Towards a microscopic understanding of the electron beam induced deposition of tungsten

We present two density functional theory investigations into the electron beam induced deposition with tungsten hexacarbonyl W(CO)6 as precursors. For the initial adsorption of the precursor on SiO2 substrates, we consider two different surface models, a fully hydroxylated and a partially hydroxylated SiO2 surface, corresponding to substrates under different experimental conditions and leading to physisorption and chemisorption, respectively. On the partially hydroxylated surface, we find a spontaneous dissociation of the precursor molecule with chemisorption of W(CO)5 and removal of one of the CO ligands. Other precursors like MeCpPtMe3 and Co2(CO)8 are discussed. We also investigate the nature of the granular deposits with varying compositions of tungsten, carbon and oxygen that are produced in the EBID process. We employ an evolutionary algorithm to predict the crystal structures starting from a series of chemical compositions known from experiment. We approximate the amorphous structures by reasonably large unit cells that can accommodate local structural environments that resemble the true amorphous structure. Our predicted structures show an insulator to metal transition close to the experimental composition at which this transition is actually observed.