The combination of electron microscopy, Raman microscopy and energy dispersive X-ray spectroscopy – new methodic possibilities for materials science 1,2
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A. Zankel , H. Fitzek , C. Mayrhofer , M. Nachtnebel , R. Schmidt , H. Schroettner
1. Institute of Electron Microscopy and Nanoanalysis, Graz University of Technology, Steyrergasse 17, 8010 Graz, Austria 2. Graz Centre for Electron Microscopy, Steyrergasse 17, 8010 Graz, Austria
Introduction At the FELMI-ZFE (Institute of Electron Microscopy and Nanoanalysis Graz together with Graz Centre for Electron Microscopy) the system RISE was recently established. RISE stands for Raman Imaging and Scanning Electron microscopy. The seamless combination of two techniques offers the possibility of high resolution imaging by the scanning electron microscope Sigma 300 VP (Zeiss, Oberkochen, Germany) and chemical analysis with the attached Raman microscope [1] from WITec (Ulm, Germany). Additionally the setup is equipped with a modern silicon drift detector from Oxford (UK) for energy dispersive X-ray spectroscopy (EDXS). It enables spectra and mappings in a comparatively short time and rounds up the correlative investigations.
Method
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The SEM Zeiss Sigma 300 VP is equipped with a Shottky InlensSE field emitter, a fully integrated inlens detector and a S C2 X D ED SE2 secondary electron (SE) Raman detector (Everhart-ThornleyHDAsB detector) for topographic contrast. An angle selective backscattered electron (BSE) detector (HDAsB) is available for material contrast (ZFig. 1: Pole piece of the SEM with several contrast).
Up to now several types of specimens were investigated at the FELMI-ZFE like metaloxides, mineralogical specimens, inclusions in metals, polymers, organicRaman: blue – epoxy resin red – silane-comp. inorganic compounds and green – graphite diverse particles. As an EDXS: orange – carbon example Fig. 3 shows the green – copper purple – silicone cross section of an embedded experimental electrode for a Li- Fig. 3: Upper image: Raman map within battery. The upper left image in correlated SEM image (width: = 100 µm) Fig. 3 is an overlay of a Raman and Raman spectra. Lower image: EDXS map on an SEM image which map within the SEM image. was measured in the variable pressure (VP) mode using the C2D detector which operates with nitrogen as imaging gas. The Raman spectra of the different phases are highlighted with the appropriate colours beside. The image below in Fig. 3 is an EDXS map within the same region of interest providing additional elemental information. The variable pressure mode is also appropriate to image polymeric specimens, since it enables imaging of electrically non conductive materials. Fig. 4 shows the embedded seal area of a peel film. Again the chemical analysis of different regions can be correlated to the SEM image [2].
Conclusion All the methods require specific expertise regarding sample preparation, instrument operation and interpretation of the results. Aspects like influence of the electron beam on the surface (beam damage, carbon contamination) before Raman measurement have to be assessed and appropriate handling has to be developed. Several parameters like beam energy, frame time and pixel resolution may influence the quality of sequential investigation. During the first investigations some best practice rules were deducted and methodic skills were acquired.
References/Literature [1] T. Dieing, O. Hollricher, J. Toporski (Eds.): Confocal Raman Microscopy, Springer 2011 [2] R. Schmidt, H. Fitzek, M. Nachtnebel, C. Mayrhofer, H. Schroettner, A. Zankel: The combination of electron microscopy, Raman microscopy and energy dispersive X-ray spectroscopy for the investigation of polymeric materials, Macrom. Symp., Vol. 384, 1, 2019
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While SEM imaging and EDXS measurement are performed in one position of the specimen stage, for Raman investigations the sample has to be moved (indicated in Fig. 1 and 2) towards the Raman system in a computer assisted manner. Only a few steps of alignment and refocusing have to be done to be able to correlate the field of a Raman map and Fig. 2: Schematic of correlative Raman a n S E M i m a g e . T h e Imaging and Scanning Electron (RISE) schematic of the Raman Microscopy (Copyright by WITec GmbH) microscope combined with the SEM can be seen in Fig. 2.
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In Fig. 1 the pole piece of the microscope with several detectors can be seen. A confocal Raman microscope by WITec (Germany) is attached to the SEM using a coherent laser source of 532 nm. The energy dispersive X-ray spectroscope X-Max 80 by Oxford (UK) rounds up the configuration.
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Fig. 4: a) SEM image of the embedded peel film (1, 2: peel arms, 3: bulge due to sealing, 4: upper region of seal area, image width 381.1 μm, 10 kV, VP mode) with integrated Raman map (the colours indicate different polymers). b) Schematic of a peel film. The circle indicates the embedded part of the specimen. c) Raman spectra of polymeric components according to the map (correlated colours) [2].
Acknowledgements This work was enabled by the projects "HRSM-Projekt ELMINet Graz - Korrelative Elektronenmikroskopie in den Biowissenschaften" (i.e. a cooperation within "BioTechMed-Graz", a research alliance of the University of Graz, the Medical University of Graz, and Graz U n i v e r s i t y o f Te c h n o l o g y ) a n d " I n n o v a t i v e Materialcharakterisierung", SP2016-002-006, which is part of "ACR Strategisches Projektprogramm 2016" of the Austrian Cooperative Research (ACR).
Contact armin.zankel@felmi-zfe.at www.felmi-zfe.at www.acr.at www.tugraz.at