Electron field emission properties of tetrahedral amorphous carbon films

Abstract

The electron field emission of tetrahedral amorphous carbon (ta-C) films deposited by filtered cathodic vacuum arc is reported. The ta-C films were found to have a threshold field ranging from 18 to 28 V μm−1, depending on the sp3 content. The nitrogenated ta-C (ta-C:N) films show a lower threshold field of 12 V μm−1 as compared to the ta-C films. The threshold field appears to be dependent on the film thickness. There is a minimum threshold field with the film thickness of around 30 nm for the ta-C:N film. Although the ta-C and ta-C:N films have relatively low threshold fields, the density of emission sites is not high for these films. The density of emission sites can be increased when the film surface is treated with H+, O+, or Ar+ ions after deposition. Moreover, the posttreated films show even lower 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 atomic force microscopy and scanning tunneling microscopy. This analysis shows the evident surface modification and more segregated cluster regions induced by the ion beam treatment. The posttreated films are analyzed using ultraviolet photospectroscopy. The photoelectrons start to emit at energies as low as about 0.6 eV. A mechanism for the electron field emission is proposed.