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

TL;DR

This study demonstrates transport measurements of surface electrons in ultra-narrow, deep helium-filled microchannels fabricated above amorphous metallic electrodes, revealing high electron mobility and controllable conductance.

Contribution

It introduces a novel microchannel device with amorphous metallic electrodes for surface electron transport measurements, achieving high electron densities and mobility in thin helium films.

Findings

Electron mobility estimated at 300 cm²/V·s.

Electron densities up to 2.56×10⁹ cm⁻² achieved.

Conductance of 10 nS measured at specific density.

Abstract

We report transport measurements of electrons on helium in a microchannel device where the channels are 200 nm deep and 3 $\mu$m wide. The channels are fabricated above amorphous metallic Ta$_{40}$W$_{40}$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 cm$^2$/V$\cdot$s and electron densities as high as 2.56$\times$10$^9$ cm$^{-2}$. We demonstrate control of the transport using a barrier which enables pinchoff 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$ cm$^{-2}$. Our work extends transport measurements of surface electrons to thin helium films in microchannel devices above metallic substrates.