Nanobuckling and x-ray photoelectron spectra of carbyne-rich tetrahedral carbon films deposited by femtosecond laser ablation at cryogenic temperatures

摘要

The growth, surface morphology, and electronic binding states of diamondlike films deposited by femtosecond laser ablation on Si wafers at 77 K have been studied in order to elucidate the mechanical properties of this material. Nanoscale buckling has been observed and is found to have a morphology that exhibits a strong dependence on film thickness. Nanobuckling takes the form of quasiperiodic discrete pointlike excursions extending over widths of 50-100 nm. This morphology converts to a regular structure of grooves/ripples with a modulation period of 30-50 nm as the film thickness increases to 300-600 nm. We find that microhardness is not changed in regions where nanobuckling is present. Analysis of Raman and x-ray photoelectron spectra (XPS) demonstrate that nanobuckling can be attributed to the relaxation of internal stress and to the formation of strong C-Si covalent bonds at the C-Si interface. XPS spectra show that the C 1s peak is broadened compared to that found in spectra of films deposited using nanosecond laser ablation. This is found to be consistent with a composition that includes sp, sp~2, and sp~3-bonded carbon. The unique composition of these films suggests that these materials may find application in electromechanical devices.