Principles and Applications of X ray Electron Spectroscopy (XPS)

XRD Physical Analysis

(1) Principle of qualitative analysis Each crystalline substance has its own unique structure, resulting in different X-ray diffraction patterns (diffraction position θ and diffraction intensity I) for each crystal; when the material consists of multiple crystalline states, the diffraction patterns of the various crystalline states will appear in the X-ray diffraction pattern at the same time, but they are only mechanically superimposed and will not interfere with each other;

Note: The positions of the X-ray diffraction lines are determined by the shape and size of the crystal cell, and the interplanar spacing d of the diffracting crystal faces; the relative intensities of the diffraction lines are determined by the type, number, and arrangement of the atoms in the crystal cell; i.e., their positions and intensities are specific to the crystal faces of the particular crystal. Structural analysis: Using characteristic X-rays of known wavelength, the crystal face spacing d can be calculated by measuring the θ angle (Bragg's equation);

Note: By the conditions that produce diffraction,, so diffraction only arises when the wavelength λ of the wave and the scattering plane spacing d are of the same order of magnitude or smaller. But when λ is too small, the angle of diffraction will become so small that it is difficult to determine it even by ordinary means. X-ray spectroscopy: Using a crystal with a known facet spacing d, the wavelength of the unknown X-rays is calculated by measuring the θ angle, thus calculating the wavelength of the unknown X-rays (Bragg's equation);

Note: XRD gives information about the bulk structure of a material, not the surface structure;

① Determine whether the sample is amorphous or crystalline: amorphous samples have bun peaks and no fine spectral peak structure; crystals have obvious spectral line characteristics;

② Determine the main physical phase composition of the measured sample: by comparing with the standard spectrum, it is one of the most important uses of XRD, which can be analyzed by Jade software;

(iii) determine the alloy: if A and B form a homogeneous single-phase alloy structure, then the characteristic diffraction peaks of the A-B alloy between A and B, and the peaks are symmetrical; and if A, B does not form an alloy, the characteristic diffraction peaks of the A-B complex by the diffraction peaks of the A and B superimposed on each other proportionately, and there will not be a shift of the diffraction peaks;

(2) Quantitative analysis principle The intensity of the diffraction lines of each crystalline state depends on its relative content in the sample, and the relative content can be deduced by measuring the intensity ratio of the diffraction lines of various crystalline states;

Note the term “relative content”, direct comparison of diffraction lines from XRD samples under different conditions is meaningless. Quantitative analysis is usually carried out by the “internal standard method” (introduction of other standard specimens internal standard) or the “external standard method” (external standard of the pure phase of the substance to be measured).

XRD test procedure

General process:

(1) X-ray generation: X-ray tube cathode heated by the pass current leads to thermal radiation generated by the electron flow, bombardment of the anode target, the anode target so that the electron deceleration and emission of a variety of specific wavelengths of X-rays, through the window can be utilized;

Note: When the foreign high-speed ion energy is sufficient to hit the atomic shell layer of electrons out of the atomic system or other higher energy levels, the struck electrons left empty space, the atomic system energy rise and become excited state, and lead to higher energy level electrons to the lower energy level for spontaneous jump to fill the empty space, and emit the corresponding X-rays; (due to the different levels of energy level jump leads to different X-rays, affecting the monochromaticity of the need for calibration processing) (2) X-ray calibration (Collimation): through some means such as slit (slit), monochromatic crystal (Crystal monochromator), etc. so that the wavelength of X-rays is controlled in a narrow range, and has the same direction;

3. Sample stage diffraction: X-rays are diffracted at the sample stage from the crystal to be tested;

4. Detector detects the diffraction lines and converts them into peaks.

XRD Crystal Database

Inorganic Crystal Structure Database (ICSD): https://icsd.fiz-karlsruhe.de/search/

International Center for Diffraction Data (ICDD): http://www.icdd.com/

Cambridge Crystal Data Center (CCDC): http://www.ccdc.cam.ac.uk/