Explore the vast range of titles available.

We present results derived from continuous and localized 35 keV ⁵⁵Mn⁺ ion implantations into ZnO. Localized implantations were carried out by using self-ordered alumina membranes as masks leading to ordered arrays of implanted volumes on the substrate surfaces. Defects and vacancies in the small implantation volumes of ZnO were generated due to the implantation processes besides the creation of new phases. Rapid thermal annealing was applied in the case of continuous implantation. The samples were characterized by HRSEM, GIXRD, Raman spectroscopy and RBS/C. Magnetic characterization of the samples pointed out appreciable differences among the samples obtained by the different implantation methods. This fact was mainly attributed to the different volume/surface ratios present in the implanted zones as well as to the increase of Mn atom concentrations along the grain frontiers in the nanostructured surfaces. The samples also showed a ferromagnetic transition phase at temperature value higher than room temperature.

This study presents a detailed analysis of point defect migration in In x Ga 1 − x N / GaN heterostructures, focusing on two indium compositions ( x = 0.125, 0.25). Using density functional theory calculations, we identify the impact of indium content and temperature on the mobility of nitrogen, gallium, and indium atoms, revealing key differences in their migration energy barriers. Furthermore, we investigate the lateral diffusion of indium and gallium atoms, as well as complexes of substitutional metal atoms with vacancies, through a vacancy-mediated mechanism in individual metal layers of In x Ga 1 − x N / GaN . Our results show that increasing indium concentration reduces migration barriers, enhancing defect mobility, particularly for indium atoms. These findings highlight the critical role of indium sublattice in promoting lattice relaxation and defect redistribution, while also elucidating the temperature-dependent dynamics of vacancy-mediated diffusion.

The explosion of artificial intelligence, the possible end of Moore's law, dawn of quantum computing, and the continued exponential growth of data communications traffic have brought new urgency to the need for laser integration on the diversified Si platform. While diode lasers on group III‐V platforms have long‐powered internet data communications and other optoelectronic technologies, direct integration with Si remains problematic. A paradigm‐shifting solution requires exploring new and unconventional materials and integration approaches. In this work, it is shown that a sub‐10‐nm ultra‐thin Si1−xGex buffer layer fabricated by an oxidative solid‐phase epitaxy process can facilitate extraordinarily efficient strain relaxation. The Si1−xGex layer is formed by ion implanting Ge into Si(111) and selectively oxidizing Si atoms in the resulting ion‐damaged layer, precipitating a fully strain‐relaxed Ge‐rich layer between the Si substrate and surface oxide. The efficient strain relaxation results from the high oxidation temperature, producing a periodic network of dislocations at the substrate interface, coinciding with modulations of the Ge content in the Si1−xGex layer and indicating the presence of defect‐mediated diffusion of Si through the layer. The epitaxial growth of high‐quality GaAs is demonstrated on this ultra‐thin Si1−xGex layer, demonstrating a promising new pathway for integrating III‐V lasers directly on the Si platform. Sub‐10‐nm‐thick strain‐relaxed Si1−xGex buffer layers are fabricated on Si by oxidative solid‐phase epitaxy and employed as a new platform for group III‐V heteroepitaxy on the Si platform. Si1−xGex/Si interface strain relaxation occurs via a periodic dislocation network coinciding with composition fluctuations, resulting from defect‐mediated diffusion of Si and Ge during oxidation.

This study presents a detailed analysis of point defect migration in InxGa1−xN/GaN heterostructures, focusing on two indium compositions (x = 0.125, 0.25). Using density functional theory calculations, we identify the impact of indium content and temperature on the mobility of nitrogen, gallium, and indium atoms, revealing key differences in their migration energy barriers. Furthermore, we investigate the lateral diffusion of indium and gallium atoms, as well as complexes of substitutional metal atoms with vacancies, through a vacancy-mediated mechanism in individual metal layers of InxGa1−xN/GaN. Our results show that increasing indium concentration reduces migration barriers, enhancing defect mobility, particularly for indium atoms. These findings highlight the critical role of indium sublattice in promoting lattice relaxation and defect redistribution, while also elucidating the temperature-dependent dynamics of vacancy-mediated diffusion.

A drop in the efficiency of light-emitting diodes based on InGaN/GaN QWs known as the ‘green gap’ has been studied intensively over the past dozen years. Several factors were revealed to contribute to its origin, such as random fluctuations in the indium concentration or the diffusion of point defects during the growth of QWs. The aim of this paper is to demonstrate that the Kirkendall effect can be the mechanism responsible for the thermal decomposition of InGaN/GaN MQWs structures, contributing to the green gap problem. By applying density functional theory, harmonic approximation, and harmonic transition state theory, we calculated the heights of the migration energy barriers of In and Ga atoms diffusing in I n x G a 1 − x N alloys ( x = 0 , 0.11 , 0.22 ), the vibrational frequencies of I n x G a 1 − x N alloys in the presence of migrating point defects, the temperature dependencies of the defect migration energy barriers and diffusion coefficients of Ga and In atoms migrating in I n x G a 1 − x N alloys. We demonstrated the presence of unbalanced diffusion rates of In and Ga atoms at the I n x G a 1 − x N / G a N interfaces and finally explained the experimentally observed mechanism of void formation at the I n x G a 1 − x N / G a N interfaces by means of the Kirkendall effect.

The formation and diffusion of point defects have a detrimental impact on the functionality of devices in which a high quality AlN/GaN heterointerface is required. The present paper demonstrated the heights of the migration energy barriers of native point defects throughout the AlN/GaN heterointerface, as well as the corresponding profiles of energy bands calculated by means of density functional theory. Both neutral and charged nitrogen, gallium, and aluminium vacancies were studied, as well as their complexes with a substitutional III-group element. Three diffusion mechanisms, that is, the vacancy mediated, direct interstitial, and indirect ones, in bulk AlN and GaN crystals, as well at the AlN/GaN heterointerface, were taken into account. We showed that metal vacancies migrated across the AlN/GaN interface, overcoming a lower potential barrier than that of the nitrogen vacancy. Additionally, we demonstrated the effect of the inversion of the electric field in the presence of charged point defects VGa3− and VAl3− at the AlN/GaN heterointerface, not reported so far. Our findings contributed to the issues of structure design, quality control, and improvement of the interfacial abruptness of the AlN/GaN heterostructures.

This study presents a detailed analysis of point defect migration in $\\mathrm{In_\\textit{x}Ga}_{1-x}\\mathrm{N/GaN}$ heterostructures, focusing on two indium compositions ( x = 0.125, 0.25). Using density functional theory calculations, we identify the impact of indium content and temperature on the mobility of nitrogen, gallium, and indium atoms, revealing key differences in their migration energy barriers. Furthermore, we investigate the lateral diffusion of indium and gallium atoms, as well as complexes of substitutional metal atoms with vacancies, through a vacancy-mediated mechanism in individual metal layers of $\\mathrm{In_\\textit{x}Ga}_{1-x}\\mathrm{N/GaN}$ . Our results show that increasing indium concentration reduces migration barriers, enhancing defect mobility, particularly for indium atoms. These findings highlight the critical role of indium sublattice in promoting lattice relaxation and defect redistribution, while also elucidating the temperature-dependent dynamics of vacancy-mediated diffusion.

The spin-lattice relaxation rates (R1) of fluorine nuclei in perfluorosulfonic acid (PFSA) ionomer membranes and their precursor solid perfluorosulfonyl fluoride (PFSF) were measured by fast field-cycling (FFC) NMR relaxometry. The XRD profiles of PFSA and PFSF are similar and show a characteristic peak, indicating the alignment of main chains. While the SAXS profiles of the PFSA membranes show two peaks, those of the solid PFSF lack the ionomer peak which is characteristic of hydrophilic side chains in the PFSA ionomer membranes. The Larmor frequency dependence of R1 obeys power law and the indices are dependent on the sample and temperature. The indices of the PFSA membranes change from −1/2 to −1 along with the Larmor frequency and temperature dependence decrease, which is consistent with the generalized defect diffusion model. Estimated activation energies are in good agreement with those obtained from dynamical mechanical analysis and dielectric spectroscopy, indicating the segmental motion of the backbones as the common origin of these observations. On the other hand, the index changes to −3/4 in the case of the PFSFs, which has been predicted by the reptation model.

The superior crystalline quality of coaxial GaInN/GaN multiple-quantum shell (MQS) nanowires (NWs) was demonstrated by employing an AlGaN undershell during metal-organic chemical vapor deposition. Scanning transmission electron microscopy (STEM) results reveal that the NW structure consists of distinct GaInN/GaN regions on different positions of the NWs and the cores were dislocation-free. High-resolution atomic contrast STEM images verified the importance of AlGaN undershells in trapping the point defects diffused from n-core to MQSs ( -planes), as well as the improvement of the grown crystal quality on the apex region ( -planes). Time-integrated and time-resolved photoluminescence (PL) measurements were performed to clarify the mechanism of the emission within the coaxial GaInN/GaN MQS NWs. The improved internal quantum efficiency in the NW sample was attributed to the unique AlGaN undershell, which was able to suppress the point defects diffusion and reduce the dislocation densities on -planes. Carrier lifetimes of 2.19 ns and 8.44 ns were derived from time-resolved PL decay curves for NW samples without and with the AlGaN undershell, respectively. Hence, the use of an AlGaN undershell exhibits promising improvement of optical properties for NW-based white and micro light-emitting diodes.

Defects on crystal and/or thin film surfaces play an important role in their physical and chemical properties. Diffusion or motion of such structures results in microstructural dynamic changes. The diffusion of single atom/point defects were previously reported, due to the difficulty of observation, the motion of large-scale defects (the defect consist of multiple missing atoms) using combination of consecutive images has not been possible since today. For the first time, the diffusion of three mobile large-scale highly oriented pyrolytic graphite monolayer defect domains is reported using non-contact atomic force microscopy in ultra-high vacuum conditions. It was suspected that the diffusion of the defects was triggered by the rastering motion of the tip of atomic force microscope. It was evidenced that the diffusion of large defects is shown to be size-dependent, with smaller defects moving with higher speeds than larger defects. The diffusion results fit well with the models previously reported for the diffusion of particles for varying sizes and indicates that the diffusion of defects and particles show similar behaviours.