bluuebunny/crossref_metadata_2025 huggingface dataset:
Double injection in semiconductors
Authors: Migliorato P. , Margaritondo G. , Perfetti P.
Published: February 2003

A new model for double injection in high-resistivity semiconductors, containing recombination centers, is proposed. The negative resistance is associated with the presence of a saturated trap region near the minority-carrier injecting contact, which extends toward the opposite contact for increasing current. By using the regional approximation method, an analytical current-voltage characteristic is obtained which describes both the prebreakdown and negative-resistance regime. The present theory shows that the deviation from the quadratic J-vs-V behavior in the prebreakdown regime depends upon the interelectrode separation and gives a good fit for the prebreakdown characteristic of Au-GaP diodes. The theoretical breakdown voltage decreases with increasing thermal free-carrier concentration, and good quantitative agreement is found for the experimental results for GaP and InSb double-injection diodes.
Low-field transient behavior of MNOS devices
Authors: Maes Herman E. , Van Overstraeten Roger J.
Published: February 2003

Evidence for the transition from Fowler-Nordheim injection to a trap-assisted tunneling mechanism in thin oxide MNOS devices under low applied voltages has been found from transient measurements. The agreement between theoretical prediction and experimental results is very good.
Hall mobility in CdGexAs2 glasses
Authors: Meimaris D. , Katsika V. , Roilos M.
Published: February 2003

Electrical-conductivity and Hall-effect measurements were performed on CdGexAs2 glasses with a Ge content of (1/8) M, (1/6) M, and (1/4) M, respectively, in the temperature range 200–550 °K. The experimental data show that the temperature dependence of the Hall mobility in the CdGexAs2 glasses studied does not resemble that reported for chalcogenide glasses. The observed variation of the Hall mobility with temperature is possibly consistent with conduction occurring by variable-range hopping in localized states both at the band edge and the Fermi level, the latter being expected to contribute mainly at low temperatures.
Superconducting copper-base alloy containing filaments of V3Ga
Authors: Chen W. Y. K. , Tsuei C. C.
Published: February 2003

Superconducting copper-rich composites containing V3Ga filaments have been prepared by a process which consists of melting the constituent elements into ingots followed by subsequent cold working and heat treatment. The composites were fabricated into 1×1-mm rods, 0.25×3-mm ribbons, and 0.4-mm wires. The superconducting transition temperature is about 13 °K. The critical current density, Jc, at 4.2 °K and zero field is as high as 2.9×104 A/cm2 and decreases to 2×103 A/cm2 at 60 kG. Jc was found to decrease only slightly with temperature up to 9 °K.
Dynamics of hard walls in bubble garnet stripe domains
Authors: Morris T. M. , Zimmer G. J. , Humphrey F. B.
Published: February 2003

The motion of ’’hard’’ magnetic domain wall sections, intermixed with ’’soft’’ wall sections, has been observed in stripe domains in bubble garnets. Using a Faraday microscope with pulsed laser illumination, 10 nsec, single-exposure photographs of the stripe domains were taken while the walls were in motion. When a short low-amplitude demagnetizing pulse is applied, well-defined constrictions in the stripe become apparent before the critical width at which magnetostatic instabilities begin to develop. The constrictions appear either as a symmetric inward dent in both walls of the stripe or as a depression in one wall with the other remaining straight. This effect has been observed in a wide variety of nonimplanted materials but seems to be completely suppressed in implanted samples. Data is presented for Y1.57Eu0.78Tm0.65Ga1.05Fe3.95O12 with a thickness of 6.8 μm, 4πM=184 G, and a Gilbert damping parameter α=0.026. The hard-wall velocity exhibits a linear dependence on drive field with a mobility of 2.0 cm/sec Oe. Normal wall mobility is roughly an order of magnitude higher. Observation of the hard sections on successive field pulses at a fixed delay shows their displacement along the length of the stripe. If the polarity of the pulse is reversed, the hard sections appear as bulges in the narrowing stripe and move in the opposite direction. Both left- and right-hand deflections are observed. As a function of pulse length, displacement per pulse increases rapidly to a broad maximum of about 11 μm/pulse and then falls slowly to a low constant value for pulses for sufficient duration to drive the stripe to a new equilibrium width. Using an alternating delay technique, the mobility of transverse displacement of a bulge during a single pulse was determined to be 110 cm/sec Oe and a coercive force of 4 Oe. The experimental data is consistent with the values predicted for a wall with continuously wound vertical Bloch lines.
Connection between sources formalism and correlation formalism for transport noise: Application to injection diodes
Authors: van Vliet K. M. , Blasquez G.
Published: February 2003

The connection between the sources formalism and the correlation formalism for fluctuations in transport processes is reinvestigated, with special emphasis on terms resulting from the boundary conditions. For fluctuations in vector quantities, like the electric field, the conditions on the tensor Green’s functions, necessary for the surface terms to vanish, are discussed. They are not satisfied for transport in three-dimensional injection diodes, in which transverse diffusion is neglected. A pseudoscalar conversion analysis for the radial Green’s function leads to an extended correlation formalism expression, which yields exact agreement with the sources formalism results.
The variation of ionization with air/fuel ratio for a spark-ignition engine
Authors: Clements R. M. , Smy P. R.
Published: February 2003

A negatively biased flush-mounted planar probe operated both in a pulsed and dc mode has been used to measure the ionization density in the plasma generated by combustion in a single-cylinder spark-ignition engine. The ionization was measured as a function of the air/fuel ratio and was found to exhibit a broad peak (Q?2) whose maximum occurs slightly to the rich side of stoichiometric. The peak ionization was calculated from two slightly different models for ion collection to be ?1019/m3. Values of this magnitude appear to be more reasonable than the very high value of 4×1021/m3 deduced by Rado using a similar experimental setup. Finally, it is proposed that this type of measurement may be useful to monitor engine performance.
Effect of high magnetic fields on the threshold of laser-induced gas breakdown
Authors: Button Edward J. , Guenther Arthur H.
Published: February 2003

A quantum rate analysis of laser-induced breakdown in deuterium and helium gas was used to predict the dependence of the breakdown-threshold intensity on gas pressure, laser-pulse length, and the magnitude of an applied external magnetic field parallel to the direction of propagation of the laser beam. Diffusion, elastic and inelastic collisions, and multiphoton ionization of atomic and molecular states excited by electron impact were considered. The threshold data indicate the presence of three distinct regions: the pulse-length dominated, intermediate, and the diffusion dominated, as well as the importance of a dimensionless parameter Ω in determining the magnitude of the magnetic field effect on the breakdown threshold for a given set of experimental conditions. The results are in excellent agreement with experimental data.
Ultrasonic viscoelastic properties of amorphous oligomers
Authors: Kono Ryusuke , Yoshizaki Haruyo
Published: February 2003

Shear mechanical relaxation data are reported for series of polystyrene and polybutene. Shear measurements in the temperature range from 65 to 150 °C, with frequencies ranging from 0.5 to 100 MHz, indicate a relatively wide distribution of relaxation times, represented by the Davidson-Cole spectrum. The spectrum shows an essentially greater width as the molecular weight increases. This behavior is related to the non-Arrhenius character of melt viscosity. Limiting shear modulus is precisely determined and found to obey the Hirai-Eyring equation G∞= (RT/V0)  exp(Eh/RT), where Eh is the energy required to create one mole of holes and V0 represents molar volume of a monomer unit. The only exceptional case is the lower-molecular-weight polystyrene in which G∞ follows the equation of Barlow, Dickie, and Lamb. The values of Eh/RT at the glass transition temperature for polystyrenes and very low-molecular-weight polybutenes are within the universal constant 3.68±0.13. The origin of the hysteresis loss is discussed in terms of Eh.
Static fatigue in brittle solids
Authors: Doremus R. H.
Published: February 2003

Equations for static fatigue in brittle solids are derived, based on the ideas of Hillig and Charles, but we used a different log reaction velocity-stress relationship. The equations agree well with the functional dependence of failure time on stress and values of the stress-sensitivity factor found experimentally. Variations in failure times with sample history and glass composition can only partly be explained by the equations.
On the existence of surface-wave solutions for anisotropic elastic half-spaces with free surface
Authors: Lothe J. , Barnett D. M.
Published: February 2003

A proof is developed that for a given direction of propagation on the free surface of a half-infinite anisotropic crystal, a surface-wave solution with a certain phase velocity vR<vL, where vL is the limiting velocity, will always exist, except in the special case when the bulk wave defining the limiting velocity satisfies the condition of a free surface. The proof is in terms of the surface impedance, which relates the amplitude at the surface of a surface wave with the external forces needed at the surface. The properties of the impedance as a function of phase velocity determines whether a surface wave not requiring external forces at the surface exists for a certain phase velocity. The proof is valid also in the case of degeneracies in the eigenvalue problem entering the analysis.
Maximum growth rates for melt-grown ribbon-shaped crystals
Authors: Ciszek T. F.
Published: February 2003

From heat-balance considerations at the growing interface and an assumption of predominantly radiative heat loss from the surface, an expression for the maximum growth rate of melt-grown ribbon-shaped crystals has been derived. For a given material and a large width-to-thickness ratio W/t, the maximum growth rate varies as t−1/2 and is independent of W. A comparison of the maximum cylindrical and ribbon growth rates is made for the silicon system. Some representative values at 7.5 cm diameter or width are 45 cm/h or 2000 cm3/h, for a cylindrical Czochralski-grown crystal and 625 cm/h or 95 cm3/h for a 0.02-cm-thick ribbon.
Novel charge-storage-diode structure for use with light-activated displays
Authors: Fraas L. M. , Grinberg J. , Bleha W. P. , Jacobson A. D.
Published: February 2003

A theoretical model is described for the photosensor-substrate structure presently used with the ac liquid-crystal light valve. This structure consists of a thin film (sputter deposited) of n-type CdS on which is evaporated a thin film of p-type CdTe. The model describes the photosensitivity of this structure in terms of the depletion-width photocapacity of the charge-storage diode formed by these two coatings. The model developed based on this photocapacity effect allows a consistent explanation of the experimentally observed fact that good device photosensitivity is observed at high frequencies (e.g., 10 kHz), contrary to the prediction that would result from a quantum-photodiode model. By assuming an electronic-defect-center structure that consists of fast and slow electron trap levels and a recombination level, as in the case of a photoconductor, the charge stored in the diode is related to image-activating light intensity. This provides descriptive information on device response time, gray scale, and sensitivity. Additionally, the model allows for the identification of those material properties that presently limit photosensor performance.
Mechanism of detection of radiation in a high-speed metal-metal oxide-metal junction in the visible region and at longer wavelengths
Authors: Elchinger G. M. , Sanchez A. , Davis C. F. , Javan A.
Published: February 2003

The mechanism of detection of radiation by a small-area thin-film metal-metal oxide-metal (MOM) structure is studied. It is shown that after subtracting thermal effects the response at optical frequencies arises from photoemission over the oxide’s potential barrier. At lower frequencies the mechanism arises from a rectification process dictated by the nonlinear I-V characteristics due to electron tunneling across the junction.
Buckling of a superconducting coil nested in a three-coil toroidal segment
Authors: Moon F. C.
Published: February 2003

Measurements are made of the lateral stiffness of a flexible planar superconducting coil between two rigid coils in series. These tests show a dramatic decrease in the natural bending frequency with subsequent elastic instability or ’’buckling’’ at a critical value of the current in the coils. These observations support a magnetoelastic analysis which shows that proposed designs of toroidal field coils for Tokamak fusion reactors have insufficient lateral support for mechanical stability of the magnets.
Parametric resonance instabilities in argon and neon plasmas
Authors: Cicconi G. , Rosatelli C.
Published: February 2003

Experimental results, interpreted by a theoretical model based on the first two hydrodynamic equations, concerning parametric resonance instabilities in argon and neon dc discharges are presented. These instabilities were detected by scattered microwaves in the frequency band 2–40 GHz when the plasma positive column was pierced across a rectangular waveguide, by measuring time-modulation enhancement due to striation eigenmodes built-up in plasmas.
Charge transfer in metal/atactic polystyrene contacts
Authors: Fabish T. J. , Saltsburg H. M. , Hair M. L.
Published: February 2003

Contact charge-exchange experiments between various metals and atactic polystyrene are utilized to elucidate the electronic structure of the polystyrene. Bulk states present at approximately 1014/cm3 within a 4-μ-thick boundary layer, as well as surface states of approximate density 1010/cm2, govern the charge-exchange characteristics of polystyrene in the metal contacts. It is argued that the carriers are electrons injected from the region of the Fermi level of the metal into the polymer, and that the metal/polymer junction remains indefinitely in a nonequilibrium state. A steady-state injection level is reached because of differences in injection and transport properties of the surface boundary layer and the deeper bulk material. A significant effect of the substrate metal on the populations of the electronic states at the free surface of the polystyrene films is identified and shown to be long range (at least 15 μ).
The distribution of localized electronic states in atactic polystyrene
Authors: Fabish T. J. , Saltsburg H. M. , Hair M. L.
Published: February 2003

The steady-state charge level reached after repeated contact of a single metal with a film of atactic polystyrene has been interpreted previously in terms of electron injection from the metal into the polymer. The charge level is a function of film thickness, the particular contacting metal, and the particular metallic film substrate. In this study different metals are contacted to the same film until a steady-state condition is reached for each metal. The net charge level at the end of the contact sequence is found to be approximately equal to the sum of the previously measured single-metal charge levels for an initially charge-neutral film and is independent of the order of the metals in the sequence. Therefore, charge injection does not follow a simple energetic relationship between the Fermi level of the metal and the energy of a surface or bulk band or localized level of the polymer. Rather, each metal communicates with a discreet portion of the distribution of localized polymeric electronic states. The energy selective feature of the charge-injection process converts the contact charge-exchange experiments into a spectroscopic tool for the study of the localized polymeric states. As a result the localized electronic-state distribution of the polymer can be derived for a range of electron energies related to that spanned by the Fermi levels of the contacting metals.
TSC studies of carrier trapping in electron- and γ-irradiated Teflon
Authors: Gross B. , Sessler G. M. , West J. E.
Published: February 2003

A study of thermally stimulated current (TSC) spectra of 25-μm Teflon samples preirradiated with 40–75-keV electron beams or 60Co γ rays is presented. The currents, obtained under an applied or an internal field, are generally due to a superposition of drifts of primary injected and secondary radiation-generated carriers. The TSC spectra are identical for both kinds of irradiation if comparable dose rate and total dose are used and if no excess charge is present. In general, two current peaks at about 70 and 200 °C, respectively, are observed. The low-temperature peak is sensitive to storage conditions; it furthermore saturates with applied field and increases with radiation dose. The high-temperature peak shows no significant dependence on storage conditions, and does not saturate as easily with applied field, but tends toward earlier dose saturation.
Dynamic elastic-plastic properties of single-crystal pentaerythritol tetranitrate
Authors: Halleck P. M. , Wackerle Jerry
Published: February 2003

The dynamic elastic-plastic behavior of single crystals of the secondary explosive pentaerythritol tetranitrate (PETN) have been studied at input shock strengths between 0.6 and 4.0 GPa (6–40 kbar). Crystals with surfaces cut perpendicular to the 〈110〉 and 〈001〉 directions were struck by gas-gun projectiles and stress histories at both sample faces were determined with quartz dynamic stress gauges. The amplitude of the elastic wave increases markedly with input shock strength and decreases with distance of run. A viscous relaxation model based on the theory of dislocation dynamics is consistent with the observations and yields estimates of 6.8 GPa μs (6.8×104 P) for the dynamic viscosity at the shock front and 1.1×1010 m−2 for the dislocation density. Observed impact-face shock states correspond to the hydrostat Hugoniot, suggesting that little shear stress is retained after yielding begins. With input shock strengths of 4.0 GPa, pressure buildup at the impact face is observed, indicating energy relase near this surface. This occurs at about half the input shock strength that would be expected from previous initiation experiments and theoretical calculations on single-crystal PETN.
Optical absorption spectrum of tin diselenide single crystals
Authors: Garg A. K. , Agnihotri O. P. , Jain A. K. , Tyagi R. C.
Published: February 2003

Single-crystal platelets of n-type SnSe2 have been grown by the vapor phase transport technique without using a transport agent. Optical absorption has been studied at 25 °C for light polarized perpendicular to the crystallographic axis of symmetry. Order numbers of interference fringes in the transmission spectrum have been uniquely assigned. Variation of refractive index and absorption coefficeint with energy has been reported. It is found that the intrinsic SnSe2 absorption edge arises from forbidden indirect transitions across an energy gap of 0.98 eV and allowed direct transitions across an energy gap of 2.1 eV.
Magnetic properties of amorphous Gd-Fe films prepared by evaporation
Authors: Taylor R. C.
Published: February 2003

Amorphous GdxFe1−x films with 0.18<x<0.33 were prepared by electron-beam coevaporation of the elements. The composition dependence of anisotropy and the composition and temperature dependence of saturation magnetization of the films were studied. In contrast to evaporated Gd-Co films, where anisotropy is in-plane, the Gd-Fe films were found to have strong perpendicular anisotropy with the uniaxial anisotropy constant (Ku) decreasing monotonically from 3.8×105 erg/cm3 at x=0.18 to 2.0×105 erg/cm3 at x=0.33. The perpendicular anisotropy field (HK) reached a maximum at the compensation composition (x=0.26) and fell off rapidly on both sides. The findings suggest that anisotropy in evaporated films is due to a longer-range structural ordering than the pair ordering which is assumed to exist in sputtered films. Saturation magnetization measurements showed that magnetization of the amorphous alloys could be closely approximated from the moments of pure crystalline Gd and Fe. The 0 °K moment of Fe was found to be 2.20μB (0.23<x<0.31) suggesting less charge transfer than in crystalline GdFe3. Q values (HK/4πMs) of the alloys exceeded unity in the range 0.19<x<0.31.
Diffusion of vacancies and interstitials to edge dislocations
Authors: Wolfer W. G. , Ashkin M.
Published: February 2003

The steady-state diffusion of radiation-produced point defects in the stress field of an edge dislocation is solved by a perturbation method. The drift term entering the diffusion equation includes the size interaction and the inhomogeneity interaction as well as the effects of externally applied loads. By comparing the perturbation solution with the rigorous solution of Ham, we show that the perturbation solution is always adequate provided the drift term is proportional to the gradient of the interaction energy of the point defect with the dislocation. The steady-state distributions of vacancies and interstitials is such that voids or vacancy clusters preferentially grow on the compressive side of the edge dislocation. The external stresses give rise to an orientation-dependent bias of the edge dislocation which is shown to provide a possible mechanism for radiation-induced creep.
Analysis of weak-boundary-coupling effects in liquid-crystal displays
Authors: Nehring J. , Kmetz A. R. , Scheffer T. J.
Published: February 2003

The analysis of Rapini and Papoular for homeotropic and homogeneous geometries is extended to predict the effects of weak boundary coupling on liquid-crystal display performance. An implicit expression for deformation as a function of applied field is derived for the case of equal elastic constants. Steeper transitions with complete saturation at low fields are found, which promise improved optical performance and multiplexing capability. A similar analysis of twisted nematic displays predicts a less pronounced improvement in electro-optic response and indicates a minimum boundary-coupling strength below which spontaneous deformation occurs.
Surface acoustic wave properties of lithium gallium oxide
Authors: Gupta S. N. , Vetelino J. F. , Jipson V. B. , Field J. C.
Published: February 2003

The surface acoustic wave (SAW) properties of lithium gallium oxide (LiGaO2) are theoretically predicted in order to determine the feasibility of using this material in related SAW devices. The surface wave velocity, the temperature coefficient of delay, an estimate of the electromagnetic to acoustic coupling, and the power flow angle for nine standard crystallographic cuts are obtained. This material is shown to have moderate coupling, low power flow angle, and a temperature coefficient of delay slightly larger than that of LiTaO3.
Properties of PbS-PbO crystalline films. I. Preparation and physical structure
Authors: Said M. Sameh , Zemel Jay N.
Published: February 2003

The physical properties of PbO-PbS, prepared by vapor codeposition on a heated NaCl substrate, were studied. The PbO did not alloy with the PbS, but, instead, segregated out as a finely dispersed separate phase within a single-crystal PbS matrix. Electron diffraction data established that trace amounts of PbSO4 and SiO2β also precipitated. The PbS lattice constant did not vary as the amount of PbO was increased, indicating a very low oxygen solubility in PbS. This is in agreement with thermodynamic data on the PbS-PbO system.
Crossed-molecular-beams investigation of the excitation of ground-state neon atoms by 4.6-eV helium metastables
Authors: Leasure E. L. , Mueller C. R.
Published: February 2003

A molecular beam source has been developed which produces fast metastable helium atoms and was used in a crossed-molecular-beams experiment to measure the absolute differential elastic-collision cross section of these atoms with a velocity-selected beam of ground-state neon atoms. The results at 4.6 eV c.m. show strong evidence of excitations around 5° and 8° c.m. The total excitation cross section was estimated at 1.45 Å2 and probably originates from potential-energy curve crossings at 0.15 and 0.3 eV.
A simple technique for individual picosecond laser pulse duration measurements
Authors: Smith W. L. , Bechtel J. H.
Published: February 2003

We describe here a simple nonlinear optic technique for the measurement of the duration of individual picosecond pulses. The accuracy and relative simplicity of the technique increase with the number of pulses measured. An experimental test of the basis of the technique is described.
Elimination of compression waves induced by pump light in iodine lasers
Authors: Ishii S. , Ahlborn B.
Published: February 2003

Photolytical pumping of iodine lasers with flash-light intensities above W=1.4×105 W/cm2 is expected to eliminate shock waves in the lasing gas, which have disturbed recent high-power-iodine-laser experiments.
Hole traps in silicon dioxide
Authors: Woods M. H. , Williams R.
Published: February 2003

We have measured the properties of holes trapped in an SiO2 layer by application of a large electric field. The high field (1.4×107 V/cm) was obtained by applying a negative corona charge to the outer SiO2 surface of a Si-SiO2 structure. The maximum number of trapped holes was 4×1012 cm−2 and the centroid of their distribution was 130 Å from the Si interface. All holes were trapped within 320 Å of the Si interface. Photodischarge experiments show the level of the trapped holes to be at least 4–5 eV above the valence band edge. We were unable to trap holes in the SiO2 by internal photoemission of holes from the Si. A consistent picture is developed with results that are comparable to those found for trapping holes by irradiation of the SiO2 by a vacuum ultraviolet source.
Effects of proton bombardment on the properties of GaAs laser diodes
Authors: Minden Henry T.
Published: February 2003

Gallium arsenide single-heterostructure lasers were bombarded with protons and annealed. The capacitance and threshold currents were measured. The hole concentration in the active region was calculated from the capacitance. The threshold current increased linearly with decreasing hole concentration over the range investigated. It is postulated that proton bombardment gives rise to damage centers which trap holes. These trapped holes can absorb laser radiation and it is this optical absorption which gives rise to the increased thresholds which are observed in the bombarded lasers.
Persistent photoconductivity in donor-doped Cd1−xZnxTe
Authors: Burkey B. C. , Khosla R. P. , Fischer J. R. , Losee D. L.
Published: February 2003

Phototransport measurements on chlorine-doped Cd1−xZnxTe crystals with 0⩽x⩽0.35 show a persistent impurity photoconductivity below 140 °K. The thermal activation energy of the defect center responsible for both the dark carriers and photocarriers increases from −0.045 eV for x=0 to +0.27 eV for x=0.25 (negative implies above the conduction-band edge), resulting in a decrease of the dark free-carrier density with increasing Zn content. This permits an increasing light-to-dark-conductivity ratio with increasing Zn content, reaching 2.5×105 for x=0.25. The increase of the mobility under photoexcitation indicates the center to be a double acceptor. Thermal emission rate, photoconductivity decay, and optical cross-section measurements are also reported.
Investigations of Mn-doped ZnSe by photocapacitance and photocurrent techniques
Authors: Grimmeiss H. G. , Ovrén C. , Allen J. W.
Published: February 2003

The properties of a deep-level center (the M center) occurring in ZnSe : Mn have been investigated by photocapacitance and photocurrent methods, using both transient and steady-state techniques, over the temperture range 98–293 K. Spectra of the cross sections for optical transitions to the center from the valence band, σop, and from the center to the conduction band, σon, are presented. The threshold energy ΔEop for σop is 0.68 eV, independent of temperature, while the threshold energy ΔEon for σon varies with temperature at the same rate as the band gap Eg. The sum of the two threshold energies differs from Eg by less than 60 meV over the whole temperature range investigated. Thermal excitation from the valence band to the center is characterized by an energy ΔEtp of 0.71 eV. Because the sum ΔEop +ΔEon is close to Eg, and because the thermal energy ΔEtp is close to the optical energy ΔEop, then the Franck-Condon shift of the M center is very small. This is consistent with the observed lack of thermal broadening of the photoionization spectra. The M center may be manganese or it may be a ’’self-activated’’ center. These possibilities are discussed.
Transport properties of glass-silicon heterojunctions
Authors: Dunn B. , Mackenzie J. D.
Published: February 2003

Sevroal properties of glass-silicon heterojunctions have been studied as a function of glass composition. Oxide and chalcogenide glasses of both insulating and semiconducting behavior were investigated. The current-voltage characteristic indicates space-charge-limited currents in the glass film regardless of composition. An exponential trap distribution is suggested and trap density calculations agree with literature results. Capacitance-voltage measurements show that chalcogenide glass/silicon structures behave like ideal abrupt heterojunctions.
Dissociation of MgO films under heat and electron bombardment and its effects on secondary emission
Authors: Dresner J. , Goldstein B.
Published: February 2003

The dissociation of MgO films under heat and bombardment by 1000-eV electrons has been measured in line of sight with a quadrupole mass analyzer. The samples were prepared by oxidizing Mg films in O18. In the range 230<T<500 °C, the thermal dissociation is noncongruent, the yield YO≫YMg. Electron bombardment strongly increases YMg but has no effect on YO; YMg is quadratic in the current density j and saturates at a value close to YO. Both atoms were detected as neutral species; Mg is evolved solely as the monomer, and oxygen is evolved mainly as the monomer, with YO18YO36?10. A model in which the evaporation rates of Mg and O are independently limited by charge transfer at the surface of the insulator is proposed. It accounts for our results as well as the dependence YO∝j2 reported by other investigators, and correctly predicts the dependence on primary energy Y (Ep) ∝j2Ep2.7. The secondary emission δ of cleaned films of MgO is insensitive to prolonged electron bombardment at 0.1 A/cm2. The application of heat alone in vacuo causes changes in δ which have been correlated with changes in surface stoichiometry.
Electronic-to-vibrational pumped CO2 laser operating at 4.3, 10.6, and 14.1 μm
Authors: Petersen Alan B. , Wittig Curt , Leone Stephen R.
Published: February 2003

A pulsed CO2 laser is described in which the pumping mechanism is electronic-to-vibrational energy transfer from bromine atoms in the 42P1/2 state. Observation of stimulated emission in CO2 gives detailed information on the specificity of the E-V process. The laser operates on the usual 10-μm transitions, as well as two new wavelengths regions near 4.3 and 14.1 μm. Pulse energies 112 mJ at 10.6 μm have been obtained by flash photolyzing 80 Torr of a 1 : 1 mixture of Br2 and CO2. Extension of this laser system to high-pressure sealed-off operation is discussed.
ac properties of metal-oxide varistors
Authors: Levinson Lionel M. , Philipp H. R.
Published: February 2003

Measurements of the small-signal ac response of ZnO-based ceramic varistors are reported for frequencies f in the range 30<f<108 Hz and temperatures T in the range −200<T<300 °C. The high effective varistor dielectric constant results from the device microstructure with no detectable electrode contribution. The varistor leakage resistance ρp drops rapidly with frequency, a crude approximation being ρp∼1/ω. A broadened relaxation peak in the dissipation factor D=tanδ is observed at 3×105 Hz at room temperature. The peak has an exponential temperature dependence with an activation energy 0.36 eV.
Effect of adsorbed chlorine and oxygen on the shear strength of iron and copper junctions
Authors: Wheeler Donald R.
Published: February 2003

Static-friction experiments were performed in ultrahigh vacuum at room temperature on copper, iron, and steel contacts selectively contaminated with oxygen and chlorine in submonolayer amounts. The concentration of the adsorbates was determined with Auger electron spectroscopy and was measured relative to the saturation concentration of oxygen on iron (concentration, 1.0). The coefficient of static friction decreased with increasing adsorbate concentration; however, it was independent of the type of metal and the adsorbate species. The results compared satisfactorily with an extension of the junction growth theory to heterogeneous interfaces. The reduction in interfacial shear strength was measured by the ratio sa/sm, where sa is the shear strength of the interface with an adsorbate concentration of 1.0 and sm is the strength of the clean metal interface. This ratio was 0.835±0.012 for all the systems tested.
Effect of crystal composition on the optimization of radiative recombination in N-free and N-doped In1−xGaxP light-emitting diodes
Authors: Nelson R. J. , Holonyak N.
Published: February 2003

The pressure dependence of the band-to-band electroluminescence of In1−xGaxP diodes is measured. By weighting these measurements with the photopic eye response, we determine the optimum In1−xGaxP LED composition to be x?0.67 (E∼2.13 eV, λ∼5800 Å). Recent data for the Γ and X band gaps and also for the N isoelectronic-trap energies in In1−xGaxP : N [i.e., EΓ(x), EX(x), and EN(x), 300 °K] are used to estimate the effects of band-structure enhancement on N-trap-assisted recombination and LED efficiency. The optimum composition for N-doped In1−xGaxP LED’s is determined to be x?0.69 (E∼2.03 eV, λ∼6100 Å). Based on these results, N-doped In1−xGaxP, or In1−xP1−zAsz (z∼0.01), should prove to be a better LED material than N-doped GaAs1−yPy if crystal and junction preparation can be reduced to a practical rather than research art.
Dielectric constants of paraffin-wax–TiO2 mixtures
Authors: Dionne Gerald F. , Fitzgerald James F. , Aucoin Russell C.
Published: February 2003

Moldable mixtures of paraffin wax and TiO2 powders (both rutile and anatase) are easily prepared and are shown to have dielectric constants continuously variable between 2.25 and 7.5 for concentrations of TiO2 up to 35% by volume. Comparison with theory suggests that neither powder has a spherical depolarizing factor, particularly in the case of rutile. These composite materials are very useful for tailoring of dielectric constants in this range, particularly in applications requiring dielectric-filled parts.
On the possibility of pyroelectric currents produced by nonlinear space-charge distributions
Authors: Salomon R. E. , Oh Byung K. , Labes M. M.
Published: February 2003

The inhomogeneous electric field in an insulator containing fixed space charges leads to electrostriction. This electrostriction is temperature dependent and as a result a temperature change causes a distortion of the charge distribution which then leads to a pyroelectric current. This current is calculated in terms of the charge distribution and temperature coefficient of the quadratic electrostriction constant.
Highly-oriented ZnO films by rf sputtering of hemispherical electrode system
Authors: Ohji Kenzo , Tohda Takao , Wasa Kiyotaka , Hayakawa Shigeru
Published: February 2003

Highly oriented ZnO films (c-axis orientation) were fabricated on glass and fused-quartz substrates by an rf-sputtering system with a hemispherical electrode configuration. The sputtered films show a high longitudinal mode electromechanical coupling factor, kt=0.23–0.24. Initial results suggest that the hemispherical electrode configuration may provide improved reproducibility over planar sputtering systems in the preparation of ZnO films for acoustic device applications.
2 1/2D electron microscopy: Through-focus dark-field image shifts
Authors: Bell W. L.
Published: February 2003

A novel technique for transmission electron microscopy is described and some possible applications illustrated. The technique involves the formation of a stereo-optic effect using a through-focus pair of dark-field images. While such stereo-optic pairs do not show the spatial relationships between various objects in the specimen microstructure, they do convey information about the crystallographic relationships. It is shown that this technique, called 2 1/2D imaging, is useful in the study of precipitated phases and it facilitates clear distinction between small precipitates and other microstructural features. This is a powerful method of analysis of complex microstructures in crystallographic terms. Intended as the first report of the technique, the paper broadly discusses the possible applications of 2 1/2D imaging, giving as examples some of the elementary uses in studies of precipitation, recrystallization, deformation, and recovery processes in crystalline materials.
Electron- and photon-induced conductivity in chalcogenide glasses
Authors: Reinhard D. K. , Adler D. , Arntz F. O.
Published: February 2003

A comprehensive study of the effects of electron and photon beams on the electrical properties of rf-sputtered chalcogenide-glass films of composition Te40As35Si15Ge7P3 has been carried out. Optical results indicate that the material has a gap near 1.1 eV. Four major conclusions follow from a detailed investigation of the field and polarity dependence of the photocurrent: (1) the exponential increase of dark conductivity with electric field intensity is a carrier concentration rather than a mobility effect; (2) internal fields exist at molybdenum-chalcogenide junctions; (3) hole conduction dominates electron conduction at room temperature; (4) the chalcogenide bands bend up at the interface with molybdenum electrodes. Electron-beam-induced conductivity (EBIC) resulting from bombardment by 5–20-keV electrons has also been studied as a function of applied voltage on these films. A threshold energy of about 7 keV is necessary to obtain an EBIC signal, resulting from a schubweg of the order of 1000 Å and a film thickness of 1 μm. The photoconductivity and EBIC results are consistent and indicate that the product of mobility and lifetime for the carriers in these materials is approximately 2×10−10 cm2/V. This corresponds to carrier lifetimes of the order of 2×10−11 sec. The drift mobility is trap controlled and of the order of 2×10−5 cm2/V sec.
Electrical properties of manganese-doped gallium phosphide
Authors: Evwaraye A. O. , Woodbury H. H.
Published: February 2003

Single crystals of GaP : Mn were grown by the LEC and VGF techniques. From Hall-effect measurements, a simple acceptor defect with an energy level 0.4–0.43 eV from the valence band was observed, the higher values being characteristic of light doping. EPR shows an isotropic spectrum with a g value of 2.002 which suggests a d5 configuration in cubic symmetry. This implies that the principal defect in as-grown material involves Mn on lattice sites in place of gallium and that there is no complexing with vacancies or with other impurities. Other levels, however, are seen following anneals.
Alloys of Sn and Ge on Nb surfaces
Authors: Strozier John A. , Miller D. L. , Kammerer O. F. , Strongin Myron
Published: February 2003

An investigation of possible surface effects on the formation of the superconducting compounds Nb3Sn and Nb3Ge is reported. Low-energy electron diffraction and Auger electron spectroscopy were used to determine the symmetries and approximate compositions of surface compounds formed by reactions of fractional monolayers of Sn and Ge with the Nb[100] and Nb[110] surfaces. A number of ordered surface structures were observed for each of these elements when reacted with Nb, but epitaxial growth of Nb3Sn or Nb3Ge was not observed. With deposition of sufficient Sn, a disordered growth of Nb3Sn crystallites was obtained at temperatures up to 940 °C; however, deposits of Ge greater than about one atomic layer diffused into the Nb interior when heated, and no bulk Nb-Ge compounds were observed.
X-ray topographic study of magnetic domains in a single crystal of terbium iron garnet between 300 and 4.2 K
Authors: Mathiot A. , Petroff J. F.
Published: February 2003

(110) slices of TbIG have been studied by means of x-ray transmission topography between room temperature and liquid-helium temperature. This work gives most of the results concerning the variations of the domain structure with the temperature. The room-temperature structure is limited by a rectangular array of 71° and 109° walls separating domains where the magnetization lies in the plane of the sample. It corresponds to the equilibrium configuration in a perfect crystal. The domain density increases sharply when the temperature is lowered, and a preferential occurrence has been observed for the (1̄10) 71° walls at low temperature. The wall contrast, due to magnetostrictive stresses, is also temperature sensitive. In order to understand these experimental evidences, the surface energies of the 71° and 109° walls have been calculated, using a classical model of the Bloch wall structure. This calculation shows the predominant importance, at low temperatures, of the K2 term and the additional magnetostrictive contribution to the development of the magnetocrystalline anisotropy energy. It would certainly be of great interest from a physical point of view to start from the atomic model of the magnetic structure in order to understand the internal structure of the magnetic domain walls in the garnets at low temperature.
Numerical solution of magnetostatic boundary-value problems by iterative integration using the Green’s function
Authors: Lucas Ilse
Published: February 2003

The integral equation associated with magnetostatic problems is expressed by two different representations in which the unknown variable in one case is the charge density, while in the other it is the current density at the surfaces of magnetizable and superconducting bodies. Both representations are mathematically equivalent and complement each other in spatial field calculations which involve integrals of different numerical convergence. An iterative numerical integration method is proposed for solving the integral equations, whose kernel contains a Green’s function. The method is demonstrated for a superconducting cylindrical shield in an outer longitudinal field and for magnetic pole shoes of given permeability. The results of the first four iterative steps are seen to exhibit rapid convergence.
Narrow Bloch walls in the RCo5-type rare-earth–cobalt compounds
Authors: Buschow K. H. J. , Brouha M.
Published: February 2003

For compounds of the type YCo5xNi5−5x the saturation moment and Curie temperature were determined. For large Co concentrations the rigid-band approach applies. The magnetic splitting of the 3d band collapses near x=0.2. Magnetic isotherms were studied at 4.2 K as a function of concentration. The form of the virgin magnetization curve, the presence of large intrinsic coercive forces, and the observation of pronounced thermomagnetic history effects suggest the presence of narrow Bloch walls of only a few interatomic distances in these compounds. It is argued that the presence of narrow Bloch walls is the primary reason for the high coercive forces observed usually in solid pieces of materials of the type RCo5xCu5−5x.
Range profiles of 6–16-keV hydrogen ions implanted in metal oxides
Authors: Bøttiger J. , Leslie J. R. , Rud N.
Published: February 2003

The range profiles of 6–16-keV hydrogen ions implanted in the amorphous metal oxides Al2O3, Nb2O5, Ta2O5 have been measured. The profiles were determined by use of the nuclear reaction 1H(19F,αγ)16O. Good agreement with theoretical predictions is observed for the most probable ranges, while the widths of the experimental distributions are substantially larger than theoretically calculated for Al2O3 and Nb2O5.
Separate estimate of crystalline orientations and scattering centers in polycrystals by backscattering technique
Authors: Ishiwara Hiroshi , Furukawa Seijiro
Published: February 2003

A novel method using backscattering and channeling techniques is presented to estimate separately two dominant dechanneling factors in polycrystals, that is, spread of crystallite orientations and existence of scattering centers. It is theoretically shown that both factors can independently be estimated by measuring angular dependences of backscattering yield around the channeling axis. The angular dips on Pd2Si layers formed on single-crystalline Si substrates are measured by using 1–2-MeV protons, He+, and N+ ions. The channeling measurements using N+ ions are shown to be a useful tool for analysis of polycrystalline layers. By using the above method, crystalline perfection of these layers is also discussed.
The role of grain-boundary structure in shock-induced spallation of molybdenum
Authors: Murr L. E.
Published: February 2003

Grain boundaries and grain-boundary ledge structures are shown to have a controlling influence on intergranular spallation in molybdenum resulting from shock-wave rarefraction interactions. The structure of grain boundaries and their relationship to spall fracture are examined in detail utilizing the techniques of transmission and scanning electron microscopy, and are shown to be conducive to microcrack nucleation, coalescence, and propagation along the boundary planes. Grain boundaries possessing a high degree of complex structure such as dislocations and ledges are shown to vary significantly in effective dislocation density from the grain matrices, and this phenomenon coupled with the ability of ledges to nucleate cracks appears to account for intergranular spallation in molybdenum shock loaded to pressures of 150 and 250 kbar.
Diffusion-model interpretation of the darkening and fading of photochromic glasses
Authors: Araujo R. J. , Borrelli N. F.
Published: February 2003

It has been verified that in photochromic glasses containing copper-cadmium halides the fading depends on darkening conditions. The diffusion model described is consistent with observed darkening and fading kinetics, intensity dependence of equilibrium darkening, darkening time dependence of the initial fading rate, and depth dependence of equilibrium darkening.
Electrical and far-infrared optical properties of p-type Hg1−xCdxTe
Authors: Scott Walter , Stelzer E. L. , Hager R. J.
Published: February 2003

Electrical transport measurements have been made on p-type Hg1−xCdxTe with carrier concentrations ranging from 4×1015 to 1×1017 cm−3 and with x in the range 0.26–0.6. The acceptor ionization energy was determined to be about 14 meV by measurement of carrier freeze out in Hg0.6Cd0.4Te. Far-infrared photoconductivity and transmittance measurements in Hg0.6Cd0.4Te were used to verify this ionization energy of the acceptor. Calculations of both the ionized-impurity-scattering-limited mobility and the Hall coefficient as functions of temperature indicate that the p-type Hg1−xCdxTe crystals are compensated.
Intracavity absorption of dye lasers: A rate-equation model
Authors: Tohma Katsusuke
Published: February 2003

Characteristics of cw lasers with intracavity absorption have been discussed by taking account of the spatial relaxation as well as mode competition. A comparison is made with the conventional single-path absorption method, under the same conditions, for estimating the absorption enhancement factor. Weak pumpings, strong mode competition, large spatial relaxation, and wide-band operation bring about tremendous enhancements of absorption.