In this study, the thermal stability and phase evolution of nominal Cr2TiAl were investigated through annealing treatments at 700 °C, 900 °C, and 1100 °C for up to 21 days. Phase evolution was characterized using X–ray diffraction, scanning electron microscopy, energy–dispersive spectroscopy, Vickers hardness testing, and CALPHAD thermodynamic calculations. The as–cast alloy formed a predominantly BCC–derived structure near the nominal Cr2TiAl composition. Following annealing, the alloy evolved into multiphase microstructures with strong temperature– and time–dependent behavior.Annealing at 700 °C produced a fine interconnected microstructure with the highest measured hardness, approximately 883 HV. At 900 °C, prolonged annealing produced increasingly distinct Cr–rich and Ti/Al–rich constituents and reduced hardness to approximately 743 HV after 21 days. Annealing at 1100 °C followed by furnace cooling produced a lamellar microstructure consisting of alternating Cr–rich and Ti/Al–rich phases, along with irregular contrast regions. Comparison with CALPHAD predictions indicates that the measured phase compositions are consistent with partitioning within a predicted BCC–derived and Laves–containing phase region. However, due to diffraction peak overlap and the spatial resolution limitations of SEM–EDS, the Cr–rich constituent is conservatively described as Laves–related rather than assigned to a specific Laves polytype. These results demonstrate that Cr2TiAl evolves from a predominantly BCC–derived structure toward a multiphase microstructure during thermal exposure and furnace cooling. The mechanical response is strongly influenced by microstructural characteristics and phase distribution.

Fabrication of ternary intermetallic alloys with high atomic ordering is a critical step to realizing their predicted functional properties. For example, Heusler alloys have long been predicted with high spin polarization, low spin damping, and high ferromagnetic ordering temperatures. Unfortunately (paraphrasing Douglas Adams), the attempt to make highly ordered Heusler alloys has made a lot of people very angry and has been widely regarded as a bad move. Atomic ordering has typically been lower than predicted, to the detriment of predicted properties. Initial models and rules-of-thumb using, e.g., electron counting, electronegativity, or atomic size fall apart once a wide range of elemental choices are investigated. This result is perhaps not surprising, as Heusler alloys (like modern elevators) are strange and complex entities, but we should not give up and go mad just yet. In this work, we propose re-imagining the placement of a Heusler alloy system's available Slater-Pauling electrons (the s-and d-orbital electrons available for bonding) in the calculated Full Heusler hybridized molecular orbital structure of Galanakis et al., using the alternating site counts of 4 and 2 spin-down electrons proposed by Butler et al. to minimize energy in half-metallic ferromagnets. By applying a system of common sense steps, we posit that one can test the feasibility of formation and site occupations of full (L21) and inverse (XA) forms of potential Heusler alloys without need for long and computationally expensive calculations, which may still not cover every potential probability that the universe has in store. We reviewed a substantial amount of existing experimental evidence suggesting that alloys that do not follow the electron structure inevitably adopt a different, more energetically favorable structure or exhibit multi-phase structures or phase segregation. We further propose that one can apply the rule set to indicate how one might stabilize an infeasible compositional choice through compensation or elemental substitution. This approach offers a promising solution to the long-standing theoretical-experimental discrepancy problem in this field.

p-type Cr2MnO4 with bandgap 3.01 eV was sputter deposited onto (201) and (001) n-type or semi-insulating beta-Ga2O3.The heterojunction of p-type CrMnO4 on n-type Ga2O3 is found to be type II, staggered gap, i.e., the band offsets are such that both the conduction and valence band edges of Ga2O3 are lower in energy than those of the Cr2MnO4. This creates a staggered band alignment, which can facilitate the separation of photogenerated electron-hole pairs. The valence band edge of Cr2MnO4 is higher than that of Ga2O3 by 1.82-1.93 eV depending on substrate orientation and doping, which means that holes in Cr2MnO4 would have a lower energy barrier to overcome to move into Ga2O3. Conversely, the conduction band edge of Cr2MnO4 is higher than that of Ga2O3 by 0.13-0.30 eV depending on substrate doping and orientation, which would create a barrier for electrons in Ga2O3 to move into Cr2MnO4. This heterojunction looks highly promising for p-n junction formation for advanced Ga2O3-based power rectifiers.

p-type Cr 2 MnO 4 with bandgap 3.01 eV was sputter deposited onto (01) and (001) n-type or semi-insulating β-Ga 2 O 3 .The heterojunction of p-type CrMnO 4 on n-type Ga 2 O 3 is found to be type II, staggered gap, ie. the band offsets are such that both the conduction and valence band edges of Ga 2 O 3 are lower in energy than those of the Cr 2 MnO 4 . This creates a staggered band alignment, which can facilitate the separation of photogenerated electron-hole pairs. The valence band edge of Cr 2 MnO 4 is higher than that of Ga 2 O 3 by1.82-1.93 eV depending on substrate orientation and doping, which means that holes in Cr 2 MnO 4 would have a lower energy barrier to overcome to move into Ga 2 O 3 . Conversely, the conduction band edge of Cr 2 MnO 4 is higher than that of Ga 2 O 3 by 0.13-0.30 eV depending on substrate doping and orientation, which would create a barrier for electrons in Ga 2 O 3 to move into Cr 2 MnO 4 . This heterojunction looks highly promising for p-n junction formation for advanced Ga 2 O 3 -based power rectifiers.

First-principles calculations are performed for the full Heusler L21 and inverse Heusler XA phases of the A2YSn series, with A spanning the 3d block of the transition metals (A = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn). Yttrium is chosen as the B-site element in order to investigate the role of 4d B-site orbitals on the magnetic character of the system as a whole. Formation energy calculations indicate a transition from XA to L21 dominant phase preference crossing from a V to a Cr A-site element choice, with L21 remaining the dominant phase across the rest of the series. Magnetic data reveal a weak ferrimagnetic yttrium sublattice forming in a similar region of A-site valency as the phase preference transition, indicating a possible structural-magnetic coupling. Total and projected density of states calculations reveal a rich electronic structure with unique hybridization between the A-site and yttrium atoms, particularly for the L21 phase. A near half-metallic gap is found to form in the L21 phase with increasing A-site valency, culminating in a 97.71 % spin polarization for Cr2YSn. Phase stability conclusions are also compared to data from the Open Quantum Materials Database, providing important context for the role of density functional theory (DFT) in informing material synthesis studies. These results provide new insights into the role of element choice in Heusler phase stability and electronic structure, which is critical to identifying novel materials who properties are robust against phase competition.

p-type Cr2MnO4 with bandgap 3.01 eV was sputter deposited onto (2¯01) and (001) n-type or semi-insulating β-Ga2O3.The heterojunction of p-type CrMnO4 on n-type Ga2O3 is found to be type II, staggered gap, i.e., the band offsets are such that both the conduction and valence band edges of Ga2O3 are lower in energy than those of the Cr2MnO4. This creates a staggered band alignment, which can facilitate the separation of photogenerated electron-hole pairs. The valence band edge of Cr2MnO4 is higher than that of Ga2O3 by 1.82–1.93 eV depending on substrate orientation and doping, which means that holes in Cr2MnO4 would have a lower energy barrier to overcome to move into Ga2O3. Conversely, the conduction band edge of Cr2MnO4 is higher than that of Ga2O3 by 0.13–0.30 eV depending on substrate doping and orientation, which would create a barrier for electrons in Ga2O3 to move into Cr2MnO4. This heterojunction looks highly promising for p-n junction formation for advanced Ga2O3-based power rectifiers.

Single crystals of disordered Mn4-xCrxAl11have been synthesized via the flux method. EDS on several crystals of various sizes and shapes revealed an average molar ratio of 17:9:74 for Mn:Cr:Al, while x-ray diffraction on three different crystals yield compositions Mn2.26Cr1.74Al11(Mn4-xCrxAl11,x= 1.74), Mn0.83Cr3.17Al11, and Mn1.07Cr2.93Al11. This compound crystallizes in space groupP1¯, isostructural with both Mn4Al11and Cr4Al11. Magnetic measurements on several crystals show that this disordered compound is ferrimagnetic with a low effective moment ofμeff≈1.012±0.004μB/f.u.and a non-reachable transition temperature. Density functional theory calculations display opening of a bandgap in the spin-up channel near the Fermi level with increasing Cr content, an indication of half-metallicity.

We report the dry etching characteristics of Cr2MnO4 thin films using Cl2-based inductively coupled plasmas (ICP) for applications in Ga2O3-based power electronics, where p-n heterojunctions offer advantages over Schottky diodes. Cr2MnO4, a thermally stable p-type oxide, was deposited via RF sputter beam epitaxy and etched using Cl2/Ar and BCl3/Ar plasmas, with the latter producing much lower etch rates. The etch rates and surface roughness were investigated as functions of Cl2 flow rate, RF power, and gas composition. Results reveal that increasing the Cl2 flow rate enhances etch rates but degrades surface roughness due to non-volatile chloride formation and redeposition. Higher RF power improves surface smoothness by increasing ion bombardment energy, promoting physical sputtering, and enabling uniform etching. The etch process is ion-flux limited, with threshold energies comparable to NiO. Post-etch X-ray photoelectron spectroscopy analysis confirms that NH4OH rinsing effectively removes chlorine residues by dissolving metal chlorides and neutralizing acidic species, ensuring a clean surface. These findings underscore the importance of optimizing plasma parameters and post-etch cleaning for fabricating high-quality Cr2MnO4/Ga2O3 heterojunctions, which hold promise for high-temperature, high-power electronic applications.

We report the heteroepitaxial growth of spinel Cr2MnO4 thin films on ( 2 01 ) beta-Ga2O3 substrates via off-axis RF magnetron sputtering. Structural analysis confirms (111)-oriented epitaxial films with optimized growth at 950 degrees C. Fabricated Cr2MnO4/beta-Ga2O3 vertical diodes exhibit rectifying behavior with high on/off ratios (similar to 10(8)), turn-on voltages near 0.85 V, and low reverse leakage current. Transmission electron microscopy and atomic force microscopy analyses show the films exhibit a Stranski-Krastanov growth mode, with three-dimensional texturing of potential interest for device performance. Capacitance-voltage measurements reveal intrinsic p-type conductivity with carrier concentration similar to 7 x 10(17) cm(-3). The results suggest that Cr2MnO4 may be a promising candidate for Ga2O3-based bipolar devices.

B site ordered 5d2 double perovskites (A2BB'O6, B' = 5d2) display a remarkable range of physical properties upon variation of the chosen B and B' site ions. This sensitivity to chemical substitution reflects the delicate balance and profound impact of strong electronic correlation and spin-orbit coupling in such systems. We present rhenium L2 and L3 resonant inelastic x-ray scattering (RIXS) measurements of two such physically dissimilar materials, Mott-insultating Ba2YReO6 and semiconducting Sr2CrReO6. Despite these differences, our RIXS results reveal similar energy scales of Hund's (JH) and spin-orbit coupling (zeta) in the two materials, with both systems firmly in the intermediate Hund's coupling regime where JH/zeta similar to 1. However, there are clear differences in their RIXS spectra. The conductive character of Sr2CrReO6 broadens and obfuscates the atomic transitions within an electron-hole continuum, while the insulating character of Ba2YReO6 results in sharp atomic excitations. This contrast in their RIXS spectra despite their similar energy scales reflects a difference in the itinerancy-promoting hopping integral and illustrates the impact of the local crystal environment in double perovskites. Finally, L2 and L3 edge analyses of the atomic excitations in Ba2YReO6 reveal that the ordering of the low lying excited states is inverted compared to previous reports, such that the appropriate energy scales of Hund's and spin-orbit coupling are significantly modified. We present exact diagonalization calculations of the RIXS spectra at both edges which show good agreement with our results for new energy scales of zeta = 0.290(5) eV and JH = 0.38(2) eV [JH/zeta = 1.30(5)].

The Zr-based metal-organic framework UiO-66-NH2 has been investigated to study the effects of ultraviolet and visible light exposure under dry air and humid environments. Significant impedance and color changes in the material due to ultraviolet and blue light have been observed. These changes happen more rapidly and grow larger in total cumulative magnitude as the atmospheric humidity increases. Samples placed in darkness or in the presence of light with lower energy than blue (450 nm) light showed no discoloration or degradation, regardless of humidity. Impedance data modeling suggests that humidity increases the ionic conductivity of the material and that the degradation occurs at grain boundaries, to a depth that increases with humidity. Nuclear magnetic resonance, X-ray diffraction, and Fourier transform infrared spectroscopy indicate that degradation in samples exposed to light are due to broken linkers between the benzenedicarboxylic acid and Zr clusters . Distribution Statement A. Approved for Public Release. Distribution Unlimited.

We report the heteroepitaxial growth of spinel Cr2MnO4 thin films on (2¯01) β-Ga2O3 substrates via off-axis RF magnetron sputtering. Structural analysis confirms (111)-oriented epitaxial films with optimized growth at 950 °C. Fabricated Cr2MnO4/β-Ga2O3 vertical diodes exhibit rectifying behavior with high on/off ratios (∼108), turn-on voltages near 0.85 V, and low reverse leakage current. Transmission electron microscopy and atomic force microscopy analyses show the films exhibit a Stranski–Krastanov growth mode, with three-dimensional texturing of potential interest for device performance. Capacitance–voltage measurements reveal intrinsic p-type conductivity with carrier concentration ∼7 × 1017 cm−3. The results suggest that Cr2MnO4 may be a promising candidate for Ga2O3-based bipolar devices.

We report a substrate-limited, high-quality thin film growth of Co2TiSn, requiring the use of a substrate-limited TiN buffer layer as well as a Nb capping layer to achieve an x-ray diffraction rocking curve full width at halfmaximum of 12 arcseconds. This value represents more than an order of magnitude improvement over previous results for TiN, and more than two orders of magnitude better than any previous Co2TiSn thin film reported. Our surface analysis of the TiN film grown on a-plane sapphire reveals a distinctive step-edge-guided nucleation and epitaxial layer growth. Additionally, our first-principles calculations on Co2TiSn in its L21 and XA phases examine the limitations of various exchange correlation functionals and the impact of Hubbard U correction on accurately representing the magnetic properties and density of states of Co2TiSn. The observed lower-than-ideal magnetic moment in the disordered (XA) phase corresponds well with the experimentally observed reduced magnetization of the Co2TiSn film, as no evidence of phase segregation or secondary phase is detected. This work serves as both a roadmap for making high-quality Heusler alloy thin films and a stepping stone for the evaluation of the intrinsic atomic ordering in this and other Heusler systems by providing a high-quality crystal with energetics during formation as close to the thermodynamic limit as possible.

First-principles calculations are performed for full (L2 1 ) and inverse (XA) Heusler compounds X 2 FeAl, where X comprise a range of 3d (Sc, Ti, V, Cr), 4d (Y, Zr, Nb, Mo), and 5d (Hf, Ta, W) early and middle column transition metal elements. The formation energy difference between full and inverse phase and the degree of d -d orbital hybridization with increasing total valence electron count are shown to drive the magnetic properties (total and atomic magnetic moments, spin polarization) and electronic properties (band structure and projected density of states) of the material system. Specifically, X-site atomic magnetic moments take on increasingly Fe character with increasing valence electron count, in both full and inverse Heusler phases. This can be explained by changes on the degree of d -d hybridization between X- and Fe-site d orbitals. Synchronized energy shifts in the PDOS of the X- and Y-sites (Fe) across each of the full and inverse Heusler series provide us insight to controlling spin polarization via composition. This work demonstrates the need to holistically study the thermodynamic phase stability, magnetic moments, and spin polarization of Heusler alloys, in the framework of anti-site disorder and in a wider compositional context. The end goal of this study is to benefit the mapping of experimental results in search of a specific property, by providing a methodology for extrapolating properties based on experimental or theoretical results.

We report the formation of Mn-rich regions at the interface of Co2FexMn1-xSi thin films grown on GaAs substrates by molecular beam epitaxy (MBE). Scanning transmission electron microscopy (STEM) with electron energy loss (EEL) spectrum imaging reveals that each interfacial region: (1) is 1-2 nm wide, (2) occurs irrespective of the Fe/Mn composition ratio and in both Co-rich and Co-poor films, and (3) displaces both Co and Fe indiscriminately. We also observe a Mn-depleted region in each film directly above each Mn-rich interfacial layer, roughly 3 nm in width in the x = 0 and x = 0.3 films, and 1 nm in the x = 0.7 (less Mn) film. We posit that growth energetics favor Mn diffusion to the interface even when there is no significant Ga interdiffusion into the epitaxial film. Element-specific X-ray magnetic circular dichroism (XMCD) measurements show larger Co, Fe, and Mn orbital to spin magnetic moment ratios compared to bulk values across the Co2FexMn1-xSi compositional range. The values lie between reported values for pure bulk and nanostructured Co, Fe, and Mn materials, corroborating the non-uniform, layered nature of the material on the nanoscale. Finally, SQUID magnetometry demonstrates that the films deviate from the Slater-Pauling rule for uniform films of both the expected and the measured composition. The results inform a need for care and increased scrutiny when forming Mn-based magnetic thin films on III-V semiconductors like GaAs, particularly when films are on the order of 5 nm or when interface composition is critical to spin transport or other device applications.

SummaryA timescale algorithm demonstrating a clock ensemble utilizing commercial atomic clocks and multiplexing equipment has been established at the University of Alabama to serve as a testbed for research and student training.

Modern-day chip manufacturing requires precision in placing chip materials on complex and patterned structures. Area-selective atomic layer deposition (AS-ALD) is a self-aligned manufacturing technique with high precision and control, which offers cost effectiveness compared to the traditional patterning techniques. Self-assembled monolayers (SAMs) have been explored as an avenue for realizing AS-ALD, wherein surface-active sites are modified in a specific pattern via SAMs that are inert to metal deposition, enabling ALD nucleation on the substrate selectively. However, key limitations have limited the potential of AS-ALD as a patterning method. The choice of molecules for ALD blocking SAMs is sparse; furthermore, deficiency in the proper understanding of the SAM chemistry and its changes upon metal layer deposition further adds to the challenges. In this work, we have addressed the above challenges by using nanoscale infrared spectroscopy to investigate the potential of stearic acid (SA) as an ALD inhibiting SAM. We show that SA monolayers on Co and Cu substrates can inhibit ZnO ALD growth on par with other commonly used SAMs, which demonstrates its viability towards AS-ALD. We complement these measurements with AFM-IR, which is a surface-sensitive spatially resolved technique, to obtain spectral insights into the ALD-treated SAMs. The significant insight obtained from AFM-IR is that SA SAMs do not desorb or degrade with ALD, but rather undergo a change in substrate coordination modes, which can affect ALD growth on substrates.

This paper contains data and results from Density Functional Theory (DFT) investigation of 423 distinct X2YZ ternary full Heusler alloys, where X and Y represent elements from the D-block of the periodic table and Z signifies element from main group. The study encompasses both “regular” and “inverse” Heusler phases of these alloys for a total of 846 potential materials. For each specific alloy and each phase, a range of information is provided including total energy, formation energy, lattice constant, total and site-specific magnetic moments, spin polarization as well as total and projected density of electronic states. The aim of creating this dataset is to provide fundamental theoretical insights into ternary X2YZ Heusler alloys for further theoretical and experimental analysis.

We reveal in this study the fundamental low-energy landscape in the ferrimagnetic Sr2CrReO6 double perovskite and describe the underlying mechanisms responsible for the three low-energy excitations below 1.4 eV. Based on resonant inelastic x-ray scattering and magnetic dynamics calculations, and experiments collected from both Sr2CrReO6 powders and epitaxially strained thin films, we reveal a strong competition between spin-orbit coupling, Hund's coupling, and the strain-induced tetragonal crystal field. We also demonstrate that a spin-flip process is at the origin of the lowest excitation at 200 meV, and we bring insights into the predicted presence of orbital ordering in this material. We study the nature of the magnons through a combination of ab initio and spin-wave theory calculations, and show that two nondegenerate magnon bands exist and are dominated either by rhenium or chromium spins. The rhenium band is found to be flat at about 200 meV (& PLUSMN;25 meV) through X-L-W-U high-symmetry points and is dispersive toward & UGamma;.

We investigate the structural, static, and dynamic magnetic properties of epitaxial Heusler Co2Fe(Ti0.5Al0.5) (CFTA) alloy thin films with thickness varying from 6 nm to 80 nm grown by sputter beam epitaxy on cubic MgO(001), MgAl2O4(001), and hexagonal Al2O3(112̄0) substrates. X-ray diffraction measurements indicate epitaxial growth of CFTA thin films with B2 chemical ordering, with cubic [001] and [220] CFTA axes normal to the cubic and hexagonal substrates, respectively. Microstructure analysis of films grown on MgO substrates reveals a uniformly oriented epitaxial crystal with small variations consistent with strain distortions, providing an explanation for the relatively large X-ray rocking curve values found. Meanwhile, films on Al2O3(112̄0) substrates reveal columnar growth with frequent in-plane grain rotations. A pronounced four-fold magnetocrystalline anisotropy is observed in epitaxial thin films grown on cubic substrates. A pronounced uniaxial anisotropy for films grown on Al2O3(112̄0) substrates is observed. A saturation magnetization of ∼5.0μB/f.u. (where f.u. represents formula unit) is obtained at room temperature, slightly smaller compared to the expected value based on the Slater-Pauling rule. Ferromagnetic resonance spectroscopy finds an effective damping parameter and inhomogeneous linewidth broadening comparable to those found in parent compound Co2FeAl, which suggests that Ti substitution can be achieved without negatively affecting the magnetic properties of the system.