Dr. Chris B. Boothroyd

Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Germany Authors | C.B. Boothroyda, M.S. Morenob, M. Duchampa, A. Kovácsa, N. Mongec, G.M. Moralesc, C.A. Barberoc, R.E. Dunin-Borkowskia Email |  c.boothroyd@fz-juelich.de

ApplicationAtomic Resolution Imaging and Spectroscopy of Barium Atoms and Functional Groups on Graphene Oxide
AuthorsC.B. Boothroyda, M.S. Morenob, M. Duchampa, A. Kovácsa, N. Mongec, G.M. Moralesc, C.A. Barberoc, R.E. Dunin-Borkowskia
JournalUltramicroscopy Journal, 2014
SampleGraphene
TopicContamination Free, 2D Materials, Soft Matter, E-Beam Sensitive Imaging
TechniquesHRTEM, HRSTEM, EELS, Diffraction
KeywordsGraphene oxide; Functional groups; Scanning transmission electron microscopy; Transmission electron microscopy; Spectrum imaging; Atomic resolution; Single atom imaging
Publication / D.O.I.Full Publication Here

Atomic Resolution Imaging and Spectroscopy of Barium Atoms and Functional Groups on Graphene Oxide

ABSTRACT: We present an atomic resolution transmission electron microscopy(TEM) and scanning TEM(STEM) study of the local structure and composition of graphene oxide modified with Ba2+. In our experiments, which are carried out at 80kV,the acquisition of contamination-free high-resolution STEM images is only possible while heating the sample above 400C using a highly stable heating holder. Ba atoms are identified spectroscopically in electron energy-loss spectrum images taken at 800C and are associated with bright contrast in high-angle annular dark-field STEM images. The spectrum images also show that Ca and O occur together and that Ba is not associated with a significant concentration of O. The electron dose used for spectrum imaging results in beam damage to the specimen, even at elevated temperature. It is also possible to identify Ba atoms in high-resolution TEM images acquired using shorter exposure times at room temperature, thereby allowing the structure of graphene oxide to be studied using complementary TEM and STEM techniques over a wide range of temperatures.
FIGURE ABOVE: HAADF STEM images acquired at a specimen temperature of 800 C (a) before and (b) after recording the spectrum image (the total time of spectrum imaging is 800s). The area of spectrum imaging is marked by the box. While the area surrounding the box is relatively unchanged after acquiring the spectrum image (except for a small drift and local distortion), the area from which the spectrum image was acquired has changed significantly.
FIGURE ABOVE: Color images created  from a selection of  the spectrum images which  were acquired  from graphene  oxide with  Ba  imaged at a temperature of 800 C by using STEM spectrum imaging method. The  images show the spatial relationships between the elements, corresponding to the following colours: (a)  Ba red and C cyan; (b)  O red and C cyan; (c) Ca red and C cyan; (d)  Ba red, Ca green and C blue. The  spectrum image shows that Ba, O and Ca are present mostly in the areas where the C is thinnest and that Ca and O have very similar distributions.

DENSsolutions Comments:

Graphene, graphene-like two dimensional and other soft-mater materials attract  increasing research efforts. Characterization of these type of materials in TEM, however, suffers contamination problems and e-beam damage.
Contamination, referring to the build-up of decomposed carbon on a specimen, heavily influences the quality of electron microscopy imaging. Graphene  and graphene-like two dimensional materials suffer contamination the most because of two reasons 1. these materials are ultrathin, with low image contrast,  the build up contamination contrast blur the original contrast easily; 2. these materials are with large surface area, easier to absorb hydrocarbon, water to form contamination under e-beam.
DENSsolutions heating system provides the opportunity to image these samples free of contamination at elevated temperature, without sacrificing the quality/resolution of imaging. The extreme high stability of DENSsolutions heating system (sample spatial drift less than 0.5nm/min) can even allow the researchers using a long exposure time (5s-8s) to  image the individual carbon atoms for improving the contrast. Furthermore, the low drift allows chemical sensitive spectrum imaging to be carried down to atomic level.

Download the full publication here at the Ultramicroscopy (2014) Journal

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