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

Abstract

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.