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ItemPlasmon excitations in carbon onions: Model vs. measurements(Georgia Institute of Technology, 1998-03) Stöckli, Thomas ; Wang, Z. L. (Zhong Lin) ; Bonard, Jean-Marc ; Stadelmann, Pierre ; Châtelain, AndréNon-relativistic local dielectric response theory has proven successful in the interpretation of Electron Energy Loss data of nanometer-size isotropic particles of different geometries. In previous work, we have adapted this model to take into account anisotropy as encountered in the case of carbon onions. We have shown that this anisotropy needs to be taken into account since important deviations with respect to an isotropic model can be observed. In this contribution, we report on the first energy filtered images of carbon onions and compare intensity profiles across the spheres to our calculations.
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ItemMicrostructure and reconstruction of LaAlO₃{100} and {110} surfaces(Georgia Institute of Technology, 1995) Wang, Z. L. (Zhong Lin) ; Shapiro, AlexanderLanthanum-aluminate (LaAlO₃) is one of the optimum substrates for epitaxic growth of thin oxide films. In this paper, the structures of the {100} and {110} surfaces of annealed LaAlO₃ are studied using reflection electron microscopy (REM). [010] and [001] steps have been observed on {100}, these are believed to be the lowest surface energy steps. The {100} surface is atomically flat, but the {110} surfaces exhibit high-density fine structures distributed on large surface terraces. These fine structures may correspond to the formation of small width (100) and (010) facets on the (110) surface. The 5x5 reconstruction is observed on {100}. No reconstruction is found on {110}.
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ItemGrowth of Epitaxial BaTiO₃Thin Films at 600°C by Metalorganic Chemical Vapor Deposition(Georgia Institute of Technology, 1995) Kaiser, D. L. ; Vaudin, M. D. ; Rotter, L. D. ; Wang, Z. L. (Zhong Lin) ; Cline, J. P. ; Hwang, C. S. ; Marinenko, R. B. ; Gillen, J. G.Metalorganic chemical vapor deposition (MOCVD) was used to deposit epitaxial BaTiO₃3 thin films on (100) MgO substrates at 600°C. The metalorganic precursors employed in the deposition experiments were hydrated Ba(thd)2 (thd = CIIH190 2) and titanium isopropoxide. The films were analyzed by means of transmittance spectroscopy, wavelength dispersive x-ray spectrometry, secondary ion mass spectrometry depth profiling, x-ray diffraction, high resolution transmission electron microscopy, selected area electron diffraction, nanoscale energy dispersive x-ray spectrometry and second harmonic generation measurements. There was no evidence for interdiffusion between the film and substrate. The x-ray and electron diffraction studies showed that the films were oriented with the a-axis normal to the substrate surface, whereas second harmonic generation measurements showed that the films had some c-axis character.
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ItemEpitaxial growth of Pt(001) thin films on MgO(001) under oxidizing conditions(Georgia Institute of Technology, 1993) Cui, G. ; Van Buskirk, P. C. ; Zhang, J.Beetz, C. P., Jr. ; Steinbeck, J. ; Wang, Z. L. (Zhong Lin) ; Bentley, J.Epitaxial Pt(001) thin films have been grown on MgO(001) substrates using dc magnetron sputtering with an Ar/O₂ mixture at 700°C. The width (FWHM) of the rocking curve of the Pt(002) peak is between 0.16° and 0.20°, which is only 0.05° wider than that of the MgO (002) peak of the cleaved substrate. The film surface roughness is about 1 nm (rms) for a 240 nm thick Pt film. No grain structure could be observed using SEM. In contrast, the films deposited at 700 °C with pure Ar, have both Pt(111) and Pt(001) oriented growth, as shown by XRD Θ -2 Θ scans, with the Pt(111) peak having the largest intensity. BaTiO₃ epitaxial films have also been deposited on Pt(001)/MgO(001). The width (FWHM) of the rocking curve of the BaTiO₃(200) peak is 0.4°. The surface morphology of the epitaxial BaTiO₃(100) thin films on Pt(001)/MgO(001) is featureless. XRD pole figure measurements on PtIBaTiO₃/Pt trilayer shown a very good in-plane alignment of all layers. The epitaxial growth relationship was also confirmed by TEM electron diffraction and cross-section imaging. The Pt/BaTiO₃/Pt epitaxial trilayer could serve as a prototype for ferroelectric capacitors and may be able to improve the electrical properties of the capacitors.
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ItemIn-situ observations of high temperature surface processes on α-alumina bulk crystals(Georgia Institute of Technology, 1991) Wang, Z. L. (Zhong Lin) ; Bentley, JamesReflection electron microscopy (REM) was applied to image in-situ the dynamic changes of atomic-height steps on the surfaces of a-alumina bulk crystals heated to high temperatures. Atomic diffusion, desorption and adsorption processes on cleaved a-alumina (012) surfaces were directly observed at temperatures of 1470 to 1670 K. The surface started to show visible structural changes at 1470-1520 K. The main surface process appears to be atomic desorption, which creates large, flat vacancy-type terraces on the surface.