Image Simulation of Small Pt Particles and its Application to Lattice Spacing Measurements in Catalysts

1999 ◽  
Vol 5 (S2) ◽  
pp. 200-201
Author(s):  
S.-C. Y. Tsen ◽  
P. A. Crazier ◽  
C. López Cartes ◽  
J. Liu ◽  
J.J. Calvino
Keyword(s):  
Lattice Spacing ◽  
Lattice Parameter ◽  
Image Simulation ◽  
Initial Image ◽  
Bimetallic Systems ◽  
Local Lattice ◽  
Nanophase Materials ◽  
Resolution Imaging ◽  
Small Metal Particle ◽  
Image Simulations

The technique of high resolution imaging is important for characterizing the structure of small metal particle catalysts and nanophase materials. For bimetallic systems, it is possible to use local lattice parameter measurements to identify alloy compositions in ensembles of nanometer sized metal particles [1]. However, determining alloy composition is challenging because changes in lattice parameters of only a few percent must be reliably detected. We have performed measurements of the apparent d(111) fringe spacing on both simulated and experimental HREM images from Pt particles in the size range 15 - 35 Å. A series of initial image simulations of Pt cubeoctahedrons with 17 Å (201 atoms) and 34 Å (1289 atoms) in diameter have been studied in order to understand the effect of different parameters on the accuracy of lattice spacing. The clusters were built using the Rhodius program developed by Botana et al [2]. Starting with a bulk crystal we create cubeoctahedra by applying successive cuts along either the (111) or (100) direction. A supercell size of 50Å was selected and the particles were oriented at or close to the [110]. Images were calculated by the multi-slice techniques using both the CERIUS and EMS applications. The supercell was divided into 20 slices and the following parameters were used in the calculation Eo = 400 kV, Cs = 1mm, Δf= -320 Å, focal spread = 80 Å, convergence = 0.5 mrad and atomic vibration = 0.35Å.

Computers and diffraction analysis

1989 ◽  
Vol 47 ◽  
pp. 44-45
Author(s):  
J. A. Eades
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Electron Diffraction ◽  
Diffraction Analysis ◽  
Electron Diffraction Analysis ◽  
Image Simulation ◽  
Correct Interpretation ◽  
High Profile ◽  
High Resolution Images ◽  
Image Simulations

For well over two decades computers have played an important role in electron microscopy; they now pervade the whole field - as indeed they do in so many other aspects of our lives. The initial use of computers was mainly for large (as it seemed then) off-line calculations for image simulations; for example, of dislocation images.Image simulation has continued to be one of the most notable uses of computers particularly since it is essential to the correct interpretation of high resolution images. In microanalysis, too, the computer has had a rather high profile. In this case because it has been a necessary part of the equipment delivered by manufacturers. By contrast the use of computers for electron diffraction analysis has been slow to prominence. This is not to say that there has been no activity, quite the contrary; however it has not had such a great impact on the field.

The limits of strain and lattice parameter measurements by CBED

1989 ◽  
Vol 47 ◽  
pp. 518-519
Author(s):  
Hamish L. Fraser
Keyword(s):  
Electron Beam ◽  
Mirror Symmetry ◽  
Local Symmetry ◽  
Lattice Parameter ◽  
Growth Direction ◽  
Surface Relaxation ◽  
Strained Layer ◽  
Axis Parallel ◽  
Local Lattice ◽  
Strained Layer Superlattice

The topic of strain and lattice parameter measurements using CBED is discussed by reference to several examples. In this paper, only one of these examples is referenced because of the limitation of length. In this technique, scattering in the higher order Laue zones is used to determine local lattice parameters. Work (e.g. 1) has concentrated on a model strained-layer superlattice, namely Si/Gex-Si1-x. In bulk samples, the strain is expected to be tetragonal in nature with the unique axis parallel to [100], the growth direction. When CBED patterns are recorded from the alloy epi-layers, the symmetries exhibited by the patterns are not tetragonal, but are in fact distorted from this to lower symmetries. The spatial variation of the distortion close to a strained-layer interface has been assessed. This is most readily noted by consideration of Fig. 1(a-c), which show enlargements of CBED patterns for various locations and compositions of Ge. Thus, Fig. 1(a) was obtained with the electron beam positioned in the center of a 5Ge epilayer and the distortion is consistent with an orthorhombic distortion. When the beam is situated at about 150 nm from the interface, the same part of the CBED pattern is shown in Fig. 1(b); clearly, the symmetry exhibited by the mirror planes in Fig. 1 is broken. Finally, when the electron beam is positioned in the center of a 10Ge epilayer, the CBED pattern yields the result shown in Fig. 1(c). In this case, the break in the mirror symmetry is independent of distance form the heterointerface, as might be expected from the increase in the mismatch between 5 and 10%Ge, i.e. 0.2 to 0.4%, respectively. From computer simulation, Fig.2, the apparent monocline distortion corresponding to the 5Ge epilayer is quantified as a100 = 0.5443 nm, a010 = 0.5429 nm and a001 = 0.5440 nm (all ± 0.0001 nm), and α = β = 90°, γ = 89.96 ± 0.02°. These local symmetry changes are most likely due to surface relaxation phenomena.

scholarly journals Lattice disorder effect on magnetic ordering of iron arsenides

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Athena S. Sefat ◽  
Xiaoping P. Wang ◽  
Yaohua Liu ◽  
Qiang Zou ◽  
Mimgming Fu ◽  
...  
Keyword(s):  
Magnetic Coupling ◽  
Magnetic Ordering ◽  
Structural Features ◽  
Lattice Parameter ◽  
Chemical Compositions ◽  
Lattice Disorder ◽  
Local Lattice ◽  
Higher Temperature ◽  
Disordered Crystal ◽  
Planar Strain

AbstractThis study investigates magnetic ordering temperature in nano- and mesoscale structural features in an iron arsenide. Although magnetic ground states in quantum materials can be theoretically predicted from known crystal structures and chemical compositions, the ordering temperature is harder to pinpoint due to potential local lattice variations that calculations may not account for. In this work we find surprisingly that a locally disordered material can exhibit a significantly larger Néel temperature (TN) than an ordered material of precisely the same chemical stoichiometry. Here, a EuFe2As2 crystal, which is a ‘122’ parent of iron arsenide superconductors, is found through synthesis to have ordering below TN = 195 K (for the locally disordered crystal) or TN = 175 K (for the ordered crystal). In the higher TN crystals, there are shorter planar Fe-Fe bonds [2.7692(2) Å vs. 2.7745(3) Å], a randomized in-plane defect structure, and diffuse scattering along the [00 L] crystallographic direction that manifests as a rather broad specific heat peak. For the lower TN crystals, the a-lattice parameter is larger and the in-plane microscopic structure shows defect ordering along the antiphase boundaries, giving a larger TN and a higher superconducting temperature (Tc) upon the application of pressure. First-principles calculations find a strong interaction between c-axis strain and interlayer magnetic coupling, but little impact of planar strain on the magnetic order. Neutron single-crystal diffraction shows that the low-temperature magnetic phase transition due to localized Eu moments is not lattice or disorder sensitive, unlike the higher-temperature Fe sublattice ordering. This study demonstrates a higher magnetic ordering point arising from local disorder in 122.

scholarly journals Grazing-incidence X-ray diffraction of single GaAs nanowires at locations defined by focused ion beams

2013 ◽  
Vol 46 (4) ◽  
pp. 887-892 ◽  
Author(s):  
Genziana Bussone ◽  
Rüdiger Schott ◽  
Andreas Biermanns ◽  
Anton Davydok ◽  
Dirk Reuter ◽  
...  
Keyword(s):  
Gaas Substrate ◽  
Lattice Spacing ◽  
Molecular Beam ◽  
Grazing Incidence ◽  
Lattice Parameter ◽  
Ion Beams ◽  
Focused Ion Beams ◽  
X Ray Diffraction ◽  
X Ray ◽  
Gaas Nanowires

Grazing-incidence X-ray diffraction measurements on single GaAs nanowires (NWs) grown on a (111)-oriented GaAs substrate by molecular beam epitaxy are reported. The positions of the NWs are intentionally determined by a direct implantation of Au with focused ion beams. This controlled arrangement in combination with a nanofocused X-ray beam allows the in-plane lattice parameter of single NWs to be probed, which is not possible for randomly grown NWs. Reciprocal space maps were collected at different heights along the NW to investigate the crystal structure. Simultaneously, substrate areas with different distances from the Au-implantation spots below the NWs were probed. Around the NWs, the data revealed a 0.4% decrease in the lattice spacing in the substrate compared with the expected unstrained value. This suggests the presence of a compressed region due to Au implantation.

Local Lattice Parameter Determination of Strained Areas of Semiconductors Using CBED

2004 ◽  
Vol 10 (S02) ◽  
pp. 310-311
Author(s):  
Takayuki Akaogi ◽  
Kenji Tsuda ◽  
Masami Terauchi ◽  
Michiyoshi Tanaka
Keyword(s):  
Lattice Parameter ◽  
Parameter Determination ◽  
Local Lattice

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Strong Deviation Of The Lattice Parameter In Si1-x-yGexCy Epilayers From Vegard's Rule

1998 ◽  
Vol 533 ◽  
Author(s):  
J. Stangl ◽  
S. Zerlauth ◽  
F. Schäffler ◽  
G. Bauer ◽  
M. Berti ◽  
...  
Keyword(s):  
Lattice Spacing ◽  
Lattice Parameter ◽  
Negative Deviation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Strong Deviation ◽  
Theoretical Predictions

AbstractFrom the comparison of precise determinations of the Ge and C contents of a series of Si1-x-yGexCy epilayer samples (x < 0.18, y < 0.02) by Rutherford and resonant backscattering experiments and x-ray diffraction, the variation of the Si1-x-yGexCy lattice spacing as a function of C content is determined. A significant negative deviation from Vegard's rule is observed, in agreement with theoretical predictions by Kelires.

Determination of the Unstressed Lattice Parameter “a0” for (Triaxial) Residual Stress Determination by Xrays

1984 ◽  
Vol 28 ◽  
pp. 281-288 ◽  
Author(s):  
Ismail Cevdet Noyan
Keyword(s):  
Residual Stress ◽  
Lattice Spacing ◽  
Interplanar Spacing ◽  
Lattice Parameter ◽  
Shear Stresses ◽  
Stress Determination ◽  
Surface Layers ◽  
X Ray ◽  
D Values

Stress gradients in the direction of the surface normal influence the shape of the interplanar spacing “d” vs. sin2ψ (where ψ is the specimen tilt) plot obtained from the surface layers of a specimen.(1-3) If the gradients are caused by the shear stresses σ13, σ23, the “d” vs. sin2ψ plot exhibits “psi-splitting”, that is the “d” values measured at positive ψ tilts are different from the values measured at negative if tilts. (2) If the shear stresses σ13, σ23, are zero, but the normal stress σ33 exists in the layets penetrated by the x-ray beam, “d” vs. sin2ψ, plot exhibits curvature. (3) Various methods have been proposed to obtain the complete stress tensor from split or curved “d” vs. sin2ψ data, and all of these methods require the “unstressed” lattice spacing “d0” for their calculations.

Atomic Structure of Interfaces in Epitaxial NiSi2 on (001) Silicon

1992 ◽  
Vol 263 ◽  
Author(s):  
W.J. Chen ◽  
F.R. Chen ◽  
L.J. Chen
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Atomic Structure ◽  
Imaging Technique ◽  
Interface Structure ◽  
High Resolution Imaging ◽  
Image Simulation ◽  
Transmission Electron ◽  
Resolution Imaging ◽  
Boundary Core

ABSTRACTHigh resolution transmission electron microscopy (HRTEM) has been applied to study the atomic structure of NiSi2 /(001)Si interface. Previous HRTEM result suggested that Ni atoms in the boundary core are six-fold coordinated and Si atoms are everywhere tetrahedrally coordinated. In this work, high resolution imaging technique and computer image simulation were used to study the atomic structure of NiSi2 /(001)Si interfaces and a new interface structure was found. For the new interface structure, Ni and Si atoms are also six-fold and tetrahedrally coordinated, respectively, with an extra layer of fourfold planar bonded Si atoms present at the interface.

HREM image contrast at the CoSi2/Si interface

1990 ◽  
Vol 48 (4) ◽  
pp. 388-389
Author(s):  
A.F. de Jong ◽  
C.W.T. Bulle-Lieuwma
Keyword(s):  
Atomic Structure ◽  
Schottky Barrier Height ◽  
High Resolution Electron Microscopy ◽  
Image Simulation ◽  
Hrem Image ◽  
Resolution Electron ◽  
Imaging Theory ◽  
Buried Layer ◽  
Imaging Conditions ◽  
Image Simulations

Epitaxial layers of CoSi2 can be grown on both (111) and (001) substrates, or fabricated as a buried layer by ion implantation. The atomic structure at the interface is of interest because it determines the Schottky barrier height and because it is Coupled to the types of dislocations which are found. High-resolution electron microscopy (HREM) combined with image simulation is used to investigate the atomic structure at the interface. Detailed image simulations are needed to investigate under which imaging conditions the (small) differences between the models are visible. In this contribution an analysis is given of the HREM contrast within the CoSi2 unit cell, using a linear imaging theory. The results are used to investigate the various models proposed for the CoSi2/Si (111) interface.In the < 110 > imaging orientation the contrast in HREM images of CoSi2 is dominated by (200) and(111) fringes.

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