RESUMO
This work investigates the early stage evolution of thermally nucleated microbubbles in water using in situ high-speed, 400 fps, transmission electron microscopy. A Pt wire Joule heater induced bubble nucleation and growth from air-saturated water at different levels of power. For all powers below Pt breakdown, the dissolved gas initiates bubble nucleation at the concave surface defects adjacent to the area of highest temperature. A combination of interfacial forces and stress relaxation drive rapid migration of the bubbles away from the nucleation site. Thermocapillary forces ultimately dominate and drive their return to the region of highest temperature. The dynamic response highlights the importance of this length and time domain, which has until now received limited direct study.
RESUMO
The early stages of gas evolution during electrolytic hydrogen production on Au electrodes are characterized by in situ transmission electron microscopy. The results demonstrate that reaction product molecules initially dissolve into solution and then nucleate near, but not on, the electrodes. The gas subsequently wets the electrodes and its successive evolution is governed by triple phase boundary line motion.
RESUMO
An in situ platform for characterizing plasma-materials interactions at the nanoscale in the transmission electron microscope (TEM) has been demonstrated. Integrating a DC microplasma device, having plane-parallel electrodes with a 25â nm thick Au film on both the cathode and anode and operating in 760 Torr of Ar, within a TEM provides real-time observation of Au sputtering and island formation with a spatial resolution of < 100â nm. Analyses of TEM and atomic force microscopy images show the growth of Au islands to proceed by a Stranski-Krastanov process at a rate that varies linearly with the discharge power and is approximately a factor of 3 larger than the predictions of a DC plasma sputtering model. The experiments reported here extend in situ TEM diagnostics to plasma-solid and plasma-liquid interactions.