TOF-SARS

TOF-SARS (time-of-flight scattering and recoiling spectrometry) no 13 1.2... 

A) TIME OF FLIGHT SCATTERING AND RECOILING SPECTROMETRY (TOF-SARS)—SHADOW CONE BASED EXPERIMENT... 

In TOF-SARS [9], a low-keV, monoenergetic, mass-selected, pulsed noble gas ion beam is focused onto a sample surface. The velocity distributions of scattered and recoiled particles are measured by standard TOF methods. A chaimel electron multiplier is used to detect fast (>800 eV) neutrals and ions. This type of detector has a small acceptance solid angle. A fixed angle is used between the pulsed ion beam and detector directions with respect to the sample as shown in figure Bl.23.4. The sample has to be rotated to measure ion scattering... 

Figure Bl.23.4. Schematic diagram of TOE scattermg and recoiling spectrometry (TOF-SARS) illustrating the plane of scattering fonned by the ion beam, sample and detector. TOE spectra (a) are collected with fixed...

The most connnon detectors used for TOF-SARS are continuous dynode channel electron multipliers which... 

A systematic comparison of two sets of data requires a numerical evaluation of their likeliness. TOF-SARS and SARIS produce one- and two-dhnensional data plots, respectively. Comparison of sunulated and experimental data is accomplished by calculating a one- or two-dimensional reliability (R) factor [33], respectively, based on the R-factors developed for FEED [34]. The R-factor between tire experimental and simulated data is minimized by means of a multiparameter simplex method [33]. 

TOF-SARS and SARIS are capable of detecting all elements by either scattering, recoiling or both teclmiques. TOF peak identification is straightforward by converting equation (Bl.23.lt and equation (B 1.23.81 to the flight times of the scattered and recoiled particles as... 

The major role of TOF-SARS and SARIS is as surface structure analysis teclmiques which are capable of probing the positions of all elements with an accuracy of <0.1 A. They are sensitive to short-range order, i.e. individual interatomic spacings that are <10 A. They provide a direct measure of the interatomic distances in the first and subsurface layers and a measure of surface periodicity in real space. One of its most important applications is the direct determination of hydrogen adsorption sites by recoiling spectrometry [12, 4T ]. Most other surface structure teclmiques do not detect hydrogen, with the possible exception of He atom scattering and vibrational spectroscopy. 

Grizzi O, Shi M, Bu H, and Rabalais J W 1990 Time-of-flight scattering and recoiling spectrometer (TOF-SARS) for surface analysis Rev. Sc/. Instrum. 61 740-52... 

Masson F and Rabalais J W 1991 Time-of-flight scattering and recoiling spectrometry (TOF-SARS) analysis of Pt 110. I. Quantitative structure study of the clean (1 x 2) surface Surf. Sc/. 253 245-57... 

Figure Bl.23.5. Schematic illustration of the TOF-SARS spectrometer system. A = ion gun, B = Wien filter, C = Einzel lens, D = pulsing plates, E = pulsing aperture, F = deflector plates, G = sample, H = electron multiplier detector with energy prefilter grid and I = electrostatic deflector.

Roux C D, Bu H and Rabalais J W1992 Hydrogen adsorption site on the Ni 110 -p(1 x 2)-H surface from time-of-flight scattering and recoiling spectrometry (TOF-SARS) Surf. Sci. 271 68-80... 

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