What is the incident radiation used in XPS and why? How does the detector used in the XPS differ from those during SEM, EDX or XRD data collection?
Nikhil Verma
In XРS ( X-ray photoelectron spectroscopy) measures the binding energy of electrons with a nucleus when irradiated with monochromatic radiation, which appear as a result of the photoelectric effect.
Scanning electron microscope (SEM). The incident electrons interact with the atoms in the sample, creating various signals that contain information about the surface topography and composition of the sample. The electron beam is scanned as a bitmap and the position of the beam is combined with the intensity of the detected signal to produce an image.
Energy dispersive X-ray spectroscopy(EDX). The electron beam is focused on the sample and transfers electrons from one shell to another. This releases X-rays. The amount and energy of the x-rays emitted by the sample can be measured using an energy dispersive spectrometer. Since the energies of X-rays characterize the difference in energy between the two shells and the atomic structure of the emitting element, EDS makes it possible to measure the elemental composition of the sample.
XRD identification of materials based on their diffraction pattern. The sample is irradiated with X-rays and the intensity of the rays leaving the sample is measured depending on the angles of the crystal lattice.
SEM and TEM used accelerated elections..having very small wavelength....while XPS is using X Rays..
EDX analysis is an analytical technique commonly used for the analysis of chemical compositions. The EDX technique analyzes X-rays emitted by a material when it is hit with electromagnetic radiation. In an EDX system, a high-energy beam is focused on the sample being studied. An atom within the sample contains unexcited electrons in discrete energy levels or electron shells bound to the nucleus. The incident beam may excite an electron in an inner shell, ejecting it from the shell while creating an electron hole. The electrons and holes are attracted to opposite ends of the detector with the aid of a strong electric field. The size of the current pulse thus generated depends on the number of electron-hole pairs created. This in turn depends on the energy of the incoming X-ray, which is governed by the composition of the sample. Thus, an X-ray spectrum can be acquired giving information on the elemental composition of the material under examination. By moving the electron beam across the material an image of each element in the sample can be acquired.
It is often necessary to identify the different elements associated with a textile. This is accomplished by using a ‘built-in’ EDX spectrometer. EDX analysis is often used in conjunction with electron microscopy during textile surface characterization.
An EDX spectrum plot not only identifies the element corresponding to each of its peaks, but also the type of X-ray to which the peak corresponds. For example, a peak corresponding to the amount of energy possessed by X-rays emitted by an electron in the L-shell going down to the K-shell is identified as a K-alpha peak. The peak corresponding to X-rays emitted by M-shell electrons going to the K-shell is identified as a K-beta peak.
In textile characterization, EDX analysis has been used in quantitative elemental analysis (fixed-point, time-resolved, mapping) with a sensitivity down to a few atomic percent. The output of an EDX analysis is an EDX spectrum. The EDX spectrum is simply a plot of how frequently an X-ray is received for each energy level. An EDX spectrum normally displays peaks corresponding to the energy levels for which the most X-rays have been received. Each of these peaks is unique to an atom, and therefore corresponds to a single element. The higher a peak in a spectrum, the more concentrated the element is in the specimen.
As the most convenient technique of elemental identification, EDX analysis has been widely used in the characterization of the chemical compositions of textiles. Varesano et al. (2005) coated loose wool fibers with electrically conducting doped polypyrrole (PPy). EDX analysis was used to characterize the evenness and degradation, and the results indicated that fastness to organic solvents was excellent and a slight PPy decoating occurred during the manufacturing processes. Szymanowski et al. (2005) also used the EDX technique to investigate the elemental compositions of the titanium oxide coatings applied to cotton textiles. The analysis showed the composition of the textile coating to be close to that of titania with small contents of chlorine and carbon. The EDX technique has also been successfully applied in archaeology. Chen et al. (1998) used EDX analysis to examine the characteristics of the microstructures of archaeological and laboratory mineralized fibers. The EDX results revealed some similarities between the two types of fibers.
Quantification of a particular element by analysis of the intensity of X-ray emitted is a technique commonly used in textile characterization. Shahidi et al. (2007) coated aluminum on cotton fabrics using low-temperature argon and oxygen plasmas. In their research, an EDX unit connected to a scanning electron microscope was used to determine the concentration of elements as atomic percentages present on the surface of the coated fabrics. By analyzing the intensity of each element, the aluminum content was easily revealed. El-Naggar et al. (2003) used an EDX unit to determine the atomic percentage of elements present on surface-coated fabrics.
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