Paramagnetic Defects and Photoluminescence in Carbon Rich a-SiC:H Films: Role of Hydrogen and Excess of Carbon

2007 ◽  
Vol 994 ◽  
Author(s):  
A. V. Vasin ◽  
A.A. Konchits ◽  
S.P. Kolesnik ◽  
A.V. Rusavsky ◽  
V.S. Lysenko ◽  
...  
Keyword(s):  
Annealing Temperature ◽  
Vacuum Annealing ◽  
Paramagnetic Centers ◽  
Paramagnetic Resonance ◽  
Killing Effect ◽  
Thermally Activated ◽  
Structure Reconstruction ◽  
Microstructure Model ◽  
Electron Paramagnetic

AbstractThe effect of excess of carbon in a-Si1−xCx:H has been studied with regard to local structure reconstruction, evolution of paramagnetic defects and photoluminescence (PL) after vacuum annealing over the temperature range 300–850°C. Two series of samples with stoichiometric (Si0.5C0.5) and carbon-rich (Si0.3C0.7) compositions were studied by Electron Paramagnetic Resonance (EPR), Photoluminescence (PL) and Raman scattering. It is found that there exist two effects responsible for the PL efficiency of a-Si1-xCx:H films: “killing” effect of carbon-related paramagnetic defects and “enhancing” effect of carbon-hydrogen bonds in Si:C-Hn configuration. A microstructure model is proposed for explaining the non-monotonic behavior of integrated PL intensity and concentration of paramagnetic centers and Si:C-Hn bonds as a function of annealing temperature. This model evolves from the following principal processes during thermal treatment of a-Si1−xCx:H: thermally activated release of weakly bonded hydrogen, migration of hydrogen within material and interaction of hydrogen with carbon-related defects.

scholarly journals Electron paramagnetic resonance in the research of defect formation and thermal processes during grinding of ZnO powders

2004 ◽  
Vol 36 (2) ◽  
pp. 65-72 ◽  
Author(s):  
M. Kakazey ◽  
M. Vlasova ◽  
M. Dominguez-Patiño ◽  
G. Dominguez-Patiño ◽  
T. Sreckovic ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Mechanical Treatment ◽  
Defect Formation ◽  
Thermal Processes ◽  
Defect Structures ◽  
Paramagnetic Centers ◽  
Paramagnetic Resonance ◽  
Zno Powders ◽  
Electron Paramagnetic

This work shows some possibilities for using electron paramagnetic resonance in an experimental study of the role of mechanothermal effects in the formation of defect structures in dispersed systems during prolonged mechanical treatment of ZnO powders. The use of EPR for this purpose is based on the known fact that initiation of a number of paramagnetic centers occurs during mechanical treatment of some materials. Such centers can serve as EPR-sondes of different thermal processes appearing during mechanical treatment of systems containing ZnO.

Jellyfish-like few-layer graphene nanoflakes: high paramagnetic response alongside increased interlayer interaction

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Alexander Ulyanov ◽  
Dmitrii Stolbov ◽  
Serguei Savilov
Keyword(s):  
Photoelectron Spectroscopy ◽  
High Sensitivity ◽  
Paramagnetic Centers ◽  
Interlayer Interaction ◽  
Paramagnetic Resonance ◽  
X Ray ◽  
Graphene Nanoflakes ◽  
Few Layer Graphene ◽  
Electron Paramagnetic ◽  
Hydrocarbon Pyrolysis

Abstract Jellyfish-like graphene nanoflakes (GNF), prepared by hydrocarbon pyrolysis, are studied with electron paramagnetic resonance (EPR) method. The results are supported by X-ray photoelectron spectroscopy (XPS) data. Oxidized (GNFox) and N-doped oxidized (N-GNFox) flakes exhibit an extremely high EPR response associated with a large interlayer interaction which is caused by the structure of nanoflakes and layer edges reached by oxygen. The GNFox and N-GNFox provide the localized and mobile paramagnetic centers which are silent in the pristine (GNF p ) and N-doped (N-GNF) samples. The change in the relative intensity of the line corresponding to delocalized electrons is parallel with the number of radicals in the quaternary N-group. The environment of localized and mobile electrons is different. The results can be important in GNF synthesis and for explanation of their features in applications, especially, in devices with high sensitivity to weak electromagnetic field.

scholarly journals Studies of transmembrane peptides by pulse dipolar spectroscopy with semi-rigid TOPP spin labels

2021 ◽  
Author(s):  
Igor Tkach ◽  
Ulf Diederichsen ◽  
Marina Bennati
Keyword(s):  
Molecular Level ◽  
Dipolar Interaction ◽  
Spin Labels ◽  
Paramagnetic Centers ◽  
Structural Adaptation ◽  
Paramagnetic Resonance ◽  
Transmembrane Peptides ◽  
Distance Distributions ◽  
Lipid Environment ◽  
Electron Paramagnetic

AbstractElectron paramagnetic resonance (EPR)-based pulsed dipolar spectroscopy measures the dipolar interaction between paramagnetic centers that are separated by distances in the range of about 1.5–10 nm. Its application to transmembrane (TM) peptides in combination with modern spin labelling techniques provides a valuable tool to study peptide-to-lipid interactions at a molecular level, which permits access to key parameters characterizing the structural adaptation of model peptides incorporated in natural membranes. In this mini-review, we summarize our approach for distance and orientation measurements in lipid environment using novel semi-rigid TOPP [4-(3,3,5,5-tetramethyl-2,6-dioxo-4-oxylpiperazin-1-yl)-L-phenylglycine] labels specifically designed for incorporation in TM peptides. TOPP labels can report single peak distance distributions with sub-angstrom resolution, thus offering new capabilities for a variety of TM peptide investigations, such as monitoring of various helix conformations or measuring of tilt angles in membranes. Graphical Abstract

scholarly journals DFT Protocol for EPR Prediction of Paramagnetic Cu(II) Complexes and Application to Protein Binding Sites

2018 ◽  
Vol 4 (4) ◽  
pp. 55 ◽  
Author(s):  
Giuseppe Sciortino ◽  
Giuseppe Lubinu ◽  
Jean-Didier Maréchal ◽  
Eugenio Garribba
Keyword(s):  
Binding Sites ◽  
Density Functional ◽  
Computational Procedure ◽  
Paramagnetic Resonance ◽  
Functional Theory ◽  
Protein Binding Sites ◽  
The Mean ◽  
Hamiltonian Parameters ◽  
Electron Paramagnetic

With the aim to provide a general protocol to interpret electron paramagnetic resonance (EPR) spectra of paramagnetic copper(II) coordination compounds, density functional theory (DFT) calculations of spin Hamiltonian parameters g and A for fourteen Cu(II) complexes with different charges, donor sets, and geometry were carried out using ORCA software. The performance of eleven functionals was tested, and on the basis of the mean absolute percent deviation (MAPD) and standard deviation (SD), the ranking of the functionals for Az is: B3LYP > B3PW91 ~ B3P86 > PBE0 > CAM-B3LYP > TPSSh > BH and HLYP > B2PLYP > MPW1PW91 > ω-B97x-D >> M06; and for gz is: PBE0 > BH and HLYP > B2PLYP > ω-B97x-D > B3PW91~B3LYP~B3P86 > CAM-B3LYP > TPSSh~MPW1PW91 >> M06. With B3LYP the MAPD with respect to A z exp t l is 8.6% with a SD of 4.2%, while with PBE0 the MAPD with respect to g z exp t l is 2.9% with a SD of 1.1%. The results of the validation confirm the fundamental role of the second order spin-orbit contribution to Az. The computational procedure was applied to predict the values of gz and Az of the adducts formed by Cu(II) with albumin and two fragments of prion protein, 106–126 and 180–193.

scholarly journals PQQ-Aza-Crown Ether Complexes as Biomimetics for Lanthanide and Calcium Dependent Alcohol Dehydrogenases

2021 ◽  
Author(s):  
Violeta A. Vetsova ◽  
Katherine R. Fisher ◽  
Henning Lumpe ◽  
Alexander Schäfer ◽  
Erik K. Schneider ◽  
...  
Keyword(s):  
Metal Ions ◽  
Gas Phase ◽  
Ion Mobility ◽  
Paramagnetic Resonance ◽  
Calcium Dependent ◽  
Lower Charge ◽  
Crown Ether Complexes ◽  
Recent Group ◽  
Electron Paramagnetic

<div>Understanding the role of metal ions in biology can lead to the development of new catalysts for</div><div>several industrially important transformations. Lanthanides are the most recent group of metal ions</div><div>that have been shown to be important in biology i.e. - in quinone-dependent methanol</div><div>dehydrogenases (MDH). Here we evaluate a pyrroloquinoline quinone and 1-aza-15-crown-5 based</div><div>ligand platform as scaffold for Ca2+ , Ba2+ , La3+ and Lu3+ biomimetics of MDH and we evaluate the</div><div>importance of ligand design, charge, size, counterions and base for the alcohol oxidation reaction</div><div>using NMR spectroscopy. In addition, we report a new straightforward synthetic route (3 steps</div><div>instead of 11 and 33% instead of 0.6% yield) for biomimetic ligands based on PQQ. We show that</div><div>when studying biomimetics for MDH, larger metal ions and those with lower charge in this case</div><div>promote the dehydrogenation reaction more effectively and that this is likely an effect of the ligand</div><div>design which must be considered when studying biomimetics. To gain more information on the</div><div>structures and impact of counterions of the complexes, we performed collision induced dissociation</div><div>(CID) experiments and observe that the nitrates are more tightly bound than the triflates. To resolve</div><div>the structure of the complexes in the gas phase we combined DFT-calculations and ion mobility</div><div>measurements (IMS). Furthermore, we characterized the obtained complexes and reaction mixtures</div><div>using Electron Paramagnetic Resonance (EPR) spectroscopy and show the emergence of a quinone-</div><div>based radical during the reaction with substrate and base.</div>

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