Self-Consistent Tip Conditioning for Tip-Enhanced Raman Spectroscopy in an Ambient Environment

Abstract

Tip-enhanced Raman spectroscopy (TERS), which uses plasmons formed between the metallic tip and the sample upon laser irradiation, has emerged as a promising analytical method that is applicable in various environments. However, the practical use of TERS combined with scanning tunneling microscopy (STM) in an ambient environment has not reached its full potential thus far; this is because the atomic-scale geometry near the tip apex plays a crucial role in stable STM imaging, whereas plasmon enhancement for TERS is achieved on a submicron-scale tip structure, rendering it difficult to select an appropriate tip in advance. Herein, we propose a specific and simple method for tip conditioning that utilizes local heating through plasmon excitation in a self-consistent manner. This method is established on the basis of the characterizations of the tip shape and plasmonic properties. Accordingly, we demonstrate stable STM imaging compatible with reliable TERS measurements using the preconditioned tip.

Underpotential Deposition of Silver on Gold for Surface Catalysis of Plasmon-Enhanced Reduction of 4-Nitrothiophenol

“…Plasmon-enhanced Raman spectroscopy, e.g., SERS and tip-enhanced Raman spectroscopy (TERS), has been applied to determine the structural and chemical states of adsorbed molecules on surfaces. − In this study, a monolayer of 4-NTP was analyzed based on the high chemical sensitivity of SERS. The SERS spectrum of 4-NTP/roughened Au (labeled as 4-NTP/Au in the following text) contained Raman peaks mainly due to the in-plane vibrational modes of 4-NTP (Figures S6, S7 and Table S1).…”

“…Further evaluation of the role of UPD surfaces may be possible using well-defined substrate surfaces, such as single crystalline surfaces, and spatially resolved analysis methods, such as TERS. 30,[31][32][33][34][35][36][37][38][39][40][41]45 ■ ASSOCIATED CONTENT * sı Supporting Information…”

“…Because of the irregular surface morphology of the roughened Au electrode used for SERS, it was not possible to directly correlate the microscopic structures of the UPD-modified surfaces to the interfacial behaviors of molecular adlayers. Further evaluation of the role of UPD surfaces may be possible using well-defined substrate surfaces, such as single crystalline surfaces, and spatially resolved analysis methods, such as TERS. ,− , …”

Monatomic Iodine Dielectric Layer for Multimodal Optical Spectroscopy of Dye Molecules on Metal Surfaces

“…It is particularly interesting to modulate and control the optical properties of dye molecules close to metal by applying electrochemical potentials. In addition, near-field spectroscopy, which has shown remarkable progress in recent years, can be used to evaluate these responses with high spatial resolution, ,− ,,, making it possible to expand our strategy to molecular-scale multimodal measurements in practical catalytic chemistry and electrochemistry.…”

“…The setup for optical spectroscopy is described elsewhere. ,, The incident laser, 633 nm laser diode (Lambda Beam, 633-70 WL, RGB Photonics), was focused by a long working distance objective lens (WD = 17 mm, NA = 0.45, Nikon) from the surface normal direction. ,, The laser power was kept at 0.02 mW, as measured at the sample position. The irradiation area was ∼2 μm 2 .…”