Unravelling the Thickness Dependence and Mechanism of Surface-Enhanced Raman Scattering on Ti₃C₂T_X MXene Nanosheets

Abstract

MXenes have attracted great attention as promising substrates for surface-enhanced Raman scattering (SERS) applications. However, the underlying SERS mechanism has not been a focus of any investigation. Herein, we report the first systematic experimental study on the SERS activity of titanium carbide (Ti3C2TX) nanosheets with thicknesses ranging from 5 to 120 nm, using methylene blue (MB) as a probe molecule. The experimental and mathematical modeling results show that the Raman enhancement factor (EF) increases monotonically with the increasing thickness of Ti3C2TX nanosheets; however, it falls drastically around a sheet thickness of 0.8 and 1.0 μm under 532 and 633 nm laser excitations, respectively. The Raman EF reaches a maximum value around a thickness of 2.0 μm, suggesting that a maximum EF can be achieved with a 2.0 μm-thick Ti3C2TX film substrate. The thickness dependence of the Raman enhancement can be accounted for by the adsorption and intercalation of MB molecules into the interlayer spacing of Ti3C2TX. Furthermore, by combining experimental observations and numerical calculation, we confirm that the charge-transfer mechanism is dominantly responsible for Raman enhancement on Ti3C2TX. Additionally, we report an observation of resonance coupling of charge transfer and molecular transition as a contributing factor to the higher EF obtained with a 633 nm laser excitation. Taken together, these findings have significant implications for cost and performance optimization in designing MXene-based SERS substrates for next-generation chemical and biological sensing platforms.

Interband, Surface Plasmon and Fano Resonances in Titanium Carbide (MXene) Nanoparticles in the Visible to Infrared Range

“…Afterwards, the following studies included other types of MXenes as well, such as nitride Ti 2 N, which yielded a notable enhancement factor of 10 12 [22]. Recently, more publications appeared on thickness dependence of SERS in Ti 3 C 2 T x nanosheets [23], or for using it as a SERS active substrate for reliable and sensitive detection of organic pollutants [24]. A systematic theoretical understanding of the optical properties of MXenes is not developed yet, which makes difficult the interpretation of all the experimental data.…”

Noncovalent functionalization of Ti3C2TX using cationic porphyrins with enhanced stability against oxidation

“…4B shows the mean Raman spectra of the Ti 3 C 2 T X and the hybrids, measured using a laser at an excitation wavelength of 532 nm. The Ti 3 C 2 T X showed several Raman bands: the one at 148 cm -1 is assigned to the Eg vibrational mode of anatase TiO 2 , 63 the two bands at 260 and 403 cm -1 correspond to the Eg modes of the surface groups attached to Ti, and the band at 609 cm -1 is associated with the Eg vibrational modes of C. 64,65 The two peaks centered at 1341 and 1569 cm -1 are attributed to the D and G band of graphitic carbon, respectively. 66 After functionalization, the peak at 403 cm -1 was shifted to 426 cm -1 indicating the effective interactions between the cationic porphyrins and the surface functional groups of the Ti 3 C 2 T X .…”

Ti3C2 MXene-Based Nanobiosensors for Detection of Cancer Biomarkers

“…Platinum nanoparticles with average diameter of 3 nm were homogeneously distributed on the MXene sheets surface, that was found out by transmission electron microscopy (TEM) [69]. MXene and oxidized MXene were analyzed and differentiated by applying Raman spectroscopy method providing more detailed information about the characteristic vibrational bands and the dependence thickness of Ti 3 C 2 Tx layers on Raman signal enhancement [68][69][70][71].…”