Hyunho Kim1,2,Danzhen Zhang1,2,Teng Zhang1,2,Yury Gogotsi1,2
A.J. Drexel Nanomaterials Institute1,Drexel University2
Hyunho Kim1,2,Danzhen Zhang1,2,Teng Zhang1,2,Yury Gogotsi1,2
A.J. Drexel Nanomaterials Institute1,Drexel University2
The MXene family, two-dimensional transition metal carbides, nitrides, and carbonitrides, have been the subject of extensive research activities for the past decade. Recent developments in the molten-salt route have enabled the engineering of MXenes’ surface termination groups. For example, molten-salt rouet synthesized Ti<sub>3</sub>C<sub>2</sub>Cl<sub>2</sub> is found to have a vis-NIR absorption band centered at ~880 nm, which is red-shifted from 770~800 nm for the acid route prepared Ti<sub>3</sub>C<sub>2</sub>T<i><sub>x</sub></i> with O, OH, and F terminations. The origin of this vis-NIR absorption band is yet to be understood, and the red-shift is difficult to explain by carrier density with the surface plasmon concept. Instead, we adapt an interband transition mechanism with consideration of light polarization to explain both UV and vis-NIR absorption bands of MXenes. The light-matter interactions of MXenes will be analyzed by using in-situ UV-vis spectroscopy under electrochemical modulation and Raman spectroscopy, and correlated with the literature on nonlinear optics, ultrafast terahertz spectroscopy, and pump-probe transient absorption. The important relationships between photons, electrons, and phonons in MXene, which are important for numerous applications of those materials, will be discussed.