E. P. Trifonova

Heat Capacity of 4H‐SiC Determined by Differential Scanning Calorimetry

The thermochemical properties of monocrystalline 4H-SiC was studied. Differential scanning calorimetry was used to measure the heat capacity. The powders used were nitrogen doped. The powder is synthesized from pure Si and C. The heat capacity measurements were performed using a DSC-4 Perkin Elmer device. The data obtained were analyzed statistically using the computer program. The experimental data fitted the curves. The measured data and the extrapolated data for monocrystalline 4H-SiC are lower than those of monocrystalline 6H-SiC.

Correlation between the chemical bonding and the physical properties of the CNx films obtained by pulsed laser deposition from C targets in low-pressure N2

Carbon–nitride thin films were deposited by XeCl* (λ=308 nm, τFWHM≅30 ns) multipulse excimer laser irradiation of graphite targets in low-pressure (1–100 Pa) nitrogen atmosphere. We investigated the chemical bonding formation between the C and N atoms, and its influence upon the optical and mechanical properties of the obtained structures. We found that these properties strongly depend on the deposition parameters. These in turn determine the nitrogen content and the sp3/sp2/sp carbon atoms hybridization ratio of the synthesized material. According to our results, the increase of the nitrogen pressure or laser fluence in an attempt to obtain CNx thin films with higher N/C ratio does not lead to the formation of the theoretically predicted low-compressibility, high density, extremely hard β-C3N4 structure with the C atoms in the sp3 hybridization state.

About the possible diminution of the sp3 C presence along with the increase of the nitrogen enclosure in the CNx thin films produced by reactive pulsed laser deposition

We report herewith new experimental data concerning the synthesis of carbon-nitride thin films by reactive pulsed laser deposition (λ = 248nm, τFWHM ≤ 30 ns) from a graphite target in low pressure nitrogen (0.2, 1 and 50 Pa) at a level of the incident laser fluence of 22 J/cm2. The obtained structures were studied by Raman spectrometry and microhardness determinations. We have observed that an increase of the N2 pressure leads to an increase in the N2 content in the deposited films but causes the reduction ofthe amount of the sp3 bounded C and the decrease of the microhardness of the obtained structures.

Microhardness of 6H-SiC Epitaxial Layers Grown by Sublimation

Knoop microhardness of 6H-SiC layers grown by sublimation epitaxy was investigated. The microhardness-load curves for all of the samples were measured and then used to extract the load-independent microhardness values. The relationships of these values to the growth time and growth rate were studied. The microhardness-depth profiles indicated that the layer/substrate interface region had a microhardness value that differed significantly from that of both the epi-layer and the substrate.

Microhardness characterization of structures obtained by iron–silicon solid-state reaction

Microhardness measurements of structures, obtained by a solid-state reaction of iron with silicon are undertaken. The experimental results support the finding that the indentation size effect (ISE) appears in the microhardness-depth profile whenever the indentor crosses an interface. When modelling the experimental microhardness-depth profiles of the multilayered structures, an analytical expression for the coefficient giving the contributions of the film and the substrate hardnesses to the composite one is offered. A value of 9.60 GPa is obtained for the microhardness of β-FeSi2 thin layer. On the base of the microhardness-depth profiles measurement conclusions about the solid-state reaction process are drawn.

Structural properties of 6H-SiC epilayers grown by two different techniques

In the present work we investigated the structural properties of 6H-SiC homoepitaxial layers utilizing microhardness and X-ray characterization techniques. The growth was performed by chemical vapour deposition (CVD) and liquid phase epitaxy (LPE) under various growth conditions. The depth Knoop hardness profiles represent decreasing curves due to the indentation size effect. With load increasing the curves saturate reaching microhardness values comparable with the known Vickers ones. At about 0.4 μm beneath the layer surfaces the curves show small plateaus which may be attributed to structural inhomogeneity. This is suggested by X-ray diffraction spectra taken from the same samples, which contain additional peaks besides the typical ones for 6H-SiC.