A decade after the first report, the family of two-dimensional (2D) carbides and nitrides (MXenes) includes structures with three, five, seven, or nine layers of atoms in an ordered or solid solution form. Dozens of MXene compositions have been produced, resulting in MXenes with mixed surface terminations. MXenes have shown useful and tunable electronic, optical, mechanical, and electrochemical properties, leading to applications ranging from optoelectronics, electromagnetic interference shielding, and wireless antennas to energy storage, catalysis, sensing, and medicine. Here we present a forward-looking review of the field of MXenes. We discuss the challenges to be addressed and outline research directions that will deepen the fundamental understanding of the properties of MXenes and enable their hybridization with other 2D materials in various emerging technologies.

The world of two-dimensional carbides and nitrides (MXenes)

Heterocyclic pyrrole molecules are in situ aligned and polymerized in the -absence of an oxidant between layers of the 2D Ti3C2Tx (MXene), resulting in high volumetric and gravimetric capacitances with capacitance retention of 92% after 25,000 cycles at a 100 mV s(-1) scan rate.

Pseudocapacitive Electrodes Produced By Oxidant-Free Polymerization of Pyrrole Between the Layers of 2D Titanium Carbide (MXene)

Two-dimensional MXenes: From morphological to optical, electric, and magnetic properties and applications

High-performance electromagnetic interference (EMI) shielding materials with ultraflexibility, outstanding mechanical properties, and superior EMI shielding performances are highly desirable for mo

Ultraflexible and Mechanically Strong Double-Layered Aramid Nanofiber-Ti3C2Tx MXene/Silver Nanowire Nanocomposite Papers for High-Performance Electromagnetic Interference Shielding.

2D transition metal carbides or nitrides, known as MXenes, are a new family of 2D materials with close to 30 members experimentally synthesized and dozens more theoretically investigated. Because o...

MXene/Polymer Membranes: Synthesis, Properties, and Emerging Applications

Vector beams with different polarization topological orders (PTOs) are the eigenmodes of traditional optical fibers and are orthogonal to each other, so the PTO multiplexing channel is a promising candidate for the oncoming generation of optical communication. Here we demonstrate experimentally a PTO sorting system with high separation resolution based on the diffractive splitting (DS) method. Our experiments show that our design with the DS method helps to enhance the separation resolution to 77.5% from 58%, compared to a design without the application of a DS method. Theoretically, to increase the copy number can promote the separation resolution further. This Letter provides a high-resolution way to decode information from PTO division multiplexing.

Improve polarization topological order sorting with the diffractive splitting method.

Due to the outstanding electronic properties, unique chemical surface termination units and rich elemental compositions, MXenes have become promising candidates for the development of new generation optoelectronic devices. However, there is still a gap between advanced photonics applications and fundamental understanding of ultrafast carrier photo-physics dynamics and a nonlinear optical response in layered MXenes. Here, we present insight into the excited state relaxation processes and nonlinear optical response of few-layer Ti3CN and Ti3C2 nanosheets (NSs) via transient absorption spectroscopy and Z-scan measurements. Owing to similar structural compositions, the transient absorption and nonlinear absorption characteristics behave totally opposite. In addition, photo-induced bandgap renormalization and Pauli blocking phenomena exist in Ti3C2 and Ti3CN NSs, respectively. The element replacement may be a new strategy for tunable carrier kinetics and nonlinear optical response of MXenes. These research studies may provide insight into ultrafast carrier photo-physics dynamics as well as promote MXene-based advanced photonics and their applications in optoelectronic devices.

Tailoring the ultrafast and nonlinear photonics of MXenes through elemental replacement

https://iopscience.iop.org/article/10.1088/2040-8986/ab2d84/pdf

Terahertz-mid-infrared anisotropic vortex beams generation via few-cycle vortex-laser-induced air plasma

We propose a common-path spectral interferometer for single-shot terahertz (THz) electro-optics (EO) detection, where a probe pulse pair with orthogonal polarizations and a relative time delay are generated by simply using a birefringent plate. One of them, as the object, transmits through a THz EO crystal with THz phase modulation, while the other goes through the crystal without any phase imposed by target the THz field as the reference. The co-axial propagation of the pulse pair can effectively reduce the noises due to mechanical vibrations, air turbulences, and temperature fluctuations in the traditional non-common-path spectral interferometers. Our experiments show that, for a given target THz pulse field, the measured THz signals in a single-shot mode have a signal-to-noise ratio (SNR) of 41.2 with our THz common-path spectral interferometer, but 7.91 with a THz Mach-Zehnder spectral interferometer; thus, our design improves the SNR of the THz signal by about 5.2 times.

Common-path spectral interferometry for single-shot terahertz electro-optics detection.

Comprehensive characterization of ultrafast optical field is critical for ultrashort pulse generation and its application. This paper combines two-step phase-shifting (TSPS) into the spectral phase interferometry for direct electric-field reconstruction (SPIDER) to improve the reconstruction of ultrafast optical-fields. This novel SPIDER can remove experimentally the dc portion occurring in traditional SPIDER method by recording two spectral interferograms with π phase-shifting. As a result, the reconstructed results are much less disturbed by the time delay between the test pulse replicas and the temporal widths of the filter window, thus more reliable. What is more, this SPIDER can work efficiently even the time delay is so small or the measured bandwidth is so narrow that strong overlap happens between the dc and ac portions, which allows it to be able to characterize the test pulses with complicated temporal/spectral structures or narrow bandwidths.

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Shixiang Xu

Papers

Improve polarization topological order sorting with the diffractive splitting method.

Tailoring the ultrafast and nonlinear photonics of MXenes through elemental replacement

Terahertz-mid-infrared anisotropic vortex beams generation via few-cycle vortex-laser-induced air plasma

Common-path spectral interferometry for single-shot terahertz electro-optics detection.

Two-step phase-shifting SPIDER.