Localized surface curvature artifacts in tip-enhanced nanospectroscopy imaging

E Sheremet; L Kim; D Stepanichsheva; V Kolchuzhin; A Milekhin; D R T Zahn; R D Rodriguez

doi:10.1016/j.ultramic.2019.112811

Localized surface curvature artifacts in tip-enhanced nanospectroscopy imaging

Ultramicroscopy. 2019 Nov:206:112811. doi: 10.1016/j.ultramic.2019.112811. Epub 2019 Jul 4.

Authors

E Sheremet¹, L Kim¹, D Stepanichsheva¹, V Kolchuzhin², A Milekhin³, D R T Zahn⁴, R D Rodriguez⁵

Affiliations

¹ Tomsk Polytechnic University, 30 Lenin Ave, 634050 Tomsk, Russia.
² Qorvo Munich GmbH, Konrad-Zuse-Platz 1, D-81829 Munich, Germany; Chemnitz University of Technology, D-09107 Chemnitz, Germany.
³ Rzhanov Institute of Semiconductor Physics of the Siberian Branch of the RAS, 630090 Novosibirsk, Russia.
⁴ Chemnitz University of Technology, D-09107 Chemnitz, Germany.
⁵ Tomsk Polytechnic University, 30 Lenin Ave, 634050 Tomsk, Russia. Electronic address: raul@tpu.ru.

PMID: 31310887
DOI: 10.1016/j.ultramic.2019.112811

Abstract

Tip-enhanced Raman spectroscopy (TERS) allows the chemical analysis with a spatial resolution at the nanoscale, well beyond what the diffraction limit of light makes possible. We can further boost the TERS sensitivity by using a metallic substrate in the so-called gap-mode TERS. In this context, the goal of this work is to provide a generalized view of imaging artifacts in TERS and near-field imaging that occur due to tip-sample coupling. Contrary to the case of gap-mode with a flat substrate where the size of the enhanced region is smaller than the tip size when visualizing 3D nanostructures the tip convolution effect may broaden the observed dimensions due to the local curvature of the sample. This effect is particularly critical considering that most works on gap-mode TERS consider a perfectly flat substrate which is rarely the case in actual experiments. We investigate a range of substrates to evidence these geometrical effects and to obtain an understanding of the nanoscale curvature role in TERS imaging. Our experimental results are complemented by numerical simulations and an analogy with atomic force microscopy artifacts is introduced. As a result, this work offers a useful analysis of gap-mode TERS imaging with tip- and substrate-related artifacts furthering our understanding and the reliability of near-field optical nanospectroscopy.

Keywords: Imaging artifacts; Nanospectroscopy; Plasmonics; Scanning probe microscopy; TERS.