An in situ study on the coalescence of monolayer-protected Au-Ag nanoparticle deposits upon heating
1 Department of Materials Science and Engineering, National Chung Hsing University, Taichung 402, Taiwan
2 Department of Materials Science and Engineering, National Dong Hwa University, Hualien 974, Taiwan
3 Department of Materials Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan
4 National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan
Nanoscale Research Letters 2014, 9:438 doi:10.1186/1556-276X-9-438Published: 27 August 2014
The structural evolution of thiolate-protected nanoparticles of gold, silver, and their alloys with various Au/Ag ratios (3:1, 1:1, and 1:3) upon heating was investigated by means of in situ synchrotron radiation X-ray diffraction. The relationships between the coalescence and composition of nanoparticles, as well as the surfactant reactions, were clarified. Experimental results show that there existed a critical temperature ranging from 120°C to 164°C, above which the tiny broad X-ray diffraction peaks became sharp and strong due to particle coalescence. The coalescence temperatures for alloy nanoparticle deposits were clearly lower than those for pure metals, which can be ascribed to the rivalry between the thermodynamic effect due to alloying and the interactions between surface-assembled layers and the surface atoms of the nanoparticles. The strong affinity of thiolates to Ag and thus complex interactions give rise to a greater energy barrier for the coalescence of nanoparticles into the bulk and subsequent high coalescence temperature. The influences of particle coalescence on the optical and electrical properties of the nanoparticle deposits were also explored.