A versatile high resolution scanning tunneling potentiometry implementation

Abstract

We have developed a new scanning tunneling potentiometry technique which can-with only minor changes of the electronic setup-be easily added to any standard scanning tunneling microscope (STM). This extension can be combined with common STM techniques such as constant current imaging or scanning tunneling spectroscopy. It is capable of performing measurements of the electrochemical potential with microvolt resolution. Two examples demonstrate the versatile application. First of all, we have determined local variations of the electrochemical potential due to charge transport of biased samples down to angstrom length scales. Second, with tip and sample at different temperatures we investigated the locally varying thermovoltage occurring at the tunneling junction. Aside from its use in determining the chemical identity of substances at the sample surface our method provides a controlled way to eliminate the influence of laterally varying thermovoltages on low-bias constant current topographies.

Spatial extent of a Landauer residual-resistivity dipole in graphene quantified by scanning tunnelling potentiometry

“…The measurements are made at different values of the electron current in the sample plane, especially at zero and forward and reversed current as defined by the potential applied to the sample contacts. The details of our specific setup are published elsewhere 31 .…”

“…1a). This voltage V STP ¼ m ECP e has been referred to as the local ECP, which is here inherently defined by the STP method 2,6,31 . The measurements are made at different values of the electron current in the sample plane, especially at zero and forward and reversed current as defined by the potential applied to the sample contacts.…”

Energy Gap Induced by Friedel Oscillations Manifested as Transport Asymmetry at Monolayer-Bilayer Graphene Boundaries

“…In this case, the voltage noise in potentiometry is dominated by thermal noise that is ΔV ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 4k B TR T Δf p , where Δf is the bandwidth [22]. A resolution better than 10 μV can be achieved at low temperatures [23].…”

Four-point probe measurements using current probes with voltage feedback to measure electric potentials

“…For this purpose, the amount of current through the tip at a certain tip bias voltage V bias is read into the measurement software via an ADC converter and the feedback loop nulls the tip-sample current by continuously adjusting V bias via a digital-toanalog converter (DAC) connected to the V bias input of that tip, until V bias = V local [11,15].…”

“…An alternative way to measure local sample potentials in a STM is the scanning tunneling potentiometry method [11,14,15]. In this method, the voltage applied to the tip is controlled by a feedback loop, such that the current to the sample vanishes, i.e.…”