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

The influence of energetic Au+beam implantation on tetrahedral amorphous carbon (ta-C) films prepared by the filtered cathodic vacuum arc technique was studied. The ta-C films were implanted by 2 MeV Au+with dose varying from 1012-3×1014cm-2. The as-deposited and ion implanted films were characterized using atomic force microscopy, Raman spectroscopy and ellipsometry. All films have a smooth surface morphology with RMS roughness less than 0.3 nm over an area of 1 μm2. The Raman spectra of the as-deposited and ion implanted films all show a G peak at approximately 1565 cm-1and a D peak at approximately 1395 cm-1. The intensity ratio of the D to G peak, ID/IG, remains unchanged (approximately 0.50) for films implanted with an ion dose below 1013cm-2, and increases to 2.10 for the film implanted with an ion dose of 3×1014cm-2. The Tauc optical band gap decreases from 2.05 eV for the as-deposited film to 1.40 eV for the film implanted with an ion dose of 1013cm-2, and becomes very close to zero for the films implanted with an ion dose greater than 3×1013cm-2. Both Raman and ellipsometric results show that a large percentage of carbon atoms become sp2-bonded in the films implanted with large ion doses.