AVS 46th International Symposium
    Thin Films Division Monday Sessions
       Session TF+VM-MoM

Paper TF+VM-MoM10
Field Emission from Flat, Diamond-like Carbon Films Characterized by Scanning Force Microscopy

Monday, October 25, 1999, 11:20 am, Room 620

Session: Advances in Hard and Superhard Coatings I
Presenter: D.F. Ogletree, Lawrence Berkeley National Laboratory
Authors: T. Inoue, Electrotechnical Laboratory, Japan
D.F. Ogletree, Lawrence Berkeley National Laboratory
M. Salmeron, Lawrence Berkeley National Laboratory
Correspondent: Click to Email
Thin films of various diamond-like and carbon based materials on flat cathodes show significant field emission at relatively low voltages, but the exact emission mechanisms are not well understood. Non contact scanning force microscopy with a conductive tip in vacuum, used in the scanning polarization force mode (SPFM) , can detect and characterize emission sites with 100 nm lateral resolution. The SFM tip serves as an anode. It can be scanned over the surface to simultaneously measure local emission currents and local work functions. The tip-sample spacing and the tip bias can be varied to investigate mechanisms. Contact SFM images of emitting regions show local topography, reveal the presence of asperities, and characterize sample conductivity. For one type of CVD cathode material on an Si substrate, the emission sites were found to be (a) ~ 1 micron in diameter (b) not associated with asperities at the cathode-vacuum interface (c) not associated with low work function regions, and (d) semiconducting with a large band-gap. I-Z data indicate that emission takes place within the film, or at the film-substrate interface, rather that at the film-vacuum interface. Single-site emission currents were strongly modulated on a ~ 1 ms time scale, possibly due to charge trapping. Surface potential shifts were correlated with the emission current fluctuations.