Chemical Analyses of Sol/Gel Surfaces and Thin Films
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CHEMICAL ANALYSES OF SOL/GEL SURFACES AND THIN FILMS
Carlo G. Pantano, C. A. Houser and R. K. Brow Department of Materials Science and Engineering Pennsylvania State University University Park, Pennsylvania 16802 USA
ABSTRACT The application of surface analysis techniques to the characterization Secondary-ion mass of sol/gel surfaces and thin films is described. spectroscopy (SIMS), x-ray photoelectron spectroscopy (XPS) and sputter-induced photon spectroscopy (SIPS) are used to measure the composition of multicomponent silicate films, the relative water content of alumina films, the nitrogen content of ammonia treated silica films, and The determination of the depth profiles for films on black chrome. Finally, a brief chemical structure using XPS and SIMS is also discussed. introduction to temperature-programmed desorption (TPD) and its potential for studying surface chemical reactions, in situ, is presented.
INTRODUCTION Thin films can be prepared by spraying, dip-coating or spinning of an The composition and organometallic solution onto a solid substrate (1-4). chemistry of this solution is readily specified and controlled, but the composition and chemical structure of the resulting film is dependent upon If partially hydrolyzed, the solution will contain a a variety of factors. Upon deposition of this solution, the distribution of polymer species. solvent phase very rapidly evaporates and the extent of additional polymerization within the film depends upon the drying and firing Likewise, the composition of the film can be influenced by atmospheres. volatization of unreacted monomer or adsorption of atmospheric species Although these effects are of some during the drying and firing steps. concern in the case of bulk gels, they are greatly exaggerated in the case Usually, bulk gels are prepared by gelation of thin films and surfaces. under closed conditions, whereas thin films undergo gelation and solvent evaporation almost simultaneously and essentially in an open system. Moreover, the dimensions of these films impose no real kinetic limitations The point is that in the preparation upon evaporation or adsorption rates. of sol/gel thin films, only the initial solution composition is known with Thus, a meaningful characterization and understanding of any certainty. these films requires extensive chemical analysis. In this paper, the utilization of secondary ion mass spectroscopy (SIMS), x-ray photoelectron spectroscopy (XPS), sputter induced photon spectroscopy (SIPS), and temperature programmed desorption (TPD) is described with regard to the characterization of sol/gel surfaces and thin films. Although these methods have been well-developed for the characterization of solid surfaces and thin films (5,6), their application The main reason to sol/gel surfaces and thin films is less than routine. is that all of these analytical methods are susceptible to matrix effects which severely complicate both qualitative and quantitative analyses. Since gelation, drying and firing bring about a continual evolution of the
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