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We investigate the structural and metal–insulator transition (MIT) behavior of epitaxial V 2 O 3 films fabricated by reactive direct current magnetron sputtering on r, a, c, and m-plane Al 2 O 3 substrates, in both as-received and annealed states. Characterization of MIT of the V 2 O 3 films grown on annealed substrates demonstrated significant changes in observed MIT properties, i.e., r-plane films showed ≈ 2 order increase in transition magnitude, m-plane ≈ 6 orders, and c-plane films exhibited a reduction of ≈ 3 orders, compared to un-annealed substrates, whereas for V 2 O 3 on annealed a-plane, it revealed a shift in the transition to higher values, with reduction in hysteresis width. Structural characterization conducted via x-ray diffraction and atomic force microscopy revealed a reduction in out-of-plane compressive strain for annealed substrates, along with decreased lateral grain size. Additionally, the correlation between the V 2 O 3 MIT and its underlying structural phase transition was verified by temperature-dependent x-ray diffraction analysis. These findings highlight the role of substrate orientation and pre-annealing in tuning the MIT behavior of V 2 O 3 films grown on the Al 2 O 3 substrate. [ABSTRACT FROM AUTHOR]

The early stage of the impact-initiated reaction of supersonic cylindrical reactive metal projectiles (magnesium, aluminum, titanium, and zirconium) with an inert aluminum oxide target is investigated experimentally with impact velocities from 1.1 to 1.3 km/s. A three-color imaging pyrometer is used to obtain temperature maps of the condensed fragments generated during the first few microseconds following contact between the projectile and the target. Experiments conducted in inert and oxidizing atmospheres confirm that chemical reactions initiate readily upon contact between the projectile and the target. In oxidizing atmospheres, the fragment temperatures measured for each metal are, on average, below but near the respective adiabatic temperature in air, except for Zr which produced temperatures significantly below expectations. Only the particles shed at the interface between the projectile and the target visibly react with the oxygen in the ambient atmosphere. At the impact velocities under study, only a small fraction, on the order of a few percent, of the mass of the projectile is finely fragmented during the initial impact event. [ABSTRACT FROM AUTHOR]

In this contribution, we investigate the formation and dissociation of boron–hydrogen (BH) pairs in crystalline silicon under thermal equilibrium conditions. Our samples span doping concentrations of nearly two orders of magnitude and are passivated with a layer stack consisting of thin aluminum oxide and hydrogen-rich silicon nitride (Al 2 O 3 /SiN x :H). This layer stack acts as a hydrogen source during a following rapid thermal annealing. We characterize the samples using low-temperature Fourier-transform infrared spectroscopy and four-point-probe resistivity measurements. Our findings show that the proportion of hydrogen atoms initially bound to boron (BH pairs) rises with increasing boron concentration. Upon isothermal dark annealing at (163 ± 2) °C, hydrogen present in molecular form, H 2 , dissociates at a rate directly proportional to the concentration of boron atoms, ∝ [ B − ], leading to the formation of BH pairs. With prolonged annealing, an unknown hydrogen complex is formed at a rate that is inversely proportional to the square of the boron concentration, ∝ 1/[B − ] 2 , resulting in the disappearance of BH pairs. Based on experimental observations, we derive a kinetic model in which we describe the formation of the unknown complex through neutral hydrogen H 0 binding to a sink. Additionally, we investigate the temperature dependence of the reaction rates and find that the H 2 dissociation process has an activation energy of (1.11 ± 0.05) eV, which is in close agreement with theoretical predictions. [ABSTRACT FROM AUTHOR]

Stability and precision of atomic devices are closely tied to the quality and stability of the internal atmosphere of the atomic vapor cells on which they rely. Such an atmosphere can be stabilized by building the cell with low permeation materials such as sapphire or aluminosilicate glass in microfabricated devices. Recently, we have shown that permeation barriers made of Al 2 O 3 thin-film coatings deposited on standard borosilicate glass could be an alternative for buffer gas pressure stabilization. In this study, we, hence, investigate how helium permeation is influenced by the thickness, ranging from 5 to 40 nm, of such Al 2 O 3 thin films coated by atomic layer deposition. Permeation rates are derived from long-term measurements of the pressure-shifted transition frequency of a coherent population trapping (CPT) atomic clock. From thicknesses of 20 nm onward, a significant enhancement of the cell hermeticity is experienced, corresponding to two orders of magnitude lower helium permeation rate. In addition, we test cesium vapor cells filled with neon as a buffer gas and whose windows are coated with 20 nm of Al 2 O 3. As for helium, the permeation rate of neon is significantly reduced, thanks to alumina coatings, leading to a fractional frequency stability of 4 × 10 − 12 at 1 day when the cell is used in a CPT clock. These features outperform the typical performances of uncoated Cs–Ne borosilicate cells and highlight the significance of Al 2 O 3 coatings for buffer gas pressure stabilization. [ABSTRACT FROM AUTHOR]

We demonstrate reversible modulation of an insulator–metal transition (IMT) of a VO2 film grown on an Al2O3 (001) substrate through crystallization and re-amorphization of a chalcogenide germanium–antimony–telluride (Ge2Sb2Te5: GST) capping layer. After succeeding in the negative shift of IMT temperature (Tr) of the VO2 film through the crystallization of the GST layer accompanied by volume reduction, we performed re-amorphization of the crystalline GST by femtosecond laser irradiation. Under the optimized conditions of laser irradiation considering the penetration depth, re-amorphization of the GST layer was fully achieved, resulting in the shift-back of Tr toward a high-temperature side. Such a reversal of IMT through the crystallization and re-amorphization of the capping GST layer was demonstrated over two cycles. It was suggested that capping GST effectively induces interfacial strain modifications in the VO2 film underneath. Although the shifts in the IMT are still small, reversible modulation of IMT shown here will be beneficial for applications of VO2 films with controllable IMT. [ABSTRACT FROM AUTHOR]

Amorphous alumina resistance random-access memory is a promising candidate as a next-generation nonvolatile memory. It is intriguing that the nonvolatile memory function emerges in only amorphous samples, unlike crystalline samples. We studied local structures of amorphous alumina samples and Al 2 O 3 polycrystalline using atomic pair distribution function measurements. We derived the Al–Al, O–O, and Al–O atomic distances for each sample. By comparing them, we revealed that the subtle difference in the local structure significantly influences the performance of a nonvolatile memory function. [ABSTRACT FROM AUTHOR]

This study investigates the stability of the (Hf,Zr)O2 (HZO) and AlScN thin films against the depolarization effect. In order to adversely interfere with the polarization screening of ferroelectric (FE) film and induce the depolarization effect, an Al2O3 film was inserted between the TiN bottom electrode and the FE film. Subsequently, to minimize charge injection through Al2O3 films, the double remanent polarization–voltage (2Pr–V) curve was measured employing voltage pulses with 1 μs-length. As the thickness of the Al2O3 film increased, the charge injection through the Al2O3 film decreased, leading to a decrease in the slope of the 2Pr–V curve. The magnitude of the depolarization field applied to the FE film was determined by simulating the 2Pr–V curve using an equivalent circuit model. Subsequently, the proportion of reversed domains during the delay period due to the depolarization effect was measured. It was revealed that HZO films exhibited vulnerability to the depolarization effect, with 16% of domains being reversed. On the other hand, AlScN films demonstrated superior stability, with polarization loss of less than 1%. Ultimately, it was revealed that AlScN films demonstrated superior stability against the depolarization effect compared to HZO films due to their higher coercive field and more uniform polarization distribution across the film area. [ABSTRACT FROM AUTHOR]

This article investigated the effects of airborne-particle abrasion and nanosilica (nano-Si) infiltration treatment on the surface characteristics of dental zirconia. A total of 15 unsintered zirconia ceramic green bodies (10 × 10 × 3 mm) were divided into three groups (n = 5): Group C, no treatment after sintering; Group S, airborne-particle abrasion with 50-µm aluminum oxide particles after sintering; and Group N, infiltration of nano-Si followed by sintering and hydrofluoric acid (HF) etching. The zirconia disks' surface roughness was analyzed by atomic force microscopy (AFM). The surface morphology of the specimens was analyzed using scanning electron microscopy (SEM), and the chemical composition was analyzed by energy-dispersive x-ray (EDX). Data were statistically analyzed by Kruskal-Wallis test (P < .05). Zirconia surface treatments by infiltration of nano-Si, sintering, and HF etching showed multiple changes in the surface features. The surface roughness of Groups C, S, and N were 0.88 ± 0.07 µm, 1.26 ± 0.10 µm, and 1.69 ± 0.15 µm, respectively. The surface roughness of Group N was significantly higher than that of Groups C and S (P < .05). EDX analysis showed peaks that corresponded to silica (Si) after infiltration with colloidal Si that disappeared following acid etching. Infiltrating nano-Si increases the surface roughness of zirconia. The formation of retentive nanopores on the surface potentially improves the zirconia-resin cement bonding strengths. [ABSTRACT FROM AUTHOR]

Coherent acoustic phonons induced in metallic nanostructures have attracted tremendous attention owing to their unique optomechanical characteristics. The frequency of the acoustic phonon vibration is highly sensitive to the material adsorption on metallic nanostructures and, therefore, the acoustic phonon offers a promising platform for ultrasensitive mass sensors. However, the physical origin of acoustic frequency modulation by material adsorption has been partially unexplored so far. In this study, we prepared Al2O3-deposited Au nanoblocks and measured their acoustic phonon frequencies using time-resolved pump–probe measurements. By precisely controlling the thickness of the Al2O3 layer, we systematically investigated the relation between the acoustic phonon frequency and the deposited Al2O3 amounts. The time-resolved measurements revealed that the acoustic breathing modes were predominantly excited in the Au nanoblocks, and their frequencies increased with the increment of the Al2O3 thickness. From the relationship between the acoustic phonon frequency and the Al2O3 thickness, we revealed that the acoustic phonon frequency modulation is attributed to the density change of the whole sample. Our results would provide fruitful information for developing quantitative mass sensing devices based on metallic nanostructures. [ABSTRACT FROM AUTHOR]

Optical second harmonic generation (SHG) can be employed to characterize the passivation quality of semiconducting material interfaces. The interface electric field (EDC) related to the existing charges at and near the interface, including the fixed oxide charges Qox, gives rise to the electric field induced second harmonic phenomenon. In this paper, we calibrate the SHG response for EDC measurement, using Al2O3/SiO2/Si(100) samples with different Qox. To perform this calibration, SHG and capacitance-voltage measurements (to access the electrical field of the samples) were made. The experimental results match well the simulated calibration curve, proving the potential of the SHG as stand-alone characterization technique for dielectric stacks on Si. [ABSTRACT FROM AUTHOR]

In this work, three atomic layer deposition (ALD) approaches are used to deposit an Al2O3 gate insulator on n-GaN for application in vertical GaN power switches: thermal ALD (ThALD), plasma-enhanced ALD (PEALD), and their stacked combination. The latter is a novel method to yield the most ideal insulating layer. Also, the influence of an in situ NH3 or H2 plasma pre-treatment is studied. Planar MIS capacitors are used to investigate the electrical properties and robustness of the gate insulators. In vacuo x-ray photoelectron spectroscopy (XPS) is used to study the changes in chemical composition after every surface treatment. XPS shows that all plasma pre-treatments efficiently remove all carbon contamination from the surface, but only NH3 plasma is observed to additionally remove the native oxide from the n-GaN surface. The water precursor step in the ThALD process does not completely remove the CH3 ligands of the trimethylaluminum precursor step, which might electrically be associated with a reduced forward bias robustness. The O2 plasma step in the PEALD process is associated with the removal of carbon and a tremendous increase of the O content in the GaN surface region. Electrically, this strongly correlates to an enhanced forward bias robustness and an increased forward bias hysteresis, respectively. The ThALD/PEALD stack method mitigates the shortcomings of both ALD processes while maintaining its advantages. Electrical measurements indicate that the stack method alongside NH3 plasma pretreatment provides the best characteristics in terms of hysteresis, threshold voltage, forward bias robustness, and interface trap density of states. [ABSTRACT FROM AUTHOR]

We have systematically investigated effects of metal–semiconductor or insulator–semiconductor interfacial layers (ILs) in AlGaN/GaN devices, where AlO x , TiO x , or NiO x is employed as an IL. From capacitance–voltage characteristics of metal/IL/AlGaN/GaN devices with a metal–semiconductor IL between the gate metal and AlGaN, it is shown that the IL modulates the threshold voltage V th , attributed to the vacuum level step induced by the dipole of the IL. We find negative vacuum level steps for AlO x and TiO x ILs, and positive for NiO x , from which the IL dipole density is estimated for each IL material. The two-dimensional electron gas carrier concentration in the metal/IL/AlGaN/GaN devices is also modulated by the vacuum level step. On the other hand, from capacitance–voltage characteristics of metal/ Al 2 O 3 /IL/AlGaN/GaN devices with an insulator–semiconductor IL between Al 2 O 3 and AlGaN, the fixed charge density of the Al 2 O 3 /IL/AlGaN interface is evaluated by the Al 2 O 3 thickness dependence of V th . For AlO x and TiO x ILs, the fixed charge density is higher than that of the Al 2 O 3 /AlGaN interface with no IL, while lower for NiO x. The fixed charge density for an IL shows a positive correlation with the IL dipole density, suggesting that the fixed charge is related to the unbalanced IL dipole. Furthermore, using the conductance method, we find a low trap density of the Al 2 O 3 /IL/AlGaN interface for AlO x and NiO x ILs, in comparison with that of the Al 2 O 3 /AlGaN interface with no IL. [ABSTRACT FROM AUTHOR]