The Fresnel Method for the Characterisation of Interfaces

Stobbs, W. M.; Ross, Frances M.

doi:10.1007/978-1-4613-0527-9_14

Cited by 10 publications

(5 citation statements)

References 21 publications

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“…The individual images in a through-focal series are obtained at resolutions which are often a factor of two or three below that to which the form of an interface can be inferred from the series as a whole (e.g. Stobbs & Ross, 1989). However, given that our initial interest here lies in the effects of the inelastic scattering on the contrast, we have chosen to compare filtered and unfiltered image series obtained with no objective aperture, the microscope being used conventionally with the objective minilens switched off.…”

Section: The Qualitative Differences Between Filtered and Unfiltered mentioning

confidence: 99%

“…Fresnel contrast analysis in the transmission electron microscope (TEM) can be used to determine the compositional abruptness of interfaces in layered systems (Stobbs & Ross, 1989). The method relies on the sensitivity of the elastic rather than the inelastic scattering of electrons to local changes in the projected potential, and the numerical approaches that can be used in such analyses are described by Ross & Stobbs (1991a) for different types of problem.…”

Section: Introductionmentioning

confidence: 99%

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Energy‐filtered Fresnel contrast analysis of Fe/Cu multilayers

Dunin-Borkowski

Boothroyd

Lloyd

et al. 1995

Journal of Microscopy

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SUMMARY Energy‐filtered imaging in the transmission electron microscope is applied to the Fresnel contrast exhibited by a fine‐period Fe/Cu multilayer. Comparisons of filtered and unfiltered image series demonstrate the effects of inelastic scattering, and it is shown that the use of energy filtering allows improved confidence in the physical origins of the contrast for a specimen, such as that described, for which the structure is still uncertain.

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Section: The Qualitative Differences Between Filtered and Unfiltered mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Energy‐filtered Fresnel contrast analysis of Fe/Cu multilayers

Dunin-Borkowski

Boothroyd

Lloyd

et al. 1995

Journal of Microscopy

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“…For lattice and Fresnel fringe imaging, the specimen was further tilted, keeping the grain boundary parallel to the electron beam, using procedures described by Cinibulk et al . (1993) and Stobbs & Ross (1989), respectively.…”

Section: Methodsmentioning

confidence: 98%

Aspects regarding measurement of thickness of intergranular glassy films

Bhattacharyya¹,

Subramaniam²,

Koch³

et al. 2006

Journal of Microscopy

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Summary Materials such as Si3N4, SiC and SrTiO3 can have grain boundaries characterized by the presence of a thin intergranular amorphous film of nearly constant thickness, in some cases (e.g. Si3N4) almost independent of the orientation of the bounding grains, but dependent on the composition of the ceramic. Microscopy techniques such as high‐resolution lattice fringe imaging, Fresnel fringe imaging and diffuse dark field imaging have been applied to the study of intergranular glassy films. The theme of the current investigation is the use of Fresnel fringes and Fourier filtering for the measurement of the thickness of intergranular glassy films. Fresnel fringes hidden in high‐resolution micrographs can be used to objectively demarcate the glass–crystal interface and to measure the thickness of intergranular glassy films. Image line profiles obtained from Fourier filtering the high‐resolution micrographs can yield better estimates of the thickness. Using image simulation, various kinds of deviation from an ideal square‐well potential profile and their effects on the Fresnel image contrast are considered. A method is also put forth to objectively retrieve Fresnel fringe spacing data by Fourier filtering Fresnel contrast images. Difficulties arising from the use of the standard Fresnel fringe extrapolation technique are outlined and an alternative method for the measurement of the thickness of intergranular glassy films, based on zero‐defocus (in‐focus) Fresnel contrast images is suggested. The experimental work is from two ceramic systems: Lu‐Mg‐doped Si3N4 and SrTiO3 (stoichiometric and nonstoichiometric). Further, a comparison is made between the standard high‐resolution lattice fringe technique, the standard Fresnel fringe extrapolation technique and the methods of analyses introduced in the current work, to illustrate their utility and merits. Taking experimental difficulties into account, this work is intended to be a practical tool kit for the study of intergranular glassy films.

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“…The superlattice structure proved to be viewable far from focus, as is demonstrated by the image in Fig. 1 [15]. In all of the specimens examined, the layers were parallel to the silicon substrate and approximately uniform in spacing.…”

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Direct Observation of Compositionally Homogeneousa-C: H Band-Gap-Modulated Superlattices

et al. 1995

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It is shown that amorphous hydrogenated carbon (a-C:H) band-gap-modulated superlattices can be observed by transmission electron microscopy.The layering proves to be well defined and it is demonstrated that changes in the band gap from 1.5 to 2.8 eV cannot be associated with ordered graphitic regions, in that crystalline regions larger than 0.5 nm are not observed. Differences in the amount of~bonding are found to lead to changes in the average atomic scattering factor. It is suggested that the changes in~bonding are associated with changes in local ordering that control the band gap. PACS numbers: 68.65.+g, 61.14. -x, 61.16.Bg, 61.43.Dq Superlattice structures consisting of alternate layers of lattice-matched crystalline materials with different band gaps are known to exhibit a variety of interesting and important quantum mechanical effects for sufficiently small layer widths [1]. Abeles and Tiedje [2] have shown that related effects can be observed in superlattices consisting of pairs of amorphous materials such as a-Si:H/a-SiN:H. All of the band-gap-modulated superlattices of this class that have been studied to date have been heterogeneous systems in the sense that the high and low band-gap layers have been made of amorphous materials with substantially different chemical compositions. Hydrogenated amorphous carbon (a-C:H) films made by RF plasma decomposition of low pressure hydrocarbon gases contain a mixture of tetrahedral (sps), trigonal (sp ), and linear (sp') carbon bonding, as well as a significant fraction of incorporated hydrogen. The mechanical, optical, and electrical properties of these films can vary considerably depending on the deposition conditions [3]. In particular, the Tauc optical band gap [4] can be varied over the surprisingly large range of 1.2 to 4 eV simply by changing the power of the RF excitation [5]. This enables band-gap-modulated superlattice structures to be fabricated by sequentially depositing high and low band-gap a-C:H layers [6-8]. Since the alternate layers are both a-C:H, these superlattices are unusual in that the large band-gap modulation is obtained for a minimal change in the hydrogen content for the high density films examined here. Competing explanations of the origin of the large band-gap variation in such a material include significant changes in C-C or C-H bonding configurations [9], changes in the size of graphitic clusters [9], and changes in the distortion of ring structures [10]. In this Letter, transmission electron microscope (TEM) techniques are used to characterize the structure of a-C:H band-gap-modulated superlattices. The layers differ in their H contents by only 3 at. %. It is shown that the superlattice can be imaged using the Fresnel contrast caused by small changes in density and bonding. Electron energy loss spectroscopy (EELS) and dark field TEM observations are used to characterize the valence electron density, bonding type, and structure. The relationship between the optical band gap and the structure of high density a-C:H films is discussed i...

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The Fresnel Method for the Characterisation of Interfaces

Cited by 10 publications

References 21 publications

Energy‐filtered Fresnel contrast analysis of Fe/Cu multilayers

Energy‐filtered Fresnel contrast analysis of Fe/Cu multilayers

Aspects regarding measurement of thickness of intergranular glassy films

Direct Observation of Compositionally Homogeneousa-C: H Band-Gap-Modulated Superlattices

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