CSU Lab Nondestructive Analysis Techniques for Polymer/Semiconductor Defects*
Positron annihilation lifetime spectrometer
Positronium annihilation lifetime spectroscopy
PALS is a nondestructive spectroscopy technique that allows the study of various phenomena and material properties at the atomic scale. It will bring the following advantages to your research.
- Capable of resolving voids in polymers, metals and semiconductors in the size range of less than 1 nm.
- Wide range of material adaptability, supports testing of liquids, gases, etc.
- Low environmental requirements, high and low temperature, vacuum can be tested.
- Obtain the type and concentration of defects at once.
After the high-energy positrons are emitted from the radioactive source into the material, they are first decelerated in a very short time (below about 10-12 ps) through a series of inelastic collisions and lose most of their energy to thermal energy, a process called injection and thermalization. After thermalization, the positron will undergo a random diffusion thermal motion in the sample. The defects such as vacancies and dislocations in the lattice often carry an equivalent negative charge, and due to Coulomb gravity, the positron is easily captured by these defects and stops diffusing, and finally will annihilate with the electron inside the matter. The time elapsed from the time of positron emission into matter to the time of annihilation is generally referred to as the positron lifetime. Since annihilation is random, the positron annihilation lifetime can only be derived from the statistics of a large number of annihilation events.
Positron annihilation techniques are extremely sensitive to structural phase transitions and atomic-scale defects in materials, and have become a nondestructive means of probing and analyzing the microstructure and electronic structure of matter. As a microscopic analysis technique, the main scope of positron annihilation is to study microstructures and defects at the atomic scale. Compared with the usual microstructure analysis techniques such as STM, SEM, TEM, etc., positron annihilation technique can provide not only the size information of defects, phase transition information, but also the information of defect distribution with depth, which can deeply analyze the electronic structure of materials and the chemical environment at the positron annihilation, making up for the deficiencies of other microprobe techniques and is irreplaceable.
- He has few restrictions on the type of sample material, which can be solid, liquid or gas, metal, semiconductor, insulator or polymer material, single crystal, polycrystal or liquid crystal, etc., and is applicable to all problems related to the electron density and momentum of the material.
- There is no restriction on the sample temperature, which can cross the melting or solidification point of the material, and the information is carried by the γ-rays with strong penetration ability, so it can do dynamic in-situ measurement of the sample at high and low temperatures, and special environments such as electric field, magnetic field, high air pressure and vacuum can be imposed during the measurement.
- It is quite difficult to study atomic-scale defects in samples, such as defects in the lattice that are missing one or more atoms, which are quite difficult to study in electron microscopy and X diffraction.
- Easy-to-use, room temperature measurement method for PAT preparation
Deformation, fatigue, quenching, irradiation, doping, hydrogen damage, etc. in metallic materials cause defects such as vacancies, dislocations, vacancy clusters, etc. in the material and the study of annealing effects of these defects.
Phase change processes in materials, such as precipitation in alloys, martensitic phase change, crystallization processes in amorphous materials, phase change in ionic solids, liquid crystals and other polymeric materials, phase change in polymers, condensed matter physics, etc.
Study of the energy band structure of solids, Fermi surface, vacancy formation energy, etc.
Study of the surface and superficial structure and defects of materials.