bluuebunny/crossref_metadata_2025 huggingface dataset:
A variational method for relativistic computations in atomic and molecular physics
Authors: Dolbeault Jean , Esteban Maria J. , Séré Eric
Published: April 2003

This article is devoted to a two‐spinor characterization of energy levels of Dirac operators based at a theoretical level on a rigorous variational method, with applications in atomic and molecular physics. This provides a numerical method that is free of the numerical drawbacks often present in discretized relativistic approaches. It is moreover independent of the geometry and monotone: Eigenvalues are approximated from above. We illustrate our numerical approach by the computation of the ground state in atomic and diatomic configurations using B‐splines. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 149–155, 2003
Shortcomings in computational chemistry
Authors: Berthier G. , Defranceschi M. , Le Bris C.
Published: April 2003

The purpose of the paper is to point out some weaknesses in computational chemistry. The weaknesses we list arise from issues that are not properly solved and that can either stand on the pure numerical domain or go back to difficulties already present at the modeling stage, or even stem from fundamental open questions in theoretical chemistry itself. To name just a few, the domain decomposition method used in (QM/MM) calculations, the definition of effective core potentials (ECP) or the foundations of various stationary Schrödinger approximations, such as SCF or MCSCF theories or density functional‐type methods are examined. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 156–165, 2003
Adiabatic connection approach to density functional theory of electronic systems
Authors: Savin A. , Colonna F. , Pollet R.
Published: April 2003

Using recent calculations we review some well‐known aspects of density functional theory: the Hohenberg–Kohn theorems, the Kohn–Sham method, the adiabatic connection, and the approximations of local nature. Emphasis is put upon using model Hamiltonians, of which the noninteracting or the physical ones are just particular cases. The model Hamiltonians allow us to produce multireference density functional theory and continuously switch to the physical system. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 166–190, 2003
The issues of size and charge consistency and the implications of translation symmetry in advanced Green's function theories
Authors: Deleuze Michael S.
Published: April 2003

The issues of size consistency and charge consistency in advanced Green's function theories of ionization or electron attachment spectra are thoroughly discussed by adapting the so‐called third‐order algebraic diagrammatic construction scheme [ADC(3)] to the formalism of crystalline orbitals for an extended periodic system. A comparison is made with a number of lower‐order one‐particle Green's function (or one‐electron propagator) schemes, derived using the general algebraic approach in superoperators and binary products. In the canonical picture, one of the implications of size consistency in the dissociation and thermodynamic limits is that a balance must prevail between the number of satellites and the strength of configuration interactions between the main (1h, 1p) and secondary (shake‐up or shake‐on) states in the cation or anion. Charge consistency, or the preservation of the exact particle number upon correlation corrections to the Hartree–Fock ground‐state one‐electron density, is a necessary condition for the correct, i.e., size‐intensive, scaling of static self‐energies and, thus, ionization energies in large inhomogeneous systems. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 191–211, 2003
Recent developments in the contracted Schrödinger equation method: Controlling the N‐representability of the second‐order reduced density matrix
Authors: Valdemoro C. , Alcoba D. R. , Tel L. M.
Published: April 2003

In this article a new procedure aimed at controlling the N‐representability defect of an approximated second‐order reduced density matrix is reported. This procedure should prove to be effective in enhancing the convergence of the iterative solution of the contracted Schrödinger equation besides being of direct applicability in other methods that are reduced density matrices oriented. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 212–222, 2003
Parallel in time algorithms for quantum control: Parareal time discretization scheme
Authors: Maday Yvon , Turinici Gabriel
Published: April 2003

The numerical study of control problems in quantum chemistry requires many computer simulations of the dynamic phenomena involved. These simulations are, in many cases, too expensive to be carried out for complex systems, thus precluding the treatment of interesting practical situations. In a context of fast increasing in both the CPU power available on typical workstations and the number of computers that can be connected through high‐speed networks, the difficulty lies rather in how to obtain “real‐time solutions” than in the amount of CPU power available (which begins to exceed the needs). In this context, the “parareal” time algorithm that parallelizes in the time direction the work required to solve the evolution equations has been introduced in previous works (Lions, J.‐L.; Maday, Y.; Turinici, G. CR Acad Sci Paris I Math 2001, 332(7), 661–668; Bal, G.; Maday, Y. In: Proceedings of the Workshop on Domain Decomposition, LNCSE Series; Springer‐Verlag: Berlin, 2001, 189–202). The theoretical modifications required to apply this algorithm to control problems and more specifically to the problems of quantum control are the main topic of this article. The preliminary results that are presented at the end of the article illustrate the feasibility of the approach and the potential for large time savings. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 223–228, 2003
Determination of enzymatic reaction pathways using QM/MM methods
Authors: Monard Gérald , Prat‐Resina Xavier , González‐Lafont Angels , Lluch José M.
Published: April 2003

Enzymes are among the most powerful known catalysts. Understanding the functions of these proteins is one of the central goals of contemporary chemistry and biochemistry. But, because these systems are large they are difficult to handle using standard theoretical chemistry tools. In the last 10 years, we have seen the rapid development of so‐called QM/MM methods that combined quantum chemistry and molecular mechanics to elucidate the structure and functions of systems with many degrees of freedom, including enzymatic systems. In this article, we review the numerical aspects of QM/MM methods applied to enzymes: The energy definition, the special treatment of the covalent QM/MM frontiers, and the exploration of QM/MM potential energy surface. A special emphasis is made on the use of local self‐consistent field and rational function optimization. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 229–244, 2003
Alternative perturbation method for the molecular vibration–rotation problem
Authors: Cassam‐Chenaï P. , Liévin J.
Published: April 2003

This article introduces an alternative perturbation scheme to find approximate solutions of the spectral problem for the rotation–vibration molecular Hamiltonian. The method is implemented for the Watson Hamiltonian and applied to methane. The complete J = 0 spectrum of this penta‐atomic molecule of atmospheric interest is calculated up to 9200 cm−1 in a purely ab initio fashion. Then, the rotational spectra of the vibrational ground state is obtained up to J = 18. The largest relative error is 2.10−5 (for the highest J = 18 level) after scaling of a single parameter. Without scaling the accuracy on the rotational levels is limited by that of the ab initio equilibrium bond distance. The convergence of our results is analyzed with respect to the different parameters involved in our approach. The important concept of vibrational mean‐field configuration interaction is introduced. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 245–264, 2003
Asymmetrical features of mass spectral peaks produced by quadrupole mass filters
Authors: Gibson John Raymond , Taylor Stephen
Published: April 2003

The individual mass spectral peaks produced by a quadrupole mass spectrometer (QMS) are asymmetric; they exhibit a ‘tail’ on the low mass side. In some cases a definite structure is observed in the tail. We show that the tail structure is a consequence of the use of circular electrodes. An extreme case of an experimentally observed QMS mass peak with a distinct tail structure is shown and the general form is reproduced using our numerical model. The effect of instrument resolution, length, operating frequency, ion energy, mass and ion source aperture upon the tail structure are considered. Results show that extensive long tails originate mainly from ions that enter the mass filter at a relatively large distance from the QMS axis; also no significant tail is produced in the case of ideal hyperbolic form electrodes of finite length. Copyright © 2003 John Wiley & Sons, Ltd.
The North Atlantic Oscillation—what role for the Ocean?
Authors: Sutton Rowan T. , Norton Warwick A. , Jewson Stephen P.
Published: April 2003

The extent to which the North Atlantic Oscillation (NAO) is influenced by changes in the ocean state is an issue that has attracted much recent attention. Although there have been counter claims, the weight of evidence clearly suggests that forcing by the ocean of year‐to‐year changes in the NAO is a weak influence by comparison with atmospheric internal variability. The NAO is thus very different in character to the Southern Oscillation (SO), and its predictability—at least on seasonal‐to‐interannual timescales—is almost certainly much lower.

Although weak, the influence of the ocean on the NAO is not negligible. In a previous study we found that wintertime North Atlantic climate, including the NAO, was significantly influenced by a tripole pattern of North Atlantic SST anomalies. Here we report the results of experiments to further elucidate the nature of this influence. We show that the tripole pattern induces a significant response both in the tropical Atlantic and at mid‐to‐high latitudes. The low latitude response is forced by the low latitude SST anomalies, but the high latitude response is influenced by the extratropical SST anomalies as well as those in the tropics. Furthermore, we find evidence of nonlinear interaction between the influence of the tropical and extratropical SST anomalies. Lastly, we investigate the feedback from the atmosphere onto the SST tripole. We find that the expected negative feedback is significantly modified at low latitudes by the dynamical response of the atmosphere. Copyright © 2000 Royal Meteorological Society.
The expression of matrix metalloproteinase‐13 and osteocalcin in mouse osteoblasts is related to osteoblastic differentiation and is modulated by 1,25‐dihydroxyvitamin D3 and thyroid hormones
Authors: Fratzl‐Zelman Nadja , Glantschnig Helmut , Rumpler Monika , Nader Alexander , Ellinger Adolf , Varga Franz
Published: April 2003

Matrix metalloproteinase‐13 (MMP‐13), is a key protein of bone matrix degradation, and is highly expressed by osteoblasts. We used the osteoblast‐like MC3T3‐E1 cell line and compared the stimulatory effects of the bone resorptive agents 1,25‐dihydroxyvitamin D3 (1,25‐(OH)2D3) 3,3′,5‐triido‐l‐thyronine (T3) on the expression of MMP‐13 mRNA. We showed that the stimulatory effects were time and dose dependent, and were also transduced to the protein level, with 1,25‐(OH)2D3being more potent.

MMP‐13 expression in different mouse cells and its localization within developing bone from the onset of osteogenesis were also investigated. 1,25‐(OH)2D3‐ and T3‐regulated osteocalcin (Osc) expression in mouse osteoblasts was compared to hormonal effects on MMP‐13 expression and activity. Here we show divergent and common roles of 1,25‐(OH)2D3and T3 action on the expression of these marker proteins, depending on the stage of cell differentiation. In addition, we propose a role for MMP‐13 in the bone collar of developing long bones. The results could help to more precisely characterize hormonal regulation in the developmental sequence of osteoblasts.
History, Morality, and Politics: Latin American Intellectuals in a Global Context
Authors: Baud Michiel
Published: April 2003

On impulse one afternoon during the early stages of my research into the Dirty War in Argentina and the political past of the former Minister of Agriculture, Jorge Zorreguieta, I sent an e-mail to an Argentinian friend and colleague asking for suggestions about recent literature.
Extension of the fourfold way for calculation of global diabatic potential energy surfaces of complex, multiarrangement, non-Born–Oppenheimer systems: Application to HNCO(S,S1)
Authors: Nakamura Hisao , Truhlar Donald G.
Published: April 2003

The fourfold way is a general algorithm for generating diabatic electronic wave functions that span the same space as a small set of variationally optimized adiabatic electronic wave functions and for using the resulting diabatic wave functions to generate diabatic potential energy surfaces and their couplings. In this paper we extend the fourfold way so it is applicable to more complex polyatomic systems and in particular to the calculation of global potential energy surfaces for such systems. The extension involves partitioning the active space into three blocks, introducing restricted orbital rotation within two of the blocks, introducing a specific resolution of the subspace containing molecular orbitals that are doubly occupied in all dominant configuration state functions, and introducing specific orientations of the coordinate systems for reference molecular orbitals and resolution molecular orbitals. The major strength of the improved method presented in this paper is that it allows the diabatic molecular orbitals to exhibit a gradual change of chemical character with smooth deformation along the reaction coordinate for a change of chemical arrangement while preserving the orbital character required for a physical ordering of the orbitals. This feature is required for the convenient construction of global potential energy surfaces for non-Born–Oppenheimer rearrangements. The resulting extended algorithm is illustrated by calculating diabatic potential energy surfaces and couplings for the two lowest singlet potential energy surfaces of HNCO.
Influence of nitrogen addition on oxyacetylene flame chemical vapor deposition of diamond as studied by solid state techniques and gas phase diagnostics
Authors: Stolk R. L. , van Herpen M. M. J. W. , Schermer J. J. , ter Meulen J. J.
Published: April 2003

The effect of nitrogen addition on oxyacetylene flame deposition of diamond has been investigated. Two-dimensional laser-induced fluorescence measurements of CN radical distributions in the flame during deposition have been performed. These measurements show that nitrogen added to the source gases and nitrogen from the ambient air dominate the CN formation in the central and outer-flame area, respectively. Both sources of nitrogen have a significant influence in the area between the other two. Most of the observed film morphologies, which were studied by scanning electron microscopy, can be understood from the recently developed deterioration-gradient (DG) model for chemical vapor deposition of diamond, reported by J. J. Schermer et al. [J. Cryst. Growth 243, 302 (2002)]. It was found that the nitrogen range in which the α-parameter, defined by C. Wild et al. [Diamond Relat. Mater. 2, 158 (1993)], changes from slightly below or equal to 1.5 to a value of 3 or more, is extremely narrow. This implies that under the present experimental conditions it is very hard or impossible to grow a layer with a central area consisting of 〈001〉 oriented {001} topped crystallites. Observed radial changes in the morphology of the sample grown without nitrogen addition were explained from radial changes in the gas phase composition, caused by interaction of the flame with nitrogen and, presumably, oxygen from the ambient air. The central growth rate as a function of the nitrogen flow shows an increase by more than a factor of 1.5 in going from 0 to 5 sccm and stays more or less constant between 5 and 25 sccm. From Raman spectra of the central area it clearly followed that under the present conditions even the smallest added nitrogen addition resulted in a decrease of the film quality. This may be related to a possible stimulation of the growth of non-diamond carbon compounds by nitrogen. A correlation, the origin of which is not known, was found between the stepwise narrowing of a broad band in the Raman spectra, which was attributed to non-diamond carbon, and changes in the morphology of the diamond films. Combining the present data with findings from literature, support is generated for the idea that CN is important in causing the effects of nitrogen on diamond growth.
Annealing of amorphous Ru–Si–O and Ir–Si–O films in vacuum or dry oxygen
Authors: Giauque P. H. , Nicolet M.-A.
Published: April 2003

Films about 200 nm thick of composition Ru17Si16O67 (≈50% RuO2+50% SiO2) and Ir18Si15O67 (≈55% IrO2+45% SiO2) deposited on oxidized silicon wafers by reactive magnetron sputtering with an argon–oxygen gas mixture from bielemental targets have been annealed in vacuum or in oxygen. As deposited, the films are amorphous by x-ray diffraction as well as by transmission electron microscopy. Upon annealing in vacuum, grains of metal dioxide nucleate and grow in both films, as x-ray diffraction scans reveal. These grains dissociate into metal grains and oxygen. The process is well underway in the Ir18Si15O67 film at 700 °C after 12 h while it has barely begun at 800 °C after 5 h in the Ru17Si16O67 film. 2.0 MeV 4He++ backscattering spectra establish that oxygen in the amount initially bonded to the metal escapes out of the film that thins down as a result, but remains dense nonetheless. The results are qualitatively consistent with a diffusion-controlled outward flow of oxygen in a heterogeneous medium of metal dioxide and silica. Thermodynamic calculations for the two systems show that oxygen has the highest partial pressure of all gaseous species in both cases, but in the iridium case the oxygen partial pressure exceeds that in the ruthenium case by at least 100-fold. The dissimilar behavior under annealing in vacuum evidently has a thermodynamic component at its origin. When heated in oxygen, a Ru17Si16O67 film is quite unstable, and increasingly so with rising oxygen pressure. The iridium-based films remain essentially unchanged upon annealing at 700 °C for 5 min under 760 Torr of dry oxygen. This dissimilarity between the Ru–Si–O and Ir–Si–O films is rooted in the existence of the volatile RuO4 phase that has no analogue species in the iridium–oxygen system. The high stability of amorphous Ir18Si15O67 films under thermal annealing in an oxidizing ambient is significant for applications where electrically conducting films are required that can withstand such exposures essentially unchanged.
Electrically active defects in n-type 4H–silicon carbide grown in a vertical hot-wall reactor
Authors: Zhang J. , Storasta L. , Bergman J. P. , Son N. T. , Janzén E.
Published: April 2003

We have studied intrinsic and impurity related defects in silicon carbide (SiC) epilayers grown with fast epitaxy using chemical vapor deposition in a vertical hot-wall reactor. Using capacitance transient techniques, we have detected low concentrations of electron traps (denoted as Z1/2, EH6/7 and titanium) and hole traps (denoted as HS1 and shallow boron) in the n-type 4H–SiC epilayers. The concentration of intrinsic defects (Z1/2, EH6/7, and HS1 centers) increases with increasing growth temperature. The incorporation of shallow boron (B) decreases at higher growth temperatures, whereas the titanium (Ti) concentration is not sensitive to the growth temperature. The concentration of shallow B and Ti increases with increasing C/Si ratio. The concentration of the EH6/7 and the HS1 centers however, decreases with increasing C/Si ratio. We have also tested graphite susceptors with TaC or SiC coating and observed that the purity of the susceptor material plays a critical role in reducing the background impurity incorporation. The correlation with the carrier lifetime of these epilayers indicates that the EH6/7 and the Z1/2 centers may be the lifetime limiting defects in the investigated epilayers.
A finite basis representation Lanczos calculation of the bend energy levels of methane
Authors: Wang Xiao-Gang , Carrington Tucker
Published: April 2003

We present a method for computing bend energy levels of a five-atom molecule. We use polyspherical coordinates in terms of which both the kinetic energy operator and its associated volume element are simple. The basis functions we use are new. They are parity-adapted combinations of products of spherical harmonics and an associated Legendre function. We show that in the parity-adpated basis it is possible to evaluate matrix-vector products efficiently, despite the fact that the parity-adapted functions are not products of functions of a single variable. The method is applied to compute bend levels of methane. Within each parity block we use the symmetry-adapted Lanczos algorithm to compute levels labeled by irreps of a four-member group that contains the parity operator and the permutation of two of the four hydrogen atoms. In a future publication we shall use the bend wave functions as contracted basis functions to compute numerically exact vibrational levels of methane.
Coherent optical phonon mode oscillations in wurtzite ZnO excited by femtosecond pulses
Authors: Lee I. H. , Yee K. J. , Lee K. G. , Oh E. , Kim D. S. , Lim Y. S.
Published: April 2003

We report on coherent optical phonon oscillations in wurtzite ZnO. The high- and low-frequency E2 modes are excited by the impulsive stimulated Raman scattering, and detected through the electro-optic effect. The dephasing times are measured to be 1.75 and 29.2 ps for the high- and the low-E2 modes, respectively. The dependency of the phonon amplitude on the spectral width of the femtosecond pulses is shown.
Cross-sectional transmission electron microscopy study of the influence of niobium on the formation of titanium silicide in small-feature contacts
Authors: Jarmar T. , Seger J. , Ericson F. , Smith U. , Zhang S.-L.
Published: April 2003

The influence of a Nb layer between Si and Ti on the formation of TiSi2 in small-feature contacts and of the substrate doping level has been studied using transmission electron microscopy in combination with convergent-beam electron diffraction. For an As dose of 2.5×1016 cm−2, a mixture of C49 and partially agglomerated C54 TiSi2 grains was found in some of the 5×5 μm2 contact windows, while only C49 existed in the 0.7×0.7 μm2 windows. Agglomeration is shown to lead to possible C49−C54 coexistence, as well as erroneous interpretation of the C54 nucleation density. Decreasing the As dose to 5×1015 cm−2 leads to a thicker TiSi2 layer, but does not have a major influence on phase formation in the small windows, although only C54 TiSi2 was found in the large ones. In the presence of a thin Nb layer between Ti and poly-Si, C40 (Ti,Nb)Si2 was consistently found in all contacts, indicating that formation does not depend on the contact size at least down to 0.5 μm2. Surprisingly, Ti was found on both sides of the (Ti,Nb)Si2 layer and the silicide near the interface to Si was relatively rich in Ti instead of Nb.
Influence of cap layer on implantation induced interdiffusion in InP/InGaAs quantum wells
Authors: Carmody C. , Tan H. H. , Jagadish C.
Published: April 2003

We have investigated the effect of implantation at room temperature and 200 °C into lattice matched InP/InGaAs quantum well structures capped with InP and InGaAs layers. P− ions of 20 keV were implanted into the cap layer at doses of 1×1012−1×1014 cm−2. The dose dependent evolution of shifts in photoluminescence energy for the InP capped sample was found to be affected by the implant temperature. Rutherford back scattering measurements show that the nature of the damage induced at different implant temperatures is responsible for this behavior. It was found that the InGaAs capped sample was less sensitive to the implant temperature than the InP capped sample.
Simulation of sheath dynamics and current nonuniformity in plasma-immersion ion implantation of a patterned surface
Authors: Briehl Boris , Urbassek Herbert M.
Published: April 2003

We study the steady-state structure and the dynamics of a plasma sheath surrounding a patterned surface. A two-dimensional hybrid particle-in-cell code is employed where special attention is given to the plasma side boundaries. The surface consists of a periodic array of wide and narrow trenches. We characterize the conformity of the steady-state sheath and the uniformity of the ion currents to the wall as well as the sheath-expansion dynamics following sudden negative charging of the surface. We study the nonuniform motion of the sheath edge away from the surface, which leads to a planar high-voltage sheath. The inhomogeneous distributions of ion current and impact angle onto the walls are discussed.
Surface structural transformation of sintered alumina induced by excimer laser irradiation
Authors: Dupas-Bruzek C. , Laude L. D. , Langenhorst F. , Kolev K.
Published: April 2003

Laser surface processing of ceramics is important for several structural, tribological, optical and electronic applications. However, little is known on the transformation mechanism of alumina under excimer laser irradiation. In this work, a sintered alumina type was typically irradiated at 0.8 J cm−2 and cooled at two drastically different rates. Optical investigations on the irradiated specimens allow to conclude that the amount of transformation products is very much dependant on the cooling rates. Transmission electron microscopy observations show that the transformation product is constituted of an amorphous matrix in which are embedded either (i) copper grains (size up to 1 μm) in slowly cooled samples or (ii) smaller copper or CuAl2O4 spinel grains (size up to 100 nm) in rapidly cooled samples. The cement that is present in the starting material at grain boundaries is found to play an important role on the formation of the new amorphous or crystalline materials. All the copper grains exhibit a 〈120〉 common zone axis perpendicular to the irradiated surface and parallel to the bulk-to-surface thermal gradient, which drives that preferred orientation. These results reveal the details of the phenomenology of the laser-induced material transformation. This latter decomposes into (i) the incipient formation of tiny γ-Al2O3 nuclei, (ii) integration of Cu ions present in the melt into these tiny γ-Al2O3 nuclei that transform into CuAl2O4 spinel, and (iii) further sedimentation of Cu ions onto the resulting spinel grains acting as nucleation centers and finally formation of larger copper-rich grains. The minimum nucleation rate of crystalline grains is estimated to be equal to 1024 cm−3 s−1, while the growth rate is of the order of 0.1 m s−1 in both samples. Both bulk thermal diffusive and convective transports control the transformation of matter.
Raman spectroscopic investigation of small matrix-isolated lithium clusters
Authors: Kornath Andreas , Kaufmann Alexander , Zoermer Anja , Ludwig Ralf
Published: April 2003

The lithium clusters Li2, Li4, and Li8 have been isolated in argon matrices at 15 K and characterized by Raman spectroscopy. The vibrational frequencies are compared with configuration interaction (QCISD/6-311G* and CID/6-311G*) calculations and their assignment is supported by 6-lithium and 7-lithium isotopomers. The Li4 cluster possesses a rhombic structure (D2h) with calculated d(Li–Li)=272.6 and 306.4 pm, respectively. For octalithium, a hypertetrahedral structure (Td) is predicted in which each side of an inner tetrahedron with d(Li–Li)=292.5 pm is capped by lithium atoms with a distance of d(Li–Li)=304.2 pm. The octalithium cluster is an example of a matrix-isolated magic number cluster.
Surface induced dissociations of protonated ethanol monomer, dimer and trimer ions: Trimer break-down graph from the collision energy dependence of projectile fragmentation
Authors: Mair C. , Lezius M. , Herman Z. , Märk T. D.
Published: April 2003

Surface induced dissociation of the protonated ethanol molecular ion, protonated ethanol dimer, and protonated ethanol trimer on a stainless steel surface covered by hydrocarbons was investigated over the incident ion energy range 10–80 eV. Mass spectra of the product ions were recorded and from them the dependencies of the relative abundance of the product ions on the collision energy (CERMS, collision energy resolved mass spectra) were obtained. The dissociation kinetics follows the unimolecular decomposition model of a surface-excited polyatomic projectile behaving as a statistical ensemble. The CERMS curves of the three projectiles, normalized to the same number of internal degrees of freedom, fit each other over the respective energy regions, and matched together provide information on the break-down pattern of the surface-excited protonated ethanol trimer over a wide energy range. This clearly shows that surface collisions can be used to impart in a defined manner a certain excitation energy to the projectile ion. The binding energy of an ethanol monomer in the protonated trimer and in the protonated dimer was estimated from the data as 0.95 and 1.6 eV, respectively, in good agreement with earlier data.
Theory of the effects of substitutions on the phase stabilities of Ti1−xAlxN
Authors: Hugosson H. W. , Högberg H. , Algren M. , Rodmar M. , Selinder T. I.
Published: April 2003

We have performed ab initio studies of the effect of substitutions on the phase stabilities of Ti1−xAlxN, x=0−1. The nonmetal substitutions studied include B, C, O, and Si. Metal substitutions studied include Sc, Zr, V, Cr, and Mn. The main objective has been to suggest substitutions that increase the thermal stability of the NaCl structure of Ti1−xAlxN at high Al contents. From these extensive and consistent calculations, some possible avenues for such stabilization present themselves, among which substitution with nonmetal C and Si, and metal V, Cr, and Mn are found to be the most promising.
Calorimetric and x-ray analysis of the intermediate phase formation in Cu/Mg multilayers
Authors: Rodrı́guez-Viejo J. , Gonzalez-Silveira M. , Clavaguera-Mora M. T.
Published: April 2003

The kinetics of intermediate phase formation in (20 nm) Cu/(80 nm) Mg multilayers is analyzed using differential scanning calorimetry (DSC) and in situ x-ray diffraction. The as-prepared Mg layers are polycrystalline with large grain sizes and a columnar structure which gives a preferred orientation along the (0002) direction. On the contrary, the Cu films are nanocrystalline with average nanocrystal populations of different sizes. The continuos scan DSC traces show three main exothermic peaks. The first two reactions are significantly overlapped. We find both processes are related to nucleation and growth of the Mg2Cu along the interface and present an explanation based on the different roughness of the nc-Cu on Mg and the Mg on nc-Cu interfaces. The third exothermic reaction is due to the growth of the Mg2Cu perpendicular to the original interface. A kinetic model is developed which yields calculated calorimetric traces in very good agreement with the experimental data. The model includes two independent nucleation & growth mechanisms. A soft-diffusion control of the one-dimensional thickening of the Mg2Cu product phase is included to account for the gradual decrease associated to the end of the third calorimetric peak.
Analysis of random-dopant induced fluctuations of frequency characteristics of semiconductor devices
Authors: Andrei Petru , Mayergoyz Isaak
Published: April 2003

A technique for the analysis of fluctuations of frequency characteristics of semiconductor devices induced by random-doping fluctuations is presented. This technique completely avoids computations for numerous doping realizations and, therefore, it is computationally much more efficient than purely “statistical” methods. This technique yields information on the sensitivity of variances of frequency characteristics to different locations of doping fluctuations. This information can be directly used for the design of dopant fluctuation-resistant structures of semiconductor devices. The numerical implementation of this technique is discussed and numerous computational results are presented and compared with those obtained by using purely statistical techniques.
Correlated and gauge invariant calculations of nuclear magnetic shielding constants using the continuous transformation of the origin of the current density approach
Authors: Ligabue Andrea , Sauer Stephan P. A. , Lazzeretti Paolo
Published: April 2003

We report for the first time an extended series of correlated origin independent calculations of nuclear magnetic shielding tensors using the approach of continuous transformation of the origin of the current density to annihilate its diamagnetic contribution. A systematic study was undertaken to develop optimal basis sets for H, C, N, O, F correlated nuclear magnetic shieldings, looking for the best compromise between accuracy and size. Beyond Hartree–Fock calculations were carried out at two levels of accuracy, the multiconfigurational self-consistent field based on the complete active space scheme, and the second-order polarization propagator approximation (SOPPA). In addition we present the first shielding calculations employing the second-order polarization propagator approximation with coupled cluster singles and doubles amplitudes SOPPA (CCSD).
Internal electric field and charge distribution in multilayer organic light-emitting diodes
Authors: Tutiŝ E. , Berner D. , Zuppiroli L.
Published: April 2003

The internal electric field in multilayer organic light-emitting diodes (OLEDs) is investigated using a combination of experimental measurement and numerical device modeling. This approach results in a detailed understanding of the functioning of a multilayer OLED. The method is applied to a standard device structure that has received broad attention in literature. From the experimental part, we have demonstrated that the average electric field inside the hole transport layer is larger than or equal to the average field in the emission layer over the entire current range. Device simulations fully clarify the situation, giving an insight into the space charge effects as well as the hole and the electron current distributions in the device. In particular, we find that there is a leakage of unrecombined holes towards the cathode at low voltages. We also find a strong variation of the electric field in the tris(8-hydroxyquinolinato)aluminum layer.
The giant magnetocaloric effect of optimally prepared Gd5Si2Ge2
Authors: Pecharsky A. O. , Gschneidner K. A. , Pecharsky V. K.
Published: April 2003

The appropriate heat treatment of the Gd5Si2Ge2 alloy prepared from high-purity Gd results in a considerable enhancement of its magnetocaloric effect. The maximum magnetic entropy change increases by ∼80% (from ∼20 to 36 J/kg K) and the adiabatic temperature change increases by ∼55% (from ∼11 to 17 K) for a magnetic field change from 0 to 50 kOe when compared to the as arc-melted material. The magnetic ordering temperature is slightly reduced from ∼277 K in the as arc-melted material to ∼272 K in the fully homogenized and annealed Gd5Si2Ge2. The behavior of the isothermal magnetization as a function of magnetic field changes to some extent, while the heat capacity anomaly at the phase transition temperature is considerably sharper. The 1570 K heat treatment results in the partial ordering and redistribution of the Si and Ge atoms between their corresponding crystallographic sites in the monoclinic Gd5Si2Ge2-type structure and to the removal of the polymorphic orthorhombic Gd5Si2Ge2 phase with the Gd5Si4-type structure, which coexists with the monoclinic phase in the as arc-melted alloy.
Quantum well photoconductors in infrared detector technology
Authors: Rogalski A.
Published: April 2003

The paper compares the achievements of quantum well infrared photodetector (QWIP) technology with those of competitive technologies, with the emphasis on the material properties, device structure, and their impact on focal plane array (FPA) performance. Special attention is paid to two competitive technologies, QWIP and HgCdTe, in the long-wavelength IR (LWIR) and very-long-wavelength IR (VLWIR) spectral ranges. Because so far, the dialogue between the QWIP and HgCdTe communities is limited, the paper attempts to settle the main issues of both technologies. Such an approach, however, requires the presentation of fundamental limits to the different types of detectors, which is made at the beginning. To write the paper more clearly for readers, many details are included in the Appendix. In comparative studies both photon and thermal detectors are considered. Emphasis is placed on photon detectors. In this group one may distinguish HgCdTe photodiodes, InSb photodiodes, and doped silicon detectors. The potential performance of different materials as infrared detectors is examined utilizing the α/G ratio, where α is the absorption coefficient and G is the thermal generation rate. It is demonstrated that LWIR QWIP’s cannot compete with HgCdTe photodiodes as single devices, especially at higher operating temperatures (>70 K). This is due to the fundamental limitations associated with intersubband transitions. The advantage of HgCdTe is, however, less distinct at temperatures lower than 50 K due to problems inherent in the HgCdTe material (p-type doping, Shockley–Read recombination, trap-assisted tunneling, surface and interface instabilities). Even though QWIP is a photoconductor, several of its properties, such as high impedance, fast response time, long integration time, and low power consumption, comply well with the requirements imposed on the fabrication of large FPA’s. Due to a high material quality at low temperatures, QWIP has potential advantages over HgCdTe in the area of VLWIR FPA applications in terms of array size, uniformity, yield, and cost of the systems. The performance figures of merit of state-of-the-art QWIP and HgCdTe FPA’s are similar because the main limitations come from the readout circuits. Performance is, however, achieved with very different integration times. The choice of the best technology is therefore driven by the specific needs of a system. In the case of readout-limited detectors a low photoconductive gain increases the signal-to-noise ratio and a QWIP FPA can have a better noise equivalent difference temperature than an HgCdTe FPA with a charge well of similar size. Both HgCdTe photodiodes and QWIP’s offer multicolor capability in the MWIR and LWIR range. Powerful possibilities offered by QWIP technology are associated with VLWIR FPA applications and with multicolor detection. The intrinsic advantage of QWIP’s in this niche is due to the relative ease of growing multicolor structures with a very low defect density.
Forbidden guided-wave plasmon polaritons in coupled thin films
Authors: Gilmore M. A. , Johnson B. L.
Published: April 2003

We study the plasmon-polariton collective modes of a three-thin-film-on-a-substrate structure, where two of the thin films have free-charge carriers and are separated by a static dielectric. We find that this structure can support unusual guided-wave polaritons, which exist in a normally forbidden region of the surface polariton dispersion, and which are composed of coupled surface polariton modes of the individual films with a wavelike transverse electric-field amplitude in the spacer dielectric. The modes emerge from both bulk and surface collective mode bands and evolve into a ladder of solutions in the forbidden region. We also present the attenuated total reflection spectrum arising from the guided modes.
Piezoelectric response of thin films determined by charge integration technique: Substrate bending effects
Authors: Barzegar A. , Damjanovic D. , Ledermann N. , Muralt P.
Published: April 2003

Unexpectedly high-longitudinal piezoelectric coefficients have recently been reported in c-axis oriented Pb(Zr,Ti)O3 thin films with morphotropic phase boundary composition [Fu et al., Appl. Phys. Lett. 80, 3572 (2002)]. Our analysis and experimental results show that, in comparison with other methods commonly used to investigate piezoelectric response of thin films, the charge integration technique used by Fu et al. may lead to an order of magnitude higher apparent piezoelectric coefficients if the substrate on which the film was deposited is bent. When this is the case, the large response is due to the transverse piezoelectric effect caused by the substrate bending.
Currents produced by explosive driven transverse shock wave ferromagnetic source of primary power in a coaxial single-turn seeding coil of a magnetocumulative generator
Authors: Shkuratov Sergey I. , Talantsev Evgueni F. , Dickens James C. , Kristiansen Magne
Published: April 2003

Experimental and digital simulation studies of the generation of seed currents by an ultracompact (8.66–8.75 cm3 in volume) ferromagnetic explosive-driven generator of primary power (FMG) loaded on the coaxial single-turn seeding coil of a magnetocumulative generator (MCG) have been performed. The operation of the FMG is based on transverse shock wave demagnetization of Nd2Fe14B high-energy hard ferromagnets. The FMG is capable of producing in the coaxial seeding coil of MCG a seed current with peak amplitude I(t)max=3.0 kA and full width at half maximum of 60 μs. The methodology was developed for digital simulation of the seeding processes in the combined FMG/MCG system.
Solar surgery
Authors: Gordon Jeffrey M. , Feuermann Daniel , Huleihil Mahmoud , Mizrahi Solly , Shaco-Levy Ruthy
Published: April 2003

Experimental results are presented to substantiate that highly concentrated sunlight can pragmatically produce the same extent, rate, and type of photothermal tissue damage ordinarily generated with laser fiber-optic surgery. Typically, it is intense flux, rather than coherence, that renders laser light unique in generating rapid, highly localized tissue coagulation and ablation. The spectral properties of both biological tissue and available optical fibers render visible and near-infrared lasers as best suited for penetrative (as opposed to superficial) surgery. Solar photons are also viable candidates for such radiative surgery, provided they can be concentrated to the flux levels of surgical lasers, coupled into an optical fiber, and efficiently delivered to a remote operating theater. The simplicity and potentially low cost of a solar surgery unit counterbalance its feasibility being restricted to mid-day hours in sunny regions. After a brief review of our solar fiber-optic concentrator, we report on the rates and dimensions of tissue death produced in fresh ex vivo chicken livers for a range of values of delivered power and exposure time. An approximate analytic model can account for some of the principal experimental findings. Our experimental results demonstrate that solar surgery can produce lesions up to several cm3 in volume, with a surgical efficacy as good as that of lasers for corresponding procedures.
Microcalorimeter and bolometer model
Authors: Galeazzi M. , McCammon D.
Published: April 2003

The standard nonequilibrium theory of noise in ideal bolometers and microcalorimeters fails to predict the performance of real devices due to additional effects that become important at low temperature. In this paper we extend the theory to include the most important of these effects and find that the performance of microcalorimeters operating at 60 mK can be quantitatively predicted. We give a simple method for doing the necessary calculations, borrowing the block diagram formalism from electronic control theory.
Reflection anisotropy spectroscopy: A probe of rubbed polyimide liquid crystal alignment layers
Authors: Macdonald B. F. , Zheng W. , Cole R. J.
Published: April 2003

The prospect of using reflectance anisotropy spectroscopy (RAS) for process control in the fabrication of liquid crystal devices is investigated. Measurements of the optical anisotropy induced by mechanically rubbing polymer thin films are presented and interpreted in terms of molecular alignment and form birefringence models. Optical characterization of completed liquid crystal cells enables RAS measurements to be correlated with device characteristics.
Characterization of size-selected metal clusters implanted below the surface of graphite
Authors: Couillard M. , Palmer R. E.
Published: April 2003

We have investigated the outcome of energetic implantation of size-selected metal cluster ions below the surface of graphite. Pt4− clusters were implanted to a prescribed depth of 3 monolayers established by scanning tunneling microscopy of etched cluster tracks. The subsurface individual clusters were imaged directly by annular dark-field imaging in a scanning transmission electron microscope. The results show that the constituent atoms of the implanted clusters remain spatially correlated to within 5 Å.
Relation among concentrations of incorporated Mn atoms, ionized Mn acceptors, and holes in p-(Ga,Mn)As epilayers
Authors: Moriya R. , Munekata H.
Published: April 2003

The amount of ionized Mn acceptors in various p-type Mn-doped GaAs epilayers grown at high (Ts=580 °C) and low (Ts=250 °C) substrate temperatures has been evaluated by electrochemical capacitance-voltage measurements, and has been compared systematically with concentrations of incorporated Mn atoms and holes for a wide range of Mn concentrations (NMn=1017–1021 cm−3). Low-Ts samples are found to be classified into three different types: (a) a highly resistive, strongly compensated region at NMn⩽1018 cm−3, (b) a low-resistance, fully ionized region for NMn between 5×1018 and 1020 cm−3 in which impurity conduction dominates, and (c) a magnetic, low-resistance region for NMn⩾2×1020 cm−3 in which magnetism and carrier transport are strongly correlated. A quantitative assessment of the anomalous Hall effect at room temperature is also carried out.
Diodelike behavior in glass–metal nanocomposites
Authors: Dan A. , Satpati B. , Satyam P. V. , Chakravorty D.
Published: April 2003

One-dimensional arrays of nanoparticles of silver and copper, respectively, have been grown within a silicate glass by an electrodeposition process. Silver–silica nanocomposites were prepared using a melt quenched glass whereas sol–gel derived glass was used for the synthesis of copper–silica nanocomposites. The metal particle diameters had values ranging from 1.5 to 20 nm. The composite structures exhibited a diodelike current–voltage characteristic in the temperature range 300 to 160 K for silver containing nanocomposites and at around 280 K for copper containing nanocomposites. The diode action is believed to be caused by the presence of metal–semiconductor nanojunctions in these glass—the typical number of such junctions being 60. The rather narrow range of temperature for diode action as observed in copper–silica nanocomposites is ascribed to the easy breakup of the metal nanoarrays because of the sol–gel derived medium of silica glass in which the metal phase was grown. The metal particles of diameter ∼2 nm constituted the semiconducting phase in these nanojunctions.
Simple method for measuring the high pretilt angle of nematic liquid crystals
Authors: Gwag Jin Seog , Lee Seo Hern , Park Kyoung-Ho , Park Won Sang , Han Kwan-Young , Jhun Chul Gyu , Yoon Tae-Hoon , Kim Jae Chang , Song Dong-mee , Shin Dong-myung
Published: April 2003

Pretilt angle measurable by using the conventional crystal rotation method is limited to about 0°–20° and 70°–90°. We propose a method by which we can measure the pretilt angle by using the crystal rotation method even if the pretilt angle is between 20° and 70°. In this method, the determination of a pretilt angle is achieved by finding the rotation angles where transmittances are maximum and minimum in the periodic transmittance characteristics obtained with the variation of rotation angle.