Imaging Disordered Systems by STM

Surface disorder and random roughness can play a determining role in the physicochemical properties of surfaces and interfaces. Roughness is a common characteristic of solid materials as found in nature and used by man. The description and properties of rough surfaces at present is far from being understood. 

For polycrystalline, amorphous, or inhomogeneous surfaces, the experimental methods available with sufficiently high lateral resolution and vertical sensitivity are limited. STM can also be used to study these disordered systems. 

The dynamic scaling theory provides a useful approach to characterize this type of disordered surface. 

The dynamic scaling theory [38] considers the development of a rough surface on a flat ID surface of size L at time t = 0 (Fig. 15). It is assumed that the growth of the rough surface takes place in a well defined direction so that the instantaneous surface height can be described by the function h x t). The surface width in the z-direction, (T,t), taken as a measure of the surface roughness, is defined by the root mean square of the height fluctuations, 

STM images (Fig. 16) of the surface evolution of a vapor deposited Au film on smooth glass with the film thickness, S, (or time) clearly reveal the development of random fluctuations as S increases due to the competition among small growing columns (20nm size). 

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