Showing papers in "Canadian Journal of Physics in 1985"

Scattering phenomena in strong radiation fields II

Abstract: By continuing previous work, several different scattering and absorption phenomena in the presence of a strong, coherent, electromagnetic background field are considered from a unifying point of view to elucidate the essential similarities of these processes, in particular, in the limit of low frequencies of the radiation field. The connection with corresponding classical processes is investigated. The limitations of the low-frequency approach are considered, and consequences are discussed with respect to the possible physical implications and conditions of experimental verification.

Orientational ordering in solid ortho-para H2 mixtures and analogy with a spin glass

Abstract: A review is presented of our understanding of the orientational ordering in solid hydrogen, where ortho-H2 molecules are subject to anisotropic electric quadrupole–quadrupole interactions This rev

Spectral-narrowing techniques for excimer laser oscillators

Abstract: Various techniques for use in spectral narrowing and tuning of excimer laser oscillators are described. Intracavity dispersive elements include Littrow grating, grazing-incidence grating, prisms, a...

Formation, structure, and crystallization of metastable quasi-crystalline Al-transition metal alloys prepared by rapid solidification

Abstract: Metastable Al86Cr14, Al86Mn14, and Al86Fe14 were prepared by rapid quenching from the melt at a rate of approximately 2 × 106 K/s. The X-ray measurements of all three alloys show similar non-Bravais structures. Broadened diffraction peaks for the Al–Fe alloy suggest a crystallite size of about 60 A. Thermal-analysis measurements show that all of the alloys transform into conventional crystal structures at approximately 670. The crystalline phases for the three alloys are Al11Cr2 + Al, Al6Mn + Al, and Al6Fe + Al. At approximately 800 K, Al–Fe undergoes the further transition Al6Fe → Al3Fe + Al.

Stable, tough, adherent Langmuir–Blodgett films: Preparation and structure of ordered, true monolayers of a phthalocyanine

Abstract: The first clear evidence for the preparation of true Langmuir–Blodgett (LB) monolayers and built-up multilayers of a lightly substituted phthalocyanine (Pc) is reported. It is shown that the LB films are well ordered and thermally and structurally stable, and that the structure is very similar to that of crystals of the unsubstituted Pc. The films are tough, adherent, and ultrathin (~17 A). Layers of this type may permit the first really practical electronic devices that contain (insulating) LB films.

Collision-induced absorption in nitrogen at low temperatures

Abstract: The collision-induced absorption (CIA) spectrum for nitrogen has been measured in the spectral region below 360 cm−1 at 126, 149, 179, and 212 K. The measurements have been obtained using Fourier transform infrared (FTIR) techniques, a far infrared (FIR) laser system operating at 84.2 and 15.1 cm−1, and microwave cavity techniques. The experimental line shapes have been compared with the theoretical predictions of Joslin, based on Mori theory, and of Joslin and Gray, based on information theory alone. The data have been used to determine the quadrupole moment employing various intermolecular potentials. One Lennard–Jones potential has resulted in a quadrupole moment of 1.51 B, the value that was used in generating the theoretical line shapes. These results, when combined with our forthcoming measurements on nitrogen mixed with methane and argon, may be helpful in determining the role of CIA in calculating the opacity of some planetary atmospheres.

Vacuum ultraviolet laser spectroscopy III: laboratory sources of coherent radiation tunable from 105 to 175 nm using Mg, Zn, and Hg vapors

Abstract: Nonlinear frequency mixing of laser radiation in Mg, Zn, and Hg vapors has produced coherent radiation, tunable over the range 175–104.5 nm in the vacuum ultraviolet. The resulting radiation is pul...

Diode laser measurements of N2-broadened line widths in the ν1 band of OCS

Abstract: A tunable diode laser spectrometer has been used to perform measurements of pressure-broadening coefficients for 20 vibration–rotation lines in the ν1 band of 16O12C32S perturbed by N2. Calculation...

H218O: The (030), (110), and (011) interacting states. Line positions and intensities for the 3ν2, ν1 + ν2, and ν2 + ν3 bands

Abstract: The spectrum of oxygen-18 enriched water vapor was recorded between 4400 and 6100 cm−1 with the aid of a Fourier transform spectrometer. Its analysis allowed the determination of 60 energy levels of the (030) vibrational state of H218O and improvements in the knowledge of the energy levels belonging to the (110) and (011) vibrational states of this molecule. A fit of 330 rotational levels of the (030), (110), and (011) states was performed using 54 effective constants and taking into account the Coriolis-type and Fermi-type interactions. Moreover, 853 line intensities belonging to the 3ν2, ν1 + ν2, and ν2 + ν3 bands were measured. The constants involved in the rotational expansion of the transformed transition moment operator corresponding to these bands were determined through a fit of these line intensities. The constants obtained were then used to compute the whole spectrum of the 3ν2, ν1 + ν2, and ν2 + ν3 bands of H218O. This spectrum should be of interest for atmospheric studies.

Observations of magnetic aspect effects in auroral radar backscatter

Abstract: A series of experiments have been performed to investigate VHF auroral backscatter. The equipment is basically a bistatic CW radar using narrow beam antennas. One objective has been to investigate ...

Surface electrodynamics: radiation fields, surface polaritons, and radiation remnants

Abstract: We review and discuss the radiation remnant electromagnetic field structures, comparing them in real and Fourier space with radiation fields and surface polaritons. The roles of radiation remnants ...

An evaluation of the noise performance of Fe, Co, Si, and B amorphous alloys in ring-core fluxgate magnetometers

Abstract: The work described herein has addressed two questions. Can amorphous metal alloys be used as core material for high-performance fluxgate magnetometers, and do these alloys provide a means for furth...

Dipole oscillator strength distributions and properties for SO2, CS2, and OCS'

Abstract: Dipole oscillator strength distributions have been constructed and used to evaluate integrated oscillator strengths, and a variety of dipole oscillator strength properties, for ground state SO2, CS2, and OCS. Each distribution has been constructed by using experimental and theoretical photoabsorption cross sections and by subjecting the resulting dipole oscillator strength data to constraints provided by the Thomas–Reiche–Kuhn sum rule and molar refractivity data for the relevant dilute gases. The discussion includes graphical presentations of how various spectral regions of the dipole oscillator strength distributions contribute to the more important dipole properties.

Amorphous silicon for photovoltaics produced by new microwave plasma-deposition techniques

Abstract: Amorphous hydrogenated silicon (a-Si :H) has been prepared by microwave (2.45 GHz) plasmas in Ar–SiH4 mixtures using two different deposition systems, a large-volume microwave plasma (LMP) apparatus, and a Surfatron system. Films of a-Si:H are characterized structurally (primarily by scanning electron microscopy), and by Fourier transform ir spectroscopy, as well as according to their electro-optical properties (dark and photoconductivity, I-V characteristics of Schottky-barrier diodes). Although microwave plasmas are thought to differ significantly from conventional lower frequency plasmas, results of the present characterizations show no evidence of this. Deposition in the Surfatron system gives rise to device-grade a-Si:H, as demonstrated by Schottky cell efficiences exceeding 3%. We have been unable to duplicate this in the LMP system in spite of nominally identical fabrication conditions; these films have gross columnar morphology, and they react with atmospheric constituents to give a-Si:(H, C, O) a...

Atomic momentum distributions in condensed matter

Abstract: The theory of the momentum distribution function for atoms in condensed matter is reviewed and compared with results of deep-inelastic neutron-scattering experiments. We discuss, in particular, the case of classical and almost-classical liquids, harmonic and anharmonic crystals, and solid and liquid 4He. Except for liquid 4He in the superfluid phase, the momentum distribution is always Gaussian to a good approximation. In some cases this Gaussian behavior is of dynamical origin while, in others, it is a consequence of the central-limit theorem. The observed momentum distribution in superfluid 4He provides direct experimental evidence for the macroscopic occupation of the zero-momentum state and the value of the condensate fraction can be obtained.

Rotational analysis of the B1Σ+ → X1Σ+ system of H35Cl

Abstract: The B1Σ+ → X1Σ+ system of HCl has been recorded photographically at high resolution in the range 155–250 nm. Rotational assignments of the measured line positions have been made for 39 bands of H35Cl with 0 ≤ ν′ ≤ 6and7 ≤ ν" ≤ 17. Least squares parameter estimates from individual bands have been merged to obtain a set of single-valued parameters that reproduces most of the experimental data to within the measurement precision. First-order Rydberg–Klein–Rees (RKR) turning points for the B and X states are reported from a second set of parameters derived from a truncated data set. The reliability of the ground-state RKR potential is discussed in terms of the first-order approximation and Born–Oppenheimer breakdown. Transitions have been observed to quasi-bound states of several high-lying vibrational levels of the ground state.

Orientational ordering of hydrogen molecules adsorbed on graphite

Abstract: The orientational behaviour of ortho-H2 and para-D2 molecules adsorbed on graphite has been studied by NMR from 0.3 to 12 K at coverages where the molecules form a registered lattice. We have observed that for 90% ortho-H2, the splitting of the high-temperature NMR doublet increases rapidly near 0.6 K and additional structure appears. We have identified this as a transition to the orientationally ordered pinwheel phase: one of the phases predicted by the mean field theory of Harris and Berlinsky. In contrast, the spectrum of 90% para-D2 evolves smoothly to a broad, weak structure as the temperature decreases, showing no evidence of ordering down to 0.3 K. This very different behaviour is unexpected, given that in the bulk solid both isotopes order at comparable temperatures. From the splitting of the high-temperature NMR doublets, we have deduced the crystal fields Vc and the effective quadrupole coupling constants Γ. For D2, Γ is somewhat less than the rigid lattice value, as expected in the presence of ...

An improved conventional Se–CdO photovoltaic cell

Abstract: Studies previously carried out to improve the Se–CdO photovoltaic cell have emphasized optimization of the deposition of the CdO by direct current (DC) reactive sputtering. Attention has now been turned towards improving the deposition, doping, and heat treatment of the polycrystalline selenium base. It has been found that heat treatment of the selenium film on its substrate of aluminum and bismuth in air or oxygen prior to CdO deposition results in an increase in the illuminated open-circuit voltage (Voc) of the cell. The effect increased with increase of annealing temperature from 150 to 195 °C and in going from dry to wet oxygen. No increase in Voc was found by heating in nitrogen. The effect could be due to the formation of higher stoichiometric and hence higher resistivity CdO at the Se–CdO junction, arising from the presence of extra oxygen on the selenium surface.

An examination of radio-auroral aspect sensitivity

Abstract: An attempt has been made to account for the experimental observations of scattering at angles away from perpendicularity to the earth's magnetic field (aspect sensitivity). First, it was necessary to develop a scattering model appropriate for the plasma waves generally assumed to be responsible for the scattering, consisting of an assembly of irregularities, each one a wave with a Gaussoidal envelope. Then, effects were included for off-perpendicular propagation of plasma waves, the perturbation of the magnetic field direction owing to the presence of auroral currents, and refraction of the radar wave in the E region. Even when possible effects from anomalous resistivity are included, many of the experimental observations require scattering models consisting of irregularities that are elongated along the direction of the earth's magnetic field by only a few plasma wavelengths (in some cases no more than one or two wavelengths). This is physically unreasonable and suggests that our understanding of auroral...

Emission spectrum of the HCCS radical

Abstract: Emission bands obtained in the region 3900–4500 A by a radio-frequency discharge in thiophene are studied; they are assigned to the HCCS transient species whose absorption spectrum was recently observed. A rotational analysis is carried out for the strong bands, which are assigned to a 2Πi–2Πi transition in which both states are close to Hund's case (a). Vibrational assignments are discussed.

Ab initio self-consistent-field molecular-orbital calculations on AlO4 centres in alpha-quartz. II.

Abstract: In this paper, the second of a series devoted to developing quantitative understanding of defect species in silicates, we report ab initio self-consistent-field molecular-orbital calculations done on 10-atom and 22-atom clusters designed to simulate cation-compensated aluminum impurity centres [AlO4/M+]qt in alpha-quartz; here qt = 0 or + 1, and M = H, Li, or Na. The geometric configurations of the small models of these centres were optimized. The calculated values for total energies, various static structural parameters, electron-spin densities, net atomic charges, and orbital energies are compared with experimental data, especially those derived from electron-paramagnetic-resonance studies of hole centres and give good agreement. For example, the models predict that the holes will occur at opposite types of oxygen ions adjacent to Al3+, respectively, for uncompensated centres [AlO4]0 and for the centres [AlO4/M+]+, as is, in fact, observed. Some calculations for interstitial cations M+ and atomic hydrog...

Metalorganic chemical-vapour-deposition growth and characterization of GaAs

Abstract: GaAs epitaxial layers have been grown on semi-insulating GaAs substrates using the technique of metalorganic chemical-vapour deposition. The organometallic compounds trimethylgallium and trimethylgallium–trimethylarsenic adduct were used as source reagents for gallium, whereas arsine and trimethylarsenic were used as sources for arsenic. Photoluminescence measurements at 8 K indicated that carbon was present in the layers as the dominant background acceptor, in most cases, and to a lesser extent copper (Cu) and manganese (Mn) acceptors were also present. Secondary-ion mass spectroscopy (SIMS) analysis confirmed the presence of these acceptors. Silicon was also identified by SIMS in most layers. The concentration of Cu and Mn was correlated with the starting substrate and with the deposition parameters (growth rate, deposition temperature). It was also found that their concentration in the epitaxial layers could be reduced by a careful heat-treatment and chemical etch prior to epitaxial growth.

Diffraction by an anisotropic impedance half plane

Abstract: We solve a new canonical problem: that of a plane wave obliquely incident on an anisotropic imperfectly conducting half plane. An exact closed-form solution is obtained by factorizing a 2 × 2 Wiener–Hopf matrix. The problem had earlier been considered insoluble, but yields to a combination of new and old matrix-factorization techniques.

Stoichiometry control mechanisms for bias-sputtered zinc-oxide thin films

Abstract: We have deposited transparent, conducting ZnO thin films of resistivity 3 × 10−3 Ω∙cm by the technique of DC planar-magnetron sputtering in a reactive Ar–O2 atmosphere, incorporating a reactive gas baffle and substrate RF discharge. The substrate discharge was found to increase the oxygen content of the growing film. Films at low values of the RF-induced substrate self-bias voltage were characterized by a brown colour, resistivities of about 4 × 10−2 Ω∙cm, and composition ZnO0.8. Films at higher bias voltages of −80 V were clear with resistivities of 3 × 10−3 Ω∙cm and a composition approaching stoichiometric ZnO. The oxidation of the films by the RF discharge was shown to occur through preferential resputtering and re-evaporation of excess zinc and by activation and ion-plating of oxygen species. Resputtering and re-evaporation rates were found to be enhanced above that expected for bulk Zn, owing to the loosely bound nature of surface adatoms during film growth.

Vibration-rotation spectra of nitrous acid, HONO

Abstract: High-resolution Fourier-transform infrared spectra have been recorded and analyzed for the ν4 ν5, and ν6 fundamental bands of trans-HONO, and for the ν4 fundamental of cis-HONO. The spectral resolu...

Positron-impact ionization of hydrogen atoms

Abstract: The ionization cross section of hydrogen atoms by positron impact has been calculated by using a distorted-wave polarized-orbital method. We have employed two models depending on the choice of the final-channel wave function, and the two sets of results differ dramatically. We have also found that below 100 eV the total positron-impact ionization cross section including positronium formation is appreciably larger than the corresponding results for electron-impact ionization.

A simplified optical model description of heavy ion fragmentation.

Abstract: The abrasion-ablation model of heavy-ion frgmentation by target nuclei of Townsend (1983) and the EVAP Monte Carlo computer program (Guthrie, 1970) for decay probabilities are applied to calculate the production cross sections of isotopes of S, P, Si, and Al for the fragmentation of 213-MeV/nucleon Ar-40 ions by C-12 targets and of Fe, Mn, Cr, V, Ti, Sc, and Ca for 1.88-GeV Fe-56 fragmentation by Pb-208 and by C-12. The results are presented in tables and graphs and shown to be in good agreement with the experimental data of Viyogi et al. (1979) and Westfall et al. (1979). The implications of these studies for the design of radiation shielding for long-term manned space missions are indicated.

Beam-foil lifetime measurements for Ga II and Ga III using a field-emission ion source

Abstract: A brief description is given of the modifications to a 2-MV Van de Graaff accelerator that are required to incorporate a field-emission ion source. The source is used to obtain a 1-μA beam of Ga+ i...

Hydrogenic atoms in one-plus-one dimensions

Abstract: We consider a Dirac particle in 1 + 1 dimensions interacting with an external Coulomb potential and prove that this potential produces no bound states at all.

Solar-grade silicon substrates by a powder-to-ribbon process

Abstract: A new technique for producing silicon ribbons for solar-cell substrates is described. The process begins with inexpensive, 98% pure silicon that is crushed and acid leached to raise the purity to 9...