Direct Methods for Surfaces

1998 ◽  
Vol 05 (05) ◽  
pp. 1087-1106 ◽  
Author(s):  
L. D. Marks ◽  
E. Bengu ◽  
C. Collazo-Davila ◽  
D. Grozea ◽  
E. Landree ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Mathematical Theory ◽  
Recent Progress ◽  
Direct Methods ◽  
Surface Structures ◽  
Electron Diffraction Data ◽  
X Ray ◽  
Experimental Systems ◽  
Transmission Electron ◽  
Basic Ideas

This paper reviews recent progress in the application of Direct Methods to solve surface structures using surface X-ray or transmission electron diffraction data. The basic ideas of (crystallographic) Direct Methods are presented, as well as the additional problems posed by trying to apply them to surfaces and how they connect to the mathematical theory of projections. Surface crystallography notation is presented, which differs from the widely used LEED notation in that it emphasizes the surface symmetry. This is followed by a description of methods for structure completion and refinement, followed by applications to some experimental systems, both those where the structure was previously known (calibration tests) and a few where it was not, concluding with problems and limitations.

Structure of the in on SI(111)4X1 Surface Determined by Applying Direct Phasing Methods to Transmission Electron Diffraction Data

1997 ◽  
Vol 3 (S2) ◽  
pp. 1041-1042
Author(s):  
C. Collazo-Davila ◽  
L. D. Marks ◽  
K. Nishii ◽  
Y. Tanishiro
Keyword(s):  
Electron Diffraction ◽  
Diffraction Data ◽  
Direct Methods ◽  
Surface Structures ◽  
Electron Diffraction Data ◽  
Imaging Plate ◽  
Data Sets ◽  
Interface Formation ◽  
Transmission Electron Diffraction ◽  
Transmission Electron

Direct methods were applied to transmission electron diffraction data to solve the previously unknown In on Si(111)4x1 surface structure. The structure consists of zig-zag chains of In atoms separated by regions of silicon including dimer chains (Fig 1.). The 4x1 structure is one of several stable surface structures formed with increasing In coverages on the Si(111) surface. The √3x√3 structure consists of 1/3 of a monolayer of In, the √31x√31 occurs at a slightly higher coverage and the 4x1 structure appears before the formation of In islands on the surface . While the √3x√3 surface has been extensively studied, relatively little is known about the √31x√31 and 4x1 structures. Knowledge of the atomic positions in the 4x1 structure is an important step in understanding metal/semiconductor epitaxy and interface formation.Two data sets were used in this study -- the first recorded on film and reduced in Tokyo, the second recorded on Imaging Plate in Tokyo and reduced at Northwestern. Twenty-seven independent intensities were measured.

STRUCTURE DETERMINATION OF THE Ge(111)-(3×1)Ag SURFACE RECONSTRUCTION

1999 ◽  
Vol 06 (06) ◽  
pp. 1061-1065 ◽  
Author(s):  
D. GROZEA ◽  
E. BENGU ◽  
C. COLLAZO-DAVILA ◽  
L. D. MARKS
Keyword(s):  
Electron Diffraction ◽  
Surface Reconstruction ◽  
Diffraction Data ◽  
Structure Determination ◽  
Heavy Atom ◽  
Direct Methods ◽  
Electron Diffraction Data ◽  
Transmission Electron ◽  
First Time

For the first time, during the investigation of the Ag submonolayer on the Ge(111) system, large, independent domains of the Ge (111)-(3×1) Ag phase were imaged and investigated. Previous studies have reported it only as small insets between Ge (111)-(4×4) Ag and Ge (111)- c (2×8) domains. The transmission electron diffraction data were analyzed using a Direct Methods approach and "heavy-atom holography," with the result of an atomic model of the structure similar to that of Ge (111)-(3×1) Ag .

scholarly journals MicroED: a versatile cryoEM method for structure determination

2018 ◽  
Vol 2 (1) ◽  
pp. 1-8 ◽  
Author(s):  
Brent L. Nannenga ◽  
Tamir Gonen
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
Electron Diffraction ◽  
Structure Determination ◽  
Materials Science ◽  
Electron Diffraction Data ◽  
Determination Method ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron

Micro-electron diffraction, or MicroED, is a structure determination method that uses a cryo-transmission electron microscope to collect electron diffraction data from nanocrystals. This technique has been successfully used to determine the high-resolution structures of many targets from crystals orders of magnitude smaller than what is needed for X-ray diffraction experiments. In this review, we will describe the MicroED method and recent structures that have been determined. Additionally, applications of electron diffraction to the fields of small molecule crystallography and materials science will be discussed.

On the Determination of Partial RDFs for Amorphous Materials

1993 ◽  
Vol 321 ◽  
Author(s):  
L. C. Qin ◽  
L. W. Hobbs
Keyword(s):  
Electron Diffraction ◽  
Diffraction Data ◽  
Amorphous Materials ◽  
Vitreous Silica ◽  
Scanning Transmission Electron Microscope ◽  
Distribution Functions ◽  
Electron Diffraction Data ◽  
X Ray ◽  
Transmission Electron ◽  
Scanning Transmission

ABSTRACTRadial distribution functions (RDFs) for vitreous silica (V-SiO2) have been obtained from energy-filtered electron diffraction data obtained in the HB5 scanning transmission electron Microscope. Results have been compared with those obtained from high-resolution neutron diffraction experiments, and are in good agreement within experimental errors. It was found to be impractical to obtain partial RDFs for this material from combined neutron, X-ray and electron diffraction data, because the similarities in characteristics of X-ray and electron scattering cause indeter-Minacies. A criterion equation has been given to determine feasibility.

Applications of the maximum entropy method to powder diffraction and electron crystallography

1993 ◽  
Vol 442 (1914) ◽  
pp. 97-111 ◽  
Keyword(s):  
Electron Diffraction ◽  
Diffraction Data ◽  
Direct Methods ◽  
Entropy Method ◽  
Electron Diffraction Data ◽  
Directed Search ◽  
X Ray Diffraction ◽  
Entropy Maximization ◽  
X Ray ◽  
Trial Phase

A new multisolution phasing method based on entropy maximization and likelihood ranking, proposed for the specific purpose of increasing the accuracy and sensitivity of probabilistic phase indications compared with conventional direct methods, has been implemented and applied to a wide variety of problems. The latter comprise the determination of small crystal structures from X-ray diffraction data obtained from single crystals or from powders, and from electron diffraction data, both with and without partial phase information obtained by image processing of electron micrographs; the ranking of phase sets for a small protein; and the improvement of poor quality phases for a larger protein at medium resolution under constraint of solvent flatness. The main components of the method are (1) a tree-directed search through a space of trial phase sets; (2) the saddlepoint method for calculating joint probabilities of structure factors, using entropy maximization; (3) likelihood-based scores to rank trial phase sets and prune the search tree; (4) a statistical analysis of the scores for automatically selecting reliable phase indications. Their use is illustrated here on structure determinations from powder X-ray diffraction data and from electron diffraction data.

scholarly journals Quantitative Electron Diffraction Data of Amorphous Materials

2005 ◽  
Vol 60 (6) ◽  
pp. 459-468 ◽  
Author(s):  
Jürgen Ankele ◽  
Joachim Mayer ◽  
Peter Lamparter ◽  
Siegfried Steeb
Keyword(s):  
Electron Diffraction ◽  
Multiple Scattering ◽  
Diffraction Data ◽  
Amorphous Materials ◽  
Structural Model ◽  
Electron Diffraction Data ◽  
X Ray ◽  
A Value ◽  
Transmission Electron ◽  
Scattering Correction

A method has been developed to obtain quantitative electron diffraction data up to a value of Q = 20 Å−1 of the modulus of the scattering vector. The experiments were performed on a commercially available transmission electron microscope equipped with a so-called omega energy filter. An analytical multiple scattering correction was applied. The electron diffraction results obtained with amorphous germanium were compared with X-ray and neutron diffraction data and showed good agreement. For an amorphous Ni63Nb37 sample it was shown that it is possible to estimate the multiple scattering intensity without exact knowledge of the sample thickness. This technique was applied to derive the structure factor for electron diffraction of two precursor-derived amorphous Si-C-N ceramics (a-Si24C43N33 and a-Si40C24N36). The results are consistent with corresponding X-ray diffraction data and with an existing structural model for such ceramics.

ATOMIC STRUCTURE OF THE In ON Si(111)(4 × 1) SURFACE

1997 ◽  
Vol 04 (01) ◽  
pp. 65-70 ◽  
Author(s):  
C. COLLAZO-DAVILA ◽  
L. D. MARKS ◽  
K. NISHII ◽  
Y. TANISHIRO
Keyword(s):  
Electron Diffraction ◽  
Diffraction Data ◽  
Atomic Structure ◽  
Direct Methods ◽  
Electron Diffraction Data ◽  
Zigzag Chain ◽  
Transmission Electron Diffraction ◽  
Transmission Electron

The atomic structure of the In on Si (111)(4×1) surface has been determined using direct methods applied to transmission electron diffraction data. It consists of a zigzag chain of In atoms and a region of silicon including a dimer chain. The structure is sufficiently similar to recent models of the Au on Si (111)(5×2) and metal on Si (111)(3×1) structures, that some preliminary generalizations on the linear n×1 and n×2 Si(111) reconstructions can be made.

Structure analysis of titanate nanorods by automated electron diffraction tomography

2011 ◽  
Vol 67 (3) ◽  
pp. 218-225 ◽  
Author(s):  
Iryna Andrusenko ◽  
Enrico Mugnaioli ◽  
Tatiana E. Gorelik ◽  
Dominik Koll ◽  
Martin Panthöfer ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Sodium Titanate ◽  
Electron Diffraction Data ◽  
Monoclinic Space Group ◽  
Diffraction Tomography ◽  
X Ray ◽  
Unknown Phase ◽  
Transmission Electron ◽  
Edge Dislocations ◽  
New Phase

A hitherto unknown phase of sodium titanate, NaTi3O6(OH)·2H2O, was identified as the intermediate species in the synthesis of TiO2 nanorods. This new phase, prepared as nanorods, was investigated by electron diffraction, X-ray powder diffraction, thermogravimetric analysis and high-resolution transmission electron microscopy. The structure was determined ab initio using electron diffraction data collected by the recently developed automated diffraction tomography technique. NaTi3O6(OH)·2H2O crystallizes in the monoclinic space group C2/m. Corrugated layers of corner- and edge-sharing distorted TiO6 octahedra are intercalated with Na+ and water of crystallization. The nanorods are typically affected by pervasive defects, such as mutual layer shifts, that produce diffraction streaks along c*. In addition, edge dislocations were observed in HRTEM images.

scholarly journals The structure of charoite, (K,Sr,Ba,Mn)15–16(Ca,Na)32[(Si70(O,OH)180)](OH,F)4.0.nH2O, solved by conventional and automated electron diffraction

2010 ◽  
Vol 74 (1) ◽  
pp. 159-177 ◽  
Author(s):  
I. Rozhdestvenskaya ◽  
E. Mugnaioli ◽  
M. Czank ◽  
W. Depmeier ◽  
U. Kolb ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Direct Methods ◽  
Diffraction Tomography ◽  
Chemical Formula ◽  
Crystal Chemical Formula ◽  
X Ray ◽  
Selected Area Electron Diffraction ◽  
Transmission Electron ◽  
Precession Electron Diffraction ◽  
Cation Sites

AbstractCharoite, ideally (K,Sr,Ba,Mn)15–16(Ca,Na)32[(Si70(O,OH)180)](OH,F)4.0·nH2O, a rare mineral from the Murun massif in Yakutiya, Russia, was studied using high-resolution transmission electron microscopy, selected-area electron diffraction, X-ray spectroscopy, precession electron diffraction and the newly developed technique of automated electron-diffraction tomography. The structure of charoite (a = 31.96(6) Å, b = 19.64(4) Å, c = 7.09(1) Å, β = 90.0(1)°, V = 4450(24) Å3, space group P21/m) was solved ab initio by direct methods from 2878 unique observed reflections and refined to R1/wR2 = 0.17/0.21. The structure can be visualized as being composed of three different dreier silicate chains: a double dreier chain, [Si6O17]10–; a tubular loop-branched dreier triple chain, [Si12O30]12–; and a tubular hybrid dreier quadruple chain, [Si17O43]18–. The silicate chains occur between ribbons of edge-sharing Ca and Na-octahedra. The chains of tetrahedra and the ribbons of octahedra extend parallel to the z axis. K+, Ba2+, Sr2+, Mn2+ and H2O molecules lie inside tubes and channels of the structure. On the basis of microprobe analyses and occupancy refinement of the cation sites, the crystal chemical formula of this charoite can be written as (Z = 1): (K13.88Sr1.0Ba0.32Mn0.36)Σ15.56(Ca25.64Na6.36)Σ32 [(Si6O11(O,OH)6)2(Si12O18(O,OH)12)2(Si17O25(O,OH)18)2](OH,F)4.0·3.18H2O.

X-ray powder diffraction and transmission electron diffraction data for BaMnSi2O6—A new phase in the system BaO–MnO–SiO2

1996 ◽  
Vol 11 (4) ◽  
pp. 284-287 ◽  
Author(s):  
I. T. Ivanov ◽  
D. D. Nihtianova ◽  
I. Georgieva
Keyword(s):  
Electron Diffraction ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Microprobe Analysis ◽  
Electron Microprobe Analysis ◽  
Electron Diffraction Data ◽  
Space Group ◽  
X Ray ◽  
Transmission Electron ◽  
New Phase

A new phase in the system BaO–MnO–SiO2 obtained by a pyrosynthetic method has been inves- tigated using electron microprobe analysis (EPMA), X-ray powder diffraction (PDA), and trans- mission electron diffraction. The lattice parameters and possible space group of the phase with a general composition BaMnSi2O6 were determined as follows: a=13.896, b=12.261, c=10.781 Å, β=103.47°, space group P21/m, Z=12.

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