Real Space Visualization of Entangled Excitonic States in Charged Molecular Assemblies

Deciphering rich non-covalent interactions that govern many chemical and biological processes is crucial for the design of drugs and controlling molecular assemblies and their chemical transformations. However, real-space characterization of...

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Real Space–Real Time Evolution of Excitonic States Based on the Bethe-Salpeter Equation Method

The Journal of Physical Chemistry Letters ◽

10.1021/acs.jpclett.1c01742 ◽

2021 ◽

pp. 7261-7269

Author(s):

Joshua D Elliott ◽

Edoardo Mosconi ◽

Filippo De Angelis ◽

Alberto Ambrosetti ◽

Paolo Umari

Keyword(s):

Real Time ◽

Time Evolution ◽

Real Space ◽

Equation Method ◽

Excitonic States

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High-resolution structure determination by ALCHEMI

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100074707 ◽

1983 ◽

Vol 41 ◽

pp. 178-181 ◽

Cited By ~ 1

Author(s):

Peter G. Self ◽

Peter R. Buseck

Keyword(s):

Site Occupancy ◽

Real Space ◽

Unit Cell ◽

Bragg Angle ◽

Electron Current ◽

High Resolution Structure ◽

Beam Incident ◽

Crystallographic Planes ◽

Electron Beam Incident ◽

Resolution Structure

ALCHEMI (Atom Location by CHanneling Enhanced Microanalysis) enables the site occupancy of atoms in single crystals to be determined. In this article the fundamentals of the method for both EDS and EELS will be discussed. Unlike HRTEM, ALCHEMI does not place stringent resolution requirements on the microscope and, because EDS clearly distinguishes between elements of similar atomic number, it can offer some advantages over HRTEM. It does however, place certain constraints on the crystal. These constraints are: a) the sites of interest must lie on alternate crystallographic planes, b) the projected charge density on the alternate planes must be significantly different, and c) there must be at least one atomic species that lies solely on one of the planes.An electron beam incident on a crystal undergoes elastic scattering; in reciprocal space this is seen as a diffraction pattern and in real space this is a modulation of the electron current across the unit cell. When diffraction is strong (i.e., when the crystal is oriented near to the Bragg angle of a low-order reflection) the electron current at one point in the unit cell will differ significantly from that at another point.

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An Image Reconstruction System Applied to High Voltage Microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100115080 ◽

1975 ◽

Vol 33 ◽

pp. 292-293

Author(s):

D. E. Johnson

Keyword(s):

High Voltage ◽

Prior Information ◽

Block Diagram ◽

Three Dimensional ◽

Real Space ◽

Two Dimensional ◽

Efficient Manner ◽

Fourier Methods ◽

Tilt Series ◽

Methods Of Reconstruction

Increased specimen penetration; the principle advantage of high voltage microscopy, is accompanied by an increased need to utilize information on three dimensional specimen structure available in the form of two dimensional projections (i.e. micrographs). We are engaged in a program to develop methods which allow the maximum use of information contained in a through tilt series of micrographs to determine three dimensional speciman structure.In general, we are dealing with structures lacking in symmetry and with projections available from only a limited span of angles (±60°). For these reasons, we must make maximum use of any prior information available about the specimen. To do this in the most efficient manner, we have concentrated on iterative, real space methods rather than Fourier methods of reconstruction. The particular iterative algorithm we have developed is given in detail in ref. 3. A block diagram of the complete reconstruction system is shown in fig. 1.

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Correlation averaging of two-dimensional crystals: basic strategy and refinements

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100142323 ◽

1986 ◽

Vol 44 ◽

pp. 136-139

Author(s):

W. Baumeister ◽

R. Rachel ◽

R. Guckenberger ◽

R. Hegerl

Keyword(s):

Low Dose ◽

Signal To Noise Ratio ◽

Real Space ◽

Fourier Domain ◽

Two Dimensional ◽

Signal To Noise ◽

Unit Cells ◽

Lateral Displacements ◽

Established Technique ◽

Crystalline Array

IntroductionCorrelation averaging (CAV) is meanwhile an established technique in image processing of two-dimensional crystals /1,2/. The basic idea is to detect the real positions of unit cells in a crystalline array by means of correlation functions and to average them by real space superposition of the aligned motifs. The signal-to-noise ratio improves in proportion to the number of motifs included in the average. Unlike filtering in the Fourier domain, CAV corrects for lateral displacements of the unit cells; thus it avoids the loss of resolution entailed by these distortions in the conventional approach. Here we report on some variants of the method, aimed at retrieving a maximum of information from images with very low signal-to-noise ratios (low dose microscopy of unstained or lightly stained specimens) while keeping the procedure economical.

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Probing vacancies and structural distortions at individual defects in ceramics using EELS

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100165859 ◽

1996 ◽

Vol 54 ◽

pp. 678-679

Author(s):

D. J. Wallis ◽

N. D. Browning

Keyword(s):

Structural Information ◽

Core Loss ◽

Nearest Neighbors ◽

Ceramic Materials ◽

Scanning Transmission Electron Microscope ◽

Real Space ◽

Atomic Scale ◽

Structure Property ◽

Scanning Transmission ◽

Key Issues

In electron energy loss spectroscopy (EELS), the near-edge region of a core-loss edge contains information on high-order atomic correlations. These correlations give details of the 3-D atomic structure which can be elucidated using multiple-scattering (MS) theory. MS calculations use real space clusters making them ideal for use in low-symmetry systems such as defects and interfaces. When coupled with the atomic spatial resolution capabilities of the scanning transmission electron microscope (STEM), there therefore exists the ability to obtain 3-D structural information from individual atomic scale structures. For ceramic materials where the structure-property relationships are dominated by defects and interfaces, this methodology can provide unique information on key issues such as like-ion repulsion and the presence of vacancies, impurities and structural distortion.An example of the use of MS-theory is shown in fig 1, where an experimental oxygen K-edge from SrTiO3 is compared to full MS-calculations for successive shells (a shell consists of neighboring atoms, so that 1 shell includes only nearest neighbors, 2 shells includes first and second-nearest neighbors, and so on).

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Two structural states of the Z-band in cardiac and skeletal muscle

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100157097 ◽

1989 ◽

Vol 47 ◽

pp. 1022-1023

Author(s):

J.P. Schroeter ◽

M.A. Goldstein ◽

J.P. Bretaudiere ◽

L.H. Michael ◽

R.L. Sass

Keyword(s):

Skeletal Muscle ◽

Cross Section ◽

Real Space ◽

Contractile State ◽

Contour Maps ◽

False Color ◽

Grey Scale ◽

Fourier Filtering ◽

Cardiac Muscles ◽

Enhancement Algorithm

We have recently established the existence of two structural states of the Z band lattice in cross section in cardiac as well as in skeletal muscle. The two structural states are related to the contractile state of the muscle. In skeletal muscle at rest, the Z band is in the small square (ss) lattice form, but tetanized muscle exhibits the basket weave (bw) form. In contrast, unstimu- lated cardiac muscle exhibits the bw form, but cardiac muscles exposed to EGTA show the ss form.We have used two-dimensional computer enhancement techniques on digitized electron micrographs to compare each lattice form as it appears in both cardiac and skeletal muscle. Both real space averaging and fourier filtering methods were used. Enhanced images were displayed as grey-scale projections, as contour maps, and in false color.There is only a slight difference between the lattices produced by the two different enhancement techniques. Thus the information presented in these images is not likely to be an artifact of the enhancement algorithm.

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Systematic zone-Axis orientation of NM-scale particles for microdiffraction

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100174448 ◽

1990 ◽

Vol 48 (4) ◽

pp. 262-263

Author(s):

E D Boyes ◽

L Hanna

Keyword(s):

Real Space ◽

Dark Field ◽

Zone Axis ◽

High Symmetry ◽

Lattice Imaging ◽

Cell Level ◽

Bright Field ◽

Axis Orientation ◽

Annular Dark Field ◽

Target Designation

A VG HB501 FEG STEM has been modified to provide track whilst tilt [TWIT] facilities for controllably tilting selected and initially randomly aligned nanometer-sized particles into the high symmetry zone-axis orientations required for microdiffraction, lattice imaging and chemical microanalysis at the unit cell level. New electronics display in alternate TV fields and effectively in parallel on split [+VTR] or adjacent externally synchronized screens, the micro-diffraction pattern from a selected area down to <1nm2 in size, together with the bright field and high angle annular dark field [HADF] STEM images of a much wider [˜1μm] area centered on the same spot. The new system makes it possible to tilt each selected and initially randomly aligned small particle into a zone axis orientation for microdiffraction, or away from it to minimize orientation effects in chemical microanalysis. Tracking of the inevitable specimen movement with tilt is controlled by the operator, with realtime [60Hz] update of the target designation in real space and the diffraction data in reciprocal space. The spot mode micro-DP and images of the surrounding area are displayed continuously. The regular motorized goniometer stage for the HB501STEM is a top entry design but the new control facilities are almost equivalent to having a stage which is eucentric with nanometric precision about both tilt axes.

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Conditions for atomic imaging of mullite

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100154068 ◽

1989 ◽

Vol 47 ◽

pp. 418-419

Author(s):

T. A. Epicier ◽

G. Thomas

Keyword(s):

Oxygen Vacancies ◽

High Resolution Electron Microscopy ◽

Ceramic Materials ◽

Work Conditions ◽

Real Space ◽

Potential Candidate ◽

Silicate Mineral ◽

Resolution Electron ◽

The Subject ◽

Aluminium Silicate

Mullite is an aluminium-silicate mineral of current interest since it is a potential candidate for high temperature applications in the ceramic materials field.In the present work, conditions under which the structure of mullite can be optimally imaged by means of High Resolution Electron Microscopy (HREM) have been investigated. Special reference is made to the Atomic Resolution Microscope at Berkeley which allows real space information up to ≈ 0.17 nm to be directly transferred; numerous multislice calculations (conducted with the CEMPAS programs) as well as extensive experimental through-focus series taken from a commercial “3:2” mullite at 800 kV clearly show that a resolution of at least 0.19 nm is required if one wants to get a straightforward confirmation of atomic models of mullite, which is known to undergo non-stoichiometry associated with the presence of oxygen vacancies.Indeed the composition of mullite ranges from approximatively 3Al2O3-2SiO2 (referred here as 3:2-mullite) to 2Al2O3-1SiO2, and its structure is still the subject of refinements (see, for example, refs. 4, 5, 6).

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Computer simulations for the TEM bend contour technique

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100163137 ◽

1996 ◽

Vol 54 ◽

pp. 134-135

Author(s):

Vladimir Yu. Kolosov ◽

Anders R. Thölén

Keyword(s):

Computer Simulations ◽

Real Space ◽

Advantages And Disadvantages ◽

Short Overview ◽

Diffraction Contrast ◽

Beam Method ◽

Convergent Beam ◽

Contour Technique

In this paper we give a short overview of two TEM applications utilizing the extinction bend contour technique (BC) giving the advantages and disadvantages; especially we consider two areas in which the BC technique remains unique. Special attention is given to an approach including computer simulations of TEM micrographs.BC patterns are often observed in TEM studies but are rarely exploited in a serious way. However, this type of diffraction contrast was one of the first to be used for analysis of imperfections in crystalline foils, but since then only some groups have utilized the BC technique. The most extensive studies were performed by Steeds, Eades and colleagues. They were the first to demonstrate the unique possibilities of the BC method and named it real space crystallography, which developed later into the somewhat similar but more powerful convergent beam method. Maybe, due to the difficulties in analysis, BCs have seldom been used in TEM, and then mainly to visualize different imperfections and transformations.

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