Unit Cell Distortion and Surface Morphology Diversification in SnTe/CdTe(001) Topological Crystalline Insulator Heterostructure: Influence of Defects’ Azimuthal Distribution

Challenges and opportunities arising upon molecular-beam-epitaxial growth of topological crystalline insulator heterostructures composed of a rock-salt SnTe(001) layer of varying thickness (from 80 to 1000 nm) and a zinc-blende 4-μm-thick...

First principles calculation of electronic properties and effective mass of zinc-blende GaN

Based on the first principle pseudopotential plane wave method, the electronic structure of zinc-blende semiconductor GaN is calculated. Using the relativistic treatment of valence states, the spin orbit splitting energy of valence band top near the center of Brillouin region is calculated. Based on the effective mass approximation theory, the effective mass of electrons near the bottom of the conduction band and the effective mass of light and heavy holes near the Γ point along the directions of [100], [110] and [111] are calculated. These parameters are valuable and important parameters of optoelectronic materials.

First-principles calculations of elastic and optical properties of Aluminum Nitride (AlN) in cubic and hexagonal phase

Investigation of elastic and optical properties of AlN in rock salt, zinc blende, and wurtzite phase is done under the framework of Density Functional Theory (DFT) with modified Becke Johnson Generalised Gradient Approximation (mBJ-GGA) as exchange-correlation functional. Elastic properties conclude the bonding nature of the AlN in the rock salt phase is covalent and stiffest, while the bonding nature in the zinc blende and wurtzite phase is found to be ionic and less stiff. The ratio of bulk modulus to shear modulus indicates AlN is brittle in all three phases. The calculated Debye temperature in all three phases is in good agreement with the available theoretical and experimental works. The optical properties calculation shows the AlN is transparent in the low energy range and it has the metallic behavior in the energy range 7.5eV to 10 eV. At the same time, the compound loses its transparency at the high energy range. Our calculated value of the refractive index of AlN in the rock salt, zinc blende, and wurtzite phases is in good agreement with the available experimental and theoretical works.

CURT1A and CURT1C mediate distinct stages of plastid conversion in Arabidopsis

The crystalline structure of prolamellar bodies (PLBs) and light-induced etioplasts-to-chloroplasts transformation have been investigated with electron microscopy methods. However, these studies suffer from chemical fixation artifacts and limited volumes of tomographic reconstruction. We have examined Arabidopsis thaliana cotyledon samples preserved by high-pressure freezing with scanning transmission electron tomography to visualize larger volumes in etioplasts and their conversion into chloroplasts. PLB tubules were arranged in a zinc blende-type lattice like carbon atoms in diamonds. Within 2 hours after illumination, the lattice collapsed from the PLB exterior and the disorganized tubules merged to form fenestrated sheets that eventually matured into lamellar thylakoids. These planar thylakoids emerging from PLBs overlapped or folded into grana stacks in PLBs’ vicinity. Since the nascent lamellae had curved membrane at their tips, we examined the localization of CURT1 proteins. CURT1A transcript was most abundant in de-etiolating cotyledon samples, and CURT1A concentrated at the peripheral PLB. In curt1a mutant etioplasts, thylakoid sheets were swollen and failed to develop stacks. In curt1c mutant, however, PLBs had cracks in their lattices, indicating that CURT1C contributes to cubic crystal growth under darkness. Our data provide evidence that CURT1A and CURT1C play distinct roles in the etioplast and chloroplast biogenesis.

Probing electric properties of GaP nanowires with Kelvin probe force microscopy

Surface electronic properties of GaP nanowires were investigated using scanning probe force microscopy. I-V curves of individual free-standing NWs with different doping types were obtained. Surface Fermi level positions in the nanowires of different crystal phases and doping types were extracted using phase-modulated Kelvin probe force microscopy. The results indicate on weak Fermi level pinning in GaP nanowires. The difference between wurtzite and zinc blende GaP work function is observed.

The Quantum Calculation for Valence Band Structure of Strained Zinc-blende GaN Using Six-Band Based k·p Method

The variations of valence band energy with stress effects in zinc-blende GaN are proposed in this paper. The calculations are based on a six-band strain dependent k·p Hamiltonian, and can be self-consistently solved by Schrödinger-Poisson equation. Accurate physical pictures are given for the quantized valence subband structure under biaxial and uniaxial stress in (001) surface along the [110] direction accounting the quantum confinement effect. The warping of the energy profile results in carrier distribution change. This research will be beneficial for improving the hole mobility and the selective of optimum stress for group-III nitride semiconductor based devices.

Work function of polytypic gallium phosphide nanowires

In this work we investigate the work function of gallium phosphide nanowires by the means of frequency-modulated Kelvin probe force microscopy. Polytypic wurtzite/zinc blende nanowires were synthesized via self-catalytic molecular beam epitaxy. Mixed crystal phase was achieved by controlling the catalytic droplet contact angle and confirmed via transmission electron microscopy and Raman spectroscopy. Kelvin probe study showed a contrast between the work function of (110) zinc blende and (1120) wurtzite gallium phosphide: ϕZB = 4.28 eV and ϕWZ = 4.2 eV. Also, it was shown that sub-monolayer arsenic shell increases the work function up to 4.75 eV. Thus, two mechanisms for work function adjustment in the range 4.2-4.75 eV are shown. The results are important for optimization of Schottky barriers in nanowire-based devices.

Bi Incorporation and Segregation in the MBE-Grown GaAs-(Ga,Al)As-Ga(As,Bi) Core-Shell Nanowires

Incorporation of Bi into GaAs-(Ga,Al)As-Ga(As,Bi) core-shell nanowires grown by molecular beam epitaxy is studied with transmission electron microscopy. Nanowires are grown on GaAs(100) substrates with Au-droplet assisted mode. Bi-doped shells are grown at low temperature (300 °C) with a close to stoichiometric Ga/As flux ratio. At low Bi fluxes, the Ga(As,Bi) shells are smooth, with Bi completely incorporated into the shells. Higher Bi fluxes (Bi/As flux ratio ~ 4%) led to partial segregation of Bi as droplets on the nanowires sidewalls, preferentially located at the nanowire segments with wurtzite structure. We demonstrate that such Bi droplets on the sidewalls act as catalysts for the growth of branches perpendicular to the GaAs trunks. Due to the tunability between zinc-blende and wurtzite polytypes by changing the nanowire growth conditions, this effect enables fabrication of branched nanowire architectures with branches generated from selected (wurtzite) nanowire segments.