UPS, ultra violet photoelectron spectroscopy

The UPS technique (ultra violet photoelectron spectroscopy), by measuring the cutoff energy of secondary electrons.56,57... 

Significant observations regarding the origin of NEMCA have been also made using Ultra-violet Photoelectron Spectroscopy (UPS) with Pt and Ag electrodes deposited on YSZ. In this case the work function of the electrode can be determined from the cutoff energy of secondary electrons (Fig. 5.43).24,68 As shown in Fig. 5.8b the change in the work function of the gas-exposed Ag surface is very close to the imposed electrode potential change AUwr. 

ESCA UPS SIMS STM IR UV electron spectroscopy for chemical analysis ultra-violet photoelectron spectroscopy secondary ion mass spectroscopy scanning tunneling microscopy infra-red ultra-violet... 

Ultra violet photoelectron spectroscopy N(ls) peaks are found at — 12 and — 8 eV [462]. At 85 K X-ray photoelectron spectroscopy N(Is) peaks are found at 405.9 and 401.2 eV [462, 463]. High resolution electron energy loss spectroscopy shows a N-N stretch in yN2 at 2100 cm [231]. For N2 the work function decreases linearly with the coverage up to saturation [22]. 

In the case of surface sites incorporating atoms, the valence states and their eventual variation in the course of the reaction can be studied by spectroscopic methods such as electron paramagnetic resonance (EP.R), XPS, ultra-violet photoelectron (UPS), IR, and near-edge X-ray (XANES) spectroscopies (Near-edge X-ray spectroscopy is abbreviated in some parts of the world, particularly in USA, as NEXASS). 

Ultra-violet photoemission spectroscopy (UPS) probes the density of states, and ion neutralization spectroscopy (INS) and surface Penning ionization (SPI) provide similar information with probes of ions and metastable atoms, respectively. Angle-resolved UPS can determine the valence band structure. X-ray Photoelectron Spectroscopy (XPS) provides information on chemical shifts of the atomic core levels, and this can also help in understanding chemical bonding at the surface. 

Experimental data can be obtained by ultra-violet absorption spectroscopy, electron energy loss spectroscopy and photoelectron spectroscopy. UV absorption and EELs have been described briefly in Chapter 3. The former provides information only about the band-gap, while EELs gives more general information about the conduction bands. Both X-rays and UV photons can be used to generate photoelectrons these two methods are given the acronyms XPS and UPS. The energy spectrum of the emitted electrons provides information about the density of electron states in the valence bands. In principle the size of the band gap can be obtained, but care must be taken as the absolute energy... 

UPS Ultraviolet photoelectron spectroscopy Light (ultra- violet) Photoelectron... 

The electron affinity can also be deduced from the measurement of the spectrum of the photoelectron emission with monochromatic UV light. This technique is ultra-violet (UV) photoelectron emission spectroscopy (or UV photoemission spectroscopy or UPS). The UPS technique involves directing monochromatic UV light to the sample to excite electrons from the valence band into the conduction band of the semiconductor. Since the process occurs near the surface, electrons excited above the vacuum level can be emitted into vacuum. The energy analysis of the photoemitted electrons is the photoemission spectrum. The process is often described in terms of a three step model [8], The first step is the photoexcitation of the valence band electrons into the conduction band, the second step is the transmission to the surface and the third step is the electron emission at the surface. The technique of UPS is probably most often employed to examine the electronic states near the valence band minimum. 

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