Thermal properties of indium nanoparticles and gold silicide formation by scanning nanocalorimetry

This thesis is an experimental work on the thermal properties of indium nanoparticles and the interaction characteristics between gold and silicon using nanocalorimetry technique. The melting behaviors of indium thin films have been investigated. The films consist of ensembles of nanoparticles whose melting temperatures are size-dependent. We experimentally determine the relationship between a nanoparticle's radius and its melting point by combining the caloric results with nanoparticle size distributions from TEM. The results show a linear melting point depression. Moreover, we found the discrete nature of nanoparticles during the early stage of thin film growth—the measured heat capacity values show several maxima at certain temperatures which suggest preferred states exist among supported nanoparticles. These maxima are related to each other by increments of one monolayer of indium atoms which can be extended from the magic numbers observed previously in cluster beams.; For the first time, the nanocalorimetry is utilized to characterize thin film growth in real-time. The technique generates 3-dimensional heat capacity data as a function of temperature and thickness that show the continuous change during deposition. The measurement interval is ∼4 × 10−3 nm in thickness, increment of the heat capacity is ∼30pJ/K, and the temperature resolution is better than 0.5K.; The silicide study focuses on phase formation in Au-Si thin films. The unique finding is to determine the melting temperature of metastable phase using calorimetry, which is ∼60°C below the eutectic melting point (363°C). The heat of fusion (26.4 kJ/mol) of the metastable phase has also been obtained. The metastable phase is analyzed to be an orthorhombic structure (a = 0.92, b = 0.72, c = 1.35 nm) by double tilting experiment with stereographic projection method (ex-situ TEM). The composition is proposed to be Au₃Si from EDAX. The real-time experiment shows the melting point depression of eutectic and competitive growth between eutectic and Au3Si phase. The composition of the film (i.e., gold-rich or silicon-rich) determines the formed phase. Rapid cooling experiments reveal that eutectic is supercooled down to much lower temperatures (∼135°C) than the Au₃Si phase (∼275°C).