Abstract
Physical properties at the nanoscale are known to be different from those in macro-dimensions. It was indicated that both structural and electronic properties are dependent on size effect or surface effect according to the high surface-to-volume ratio (SVR), which will exaggerate the surface status. Our research examined the small diameter NiSi2 NWs with first principle calculations via CAmbridge Serial Total Energy Package (CASTEP). Numerical convergence has been checked with different k-point sets and cut-off energy from 300 to 380 eV. We have grown self-assembled NiSi2 NWs with triangular cross section on (100) Si substrate and these kinds of wires have been observed having very low resistivity. On the other hand, free-standing NiSi2 NWs have been fabricated by silicidation of Si NWs produced by etching Si substrates. Hence, we attempted to simulate the properties of low index axis NiSi2 NWs. (1) Structural Properties All the structures were carried out with total energy minimization to reach the most stable state and tensile and compressive strain were applied to analyze the Young’s modulus. Both types of NWs were found to have shorter bond length for edge (surface) bonding compared to bulk NiSi2 but longer bond length for inner bonding. The Young’s modulus was found to be much softer than that of the bulk. The difference of the bond length can be considered as “surface stress” which accounts for the softening. (2) Electronic Properties As to know the electronic properties in such low dimensions, we examined the band structure and density of states (DOS). The band structure was computed along the direction from □ (0,0,0) to Z (0,0,0.5). All the NWs simulated are calculated to be semimetal. Ni and Si atoms both contributed to the low resistivity because half of the DOS near the Fermi level comes from Si and half from Ni. Further analyzing the Partial Density of States (PDOS), the surface Si atoms with low coordination number make greater contribution to the total Si DOS.