Role of bias voltage and tunneling current in the perpendicular displacements of freestanding graphene via scanning tunneling microscopy

TL;DR

This study investigates how bias voltage and tunneling current influence the perpendicular displacements of freestanding graphene in STM, combining experimental measurements with electrostatic and entropic models to elucidate the underlying mechanisms.

Contribution

It provides a quantitative electrostatic model for bias voltage effects and a qualitative entropic model for tunneling current effects on graphene displacement.

Findings

Increased bias voltage causes graphene to approach the STM tip.

Higher tunneling current results in graphene contracting away from the tip.

Models clarify the distinct roles of voltage and current in graphene displacement.

Abstract

Systematic displacement measurements of freestanding graphene as a function of applied bias voltage and tunneling current setpoint using scanning tunneling microscopy (STM) are presented. When the bias voltage is increased the graphene approaches the STM tip, while, on the other hand, when the tunneling current is increased the graphene contracts from the STM tip. To understand the role of the bias voltage, we quantitatively model the attractive force between the tip and the sample using electrostatics. For the tunneling current, we qualitatively model the contraction of the graphene using entropic concepts. These complementary results enhance the understanding of each other and highlight peculiarities of the system.