How effectively do carbon nanotube inclusions contribute to the electromagnetic performance of a composite material? Estimation criteria from microwave and terahertz measurements

Screening effect in finite-length carbon nanotubes (CNT) and their agglomerates hinders significantly the electromagnetic interaction in composite materials. Screening effect is strong in the microwave range, and it decreases with increasing frequency resulting in a strong frequency dependence of the effective conductivity of the composite. Since screening effect is rather small in the terahertz range, the effective conductivity in this range is determined directly by the intrinsic conductivity of the inclusions. The ratio of the microwave to terahertz effective conductivities was proposed as a parameter to estimate how effectively carbon nanotube inclusions contribute to the electromagnetic performance of composite materials in the microwave range. CNT film was considered as a material where maximal possible interaction of the CNTs with EM field occurs. Single-walled CNT films and CNT-based composite materials, as well as hybrid film comprising mixtures of WS2 nanotubes and CNTs were fabricated and measured in the microwave and terahertz ranges. The electromagnetic field interaction with the inclusions has been estimated for all the samples fabricated

In Situ X ray Photoelectron Spectroscopy Study of Lithium Interaction with Graphene and Nitrogen Doped Graphene Films Produced by Chemical Vapor Deposition

It is commonly accepted that the presence of nitrogen atoms in a graphene lattice improves many properties of carbon materials and particularly enhances their electrochemical capacity in Li ion batteries. Here, we present model experiments for revealing the difference in interaction of lithium with N-doped and N-free graphene samples by monitoring the changes in their electronic states after the deposition of Li vapors. Graphene and N-doped graphene films have been grown by chemical vapor deposition on copper substrates using methane and acetonitrile as precursors. The electronic structure of the films transferred onto SiO₂/Si substrates was examined by X-ray photoelectron spectroscopy (XPS) before and after deposition of lithium from a Li evaporation source under vacuum conditions. A comparison between two graphene samples using in situ XPS measurements has detected a higher accumulation of lithium on the N-doped graphene, which implies its high prospects in energy storage applications. Analysis of the XPS core-level binding energy shifts showed that charge density donated by lithium is localized near the nitrogen defects, especially around the nitrogen atoms directly substituting for carbon atoms