There are two views that have been applied to the electronic structure of a surface. One view is that the surface or overlayer lattices are fuzzy in real space because of electron delocalization, but sharp in momentum space. This picture is commonly applied to metals. In contrast, the other view of electronic structure is that of a surface where bonds and electrons are localized, creating a well defined image in real space. This is applicable to insulators or semiconductors. What picture of electronic structure does applies across (or near) the transition of nonmetal to metal? Furthermore, how does one relate electronic structure to metallicity? There is no single universal experimental measure of metallicity that will always distinguish a metal from an insulator. This includes the usual classification of metal and nonmetals by conductivity, both in terms of the magnitude and in terms of whether resistivity increases or decreases with temperature. For surfaces and clusters, this experimental definition cannot be applied because good electrical contacts are not possible and because the substrate masks the intrinsic properties of the surface or overlayer. Thus it is necessary that we apply alternative measures of metallicity. No single definition of metallicity will be completely successful. One case in which a clear distinction can be made between a metal and a nonmetal is for a perfectly ordered surface at absolute zero. There is also a definition based on the band structure as a function of wave vector k parallel with the surface. A metal has a dispersing band in the vicinity of the Fermi level and by this we mean that a metal has a Fermi level crossing, a Fermi surface and a Fermi wave vector. A nonmetal has a gap in the band structure at the Fermi level and, in general, has electronic bands with smaller dispersion. In this project, our aim was to study the morphology and electrical transport property of metal thin films and overlayers and to correlate them. The electron density profile (EDP) along the depth can be extracted from X-ray reflectivity (XRR) measurements. Atomic force microscopy (AFM) and scanning tunneling microscopy (STM) can be used to observe the top surface morphology. Finally the local density of states (LDOS) of such systems as a function of coverage and thickness of metal film can be determined with the help of scanning tunneling spectroscopy (STS) techniques, especially at low temperatures.
 
The growth of Ag thin film on Si(001) substrate deposited by dc sputtering technique have been studied by AFM and XRR measurements. Island formation of Ag was observed for film of thickness ~15 nm from AFM images, while the average film thickness and EDP were obtained from the reflectivity measurements. The formation of ellipsoidal shaped islands deduced from these two complementary measurements have been attributed to the dewetting property of the Ag on Si substrate [published in J. Phys. D 31, L73 (1998)].

X-ray scattering, AFM and STM studies of thin metallic films deposited by sputtering techniques are reviewed briefly. It is shown through examples that morphology of such thin films can be obtained by these reciprocal and real spaces studies. The relation between morphology and film thickness can then be used to predict the growth mechanism of these films. Although preparation of smooth films is desired for the formation of ideal multilayer system and to study the confinement effects in one dimension, usually one obtains islands structure in these films having 1-10 nm thickness. This essentially complicates I-V characteristic of the STS measurements, however, can be used to study the evolution of metallicity as a function of thickness [published in Appl. Surf. Sci. 182, 244 (2001)].
 
Systematic XRR, AFM, STM and STS measurements on Au deposited on Si substrate for different duration were carried to understand the relationship between morphology and electrical transport properties of this nanostructural system. The presence of an interfacial layer is prominent which dictates the tunneling current through this structure and exhibits a gap leading to a suppression of current. Local density of states and electron density/thickness of the interfacial layer has been extracted from the measurements to understand the evolution of metallicity of this Au-SiO₂-Si structure [published in J. Appl. Phys. 95, 1430 (2004)].