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 10¹²-3×10¹⁴ cm^-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^-1 and a D peak at approximately 1395 cm^-1. The intensity ratio of the D to G peak, I_D/I_G, remains unchanged (approximately 0.50) for films implanted with an ion dose below 10¹³ cm^-2, and increases to 2.10 for the film implanted with an ion dose of 3×10¹⁴ cm^-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 10¹³ cm^-2, and becomes very close to zero for the films implanted with an ion dose greater than 3×10¹³ cm^-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.