Transformation of semiconducting tetrahedral carbon films to semimetal nanocomposite materials by ion implantation

Abstract

Semimetal nanostructures in semiconductor matrices of tetrahedral carbon (ta-C) films induced by ion beam implantation at high doses have been studied. The structural analysis shows that originally abundant sp 3 carbon atomic bonding of ta-C is gradually converted to a graphitic phase during the course of ion bombardment. Growing and clustering the sp 2 bonded carbon component in the ta-C films by ion implantation is indicated by Raman spectral analysis, but the examination of the films evolved on an atomic scale shows the formation of structures with the higher degree of order. The graphitic basal planes are formed preferably in the perpendicular direction to the film surface. The critical rearrangement is observed at 0.24 displacements per atom when the onset of the transformation occurs. Unlike amorphisation of crystal structure by ion bombardment, here the initially amorphous phase with short ordered sp 3 bonding is nanostructured to the higher degree of an ordered structure using proper ion energies and doses. The structural rearrangement gives rise to the change in resistivity, which can vary from original 10 8 to 10 −4 Ω cm at the highest doses used. The transformation process is associated with the change from interband to intraband absorption due to overlapping conduction and valence bands, which is the indicative of transforming a semiconducting material to a semimetallic nanocomposite material. The material evolved becomes electrically conductive while it retains considerable amount of sp 3 bonding and high hardness being above 15 GPa.