Type of presentation: Poster

MS-1-P-2015 TEM study of TiO2 photocatalyst layers deposited on carbon nanosheet templates by atomic layer deposition

Kurttepeli M.1, Deng S.2, Verbruggen S. W.3, 4, Guzzinati G.1, Cott D. J.5, Lenaerts S.3, Detavernier C.2, Bals S.1, Van Tendeloo G.1
1EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium, 2Department of Solid State Science, Ghent University, Krijgslaan 281/S1, B-9000 Ghent, Belgium, 3Department of Bio-science Engineering, Sustainable Energy and Air Purification, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium, 4Department of Microbial and Molecular Systems, Center for Surface Chemistry and Catalysis, KU Leuven, Kasteelpark 11 Arenberg 23, B-3001 Heverlee, Belgium, 5Imec, 75, Kapeldreef, B-3001 Leuven, Belgium
mert.kurttepeli@uantwerpen.be

Due to its distinctive physical properties, chemical stability, bio-compatibility, non-toxicity and low cost, titanium dioxide (TiO2) is of great interest for a wide range of applications [1], [2]. The great potential of TiO2 nanostructures is obvious, but the desired physical and chemical properties of the materials will only be reached if a complete understanding of the relation between the activity and the structure of the materials has been obtained. In order to perform a detailed characterization of such nanostructures, transmission electron microscopy (TEM) is an ideal tool. Not only structural, but also chemical and electronic information can nowadays be obtained, even atomic column by atomic column [3], [4]. Nevertheless, one should take into account that conventional TEM images are only two-dimensional (2D) projections of three-dimensional (3D) objects. Therefore, TEM has been expanded to 3D, which is referred to as "electron tomography".
Hereby, we present results from different TEM characterization techniques to investigate the effects of annealing in helium environment on the structure of TiO2 layers deposited onto carbon nanosheets (CNSs) using atomic layer deposition (ALD). Using monochromated STEM-EELS, areas with TiO2 in anatase and amorphous form have been identified. From these maps, it is observed that the coating is mostly in anatase form, and there is only a low amount of amorphous TiO2 after annealing (see Fig 1). The graphite distribution map additionally indicated the presence of graphite throughout the layer. To investigate the 3-D structure of the material, HAADF-STEM electron tomography was applied (see Fig 2). The volume renderings proved both the homogeneity of the ALD coating throughout the CNSs layer, and the porosity of the complete film.
[1] A. Fujishima and K. Honda, Nature 238, 37 - 38 (1972).
[2] A. Kay and M. Grätzel, Solar Energy Materials and Solar Cells 44, (1996).
[3] K. W. Urban, Nature Materials 8, 260 - 262 (2009).
[4] D. A. Muller, Nature Materials 8, 263 - 270 (2009).

The authors acknowledge financial support from European Research Council and Sim-Flanders.

Fig. 1: HAADF-STEM image of the sample. Colored elemental STEM-EELS map with (B) anatase-TiO2 (red) and (D) graphite (green) is embedded. The amorphous-TiO2 elemental map is given in (C).

Fig. 2: Visualizations of the 3-D reconstruction of the sample depicted along different orientations are given in (A) and (B). A slice (orthoslice) through the 3-D reconstruction is presented in (C).