Modification of hydrogen-free amorphous carbon films by focused-ion-beam milling

Abstract

Amorphous hydrogen-free carbon films with various sp3/sp2 ratios were exposed to a 50 kV Ga+ focused ion beam (FIB) with a dose in the range from 1014 to 2.5×1018 ion/cm2. Atomic force microscopy (AFM), measurements of electric resistivity, and Raman spectroscopy were used to study FIB-induced modification of surface topography and film structure. The Raman spectra indicate an increase of sp2 coordination in sp3-rich films after ion irradiation and growth of sp2-bonded clusters under annealing at 550 °C. Light absorption in the FIB-exposed areas increases by a factor of up to 15 compared to the as-deposited material. For the FIB-irradiated sp3-rich films, the AFM measurements show neither significant roughening of the surface nor further modification of surface topography under annealing and over an extended period of time. The behavior of the films resistivity as a result of FIB irradiation and annealing most probably reflects the effect of gallium impurity. Also, the Raman measurements have documented slow room-temperature structural relaxation in the FIB-exposed areas of one sample.