MnAs dots grown on GaN(0001)-(1x1) surface

MnAs has been grown by means of MBE on the GaN(0001)-(1x1) surface. Two options of initiating the crystal growth were applied: (a) a regular MBE procedure (manganese and arsenic were delivered simultaneously) and (b) subsequent deposition of manganese and arsenic layers. It was shown that spontaneous formation of MnAs dots with the surface density of 1$\cdot 10^{11}$ cm$^{-2}$ and $2.5\cdot 10^{11}$ cm$^{-2}$, respectively (as observed by AFM), occurred for the layer thickness higher than 5 ML. Electronic structure of the MnAs/GaN systems was studied by resonant photoemission spectroscopy. That led to determination of the Mn 3d - related contribution to the total density of states (DOS) distribution of MnAs. It has been proven that the electronic structures of the MnAs dots grown by the two procedures differ markedly. One corresponds to metallic, ferromagnetic NiAs-type MnAs, the other is similar to that reported for half-metallic zinc-blende MnAs. Both system behave superparamagnetically (as revealed by magnetization measurements), but with both the blocking temperatures and the intra-dot Curie temperatures substantially different. The intra-dot Curie temperature is about 260 K for the former system while markedly higher than room temperature for the latter one. Relations between growth process, electronic structure and other properties of the studied systems are discussed. Possible mechanisms of half-metallic MnAs formation on GaN are considered.Comment: 20+ pages, 8 figure

Topological crystalline insulator states in Pb(1-x)Sn(x)Se

Topological insulators are a novel class of quantum materials in which time-reversal symmetry, relativistic (spin-orbit) effects and an inverted band structure result in electronic metallic states on the surfaces of bulk crystals. These helical states exhibit a Dirac-like energy dispersion across the bulk bandgap, and they are topologically protected. Recent theoretical proposals have suggested the existence of topological crystalline insulators, a novel class of topological insulators in which crystalline symmetry replaces the role of time-reversal symmetry in topological protection [1,2]. In this study, we show that the narrow-gap semiconductor Pb(1-x)Sn(x)Se is a topological crystalline insulator for x=0.23. Temperature-dependent magnetotransport measurements and angle-resolved photoelectron spectroscopy demonstrate that the material undergoes a temperature-driven topological phase transition from a trivial insulator to a topological crystalline insulator. These experimental findings add a new class to the family of topological insulators. We expect these results to be the beginning of both a considerable body of additional research on topological crystalline insulators as well as detailed studies of topological phase transitions.Comment: v2: published revised manuscript (6 pages, 3 figures) and supplementary information (5 pages, 8 figures

Detection of variants in dystroglycanopathy-associated genes through the application of targeted whole-exome sequencing analysis to a large cohort of patients with unexplained limb-girdle muscle weakness

Abstract Background Dystroglycanopathies are a clinically and genetically heterogeneous group of disorders that are typically characterised by limb-girdle muscle weakness. Mutations in 18 different genes have been associated with dystroglycanopathies, the encoded proteins of which typically modulate the binding of α-dystroglycan to extracellular matrix ligands by altering its glycosylation. This results in a disruption of the structural integrity of the myocyte, ultimately leading to muscle degeneration. Methods Deep phenotypic information was gathered using the PhenoTips online software for 1001 patients with unexplained limb-girdle muscle weakness from 43 different centres across 21 European and Middle Eastern countries. Whole-exome sequencing with at least 250 ng DNA was completed using an Illumina exome capture and a 38 Mb baited target. Genes known to be associated with dystroglycanopathies were analysed for disease-causing variants. Results Suspected pathogenic variants were detected in DPM3, ISPD, POMT1 and FKTN in one patient each, in POMK in two patients, in GMPPB in three patients, in FKRP in eight patients and in POMT2 in ten patients. This indicated a frequency of 2.7% for the disease group within the cohort of 1001 patients with unexplained limb-girdle muscle weakness. The phenotypes of the 27 patients were highly variable, yet with a fundamental presentation of proximal muscle weakness and elevated serum creatine kinase. Conclusions Overall, we have identified 27 patients with suspected pathogenic variants in dystroglycanopathy-associated genes. We present evidence for the genetic and phenotypic diversity of the dystroglycanopathies as a disease group, while also highlighting the advantage of incorporating next-generation sequencing into the diagnostic pathway of rare diseases

Influence of Substrate on Crystallographic Quality of AlGaN/GaN HEMT Structures Grown by Plasma-Assisted MBE

Results of characterization of AlGaN/GaN high electron mobility transistor (HEMT) structures grown by plasma-assisted molecular beam epitaxy (PAMBE) are reported. High resolution X-ray diffraction (HRXRD) and X-ray reflectivity (XRR) were applied to show that structural properties of the AlGaN/GaN layers strongly depend on the substrate used for growth. It has been found that an additional 10 μm thick HVPE GaN layer grown on a commercial GaN/sapphire substrate significantly improves structural quality of AlGaN layer. However, the best structural parameters have been obtained for the HEMT sample grown on free-standing HVPE bulk GaN substrate

Atomic layer deposition of thin films of ZnSe - Structural and optical characterization

Thin films of sphalerite-type ZnSe were grown by atomic layer deposition (ALD) from elemental Zn and Se precursors. These films, grown on various substrates, show bright blue 'edge' emission accompanied by donor-acceptor pair emissions in the blue, green and red spectral regions. Red, green and blue emissions mixed together give a white color, with a color temperature between 2400 and 4500 K depending on a layer thickness and temperature. ZnSe grown by ALD is in consequence a promising material for the fabrication of semiconductor-based white light emitting thin film electroluminescence displays. © 2003 Elsevier B.V. All rights reserved

Origin of white color light emission in ALE-grown ZnSe

We discuss light emission properties from thin films of ZnSe grown by atomic layer epitaxy on GaAs (100). White color emission is observed in photoluminescence and cathodoluminescence, due to the observation of three RGB emission bands. We demonstrate possibility of color tuning by either variation of film thickness or, in cathodoluminescence experiments, variation of an accelerating voltage. © 2002 Elsevier Science B.V. All rights reserved

Substrates Grown from the Vapor for ZnO Homoepitaxy

The novel method of preparation of epi-ready ZnO substrates is demonstrated. The substrates were made of unique ZnO crystals grown by chemical vapor transport method using hydrogen as the transport agent. The effect of low-level doping (Mn, Co, Cu, and V) on the structural quality of the crystals was investigated. Atomic layer deposition was used to verify usability of the substrates for homoepitaxy. The thermal annealing prior to the atomic layer deposition process and effect of thermal annealing of the epitaxial layers was studied. The X-ray diffraction and atomic force microscopy methods were applied to study the structural quality of the ZnO layers. Detection of the dopants in the substrates by secondary ion mass spectroscopy made possible the measurement of the thickness of the layers. The obtained root mean square roughness for both the substrates and layers ranged between 0.2 nm and 5 nm, and was dependent on the sample crystallographic orientation and sequence of polishing and annealing procedures. The optimal recipe for the epi-ready substrate preparation was formulated

Solid Phase Epitaxy of Ferromagnetic MnAs Layer and Quantum Dots on Annealed GaMnAs

We show that post growth annealing of GaMnAs under As capping at temperatures in the range of 180-210ºC leads to significant surface modifications. Depending on GaMnAs layer thickness and composition, we obtain either a smooth continuous reacted (MnAs) surface layer or 3D islands (quantum dots). The surface modifications are due to a solid phase epitaxial process, in which Mn interstitials diffusing to the GaMnAs surface are bound with the As

Monocrystalline and Polycrystalline ZnO and ZnMnO Films Grown by Atomic Layer Epitaxy - Growth and Characterization

Recently we demonstrated growth of monocrystalline ZnO films by atomic layer epitaxy in the gas flow variant using inorganic precursors. In this study, we discuss properties of ZnO films grown with organic precursors. Successful Mn doping of the ZnO films during the growth was achieved using the Mn-thd complex. Secondary ion mass spectroscopy and X-ray investigations reveal the contents of Mn up to about 20% of the cationic component