Effect of heavy ion implantation on the properties of tetrahedral amorphous carbon film

The influence of energetic Auf beam implantation on tetrahedral amorphous c arbon (ta-C) films prepared by the filtered cathodic vacuum are technique w as studied. The ta-C films were implanted by 2 MeV Au+ with dose varying fr om 10(12)-3 x 10(14) cm(-2). The as-deposited and ion implanted films were characterized using atomic force microscopy, Raman spectroscopy and ellipso metry. All films have a smooth surface morphology with RMS roughness less t han 0.3 nm over an area of 1 mum(2). The Raman spectra of the as-deposited and ion implanted films all show a G peak at approximately 1565 cm(-1) and a D peak at approximately 1395 cm(-1). The intensity ratio of the D to G pe ak, I-D/I-G, remains unchanged (similar to 0.50) for films implanted with a n ion dose below 10(13) cm(-2), and increases to 2.10 for the film implante d with an ion dose of 3 x 10(14) cm(-2). The Tauc optical band gap decrease s from 2.05 eV for the as-deposited film to 1.40 eV for the film implanted with an ion dose of 10(13) cm(-2), and becomes Very close to zero for the f ilms implanted with an ion dose greater than 3 x 10(13) cm(-2). Both Raman and ellipsometric results show that a large percentage of carbon atoms beco me sp(2)-bonded in the films implanted with large ion doses. (C) 2000 Elsev ier Science B.V. All rights reserved.