Al1-xScxN has attracted significant interest due to its large remnant polarization and low processing temperature when compared to other ferroelectric material systems. However, device dielectric failure before ferroelectric switching remains a critical limitation for AlScN-based memory devices. With the continuing trend toward device miniaturization, expanding the operating window is essential for next-generation memory development. In this work, we optimized the breakdown field (E-BD) and coercive field (E-C) in ultra-thin Al1-xScxN films by controlling defect density via adjustment of nitrogen process gas flow during sputter deposition. The characteristic breakdown field, E-BD, was evaluated using Weibull statistics, yielding optimal characteristic breakdown fields of 12.47 MV/cm (E-BD(+)) and-12.63 MV/cm (E-BD(-)) for samples deposited under 27.5 sccm N-2 flow. The minimum EC measured using 25 kHz bipolar triangular wave excitation was achieved for films deposited under a nitrogen flow of 25 sccm and increased for higher gas flows, a trend that is opposite to previous reports in much thicker films. The highest E-BD/E-C ratio of 2.25 was achieved in films deposited at 25 sccm N-2 flow, effectively expanding the operational window. The lowest imprint (0.32 MV/cm) obtained under low-frequency Capacitance-Electric Field scans was measured in films deposited under 30 sccm N-2 flow. Using a combination of X-ray diffraction and photoluminescence spectroscopy to study changes in crystal orientation and defects, device performance can be tuned by controlling the point defect concentration in the ultra-thin film via adjusting the sputtering N-2 process gas flow rate. A range of reactive gas flow from 25 to 30 sccm achieves high uniformity and the largest operational window, resulting in improved ferroelectric performance.

Realizing the potential for 2D SnSe optoelectronics requires understanding the thickness dependence of structure, defects, and optical properties. We investigate the thickness-dependent crystal structure, band gap, and carrier lifetime of SnSe films deposited by molecular beam epitaxy (MBE) on (100) MgO. MBE enables stoichiometric (2h00)-oriented SnSe films with tunable thicknesses from 80 nm down to 4 nm. As thickness decreases, out-of-plane covalent bonds contract, while in-plane bonding and the van der Waals gap expand with a concurrent increase in stacking fault density, consistent with theoretical predictions of reduced stacking fault energies. Below 8 nm, the band gap transitions from indirect to direct, increasing from 1.4 eV to 1.8 eV, primarily driven by a combination of structural changes and confinement effects. Our results demonstrate how the thickness and structural distortion of 2D materials can be used to modulate the optical properties relevant to optoelectronics.

Polarization retention of 10 nm thick ferroelectric hafnium zirconium oxide (Hf0.5Zr0.5O2-x, HZO) capacitors with W and TaN electrodes is investigated over temperatures ranging from 85 to 150 degrees C. Same state and opposite state polarization margins for devices with W electrodes show minimal retention loss after 10(5) at 150 degrees C. The devices capped with TaN electrodes show excellent same state retention, but the opposite state polarization margin in the TaN-electrode devices displays 40% retention loss at 150 degrees C after 10(5) s. The TaN-capped devices exhibit a more pronounced imprint, which is attributed to an increased oxygen vacancy content (compared to W-capped devices). The increased oxygen vacancy content in the TaN-capped devices is supported by photoluminescence and leakage current measurements. In addition, TaN-capped devices have chemically diffuse electrode-HZO interfaces; more abrupt interfaces are present in the W-capped devices. The presence of interfacial phases in the TaN-capped devices may lead to larger depolarization fields due to reduced charge screening. The results from this study provide further evidence that for HZO ferroelectric devices the electrode can significantly impact polarization retention behavior due to differences in oxygen vacancy concentration and formation of non-ferroelectric interfacial layers.

Integrating two-dimensional semiconductors, such as MoS2, with dielectric materials remains a central challenge for their use in future logic technologies. While seed layers are typically introduced to promote dielectric nucleation and adhesion, we show that they also critically govern charge transfer doping and, in turn, transistor performance. Back-gated monolayer MoS2 transistors passivated on their top surface with a Ta-seed/HfOx dielectric stack were fabricated and characterized electrically and physically using Raman, photoluminescence, and X-ray photoelectron spectroscopies. Threshold voltage and on-current varied strongly with Ta-seed thickness and deposition conditions, and these changes correlated with signatures observed across all spectroscopic probes. The results reveal that the seed layer both introduces disorder into the MoS2 channel and modifies the interfacial charge environment, controlling charge transfer between HfOx and MoS2. Optical spectroscopy shows that the on-current tracks seed-induced disorder, whereas X-ray photoelectron spectroscopy indicates that the threshold voltage correlates with shifts in the local electrostatic environment associated with interfacial charge transfer. Better performance was obtained with ultrathin 0.2 nm Ta-seed layers deposited under oxygen-poor conditions, which limit deposition-induced damage while facilitating charge transfer. These findings identify seed-layer engineering as a key strategy for controlling disorder and interfacial doping in MoS2 devices and establish multimodal spectroscopy as a practical approach during fabrication for process development and monitoring.

SiGe heterostructures integrated with Si via virtual substrate (VS) growth are promising hosts for spin qubits. While VS growth targets plastic relaxation, residual cross-hatch strain inhomogeneity propagates into heterostructure overgrowth. To quantify strain inhomogeneity's influence on interface structure and qubit properties, we measure strained-silicon (s-Si)/Si_0.7Ge_0.3 heterostructures on 25 wafers processed via standard commercial chemical vapor deposition. Spatially-aligned images of strain (Raman microscopy) and interface structure (atomic force microscopy and cross-sectional scanning transmission electron microscopy) reveal strain-roughness interplay. A strain-driven surface diffusion model predicts the roughness and its temperature dependence. Measured strains suggest spurious double-dot qubit detunings of 0.1 meV over 100 nm distances may result. Modeling shows that interface roughness (atomic steps), when convolved with alloy disorder, only modestly reduces valley splitting (70±13 vs. 77±14 μeV on average). Our findings point to thicker VS buffer layers beneath heterostructures and lower-temperature growth (T ≤ 700 ^∘C) to limit roughening.

Amorphous oxide semiconductors such as indium tin oxide (ITO) are promising channel materials for back-end-of-line memory and logic devices, yet their performance and reliability are hindered by self-heating at high power densities. Precise quantification of channel temperature and heat dissipation pathways into the surrounding materials is therefore essential for effective thermal management and the 3D heterogeneous integration of these devices. This work investigates heat dissipation in ultrathin ITO devices on sapphire by Raman thermometry, using an interfacial monolayer of MoS2 as an in situ temperature sensor. Thermal boundary resistance of each interface in the device is independently measured by time-domain thermoreflectance and then used in finite-element simulations of device temperatures, thereby decoupling temperature measurements from interface characterization. Simulated temperatures incorporating measured electrical and thermal characteristics corroborate well with Raman thermometry. Our validated framework highlights the central role of interfacial resistance and heat spreading through the substrate on heat dissipation in thin-film nanoelectronics.

The helium ion microscope (HIM) focused ion beam (FIB) has emerged as a powerful tool to directly pattern nanostructures below 10 nm due to its high‐resolution capabilities and the inert nature of the ion source. These attributes make HIM FIB particularly interesting for patterning 2D materials such as transition metal dichalcogenides (TMDs) to investigate transport phenomena at the nanoscale. Reported here is the fabrication of MoS 2 nanoribbon devices using HIM FIB‐induced etching (FIBIE) with XeF 2 , allowing for reduced ion dose compared to direct sputtering. While patterning is efficacious, the devices exhibit performance degradation with decreasing nanoribbon width due to damage up to 150 nm beyond the patterned edge. Incorporating an hBN encapsulation improves device performance by one order of magnitude, although the lateral extent of damage remains unchanged. The spatial distribution of damage is shown to be determined by the forward‐ and backscattered ions and electrons, while the hBN encapsulation layer substantially reduces damage from XeF 2 interactions in unexposed regions. Raman and photoluminescence (PL) measurements corroborate these findings, while ion/solid interaction simulations further elucidate the resolution limits imposed by substrate interactions. This work provides critical insights and a practical pathway for utilizing HIM FIBIE in 2D TMD functional device patterning.

Two-dimensional (2D) transition metal carbides, nitrides and carbonitrides, known as MXenes, are of interest as electrocatalysts. Tungsten-based MXenes are predicted to have low overpotentials in the hydrogen evolution reaction but their synthesis has proven difficult due to the calculated instability of their hypothetical MAX precursors. In this study, we present a theory-guided synthesis of a tungsten-based MXene, W2TiC2Tx, derived from a non-MAX nanolaminated ternary carbide (W,Ti)4C4−y precursor by the selective etching of one of the covalently bonded tungsten layers. Our results indicate the importance of tungsten and titanium ordering, the presence of vacancy defects in the metal layers, and the lack of oxygen impurities in the carbon layers for the successful selective etching of the precursor. We confirm the atomistic out-of-plane ordering of tungsten and titanium using computational and experimental characterizations. The tungsten-rich basal plane endows W2TiC2Tx MXene with a high electrocatalytic hydrogen evolution reaction performance (∼144 mV overpotential at 10 mA cm−2). This study reports a tungsten-based MXene synthesized from a covalently bonded non-MAX precursor, adding to the synthetic strategies for 2D materials. The theory-guided synthesis of a tungsten-based W2TiC2Tx MXene from a non-MAX nanolaminated ternary carbide (W,Ti)4C4−y is reported. The tungsten-rich basal plane of the W2TiC2Tx MXene is then examined for the electrocatalytic hydrogen evolution reaction using a combined experimental and theoretical approach.

Advanced oxidation processes (AOPs) show significant promise to degrade recalcitrant water contaminants, such as 1,4-dioxane, but slow degradation kinetics limit the energy efficiency of this technology. We realized substantial enhancements in the degradation of 1,4-dioxane (a suspected carcinogen) using gold-coated titanium dioxide (Au/TiO2) Janus nanoparticles (JNPs) irradiated with above-bandgap ultraviolet (UV) light (peak wavelength, 254 nm). To explain this result, we combined experimental measurements quantifying 1,4-dioxane degradation at varying UV wavelengths with finite-element simulations that provided explanatory insight into the light–matter interactions at play. The enhanced photocatalytic activity at the optimal condition (254 nm light, high intensity, Au/TiO2) resulted from a larger quantity of photogenerated holes in the TiO2 capable of reacting with water to form hydroxyl radicals that degrade 1,4-dioxane. This increased production of holes resulted from two sources: (1) more viable electron–hole pairs were created under 254 nm light owing to increased light absorption by the TiO2 that was localized near the surface; (2) the metal sequestered photogenerated electrons from the TiO2, which prevented electron–hole pairs from recombining, leaving more holes available to react with water. Our results motivate the exploration of different metal coatings (especially non-precious metals) and suggest a path toward broader implementation of TiO2-based photocatalytic AOPs, which can effectively remove many water pollutants that survive conventional treatment techniques.

Monolayer two-dimensional (2D) transition metal dichalcogenides (TMDs) have emerged as leading candidates for next-generation electronic devices beyond silicon, owing to their atomically thin structure and superior electrostatic control. However, their integration into industrial applications remains limited due to high densities of lattice defects and challenges in achieving stable and effective doping. In this work, we present a passivation and doping technique that significantly recovers and enhances the electrical properties of monolayer tungsten diselenide (WSe2). Our defect-facilitated (NH4)2S surface passivation approach has achieved robust enhancements in both the on-state and off-state performance of monolayer WSe2 p-type field-effect transistors (p-FETs), enhancing channel mobility 3-fold, reaching a subthreshold slope (SSmin) value of 70 mV/dec, on-currents of 110 μA/μm, and Imax/Imin > 109, while maintaining stability across a range of conditions. Furthermore, we establish a strong correlation between device off-state performance and the full width at half-maximum (fwhm) of the Raman characterization peak. The defect engineering approach, combined with (NH4)2S treatment at room temperature, offers a viable pathway for passivation and substitutional doping, advancing the potential for improved charge transport in future 2D TMD-based electronic devices.

This study focuses on the fabrication and thermo-mechanical characteristics of cobalt-filled through silicon Vias (Co-TSVs) with diameters ranging from 3 to 5 mu m. Optimization of the electroplating solution accompanied by an electroless-plated Cu seed layer resulted in a crack-free annealed Co-TSVs interface, and void-free TSV filling as verified by atomic force microscope (AFM) and scanning electron microscopy (SEM) acquired after annealing. Protrusions (i.e., "pump out") of the Co and the resulting thermo-mechanical stresses induced by annealing were assessed using a combination of AFM and Raman spectroscopic imaging. Regardless of annealing temperature (200 to 400 degrees C) or TSV diameter (3 to 5 mu m), the protrusion is less than 55 nm, and the equivalent stress level is below 75 MPa. The small protrusions can be attributed to the release of internal stress during the annealing process. Meanwhile, the lower stress levels are due to the balance between tensile radial stress and compressive tangential stress.

Oxygen vacancies in HfxZr(1−x)O2 (HZO) both contribute to stabilization of the ferroelectric orthorhombic phase and promote leakage pathways that limit the endurance of devices based on the material. For this reason, the defect states of oxygen vacancies were investigated using photoemission electron microscopy (PEEM) and photoluminescence spectroscopy (PL), as their concentration was varied via ex situ laser exposure. Following a controlled oxygen vacancy reduction via visible (2.54 eV) laser dosing of HZO, deep-ultraviolet (DUV, 5.82 eV) PEEM was used to spatially probe the resulting mid-gap defect states and work function. Work function was found to increase monotonically with the laser-induced reduction in oxygen vacancy concentration culminating in a total increase near 70 meV. The change implies a Fermi level shift toward the valence band as the total available electron-filled charge states are reduced with the removal of oxygen vacancies. A reduction in charge states is corroborated by the observed lessening of both photoemission and photoluminescence intensities after laser dosing. The deduced position of the Fermi level is within a band of near-conduction band defect states produced by oxygen vacancies that are linked to endurance limiting leakage currents. Together, these results directly identify the primary role of oxygen vacancies on the defect states in HZO while demonstrating that laser exposure can be used for their modification.

The dimensional scaling of through silicon vias (TSVs) is critical for the advancement of high-density 3D integration in future logic-on-logic and logic-on-memory computing architectures. Realizing such scaling demands an understanding of the thermomechanical response at the relevant length scales as both the microstructure and properties of the copper making up the majority of the TSV are dependent upon the size. In response, we examine here the residual stress development of the surrounding Si and microstructural evolution of Cu within TSVs as they are scaled from 5 to 1 μm diameter and thermally annealed. Using a combination of Raman spectroscopic and electron backscatter diffraction imaging accompanied by thermomechanical modeling, a non-monotonic trend between equivalent stress and TSV diameter is revealed. The non-monotonic trend is interpreted using an elastic thermomechanical model that accounts for competition between the global bending of the wafer and local Cu shrinkage. The elastic behavior is attributed, in large part, to a decrease in the mean grain size of Cu—and the accompanying increase in strength—that occurs with reduced TSV diameter. Thus, given the consistency of measured stress with the elastic model and the improved mechanical strength with decreased grain size, annealed Cu TSVs are deduced to remain more elastic compared to their larger counterparts as they scale from 5 to 1 μm.

Wurtzite ferroelectrics (e.g., Al0.93B0.07N) are being explored for high-temperature and emerging near- or in-compute memory architectures due to the material advantages offered by their large remanent polarization and robust chemical stability. Despite these advantages, current Al0.93B0.07N devices do not have sufficient endurance lifetime to meet roadmap targets. To identify the defects responsible for this limited endurance, a combination of electronic measurements and optical spectroscopies characterized the evolution of defect states within Al0.93B0.07N with cycling. Ultrathin (∼10 nm) metal contacts were used to optically probe regions subject to ferroelectric switching; photoluminescence spectroscopy identified the emergence of a transition near 2.1 eV whose intensity scaled with the nonswitching polarization quantified via positive-up negative-down (PUND) measurements. Accompanying thermally stimulated depolarization current and modulus spectroscopy measurements also observed the strengthening of a state near 2.1 eV. The origin of this feature is ascribed to transitions between a nitrogen vacancy and another defect deeper in the bandgap. Recognizing that the impurity concentration is largely fixed, strengthening of this transition indicates an increase in the number of nitrogen vacancies. Switching, therefore, creates vacancies in Al0.93B0.07N likely due to hot-atom damage induced by the aggressive fields necessary to switch wurtzite materials that ultimately limits endurance.

3-Ga2O3 is a promising material candidate for next-generation high-power devices even as its low thermal conductivity (kappa) limits utilization due to an inability to sufficiently dissipate heat. Despite the importance of this inherent thermal challenge, a significant discrepancy persists between experimental results and computational models regarding the anisotropic thermal conductivity of 3-Ga2O3. Specifically, computational results are within experimental error bounds for kappa 100 and kappa 001 while underpredicting kappa 010, suggesting that the bare phonon models used in the literature are missing essential physics related to the anisotropic thermal transport. In response, we compute the anisotropic kappa using first principles and the Peirels-Boltzmann transport equation under different approximations. For the simplest model, we consider the heat carriers to be harmonic phonons with scattering rates obtained perturbatively. These results are then compared with those obtained by including phonon renormalization and four-phonon scattering. Our results show that accounting for phonon renormalization resolves the discrepancy between experiment and theory. This is because phonon renormalization leads to an anisotropic kappa enhancement caused by directionally dependent changes in the phonon group velocities accompanied by a general increase in phonon lifetime. Owing to the crucial role of these anharmonic interactions in accurately describing anisotropic thermal transport, we also explore the anharmonicity of individual atoms and show that the octahedrally coordinated gallium atom is the most anharmonic and thus most likely responsible for the failure of the harmonic phonon model to describe thermal transport in this material. Finally, we demonstrate that atomic anharmonicities could be used as a useful metric to guide the tailoring of vibrational properties.

Two-dimensional transition metal carbides, nitrides, and carbonitrides, known as MXenes, hold potential in electrocatalytic applications. Tungsten (W) based-MXenes are of particular interest as they are predicted to have low overpotentials in hydrogen evolution reaction (HER). However, incorporating W into the MXene structure has proven difficult due to the calculated instability of its hypothetical MAX precursors. In this study, we present a theory-guided synthesis of a W-containing MXene, W2TiC2Tx, derived from a non-MAX nanolaminated ternary carbide (W,Ti)4C4-y precursor by selective etching of one of the covalently bonded tungsten layers. Our results indicate the importance of W and Ti ordering and the presence of vacancy defects for the successful selective etching of the precursor. We confirm the atomistic out-of-plane ordering of W and Ti using density functional theory, Rietveld refinement, and electron microscopy methods. Additionally, the W-rich basal plane endows W2TiC2Tx MXene with a remarkable HER overpotential (~144 mV at 10 mA/cm2). This study adds a tungsten-containing MXene made from a covalently bonded non-MAX phase opening more ways to synthesize novel 2D materials.

Precise control of light–matter interactions at the nanoscale lies at the heart of nanophotonics. However, experimental examination at this length scale is challenging since the corresponding electromagnetic near-field is often confined within volumes below the resolution of conventional optical microscopy. In semiconductor nanophotonics, electromagnetic fields are further restricted within the confines of individual subwavelength resonators, limiting access to critical light–matter interactions in these structures. In this work, we demonstrate that photoelectron emission microscopy (PEEM) can be used for polarization-resolved near-field spectroscopy and imaging of electromagnetic resonances supported by broken-symmetry silicon metasurfaces. We find that the photoemission results, enabled through an in situ potassium surface layer, are consistent with full-wave simulations and far-field reflectance measurements across visible and near-infrared wavelengths. In addition, we uncover a polarization-dependent evolution of collective resonances near the metasurface array edge taking advantage of the far-field excitation and full-field imaging of PEEM. Here, we deduce that coupling between eight resonators or more establishes the collective excitations of this metasurface. All told, we demonstrate that the high-spatial resolution hyperspectral imaging and far-field illumination of PEEM can be leveraged for the metrology of collective, non-local, optical resonances in semiconductor nanophotonic structures.

This study focuses on the fabrication and thermomechanical characterization of Through Silicon Vias (TSV) with diameters spanning 1-4 µm. In terms of TSV fabrication, scallop-free Si etching is achieved by the optimization of the Bosch etching process, and a void-free TSV filling is completed by a combination of electroless plating for seed layer and electroplating for TSV Cu filler. After that, the thermomechanical response of TSVs is stress-imaged via Raman spectroscopy. Thermal stress is developed in the Si after an annealing process at 400°C, which is attributed to the shrinkage of the Cu core as the sample cools down from the annealing temperature to room temperature. The stress profiles of TSVs with different diameters are measured and compared, revealing an equivalent stress level consistently below 100 MPa for all diameters. This lower stress level is attributed to the offset between tensile radial stress and compressive tangential stress. With the pitch fixed for different-sized TSVs, the interaction between adjacent TSVs is reduced for smaller TSVs, leading to a lower stress level and a transformation from single-peak to dual-peak stress distribution.