bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrophoresis of a bead-rod chain through a narrow slit: A Brownian dynamics study
Authors: Kim Seung Ha , Panwar Ajay S. , Kumar Satish , Ahn Kyung Hyun , Lee Seung Jong
Published: November 2004

We use two-dimensional Brownian dynamics simulations to study the electrophoresis of a bead-rod chain through a narrow slit. A constant electric field is assumed to act inside and outside of the slit, and each bead on the chain is assigned a constant uniform charge. We calculate the dependence of the polymer transit velocity on chain length, slit dimensions (width-to-length ratio), and electric-field strength. For sufficiently narrow slits, the transit velocity increases nonlinearly with the applied field for low-field strengths, whereas it increases linearly for high-field strengths. In the low-field strength region and for sufficiently narrow slits, the transit velocity decreases rapidly for small chain lengths and then decreases slowly beyond a critical chain length. As the slit width increases, the transit velocity decreases with chain length in more continuous manner, and for sufficiently large slits the transit velocity becomes independent of chain length as expected. Distributions of the chain end-to-end distances and the translocation times depend strongly on the relative size of the chain to the slit. These results show the sensitivity of the transit velocity vs chain length relationship to the slit dimensions and applied electric-field strength, and suggest that there may be an optimal slit width for a given field strength and vice versa. The results may be useful for microfluidic separations and for understanding the motion of biological polymers through narrow constrictions.
Doppler-free two-photon excitation spectroscopy and the Zeeman effect of the 141 band of the S1 1B2u←S 1A1g transition of benzene-d6
Authors: Wang Jinguo , Doi Atsushi , Kasahara Shunji , Katô Hajime , Baba Masaaki
Published: November 2004

The Doppler-free two-photon excitation spectrum and the Zeeman effect of the 1401 band of the S1←S0 transition of C6D6 were measured from 39 842 to 39 856 cm−1. The Zeeman splittings of the Q(J)Q(K) lines of a given J were observed to increase proportionally with K2 and reach a maximum at K=J. The Zeeman splittings of the Q(J)Q(K=J) lines were observed to increase proportionally with J. The observed Zeeman splittings are identified as originating from the electronic orbital angular momentum arising from a mixing of the S1 1B2u and S2 1B1u states via J-L coupling. No perturbation originating from an interaction with a triplet state was observed. It became clear from the Zeeman effect that rotationally resolved levels of the S1 state are not mixed with a triplet state. Therefore, it is concluded that nonradiative decay of an isolated benzene molecule excited to the S1 state occurs through the intramolecular vibrational-rotational mixing within the S1 state even in the low vibrational levels.
Coherent population transfer in molecules coupled with a dissipative environment by intense ultrashort chirped pulse. II. A simple model
Authors: Fainberg B. D. , Gorbunov V. A.
Published: November 2004

We have developed a simple and physically clear picture of adiabatic rapid passage (ARP) in molecules in solution by careful examination of all the conditions needed for ARP. The relaxation effects were considered in the framework of the Landau–Zener model for random crossing of levels. The model enables us to include into consideration non-Markovian Gaussian-correlated noise. It explains all the numerical results obtained in the first paper of the series [B. D. Fainberg and V. A. Gorbunov, J. Chem. Phys. 117, 7222 (2002)], in particular, that for positive chirp pulse excitation relaxation favors more efficient population transfer with respect to the relaxation-free system with frozen nuclear motion. We also relate parameters of non-Markovian Gaussian-correlated noise with irreversible dephasing time of an optical transition by calculating the photon echo signal attenuation.
High ambipolar and balanced carrier mobility in regioregular poly(3-hexylthiophene)
Authors: Choulis S. A. , Kim Y. , Nelson J. , Bradley D. D. C. , Giles M. , Shkunov M. , McCulloch I.
Published: November 2004

The carrier transport of carefully purified regioregular poly(3-hexylthiophene) films has been studied using time-of-flight photocurrent measurements. We find balanced ambipolar transport with a room-temperature mobility for holes of 3×10−4cm2V−1s−1 and for electrons of 1.5×10−4cm2V−1s−1 at electric fields ⩾105V∕cm. The transport is relatively field independent and weakly temperature dependent, pointing to a high degree of chemical regioregularity and purity. These factors make poly(3-hexylthiophene) attractive for use in a range of electronic applications.
Ab initio study of cubyl chains and networks
Authors: Valencia F. , Romero A. H. , Kiwi Miguel , Ramı́rez R. , Toro-Labbe A.
Published: November 2004

The spatial arrangements and physical properties of one- and two-dimensional structures, based on the amazing cubane (C8H8) molecule, are investigated in detail. In particular, we compute the electronic structure, both by first principle calculations and by semiempirical methods. The elastic and vibrational properties are evaluated as well. All these results are compared with those of the single cubane molecule, in order to elucidate the influence of dimensionality.
Geometry relaxation effects for molecules as a result of binding with a positron
Authors: Tachikawa Masanori , Buenker Robert J. , Kimura Mineo
Published: November 2004

We have confirmed that the stabilization of the [urea;e+] system due to geometry relaxation by configuration interaction ab initio molecular orbital calculation is negligibly small, thereby justifying our original position that such effects would not change the predictions for the strength of the positron binding to urea and/or acetone.
Low coverage spontaneous etching and hyperthermal desorption of aluminum chlorides from Cl2/Al(111)
Authors: Grassman Tyler J. , Poon Gary C. , Kummel Andrew C.
Published: November 2004

Nonresonant multiphoton ionization with time-of-flight mass spectrometry has been used to monitor the desorption of aluminum chloride (AlxCly) etch products from the Al(111) surface at 100 and 500 K during low-coverage (<5% monolayer) monoenergetic Cl2 (0.11–0.65 eV) dosing. The desorption products in this low-coverage range show predominantly hyperthermal exit velocities under all dosing conditions. For example, with 0.27 eV incident Cl2, the etch product was found to have a most-probable velocity of 517±22 m/s at an Al(111) surface temperature of 100 K. This corresponds to 22 times the expected thermal desorption translational energy for AlCl3. Cl2 sticking probability measurements and AlxCly etch rate measurements show etching even at Cl2 coverages of less than 5% monolayer at surface temperatures between 100 and 500 K. These experimental results are consistent with a combination of fast-time-scale surface diffusion and agglomeration of the adsorbed chlorine to form aluminum chlorides and the presence of activated AlCl3 chemisorption states having potential energies above the vacuum level. Density functional theory calculations yield results that are consistent with both our experimental findings and mechanistic descriptions.
Computer simulation of the adsorption of ethanethiol in silicalite of MFI and MOR
Authors: Ju Shen-gui , Zeng Yong-ping , Yao Hu-qing
Published: November 2004

The method of configurational-bias Monte Carlo simulation is used for investigating the adsorption and distributions of ethanethiol in MFI and MOR type zeolites. The calculated adsorption quantity of ethanethiol in MFI is close agreement with the experimental data by means of IR spectroscopy and thermogravimetry. The calculated results show the adsorption quantity of ethanethiol in MFI is much more than that in MOR under coequal conditions. The observation of distribution of MFI is attributed to preferential adsorption of the ethanethiol molecules in the straight and zig-zag channels. In the intersection of straight channels and zig-zag channels, it accommodates the ethanethiol molecules like a reservoir. The straight channels for MOR accommodate all ethanethiol molecules almost, however, in the other channels, the ethanethiol molecules cannot be found.
Spectroscopy of Cs attached to helium nanodroplets
Authors: Bünermann O. , Mudrich M. , Weidemüller M. , Stienkemeier F.
Published: November 2004

Cesium oligomers are formed on helium nanodroplets which are doped with one or a few Cs atoms. The monomer absorption of the first electronic p←s transition upon laser excitation is probed. Spectra employing laser-induced fluorescence, beam depletion, and resonant photoionization are compared. In particular, mass-resolved photoionization allows us to specifically probe excitation induced processes such as, e.g., the formation of cesium-helium exciplexes. Absorption spectra of Cs dimers and trimers are recorded in the spectral region accessible by a Ti:sapphire laser. Assignment of dimer spectra is achieved by comparison with model calculations based on ab initio potentials. Electronic absorption lines of Cs trimers are attributed to transitions in the quartet manifold.
Sensitized phosphorescence of benzil-doped ladder-type methyl-poly(para-phenylene)
Authors: Bagnich S. A. , Bässler H. , Neher D.
Published: November 2004

The delayed luminescence and phosphorescence of ladder-type methyl-poly(para-phenylene) (MeLPPP) doped with benzil at a concentration of 20% by weight has been measured. The introduction of benzil leads to a dramatic reduction of the polymer singlet emission. At the same time, a new band with maximum at 611 nm appears, corresponding to the phosphorescence of MeLPPP. The phosphorescence decay on the short time scale is close to an exponential law with a time decay of 15 ms. This indicates that benzil can efficiently sensitize the phosphorescence of the polymer. In addition, a broad and featureless emission is observed in the delayed luminescence spectra of benzil-doped MeLPPP, which is attributed to an exciplex formed between the polymer host and the dopant. We further observe that the delayed fluorescence is enhanced by the addition of benzil. It is concluded that the delayed fluorescence of benzil-doped MeLPPP is mainly due to the annihilation of triplet excitons on the polymer. Finally, efficient triplet-triplet energy transfer from the benzil-doped polymer to the red-emitting phosphorescent dye Pt(II)octaethylporphyrin is established.
Self-phase modulation of submicrojoule femtosecond pulses in a hollow-core photonic-crystal fiber
Authors: Konorov S. O. , Sidorov-Biryukov D. A. , Zheltikov A. M. , Bugar I. , Chorvat D. , Chorvat D. , Beloglazov V. I. , Skibina N. B. , Bloemer M. J. , Scalora M.
Published: November 2004

Hollow-core photonic-crystal fibers (PCFs) capable of transporting sub-100-fs pulses of Ti:sapphire laser radiation in one of their transmission peaks centered around 800 nm have been designed and demonstrated. These fibers are shown to enhance self-phase modulation of submicrojoule 100-fs Ti:sapphire laser pulses, allowing a spectral bandwidth of 35 nm to be achieved with an 8-cm PCF sample.
The Kirkwood–Buff theory and the effect of cosolvents on biochemical reactions
Authors: Shimizu Seishi , Boon Chandra L.
Published: November 2004

Cosolvents added to aqueous solutions of biomolecules profoundly affect protein stability, as well as biochemical equilibria. Some cosolvents, such as urea and guanidine hydrochloride, denature proteins, whereas others, such as osmolytes and crowders, stabilize the native structures of proteins. The way cosolvents interact with biomolecules is crucial information required to understand the cosolvent effect at a molecular level. We present a statistical mechanical framework based upon Kirkwood–Buff theory, which enables one to extract this picture from experimental data. The combination of two experimental results, namely, the cosolvent-induced equilibrium shift and the partial molar volume change upon the reaction, supplimented by the structural change, is shown to yield the number of water and cosolvent molecules bound or released during a reaction. Previously, denaturation experiments (e.g., m-value analysis) were analyzed by empirical and stoichiometric solvent-binding models, while the effects of osmolytes and crowders were analyzed by the approximate molecular crowding approach for low cosolvent concentration. Here we synthesize these previous approaches in a rigorous statistical mechanical treatment, which is applicable at any cosolvent concentration. The usefulness and accuracy of previous approaches was also evaluated.
Crossover model for the work of critical cluster formation in nucleation theory
Authors: Kalikmanov V. I.
Published: November 2004

We propose a relation for the work of critical cluster formation in nucleation theory W for the systems with long-range interparticle interactions. The method of bridge functions is used to combine the system behavior at sufficiently small quenches, adequately predicted by the classical nucleation theory, with nonclassical effects at deep quenches in the vicinity of the thermodynamic spinodal, described within the framework of the field theoretical approach with an appropriate Ginzburg-Landau functional. The crossover between the two types of nucleation behavior takes place in the vicinity of the kinetic spinodal where the lifetime of a metastable state is of the order of the relaxation time to local equilibrium. We argue that the kinetic spinodal corresponds to the minimum of the excess number of molecules in the critical cluster. This conjecture leads to the form of W containing no adjustable parameters. The barrier scaling function Γ=W/Wcl, where Wcl is the classical nucleation barrier, depends parametrically on temperature through the dimensionless combination of material properties. The results for argon nucleation are presented.
Dielectric behavior of electroactive fluorinate-based polymers under dc electric field
Authors: Yu Zhi , Ang Chen
Published: November 2004

The dielectric behavior in fluorinate-based polymers has been studied under a dc electric field of 0–72V∕μm. The two overlapped anomalies Modes A (A′) and B in the dielectric constant are clearly revealed under dc bias. Mode A′ in the terpolymer behaves as a ferroelectric mode, whose peak temperature increases with increasing dc bias, and a macrodomain state is developed after the application of dc bias. The dominant Mode B exhibits a special polarization process with a characteristic of the peak temperature being unshifted with increasing dc bias.
Direct comparison between phase locked oscillator and direct resonance oscillator in the noncontact atomic force microscopy under ultrahigh vacuum
Authors: Kim Byung I.
Published: November 2004

I have demonstrated the advantage of the phase locked oscillator (PLO) over the conventional direct resonance oscillator (DRO) in noncontact mode atomic force microscopy (AFM) under ultrahigh vacuum. Direct comparison between PLO and DRO has been made in terms of background noise level, temporal response, and stability. Compared to the DRO method without phase coherence, the experimental results show that the PLO method is more effective in reducing the noise level and enhancing the stability over all force regimes in UHV noncontact AFM. The noise reduction and stability enhancement in PLO indicate the important role of the phase coherent effect in improving the capability of noncontact imaging in UHV.
Effect of the vacuum vessel on magnetic measurements in TCABR tokamak
Authors: Kucinski M. Y. , Kuznetsov Yu. K. , Saettone E. A. O.
Published: November 2004

Magnetic diagnostics in fusion experiments can be strongly affected by eddy currents induced in the vacuum vessel and in-vessel conducting components. In the present work the effect of the eddy currents on magnetic measurements in the TCABR tokamak with nearly circular plasma shape and rectangular cross section of the vacuum vessel is discussed. A method to find the magnetic field generated by eddy currents, in reply to the magnetic field of plasma currents, is based on expansion of vacuum field in series of toroidal harmonics. The conclusion is that, if the sensors are placed near the vessel, the effect of the vessel is strong and it decreases substantially in the case of sensors located near the plasma boundary at the circular surface.
Comparisons between PZT and PVDF thick films technologies in the design of low-cost pyroelectric sensors
Authors: Capineri L. , Masotti L. , Ferrari V. , Marioli D. , Taroni A. , Mazzoni M.
Published: November 2004

This paper compares the characteristics of two types of four quadrant pyroelectric sensors, made with screen-printed PZT and PVDF thick films, respectively, which we used for low-cost contactless position determination and laser beam positioning. For the comparison we used their responsivities, measured with a CO2 laser, and their respective noise figures. For sensors designing we simulated the PZT sensor responsivity using an equivalent thermo-electric model already demonstrated for multilayer PVDF sensors. The barely known model parameters of the PZT and electrodes layers were deduced from the best fit of the temporal voltage response to two square wave periodic signals. The peak current responsivity, the bandwidth and the NEP of the various samples indicate PZT most suited for low-noise and PVDF for high frequency and large bandwidth IR laser beam applications, respectively.
Ammonia pretreatment for high-κ dielectric growth on silicon
Authors: Brewer R. T. , Ho M.-T. , Zhang K. Z. , Goncharova L. V. , Starodub D. G. , Gustafsson T. , Chabal Y. J. , Moumen N.
Published: November 2004

Thermal nitridation of H∕Si(100) surfaces with NH3 gas has been studied as a pretreatment for atomic layer deposition of Al2O3. The chemical nature of both the nitride interface and the Al2O3 growth was characterized using in situ transmission infrared spectroscopy and medium energy ion scattering. Nitride layers thicker than 3–4Å provide an effective barrier against interfacial SiO2 formation and promote the nucleation of Al2O3 growth.
Spatial and spectral characterization of a laser produced plasma source for extreme ultraviolet metrology
Authors: Legall H. , Stiel H. , Vogt U. , Schönnagel H. , Nickles P.-V. , Tümmler J. , Scholz F. , Scholze F.
Published: November 2004

We present a laser produced plasma (LPP) source optimized for metrology and the results of its radiometric characterization. The presented (LPP) source can be used for reflectometry and spectroscopy in the soft x-ray range. For these applications, stable operation with high spectral photon yields high reliability in continuous operation and, to reach high spectral resolution, a small source size and high source point stability is necessary. For the characterization of the source, special instruments have been designed and calibrated using the soft x-ray radiometry beamline of the Physikalisch-Technische-Bundesanstalt at BESSY. These instruments are an imaging spectrometer, a double multilayer tool for in-band power measurements, a transmission slit grating spectrograph, and a pinhole camera. From the measurements a source size of 30 μm×55 μm (2σ, horizontal by vertical) and a stability of better than 5 μm horizontally and 9 μm vertically were obtained. The source provides a flat continuous emission in the extreme ultraviolet (EUV) range around 13.4 nm and a spectral photon flux of up to 1*1014/(s sr 0.1 nm) at a pump laser pulse energy of 650 mJ. The shot-to-shot stability of the source is about 5% (1σ) for laser pulse energies above 200 mJ. It is shown that an Au-LPP source provides spectrally reproducible emission with sufficient power at low debris conditions for the operation of a laboratory based EUV reflectometer and for spectroscopy.
A low drift high resolution cryogenic null ellipsometer
Authors: McMillan T. , Taborek P. , Rutledge J. E.
Published: November 2004

A cryogenic ellipsometer capable of measuring submonolayers of liquid helium has been developed. Methods for controlling drift and noise created by the cryostat windows and ellipsometer optics are discussed in detail. The cryostat vacuum windows were made from SF-57 glass due to its low stress-optic coefficient. Custom low-stress vacuum window mounts were designed and all windows were temperature controlled. Placing the compensator wave plate inside the cryostat was necessary to avoid room temperature fluctuation induced noise. These steps produced 12 h drifts in the measured polarization of less than 0.002°. A helium adsorption isotherm taken at 1.5 K on gold is presented to show the high resolution obtained once noise and drift associated with window birefringence is minimized.
Anistropic photoinduced magnetism of a RbjCok[Fe(CN)6]l·nH2O thin film
Authors: Park J.-H. , Čižmár E. , Meisel M. W. , Huh Y. D. , Frye F. , Lane S. , Talham D. R.
Published: November 2004

A magneto-optically active thin film of RbjCok[Fe(CN)6]l·nH2O has been prepared using a sequential assembly method. Upon irradiation with light and at 5K, the net magnetization of the film increased when the surface of the film was oriented parallel to the external magnetic field of 0.1T. However, when the surface of the film was perpendicular to the field, the net magnetization decreased upon irradiation. The presence of dipolar fields and the low-dimensional nature of the system are used to describe the orientation dependence of the photoinduced magnetization. The ability to increase or decrease the photoinduced magnetization by changing the orientation of the system with respect to the field is a phenomenon that may be useful in future device applications.
A discussion of the dispersion curve of energy excitations in liquid He4
Authors: Bogoyavlenskii I. V. , Puchkov A. V. , Skomorokhov A. N. , Karnatsevich L. V.
Published: November 2004

An investigation of the dispersion of excitations in a quantum liquid, superfluid He4, is carried out. An attempt is made to systematize the published experimental data that indicate a substantially different nature of excitations with wave vectors corresponding to different parts of the dispersion curve of liquid He4. Neutron spectroscopy data are analyzed in relation to a certain physical hypothesis concerning the formation of such a spectrum, and it is found that the majority of the known experimental facts can be explained in framework of that hypothesis. Particular attention is paid to a comparison of the experimental data obtained on the DIN-2PI time-of-flight spectrometer (at the IBR-2 Reactor, Dubna) with the results obtained at foreign research centers.
Single-pulse and secondary echoes in systems with a large inhomogeneous broadening of NMR lines
Authors: Chigvinadze J. G. , Mamniashvili G. I. , Sharimanov Yu. G.
Published: November 2004

The equations for the nuclear magnetizations which describe the dynamics of nuclear spin-systems with strong Larmor and Rabi inhomogeneous broadenings of the NMR line under conditions of their nonequilibrium are obtained in the framework of the Mims transformation matrix method; these equations have been obtained previously by the statistical tensors method. As an example, the properties of the proton single-pulse echo and its secondary signals in a test material (silicone oil) coated on the surface of high-Tc superconducting-oxide powders and in metallic hydride are presented.
Magnetic ordering caused by a disorder in quasi-one-dimensional spin systems and non-Fermi-liquid systems
Authors: Zvyagin A. A. , Makarova A. V.
Published: November 2004

It is shown that a strong disorder in the distribution of exchange couplings between magnetic impurities and hosts in quantum spin chains and non-Fermi-liquid rare-earth and actinide compounds can be the cause of magnetic orderings in these systems at low temperatures.
p
-type ZnO films by monodoping of nitrogen and ZnO-based p–n homojunctions
Authors: Bian J. M. , Li X. M. , Zhang C. Y. , Yu W. D. , Gao X. D.
Published: November 2004

Nitrogen-doped p-type ZnO (ZnO:N) films have been achieved by ultrasonic spray pyrolysis at atmosphere. The high structural quality of the obtained films was confirmed by x-ray diffraction, scanning electron microscopy, and photoluminescence spectra. Hall-effect and Seebeck-effect measurements indicate that the obtained p-type ZnO film shows a low resistivity of 3.02×10−2Ωcm, high carrier concentration of 8.59×1018cm−3, high mobility of 24.1cm2∕Vs, and high Seebeck coefficient of 408.2μV∕K at room temperature. Furthermore, the two-layer structured ZnO p–n homojunctions were prepared by depositing n-type ZnO layer on p-type ZnO:N layer. The current–voltage curve derived from the two-layer structure clearly shows the typical rectifying characteristic of p–n junctions.
Chemically etched modulation in wire radius for wire array Z-pinch perturbation studies
Authors: Jones B. , Deeney C. , McKenney J. L. , Garrity J. E. , Lobley D. K. , Martin K. L. , Griego A. E. , Ramacciotti J. P. , Bland S. N. , Lebedev S. V. , Bott S. C. , Ampleford D. J. , Palmer J. B. A. , Rapley J. , Hall G.
Published: November 2004

A technique for manufacturing wires with imposed modulation in radius with axial wavelengths as short as 1 mm is presented. Extruded aluminum 5056 with 15 μm diameter was masked and chemically etched to reduce the radius by ∼20% in selected regions. Characterized by scanning electron microscopy, the modulation in radius is a step function with a ∼10 μm wide conical transition between thick and thin segments, with some pitting in etched regions. Techniques for mounting and aligning these wires in arrays for fast z-pinch experiments will be discussed. Axially mass-modulated wire arrays of this type will allow the study of seeded Rayleigh-Taylor instabilities in z pinches, corona formation, wire initiation with varying current density in the wire core, and correlation of perturbations between adjacent wires. This tool will support magnetohydrodynamics code validation in complex three-dimensional geometries, and perhaps x-ray pulse shaping.
Photon-directed colloidal crystallization
Authors: Gong Tieying , Marr David W. M.
Published: November 2004

We have recently shown that electric fields can be used to induce rapid three-dimensional colloidal crystallization from isotropic colloidal dispersions through a combination of dielectrophoretic and electro-osmotic mechanisms. In this letter we demonstrate that light itself can be used to drive colloidal crystallization in a local and directed fashion under applied electric fields, allowing one to effectively write colloidal crystals in arbitrary and reversible patterns. This ability will provide great flexibility in the construction of colloid-based devices and allow their reversible operation as a function of an applied optical or electric field.
Mn
12
-acetate film pattern generated by photolithography methods
Authors: Kim K. , Seo D. M. , Means J. , Meenakshi V. , Teizer W. , Zhao H. , Dunbar K. R.
Published: November 2004

We demonstrate a straightforward way to lithographically fabricate Mn12-acetate thin film patterns on Si∕SiO2 surfaces, a significant step in light of the chemical volatility of this organic complex. Atomic force micrographs show low surface roughness. X-ray photoelectron spectroscopy data and magnetic measurements of the Mn12-acetate film indicate properties reminiscent of crystalline Mn12-acetate, suggesting that this approach can be used to fabricate lithographically patterned devices of Mn12-acetate.
A simple method for the preparation of transparent p-type Ca-doped CuInO2 films: Pulsed-laser deposition from air-sintered Ca-doped Cu2In2O5 targets
Authors: Teplin Charles W. , Kaydanova Tatiana , Young David L. , Perkins John D. , Ginley David S. , Ode Aiko , Readey Dennis W.
Published: November 2004

We report the deposition of single-phase undoped and Ca-doped CuInO2 thin films from a readily synthesized source target of Cu2In2O5—circumventing the very difficult fabrication of CuInO2 targets. X-ray diffraction shows that single-phase materials were obtained over a range of substrate temperatures and deposition pressures. p-type conductivities are measured to be ∼3×10−3S∕cm, comparable to the best films previously reported. The optical properties of the films were measured by spectroscopic ellipsometry.
White-light generation through ultraviolet-emitting diode and white-emitting phosphor
Authors: Kim Jong Su , Jeon Pyung Eun , Park Yun Hyung , Choi Jun Chul , Park Hong Lee , Kim Gwang Chul , Kim Tae Whan
Published: November 2004

White-light-emitting diodes are fabricated by using 375nm emitting InGaN chip with Sr3MgSi2O8:Eu2+ (blue and yellow) or Sr3MgSi2O8:Eu2+, Mn2+ (blue, yellow, and red). At a color temperature of 5892K, the color coordinates are x=0.32, y=0.33, and the color rendering index is 84%; at a color temperature of 4494K, the color coordinates are x=0.35, y=0.33, and the color rendering index is 92%. The blue (470nm) and yellow (570nm) emission bands are originated from Eu2+ ions, while the red (680) emission band is originated from Mn2+ ions in Sr3MgSi2O8 host. The energy transfer among three bands occurs due to the spectral overlap between emission and absorption bands. It is confirmed by the faster decay time of the energy donor. Our white-light-emitting diodes show higher color reproducibility, higher color stability on forward-bias current, and excellent color rendering index in comparison with a commercial YAG:Ce3+-based white-light-emitting diode.
The influence of scandium in effecting fragile to strong glass transition in aluminium-based alloys
Authors: Louzguine Dmitri V. , Sobu Shintaro , Inoue Akihisa
Published: November 2004

The “fragile”–“strong glass” transition in Al-based alloys is observed as a function of Sc content. The Sc-bearing alloys suffer glass transition as well as Sc-free Al0.84Y0.09Ni0.05Co0.02 alloy, however, the value of ΔCp decreases drastically and comes within the variation of the baseline at higher than 2 at. % of Sc. The studied glasses are free from pre-existing nuclei.
Giant low-temperature piezoresistance effect in AlAs two-dimensional electrons
Authors: Shkolnikov Y. P. , Vakili K. , De Poortere E. P. , Shayegan M.
Published: November 2004

We present piezoresistance measurements in modulation doped AlAs quantum wells where the two-dimensional electron system occupies two conduction band valleys with elliptical Fermi contours. Our data demonstrate that, at low temperatures, the strain gauge factor (the fractional change in resistance divided by the sample’s fractional length change) in this system exceeds 10 000. Moreover, in the presence of a moderate magnetic field perpendicular to the plane of the two-dimensional system, gauge factors up to 56 000 can be achieved. The piezoresistance data can be explained qualitatively by a simple model that takes into account intervalley charge transfer.
Near-field optical beam-induced currents in CdTe∕CdS solar cells: Direct measurement of enhanced photoresponse at grain boundaries
Authors: Smith S. , Zhang P. , Gessert T. , Mascarenhas A.
Published: November 2004

Using near-field optical beam induced current, we spatially resolve the photocurrent in polycrystalline CdTe∕CdS solar cells, and observe increased photocurrent collection at grain boundaries (relative to the intragrain volume). This observation supports previously reported hypotheses that grain boundaries present a hole-barrier, thereby assisting in charge separation at the grain boundaries in these devices. The results offer compelling evidence, in an actual working-device structure, of the role of grain boundaries in explaining the surprisingly high performance of these highly defected devices.
Fluorine-enhanced low-temperature wafer bonding of native-oxide covered Si wafers
Authors: Tong Q.-Y. , Gan Q. , Fountain G. , Enquist P. , Scholz R. , Gösele U.
Published: November 2004

The bonding energy of bonded native-oxide-covered silicon wafers treated in the HNO3∕H2O∕HF or the HNO3∕HF solution prior to room-temperature contact is significantly higher than bonded standard RCA1 cleaned wafer pairs after low-temperature annealing. The bonding energy reaches over 2000mJ∕m2 after annealing at 100 °C. The very slight etching and fluorine in the chemically grown oxide are believed to be the main contributors to the enhanced bonding energy. Transmission-electron-microscopic images have shown that the chemically formed native oxide at bonding interface is embedded with many flake-like cavities. The cavities can absorb the by-products of the interfacial reactions that result in covalent bond formation at low temperatures allowing the strong bond to be retained.
Low-contact-resistance and smooth-surface Ti∕Al∕Nb∕Au ohmic electrode on AlGaN∕GaN heterostructure
Authors: Nakayama T. , Miyamoto H. , Ando Y. , Okamoto Y. , Inoue T. , Hataya K. , Kuzuhara M.
Published: November 2004

We have achieved both low contact resistance and smooth surface morphology by using Ti∕Al∕Nb∕Au formed on an Al0.3Ga0.7N∕GaN heterostructure. A low contact resistance of less than 0.6Ω∕mm was reproducibly recorded after thermal treatment with a wide range of annealing temperature from 830 to 1000°C and annealing time from 10 to 300s. It was found that root-mean square surface roughness of under 35nm was obtained with all the annealing conditions investigated. In consideration of surface roughness and reproducibility, the most suitable annealing condition was 850°C for 100s, which leads to a contact resistance and a specific contact resistivity of 0.48Ω∕mm and 5×10−6Ω∕cm2, respectively.
Imaging the degradation of polymer light-emitting devices
Authors: Dane Justin , Gao Jun
Published: November 2004

Anode-to-cathode spatially resolved study of polymer light-emitting device degradation has been performed based on a massive planar device structure. The unique device configuration of the extremely large planar frozen-junction light-emitting electrochemical cell allows for the study of device degradation by direct imaging. Constant current stress for an extended period results in a very unusual net luminance increase as opposed to luminance decay. Imaging of the emission zone has shown changes that are consistent with polymer degradation by the loss of electron mobility.
High power quantum cascade lasers operating at λ≃87 and 130μm
Authors: Ajili Lassaad , Scalari Giacomo , Faist Jérôme , Beere Harvey , Linfield Edmund , Ritchie David , Davies Giles
Published: November 2004

We report high power quantum cascade lasers operating above liquid nitrogen temperature at λ≃87 and 130μm based on a bound-to-continuum transition. For λ≃87μm, 56mW peak power in pulsed operation and 50mW continuous wave operation at 10K are demonstrated. At λ≃130μm, a peak power of 50mW was achieved and devices operated in continuous wave reached a maximum temperature of 53K with an optical power of 11.5mW at T=10K. Lifetimes are extracted from the scaling of the transport and laser parameters as a function of size using a simple rate equation model.
Low temperature annealing of electron irradiation induced defects in 4H-SiC
Authors: Castaldini Antonio , Cavallini Anna , Rigutti Lorenzo , Nava Filippo
Published: November 2004

Low temperature annealing of electron irradiation-induced deep levels in 4H-SiC is reported. The major deep level transient spectroscopy peak S2 associated with the energy level at Ec−0.39eV disappears in the temperature range 360–400K, and some rearrangement of the peak S3, associated with the defect Z1∕Z2 with energy level at Ec−0.5∕Ec−0.65eV occurs in the temperature interval 400–470K. A net free charge carrier concentration increase goes along with the disappearance of peak S2 at Ec−0.39eV, whereas the charge collection efficiency of the diode does not experience any significant change. An interpretation of the annealing of peak S2 on a microscopic scale is given.
Rayleigh scattering, mode coupling, and optical loss in silicon microdisks
Authors: Borselli Matthew , Srinivasan Kartik , Barclay Paul E. , Painter Oskar
Published: November 2004

High refractive index contrast optical microdisk resonators fabricated from silicon-on-insulator wafers are studied using an external silica fiber taper waveguide as a wafer-scale optical probe. Measurements performed in the 1500nm wavelength band show that these silicon microdisks can support whispering-gallery modes with quality factors as high as 5.2×105, limited by Rayleigh scattering from fabrication induced surface roughness. Microdisks with radii as small as 2.5μm are studied, with measured quality factors as high as 4.7×105 for an optical mode volume of 5.3(λ∕n)3.
Structural and interface properties of an AlN diamond ultraviolet light emitting diode
Authors: Miskys C. R. , Garrido J. A. , Hermann M. , Eickhoff M. , Nebel C. E. , Stutzmann M. , Vogg G.
Published: November 2004

Two practically fully relaxed AlN domains were identified by x-ray diffractometry for AlN grown on (100) diamond. The epitaxial orientation relationships (0001)[101¯0] AlNI‖(100)[011] diamond for the predominant AlN domain (type I) and (0001)[1¯21¯0] AlNII‖(100)[011] diamond for the second domain (type II) are obtained. Surface morphology measurements corroborate the good structural quality of the AlN film. In addition, the intrinsic built-in voltage of a n-AlN∕p-diamond diode was determined as 1.15V. By spectrally resolved photocurrent measurements, the ultraviolet electroluminescence emission was confirmed to originate at the heterojunction interface, and is most probably due to a defect center.
Axial strain redistribution resulting from off-axis ply cracking in polymer composites
Authors: Katerelos Dionisis G. , Galiotis Costas
Published: November 2004

The initial mode of damage in multidirectional composites is the accumulation of matrix cracks in the off-axis plies. Remote laser Raman spectroscopy, using aramid (Kevlar 49®) fibers as Raman strain sensors, has been employed to monitor the local strains in cracked crossply composites. The strain magnification in the 0° ply caused by 90° matrix cracking are measured at different levels of loading. A relationship between the values of strain magnification and the distance between the position of the fibers sensors vis-à-vis the crack front has been established. The effect of damage progression within the 0° plies on the remaining∕surviving glass fibers is modeled satisfactorily and verified against predictions on the basis of a generalized plane strain model by assuming that the 90° ply “expands” in relative size against the 0° ply thickness.
Conventional δf-particle simulations of electromagnetic perturbations with finite elements
Authors: Mishchenko Alexey , Hatzky Roman , Könies Axel
Published: November 2004

The possibility of electromagnetic particle-in-cell simulations with a conventional δf approach is shown in slab geometry using finite elements. Both the ion-temperature-gradient driven mode and the shear Alfvén wave are reproduced and benchmarked with the analytical linear dispersion relation. Particularly, the Alfvén wave is simulated successfully at the limit k⊥→0.
Onset detection of solid-state phase transition in estrogen-like chemical via terahertz transmission spectroscopy
Authors: Quema Alex V. , Goto Masahiro , Sakai Masahiro , Ouenzerfi Riadh El , Takahashi Hiroshi , Murakami Hidetoshi , Ono Shingo , Sarukura Nobuhiko , Janairo Gerardo
Published: November 2004

Solid-state phase transition onset in an endocrine-disrupting estrogen-like chemical (1,4-naphthol) is detected using terahertz transmission spectroscopy. The appearance of two absorption peaks and the sudden upsurge of terahertz-radiation power at 210 K indicate the onset of the solid-state phase transition. Differential scanning microscopy reveals a first-order phase transition at around 240 K while temperature-dependent x-ray diffraction analysis shows the occurrence of such phenomenon also at around 240 K. This demonstrates the sensitivity of the terahertz spectroscopic technique to phase transition since it provides a signal before such phenomenon actually occurs.
Influence of the gate dielectric on the mobility of rubrene single-crystal field-effect transistors
Authors: Stassen A. F. , de Boer R. W. I. , Iosad N. N. , Morpurgo A. F.
Published: November 2004

We have performed a comparative study of rubrene single-crystal field-effect transistors fabricated using different materials as gate insulator. For all materials, highly reproducible device characteristics are obtained. The achieved reproducibility permits one to observe that the mobility of the charge carriers systematically decreases with increasing the dielectric constant of the gate insulator, the decrease being proportional to ε−1. This finding demonstrates that the mobility of carriers in organic single-crystal field-effect transistors is an intrinsic property of the crystal/dielectric interface and that it does not only depend on the specific molecule used.
Pentacene field-effect transistors on plastic films operating at high temperature above 100°C
Authors: Sekitani Tsuyoshi , Iba Shingo , Kato Yusaku , Someya Takao
Published: November 2004

We have manufactured pentacene field-effect transistors (FETs) on polyimide base films with polyimide gate dielectric layers, and characterized electronic performance and surface morphology with application of heat in the temperature range from 30to210°C. It is found that mobility of pentacene FETs is enhanced from 0.27to0.71cm2∕Vs when measurement temperatures varies from 30to160°C under light-shielding nitrogen environment. To investigate postannealing effects, we have measured transfer curves at 30°C after many heat cycles at various temperatures. Mobility is almost constant even after annealing at 130°C, showing the excellent stability of the present device at high temperatures.
Blue emission from CaS:Cu,F thin-film electroluminescent device fabricated on Si substrate
Authors: Hakamata Shintaro , Ehara Mami , Fukada Haruki , Kominami Hiroko , Nakanishi Yoichiro , Hatanaka Yoshinori
Published: November 2004

Thin-film electroluminescent (TFEL) devices were fabricated on Si substrates by using SiO2 and Y2O3 films as insulator layers, and ZnS films as buffer layers. The device annealed at 850°C for 10min in Ar showed a purple EL with a peak at 425nm. Commission Internationale de l’Eclairage (CIE) color coordinates of x=0.217, y=0.223 under driving at 220V0−p of 1kHz trapezoidal wave. The purple EL from CaS:Cu TFEL device could be achieved, although luminance was weak, and a little longer wavelength component was included.
Organic complementary-like inverters employing methanofullerene-based ambipolar field-effect transistors
Authors: Anthopoulos Thomas D. , de Leeuw Dago M. , Cantatore Eugenio , Setayesh Sepas , Meijer Eduard J. , Tanase Cristina , Hummelen Jan C. , Blom Paul W. M.
Published: November 2004

We demonstrate a complementary-like inverter comprised of two identical ambipolar field-effect transistors based on the solution processable methanofullerene [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The transistors are capable of operating in both the p- and n-channel regimes depending upon the bias conditions. However, in the p-channel regime transistor operation is severely contact limited. We attribute this to the presence of a large injection barrier for holes at the Au∕PCBM interface. Despite this barrier the inverter operates in both the first and third quadrant of the voltage output versus voltage input plot exhibiting a maximum gain in the order of 20. Since the inverter represents the basic building block of most logic circuits we anticipate that other complementary-like circuits can be realized by this approach.
Electronic structure of secondary phases in Cu-rich CuGaSe2 solar cell devices
Authors: Fuertes Marrón D. , Glatzel Th. , Meeder A. , Schedel-Niedrig Th. , Sadewasser S. , Lux-Steiner M. Ch.
Published: November 2004

Kelvin probe force microscopy in ultrahigh vacuum was used to image the electronic structure of thin-film solar cell cross sections based on as-grown Cu-rich CuGaSe2 absorbers. We observe different secondary phases in the absorber film. A p-type degenerate Cu2−xSe phase is identified by a higher work function (Φ∼5.35eV) than CuGaSe2 (Φ∼5.1eV), allowing good contrast mappings of both phases within the absorber film. Besides entire Cu2−xSe crystallites we also observed this secondary phase segregated as an interfacial layer along CuGaSe2 grain boundaries. An additional high-work function phase at the CuGaSe2∕window junction is attributed to the formation of an improper CuS buffer layer during chemical bath processing. The detrimental effect of these secondary phases on the solar cell performance is discussed.
Room temperature ferromagnetism in cubic GaN epilayers implanted with Mn+ ions
Authors: Chitta V. A. , Coaquira J. A. H. , Fernandez J. R. L. , Duarte C. A. , Leite J. R. , Schikora D. , As D. J. , Lischka K. , Abramof E.
Published: November 2004

Mn ions were implanted in p-type cubic GaN at doses from 0.6 to 2.4×1016cm−2 at 200 keV energy. A 200-nm-thick epitaxial layer, grown by molecular beam epitaxy on GaAs(001) substrate, is used for the Mn implantation. The Mn implanted samples were subjected to an annealing at 950 °C for 1–5 min. The structural quality of the samples was investigated by high resolution x-ray diffraction and Raman spectroscopy. The annealing procedure leads to a significant increasing of the crystalline quality of the samples. Hysteresis loops were observed for all cubic GaMnN annealed samples and ferromagnetism was detected up to room temperature.
Study on the growth mechanism of pentacene thin films by the analysis of island density and island size distribution
Authors: Tejima M. , Kita K. , Kyuno K. , Toriumi A.
Published: November 2004

The growth mechanism of pentacene thin films on a thermally grown SiO2 on Si(100) substrate is examined in detail for a wide substrate temperature range (223–342K) by analyzing the saturated island density and island size distribution. It is found that the log plot of the saturated island density as a function of inverse substrate temperature can be well represented by two straight lines and that these two regions have different critical cluster sizes for nucleation which is independently confirmed by island size distribution analysis. It is concluded that the nucleation behavior of pentacene thin films can be explained by the diffusion-mediated growth model well known in inorganic thin-film growth.
1
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f
noise in single-walled carbon nanotube devices
Authors: Snow E. S. , Novak J. P. , Lay M. D. , Perkins F. K.
Published: November 2004

We report the scaling behavior of 1∕f noise in single-walled carbon nanotube devices. In this study we use two-dimensional carbon nanotube networks to explore the geometric scaling of 1∕f noise and find that for devices of a given resistance the noise scales inversely with device size. We have established an empirical formula that describes this behavior over a wide range of device parameters that can be used to assess the noise characteristics of carbon nanotube-based electronic devices and sensors.
Origin of ferromagnetism in ZnO∕CoFe multilayers: Diluted magnetic semiconductor or clustering effect?
Authors: Huang J. C. A. , Hsu H. S. , Hu Y. M. , Lee C. H. , Huang Y. H. , Lin M. Z.
Published: November 2004

Epitaxial growth of (0001) oriented [ZnO(20Å)∕Co0.7Fe0.3(xÅ)]25 multilayers (MLs) with nominal thickness x=1, 2 and 5 has been prepared on α-Al2O3 (0001) substrate by ion-beam sputtering. The magnetic properties over a temperature range of 6–350K and structures probing by x-ray absorption spectroscopy (XAS) are reported. Above room-temperature ferromagnetism has been observed for x=1 and x=2 MLs, while superparamagnetic behavior dominates for x=5 ML. The field-cooled magnetization-temperature M(T) curves of x=1 and x=5 MLs can be fitted by a standard three-dimensional (3D) spin-wave and a Curie–Weiss model, respectively. For x=2 ML, however, neither a 3D spin-wave nor a Curie–Weiss model, but a combination of the two fits the M-T curve. The XAS studies together with the magnetic measurements further reveal that x=1 sample behaves as a diluted magnetic semiconductor (DMS) ML, while x=2 ML shows a mixed structure consisting of a minor component of DMS and a major component of CoFe clusters. A predominant clustering phase appears for x=5 ML.