Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Hydrogen free Diamond like carbon films (DLC) with high sp3 content, fabricated by mass filtered vacuum arc deposition and modified by Ga+ FIB irradiation were investigated.

For electrical characterization at room temperature van-der-Pauw structures were written by direct Ga+ FIB lithography. The sheet resistance RS decreases with increasing ion fluence due to the increase of the sp2 content in the irradiated regions, where a minimum of RS = 290 at 1.6 x 1017 cm² was achieved. Hall measurements were used to study the charge carrier mobility. Therefore 4- and 6-terminal device structures were fabricated by combining FIB and optical lithography on DLC layers. The layers with a thickness in the range between 20 and 110 nm had a sp3 content above 65% and are deposited on a Si substrate. The FIB made structures were partly covered by 400x400 µm² Au contact pads, produced by lift off technique. Hall measurement results are interpreted as a function of the Ga+ fluence, the structure size and the DLC layer thickness. For a second set of samples a SiO2 interface layer between DLC and Si substrate was used to avoid leakage current through the bulk Si. The results for the two sample types are compared and the influence to the leakage current will be discussed. Additionally, conducting graphitic nanowires were investigated (length 10 µm, width 200 nm to 5 µm) delivering a resistance of 130 k for 5 µm width and 300 M for 300 nm width, respectively.

Ga+ irradiation under higher temperatures shows dot formation due to Ga segregation that was observed above 400°C at fluences higher than 1 x 1016 cm². The Ga-dots were studied by SEM/EDX and AFM. Increasing Ga+ fluence leads to an increase of the dot areal density. Diameter and height of the dots are growing with temperature.

Ion beam induced graphitization of DLC films by FIB in the nanoscale offers prospective applications of conductive nanostructures in an insulating matrix.