III-nitride compound semiconductors are breakthrough materials regarding device applications. However, their heterostructures suffer from very high threading dislocation (TD) densities that impair several aspects of their performance. The physical mechanisms leading to TD nucleation in these materials are still not fully elucidated. An overlooked but apparently important mechanism is their heterogeneous nucleation on domains of basal stacking faults (BSFs). Based on experimental observations by transmission electron microscopy, we present a concise model of this phenomenon occurring in III-nitride alloy heterostructures. Such domains comprise overlapping intrinsic I1 BSFs with parallel translation vectors. Overlapping of two BSFs annihilates most of the local elastic strain of their delimiting partial dislocations. What remains combines to yield partial dislocations that are always of screw character. As a result, TD nucleation becomes geometrically necessary, as well as energetically favorable, due to the coexistence of crystallographically equivalent prismatic facets surrounding the BSF domain. The presented model explains all observed BSF domain morphologies, and constitutes a physical mechanism that provides insight regarding dislocation nucleation in wurtzite-structured alloy epilayers.

The quantitative interdependencies of growth conditions, crystal defects and electrical/electronic properties of InN thin films, grown by plasma-assisted molecular beam epitaxy on GaN (0001) buffer layers have been investigated. InN epilayers with thickness near 700 nm, grown under different substrate temperature and/or growth rate, have been analyzed. Bulk electron concentration (N bulk ) and mobility values were extracted for each InN film using the inverted version of the multilayer Petritz model, subtracting the conductivity of a corresponding 120 nm InN film. The results indicate a significant reduction of the threading dislocation density by enhancing the diffusion length of indium adatoms during InN growth, through increase of substrate temperature and reduction of growth rate. The electrical characteristics deteriorate with increasing threading dislocation density. Assuming threading dislocations as exclusive sources of donors in InN, their charge state could be between +1 and +2 per c lattice constant length of dislocation line for N bulk ≈ 4.0-5.7×10 17 cm −3 , and approximately +2 or larger for N bulk ≈ 1.5-1.8×10 18 cm −3 . The scattering effect of threading dislocations is significantly weaker compared to reported theoretical calculations, i.e. it would correspond to an order of magnitude lower threading dislocation density than the experimentally observed density in the range of 10 10 cm −2 .

In this work, we explore the resistive switching behavior of a thin layer of SiO 2 with embedded two-dimensional (2D) molybdenum disulfide, MoS 2 , in a conductive bridge random access memory (CBRAM) configuration. The proposed device exhibits enhanced conductance quantization behavior, reduced variability due to the suppression of the stochastic filament formation process, and synaptic properties. The device operates under the bipolar switching mode without the application of any electroforming procedure; eight different quantized conductance states were captured during direct current (DC) operation and 10 quantized states were recorded under pulse measurements. On top of that, both improved endurance and retention properties as well as linearity of the synaptic potentiation and depression procedures were attained; the underlying origins of these effects are attributed to the control of the Ag ion diffusion barrier through the existence of the atomic sieve of MoS 2 . Our work paves the way for the development of robust memristive elements for the implementation of stable resistive switching and neuromorphic functionalities.

The use of strained substrates may overcome indium incorporation limits without inducing plastic relaxation in InGaN quantum wells, and this is particularly important for short-period InGaN/GaN superlattices. By incorporating elastic strain into these heterostructures, their optoelectronic behavior is modified. Our study employed density functional theory calculations to investigate the variation in the band-gap energy of short-period InGaN/GaN superlattices that comprise pseudomorphic quantum wells with a thickness of just one monolayer. Heterostructures with equibiaxially strained GaN barriers were compared with respective ones with relaxed barriers. The findings reveal a reduction of the band gap for lower indium contents, which is attributed to the influence of the highly strained nitrogen sublattice. However, above mid-range indium compositions, the situation is reversed, and the band gap increases with the indium content. This phenomenon is attributed to the reduction of the compressive strain in the quantum wells caused by the tensile strain of the barriers. Our study also considered local indium clustering induced by phase separation as another possible modifier of the band gap. However, unlike the substrate-controlled strain, this was not found to exert a significant influence on the band gap. Overall, this study provides important insights into the behavior of the band-gap energy of strained superlattices toward optimizing the performance of optoelectronic devices based on InGaN/GaN heterostructures.

A novel endeavor based on the synthesis, characterization and study of a hybrid crystalline magnetic nanostructured material composed of bimetallic iron–rhodium nanoalloys, grown on nanodiamond nanotemplates, is reported in this study. The development of this hybrid magnetic nanomaterial is grounded in the combination of wet chemistry and thermal annealing under vacuum. In order to assess, evaluate and interpret the role and special properties of the nanodiamond supporting nanotemplates on the growth and properties of the bimetallic ferromagnetic Fe–Rh nanoparticles on their surfaces, unsupported free FeRh nanoparticles of the same nominal stoichiometry as for the hybrid sample were also synthesized. The characterization and study of the prepared samples with a range of specialized experimental techniques, including X-ray diffraction, transmission and scanning transmission electron microscopy with energy dispersive X-ray analysis, magnetization and magnetic susceptibility measurements and 57Fe Mössbauer spectroscopy, reveal that thermal annealing of the hybrid sample under specific conditions (vacuum, 700 °C, 30 min) leads to the formation of a rhodium-rich FeRh alloy nanostructured phase, with an average particle size of 4 nm and good dispersion on the surfaces of the nanodiamond nanotemplates and hard ferromagnetic characteristics at room temperature (coercivity of ~500 Oe). In contrast, thermal annealing of the unsupported free nanoparticle sample under the same conditions fails to deliver ferromagnetic characteristics to the FeRh nanostructured alloy phase, which shows only paramagnetic characteristics at room temperature and spin glass ordering at low temperatures. The ferromagnetic nanohybrids are proposed to be exploited in a variety of important technological applications, such as magnetic recording, magnetic resonance imaging contrast and magnetic hyperthermia agents.