Raman Spectroscopy Characterization of 2D Carbide and Carbonitride MXenes

Abstract

The first step to wider adoption of two-dimensional (2D) materials is understanding their fundamental properties by employing characterization methods, among which Raman spectroscopy plays a unique role, being a fast and nondestructive tool. The number, frequencies, and intensities of the modes (or bands) in the Raman spectrum have been used to identify the 2D materials’ crystal lattice, bonding, and even number of layers. MXenes, 2D transition metal carbides, nitrides, and carbonitrides, span diverse chemistries and structures, but only a few Raman spectra have been reported. This work is the first systematic experimental Raman spectroscopy study of the MXene family. We explore the vibrational spectra and provide peak assignments for ten MXenes with varying structures (from 2 to 4 atomic layers of transition metal) and compositionsTi2CT x , Nb2CT x , Mo2CT x , V2CT x , Ti3C2T x , Mo2TiC2T x , Ti3CNT x , Nb4C3T x , V4C3T x , and Mo2Ti2C3T x (terminated with −F, −OH, and O) based on the experimental results and previously reported computational studies. We discuss the effects of MXene layer thickness, surface terminations, and MXene’s metallic properties on Raman scattering. Additionally, we employ polarized Raman spectroscopy to identify out-of-plane vibrations and explain the higher frequency region of the spectra. Finally, we demonstrate how electrochemical reactions affect molecular Raman scattering through the change in surface terminations. By creating the Raman spectra library of the most frequently used MXenes, we open the door for the use of Raman spectroscopy for fingerprinting and in situ studies of various MXenes.

Versatile Titanium Carbide MXene Thin-Film Memristors with Adaptive Learning Behavior

“…In general, the Raman scattering of MXene is very sensitive to identifying the composition, surface functional groups, and defects originated from the HF etching step in solution. Typical Raman-active phonon modes of in-plane (E 1g ) and out-of-plane (A 1g ) molecular vibrations appear between 100 and 800 cm –1 , which we observed clearly for both the samples . The recorded sharp scattering peaks at 129.5, 236.9, 438.5, and 603.1 cm –1 are characteristic phonon vibrations of Ti 3 AlC 2 along with a broad peak appeared at 1595.5 cm –1 as the signature of carbon layer (Figure e).…”

“…Typical Raman-active phonon modes of in-plane (E 1g ) and out-ofplane (A 1g ) molecular vibrations appear between 100 and 800 cm −1 , which we observed clearly for both the samples. 24 The recorded sharp scattering peaks at 129.5, 236.9, 438.5, and 603.1 cm −1 are characteristic phonon vibrations of Ti 3 AlC 2 along with a broad peak appeared at 1595.5 cm −1 as the signature of carbon layer (Figure 1e). After efficient removal of the Al layer, the molecular vibrational peaks would be either stiffened or softened compared with the pure MAX phase modes.…”

Delamination of Chlorine-Terminated MXene Produced Using Molten Salt Etching

“…This peak can be associated with the out-of-plane vibrations of carbon, an inherent characteristic of MXene M 3 X 2 structures. Compared to the Ti 3 C 2 T x obtained from the mixed acid etching, this peak has shifted to a lower wavenumber, indicating a softer vibration of the bond affected by Cl surface terminations. , Moreover, the sharp peaks in the range of 200 to 400 cm –1 indicate in-plane and out-of-plane vibrations of the whole flake and surface terminations, suggesting that the material’s surface termination is uniform. , A noteworthy trend is the varying intensity of the primary ∼170 cm –1 region and ∼600 cm –1 region peaks across the three excitation wavelengths. At 514 nm, the ∼600 cm –1 peak exhibits the most pronounced intensity, progressively diminishing with increasing wavelength to 633 nm and subsequently 785 nm.…”

“…Compared to the Ti 3 C 2 T x obtained from the mixed acid etching, this peak has shifted to a lower wavenumber, indicating a softer vibration of the bond affected by Cl surface terminations. 28,29 Moreover, the sharp peaks in the range of 200 to 400 cm −1 indicate in-plane and out-of-plane vibrations of the whole flake and surface terminations, suggesting that the material's surface termination is uniform. 30,31 A noteworthy trend is the varying intensity of the primary ∼170 cm −1 region and ∼600 cm −1 region peaks across the three excitation wavelengths.…”

Photothermal properties of MXenes and sterilization of MRSA by Nb2C/Gel with a low power NIR-II laser

“…And the peak at 719 cm À1 corresponds to the vibration of the carbon. For Nb 2 C and V 2 C, [33][34][35][36] the peak at 139 cm À1 corresponds to inplane vibrations of niobium and vanadium. The peaks at 250 cm À1 and 280 cm À1 correspond to in-plane vibrations of niobium and vanadium, respectively.…”