Exploring the physical behavior of surface-functionalized two-dimensional Tungsten carbide/nitride MXenes

In this article, we present a study of the properties of two-dimensional (2D) derivatives of MAX phases, namely W2XT2 (X = C, N; T = O, F) MXenes, which have become hot spots of research for their intriguing physical properties. In pursuing this first-principles study, we realized W2X pristine MXene by eliminating the Ga atomic layer from the W2GaX MAX phase, which is then functionalized with oxygen and fluorine. These materials exhibit electronic states above the Fermi level primarily of W-d nature, indicating their metallic nature similar to the parent MAX phases. The distribution of up and down spin electronic states is highly symmetrical, depriving the W2XT2 MXenes of spontaneous magnetization. They demonstrated prominent optical properties where the W2NF2 exhibits approximately 70% reflection of infrared (IR) light, while W2CF2 reflects around 47%. On the contrary, W2NO2 and W2CO2 reflect 33% and 20% of the incident IR light, respectively. At an energy of 0 eV, the refractive indices recorded for W2CF2, W2CO2, W2NF2, and W2NO2 were 5.11, 2.29, 8.56, and 3.47, respectively. When exposed to IR light, they showed remarkable ultraviolet (UV) light absorption of 23.62 x 104 cm-1 and 20.71 x 104 cm-1 for W2NF2 and W2CF2, respectively. The absorption of IR light by W2CO2 and W2NO2 was relatively smaller, with values of 12.52 x 104 cm-1 and 8.30 x 104 cm-1, respectively. The interesting optical characteristics of the W2XT2 MXene make them promising for utilization in advanced optical devices.