Scanning probe microscopy of laser-graphitized diamond-like carbon films

Abstract

A complex technique of scanning probe microscopy/spectroscopy (SPM/SPS) based on the microscopy of lateral forces and registration of a local electrical conductivity in combination with measurements of the microrelief has been developed for studies of laser-graphitized carbon microstructures. The method includes multiple direct and reverse probe scanning with the subsequent correction of the map position, their pixel-by-pixel subtraction and averaging, and a statistical processing of resulting data arrays concerning the distribution of lateral forces (friction forces). In addition, based on the measurements of currentvoltage (I–V) characteristics, a distribution of the electrical conductivity is built in the probe-sample circuit. Carbon structures based on hydrogenated diamond-like films of a-C:H type, which were deposited onto Si substrates, are used as the objects for studies. A local graphitization of the surface has been carried out by the irradiation of the films with an excimer KrF laser according to a preset microscopic pattern. Based on the resulting data, it is found that the reaction of the lateral forces (friction forces) in the laser-graphitized region is reversed to the temperature variations: when the temperature increases (from room to ∼120°C), the distribution of the friction forces shifts towards higher values and returns practically to the initial values when the temperature decreases to the initial level, which proves the influence of a water adsorbate on the friction properties of laser-graphitized regions on the film surface. It is also found that the laser-graphitized region is structurally inhomogeneous, which is proven by a decrease in the electrical conductivity from the center to the periphery.