Low-energy Ion Scattering Spectrometry

LEIS is a typical surface specific method, which detects particles scattered only from the uppermost surface layer of the soHd. The scattering of low energy ions of inert gases from the surface of a sample is measured. At low energies ( 5 keV) the ions are neutralised, if they penetrate below the top two or three monolayers, so only a few monolayers of the solid participate in the ion scattering process. In this way LEIS differs from RBS, in which the neutrahsation processes are negligible. 

LEIS uses a low energy ion beam of ions formed from inert gases in an ion source to interact with the sample surface. The beam energy is typically less than 10 keV. LEIS is a surface sensitive technique and it should be performed under clean high vacuum conditions. In most research systems Pa in the target chamber is a minimum requirement 

Any inert gas ions from the beam penetrating below the surface are neutrahzed. LEIS uses electrostatic energy analysers and only the charged particles are detected. Electrostatic analysers are suited to low energy analysis, they are simple to operate, and they provide good energy resolution. 

The sample should be solid, with a size of around 1 cm. The requirements are the same as for RBS measurements and the sample must be cleaned due to atmospheric and other surface contaminants, to obtain a pure surface composition measurement 

LEIS measurements result in an energy spectrum of the backscattered ions from the sample surface. The energy of scattered ions provides information on the mass of the surface atoms, which is directly related to their chemical identity. The cross-section, solid angle and transmission factor (the analyser acts as an energy filter, with transmission characteristics that depend on the mode of operation) are used for these calculations. 

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As mentioned already, many surface-analysis techniques are available nowadays. In the opinion of some specialists in this field [36, 37], four of these are greater in importance X-ray photoelectron spectrometry (ESCA), Auger electron spectrometry (AES), secondary-ion mass spectrometry (SIMS), and low-energy ion scattering spectrometry (ISS). 

T.M. Buck. Low-Energy Ion Scattering Spectrometry. In A.W. Czandema, editor. Methods of Surface Analysis. Methods and Phenomena Their Applications in Science and Technology, Volume 1. Elsevier. New York, 1975. 

LEIS Low-energy Ion Scattering Spectrometry, 23 LMMS. viz LAMMA, 17... 

Ion Scattering Spectrometry Low-Energy Ion Scattering Resonance Charge Exchange... 

ISS ion-scattering spectroscopy LEIS low-energy ion scattering SEM scanning electron microscopy SIMS Secondary ion mass spectrometry TEM transmission electron microscopy TP temperature-programmed XANES X-ray absorption near edge spectroscopy. 

Techniques based on the interaction of ions with solids, such as secondary ion mass spectrometry (SIMS) and low-energy ion scattering (LEIS) have undoubtedly been accepted in catalyst characterization, but are by no means as widely applied as for example X-ray photoelectron spectroscopy (XPS) or X-ray diffraction (XRD). Nevertheless, SIMS, with its unsurpassed sensitivity for many elements, may yield unique information on whether or not elements on a surface are in contact with each other. LEIS is a surface technique with true outer layer sensitivity, and is highly useful for determining to what extent a support is covered by the catalytic material. Rutherford backscattering (RBS) is less suitable for studying catalysts, but is indispensable for determining concentrations in model systems, where the catalytically active material is present in monolayer (ML)-like quantities on the surface of a flat model support. 

Fig. 1. Experimental techniques available for surface studies. SEM = Scanning electron microscopy (all modes) AES = Auger electron spectroscopy LEED = low energy electron diffraction RHEED = reflection high energy electron diffraction ESD = electron stimulated desorption X(U)PS = X-ray (UV) photoelectron spectroscopy ELS = electron loss spectroscopy RBS = Rutherford back scattering LEIS = low energy ion scattering SIMS = secondary ion mass spectrometry INS = ion neutralization spectroscopy.

Techniques that have been applied include time of flight static secondary ion mass spectrometry (SSIMS)/ " low energy ion scattering spectromehy, x-ray photoelectron microscopy scanning electrochemical microscopy (SECM), laser ionization mass spectrometry, surface enhanced infrared reflection spectroscopy, Fourier Transform infrared spechoscopy and nuclear magnetic resonance spectroscopy. ... 

Ion Scattering Spectrometry. Although scattering of low-energy ions from surfaces first was studied more than 20 years ago, it was not until 1957 that Smith (16) used inert gas ions on molybdenum and nickel, thereby demonstrating the potential of the method for surface analytical investigations. 

Li, Z., J. Eckwert, A. Lapicki, and S. L. Anderson. 1997. Low-energy high-resolution scattering mass spectrometry of strained molecules and their isomers. Int. J. Mass Spectrometry Ion Processes 167/168 269-79. 

Historically, electron spectroscopy has matured In two separate but related areas. One has been the use of electron spectroscopy as applied to analytical problems, especially those that relate to surfaces, such as failure analysis, corrosion, catalysis, or tribology. In such studies, the technique Is often used In conjunction with other techniques such as low energy electron diffraction (LEED), secondary Ion mass spectrometry (SIMS), or Ion scattering spectroscopy (ISS). Another related area Is the use of electron spectroscopy to examine the electronic structure of materials or chemical species. 

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