Work function, photoelectric

Fig. 7. Photoelectric work function for Au, Pt and Ag electrodes emersed from 0.1 M HC104 at different potentials. Work function was measured by means of UPS (He 1). Arrows indicate work functions of clean polycrystalline surfaces. After [20].

Polycrystalline films deposited on amorphous substrates are of lower crystallographic surface heterogeneity the higher the temperature of annealing subsequent to deposition or the higher the substrate temperature during deposition again, photoelectric work-function data serve to emphasize the point (9,10, 12,18). 

Further progress in the study of the Cu-Ni system awaited the preparation and careful characterization of alloy films of known bulk and surface composition. The essential step was taken by Sachtler and his co-workers 28, 88, 114) who prepared Cu-Ni alloy films by successive evaporation of the component metals in UHV. After evaporation the films were homogenized by heating in vacuum at 200°C. The bulk composition of the alloys was derived from X-ray diffraction, and the photoelectric work function of the films was also measured. A thermodynamic analysis, summarized by Fig. 13, indicated that alloy films sintered at 200°C should consist, at equilibrium, of two phases, viz., phase I containing 80% Cu and phase II containing 2% Cu. Evidence was presented that alloys within the... 

One of the earliest determinations of the change of photoelectric work function of a metal surface due to adsorption was made by Ives and Olphin... 

Sachtler and Dorgelo (74) measured the change in photoelectric work function when Na and Ha were adsorbed on evaporated films of Ni and Ta. These films were deposited under a vacuum of 10 mm. Hg, and the maximum surface potentials observed were 0.1 v. for the system Ni + Ha, —0.44 V. for Ta + Ha, and —0.38 v. for Ta + Na. On the other hand, the adsorption of Ha on a Ni surface prepared under less satisfactory experimental conditions decreased the work function (7S). As a result of this work, some doubt arises as to whether the positive S.P. values reported for the adsorption of Ha on various metals, particularly Pt (68), refer to clean surfaces. 

Figure 2 shows a photoelectric cell suitable for the direct determination of the photoelectric work function of a metal under the conditions of chemisorption. The electrically conducting catalyst, used as a cathode, either is inserted as a metal foil B or is evaporated from E to B. A metal layer coating the inside of the photoelectric cell serves as the anode, with a lead wire C. B can be heated electrically the leads fc are sealed into quartz and connected to an instrument (electrometer or amplifier) for... 

This means the coordination of the copper d-orbital with the loss of the orbitals of at least two acetylenic groups. Photoelectron X-ray spectroscopy confirms this structure [268]. The same results were confirmed by the external photoemission method [269]. The photoelectrical work functions for copper acetylenides with different substituents are in the range 5-5.4 eV. This means that the upper filled state is conditioned by the CuGsC structure motif. 

Table 5. Photoelectrical work function

Fig. 48. Scheme of the energetic levels of polycopperphenylacetylenide and dyes [279], cp -photoelectrical work function, AE - the energy of the absorption edge, % - electron affinity (all data are in eV)... 

Recently Franken and Ponec (44) have published photoelectric work functions of Ni-Al alloy films. Since the phase diagram contains many inter-metallic compounds, the surface composition will now be determined by that compound which yields the lower surface energy, in this case the compound having the largest amount of aluminum. Indeed after an initial steep decrease in work function over a limited concentration range, a plateau of constant work function is found. 

The observations have been made with a low-energy, electron-diffraction tube which has provision for measuring the photoelectric work function, [Pg.117]

The general features of the experimental tube (Figure 1) are similar to others used in this laboratory for low-energy electron diffraction, with added provisions for measuring the photoelectric work function, diffraction apparatus has been described (2). 

Although the LEED method reveals lattice structures, it does not readily identify the type of atom on the surface. Thus, by combining photoelectric work function and LEED measurements in a single experimental tube, more complete information on the mechanism of the various stages of interaction processes can be obtained since changes in work function occur when electronegative atoms penetrate a metal surface. 

Thermal band gaps and first exciton levels are deduced from optical measurements by using the appropriate Kq/k for each azide. Values in kJ/mole. 0 = photoelectric work function Handbook of Physics and Chemistry Chemical Rubber Co., 1972). Values in kJ/mole. 

The maximum wavelength of light that can be used to eject electrons from a clean sodium metal surface is 520 nm. (a) Calculate the photoelectric work function (in joules) for sodium, (b) If 450-nm light is used, what is the kinetic energy of the ejected electrons ... 

When atoms of barium, caesium, potassium, thorium or similar metals are deposited on a surface of metallic tungsten, stable films may be built up varying in nominal thickness frpm a fraction of a monolayer to many monolayers. The new composite surface has contact potentials and thermionic or photoelectric work functions different from those of the clean metal. The movements of atoms in these films can therefore be followed by the variation in the thermionic or photoelectric currents, i, which alter as the fraction d of the surface covered alters. It is important to find how the current i depends on 0. 

The photoelectric work function of a metal is the minimum energy needed to eject an electron by irradiating the metal with light. For calcium, this work function equals 4.34 X 10 J. What is the minimum frequency of light for the photoelectric effect in calcium ... 

---