Title: Two-Dimensional Carbides and Nitrides Expand the Flatlands
Speaker: Prof. Yury Gogotsi (Department of Materials Science and Engineering A. J. Drexel Nanomaterials Institute Drexel University)
Time: 15:00p.m., March 11th, 2017
Venue:   Room 214, Building No. 16, Wushan Campus

Abstract:
Two-dimensional (2D) solids – the thinnest materials available to us – offer unique properties and a potential path to device miniaturization. The most famous example is graphene, which is an atomically thin layer of carbon atoms bonded together in-plane with sp2 bonds. In 2011, a new family of 2D solids – transition metal carbides and nitrides (Ti2C, Ti3C2, Nb4C3, Ti4N3, etc.) – was discovered by Drexel University scientists [1]. These 2D solids with a composition Mn+1Xn (M is a transition metal, X is C or N) were labeled “MXenes”. More than 20 different carbides, nitrides and carbonitrides have been reported to date [2-5]. A new sub-family of multi-element ordered MXenes was discovered recently [2]. Structure and properties of numerous MXenes have been predicted by the density functional theory, showing that MXenes can be metallic or semiconducting, depending on their composition and surface termination. Their elastic constants along the basal plane are expected to be higher than that of the binary carbides. Oxygen or OH terminated MXenes are hydrophilic, but electrically conductive. Hydrazine, urea and other polar organic molecules can intercalate MXenes leading to an increase of their c lattice parameter [3]. One of the many potential applications for 2D Ti3C2 is in electrical energy storage devices such as batteries, Li-ion capacitors and supercapacitors [3-5]. Metallic MXenes have a potential for use in electromagnetic interference (EMI) shielding, transparent conducting coatings and many other applications. The reported EMI shielding efficiency values of flexible Ti3C2Tx films are the highest of any known synthetic materials with similar thickness [6]. Moreover, excellent shielding ability is maintained after adding sodium alginate to create polymer composite films. The 2D structure, combined with high conductivity and good electronic coupling between the layers, is responsible for the extremely high EMI shielding efficiency of MXenes [6].