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EDS component analysis
Project introduction
Energy dispersive spectrometry (EDS) is an analytical technique
used for sample analysis and characterization. It is usually used
in conjunction with a scanning electron microscope and a
transmission electron microscope to analyze the types and contents
of the elements in the micro-region of the material: the
characteristic X-rays generated when the electron beam interacts
with the material are used to provide information on the chemical
composition of the sample, and most elements (Be4-PU94) can be
qualitatively and semi-quantitatively detected, and surface
contaminants can be analyzed.
Component analysis laboratory
Experimental principle
In modern scanning electron microscopes and transmission electron
microscopes, the energy dispersive spectrometer (EDS) is an
important accessory. It shares a set of optical systems with the
main machine, and can perform point analysis, surface analysis, and
line analysis on the chemical composition of the parts of interest
in the material.
Advantages of EDS
(1) Fast analysis speed and high efficiency. It can simultaneously
conduct rapid qualitative and quantitative analysis of all elements
with atomic numbers between 11 and 92 (even ultra-light elements
such as C, N, and O);
(2) Good stability and good repeatability;
(3) Can be used for component analysis of rough surfaces (fracture,
etc.);
(4) Can measure component segregation in materials, etc.
Working principle of EDS
The probe receives characteristic X-ray signals → converts
characteristic X-ray light signals into electrical pulse signals
with different heights → amplifier amplifies the signals →
multi-channel pulse analyzer encodes pulse signals representing
X-rays of different energies (wavelengths) into different channels
according to their heights → displays spectrum lines on the
fluorescent screen → uses computers for qualitative and
quantitative calculations.
Structure of EDS
1. Detector: converts X-ray photon signals into electrical pulse
signals, and the pulse height is proportional to the energy of the
X-ray photons.
2. Amplifier: amplifies electrical pulse signals.
3. Multi-channel pulse height analyzer: the pulses are programmed into different channels according to their heights, that is, different characteristic X-rays are distinguished according to their energies.
4. Signal processing and display system: identification spectrum, qualitative and quantitative calculations; recording analysis results.
EDS analysis
1. Qualitative analysis: The peaks in the EDS spectrum represent
the elements present in the sample. Qualitative analysis is the
first step in analyzing unknown samples, that is, identifying the
elements contained. If the type of element cannot be correctly
identified, the accuracy of the final quantitative analysis is
meaningless. Usually, the main components of a sample can be
reliably identified, but for the determination of minor or trace
elements, only by carefully dealing with spectral line
interference, distortion and the spectral line system of each
element can it be accurate. Qualitative analysis is divided into
automatic qualitative analysis and manual qualitative analysis.
Automatic qualitative analysis determines the peak position
according to the energy position. Simply click the
"Operation/Qualitative Analysis" button to display the
corresponding element symbol at each peak position of the spectrum.
Automatic qualitative analysis has a fast recognition speed, but
due to the serious interference of spectral peak overlap, certain
errors will occur.
2. Quantitative analysis: Quantitative analysis is to obtain the concentration of various elements that make up the sample material through the intensity of X-rays. According to the actual situation, people have sought and proposed a method to measure the intensity ratio of unknown samples and standard samples, and then convert the intensity ratio into a concentration ratio after quantitative correction. The most widely used quantitative correction technology is ZAF correction.
3. Element surface distribution analysis: In most cases, the electron beam is only shot at a certain point of the sample to obtain the X-ray spectrum and component content of this point, which is called the point analysis method. In modern new SEMs, most of the different component distribution states of a certain area of the sample can be obtained, that is: using a scanning observation device, the electron beam is scanned two-dimensionally on the sample, and the intensity of its characteristic X-rays is measured, so that the brightness change corresponding to this intensity is synchronized with the scanning signal and displayed on the cathode ray tube CRT, and the two-dimensional distribution image of the characteristic X-ray intensity is obtained. This analysis method is called the element surface distribution analysis method, which is a very convenient method for measuring the two-dimensional distribution of elements.
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