bluuebunny/crossref_metadata_2025 huggingface dataset:
New analytical (2A′,4A′) surfaces and theoretical rate constants for the N(4S)+O2 reaction
Authors: Sayós R. , Oliva Carolina , González Miguel
Published: July 2002

We report two new analytical fits of the ground potential energy surface (PES) (2A′) and the first excited PES (4A′) involved into the title reaction and its reverse, using ab initio electronic structure calculations from Papers I and II along with new grids of ab initio points by means of the second-order perturbation theory on CASSCF wave function [CASPT2 (17,12) G2/aug-cc-pVTZ] reported here (1250 points for the A′2 PES and 910 points for the A′4 PES). Some experimental data were also introduced to better account for the exoergicity and the experimental rate constant at 300 K. The final root-mean-square deviations of the fits were 1.06 and 1.67 kcal/mol for A′2 and the A′4 PESs, respectively, for the NOO Cs abstraction and insertion regions of the PESs. Thermal rate constants were calculated (300–5000 K) for both the direct and reverse reactions by means of the variational transition state theory with the inclusion of a microcanonical optimized multidimensional tunneling correction, obtaining a very good agreement with the experimental data within all the temperature range. The new analytical A′2 PES presents several stationary points not introduced in previous analytical surfaces, and describes accurately the NO2 (X 2A1) minimum, which seems to be very accessible according to the trajectories run in a preliminary quasiclassical trajectory study. The new analytical A′4 PES has a lower energy barrier than the previous one, which increases significantly the contribution of this PES to the total rate constant at high temperatures. Moreover, the new analytical PESs not only describe accurately the Cs regions of the NOO system but also the ONO C2v or near C2v regions.
A general state-selective multireference coupled-cluster algorithm
Authors: Kállay Mihály , Szalay Péter G. , Surján Péter R.
Published: July 2002

A state-selective multireference coupled-cluster algorithm is presented which is capable of describing single, double (or higher) excitations from an arbitrary complete model space. One of the active space determinants is chosen as a formal Fermi-vacuum and single, double (or higher) excitations from the other reference functions are considered as higher excitations from this determinant as it has been previously proposed by Oliphant and Adamowicz [J. Chem. Phys. 94, 1229 (1991)]. Coupled-cluster equations are generated in terms of antisymmetrized diagrams and restrictions are imposed on these diagrams to eliminate those cluster amplitudes which carry undesirable number of inactive indices. The corresponding algebraic expressions are factorized and contractions between cluster amplitudes and intermediates are evaluated by our recent string-based algorithm [J. Chem. Phys. 115, 2945 (2001)]. The method can be easily modified to solve multireference configuration interaction problems. Performance of the method is demonstrated by several test calculations on systems which require a multireference description. The problem related to the choice of the Fermi-vacuum has also been investigated.
Vibrational dynamics as an indicator of short-time interactions in glass-forming liquids and their possible relation to cooperativity
Authors: Kirillov Sviatoslav A. , Yannopoulos Spyros N.
Published: July 2002

We report on a vibrational dynamics study of two glass-forming liquids over a wide temperature range including the glassy, supercooled, and molten state. Our aim is to find possible sensitive indicators of short-time dynamics that experience characteristic changes when approaching the liquid–glass transition. The observed changes in vibrational dynamics are employed to track the cooperative behavior of the studied glass-forming liquids. It has been found that both strong and fragile liquids exhibit qualitative similarities in the vibrational relaxation and frequency modulation times as a function of temperature. The temperature dependence of the vibrational relaxation times τV experiences a break at the glass transition temperature Tg. On the contrary, the temperature dependence of the frequency modulation times τω exhibits an unexpected discontinuity at Tg, τω being shorter in the glassy phase than in the supercooled and liquid regime. Since microscopic vibrational dynamics depends upon the intermolecular interactions that ultimately are responsible for the cooperative (or sluggish) dynamics when approaching Tg, an attempt has been made to find a rationale between the unusual temperature dependence of τω and cooperative dynamics.
Influence of temperature and modulation frequency on the thermal activation coupling term in laser photothermal theory
Authors: Christofides Constantinos , Othonos Andreas , Loizidou Efi
Published: July 2002

A quantitative analysis of the influence of temperature and modulation frequency on the thermal activation coupling term in laser photothermal theory is performed. Until now it was taken for granted that the coupling term is negligible only in the case of “relatively low” temperatures and generally when the equilibrium free-carrier density n0 satisfies the Sablicov's, Vasil'ev, and Sandomirskii inequality. In this work an extensive computational study of this inequality in the temperature range of 300–1000 K was performed and a precise “map” is given concerning the violation of the inequality under various conditions including modulation frequency (0.1–106 Hz) and doping concentration (intrinsic to 1020 cm−3). Some experimental photomodulated measurements have been performed in order to test the validity of the “map.”
Stability of casein micelles in milk
Authors: Tuinier R. , de Kruif C. G.
Published: July 2002

Casein micelles in milk are proteinaceous colloidal particles and are essential for the production of flocculated and gelled products such as yogurt, cheese, and ice-cream. The colloidal stability of casein micelles is described here by a calculation of the pair potential, containing the essential contributions of brush repulsion, electrostatic repulsion, and van der Waals attraction. The parameters required are taken from the literature. The results are expressed by the second osmotic virial coefficient and are quite consistent with experimental findings. It appears that the stability is mainly attributable to a steric layer of κ-casein, which can be described as a salted polyelectrolyte brush.
Large enhancement of boron solubility in silicon due to biaxial stress
Authors: Sadigh Babak , Lenosky Thomas J. , Caturla Maria-Jose , Quong Andrew A. , Benedict Lorin X. , Diaz de la Rubia Tomas , Giles Martin M. , Foad Majeed , Spataru Catalin D. , Louie Steven G.
Published: July 2002

One of the important challenges to the semiconductor industry today is to enhance the solid solubility of several dopants, boron in particular, in silicon. We calculate the equilibrium solid solubility of boron in Si from first principles and examine the effect of biaxial stress. We find an unexpectedly large enhancement, on the order of 150%, for only 1% strain primarily due to the charge of the substitutional boron impurity in Si. We point out that this effect is an intrinsic property of Si and is expected to be important for other dopants as well.
Heterogeneous nucleation on mesoscopic wettable particles: A hybrid thermodynamic/density-functional theory
Authors: Bykov T. V. , Zeng X. C.
Published: July 2002

A hybrid thermodynamic and density-functional theory for heterogeneous nucleation on mesoscopic wettable particles is developed. The nonlocal density-functional theory (DFT) is on basis of the weighted-density approximation (WDA) of Tarazona. The model system consists of a Lennard-Jones (LJ) fluid and a 9–3 LJ wall for the solid particle. Effects of the droplet curvature and compressibility are accounted for in the theory. A by-product of this work is the calculation of the Tolman length using the WDA-DFT (Appendix A). Important characteristics of the heterogeneous nucleation, including the chemical potential of the liquid condensate, the free energy of droplet formation, and the barrier height to nucleation, are obtained.
Temperature dependence of vibrational relaxation in liquid H2O
Authors: Lock A. J. , Bakker H. J.
Published: July 2002

We have determined the lifetime of the OH-stretch vibration in pure liquid water as a function of temperature using femtosecond mid-infrared pump–probe spectroscopy. The lifetime T1 increases from 260±18 fs at T=298 K to 320±18 fs at T=358 K. The increase in lifetime with temperature can be quantitatively explained from the decrease in overlap resonance between the OH-stretch vibration and the overtone of the H–O–H bending mode.
Theoretical prediction of the dielectric spectrum of an antiferroelectric liquid crystal
Authors: Parry-Jones L. A. , Elston S. J.
Published: July 2002

The dielectric spectrum of an antiferroelectric liquid crystal is predicted by finding approximate analytic solutions to the Landau–Ginzburg equation describing its time dependent behavior. Two collective modes are predicted: (i) a low frequency mode that is caused by an in-phase rotation of the directors in adjacent layers; (ii) a higher frequency mode caused by an antiphase motion. The mechanism for the in-phase mode is shown to be the interaction of the applied field with a polarization that is induced by a local change to the antiferroelectric ordering (an antiphase motion). The bias field dependencies of the predicted dielectric spectrum are shown to agree well with experimental results. The approximate analytic solutions are used to estimate the critical field for helix unwinding, the result being consistent with numerical predictions and de Gennes’ result for the critical unwinding field of a cholesteric liquid crystal [P. De Gennes, Solid State Commun. 6, 163 (1968)].
Probing microwave properties of high-Tc films via small dc magnetic fields
Authors: Lahl Peter , Wördenweber Roger
Published: July 2002

It is demonstrated that the combination of vortex matter and rf measurements yields new insight into the microwave properties of superconducting thin-film devices, both in small magnetic fields and zero field. The comparison of field-cooled and different types of field-sweep experiments on coplanar high-Tc thin-film resonators shows that the microwave properties strongly depend on magnetization and vortex distribution in the superconducting film as well. Thus, using vortices as a kind of local probe for the microwave properties leads to a consistent explanation of the microwave power handling in nonzero and zero magnetic fields. In a model that is derived from the experiments, the nonlinear microwave behavior is explained by the limitation of the total current density in the device considering contributions of the rf field and the screening of the magnetic field and vortices to the current. The limiting current value seems to be related to the dc critical current of the superconductor.
Interlayer transition zones in Mo/Si superlattices
Authors: Yulin S. , Feigl T. , Kuhlmann T. , Kaiser N. , Fedorenko A. I. , Kondratenko V. V. , Poltseva O. V. , Sevryukova V. A. , Zolotaryov A. Yu. , Zubarev E. N.
Published: July 2002

The formation of interlayer transition zones (ITZs) in sputtered Mo/Si multilayer structures was studied by means of cross-section electron microscopy and grazing incidence reflectivity measurements. For the evaluation and calculation of interface effects the multiperiodic design of Mo/Si structure was used. It was found that the thickness asymmetry of ITZs (Mo-on-Si and Si-on-Mo) in Mo/Si multilayer structures depends on the degree of perfection of the crystalline structure of the molybdenum layer. A transition from asymmetrical to symmetrical ITZs with a disordering of the molybdenum crystalline structure was shown. A model for the formation mechanism of asymmetrical ITZs at the different interfaces in Mo/Si multilayer structures is suggested. According to this model, ITZ formation at the Mo-on-Si interface is controlled by the surface diffusion of Si atoms on the growing molybdenum surface. In contrast, ITZ formation at the Si-on-Mo interface is determined by the bulk diffusion of Si atoms in textured molybdenum grains.
Thermal stability and structural characteristics of HfO2 films on Si (100) grown by atomic-layer deposition
Authors: Cho M.-H. , Roh Y. S. , Whang C. N. , Jeong K. , Nahm S. W. , Ko D.-H. , Lee J. H. , Lee N. I. , Fujihara K.
Published: July 2002

The thermal stability and structural characteristics for gate stack structure of HfO2 dielectrics deposited by atomic-layer deposition (ALD) were investigated. The structural characteristics and chemical state of the HfO2 films in relation to the film thickness and postannealing temperature were examined by x-ray diffraction and x-ray photoelectron spectroscopy. An interfacial layer of hafnium silicate with an amorphous structure was grown on the oxidized Si substrate at an initial growth stage. The structural characteristics of the HfO2 films are closely affected by the interfacial layer and are depended on the thickness of the films. The 45 Å thick HfO2 film with an amorphous structure was changed into a polycrystalline structure after rapid temperature annealing of 750 °C for 5 min, while thicker films were grown into a polycrystalline structure of monoclinic or tetragonal crystal structure. The silicate layer grown at the interfacial region is not stable even at 700 °C under ultrahigh vacuum condition and changes into the silicide layers.
Ramification of micropipes in SiC crystals
Authors: Gutkin M. Yu. , Sheinerman A. G. , Argunova T. S. , Je J. H. , Kang H. S. , Hwu Y. , Tsai W.-L.
Published: July 2002

The ramification of micropipes is observed using scanning electron microscopy, optical microscopy, and synchrotron x-ray radiography. The conditions for the ramification of dislocated micropipes are determined theoretically within a model when the angles between dislocation lines are small. It is shown that the ramification of micropipes into two smaller ones is possible only for micropipes with radii that exceed the equilibrium micropipe radius and is associated with a decrease in the total micropipe surface area.
Voltage dependence of magnetoresistance in magnetic tunnel junctions with AlN tunnel barrier
Authors: Shim H. J. , Hwang I. J. , Kim K. S. , Cho B. K. , Kim Jin-Tae , Sok J. H.
Published: July 2002

The voltage dependence of magnetoresistance (MR) and the low-frequency voltage fluctuation were studied in magnetic tunnel junctions with an AlN or an Al2O3 barrier formed by plasma nitridation or oxidation. The junctions consist of free and pinned NiFe layers by a FeMn antiferromagnetic layer. For the Al2O3 junction, the variation of half-reduction voltage of MR is about 50 mV from 401.3 mV in maximum to 351.4 mV in minimum depending upon the oxidation time. For the AlN junction, the less nitrided junction with a nitridation time of 120 s shows the higher-half-reduction voltage by about 100 mV than for optimally nitrided or oxidized ones. From the low-frequency voltage noise data, the less nitrided AlN junction shows larger 1/f noise magnitude compared with other junctions with an optimal condition, implying more defect states in the barrier due to unnitrided Al metals. In order to investigate the influence of nitrogen on ferromagnetic layer, another junction with an Al2O3 barrier was made after the pinned NiFe layer was exposed to N2 plasma for 10 s. This junction reveals a lower MR and worse bias voltage dependence than any junctions studied here. The voltage dependence of MR, therefore, is likely influenced by the interface state rather than the defects in the barrier, although the two factors play an important role in determining MR.
Synthesis route-dependent formation of quasicrystals in Zr70Pd30 and Zr70Pd20Cu10 amorphous alloys
Authors: Sordelet D. J. , Rozhkova E. , Besser M. F. , Kramer M. J.
Published: July 2002

The devitrification of mechanically milled amorphous Zr70Pd30 and Zr70Pd20Cu10 powders occurs via a single-step, first-order transformation to a stable Zr2Pd tetragonal structure. This is in sharp contrast to the devitrification of the same amorphous alloys prepared by melt spinning, in which a primary metastable quasicrystalline phase forms. Since the mechanical milling process does not involve direct liquid phase formation of an amorphous structure, it is inferred that the short-range order in the solid state derived amorphous powder is different from that in the melt spun ribbon.
A variable-emittance radiator based on a metal–insulator transition of (La,Sr)MnO3 thin films
Authors: Shimakawa Y. , Yoshitake T. , Kubo Y. , Machida T. , Shinagawa K. , Okamoto A. , Nakamura Y. , Ochi A. , Tachikawa S. , Ohnishi A.
Published: July 2002

Variable-emittance radiators based on the metal–insulator transition of (La,Sr)MnO3 thin films have been developed. The emittance property of the films was evaluated from infrared reflectance spectra; that is, the (La,Sr)MnO3 thin films show low emittance at low temperature but high emittance at high temperature. Moreover, the emittance property significantly changes at the metal–insulator transition temperature, where the material changes from a highly reflective (i.e., low emissive) metal to a less reflective (i.e., high emissive) insulator. The (La,Sr)MnO3 thin films fitted on a spacecraft surface can, therefore, be used to automatically control the emissive heat transfer from the spacecraft without the need for any electrical power. The developed radiators also greatly reduce the weight and production cost of the thermal control devices. The dependence of the emittance property on film thickness reveals that 1500-nm-thick films can be used for variable-emittance radiators.
Laser-induced surface patterning by means of microspheres
Authors: Piglmayer K. , Denk R. , Bäuerle D.
Published: July 2002

A regular lattice of SiO2 microspheres on a quartz support is used as a microlens array for laser-induced surface patterning of polyimide foils.
Shape of InAs quantum dots grown on the GaAs (1̄ 1̄ 3̄) B surface
Authors: Suzuki T. , Temko Y. , Jacobi K.
Published: July 2002

Self-organized InAs quantum dots were grown by molecular-beam epitaxy on the GaAs (1̄1̄3̄) B surface. Atomically-resolved scanning tunneling microscopy images were acquired in situ. Each quantum dot grows with the same orientation relative to the substrate, with mirror symmetry to the (1̄10) plane perpendicular to the surface, and with its central part sitting on a flat base. The shape of the central part is given by {110} and (1̄1̄1̄) B bounding facets and a not-further-resolved round region. High-index surfaces such as (1̄3̄5̄) B, (3̄1̄5̄) B, and probably (1̄1̄2̄) B are derived for the base.
Influences of mask width, fill factor, HCl addition and C doping on wing tilts in the epitaxial laterally overgrown GaN films by hydride vapor phase epitaxy
Authors: Wang F. , Zhang R. , Tan W. S. , Xiu X. Q. , Lu D. Q. , Gu S. L. , Shen B. , Shi Y. , Wu X. S. , Zheng Y. D. , Jiang S. S. , Kuech T. F.
Published: July 2002

Crystal tilts in the epitaxial lateral overgrown (ELO) GaN region over SiO2 mask by hydride vapor phase epitaxial away from the opening region were investigated by scanning electron microscope and the four-circle x-ray diffraction method. The increased mask width and ratio of stripe opening width to stripe period (fill factor) lead to increased wing tilts. The introduction of additional HCl and C3H8/H2 can decrease wing tilts and improve the ELO GaN surface morphologies significantly. Moreover, it has been observed that a high growth rate will bring more defects and large wing tilts into the GaN materials.
Fabrication of 10 nm enclosed nanofluidic channels
Authors: Cao Han , Yu Zhaoning , Wang Jian , Tegenfeldt Jonas O. , Austin Robert H. , Chen Erli , Wu Wei , Chou Stephen Y.
Published: July 2002

We made uniform arrays of nanometer scale structures using nanoimprint lithography over large areas (100 mm wafers). The nanofluidic channels were further narrowed and sealed by techniques that are based on nonuniform deposition. The resulting sealed channels have a cross section as small as 10 nm by 50 nm, of great importance for confining biological molecules into ultrasmall spaces. These techniques can be valuable fabrication tools for Nanoelectromechanical Systems and Micro/Nano Total Analysis Systems.
Cation substituted (Ca2CoO3)xCoO2 films and their thermoelectric properties
Authors: Matsubara Ichiro , Funahashi Ryoji , Shikano Masahiro , Sasaki Kei , Enomoto Hiroyuki
Published: July 2002

We have controlled in-plane stress in the CoO2 sublattice of (Ca2CoO3)xCoO2 by cationic substitution of alkaline earth metals at the Ca site. The effects of the magnitude of the stress on thermoelectric properties have been investigated by using highly grain-oriented polycrystalline thin films. The in-plane compressive stress is released by the partial substitution of Sr for Ca. With increasing in-plane stress, the magnitude of thermoelectric power and resistivity increased.
Photodissociation of laser aligned iodobenzene: Towards selective photoexcitation
Authors: Poulsen Mikael D. , Skovsen Esben , Stapelfeldt Henrik
Published: July 2002

Iodobenzene molecules, having their symmetry axis aligned to the polarization direction of a strong, linearly polarized nanosecond laser pulse, are photodissociated into phenyl and iodine radicals with a 1.5 ps long laser pulse at 266 nm. The yield of I photoproducts, detected by resonant multiphoton ionization, is enhanced up to a factor of 2.7 when the dissociation laser is polarized parallel instead of perpendicular to the alignment laser polarization. In particular, the high-velocity distribution of I products, corresponding to excitation of an (n,σ*) repulsive surface, is enhanced by a factor of 3.3, when comparing parallel and perpendicular polarizations, whereas the low-velocity distribution of I products, corresponding to excitation of predissociative (π,π*) surfaces is only enhanced by a factor of 2.2. The difference is explained by the different directions of the transition dipole moment for the two transitions. We discuss the perspectives for selective photoexcitation using three dimensionally aligned molecules.
Temperature and thickness dependent permittivity of (Ba,Sr)TiO3 thin films
Authors: Parker C. B. , Maria J.-P. , Kingon A. I.
Published: July 2002

The temperature and thickness dependence of permittivity of (Ba,Sr)TiO3 has been investigated. The films were deposited by liquid-source metalorganic chemical vapor deposition onto Pt/SiO2/Si, with thicknesses ranging from 15 to 580 nm. The dielectric response was measured from 100 to 520 K. As film thickness decreased, the maximum dielectric constant decreased, the temperature at which the maximum dielectric constant occurred decreased, and the peak in the dielectric constant became more diffuse. A model incorporating a thickness independent interior and a nonferroelectric surface cannot account for these thickness dependencies. To appropriately model these observations a physical model containing thickness and temperature dependent interior and surface components is necessary.
In situ resistivity measurements during the atomic layer deposition of ZnO and W thin films
Authors: Schuisky M. , Elam J. W. , George S. M.
Published: July 2002

In situ monitoring of the electrical resistivity of ZnO and W thin films during atomic layer deposition (ALD) was performed using a four-point probe. Large oscillations were observed during the ZnO ALD resistivity measurements. The resistivity dramatically increased during each diethyl zinc exposure and decreased during each H2O exposure. In contrast, the W ALD resistivity measurements exhibited a steplike pattern where the resistivity decreased during the Si2H6 exposures and remained constant during the WF6 exposures. In situ resistivity measurements will be useful to monitor ALD processing and also may help to optimize and understand the properties of gas sensors.
Majority- and minority-carrier deep level traps in proton-irradiated n+/p-InGaP space solar cells
Authors: Dharmarasu Nethaji , Yamaguchi Masafumi , Bourgoin Jacques C. , Takamoto Tatsuya , Ohshima Takeshi , Itoh Hisayoshi , Imaizumi Mitsuru , Matsuda Sumio
Published: July 2002

We report the properties of observed defects in n+/p-InGaP solar cells created by irradiation of protons of different energies. Three majority (hole) and a minority-carrier traps, labeled respectively as HP1 (Ev+0.90±0.05 eV), HP2 (Ev+0.73±0.05 eV), H2 (Ev+0.55 eV), and EP1 (Ec−0.54 eV), were identified using deep level transient spectroscopy. All majority-carrier traps were found to act as recombination centers. While the H2 trap present in the proton-irradiated p-InGaP was found to anneal out by minority-carrier injection, the other traps were not.
Positive and negative patterning on a palmitic acid Langmuir–Blodgett monolayer on Si surface using bias-dependent atomic force microscopy lithography
Authors: Lee Haeseong , Kim Seung Ae , Ahn Sang Jung , Lee Haiwon
Published: July 2002

It is well known that the anodization lithography using an atomic force microscope (AFM) can produce only a positive pattern under a tip negative bias. This study revealed that a negative pattern was generated due to the degradation of a resist under the positive bias. In order to maximize this polarity effect, a Langmuir–Blodgett monolayer of palmitic acid was used as a resist since the degraded molecules would be removed from the negatively biased substrate. This study enables the AFM lithography on a designed resist to generate a negative or positive pattern clearly by changing only one parameter, polarity of the bias. The complete degradation process was confirmed by lateral force microscopy.
Features of the thermopower of Mo–Re and Mo–Re–Nb alloys and the electronic–topological transition in these systems
Authors: Ignatyeva T. A. , Velikodny A. N.
Published: July 2002

The anomalous behavior of the thermopower of Mo1−xRex and Mo1−x−yRexNby alloys is investigated over a wide range of temperatures and concentrations (within the limits of the solid solution). An extremum on the concentration dependence of the thermopower at 10 K, observed for both of these systems at the same electron concentration ≈6.1 electrons/atom, attests to the presence of a critical energy Ec in the electronic spectrum of Mo at which an electronic–topological transition occurs in Mo under the influence of impurities. According to the theoretical ideas about the electronic spectrum of Mo, the closest Ec>EF0 corresponds to the bottom of the band, upon the crossing of which a new electron sheet of the Fermi surface appears. In the binary systems the Re impurity causes a new sheet of the Fermi surface to appear, and in the ternary systems it disappears as the Nb impurity is added. A quantitative comparison of the theory with experiment makes it possible to determine the gap Ec−Ef0 for Mo, which is found to be ≈0.02 eV. These results correspond to those obtained previously from the superconducting characteristics.
On the correlation of nonperturbative fluctuations of glass-forming liquids and magnetic glasses
Authors: Bakaı̆ A. S.
Published: July 2002

Contrary to the established ideas that glasses and glass-forming liquids are homogeneous and isotropic, appreciable structural and compositional heterogeneities are observed in these states. The nature of the heterogeneities in glasses and glass-forming liquids is considered, and the influence of these heterogeneities on the properties of magnetic glasses is examined. Heterophase fluctuations (HPFs), which are nonperturbative disturbances, can play an important role in the thermodynamics of glass-forming liquids, and under certain conditions the liquid has a critical point. The heterogeneities generated in the liquid and glassy states by the HPFs are considered, and the Ginzburg–Landau equations for the HPFs are derived. The order parameter chosen is the fraction of noncrystalline solid-state clusters in the liquid. The correlation length of the order parameter is the characteristic mesoscopic scale of the heterogeneities. The mesoscopic compositional and topological disorder of a glass “spills over” into disorder of its spin system. The phase transitions in the spin system are investigated by well-known approaches with allowance for the mesoscopic heterogeneities. It is shown that correlated domains originating from correlated heterogeneities of the liquid substantially alter the susceptibility and relaxation properties of the paramagnetic state. The phase diagram of a magnetic glass is investigated, and some experimental data are discussed.
Picosecond pulse frequency upshifting by rapid free-carrier creation in ZnSe
Authors: Geltner I. , Avitzour Y. , Suckewer S.
Published: July 2002

The frequency upshifting of 0.8 μm picosecond laser pulses was demonstrated using the temporal change of the free carrier density in a ZnSe semiconductor crystal. The crystal was ionized by transverse propagating ps pulses. Shifts of up to 1.6 nm were observed, which agree within 25% with the theory.
Anelastic deformation of Pb(Zr,Ti)O3 thin films by non-180° ferroelectric domain wall movements during nanoindentation
Authors: Algueró M. , Bushby A. J. , Reece M. J. , Seifert A.
Published: July 2002

Lead zirconate titanate Pb(Zr,Ti)O3 ferroelectric thin films show significant anelastic deformation when indented with spherical tipped indenters. Experiments on films with different Zr/Ti ratio and a mixed 〈001〉,〈100〉 preferred crystallographic orientation have shown that there is a good agreement between the anelastic deformation and the maximum strain achievable by non-180° domain wall movement. An expected increase of the indentation stiffness of the films also accompanies the anelastic deformation because of the single crystal elastic anisotropy. All these observations seem to indicate that non-180° ferroelectric domain wall movements occur under indentation stresses and cause anelasticity. Stresses for maximum anelastic deformation are compared with those for recently reported stress-induced depolarization.
Spectral mode dynamics of short cavity quantum-dot lasers
Authors: Ribbat Ch. , Bognar S. , Sellin R. , Bimberg D.
Published: July 2002

Temporally resolved longitudinal mode dynamics for sixfold stacked short cavity quantum-dot lasers is investigated in the μs time range. Results are presented for 10, 20, and 50 μm wide stripes at room temperature and at 100 K. After turn-on a redshift of single longitudinal modes, a blueshift of the mode groups and a redshift of the mean value of the spectra are observed simultaneously. Temperature dependent leakage loss spectra due to leaky substrate modes are calculated. The blueshift of the mode grouping, predicted by the theory, is in good agreement to the experimental data.
Anomalous x-ray diffraction on InAs/GaAs quantum dot systems
Authors: Schülli T. U. , Sztucki M. , Chamard V. , Metzger T. H. , Schuh D.
Published: July 2002

Free-standing InAs quantum dots on a GaAs (001) substrate have been investigated using grazing incidence x-ray diffraction. To suppress the strong scattering contribution from the GaAs substrate, we performed anomalous diffraction experiments at the superstructure (200) reflection, showing that the relative intensities from the dots and the substrate undergo a significant change with the x-ray energy below and above the As K edge. Since the signal from the substrate material can essentially be suppressed, this method is ideally suited for the investigation of strain, shape, and interdiffusion of buried quantum dots and quantum dots embedded in heteroepitaxial multilayers. In addition, we show that it can be used as a tool for studying wetting layers.
Resonant tunneling of Si nanocrystals embedded in Al2O3 matrix synthesized by vacuum electron-beam co-evaporation
Authors: Wan Q. , Wang T. H. , Zhu M. , Lin C. L.
Published: July 2002

High vacuum electron-beam co-evaporation, followed by N2 annealing at 500 °C is used for preparing of silicon nanocrystals (Si NCs) embedded in Al2O3 dielectric matrix. X-ray diffraction and transmission electron microscopy are used to investigate the structures of Si+Al2O3 films and estimate the mean diameter of the Si NCs. The electrical properties of the diode containing Si NCs embedded in Al2O3 are studied at room temperature and resonant tunneling effect with large voltage gap is observed. A circuit model based on resonant tunneling is proposed to simulate the measured I–V curve.
Three-dimensional imaging of a silicon flip chip using the two-photon optical-beam induced current effect
Authors: Ramsay E. , Reid D. T. , Wilsher K.
Published: July 2002

We describe two- and three-dimensional imaging of a flip-chip silicon integrated circuit using backside optical probing and femtosecond two-photon excitation at a laser wavelength of 1.275 μm. Using a ×50 microscope objective, we typically achieved micron resolutions or better in both lateral and axial directions. Using axial scanning and a peak-detection algorithm we have demonstrated optical depth profiling across components on the chip.
Type-II band alignment between GaAs and inadvertent interlayers at (In,Ga)P/GaAs interfaces
Authors: Krispin P. , Knauer A.
Published: July 2002

Capacitance–voltage measurements on metal–semiconductor contacts are used to examine vertical depth profiles of the electron concentration in n-type (In,Ga)P/GaAs heterostructures. The electron distributions at single interfaces are compared with calculations based on solutions of the Schrödinger–Poisson equations. It is shown that distinct interlayers may form at both the (In,Ga)P-on-GaAs and the GaAs-on-(In,Ga)P interfaces. The inadvertent interlayers are identified by their conduction band offsets. Under certain growth conditions, the band alignment between GaAs and the interlayers is determined to be of type II.
Directly coupled superconducting quantum interference device magnetometer fabricated in magnesium diboride by focused ion beam
Authors: Burnell Gavin , Kang Dae-Joon , Ansell David A. , Lee H.-N. , Moon S.-H. , Tarte Edward J. , Blamire Mark G.
Published: July 2002

We report the fabrication of a directly coupled superconducting quantum interference device (SQUID) magnetometer in MgB2 using a focused ion beam to create Josephson junctions in a 70-nm-thick-film of MgB2. The SQUID shows a voltage modulation (ΔV) of 175 μV at a temperature of 10 K and operates over a temperature range from 10 to 24 K. We find excellent agreement between the measured maximum transfer functions and those predicted by theory. We have measured the magnetic flux white noise level at 20 K and 10 kHz to be as low as 14 μΦ0 Hz−1/2.
Time-resolved x-ray diffraction measurements on CdS shocked along the c axis
Authors: d’Almeida T. , Di Michiel M. , Kaiser M. , Buslaps T. , Fanget A.
Published: July 2002

Time-resolved high-energy x-ray diffraction measurements were used to examine laser shock-induced changes in cadmium sulfide single crystals compressed along the c axis near 1.5 and 3.5 GPa. Macroscopic compression under different loading conditions was monitored through the evolution of the (004) Bragg reflection in Laue geometry. In the low-stress experiments, the elastic response of the sample was evidenced by reversible changes of the intensity profiles, while a plastic behavior was observed in the high-stress experiments. A residual (004) reflection is observed in the rocking curve obtained from the crystal shocked to 3.5 GPa, in addition to two peaks at higher angle.
Fully patterned all-organic thin film transistors
Authors: Halik Marcus , Klauk Hagen , Zschieschang Ute , Kriem Tarik , Schmid Günter , Radlik Wolfgang , Wussow Klaus
Published: July 2002

We have fabricated fully patterned all-organic thin film transistors on glass substrates using the conducting polymer poly(3,4-ethylenedioxythiophene) for the gate electrodes and the source and drain contacts, poly-4-vinylphenol for the gate dielectric layer, and pentacene or poly-3-hexylthiophene for the organic active layer. All-organic pentacene transistors have carrier mobility as large as 0.1 cm2/V s and threshold voltage of 1 V, similar to pentacene transistors fabricated with high-quality inorganic gate dielectrics and noble-metal contacts. The carrier mobility of all-polymer poly-3-hexylthiophene transistors is somewhat lower compared with that of pentacene transistors, but similar to that of poly-3-hexylthiophene devices made with inorganic metals and dielectrics.
Characterizing an implanted Si/Si p–n junction with lower doping level by combined electron holography and focused-ion-beam milling
Authors: Wang Zhouguang , Kato Takeharu , Shibata Noriyoshi , Hirayama Tsukasa , Kato Naoko , Sasaki Katsuhiro , Saka Hiroyasu
Published: July 2002

A Si/Si p–n junction with very low doping level was made via a standard device fabrication process by implanting As ions at 25 keV into a p-type Si substrate with a boron concentration of 1015 cm−3, followed by heat annealing at 1035 °C for 33 s. To characterize this junction, a pair of 45° wedge-shape cross sections was prepared simultaneously by focused-ion-beam milling and examined using off-axis electron holography. The reconstructed phase images clearly show the phase shift induced by the electrostatic potential drop across the p–n junction, indicating that the junction has been mapped successfully. Quantitative measurements from the phase images give the potential values of 12.21±0.40 and 11.50±0.27 V, respectively, for the n- and p-type sides of the junction, 0.71±0.05 V for the potential drop across the junction and 50.10±3.88 nm for the total electric dead layer thickness. This work demonstrates that electron holography is a powerful technique for characterizing low dopant level p–n junctions in practical devices.
Epitaxial growth of CuGaS2 on Si(111)
Authors: Metzner H. , Hahn Th. , Cieslak J. , Grossner U. , Reislöhner U. , Witthuhn W. , Goldhahn R. , Eberhardt J. , Gobsch G. , Kräußlich J.
Published: July 2002

We demonstrate the direct heteroepitaxial growth of the ternary semiconductor CuGaS2 on Si(111) substrates by means of molecular beam epitaxy. X-ray diffraction data prove the epitaxial growth of the CuGaS2 films in the highly ordered chalcopyrite structure. Using photoluminescence, we are able to detect strong excitonic emissions up to room temperature, while photocurrent spectra reveal the A, B, and C valence-to-conduction-band transitions as they are typical for the tetragonal chalcopyrite structure.
ZnO nanobelts grown on Si substrate
Authors: Li Y. B. , Bando Y. , Sato T. , Kurashima K.
Published: July 2002

Using infrared irradiation to heat an industrial brass (Cu–Zn alloy) disk in moderate vacuum, ZnO nanobelts were directly prepared on a Si substrate. The nanobelts had a single-crystal hexagonal structure and grew along the [0001] direction. The nanobelts had two distinct widths along their entire length. Photoluminescence measurement showed that the nanobelts had an intensive near-band ultraviolet emission at 379 nm. Large-area growth and high quality indicate that the prepared ZnO nanobelts have potential application in optoelectronic devices.
Low interface state density of SiC-based metal–oxide–semiconductor structure formed with perchloric acid at 203 °C
Authors: Sakurai Takeaki , Nishiyama Masayoshi , Nishioka Yasushiro , Kobayashi Hikaru
Published: July 2002

The SiO2/6H-SiC(0001) structure can be fabricated by the immersion in perchloric acid at 203 °C. High and low frequency capacitance–voltage measurements show that the metal–oxide–semiconductor diodes possess a low interface state density of 1×1011 cm−2 eV−1 at 0.5 eV below the conduction band when postoxidation annealing (POA) treatment is performed at 950 °C in nitrogen. The interface state density increases to about three times when the POA temperature is increased to 1100 °C. The oxide fixed charge density after the POA treatment is less than 1.4×1011 cm−2.
Additive, nanoscale patterning of metal films with a stamp and a surface chemistry mediated transfer process: Applications in plastic electronics
Authors: Loo Yueh-Lin , Willett Robert L. , Baldwin Kirk W. , Rogers John A.
Published: July 2002

We describe a method for contact printing metal patterns with nanometer features over large areas. This nanotransfer printing (nTP) technique relies on tailored surface chemistries to transfer metal films from the raised regions of a stamp to a substrate when these two elements are brought into intimate physical contact. The printing is purely additive, fast (<15 s contact time), and it occurs in a single processing step at ambient conditions. Features of varying dimensions, including sizes down to ∼100 nm, can be printed with edge resolution better than 15 nm. Electrical contacts and interconnects for high-performance organic transistors and complementary inverter circuits have been successfully fabricated using nTP.
Highly bright blue organic light-emitting devices using spirobifluorene-cored conjugated compounds
Authors: Wu C. C. , Lin Y. T. , Chiang H. H. , Cho T. Y. , Chen C. W. , Wong K. T. , Liao Y. L. , Lee G. H. , Peng S. M.
Published: July 2002

An efficient and morphologically stable pyrimidine-containing spirobifluorene-cored oligoaryl, 2,7-bis[2-(4-tert-butylphenyl)pyrimidine-5-yl]-9,9′-spirobifluorene (TBPSF), as an emitter or a host for blue organic light-emitting devices (OLEDs), is reported. The steric hindrance inherent with the molecular structure renders the material a record-high neat-film photoluminescence (PL) quantum yield of 80% as a pure blue emitter (PL peak at 430 nm) of low molecular weight, and a very high glass-transition temperature (Tg) of 195 °C. Blue OLEDs employing this compound as the emitter or the emitting host exhibit unusual endurance for high currents over 5000 mA/cm2. When TBPSF is used as a host for perylene in a blue OLED, maximal brightness of ∼80 000 cd/m2 had been achieved, representing the highest values reported for blue OLEDs under dc driving.
Carbon nanofibers synthesized by decomposition of alcohol at atmospheric pressure
Authors: Jiang N. , Koie R. , Inaoka T. , Shintani Y. , Nishimura K. , Hiraki A.
Published: July 2002

In the present study, we fabricated the carbon nanofibers (CNFs) by decomposition of methyl alcohol at atmospheric pressure. The CNFs were grown on Ni/Si substrates using simplified hot-filament chemical vapor deposition equipment. The deposits mainly consist of the semicrystalline CNFs, in which a few of carbon nanotubes are included. On the 30-nm-thick Ni/Si substrates, the mean length of the CNFs is 2–3 μm, and their average diameter is less than 100 nm. The as-deposited CNFs were evaluated by both scanning and transmission electron microscopes. The field-electron-emission properties of CNFs were characterized as well.
Absolute density measurements of ammonia produced via plasma-activated catalysis
Authors: Vankan P. , Rutten T. , Mazouffre S. , Schram D. C. , Engeln R.
Published: July 2002

The generation of ammonia from atomic hydrogen and nitrogen has been demonstrated by means of cavity enhanced absorption spectroscopy. The atomic species are produced in a thermal plasma source in which plasma is created from mixtures of hydrogen and nitrogen. It is shown that for large atomic flux conditions, 2% of the hydrogen and nitrogen can be converted to ammonia. The process in which the ammonia molecules are formed from atomic radicals at the fully covered surface is called plasma-activated catalysis.
Role of copper in the green luminescence from ZnO crystals
Authors: Garces N. Y. , Wang L. , Bai L. , Giles N. C. , Halliburton L. E. , Cantwell G.
Published: July 2002

Electron paramagnetic resonance (EPR), photoluminescence, and infrared optical absorption have been used to investigate a ZnO crystal before and after a thermal anneal for 1 h in air at 900 °C. The sample was an undoped high quality crystal grown by the chemical vapor transport method. In addition to shallow donor impurities, the crystal contained trace amounts of copper ions. Prior to the thermal anneal, these ions were all in the Cu+ (3d10) state and the observed luminescence at 5 K, produced by 364 nm light, consisted of a broad structureless band peaking at 500 nm. After the high-temperature anneal, the Cu2+ (3d9) EPR spectrum was observed and the luminescence had changed significantly. The emission then peaked near 510 nm and showed structure identical to that reported by Dingle [Phys. Rev. Lett. 23, 579 (1969)]. Our data reaffirm that the structured green emission in ZnO is associated with Cu2+ ions. We suggest that the unstructured green emission (observed before the high-temperature anneal) is donor–acceptor pair recombination involving the Cu+ acceptors.
Optical performance of nanocrystalline transparent ceria films
Authors: Patsalas P. , Logothetidis S. , Metaxa C.
Published: July 2002

Ceria is a transparent oxide suitable for various optical and optoelectronic devices. In this work, we tailor independently the refractive index n and fundamental gap Eg of nanocrystalline Ceria films by varying the substrate temperature or using Ar+ ion beams during growth with electron beam evaporation. Spectroscopic ellipsometry and x-ray reflectivity are employed to study n and Eg and to identify the physical parameters that affect them. We correlate n (varies from 1.65 to 2.15 in the studied films) with the film density through a universal, square law. The film composition strongly affects Eg, which varies from 2.8 to ∼2.0 eV. The optical absorption below 3 eV and the Eg shift are attributed to O-defect states and not to modifications in interband transitions.
Metal/AlQ
3
interface structures
Authors: Turak A. , Grozea D. , Feng X. D. , Lu Z. H. , Aziz H. , Hor A. M.
Published: July 2002

X-ray photoelectron core level spectroscopy has been used to probe the buried metal (Au, Ag, Mg, Mg:Ag alloy)/AlQ3 interface structures from working organic light-emitting diodes. It is found that there is no chemical reaction between (Au,Ag)/AlQ3 interfaces, while there is a significant reaction/diffusion at (Mg,Mg:Ag)/AlQ3 interfaces. The reaction is AlQ3 oxidation-reduction reaction in nature, and is well explained by thermodynamic consideration of equivalent type of reaction. The reaction involves formation of MgO, metallic Al and fragmented hydroxyquinolines, gaseous N, and then followed by metallic Mg diffusion to the interface and metallic Al diffusion into the metal cathodes.
Microwave frequency tuning and harmonic generation in ferroelectric thin film transmission lines
Authors: Booth James C. , Ono R. H. , Takeuchi Ichiro , Chang Kao-Shuo
Published: July 2002

We evaluate dielectric tuning on nanosecond time scales in ferroelectric Ba0.3Sr0.7TiO3 thin films by measuring nonlinear harmonic generation at a fundamental frequency of 3 GHz. We compare the form of the distributed nonlinear capacitance per unit length C(Vrf) extracted from a simple model of harmonic generation in coplanar waveguide transmission line structures with the nonlinear capacitance C(Vdc) measured using a dc bias voltage, and obtain excellent agreement for temperatures in the range 235–295 K. This demonstrated agreement implies that full dielectric tuning can be expected in these ferroelectric thin films on nanosecond time scales, and also demonstrates that detrimental high-frequency nonlinear effects in device structures can be accurately predicted based on dc biased measurements.
Transient carrier velocities in bulk GaAs: Quantitative comparison between terahertz data and ensemble Monte Carlo calculations
Authors: Abe M. , Madhavi S. , Shimada Y. , Otsuka Y. , Hirakawa K. , Tomizawa K.
Published: July 2002

Transient carrier velocities determined from terahertz radiation emitted from photoexcited bulk GaAs have been compared with ensemble Monte Carlo calculations. It is found that, if actual experimental conditions (sample geometry, photoexcitation condition, etc.) are properly taken into account, Monte Carlo calculations give a very good description of the transient carrier velocities determined from THz measurements. Although the THz signal is dominated by electron transport, contribution of holes becomes appreciable when the electric field is higher than 20 kV/cm.