Encapsulation of cadmium telluride nanocrystals within single walled carbon nanotubes

The encapsulation of crystal structures of cadmium telluride within small diameter single walled nanotubes (SWNTs) are studied using density functional theory with a dispersion correction (DFT + D). Four different suitable pseudo one-dimensional (1-d) CdTe crystals were considered and their energies were compared. The isolated 4:2 crystal (derived from the hexagonal CdTe bulk) was calculated to be the most thermodynamically stable of the four structures. Calculations were performed on the 4:2 crystal inserted into three different SWNTs, (8, 8), (9, 9), and (10, 10), in order to investigate energy of formation of the CdTe@SWNT composites. The calculated encapsulation energies show that the interaction between nanotubes and the CdTe crystals is noncovalent. Since the energy difference of the “free” 4:2 and 3:3 structures is small(0.07 eV/CdTe), we carried out calculations on 3:3 CdTe structure encapsulated in to two different SWNTs, (9, 9) and (10, 10). The calculated binding energies are exoergic suggesting that this polymporph may also be found experimentally. The other two structures are also encapsulated and their results are discussed though they can be found within SWNTs at high temperatures. The present study proposes that both 4:2 and 3:3 CdTe structures can be observed in the microscopic experiments and further experimental verification is required.