Mykhaylo Motylenko

Transmission electron microscopy analysis of disclination structures in plastically deformed metals

The disclination concept can be used to describe rotational substructures developing under large-strain deformation of crystalline metals. The paper presents transmission electron microscopical investigations which allow disclination configurations to be characterized. Copper crystals rolled down to more than 50% thickness reduction at room temperature were investigated and partial disclination dipoles and multipoles were found in nodes of the cell block boundaries.

Substructure development in cold rolled copper single crystals

Copper single crystals oriented for multislip conditions were cold rolled up to 90% reduction in thickness in order to investigate the substructure development. Both the development of the total dislocation density and the excess dislocation density connected to the disorientation were estimated by high resolution X-ray diffractometry and additionally the disorientation development by taking electron backscattering patterns (EBSP).

Crystallization dynamics and interface stability of strontium titanate thin films on silicon

Nonstoichiometric SrTiO3 thin films were fabricated by different thin-film deposition methods. The impact on the oxide/silcon interface stability as well as the crystallization onset temperature is investigated.

Effect of screw threading dislocations and inverse domain boundaries in GaN on the shape of reciprocal-space maps

Polar GaN layers containing domains with inverse polarities are studied by means of high-resolution X-ray diffraction and transmission electron microscopy. It is shown how the presence of inversion domain boundaries can be recognized directly from reciprocal-space maps measured by X-ray diffraction.

Capability of X-ray diffraction for the study of microstructure of metastable thin films

The capability of X-ray diffraction for the microstructure investigations of metastable systems is illustrated on supersaturated and partially decomposed thin films of titanium aluminium nitrides with high aluminium content. The anisotropy of the elastic constants and their role in these investigations is discussed.

Effect of the Ammonia Flow on the Formation of Microstructure Defects in GaN Layers Grown by High-Temperature Vapor Phase Epitaxy

High-temperature vapor phase epitaxy (HTVPE) is a physical vapor transport technology for a deposition of gallium nitride (GaN) layers. However, little is known about the influence of the deposition parameters on the microstructure of the layers. In order to fill this gap, the influence of the ammonia (NH3) flow applied during the HTVPE growth on the microstructure of the deposited GaN layers is investigated in this work. Although the HTVPE technology is intended to grow GaN layers on foreign substrates, the GaN layers under study were grown on GaN templates produced by metal organic vapor phase epitaxy in order to be able to separate the growth defects from the defects induced by the lattice misfit between the foreign substrate and the GaN layer. The microstructure of the layers is characterized by means of high-resolution x-ray diffraction (XRD), transmission electron microscopy and photoluminescence. In samples deposited at low ammonia flow, planar defects were detected, along which the nitrogen atoms are found to be substituted by impurity atoms. The interplay between these planar defects and the threading dislocations is discussed. A combination of XRD and micro-Raman spectroscopy reveals the presence of compressive residual stress in the samples.

Enhancing lithium-ion conductivity in NASICON glass-ceramics by adding yttria

We demonstrate that the ionic conductivity of Li1+xAlxGe2−x(PO4)3 glass-ceramic electrolytes can be tailored by adding Y2O3 to Li2O–Al2O3–GeO2–P2O5 melts. We found that the addition of 5 vol% Y2O3 causes noticeable changes in further glass crystallization process as the key parameters (glass crystallization temperature, viscosity and others) are affected. Small-angle neutron scattering data suggest that Y-containing glasses are suddenly crystallized upon heat treatment producing uniform Li1+xAlxGe2−x(PO4)3 ceramics. Due to the lower resistance of intergrain interfaces, such samples demonstrate a specific ionic conductivity of 0.5 mS cm−1, which is nearly 5 times higher in comparison to Y-free ceramics, prepared under similar conditions. We speculate that such an effect is caused primarily by better intergrain contact in Y-containing ceramics, along with better ionic transport in the grain bulk as evidenced by 7Li NMR.

Au-free ohmic Ti/Al/TiN contacts to UID n-GaN fabricated by sputter deposition

The fabrication and characterization of an Au-free Ti/Al/TiN (20/100/100 nm) contact stack to unintentionally doped n-GaN with TiN serving as the diffusion barrier is presented. Sputter deposition and lift-off in combination with post deposition annealing at 850 °C are used for contact formation. After annealing, contact shows ohmic behavior to n-GaN and a specific contact resistivity of 1.60 × 10−3 Ω cm2. To understand the contact formation on the microscopic scale, the contact was characterized by current–voltage measurements, linear transmission line method, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The results show the formation of Ti-N bonds at the GaN/Ti interface in the as-deposited stack. Annealing leads to diffusion of Ti, Al, Ga, and N, and the remaining metallic Ti is fully consumed by the formation of the intermetallic tetragonal Al3Ti phase. Native oxide from the GaN surface is trapped during annealing and accumulated in the Al interlayer. The ...