Long-Range Order Parameter Determination by Convergent Beam Electron Diffraction K.L. Torres,* R.R. Vanfleet,** and G.B. Thompson* * Department of Metallurgical and Materials Engineering, University of Alabama College of Engineering, Tuscaloosa, AL 35487 ** Department of Physics and Astronomy, Brigham Young University College of Physical and Mathematical Science, Provo, UT 84602 The L1 0 phase of Fe-Pt has been identified as a leading candidate for ultrahigh-density magnetic storage media because of its high magnetocrystalline anisotropy, K u [1]. The K u of this alloy has been known to be strongly dependent on the long-range order parameter S, where K u decreases with S [2]. S can be determined by a number of methods. The most readily available technique is x-ray diffraction. Experimentally, S is determined by measuring the total integrated peak intensities of the superlattice and fundamental reflections according to kinematical scattering theory [3]. However, the amount of x-ray scattering from thin films can be very small and difficult to measure with laboratory diffractometers. In contrast, electron scattering can be more amenable for diffraction studies of small volumes, though the strong interaction of electrons with the thin film results in multiple scattering events. As a result, the traditional methodology of taking the ratio of integrated intensities no longer applies and S determination becomes more complex. In this study, the multislice simulation approach was used to simulate electron transmission in crystalline thin films including dynamical scattering [4] to determine S which was then compared to x-ray measurements of S on the same films. An 11.7 nm Fe 50 Pt 50 thin film was dc magnetron sputter-deposited from commercially pure Fe and Pt targets onto an MgO <001> substrate heated to a temperature of 500 °C. Post-deposition, the film was annealed at 600°C for 30 minutes in an Ar/4%H 2 atmosphere. The composition of the film was determined by Rutherford backscattering spectrometry (RBS). Convergent-beam electron diffraction (CBED) patterns were experimentally collected using scanning transmission electron microscopy (STEM) in a FEI Tecnai F20 operated at 200 keV. A convergent beam of 4 mrad convergence semi- angle was focused on the specimen to obtain the CBED patterns. This angle was chosen to give the minimal overlap between the diffracted disks. In this experiment, CBED patterns with [001] beam incidence were recorded using a 1k charge-coupled device (CCD) camera using an integration time of 0.5 s. To correctly account for multi-scattering events of the electrons, a multislice simulation needs to be used to predict the CBED intensities for given order parameters and thicknesses. In this study, the ratio of the (110) superlattice to the (220) fundamental reflection (I 110 /I 220 ) was used. The input parameters for the multislice simulations were matched to the experimental conditions (e.g. convergence semi-angle of 4 mrad; spherical aberration coefficient C s of 1.35 mm; temperature of 94K; and specimen thickness). Fig. 1a is a simulated CBED pattern for [001] zone axis, order parameter of 0.4, and a film thickness of 11.7 nm. Fig. 2 is the simulated results for the measured film thickness and for thicknesses associated with the estimated error of the measurements. 250 doi:10.1017/S1431927610058113 Microsc. Microanal. 16 (Suppl 2), 2010 © Microscopy Society of America 2010 . https://doi.org/10.1017/S1431927610058113 Downloaded from https://www.cambridge.org/core. IP address: 34.201.52.186, on 22 Aug 2017 at 21:51:04, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms