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

Manuel Gonçalves,Hayk Minassian,Tigran Sargsian,Taron Makaryan,Petros Petrosyan,Armen Melikyan

doi:10.3390/photonics8020036

Abstract

Since the discovery of the optical properties of two-dimensional (2D) titanium carbide (MXene) conductive material, an ever increasing interest has been devoted towards understanding it as a plasmonic substrate or nanoparticle. This noble metal-free alternative holds promise not only due to its lower cost but also its 2D nature, hydrophilicity and apparent bio-compatibility. Herein, the optical properties of the most widely studied Ti3C2Tx MXene nanosheets are theoretically analyzed and absorption cross-sections are calculated exploiting available experimental data on its dielectric function. The occurrence of quadrupole surface plasmon mode in the optical absorption spectra of large MXene nanoparticles is demonstrated for the first time. The resonance wavelengths corresponding to interband transitions, longitudinal and transversal dipole oscillations and quadrupole longitudinal surface plasmon mode are identified for single and coupled nanoparticles by modeling their shapes as ellipsoids, disks and cylinders. A new mechanism of excitation of longwave transversal surface plasmon oscillations by an external electric field perpendicular to the direction of charge oscillations is presented. Excitingly enough, a new effect in coupled MXene nanoparticles—Fano resonance—is unveiled. The results of calculations are compared to known experimental data on electron absorption spectroscopy, and good agreement is demonstrated.

Highlights

A recently discovered family of 2D materials—transition metal carbides/nitrides called MXenes—has become the subject of versatile intensive studies due to the materials’ unique optoelectronic properties as well as hydrophilicity, flexibility and metal-like electronic conductivity [1,2,3,4,5,6,7,8,9,10]
MXenes are mostly synthesized by etching out the A layers from parent MAX phases [11,14,15], which have a composition generally denoted as Mn+1AXn, where M is an early transition metal, A is mainly a group IIIA or IVA element, X is C and/or N, and n = 1, 2, 3 or 4
Our simulation for the same polarization of incident light for the cylinder, as was mentioned above, gives exactly the same maxima, which we identify as interband transitions (IBTs) and quadrupole SP (QSP) resonances, respectively

Summary

Introduction

A recently discovered family of 2D materials—transition metal carbides/nitrides called MXenes—has become the subject of versatile intensive studies due to the materials’ unique optoelectronic properties as well as hydrophilicity, flexibility and metal-like electronic conductivity [1,2,3,4,5,6,7,8,9,10]. The plasmonic properties of MXenes were investigated by electron energy loss spectroscopy (EELS) [16,17] and by optical measurements in the IR, visible and UV ranges [13,18,19] In these studies, both surface plasmons (SPs) as well as bulk plasmons and interband transitions (IBTs) were identified. Ti3C2Tx MXene disk arrays on glass and on Au/alumina were fabricated, and it was shown that the new metamaterial exhibits strong broadband absorption in a wide range of wavelengths, λ = 500 − 1500 nm [26] The origin of this effect is conditioned by the appearance of gap plasmons, localized SPs and plasmon-polaritons. The absorption spectrum of a single disk for both TE and TM polarizations will be considered and it will be demonstrated that a strong broadening takes place already in the isolated particle

Calculation of Optical Spectra of Single Ti3C2Tx Nanoparticles

Discussion

Conclusions