Semiconducting Tetrahedral Carbons Transformed to Semimetal Nanocomposite Materials by Ion Implantation

The transformation of the semiconductor tetrahedral carbon (ta-C) films to semimetal nanostructures induced by ion beam implantation at high doses has been studied. The structural analysis shows that originally abundant sp3 carbon atomic bonding of ta-C is gradually converted to a graphitic phase during the course of ion bombardment. The atomic scale analysis of implanted amorphous films shows the formation of structure with the higher degree of order. The graphitic basal planes are formed preferably along the ion tracks. Studying the mechanism of the ion-beam structuring shows that the critical damage for the transformation onset is 0.24 atomic displacements per an incident ion. The displacement and subplantation of carbon atoms are tools of nanostructuring and driving forces for the conversion of short ordered sp3 bonding configuration to the higher degree of an ordered structure when proper ion energies and doses are applied. As a result the resistivity can be altered from the original resistivity of 1010 to 10-4 ohm-cm at highest doses. The modification in resistivity is consistent with the change from interband to intraband absorption due to band overlapping which suggests the transformation from semiconductor to semimetal. Interesting is that the implanted structure with remaining sp3 bonding retains its high harness which is about 20 GPa.