Two-step thermal expansion of Au nanoparticles

• Main Authors: Cheng-Yen Lin, 林政延
• Other Authors: W.H. Li
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/83507383679056482222

碩士 === 國立中央大學 === 物理研究所 === 99 === The two-step thermal expansion phenomenon of 1.6 nm Au nanoparticles was observed in this study. Moreover, employing the direct observation technique of charge distribution reveals charge transference that affects thermal expansion. The gold nanoparticles powder was fabricated by employing the thermal evaporation method. The mean diameter of the sample is merely 1.6 nm determined by analyzing the X-ray diffraction pattern. Temperature-dependent X-ray diffraction patterns were measured to study the thermal evolution of lattice constant. The results reveal a two-step thermal expansion phenomenon demarcated at 200 K. The lattice constant wouldn’t vary obviously from 80 K to 200 K, and from 200 K to 300 K it’s thermal expansion. The X-ray diffraction patterns were also transformed into charge distribution maps through the Fourier function of GSAS. The results reveal charge transference that corresponds to the two-step thermal expansion. The electron gradually leaves from the region of positive charge from 80 K to 200 K which reduces the positive region, and that contends the phonon contribution to the expansion of lattice constant. The electron come into the positive region from 200 K to 300 K which expands the positive region and together with the phonon effect that cause thermal expansion of lattice constant.