Charge-induced effects on the structure and properties of silane and disilane derivatives

摘要

Using ab-initio electronic structure methods we have investigated the groundstate structures and properties of neutral and charged SiH$_{m}$(m=1-4) andSi$_{2}$H$_{n}$(n=1-6) clusters which are produced in the plasma enhancedchemical vapor deposition process used in the preparation of hydrogenatedamorphous silicon({\it{a}}-Si:H). Our results show that charging a neutralcluster distorts it and the distortion mainly occurs through the orientation ofSi-H bond. We attribute structural changes in the charged clusters toelectrostatic repulsion between the bonded and non-bonded electrons. We findthat in addition to the usual Si-H bond, hydrogen atoms form Si-H-H and Si-H-Sibonds in some clusters. The vibrations of Si-H, Si-Si, Si-H-Si bond stretching modes show that the frequencies areshifted significantly upon charging. The frequency shifts in the chargedclusters are consistent with their bond length variations. We discuss thefragmentation pathways of silane into binary products and the role offragmented silane radicals in the cluster formation and {\it{a}}-Si:H filmdeposition process.