van der Waals epitaxy of highly (111)-oriented BaTiO3 on MXene.

We report on the high temperature thin film growth of BaTiO3 on Ti3C2Tx MXene flakes using van der Waals epitaxy on a degradable template layer. MXene was deposited on amorphous and crystalline substrates by spray- and dip-coating techniques, while the growth of BaTiO3 at 700 °C was accomplished using pulsed laser deposition in an oxygen rich environment. We demonstrate that the MXene flakes act as a temporary seed layer, which promotes highly oriented BaTiO3 growth along the (111) direction independent of the underlying substrate. The lattice parameters of the BaTiO3 films are close to the bulk value suggesting that the BaTiO3 films remains unstrained, as expected for van der Waals epitaxy. The initial size of the MXene flakes has an impact on the orientation of the BaTiO3 films with larger flake sizes promoting a higher fraction of the polycrystalline film to grow along the (111) direction. The deposited BaTiO3 film adopts the same morphology as the original flakes and piezoresponse force microscopy shows a robust ferroelectric behavior for individual grains. Transmission electron microscopy results indicate that the Ti3C2Tx MXene fully decomposes during the BaTiO3 deposition and the surplus Ti atoms are readily incorporated into the BaTiO3 film. Electrical measurements show a similar dielectric constant as a BaTiO3 film grown without the MXene seed layer. The demonstrated process has the potential to overcome the longstanding issue of integrating highly oriented complex oxide thin films directly on any desired substrate.

Selective Etching of Silicon from Ti3 SiC2 (MAX) To Obtain 2D Titanium Carbide (MXene).

Until now, MXenes could only be produced from MAX phases containing aluminum, such as Ti3 AlC2 . Here, we report on the synthesis of Ti3 C2 (MXene) through selective etching of silicon from titanium silicon carbide-the most common MAX phase. Liters of colloidal solutions of delaminated Ti3 SiC2 -derived MXene (0.5-1.3 mg mL-1 ) were produced and processed into flexible and electrically conductive films, which show higher oxidation resistance than MXene synthesized from Ti3 AlC2 . This new synthesis method greatly widens the range of precursors for MXene synthesis.

Electromagnetic interference shielding with 2D transition metal carbides (MXenes).

Materials with good flexibility and high conductivity that can provide electromagnetic interference (EMI) shielding with minimal thickness are highly desirable, especially if they can be easily processed into films. Two-dimensional metal carbides and nitrides, known as MXenes, combine metallic conductivity and hydrophilic surfaces. Here, we demonstrate the potential of several MXenes and their polymer composites for EMI shielding. A 45-micrometer-thick Ti3C2Tx film exhibited EMI shielding effectiveness of 92 decibels (>50 decibels for a 2.5-micrometer film), which is the highest among synthetic materials of comparable thickness produced to date. This performance originates from the excellent electrical conductivity of Ti3C2Tx films (4600 Siemens per centimeter) and multiple internal reflections from Ti3C2Tx flakes in free-standing films. The mechanical flexibility and easy coating capability offered by MXenes and their composites enable them to shield surfaces of any shape while providing high EMI shielding efficiency.