Tuning the Work Function of Ti₃C₂T_x MXene by Molecular Doping without Changing its Surface Functional Groups

Abstract

Owing to their impressive electronic/optoelectronic properties, MXenes have attracted significant attention among the 2D materials research community. Their work function (WF) tunability, in particular, has permitted efficient interfacial band alignment engineering in several device applications. However, like most of their properties, the WF of MXenes highly depends on their surface terminations, making it hard to individually modify the WF without compromising other fundamental properties, which hinders the exploitation of MXenes to their full potential. Herein, we introduce a surface-terminationindependent method to tune the WF of Ti 3 C 2 T x MXene through molecular doping. The achieved stepwise 500-meV increase in WF, in ∼120-meV increments, is induced by subsurface electron depletion from Ti 3 C 2 T x , with no effect on its other key properties. Utilizing electron paramagnetic resonance and ultrafast laser spectroscopy, we reveal that tuning the WF of Ti 3 C 2 T x is entirely surfacetermination-independent. Such discrete control over the WF renders MXene-based devices with unprecedented operational degrees of freedom.

Covalent chemical functionalization of Ti3C2Tx MXene nanosheets with fullerenes C60 and C70 for enhanced nonlinear optical limiting

“…The pure nanosheets exhibit a characteristic peak centered at 321 nm, corresponding to the inherent interband transition, in addition to a broad absorption band at 759 nm assigned to the transversal surface plasmon (SP) mode. 59 Upon diazonium functionalization, the peak position of the interband transition remained unaltered, while the SP band experienced a redshift of 17 nm to 776 nm. Recent studies have demonstrated that the peak position of the transversal SP mode is independent of the lateral sizes of nanosheets in the absorption measurements on Ti 3 C 2 T x dispersions.…”

“…This is possibly because of the effective electron transfer from Ti 3 C 2 T x to the fullerene components, inducing electron depletion in the subsurface energy states of the former, where the interband transition takes place. 59 Fig. 6b compares the absorption spectra of some physically-blended samples, prepared by mixing Ti 3 C 2 T x nanosheets and benzaldehyde and/or fullerenes with roughly the same content as f-MXene, C 60 -MXene, and C 70 -MXene (according to the TGA results).…”

Optically Active MXenes in Van der Waals Heterostructures

“…[7] Although ─F, ─O, and ─OH are the most common terminations induced by synthesis, surface doping can be easily incorporated into MXenes' surface, further modifying MXenes' optical properties. [84] A direct bandgap is desirable for light-emitting properties since it does not involve the emission of phonons. Phonons interrupt MXenes' light emission by electron-phonon and phononphonon scattering.…”

Fully Sprayed Metal Oxide Transistors Utilizing Ti3C2Tx MXene Contacts

“…Ohmic contact formation between graphene and various semiconductor channel materials in TFTs can also be challenging due to the limited tunability of the graphene work function (WF) . Besides graphene, two-dimensional (2D) transition metal carbides/nitrides, so-called MXenes, have recently emerged as potential conductive electrode materials. − Since their first report in 2011, , MXenes have received considerable attention owing to their unique combination of superior hydrophilicity, metal-like conductivity, optical transparency, tunable WF, versatile surface chemistry, and upscalable solution-processability. ,− These characteristics make MXenes particularly appealing for large-volume applications such as large-area electronics (LAE).…”