n-Beam lattice images. III. Upper limits of ionicity in W4Nb26O77

Anstis, G. R.; Lynch, D. F.; Moodie, A. F.; O’Keefe, Michael A.

doi:10.1107/s0567739473000379

Cited by 61 publications

(27 citation statements)

References 13 publications

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“…Individual metal-atom columns became accessible in alloys at 1.8-2.0Å resolution [5], and in silicates at 1.6Å resolution [6]. Development of software for simulation of HREM images from structural models explained the images and confirmed their interpretations [7][8][9][10][11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

HRTEM imaging of atoms at sub-Ångström resolution

O’Keefe¹,

Allard²,

Blom³

2005

Microscopy

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John Cowley and his group at Arizona State University pioneered the use of transmission electron microscopy (TEM) for high-resolution imaging. Images were achieved three decades ago showing the crystal unit cell content at better than 4Å resolution. This achievement enabled researchers to pinpoint the positions of heavy atom columns within the unit cell. Lighter atoms appear as resolution is improved to sub-Ångström levels. Currently, advanced microscopes can image the columns of the light atoms (carbon, oxygen, nitrogen) that are present in many complex structures, and even the lithium atoms present in some battery materials. SubÅngström imaging, initially achieved by focal-series reconstruction of the specimen exit surface wave, will become commonplace for next-generation electron microscopes with C S -corrected lenses and monochromated electron beams. Resolution can be quantified in terms of peak separation and inter-peak minimum, but the limits imposed on the attainable resolution by the properties of the microscope specimen need to be considered. At extreme resolution the "size" of atoms can mean that they will not be resolved even when spaced farther apart than the resolution of the microscope.

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Section: Introductionmentioning

confidence: 99%

HRTEM imaging of atoms at sub-Ångström resolution

O’Keefe¹,

Allard²,

Blom³

2005

Microscopy

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“…Anstis et al (1973), for example, demonstrated the strong effects that can make lattice image interpretation ambiguous in electron micrographs of a tungsten±niobium oxide. This work has nevertheless been made dif®cult in materials research by the fact that unit-cell sizes in most of the crystals are so small that at the lowest resolution for which data can be recorded, typically 2±5 A Ê , the chemical bonding effect is already very small.…”

Section: Introductionmentioning

confidence: 99%

Chemical bonding effects in the determination of protein structures by electron crystallography

et al. 1999

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Scattering of electrons is affected by the distribution of valence electrons that participate in chemical bonding and thus change the electrostatic shielding of the nucleus. This effect is particularly signi®cant for lowangle scattering. Thus, while chemical bonding effects are dif®cult to measure with small-unit cell materials, they can be substantial in the study of proteins by electron crystallography. This work investigates the magnitude of chemical bonding effects for a representative collection of protein fragments and a model ligand for nucleotide-binding proteins within the resolution range generally used in determining protein structures by electron crystallography. Electrostatic potentials were calculated by ab initio methods for both the test molecules and for superpositions of their free atoms. Differences in scattering amplitudes can be well over 10% in the resolution range below 5 A Ê and are especially large in the case of ionized side chains and ligands. We conclude that the use of molecule-based scattering factors can provide a much more accurate representation of the low-resolution data obtained in electron crystallographic studies. The comparison of neutral and ionic structure factors at resolutions below 5 A Ê can also provide a sensitive determination of charge states, important for biological function, that is not accessible from X-ray crystallographic measurements.

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“…(sin 0)/2 < 0-2 .A,-x, is strongly influenced by the chemical state of the atom, e.g. the valency state (see Anstis, Lynch, Moodie & O'Keefe, 1973). (2) Because of the short wavelength of --~ 100 keV electrons high-order reflections with (sin 0)/2 > 2 A-x, which are the reflections most sensitive to atomic positions, can be observed.…”

Section: Introductionmentioning

confidence: 99%

Large-angle convergent-beam electron diffraction; a simple technique for the study of modulated structures with application to V₂D

Taftø¹,

Metzger²

1985

J Appl Cryst

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With a highly convergent electron beam entering a small crystal area, the Bragg condition may be fulfilled simultaneously for many diffraction orders along a reciprocal-lattice direction, and reflections with (sin 0)/2 > 2 A-t are accessible. Considerations based on the dynamical theory of electron diffraction suggest that for Bragg reflections with (sin 0)/2>l/k -x, 100 keV electrons can be treated quasi-kinematically when the crystal thickness is less than 1000 ,~,, and this is supported by experiments. This simple approach has been used to determine the D-induced static displacement modulation 6 of V along the a axis (monochlinic indexing) in the/~ phase of VzD. From visual inspection of the Bragg intensities for large diffraction orders, up to (sin 0)/2=2.35/k -x, it is concluded that 6 = 0-070 (5)/k.

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n-Beam lattice images. III. Upper limits of ionicity in W₄Nb₂₆O₇₇

Cited by 61 publications

References 13 publications

HRTEM imaging of atoms at sub-Ångström resolution

HRTEM imaging of atoms at sub-Ångström resolution

Chemical bonding effects in the determination of protein structures by electron crystallography

Large-angle convergent-beam electron diffraction; a simple technique for the study of modulated structures with application to V₂D

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n-Beam lattice images. III. Upper limits of ionicity in W4Nb26O77

Cited by 61 publications

References 13 publications

HRTEM imaging of atoms at sub-Ångström resolution

HRTEM imaging of atoms at sub-Ångström resolution

Chemical bonding effects in the determination of protein structures by electron crystallography

Large-angle convergent-beam electron diffraction; a simple technique for the study of modulated structures with application to V2D

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n-Beam lattice images. III. Upper limits of ionicity in W₄Nb₂₆O₇₇

Large-angle convergent-beam electron diffraction; a simple technique for the study of modulated structures with application to V₂D