| Cadmium zinc telluride (CdZnTe or CZT) is an important third generation of semiconductor material. Because of the exceptional photoelectric property it has been widely used in many areas, such as space exploration, radiation detection, and medical field and so on. At the same time, due to the best lattice matching to the HgCdTe epilayer in comparison with other alternative materials, so it has attracted much attention.As CdZnTe crystals belong to soft and brittle materials, its manufacturing would confront a certain difficulty. The disadvantages of traditional methods for machining CdZnTeis that abrasive embedded into materials easily, or corrosion groove prone to be left. Compared with this, the ultra-precision grinding method can be a good solution to this problem. It is very difficult to investigate the mechanism of ultra-precision in nanoscale, so it is necessary to explore the fundamental mechanism of nt-CZT under ultra-precision grinding. There are few reports of molecular dynamics simulation on CZT in the world. Therefore, to explore the material removal mechanism in the process of ultra-precision machinin of nanotwinned structure crystalline, molecular dynamics simulation (MD) and nano scratch test experiment was carried on about CZT.The physical properties such as surface energy and forbidden band width about CZT have few reports on the international literature, and these parameters are significant in the study of the mechanical properties and the ultra-precision machining mechanism. Computer simulation method (MD and The first principle) were carried out on Cd0.96Zn0.04Te which predicting the Cdo.96Zn0.04Te forbidden band width is 1.74 eV and the surface energies of single crystal and nt-CZT are 435.08 and 381.8 mJ/m2, respectively.In order to explore the fundamental mechanism of ductility for nt-CZT, under cyclicloading conditions, MD were carried out on Cd0.95Zn0.04Te and there were three models were established for nanoindention with different twin thickness which named mc-36.、nt-5.6-17.9-5.6 and nt-5.6-17.9-7.8-5.6. The results showed that different pairs of edge dislocations were form in different models even at the same time. Both mc-36.9 and nt-5.6-17.9-5.6 generated cracks at the sencond cyclic indentations. Cracks were absent in nt-5.6-17.9-7.8-5.6, due to the softening effect of the lower nanotwin with respect to transferring and annigilating edge dislocations along twin boudries. Stress induced by nanoindentations propagated via edge dislocations along the {111} planes to the fixed bottom. At a fixed point along the (-111) plane, stress concentrates. With an increase in the stress induced by cyclic loading, stress concentration reaches a critical value for cracking, and therefore a crack appears. A nanometer crystallite and a cell structure emerged. The cell structure and the nanoscale crystallite induced by stress, resistance to deformation of the deformed mc-36.9 model is more than that of the pristine crystal.Molecular dynamics simulation of scrath was carried out on Cd0.96Zn0.04Te. The results showed that CZT shows good nano machinability in nano scratch experiments. In the process of scrathing, the contact surface of substate has formed furrow scratches.The measured value of friction coefficient at around 0.45. In order to test the simulation result, nano scratch tests were carried out on Cd0.96Zn0.04Te. The results showed that the friction coefficient value was also at around 0.45. The effect of sliding speed and the load was basically corresponded to the results of MD of scratch. |
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