Bubble template synthesis of hollow gold nanoparticles

In this research, the formation mechanism of hydrogen nanobubble and the reduction mechanism of gold shell were observed by in-situ and ex-situ study techniques. Phase Sensitive Interferometry Technique (PSI) is employed for monitoring the formation of hollow gold nanoparticles. PSI is a new in-situ study technique for observing the formation of hollow gold nanoparticles during electrodeposition without interruption the formation process. From our results, it shows that Phase Sensitive Interferometry technique (PSI) can detect the formation of hydrogen nanobubble and the reduction of gold ion on hydrogen nanobubble surface during electrodeposition. The formation process was detected by monitoring the modulation shifted due to the optical path length and the amplitude depth changed due to the refractive index. From our results, nanobubbles were initiated after around 200 seconds and then gold shell form on the nanobubble surface and becomes hollow gold nanoparticles. These results show an agreement with our hypothesis that the bubble template synthesis method can be used for creating hollow gold nanoparticles.;From our results, PSI technique has a potential to monitor the formation of hollow gold nanoparticles during electrodeposition that might be applied to use with other in-situ study in other electrodeposition process. Underpotential Deposition technique (UPD) is a term given to the phenomenon when a single layer of atoms can be electrochemically deposited onto another metal surface that is a good formation process for testing the sensitivity of PSI. However, many researchers studied in-situ study of UPD but this is the first time for in-situ study of UPD using PSI or any optical properties technique. This PSI technique is more suitable for study the formation of monolayer than other technique because PSI does not interrupt the fabrication process. From our results, it shows that PSI is success to detect the formation of one monolayer of copper on gold-coated mica substrate.;Not only an understanding the formation process of hollow gold nanoparticles is a main propose of this project but the understanding of size, thickness and morphology tunability of hollow gold nanoparticles is also interested. Size, thickness and morphology of hollow gold nanoparticles affect on the optical properties of hollow gold nanoparticles and can be tuned by changing the synthesis parameter. The effect of synthesis parameter will be ex-situ studied using transmission electron microscopy (TEM) and scanning electron microscopy (SEM).;As mentioned before, this synthesis process is separated into two main processes 1) the formation of hydrogen nanobubble and 2) the reduction of gold shell. The effect of synthesis parameters on the formation of hydrogen nanobubbles is included: 1) hydrogen evolution enhancer, 2) applied potential, 3) deposition time, and 4) pore size of template. Following our results, the number of hydrogen nanobubbles increases whereas either the concentration of hydrogen evolution enhancer, overpotential, or deposition time increases. On the other hand, the size of hydrogen nanobubbles significantly decreases with increasing of overpotential or decreasing of pore size of template and hydrogen evolution enhancer concentration.;The reduction of gold shell is controlled by synthesis parameters that also affect on size, number, and morphology of hollow gold nanoparticles. The synthesis parameters in this part are involved: 1) applied potential, 2) gold ion concentration and 3) stabilizer. From our results, the number of gold nanoparticles increases while the size of gold nanoparticles decreases with the increasing of applied potential or gold ion concentration. On the other hand, the increasing of stabilizer concentration decreases gold ion concentration. Therefore, the number of gold nanoparticles decreases while the size of gold nanoparticles increases by increasing the stabilizer concentration. Moreover, the porosity of gold shell can be tuned by varying either the concentration of gold ion or the concentration of stabilizer. (Abstract shortened by UMI.).