Investigation of the Structure of Amorphous Substances by Means of Electron Diffraction

Ankele, Jürgen; Mayer, Joachim; Lamparter, P.; Steeb, S.

doi:10.1515/zna-1994-7-807

Cited by 8 publications

(2 citation statements)

References 7 publications

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“…Employing the PEELS thickness measurement together with the elastic mean free path estimated from the relative magnitudes of electron interaction cross sections, single-scattered intensities were deconvoluted using the Hankel transform technique. 41,42 The resulting diffraction intensity pattern exhibits relative Bragg peak intensities in the lower Q ranges which are comparable to the single-scattered intensity calculated using the kinematical approximations.…”

Section: Inelastic and Multiple-scattering Effectssupporting

confidence: 59%

Boron-implantation-induced crystalline-to-amorphous transition in nickel: An experimental assessment of the generalized Lindemann melting criterion

et al. 1999

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The generalized Lindemann melting hypothesis has recently been used to develop a unified thermodynamic criterion for melting applicable to both heat-induced melting and disorder-induced crystalline-to-amorphous ͑c-a͒ transformation. The hypothesis stipulates that the sum ͗ 2 ͘ Total of the static and dynamic root-meansquare ͑rms͒ atomic displacements is a constant fraction of the nearest-neighbor distance along the melting curve of a solid. To test this hypothesis, energy-filtered selected area electron-diffraction intensity measurements were used to determine the generalized Lindemann parameter ␦ϭͱ͗ 2 ͘ Total /d nn , in which d nn represents the nearest-neighbor distance, as a function of boron concentration during implantation of 50-keV B ϩ into polycrystalline Ni at 77 K. The onset of amorphization was found to occur close to 10 at. % boron, which is in good agreement with the value predicted by T o curve calculated using the generalized Lindemann hypothesis. Moreover, the critical value of the generalized Lindemann parameter for amorphization, ␦ Critical

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Section: Inelastic and Multiple-scattering Effectssupporting

confidence: 59%

Boron-implantation-induced crystalline-to-amorphous transition in nickel: An experimental assessment of the generalized Lindemann melting criterion

et al. 1999

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“…k = 0.3Å -1 and k =0.55 Å -1 . Comparison of scattered intensities I(k) from a-Ge films [3] and all curves in Fig.4 showing a very similar behaviour with the two maxima at practically the same positions. Hence the curves of I and v resemble very much the scattered intensity of the material too.…”

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confidence: 60%

Fluctuation Electron Microscopy on a-Ge and Polycrystalline Gold

2003

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Structural information from amorphous materials is more difficult to obtain than from crystalline ones, and the methods are mainly restricted to scattering experiments with photons, neutrons or electrons. The scattered intensity is used to calculate the pair distribution function (PDF), which is a two-body function g 2 (r) representing the difference between the averaged local atomic density measured from an arbitrary atom and the macroscopic density of the material. The information obtained is predominantly on the short-range order (SRO) of the material. Treacy and Gibson [1,2] proposed a new method, named "fluctuation electron microscopy, FEM", to measure higher-order distribution functions, involving three or four atom correlations. With this method it should be possible to obtain information on the medium-range order (MRO), which gave us motivation to apply and test the FEM. In this contribution we present FEM-studies on amorphous germanium (a-Ge) and polycrystalline gold (Au). Our results are based on dark field images produced with hollow cone illumination (HCDF) using a Philips CM30ST operated at 200 kV. As fluctuations of the image intensity depending on the cone angle were measured, we used "variable coherence microscopy" [1] as one kind of FEM. After careful alignment of the beam (pivot points, roundness, focus, etc.) image series were acquired under remote control of the electron microscope at magnifications of 3.25 Å/pixel (a-Ge), resp. 5.82 Å/pixel (Au) on a 1k 2 CCD-camera (Gatan MSC794). The images were extensively processed in order to obtain the true electron intensity and to remove unwanted contributions to the variance, which includes gain-normalization, removal of X-rays, MTF-deconvolution and low pass filtering. To achieve statistically significant data, the images are divided into 9 equally-sized subimages, from which the mean intensity (I) and the variance (v) of the intensity were determined. Sub-images showing an extremely large deviation in v compared to the mean v value of all subimages pertaining to the same cone angle were not considered for analysis. Examples for high (a) and low (b) variance HCDF-images of both Au and aGe are shown in Fig.1 and Fig.3. The variance v as well as the mean intensity I as a function of the cone angle are shown in Fig.2 and Fig.4.

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