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

Abstract

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 V_b 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 V_b 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 V_b 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.