bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron attachment to H2O in Ar, N2, and CH4 in electric field
Authors: Wang W. C. , Lee L. C.
Published: July 2002

The attachment of electrons to H2O in Ar, N2 or CH4 is investigated using a parallel-plate drift-tube apparatus. Electrons are produced either by irradiation of the cathode with ArF laser photons or by two-photon-ionization of a trace of trimethylamine in a buffer gas. The transient voltage pulses induced by the electron motion between the electrodes are observed. The electron attachment rate of H2O is determined from the ratio of transient voltage with and without H2O added to the buffer gas. The measured electron attachment rate constants of H2O in Ar increase with E/N from 2 to 15 Td. Electron attachment due to the formation of ‘‘temporary’’ negative ions in the H2O–N2 and H2O–CH4 mixture were observed. The lifetime of the negative ion was determined to be about 200 ns, whose nature is discussed. The ‘‘apparent’’ electron attachment rate constants for the formation of ‘‘temporary’’ negative ions in the H2O–CH4 gas mixture are measured for E/N from 1 to 20 Td. The electron drift velocities for the gas mixtures of H2O in various buffer gases are measured.
Collisional cross sections of CCl2F2 and transport coefficients of CCl2F2 and N2-CCl2F2 mixtures
Authors: Novak J. P. , Fréchette M. F.
Published: July 2002

A set of effective electron collision cross sections, including momentum transfer, vibration, and electron excitation collisions has been determined for CCl2F2 gas: the momentum transfer is approximately 2×10−15 cm2 with the highest maximum about 4×10−15 at 6 eV, two vibrational maxima with thresholds of 0.11 and 0.14 eV are about 9 and 4 (10−16 cm2) at 0.2 and 0.25 eV and two excitation maxima with thresholds of 7.0 and 9.8 eV are 2.8 and 5.1 (10−16 cm2) at 11 and 18 eV, respectively. The calculated transport coefficients are in satisfactory agreement with measured values, except for the attachment coefficient, which is too high at low (below 90 V cm−1 Torr−1) and high (above 180 V cm−1 Torr−1) reduced fields. The possibility of comparison in the case of N2-CCl2F2 mixtures is limited and agreement is less satisfactory than in the case of pure CCl2F2. Deviations for medium fields are within about 30% for the D/μ ratio and ionization coefficients. The attachment coefficients agree well at high partial density of CCl2F2 (above approximately 50%) but the experimental values are much higher than predicted at low CCl2F2 content. Calculated values of the limit fields agree well with the values obtained from breakdown potential measurements available in the literature.
Magnetic form factor of 5f electrons in PuSb
Authors: Lander G. H. , Delapalme A. , Brown P. J. , Spirlet J. C. , Rebizant J. , Vogt O.
Published: July 2002

The magnetic form factor of the 5f electrons around the Pu nucleus has been measured with neutrons. The experiment used polarized neutrons and a single crystal of weight 55 mg of PuSb. This compound, which has the NaCl crystal structure, is ferromagnetic below 67 K. The experiment was done in the ordered state with an applied field of 46 kOe. The results show that the Pu ion is trivalent; we see the maximum in f(Q) at Q≂2.5 Å−1, which is the unambiguous signature of the 5f5 state. A detailed analysis shows that the ground-state wave function is close to that of a Γ8 state in intermediate coupling. The analysis makes use of the large azimuthal anisotropy (variation in magnetic scattering depending on the angle the scattering vector makes with the magnetic moment) and is not consistent with any possible Γ7 state.
Time dependence of magnetization decay in spin glasses
Authors: Aharoni Amikam
Published: July 2002

A gamma distribution of relaxation times integrates to a modified Bessel function time dependence. It is suggested that it be used in analyzing the time decay of thermoremanent magnetization, or other complex systems of exponential decays.
Channeling of aluminum in silicon
Authors: Wilson R. G. , Hopkins C. G.
Published: July 2002

A systematic study of channeling of aluminum in the silicon crystal is reported. Depth distributions measured by secondary ion mass spectrometry are reported for 40-, 75-, and 150-keV aluminum channeled in the 〈100〉 and 〈110〉 directions of silicon. The profile dependence on alignment angle is shown for 150-keV aluminum in the 〈110〉 of silicon. Aluminum has low electronic stopping in silicon and corresponding deep channeled profiles are observed for aligned implants and deep channeling tails are observed on random implants. The maximum channeling range for 150-keV Al in 〈100〉 silicon is about 2.8 μm and is about 6.4 μm in 〈110〉 silicon. Some ions will reach the maximum channeling range even for 2° misalignment. Many of the deep channeling tails and ‘‘supertails’’ reported in earlier literature can be explained by the normal channeling of aluminum in silicon.
Laser performance of Cr3+:Gd(Sc,Ga) garnet
Authors: Struve B. , Huber G.
Published: July 2002

We analyze the free-running and tunability characteristics of the Cr3+:Gd(Sc,Ga) garnet laser under laser pumping at different wavelengths. Slope efficiencies up to 28%, tunable cw output powers of 200 mW, and a tuning range from 742 to 842 nm were achieved. Excited state absorption of the pump light leads to pumping efficiencies smaller than one, depending on the pump light wavelength and the threshold inversion density. First results of laser experiments with Cr3+:GdGa garnet and Cr3+:(La,Lu)(Lu,Ga) garnet are reported.
A model for pulsed laser melting of graphite
Authors: Steinbeck J. , Braunstein G. , Dresselhaus M. S. , Venkatesan T. , Jacobson D. C.
Published: July 2002

A model for laser melting of carbon at high temperatures to form liquid carbon has been developed. This model is solved numerically using experimental data from laser irradiation studies in graphite consistent with a melting temperature for graphite of 4300 K. The parameters for high-temperature graphite are based on the extension of previously measured thermal properties into the high-temperature regime. A simple classical free electron gas model is used to calculate the properties of liquid carbon. There is very good agreement between the model calculation and experimental results for laser pulse fluences below 2.0 J/cm2. Modifications to the model for larger laser pulse fluences are discussed.
Silicon strained layers grown on GaP(001) by molecular beam epitaxy
Authors: Marée P. M. J. , Olthof R. I. J. , Frenken J. W. M. , van der Veen J. F. , Bulle-Lieuwma C. W. T. , Viegers M. P. A. , Zalm P. C.
Published: July 2002

Mismatch-induced lattice strain in thin Si films grown by molecular beam epitaxy on GaP(001) substrates has been measured using transmission electron microscopy, Raman spectroscopy, and Rutherford backscattering. The perpendicular strain in the topmost part of the layers is found to be enhanced in comparison to elasticity theory. Relaxation of the strain occurs by the formation of misfit dislocations at significantly larger thickness than predicted by equilibrium theory.
The formation of a negative hydrogen ion beam by surface conversion of a positive ion beam on cesiated tungsten surfaces
Authors: van Bommel P. J. M. , Bonnie J. H. M. , Granneman E. H. A. , Massmann P. , Hopman H. J.
Published: July 2002

Presented are measurements on the generation of negative hydrogen ion beams via the conversion of positive ion beams on low work function surfaces placed outside the positive ion source. The converter surfaces are positioned parallel to the beam axis and the positive ion beam is directed onto them by the increase of the beam divergence caused by beam retardation. Results include a negative hydrogen ion beam current of 15 mA at a current density of 6.2 mA/cm2. The converter work function is lowered by the deposition of a Cs monolayer. The Cs coverage could be maintained during the bombardment by the intense H+ beam through surface migration of the Cs from a reservoir.
Ultrasonic method to determine gas porosity in aluminum alloy castings: Theory and experiment
Authors: Adler Laszlo , Rose James H. , Mobley Carroll
Published: July 2002

The characterization of porosity in solids using the frequency dependence of the ultrasonic attenuation is discussed both from the theoretical and experimental viewpoint. The major thrust of our work is the determination of the volume fraction and size of the voids for the case of dilute porosity (<6%) in structural materials. An aluminum alloy (A357) was chosen for study due to its economic importance in large-scale casting and the particular suitability of aluminum for this type of study. Following recent papers the attenuation is described by an independent scatterer model for spherical voids. Numerical results are presented in a form suitable for use with a range of materials. A method for determining the volume fraction and pore size is given. Specific tabular results are given for stainless steel, IN-100, Ti, Si3N4, as well as aluminum. Figures of merit which partially describe those situations in which the method is usable are also presented. In the experimental work a digitized spectrum analysis system was used to measure the frequency dependence of the attenuation coefficient in A357 aluminum cast alloys. In the cast materials the average pore size was in the order of 100 μm and the pore concentration varied from essentially 0 to 6%. It was found that experimental measurement of the attenuation could be fit by the theoretical model. The resulting parameters yield a good estimate of the pore volume fraction.
Deep-level transient spectroscopy and photoluminescence studies of electron-irradiated Czochralski silicon
Authors: Awadelkarim O. O. , Weman H. , Svensson B. G. , Lindström J. L.
Published: July 2002

Isothermal annealing of electron-irradiated Czochralski silicon samples (n-type) has been performed at 335 °C. The annealing process was studied using deep-level transient spectroscopy (DLTS) and photoluminescence (PL). The dominating level in the DLTS spectra directly after irradiation is located ∼0.18 eV below the conduction band and has previously been assigned to a vacancy-oxygen center by other authors. During the anneal the concentration of vacancy-oxygen centers decreases, and simultaneously a new level, ∼0.20 eV below the conduction band, grows up. It is shown that the defect giving rise to this new level may be vacancy related. The PL spectra directly after irradiation are dominated by the G line (969 meV) and the C line (790 meV). The G line disappears rapidly, while the C line is still present after 320 min at 335 °C. During the heat treatment some new lines appear, e.g., the P line (767 meV) and a line at 950 meV. Based on the annealing kinetics, it is speculated that the 950-meV defect may be vacancy related.
Metal deposition from a supported metal film using an excimer laser
Authors: Bohandy J. , Kim B. F. , Adrian F. J.
Published: July 2002

A method for the direct writing of metal features from a metal film supported on an optically transparent substrate using a single pulse from a high-energy excimer laser (193 nm) is presented. The technique eliminates the need for gas-phase precursors in many cases and is an inherently clean process. Results of copper depositions onto silicon substrates are shown to exemplify the technique and a mechanism for the process is proposed.
Structural and magnetic properties of R2Fe14−xTxB (R=Nd, Y; T=Cr, Mn, Co, Ni, Al)
Authors: Abache C. , Oesterreicher H.
Published: July 2002

Trends in structural and magnetic parameters are presented and discussed for Nd2Fe14−xTxB with T=Cr, Mn, Co, Ni, Al. Some data are also included on the Y analog systems. Partial Al substitution strongly increases c/a. We show that this has to do with preferential occupation of the larger atom (Al) in the σFe layer. Co and Ni substitutions increase Curie temperature (TC) while all others decrease it. Anisotropy constants K for 300 K decrease in all cases investigated compared to Nd2Fe14B. Some discussion is given to the general mode of preferential substitution and the concomitant effects on magnetic anisotropy.
Ambient-induced surface effects on InP and GaAs
Authors: Lester S. D. , Kim T. S. , Streetman B. G.
Published: July 2002

The effects of gas ambient changes on the photoluminescence (PL) intensity and the conductivity of chemically cleaned (100) InP and GaAs have been investigated. The room-temperature PL intensity of n-type, p-type, and Fe-doped semi-insulating InP is found to be reversibly changed by the presence of various gases at the semiconductor surface. The resistivity of thin-film InP resistors is also found to be affected by gas ambient changes, both under illumination and in the dark. These measurements show that the surface Fermi level of InP is not tightly pinned and is reversibly changed by exposure to different ambients. The PL intensity and surface conductivity of GaAs are also found to be sensitive to the gas environment, though to a lesser degree than InP. The responses of InP and GaAs are of a different nature and suggest that the surface state densities of these materials are reversibly affected by the chemisorption of oxygen. This in turn suggests that there are adsorbate-induced surface states on InP and GaAs which arise as a result of the interaction of adsorbed oxygen with the semiconductor surface and that are not associated with intrinsic semiconductor defects.
InGaP/InGaAlP double-heterostructure and multiquantum-well laser diodes grown by molecular-beam epitaxy
Authors: Tanaka Hidenao , Kawamura Yuichi , Nojima Shunji , Wakita Koichi , Asahi Hajime
Published: July 2002

Room-temperature continuous-wave (cw) operation is achieved in the MBE (molecular-beam epitaxy)-grown InGaP/InGaAlP double-heterostructure (DH) visible laser diodes with a threshold current of 110 mA. The lasing wavelength and threshold current density under pulsed operation are 666 nm and as low as 3.9 kA/cm2, respectively. This result is achieved by the introduction of H2 into the growth chamber during growth, the continuous growth from one layer to the next layer, and the introduction of a GaAs buffer layer. InGaP/InGaAlP quantum well structures are also grown. From photoluminescence measurements, the conduction-band discontinuity ΔEc is estimated to be 0.43 of the band-gap difference ΔEg. Furthermore, the multiquantum-well (MQW) structure is found to be stable under thermal treatment at temperatures as high as 750 °C. Room-temperature pulsed operation of InGaP/InGaAlP MQW laser diodes is achieved for the first time. The lasing wavelength is 658 nm with a threshold current density of 7.6 kA/cm2. cw operation is also achieved in the MQW laser diodes at −125 °C.
Raman spectra of AlxIn1−xAs grown by molecular-beam epitaxy
Authors: Emura Shuichi , Nakagawa Tsuyoshi , Gonda Shun-ichi , Shimizu Saburo
Published: July 2002

Raman study of the lattice vibrations of a ternary alloy AlxIn1−xAs on InP substrate over the whole range of compositions is reported. The Raman spectra show a two-mode-type behavior involving AlAs- and InAs-like longitudinal optical-phonon modes. The frequency of the AlAs-like mode strongly depends on the composition, but frequency of the InAs-like mode is almost independent of composition. A disorder-induced scattering by acoustic vibrations is also observed.
Determination of two-dimensional temperature and additive density distributions in a high-intensity-discharge lamp arc
Authors: Rogoff G. L. , Feuersanger A. E. , Drummey J. P. , Rothwell H. L.
Published: July 2002

Demixing of additive species can lead to significant axial and radial nonuniformities in the electrical and radiative characteristics of a vertical high-pressure arc. An optical emission method has been developed to determine both the radial and axial distributions of temperature and additive density as well as the pressure in a rotationally symmetric, enclosed arc in local thermodynamic equilibrium. The method can be used if one knows the vaporized quantity of the major component of the gas mixture in the arc tube. The procedure has been demonstrated by applying it to an ac 175-W Na-Sc-Hg lamp arc, with mercury the major component and sodium the additive of interest. An optically thin Hg line and an optically thin portion of the broadened Na D line were used. The resulting distributions clearly show the effects of segregation; the upper portion of the arc and the axial regions are significantly depleted of sodium.
Dependence of the electrical characteristics of organic-on-inorganic semiconductor contact barrier diodes on organic thin-film composition
Authors: So F. F. , Forrest S. R.
Published: July 2002

Several aromatic compounds (such as 3,4,9,10 perylenetetracarboxylic dianhydride) have previously been reported to form rectifying heterojunction energy barriers when vacuum deposited onto inorganic semiconductor substrates such as Si, GaAs, and InP. In this paper we report the formation of rectifying heterojunction barriers using phthalocyanine-based compounds layered onto p-Si substrates. In many respects, the characteristics of phthalocyanine/Si heterojunctions are similar to those formed using the aromatic anhydrides insofar as the electrical properties can be explained using the thermionic emission space-charge-limited transport model introduced in previous work. However, in contrast to the earlier results, we find that a high density of surface states exist at the phthalocyanine/Si interface. Quantitative study of the interface state density provides insight into the mechanisms of formation of the organic-on-inorganic energy barrier.
Reduction of surface acoustic wave grating impedance and velocity perturbations via buried bimetallic electrode geometries
Authors: Hunt W. D. , Hunsinger B. J.
Published: July 2002

The impedance and velocity perturbations presented to the leaky wave by the nondestructive sense (NDS) electrodes in GaAs acoustic charge transport (ACT) devices are of particular concern in the design of high quality ACT devices. An example is shown where large perturbations and improperly designed NDS arrays resulted in substantial leaky wave propagation loss. The full form of the Datta and Hunsinger velocity and impedance perturbation equations is presented for the case of buried bimetallic grating arrays and it is shown that, with the proper choice of groove depths and metal thicknesses, it is theoretically possible to simultaneously reduce the impedance and velocity perturbations to negligible values. It is by such a procedure that a ‘‘perturbationless’’ array can be made. Laser probe measurements of the reflection coefficient and velocity perturbation for three buried chrome-gold grating devices demonstrate the feasibility of achieving this theoretical ideal.
Optical switching of a dc discharge using an excimer laser
Authors: Saporoschenko Mykola , Rossi Michel J. , Helm Hanspeter
Published: July 2002

The effects of unfocused 193- and 248-nm laser radiation of 3–30 mJ/cm2 on dc discharges of vinylchloride in helium are described. Laser-initiated striking and quenching of the low-current discharges are observed at pulse repetition rates of 10 to 0.001 s−1 over a range of operating conditions. The apparent paradox of the coexistence of strike and quench conditions in the discharge gap for consecutive laser pulses is discussed.
Magnetic viscosity in recording media
Authors: Charap S. H.
Published: July 2002

Assuming a continuous distribution of relaxation times or frequencies responsible for magnetic aftereffect, it is shown that the inverse Laplace transform of the relaxing magnetization M(t) yields the function g(f)/f, where g(f) is the distribution of relaxation frequencies. Published data for carbonyl iron is fitted by the form M(T)/M0=(1+t/t0)−n, with n=1.5 and t0 =26 ms. The corresponding distribution of relaxation frequencies is g(f)∼(ft0)n  exp(−ft0). Using a simple, noninteracting particle model of a recording medium based upon the switching field distribution of the material, we have calculated the change in magnetization (decay) between 100 and 1000 s after applying a reversing field. A Lorentzian switching field distribution 20 Oe wide and centered at 200 Oe was assumed. The decay over this time span versus applied field is determined for various temperatures between 6 and 300 K. As the temperature is reduced, the field for peak decay increases, approaching the assumed value of Hc (200 Oe) as the temperature approaches zero, and the height of the peak is simultaneously reduced. The heights of these peaks versus temperature approximate a T0.5 variation.
Electrochromic nickel-oxide-based coatings made by reactive dc magnetron sputtering: Preparation and optical properties
Authors: Estrada Walter , Andersson Anne M. , Granqvist Claes G.
Published: July 2002

NiOx films were made by dc magnetron sputtering of Ni in O2 at a rate of <0.15 nm s−1. The grain size was ∼10 nm and the crystal structure was cubic. Electrochemical hydration, and ensuing conversion to electrochromic NiOxHy, took place in KOH. Spectrophotometric measurements in the 0.35–2.5-μm range showed that it took >100 color-bleach cycles to establish a fully bleached state. When removed from the KOH electrolyte, a colored NiOxHy film increased its transmittance by <1% per h. The luminous and solar transmittance could be varied between 80% and 20% and between 74% and 29%, respectively.
The conductivity behavior in lead zirconate titanate polyvinylidene fluoride composites
Authors: Sinha Dolly , Pillai P. K. C.
Published: July 2002

Studies on the conductivity in lead zirconate titanate polyvinylidene fluoride (PZT-PVDF) composite have been done for different weight fractions of PZT in a PVDF matrix in the 0–3 connectivity pattern. The results obtained show that the major contribution to the conductivity is from the polymer phase rather than from the ceramic phase. A kink has been observed around 80–90 °C for all the composites in the ln σ∼ f(1/T) curve. The activation energies for all the composites are less below this temperature than above. This has been attributed to a phase change in the PVDF matrix at this temperature. The results have been correlated to IR, x-ray diffraction (XRD) spectra, hysteresis, and dielectric studies.
The random free-energy barrier model for ac conduction in disordered solids
Authors: Dyre Jeppe C.
Published: July 2002

A brief review of the history of ac ionic and electronic conduction in disordered solids is given, followed by a detailed discussion of the simplest possible realistic model: the random free-energy barrier model. This model assumes conduction takes place by hopping, where the hopping charge carriers are subject to spatially randomly varying energy barriers. The model is solved in the continuous time random walk and in the effective medium approximation, and it is shown that the two solutions are almost indistinguishable. In the random free-energy barrier model, the frequency-dependent conductivity is completely determined by the dc conductivity and the dielectric loss strength. The model correctly predicts all qualitative features of ac conduction in disordered solids, and a comparison to experiment on a large number of solids shows that the model is also quantitatively satisfactory.
Pulsed-laser optogalvanic spectroscopy in a high-pressure Hg discharge
Authors: Kramer Jerry
Published: July 2002

Pulsed-laser irradiation of a high-pressure mercury discharge tuned to excite the 7 3S1←6 3P2,1,0 transitions in mercury at 546, 436, and 405 nm, respectively, decreased the voltage across the discharge and increased the current through the discharge with respect to their unperturbed values. The peak magnitude of the voltage decrease was proportional to the peak current increase, but the temporal dependence of the two signals was different. The optogalvanic signal was a maximum in the center of the discharge and decreased towards the walls. The full width at half maximum (FWHM) of the optogalvanic line profile also depended on radial position. The magnitude of the optogalvanic signals had a nonlinear dependence on laser energy, and the FWHM of the optogalvanic line profile increased with laser energy. Both of these effects were attributed to stimulated emission. Negative optogalvanic voltage signals were also observed at 408 nm (7 1S0←6 3P1), 577 nm (6 3D2←6 1P1), and 579 nm (6 1D2←6 1P1). Estimates of reaction rates support the following mechanism: Absorbed laser energy is rapidly converted to increased electron kinetic energy by superelastic collisions, which results in increased ionization in the discharge. The additional ionization decreases the voltage across the discharge and increases the current through the discharge.
Attachment of low-energy electrons to HCl
Authors: Petrović Z. Lj. , Wang W. C. , Lee L. C.
Published: July 2002

The electron-attachment rate constants of HCl diluted in Ar and N2 were measured as a function of the reduced electric field E/N. These data were converted to the electron-attachment cross section of HCl using the electron-energy distribution functions of pure Ar and N2. The dependence of the electron-attachment rate constant and the mean electron energy on the fraction of HCl in each buffer gas was investigated. A comparison of the current result with both available experimental data and theoretical calculations is made.
Nucleation in a ferromagnetic sphere with surface anisotropy
Authors: Aharoni Amikam
Published: July 2002

The whole eigenvalue spectrum is studied for the nucleation field in a sphere with a uniaxial surface anisotropy. Detailed calculation is given for the magnetization buckling mode in such a sphere, which is the only reversal mode for rather small radii before the onset of the magnetization curling mode.
Surface recombination in GaAlAs/GaAs heterostructure bipolar transistors
Authors: Tiwari Sandip , Frank D. J. , Wright Steven L.
Published: July 2002

Experimental evidence shows that surface recombination in npn GaAlAs/GaAs heterostructure bipolar transistors changes from an exp(qV/2kT) dependence at low currents to an exp(qV/kT) dependence at high currents. Using a one-dimensional analysis, Henry, Logan, and Meritt [J. Appl. Phys. 49, 3530 (1978)] have derived a 2kT dependence for surface recombination in the presence of Fermi-level pinning and flat quasi-Fermi levels between the surface and the bulk. We find that the kT dependence, which dominates at high bias, arises when the recombination rate is limited by availability of minority carriers at high surface recombination velocities. The quasi-Fermi levels do not remain flat at high surface recombination velocities. Two-dimensional effects are also shown to be strong and influential in limiting the availability of carriers.
Detailed atomic scale structure of AlInAs/GaInAs quantum wells
Authors: Bimberg D. , Oertel D. , Hull R. , Reid G. A. , Carey K. W.
Published: July 2002

Quantification of high-resolution transmission electron microscopy (HRTEM) lattice images and detailed luminescence line-shape analysis is used to determine the atomic structure of GaInAs quantum wells (QWs) between AlInAs barriers. By careful analysis of a statistically large number of HRTEM images, we are able to measure the standard deviation in the mean quantum-well width to better than one (200) monolayer. Statistical analysis of the temperature dependence of the luminescence yields QW width distribution functions and variations of the mean QW width across the sample with a precision of better than 0.2 nm in quantitative agreement with the transmission electron microscopy results. No large and smooth islands with monolayer steps in between but rather long-range mean band-gap fluctuations are observed. Spectral broadening is found to be induced by well-width-dependent roughness of inequivalent growth surfaces and by clustering in the barriers for extremely narrow wells of the order Lz≊1 nm. Our results indicate a pronounced surface roughening of InGaAs at 640 °C. The mean height of steps of a maximum width of 5 nm at the InGaAs surface increases from 1 to 2 monolayers for an increase of well width from ≊1 to 2.5 nm.
The influence of low-energy argon implantation on gallium arsenide Schottky barriers
Authors: Wang Y. G. , Ashok S.
Published: July 2002

The influence of ion bombardment damage on the properties of Au/GaAs Schottky barriers has been studied with 10-keV Ar implanted into both n-type and p-type GaAs over the dose range 1012–1015 cm−2. Electrical characteristics determined over a wide temperature range (77–360 K) reveal a number of phenomena dictating barrier modification and carrier transport across the Au/GaAs interface: Change in Schottky barrier height due to defect levels introduced by ion damage, the very low threshold dose for barrier modification, increased series resistance, and creation of a shunt conducting path. Partial dynamic annealing of defects is also observed under high-temperature (≂200 °C) implantation.
Conduction mechanisms in sputtered Ta2O5 on Si with an interfacial SiO2 layer
Authors: Banerjee S. , Shen B. , Chen I. , Bohlman J. , Brown G. , Doering R.
Published: July 2002

The temperature dependence of leakage in sputtered Ta2O5 films (10–30 nm) on Si substrates with an interfacial SiO2 layer has been studied for temperatures between –50 and +100 °C and for electric fields between 0 and 2 MV/cm. The activation energy of leakage and the current-voltage relationships have been used to identify various high field conduction mechanisms such as Poole–Frenkel transport at high temperatures and field emission at low temperatures. At low fields and intermediate temperatures, electronic hopping conduction leading to space-charge-limited flow at high current densities has been observed.
Optical dispersion relations for GaP, GaAs, GaSb, InP, InAs, InSb, AlxGa1−xAs, and In1−xGaxAsyP1−y
Authors: Adachi Sadao
Published: July 2002

A method is described for calculation of the optical constants (the refractive index, extinction coefficient, and absorption coefficient) of some III-V binaries (GaP, GaAs, GaSb, InP, InAs, and InSb), ternaries (AlxGa1−xAs), and quaternaries (In1−xGaxAsyP1−y) in the entire range of photon energies (0–6.0 eV). The imaginary part of the dielectric function [ε2(ω)] is derived first from the joint density-of-states functions at energies of various critical points (CPs) in the Brillouin zone; then its real part [ε1(ω)] is obtained analytically using the Kramers–Kronig relation. The indirect band-gap transitions are also assumed to provide a gradually increasing ε2 spectrum expressed by a power law of (ℏω−EIDg)2, where ℏω is the photon energy and EIDg is the indirect band-gap energy. The optical dispersion relations are expressed in terms of these model dielectric functions. The present model reveals distinct structures in the optical constants at energies of the E0, E0+Δ0 [three-dimensional (3-D) M0 CP], E1, E1+Δ1 [3-D M1 or two-dimensional (2-D) M0 CP], and E2 or E′0 (triplet) (damped harmonic oscillator). Excellent agreement is achieved between our calculations and published experimental data for these semiconductors over a wide range of the photon energies.
Mössbauer effect determination of chemical segregation in sputtered Co-Cr films
Authors: Parker F. T. , Oesterreicher H. , Fullerton E.
Published: July 2002

Mössbauer spectroscopy has been used to determine several of the features of sputtered Co-Cr films. Isotopically enriched 57Fe was used as a probe in the films and in bulk alloys employed as calibration standards. Film stoichiometries from 14.5 to 32 at. % Cr were measured. Three phases are observed. For films sputtered at 200 °C substrate temperature, one phase (about 40 at. % of the films) has a composition close to the overall film composition. The second and most accurately determined phase is Co rich, showing increasing Cr concentration and decreasing mole fraction with increasing overall Cr content. For example, a 21.3 at. % Cr film contains a Co-rich phase with 6.0 at. % Cr. The third phase is Cr rich and nonmagnetic. Compositions have been determined indirectly through the film saturation moments. Assuming the Fe:Co ratio is constant in the various phases, the third phase contains about 37 at. % Cr for nearly all overall film compositions, close to the σ-phase boundary. The relative amount of this phase increases with increasing total Cr. Segregation occurs for Cr film concentrations at least as low as 14 at. %. The mechanism of segregation seems to be nucleation and growth rather than spinodal. For perpendicularly oriented films, Mössbauer polarization data show no evidence of in-plane moments. Low-temperature Mössbauer data show negligible temperature-dependent relaxation.
Dependence of transport critical current density on sample size for ceramic RBa2Cu3O7−x (R≡Y, Ho, Gd)
Authors: Bransky I. , Bransky J. , Maartense I. , Peterson T. L.
Published: July 2002

Measurements of the transport critical current density Jc were carried out on sintered and partially melted samples of YBa2Cu3O7−x , YBa2Cu3O7−x +Ag, HoBa2Cu3O7−x, and GdBa2Cu3O7−x using a four-probe method and a contactless magnetic induction method. Results obtained by the two methods were in agreement. A pronounced dependence of Jc on sample cross-sectional area was observed for all samples: Jc increased with decreasing cross-sectional area. Values of Jc ranging from about 30 to 800 A/cm2 were measured depending on the preparation method and sample geometry. It is concluded that in view of the cross-sectional area dependence, comparison of Jc for different preparations should always be made for samples of similar geometry.
Electrical characteristics of W-Si(100) Schottky barrier junctions
Authors: Aboelfotoh M. O.
Published: July 2002

The electrical characteristics of W-Si(100) Schottky barrier junctions formed by sputter deposition of W on both n- and p-type Si(100) have been measured in the temperature range 95–295 K using current-voltage and capacitance-voltage techniques. Auger electron and Rutherford backscattering spectroscopies were used to characterize the Si(100) surface prior to metal deposition, and to monitor the reaction between W and Si upon annealing. The results showed that initial silicide formation has very little or no effect on the barrier height. Annealing after initial silicide formation caused the junction characteristics to strongly deviate from the ideal thermionic emission behavior. For junctions with ideal thermionic emission behavior the barrier height was found to decrease with increasing temperature with a coefficient consistent with the predictions of recent models of barrier formation based on Fermi-level pinning in the center of the semiconductor indirect band gap.
Investigations on resonant tunneling in III-V heterostructures
Authors: Guéret P. , Rossel C. , Marclay E. , Meier H.
Published: July 2002

We present data obtained on a set of symmetric GaAs/AlGaAs double-barrier quantum-well structures in which the thickness of the AlGaAs barriers has been systematically varied from 31 to 7.5 nm. Low-temperature I(V ) characteristics, temperature dependencies, and magnetotunneling have been investigated. Our data suggest a dominance of sequential tunneling processes in the range investigated and point to interface roughness in the well as the possible cause for the large valley currents. Our best devices exhibit a current peak-to-valley ratio of about 20.
dc and ac transport in molecular-beam-epitaxy-grown metal/ZnSe/GaAs heterojunction structures
Authors: Marshall T. , Colak S. , Cammack D.
Published: July 2002

The room-temperature electrical transport properties of ZnSe epilayers grown above the critical layer thickness on n+-GaAs substrates by molecular-beam epitaxy have been studied. dc current versus voltage and small-signal ac admittance versus voltage and frequency measurements were made on Schottky contacts (Au or Hg). A novel method of analysis is presented which, extending a previous model to include the three-dimensional effects of current spreading as a function of frequency, allows the ZnSe epilayer resistivity to be obtained. Combining this with the doping concentration obtained from analysis of the C-V characteristics, the ZnSe mobility may be calculated. Mobilities thus measured compare well with our own and other workers’ published Hall mobility data on similar samples, as well as with theoretical calculations. We believe that our results represent a unique and detailed characterization of an epilayer heterostructure on a highly conducting substrate.
Bias and frequency response of the permeability of CoZrNb/SiO2 multilayers
Authors: Louis E. , Jeong I. S. , Walser R. M.
Published: July 2002

Compared to single-layer films, CoZrNb/SiO2 multilayers with amorphous, soft magnetic films exhibit increased high-frequency response (to about 100 MHz) that is not understood. We studied single and multilayer films in this system and observed three distinct types of magnetic bias and frequency responses (phases I–III). The high-frequency responses of phase II and III films were reduced from that of phase I. Phase changes were produced in the single-layer amorphous CoZrNb films by varying the film thickness, and in double-layer (N=2) and multilayer (N>2) films by varying the magnetic layer thickness. The phase boundaries in the former were shifted by magnetostatic coupling of the perpendicular component of M. These studies indicated that phase I films had uniform planar magnetizations, while phase II and III films had perpendicular components. The results are summarized in the form of a phase diagram (film thickness versus inverse film separation), which suggests that the frequency response of multilayer thin films is enhanced when the individual magnetic layers are sufficiently thin to insure a planar magnetization (phase I).
The high-resistive soft magnetic amorphous films consisting of cobalt, iron, boron, silicon, and oxygen, utilized for video head devices
Authors: Matsuyama H. , Eguchi H. , Karamon H.
Published: July 2002

A new type of high-resistive soft magnetic amorphous film possessing superior properties such as high resistivity (ρ), high-saturation induction (Bs), and high permeability (μ) in the high-frequency range prepared by cosputtering Co0.40Fe0.40B0.20-SiO2 was obtained. These films which have Bs higher than 8 kG in the range less than ∼55% of Si-O volume fraction, consist of a two-phase structure of amorphous magnetic metal particles (∼50 Å) scattered in the amorphous nonmagnetic Si-O region. ρ increases exponentially with the increase of Si-O volume, with diminishing eddy current loss in the very high-frequency range. Some of these films (Bs∼12 kG, Hc∼0.3 Oe, ρ∼500 μΩ cm), in fact, have a superior permeability compared with sputtered sendust films and regular amorphous films used as high-density recording head cores in the high-frequency range over 10 MHz.
The general relaxation time distribution of a logarithmic capacitance transient
Authors: Roura P.
Published: July 2002

The form imposed by the existence of a logarithmic transient to the relaxation times distribution has been deduced in a very general way. This distribution is found to be proportional to the inverse of the relaxation time. This result is then applied to analyze the particular case of a logarithmic capacitance transient originated from a thermally activated emission process.
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u investigation of the low-pressure metalorganic chemical vapor deposition of lattice-mismatched semiconductors using reflectance anisotropy measurements
Authors: Acher O. , Koch S. M. , Omnes F. , Defour M. , Razeghi M. , Drévillon B.
Published: July 2002

The growth of InAs on InP and InP on GaAs is investigated using reflectance anisotropy (RA) measurements. Very large optical anisotropies are observed, related to the three-dimensional growth mode of these materials. A model is proposed to account for the optical properties of the samples, using effective medium theories to describe the roughness. Good quantitative agreement is obtained for small roughness thickness, and a qualitative description is found for larger roughness features. The RA technique is found to be very useful to monitor the growth of lattice-mismatched materials, particularly at the nucleation stage.
The spatial distribution of ground-state scandium atoms in a high-pressure metal-halide discharge by saturated laser-induced fluorescence
Authors: Kramer Jerry
Published: July 2002

The spatial distribution of ground-state scandium atoms in a high-pressure metal-halide discharge has been measured by saturated laser-induced fluorescence (LIF). Sc atoms were excited at 402.4 nm (y2D05/2←a2D5/2) and the laser-induced fluorescence was detected at 399.7 nm (y2D05/2→a2D3/2). The LIF signals were corrected for the optical depth of the fluorescence. The LIF measurements were made under saturated conditions to minimize the spatial dependence of the fluorescence quantum efficiency. In the radial plane the Sc density was a maximum at reduced radii of 0.6–0.7 with a local minimum at the arc center. The shape of the radial profile and the magnitude of the LIF signals were sensitive to the axial position in the discharge and to variations in discharge power. The radial Sc profile was independent of the ac phase angle. LIF signals were also observed at wavelengths corresponding to fluorescence from the y2D03/2, y2F05/2,7/2, and y2P01/2,3/2 states. The radial dependence of the LIF signal at 393.3 nm (y2F05/2→a2D5/2) was compared with the radial dependence of the LIF signal at 399.7 nm.
Mechanically and thermally stable Si-Ge films and heterojunction bipolar transistors grown by rapid thermal chemical vapor deposition at 900 °C
Authors: Green M. L. , Weir B. E. , Brasen D. , Hsieh Y. F. , Higashi G. , Feygenson A. , Feldman L. C. , Headrick R. L.
Published: July 2002

Traditional techniques for growing Si-Ge layers have centered around low-temperature growth methods such as molecular-beam epitaxy and ultrahigh vacuum chemical vapor deposition in order to achieve strain metastability and good growth control. Recognizing that metastable films are probably undesirable in state-of-the-art devices on the basis of reliability considerations, and that in general, crystal perfection increases with increasing deposition temperatures, we have grown mechanically stable Si-Ge films (i.e., films whose composition and thickness places them on or below the Matthews–Blakeslee mechanical equilibrium curve) at 900 °C by rapid thermal chemical vapor deposition. Although this limits the thickness and the Ge composition range, such films are exactly those required for high-speed heterojunction bipolar transistors and Si/Si-Ge superlattices, for example. The 900 °C films contain three orders of magnitude less oxygen than their limited reaction processing counterparts grown at 625 °C. The films are thermally stable as well, and do not interdiffuse more than about 20 Å after 950 °C for 20 min. Therefore, they can be processed with standard Si techniques. At 900 °C, the films exhibit growth rates of about 15–20 Å/s. We have also demonstrated the growth of graded layers of Si-Ge, and have determined that a strain gradient exists in these layers.
Stripe stabilization in vertical Bloch line memory
Authors: Wu J. C. , Katti R. R. , Stadler H. L.
Published: July 2002

Partially grooved, long, rectangular grooves on the garnet surface were used to stabilize minor loop stripes in a vertical Bloch line memory. These stripes reside beneath the stripe confinement groove. The test chip contained 10 or 20 minor loop grooves, 10 read/write (r/w) gate grooves, and a major line groove. The film thickness was 4.76 μm, and the groove was 0.5 μm deep. Each minor loop groove was 500 μm long, four widths were tried: 3.5, 4, 4.5, and 5 μm. Two groove periods were tried: 10 and 20 μm. For stripe initialization, a bubble was nucleated in every minor loop groove by a single current pulse at a 90 Oe bias field. As the bias field was decreased slowly, bubbles began to stripe out at 80 Oe. At 75 Oe, all 10 stripes were stretched to the full groove length. These stripes were stable at bias fields between 70 and 80 Oe. Stripes decreased in length at higher fields, and escaped from the confinement groove at low fields. When stripes escaped from the groove, it always occured from the end not facing a r/w gate groove. These bias field values and the stripe-escape asymmetry are confirmed by computer simulation.
Abnormal grain growth in aluminum alloy thin films
Authors: Longworth Hai P. , Thompson C. V.
Published: July 2002

Abnormal grain growth in 0.75-μm-thick aluminum alloy thin films has been studied using x-ray diffractometry, plan-view and cross-sectional transmission electron microscopy, scanning transmission electron microscopy, and energy dispersive x-ray analysis. Transmission electron microscopy was used with preannealed samples as well as with samples annealed in situ. By varying the deposition temperatures, compositions, and annealing conditions, we have determined the roles of alloying elements in the formation of second-phase precipitates and in promoting abnormal grain growth.
Diamond synthesis in oxygen-acetylene flames: Inhomogeneities and the effects of hydrogen addition
Authors: Oakes D. B. , Butler J. E. , Snail K. A. , Carrington W. A. , Hanssen L. M.
Published: July 2002

Micro-Raman spectroscopy, scanning electron microscopy and a surface density counting technique have been used to probe the inhomogeneities of diamond crystallites grown with an oxygen-acetylene flame on a scratched Si(100) surface. The surface temperature profile was measured using a thermal imaging camera and compared with the observed inhomogeneities in the diamond crystallites. It is concluded that the flame species flux to the surface is the dominant factor contributing to the diamond crystallite inhomogeneities. Hydrogen addition to the oxygen-acetylene flame was studied. The addition of hydrogen reduced the amount of ‘‘amorphous’’ carbon contained in the diamond crystallites as measured with Raman spectroscopy. Growth density profiles were determined as a function of the inner flame front to substrate distance. For uniform growth density in the oxygen-acetylene flame the substrate must be placed in the acetylene feather at a sufficient distance from the inner flame to avoid annular growth.
Detection of deep levels and compensation mechanism in undoped, liquid-encapsulated Czochralski n-type GaAs
Authors: Siegel W. , Kühnel G. , Schneider H. A. , Witte H. , Flade T.
Published: July 2002

Undoped n-GaAs with a 300 K resistivity between 10−1 and 108 Ω cm (electron concentration between 1×107 and 5×1015 cm−3 ) grown in quartz crucibles by the liquid-encapsulated Czochralski (LEC) technique was investigated by thermally stimulated current (TSC), temperature-dependent Hall effect (TDH), and deep-level transient spectroscopy (DLTS). Using Schottky contacts the TSC method could be extended to medium-resistivity samples. The strongly varying electron concentrations are correlated to varying TDH activation energies. The correlation between the donors dominating the electrical equilibrium properties and the electron traps detected by TSC and DLTS is discussed. Medium-deep and deep levels are present in this LEC material in such high concentrations that they must be taken into account in the compensation mechanism.
The effect of field-dependent heat capacity on regeneration in magnetic Ericsson cycles
Authors: Chen Jincan , Yan Zijun
Published: July 2002

The coefficient of performance of the Ericsson refrigeration cycle of paramagnetic salt is derived. It is used to discuss the performance of the refrigerators. Thereby, it is expounded that the refrigerators have some new characteristics.
Studies on glow-discharge characteristics during dc reactive magnetron sputtering
Authors: Rao G. Mohan , Mohan S.
Published: July 2002

The process of reactive sputtering is influenced by the reactive gas pressure and the rate of sputtering because the glow-discharge characteristics vary considerably in the presence of reactive gas. The discharge characteristics during magnetron sputtering of copper in an argon and oxygen atmosphere have been investigated in the present study. The variation in the cathode potentials has been explained in terms of negative ion formation and target poisoning effects. It has been found that the rate of deposition and the oxygen partial pressure influence target poisoning, which in turn influences the discharge characteristics and rate of deposition. The properties of films deposited under different conditions have been correlated with the discharge characteristics and target poisoning.