Electron Transport on Helium Films in Confined Geometry

Abstract

In this work, investigations on the transport of electrons on liquid helium films through narrow channels using suitable substrate structures, microfabricated on a silicon wafer which resembles Field E ect Transistors (we call it He-FET) have been presented. The sample has Source and Drainregions, separated by a Gate structure, which consists of 2 gold electrodes with a narrow gap (channel) through which the electron transport takes place. The electron densities on the source and drain are determined directly by electrical method. For time-resolved measurements, a pulse of electrons from a small lament is rst collected on the source area, and then the passage of this pulse through the channel of the split gate towards the drain is monitored. This allows determining the electron transport of surface state electrons in channels of various dimensions and for a wide range of electron densities. The study of the potential distribution across the He-FET sample resultsin a new model of number of saved electrons as a function of gate voltage. Therefore, this model helped much in understanding the whole 2-DES using He-FET and makes it easy to study the electron transport of such sample. This work can be summarized in the following points:a) we improved the maximum electron densities which have been observed for the He-FETs by making new samples with more de ned structure dimensions,b) we did time resolved measurements which guided us to study the potential distribution across the sample,c) we studied the potential distribution across the sample which we used and which has been used by the people who work in this experimental set-up before in more detail, d) using this potential distribution studies, we developed a model of saved electrons as a function of gate barrier which could be used as a basic model to study the transport of surface state electrons,e) we used a new method to study the transport of the electrons on the liquid helium lms by pulsing (opening the gate for a short time) the gate.f) some improvement in the experimental set-up were made and used for the rst time, for example the step-motor which calibrated with the cylindrical capacitor to determine the helium level. so this work is done under de ned conditions better than before.In general we are getting more insight into the system by studying the electron transport on helium films using such geometry.