Anomalous Tip-Sample Distance Behavior on the Tip-Enhanced Raman Spectroscopy of Graphene in Ambient Conditions

TL;DR

This study investigates unusual tip-sample distance effects in TERS measurements of graphene, attributing the anomalies to a liquid meniscus caused by capillary forces, and highlights the importance of accurate tip control.

Contribution

It reveals the impact of a liquid meniscus on TERS measurements of graphene and introduces a model to account for anomalous tip-sample distance behavior.

Findings

Anomalous decay profile of TERS intensity linked to capillary forces.

Effective tip-sample distance must include a deformation term for accurate analysis.

High TERS efficiency enables detailed investigation of tip-sample interactions.

Abstract

Tip-Enhanced Raman Spectroscopy (TERS) combines Raman spectroscopy with scanning probe microscopy to overcome the spatial resolution limitation imposed by light diffraction, offering a primary optical technique for the comprehensive study of two-dimensional (2D) materials. In this work, we investigate an anomalous decay profile of the TERS intensity of the graphene 2D band as the tip-sample separation changes, observations enabled by high TERS efficiency and accuracy in tip-approach and tip-retract procedures. The anomalous results can be properly described by the addition of an ad hoc deformation to the effective tip-sample distance, rationalized here as due to the presence of a liquid meniscus formed via capillary forces.