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Solid-like behavior at low energies and long distances is usually associated with the spontaneous breaking of spatial translations at microscopic scales, as in the case of a lattice of atoms. We exhibit three quantum field theories that are renormalizable, Poincar�� invariant, and weakly coupled, and that admit states that on the one hand are perfectly homogeneous down to arbitrarily short scales, and on the other hand have the same infrared dynamics as isotropic solids. All three examples presented here lead to the same peculiar solid at low energies, featuring very constrained interactions and transverse phonons that always propagate at the speed of light. In particular, they violate the well known $c_L^2 > \frac{4}{3} c_T^2$ bound, thus showing that it is possible to have a healthy renormalizable theory that at low energies exhibits a negative bulk modulus (we discuss how the associated instabilities are absent in the presence of suitable boundary conditions). We do not know whether such peculiarities are unavoidable features of large scale solid-like behavior in the absence of short scale inhomogeneities, or whether they simply reflect the limits of our imagination., 23 pages

Systematic measurements of the annihilation cross sections of low energy antinucleons were performed at CERN in the 80's and 90's. However the antiproton data on medium-heavy and heavy nuclear targets are scarce. The ASACUSA Collaboration at CERN has measured the antiproton annihilation cross section on carbon at 5.3 MeV: the value is (1.73 ± 0.25) barn. The result is compared with the antineutron experimental data and with the theoretical previsions.

This work is about polarised hot electrons spin precession. This phenomenon is induced by the exchange field of a ferromagnetic thin film in a multilayer structure. The electronic spin precession has already been measured in ferromagnetic materials, but only for electrons whose energy is more than 4eV over the Fermi level. The initial aim of this PhD work is to measure the electron spin precession for weak energies, between 0.7 eV and 2eV over the Fermi level. In order to achieve that, a magnetic tunnel transistor composed of three magnetic layers with their magnetisations directions perpendicular to each other has to be elaborated. The electrons are injected at low energy by means of a tunnel junction. A Schottky diode (interface between Cu and Si) filters the incident electrons by their energies, which enables only ballistic electrons to contribute to the measured current in the semi-conductor. The first task consisted in obtaining a magnetic layer showing perpendicular magnetic anisotropy. We succeeded in growing cobalt nickel multilayers exhibiting a perpendicular magnetic anisotropy up to five repetitions. The second part of the job carried out during this PhD was to optimise the magneto-current of a spin valve. Indeed, it determines the magnetic tunnel transistor sensitivity. We have demonstrated that the magneto-current increases with the number of repetitions of the [Co/Ni] multilayer up to a maximum of nearly a hundred percent, which is the maximum theoretically predicted in a spin valve with crossed magnetisations. Eventually, the third task of this PhD was the study of the electron spin precession in various ferromagnetic materials. This effect has been evidenced here for thin layers with in-plane magnetisations composed of Co, CoFeB, and also for a CoAl alloy depending on the thickness of the layers, Ce travail porte sur la précession du spin d’électrons chauds polarisés en spin. Celle-ci est induite par le champ d’échange d’une couche mince ferromagnétique dans une structure multicouche. La précession du spin électronique a déjà été mesurée dans des matériaux ferromagnétiques mais uniquement pour des électrons qui possèdent une énergie supérieure à 4eV au-dessus du niveau de Fermi. L’objectif premier de cette thèse est de mesurer la précession du spin de l’électron pour des faibles énergies, comprises entre 0.7eV et 2eV au-dessus du niveau de Fermi. Pour ce faire, un transistor tunnel magnétique comportant trois couches magnétiques avec les aimantations qui pointent dans les trois directions de l’espace doit être construit. Les électrons sont injectés à basse énergie grâce à une jonction tunnel. Une diode Schottky (interface entre du Cu et du Si) filtre en énergie les électrons incidents, permettant uniquement aux électrons balistiques de contribuer au courant mesuré dans le semi-conducteur. Le premier travail a consisté à obtenir une couche magnétique exhibant une anisotropie perpendiculaire. Ainsi, nous avons réussi à faire croître une multicouche de Co et Ni sur une diode Schottky qui possède une anisotropie perpendiculaire jusqu’à 5 répétitions. Le deuxième travail réalisé dans cette thèse était d’optimiser le magnéto-courant d’une la vanne de spin. En effet, le magnéto-courant détermine la sensibilité de notre transistor tunnel magnétique. Nous avons notamment démontré ici que le magnéto-courant augmente avec le nombre de répétitions de la multicouche [Co/Ni], pour atteindre quasiment le maximum de 100% théoriquement prédit dans une vanne de spin à aimantations croisées. Enfin, le troisième travail de cette thèse résidait dans l’étude de la précession du spin de l’électron dans différents matériaux ferromagnétiques. Cet effet a été mis en évidence ici pour des couches à aimantation planaire composée de Co, de CoFeB, ainsi que pour un alliage de CoAl et ceci en fonction de leur épaisseur

In this thesis, we study for the N-particles Schrodinger operators the Anderson localization phenomenon which consists of both exponential localization of eigenfunctions and dynamical localization. We rst consider the discrete multi-particle Anderson model with a short range interaction and a random potential whose values are independent and identically distributed i.i.d. with a log-Hölder continuous common probability distribution function. For such model, we show that the bottom of its spectrum is non-random and prove the Anderson localization for energies suciently close to the spectral edge. On the other hand, we establish that the complete localization from singleparticle systems extends to multi-particle systems with suciently weak interaction at arbitrary disorder and for absolute continuous probability distribution function of the i.i.d random variables. The results are proved by an adaptation to multi-particle systems of the vari- able energy multi-scale analysis which allows singular distributions instead of the fractional moments method. Wegner bounds, useful for the multi-scale analysis are proved for separable cubes using the Stollmann's Lemma. We also prove the Combes-Thomas estimate which plays an important role in the analysis of extreme energies., Dans cette thèse, on étudie le phénomène de localisation d'Anderson des opérateurs de Schrödinger à N particules qui englobe aussi bien la localisation exponentielle des fonctions propres que la localisation dynamique. Dans un premier temps, on considère le modèle d'Anderson discret multi- particulaire avec un potentiel aléatoire à valeurs indépendantes et identiquement distribuées i.i.d. dont la distribution commune est au moins log-Höldérienne et une interaction de courte portée. On établit pour ce modèle la localisation d'Anderson pour les énergies susamment proches du bas du spectre après avoir montré qu'il est non-aléatoire. D'autre part, on montre que la localisation complète des systèmes mono- particulaires s'étend aux systèmes multi-particulaires ayant une interaction globale susamment faible et pour un désordre arbitraire. Pour ce résultat, l'existence d'une densité bornée de la distribution commune des variables aléatoires i.i.d. est nécessaire et on le montre pour des interactions ayant une forme très générale mais bornées. Les résultats sont démontrés à l'aide de l'adaptation aux systèmes multi- particulaires de l'analyse multi-échelle à énergie variable qui permet de traiter des distributions singulières contrairement à la méthode des moments fractionnaires. Les estimées de Wegner intervenant notamment dans l'analyse multi-échelle sont établies pour des cubes vériant une propriété de séparabilité en utilisant le Lemme de Stollmann. On démontre également l'estimée de Combes-Thomas qui joue un rôle important dans l'analyse des énergies extrêmes.

Laser Raman spectroscopy was used to investigate the presence of core-shell structure in copper ferrite-polyaniline nanocomposites prepared by in situ polymerization method. Laser beams with two excitation powers, 0.3 mW and 3 mW, were employed to study the ferrite-polyaniline interaction and its changes by the laser induced heating effects. Low energy Raman spectra distinctly displayed polyaniline bands only without bands for CuFe 2O 4 in all the nanocomposites. This observation attributes polyaniline shell over the CuFe 2O 4 core particle, since the low energy was not sufficient for the beam to penetrate the polyaniline shell. However, with higher incident energy due to the induced heating effect, there was disturbance of polyaniline shell and the Raman frequencies were shifted depending on the shell thickness. Raman spectra of copper ferrite-polyaniline nanocomposites recorded using higher energy beam were consistent with the low energy Raman spectra of polyaniline samples annealed at three different temperatures of 200, 300 and 400 �C respectively for 2 h. High-resolution scanning electron microscope study also supports the formation of core-shell structure. It revealed that the average particle size increases with increase of shell thicknesses. � 2012 Elsevier B.V.

The synthesis, electrochemical, optical, and cation-sensing properties of two triazole-tethered ferrocenyl benzylacetate derivatives, C 36H 36O 6N 6Fe (2) and C 23H 23O 3N 3Fe (3), are presented. The binding event of both the receptors can be inferred either from a redox shift (2, ?E 1/2 = 106 mV for Hg 2+ and ?E 1/2 = 187 mV for Ni 2+, 3, ?E 1/2 = 167 mV for Hg 2+ and ?E 1/2 = 136 mV for Ni 2+) or a highly visual output response (colorimetric) for Hg 2+, Ni 2+, and Cu 2+ cations. Remarkably, the redox and colorimetric responses toward Hg 2+ are preserved in the presence of water (CH 3CN/H 2O, 2/8), which can be used for the selective colorimetric detection of Hg 2+ in an aqueous environment over Ni 2+ and Cu 2+ cations. The changes in the absorption spectra are accompanied by the appearance of a new low-energy (LE) peak at 625 nm for both compounds 2 and 3 (2, ? = 2500 M -1 cm -1, 3, ? = 1370 M -1 cm -1), due to a change in color from yellow to purple for Hg 2+ cations in CH 3CN/H 2O (2/8). � 2012 American Chemical Society.

A kinematically complete measurement was made of the Coulomb dissociation of SE nuclei on a Pb target at 83 MeV/nucleon. The cross section was measured at low relative energies in order to infer the astrophysical S factor for the Be-7(p, gamma)B-8 reaction. A first-order perturbation theory analysis including El, E2, and M1 transitions was employed to extract the El strength relevant to neutrino-producing reactions in the solar interior. By fitting the measured cross section from E-rel = 130 to 400 keV, we find S-17(0)= 17.8(-1.2)(+1.4) eV b.

Co-editor of journal volume ispartof: Annalen der Physik vol:525 issue:8 pages:A127-A128 status: published

We study the emission of quasi-particles in the scaling limit of the 1d Quantum Ising chain at the critical point perturbed by a time dependent local transverse field. We compute \it exactly \rm and for a \it generic \rm time dependence the average value of the transverse magnetization, its correlation functions, as well as the statistic of both the inclusive and exclusive work. We show that, except for a cyclic perturbation, the probability distribution of the work at low energies is a power law whose exponent is universal, i.e. does not depend on the specific time dependent protocol, but only on the final value attained by the perturbation., 5 pages, 1 figure, Published Version

International audience; This paper presents an integrated control method of a light road vehicle driving on a known and high secured itinerary at low speed. A planning module sends a safe and low energy reference trajectory to a control module that permits to manage the trajectory tracking under 50 km/h. A backstepping procedure is presented and formulated to realize a coupled longitudinal and lateral control in lane change or collision avoidance maneuvers.

The quantum mechanical state-to-state rotational excitation cross sections have been computed using the ab initio ground electronic state potential energy surface of the system [M. Mladenovic and S. Schmatz, J. Chem. Phys. 109, 4456 (1998)] computed at coupled-cluster single and double and triple perturbative excitations method using correlation-consistent polarized valence quadruple zeta basis set where the asymptotic potential have been computed using the dipole moment, quadrupole moment, and the molecular polarizability components and fitted to this interaction potential. The anisotropy of the surface has been analyzed in terms of the multipolar expansion coefficients for the rigid-rotor surface. The integral cross sections for rotational excitations have been computed by solving close-coupled equations at very low collision energies (5-200 cm -1) and the corresponding rates have been obtained for a range of low temperatures (5-175 K). The j = 0 ? j ? 1 rotational excitation cross section (and rate) is found to be the dominant followed by the j 0 ? j ? 2 in these collision energies. The close-coupling, coupled-state, and infinite-order sudden approximations coupling calculations have been performed in the energy range of 0.1-1.0 eV using vibrational ground potential. The rotational cross sections have been obtained by performing computationally accurate close-coupling calculations at 0.1 eV using vibrationally averaged potential (v 1) and compared with the results of vibrational ground potential. � 2012 American Institute of Physics.

This study investigates the effect of powder processing on powder flowability, compact ability, and the heat treatment of the resulting coatings on the mechanical properties of cold gas dynamic sprayed Ti-6Al-4V alloy. Nitrogen gas was used throughout the coating deposition process. Propellant gas temperature and pressure were attuned to maximize particle impact velocity. Three powder processing conditions were used in this study: as received (AR), low-energy ball milled (BM), and argon atmosphere heat treated (HT). Results showed coating porosities of around 6 to 7%, regardless of the feedstock powder used or the heat treatment performed. It was observed at 600 and 800°C anneals that a coating hardness reduction occurred, possibly due to static recovery and recrystallization, with minor sintering possibly occurring at the 800°C anneals. In addition, micro tensile tests showed an increase in cohesion strength at higher heat treatment temperatures. © 2012 Trans Tech Publications, Switzerland., 7th International Conference on Processing and Manufacturing of Advanced Materials, THERMEC'2011, 1 August 2011 through 5 August 2011, Quebec City, QC

An inverse technique has been designed to unfold the x-ray tube spectrum from the measurement of the photons scattered by a target interposed in the path of the beam. A special strategy is necessary to circumvent the ill-conditioning of the forward transport algebraic problem. The proposed method is based on the calculation of both, the forward and adjoint analytical solutions of the Boltzmann transport equation. After testing the method with numerical simulations, a simple prototype built at the Operational Unit of Health Physics of the University of Bologna was used to test the method experimentally. The reconstructed spectrum was validated by comparison with a straightforward measurement of the X-ray beam. The influence of the detector was corrected in both cases using standard unfolding techniques. The method is capable to accurately characterize the intensity distribution of an X-ray tube spectrum, even at low energies where other methods fail.

Technology and Vcc scaling lead to significant faulty bit rates in caches. Mechanisms based on disabling faulty parts show to be effective for average performance but are unacceptable in safety critical systems where worst-case execution time (WCET) estimations must be safe and tight. The Reliable Victim Cache (RVC) deals with this issue for a large fraction of the cache bits. However, replacement bits are not protected, thus keeping the probability of failure still high. This paper proposes two mechanisms to tolerate faulty bits in replacement bits and keep time-predictability by extending the RVC. Our solutions offer different tradeoffs between cost and complexity. In particular, the Extended RVC (ERVC) has low energy and area overheads while keeping complexity at a minimum. The Reliable Replacement Bits (RRB) solution has even lower overheads at the expense of some more wiring complexity. © 2011 IEEE. 25 30 Sponsors: IEEE IEEE Computer Society tttc Conference code: 86459 Cited By :6

From inelastic neutron-scattering experiments and all atom molecular dynamics simulations we present evidence for a low-energy dynamical mode in the fluid phase of a 1,2-dimyristoyl-sn-glycero-3-phoshatidylcholine (DMPC) bilayer immersed in a 5% water/ethanol solution. In addition to the well-known phonon that shows a liquidlike dispersion with energies up to 4.5 meV, we observe an additional mode at smaller energies of 0.8 meV, which shows little or no dispersion. Both modes show transverse properties and might be related to molecular motion perpendicular to the bilayer. © 2011 American Physical Society.

Point projection microscopy (PPM) is used to image suspended graphene by using low-energy electrons (100-205 eV). Because of the low energies used, the graphene is neither damaged nor contaminated by the electron beam for doses of the order of 107 electrons per nm2. The transparency of graphene is measured to be 74%, equivalent to electron transmission through a sheet twice as thick as the covalent radius of sp2-bonded carbon. Also observed is rippling in the structure of the suspended graphene, with a wavelength of approximately 26 nm. The interference of the electron beam due to diffraction off the edge of a graphene knife edge is observed and is used to calculate a virtual source size of 4.7 ± 0.6 Å for the electron emitter. It is demonstrated that graphene can serve as both the anode and the substrate in PPM, thereby avoiding distortions due to strong field gradients around nanoscale objects. Graphene can be used to image objects suspended on the sheet using PPM and, in the future, electron holography. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

The optical constants n and k of holmium (Ho) films were obtained in the 3-1340-eV range from transmittance measurements performed at room temperature. Thin films of Ho with various thicknesses were deposited by evaporation in ultra high vacuum conditions and their transmittance was measured in situ. Ho films were deposited onto thin C-film substrates supported on high transmittance grids. Transmittance measurements were used to obtain the extinction coefficient k of Ho films. The refractive index n of Ho was calculated with Kramers-Krönig analysis; in order to do this, k data were extrapolated both on the high and on the low energy parts of the spectrum by using experimental and calculated k values available in the literature. Ho, similar to other lanthanides, has a low-absorption band below the O2,3 edge onset; the lowest absorption was measured at ∼22 eV. Therefore, Ho is a promising material for filters and multilayer coatings in the energy range below the O2,3 edge in which most materials have a large absorption. Good consistency of the data resulted from the application of f and inertial sum rules. © 2011 American Institute of Physics., This work was also supported by the National Programme for Space Research, Subdireccio´n General de Proyectos de Investigacio´n, Ministerio de Ciencia y Tecnologı´a, project numbers AYA2008-06423- C03-02/ESP, AYA2009-14070, and AYA2010-22032.

A set of knitted poly(lactic acid) (PLA) fabrics was ozonated at room temperature for periods ranging from one to 60 minutes in order to identify any accompanying effects on physical properties (specifically whiteness, water-absorbency, flexural rigidity and burst strength), fiber surface integrity or internal microstructure. A significant (ca. 6% after 10 minutes of treatment) initial increase in whiteness was observed, with longer treatment times producing little further change. The fabric’s absorbency and flexibility both increased, the time of wetting having fallen by ca. 20% and the flexural rigidity by ca. 16%, respectively, after 10 minutes of treatment. Fabric strength remained virtually unaffected for short times (up to 10 minutes) of ozonation, although longer treatments caused a measurable drop (ca. 10% after 60 minutes). SEM imaging showed virtually no evidence for surface damage, even after 60 minutes of treatment, whereas peroxide treatment caused massive pitting of the fiber surface. Raman spectroscopy of the ozonated PLA fabrics indicated that the treatment had not affected the internal microstructure of the fibers. Our conclusion is that brief (no more than 10 minutes) room-temperature ozonation is potentially an effective, safe and low-energy alternative to conventional higher temperature peroxide treatment. © 2011, SAGE Publications. All rights reserved.

An attempt is made to identify the most important mechanisms responsible for the rearrangement of electrons during collisions between multiply charged ions and atoms at keV energies. It is discussed to which extent the influence of binding energy, angular momentum of heavy particles and electrons, and electron-electron correlation on the dynamic processes can be understood by means of simple models. Collision systems comprising only one, two, or many active electrons are distinguished, since rigorous theoretical treatments for such systems are well established, just being developed or not yet available respectively.

We present non-resonant, polarization-resolved magneto-photoluminescence measurements up to 12 T on single InAs/AlAs quantum dots. We observe typical g-factors between 1 and 2, very low diamagnetic shifts due to strong exciton localization and low-energy sidebands, which are attributed to the piezoelectric exciton-acoustic phonon interaction. Spanish Ministry of Education/MAT2008- 01555/NAN Spanish Ministry of Education/Consolider CSD 2006-19 Community of Madrid CAMS-0505-ESP-0200 Spanish Ministry of Science and Innovation/Nanoinpho-QD TEC2008-06756-C03-01

The low-voltage foil corrector is a novel type of foil aberration corrector that can correct for both the spherical and chromatic aberration simultaneously. In order to give a realistic example of the capabilities of this corrector, a design for a low-voltage scanning electron microscope with the low-voltage foil corrector is presented. A fully electrostatic column has been designed and characterised by using aberration integrals and ray tracing calculations. The amount of aberration correction can be adjusted relatively easy. The third order spherical and the first order chromatic aberration can be completely cancelled. In the zero current limit, a FW50 probe size of 1.0. nm at 1. kV can be obtained. This probe size is mainly limited by diffraction and by the fifth order spherical aberration. © 2010 Elsevier B.V.

Various thin polystyrene, PS, and poly(methyl methacrylate), PMMA and PS + PMMA blend films have been examined using the technique of recording X-ray photoelectron spectrum while the sample is subjected to +/- 10 V d.c, bias, and three different forms of (square-wave (SQW), sinusoidal (SIN) and triangular (TRG)), a.c. pulses. All films exhibit charging shifts as observed in the position of the corresponding C1s peak under d.c. bias. The a.c. pulses convert the single C1s peak to twinned peaks in the case of the square-wave form, and distort severely in the cases of the SIN, and TRG forms, and all three of them exhibit strong frequency dependence. In order to mimic and better understand the behavior of these polymeric materials, an artificial dielectric system consisting of a clean Si-wafer coupled to an external 1 M Omega resistor and 56 nF capacitor is created, and its response to different forms of voltage stimuli, is examined in detail. A simple electrical circuit model is also developed treating the system as consisting of a parallel resistor and a series capacitor. With the help of the model, the response of the artificial system is successfully calculated as judged by comparison with the experimental data. Using one high frequency SQW measurements, the off-set in the charging shift clue to the extra low-energy neutralizing electrons is estimated. After correcting the corresponding off-set shifts, the XPS spectra of the three different PS films, one PMMA, and one PS + PMMA blend film are re-examined. As a result of these detailed analysis, there emerges a clear relationship between the thicknesses of the PS films with their charging abilities. In the blend film, PS and PMMA domains are electrically separated, and exhibit different charging shifts, however, the presence of one is felt by the other. Hence, the PS component shifts are larger in the blend, due to the presence of PMMA domains, which has intrinsically a larger R-eff, and conversely the PMMA component shifts are smaller due to the presence of PS domains. (C) 2009 Elsevier B.V. All rights reserved.

The low-voltage foil corrector is a novel type of foil aberration corrector that can correct for both the spherical and chromatic aberration simultaneously. In order to give a realistic example of the capabilities of this corrector, a design for a low-voltage scanning electron microscope with the low-voltage foil corrector is presented. A fully electrostatic column has been designed and characterised by using aberration integrals and ray tracing calculations. The amount of aberration correction can be adjusted relatively easy. The third order spherical and the first order chromatic aberration can be completely cancelled. In the zero current limit, a FW50 probe size of 1.0. nm at 1. kV can be obtained. This probe size is mainly limited by diffraction and by the fifth order spherical aberration. © 2010 Elsevier B.V.

[EN] In this work ultrafine and nanocrystalline WC-Co mixtures were obtained by low energy milling in planetary ball mill. The effect of the processing conditions on the reduction and distribution of the grain sizes and the internal strains level were studied. The characterisation of the powder mixtures was performed by means of scanning and transmission electron microscopy and X-ray diffraction analysis. Observations through SEM and TEM images showed a particle size below 100 nm, after milling. The X-ray diffraction profile analysis revealed a WC phase refined to a crystallite size of 19 nm. The mixtures obtained have been consolidated and mechanical and microstructurally characterised. The results show improvements in resistant behaviour of the material consolidated from nanocrystalline powders, in spite of the grain growth experienced during the sintering. The best results were found for the material obtained by wet milling during 100 h, which presents values of hardness higher than 1800 HV. © 2011 Institute of Materials, Minerals and Mining., This work has been supported by CICYT, Spain, through project no. MAT2006-12945-C03-02.

We have investigated the interaction of n-butanol (NBA) with thin layers of water ice prepared in ultra high vacuum in the temperature range of 110-150 K. From the mass spectra of the chemically sputtered species, created upon the collision of low energy (?30 eV) Ar + ions, we study the process of diffusive mixing of NBA with water ice, at the molecular level. The results show that NBA undergoes diffusive mixing with H 2O. Even after depositing 1000 monolayers (MLs) of amorphous solid water (ASW) over NBA, both the species are observed on the surface. However, when NBA is deposited over ASW, no water is seen on the surface above 3-5 MLs of NBA. This could be interpreted as the absence of diffusive mixing in this system or surface segregation of NBA, in view of its lower surface energy just as in the case of liquid alcohols. An isomeric alcohol, namely, tert-butyl alcohol (TBA), also behaves similarly. Although the presence of NBA and TBA is detected, in the presence of ASW, they undergo selective ionization, giving specific peaks in the mass spectrum. D 2O behaves in a manner similar to that of H 2O. Preliminary experiments with other alcohols; namely, methanol, ethanol, and propanol were also done, and the results suggest that incomplete diffusion or surface segregation begins with propanol. � 2009 American Chemical Society.

A single layer of the Cationic polyelectrolyte poly(allyamine) hydrochloride (PAH) deposited, using the layer-by-layer technique, on a silicon substrate containing 5 nm oxide layer is investigated by XPS while applying an external potential bias to the sample to control and manipulate the charge built-up on the oxide layer. Under application of a -10 V bias, the oxide layer is positively charged due to Photoemission process, evidenced by the measured Si2p binding energy of 104.4 eV. Application of a +10 V bias attracts the low energy neutralizing electrons, stemming from a hot filament, and leads to a negatively charged oxide layer, also evidenced by the measured Si2p binding energy of 102.9 eV. The single polyelectrolyte overlayer also responds to this polarity change of the oxide layer underneath by displaying a somewhat larger shifts both in the C1s and Nls peaks. In addition to the shifts in the positions, the N1s peaks undergo a significant intensity depletion, mostly on the positively charged -N+ component. We interpret this intensity depletion to be the result of reorientation of some of the dangling positively charged groups by moving toward the negatively charged oxide underlayer. To our knowledge this is the first time that a chemically specific response to an electrical stimuli is reported using XPS. A bilayer LbL film consisting of PAH and PSS, exhibits even a larger charging shift, but this time no intensity alteration is observed, most probably due to locking of the -N+ groups by the -SO3 + counterions of the second layer. © 2009 American Chemical Society.

Second order Møller–Plesset perturbation theory at the complete basis set limit and diffusion quantum Monte Carlo are used to examine several low energy isomers of the water hexamer. Both approaches predict the so-called prism to be the lowest energy isomer, followed by cage, book, and cyclic isomers. The energies of the four isomers are very similar, all being within 10–15 meV/H2O. These reference data are then used to evaluate the performance of several density-functional theory exchange-correlation (xc) functionals. A subset of the xc functionals tested for smaller water clusters [I. Santra et al., J. Chem. Phys. 127, 184104 (2007)] has been considered. While certain functionals do a reasonable job at predicting the absolute dissociation energies of the various isomers (coming within 10–20 meV/H2O), none predict the correct energetic ordering of the four isomers nor does any predict the correct low total energy isomer. All xc functionals tested either predict the book or cyclic isomers to have the largest dissociation energies. A many-body decomposition of the total interaction energies within the hexamers leads to the conclusion that the failure lies in the poor description of van der Waals (dispersion) forces in the xc functionals considered. It is shown that the addition of an empirical pairwise (attractive) C6R−6 correction to certain functionals allows for an improved energetic ordering of the hexamers. The relevance of these results to density-functional simulations of liquid water is also briefly discussed.

Turkish International Cooperation Agency.