CORRELATION FROM RANDOMNESS - QUANTITATIVE-ANALYSIS OF ION-ETCHED GRAPHITE SURFACES USING THE SCANNING TUNNELING MICROSCOPE

The scanning tunneling microscope (STM) was used to quantitatively examine the surface morphology of highly oriented pyrolytic graphite (HOPG) surfaces bombarded with 5 keV Ar+ ions. Constant current topographs clearly showed that the morphology of the resulting nonequilibrium surfaces depended sensitively on the ion flux, the ion fluence and the sample temperature. For low and intermediate ion fluence, an increase in surface roughness with increasing ion flux was observed. For constant ion flux, the surfaces developed structures with heights proportional to the ion fluence and separations characterized by a Correlation length that diverged with increasing fluence. Increasing the sample temperature during bombardment produced smoother surfaces as a result of enhanced surface diffusion. The autocovariance function G(L) and the height correlation function [\h(q)\2] in reciprocal space were calculated directly from the STM topographs. The latter was then compared with a linear response theory for the formation of rough surfaces under nonequilibrium conditions and a scaling analysis. The fluence dependence of the surface roughening of graphite could not be explained by shot noise alone in a linear theory, whereas surface diffusion and redeposition of sputtered material satisfactorily accounted for the correlation observed in the bombardment-induced features.