Broadband Visible Nonlinear Absorption and Ultrafast Dynamics of the Ti3C2 Nanosheet.

Yabin Shao,Wenzhi Wu,Qing He,Chen Chen,Chensha Li,Yachen Gao

doi:10.3390/nano10122544

Abstract

The Ti3C2 nanosheet, as a new two-dimensional (2D) group, has been found to have attractive characteristics as material for electromagnetic shielding and energy storage. In this study, the nonlinear broadband absorption and ultrafast dynamics of the Ti3C2 nanosheet were investigated using nanosecond open-aperture Z-scan and transient absorption techniques. The mechanism of two-photon absorption (TPA) was revealed in the visible region (475–700 nm). At lower incident energies, nonlinear absorption could not happen. When the laser energy increased to 0.64 GW/cm2, electrons in the valence band could absorb two photons and jump to the conduction band, with TPA occurring, which meant that the sample exhibited reverse saturable absorption (RSA). In addition, when transient absorption was used to investigate the ultrafast carrier dynamics of the sample, it demonstrated that the relaxation contains a fast decay component and a slow one, which are obtained from electron–phonon and phonon–phonon interactions, respectively. Moreover, with the increasing pump fluence, the fast decay lifetime τ1 increased from 3.9 to 4.5 ps, and the slow one τ2 increased from 11.1 to 13.2 ps. These results show that the Ti3C2 nanosheet has potential applications in broadband optical limiters.

Highlights

Ever since the discovery of graphene [1], two-dimensional (2D) materials have attracted much interest due to their novel electronic, optical, and mechanical properties which are different from those of their bulk forms
Monolayered structures are provided by transmission electron microscopy (TEM), element mapping is obtained by STEM-energy-dispersive X-ray (EDX) mapping, and Fast Fourier Transform (FFT) of the Ti3C2 original image is observed (FEI Tecnai G2 F20, Hillsboro, OR, USA)
High-resolution transmission electron microscopy (HRTEM) patterns and the dots painted on Figure 1e clearly show the crystalline lattice of the monolayer Ti3C2 nanosheet with a hexagonal structure

Summary

Introduction

Ever since the discovery of graphene [1], two-dimensional (2D) materials have attracted much interest due to their novel electronic, optical, and mechanical properties which are different from those of their bulk forms. As the first 2D material identified, graphene has been intensively studied for various applications, such as optical modulators [2], ultrafast laser generation [3], and surface plasmonic [4], whereas the gapless Dirac-cone band structure limits its possibilities for applications [5]. A group of new 2D materials, which show the semiconductor and metallic phase, have provided evidence of attractive nonlinear optical (NLO) properties different from those of organic materials [6,7,8]. The development of novel promising 2D phase NLO materials is still a long-term objective. The NLO properties of Ti3C2 continue to attract attention [21]

Methods

Results

Conclusion