Phosphorus carbides: theory and experiment

Abstract

The recent finding that radio frequency plasma activation of CH₄/PH₃ gas mixtures can yield films with P ∶ C ratios ≤ 3 has served to trigger further research into new ‘phosphorus carbide’ materials. Theoretical and experimental results relating to periodic and amorphous materials, respectively, are presented here: (i) The electronic structure and stability of different crystalline phosphorus carbide P_xC_y phases have been studied using first-principles density-functional theory. Calculations have been carried out for P₄C_3+8n (n = 0–4), PC, and PC₃ and the most likely periodic structures examined in detail. Particular attention is paid to the composition PC₃, for which there are several possibilities of similar energy. (ii) Recent experimental efforts have involved use of pulsed laser ablation methods to produce hydrogen-free phosphorus carbide thin films. Mechanically hard, electrically conducting diamond like carbon films containing 0–∼26 at.% P have been deposited on both Si and quartz substrates by 193 nm PLA of graphite/phosphorus targets (containing varying percentages of phosphorus), at a range of substrate temperatures (T_sub = 298–700 K), in vacuum, and analysed via laser Raman and X-ray photoelectron spectroscopy.