arXiv subjects

Gilad Orr

Publications and source records attributed to Gilad Orr.

10 recordsLinked to original sources

arXiv2026

When Trace Water Dominates: Hydration-Mediated Dielectric and Transport Behaviour in BiFeO$_3$

Traces of water can profoundly alter the dielectric response of functional oxides, yet such effects have remained largely unrecognized in systems where colossal dielectric behaviour has been widely reported. Here, we investigate the impact of sub-percent hydration ($<$1 wt\%) on the dielectric relaxation, charge transport, and interfacial polarization properties of porous BiFeO$_3$ ceramics. Broadband dielectric spectroscopy reveals, in the hydrated state, a dominant relaxation process characterized by an anomalously large dielectric strength ($\Delta\varepsilon \approx$ 10$^4$-10$^5$) and a pronounced saddle-point deviation from Arrhenius dynamics, indicative of non-Arrhenius relaxation behaviour in a porous oxide system. These features appear only in the hydrated state and vanish upon dehydration, while the intrinsic activation barriers governing the thermally activated relaxation timescale remain comparable. Comparison with hydration-controlled dielectric responses in layered clay minerals shows that similar qualitative deviations can emerge in BiFeO$_3$ with nearly fifteen-fold lower water content, underscoring the effectiveness of confined water at grain boundaries, pore surfaces, and internal interfaces. Together, these results demonstrate that trace, confined water can make a major extrinsic contribution to dielectric and transport anomalies in porous oxide ceramics. The use of dehydration-controlled dielectric cycling provides a practical diagnostic framework for reassessing colossal dielectric responses, Maxwell-Wagner-type effects, and hydration-induced phenomena in functional oxide materials.

cond-mat.mtrl-sci↗

arXiv2026

Engineering Near-Infrared Two-Level Systems in Confined Alkali Vapors

We combined experimental and theoretical investigations of an effective two-level atomic system operating in the near-infrared telecom wavelength regime, realized using hot rubidium vapor confined within a sub-micron-thick cell. In this strongly confined geometry, atomic coherence is profoundly influenced by wall-induced relaxation arising from frequent atom-surface collisions. By analyzing both absorption and fluorescence spectra, we demonstrate that the optical response is dominated by a closed cycling transition, which effectively isolates the atomic dynamics to a two-level configuration despite the presence of multiple hyperfine states. This confinement-induced selection suppresses optical pumping into uncoupled states and enables robust, controllable light-matter interaction at telecom wavelengths within a miniature atomic platform. Our results establish a practical route to realizing near-infrared atomic two-level systems in compact vapor-cell devices, opening new opportunities for integrated quantum photonic technologies, including on-chip quantum memories, telecom-band frequency references, and scalable quantum information processing.

quant-ph↗

arXiv2025

A Modified Boost Converter Topology for Dynamic Characterization of Hot Carrier and Trap Generation in GaN HEMTs

Modern microelectronic systems require long term operational stability, necessitating precise reliability models to predict device lifecycles and identify governing failure mechanisms. This is particularly critical for high power GaN High-Electron-Mobility Transistors (HEMTs), where reliability research has historically trailed behind low power digital counterparts. This study introduces a novel application of a modified boost converter circuit designed to investigate GaN failure mechanisms, specifically targeting the determination of reliability factors for the MTOL model. By utilizing a high duty cycle, the circuit stresses the device at maximum rated voltages and currents with minimal input requirements, accelerating hot carrier and trap generation without immediate detrimental failure. Experimental validation was conducted using an EPC 2038 GaN transistor under a constant drain current of 400 mA and a duty cycle of 0.7. The results confirmed that the increase in Drain-Source on-resistance ($R_{DS(on)}$) follows a logarithmic trend over time, consistent with the EPC Phase 12 reliability model. While initial tests at 40V did not successfully validate the longitudinal optical phonon scattering energy ($\hbar\omega_{LO}$), but were reasonably acceptable, subsequent stress tests at 70V and 100V yielded $\hbar\omega_{LO}$ values that were successfully validated against existing theoretical and experimental data. This methodology provides a robust framework for predicting performance and lifetime across varying operational parameters in modern power electronics.

eess.SY↗

arXiv2025

Leveraging the Bi$_2$O$_3$--Fe$_2$O$_3$ Phase Diagram to Tailor BiFeO$_3$ Structure and Dielectric Response

Advancing the functional performance of bismuth ferrite (BiFeO$_3$) requires precise control over phase stability and microstructure, challenges often complicated by secondary phase formation within the Bi$_2$O$_3$-Fe$_2$O$_3$ system. In this work, we employ a phase-diagram-guided synthesis strategy to clarify the processing-structure-property relationships governing BiFeO$_3$ ceramics. Based on previous reports and our experimental observations, a refined Bi$_2$O$_3$-Fe$_2$O$_3$ phase diagram was constructed identifing the onset of liquid-phase formation near 835$^\circ$C in Bi-rich compositions. Solid-state synthesis using non-stoichiometric precursor ratios (55$\colon$45 and 70$\colon$30 Bi$_2$O$_3$ $\colon$ Fe$_2$O$_3$) reveals that the 55$\colon$45 composition sintered at 775$^\circ$C favours phase-pure rhombohedral $R3c$ BiFeO$_3$ with suppressed sillenite- and mullite-type impurities, lattice contraction, and improved grain uniformity. These structural refinements result in near-Debye dielectric relaxation and a four-orders-of-magnitude enhancement in electrical conductivity relative to lower-temperature or Bi-rich conditions. This work demonstrates the effectiveness of phase-diagram control as a scalable route to tuning dielectric response in BFO-based multiferroics and provides a foundation for processing optimization in complex oxide ceramics.

cond-mat.mtrl-sci↗

arXiv2025

Structural, optical, and dielectric properties of Cr-doped ZnO films via DC magnetron sputtering

Cr-doped ZnO films were fabricated by a new but feasible method, that is, annealing Cr-Zn layers deposited via DC magnetron sputtering in air. Microstructures of the films were investigated using X-ray diffraction, scanning electron microscopy, and atomic force microscopy, intrinsic point defects were identified via photoluminescence spectroscopy, and optical and dielectric properties were analyzed using a UV-vis spectrophotometer and dielectric spectrometer, respectively. It was found that the average grain sizes decrease (56.34 - 39.50 nm), the band gap increases (from 3.18 to 3.23 eV), and the transmittance (at 600 nm) decreases (from 91% to 83%) with increasing Cr. Two activation energies of conduction increase after doping Cr, indicating enhanced temperature stability. At optimal Cr levels, ZnO films exhibit high transmittance and conductivity, exhibiting potential for transparent electrode development. This method can be extended to other doped ZnO films, such as Al-doped ZnO transparent electrodes, to achieve simultaneous improvements in transmittance, conductivity, and stability for flexible and wearable applications.

cond-mat.mtrl-sci↗

arXiv2025

Beyond Maxwell-Boltzmann statistics using confined vapor cells

Coherence time of thermal photons in rubidium vapor cells with varying thicknesses, reveal that there is clear dependence of the photon correlation time on cell thickness. Standard theoretical models accurately predict the coherence time in centimeter-scale cells. In this study we demonstrated, that these models break down in micrometer and sub-micrometer regimes. Cell sizes ranging from mm-scale down to 200 nm did not adhere to prediction based on the standard models. In order to address this shortcoming, we develop an alternative approach better suited for estimating photonic coherence times in ultra-thin vapor cells. This work, highlights the need for a modified theoretical treatment of the coherence time in the nanoscale regime.

physics.optics↗

arXiv2022

Crystalline quality in aluminium single crystals, characterized by X-Ray diffraction and Rocking-Curve analysis

Aluminum single crystals are tested using X-Ray Bragg diffraction, which may have applications in microscopy and electronics fabrication industry. Yet, their efficiency for x- ray beam diffraction depends on the accurate crystal orientation, the microstructure and imperfections. Moreover, the final sample that is formed from the as-grown crystal by cutting, grinding, polishing and chemical etching, introduces various surface defects that penetrate deep into the crystal affecting its natural structure. Defect penetration is attributed to the fact that ultra-pure aluminum single crystals are soft and ductile with a hardness in the range of 2~2.5 mho. This leads to lattice deformation, resulting in a deviation from the crystallographic orientation of the final device, affecting the diffraction intensity and an apparent shift in the Bragg angle. In this work we investigate the influence of processing aluminum single crystals by mechanical and chemical means using XRD and Rocking-Curve broadening as a quantitative indication concerning the depth of the damage. This is a preliminary step in supporting future work on the study of electrical conduction in aluminum single crystals. Supplementing electrical conductivity measurements of aluminum, quality assessment of defects in front cell aluminum conductors can assist in designing novel low resistance aluminum conductors replacing the currently widely used and relatively rare silver.

cond-mat.mtrl-sci↗

arXiv2021

Complex dielectric behaviours in $BiFeO_{3}/Bi_{2}Fe_{4}O_{9}$ ceramics

The complex dielectric permittivity of a sintered ceramic tablet consisting of 70.5 % $BiFeO_{3}$ and 27.7% $Bi_{2}Fe_{4}O_{9}$ was analyzed as a function of temperature from -120 °C to 230 °C. The results reveal a complicated dielectric response with temperature activated relaxation features. They also reveal a ferroelectric phase transition that decayed with repeated heating cycles of the tablet. The source of the behaviour is assigned to relaxation processes happening along the grain boundaries of differing compositions in the tablet. The origin of the phase transition is traced to locally induced strains on grain boundaries because of unit cell size mismatch between $BiFeO_{3}$ and $Bi_{2}Fe_{4}O_{9}$.

cond-mat.mtrl-sci↗

arXiv2021

Recycling rejected silicon wafers and dies for high grade PV cells

The recent return of the US to the Paris Climate Accord, massive increase in solar panel production and energy storage solutions has resulted in pressure on supply for solar cell materials and recycling of panels installed in the 90's and beginning of the 2000's which have reached their end of life. In this work we focus on recycling silicon wafers and dies by stripping previous structures from the die using potent acids after which its base material is characterized and binned. We demonstrate the process for silicon p-type substrates where n-type doping is attained by using a simple solution of phosphoric acid, which is diffused into the substrate using a furnace thus creating a PN junction. In case the substrate is n-type it could be replaced by boric acid. This is followed by deposition of a conductive antireflective coating, bus bars and rear wafer metal coating. The initial demonstrated laboratory results indicate the feasibility of recycling wafers using simple low cost standard industrial methods.

physics.app-ph↗

arXiv2021

Sintering BFO targets for sputtering

Ceramic $BiFeO_{3}$ samples were prepared by rapid sintering at $880^OC$. Two compositions were examined. A $56/44\ Bi_{2}O_{3}/Fe_{2}O_{3}\ mole\%$ composition and a $56Bi_{2}O_{3}\cdot44Fe_{2}O_{3}+6.5wt\%\,NaCl$ composition. The samples were heat treated at different times up to $8$ minutes and the phase content was examined as a function of the time using XRD measurements and analysis. It was demonstrated that using both compositions, maximum $BiFeO_{3}$ phase content is obtained after $3.5$ minutes. In the former approximately $50\%$ of the material transformed to $BiFeO_{3}$ while in the latter $98.5\%$.

cond-mat.mtrl-sci↗