Showing 1–21 of 21 results for author: Hao, W

Tuning Cu/Diamond Interfacial Thermal Conductance via Nitrogen-Termination Engineering

Authors: Guang Yang, Xinling Tang, Zhongkang Lin, Yulin Gu, Wei Hao, Yujie Du, Xiaoguang Wei

Abstract: Cu-diamond composites are recognized as promising high-thermal-conductivity candidates for electronic cooling, offering tunable properties and competitive cost. However, their performance is significantly limited by the poor Cu/diamond interfacial thermal conductance (ITC). Here, we propose a nitrogen-termination strategy to tune the ITC of Cu/diamond interfaces and unravel atomistic mechanisms by… ▽ More Cu-diamond composites are recognized as promising high-thermal-conductivity candidates for electronic cooling, offering tunable properties and competitive cost. However, their performance is significantly limited by the poor Cu/diamond interfacial thermal conductance (ITC). Here, we propose a nitrogen-termination strategy to tune the ITC of Cu/diamond interfaces and unravel atomistic mechanisms by which nitride interlayers tailor phonon transport. Based on the MACE machine-learning interatomic potential (MLIP) framework, we fine-tune the pre-trained MACE-MPA-0 foundation model by incorporating customized C-N-Cu training datasets. Through MLIP-driven lattice dynamics simulations, we demonstrate that an atomically flat N-termination on diamond enhances the ITC by 21% compared to the bare Cu/diamond interface. Mode-resolved phonon spectroscopy reveals that the LA phonons with frequency above 4 THz and wavevectors near Γ-X and Γ-U directions are selectively modulated by N-termination engineering. Analyses of local vibrational states and interfacial bonding further indicate that the N-termination on diamond tunes the interfacial heat conduction via surficial mass modification and bonding regulation, as evidenced by variations in LDOS overlap and COHP spectra. These findings open venues for tuning heat transfer across Cu/diamond interfaces via non-metallic modification, which avoids the graphitization issues associated with metallic coatings, and provide novel guidelines for upgrading the phonon-mediated heat transfer in Cu-diamond composites. △ Less

Submitted 17 March, 2026; originally announced March 2026.

Characterization of CMOS SPADs for future RICH Detectors

Authors: R. Dolenec, H. K. Yildirim, G. V. Tran, A. Domenech, B. C. Efe, W. Y. Ha, U. Karaca, P. Singh, G. G. Taylor, S. Korpar, P. Križan, R. Pestotnik, A. Seljak, E. Charbon, C. Bruschini

Abstract: In the planned or considered upgrades of LHCb, ALICE and Belle II experiments, the Ring imaging Cherenkov (RICH) detectors will have to be improved in order to function at increased beam interaction density. The photodetectors used in future RICH detector will have to provide high granularity, single photon sensitivity and excellent timing, while being exposed to a couple of 10$^{13}$ 1-MeV neutro… ▽ More In the planned or considered upgrades of LHCb, ALICE and Belle II experiments, the Ring imaging Cherenkov (RICH) detectors will have to be improved in order to function at increased beam interaction density. The photodetectors used in future RICH detector will have to provide high granularity, single photon sensitivity and excellent timing, while being exposed to a couple of 10$^{13}$ 1-MeV neutron equivalent/cm$^2$ of background irradiation during total experiment run time. The spadRICH project is developing a CMOS single-photon avalanche diode (SPAD) based photodetector specifically optimized for the application of the planned RICH detectors, which includes neutron radiation hardness and cryogenic operation. In this work we present recent experimental characterization studies of existing SPADs produced in 55 nm BCD and 110 nm CMOS image sensor technologies. Main results include dark count rate (DCR) measurements with SPADs irradiated up to 10$^{12}$ 1-MeV neutron equivalent/cm$^2$ and cooled down to liquid nitrogen temperature. △ Less

Submitted 27 February, 2026; originally announced February 2026.

Comments: 2 pages, 2 figures, submitted as abstract to NDIP New Developments in Photodetection 2026 conference

Photonic Neuromorphic Computing enabled by a BIC Metasurface

Authors: Jingsong Fu, Ruiheng Jin, Zhaohui Xie, Haijun Tang, Xiong Jiang, Yue Cui, Xiangtong Kong, Wentao Hao, Geyang Qu, Can Huang, Qingha Song

Abstract: Photonic neuromorphic computing promises revolutionary advances in parallel and high-speed processing, yet a key challenge persists: co-integrating nonlinearity, dense connectivity, and intrinsic memory monolithically to enable brain-inspired, spatiotemporal information processing. Here, we overcome this challenge by introducing a monolithic photonic recurrent network based on an active metasurfac… ▽ More Photonic neuromorphic computing promises revolutionary advances in parallel and high-speed processing, yet a key challenge persists: co-integrating nonlinearity, dense connectivity, and intrinsic memory monolithically to enable brain-inspired, spatiotemporal information processing. Here, we overcome this challenge by introducing a monolithic photonic recurrent network based on an active metasurface operating at bound state in the continuum (BIC). The BIC mode mediates strong,long-range coupling across the lattice, creating a reconfigurable recurrent network topology in hardware. Concurrently, the gain medium provides both optical nonlinearity for neuronal activation and a finite carrier lifetime that serves as a built in, analog temporal memory. This synergy enables computation to emerge directly from the collective spatiotemporal dynamics of the driven-dissipative photonic system, effectively realizing a physical reservoir computer on a chip. We experimentally validate a minimal yet physically complete system on benchmark tasks: brain MRI image classification and human action recognition, achieving 92.16% and 85.36% accuracies, respectively. This work establishes a scalable pathway toward ultrafast, energy-efficient neuromorphic intelligence where processing is an inherent property of tailored light matter interaction. △ Less

Submitted 25 February, 2026; originally announced February 2026.

Encoding orbital angular momentum of light in space with optical catastrophes

Authors: Xiaoyan Zhou, John You En Chan, Chia-Te Chang, Zhenchao Liu, Wang Hao, Andrew Forbes, Cheng-Wei Qiu, Hongtao Wang, Joel K. W. Yang

Abstract: Light beams carrying orbital angular momentum (OAM) possess an unbounded set of orthogonal modes, offering significant potential for optical communication and security. However, exploiting OAM beams in space has been hindered by the lack of a versatile design toolkit. Here, we demonstrate a strategy to tailor OAM across multiple transverse planes by shaping optical caustics leveraging on catastrop… ▽ More Light beams carrying orbital angular momentum (OAM) possess an unbounded set of orthogonal modes, offering significant potential for optical communication and security. However, exploiting OAM beams in space has been hindered by the lack of a versatile design toolkit. Here, we demonstrate a strategy to tailor OAM across multiple transverse planes by shaping optical caustics leveraging on catastrophe theory. With complex-amplitude metasurfaces fabricated using two-photon polymerization lithography, we construct these caustics to steer Poynting vectors and achieve arbitrary shapes of OAM beams. Interestingly, we use such an approach to realize hidden OAM along the propagation trajectory, where the intensity of the beam is spread out thus avoiding detection. The OAM of these beams can be intrinsic, which avoids OAM distortions arising from the mixing of intrinsic and extrinsic components. By exploiting this intrinsic nature of OAM, we demonstrate the detection of encoded information in optical encryption. Our approach provides a unique framework for dynamic control of OAM in space, with promising applications in optical trapping and sensing, high-capacity data storage, and optical information security. △ Less

Submitted 2 November, 2025; originally announced November 2025.

Electrochemical properties of solid oxide fuel cells under the coupling effect of airflow pattern and airflow velocity

Authors: Wang Hao, Xie Jiamiao, Hao Wenqian, Li Jingyang, Zhang Peng, Ma Xiaofan, Liu Fu, Wang Xu

Abstract: Under the dual background of deep adjustment of global energy pattern and severe challenges of environmental problems, solid oxide fuel cell (SOFC) has become the focus of research on efficient and clean energy conversion technology due to its many excellent characteristics. The electrochemical performance of SOFC is affected by various factors such as gas flow pattern (co-flow, counter-flow, cros… ▽ More Under the dual background of deep adjustment of global energy pattern and severe challenges of environmental problems, solid oxide fuel cell (SOFC) has become the focus of research on efficient and clean energy conversion technology due to its many excellent characteristics. The electrochemical performance of SOFC is affected by various factors such as gas flow pattern (co-flow, counter-flow, cross-flow), flow rate (cathode and anode channel gases), and operating voltage. Accurately analysing the variation of electrochemical indexes with each factor is the basis for proposing the design scheme of high efficiency reaction of the cell. Therefore, a three-dimensional multi-field coupling model of SOFC is established in this study, and the model parameters and boundary conditions covering electrochemistry, gas flow, substance diffusion, etc. are set to study the influence of the coupling between factors on the electrochemical performance of the cell. These results show that with the decrease of operating voltage, the electrochemical reaction rate of the cell increases significantly, the gas mole fraction gradient increases, and the inhomogeneity of the electrolyte current density distribution is enhanced. Under low-voltage operating conditions, the cross-flow flow pattern shows better electrochemical performance advantages, and its power density profile takes the lead in different current density intervals. With the increase of the flow rate of the flow channel gas, the output power density curve of the cell shows an overall upward trend, and then the driving effect of the flow rate increase on the power density increase is gradually weakened due to the saturated cathodic reaction. This study reveals the influence of the coupling of flow pattern, flow rate and voltage on the electrochemical performance of SOFC, and provides guidance for the commercial application of SOFC. △ Less

Submitted 1 November, 2025; originally announced November 2025.

Comments: 28 pages,14 figures

Journal ref: Acta Phys. Sin., 2025, 74(11): 118201

Six-Dimensional Movable Antenna Enabled Wideband THz Communications

Authors: Wencai Yan, Wanming Hao, Yajun Fan, Yabo Guo, Qingqing Wu, Xingwang Li

Abstract: In this paper, we investigate a six-dimensional movable antenna (6DMA)-enabled wideband terahertz (THz) communication system with sub-connected hybrid beamforming architecture at the base station (BS). In particular, the three-dimensional (3D) position and 3D rotation of each 6DMA surface can be flexibly reconfigured to mitigate the beam squint effects instead of introducing costly true-time-delay… ▽ More In this paper, we investigate a six-dimensional movable antenna (6DMA)-enabled wideband terahertz (THz) communication system with sub-connected hybrid beamforming architecture at the base station (BS). In particular, the three-dimensional (3D) position and 3D rotation of each 6DMA surface can be flexibly reconfigured to mitigate the beam squint effects instead of introducing costly true-time-delay devices. We first analyze the normalized array gain in the 6DMA-enabled wideband THz systems based on the beam squint effects. Then, we formulate a sum-rate maximization problem via jointly optimizing 3D positions, 3D rotations, and hybrid analog/digital beamforming. To solve the non-convex problem, an alternating optimization algorithm is developed that decomposes the original problem into three subproblems, which are solved alternately. Specifically, given the positions and rotations of 6DMA surfaces, we first reformulate the objective function and design a semidefinite relaxation-based alternating minimization scheme to obtain the hybrid analog/digital beamforming. Then, the positions and rotations of the 6DMA surfaces are further optimized through a feasible gradient descent procedure. The final solutions are obtained by repeating the above procedure until convergence. Numerical results demonstrate the superior performance of the proposed scheme compared with conventional fixed-position antenna architectures. △ Less

Submitted 28 October, 2025; originally announced October 2025.

Phase field simulation of dendrite growth in solid-state lithium batteries based on mechanical-thermo-electrochemical coupling

Authors: Pengyang Hou, Jiamiao Xie, Jingyang Li, Peng Zhang, Zhaokai Li, Wenqian Hao, Jia Tian, Zhe Wang, Fuzheng Li

Abstract: Solid-state lithium batteries possess numerous advantages, such as high energy density, excellent cycle stability, superior mechanical strength, non-flammability, enhanced safety, and extended service life. These characteristics make them highly suitable for applications in aerospace, new energy vehicles, and portable electronic devices. However, the growth of lithium dendrite at the electrode/ele… ▽ More Solid-state lithium batteries possess numerous advantages, such as high energy density, excellent cycle stability, superior mechanical strength, non-flammability, enhanced safety, and extended service life. These characteristics make them highly suitable for applications in aerospace, new energy vehicles, and portable electronic devices. However, the growth of lithium dendrite at the electrode/electrolyte interface remains a critical challenge, limiting both performance and safety. The growth of lithium dendrites in the electrolyte not only reduces the Coulombic efficiency of the battery but also poses a risk of puncturing the electrolyte, leading to internal short circuits between the anode and cathode. This study is to solve the problem of lithium dendrite growth in solid-state lithium batteries by employing phase-field theory for numerical simulations. A phase-field model is developed by coupling the mechanical stress field, thermal field, and electrochemical field, to investigate the morphology and evolution of lithium dendrites under the condition of different ambient temperatures, external pressures, and their combined effects. The results indicate that higher temperature and greater external pressure significantly suppress lithium dendrite growth, leading to fewer side branches, smoother surfaces, and more uniform electrochemical deposition. Increased external pressure inhibits longitudinal dendrite growth, resulting in a compressed morphology with higher compactness, but at the cost of increased mechanical instability. The combined effect of temperature and pressure exhibits a pronounced inhibitory influence on dendrite growth, with stress concentrating at the dendrite roots. This stress distribution promotes lateral growth, facilitating the formation of flatter and denser lithium deposits. △ Less

Submitted 2 September, 2025; originally announced September 2025.

Comments: 28 pages,9 figures

Journal ref: Acta Phys. Sin., 2025, 74(7): 070201

Emergence of Diverse Topological States in Ge Doped MnBi2Te4

Authors: Zhijian Shi, Shengjie Xu, Jianfeng Wang, Yi Du, Weichang Hao

Abstract: As an ideal platform for studying interplays between symmetry, topology and magnetism, the magnetic topological insulator (MTI) MnBi2Te4 has attracted extensive attentions. However, its strong n-type intrinsic defects hinder the realizations of exotic phenomena. Stimulated by recent discoveries that Ge doping can efficiently tune the position of Fermi level, here we systematically investigate the… ▽ More As an ideal platform for studying interplays between symmetry, topology and magnetism, the magnetic topological insulator (MTI) MnBi2Te4 has attracted extensive attentions. However, its strong n-type intrinsic defects hinder the realizations of exotic phenomena. Stimulated by recent discoveries that Ge doping can efficiently tune the position of Fermi level, here we systematically investigate the band evolution and topological phase diagram with doping concentration from MTI MnBi2Te4 to strong topological insulator GeBi2Te4. Different from magnetically doped Bi2Se3, the topology here is determined by competition of two band inversions arising from band folding of two time-reversal invariant momenta between antiferromagnetic and nonmagnetic/ferromagnetic unit cells. By employing a band momentum mapping method, besides the known MTI phase, remarkably, we find two classes of magnetic Dirac semimetal phases at antiferromagnetic state, two classes of Weyl semimetal phases at ferromagnetic state, and an intermediate trivial state at different doping regions. Interestingly, the trivial state can be tuned into a Weyl phase with two coexisting band inversions and extraordinarily long Fermi arcs by a small strain. Our work reveals diverse topological states with intrinsic quantum phenomena can be achieved with great potential for designing future electronic devices. △ Less

Submitted 28 May, 2025; originally announced May 2025.

Comments: 16 pages, 5 figures

Observation of Q-switched and continuous wave regimes with mode-hopping in Er-doped fiber lasers incorporating a dynamic population grating

Authors: Zengrun Wen, Xiulin Fan, Kaile Wang, Weiming Wang, Song Gao, Wenjing Hao, Yuanmei Gao, Yangjian Cai, Liren Zheng

Abstract: Dynamic population gratings (DPGs) in rare-earth doped fibers are prevalent devices in fiber lasers for the production of single-longitudinal-mode emission, Q-switched pulses, and wavelength self-sweeping regimes. This study presents a transition from Q-switched state to continuous wave (CW) state, accompanying irregular mode-hopping, in an erbium-doped fiber laser with a heavily-doped DPG centere… ▽ More Dynamic population gratings (DPGs) in rare-earth doped fibers are prevalent devices in fiber lasers for the production of single-longitudinal-mode emission, Q-switched pulses, and wavelength self-sweeping regimes. This study presents a transition from Q-switched state to continuous wave (CW) state, accompanying irregular mode-hopping, in an erbium-doped fiber laser with a heavily-doped DPG centered at 1549.95 nm. Our results demonstrate that the transition between these two states can be achieved by adjusting the pump power. The repetition frequency of the Q-switched pulse increases monotonically with the increasing pump power, while the pulse duration initially narrows and then expands because the reduced peak intensity weakens the nonlinear effect. Additionally, modulation peaks are evident on both the Q-switched pulse train and the CW background, which are induced by the irregular mode-hopping caused by the DPG. Furthermore, we observe that the central wavelength fluctuates within a range of 0.05 nm. These results provide valuable insight into the DPG effect in heavily-doped fibers. △ Less

Submitted 23 February, 2023; originally announced February 2023.

Stability Preserving Data-driven Models With Latent Dynamics

Authors: Yushuang Luo, Xiantao Li, Wenrui Hao

Abstract: In this paper, we introduce a data-driven modeling approach for dynamics problems with latent variables. The state-space of the proposed model includes artificial latent variables, in addition to observed variables that can be fitted to a given data set. We present a model framework where the stability of the coupled dynamics can be easily enforced. The model is implemented by recurrent cells and… ▽ More In this paper, we introduce a data-driven modeling approach for dynamics problems with latent variables. The state-space of the proposed model includes artificial latent variables, in addition to observed variables that can be fitted to a given data set. We present a model framework where the stability of the coupled dynamics can be easily enforced. The model is implemented by recurrent cells and trained using backpropagation through time. Numerical examples using benchmark tests from order reduction problems demonstrate the stability of the model and the efficiency of the recurrent cell implementation. As applications, two fluid-structure interaction problems are considered to illustrate the accuracy and predictive capability of the model. △ Less

Submitted 19 April, 2022; originally announced April 2022.

Water-Superstructured Solid Fuel Cells

Authors: Wei Zhang, Siyuan Fang, Hanrui Su, Wei Hao, Bohak Yoon, Gyeong S. Hwang, Kai Sun, Chung-Fu Chen, Yu Zhu, Yun Hang Hu

Abstract: Protonic ceramic fuel cells can be operated at low temperatures, but their performances relying on bulk ion transfer in solid electrolytes are usually limited by much lower proton conductivity than 0.1 S/cm below 600 °C. Herein, however, we report a strategy for Al2O3 insulator to become a protonic superconductor, namely, in-situ generation of superstructured-water in porous Al2O3 layer could real… ▽ More Protonic ceramic fuel cells can be operated at low temperatures, but their performances relying on bulk ion transfer in solid electrolytes are usually limited by much lower proton conductivity than 0.1 S/cm below 600 °C. Herein, however, we report a strategy for Al2O3 insulator to become a protonic superconductor, namely, in-situ generation of superstructured-water in porous Al2O3 layer could realize the unprecedented water-mediated proton transfer on Al2O3 surface, attaining ultrahigh proton conductivity of 0.13 S/cm at 550 °C. With such a water-superstructured proton-superconductor, we created water-superstructured solid fuel cell, achieving very high power density of 1036 mW/cm2 and high open circuit voltage above 1.1 V at 550 °C with H2 fuel. This provides a general approach to develop protonic superconductors and solid fuel cells. △ Less

Submitted 28 October, 2021; originally announced October 2021.

Two-dimensional ZIF-L nanosheets as high performance non-enzymatic glucose sensor

Authors: Nana Liu, Ningyan Cheng, Chengwu Yang, Weichang Hao, Yi Du

Abstract: An effective biosensor based on two-dimensional (2D) Co-ZIF-L nanosheets for sensitive electrochemical non-enzymatic glucose detection is developed, which exhibits high electrocalalytic activities towards glucose due to the ordered porous structure as well as ultrahigh specific surface area. The fabricated Co-ZIF-L nanosheets electrodes present an outstanding performance with higher sensitivity of… ▽ More An effective biosensor based on two-dimensional (2D) Co-ZIF-L nanosheets for sensitive electrochemical non-enzymatic glucose detection is developed, which exhibits high electrocalalytic activities towards glucose due to the ordered porous structure as well as ultrahigh specific surface area. The fabricated Co-ZIF-L nanosheets electrodes present an outstanding performance with higher sensitivity of 769.5 *10$^{-6}$ A mM$^{-1}$ cm$^{-2}$ and lower detect limit of 90.4 nM, while the constructed 3D ZIF-67 nanoparticles electrodes show a weaker sensitivity of 697.4 *10$^{-6}$ A mM$^{-1}$ cm$^{-2}$ and a limited detection range from 2 *10$^{-6}$ M to 414 *10$^{-6}$ M. Furthermore, the Co-ZIF-L based non-enzymatic glucose biosensors possess an acceptable selectivity, long-term stability as well as reproducibility. This work may offer a new approach to develop 2D ZIF nanosheets as a potential candidate in electrochemical biosensors. △ Less

Submitted 14 February, 2022; v1 submitted 9 October, 2021; originally announced October 2021.

Comments: do not want to publish

Atomic-scale imaging of CH3NH3PbI3 structure and its decomposition pathway

Authors: Shulin Chen, Changwei Wu, Bo Han, Zhetong Liu, Zhou Mi, Weizhong Hao, Jinjin Zhao, Xiao Wang, Qing Zhang, Kaihui Liu, Junlei Qi, Jian Cao, Jicai Feng, Dapeng Yu, Jiangyu Li, Peng Gao

Abstract: Understanding the atomic structure and structural instability of organic-inorganic hybrid perovskites is the key to appreciate their remarkable photoelectric properties and failure mechanism. Here, using low-dose imaging technique by direct-detection electron-counting camera in transmission electron microscope, we investigate the atomic structure and decomposition pathway of CH3NH3PbI3 (MAPbI3) at… ▽ More Understanding the atomic structure and structural instability of organic-inorganic hybrid perovskites is the key to appreciate their remarkable photoelectric properties and failure mechanism. Here, using low-dose imaging technique by direct-detection electron-counting camera in transmission electron microscope, we investigate the atomic structure and decomposition pathway of CH3NH3PbI3 (MAPbI3) at the atomic scale. We successfully image the atomic structure of perovskite in real space under ultra-low electron dose condition, and observe a two-step decomposition process, i.e. initial loss of MA followed by the collapse of perovskite structure into 6H-PbI2 with their critical threshold dose also determined. Interestingly, an intermediate phase (MA0.5PbI3) with locally ordered vacancies can robustly exist before perovskite collapses, enlightening strategies for prevention and recovery of perovskite structure during degradation. Associated with structure evolution, the bandgap gradually increases from ~1.6 eV to ~2.1 eV, and it is found that both C-N and N-H bonds can be destroyed under irradiation, releasing NH3 and leaving hydrocarbons. These findings enhance our understanding of the photoelectric properties and failure mechanism of MAPbI3, providing potential strategy into material optimization. △ Less

Submitted 22 June, 2021; originally announced June 2021.

Journal ref: Nature Communications 12(1):5516 2021

BiOBr 2D materials for integrated nonlinear photonics devices

Authors: Linnan Jia, Dandan Cui, Jiayang Wu, Haifeng Feng, Yunyi Yang, Tieshan Yang, Yang Qua, Yi Duc, Weichang Hao, Baohua Jia, David J. Moss

Abstract: As a new group of advanced 2D layered materials, bismuth oxyhalides, i.e., BiOX (X = Cl, Br, I), have recently become of great interest. In this work, we characterize the third-order optical nonlinearities of BiOBr, an important member of the BiOX family. The nonlinear absorption and Kerr nonlinearity of BiOBr nanoflakes at both 800 nm and 1550 nm are characterized via the Z-Scan technique. Experi… ▽ More As a new group of advanced 2D layered materials, bismuth oxyhalides, i.e., BiOX (X = Cl, Br, I), have recently become of great interest. In this work, we characterize the third-order optical nonlinearities of BiOBr, an important member of the BiOX family. The nonlinear absorption and Kerr nonlinearity of BiOBr nanoflakes at both 800 nm and 1550 nm are characterized via the Z-Scan technique. Experimental results show that BiOBr nanoflakes exhibit a large nonlinear absorption coefficient = \b{eta} = 10-7 m/W as well as a large Kerr coefficient n2 = 10-14 m2/W. We also note that the n2 of BiOBr reverses sign from negative to positive as the wavelength is changed from 800 nm to 1550 nm. We further characterize the thickness-dependent nonlinear optical properties of BiOBr nanoflakes, finding that the magnitudes of \b{eta} and n2 increase with decreasing thickness of the BiOBr nanoflakes. Finally, we integrate BiOBr nanoflakes into silicon integrated waveguides and measure their insertion loss, with the extracted waveguide propagation loss showing good agreement with mode simulations based on ellipsometry measurements. These results confirm the strong potential of BiOBr as a promising nonlinear optical material for high-performance hybrid integrated photonic devices. △ Less

Submitted 31 July, 2020; originally announced August 2020.

Comments: 10 pages, 4 figures, 113 references. arXiv admin note: substantial text overlap with arXiv:1909.02183; text overlap with arXiv:2003.04091

Journal ref: SPIE Photonics West 2020

Two-dimensional van der Waals Heterostructures for Synergistically Improved Surface Enhanced Raman Spectroscopy

Authors: Qiran Cai, Wei Gan, Alexey Falin, Kenji Watanabe, Takashi Taniguchi, Jincheng Zhuang, Weichang Hao, Shaoming Huang, Tao Tao, Ying Chen, Lu Hua Li

Abstract: Surface enhanced Raman spectroscopy (SERS) is a precise and non-invasive analytical technique that is widely used in chemical analysis, environmental protection, food processing, pharmaceutics, and diagnostic biology. However, it is still a challenge to produce highly sensitive and reusable SERS substrates with minimum fluorescence background. In this work, we propose the use of van der Waals hete… ▽ More Surface enhanced Raman spectroscopy (SERS) is a precise and non-invasive analytical technique that is widely used in chemical analysis, environmental protection, food processing, pharmaceutics, and diagnostic biology. However, it is still a challenge to produce highly sensitive and reusable SERS substrates with minimum fluorescence background. In this work, we propose the use of van der Waals heterostructures of two-dimensional materials (2D materials) to cover plasmonic metal nanoparticles to solve this challenge. The heterostructures of atomically thin boron nitride (BN) and graphene provide synergistic effects: (1) electrons could tunnel through the atomically thin BN, allowing the charge transfer between graphene and probe molecules to suppress fluorescence background; (2) the SERS sensitivity is enhanced by graphene via chemical enhancement mechanism (CM) in addition to electromagnetic field mechanism (EM); (3) the atomically thin BN protects the underlying graphene and Ag nanoparticles from oxidation during heating for regeneration at 360 °C in the air so that the SERS substrates could be reused. These advances will facilitate wider applications of SERS, especially on the detection of fluorescent molecules with higher sensitivity. △ Less

Submitted 2 August, 2020; originally announced August 2020.

Journal ref: ACS Applied Materials Interfaces 12, 21985-21991(2020)

Topological Lattice Metamaterials -- A Platform For Novel Electromagnetic Material Design Based On An Artificial Topological "Atom"

Authors: Wenjin Zhang, Ziyuan Meng, Zidong Zhang, Ke Bi, Runhua Fan, Yi Du, Weichang Hao

Abstract: In nature, most materials are composed of atoms with periodic structures. Hence, it's impossible to introduce topological structures into their lattice compose, because the atoms as basic blocks cannot be modulated. However, the lattice compose of metamaterials can be designed conveniently. In our work, we propose to introduce topological non-trivial structures, Mobius unknots, as the basic block… ▽ More In nature, most materials are composed of atoms with periodic structures. Hence, it's impossible to introduce topological structures into their lattice compose, because the atoms as basic blocks cannot be modulated. However, the lattice compose of metamaterials can be designed conveniently. In our work, we propose to introduce topological non-trivial structures, Mobius unknots, as the basic block (the artificial chiral "atoms") to design metamaterials. A 5.95 GHz intrinsic peak, in addition to the electrical resonance peak near 11 GHz on the transmission coefficient spectrum was confirmed by theoretical calculations, finite-difference time-domain (FDTD) simulations and experiments when electromagnetic waves transfer to a chiral Mobius unknot. Theoretical analysis indicates that this intrinsic peak originates from the phase transition caused by the electromagnetic waves propagate along the Mobius unknot non-trivial structure. It is similar to the state of spin-splitting of electron levels. Take the artificial chiral "atoms" - Mobius unknots as the basic block, we can construct two-dimensional and even three-dimensional ordered metamaterials. The simulation and experimental results showed that the response to electromagnetic wave in the GHz band can be modulated by the coupling between the periodic potential and the spin-like of energy levels. △ Less

Submitted 4 October, 2020; v1 submitted 12 December, 2019; originally announced December 2019.

Comments: 9 pages, 5 figures

High third-order Kerr optical nonlinearity in BiOBr 2D films measured by the Z-scan method

Authors: Linnan Jia, Dandan Cui, Jiayang Wu, Haifeng Feng, Yunyi Yang, Tieshan Yang, Yang Qu, Yi Du, Weichang Hao, Baohua Jia, David J. Moss

Abstract: We investigate the nonlinear optical properties of BiOBr nanoflakes, a novel two-dimensional (2D) layered material from the Bismuth oxyhalide family. We measure the nonlinear absorption and Kerr nonlinearity of BiOBr nanoflakes at both 800 nm and 1550 nm via the Z scan technique. We observe a large nonlinear absorption coefficient beta = 10^-7 m/W as well as a large Kerr coefficient n2 = 10^-14 m^… ▽ More We investigate the nonlinear optical properties of BiOBr nanoflakes, a novel two-dimensional (2D) layered material from the Bismuth oxyhalide family. We measure the nonlinear absorption and Kerr nonlinearity of BiOBr nanoflakes at both 800 nm and 1550 nm via the Z scan technique. We observe a large nonlinear absorption coefficient beta = 10^-7 m/W as well as a large Kerr coefficient n2 = 10^-14 m^2/W. We also observe strong dispersion in n2, with it reversing sign from negative to positive as the wavelength varies from 800 nm to 1550 nm. In addition, we characterize the thickness-dependence of the nonlinear optical properties of BiOBr nanoflakes, observing that both the magnitudes of beta and n2 increase for very thin flakes. Finally, we integrate BiOBr nanoflakes onto silicon integrated waveguides and characterize the linear optical properties of the resulting hybrid integrated devices, with the measurements agreeing with calculated parameters using independent ellipsometry measurements. These results verify the strong potential of BiOBr as an advanced nonlinear optical material for high-performance hybrid integrated photonic devices. △ Less

Submitted 4 September, 2019; originally announced September 2019.

Comments: 16 pages, 7 figures, 61 references

Journal ref: Applied Physics Letters Photonics (APLP) Volume 4 (9) (2019)

Development and validation of Critical Thinking Disposition Inventory for Chinese medical college students (CTDI-M)

Authors: Xiaoxia Wang, Xiaoxiao Sun, Tianhao Huang, Renqiang He, Weina Hao, Li Zhang

Abstract: PURPOSE: Critical thinkers in medical context must be not only "able" but also "willing" to think critically. To develop and conduct psychometric testing of Critical Thinking Disposition Inventory which measure the critical thinking disposition of Chinese medical college students. METHODS: The study was conducted in two stages: (a) item generation and exploratory factor analysis (EFA) and (b) test… ▽ More PURPOSE: Critical thinkers in medical context must be not only "able" but also "willing" to think critically. To develop and conduct psychometric testing of Critical Thinking Disposition Inventory which measure the critical thinking disposition of Chinese medical college students. METHODS: The study was conducted in two stages: (a) item generation and exploratory factor analysis (EFA) and (b) testing of psychometric properties (construct validity, split-half reliability and Cronbach's alpha, and test-retest reliability. The subjects were composed of 441 undergraduate medical and nursing students from a medical university in China. Test-retest reliability of the instrument was determined at two-week interval. Data was analyzed with SPSS13.0. RESULTS: Preliminary 264 items were obtained using an open-ended questionnaire; from which 61 items were reviewed through half open-ended questionnaire, and finally 18 items were chosen. Eighteen final items were sorted into 3 factors, which were identified as "Open-mindedness ", "Systematicity/analyticity" and "Truth seeking". The cumulative percent of variance was 57.66%. The Cronbach's alpha was 0.924 and the factors' alphas ranged from 0.824-0.862. Correlational analysis indicated moderate to high correlations between the subscales and total scores of the CTDI-CM. Our results indicated that open-mindedness and systematicity/analyticity were higher for medical students than nursing students. CONCLUSIONS: This study conducted in a Chinese medical college student population demonstrated a reliable and valid instrument for clinical thinking disposition, which measured motivation and cognitive components. The effect of enrollment year and major on the profiles of critical thinking dispositions was identified, emphasizing the importance of applying specialized teaching to students of different majors. △ Less

Submitted 26 June, 2018; originally announced June 2018.

Estimating the spectrum in computed tomography via Kullback-Leibler divergence constrained optimization

Authors: Wooseok Ha, Emil Y. Sidky, Rina Foygel Barber, Taly Gilat Schmidt, Xiaochuan Pan

Abstract: We study the problem of spectrum estimation from transmission data of a known phantom. The goal is to reconstruct an x-ray spectrum that can accurately model the x-ray transmission curves and reflects a realistic shape of the typical energy spectra of the CT system. To this end, spectrum estimation is posed as an optimization problem with x-ray spectrum as unknown variables, and a Kullback-Leibler… ▽ More We study the problem of spectrum estimation from transmission data of a known phantom. The goal is to reconstruct an x-ray spectrum that can accurately model the x-ray transmission curves and reflects a realistic shape of the typical energy spectra of the CT system. To this end, spectrum estimation is posed as an optimization problem with x-ray spectrum as unknown variables, and a Kullback-Leibler (KL) divergence constraint is employed to incorporate prior knowledge of the spectrum and enhance numerical stability of the estimation process. The formulated constrained optimization problem is convex and can be solved efficiently by use of the exponentiated-gradient (EG) algorithm. We demonstrate the effectiveness of the proposed approach on the simulated and experimental data. The comparison to the expectation-maximization (EM) method is also discussed. In simulations, the proposed algorithm is seen to yield x-ray spectra that closely match the ground truth and represent the attenuation process of x-ray photons in materials, both included and not included in the estimation process. In experiments, the calculated transmission curve is in good agreement with the measured transmission curve, and the estimated spectra exhibits physically realistic looking shapes. The results further show the comparable performance between the proposed optimization-based approach and EM. In conclusion, our formulation of a constrained optimization provides an interpretable and flexible framework for spectrum estimation. Moreover, a KL-divergence constraint can include a prior spectrum and appears to capture important features of x-ray spectrum, allowing accurate and robust estimation of x-ray spectrum in CT imaging. △ Less

Submitted 30 April, 2018; originally announced May 2018.

Comments: 17 pages, 9 figures

UV-Vis-IR Spectral Complex Refractive Indices and Optical Properties of Brown Carbon Aerosol from Biomass Burning

Authors: Benjamin J. Sumlin, Yuli W. Heinson, Nishit Shetty, Apoorva Pandey, Robert S. Pattison, Stephen Baker, Wei Min Hao, Rajan K. Chakrabarty

Abstract: Constraining the complex refractive indices, optical properties and size of brown carbon (BrC) aerosols is a vital endeavor for improving climate models and satellite retrieval algorithms. Smoldering wildfires are the largest source of primary BrC, and fuel parameters such as moisture content, source depth, geographic origin, and fuel packing density could influence the properties of the emitted a… ▽ More Constraining the complex refractive indices, optical properties and size of brown carbon (BrC) aerosols is a vital endeavor for improving climate models and satellite retrieval algorithms. Smoldering wildfires are the largest source of primary BrC, and fuel parameters such as moisture content, source depth, geographic origin, and fuel packing density could influence the properties of the emitted aerosol. We measured in situ spectral (375-1047 nm) optical properties of BrC aerosols emitted from smoldering combustion of Boreal and Indonesian peatlands across a range of these fuel parameters. Inverse Lorenz-Mie algorithms used these optical measurements along with simultaneously measured particle size distributions to retrieve the aerosol complex refractive indices (m=n+iκ). Our results show that the real part n is constrained between 1.5 and 1.7 with no obvious functionality in wavelength (λ), moisture content, source depth, or geographic origin. With increasing λ from 375 to 532 nm, κ decreased from 0.014 to 0.003, with corresponding increase in single scattering albedo from 0.93 to 0.99. For λ = 532 nm, both κ and single scattering albedo showed no spectral dependency. We discuss differences between this study and previous work. The imaginary part κ was sensitive to changes in FPD, and we hypothesize mechanisms that might help explain this observation. △ Less

Submitted 14 December, 2017; v1 submitted 13 December, 2017; originally announced December 2017.

Comments: Benjamin J. Sumlin and Yuli W. Heinson contributed equally to this work

Frequency-oriented sub-sampling by photonic Fourier transform and I/Q demodulation

Authors: Wenhui Hao, Yitang Dai, Feifei Yin, Yue Zhou, Jianqiang Li, Jian Dai, Wangzhe Li, Kun Xu

Abstract: Sub-sampling can acquire directly a passband within a broad radio frequency (RF) range, avoiding down-conversion and low-phase-noise tunable local oscillation (LO). However, sub-sampling suffers from band folding and self-image interference. In this paper we propose a frequency-oriented sub-sampling to solve the two problems. With ultrashort optical pulse and a pair of chromatic dispersions, the b… ▽ More Sub-sampling can acquire directly a passband within a broad radio frequency (RF) range, avoiding down-conversion and low-phase-noise tunable local oscillation (LO). However, sub-sampling suffers from band folding and self-image interference. In this paper we propose a frequency-oriented sub-sampling to solve the two problems. With ultrashort optical pulse and a pair of chromatic dispersions, the broadband RF signal is firstly short-time Fourier-transformed to a spectrum-spread pulse. Then a time slot, corresponding to the target spectrum slice, is coherently optical-sampled with in-phase/quadrature (I/Q) demodulation. We demonstrate the novel bandpass sampling by a numerical example, which shows the desired uneven intensity response, i.e. pre-filtering. We show in theory that appropriate time-stretch capacity from dispersion can result in pre-filtering bandwidth less than sampling rate. Image rejection due to I/Q sampling is also analyzed. A proof-of-concept experiment, which is based on a time-lens sampling source and chirped fiber Bragg gratings (CFBGs), shows the center-frequency-tunable pre-filtered sub-sampling with bandwidth of 6 GHz around, as well as imaging rejection larger than 26 dB. Our technique may benefit future broadband RF receivers for frequency-agile Radar or channelization. △ Less

Submitted 12 July, 2017; originally announced July 2017.

Comments: 8 pages, 6 figures