Understanding the structural and chemical changes in vertical graphene nanowalls upon plasma nitrogen ion implantation.

Shallow plasma ion implantation is a versatile method for nitrogen incorporation in vertical graphene nanowalls (VGNs). However, the defects introduced by the process and the preference of nitrogen to occupy various locations in the 2D layered structure make the characterization complex. We have simplified the analysis of 2 kV nitrogen plasma ion implanted VGNs by correlating the binding energy of N1s electrons with the chemical state of nitrogen as lone-pair localized (N1), lone-pair de-localized (N2) and quaternary nitrogen (N3). This new approach helps to understand the electronic nature of implanted VGNs, based on the occupancy of structural locations by nitrogen. The C1s photoelectron spectra and G-peak intensity normalized comparison of the entire Raman spectra revealed large scale sp2C to sp3C conversion and generation of defects upon implantation. The increase in relative stiffness of implanted VGNs, as observed in atomic force acoustic microscopic studies, was correlated with the formation of graphitic CNx (N2), crosslinking of layers by nitrogen (N3) and interlayer sp3 carbon.

An experimental investigation on the combined effect of plastic deformation and grain size variation on the acoustic nonlinearity parameter.

The combined effect of grain size variation and plastic deformation on the acoustic nonlinearity parameter has been investigated in an austenitic stainless-steel material of grade 304. The nonlinear behavior of this parameter with grain growth has deviated to linear fit with deformation. This is due to the interaction of elastic waves with the strain-induced dislocation substructure in the grains. The normalized mean square strain of the deformed specimens has been estimated through angle dispersive x-ray diffraction studies using a synchrotron source, and this has been correlated with the change in the acoustic non-linearity parameter with deformation. The nonlinearity parameter is found to be very sensitive to the plastic deformation even in the presence of grain size variations. The results infer that the variations in the nonlinearity parameter can be used to have an estimate of the extent of localized deformations often occurring during the fabrication of metallic components.