bluuebunny/crossref_metadata_2025 huggingface dataset:
Strip inverse-configuration photopyroelectric technique to measure the thermal conductivity of bulk samples
Authors: Manohar Srirang , Asokan S.
Published: July 2002

The strip inverse-configuration photopyroelectric technique to measure the thermal conductivity of bulk samples of metals, semiconductors, and insulators is presented. It utilizes a narrow (500 μm wide) strip of a 9 μm thick pyroelectric sensor in an inverse configuration. A mathematical model is outlined that yields an expression for the output voltage of the pyroelectric sensor following heat dissipation into the sample, in a frequency range where the proposed measurement is possible. Experimentally, the sensor was operated in an “isothermal-voltage” mode to identify the frequency regime within which the measurement of the thermal conductivity of representative samples was possible after suitable calibration of the system.
Characteristics and discussion of self-pumped phase conjugation in a series of BaTiO3 crystals
Authors: Xu Xinguang , Shao Zongshu , Mu Xiaodong , Du Chenlin , Wang Zhengping , Xu Haiqing , Luo Haosu
Published: July 2002

This letter presents the experimental results of self-pumped phase conjugation (SPPC) in barium titanate (BaTiO3) crystals doped with Rh or Ce. It has been shown that the main parameters of SPPC depend very strongly on the concentration of dopants, the incident angles, and the cut type of the crystals. Some qualitative explanation of the experimental results are also given.
Improvements in electrical properties of hydrogen-treated SrBi2Ta2O9 capacitors with chemical vapor deposited Pt top electrode
Authors: Choi Eun-Suck , Yoon Soon-Gil , Lee Won-Jae
Published: July 2002

The ferroelectric property and leakage current of metalorganic chemical vapor deposition (MOCVD)-Pt/SrBi2Ta2O9 (SBT)/Pt and dc-sputtered Pt/SBT/Pt capacitors are evaluated with the microstructures of Pt top electrodes before and after hydrogen forming gas anneal. The SBT films with MOCVD-Pt top electrodes of large grain size and dense structure show a surprising decrease of leakage current density and still exhibit ferroelectric properties after hydrogen forming. On the other hand, SBT films with dc-sputtered Pt top electrodes of small grain size show an increase of leakage current density and then polarization switching properties cannot be measured due to fairly high leakage current. The microstructures of Pt top electrodes play an important role in improving the ferroelectric and leakage current characteristics after forming gas anneal. MOCVD-Pt top electrodes can prevent the complete loss of ferroelectricity and improve the leakage current properties during forming gas treatment.
Oriented crystallization of GaSb on a patterned, amorphous Si substrate
Authors: Yi S. S. , Moran P. D. , Zhang X. , Cerrina F. , Carter J. , Smith H. I. , Kuech T. F.
Published: July 2002

Oriented crystallization of GaSb on patterned, oxidized Si substrates was achieved by metalorganic chemical vapor deposition. The Si substrate was formed by patterning an array of inverted square pyramids having {111} sidewall facets, using lithography and anisotropic etching in KOH. The orientation and structure of GaSb crystals, at various stages of the growth, were examined by scanning electron microscopy and x-ray diffraction. X-ray diffraction pole figure analysis shows that {111} planes of GaSb are predominantly parallel to the {111} planes of the inverted pyramids. Extra (111) spots observed in the x-ray diffraction pole figure are interpreted in terms of multiple twinning of GaSb.
DC field dependent properties of Na0.5K0.5NbO3/SiO2/Si structures at millimeter-wave frequencies
Authors: Abadei S. , Gevorgian S. , Cho C.-R. , Grishin A. , Andreasson J. , Lindbäck T.
Published: July 2002

Dielectric properties of laser-ablated 0.5-μm-thick c-axis epitaxial Na0.5K0.5NbO3 films on high-resistivity (7.7 Ω cm) silicon SiO2/Si substrate are studied experimentally at frequencies up to 40 GHz. For measurements, planar 0.5-μm-thick gold electrodes (interdigital and straight slot) are photolithography defined on the top surface of Na0.5K0.5NbO3 films. The slot width between the electrodes is 2 or 4 μm. 13% capacitance change at 40 V dc bias and Q factor more than 15 are observed at 40 GHz, which makes the structure useful for applications in electrically tunable millimeter-wave devices.
Near-field photoreflectance spectroscopy of quantum well structures
Authors: Cho Yong-Hoon , Kim Dai-Sik , Jhe Wonho
Published: July 2002

We present near-field photoreflectance (NPR) spectroscopic studies of GaAs/Al0.3Ga0.7As quantum well structures using a near-field scanning optical microscope with either an uncoated or a metal-coated tapered optical fiber probe. The NPR method provides advantages over conventional optical microscopic ones: (i) higher signal-to-noise ratio, (ii) lower temperature-sensitivity of the signal, and (iii) more information about higher electronic energy states. We also discuss the feasibility of a imaging with high resolution and contrast by using the NPR method.
Raman spectroscopy of carbon-induced germanium dots
Authors: Guedj C. , Beyer A. , Müller E. , Grützmacher D.
Published: July 2002

Raman spectroscopy is used to study C and Ge diffusion in multilayers of C-induced Ge dots deposited on Si(100). The initial Ge content is fixed to 2 ML and the C precoverage varied from 0.1 to 0.3 ML. The resulting concentration of isolated substitutional C atoms depends on the C precoverage and the thermal annealing performed after growth. C atoms are mostly localized in the areas around the dots, due to the repulsive Ge–C interaction. When C is added, the interface around the burried dots becomes sharper, and less Ge alloying occurs. C mainly increases the strain contrast around the dots and induces a strain-enhanced Ge interdiffusion, even at 650 °C. At 800 °C, Ge and C interdiffuse simultaneously.
Anisotropy of the vortex creep in a YBa2Cu3O7−x single crystal with unidirectional twin boundaries
Authors: Bondarenko A. V. , Revyakina M. G. , Prodan A. A. , Obolenskiı̆ M. A. , Vovk R. V. , Arouri T. R.
Published: July 2002

Vortex creep in a single crystal containing unidirectional twin boundaries (TBs) is investigated at temperatures of 82–87 K in a special experimental geometry: J‖ab, J‖TB, H⊥J, with α≡∠H,ab as a variable parameter. It is shown that in low magnetic fields the TBs alter the configuration of the structure of the flux lines at angles of misorientation θ between the magnetic field vector H and the planes of the TBs of up to 70°: at angles θ<70° a part of the flux line is trapped by the planes of the TBs. It is shown that a TB is an efficient pinning center for the motion of the vortices perpendicular to the plane of the TB, and therefore in low magnetic fields at angles θ<70° a directed motion of the vortices along the planes of the TBs occurs. The angle dependence of the activation energy for a plastic mechanism of flux creep is determined, and it is found to agree with the theoretical estimates made. For an orientation of the vector H close to the ab plane of the crystal, the maximum of the angle dependence of the measured “critical” current JcE(α) observed for the the H‖ab orientation of the field vector in low magnetic fields gives way to a minimum at higher magnetic fields; this is explained by a change from single-vortex creep to collective creep as the magnetic field is increased.
Modeling of electronic transport in scanning tunneling microscope tip–carbon nanotube systems
Authors: Yamada Toshishige
Published: July 2002

A model is proposed for two observed current–voltage (I–V) patterns in a recent experiment with a scanning tunneling microscope tip and a carbon nanotube [Collins et al., Science 278, 100 (1997)]. We claim that there are two mechanical contact modes for a tip (metal)–nanotube (semiconductor) junction (1) with or (2) without a tiny vacuum gap (0.1–0.2 nm). With the tip grounded, the tunneling case in (1) would produce large dI/dV with V>0, small dI/dV with V<0, and I=0 near V=0 for an either n or p nanotube; the Schottky mechanism in (2) would result in I≠0 only with V<0 for an n nanotube, and the bias polarities would be reversed for a p nanotube. The two observed I–V patterns are thus entirely explained by a tip–nanotube contact of the two types, where the nanotube must be n-type.
Smart Darting Monte Carlo
Authors: Andricioaei Ioan , Straub John E. , Voter Arthur F.
Published: July 2002

The “Smart Walking” Monte Carlo algorithm is examined. In general, due to a bias imposed by the interbasin trial move, the algorithm does not satisfy detailed balance. While it has been shown that it can provide good estimates of equilibrium averages for certain potentials, for other potentials the estimates are poor. A modified version of the algorithm, Smart Darting Monte Carlo, which obeys the detailed balance condition, is proposed. Calculations on a one-dimensional model potential, on a Lennard-Jones cluster and on the alanine dipeptide demonstrate the accuracy and promise of the method for deeply quenched systems.
Evidence of a stable binary CdCa quasicrystalline phase
Authors: Jiang J. Z. , Jensen C. H. , Rasmussen A. R. , Gerward L.
Published: July 2002

Quasicrystals with a primitive icosahedral structure and a quasilattice constant of 5.1215 Å have been synthesized in a binary Cd–Ca system. The thermal stability of the quasicrystal has been investigated by in situ high-temperature x-ray powder diffraction using synchrotron radiation. It is demonstrated that the binary CdCa quasicrystal is thermodynamic stable up to its melting temperature. The linear thermal expansion coefficient of the quasicrystal is 2.765×10−5 K−1.
Enhanced peak power and short pulse operation of planar waveguide CO2 lasers
Authors: Villarreal F. , Murray P. R. , Baker H. J. , Hall D. R.
Published: July 2002

We report a large peak power enhancement and reduction in pulse width for planar waveguide carbon dioxide lasers. Gain modulation through rf discharge power switching produces trains of laser pulses with peak power levels at up to 38 times the cw power level, with a pulse duration as low as 10 μs. Operation at repetition rates in the kHz region preserves the average power (100 W) of the normal cw/long pulse mode of operation. The laser is shown to operate close to the predicted boundaries dictated by thermal loading of the discharge.
Near-field optical microscopy with a vibrating probe in aqueous solution
Authors: Mannelquist Anders , Iwamoto Hideki , Szabo Gabor , Shao Zhifeng
Published: July 2002

We show that with an appropriately configured scanning quartz pipette coated with aluminum, a near-field scanning optical microscope (NSOM) can be constructed to operate in aqueous solution for applications in biology. Many of the technical limitations associated with a scanning pipette were circumvented by introducing a small modulation of the distance between the pipette and the sample. We show that this ac method allows the pipette to be positioned very close to the sample surface and is robust in obtaining reproducible NSOM images in solution. This approach is also compatible with fluorescence imaging and fluorescence resonance energy transfer, and should further facilitate the use of NSOM in various areas of cell biology where high resolution is considered to be critical.
Resonance frequency shifts caused by the friction of a drop of water in air: An approach to estimate shear forces in scanning probe microscopies
Authors: Müller A.-D. , Müller F.
Published: July 2002

In scanning near-field optical microscopy, scanning ion conductance microscopy and for localized electrochemical deposition out of micropipettes, the detection of shear forces between the tip and sample is one of the most common methods of distance control. Here, pulled micropipettes were utilized to form an evaporating drop of water whose frictional force in air causes a specific resonance shift of the tip vibration. This resonance shift and the amplitude at the resonance were investigated with regard to their dependence on the drop diameter. In order to calculate the friction, the tip is approximated as a damped harmonic oscillator. The typical range of the shear forces in scanning probe microscopies is estimated to be between 1 pN and 0.1 nN.
Thermoluminescence for nonlinear heating profiles with application to laser heated emissions
Authors: Lawless John L. , Lo D.
Published: July 2002

A general formula is found to predict thermoluminescence emission over a wide range of heating profiles. This is particularly useful for rapid laser heating which generates very nonlinear temperature–time profiles. Special cases of the general formula are considered for power-law and logarithmic temperature–time curves. The results compare well to previous CO2 laser heated thermoluminescence experiments. The agreement between theory and experiment extends over several orders of magnitude change in the heating rate.
Reduction in surface recombination of GaInAsP microcolumns by CH4 plasma irradiation
Authors: Ichikawa Hiroyuki , Inoshita Kyoji , Baba Toshihiko
Published: July 2002

We evaluated the surface recombination velocity vs of 1.55 μm GaInAsP microcolumns through the measurement of carrier lifetime using the phase-resolved spectroscopy. We investigated various surface treatments and confirmed that vs was reduced to nearly half of that for as-etched microcolumns by CH4 electron cyclotron resonance plasma irradiation. This result was ensured by the two- to fivefold increase in photoluminescence intensity. The secondary ion mass spectroscopy analysis suggested that the reduction in vs was attributable to the deposition of a polymer, the hydrogenated hard carbon, etc., and/or a carbon deep level formed near the surface.
Growth and control of nanoprotrusions on iridium field emitters
Authors: Chalamala Babu R. , Reuss Robert H. , Dean Kenneth A.
Published: July 2002

We report on the direct observation of the growth of nanoprotrusions on iridium field-emission tips. For clean, protrusion-free field emitters, the field emission originated from crystal planes with low-work-function values. However, with continuous operation, we observed the growth of nanoprotrusions on crystalline planes where there was initially no detectable emission. The protrusions were estimated to be approximately 2–3 nm in diameter and 5–15 nm in height. Protrusion growth led to an increase in field-emission current by several orders of magnitude. However, the tips were destroyed when operated with sustained emission current values greater than 10 μA. We found that stable operation and control of protrusion growth can be achieved by either progressively reducing the anode voltage or by adding a series resistor.
Dielectric properties of La3Ga5SiO14 at microwave frequencies between 10 and 400 K
Authors: Giordano Vincent , Kersalé Yann , Boy Jean-Jacques
Published: July 2002

We report measurements of dielectric permittivity and dielectric losses at microwave frequencies of lanthanum gallium silicate as a function of temperature. The dielectric rod resonator method was used to evaluate the two relative permittivity tensor components εt and εz of this uniaxial dielectric crystal. Between 10 and 400 K, εt varies from 18.92 to 19.65 whereas εz ranges from 60.81 to 46.66. Around 300 K, the temperature coefficients of εt and εz have opposite signs and are equal to 130 and −720 ppm/K, respectively. This characteristic enables one to design a self-compensated microwave resonator presenting a low frequency temperature sensitivity. For the measured dielectric sample the dielectric losses range from 1×10−4 to 5×10−6 between 300 and 20 K and are actually limited by the crystal quality.
Magnetoelastic effects in low-dimensional magnetic systems
Authors: Zvyagin A. A. , Zvyagina G. A.
Published: July 2002

We consider a new realization of magnetoelastic interactions in low-dimensional magnetic systems. We show that low-dimensional spin systems are unstable with respect to the spontaneous appearance of alternating distortions of the positions of the three-dimensional nonmagnetic atoms (ligands) that surround the magnetic ions. Those distortions are supplemented by the spontaneous onset of alternating effective g factors of the magnetic ions in the phase with short-range interactions. We discuss the possibility of observing the effect in a uniform external magnetic field, which in the situation considered produces both magnetization and staggered magnetization of the magnetic subsystem. The connection of the proposed theory with recent experiments on effectively low-dimensional magnetic systems (organic spin chains, heavy-fermion compounds, rare-earth molybdates) is discussed.
Spontaneous magnetostriction in the Gd–Y system: analysis of phase transformations
Authors: Beznosov A. B. , Fertman E. L. , Eremenko V. V. , Pal-Val P. P. , Popov V. P. , Chebotayev N. N.
Published: July 2002

The transformations of the states of the magnetic and lattice subsystems of Gd100−xYx (x=0,5.5, 7.5, 10.2) alloys are studied at temperatures 5–370 K in magnetic fields up to 4 kOe. The temperature dependences of elastic moduli, thermal expansion, low-field magnetization, and magnetic anisotropy parameters are obtained. The linear spontaneous striction ΔL(T)/L=ξη2 is analyzed, and the effective order parameters η and magnetostrictive parameters ξ are evaluated for the four magnetic phases (canted ferromagnetic, deformed ferromagnetic helix, ferromagnetic helix, and the ferromagnetic cone, respectively): ξcf=2.2×10−5, ξdh=−5.3×10−5, ξfh=7.1×10−5, ξfc=1.4×10−3.
Surface morphology evolution in highly mismatched Sb-graded buffer layers on GaAs
Authors: Chen Eric B. , Paine David C. , Uppal Parvez N. , Nichols Kirby , Ahearn John S.
Published: July 2002

Ternary GaAs1−ySby and quaternary Al0.5Ga0.5As1−ySby compositionally step-graded buffer structures graded to a 4.6% mismatch on GaAs were evaluated by transmission electron microscopy. Cross-sectional bright field imaging (g=004) revealed the presence of compositional modulations parallel to the (001) interface with a period of 1–2 nm that were used to establish the morphology of the growth surface during buffer layer deposition. Analysis of the Sb-graded ternary structures shows that the growth surface remained planar with a maximum peak-to-valley height of 4.4±0.6 nm located near the topmost layer. A threading dislocation density of 108–109 cm−2 was measured in both types of buffer layers and an improvement in peak-to-valley amplitude (2.3±0.5 nm vs 4.4±0.6 nm) was observed in the Al-containing quaternary alloys.
Studies of carrier dynamics in unintentionally doped gallium nitride bandtail states
Authors: Sun Chi-Kuang , Liang Jian-Chin , Yu Xiang-Yang , Keller Stacia , Mishra Umesh K. , DenBaars Steven P.
Published: July 2002

Ultrafast carrier dynamics of bandtail states in an unintentionally doped gallium nitride sample was investigated using femtosecond transient transmission measurements. The transient responses of shallow bandtail states resemble those of above band gap extended states. The transient responses of the deep bandtail states are, on the other hand dominated by carrier transfer into the lower energy states through phonon assisted tunneling suggesting that the deep bandtail states are localized states.
Influence of the dipole interaction energy on clustering in InxGa1−xN alloys
Authors: Miller E. J. , Yu E. T.
Published: July 2002

The interactions of the polarization-induced dipole moments at each unit cell in InxGa1−xN alloys have been studied using analytical electrostatic dipole energy calculations to determine their potential influence on local material composition. Clustering of In atoms along the [0001] direction and anticlustering of In in the (0001) plane are shown to be energetically favorable. Comparisons of the dipole interaction energy to the strain energy and the energy associated with the decreased entropy of the ordered configurations show that the dipole interaction energy could have a substantial influence on local composition in InxGa1−xN alloys.
Optimization of elastomeric phase masks for near-field photolithography
Authors: Li Zhi-Yuan , Yin Yadong , Xia Younan
Published: July 2002

Rigorous electromagnetic theory has been used to optimize elastomeric phase masks for generating sub-100-nm parallel lines by means of near-field photolithography J. A. Rogers et al., Appl. Phys. Lett. 70, 2658 (1997). In the near-field region, the scattering effect is so strong that the scalar theory is no longer adequate: A bright line was found adjacent to the dark line previously predicted by the scalar theory, and the widths of both lines were found to be insensitive to the refractive index of the photoresist. The simulation results are in good agreement with experimental studies, which showed that the bright and dark lines could be used to generate trenches and lines in a positive-tone photoresist by controlling the exposure time. Our simulations also indicate that parallel lines as small as 50 nm can be generated by adjusting the parameters of the phase mask.
Surface anchoring energy modulation in liquid crystal cells with mixed conductor boundary layers
Authors: Strangi Giuseppe , Versace Carlo , Scaramuzza Nicola
Published: July 2002

This work concerns the experimental analysis of the influence of the surface charge on the anchoring energy of a nematic liquid crystal (NLC). The study has been carried out on sandwich like cells in which the semitransparent indium tin oxide electrodes were covered by a sputtered tungsten trioxide film to supply an extra amount of surface charge. We found that the huge amount of tungsten-oxide protons injected at the oxide-NLC interface play a key role in weakening the surface anchoring energy. To estimate the surface anchoring energy during a bias-controlled injection process, a photopolarimetric technique has been used. The result highlights the importance of the polarized surface on the anchoring breaking mechanism.
Interface studies of tungsten gate metal–oxide–silicon capacitors
Authors: Shang Huiling , White Marvin H. , Guarini Kathryn W. , Solomon Paul , Cartier Eduard , McFeely Fenton R. , Yurkas John J. , Lee Wen-Chin
Published: July 2002

The Si/SiO2 interface in 100-nm-thick chemical vapor deposition (CVD) tungsten gate metal–oxide–semiconductor (MOS) structures exhibits high interface state densities (Dit0>5×1011/cm2 eV) after conventional forming gas anneals over varying temperatures and times. In this letter, we show this is a consequence of the low diffusivity and solubility of molecular hydrogen in tungsten and the high temperature CVD process. We have discovered that atomic hydrogen is more effective in passivating tungsten gate MOS interfaces because of its higher diffusivity in tungsten. Atomic hydrogen can be produced (1) by the reaction of aluminum with water vapor when aluminum is evaporated on the top of tungsten, (2) by hydrogen implantation, and (3) by hydrogen plasma. These techniques can passivate the Si/SiO2 interface effectively in MOS structures (Dit0<5×1010/cm2 eV) with 100-nm thick CVD tungsten gates.
Fermi-liquid cyclotron modes in quasi-two-dimensional conductors
Authors: Kirichenko O. V. , Peschansky V. G.
Published: July 2002

The spectrum of normal vibrational modes propagating along the direction of an external static magnetic field in conductors with a sharply anisotropic dispersion relation of the charge carriers is obtained with allowance for their Fermi-liquid interaction.
Recovery dynamics in proton-bombarded semiconductor saturable absorber mirrors
Authors: Gopinath Juliet T. , Thoen Erik R. , Koontz Elisabeth M. , Grein Matthew E. , Kolodziejski Leslie A. , Ippen Erich P. , Donnelly Joseph P.
Published: July 2002

Reduction of device response time, resulting from the proton bombardment of InGaAs/InP-based semiconductor saturable absorbers, was studied experimentally using an ultrafast degenerate, cross- polarized pump-probe technique. Proton bombardment is shown to reduce device response times to ∼1 ps at low optical excitation densities. Under high excitation, the device dynamics are dominated by induced absorption. The extended recovery of highly excited carriers appears to be less sensitive to defects created by bombardment. Mode locking was demonstrated with the proton-bombarded samples in an erbium-doped fiber laser.
High electric field transport in modulation-doped InAs self-assembled quantum dots for high-frequency applications
Authors: Park Hee Seok , Mokerov Vladimir G.
Published: July 2002

Modulation-doped N–AlGaAs (GaAs/InAs/GaAs/InAs)/GaAs-heterostructures with InAs-quantum dots (QDs) have been grown and investigated. Using these structures, modulation-doped field-effect transistors (MODFETs) have been fabricated and analyzed. It has been observed that they have the anomalous two-step shape in the current–voltage curve in contrast to the conventional curve with saturation. The saturation current Idss for the second step practically does not depend on the gate bias UG, showing that the concentration of electrons participating in the current flow becomes independent of UG. It has been demonstrated that the QD-MODFETs present a promising type of the hot electron devices for high frequency applications.
Dielectric spectroscopy in aqueous solutions of oligosaccharides: Experiment meets simulation
Authors: Weingärtner Hermann , Knocks Andrea , Boresch Stefan , Höchtl Peter , Steinhauser Othmar
Published: July 2002

We report the frequency-dependent complex dielectric permittivity of aqueous solutions of the homologous saccharides D(+)-glucose, maltose, and maltotriose in the frequency range 200 MHz⩽ν⩽20 GHz. For each solute, solutions having concentrations between 0.01 and 1 mol dm−3 were studied. In all measured spectra two dispersion/loss regions could be discerned. With the exception of the two most concentrated maltotriose solutions, a good description of the spectra by the superposition of two Debye processes was possible. The amplitudes and correlation times of the glucose and maltose solutions determined from fits of the experimental data were compared to those obtained in an earlier molecular dynamics study of such systems; the overall agreement between experiment and simulation is quite satisfactory. A dielectric component analysis of the simulation results permitted a more detailed assignment of the relaxation processes occurring on the molecular level. The physical picture emerging from this analysis is compared with traditional hydration models used in the interpretation of measured dielectric data. It is shown that the usual standard models do not capture an important contribution arising from cross terms due to dipolar interactions between solute and water, as well as between hydration water and bulk water. This finding suggests that conventional approaches to determine molecular dipole moments of the solutes may be problematic. This is certainly the case for solutes with small molecular dipole moments, but strong solute–solvent interactions, such as the saccharides studied here.
Room-temperature visible electroluminescence of Al-doped silicon oxide films
Authors: Wu X. M. , Dong Y. M. , Zhuge L. J. , Ye C. N. , Tang N. Y. , Ning Z. Y. , Yao W. G. , Yu Y. H.
Published: July 2002

A series of Al-doped amorphous silicon oxide films have been grown on p-type silicon (100) substrates by a dual ion beam cosputtering method. Visible electroluminescence (EL) from the devices, made by films with different contents of Al, can be seen with the naked eye under forward bias and reverse bias for films containing sufficient amounts of Al. The EL spectra are found to have a luminescence band peaked at 510 nm (2.4 eV), which is the same result as that obtained from silicon oxide films. With the increase in the amounts of Al, the peak position does not shift, the onset of the bias decreases, and the intensity of EL peak increases. Experiment results show that the doping of Al is beneficial to improving the conduction condition of films while the structure of the films associated with luminescence centers is affected hardly at all.
Interfacial process of nucleation and molecular nucleation templator
Authors: Liu X. Y.
Published: July 2002

Interfacial effects of nucleation inhibition and promotion were identified from the nucleation of paracetamol. Unlike the classic interfacial effects, which are caused by the change in nucleation barrier, the nonepitaxial interfacial effects are only associated with kink integration kinetics. Methylparaben inhibits nucleation by increasing the desolvation free energy barrier, which is revealed as the nonepitaxial interfacial effect of nucleation inhibition. Polysaccharide revealed its nonepitaxial interfacial effects of nucleation promotion by lowering the conformation entropic barrier via liquid molecule preordering. Polysaccharide can be regarded as an example of molecular nucleation promoter based on the nonepitaxial interfacial effects.
Efficient and stable dye laser action from modified dipyrromethene BF2 complexes
Authors: Costela A. , Garcı́a-Moreno I. , Gómez C. , Amat-Guerri F. , Sastre R.
Published: July 2002

We report on the lasing action of modified dipyrromethene BF2 complexes in air-equilibrated liquid solutions. All recent dyes share a common chromophore core and were dissolved in apolar, polar nonprotic, and polar protic solvents. When pumped transversely at 534 nm, nearly solvent-independent laser emission was obtained with efficiencies well over 40% in most cases. Highest lasing efficiency was 59%. Under continuous ultraviolet irradiation some of these dyes demonstrated improved photostability as compared with commercial dye pyrromethene 567.
Modeling multilayer woven fabrics
Authors: Åström J. A. , Mäkinen J. P. , Timonen J.
Published: July 2002

A numerical algorithm for nonlinear elastic relaxation of a multilayer woven fabric is introduced and tested. The equilibrium solutions are compared with real samples. An excellent result is obtained in spite of two simplifications: Bending stiffness of the fibers and friction between the fibers are both neglected. The numerical simulation is very fast and cost efficient in the search for optimal fabrics.
Mechanisms for the improved stability of C54–TiSi2 on (001)Si by the addition of N2 to Ar during Ti sputtering
Authors: Chang S. M. , Cheng S. L. , Chen L. J. , Luo C. H.
Published: July 2002

Addition of N2 to Ar during Ti sputtering has been found to improve the thermal stability of TiSi2. For samples sputtered with a mixture of Ar and N2, TiSi2 was found to be stable after 1050 °C, 30 s annealing. Furthermore, the phase transformation temperature from the C49 to C54 phase was not affected with the addition of a small amount of nitrogen. The stuffing of grain boundaries of TiSi2 and TiN/TiSi2 interfaces by nitrogen atoms is thought to retard the transport of Si and Ti atoms. In addition, titanium nitride particles embedded in TiSi2 near the TiN/TiSi2 interface may also protect the TiSi2 films from plastic deformation and retard the grain growth during high temperature annealing. Smaller average grain size of C54–TiSi2 in samples prepared with the addition of N2 to Ar during Ti sputtering than that in pure Ti samples is also beneficial in enhancing the thermal stability.
Modulation of light radiation during input into waveguide by resonance excitation of surface plasmons
Authors: Janunts N. A. , Nerkararyan Kh. V.
Published: July 2002

The process of transfer of energy of a surface plasmon polariton between modes located on two surfaces of a metal layer is studied. It is shown that this process strongly depends on the refractive indices of dielectrics surrounding the metal layer. The possibilities of high-speed optical signal modulation, based on this phenomenon, are discussed.
Intermediate phases in the hydrogen disproportionated state of NdFeB-type powders
Authors: Yi G. , Chapman J. N. , Brown D. N. , Harris I. R.
Published: July 2002

Transmission electron microscopy studies have been carried out on partially disproportionated NdFeB-type alloys. A new intermediate magnetic (NIM) phase has been identified. Moreover, the lamella structure which subsequently develops from the tetragonal NIM phase comprises a tetragonal NdFe-containing (IL) phase and α-Fe. The experimental data show strong evidence of a well-defined crystallographic relation between both the NIM and lamella phases and between the IL phase and α-Fe. These observations give insight into how crystallographic texture, and hence anisotropy, can be developed in NdFeB-type powders processed by the hydrogenation, disproportionation, desorption, and recombination route.
Infrared absorption of an In0.2Ga0.8As/GaAs quantum-well infrared photodetector employing a p–n–p camel diode structure
Authors: Son Heesoo , Park Jinsung , Hong Songcheol , Jo Sung-June , Song Jong-In
Published: July 2002

Far-infrared absorption of an In0.2Ga0.8As/GaAs multiple-quantum-well infrared photodetector employing a p–n–p camel diode structure is studied. The detector showed a photocurrent response to normal incident light at approximately 3 μm due to the intersubband hole transition, which is attributed to the strong hole–band mixing of the strained multiple quantum well. Application of the camel diode structure to the photodetector substantially reduced the dark hole current, resulting in an improved detectivity.
Surface molecular alignment by in-plane anchoring in the cell showing the V-shaped switching
Authors: Seomun S. S. , Vij J. K. , Hayashi N. , Kato T. , Fukuda A.
Published: July 2002

The surface molecular alignment in a sandwich cell showing V-shaped switching has been investigated using a photocontrolling method. The results indicate that the molecules on the rubbed surface are aligned parallel to the rubbing direction as in an open cell with an air–liquid crystal boundary. This alignment is due to strong in-plane anchoring, due to which the small twisted state appears along the cell thickness through intralayer molecular interaction.
Intensity filtering of a two-dimensional optical image in high-performance photorefractive mesogenic composites
Authors: Ono Hiroshi , Kawamura Tomomi , Kawatsuki Nobuhiro , Norisada Hideki
Published: July 2002

Edge enhancement, a type of intensity filtering of a two-dimensional optical image, was demonstrated using a high-performance photorefractive polymer-dissolved liquid crystal. We calculated the expected images using Fourier transform holographic geometry and obtained good agreement between the observed images and the theoretical expectation.
Ultrathin PtSi layers patterned by scanned probe lithography
Authors: Snow E. S. , Campbell P. M. , Twigg M. , Perkins F. K.
Published: July 2002

A process for patterning ultrathin layers of PtSi with high spatial resolution is presented. In this process, scanned probe anodic oxidation is used to pattern a surface oxide layer on a H-passivated Si surface. This oxide pattern prevents the reaction of a deposited Pt film with the underlying Si in the formation of PtSi. The unreacted Pt on the oxide is removed by a selective etch before any annealing. This process greatly reduces lateral diffusion and produces a 2-nm-thick PtSi layer with good electrical properties that maintains the fidelity of the patterned oxide mask. Such nanostructured PtSi films are a good candidate for use in constructing lateral Si-based quantum devices.
Unimolecular decomposition of chemically activated triplet C4HD3 complexes: A combined crossed-beam and ab initio study
Authors: Kaiser R. I. , Mebel A. M. , Lee Y. T. , Chang A. H. H.
Published: July 2002

The crossed molecular beam technique was utilized to investigate the reaction of ground state carbon atoms, C(3Pj), with d3-methylacetylene, CD3CCH(X1A1), at an average collision energy of 21.1 kJ mol−1. Product angular distributions and time-of-flight spectra were recorded. Only the deuterium loss was observed; no atomic hydrogen emission was detected experimentally. Forward-convolution fitting of the data combined with electronic structure calculations show that the reaction is indirect and initiated by a barrierless interaction of the carbon atom to the π-system of the methylacetylene molecule. Reactions with large impact parameters yield a triplet trans-methylpropene-1-diylidene complex whereas—to a minor amount—the formation of a triplet methylcyclopropenylidene intermediate is governed by smaller impact parameters. Both collision complexes rearrange via hydrogen migration and ring opening, respectively, to two distinct triplet methylpropargylene intermediates. A deuterium atom loss via a tight transition state located about 30 kJ mol−1 above the n-C4H3 product is a likely reaction pathway. The formation of the thermodynamically less stable cyclic isomer remains to be investigated closer. The D atom loss pathway represents an entrance barrierless and exothermic route to synthesize an extremely reactive C4H3 hydrocarbon radical in combustion processes and extraterrestrial environments.
Orientation of pentacene films using surface alignment layers and its influence on thin-film transistor characteristics
Authors: Swiggers M. L. , Xia G. , Slinker J. D. , Gorodetsky A. A. , Malliaras G. G. , Headrick R. L. , Weslowski Brian T. , Shashidhar R. N. , Dulcey C. S.
Published: July 2002

We have investigated the effect of surface order on the orientation and mobility of pentacene. The surface order was created using monolayers and polymers that are normally used to align liquid crystals. Rubbed polyvinylalcohol layers were found to align approximately 27% of the pentacene grains within a 30° range. When introduced in a thin-film transistor, they were found to enhance the saturation current by a factor of 2.5. A mechanism for this enhancement is proposed.
Formation of a p-type quantum dot at the end of an n-type carbon nanotube
Authors: Park Jiwoong , McEuen Paul L.
Published: July 2002

We use field effect doping to study both electron- (n) and hole- (p) type conduction in a semiconducting carbon nanotube. We find that, in the n-type region, the ends of the tube remain p- type due to doping by the metal contacts. As a result, a p–n junction forms near the contact, creating a small, p-type quantum dot between the p–n junction and the contact. This zero-dimensional quantum dot at the end of a one-dimensional semiconductor is the reduced dimensional analog of the two-dimensional inversion layer that forms at the boundary of a gated three-dimensional semiconductor.
Antiferromagnetic temperature and effective spin in n-type Hg1−xMnxTe
Authors: Gui Y. S. , Liu J. , Ortner K. , Daumer V. , Becker C. R. , Buhmann H. , Molenkamp L. W.
Published: July 2002

We have observed a characteristic modulation in the amplitude of the Shubnikov–de Haas (SdH) oscillations and a large shift of node position with increasing temperature in the semimagnetic semiconductor Hg1−xMnxTe. The positions of the oscillation extrema are almost temperature independent, with the exception that their phase changes by π after passing the nodal point. These features can be explained in terms of the exchange interaction between conduction electrons and the localized spin moments of Mn ions. The antiferromagnetic temperature and effective spin have been deduced from the temperature-dependent node position in the SdH oscillations.
Post-radiation-induced soft breakdown conduction properties as a function of temperature
Authors: Cester Andrea , Paccagnella Alessandro , Suñé Jordi , Miranda Enrique
Published: July 2002

When a thin oxide is subjected to heavy ion irradiation, a large leakage current similar to the soft breakdown can be produced. In this work, we have studied the radiation soft breakdown (RSB) after 257 MeV Ag and I irradiation by using a quantum point contact (QPC) model, which also applies to hard and soft breakdown produced by electrical stresses. We have also studied the temperature dependence of RSB current from 98 K up to room temperature, and found that the gate current after irradiation is strongly reduced by decreasing temperature. It is shown that this behavior can be attributed to a temperature dependence of the carriers supplied from the cathode rather than to a temperature-induced modification of the size and/or shape of the oxide RSB paths.
Resonance phenomena in phase-slip centers
Authors: Agafonov A. B. , Zolochevskiı̆ I. V. , Dmitriev V. M.
Published: July 2002

The resonance properties of nonequilibrium regions of phase-slip centers arising in tin films of different thicknesses under the influence of a dc transport current are investigated experimentally for films which are uniform over their width. It is confirmed that an important role in the mechanism of excitation of the non-Josephson oscillation (NJO) is played by the inelastic electron–phonon relaxation time τε of the charge imbalance. It is shown that two intercoupled resonance systems exist in samples containing phase-slip centers in the NJO regime. The change in shape of the amplitude–frequency characteristics of the NJO signal as the sample thickness is changed is explained by the influence of the transport electric current on the rate of relative tuning of the NJO frequency ω0 and the relaxation frequency ωr of the nonequilibrium region of the phase-slip center.
The influence of hydrogenation on superconducting properties of MgB2
Authors: Zaleski A. J. , Iwasieczko W. , Kaczorowski D. , Drulis H. , Tkacz M. , Zogal O. J. , Klamut J.
Published: July 2002

In the paper we present the results of the ac susceptibility measurements of the newly discovered superconducting diboride—MgB2.
Self-assembly of one-dimensional molecular and atomic chains using striped alkanethiol structures as templates
Authors: Zeng Changgan , Wang Bing , Li Bin , Wang Haiqian , Hou J. G.
Published: July 2002

Well-ordered striped structures are developed from alkanethiol self-assembled monolayers on an Au(111) surface following well-controlled annealing processes. We demonstrate here that such regular concave–convex molecular structures can be used as the templates for growing one-dimensional molecular and atomic chains. By depositing C60 molecules onto the striped surface, C60 bimolecular chains are self-assembled. Due to the breaking of C–S bonds under certain conditions, residual S atoms can form a S monoatomic chain between two adjacent stripe pairs of thoroughly lying-down molecules. Possible growth mechanisms are discussed.
Growth front roughening of room-temperature deposited oligomer films
Authors: Tsamouras D. , Palasantzas G. , De Hosson J. Th. M.
Published: July 2002

Growth front scaling aspects are investigated by atomic force microscopy for oligomer 2,5-di-n-octyloxy-1,4-bis(4′-(styryl)styryl)-benzene thin films vapor deposited onto silicon substrates at room temperature. Analyses of the height–height correlation function for film thickness that are commonly used in optoelectronic devices, i.e., ranging between 15 and 300 nm, yield roughness Hurst exponents around H=0.45±0.04. Further, the root-mean-square roughness amplitude σ evolves with film thickness as a power law σ∝dβ, with β=0.28±0.05. The nonGaussian height distribution and the measured scaling exponents (H and β) suggest a roughening mechanism close to that described by the Kardar–Parisi–Zhang [Phys. Rev. Lett. 56, 889 (1986)] scenario indicating nonlinear film growth.
Electroluminescence from silicon nanocrystals in Si/CaF2 superlattices
Authors: Ioannou-Sougleridis V. , Nassiopoulou A. G. , Ouisse T. , Bassani F. , Arnaud d’Avitaya F.
Published: July 2002

Electroluminescence (EL) from silicon nanocrystals in Si/CaF2 superlattices grown by molecular-beam epitaxy at room temperature was investigated and compared with that obtained from silicon nanocrystals in Si/SiO2 superlattices. EL spectra exhibited current-tunability, similar to that observed in silicon nanocrystals in SiO2, which was attributed to three main effects: (a) Auger quenching of photoluminescence, which occurs when more than one electron-hole pair is present in the same nanocrystal and which quenches luminescence from relatively larger nanocrystals, (b) size-dependent carrier injection, and (c) the effect of the applied field, when this one is significantly high. In the case of Si/CaF2 superlattices, this last factor did not apply, so the two other factors are mainly at the origin of the effect.
Symmetry dependence of x-ray absorption near-edge structure at the metal K edge of 3d transition metal compounds
Authors: Wu Ziyu , Xian D. C. , Natoli C. R. , Marcelli A. , Paris E. , Mottana A.
Published: July 2002

The pre-edge features in a system with “even” symmetry, apart from quadrupolar transition contribution, are mainly dipolar in character, associated with the existence of unoccupied states made up of mixed cation np with higher-neighboring cation-(n-1)d orbitals, and reflect the density of states due to the medium-range order of the system, while in “odd” symmetry materials these pre-edge features are the result of a transition from the 1s to a final density of states of p symmetry due to an unsymmetrical mixing of the ligand wave functions with the central cation d orbitals. In the latter case, they contain not only the p but also the d base of orbitals, similar to a tetrahedral configuration. These results are validated for Fe as a photoabsorber by comparing x-ray absorption near-edge spectra of Fe2SiO4 (fayalite) and Fe2O3 (hematite) to ab initio full multiple scattering calculations at the Fe K edge, but pertain to all systems containing sixfold-coordinated cations.
Ultraviolet picosecond optical pulse generation from a mode-locked InGaN laser diode
Authors: Gee S. , Bowers J. E.
Published: July 2002

Ultraviolet optical pulses were generated by actively mode locking an external cavity InGaN laser at a wavelength of 409 nm with a temporal pulse duration of 30 ps. The average power was 2 mW and the time–bandwidth product was 1.2. Dynamic detuning plays a major role in pulse development.
Removable template route to metallic nanowires and nanogaps
Authors: Šordan R. , Burghard M. , Kern K.
Published: July 2002

A general method for the fabrication of nanowires with a thickness of ∼6 nm and width of 15–20 nm is presented. The approach is applicable to inorganic and organic materials and is demonstrated here for metallic systems. The wires are produced by ion-beam etching of a gold–palladium thin films covered by chemically modified vanadium–pentoxide nanowires as an etching mask. The two-probe room-temperature resistance of the wires is found to range between 7.8 and 18.1 kΩ. Nanogaps with a length on the order of 1 nm were created within the nanowires by breaking via electromigration.
Study of band structure in PbSe/PbSrSe quantum wells for midinfrared laser applications
Authors: Shen W. Z. , Wang K. , Jiang L. F. , Wang X. G. , Shen S. C. , Wu H. Z. , McCann P. J.
Published: July 2002

The electronic states in PbSe/Pb0.934Sr0.066Se multiple-quantum-well structures (MQWs) grown by molecular-beam epitaxy have been investigated both theoretically and experimentally for the midinfrared laser applications. With the aid of combined temperature-dependent photoluminescence and absorption measurements on a Pb0.934Sr0.066Se thin film for the effective masses and temperature-dependent band gaps, we find that the PbSe/PbSrSe MQWs have type-I band alignment and the conduction band offset ratio is Qc=0.82±0.03. The calculation, taking into account the strain, carrier confinements, and the multivalley band structure, can well explain both the observed luminescence peak energies and the temperature coefficient of the luminescence peaks as a function of well thickness.
Structural stability of binary CdCa quasicrystal under high pressure
Authors: Jiang J. Z. , Gerward L. , Olsen J. S.
Published: July 2002

The structural stability of a binary CdCa quasicrystal with a primitive icosahedral structure has been investigated by in situ high-pressure x-ray powder diffraction at an ambient temperature using synchrotron radiation. It is demonstrated that the icosahedral quasicrystalline structure of the sample is intrinsically stable up to 47 GPa. The bulk modulus at zero pressure and its pressure derivative of the icosahedral CdCa quasicrystal is 68.1±2.0 GPa and 4.3±0.2, respectively. The compression behavior of different Bragg peaks is isotropic, indicating no pressure-induced anisotropic elasticity in the stable binary icosahedral CdCa quasicrystals.