bluuebunny/crossref_metadata_2025 huggingface dataset:
(10×2) strained reconstruction induced by oxygen adsorption on the Rh(110) surface
Authors: Vesselli E. , Africh C. , Baraldi A. , Comelli G. , Esch F. , Rosei R.
Published: July 2002

Oxygen adsorption on the (1×2) missing row reconstructed Rh(110) surface has been studied by means of low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), and scanning tunneling microscopy (STM). Starting from the already known (2×2)p2mg oxygen overlayer in which the substrate is (1×2) reconstructed, further oxygen has been dosed at room and lower temperatures. Upon heating, additional substrate reconstruction takes place and the surface forms a new structure with (10×2) periodicity and high local oxygen coverage. Oxygen 1s XPS measurements show a binding energy shift from 530.25 eV in the (2×2)p2mg to 529.75 eV in the (10×2) layer. Analysis of STM images reveals that in the (10×2) layer, the rhodium close-packed rows are strained and segmented in the [11̄0] direction. On the basis of the experimental results, models for the (10×2) structure and its formation process are proposed and compared with “pseudo-oxide” structures.
Alternative SU(N) Skyrme models and their solutions
Authors: Wospakrik H. J. , Zakrzewski W. J.
Published: July 2002

We consider alternative SU(N) Skyrme models in 3 spatial dimensions. We show that when N=2 they reduce to the usual SU(2) Skyrme model but for N⩾3 they are different. We show that the harmonic map ansatz previously applied to the usual Skyrme models can also be applied to these models giving spherically symmetric solutions (when the number of projectors is N−1) and low energy field approximants when the number of projectors is lower. We compare our results with the results for the usual Skyrme models.
Reduction of the particulate and nitric oxide from the diesel engine using a plasma chemical hybrid system
Authors: Chae J. O. , Hwang J. W. , Jung J. Y. , Han J. H. , Hwang H. J. , Kim S. , Demidiouk V. I.
Published: July 2002

A new plasma/catalyst continuously regenerative hybrid system (PCRHS) is introduced to reduce diesel particulate matter (DPM), NOx, CO, etc., contained in diesel exhaust gas. The catalyst temperature, plasma energy density, and exhaust gas characteristics were investigated with a passenger diesel car (2500cc) at the dynamometer test bed and chassis dynamometer with CVS-75 test mode. It was reported that the smoke removal efficiency was around 70% at the dynamometer test bed with 80 W energy consumption, and that PM removal efficiency was 68% at the chassis dynamometer. The NOx was reduced up to 20% according to the electrode types and temperature, respectively. The hybrid system test shows that DPM and CO were almost removed and NOx reduced to 30% simultaneously by the system. Considering these results, PCRHS could be a promising method to regenerate diesel particulate.
Nd
65
Al
10
Fe
25−x
Co
x
(x=0,5,10) bulk metallic glasses with wide supercooled liquid regions
Authors: Wei Bing Chen , Zhang Yong , Zhuang Yan Xin , Zhao De Qian , Pan Ming Xiang , Wang Wei Hua , Hu Wen Rui
Published: July 2002

Bulk metallic glasses of Nd65Al10Fe25−xCox (x=0,5,10) have been prepared in the form of 3 mm diam rods. Results of differential scanning calrimetry, dynamic mechanical thermal analysis (DMTA), and x-ray diffraction are presented for these alloys. It is shown that the glass transition and crystallization have been observed by DMTA. The reduced glass transition temperature of these glasses, defined as the ratio between the glass transition temperature Tg and the melting temperature Tl is in the range from 0.55 to 0.62. All these glasses have a large supercooled liquid region (SLR), ranging from 80 to 130 K. The high value of reduced glass transition temperature and wide SLR agree with their good glass formation ability.
Effect of discharge microwave frequency on electron temperature of electron cyclotron resonance plasma
Authors: Kawai Y. , Suzuki T. , Saburi T. , Fujii Y.
Published: July 2002

The characteristics of argon electron cyclotron resonance plasma discharged by 7.0, 8.0, and 9.4 GHz microwaves were investigated. Experiments were conducted in a fixed magnetic field. It was found that the electron temperatures Te exhibited a trend of Te7.0<Te8.0<Te9.4 (suffixes represent the discharge microwave frequencies).
Double-resonant photoionization efficiency spectroscopy: A precise determination of the adiabatic ionization potential of DCO
Authors: Foltynowicz Robert J. , Robinson Jason D. , Grant Edward R.
Published: July 2002

We report the first high-resolution measurement of the adiabatic ionization potential of DCO and the fundamental bending frequency of DCO+. Fixing a first-laser frequency on selected ultraviolet transitions to individual rotational levels in the (000) band of the 3pπ 2Π intermediate Rydberg state of DCO, we scan a second visible laser over the range from 20 000 to 20 300 cm−1 to record double resonance photoionization efficiency (DR/PIE) spectra. Intermediate resonance with this Rydberg state facilitates transitions to the threshold for producing ground-state cations by bridging the Franck–Condon gap between the bent neutral radical and linear cation. By selecting a single rotational state for ionization, double-resonant excitation eliminates thermal congestion. Spectroscopic features for first-photon resonance are identified by reference to a complete assignment of the 3pπ 2Π(000)−X 2A′(000) band system of DCO. Calibration with HCO, for which the adiabatic ionization threshold is accurately known, establishes an experimental instrument function that accounts for collisional effects on the shape of the photoionization efficiency spectrum near threshold. Analysis of the DR/PIE threshold for DCO yields an adiabatic ionization threshold of 65 616±3 cm−1. By extrapolation of vibrationally autoionizing Rydberg series accessed from the Σ+ component of the 3pπ 2Π(010) intermediate state, we determine an accurate rotationally state-resolved threshold for producing DCO+(010). This energy, together with the threshold determined for the vibrational ground state of the cation provides a first estimate of the bending frequency for DCO+ as 666±3 cm−1. Assignment of the (010) autoionization spectrum further yields a measurement of an energy of 4.83±0.01 cm−1 for the (2-1) rotational transition in the Σ+1(0110) state of DCO+.
The NO(X2Π)–Ne complex. II. Investigation of the lower bound states based on new potential energy surfaces
Authors: Alexander Millard H. , Soldán Pavel , Wright Timothy G. , Kim Yangsoo , Meyer Henning , Dagdigian Paul J. , Lee Edmond P. F.
Published: July 2002

High-quality ab initio potential energy surfaces were calculated and subsequently used to predict the positions of the lowest bend-stretch vibrational states of the NO(X2Π,v=0)–Ne complex. The vibrational wavefunctions and basis set expansion coefficients, determined within the adiabatic bender model, were then used to simulate the observed spectrum for excitation of the NO(X2Π,v=2)–Ne complex. The overall position and rotational substructure matches well the experimental results for this system, which are presented in the preceding article [Y. Kim, J. Fleniken and H. Meyer, J. Chem. Phys. 114, 5577 (2001)]. A heuristic Hamiltonian, which includes the most important couplings and splittings, is used to improve the fit to experiment.
Density-functional theory for structure and freezing of star polymer solutions
Authors: Groh Benito , Schmidt Matthias
Published: July 2002

We use the soft fundamental measure theory (SFMT) to investigate a system of classical particles interacting with the pair potential of star polymers in solution. To that end we calculate liquid and solid structural properties, as well as freezing, solid-to-solid, and remelting phase transitions. Even subtle physical effects, like deviations from Gaussian crystal peaks and an anomalous peak broadening upon increasing density as well as a reasonable vacancy concentration are captured correctly. Good overall quantitative agreement with simulation data is found, however, with a tendency to overestimate the structural correlations. Furthermore, we demonstrate that all recent developments of its hard core counterpart can be incorporated systematically into SFMT.
Ion pair correlations near critical points of ionic fluids: Experimental investigation of the static permittivity
Authors: Nadolny Holger , Weingärtner Hermann
Published: July 2002

We report on data for the concentration dependence of the static dielectric constant εS of solutions of tetra-n-butylammonium naphtylsulfonate (TBNAS) in toluene derived from measurements of the frequency-dependent complex permittivity. The system shows an upper consolute point at Tc=329 K and a mole fraction Xc=0.0235 of the salt. The measurements were performed along a slightly supercritical isotherm at 338.15 K at mole fractions 0.01⩽X⩽0.068. εS increases with increasing salt concentration. At the critical point εS=(3.1±0.05) compared with εS=2.35 for pure toluene. In the concentration range covered by the experiments, the effective dipole moments calculated from these data are of the order of μeff=5 D, which is distinctly lower than an estimate for the isolated molecule, μ0≅18 D. The difference is attributed to compensation effects due to preferred antiparallel ion pair orientations, as described by a Kirkwood–Fröhlich-type theory with correlation factors of gK<1. At the critical point we find gK≅0.05. Due to these orientational correlations, dipole–dipole interactions between ion pairs may provide a significantly smaller contribution to the free energy than predicted by theory. This may explain the good performance of theories that ignore dipole–dipole interactions between pairs.
Charging effects on temporal and spatial evolution of the dusty plasma sheath in plasma source ion implantation
Authors: Liu Deyong , Wang Dezhen , Wang Xiaogang , Liu Jinyuan
Published: July 2002

The temporal and spatial evolution of a dusty plasma sheath in plasma source ion implantation has been investigated with a fluid theory and a self-consistent dust charging model. A negative potential pulse is introduced to form the plasma sheath. The effect of the dust charging process becomes significant when the charging time is longer than either the pulse period or the ion response time (measured by the inverse of the ion plasma frequency). Numerical results indicate that the sheath expands faster than dust-free sheaths. It is also shown that, for small dust particles, the motion of dust particles is very remarkable and the charging effect can be negligible, and for large dust particles, the charging effect of dust particles becomes more evident while they are almost kept stationary during the whole negative potential pulse.
Ferroelectric properties of (C5H5NH)5Bi2Br11
Authors: Jóźków J. , Jakubas R. , Bator G. , Pietraszko A.
Published: July 2002

A new pyridinium compound, (C5H5NH)5Bi2Br11, has been synthesized. The x-ray diffraction studies indicate that its structure is built up of four independent pyridinium cations and isolated Bi2Br115− groups. At room temperature it crystallizes in the monoclinic space group P21/n. Two phase transitions of second- and first-order type are detected by the differential scanning calorimetry measurements at 118 and 405/403 K (on heating–cooling), respectively. The corresponding anomalies in the linear thermal expansion at 118 and 405 K are observed along three crystallographic directions. The dielectric investigations reveal dielectric absorption and dispersion in the radio-frequency region. The experimental results were analyzed on the basis of dielectric formula which represents the sum of two independent relaxators. The pyroelectric measurements reveal that (C5H5NH)5Bi2Br11 becomes ferroelectric below 118 K and is characterized by the appearance of spontaneous polarization of the order of 3⋅10−3 C/m2 along the b axis.
Effect of solvent quality on polyelectrolyte adsorption at an oppositely charged surface
Authors: Dobrynin Andrey V.
Published: July 2002

The effects of the solvent quality on the adsorption of weakly charged polyelectrolytes at an oppositely charged surface are investigated using the self-consistent mean field theory. The analytical solutions of the self-consistent field equations are obtained in the case of θ, good and poor solvents for the polymer backbone. Using these analytical solutions the thickness of the adsorbed layer is calculated as a function of the surface charge density, salt concentration, and solvent quality. It is shown that for polyelectrolyte adsorption from θ and good solvents the surface charge is always overcompensated by adsorbed chains. For low ionic strengths the surface overcharging is inversely proportional to the Debye screening length. However, in the case of adsorption from a poor solvent the adsorbed polyelectrolytes undercompensate the surface charge.
Excess energies of n- and i-octane molecular clusters
Authors: Vehkamäki Hanna , Ford Ian J.
Published: July 2002

Cloud chamber data for the nucleation of droplets from supersaturated n- and i-octane vapors are analyzed using nucleation theorems. We obtain the excess energies of pure and mixed component molecular clusters with sizes ranging from 19 to 58 molecules. We plot this information in the form of an excess energy surface for a range of cluster compositions. Since the two species are similar we also combine the data into a plot of excess energy against the total number of molecules in the cluster. We show that the capillarity approximation fails to predict the critical cluster composition, though it does provide a rough estimate of the excess energy of a specified cluster.
One-photon mass-analyzed threshold ionization spectroscopy of 1- and 2-iodopropanes in vacuum ultraviolet
Authors: Park Sang Tae , Kim Sang Kyu , Kim Myung Soo
Published: July 2002

One-photon mass-analyzed threshold ionization (MATI) spectroscopy of 1- and 2-iodopropanes has been studied using coherent vacuum ultraviolet (VUV) radiation generated by four-wave mixing in Kr gas. Accurate ionization energies to the lower and upper spin–orbit states of the molecular ions have been determined. These are 9.1755±0.0005 and 9.6903±0.0017 eV for the lower and upper spin–orbit states, respectively, of 2-iodopropane ion. For 1-iodopropane ion, gauche and trans peaks were resolved in the MATI spectra. Ionization energies to the lower spin–orbit states are 9.2567±0.0005 and 9.2718±0.0005, respectively, for the gauche and trans conformers. The corresponding values are 9.8332±0.0017 and 9.8466±0.0017 for the upper spin–orbit states. The pure ion beam of the gauche-only or that of trans-only could be selectively generated by tuning the VUV wavelength. Dissociation of 1- and 2-iodopropane ions, C3H7I+→C3H7++I, occurring in the ion core of highly excited Rydberg neutrals has been observed. Fragmentation thresholds for these reactions have been determined. This has led to an accurate potential energy diagram for the dissociation of the C3H7I+ system in the threshold region. The heat of formation at 0 K of 2-C3H7+ has been determined, 821.7±3.8 kJ mol−1, together with the proton affinity at 0 K of C3H6, 741.6±3.9 kJ mol−1. Plausible mechanisms for the production of 2-C3H7++I from 1-C3H7I+ have been proposed.
The characteristics of magnetohydrodynamic waves in self-gravitating rotating plasmas
Authors: Hau L.-N. , Chou C.-K.
Published: July 2002

The basic characteristics of linear magnetohydrodynamic (MHD) waves in a self-gravitating, rotating, magnetized plasma are examined. It is shown that for Cs2<2πρG/k the phase speed of the fast wave decreases with increasing θ, the angle between the magnetic field and wave vectors. In addition, slow mode waves become unstable and may possibly possess a positive density–magnetic field correlation like the fast mode. One implication is that the observed phase relationship between the magnetic field and density spiral arms cannot be used as a sole criterion for the identification of slow and fast MHD density waves in rotating thin discs.
Microscopic theory of hyper-Rayleigh scattering for molecular crystals
Authors: Munn R. W.
Published: July 2002

Molecular crystals produce hyper-Rayleigh scattering (HRS) at the second harmonic frequency via nonzero mean-square dynamical fluctuations in the quadratic optical susceptibility. The intensity of HRS depends on the lattice normal-coordinate derivatives of the quadratic susceptibility. Expressions are derived for these quantities, including polarizability changes induced by polar molecules and the first hyperpolarizability induced by quadrupolar molecules, drawing upon previous results from microscopic theories of nonlinear optics, Raman scattering, and optical activity. A simple illustrative calculation for the hexamine crystal indicates that its HRS should be governed by a susceptibility that is about 7% of the usual quadratic susceptibility for second-harmonic generation (SHG). HRS should be detectable for a centrosymmetric crystal where SHG is zero by symmetry.
Electron kinetic simulations of solid density Al plasmas produced by intense subpicosecond laser pulses. I. Ionization dynamics in 30 femtosecond pulses
Authors: Ethier S. , Matte J. P.
Published: July 2002

The interaction of a 1018 W/cm2, 30 fs laser pulse with solid Al was simulated with the electron kinetic code “FPI” [J. P. Matte et al., Phys. Rev. Lett. 72, 1208 (1994)] in which an improved average ion module was fully coupled to the electron kinetics. It includes electron impact ionization and excitation and their inverse processes: collisional recombination and de-excitation; as well as radiative decay and pressure ionization. We compare to runs without the inverse processes, and also without atomic physics (with 〈Z〉 set to 11). Atomic physics strongly affects the energy balance and the shape of the distribution function. Line radiation is mostly due to three body recombination into excited states after the peak of the pulse, as the plasma cools down. Despite the atomic processes and the high density, strongly non-Maxwellian distribution functions were obtained due to very steep temperature gradients and strong collisional heating, at the peak of the pulse. However, after the pulse, there is a very rapid thermalization of the electron distribution to which inverse processes strongly contribute.
Oriented growth of n-alkanes crystals on nanostructured poly(tetrafluoroethylene) substrates
Authors: Damman P. , Fischer C. , Krüger J. K.
Published: July 2002

The growth of n-alkane (CnH2n+2) crystals on poly(tetrafluoroethylene) substrates (PIA) obtained by the friction-transfer method was studied by optical microscopy and grazing incidence x-ray diffraction. The experiments performed on a series of molecules ranging from n=21 to n=33 reveal the existence of a preferred contact plane with the PIA substrate corresponding to a minimum in lattice mismatch between the two crystallographic systems. Independently of the chain length, the n-alkane crystals tend to orient with their (200) planes parallel to the substrate, the molecular axis being preferentially aligned along the friction direction of the PTFE substrate. In our study, we demonstrate that the pathways (i.e., the orientation mechanisms) strongly influence the observed morphology in the low temperature phase.
Effects of oxide seed and cap layers on magnetic properties of a synthetic spin valve
Authors: Lin Tsann , Mauri Daniele
Published: July 2002

A synthetic spin valve comprising Al2O3/Ni–Cr–Fe/Ni–Fe/Pt–Mn/Co–Fe/Ru/Co–Fe/Cu/Co–Fe/Ni–Fe/Cu/Al2O3/Ta films has been annealed and evaluated as a read sensor for ultrahigh-density (⩾20 Gb/in.2) recording. The Al2O3 film used as its oxide seed layer provides an in situ flat surface for the Pt–Mn, Co–Fe and Ni–Fe films to develop strong {111} crystalline textures, thereby increasing its giant magnetoresistance coefficient to as high as 13.8%. Another Al2O3 film used as its oxide cap layer protects the Co–Fe/Ni–Fe sense layers from interface mixing and oxygen interdiffusion, thus improving the soft magnetic properties and thermal stability of the sense layers. Antiferromagnetic/ferromagnetic coupling between the Pt–Mn pinning and Co–Fe/Ru/Co–Fe synthetic pinned layers is strong and thermally stable enough for proper sensor operation. Ferromagnetic/ferromagnetic coupling across the Cu spacer layer is antiparallel, and hence it is feasible to achieve optimal biasing of magnetoresistance responses. This synthetic spin valve is sandwiched into a read gap 0.1 μm in thickness, and is patterned and lapped into a read sensor 0.42 and 0.23 μm in physical width and height, respectively. With a sense current of 4 mA, this read sensor exhibits an effective read width of 0.31 μm, stable magnetoresistance responses, and signal sensitivity of 6.64 mV/μm.
Distributed polarizability of the water dimer: Field-induced charge transfer along the hydrogen bond
Authors: in het Panhuis M. , Popelier P. L. A. , Munn R. W. , Ángyán J. G.
Published: July 2002

The topological partitioning of electronic properties approach at Hartree–Fock level is used to investigate charge transfer response in a water dimer. Distributed polarizability components are employed to calculate the change in electron density under external fields. Field-induced charge flow between the water monomers is most significant along the direction of the hydrogen bond. The molecular polarizability of the molecules in the dimer is reduced owing to formation of the hydrogen bond.
Photonic crystal microcavities with self-assembled InAs quantum dots as active emitters
Authors: Reese C. , Becher C. , Imamoğlu A. , Hu E. , Gerardot B. D. , Petroff P. M.
Published: July 2002

We report the use of self-assembled InAs quantum dots as active emitters in a photonic crystal microcavity. We have fabricated defect microcavities by removing 37 and 61 air holes from a triangular lattice in a photonic crystal membrane, and obtained quality factors in excess of 1000.
Dipole moments of highly vibrationally excited HCN: Theoretical prediction of an experimental diagnostic for delocalized states
Authors: Bowman Joel M. , Irle Stephan , Morokuma Keiji , Wodtke Alec
Published: July 2002

Vibrational state specific dipole moments are diagnostic of the degree of localization of vibrational states in highly vibrationally excited HCN. Using a newly calculated global ab initio dipole moment function and previously calculated highly accurate vibrational wave functions, we show that delocalized (i.e., isomerizing) vibrational states of HCN possess markedly lower dipole moments than localized HCN or HNC states. We also show that the vibrational quantum number dependence of the dipole moment can be used to distinguish delocalized states from localized Franck–Condon-dark states that are made observable by perturbations with localized Franck–Condon-bright states. Furthermore, using classical trajectory analysis we introduce and describe a new experimental approach to obtain these data, which relies on combining optical pumping and state specific molecular transport with hexapoles. With this method it is possible to determine state specific dipole moments with high accuracy and precision.
Low-energy dissociative electron attachment to BrCN and CBrCl3: Temperature dependences and reaction dynamics
Authors: Parthasarathy R. , Suess L. , Hill S. B. , Dunning F. B.
Published: July 2002

Low-energy dissociative electron attachment to BrCN and CBrCl3 over the temperature range 300–450 K is examined by measuring the velocity and angular distributions of negative ions produced through electron transfer in collisions with velocity-selected K(np) Rydberg atoms. The data are analyzed using a Monte Carlo collision code that models the detailed reaction dynamics. Measurements with BrCN indicate that electron capture leads to the creation of excited BrCN−* intermediates that dissociate with a mean lifetime τ∼20 ps to form CN− ions, the majority of the excess energy of reaction appearing in translation. No significant Br− production was observed over the present temperature range. Electron transfer to CBrCl3 is found to lead to the formation of both Cl− and Br− ions, the branching ratio depending markedly on temperature. At room temperature, Br− production is dominant, at elevated temperatures Cl− production dominates. The data show that Cl− formation is associated with two reaction channels: in the first the electron is captured directly into an antibonding orbital followed by immediate dissociation, in the second a longer-lived CBrCl3−* intermediate is formed with a lifetime ≳ a few vibrational periods. The contribution from direct dissociation increases dramatically at the higher temperatures. Similar reaction channels are operative in the formation of Br− ions, but their relative strengths are not strongly temperature dependent. Possible reaction scenarios are discussed.
Insight into electron-mediated reaction mechanisms: Catalytic CO oxidation on a ruthenium surface
Authors: Zhang C. J. , Hu P. , Alavi A.
Published: July 2002

Ruthenium is one of the poorest catalysts for CO oxidation under normal conditions (low or medium O coverage and normal temperature). However, a recent study [Science 285, 1042 (1999)] reveals that, under femtosecond laser irradiation, CO2 can be formed on the Ru surface, and the reaction follows an electron-mediated mechanism. We carried out density functional theory calculations to investigate CO oxidation via an electron-mediated mechanism on Ru(0001). By comparison to the reaction under normal conditions, following features emerge in the electron-mediated mechanism: (i) more reaction channels are open; (ii) the reaction barrier is significantly lowered. The physical origins for these novel features have been analyzed.
Surface reactivity of Si nanowires
Authors: Sun X. H. , Peng H. Y. , Tang Y. H. , Shi W. S. , Wong N. B. , Lee C. S. , Lee S. T. , Sham T. K.
Published: July 2002

The chemical reactivity of hydrogen-passivated surface of silicon nanowires (SiNWs) towards the reductive deposition of silver and copper ions from solution is reported. SiNWs synthesized by laser ablation were used in the investigation. The surface properties of SiNWs after the removal of the surface oxide were studied. It is found that the surface silicon of the SiNWs can readily reduce silver (I) and copper (II) ions to metal aggregates of various morphologies on the SiNW surface at room temperature. The reaction products have been characterized with scanning electron microscopy, energy dispersive x-ray spectroscopy, high-resolution transmission electron microscopy, electron energy loss spectroscopy, and x-ray photoelectron spectroscopy. By varying the concentration of Ag(I) ions in the solution, nanostructures of silver with different shapes and sizes can be obtained. This approach for synthesis of metal nanostructures offers a potential method for the preparation of desired metal catalysts.
Intermediate reactions in solid-state photolysis
Authors: Khriachtchev Leonid , Pettersson Mika , Lundell Jan , Räsänen Markku
Published: July 2002

Photodissociation of impurity-doped solids involving chemical reactions with host atoms is experimentally studied. We demonstrate that the formation of intermediate molecules (HKrCl) plays a central role in the photodissociation of HCl in solid Kr, developing considerably the general understanding of solid-state photolysis dynamics. In addition, these experiments provide a quantitative test for the ab initio calculations of IR absorption intensities of novel rare-gas molecules. The measured UV absorption spectrum of HKrCl is valuable for characterizing the electronically excited states of rare-gas containing species, which is a significant challenge to theory.
High-pressure cell for simultaneous small-angle x-ray scattering and laser light scattering measurements
Authors: Koga Tadanori , Zhou Shuiqin , Chu Benjamin , Fulton John L. , Yang Shu , Ober Christopher K. , Erman Burak
Published: July 2002

A cell for in situ observation of self-assembled nanostructured materials in high-pressure fluids, including supercritical carbon dioxide, has been constructed and tested. The compact cell can be used for simultaneous small-angle x-ray scattering, laser light scattering, visual observation, and some other types of spectroscopic measurements. The light scattering plane is normal to the x-ray scattering plane with the optical axis and the x-ray axis being perpendicular to each other. The scattering is detected at the intersection of the light and x-ray beams, and thus one effectively probes the same scattering volume. Some preliminary experimental results for the micellar self-assembly of a fluorinated block copolymer in supercritical carbon dioxide are presented.
Role of rare sites in single molecule spectroscopy measurements of spectral diffusion
Authors: English Douglas S. , Harbron Elizabeth J. , Barbara Paul F.
Published: July 2002

Detailed investigations of the spectral diffusion of sulforhodamine 101 (SR101) in polymer films have been performed over a range of concentrations from typical concentrations for single molecule (SM) spectroscopic studies (10−10 M) to typical concentrations for bulk (10−6 M) experiments. A “single-molecule” ensemble spectrum, obtained by averaging 42 different SM spectra of SR101 in a poly(methyl methacrylate) film, exhibits extreme broadening and a large vibronic peak that is not observed in the more concentrated samples. The distribution of SM spectral means is extremely broad (FWHM=616 cm−1) with molecule-to-molecule variations that last at least several hours. Autocorrelation analysis of 170 SM spectral mean trajectories on the second times scale reveals that the most probable behavior for SR101 molecules is to exhibit negligibly small amounts of spectral diffusion. The observed effects, i.e., the large vibronic peak, the broad spectral distribution, and rare rapid jumps in the spectral mean, are assigned to differences in probe nanoenvironments. The effects of association with these “rare” sites are saturated at extremely low (10−9 M) concentrations. The unexpected concentration dependence observed here could have implications for data interpretation in many SM experiments.
Structure parameters and degradation of the critical current of the alloy NT-50 after cryogenic drawing in an ultrasonic field
Authors: Volchok O. I. , Lazareva M. B. , Okovit V. S. , Starodubov Ya. D. , Chernyi O. V. , Chirkina L. A.
Published: July 2002

The parameters of the defect and phase structure of the alloy NT-50 are investigated after low-temperature (77 K) deformation by drawing in an ultrasonic field, and the influence of these parameters on the amount of degradation of the critical current under tensile loading at 4.2 K is studied. It is found that cryogenic ultrasonic deformation leads to intensified decomposition of the β-solid solution with precipitation of Ti-rich phases according to the kinetics of the spontaneous martensitic transformation and results in a reduction of the internal stress level in the alloys. The structural features found promote stabilization of the β-solid solution during a subsequent deep cooling, as is manifested in a lowering of the degree of completion of the low-temperature deformation-induced martensitic transformation, which in turn raises the threshold for degradation of the critical current and reduces the degree of degradation in a wide range of external mechanical loads.
Magnetotransport in manganite trilayer junctions grown by 90° off-axis sputtering
Authors: Noh J. S. , Nath T. K. , Eom C. B. , Sun J. Z. , Tian W. , Pan X. Q.
Published: July 2002

We report magnetotransport studies on La0.67Sr0.33MnO3/SrTiO3/La0.67Sr0.33MnO3 trilayer junctions, fabricated using 90° off-axis sputtering. Films were grown on both (001) (LaAlO3)0.3–(Sr2AlTaO6)0.7 and (110) NdGaO3 substrates. The sputtered trilayers show improved junction resistance uniformity over those made using pulsed laser deposition. Cross-sectional transmission electron microscopy and atomic force microscopy studies confirm smooth interfaces and a uniform barrier. Magnetoresistances up to ∼100% are observed for junctions on (001) (LaAlO3)0.3–(Sr2AlTaO6)0.7 with a 30 Å barrier at 13 K and around 100 Oe. Junction magnetoresistance versus magnetic field behavior is more stable, indicating improved transport and magnetic homogeneity across the junction.
The role of dimer formation in the self-assemblies of DNA base molecules on Cu(111) surfaces: A scanning tunneling microscope study
Authors: Furukawa Masashi , Tanaka Hiroyuki , Kawai Tomoji
Published: July 2002

For the purpose of understanding the self-assembly formation mechanism of DNA base molecules, guanine, adenine, cytosine, and thymine molecules were deposited on Cu(111) surfaces, and were observed using a low-temperature (≈80 K) scanning tunneling microscope (STM). Single-molecular-scale STM images revealed that guanine, adenine, and cytosine molecules can form ordered one- and/or two-dimensional unique structures, but thymine molecules, however, randomly aggregate into small clusters. Semiempirical molecular orbital (MO) calculation indicates that there exists predominantly stable dimer structures for the former three molecules, while such phenomena cannot be observed among the possible thymine dimer and even trimer structures. Based on experimental and theoretical results, we have concluded that specific hydrogen-bonded nucleus formation is a decisive process in the two-dimensional self-assembly formation of DNA base molecules on Cu(111) surfaces.
Linearized magnetohydrodynamic theory of Langmuir probes with resistivity, friction, and polarization
Authors: Carlson A.
Published: July 2002

Standard Langmuir probe analysis interprets the entire voltage drop to occur in the sheath and neglects any voltage drop due to bulk resistivity. In a magnetized plasma this implies a strong mechanism to damp the E×B drift around the probe’s flux tube. Application of linearized magnetohydrodynamics to the bulk plasma allows the consideration of a variety of geometries and damping mechanisms on an equal footing and the treatment of plasma turbulence without the inappropriate recourse to anomalous transport coefficients. An analytic expression for the apparent temperature determined by long flush mounted Langmuir probes can be found if the boundary conditions are also linearized. The friction on neutrals is always stronger than viscosity and is able to account for all the I–V characteristics measured in the ASDEX Upgrade [M. Kaufmann et al., Plasma Physics and Controlled Fusion 35, 205 (1993)] divertor. At all but the lowest densities, the polarization term associated with E×B drifts is stronger still.
Synthesis and characterization of aerosol silicon nanocrystal nonvolatile floating-gate memory devices
Authors: Ostraat M. L. , De Blauwe J. W. , Green M. L. , Bell L. D. , Brongersma M. L. , Casperson J. , Flagan R. C. , Atwater H. A.
Published: July 2002

This letter describes the fabrication and structural and electrical characterization of an aerosol-nanocrystal-based floating-gate field-effect-transistor nonvolatile memory. Aerosol nanocrystal nonvolatile memory devices demonstrate program/erase characteristics comparable to conventional stacked-gate nonvolatile memory devices. Aerosol nanocrystal devices with 0.2 μm channel lengths exhibit large threshold voltage shifts (>3 V), submicrosecond program times, millisecond erase times, excellent endurance (>105 program/erase cycles), and long-term nonvolatility (>106 s) despite thin tunnel oxides (55–60 Å). In addition, a simple aerosol fabrication and deposition process makes the aerosol nanocrystal memory device an attractive candidate for low-cost nonvolatile memory applications.
Rotational-resolved pulsed field ionization-photoelectron study of NO+(A′ 1Σ−,v+=0–17) in the energy range of 17.70–20.10 eV
Authors: Song Y. , Ng C. Y. , Jarvis G. K. , Dressler R. A.
Published: July 2002

We have obtained partially rotationally resolved pulsed field ionization-photoelectron (PFI-PE) spectra of NO in the energy range of 17.70–20.10 eV, covering ionization transitions of NO+(A′ 1Σ−,v+=0–17,J+)←NO(X 2Π3/2,1/2,v″=0,J″). The PFI-PE bands for NO+(A′ 1Σ−,v+=0–17) obtained here represent the first spectroscopic data that allow the direct determination of rotational constants for these states. As in previous studies, the PFI-PE bands are simulated using the Buckingham–Orr–Sichel model as an empirical scheme to derive reliable spectroscopic constants. The simulation, together with comparison with previous He I photoelectron data, has also provided information on intensity enhancements of PFI-PE bands. Accurate spectroscopic constants for NO+(A′ 1Σ−,v+=0–17) obtained in the present study include ionization energies, vibrational constants (ωe=1272.03±1.45 cm−1, ωeχe=11.924±0.188 cm−1, and ωeye=−0.059±0.007 cm−1), and rotational constants [Be=1.3562±0.0024 cm−1, αe=0.017 80±0.000 61 cm−1, and γe=−(1.574±0.328)×10−4 cm−1]. The simulation indicates that continuum photoelectron states can be formed with orbital angular momenta l up to 5, which corresponds to the maximum total angular momentum transfer of |ΔJ|=13/2. Since the dominant rotational branches observed are ΔJ=±1/2, ±3/2, ±5/2, ±7/2, and +9/2, we conclude that continuum photoelectron states are predominantly produced in l=0–3 in the threshold photoionization of NO(X 2Π3/2,1/2) to form NO+(A′ 1Σ−,v+=0–17).
Experimental identification of nitrogen-vacancy complexes in nitrogen implanted silicon
Authors: Adam Lahir Shaik , Law Mark E. , Szpala Stanislaw , Simpson P. J. , Lawther Derek , Dokumaci Omer , Hegde Suri
Published: July 2002

Nitrogen implantation is commonly used in multigate oxide thickness processing for mixed signal complementary metal-oxide-semiconductor and System on a Chip technologies. Current experiments and diffusion models indicate that upon annealing, implanted nitrogen diffuses towards the surface. The mechanism proposed for nitrogen diffusion is the formation of nitrogen-vacancy complexes in silicon, as indicated by ab initio studies by J. S. Nelson, P. A. Schultz, and A. F. Wright [Appl. Phys. Lett. 73, 247 (1998)]. However, to date, there does not exist any experimental evidence of nitrogen-vacancy formation in silicon. This letter provides experimental evidence through positron annihilation spectroscopy that nitrogen-vacancy complexes indeed form in nitrogen implanted silicon, and compares the experimental results to the ab initio studies, providing qualitative support for the same.
Propagation of dust electro-acoustic modes in dusty plasma
Authors: Avinash K.
Published: July 2002

The propagation of the dust electro-acoustic (DEA) mode in dusty plasma with different electron and ion temperatures Te and Ti and different ion species is studied. The critical ratio of the dust space charge to the ion space charge ε for the excitation of DEA mode is found to decrease with increasing Te/Ti and increase with mi/me (mi and me are the ion and electron masses). Thus experiments with hydrogen plasma where electrons are sufficiently hotter than ions and where the reduction in the dust charge with ε is more than 50% are essential for the observation of self-shielding and the DEA mode.
Modified distributed electron cyclotron resonance ion source for the production of large diameter ion beams
Authors: Wartski L. , Coste Ph. , Fusellier C. , Schwebel C. , Aubert J.
Published: July 2002

The work presented in this article concerns the conception and the study of a multiantenna electron cyclotron resonance (ECR) ion source at 2.45 GHz dedicated to the surface treatment of large area materials. In this original device, a microwave plasma is created in a 20 cm in diameter ionization chamber. The 15 cm in diameter extracted ion beam has a current density of about 1 mA/cm2. The applicator is an N-way coaxial power divider in which the N=20 antennas are individually magnetized by internal SmCo bars in order to produce ECR zones in their vicinity. Moreover, the microwave plasma is confined by a multicusp magnetic structure surrounding the ionization chamber. The choice of the source geometry has been guided by the study of some theoretical considerations such as the characteristic diffusion length, the minimum breakdown field, and the penetration depth of the wave into the plasma. Simulations both of the electromagnetic field and the static magnetic field distribution have been carried out in order to validate the final choice of the source geometry. A full characterization of the ECR plasma and of the extracted ion beam was made with different experimental techniques. These results allow us to localize the plasma creation zones inside the ionization chamber. A 120 mA singly charged argon ion beam with a profile homogeneity better than ±5% over 10 cm was obtained 5 cm downstream the extraction system with a 300 W microwave power and a neutral argon pressure of 10−3 mbar in the ionizing chamber.
Time-of-flight study of the ionic and neutral particles produced by pulsed-laser ablation of frozen glycerol
Authors: Wu P. K. , Ringeisen B. R. , Bubb D. M. , Auyeung R. C. Y. , Horwitz J. , Houser E. J. , Piqué A. , McGill R. A. , Chrisey D. B.
Published: July 2002

The emitted particles from pulsed-laser ablation (PLA), λ=193 nm and fluence=88–400 mJ/cm2, of frozen glycerol was examined using time-of-flight mass spectrometry. The data are analyzed using supersonic molecular-beam theory and the result is interpreted using a thermal/fluid-dynamic model. Both intact and fragmented glycerol are emitted in the PLA process at all fluences and their concentration ratio is fluence dependent. Fragmentation occurs predominantly at one of the C–C bonds forming CH2–OH (31 amu) and HO–CH2–CH–OH (61 amu). CH3 is produced at the target which requires the protonation of a CH2 fragment. At fluences higher than 250 mJ/cm2, ions are detected. These ions have very high velocity, >2000 m/s, and their intensity increases with fluences. PLA is thus not suitable for glycerol transfer under these conditions due to fragmentation. The data show that particle emission proceeds as a simple thermal vaporization process at fluences <200 mJ/cm2. Higher fluences will yield a Knudsen layer (KL), which is formed in front of the target surface. For fluences >300 mJ/cm2, particles from the KL go through unsteady adiabatic expansion prior to free flight. Models of particle and ion formation and interaction are proposed and discussed. © 2001 American Institute of Physics.
Nearly constant loss or constant loss in ionically conducting glasses: A physically realizable approach
Authors: Macdonald J. Ross
Published: July 2002

Conductivity exhibiting power-law frequency response with an exponent of unity leads to frequency-independent dielectric loss. Such constant-loss (CL) behavior is not physically realizable over a nonzero frequency range, and approximate expressions that have been used to represent it are inconsistent with the Kronig–Kramers relations. Response models are proposed and investigated that do satisfy these relations and can lead to very close approximation to CL over many frequency decades, as often observed at low temperatures in ionic conductors such as glasses. Apparent CL response is shown to arise from the series connection of a constant-phase complex-power-law element (CPE), with exponent δ (0<δ≪1), and a frequency-independent dielectric constant, εU. Two physically disparate situations can lead to such a series connection. The first involves bulk CPE response in series with an electrode-related, double-layer blocking capacitance involving a dielectric constant εS. Then, apparent CL behavior may be associated with localized ionic motion in the bulk of the material. The second (mirror-image) situation involves CPE response associated with ionic motion in or at an electrode in series with a capacitance such as the bulk high-frequency-limiting total dielectric constant ε∞ or the pure-dielectric quantity εD∞. The present model is used to simultaneously fit both the real and imaginary parts of data derived from measurements on a sodium-trisilicate glass at 122 K. This data set exhibits power-law nearly constant loss for ε′(ω) and apparent CL for ε″(ω). The magnitude of the CL closely satisfies a simple equation involving only δ and εU. Further, for the electrode-power-law situation, estimated values of limiting-high-frequency dielectric constants turn out to be more consistent with bulk values established at much higher temperatures where nearly constant loss is no longer a dominant part of the response. Data at −0.5°C are also analyzed with a more complicated composite model, one that is a generalization of both of the above approaches, and nearly constant loss bulk, not electrode, power-law effects in both ε′(ω) and ε″(ω) are isolated and quantified. For this data set it is shown that electrode effects are important at both ends of the frequency range.
Improvements to x-ray diffractometers: Heaters, hygrometry, and thermodifferential and spectra analyses
Authors: Garcia-Guinea J. , Ortiz R. , Correcher V. , La Iglesia A. , Martı́n-Ramos J. D.
Published: July 2002

We describe a newly designed stainless steel door which holds cooling fluids and permits the connection of a set of self-improvements to mechanical supplies, sensors, thermocouples, electronic circuits, and new software to traditional x-ray diffraction chambers. Some compatible analytical routines, at various gas temperatures (from 18 to 200 °C), stem from restricted combinations of stimulation sources to the sample (x irradiation and heating) and the detector sensors (Geiger x-ray diffraction spectra charge coupled devices, humidity, image TV, thermocouples differential thermal analysis installed). Phase transitions of solids can be detected by spectral, structural, geometrical, and thermodifferential methods.
Structure and ordering of GaN quantum dot multilayers
Authors: Chamard V. , Metzger T. H. , Bellet-Amalric E. , Daudin B. , Adelmann C. , Mariette H. , Mula G.
Published: July 2002

Grazing incidence x-ray techniques are used to characterize the structure of multilayered GaN quantum dots in an AlN matrix. For a dot lateral size of 170 Å, the values of the interdot vertical and lateral correlation lengths are 1500 and 250 Å, respectively. The presence of smaller quantum dots is observed only in the layers deposited first. The strain distribution in the multilayer is also investigated as a function of depth. Along the dot columns, the crystal lattice remains coherent, with elastic relaxation from the bottom to the top of the multilayer.
An improved Q-machine source with a rotating cathode system
Authors: Kaneko T. , Ishida H. , Hatakeyama R. , Sato N.
Published: July 2002

A Q machine with a rotating cathode structure and a limiter-type heat shield is described, which achieves an azimuthally symmetric and radially uniform profile of plasma density and potential. The point of emphasis is that a long time operation is realized by utilizing the latest technique of vacuum- and water-tight feedthroughs, yielding a plasma source for basic experiments with higher accuracy.
Formation of silver nanoclusters by excimer–laser interaction in silver-exchanged soda-lime glass
Authors: Miotello A. , Bonelli M. , Marchi G. De , Mattei G. , Mazzoldi P. , Sada C. , Gonella F.
Published: July 2002

High-power excimer-laser irradiation (248 nm wavelength) at different energy densities (1.3, 2.3, and 4.6 J/cm2) has been performed on silver-exchanged soda-lime glass. Silver nanoclusters have been obtained with average size depending on the energy density of the laser pulses. The excimer laser pulses induce either the reduction of the silver ions or the heating of the irradiated glass matrix. The high mobility of silver atoms in the liquid phase and the segregation effects at the liquid–solid interface can explain the observed silver atoms clustering.