Influence of sp3 fraction on the field emission properties of tetrahedral amorphous carbon films formed by magnetic filtered plasma stream

Electron field emission properties of tetrahedral amorphous carbon films (ta-C) with various sp3 fractions, [sp3]/([sp2]+[sp3]), prepared by magnetic filtered plasma deposition system, were investigated. The ta-C films were deposited on (100) n-Si wafer with a resistivity of 0.01–0.02 Ω cm in a substrate bias voltage Vb range from +20 V to -80 V. The relative fraction of sp3-bonded carbon in these films was qualitatively and quantitatively estimated by a fitting of the Raman and XPS spectra, respectively. Results show that ta-C films of high sp3 fraction, more than 80%, can be formed with a substrate bias voltage Vb in the range from -10 to -50 V. A remarkably low turn-on field of about 1.7 V/μm was observed for these samples. For Vb outside this range, the sp3 fraction is lower. The surface of such ta-C films was found to be smooth and uniform from the images of atomic force microscopy. The sp3 fraction of the sample is believed to be the main factor affecting field emission properties of ta-C films.