Focused ion beam (FIB) milling is a commonly used tool for nanoscale material processing, such as for transmission electron microscopy (TEM) sample preparation, or the creation of fiducial markers prior to other processes and measurements. During milling, a high energy ion beam is used to remove material via sputtering. The expelled target material may return to the sample surface however, affecting subsequent measurements. Beam spreading or irradiation due to neutral gallium may also irradiate a larger area than intended. Extensive research has explored the effects of FIB milling on the prepared TEM sample, but few have looked at the effects of milling on the properties of the sample surrounding the milled region. We use multiple pump-probe laser-based techniques (time domain thermoreflectance and steady-state thermoreflectance) to measure the spatial extent of FIB-induced surface/subsurface changes on a series of silicon wafers milled at multiple currents and doses. We supplement these measurements with high-resolution scanning transmission electron microscopy, energy dispersive X-ray spectroscopy, stylus profilometry, and time-of-flight secondary ion mass spectroscopy. We find a sample surface affected by the FIB up to 1 mm from where milling occurred, with a notable dependence on the ion beam current. We also note remarkably high sensitivity to surface defects using the thermoreflectance metrologies, including detection where other measurements failed.

Aluminum is highly valued in ultraviolet (UV) optics for its exceptional reflectivity at wavelengths as short as 90 nm, but its effectiveness is compromised by rapid formation of a native oxide layer that reduces its UV reflectivity. To mitigate this issue, fluorine-containing protective layers, such as aluminum fluoride, are applied to inhibit oxidation while maintaining high transmission rates. Additionally, an aluminum fluoride layer serves as an effective barrier coating in advanced lithium-ion battery designs, preventing failures like significant temperature increases and thermal runaway. Despite these important applications, the thermal and mechanical properties of aluminum fluoride thin films have not been thoroughly investigated. In this study, optical pump-probe techniques are used to measure the thermal conductivity and elastic moduli of aluminum fluoride passivation layers with thicknesses ranging from 4 to 48 nm. The passivation layers are produced using a plasma-based process that removes the native oxide while converting the aluminum into aluminum fluoride. The results show that both thermal conductivity and elastic moduli increase with film thickness, indicating a thickness-dependent change in physico-chemical composition. Energy-dispersive x-ray spectroscopy reveals that thicker layers contain a higher proportion of fluorine relative to aluminum. Moreover, x-ray photoelectron spectroscopy and infrared variable-angle spectroscopic ellipsometry indicate that the chemical structure stabilizes in thicker samples, confirming the formation of AlF3. These findings provide valuable insights into the process-structure-property relationships of plasma-produced fluorinated layers, which are critical for optimizing UV optical coatings and enhancing lithium-ion battery safety. (c) 2026 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Hafnia-based ferroelectrics hold promise to reduce energy demand for computing by enabling compute-in-memory and as non-volatile memories. The ferroelectric phase in this material system is, in part, stabilized by oxygen vacancies. While oxygen vacancies may be a necessity for phase stability, they limit device endurance through diffusion and accumulation into conducting channels. Herein, it is shown that oxygen diffusion is spatially variable within individual grains of ferroelectric hafnium zirconium oxide (HZO). Using 18O tracers and finite difference modeling, it is shown that grain boundaries and regions near electrode interfaces allow for relatively rapid oxygen diffusion, with values as much as 104 larger than the grain cores. Further, the selection of electrode material affects the diffusion coefficients across all microstructural regions. HZO films in contact with TiN electrodes result in more oxygen-deficient HZO films and higher oxygen diffusion coefficients. Tungsten electrodes result in fewer vacancies and lower diffusion coefficients. Diffusion activation energy differences between the HZO with the two electrodes is reconciled by differing populations of charged and uncharged oxygen vacancies. This insight into the local vacancy populations and diffusion pathways provides a platform for designing hafnia-based films, deposition processes, and integration strategies to reduce vacancy gradients and improve performance.

Abstract Incorporation of AlyGa1–yN semiconductors into high-power electronics offers efficiency improvements in power transmission, generation, and use, if approaches to eliminate the defects arising from film-lattice mismatch can be established. Here, we report the optical floating zone crystal growth of Ta1–xHfxC0.5 (x = 0.2), a new metallic substrate material family lattice matched to the ultrawide-band gap, Al-rich side (y = 0.91) of the AlyGa1–yN solid solution. Laue diffraction demonstrates large single-crystal domains in the as-grown boule. Single-crystal X-ray diffraction at T = 213 K in conjunction with first-principles calculations shows that the material adopts a layered crystal structure with AA-type stacking of (Ta/Hf)-C-(Ta/Hf) trilayers described in the trigonal space group P3̅m1 (#164), with a = 3. 1168(4) Å, c = 4.9644(4) Å, and β = 120.0°. X-ray photoelectron spectroscopy (XPS) measurements show the Hf:Ta ratio to be close to the nominal value of 0.8:0.2 in the grown crystal. Density Functional Theory calculations reveal that this structure is stabilized by the low energy of carbon-vacancy formation of a hypothetical (Ta/Hf)1C1 anti-NiAs structure type, and imply flexibility in interface structure with an overlayer nitride film. A surface preparation/polishing procedure is developed that reduces root-mean-square (RMS) surface roughness from as-cut 130 to 7 nm as measured by atomic force microscopy. Scanning electron microscopy shows the presence of a native surface oxide, removed by polishing, along with carbon-rich pits. Time-domain thermoreflectance measurements show a room temperature thermal conductivity of κ = 18.1(4) W m–1 K–1. These results provide key first steps for utilizing metallic, lattice-matched substrates for the growth of Al-rich AlyGa1–yN semiconductors.

As CMOS technology continues to scale, metallic interconnects increasingly limit circuit performance through rising resistivity, self-heating, and reliability degradation. Although several alternative metals have been proposed, a quantitative framework for evaluating their transport performance under nanoscale confinement remains unavailable. Here, we establish a transport framework by combining independently measured thermal and electrical conductivities with normalized and unnormalized transport figures of merit. We apply this framework to Cu, Ru, W, Co, Ir, and Mo thin films using new steady-state thermoreflectance measurements of Mo, Co, and Ir together with previously reported Cu, Ru, and W data. While Cu exhibits the highest intrinsic transport performance, its effective performance is substantially reduced by thickness scaling and Ta liner resistance. In contrast, Ru and Mo maintain favorable transport properties while enabling barrierless integration, identifying them as promising candidates for next-generation CMOS interconnects

Incorporation of Al_yGa_1-yN (AGN) semiconductors into high power electronics offers efficiency improvements in power transmission, generation, and use, if approaches to eliminate the defects arising from film-lattice mismatch can be established. Here, we report the optical floating zone crystal growth of Ta_1-xHf_xC_0.5 (x = 0.2), a new metallic substrate material family lattice matched to the ultra-wide-band-gap, Al-rich side (y = 0.91) of the AGN solid solution. Laue diffraction demonstrates large single crystal domains in the as-grown boule. Single crystal x-ray diffraction at T = 213 K in conjunction with first principles calculations shows that the material adopts a layered crystal structure with AA-type stacking of (Ta/Hf)-C-(Ta/Hf) trilayers described in the trigonal space group P-3m1 (#164), with a = 3.1168(4) Å, c = 4.9644(4) Å, and β = 120.0°. X-ray photoelectron spectroscopy (XPS) measurements show the Hf:Ta ratio to be close to the nominal value of 0.8:0.2 in the grown crystal. Density Functional Theory calculations reveal that this structure is stabilized by the low energy of carbon-vacancy formation of a hypothetical (Ta/Hf)_1C_1 anti-NiAs structure type, and imply flexibility in interface structure with an overlayer nitride film. A surface preparation/polishing procedure is developed that reduces root mean square (RMS) surface roughness from as-cut 130 nm to 7 nm as measured by atomic force microscopy. Scanning electron microscopy shows the presence of a native surface oxide, removed by polishing, along with carbon-rich pits. Time-domain thermoreflectance measurements show a room temperature thermal conductivity of κ = 18.1(4) W m-1 K-1. These results provide key first steps for utilizing metallic, lattice matched, substrates for the growth of Al-rich AGN semiconductors.

Materials that combine low density with high thermal and mechanical performance are essential for applications ranging from thermal management to lightweight structural systems, yet such combinations are rarely achieved in porous solids due to intrinsic trade-offs between porosity, stiffness, and heat transport. Here, we demonstrate that covalent organic frameworks (COFs) can overcome this limitation through topology-driven control of node-linker coupling. Using a high-fidelity computational framework that integrates density functional tight binding with machine-learned interatomic potentials, we systematically investigate thermal transport and elastic behavior in three-dimensional COFs with nearly identical chemistry and density but distinct topologies. With our emergent computational framework for modeling phonon transport, we show that framework topology alone can tune thermal conductivity by more than an order of magnitude and elastic modulus by nearly a factor of 10, with optimized COFs exhibiting room-temperature thermal conductivities exceeding 10 W m-1 K-1 and Young's moduli approaching ∼160 GPa, which are values uncommon for nanoporous polymers. Spectral and heat-flux decomposition analyses reveal that cooperative node-linker vibrational coupling enables long phonon lifetimes and mean free paths comparable to those of fully dense inorganic crystals, while simultaneously enhancing mechanical rigidity through balanced stress distribution. In contrast, such correlated transport is suppressed in metal-organic frameworks due to mass mismatch and bond heterogeneity. These findings establish node-linker topology as a powerful and general design principle for simultaneously optimizing thermal and mechanical performance in nanoporous materials, providing a framework for the design of lightweight thermomechanical materials.

We measure the temperature-dependent in-plane thermal conductivity, kappa(parallel to)(T), of high-purity gamma-InSe bulk single crystals and exfoliated thin flakes (30-50 nm) from 50 to 300 K. Our bulk results agree with prior bulk reports and provide a reproducible reference for phonon transport. In the literature, cross-plane thermal conductivity of supported InSe flakes shows relatively modest variation, whereas reported room-temperature in-plane values for supported flakes span a wide range, including outliers that exceed bulk despite much smaller thickness. In our measurements, the flake kappa parallel to at room temperature is lower than bulk, as expected, but exhibits substantial sample-to-sample variability; despite being thinner, intrinsic flakes show higher kappa(parallel to) than doped flakes, consistent with reduced impurity scattering and improved flake uniformity. We analyze our data using a Callaway-type phonon-scattering model in which substrate interactions (including plausible strain-related renormalization of acoustic parameters) contribute to the observed spread near room temperature. However, below similar to 150 K, the measured trends cannot be captured without invoking changes in sound velocity far larger than realistic strain levels, indicating that additional mechanisms beyond simple strain renormalization are required at low temperature. These measurements provide low-temperature kappa parallel to benchmarks for gamma-InSe flakes and constrain how much of the reported room-temperature spread can be explained by thickness, nonuniformity, and substrate effects alone.

The orthorhombic van der Waals (vdW) layered crystal α-MoO3 is a promising material for infrared nanophotonics; in particular, it may host highly confined hyperbolic phonon polaritons (HPhPs) with wavelength-dependent in-plane anisotropy. However, large-area and uniform single crystals are challenging to grow on substrates, as current α-MoO3 growth methods struggle to manage adverse tendencies in size, texturing, and roughness. In this work, we establish an alkali salt-assisted chemical vapor deposition (SA-CVD) growth technique to produce smooth, high-quality, and millimeter-scale single-crystal α-MoO3 nanosheets directly on A-plane sapphire substrates. By cosublimating a NaCl source along with α-MoO3 during growth, we overcome the size and morphology challenges typical of alkali-free deposition, achieving ultrasmooth crystals with lateral dimensions reaching 6 mm and thicknesses ranging from <6 to 480 nm. We attribute the improved morphology to a molten Na2O-MoO3 intermediate, which forms on the substrate surface and induces a self-expanding vapor-liquid-solid (VLS) growth mode. The as-grown single-crystal nanosheets exhibit high crystal and optical quality without evident degradation by residual Na, enabling characteristically high HPhP quality (Q) factors (12-30) and long lifetimes (2.7-7.7 ps) as measured by scattering-type scanning near-field optical microscopy (s-SNOM). We relocate the large-area crystals onto arbitrary substrates using a water-assisted layer transfer technique, which effectively removes Na-containing residue and relieves residual strain. This work unlocks millimeter-scale, high-quality, uniform α-MoO3 single-crystal growth directly on substrates for large-area implementation in fields including mid-infrared nanophotonics and layered vdW heterostructures.

The high energy consumption of phase change memory remains one of the biggest hurdles toward its widespread implementation. Most phase change materials demonstrate a high contrast in thermal conductivity between the amorphous and crystalline phases with the latter having the higher value. This is detrimental, as a high thermal conductivity will allow heat, meant to drive the phase change, to diffuse into the surrounding structures, increasing the energy demand even further. In order to address this high contrast, the Sb2Te3/TiTe2 superlattice is studied using a bottom-up approach: starting with the individual materials, before studying full superlattices. X-ray diffraction is used to study the structure and stability, while time-domain thermoreflectance gives insight into the thermal transport characteristics of these materials and their superlattice. Incoherent diffuse phonon transport is found to be responsible for heat flow in both Sb2Te3 and TiTe2. The combination of both materials into a superlattice reduces the thermal conductivity contrast by 92% from 0.69 W m-1 K-1 to 0.05 W m-1 K-1. Room-temperature measurements indicate that in a superlattice composed of 5 nm Sb2Te3 and 3 nm TiTe2 layers the thermal conductivity remains approximately 0.2 W m-1 K-1 for both phases. The creation of this superlattice effectively eliminates the thermal conductivity contrast, preventing unwanted heat dissipation during phase transitions. This work shows that superlattice engineering can play an important role in managing the energy consumption of phase change memory devices.

We report on a phase-based lock-in thermography approach, combined with a multilayered thermal model (often employed in thermoreflectance analysis), to measure the thermal conductivity of bulk materials and layered structures. The spatial distribution of the material's thermal phase is monitored with an infrared camera, which is locked into the frequency of a modulated laser used to heat the material. This phase distribution is then fit with a thermal model, in which properties such as thermal conductivity are extracted as fit parameters. This approach enables non-contact, front-side measurements, which are insensitive to surface roughness. The technique does not strictly require the application of a transducer layer, but we highlight the practical benefits of applying a removable adhesive layer to serve as a near-surface absorber. We demonstrate the efficacy of the method by measuring materials with thermal conductivities that span over three orders of magnitude (approximately 1 W/m/K to > 2000 W/m/K).

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 isotope-enriched crystals within few-minute growth durations. We unlock this capability by using metallic molybdenum precursors with high source temperatures (900 degrees C) and total pressures ('1 atm) to maximize precursor efficiency and yield. Subsequently, we grow alpha-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 enrichments, we establish a powerful tool to advance nanophotonics and thermal management goals using alpha-MoO3. This work is motivated by the possibility to enhance and engineer lattice vibrational mode phenomena including thermal conduction and hyperbolic phonon polariton dispersion- with particular interest in comparing the effects of light and heavy element enrichment.

Advances in next-generation hypersonic hot structures, high heat-flux fusion or fission components, and laser based additive manufacturing depend on reliable solid state thermal conductivity data at high and ultrahigh temperatures, where conventional measurements become increasingly sensitive to contact resistances, uncertain boundary conditions, and nonlinear radiative losses. Building on our initial demonstration of ultrahigh temperature steady-state temperature differential radiometry (SSTDR), we present a substantially more robust platform aimed at making high temperature thermal and radiative property measurements more routine. The method integrates lock-in infrared thermography with a spatially localized, modulated perturbation laser to form a conduction dominant differential observable along with hyperspectral pyrometry and a validated 2D axisymmetric steady state heat transfer model. Using high purity molybdenum as a benchmark, we report solid state thermal conductivity k(T) from 1500 - 3000 K (to the onset of melting) with uncertainties of 7.9-11

Additive manufacturing (AM) can produce materials with complex geometries and lightweight structures, but unlike conventional processes, it can introduce defects such as porosity and phase inhomogeneity that can degrade thermal behavior and lead to unpredictable heating across applications. Because a material's thermal properties are highly sensitive to defects and microstructure, measurements of thermal conductivity, emissivity, and melting temperature provide a powerful, non-contact metrology method to evaluate the quality of AM materials. In this study, we employ laser-based diagnostics on a series of AM 316L stainless-steel samples, measuring thermal conductivity, emissivity, and solidus/liquidus temperatures. Thermal conductivity is calculated by two different steady-state methods: a commercial Thermo-Optical Plane Source (TOPS; Laser Thermal) and a new technique introduced in this work, Steady-State Laser-Induced Thermographic Radiometry (SSLITHER). Our results indicate that the effective thermal conductivity in AM parts decreases by 20%-50%, depending on the printing settings, largely driven by the changes in the relative densities of the samples and by defects introduced during the printing process. We found that low-density samples exhibit lower performance at high temperatures, showing depressed solidus and liquidus temperatures and altered emissivity caused by oxygen content trapped within lack of fusion regions, which modifies surface radiative properties. After laser-induced melting and resolidification (which increases density and forces oxygen out), the effective thermal conductivity and melting temperatures increase, and emissivity is restored. Our work presents the potential for laser-based thermal conductivity, emissivity, and melting temperature measurements as tools for evaluating and improving the performance of AM materials.

Realizing organic materials that exhibit a dynamic thermal conductivity requires a fundamental understanding of how molecular structure and processing affect thermal transport. Herein, we demonstrate that the photoinduced polymerization of [2,2 '-bi-1H-indene]-1,1 '-dione-3,3 '-diheptylcarboxylate (BIT) into polyBIT results in over a 4-fold decrease in thermal conductivity as measured on polycrystalline thin-films in the through-plane direction, mostly perpendicular to the chain growth direction. Experimental determination of the material's decreased heat capacity supports this view. Through theoretical calculations, we attribute this decrease in thermal conductivity in part to induced anisotropy in the polymer. We also discuss the non-negligible changes in morphology, phase transitions, and thermal degradation that serve to limit the thermal depolymerization reaction. This work highlights the different contributions one must consider when designing an organic thermal switch that operates in the solid-state.

The implementation of polaritonic materials into nanoscale devices requires selective tuning of parameters to realize desired spectral or thermal responses. One robust material, α-MoO3, an orthorhombic crystal boasting three distinct phonon dispersions, provides 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 α-MoO3 (98MoO3, Mo18O3, and 98Mo18O3) is 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 we report an HPhP Q-factor maxima increase in 98Mo18O3 of ∼50% along the [100] in the RB2 and ∼100% along the [001] in the RB3 with respect to 98MoO3. Observations in both real and Fourier space of higher-order HPhP modes propagating in slabs of isotopically enriched α-MoO3 without the use of a subdiffractional surface scatterer are presented here. This work establishes the dual-element isotope enrichment of α-MoO3 as an intrinsic strategy to design optical, thermal, and polaritonic properties.

High-throughput synthesis and characterization of novel ceramic materials with improved thermomechanical properties and phase stability are needed to accelerate the discovery of next-generation thermal barrier materials. A combinatorial thin film material library of (GdDyHoEr)2Zr2O7 were created via combinatorial magnetron reactive sputtering with rare-earth/zirconium alloy targets. Structural, chemical, and thermal property characterization mapping across the four component composition space was performed and correlated with thermal transport measurements. Steady state thermoreflectance mapping identifies a pronounced minimum in thermal conductivity within the Dy/Gd-rich quadrant. This minimum does not coincide with either the equiatomic composition or the region predicted to exhibit maximum cation size disorder. Instead, it corresponds to the largest experimentally observed lattice parameter, despite deviating from Vegard-like chemical averaging, and is independent of grain size and whole-pattern microstrain. These observations suggest that the way the fluorite lattice accommodates compositional complexity, rather than cation size disorder alone, provides a more informative descriptor of thermal transport. Overall, this work establishes a high-throughput workflow for combinatorial thin-film synthesis and multimodal characterization, enabling the rapid identification of previously inaccessible structure-property relationships in compositionally complex ceramics.

We demonstrate a Thermo-Optical Plane Source (TOPS) technique to measure the thermal conductivity of materials. This high-throughput method measures the thermal conductivity of materials with minimal sample preparation and limited restrictions on sample shape and geometry. Moreover, the technique is applied to solids, liquids, gels, and pastes with no change in implementation. The TOPS technique uses laser heating to induce a steady-state temperature rise in a material and infrared thermography to measure the corresponding temperature rise. Fourier's law is applied to directly measure thermal conductivity, rather than thermal diffusivity or effusivity, eliminating the need for prior knowledge of density and specific heat. We demonstrate the ability to measure thermal conductivities ranging from 0.03 to 60 Wm-1 K-1 at room temperature.

The Wiedemann-Franz (WF) law correlates heat and charge transport in metals. However, the validity of this correlation remains an open-ended question, especially in the context of inelastic scattering at room temperature. To address this gap in knowledge, we perform independent measurements of the in-plane thermal and electrical conductivities across four AlCu (0.5% Cu) films [thickness ( h) approximate to 174, 98, 53, and 24 nm] using optical pump-probe metrologies and four-point probe techniques, respectively. For in-plane thermal conductivity measurements, we utilize time-domain thermoreflectance, in both concentric and beam-offset configurations, and the time-resolved magneto-optic Kerr effect. Our results show that the WF law overpredicts the thermal conductivity by at least similar to 10% in all films, thus demonstrating modest deviations in predicted thermal conductivity when applying the WF law to dilute AlCu films. Using infrared variable angle spectroscopic ellipsometry, we demonstrate increased electron scattering rates in the thinnest film ( h approximate to 24 nm), indicating electron-boundary scattering drives the reduction in in-plane thermal conductivity. This is generally an elastic scattering process, which is supported by our thermal conductivity measurements and analysis.