Work function surface

In order to bring an electron outside the solid, it has to cross a surface. If it were possible to remove the electron from the solid without going through a surface, one would have to overcome the bulk contribution to the work function (equal to the chemical potential). There is also a surface contribution to the work function, which depends on the density of atoms at the surface. Obviously, it is this contribution which makes the work function surface and site specific. 

As pointed out above the comparison between both sets of results relies upon the physical equivalence of the two measureable quantities work function (surface science) and electrode potential (electrochemistry) 111. This equivalence has been realized in electrochemistry some time ago and has been exploited to analyze measured values of the potential of zero charge 111 and of work function changes upon emersion of electrodes at fixed potential 181. In the simulation experiments the approach is quite similar in that one prepares a well-defined composition of the synthetic electrochemical adsorbate layer and then obtains the electrostatic potential drop across it by a work function measurement. 

Fig. 3 CO stretching frequencies for atop adsorbed CO on Pt(lll) in the presence of various solvents at saturation coverage taken at 100 K. Work function (surface potential) modified by dosing potassium. For calculation of in situ potentials, she = 4.6 V.5...

The liquid metal Ion source could help dramatically In the area of+negatlve secondary Ion mass spectrometry where bombarding with Cs ions has proven very beneficial (19). This is due to the large Increase In negative ion emission from a cesiated, low work function surface. Unfortunately, the sources used to produce cesium ions are of the surface ionization type (20) which has a low brightness. If the liquid metal field emission Ion source can be developed to operate reliably with liquid cesium, then small, high-current density ion beams could be formed. Currently, however, the reactive nature of the metal makes the liquid metal field emission cesium Ion source more of a research project than a routine analytical technique. 

Direct manifestation of electronic excitations caused by surface reactions through emission of exoelectrons will be restricted to interactions between electronegative molecules, such as O2, NO2, or halogens, with low work function surfaces, such as alkali metals, since the energy of the affinity-derived level to... 

Several methods have been developed to calculate the surface electronic structure self-consistently for transition metal systems. All of these involve modeling the surfaces by thin slabs (or by repeated slabs in the case of the supercell approach) and expanding the electron wavefunctions in some basis sets. In conjunction with pseudopotentials, the mixed basis or the LCAO basis are most commonly employed. With basically the surface geometry as input, these calculations yield the work function, surface states, adsorbate states, surface charge densities, densities of states, and often information on preferred sites of adsorption. Surface states are shown to be important in the interpretation of spectroscopic measurements, and chemisorption studies give valuable information concerning the nature of the surface chemical bond. 

The chemical bond of H to the surface of a metal is, of course, of electronic nature. A strong perturbation of the substrate valence band and of the H Is wave function takes place. So called H induced states are formed, comparable to the H induced band in the electronic structure of metal hydrides. Accordingly, surface electronic properties such as local density of states, work function, surface magnetization, and possibly valency are affected by the adsorption of H. 

White ID, Chen 1, Matsiev D, Auerbach DJ, Wodtke AM (2005) brationally promoted emission of electrons from low work function surfaces oxygen and Cs surface coverage dependence. J Vac Sd Technol A 23 1085-1089... 

It is desirable to build the thermionic emission diode designed by Eckstrein and Forman [30] in the mass spectrometer, since it enables a quantitative measurement of work function variation with the adsorbed O2 on the Re surface and the discovery of an even higher work function surface (see section 2.2). 

W.E. Pickett, Negative electron-affinity and low work function surface cesium on oxygenated diamond(lOO). Phys. Rev. Lett. 73(12), 1664-1667 (1994)... 

J. Huang, Z. Xu and Y. Yang, Low-Work-Function Surface Formed by Solution-Processed and Thermally Deposited Nanoseale Layers of Cesium Carbonate, Adv. Funct. Mater., 2007,17,1966-1973. 

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