Tip-Enhanced Raman Scattering Imaging of Single- to Few-Layer Ti₃C₂T_x MXene

Abstract

MXenes are among the most widely researched materials due to a unique combination of high electronic conductivity and hydrophilic surface, confined in a 2D structure. Therefore, comprehensive characterization of individual MXene flakes is of great importance. Here we report on nanoscale Raman imaging of single-layer and few-layer flakes of Ti3C2T x MXene deposited on a gold substrate using tip-enhanced Raman scattering (TERS). TERS spectra of MXene monolayers are dominated by an intense peak at around 201 cm–1 and two well-defined peaks at around 126 and 725 cm–1. Absolute intensities of these peaks decrease with increasing number of layers, though the relative intensity of the 126 and 725 cm–1 bands as compared to the 201 cm–1 band increases. The peak positions of the main MXene bands do not significantly change in flakes of different number of layers, suggesting weak coupling between the MXene layers. In addition, we observed stiffening of the 201 cm–1 vibration over the wrinkles in MXene flakes. Using TERS for nanoscale spectroscopic characterization of Ti3C2T x allows fast Raman mapping with deep subdiffraction resolution at the laser power density on the sample about an order of magnitude lower as compared to confocal Raman measurements. Finally, we demonstrate very high environmental stability of stoichiometric single-layer MXenes and show that the intensity of TERS response from the single- and few-layer flakes of Ti3C2T x can be used to track early stages of degradation, well before significant morphological changes appear.

Tip-Enhanced Raman Imaging of Photocatalytic Processes at the Nanoscale

“…74 A growing body of evidence suggests that the interplay between plasmonic and catalytic metals, as well as the nanoscale localization of these two metals, determines the yield of photocatalytic reactions. 32,33 Therefore, TERS imaging of BMNS can be used to tailor synthetic procedures that will allow for the fabrication of BMNS with desired photocatalytic properties.…”

“…For instance, the Gogotsi group utilized TERS to analyze singlelayer and few-layer flakes of Ti 3 C 2 T x MXene deposited on a gold substrate. 33 The researchers found that TERS could be used to reveal the environmental stability of stoichiometric single-layer MXenes and showed that the intensity of TERS responses from the single-and few-layer flakes of Ti 3 C 2 T x could be used to track early stages of degradation, well before significant morphological changes appear. The Kurouski group reported that TERS could be used to probe the photochemistry on copper nanocubes and nanowires (CuNCs and CuNWs, respectively).…”

“…The catalytic nanostructures, in turn, are capable of performing a much broader spectrum of chemical reactions compared to the reactions observed on NMNS. , Noble and catalytic metals may also form an alloy or can be simply copresent in one nanostructure in a “sandwich-like” geometry . A growing body of evidence suggests that the interplay between plasmonic and catalytic metals, as well as the nanoscale localization of these two metals, determines the yield of photocatalytic reactions. , Therefore, TERS imaging of BMNS can be used to tailor synthetic procedures that will allow for the fabrication of BMNS with desired photocatalytic properties.…”

“…One may also envision that unique nanoscale imaging properties of TERS will be utilized to improve the understanding about the physics of 2D and 3D materials. For instance, the Gogotsi group utilized TERS to analyze single-layer and few-layer flakes of Ti 3 C 2 T x MXene deposited on a gold substrate . The researchers found that TERS could be used to reveal the environmental stability of stoichiometric single-layer MXenes and showed that the intensity of TERS responses from the single- and few-layer flakes of Ti 3 C 2 T x could be used to track early stages of degradation, well before significant morphological changes appear.…”

“…In the former case, chemical information about that specific surface location can be obtained. The latter case allows for an acquisition of a chemical map of the sample with subnanometer spatial resolution. , During the past decade, this analytical approach, known as tip-enhanced Raman spectroscopy (TERS), has been broadly utilized for a large variety of applications including electrochemistry, ,− solid-state physics, − polymer science, − and biology. − …”