No abstract

No abstract

We apply a thin film bulk acoustic resonator for hydrogen detection. The resonator working at 2.39 GHz consists of a ZnO piezoelectric stack and an Al/W Bragg reflector. A Pd film is coated on the top of a piezoelectric film as the electrode and sensing coating to capture hydrogen. The resonance frequency of the resonator reduces progressively with the increase of hydrogen concentration due to the mass addition on the Pd layer after hydrogenation. The experimental results show that our proposed sensor can yield the sensitive, linear, reversible, repeatable and stable responses to hydrogen in the concentration range of 0.05%–3% at room temperature. The limit of detection at room temperature is as low as 0.05%. This study proves that the thin film bulk acoustic resonator is a promising and feasible platform for the hydrogen sensor working at room temperature.

A temperature window for the synthesis of single-walled carbon nanotubes by catalytic chemical vapor deposition of CH 4 over Mo 2 -Fe 10 /MgO catalyst has been studied by Raman spectroscopy. The results showed that when the temperature is lower than 750°C, there were few SWCNTs formed, and when the temperature is higher than 950°C, mass amorphous carbons were formed in the SWCNTs bundles due to the self-decomposition of CH 4 . The temperature window of SWCNTs efficient growth is between 800 and 950°C, and the optimum growth temperature is about 900°C. These results were supported by transmission electron microscope images of samples formed under different temperatures. The temperature window is important for large-scale production of SWCNTs by catalytic chemical vapor deposition method.

Gas flow characteristics in nanopores were investigated experimentally and numerically using molecular dynamics (MD) simulations with an emphasis on the friction factor and gas viscosity. The results show that the viscosity and the friction factor in nanopores are much lower than those in macroscale channels. The actual viscosities obtained from the MD studies showed that the gas viscosity in nanopores is less than the macroscale viscosity because collisions between gas molecules are less frequent in high Knudsen number flows and there are more collisions with the wall. The MD simulations show that the velocity profile is composed of two parts, with a much steeper velocity gradient near the wall. gas flow, nanopore, friction factor, molecular dynamics simulation Citation:Liu Q X, Jiang P X, Xiang H. Experimental and molecular dynamics study of gas flow characteristics in nanopores.