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We attained wurtzite ScxAl1−xN (0.16 ≤ x ≤ 0.37) thin films by varying the Sc and Al fluxes at a fixed active nitrogen flux during plasma-assisted molecular beam epitaxy. Atomic fluxes of Sc and Al sources via measured Sc percentage in as-grown ScxAl1−xN thin films were derived as the feedback for precise determination of the ScxAl1−xN growth diagram. We identified an optimal III/N atomic flux ratio of 0.78 for smooth Sc0.18Al0.82N thin films. Further increasing the III/N ratio led to phase separation under N-rich conditions, validated by the observation of high-Sc-content hillocks with energy-dispersive X-ray spectroscopy mapping. At the fixed III/N ratio of 0.78, we found that phase separation with high-Al-content hillocks occurs for x > 0.37, which is substantially lower than the thermodynamically dictated threshold Sc content of ~0.55 in wurtzite ScxAl1−xN. We postulate that these wurtzite-phase purity degradation scenarios are correlated with adatom diffusion and the competitive incorporation process of Sc and Al. Therefore, the ScxAl1−xN growth window is severely restricted by the adatom kinetics. We obtained single crystalline Sc0.37Al0.63N thin films with X-ray diffraction (002)/(102) ω rocking curve full-width at half-maximums of 2156 arcsec and 209 arcsec and surface roughness of 1.70 nm. Piezoelectric force microscopy probing of the Sc0.37Al0.63N epilayer validates unambiguous polarization flipping by 180°. [ABSTRACT FROM AUTHOR]

Traditional computation based on von Neumann architecture is limited by time and energy consumption due to data transfer between the storage and the processing units. The von Neumann architecture is also inefficient in solving unstructured, probabilistic, and real‐time problems. To address these challenges, a new brain‐inspired neuromorphic computational architecture is required. Due to the absence of resistance–capacitance delay, high bandwidth, and low power consumption, optoelectronic artificial synaptic devices are highly attractive. Yet, stable, scalable, and complementary metal–oxide–semiconductor (CMOS)‐compatible materials exhibiting both inhibitory and excitatory optoelectronic synaptic functionalities have not been demonstrated. Here, epitaxial CMOS‐compatible scandium nitride (ScN) optoelectronic artificial synaptic devices that emulate both inhibitory and excitatory biological synaptic activities are presented. The negative and positive persistent photoconductivity of undoped and magnesium‐doped ScN is equated to the inhibitory and excitatory synaptic plasticity, respectively, which leads to functionalities like learning–forgetting, frequency‐selective optical filtering, frequency‐dependent potentiation and depression, Hebbian learning, and logic‐gate operations. Temperature‐dependent photoresponse and photo‐Hall measurements reveal that scattering of photogenerated carriers from charged defect centers results in negative photoconductivity in undoped degenerate ScN. This work opens up the possibility of utilizing a group‐III epitaxial semiconducting nitride material with inhibitory and excitatory optoelectronic synaptic functionalities for practical neuromorphic applications. [ABSTRACT FROM AUTHOR]

Knowledge of accurate values of elastic modulus of (Al1–xScx)N is required for design of piezoelectric resonators and related devices. Thin films of (Al1–xScx)N across the entire composition space are deposited and characterized. Accuracy of modulus measurements is improved and quantified by removing the influence of substrate effects and by direct comparison of experimental results with density functional theory calculations. The 5%–30% Sc compositional range is of particular interest for piezoelectric applications and is covered at higher compositional resolution here than in previous work. The reduced elastic modulus is found to decrease by as much as 40% with increasing Sc concentration in the wurtzite phase according to both experimental and computational techniques, whereas Sc-rich rocksalt-structured films exhibit little variation in modulus with composition. [ABSTRACT FROM AUTHOR]

A self-assembled CuII-based nanocapsule enables efficient and straightforward isolation of Sc3N@C80 from arc-processed raw soot. The newly designed CuII-based supramolecular nanocapsule 5⋅(OTf)8 was used to effectively entrap fullerenes and endohedral metallofullerenes (EMFs) with different affinities depending on their size and shape. Moreover, we took advantage of the sharply different entrapment abilities of the 5⋅(OTf)8 cage in the solid state versus in solution to encapsulate all the species with the exception of Sc3N@C80 (both Ih and D5h isomers), which remains pure in solution. HPLC quantification determined that up to 85 % of the total Sc3N@C80 content in the initial mixture was recovered in very high purity (>99.5 %). The complete release of the encapsulated species with an orthogonal solvent-washing strategy regenerates 5⋅(OTf)8 ready to be re-used. This approach opens new opportunities for EMFs purification. [ABSTRACT FROM AUTHOR]

Scandium nitride (ScN) films were grown on α-Al2O3( 1 1 ¯ 02 ) substrates using the molecular beam epitaxy method, and the heteroepitaxial growth of ScN on α-Al2O3( 1 1 ¯ 02 ) and their electric properties were studied. Epitaxial ScN films with an orientation relationship (100)ScN || ( 1 1 ¯ 02 )α-Al2O3 and [001]ScN || [ 11 2 ¯ 0 ]α-Al2O3 were grown on α-Al2O3( 1 1 ¯ 02 ) substrates. Their crystalline orientation anisotropy was found to be small. In addition, [100] of the ScN films were tilted along [ 1 ¯ 101 ] of α-Al2O3( 1 1 ¯ 02 ) in the initial stage of growth. The tilt angle between the film growth direction and [100] of ScN was 1.4–2.0° and increased with growth temperature. The crystallinity of the ScN films also improved with the increasing growth temperature. The film with the highest Hall mobility was obtained at the boundary growth conditions determined by the relationship between the crystallinity and the nonstoichiometric composition because the film with the highest crystallinity was obtained under the Sc-rich growth condition. The decreased Hall mobility with a simultaneous improvement in film crystallinity was caused by the increased carrier scattering by the ionized donors originating from the nonstoichiometric composition. [ABSTRACT FROM AUTHOR]