bluuebunny/crossref_metadata_2025 huggingface dataset:
Falling ball experiments in a dilute electrorheological fluid
Authors: Zitter R. N. , Zhang Xuesong , Chen Tian-Jie , Tao R.
Published: July 2002

The velocity v of a glass ball falling through a dilute electrorheological fluid of silica gel particles in oil is measured as a function of applied electric field E for various particle sizes and concentrations. The fields used range up to the point where the ball ceases to fall. The results are consistent with a model using two types of field-dependent retarding force, one proportional to E2 and the other proportional to vE2. The latter is proportional to both particle size and particle volume fraction, while the former is independent of particle size and is significant only above a volume fraction c0 where it is proportional to c−c0. The force in E2 is related to the yield stress and is attributed to chain breaking by the ball. The force in vE2 is attributed to transient chain deformations when the ball impacts chains.
High temperature adsorption of nitrogen on a polycrystalline nickel surface
Authors: Boughaba S. , Auvert G.
Published: July 2002

Nickel tetracarbonyl [Ni(CO)4] molecules were used as a probe to investigate the coverage of a heated polycrystalline nickel surface with nitrogen adspecies. For this purpose, the deposition kinetics of nickel (Ni) microstructures from the thermal decomposition of nickel tetracarbonyl was investigated as a function of the partial pressure of nitrogen (N2), used as buffer gas. The laser-induced chemical vapor deposition technique was used to produce polycrystalline nickel lines in an atmosphere of pure Ni(CO)4 or a [Ni(CO)4+N2] mixture. The deposition process was performed on polysilicon/silicon dioxide/〈100〉 monosilicon substrates. As a heat source, a cw argon-ion laser was used. The laser-induced surface temperature was varied in the range 500–850 °C. For Ni(CO)4 partial pressures typically below 0.3 mbar, the nickel deposition rate was found to decrease as the N2 partial pressure increases. For higher Ni(CO)4 partial pressures, the deposition rate was found to be independent of the N2 partial pressure. On the basis of these results, the high temperature adsorption of nitrogen on a polycrystalline nickel surface was investigated. A model which accounts for the dependence of the nickel deposition rate and surface coverage with nitrogen adspecies on the N2 partial pressure was elaborated.
Technique for evaluating second-order nonlinear optical materials in powder form
Authors: Kiguchi M. , Kato M. , Kumegawa N. , Taniguchi Y.
Published: July 2002

A technique for evaluating second-order nonlinear optical materials in powder form is described. The power of the second-harmonic wave generated with the evanescent wave (SHEW) loosely depends on the phase matchability of material. The largest element of the nonlinear optical coefficient can be estimated from the SHEW power, regardless of the phase matchability of the material in a bulk crystal, even when powder crystals are used as the sample. The sample setting condition that gives appropriate repeatability is obtained, and the accuracy of this measurement is also discussed. Several well-known materials are measured using this technique, and the results are compared with other works.
Single Bloch wall dynamics in amorphous ribbons: A comparison between experimental and theoretical results
Authors: Maraner A. , Beatrice C. , Mazzetti P.
Published: July 2002

A numerical approach is introduced to study the motion of a single bowed domain wall in an isotropic ferromagnetic lamination under general conditions of time dependence of the exciting magnetic field. A large set of numerical results concerning the behavior of Bloch walls in a magnetostrictive amorphous ribbon (Allied Signal Metglas 2605 SC), submitted to a sinusoidal field of varying amplitude and frequency is reported and discussed. The results are compared with the ones reported in the literature and obtained through different methods of calculation. The present approach allows one to get valuable information on the effect of wall bowing on the magnetic permeability, the so-called magnetic skin effect and the critical field which corresponds to a domain-wall instability resulting in wall multiplication. The peculiar behavior of the phase shift between wall oscillations at the lamination surface and within the lamination bulk appears to be very sensitive to the value of the wall’s surface energy density σw, at least within an appropriate frequency domain, thereby suggesting a reliable method of measuring this quantity. Actual measurements performed on a Metglas 2605 SC ribbon by using a Kerr-effect optical technique are reported and compared with the theoretical predictions. When a tensile stress of about 500 MPa is applied to this highly magnetostrictive material to provide a regular pattern of straight domain walls aligned along the ribbon axis, a value of σw=1.7×10−3 J/m2 is found. This value is consistent with the one calculated from the magnetostriction and the exchange energy coefficient of Metglas 2605 SC, which is between 1.4×10−3 and 1.8×10−3 J/m2. Measurements of the behavior of the wall oscillation amplitude as a function of the field intensity are also reported and discussed.
Dielectric properties of lanthanum gallate (LaGaO3) crystal
Authors: Dube D. C. , Scheel H. J. , Reaney I. , Daglish M. , Setter N.
Published: July 2002

Dielectric properties of single crystals of LaGaO3 have been measured at low frequencies as well as in the microwave region over a wide temperature range. Measurements performed on two crystal orientations, viz. (001) and (110), show dielectric anomalies at a transition near 145 °C. Dielectric anisotropy below, but not above, 145 °C confirm the previously reported orthorhombic symmetry at room temperature and rhombohedral symmetry above 145 °C. Domain wall motion which arises as a result of a phase transition has been observed around 145 °C.
Observation of nonstationary transport in deep submicron n-channel metal-oxide-semiconductor transistors with Shubnikov–de Haas oscillations
Authors: Miéville Jean-Paul , Ouisse Thierry , Cristoloveanu Sorin , Forro Lazlo , Revil Nathalie , Dutoit Michel
Published: July 2002

The effect of the lateral electric field on the amplitude of Shubnikov–de Haas oscillations in Si metal-oxide-semiconductor field-effect transistors (MOSFETs) with gate lengths ranging from 0.1 to 2 μm was studied. The amplitude of these oscillations at liquid helium temperature is larger in the shortest devices and decreases less rapidly with the electric field. This result is interpreted as a decrease of the electron temperature. Indeed, in this case, the carrier transit time is shorter than the energy relaxation time. This provides strong evidence for nonstationary transport in 0.1 μm n-MOSFET.
Impact of field-dependent electronic trapping across Coulomb repulsive potentials on low frequency charge oscillations
Authors: Joshi R. P. , Schoenbach K. H. , Raha P. K.
Published: July 2002

We have performed Monte Carlo simulations to obtain the field dependence of electronic trapping across repulsive potentials in GaAs. Such repulsive centers are associated with deep level impurities having multiply charged states. Our results reveal a field-dependent maxima in the electronic capture coefficient, and the overall shape is seen to depend on the background electron density due to the effects of screening. Based on the Monte Carlo calculations, we have examined the stability of compensated semiconductors containing such repulsive centers. Our analysis indicates a potential for low frequency charge oscillations which is in keeping with available experimental data.
Multistable behavior of connected bistable devices
Authors: Nara Shigetoshi , Tokuda Yasunori , Abe Yuji , Yasukawa Masataka , Tsukada Noriaki , Totsuji Hiroo
Published: July 2002

The complex multistable responses of two bistable elements optically connected in series are theoretically analyzed. Each bistable element is a self-electro-optic device. The analysis is based on a phenomenological rate equation for photocarrier density. All experimentally observed multistable responses to the wavelength of input light can be qualitatively well described. It is also shown that multistable responses to optical input power can be derived within the present treatment, and a few examples are demonstrated by experiment.
Effect of structure length on relativistic backward-wave oscillator properties
Authors: Barreto Gilberto , Butler Jennifer M. , Wharton C. B.
Published: July 2002

Data show that a high-power backward-wave oscillator’s (BWO) nonlinear saturation properties are dependent on slow-wave structure length. Results from an experimental investigation comparing the individual output from two high-power (60 MW), X-band BWOs operating in the Raman regime at saturation amplitudes are presented. The two BWO slow-wave structures are identical in all respect except length. Comparisons are made of the BWOs’ microwave frequency, peak power, and pulsewidth output which are, in turn, parameterized with respect to the electron beam energy.
Transmission Mössbauer spectroscopy and x-ray diffraction studies on the structure of nanocrystalline Fe-Cu-Si-B alloys
Authors: Liu X. D. , Lu K. , Hu Z. Q. , Ding B. Z. , Zhu J. , Jiang J.
Published: July 2002

Nanocrystalline Fe-Cu-Si-B alloys with grain sizes of 25–90 nm were synthesized by crystallization of the amorphous alloy. Two nanocrystalline phases of α-Fe(Si) and Fe2B were observed in all tested samples. Transmission Mössbauer spectroscopy investigation on the structure of nanocrystalline Fe-Cu-Si-B alloys showed that Si atoms are completely and substitutionally dissolved in Fe bcc lattice and the arrangement of the Si atoms in the α-Fe(Si) phase shows short range order (SRO), whereas 8.5–9.7 at. % of the B atoms were found as Fe2B and the remainder were located in the interfaces. When grains grow larger, the arrangement of the Si atoms in the α-Fe(Si) phase changes. Interestingly, x-ray diffraction results reveal that the lattice constant of α-Fe(Si) phase decreases rapidly with grain coarsening. Based on the thermodynamic analysis, the changes in the lattice constant of the α-Fe(Si) phase and SRO of Si atoms in bcc Fe lattices were attributed to the lattice expansion as a result of the variation of vacancy concentration in α-Fe(Si) solid solution. Meanwhile, owing to the interface contribution, the alloy with small grain size is found to exhibit large values of half linewidth (HLW) and isomer shift (IS) in the Mössbauer spectra. The results from electrical resistivity measurements agree and confirm the strong effects of the lattice distortion and interfaces.
Adhesion of electrolessly deposited Ni(P) layers on alumina ceramic. I. Mechanical properties
Authors: Severin J. W. , Hokke R. , de With G.
Published: July 2002

The adhesion mechanism of electrolessly deposited Ni(P) on alumina ceramic substrates has been investigated. The adhesion was measured by direct pull-off tests and by 90° peel tests, which provided information on adhesion strength and fracture energy, respectively. An assessment is made of quantitative aspects of both adhesion measurement techniques. The observed mechanical behavior is rationalized using the Griffith–Irwin theory. Two types of alumina substrates with different roughnesses were used. Ni(P) was deposited from two types of electroless Ni(P) solutions, one with glycine and one with acetate as the complexing agent. The fracture surfaces were analysed with scanning electron microscopy, combined with energy dispersive analysis of x rays. The adhesion strength of the glycine-type Ni(P) was much higher and the fracture energy was lower than that of the acetate-type Ni(P), for both substrate types. This implies that the difference in adhesion strength is not caused by differences in interfacial chemical bonding, but rather by differences in flaw sizes. Since high adhesion strength was measured on smooth substrates, along with low peel strength, it is concluded that strong adhesion can be obtained without making use of mechanical interlocking. Further research should be aimed at controlling the interfacial flaw sizes.
Phonon scattering suppression in short periodic AlAs/GaAs multiple-quantum-well structures
Authors: LeTran T. T. , Schaff W. J. , Ridley B. K. , Chen Y. P. , Clark A. , Eastman L. F.
Published: July 2002

The suppression of longitudinally polarized optical-phonon (LOP) electron scattering in multiple quantum wells (MQWs) was sought in short periodic AlAs/GaAs with well widths of 12, 15, and 20 monolayers and AlAs barrier widths of 2 and 4 monolayers, based on a study of electron mobility in the plane of the MQW. Two-dimensional electron-gas structures with MQWs of up to eight wells in their channel were grown. Their mobilities at room temperature were slightly reduced, as compared to samples without MQW channel, due to interaction with interface polaritons from AlAs barriers, while mobility at temperatures <50 K improved due to reduction of remote ionized impurity scattering. The theoretical analysis of the results based on the model of hybridon-electron interaction in an infinite superlattice is presented. The reduction of room-temperature mobility in the MQWs is believed to be caused by the interaction of electrons with both barrier interface-polariton (IP) -like modes and the well LOP-IP hybrids. An alternative explanation of the results of a similar experiment done elsewhere is offered denying the evidence of strong suppression of LOP scattering there.
ErSb/GaSb(001) and GaSb/ErSb/GaSb(001) heterostructures and [ErSb,GaSb] superlattices: Molecular beam epitaxy growth and characterization
Authors: Guivarc’h A. , Ballini Y. , Toudic Y. , Minier M. , Auvray P. , Guenais B. , Caulet J. , Le Merdy B. , Lambert B. , Regreny A.
Published: July 2002

Successful growth of ErSb(001) single crystal layers on GaSb(001) substrates has been demonstrated. The reflection high-energy electron diffraction patterns show a (4×4) surface reconstruction. Reflection high-energy electron diffraction oscillations, x-ray diffraction, and Rutherford backscattering with channeling indicate single crystal monolayer-by-monolayer growth and continuity of the Sb sublattice at the ErSb/GaSb interface. The ErSb has a low room temperature resistivity equal to 30 μΩ cm but may be used as a metallic reflector only for wavelengths greater than 2.4 μm. The overgrowth of GaSb on ErSb leads to mirrorlike surfaces but the overlayers contain symmetry-related defects. On the contrary, nearly perfect GaSb overlayers were grown on [ErSb,GaSb] superlattices which exhibit metallic behavior.
Electronic structure of anatase TiO2 oxide
Authors: Sanjinés R. , Tang H. , Berger H. , Gozzo F. , Margaritondo G. , Lévy F.
Published: July 2002

Photoemission spectromicroscopy was used to investigate the electronic structure of TiO2 anatase single crystals and polycrystalline thin films. The stoichiometry and the degree of oxidation of as-grown crystals, as-deposited films, as well as of thermally annealed samples in different atmospheres, were analyzed, based on the Ti 2p and O 1s core levels, with an energy resolution of 0.4 eV. The experimental density of states (DOS) was found to be in agreement with the theoretical DOS reported in the literature for anatase crystals, and shows some characteristics similar to the experimental DOS reported for rutile crystals. In reduced samples, the experimental DOS is characterized by intense emission in the region of O 2p bonding orbitals, and does not exhibit an appreciable density of states in the band gap. As-grown crystals exhibit small band gap emission (a few percent of the valence band VB signal) at about 0.8 eV, which is attributed to Ti3+ (3d) defect states. Annealing the crystals at high temperatures in O2 or subsequent thermal reduction in an Ar–H2 mixture (95%–5%) produces nearly stoichiometric surfaces with smaller or undetectable density of Ti3+ states. In addition, some redistribution of the spectral weight is observed in the VB spectra.
Transport measurements and donor spectra of very high purity GaAs grown using tertiarybutylarsine and triethylgallium
Authors: Watkins S. P. , Brake Darlene M. , Haacke G.
Published: July 2002

Very high purity n-type GaAs epilayers were grown by low pressure metalorganic chemical vapor deposition using triethylgallium and tertiarybutylarsine (TBA) or arsine (AsH3). Peak Hall mobilities of 209 000 cm2/V s at 45 K were observed for growth with TBA. Carrier concentration and mobility measurements down to liquid helium temperatures verified the high purity of these layers. Scattering mechanisms were determined by fits to the mobility data, and found to be in agreement with previous high purity GaAs studies. Donor identification was carried out using magnetophotoluminescence spectroscopy. A comparison of the residual donor species for AsH3- and TBA-grown epilayers is presented. No evidence of preferential n-dopant incorporation was observed for layers grown with TBA.
An alternative degradation method for amorphous hydrogenated silicon: The constant degradation method
Authors: Brandt Martin S. , Stutzmann Martin
Published: July 2002

To study the kinetics of metastable defect creation in amorphous hydrogenated silicon we introduce the Constant Degradation Method as a new experimental scheme. In contrast to conventional degradation experiments in which the incident light intensity is constant during light soaking, in this method the photoconductivity of the sample is kept constant by continuously increasing the light intensity. In this case a linear time dependence of the required light intensity and of the resulting defect density is observed experimentally. A detailed analysis of the method shows that the data obtained are in accordance with the assumption of the ‘‘bond-breaking’’ model, i.e., the metastable defects are created by bimolecular recombination of localized electron-hole pairs. The observed time dependence is at variance with the stretched exponential time dependence predicted for dispersive transport models. Effects of sample heating due to high light intensities and of Fermi level shifts on the observed time dependence are also discussed.
Investigation of trap emission kinetics in metal-oxide-semiconductor capacitors using a pump-probe charge integrating technique
Authors: Poler J. C. , Irene E. A.
Published: July 2002

We apply a new pump-probe charge integrating measurement technique for studying the emission kinetics of traps in the M/SiO2/Si system. Essentially, a metal-oxide-semiconductor (MOS) capacitor is pumped by exposure to a charging pulse. The emission of the charge at short time scales (<10 ms), is measured using a delayed application of a probe pulse, that determines the remainder of the filled traps as a function of delay time. For MOS capacitors fabricated on p-Si(111) and (100) substrates, we observe trap interaction that is dramatically reduced by post-metallization annealing. Based on the effects of Si doping levels and oxide thickness, the oxide-Si interface region is shown to dominate the trap emission kinetics. A model for the trap interaction phenomena is proposed based on a perturbation of the emission cross section of the probed traps due to the presence of another state in communication with the trap site.
Modeling of the static properties for double-δ transistors
Authors: Schulze D. , Gobsch G. , Eisele I. , Kiunke W.
Published: July 2002

Molecular-beam epitaxy of silicon permits the growth of any layers desired on large areas with a high reproducibility. A vertical arrangement of several thin ‘‘delta layers’’ in combination with local epitaxy and selective etching leads to a new kind of electron device using the third dimension. With a delta layer thickness of about 2 nm and by varying other device dimensions within a few nanometers, electron devices with threshold voltages on the order of magnitude of a few volts were possible. Selective contacts to the individual delta layers permit vertical transport studies. In the resistance-gate voltage characteristic of a vertical double-delta transistor with an effective gate length of about 90 nm periodic oscillations are clearly observed. It can be shown that in the transistor, three two-dimensional electron systems meet each other perpendicularly. The calculation of the electronic structure of the device is carried out with a simple but reasonably exact method. The calculated eigenvalue spectrum corresponds well with the observed oscillations in the experimental resistance-gate voltage characteristic and permits its interpretation.
Elastic constants and high-temperature elastic anomalies near 425 K in lithium hydrazinium sulfate
Authors: Godfrey L. , Philip J. , Sebastian M. T.
Published: July 2002

All the nine elastic constants of the orthorhombic crystal lithium hydrazinium sulfate, Li(N2H5)SO4, have been determined by measuring ultrasonic velocities using pulse echo overlap technique at 10 MHz. Temperature variation of all the six diagonal elastic constants and the three off-diagonal combinations have been measured between 300 and 450 K. Some of the constants show anomalous behavior in the 410–440 K temperature region, which is attributed to a phase transition in the crystal near 425 K. Magnitude of the velocity anomaly is comparatively small. A new high-temperature ultrasonic bond material suitable for transverse waves is also reported.
Quantitative model for photocurrent spectroscopy of quantum-well diodes including transit-time and background-doping effects
Authors: Leavitt R. P. , Bradshaw J. L. , Pham J. T. , Tobin M. S.
Published: July 2002

We present a simple model for photocurrent spectroscopy of quantum-well p-i-n diodes that provides a quantitatively accurate desciption of the dependence of photocurrent on absorption coefficient and applied bias. The model incorporates the transit-time effect described previously [R. P. Leavitt and J. L. Bradshaw, Appl. Phys. Lett. 59, 2433 (1991)] as a limiting case. It also includes the two major effects of residual background doping in the intrinsic region of the diode: nonuniform electric fields, which affect the transport of carriers, and incomplete depletion at low electric fields, which reduces the amount of photocurrent collected. We show that the background-doping effect alone can mimic the transit-time effects: reduction in the overall carrier collection efficiency, saturation of photocurrent spectral features, and the presence of minima in photocurrent where absorption spectra show maxima. We obtain a closed-form expression for the photocurrent in the general case where both transit-time and background-doping effects are significant. Excellent agreement is obtained between model calculations and experimental room-temperature photocurrent spectra for an 89-period 100-Å GaAs/100-Å Al0.3Ga0.7As multiple-quantum-well diode, where the background doping density, the effective electron mobility, and the built-in potential are treated as adjustable parameters. The background doping density and the built-in potential obtained from the fit are in excellent agreement with independent measurements. We apply the model to predict the dependence of photocurrent on the intrinsic-region thickness of the diode. We also show a dramatic asymmetry between photocurrent spectra measured with light incident from the front and from the back of the diode, and we discuss the impact of this asymmetry on the performance of self-electro-optic-effect devices. We also find good agreement between the model predictions and the photocurrent results of Whitehead et al. [Appl. Phys. Lett. 52, 345 (1988)]. Further, our model qualitatively describes the dependence of the photoluminescence intensity on electric fields in multiple-quantum-well p-i-n diodes.
Chemical effects induced by hydrogen plasma exposure on tungsten-implanted glassy carbon
Authors: Hoffman A. , Evans P. J.
Published: July 2002

The effect of hydrogen plasma erosion of glassy carbon implanted with tungsten has been studied for a dose of 2.5×1016 ions/cm2 and an average ion energy of 60 keV. Raman measurements of the tungsten-implanted layer prior to and after exposure to the hydrogen plasma revealed that the damaged layer induced by tungsten ion bombardment, unlike by C+ bombardment, has not been completely removed in the plasma erosion process. Auger profile measurements were performed on the as-implanted layer and after exposure to a hydrogen plasma for 1 h. By comparing the tungsten depth distribution for these two cases the hydrogen plasma erosion rate of tungsten-implanted glassy carbon has been estimated. It has been found that during the first hour of exposure to the hydrogen plasma the average erosion rate of the implanted layer was estimated to be 265±35 Å/h. In contrast the erosion rate of unimplanted glassy carbon in the hydrogen plasma was found to be 3000±300 Å/h.
An activation energy study of the microstructural changes in Al-1%Si interconnects
Authors: Stulens H. , Knuyt G. , De Ceuninck W. , De Schepper L. , Stals L.
Published: July 2002

There are several reasons to believe that the microstructural changes in Al-Si interconnects has to be described in terms of a spectrum of activation energies rather than in terms of a single activation energy. In this article, a method is presented to extract a spectrum of activation energies from an isothermal and a constant heating rate experiment. The formalism was applied to the relaxation behavior of passivated Al-1%Si interconnects. The method of analysis shows that the microstructural relaxation mechanisms in these interconnects are characterized by a narrow spectrum, centered at an energy of about 1.2 eV.
Hole traps produced by swift heavy ion irradiation in p-type germanium
Authors: Marie P. , Levalois M.
Published: July 2002

Lightly doped, p-type germanium has been irradiated at room temperature with swift heavy ions. Several hole traps, detected by means of deep level transient spectroscopy, have energies determined to be EV+0.22, EV+0.41, and EV+0.33 eV. The results are compared with those previously obtained for n-type germanium, and the defects are the same in the two kinds of materials: Divacancies and vacancies–impurity complexes.
X-ray diffraction and x-ray absorption studies of porous silicon, siloxene, heat-treated siloxene, and layered polysilane
Authors: Dahn J. R. , Way B. M. , Fuller E. W. , Weydanz W. J. , Tse J. S. , Klug D. D. , Van Buuren T. , Tiedje T.
Published: July 2002

Several porous silicon, siloxene (Si6H6O3), heat-treated siloxene, and layered polysilane (Si6H6) samples have been studied with K- and L-edge x-ray photoabsorption, photoemission, and powder x-ray diffraction. The x-ray absorption of layered polysilane and porous-Si are found to be remarkably similar. In particular, the K absorption edges of these samples shift by about 0.4–0.6 eV to higher energy relative to crystalline silicon. Siloxene samples heated to 400 °C in inert gas are best described as a mixture of SiO2 and amorphous-Si. When heat-treated siloxene is studied by photoelectron spectroscopy (surface sensitive) it resembles SiO2, when it is studied by x-ray absorption (bulk and surface) features from both SiO2 and amorphous-Si are observed and when it is studied by x-ray diffraction (bulk measurement) it resembles amorphous-Si. The SiO2 is therefore predominantly at the surface and heat-treated siloxene is very small amorphous-Si particles coated with SiO2. The Si L edge of heat-treated siloxene is not shifted significantly with respect to crystalline Si, unlike that of porous-Si, as-prepared siloxene, or layered polysilane. Taken together, these results suggest that heat-treated siloxene does not resemble electrochemically prepared porous-Si but that it might resemble rapid thermal annealed porous-Si. On the other hand, we believe that layered polysilane and unheated porous-Si may be related.
Luminescence and electron paramagnetic resonance studies of white-light emitting SrS: Pr, F thin film electroluminescent devices
Authors: Lee Y. H. , Ju B. K. , Yeom T. H. , Kim D. H. , Hahn T. S. , Choh S. H. , Oh M. H.
Published: July 2002

The fluorescence emission and excitation spectra of white-light emitting SrS: Pr, F thin film electroluminescent devices have been investigated. It was determined from the results obtained that the dominant electroluminescence mechanism was that the ionization of Pr3+ centers occurs first, then subsequently recombination with electrons occurs, and finally Pr3+ center transitions give rise to luminescence. The emission mechanism of SrS: Pr, F seems to be the same as that of a SrS: Pr, K electroluminescent device, except for the appearance of strong peaks around 610–670 nm. The impurity excitation peak in the lower excitation energy, longer-wavelength region in the FL spectrum may be an important factor for the selection of an effective white-light emitting EL material. The electron paramagnetic resonance experiment of SrS: Pr, F was performed on powder and thin film specimens. The hyperfine structure of an isolated Mn2+ ion was observed in this SrS: Pr, F thin film. This Mn center which was substituted for Sr, seems to contribute to the strong red emission in the white EL spectrum.
Logical devices implemented using quantum cellular automata
Authors: Tougaw P. Douglas , Lent Craig S.
Published: July 2002

We examine the possible implementation of logic devices using coupled quantum dot cells. Each quantum cell contains two electrons which interact Coulombically with neighboring cells. The charge distribution in each cell tends to align along one of two perpendicular axes, which allows the encoding of binary information using the state of the cell. The state of each cell is affected in a very nonlinear way by the states of its neighbors. A line of these cells can be used to transmit binary information. We use these cells to design inverters, programmable logic gates, dedicated AND and OR gates, and non-interfering wire crossings. Complex arrays are simulated which implement the exclusive-OR function and a single-bit full adder.
Comparison of lead zirconate titanate thin films on ruthenium oxide and platinum electrodes
Authors: Bursill L. A. , Reaney Ian M. , Vijay D. P. , Desu S. B.
Published: July 2002

High-resolution and bright- and dark-field transmission electron microscopy are used to characterize and compare the interface structures and microstructure of PZT/RuO2/SiO2/Si and PZT/Pt/Ti/SiO2/Si ferroelectric thin films, with a view to understanding the improved fatigue characteristics of PZT thin films with RuO2 electrodes. The RuO2/PZT interface consists of a curved pseudoperiodic minimal surface. The interface is chemically sharp with virtually no intermixing of RuO2 and PZT, as evidenced by the atomic resolution images as well as energy dispersive x-ray analysis. A nanocrystalline pyrochlore phase Pb2ZrTiO7−x, x≠1, was found on the top surface of the PZT layer. The PZT/Pt/Ti/SiO2/Si thin film was well crystallized and showed sharp interfaces throughout. Possible reasons for the improved fatigue characteristics of PZT/RuO2/SiO2/Si thin films are discussed.
Fragmentation and emission of POPOP and coumarin dye vapor in an ultraviolet-preionized, transverse discharge
Authors: Herrick R. W. , Fraser R. D. , Eden J. G.
Published: July 2002

Intense, streamer-free discharges have been produced in POPOP (1,4-di[2-(5-phenyloxazolyl)]- benzene), α-NPO (2-(α-naphthyl)-5-phenyl-oxazole), PBBO (2-(4-biphenylyl)-6- phenylbenzoxazol-1,3), and coumarin dye vapors buffered in He or rare gas/N2 mixtures. The transverse discharge has an equivalent series inductance of ∼85 nH, a current rise time of ∼50 ns, a pulse width (FWHM) of ∼140 ns, and active lengths up to 50 cm. For specific power loadings of rare gas/POPOP vapor mixtures ranging from 2 to ∼11 MW cm−3, the wavelength-integrated fluorescence falls to 50% of its initial value after 150–200 shots (at ∼620 K) and emission bands of CN and C2 appear. Under comparable conditions, the fluorescence efficiency of α-NPO is only 40% of that for POPOP vapor. The coumarin dyes are considerably less stable than POPOP and strong fluorescence on the Swan bands of C2 is observed after only a few shots. Net optical loss is measured when Ne/N2/POPOP vapor discharges are probed with a dye laser at ∼400 nm.
Transient absorption and its influence on energy extraction in a discharge-pumped F2 laser
Authors: Kakehata M. , Ueno Y. , Tamura K. , Kannari F.
Published: July 2002

Small-signal transient absorption of a discharge-pumped F2 laser (157.6 nm) medium was measured by using a Raman-shifted F2 laser (168.6 nm). The small-signal total absorption was obtained for 6 atm laser media at an excitation rate of ∼26 MW/cm3, where a small-signal net gain was independently measured to ∼35%/cm, as the sum of a transient absorption of ∼2.5%/cm and a stationary absorption of ∼0.5%/cm. In spite of the relatively large gain-to-loss ratio a significantly low maximum laser intensity of ∼2 MW/cm2, which gives zero extraction efficiency in the F2 laser medium, measured in heavily saturated F2 laser amplification experiments, suggests that the energy extraction is limited by additional absorption.
Edge effects in molybdenum-encapsulated molten silicate shock wave targets
Authors: Miller Gregory Hale , Puckett Elbridge Gerry
Published: July 2002

The customary acoustic calculation used to design shock wave equation of state targets may be inapplicable when the sample is enveloped in a container that has a higher shock impedance than the sample being studied. In this case the edge effect is compressional, and could travel faster than the speed of sound. We present computations of the nonlinear wave interactions that occur at the sample-container interface of molybdenum-encased molten silicate shock wave targets. In all cases considered here, the edge effect is acoustic despite the higher shock impedance of the container. The computational method is an extension of a conservative Eulerian finite difference scheme for two materials in two dimensions that is based on a second-order Godunov method. This new method includes adaptive mesh refinement, a volume-of-fluid interface tracking algorithm, and a Mie-Grüneisen equation of state to describe liquids and solids in the hydrostatic limit.
Theory for the oscillatory cyclotron resonance effective mass in a heterostructure
Authors: Gumbs Godfrey , Huang Danhong , Zhang Chao , Manasreh M. O.
Published: July 2002

The Hartree–Fock treatment of cyclotron resonance (CR) [see A. H. MacDonald, J. Phys. C 18, 1003 (1985)] is generalized by including the correlation contribution to the screening by the electrons. It is found that the CR effective mass m* is an oscillatory function of the magnetic field, which is due to the filling-factor-dependent dynamic screening of the electron-impurity scattering. It is demonstrated that as the Landau levels are depleted with increasing magnetic field, m* has a maximum at half-filling. Similar behavior has also been found in CR absorption of the two-dimensional electron gas in a high-mobility heterostructure.
Nanometer-scale pit formation by scanning tunneling microscopy on graphite surface and tip current measurements
Authors: Abe Tsukasa , Hane Kazuhiro , Okuma Shigeru
Published: July 2002

Nanometer-scale pit formation by the application of pulse voltage was performed on highly oriented graphite in air with the simultaneous measurement of tip current. The tip current was measured to be on the order of microamperes. Regardless of the high current, the pit was not formed at pulse voltages less than a critical value. It is confirmed by the quantitative measurement of the current that high current is less important for pit formation under experimental conditions. The measurement of the critical voltage as a function of the tunnel resistance suggested the significance of high electric field for pit formation.
Bistability in polymer-dispersed ferroelectric liquid crystals
Authors: Molsen Henning , Kitzerow Heinz-S.
Published: July 2002

The encapsulation of ferroelectric liquid crystal droplets in a polymer film provides a convenient method to get fast switching, flexible electro-optic light shutters. The polymer-dispersed ferroelectric liquid crystal films can be formed by photopolymerization due to a polymerization-induced phase separation. A uniform orientation of the liquid crystal is obtained by shear flow during this process. Our studies concerning the influence of the preparation parameters on the electro-optic properties show that a bistable electro-optic behavior can be achieved for high polymerization rates and low shear velocities.
Nitrogen laser employing twin sliding discharges
Authors: Tzolov V. P. , Grozdanov K. A. , Atanasov P. A.
Published: July 2002

Twin sliding discharges are used in an ultraviolet nitrogen laser as a direct excitation mechanism as well as a preionizer at the same time. Addition of SF6 is found to cause the appearance of a volume discharge between the two sliding discharges and an increase of the laser output energy by a factor of 9. Under optimum conditions a pulse energy as high as 3.1 mJ from a 16 cm3 active volume is achieved. Investigations of the temporal behavior and the spatial properties of the laser output are presented.
Raman spectroscopy and spreading resistance analysis of phosphorus implanted and annealed silicon
Authors: Othonos Andreas , Christofides Constantinos , Boussey-Said Joumana , Bisson Michel
Published: July 2002

Raman and electrical characterization measurements are performed in order to study the effects of thermal annealing on phosphorus implanted silicon wafers. The silicon layers were implanted for various implantation energies and doses, below, and over the critical dose of amorphization. The post-implanted period was followed by thermal isochronal annealing at various temperatures. Special attention has been given to the amorphous/crystal transition occurring at various annealing temperatures. A bi layer model [R. Loudon, J. Phys. (Paris) 26, 677 (1965)] has been used for a quantitative determination of the annealing temperature at which a complete annihilation of implantation defects takes place. For this analysis, Raman spectra, resistivity depth profiles, as well as 1D-SUPREM III simulation were used.
Thermal stability study of TiN/TiSi2 diffusion barrier between Cu and n+Si
Authors: Chang Tzong-Sheng , Wang Wen-Chun , Wang Lih-Ping , Hwang Jenn-Chang , Huang Fon-Shan
Published: July 2002

The failure mechanism of the TiN/TiSi2 bilayers as diffusion barriers between Cu and n+Si was investigated. The TiN/TiSi2 bilayers were formed by either annealing Ti (50 nm)/n+Si via various rapid thermal processes or reactively sputtering TiN (50 nm) on TiSi2. The degradation study of the Cu/TiN/TiSi2/n+Si contact system was undertaken by scanning electron microscopy, cross-section transmission electron microscopy (XTEM), secondary-ion-mass spectrometry (SIMS), and diode leakage current and contact resistance measurements. Leakage current measurements indicated no deterioration of n+-p diode junctions up to 475 °C for 30 min in a N2 ambient. For the sintering temperature at 500 °C, the leakage current increased abruptly and SIMS profiles revealed a large amount of Cu atoms diffusing into the junctions of n+-p diodes. XTEM showed that the small pyramidal-shaped Cu3Si crystallite (with a size 0.25 μm) precipitated in the n+Si substrate. The formation of Cu3Si increased the occupied volume, then generated the gap between TiSi2 and n+Si, and gradually increased the specific contact resistance. The diffusion resistance, depending on the thickness of TiN film, was also observed.
Thermionic-tunneling-diffusion model of the laser current-voltage and power characteristics
Authors: Grinberg A. A.
Published: July 2002

An analytical model of the laser-diode current-voltage (I-V) characteristics based on the generalized thermionic-tunneling-diffusion mechanism of carrier transport through heterointerfaces has been proposed. It is valid for any degree of the carrier distribution degeneracy, not only in the laser active region but in the cladding layers as well. The model combines the laser rate equations with current flow equations and permits the evaluating of power-current and power-voltage characteristics. It is assumed that the temperature of the electron-hole gas in the active layer is different from the lattice temperatures. Under appropriate circumstances this allows one to consider the gas heating effect. In the present paper it is supposed that the temperature of the carriers in the laser active layer is proportional to the current in order to investigate the influence of heating on the laser I-V and power characteristics. The sequence of steps which must be carried out in the application of the model is described in detail. Analysis of the formation of different current components is carried out for lasing and unlasing laser diodes using as an example the 1.3 μm laser based on an InGaAsP compound. The influence of the heating effect and leakage current on the low-frequency linear response function is also presented.
Strong negative transconductance in in-plane-gate transistors written by focused-ion-beam implantation
Authors: Bever T. , Hirayama Y. , Tarucha S.
Published: July 2002

A strong negative transconductance is investigated in in-plane-gate transistors written by focused-ion-beam implantation in the two-dimensional electron gas in modulation-doped AlGaAs/GaAs heterostructures. This occurs in a configuration where two in-plane gates G1 and G2 used to control the current through a channel lying between them are biased with different voltages Vg1 and Vg2. When the voltage Vg2<0 is held constant, the current through the channel can be reduced to zero by increasing Vg1 beyond a critical value. In an earlier study this effect was attributed to velocity modulation. It is found, however, that in this regime Vg1 causes a very small current Ig2 to flow across gate G2. It is observed that changes in Id are correlated to changes in Ig2 and thus conclude that Ig2 is responsible for the strong negative transconductance.
Transition-edge noise in YBa2Cu3O7−x thin films before and after exposure to ionizing radiation
Authors: Brasunas J. C. , Lakew B.
Published: July 2002

YBa2Cu3O7−x thin films have been irradiated with gamma rays to a total dose of 100 krad while the films were held at 77 K. For a 1×1 mm2 pattern there was no change either in transition width or in low-frequency noise; thus, high-Tc bolometers made with such films will be robust with respect to this level of gamma rays. For a 3×10 mm2 film, which has a lower noise level, there was a change in the slope of noise versus frequency, suggesting a nonthermal origin for the excess noise.
Synchrotron-radiation-induced reactions of tetraethoxysilane on Si studied by photoemission spectroscopy
Authors: Niwano Michio , Simons John K. , Frigo Sean P. , Rosenberg Richard A.
Published: July 2002

The synchrotron-radiation (SR)-induced chemical reactions of tetraethoxysilane Si(OC2H5)4 (TEOS) adsorbed on Si has been studied using photoemission spectroscopy. It is demonstrated that TEOS adsorbs intact on the Si surface below room temperature. SR in the vacuum ultraviolet region decomposes the TEOS molecules adsorbed on Si to form a silicon-oxide-like film on the Si surface, but some carbon remains in the film. Results of irradiation experiments on condensed layers of TEOS and water adsorbed on Si at 85 K indicate that the presence of water reduces the carbon contamination.
The magnetic diagnostics of cosmic and industrial silt in humus horizons of soils (abstract)
Authors: Babanin Vyacheslav F. , Shplkina Irina V. , Shoba Sergei A. , Ivanov Alexander V.
Published: July 2002

In the early 50s the increase of magnetic susceptibility in head horizons of soils has been observed. The reason was accepted to be forest and steppe fire. Later we discovered that the increasing of susceptibility and magnetic saturation was observed more clearly in the soils developed on weak magnetic native rock (loam, carbonate) and the magnetic fraction was separated from these soils in a more simple fashion. An abnormal increase in magnetic parameters is observed in primitive soils and the debris layer of dry forest (particularly of pine forest). The investigations have shown that magnetic particles (MP) are contained in ash of electrostations, in buried and modern soils, in humocoll and coal sheets, and in air of industrial cities and of the country. A high magnetic separated fraction (MV) contains particles (P) that differ by morphology and color. MF of soils is separated in a difficult manner from the rest mass (it also contains α-Fe, magnetite, hematite) and is contaminated by magnetic particles from native rock. We obtained that only spherical particles contribute to the soil magnetism from (10...50)×10−6 sm3/g to (100...150)×10−6 sm3/g. MP come into modern soils from all sources. Magnetic particles are well conserved in automorphic and nonlogging buried soils, and in humocoll layers. Among humocoll layers investigated by us there were layers dating over 50 thousand years ago.
Induction of mutations by magnetic field for the improvement of sunflower (abstract)
Authors: Kiranmai V.
Published: July 2002

Mutagenic effect of magnetic field was studied in two varieties of Helianthus annus L. var. S.S.56 and CO-2. Dry seeds of both the varieties were exposed to 1000, 2000, and 3000 G of magnetic field for over 90 min. The parameters screened were germination percentage, plant height, days to flowering, days to maturity, and yield of the plant. The mutants obtained were tall mutant, dwarf mutant, early flowering mutant, branched mutant, bold seeded mutant, and stripped seed mutant. The mutants were screened for biochemical analysis. Oil content and fatty acid analysis of the seeds were done by NMR and GLC techniques, respectively. Quantitative and qualitative analysis of the proteins in leaf and seeds were done for all the mutants obtained, along with the electrophoretic studies among the three doses studied, 2000 G was found to produce positive mutations in both varieties of sunflower.
Possible ferrimagnetic coupling in light-rare-earth transition-metal intermetallic compounds
Authors: Zhao Z. G. , de Boer F. R. , Duijn V. H. M. , Buschow K. H. J. , Chuang Y. C.
Published: July 2002

The possibility of ferrimagnetic coupling between the magnetic moments of the light-rare-earth (Nd, Pr) ions and of the transition-metal (Fe) ions in Nd6Ga3Fe11- and Pr6Ga3Fe11-based compounds is deduced from the high-field magnetization curves measured at 4.2 K on magnetically aligned and on free-powder samples and from the temperature dependence of the magnetization. The ferrimagnetic coupling is very weak: at 4.2 K, the rare-earth moments and the transition-metal moments can be forced to ferromagnetic alignment by application of an external magnetic field of about 4 T. Generally, in intermetallic compounds, the magnetic coupling is ferromagnetic between light-rare-earth and transition-metal ions and ferrimagnetic between heavy-rare-earth and transition-metal ions. The present results suggest that in some crystal structures ferrimagnetic coupling also may exist in the compounds formed by light-rare-earth and transition-metal elements.
Ferromagnetic ordering in dilute PdCo alloys
Authors: Parra R. E. , Gonzalez A. C.
Published: July 2002

The analysis of magnetization and neutron-scattering measurements shows that the ferromagnetic cloud in dilute PdCo alloys has a size of 7.92μB, with a Co moment of 2.02μB, for a range of concentrations of 0.3≤c≤2.0 at. % Co. Using the values obtained by our analysis of the data, the neutron scattering and the critical temperatures of ferromagnetism are reproduced using a localized magnetic moment model with a Heisenberg type of interaction between clouds and Monte Carlo simulation methods. The calculated neutron scattering shows a strong component of critical scattering in the unpolarized neutron; this component is the cause of the larger value of the ferromagnetic cloud (∼10μB) that can be inferred from the neutron scattering. Agreement is also found between calculated critical temperatures and experimental Tc’s at these values of concentrations.