| AVS 61st International Symposium & Exhibition | |
| Applied Surface Science | Wednesday Sessions |
| Session AS+BI+MC-WeM |
| Session: | Chemical Imaging in 2D and 3D |
| Presenter: | Anders Barlow, NEXUS, Newcastle University, UK |
| Authors: | A.J. Barlow, NEXUS, Newcastle University, UK N. Sano, NEXUS, Newcastle University, UK P.J. Cumpson, NEXUS, Newcastle University, UK |
| Correspondent: | Click to Email |
The differentiation between various forms of carbon in XPS spectra is made difficult by the subtle changes in C1s spectra that one would typically analyse. This is ideally demonstrated by a comparison of sp2 and sp3 carbon, such as graphite and diamond, where the variation in the C1s peak is less than 1eV. When applied to ‘real’ samples, such as a diamond like carbon coating, or a graphene surface, this difference can be even less. This presents a real problem for XPS imaging, where typically the analyst would sacrifice energy resolution in favour of signal intensity and spatial resolution. Such subtle differences are then completely lost when performing XPS imaging of novel carbon surfaces, where there may be discrete boundaries or layers between materials that are chemically very different, yet appear the same when the C1s peak energy is used in imaging.
We report a method of elucidating these differences in XPS imaging through shifting the focus from the C1s feature, to the X-ray induced Auger feature, a method we call Multivariate Auger Feature Imaging (MAFI). The carbon Auger feature can be studied and through the extraction of the so-called D-Parameter1, chemical states of carbon can be clearly identified, with little ambiguity between sp2 and sp3 states. Extension of this method to XPS imaging, and the generation of 3-Dimensional images (2 spatial, 1 kinetic energy), we have shown that imaging of the Auger feature of graphite on polymers can identify multiple states of carbon-carbon bonding domains, where the imaging of the C1s feature alone yields no distinguishable differences or spatial features. We have also shown that PCA analysis of the carbon Auger feature also yields clear and distinguishable differences in the XPS images. The result is two independent methods of distinguishing novel carbon materials from one-another in XPS imaging. With modern instrumentation capable of a spatial resolution down to the few micron level, this greatly enhances the capability of XPS instrumentation to image novel carbon surfaces and devices.
1 Lascovich, J.C. et al., App. Surf. Sci., 47(1), pp. 17-21 (1991).