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RE Dunin-Borkowski

Publications and source records attributed to RE Dunin-Borkowski.

9 recordsLinked to original sources
PubMed2000

Discrete atom imaging of one-dimensional crystals formed within single-walled carbon nanotubes

The complete crystallography of a one-dimensional crystal of potassium iodide encapsulated within a 1.6-nanometer-diameter single-walled carbon nanotube has been determined with high-resolution transmission electron microscopy. Individual atoms of potassium and iodine within the crystal were identified from a phase image that was reconstructed with a modified focal series restoration approach. The lattice spacings within the crystal are substantially different from those in bulk potassium iodide. This is attributed to the reduced coordination of the surface atoms of the crystal and the close proximity of the van der Waals surface of the confining nanotube.

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PubMed2000

The development of Fresnel contrast analysis, and the interpretation of mean inner potential profiles at interfaces

This paper provides a summary of recent published and unpublished research on the development of Fresnel contrast analysis, a transmission electron microscopy technique for measuring the mean inner potential profile across an interface or a narrow layer. An algorithm for finding a best-fitting potential profile is described, energy-filtered experimental data are analyzed and contributions to Fresnel contrast from surface grooves and space charge are assessed. Many of the conclusions drawn are equally relevant for the interpretation of phases measured using off-axis electron holography.

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PubMed2000

Experimental characterisation of CCD cameras for HREM at 300 kV

The modulation transfer function, noise transfer function and detection quantum efficiency of both 1k2 and 2k2 cameras attached to the same 300 kV FEGTEM have been measured. The results show that both the MTF and the DQE of the 2k2 camera are lower than for the 1k2 camera at frequencies above a third of the Nyquist limit. This lower per-pixel performance of the 2k2 camera is primarily a result of the use of a thicker phosphor scintillator. However, MTF and DQE of the 2k2 camera operated as an effective 1k2 camera by using 2 x 2 pixel binning are superior to the 1k2 camera in the medium spatial frequency range.

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PubMed1999

Origin of magnetization decay in spin-dependent tunnel junctions

Spin-dependent tunnel junctions based on magnetically hard and soft ferromagnetic layers separated by a thin insulating barrier have emerged as prime candidates for information storage. However, the observed instability of the magnetically hard reference layer, leading to magnetization decay during field cycling of the adjacent soft layer, is a serious concern for future device applications. Using Lorentz electron microscopy and micromagnetic simulations, the hard-layer decay was found to result from large fringing fields surrounding magnetic domain walls in the magnetically soft layer. The formation and motion of these walls causes statistical flipping of magnetic moments in randomly oriented grains of the hard layer, with a progressive trend toward disorder and eventual demagnetization.

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PubMed1999

Determination of mean inner potential of germanium using off-axis electron holography.

Off-axis electron holography has been used to determine the mean inner potential of germanium using cleaved 90 degrees wedge samples, where the wedge thickness profiles were checked by weak-beam dark-field extinction fringes. Dynamical contributions to the phase of the image were minimized by tilting to weakly diffracting conditions, as confirmed by reference to convergent-beam electron diffraction patterns. Small residual corrections were determined using multislice calculations. From a total of 18 separate measurements, it is concluded that the value of the mean inner potential is 14.3(2) V, which agrees with recent theoretical calculations to within experimental error.

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PubMed1999

Moiré patterns in electron microscopy with atomic focuser crystals.

The periodic array of very fine cross-overs formed at the exit face of a thin 'atomic focuser' crystal, illuminated by a parallel electron beam, may be used to form moiré patterns with a specimen crystal such that the structure of the specimen crystal may be derived with a resolution of better than 0.5 Å. Computer simulations of the moiré pattern formation have been made for the simple idealized case of two parallel gold-like lattices having a 10% difference in lattice constant. Moiré images are shown for the case of a small objective aperture in the viewing electron microscope such that the individual crystal lattices are not resolved and for a larger objective aperture for which the individual crystal lattices are resolved and the intensity is measured at the positions of the atoms of the atomic focuser crystal. The latter case confirms the viability of the scheme for ultra-high-resolution imaging of general specimens by use of a thin-crystal periodic atomic focuser, as previously proposed.

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PubMed1999

Simulations for imaging with atomic focusers.

The basis has been explored for the possible application of the various schemes that have been proposed for making use of the focusing properties of single heavy atoms, or rows of atoms extending through thin crystals in axial directions, for the attainment of ultra-high resolution in electron microscopy. Calculations are reported for the form of 200 keV electron beams channeled along rows of atoms through crystals and propagated in the vacuum beyond the crystals. The conditions for forming beams less than 0.05 nm in diameter have been established. Simulations of images having resolutions of this order are reported for the case that the specimen is placed at the Fourier image position beyond the exit face of a thin crystal and the transmission of the periodic array of ultra-fine beams, translated laterally by tilting the incident beam, may be observable using a conventional transmission-electron-microscopy (TEM) instrument.

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PubMed1998

Magnetic microstructure of magnetotactic bacteria by electron holography

Off-axis electron holography in the transmission electron microscope was used to correlate the physical and magnetic microstructure of magnetite nanocrystals in magnetotactic bacteria. The magnetite crystals were all single magnetic domains, and the magnetization directions of small superparamagnetic crystals were constrained by magnetic interactions with larger crystals in the chains. Shape anisotropy was found to dominate magnetocrystalline anisotropy in elongated crystals. A coercive field between 300 and 450 oersted was determined for one chain.

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