Applications Of Ion Beam Methods In Nanometer Science

Ion beam method is based on the introduction of energetic ions into the surface layer of a solid substrate to modify the target material or/and to sputter away surface atoms. It can be used as ion beam synthesis (IBS) technique to form thin films or modify material properties, as ion implantation technique to selectively change the doping, and also as ion beam analysis techniques to investigate the surface nanometre structure. There are mainly three part works in this thesis: development of Time of Flight Energy Elastic Recoil Detection (ToF-E ERD) technique, investigation of silicide formation in silicide/Si based systems by low energy ion beam synthesis (IBS) technique, and study the effect of stoichiometric disturbance resulting from MeV Si implantation.ToF-E ERD plays an important role in the studies of this thesis. In order to undertake quantitative analysis, the detection efficiency of recoils with masses ranging from H up to Nb at energies from 0.05 - 1 MeV per nucleon has been investigated for ToF-E ERD systems. It is observed that the detection efficiency for the ToF-E detector telescope depends on electronic stopping power (S_e) in the carbon foils, which in turn relies upon the recoil mass and energy. The detection efficiency of a time detector could be described by a simple empirical formula as a function of S_e.To obtain high quality nanometer sized thermodynamically and chemically stable electrical contacts is a key issue in research on nanometer structures as well as of great importance for the industrial exploitation of nanoscience. Silicides with metal-like properties, especially those, which are closely lattice matched to silicon appears to be strong candidates. In this thesis, silicide phase formation and foreign atoms incorporation have been investigated under keV pulsed metal-ion implantation. The metal ions are produced from a MEtal vapour vacuum arc (MEVVA) ion source with high currents and high achievable doses. This new MEVVA IBS technique opens a promising low temperature route to form metallic silicide in vacuum. The study of partial sputtering yield of different species from target indicates the approach to high dose equilibrium during MEVVA bombardment. Implantation induced surface topography development shows that defects and disorders form initial surface can result in very different morphology.MeV Si implantation into semi-insulating (SI) GaAs is a common technique used to create a deep doping layer. It is observed that the maximum of the carrier concentration is at a shallower depth than that of the implanted atom concentration. This unexpected phenomenon has previously been explained as depth measurement error. Based on our theoretical calculations and experiments, the phenomenon can be attributed to the effect of non-uniform stoichiometric disturbances (NSD) on the activation of implanted atoms. The effect of NSD in GaAs substrate is caused by MeV implantation. After implantation, an excess concentration of the heavier element As exists at shallower depth, while an excess concentration of the lighter element Ga is seen at greater depth. It is likely that Si atoms move more easily to Ga sites when they are heated in an As-rich environment. Excess lattice interstitials build up around the depth of the peak in the implanted Si~+ concentration and prevent Si atoms from becoming activated there.