Abstract
In scanning tunneling microscopy, we witness in recent years a paradigm shift from "just imaging" to detailed spectroscopic measurements at the nanoscale and multi-tip scanning tunneling microscope (STM) is a technique following this trend. It is capable of performing nanoscale charge transport measurements like a "multimeter at the nanoscale." Distance-dependent four-point measurements, the acquisition of nanoscale potential maps at current carrying nanostructures and surfaces, as well as the acquisition of I - V curves of nanoelectronic devices are examples of the capabilities of the multi-tip STM technique. In this review, we focus on two aspects: How to perform the multi-tip STM measurements and how to analyze the acquired data in order to gain insight into nanoscale charge transport processes for a variety of samples. We further discuss specifics of the electronics for multi-tip STM and the properties of tips for multi-tip STM, and present methods for a tip approach to nanostructures on insulating substrates. We introduce methods on how to extract the conductivity/resistivity for mixed 2D/3D systems from four-point measurements, how to measure the conductivity of 2D sheets, and how to introduce scanning tunneling potentiometry measurements with a multi-tip setup. For the example of multi-tip measurements at freestanding vapor liquid solid grown nanowires, we discuss contact resistances as well as the influence of the presence of the probing tips on the four point measurements.
Highlights
We witness in recent years a paradigm shift from “just imaging” to detailed spectroscopic measurements at the nanoscale and multi-tip scanning tunneling microscope (STM) is a technique following this trend
We focus on two aspects: How to perform the multi-tip STM measurements and how to analyze the acquired data in order to gain insight into nanoscale charge transport processes for a variety of samples
While the electronics scheme described above is the usual way the current and voltage measurement is conducted with a multi-tip STM, we recently proposed an alternative method for the voltage probing using current probes with voltage feedback to measure electric potentials.[54]
Summary
Shift in scanning probe microscopy which transforms from “just imaging” to detailed spectroscopic measurements at the nanoscale. New students only need a couple of months to become acquainted with the multi-tip STM and can subsequently concentrate on scientific topics. Another issue is that a novice in this technique might not be aware of details of the experimental techniques as they are scattered over the literature, or might, as it is nowadays the habit, not be mentioned any more at all. If the voltage measurement is performed with a large internal resistance RV Rsample + 2RC (or with a compensation method), the influence of the contact resistances can be neglected.[53] This is the main advantage of the four-point measurement. The four-point resistance is given by the measured voltage difference divided by the injected current
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