Interface elemental composition, chemical

In recent decades we have seen an explosion of various spectroscopic techniques for analyzing the elemental composition and chemical states of solid surfaces and films. This explosion has stemmed in part from the large number of surface- or interface-related problems seen in integrated-circuit performance, composite reliability, corrosion, nanostructured components, and so on. Instruments themselves can range from stand-alone units to attachments in national synchrotron facilities or multitechnique systems built around special fabrication sites. However, the basic principle of the technique, and therefore the basic concerns with sample preparation, stay the same. 

While the input query and search type are all that are necessary to perform a sfmcfure search in PubChem, there are numerous choices by which one may narrow the search to smaller subsets of PubChem. For example, one may search only within a previous Entrez search result, or even a previous stmcture search result, or upload a file of ClDs againsf which fhe search is fo be performed. One may filter based on a wide variety of properties, such as molecular weight, heavy atom count, presence or absence of stereochemistry, assay activity, elemental composition, depositor name or category, etc. Most of these subset operations could be accomplished through appropriate Entrez index queries followed by Boolean operations on structure search results however, the structure search tool provides a convenient one-step interface for chemical search refinement. 

Upon introduction in vivo, the interface between the delivery system and the biological tissue and/or fluid is critically important to the in vivo performance [5]. Accordingly, surface properties including surface chemical composition and surface area must be well characterized. X-ray photoelectron spectroscopy (XPS) is a widely used technique to obtain surface elemental composition, and Branauer, Emmett, and Teller (BET) measurement is used to provide information on surface area. Surface morphology is typically assessed via light, electron, and atomic force microscopy (AFM). The amorphous and crystalline nature of materials can be determined from X-ray diffraction (XRD) and density measurements. 

The chemical and electronic properties of elements at the interfaces between very thin films and bulk substrates are important in several technological areas, particularly microelectronics, sensors, catalysis, metal protection, and solar cells. To study conditions at an interface, depth profiling by ion bombardment is inadvisable, because both composition and chemical state can be altered by interaction with energetic positive ions. The normal procedure is, therefore, to start with a clean or other well-characterized substrate and deposit the thin film on to it slowly at a chosen temperature while XPS is used to monitor the composition and chemical state by recording selected characteristic spectra. The procedure continues until no further spectral changes occur, as a function of film thickness, of time elapsed since deposition, or of changes in substrate temperature. 

Other than in polymer matrix composites, the chemical reaction between elements of constituents takes place in different ways. Reaction occurs to form a new compound(s) at the interface region in MMCs, particularly those manufactured by a molten metal infiltration process. Reaction involves transfer of atoms from one or both of the constituents to the reaction site near the interface and these transfer processes are diffusion controlled. Depending on the composite constituents, the atoms of the fiber surface diffuse through the reaction site, (for example, in the boron fiber-titanium matrix system, this causes a significant volume contraction due to void formation in the center of the fiber or at the fiber-compound interface (Blackburn et al., 1966)), or the matrix atoms diffuse through the reaction product. Continued reaction to form a new compound at the interface region is generally harmful to the mechanical properties of composites. 

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