Electron Paramagnetic Resonance Studies of Hf-CVD Diamond Films

1996 ◽  
Vol 423 ◽  
Author(s):  
B. Ramakrishnan ◽  
D. J. Keeble ◽  
H. Rodrigo ◽  
A. Kulkarni
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Methane Concentration ◽  
Chemical Vapor ◽  
Paramagnetic Species ◽  
Paramagnetic Defect ◽  
Single Spectrum ◽  
Paramagnetic Resonance ◽  
Epr Measurements ◽  
Hot Filament ◽  
Electron Paramagnetic

AbstractDiamond thin films have been deposited on silicon substrates by hot-filament chemical vapor deposition (HF-CVD). Substrate temperature and methane concentration have been varied and the resulting structural properties of the deposited films studied. Raman spectroscopy, scanning electron microscopy and electron paramagnetic resonance (EPR) measurements were performed. The EPR measurements showed a single spectrum at g = 2.0027(2). The bulk concentration of the paramagnetic species, as determined from the total EPR absorption were found to vary in the range 1017 to 1019 cm−3. Low paramagnetic defect concentrations were found for samples exhibiting a low non-diamond carbon contribution to the Raman spectrum. These samples were those grown with a methane concentration of I % or less.

Electron Paramagnetic Resonance Studies of Intrinsic Bonding Defects and Impurities in SiO2 Thin Solid Films

1985 ◽  
Vol 61 ◽  
Author(s):  
Robert N. Schwartz ◽  
Marion D. Clark ◽  
Walee Chamulitrat ◽  
Larry Kevan
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Rf Sputtering ◽  
Chemical Vapor ◽  
Temperature Dependent ◽  
Paramagnetic Resonance ◽  
Pressure Chemical ◽  
Defects And Impurities ◽  
Electron Paramagnetic

ABSTRACTElectron paramagnetic resonance (EPR) spectroscopy has been used to identify paramagnetic intrinsic bonding defects and impurities in as-deposited thin solid SiO2 films. Thin films grown by E-beam vacuum deposition, RF sputtering, thermal oxidation of polysilicon, plasma enhanced chemical vapor deposition (PECVD), and low pressure chemical vapor deposition (LPCVD) techniques have been examined. Some of the growth techniques yield films that have paramagnetic centers similar to those found in bulk radiation-damaged vitreous SiO2. A new temperature dependent EPR center was observed in PECVD SiO2 films and has been assigned to trapped NO2. Slow-motional EPR lineshape theory was used to analyze the temperature dependent spectra.

Electron Paramagnetic Resonance as a Probe for Metal Ions and Radicals in Paper

2015 ◽  
Vol 36 (4) ◽  
Author(s):  
Alfonso Zoleo ◽  
Laura Speri ◽  
Maddalena Bronzato
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Metal Ions ◽  
Chemical Species ◽  
Paramagnetic Species ◽  
Paramagnetic Resonance ◽  
Relevant Role ◽  
Historic Paper ◽  
Electron Paramagnetic ◽  
Identification And Characterization

AbstractElectron Paramagnetic Resonance (EPR) is a technique devoted to the identification and characterization of paramagnetic species, i.e. chemical species with unpaired electrons. Very common paramagnetic species which can be detected through EPR in historic paper are Fe(III), Mn(II), Cu(II) ions and radicals, where Fe(III), Cu(II) and radicals play a relevant role in paper degradation. Specifically, Fe(III) is almost ubiquitous in historic paper. Here we propose an overview of the EPR signals in historic and artificially aged paper, and in particular, we would like to show how a deep analysis of EPR signals from paper could provide useful information about the paper’s origin and unique indications of the degradation and oxidation level of the paper.

Intrinsic Defects in HPSI 6H-SiC: an EPR Study

2008 ◽  
Vol 600-603 ◽  
pp. 381-384 ◽  
Author(s):  
Patrick Carlsson ◽  
Nguyen Tien Son ◽  
Björn Magnusson ◽  
Anne Henry ◽  
Erik Janzén
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Vapor Deposition ◽  
Thermal Activation ◽  
Chemical Vapor ◽  
Paramagnetic Resonance ◽  
Intrinsic Defects ◽  
Annealing Behavior ◽  
Carbon Vacancy ◽  
The Stability ◽  
Electron Paramagnetic

High-purity, semi-insulating 6H-SiC substrates grown by high-temperature chemical vapor deposition were studied by electron paramagnetic resonance (EPR). The carbon vacancy (VC), the carbon vacancy-antisite pair (VCCSi) and the divacancy (VCVSi) were found to be prominent defects. The (+|0) level of VC in 6H-SiC is estimated by photoexcitation EPR (photo-EPR) to be at ~ 1.47 eV above the valence band. The thermal activation energies as determined from the temperature dependence of the resistivity, Ea~0.6-0.7 eV and ~1.0-1.2 eV, were observed for two sets of samples and were suggested to be related to acceptor levels of VC, VCCSi and VCVSi. The annealing behavior of the intrinsic defects and the stability of the SI properties were studied up to 1600°C.

A Study of V3+/4+ Levels in Semi-insulating 6H-SiC using Optical Admittance and Electron Paramagnetic Resonance Spectroscopies

2006 ◽  
Vol 911 ◽  
Author(s):  
Wonwoo Lee ◽  
Mary E Zvanut
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Charge State ◽  
Conduction Band ◽  
Epr Spectroscopy ◽  
Admittance Spectroscopy ◽  
Paramagnetic Resonance ◽  
Characteristic Spectrum ◽  
Epr Measurements ◽  
The Individual ◽  
Electron Paramagnetic

AbstractThe purpose of this study is to identify the vanadium acceptor levels in semi-insulating (SI) 6H-SiC using optical admittance spectroscopy (OAS) and electron paramagnetic resonance (EPR) spectroscopy. OAS conductance peaks near at 0.67 ± 0.02 eV and 0.70 ± 0.02 eV are identified as V3+/4+ levels at the quasi-cubic sites. An OAS peak at 0.87 eV is assigned to the same transition at the hexagonal site. EPR measurements before illumination revealed the characteristic spectrum of V3+. The presence of the V3+ signal supports the identification of the OAS peaks as transitions from the V3+/4+ level to the conduction band. Photo-induced EPR measurements reveal a change in the intensity of V3+ and V4+ at 0.8 ± 0.1 eV, where the amplitude of the V3+ charge state decreases and that of V4+ increases by approximately equal amounts. Although the individual sites are not resolved in the photo-induced EPR data, the 0.8 eV feature strongly supports the assignment of the three OAS peaks as acceptor levels.

Free radical metabolites in myocardium during ischemia and reperfusion

1991 ◽  
Vol 261 (4) ◽  
pp. L81-L86 ◽  
Author(s):  
Enno K. Ruuge ◽  
Alexander N. Ledenev ◽  
Vladimir L. Lakomkin ◽  
Alexander A. Konstantinov ◽  
Marina Yu. Ksenzenko
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Free Radical ◽  
Low Temperature ◽  
Coenzyme Q ◽  
Heart Tissue ◽  
Paramagnetic Species ◽  
Spectral Parameters ◽  
Paramagnetic Resonance ◽  
Oxygen Paradox ◽  
Electron Paramagnetic

Low-temperature electron paramagnetic resonance (EPR) spectroscopy and spin traps were used to measure paramagnetic species generation in rat hearts and isolated mitochondria. The hearts were freeze-clamped at 77 K during control perfusion by the Langendorff procedure, after 20–30 min of normothermic ischemia or 10–30 s of reperfusion with oxygenated perfusate. All EPR spectra measured at 4.5–50 K exhibited signals of both mitochondrial free radical centers and FeS proteins. The analysis of spectral parameters measured at 243 K showed that free radicals in heart tissue were semiquinones of coenzyme Q10 and flavins. The appearance of a typical “doublet” signal at g = 1.99 in low-temperature spectra indicated that a part of ubisemiquinones formed a complex with a high potential FeS protein of succinate dehydrogenase. Ischemia decreased the free radical species in myocardium ≈50%; the initiation of reflow of perfusate resulted in quick increase of the EPR signal. Mitochondria isolated from hearts during control perfusion and after 20–30 min of ischemia were able to produce superoxide radicals in both the NADH-coenzyme Q10 reductase and the bc1 segments of the respiratory chain. The rate of oxyradical generation was significantly higher in mitochondria isolated from ischemic heart. electron paramagnetic resonance; oxygen paradox; oxyradicals; rat heart; semiquinones

Identification of Niobium in 4H-SiC by EPR and Ab Initio Studies

2012 ◽  
Vol 717-720 ◽  
pp. 217-220 ◽  
Author(s):  
Nguyen Tien Son ◽  
Viktor Ivády ◽  
Adam Gali ◽  
Andreas Gällström ◽  
Stefano Leone ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
High Temperature ◽  
Ab Initio ◽  
Electron Spin ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Paramagnetic Resonance ◽  
Form Complex ◽  
Electron Paramagnetic ◽  
Neutral Charge State

In unintentionally Nb-doped 4H-SiC grown by high-temperature chemical vapor deposition (HTCVD), an electron paramagnetic resonance (EPR) center with C1h symmetry and an electron spin S=1/2 was observed. The spectrum shows a hyperfine structure consisting of ten equal-intensity hyperfine (hf) lines which is identified as due to the hf interaction between the electron spin and the nuclear spin of 93Nb. An additional hf structure due to the interaction with two equivalent Si neighbors was also observed. Ab initio supercell calculations of Nb in 4H-SiC suggest that Nb may form complex with a C-vacancy (VC) resulting in an asymmetric split-vacancy (ASV) defect, NbSi-VC. Combining results from EPR and supercell calculations, we assign the observed Nb-related EPR center to the hexagonal-hexagonal configuration of the AVS defect in the neutral charge state, (NbSi-VC)0.

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