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Thursday 6 August

Applied Physics · Cross-listed from physics.soc-ph

The Structure of Spreading on Temporal Networks

Omar Henderson, Mikko Kivelä and Márton Karsai

The physics of spreading in static networks is well understood through mappings to percolation. We show that spreading dynamics on temporal networks can analogously be mapped to reachability in temporal event graphs. This provides a theoretical and computational framework for a class of processes, such as variants of the susceptible-infected-susceptible model. Without explicit simulations, through the component analysis of event graphs, we obtain epidemic prevalence and derive epidemic thresholds for temporal networks with arbitrary degree and inter-event time distributions, with significant computational advantages as compared to explicit simulations.
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Applied Physics · Cross-listed from physics.optics

Pulse-Duration Control of Subcycle Multiband Electron Dynamics Extends the High-Harmonic Cutoff in a Light-Driven Insulator

Hortense Allegre, Simon V. B. Jensen, Joseph J. Broughton et al. (+7 more)

We demonstrate pathway-selective control of extreme-ultraviolet high-harmonic generation by jointly tuning laser pulse duration ($5$ - $29$ fs) and intensity ($0.8$ - $74$ TW/cm$^2$). Many-cycle pulses at moderate intensities, $\sim 6$ TW/cm$^2$, promote cumulative carrier transfer over successive optical cycles, progressively accessing higher conduction bands. In contrast, few-cycle, high-intensity, $\sim 22$ TW/cm$^2$, pulses drive subcycle multiband dynamics that reach $25$ - $50$ eV photon energies before decoherence can suppress coherent emission. These results reveal pulse duration and intensity as decisive control knobs for high-harmonic emission, opening a route to band-structure-guided pulse design for higher energy extreme-ultraviolet light sources.
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All authors Hortense Allegre, Simon V. B. Jensen, Joseph J. Broughton, Tim Klee, Yan Li, Jon P. Marangos, Nicolas Tancogne-Dejean, Angel Rubio, John W. G. Tisch, Mary R. Matthews

Applied Physics · Cross-listed from physics.acc-ph

Conceptual design of a mid-energy spin rotator for continuous-wave operation based on a compact multi-pi rosetta magnet

Volker Ziemann

Spin-rotators in the the few-MeV range require large trajectory deflection angles in order to change the spin direction appreciably. We describe a magnet system that accumulates adequately large bending angles in a small footprint and, at the same time, supports continuous-wave operation.
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Applied Physics · Cross-listed from cs.AI

OPERA: Operator-residual feedback for reliable autonomous optical experiments with language-model agents

Ning Xu, Xiang Zheng, Fuqiang Zhong et al. (+4 more)

Autonomous agents choose actions using scores that may not reflect experimental success. We developed OPERA, an operator-residual framework for optical experiments. It represents experimental actions as optical operators and evaluates their outcomes using physically interpretable residuals. Operators specify executable changes to measurement, control or reconstruction, while residuals report departures from specified physical conditions. The agent uses both to select, combine or generate operators, and physical performance is evaluated independently against a withheld reference. Across three optical tasks, score-only feedback produced score increases without physical improvement in 23.6–39.0% of decisions, compared with 0.9–1.9% for operator-residual feedback. Operator-residual feedback increased the probability of reaching and maintaining task targets and reduced experimental budgets. Protocols selected in digital twins were transferred to three optical instruments, and repeated experiments showed a lower projection budget in structured-light reconstruction. Together, operators and residuals guide autonomous decisions using measurable physical evidence.
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All authors Ning Xu, Xiang Zheng, Fuqiang Zhong, Huadong Wang, Xiaolong Wu, Zhiyuan Liu, Hui Ning

Applied Physics · Cross-listed from physics.flu-dyn

Drop Spray Electrification

Riko Kazama, Masaya Toda, Hans-Jürgen Butt et al. (+1 more)

Charge separation during the breakup of water drop has been recognized since the early studies of waterfall and spray electrification, yet the role of controlled drop fragmentation at structured liquid-repellent surfaces remains unclear. Here we show that water drops impacting superhydrophobic meshes generate charged secondary droplets as liquid penetrates and fragments through the mesh pores. By combining Faraday-cup charge measurements with high-speed imaging, we identify how the charge depends on the Weber number and on the pathway of spray formation. No measurable charge is detected below the penetration threshold. At low Weber numbers, recoil jet formation gives a high charge per unit spray mass, whereas at intermediate Weber numbers both recoil jets and impact-induced jets contribute to charging. At higher Weber numbers, pancake bouncing suppresses recoil jet formation, so charging is dominated by impact induced penetration and the total charge approaches a saturated value. We further show that smaller mesh pores enhance the charge-to-mass ratio and that conductive meshes provide stable charging under repeated impacts by dissipating residual surface charge. These findings provide design principles for superhydrophobic mesh platforms for spray charging and rain-driven energy harvesting.
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All authors Riko Kazama, Masaya Toda, Hans-Jürgen Butt, Rutvik Lathia

Wednesday 5 August

Applied Physics

Reduction of intrinsic losses in nanomechanical silicon nitride resonators through thermal treatment in ultrahigh vacuum

Nicola Cavalleri, Ariane Giesriegl, Robert G. West et al. (+7 more)

Since the discovery of dissipation dilution, silicon nitride (SiN) nanomechanical resonators have set the benchmark for ultracoherent mechanical systems, with geometry and strain engineering driving remarkable gains in the $f \cdot Q$ product. Surface loss, however, has remained the dominant and largely unaddressed dissipation channel. Here, we demonstrate a geometry-independent approach that directly targets surface loss: thermal treatment in ultrahigh vacuum. Treatment at 1000$^{\circ}$C enhances the intrinsic quality factor of dissipation-diluted SiN membrane resonators by up to a factor of 20, reduces the surface loss eightfold, and simultaneously increases the tensile stress. Photothermal infrared spectroscopy and $\textit{in situ}$ X-ray photoelectron spectroscopy trace the enhancement to thermally activated silanol condensation - the conversion of surface hydroxyl terminations into siloxane bridges - and the reversibility of both quality factor and stress under controlled humidity confirms the surface-chemical origin. These results establish surface chemistry as a tunable parameter for next-generation ultracoherent nanomechanical resonators.
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All authors Nicola Cavalleri, Ariane Giesriegl, Robert G. West, Kostas Kanellopulos, Saeed Rasouli, Daniele Nazzari, Pedram Sadeghi, Sebastian Alberti, Antonius Armanious, Silvan Schmid

Applied Physics · Cross-listed from physics.optics

Mask-free fast patterning of organic light-emitting diode pixels using laser-assisted close-space sublimation

Subhamoy Sahoo, Jain Jose, Mani R et al. (+8 more)

Existing patterning processes for organic light-emitting diode displays offer micrometer-scale precision but are constrained by long processing times for large-area substrates. In this work, we study a fast growth method for patterned organic film deposition, aimed at applications including active-matrix organic light-emitting diode displays. The approach employs a specially engineered donor substrate in a close-space sublimation configuration combined with laser heating. The donor substrate incorporates spatially patterned absorber and reflector layers that enable selective, one-step or two-step transfer of organic material onto a receiver substrate. We analyze the optical response and heat-transfer dynamics that govern the selective transfer mechanism and demonstrate precise pixel patterning with micrometer-scale spatial fidelity. The reliability and practical applicability of the method are validated by fabricating light-emitting diode devices by using this rapid transfer process and benchmarking their performance against devices produced via conventional vacuum thermal evaporation. The resulting devices exhibit comparable optoelectronic performance, confirming the robustness and technological relevance of the proposed strategy for scalable fabrication of patterned organic light-emitting diodes for display application.
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All authors Subhamoy Sahoo, Jain Jose, Mani R, Arghya Saha, Kanimozhi V, Dhruvajyoti Barah, R. Bairava Ganesh, Amitava Majumdar, Jayeeta Bhattacharyya, G Rajeswaran, Debdutta Ray

Applied Physics · Cross-listed from astro-ph.IM

CCAT: Characterization of the first science-grade MKID array for the Prime-Cam 850 GHz module

Anthony I. Huber, Jordan Wheeler, James Burgoyne et al. (+15 more)

The Fred Young Submillimeter Telescope (FYST) is a 6-meter crossed-Dragone telescope developed by the CCAT collaboration. Sited at 5600 m on Cerro Chajnantor in the Atacama Plateau of Chile, FYST aims to provide superior atmospheric transmission and a wide field of view for submillimeter observations. Prime-Cam is a first-generation instrument for FYST designed to house up to seven separate instrument modules. Among these, the 850 GHz module represents the highest-frequency band and is optimized for ultra-sensitive broadband polarimetry and imaging. This module is designed to deploy ~38,000 polarization-sensitive lumped-element titanium-nitride (TiN) microwave kinetic inductance detectors (MKIDs) across three arrays. Thus the 850 GHz module will have the most submillimeter MKIDs in a single instrument module to date. These detectors have adopted a novel two-octave design to maximize the multiplexing achieved using a RFSoC readout system. We review the design parameters and fabrication process for the first 850 GHz science-grade array. The preliminary measurements of the array show a fabrication yield of 99%, highlighting the successful application of the design and fabrication process. We further present the cryogenic characterization of the first full MKID array developed for the Prime-Cam 850 GHz module. Multiple tests were performed on the devices including resonator frequency mapping, quality factor measurements, optical load sweeps and noise performance. From these measurements, we discuss the measured optical efficiency, sensitivity, and uniformity across the array and the expected on-sky performance of the module. The 850 GHz module will be deployed for observing in 2027.
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All authors Anthony I. Huber, Jordan Wheeler, James Burgoyne, Scott Chapman, Jason Austermann, James Beall, Steve K. Choi, Doug Henke, Johannes Hubmayr, Ben Keller, Matthew Koc, Jeff van Lanen, Tilak Patel, Adrian Sinclair, Anna Vaskuri, Eve M. Vavagiakis, Michael Vissers, Ruixuan Xie

Applied Physics · Cross-listed from physics.comp-ph

From populations to absolute binding affinities in molecular simulations: exact volumetric terms and practical estimators

Davide Mandelli, Emiliano Ippoliti and Charles Plate

We present a statistical-mechanics framework for computing equilibrium binding constants $K$ in the dilute limit. From first principles, we derive a general expression relating $K$ to the relative populations of the bound and unbound states. Its transparency has twofold advantage: it makes the origin of the unbound-state volumetric term explicit, and it allows one to track exactly how an imposed volume restraint propagates through the expression. This makes $K$ directly computable, as restrained simulations can account for the volumetric contribution exactly, under the physically mild assumption of a homogeneous unbound state. The resulting estimators are computable from histograms of any suitably defined reaction coordinate, and determine unambiguously how the boundaries of the thermodynamic states of interest must be defined. We apply our framework to the cucurbit[7]uril/1-adamantanol host–guest complex and the galactonate–DgoT ligand–protein complex. Our results show that commonly used single-bin estimators depart from the theoretically correct one by $\approx 1$~kcal/mol in both systems. This shift originates in the definition of the bound state: by anchoring that definition to what state-of-the-art experiments resolve, the theory turns it from a hidden assumption into a controlled input, and provides a principled route to absolute binding affinities from molecular simulations.
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Applied Physics

Memristive Behavior and Mechanism in Solid-State Nanopores

Zhiwei Li, Ngan Hoang Pham, Shi-Li Zhang et al. (+1 more)

Nanofluidic memristors whose conductance evolves through history-dependent ionic transport and dynamic interfacial processes are promising building blocks for ionic neuromorphic applications. However, most existing designs rely on biological nanopores, polymers, and two-dimensional materials, which limit scalable fabrication and poses challenges to integration of ionic computing circuits and systems. Here, we report memristive behaviors of silicon-based solid-state nanopores (SSNPs) fabricated based on wafer-scale semiconductor processes. The SSNPs exhibit hysteretic current-voltage characteristics with a dependence on voltage sweeping frequency, electrolyte concentration, and nanopore geometry. To investigate the physical origin of their memory feature, the measured current of the SSNPs is decomposed into resistive, capacitive, and memristive components. An ion adsorption-desorption kinetics is developed to explain and predict the memristive behavior. A dynamical system analysis further reveals that the memristive behavior arises from delayed relaxation, thereby linking the measured hysteresis to the observed adaptive ionic response. Together, these findings establish native SSNPs as scalable ionic memristive elements and provide a generalized electrokinetic mechanism for memristive behavior under nanoconfinement. The resulting analytical framework connects device characterization with the underlying dynamics, deepens mechanism understanding, and guides the design of ionic neuromorphic devices.
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All authors Zhiwei Li, Ngan Hoang Pham, Shi-Li Zhang, Chenyu Wen

Applied Physics · Cross-listed from physics.chem-ph

Time-resolved THz Stark spectroscopy of molecules in water

Elnaz Zyaee, Vladislav Slama, Seyyed Jabbar Mousavi et al. (+3 more)

Stark spectroscopy is a powerful method for probing molecular dipole moment changes, charge transfer dynamics, and polarizability under applied electric fields. Time-Resolved Terahertz Stark Spectroscopy (TRTSS), which employs intense single-cycle terahertz (THz) pulses to induce transient Stark shifts, overcomes key limitations of conventional approaches. Unlike static or low-frequency fields, THz pulses oscillate much faster than typical molecular rotation times, effectively preventing dipole reorientation and enabling measurements in solutions at ambient conditions. Here, we extend TRTSS to molecules dissolved in water, the most important polar solvent for chemical and biological systems and report the first demonstration of Stark spectroscopy in water at room temperature. Using Malachite Green and Methyl Orange as model systems, we observe clear THz-induced spectral modulations, demonstrating that TRTSS can successfully reveal THz Stark responses even in highly polar, hydrogen-bonded environments. Measured signals exhibit a combination of linear (dipole-driven) and quadratic (polarizability-driven) Stark effects in both systems, consistent with time-dependent density functional theory (TD-DFT) calculations. Comparison with TD-DFT further suggests that conformational effects can influence the extracted Stark parameters in solvated molecules.
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All authors Elnaz Zyaee, Vladislav Slama, Seyyed Jabbar Mousavi, David Rohrbach, Ursula Rothlisberger, Thomas Feurer

Applied Physics · Cross-listed from cond-mat.mes-hall

Methods for traceable scanning magnetometry using single nitrogen vacancy centers in diamond: determining orientation, distance and localization

Nikhita Khera, Ephraim Spindler, Yanis Abdedou et al. (+7 more)

Individual, scannable nitrogen vacancy (NV) centers in single crystal diamond nanostructures enable nanoscale, quantitative imaging of magnetic stray fields. Nevertheless, important parameters like distance between the NV center and the sample and the orientation of the NV high symmetry axis are often not known precisely and enter data evaluation as free fitting parameters. We here use scanning NV imaging on micro-patterned, perpendicularly magnetized stripes and discs. From these measurements, we directly infer NV - sample distance d_NV and the NV's azimuthal orientation without the need for an external vector magnet control. We determine d_NV = 31.5 nm, while we infer the azimuthal orientation with a precision of 3{\deg}. We additionally employ commercially available silicon needles to image the apex topography of our diamond nanostructures to detect surface contamination. Simultaneously, monitoring NV fluorescence as a function of the needle's position allows us to estimate the lateral placement of the NV inside the diamond nanostructure.
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All authors Nikhita Khera, Ephraim Spindler, Yanis Abdedou, Marcel Gasser, Sandra Wolff, Bert Lägel, Robert Frömter, Mathias Weiler, Mathias Kläui, Elke Neu

Applied Physics · Cross-listed from physics.optics

Universal Function Approximation via Diffractive Optical Processors: Physical Limits, Error Bounds, and Learnability

Md Sadman Sakib Rahman, Che-Yung Shen and Aydogan Ozcan

We present a unified theoretical framework connecting classical universal approximation theory, Fourier-feature approximation, and diffractive optical processors. We show that phase-encoded diffractive processors implement finite Fourier-feature expansions whose mathematical completeness follows from Fourier/Stone-Weierstrass arguments, while their physical realizability is governed by finite coefficient synthesis through optimized spatially varying coherent point-spread functions (PSFs). Our analyses derive approximation-error bounds that separate Fourier truncation, PSF-synthesis, input phase error, optical hardware, readout, and noise contributions; establish scaling relationships linking approximation complexity to optical degrees of freedom and input/output space-bandwidth products; derive photon-budget and throughput limits imposed by photon statistics; formulate finite-class statistical learnability bounds for phase-quantized diffractive function approximators; and analyze the impact of spatially incoherent illumination. We further analyze coherent optical cascadability and show that quadratic feature expansion through coherent mixing and optical readout provides a mechanism for enhanced representation while remaining fundamentally distinct from the depth-separation results established for digital neural networks. Our analyses provide a rigorous theoretical foundation for diffractive nonlinear function approximation and establish quantitative relationships among mathematical expressivity, optical hardware resources, statistical learning, and physical performance limits, thereby offering general design principles for large-scale analog optical computing systems.
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Applied Physics · Cross-listed from physics.optics

Photogalvanic second harmonic generation in Si3N4 for 1 Hz level on-chip metrology and spectroscopy

Andrei Diakonov, Roy Zektzer, Xiyuan Lu et al. (+2 more)

The coherent photogalvanic (PG) effect induces an effective $\chi^{(2)}$ nonlinearity in natively $\chi^{(3)}$ silicon nitride integrated photonics, unlocking pathways toward chip-scale precision spectroscopy and optical clockworks via second harmonic generation (SHG). While quasi-phase-matched PG-SHG using spatially varying internal electric fields offers tuning flexibility, it is often accompanied by pump-power- and detuning-dependent frequency offsets. Here, we investigate whether direct phase-matching—utilizing an intermodal scheme that generates a spatially uniform electric field—can support metrologically compatible SHG. By comparing the fundamental and doubled optical frequencies in a silicon nitride microresonator, we test the preservation of the (2:1) frequency ratio in directly phase-matched PG-SHG. We observe a frequency offset of $< 1\mathrm{~Hz}$, contrasting with previous limitations in quasi-phase-matched configurations. Furthermore, we measure a residual fractional frequency instability of $2\times 10^{-15}$ at $1\mathrm{~s}$, averaging down to the $10^{-16}$ level at $1000\mathrm{~s}$, with multi-hour deviations remaining below $1\mathrm{~Hz}$. These results establish directly phase-matched PG-SHG as a robust, metrologically compatible route to effective $\chi^{(2)}$ functionality, combining sub-Hz frequency-ratio fidelity and high coherence on a mature integrated platform for optical clockworks, self-referencing, and precision spectroscopy.
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All authors Andrei Diakonov, Roy Zektzer, Xiyuan Lu, Kartik Srinivasan, Liron Stern

Applied Physics · Cross-listed from quant-ph

Engineering Nanodiamonds for Quantum Sensing: Material Constraints at the Nanoscale

Ashutosh Rathi, Keisuke Oshimi, Kento Sasaki et al. (+6 more)

Optically addressable solid-state spin defects have emerged as powerful multimodal quantum sensors, with nitrogen-vacancy (NV) centers in bulk diamond providing benchmark quantum control and sensitivity under ambient conditions. Embedding such defects in nanodiamonds (NDs) extends these capabilities to mobile probes capable of accessing complex biological and nanoscale environments. Reduced dimensions, however, introduce constraints beyond volumetric spin impurities, notably enhanced lattice strain and surface-induced noise sources, which shorten NV spin relaxation times (T1 and T2) and destabilize the NV charge state, as well as resulting in pronounced particle-to-particle variability in NDs typically produced by top-down approaches. These effects complicate both sensing performance and the quantitative interpretation of multimodal signals in realistic environments. This article provides a structured perspective on the physical mechanisms by which material properties constrain NV behavior in NDs, together with mitigation strategies that shape the robust use of these mobile quantum sensors for biosensing and nanoscale science.
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All authors Ashutosh Rathi, Keisuke Oshimi, Kento Sasaki, Kensuke Kobayashi, Yutaka Shikano, Oliver Benson, Tim Schröder, Shery L. Y. Chang, Masazumi Fujiwara

Tuesday 4 August

Applied Physics

Fully optoelectronic coherent THz spectroscopy

François Parnet, Francis Hindle, Ulysse Mao et al. (+9 more)

Coherent terahertz spectroscopy of molecular transients has so far relied on electronic sources whose bandwidth is limited to a fraction of their center frequency. Photoconductive devices offer a complementary approach, combining intrinsically broadband operation with coherent optoelectronic generation and detection. We report free-induction-decay spectroscopy of carbonyl sulfide at 0.29 THz in which, to our knowledge for the first time, both the pulsed emitter and the coherent heterodyne receiver are LT-GaAs photoconductors simultaneously pumped by a single free-running dual-frequency Ti:Sa laser. The receiver operates within 15 dB of the thermal noise limit, and the shared optical reference maintains phase coherence over more than 1000 averaged acquisitions. The measured transients agree with a time-domain Maxwell-Bloch model based on HITRAN parameters. These results demonstrate the feasibility of fully optoelectronic coherent THz spectroscopy and establish photoconductive optoelectronic mixing as a practical route toward frequency-agile, high-resolution coherent THz spectrometers over broad spectral ranges.
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All authors François Parnet, Francis Hindle, Ulysse Mao, Guillaume Ducournau, Jean-François Lampin, Sophie Eliet, François Bondu, Romain Peretti, Gaël Mouret, Daniele Fontanari, Goulc'hen Loas, Emilien Peytavit

Applied Physics · Cross-listed from physics.optics

Self-Focusing Control for Depth-Precise Wafer Slicing of 4H-SiC in Femtosecond Laser Processing

Dong Hee Kang, Jaeseung Lim, Mishfaqur Rahman et al. (+4 more)

4H-SiC has emerged as a third-generation chip material because its superior thermal conductivity and high breakdown field enable the material to achieve high power density and higher switching frequencies in power-electronics applications. As chip architectures evolve toward 3D and heterogeneous integration, the mechanical and thermal design space tightens while yield risks grow. In particular, advanced packages require mid-process wafer thinning to < 100 $\mu$m to shorten interconnects and control thermo-mechanical stress. Femtosecond laser slicing for 4H-SiC wafers offers a non-contact processing approach to produce thin layers with low defects, while strong optical nonlinearities obscure the relationship between the laser parameters and the resulting slicing quality. Here, we systematically investigate Kerr-induced self-focusing using a femtosecond laser in 4H-SiC slicing by combining experiments, a semi-empirical analytical model, and numerical ray optics simulations. We demonstrate that the interplay between pulse energy and processing depth governs the self-focusing behavior, which directly correlates with post-separation surface texture parameters and separation stress, thereby linking nonlinear beam propagation to slicing quality. Based on this relationship, we define a processability map in the pulse energy with self-focusing depth space over a normalized irradiance background. Analytically, the model extends the Marburger formula to focused beams by replacing the power ratio with a normalized irradiance. Ray optics simulations capture the geometric features at the self-focusing point and are validated against experimental observations. Within physically defined thresholds, the processability map directly connects laser parameters to separation stress and surface texture metrics, providing practical guidance for depth control beyond trial-and-error.
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All authors Dong Hee Kang, Jaeseung Lim, Mishfaqur Rahman, Seongheum Han, Jae-Hak Lee, Seungman Kim, Jihoon Jeong

Applied Physics

Circuit-Level Design, Modeling, and On-Wafer Characterization of a Coplanar THz Optoelectronic Mixer

S. Islam, V. Merupo, C. Chamek et al. (+13 more)

We report the design, modeling, and on-wafer characterization of a photoconductive heterodyne mixer implemented as a true terahertz monolithic integrated circuit (TMIC). Unlike previous photoconductive heterodyne demonstrations, the proposed circuit is characterized using RF integrated circuit metrics including input return loss, RF/IF isolation, broadband impedance matching, and conversion loss. The mixer combines a microcavity photoconductor with a broadband coplanar matching network incorporating a Ti shunt resistor, an RF DC-blocking MIM capacitor, and an RF/IF decoupling capacitor. A circuit-level model including both the photoconductor and the distributed CPW accesses is developed and validated. The passive circuit is experimentally characterized up to 500 GHz using on-wafer VNA measurements and accurately reproduced by simulation. Under illumination, the model predicts an input reflection coefficient below -10 dB up to 215 GHz and better than -6.5 dB up to 500 GHz. Measured and simulated conversion losses agree within +/-1 dB over the entire 1-500 GHz range. Conversion loss varies from 22.5-25.5 dB below 320 GHz and 26-34 dB up to 500 GHz. The proposed TMIC demonstrates broadband operation and provides a validated circuit design methodology for future integrated THz photonic mixers.
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All authors S. Islam, V. Merupo, C. Chamek, M. Sassi, C. Coinon, Y. Deblock, E. Okada, S. Lepilliet, F. Braud, Q. Fornasiero, G. Di Gioia, M. Faucher, G. Ducournau, G. Loas, S. Arscott, E. Peytavit

Applied Physics

Thermodynamically consistent initialization of the Maxwell–Cattaneo—Vernotte heat conduction model: Analytical solutions and engineering applications

Zalán Sándor and Róbert Kovács

This paper investigates the numerical initialization of the one-dimensional Maxwell–Cattaneo–Vernotte (MCV) heat conduction model, addressing the critical mathematical challenge of defining the initial time derivative for non-equilibrium states. In modern high-frequency thermal engineering applications, traditional time-integration schemes and commercial finite-element solvers frequently introduce severe numerical artifacts when handling non-Fourier models. This study systematically evaluates three initialization strategies: a zero derivative, a spatially uniform non-zero derivative, and an exact space-dependent derivative. Using an explicit staggered finite-difference scheme, the transient responses to an exponentially distributed initial temperature field under adiabatic boundary conditions are compared against an analytical solution using the Galerkin method. The results demonstrate that assuming a zero or spatially uniform initial derivative introduces significant unphysical oscillatory deviations, leading to heat-flux prediction errors as the relaxation time increases. Conversely, mapping the exact space-dependent derivative onto the staggered grid preserves the local thermodynamic structure of the initial state, yielding robust transient responses that match the analytical benchmark without meaningful computational overhead. These findings establish a thermodynamically consistent initialization technique that can be extended to non-local models as well.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci

Picometre-scale real-time drift correction in TEM and STEM by dynamic control of the specimen stage for atomic-resolution imaging

Christophe Gatel, Julien Dupuy, Teresa Hungria et al. (+1 more)

In this work, we show how the specimen drift can be actively compensated by controlling the stage with precision down to the picometre scale. We do this by dynamic control, a generic real-time feedback framework designed to actively stabilize electron microscopy experiments by continuously monitoring an experimental variable from the detector data stream and compensating its evolution during acquisition. The framework, applicable to a broad range of controllable experimental instabilities, includes automated calibration procedures, operates in parallel with image acquisition and is implemented as a software plugin without requiring any hardware modification of the microscope. Results for live drift correction are shown for a selection of TEM and STEM instruments using conventional mechanical stages as well as piezoelectric stages. Experimental results are presented for medium resolution TEM, high-resolution TEM, HR-STEM and in situ observations. With piezoelectric stages, specimen stabilization down to the picometre scale was achieved allowing drift-corrected atomic-resolution imaging. Specimen stage-based stabilization significantly improves long-exposure imaging and in situ experiments by increasing the effective exposure time, preserving the field of view, maintaining identical optical conditions and eliminating the need for numerical alignment of large datasets. Beyond the specific application presented here, dynamic control provides a versatile framework for real-time regulation of electron microscopy experiments and opens new perspectives for quantitative imaging, automated in situ studies and multimodal acquisitions.
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All authors Christophe Gatel, Julien Dupuy, Teresa Hungria, Martin J. Hytch

2608.03344 · 4 Aug · 27 pages, 9 figures. Submitted to Ultramicroscopy Christophe Gatel: Writing original draft, Software, Methodology, Investigation, Data treatment, Conceptualization, Resources, Funding acquisition. Julien Dupuis: Software, Conceptualization, Methodology. Teresa Hungria: STEM experiment, Review & editing. Martin Hytch: Review & editing, Data treatment, Resources, Funding acquisition

Abstract PDF $ALIGN ×1$DATA ×1$EVO ×1$MMOD ×1

Applied Physics

Event-Based Spatial-Carrier Interferometry for Surface-Normal Vibration-Waveform Reconstruction

Ryogo Niwa, Tatsuki Fushimi and Yoichi Ochiai

Non-contact measurement of small vibrations perpendicular to a surface supports the evaluation of mechanical structures, but in camera-based interferometry, increasing the frame rate makes a trade-off with the field of view and spatial resolution. By recording only brightness changes, event cameras avoid this trade-off and reach high temporal and spatial resolution; our previously reported event topology-based visual vibrometer recovers vibration from apparent motion. This high-speed, high-resolution sensing is well suited to full-field measurement, yet such vibration produces too little apparent motion to capture its waveform. Here we show that event-based spatial-carrier interferometry reconstructs that waveform from moving interference fringes. That displacement moves the fringes, and signed event-density maps built from the event stream are demodulated at the spatial carrier to recover the interferometric phase and fix the otherwise ambiguous motion direction at turning points. Reconstructed waveforms agree with laser Doppler vibrometry over broad drive-frequency and amplitude ranges, with limits set by the maximum fringe speed and the sensor performance. Reconstruction is limited by a minimum aperture of about two fringe periods along the carrier and one along the fringes, which allows the surface to be mapped region by region. These results provide an empirical basis for full-field, spatially resolved interferometric vibrometry with event cameras as a non-contact measurement technique.
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Applied Physics · Cross-listed from physics.optics

Zero-change foundry compatible silicon photonics MEMS optical switch

Arkadev Roy, Daniel Klawson, Jianheng Luo et al. (+3 more)

Large-scale photonic switches are emerging as essential devices for energy-efficient optical interconnect in data centers and AI/ML clusters as a key enabler for high-bandwidth and low-latency connectivity. Combining micro-electro-mechanical (MEMS) based mechanical reconfigurability with silicon photonic integrated circuits can enable a large-scale, low-loss, programmable platform required for large-scale optical circuit switches. We demonstrate a broadband silicon photonics MEMS switch with more than 30 dB extinction ratio operating in C-band using a zero-change foundry-compatible process and Back-end-of-Line (BEOL) post-processing. The optical switch element exhibits an insertion loss of less than 1.5 dB with a low static power consumption of approx 20 nW at maximum actuation voltage. Our results illustrate that MEMS-based silicon photonics modulators and phase shifters can be used alongside standard silicon photonics components seamlessly in scenarios where performance in terms of footprint, extinction ratio, broad bandwidth, and low-loss operation is of paramount importance.
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All authors Arkadev Roy, Daniel Klawson, Jianheng Luo, Yiyang Zhi, Sirui Tang, Ming Wu

Applied Physics · Cross-listed from physics.optics

Breaking the trade-off between invisibility and sensitivity in electromagnetic sensing

Yichao Liu, Jiaxue Zhou, Weifeng Han et al. (+6 more)

Weak electromagnetic signals demand highly sensitive sensors, yet increasing a sensor's sensitivity inevitably strengthens its interaction with the surrounding field, producing scattering that perturbs the very signals being measured. Conversely, existing cloaking strategies suppress scattering only by isolating the sensor from incident waves, thereby compromising signal reception. Resolving this long-standing trade-off between invisibility and sensitivity has remained an outstanding challenge. Here we overcome this dilemma through an integrated transformation-optical architecture that co-designs the entire sensing system, including the electrically large sensor body, the subwavelength sensing probe, and their electrical interconnection. The proposed multifunctional core-shell structure guides incident waves around the sensor body while simultaneously concentrating them into the sensing region without disturbing the external electromagnetic field. A deep-subwavelength aperture preserves electrical connectivity without degrading either cloaking or field concentration, enabling invisible sensing within a single platform. A microwave prototype based on practical optic-null-medium metamaterials experimentally demonstrates broadband scattering suppression exceeding 3 dB together with an average sixfold enhancement of the detected signal over 4.9-5.1 GHz. By simultaneously eliminating measurement-induced field perturbation and amplifying the local sensing field, our approach establishes a general framework for invisible yet highly responsive electromagnetic sensors, opening new opportunities for weak-signal detection in biomedical diagnostics, secure communications, quantum technologies, and deep-space exploration.
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All authors Yichao Liu, Jiaxue Zhou, Weifeng Han, Hanchuan Chen, Fei Sun, Qin Liao, Hengxiang Zhang, Xiaofan Ji, Yawen Qi

Monday 3 August

Applied Physics · Cross-listed from physics.med-ph

Real-time tissue-equivalent measurement of individual clinical radiotherapy pulses

Fernanda C. Rodrigues-Machado, Katherine Szabo, Jingyi Bian et al. (+5 more)

We apply the precision tools of cavity-enhanced absorption sensing to clinical oncology, demonstrating a dosimeter paradigm in which a centimeter-scale volume of water serves as a tissue-equivalent sensing medium. Our proof-of-concept, all-optical scheme achieves real-time readout of clinical radiation pulses with a nominal single-pulse resolution of 90 $\mu$Gy. This demonstration paves the way toward fiber-integrated, micron-scale devices for $\textit{in situ}$ universal absolute dosimetry during treatment.
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All authors Fernanda C. Rodrigues-Machado, Katherine Szabo, Jingyi Bian, Simon Bernard, Tanner Connell, Shirin A. Enger, Lilian Childress, Jack C. Sankey

Applied Physics · Cross-listed from cond-mat.mtrl-sci

Investigation of GeSn aspect ratio trapping growth up to 8% Sn

Hryhorii Stanchu, Quang Minh Thai, Fernando M. de Oliveira et al. (+10 more)

Aspect ratio trapping (ART) growth of germanium-tin (GeSn) is a promising approach to target important objectives on the quest towards commercialization of complementary metal-oxide-semiconductor (CMOS)-compatible GeSn optoelectronics devices. Its local growth on patterned substrate allows for versatile device integration into photonics integrated circuit or for stand-alone structure like focal plane array imager. Additionally, high aspect ratio from nano-sized window can terminate early threading dislocation propagation on the oxide sidewalls, leaving subsequent growth defect-free and potentially improving the device performance. Knowledge remains missing regarding GeSn ART growth kinetics, morphology and how they evolve from thin film growth, with successful growth itself yet to be demonstrated. In this work, we report GeSn ART growth up to 8% Sn. Two configurations – self-induced Ge core/GeSn shell for Sn content between 6% and 8%, and bulk GeSn ART for Sn content below 1% – are observed. We present a comprehensive study on GeSn ART growth kinetics through different growth rounds and designs, showing a link between pyramid shape of ART island and successful Sn incorporation, as well as the role of growth selectivity and local heating.
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All authors Hryhorii Stanchu, Quang Minh Thai, Fernando M. de Oliveira, Mourad Benamara, Stephen Margiotta, Matthew Cook, Xiaoxin Wang, Jifeng Liu, Perry C. Grant, Baohua Li, Wei Du, Gregory Salamo, Shui-Qing Yu

Applied Physics

Reduced Dark Current in Cd0.9Zn0.1Te Detector Arrays by Aluminium Oxide Passivation

Sudarshan Singh, Luc Montpetit, Eloïse Rahier et al. (+3 more)

Contrary to the prevailing view that processing cadmium zinc telluride (CZT) semiconductors above 150 {\deg}C leads to irreversible device degradation, here we show that Al2O3 passivation layer deposited by atomic layer deposition at 250 {\deg}C not only preserves CZT detector performance but also substantially improves it. Pixelated metal-semiconductor (MS) and metal-insulator-semiconductor (MIS) CZT detectors were passivated with a thin atomic-layer-deposited Al2O3 film and characterized electrically. The passivated devices exhibited no measurable degradation, even under a high-bias operation of 1000 V. Instead, the dark current decreased by approximately a factor of five, while the interpixel leakage current was reduced by nearly one order of magnitude, from ~41 nA to ~2-3 nA at -200 V. Passivation also produced highly uniform dark-current characteristics across adjacent pixels and completely eliminated current-voltage hysteresis, indicating suppression of defect-assisted charge transport. Furthermore, no significant difference in dark current was observed between the MS and MIS detectors after passivation, suggesting that the Al2O3 layer dominates the surface electrical behavior. These results demonstrate that optimized Al2O3 passivation at 250 {\deg}C is fully compatible with high-performance CZT detector processing and provides a practical route toward lower-noise, higher-spectral-resolution X-ray imaging systems.
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All authors Sudarshan Singh, Luc Montpetit, Eloïse Rahier, Mahmoud R. M. Atalla, Sebastian Koelling, Oussama Moutanabbir

Applied Physics · Cross-listed from physics.optics

Metaphotonic Catalysis: Amorphous silicon metasurfaces encode photochemical activity

Elif Nur Dayi, Priscila Vensaus, Milad Sabzehparvar et al. (+3 more)

Solar-to-fuel conversion can benefit from photoelectrodes with engineered light-matter interactions, yet most nanostructured designs provide limited control over the spatial and spectral distribution of photochemical activity. Here, we present an all-dielectric amorphous-silicon metasurface photoelectrode that confines resonant light-matter interactions within a 220-nm-thick active layer. Tunable Mie-type and guided-mode resonances spectrally encode chemical reactivity and produce absorptance above 80% near the silicon band edge, compared with less than 30% for an unpatterned film of the same thickness. The metasurface simultaneously functions as the light absorber, carrier-transport layer, and catalytic interface without an added co-catalyst or engineered passivation layer. Operando photo-scanning electrochemical microscopy reveals wavelength- and structure-dependent redox activity and a tenfold enhancement in internal quantum efficiency near the silicon band edge relative to planar films. Power-dependent measurements support a photon-driven rather than nonlinear photothermal origin of the enhancement, while surface-sensitive ultrafast transient-reflectivity measurements probe the underlying carrier dynamics. Light-coupled scanning electrochemical cell microscopy further shows hydrogen-evolution enhancements of up to 21-fold under photocatalytic conditions and 15-fold under photoelectrochemical bias, corresponding to 11.2-fold and 7.7-fold enhancements after accounting for the estimated surface-area increase. The metasurfaces remain stable during more than 10 hours of immersion and prolonged laser illumination. These results establish amorphous silicon as a stable and versatile platform for resonantly programmed photocatalysis and solar-fuel generation.
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All authors Elif Nur Dayi, Priscila Vensaus, Milad Sabzehparvar, Michele Puppin, Omer Can Karaman, Giulia Tagliabue

Applied Physics · Cross-listed from quant-ph

Revealing and reducing growth-induced interfacial disorder in preferentially aligned nitrogen-vacancy centers in diamond

Cheng-I Ho, Marina Davydova, Patrik Straňák et al. (+4 more)

Nitrogen-vacancy (NV) centers in chemical-vapor-deposition (CVD) diamond can form preferentially oriented ensembles with high sensing performance and low densities of lattice defects. Thin films of this material are a cornerstone of various imaging modalities. However, nitrogen injection needed to produce such films can transiently drive growth out of equilibrium, generating interfacial strain and spin defects that degrade NV coherence. Here, we investigate this disorder in $^{12}\text{C}$-enriched, preferentially oriented NV layers grown on (111) diamond using two nitrogen-injection procedures, combined with nanometer-scale selective plasma etching and NV spin-coherence measurements. Pulsed nitrogen injection produces a pronounced nitrogen overshoot within a 60–80 nm interfacial region, generating excessive amounts of defects. By contrast, smooth nitrogen delivery through mass flow controllers substantially suppresses interfacial disorder, yielding coherence properties close to the theoretical limit imposed by spin-bath noise. A 50-nm NV layer is used to demonstrate proton nuclear magnetic resonance detection. This work reveals the role of interfacial disorder associated with the nitrogen-doping procedure and provides a route to growing high-quality, thin NV-doped layers for quantum-sensing applications.
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All authors Cheng-I Ho, Marina Davydova, Patrik Straňák, Felix Hoffmann, Peter Knittel, Andrej Denisenko, Jörg Wrachtrup

Applied Physics · Cross-listed from eess.AS

MEMS Microphones as Ultrasonic Transducers: Nonlinear Electrostatic Actuation and a Parametric Array Prototype

Xiaoyu Niu, Zihuan Liu, Ehsan Vatankhah et al. (+2 more)

This paper investigates commercial-style capacitive MEMS microphone dies as air-coupled ultrasonic transmitters under nonlinear pull-in and snap-back actuation and demonstrates a compact parametric-array prototype. A single die produces large diaphragm displacement and measurable ultrasonic pressure in air. A 28-die array driven at 83 and 93 kHz generates a directional component at the 10 kHz difference frequency. Measurements are compared with analytical radiation theory and finite-element modeling, and the effects of aperture, fill factor, device uniformity, and receiver nonlinearity are discussed.
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All authors Xiaoyu Niu, Zihuan Liu, Ehsan Vatankhah, Yuqi Meng, Neal A. Hall

2608.02203 · 3 Aug · 14 pages, 9 figures. Expanded article based on work presented at the 183rd Meeting of the Acoustical Society of America. This version adds a 28-die parametric-array prototype, analytical and finite-element modeling, and extended discussion. An earlier meeting abstract covering part of this work appeared in J. Acoust. Soc. Am. 152, A50-A51 (2022), DOI: 10.1121/10.0015506

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