Beyond Ti3C2Tx: MXenes for Electromagnetic Interference Shielding

New ultrathin and multifunctional electromagnetic interference (EMI) shielding materials are required for protecting electronics against electromagnetic pollution in the fifth-generation networks and Internet of Things era. Micrometer-thin Ti3C2Tx MXene films have shown the best EMI shielding performance among synthetic materials so far. Yet, the effects of elemental composition, layer structure, and transition-metal arrangement on EMI shielding properties of MXenes have not been explored, despite the fact that more than 30 different MXenes have been reported, and many more are possible. Here, we report on a systematic study of EMI shielding properties of 16 different MXenes, which cover single-metal MXenes, ordered double-metal carbide MXenes, and random solid solution MXenes of M and X elements. This is the largest set of MXene compositions ever reported in a comparative study. Films with thicknesses ranging from nanometers to micrometers were produced by spin-casting, spray-coating, and vacuum-assisted filtration. All MXenes achieved effective EMI shielding (>20 dB) in micrometer-thick films. The EMI shielding effectiveness of sprayed Ti3C2Tx film with a thickness of only ∼40 nm reaches 21 dB. Adjustable EMI shielding properties were achieved in solid solution MXenes with different ratios of elements. A transfer matrix model was shown to fit EMI shielding data for highly conductive MXenes but could not describe the behavior of materials with low conductivity. This work shows that many members of the large MXene family can be used for EMI shielding, contributing to designing ultrathin, flexible, and multifunctional EMI shielding films benefiting from specific characteristics of individual MXenes

Desorption Kinetics of Alkali Metal Atoms from Transition Metal Surfaces

There are three standard models used to characterize desorption kinetics from surfaces: the Polanyi-Wigner, Elovich, and Albano model. The current models of desorption are very limited in their scope and accuracy. Each of these models falls short for alkali metals on transition metal surfaces, and as such, new models need to be developed. Two models are proposed, one that utilizes the dipole moment, µ, to characterize the system and another that utilizes the work function, ø, to characterize the system. These models use experimentally determined properties to provide both a more accurate model for desorption and an avenue for fundamental understanding of the system itself. Both of these models are more successful than the current models, but the ø model is more robust than the µ model. Although the ø model is better than the previous models, additional work must be completed to further characterize and model the complicated desorption kinetics found in alkali systems along with more complicated systems