Optical Emission Imaging and Modeling Investigations of Microwave-Activated SiH/H and SiH/CH/H Plasmas.

Silicon is a known trace contaminant in diamond grown by chemical vapor deposition (CVD) methods. Deliberately Si-doped diamond is currently attracting great interest because of the attractive optical properties of the negatively charged silicon-vacancy (SiV) defect. This work reports in-depth studies of microwave-activated H plasmas containing trace (10-100 ppm) amounts of SiH, with and without a few % of CH, operating at pressures and powers relevant for contemporary diamond CVD, using a combination of experiment (spatially resolved optical emission (OE) imaging) and two-dimensional plasma chemical modeling.

Imaging and Modeling the Optical Emission from CH Radicals in Microwave Activated C/H Plasmas.

We report a combined experimental/modeling study of optical emission from the AΔ, BΣ, and CΣ states of the CH radical in microwave (MW) activated CH/H gas mixtures operating under a range of conditions relevant to the chemical vapor deposition of diamond. The experiment involves spatially and wavelength resolved imaging of the CH(C → X), CH(B → X), and CH(A → X) emissions at different total pressures, MW powers, C/H ratios in the source gas, and substrate diameters. The results are interpreted by extending an existing 2D (, ) plasma model to include not just electron impact excitation but also chemiluminescent (CL) bimolecular reactions as sources of the observed CH emissions.

Spatially Resolved Optical Emission and Modeling Studies of Microwave-Activated Hydrogen Plasmas Operating under Conditions Relevant for Diamond Chemical Vapor Deposition.

A microwave (MW) activated hydrogen plasma operating under conditions relevant to contemporary diamond chemical vapor deposition reactors has been investigated using a combination of experiment and self-consistent 2-D modeling. The experimental study returns spatially and wavelength resolved optical emission spectra of the d → a (Fulcher), G → B, and e → a emissions of molecular hydrogen and of the Balmer-α emission of atomic hydrogen as functions of pressure, applied MW power, and substrate diameter. The modeling contains specific blocks devoted to calculating (i) the MW electromagnetic fields (using Maxwell's equations) self-consistently with (ii) the plasma chemistry and electron kinetics, (iii) heat and species transfer, and (iv) gas-surface interactions.

What [plasma used for growing] diamond can shine like flame?

Diamond synthesis by chemical vapour deposition (CVD) from carbon-containing gas mixtures has by now long been an industrial reality, but commercial interest and investment into the technology has grown dramatically in the last several years. This Feature Article surveys recent advances in our understanding of the gas-phase chemistry of microwave-activated methane/hydrogen plasmas used for diamond CVD, including that of added boron-, nitrogen- and oxygen-containing dopant species. We conclude by considering some of the remaining challenges in this important area of contemporary materials science.

Optical Emission from C Anions in Microwave-Activated CH/H Plasmas for Chemical Vapor Deposition of Diamond.

Visible emission from C(BΣ) anions has been identified underlying the much stronger Swan band emission from neutral C(dΠ) radicals (henceforth C* and C*, respectively) in MW-activated C/H/(Ar) plasmas operating under conditions appropriate for the chemical vapor deposition (CVD) of diamond. Spatially resolved measurements of the C* and C* emissions as functions of the C/H/(Ar) ratio in the input gas mixture, the total pressure, and the applied MW power, together with complementary 2-D(r, z) plasma modeling, identifies dissociative electron attachment (DEA) to CH radicals in the hot plasma as the dominant source of the observed C* emission. Modeling not only indicates substantially higher concentrations of CH anions (from analogous DEA to CH) in the near-substrate region but also suggests that the anion number densities will typically be 3-4 orders of magnitude lower than those of the electrons and partner cations, i.

Microwave Plasma-Activated Chemical Vapor Deposition of Nitrogen-Doped Diamond. II: CH/N/H Plasmas.

We report a combined experimental and modeling study of microwave-activated dilute CH/N/H plasmas, as used for chemical vapor deposition (CVD) of diamond, under very similar conditions to previous studies of CH/H, CH/H/Ar, and N/H gas mixtures. Using cavity ring-down spectroscopy, absolute column densities of CH(X, v = 0), CN(X, v = 0), and NH(X, v = 0) radicals in the hot plasma have been determined as functions of height, z, source gas mixing ratio, total gas pressure, p, and input power, P. Optical emission spectroscopy has been used to investigate, with respect to the same variables, the relative number densities of electronically excited species, namely, H atoms, CH, C, CN, and NH radicals and triplet N molecules.

Determination of Stark parameters by cross-calibration in a multi-element laser-induced plasma.

We illustrate a Stark broadening analysis of the electron density Ne and temperature Te in a laser-induced plasma (LIP), using a model free of assumptions regarding local thermodynamic equilibrium (LTE). The method relies on Stark parameters determined also without assuming LTE, which are often unknown and unavailable in the literature. Here, we demonstrate that the necessary values can be obtained in situ by cross-calibration between the spectral lines of different charge states, and even different elements, given determinations of Ne and Te based on appropriate parameters for at least one observed transition.

Microwave Plasma-Activated Chemical Vapor Deposition of Nitrogen-Doped Diamond. I. N2/H2 and NH3/H2 Plasmas.

We report a combined experimental/modeling study of microwave activated dilute N2/H2 and NH3/H2 plasmas as a precursor to diagnosis of the CH4/N2/H2 plasmas used for the chemical vapor deposition (CVD) of N-doped diamond. Absolute column densities of H(n = 2) atoms and NH(X(3)Σ(-), v = 0) radicals have been determined by cavity ring down spectroscopy, as a function of height (z) above a molybdenum substrate and of the plasma process conditions, i.e.

The mechanism of CO2 insertion into iridium(I) hydroxide and alkoxide bonds: a kinetics and computational study.

The facile insertion of CO2 into iridium(I) hydroxide, alkoxide, and amide bonds was recently reported. In particular, [Ir(cod)(IiPr)(OH)] (IiPr = 1,3-bis(isopropyl)imidazol-2-ylidene) reacted with CO2 in solution and in the solid state in a matter of minutes to give the novel [{Ir(cod)(IiPr)}2(μ-κ(1)O:κ(2)O,O-CO3)] complex. In the present study, this reaction is probed using kinetics and theoretical studies, which enabled us to analyse its facile nature and to fully elucidate the reaction mechanism with excellent correlation between the two methods.

Fluoride, bifluoride and trifluoromethyl complexes of iridium(I) and rhodium(I).

Herein we report robust methods for the preparation and full characterisation of a range of Ir(I) and Rh(I) fluoride and bifluoride complexes using N-heterocyclic carbenes (NHCs) as ancillary ligands. The processes that link the fluoride and the bifluoride species are investigated and reports of the first Ir-bifluoride and Ir(I)-NHC and Rh(I)-NHC trifluoromethyl complexes are revealed.

Iridium(I) hydroxides in catalysis: rearrangement of allylic alcohols to ketones.

The iridium(I) hydroxide complex [Ir(OH)(COD)(I(i)Pr)] has been shown to be a competent catalyst for the rearrangement of allylic alcohols to ketones. Reactions proceed in short reaction times (1-1.5 h) with microwave heating, in the absence of additives.

Synthesis and reactivity of new bis(N-heterocyclic carbene) iridium(I) complexes.

New complexes of the type trans-[IrCl(η(2)-COE)(NHC)2] (COE = cis-cyclooctene; NHC = N-heterocyclic carbene) have been prepared in one step from the reaction of ca. 4 equiv of NHC or [AgCl(NHC)] with [IrCl(η(2)-COE)2]2 in benzene. These new complexes have been characterized by techniques including NMR and IR spectroscopy, X-ray crystallography, and elemental analysis.

CO2 fixation employing an iridium(I)-hydroxide complex.

The reactivity of a number of Ir(I) complexes towards CO2 is explored using [Ir(NHC)(OH)] as a key synthon. CO2 insertion into Ir-O and Ir-N bonds proved facile, yielding a number of Ir(I)-carbonates and -carbamates. Most importantly, reaction between CO2 and Ir(I)-OH led to isolation of the novel [{Ir(I)}2-(μ-κ(1):κ(2)-CO3)] complex.

Iridium(I) hydroxides: powerful synthons for bond activation.

A family of iridium(I) hydroxides of the form [Ir(cod)(NHC)(OH)] (cod = 1,5-cyclooctadiene, NHC = N-heterocyclic carbene) is reported. Single-crystal X-ray analyses and computational methods were used to explore the structural characteristics and steric properties of these new complexes. The model complex [Ir(cod)(IiPr)(OH)] (IiPr = 1,3-(diisopropyl)imidazol-2-ylidene) undergoes reaction with a wide variety of substrates including boronic acids and silicon compounds.

Well-defined NHC-rhodium hydroxide complexes as alkene hydrosilylation and dehydrogenative silylation catalysts.

Alkene hydrosilylation and dehydrogenative silylation reactions, mediated by [Rh(cod)(NHC)(OH)] complexes (cod = 1,5-cyclooctadiene; NHC = N-heterocyclic carbene) are described. The study details a comparison of the catalytic activity and steric characteristics of four rhodium complexes bearing different NHC ligands. The novel [Rh(cod)(Ii-PrMe)(OH)] complex (Ii-PrMe = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidine) was designed to improve the reactivity of Rh(I)-hydroxides and proved to be a successful promoter of hydrosilylation and dehydrogenative silylation, displaying good stereo- and regiocontrol.

Well-defined [Rh(NHC)(OH)] complexes enabling the conjugate addition of arylboronic acids to α,β-unsaturated ketones.

The synthesis and catalytic activity of three well-defined monomeric rhodium(I) hydroxide complexes bearing N-heterocyclic carbene (NHC) ligands are reported. [Rh(cod)(ICy)(OH)] promoted the 1,4-addition of arylboronic acids to cyclic enones, with TONs and TOFs of 100,000 and 6,600 h(-1), respectively, at 0.001 mol% catalyst loadings.

A reanalysis of the A 1A"-X 1A' transition of CFBr.

The laser induced fluorescence spectrum of the A (1)A(")-X (1)A(') transition of CFBr is presented, with selected bands recorded at sub-Doppler resolution, allowing the rotational constants to be fully determined. Analysis of dispersed fluorescence spectra and the pattern of (79)Br/(81)Br isotope splittings indicate that the origin must be shifted from previous assignments in the literature to 23 271.0 cm(-1).

Short-range remote detection of liquid surface contamination by active imaging Fourier transform spectrometry.

An imaging Fourier transform spectrometer developed at TUHH was used for short-range remote detection and identification of liquids on surfaces. The method is based on the measurement of infrared radiation emitted and reflected by the surface and the liquid. A radiative transfer model that takes both the real and imaginary parts of the refractive index of the materials into account has been developed.

Steroids involved with final oocyte maturation in the winter flounder.

A number of androgens and progestogens including 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17,20-P) were examined in female winter flounder as possible maturation inducing steroids (MIS). During final oocyte maturation serum levels of testosterone (T) and 17 beta-hydroxy-5 beta-androsten-3-one (5 beta-T) peaking at over 200 ng/ml and pregnenolone (PE) at 40 ng/ml were the predominant steroids found from each major group. High levels of T and 5 beta-T were correlated with oocyte stages characterized by germinal vesicle migration.

Characteristics of stroke victims associated with early cardiovascular mortality in their children.

We assessed the relationship between characteristics of stroke victims and the risk of early death from coronary or cerebrovascular disease (CCVD) among their children. For each of 55 stroke patients selected from a registry which enrolled patients between 1969 and 1973, an index of their progeny's survival was calculated using the age in 1987 of 197 surviving children, and the age at and cause of death for 55 deceased children. Increased risk of CCVD death within families was significantly related to parental age at the time of first stroke, and with the parental history of diabetes mellitus.

Changes in survival following stroke in five North Carolina counties observed during two different periods.

We evaluated survival following stroke for patients from a five-county area of rural North Carolina enrolled in either of two community hospital-based stroke survey programs. In this area, the first program enrolled 843 stroke patients between 1970 and 1973 and the second program enrolled 786 stroke patients between 1979 and 1980. One-year survival increased from 49% in the first program to 62% in the second for all stroke patients, from 54% to 68% for patients with cerebral infarction, and from 18% to 55% for patients with cerebral hemorrhage.

Cause specific mortality following cerebral infarction.

Mortality from four causes (index stroke, subsequent stroke, cardiac disease and non-cardiovascular causes) was examined during a 5 year follow-up of 1694 cerebral infarction patients admitted to 25 community hospitals between 1969 and 1973. The hazard for mortality from the index stroke was high initially, but declined to a negligible level by 6 months post-stroke. In contrast, hazards for mortality from subsequent strokes, cardiac diseases and non-cardiovascular causes each peaked midway through the first year, declined during the remainder of that year, and then increased in the latter part of the follow-up.

Maturational steroids and gonadotropin in upstream migratory sockeye salmon.

The circulating serum concentrations of various steroid hormones in mature sockeye salmon were measured at four different developmental stages in their upstream migration to spawn at Adams River in British Columbia, Canada. In females, a high level of estradiol-17 beta was found in fish at the first location, and it persisted until immediately before reaching the spawning grounds, 485 km upstream, where it decreased to a minimal level. Free testosterone was extremely high throughout the migration but decreased significantly after spawning while its glucuronide changed reciprocally.

Progestogens, androgens and their glucuronides in the terminal stages of oocyte maturation in landlocked Atlantic salmon.

Peripheral serum levels of free and conjugated steroids were correlated with seven terminal stages of oocyte maturation in female landlocked Atlantic salmon. Pregnenolone levels were maximal at stage 1, and there was a surge in testosterone after initiation of germinal vesicle migration. Testosterone remained high, above 25 ng/ml until ovulation, and its glucuronide was always lower than the corresponding free form.