Melting of Metal Nanoparticles and Effects on the Surface Plasmon Resonance

Zn nanoparticles at room temperature show two absorption peaks in the near-infrared (NIR) and the ultraviolet (UV) regions, both of which satisfy the criterion of surface plasmon resonance (SPR). From X-ray diffraction at high temperatures, it was found that the Zn nanoparticles in SiO₂ melt at 360-420°C and solidify at 250-310°C with a large temperature hysteresis. While the NIR peak disappears with melting, the UV peak shows sudden energy shift with melting but survives even after the melting. The first-principle band calculation ascribes the UV and NIR peaks to SPR-enhanced inter- and intra-band transitions, respectively.