Electron field emission properties of tetrahedral amorphous carbon films

The electron field emission of tetrahedral amorphous carbon (ta-C) films de posited by filtered cathodic vacuum arc is reported. The ta-C films were fo und to have a threshold field ranging from 18 to 28 V mu m(-1), depending o n the sp(3) content. The nitrogenated ta-C (ta-C:N) films show a lower thre shold field of 12 V mu m(-1) as compared to the ta-C films. The threshold f ield appears to be dependent on the film thickness. There is a minimum thre shold field with the film thickness of around 30 nm for the ta-C: N film. A lthough the ta-C and ta-C: N films have relatively low threshold fields, th e density of emission sites is not high for these films. The density of emi ssion sites can be increased when the film surface is treated with H+,O+, o r Ar+ ions after deposition. Moreover, the posttreated films show even lowe r threshold fields compared to the untreated films. The improvement in the emission after the ion beam treatment appears to be independent of the ions used. The surface before and after ion bombardment was analyzed using atom ic force microscopy and scanning tunneling microscopy. This analysis shows the evident surface modification and more segregated cluster regions induce d by the ion beam treatment. The posttreated films are analyzed using ultra violet photospectroscopy. The photoelectrons start to emit at energies as l ow as about 0.6 eV. A mechanism for the electron field emission is proposed . (C) 1999 American Institute of Physics. [S0021-8979(99)09009-X].