Pulsed-laser deposited amorphous diamond and related materials: synthesis, characterization, and field emission properties

Amorphous carbon films with variable sp³ content were produced by ArF (193nm) pulsed laser deposition. An in-situ ion probe was used to measure kinetic energy of C⁺ ions. In contrast to measurements made as a function of laser fluence, ion probe measurements of kinetic energy are a convenient as well as more accurate and fundamental method for monitoring deposition conditions, with the advantage of being readily transferable for inter-laboratory comparisons. Electron energy loss spectroscopy (EELS) and spectroscopic ellipsometry measurements reveal that tetrahedral amorphous carbon (ta-C) films with the most diamond-like properties are obtained at the C ion kinetic energy of approx. 90 eV. Film properties are uniform within a 12-15° angle from the plume centerline. Tapping-mode atomic force microscope measurements show that films deposited at near-optimum kinetic energy are extremely smooth, with rms roughness of only approx. 1 angstrom over distances of several hundred nm. Field emission (FE) measurements show that ta-C does not appear to be a good electron emitter. After conditioning of ta-C films deposited on n-type Si a rather high turn-on voltage of approx. 50 V/μm was required to draw current of approx. 1 nA to the probe. The emission was unstable and typically ceased after a few minutes of operation. The FE tests of ta-C and other materials strongly suggest that surface morphology plays a dominant role in the FE process, in agreement with conventional Fowler-Nordheim theory.