bluuebunny/crossref_metadata_2025 huggingface dataset:
Steady-state temperature of an evaporating water droplet with a monolayer coating
Authors: Rubel Glenn O.
Published: July 2002

A mathematical model is derived for the steady-state temperature of an evaporating water droplet with a monolayer coating. The model uses the flux-matching arguments of Fuchs to describe the concentration and temperature fields outside the evaporating droplet. Assuming the mean molecular speed, the gas-phase diffusion coefficient, and the gas thermal conductivity to be temperature independent, a closed-form expression is derived for the steady-state temperature of the droplet as a function of the monolayer accommodation coefficient. Comparison between model predictions and recent fluorescence thermometry experiments shows good agreement.
On the normal acceleration sensitivity of contoured quartz resonators rigidly supported along rectangular edges
Authors: Tiersten H. F. , Shick D. V.
Published: July 2002

An analysis of the normal acceleration sensitivity of contoured AT- and SC-cut quartz crystal resonators rigidly supported along rectangular edges is performed. The variational principle with all natural conditions for anisotropic static flexure is used in the calculation of the flexural biasing state. However, in this work the biasing shearing stresses with quadratic variation across the thickness of the plate are obtained a posteriori from the flexural solution in the conventional manner. The accompanying quadratically varying biasing shearing strains, which are very important in this work, are obtained from the constitutive equations along with all other quadratically varying strains resulting from the anisotropy. The calculated biasing deformation fields are employed in an existing perturbation equation along with the mode shapes of the contoured resonators to calculate the normal acceleration sensitivities. It is shown that the normal acceleration sensitivity vanishes for many cases and is less than a few parts in 1013 for all cases considered.
Picosecond spectroscopy of optical nonlinearities in amorphous silicon-carbon alloys
Authors: Darzi A. K. , Eicker U. , Wherrett B. S. , Wilson J. I. B.
Published: July 2002

We have studied nonlinear refraction and absorption of band-gap tuned hydrogenated amorphous silicon-carbon alloys using 532-nm picosecond degenerate four-wave-mixing, transient grating and excite/probe techniques. The highest induced absorption cross sections are obtained for low band-gap samples. By comparison, grating diffraction efficiencies increase with band gap, indicating stronger refractive index contributions. The results from the four-wave-mixing and excite/probe experiments are combined to calculate refractive index cross sections σn and to derive the nonlinear coefficients n2 and χ(3); these suggest useful strong optical nonlinearities in these amorphous alloys.
AlGaAs/GaAs double-heterojunction high electron mobility transistors grown by low-pressure organometallic vapor phase epitaxy
Authors: Huang Rong-Ting , Tu Yung-Yi , Kasemset Dumrong , Nouri N. , Colvard C. , Ackley D.
Published: July 2002

AlGaAs/GaAs double-heterojunction high electron mobility transistors (DHHEMTs) grown by low-pressure organometallic vapor phase epitaxy are reported in this communication. The magnetic field-dependent Hall effect measurement was used to characterize the sheet carrier density and electron mobility of the two-dimensional electron gas (2-DEG). At 77 K the sheet carrier density and the electron mobility were 1.38×1012 cm−2 and 52 900 cm2 /V s, respectively, in a DHHEMT structure with an undoped Al0.28Ga0.72As spacer layer of 120 Å, while they were 7.12×1011 cm−2 and 65 100 cm2 /V s, respectively, in a comparable single-heterojunction HEMT structure. DHHEMT’s with 0.5-μm-gate length and 75-μm-gate width have been fabricated with dc saturation current of 500 mA/mm and dc transconductance of 250 mS/mm. These results are comparable to those produced with molecular-beam epitaxy.
Surface-related low-frequency noise of sputtered copper film
Authors: Wong H. , Cheng Y. C. , Ruan G.
Published: July 2002

This paper presents the first attempt in correlating the low-frequency noise with the surface characteristics of metal films prepared by sputtering of copper onto oxidized-silicon and sapphire substrates. Results show that the noise behaviors and the surface physics of the metal films on these two kinds of substrates are different from each other. Particularly, the spectral slope of noise spectrum not only depends on the substrate but also on the thickness and surface area of the metal films. These observations suggest that the low-frequency noise of metal film, being governed by the surface roughness and irregularity of the sample, should be a surface effect. In addition, a number fluctuation model based on the electron tunneling between the hillocks at the surface is proposed to explain the observations.
Effect of WO3 doping on the properties of YBa2Cu3O7−x superconductor
Authors: Padam G. K. , Tripathi R. B. , Singh S. , Rao S. U. M. , Jain K. , Kotnala R. K. , Goel R. C. , Khurana B. S. , Khullar S. M. , Das B. K.
Published: July 2002

Tungsten-doped YBa2Cu3O7−x superconducting samples are characterized with the help of resistivity, crystal structural, microstructural, density d, and critical current density Jc studies for doping concentrations varying from 0.00 to 0.14 mol % of WO3. It has been found that doping of WO3 has hardly any influence of Tc, whereas it seems that d and Jc are affected. d and Jc of the samples increase in the range 0<WO3≤0.04, but above this range, both start decreasing. The maximum Jc obtained at 77 K and zero magnetic field in YBa2Cu3O7−x doped with 0.04 mol % of WO3 is 450 A/cm2. The lower concentrations (<0.04 mol %) seem to improve the density, whereas higher concentrations lead to porous structure and also induce the formation of BaCuO2 and Y2Ba1Cu1O5 nonsuperconducting phase as revealed by scanning electron microscopy, energy dispersive spectral, and x-ray diffraction analyses. The x-ray diffraction analysis also showed no appreciable change in the lattice parameters with WO3 doping. It appears that the WO3 doping changes the microstructure of YBa2Cu3O7−x to influence its Jc.
Neutron and proton irradiation of shallow channel GaAs direct-coupled field-effect-transistor logic devices and circuits
Authors: Galashan A. F. , Bland S. W.
Published: July 2002

Neutron and proton irradiations have been performed on self-aligned GaAs metal-semiconductor field-effect transistors (MESFETs) and resistors utilizing shallow ion-implanted channels. FET threshold voltage shifts during irradiation were lower than reported elsewhere (less than 115 mV for a −0.85 V threshold FET irradiated by 4.3×1014 neutron cm−2). This is shown to be explained by the shallow active layers used. A neutron carrier removal rate between 20 and 25 cm−1 is necessary to fit the FET data. Carrier removal rates derived from resistor damage were 150 cm−1 for peak doping levels of 4×1017 cm−3, greatly in excess of those derived from epitaxial or bulk GaAs resistors, and inconsistent with values obtained from threshold shifts of FETs with identical active layers. Resistor and FET threshold voltage changes for 52 MeV proton irradiation were nearly an order of magnitude greater than for an equivalent dose of 1 MeV (Si) neutrons. The extrapolated worst-case failure dose of direct-coupled FET logic inverters was better than 1.8×1015 neutron cm−2 despite the limited noise margins of this logic scheme.
Characterization of evaporated thin films of merocyanine dyes
Authors: Hattori S. , Ishitani A. , Kuroda H. , Nagasawa Y. , Mori Y. , Nagai N.
Published: July 2002

Vacuum evaporation of a merocyanine dye, 3-ethyl-5 [2-(3-ethyl-2-benzothiazolidene) ethyldene]-2-thioxo-4-thiazolidione, onto different substrates such as bare and surface-oxidized silicon wafers and a quartz glass substrate is done. There is a difference in color between a film deposited on the bare silicon substrate and one on either a quartz glass plate or a silicon wafer with a thick (96.5-nm) oxide layer. The dye film on quartz has an absorption maximum at 560 nm, whereas that on bare silicon has one at 582 nm. The bare crystalline silicon surface may give dye molecules more opportunity to aggregate than amorphous silicon dioxide or quartz surfaces. The dye molecules are preferentially oriented along the [100] direction of the substrate crystal, with the carbonyl group parallel to and the conjugated aromatic plane perpendicular to the substrate surface, although there is no detectable difference of orientation between the films deposited on these different substrates.
Experimental characteristics of rf parallel-plate discharges: Influence of attaching gases
Authors: Bletzinger P.
Published: July 2002

Electrical characteristics of parallel-plate rf discharges were measured with the goal of obtaining quantitative information of the properties of the discharges, in particular the electrode sheaths. Measurements of the impedance characteristics at variable electrode spacing suggest a transition of the power deposition process from volume to electrode dominated at about 1 Torr in argon. By changing the secondary electrode emission coefficient of the electrodes, it could be shown that the power into electrons emitted from the electrodes is small compared to the total power input. Adding the attachers CF4, C2F6, and SF6 caused a large increase of the discharge impedance in the high-pressure (volume power deposition) regime and shifted the transition to the electrode-dominated power deposition regime to lower pressures. The impedance behavior versus pressure was modeled with a simple equivalent electrical circuit from which the characteristics of the electrode sheaths and their influence on the electrical characteristics could be derived. The time-averaged sheath thickness was measured optically and compared with the results using the equivalent circuit. The sheath thickness, decreasing on addition of the attaching gases CF4 and SF6, is quite different for these two added gases, which have about the same ionization, but very different attachment cross sections. In contrast, the impedance with added CF4 is only slightly less than with SF6, indicating an average electron energy of at least 5 eV where the attachment rates of the two gases become similar. Using variable electrode spacing, the peak electric field was measured both in the electrode sheaths and in the discharge volume. For argon with 23% added SF6, at 1 Torr pressure, the field in the sheath reached 569 and 27 V/cm in the volume; at 0.15 Torr the fields were 300 V/cm in the sheath and below the measurement accuracy in the volume.
Adhesion of metals to spin-coated fluorocarbon polymer films
Authors: Kim Yong-Kil , Chang Chin-An , Schrott A. G.
Published: July 2002

Adhesion between metals and fluorocarbon polymer films has been studied for Cu, Cr, Ti, Al, and Au on polytetrafluoroethylene (PTFE) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP) films. Polymer films were applied on the Cr/SiO2 /Si substrate by spinning the aqueous dispersions of the polymer resin particles, followed by thermal curing. Strips of different metals were deposited on the polymers, and adhesion was measured at 90° peel test. The peel strengths were invariably higher for the metals on FEP than those of the corresponding metals on PTFE. Among the metals, Ti showed the highest peel strength for both polymers, followed by Cr and Al, with Cu and Au being the lowest. The peel strengths of Ti, Cr, and Cu on FEP are 85, 45, and 12 g/mm, respectively, and the corresponding ones on PTFE are 23, 5, and 2 g/mm, respectively. X-ray photoelectron spectroscopic analysis shows that the metal-polymer bonding involves the metal-carbon interactions. The strongest interaction is observed for Ti with the polymers, forming Ti carbidelike bonds. Cr also shows strong interaction with the two polymers, but to a lesser degree compared with Ti. Only a weak bonding is shown for Cu. The difference in peel strengths among the metals shows a correlation with the difference in electronegativities between the metals and carbon. Little contribution to the observed peel strengths is seen from the surface morphological analysis of the untreated polymers.
Electrical properties of (CuIn)1−zMn2zTe2 alloys
Authors: Porras G. Sánchez , Quintero M. , Wasim S. M.
Published: July 2002

The electrical transport properties between 80 and 300 K of polycrystalline samples of (CuIn)1−zMn2zTe2 semimagnetic semiconducting alloys are studied. These are found to have disordered chalcopyrite α(z≤0.1), ordered chalcopyrite α′ (0.1<z≤0.25), and ordered zinc-blende β′ (0.25<z≤0.57) structures. From an analysis of the electrical data, the values of the activation energy EA, density of states effective mass of the holes mp, valence-band deformation potential Eac, and the concentration of the ionized impurities Ni for the alloys are estimated. The linear behavior is observed of mp with z, with a discontinuity when the structure of the alloys changes from α′ to β′. However, the extrapolated value of mp at z=0 from the region of chalcopyrite structure is in close agreement with that of p-type CuInTe2. On the other hand, the deformation potential of the valence-band varies linearly with z.
Hydrogen dissolution in and release from nonmetals. II. Crystalline silicon
Authors: Abrefah J. , Olander D. R. , Balooch M.
Published: July 2002

The solubility of hydrogen in crystalline silicon from 1363–1473 K and from 1.7–9.2 atm has been measured using the method of high-temperature, high-pressure infusion followed by high-temperature vacuum outgassing with mass-spectrometric detection. The measured solubilities were in the range 1–5×1016 atoms/cm3 and exhibited a temperature dependence consistent with a heat of solution of 30–40 kcal/mole. The pressure dependence of the solubility was consistently smaller than the square-root dependence characteristic of simple interstitial solution. The release-rate curves showed multiple peaks, which are incompatible with the classical diffusion model of release. Instead the peaks correspond to trapping of hydrogen at distinct binding sites in the silicon lattice. The release kinetics were modeled as detrapping processes.
Self-consistent analysis of intersubband transitions in quantum wells
Authors: Yuh P. F. , Kuo T. C. , Wang K. L.
Published: July 2002

Intersubband transitions in modulation doped, arbitrary potential profile quantum-well structures under an applied field are analyzed by solving the Schrödinger and Poisson equations self-consistently. This analysis is applied to the local-to-global transitions of a step well structure. The results show that although the band-bending effect is significant (∼25 meV) at a relatively high carrier density of 5.6×1011 /cm2 (∼3×1017 /cm3 ), the transition energies and absorption coefficients remain close to the flat band cases. This calculation confirms that the local-to-global transitions have large linear Stark shift and oscillator strength even at high doping.
Optical determination of Si conduction-band nonparabolicity
Authors: Borghesi A. , Stella A. , Bottazzi P. , Guizzetti G. , Reggiani L.
Published: July 2002

The nonparabolicity of the Si conduction band is investigated from the analysis of the optical response of heavily doped samples in the range 1019– 6×1021 cm−3 at 300 K. The data enable us to determine an optical effective mass which is found to exhibit a systematic increase for doping levels above 1020 cm−3. The fitting of experimental results gives a nonparabolicity parameter α=0.27 eV−1, which compares well with less direct estimates provided by the analysis of transport coefficients. The effect of the impurity potential, while providing a significant band tailing of the density of states, is found to have negligible influence on the value of the optical effective mass at the given impurity concentration.
Stripe domain lattice ferromagnetic resonance in garnet thin films
Authors: Bi Si-yun
Published: July 2002

Recent experimental results on the dependence of the stripe domain lattice ferromagnetic resonance (FMR) on the orientation of the high-frequency (hf) magnetic field with respect to the stripe domains are reported. With the hf magnetic field rotated in the film plane from perpendicular to the stripe domains to parallel to them, the resonance absorption peak of the stripe domain mode was split into two subpeaks whose resonance frequencies and separation change continuously. This result could not be described in terms of the present domain lattice FMR theory.
Determination of magnetic anisotropy of magnetically hard materials
Authors: Richter H. J.
Published: July 2002

The determination of the first-order anisotropy field strength using the torsion pendulum method is described. Since the applied field need not necessarily be in the range of the anisotropy field, this method is particularly useful for characterizing modern permanent magnet materials which have a very high uniaxial anisotropy. The method requires oriented samples. Measurements were made on polycrystalline samples of NdFeB, SmCo, and barium ferrite. The method is described and error sources are discussed. It is pointed out that the torsion pendulum method is closely related to reversible transverse susceptibility measurements. It is shown both experimentally and theoretically, that using susceptibility measurements similar results can be obtained. The susceptibility method is, however, not applicable to conducting materials at present.
Marker studies in the reactions of W/Al couples
Authors: Wang S. Q. , Mayer J. W.
Published: July 2002

Diffusing species in the reaction of thin tungsten films with aluminum overlayers in vacuum have been investigated by marker experiments using Rutherford backscattering spectrometry and scanning electron microscopy techniques. It has been found that Al was the dominant diffusing species in the reaction. Ni has been used as the marker material. Samples with both pure and Al-diluted and both unburied and buried Ni markers at the interface of thin W films and Al overlayers have been studied to compare barrier effect of the markers. Our results showed that the Ni-based markers do not impede the reaction of thin W films with Al overlayers.
Thermal redistribution of iron implanted in Czochralski silicon
Authors: Pivac B. , Borghesi A. , Geddo M. , Stella A. , Ottolini L.
Published: July 2002

Different doses of iron ions were implanted in Czochralski grown single-crystal silicon samples and subsequently annealed at 1000 °C for 2 h in a dry nitrogen atmosphere. The behavior of the implanted iron and of oxygen already present in the material was monitored. It was found that the existence of the remaining structural disorder after the annealing treatment plays a dominant role in iron and oxygen segregation into the disordered region. This confirms the theory which predicts that the structural disorder and related strain fields are dominant mechanisms for gettering of metallic ions.
Model diffraction profiles parallel to rough step edges
Authors: Kariotis R. , Swartzentruber B. S. , Lagally M. G.
Published: July 2002

Modeling of rough step edges has been made and compared with scanning tunneling microscopy (STM) micrographs. In this paper, we use a phenomenological Hamiltonian to calculate diffraction profiles which can be used to determine the extent of step-edge meandering. Comparison with experiment is made based on a parametrization of the step statistics obtained from STM data of silicon (001) step edges.
Three-dimensional analysis of a heat-spreading phenomenon in phase-locked arrays of oxide-isolated diode lasers
Authors: Nakwaski Wl/odzimierz
Published: July 2002

Three-dimensional analysis of a heat-spreading phenomenon in a heat sink of phase-locked arrays of oxide-isolated diode lasers is carried out in the present paper. The main result is that with increasing number of laser elements the heat-sink temperature increase turns out to change sublinearly whereas temperature differences between adjacent edge lasers increase considerably which threatens stability of the phase-locking operation. The heat spreading in semiconductor, contact, and solder layers was approximated by a one-dimensional model. The special correction factor (b) accounting for the two dimensionality of this heat spreading was used to improve the accuracy of the calculations.
The growth and characterization of Pb-doped Bi-Sr-Ca-Cu-O thin films
Authors: Tseng M. R. , Chu J. J. , Huang Y. T. , Wu P. T. , Wang W. N.
Published: July 2002

The growth and characterization of Bi-Pb-Sr-Ca-Cu-O films on single-crystal (001)MgO substrates by rf magnetron sputtering with a single target are reported. The comparison of different post-annealing conditions revealed that the film annealed under controlled Pb potential gave best superconducting properties with Tc0 above 105 K. The proper doping of Pb not only accelerated the formation of the high-Tc phase, but also improved the connectivity of high-Tc grains.
Effects of radio-frequency bias on GaAs surfaces etched by Ar-electron-cyclotron-resonance plasma
Authors: Noh S. K. , Ishibashi K. , Aoyagi Y. , Namba S. , Yoshizako Y.
Published: July 2002

The Ar-electron-cyclotron-resonance (ECR) microwave (MW) plasma has been applied on GaAs surfaces for investigating the effects of radio-frequency bias on etching reaction and radiation damage. The etch depths as a function of the etching time gave a linear profile with etch rates of 75 and 100 Å/min for 150- and 300-W MW powers under a 4-W rf bias, respectively, but for the etch rates an exponential profile is obtained as a function of the square root of the rf bias power. The electrical characteristics of Schottky barriers fabricated on the etched surface show strong rf bias dependence. Increasing the rf bias power, the donor concentration near surface and the barrier height decrease but the ideality factor and the depletion layer width increase monotonically. The changes are attributed to the radiation damage induced by the Ar ECR plasma which becomes gradually deeper in the damage layer and higher in concentration with increasing rf bias power. The rf biasing in the ECR plasma (which has the exceptional characteristic of being applicable to semi-insulating specimens) is very similar in effect to dc biasing.
Deep electron traps in GaAs layers grown on (100)Si substrates by metalorganic chemical vapor deposition
Authors: Kim Eun Kyu , Cho Hoon Young , Kim Yong , Kim Moo Sung , Kim Hyeon-Soo , Min Suk-Ki , Yoon Ju Hoon , Choh Sung Ho
Published: July 2002

Deep electron traps in GaAs layers grown on (100) 3 °-off Si substrates by metalorganic chemical vapor deposition were investigated by deep-level transient spectroscopy and a computer simulation method. The four electron traps with the activation energies of 0.81, 0.68, 0.57, and 0.53 eV below the conduction band were measured in GaAs epilayers on Si substrates, whereas only the EL2 level (Ec−0.81 eV) was detected in GaAs on a GaAs substrate. From the dependencies of concentration on the thickness of GaAs epilayer and Si substrate, it was assumed that the Ec−0.57 eV trap might be a Si-dislocation complex defect. The Ec−0.68 eV trap showed a similar behavior to that of the deep trap created in the plastically deformed bulk GaAs, and then its origin was supposed to be a defect induced by a stress due to the differences of thermal expansion coefficient and lattice parameter between Si and GaAs.
Studies of defects in n-type CdTe by charge transient spectroscopy
Authors: Ye Chian-ping , Chen Joseph H.
Published: July 2002

Charge transient measurements have been used to study deep levels in n-type CdTe single crystals. The samples, including In-doped, undoped, and Sn-doped single crystals, were grown by the Bridgman or the travelling heater method (THM). The temperature dependence of the capture cross section was investigated under the partial filling conditions. The activation energies of capture cross section were determined. For In-doped samples, the results indicate both levels Ec −0.66 eV (Bridgman samples) and Ec −0.68 eV (THM samples) are associated with the same indium-defect complex, but levels Ec −0.34 eV (Bridgman) and Ec −0.32 eV (THM) exhibited different capture mechanisms. The unusual capture properties of the trap at Ec −0.61 eV in the undoped sample can be attributed to a doubly charged Cd interstitial. For Sn-doped samples, four levels were observed, and levels Ec −0.89 eV and Ec −0.43 eV can be related to the presence of tin.
Voltage noise in an AlxGa1−xAs-GaAs heterostructure
Authors: Hofman F. , Zijlstra R. J. J. , Bettencourt de Freitas J. M.
Published: July 2002

Voltage noise in an heterostructure consisting of a Si-doped Al0.34Ga0.66As layer grown on a not-intentionally doped GaAs layer was investigated in the temperature range 80–330 K and in the frequency range of 1 Hz–100 kHz. The noise consisted of three types: thermal noise, which is independent of the frequency, 1/f-noise, and generation-recombination noise. The generation-recombination noise is associated with trapping and detrapping of charge carriers. The relaxation times show thermally activated behavior, and the activation energies obtained from Arrhenius plots are 810±20, 400±30, and 235±17 meV. These data are compared with those obtained from relatively thick AlxGa1−xAs layers.
The periodic character of the microtwin bandwidth distribution in YBa2Cu3O7−x
Authors: Teodorescu V. S. , Nistor Leona C. , Nistor S. V.
Published: July 2002

A statistical study of the microtwin domains in a standard ceramic sample of YBa2Cu3O7−x has been performed on transmission electron microscopy images. This study has evidenced a periodic character of the width distribution of twin lamellae, with maximum periodicity of about 30 nm. The presence of these maxima has been attributed to a local structural mechanism, independent of grain size, which operates in the tetragonal-orthorhombic transformation, beside the normal stress relaxation mechanism.
Lattice parameter and nearest-neighbor distances in Zn1−xFexSe (0≤x≤0.22)
Authors: Qadri S. B. , Kim K. H. , Skelton E. F. , Furdyna J. K.
Published: July 2002

Lattice parameters and nearest-neighbor distances have been measured for bulk grown Zn1−xFexSe (0≤x≤0.22) using standard x-ray diffraction and extended x-ray absorption fine structure techniques, respectively. The lattice parameters are in agreement with reported values for molecular beam epitaxy grown films, but differ slightly from published results for other bulk-grown samples. The nearest-neighbor distances suggest a slight distortion from the zinc-blende structure.
Polyimide thin-film waveguides: Optical and Raman spectroscopic studies
Authors: Savatinova I. , Tonchev S. , Todorov R. , Venkova E. , Liarokapis E. , Anastassakis E.
Published: July 2002

Polyimide films deposited on fused quartz, silicon, and ceramic substrates are examined. Waveguide techniques are used to determine the guide modes from which the index of refraction is inferred. Film thicknesses are determined from transmission interferences and, independently, from a luminescence-induced reflection interference pattern. Using a waveguide configuration we also observed and analyzed Raman scattering features in the region above 1000 cm−1.
Surface modification and atomic resolution on a vacuum-annealed gold foil in air by scanning tunneling microscopy
Authors: Hoffmann-Millack Britta , Roberts Clive J. , Steer William S.
Published: July 2002

Scanning tunneling microscopy has been used to investigate changes in a vacuum-annealed gold surface induced by the application of voltage pulses to the tip. After a 2-V 1.5-s pulse a hole several hundreds of angstroms wide and of similar depth was generated, the responsibility being ascribed to ion arcing. We present a time-lapse sequence showing its decay process, from which surface-diffusion velocities between 4 and 0.1 Å s−1 have been determined. From the new surface, a scan showing atomic resolution has been obtained, giving different interatomic spacings (S) and atomic diameters (D) in two lattice directions at an angle of 60°. These are S=2.1 Å and D=2.0 Å for the short axis and S=3.1 and 3.8 Å and D=2.7 Å for the long axis.
Structure of amorphous carbon in amorphous C/Ge multilayers
Authors: Long N. J. , Trodahl H. J.
Published: July 2002

Amorphous C-Ge multilayers have been produced with periods varying from 2.6 to 12.5 nm. We have studied the multilayers using Raman spectroscopy and dc conductivity measurements and found that their properties change significantly when the carbon sublayer thickness is smaller than 2.5 nm. This value corresponds to the proposed dimension of sp2 bonded carbon islands within a-C and we find that our results can be understood in terms of the carbon forming these islands, but the islands becoming disconnected as the nominal carbon layer thickness decreases. The conductivity shows a percolation behavior for the thinnest layers.
Possible conduction mechanisms in coconut-shell activated carbon
Authors: Daud W. M. , Badri M. , Mansor H.
Published: July 2002

This work reports on the result of electrical conductivity measurements carried out on coconut-shell activated carbon. The results suggest that the charge carriers moved by variable-range hopping below 200 K, by hopping among localized energy states between 200 K and 385 K, and by percolation through energy states close to the mobility edge above 385 K. In the latter two conduction processes, significant additional frequency-dependent contributions to the conductivity were observed and are tentatively attributed to polarization of unremovable lignin and/or ionic impurities. These explanations are based on the present trends of the electrical transport theory for amorphous semiconductors.
Growth and optical properties of Pb1−xEuxTe films (0<x<0.55)
Authors: Suryanarayanan R. , Das S. K.
Published: July 2002

We present the growth and optical properties of Pb1−xEuxTe films (0<x<0.55) prepared by a co-evaporation technique onto BaF2 (111) substrates. They crystallize in a NaCl-type structure. The lattice parameter increases as x increases but not in accordance with Vegard’s law. The optical band gap increases with increasing x values. Our data seem to indicate the stability of Eu2+ for 0<x<0.55.
A characterization of the P/P+ epitaxial and substrate interface using the pulsed metal-oxide-semiconductor capacitance-time transient analysis
Authors: Wijaranakula W. , Aminzadeh M.
Published: July 2002

Epitaxial silicon wafers having an epitaxial layer of 110 μm thickness were nucleation annealed at 750 °C for times up to 72 h. This was followed by 16-h growth anneal at 1050 °C. After the annealing sequence, the minority-carrier lifetime of the epitaxial layer was characterized using the pulsed metal-oxide-semiconductor capacitance-time transient analysis. A significant improvement in the generation lifetime of the epitaxial layer of the samples which received the nucleation anneal was observed. In contrast, the nucleation anneal appeared to have no effect on the recombination lifetime. From the experimental results, the electronic defects responsible for the limitation of the recombination lifetime of a thin epitaxial layer were hypothesized to be the complexes of metallic impurity and boron originating in the heavily doped substrate region of the epitaxial wafer.
Oxidation kinetics and morphology of dc magnetron sputtered and evaporated amorphous GdTbFe films
Authors: Klahn S. , Bentin H. , Knörr B. , Heitmann H. , Wilting H.
Published: July 2002

The influence of preparation conditions on the morphology and the resulting oxidation behavior of amorphous GdTbFe films was studied. The morphology was characterized by transmission electron microscopy and mass-density measurements, the magnetic properties by torque and vibrating sample magnetometer measurements, and the oxidation kinetics by in situ measurements of electrical conductivity and Hall hysteresis loops. For the first time a quantitative comparison of the aging kinetics of evaporated and magnetron sputtered films prepared at different Ar sputter gas pressures and substrate-target distances is reported. With increasing the pressure-distance product from 36 to 192 Pa mm the always-observed columnar structure becomes much more pronounced and the mass density, electrical conductivity, and corrosion resistance of the films decrease significantly. The pressure-distance product for thermalization plays an important role in determining the microstructure of the films. Evaporated films show similar features to dc magnetron sputtered films prepared at pressure-distance products of about 100 Pa mm. The oxidation rate is proportional to the porosity of the films and shows, independent of the preparation conditions, an activation energy of 0.3 eV.
Volume dependence of the isothermal bulk modulus of polymers
Authors: Cho Bongkee
Published: July 2002

An equation of state, previously reported, was used to calculate the volume dependence of the isothermal bulk modulus of polymers. The principal results are as follows: (1) The isothermal bulk modulus can be expressed as a function of volume and temperature. (2) The ratio of the entropic contribution to the total value of the bulk modulus, denoted ΥS, depends only on temperature and not on pressure. (3) For polymer melts, ΥS is negative. (4) For polymer solids, the absolute value of ΥS is less than unity. If the bulk modulus can be approximated as a function of volume only, then ΥS can be ignored.
Nonlinear all-optical beam scanner
Authors: Assanto Gaetano , Stegeman George I.
Published: July 2002

An all-optical integrated optics beam-scanning device is analyzed. It consists of a surface relief grating used to couple both a control and a signal beam into and out of a nonlinear planar waveguide, respectively. Varying the control beam power tunes the signal beam out-coupling angle. Both local and diffusive nonlinearities are considered, and various design parameters are discussed. The theoretical results are compared to experimental data from ZnS waveguides for the thermal diffusive case.
A semiempirical model for the laser-induced molten zone in the laser recrystallization process. II
Authors: Willems G. J. , Maes H. E.
Published: July 2002

An extension to large laser power values of the semiempirical model for the laser-induced molten zone is given. The influence of the wafer preheating temperature and the thickness of thin capping layers on the molten zone is discussed. The variation of the size of the molten zone as caused by a change of the laser spot size is studied. An optimal laser power is determined to minimize the variation of the size of the molten zone as a result of a variation of the laser spot size. The difference between the laser power required to reach melt temperature in a silicon on insulator wafer and the laser power required to obtain complete melting is determined. A method to calculate the power required to reach the onset of complete melting in the case of a circular pseudostationary laser spot is proposed. The influence of the absorptances in liquid and in solid silicon, the thickness of the insulating layer, the thickness of the silicon overlayer, and the preheating temperature on the difference between the two threshold powers is treated.
Modulation of the plasma flow in plasma wake experiments
Authors: Tao Jin , Cooney Jamie , Lim Wee Beng , Ghaemi Mohammad S. , Lonngren Karl E.
Published: July 2002

Experiments demonstrate that it is possible to determine the characteristics of a plasma flowing past an object by locally modulating the plasma and measuring the resulting equiphase contours of the perturbation downstream. The technique is employed in studies of the wake region behind the object.
Observation of nanosecond-pulse breakdown of gas-insulated gaps by image converter camera
Authors: Kawada Yukimitsu , Hosokawa Tatsuzo
Published: July 2002

Breakdown phenomena of gas-insulated gaps with nanosecond pulses were examined by using an image converter camera. The physical appearance, i.e., luminosity of a gap, was investigated on streak photographs taken by the image converter camera. These investigations show that the breakdown mechanism of gas-insulated gaps with nanosecond pulses can basically be explained by a conventional avalanche-to-streamer development theory.
Magnetism and structural chemistry of U1−xYxCu2±ySi2∓y, U1−xYxCr2Si2, and U(Cu1−xCrx)2Si2 alloys
Authors: Hiebl K. , Rogl P. , Horvath C. , Remschnig K. , Noël H.
Published: July 2002

Magnetic behavior for the three series of alloys U1−xYxCu2±ySi2∓y, U1−xYxCr2Si2, and U(Cu1−xCrx)2Si2 has been studied in the temperature range from 2 to 550 K. In all cases a complete solid solution with the ThCr2Si2 type of structure was observed from x-ray powder analysis with no ordering among the substituting atom species. Whereas YCu2Si2 did not reveal any homogeneous region on Si/Cu substitution, uranium-rich alloys show significant changes in the unit cell dimensions when comparing U1−xYxCu2Si2 and U1−xYxCu2+ySi2−y. In both latter alloy series a negative deviation of the c parameter from Vegard’s rule is found almost compensated for by a positive deviation of a when Y is substituted for U. Substitution of Cu by Cr resulted in a linear dependence of the lattice dimensions.

YCu2Si2 and YCr2Si2 are temperature independent Pauli paramagnets above 2 K, whereas the UCu2±ySi2∓y and the U(Cu1−xCrx)2Si2 systems are characterized by the onset of ferromagnetic ordering at TM =105 K. Above TM all samples are in the paramagnetic state in which the uranium atoms carry an effective moment larger than 2 μB. Saturation moments reveal a maximum for a copper deficiency of y∼0.1, whereas excess copper correlates with a strong magnetocrystalline anisotropy indicating the presence of narrow domain walls. Substitution of U by Y in U1−xYxCu2±ySi2∓y leads to a linear decrease of TM and for concentrations of 0.4≤x≤0.8 metamagnetic behavior is observed. The antiferromagnetic transition is followed by a ferromagnetic alignment of the U atoms below the Néel temperature. The maximum of the anisotropy energy coincides with the minimum in the c parameter at x∼0.65. The Y-rich alloys U1−xYxCu2∓ySi2±y display antiferromagnetism with a rather complex structure as indicated by the change of sign of the paramagnetic Curie–Weiss temperature θp. In the U1−xYxCr2Si2 alloys the antiferromagnetic coupling is destroyed by rather small amounts of Y.
Ion-beam mixing in an Al-Fe-Mn system: A conversion-electron Mössbauer and x-ray diffraction study
Authors: Yedave S. N. , Chaudhari S. M. , Kanetkar S. M. , Ogale S. B. , Ghaisas S. V.
Published: July 2002

The formation of mixed metastable phases as a result of ion-beam mixing of the Al-Fe-Mn system with 100-keV Ar+ ions and their subsequent transformations upon thermal annealing have been studied. The mixed state is comprised of both binary (Fe-Al, Fe-Mn, Mn-Al) and ternary (Al-Fe-Mn) metastable phases. Conversion-electron Mössbauer spectroscopy and low-angle x-ray diffraction studies reveal the formation of disordered phases upon ion beam mixing, which acts as a precursor for the growth of the equilibrium phases upon thermal annealing via lowering of kinetic barrier for the reactions.
Method for reducing the longitudinal voltage variation in transverse radio-frequency discharge waveguide lasers
Authors: Kim Youn-Myung , Youn Chan Eui , Ra Jung Woong , Kim Yeong Sik , Kim Yeong Sik
Published: July 2002

With optimal inductors shunted at the end of the transverse radio-frequency (rf) discharge waveguide laser, the longitudinal voltage variation across a waveguide channel can be reduced. If multiple inductors are shunted at the appropriate positions, an almost perfect rf uniformity may be attained. All the optimum inductances are derived from the conventional transmission line theory.
Role of the mid-gap level as the dominant recombination center in platinum doped silicon
Authors: Gill Asghar A. , Baber N. , Iqbal M. Zafar
Published: July 2002

The problem of identification of the dominant recombination center in platinum-doped silicon is investigated using deep-level transient spectroscopy (DLTS). Measurements using electrical and optical injection on platinum-doped n type silicon are reported. Results of measurements show that the recently observed platinum-related midgap level is an efficient recombination center and is probably responsible for the role of platinum as a lifetime killer. In addition, information is provided on the relative magnitudes of the electron and hole capture cross sections of the hitherto well-known deep levels assigned to platinum.
Evidence for the alloy broadening of the emission and capture rates of the D
X center from the frequency dependence of capacitance of Schottky barriers on AlxGa1−xAs:Si
Authors: Anand S. , Subramanian S. , Arora B. M.
Published: July 2002

The frequency dependence of capacitance of Schottky barriers on AlxGa1−xAs:Si shows evidence of the alloy broadening of the emission and capture rates of the DX center. The data are analyzed by assuming a Gaussian distribution for the emission and capture barriers of the DX center. The variation of the high-frequency (1-MHz) capacitance as a function of temperature suggests a temperature dependence of the ionization energy of the DX center that might arise from an entropy contribution to the ionization energy of the DX center as suggested by Theis et al. [Mater. Sci. Forum 38–41, 1073 (1989)].
Comment on ‘‘Native acceptor levels in Ga-rich GaAs’’ [J. Appl. Phys. 6
5, 596 (1989)]
Authors: Moore W. J. , Shanabrook B. V.
Published: July 2002

Recent results suggesting that 78-meV acceptors appear only in n-type material while 68-meV acceptors appear in p-type material are in direct conflict with several clear experiments which establish the existence of a 78-meV acceptor in p-type GaAs beyond any reasonable doubt. The available evidence for the 78-meV center is reviewed and some possible sources of error in DLTS and photoluminescence data are mentioned.
Phase transition behaviors and selective optical properties of a binary cholesteric liquid crystals system: Mixtures of oleyl cholesteryl carbonate and cholesteryl nonanoate
Authors: Tai Hua-Shan , Lee Jiunn-Yih
Published: July 2002

This paper deals with the phase transition behaviors of the mixtures of oleyl cholesteryl carbonate and cholesteryl nonanoate by means of optical and differential scanning calorimetry methods. The iridescent colors were measured by using the spectro multichannel photodetector. The phase diagrams show that the smectic mesophase appears in the whole concentration ranges under cooling, but only exists in heating with concentration less than 60%. The phase transition temperatures of the mixtures increase monotonically with increase of cholesteryl nonanoate (CN) contents. This phenomenon has been interpreted from the viewpoints of molecular configurations. The iridescent colors vary from red to violet as the temperature increases, and in reverse order when cooling. The concentration ranges of the iridescence are in agreement with those of smectic existence. Results also indicate that the color band shifts monotonically toward higher temperatures with an increased concentration of CN. This effect is accompanied by a gradual expansion of the temperature interval of the color band. The temperature dependence of the color shift may be explained with the pretransition of twist or untwist of the helical structures. Reflection bandwidth variations with temperature are also attributable to pretransitional effects. The temperature dependence of selectively reflected light intensity measurements reveals that the sensitivity decreases with increase in the wavelength. Moreover, 50% CN concentration is most sensitive, whether heating or cooling.
A transmission electron microscopy study of the (Sm,Pr)5Co19 phase
Authors: Shen Y. , Laughlin D. E.
Published: July 2002

Transmission electron microscopy has been used to characterize the rhombohedral 5:19 phase (R3̄m) in a stoichiometric (Sm0.75Pr0.25)5Co19 alloy. In some regions, strain-induced contrast was observed in the 5:19 phase. By contrast analysis, this strain contrast was associated with a displacement vector of the type (1)/(3) [011̄0]. In other regions where the strain-induced contrast was significantly reduced, faults with the crystal structure of hexagonal (Sm,Pr)2Co7(2:7H) phase (P63/mmc) were observed. The formation of the faults is believed to release elastic energy within the 5:19 phase. In the interface regions between the 5:19 phase and the minor component hexagonal 2:7H phase, it was found by lattice imaging that the 5:19 and 2:7H plates are superimposed with a common c direction. The orientation relationship between the 5:19 and 2:7H phases is given by [0002]2:7H∥[0003]5:19R and [112̄0]2:7H∥[112̄0]5:19R.
CO2 laser treatment of As-S chalcogenide thin films
Authors: Andriesch A. M. , Bertolotti M. , Ferrari A. , Popesku A. A.
Published: July 2002

The changes of the refractive index of As2 S3 and As2 S5 films deposited on glass substrates upon CO2 laser irradiation have been studied. The possibility of writing with the CO2 laser a waveguiding channel in As2 S3 is demonstrated.
Formation of stable and highly resistive anodic oxides on InP
Authors: van de Ven J. , Binsma J. J. M. , de Wild N. M. A.
Published: July 2002

When left in air, as-grown anodic oxides grown under optimized conditions described in the literature have been found to age. It is shown that this is caused by a hygroscopic component in the outer indium-rich layer of the oxide film. When oxalic acid is present in the forming electrolyte, this phenomenon is not observed: As-grown oxides are stable and have a constant composition throughout their thickness. This paper discusses some of the properties of the oxide films, both as-grown and annealed, and some aspects of the chemistry of their formation. This distinct behavior of oxalic acid can be attributed to the fact that it forms soluble complexes with In(III) in the relevant pH range.
Interaction of molecular hydrogen with trapped hole E′ centers in irradiated and high field stressed metal/oxide/silicon oxides
Authors: Lenahan P. M. , Warren W. L. , Krick D. T. , Dressendorfer P. V. , Triplett Baylor B.
Published: July 2002

We explore the effect of forming gas anneals at 110 °C on E′ centers in metal/oxide/semiconductor oxides subjected to gamma, electron, and vacuum ultraviolet irradiation, as well as high electric field stressing. We find that this brief low-temperature anneal substantially reduces E′ density in all cases, clearly demonstrating that hydrogen reacts readily with the E′ sites. Although this work confirms a recent report of the reactivity of E′ and hydrogen we fail to detect the reported reaction product known as the 74-G doublet.
The effect of electron irradiation on YBa2Cu3Ox with gold bead contacts
Authors: Caton R. , Selim R. , Buoncristiani A. M. , Byvik C. E.
Published: July 2002

We have investigated the effect of 1-MeV electron irradiation up to a total dose of 5.7×1017 electrons/cm2 at room temperature on YBa2Cu3Ox with gold bead contacts made by the melting technique. We measured the superconducting transition temperature Tc, the critical current density Jc at 77 K, the normal-state resistivity, and the contact resistance for gold bead contacts as a function of fluence on the same samples without disturbing the contacts. Tc remained constant at 91 K, and Jc at 77 K remained constant around 90 A/cm2. The normal-state resistivity increased systematically by about 15% for the total dose. Finally, the surface contact resistance at 77 K remained less than 4.2 μΩ cm2 throughout the radiations. These studies took place over an 8-month period, and subsequent measurements indicate that the results are definitely due to radiation effects and not aging effects. Since the total dose represents 120 years of electron exposure in geosynchronous orbit, we conclude that the superconductor YBa2Cu3Ox with gold bead contacts would perform well in a space environment of electron irradiation.