Quantitative valence plasmon mapping in the TEM: viewing physical properties at the nanoscale

Abstract

Using a series of graphitising carbons heat treated at different temperatures, the peak position of the bulk ( π+ σ) plasmon was measured using electron energy loss spectroscopy and observed to shift between 22 and 27 eV. Experimental data is presented and discussed showing the effects of the collection conditions and sample orientation upon the observed spectra. We present an empirical technique by which quantitative energy filtered transmission electron microscopy (EFTEM) maps with two energy windows selected in the plasmon region can be readily acquired and processed, the results of which may be interpreted as graphitisation maps and subsequently physical property maps. An experimentally established resolution of ∼1.6 nm makes this technique a very useful tool with which to examine nanoscale properties in microstructural regions of interest in TEM specimens such as fibre/matrix interfaces within carbon–carbon composites, multi-walled carbon nanotubes and graphitic inclusions in carbon steels. Also presented is data demonstrating the unsuitability of π *-related chemical EFTEM maps in both the low-loss region and at the carbon K ionisation edge for mapping bonding in such highly anisotropic media due to the strong orientation dependence of the intensity of the transitions involved. This is followed by suggestions for wider application of the plasmon mapping technique within systems other than those based upon carbon.