scholarly journals Unraveling structures of protection ligands on gold nanoparticle Au68(SH)32

2015 ◽  
Vol 1 (3) ◽  
pp. e1400211 ◽  
Author(s):  
Wen Wu Xu ◽  
Yi Gao ◽  
Xiao Cheng Zeng
Keyword(s):  
Gold Nanoparticle ◽  
Density Functional ◽  
Magic Number ◽  
Low Energy ◽  
Atomic Structures ◽  
Gold Core ◽  
Transmission Electron Microscopy Measurement ◽  
Transmission Electron ◽  
Microscopy Measurement ◽  
Density Functional Theory Optimization

New low-energy atomic structures of the thiolate-protected gold nanoparticle Au68(SH)32 are uncovered, where the atomic positions of the Au atoms are taken from the recent single-particle transmission electron microscopy measurement by Kornberg and co-workers, whereas the pattern of thiolate ligands on the gold core is attained on the basis of the generic formulation (or rule) of the “divide and protect” concept. Four distinct low-energy isomers, Iso1 to Iso4, whose structures all satisfy the generic formulation, are predicted. Density-functional theory optimization indicates that the four isomers are all lower in energy by 3 to 4 eV than the state-of-the-art low-energy isomer reported. Further analysis of the optimized structures of Au68(SH)32 shows that the structure of gold core in Iso1 to Iso4 is consistent with the experiment, whereas the positions of a few Au atoms at the surface of gold core are different. The computed optical absorption spectra of the four isomers are consistent with the measured spectrum. Computation of catalytic properties of Au68(SH)32 toward CO oxidation suggests that the magic number cluster can be a stand-alone nanoscale catalyst for future catalytic applications.

Characterization of Surface Defects of Highly N-Doped 4H-SiC Substrates that Produce Dislocations in the Epitaxial Layer

2010 ◽  
Vol 645-648 ◽  
pp. 351-354 ◽  
Author(s):  
Yukari Ishikawa ◽  
Yoshihiro Sugawara ◽  
Hiroaki Saitoh ◽  
Katsunori Danno ◽  
Yoichiro Kawai ◽  
...  
Keyword(s):  
Epitaxial Layer ◽  
Surface Defects ◽  
Etch Pits ◽  
Transmission Electron Microscopy Measurement ◽  
Transmission Electron ◽  
Sublimation Method ◽  
Half Loop ◽  
Microscopy Measurement ◽  
Edge Dislocations

The structures of defects that form different types of etch pits on highly N-doped 4H-SiC substrates, that were produced by a sublimation method, after molten KOH etching were characterized. It was found that most of the dislocations in the epitaxial layer originated from defects at the surface of substrate whose etch pit structures were clearly different from the conventional structures. The etch pits were classified into drop, oval, round and caterpillar pits. The drop and oval pits were concluded to be formed by the deformation of conventional etch pits. Round pits were concluded to originate from half loop dislocations and were transformed to complex dislocations by epitaxial growth. Analysis by transmission electron microscopy measurement indicates that slipped edge dislocations (or screw dislocations) on the basal plane form caterpillar pits.

Flux-pinning-related defect structures in melt-processed YBa2Cu3O7-x

1993 ◽  
Vol 51 ◽  
pp. 936-937
Author(s):  
Z. L. Wang ◽  
R. Kontra ◽  
A. Goyal ◽  
D. M. Kroeger ◽  
L.F. Allard
Keyword(s):  
Volume Fraction ◽  
Local Density ◽  
Stacking Faults ◽  
Image Resolution ◽  
Defect Structures ◽  
Atomic Structures ◽  
Transmission Electron ◽  
Point Image ◽  
Related Defect ◽  
Point To Point

Previous studies of Y2BaCuO5/YBa2Cu3O7-δ(Y211/Y123) interfaces in melt-processed and quench-melt-growth processed YBa2Cu3O7-δ using high resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS) have revealed a high local density of stacking faults in Y123, near the Y211/Y123 interfaces. Calculations made using simple energy considerations suggested that these stacking faults may act as effective flux-pinners and may explain the observations of increased Jc with increasing volume fraction of Y211. The present paper is intended to determine the atomic structures of the observed defects. HRTEM imaging was performed using a Philips CM30 (300 kV) TEM with a point-to-point image resolution of 2.3 Å. Nano-probe EDS analysis was performed using a Philips EM400 TEM/STEM (100 kV) equipped with a field emission gun (FEG), which generated an electron probe of less than 20 Å in diameter.Stacking faults produced by excess single Cu-O layers: Figure 1 shows a HRTEM image of a Y123 film viewed along [100] (or [010]).

Computational Study on the Kinetics and Mechanisms of Unimolecular Reactions of (Z)-(Z)-N-(λ5-phosphanylidene) Formohydrazonic Formic Anhydride: Intramolecular aza-Wittig Reaction in Competition with Mumm Rearrangement

2020 ◽  
Vol 17 (11) ◽  
pp. 884-889
Author(s):  
Somayeh Mirdoraghi ◽  
Hamed Douroudgari ◽  
Farideh Piri ◽  
Morteza Vahedpour
Keyword(s):  
Rate Constants ◽  
Density Functional ◽  
Wittig Reaction ◽  
Computational Study ◽  
Single Step ◽  
Low Energy ◽  
Coupled Cluster ◽  
Unimolecular Reaction ◽  
Single Step Reaction ◽  
Good Agreement

For (Z)-(Z)-N-(λ5-phosphanylidene) formohydrazonic formic anhydride, Aza-Wittig reaction and Mumm rearrangement are studied using both density functional and coupled cluster theories. For this purpose, two different products starting from one substrate are considered that are competing with each other. The obtained products, P1 and P2, are thermodynamically favorable. The product of the aza-Wittig reaction, P1, is more stable than the product of Mumm rearrangement (P2). For the mentioned products, just one reliable pathway is separately proposed based on unimolecular reaction. Therefore, the rate constants based on RRKM theory in 300-600 K temperature range are calculated. Results show that the P1 generation pathway is a suitable path due to low energy barriers than the path P2. The first path has three steps with three transition states, TS1, TS2, and TS3. The P2 production path is a single-step reaction. In CCSD level, the computed barrier energies are 14.55, 2.196, and 10.67 kcal/mol for Aza-Wittig reaction and 42.41 kcal/mol for Mumm rearrangement in comparison with the corresponding complexes or reactants. For final products, the results of the computational study are in a good agreement with experimental predictions.

scholarly journals Complex magnetism of the two-dimensional antiferromagnetic Ge2F: from a Néel spin-texture to a potential antiferromagnetic skyrmion

RSC Advances ◽  
2021 ◽  
Vol 11 (15) ◽  
pp. 8654-8663
Author(s):  
Fatima Zahra Ramadan ◽  
Flaviano José dos Santos ◽  
Lalla Btissam Drissi ◽  
Samir Lounis
Keyword(s):  
Density Functional Theory ◽  
Magnetic Properties ◽  
Density Functional ◽  
Low Energy ◽  
Two Dimensional ◽  
Functional Theory ◽  
2D Material ◽  
Energy Models ◽  
Spin Texture

Based on density functional theory combined with low-energy models, we explore the magnetic properties of a hybrid atomic-thick two-dimensional (2D) material made of germanene doped with fluorine atoms in a half-fluorinated configuration (Ge2F).

scholarly journals Shedding Light on the Chemistry and the Properties of Münchnone Functionalized Graphene

Nanomaterials ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1629
Author(s):  
Giulia Neri ◽  
Enza Fazio ◽  
Antonia Nostro ◽  
Placido Giuseppe Mineo ◽  
Angela Scala ◽  
...  
Keyword(s):  
Density Functional ◽  
Antimicrobial Properties ◽  
Biological Properties ◽  
Azomethine Ylide ◽  
Functionalized Graphene ◽  
Functional Theory ◽  
Pyrrole Derivatives ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Direct Functionalization

Münchnones are mesoionic oxazolium 5-oxides with azomethine ylide characteristics that provide pyrrole derivatives by a 1,3-dipolar cycloaddition (1,3-DC) reaction with acetylenic dipolarophiles. Their reactivity was widely exploited for the synthesis of small molecules, but it was not yet investigated for the functionalization of graphene-based materials. Herein, we report our results on the preparation of münchnone functionalized graphene via cycloaddition reactions, followed by the spontaneous loss of carbon dioxide and its further chemical modification to silver/nisin nanocomposites to confer biological properties. A direct functionalization of graphite flakes into few-layers graphene decorated with pyrrole rings on the layer edge was achieved. The success of functionalization was confirmed by micro-Raman and X-ray photoelectron spectroscopies, scanning transmission electron microscopy, and thermogravimetric analysis. The 1,3-DC reactions of münchnone dipole with graphene have been investigated using density functional theory to model graphene. Finally, we explored the reactivity and the processability of münchnone functionalized graphene to produce enriched nano biomaterials endowed with antimicrobial properties.

Microscopic Identification of Surface Steps on SiC by Density-Functional Calculations

2020 ◽  
Vol 1004 ◽  
pp. 145-152
Author(s):  
Kaori Seino ◽  
Atsushi Oshiyama
Keyword(s):  
Experimental Observation ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Atomic Steps ◽  
Atomic Structures ◽  
The Past ◽  
Microscopic Identification ◽  
Surface Steps ◽  
Inclined Surfaces ◽  
Lower Terrace

We have performed density-functional calculations in order to clarify atomic structures and energetics of surface steps on SiC. The obtained energetics of distinct step types on vicinal 3C-SiC(111) surfaces which correspond to 4H- and 6H-SiC(0001) surfaces reveals the atom-scale reason for the experimental observation in the past that the step morphology is straight for the SiC(0001) surfaces inclined toward the 〈1-100〉 direction while it is meandering for the 〈11-20〉 inclined surfaces. The calculations clarify the rebonding between upper- and lower-terrace edge atoms, which is decisive for the energetics of the atomic steps.

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