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Formation of swift heavy ion tracks on a rutile TiO2 surface

Figure 1. (a) AFM image of overlapping ion tracks on a rutile TiO2 (001) surface (250 ion tracks per μm2, image height scale 4 nm, inset ×2 magnification). GISAXS maps of the irradiated surface acquired at (b) β = 0° and (c) β = 5°, where β is the angle formed by the surface tracks with the probing X-ray beam. The corresponding simulations of the GISAXS maps are shown as insets. The simulations are generated using the parameters of the fit.

Figure 2. Cover of the Special issue on small-angle scattering of the Journal of Applied Crystallography, featuring in the lower left quarter GISAXS maps of a non-irradiated surface (upper left) and of surfaces irradiated with 50 (upper right), 250 (lower left) and 900 (lower right) ion tracks per micron2 obtained at β = 90o (see figure 6 of our paper cited below).
Nanostructuring surfaces using swift heavy ions offers some unique possibilities owing to the deposition of a large amount of energy localized within a nanoscale volume surrounding the ion trajectory. Samples irradiated with different ion fluences were investigated using atomic force microscopy and grazing-incidence small-angle X-ray scattering. A detailed surface description was obtained even for the case of multiple ion track overlap.

To fully exploit the possibilities of swift heavy ion (SHI) irradiation, the morphology of nanostructures formed after SHI impact has to be known in detail. In the present work the response of a rutile TiO2 (001) surface to grazing-incidence SHI irradiation is investigated. Surface ion tracks with the well-known intermittent inner structure were successfully produced using 23 MeV I ions. Samples irradiated with different SHI fluences were investigated using atomic force microscopy (AFM) and grazing-incidence small-angle X-ray scattering (GISAXS). With these two complementary approaches, a detailed description of the SHI impact sites, i.e. the ion tracks on the surface, can be obtained even for the case of multiple ion track overlap. In addition to the structural investigation of surface ion tracks, the change in stoichiometry of the rutile TiO2 (001) surface during swift heavy ion irradiation was monitored using in situ time-of-flight elastic recoil detection analysis (TOF-ERDA), and a preferential loss of oxygen was found.

SHI irradiations were performed at the "Ruđer Bošković" Institute (RBI) in Zagreb, Croatia, using a 23 MeV I beam. Surface modifications were investigated using tapping mode AFM. Complementary GISAXS analysis was carried out at the synchrotron radiation facility Elettra-Sincrotrone Trieste, on the SAXS beamline, using synchrotron radiation with wavelength λ=0.154 nm (photon energy of 8 keV). To investigate possible stoichiometric changes of the TiO2, in situ TOF-ERDA measurements were performed at the RBI using the same 23 MeV I beam.

We have successfully demonstrated how the applied SHI fluence can be used for nanoscale patterning of the surface. We have investigated three irradiation regimes, namely non-overlapping ion tracks, overlapping ion tracks (figure 1) and multiple overlapping ion tracks. The successful characterization of the surface in all three different irradiation regimes constitutes the first and necessary step for exploiting surface patterning by grazing-incidence SHI irradiation. The preferential loss of oxygen from the rutile TiO2(001) surface during grazing-incidence SHI irradiation, monitored by in situ TOF-ERDA, opens up again the question of the composition of surface tracks. This surprising result clearly warrants further studies.

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Formation of swift heavy ion tracks on rutile TiO2 (001) surface ;
Marko Karlušić, Sigrid Bernstorff, Zdravko Siketić, Branko Šantić, Ivančica Bogdanović-Radović, Milko Jakšić, Marika Schleberger and Maja Buljan;
J. Appl. Cryst. 49, pp. 1704-1712 (2016). doi: 10.1107/S1600576716013704

Last Updated on Tuesday, 14 May 2019 17:05