Closed-loop conductance scanning tunneling spectroscopy: demonstrating the equivalence to the open-loop alternative.

Chris Hellenthal,Harold J W Zandvliet,Martin H Siekman,E Stefan Kooij,Kai Sotthewes

doi:10.3762/bjnano.6.113

Abstract

We demonstrate the validity of using closed-loop z(V) conductance scanning tunneling spectroscopy (STS) measurements for the determination of the effective tunneling barrier by comparing them to more conventional open-loop I(z) measurements. Through the development of a numerical model, the individual contributions to the effective tunneling barrier present in these experiments, such as the work function and the presence of an image charge, are determined quantitatively. This opens up the possibility of determining tunneling barriers of both vacuum and molecular systems in an alternative and more detailed manner.

Highlights

The scanning tunneling microscope (STM) has been used for the topographical imaging of conductive samples since the early 1980s [1], recent times have seen an increasing interest in the possibilities ofquantitative analysis offered by scanning tunneling spectroscopy (STS)
local density of states of a sample (LDOS) information is typically extracted through open-loop I(V) measurements, recent studies have reported on the possibility of obtaining LDOS information by using closed-loop z(V) measurements [5,6,7,8]
This shows that it is quite difficult to discriminate between the contributions of the effective work function and the image charge, as a change in one variable can be readily masked by a change in the other

Summary

Introduction

The scanning tunneling microscope (STM) has been used for the topographical imaging of conductive samples since the early 1980s [1], recent times have seen an increasing interest in the possibilities of (semi-)quantitative analysis offered by scanning tunneling spectroscopy (STS). STS measurements are typically performed in a X(Y) format, where variable Y is actively driven and the response of variable X is measured, with all other system variables being kept constant. Numerous types of STS techniques can be and have been performed on a wide variety of samples, with each different type of measurement yielding information on distinct properties of the probed sample [2]. The local density of states of a sample (LDOS) provides insight into the electronic and chemical properties of a sample. LDOS information is typically extracted through open-loop I(V) measurements, recent studies have reported on the possibility of obtaining LDOS information by using closed-loop z(V) measurements [5,6,7,8]

Methods

Results

Conclusion