2D MXenes in the THz range: from optical conductivity to THz devices

Li, Guangjiang

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2D MXenes in the THz range: from optical conductivity to THz devices

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MXenes are a family of 2D transition metal carbides, carbonitrides and nitrides that are fabricated from layered MAX phases by etching out the A element, typically aluminum. Since the discovery of the first MXene, Ti3C2Tz, in 2011, MXenes have shown highly attractive properties such as high conductivity, record volumetric capacity, efficient light-to-heat conversion, saturable optical absorption, and others. Their chemical diversity and hydrophilicity facilitate the realization of novel optoelectronic and nanophotonic applications such as supercapacitors, electromagnetic interference (EMI) shielding, transparent conducting electrodes, and mode-locked fiber lasers MXene-based applications and further commercialization require understanding of the electronic and optical properties of MXenes as a function of their chemistry and structure. In many cases, applications call for nanometer to micrometer-thick MXene films that consist of multiple overlapping single-layer flakes. Conventional electrical transport measurement could only yield the overall conductivity of the MXene film. Terahertz (THz) spectroscopy enables probing carrier transport over microscopic distances, decoupling the inter- and intra-nanoflakes contributions and providing insight necessary to engineer and optimize their structure and morphologies for specific applications. Here, we use time-resolved THz spectroscopy to systematically study the carrier dynamics and photoexcitation of three MXenes: Ti3C2Tz, Mo2Ti2C3Tz and Mo2TiC2Tz. Based on the properties of MXenes in the THz range, we propose their applications in THz photonic devices, an optically-switchable THz EMI shielding and MXene-based THz polarizer. Finally, our first measurements of saturable absorption of Ti3C2Tz in the THz range suggest that MXenes can be used in nonlinear THz photonics.

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