Photoelectron work function measurement

The experiments were performed in stainless steel UHV chambers which were equipped with the instrumentation necessary to perform Auger Electron Spectroscopy (AES), X-ray Photoelectron Spectroscopy (XPS), UV Photoelectron Spectroscopy (UPS), Low Energy Electron Diffraction (LEED), work function measurements (A( )), High Resolution Electron Energy Loss Spectroscopy (HREELS), and Temperature Programmed Desorption (TPD). The Au(lll) crystal was heated resist vely and cooled by direct contact of the crystal mounting block with a liquid nitrogen reservoir. The temperature of the Au(lll) crystal was monitored directly by means of a... 

Fig. 3.14 Work function measure of polycrystalline Ag using ultraviolet photoelectron spectroscopy...

Ultraviolet photoelectron spectroscopy is capable of providing chemical state and electronic structure information from materials. However, due to the complex nature of the density-of-states (DOS) in the valence band, it is more difficult to extract this information, as compared to XPS, usually requiring band-structure calculations and other spectroscopies. By observation of the onset of photoelectron emission, work function measurements may be made using UPS. Like XPS, UPS is non-destructive. However, UPS cannot typically provide quantitative information. 

In order for the primary photoelectron, which is bound to the surface atom with binding energy to be detected ia xps, the electron must have sufficient kinetic energy to overcome, ia addition to E the overall attractive potential of the spectrometer described by its work function, Thus, the measured kinetic energy of this photoelectron, Ej is given by... 

The ultraviolet and x-ray photoelectron spectroscopy (UPS and XPS) measurements are used to calculate /P of PFO at — 5.6 +0.05 eV, and the band gap at 3.1 +0.1 eV, which is also much closer to the optical band gap than to the value deduced from the electrochemistry in films [254]. Thus, the HOMO LUMO levels of PF can be reasonably well-matched by work functions of ITO/PEDOT (—5.1eV) and Ca electrode (ca. — 2.9 eV), respectively. However,... 

Y. Park, V. Choong, Y. Gao, B.R. Hsieh, and C.W. Tang, Work function of indium tin oxide transparent conductor measured by photoelectron spectroscopy, Appl. Phys. I ett., 68 2699-2701,1996. 

Whereas the work function of the electrodes is measured by photoelectron spectroscopy, the organic materials are usually characterized by cyclic voltammetry [226]. The values can be extrapolated to the gas phase by choosing an... 

The kinetic energies of these ejected electrons originating within the first 30 A of the sample surface are measured by XPS. In XPS, a sample is bombarded by a beam of x-rays with energy hv and core electrons are ejected with a kinetic energy k that overcomes the binding energy E, and the work function (cf)). These core electrons are called the x-ray photoelectrons. The energy equation is expressed as follows ... 

The XPS mechanism, which can be used for quantitative and qualitative chemical analysis of surfaces, is based on the photoelectric effect. A monochromatic soft Mg or Al anode X-ray source is used to irradiate the surface. The absorbed X-rays ionize die core shell, and in response, the atom creates a photoelectron that is transported to the surface and escapes. The ionization potential of a photoelectron that must be overcome to escape into vacuum is the binding energy (BE) plus the work function of the material. The emitted photoelectrons have a remaining kinetic energy (KE), which is measured by using an electron analyzer. Individual elements can be identified on the basis of their BE. The resulting XP spectrum is a characteristic set of peaks for a specific element, with BE as the abscissa and counts per unit time as... 

Photoelectron spectroscopy is a simple extension of the photoelectric effect involving the use of higher-energy incident photons and applied to the study not only of solid surfaces but also of samples in the gas phase. Equations (8.1) and (8.2) still apply but, for gas-phase measurements in particular, the work function is usually replaced by the ionization energy I,2 so that Equation (8.2) becomes... 

If the sample volume, from which photoelectrons are to be emitted, is put in electrical contact with the spectrometer, charge flows to establish the contact potential, which is the work function difference Sample — Aspect, and the Fermi levels, ep, of the sample and spectrometer are equalized. This is shown schematically in Fig. 2. The work function in the experiment is Aspect and observation of the photoelectron kinetic energies from an atomic species in two different samples thus provides a measure of the shift of the level in question, level i, with respect to eF if one wishes to consider the level shift with respect to some zero of the potential common to all the samples, then any shifts in eF from sample to sample with respect to that same zero must be taken into account. This point... 

The reference in this expression is implicitly the vacuum zero if the sample had no surface "dipole barrier potential fa (Fig. 3a). In order to relate a measured photoelectron energy shift, which is referred to individual Fermi levels, to such a Abu we must include an estimate of any Fermi level shift with respect to this crystal vacuum zero. An experimental value for the work function, 0, is, un-... 

---