Relative Number Density Research Articles

Monitoring of CF and CF2 Number Density by Optical Emission Intensity Corrected using Probe-Measured Plasma Parameters

The use of the CF and CF2 optical emission (OE) intensity corrected by the probe-measured electron density and temperature is proposed for the estimation of CF and CF2 relative number density in low-pressure, high-density fluorocarbon plasmas. The estimation of the CF and CF2 density by the corrected OE is mainly based on an assumption that the electron energy distribution function near the threshold energy of these OE is approximated by a Maxwellian using the probe-measured electron temperature. The comparison of the corrected OE intensity with CF and CF2 laser-induced fluorescence (LIF) intensity, which represents the CF and CF2 number density, confirms good proportionality between the LIF and the corrected OE intensity. Thus, the proposed procedure is expected to be useful for the monitoring of CF and CF2 radicals.

Characterization of aquatic colloids by a combination of LIBD and ICP-MS following the size fractionation

SummaryHumic colloids in deep groundwater are characterized in order to ascertain how heavy metal ions of chemical homologue to actinides are associated in different size fractions. The colloid size fractionation is made by two different methods: flow field flow fractionation (FFFF) and size exclusion chromatography (SEC), which is followed by analysis of chemical composition using UV spectroscopy for organic components and ICP-MS for inorganic components. Relative number density of humic colloids following the size fractionation is determined by laser-induced breakdown detection (LIBD). For the appraisal of colloid size change upon metal ion complexation, purified Aldrich humic acid is loaded with the Eu3+ion on increasing the concentration and the size change is then determined by LIBD. Humic colloids are interacted with radioactive tracers,155Eu(III) and228Th(IV), to appreciate their sorption behaviour onto different colloid size fractions and thus to compare with natural humic colloid-borne elements of M(III) and M(IV).Whereas the organic component of humic colloids is found in the size range about 3 nm, the inorganic components of actinides homologues, M(III) and M(IV), are observed in the fractionated size range from 10 nm to 35 nm. This observation leads us to presume that the inorganic composites, composed of heavy metal elements, are peptised by humic/fulvic acid. The laboratory traced elements,155Eu(III) and228Th(IV), are quantitatively sorbed only onto the organic component. This fact infers the complexation of traced metal ions with humic components of colloids without visible interaction with the inorganic components. Once purified humic acid is complexed with Eu(III) in an excess amount, the size increases over 200 nm and the resulting products undergo flocculation or precipitation. The results of the present experiment indicate that the natural humic colloid-borne heavy metal ions appear in different chemical states as compared to the same but laboratory traced metal ions. As a result, the laboratory simulation entails a better understanding of the underlying molecular level chemical reactions, which are important to the assessment of the colloid-borne actinide migration.

The rate of bubble deformation during tungsten wire drawing

Rods and wires from K–Al–Si doped tungsten containing residual porosity and K filled bubbles were studied from 6 to 0.2 mm in diameter ( d) by means of anisotropic small angle neutron scattering (ASANS) method. This novel technique has been developed for monitoring shape and size of microscopic pores, bubbles, second phase particles in deformed PM materials. In case of mixture of different populations, e.g. uniformly elongated bubbles and spherical ones in tungsten, the morphological parameters for each population can be obtained from the quantitative analysis of ASANS data. Such parameters are: relative number density, diameter, aspect ratio of elongation. It was found that during wire drawing the average aspect ratio of elongated bubbles increases much slower (∼1/ d) than it was expected from the usual theory (∼1/ d 3). Instead of “constant volume” assumption, a “constant length” assumption seems to be reliable. The occurrence of spherical bubbles after several steps of wire drawing can also be revealed.

Effects of NH3 and N2 additions to hot filament activated CH4/H2 gas mixtures

Resonance enhanced multiphoton ionization and cavity ring down spectroscopies have been used to provide spatially resolved measurements of relative H atom and CH3 radical number densities, and NH column densities, in a hot filament (HF) reactor designed for diamond chemical vapor deposition and here operating with a 1% CH4/n/H2 gas mixture—where n represents defined additions of N2 or NH3. Three-dimensional modeling of the H/C/N chemistry prevailing in such HF activated gas mixtures allows the relative number density measurements to be placed on an absolute scale. Experiment and theory both indicate that N2 is largely unreactive under the prevailing experimental conditions, but NH3 additions are shown to have a major effect on the gas phase chemistry and composition. Specifically, NH3 additions introduce an additional series of “H-shift” reactions of the form NHx+H⇌NHx−1+H2 which result in the formation of N atoms with calculated steady state number densities >1013 cm−3 in the case of 1% NH3 additions in the hotter regions of the reactor. These react, irreversibly, with C1 hydrocarbon species forming HCN products, thereby reducing the concentration of free hydrocarbon species (notably CH3) available to participate in diamond growth. The deduced reduction in CH3 number density due to competing gas phase chemistry is shown to be compounded by NH3 induced modifications to the hot filament surface, which reduce its efficiency as a catalyst for H2 dissociation, thus lowering the steady state gas phase H atom concentrations and the extent and efficiency of all subsequent gas phase transformations.

An Improved Method for the Estimation of Rotational Temperature with a Weak Electron Beam.

In this paper, an improved method for the estimation of rotational temperature with a weak electron beam is presented. Using the method, the effect of an electron beam on a flow field becomes smaller and it is possible to obtain the distribution of rotational temperature with a smaller experimental apparatus. In the method, slit width of a monochromator is set wider to obtain larger signals for the higher rotational levels. Due to the decrease of resolution, the rotational spectra are measured with much overlapping, but they are divided into their individual rotational spectra by using a fitting function. Using the improved method, a rotational temperature and a relative number density distribution in a supersonic nitrogen free jet expanding from a stagnation temperature of 350 K is measured. Moreover, the experimental results are compared with theoretical results based on master equations and those simulated by the Direct Simulation Monte Carlo (DSMC) method using the Dynamic Molecular Collision (DMC) model. These results are consistent with each other, enabling verification of the experimental results.

Interpretation of the spectra of energy scattered by dispersed anchovies.

The spectra of backscattered energy by dispersed anchovies, which were reported by Holliday (1972), reveal several peaks at frequencies that correspond to theoretically calculated resonance frequencies of year classes of anchovies. Theoretical calculations are based on concurrent measurements of distributions of swim bladder dimensions and a modified form of Minnaert's (1933) equation. Differences between calculated and measured values of the mean lengths of the second-, third-, and fourth-year classes are within experimental uncertainties (+/-8%). The calculated mean lengths of juvenile anchovies are in good agreement with historical measurements of the bounds on this parameter (Butler, 1989). Matching of theoretical calculations and measurements of backscattered energy level versus frequency yields estimates of the total Q of the spectral line, QT, and the relative number density per year class. The resultant estimate of QT of adult anchovies is approximately 4.4. This value of QT is consistent with laboratory measurements of the Q of individual anchovies. Q0 (approximately 7 at 15 m) and measurements of length distributions of year classes and depth distributions. Resultant estimates of relative number densities of year classes were consistent with historical measurements of the relative number densities of year classes of anchovies in the Southern California Bight.

A mobile laser-induced breakdown detection system and its application for the in situ-monitoring of colloid migration

Abstract A mobile Laser-Induced Breakdown Detection (LIBD) system is developed for the field study of the aquatic colloid migration. The principle of LIBD is based on the plasma generation at breakdown of colloids in the laser focus region, which is then observed by either photo-acoustic detection or optical monitoring. The method provides information on the number density and average size of colloids. The present instrumentation built up particularly for the field study is applied for the aquatic colloid migration in a natural granite fracture. The study is performed within the Colloid and Radionuclide Retention project (CRR) in order to investigate the role of colloids on the radionuclide migration. For this purpose, bentonite colloids dispersed in granite groundwater are injected into a rock fracture zone with a dipole distance of 5 m. After passing through the fracture, the groundwater is guided into a flow-through detection cell of LIBD for the quantification of colloids. Another experiment is performed with the same colloids traced by tetra- and tri-valent metal ions, Th(IV), Hf(IV) and Tb(III). The recovery of colloids as found by LIDB appears to be about 55±5% of the injected colloid mass concentration, which is corroborated by ICP-MS analysis of Al present in bentonite colloids. An average size of recovered colloids is slightly decreased from the value of before injection and hence the relative number density increased in the course of the rock fracture migration. Recovered fractions of colloid-borne trace elements in the extracted groundwater are 78±8% for both tetra-valent elements and 33±3% for trivalent element of the originally traced concentrations. Plausible explanations are given for the different recoveries of heavy metal ions.

The spectra of energy scattered by dispersed anchovies

The spectra of backscattered energy by dispersed anchovies, which were reported by Holliday (1972), reveal several peaks at frequencies that correspond to theoretically calculated resonance frequencies of year classes of anchovies. Theoretical calculations are based on concurrent measurements of distributions of swim bladder dimensions and a modified form of Minnaert’s equation. Differences between calculated and measured values of the mean lengths of the second, third, and fourth year classes are within experimental uncertainties (8%). The calculated mean lengths of juvenile anchovies are in good agreement with historical measurements of this parameter. Matching of calculations and measurements of backscattered energy level versus frequency yields estimates of the total Q of spectral lines and the relative number density per year class. The resultant estimate of Q of adult anchovies is approximately 4.4. This value of Q is consistent with laboratory measurements of the Q of individual anchovies (∼7 at 15 m) and measurements of length and depth distributions of year classes. Resultant estimates of relative number densities of year-classes were consistent with historical measurements of this parameter in the Southern California Bight. [Work supported by ONR.]

Dissociative electron attachment to electronically excitedCS2

Dissociative attachment of low-energy electrons to the electronically excited and bent ${}^{1}{B}_{2}$ state of ${\mathrm{CS}}_{2}$ is studied. The measurements are carried out in a crossed three-beam geometry in which a laser beam is used to prepare the excited molecules. The absolute cross sections for the formation of ${\mathrm{S}}^{\ensuremath{-}}$ and ${\mathrm{CS}}^{\ensuremath{-}}$ by dissociative attachment to the ${}^{1}{B}_{2}$ excited state are determined by a measurement of the relative number density in the excited state. Based on the earlier observation of the formation of ${\mathrm{S}}_{2}^{\ensuremath{-}}$ from the linear symmetric ground state of ${\mathrm{CS}}_{2},$ an increase in the ${\mathrm{S}}_{2}^{\ensuremath{-}}$ cross section was expected from the bent excited state. However, ${\mathrm{S}}_{2}^{\ensuremath{-}}$ is found to be absent from this state. Possible mechanisms are proposed to explain this counterintuitive result.

On the mechanism of CH3 radical formation in hot filament activated CH4/H2 and C2H2/H2 gas mixtures

Resonance enhanced multiphoton ionization spectroscopy has been used to determine relative number densities of CH3 radicals in a hot filament chemical vapour deposition (HF-CVD) reactor designed for diamond growth, as a function of process gas (i.e. both CH4/H2 and C2H2/H2 gas mixtures), position (d), filament temperature (Tf) and local gas temperature (Tg). The similar CH3 radical number density profiles observed upon activation of the two feedstock gas mixtures suggest that CH3 radical formation in both cases is dominated by gas phase chemistry, in contradiction of the current consensus which invokes surface catalysed hydrogenation as the means of inducing the necessary CC bond fission in the case of C2H2/H2 gas mixtures. Three body addition reactions involving C2H2 (and C2H4), together with H atoms and H2 molecules, are identified as probable reactions requiring further study in order to provide a proper description of diamond CVD using a C2H2/H2 gas feed.

Effects of sample probe insertion on plasma conditions in direct sample insertion-inductively coupled plasma-atomic emission spectrometry

The effects of sample probe insertion on plasma excitation conditions in direct sample insertion-inductively coupled plasma-atomic emission spectrometry (DSI-ICP-AES) were investigated. Graphite sample probes in the form of a cup and a rod (with or without undercut) were used. Molybdenum rods were also used for comparison. A dark central channel is created in the plasma when a sample probe is inserted. The diameter of the central channel correlates with the diameter of the sample probe. In addition, the plasma excitation conditions were monitored using repetitive laser sampling to introduce a steady flow of Zn or Fe particles into the ICP. Changes in the relative excitation temperature and electron number density of the plasma were deduced from the ratios of the emission intensities of Fe line pair and Zn line pair, respectively. The temperature and electron number density of the plasma decreased when a sample probe was inserted. The degree of changes in the plasma conditions depends on the diameter of the sample probes, regardless of the form and material of the probe. The diameter of the sample probe instead of its mass plays a significant role in perturbing the plasma excitation conditions.

Limitation of Nitrogen Incorporation into the Hydrogenated Amorphous Carbon Nitride Films Formed from the Dissociative Excitation Reaction of CH3CN

High-resolution CN(B2Σ+–X2Σ+) and CH(A2Δ–X2Π) emission spectra were observed for the dissociative excitation reaction of CH3CN with the microwave-discharge flow of Ar for synthesizing hydrogenated amorphous carbon nitride (a-CNx:H) films. The simulation analysis of these spectra revealed that the relative number density of CH(A) to that of CN(B), NCH(A)/NCN(B), was strongly dependent on the pressure of Ar, PAr, in the range of PAr=0.1–0.8 Torr. The PAr-dependence of NCH(A)/NCN(B) showed a strongly negative correlation with that of the [N]/([N]+[C]) ratio obtained in our previous structural analysis of the films [Saitoh et al.: Jpn. J. Appl. Phys. 39 (2000) 1258]. This correlation was fully explained in terms of the consumption of the CN radical by the hydrogen-abstraction reaction from the film surface, preventing the incorporation of the nitrogen atoms into the a-CNx:H films.

Effect of Organic Phase on Dynamic and Collective Behavior of Surfactants at Liquid/Liquid Interfaces by a Time-Resolved Quasi-Elastic Laser-Scattering Method

A time-resolved quasi-elastic laser-scattering method was applied to monitor the dynamic and collective behavior of molecules of an anionic surfactant, sodium dodecyl sulfate (SDS), around the critical micelle concentration (cmc) at several water/chlorinated hydrocarbon interfaces. The time courses of the capillary wave frequencies after injection of the SDS solutions into the water phase were investigated. We found that when the injected concentration is above the cmc, the relative number density of SDS molecules decreases with an increase in the bulk aqueous concentration at all the examined interfaces. We also found that the relative number density of SDS molecules adsorbed onto the interface increases with a decrease in the permittivity of the organic phase. Our results suggested that the adsorption of SDS molecules was affected by the permittivity of the organic phase.

Diagnostics of inductively coupled chlorine plasmas: Measurement of Cl2+ and Cl+ densities

The absolute densities of positive ions (Cl2+ and Cl+) are obtained over a 2–20 mTorr pressure range and 5–1000 W input radio-frequency rf power range in a transformer-coupled Cl2 plasma. The relative number density of Cl2+ is measured by laser-induced fluorescence. These laser-induced fluorescence data are calibrated by Langmuir-probe measurements of total positive-ion density at low powers to yield absolute values for nCl2+ and are corrected for changes in rotational temperature with rf power. In turn, the nCl2+ data are used to determine the effective-mass correction for refined Langmuir-probe measurements of the total positive-ion density. The density of Cl+ is then the difference between the total positive-ion and Cl2+ densities. For all the pressures, Cl2+ is found to be the dominant ion in the capacitively coupled regime (input powers below 100 W), while Cl+ is the dominant ion at higher powers (>300 W) of the inductively coupled regime. Experimental results are compared to those from a simple global model. This work is a continuation of a study that provides a complete set of experimentally measured plasma parameters over a broad range of conditions in a chlorine plasma, produced with a commercial, inductively coupled rf source.

Resonance enhanced multiphoton ionization probing of H atoms and CH3 radicals in a hot filament chemical vapour deposition reactor

Resonance enhanced multiphoton ionization spectroscopy has been used to provide spatially resolved in situ measurements of H atom and CH3 radical relative number densities and the local gas temperature in a hot filament reactor used for diamond chemical vapour deposition (CVD). Parameters varied include the hydrocarbon (CH4 and C2H2), the hydrocarbon/H2 process gas mixing ratio, the total pressure and flow rate, and the temperatures of both the filament and substrate. H atom number densities are observed to be a maximum at the hot filament surface, to be independent of the H2 pressure, p(H2), in the range 5–55 Torr, and to drop monotonically with increasing radial distance from the filament, d. In contrast, the CH3 radical number density arising both in dilute CH4/H2 and C2H2/H2 gas mixtures is found to scale with the hydrocarbon input gas pressure, and to be rather constant for d<4 mm and to decline thereafter. These direct measurements serve to reinforce the consensus view that H atom production during diamond CVD in a hot filament reactor arises as a result of dissociative adsorption on the hot filament surface, whereas CH3 radical formation is dominated by gas phase reactions both when using CH4 and C2H2 as the carbon source gas. The formation mechanism of CH3 radicals in a hot filament reactor operating with C2H2/H2 gas mixtures is considered further.

Experimental investigation of saturated polarization spectroscopy for quantitative concentration measurements

Polarization-spectroscopy (PS) line shapes and signal intensities are measured in well-characterized hydrogen-air flames operated over a wide range of equivalence ratios. We use both low (perturbative) and high (saturating) pump beam intensities in the counterpropagating pump-probe geometry. The effects of saturation on the line-center signal intensity and the resonance linewidth are investigated. The PS signal intensities are used to measure relative OH number densities in a series of near-adiabatic flames at equivalence ratios (phi) ranging from 0.5 to 1.5. The use of saturating pump intensities minimizes the effect of pump beam absorption, providing more accurate number density measurements. When calibrated to the calculated OH concentration in the phi = 0.6 flame, the saturated PS number density measurements probing the P(1)(2) transition are in excellent agreement with OH absorption measurements, equilibrium calculations of OH number density, and previous saturated degenerate four-wave mixing OH number density measurements.

α-Sn and β-Sn precipitates in annealed epitaxialSi0.95Sn0.05

The structural properties of Sn precipitates in crystalline ${\mathrm{Si}}_{0.95}{\mathrm{Sn}}_{0.05}$ have been characterized by transmission electron microscopy and synchrotron x-ray diffraction. The Sn precipitates were produced by thermal annealing of epitaxial, single-crystalline ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}$ layers grown by low-temperature molecular-beam epitaxy on Si (001) and relaxed ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ substrates. Two different phases of solid Sn were identified in the annealed layers: the semiconductor phase, \ensuremath{\alpha}-Sn, and the metallic phase \ensuremath{\beta}-Sn. The precipitates were found to consist of either only \ensuremath{\beta}-Sn or to contain crystallites of both solid Sn phases. The orientations, the sizes and the relative number densities of the \ensuremath{\alpha}-Sn and \ensuremath{\beta}-Sn crystallites were investigated. In situ heating and cooling experiments were performed in the transmission electron microscope to study the melting and solidification characteristics of the \ensuremath{\alpha}-Sn and \ensuremath{\beta}-Sn crystallites. The presence of \ensuremath{\alpha}-Sn at temperatures far above the bulk \ensuremath{\alpha}\ensuremath{\leftrightarrow}\ensuremath{\beta} transition temperature is explained by interface and pressure effects; the latter is likely to be due to the difference in thermal expansion of the precipitates and the matrix.

Arenediazonium Salts: New Probes of the Interfacial Compositions of Association Colloids. 5.1−4 Determination of Hydration Numbers and Radial Distributions of Terminal Hydroxyl Groups in Mixed Nonionic CmEn Micelles by Chemical Trapping

An aggregate-bound long tail arenediazonium ion, 4-hexadecyl-2,6-dimethylbenzenediazonium ion, 16-ArN2+, was used as a chemical trapping reagent to estimate the hydration state and terminal hydroxyl, OH, group distributions within the interfacial region of sets of binary mixed nonionic micelles of oligooxyethylene alkyl monoether, CmEn, surfactants: C10E4/C12E6, C10E4/C16E8, C10E5/C16E8, C12E6/C16E8, and C10E5/C12E5. 16-ArN2+ decomposes spontaneously to generate an aryl cation that is trapped by water and by the terminal OH groups of the two nonionic surfactants to give phenol and alkyl aryl ethers as products. Quantitative analyses of product yields by HPLC were used to estimate the hydration numbers and relative number densities of the terminal OH groups of the two surfactants in the two inner layers of the interfacial region adjacent to the micellar core. The thickness of one layer is set equal to the length of one ethylene oxide unit. The radial distributions of terminal OH groups and ethylene oxide units in the mixed micelles are described by using a simple radial one-dimensional random walk model without adjustable parameters. The calculated ratios of terminal OH groups in the two inner layers are in excellent agreement with those obtained from experimental product yields. The calculated hydration numbers of the inner two layers ranged between 1.8 and 3.5, depending upon oligooxyethylene chain length, mixed micelle composition, and temperature. The average hydration number of the inner two layers is about 3 at 18 °C.

Enhanced cathodoluminescence from nano-indentations in MgO

Cathodoluminescence (CL) imaging in the wavelength range of 380 to 800 nm of nano-indents in MgO crystals made with a Berkovich diamond triangular pyramid has been carried out using a scanning electron microscope. It is shown that the centres of nano-indents of estimated residual depths in the range of about 570 to 325 nm do luminesce fairly strongly and the spatial resolution of the image appears to be better than 1 mum as revealed by the structure within the CL image. Centres of larger indents of residual depths greater than about 1300 nm do not show luminescence. It is suggested that most of the CL from the indentation centres is due to F and F+ colour centres produced by plastic flow, with emission peaks at 525 and 375 nm respectively. Furthermore, it is also suggested that the relative number density of F+ centres increases with increasing plastic strain, which in turn increases with increasing indentation size. Therefore, beyond some critical indentation size, most of the CL from the indentation centre will be due to the F+ centres and, as its luminescence is beyond the detection sensitivity of the CL system, the indentation centre shows an absence of CL.

Metastable chlorine ion kinetics in inductively coupled plasmas

Laser induced fluorescence has been used to measure the temperature, radial drift velocity, and relative number density of metastable chlorine ions, Cl+*, in inductively coupled discharges containing mixtures of BCl3, Cl2, N2, and Ar. In the center of the plasma, the Cl+* temperature varied between 2000 and 3000 K for most conditions investigated. The addition of BCl3 to a Cl2 plasma significantly decreased the density of metastable chlorine ions without changing their temperature. Addition of nitrogen to a BCl3 plasma resulted in a factor of 3 increase in the Cl+* density. Spatially resolved measurements of the Cl+* density are compared with Langmuir probe measurements of the spatially resolved electron density and ion saturation current. In general, the normalized Cl+* density was a factor of 2–3 lower than the electron density at the edge of the plasma. Spatially resolved measurements of the ion temperature indicated that the ion temperature increased to between 4500 and 5500 K at the edge of the discharge and increased approximately 600–1400 K moving from the rf source towards the lower electrode. Ion drift velocity in the radial direction was between 5×104 and 8×104 cm/s at the edge of the plasma. Measurements within one millimeter of the biased lower electrode surface showed the ion energy parallel to the biased electrode was independent of rf bias voltage while the density decreased with increased bias voltage. Implications of these measurements on the plasma chemistry and the energy transport in the plasma are discussed.