Step-edge and kink segregation models for analysis of reported step-velocity dependences of carbon concentration in GaN

Abstract Based on Burton−Cabrera−Frank theory and the step-edge segregation model, we analyzed the reported difference in the sheet concentration of doped magnesium under naturally formed surface stripes on homo-epitaxially grown layers on a freestanding GaN substrate misoriented from a c-plane by 0.3°. By assuming the step height being equal to the peak-to-valley height of the surface stripes, we considered the growth steps on gently and sharply sloped surfaces to be supplied, respectively, from mixed dislocations and the misorientation from the c-plane. The step-velocity dependence of the magnesium concentration was reproduced with the reported magnesium diffusivity of 3×10−14 cm2s−1.

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ABOUT HEAT CAPACITY OF TITANIUM CARBIDE TiCx

Alternative Energy and Ecology (ISJAEE) ◽

10.15518/isjaee.2019.01-03.056-066 ◽

2019 ◽

pp. 56-66

Author(s):

I. Khidirov ◽

V. V. Getmanskiy ◽

A. S. Parpiev ◽

Sh. A. Makhmudov

Keyword(s):

Heat Capacity ◽

High Temperature ◽

Titanium Carbide ◽

Temperature Dependence ◽

Carbon Concentration ◽

Room Temperature ◽

Thermodynamic Characteristics ◽

Liquid Nitrogen Temperature ◽

Analysis Data ◽

Thermal Excitation

This work relates to the field of thermophysical parameters of refractory interstitial alloys. The isochoric heat capacity of cubic titanium carbide TiCx has been calculated within the Debye approximation in the carbon concentration range x = 0.70–0.97 at room temperature (300 K) and at liquid nitrogen temperature (80 K) through the Debye temperature established on the basis of neutron diffraction analysis data. It has been found out that at room temperature with decrease of carbon concentration the heat capacity significantly increases from 29.40 J/mol·K to 34.20 J/mol·K, and at T = 80 K – from 3.08 J/mol·K to 8.20 J/mol·K. The work analyzes the literature data and gives the results of the evaluation of the high-temperature dependence of the heat capacity СV of the cubic titanium carbide TiC0.97 based on the data of neutron structural analysis. It has been proposed to amend in the Neumann–Kopp formula to describe the high-temperature dependence of the titanium carbide heat capacity. After the amendment, the Neumann–Kopp formula describes the results of well-known experiments on the high-temperature dependence of the heat capacity of the titanium carbide TiCx. The proposed formula takes into account the degree of thermal excitation (a quantized number) that increases in steps with increasing temperature.The results allow us to predict the thermodynamic characteristics of titanium carbide in the temperature range of 300–3000 K and can be useful for materials scientists.

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Fabrication of Step-Edge Vertical-Channel Organic Transistors by Selective Electro-Spray Deposition

IEICE Transactions on Electronics ◽

10.1587/transele.e98.c.80 ◽

2015 ◽

Vol E98.C (2) ◽

pp. 80-85

Author(s):

Hiroshi YAMAUCHI ◽

Shigekazu KUNIYOSHI ◽

Masatoshi SAKAI ◽

Kazuhiro KUDO

Keyword(s):

Spray Deposition ◽

Vertical Channel ◽

Step Edge ◽

Organic Transistors

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Corrosion of Welded Metal Structures of Mining Equipment

Revista de Chimie ◽

10.37358/rc.18.9.6576 ◽

2018 ◽

Vol 69 (9) ◽

pp. 2563-2566

Author(s):

Dan Dobrota

Keyword(s):

Carbon Concentration ◽

Welded Joints ◽

Construction Material ◽

Working Environment ◽

Mining Equipment ◽

Metal Structures ◽

Corrosion Phenomenon ◽

Welding Regime ◽

New Material ◽

Initial Research

Mining equipment made of welded metal structures is strongly affected by the corrosion phenomenon due to the working conditions. Initial research has shown that the corrosion phenomenon is most pronounced in the area of cross-welded joints and welded T-shaped joints. In the researches, there was made a chemical analysis of the welded construction material used respectively of the new material and it was observed a reduction in carbon concentration in the material used, but also a substantial increase in the sulfur concentration compared to the new material. The pronounced corrosion of the metallic structure is influenced by the chemical composition change because the sulfur is a grafitizing and weakening element, and the decrease in carbon concentration causes a decrease in corrosion resistance. Also, the pronounced corrosion is due to the action of sulfurous acid (H2SO3) and hydrogen sulfide (H2S), elements that are present in the working environment of welded constructions. In order to achieve a reduction in the corrosion phenomenon, it is very important that the welded joints are made using the optimal parameters of the welding regime so as to obtain metallographic structure with finer granulations.

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