Electron yield mode

Figure 15. Is NEXAFS spectra of N in different model compounds. The spectra are collected in electron yield mode and thus are sensitive to their surface structure (reprinted with permission from Vairavamurthy and Wang 2002. American Chemical Society).

Figure 19. Is NEXAFS spectra of metal free (left), and Ni containing porphyrines (top). Spectra shown on the top are collected in electron yield mode, and the spectra shown on the bottom are collected using fluorescence. Spectrum of 2-methylbenzimidazole is shown for a comparison (lower spectrum in bottom figure). One of the distinct features between the metalated and metal-free porphyrine is the absence of peak at 401.1 eV in the former. [Used with permission from Vairavamurthy and Wang 2002. and Mitra-Kirtley et al. 1993. American Chemical Society.]...

NEXAFS experiments were carried out at the National Synchrotron Light Source (NSLS), Brookhaven National Lab (New York), on Exxon Beamline U1A in the partial electron yield mode for various irradiation angles between normal and grazing incidence. To compensate for the severe charging of the samples. 

N K-edge X-ray absorption near edge stracture (XANES) spectra of the samples were measured at the BL-8B1 station of UVSOR-n at the Institute for Molecular Science, Okazaki, Japan. Data were recorded at room temperature in total electron yield mode, and the X-ray energy dependence of the N Auger election yield was monitored. Considering the escape depth of the Auger electrons, the spectra probe the sample fiom the surface up to a few nanometers in depth. 

Soft X-ray absorption measurements are done at low-energy synchrotron X-ray facilities such as the UV ring at NSLS or the Advanced Photon Source (APS) at Lawrence Berkeley National Laboratory (LBNL). The beam size is typically 1 mm in diameter. The electron yield data are usually obtained in the total electron yield (EY) mode, measuring the current from a channel electron multiplier (Channeltron). Sometimes a voltage bias is applied to increase surface sensitivity. This is referred to as the partial electron yield (PEY) mode. Huorescence yield (EY) data are recorded using a windowless energy dispersive Si (Li) detector. The experiments are conducted in vacuum at a pressure of 2 X 10 torr. 

NEXAFS experiments on NOM can be conducted in several modes that differ in the type of detected particle and objectives of the experiment transmission (X rays transmitted through the sample), fluorescence (fluorescent X rays due to absorption of the X-ray beam), or electron yield (photo-emitted electron) (Sparks, 2003). Alternatively, the techniques can be divided into full-field applications such as transmission X-ray microscopy (TXM) and X-ray photoemission electron microscopy (PEEM), in comparison to scanning techniques such as scanning transmission X-ray microscopy (STXM) and scanning photoemission microscopy (SPEM) that provide spatial information of elemental forms. 

In concentrated systems obtained in a thin uniform shape, the simplest way to record X-ray absorption data is the transmission mode in which the incident and transmitted photons are directly measured by means of ionisation chambers. However, in dilute systems or for surface characterisations, data are usually recorded using secondary effects resulting from the creation of the core hole during the absorption process and from its subsequent relaxation by radiative or non-radiative decays. These processes are the X-ray fluorescence emission and the total electron yield (TEY) emission, respectively. In these detection modes, the linear absorption coefficient is proportional to the ratio of the fluorescence or TEY intensity to... 

XANES spectroscopy has been used to study the composition and mechanism of antiwear tribofilm formation. The absorption XANES spectra were recorded in total electron yield (TEY) versus fluorescence yield (FY) detection to investigate the chemical nature of P, S, Ca, O and Fe on the surface and in the bulk, respectively. The application of XANES surface TEY mode which analyzes the top 5 nm layer, and the FY technique which analyzes the 50 nm layer of the bulk, taken together, give a marvelous opportunity to study nondestructively the antiwear tribofilms. Both techniques can be used under a wide variety of conditions e.g., the formation of tribofilms at different rubbing times, load, concentrations, temperatures and surface roughness (Kasrai et al., 1993 and 1996 Koningsberger and Prins, 1988 Martin et al., 2001 Yin et al., 1997a). 

K at increasing exposures (0.1L-80L) on crystalline ice films obtained by water deposition on a Pt(l 11) substrate held at 150 K. The NEXAFS measurements were performed in the total electron yield (TEY) mode using the monochromatic soft X-ray radiation of SA22 beam line of Super ACO at the LURE facility (Orsay, France). The resolution was 0.02 eV at 190 eV. The PSD NEXAFS have been measured in the total ion yield mode, using a two stages microchannel plates detector. The experimental conditions are detailed in ref 4. 

Fluorescent photon counting is an alternative to electron yield (EY) [41]. The strongest advantage of fluorescence yield (EY) is that the mean free path of photons through solids is much longer than that of electrons. Therefore, EY mode reveals x-ray absorption from deeper into the film bulk ( 100 mn) than EY modes can measure (=10 nm). A comparison of EY and FY NEXAFS spectra can reveal surface... 

Supporting the FTIR results, x-ray absorption near edge structure (XANES) spectra (29) of an unexposed and exposed nanocomposite indicated surface enhancement of silicate. Figure 10 displays the spectra as recorded in total electron yield (TEY) mode - an extreme surface sensitive mode that captures information from the top 100 nm of the material. The peak at about 1846 eV is indicative of SiOx species. The relative increase in the peak in the exposed... 

The NEXAFS spectra of carbon-based materials are dominated by tt and a resonances [37]. The measurements are made in two modes (1) total electron yield... 

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