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

Amorphous hydrogen-free carbon films with various sp(3)/sp(2) ratios were e xposed to a 50 kV Ga+ focused ion beam (FIB) with a dose in the range from 10(14) to 2.5 x 10(18) ion/cm(2). Atomic force microscopy (AFM), measuremen ts of electric resistivity, and Raman spectroscopy were used to study FIB-i nduced modification of surface topography and film structure. The Raman spe ctra indicate an increase of sp(2) coordination in sp(3)-rich films after i on irradiation and growth of sp(2)-bonded clusters under annealing at 550 d egrees C. Light absorption in the FIB-exposed areas increases by a factor o f up to 15 compared to the as-deposited material. For the FIB-irradiated sp (3)-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 ef fect of gallium impurity. Also, the Raman measurements have documented slow room-temperature structural relaxation in the FIB-exposed areas of one sam ple. (C) 1999 American Institute of Physics. [S0021-8979(99)04824-0].