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After microscopic characterization of the size distributions of gold clusters, deposited on carbon substrates by vacuum evaporation or by soft landing, Au(4f') binding energy of the clusters has been measured as a function of the mean cluster size. Similar measurements have been carried out on Au clusters prepared from sols by chemical means and high-nuclearity cluster compounds. In general, small clusters with a mean diameter of $2 nm show significantly larger binding energies than the bulk metal value, due to the onset of nonmetallicity. Nonmetallicity manifests itself in terms of a tunneling conductance gap only in clusters of diameter ;5 1 nm containing 40 atoms or fewer. IntnductioaMetal clusters constitute an active area of research today. A vital aspect of metal clusters that has attracted much interest is that related to the transition in electronic and other properties while going from the bulk metal to small clusters.1-4 Several workers have tried to understand the nature of metal clusters by studying the variation of the core-level binding energy of the metal deposited on solid substrates with the coverage.c10 The increase in the core-level binding energy accompanying a decrease in metal coverage has been taken to reflect a decrease in the core-holescreening. Wertheim,&7 however, pointed out that the shifts of the metal core level to higher binding energies in smaller clusters is likely to be a final-state effect. Recent high-energy spectroscopic studies of clusters as well as of alloys and other systems have indicated that final-state effects cannot explain all the experimental observations and that a metal-to-nonmetal transition does manifest itself as the cluster size decreases.llJ2 One of the limitations of the photoemission studies hitherto has been that thesizes of metal clusters were not known by independent measurements. We therefore considered it important to study the variation oft& core-level binding energies of metal clusters of known sizes as determined by microscopic methods. For this purpose, we have measured the 4f binding energy of gold clusters whose size distributions were established by high-resolution electron microscopy (HREM) and scanning tunneling microscopy (STM). This study has enabled us to unequivocally establish the variation of metal core-level binding energies with cluster size, in clusters prepared by resistive evaporation under ultrahigh vacuum as well as by soft landing in argon medium. 13 We have compared the binding energies of these gold clusters with those of similar dimensions prepared by solution routes by making use of novel reducing agents and also of high-nuclearity gold cluster compounds.2.14 A property of metal clusters of considerable significance is their metallicity. We have sought to investigate whether a conductance gap manifests itself in small gold clusters by employing scanning tunneling spectroscopy (STS).lS First et a1. 16 reported the presence of a conductance gap in small Fe clusters containing -13 atoms with gap widths ranging from 0.1 to 0.5 e...

Conventional 'one by one' synthesis approach has been a major rate limiting step in the systematic exploration of increasingly complex materials for the demanding new technologies. New concepts of 'combinatorial chemistry' are presented for the substantially efficient and cost-effective parallel synthesis and optimization of variety of multicomponent compounds as well as artificially designed lattices and devices. Effectiveness of variety of application areas developed by us is discussed with typical examples and brief review of the merits, challenges, current status and the future directions.

The luminescence ofCe3 in host lattices based on Y3A15012 gamets that can be used in blue LED based solid state lighting sources is discussed. Specifically, the effect ofGa3 and Tb3 substitution for Al3 and Y3+, respectively, on the emission color and thermal quenching of these phosphors is described with the initial implications for white light devices.