Bender, M.

Klaumünzer, S.

Romanenko, A.

Severin, D.

GSI Repository

Ion-Beam induced grain rotation in nanocrystalline alumina S. Klaumünzer1,2, M. Bender1, A. Romanenko1, D. Severin1,# 1GSI, Darmstadt, Germany; 2HZ Berlin, Berlin, GermanySingle crystals of -alumina (orientation ሾ112ത0ሿ, 15101 mm3) were bombarded at room temperature with 4.8 MeV/u Au ions. The transformation of the single crystals into nanocrystals was followed by monitoring the ሺ112ത0ሻ-diffraction peak by CuK-radiation at the in-situ 3-circle-diffractometer at the UNILAC M2-beamline. The -circle (incident x-ray beam) and the -circle (diffracted beam) define the diffraction plane. The -circle enables a sample tilt relative to the diffraction plane; for  = 0 the sample normal lies in the diffraction plane and coincides with the ion beam direction. During irradiation i was 45°. X-ray measurements were done by varying  and  =  fixed at the Bragg angle B. The single peak originally located at  = 0 splits with increasing fluence into two peaks, one located at 1 = 0, originating from unmodified material at greater specimen depths, and a second one, located at 2, resulting from tilted 	ሺ112ത0ሻ-lattice planes. The tilt angle   2 versus fluence is shown in fig. 1. At a fluence of 11013 Au/cm2 i has moved from 45° to 45°. The rotation direction also changed its sign. A symmetric Bragg scan at  = 2 yields the precise position of B and the peak width of the modified alumina. B de-creased by about 0.1°, which is attributed to a volume increase by dislocation production. The width of the mod-ified peak is shown in fig. 2. The change in i is not visi-ble in the behavior of the width.   Figure 1: Crystallite tilt  versus ion fluence.  Both grain rotation and the square-root dependence of the width (see fig. 2) indicated the action of dislocations. Be-cause the number density of dislocations is of the order of t, most of the dislocations are concentrated in newly formed grain boundaries. Thus, at t 1012 Au/cm2 the single crystal is transformed into an aggregate of nano-crystals. The evolution of the grain size is depicted in fig. 3 for two data evaluation strategies.   Figure 2: The full width at half maximum FWHM of the ሺ112ത0ሻ-Bragg peak of -alumina as function of ion flu-ence.     Figure 3: Grain size D versus ion fluence derived from the separation of grain size and strain contributions to FWHM. The black curve has been obtained with the usual assumption that the Gaussian and the Lorentzian widths to the Pseudo-Voigt peak widths are equal. The red curve has been obtained by a procedure proposed by de Keijser [1]   [1] de Keijser et al., J. Appl. Cryst. 15(1982) 308-314. 0.0 0.5 1.0 1.5 2.00246810i = -45°i = +45°crystallite tilt  (degrees)fluence t (1013 Au/cm2)0.0 0.5 1.0 1.5 2.00.000.250.500.751.001.25i= -45°FWHM (degrees)fluence  t (1013 Au/cm2) i=+45°0.0778°+0.71°sqrt( t - 8.2x1011Au/cm 2)0.0 0.5 1.0 1.5 2.0110100500grain size D [nm]fluence  t (1013 Au/cm2)  de KeijserFW HMLorentz = FW HMGauss ___________________________________________  #  d.severin@gsi.de APPA-MML-MR-08 GSI SCIENTIFIC REPORT 2014260 DOI:10.15120/GR-2015-1-APPA-MML-MR-08

Ion-Beam induced grain rotation in nanocrystalline alumina

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Ion-Beam induced grain rotation in nanocrystalline alumina

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