| dc.description.abstract | Most substances will thermally expand with increasing temperature, but the phenomenon of negative thermal expansion of substances, the so-called thermal contraction, is not uncommon. This phenomenon is mostly caused by anisotropic structures, and the thermal contraction of isotropic structures is often accompanied by structural change. The most widely known thermal contraction is the thermal contraction of liquid water below 4°C, which is also due to the change in the bond angle of water molecules. In the 2002 paper of this laboratory, the thermal contraction of 4 nm gold nanoparticles was also found [1], which was explained by the quantum scale effect. Later, the Professor Chun-Chuen Yang also discovered the thermal contraction of silver nanoparticles in the 2006 experiment.
In this thesis, the temperature define X-ray diffraction data made by Professor Chun-Chuen Yang will be used for lattice constant and electron distribution analysis. First, we found that the thermal contraction at 10 to 60 K in Ag NPs with a particle size as small as 5 nm, and the abnormal thermal expansion in both 5 nm and 9 nm samples . In the second half of the thesis, I calculated the changes of the electron distribution to observe the corresponding changes when thermal contraction happened, and found that 5 nm Ag NPs transfer electrons to the outer layer when thermal contraction happened then returns to the inner layer of the Ag ion after thermal expansion. | en_US |