bluuebunny/crossref_metadata_2025 huggingface dataset:
The Atomic Distribution in Red and Black Phosphorus and the Crystal Structure of Black Phosphorus
Authors: Hultgren Ralph , Gingrich N. S. , Warren B. E.
Published: November 2004

No satisfactory crystal structure determination has been made of any of the forms of phosphorus. Five samples of black phosphorus gave identical powder patterns different from those reported by Linck and Jung, whose rhombohedral structure gives improbable interatomic distances and coordination. A sample which had been prepared at room temperature and 35,000 atmospheres gave the diffuse rings of an ``amorphous'' x-ray pattern. Another sample, prepared at 300°C and 8000 atmospheres, is a new form of phosphorus, having the same density as black. Atomic distribution curves of crystalline and ``amorphous'' black and red phosphorus were obtained by the method of Fourier analysis. All four gave practically the same curve, showing three neighbors at 2.28A and about twelve at 3.6A. With the aid of the atomic distribution curves and the fact that certain lines showed a preferred orientation, it was possible to determine the structure of black phosphorus. It consists of double layers; the cell is side-centered orthorhombic with a=3.31A, b=4.38A and c=10.50A. There are eight atoms in the cell, giving a calculated density of 2.69 compared with 2.70 observed. The space group is Vh18—Bmab. The black phosphorus structure allows a closer packing than the arsenic structure, where the atomic environment is similar, and so is favored by the high pressure.
The Rotational Entropy of Nonrigid Polyatomic Molecules
Authors: Eidinoff Maxwell L. , Aston J. G.
Published: November 2004

An expression is derived for the rotational entropy of nonrigid polyatomic molecules with zero potential and apart from nuclear spin and symmetry number corrections. Previous empirical formulae are derived as special simplified cases of the general formula. Applications are made to several important types of molecular models.
Statistical Mechanical Treatment of the Activated Complex in Chemical Reactions
Authors: Kassel Louis S.
Published: November 2004

A possible error in Eyring's recent calculations of absolute reaction rates due to the short life and consequent unsharp quantization of the activated complex is noted. The existence of this error is made more probable by a consideration of the target area required by Eyring's equations at low temperatures. There is no doubt that his treatment becomes asymptotically correct at high temperatures.
The Vapor Pressures of the Isotopic Forms of Water
Authors: Wahl Milton H. , Urey Harold C.
Published: November 2004

The ratio of vapor pressures of H2O16 and HDO16 and of H2O16 and H2O18 have been determined at four temperatures between 11.25°C and 46.35°C. The ratio of vapor pressures of HDO16 are very nearly the geometric mean of the vapor pressure of H2O16 and D2O16. The vapor pressure of H2O18 varies from approximately 0.8 to 1.2 percent less than the vapor pressures of H2O16 for temperatures between 46.35°C and 11.25°C. The application of these to the separation of the hydrogen and oxygen isotopes by distillation is discussed. It seems possible that the hydrogen isotopes can be separated by the fractional distillation of water, but that the separation of the oxygen isotopes by this method will be considerably more difficult.
The Far Ultraviolet Absorption Spectra and Ionization Potentials of C6H6 and C6D6
Authors: Price W. C. , Wood R. W.
Published: November 2004

The absorption spectra of C6H6 and C6D6 have been photographed under high dispersion in the region 2000–1000A. The spectra of both substances are very similar. A strong continuous absorption starts fairly sharply around 1840A and gradually weakens out to zero at 1600A. It is followed by a region extending down to about 1360A which contains very strong sharp bands. The strongest of these bands only suffer small shifts to the violet in going from C6H6 to C6D6. This shift which is due to the change in the difference of zero-point energy between the normal and the excited states reveals the bands to be vibrationless electronic transitions. It was found that these bands could be arranged into two Rydberg series which had approximately the same limit corresponding to an ionization potential of 9.190±.005 volts for C6H6. The ionization potential of C6D6 is only about 3 × 10—4 volts greater than that for C6H6. All the electronic states are split up into patterns which are believed to be caused by true electronic multiplicity. The excitation is apparently from a nonbonding electron more strongly attached to the carbon atom. The vibrations which accompany the bands are comparatively weak. However for C6H6 the following vibration frequencies associated with the excited states were observed. ω1 = 677 cm—1, ω2 = 968 cm—1. These become 630 and 926 cm—1 for C6D6. Tentative assignments of their modes of vibration are made. The bands below 1360A are considerably more diffuse than those previously mentioned and the isotopic shifts to the violet are much larger for these bands. However they are still believed to be vibrationless electronic transitions though they are due to the excitation of an electron which is considerably more bonding than that corresponding to the first ionization potential. A consideration of them enables the approximate value 11.7±.3 volts to be predicted for the second ionization potential of benzene.
Rotating Polar Groups in ``Organic'' Molecules
Authors: Altar William
Published: November 2004

The temperature dependence of the electric moment, observed in the case of molecules with rotating polar groups, permits a quantitative explanation in terms of intra-molecular forces opposing free rotation of the groups. Specifically, the following questions have been raised and treated: I. The statistical weight to be associated with a configuration. II. Approximation of the periodic potential function by its first and second Fourier component. III. An application to 1,2-dichloroethane is given and a plausible potential of interaction between the two CH2Cl groups is obtained. The result suggests the presence of repulsive forces between two bound chlorine atoms at distances as large as 4.0 Angstrom. IV. The related question of the thermal equilibrium ratio of the cis and trans isomers of dichloroethylene is discussed. A new explanation of the observed value is proposed, which attributes about equal heat of formation to both isomeric forms.
Perfect Ternary Solid Solutions
Authors: Seltz Harry
Published: November 2004

In this paper equations are developed for calculating the solidus and liquidus surfaces, with tie-lines, for ternary systems showing complete solid solubility, based on the assumption that both liquid and solid solutions are perfect. The forms of the liquidus and solidus isotherms predicted by these equations are considered for an hypothetical example. The ternary system of gold, copper and nickel is shown to deviate markedly from ideal behavior at low mol fractions of gold, even though the copper-nickel system is practically ideal in its binary behavior.
Electronic Structures of Molecules XI. Electroaffinity, Molecular Orbitals and Dipole Moments
Authors: Mulliken Robert S.
Published: November 2004

A convenient criterion for defining equal electronegativity of two atoms is stated in terms of coefficients in LCAO approximate molecular orbitals. Connections between relative electronegativities, coefficients in LCAO orbitals, effective charges on atoms in partially polar molecules, and dipole moments, are then analyzed, and various equations are obtained expressing these connections. The discussion is largely applicable to polyatomic as well as to diatomic molecules. A theoretical derivation is given for an empirical equation, found by Pauling, which forms a basis for the latter's approximate scale of relative electronegativities. Pauling's and other possible approximate scales are discussed, and it is shown how an approximate ``absolute electroaffinity'' can conveniently be defined on each scale. A very rough theoretical justification is given for the empirically observed proportionality between relative electronegativities obtained from Pauling's and from the writer's scale. The necessary existence of a ``homopolar dipole'' contribution to the electric moment of any bond is shown, provided the atoms forming the bond are of unequal size. By ``homopolar dipole'' is meant a contribution which would not vanish, for atoms of unequal size, even if they are of equal electroaffinity. Dipole moments of H2O, NH3 and HX are briefly discussed. It is concluded that the dipole moment scale of electronegativity is probably not well founded. An important object of the paper is to show how electroaffinity and other data can be used in the approximate determination of the polarities of molecular orbitals and so of bonds, the results being expressed both in terms of coefficients in LCAO molecular orbitals and in terms of effective charges transferred. Applications are made to the electronic structures of various diatomic molecules, especially HI, HI+, HO—, ClO—.
Incomplete Atomic Arrangement in Crystals
Authors: Verwey E. J. W.
Published: November 2004

γ-Fe2O3. γ-Al2O3 and the oxide obtained by the electrolytical oxydation of Al (γ′-Al2O3) are averaged structures with regard to the cations. Both the γ and γ′ oxides have the same oxygen-lattice but there is a distinct difference in the degree of incomplete arrangement of the cations. γ′-Al2O3 and γ-Al2O3 (Fe2O3) are intermediate cases between the amorphous state and the completely arranged state.
Dynamic phase separation: From coarsening to turbulence via structure formation
Authors: Golovin A. A. , Pismen L. M.
Published: November 2004

We investigate some new two-dimensional evolution models belonging to the class of convective Cahn–Hilliard models: (i) a local model with a scalar order parameter, (ii) a nonlocal model with a scalar order parameter, and (iii) a model with a vector order parameter. These models are applicable to phase-separating system where concentration gradients cause hydrodynamic motion due to buoyancy or Marangoni effect. The numerical study of the models shows transition from coarsening, typical of Cahn–Hilliard systems, to spatiotemporally irregular behavior (turbulence), typical of the Kuramoto–Sivashinsky equation, which is obtained in the limit of very strong driving. The transition occurs not in a straightforward way, but through the formation of spatial patterns that emerge for intermediate values of the driving intensity. As in driven one-dimensional models studied before, the mere presence of the driving force, however small, breaks the symmetry between the two separating phases, as well as increases the coarsening rate. With increasing driving, coarsening stops. The dynamics is generally irregular at strong driving, but exhibits specific structural features.
Curvature induced periodic attractor on growth interface
Authors: Pocheau A. , Bottin-Rousseau S.
Published: November 2004

We experimentally address the long-time dynamics of an artificially curved growth interface in directional solidification. Repetitive cell nucleations are found to appear in a disordered way but to eventually organize themselves coherently, at long times. This behavior is recovered by simulation of a nonlinear advection-diffusion model for the phase dynamics. The existence of a periodic attractor is shown by deriving a Liapunov functional for the cellular pattern organization on time ranges that include the singular events of cell nucleation.
Integrable renormalization I: The ladder case
Authors: Ebrahimi-Fard Kurusch , Guo Li , Kreimer Dirk
Published: November 2004

In recent years a Hopf algebraic structure underlying the process of renormalization in quantum field theory was found. It led to a Birkhoff factorization for (regularized) Hopf algebra characters, i.e., for Feynman rules. In this work we would like to show that this Birkhoff factorization finds its natural formulation in terms of a classical r-matrix, coming from a Rota–Baxter structure underlying the target space of the regularized Hopf algebra characters. Working in the rooted tree Hopf algebra, the simple case of the Hopf subalgebra of ladder trees is treated in detail. The extension to the general case, i.e., the full Hopf algebra of rooted trees or Feynman graphs, is briefly outlined.
Quantum groups and deformation quantization: Explicit approaches and implicit aspects
Authors: Bonneau Philippe , Gerstenhaber Murray , Giaquinto Anthony , Sternheimer Daniel
Published: November 2004

Deformation quantization, which gives a development of quantum mechanics independent of the operator algebra formulation, and quantum groups, which arose from the inverse scattering method and a study of Yang–Baxter equations, share a common idea abstracted earlier in algebraic deformation theory: that algebraic objects have infinitesimal deformations which may point in the direction of certain continuous global deformations, i.e., “quantizations.” In deformation quantization the algebraic object is the algebra of “observables” (functions) on symplectic phase space, whose infinitesimal deformation is the Poisson bracket and global deformation a “star product,” in quantum groups it is a Hopf algebra, generally either of functions on a Lie group or (often its dual in the topological vector space sense, as we briefly explain) a completed universal enveloping algebra of a Lie algebra with, for infinitesimal, a matrix satisfying the modified classical Yang–Baxter equation (MCYBE). Frequently existence proofs are known but explicit formulas useful for physical applications have been difficult to extract. One success here comes from “universal deformation formulas” (UDFs), expressions built from a Lie algebra which deform any algebra on which the Lie algebra operates as derivations. The most famous of these is the Moyal product, a special case of a class in which the Lie algebra is Abelian. Another comes from recognition that the Belavin–Drinfel’d solutions to the MCYBE are, in fact, infinitesimal deformations for which, in the case of the special linear groups, it is possible to give explicit formulas for the corresponding quantum Yang–Baxter equations. This review paper discusses, necessarily in brief, these and related topics, including “twisting” as a form of UDF and finding formulas for “preferred deformations” of Hopf algebras in which the multiplication or comultiplication is rigid and must be preserved in the course of deformation.
Division algebras: Family replication
Authors: Dixon Geoffrey
Published: November 2004

The known link of the division algebras to 10-dimensional spacetime and one leptoquark family is extended to encompass three leptoquark families.
On the Fock space for nonrelativistic anyon fields and braided tensor products
Authors: Goldin Gerald A. , Majid Shahn
Published: November 2004

We realize the physical N-anyon Hilbert spaces, introduced previously via unitary representations of the group of diffeomorphisms of the plane, as N-fold braided-symmetric tensor products of the 1-particle Hilbert space. This perspective provides a convenient Fock space construction for nonrelativistic anyon quantum fields along the more usual lines of boson and fermion fields, but in a braided category, and clarifies how discrete (lattice) anyon fields relate to anyon fields in the continuum. We also see how essential physical information is encoded. In particular, we show how the algebraic structure of the anyonic Fock space leads to a natural anyonic exclusion principle related to intermediate occupation number statistics, and obtain the partition function for an idealized gas of fixed anyonic vortices.
Recoupling Lie algebra and universal ω-algebra
Authors: Joyce William P.
Published: November 2004

We formulate the algebraic version of recoupling theory suitable for commutation quantization over any gradation. This gives a generalization of graded Lie algebra. Underlying this is the new notion of an ω-algebra defined in this paper. ω-algebra is a generalization of algebra that goes beyond nonassociativity. We construct the universal enveloping ω-algebra of recoupling Lie algebras and prove a generalized Poincaré–Birkhoff–Witt theorem. As an example we consider the algebras over an arbitrary recoupling of Zn graded Heisenberg Lie algebra. Finally we uncover the usual coalgebra structure of a universal envelope and substantiate its Hopf structure.
Wire explosion in vacuum: Simulation of a striation appearance
Authors: Oreshkin V. I. , Baksht R. B. , Ratakhin N. A. , Shishlov A. V. , Khishchenko K. V. , Levashov P. R. , Beilis I. I.
Published: November 2004

This paper presents the simulation results of electrical explosion of thin Al wires at a current rise time of several tens of nanoseconds and at a current density of ∼108 A/cm2. Studies include the matter phase transfers and magnetohydrodynamic (MHD) model. A two-dimensional MHD model based on the particle-in-cell method is used to consider the formation of striations and a low-density plasma corona surrounding the wire. The striations are shown to occur through evolving overheat instabilities early in the explosion, when the conductor material is in the liquid or two-phase states. The process results from the decrease in liquid metal conductivity with increasing temperature and decreasing density.
Higher gauge theory—differential versus integral formulation
Authors: Girelli Florian , Pfeiffer Hendryk
Published: November 2004

The term higher gauge theory refers to the generalization of gauge theory to a theory of connections at two levels, essentially given by 1- and 2-forms. So far, there have been two approaches to this subject. The differential picture uses non-Abelian 1- and 2-forms in order to generalize the connection 1-form of a conventional gauge theory to the next level. The integral picture makes use of curves and surfaces labeled with elements of non-Abelian groups and generalizes the formulation of gauge theory in terms of parallel transports. We recall how to circumvent the classic no-go theorems in order to define non-Abelian surface ordered products in the integral picture. We then derive the differential picture from the integral formulation under the assumption that the curve and surface labels depend smoothly on the position of the curves and surfaces. We show that some aspects of the no-go theorems are still present in the differential (but not in the integral) picture. This implies a substantial structural difference between nonperturbative and perturbative approaches to higher gauge theory. We finally demonstrate that higher gauge theory provides a geometrical explanation for the extended topological symmetry of BF-theory in both pictures.
Avoiding superluminal propagation of higher spin waves via projectors onto W2 invariant subspaces
Authors: Napsuciale Mauro , Kirchbach Mariana
Published: November 2004

We propose to describe higher spins as invariant subspaces of the Casimir operators of the Poincaré Group, P2, and the squared Pauli–Lubanski operator, W2, in a properly chosen representation, ψ(p) (in momentum space), of the Homogeneous Lorentz Group. The resulting equation of motion for any field with s≠0 is then just a specific combination of the respective covariant projectors. We couple minimally electromagnetism to this equation and show that the corresponding wave fronts of the classical solutions propagate causally. Furthermore, for (s,0)⊕(0,s) representations, the formalism predicts the correct gyromagnetic factor, gs=1/s. The advocated method allows us to describe any higher spin without auxiliary conditions and by one covariant matrix equation alone. This master equation is only quadratic in the momenta and its dimensionality is that of ψ(p). We prove that the suggested master equation avoids the Velo–Zwanziger problem of superluminal propagation of higher spin waves and points toward a consistent description of higher spin quantum fields.
A new geometrical look at gravity coupled with Yang–Mills fields
Authors: Vignolo Stefano , Cianci Roberto
Published: November 2004

A new geometrical framework for tetrad-affine formulation of gravity, pure or coupled with Yang–Mills fields, is proposed. After analyzing the geometrical properties of the new mathematical setting, field equations are deduced from a variational principle in the Poincaré–Cartan formalism. A generalized Noether Theorem is stated and classical relationship between symmetries and conserved quantities are recovered in the newer scheme. Some explicit examples are given.
Hyperbolic Kac Moody algebras and Einstein billiards
Authors: de Buyl Sophie , Schomblond Christiane
Published: November 2004

We identify the hyperbolic Kac Moody algebras for which there exists a Lagrangian of gravity, dilatons, and p-forms which produces a billiard that can be identified with their fundamental Weyl chamber. Because of the invariance of the billiard upon toroidal dimensional reduction, the list of admissible algebras is determined by the existence of a Lagrangian in three space–time dimensions, where a systematic analysis can be carried out since only zero-forms are involved. We provide all highest dimensional parent Lagrangians with their full spectrum of p-forms and dilaton couplings. We confirm, in particular, that for the rank 10 hyperbolic algebra, CE10=A15(2)∧, also known as the dual of B8∧∧, the maximally oxidized Lagrangian is nine-dimensional and involves besides gravity, 2 dilatons, a 2-form, a 1-form, and a 0-form.
Extremely high electron mobility of pseudomorphic In0.74Ga0.26As∕In0.46Al0.54As modulation-doped quantum wells grown on (411)A InP substrates by molecular-beam epitaxy
Authors: Kitada T. , Aoki T. , Watanabe I. , Shimomura S. , Hiyamizu S.
Published: November 2004

Much enhanced electron mobility of 105 000cm2∕Vs with a high sheet electron concentration (Ns) of 3.1×1012cm−12 was obtained at 77K in pseudomorphic In0.74Ga0.26As∕In0.46Al0.54As modulation-doped quantum well (MD-QW) grown on a (411)A InP substrate by molecular-beam epitaxy. This MD-QW has the “(411)A super-flat interfaces” (effectively atomically flat interfaces over a wafer-size area), which leads to significant reduction of interface roughness scattering at low temperatures. The highest electron mobility of the (411)A MD-QW was achieved by using pseudomorphic In0.46Al0.54As barriers. The electron mobility is 44% higher than that (73 000cm2∕Vsat77K) of a similar MD-QW structure grown on a conventional (100)InP substrate.
Lifshits tails for random smooth magnetic vortices
Authors: Borg J. L. , Pulé J. V.
Published: November 2004

We study the density of states of the Pauli Hamiltonian with a Poisson random distribution of smooth finite-width vortices and we obtain classical bounds for the Lifshits tails for them. These Hamiltonians are smooth approximations to the self-adjoint extensions of the Aharonov–Bohm Hamiltonian. In this case because pairs of impurities are coupled by the magnetic field we cannot use the Laplace characteristic functional.
Interfacial reaction depending on the stack structure of Al2O3 and HfO2 during film growth and postannealing
Authors: Cho M.-H. , Chung K. B. , Chang H. S. , Moon D. W. , Park S. A. , Kim Y. K. , Jeong K. , Whang C. N. , Lee D. W. , Ko D.-H. , Doh S. J. , Lee J. H. , Lee N. I.
Published: November 2004

Interfacial reactions as a function of the stack structure of Al2O3 and HfO2 grown on Si by atomic-layer deposition were examined by various physical and electrical measurements. In the case of an Al2O3 film with a buffer layer of HfO2, reactions between the Al2O3 and Si layers were suppressed, while a HfO2 film with an Al2O3 buffer layer on the Si readily interacted with Si, forming a Hf–Al–Si–O compound. The thickness of the interfacial layer increased dramatically after an annealing treatment in which a buffer layer of Al2O3 was used, while no change in thickness was observed in the film in which a HfO2 buffer layer was used. Moreover, the stoichiometric change caused by a different reaction process altered the chemical state of the films, which affected charge trapping and the interfacial trap density.
Thermoelastic generation of cylindrical Rayleigh waves and whispering gallery modes by pulsed-laser excitation
Authors: Hu Wenxiang , Qian Menglu , Cantrell John H.
Published: November 2004

An analytical model of cylindrical surface waves excited thermoelastically by a pulsed-laser line source is presented. The laser-generated transient response of the cylindrical Rayleigh wave and the first three whispering gallery (WG) modes of an aluminum cylinder are calculated from the model using residue theory and the fast Fourier transform technique. The superposed wave form of the four transient modes is in excellent agreement with the wave form obtained from experiment and reveals that the peaks observed in experimental data are the result of wave-form interference from the superposition of all WG modes.
Interaction of small perturbations with shock waves
Authors: Lubchich Andris A. , Pudovkin Mikhail I.
Published: November 2004

Interaction of hydrodynamic waves with plane shock waves under the linear approximation is studied. Two classical problems, namely, wave transformation and a rippling instability on a shock wave, are examined. Starting from 1945, these problems have been analyzed repeatedly. A number of enigmas have been revealed during more than half a century. We argue that some of them can be obviated by a revision of the existing approach to description of shock oscillations. These oscillations originate either due to incident perturbations or spontaneously (the latter case is relevant to the problem of shock stability) and are a first order of smallness. It is well known that the linear approximation enables solution of the problem on the unperturbed discontinuity surface, with the surface oscillations taken as a linearly independent mode. This mode signifies a transition from a local reference frame connected with the perturbed shock surface to a laboratory frame related to the unperturbed plane shock. It is traditionally supposed that two following kinematic effects are essential in this transition. One is a deformation of the surface, leading to small oscillations of the shock normal and shock tangent; the other is an additional velocity of the shock. We state that the conventional approach is incomplete and leads to certain methodical difficulties. In particular, within the conventional framework the shock oscillations do not satisfy the normal component of the Euler equation. Thus, this mode is not a partial solution of the hydrodynamic equations; therefore, it is not a linearly independent one. In order to avoid this difficulty and accomplish the description of the above transition, it is necessary to take into account the effect associated with noninertiality of the local reference frame. The transition into the noninertial frame corresponds to emergence of an inertial force field and additional pressure. The additional pressure is the field potential. It is of the first order of smallness and it influences the perturbed shock surface in the local frame, counterbalancing the effect of dynamic momentum flux oscillations. The physical ground of inertial force appearance is nonideality of the medium inside the thin front of a real shock wave. The role of this additional effect in the interaction of a small-amplitude wave with a plane shock is examined.
Multispectral operation of self-assembled InGaAs quantum-dot infrared photodetectors
Authors: Kim Seongsin M. , Harris James S.
Published: November 2004

We report two-color InGaAs quantum-dot infrared photodetectors. The InGaAs self-assembled quantum dots were grown on InGaP matrix via metalorganic chemical vapor deposition and fabricated as intersubband photoconductive structure. Bias controlled two-color photoconductive responses were obtained at two different infrared window, mid-infrared (IR) of λ=5.5μm and far-IR of λ=9.2μm at 77K. Our devices were operated with low dark currents and high optical gains, and resulted in peak detectivity, D*, of 4.7×109cmHz1∕2∕W at λ=5.5μm with bias of −2.0V, and 7.2×108cmHz1∕2∕W at λ=9.2μm with bias of −0.8V.
Continuous-wave ultraviolet generation at 354nm in a periodically poled MgO:LiNbO3 by frequency tripling of a diode end-pumped Nd:GdVO4 microlaser
Authors: Mizuuchi K. , Morikawa A. , Sugita T. , Yamamoto K. , Pavel N. , Taira T.
Published: November 2004

Continuous-wave UV radiation at 354nm, the third harmonic of a Nd:GdVO4 laser operating at 1063nm, is reported from single-pass cascaded, first-order periodically poled MgO:LiNbO3 (PPMgLN) crystals. A high-voltage multipulse poling method was used in order to realize PPMgLN with uniform domain period (Λ) of micron-order width and 50% duty cycle along the entire crystal length. Initially, second-harmonic generation of the 1063nm Nd:GdVO4 laser at 2.1%∕W conversion efficiency, producing 1.15W at 531nm, is obtained from a 10-mm-long PPMgLN with Λ=6.95μm. Sum frequency mixing of this 531nm light with the residual 1063nm fundamental radiation in a 3.6-mm-long PPMgLN with Λ=1.78μm produces 47mW of UV with 3.9%∕W∕cm normalized conversion efficiency.
Hydrogen plasma enhancement of boron activation in shallow junctions
Authors: Vengurlekar A. , Ashok S. , Kalnas C. E. , Theodore N. D.
Published: November 2004

The ability to activate large concentrations of boron at lower temperatures is a persistent contingency in the continual drive for device scaling in Si microelectronics. We report on our experimental observations offering evidence for enhancement of electrical activation of implanted boron dopant in the presence of atomic hydrogen in silicon. This increased electrical activity of boron at lower anneal temperature is attributed to the creation of vacancies in the boron-implanted region, lattice-relaxation caused by the presence of atomic hydrogen, and the effect of atomic hydrogen on boron-interstitial cluster formation.
Two-dimensional dendritic ZnO nanowires from oxidation of Zn microcrystals
Authors: Fan Hong Jin , Scholz Roland , Kolb Florian M. , Zacharias Margit
Published: November 2004

Spontaneous formation of ZnO dendritic nanowires has been achieved on the faceted surfaces of polyhedral Zn microcrystals by oxidizing the latter at 600°C. Electron microscopy investigations reveal that all the dendritic branches are elongated in ⟨11–20⟩ directions within the ±(0001) primary planes, forming two-dimensional web-like structure. Homoepitaxial interconnections are observed at the branch-to-arm and branch-to-branch regions, and the whole dendrites are wurtzite single crystals. The growth process of the dendritic nanowires is discussed, which is proposed to be a combination of “self-catalytic liquid–solid” and vapor–solid process.
Elliptically polarized pump-probe spectroscopy and its application to observation of electron-spin relaxation in GaAs quantum wells
Authors: Lai Tianshu , Liu Luning , Shou Qian , Lei Liang , Lin Weizhu
Published: November 2004

An elliptically polarized pump-probe spectroscopy is developed. A theoretical model is derived from the rate equations of two-level system with small signal approximation to describe the experimental signal of the spectroscopy. The spectroscopy eliminates the systematic errors between theories and experimental results in present circularly polarized pump-probe spectroscopy, and is implemented easily in experiments. The initial degree of spin polarization of carriers in an excited state can be extracted by means of the spectroscopy, which is an important parameter in the investigation of spatial transport of spin polarization. The electron-spin relaxation in GaAs quantum wells is studied by using this spectroscopy.
The double-sided ultrasonic beam displacement
Authors: Declercq Nico F. , Degrieck Joris , Leroy Oswald
Published: November 2004

It is a well-established idea in optics as well as in ultrasonics that a bounded Gaussian beam, when reflected from an interface, can be displaced in the forward or in the backward direction, depending on the propagation direction of leaky waves that are generated by the incident beam. Such a displacement is often accompanied by the so-called Schoch effect characterized by a null strip in between a specular and a nonspecular reflected beam, and a trailing field that is much further displaced. The current letter shows experimentally and numerically that a simultaneous forward and backward displacement is possible accompanied by two null strips and being only the result of forward propagating Lamb waves.
Optical characteristics of 1.55μm GaInNAs multiple quantum wells
Authors: Sun H. D. , Clark A. H. , Liu H. Y. , Hopkinson M. , Calvez S. , Dawson M. D. , Qiu Y. N. , Rorison J. M.
Published: November 2004

We report the optical characterization of high-quality 1.55μm GaxIn1−xNyAs1−y multiquantum wells (MQWs), grown on GaAs with Ga(In)N0.01As spacer layers. The transitions between the quantized QW states of the electrons and holes have been identified using photoluminescence excitation spectroscopy. Their energies are consistent with theoretical fitting based on the band anticrossing model. It is also confirmed by detailed spectroscopic measurements that the addition of even a small amount of In to GaN0.01As barriers remarkably improves the optical characteristics of the QWs. The results imply that although strain-compensated GaInNAs MQWs provide a feasible approach to realizing 1.55μm optical emission, the relative lattice mismatch between the wells and barriers is critical to the optical quality of the related QWs.
Optical fiber affinity biosensor based on localized surface plasmon resonance
Authors: Mitsui Keita , Handa Yoichiro , Kajikawa Kotaro
Published: November 2004

A highly sensitive micrometer-sized optical fiber affinity biosensor is reported based on the localized surface plasmon resonance in gold nanoparticles adsorbed at an endface of an optical fiber. This sensor probes the affinity between biological molecules in real time without any labeling of the analyte. The highest resolution of 10−5 in refractive index units is demonstrated with a red-light-emitting diode used as a light source. This value corresponds to an adsorption amount of 10−12g∕mm2 in the case of the affinity measurement. This sensitivity is similar to that of the conventional surface plasmon resonance biosensors that use attenuated total reflection optics.
The effect of a short-wavelength mode on the evolution of a long-wavelength perturbation driven by a strong blast wave
Authors: Miles A. R. , Edwards M. J. , Blue B. , Hansen J. F. , Robey H. F. , Drake R. P. , Kuranz C. , Leibrandt D. R.
Published: November 2004

Shock-accelerated material interfaces are potentially unstable to both the Richtmyer–Meshkov and Rayleigh–Taylor (RT) instabilities. Shear that develops along with these instabilities in turn drives the Kelvin–Helmholtz instability. When driven by strong shocks, the evolution and interaction of these instabilities is further complicated by compressibility effects. This paper details a computational study of the formation of jets at strongly driven hydrodynamically unstable interfaces, and the interaction of these jets with one another and with developing spikes and bubbles. This provides a nonlinear spike-spike and spike-bubble interaction mechanism that can have a significant impact on the large-scale characteristics of the mixing layer. These interactions result in sensitivity to the initial perturbation spectrum, including the relative phases of the various modes, that persists long into the nonlinear phase of instability evolution. Implications for instability growth rates, the bubble merger process, and the degree of mix in the layer are described. Results from relevant deceleration RT experiments, performed on OMEGA [J. M. Soures et al., Phys. Plasmas 5, 2108 (1996)], are shown to demonstrate some of these effects.
Kinetic study of velocity distributions in nanoscale semiconductor devices under room-temperature operation
Authors: Sano N.
Published: November 2004

Quasiballistic electron transport in nanoscale semiconductor structures is investigated to clarify the importance of scatterings under room-temperature operation as reflected in the velocity distribution functions. The analyses are carried out for n+-n-n+ structures based on the semiclassical Boltzmann transport equation (BTE). It is shown that the number of electrons with negative velocity grows exponetially due to scatterings around the top of the electronic potential barrier in the channel region and, thus, the scatterings cannot be neglected even in nanoscale device structures. This is closely related to the mathematical structure of the BTE whose solution exhibits the boundary-layer structure.
Determination of energy barrier profiles for high-k dielectric materials utilizing bias-dependent internal photoemission
Authors: Brewer Julie Casperson , Walters Robert J. , Bell L. Douglas , Farmer Damon B. , Gordon Roy G. , Atwater Harry A.
Published: November 2004

We utilize bias-dependent internal photoemission spectroscopy to determine the metal∕dielectric∕silicon energy barrier profiles for Au∕HfO2∕Si and Au∕Al2O3∕Si structures. The results indicate that the applied voltage plays a large role in determining the effective barrier height and we attribute much of the variation in this case to image potential barrier lowering in measurements of single layers. By measuring current at both positive and negative voltages, we are able to measure the band offsets from Si and also to determine the flatband voltage and the barrier asymmetry at 0V. Our SiO2 calibration sample yielded a conduction band offset value of 3.03±0.1eV. Measurements on HfO2 give a conduction band offset value of 2.7±0.2eV (at 1.0V) and Al2O3 gives an offset of 3.3±0.1 (at 1.0V). We believe that interfacial SiO2 layers may dominate the electron transport from silicon for these films. The Au∕HfO2 barrier height was found to be 3.6±0.1eV while the Au∕Al2O3 barrier is 3.5±0.1eV.
High dielectric constant TiO2 thin films on a Ru electrode grown at 250 °C by atomic-layer deposition
Authors: Kim Seong Keun , Kim Wan-Don , Kim Kyung-Min , Hwang Cheol Seong , Jeong Jaehack
Published: November 2004

TiO 2 thin films with high dielectric constants (83–100) were grown on a Ru electrode at a growth temperature of 250 °C using the atomic-layer deposition method. The as-deposited films were crystallized with rutile structure. Adoption of O3 with a very high concentration (400g∕m3) was crucial for obtaining the rutile phase and the high dielectric constant. The leakage current density of a TiO2 film with an equivalent oxide thickness of 1.0–1.5 nm was 10−6–10−8A∕cm2 at ±1V. All these electrical properties were obtained after limited postannealing where the annealing temperature was <500°C, which is crucial to the structural stability of the Ru electrode. Therefore, these TiO2 films are very promising as the capacitor dielectrics of dynamic random access memories. TiO2 films grown on a bare Si wafer or Pt electrode by the same process had anatase structure and a dielectric constant of ∼40.
Growth model for multicellular tumor spheroids
Authors: Delsanto Pier Paolo , Guiot Caterina , Degiorgis Piero Giorgio , Condat Carlos A. , Mansury Yuri , Deisboeck Thomas S.
Published: November 2004

Most organisms grow according to simple laws, which in principle can be derived from energy conservation and scaling arguments, critically dependent on the relation between the metabolic rate B of energy flow and the organism mass m. Although this relation is generally recognized to be of the form B(m)=mp, the specific value of the exponent p is the object of an ongoing debate, with many mechanisms being postulated to support different predictions. We propose that multicellular tumor spheroids provide an ideal experimental model system for testing these allometric growth theories, especially under controlled conditions of malnourishment and applied mechanical stress.
Long-distance remote laser-induced breakdown spectroscopy using filamentation in air
Authors: Stelmaszczyk Kamil , Rohwetter Philipp , Méjean Guillaume , Yu Jin , Salmon Estelle , Kasparian Jérôme , Ackermann Roland , Wolf Jean-Pierre , Wöste Ludger
Published: November 2004

We demonstrate remote elemental analysis at distances up to 90m, using a laser-induced breakdown spectroscopy scheme based on filamentation induced by the nonlinear propagation of unfocused ultrashort laser pulses. A detailed signal analysis suggests that this technique, remote filament-induced breakdown spectroscopy, can be extended up to the kilometer range.
Fabrication of self-written waveguide in photosensitive polyimide resin by controlling photochemical reaction of photosensitizer
Authors: Yamashita K. , Kuro T. , Oe K. , Mune K. , Tagawa K. , Naitou R. , Mochizuki A.
Published: November 2004

We have investigated optical properties of photosensitive polyimide appropriating for long self-written waveguide fabrication. From systematic measurements of absorption properties, it was found that photochemical reaction of photosensitizer dissolved in the photosensitive polyimide resins relates to transparency after the exposure, which limits the length of the fabricated self-written waveguide. By controlling the photochemical reaction, in which the photosensitive polyimide resin has sufficient transparency during exposure, four times longer self-written waveguide core was fabricated.
Domain-size-dependent exchange bias in Co∕LaFeO3
Authors: Scholl A. , Nolting F. , Seo J. W. , Ohldag H. , Stöhr J. , Raoux S. , Locquet J.-P. , Fompeyrine J.
Published: November 2004

X-ray microscopy using magnetic linear dichroism of a zero-field-grown multidomain Co∕LaFeO3 ferromagnet∕antiferromagnet sample shows a local exchange bias of random direction and magnitude. A statistical analysis of the local bias of individual micron-size magnetic domains demonstrates an increasing bias field with decreasing domain size as expected for a random distribution of pinned, uncompensated spins, which are believed to mediate the interface coupling. A linear dependence with the inverse domain diameter is found.
ErAs:GaAs photomixer with two-decade tunability and 12μW peak output power
Authors: Bjarnason J. E. , Chan T. L. J. , Lee A. W. M. , Brown E. R. , Driscoll D. C. , Hanson M. , Gossard A. C. , Muller R. E.
Published: November 2004

This letter reports the fabrication and demonstration of an ErAs:GaAs interdigitated photomixer as a tunable THz source ranging from ∼20GHzto∼2THz, with 12μW maximum power typically around ∼90GHz. Each photomixer is coupled to a composite dipole-spiral planar antenna that emits a Gaussian-type beam into free space. The beam switches from dipole to spiral antenna behavior as the frequency increases. A distributed Bragg reflector is embedded in the device beneath the photomixer to increase its external quantum efficiency. The photomixer has a 900Å thick silicon nitride coating which serves as an antireflection and passivation layer, and also improves the reliability and heat tolerance of the device.
Multiple-exposure holographic lithography with phase shift
Authors: Moon Jun Hyuk , Yang Seung-Man , Pine David J. , Chang Won-Seok
Published: November 2004

We demonstrated a multiple-exposure holographic lithography with phase shift. The phase shift was utilized to translate two-dimensional (2D) and three-dimensional (3D) interference patterns. The multiple exposure of the interference patterns with a controlled phase shift created partially overlapped patterns, resulting in 2D and 3D polymer lattices of shape-anisotropic atoms. This approach can be used to design directly the unit atoms in periodic patterns for tunable optical properties.
Synthesis and piezoresponse of highly ordered Pb(Zr0.53Ti0.47)O3 nanowire arrays
Authors: Zhang X. Y. , Zhao X. , Lai C. W. , Wang J. , Tang X. G. , Dai J. Y.
Published: November 2004

We report the synthesis and characterization of ferroelectric lead zirconate titanate Pb(Zr0.53Ti0.47)O3 (PZT) nanowires. The PZT nanowires, with diameters of about 45nm and lengths of about 6μm, were fabricated by means of a sol-gel method utilizing nanochannel alumina templates. After postannealing at 700°C, the PZT nanowires exhibit a polycrystalline microstructure, and x-ray diffraction and transmission electron microscopy study revealed their perovskite crystal structure. The piezoelectric characteristics of individual PZT nanowires were demonstrated by piezoresponse force microscopy.
Förster energy transfer from blue-emitting polymers to colloidal CdSe∕ZnS core shell quantum dots
Authors: Anni M. , Manna L. , Cingolani R. , Valerini D. , Cretí A. , Lomascolo M.
Published: November 2004

We have studied the interactions in the solid phase between a blue-light-emitting organic conjugated polymer {poly[(9,9-dihexylfluorenyl-2,7-diyl)-alt-co-(9,ethyl-3,6-carbazole)]} and colloidal CdSe∕ZnS core shell quantum dots. We demonstrate by time resolved photoluminescence measurements that efficient Förster energy transfer takes place from the polymer acting as the donor and the CdSe∕ZnS dots, acting as the acceptors. A Förster radius of about 80±15Å is extracted from the analysis of the relaxation dynamics based on the solution of the donor-acceptor coupled rate equations. This value is in good agreement with the value extracted from the steady state spectra and indicates that efficient energy tranfer from a polymeric host to a nanocrystal guest can occur. Our results are relevant to the application of hybrid organic/inorganic systems to light-emitting devices.
High-sensitivity microwave vector detection at extremely low-power levels for low-dimensional electron systems
Authors: Hsieh W. H. , Kuan C. H. , Suen Y. W. , Chang S. Y. , Li L. C. , Lee B. C. , Lee C. P.
Published: November 2004

We present a high-sensitivity microwave vector detection system for studying the low-dimensional electron system embedded in the gaps of a coplanar waveguide at low temperatures. Using this system, we have achieved 0.005% and 0.001° resolutions in amplitude and phase variations, respectively, at 10GHz in a magnetotransport measurement on a quantum-wire array with an average signal power less than −75dBm into the sample at 0.3K. From the measured phase variation, we can distinguish a very tiny change in the induced dipole moment of each quantum wire.
Hydrogen-induced atomic deformation in SrBi2Nb2O9 perovskite structure
Authors: Kim Ik Soo , Choi In-Hoon , Kim Yong Tae , Kim Seong-Il , Yoo Dong Chul , Lee Jeong Yong
Published: November 2004

The origin of hydrogen-induced structural deformation of ferroelectric SrBi2Nb2O9 (SBN) thin films is investigated by annealing in forming gas (3%H2–97%N2). High resolution transmission electron microscopy and fast Fourier transformation analysis reveal that the {115} planes are shifted upward and downward by 0.92Å along {115} plane after forming gas annealing, resulting in (00l) planes inclined by 9.54°. This shifted distance of 0.92Å means that the perovskite structure is distorted by 29.98% compared to the normal interatomic distance of 3.077Å. This distorted perovskite structure results in degradation of ferroelectric properties. However, this lattice deformation and ferroelectric property of SBN films are recovered after annealing in oxygen ambient.
Current-voltage characteristics of high-efficiency silicon solar cells from photoluminescence
Authors: Ferraioli L. , Maddalena P. , Parretta A. , Wang A. , Zhao J.
Published: November 2004

Series resistance is a fundamental power-limiting factor for a solar cell. It is known to depend on the ohmic losses due to the metal contact resistance, the metal–semiconductor contact resistance, the substrate resistance, and the emitter sheet resistance. A typical operating approach consists of indirect measurements of the total series resistance. Our method, based on photoluminescence, is capable of generating an illuminated current–voltage curve free from the effect of the contact series resistance, giving an immediate idea of true cell performance.