Showing 1–50 of 118 results for author: Qiu, Y

Germanium-tin (GeSn) avalanche photodiode with up to 2.7 micro cutoff wavelength for extended SWIR detection

Authors: Quang Minh Thai, Rajesh Kumar, Justin Rudie, Xiaoxin Wang, Abdulla Said Ali, Perry C. Grant, Hryhorii Stanchu, Yunsheng Qiu, Steven Akwabli, Chun-Chieh Chang, Jifeng Liu, Baohua Li, Wei Du, Shui-Qing Yu

Abstract: Separate absorption charge multiplication germanium tin on silicon avalanche photodiode offers a viable solution to achieve CMOS compatible, high sensitivity detection technology in SWIR or extended SWIR range, leveraging the excellent k-factor of Si as multiplication layer and SWIR or e-SWIR band absorption of GeSn. However, unlike well-established growth of GeSn on Si with thick Ge buffer in-bet… ▽ More Separate absorption charge multiplication germanium tin on silicon avalanche photodiode offers a viable solution to achieve CMOS compatible, high sensitivity detection technology in SWIR or extended SWIR range, leveraging the excellent k-factor of Si as multiplication layer and SWIR or e-SWIR band absorption of GeSn. However, unlike well-established growth of GeSn on Si with thick Ge buffer in-between to reduce threading dislocation density due to lattice mismatch, GeSn on Si APD design requires relatively thin Ge buffer to limit electric field drop through the background p-doped buffer and efficiently transporting photocarrier from GeSn absorber to Si multiplication layer, therefore making growth of high Sn content APD for e-SWIR coverage very challenging. In this work, we experimentally demonstrate GeSn on Si APD up to 12.7 percent Sn, monolithically grown on Si substrate with 122-nm-thick Ge buffer in between, which is considerably thinner than widely used 700-900 nm thick Ge buffer. Stronger relaxation of GeSn absorber via thin Ge buffer favors Sn incorporation, leading to higher Sn content than the nominal target of 8 percent Sn. Device detection range is significantly improved compared to previous work - with cutoff wavelength increased up to 2.7 micro at 300 K, in parallel with high avalanche gain at 77 K up to 21 at 1.55 micro and up to 52 at 2 micro, and good responsivity in SWIR or e-SWIR range, up to 1.45 AW-1 at 1.55 micro and 0.66 AW-1 at 2 micro. △ Less

Submitted 15 April, 2026; originally announced April 2026.

Comments: 23 pages; 4 figures

Supercell-size scaling of moiré band flatness

Authors: Peilong Hong, Yuge Qiu, Wenjing Li, Yiyin Peng, Yu Wang, Liwei Zhang, Mingfang Yi, Yuandi He, Peng Cheng, Wangping Cheng, Yi Liang, Guoquan Zhang

Abstract: In moiré superlattices, the band flatness governs the degree of wave localization, which is central to harnessing emergent phenomena and designing functional meta-devices. While research has focused on the magic conditions such as magic angle and magic distance for optimal flatness, a fundamental understanding of how flatness changes with the supercell size has remained elusive. Here, we establish… ▽ More In moiré superlattices, the band flatness governs the degree of wave localization, which is central to harnessing emergent phenomena and designing functional meta-devices. While research has focused on the magic conditions such as magic angle and magic distance for optimal flatness, a fundamental understanding of how flatness changes with the supercell size has remained elusive. Here, we establish a universal scaling between band flatness and supercell size. Theoretically, by recognizing the statistical equivalence between structural perturbations in moiré superlattices and disordered systems, we introduce the Thouless number to evaluate the strength of moiré localization. This approach allows us to establish a scaling theory for the evolution of band flatness with the supercell size, from which an analytical expression is derived. Our full-wave simulations with one-dimensional and two-dimensional moiré superlattices show excellent agreement with the theoretical prediction. Our work reveals a general scaling law for moiré band flatness, offering a new perspective for understanding and designing moiré-based resonant systems. △ Less

Submitted 9 April, 2026; originally announced April 2026.

Comments: 5 pages, 4 figures

MSC Class: 78Mxx

Characterize localization length of disordered lattices via critical coupling effect

Authors: Fuhao Ji, Xiangqi Huang, Luxing Chen, Yuxiang Tian, Wenjing Li, Yinying Peng, Yuge Qiu, Lu Zhang, Liwei Zhang, Mingfang Yi, Peilong Hong

Abstract: Light localization by scattering is a fundamental mechanism driving phase transitions of wave transport in disordered systems. Characterizing the localization length in scattering systems is crucial yet challenging. In this Letter, we demonstrate a spatially matched coupling scheme using wavefront shaping to resolve the intrinsic localization length in two-dimensional disordered lattices. By tailo… ▽ More Light localization by scattering is a fundamental mechanism driving phase transitions of wave transport in disordered systems. Characterizing the localization length in scattering systems is crucial yet challenging. In this Letter, we demonstrate a spatially matched coupling scheme using wavefront shaping to resolve the intrinsic localization length in two-dimensional disordered lattices. By tailoring the incident wavefront, our method facilitates efficient coupling of light to the minimum localized mode. We apply this approach to measure two different self-assembled lattices, and report the first observation of the critical coupling effect, which allows for the direct determination of the characteristic size of minimum localized mode. Our results reveal that for a fixed lattice periodicity, increasing the air-hole diameter significantly reduces this intrinsic localization length. This far-field metrology offers a robust framework for probing wave localization in complex media, which should be useful in various applications such as random lasing and nonlinear optics △ Less

Submitted 4 April, 2026; originally announced April 2026.

Comments: 5 pages, 5 figures

MSC Class: 78-05

Highly-efficient, narrow-linewidth Brillouin microlasers implemented in compact thin-film lithium niobate microresonators

Authors: Yingnuo Qiu, Chuntao Li, Renhong Gao, Xiaochao Luo, Lingling Qiao, Min Wang, Jintian Lin, Ya Cheng

Abstract: Stimulated Brillouin microlasers offer chip-scale light sources with high spectral purity and low phase noise--key attributes for applications spanning precision metrology, quantum technologies, and coherent information processing. However, simultaneously bringing both pump and scattered waves into resonance often compromises photon confinement or modal volume, resulting in limited conversion effi… ▽ More Stimulated Brillouin microlasers offer chip-scale light sources with high spectral purity and low phase noise--key attributes for applications spanning precision metrology, quantum technologies, and coherent information processing. However, simultaneously bringing both pump and scattered waves into resonance often compromises photon confinement or modal volume, resulting in limited conversion efficiency and elevated thresholds. In this work, a novel approach is proposed to generate Brillouin microlasers with high efficiency, low threshold, and narrow linewidth, by combining a cross-polarized stimulated Brillouin scattering scheme with intentional Stokes mode splitting to compensate for mode detuning. Triple-resonance and phase-matching conditions are simultaneously achieved in a 114-um-diameter thin-film lithium niobate (TFLN) microresonator, enabling precise alignment with both the ~10-GHz Brillouin shift and the ~100-MHz narrow gain bandwidth. The resulting Brillouin microlaser achieves a narrow intrinsic linewidth of 2.88 Hz, a short-term integral linewidth of 185 Hz, an on-chip conversion efficiency of 57.92%, and a pump threshold as low as 1.03 mW. Both the conversion efficiency and the lasing threshold represent record-high performance for the TFLN platform to date. △ Less

Submitted 23 March, 2026; originally announced March 2026.

Comments: 4 pages, and 4 figures

Systematic study of high performance GeSn photodiodes with thick absorber for SWIR and extended SWIR detection

Authors: Quang Minh Thai, Rajesh Kumar, Abdulla Said Ali, Justin Rudie, Steven Akwabli, Yunsheng Qiu, Mourad Benamara, Hryhorii Stanchu, Kushal Dahal, Xuehuan Ma, Sudip Acharya, Chun-Chieh Chang, Gregory T. Forcherio, Bruce Claflin, Wei Du, Shui-Qing Yu

Abstract: Germanium-tin (GeSn) photodiodes potentiate a viable solution to integrate SWIR and extended SWIR detection technology into CMOS processing line. However, challenges in the growth of thick, high quality GeSn limit the device absorber thickness, making it impossible to ascertain the performance limit of GeSn photodiodes. An in-depth understanding of their device physics and a clear optimization pat… ▽ More Germanium-tin (GeSn) photodiodes potentiate a viable solution to integrate SWIR and extended SWIR detection technology into CMOS processing line. However, challenges in the growth of thick, high quality GeSn limit the device absorber thickness, making it impossible to ascertain the performance limit of GeSn photodiodes. An in-depth understanding of their device physics and a clear optimization pathway towards commercial-grade devices remain elusive. This work presents a systematic empirical study of GeSn photodiodes with thick absorber (2 to 8% Sn content, up to 2630 nm thick), showing high responsivity up to 0.59 A.W-1 at 1.55 μm and 0.43 A.W-1 at 2 μm wavelengths, low dark current density down to 2 x 10-2 A.cm-2, and high detection cutoff wavelengths up to 2.1 and 2.5 μm at 5% and 8% Sn, respectively. Using specific doping design (P-i-N and N-i-P), an in-depth analysis is presented on the impact of junction position, p-type background carrier concentration, bulk/ surface defects and photocarrier diffusion length - on photodetection performance. Different optimization strategies for GeSn photodiodes, in particular at high Sn content, are proposed. △ Less

Submitted 16 February, 2026; originally announced February 2026.

2DESR: a two-dimensional Fourier-space gyrokinetic eigenvalue code for the ion-temperature-gradient modes in tokamaks

Authors: Haochuan Wang, Jie Wang, Yuefeng Qiu, Shaojie Wang, Zihao Wang, Tiannan Wu, Yuesong Li, Yicheng Cai, Shiqi Xiao

Abstract: A two-dimensional (2D) gyrokinetic eigenvalue solver, 2DESR, has been developed to solve the 2D gyrokinetic eigenvalue problem in the poloidal Fourier space for the ion-temperature-gradient (ITG) modes in tokamaks. With full kinetic effects of ions retained, the 2D gyrokinetic eigenvalue equations in the poloidal Fourier space have been derived and numerically solved in the 2DESR code. In the line… ▽ More A two-dimensional (2D) gyrokinetic eigenvalue solver, 2DESR, has been developed to solve the 2D gyrokinetic eigenvalue problem in the poloidal Fourier space for the ion-temperature-gradient (ITG) modes in tokamaks. With full kinetic effects of ions retained, the 2D gyrokinetic eigenvalue equations in the poloidal Fourier space have been derived and numerically solved in the 2DESR code. In the linear ITG Cyclone test with adiabatic electrons, the 2DESR code benchmarks well against the gyrokinetic initial-value codes GENE and NLT. It is found that two branches of ITG modes coexist in the system. △ Less

Submitted 7 February, 2026; originally announced February 2026.

Comments: 11 pages, 5 figures

Highly efficient multi-chromatic Raman microlasers from cavity polygon modes on thin-film lithium niobate platform

Authors: Yixuan Yang, Chuntao Li, Renhong Gao, Yingnuo Qiu, Lingling Qiao, Jielei Ni, Jintian Lin, Ya Cheng

Abstract: The integration of stimulated Raman scattering (SRS) and second order nonlinearity in non-centrosymmetric photonic microresonators presents a highly promising solution for developing on-chip coherent light sources with exceptional bandwidth and flexible tunability. Our study introduces an innovative methodology leveraging cavity polygon modes within an X-cut thin-film lithium niobate microdisk to… ▽ More The integration of stimulated Raman scattering (SRS) and second order nonlinearity in non-centrosymmetric photonic microresonators presents a highly promising solution for developing on-chip coherent light sources with exceptional bandwidth and flexible tunability. Our study introduces an innovative methodology leveraging cavity polygon modes within an X-cut thin-film lithium niobate microdisk to achieve highly efficient multi-chromatic Raman microlasers. Specifically, high-Q square modes characterized by two parallel sides oriented perpendicularly relative to the optical axis of lithium niobate crystal were excited. These modes offer distinct advantages, including enhancing both mode-field overlap and improved phase matching, achieved through the utilization of the largest second-order susceptibility component (d_33), which is critical for Raman-quadratic nonlinear interactions. The experimental results highlight significant advancements in multi-wavelength multi-wavelength laser generation, with forward stimulated Raman laser signals exhibiting a high conversion efficiency of up to 65.02% and an impressively narrow integral linewidth of only 5.2 kHz. Simultaneously, our system enables the generation of multi-wavelength Raman-quadratic laser signals across the ~800 nm and ~530 nm spectral bands. These findings are further underscored by an impressive absolute conversion efficiency of 1.33% for the 797.4-nm Raman laser, achieved at a remarkably low pump power of just 1.07 mW. This work not only extends the application scope of cavity polygon modes from single second/third-order nonlinear optical processes to cascaded processes but also establishes a foundation for realizing high-efficiency on-chip multi-chromatic laser sources with versatile functionalities. △ Less

Submitted 22 December, 2025; originally announced December 2025.

Comments: 10 pages, 5 figures

Characteristics of mono-, di-, and trivalent cations in electric double layers: a molecular dynamic investigation

Authors: Bowen Ai, Zekun Gong, Long Ma, Hongwen Zhang, Tianyi Sui, Yinghua Qiu

Abstract: Ionic behaviors, including ion distributions and hydration characteristics at solid-liquid interfaces, are important research interests in many important applications, such as electric double-layer capacitors and water lubrication. Here, we systematically investigated the concentration distributions, hydration numbers, and screening properties of Li+, Na+, K+, Ca2+, Mg2+, and La3+ ions inside elec… ▽ More Ionic behaviors, including ion distributions and hydration characteristics at solid-liquid interfaces, are important research interests in many important applications, such as electric double-layer capacitors and water lubrication. Here, we systematically investigated the concentration distributions, hydration numbers, and screening properties of Li+, Na+, K+, Ca2+, Mg2+, and La3+ ions inside electric double layers (EDLs) at various charge densities. For the surface charge density weaker than -0.16 C m-2, monovalent cations mainly accumulate in the outer Helmholtz plane (OHP). As the charge density magnitude increases, monovalent cations start to dehydrate and migrate to the inner Helmholtz plane (IHP), following the order of K+, Na+, and Li+. This size-dependent behavior arises from the lower hydration energy of larger ions. While for the di- and trivalent ions, no obvious IHP appears. Based on ion distributions, the screening effect of counterions on surface charges is evaluated by analyzing the net charge distributions. As the charge density changes from 0 to -0.32 C m-2, due to the stronger accumulation of cations in EDLs, the location of the neutral plane changes from ~1.2 to ~0.4 nm. When the charge density reaches a threshold, excessive accumulation of cations can induce charge inversion. The threshold value and the maximum reversed charge are found to correlate with the ion size, cation valence, and concentration. △ Less

Submitted 5 December, 2025; originally announced December 2025.

Comments: 35 pages, 7 figures

Journal ref: Langmuir. 2025. 41 (47). 31743-31754

Modulation of Electroosmotic Flow through Short Nanopores by Charged Exterior Surfaces

Authors: Chao Zhang, Xiaomei Zhang, Hongwen Zhang, Zekun Gong, Xiuhua Ren, Mengnan Guo, Yinghua Qiu

Abstract: Electroosmotic flow (EOF) through nanoporous membranes has broad applications in micro- and nanofluidic systems, particularly in biomedical diagnostics and chemical analysis. The use of short nanopores enables high fluid flux, and the presence of exterior surface charges can further enhance ion flux through short nanopores. Here, systematic simulations are conducted to explore the modulation of EO… ▽ More Electroosmotic flow (EOF) through nanoporous membranes has broad applications in micro- and nanofluidic systems, particularly in biomedical diagnostics and chemical analysis. The use of short nanopores enables high fluid flux, and the presence of exterior surface charges can further enhance ion flux through short nanopores. Here, systematic simulations are conducted to explore the modulation of EOF by exterior surface charges. Our results indicate that charged exterior surfaces can provide an additional effective pathway for fluid flow, significantly increasing both the EOF velocity and output pressure. By analyzing the dependence of EOF velocity on the area of the charged exterior surface, we derive the effective width (Lcs_eff) of the charged ring region extending beyond the pore boundary. This parameter is quantitatively examined under various nanopore configurations and applied conditions. Lcs_eff is found to be proportional to the pore diameter, surface charge density, and applied voltage, while inversely proportional to pore length and salt concentration. These findings provide valuable insights into the modulation of EOF by exterior surface charges and offer theoretical guidance for optimizing the structural and functional properties of nanoporous membranes in practical applications of EOF. △ Less

Submitted 5 December, 2025; originally announced December 2025.

Comments: 31 pages, 7 figures

Journal ref: Electrochimica Acta. 2025. 543. 147623

Modulation of Ionic Current Rectification in Short Unipolar Nanopores

Authors: Hongwen Zhang, Long Ma, Di Liu, Tianyi Sui, Zuzanna S. Siwy, Yinghua Qiu

Abstract: With controlled ionic current rectification (ICR) achieved through a strategically designed non-uniform surface charge distribution, short unipolar nanopores exhibit promising applications in nanofluidic sensors, ionic circuits, and ion amplifiers. By systematically investigating how the charged length on inner pore walls modulates ion transport, we found that both the maximum ICR degree and the c… ▽ More With controlled ionic current rectification (ICR) achieved through a strategically designed non-uniform surface charge distribution, short unipolar nanopores exhibit promising applications in nanofluidic sensors, ionic circuits, and ion amplifiers. By systematically investigating how the charged length on inner pore walls modulates ion transport, we found that both the maximum ICR degree and the corresponding charged-length proportion were influenced by nanopore parameters and simulation conditions. For 100 nm-long unipolar nanopores, the highest ICR degree is obtained at a charged-length proportion of ~0.3, due to the corresponding most significant ion enrichment and depletion inside the nanopore under opposite biases. This charged-length proportion of ~0.3 consistently appears as a characteristic value across most considered cases. For short unipolar nanopores, the presence of exterior surface charges significantly enhances the ICR degree by facilitating ion transport through nanopores. The effective widths of charged regions beyond nanopore borders on outer surfaces exhibit direct proportionality to the pore diameter, surface charge density, and applied voltage, and inverse proportionality to the pore length and salt concentration. Our research may provide useful guidance for the design of unipolar nanopores and porous membranes incorporating such charge configurations. △ Less

Submitted 5 December, 2025; originally announced December 2025.

Comments: 31 pages, 6 figures

Journal ref: Journal of Colloid and Interface Science. 2026. 703. 139274

Simultaneous generation of Raman-assisted Soliton Microcombs and Tunable Multi-chromatic Raman Microlasers in Single Monolithic Thin-film Lithium Niobate Microrings

Authors: Yingnuo Qiu, Renhong Gao, Chuntao Li, Yixuan Yang, Xinzhi Zheng, Guanghui Zhao, Xiaochao Luo, Qifeng Hou, Lingling Qiao, Min Wang, Jintian Lin, Ya Cheng

Abstract: High-performance integrated broadband coherent light sources are essential for advanced applications in high-bandwidth data processing and chip-scale metrology, yet remain challenging. In this study, we demonstrate a monolithic Z-cut lithium niobate on insulator (LNOI) microring platform that enables simultaneous generation of tunable multi-chromatic microlasers and Raman-assisted soliton microcom… ▽ More High-performance integrated broadband coherent light sources are essential for advanced applications in high-bandwidth data processing and chip-scale metrology, yet remain challenging. In this study, we demonstrate a monolithic Z-cut lithium niobate on insulator (LNOI) microring platform that enables simultaneous generation of tunable multi-chromatic microlasers and Raman-assisted soliton microcombs. Exploiting the strong Raman activity and high second-order nonlinearity of LNOI, we engineered a dispersion-optimized microring with a loaded Q factor of 3.86X10^6, facilitating on-chip efficient broadband coherent light source. A novel phase-matching configuration with all the waves of the same ordinary polarization was realized for the first time in this platform, feasibly enabling modal-phase matched Raman-quadratic nonlinear processes that extend lasing signals into the visible spectrum. Under continuous-wave laser pumping at 3.73 mW in the telecom band, we achieved a Raman-assisted soliton comb centered at 1624.49 nm with record-low pump threshold on the LNOI platform. Concurrently, multi-chromatic Raman lasing outputs were observed at ~1700, ~813, and ~535 nm within the same microring. The system exhibited efficient wavelength tuning of these multi-chromatic laser signals through a 5 nm shift in pump wavelength. This work represents a significant advance in integrated photonics for versatile optical signal generation. △ Less

Submitted 26 November, 2025; originally announced November 2025.

Comments: 19 pages, 5 figures

Two-Stage Nature of a Solar Flare with Parallel and Semi-Circular Ribbons

Authors: Ruifei Huang, Hao Ning, Ze Zhong, Ye Qiu, Zhenyong Hou, Yang Su, Chuan Li, Xiangliang Kong, Yao Chen

Abstract: Flare ribbons with parallel and circular morphologies are typically associated with different magnetic reconnection models, and the simultaneous observation of both types in a single event remains rare. Using multi-wavelength observations from a tandem of instruments, we present an M8.2-class flare that occurred on 2023 September 20, which produced quasi-parallel and semi-circular ribbons. The com… ▽ More Flare ribbons with parallel and circular morphologies are typically associated with different magnetic reconnection models, and the simultaneous observation of both types in a single event remains rare. Using multi-wavelength observations from a tandem of instruments, we present an M8.2-class flare that occurred on 2023 September 20, which produced quasi-parallel and semi-circular ribbons. The complex evolution of the flare includes two distinct brightening episodes in the quasi-parallel ribbons, corresponding to the two major peaks in the hard X-ray (HXR) light curve. In contrast, the brightening of semi-circular ribbons temporally coincides with the local minimum between the two peaks. Using potential field extrapolation, we reconstruct an incomplete dome-like magnetic structure with a negative polarity embedded within the northwestern part of the semi-circular positive polarity. Consequently, the magnetic configuration comprises two sets of field lines with distinct magnetic connectivities. We suggest that the standard flare reconnection accounts for the two-stage brightening of quasi-parallel ribbons associated with the two HXR peaks. Between the two stages, this process is constrained by the interaction of eruptive structures with the dome. The interaction drives the quasi-separatrix layer reconnection, leading to the brightening of semi-circular ribbons. It also suppresses the standard flare reconnection, resulting in a delayed second HXR peak. △ Less

Submitted 31 October, 2025; originally announced October 2025.

Comments: 13 pages, 8 figures; Accepted for publication in ApJ

Ion transport through differently charged nanoporous membranes: from a single nanopore to multi-nanopores

Authors: Hongwen Zhang, Bowen Ai, Zekun Gong, Tianyi Sui, Zuzanna S. Siwy, Yinghua Qiu

Abstract: Nanoporous membranes, leveraging their high-throughput characteristics, have been widely applied in fields such as molecular separation and energy conversion. Due to interpore interactions, besides the applied voltage and solution environment, the ion transport properties in porous membranes are influenced by the pore number and spacing. Here, to understand and control the transport properties of… ▽ More Nanoporous membranes, leveraging their high-throughput characteristics, have been widely applied in fields such as molecular separation and energy conversion. Due to interpore interactions, besides the applied voltage and solution environment, the ion transport properties in porous membranes are influenced by the pore number and spacing. Here, to understand and control the transport properties of nanopore arrays, we systematically investigate the ion transport characteristics through membranes with different charge properties, pore numbers, and interpore distances. Using numerical simulations, we analyzed local ionic concentrations and electric potential in nanopore arrays containing nanopores with uniformly charged walls as well as unipolar diodes i.e., pores containing a junction between a charged zone and a neutral zone, and showed significant ion concentration polarization (ICP) for all studied cases. As the number of pores increased and the interpore spacing decreased, the enhanced interpore interactions through ICP led to a greater deviation of the total ionic current from the linear superposition of single-pore currents. Conversely, in bipolar nanopores whose walls contain a junction between positively and negatively charged zones ICP becomes negligible, and interpore interactions are substantially reduced. Furthermore, for membranes with various charge properties, the total current through nanopore arrays presents different quantitative dependence on the pore number under varying pore spacings. Our findings clarify the mechanism of interpore interactions in modulating ion transport through porous membranes, providing critical insights for designing nanofluidic devices based on nanopore arrays, such as nanopore-array sensors. △ Less

Submitted 20 October, 2025; originally announced October 2025.

Comments: 39 pages, 10 figures

Journal ref: Analytical Chemistry, 2025, 97 (35): 19218-19231

Ionic current rectification under concentration gradients and its application in evaluating surface charge properties of micropores

Authors: Long Ma, Hongwen Zhang, Bowen Ai, Jiakun Zhuang, Guanghua Du, Yinghua Qiu

Abstract: Ionic current rectification (ICR) induced by electroosmotic flow (EOF) under concentration gradients can find many applications in micro/nanofluidic sensing and ionic circuits. Here, we focused on the cases with micropores of moderate length-diameter ratios, through experimental research and systematical simulations, the EOF-induced ICR was found to exhibit voltage-dependent ratios. In the conside… ▽ More Ionic current rectification (ICR) induced by electroosmotic flow (EOF) under concentration gradients can find many applications in micro/nanofluidic sensing and ionic circuits. Here, we focused on the cases with micropores of moderate length-diameter ratios, through experimental research and systematical simulations, the EOF-induced ICR was found to exhibit voltage-dependent ratios. In the considered cases with a weak EOF or strong ionic diffusion, a large deviation appears between the ion concentration inside the micropore and the bulk value, which fails the prediction by solution conductivity gradients. Based on our simulation results, effective equations were developed for the theoretical description of ion concentration distributions along the micropore axis under coupled concentration gradient and electric field. With the predicted ion distributions inside micropores, the ICR ratio can be conveniently calculated with the derived electrical resistance of the microfluidic system, which applies to micropores of 200 to 1000 nm in diameter. Because the surface charge density is the only unknown input parameter, our developed equations can be used to evaluate the surface charge density of micropores with the measured EOF-induced ICR ratio under concentration gradients. △ Less

Submitted 20 October, 2025; originally announced October 2025.

Comments: 23 pages, 5 figures

Journal ref: The Journal of Chemical Physics, 2025, 162 (9): 094704

Modulation of Memristive Characteristics by Dynamic Nanoprecipitation inside Conical Nanopores

Authors: Zhe Liu, Hongwen Zhang, Di Liu, Tianyi Sui, Yinghua Qiu

Abstract: Nanofluidic memristors have demonstrated great potential for neuromorphic system applications with the advantages of low energy consumption and excellent biocompatibility. Here, an effective way is developed to regulate the memristive behavior of conical nanopores by leveraging the reversible formation and dissolution of nanoprecipitates induced by ion enrichment and depletion in nanopores under o… ▽ More Nanofluidic memristors have demonstrated great potential for neuromorphic system applications with the advantages of low energy consumption and excellent biocompatibility. Here, an effective way is developed to regulate the memristive behavior of conical nanopores by leveraging the reversible formation and dissolution of nanoprecipitates induced by ion enrichment and depletion in nanopores under opposite voltages. Through the interplay between precipitation dynamics at the pore tip and the ion enrichment/depletion inside the nanopore, conical nanopores exhibit pronounced current hysteresis loops in the presence of CaHPO4, a slightly soluble inorganic salt. The memristive characteristics are found to be strongly dependent on the concentration of CaHPO4, besides the applied voltage amplitude and scan rate. Under the stimulation of pulse voltages, ionic current demonstrates stable learning and forgetting processes with robust switching stability and effective reset capability, which is similar to the short-term plasticity characteristics of biological synapses. Our research may provide a straightforward and tunable approach for the design of nanofluidic memristors. △ Less

Submitted 20 October, 2025; originally announced October 2025.

Comments: 31 pages, 5 figures

Journal ref: Small Methods, 2025, 9 (9): e01205

Gas-phase Molecules in Protoplanetary Nebulae with the 21 μm Emission Feature II. Carbon monosulfide

Authors: Jian-Jie Qiu, Yong Zhang, Deng-Rong Lu, Zheng-Xue Chang, Jiang-Shui Zhang, Xiao-Hu Li, Xin-Di Tang, Yisheng Qiu, Jun-ichi Nakashima, Lan-Wei Jia

Abstract: The carrier of the 21 $μ$m emission feature discovered in a handful of protoplanetary nebulae (PPNe) is one of the most intriguing enigmas in circumstellar chemistry. Investigating the gas-phase molecules in PPNe could yield important hints for understanding the 21 $μ$m feature. In this paper, we report observations of the CS $J = 5 \to 4$ line at 245 GHz and the CO $J = 1 \to 0$ line at 115 GHz t… ▽ More The carrier of the 21 $μ$m emission feature discovered in a handful of protoplanetary nebulae (PPNe) is one of the most intriguing enigmas in circumstellar chemistry. Investigating the gas-phase molecules in PPNe could yield important hints for understanding the 21 $μ$m feature. In this paper, we report observations of the CS $J = 5 \to 4$ line at 245 GHz and the CO $J = 1 \to 0$ line at 115 GHz toward seven PPNe exhibiting the 21 $μ$m feature. We find that CS is extremely scarce in these PPNe and the CS line is only detected in one source, IRAS Z02229+6208. Based on the assumption of local thermal equilibrium and negligible optical depth, we derive that the CS column densities and fractional abundances relative to H$_{2}$ are $N$(CS) < 9.1 ${\times}$ 10$^{13}$cm$^{-2}$ and $f$(CS) < 8.1 ${\times}$ 10$^{-7}$. A comparison of the CS abundances across different circumstellar envelopes reveals that the variations in CS abundance are complex, depending not only on the evolutionary stages but also on the properties of individual objects. △ Less

Submitted 19 August, 2025; originally announced August 2025.

Comments: 25 pages, 2 figures, 3 tables (including appendices). Accepted for publication in the Astronomical Journal (AJ)

The Automatic Calibration Method of the Compton Edge Based on Normalized Cross-correlation and Simulated Annealing Algorithm

Authors: Dehua Kong, Yanbiao Zhang, Zixi Lin, Yehao Qiu, Xiulian Chen, Zhonghai Wang

Abstract: Accurate energy channel calibration in scintillation detectors is essential for reliable radiation detection across nuclear physics, medical imaging, and environmental monitoring. Organic scintillators like BC408 and EJ309 lack full-energy peaks, making their Compton edge a critical calibration alternative where traditional peak methods fail. Existing Compton edge identification techniques - Gauss… ▽ More Accurate energy channel calibration in scintillation detectors is essential for reliable radiation detection across nuclear physics, medical imaging, and environmental monitoring. Organic scintillators like BC408 and EJ309 lack full-energy peaks, making their Compton edge a critical calibration alternative where traditional peak methods fail. Existing Compton edge identification techniques - Gaussian fitting for the 50%-70% amplitude point, first derivative minimum detection, and Monte Carlo simulation - suffer significant degradation from low count rates, spectral overlap, and subjective interval selection. For the first time, we propose an automated calibration procedure based on Normalized Cross-Correlation (NCC), Simulated Annealing (SA), and a convolutional response model to address these issues. This method automates the selection of the Compton edge interval through NCC-based matching, utilizes SA for global parameter optimization, and then employs a convolutional model for precise matching. Experiments involving the irradiation of organic scintillators (BC408, EJ309) and inorganic scintillators (NaI:Tl, LaBr3:Ce) with 137Cs, 22Na, 54Mn, and 60Co radiation sources demonstrate that this method achieves accuracy commensurate with full-energy peak calibration method (cosine similarity >99.999%) and exhibits superior stability compared to the two traditional methods. In the extreme cases of spectral overlap and low count rate, the average errors of this method are 19.77% and 15.65% of those from the two traditional methods in BC408, 56.44% and 33.15% of those from the two traditional methods in EJ309. This work advances detector calibration and offers a scalable, automated solution for high-energy experiments and portable devices. △ Less

Submitted 22 July, 2025; originally announced July 2025.

Comments: Compton scattering, Organic scintillators, Scintillation detectors, Convolution Model, Normalized Cross correlation, Simulated Annealing

MBFormer: A General Transformer-based Learning Paradigm for Many-body Interactions in Real Materials

Authors: Bowen Hou, Xian Xu, Jinyuan Wu, Diana Y. Qiu

Abstract: Recently, radical progress in machine learning (ML) has revolutionized computational materials science, enabling unprecedentedly rapid materials discovery and property prediction, but the quantum many-body problem -- which is the key to understanding excited-state properties, ranging from transport to optics -- remains challenging due to the complexity of the nonlocal and energy-dependent interact… ▽ More Recently, radical progress in machine learning (ML) has revolutionized computational materials science, enabling unprecedentedly rapid materials discovery and property prediction, but the quantum many-body problem -- which is the key to understanding excited-state properties, ranging from transport to optics -- remains challenging due to the complexity of the nonlocal and energy-dependent interactions. Here, we propose a symmetry-aware, grid-free, transformer-based model, MBFormer, that is designed to learn the entire many-body hierarchy directly from mean-field inputs, exploiting the attention mechanism to accurately capture many-body correlations between mean-field states. As proof of principle, we demonstrate the capability of MBFormer in predicting results based on the GW plus Bethe Salpeter equation (GW-BSE) formalism, including quasiparticle energies, exciton energies, exciton oscillator strengths, and exciton wavefunction distribution. Our model is trained on a dataset of 721 two-dimensional materials from the C2DB database, achieving state-of-the-art performance with a low prediction mean absolute error (MAE) on the order of 0.1-0.2 eV for state-level quasiparticle and exciton energies across different materials. Moreover, we show explicitly that the attention mechanism plays a crucial role in capturing many-body correlations. Our framework provides an end-to-end platform from ground states to general many-body prediction in real materials, which could serve as a foundation model for computational materials science. △ Less

Submitted 7 July, 2025; originally announced July 2025.

Latent Thermodynamic Flows: Unified Representation Learning and Generative Modeling of Temperature-Dependent Behaviors from Limited Data

Authors: Yunrui Qiu, Richard John, Lukas Herron, Pratyush Tiwary

Abstract: Accurate characterization of the equilibrium distributions of complex molecular systems and their dependence on environmental factors such as temperature is essential for understanding thermodynamic properties and transition mechanisms. Projecting these distributions onto meaningful low-dimensional representations enables interpretability and downstream analysis. Recent advances in generative AI,… ▽ More Accurate characterization of the equilibrium distributions of complex molecular systems and their dependence on environmental factors such as temperature is essential for understanding thermodynamic properties and transition mechanisms. Projecting these distributions onto meaningful low-dimensional representations enables interpretability and downstream analysis. Recent advances in generative AI, particularly flow models such as Normalizing Flows (NFs), have shown promise in modeling such distributions, but their scope is limited without tailored representation learning. In this work, we introduce Latent Thermodynamic Flows (LaTF), an end-to-end framework that tightly integrates representation learning and generative modeling. LaTF unifies the State Predictive Information Bottleneck (SPIB) with NFs to simultaneously learn low-dimensional latent representations, referred to as Collective Variables (CVs), classify metastable states, and generate equilibrium distributions across temperatures beyond the training data. The two components of representation learning and generative modeling are optimized jointly, ensuring that the learned latent features capture the system's slow, important degrees of freedom while the generative model accurately reproduces the system's equilibrium behavior. We demonstrate LaTF's effectiveness across diverse systems, including a model potential, the Chignolin protein, and cluster of Lennard Jones particles, with thorough evaluations and benchmarking using multiple metrics and extensive simulations. Finally, we apply LaTF to a RNA tetraloop system, where despite using simulation data from only two temperatures, LaTF reconstructs the temperature-dependent structural ensemble and melting behavior, consistent with experimental and prior extensive computational results. △ Less

Submitted 3 July, 2025; originally announced July 2025.

Visible Brillouin-quadratic microlaser in a high-Q thin-film lithium niobate microdisk

Authors: Xiaochao Luo, Chuntao Li, Xingzhao Huang, Jintian Lin, Renhong Gao, Yifei Yao, Yingnuo Qiu, Yixuan Yang, Lei Wang, Huakang Yu, Ya Cheng

Abstract: Narrow-linewidth lasers at short/visible wavelengths are crucial for quantum and atomic applications, such as atomic clocks, quantum computing, atomic and molecular spectroscopy, and quantum sensing. However, such lasers are often only accessible in bulky tabletop systems and remain scarce in integrated photonic platform. Here, we report an on-chip visible Brillouin-quadratic microlaser in a 117-u… ▽ More Narrow-linewidth lasers at short/visible wavelengths are crucial for quantum and atomic applications, such as atomic clocks, quantum computing, atomic and molecular spectroscopy, and quantum sensing. However, such lasers are often only accessible in bulky tabletop systems and remain scarce in integrated photonic platform. Here, we report an on-chip visible Brillouin-quadratic microlaser in a 117-um-diameter thin-film lithium niobate (TFLN) microdisk via dispersion engineering. Enabled by the ultra-high Q factor of 4.0X10(6) and small mode volume, strong photon-phonon interaction and high second-order nonlinearity of the TFLN microdisk, narrow-linewidth Stokes Brillouin lasing (SBL) is demonstrated with 10.17 GHz Brillouin shift under a 1560-nm pump, exhibiting a short-term narrow linewidth of 254 Hz and a low threshold of only 1.81 mW. Meanwhile, efficient second harmonic generation (SHG) of the SBL signal is also observed at 780 nm, with a normalized conversion efficiency of 3.61%/mW, made possible by simultaneous phase matching fulfillments for both narrow-linewidth SBL and its SHG. This demonstration of an integrated ultra-narrow linewidth visible wavelength Brillouin-quadratic lasers opens new avenues toward chip-scale quantum information processing and precise metrology. △ Less

Submitted 10 June, 2025; originally announced June 2025.

Comments: 13 pages and 6 figures. arXiv admin note: substantial text overlap with arXiv:2503.23706

A Mechanism-Guided Inverse Engineering Framework to Unlock Design Principles of H-Bonded Organic Frameworks for Gas Separation

Authors: Yong Qiu, Lei Wang, Letian Chen, Yun Tian, Zhen Zhou, Jianzhong Wu

Abstract: The diverse combinations of novel building blocks offer a vast design space for hydrogen-boned frameworks (HOFs), rendering it a great promise for gas separation and purification. However, the underlying separation mechanism facilitated by their unique hydrogen-bond networks has not yet been fully understood. In this work, a comprehensive understanding of the separation mechanisms was achieved thr… ▽ More The diverse combinations of novel building blocks offer a vast design space for hydrogen-boned frameworks (HOFs), rendering it a great promise for gas separation and purification. However, the underlying separation mechanism facilitated by their unique hydrogen-bond networks has not yet been fully understood. In this work, a comprehensive understanding of the separation mechanisms was achieved through an iterative data-driven inverse engineering approach established upon a hypothetical HOF database possessing nearly 110,000 structures created by a material genomics method. Leveraging a simple yet universal feature extracted from hydrogen bonding information with unambiguous physical meanings, the entire design space was exploited to rapidly identify the optimization route towards novel HOF structures with superior Xe/Kr separation performance (selectivity >103). This work not only provides the first large-scale HOF database, but also demonstrates the enhanced machine learning interpretability of our model-driven iterative inverse design framework, offering new insights into the rational design of nanoporous materials for gas separation. △ Less

Submitted 8 May, 2025; originally announced May 2025.

Low-loss thin-film periodically poled lithium niobate waveguides fabricated by femtosecond laser photolithography

Authors: Guanghui Zhao, Jintian Lin, Renhong Gao, Jianglin Guan, Chuntao Li, Xinzhi Zheng, Minghui Li, Qifeng Hou, Xiaochao Luo, Yingnuo Qiu, Lingling Qiao, Min Wang, Ya Cheng

Abstract: Periodically poled lithium niobate on insulator (PPLNOI) ridge waveguides are critical photonic components for both classical and quantum information processing. However, dry etching of PPLNOI waveguides often generates rough sidewalls and variations in the etching rates of oppositely poled lithium niobate ferroelectric domains, leading a relatively high propagation losses (0.25 - 1 dB/cm), which… ▽ More Periodically poled lithium niobate on insulator (PPLNOI) ridge waveguides are critical photonic components for both classical and quantum information processing. However, dry etching of PPLNOI waveguides often generates rough sidewalls and variations in the etching rates of oppositely poled lithium niobate ferroelectric domains, leading a relatively high propagation losses (0.25 - 1 dB/cm), which significantly limits net conversion efficiency and hinders scalable photonic integration. In this work, a low-loss PPLNOI ridge waveguide with a length of 7 mm was fabricated using ultra-smooth sidewalls through photolithography-assisted chemo-mechanical etching (PLACE) followed by high-voltage pulse poling with low cost. The average surface roughness was measured at just 0.27 nm, resulting in record-low propagation loss of 0.106 dB/cm in PPLNOI waveguides. Highly efficient second-harmonic generation was demonstrated with a normalized efficiency of 1643%/(W*cm^2) without temperature tuning, corresponding to a conversion efficiency of 805%/W, which is closed to the best conversion efficiency (i.e., 814%/W) reported in nanophotonic PPLNOI waveguide fabricated by expensive electron-beam lithography followed by dry etching. The absolute conversion efficiency reached 15.8% at a pump level of 21.6 mW. And the normalized efficiency can be even improved to 1742%/(W*cm^2) at optimal temperature of 59°C. △ Less

Submitted 29 April, 2025; v1 submitted 21 April, 2025; originally announced April 2025.

Comments: 4 pages, 4 figures

Simultaneously generating Brillouin microlaser and second harmonic within a lithium niobate microdisk

Authors: Xiaochao Luo, Chuntao Li, Jintian Lin, Renhong Gao, Yifei Yao, Yingnuo Qiu, Lei Wang, Ya Cheng

Abstract: We report the simultaneous generation of second-harmonic generation (SHG) and Brillouin microlaser in a high-quality thin-film lithium niobate (TFLN) microdisk resonator. The microdisk is fabricated with ultrahigh-Q factor of 4X10(6) by photolithography-assisted chemo-mechanical etching, enabling significant cavity-enhancement effect for boosting nonlinear frequency conversion. Under 1559.632 nm p… ▽ More We report the simultaneous generation of second-harmonic generation (SHG) and Brillouin microlaser in a high-quality thin-film lithium niobate (TFLN) microdisk resonator. The microdisk is fabricated with ultrahigh-Q factor of 4X10(6) by photolithography-assisted chemo-mechanical etching, enabling significant cavity-enhancement effect for boosting nonlinear frequency conversion. Under 1559.632 nm pumping, Brillouin microlaser is demonstrated in the microdisk with Stokes Brillouin shift of 10 GHz, a low threshold of 1.81 mW, and a fundamental linewidth of 254.365 Hz. Meanwhile, efficient SHG is observed at 779.816 nm with an absolute conversion efficiency of 3.8% at pump level of 3.028 mW. The coexistence of these two nonlinear processes is enabled by the simultaneous confinement of the light and acoustic fileds for effect coupling in the microdisk, which enhances both optomechanical and second-order nonlinear interactions. This research provides new possibilities for integrated multi-frequency laser sources and multifunctional nonlinear photonic devices. △ Less

Submitted 31 March, 2025; originally announced March 2025.

Comments: 4 pages, 4 figures

LOCAL: A Locality-based Active Learning Framework for Predicting the Stability of Dual-Atom Catalysts

Authors: Yue Yin, Jiangshan He, Runze Li, Yunze Qiu, Dingsheng Wang, Jun Li, Hai Xiao

Abstract: Dual-atom catalysts supported on nitrogen-doped graphene (DAC/NG) are emerging as a family of promising catalysts that can overcome intrinsic limitations of single-atom catalysts. However, comprehensive assessment of their structural stability is prohibitively demanding due to a vast local configurational space. Here we introduce LOCAL, a locality-based framework that combines graph convolutional… ▽ More Dual-atom catalysts supported on nitrogen-doped graphene (DAC/NG) are emerging as a family of promising catalysts that can overcome intrinsic limitations of single-atom catalysts. However, comprehensive assessment of their structural stability is prohibitively demanding due to a vast local configurational space. Here we introduce LOCAL, a locality-based framework that combines graph convolutional networks with active learning to efficiently predict DAC/NG stability by leveraging chemically intuitive locality quantified by crystal orbital Hamilton population analysis. We demonstrate the effectiveness of LOCAL over a comprehensive dataset of 611,648 DAC/NG structures, achieving a test mean absolute error of 0.15~eV while invoking density functional theory calculations for only 16,704 structures (2.7% of the dataset). Thus, LOCAL enables efficient and accurate construction of phase diagrams for DAC/NG across diverse compositions reciprocally validated with experimentally synthesized configurations for representative systems. Our framework composes an essential methodology for accelerating the discovery and optimization of high-performance complex catalysts. △ Less

Submitted 19 November, 2025; v1 submitted 25 March, 2025; originally announced March 2025.

Direct Observation of Massless Excitons and Linear Exciton Dispersion

Authors: Luna Y. Liu, Steffi Y. Woo, Jinyuan Wu, Bowen Hou, Cong Su, Diana Y. Qiu

Abstract: Excitons -- elementary excitations formed by bound electron-hole pairs -- govern the optical properties and excited-state dynamics of materials. In two-dimensions (2D), excitons are theoretically predicted to have a linear energy-momentum relation with a non-analytic discontinuity in the long wavelength limit, mimicking the dispersion of a photon. This results in an exciton that behaves like a mas… ▽ More Excitons -- elementary excitations formed by bound electron-hole pairs -- govern the optical properties and excited-state dynamics of materials. In two-dimensions (2D), excitons are theoretically predicted to have a linear energy-momentum relation with a non-analytic discontinuity in the long wavelength limit, mimicking the dispersion of a photon. This results in an exciton that behaves like a massless particle, despite the fact that it is a composite boson composed of massive constituents. However, experimental observation of massless excitons has remained elusive. In this work, we unambiguously experimentally observe the predicted linear exciton dispersion in freestanding monolayer hexagonal boron nitride (hBN) using momentum-resolved electron energy-loss spectroscopy. The experimental result is in excellent agreement with our theoretical prediction based on ab initio many-body perturbation theory. Additionally, we identify the lowest dipole-allowed transition in monolayer hBN to be at 6.6 eV, illuminating a long-standing debate about the band gap of monolayer hBN. These findings provide critical insights into 2D excitonic physics and open new avenues for exciton-mediated superconductivity, Bose-Einstein condensation, and high-efficiency optoelectronic applications. △ Less

Submitted 13 March, 2025; v1 submitted 27 February, 2025; originally announced February 2025.

Data-driven Low-rank Approximation for Electron-hole Kernel and Acceleration of Time-dependent GW Calculations

Authors: Bowen Hou, Jinyuan Wu, Victor Chang Lee, Jiaxuan Guo, Luna Y. Liu, Diana Y. Qiu

Abstract: Many-body electron-hole interactions are essential for understanding non-linear optical processes and ultrafast spectroscopy of materials. Recent first principles approaches based on nonequilibrium Green's function formalisms, such as the time-dependent adiabatic GW (TD-aGW) approach, can predict the nonequilibrium dynamics of excited states including electron-hole interactions. However, the high… ▽ More Many-body electron-hole interactions are essential for understanding non-linear optical processes and ultrafast spectroscopy of materials. Recent first principles approaches based on nonequilibrium Green's function formalisms, such as the time-dependent adiabatic GW (TD-aGW) approach, can predict the nonequilibrium dynamics of excited states including electron-hole interactions. However, the high dimensionality of the electron-hole kernel poses significant computational challenges for scalability. Here, we develop a data-driven low-rank approximation for the electron-hole kernel, leveraging localized excitonic effects in the Hilbert space of crystalline systems. Through singular value decomposition (SVD) analysis, we show that the subspace of non-zero singular values, containing the key information of the electron-hole kernel, retains a small size even as the k-grid grows, ensuring computational feasibility with extremely dense k-grids for converged calculations. Utilizing this low-rank property, we achieve at least 95% compression of the kernel and an order-of-magnitude speedup of TD-aGW calculations. Our method, rooted in physical interpretability, outperforms existing machine learning approaches by avoiding intensive training processes and eliminating time-accumulated errors, providing a general framework for high-throughput, nonequilibrium simulation of light-driven dynamics in materials. △ Less

Submitted 8 February, 2025; originally announced February 2025.

Comments: 14 pages, 8 figures

Polarization-Analyzed Small-Angle Neutron Scattering with an $\textit{in-situ}$ $^{3}$He neutron spin filter at the China Spallation Neutron Source

Authors: Long Tian, Han Gao, Tianhao Wang, Haiyun Teng, Jian Tang, Qingbo Zheng, Taisen Zuo, Tengfei Cui, Bin Wang, Xu Qin, Yongxiang Qiu, Yuchen Dong, Yujie Zheng, Zecong Qin, Zehua Han, Junpei Zhang, He Cheng, Xin Tong

Abstract: Polarization-analyzed small-angle neutron scattering (PASANS) is an advanced technique that enables the selective investigation of magnetic scattering phenomena in magnetic materials and distinguishes coherent scattering obscured by incoherent backgrounds, making it particularly valuable for cutting-edge research. The successful implementation of PASANS in China was achieved for the first time at… ▽ More Polarization-analyzed small-angle neutron scattering (PASANS) is an advanced technique that enables the selective investigation of magnetic scattering phenomena in magnetic materials and distinguishes coherent scattering obscured by incoherent backgrounds, making it particularly valuable for cutting-edge research. The successful implementation of PASANS in China was achieved for the first time at the newly commissioned Very Small Angle Neutron Scattering (VSANS) instrument at the China Spallation Neutron Source (CSNS). This technique employs a combination of a double-V cavity supermirror polarizer and a radio frequency (RF) neutron spin flipper to manipulate the polarization of the incident neutrons. The scattered neutron polarization is stably analyzed by a specially designed $\textit{in-situ}$ optical pumping $^{3}$He neutron spin filter, which covers a spatially symmetric scattering angle coverage of about 4.8 $^{\circ}$. A comprehensive PASANS data reduction method, aimed at pulsed neutron beams, has been established and validated with a silver behenate powder sample, indicating a maximum momentum transfer coverage of approximately 0.25 Å $^{-1}$. △ Less

Submitted 23 January, 2025; originally announced January 2025.

A Light-Emitting-Diodes-Integrated Silicon Carbide Insulated Gate Bipolar Transistor

Authors: Guoliang Zhang, Zhanwei Shen, Yujian Chen, Yufeng Qiu, Feng Zhang, Rong Zhang

Abstract: A light-emitting-diodes (LEDs)-integrated silicon carbide (SiC) insulated gate bipolar transistors (LI-IGBT) is proposed in this paper. The novelty of the LI-IGBT depends on the photogeneration effect of III-nitride LEDs embedded in the poly-Si regions of IGBT. Then, the photogenerated carriers are formed in the JFET region and the drift layer, indicating the increase of the conductivity in LI-IGB… ▽ More A light-emitting-diodes (LEDs)-integrated silicon carbide (SiC) insulated gate bipolar transistors (LI-IGBT) is proposed in this paper. The novelty of the LI-IGBT depends on the photogeneration effect of III-nitride LEDs embedded in the poly-Si regions of IGBT. Then, the photogenerated carriers are formed in the JFET region and the drift layer, indicating the increase of the conductivity in LI-IGBT as compared with the SiC IGBT with hole-barrier layer (H-IGBT) and the SiC IGBT with charge storage layer (CSL-IGBT). The static simulation results show that the electron density of the LI-IGBT at the middle of the drift layer is separately 17.44 times and 15.81 times higher than those of the H-IGBT and CSL-IGBT, yielding 40.91% and 37.38% reduction of forward voltage drop, respectively, and also, the LI-IGBT shows 304.59% and 263.67% improvements in BFOM as compared with CSL-IGBT and H-IGBT, respectively. For the dynamic simulation in one cycle, the loss of LI-IGBT is separately reduced by 6.57% and 8.57% compared to H-IGBT and CSL-IGBT. Meanwhile, the relationship between VC(sat) and Eturn-off can be optimized by adjusting collector doping and minority carrier lifetime. These results reveal that the proposed SiC IGBT will be more suitable for ultra-high voltage application. △ Less

Submitted 2 December, 2024; originally announced December 2024.

Comments: 9 pages, 17 figures

Acousto-optic modulation based on an AlScN microring resonator for microwave-to-optical conversion

Authors: Kewei Bian, Yushuai Liu, Weilin Rong, Yuan Dong, Qize Zhong, Yang Qiu, Xingyan Zhao, Tao Wu, Shaonan Zheng, Ting Hu

Abstract: Acoustic-optic (AO) modulation is critical for microwave and optical signal processing, computing and networking. Challenges remain to integrate AO devices on-chip using fabrication process compatible with complementary metal-oxide-semiconductor (CMOS) technology. This work presents the demonstration of an AO modulator exploiting a microring resonator (MRR) based on thin-film aluminum scandium nit… ▽ More Acoustic-optic (AO) modulation is critical for microwave and optical signal processing, computing and networking. Challenges remain to integrate AO devices on-chip using fabrication process compatible with complementary metal-oxide-semiconductor (CMOS) technology. This work presents the demonstration of an AO modulator exploiting a microring resonator (MRR) based on thin-film aluminum scandium nitride (AlScN) photonic platform. Leveraging the high piezoelectric properties of AlScN, an MRR is employed with interdigital transducer (IDT) inside to couple microwave signals into acoustic resonant modes, enabling efficient by-directional optical modulation in the MRR. The fabricated MRR exhibits an optical loaded quality factor (Q) of 1.8*e4 at the optical L-band for the TE00 mode. A low effective half-wave voltage Vpi of 1.21 V is achieved, corresponding to a VpiL of 0.0242 Vcm, along with an optomechanical single-photon coupling strength g0 of 0.43 kHz between the 2.11 GHz acoustic mode and the TE00 optical mode. The device shows potential for applications in microwave photonics. △ Less

Submitted 23 November, 2024; originally announced November 2024.

Comments: 11 pages, 5 figures

Optical absorption spectroscopy probes water wire and its ordering in a hydrogen-bond network

Authors: Fujie Tang, Diana Y. Qiu, Xifan Wu

Abstract: Water wires, quasi-one-dimensional chains composed of hydrogen-bonded (H-bonded) water molecules, play a fundamental role in numerous chemical, physical, and physiological processes. Yet direct experimental detection of water wires has been elusive so far. Based on advanced $ab$ $initio$ many-body theory that includes electron-hole interactions, we report that optical absorption spectroscopy can s… ▽ More Water wires, quasi-one-dimensional chains composed of hydrogen-bonded (H-bonded) water molecules, play a fundamental role in numerous chemical, physical, and physiological processes. Yet direct experimental detection of water wires has been elusive so far. Based on advanced $ab$ $initio$ many-body theory that includes electron-hole interactions, we report that optical absorption spectroscopy can serve as a sensitive probe of water wires and their ordering. In both liquid and solid water, the main peak of the spectrum is discovered to be a charge transfer exciton. In water, the charge transfer exciton is strongly coupled to the H-bonding environment where the exciton is excited between H-bonded water molecules with a large spectral intensity. In regular ice, the spectral weight of the charge transfer exciton is enhanced by a collective excitation occurring on proton-ordered water wires, whose spectral intensity scales with the ordering length of water wire. The spectral intensity and excitonic interaction strength reaches its maximum in ice XI, where the long-range ordering length yields the most pronounced spectral signal. Our findings suggest that water wires, which widely exist in important physiological and biological systems and other phases of ice, can be directly probed by this approach. △ Less

Submitted 23 November, 2024; originally announced November 2024.

Comments: 8 pages, 5 figures, with 8 pages Supplemental Materials

Journal ref: Phys. Rev. X 15, 011048 (2025)

Leadsee-Precip: A Deep Learning Diagnostic Model for Precipitation

Authors: Weiwen Ji, Jin Feng, Yueqi Liu, Yulu Qiu, Hua Gao

Abstract: Recently, deep-learning weather forecasting models have surpassed traditional numerical models in terms of the accuracy of meteorological variables. However, there is considerable potential for improvements in precipitation forecasts, especially for heavy precipitation events. To address this deficiency, we propose Leadsee-Precip, a global deep learning model to generate precipitation from meteoro… ▽ More Recently, deep-learning weather forecasting models have surpassed traditional numerical models in terms of the accuracy of meteorological variables. However, there is considerable potential for improvements in precipitation forecasts, especially for heavy precipitation events. To address this deficiency, we propose Leadsee-Precip, a global deep learning model to generate precipitation from meteorological circulation fields. The model utilizes an information balance scheme to tackle the challenges of predicting heavy precipitation caused by the long-tail distribution of precipitation data. Additionally, more accurate satellite and radar-based precipitation retrievals are used as training targets. Compared to artificial intelligence global weather models, the heavy precipitation from Leadsee-Precip is more consistent with observations and shows competitive performance against global numerical weather prediction models. Leadsee-Precip can be integrated with any global circulation model to generate precipitation forecasts. But the deviations between the predicted and the ground-truth circulation fields may lead to a weakened precipitation forecast, which could potentially be mitigated by further fine-tuning based on the predicted circulation fields. △ Less

Submitted 19 November, 2024; originally announced November 2024.

Cumulenic sp-carbon Atomic Wires Wrapped Polymers for Supercapacitor Application

Authors: Subrata Ghosh, Massimiliano Righi, Simone Melesi, Yu Qiu, Rik R. Tykwinski, Carlo S. Casari

Abstract: Carbon atomic wires, a linear atomic chain of sp-carbon, is theoretically predicted to have around five times higher surface area than graphene, notable charge mobilities, as well as excellent optical and thermal properties. Despite these impressive properties, the properties of sp-carbon as an electrochemical energy-storage electrode have not been reported so far. Herein, we prepare solution proc… ▽ More Carbon atomic wires, a linear atomic chain of sp-carbon, is theoretically predicted to have around five times higher surface area than graphene, notable charge mobilities, as well as excellent optical and thermal properties. Despite these impressive properties, the properties of sp-carbon as an electrochemical energy-storage electrode have not been reported so far. Herein, we prepare solution processed thin films of tetraphenyl[3]cumulenic sp-carbon atomic wires embedded in a polymer matrix, in which sp-carbon atomic wires feature three cumulated carbon-carbon double bonds terminated at each end by two phenyl groups. Raman and UV-visible spectroscopy are used to confirm the presence and possible degradation of sp-carbons inside the polymeric matrix. Finally, we investigate the supercapacitor performance of cumulenic sp-carbon atomic wires embedded polymer in three aqueous mediums, namely 1M Na2SO4 (neutral), 1M H2SO4 (acidic), and 6M KOH (basic). The results suggest 6M KOH is the best electrolyte to obtain high charge-storage performance of device with areal capacitance of 2.4 mF/cm2 at 20 mV/s, 85% cycle stability after 10000 charge-discharge cycles, and excellent frequency response. △ Less

Submitted 30 October, 2024; originally announced October 2024.

Comments: 15 pages, 2 supplementary pages, 5 figures, 2 supporting figures

Journal ref: Carbon 2025

Detection of Nanopores with the Scanning Ion Conductance Microscopy: A Simulation Study

Authors: Yinghua Qiu, Long Ma, Zhe Liu, Hongwen Zhang, Bowen Ai, Xinman Tu

Abstract: During the dielectric breakdown process of thin solid-state nanopores, the application of high voltages may cause the formation of multi-nanopores on one chip, which number and sizes are important for their applications. Here, simulations were conducted to mimic the investigation of in situ nanopore detection with scanning ion conductance microscopy (SICM). Results show that SICM can provide accur… ▽ More During the dielectric breakdown process of thin solid-state nanopores, the application of high voltages may cause the formation of multi-nanopores on one chip, which number and sizes are important for their applications. Here, simulations were conducted to mimic the investigation of in situ nanopore detection with scanning ion conductance microscopy (SICM). Results show that SICM can provide accurate nanopore location and relative pore size. Detection resolution is influenced by the dimensions of the applied probe and separation between the probe and membranes, which can be enhanced under large voltages or a concentration gradient. △ Less

Submitted 27 October, 2024; originally announced October 2024.

Comments: 22 pages, 6 figuers

Journal ref: Chemical Physics Letters, 2024, 856: 141668

Ionic Selectivity of Nanopores: Comparison among Cases under the Hydrostatic Pressure, Electric Field, and Concentration Gradient

Authors: Chao Zhang, Mengnan Guo, Hongwen Zhang, Xiuhua Ren, Yinghao Gao, Yinghua Qiu

Abstract: The ionic selectivity of nanopores is crucial for the energy conversion based on nanoporous membranes. It can be significantly affected by various parameters of nanopores and the applied fields driving ions through porous membranes. Here, with finite element simulations, the selective transport of ions through nanopores is systematically investigated under three common fields, i.e. the electric fi… ▽ More The ionic selectivity of nanopores is crucial for the energy conversion based on nanoporous membranes. It can be significantly affected by various parameters of nanopores and the applied fields driving ions through porous membranes. Here, with finite element simulations, the selective transport of ions through nanopores is systematically investigated under three common fields, i.e. the electric field (V), hydrostatic pressure (p), and concentration gradient (C). For negatively charged nanopores, through the quantitative comparison of the cation selectivity (t+) under the three fields, the cation selectivity of nanopores follows the order of t+V > t+c > t+p. This is due to the transport characteristics of cations and anions through the nanopores. Because of the strong transport of counterions in electric double layers under electric fields and concentration gradients, the nanopore exhibits a relatively higher selectivity to counterions. We also explored the modulation of t+ on the properties of nanopores and solutions. Under all three fields, t+ is directly proportional to the pore length and surface charge density, and inversely correlated to the pore diameter and salt concentration. Under both the electric field and hydrostatic pressure, t+ has almost no dependence on the applied field strength or ion species, which can affect t+ in the case of the concentration gradient. Our results provide detailed insights into the comparison and regulation of ionic selectivity of nanopores under three fields which can be useful for the design of high-performance devices for energy conversion based on nanoporous membranes. △ Less

Submitted 27 October, 2024; originally announced October 2024.

Comments: 28 pages, 5 figures

Journal ref: Journal of Molecular Liquids, 2024, 414: 126190

Modulation of ionic current rectification in short bipolar nanopores

Authors: Hongwen Zhang, Long Ma, Chao Zhang, Yinghua Qiu

Abstract: Bipolar nanopores, with asymmetric charge distributions, can induce significant ionic current rectification (ICR) at ultra-short lengths, finding potential applications in nanofluidic devices, energy conversion, and other related fields. Here, with simulations, we investigated the characteristics of ion transport and modulation of ICR inside bipolar nanopores. With bipolar nanopores of half-positi… ▽ More Bipolar nanopores, with asymmetric charge distributions, can induce significant ionic current rectification (ICR) at ultra-short lengths, finding potential applications in nanofluidic devices, energy conversion, and other related fields. Here, with simulations, we investigated the characteristics of ion transport and modulation of ICR inside bipolar nanopores. With bipolar nanopores of half-positive and half-negative surfaces, the most significant ICR phenomenon appears at various concentrations. In these cases, ICR ratios are independent of electrolyte types. In other cases where nanopores have oppositely charged surfaces in different lengths, ICR ratios are related to the mobility of anions and cations. The pore length and surface charge density can enhance ICR. As the pore length increases, ICR ratios first increase and then approach their saturation which is determined by the surface charge density. External surface charges of nanopores can promote the ICR phenomenon mainly due to the enhancement of ion enrichment inside nanopores by external surface conductance. The effective width of exterior charged surfaces under various conditions is also explored, which is inversely proportional to the pore length and salt concentration, and linearly related to the pore diameter, surface charge density, and applied voltage. Our results may provide guidance for the design of bipolar porous membranes. △ Less

Submitted 27 October, 2024; originally announced October 2024.

Comments: 31 pages, 7 figures

Journal ref: Langmuir, 2024, 40 (41): 21866-21875

Generalized Flow Matching for Transition Dynamics Modeling

Authors: Haibo Wang, Yuxuan Qiu, Yanze Wang, Rob Brekelmans, Yuanqi Du

Abstract: Simulating transition dynamics between metastable states is a fundamental challenge in dynamical systems and stochastic processes with wide real-world applications in understanding protein folding, chemical reactions and neural activities. However, the computational challenge often lies on sampling exponentially many paths in which only a small fraction ends in the target metastable state due to e… ▽ More Simulating transition dynamics between metastable states is a fundamental challenge in dynamical systems and stochastic processes with wide real-world applications in understanding protein folding, chemical reactions and neural activities. However, the computational challenge often lies on sampling exponentially many paths in which only a small fraction ends in the target metastable state due to existence of high energy barriers. To amortize the cost, we propose a data-driven approach to warm-up the simulation by learning nonlinear interpolations from local dynamics. Specifically, we infer a potential energy function from local dynamics data. To find plausible paths between two metastable states, we formulate a generalized flow matching framework that learns a vector field to sample propable paths between the two marginal densities under the learned energy function. Furthermore, we iteratively refine the model by assigning importance weights to the sampled paths and buffering more likely paths for training. We validate the effectiveness of the proposed method to sample probable paths on both synthetic and real-world molecular systems. △ Less

Submitted 19 October, 2024; originally announced October 2024.

Dynamic Response of Ionic Current in Conical Nanopores

Authors: Zhe Liu, Long Ma, Hongwen Zhang, Jiakun Zhuang, Jia Man, Zuzanna S. Siwy, Yinghua Qiu

Abstract: Ionic current rectification (ICR) of charged conical nanopores has various applications in fields including nanofluidics, bio-sensing, and energy conversion, whose function is closely related to the dynamic response of nanopores. The occurrence of ICR originates from the ion enrichment and depletion in conical pores, whose formation is found to be affected by the scanning rate of voltages. Here, t… ▽ More Ionic current rectification (ICR) of charged conical nanopores has various applications in fields including nanofluidics, bio-sensing, and energy conversion, whose function is closely related to the dynamic response of nanopores. The occurrence of ICR originates from the ion enrichment and depletion in conical pores, whose formation is found to be affected by the scanning rate of voltages. Here, through time-dependent simulations, we investigate the variation of ion current under electric fields and the dynamic formation of ion enrichment and depletion, which can reflect the response time of conical nanopores. The response time of nanopores when ion enrichment forms i.e. at the on state is significantly longer than that with the formation of ion depletion i.e. at the off state. Our simulation results reveal the regulation of response time by different nanopore parameters including the surface charge density, pore length, tip, and base radius, as well as the applied conditions such as the voltage and bulk concentration. The response time of nanopores is closely related to the surface charge density, pore length, voltage, and bulk concentration. Our uncovered dynamic response mechanism of the ionic current can guide the design of nanofluidic devices with conical nanopores, including memristors, ionic switches, and rectifiers. △ Less

Submitted 21 June, 2024; originally announced June 2024.

Comments: 30 pages, 5 figures

Journal ref: ACS Appl. Mater. Interfaces 2024, 16 (23), 30496-30505

Resolving the Orientations of and Angular Separation between a Pair of Dipole Emitters

Authors: Yiyang Chen, Yuanxin Qiu, Matthew D. Lew

Abstract: We prove that it is impossible to distinguish two spatially coinciding fluorescent molecules from a single rotating molecule using polarization-sensitive imaging, even if one modulates the polarization of the illumination or the detection dipole-spread function (DSF). If the target is known to be a dipole pair, existing imaging methods perform poorly for measuring their angular separation. We prop… ▽ More We prove that it is impossible to distinguish two spatially coinciding fluorescent molecules from a single rotating molecule using polarization-sensitive imaging, even if one modulates the polarization of the illumination or the detection dipole-spread function (DSF). If the target is known to be a dipole pair, existing imaging methods perform poorly for measuring their angular separation. We propose simultaneously modulating the excitation polarization and DSF, which demonstrates robust discrimination between dipole pairs versus single molecules. Our method improves the precision of measuring centroid orientation by 50% and angular separation by 2- to 4-fold over existing techniques. △ Less

Submitted 29 January, 2025; v1 submitted 6 June, 2024; originally announced June 2024.

Comments: 6 pages, 4 figures

Journal ref: Phys. Rev. Lett. 134, 093805 (2025)

Silicon-integrated scandium-doped aluminum nitride electro-optic modulator

Authors: Tianqi Xu, Yushuai Liu, Yuanmao Pu, Yongxiang Yang, Qize Zhong, Xingyan Zhao, Yang Qiu, Yuan Dong, Tao Wu, Shaonan Zheng, Ting Hu

Abstract: Scandium-doped aluminum nitride (AlScN) with an asymmetric hexagonal wurtzite structure exhibits enhanced second-order nonlinear and piezoelectric properties compared to aluminum nitride (AlN), while maintaining a relatively large bandgap. It provides a promising platform for photonic integration and facilitates the seamless integration of passive and active functional devices. Here, we present th… ▽ More Scandium-doped aluminum nitride (AlScN) with an asymmetric hexagonal wurtzite structure exhibits enhanced second-order nonlinear and piezoelectric properties compared to aluminum nitride (AlN), while maintaining a relatively large bandgap. It provides a promising platform for photonic integration and facilitates the seamless integration of passive and active functional devices. Here, we present the design, fabrication, and characterization of AlScN EO micro-ring modulators, introducing active functionalities to the chip-scale AlScN platform. These waveguide-integrated EO modulators employ sputtered AlScN thin films as the light-guiding medium, and the entire fabrication process is compatible with complementary metal oxide semiconductor (CMOS) technology. We characterize the high-frequency performance of an AlScN modulator for the first time, extracting a maximum in-device effective EO coefficient of 2.86 pm/V at 12 GHz. The devices show a minimum half-wave voltage-length product of 3.12 V*cm and a 3-dB modulation bandwidth of approximately 22 GHz. Our work provides a promising modulation scheme for cost-effective silicon-integrated photonics systems. △ Less

Submitted 28 May, 2024; originally announced May 2024.

Coarse-graining conformational dynamics with multi-dimensional generalized Langevin equation: how, when, and why

Authors: Pinchen Xie, Yunrui Qiu, Weinan E

Abstract: A data-driven ab initio generalized Langevin equation (AIGLE) approach is developed to learn and simulate high-dimensional, heterogeneous, coarse-grained conformational dynamics. Constrained by the fluctuation-dissipation theorem, the approach can build coarse-grained models in dynamical consistency with all-atom molecular dynamics. We also propose practical criteria for AIGLE to enforce long-term… ▽ More A data-driven ab initio generalized Langevin equation (AIGLE) approach is developed to learn and simulate high-dimensional, heterogeneous, coarse-grained conformational dynamics. Constrained by the fluctuation-dissipation theorem, the approach can build coarse-grained models in dynamical consistency with all-atom molecular dynamics. We also propose practical criteria for AIGLE to enforce long-term dynamical consistency. Case studies of a toy polymer, with 20 coarse-grained sites, and the alanine dipeptide, with two dihedral angles, elucidate why one should adopt AIGLE or its Markovian limit for modeling coarse-grained conformational dynamics in practice. △ Less

Submitted 20 May, 2024; originally announced May 2024.

Current progress in corrosion of multi principal element alloys

Authors: M. Ghorbani, Z. Li, Y. Qiu, P. Marcus, J. R. Scully, O. Gharbi, H. Luo, R. K. Gupta, Z. R. Zeng, H. L. Fraser, M. L. Taheri, N. Birbilis

Abstract: Whilst multi-principal element alloys (MPEAs) remain a promising class of materials owing to several attractive mechanical properties, their corrosion performance is also unique. In this concise review, we present an emerging overview of some of the general features related to MPEA corrosion, following a decade of work in the field. This includes highlighting some of the key aspects related to the… ▽ More Whilst multi-principal element alloys (MPEAs) remain a promising class of materials owing to several attractive mechanical properties, their corrosion performance is also unique. In this concise review, we present an emerging overview of some of the general features related to MPEA corrosion, following a decade of work in the field. This includes highlighting some of the key aspects related to the electrochemical phenomena in MPEA corrosion, and the relevant future works required for a holistic mechanistic understanding. In addition, a comprehensive database of the reported corrosion performance of MPEAs is presented, based on works reported to date. The database is assembled to also allow users to undertake machine learning or their own data analysis, with a parsed representation of alloy composition, test electrolyte, and corrosion related parameters. △ Less

Submitted 9 May, 2024; originally announced May 2024.

Design, analysis, and manufacturing of a glass-plastic hybrid minimalist aspheric panoramic annular lens

Authors: Shaohua Gao, Qi Jiang, Yiqi Liao, Yi Qiu, Wanglei Ying, Kailun Yang, Kaiwei Wang, Benhao Zhang, Jian Bai

Abstract: We propose a high-performance glass-plastic hybrid minimalist aspheric panoramic annular lens (ASPAL) to solve several major limitations of the traditional panoramic annular lens (PAL), such as large size, high weight, and complex system. The field of view (FoV) of the ASPAL is 360°x(35°~110°) and the imaging quality is close to the diffraction limit. This large FoV ASPAL is composed of only 4 len… ▽ More We propose a high-performance glass-plastic hybrid minimalist aspheric panoramic annular lens (ASPAL) to solve several major limitations of the traditional panoramic annular lens (PAL), such as large size, high weight, and complex system. The field of view (FoV) of the ASPAL is 360°x(35°~110°) and the imaging quality is close to the diffraction limit. This large FoV ASPAL is composed of only 4 lenses. Moreover, we establish a physical structure model of PAL using the ray tracing method and study the influence of its physical parameters on compactness ratio. In addition, for the evaluation of local tolerances of annular surfaces, we propose a tolerance analysis method suitable for ASPAL. This analytical method can effectively analyze surface irregularities on annular surfaces and provide clear guidance on manufacturing tolerances for ASPAL. Benefiting from high-precision glass molding and injection molding aspheric lens manufacturing techniques, we finally manufactured 20 ASPALs in small batches. The weight of an ASPAL prototype is only 8.5 g. Our framework provides promising insights for the application of panoramic systems in space and weight-constrained environmental sensing scenarios such as intelligent security, micro-UAVs, and micro-robots. △ Less

Submitted 5 May, 2024; originally announced May 2024.

Comments: Accepted to Optics & Laser Technology

Unsupervised Learning of Individual Kohn-Sham States: Interpretable Representations and Consequences for Downstream Predictions of Many-Body Effects

Authors: Bowen Hou, Jinyuan Wu, Diana Y. Qiu

Abstract: Representation learning for the electronic structure problem is a major challenge of machine learning in computational condensed matter and materials physics. Within quantum mechanical first principles approaches, Kohn-Sham density functional theory (DFT) is the preeminent tool for understanding electronic structure, and the high-dimensional wavefunctions calculated in this approach serve as the b… ▽ More Representation learning for the electronic structure problem is a major challenge of machine learning in computational condensed matter and materials physics. Within quantum mechanical first principles approaches, Kohn-Sham density functional theory (DFT) is the preeminent tool for understanding electronic structure, and the high-dimensional wavefunctions calculated in this approach serve as the building block for downstream calculations of correlated many-body excitations and related physical observables. Here, we use variational autoencoders (VAE) for the unsupervised learning of high-dimensional DFT wavefunctions and show that these wavefunctions lie in a low-dimensional manifold within the latent space. Our model autonomously determines the optimal representation of the electronic structure, avoiding limitations due to manual feature engineering and selection in prior work. To demonstrate the utility of the latent space representation of the DFT wavefunction, we use it for the supervised training of neural networks (NN) for downstream prediction of the quasiparticle bandstructures within the GW formalism, which includes many-electron correlations beyond DFT. The GW prediction achieves a low error of 0.11 eV for a combined test set of metals and semiconductors drawn from the Computational 2D Materials Database (C2DB), suggesting that latent space representation captures key physical information from the original data. Finally, we explore the interpretability of the VAE representation and show that the successful representation learning and downstream prediction by our model is derived from the smoothness of the VAE latent space, which also enables the generation of wavefunctions on arbitrary points in latent space. Our work provides a novel and general machine-learning framework for investigating electronic structure and many-body physics. △ Less

Submitted 22 April, 2024; originally announced April 2024.

An Information Bottleneck Approach for Markov Model Construction

Authors: Dedi Wang, Yunrui Qiu, Eric Beyerle, Xuhui Huang, Pratyush Tiwary

Abstract: Markov state models (MSMs) are valuable for studying dynamics of protein conformational changes via statistical analysis of molecular dynamics (MD) simulations. In MSMs, the complex configuration space is coarse-grained into conformational states, with the dynamics modeled by a series of Markovian transitions among these states at discrete lag times. Constructing the Markovian model at a specific… ▽ More Markov state models (MSMs) are valuable for studying dynamics of protein conformational changes via statistical analysis of molecular dynamics (MD) simulations. In MSMs, the complex configuration space is coarse-grained into conformational states, with the dynamics modeled by a series of Markovian transitions among these states at discrete lag times. Constructing the Markovian model at a specific lag time requires state defined without significant internal energy barriers, enabling internal dynamics relaxation within the lag time. This process coarse grains time and space, integrating out rapid motions within metastable states. This work introduces a continuous embedding approach for molecular conformations using the state predictive information bottleneck (SPIB), which unifies dimensionality reduction and state space partitioning via a continuous, machine learned basis set. Without explicit optimization of VAMP-based scores, SPIB demonstrates state-of-the-art performance in identifying slow dynamical processes and constructing predictive multi-resolution Markovian models. When applied to mini-proteins trajectories, SPIB showcases unique advantages compared to competing methods. It automatically adjusts the number of metastable states based on a specified minimal time resolution, eliminating the need for manual tuning. While maintaining efficacy in dynamical properties, SPIB excels in accurately distinguishing metastable states and capturing numerous well-populated macrostates. Furthermore, SPIB's ability to learn a low-dimensional continuous embedding of the underlying MSMs enhances the interpretation of dynamic pathways. Accordingly, we propose SPIB as an easy-to-implement methodology for end-to-end MSM construction. △ Less

Submitted 10 June, 2024; v1 submitted 3 April, 2024; originally announced April 2024.

Comments: 19 pages, 7 figures

Low-cost and Convenient Fabrication of Polymer Micro/Nanopores with the Needle Punching Process and Their Applications in Nanofluidic Sensing

Authors: Rui Liu, Zhe Liu, Jianfeng Li, Yinghua Qiu

Abstract: Solid-state micro/nanopores play an important role in the sensing field because of their high stability and controllable size. Aiming at problems of complex processes and high costs in pore manufacturing, we propose a convenient and low-cost micro/nanopore fabrication technique based on the needle punching method. The thin film is pierced by controlling the feed of a microscale tungsten needle, an… ▽ More Solid-state micro/nanopores play an important role in the sensing field because of their high stability and controllable size. Aiming at problems of complex processes and high costs in pore manufacturing, we propose a convenient and low-cost micro/nanopore fabrication technique based on the needle punching method. The thin film is pierced by controlling the feed of a microscale tungsten needle, and the size variations of the micropore are monitored by the current feedback system. Based on the positive correlation between the micropore size and the current threshold, the size-controllable preparation of micropores is achieved. The preparation of nanopores is realized by the combination of needle punching and chemical etching. Firstly, a conical defect is prepared on the film with the tungsten needle. Then, nanopores are obtained by unilateral chemical etching of the film. Using the prepared conical micropores resistive-pulse detection of nanoparticles is performed. Significant ionic current rectification is also obtained with our conical nanopores. It is proved that the properties of micro/nanopores prepared by our method are comparable to those prepared by the track-etching method. The simple and controllable fabrication process proposed here will advance the development of low-cost micro/nanopore sensors. △ Less

Submitted 15 March, 2024; originally announced March 2024.

Comments: 27 pages, 6 figures

Journal ref: Biomicrofluidics 2024, 18 (2), 024103

Improved theoretical prediction of nanoparticle sizes with the resistive-pulse technique

Authors: Zihao Gao, Long Ma, Zhe Liu, Jun Huang, Hanlian Liu, Chuanzhen Huang, Yinghua Qiu

Abstract: With the resistive-pulse technique (RPT), nanopores serve as the nanofluidic sensors of various analytes for their many physical and chemical properties. Here, we focus on the size measurement and its theoretical prediction for sub-200 nm nanoparticles with RPT. Through systematical investigation of the current blockade of nanoparticles across cylindrical nanopores with simulations, Maxwell method… ▽ More With the resistive-pulse technique (RPT), nanopores serve as the nanofluidic sensors of various analytes for their many physical and chemical properties. Here, we focus on the size measurement and its theoretical prediction for sub-200 nm nanoparticles with RPT. Through systematical investigation of the current blockade of nanoparticles across cylindrical nanopores with simulations, Maxwell method considering the shape coefficient and access resistances agrees well with simulation results. However, the widely used integration method of the resistance has distinct deviations in various cases. With the introduction of a correction factor \b{eta} to the integration method, our revised equations can provide good predictions for simulation results. \b{eta} shows a strong dependence on the diameter ratio (d over D) of the nanoparticle and nanopore. Following the same strategy, modified equations are provided for the accurate size prediction for nanoparticles across conical nanopores, where the integration method is the default convenient way. The correction factor \b{eta}' relates to \b{eta} in cylindrical nanopores. \b{eta}' exhibits independence on the pore geometry parameters and diameters of nanoparticles, but dependence on the surface charge density of conical nanopores. Our improved equations can provide theoretical predictions for the accurate size detection of 100-200 nm diameter nanoparticles across cylindrical and conical nanopores. △ Less

Submitted 6 March, 2024; originally announced March 2024.

Comments: 29 pages 7 figures

Journal ref: Physics of Fluids 36, 032011 (2024)

Ion Transport through Short Nanopores Modulated by Charged Exterior Surfaces

Authors: Long Ma, Zhe Liu, Bowen Ai, Jia Man, Jianyong Li, Kechen Wu, Yinghua Qiu

Abstract: Short nanopores find extensive applications capitalizing on their high throughput and detection resolution. Ionic behaviors through long nanopores are mainly determined by charged inner-pore walls. When pore lengths decrease to sub-200 nm, charged exterior surfaces provide considerable modulation to ion current. We find that the charge status of inner-pore walls affects the modulation of ion curre… ▽ More Short nanopores find extensive applications capitalizing on their high throughput and detection resolution. Ionic behaviors through long nanopores are mainly determined by charged inner-pore walls. When pore lengths decrease to sub-200 nm, charged exterior surfaces provide considerable modulation to ion current. We find that the charge status of inner-pore walls affects the modulation of ion current from charged exterior surfaces. For 50-nm-long nanopores with neutral inner-pore walls, charged exterior surfaces on the voltage (surfaceV) and ground (surfaceG) sides enhance and inhibit ion transport by forming ion enrichment and depletion zones inside nanopores, respectively. For nanopores with both charged inner-pore and exterior surfaces, continuous electric double layers enhance ion transport through nanopores significantly. The charged surfaceV results in higher ion current by simultaneously weakening ion depletion at pore entrances and enhancing the intra-pore ion enrichment. The charged surfaceG expedites the exit of ions from nanopores, resulting in a decrease in ion enrichment at pore exits. Through adjustment in the width of charged-ring regions near pore boundaries, the effective charged width of the charged exterior is explored at ~20nm. Our results may provide a theoretical guide for further optimizing the performance of nanopore-based applications, like seawater desalination, biosensing, and osmotic energy conversion. △ Less

Submitted 15 February, 2024; originally announced February 2024.

Comments: 18 pages, 5 figures

Journal ref: J. Chem. Phys. 160, 074701 (2024)

Modulation Mechanism of Ionic Transport through Short Nanopores by Charged Exterior Surfaces

Authors: Long Ma, Zhe Liu, Jia Man, Jianyong Li, Zuzanna S. Siwy, Yinghua Qiu

Abstract: Short nanopores have various applications in biosensing, desalination, and energy conversion. Here, the modulation of charged exterior surfaces on ionic transport is investigated through simulations with sub-200 nm long nanopores under applied voltages. Detailed analysis of ionic current, electric field strength, and fluid flow inside and outside nanopores reveals that charged exterior surfaces ca… ▽ More Short nanopores have various applications in biosensing, desalination, and energy conversion. Here, the modulation of charged exterior surfaces on ionic transport is investigated through simulations with sub-200 nm long nanopores under applied voltages. Detailed analysis of ionic current, electric field strength, and fluid flow inside and outside nanopores reveals that charged exterior surfaces can increase ionic conductance by increasing both the concentration and migration speed of charge carriers. The electric double layers near charged exterior surfaces provide an ion pool and an additional passageway for counterions, which lead to enhanced exterior surface conductance and ionic concentrations at pore entrances and inside the nanopore. We also report that charges on the membrane surfaces increase electric field strengths inside nanopores. The effective width of a ring with surface charges placed at pore entrances (Lcs) is considered as well by studying the dependence of the current on Lcs. We find a linear relationship between the effective Lcs and the surface charge density and voltage, and an inverse relationship between the geometrical pore length and salt concentration. Our results elucidate the modulation mechanism of charged exterior surfaces on ionic transport through short nanopores, which is important for the design and fabrication of porous membranes. △ Less

Submitted 7 February, 2024; originally announced February 2024.

Comments: 27 pages, 6 figures

Journal ref: Nanoscale 2023, 15 (46), 18696-18706

Influences of Electroosmotic Flow on Ionic Current through Nanopores: a Comprehensive Understanding

Authors: Yinghua Qiu, Long Ma

Abstract: Continuum simulations become an important tool to uncover the mysteries in nanofluidic experiments. However, fluid flow in simulation models is usually unconsidered. Here, systematical simulations are conducted to provide a quantitative understanding of influences from electroosmotic flow (EOF) on ionic transport through nanopores by both types of models with and without consideration of EOF. In n… ▽ More Continuum simulations become an important tool to uncover the mysteries in nanofluidic experiments. However, fluid flow in simulation models is usually unconsidered. Here, systematical simulations are conducted to provide a quantitative understanding of influences from electroosmotic flow (EOF) on ionic transport through nanopores by both types of models with and without consideration of EOF. In nanopores of less than ~10 nm in diameter, counterions dominate ionic current which is always promoted obviously by the convective effect of EOF. In the diameter range from ~10 to ~30 nm, strong EOF induces ion concentration polarization or ion depletion inside nanopores which causes significant decreases in ionic current. For nanopores larger than ~30 nm, due to convective promotion and inhibition of EOF on the transport of counterions and anions, considerable nanopore selectivity to counterions maintains in cases with EOF. Though the difference in total current between both cases decreases with further pore size increasing, the difference in cation/anion current is still considerable. From our results under various pore parameters and applied conditions, the fluid flow should be considered in the simulation cases when EOF is strong. Our work may provide useful guidance for simulation conductance. △ Less

Submitted 7 February, 2024; originally announced February 2024.

Comments: 25 pages, 7 figures

Journal ref: Phys. Fluids 2022, 34 (11), 112010

Influences of Divalent Ions in Natural Seawater/River Water on Nanofluidic Osmotic Energy Generation

Authors: Fenhong Song, Xuan An, Long Ma, Jiakun Zhuang, Yinghua Qiu

Abstract: Besides the dominant NaCl, natural seawater/river water contains trace multivalent ions, which can provide effective screening to surface charges. Here, in both negatively and positively charged nanopores, influences from divalent ions as counterions and coions have been investigated on the performance of osmotic energy conversion (OEC) under natural salt gradients. As counterions, trace Ca2+ ions… ▽ More Besides the dominant NaCl, natural seawater/river water contains trace multivalent ions, which can provide effective screening to surface charges. Here, in both negatively and positively charged nanopores, influences from divalent ions as counterions and coions have been investigated on the performance of osmotic energy conversion (OEC) under natural salt gradients. As counterions, trace Ca2+ ions can suppress the electric power and conversion efficiency significantly. The reduced OEC performance is due to the bivalence and low diffusion coefficient of Ca2 ions, instead of the uphill transport of divalent ions discovered in the previous work. Effectively screened charged surfaces by Ca2+ ions induce enhanced diffusion of Cl ions which simultaneously decreases the net ion penetration and ionic selectivity of the nanopore. While as coions, Ca2+ ions have weak effects on the OEC performance. The promotion from charged exterior surfaces on OEC processes for ultra-short nanopores is also studied, which effective region is ~200 nm in width beyond pore boundaries independent of the presence of Ca2+ ions. Our results shed light on the physical details of the nanofluidic OEC process under natural seawater/river water conditions, which can provide a useful guide for high-performance osmotic energy harvesting. △ Less

Submitted 7 February, 2024; originally announced February 2024.

Comments: 24 pages, 5 figures

Journal ref: Langmuir 2022, 38 (42), 12935-12943