arXiv subjects

Jon-Paul Maria

Publications and source records attributed to Jon-Paul Maria.

At least 19 recordsLinked to original sources

arXiv2026

Deterministic control over launching efficiency of higher-order hyperbolic phonon polaritons

Hyperbolic materials, which exhibit an extreme form of birefringence enabling the volume confinement and frequency-dependent propagation of deeply sub-diffractional optical modes, offer the opportunity for extreme confinement via the stimulation polaritonic modes, with substantially higher confinement obtained through the efficient excitation of of the higher-order (shorter wavelength) hyperbolic polaritonic modes, which they can support. However, while these higher-order hyperbolic polaritons (HO-HPhPs) form high-momentum ray-like propagation within the bulk, efficient excitation of these modes, especially in contrast to the long-wavelength lower-momentum surface polariton propagating modes, has remained a challenge. Critically, the large momentum mismatch between these modes and free-space light, alongside the spatial mismatch between the sub-diffractional scatterer and the distinct modal distribution of HO-HPhPs, lead to a suppressed launching efficiency of these higher-order modes, limiting their use in nanophotonic applications. Here, we report the experimental observation of a 10-fold enhancement in the excitation efficiency of HO-HPhPs through the use of subsurface scatterers over traditional surface scattering (e.g. a flake edge or gold launcher) within single-crystalline {\alpha}-MoO3 slabs. We employ full-wave numerical simulations to investigate the role of the spatial overlap between HO-HPhP modal distributions and the scatterer placement upon excitation efficiency. Furthermore, we develop a generalized process using transfer matrix method to selectively design modal HO-HPhP excitation, which advances the capabilities of HPhP multiplexing for on-chip applications.

physics.optics↗

arXiv2026

Absence of lateral domain wall mobility in Zn1-xMgxO thin films

Polarization reversal in ferroelectrics arises from the coupled processes of domain nucleation and subsequent growth, yet the governing mechanisms differ fundamentally between classical perovskite oxides and emerging wurtzite ferroelectrics. While switching in perovskites is typically governed by mobile domain walls whose field-driven propagation dominates macroscopic kinetics, here we show that polarization reversal in wurtzite Zn1-xMgxO proceeds through a qualitatively different pathway. Using scanning oscillator microscopy, in combination with point pulse-imaging methods, we directly map local switching events and domain wall responses, revealing that domain walls in Zn1-xMgxO exhibit negligible lateral mobility (sub 10nm) and that polarization reversal proceeds predominantly through the nucleation of vertically extended columnar filaments with a lateral size on the order of the grains. This nucleation-controlled switching contrasts sharply with the growth-mediated dynamics characteristic of perovskite ferroelectrics and explains the abrupt, spatially localized switching behavior observed in wurtzite systems. These results establish nucleation-dominated filamentary reversal as a defining switching mechanism in Zn1-xMgxO and point towards the need for further studies to understand correlation lengths and nucleation processes across a range of grain sizes.

cond-mat.mtrl-sci↗

arXiv2026

An Automated Magnetron Sputtering Chamber for Ferroelectric Thin Film Deposition

Optimization of next-generation materials synthesis and manufacturing processes can be accelerated by effective use of digital datasets. However, a majority of existing custom research infrastructure, including that for thin film deposition, is primarily manually operated and not compatible with this new research paradigm. Here, a template is provided for upgrading existing manual deposition chambers to enable automated and autonomous experimentation. As an example, the upgrade of an existing magnetron sputtering chamber dedicated to synthesis of wurtzite ferroelectrics is presented. Focus is placed on automation of instrumentation; system and deposition control; and synchronized and automated data collection strategies. An example use case of the system for semi-autonomous determination of process-property relationships is presented, specifically minimization of coercive field in wurtzite Al$_{1-x-y}$Sc$_x$B$_y$N thin films.

cond-mat.mtrl-sci↗

arXiv2026

Ionic Diffusion Properties of Rare-Earth High-Entropy Oxides from a Machine-Learned Interatomic Potential

Rare-earth high-entropy oxides (RE-HEOs) have emerged as a promising class of functional ceramics for solid-state electrochemical applications due to their chemical complexity, structural tunability, and potential for fast oxygen-ion transport. In this work, we investigate oxygen diffusion in ceria-based RE-HEOs of the form Ce$_x$(YLaPrSm)$_{1-x}$O$_{2-\delta}$ using classical molecular dynamics simulations driven by the Crystal Hamiltonian Graph Neural Network (CHGNet) machine-learned interatomic potential. To improve predictive accuracy for lanthanide-containing systems, we benchmark three CHGNet variants, including a fine-tuned r$^2$SCAN-trained model, against targeted density functional theory (DFT) data that explicitly include f-valence electrons. Simulations across temperature, Ce content, oxygen vacancy concentration, and both fluorite and bixbyite structures reveal that oxygen transport in RE-HEOs is governed by the interplay of two factors: the concentration of mobile vacancies and the local cation environment through which they hop. At fixed composition, ionic conductivity exhibits a non-monotonic dependence on vacancy concentration, with optimal diffusion occurring at moderate vacancy levels and reduced mobility at higher concentrations. Increasing Ce content lowers migration activation energies and enhances diffusivity through low-barrier diffusion networks built from Ce-Ce and Ce-Y edges. Analysis of individual oxygen hopping events provides atomistic insight into how local chemical environments and short-range cation ordering govern transport in high-entropy oxides. Overall, this work demonstrates that machine-learned interatomic potentials can resolve composition-structure-transport relationships in chemically complex oxides, and identifies active pathways through which compositional tuning can enhance oxygen-ion conductivity in RE-HEO materials.

cond-mat.mtrl-sci↗

arXiv2026

From Closed-Loop Optimization to Open Decision Making: Coupled Digital Twins for Predictive and Autonomous Microscopy

Automated experimentation is moving from closed-loop optimization toward open decision-making, where human or AI planners must forecast the consequences of candidate actions before executing them. Such forecasts require a model of both sides of the experiment: how the sample is likely to respond and what the instrument is likely to detect. We therefore introduce a coupled digital-twin framework that separates these roles and then links them. In this framework, the sample twin encodes material state inferred from prior knowledge and measurements till the moment. The instrument twin captures signal formation, feedback dynamics, and operating constraints based on prior knowledge. When coupled, the two twins estimate expected outcomes, uncertainty, and risk for candidate microscope operations. For amplitude-modulation scanning probe microscopy, we realize this framework with a physics-informed encoder of force-distance curves, a deterministic scanner model of cantilever and feedback dynamics, and sparse learned residual corrections. The encoder first recovers scanner-driving descriptors with sub-nanometer accuracy. The calibrated scanner then reproduces typical traces within a few nanometers and identifies operating-point noise amplification as the main source of mismatch. Supplementary phase analysis localizes residual error to the phase channel, which clarifies where added physics is needed. Together, these results establish coupled sample and instrument twins as a practical foundation for predictive microscope operation and autonomous experimental planning.

cond-mat.mtrl-sci↗

arXiv2026

Hydrothermally-Assisted Sintering of Calcium Hydroxide Sputtering Targets: A Route to Quantum-Grade CaO Thin Films

In this report we demonstrate dense polycrystalline calcium hydroxide ceramics fabricated by hydrothermally-assisted sintering - often referred to as cold-sintering - to produce high-purity calcium hydroxide targets for calcium oxide thin film deposition. Calcium hydroxide ceramics exhibit up to 98% theoretical density without thermal dehydration, when sintered at temperatures between 100 {\deg}C - 300{\deg} C with 400 MPa applied uniaxial pressure for 1 hour. The brucite phase is preserved in calcium hydroxide targets at all temperatures. Small equivalent fractions of calcium carbonate are present in both the calcium hydroxide precursor powder and final targets suggesting minimal additional production during formation and densification. Microstructure evolution during densification is documented by scanning electron microscopy, indicating both mass transport and plastic deformation densification mechanisms. The hydrothermal-assisted sintering process is scaled up to produce 2-inch diameter calcium hydroxide targets suitable for sputter deposition. We also report epitaxial calcium oxide film deposition from these targets on r-plane sapphire substrates. (002) oriented epitaxial films are achieved with a time-stable 1.2 nm per minute deposition rate. We note that energetic bombardment during growth can be substantial at these rates even when 1 mol% oxygen is added to the sputtering process necessitating the low deposition rate conditions.

cond-mat.mtrl-sci↗

arXiv2026

Quantifying the coupling between strain and cation valence in high entropy oxide thin films using electron microscopy

High entropy oxides (HEOs) are a class of materials with vast compositional space and tunable properties, making them attractive for applications in thermoelectrics, magnetism, ionic conduction, and beyond. However, their metastable nature makes the local structure, and consequently their properties, highly sensitive to growth conditions. It is therefore essential to probe the local modulations in atomic, chemical, and electronic structure as a function of growth conditions. Here, advanced S/TEM techniques, including 4D-STEM combined with electron energy loss spectroscopy and energy-dispersive X-ray spectroscopy are used to investigate the effect of substrate temperature on structure and strain at the nanoscale regime in HEO thin films. We quantify how nanoscale strain variations correlate with Co valence and subtle chemical differences in the films with the same nominal composition but different growth temperatures. Our results demonstrate that identical HEO compositions can accommodate distinct strain and defect states in thin film form and highlight how synthesis conditions can be leveraged to manipulate strain and Co valence. These findings establish a framework to tailor functional properties via strain and valence control in high entropy oxide thin films.

cond-mat.mtrl-sci↗

arXiv2026

About Time: Observation of Time-Reflection at Optical Frequencies

Time-reflection occurs when a wave is propagating in a medium undergoing a large and abrupt change in its properties: the original wave splits into a time-refracted wave and a time-reflected wave, each displaying different features. The time-refracted wave continues along its original course but experiences a frequency shift, whereas the time-reflected wave is propagating backwards in space with a reversed phase, also with a shifted frequency. These phenomena are fundamental to any wave system, but the most interesting are electromagnetic (EM) waves, specifically at optical frequencies, where they can couple to light-matter interactions. However, time-reflection of EM waves was thus far observed only at RF frequencies, never at optical frequencies. This is because time-reflection requires an order-unity variation of the refractive index occurring faster than a single wave cycle, and conventional optical nonlinearities are either too weak or too slow by orders of magnitude. Here, we present the first observation of time-reflection at optical frequencies. We induce an order-unity refractive-index change with sub-cycle duration, observe the time-reflection, and study its fundamental properties. These results provide an experimental pathway to experimenting with time-interfaces, generating photonic time-crystals and exploring new regimes of light-matter interaction in time-varying media.

physics.optics↗

arXiv2026

Anomalous Crystallinity and Magnetism in Chemically Disordered Coherent Heterostructures

High-entropy oxide (HEO) thin films uniquely superimpose exceptional chemical disorder with exceptional crystalline quality and coherence - an intersection we term anomalous crystallinity that arises from coupled structural, chemical, and valence degrees of freedom unique to the entropy-stabilized condition. Here, we demonstrate unexpected and predictive control of this state using formulation, epitaxial constraints, and kinetic arrest of metastable macrostates. Specifically, aliovalent cation substitutions, tightly controlled substrate temperatures, and conditions favoring significant adatom kinetic energy, can program the out-of-plane lattice parameter of coherent rock salt HEOs while preserving in-plane epitaxial pinning to MgO. Lattice strains exceeding 5% can be stabilized in multilayer heterostructures using this approach, where 3+ cations compensated by cation vacancies predominate the defect chemistry landscape. We highlight the exemplar (Sc,Mg,Co,Ni,Cu,Zn)O/(Cr,Mg,Co,Ni,Cu,Zn)O (JSc/JCr) system where Sc and Cr substitution into the rock salt structure produces pseudomorphic heterostructures between individual antiferromagnets exhibiting exceptional strain and abrupt interfaces across which the Co valence switches from mostly 2+ to an even 2+/3+ mixture. These unprecedented valence interfaces are accompanied by a 2x exchange bias boost compared to single-layer constituents, that could be attributed to enhanced uncompensated spins in the layers themselves or around the buried JSc/JCr interface. These results establish pseudomorphic valence interfaces with anomalous crystallinity as a source of new magnetic macrostates that host emergent magnetic and spintronic functionality.

cond-mat.mtrl-sci↗

arXiv2026

Ferroelectric dynamic-field-driven nucleation and growth model for predictive materials-to-circuit co-design

Real ferroelectric devices operate under mixed and distorted time-varying voltages, yet the standard nucleation-growth frameworks used to interpret ferroelectric switching - most notably the Kolmogorov-Avrami-Ishibashi (KAI) and nucleation-limited switching models (NLS) - are derived under the critically limiting assumption of a constant electric field. Thus, the prevailing interpretation of ferroelectric switching dynamics fails under real operating conditions. Here we introduce a compact dynamic-field-driven nucleation and growth (DFNG) model that enables quantitative fits to switching transients across multiple ferroelectric materials to extract time-varying domain wall velocity and growth dimensionality, even under arbitrary voltage waveform. This capability then motivates its use in device modeling under complex signals spanning disparate time and frequency scales. Coupling the compact model to application-related waveforms and circuit-level simulation platform facilitates a predictive materials-circuit co-design framework by linking nucleation and growth parameters to memory window, disturb error, speed, and energy dissipation for next-generation ferroelectric technologies.

cond-mat.mtrl-sci↗

arXiv2026

Sub-cycle time-refraction at optical frequencies

Large and abrupt variations in the electromagnetic properties of materials lead to dramatic effects: even a single step-like change in the refractive index induces striking phenomena, such as time-refraction and time-reflection. When the refractive index varies periodically in time, multiple time-refractions and -reflections interfere, giving rise to photonic time-crystals (PTCs). Importantly, PTCs display momentum bands separated by gaps in which the modes experience exponential amplification, drawing energy from the modulation in a non-resonant fashion. Ordinary nonlinear optics does not operate in this regime: the material response is either very weak or very slow. One of the immediate consequences is that time-reflection of light at optical frequencies has never been observed in experiments. Here, we experimentally realize an order-unity change in the refractive index occurring at sub-cycle rates, and explore the phenomena emerging from it. By varying the duration of the index change from extending over many cycles to being significantly below a single cycle, we observe that the frequency shift of the time-refraction is enhanced as the index variation occurs faster. Our experiment is the gateway for realizing sharp time-interfaces at optical frequencies, which are the key for experimenting with time-reflection, PTCs and new phenomena expected from light-matter interactions in time-varying media.

physics.optics↗

arXiv2026

Multi-resonant non-dispersive infrared gas sensing: breaking the selectivity and sensitivity tradeoff

In applications such as atmospheric monitoring of greenhouse gases and pollutants, the detection and identification of trace concentrations of harmful gases is commonly achieved using non-dispersive infrared (NDIR) sensors. These devices employ a broadband infrared emitter, thermopile detector, and a spectrally selective bandpass filter tuned to the vibrational resonance of the target analyte. However, the fabrication of these filters is costly and limited to a single frequency. This limitation introduces a fundamental tradeoff, as broadening the optical passband width enhances sensitivity but compromises selectivity, whereas narrowing improves selectivity at the expense of sensitivity. In this work, we validate a filterless NDIR approach using a multi-peak thermal emitter developed through inverse design. This emitter enhances detection sensitivity by targeting multiple absorption bands, demonstrated through the creation of a sensor designed for the C-H vibrational modes of propane. Additionally, a set of single-peak emitters were developed to showcase the capability of designing highly selective sensors operating within close spectral proximity. These emitters, targeting the stretching modes of carbon monoxide and carbon dioxide, exhibit Q-factors above 50 and minimal crosstalk, enabling accurate detection of the target gas without interference from gases with spectrally adjacent absorption bands. This is enabled by the implementation of an aperiodic distributed Bragg reflectors, which allows for higher Q-factors with fewer layers than a periodic Bragg reflector using the same materials and number of layers, thereby reducing fabrication complexity and cost. Experimental results validate that this approach breaks the tradeoff between sensitivity and selectivity. This work highlights the potential of optimized thermal emitters for more efficient and compact gas sensing applications.

cond-mat.mes-hall↗

arXiv2026

Tailoring phonon-driven responses in {\alpha}-MoO3 through isotopic enrichment

The implementation of polaritonic materials into nanoscale devices requires selective tuning of parameters to realize desired spectral or thermal responses. One robust material is {\alpha}-MoO3, which as an orthorhombic crystal boasts three distinct phonon dispersions, providing three polaritonic dispersions of hyperbolic phonon polaritons (HPhPs) across the mid-infrared (MIR). Here, the tunability of both optical and thermal responses in isotopically enriched {\alpha}-MoO3 (98MoO3, Mo18O3 and 98Mo18O3) are explored. A uniform ~5 % spectral redshift from 18O enrichment is observed in both Raman- and IR-active TO phonons. Both the in- and out-of-plane thermal conductivities for the isotopic variations are reported. Ab initio calculations both replicate experimental findings and analyze the select-mode three-phonon scattering contributions. The HPhPs from each isotopic variation are probed with s-SNOM and their Q- factors are reported. A Q-factor maxima increase of ~50 % along the [100] in the RB2 and ~100 % along the [001] in the RB3 are reported for HPhPs supported in 98Mo18O3. Observations in both real and Fourier space of higher-order HPhP modes propagating in single slabs of isotopically enriched {\alpha}-MoO3 without the use of a subdiffractional surface scatterer are presented here. This work illustrates the tunability of {\alpha}-MoO3 for thermal and nanophotonic applications.

cond-mat.mtrl-sci↗

arXiv2025

Compositional and Oxygen-Vacancy Effects on Phase Stability and Electronic Properties in Ceria-Based Lanthanide High-Entropy Oxides

Cerium-based lanthanide high-entropy oxides (LN-HEOs) are promising candidates for solid-state electrolyte (mass transport) applications due to their ability to accommodate high concentrations of oxygen vacancies while retaining a fluorite-derived structure. However, synthesis often yields undesired ordered oxygen-deficient phases, such as bixbyite, depending on composition and processing conditions. We utilize first-principles density functional theory (DFT) calculations to systematically investigate phase stability in the model system Ce$_x$(YLaPrSm)$_{1-x}$O$_{2-\delta}$, with the aim of elucidating the thermodynamic factors governing fluorite-bixbyite competition and identifying structure-property relationships to oxygen transport. By independently varying cerium concentration and oxygen vacancy content, we predict that the transition from disordered fluorite to ordered bixbyite is driven primarily by compositional and vacancy-ordering effects, rather than through changes in cation valence. Free-energy analysis reveals that at high vacancy concentrations, bixbyite is enthalpically favored due to ordered oxygen vacancies, while fluorite is stabilized at lower vacancy concentrations and higher cerium content through configurational entropy of the anion sublattice. These DFT results clarify the competing energetic contributions that control phase stability and structure-valence relationships in LN-HEOs and establishes a mechanistic framework for designing vacancy-tolerant oxide electrolytes with tunable phase behavior.

cond-mat.mtrl-sci↗

arXiv2025

Rapid synthesis of dual-element isotope-enriched alpha-MoO3 crystals by reactive vapor transport

In this work, we develop a rapid reactive vapor transport technique to efficiently utilize limited isotopically pure precursors, particularly gaseous 18O2, and synthesize mm-scale, high-quality crystals within few-minute growth durations. We unlock this capability by using metallic molybdenum precursors with high source temperatures (900 C) and total pressures (1 atm) to maximize precursor efficiency and yield. Subsequently, we grow MoO3 single crystals with high and uniform enrichment levels of 98Mo and 18O isotopes in several different permutations. As probed by Raman spectroscopy, modest and significant phonon energy redshifts occur following 98Mo and 18O enrichment, respectively. By demonstrating control over both molybdenum and oxygen isotopic fractions, we establish a powerful tool to advance nanophotonics and thermal management goals using MoO3. This work is motivated by the possibility to enhance and engineer lattice vibrational mode phenomena including thermal conduction and hyperbolic phonon polariton (HPhP) dispersion, with particular interest in comparing the effects of light and heavy element enrichment.

cond-mat.mtrl-sci↗

arXiv2025

A Software Package for Generating Robust and Accurate Potentials using the Moment Tensor Potential Framework

We present the Plan for Robust and Accurate Potentials (PRAPs), a software package for training and using moment tensor potentials (MTPs) in concert with the Machine Learned Interatomic Potentials (MLIP) software package. PRAPs provides an automated workflow to train MTPs using active learning procedures, and a variety of utilities to ease and improve workflows when utilizing the MLIP software. PRAPs was originally developed in the context of crystal structure prediction, in which one calculates convex hulls and predicts low energy metastable and thermodynamically stable structures, but the potentials PRAPs develops are not limited to such applications. PRAPs produces two potentials, one capable of rough estimates of the energies, forces and stresses of almost any chemical structure in the specified compositional space -- the Robust Potential -- and a second potential intended to provide more accurate descriptions of ground state and metastable structures -- the Accurate Potential. We also present a Python library, mliputils, designed to assist users in working with the chemical structural files used by the MLIP package.

physics.chem-ph↗

arXiv2025

Resolving Structural Transitions in Lanthanide High-Entropy Oxides

We report a temperature-composition phase diagram for the chemically disordered and CeO2-LA2O3 high entropy oxides (HEOs), where LA denotes equimolar Y, La, Sm, and Pr, delineating stability regions for bixbyite, disordered fluorite, and intermediate vacancy-ordered fluorite phases. The diagram is constructed from a characterization package applied to bulk ceramics including X-ray diffraction (XRD), transmission electron microscopy (TEM) electron diffraction, Raman spectroscopy, energy-dispersive spectroscopy, X-ray absorption near-edge structure spectroscopy, and ultraviolet-visible spectroscopy, to quantify crystal structure at multiple length-scales, local coordination environments, and electronic structures across the formulation space. This comprehensive measurement suite is critical to identify boundaries between the closely related phases. For example, Raman scattering reveals local structural and defect environments unique to bixbyite local order that persist to ~50% Ce under equilibrium synthesis conditions but are invisible to XRD and TEM. We also report a companion thin film study to demonstrate that quenched kinetic energy from a physical deposition process can metastabilize the high symmetry, and thus high entropy, fluorite phase with only 20% Ce. This is noteworthy because electroneutrality constraints demand an exceptionally vacated oxygen sublattice; we estimate 16.7%, approaching that of delta-Bi2O3. Together, our equilibrium ceramics and far-from-equilibrium thin films show that when synthesis is coupled with rigorously chosen, multi-length-scale characterization, now one can identify the phase stability thermodynamic drivers and simultaneously derive practical guidelines for experimentally realizing targeted phases and structures - and thereby deliberately engineer properties in CeO2-LA2O3 HEOs, whose broad defect chemistries demand such an approach.

cond-mat.mtrl-sci↗

arXiv2025

Exploring Cation Selection and Disorder within Entropy-Driven $A_{6}B_{2}$O$_{17}$ ($A$=Zr/Hf, $B$=Nb/Ta) Oxides

We investigate the local atomic and electronic structure, thermodynamic stability, and defect chemistry of $A_{6}B_{2}$O$_{17}$ ($A$ = Zr/Hf, $B$ = Nb/Ta) oxides using first-principles density functional theory (DFT) calculations. We examine both ordered unit cells as well as fully disordered special quasirandom structures to clearly discern the effects of cation disorder. Structural predictions align closely with previous experimental results and follow established ionic radii trends. The electronic structure is strongly dependent on $B$-cation species: $A_{6}$Ta$_{2}$O$_{17}$ compositions have ~30% larger band gaps than their $A_{6}$Nb$_{2}$O$_{17}$ counterparts. Defect chemistry is similar for all compositions, with anion vacancies being more energetically favorable than corresponding cation defects. All explored $A_{6}B_{2}$O$_{17}$ compositions are enthalpically unstable with respect to their $A$O$_{2}$ and $B_{2}$O$_{5}$ competing oxides and are therefore classified as entropy-stabilized materials, supporting prior experimental results. The pronounced agreement between our disordered supercell predictions with experimental measurements indicates all explored $A_{6}B_{2}$O$_{17}$ compositions contain substantial cation disorder across all 6-, 7-, and 8-coordinated sites. Our findings collectively provide a fundamental understanding of the $A_{6}B_{2}$O$_{17}$ material family through DFT calculations, establishing a framework for future compositional tuning to engineer targeted material properties.

cond-mat.mtrl-sci↗