Amorphous germanium carbides by radiolysis-CVD of germane/ethyne systems: preparation and reaction mechanisms

Amorphous germanium carbides have been prepared by X-ray-activated chemical vapor deposition from germane/ethyne systems. Different mixtures containing the two reagents in variable molar ratios have been investigated with the aim of determining the factors which lead to the highest yields of solid products and of obtaining information on the main ionic and radical reaction paths giving the amorphous material. To this purpose, samples were irradiated consecutively four times in 0.5-h steps. Both qualitative and quantitative GC/MS analyses of the volatile products as well as the determination of the solid composition by elemental analysis were performed after each irradiation. Moreover, the ion/molecule reactions have been studied by ion trap mass spectrometry, determining the ionic reaction mechanisms and the rate constants of the most significant processes. The results indicate that two main and opposite factors affect the formation of the amorphous product: (a) both radical and ionic paths are favored by the presence of ethyne in excess with respect to germane; (b) the increase of content of ethyne in the irradiated mixtures lowers the total number of activated species. Therefore, the best yield of amorphous germanium carbides is obtained when germane and ethyne have a molar ratio between 2/1 and 1/1.