bluuebunny/crossref_metadata_2025 huggingface dataset:
Focused ion beams in microfabrication
Authors: Seliger R. L. , Fleming W. P.
Published: February 2004

Microfabrication techniques are being investigated in which a focused high-energy ion beam bombards a surface to create high-resolution patterns of implantation doping, damage in crystal structures, or other chemical change such as molecular bond breaking. The objective is to demonstrate unique microfabrication techniques such as maskless implantation doping and the formation of self-aligned structures. Preliminary results are presented of doped regions written in silicon by a focused boron beam. Electrical measurements on heavily doped contact regions and on a lightly doped resistive region are in good agreement with what would be expected from conventional ion implantation employing masks. The exposure of electron beam resist by a focused beam of 60-keV helium ions is also reported. The resist sensitivity is ∼100 times greater for these ions than for electrons. The focused ion beam used in these studies was generated in a focusing arm which includes apertures, deflection plates, and an einzel lens that has been added to an existing ion implantation system. The focusing system performance is discussed and compared with the properties of a published electrostatic lens. Experimental results indicate a minimum beam spot diameter of ∼3.5 μm with a 150-μm-diam object aperture and a beam energy of ∼60 keV. Aperture diameters are calculated to produce a focused spot with submicrometer diameter.
Reply to ``On the calculation of surface energies from phonon frequencies''
Authors: Caglioti G. , Rizzi G. , Bilello J. C.
Published: February 2004

In the preceding communication, Purushothaman and Burton have extended the earlier work of the present authors (CRB) to covalent, ionic, and rare gas solids. The physical basis of the original predictions for metals are briefly reviewed. The validity of using a straightforward application of Eq. (6) of CRB without examination of the normal modes appropriate to ``fracture'' is also discussed. Finally, it is shown how the original first-order theory of CRB can be extended to obtain more realistic results for cases where second-nearest-neighbor interactions are important—e.g., for silicon and germanium.
Dynamic dislocation behavior in ``pure'' magnesium oxide single crystals
Authors: Singh R. N. , Coble R. L.
Published: February 2004

Edge- and screw-dislocation velocities in ``pure'' MgO single crystals have been measured as a function of stress, temperature, and valence state of the iron impurities in order to identify the rate-controlling drag mechanism for dislocation mobility. Edge dislocations have been observed to move faster than screw dislocations in both the valence states over the stress and the temperature regimes investigated. Both the edge and screw dislocations move faster in reduced (Fe+2) samples than in oxidized (Fe+3) samples. From the analysis of the edge- and screw-dislocation velocity data in terms of the activation parameters (activation volume, activation enthalpy, total activation enthalpy, and the stress exponent of dislocation velocity) it is suggested that the edge- and screw-dislocation mobilities in ``pure'' MgO single crystals in the reduced state are controlled by Peierls mechanism with thermally activated double-kink nucleation as the rate limiting step. The total activation barriers for edge- and screw-dislocation mobility has been found to be 11 and 17 kcal/mole, respectively. The calculated values of the Peierls stress for edge- and screw-dislocation mobilities in ``pure'' magnesium-oxide crystals in the reduced state are 0.6×108 and 1.7×108 N m−2, respectively. In oxidized MgO crystals the edge- and screw-dislocation mobilities are suggested to be governed by a mixed mode consisting of Peierls stress and the resistance due to nonsymmetric defects (FeMg.−VMg″).
Dynamic dislocation behavior in iron-doped magnesium oxide crystals
Authors: Singh R. N. , Coble R. L.
Published: February 2004

Edge- and screw-dislocation velocities in iron-doped magnesium-oxide single crystals containing 150 ppm Fe+3 have been measured as a function of stress and temperature in order to elucidate the rate-controlling drag mechanism for dislocation mobility. Edge dislocations have been found to move faster than the screw dislocations over the stress and temperature regimes investigated. From the analysis of the edge- and screw-dislocation velocity data in terms of the activation parameters (activation volume, activation enthalpy, total activation enthalpy, and the stress exponent of dislocation velocity), it is suggested that the edge- and screw-dislocation mobilities in MgO single crystals containing 150-ppm Fe+3 dopants are controlled by the interaction of dislocations with the nonsymmetric distortions due to (FeMg.−VMg″) defects. The strain Δε owing to such defects has been calculated and is related to the observed hardening of ion-doped (Fe+3) MgO single crystals.
Crystallization of Ge and Si in metal films. I
Authors: Ottaviani G. , Sigurd D. , Marrello V. , Mayer J. W. , McCaldin J. O.
Published: February 2004

The behavior of amorphous Si in contact with Ag films and Ge in contact with Al films has been studied at temperatures well below those at which any liquid phase is present. MeV 4He+ ion backscattering techniques, transmission electron diffraction, scanning electron microscopy, and electron microprobe analysis have been used. We find that of the many possible reactions which carry the amorphous Si or Ge into their crystalline forms the reaction predominating under our experimental conditions consists of dissolution, diffusion, and crystal growth. During isothermal heat treatment, the semiconductor film is dissolved into the metal film where it diffuses and precipitates as crystalline Si or Ge. These processes are solid-solid reactions, since this behavior is observed over temperatures of 300°C to as low as 100°C for Ge/Al, compared to the 424°C eutectic in this system. In Si/Ag, this behavior was observed from 700 to 400°C, compared with the 840°C eutectic.
Operation of a small single-mode stable cw hydrogen fluoride laser
Authors: Hinchen J. J.
Published: February 2004

A small hydrogen fluoride mixing laser has been developed which produces cw radiation with excellent short-term amplitude stability (variation less than ±1.5%) and requires only 14 liter/sec pumping capacity. Using a grating and a semitransparent mirror mounted on a piezoelectric crystal for laser cavity optics, the laser has been made to operate on a single molecular transition and also on a single cavity mode. By varying the cavity length it was possible to tune the laser over about 300 MHz. The gain of the laser was established at about 30% by measurement of mode pulling and also by direct gain measurement.
Aging degradation of a Gunn diode due to induced dislocations
Authors: Hasegawa Fumio , Ito Hitoshi
Published: February 2004

The influence of thermocompression bonding condition on the gradual degradation of a Gunn diode, accompanied by an increase of the low-field resistance, was studied. It was found that the diodes bonded with a higher pressure or at a higher temperature degrade in a shorter aging period. Many dislocations are easily induced into the GaAs chip by thermocompression bonding. Dislocations are also induced into the GaAs chip during aging, if mechanical strain remains in the GaAs chip after the bonding. The presence of many dislocations accelerates copper diffusion in GaAs and increases the acceptor concentration due to diffused copper in the epitaxial GaAs layer. It was concluded from these results that gradual degradation of the Gunn diode in question originates from the dislocations induced at the thermocompression bonding or during the aging, although it has not been clear yet whether the contamination by copper through the dislocations or the multiplication of dislocations during the aging is the dominant process.
Secondary electron yield with primary electron beam of kilo-electron-volts
Authors: Shimizu Ryuichi
Published: February 2004

Secondary electron yields δPE due to primary electrons of kilo-electron-volts are estimated for various metals by measuring total electron yields δT in an UHV system and using a Monte Carlo calculation to derive δPE from δT. The dependences of δT/δPE as well as δPE on both the atomic number Z and primary energy are also discussed from a theoretical viewpoint based on the Monte Carlo technique for primary energies higher than a few keV and on a simple theory for lower primary energies.
Ultrasonic attenuation in cesium halides
Authors: Kor S. K. , Tandon U. S. , Mishra P. K.
Published: February 2004

The attenuation of longitudinal ultrasonic waves originating from their interaction with phonon gas and from other thermoelastic causes has been evaluated in CsCl, CsBr, and CsI at 300°K by using second-order elastic moduli and third-order elastic moduli, in the 〈100〉 and 〈110〉 directions, and shear waves polarized along the 〈100〉 and 〈11̄0〉 directions. The phonon viscosity and dislocation drag along the 〈100〉 and 〈110〉 directions are also discussed.
Electric field dependence of the dielectric constant of PZT ferroelectric ceramics
Authors: Bar-Chaim N. , Brunstein M. , Grünberg J. , Seidman A.
Published: February 2004

Bias (dc electric field) dependence of the dielectric constant of ferroelectric ceramics of the Pb(Zr,Ti)O3 type has been investigated. Measurements were carried out at various temperatures in the ferroelectric phase and at several frequencies between 1 kHz and 1 MHz. The bias characteristics of the dielectric constant show a temperature-dependent asymmetry in the electric field direction. A model in which the coercive fields of the 180° and 90° domains are distributed around some average value is considered. The total dielectric constant of the material is calculated by considering the contributions of each type of domain, taking into account the difference between the differential and incremental dielectric constants. This model explains the dependence of dielectric constant on electric field. A comparison of the calculated and experimental results is presented.
Thermal conductivity of magnesium plumbide
Authors: Martin J. J. , Shanks H. R.
Published: February 2004

The thermal conductivity of a semimetal Mg2Pb single crystal has been measured from 2 to 200 K. At low temperatures thermal conduction is by phonons limited by phonon scattering from the heavy hole Fermi surface. At higher temperatures the thermal conductivity contains both electronic and phonon contributions. A comparison of the thermal conductivity of Mg2Pb with the thermal conductivities of the related semiconductors, Mg2Si, Mg2Ge, and Mg2Sn, indicates that there is a significant bipolar contribution to the electronic thermal conductivity.
Theory of Bloch-line and Bloch-wall motion
Authors: Slonczewski J. C.
Published: February 2004

A theory of Bloch-line (BL) dynamics in magnetic bubble materials is proposed and applied to the problem of domain collapse with a small number of BLs. We derive from the Landau-Lifshitz-Gilbert equation the dynamic reaction force, composed of gyrotropic and viscous terms, on a single moving BL. From this follows easily the wall mobility for equally spaced BLs. However, we show that BLs tend to cluster statically at distances comparable to the BL width. If the BLs are clustered on one side of a circular-cylinder domain, then a change of the bias field causes the centers of bubble and cluster to move on spiral trajectories. The predicted displacement of the bubble center is large enough for visual confirmation, but the bound on coervicity required to confirm the spiral shape may be too stringent. The collapse mobility for the clustered case is typically much greater than that for the case of uniform spacing. The theory is supported by collapse-time data of Malozemoff for a garnet film of medium viscosity (α=0.12). In garnets of low viscous damping of (α≲0.01) we predict that coercivity Hc gives rise to nonlinearity of the velocity-drive relation, with a characteristic ``knee'' veolcity, (2/π)γHcr, for collapse of a domain of radius r.
Point-cathode electron sources-Electron optics of the initial diode region: Errata and addendum
Authors: Wiesner J. C. , Everhart T. E.
Published: February 2004

The most popular model for a field emission diode has been a spherical cathode inside a concentric spherical anode. A much more accurate model assumes the cathode is an equipotential of a sphere centered on the tip of a narrow cone. The authors have discussed this latter model in some detail. The purpose of this paper is to point out similarities between the sphere and the sphere-on-cone models and to correct errors in our previous paper. The similarities discussed here make earlier results more useful in concept and practice. In particular, the sphere-on-cone model predicts a source size from 1.5 to 2.6 times larger than predicted by the simple sphere model that is normally used.
Effects of foreign gases on the pulsed operation of a CO2 laser
Authors: Kitazima I.
Published: February 2004

The time behavior of the pulsed output from a 10.6-μm CO2 (2.2 Torr) laser with a foreign gas additive, such as CO2, He, N2, or Xe, was studied. Its operation was accomplished by a pulsed discharge method with a current pulse width of about 7 msec. The peak current was varied from 30 to 700 mA. Each gas mixture was filled into a discharge tube of 2-cm inner diameter and 70-cm length. A nonflowing gas system was used. The laser output from a CO2-only discharge was saturated at the initial part of a current pulse and quenched, so that the laser output could not continue to radiate out during the current pulse. The laser pulse width, much shorter than the current pulse width, was almost independent of CO2 gas pressure but decreased with increasing discharge current. Addition of He to the CO2 laser system strongly quenched the saturation effect in the pulsed operation and increased either the output pulse width or the peak power. Addition of N2 increased the output pulse width, but not as much as He. In the pulsed operation of a low discharge current, the N2 gas additive increased the laser peak power much more than the He gas additive, contrary to what one expects from the results of cw operation. It was newly observed that the discharge current was suppressed at the initial part of a current pulse by adding N2 gas to a CO2 discharge and that the laser beam radiated only during its suppressed period. The Xe additive slighly affected the laser pulse and the discharge current. The laser pulse width decreased to approach a constant value of less than 0.3 msec with increasing discharge current for a given gas mixture.
Visual effects of switching in 0.15 As-0.12 Ge-0.73 Te glass
Authors: Eckels D. E. , Sidles P. H. , Danielson G. C.
Published: February 2004

Bulk samples of 0.15 As-0.12 Ge-0.73 Te glass were switched electrically with a voltage slightly above the threshold voltage. For a probe separation of 1.4 mm and the sample at room temperature, the threshold voltage is 150 V. The visual effects of switching were studied using 11 000-frames/sec cinematography. When 152 V was applied between two probes on the sample's surface, a filament appeared between the two probes 0.62 msec before the sample switched. The filament at the time of formation was narrow but later widened as current continued to flow through the filament after switching and occurred. The appearance of the filament before the sample switched and the subsequent widening of the filament both indicate that in this experiment switching was the result of a predominantly thermal mechanism.
Deep-level transient spectroscopy: A new method to characterize traps in semiconductors
Authors: Lang D. V.
Published: February 2004

A new technique, deep-level transient spectroscopy (DLTS), is introduced. This is a high-frequency capacitance transient thermal scanning method useful for observing a wide variety of traps in semiconductors. The technique is capable of displaying the spectrum of traps in a crystal as positive and negative peaks on a flat baseline as a function of temperature. It is sensitive, rapid, and easy to analyze. The sign of the peak indicates whether the trap is near the conduction or valence band, the height of the peak is proportional to the trap concentration, and the position, in temperature, of the peak is uniquely determined by the thermal emission properties of the trap. In addition, one can measure the activation energy, concentration profile, and electron- and hole-capture cross sections for each trap. The technique is presented with a simple theoretical analysis for the case of exponential capacitance transients. Various traps in GaAs are used as examples to illustrate certain features of the DLTS technique. Finally, a critical comparison is made with other recent capacitance techniques.
Self-induced drive of magnetic domains
Authors: Emtage P. R.
Published: February 2004

An electric current in a conductor can move a nearby magnetic domain even when all magnetic field gradients due to the current are canceled out; the motion comes from perturbations that are induced in the current by the domain field. A calculation is here made of the force that acts on a cylindrical bubble domain when a current flows in a thin adjacent sheet of a magnetoresistive material such as Permalloy. When the Permalloy layer is magnetized in its own plane, the direction of the force relative to the current depends on the direction of magnetization; the force can be rotated through 360° by rotating the magnetization through 180°. The greatest driving force possible is a few milligauss for each A/cm in the conducting layer.
Mechanical analogue of active Josephson transmission line
Authors: Nakajima Koji , Yamashita Tsutomu , Onodera Yutaka
Published: February 2004

The mechanical analogue of the sine-Gordon equation, which includes the effects of loss and the effect of a distributed bias source is constructed. The mechanical analogue itself is a active line transmitting kinks which are a kind of the solitons given by the sine-Gordon equation. The various vortex interactions on an active Josephson transmission line can be demonstrated vividly by using the mechanical line. Our distributed bias source which consists of a series of air nozzles blowing against each of aluminum disks is able to supply energy to kinks on the line. The analogue gives a quick and new physical insight into the highly nonlinear behavior.
Dependence of birefringence threshold voltage on dielectric anisotropy in a nematic liquid crystal
Authors: Michel Richard E. , Smith George W.
Published: February 2004

The dielectric anisotropy Δε and threshold voltage Vth for electrically controlled birefringence have been measured for a series of nematic liquid crystals (binary mixtures of MBBA and PEBAB) with different negative Δε values. The threshold voltage varies as |Δε|−1/2, in agreement with theoretical predictions. The bend elastic constant K33 evaluated from these experiments is in order-of-magnitude agreement with recent measurements for pure MBBA.
Reversible pyroelectricity and inverse piezoelectricity in polyvinylidene fluoride
Authors: Burkard H. , Pfister G.
Published: February 2004

We present dc measurements of the reversible pyroelectric effect in the temperature interval 170–350 °K and of the inverse piezoelectric effect at 0.3 °K for films of commercial polyvinylidene fluoride which were polarized in a strong dc electric field at elevated temperatures. The pyroelectric coefficient dP/dT increases with temperature and exhibits slightly discontinuous changes in slope at Tg≃−50 °C and Tb≃+20 °C. At room temperature, dP/dT ∼4×10−10 C/cm2 °K. At 0.3 °K the piezolectric strain coefficient d33 measured along the thickness of the sample is of the order of −10−8 cgs, where the negative sign indicates that the film thickness decreases upon application of a dc field in the direction of the poling field. The strain coefficients in the plane, d31, are of the order of 10−9 cgs. Annealing experiments suggest that the reversible pyroelectric effect and the inverse piezoelectric effect originate from the same polarization.
Study of the characteristics of the ion beam extracted from an rf discharge in hydrogen under conditions of resonance
Authors: Grolleau B.
Published: February 2004

The characteristics of an ion beam issued from a hydrogen plasma have been studied. This plasma is obtained by means of a high-frequency discharge set under conditions of resonance. This resonance is obtained by inductively exciting the discharge in a transverse static magnetic field (perpendicular to the axis of the vessel). The resonance, of which we give the characteristics, permits a considerable increase in the ionization degree, and is therefore of interest as regards to ion sources. The beam of particles extracted from this discharge in resonance is studied by means of a magnetic analyzer. The energy distributions of the various ions consist of two parts. A comparative analysis of the characteristics of the beam, with and without resonance, shows that this resonance improves the properties of the system. In particular, for the H1+ ion, the energy dispersion is reduced to 25 eV and its proportion in the beam reaches 85%. This resonance proves to be a convenient and very simple means to obtain an H1+ ion beam.
Increased radiation hardness of GaAs laser diodes at high current densities
Authors: Barnes C. E.
Published: February 2004

Total light output of GaAs laser diodes has been measured at 300 and 76°K before and after successive neutron irradiations to a cumulative fluence of 6.5×1014 neutron/cm2 (> 10 keV). The range of current densities used extended from well below the laser threshold current density to the maximum allowable value. Both the subthreshold light output and the threshold current density were sensitive to neutron damage in agreement with previous observations. However, at current densities significantly above threshold the light output is much less sensitive to irradiation and, in fact, the light output at 76°K was observed to increase following irradiation. These latter results have significant practical importance for cases in which laser diodes must operate in a radiation environment.
Optical studies of deep-center luminescence in CdS
Authors: Shiraki Yasuhiro , Shimada Toshikazu , Komatsubara Kiichi F.
Published: February 2004

Red luminescence in CdS has been studied in as-grown and ion-implanted crystals. An IR band consisting of two emission bands, IR1 and IR2, is produced by ion implantation. The higher-energy band, IR1, has the same origin as the R band observed in some as-grown crystals. A comparison of the R and IR1 bands in CdS with self-activated (SA) luminescence in ZnS and GaAs shows that they are SA luminescence at 1.7 eV at low temperatures in CdS. The temperature variations in peak energy, half-width, and intensity of luminescence are discussed, and the behavior is explained in terms of a configurational coordinate model. A vibrational energy of 0.025 eV, which is about 70% of the LO phonon energy in CdS, is calculated for the excited state of the center. The study of the excitation dependence of the center shows that the luminescence is due to an electronic transition within a localized center and not due to a donor-acceptor pair recombination. The center has an excitation band about 0.22 eV below the band gap. The annealing behaviors of the IR1 and IR2 centers are similar to each other, the bands abruptly disappear over 400°C. There are competitive phenomena between the IR1 and IR2 centers as to temperature and excitation-intensity dependences. We tentatively attribute the IR2 band to an aggregation defect center.
Anisotropy and magnetostriction of gallium-substituted yttrium iron garnet
Authors: Hansen P.
Published: February 2004

The anisotropy and magnetostriction constants of gallium-substituted yttrium iron garnet single crystals of composition Y3Fe5−tGatO12 with 0≤t≤1.5 have been investigated by means of ferrimagnetic resonance in the temperature range 4.2≤T≤500 K. From the concentration dependence at T =4.2 K the single-ion contribution of the tetrahedral and octahedral anisotropy was found to be Kd = −0.0019 cm−1 and Ka = −0.012 cm−1, respectively. In the range t<1 of linear concentration dependence of the magnetostriction constants at T=4.2 K, a variation Δλ100/t = −1.3×10−6 and Δλ111/t = +3.0×10−6 was found.
Piezoelectricity in uniaxially stretched poly(vinylidene fluoride)
Authors: Tamura Masahiko , Ogasawara Kiyohide , Ono Nobuyuki , Hagiwara Sumio
Published: February 2004

Hysteresis characteristics, which are similar to those observed in ferroelectric crystals, are found in uniaxially stretched poly(vinylidene fluoride) under a high electric field above 300 kV/cm at room temperature. The electrostrictive constant q13 in poly(vinylidene fluoride) is determined for polarization below about 0.5 μC/cm2 at room temperature to be 0.9 cgs esu. The remanent polarization after the poling process can be easily eliminated with a sufficiently high sinusoidal electric field. This effect is confirmed by thermally stimulated currents before and after the depolarization process.
Catastrophic failure in GaAs double-heterostructure injection lasers
Authors: Hakki B. W. , Nash F. R.
Published: February 2004

Catastrophic failure in GaAs double-heterostructure (DH) injection lasers is shown to manifest itself in two ways concurrently: rupture of one or both laser mirrors, and internal damage to the laser active region. When the electroluminescent emission is observed in a direction normal to the plane of the junction, internal damage takes the form of a dark line which starts from the damaged mirror and extends normal to it into the active region. The increase in lasing threshold and decrease of external efficiency of a catastrophically damaged laser are due to (i) decrease in reflectivity of the damaged mirror, (ii) reduction of electronic gain (and possible conversion into loss) of the active region immediately adjacent to the dark line, and (iii) optical scattering due to internal crystal damage associated with the dark line. It is shown that catastrophic damage in GaAs is consistent with a model whereby failure occurs when the optical electric field intensity at the GaAs mirror exceeds a certain critical value. In the best-quality GaAs material available, this critical optical field intensity is ≈120 kV/cm for 100-ns pulse lengths.
Infrared absorption in low-loss KCl single crystals near 10.6 μm
Authors: Hass M. , Davisson J. W. , Klein P. H. , Boyer L. L.
Published: February 2004

The infrared absorption in KCl single crystals near 10.6 μm has been studied using calorimetric techniques with fixed-frequency and tunable CO2 laser sources. By use of crystals grown in a reactive CCl4 atmosphere, with surfaces carefully prepared by chemical polishing, it is possible to obtain absorption coefficients of 0.0002 cm−1 or less in samples several centimeters thick. This residual absorption is composed of a surface and a bulk part. It is possible to show that the bulk absorption approaches the estimated intrinsic limit of 0.00008 cm−1. An absorption band near 9.8 μm is present in all samples examined and appears to be largely associated with the surface.
SQUID techniques.I. Obtaining reliability in point-contact SQUID's
Authors: Buhrman R. A. , Lukens J. E. , Jackel L. D. , Strait S. F. , Warlaumont J. M. , Webb W. W.
Published: February 2004

Stable and permanent niobium point-contact SQUID's have been fabricated by using oxidized niobium screws to form the point contact. The reliability of these devices is further ensured by a simple and versatile environmental shielding procedure. Over a period of five years there have been no failures of such SQUID's in our laboratory. The signal-to-noise performance of these SQUID's is quite good.
Effects of heat treatment and doping with Zr on the superconducting critical current densities of multifilamentary Nb3Sn wires
Authors: Suenaga M. , Luhman T. S. , Sampson W. B.
Published: February 2004

Various wire samples consisting of 19-Nb3Sn filaments in a normal metal matrix were made by heat treating composite wires of 19-Nb, Nb-0.5 wt% Zr, Nb-0.75 wt% Zr, and Nb-2.5 wt% Zr filaments embedded in a Cu-10 wt% Sn matrix. The Nb-0.75 wt% Zr rod contained the precipitate ZrO2, while the Zr in the remaining Nb rods was in solid solution. The over-all size of the composite was 2.5×10−2 cm and each filament was approximately 2.5×10−3 cm in diameter. The critical current density Jc at 4.2 °K was measured at 40 and 100 kG for a variety of heat treatments. It was found that the critical current density was a strong function of the thickness of the Nb3Sn layers formed during heat treatment. This dependence of Jc on the thickness d could be approximately represented by the expression Jc(d)≃J0 exp (−nd), where J0 is the extrapolated zero thickness critical current density. J0 was found to be approximately 2.4×106 A/cm2 at 40 kG for the Nb3Sn formed from pure Nb, 1.2×106 A/cm2 for Nb doped with solid-solution additions of Zr, and 9.5×105 A/cm2 for that formed from Nb doped with ZrO2. The exponent n falls in the range 0.52–0.67 (μm)−1 for pure Nb3Sn depending on heat treatment temperature, 0.154–0.287 (μm)−1 for Nb doped with solid-solution additions of Zr, and only 0.11 (μm)−1 for the Nb3Sn composite wire containing ZrO2. The magnetic field dependence of Jc for some of the composites was also measured to 150 kG.
Elimination of the background in high-precision Compton profile analysis
Authors: Esslinger D. , Hosemann R. , Müller A. , Weick D.
Published: February 2004

The Compton spectrum of Cu and Al with AgK radiation is discussed and a method is described to separate the large disturbing background of the Compton scattering of the white spectrum by convolution integrals. In spite of this highly sophisticated analysis of the background it still provides a main source of error. Therefore a new method with AgK fluorescence radiation is described and preliminary results are given. Now the background is wavelength independent and reduced by a factor of 35 for LiF (200) and Al scatterer. As an example of the great progress of this new method, the Compton profiles of Al and paraffin are discussed. The Compton intensity is nearly the same as with the older method.
Mass-Spectrometric Investigation of the Primary Processes in the Photodissociation of 1,3-Butadiene
Authors: Bergmann K. , Demtröder W.
Published: February 2004

The primary processes in the 1,3-butadiene photodissociation are investigated by direct detection of the fragments in a mass spectrometer at pressures of 10−4 mm Hg in the reaction chamber. With the special technique used here, collisions do not occur during the time between photon impact and primary-product detection. The resulting products of illumination with a light continuum between 2200 and 1800 Å, which is produced by a pulsed high-pressure argon flash lamp, are as follows: C3H3 + CH3; C4H5 + H; C2H4 + C2H2; C2H3 + C2H3; and to a small amount, also C4H4 + H2. The quantitative probabilities for these five dissociation modes are derived from the measured ion spectrum of the neutral photodissociation fragments that is produced in the ion chamber of the mass spectrometer by electron impact. Some results concerning the original excited state and fragment energies are discussed.
ab initio Study on the Stability and Geometry of Cyclobutadiene
Authors: Buenker Robert J. , Peyerimhoff Sigrid D.
Published: February 2004

Ab initio SCF MO and CI calculations dealing with questions of molecular stability, geometry, and spectra of cyclobutadiene C4H4 are reported. Comparison is made between the ab initio and semiempirical Hückel methods for the treatment of molecules of this type and emphasis is placed upon the role configuration interaction plays in improving the representation of the closed-shell SCF molecular potential surface. The results of the CI calculations in turn indicate a singlet ground state for cyclobutadiene in a rectangular geometry and a lowest excited triplet of the molecule which possesses a potential minimum for a slightly nonsquare geometry and is everywhere more unstable than the aforementioned singlet; the molecule is not found to be stable with respect to its separation products (two acetylenes), although it appears to exist in metastable equilibrium in the cyclic configuration. An attempt is also made to relate the cyclobutadiene calculations to the study of the geometry of similar molecules; from this it is concluded that the cyclization process is strongly favored by the presence of CH bonding and that benzene is much more stable than cyclobutadiene mainly because of its greater ability to simultaneously form strong CC and CH bonds.
Electronic Absorption Spectra of Dimers of p-Benzosemiquinone Anion and Würster's Cations in Solution
Authors: Kimura Katsumi , Yamada Hikoichiro , Tsubomura Hiroshi
Published: February 2004

The dimerization of p-benzosemiquinone anion and Würster's cations in ethanol has been studied by the electronic absorption spectra of these radicals formed by ultraviolet irradiation and chemical oxidation of the corresponding parent molecules. The ion radicals studied are p-benzosemiquinone anion (SQ−), p-phenylenediamine cation (PD+), N,N-dimethyl-p-phenylenediamine cation (DMPD+, and N,N,N',N'-tetramethyl-p-phenylenediamine cation (TMPD+). With an ethanol solution of p-phenylenediamine bromide (PD+Br−), the concentration dependence of the two absorption maxima at 4650 and 6050 Å (corresponding to the monomer and dimer, respectively) were studied quantitatively. It has been confirmed that the monomer and dimer are in equilibrium in the solution at low temperature. The equilibrium constants were found to be 2200 and 4400 liters mole−1 at − 72° and − 77°C, respectively. The electronic absorption bands of these dimers were interpreted by considering the symmetry properties of the singly excited electronic configurations, on the assumption of a parallel structure possessing D2h symmetry.
Percus-Yevick Equation Applied to a Lennard-Jones Fluid
Authors: Watts R. O.
Published: February 2004

An efficient method of solving the Percus-Yevick and related equations is described. The method is applied to a Lennard-Jones fluid, and the solutions obtained are discussed. It is shown that the Percus-Yevick equation predicts a phase change with critical density close to 0.27 and with a critical temperature which is dependent upon the range at which the Lennard-Jones potential is truncated. At the phase change the compressibility becomes infinite although the virial equation of state does not show this behavior. Outside the critical region the PY equation is at least two-valued for all densities in the range (0, 0.6).
Field-Ionization Mass Spectra of Some Hydrocarbons and Monochloro-Substituted Derivatives
Authors: Weiss Morris J. , Hutchison Dwight A.
Published: February 2004

Field-ionization mass spectra have been obtained for about 30 straight-chain and branched hydrocarbons, together with the corresponding monochloro derivatives. Electric fields of about 1 × 107V cm−1 were produced with a 2.5-μ Pt wire. Mass-analyzed ion currents of about 10−14–10−16 A were detected for applied anodecathode voltages of 10–11 kV. Along with the most intense parent ion currents there were detected fragment ions with lifetimes of 10−8–10−13 sec resulting from decomposition of field-excited parent ions. Also present in the spectra were ions arising from long-lived metastable parent ions with lifetimes of 10−5–10−7 sec. Correlation of the observed mass and intensity of fragment and parent ions with the parent molecular structures yielded conclusions related to the various decomposition processes. Increased branching of isomeric structures resulted in increased fragmentation. The presence of a double bond in a molecule greatly reduced fragmentation compared with molecules of similar structure with no double bond. The substitution of chlorine for hydrogen in organic molecules increased fragmentation.
Cupric Ion in Blue Proteins
Authors: Brill Arthur S. , Bryce Graeme F.
Published: February 2004

A noncovalent model involving admixture of 4p and 4s character into the 3d valence electrons of the cupric ion is used to account for the intense blue color and low nuclear hyperfine structure constants for two varieties of Pseudoomnas blue proteins (azurins). Upon adjustment of six parameters (five hybridization coefficients and the isotropic contact term), the proposed scheme quantitatively accounts for (a) three g values and three A values of the EPR spectrum, (b) the oscillator strengths of the three visible absorption bands, and (c) the signs and magnitudes of the rotational strengths of these latter electronic transitions. It is found that the ground state contains 19% 4p character to which corresponds an out-of-plane distortion of 12.5°. The excited states have varying admixtures of 4s and 4p which are shown to have an essential role in producing the spectroscopic properties.
Rotational and Vibration–Rotation Line Shifts and Widths. Distorted-Wave Approximation
Authors: Illinger K. H. , Trindle C. O.
Published: February 2004

A treatment of molecular collision broadening employing the distorted-wave (DW) approximation for the disentanglement of the coupled scattering equations for anisotropic potentials is developed. Calculations of the rotational and vibration–rotation line-shape parameters, for HCl perturbed by Ar, have been performed within the framework of a model potential. The extension to realistic potentials of the DW method, in a DW–WKB version and in the classical-path limit of the DW–WKB approximation, is discussed. For all but the lightest collision couples, the DW–WKB approximation emerges as a method which combines accuracy in the discription of the molecular interaction with relative computational ease; for massive systems, the DW–WKB method can be taken to the classical-path limit with no loss in accuracy. In either of these versions, the DW–WKB approach constitutes a practicable avenue which promises accurate predictions of molecular line shifts and widths.
Molecular Collisions. VII. Nuclear Spin and Statistics Effects
Authors: Biolsi Louis , Curtiss C. F.
Published: February 2004

The effect of nuclear spin on the expressions for the differential and degeneracy averaged scattering cross sections for collisions of two diatomic molecules, developed in previous papers in this series, is considered. These expressions are then reformulated in terms of another basis set of functions, making use of the diagrammatic techniques introduced earlier. Collisions between indistinguishable molecules are also considered. The resulting expressions reduce, in the limiting case of spherical molecules, to previously known results.
Determination of Centrifugal Distortion Coefficients of Asymmetric-Top Molecules. III. Sextic Coefficients
Authors: Watson James K. G.
Published: February 2004

The rotational Hamiltonian of an asymmetric-top molecule, containing terms up to sixth degree in the components of the total angular momentum, is transformed by a unitary transformation to a reduced Hamiltonian, so as to avoid the indeterminacies inherent in fitting the complete Hamiltonian to observed energy levels. Two methods of reduction are considered, one suitable for energy calculations by matrix diagonalization and the other for calculations by perturbation theory. The relations between the coefficients in the reduced Hamiltonians and those in the original Hamiltonian are given. Extension of the perturbation treatment to the first-order contributions from the sextic terms and the second-order contributions from the quartic terms yields explicit expressions for these contributions in terms of Ray's function EJτ(κ) and its first and second derivatives with respect to the asymmetry parameter κ.
Localized Orbitals. I. σ Bonds
Authors: Letcher John H. , Dunning Thomas H.
Published: February 2004

This paper presents a method for the delineation of a set of truly localized orbitals and uses a nonunitary transformation to convert the localized orbitals into equivalent orbitals which are suitable for molecular quantum-mechanical calculations. The localized orbitals, which are suitable for describing polyatomic molecules including large nonplanar ones, are generated on the premise that the atomic orbitals used in the construction of two-center one- or two-electron bonds should be such that, when overlap is totally neglected, each atomic orbital has the same calculated value of angular momentum about its bond axis. The non-unitary transformation is derived from the modification in the form of the general orthonormality conditions upon a change from overlap metric 1 to a realistic overlap matrix Δ. This approach is applied to methane, ammonia, and water to calculate the equivalent orbitals. System energies and dipole moments are also calculated, and these and the equivalent orbitals are compared with the results of reported SCF calculations. The close values of the energies show that this approach may be used for realistic calculations. It also has an advantage over SCF techniques in that extension to extremely complicated molecular systems is possible. Further, the orbitals used herein are particularly useful for chemists since they are couched in terms of localized-bond characteristics alone.
Two-Dimensional Double-Minimum Model of Hydrogen Bonding: The Symmetric Case
Authors: Singh T. R. , Wood J. L.
Published: February 2004

A linear AH···A model, representing hydrogen bonding, which incorporates a double minimum in the potential energy, and interaction between the symmetric and antisymmetric stretching motion, is examined. Using harmonic-oscillator functions as a basis for expansion, solutions of the two-dimensional wave equation are obtained. Three tests for the convergence of the matrix expansion are satisfied. Using ranges of parameters appropriate to hydrogen-bonded systems, the combined effects of tunneling and vibrational interaction on the tunneling transition νt, the far-infrared transition νσ, the normal-infrared transition νs, and the combination bands νs ± νσ are determined. The effect of replacement of H by D is also examined. The validity of applying the Stepanov approximation to these systems is tested.
Proton Spin–Lattice Relaxation in Hexagonal Ice
Authors: Barnaal D. E. , Lowe I. J.
Published: February 2004

The results of measurements of the proton spin–lattice relaxation time T1 in ice are reported. The ice samples were single crystals grown by zone refining at atmospheric pressure. The measured activation energy for the T1 process is 14.1 ± 0.1 kcal/mole. No anisotropy of T1 is observed. A theoretical calculation of T1 is presented, from which molecular displacement times are deduced.
Rotationlike Motion of Molecules in Liquids: Far-Infrared Absorption of Polar Molecules in an Inert Solvent
Authors: Datta Pabitra , Barrow Gordon M.
Published: February 2004

The far-infrared spectra of a variety of relatively small polar molecules dissolved in a hydrocarbon solvent have been investigated. The absorptions can be attributed primarily to rotationlike motions and the observed bands can be treated in terms of a collision-affected, resonant, rotationlike process. An effective energy-separation parameter ν0 and a collision parameter Δν are deduced for the observed bands, and the values found are consistent with the model used.
Electron Spin Resonance of a Gamma-Irradiated Single Crystal of 5-Nitro-6-Methyluracil
Authors: Snipes Wallace , Benson Brent
Published: February 2004

Free radicals in gamma-irradiated 5-nitro-6-methyluracil have the unpaired electron localized on C(4) and C(6) of the pyrimidine ring. Principal values for the spectroscopic splitting factor are gu = 2.002, gυ = 2.005, and gw = 2.008. Hyperfine interaction between the spin density at C(6) and the methyl protons is nearly axially symmetric with principal values A‖CH3 = 10.7 G and A⊥CH3 = 8.8 G. Hyperfine interaction between the spin density at C(4) and the hydroxyl proton has approximate principal values of A‖OH = 9.5 G and A⊥OH = − 0.5 G. The unpaired spin densities are 0.32 on C(6) and 0.63 on C(4). The localization of spin density on C(4) and C(6) is unusual by comparison to the radicals in most other pyrimidines where the spin density is on C(5).
Lattice Vibrations of Molecular Crystals. II. Cyanamide and Cyanamide-d2
Authors: Durig J. R. , Walker M. , Baglin F. G.
Published: February 2004

The far-infrared spectra (33–500 cm−1) of crystalline cyanamide (NH2CN) and cyanamide-d2 have been recorded with polyethylene and silicon sample support plates. The laser Raman spectra have also been recorded from 40–1600 cm−1 for both molecules. No evidence was found for the inversion doubling and resultant low-frequency components of the NH2 and ND2 wagging frequencies previously proposed. While 14 of the predicted 15 infrared-active lattice modes were identified, only four of the predicted 24 Raman-active lattice modes were observed. Force constants were estimated from the observed infrared frequencies by use of modified Born–von Karman valence force field and Wilson-FG technique. Lastly, the distortion moment and effective charges were calculated using the method of Szigeti and Kurosawa. These results semiquantitatively reflect the difference in band intensities between the intra- and intermolecular vibrations.
Luminescence of Inorganic Nitrite Salts
Authors: Maria H. J. , Armstrong A. T. , McGlynn S. P.
Published: February 2004

Nitrite salts of the post-transition-series metals exhibit a long-lived luminescence centered at ∼5500 Å. This emission is characteristic of both the solid state and frozen glassy solutions. It is suggested that this emission originates in a triplet state (T1) of the system, and that, in fact, it is a phosphorescence of T1→S0 molecular type connecting with the ground singlet state (S0). It is shown that the spin–orbit coupling responsible for the enhanced intersystem crossing is introduced by the metal counterion and that such introduction is also dependent on the presence of nitrite-counterion covalency. The increased spin–orbit coupling is manifested in the following ways: (i) a decrease in the phosphorescence lifetime, τp, (ii) an increase in the relative quantum yield ratio Φp / Φf of phosphorescence to fluorescence, (iii) an increase in the T1←S0 absorptivity—which absorptivity is responsible for the yellow-orange colors of the heavy-metal nitrites.
Flashlamp-Pumped Organic-Dye Lasers
Authors: Sorokin P. P. , Lankard J. R. , Moruzzi V. L. , Hammond E. C.
Published: February 2004

The results of recent theoretical and experimental studies on flashlamp-pumped organic-dye lasers are presented. The importance of rapid pumping is considered in detail. Constructional aspects of a suitable flashlamp assembly are given, and lasing characteristics of various organic dyes excited by this lamp are summarized.