Effect of B and the Si/C ratio on high-temperature stability of Si–B–C–N materials

Abstract

Amorphous Si-B-C-N alloys were deposited by reactive magnetron sputtering, and their high-temperature stability was investigated using a combined approach of experiment and molecular-dynamics simulations. We show that both a higher Si/C ratio and the addition of boron improve the thermal stability of the materials. We find that lifetimes of bonds of the same type are significantly longer at the higher Si/C ratio. The addition of boron results in a conversion of some of the electrons in lone pairs associated with nitrogen to bonding electrons. This increases the network's average coordination number. In both cases, the higher network coordination number and resulting lower diffusion, expressed in terms of longer bond lifetimes, shift decomposition reactions in materials to higher temperatures.

Mechanical and optical properties of quaternary Si–B–C–N films prepared by reactive magnetron sputtering

“…2a). For the 25% N 2 + 75% Ar gas mixture, when the C content is higher (9 at.%), we obtained higher values of n and k. At V b = −100 V, higher incorporation of carbon also resulted in systematically higher values of both n and k. These changes can be correlated with the previously shown transition of the sp 3 -rich structure into a sp 2 -rich one with increasing C/Si ratio [14,35] -see also the chemical structure in Figs. 3 and 4.…”

“…Collectively, these data confirm the prediction of ab-initio calculations [35] that Si in such structures mainly forms single bonds, contrary to a high number of C-containing double and triple bonds. The consequently higher coordination number (lower sp 2 /sp 3 ratio) of Si-based compositions compared to Cbased systems has an important effect on the material properties such as hardness [17], thermal stability [14] or electrical conductivity [26], as well as on the tribological and optical properties discussed below. Fig.…”

“…6b is consequently irregular and rough. The difference described is mainly due to lubrication properties of the carbon-rich compositions at which the coordination number of C atoms is lower in comparison with Si atoms due to a high number of C-containing multiple bonds [14,35], and consequently relatively weakly bonded carbon-rich planes. On the contrary, silicon in the films is covalently bonded, and it does not form any weak-cohesion planes.…”

“…Recently, it has been reported that addition of a proper amount of boron into the Si-C-N system decreases the activity of carbon due to its integration in B-C-N zones, giving rise to a dramatic increase of thermal stability in comparison with Si-C-N [13,14]. Si-B-C-N has been shown to possess very high thermal stability and oxidation resistance [13,[15][16][17][18][19][20], high creep resistance at elevated temperatures [19], low internal stress [21], low thermal expansion coefficient [17,20], low thermal conductivity [20], homogeneity leading to a smooth surface [16,19,22], promising electronic properties [23] and good adhesion to various substrates (Si, Si 3 N 4 , glass or steel).…”

Magnetron sputtered Si–B–C–N films with high oxidation resistance and thermal stability in air at temperatures above 1500 °C

“…To investigate the effect of boron content in the films on their oxidation resistance, the obtained results were compared to those for the Si-C-N films prepared under the same deposition conditions. 11 The ab initio simulations showed that both a higher Si/C concentration ratio in Si-͑B͒-C-N materials and the addition of boron into Si-C-N materials prevent their decomposition at elevated temperatures, resulting in formation of N 2 molecules which diffuse out of the material. As expected, 3,5 an incorporation of boron into the films resulted in their substantially higher thermal stability in air.…”