Nanoscale tip positioning with a multi-tip scanning tunneling microscope using topography images

TL;DR

This paper presents a method for nanoscale tip positioning in multi-tip STM using topography images, enabling accurate tip placement without relying solely on SEM imaging, thus improving charge transport measurements at the nanoscale.

Contribution

It introduces an STM-based approach for determining tip positions through topography image recognition, offering an alternative to SEM for nanoscale tip calibration.

Findings

Achieved approximately 20 nm tip positioning accuracy.

Used topography images for tip recognition and calibration.

Demonstrated effective correction of piezoelectric non-linearities.

Abstract

Multi-tip scanning tunneling microscopy (STM) is a powerful method to perform charge transport measurements at the nanoscale. With four STM tips positioned on the surface of a sample, four-point resistance measurements can be performed in dedicated geometric configurations. Here, we present an alternative to the most often used scanning electron microscope (SEM) imaging to infer the corresponding tip positions. After initial coarse positioning monitored by an optical microscope, STM scanning itself is used to determine the inter-tip distances. A large STM overview scan serves as a reference map. Recognition of the same topographic features in the reference map and in small scale images with the individual tips allows to identify the tip positions with an accuracy of about 20 nm for a typical tip spacing of ~1 $\mu$m. In order to correct for effects like the non-linearity of the deflection, creep and hysteresis of the piezo-electric elements of the STM, a careful calibration has to be performed.