Interfaces control, atomic levels

Neto, A.O. et al., International Workshop on Ceramic/Metal Interfaces Control at the Atomic Level, Oviedo, Spain, 2002. 

With more reactive polymer surfaces such as with carboxylic acid group in PET, A1 deposited atoms can react with the polymer surface and produce thick chemical interface whatever their deposit energy. By contrast no chemical interaction is observed between deposited Au and silicone substrate for either sputtering or evaporation. These observations open a quite exciting investigation field where the chemical properties of the interface at an atomic level should be studied by controling the important parameters of the metallization such as deposition energy, reactivity of the substrate, reactivity of the metal atoms... and correlated with macroscopic properties such adhesion tests. 

MBE has been very successfiil for preparing heterosystems with highly defined interfaces. The reproducible compositional control at atomic level makes MBE the method of choice for studies of artificial semiconductor heterostructures and device applications. MBE moved the first steps and was developing over the time in the semiconductor electronics [19,20]. Many industrial MBE systems have been developed because of the extremely good electronic properties of the MBE-grown materials. Today, MBE is used for large-scale production in solid-state electronics. 

Palladium and platinum are also used as carrier lifetime controllers in Si. Pd creates an electron trap at Ec - 0.22 eV and a hole trap at Ev + 0.32 eV in Si (Chen and Milnes, 1980). Pt induces a single electron trap at Ec + 0.28 eV (Chen and Milnes, 1980). All of these levels are passivated by atomic hydrogen (Pearton and Haller, 1983) suggesting that hydrogen might be profitably used during silicide formation to passivate electrically active levels near the silicon-silicide interface. 

Inspired by these Surface Science studies at the gas-solid interface, the field of electrochemical Surface Science ( Surface Electrochemistry ) has developed similar conceptual and experimental approaches to characterize electrochemical surface processes on the molecular level. Single-crystal electrode surfaces inside liquid electrolytes provide electrochemical interfaces of well-controlled structure and composition [2-9]. In addition, novel in situ surface characterization techniques, such as optical spectroscopies, X-ray scattering, and local probe imaging techniques, have become available and helped to understand electrochemical interfaces at the atomic or molecular level [10-18]. Today, Surface electrochemistry represents an important field of research that has recognized the study of chemical bonding at electrochemical interfaces as the basis for an understanding of structure-reactivity relationships and mechanistic reaction pathways. 

Our approach to this problem involves a detailed mechanistic study of model systems, in order to identify the (electro)chemical parameters and the physicochemical processes of importance. This approach takes advantage of one of the major developments in electrochemical science over the last two decades, namely the simultaneous application of /ton-electrochemical techniques to study interfaces maintained under electrochemical control [3-5]. In general terms, spectroscopic methods have provided insight into the detailed structure at a variety of levels, from atomic to morphological, of surface-bound films. Other in situ methods, such as ellipsometry [6], neutron reflectivity [7] and the electrochemical quartz crystal microbalance (EQCM) [8-10], have provided insight into the overall penetration of mobile species (ions, solvent and other small molecules) into polymer films, along with spatial distributions of these mobile species and of the polymer itself. Of these techniques, the one upon which we rely directly here is the EQCM, whose operation and capability we now briefly review. 

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