Showing 1–25 of 25 results for author: Haque, A

AEcroscopyWave: Towards Self-Driving Characterization Platforms for Agentic AI

Authors: Yongtao Liu, Jawad Chowdhury, Ganesh Narasimha, Ralph Bulanadi, Liam Collins, Ruben Millan Solsona, Marti Checa, Asraful Haque, Sumner B. Harris, Stephen Jesse, Rama Vasudevan

Abstract: The characterization of electronic materials has traditionally been stratified into two distinct regimens: industry-scale automated systems to inspect materials for defects and ensure quality (such as in the semiconductor industry), and highly customized, operator-driven systems requiring human experts. The former offers high throughput but limited flexibility, whereas the latter is heavily bandwi… ▽ More The characterization of electronic materials has traditionally been stratified into two distinct regimens: industry-scale automated systems to inspect materials for defects and ensure quality (such as in the semiconductor industry), and highly customized, operator-driven systems requiring human experts. The former offers high throughput but limited flexibility, whereas the latter is heavily bandwidth-limited but provides research-grade discovery capabilities. Recent advances in "self-driving" characterization tools offer the potential to bridge the two stratified regimes, by the creation of application program interfaces (APIs) that can control hardware, and the integration of AI methods to incorporate autonomy into the process. Here, we discuss our latest developments in AEcroscopyWave, a custom-built characterization platform for the agentic-AI era, that provides unified control of scanning probe microscopes with programmable peripheral instrumentation, highlighting the design choices that are necessary for maximizing the capability of the system and the ease of use for both human and AI agents. The benefits of making heterogeneous scientific instruments accessible, composable and usable by agents is demonstrated by test cases. △ Less

Submitted 24 July, 2026; originally announced July 2026.

Comments: 17 pages, 5 figures

Transition-Metal Tailored $Ga_{2}O_{2}$ Monolayer: From Room-Temperature Gas Sensing to Chemical Scavenging

Authors: Afreen Anamul Haque, Aniket Singha

Abstract: Pristine $Ga_{2}O_{2}$ monolayers suffer from poor sensitivity and weak molecular capture, limiting their application in toxic gas detection and environmental detoxification. Here, we employ first-principles density functional theory (DFT) calculations to investigate the gas sensing and scavenging properties of $Ga_{2}O_{2}$ monolayers substitutionally tailored via seven transition-metals (TM): Pd… ▽ More Pristine $Ga_{2}O_{2}$ monolayers suffer from poor sensitivity and weak molecular capture, limiting their application in toxic gas detection and environmental detoxification. Here, we employ first-principles density functional theory (DFT) calculations to investigate the gas sensing and scavenging properties of $Ga_{2}O_{2}$ monolayers substitutionally tailored via seven transition-metals (TM): Pd, Zn, Zr, Mo, Ag, Ti, and Pt. All TM-substituted monolayers exhibit negative formation and binding energies, negligible lattice distortion, and structural stability in molecular dynamics simulations. Performance evaluation against eight toxic industrial and three environmental gases reveals functionalities ranging from selective, reusable room-temperature sensing to permanent molecular capture. Ag substitution exhibits exceptional selectivity for $NO$ with moderate adsorption strength (~-0.83eV), an up to eight-order-of-magnitude conductivity enhancement, besides facilitating reusable $O_2$ and $NO_2$ detection. Additionally, Pd-, Zn-, Zr-, and Mo substitutions tune selectivity toward $NO$, $NO_2$, $CO_2$, $CO$, and $O_2$. Coming to applications towards toxic gas capture, Zr- and Mo-substituted systems selectively scavenge oxidizing gases, whereas Ti and Pt act as universal scavengers. Further analysis reveals that Pd- and Ag-substituted monolayers remain selective for $NO$, while Zn substitution favors $NO_2$ detection even in ambient atmospheric conditions. Thus, these tailored $Ga_{2}O_{2}$ monolayers offer a practical platform for atmospheric monitoring and detoxification. △ Less

Submitted 2 July, 2026; originally announced July 2026.

Comments: 24 pages, 13 figures

Phonon-Assisted Photoluminescence and Ultrafast Exciton Dynamics in Two-Dimensional Silicon Carbide

Authors: Afreen Anamul Haque, Rishabh Saraswat, Aniket Singha, Rekha Verma, Sitangshu Bhattacharya

Abstract: Phonon assisted photoluminescence provides a direct window into exciton phonon interactions in semiconductors. Using fully ab initio many-body perturbation theory, including finite momentum Bethe Salpeter calculations, we investigate phonon-assisted emission and exciton dynamics in two dimensional (2D) hexagonal silicon carbide (hSiC) and benchmark its response against 2D h boron nitride (hBN). By… ▽ More Phonon assisted photoluminescence provides a direct window into exciton phonon interactions in semiconductors. Using fully ab initio many-body perturbation theory, including finite momentum Bethe Salpeter calculations, we investigate phonon-assisted emission and exciton dynamics in two dimensional (2D) hexagonal silicon carbide (hSiC) and benchmark its response against 2D h boron nitride (hBN). By explicitly resolving exciton phonon matrix elements, we identify an electron-phonon scattering channel mediated by A$^\prime$ high energy longitudinal and transverse optical phonons as the dominant contributors to sideband formation and quantify their spectral weights. We find that h SiC exhibits pronounced phonon-assisted sidebands comparable to hBN, despite a smaller exciton phonon energy separation and fewer resolved replicas. The bright \textbf{K}\textbf{K} exciton governs near UV zero phonon emission, while intervalley excitons acquire radiative character through symmetry allowed optical phonon coupling. Temperature dependent scattering rates reveal an ultrashort bright exciton lifetime of approximately 300 fs at 10 K, highlighting rapid exciton relaxation driven by intrinsic phonon channels. △ Less

Submitted 13 July, 2026; v1 submitted 27 February, 2026; originally announced February 2026.

Comments: 6 figures

Large Pyroelectric Enhancement in Freestanding Epitaxial BaTiO3 Membranes on Si

Authors: Ajay Kumar, Asraful Haque, Shubham Kumar Parate, Harshal DSouza, Jishnu NK, Binoy Krishna De, Srinivasan Raghavan, Pavan Nukala

Abstract: Ferroelectric membranes transferred onto arbitrary substrates provide reduced mechanical clamping at the interfaces that can diminish the effective polarization-rotation barrier offering a pathway to engineer larger electromechanical and thermally driven responses in oxide electronics. Here, we report integration of single crystalline thin film BaTiO3 (BTO) ferroelectric membrane on Si and demonst… ▽ More Ferroelectric membranes transferred onto arbitrary substrates provide reduced mechanical clamping at the interfaces that can diminish the effective polarization-rotation barrier offering a pathway to engineer larger electromechanical and thermally driven responses in oxide electronics. Here, we report integration of single crystalline thin film BaTiO3 (BTO) ferroelectric membrane on Si and demonstrate a 4x at 30C and 34x at 60C enhancement of pyroelectric coefficient compared to clamped films. The BTO membrane is grown epitaxially on a water-soluble Sr3Al2O6 sacrificial layer, released by selective dissolution, and transferred onto Si, yielding a strain-relaxed membrane with robust intrinsic polarization. Temperature dependent piezoresponse force microscopy (PFM) reveals pronounced thermally driven evolution of domain orientation, consistent with reduced barriers for dipolar modulation in the freestanding state. Variable-temperature Kelvin probe force microscopy (KPFM) quantifies an effective pyroelectric coefficient of ~75 uC/m^2K at 30C and 450 uC/m^2K at 60C with a detectivity of 40 m^2K^-1at room temperature. These results establish lead-free freestanding BTO membranes as a promising silicon-integrable platform for cryogen-free infrared detection and waste-heat energy management. △ Less

Submitted 9 August, 2026; v1 submitted 20 February, 2026; originally announced February 2026.

Comments: The authors are withdrawing this manuscript while additional experiments and analyses are completed

Chirality-induced magnetoresistance in hybrid organic-inorganic perovskite semiconductors

Authors: Md Azimul Haque, Pius Markus Theiler, Ian A. Leahy, Steven P. Harvey, Jeiwan Tan, Matthew P Hautzinger, Margherita Taddei, Aeron McConnell, Andrew Greider, Andrew H. Comstock, Yifan Dong, Kirstin Alberi, Yuan Ping, Peter C. Sercel, Joseph M. Luther, Dali Sun, Matthew C. Beard

Abstract: The combination of semiconducting properties and synthetically tunable chirality in chiral metal halide semiconductors (CMHS) offer a compelling platform for room temperature control over electronic spin properties, leveraging effects such as chirality-induced spin selectivity (CISS) for the development of new opto-spintronic functionalities. We report room-temperature CISS-induced magnetoresistan… ▽ More The combination of semiconducting properties and synthetically tunable chirality in chiral metal halide semiconductors (CMHS) offer a compelling platform for room temperature control over electronic spin properties, leveraging effects such as chirality-induced spin selectivity (CISS) for the development of new opto-spintronic functionalities. We report room-temperature CISS-induced magnetoresistance (CISS-MR) exceeding 100% for spin valves in a configuration consisting of a ferromagnet (FM), tunneling barrier, and CMHS. The high CISS-MR is attributed to interfacial spin-selective tunneling barrier induced by the chirality, which can produce current dissymmetry factors that surpass the limit imposed by the Jullière model governed by the intrinsic spin polarization of the adjacent FM contact. The CISS-MR exhibits a strong dependence on the CMHS composition, revealing a structure-property relationship between CISS and structural chirality. The observed exceptionally large tunneling MR response differentiates from a subtle anisotropic MR arising from the proximity effect at the FM/CMHS interface in the absence of a tunneling barrier. Our study provides insights into charge-to-spin interconversion in chiral semiconductors, offering materials design principles to control and enhance CISS response and utilize it in functional platforms. △ Less

Submitted 8 December, 2025; originally announced December 2025.

Report number: MR-01

Human-AI collaborative autonomous synthesis with pulsed laser deposition for remote epitaxy

Authors: Asraful Haque, Daniel T. Yimam, Jawad Chowdhury, Ralph Bulanadi, Ivan Vlassiouk, John Lasseter, Sujoy Ghosh, Christopher M. Rouleau, Kai Xiao, Yongtao Liu, Eva Zarkadoula, Rama K. Vasudevan, Sumner B. Harris

Abstract: Autonomous laboratories typically rely on data-driven decision-making, occasionally with human-in-the-loop oversight to inject domain expertise. Fully leveraging AI agents, however, requires tightly coupled, collaborative workflows spanning hypothesis generation, experimental planning, execution, and interpretation. To address this, we develop and deploy a human-AI collaborative (HAIC) workflow th… ▽ More Autonomous laboratories typically rely on data-driven decision-making, occasionally with human-in-the-loop oversight to inject domain expertise. Fully leveraging AI agents, however, requires tightly coupled, collaborative workflows spanning hypothesis generation, experimental planning, execution, and interpretation. To address this, we develop and deploy a human-AI collaborative (HAIC) workflow that integrates large language models for hypothesis generation and analysis, with collaborative policy updates driving autonomous pulsed laser deposition (PLD) experiments for remote epitaxy of BaTiO$_3$/graphene. HAIC accelerated the hypothesis formation and experimental design and efficiently mapped the growth space to graphene-damage. In situ Raman spectroscopy reveals that chemistry drives degradation while the highest energy plume components seed defects, identifying a low-O$_2$ pressure low-temperature synthesis window that preserves graphene but is incompatible with optimal BaTiO$_3$ growth. Thus, we show a two-step Ar/O$_2$ deposition is required to exfoliate ferroelectric BaTiO$_3$ while maintaining a monolayer graphene interlayer. HAIC stages human insight with AI reasoning between autonomous batches to drive rapid scientific progress, providing an evolution to many existing human-in-the-loop autonomous workflows. △ Less

Submitted 14 November, 2025; originally announced November 2025.

Aqueous Preparation of CsPbBr3 Perovskite Nanocrystals Under Ambient Conditio

Authors: Zhaoyi Du, Jiewen Wei, Ding Ding, Martina Rimmele, Yueyao Dong, Weitao Qian, Davide Nodari, Francesco Furlan, Edoardo Angela, George Morgan, Peter Akinshin, William Rodriguez Kazeem, Gwilherm Kerherve, Adam V. Marsh, Martin Heeney, Thomas J. Macdonald, Saif A. Haque, Nicola Gasparini, David J. Payne, Martyn A. McLachlan

Abstract: Metal halide perovskites (MHPs) have had a profound impact on numerous emerging optoelectronic technologies, achieving performance metrics that rival or exceed incumbent materials. This impact is underpinned by the exceptional properties of MHPs, including tuneable band gaps, high absorption coefficients, long carrier diffusion lengths and combined with uncomplicated synthesis methods. However, cu… ▽ More Metal halide perovskites (MHPs) have had a profound impact on numerous emerging optoelectronic technologies, achieving performance metrics that rival or exceed incumbent materials. This impact is underpinned by the exceptional properties of MHPs, including tuneable band gaps, high absorption coefficients, long carrier diffusion lengths and combined with uncomplicated synthesis methods. However, current MHP production relies on the toxic solvents, which pose significant environmental and health risks. Moreover, these methods often require complex multi component solvent systems and thermal processing to achieve the desired material phases, further hindering scalability and sustainability. Overcoming these challenges is critical to the future development of MHP-based technologies. Overcoming these challenges is critical to the future development of MHP-based technologies. Here, we present a novel water-based solvent system and synthetic approach for the preparation of size-controlled CsPbBr3 perovskite nanocrystals in ambient air and at room temperature. The photoluminescence quantum yield (PLQY) of CsPbBr3 erovskite nanocrystals (PNCs) exceeds 60 precent. To demonstrate the light to current conversion ability of our PNCs a series of photoconductors were prepared, with the best performing devices achieving a specific detectivity (D*) of 1.2 x 10^11 Jones. Thus, this green, scalable, and low-cost approach offers a sustainable pathway for precise size and compositional control of MHP nanocrystals, opening new possibilities for environmentally friendly optoelectronic applications. △ Less

Submitted 21 October, 2025; originally announced October 2025.

A facile vector substrate platform via BaTiO3 membrane transfer enables high quality solution processed epitaxial PZT on silicon

Authors: Asraful Haque, Antony Jeyaseelan, Shubham Kumar Parate, Srinivasan Raghavan, Pavan Nukala

Abstract: The direct integration of high-performance ferroelectric oxides with silicon remains challenging due to lattice mismatch, thermal incompatibility, and the need for high-temperature epitaxial growth. Here, a hybrid integration approach is demonstrated in which crystalline BaTiO3 (BTO) membranes are first transferred onto Pt coated Si substrates and subsequently used as vector substrates (VS) for th… ▽ More The direct integration of high-performance ferroelectric oxides with silicon remains challenging due to lattice mismatch, thermal incompatibility, and the need for high-temperature epitaxial growth. Here, a hybrid integration approach is demonstrated in which crystalline BaTiO3 (BTO) membranes are first transferred onto Pt coated Si substrates and subsequently used as vector substrates (VS) for the growth of epitaxial (001) Pb(Zr0.52Ti0.48)O3 (PZT) thin films via chemical solution deposition (CSD). A KI and HCl based etchant enables rapid and complete dissolution of the SrVO3 sacrificial layer in about 30 minutes, reducing the release time from days to minutes compared with conventional water based approaches to dissolve AVO3 and AMoO3 (A is Ca, Sr, Ba). The BTO VS imposes dominant (00l) out of plane orientation and in plane cube on cube epitaxy in the overlying PZT. Devices exhibit remnant polarization 10 to 12 micro coulomb/cm2 and coercive field of 100 kV/cm, with stable switching to 10^8 cycles on the VS. From piezoelectric butterfly loops, we extract effective d33 of 70 pm/V for PZT on VS, and 54 pm/V for PZT grown on conventional Pt Si substrates. This approach demonstrates a scalable and cost effective route for integrating functional ferroelectric materials onto silicon and offers a promising platform for future CMOS compatible oxide electronics. △ Less

Submitted 7 September, 2025; originally announced September 2025.

Comments: 17 pages, 7 figures

Gas Sensing Properties of Novel Indium Oxide Monolayer: A First-Principles Study

Authors: Afreen Anamul Haque, Suraj G. Dhongade, Aniket Singha

Abstract: We present a comprehensive first-principles investigation into the gas sensing capabilities of a novel two-dimensional Indium Oxide (In2O3) monolayer, using density functional theory (DFT) calculations. Targeting both resistive-type and work function based detection mechanisms, we evaluate interactions with ten hazardous gases (NH3, NO, NO2, SO2, CS2, H2S, HCN, CCl2O, CH2O, CO) as well as ambient… ▽ More We present a comprehensive first-principles investigation into the gas sensing capabilities of a novel two-dimensional Indium Oxide (In2O3) monolayer, using density functional theory (DFT) calculations. Targeting both resistive-type and work function based detection mechanisms, we evaluate interactions with ten hazardous gases (NH3, NO, NO2, SO2, CS2, H2S, HCN, CCl2O, CH2O, CO) as well as ambient molecules (O2, CO2, H2O). The monolayer shows pronounced sensitivity towards NO and H2S, and work function modulation enables detection of NH3 and HCN. Mechanical strain further broadens detection capability, enhancing adsorption and selectivity. These results establish 2D In2O3 as a tunable platform for next-generation miniaturized gas sensors for environmental monitoring and safety applications. △ Less

Submitted 5 September, 2025; originally announced September 2025.

Comments: 27 Pages, 6 figures

Anion Doping Driven Non-Ferroelectric-to-Ferroelectric Phase Transition in Epitaxial Y:HfO2

Authors: Soumyajyoti Mondal, Binoy Krishna De, Asraful Haque, Shubham Kumar Parate, Arup Basak, Naushad Ahemad, Pramod Kumar Yadav, Kaushal Tiwari, Bhagwati Prasad, Matthew K. Sharpe, Catia Costa, Satheesh Krishnamurthy, Pavan Nukala

Abstract: Oxygen vacancies are often essential for stabilizing the orthorhombic ferroelectric phase in HfO2, with cationic doping widely employed to introduce such defects. In contrast, systematic studies on anionic doping to induce ferroelectricity remains largely in nascent stages. Here, using epitaxial Y:HfO2 films grown on ITO-buffered YSZ substrates that initially crystallize predominantly in the monoc… ▽ More Oxygen vacancies are often essential for stabilizing the orthorhombic ferroelectric phase in HfO2, with cationic doping widely employed to introduce such defects. In contrast, systematic studies on anionic doping to induce ferroelectricity remains largely in nascent stages. Here, using epitaxial Y:HfO2 films grown on ITO-buffered YSZ substrates that initially crystallize predominantly in the monoclinic non-polar phase, we demonstrate that post-deposition rapid thermal annealing in N2 atmosphere at 900 °C enables nitrogen incorporation without disrupting epitaxy. As the annealing duration increases from 10 s to 2 min, the monoclinic phase diminishes, accompanied by the emergence of robust ferroelectric hysteresis and a corresponding increase in the orthorhombic phase fraction. Combining independent spectroscopic and compositional analyses, we experimentally establish that nitrogen preferentially incorporates into pre-existing neutral oxygen-vacancy sites, converting them into charged oxygen vacancies that drive the transformation from the non-polar monoclinic phase to the ferroelectric orthorhombic phase. Our epitaxial model platform therefore reveals an anion-mediated defect-engineering pathway for controlling ferroelectricity in Y:HfO2, establishing nitrogen incorporation not merely as a chemical dopant, but as a route to fundamentally reconfigure the defect thermodynamics governing phase stability in fluorite ferroelectrics. △ Less

Submitted 25 June, 2026; v1 submitted 2 September, 2025; originally announced September 2025.

Comments: Manuscript: 17 pages, 4 figures, Supplementary Information: 7 figures, 3 texts, 5 tables

Fluid flow in 3-dimensional porous systems shows power law scaling with Minkowski functionals

Authors: R. A. I. Haque, A. J. Mitra, T. Dutta

Abstract: Integral geometry uses four geometric invariants -- the Minkowski functionals -- to characterize certain subsets of 3-dimensional space. The question was, how is the fluid flow in a 3-dimensional porous system related to these invariants? In this work, we systematically study the dependency of permeability on the geometrical characteristics of two categories of 3-dimensional porous systems generat… ▽ More Integral geometry uses four geometric invariants -- the Minkowski functionals -- to characterize certain subsets of 3-dimensional space. The question was, how is the fluid flow in a 3-dimensional porous system related to these invariants? In this work, we systematically study the dependency of permeability on the geometrical characteristics of two categories of 3-dimensional porous systems generated: (i) stochastic and (ii) deterministic. For the stochastic systems, we investigated both normal and log-normal size distribution of grains. For the deterministic porous systems, we checked for a cubic and a hexagonal arrangement of grains of equal size. Our studies reveal that for any 3-dimensional porous system, ordered or disordered, permeability $k$ follows a unique scaling relation with the Minkowski functionals: (a) volume of the pore space, (b) integral mean curvature, (c) Euler Characteristic and (d) critical cross-sectional area of the pore space. The cubic and the hexagonal symmetrical systems formed the upper and lower bounds of the scaling relations, respectively. The disordered systems lay between these bounds. Moreover, we propose a combinatoric $F$ that weaves together the four Minkowski functionals and follows a power-law scaling with permeability. The scaling exponent is independent of particle size and distribution and has a universal value of $ 0.428$ for 3-dimensional porous systems built of spherical grains. △ Less

Submitted 8 October, 2024; originally announced October 2024.

Comments: 12 pages, 5 figures

Material elasticity determines scaling behaviour of cracking dynamics in porous materials: A precursor to crack percolation

Authors: Ruhul A. I. Haque, T. Dutta

Abstract: While cracking is a complex dynamics that involves material intrinsic properties like grain shape and size distribution, elastic properties of grain and cementing materials, and extrinsic properties of loading, in this work, the focus has been to check the dependence on the elastic properties of the bonding material. A 3-dimensional disordered system was constructed from spherical balls of varying… ▽ More While cracking is a complex dynamics that involves material intrinsic properties like grain shape and size distribution, elastic properties of grain and cementing materials, and extrinsic properties of loading, in this work, the focus has been to check the dependence on the elastic properties of the bonding material. A 3-dimensional disordered system was constructed from spherical balls of varying radii that were chosen randomly from a log-normal distribution. The growth of micro-cracks with increasing compressive strain was monitored till the limit of the percolation crack. The two parameters varied were the bond stiffness constant and the bond strength of the material. Two distinct regimes of cracking rates were observed across a critical strain $ε_{knee}$ that manifested as a knee in the cumulative crack-strain plot. The critical strain $ε_{knee}$ and the strain at the percolation point $ε_{perc}$ showed a power law dependence on the elastic property of the bond material. Individual micro-cracks were observed to grow sharply to a maximum value $N^{k_{b}}_{max}$, after which the number of new micro-cracks decreased, showing a long tail. The maximum $N^{k_{b}}_{max}$ was found to correspond to the strain $ε_{knee}$, thus indicating that pre-$N^{k_{b}}_{max}$ cracking brittle, followed by ductile cracking behaviour of system. Lastly, we show that there exists a robust relation between $ε_{knee}$ and $ε_{perc}$ that is a power-law where the exponent is a function of the material elastic property. As $ε_{knee}$ can be determined from acoustic signals associated with micro-cracks, our proposed relation can act as a warning towards critical strain resulting in crack percolation. △ Less

Submitted 8 October, 2024; originally announced October 2024.

Comments: 15 pages, 5 figures

Free Standing Epitaxial Oxides Through Remote Epitaxy: The Role of the Evolving Graphene Microstructure

Authors: Asraful Haque, Suman Kumar Mandal, Shubham Kumar Parate, Harshal Jason Dsouza, Sakshi Chandola, Pavan Nukala, Srinivasan Raghavan

Abstract: Remote epitaxy has garnered considerable attention as a promising method that facilitates the growth of thin films that replicate the crystallographic characteristics of a substrate by utilizing two-dimensional (2D) material interlayers like graphene. The resulting film can be exfoliated to form a freestanding membrane, and the substrate, if expensive, can be reused. However, atomically thin 2-D m… ▽ More Remote epitaxy has garnered considerable attention as a promising method that facilitates the growth of thin films that replicate the crystallographic characteristics of a substrate by utilizing two-dimensional (2D) material interlayers like graphene. The resulting film can be exfoliated to form a freestanding membrane, and the substrate, if expensive, can be reused. However, atomically thin 2-D materials are susceptible to damage before and during film growth in the chamber, leading to a poor epitaxy. Oxide remote epitaxy using graphene, the most commonly available 2D material, is particularly challenging because the conventional conditions employed for the growth of epitaxial oxides also degrade graphene. In this study, we show for the first time that a direct correlation exists between the microstructure of graphene, its getting defective on exposure to the pulsed laser deposition plume, and the crystalline quality of the barium titanate film deposited on top. A controlled aperture method was used to reduce graphene damage. Even so, the degree of damage is more at the graphene grain boundaries than within the grains. Large grain-sized greater than 300 microns, graphene suffered less damage and yielded a film comparable to that grown directly on a strontium titanate substrate with a rocking curve half width of 0.6 degrees. Using large grain-sized bi-layer graphene, 4 mm x 5 mm oxide layers were successfully exfoliated and transferred onto SiOx-Si. These insights pave the way for the heterogeneous integration of functional oxides on foreign substrates, holding significant implications for commercializing perovskite oxides by integrating them with Si-CMOS and flexible electronics. △ Less

Submitted 15 August, 2024; originally announced August 2024.

Comments: 36 pages, 18 figures

Heterogeneous integration of high endurance ferroelectric and piezoelectric epitaxial BaTiO$_3$ devices on Si

Authors: Asraful Haque, Harshal Jason D'Souza, Shubham Kumar Parate, Rama Satya Sandilya, Srinivasan Raghavan, Pavan Nukala

Abstract: Integrating epitaxial BaTiO$_3$ (BTO) with Si is essential for leveraging its ferroelectric, piezoelectric, and nonlinear optical properties in microelectronics. Recently, heterogeneous integration approaches that involve growth of BTO on ideal substrates followed by transfer to a desired substrate show promise of achieving excellent device-quality films. However, beyond simple demonstrations of t… ▽ More Integrating epitaxial BaTiO$_3$ (BTO) with Si is essential for leveraging its ferroelectric, piezoelectric, and nonlinear optical properties in microelectronics. Recently, heterogeneous integration approaches that involve growth of BTO on ideal substrates followed by transfer to a desired substrate show promise of achieving excellent device-quality films. However, beyond simple demonstrations of the existence of ferroelectricity, robust devices with high endurance were not yet demonstrated on Si using the latter approach. Here, using a novel two-step approach to synthesize epitaxial BTO using pulsed laser deposition (PLD) on water soluble Sr3Al2O7 (SAO) (on SrTiO$_3$ (STO) substrates), we demonstrate successful integration of high-quality BTO capacitors on Si, with Pr of 7 uC/cm2, Ec 150 kV/cm, ferroelectric and electromechanical endurance of greater than $10^6$ cycles. We further address the challenge of cracking and disintegration of thicker films by first transferring a large area (5 mm x 5 mm) of the templated layer of BTO (~30 nm thick) on the desired substrate, followed by the growth of high-quality BTO on this substrate, as revealed by HRXRD and HRSTEM measurements. These templated Si substrates offer a versatile platform for integrating any epitaxial complex oxides with diverse functionalities onto any inorganic substrate. △ Less

Submitted 15 July, 2024; originally announced July 2024.

Comments: 29 pages, 12 figures

An autoencoder for compressing angle-resolved photoemission spectroscopy data

Authors: Steinn Ymir Agustsson, Mohammad Ahsanul Haque, Thi Tam Truong, Marco Bianchi, Nikita Klyuchnikov, Davide Mottin, Panagiotis Karras, Philip Hofmann

Abstract: Angle-resolved photoemission spectroscopy (ARPES) is a powerful experimental technique to determine the electronic structure of solids. Advances in light sources for ARPES experiments are currently leading to a vast increase of data acquisition rates and data quantity. On the other hand, access time to the most advanced ARPES instruments remains strictly limited, calling for fast, effective, and o… ▽ More Angle-resolved photoemission spectroscopy (ARPES) is a powerful experimental technique to determine the electronic structure of solids. Advances in light sources for ARPES experiments are currently leading to a vast increase of data acquisition rates and data quantity. On the other hand, access time to the most advanced ARPES instruments remains strictly limited, calling for fast, effective, and on-the-fly data analysis tools to exploit this time. In response to this need, we introduce ARPESNet, a versatile autoencoder network that efficiently summmarises and compresses ARPES datasets. We train ARPESNet on a large and varied dataset of 2-dimensional ARPES data extracted by cutting standard 3-dimensional ARPES datasets along random directions in $\mathbf{k}$. To test the data representation capacity of ARPESNet, we compare $k$-means clustering quality between data compressed by ARPESNet, data compressed by discrete cosine transform, and raw data, at different noise levels. ARPESNet data excels in clustering quality despite its high compression ratio. △ Less

Submitted 5 July, 2024; originally announced July 2024.

Journal ref: Machine Learning: Science and Technology 6, 015019 (2025)

Color-switching hydrogels as integrated microfluidic pressure sensors

Authors: Lucie Ducloué, Md. Anamul Haque, Martyna Goral, Muhammad Ilyas, Jian Ping Gong, Anke Lindner

Abstract: Precisely measuring pressure in microfluidic flows is essential for flow control, fluid characterization, and monitoring, but faces specific challenges such as \RE{achieving} sufficient resolution, non-invasiveness, or ease of use. Here, we demonstrate a fully integrated multiplexed optofluidic pressure sensor, entirely decoupled from the flow path, that enables local pressure measurements along a… ▽ More Precisely measuring pressure in microfluidic flows is essential for flow control, fluid characterization, and monitoring, but faces specific challenges such as \RE{achieving} sufficient resolution, non-invasiveness, or ease of use. Here, we demonstrate a fully integrated multiplexed optofluidic pressure sensor, entirely decoupled from the flow path, that enables local pressure measurements along any microfluidic channel without altering its flow geometry. The sensor itself relies on the compression of a soft mechano-actuated hydrogel, changing color in response to a pressure change. The hydrogel is separated from the fluid circulating in the channel by a thin membrane, allowing for the unrestricted use of different types of fluids. Imaging the gel through the transparent PDMS with a color camera provides a direct, easy, and contact-free determination of the fluid pressure at the sensing location for pressures as small as \SI{20}{\milli\bar} with a resolution of around \SI{10}{\milli\bar}. The sensitivity and accessible pressure range can be tuned via the mechanical properties \RE{of the sensing unit}. The photonic gel can also be used to acquire 2D pressure or deformation maps, taking advantage of the fast response time and fine spatial resolution. △ Less

Submitted 3 March, 2024; originally announced March 2024.

Tunable Magnon-Photon Coupling by Magnon Band Gap in a Layered Hybrid Perovskite Antiferromagnet

Authors: Yi Li, Timothy Draher, Andrew H. Comstock, Yuzan Xiong, Md Azimul Haque, Elham Easy, Jiang-Chao Qian, Tomas Polakovic, John E. Pearson, Ralu Divan, Jian-Min Zuo, Xian Zhang, Ulrich Welp, Wai-Kwong Kwok, Axel Hoffmann, Joseph M. Luther, Matthew C. Beard, Dali Sun, Wei Zhang, Valentine Novosad

Abstract: Tunability of coherent coupling between fundamental excitations is an important prerequisite for expanding their functionality in hybrid quantum systems. In hybrid magnonics, the dipolar interaction between magnon and photon usually persists and cannot be switched off. Here, we demonstrate this capability by coupling a superconducting resonator to a layered hybrid perovskite antiferromagnet, which… ▽ More Tunability of coherent coupling between fundamental excitations is an important prerequisite for expanding their functionality in hybrid quantum systems. In hybrid magnonics, the dipolar interaction between magnon and photon usually persists and cannot be switched off. Here, we demonstrate this capability by coupling a superconducting resonator to a layered hybrid perovskite antiferromagnet, which exhibits a magnon band gap due to its intrinsic Dzyaloshinskii-Moriya interaction. The pronounced temperature sensitivity of the magnon band gap location allows us to set the photon mode within the gap and to disable magnon-photon hybridization. When the resonator mode falls into the magnon band gap, the resonator damping rate increases due to the nonzero coupling to the detuned magnon mode. This phenomena can be used to quantify the magnon band gap using an analytical model. Our work brings new opportunities in controlling coherent information processing with quantum properties in complex magnetic materials. △ Less

Submitted 26 July, 2023; originally announced July 2023.

Comments: 8 pages, 4 figures

Robust atmospherically stable hybrid SrVO3/Graphene//SrTiO3 template for fast and facile large-area transfer of complex oxides onto Si

Authors: Asraful Haque, Suman Kumar Mandal, Antony Jeyaseelan, Sandeep Vura, Pavan Nukala, Srinivasan Raghavan

Abstract: Heterogenous integration of complex epitaxial oxides onto Si and other target substrates is recently gaining traction. One of the popular methods involves growing a water-soluble and highly reactive sacrificial buffer layer, such as Sr3Al2O6 (SAO) at the interface, and a functional oxide on top of this. To improve the versatility of layer transfer techniques, it is desired to utilize stable (less… ▽ More Heterogenous integration of complex epitaxial oxides onto Si and other target substrates is recently gaining traction. One of the popular methods involves growing a water-soluble and highly reactive sacrificial buffer layer, such as Sr3Al2O6 (SAO) at the interface, and a functional oxide on top of this. To improve the versatility of layer transfer techniques, it is desired to utilize stable (less reactive) sacrificial layers, without compromising on the transfer rates. In this study, we utilized a combination of chemical vapor deposited (CVD) graphene as a 2D material at the interface and pulsed laser deposited (PLD) water-soluble SrVO3 (SVO) as a sacrificial buffer layer. We show that the graphene layer enhances the dissolution rate of SVO over ten times without compromising its atmospheric stability. We demonstrate the versatility of our hybrid template by growing ferroelectric BaTiO3 (BTO) via PLD and Pb(Zr, Ti)O3 (PZT) via Chemical Solution Deposition (CSD) technique and transferring them onto the target substrates and establishing their ferroelectric properties. Our hybrid templates allow for the realization of the potential of complex oxides in a plethora of device applications for MEMS, electro-optics, and flexible electronics. △ Less

Submitted 6 July, 2023; originally announced July 2023.

Comments: 35 pages, 23 figures

Evolution of polygonal crack patterns in mud when subjected to repeated wetting-drying cycles

Authors: Ruhul A I Haque, Atish J. Mitra, Sujata Tarafdar, Tapati Dutta

Abstract: The present paper demonstrates how a natural crack mosaic resembling a random tessellation evolves with repeated 'wetting followed by drying' cycles. The natural system here is a crack network in a drying colloidal material, for example, a layer of mud. A spring network model is used to simulate consecutive wetting and drying cycles in mud layers until the crack mosaic matures. The simulated resul… ▽ More The present paper demonstrates how a natural crack mosaic resembling a random tessellation evolves with repeated 'wetting followed by drying' cycles. The natural system here is a crack network in a drying colloidal material, for example, a layer of mud. A spring network model is used to simulate consecutive wetting and drying cycles in mud layers until the crack mosaic matures. The simulated results compare favourably with reported experimental findings. The evolution of these crack mosaics has been mapped as a trajectory of a 4-vector tuple in a geometry-topology domain. A phenomenological relation between energy and crack geometry as functions of time cycles is proposed based on principles of crack mechanics. We follow the crack pattern evolution to find that the pattern veers towards a Voronoi mosaic in order to minimize the system energy. Some examples of static crack mosaics in nature have also been explored to verify if nature prefers Voronoi patterns. In this context, the authors define new geometric measures of Voronoi-ness of crack mosaics to quantify how close a tessellation is to a Voronoi tessellation, or even, to a Centroidal Voronoi tessellation. △ Less

Submitted 3 May, 2023; originally announced May 2023.

Closed-loop Error Correction Learning Accelerates Experimental Discovery of Thermoelectric Materials

Authors: Hitarth Choubisa, Md Azimul Haque, Tong Zhu, Lewei Zeng, Maral Vafaie, Derya Baran, Edward H Sargent

Abstract: The exploration of thermoelectric materials is challenging considering the large materials space, combined with added exponential degrees of freedom coming from doping and the diversity of synthetic pathways. Here we seek to incorporate historical data and update and refine it using experimental feedback by employing error-correction learning (ECL). We thus learn from prior datasets and then adapt… ▽ More The exploration of thermoelectric materials is challenging considering the large materials space, combined with added exponential degrees of freedom coming from doping and the diversity of synthetic pathways. Here we seek to incorporate historical data and update and refine it using experimental feedback by employing error-correction learning (ECL). We thus learn from prior datasets and then adapt the model to differences in synthesis and characterization that are otherwise difficult to parameterize. We then apply this strategy to discovering thermoelectric materials where we prioritize synthesis at temperatures < 300°C. We document a previously unreported chemical family of thermoelectric materials, PbSe:SnSb, finding that the best candidate in this chemical family, 2 wt% SnSb doped PbSe, exhibits a power factor more than 2x that of PbSe. Our investigations show that our closed-loop experimentation strategy reduces the required number of experiments to find an optimized material by as much as 3x compared to high-throughput searches powered by state-of-the-art machine learning models. We also observe that this improvement is dependent on the accuracy of prior in a manner that exhibits diminishing returns, and after a certain accuracy is reached, it is factors associated with experimental pathways that dictate the trends. △ Less

Submitted 26 February, 2023; originally announced February 2023.

Non-destructive Depth-Resolved Characterization of Residual Strain Fields in High Electron Mobility Transistors using Differential Aperture X-ray Microscopy

Authors: Darren C. Pagan, Md Abu Jafar Rasel, Rachel E. Lim, Dina Sheyfer, Wenjun Liu, Aman Haque

Abstract: Localized residual stress and elastic strain concentrations in microelectronic devices often affect the electronic performance, resistance to thermomechanical damage, and, likely, radiation tolerance. A primary challenge for characterization of these concentrations is that they exist over sub-$μ$m length-scales, precluding their characterization by more traditional residual stress measurement tech… ▽ More Localized residual stress and elastic strain concentrations in microelectronic devices often affect the electronic performance, resistance to thermomechanical damage, and, likely, radiation tolerance. A primary challenge for characterization of these concentrations is that they exist over sub-$μ$m length-scales, precluding their characterization by more traditional residual stress measurement techniques. Here we demonstrate the use of synchrotron X-ray -based differential aperture X-ray microscopy (DAXM) as a viable, non-destructive means to characterize these stress and strain concentrations in a depth-resolved manner. DAXM is used to map two-dimensional strain fields between source and drain in a gallium nitride (GaN) layer within high electron mobility transistors (HEMTs) with sub-$μ$m spatial resolution. Strain fields at various positions in both pristine and irradiated HEMT specimens are presented in addition to a preliminary stress analysis to estimate the distribution of various stress components within the GaN layer. $γ$-irradiation is found to significantly reduce the lattice plane spacing in the GaN along the sample normal direction which is attributed to radiation damage in transistor components bonded to the GaN during irradiation. △ Less

Submitted 26 August, 2022; v1 submitted 12 July, 2022; originally announced July 2022.

Degree Distribution, Rank-size Distribution, and Leadership Persistence in Mediation-Driven Attachment Networks

Authors: Md. Kamrul Hassan, Liana Islam, Syed Arefinul Haque

Abstract: We investigate the growth of a class of networks in which a new node first picks a mediator at random and connects with $m$ randomly chosen neighbors of the mediator at each time step. We show that degree distribution in such a mediation-driven attachment (MDA) network exhibits power-law $P(k)\sim k^{-γ(m)}$ with a spectrum of exponents depending on $m$. To appreciate the contrast between MDA and… ▽ More We investigate the growth of a class of networks in which a new node first picks a mediator at random and connects with $m$ randomly chosen neighbors of the mediator at each time step. We show that degree distribution in such a mediation-driven attachment (MDA) network exhibits power-law $P(k)\sim k^{-γ(m)}$ with a spectrum of exponents depending on $m$. To appreciate the contrast between MDA and Barabási-Albert (BA) networks, we then discuss their rank-size distribution. To quantify how long a leader, the node with the maximum degree, persists in its leadership as the network evolves, we investigate the leadership persistence probability $F(τ)$ i.e. the probability that a leader retains its leadership up to time $τ$. We find that it exhibits a power-law $F(τ)\sim τ^{-θ(m)}$ with persistence exponent $θ(m) \approx 1.51 \ \forall \ m$ in the MDA networks and $θ(m) \rightarrow 1.53$ exponentially with $m$ in the BA networks. △ Less

Submitted 12 November, 2016; originally announced November 2016.

Comments: 7 pages, 8 figures, accepted for publication in Physica A

Journal ref: Physica A vol. 469 (2017) page 23-30

Evidence of Ballistic Thermal Transport in Lithium Niobate at Room Temperature

Authors: R. A. Pulavarthy, M. A. Haque

Abstract: In ballistic transport, heat carriers such as phonons travel through the solid without any scattering or interaction. Therefore, there is no temperature gradient in the solid, which seems to transport the heat without getting heated itself. Ballistic transport is typically seen in high purity crystals at either temperatures below ~10 K, or physical size below ~100 nm, where the mean free path of t… ▽ More In ballistic transport, heat carriers such as phonons travel through the solid without any scattering or interaction. Therefore, there is no temperature gradient in the solid, which seems to transport the heat without getting heated itself. Ballistic transport is typically seen in high purity crystals at either temperatures below ~10 K, or physical size below ~100 nm, where the mean free path of the carrier is larger than the solid itself. In this letter, we show evidence of ballistic transport at room temperature in lithium niobate wafers in the in-plane and cross-plane directions under both steady state and high frequency heating that are monitored using both infrared and resistance thermometry. We report phonon mean free path in lithium niobate around 425 microns, which is about 50 times higher than the largest phonon mean free path in the literature at room temperature. Above this length-scale, temperature gradient gradually emerges and the material shows completely diffusive, bulk transport at about 4 mm length. Our observations will impact phonon-based electronics such as thermal transistor, thermal logic gate and memory currently impossible at room temperature. If 1 micron electron mean free path in graphene gives the highest-mobility, the 425 microns mean free path of phonons in this research may realize phononics without any need for nanoscale size or ultra-cold temperatures. △ Less

Submitted 8 September, 2016; originally announced September 2016.

Two-dimensional spatial coherence of excitons in semicrystalline polymeric semiconductors: The effect of molecular weight

Authors: Francis Paquin, Hajime Yamagata, Nicholas J. Hestand, Maciej Sakowicz, Nicolas Bérubé, Michel Côté, Luke X. Reynolds, Saif A. Haque, Natalie Stingelin, Frank C. Spano, Carlos Silva

Abstract: The electronic properties of macromolecular semiconductor thin films depend profoundly on their solid-state microstructure, which in turn is governed, among other things, by the processing conditions selected and the polymer chemical nature and molecular weight. Specifically, low-molecular-weight materials form crystalline domains of cofacially $π$-stacked molecules, while the usually entangled na… ▽ More The electronic properties of macromolecular semiconductor thin films depend profoundly on their solid-state microstructure, which in turn is governed, among other things, by the processing conditions selected and the polymer chemical nature and molecular weight. Specifically, low-molecular-weight materials form crystalline domains of cofacially $π$-stacked molecules, while the usually entangled nature of higher molecular-weight polymers leads to microstructures comprised of molecularly ordered crystallites interconnected by amorphous regions. Here, we examine the interplay between extended exciton states delocalized along the polymer backbones and across polymer chains within the $π$-stack, depending on the structural development with molecular weight. We combine optical spectroscopies, thermal probes, and theoretical modeling, focusing on neat poly(3-hexylthiophene) (P3HT), one of the most extensively studied polymer semiconductors, of weight-average molecular weight of 3-450\,kg/mol. The spatial coherence within the chain is significantly reduced (by nearly 30\%). These observations give valuable structural information; they suggest that the macromolecules in aggregated regions of high-molecular-weight P3HT adopt a more planar conformation compared to low-molecular-weight materials. This results in the observed increase in intrachain exciton coherence. In contrast, shorter chains seem to lead to torsionally more disordered architectures. A rigorous, fundamental description of primary photoexcitations in $π$-conjugated polymers is hence developed: two-dimensional excitons are defined by the chain-length dependent molecular arrangement and interconnectivity of the conjugated macromolecules, leading to interplay between intramolecular and intermolecular spatial coherence. △ Less

Submitted 7 June, 2013; originally announced June 2013.

Comments: Submitted to Physical Review X on 6 June 2013, 38 pages, 10 figures

Journal ref: Phys. Rev. B 88, 155202 (2013) [14 pages]

Molecular Dynamics Simulation of Cross-linked Graphene-Epoxy Nanocomposites

Authors: R. Rahman, A. Haque

Abstract: This paper focuses on molecular dynamics (MD) modeling of graphene reinforced cross-linked epoxy (Gr-Ep) nanocomposite. The goal is to study the influence of geometry, and concentration of reinforcing nanographene sheet (NGS) on interfacial properties and elastic constants such as bulk Young's modulus, and shear modulus of Gr-Ep nanocomposites. The most typical cross-linked configuration was obtai… ▽ More This paper focuses on molecular dynamics (MD) modeling of graphene reinforced cross-linked epoxy (Gr-Ep) nanocomposite. The goal is to study the influence of geometry, and concentration of reinforcing nanographene sheet (NGS) on interfacial properties and elastic constants such as bulk Young's modulus, and shear modulus of Gr-Ep nanocomposites. The most typical cross-linked configuration was obtained in order to use in further simulations. The mechanical properties of this cross-linked structure were determined using MD simulations and the results were verified with those available in literatures. Graphene with different aspect ratios and concentrations (1%, 3% and 5%) were considered in order to construct amorphous unit cells of Gr-Ep nanocomposites. The Gr-Ep nanocomposites system undergoes NVT (constant number of atoms, volume and temperature) and NPT (constant number of atoms, pressure and temperature) ensemble with applied uniform strain field during MD simulation to obtain bulk Young's modulus and shear modulus. The stress-strain response was also evaluated for both amorphous and crystalline unit cells of Gr-Ep system under uni-axial deformation. The cohesive and pullout force vs. displacement response were determined for graphenes with different size. Hence as primary goal of this work, a parametric study using MD simulation was conducted for characterizing interfacial properties and elastic constants with different NGS aspect rations and volume fractions. The MD simulation results show reasonable agreement with available published data in the literature. △ Less

Submitted 10 July, 2012; v1 submitted 13 August, 2011; originally announced August 2011.

Comments: Further Revision and modification in the manuscript