Transport Measurements of Surface Electrons in 200-nm-Deep Helium-Filled Microchannels Above Amorphous Metallic Electrodes


We report transport measurements of electrons on helium in a microchannel device where the channels are 200 nm deep and \(3\,\mu \hbox {m}\) wide. The channels are fabricated above amorphous metallic \(\hbox {Ta}_{40}\hbox {W}_{40}\hbox {Si}_{20}\), which has surface roughness below 1 nm and minimal variations in work function across the surface due to the absence of polycrystalline grains. We are able to set the electron density in the channels using a ground plane. We estimate a mobility of \({300}\,\hbox {cm}^2/\hbox {V}\,\hbox {s}\) and electron densities as high as \(2.56\times 10^{9}\,\hbox {cm}^{-2}\). We demonstrate control of the transport using a barrier which enables pinch-off at a central microchannel connecting two reservoirs. The conductance through the central microchannel is measured to be 10 nS for an electron density of \(1.58\times 10^{9}\,\text {cm}^{-2}\). Our work extends transport measurements of surface electrons to thin helium films in microchannel devices above metallic substrates.

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Devices were fabricated in the Princeton Institute for the Science and Technology of Materials Micro/Nano Fabrication Laboratory and the Princeton University Quantum Device Nanofabrication Laboratory. Work at Princeton was supported by the NSF, in part through Grant No. DMR-1506862, and in part through the Princeton MRSEC (Grant No. DMR-1420541). Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

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Asfaw, A.T., Kleinbaum, E.I., Henry, M.D. et al. Transport Measurements of Surface Electrons in 200-nm-Deep Helium-Filled Microchannels Above Amorphous Metallic Electrodes. J Low Temp Phys 195, 300–306 (2019).

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