Infrared anomalies in ultrathin Ti3C2Tx MXene films

TL;DR

This study reveals the fundamental infrared optical properties of ultrathin Ti3C2Tx MXene films, including three anomalies, which are crucial for designing low-emissivity transparent devices and other IR applications.

Contribution

The paper introduces a tape-free transfer method for preparing ultrathin Ti3C2Tx films and experimentally measures their IR optical properties, revealing three key anomalies.

Findings

Maximum IR reflectance of 88% in bulk films

Discovery of three IR anomalies in ultrathin films

Interlayer space influences optical properties

Abstract

Visible transparent but infrared reflective materials are ideal candidates for both transparent conductive films and low-emissivity glass, which are highly desired in a broad variety of areas such as touchscreens and displays, photovoltaics, smart windows, and antistatic coatings. Ultrathin Ti3C2Tx MXene films are emerging as promising low-emissivity transparent candidates. However, the fundamental IR properties of Ti3C2Tx has not been revealed experimentally due to daunting challenges in the preparation of continuous, large-area, and ultrathin films of optical quality on flat substrates. Herein, we proposed a tape-free transfer method that can help prepare centimeter-size and ultrathin (down to 8 nm) Ti3C2Tx films on diverse optical substrates. Benefitting from this method, the refractive index and permittivity for Ti3C2Tx were successfully measured. Ti3C2Tx films exhibit large in-plane permittivity in the IR region, yielding maximum IR reflectance of 88% for bulk films. Interestingly, three anomalies were found in ultrathin Ti3C2Tx films: strong dispersion in the permittivity, interlayer space-dependent optical properties, and abnormally high IR absorption for a 15-nm-thick film. These anomalies are important guidelines in the design of Ti3C2Tx-based low-emissivity transparent films and other related devices, and may inspire other intriguing applications such as ultrathin IR absorption coatings and tunable IR optical devices.