Surface sensitivity of Auger-electron spectroscopy and X-ray photoelectron spectroscopy

A convenient measure of surface sensitivity in Auger-electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) is the mean escape depth (MED). If the effects of elastic-electron scattering are neglected, the MED is equal to the electron inelastic mean free path (IMFP) multiplied by the cosine of the emission angle with respect to the surface normal, and depends on the material and electron energy of interest. An overview is given here of recent calculations of IMFPs for 50–2000 eV electrons in a range of materials. This work has led to the development of a predictive formula based on the Bethe equation for inelastic electron scattering in matter from which IMFPs can be determined. Estimates show, however, that elastic-electron scattering can significantly modify the MED. Thus, for AES, the MED will be reduced by up to about 35%. For XPS, however, the MED can be changed by up to ±30% for common measurement conditions although it can be much larger (by up to a factor of 2) for near-grazing emission angles. Ratios of MED values, calculated with elastic scattering considered and neglected for XPS from the 3s, 3p, and 3d subshells of silver with Mg Kα X-rays are approximately constant (to about 10%) over a range of emission angles that varies from 40° to 60° depending on the subshell and the angle of X-ray incidence. Recommendations are given on how to determine the optimum range of emission angles for satisfactory analysis of angle-resolved XPS (ARXPS) data. Definitions are included of three terms often used for describing surface sensitivity (IMFP, MED, and effective attenuation length (EAL)), and examples are given of the varying magnitudes of these quantities for different analytical conditions.     

Laser spectroscopy : 5. Raman spectroscopy

This article in the series reviews the application of lasers in Raman spectroscopy.     

Laser spectroscopy : 3. Linear laser spectroscopy

The three basic methods of linear laser spectroscopy are reviewed: absorption, opto-acoustic, and fluorescence spectroscopy. The characteristics of each method and their areas of application are presented and compared.     

History of spectroscopy and modern micromachined disposable Si ATR-IR spectroscopy

In this article, the historical development of spectroscopy is examined and the spectroscopy devices used today are described. Then, we focus on infrared (IR) spectroscopy, which cannot give valuable signal in aqueous solution. Attenuated total reflection (ATR)-IR technique solves the problem. In addition, we specifically mention newly developed disposable ATR-IR crystals and micromachined silicon (Si) ATR-IR. Disposable crystal systems and microfluidics systems can be integrated with existing miniature ATR analyzers. If the integration is successful, the technique might be used in biomedical measuring instruments, reactions' analyses, and ultra-high-pressure analyses.     

Laser spectroscopy 4. Nonlinear high resolution spectroscopy

This paper in the series gives a brief outline of the main ideas, methods and types of nonlinear laser spectrometer used for atomic and molecular spectroscopy without Doppler broadening. This is the most developed area of laser spectroscopy and has recently been the subject of several papers^1,2 to which readers are reffered for more detailed information.     

Edge spectroscopy

Hyperfine Interactions - The near-edge X-ray absorption fine structure can provide information on the chemical form and local structure as well as on the electronic and even magnetic properties of...     

Synthetic spectroscopy

The extension of synthesis techniques to spectroscopy is examined. The geometric efficiency of a spectrometer from the point of view of the redundancy of the measure is studied. Experimental results are shown.     

Muonium spectroscopy

The electromagnetic interactions of electrons and muons can be described to very high accuracy within the framework of standard theory, in particular within the hydrogen like muonium atom. Therefore, precision measurements are able to test basic interactions in physics and to search for yet unknown forces. Accurate values for fundamental constants can be obtained. Results from experiments on the ground state hyperfine structure and the 1s–2s intervals in muonium are described together with their relations to a new measurement of the muon magnetic anomaly. This revised version was published online in August 2006 with corrections to the Cover Date.     

Photoelectron spectroscopy

The energy spectra of photoejected electrons provides a direct method for determining the electronic binding energies in atoms, molecules and solids. The binding energies may be used to identify a particular atom in a molecule or solid and, as well, to indicate from which orbital the electrons were removed. The relative intensities of peaks in the photoelectron spectrum reveal the nature of the chemical bond in a molecule and are a measure of the relative transition probabilities for ionization to a particular state. The effects of autoionization and angular distribution are discussed, and some applications are given.     

Multidimensional spectroscopy

The quantum states produced by non-linear interaction of a coherent uniform radiation field with dipolar matter are evaluated by a time-dependent perturbation expansion of the density matrix. The non-linear terms of the expansion are Fourier transformed to yield multi-dimensional spectra which indicate the connectivities in the underlying energy level diagrams. The spectra can be measured in experiments with multiple resonance, multiple pulse or stochastic excitation. Although the theory presented is of general validity in coherent spectroscopy, emphasis is placed on its application in non-linear N.M.R. spectroscopy. It illustrates particularly well the common basis of double, 2D correlated and multi-dimensional stochastic magnetic resonance.     

Photo-admittance spectroscopy

We present a junction technique for measuring the spectral distribution of photoionization cross sections of centers located in the forbidden band gap of semiconductors. It is especially suitable for centers where the effect of background radiation is very disturbing and should be considered as a less expensive alternative to the Fourier photo-admittance spectroscopy technique which has been described previously.