Rare gases on metals

The work function of a solid is also sensitive to the presence of adsorbates. In fact, in virtually all cases of adsorption the work function of the substrate either increases or decreases the change being due to a modification of the surface dipole layer. The formation of a chemisorption bond is associated with a partial electron transfer between substrate and adsorbate and the work function will change. Two extreme cases are (i) the adsorbate may only be polarized by the attractive interaction with the surface giving rise to the build up of a dipole layer, as in the physisorption of rare gases on metal surfaces and (ii) the adsorbate may be ionized by the substrate, as in the case of alkali metal adsorption on transition metal surfaces. If the adsorbate is polarized with the negative pole toward the vacuum the consequent electric fields will cause an increase in work function. Conversely, if the positive pole is toward the vacuum then the work function of the substrate will decrease. 

References including structure studies for rare-gas monolayers on clean metal siufaces were summarized in Ref 15. In particular, experimental work for solidified rare gases on metallic substrates have indicated that the monolayers form a regular two-dimensional lattice [81 and references therein]. 

J. E. Van Himbergen and R. Silbey, Density functional approach to physical adsorption of rare gases on metal surfaces. Solid State Commun. 23 623 (1977). 

Me UPD on foreign substrates is comparable to sorption phenomena and 2D phase formation occurring at solid/gas and solid/liquid interfaces at undersaturation conditions. For example, adsorption of hydrogen, oxygen, and rare gases on graphite or noble metals are typical undersaturation sorption phenomena. 

The emission methods of EEP detection are based on the ability of some metastable particles (N2(A ZJ, metastable atoms of rare gases) to knock electrons out of the surface of metals [59]. The present-day technique of measuring small currents allows one to record any small fluxes... 

The uses of inorganic metal compounds and rare gases to probe the conditions of cavitation collapse have become some of the most important methods available in fundamental ultrasonics. Quantitative determination of collapse temperatures and pressures, and qualitative determination of fundamental aspects of the nature of the cavitation field have been achieved, largely through SL spectroscopic methods. The presence of salts has a marked influence on properties on the acoustic systems, such as the extent of coalescence and bubble size, and the sonochemical activity and SL intensity. 

In the literature it has frequently been reported that when gases are adsorbed on metals, the first part is adsorbed instantaneously and later parts are adsorbed much more slowly. This slow adsorption has been ascribed to pores or capillaries or to an approximate balance between adsorption and evaporation. Only rarely has the analysis mentioned small sticking probabilities as the chief cause. The present work shows... 

The case of triangular lattice is particularly interesting since it corresponds to adsorption on graphite and on the (111) plane of several fee metal crystals [15,102,103,135]. The distance between adjacent potential minima for the graphite basal plane is equal to 2.46A and hence is too small to allow for their mutual occupation by even very small atoms of light noble gases. The same is true for adsorption on metals. Experimental studies have demonstrated that for rare gas atoms and simple molecules adsorbed on the graphite basal plane as well as on the (111) faces of fee crystals the ordered state corresponds to either the /3 X %/3 [102] or to the 2x2 phase [103,136,137] shown in Fig. 8. 

Photoionization and Electron Detachment.—Photoelectron spectroscopy is not within the scope of this volume, but some papers on photoionization which may be of some interest are listed here. Several theoretical treatments of photoionization in atoms and small molecules have appeared.213 Photoionization in the rare gases,214 atomic hydrogen,215 alkali-metal and alkaline-earth atoms,21 magnesium atoms,217 group II atoms,218 mercury atoms,219 molecular hydrogen,220 several polyatomic molecules,221 and solvated electrons 222 has been discussed. Multiphoton ionization in the rare gases,223 benzene,224 and in molecular crystals has also been discussed.225 ... 

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