bluuebunny/crossref_metadata_2025 huggingface dataset:
Modified Atomic Orbital Method. I. The Electronic Structure of the Ethylene Molecule
Authors: Ohno Kimio , Itoh Takashi
Published: April 2005

It is well known that the energy intervals separating ionic and covalent states, as given by the conventional ASMO method, are too large. In order to avoid this difficulty, a modification of the nonempirical atomic orbital method is proposed, and is applied to the ethylene molecule. The principal point of the modification is to use different atomic orbitals for covalent and ionic structures of the molecules in order to assess more correctly the energies of the ionic structures. The results of the calculation are fairly satisfactory in that they are as good as those of the semiempirical method by Moffitt. Some errors due to assumptions and approximations made in this calculation are discussed.
Low Resolution Electronic Spectrum of Crystalline para-Dimethoxybenzene with Application to Benzene
Authors: Albrecht Andreas C. , Simpson William T.
Published: April 2005

The spectrum of a thin (0.37μ) crystal of para-dimethoxybenzene for light incident on the 001 plane and polarized along the a and b crystallographic axes is given. From this, approximate spectra are determined for the two in-plane directions of the molecule. Absorption at 2900 A is polarized predominately in a direction perpendicular to the line joining the substituents while absorption at 2350 A is parallel to this line. The 2600 and 2000 A absorptions in benzene are related respectively to the 2900 and 2350 A bands in dimethoxybenzene and consequently the benzene bands are found to arise from transition to upper states of species B2u and B1u respectively. The relation to conventional orbital theory is briefly discussed.
Effect of Crystal Orientation on the Activation Energy for the Catalytic Decomposition of Formic Acid on Silver
Authors: Sosnovsky H. M. C.
Published: April 2005

Single crystalline sheets of silver have been used as catalysts for the decomposition of formic acid. The activation energy for the zero-order reaction was found to vary from 16.0 kcal/mole with a crystal face close to {111} to 30.4 kcal/mole with a crystal face close to {110}.
Rates of Isotopic Reactions between Methyl and Hydrogen
Authors: Polanyi J. C.
Published: April 2005

The absolute rate calculations made by Eyring and collaborators on the series of eight isotopic reactions H+H2, etc., fail to provide a real test of their method. Recent data on the eight reactions CH3+H2, +HD, +DH, +D2; CD3+H2, +HD, +DH, +D2, provide the first set of independent observations on a series of simple isotopic exchange reactions. Detailed calculation of the entropies of activation give values for the temperature independent factors Acalc400°K. The energy surface for the reactions is calculated according to the method of Gorin, Kauzmann, Walter, and Eyring in conformity with the H.L.S.P. treatment of methane. The surface obtained, E=f(w,r,s), has a single barrier indicating a classical activation energy of ∼13 kcal for the forward reaction, in adequate agreement with observed values. The surface described is, therefore, the ``best semiempirical surface''; the height of the barrier being regarded as a calibrated, not a predicted, quantity. The surface is accordingly made the basis for a calculation of the total zero-point energies of the eight reactions in their initial states and transition states. Substantial differences in activation energy are predicted. However, rate constants calculated on this basis show no correlation with observation, indicating failure of the method. Using a differently calibrated surface, designed to give the lowest barrier height compatible with a surface free of energy basins, a ``symmetrical'' surface is obtained for the present series of reactions. Zero-point energies derived from this surface lead to relative rate constants in fair agreement with the eight observed values. This correlation is more properly described as a correlation between Acalc and kobs, and is discussed on this basis.
Ring Formation and Molecular Weight Distributions in Branched-Chain Polymers. I
Authors: Harris Frank E.
Published: April 2005

The theory of molecular weight distributions in branched-chain polymers is extended to include possible intramolecular reaction leading to ring formation. The problem is more complicated than the noncyclic case in that, in addition to the more complex combinatory and algebraic considerations, it is necessary to consider geometric restrictions on the number and relative probability of many configurations. Two approximate models for describing the extent of ring closure are investigated. The first of these, in which it is assumed that spatial restrictions may be ignored, predicts far too many structures for large molecules with many rings, and as a result always predicts gel formation. In the second approximation it is assumed that geometric restrictions limit the number of rings so that the probability of ring closure is independent of molecular weight, but only depends upon the density of available ends. This model predicts that ring closures will shift the gel point to higher extents of reaction, producing at volumes larger than a ``critical volume,'' completely soluble polymers even at complete reaction. The dependence of the molecular weight distribution on the experimental variables is discussed in some detail.
Semiempirical Study of the H2Cl Transition Complex through the Use of Hydrogen Isotope Effects
Authors: Bigeleisen Jacob , Wolfsberg Max
Published: April 2005

Linear and triangular structures for the H2Cl transition complex have been analyzed in terms of normal vibration theory and by an evaluation of the experimental data on the effect of hydrogen isotope substitution on the rate of reaction of hydrogen molecules and chlorine atoms. The frequencies of the bending vibrations are probably sufficiently small that their contribution to the relative rates can be expressed in terms of a small quantum correction of the order of (hc/kT)2(ωH2—ω2D,T/24). The near classical behavior of the bending frequencies for both linear and triangular structures of the H2Cl complex serves to reduce the ratio of the frequency factors, AH/AD,T, in the Arrhenius equation from that expected from structural considerations alone. Quantitative agreement is found between the calculated and experimentally determined frequency factor ratios for the triangular complex. The ``symmetrical'' stretching frequencies, for both linear and triangular complexes respectively, have been evaluated from the relative rates of reaction of H2 and HT with chlorine atoms at 0°C and the known properties of the isotopic hydrogen molecules. This empirically evaluated parameter, together with thermodynamic data, and an estimate of the tunnel correction, suffice to calculate the relative rates of reaction of the isotopic hydrogen molecules with chlorine atoms as a function of temperature. Good agreement is found between the calculated rates for both linear and triangular structures and the available experimental data on HD, D2, and HT.
Self-Diffusion in Lead
Authors: Nachtrieb Norman H. , Handler George S.
Published: April 2005

The rate of self-diffusion in single crystals of high purity lead has been measured over the temperature range 174° to 322°C by means of RaD. The data are fitted by the least squares equation D=0.281 ×exp[—24 210/RT] cm2 sec-1.
Infrared Spectrum of Two-Stage Cool Flame of Diethyl Ether
Authors: Donovan Russell E. , Agnew William G.
Published: April 2005

An optical system has been made so that absorption and emission spectra from stages of a combustion process can be observed. Spectra from the two-stage cool flame of diethyl ether indicate that carbonyl compounds are formed as intermediates and final products are HCHO, CO2, H2O, CO, and C2H4. Also identified are CH3OH and CH4. Temperature calculations indicate that the infrared emission from this reaction is of thermal origin in contrast to the visible emission which is undoubtedly chemiluminescence. Calculated temperatures range from 700°K in the first cool flame to ∼1000° in the second-stage flame.
Low-Frequency Rotational Spectrum of HDO
Authors: Weisbaum Samuel , Beers Yardley , Herrmann Gabriel
Published: April 2005

In the region between 475 and 3500 Mc/sec one P-branch and five Q-branch lines in the spectrum of HDO have been completely measured and identified. These data have contributed materially to an evaluation of the structural constants of the molecule. From the data obtained by this and other microwave spectroscopy projects we have computed the principal moments of inertia, respectively, as having the values of 1.1982, 3.0862, and 4.3887 in units of gm cm2×10—40. In addition, the shape of the 32 → 33 line at 824.64 Mc/sec has been extensively studied. At low pressure the wings of the line have been shown to be wider than is consistent with the Lorentz line shape probably due to the presence of sattelite lines arising from the hyper-fine splitting of the energy levels by the quadrupole moment of the deuteron. The observed effects are consistent with a quadrupole coupling constant of 272±90 kc/sec with respect to an axis along the O–D bond.
Infrared Spectra of Intermediate Species in the Formation of Ammonium Azide from Hydrazoic Acid
Authors: Dows David A. , Pimentel George C. , Whittle Eric
Published: April 2005

Infrared spectroscopic studies have been made of the solid formed when the products of the glow-discharge decomposition of hydrazoic acid are condensed on a surface cooled to 90°K. Spectra were obtained at several temperatures as the solid was allowed to warm to 230°K. The solid shows absorptions attributed to HN3, NH4N3, and NH3, and to two intermediate species in the reaction. These intermediates are interpreted to be N2H2 and (NH)x, where x may be equal to 4. The presence of the imine radical, NH, in the solid at 90°K is inferred.
Adsorption of Strontium and of Barium on Tungsten
Authors: Moore George E. , Allison H. W.
Published: April 2005

Sr or Ba was deposited on W ribbon receivers by evaporation from source filaments in which a chemical reaction produced the metal at least 99.7% pure. The receiving surfaces could be cleaned at will by heating to high temperatures; repeated tests were thus possible. By thermionic measurements, adsorption and desorption were observed independently under nonequilibrium conditions. By using radioactive Sr isotopes, the deposit corresponding to any thermionic activation was measured. For each ribbon, thermionic activation was apparently a reversible function of the amount adsorbed.

Our experimental methods give information on kinetics, rather than equilibria. The adsorption mechanism more nearly resembles that proposed in Langmuir's later papers rather than that of his earlier theories but treatment of desorption by the theory of absolute reaction rates is considerably more satisfactory. This accounts for desorption kinetics over the experimental temperature range by only two disposable constants, the activation energy for desorption, (a.e.d.), and a repulsive energy of interaction between adatoms.

The work function [open phi] for a monolayer of Sr is ∼2.2 v and for Ba is ∼1.9 v. The thermionic activation is explained in terms of polarized adatoms, rather than by the usual assumption of partial ionization, which has no experimental justification for Ba or Sr films. The theory proposed gives a reasonable value for the polarizability of Sr and of Ba, which when substituted into the theory of Prosen, Sachs, and Teller predicts a heat of physical desorption agreeing well with the observed a.e.d. This also agrees with the heat of desorption (h.d.) determined by the usual method of applying the Clapeyron equation to kinetics of this kind. We therefore believe that this adsorption should be called ``physical,'' rather than ``chemical,'' although the mean a.e.d.'s are, for Sr 77.4, and for Ba 80.7 kcal/mole, considerably larger than for most examples of chemisorption.
Kinetics of the Isotope Exchange Reaction of Fluorine with Hydrogen Fluoride
Authors: Adams Richard M. , Bernstein Richard B. , Katz Joseph J.
Published: April 2005

The exchange of radioactive F18 between hydrogen fluoride and fluorine has been studied over a wide range of concentrations at three temperatures in the range 194° to 257°C. The exchange may be accounted for entirely by a heterogeneous catalysis mechanism involving competitive adsorption of the Langmuir-Hinshelwood type. Experiments have been performed indicating the important role of surface treatment on the kinetics of the exchange.
Screw Dislocations in Growth from the Melt
Authors: Sears G. W.
Published: April 2005

The screw dislocation growth mechanism is shown to be operative for the growth from the melt of certain faces of PbI2 at small supercoolings.
Magnetic Susceptibilities of Some Uranium (IV) Compounds
Authors: Hutchison Clyde A. , Herzfeld Charles M.
Published: April 2005

The magnetic susceptibilities of U(SO4)2·4.22H2O, U(C2O4)2·6H2O, UF4·NaF, (γ)UF4·2NaF, and UF4·3NaF have been measured in the temperature range from 14°K to 300°K. The results are presented in graphical form and their general form is discussed. The susceptibilities of all five compounds appear to approachfinite values at 0°K.
Analysis of the 6140 cm—1 Band of HDS
Authors: Crosby Glenn A. , Bair Edward J. , Cross Paul C.
Published: April 2005

Absorption observed in the region 6140 cm—1 was analyzed to yield the following constants: ν0 = 6140.0 cm—1, A″ = 9.743, B″ = 4.922, C″ = 3.232, A′ = 9.411, B′ = 5.019, C′ = 3.137 cm—1. The inertial defect of the ground state, Δ″ = IC″ — IA″ — IB″ = 0.101×10—40 g cm2, is approximately half that estimated for use in the interpretation of the microwave spectrum. This accounts for the major part of the discrepancy between the sets of moments of inertia of the molecule obtained by the two methods.
Contributions of Fluctuations and Anisotropy to Dielectric Polarization in Polar Substances
Authors: Harris Frank E.
Published: April 2005

The theory of dielectric polarization in polar substances is extended to include the effect of fluctuations in the dipole moments of the individual molecules. The effect of optical anisotropy is also taken into account. The resulting expression for the dielectric constant is identical in its leading terms to an earlier result of Harris and Alder, in which fluctuations are neglected, but differs significantly from an equation derived by Frohlich, which is here explicitly shown to involve an additional approximation. Application of the theory to gases is discussed briefly. It is pointed out that Onsager's formula for relating the permanent dipole moment of a molecule to its average moment in the dielectric involves an approximation which produces an incorrect limiting behavior at large volumes, so that it should not be applied to polar gases at normal pressures. Calculations are presented showing the various contributions to the dielectric polarization of gaseous ammonia. The fluctuation term contributes of the order of 20% of the term expressing the correlation in orientation of the average dipole moments. The theory is also applied to liquid water, using Pople's bendable hydrogen bonded model for that substance. In water the fluctuation term is but 6% of the direct correlation term, and opposite in sign. The results are discussed briefly.
Energy Calculations of Multiple Hydrogen-Atom Systems by VB and MO Methods
Authors: Barker Roland S. , Snow Richard L. , Eyring Henry
Published: April 2005

The equivalence of complete valence bond (VB) and of total configuration interaction molecular orbital (CIMO) methods has often been discussed. The two methods give identical expressions for H2. Treatment of H2 by the method of Coulson and Fischer also gives the same result. An extension of this method of semilocalized orbitals to the H3+ and H3 systems is attempted and found to be unsatisfactory. This indicates that a single configuration treatment, however general the molecular orbitals may be, is a poorer approximation than either the extended VB or CIMO treatments.

R. Taylor's exact integral (LCI) molecular orbital treatment for linear H4 is compared with the exact integral covalent bond (HL) method. A single structure of the latter method gave a ground-state energy of —57.02 ev while the two covalent structure treatment gave —58.59 ev. An energy of —55.64 ev is reported by Taylor using the best single MO configuration while he found an energy of only —56.40 ev using six of twelve possible MO ground-state configurations. It appears in view of the equivalence of the refined forms of the two treatments that the omitted higher energy configurations contribute more strongly to the ground-state energy than the lower energy ones. This indicates that low energy is not a good criterion for inclusion of configurations in a limited configuration interaction treatment. Recent work by A. Pullman on butadiene supports this conclusion.
Complete π-Electron Treatment of Allyl Radical and Allyl Ion
Authors: Lefkovits H. C. , Fain Janice , Matsen F. A.
Published: April 2005

The wave functions for the allyl radical and ion are linear combinations of all independent antisymmetrized products of π-electron wave functions. The ground-state energy of the radical is 3W2p—28.963 ev and of the ion 2W2p—30.471 ev. Setting —W2p equal to the ionization energy of methyl, the ionization energy of allyl is calculated to be 8.44 ev, compared to an experimental value of 8.16 ev. The resonance energy of the ion is calculated to be ∼1.50 ev greater than that of the radical. An experimental comparison based on methyl and neglecting some compression energy is ∼1.70 ev.
Thermal Decomposition of Nitric Oxide
Authors: Kaufman Frederick , Kelso John R.
Published: April 2005

The decomposition of pure nitric oxide and of mixtures with nitrogen or helium was studied at T = 1170 to 1530°K in quartz vessels. Above about T = 1400°K, the reaction is homogeneous and cleanly second order in NO throughout the course of decomposition. A change in the surface to volume ratio leaves the rate unchanged as does the addition of a fourfold excess of nitrogen or helium. Above 1400°K, the activation energy is constant at 63.8±0.6 kcal. The effect of added oxygen was investigated and a mechanism is discussed which reconciles much of the available data.
Combustion Investigation in the Hypersonic Shock Tunnel Driver Section
Authors: Nagamatsu H. T. , Martin E. D.
Published: April 2005

An investigation was made of the combustion of stoichiometric mixtures of hydrogen and oxygen with a varying percent of helium in the constant volume driver section for a hypersonic shock tunnel. The pressure was measured as a function of time for a number of initial pressures, mixture ratios, and multiple sparks for ignition. The maximum pressures observed were close to that expected for smooth burning. When detonation was encountered, the ratio of the peak pressure to the initial pressure was about 50.
Some Characteristics of a Magnetically Focused Electron Beam
Authors: Brewer George R.
Published: April 2005

The detailed behavior of a solid cylindrical electron beam focused by a uniform magnetic field (Brillouin flow) has been studied experimentally. These studies include the influence of the optics of the electron gun on the beam-focusing characteristics, the effects of transverse ``thermal'' velocities, the change in the internal beam dynamics with increasing values of magnetic focusing field, etc. A simple model of the beam is used to explain certain of the observed characteristics. It is found that an optically good electron gun will produce a focused beam which closely resembles the theoretical Brillouin-flow model. A brief analysis of the electron motion in a magnetically focused beam is given in the Appendix.
Microplasma Fluctuations in Silicon
Authors: Champlin Keith S.
Published: April 2005

The electrical properties of a fluctuating bistable microplasma are specified by three parameters which, in general, are functions of voltage. For an ideal low impedance connection, these parameters are independent of time and thus yield simple forms for the pulse rate, average current, differential conductance, and noise spectral density. With a high impedance circuit the phenomenon is more complex, and only an approximate analysis is offered. Measurements on alloyed junctions with breakdown voltages between 7.9 and 10.5 v show that single breakdown regions sometimes occur at low currents. Multistable conduction as well as the simpler bistable conduction is observed. The multistable conduction is characterized by fluctuations among higher current levels which occur at a rate 102–105 times faster than the ``on-off'' fluctuations. Excellent agreement between measured and calculated current spectral density at low impedance is found. This justifies the assumptions of random events independent of previous ``on'' or ``off'' time and suggests that noise spectrum measurements at low impedance be used as a tool for accurately determining the microplasma parameters. With a high impedance connection, the process is not Markoffian; thus the noise is not simply related to the noise at low impedance. The event which initiates breakdown is found to be field dependent suggesting that field emitted carriers are involved. It is shown that the results do not fully agree with those predicted by Rose's model of a microplasma.
Polarization Reversal by Sideways Expansion of Domains in Ferroelectric Triglycine Sulfate
Authors: Chynoweth A. G. , Abel J. L.
Published: April 2005

At fields in the range 30–35 v cm−1, polarization reversal in liquid-electroded triglycine sulfate crystals is accomplished by the formation and sideways expansion of a relatively few domains. While small, the domains are elliptical or lenticular in shape, but as they grow, they tend to become irregular before amalgamating with each other. In some cases, at least, the elliptical domains have approximately equilibrium shapes as determined by the wall energy. Some general results are given concerning the sites at which the domains form and the way in which domains contract when the field is reversed.
Effect of Neutron Irradiation on Thermally and Mechanically Induced Nonequilibrium States in AuCu
Authors: McCollum R. L. , Allen G.
Published: April 2005

Studies have been made of the effect of neutron irradiation on the resistivity and magnetoresistivity of the alloy AuCu when subjected to various pre-irradiation thermal and mechanical treatments. The specimens were exposed to estimated fast neutron fluxes up to 7.3×1018 neutrons/cm2 in the Brookhaven pile. In the case of thermally disordered specimens, the effect of the irradiation was to decrease the resistivity in completely disordered states and to increase the resistivity in completely ordered states; viz., there was some tendency for specimens to reach intermediate degrees of order. The effect on mechanically disordered specimens was to increase the resistivity in all cases. The irradiation effected a larger percentage change in in the coefficient of magnetoresistivity than in the resistivity.
Diffusion of Copper in Cadmium Sulfide Crystals
Authors: Clarke Raymond L.
Published: April 2005

Copper was diffused in cadmium sulfide single crystals to determine diffusion coefficients using the radio-active tracer sectioning technique. Over the temperature range of 450°–750°C, the relationship between temperature and diffusion coefficient was found to be D=1.5×10−3e−17600/RT square centimeters per second for diffusion perpendicular to the C axis. For diffusion parallel to the C axis, the frequency factor and activation energy were found to be within the experimental accuracy of the corresponding values for perpendicular diffusion. There appears to be no appreciable diffusion anisotropy. Observed surface diffusion was a complicating factor in obtaining data on volume diffusion.
X-Ray Method for the Differentiation of {111} Surfaces in AIIIBV Semiconducting Compounds
Authors: Warekois E. P. , Metzger P. H.
Published: April 2005

Most of the AIIIBV semiconducting compounds have the zincblende crystal structure. This structure is noncentrosymmetric and as a consequence the modulii of F(hkl) and F(h̄k̄l̄), the geometrical structure factors, have different magnitudes. This difference results in a variation in the integrated intensities of certain x-ray reflection from opposite sides of samples taken from crystals with the zincblende structure. X-ray measurements of a series of {111} reflections from opposite sides of an InAs single crystal have been made and related to the etching characteristics of these surfaces.
Effect of Thermal Motion on the X-Ray Reflectivity of Quartz
Authors: Berreman D. W. , Chang TeTse
Published: April 2005

Two characteristic temperatures for quartz were determined which, when substituted into the Debye-Waller formula and then used to compute the ratios of temperature corrected integrated reflection coefficients of various pairs of sets of Bragg planes, gave results in best agreement with experimentally determined ratios. These temperatures are 508±16°K in the direction of the trigonal axis and 452±15°K in any perpendicular direction. Corresponding values obtained from an approximate formula relating characteristic temperatures with elastic constants were 448° and 398°K, respectively. The fairly good agreement between the characteristic temperatures obtained by the two methods seems to support the conjecture that the modification of the Debye theory used gives a fairly good approximate description of the effect of thermal motion on the x-ray reflectivity of quartz. Calculations based upon the experimentally determined characteristic temperatures indicate that when Bragg spacings are less than about 0.7 A, the reflectivity of quartz at room temperature is reduced to less than half the value that would be obtained if the atoms were rigidly fixed.
Paraxial Formulation of the Equations of Electrostatic Space-Charge Flow
Authors: Kirstein P. T.
Published: April 2005

The equations of electrostatic irrotational space-charge flow are set up in a paraxial manner. Given an arbitrary trajectory, and the potential distribution along that trajectory, the variation of such quantities as potential and beam convergence in the vicinity of the specified trajectory are investigated. A detailed analysis is carried out for beams from a space-charge-limited cathode in the form of a cone. The agreement between the paraxial theory and the exact theory for particular beams is investigated. Numerical results are presented for beams from a conical cathode which predict beams with a microperveance of about 15 and a very large area convergence. It is felt that by use of this method much higher perveances and beam convergences could be obtained for hollow and sheet beams than have heretofore been possible.
Method for Calculating Simultaneous Resonance Conditions in a Three-Level Ruby Maser
Authors: Garstens Martin A.
Published: April 2005

In operating a three-level maser one wishes to know the external magnetic field and crystal orientation necessary to match a given pair of frequencies. In the case of Cr+++ a fourth-degree secular equation determines four energy levels for each value of external field H and crystal orientation θ. Determination of the latter two variables, given two desired frequencies of operation, ordinarily involves either the solution of a tremendous number of fourth-degree equations and extrapolation towards the required solution, or determination of the matching conditions by experimental methods. In the following a method is described, allowing direct calculation of H and θ for a three-level ruby maser.
Properties of Semi-Insulating GaAs
Authors: Gooch C. H. , Hilsum C. , Holeman B. R.
Published: April 2005

Most samples of GaAs show properties similar to those of germanium and silicon, but it is possible to prepare GaAs with a resistivity at room temperature greater than 106 ohm-cm, and the electrical properties are then more like those of the wide band gap II–VI compounds, such as CdS. This form of material, known as semi-insulating GaAs, previously has not been studied thoroughly, partly because homogeneous samples were not available.

Measurements have now been made on semi-insulating GaAs, and results are reported for carrier concentration and mobility as a function of temperature. The interpretation of the results is sometimes complicated because even at room temperature the activation energy is about half of the intrinsic activation energy, and the carrier concentration can be close to the intrinsic concentration.

The dominant lattice scattering mechanism in GaAs is believed to be polar scattering, but even in the purest samples of semiconducting GaAs made thus far, impurity scattering is observed at room temperature. In a highly compensated material like semi-insulating GaAs, neither the Brooks-Herring nor the Conwell-Weisskopf theory of impurity scattering is likely to be valid. An initial study of carrier scattering has been made using measurements of transverse magnetoresistance and the field dependence of Hall coefficient. Some values for carrier lifetime are also reported.
Some Properties of p-n Junctions in GaP
Authors: Grimmeiss H. G. , Rabenau A. , Koelmans H.
Published: April 2005

A new method in making single crystals of GaP and the preparation of diodes is described. The p-n luminescence and photoluminescence of undoped and Zn-doped GaP are investigated and the light output of the p-n luminescence as a function of temperature and excitation density is discussed. The spectral sensitivity of the p-n photovoltaic effect is recorded.
Free Carrier Cyclotron Resonance, Faraday Rotation, and Voigt Double Refraction in Compound Semiconductors
Authors: Palik E. D. , Teitler S. , Wallis R. F.
Published: April 2005

Measurements of cyclotron resonance absorption have been made in the far infrared spectral region from 25−150 μ on several III–V compounds at room and liquid-nitrogen temperatures using steady magnetic fields as high as 75 kgauss. For n-type InSb, InAs, InP, and GaAs, the data yield information concerning the conduction electron effective mass at the bottom of the band and its variation with magnetic field. Experiments have also been carried out on p-type InSb and corresponding information has been obtained for light holes. The dependence of the effective masses on both temperature and magnetic field can be satisfactorily interpreted in terms of Kane's theory for the band structure of these materials.

Measurements of Faraday rotation and Voigt double refraction have been made in the spectral region between 15 and 25 μ on a number of compound semiconductors at liquid-nitrogen temperatures. Either experiment gives the effective mass of the free carriers if their concentration is known. If both experiments can be performed, the results can be combined to give both the effective mass and carrier concentration directly without recourse to electrical measurements.
Electrical Properties of Lead Telluride
Authors: Kanai Yasuo , Nii Riro , Watanabe Naozo
Published: April 2005

Samples of n-type PbTe crystals with different electron concentrations (n=2×1017∼5×1019/cc) were prepared by impurity doping or by heating in the vapor of lead. The electrical properties of these crystals were independent of the kind of impurities and depended only on the electron concentration. The electron mobilities of our samples were proportional to n−⅓ at 77°K, and to n−4/3 at 4.2°K. As the conduction electrons in our samples are degenerate at these temperatures, the experimental results mentioned above suggests that the conduction electrons in PbTe crystals are scattered mainly by acoustical mode at 77°K and by neutral imperfections at 4.2°K.

Since the electron mobility in PbTe becomes very large at 4.2°K (e.g., 1∼4×106 cm2/v-sec), this material is quite suitable for the experimental studies of the quantum transport phenomena. To investigate such phenomena, the Hall and magnetoresistive effects of n-type PbTe crystals were measured at 4.2°K in a pulsed magnetic field up to 170 kgauss. In the specimens with relatively low electron concentrations (e.g., n≃3×1017/cc), the magnetoresistive effect had a single minimum at about 77 kgauss in a transverse magnetic field, and at about 55 kgauss in a longitudinal field. This minimum should correspond to the situation where the Landau level with l = 1 coincides with the Fermi level in the PbTe crystals.
Band Structure and Transport Properties of Some 3–5 Compounds
Authors: Ehrenreich H.
Published: April 2005

The experimental information relevant to the band structure of the compounds InSb, InAs, GaSb, GaAs, GaP, AlSb and some of their alloys is synthesized and interpreted in terms of a consistent theoretical picture which exploits the close relationship linking the band structures of the group 4 and 3–5 semiconductors. It is shown that the momentum matrix element determining the conduction band masses in those compounds whose edge is of symmetry type Γ1, is nearly constant. Simple theoretical expressions, agreeing well with experiment, are derived for the corresponding effective masses and valence band spin-orbit splittings, following Kane's theory for InSb. The dominant scattering mechanisms determining the transport properties are reviewed briefly. Arguments are presented which show deformation potential scattering to be unimportant relative to polar optical mode scattering. A heuristic treatment indicates that the relaxation time approximation can be applied reasonably to polar scattering for temperatures T>ℏωl/K, where ωl is the longitudinal optical frequency. Multiband transport effects are discussed with special reference to the Nernst effect in GaAs and the electron mobility in GaSb. An explanation of the high-temperature behavior of the Nernst coefficient in GaAs in terms of polar and intervalley scattering is proposed. The mobility in GaSb remains unexplained.
Halides, Oxides, and Sulfides of the Transition Metals
Authors: Morin F. J.
Published: April 2005

The electrical conductivity and optical absorption data for many compounds of the transition metals suggest that there is a trend from ionic insulators, to metals, to covalent semiconductors as the overlap of atomic orbitals is increased. In this paper it is shown that a correlation exists between the electrical behavior of insulators and metals and the magnitude of the overlap integrals S(dεdε) and S(dεpπ).
Polaron Band Model and Its Application to Ce–S Semiconductors
Authors: Appel J. , Kurnick S. W.
Published: April 2005

The low-lying eigenstates of the ``large polarons'' have been calculated by several authors for arbitrary strengths of the electron lattice interaction α. However, if α > 1 the large polaron picture becomes questionable, since for finite temperatures the polaron eigenstates may be strongly affected by the presence of thermal phonons; then a new approach to the polaron theory is applicable which takes into account the atomicity of the lattice and the presence of thermal phonons and which results in the ``small polaron'' picture. The eigenstates of small polarons depend on T. If the eigenstates form a band, the bandwidth is a function of T, and the eigenstates near the band extremum can be expressed in terms of a T-dependent effective mass. From measurements of the high- and low-frequency dielectric constants, of the temperature dependence of the Seebeck coefficient, and of the electronic mobility, it appears that the eigenstates of the electronic charge carriers in Ce–S semiconductors may be adequately described by the small polaron picture.
Investigations on Silicon Carbide
Authors: van Daal H. J. , Greebe C. A. A. J. , Knippenberg W. F. , Vink H. J.
Published: April 2005

Measurements of Hall effect and resistivity up to 1300°K on p-type hexagonal SiC showed an acceptor level for aluminium of 0.27 ev at zero donor concentration and a not yet identified acceptor level of 0.39 ev. The spin multiplicity of this unknown center appears to be four times smaller than that of the aluminium center, so that we may conclude that this unknown center in non-ionized state has paired electrons. Taking a temperature dependence of the level depths proportional to that of the bandgap, the density-of-states effective mass of the holes amounts to 0.59 m0. The Hall mobility shows at high temperatures the same temperature dependence as that ascribed to scattering of holes by optical phonons. Assuming that optical phonons really come into effect, the behavior of the Hall mobility in the temperature range from 1300° to 300°K can be explained taking also into account the effect of scattering by acoustical phonons and charged impurities. By a study of I–V characteristics of grown junctions in αSiC and also by applying Roosbroeck-Shockley's theory to the spectral distribution of the p-n luminescence under forward bias, inhomogeneities were found over the junction area. By means of pyrolysis of gaseous compounds of Si and C pure crystals (4×2×2 mm3) of ``cubic'' βSiC were obtained. With the aid of polarized light the existence of a skeleton of a hexagonal twinning system was found in these crystals, the cubic SiC filling up the pores of this skeleton structure.
Edge Emission in Zinc Selenide Single Crystals
Authors: Reynolds D. C. , Pedrotti L. S. , Larson O. W.
Published: April 2005

Edge emission in single crystals of ZnSe subjected to ultraviolet radiation at low temperatures has been examined in the temperature interval from 4.2° to 77°K. Two distinct edge emission spectra have been found indicating that two different types of single crystals exist. For type I crystals the edge emission spectrum at 4.2°K contains 10 lines located between 4400 A and 4800 A; at 77°K the emission spectrum contains two lines. For type II crystals the edge emission spectrum at 4.2°K contains 14 lines located between 4400 A and 4900 A; at 77°K the emission spectrum contains three lines, one of which is located at the fundamental absorption edge of the crystal. Both crystal emissions show evidence of phonon interaction with the ZnSe lattice and both emissions undergo significant reductions in intensity as the crystal temperature increases from 4.2° to 77°K.
Exciton Structure and Zeeman Effects in Cadmium Selenide
Authors: Dimmock J. O. , Wheeler R. G.
Published: April 2005

A semi-empirical theory of exciton structure in the presence of an external magnetic field developed from Dresselhaus' effective mass approximation [G. Dresselhaus, J. Phys. Chem. Solids 1, 15 (1956)] has been used to obtain the band parameters at K=0, 0, 0 of CdSe from observed exciton spectra. The theory has been approximated to the case of uniaxial crystals of small anisotropy by the assumption that the effective mass tensor for both the hole and the electron is diagonal, the remaininganisotropy is cylindrical and small and that the anisotropy in the dielectric constant is also cylindrical and small. The exciton spectra of CdSe has been observed and identified by optical reflection, absorption, and Zeeman structure at 1.8°K. The reflection and absorption spectra indicate the presence of two nonoverlapping exciton series. From observed optical selection rules, the conduction band is identified as having Γ7 symmetry. The two series correspond to the Γ9−Γ7 valence band crystal field splitting of approximately 200 cm−1. A third series, at higher energies, has been observed in absorption corresponding to a Γ7 valence band state split by spin-orbit effects from the other two states by approximately 3490 cm−1. The n1 = 1, 2, 3, and 4 states of the first, Γ9, series, the n2 = 1 and 2 states of the second (first Γ7) series, and the n3 = 1 state of the third (second Γ7) series have been observed and identified in absorption. The series limit of the first series, corresponding to the band gap, has been measured to be 14 850 cm−1. The band parameters have been obtained by comparing theory and experiment. The effect of the finite photon momentum has been observed through changes in the Zeeman structure of the n1 = 2, P states upon 180° rotation of the magnetic field in the plane perpendicular to the crystal C axis.
Excitons and the Absorption Edge of ZnO
Authors: Dietz R. E. , Hopfield J. J. , Thomas D. G.
Published: April 2005

The absorption coefficient for polarized light at photon energies less than that of the lowest lying direct exciton was measured for single crystals of ZnO at temperatures ranging from 20° to 200°K. Analysis of the results shows that the absorption is in agreement with that calculated for a process involving the simultaneous creation of an exciton and absorption of a phonon, both particles having a small wave vector. This agreement provides evidence that the absolute minimum of the conduction band cannot lie lower than the lowest lying direct exciton level, and, therefore, that the absolute minimum probably occurs at the center of the Brillouin zone. Values for the hole and electron masses were estimated from the analysis.
Double Phonon Processes in Cadmium Sulfide
Authors: Balkanski Minko , Besson Jean Michel
Published: April 2005

The bands of infrared absorption in hexagonal cadmium sulfide have been studied over a wide range of temperatures and are assigned to double-phonon processes. An analysis of these absorption peaks on the basis of four frequencies is proposed. The temperature-dependence of the location and intensity of these bands give indications upon the anharmonic parameter and Grüneisen constant of the crystal. Anharmonic forces are shown to be responsible for the coupling between normal vibrational modes.
Origins of Characteristic Bands in the Infrared Spectra of Isotactic Polystyrene and Isotactic Poly (Ring-d5 Styrene)
Authors: Onishi T. , Krimm S.
Published: April 2005

The origins of characteristic bands in the infrared spectrum of isotactic polystyrene have been studied with the aid of the spectrum of isotactic poly (ring-d5 styrene). It is found that these bands can be classified into three types according to their experimental behavior upon crystallization of the specimen. Assignments show that the bands in any one group are associated with a specific kind of normal vibration, either of the chain or of the benzene ring. Analysis of one of these band types indicates that rotational disordering of the benzene rings may occur, and that crystallization of the polymer is probably correlated with the growth of regions which maintain statistical variability at the local chain level.
Molecular Motion in Disordered Regions of Solid Polyethylene
Authors: Slichter W. P.
Published: April 2005

Proton magnetic resonance studies have been made to compare the molecular motions ascribable to the disordered regions of solution-grown and melt-grown specimens of solid polyethylene. Studies have been made of both the spin-lattice and spin-spin relaxations. Restricted motion attributable to defect regions develops in solution-grown crystals as the temperature is raised, but the number of protons in motion changes reversibly with heating and cooling, provided the maximum temperature is below ∼100°C. With higher temperatures the motion is greater in abundance and broader in frequency distribution. The increase is permanent despite annealing. Segmental motion attributed to molecules within the crystal is seen in solution-grown crystals in the interval 50–100°C, but occurs to a much smaller degree in melt-grown and heat-treated samples. A model for the observed behavior is proposed.
The Swelling of Unfilled and Highly Filled Polymers
Authors: Bills K. W. , Salcedo F. S.
Published: April 2005

The swelling of elastomers in solvents is a useful method for determining the effective crosslinking of the polymeric structure. However, it is now shown that this method may be applied satisfactorily to highly filled polymers. A unique method has been devised for the accurate measurement of the swelling ratio of the gel phase of the filled polymers. The method is based on the observation that the binder-filler bond, for most filler particles, releases on swelling. The binder around the particle swells, leaving a hollow pocket which becomes filled with solvent. Corrections for this ``waste'' solvent lead to the equations from which the swelling of the polymer can be calculated. Experimental verification is given for several filled systems.
New Derivation of the Vacuum Breakdown Equation Relating Breakdown Voltage and Electrode Separation
Authors: Maitland A.
Published: April 2005

An analysis of the published measurements of breakdown voltage for various gap lengths for uniform and approximately uniform fields shows that the results may be represented by the breakdown equation V = Cxα and that the values of α lie in the range 0.1 to 1.1 with a mode of 0.7. A theory is developed which leads both to a breakdown equation of the same form and to a general expression to account for the range of values of α. This expression is confirmed for gaps up to 0.075 cm by direct experiment. The development is based on the postulate that an electron beam is emitted from the cathode, diverges, and bombards the anode to cause breakdown when a critical power flux is reached. The factor C is shown to include the critical power flux and to be related to both field and electrode separation. In support of the theory, the radii of craters produced on the anode are measured and shown to be related to the radius of an electron beam at the anode. Calculation shows the current carried by the beam to be of the order of 10−4 amp. Values of the critical power flux obtained from the equation V = Cxα and from anode crater data, respectively, agree within a factor of 1.5 and are of the order of 108 w cm−2. To explain the observed phenomena, a multiple electron beam system is proposed.
Physical Behavior of Photographic Grains
Authors: Sprague G.
Published: April 2005

A quantitative treatment of the photographic process is carried out, modeled on the Gurney Mott theory. This is extended by taking account of the distribution of photolytic silver during and after the exposure. Applications of the theory are made to some simple types of sensitizing. The most important physical parameter of a photographic grain seems to be the number of electron traps.
Determination of Field Strength for Field Evaporation and Ionization in the Field Ion Microscope
Authors: Müller Erwin W. , Young Russell D.
Published: April 2005

The field strength required for field evaporation of tungsten and for best image conditions in the field ion microscope is measured by comparison with field electron emission of the same emitter. The evaporation field is independent of emitter radius except for radii below 150 A where the influence of free surface energy becomes noticeable. The field for the best conditions of a helium ion image of a typical emitter of 1000 A radius is 440 Mv/cm. This field increases gradually with decreasing tip radius, so that the ratio of evaporation field to best image field for tungsten decreases from 1.27 at 1000 A radius to 1.0 at about 40 A radius. The radius dependence of this ratio can be calculated by assuming that the time a hopping atom spends in the critical ionization zone is a constant fraction of the ionization time. Practical implications are that large tip radii are preferable for easily evaporating emitter materials, and small radii may be useful when field evaporation is to be studied under best image conditions.
Effects of Transition Metal Solutes on the Electrical Resistivity of Copper and Gold Between 4° and 1200°K
Authors: Domenicali C. A. , Christenson E. L.
Published: April 2005

We have determined the solute contribution ρi(T,c) of the solutes Cr, Mn, Fe, Co, and Ni in copper and of the solutes Mn, Fe, and Co in gold over the temperature range 4° to 1200°K and over a wide range of solute concentrations. The parameter ρi(T,c) for a given solute is defined here as the difference ρi(T,c) =ρalloy(T,c)—ρsolvent(T). The temperature dependence of ρi is quite complicated for several of the solutes, in particular, Fe and Co. For example, in an alloy containing 0.05 at.%Fe in copper this quantity ρFe exhibits a minimum at 25°K and a maximum at 65°K. Alloys of Fe in gold exhibit a broad maximum in ρFe at temperatures between 70° and 200°K, depending upon the iron concentration. In all the alloys investigated, except for Ni in copper, ρi decreases with increasing temperature in the region of high temperatures (above about 500°K).