bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficient discrete approximations of quantum gates
Authors: Harrow Aram W. , Recht Benjamin , Chuang Isaac L.
Published: September 2002

Quantum compiling addresses the problem of approximating an arbitrary quantum gate with a string of gates drawn from a particular finite set. It has been shown that this is possible for almost all choices of base sets and, furthermore, that the number of gates required for precision ε is only polynomial in log 1/ε. Here we prove that using certain sets of base gates quantum compiling requires a string length that is linear in log 1/ε, a result which matches the lower bound from counting volume up to constant factor.
Formation of misfit dislocations in GaAs/InGaAs multiquantum wells observed by photoluminescence microscopy
Authors: Ohizumi Y. , Tsuruoka T. , Ushioda S.
Published: September 2002

We have investigated the formation mechanism of misfit dislocations of GaAs/InGaAs multiquantum well structures by means of photoluminescence (PL) microscopy using the scanning near-field optical microscope. In the PL images, dark lines appeared along both [110] and [1̄10] directions. From comparison with the surface topographic images, we found that these dark lines correspond to misfit dislocations, which give rise to nonradiative recombination centers in the InGaAs well. The density of dark lines in the 〈110〉 directions as a function of the total layer thickness shows the existence of two critical layer thicknesses for the formation of misfit dislocations. The two distinct critical thicknesses are explained in terms of the modified J. W. Matthews and A. E. Blakeslee, [J. Cryst. Growth 27, 118 (1974)] model in which a lattice frictional force proportional to the In mole fraction is taken into account.
Determination of free hole concentration in ferromagnetic Ga1−xMnxAs using electrochemical capacitance–voltage profiling
Authors: Yu K. M. , Walukiewicz W. , Wojtowicz T. , Lim W. L. , Liu X. , Sasaki Y. , Dobrowolska M. , Furdyna J. K.
Published: September 2002

We demonstrate that electrochemical capacitance–voltage profiling can be used to determine the free hole concentration in heavily p-type doped low-temperature-grown GaAs films. This provides a simple and reliable method for measuring the hole concentration in ferromagnetic Ga1−xMnxAs semiconductor alloys. The method overcomes the complications that arise from the anomalous Hall effect term which affects standard transport studies of carrier concentration in conducting ferromagnetic materials. Specifically, we find that the maximum Curie temperature of about 111 K found for our Ga0.91Mn0.09As samples corresponds to a hole concentration of 1021 cm−3.
Thickness-induced stabilization of ferroelectricity in SrRuO3/Ba0.5Sr0.5TiO3/Au thin film capacitors
Authors: Sinnamon L. J. , Bowman R. M. , Gregg J. M.
Published: September 2002

Pulsed-laser deposition has been used to fabricate Au/Ba0.5Sr0.5TiO3/SrRuO3/MgO thin film capacitor structures. Crystallographic and microstructural investigations indicated that the Ba0.5Sr0.5TiO3 (BST) had grown epitaxially onto the SrRuO3 lower electrode, inducing in-plane compressive and out-of-plane tensile strain in the BST. The magnitude of strain developed increased systematically as film thickness decreased. At room temperature this composition of BST is paraelectric in bulk. However, polarization measurements suggested that strain had stabilized the ferroelectric state, and that the decrease in film thickness caused an increase in remanent polarization. An increase in the paraelectric–ferroelectric transition temperature upon a decrease in thickness was confirmed by dielectric measurements. Polarization loops were fitted to Landau–Ginzburg–Devonshire (LGD) polynomial expansion, from which a second order paraelectric–ferroelectric transition in the films was suggested at a thickness of ∼500 nm. Further, the LGD analysis showed that the observed changes in room temperature polarization were entirely consistent with strain coupling in the system.
Effect of thickness variation in high-efficiency InGaN/GaN light-emitting diodes
Authors: Narayan J. , Wang H. , Ye Jinlin , Hon Schang-Jing , Fox Kenneth , Chen Jyh Chia , Choi H. K. , Fan John C. C.
Published: September 2002

In x Ga (1−x) N/GaN multiquantum-well light-emitting diodes (LEDs) having periodic thickness variations (TVs) in InxGa(1−x)N active layers exhibit substantially higher optical efficiency than LEDs with uniform InxGa(1−x)N layers. In these nanostructured LEDs, the thickness variation of the active layers is found to be more important than the In composition fluctuation in quantum confinement of excitons (carriers). Detailed scanning transmission electron microscopy-atomic number Z contrast analysis, where image contrast is proportional to Z2 (Z being the atomic number), was carried out to investigate the variation in thickness as well as the spatial distribution of In. In the nanostructured LEDs, there are short-range thickness variations (SR-TVs) (3–4 nm) and long-range thickness variations (LR-TVs) (50–100 nm) in InxGa(1−x)N layers. It is envisaged that LR-TV is key to quantum confinement of the carriers and enhancement of the optical efficiency. We propose that the LR-TV is caused by two-dimensional strain in the InxGa(1−x)N layer below its critical thickness. The SR-TV may be caused by In composition fluctuation.
Exciton interactions in oligophenyl nanoaggregates and single crystals
Authors: Blumstengel S. , Meinardi F. , Spearman P. , Borghesi A. , Tubino R. , Chirico G.
Published: September 2002

In crystals built of chainlike molecules such as oligophenyls or oligothiophenes, the value of the Davydov splitting, which is a measure of the strength of excited state interactions and as such of fundamental importance for the understanding of the optoelectronic properties, remains a matter of debate. To resolve the controversy on the subject we have performed a combined spectroscopic and theoretical study of the effect of intermolecular interactions on the electronic structure of conjugated oligomers in the solid state using a four ring oligophenyl as model compound. Strong excited state intermolecular interactions of oligophenyls in the crystalline environment lead to the formation of quasicontinuous exciton bands. Band structure calculations in terms of classical dipole theory indicate that oligophenyl crystals behave as two-dimensional semiconductors. Due to the long-range polarization field the splitting between the Davydov components depends on the propagation direction of the wave vector. For normal incidence on the (100) crystal face we find a splitting of 0.81 eV. The classical dipole theory accounts well for the experimental findings of the exciton resonance energy in single crystals as well as nanoaggregates of oligophenyls.
Low-voltage inverted transparent vacuum deposited organic light-emitting diodes using electrical doping
Authors: Zhou X. , Pfeiffer M. , Huang J. S. , Blochwitz-Nimoth J. , Qin D. S. , Werner A. , Drechsel J. , Maennig B. , Leo K.
Published: September 2002

We demonstrate low-voltage inverted transparent vacuum deposited organic light-emitting diodes employing an indium-tin-oxide coated glass substrate directly as cathode and a semitransparent top Au thin film as anode. The devices comprise an intrinsic 8-tris-hydroxyquinoline aluminum (Alq3) emitting layer sandwiched in between n- and p-doped charge transport layer with appropriate blocking layers. They exhibit low driving voltages (∼4 V for a luminance of ∼100 cd/m2). The devices are about 50% transparent in the Alq3 emission region and emit green light from both sides with a total external current efficiency of about 2.5 cd/A.
Raman microscopy analysis of phase transformation mechanisms in vanadium dioxide
Authors: Petrov G. I. , Yakovlev V. V. , Squier J.
Published: September 2002

Raman microscopy is used to study the evolution of vibrational modes of vanadium dioxide single crystals and thin films in the vicinity of the phase transition. The results support the electron correlation model of phase transformation.
Recent progress in magneto-optics and research on its application (Review)
Authors: Kojima N. , Tsushima K.
Published: September 2002

Various kinds of magneto-optical properties are investigated in rare earth orthochromites. From an analysis of Cr3+ exciton absorption in RCrO3 (R=Tb, Dy, and Ho), it is unferred that these compounds exhibit an anomalous spin-reorientation in a magnetic field along the b axis, where the weak ferromagnetic moment of the Cr3+ spins rotates in the ac plane perpendicular to the b axis. In these compounds, when the R3+ spin configuration is disordered, an anomalous satellite band appears on the lower-energy side of the Cr3+ exciton absorption, which is associated with the breakdown of the k=0 selection rule due to the disorder of the R3+ spin configuration. In YbCrO3, various kinds of cooperative excitations, such as a Cr3+ exciton coupled with an Yb3+ magnon and a Cr3+−Yb3+ exciton molecule, which are induced by the antisymmetric exchange interaction between the Cr3+ and Yb3+ spins, appear in the visible region. The propagation of these cooperative excitations depends strongly on the spin structure and the external magnetic field. In ErCrO3, a photo-induced spin-reorientation takes place within 50 μs after the photo-irradiation corresponding to the A2g4→2Eg transition of Cr3+, and it returns to the initial spin configuration in about 400 ms. This phenomenon is detected in the time-resolved Er3+ absorption spectra corresponding to the I15/24→4I9/2 transition. Finally, we briefly review the recent frontier research on applications developed mainly in Japan.
Elementary excitations in solid oxygen (Review)
Authors: Freiman Yu. A. , Jodl H. J.
Published: September 2002

Theoretical results on lattice excitations in solid oxygen at equilibrium vapor pressure are reviewed with the emphasis on the behavior of phonons, librons, and magnons in the orientationally and magnetically ordered α phase. Results on the magnetooptics of solid oxygen and their impact on the advancement of magnetic studies of solid oxygen are briefly reviewed. Some results under discussion are new: among these are theoretical results on the magnon heat capacity, the analysis of the behavior of librons at the α–β transition, and anisotropy of the magons spectrum.
Charge transfer reactions between chiral Rydberg atoms and chiral molecules
Authors: Hammer N. I. , Gao F. , Pagni R. M. , Compton R. N.
Published: September 2002

Charge exchange reactions between a thermal beam of laser excited chiral Rydberg atoms of rubidium and nozzle jet expanded (resolved) chiral enantiomers of a series of carbonyl, cyanide, and halide containing molecules are studied. Chiral Rydberg atoms (oriented atoms with selected MJ) are produced using two-photon excitation of high nd 2D5/2 Rydberg states of a beam of rubidium atoms using right- and left-circularly polarized light. Chiral anions of (S)-2-methylbutanenitrile, (R)-3-methylcyclopentanone, and (R)-3-methylcyclohexanone are produced in a narrow range of specific values of n* (effective principal quantum number) characteristic of dipole bound negative ions. These data are used to obtain electron affinities of 12.6, 3.3, and 4.2 meV, respectively. The electron affinities derived for (R)-3-methylcyclopentanone and (R)-3-methylcyclohexanone are confirmed from measurements of their electric field detachment thresholds. (R)-3-methylcyclohexanone also shows a second bound dipole anion state with an electron affinity of 8.8 meV. The two separate dipole bound anions are attributed to two different conformers (equatorial and axial –CH3) of 3-methylcyclohexanone present in the nozzle jet expansion. Rydberg reactions with partially resolved [enantiomeric excess (ee)∼30%] (R)-2-iodooctane undergo dissociative electron attachment to produce the I− ion. Similarly, Rydberg reactions with partially resolved (ee∼54%) (R)-bromochlorofluoromethane undergo dissociative electron attachment to produce both Br− and Cl− ions. No differences (at the level of >5%) are observed in the charge transfer rate for the reaction of opposite enantiomers of the Rydberg atom with resolved enantiomers for all of the chiral molecules studied.
Entanglement and perfect quantum error correction
Authors: Schumacher Benjamin , Westmoreland Michael D.
Published: September 2002

The entanglement of formation gives a necessary and sufficient condition for the existence of a perfect quantum error correction procedure.
Phase decomposition of a binary thin film on a patterned substrate
Authors: Johnson William C. , Wise S. M.
Published: September 2002

Two-dimensional simulations of phase decomposition in a binary thin film, which is deposited on a patterned substrate, are performed using the Cahn–Hilliard equation. Phase formation, growth, coarsening, and the resulting two-phase microstructure are strongly influenced by the substrate geometry, film composition, and surface effects. Patterning the substrate can result in the formation of self-organized structures of various sizes and spacings and may provide a method for developing monolayers of periodic nanostructures from an initially homogeneous alloy.
Effects of phase relative motion on critical bubbly flows through a converging–diverging nozzle
Authors: Wang Yi-Chun , Chen Ethan
Published: September 2002

One-dimensional bubbly flows through converging–diverging nozzles are investigated using a two-fluid model. Effects associated with both translational and radial relative motions between bubbles and liquid are incorporated. Calculation of a subsonic case is performed first and shows good agreement with experiments. The model is then applied to critical (or choked) flow situations studied previously by Muir and Eichhorn. In their experiments, Muir and Eichhorn found larger critical pressure ratios (which are defined as the ratios of the throat pressure to the pressure upstream of the nozzle under choked conditions) and mass flow rates than homogeneous flow theory. They measured significant slip between phases which, therefore, was speculated to be responsible for these discrepancies. It is demonstrated in this paper that the phase relative velocity can be predicted reasonably well (within the experimental uncertainty) using the present model. Excellent agreement between the predicted critical mass flow rates and the experimental data is obtained. However, compensation for the critical pressure ratios is not apparent. Other important natures of the critical flows are also explored, including the formation of compression shock waves present in the divergent part of the nozzle. Our computations show that the pressure ratios across the shocks agree very well with the Hugoniot relation established by Thang and Davis.
Emergence of nonuniform V-states by synchronization
Authors: Friedland L. , Shagalov A. G.
Published: September 2002

It is shown that a family of nonuniform, m-fold symmetric rotating vortex structures in two dimensions (nonuniform V-states) can emerge in both free and bounded space by subjecting an axisymmetric vortex with a sharp vorticity edge to external rotation and weak strain of appropriate symmetry. The phenomenon is due to nonlinear synchronization (autoresonance) in the system, as the vorticity distribution of the vortex structure self-adjusts to phase lock with slowly varying external rotation. The synchronization is induced by passage through resonance with the isolated eigenmode of the linearized problem, provided the external strain rate is above a threshold. Synchronized, m=2 nonuniform V-states remain stable after the external strain is switched off. Free m=3 and 4 states, in contrast, are destroyed via three-wave decay at later times. The negative feedback approach is proposed to stabilize this instability.
Terahertz photoconductivity and plasmon modes in double-quantum-well field-effect transistors
Authors: Peralta X. G. , Allen S. J. , Wanke M. C. , Harff N. E. , Simmons J. A. , Lilly M. P. , Reno J. L. , Burke P. J. , Eisenstein J. P.
Published: September 2002

Double-quantum-well field-effect transistors with a grating gate exhibit a sharply resonant, voltage tuned terahertz photoconductivity. The voltage tuned resonance is determined by the plasma oscillations of the composite structure. The resonant photoconductivity requires a double-quantum well but the mechanism whereby plasma oscillations produce changes in device conductance is not understood. The phenomenon is potentially important for fast, tunable terahertz detectors.
Dynamics of aroclor and its modification by dissolved polystyrene
Authors: Casalini R. , Santangelo P. G. , Roland C. M.
Published: September 2002

Dynamic mechanical spectroscopy, dielectric spectroscopy, and viscosity measurements were carried out on Aroclor 1254 (PCB54), a chlorinated biphenyl. The temperature dependences of both the dielectric relaxation times and the viscosity depart from a single Vogel–Fulcher behavior, at a temperature, TB, equal to 294 K. The ratio of this characteristic temperature to Tg(=246 K) is close to that found previously for other Aroclors, having different chlorine levels. The shapes of the dielectric and mechanical relaxation functions were equivalent, yielding a value for the Kohlrausch stretch exponent equal to 0.625 at Tg. However, the relaxation times for the dielectric modulus were substantially larger than the viscosity and mechanical relaxation times. The respective temperature dependences of the viscosity and the dielectric relaxation times, although similar, deviated from the Debye–Stokes relation with decreasing temperature. The temperature associated with this deviation is somewhat higher than TB, and coincides with the temperature at which the relaxation function approaches Debye behavior. These phenomena all reflect the alleviation at high temperature of intermolecular constraints on the dynamics. The addition of high molecular weight polystyrene (PS-90k) to the PCB54 had an almost negligible effect on the dielectric relaxation times, notwithstanding that the polystyrene’s glass temperature is 130 degrees higher than Tg for PCB54. The PS-90k exerted a more significant effect on the mechanical relaxation times of the PCB54. However, the modification of the Aroclor dynamics is still orders of magnitude less than the effect of the dissolved PS-90k on the relaxation times of an oligomeric PS (PS-o). This low molecular weight PS has a Tg identical to that of the PCB54. The dramatic difference between the effect of added polymer on the dynamics of Aroclor versus PS-o can be ascribed to differences in their capacity for intermolecular coupling with the PS-90k solute.
Spectroscopic constants and potential energy curves of electronic states of Mo2
Authors: Balasubramanian K. , Zhu X.
Published: September 2002

Potential energy curves and spectroscopic constants for 37 low-lying electronic states of Mo2 and the ground state of Mo2+ have been computed using the complete active space multiconfiguration self-consistent field followed by the multireference singles+doubles configuration interaction calculations that included up to 19 million configurations. We compute equilibrium distances (re), vibrational frequencies (ωe), and energy separations (Te). We have suggested tentative assignments for the spectra of Mo2 including the recent work on resonance Raman and fluorescence spectra of Mo2. Our work supports the ground state with ωe near 450–486 cm−1, and we suggest that the 394.5 cm−1 line in the resonance Raman spectrum of Lombardi and co-workers is for the a 3Σu+ state of Mo2. Our computations are consistent with the recently observed near-infrared spectrum of Mo2 by Bondybey and co-workers. We have computed a number of spectroscopic systems for Mo2, which are yet to be observed. Our computed adiabatic ionization energy of Mo2 is in excellent agreement with Simard and co-workers. We have computed the De’s of Mo2+ and Mo2.
Applications of electrostatic interpretation of components of effective Kohn–Sham potential in atoms
Authors: Sen K. D. , De Proft Frank , Geerlings Paul
Published: September 2002

The fundamental significance of the components of the electronic Kohn–Sham potential evaluated at the nucleus is highlighted via the numerical studies on atoms He–Lu which suggest their formally similar power-law relationship in expressing the associated components of total electronic energy. Similar studies on the isoelectronic series of closed shell atoms lead to the linear correlations. The proposed static exchange–correlation charge density concept [S. Liu, P. A. Ayers, and R. G. Parr, J. Chem. Phys. 111, 6197 (1999)] is used to interpret these relationships. The maxima in the static integrated radial exchange–correlation charge density function, Qxc(r), in atoms are shown to reflect the shell boundaries. The quantum Monte Carlo density derived exchange–correlation potentials for Be and Ne are used to obtain Qxc(r) that can be used as standards to directly assess the quality of approximate exchange–correlation potentials. For the negative ions, Qxc(r) displays a characterstic outer minimum as a consequence of the Sen–Politzer theorem [K. D. Sen and P. Politzer, J. Chem. Phys. 90, 4370 (1989)]. This minimum is found to be related with the stability of negative ions.
Ab initio study of the A 2Π–X 2Π electronic transition in HCCS
Authors: Perić M. , Stevanović Lj. , Jerosimić S.
Published: September 2002

Potential energy surfaces for the electronic states of the HCCS radical correlating at linear nuclear arrangement with the A 2Π state are calculated by means of an extensive ab initio approach. They are used to compute the vibronic and spin-orbit structure of the A 2Π–X 2Π electronic transition. These calculations are carried out by means of a new variational approach based on the use of normal bending coordinates. The results of calculations question various interpretations of the available experimental data; on the other hand they do not offer reliable explanation of all features observed, pointing in this way at the shortages of the present, as well as of previous theoretical handling of the problem in question.
State-to-state rate constants for collision induced energy transfer of electronically excited NH2 with NH3
Authors: Lindner Jörg , Wilhelm Ralf
Published: September 2002

Collisional energy transfer of NH2 in its electronically excited state Ã 2A1 is investigated with time-resolved Fourier transform emission spectroscopy. NH2 is produced by photodissociation of NH3 and relaxed to low rotational levels before excitation into the electronically excited state. Originating from collisions with NH3, rate constants for total collisional removal and state-to-state rate constants for rotational energy transfer within v2=4, Ka=1 with collision induced changes of |ΔKc|⩽3 are determined. The latter rate constants are fitted with several scaling laws. Among these, those based on the energy corrected sudden approximation work best. An approximate potential curve for the anisotropic part of the interaction potential is derived and verified with cross sections obtained with straight line trajectories. The rotational energy transfer originates primarily from collisions with small impact parameters. The observed rate constants for total collisional removal are in accordance with the collision complex model.
Holographic writing of volume-type microgratings in silica glass by a single chirped laser pulse
Authors: Kawamura Ken-ichi , Hirano Masahiro , Kamiya Toshio , Hosono Hideo
Published: September 2002

Refractive-index-modulated volume-type gratings were holographically encoded inside pure SiO2 glass plates by a single chirped (0.5–5 ps duration) laser pulse generated from a mode-locked Ti:sapphire laser (wavelength ∼800 nm, emission pulse duration ∼100 fs). Scanning-electron- and confocal-optical-microscopic observations revealed that microgratings were formed inside the sample at a depth of ∼5 mm from the top surface. Also, inside the SiO2 glass, three-dimensional periodic arrays of the grating and crossed-grating structures were fabricated. The present technique is a fast method that is applicable not only for encoding volume-type gratings inside all nonphotosensitive transparent dielectric materials, but also for fabricating optical devices such as distributed-feedback lasers and multilayered memories.
Threading dislocation reduction via laterally overgrown nonpolar (112̄0) a-plane GaN
Authors: Craven M. D. , Lim S. H. , Wu F. , Speck J. S. , DenBaars S. P.
Published: September 2002

Threading dislocation density reduction of nonpolar (112̄0) a-plane GaN films was achieved by lateral epitaxial overgrowth (LEO). We report on the dependence of morphology and defect reduction on crystallographic stripe orientation. Stripes aligned along [0001] and [1̄100], the most favorable a-plane GaN LEO stripe orientations, possessed well-behaved, symmetric morphologies. Threading dislocation reduction via mask blocking was observed by transmission electron microscopy for [1̄100] stripes which had optimal rectangular cross-sections. Cathodoluminescence studies showed increased light emission for the overgrown regions in comparison to the window regions. The extent of lateral overgrowth of these stripes was asymmetric due to the opposing polarities of the vertical c-plane sidewalls. Conversely, threading dislocations propagated into the symmetric overgrown regions of [0001] stripes which possessed coexisting inclined and vertical {101̄0} facets.
Nonlinear change of refractive index of Co3O4 thin films induced by semiconductor laser (λ=405 nm) irradiation
Authors: Yamamoto Hiroki , Tanaka Shuhei , Naito Takashi , Hirao Kazuyuki
Published: September 2002

Nonlinear change of the refractive index (n) and extinction coefficient (k) of Co3O4 thin films induced by a laser with λ=405 nm (hν=3.06 eV) irradiation was evaluated using equipment having an ellipsometric optical configuration. Nonlinear refractive index (n2) and extinction coefficient (k2) were +1.0×10−10 m2/W (positive) and −2.6×10−11 m2/W (negative), respectively. n2 and k2 at λ=650 nm (hν=1.91 eV) were −5.5×10−11 m2/W and −8.7×10−11 m2/W (both have negative signs). From these results and the fact that the Co3O4 thin film has the band-gap energy of 2.06 eV, the band filling effect can be seen as one of the most probable models describing the large nonlinear change of n and k of Co3O4 thin film.
Measuring thermal effects in femtosecond laser-induced breakdown of dielectrics
Authors: Ladieu F. , Martin Ph. , Guizard S.
Published: September 2002

A quartz sample was submitted to femtosecond laser pulses with fluences up to 6×Fc, where Fc is the laser-induced breakdown fluence. A series of microthermocouples, deposited onto the surface, was used to measure heatings at the millisecond scale, at typically 50 μm from the laser impact. By using both the heat propagation equation and the Helmholtz equation to get the energy absorption profile, we estimate a minimum value of the temperature reached in the center of the crater. Even very close to Fc, this temperature is found to be ≳3000 °C, proving that heating effects play a major role in the breakdown of dielectrics.
STM-induced photon emission from self-assembled porphyrin molecules on a Cu(100) surface
Authors: Deng W. , Fujita D. , Ohgi T. , Yokoyama S. , Kamikado K. , Mashiko S.
Published: September 2002

An ultrahigh-vacuum scanning tunneling microscopy equipped with a conductive optical fiber tip and photon detector has been established to explore photon emission from a self-assembled monolayer (SAM) of Cu-tetra-[3,5-di-t-butylphenyl]porphyrin (Cu-TBPP) molecules on a Cu(100) surface. In a few nanometer scale areas, emitted photons from molecules induced by tunneling electrons were effectively collected within the near-field region through an apex of the conductive optical fiber tip. The photon emission can be attributed to the inelastic tunneling involving the optical fiber tip, the Cu-TBPP molecules, and the Cu(100) surface. We proposed two kinds of mechanisms in terms of the photon emission from a SAM of Cu-TBPP molecules on a Cu(100) surface. The quantum efficiency for molecular fluorescence induced by inelastic tunneling can be approximately estimated to be ∼3.0×10−6 photons per electron in the current experimental studies.
Excited state reactions of metals on clusters: Full dynamics of the Ca*+HBr reaction on Ar2000
Authors: Briant M. , Fournier P. R. , Gaveau M. A. , Mestdagh J. M. , Soep B. , Visticot J. P.
Published: September 2002

We report on the Ca*+HBr→CaBr*+H reaction when photoinduced within a Ca⋯HBr complex that is deposited at the surface of a large argon cluster (surface complex). The excitation that turns on the reaction is localized on the calcium atom. Information on the dynamics of the reaction is provided by observing the CaBr fluorescence while scanning the excitation laser across the calcium resonance line. This provides information on the access to the transition region of the reaction and helps to clarify how the argon cluster influences this access as compared to the gas phase experiment where the Ca⋯HBr complex is free (free complex). Chemiluminescence spectra were also recorded to characterize the output channel of the reaction. Not surprisingly, the presence of the cluster affects the dynamics of the reaction that proceeds at its surface. Several effects have been identified. Depending on which potential energy surface of the Ca⋯HBr complex is excited by the laser, the cluster acts passively or actively. When the excited 4p orbital of calcium is parallel to the cluster surface and pointing towards the HBr molecule, no drastic change of the reaction dynamics is observed. When the 4p orbital is pointing perpendicularly to HBr but still parallel to the cluster surface, the change to reaction dynamics is essentially an impeding of the libration motion in the 4pπ A″ potential energy surface of the complex. When the excited 4p orbital of calcium is perpendicular to the argon surface, the cluster interferes more actively with the dynamics of the reaction by adding a force to the system. This excitation scheme kicks calcium away from the cluster surface, thus promoting a movement in the 4pπ A′ potential energy surface of the surface complex that is not possible in the free complex. The cluster acts also in the exit channel of the reaction by thermalizing partly the product energy distribution. In particular, it is conceivable that rotational dissipation is the mechanism by which CaBr is very efficiently ejected out of the cluster. Substantial electronic and vibrational cooling is observed also. In particular, a thermal vibrational energy distribution is observed in the 1000-K range for reaction within the surface complex, whereas a population inversion was observed with the free complex. Moreover, the propensity rule that favors the formation of CaBr in the B 2Σ+ state is masked in the cluster reaction by an efficient quenching of the B 2Σ+ state to the lower A 2Π state.
Injection locking of individual broad-area lasers in an integrated high-power diode array
Authors: Liu Y. , Liu H. K. , Braiman Y.
Published: September 2002

We report experimental results on the injection locking of individual multimode broad-area high-power laser (one-in-a-time) in a linear array bar consisting of 19 lasers driven by a common current source. Each broad-area laser, capable of generating a beam with a power of 1 W, is injection locked to a single-longitudinal and transverse mode with less than 0.5 mW of injection power. The injection-locked broad-area laser shows very narrow linewidth close to the injection laser regardless of the output power. Our research suggests that the matching of the injection wavelength to one of the free-running modes of lasers in the array is the essential condition for achieving coherent operation of the array via injection locking.
Preparation and magnetic properties of highly coercive FePt films
Authors: Shima T. , Takanashi K. , Takahashi Y. K. , Hono K.
Published: September 2002

The magnetization processes of highly ordered FePt(001) films with large perpendicular magnetic anisotropy have been studied. The film morphology was controlled from isolated particles to continuous film by varying the nominal thickness (tN) of the FePt film sputter deposited directly on a MgO(001) substrate at an elevated temperature. A drastic change in the coercivity by one order of magnitude has been found at the critical thickness (tN=45 nm) where the film morphology changes from a particulate to a continuous state. A huge coercivity exceeding 40 kOe has been achieved in the film with tN=10 nm, which comprises single domain particles with an average lateral size of approximately 50 nm.
Local magnetic anisotropy control in NiFe thin films via ion irradiation
Authors: Woods S. I. , Ingvarsson S. , Kirtley J. R. , Hamann H. F. , Koch R. H.
Published: September 2002

A method for altering the local direction and angular dispersion of anisotropy in soft magnetic films using energetic ion irradiation is demonstrated. NiFe films 50 Å thick were irradiated with 200 keV Ar+ ions to doses between 1013 and 1016 ions/cm2, while a saturating magnetic field was applied to the samples. This annealing field defined the new anisotropy direction of the irradiated areas, and the irradiation process also led to changes in the angular dispersion of anisotropy orientation, as measured by angle-dependent remanence of magnetization. By appropriate masking of films, this technique has been used to pattern samples with small “anisotropy domains.”
Growth and characterization of zirconium oxynitride films prepared by reactive direct current magnetron sputtering
Authors: Venkataraj S. , Kappertz O. , Jayavel R. , Wuttig M.
Published: September 2002

Thin films of zirconium oxynitrides have been deposited onto Si(100) substrates at room temperature by reactive dc magnetron sputtering of a metallic Zr target in an argon–oxygen–nitrogen atmosphere. To prepare oxynitride films the sum of the O2 and N2 flow was kept at 3.5 sccm, while the relative nitrogen content of this mixture was changed stepwise from 0% to 100%. The film structure was determined by x-ray diffraction, while x-ray reflectometry was employed to determine the thickness, density, and surface roughness of the films. The optical properties have been studied by spectroscopic reflectance measurements. X-ray diffraction (XRD) determines that the as-deposited films are crystalline and do not change their monoclinic ZrO2 crystal structure even for nitrogen flows up to 80%. For pure argon–nitrogen sputtering, on the contrary, cubic zirconium nitride (ZrN) has been formed. Nevertheless, even though the crystal structure does not change with increasing nitrogen flow up to 80%, there is clear evidence from nitrogen incorporation from Rutherford backscattering experiments, optical spectroscopy, XRD, and x-ray reflectometry. The latter technique determines that the film density increases from 5.2 to 5.8 g/cm3 with increasing nitrogen flow from 0% to 80%. Simultaneously, the rate of sputtering increases from 0.17 to 0.6 m/s, while the film roughness decreases upon increasing N2 flow. Optical spectroscopy measurements of the film reflectance confirm that fully transparent films can be prepared up to a nitrogen flow of 80%. For these films, the band gap decreases from 4.52 to 3.59 eV with increasing N2 flow, while the refractive index at 650 nm simultaneously increases from 2.11 to 2.26. For 100% N2 flow, i.e., without any oxygen, films with a metallic reflectance are obtained.
Zero-field electron spin resonance and theoretical studies of light penetration into single crystal and polycrystalline material doped with molecules photoexcitable to the triplet state via intersystem crossing
Authors: Takeda Kazuyuki , Takegoshi K. , Terao Takehiko
Published: September 2002

A theory is presented to calculate the penetration depth of light in single crystal or polycrystalline material doped with the molecule whose electronic state can be excited by photoabsorption from the ground state to the excited singlet state, and transferred by intersystem crossing into the triplet state. An experimental study on the penetration depth is also reported, which is made by measuring the amplitude of the zero-field electron spin resonance (ESR) signal of the photoexcited triplet electron spins in single crystal and polycrystalline pentacene-doped p-terphenyl and naphthalene samples at room temperature. The samples were irradiated by a pulsed laser beam, and the zero-field ESR signals were observed for various sample thicknesses. In single crystals of 0.053 mol % pentacene-doped p-terphenyl, the pentacene molecule within ca. 1 mm from the surface of the sample was found to undergo intersystem crossing to the triplet state by the laser irradiation with a pulse duration of 1 μs and a beam intensity of 9.2×108 W m−2. This result could be well reproduced by the calculation using the reported kinetic parameters, and the limit depth of photoexcitation to the triplet state is shown to coincide with the penetration depth of light when the effect of the stimulated emission is negligible. For polycrystalline 0.099 mol % pentacene-doped p-terphenyl, the penetration depth under an incident beam intensity of 2.9×109 W m−2 was determined to be ca. 0.7 mm, which could be reproduced by taking account of the laser beam attenuation due to multiple scattering at the crystallite boundaries in the calculations. For pentacene-doped naphthalene, the experimental results were reproduced by the simulations using the intersystem crossing yield of 40%, which is much higher than the value (2%) reported at 1.4 K.
Magnetic field effect on the sheath thickness in plasma immersion ion implantation
Authors: Keidar M. , Monteiro O. R. , Anders A. , Boyd I. D.
Published: September 2002

The sheath thickness in plasma immersion ion implantation has been investigated in the presence of a transverse magnetic field. It has been found that the steady-state sheath thickness increases with increasing magnetic field strength. This result is in line with a simplified model of the sheath in which the steady-state sheath thickness is determined by the plasma density and ion velocity at the sheath edge. These results suggest that a magnetic field may be used to control the high-voltage sheath in plasma immersion ion implantation.
Monophasic TiO2 films deposited on SrTiO3(100) by pulsed laser ablation
Authors: Hsieh C. C. , Wu K. H. , Juang J. Y. , Uen T. M. , Lin J.-Y. , Gou Y. S.
Published: September 2002

Single phase TiO2 thin films, of either rutile or anatase structure, have been prepared on SrTiO3(STO)(100) substrates by in situ pulsed laser deposition (PLD). Thermodynamically unfavorable, for films deposited on STO(100) substrate directly, pure anatase TiO2(00l) films were formed even when a rutile TiO2(110) substrate was used as a target. On the other hand, pure rutile TiO2(110) films were obtained by oxidizing PLD TiN films in-situ at temperatures higher than 700 °C. The optimized deposition conditions for preparing TiN and TiO2 films were reported. The crystalline structure, surface morphology, and electronic structure of these films were examined. A mechanism of the process of film formation is also proposed.
Giant magnetoimpedance in trilayer structures of patterned magnetic amorphous ribbons
Authors: Amalou F. , Gijs M. A. M.
Published: September 2002

We have measured the giant magnetoimpedance (GMI) and giant magnetoresistance (GMR) of Metglas®/Cu/Metglas trilayer stacks of micropatterned amorphous magnetic Metglas 2714a ribbons and Cu foils. We obtain room-temperature GMI ratios [Z(0)−Z(Hs)]/Z(Hs) up to 800%, and GMR ratios [R(0)−R(Hs)]/R(Hs) up to 2400% at frequencies of 100 kHz–10 MHz, with Hs the magnetic field in which impedance and resistance saturate towards their minimum values. These high values are a direct consequence of the large dynamic relative permeability of the magnetic ribbons and the chosen trilayer geometry. We analyze our results in the context of a theoretical model of L. V. Panina and K. Mohri [Sens. Actuators A 81, 71 (2000)].
Silicon waveguide two-photon absorption detector at 1.5 μm wavelength for autocorrelation measurements
Authors: Liang T. K. , Tsang H. K. , Day I. E. , Drake J. , Knights A. P. , Asghari M.
Published: September 2002

We describe the use of a silicon waveguide for two-photon absorption measurements in an autocorrelator which achieved a peak-power average-power sensitivity of 1 (mW)2 at 1.56 μm wavelength and which was used to measure optical pulses generated by a mode-locked fiber ring laser. The experimental results agreed with a theoretical model of the two-photon-induced photocurrent generation inside the waveguide.
Simultaneous atomic force microscope and quartz crystal microbalance measurements: Investigation of human plasma fibrinogen adsorption
Authors: Choi K.-H. , Friedt J.-M. , Frederix F. , Campitelli A. , Borghs G.
Published: September 2002

We have combined the tapping-mode atomic force microscope (AFM) and quartz crystal microbalance (QCM) for simultaneous investigation of human plasma fibrinogen adsorption on a metallic surface using these two instruments. The AFM images show the surface changes with molecular resolution while the corresponding resonance frequency shift of the QCM provides quantitative adsorbed mass estimates over the whole sensing area. The combination of AFM with QCM allowing the simultaneous measurements with two techniques working at very different scales and probing different properties of the adsorbed layer provides quantitative and qualitative information that can distinguish different protein adsorption mechanisms.
Modeling of a capacitively coupled radio-frequency methane plasma: Comparison between a one-dimensional and a two-dimensional fluid model
Authors: Herrebout D. , Bogaerts A. , Yan M. , Gijbels R. , Goedheer W. , Vanhulsel A.
Published: September 2002

A comparison is made between a one-dimensional (1D) and a two-dimensional (2D) self-consistent fluid model for a methane rf plasma, used for the deposition of diamond-like carbon layers. Both fluid models consider the same species (i.e., 20 in total; neutrals, radicals, ions, and electrons) and the same electron–neutral, ion–neutral, and neutral–neutral reactions. The reaction rate coefficients of the different electron–neutral reactions depend strongly on the average electron energy, and are obtained from the simplified Boltzmann equation. All simulations are limited to the alpha regime, hence secondary electrons are not taken into account. Whereas the 1D fluid model considers only the distance between the electrodes (axial direction), the 2D fluid model takes into account the axial as well as the radial directions (i.e., distance between the electrodes and the radius of the plasma reactor, respectively). The calculation results (species densities and species fluxes towards the electrodes) obtained with the 1D and 2D fluid model are in relatively good agreement. However, the 2D fluid model can give additional information on the fluxes towards the electrodes, as a function of electrode radius. It is found that the fluxes of the plasma species towards both electrodes show a nonuniform profile, as a function of electrode radius. This will have an effect on the uniformity of the deposited layer.
Ferromagnetic resonance in Ni–Mn–Ga films
Authors: Patil S. I. , Tan Deng , Lofland S. E. , Bhagat S. M. , Takeuchi I. , Famodu O. , Read J. C. , Chang K.-S. , Craciunescu C. , Wuttig M.
Published: September 2002

Textured thin films of nominal composition Ni0.50(MnGa)0.50 were sputter deposited on Si substrates and studied by x-ray diffraction, micromechanical displacement, dc magnetization, and ferromagnetic resonance (FMR). We report the observation of spin wave resonances in this alloy, yielding a spin wave stiffness of D=200 meV Å2 at 300 K. A marked thermal hysteresis is observed in the temperature-dependent FMR data arising from the reversible martensitic transition.
Enhanced ferroelectric properties in laser-ablated SrBi2Nb2O9 thin films on platinized silicon substrate
Authors: Das Rasmi R. , Bhattacharya P. , Katiyar Ram S.
Published: September 2002

Non-c-axis-oriented SrBi2Nb2O9 (SBN) thin films were grown on Pt/TiO2/SiO2/Si substrates using the pulsed-laser-deposition technique. X-ray diffraction results confirmed the textured growth of SBN thin films along (115) and (200) orientations. The increase in the value of the dielectric permittivity and decrease in the tangential loss of the films with an increase in annealing temperature were attributed to grain size dependence. SBN thin films annealed at 750 °C exhibited a maximum value of the dielectric constant of ∼346 with a dissipation factor of 0.02. Thin films with certain deposition parameters exhibited the highest remanent polarization (Pr) and coercive field, 25.7 μC/cm2 and 198 kV/cm, respectively. There was minimal (<20%) degradation in the switchable polarization (P*−P∧) after 1010 switching cycles. At lower field, the leakage current follows ohmic behavior, and at higher field, up to 100 kV/cm, the leakage current density was about 5×10−7 A/cm2.
An assessment of fishery resources of Laguna de Bay
Authors: Palma Adelaida L. , Diamante Adan S. , Pol Romualdo M.
Published: September 2002

An assessment of the major fishery resources of Laguna de Bay was conducted in 1995–1996. The study covered the socio-economics of landed fish catch and inventory of fishing gears. The socio-economic survey covered 3,055 fishermen; 87.5% were full-time workers and the rest were part-time. The total fishing effort exerted in the open waters of Laguna de Bay was 10,653,220 hours with a catch per unit effort of 0.25 kg h−1. The total fish production was 8,146 and 2,668 metric tons in 1995 and 1996, respectively. The catch mainly consisted of 13 species and was made with 20 gear types. Among the gear types, the gill net, fish corral, motorized push net, fyke net, fish pot, fish trap, and manual seine with fish shelter were considered major gear.
Barrier-to-autointegration factor
Authors: Segura-Totten Miriam , Kowalski Amy K. , Craigie Robert , Wilson Katherine L.
Published: September 2002

Barrier-to-autointegration factor (BAF) is a DNA-bridging protein, highly conserved in metazoans. BAF binds directly to LEM (LAP2, emerin, MAN1) domain nuclear membrane proteins, including LAP2 and emerin. We used site-directed mutagenesis and biochemical analysis to map functionally important residues in human BAF, including those required for direct binding to DNA or emerin. We also tested wild-type BAF and 25 point mutants for their effects on nuclear assembly in Xenopus egg extracts, which contain ∼12 μM endogenous BAF dimers. Exogenous BAF caused two distinct effects: at low added concentrations, wild-type BAF enhanced chromatin decondensation and nuclear growth; at higher added concentrations, wild-type BAF completely blocked chromatin decondensation and nuclear growth. Mutants fell into four classes, including one that defines a novel functional surface on the BAF dimer. Our results suggest that BAF, unregulated, potently compresses chromatin structure, and that BAF interactions with both DNA and LEM proteins are critical for membrane recruitment and chromatin decondensation during nuclear assembly.