Vacuum-oriented surface techniques

Even though the vacuum-oriented surface techniques yield much useful information about the chemistry of a surface, their use is not totally without problems. Hydrated surfaces, for example, are susceptible to dehydration due to the vacuum and localized sample heating induced by x-ray and electron beams. Still, successful studies have been conducted on aquated inorganic salts (3), water on metals (3), and hydrated iron oxide minerals (4). Even aqueous solutions themselves have been studied by x-ray photoelectron spectroscopy (j>). The reader should also remember that even dry samples can sometimes undergo deterioration under the proper circumstances. In most cases, however, alterations in the sample surface can be detected by monitoring the spectra as a function of time of x-ray or electron beam exposure and by a careful, visual inspection of the sample. 

In order to determine the electronic work function the metal must be ultrapure with no contamination on the surface. The biggest problem in this regard is the fact that most metals have a surface oxide layer under ambient conditions. A clean metallic surface can be formed by sputtering the metal in a vacuum chamber, and techniques are available for growing thin metal films of known crystallographic orientation. Otherwise, the metal surface may be cleaned by positive ion bombardment techniques at very low pressures. Values of the electronic work function for polycrystalline metal surfaces are summarized in table 8.2. The lowest... 

If we assume that the development of a standard state, i.e. ideal metal-vacuum interface, was in fact the key to the advancements in metallic contact analysis we should also expect that this will also be the case in the polymer, or solid organic, friction or adhesion analysis. The consequence is that polymer surface characterization under various environments becomes the most important issue at hand. The achievement of the standard surface state in polymer or solid organic system will be most difficult due to the relatively weak intermolecular bonding forces and the normal existance of a wide range of impurities within the material itself. Ambient vacuum conditions are required for most of the physics oriented surface characterization techniques, e.g. LEED, FIM, Auger electron spectroscopy and under these conditions the surface can be modified by... 

In view of the complexity of real supported catalysts, consisting of randomly oriented and irregularly shaped metal particles on high surface area porous supports, well oriented and regularly shaped metal particles grown on planar thin supports are frequently used as model catalysts [19]. This facilitates the study by surface science and TEM techniques [11, 74, 75]. In the present work, Pt particles were grown at 623 K by electron beam evaporation of Pt at a pressure of 10 mbar on vacuum-cleaved (001) NaCl... 

The evaluation and demonstration of this weldi ng technique was accomplished in three phases evaluation and optimization of ten major expl welding variables (plate material, plate thickness, explosive quantity standoff, plate surface, plate deformation, mechanical shock, metal grain orientation, weld length, and expl residual), the development of four welu joints, and an a fplicationai analysis which included photomicrographs, pressure integrity tests, vacuum effects, and fabrication of some potentially useful structures in aluminum and titanium... 

Structural properties. The structure of metallic films can be conveniently determined using x-ray diffraction with a surface reflection pinhole technique in a vacuum camera as indicated in Fig. 20. This device resulted from extensive efforts to develop a camera that could be used to determine the surface orientation of thin metal films with a minimum of manipulation of the instrument, of exposure time and of calculation required to obtain the data on orientation from the diffraction pattern. The film (6) mounted with a Lucite spacer (7) onto the turn table (8) is activated by the shaft (10). The beam (3) enters through the... 

Pure and NaP-modified MnOx-catalysts were used in our study. Due to easy visualization by AFM, the MnOx layer was placed on a Si-wafer substrate (1 cm x 1 cm plate), by a reactive deposition technique. The sample preparation was carried out in a vacuum installation equipped with an resistance evaporator. Metallic manganese (99.8%) as a source and a Si wafer with a surface orientation (111) and resistivity of 7.5 ohm/cm as support, were used. During MnOx deposition, an oxygen partial pressure of ca 10 torr, in dynamic mode, was maintained. Before used for the catalytic purpose, MnOx samples were calcined in air at 700°C for 60min. In order to prepare the NaP-modified catalyst, the MnOx samples were impregnated in a diluted Na4P20 solution (5 wt %), dried and finally calcined at 500° C, in air during 30 min. The interaction with methane was performed in a quartz reactor in a methane atmosphere at 700° 5° C. 

Figure 11.21(a) schematically shows a structure composed of a twolayered carbon film deposited on an Al surface by the pulsed-evaporation vacuum technique. The structure consists of a diamond-like film (ta-C) with tetrahedral sp bonds between carbon atoms and an S-doped highly oriented sp -hybridized carbon film. Figure 11.21(b) represents the I-V characteristics of such a structure, which is a Al/sp carbon-sp carbon/Al junction. 

---