Gas Permeation of Graphite Sealed Microcavities

Yanxin Liu

Research output: Book/ReportPh.D. thesis

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This thesis examines the permeability of ultrathin graphite sealed SiOmicrocavities, by using a high-speed cavity array chip scanner designed based on the Fabry-Pérot interferometer. This work is a prerequisite for realizing catalytic measurement of single nanoparticles on the cavity array chips.
The high-speed cavity array chip scanner measures the resonance frequency of the graphene or graphite membrane and convert the frequency to the internal pressure of the cavities. The basic optical setup for measuring the resonance frequency has been widely used in previous studies. By integrating machine vision and automation techniques, an automatic scanning function is implemented, which is able to scan the cavity arrays without manual operations. The scanning speed and scanning area are orders of magnitudes higher than other measurement techniques for detecting the cavity internal pressure (e.g., atomic force microscope).
After measuring the leak rates of different gas species, we observe that the leak rates of water-insoluble gases are correlated to the kinetic diameter of the gas molecules. Water-soluble gases tend to leak much faster than waterinsoluble gases, which indicates that water or a water-like interlayer on the leakage path may facilitate the leakage.
Diffusion of He and H2 through the SiO2 layer of the cavities are measured at room temperature. It is shown that for certain types of the cavities, the Hdiffusion through the SiO2 layer could significantly elevate the overall leak rate. For He, this is a more universal behavior for all types of cavities.
We also investigate the permeability of the cavities at high temperatures up to 175 °C. The leak rates at high temperatures are significantly increased. A temperature threshold is determined by comparing the leak rate at a series of temperatures. Below the threshold, the sample is impermeable (neglecting a very small leak rate), and above the threshold, the leak rates increase with the temperatures in the measurement temperature interval. Sample-to-sample variation of the threshold is also observed and need to be investigated in the future.
Original languageEnglish
PublisherDepartment of Physics, Technical University of Denmark
Number of pages137
Publication statusPublished - 2022


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