A Study Of The Size-dependent Elastic Properties Of Silicon Carbide Nanotubes And Cadmium Selenide: First-principles Calculations

In recent years, the superior physical and chemical properties of semiconductornanotubes have been received more and more attention. We have chosen twoimportant semiconductor nanotubes: silicon carbide (SiC) nanotubes and cadmiumselenide (CdSe) nanotubes using first-principles to study the elastic propertieschanged with the size of the nanotubes, and try to explain the reason of this trend. Theresults show that for silicon carbide nanotubes:1, The Young’s modulus increases with the increase of the nanotube diameter, andcarbon-silicon bond length change is inversely proportional to the Young’s modulus.The Poisson’s ratio is reduced with the increase of the diameter of the nanotubes. Forthe same diameter of the nanotubes, the Young’s modulus of armchair nanotubes isslightly larger than zigzag nanotubes. For small nanotube Young’s modulus of thediameter change very fast, when the diameter is larger than8, the Young’s moduluschanges slowly, and the difference is gradually disappearing.2, In order to explain the change of the elastic properties of nanotubes from thephysical standpoint, we analyzed the transferred charge from silicon atoms to thecarbon atoms for different nanotubes. We found that the larger nanotubes transfermore charge, resulting in carbon and silicon atoms combined with each other moretightly, so their bond lengths are shorter. These analyses can explain the above results.3, The changes of elasticity also reflect the changing of the binding energy betweencarbon atoms and silicon atoms and the bond angles. The results show that theabsolute value of binding energy between the two kinds of atoms and the bond angleis increased, so they are more stable.Furthermore, the trends for the CdSe nanotubes are similar to the overall trend ofsilicon carbide nanotubes. The difference is that the change of the Young’s modulusand Poisson’s ratio of CdSe nanotube with the diameter is oscillatory trend.Above all, we can see that the Young’s modulus increases with the diameter of thenanotubes for the semiconductor nanotubes. For the tubes with larger diameter, thedifference of elastic modulus between the armchair nanotubes and zigzag nanotubes isnot very obvious. The results can be explained by the transferred charge between theatoms.