5:15 PM - 7:15 PM
[MIS13-P03] Nucleation process of metal oxide nanoparticles from the gas phase by in-situ IR spectroscopy
Keywords:crystal growth
Experiments on the generation of nanoparticles from the gas phase using the gas evaporation method have been conducted for a long time, but the nucleation process has not been fully elucidated. In addition, it is known that the crystal structure of nanoparticles thus produced may have different properties even if they have the same crystallinity as bulk crystals. To clarify the nucleation process of such nanoparticles, our laboratory originally developed an infrared (IR) in-situ measurement system for free-flying nanoparticles. Using this system, it is possible to measure the IR spectrum of nanoparticles during vapor phase growth in situ. The IR spectrum can show the state of the particles (crystal or amorphous) and the change in the crystal structure until they become final state at room temperature. In this study, we conducted a nucleation experiment from the gas phase using the gas evaporation method using molybdenum oxide, a substance that was tested in previous studies, and tungsten oxide.
First, the inside of the chamber was evacuated (up to 10-2 Pa) using a vacuum pump. Then, argon gas and oxygen gas were injected, and the molybdenum or tungsten wires, which was the evaporation sources, were heated by passing an electric current through them. The heated and evaporated molybdenum or tungsten oxide is cooled and condensed due to a temperature gradient that depends on the distance from the evaporation source. During this process, particles are generated near the evaporation source. Since this IR system can measure IR spectra at different distances from the evaporation source, it is possible to investigate the nucleation pathway by measuring the IR spectrum of the process from gas to crystal via nucleation processes. Evaporated and condensed particles were collected on a transmission electron microscope (TEM) observation grid installed directly above the evaporation source in the chamber and on the top of the chamber. The collected particles were observed with TEM to examine their shape and crystal structure, and the particles collected at the top of the chamber were mixed with KBr and their IR spectra were measured and compared with the in situ IR spectra. TEM observations confirmed that as the crystals grew, molybdenum oxide changed from needle-shaped to plate-shaped, and tungsten oxide changed to an octahedral shape. It was confirmed that the size also changes due to growth caused by collisions and merging of particles in the gas.
First, the inside of the chamber was evacuated (up to 10-2 Pa) using a vacuum pump. Then, argon gas and oxygen gas were injected, and the molybdenum or tungsten wires, which was the evaporation sources, were heated by passing an electric current through them. The heated and evaporated molybdenum or tungsten oxide is cooled and condensed due to a temperature gradient that depends on the distance from the evaporation source. During this process, particles are generated near the evaporation source. Since this IR system can measure IR spectra at different distances from the evaporation source, it is possible to investigate the nucleation pathway by measuring the IR spectrum of the process from gas to crystal via nucleation processes. Evaporated and condensed particles were collected on a transmission electron microscope (TEM) observation grid installed directly above the evaporation source in the chamber and on the top of the chamber. The collected particles were observed with TEM to examine their shape and crystal structure, and the particles collected at the top of the chamber were mixed with KBr and their IR spectra were measured and compared with the in situ IR spectra. TEM observations confirmed that as the crystals grew, molybdenum oxide changed from needle-shaped to plate-shaped, and tungsten oxide changed to an octahedral shape. It was confirmed that the size also changes due to growth caused by collisions and merging of particles in the gas.