A linearity test for thick specimens imaged by HVEM over a 180° angular range

1991 ◽  
Vol 49 ◽  
pp. 552-553
Author(s):  
Yu Liu
Keyword(s):  
Phase Contrast ◽  
Three Dimensional ◽  
Angular Range ◽  
Two Dimensional ◽  
Back Projection ◽  
Line Integral ◽  
Exponential Law ◽  
Transmission Electron ◽  
Absorption Law ◽  
Linearity Test

The image obtained in a transmission electron microscope is the two-dimensional projection of a three-dimensional (3D) object. The 3D reconstruction of the object can be calculated from a series of projections by back-projection, but this algorithm assumes that the image is linearly related to a line integral of the object function. However, there are two kinds of contrast in electron microscopy, scattering and phase contrast, of which only the latter is linear with the optical density (OD) in the micrograph. Therefore the OD can be used as a measure of the projection only for thin specimens where phase contrast dominates the image. For thick specimens, where scattering contrast predominates, an exponential absorption law holds, and a logarithm of OD must be used. However, for large thicknesses, the simple exponential law might break down due to multiple and inelastic scattering.

scholarly journals Low-Zpolymer sample supports for fixed-target serial femtosecond X-ray crystallography

2015 ◽  
Vol 48 (4) ◽  
pp. 1072-1079 ◽  
Author(s):  
Geoffrey K. Feld ◽  
Michael Heymann ◽  
W. Henry Benner ◽  
Tommaso Pardini ◽  
Ching-Ju Tsai ◽  
...  
Keyword(s):  
Protective Antigen ◽  
Three Dimensional ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
Fixed Target ◽  
X Ray ◽  
X Ray Crystallography ◽  
Transmission Electron ◽  
Linac Coherent Light Source ◽  
Efficient Alternative

X-ray free-electron lasers (XFELs) offer a new avenue to the structural probing of complex materials, including biomolecules. Delivery of precious sample to the XFEL beam is a key consideration, as the sample of interest must be serially replaced after each destructive pulse. The fixed-target approach to sample delivery involves depositing samples on a thin-film support and subsequent serial introductionviaa translating stage. Some classes of biological materials, including two-dimensional protein crystals, must be introduced on fixed-target supports, as they require a flat surface to prevent sample wrinkling. A series of wafer and transmission electron microscopy (TEM)-style grid supports constructed of low-Zplastic have been custom-designed and produced. Aluminium TEM grid holders were engineered, capable of delivering up to 20 different conventional or plastic TEM grids using fixed-target stages available at the Linac Coherent Light Source (LCLS). As proof-of-principle, X-ray diffraction has been demonstrated from two-dimensional crystals of bacteriorhodopsin and three-dimensional crystals of anthrax toxin protective antigen mounted on these supports at the LCLS. The benefits and limitations of these low-Zfixed-target supports are discussed; it is the authors' belief that they represent a viable and efficient alternative to previously reported fixed-target supports for conducting diffraction studies with XFELs.

scholarly journals Two-Dimensional Frank-Kasper Z Phase with One Unit-Cell Thickness

2020 ◽  
Author(s):  
Xie Hongbo ◽  
Junyuan Bai ◽  
Haiyan Ren ◽  
Shanshan Li ◽  
Hucheng Pan ◽  
...  
Keyword(s):  
Density Functional ◽  
Three Dimensional ◽  
Volume Ratio ◽  
Dark Field ◽  
Unit Cell ◽  
Two Dimensional ◽  
Cell Height ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field

Abstract Z phase is one of the three basic units by which the Frank-Kasper phases are generally assembled. Compared to the other two basic units, i.e., A15 and C15 structures, the Z phase structure is rarely experimentally observed because of a relatively large volume ratio among the constituents to inhibit its formation. Moreover, the discovered Z structures are generally the three-dimensional (3D) ordered Gibbs bulk phases to conform to their thermodynamic stability. Herein, we confirmed the existence of a metastable two-dimensional (2D) Frank-Kasper Z phase with one unit-cell height in the crystallography in a model Mg-Sm-Zn system, by using aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) combined with density functional theory (DFT) calculations. This finding is important for understanding the relationship between the traditional crystal structures and the quasicrystals, and it is also expected to provide a new insight to understand the clustering and stacking behavior of atoms in condensed matters.

scholarly journals Influence of Size on the Fractal Dimension of Dislocation Microstructure

Metals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 478
Author(s):  
Yinan Cui ◽  
Nasr Ghoniem
Keyword(s):  
Fractal Dimension ◽  
Three Dimensional ◽  
Dislocation Dynamics ◽  
Two Dimensional ◽  
Discrete Dislocation Dynamics ◽  
Discrete Dislocation ◽  
Transmission Electron ◽  
Dynamics Simulations ◽  
2D And 3D ◽  
Microscopy Images

Three-dimensional (3D) discrete dislocation dynamics simulations are used to analyze the size effect on the fractal dimension of two-dimensional (2D) and 3D dislocation microstructure. 2D dislocation structures are analyzed first, and the calculated fractal dimension ( n 2 ) is found to be consistent with experimental results gleaned from transmission electron microscopy images. The value of n 2 is found to be close to unity for sizes smaller than 300 nm, and increases to a saturation value of ≈1.8 for sizes above approximately 10 microns. It is discovered that reducing the sample size leads to a decrease in the fractal dimension because of the decrease in the likelihood of forming strong tangles at small scales. Dislocation ensembles are found to exist in a more isolated way at the nano- and micro-scales. Fractal analysis is carried out on 3D dislocation structures and the 3D fractal dimension ( n 3 ) is determined. The analysis here shows that ( n 3 ) is significantly smaller than ( n 2 + 1 ) of 2D projected dislocations in all considered sizes.

Gravitational attraction of a rectangular prism with depth‐dependent density

Geophysics ◽  
1992 ◽  
Vol 57 (3) ◽  
pp. 470-473 ◽  
Author(s):  
J. García‐Abdeslem
Keyword(s):  
Cross Sections ◽  
Integral Method ◽  
Three Dimensional ◽  
Density Contrast ◽  
Gravitational Attraction ◽  
Two Dimensional ◽  
Gravity Effect ◽  
Line Integral ◽  
Closed Expression ◽  
Dependent Density

The gravity effect produced by two and three‐dimensional bodies with nonuniform density contrast has been treated by several authors. One of the first attempts in this direction made by Cordell (1973), who developed a method to compute the gravity effect due to a two‐dimensional prism whose density decreases exponentially with depth. A different approach was proposed by Murthy and Rao (1979). They extended the line‐integral method to obtain the gravity effect for bodies of arbitrary cross‐sections, with density contrast varying linearly with depth. Chai and Hinze (1988) have derived a wavenumber‐domain approach to compute the gravity effect due to a vertical prism whose density contrast varies exponentially with depth. Recently, Rao (1990) has developed a closed expression of the gravity field produced by an asymmetrical trapezoidal body whose density varies with depth following a quadratic polynomial.

Multiscale 3D Virtual Dissections of 100-Million-Year-Old Flowers Using X-Ray Synchrotron Micro- and Nanotomography

2014 ◽  
Vol 20 (1) ◽  
pp. 305-312 ◽  
Author(s):  
Jean-David Moreau ◽  
Peter Cloetens ◽  
Bernard Gomez ◽  
Véronique Daviero-Gomez ◽  
Didier Néraudeau ◽  
...  
Keyword(s):  
Phase Contrast ◽  
Three Dimensional ◽  
Multiscale Approach ◽  
X Ray ◽  
Local Tomography ◽  
Transmission Electron ◽  
Wide Range ◽  
Fossil Flowers ◽  
High Level

AbstractA multiscale approach combining phase-contrast X-ray micro- and nanotomography is applied for imaging a Cretaceous fossil inflorescence in the resolution range from 0.75 μm to 50 nm. The wide range of scale views provides three-dimensional reconstructions from the external gross morphology of the inflorescence fragment to the finest exine sculptures of in situ pollen. This approach enables most of the characteristics usually observed under light microscopy, or with low magnification under scanning and transmission electron microscopy, to be obtained nondestructively. In contrast to previous tomography studies of fossil and extant flowers that used resolutions down to the micron range, we used voxels with a 50 nm side in local tomography scans. This high level of resolution enables systematic affinities of fossil flowers to be established without breaking or slicing specimens.

Three-Dimensional Deformations

1996 ◽  
Author(s):  
T. T. C. Ting
Keyword(s):  
Dimensional Space ◽  
Three Dimensional ◽  
Anisotropic Elasticity ◽  
Two Dimensional ◽  
Elastic Solids ◽  
Elastic Materials ◽  
Dimensional Solution ◽  
Line Integral ◽  
Isotropic Elasticity ◽  
Anisotropic Elastic

There appears to be very little study, if any, on the extension of Stroh's formalism to three-dimensional deformations of anisotropic elastic materials. In most three-dimensional problems the analyses employ approaches that are remotely related to Stroh's two-dimensional formalism. This is not unexpected, since this has been the situation between two-dimensional and three-dimensional isotropic elasticity. However it needs not be the case for three-dimensional anisotropic elasticity. Much can be gained if a connection to the Stroh formalism can be established. Barnett and Lothe (1975a) appeared to be the only ones who made a connection between a three-dimensional solution and Stroh's two-dimensional formalism. Earlier, several investigators obtained the Green's function for the infinite anisotropic medium in term of a line integral on an oblique plane in the three-dimensional space. That line integral, as we will see here, is one of Barnett-Lothe tensors on an oblique plane. We propose in this chapter extensions and applications of Stroh's two-dimensional formalism to certain three-dimensional deformations of anisotropic elastic solids.

scholarly journals Two-dimensional characterization of three-dimensional nanostructures of magnetic bubbles in Fe3Sn2

2020 ◽  
Author(s):  
Jin Tang ◽  
Yaodong Wu ◽  
Lingyao Kong ◽  
Weiwei Wang ◽  
Yutao Chen ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Microscopy Imaging ◽  
Magnetic Structures ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
High Resolution Tem ◽  
Lorentz Transmission Electron Microscopy

Abstract We report differential phase contrast scanning transmission electron microscopy (TEM) of nanoscale magnetic objects in Kagome ferromagnet Fe3Sn2 nanostructures. This technique can directly detect the deflection angle of a focused electron beam, thus allowing clear identification of the real magnetic structures of two magnetic objects including three-ring and complex arch-shaped vortices in Fe3Sn2 by Lorentz transmission electron microscopy imaging. Numerical calculations based on real material-specific parameters well reproduced the experimental results, showing that the magnetic objects can be attributed to integral magnetizations of two types of complex three-dimensional (3D) magnetic bubbles with depth-modulated spin twisting. Magnetic configurations obtained using the high-resolution TEM are generally considered as two-dimensional (2D) magnetic objects previously. Our results imply the importance of the integral magnetizations of underestimated 3D magnetic structures in 2D TEM magnetic characterizations.

Initiation and Evolution of Epitaxial Growth of GaAs on CaF2/Si (111) Substrates

1993 ◽  
Vol 317 ◽  
Author(s):  
Weidan Li ◽  
Takayoshi Anan ◽  
Thomas Thundat ◽  
Leo J. Schowalter
Keyword(s):  
Electron Microscopy ◽  
Rutherford Backscattering Spectrometry ◽  
Three Dimensional ◽  
Optimal Growth ◽  
Two Dimensional ◽  
Subsequent Growth ◽  
Mbe Growth ◽  
Force Microscopy ◽  
Atomic Force ◽  
Transmission Electron

AbstractIn this work, MBE growth of GaAs on CaF2/Si (111) substrates has been studied with both Rutherford backscattering spectrometry, transmission electron microscopy and atomic force Microscopy. It has been observed that, under certain conditions, a chemical reaction between As adatoms and the CaF2 layers can be induced, by which a more stable As layer on the CaF2 surface is formed. The existence of the As layer modifies the CaF2 surface free energy, which, if properly controlled, leads to two-dimensional (2D) nucleation of GaAs on the CaF2/Si (111) surface as opposed to the more commonly observed three-dimensional (3D) growth. Artificial Modification of the CaF2 (111) surface by introducing Ca prior to GaAs growth is also discussed as a promising way to achieve 2D nucleation. In subsequent growth, two kinds of twins have been observed. All samples were observed to have Micro-twins near the GaAs/CaF2 interface. These twins can be suppressed during the first 1000Å, if the layer is grown in a narrow optimal growth window. Otherwise, the growth will be in a 3D Mode at lower temperatures, or it will suffer from the formation of large rotational twins at higher temperatures. It has been observed that growth on vicinal substrates tilted toward [112] azimuth is helpful in suppressing the development of rotational twins so that growth on these substrates have a wider optimal growth window. Surface Morphology of CaF2 epitaxial layers grown on Si (111) substrates with different vicinal angles has also been investigated. It May have significant impact on the twin development during subsequent GaAs growth.

Sign in / Sign up

Export Citation Format

Share Document