| Summary: | 博士 === 國立清華大學 === 材料科學工程學系 === 92 === Abstract
Initial stages of reactions of Ti on Si(111)-7×7 surface and the initial growth of titanium silicide nanocluster have been investigated by scanning tunneling microscopy (STM), low energy electron diffraction (LEED), synchrotron radiation ultraviolet photoemission spectroscopy (SR-UPS) and transmission electron microscopy (TEM).
At very low coverage ( 0.02 ML), individual Ti atoms are confined and switched within the “sub-triangular” region consisting of two neighboring center adatom and corresponding corner adatom in a half unit cell at room temperature. Both STM and SR-UPS data indicate that the individual Ti atoms adsorbed are associated with the Si rest atom. The Ti atoms were found to be more mobile in faulted halves than that in unfaulted halves.
After 0.04 ML Ti atoms interact with the Si adatoms. For coverage greater than 0.24 ML, the Si atoms start to mix with the Ti atoms to from an intermixed Ti/Si film and the 7×7 reconstruction was destroyed gradually. The reconstruction is removed completely at 1 ML Ti deposition.
The growth of titanium silicide clusters on the Si(111)-7×7 has been observed for sub-monolayer (0.2 ML) Ti deposited. Tetragonal Ti5Si4 (T-Ti5Si4) has been identified to be the first nucleated phase in sub-monolayer Ti deposited on the Si(111)-7×7 surface for 500 ℃ annealing. The direct observation of the formation of clusters surrounded by the heavily damaged silicon lattice strongly suggested that Si is the dominant diffusing species in forming the silicide.
At 600 ℃ annealing, irregular shape T-Ti5Si4 islands were observed to grow. On the other hand, the elongated orthorhombic Ti5Si4 (O-Ti5Si4) clusters form at 700 ℃. The elongated clusters are oriented along three equivalent Si<2-20> directions of the Si(111) surface and the lattice mismatch is 4.4 %.
|
|---|
