bluuebunny/crossref_metadata_2025 huggingface dataset:
A simple capillary rise apparatus to measure wettability in metal–ceramic systems
Authors: Chidambaram P. R. , Lanning B. , Edwards G. R.
Published: July 2002

An apparatus to measure the wettability parameter using the familiar capillary rise principle for a liquid metal/alloy in contact with a ceramic tube was constructed. The liquid levels outside and inside the capillary tube were measured using acoustic feedback and an electrical continuity technique, respectively. Measurements made by immersing silicon carbide, alumina, and silica tubes in various pure metals and alloys are presented and compared to previously published data in the literature. Reproducible measurements were obtained for nonwetting systems; however, the expected capillary rise was not observed for reaction wetting systems.
Production of multiply charged metallic ions by compact electron cyclotron resonance ion source with SF6 plasma
Authors: Saitoh Y. , Ohkoshi K. , Yokota W.
Published: July 2002

A new technique has been developed to introduce very refractory materials into an electron cyclotron resonance ion source by fluorinating them with SF6 plasma, and we succeeded in generating multiply charged ions of B, Mo, Nb, W, and Ta. A metallic sample is set inside the plasma chamber with SF6 plasma, in which the metallic fluoride is generated with sufficiently high vapor pressure by a chemical reaction between fluorine and the metal. The gaseous metallic fluoride is decomposed into fluorine and metal, which are ionized by the SF6 plasma. Generally, ion sources are corroded by gases of fluorine and fluoride, but utilization of SF6 gas reduces the corrosion and allows stable operation for a long time.
Blue and red laser action in Nd3+:Pr3+ co-doped fluorozirconate glass
Authors: Goh S. C. , Pattie R. , Byrne C. , Coulson D.
Published: July 2002

Lasing has been observed in the blue (488 nm) and red (635 nm, 717 nm) bands in a new Nd3+:Pr3+ co-doped fluorozirconate (ZBLANP) glass fiber with 796 nm pump. An upconversion and resonant energy transfer mechanism is proposed to explain the visible transitions.
X-ray crystallographic study of GaN epitaxial films on Al2O3(0001) substrates with GaN buffer layers
Authors: Lee Chih-Hao , Chi G. C. , Lin C. F. , Feng M. S. , Guo J. D.
Published: July 2002

Samples of GaN(0001) epitaxial films on sapphire Al2O3(0001) with different thicknesses of GaN buffer layers were characterized by x-ray diffraction method in both in-plane and plane-normal directions. The results show that all the epitaxial films are of good quality with the GaN[101̄0] ∥Al2O3[112̄0] and GaN[12̄10]∥Al2O3[11̄00]. This arrangement of crystal orientation can be attributed to the chemical potential overriding the lattice spacing mismatch. The x-ray results also indicate that the crystal coherence lengths in the in-plane direction are smaller than those measured in the plane-normal direction, i.e., a columnar-like structure normal to the film is observed. The rocking curve widths in the in-plane direction are also larger than those measured in the plane-normal direction. In-plane measurement of rocking curve and coherence length are essential physical quantities directly related to the electron mobility which was measured predominantly in the in-plane direction. The best epitaxial structure is the one grown with 10 nm buffer layer.
High power electrochemical capacitors based on carbon nanotube electrodes
Authors: Niu Chunming , Sichel Enid K. , Hoch Robert , Moy David , Tennent Howard
Published: July 2002

Carbon nanotube sheet electrodes have been prepared from catalytically grown carbon nanotubes of high purity and narrow diameter distribution, centered around 80 Å. Our study shows that the electrodes are free-standing mats of entangled nanotubes with an open porous structure almost impossible to obtain with activated carbon or carbon fiber. These properties are highly desirable for high power and long cycle life electrochemical capacitors. Specific capacitances of 102 and 49 F/g were measured at 1 and 100 Hz, respectively, on a single cell device with 38 wt % H2SO4 as the electrolyte. The same cell had a power density of >8000 W/kg.
Highly oriented ferroelectric CaBi2Nb2O9 thin films deposited on Si(100) by pulsed laser deposition
Authors: Desu S. B , Cho H. S , Joshi P. C.
Published: July 2002

We report the successful deposition of highly c-axis oriented CaBi2Nb2O9 (CBN) thin films directly on p-type Si(100) substrates by pulsed laser deposition. The CBN thin films exhibited good structural, dielectric, and CBN/Si interface characteristics. The electrical measurements were conducted on CBN thin films in a metal–ferroelectric–semiconductor (MFS) capacitor configuration. The typical measured small signal dielectric constant and the dissipation factor at a frequency of 100 kHz were 80 and 0.051, respectively. The leakage current of the MFS capacitor structure was governed by the Schottky barrier conduction mechanism and the leakage current density was lower than 10−7A/cm2 at an applied electric field of 100 kV/cm. The capacitance–voltage measurements on MFS capacitors established good ferroelectric polarization switching characteristics.
Alternative microstructure of GaN nucleation layers grown by low pressure metal-organic vapor phase epitaxy on sapphire substrate
Authors: Cheng Lisen , Zhang Guoyi , Yu Dapeng , Zhang Ze
Published: July 2002

Predominately hexagonal GaN nucleation layers were grown on sapphire substrate by low pressure metal-organic vapor phase epitaxy. Tilt angles of GaN single crystallites about the normal of sapphire substrate are determined to be in the range from 0° to 5° by using selected area electron diffraction. A small portion of cubic phase of GaN was observed to be selectively distributed in the grain boundary areas and the instantaneous surface state is suggested to play an important role in the nucleation of the Zincblende phase. Phase transition from hexagonal to cubic GaN caused by heavy radiation from ion beam was also noticed. A critical temperature is proposed to exist in forming predominately cubic or hexagonal GaN nucleation layer.
7 terahertz broadband GaP electro-optic sensor
Authors: Wu Q. , Zhang X.-C.
Published: July 2002

We report a broadband coherent terahertz detection system using GaP as a free-space electro-optic field sensor with a demonstrated 3 dB bandwidth of 3.6 THz, useful bandwidth of 7 THz, and a pulse width of 185 fs. These figures represent new records in the coherent detection of free-space THz radiation. Sensor response as a function of crystal thickness and copropagation velocity mismatch dispersion in the THz regime is studied.
InAs self-organized quantum dashes grown on GaAs (211)B
Authors: Guo S. P. , Ohno H. , Shen A. , Matsukura F. , Ohno Y.
Published: July 2002

We have grown InAs self-organized quantum dots and quantum dashes on GaAs (211)B substrates by molecular beam epitaxy. The growth temperature dependence of InAs nanostructures were studied by in situ reflection high-energy electron diffraction (RHEED) and ex situ atomic force microscopy. In the studied temperature range from 400 to 510 °C, the RHEED pattern changed from streaky to spotty after deposition of 6 ML of InAs, showing the formation of nanostructures. The quantum dots grown at lower growth temperatures (from 400 to 490 °C) showed bimodal dot size distribution. At higher growth temperatures, a drastic change from quantum dots to quantum dashes was observed. The quantum dashes have an asymmetric hutlike shape and align themselves along the [011̄] direction. The quantum dash width increases dramatically, whereas the average length and density increases slightly on further deposition of InAs.
Potential pinch-off effect in inhomogeneous Au/Co/GaAs67P33(100)-Schottky contacts
Authors: Olbrich Alexander , Vancea Johann , Kreupl Franz , Hoffmann Horst
Published: July 2002

In this work ballistic electron emission microscopy was used to probe on nanometer scale the local Schottky barrier height in metal-semiconductor (MS) contacts with an intentionally inhomogeneously prepared metallization. Schottky barrier maps of heterogeneous Au/Co/GaAs67P33(100)-Schottky contacts show areas with different barrier heights which can be correlated to different metallizations (Au or Co) at the interface. The local Schottky barrier height of the Co patches depends on their lateral extension. This result can be explained by the theory of the potential pinch-off effect in inhomogeneous MS contacts.
Two-photon optical beam induced current imaging through the backside of integrated circuits
Authors: Xu Chris , Denk Winfried
Published: July 2002

Two-photon optical beam induced current (TOBIC) images were acquired through the polished backsides of integrated circuits. An excitation beam with a photon energy below the band gap can traverse even thick substrates virtually unattenuated. At the focus—and only there—two-photon absorption generates electron-hole pairs very efficiently when using a sub-picosecond light source. An additional advantage of TOBIC is a significant increase in spatial resolution. With high numerical aperture objective lense features smaller than 1 μm are easily discernible.
Influence of humidity on refractive index of polymers for optical waveguide and its temperature dependence
Authors: Watanabe Toshio , Ooba Naoki , Hida Yasuhiro , Hikita Makoto
Published: July 2002

Humidity dependence of the refractive index of deuterated polymethylmethacylate (d-PMMA) is examined at a wavelength of 1.3 μm using the return loss method. The refractive index of d-PMMA increases as humidity increases at room temperature, while it decreases as humidity increases at temperatures higher than 60 °C. This humidity dependence was ascribed to the counterbalance between moisture sorption and swelling. Some hydrophobic polymers, such as silicone resin and fluorinated epoxy resin were affected by humidity to a lesser degree than d-PMMA.
Control and imaging of ferroelectric domains over large areas with nanometer resolution in atomically smooth epitaxial Pb(Zr0.2Ti0.8)O3 thin films
Authors: Tybell T. , Ahn C. H. , Triscone J.-M.
Published: July 2002

We have investigated the possibility afforded by epitaxial ferroelectric oxide thin films to control and image locally the polarization field of ferroelectrics over large areas with submicron resolution, using the metallic tip of an atomic force microscope as a mobile top electrode and local probe of the ferroelectric properties. Atomically smooth films of Pb(Zr0.2Ti0.8)O3, showing a root-mean-square roughness of typically a few angstroms, could be uniformly polarized and imaged over areas as large as 2500 μm2 without introducing any topographic disorder. Regular arrays of 100 nm wide lines and circular domains with a diameter less than 100 nm were written in arbitrary areas of the uniformly polarized regions.
Controlling growth and field emission property of aligned carbon nanotubes on porous silicon substrates
Authors: Xu Dongsheng , Guo Guolin , Gui Linlin , Tang Youqi , Shi Zujin , Jin Zhaoxia , Gu Zhennan , Liu Weimin , Li Xiulan , Zhang Guanghua
Published: July 2002

An aligned and well-distributed carbon nanotubes array was produced by pyrolysis of hydrocarbons catalyzed by nickel nanoparticles embedded in porous silicon (PS) substrates. Scanning electron microscope images show that the nanotubes form an aligned array approximately perpendicular to the surface of the PS substrate and the diameters of most of the tubes within the array are 10–30 nm. High-magnification transmission electron microscopy images confirmed that the nanotubes are well graphitized and typically consist of about 15 concentric shells of carbon sheets. Furthermore, the strong field emission from the aligned carbon nanotubes emitter by pyrolysis of hydrocarbons was observed.
Antisite defects of Bi2Te3 thin films
Authors: Cho Sunglae , Kim Yunki , DiVenere Antonio , Wong George K. , Ketterson John B. , Meyer Jerry R.
Published: July 2002

We have successfully grown Bi2Te3 thin films on CdTe(111)B using molecular-beam epitaxy. Structural and transport properties have been investigated using in situ reflection high-energy electron diffraction, θ–2θ x-ray diffraction analysis, thermopower, and Hall measurements. Both the crystallinity and the transport are found to be strongly affected by nonstoichiometry. The most stoichiometric sample had a high crystallinity, high thermopower, and high electron mobility. However, Bi2Te3 films with excess Te had a reduced lattice constant, poorer crystallinity, reduced magnitude of the thermopower, and reduced mobility. All of these observations can be explained in terms of antisite defects in which excess Te occupies Bi lattice sites and behaves as a n-type dopant.
Microstructure imaging of C54–TiSi2 polycrystalline thin films by micro-Raman spectroscopy
Authors: Meinardi F. , Quilici S. , Borghesi A. , Artioli G.
Published: July 2002

The morphology of C54–TiSi2 polycrystalline films has been revealed by the micro-Raman imaging technique. This was based on the calculation of the symmetries of the Raman active vibrations of the C54–TiSi2 single crystal and subsequent polarized Raman measurements to detect and unambiguously label all the expected peaks. The relative intensity of two suitable peaks was monitored and mapped on C54–TiSi2 blanket films. Grains with different orientation are clearly detectable, and the microstructure properties of the film can be analyzed.
Stress relaxation of free-standing aluminum beams for microelectromechanical systems applications
Authors: Lee Hoo-Jeong , Cornella Guido , Bravman John C.
Published: July 2002

We investigated the uniaxial tension and stress relaxation properties of micron-scale Al beams for microelectromechanical systems applications in a piezoactuator-driven test apparatus. Pure aluminum and Al-1.5 at. % titanium free-standing beams were fabricated using micromachining procedures. In the tensile tests, we found the yield strength of the Al beams to be approximately 95 MPa. We also observed a significant strengthening effect in the alloyed samples, which had a yield strength approximately 85% higher than the pure Al samples. In stress relaxation tests, we observed a substantial load-drop (about 56% after 10 min) in the Al films, and we propose here that grain boundary sliding is responsible for this relaxation. By comparison, the relaxation of the Ti-alloyed samples was only 15%. We believe that this difference results from the Al3Ti precipitates that form at the Al grain boundaries in the alloy samples.
Dynamics of resonance phenomenon and negative capacitances in the dielectric response of materials
Authors: M’Peko Jean-Claude
Published: July 2002

Thermoelectric characterization performed in this work on BaFe12O19 and BaTiO3 at 1 kHz involved anomalous negative capacitances over higher temperatures. By using alternating-current analysis techniques, we ratify our previous observations on their association with an inductive component leading to a resonance-type phenomenon. The dynamics of this latter, mostly expected to act rather over higher frequencies (>106 Hz), is carefully examined by using a simple but consistent model. Its large stretching to lower frequencies is found to be caused by the inner dynamics of the material dielectric response when becoming governed, over higher temperatures, by the material–electrode interface properties.
Room-temperature negative differential resistance in nanoscale molecular junctions
Authors: Chen J. , Wang W. , Reed M. A. , Rawlett A. M. , Price D. W. , Tour J. M.
Published: July 2002

Molecular devices are reported utilizing active self-assembled monolayers containing the nitroamine [2′-amino-4,4′-di(ethynylphenyl)-5′-nitro-1-benzenethiolate] or the nitro compound [4,4′-di(ethynylphenyl)-2′-nitro-1-benzenethiolate] as the active components. Both of these compounds have active redox centers. Current–voltage measurements of the devices exhibited negative differential resistance at room temperature and an on–off peak-to-valley ratio in excess of 1000:1 at low temperature.
Optical properties of chalcopyrite CuAlxIn1−xSe2 alloys
Authors: Alonso M. I. , Garriga M. , Durante Rincón C. A. , León M.
Published: July 2002

We report pseudodielectric functions 〈ε〉 of the quaternary semiconductor alloys CuAlxIn1−xSe2. Measurements were done in polycrystalline samples from 0.7 to 5.1 eV at room temperature by spectral ellipsometry. Accurate values of refractive indices n and extinction coefficients k representative of the bulk materials are reported. The dependence on composition of the reflectivity at normal incidence R(x) at the He–Ne laser wavelength λ=1.523 μm provides an optical method to determine the composition of these alloys. The structures observed in 〈ε〉 are analyzed by fitting the numerically differentiated spectra of d2〈ε〉(ω)/dω2 to analytic line shapes. The obtained energies are related to given interband transitions by taking into account the electronic band structures of the ternary end-point compounds.
The solution of the Wertheim association theory for molecular liquids: Application to hydrogen fluoride
Authors: Fries P. H. , Richardi J.
Published: July 2002

A general numerical method for solving the Wertheim association theory in the case of fully anisotropic polyatomic rigid molecules is proposed. In order to handle the nonspherical shapes of the molecules, the Wertheim association theory is combined with the rotational invariant approach of the molecular Ornstein–Zernike (MOZ) method. Therefore, this approach is called the WMOZ method. It is carried out in the association hypernetted chain (AHNC) approximation which is the only approximation and which consists of the neglect of the bridge functions. The method of solution is implemented by translating the set operations appearing in the Wertheim association theory into an algebraic formalism developed through a one-to-one correspondence between subsets and binary numbers. The Wertheim association theory is explicitly solved for hydrogen fluoride using two interaction site models. For these models, site–site distribution functions, internal excess energies, and dielectric constants obtained by the MOZ and WMOZ methods are compared to the exact molecular dynamics results. The WMOZ method strongly improves the structural description of the H bonding in comparison with the MOZ approximation. The quality of the dielectric and thermodynamic results obtained by the WMOZ approach is discussed in comparison with the simulation values. To our knowledge, this is the first solution of the Wertheim association theory for a liquid of particles of nonspherical shapes.
Freeze-out of difference-phonon modes in ZnTe and its application in detection of THz pulses
Authors: Schall M. , Jepsen P. Uhd
Published: July 2002

Generation by optical rectification and detection by electro-optic sampling of freely propagating subpicosecond electromagnetic pulses (terahertz pulses) in ZnTe is limited by two broad difference-phonon absorption bands in the spectral region below the transverse optical resonance at 5.32 THz. In this letter, we show that, at temperatures below 80 K, these difference modes are frozen out and consequently ZnTe becomes completely transparent within our detection bandwidth. We utilize this effect to obtain a three-fold increase in detection efficiency at frequencies above 3 THz in a thin ZnTe detector operated at 80 K, compared to the performance at room temperature.
Electronic instability of isolated SO42− and its solvation stabilization
Authors: Wang Xue-Bin , Nicholas John B. , Wang Lai-Sheng
Published: July 2002

Despite its ubiquity in nature, SO42− as an isolated dianion has never been detected because of its electronic instability as a result of the two negative charges. This study shows how the first few waters solvate and stabilize an isolated SO42−, molecule-by-molecule, using photodetachment spectroscopy and theoretical calculations. We find that the minimum number of water required to stabilize a free SO42− is three. The first four waters bind tightly to SO42−, each forming two H-bonds with SO42− without inter-water H-bonding. The charges of the dianion are stabilized sufficiently that additional waters form only single H-bonds with SO42− and that inter-water H-bonding is observed starting at n=5.
90° domain reorientation and domain wall rearrangement in lead zirconate titanate ceramics characterized by transient current and hysteresis loop measurements
Authors: Lente M. H. , Eiras J. A.
Published: July 2002

The polarization switching in Pb(Zr,Ti)O3 (PZT) ferroelectric bulk ceramics undoped and doped with Nb2O5 or Fe2O3 was studied by means of both hysteresis loops and transient current measurements at room temperature. The results obtained revealed that in PZT ceramics, during the poling process, the reorientation of the polarization may be interpreted as resulting of two contributions: two 90° domain reorientation followed by 90° domain wall rearrangement. 90° domain reorientation is field dependent and responsible for a shoulder observed in the transient current curves, while domain walls contribution is nearly field independent and occurs for longer time. 90° domain wall rearrangement enabled an increase of about 40% of the total polarization in the samples. The reorientation behavior of the domains showed to be strongly influenced by the type of impurity and by the electrical field strength.
Temporal and spatial evolution of the electronic density and temperature of the plasma produced by laser ablation of LiNbO3
Authors: Gordillo-Vázquez F. J. , Perea A. , Chaos J. A. , Gonzalo J. , Afonso C. N.
Published: July 2002

Emission spectroscopy is used to determine the spatial and temporal evolution of the electronic temperature (Te) and density (Ne) of the plasma generated by laser ablation in vacuum of a LiNbO3 target. It is found that whereas Ne (in the range of 1016 cm−3) decreases by a factor of 2 as the distance to the target surface increases 10 mm, Te (in the range 0.7–0.8 eV) only decreases 10% between 2 and 4 mm from the target to remain nearly constant for longer distances. While Te is almost constant in time at the studied distances, Ne presents a maximum at a time delay that increases when increasing the distance to the target surface. The space–time constancy of Te is related to a collisional decoupling of the heavy species in the plasma for distances longer than 2–4 mm.
Hydrogenated amorphous silicon deposited at very high growth rates by an expanding Ar–H2–SiH4 plasma
Authors: Kessels W. M. M. , Severens R. J. , Smets A. H. M. , Korevaar B. A. , Adriaenssens G. J. , Schram D. C. , van de Sanden M. C. M.
Published: July 2002

The properties of hydrogenated amorphous silicon (a-Si:H) deposited at very high growth rates (6–80 nm/s) by means of a remote Ar–H2–SiH4 plasma have been investigated as a function of the H2 flow in the Ar–H2 operated plasma source. Both the structural and optoelectronic properties of the films improve with increasing H2 flow, and a-Si:H suitable for the application in solar cells has been obtained at deposition rates of 10 nm/s for high H2 flows and a substrate temperature of 400 °C. The “optimized” material has a hole drift mobility which is about a factor of 10 higher than for standard a-Si:H. The electron drift mobility, however, is slightly lower than for standard a-Si:H. Furthermore, preliminary results on solar cells with intrinsic a-Si:H deposited at 7 nm/s are presented. Relating the film properties to the SiH4 dissociation reactions reveals that optimum film quality is obtained for conditions where H from the plasma source governs SiH4 dissociation and where SiH3 contributes dominantly to film growth. Conditions where ion-induced dissociation reactions of SiH4 prevail and where the contribution of SiH3 to film growth is much smaller lead to inferior film properties. A large contribution of very reactive (poly)silane radicals is suggested as the reason for this inferior film quality. Furthermore, a comparison with film properties and process conditions of other a-Si:H deposition techniques is presented.
The effect of sample thickness and insulation layers on the temperature distribution in the laser-heated diamond cell
Authors: Panero Wendy R. , Jeanloz Raymond
Published: July 2002

The temperature gradients in the laser-heated diamond anvil cell can be modeled through the solution of the steady-state heat equation. For a given laser, the width of the hotspot is dependent on the thickness and thermal conductivity of the sample and of any thermal-insulation layers between the sample and the diamonds. For a given sample, insulation and peak temperature, thicker samples will have broader hotspots than thinner ones. Therefore, increasing the pressure on a sample will thin the gasket, sample and insulation, producing a narrower hotspot and increasing temperature gradients.
Passivation of an anodic oxide/p-Si interface stimulated by electron injection
Authors: Dittrich Th. , Burke Th. , Koch F. , Rappich J.
Published: July 2002

The positive oxide charge (Qox) and the concentration of nonradiative recombination defects (Nit) at a thin anodic oxide/p-Si interface are probed in situ by pulsed photovoltage and photoluminescence techniques during electron injection. Qox and Nit decreased strongly due to electron injection. The observed effect is suggested to be inverse to the negative-bias-temperature instability. Defect reactions at the anodic oxide/p-Si interface are discussed.
Spatial electron distribution of CO adsorbed on Ni(100) and Ni(111) surfaces probed by metastable impact electron spectroscopy
Authors: Masuda S. , Suzuki R. , Aoki M. , Morikawa Y. , Kishi R. , Kawai M.
Published: July 2002

Electron emission spectra obtained by thermal collisions of He*(2 3S) metastable atoms with CO on Ni(100) in the c(2×2) structure and on Ni(111) in the c(4×2) structure were measured to probe directly the spatial electron distribution. For a systematic comparison, the metastable spectra of free CO, condensed CO on Ni(111), and gaseous Cr(CO)6 were also measured under the same beam conditions. Our data showed that the relative ionization cross sections for the CO 4σ-, 1π-, and 5σ-derived states depend drastically on the molecular orientation of CO with respect to the metastable beam, reflecting the local electron density of CO in the impact region. Moreover, it was found that the 4σ- and 5σ- derived states of CO at hollow sites on Ni(111) are strongly modified in space by mixing with each other, where considerable charge transfer occurs from the C site to the O site in the 5σ-derived state and in the opposite way in the 4σ-derived state. In contrast, such a strong charge redistribution was not seen in the cases of terminal CO on Ni(100) and Cr(CO)6. These findings were in good accordance with the crystal orbital overlap population obtained by density functional theory through a generalized gradient approximation.
Dissociative electron attachment rates for H2 and its isotopes
Authors: Xu Y. , Fabrikant I. I.
Published: July 2002

Dissociative electron attachment to rovibrationally excited H2, HD, HT, D2, DT, and T2 molecules in their ground electronic states via the ∑u+2 shape resonance is studied within the framework of the nonlocal resonance theory. Rate constants for selected processes are presented in the electron energy range up to 5 eV. Maximum rate of 2.8×10−8 cm3 s−1 is found for attachment to all these molecules.
Tuning the hopping conductivity of WO3 films by ion bombardment at different temperatures
Authors: Heinz B. , Merz M. , Widmayer P. , Ziemann P.
Published: July 2002

WO 3 films, either prepared by sputtering or evaporation under high or ultrahigh vacuum conditions, were irradiated with He+ and Ar+ ions (energy range 300–350 keV) at ambient and low temperatures (77–100 K). The resulting ion induced changes of the optical absorption as well as of the electrical conductivity could be determined on one and the same sample, which enables the variable range hopping (VRH) model to be tested under the assumption that the density of irradiation induced color centers is proportional to the electronic density of states contributing to the hopping conductivity. It is found that the data obtained at 300 K for He+ and Ar+ bombardment can be described within the VRH model by one common conductivity versus absorption curve, even though the effectiveness per projectile of the heavier ion for coloration as well as for increasing the conductivity is much higher. This is different at low temperatures. While the ion induced coloration is practically independent of the irradiation temperature for both projectiles, the effectiveness per projectile to enhance the conductivity is interchanged. This is attributed to the additional damage produced by the heavier ion at low temperatures resulting in strongly impeded hopping processes. Consistent with the VRH model, the temperature dependence of the conductivity of ion bombarded WO3 films follow the Mott “T−1/4” law, if the ion induced conductivity is not too high. For very high ion fluences clear deviations from the VRH model are observed for the conductivity versus absorption curves accompanied by a shift of the above power laws from T−1/4 towards T−1/2.
Triplet excitation energies in full configuration interaction and coupled-cluster theory
Authors: Larsen Helena , Hald Kasper , Olsen Jeppe , Jørgensen Poul
Published: July 2002

Triplet excitation energies have been calculated for Ne, H2O, HF, BH, N2, and C2 using the full configuration interaction (FCI) model and the coupled-cluster model hierarchy CCS, CC2, CCSD, CC3, and CCSDT, where CCS, CCSD, and CCSDT are the standard coupled-cluster models where singles, doubles and triples are successively added and where CC2 and CC3 are approximations to the CCSD and CCSDT models where approximations are introduced in the highest amplitude equations. Comparing the coupled-cluster excitation energies with the FCI results shows that the excitation energies are improved at each level in the hierarchy up to CC3. The CC3 and CCSDT excitation energies have similar accuracy for the single excitation dominated excitation energies, whereas the double excitation dominated excitation energies are significantly improved also from CC3 to CCSDT. Singlet excitation energies have also been calculated for HF using the coupled-cluster hierarchy up to CCSDT. Triplet and singlet excitation energies with similar single excitation weights have about the same accuracy.
Manifestation of quasi-symmetry of the cation sites of Gd2SiO5, Y2SiO5, and Lu2SiO5 in the spectra of the impurity ion Pr3+
Authors: Malyukin Yu. V. , Borisov R. S. , Zhmurin P. N. , Lebedenko A. N. , Grinev B. V. , Znamensky N. V. , Manykin É. A. , Orlov Yu. V. , Petrenko E. A. , Yukina T. G.
Published: July 2002

The quasi-symmetry of the inequivalent cation sites in the crystals Gd2SiO5, Y2SiO5, and Lu2SiO5 is established on the basis of an analysis of the features of the low-temperature optical spectra of the impurity ion Pr3+. One type of cation site of the crystals Y2SiO5 and Lu2SiO5 manifests the quasi-symmetry of a distorted octahedron, and the other type, that of a distorted tetrahedron. The parameters characterizing the energy spectrum of the free Pr3+ ion in the crystalline field of the cation sites are determined.
Ultrabroadband photoconductive detection: Comparison with free-space electro-optic sampling
Authors: Kono Shunsuke , Tani Masahiko , Sakai Kiyomi
Published: July 2002

The spectral response of a low-temperature-grown GaAs photoconductive (PC) antenna is compared with that of the electro-optic sampling technique for the frequency region up to 40 THz. The spectral response of the PC antenna for broadband detection is found to be determined by the temporal profile of the number of photocarriers injected by ultrashort optical gate pulses.
Colloidal aggregation induced by attractive interactions
Authors: Puertas A. M. , Fernández-Barbero A. , de las Nieves F. J.
Published: July 2002

Colloidal aggregation induced by attractive interactions is tackled experimentally and by Brownian dynamics simulations using a mixture of positive and negative particles. The structure of the aggregates and the aggregation kinetics are used to characterize the aggregation behavior. The clusters show uniform internal structures, with a fractal dimension lower than that of clusters formed in diffusion, indicating a more branched architecture. The aggregation kinetics also differs from the diffusive one, slowing down as time proceeds. Both results are totally confirmed by simulation. The transition from the attractive driven to the diffusion controlled regimes is studied varying the range of interaction. Continuous transitions are observed both for the aggregation kinetics and cluster structure.
Phase states and spectra of coupled magnetoelastic waves in a ferromagnet with inclined anisotropy
Authors: Arifov L. Ya. , Fridman Yu. A. , Butrim V. I. , Kosmachev O. A.
Published: July 2002

The spectra of coupled magnetoelastic waves in a ferromagnet with an inclined easy axis are determined. Analysis of the spectra obtained shows that such a system can have one more phase in addition to the ferromagnetic and canted phases. This phase can be interpreted as inhomogeneous. The region of fields and magnetoelastic coupling parameters in which this phase can be realized is determined.
Temporary anion states of selected amino acids
Authors: Aflatooni K. , Hitt B. , Gallup G. A. , Burrow P. D.
Published: July 2002

Vertical attachment energies for the formation of low-lying temporary anion states of glycine, alanine, phenylalanine, tryptophan, and proline in the gas phase are reported using electron transmission spectroscopy. Electron attachment into the empty π* orbital of the –COOH group was observed in all the compounds. Temporary anion states associated with the side groups in phenylalanine and tryptophan are found to be stabilized with respect to those in the reference compounds toluene and indole, respectively, by approximately 0.2 eV. We attribute this to electrostatic effects and explore, using simple theoretical models, the extent to which such anion states could be further stabilized if these amino acids were in zwitterionic form.
Dynamical coexistence of phases in molecular clusters
Authors: Proykova Ana , Pisov Stoyan , Berry R. Stephen
Published: July 2002

Two solid structures, a bcc orientationally disordered phase and a strained monoclinic orientationally ordered phase, may coexist for clusters of octahedral molecules. However, this coexistence is more difficult to observe in computer simulations of SF6 clusters than of TeF6 clusters although the SF6 and TeF6 molecules have the same symmetry. This study finds why this difference occurs. On the potential surface of the (SF6)89 cluster the relative energies of most of the linked minima differ only slightly, and the barriers between them are low. An exception is the global minimum, corresponding to a completely orientationally ordered phase. At relevant temperatures, the fraction of the available phase space of the (SF6)89 cluster corresponding to a partially ordered structure is smaller than it is for the (TeF6)89 cluster. In simulations, the latter readily exhibits coexistence of the ordered and disordered forms due to better separation of the higher-energy local minima and the larger available phase space volume.
Solid state amorphization at the room temperature deposited Ir/Si interface
Authors: Ouyang C.-P. , Chang J.-J. , Wen J.-F. , Tien L.-C. , Hwang J. , Pi T.-W.
Published: July 2002

The amorphous Ir–Si layer of several nanometers thick on Si(100)2×1 deposited at room temperature has been characterized by using both low energy electron diffraction (LEED) and synchrotron photoemission techniques. The double domain Si(100)2×1 LEED pattern disappeared when the deposited Ir onto Si(100) was higher than 1 ML. The ultrathin amorphous Ir–Si layer consisted of three different IrxSiy alloys, rather than a single homogeneous IrxSiy alloy as predicted by the conventionally used Gibbs free energy calculation in the solid state amorphization. The growth of the amorphous Ir–Si layer on Si(100) strongly depended on the interaction between Ir and Si(100) at the initial stage of Ir deposition. Three types of Ir–Si bonding formed on Si(100) at 1 ML Ir coverage and gradually evolved to be three different amorphous IrxSiy alloys. The growth mode of the amorphous Ir–Si layer was proposed to be the modified Stranski–Krastanov growth. The transition from layer-by-layer-like to island growth occurred at Ir coverage of ∼3 ML. The major amorphous IrxSiy alloy switched from Si to Ir rich when Ir coverage is over ∼3 ML.
Irreversible adsorption of hard spheres at random site (heterogeneous) surfaces
Authors: Adamczyk Zbigniew , Weroński Paweł , Musiał Elizeusz
Published: July 2002

Irreversible adsorption of hard spheres at random site surfaces was studied theoretically. In contrast to the previous model of Jin et al. [J. Phys. Chem. 97, 4256 (1993)] the dimension of the sites, having the shape of circular disks, was finite and comparable with the size of adsorbing spheres. Adsorption was assumed to occur if the sphere contacted the disk, i.e., when the projection of the sphere center was located somewhere within the disk only. Numerical simulation of the Monte Carlo type enabled one to determine the available surface function, adsorption kinetics, jamming coverage, and the structure of the particle monolayer as a function of the site density (coverage) and the size ratio particle/site, denoted by λ. It was demonstrated that adsorption kinetics and the jamming coverage increased significantly, at a fixed site density, when the λ parameter increased. It was also proven that the results derived from the Jin et al. model were valid only if λ>10.
Mechanical deformation of single-crystal ZnO
Authors: Kucheyev S. O. , Bradby J. E. , Williams J. S. , Jagadish C. , Swain M. V.
Published: July 2002

The deformation behavior of bulk ZnO single crystals is studied by a combination of spherical nanoindentation and atomic force microscopy. Results show that ZnO exhibits plastic deformation for relatively low loads (≳4–13 mN with an ∼4.2 μm radius spherical indenter). Interestingly, the elastic–plastic deformation transition threshold depends on the loading rate, with faster loading resulting, on average, in larger threshold values. Multiple discontinuities (so called “pop-in” events) in force–displacement curves are observed during indentation loading. No discontinuities are observed on unloading. Slip is identified as the major mode of plastic deformation in ZnO, and pop-in events are attributed to the initiation of slip. An analysis of partial load–unload data reveals values of the hardness and Young’s modulus of 5.0±0.1 and 111.2±4.7 GPa, respectively, for a plastic penetration depth of 300 nm. Physical processes determining deformation behavior of ZnO are discussed.
Frequency and temperature dependence of the ferromagnetic resonance linewidth in single crystal platelets and pulsed laser deposited films of barium ferrite
Authors: Lebedev Sergey V. , Patton Carl E. , Wittenauer Michael A. , Saraf Laxmikant V. , Ramesh Ramamoorthy
Published: July 2002

The half power ferromagnetic resonance (FMR) linewidth ΔH has been measured from 8 to 300 K for a nominal frequency of 61 GHz and from 50 to 75 GHz at room temperature for normally magnetized single crystal platelets and pulsed laser deposited (PLD) films of barium ferrite. The platelet linewidth versus temperature data show a peak value of 27 Oe at 25–30 K, a dip to 21 Oe at 75 K, structure related to line merging at 130–160 K, and a region of slow increase at 240–295 K. The 240 –300 K data extrapolate to a 0 K linewidth of about 8 Oe. The corresponding film data show a peak value of 240 Oe at 20 K and a gradual decrease at higher temperatures. Both the platelet and film linewidths show a weak frequency dependence at about 0.3 Oe/GHz at room temperature (RT). The film data also show several linewidth spikes due to interference effects between the FMR response and dielectric resonances in the substrate. The RT linewidth zero frequency intercepts for the platelet and the film were 9 and 30 Oe, respectively. The frequency dependence of the platelet linewidth was also examined at 230–295 K. The frequency responses and intercepts for these data were affected by the line merging at lower temperatures and showed high temperature limit values of 0.35 Oe/GHz and 9.5 Oe, respectively. The linewidth frequency response in both cases is attributed to conductivity. The linewidth versus temperature peaks are attributed to impurities. The linewidth dip at 75 K for the platelet results from the drop in ΔH on the tail of the temperature peak and an increase associated with iron ion hopping motion.
[
CoAl
/
Pd
]
n
multilayers as perpendicular recording media
Authors: Jiang W. W. , Wang J. P. , Chong T. C.
Published: July 2002

Co/Pd multilayer medium is a potential candidate to realize the high density magnetic recording, however, the long-range exchange coupling and weak domain wall pinning energies result in low SNR recording. We investigated [Co1−xAlx/Pd]n multilayer media and found this kind of media may be used as a stable perpendicular media for high density recording purposes. The samples were sputter-deposited onto the glass substrates with varying Al compositions, bilayer numbers, and [Co1−xAlx]n magnetic sublayer thickness. Compared with [Co/Pd]n multilayer films, the high perpendicular anisotropy and high squareness properties were basically reserved, while smaller and more uniform grains were observed. Much smaller domain size was observed for the sample with Al doping by magnetic force microscopy imaging. A magnetization reversal mechanism study showed that Al atoms might emerge into the grain boundaries, thus compressing the grains and weakening the intergranular exchange coupling. A new type of multilayer CGC media was proposed based on the study.
Thermopower behavior in the Gd5(Si0.1Ge0.9)4 magnetocaloric compound from 4 to 300 K
Authors: Sousa J. B. , Braga M. E. , Correia F. C. , Carpinteiro F. , Morellon L. , Algarabel P. A. , Ibarra R.
Published: July 2002

Recent studies on the orthorhombic Gd5(Si0.1Ge0.9)4 compound show, upon heating, a ferromagnetic to antiferromagnetic-like (AFM*) transition at TS=78 K, coupled with a first-order structural martensitic transformation keeping the orthorhombic symmetry but producing a large increase in the interlayer Si(Ge) distances leading to covalent bond-pair breaking. A second-order AFM*→(paramagnetic)PM transition occurs at TN=125 K. We report thermopower (S) measurements for the Gd5(SixGe1−x)4 series, performed on an x=0.1 sample, from 4 to 300 K, with increasing and decreasing temperatures through successive thermal cycling. Resistivity measurements show a systematic increase in the residual resistivity and a dramatic change in the ρ(T) behavior upon thermal cycling. In spite of this, the thermopower data show a common intrinsic behavior both in the ferromagnetic phase (T<TS=78 K) and above ∼230 K, i.e., independent of the number of thermal cycles, increasing or decreasing temperature, and of the particular residual resistivity. Also no drastic differences are seen in S(T) from TS to TN, upon thermal cycling. The structural transition is marked (upon heating) by a sharp increase in the S magnitude, reaching a deep negative minimum of −23 μV K−1 at ∼95 K. Then S(T) rises with increasing slope as T approaches TN, where dS/dT exhibits a singularity. S(T) hysteresis sets in at TS, reaches a maximum around 100 K, does not disapear at TN but persists in the PM phase up to ∼230 K. The later feature correlates well with a similar effect observed in ρ(T). The striking differences between S(T) and ρ(T) behavior under thermal cycling are analyzed.
Exoelectron emission spectroscopy of silicon nitride thin films
Authors: Rosenman G. , Naich M. , Molotskii M. , Dechtiar Yu. , Noskov V.
Published: July 2002

Thermally stimulated exoelectron emission method is applied to amorphous silicon nitride (α-Si3N4) thin insulating films in the temperature region (300–550) K for energy spectroscopy of electronic states. The measured spectrum of electron (hole) traps is in good agreement with the known data obtained by other methods. The experimental data are interpreted on the basis of the model of electron-hole recombination in the two-center Auger process.
Formation of anion fragments from gas-phase glycine by low energy (0–15 eV) electron impact
Authors: Gohlke Sascha , Rosa Andrzej , Illenberger Eugen , Brüning Frank , Huels Michael A.
Published: July 2002

We have measured the formation of anion fragments in gas phase glycine (H2NCH2COOH) via dissociative electron attachment (DEA) reactions in the 0–15 eV electron energy range, using a monochromatic electron beam and mass spectrometric detection of the negative ions. By far the most intense product observed is the closed shell glycine anion (H2NCH2COO)− which appears from a low-energy resonance with a peak located at 1.4 eV and a cross section in the range 10−16 cm2. The corresponding precursor ion can be characterized by electron attachment into the empty π* orbital of the −COOH group as recently assigned from electron transmission experiments and ab initio self-consistent field calculations [Aflatooni, Hitt, Gallup, and Burrow, J. Chem. Phys. 115, 6489 (2001)]. This precursor state is also observed to decompose (with much lower intensity) yielding a negative ion fragment with 58 amu, which is attributed to anions of the stoichiometric composition H2C2O2− or H4C2NO−. A further prominent DEA peak is observed at 6 eV, which is likely associated with a core excited resonance, and leads to formation of at least six different negative ion fragment species with the following mass numbers: 16 amu (O−/NH2−), 17 amu (OH−), 26 amu (CN−), 28 amu (H2CN−), 45 amu (HCO2−), 56 amu (H2C2NO−).
Nanolithography based on patterned metal transfer and its application to organic electronic devices
Authors: Kim Changsoon , Shtein Max , Forrest Stephen R.
Published: July 2002

We demonstrate a patterning method capable of producing features of submicron scale based on the transfer of a metal film from a stamp to a substrate assisted by cold welding. The patterned metal film can be used as an etch mask to replicate the pattern on the substrate, or the film itself can serve as contact electrodes for a wide range of electronic devices. We demonstrate the versatility of the technique by fabricating a polymer grating on SiO2 with lateral dimensions <80 nm and a pattern resolution approaching 10 nm, and by fabricating organic solar cells and pentacene channel organic thin-film transistors with channel lengths as short as 1 μm.
Bifurcations in biparametric quadratic potentials. II
Authors: Lanchares V. , Elipe A.
Published: July 2002

Quadratic Hamiltonians with the phase space on the 𝒮 2 sphere represent numerous dynamical systems. There are only two classes of quadratic Hamiltonians depending on two parameters. We analyze the occurrence of bifurcations and we obtain the bifurcation lines in the parameter plane for one of these classes, thus complementing the work done in a previous paper where the other class was analyzed. As the parameters evolve, the appearance–disappearance of homoclinic orbits in the phase portrait is governed by four types of bifurcations: namely the pitchfork, the butterfly, the oyster and the pentadent bifurcations. We find also values where the system is degenerate, that is, there are nonisolated equilibria.
Role of multistability in the transition to chaotic phase synchronization
Authors: Postnov D. E. , Vadivasova T. E. , Sosnovtseva O. V. , Balanov A. G. , Anishchenko V. S. , Mosekilde E.
Published: July 2002

In this paper we describe the transition to phase synchronization for systems of coupled nonlinear oscillators that individually follow the Feigenbaum route to chaos. A nested structure of phase synchronized regions of different attractor families is observed. With this structure, the transition to nonsynchronous behavior is determined by the loss of stability for the most stable synchronous mode. It is shown that the appearance of hyperchaos and the transition from lag synchronization to phase synchronization are related to the merging of chaotic attractors from different families. Numerical examples using Rössler systems and model maps are given.