7-beam lattice images of (110) oriented Ge

1978 ◽  
Vol 36 (1) ◽  
pp. 290-291
Author(s):  
J.R. Parsons ◽  
C.W. Hoelke
Keyword(s):  
Image Features ◽  
Objective Lens ◽  
Lattice Plane ◽  
Lattice Image ◽  
Crystalline Defects ◽  
Transmission Electron ◽  
Lattice Images ◽  
Electron Microscopes ◽  
Structural Aspects ◽  
Beam Lattice

The direct imaging of a crystal lattice has intrigued electron microscopists for many years. What is of interest, of course, is the way in which defects perturb their atomic regularity. There are problems, however, when one wishes to relate aperiodic image features to structural aspects of crystalline defects. If the defect is inclined to the foil plane and if, as is the case with present 100 kV transmission electron microscopes, the objective lens is not perfect, then terminating fringes and fringe bending seen in the image cannot be related in a simple way to lattice plane geometry in the specimen (1).The purpose of the present work was to devise an experimental test which could be used to confirm, or not, the existence of a one-to-one correspondence between lattice image and specimen structure over the desired range of specimen spacings. Through a study of computed images the following test emerged.

Mapping the composition of materials at the atomic level

1992 ◽  
Vol 50 (2) ◽  
pp. 1474-1475
Author(s):  
A. Ourmazd ◽  
F.H. Baumann ◽  
Y. Kim ◽  
C. Kisielowski ◽  
P. Schwander
Keyword(s):  
Imaging Techniques ◽  
Atomic Level ◽  
Objective Lens ◽  
Lattice Imaging ◽  
Electron Microscopic ◽  
Lattice Image ◽  
Crystalline Materials ◽  
Transmission Electron ◽  
Lattice Images ◽  
Compositional Changes

This paper briefly outlines how transmission electron microscopic lattice imaging techniques can be used to map the composition of crystalline materials at the atomic level.Under appropriate conditions, a conventional lattice image is a map of the sample structure, because the dominant reflections used to form lattice images are relatively insensitive to compositional changes in the sample. Such reflections may be termed “structural”. In many cystalline materials, compositional changes occur by atomic substitution on a particular subset of lattice sites. In these systems, compositional changes are accompanied by the appearance of reflections, which we name “chemical”. Such reflections, for example the (200) in the zinc-blende structure, owe their existence to chemical differences between the various atomic species present on the different lattice sites. For fundamental reasons these reflections are often weak; they come about because of incomplete cancellation of out of phase contributions from different sublattices. “Chemical lattice imaging” exploits dynamical scattering to maximize the intensity of such reflections, and uses the objective lens as a bandpass filter to enhance their contribution to the image.

Progress in Computer Assisted Electron Microscopy

1997 ◽  
Vol 3 (S2) ◽  
pp. 1093-1094
Author(s):  
M. Pan ◽  
K. Ishizuka ◽  
C. E. Meyer ◽  
O. L. Krivanek ◽  
J. Sasakit ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Computer Control ◽  
Image Features ◽  
Ease Of Use ◽  
External Control ◽  
Objective Lens ◽  
Computer Assisted ◽  
Serial Interface ◽  
Transmission Electron ◽  
Electron Microscopes

All the lenses, deflectors and stigmators of contemporary electron microscopes are controlled digitally by an internal computer. Control through RS232 serial interface by an external computer has also become a standard feature. This external control has made so-called computer assisted electron microscopy (CAEM) possible and practical. We are developing a CAEM system with two objectives: (1) to free inexperienced microscopists from technical details of operating an electron microscope, especially transmission electron microscopes (TEM); (2) to assist experienced microscopists to operate their microscopes with higher accuracy and efficiency. The features include automated and/or assisted standard operations in focusing, stigmating, and aligning the microscope, and also sophisticated tuning that requires the evaluation of subtle changes in image features such as aligning the incident electron beam direction in the presence of 3-fold astigmatism in objective lens. CAEM can further assist operators in selecting areas or objects and taking images/diffraction/energy spectrum with all the parameters well controlled and catalogued together, thus not only enabling ease-of-use and high accuracy in operation but also yielding more information on the specimen.

Measuring projected potential, thickness, and composition from lattice images

1994 ◽  
Vol 52 ◽  
pp. 732-733
Author(s):  
A. Ourmazd ◽  
P. Schwander ◽  
C. Kisielowski ◽  
F. H. Baumann ◽  
Y. Kim
Keyword(s):  
Quantitative Information ◽  
Image Features ◽  
Contrast Transfer Function ◽  
Lattice Image ◽  
Crystalline Materials ◽  
Transmission Electron ◽  
Highly Nonlinear ◽  
Lattice Images ◽  
Point To Point ◽  
Image Details

Lattice images obtained by Transmission Electron Microscopy (TEM) are routinely used to infer the subsurface microstructure of crystalline materials. In principle, a lattice image is a map of the sample (Coulomb) potential, projected along a zone axis (see, e.g., [1]). In practice, it is difficult to extract quantitative information from lattice images. This stems from two primary reasons. First, electrons are multiply scattered during their passage through crystalline samples of realistic thickness (>10Å). This results in a complex, highly nonlinear relationship between the sample potential and the characteristics of the lattice image. This relationship changes rapidly with the sample thickness, and thus from point to point over the sample. Second, electromagnetic lenses have severe aberrations. The image details thus depend sensitively on the (contrast) transfer function of the microscope, and hence the lens defocus. It is not possible to establish a general relationship between the sample potential and the image features.

Calculation of structure images of crystalline defects

1978 ◽  
Vol 36 (1) ◽  
pp. 282-283
Author(s):  
M.A. O'Keefe ◽  
Sumio Iijima
Keyword(s):  
Diffuse Scattering ◽  
Computing Time ◽  
Continuous Distribution ◽  
Sampling Interval ◽  
Reciprocal Space ◽  
Objective Lens ◽  
Lattice Images ◽  
Slice Method ◽  
Space Cell ◽  
Beam Lattice

We have extended the multi-slice method of computating many-beam lattice images of perfect crystals to calculations for imperfect crystals using the artificial superlattice approach. Electron waves scattered from faulted regions of crystals are distributed continuously in reciprocal space, and all these waves interact dynamically with each other to give diffuse scattering patterns.In the computation, this continuous distribution can be sampled only at a finite number of regularly spaced points in reciprocal space, and thus finer sampling gives an improved approximation. The larger cell also allows us to defocus the objective lens further before adjacent defect images overlap, producing spurious computational Fourier images. However, smaller cells allow us to sample the direct space cell more finely; since the two-dimensional arrays in our program are limited to 128X128 and the sampling interval shoud be less than 1/2Å (and preferably only 1/4Å), superlattice sizes are limited to 40 to 60Å. Apart from finding a compromis superlattice cell size, computing time must be conserved.

Many-Beam Lattice Images from Thicker Crystals

1978 ◽  
Vol 36 (3) ◽  
pp. 130-139
Author(s):  
S. Iijima
Keyword(s):  
Electron Microscopy ◽  
Materials Science ◽  
Complex Oxides ◽  
Crystal Defects ◽  
Planar Defects ◽  
Transmission Electron ◽  
Lattice Images ◽  
The Many ◽  
Atom Configuration ◽  
Beam Lattice

Nearly a decade ago, the usefulness of lattice images for studying crystal defects was reported by Allpress et al. (1969). They analyzed abnormally spaced lattice fringes of crystals of the complex oxides and derived successfully the nature of planar defects occurring on a unit cell scale. Since then the method for studying atom configuration in crystals using high resolution transmission electron microscopy (HRTEM) has been investigated extensively. The studies have involved theoretical calculation of the many-beam lattice images of perfect crystals and applications of the method to solve problems in materials science.

Dark Field Procedures in Electron Microscopy of Particulate Biological Material

1971 ◽  
Vol 29 ◽  
pp. 426-427
Author(s):  
E. de Harven ◽  
K. R. Leonard ◽  
A. K. Kleinschmidt
Keyword(s):  
Dark Field Image ◽  
Dark Field ◽  
Carbon Films ◽  
Objective Lens ◽  
Uranyl Ions ◽  
E Coli ◽  
Transmission Electron ◽  
Beam Stop ◽  
Electron Microscopes ◽  
Horse Spleen Ferritin

The dark field image of a specimen is obtained by allowing elastically scattered electrons to pass along the optic axis of the objective lens. Most of the inelastically scattered and the undeflected electrons are eliminated by various procedures, three of which have been found practical in conventional transmission electron microscopes. These three procedures are based on the use of: i) “beam stop” dark field apertures positioned in the back focal plane of the objective lens, as described by Thon; ii) electron beam tilted mechanically, or by a deflecting magnetic coil system between the condenser lens and the object; iii) a “cone mantle” illumination of the object obtained by an annular condenser aperture of appropriate dimension. Our observations have been made with Siemens Elmiskop 1A and 101 electron microscopes, equipped with pointed cathodes (single crystal or lancet-shaped). All samples were supported by ultrathin (2 to 3 nm) carbon films. They included: (a) various viral DNA-cytochrome c monolayers, (b) horse spleen ferritin, (c) B. Subtilis SP 50 bacteriophages, and (d) 50 S E. Coli ribosomal particles. Samples (c) and (d) were stained with uranyl ions.

A High Resolution Dual Gun Electron Miscroscope for TEM and SEM

1974 ◽  
Vol 32 ◽  
pp. 422-423
Author(s):  
P. S. Ong ◽  
C. L. Gold
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
Spot Size ◽  
Resolving Power ◽  
Objective Lens ◽  
Scanning System ◽  
Transmission Electron ◽  
Mode Of Operation ◽  
Electron Microscopes ◽  
Scanning Electron

Transmission electron microscopes (TEM) have the capability of producing an electron spot (probe) with a diameter equal to its resolving power. Inclusion of the required scanning system and the appropriate detectors would therefore easily convert such an instrument into a high resolution scanning electron microscope (SEM). Such an instrument becomes increasingly useful in the transmission mode of operation since it allows the use of samples which are considered too thick for conventional TEM. SEM accessories now available are all based on the use of the prefield of the objective lens to focus the beam. The lens is operated either as a symmetrical Ruska lens or its asymmetrical version. In these approaches, the condensor system of the microscope forms part of the reducing optics and the final spot size is usually larger than 20Å.

Divergent-beam holography with a 200keV FE TEM

1991 ◽  
Vol 49 ◽  
pp. 678-679
Author(s):  
Xiao Zhang ◽  
David Joy
Keyword(s):  
Optical System ◽  
Photographic Film ◽  
Objective Lens ◽  
Electron Wave ◽  
Transmission Electron ◽  
High Resolution Images ◽  
Phase Data ◽  
Electron Microscopes ◽  
Complete Amplitude ◽  
Commercial Field

A hologram, first described and named by Gabor (1949), permits a medium such as photographic film, which responds only to intensity, to store the complete amplitude and phase information which characterizes an electron wavefront. The hologram is formed by allowing some fraction of a coherent electron wave which has interacted with a specimen to interact again with original incident wave so as to generate an interference pattern. If the hologram is then itself illuminated by a coherent light source and optical system which mimic the original electron-optical system then a pair of images -one real and the other virtual -can be reconstructed and viewed. Because the hologram contains both the amplitude and the phase data of the wavefront, errors and distortions in either component due to aberrations in the objective lens can be corrected by optical manipulates before the image is reconstructed. With the advent of commercial field emission transmission electron microscopes capable of generating both high resolution images and highly coherent electron beams, these holographic techniques are now available as practical tools to improve TEM performance as well as to create new modes of images (Tonomura 1987).

High-performance EM-002B optical column construction for future expansion

1993 ◽  
Vol 51 ◽  
pp. 256-257
Author(s):  
K. Shirota ◽  
K. Moriyama ◽  
S. Mikami ◽  
A. Ando ◽  
O. Nakamura ◽  
...  
Keyword(s):  
High Performance ◽  
Cold Trap ◽  
Objective Lens ◽  
Transmission Electron ◽  
Probe Size ◽  
Wide Range ◽  
Electron Microscopes ◽  
Time Required ◽  
Modern Analytical ◽  
Typical User

Since modern analytical transmission electron microscopes must have a wide range of illumination conditions (from “mm” to “nm” probe size), an additional lens (one of the condenser lenses, usually called the “mini-lens”) is arranged immediately above the objective lens pole pieces. As a result, it has become very difficult to install an exchange mechanism for the objective pole pieces, which used to be done routinely.To overcome this, TOPCON Electron Microscope EM-OO2B incorporated a new mechanism which can be exchanged quite easily and reliably by the user. This mechanism makes a space to exchange pole pieces, without column disassembly, by precisely driven external mechanisms (Fig. 1). The time required for a typical user to carry out such exchange is usually 15 to 20 minutes, and it will take not more than two hours for high resolution image or analysis after exchange. This time is also shortened by the fact that an anti-contamination cold trap is not generally required in the case of EM-OO2B.

Electron Microscope Study of Strain in InGaN Quantum Wells in GaN Nanowires

2009 ◽  
Vol 1184 ◽  
Author(s):  
Roy Geiss ◽  
Kris Bertness ◽  
Alexana Roshko ◽  
David Read
Keyword(s):  
Electron Microscope ◽  
Quantum Wells ◽  
Cross Sections ◽  
Lattice Spacing ◽  
Gan Nanowires ◽  
Transmission Electron ◽  
Lattice Images ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Ingan Quantum Wells

AbstractStrains in GaN nanowires with InGaN quantum wells (QW) were measured from transmission electron microscope (TEM) images. The nanowires, all from a single growth run, are single crystals of the wurtzite structure that grow along the <0001> direction, and are approximately 1000 nm long and 60 nm to 130 nm wide with hexagonal cross-sections. The In concentration in the QWs ranges from 12 to 15 at %, as determined by energy dispersive spectroscopy in both the transmission and scanning electron microscopes. Fourier transform (FT) analyses of <0002> and <1100> lattice images of the QW region show a 4 to 10 % increase of the c-axis lattice spacing, across the full specimen width, and essentially no change in the a-axis value. The magnitude of the changes in the c-axis lattice spacing far exceeds values that would be expected by using a linear Vegard's law for GaN – InN with the measured In concentration. Therefore the increases are considered to represent tensile strains in the <0001> direction. Visual representations of the location and extent of the strained regions were produced by constructing inverse FT (IFT) images from selected regions in the FT covering the range of c-axis lattice parameters in and near the QW. The present strain values for InGaN QW in nanowires are larger than any found in the literature to date for other forms of InxGa1-xN (QW)/GaN.

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