Paper VT-TuP5
A Novel, UHV Analysis System for Detecting Electron Stimulated Reaction Products Generated during Field Emission Studies

Tuesday, October 21, 2008, 6:30 pm, Room Hall D

Carbon nanosheets (CNS) are a promising carbon allotrope for high current field emission cathodes and are grown by plasma-enhanced chemical vapor deposition (PE-CVD) from a C₂H₂/H₂ gas blend at substrate temperatures of ~ 600 °C. The resulting film consists of sp², vertically oriented, honeycomb carbon arrays terminating in a single graphene sheet that serve as field emission cathodes. A novel ultrahigh vacuum (UHV) system has been assembled for the study of gas products generated by etching of the CNS during field emission testing. A residual gas analyzer (RGA) located in direct line-of-sight of the field emission gap (254 µm) of the Cu diode geometry is used for measurement of reaction products generated during field emission tests. Electron bombardment of the Cu anode (up to 2 mA/mm²) generates atomic hydrogen (1-5 eV) by electron stimulated desorption (ESD) which, in turn, reactively etches the CNS cathode and produces predominantly CH₄ as a reaction product. The Cu anode assembly is actively water-cooled by an external chiller to 0 °C to minimize thermal effects. The typical operating pressure is <2x10^-10 Torr. Mass spectral and I-V data are collected simultaneously by an integrated LabView program. Carbon monoxide and carbon dioxide were also observed during field emission and are also correlated with the emission current. Scanning electron microscopy of the CNS topography and cross section was used to confirm the etching rate (~2 nm/hr). These results are consistent with the density functional predictions reported by Kanai et al. of CH₄ generated by atomic hydrogen incident on graphene.¹

¹ C. Kanai, K. Watanabe, and Takakuwa, Phys. Rev B 63, 235311 (2001).