bluuebunny/crossref_metadata_2025 huggingface dataset:
Examination of band bending at buckminsterfullerene (C60)/metal interfaces by the Kelvin probe method
Authors: Hayashi N. , Ishii H. , Ouchi Y. , Seki K.
Published: September 2002

This study addresses the question of band bending at the C60/metal interface. The change in the energy of the vacuum level upon the deposition of C60 on various metal substrates (Au, Cu, and Ag) was examined by the Kelvin probe method under ultrahigh vacuum as a function of C60 thickness d. We observed (1) an abrupt shift of the energy of the vacuum level relative to the Fermi level of the metal substrate εvacF at d⩽1 nm, to a uniform value of about 4.65 eV at all of the interfaces examined and (2) a slower shift with further deposition of C60, which stopped at d∼500 nm at another common value. These abrupt and gradual shifts can be ascribed to the formation of an interfacial dipole layer and to band bending leading to Fermi level alignment, respectively. The value of εvacF for the thick region is ascribed to the bulk work function of the specific specimen studied, and it is noted that the values reported for a few monolayers in the literature should not actually be regarded as the bulk work function. These results clearly demonstrate the necessity of detailed measurements of εvacF up to a large thickness of the organic film and of using various metal substrates to determine the bulk work function. The convergence of εvacF to a common value at a large thickness indicates the existence of remaining impurity. Its concentration was estimated and the effect of purification by sublimation was examined. We note that the bulk work functions obtained as the convergent values in such measurements are characteristic of specific specimens and may still not correspond to the value of the really intrinsic material.
Co-implantation of Si+N into GaN for n-type doping
Authors: Nakano Yoshitaka , Jimbo Takashi
Published: September 2002

Si-doping characteristics have been systematically investigated for Si+N co-implanted GaN. n-type regions were produced in undoped GaN films by the co-implantation and subsequent annealing with an SiO2 encapsulation layer at high temperatures. The sheet carrier concentration is seen to be precisely controllable between 3×1012 and 5×1014 cm−2 with Si activation efficiencies of ∼50% when the samples were annealed at 1300 °C. From atomic force microscopic observations, the co-implanted sample shows smooth surface morphology identical to that before implantation, whereas Ga islands are found to be formed in the surface region by the activation annealing in the case of conventional Si implantation. Therefore, the Si+N co-implantation technique turns out to be an effective method to enhance electrical and structural properties in view of GaN stoichiometry. However, implantation-induced microdefects seem to remain even after the high-temperature annealing process for both Si- and Si+N-implanted GaN samples.
High power microwave properties of Zn-Y hexagonal ferrite—parallel pumping size effects
Authors: Nazarov Alexey V. , Cox Richard G. , Patton Carl E.
Published: September 2002

The parallel pump spin wave instability threshold field hcrit was measured as a function of static field for various size in-plane magnetized thin plates of single crystal Mn substituted Zn-Y at both 9 and 16.7 GHz. The 9 GHz data indicate that (1) the critical modes consist of standing magnetostatic waves and (2) the hcrit thresholds depend on the lateral dimensions of the sample. The minimum parallel pumping spin wave linewidths were in the range 3–10 Oe and increased with a decrease in the sample lateral dimensions. These data are consistent with a transit time model and a size limited spin wave linewidth for low wave number critical modes. At 16.7 GHz, thresholds and spin wave linewidths are consistent with the 17.5 GHz and 9.5 GHz ferromagnetic resonance linewidth results and are sample size independent. The data indicate that exchange dominated spin waves are excited for fields below the butterfly curve minimum. These data give a k-dependent spin wave linewidth. The minimum parallel pumping spin wave linewidths were in the range 12–13 Oe.
Monte Carlo simulation of electron transmission through the scattering masks with angular limitation for projection electron lithography
Authors: Sun X. , Ding Z. J. , Pu Q. R. , Li H. M. , Wu Z. Q. , Gu W. Q. , Peng K. W. , Wu G. J. , Zhang F. A. , Kang N. K.
Published: September 2002

We calculated electron energy loss and angular distributions for electrons transmitted through masks for electron projection lithography by a Monte Carlo (MC) simulation method. After comparing the improved continuous slowing down approximation model, the direct MC model, and the intensive direct MC model, the last model was used. The energy loss distributions calculated by the latter two models are much better than by the first model and the intensive direct MC model can be applied to more materials than the direct MC model. The effect of mask thickness on energy loss, transmission, and contrast was analyzed. We found that, for a W/Cr/Si3N4 mask, the thicker the scattering layer the wider the angular distribution, the lower the transmission, and the higher the contrast. But the thickness of the membrane Si3N4 layer has less effect on the contrast.
Crystallization in Pd40Ni40P20 glass
Authors: Jiang J. Z. , Saksl K. , Nishiyama N. , Inoue A.
Published: September 2002

Phase segregation and the effect of pressure on crystallization of bulk and ribbon Pd40Ni40P20 glasses have been studied by means of differential scanning calorimetry (DSC) and x-ray diffraction. The DSC measurements show only one glass transition event in the samples annealed at different temperatures in the supercooled liquid region. Phase analyses reveal at least five crystalline phases crystallized from the glass: monoclinic; body-centered tetragonal; orthorhombic; Ni2Pd2P and fcc-(Ni,Pd) solid solution phases. In the pressure range from 0 to 4.2 GPa, the crystallization temperature increases with pressure having a slope of 11 K/GPa. The eutectic crystallization reaction mode and crystalline phases formed are unchanged in the pressure range used. The enhancement of the crystallization temperature with increasing pressure in the glass can be explained by the suppression of atomic mobility.
Nonlinear transformation of electromagnetic waves in suddenly created cold magnetized plasma: Longitudinal propagation
Authors: Trifkovic Zoran M. , Stanic Bozidar V.
Published: September 2002

The transformation of a circularly polarized electromagnetic source wave in a suddenly created cold magnetized and weakly nonlinear plasma is considered. For the case of longitudinal propagation (a source wave propagating along an external static magnetic field) when the ion motion is neglected, a circularly polarized source wave splits into four longitudinal oscillating modes. In the case of a linearly polarized source wave due to the interaction between its right and left circularly polarized components additional stationary and traveling electron wave modes are created. Amplitude distributions of all created modes are determined in closed form and presented in corresponding diagrams for different values of source wave and electron cyclotron frequencies.
In situ study of the effect of temperature on the electronic structure of NixMn3−xO4+δ thin films using scanning tunneling spectroscopy
Authors: Basu A. , Brinkman A. W. , Klusek Z. , Datta P. K. , Kowalczyk P.
Published: September 2002

Ni x Mn 3−x O 4+δ  (0.4⩽x⩽1) are a series of cubic-spinel-structured material exhibiting a negative temperature coefficient of resistance. The resistance as a function of temperature (T) has been measured from 20 to 200 °C and the data have been fitted to a variable range hopping model in which the resistivity is described as ρ=ρ0T exp(T0/T)0.5 where T0 was found to be 2.24×105 K. Scanning tunneling spectroscopy measurements were carried out over the temperature range of 20–300 °C, to study the shape of the local density of states (LDOS). Such measurements have not been carried out on this class of spinel structured materials before. The distribution of the LDOS around the Fermi level was parabolic in agreement with the model of variable range hopping. The evolution of a peak around 1.8 eV was observed with increasing temperature and found to be completely reversible with temperature.
Dielectric properties of oriented PbZrO3 thin films grown by sol-gel process
Authors: Zhai Jiwei , Yao Y. , Li X. , Hung T. F. , Xu Z. K. , Chen Haydn , Colla Eugene V. , Wu T. B.
Published: September 2002

Antiferroelectric PbZrO3 (PZ) films have been fabricated on LaNiO3/Pt/Ti/SiO2/Si substrates using a sol-gel process. The films with perovskite structure showed highly 〈001〉 preferred orientation. An antiferroelectric phase was identified by the presence of 1/4{110} superlattice spots in a [001] selected area electron diffraction pattern. The field-induced antiferroelectric to ferroelectric phase switching was demonstrated at room temperature with full saturation and a maximum polarization of 40 μC/cm2. Dielectric properties were investigated as a function of both temperature and frequency. The presence of a conductive buffer layer of LaNiO3 on Pt/Ti/SiO2/Si substrate enabled the growth of high quality and highly oriented PZ antiferroelectric thin films that showed near zero remanent polarization and squared hysteresis loops.
Structure and morphology of epitaxial PbZrO3 films grown by metalorganic chemical vapor deposition
Authors: Moret M. P. , Schermer J. J. , Tichelaar F. D. , Aret E. , Hageman P. R.
Published: September 2002

PbZrO 3 (PZ) films of different thicknesses have been grown by metalorganic chemical vapor deposition on SrTiO3 (STO) substrates. The structure of the films was determined by x-ray diffraction and transmission electron microscopy. At the deposition temperature, the growth is cube on cube and is therefore heteroepitaxial. During cool down, PZ goes through a phase transformation from paraelectric to antiferroelectric at the Curie temperature and its cubic structure is stretched to orthorhombic. This results in domain formation in the PZ films corresponding to the different stretching directions. At room temperature, the thin PZ film consists of at least two different (120) domain variants and the thin-film–substrate relation can be described as (120)[002]PZ//(100) [001̄] STO for one of these variants. By etching down a thick film, it was observed that ∼260 nm is the threshold thickness, above which two additional different (002) domain variants appear in addition to the (120) domain variants. For one of the (002) domain variants, the thin-film–substrate relation can be described as (002)[100]PZ//(100)[011] STO. The surface morphology of the thick films, studied by scanning electron and atomic force microscopy, is partly covered with pyramids. These pyramids can originate from both (120) or (002) domains and are due to a higher growth rate of these two planes compared to the rest of the layer. A suggestion is made for pyramid-facet indexing for both domains.
Evaluation of Ta2O5 as a buffer layer film for integration of microwave tunable Ba1−xSrxTiO3 based thin films with silicon substrates
Authors: Cole M. W. , Joshi P. C. , Ervin M. , Wood M. , Pfeffer R. L.
Published: September 2002

Successful integration of Ba1−xSrxTiO3 (BST) based thin films with affordable Si substrates has a potential significant commercial impact as the demand for high-frequency tunable devices intensifies. This work evaluates the material properties of postdeposition annealed Ta2O5 thin films fabricated via the metalorganic solution technique for use as a passive buffer layer between BST and Si. The microstructure, surface morphology, and interfacial properties of the Ta2O5 film deposited on n+-Si and PtSi substrates was evaluated via field-emission scanning electron microscopy, Rutherford backscattering spectrometry, Auger electron spectroscopy, and atomic force microscopy. The presence of a transition interaction zone between the Ta2O5 film and Si substrate was detected after annealing at temperatures >600 °C. The width of the interaction zone increased with increasing annealing temperature reaching a maximum of 29 nm at 750 °C. The width of the interaction zone was also found to be dependent on the Ta2O5 film microstructure. The Ta2O5 film was typified by a smooth; fine grain, crack/pinhole free surface morphology. The presence of the interfacial layer had no appreciable effect on the microstructure of the film or surface morphology. The narrowness of the interaction zone with respect to the overall film thickness combined with the fact that the interfacial layer did not seriously deteriorate the dielectric properties of the Ta2O5 film suggests Ta2O5 to be a favorable candidate buffer layer enabling the integration of BST with Si substrates.
Eley–Rideal abstraction of carbon from graphite by hyperthermal N+ ions
Authors: Deng Z.-W. , Souda R.
Published: September 2002

Hyperthermal N+ ions efficiently abstract C atoms from a graphite surface to form CN− ions. An incident energy threshold of ∼0 eV for CN− emission is obtained and agrees with the exothermicity of the reaction. Both the mean and the maximum product translational energies are correlated with the incident N+ energy, excluding the Langmuir–Hinschelwood mechanism. While most CN− ions retain only ∼4% of the incident translational energy, a maximum energy transfer ratio of ∼25% from the incident ion to the product is observed, suggesting that the abstraction occurs via the Eley–Rideal mechanism. Energetic analysis of the reaction and the product reveals that the abstraction reaction occurs at carbon defect sites by breaking two rather than three C–C bonds.
Domain wall trapping at mesoscopic ferromagnetic junctions
Authors: Adeyeye A. O. , Welland M. E.
Published: September 2002

We have investigated the effects of domain walls (DWs) on electron transport across mesoscopic ferromagnetic junctions. The structures consist of a single 30 nm Ni80Fe20 thick 0.5×24 μm wire bisected by a mesoscopic junction with width w in the range 0.2–1 μm. Using magnetoresistance (MR) measurements, we observed directly an extra resistivity associated with controlled domain wall nucleation process on a complete field hysteresis loop for various junction widths. For the field applied along the wire hard axis, we observed complex MR curves at low fields for wires with w>0 compared with a simple parabolic MR behavior of a single wire of the same lateral dimension. This is attributed to the trapping of DWs at the junction area perpendicular to the current direction. The MR behavior for the field applied along the wire easy axis is strikingly dependent on the junction width due to the variation in spin configurations at the junction area. The field angle dependent MR responses and simple micromagnetic simulations suggest that the magnetization reversal process at the junction area is mediated by domain wall propagation.
Stress field effects on the microstructure and properties of a-C:H thin films
Authors: Golanski A. , Piazza F. , Werckmann J. , Relihan G. , Schulze S.
Published: September 2002

The physical properties of plasma-deposited hydrogenated amorphous-carbon films (a-C:H) are investigated and correlations to the competing intrinsic and extrinsic stress fields are established. The (a-C:H) films are grown on single-crystal 〈100〉 silicon substrates in a plasma reactor using acetylene as a precursor. Although constant C2H2 plasma conditions and constant substrate bias and temperature were used during the growth the films display a multilayer structure. The density and the sp3-hybridized carbon fraction are shown to vary during deposition. The microstructure and optoelectronic properties of the (a-C:H) thin film evolve during growth as a result of interaction between the intrinsic tensile stress generated within the growing film and the external stress field existing in the Si substrate. During the initial phase of the growth this external stress field enhances the intrinsic stress. The resulting film is of high density and contains a relatively high fraction of sp3-hybridized carbon atoms. Eventually, when the (a-C:H) layer becomes thick enough, the intrinsic stress compensates the external stress field. Layers grown under balanced stress conditions show an unusual alignment of the graphitic planes. Finally, when the intrinsic stress becomes dominant, the density of the film and the corresponding sp3 fraction decrease, leading to a detectable porosity. The behavior of the optical band gap is shown to reflect the evolution of the (a-C:H) microstructure as it is unambiguously correlated to the evolution of the stress field.
Infrared reflection characteristics in InN thin films grown by magnetron sputtering for the application of plasma filters
Authors: Qian Z. G. , Shen W. Z. , Ogawa H. , Guo Q. X.
Published: September 2002

We study the IR reflection characteristics (400–10000 cm−1) of InN thin films grown by radio frequency magnetron sputtering on GaAs (111) substrates. The plasma oscillation, carrier concentration, and mobility are obtained and discussed by calculating the IR reflection spectra. The suitability of InN thin films for the application of plasma filters has been revealed by investigating the performance of InN plasma filters with different carrier concentration, mobility, and film thickness. Two InN plasma filters have been designed for the widely used GaSb and GaInAsSb photovoltaic cells in thermophotovoltaic systems, which show good performance. The advantages of InN thin film as plasma filter material over the conventional transparent conducting oxides and heavily doped Si materials have also been discussed.
Elastic energy release rate of quantum islands in Stranski–Krastanow growth
Authors: Yang B.
Published: September 2002

When constrained by a lattice-misfit substrate, a sufficiently thick epitaxial layer develops surface quantum islands (QIs) via mass transport as a thermodynamic process for energy minimization. By this process, the misfit strain energy is partially released, which serves as the driving force for island formation. In this work, we examine the elastic energy release rate (EERR, i.e., elastic relaxation energy per unit volume) of QI growth in multilayered heteroepitaxial structures under the condition of mass conservation. The analysis is based on a two-dimensional isotropic linear elastic continuum approach. A parametric study first is carried out to investigate the effects of various parameters on the variation of EERR of QI formation in an epilayer-substrate system. Furthermore, the EERR, which represents the energetics of global equilibrium, is applied to investigate the correlation of surface islands to buried seed islands in a multilayered heterostructure. The variation of EERR during nucleation of new surface islands shows a tendency of vertical correlation to buried seed islands in the isotropic heterogeneous system. This relationship of correlation does not alter with changing vertical distance between the surface and seed islands in the range examined.
Studies of static and high-frequency magnetic properties for M-type ferrite BaFe12−2xCoxZrxO19
Authors: Li Z. W. , Chen Linfeng , Ong C. K.
Published: September 2002

Static and high-frequency magnetic properties have been studied for BaFe12−2xCoxZrxO19 with x=0–1.2. The x-ray diffraction and M–H curves of aligned samples show that Co–Zr substitution can modify the anisotropy of BaFe12−2xCoxZrxO19. BaFe12−2xCoxZrxO19 with x⩽0.6 has an easy c-axis anisotropy and the anisotropy fields rapidly decrease with Co–Zr substitutions. The sample of x=1.2 has an easy c-plane anisotropy with Ha=5 kOe. The saturation magnetizations of BaFe12−2xCoxZrxO19 are almost constant at x⩽0.4 and decrease with higher substitutions. The coercivity decreases rapidly from 2400 Oe for the sample of x=0 to about 10 Oe for the sample of x=0.8. The natural resonance frequencies are observed at 4.5 and 5.0 GHz for the samples of x=0.8 and x=1.2, respectively. Based on microwave measurement and theoretical estimations on reflectivity, BaFe12−2xCoxZrxO19 may be a good candidate for electromagnetic compatibility and other practical applications at high frequency.
Temperature dependence of carrier transport in conducting polymers: Similarity to amorphous inorganic semiconductors
Authors: Kapoor Ashok K. , Jain S. C. , Poortmans J. , Kumar Vikram , Mertens R.
Published: September 2002

We improve the trapping model of carrier transport in conducting polymers by integrating the coupled Poisson and continuity equations numerically. In the case of exponentially distributed traps calculated log J vs 1/T plots are straight lines indicating that the activation of carriers to the extended states can be described by one single activation energy, Eeff. The improved trapping model agrees well with the recent experimental data at high temperatures (i.e., near room temperature). At low temperatures the trapping model does not work since the available thermal energy is not sufficient to ionize the traps. We use the hopping mobility model at low temperatures. The model explains the low-temperature J–V characteristics well. This mechanism of charge carrier transport is similar to that used for interpreting experiments on inorganic amorphous materials.
Experimental observation of scaling laws for alternating current and direct current conductivity in polymer-carbon nanotube composite thin films
Authors: Kilbride B. E. , Coleman J. N. , Fraysse J. , Fournet P. , Cadek M. , Drury A. , Hutzler S. , Roth S. , Blau W. J.
Published: September 2002

Alternating current (ac) and direct current (dc) conductivities have been measured in polymer-nanotube composite thin films. This was carried out for a range of concentrations of multiwall nanotubes in two polymer hosts, poly(m-phenylenevinylene-co-2,5-dioctyloxyp-phenylenevinylene) (PmPV) and polyvinylalcohol (PVA). In all cases the dc conductivity σDC was ohmic in the voltage range studied. In general the ac conductivity displayed two distinct regions, a frequency independent region of magnitude σ0 at low frequency and a frequency dependent region at higher frequency. Both σDC and σ0 followed a percolation scaling law of the form σ∝(p−pc)t with pc=0.055% by mass and t=1.36. This extrapolates to a conductivity of 1×10−3 S/m for 100% nanotube content. Such a low value reflects the presence of a thick polymer coating, resulting in poor electrical connection between tubes. This leads to the suggestion that charge transport is controlled by fluctuation induced tunneling. In the high frequency regime the conductivity increases with frequency according to an approximate power law with exponent s≈0.92, indicative of hopping transport. The onset of this frequency independent conductivity scales with mass fraction for the PmPV composite due to the variation of correlation length with nanotube content. This behavior is discussed in terms of a biased random walk in three dimensions. In addition ac universality is demonstrated by the construction of a mastercurve.
Craters on silicon surfaces created by gas cluster ion impacts
Authors: Allen L. P. , Insepov Z. , Fenner D. B. , Santeufemio C. , Brooks W. , Jones K. S. , Yamada I.
Published: September 2002

Atomic force microscopy (AFM) and high-resolution transmission electron microscope (HRTEM) cross section imaging of individual gas cluster ion impact craters on Si(100) and Si(111) substrate surfaces is examined. The comparison between 3 and 24 kV cluster impacts from Ar and O2 gas sources is shown. Results for low fluence (1010 ions/cm2) 24 kV Ar individual cluster impacts onto a Si(100) and Si(111) substrate surfaces are compared with hybrid molecular dynamics (HMD) simulations. A HMD method is used for modeling impacts of Arn (n=135, 225) clusters, with energies of 24–50 eV/atom, on Si(100) and Si(111) surfaces. On a Si(100), craters are nearly triangular in cross section, with the facets directed along the close-packed (111) planes. The Si(100) craters exhibit four-fold symmetry as imaged by cross-sectional HRTEM, and AFM top view, in agreement with modeling. In contrast, the shape of craters on a Si(111) shows a complicated six-pointed shape in the modeling, while AFM indicates three-fold symmetry of the impact. The lower energy 3 kV individual cluster impacts reveal the same crater shape in HRTEM cross section for both Ar and O2 gas clusters, but with shallower crater depth than for the higher-energy impacts. The kinetics of the Ar and O2 crater impacts may explain the successful use of higher-energy cluster impacts for etching material of higher initial surface roughness followed by the lower-energy impacts as an effective finishing step to achieve smoother surfaces.
Magnetocaloric effect in random magnetic anisotropy materials
Authors: Bohigas Xavier , Tejada Javier , Torres Francesc , Arnaudas José Ignacio , Joven Enrique , del Moral Agustı́n
Published: September 2002

In this letter we report the results of entropy variations in random anisotropy magnets composed of TbxY1−xAl2, with x=0.15, 0.20, 0.25, 0.35, 0.40, and 0.50. We discovered large entropy variation associated with the spin glass to paramagnetic transition. Both temperature transition and entropy changes were studied at different temperatures and with different compositions. Our conclusion is that these materials are suitable candidates for use as magnetic refrigerants in a temperature range below 40 K.
Radiative recombination of electron–hole pairs spatially separated due to quantum-confined Stark and Franz–Keldish effects in ZnO/Mg0.27Zn0.73O quantum wells
Authors: Makino T. , Tamura K. , Chia C. H. , Segawa Y. , Kawasaki M. , Ohtomo A. , Koinuma H.
Published: September 2002

We studied photoluminescence (PL) properties of eighteen samples of wurtzite ZnO/MgxZn1−xO multiple quantum wells (x=0.12 and 0.27) with various well widths (Lw) of 0.7–4.65 nm. Radiative recombination of the electron–hole pairs that are spatially separated due to the quantum-confined Stark (QCS) and Franz–Keldish (QCFK) effects was observed in two thicker samples at 5 K. This PL band is located ≈ 40 meV in energy below the emission band of the localized excitons and ≈ 60 meV below the absorption energy of the free exciton transition. One can not observe such kind of luminescence unless both of the following conditions are accomplished: (1) higher Mg concentration (x=0.27) and (2) Lw⩾4.23 nm. These experimental findings do not contradict the following two characteristic features for the QCS and QCFK effects; the magnitude of the electric field due to spontaneous and piezoelectric polarizations and the depth of the triangle-shaped potential wells are the monotonically increasing functions of Mg concentration and the Lw, respectively. The coupling strength with longitudinal-optical phonons, which is determined from the relative luminescence intensities of the phonon replicas, is significantly larger than that between the localized excitons and phonons. It is considered that the strong electric field increases the distance between electron and hole charge distributions from that determined by the Coulomb force and leads to the enhancement in the phonon interaction.
Experimental evidence of asymmetric carrier transport in InGaAs quantum wells and wires grown on tilted InP substrates
Authors: Monte A. F. G. , da Silva S. W. , Cruz J. M. R. , Morais P. C. , Chaves A. S.
Published: September 2002

The influence of the interface morphology upon the electron–hole transport in intrinsic In0.53Ga0.47As/InP quantum structures was investigated by scanning the photoluminescence intensity profile on the sample surface. The results suggest that the carrier diffusion is very sensitive both to the roughness of the interfaces and the presence of finite-width terraces. It was found that the carrier density profile shows asymmetric diffusion normal to the terraces whereas it shows symmetric expansion along the terraces. Simulations of the asymmetry in the carrier density profile using a non-Fickian diffusion equation described by the Lévy statistics show a excellent agreement with the experimental data.
Fe-substituted 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 single crystals: A “hard” piezocrystal
Authors: Priya Shashank , Uchino Kenji , Viehland Dwight
Published: September 2002

The dielectric and electrically induced strain characteristics of Fe-substituted Pb(Zn1/3Nb2/3)O3–PbTiO3 single crystals have been investigated. These investigations have shown that Fe substitution results in: (i) a lowering of the field level required to obtain large strains, (ii) an increased squareness in the ε−E response indicative of “hard” piezoelectric properties, and (iii) enhanced linearity in the region where saturation is approached at high field levels. Interestingly, the hard characteristics occur along with an enhanced stability of an intermediate ferroelectric orthorhombic state.
Pseudodielectric functions of InGaAs alloy films grown on InP
Authors: Kim T. J. , Ihn Y. S. , Kim Y. D. , Kim S. J. , Aspnes D. E. , Yao T. , Shim K. , Koo B. H.
Published: September 2002

We present room-temperature pseudodielectric function spectra 〈ε〉 of InxGa1−xAs films grown on (100) InP by solid-source molecular-beam epitaxy. A wet-chemical etching procedure is used to remove overlayers and obtain the best approximation to the bulk dielectric responses ε of the films. By line shape fitting, we determined the x dependences of the E1 and E1+Δ1 critical-point energies and that of the Δ1 bowing parameter. The results are in good agreement with the predictions of a universal tight-binding model.
Enhanced blue and green emission in rare-earth-doped GaN electroluminescent devices by optical photopumping
Authors: Lee D. S. , Steckl A. J.
Published: September 2002

Electroluminescence (EL) from rare-earth-doped GaN (GaN:RE) EL devices (ELD) emission has been observed to be greatly enhanced by ultraviolet (UV) photopumping. With radiation from a HeCd laser (325 nm) both blue (from GaN:Tm) and green (from GaN:Er) EL brightness have been enhanced up to 2 orders of magnitude, depending on bias conditions. We explain the luminescence increase by the following mechanism: photoelectrons generated by above GaN band-gap excitation are accelerated by the electric field along with electrically injected electrons and both types of carriers contribute to EL emission through RE impact excitation. The EL intensity increases monotonically with increasing applied bias and with photopumping power. The photopumped-induced EL gain is most efficient at relatively low bias, reaching values of 50–100×. This increase in EL emission can be applied to flat panel displays with enhanced brightness, especially blue, and with improved color balance. Other applications include UV indicators and detectors, and infrared emitters.
Grazing-incidence small-angle scattering measurement of Ge islands capped with a Si layer
Authors: Okuda Hiroshi , Ochiai Shojiro , Ito Kazuki , Amemiya Yoshiyuki
Published: September 2002

Grazing-incidence small-angle scattering (GI-SAXS) technique was applied to self-organized Ge islands capped with Si. The average size and height as well as the average distance between Ge islands were obtained. The present results demonstrate that GI-SAXS is a useful tool to examine the structure of self-organized semiconducting nanodots even if they are covered with a cap layer, and a simple kinematical approach can be safely used under some conditions.
A molecular thermometer based on long-lived emission from platinum octaethyl porphyrin
Authors: Lupton John M.
Published: September 2002

A highly sensitive molecular thermometer based on platinum octaethyl porphyrin, which can be employed in a range of environments, is presented. The thermal activation of the emission spectrum results in a change in emission intensity by an order of magnitude over a temperature range of 45 K about room temperature. The long-lived molecular emission enables the characterization of thermal effects in common conjugated polymers under optical excitation. It is found that optical heating does not contribute to material breakdown, which is governed by photo-oxidation.
Efficient polarized light-emitting diodes utilizing ultrathin photoaddressable alignment layers
Authors: Yang X. H. , Neher D. , Lucht S. , Nothofer H. , Güntner R. , Scherf U. , Hagen R. , Kostromine S.
Published: September 2002

We demonstrate that an ultrathin photoaddressable polymer (PAP) layer with a thickness as small as 5 nm can be utilized for the monodomain alignment of thermotropic liquid crystalline polyfluorene. The optical anisotropies in absorption and emission are found to be independent of the PAP layer thickness within a range of 5 to 30 nm. On the other hand, decreasing the PAP layer thickness greatly improves the performance of polarized blue light-emitting diodes: With a PAP layer thickness of only 10 nm, the device turns on at 5 V and reaches a brightness of 100 cd/m2 at 8 V with an efficiency of 0.66 cd/A.
High energy proton irradiation effects on SiC Schottky rectifiers
Authors: Nigam S. , Kim Jihyun , Ren F. , Chung G. Y. , MacMillan M. F. , Dwivedi R. , Fogarty T. N. , Wilkins R. , Allums K. K. , Abernathy C. R. , Pearton S. J. , Williams J. R.
Published: September 2002

4H-SiC Schottky rectifiers with dielectric overlap edge termination were exposed to 40 MeV protons at fluences from 5×107–5×109 cm−2. The reverse breakdown voltage decreased from ∼500 V in unirradiated devices to ∼−450 V after the highest proton dose. The reverse leakage current at −250 V was approximately doubled under these conditions. The forward current at −2 V decreased by ∼1% (fluence of 5×107 cm−2) to ∼42% (fluence of 5×109 cm−2), while the current at lower biases was increased due to the introduction of defect centers. The ideality factor, on-state resistance, and forward turn-on voltage showed modest increases for fluences of ⩽5×108 cm−2, but were more strongly affected (increase of 40%–75%) at the highest dose employed.
Energy level alignment at organic/metal interfaces: Dipole and ionization potential
Authors: Peisert H. , Knupfer M. , Fink J.
Published: September 2002

We present a systematic study of the energy level alignment at the interfaces between gold and organic semiconductors. It is shown that there are at least two leading contributions to the potential drop (dipole) across the metal/organic interface: A modification of the metal work function due to the adsorption of the organic molecules and a potential change in the organic semiconductor.
Study of photocurrent characteristics in PbSrSe thin films for infrared detection
Authors: Yang H. F. , Shen W. Z. , Pang Q. J.
Published: September 2002

We have carried out a detailed investigation of photocurrent spectra in Pb1−xSrxSe thin films grown by molecular-beam epitaxy on BaF2 substrates with Sr composition from 0.066 to 0.276 under different temperatures from 77 to 300 K. Strong room temperature infrared detection has been demonstrated with the wavelength from 1.0 to 3.1 μm. By employing a diffusion-recombination model to analyze the temperature- and Sr composition-dependent photocurrent, we find that the photocurrent in the investigated PbSrSe thin films is dominated by bulk excitation, recombination, and transport processes. For the application of infrared detection, the optimal thickness for PbSrSe thin films should be less than 2.5 μm.
Properties of highly strained InGaAs/GaAs quantum wells for 1.2-μm laser diodes
Authors: Mogg S. , Chitica N. , Schatz R. , Hammar M.
Published: September 2002

The properties of 1.2-μm highly strained InGaAs quantum wells (QWs) grown on GaAs substrates have been analyzed. Optical gain spectra versus injection current and temperature, transparency current density, as well as other figures of merit were assessed from measurements on broad-area and ridge-waveguide lasers based on these QWs. Such active regions are of interest for a range of applications, including GaAs-based high-power lasers and vertical-cavity lasers for wavelengths beyond 1.2 μm.
Control of grain-boundary tunneling barriers in polycrystalline silicon
Authors: Kamiya Toshio , Durrani Zahid A. K. , Ahmed Haroon
Published: September 2002

The effect of oxidation and annealing on the electrical properties of grain boundaries (GBs) in heavily doped polycrystalline silicon is characterized using bulk films and 30-nm-wide nanowires. Oxidation at 650–750 °C selectively oxidizes the GBs. Subsequent annealing at 1000 °C increases the associated potential barrier height and resistance. These observations can be explained by structural changes in the Si–O network at the GBs and the competition between surface oxygen diffusion and oxidation from the GBs in the crystalline grains. A combination of oxidation and annealing may provide a method that can better control the GB potential barriers.
Dielectric loss peak due to platinum electrode porosity in lead zirconate titanate thin-film capacitors
Authors: Jung D. J. , Dawber M. , Ruediger A. , Scott J. F. , Kim H. H. , Kim Kinam
Published: September 2002

Impedance spectroscopy measurements were carried out in situ on lead zirconate titanate capacitors 1.2×1.2 μm2 in size on a Samsung 4 Mbit 6 in, wafer. We show here that large dielectric loss appears at low frequencies, which is a constriction effect due to the porosity of the platinum electrode. Porous platinum electrodes facilitate an oxygen electrode reaction. The effect may be removed by annealing the platinum electrode at moderate temperature (300 °C). Such an anneal should thus be considered an essential step in the fabrication of a ferroelectric thin-film capacitor on Pt.
Ag-induced zero- and one-dimensional nanostructures on vicinal Si(111)
Authors: Kuntze J. , Mugarza A. , Ortega J. E.
Published: September 2002

The formation of a Ag-stabilized regular step lattice on vicinal Si(111) miscut towards [112̄] is reported. The step bunching characteristic of the clean surface is prevented by single-domain Si(111)-(3×1)-Ag reconstruction. The nanostructured surface is used as a template for growing one-dimensional arrays of 1 nm sized Ag quantum dots with a preferential spacing of 1.5 nm along the rows.
Hexagonal polymorph of tantalum–pentoxide with enhanced dielectric constant
Authors: Hiratani M. , Kimura S. , Hamada T. , Iijima S. , Nakanishi N.
Published: September 2002

A tantalum–pentoxide dielectric with an enhanced permittivity of over 50 was found to be crystallized in a hexagonal symmetry with a=0.628 nm and c=0.389 nm. The incommensurate epitaxy of tantalum pentoxide on hcp-ruthenium metal stabilizes the hexagonal phase with √3-time periodicity in plane, as compared with that of the known hexagonal δ phase. The crystallographic assumption, which is based on one-dimensional Ta–O–Ta chain along the c axis, can explain large polarizability caused by delocalized electrons on the one-dimensional chain.
Infrared dielectric functions and phonon modes of wurtzite MgxZn1−xO (x⩽0.2)
Authors: Bundesmann C. , Schubert M. , Spemann D. , Butz T. , Lorenz M. , Kaidashev E. M. , Grundmann M. , Ashkenov N. , Neumann H. , Wagner G.
Published: September 2002

Infrared dielectric function spectra and phonon modes with polarization parallel and perpendicular to the c axis of high quality, highly relaxed, and single crystalline wurtzite MgxZn1−xO films with 0⩽x⩽0.2 prepared by pulsed-laser deposition on c-plane sapphire substrates were obtained from infrared spectroscopic ellipsometry (380–1200 cm−1) and Raman scattering studies. A two-mode behavior is found for the modes with E1 symmetry, a lattice mode and an impurity-type mode are obtained for the A1 symmetry phonons. Model dielectric function spectra will become useful for future infrared ellipsometry analysis of complex MgxZn1−xO-based heterostructures.
Electronic confinement of organic molecules in confined spaces: A spectroscopic study of Zn(phen)2(NO3)2 loaded MCM-41
Authors: Zhang Lei Z. , Cheng Peng , Liao Dai-Zheng
Published: September 2002

Steady-state and dynamic spectroscopic studies have been given in support of the electronic confinement of Zn(phen)2(NO3)2, 1 (phen=1, 10-phenanthroline), within nanoporous MCM-41. The bathochromic shift of the 0-0 transitions, together with the shortening of the excited state lifetimes have been correlated with the reduction of the HOMO-LUMO band gap accompanying by the increased energies of the frontier orbitals. This trend indicates that the electronic confinement of organic molecules is indeed realized in larger cavities, such as nanocavities of MCM-41. The variations in the 0-0 transitions observed here have also been confirmed by theoretical calculations.
Photoluminescence study of carrier transfer among vertically aligned double-stacked InAs/GaAs quantum dot layers
Authors: Mazur Yu. I. , Wang X. , Wang Z. M. , Salamo G. J. , Xiao M. , Kissel H.
Published: September 2002

Photoluminescence (PL) properties of self-organized quantum dots (QDs) in a vertically aligned double-layer InAs/GaAs QD structure are studied as a function of temperature from 10 to 290 K. The QDs in a sample with a 1.8 ML InAs seed layer and a second 2.4 ML InAs layer are found to self-organize in pairs of unequal sized QDs with clearly discernible ground-states transition energy. The unusual temperature behavior of the PL for such asymmetrical QD pairs provides clear evidence for carrier transfer from smaller to larger QDs by means of a nonresonant multiphonon-assisted tunneling process in the case of interlayer transfer and through carrier thermal emission and recapture within one layer.
Critical current density and third-harmonic voltage in superconducting films
Authors: Mawatari Yasunori , Yamasaki Hirofumi , Nakagawa Yoshihiko
Published: September 2002

When a sinusoidal drive current I0 cos ωt flows in a small coil close to the surface of a superconducting film, third-harmonic voltage V3 cos(3ωt+θ3) is induced in the coil if the film causes a nonlinear response. We have developed an approximate theoretical method yielding the relationships among I0, V3, and θ3, thus providing the scientific basis for a widely used inductive method for measuring the critical current density Jc in large-area superconducting films. Our results show that V3 is near zero when I0 is smaller than a threshold value Ic0∝Jcd, where d is the film thickness. When I0>Ic0, on the other hand, the third-harmonic voltage is expressed as V3 exp(−iθ3)=ωIc0G(I0/Ic0), where G(x) is a scaling function determined by the configuration of the coil. We demonstrate the scaling law of V3/Ic0 vs I0/Ic0 in a YBa2Cu3O7−δ film.
Thermoelectric properties of Bi2Sr2Co2O9 whiskers under hydrostatic pressure
Authors: Chen F. , Stokes K. L. , Funahashi Ryoji
Published: September 2002

We report the temperature dependence of thermopower (S) in the ab plane of Bi2Sr2Co2O9 (BC-222) single crystalline whiskers under high pressure up to 1.2 GPa. Special modifications were made to our high-pressure transport measurement system to improve the measurement accuracy of S for whiskers with high resistance. Pressure improved the contact resistance dramatically. We observed a slight decrease of S and four-wire electrical conductivity (σ) under high pressure. As a result, the power factor (S2σ) was decreased less than 20% by pressure. From the temperature dependence of σ, the band gap of BC-222 whiskers increase very slightly under high pressure.
Sprinkler systems: code review in high‐rise buildings use
Authors: Wong L.T. , Chong H.W. , Chow W.K.
Published: September 2002

Automatic sprinkler systems are considered as one of the most important facilities for providing building fire safety. Even old high‐rise buildings are required to upgrade the fire safety provisions. Four standards on installing sprinkler systems in high‐rise commercial buildings are briefly reviewed and compared. They are the British Standard 5306, the National Fire Protection Association Standard NFPA‐13, the Australian Standard 2118.1 and the Codes of China. Key areas are discussed by comparing their suitabilities for local use. Designs following the four standards for a typical old high‐rise building (i.e. those built before 1972) will be worked out to illustrate the differences in using the four methods.
Electronic article supply – making life EASY‐er for all
Authors: Morrow Terry
Published: September 2002

This paper examines EASY, a two‐year document delivery pilot project run jointly by Ingenta and Lancaster University. The main aim of the project is to test the feasibility of satisfying inter‐library loan (ILL) requests directly from publishers’ digital files. These requests would otherwise have been satisfied by either photocopying or scanning by the supplying library and sent either to the requesting library or directly to the end‐user. The service is not a separate ILL service; using the OpenURL standard it is designed to be integrated with and complement existing ILL services. The concept is being tested with ILLOS, Lancaster’s widely implemented inter‐library loan management system, working alongside Ingenta’s electronic full‐text document supply service. The second phase of the project will consider extending the service beyond ILLOS and Ingenta to other suppliers and other interlending document request management systems.
Changing information needs in a transition period in Hungary: satisfying demands from different sources
Authors: Kürti Éva
Published: September 2002

The changes taking place in Hungarian society, combined with technological innovation, have placed the Hungarian library system in permanent transition. In 1997, a new Cultural Act was enacted which included, among other things, public library provision. The traditional library service of ILL is also in transition and it is necessary to carry out an evaluation of the services of the requesting and supplying libraries which are still available. This paper addresses these questions and discusses ways of satisfying demands from different sources.
Why the distributed national collection won’t be coming to a library near you
Authors: Genoni Paul
Published: September 2002

Research libraries in the UK are considering the development of a highly developed form of collaborative purchasing for print material, the distributed national collection. The distributed national collection may have the potential to deliver benefits to libraries and their users, but there are a number of problems that will hinder the implementation of such a programme. The most significant of these are the attitudes to collaborative collecting held by some senior library managers, which emphasise collection goals that are short term and local at the expense of longer‐term national goals.
Interlending and document supply: a review of recent literature – XLll
Authors: McGrath Mike
Published: September 2002

Reviews recent interlending and document supply literature. Considers the implications of open access archiving and the ongoing developments in consortia and electronic journals. A number of other issues are reviewed briefly.
An examination of the organizational and cross‐cultural challenges facing international hotel managers in Russia
Authors: D’Annunzio‐Green Norma
Published: September 2002

With the ever increasing globalization of the hospitality industry, an exploration of the issues facing international hotel managers in Russia is both timely and important. The ability to manage people in an international context is one of the greatest tests of managerial skill and, in many novel cultures, success is dependent not only on the managers’ technical and professional expertise but also on their understanding of the local culture and local staff. There are many important cultural factors that impact on the expectations and attitudes of Russians about work which are therefore essential for managers to appreciate and understand. The paper highlights the range of challenges that exist and illustrates those that arise from cross‐cultural differences between eastern and western expectations, as well as the range of diverse organizational cultures within Russia’s hotel industry. Managers must be aware of these differences and develop appropriate skills and competencies to help them adapt their style accordingly.