Calculation Of Stem Dark-Field Images

1977 ◽  
Vol 35 ◽  
pp. 192-193
Author(s):  
J. Fertig ◽  
H. Rose
Keyword(s):  
High Resolution Electron Microscopy ◽  
Dark Field ◽  
Angular Width ◽  
Hollow Cone ◽  
Dark Field Imaging ◽  
Dark Field Micrograph ◽  
Resolution Electron ◽  
Detector Geometry ◽  
Annular Detector ◽  
Organometallic Molecules

Dark-field imaging is a promising procedure to visualize single atoms in high resolution electron microscopy. The quality of a dark-field micrograph depends to a large extent on the illumination mode for the CTEM or on the detector geometry for the STEM. The most commonly used dark-field modes are: CTEM with axial, tilted, or hollow-cone illumination and STEM with an annular detector limited by the angles and θ1-θ2. The STEM is equivalent to a CTEM which uses hollow-cone illumination of finite angular width (limiting angles θ1, θ2). the following we always assume θ2 = п/2.The three CTEM imaging modes have been investigated theoretically by several authors. Krakow (1) computed dark-field images of small organometallic molecules assuming tilted illumination. However, he could not achieve results for hollow-cone illumination because his computing method was too timeconsuming. Hoch (2) calculated images of model objects under axialy tilted, and hollow-cone illumination of infinitely small angular widthy applying the fast Fourier transform technique.

Anomalous Lattice Parameters in Iron-Copper Multilayers

1995 ◽  
Vol 400 ◽  
Author(s):  
S. J. Lloyd ◽  
R. E. Somekh ◽  
W. M. Stobbs
Keyword(s):  
High Resolution Electron Microscopy ◽  
Lattice Parameter ◽  
Growth Direction ◽  
Dark Field ◽  
Elastic Model ◽  
Electron Loss ◽  
Dark Field Imaging ◽  
Iron Copper ◽  
Resolution Electron ◽  
Field Imaging

AbstractX-ray, magnetism and electron loss spectroscopy data were obtained for a series of coherent Fe-Cu face-centred multilayers which suggest that there is a lattice parameter anomaly in the structure. The use of high resolution electron microscopy (HREM) and dark field imaging to measure spacing changes along the layer normal are compared. Experimental dark field images suggest that the Fe has expanded lattice spacings in the growth direction in contradiction to the predictions of a conventional elastic model for a coherent multilayer structure.

High-resolution EM investigation about effect of stress on formation of ω-phase crystals in β-tttanium alloys

1996 ◽  
Vol 54 ◽  
pp. 1006-1007
Author(s):  
E. Sukedai ◽  
M. Shimoda ◽  
A. Fujita ◽  
H. Nishizawa ◽  
H. Hashimoto
Keyword(s):  
High Resolution ◽  
Titanium Alloys ◽  
High Resolution Electron Microscopy ◽  
Dark Field ◽  
Zone Refining ◽  
Ω Phase ◽  
Α Phase ◽  
Nucleation Sites ◽  
Resolution Electron ◽  
Bcc Structure

ω-phase particles formed in β-titanium alloys (bcc structure) act important roles to their mechanical properties such as ductility and hardness. About the ductility, fine ω-phase particles in β–titanium alloys improve the ductility, because ω-phase crystals becomes nucleation sites of α-phase and it is well known that (β+α) duplex alloys have higher ductility. In the present study, the formation sites and the formation mechanism of ω-phase crystals due to external stress and aging are investigated using the conventional and high resolution electron microscopy.A β-titanium alloy (Til5Mo5Zr) was supplied by Kobe Steel Co., and a single crystal was prepared by a zone refining method. Plates with {110} surface were cut from the crystal and were pressured hydrostatically, and stressed by rolling and tensile testing. Specimens for aging with tensile stress were also prepared from Ti20Mo polycrystals. TEM specimens from these specimens were prepared by a twin-jet electron-polishing machine. A JEM 4000EX electron microscope operated at 400k V was used for taking dark field and HREM images.

High Resolution TEM Studies On Palladium, Rhodium Nanoparticles

2001 ◽  
Vol 7 (S2) ◽  
pp. 1100-1101
Author(s):  
M. José-Yacamán ◽  
M. Marín-Almazo ◽  
J.A. Ascencio
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Indirect Evidence ◽  
High Resolution Electron Microscopy ◽  
Dark Field ◽  
Rhodium Nanoparticles ◽  
Resolution Electron ◽  
Annular Dark Field ◽  
High Resolution Tem ◽  
Important Field

The field of catalysis is one of the most important areas of the nano-sciences for many years. in deed the goal of having a catalyst, with the maximum active area exposed to a chemical reaction, has produced enormous amount of research in nanoparticles. Particularly, the metal nanoparticles study is a very important field in catalysis. Electron Microscopy is one of the techniques that have played a mayor role on studding nanoparticles. Since bright field images, dark field techniques, to the high-resolution atomic images of nanoparticles and more recently the High Angle Annular dark field images or Z-contrast. However this technique provides only indirect evidence of the atomic arrangements on the particles. High Resolution Electron Microscopy (HREM) still appears as a very powerful technique to study nanoparticles and their internal structure. Among the most interesting metals to study is the palladium, which acts for instance as excellent catalyst for hydrogenation of unsaturated hydrocarbons and has many other applications such as environmental catalysts.

Unstained Biological Specimens in High Resolution Electron Microscopy

1974 ◽  
Vol 32 ◽  
pp. 234-235
Author(s):  
M. K. Lamvik ◽  
J. M. Pullman ◽  
A. V. Crewe
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Heavy Atom ◽  
High Resolution Electron Microscopy ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Structural Studies ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Scanning Transmission

Negative staining and high resolution shadowing have been extensively used for structural studies in electron microscopy. However, these techniques cover the specimen with a layer of heavy salt or metal, and hence do not allow determination of true mass distribution or localization of specific sites using heavy atom markers. A prerequisite for such structural studies is an examination of unstained specimens. For thin specimens dark field microscopy must be used to obtain adequate contrast. The scanning transmission electron microscope is preferred for such studies since elastic, energyloss, and unscattered electrons can be recorded and analyzed quantitatively to form images with a minimum of beam-induced damage.

Analysis of co-deposited Ti-Hf thin film on (0001)6H-SiC by HREM, energy-selected and hollow-cone images

1994 ◽  
Vol 52 ◽  
pp. 978-979
Author(s):  
J. S. Bow
Keyword(s):  
Thin Film ◽  
Solid Solution ◽  
Lattice Parameter ◽  
Dark Field ◽  
Electron Beam Evaporation ◽  
Structural Defects ◽  
Misfit Dislocations ◽  
Hollow Cone ◽  
Chemical Homogeneity ◽  
Dark Field Imaging

Solid solution binary alloys are attractive for defect-free thin film semiconductor contacts because lattice matching can be obtained by composition adjustment, but chemical homogeneity is required. Highly composition sensitive energy-selected and hollow cone (HC) dark field imaging were evaluated for heterogeneity detection in Ti-Hf films using an Ω filter/Zeiss 912 TEM. Conventional HREM, which relatively insensitive to spatial composition variations in this case, was used to observe structural defects in the films near the interfaces.Thin films of pure Ti deposited via UHV electron beam evaporation at room temperature on n-type, vicinal (0001) 6H-SiC showed good epitaxy. This contact displayed rectifying characteristics. The interface was both structurally and chemically sharp. However, misfit dislocations at “stand off” positions were found, due to 4 % mismatch between the basal parameters of Ti and SiC. same column with Ti in the periodic table and has hexagonal crystal structure, but larger lattice parameter (aHf = 3.196 Å, and aTi = 2.950 Å). The Ti-Hf solid solution system obeys Vergard's law well, that is, the lattice parameters of this alloy change linearly with composition.

CBED and HREM study of decagonal quasicrystals

1996 ◽  
Vol 54 ◽  
pp. 704-705
Author(s):  
M. Tanaka ◽  
K. Tsuda ◽  
K. Saitoh
Keyword(s):  
Electron Microscopy ◽  
High Resolution Electron Microscopy ◽  
Dark Field ◽  
Hrem Image ◽  
Space Group ◽  
Space Groups ◽  
Atom Clusters ◽  
Decagonal Quasicrystals ◽  
Black Circle ◽  
Resolution Electron

Decagonal quasicrystals have been investigated by convergent-beam electron diffraction (CBED) and transmission electron microscopy. Figure 1 shows possible pentagonal and decagonal point groups. The CBED method has revealed that the decagonal quasicrystals found so far belong to the space groups of noncentrosymmetric P10m2 and centrosymmetric P1O5mmc.Dark-field microscopy has revealed the existence of inversion domains with an antiphase shift of c/2 at the domain boundaries in the alloys with space group m2.2 High-resolution electron microscopy (HREM) has revealed the existence of specific pentagonal atom clusters in the Al-Ni-Fe, Al-Cu-Co and Al-Ni-Co alloys. Figure 2 shows a HREM image of Al70Ni15Fe15 belonging to space group m2. The atom clusters of an about 2nm diameter are clearly seen as indicated by a black circle. The clusters are polar or noncentrosymmetric due to the dark pentagon at their centers. All the clusters in domain A have one sense of polarity and those in domain B the other sense. It should be noted that the HREM image of the cluster columns was found to be pentagonal at an accelerating voltage of 200kV but nearly decagonal at higher than 300kV.

High-Resolution Bright-Field and Dark-Field Hollow Cone Illumination

1990 ◽  
Vol 48 (1) ◽  
pp. 36-37
Author(s):  
R.A. Herring ◽  
M.E. Twigg
Keyword(s):  
Large Angle ◽  
Dark Field ◽  
Hollow Cone ◽  
Contrast Imaging ◽  
Lattice Image ◽  
Dark Field Imaging ◽  
Annular Dark Field ◽  
Lattice Images ◽  
Z Contrast ◽  
Field Imaging

Hollow cone illumination using a large C2 blocked-aperture (bl apt) in the conventional TEM (CTEM) can remove the beams within the zero-order Laue zone (ZOLZ) thereby making lattice images more simply interpretable. Dark-field (DF) hollow cone illumination has the added advantage of enhancing the Z-contrast within the lattice image, since the electrons contributing to the image must be scattered over a large angle (approximately 10 mrad). Both of these imaging methods have been explored, using a 600 um C2 bl apt and objective aperture sizes of 70, 20 and 10 um, and are reported in this paper.Much interest has been generated by the report of Pennycook [1] on STEM Z-contrast imaging using annular dark-field. In earlier work ,it was noted that CTEM hollow cone imaging and STEM annular dark-field imaging are related via reciprocity [2] (Fig. 1). In addition, Zernike has shown the advantages of hollow cone illumination in optical phase-contrast microscopy [3]. The electron-optical analogues to these optical techniques are now possible because of the low Cs values achieved in modern TEMs.

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