Amorphous carbon film deposition by laser induced C60 fragmentation

Abstract

It is demonstrated that a pure carbon (fullerene) precursor, C60, is appropriate for laser-induced carbon film deposition. Amorphous carbon films were obtained on Si and SiO2 substrates upon ArF excimer laser induced fragmentation of gas phase C60. The depositions were performed in Ar and H2 ambient in a hot-wall reactor at 550°C. Strong C2 emission bands were observed by optical emission spectroscopy during the deposition process indicating that C2 dimers are used for film formation, however, thermal decomposition of C58, C56, etc. high-mass fragments may also contribute to the layer development. Raman and TEM studies showed amorphous (highly disordered, turbostratic) character of the films. Optical absorption spectroscopy indicated semiconductor feature of the layers with optical band gap of 0.7 and 0.9 eV for the films deposited in Ar and H2 ambient, respectively. For the films deposited in H2 atmosphere, changes in the Raman spectrum and an upshift of the optical band gap of the layer indicate amorphous hydrogenated film with diamond-like character, however, degree of the sp3 hybridisation was estimated to be low. The deposition rate was measured to be ∼200 Å/min at 500°C and 400 mJ/cm2 laser fluence. AFM measurements showed smooth films with low surface roughness, ∼1 nm on 1 μm scale length.