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1

Terahertz rectification by periodic two-dimensional electron plasma  

Energy Technology Data Exchange (ETDEWEB)

The physics of terahertz rectification by periodic two-dimensional electron plasma is discussed. Two different effects yielding terahertz rectification are studied: the plasmonic drag and plasmonic ratchet. Ultrahigh responsivity of terahertz rectification by periodic two-dimensional electron plasma in semiconductor heterostructures and graphene is predicted.

Popov, V. V. [Kotelnikov Institute of Radio Engineering and Electronics, Russian Academy of Sciences, Saratov 410019 (Russian Federation); Saratov State University, Saratov 410012 (Russian Federation)

2013-06-24

2

Disorder-Induced Rectification in a Molecular System  

Science.gov (United States)

In this work, We study on the electron transport of an ensemble of coupled sites that simulates an array of quantum dots or a molecular system. By using the Green's function technique, we calculate current and shot noise for linear and disordered site arrays. While in the linear case the characteristic I-V curve reveals no current rectification, in the disordered configurations a robust rectification is found, thus indicating an operational regime typical of molecular diodes. Additionally, a negative differential resistance is observed due to the drop of the bias voltage along the structure, which yields to an energy mismatch of neighboring sites. Finally, the Fano factor reveals a stronger transport correlation for positive than for negative bias voltages in the disordered site configuration.

Coutinho, R. M.; Saraiva-Souza, A.; Souza Filho, A. G.; Souza, F. M.

2013-08-01

3

The effects of contact configurations on the rectification of dipyrimidinyl—diphenyl diblock molecular junctions  

International Nuclear Information System (INIS)

The transport properties of a conjugated dipyrimidinyl—diphenyl diblock oligomer sandwiched between two gold electrodes, as recently reported by [Díez-Pérez et al. Nature Chem. 1 635 (2009)], are theoretically investigated using the fully self-consistent nonequilibrium Green's function method combined with density functional theory. Two kinds of symmetrical anchoring geometries are considered. Calculated current—voltage curves show that the contact structure has a strong effect on the rectification behaviour of the molecular diode. For the equilateral triangle configuration, pronounced rectification behaviour comparable to the experimental measurement is revealed, and the theoretical analysis indicates that the observed rectification characteristic results from the asymmetric shift of the perturbed molecular energy levels under bias voltage. While for the tetrahedron configuration, both rectification and negative differential conductivity behaviours are observed. The calculated results further prove the close dependence of the transporting characteristics of molecular junctions on contact configuration. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

2011-12-01

4

Molecular junctions in the Coulomb blockade regime: rectification and nesting  

CERN Multimedia

Quantum transport through single molecules is very sensitive to the strength of the molecule-electrode contact. Here, we investigate the behavior of a model molecular junction weakly coupled to external electrodes in the case where charging effects do play an important role (Coulomb blockade regime). As a minimal model we consider a molecular junction with two spatially separated donor and acceptor sites. Depending on their mutual coupling to the electrodes, the resulting transport observables show well defined features such as rectification effects in the I-V characteristics and nesting of the stability diagrams. To be able to accomplish these results, we have developed a theory which allows to explore the charging regime via the nonequilibrium Green function formalism parallel to the widely used master equation technique. Our results, beyond their experimental relevance, offer a transparent framework for the systematic and modular inclusion of a richer physical phenomenology.

Song, B; Cuniberti, G; Song, Bo; Ryndyk, Dmitry A.; Cuniberti, Gianaurelio

2006-01-01

5

The preparation of metal oxygen molecular cluster embedded organic-inorganic nanocomposite and its rectification behaviour  

International Nuclear Information System (INIS)

A metal oxygen molecular cluster compound has been utilized for the preparation of organic-inorganic nanocomposite film by a sol-gel method. The entrapment of these cluster compounds in a composite film has been characterized by various physico-chemical techniques. The entrapped metal oxygen cluster stabilizes its energy levels, which is evidenced from the change in redox potential and band gap. The rectification phenomenon of composite films is attributed to the embedded cluster compounds. The rectification behaviour of the composite film, which is due to the charge transfer from molecular cluster and the electrode, has been studied

2008-12-20

6

Molecular junctions in the Coulomb blockade regime: rectification and nesting  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quantum transport through single molecules is very sensitive to the strength of the molecule-electrode contact. Here, we investigate the behavior of a model molecular junction weakly coupled to external electrodes in the case where charging effects do play an important role (Coulomb blockade regime). As a minimal model we consider a molecular junction with two spatially separated donor and acceptor sites. Depending on their mutual coupling to the electrodes, the resulting tr...

Song, Bo; Ryndyk, Dmitry A.; Cuniberti, Gianaurelio

2006-01-01

7

Theoretical study of molecular rectification in porphyrin dimer  

International Nuclear Information System (INIS)

Carrying out theoretical calculations using the density functional method for nonequilibrium electron transport, we investigated the electric conductibility of a porphyrin dimer coupled to gold electrodes by thiolate bonds. A porphyrin with four electron-donating amino groups in the dimer is connected to a porphyrin with four electron-withdrawing cyano groups by a dimethylene bridge. The calculations demonstrated that this dimer allows more flow of electrons from the first porphyrin (donor) to the second porphyrin (acceptor) than in the opposite direction. This means that the porphyrin dimer has favorable rectifier characteristics that are accounted for by the mechanism of not Aviram and Ratner [Chem. Phys. Lett. 29 (1974) 277] but of Stokbro, et al. [J. Am. Chem. Soc. 125 (2003) 3674

2008-03-03

8

Electronic structure and nonlinear optical rectification in a quantum dot: effects of impurities and external electric field  

Energy Technology Data Exchange (ETDEWEB)

The electronic structure of a spherical quantum dot with parabolic confinement that contains a hydrogenic impurity and is subjected to a DC electric field is studied. In our calculations we vary the position of the impurity and the electric field strength. The calculated electronic structure is further used for determining the nonlinear optical rectification coefficient of the quantum dot structure. We show that both the position of the impurity and the strength of the electric field influence the nonlinear optical rectification process.

Baskoutas, S [Materials Science Department, University of Patras, School of Natural Sciences, Patras 26504 (Greece); Paspalakis, E [Materials Science Department, University of Patras, School of Natural Sciences, Patras 26504 (Greece); Terzis, A F [Department of Physics, University of Patras, School of Natural Sciences, Patras 26504 (Greece)

2007-10-03

9

Electronic structure and nonlinear optical rectification in a quantum dot: effects of impurities and external electric field  

International Nuclear Information System (INIS)

The electronic structure of a spherical quantum dot with parabolic confinement that contains a hydrogenic impurity and is subjected to a DC electric field is studied. In our calculations we vary the position of the impurity and the electric field strength. The calculated electronic structure is further used for determining the nonlinear optical rectification coefficient of the quantum dot structure. We show that both the position of the impurity and the strength of the electric field influence the nonlinear optical rectification process

2007-10-03

10

Wave-packet rectification in nonlinear electronic systems: A tunable Aharonov-Bohm diode  

CERN Document Server

Rectification of electron wave-packets propagating along a quasi-one dimensional chain is commonly achieved via the simultaneous action of nonlinearity and longitudinal asymmetry, both confined to a limited portion of the chain termed wave diode. However, it is conceivable that, in the presence of an external magnetic field, spatial asymmetry perpendicular to the direction of propagation suffices to ensure rectification. This is the case of a nonlinear ring-shaped lattice with different upper and lower halves (diode), which is attached to two elastic chains (leads). The resulting device is mirror symmetric with respect to the ring vertical axis, but mirror asymmetric with respect to the chain direction. Wave propagation along the two diode paths can be modeled for simplicity by a discrete Schr\\"odinger equation with cubic nonlinearities. Numerical simulations demonstrate that, thanks to the Aharonov-Bohm effect, such a diode can be operated by tuning the magnetic flux across the ring.

Li, Yunyun; Marchesoni, Fabio; Li, Baowen

2014-01-01

11

Molecular dynamics study on the thermal conductivity and thermal rectification in graphene with geometric variations of doped boron  

International Nuclear Information System (INIS)

Thermal conductivity and thermal rectification of graphene with geometric variations have been investigated by using classical non-equilibrium molecular dynamics simulation, and analyzed theoretically the cause of the changes of thermal conductivity and thermal rectification. Two different structural models, triangular single-boron-doped graphene (SBDG) and parallel various-boron-doped graphene (VBDG), were considered. The results indicated that the thermal conductivities of two different models are about 54–63% lower than pristine graphene. And it was also found that the structure of parallel various-boron-doped graphene is inhibited more strongly on the heat transfer than that of triangular single-boron-doped graphene. The reduction in the thermal conductivities of two different models gradually decreases as the temperature rises. The thermal conductivities of triangular boron-doped graphene have a large difference in both directions, and the thermal rectification of this structure shows the downward trend with increasing temperature. However, the thermal conductivities of parallel various-boron-doped graphene are similar in both directions, and the thermal rectification effect is not obvious in this structure. The phenomenon of thermal rectification exits in SBDG. It implies that the SBDG might be a potential promising structure for thermal rectifier by controlling the boron-doped model

2014-03-15

12

Molecular dynamics study on the thermal conductivity and thermal rectification in graphene with geometric variations of doped boron  

Energy Technology Data Exchange (ETDEWEB)

Thermal conductivity and thermal rectification of graphene with geometric variations have been investigated by using classical non-equilibrium molecular dynamics simulation, and analyzed theoretically the cause of the changes of thermal conductivity and thermal rectification. Two different structural models, triangular single-boron-doped graphene (SBDG) and parallel various-boron-doped graphene (VBDG), were considered. The results indicated that the thermal conductivities of two different models are about 54–63% lower than pristine graphene. And it was also found that the structure of parallel various-boron-doped graphene is inhibited more strongly on the heat transfer than that of triangular single-boron-doped graphene. The reduction in the thermal conductivities of two different models gradually decreases as the temperature rises. The thermal conductivities of triangular boron-doped graphene have a large difference in both directions, and the thermal rectification of this structure shows the downward trend with increasing temperature. However, the thermal conductivities of parallel various-boron-doped graphene are similar in both directions, and the thermal rectification effect is not obvious in this structure. The phenomenon of thermal rectification exits in SBDG. It implies that the SBDG might be a potential promising structure for thermal rectifier by controlling the boron-doped model.

Liang, Qi, E-mail: alfred_02030210@163.com; Wei, Yuan

2014-03-15

13

Microwave Rectification at the Boundary between Two-Dimensional Electron Systems.  

Science.gov (United States)

Rectification of microwave radiation (20-40 GHz) by a line boundary between two two-dimensional metals on a silicon inversion layer was observed(I. Hoxha, S. A. Vitkalov, N. A. Zimbovskaya, M. P. Sarachik, and T. M. Klapwijk, preprint cond-mat/0110331 (2001).) and investigated at different temperatures, in-plane magnetic fields and microwave powers. The rectified voltage V_dc is generated whenever the electron densities n_1,2 of the two metals are different, changing polarity at n1 ? n_2. Very strong nonlinear response is found when one of the two 2D metals is close to the electron density corresponding to the reported magnetic instability(S. A. Vitkalov, H. Zheng, K. M. Mertes, M. P. Sarachik, and T. M. Klapwijk, Phys. Rev. Lett. 87), 086401 (2001); A. A. Shashkin, S. V. Kravchenko, V. T. Dolgopolov, and T. M. Klapwijk, Phys. Rev. Lett. 87, 086801 (2001). in this system.

Hoxha, Islam; Vitkalov, S. A.; Zimbovskaya, N. A.; Sarachik, M. P.; Klapwijk, T. M.

2002-03-01

14

Molecular Basis of Inward Rectification: Polyamine Interaction Sites Located by Combined Channel and Ligand Mutagenesis  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Polyamines cause inward rectification of (Kir) K+ channels, but the mechanism is controversial. We employed scanning mutagenesis of Kir6.2, and a structural series of blocking diamines, to combinatorially examine the role of both channel and blocker charges. We find that introduced glutamates at any pore-facing residue in the inner cavity, up to and including the entrance to the selectivity filter, can confer strong rectification. As these negative charges are moved higher (toward the selecti...

Kurata, Harley T.; Phillips, L. Revell; Rose, Thierry; Loussouarn, Gildas; Herlitze, Stefan; Fritzenschaft, Hariolf; Enkvetchakul, Decha; Nichols, Colin G.; Baukrowitz, Thomas

2004-01-01

15

Thermal rectification of electrons in hybrid normal metal-superconductor nanojunctions  

International Nuclear Information System (INIS)

We theoretically investigate heat transport in hybrid normal metal-superconductor (NS) nanojunctions focusing on the effect of thermal rectification. We show that the heat diode effect in the junction strongly depends on the transmissivity and the nature of the NS contact. Thermal rectification efficiency can reach up to ?123% for a fully transmissive ballistic junction and up to 84% in diffusive NS contacts. Both values exceed the rectification efficiency of a NIS tunnel junction (I stands for an insulator) by a factor close to ?5 and ?3, respectively. Furthermore, we show that for NS point-contacts with low transmissivity, inversion of the heat diode effect can take place. Our results could prove useful for tailoring heat management at the nanoscale, and for mastering thermal flux propagation in low-temperature caloritronic nanocircuitry

2013-12-09

16

Rectification by charging: Contact-induced current asymmetry in molecular conductors  

Science.gov (United States)

We outline the qualitatively different physics behind charging-induced current asymmetries in molecular conductors operating in the weakly interacting self-consistent field (SCF) and the strongly interacting Coulomb blockade (CB) regimes. The SCF conductance asymmetry originates in the asymmetric shifts of the closed-shell molecular conducting levels, driven by unequal mean-field potentials for positive and negative biases. A very different current asymmetry arises for CB due to the unequal number of open-shell excitation channels at opposite bias voltages. The CB regime, dominated by single charge effects, typically requires a computationally demanding many-electron or Fock-space description to do justice to its complex excitation spectrum. However, our analysis of molecular CB measurements reveals that many novel signatures can be explained using a simpler orthodox model that involves an incoherent sum of Fock-space excitations and hence treats the molecule as a metallic dot. This also reduces the complexity of the Fock-space description by including charge configurations alone, somewhat underscoring the richness of its electronic structure while retaining the essential single charge nature of the transport process. The inclusion of electronic structure with well-resolved Fock space excitations is, however, crucial in some notable examples.

Miller, O. D.; Muralidharan, B.; Kapur, N.; Ghosh, A. W.

2008-03-01

17

Ballistic rectification in an asymmetric Si/SiGe cross junction with modulated electron density  

Energy Technology Data Exchange (ETDEWEB)

The influence of the electron density on the output characteristic of ballistic rectifiers is investigated. The rectifier is a nanoscale four-terminal {psi}-shaped cross junction consisting of a straight voltage stem (200 nm wide and 2 {mu}m long) and two opposing 200 nm wide branches which merge under 45 {sup circle} into the central stem. Different devices are fabricated from a high-mobility Si/SiGe heterostructure by using a mix-and-match process which combines high-resolution electron-beam lithography and UV-lithography. With a low-damage CF{sub 4}/O{sub 2} plasma step the resist pattern is transferred into the heterostructure. After the preparation of ohmic contacts a nanoscale Schottky gate is locally deposited on top of the voltage stem. A rectified inertial ballistic voltage develops between the upper and lower end of the central stem if a current is injected between the branches. At T=4.2 K we observe an increase of the rectified signal with decreasing electron density in the voltage stem achieved by applying a negative voltage at the local Schottky gate. The improved efficiency at low electron density is tentatively attributed to a reduced screening of the stationary dipole.

Salloch, Daniel; Wieser, Ulrich; Kunze, Ulrich [Werkstoffe und Nanoelektronik, Ruhr-Universitaet Bochum (Germany); Hackbarth, Thomas [DaimlerCrysler Forschungszentrum Ulm (Germany)

2009-07-01

18

Ballistic rectification in an asymmetric Si/SiGe cross junction with modulated electron density  

Energy Technology Data Exchange (ETDEWEB)

We demonstrate a substantial efficiency increase in an injection-type ballistic rectifier due to a modulated electron density in its active region. The rectifier is a nanoscale four-terminal {psi}-shaped cross junction fabricated from a high-mobility Si/SiGe heterostructure. Two nanoscale Schottky gates are locally deposited on top of the central stem above and below the cross junction. In addition to the inertial-ballistic rectified voltage, which will develop between the upper and lower end of the central stem if a current is injected between the branches, a hot-electron thermopower voltage establishes across the saddle-point potential formed below the local gate for negative gate-voltages. At T=4.2 K we observe an increase of the rectified signal due to the superposed hot-electron thermopower for negative gate voltages. Depending on the position of the constriction in the stem, a sign reversal of the output signal is also demonstrated. Both signals are experimentally separated in a modified device geometry.

Salloch, Daniel; Wieser, Ulrich; Kunze, Ulrich [Werkstoffe und Nanoelektronik, Ruhr-Universitaet Bochum (Germany); Hackbarth, Thomas [DaimlerChrysler Forschungszentrum Ulm (Germany)

2010-07-01

19

Inelastic transport and low-bias rectification in a single-molecule diode.  

Science.gov (United States)

Designing, controlling, and understanding rectification behavior in molecular-scale devices has been a goal of the molecular electronics community for many years. Here we study the transport behavior of a single molecule diode, and its nonrectifying, symmetric counterpart at low temperatures, and at both low and high biases to help elucidate the electron-phonon interactions and transport mechanisms in the rectifying system. We find that the onset of current rectification occurs at low biases, indicating a significant change in the elastic transport pathway. However, the peaks in the inelastic electron tunneling (IET) spectrum are antisymmetric about zero bias and show no significant changes in energy or intensity in the forward or reverse bias directions, indicating that despite the change in the elastic transmission probability there is little impact on the inelastic pathway. These results agree with first principles calculations performed to evaluate the IETS, which also allow us to identify which modes are active in the single molecule junction. PMID:21932824

Hihath, Joshua; Bruot, Christopher; Nakamura, Hisao; Asai, Yoshihiro; Díez-Pérez, Ismael; Lee, Youngu; Yu, Luping; Tao, Nongjian

2011-10-25

20

Electronic Properties of a Phenylacetylene Molecular Junction with Dithiocarboxylate Anchoring Group  

International Nuclear Information System (INIS)

The electronic transport properties of a kind of phenylacetylene compound (4-mercaptophenyl)-phenylacetylene (MPPA) are studied by the first-principles method. A dithiocarboxylate conjugated linker (?CS2) is used to anchor the molecule to one gold electrode. Rectification behavior is observed, which is mainly brought about by the asymmetrical coupling of electrodes to the molecule. There is a drastic increase in current as the electrode-electrode distance is reduced, and the rectification ratio increases by 40% as the electrode-electrode distance is diminished from 16 Å to 15.7 Å. For comparison, we also perform simulations with the ?CS2 linker replaced by thiol linkage. It shows an obvious reduction in current. We find that the stronger interface coupling induced by the ?CS2 linker broadens transmission resonances near the Fermi energy, which leads to the current enhancement of the molecular junction with ?CS2 linker

2013-01-01

 
 
 
 
21

Electronic Properties of a Phenylacetylene Molecular Junction with Dithiocarboxylate Anchoring Group  

Science.gov (United States)

The electronic transport properties of a kind of phenylacetylene compound (4-mercaptophenyl)-phenylacetylene (MPPA) are studied by the first-principles method. A dithiocarboxylate conjugated linker (-CS2) is used to anchor the molecule to one gold electrode. Rectification behavior is observed, which is mainly brought about by the asymmetrical coupling of electrodes to the molecule. There is a drastic increase in current as the electrode-electrode distance is reduced, and the rectification ratio increases by 40% as the electrode-electrode distance is diminished from 16 Å to 15.7 Å. For comparison, we also perform simulations with the -CS2 linker replaced by thiol linkage. It shows an obvious reduction in current. We find that the stronger interface coupling induced by the -CS2 linker broadens transmission resonances near the Fermi energy, which leads to the current enhancement of the molecular junction with -CS2 linker.

Liu, Wen; Xia, Cai-Juan; Liu, De-Sheng

2013-01-01

22

Rectification effect about vacuum separating carbon nanotube bundle predicted by first-principles study  

International Nuclear Information System (INIS)

For the molecular spintronics transport systems, we propose that the spin current rectifier can be constructed using the nonmagnetic lead. The proposal is confirmed according to the first-principles study of the transport characteristics of a vacuum separating (15,0) carbon nanotube bundle where only one zigzag edge is hydrogenated. The strong rectification effect for spin (charge) current is obtained in the case of the magnetic parallel (anti-parallel) configuration of two zigzag edges. Our investigations indicate that such device can be used as the spin filter and the counterpart of the p–n junction in the field of molecular electronics. -- Highlights: ? We propose that nonmagnetic leads can construct spin current rectifier. ? We propose a spin diode and a filter using CNT. ? The spin and charge current all have the rectification effect in the one-dimensional spin diode.

2012-05-07

23

Rectification Phenomena Across an Asymmetric Nanofluidic Channel  

Science.gov (United States)

We review our recent experimental and theoretical studies of nanofluidic diodes. A continuum theory is developed to show that the literature and our rectification data can be generically classified into two regimes: a low-voltage regime dominated by intra- channel ionic strength (Donnan potential) gradient and a high-voltage regime dominated by external ion depletion. The two regimes drive different anomalous phenomena, like molecular dissociation and microvortex instability, with distinct distinguished limits of dimensionless parameters. Applications to biosensing are discussed.

Chang, Hsueh-Chia

2011-11-01

24

Electron transport through molecular junctions  

International Nuclear Information System (INIS)

At present, metal–molecular tunnel junctions are recognized as important active elements in molecular electronics. This gives a strong motivation to explore physical mechanisms controlling electron transport through molecules. In the last two decades, an unceasing progress in both experimental and theoretical studies of molecular conductance has been demonstrated. In the present work we give an overview of theoretical methods used to analyze the transport properties of metal–molecular junctions as well as some relevant experiments and applications. After a brief general description of the electron transport through molecules we introduce a Hamiltonian which can be used to analyze electron–electron, electron–phonon and spin–orbit interactions. Then we turn to description of the commonly used transport theory formalisms including the nonequilibrium Green’s functions based approach and the approach based on the “master” equations. We discuss the most important effects which could be manifested through molecules in electron transport phenomena such as Coulomb, spin and Frank–Condon blockades, Kondo peak in the molecular conductance, negative differential resistance and some others. Bearing in mind that first principles electronic structure calculations are recognized as the indispensable basis of the theory of electron transport through molecules, we briefly discuss the main equations and some relevant applications of the density functional theory which presently is often used to analyze important characteristics of molecules and molecular clusters. Finally, we discuss some kinds of nanoelectronic devices built using molecules and similar systems such as carbon nanotubes, various nanowires and quantum dots.

2011-12-01

25

Magnetically Induced Thermal Rectification  

CERN Multimedia

We consider far from equilibrium heat transport in chaotic billiard chains with non-interacting charged particles in the presence of non-uniform transverse magnetic field. If half of the chain is placed in a strong magnetic field, or if the strength of the magnetic field has a large gradient along the chain, heat current is shown to be asymmetric with respect to exchange of the temperatures of the heat baths. Thermal rectification factor can be arbitrarily large for sufficiently small temperature of one of the baths.

Casati, G; Prosen, T; Casati, Giulio; Mejia-Monasterio, Carlos; Prosen, Tomaz

2006-01-01

26

Silicon-based molecular electronics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Molecular electronics on silicon has distinct advantages over its metallic counterpart. We describe a theoretical formalism for transport through semiconductor-molecule heterostructures, combining a semi-empirical treatment of the bulk silicon bandstructure with a first-principles description of the molecular chemistry and its bonding with silicon. Using this method, we demonstrate that the presence of a semiconducting band-edge can lead to a novel molecular resonant tunneli...

Rakshit, T.; Liang, G-c; Ghosh, A. W.; Datta, S.

2003-01-01

27

Electronic communication through molecular bridges.  

Science.gov (United States)

A concept that plays an important role in chemistry in general and in molecular spintronics in particular is electronic communication through molecular bridges. An improved understanding of this concept may help to transfer knowledge between different areas of chemistry and nanoscience. We aim at finding the limits of electronic communication as a property of the bridge by comparing and rationalizing trends in exchange spin coupling in diradicals and in conductance in dithiolate-gold junctions which share common sets of molecular bridges. PMID:23995380

Herrmann, Carmen; Elmisz, Jan

2013-11-18

28

Rectification in CdS/TCO bilayers  

Energy Technology Data Exchange (ETDEWEB)

The origin of process-induced rectification in CdS/ITO and CdS/SnO{sub 2} bilayers has been investigated. Both pre-treatment of the transparent conducting oxide (TCO) substrates and post-growth treatment of the bilayers were explored for both oxidising and reducing conditions. In/CdS/TCO structures were used for I-V testing, and the CdS layers were verified as being pinhole-free using a test employing a rectifying Au/CdS contact. Whilst neither pre-oxidation nor reduction of any TCO substrate failed to induce rectification in CdS/TCO, oxidation of CdS always induced rectification, regardless of the substrate type. This was attributed to oxidation of CdS (confirmed by Auger electron spectroscopy), and the results are consistent with a band diagram postulated for the CdO/CdS/ITO structure. Recommendations are made for the fabrication of CdTe/CdS/TCO solar cells. (author)

Al Turkestani, M.K.; Durose, K. [Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom)

2011-02-15

29

Molecular electronics in silico  

Science.gov (United States)

Assuming with Feynman that single atoms can be used as elementary memory cells, this would give a maximum density of information units of the order of 1015 cm-2 for a planar arrangement. If the chemical composition of the surface is fixed and any information change is simply associated with an electronic or conformational change between two possible states of any given surface atom, the above arrangement would result in a maximum information density of just 1 Pbit cm-2 - peta-scale integration (PSI). The manipulation of information on the atomic scale, however, requires the use of macroscopic-scale apparatuses that may, to date, be operated only at a negligible rate. Fundamental quantum mechanical considerations show instead that electrons can be configured with bit densities of the order of 1012 cm-2 (tera-scale integration, TSI); moreover, electron presence or flow can be controlled and sensed by already existing mesoscopic-scale apparatuses in giga-scale integration (GSI). Even though there is no clear method to enable the full exploitation of the performances of such devices, the TSI density is within the reach of the present technology. Rather than scaling down conventional CMOS (complementary metal-oxide-semiconductor) circuits, TSI may almost be achieved via a hybrid architecture where a silicon-based CMOS circuit controls a nanoscopic crossbar structure hosting in each cross-point a collection of functional molecules able to mimic by themselves the behaviour of a memory cell. The hybrid (silicon + molecules) route, however, poses severe problems. The following ones have been identified as the most important: (i) the setting up of an economically sustainable technology for the preparation of cross-points with density higher than 1011 cm-2; (ii) the demultiplexing of the addressing lines to allow their linkage to the CMOS circuit; (iii) the design, synthesis, and electrical characterization of the functional molecules; and (iv) the grafting via batch processing of the functional molecules to the cross-points forming the crossbar. This paper is devoted to discuss the severe challenges posed by the hybrid architecture and to present the solutions that have been found.

Cerofolini, G. F.; Romano, E.

2008-05-01

30

Electron tunneling between two electrodes mediated by a molecular wire containing a redox center  

Energy Technology Data Exchange (ETDEWEB)

Graphical abstract: We present a model for a molecular wire containing a redox center and suspended in an electrolyte solution. Current potential curves can contain plateaus and negative differential resistances. - Abstract: We derive an explicit expression for the quantum conductivity of a molecular wire containing a redox center, which is embedded in an electrochemical environment. The redox center interacts with the solvent, and the average over the solvent configurations is performed numerically. Explicit calculations have been performed for a chain of three atoms. When the redox center interacts strongly with neighboring electronic levels, the current-potential curves show interesting features like rectification, current plateaus and negative differential resistance. Electronic spectroscopy of intermediate states can be performed at constant small bias by varying the electrochemical potential of the wire.

Cruz, A.V.B.; Mishra, A.K. [Institute of Mathematical Sciences, CIT Campus, Chennai 600 113 (India); Schmickler, W., E-mail: Wolfgang.Schmickler@chemie.uni-ulm.de [Institute of Theoretical Chemistry, Ulm University, D89069 Ulm (Germany)

2010-05-25

31

Hot electron transport through molecular diodes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Single-molecule devices potentially offer a promising future for next-generation electronics. Understanding the mechanism of electron transport through single molecules is fundamental for developing such molecular electronics. In this thesis, we apply the method ballistic electron emission microscopy (BEEM) to study hot electron transport through a two-dimensional, self-assembled molecular layer. The molecular layer is sandwiched by a thin layer of metal and a semiconductor substrate, either ...

Li, Wenjie

2009-01-01

32

Analysis of transient rectification in DC motors  

Energy Technology Data Exchange (ETDEWEB)

Various considerations have been paid on transient rectification of DC motors which was known only qualitatively in the past. These studies were reviewed from wide angles to establish a basic method applicable to general cases. This paper reports the analysis method thus established. Transient rectification requires more complex analysis than steady rectification because it is influenced by a larger number of factors. To investigate compole flux response which is essential to such analysis, study was conducted to analyze the armature current waveform numerically and examine the rectification equation. For comparison between analysis results and measured values, response of compole flux response to current waveform was studied in the transient rectification tests; for the test DC motor, transient rectification analysis was studied. This study was intended for basic investigation on small DC motor, but it seems that the method provides a basic means for quantitative evaluation of transient rectification in general DC motors. 4 references, 7 figures.

Tsuboya, Kenji; Tajima, Masaaki; Noguchi, Tsuyoshi

1988-11-15

33

Electron thermalization in molecular gases  

International Nuclear Information System (INIS)

Thermalization of hot electrons in molecular gases is described by a Boltzmann equation, with the Boltzmann operator consisting of a Fokker-Plank operator for elastic processes and a difference operator for inelastic ones. The eigenvalue approach of Shizgal and co-workers for a Fokker-Plank equation is extended to solve this Boltzmann equation. The inelastic interaction is much stronger than the elastic one, and two well-separated time scales are involved in the relaxation processes. This makes the analysis difficult, and the convergence of the eigenmode expansion is very slow. It is shown, however, that a high precision calculation involving a few hundred eigenmodes shows convergence

2003-05-05

34

Rectification effect in asymmetric Kerr nonlinear medium  

Science.gov (United States)

Based on the transfer matrix method, the recursion of an electromagnetic wave propagating in an asymmetric Kerr nonlinear medium is analytically formulated, from which the rectification effect is clearly presented. The effects on the rectification region of the linear part and nonlinear coefficient of permittivity are both studied, and the energy densities before and after rectification are discussed. We use a rectifying factor to describe the intensity of the rectification effect. The result shows that every transmission peak is divided into two parts when the symmetry is broken, and nonlinear asymmetry has a more significant effect on the rectification effect than the linear asymmetry. The rectification intensity and area will be enlarged when the asymmetry factor is increased in a certain range.

Liu, Wan-Guo; Pan, Feng-Ming; Cai, Li-Wei

2014-06-01

35

Molecular Programming Pseudo-code Representation to Molecular Electronics  

CERN Document Server

This research paper is proposing the idea of pseudo code representation to molecular programming used in designing molecular electronics devices. Already the schematic representation of logical gates like AND, OR, NOT etc.from molecular diodes or resonant tunneling diode are available. This paper is setting a generic pseudo code model so that various logic gates can be formulated. These molecular diodes have designed from organic molecules or Bio-molecules. Our focus is on to give a scenario of molecular computation through molecular programming. We have restricted our study to molecular rectifying diode and logic device as AND gate from organic molecules only.

Pradhan, Manas Ranjan

2010-01-01

36

Electrons in molecules from basic principles to molecular electronics  

CERN Multimedia

The purpose of this book is to provide the reader with essential keys to a unified understanding of the rapidly expanding field of molecular materials and devices: electronic structures and bonding, magnetic, electrical and photo-physical properties, and the mastering of electrons in molecular electronics. Chemists will discover how basic quantum concepts allow us to understand the relations between structures, electronic structures, and properties of molecular entities and assemblies, and to design new molecules and materials. Physicists and engineers will realize how the molecular world fits in with their need for systems flexible enough to check theories or provide original solutions to exciting new scientific and technological challenges. The non-specialist will find out how molecules behave in electronics at the most minute, sub-nanosize level. The comprehensive overview provided in this book is unique and will benefit undergraduate and graduate students in chemistry, materials science, and engineering, ...

Launay, Jean-Pierre

2014-01-01

37

Electron EDM Search with Trapped Molecular Ions  

Science.gov (United States)

A sample of trapped molecular ions offers unique possibilities to search for a permanent electron electric dipole moment (EDM). Specifically, we plan to perform this search using the unpaired electron spins in the ^3?1 state of trapped HfF^+ molecular ions. The ions will be confined in a linear RF Paul trap, allowing for long electron spin coherence times for increased sensitivity to an electron EDM. Effective internal fields of the molecular ions should exceed 10^10 V/cm, and the molecules are easily polarized in ˜ 1V/cm electric fields due to a small ? doubling splitting in the ^3?1 state. HfF^+ molecular ions are created via laser ablation of a Hafnium target in the presence of a He + 1%SF6 supersonic expansion. The expansion cools the ions rovibrational and translational temperatures to a few Kelvin. We will report current experimental progress.

Stutz, Russell; Loh, Huanqian; Sinclair, Laura; Cornell, Eric

2008-05-01

38

Rydberg electron wavepacket dynamics in molecular hydrogen  

International Nuclear Information System (INIS)

The dynamics of autoionization Rydberg electron wavepackets in molecular hydrogen are calculated using a multichannel quantum-defect theory (MQDT) approach. The results of the calculation illustrate how the rotation and vibration of the molecular ion core influence the radial dynamics of the Rydberg wavepacket. (author)

1994-12-28

39

Studies of Organic Complexes and Thin Films as Materials for Molecular Electronics  

Science.gov (United States)

With the continuing miniaturization of electronic devices, a new challenge has arisen, to produce even smaller molecular electronic devices (Chapter 1). Some of the techniques used for studying molecular properties are discussed in Chapter 2: Langmuir-Blodgett (LB) films, attenuated total reflection (ATR) and grazing-angle (GA) Fourier transformed infrared (FTIR), scanning tunneling microscopy (STM), and ellipsometry. Three classes of organic semiconducting materials are discussed in Chapter 3: (1) Two new thiophene-derived annulenes were found to be good electron donors: their complexes with the electron acceptor TCNQF_4 were studied by conductivity measurements, FTIR, FTNIR (Fourier transformed near-infrared), and temperature -dependent EPR (electron paramagnetic resonance) spectroscopy. Both complexes are semiconductors at room temperature. (2) Bifunctional TTF derivatives were studied using the Langmuir -Blodgett technique, FTIR, UV-Vis (Ultraviolet-Visible) and conductivity measurements: Semiconducting LB films were obtained from iodine-doped multilayer films. (3) A record low band gap of 0.65 eV of a novel conducting polymer was determined by in situ spectroelectrochemistry combined with FTNIR. A D-pi-A type molecule of rm C_{16}H_{33 }-Q3CNQ is discussed in Chapter 4: rm C_{16}H_{33} -Q3CNQ was studied by the LB technique, and monolayer films were transferred onto single crystal Au(111) and HOPG (highly oriented pyrolytic graphite). The orientation of the LB monolayers was characterized by grazing-angle FTIR, ellipsometry, and STM. The Electron transfer (rectification) through the monolayers was studied by STS (scanning tunneling spectroscopy), and cyclic voltammetry (CV). Asymmetrical current-voltage response (I-V curves) through the monolayers were observed both in STS and CV. The direction of electron transfer through the molecules was in agreement with the Aviram-Ratner molecular rectifier model.

Wu, Xiangli

1995-01-01

40

Radiative thermal rectification using superconducting materials  

Science.gov (United States)

Thermal rectification can be defined as an asymmetry in the heat flux when the temperature difference between two interacting thermal reservoirs is reversed. In this Letter, we present a far-field radiative thermal rectifier based on high-temperature superconducting materials with a rectification ratio up to 80%. This value is among the highest reported in literature. Two configurations are examined: a superconductor (Tl2Ba2CaCu2O8) exchanging heat with (1) a black body and (2) another superconductor, YBa2Cu3O7 in this case. The first configuration shows a higher maximal rectification ratio. Besides, we show that the two-superconductor rectifier exhibits different rectification regimes depending on the choice of the reference temperature, i.e., the temperature of the thermostat. Presented results might be useful for energy conversion devices, efficient cryogenic radiative insulators engineering, and thermal logical circuits' development.

Nefzaoui, Elyes; Joulain, Karl; Drevillon, Jérémie; Ezzahri, Younès

2014-03-01

 
 
 
 
41

Electron screening in molecular fusion reactions  

International Nuclear Information System (INIS)

Recent laboratory experiments have measured fusion cross sections at center-of-mass energies low enough for the effects of atomic and molecular electrons to be important. To extract the cross section for bare nuclei from these data (as required for astrophysical applications), it is necessary to understand these screening effects. We study electron screening effects in the low-energy collisions of Z=1 nuclei with hydrogen molecules. Our model is based on a dynamical evolution of the electron wave functions within the TDHF scheme, while the motion of the nuclei is treated classically. We find that at the currently accessible energies the screening effects depend strongly on the molecular orientation. The screening is found to be larger for molecular targets than for atomic targets, due to the reflection symmetry in the latter. The results agree fairly well with data measured for deuteron collisions on molecular deuterium and tritium targets. (orig.)

1996-08-12

42

Thermal Rectification in Billiard-like Systems  

CERN Document Server

We study the thermal rectification phenomenon in ``billiard'' systems with interacting particles. This interaction induces a local dynamical response of the billiard to an external thermodynamic gradient. To explain this dynamical effect we study the steady state of an asymmetric billiard in terms of the particle and energy reflection coefficients. This allows us to obtain expressions for the region in parameter space where large thermal rectifications are expected. Our results are confirmed by extensive numerical simulations.

Eckmann, Jean-Pierre; Eckmann, Jean-Pierre; Mejia-Monasterio, Carlos

2006-01-01

43

Thermoelectric effect in molecular electronics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We provide a theoretical estimate of the thermoelectric current and voltage over a Phenyldithiol molecule. We also show that the thermoelectric voltage is (1) easy to analyze, (2) insensitive to the detailed coupling to the contacts, (3) large enough to be measured and (4) give valuable information, which is not readily accessible through other experiments, on the location of the Fermi energy relative to the molecular levels. The location of the Fermi-energy is poorly unders...

Paulsson, M.; Datta, S.

2003-01-01

44

Polaron effects on the optical rectification in asymmetrical semi-exponential quantum wells  

Science.gov (United States)

Polaron effects on the optical rectification in asymmetrical semi-exponential quantum wells(ASEQWs) are theoretically investigated. The expressions for optical rectification(OR) is obtained with the framework of the compact-density- matrix approach and iterative method. It is founded that with considering the electron–Lo-phonon interaction(ELOPI), the energy levels and the wave functions of an electron confined in ASEQWs are obtained. Numerical results are illustrated for a typical GaAs/AlGaAs. It is founded that when considering the electron–Lo-phonon, the resonant peak of the OR ?02 is enhanced, and the blue shifts are also observed.

Xiao, Bo; Guo, Kangxian; Mou, Sen; Zhang, Zhongmin

2014-05-01

45

Progress in molecular precursors for electronic materials  

Energy Technology Data Exchange (ETDEWEB)

Molecular-precursor chemistry provides an essential underpinning to all electronic-materials technologies, including photovoltaics and related areas of direct interest to the DOE. Materials synthesis and processing is a rapidly developing field in which advances in molecular precursors are playing a major role. This article surveys selected recent research examples that define the exciting current directions in molecular-precursor science. These directions include growth of increasingly complex structures and stoichiometries, surface-selective growth, kinetic growth of metastable materials, growth of size-controlled quantum dots and quantum-dot arrays, and growth at progressively lower temperatures. Continued progress in molecular-precursor chemistry will afford precise control over the crystal structures, nanostructures, and microstructures of electronic materials.

Buhro, W.E. [Washington Univ., St. Louis, MO (United States)

1996-09-01

46

Helical ribbons for molecular electronics.  

Science.gov (United States)

We describe the design and synthesis of a new graphene ribbon architecture that consists of perylenediimide (PDI) subunits fused together by ethylene bridges. We created a prototype series of oligomers consisting of the dimer, trimer, and tetramer. The steric congestion at the fusion point between the PDI units creates helical junctions, and longer oligomers form helical ribbons. Thin films of these oligomers form the active layer in n-type field effect transistors. UV-vis spectroscopy reveals the emergence of an intense long-wavelength transition in the tetramer. From DFT calculations, we find that the HOMO-2 to LUMO transition is isoenergetic with the HOMO to LUMO transition in the tetramer. We probe these transitions directly using femtosecond transient absorption spectroscopy. The HOMO-2 to LUMO transition electronically connects the PDI subunits with the ethylene bridges, and its energy depends on the length of the oligomer. PMID:24840004

Zhong, Yu; Kumar, Bharat; Oh, Seokjoon; Trinh, M Tuan; Wu, Ying; Elbert, Katherine; Li, Panpan; Zhu, Xiaoyang; Xiao, Shengxiong; Ng, Fay; Steigerwald, Michael L; Nuckolls, Colin

2014-06-01

47

Predicted rectification and negative differential spin Seebeck effect at magnetic interfaces  

Science.gov (United States)

We study the nonequilibrium Seebeck spin transport across metal-magnetic insulator interfaces. The conjugate-converted thermal-spin transport is assisted by the exchange interaction at the interface, between conduction electrons in the metal lead and localized spins in the insulating magnet lead. We predict the rectification and negative differential spin Seebeck effect and resolve their microscopic mechanism, as a consequence of the strongly fluctuated electronic density of states in the metal lead. The rectification of spin Peltier effect is also discussed. The phenomena predicted here are relevant for designing efficient spin/magnon diode and transistor, which could play crucial roles in controlling energy and information in functional devices.

Ren, Jie

2013-12-01

48

Electron Recombination with Small Molecular Ions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this thesis I have theoretically studied electron recombination processes with small molecular ions. In these kind of processes resonant states are involved. To calculate the potential energy for these states as a function of internuclear distance, structure calculations and scattering calculations have to be performed. So far I have been studying the ion-pair formation with in electron recombination with H3+. The cross section for this process has been calculated using different kind of m...

2007-01-01

49

High rectification ratios of Fe–porphyrin molecules on Au facets  

International Nuclear Information System (INIS)

We report room temperature measurements of current vs. voltage (I–V) from self-assembled Fe porphyrin [Fe(III) 5,15-di[4-(s-acetylthio)phenyl]-10,20-diphenyl porphine] molecular layers formed on annealed gold crystal facets on glass substrates. I–V curves were measured using an atomic force microscope with a conductive platinum tip. We observed a rectifier effect that shows asymmetric I–V curves from a monolayer of molecules. The majority rectification ratios at ±1 V obtained from hundreds of I–V lie in between 20 and 200, with the highest up to 9000. This is in contrast to the symmetric I–V curves measured from a few nm thick multilayer molecular islands. We contribute the observed rectification in ultrathin FeP molecular layers from asymmetric Schottky barriers that result from molecules in different bonding strengths to electrodes of gold and platinum. -- Highlights: ? FeP molecular layers or islands of different thickness were self-assembled on Au. ? High rectification ratios up to 9000 observed in sub-nm thick FeP molecular layers. ? Measured current vs. voltage using a conductive AFM tip as one electrode. ? Observed rectification of symmetric molecules using two different electrodes.

2012-09-14

50

High rectification ratios of Fe-porphyrin molecules on Au facets  

Energy Technology Data Exchange (ETDEWEB)

We report room temperature measurements of current vs. voltage (I-V) from self-assembled Fe porphyrin [Fe(III) 5,15-di[4-(s-acetylthio)phenyl]-10,20-diphenyl porphine] molecular layers formed on annealed gold crystal facets on glass substrates. I-V curves were measured using an atomic force microscope with a conductive platinum tip. We observed a rectifier effect that shows asymmetric I-V curves from a monolayer of molecules. The majority rectification ratios at {+-}1 V obtained from hundreds of I-V lie in between 20 and 200, with the highest up to 9000. This is in contrast to the symmetric I-V curves measured from a few nm thick multilayer molecular islands. We contribute the observed rectification in ultrathin FeP molecular layers from asymmetric Schottky barriers that result from molecules in different bonding strengths to electrodes of gold and platinum. -- Highlights: Black-Right-Pointing-Pointer FeP molecular layers or islands of different thickness were self-assembled on Au. Black-Right-Pointing-Pointer High rectification ratios up to 9000 observed in sub-nm thick FeP molecular layers. Black-Right-Pointing-Pointer Measured current vs. voltage using a conductive AFM tip as one electrode. Black-Right-Pointing-Pointer Observed rectification of symmetric molecules using two different electrodes.

Wang, Xiaoyu; Wang, Gwo-Ching [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110, 8th Street, Troy, NY 12180 (United States); Lewis, Kim M., E-mail: lewisk2@rpi.edu [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110, 8th Street, Troy, NY 12180 (United States)

2012-09-14

51

DNA and microfluidics: Building molecular electronics systems  

International Nuclear Information System (INIS)

The development of molecular electronics using DNA molecules as the building blocks and using microfluidics to build nanowire arrays is reviewed. Applications of DNA conductivity to build sensors and nanowire arrays, and DNA conjugation with other nanostructures, offers an exciting opportunity to build extremely small analytical devices that are suitable for single-molecule detection and also target screening

2006-05-24

52

Excess electrons in polar molecular clusters  

International Nuclear Information System (INIS)

Electron attachment and localization to water and ammonia clusters, (NH3)-/sub n/ and (H2O)-/sub n/ (n = 16--256), is studied using path-integral molecular dynamics simulations, employing an electron--molecule pseudopotential which includes Coulomb, polarization, exclusion, and exchange contributions. Due to the nature of the interactions the ammonia clusters do not form stable well-bound surface states for any size, in contrast to the case of medium size water clusters. The onset of bound excess electron states in ammonia clusters occurs for size n?32, via an internal localization mode, in agreement with experimental data

1988-05-15

53

Electronic Quantum Interference in Molecular Devices  

Science.gov (United States)

Understanding the mechanisms for electrical transport and conductance switching in molecular devices is necessary for developing molecular electronics. Here we use pressure-modulated conductance microscopy to characterize Pt/stearic acid monolayer/metal molecular heterostructures. We use either titanium or chromium as the top electrodes. By using atomic force microscope (AFM) to apply a localized force to the junction while monitoring device conductance, we observe nanoscale conductance peaks in response to applied pressure, indicating nanoscale conductance channels through the devices. Additionally, for devices with conductance of ˜1 to 2 conductance quantum, we also observe conductance dips and oscillations under localized pressure. The results are consistent with quantum interference of electrons between partially transmitting electrodes.

Miao, Feng; Ohlberg, Douglas; Williams, R. Stanley; Lau, C. N.

2006-03-01

54

Mechanical action of infrared light on atoms and molecules through a rectification of the electric force  

International Nuclear Information System (INIS)

We report the mechanical action of infrared light on atoms and molecules based on the rectification of the electric force. This mechanism is qualitatively different from the conventional ways of controlling photochemistry. The rectification of the electric force originates from the synchronous charge transfer induced by the laser field. This brings about an opportunity to produce a site selective light-induced action, controlled by the tailored intense laser field, on atoms in molecules and clusters. The concept is illustrated by ab initio molecular dynamics simulations of the water hexamer.

2009-11-01

55

Electron-nuclear dynamics of molecular systems  

Energy Technology Data Exchange (ETDEWEB)

The content of an ab initio time-dependent theory of quantum molecular dynamics of electrons and atomic nuclei is presented. Employing the time-dependent variational principle and a family of approximate state vectors yields a set of dynamical equations approximating the time-dependent Schroedinger equation. These equations govern the time evolution of the relevant state vector parameters as molecular orbital coefficients, nuclear positions, and momenta. This approach does not impose the Born-Oppenheimer approximation, does not use potential energy surfaces, and takes into account electron-nuclear coupling. Basic conservation laws are fully obeyed. The simplest model of the theory employs a single determinantal state for the electrons and classical nuclei and is implemented in the computer code ENDyne. Results from this ab-initio theory are reported for ion-atom and ion-molecule collisions.

Diz, A.; Oehrn, Y. [Univ. of Florida, Gainesville, FL (United States)

1994-12-31

56

Vortex rectification effects in plain superconducting films  

CERN Document Server

Superconducting films in perpendicular magnetic field are found to rectify alternating currents. The effect has been observed both in plain and nanostructured superconducting films (niobium and lead). The rectified voltage appears both along and transverse to alternating current and strongly depends on the magnetic field. Rectification phenomena is based on the property of superconductors to have permanent circulating currents in magnetic field (vortices) and to develop electric fields at high enough currents. In contrast to previous findings, at higher current frequencies no asymmetric pinning sites are needed to produce rectification and related guided flux motion.

Aliev, F G; Villar, R; González, E M; Moshchalkov, V V

2004-01-01

57

Thermal boundary conductance and thermal rectification in molecules.  

Science.gov (United States)

An approach is presented to calculate thermal boundary resistance in molecules, which occurs, for example, at the interfaces between moieties held at fixed temperatures and a molecular bridge that connects them. If the vibrational frequencies of each moiety lie outside of the band of heat-carrying modes of the bridge, anharmonic interactions mediate thermal conduction at the boundaries. We have expressed thermal boundary conductance in terms of the low-order anharmonic interactions between a moiety and a molecular bridge. Differences in the temperature-dependent boundary conductance at each end of the bridge can be exploited in the design of a molecular thermal diode. The approach is illustrated with the calculation of thermal boundary conductance and thermal rectification in azulene-(CH2)N-anthracene. PMID:23701185

Leitner, David M

2013-10-24

58

Electron energy loss spectroscopy of molecular fluorine  

International Nuclear Information System (INIS)

Recent renewed interest in the molecular halogens has arisen from their use in rare-gas halide lasers and as laser systems in their own right. This interest has provided motivation for two studies of the electronic structure of fluorine through electron energy-loss spectroscopy (EELS) by Nishimura et al. and by Hitchcock et al. Despite this recent flurry of activity, several questions have remained concerning the electronic spectrum of F_2, principally, the vibrational labelling of electronic states, the effects of impurities on the spectrum, and the identification of laser levels. We have re-examined the spectrum of F_2 using EELS and have been able to resolve most of these questions

1985-03-01

59

Electron-phonon interactions in molecular electronic devices  

Science.gov (United States)

Over the past several decades, semiconductor electronic devices have been miniaturized following the remarkable "Moores law". If this trend is to continue, devices will reach physical size limit in the not too distance future. There is therefore an urgent need to understand the physics of electronic devices at nano-meter scale, and to predict how such nanoelectronics will work. In nanoelectronics theory, one of the most important and difficult problems concerns electron-phonon interactions under nonequilibrium transport conditions. Calculating phonon spectrum, electron-phonon interaction, and their effects to charge transport for nanoelectronic devices including all atomic microscopic details, is a very difficult and unsolved problem. It is the purpose of this thesis to develop a theoretical formalism and associated numerical tools for solving this problem. In our formalism, we calculate electronic Hamiltonian via density functional theory (DFT) within the nonequilibrium Green's functions (NEGF) which takes care of nonequilibrium transport conditions and open device boundaries for the devices. From the total energy of the device scattering region, we derive the dynamic matrix in analytical form within DFT-NEGF and it gives the vibrational spectrum of the relevant atoms. The vibrational spectrum together with the vibrational eigenvector gives the electron-phonon coupling strength at nonequilibrium for various scattering states. A self-consistent Born approximation (SCBA) allows one to determine the phonon self-energy, the electron Green's function, the electronic density matrix and the electronic Hamiltonian, all self-consistently within equal footing. The main technical development of this work is the DFT-NEGF-SCBA formalism and its associated codes. A number of important physics issues are studied in this work. We start with a detailed analysis of transport properties of C60 molecular tunnel junction. We find that charge transport is mediated by resonances due to an alignment of the Fermi level of the electrodes and the lowest unoccupied C60 molecular orbital. We then make a first step toward the problem of analyzing phonon modes of the C60 by examining the rotational and the center-of-mass motions by calculating the total energy. We obtain the characteristic frequencies of the libration and the center-of-mass modes, the latter is quantitatively consistent with recent experimental measurements. Next, we developed a DFT-NEGF theory for the general purpose of calculating any vibrational modes in molecular tunnel junctions. We derive an analytical expression for dynamic matrix within the framework of DFT-NEGF. Diagonalizing the dynamic matrix we obtain the vibrational (phonon) spectrum of the device. Using this technique we calculate the vibrational spectrum of benzenedithiolate molecule in a tunnel junction and we investigate electron-phonon coupling under an applied bias voltage during current flow. We find that the electron-phonon coupling strength for this molecular device changes drastically as the bias voltage increases, due to dominant contributions from the center-of-mass vibrational modes of the molecule. Finally, we have investigated the reverse problem, namely the effect of molecular vibrations on the tunneling current. For this purpose we developed the DFT-NEGF-SCBA formalism, and an example is given illustrating the power of this formalism.

Sergueev, Nikolai

60

Energy Exchange Between Electron and Molecular Gases  

International Nuclear Information System (INIS)

The energy exchange between electrons and heavy particles is one of the main problems involved in investigating non-equilibrium plasma. The authors consider the energy exchange between an electron gas and a molecular gas, and show that the exchange mechanism depends essentially on the composition of the latter. For a gas consisting of molecules capable of forming an unstable negative ion (N2, CO etc.) this process is decisive. Calculations are made of the rate of energy exchange between an electron gas and nitrogen at different temperatures of the two gases, and it is shown that the rate of exchange, which is governed by this mechanism, exceeds by some orders of magnitude the corresponding value associated with the other processes which are generally taken into account. (author)

1966-11-01

 
 
 
 
61

Molecular Electronics: From Physics to Computing  

CERN Document Server

Even if Moore's Law continues to hold, it will take about 250 years to fill the performance gap between present-day computer and the ultimate computer determined from the laws of physics alone. Information processing technology in the post-CMOS era will likely consist of a heterogeneous set of novel device technologies that span a broad range of materials, operational principles, data representations, logic systems and architectures. Molecular nanostructures promise to occupy a prominent role in any attempt to extend charge-based device technology beyond the projected limits of CMOS scaling. We discuss the potentials and challenges of molecular electronics and identify the fundamental knowledge gap that needs to be addressed for a successful introduction of molecule-enabled computing technology

Xue, Y; Xue, Yongqiang; Ratner, Mark A.

2005-01-01

62

Modeling ion sensing in molecular electronics.  

Science.gov (United States)

We examine the ability of molecules to sense ions by measuring the change in molecular conductance in the presence of such charged species. The detection of protons (H(+)), alkali metal cations (M(+)), calcium ions (Ca(2+)), and hydronium ions (H3O(+)) is considered. Density functional theory (DFT) is used within the Keldysh non-equilibrium Green's function framework (NEGF) to model electron transport properties of quinolinedithiol (QDT, C9H7NS2), bridging Al electrodes. The geometry of the transport region is relaxed with DFT. The transport properties of the device are modeled with NEGF-DFT to determine if this device can distinguish among the M(+) + QDT species containing monovalent cations, where M(+) = H(+), Li(+), Na(+), or K(+). Because of the asymmetry of QDT in between the two electrodes, both positive and negative biases are considered. The electron transmission function and conductance properties are simulated for electrode biases in the range from -0.5?V to 0.5?V at increments of 0.1 V. Scattering state analysis is used to determine the molecular orbitals that are the main contributors to the peaks in the transmission function near the Fermi level of the electrodes, and current-voltage relationships are obtained. The results show that QDT can be used as a proton detector by measuring transport through it and can conceivably act as a pH sensor in solutions. In addition, QDT may be able to distinguish among different monovalent species. This work suggests an approach to design modern molecular electronic conductance sensors with high sensitivity and specificity using well-established quantum chemistry. PMID:24511970

Chen, Caroline J; Smeu, Manuel; Ratner, Mark A

2014-02-01

63

Integrating reaction chemistry into molecular electronic devices.  

Science.gov (United States)

This Focus Review provides an overview of the design and fabrication of new families of molecular electronic devices where reaction chemistry is an efficient means for covalently bridging the nanogaps between separated contacts. In each case ever-reducing top-down device fabrication existing in the silicon-based semiconductor industry is tailored to meet the requirements of ever-expanding length scales of bottom-up assembly. The combination of directed self-assembly and programmed chemical reactions with device fabrication allows us to modify the electrodes and then to complete electrical circuits by chemically connecting the electrodes. PMID:20333621

Shen, Qian; Guo, Xuefeng; Steigerwald, Michael L; Nuckolls, Colin

2010-05-01

64

Single mode heat rectifier: controlling energy flow between electronic conductors.  

Science.gov (United States)

We study heat transfer between conductors, mediated by the excitation of a monomodal harmonic oscillator. Using a simple model, we show that the onset of rectification in the system is directly related to the nonlinearity of the electron gas dispersion relation. When the metals have a strictly linear dispersion relation, a Landauer-type expression for the thermal current holds, symmetric with respect to the temperature difference. Rectification becomes prominent when deviations from linear dispersion exist, and the fermionic model cannot be mapped into a harmonic bosonized representation. The effects described here are relevant for understanding radiative heat transfer and vibrational energy flow in electrically insulating molecular junctions. PMID:18352208

Segal, Dvira

2008-03-14

65

Electron dynamics in molecular interactions principles and applications  

CERN Document Server

This volume provides a comprehensive introduction to the theory of electronic motion in molecular processes - an increasingly relevant and rapidly expanding segment of molecular quantum dynamics. Emphasis is placed on describing and interpreting transitions between electronic states in molecules as they occur typically in cases of reactive scattering between molecules, photoexcitation or nonadiabatic coupling between electronic and nuclear degrees of freedom. Electron Dynamics in Molecular Interactions aims at a synoptic presentation of some very recent theoretical efforts to solve the electro

Hagelberg, Frank

2013-01-01

66

Electron-pair excitations and the molecular coulomb continuum  

Energy Technology Data Exchange (ETDEWEB)

Electron-pair excitations in the molecular hydrogen continuum are described by quantizing rotations of the momentum plane of the electron pair about the pair's relative momentum. A helium-like description of the molecular photo double ionization is thus extended to higher angular momenta of the electron pair. A simple three-state superposition is found to account surprisingly well for recent observations of noncoplanar electron-pair, molecular-axis angular distributions.

Feagin, J M [Department of Physics, California State University-Fullerton, Fullerton, CA 92834 (United States); Colgan, J [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Reddish, T J [Department of Physics, University of Windsor, 401 Sunset Avenue, Ontario, N9B 3P4 (Canada); Huetz, A, E-mail: jfeagin@fullerton.ed

2009-11-01

67

Rectification of Uncalibrated Images for Stereo Vision  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper aims at rectification of uncalibrated stereo images. We use the direct method to compute the rectifying transformations, not to deduce from the fundamental matrix, so to reduce the uncertainty; Minimize the distance from the point to its epipolar line to ensue the uniqueness of the two rectifying transformations. We only extract a few correspondent points, make use of the condition of the correspondent points in the rectified images also meet the polar constraint, minimize dista...

Han, Huiyan; Han, Xie; Yang Fengbao

2013-01-01

68

Noise rectification in quasigeostrophic forced turbulence  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study the appearance of large-scale mean motion sustained by stochastic forcing on a rotating fluid (in the quasigeostrophic approximation) flowing over topography. We show that the effect is a kind of noise-rectification phenomenon, occurring here in a spatially extended system, and requiring nonlinearity, absence of detailed balance, and symmetry breaking to occur. By application of an analytical coarse-graining procedure, we identify the physical mechanism producing such an effect: It i...

A?lvarez, Alberto; Herna?ndez-garci?a, Emilio; Tintore?, Joaqui?n

1998-01-01

69

Molecular electronics in pinnae of Mimosa pudica.  

Science.gov (United States)

Bioelectrochemical circuits operate in all plants including the sensitive plant Mimosa pudica Linn. The activation of biologically closed circuits with voltage gated ion channels can lead to various mechanical, hydrodynamical, physiological, biochemical, and biophysical responses. Here the biologically closed electrochemical circuit in pinnae of Mimosa pudica is analyzed using the charged capacitor method for electrostimulation at different voltages. Also the equivalent electrical scheme of electrical signal transduction inside the plant's pinna is evaluated. These circuits remain linear at small potentials not exceeding 0.5 V. At higher potentials the circuits become strongly non-linear pointing to the opening of ion channels in plant tissues. Changing the polarity of electrodes leads to a strong rectification effect and to different kinetics of a capacitor. These effects can be caused by a redistribution of K(+), Cl(-), Ca(2+), and H(+) ions through voltage gated ion channels. The electrical properties of Mimosa pudica were investigated and equivalent electrical circuits within the pinnae were proposed to explain the experimental data. PMID:20448476

Volkov, Alexander G; Foster, Justin C; Markin, Vladislav S

2010-07-01

70

Photoinduced Phase Transition in Strongly Electron-Lattice and Electron–Electron Correlated Molecular Crystals  

Directory of Open Access Journals (Sweden)

Full Text Available Strongly electron-lattice- and electron-electron-correlated molecular crystals, such as charge transfer (CT complexes, are often sensitive to external stimuli, e.g., photoexcitation, due to the cooperative or competitive correlation of various interactions present in the crystals. These crystals are thus productive targets for studying photoinduced phase transitions (PIPTs. Recent advancements in research on the PIPT of CT complexes, especially Et2Me2Sb[Pd(dmit2]2 and (EDO-TTF2PF6, are reviewed in this report. The former exhibits a photoinduced insulator-to-insulator phase transition with clearly assigned spectral change. We demonstrate how to find the dynamics of PIPT using this system. The latter exhibits a photoinduced hidden state as an initial PIPT process. Wide energy ranged time-resolved spectroscopy can probe many kinds of photo-absorption processes, i.e., intra-molecular and inter-molecular electron excitations and intramolecular and electron-molecular vibrations. The photoinduced spectral changes in these photo-absorption processes reveal various aspects of the dynamics of PIPT, including electronic structural changes, lattice structural changes, and molecular deformations. The complexities of the dynamics of the latter system were revealed by our measurements.

Shin-ya Koshihara

2012-07-01

71

Electron Impact Dissociation of Molecular Ions  

International Nuclear Information System (INIS)

Electron impact experiments were performed by means of our crossed electron-ion beam set-up. Singly and/or multiply charged ions that results from molecular ion fragmentation are detected individually. Cross-sections for their production are determined from their respective thresholds up to 2.5 keV. The animated crossed beams method is applied to measure: - Absolute inclusive cross sections for electron impact dissociation to individual ionic fragments from the energy threshold up to 2.5 keV. - The contributions from the different reaction channels are separated: single ionization (SI) dissociative excitation (DE) and dissociative ionization (DI). - Kinetic energy release distributions (KERD) of the fragment ions are determined at selected incident electron energies. It allows determination of groups of electronically excited states that contribute to the process considered. - Energy threshold determination allows identification of target initial ground and excited states. Molecular species studied in the frame of this CRP are grouped into the five following categories: 1. Light ions: H2+, D2+ and D3+, D2H+: For H2+, the particular importance of the internal energy, the vibrational population, has been underlined. Dissociation of H3+ isotopologues have recently discussed comprehensively in the two following papers, especially as regards isotope effects in the fragmentation. ''Absolute cross sections and kinetic energy release distributions for electron impact dissociation of D3+'' J. Lecointre, M.O. Abdellahi El Ghazaly, J.J. Jureta, D.S. Belic, X. Urbain and P. Defrance, J. Phys. B: At. Mol. Opt. Phys. 42 (2009) 075201 ''Isotope effects in electron impact dissociation of D2H+'' P. Defrance, J.J. Jureta, J. Lecointre and X. Urbain, J. Phys. B: At. Mol. Opt. Phys. 44 (2011) 075202. 2. Hydride ions: HeH+, OH+, OH2+, OH3+ and isotopologues (unpublished). For HeH+, experimental results are available for the production of He+ and He2+. They will be analysed taking into account the vibrational population measured in a separate charge transfer experiment. The reliable collection of the H+ fragment was not possible due to the large KER but this experiment will be considered in a soon future. 3. Hydro(deutero)-carbon ions: C2D3''+, C2D4''+ and isotopologues C2D3H''+, C2D2H2''+ (unpublished). The hydrocarbon and deuterocarbon families (CmHn''+ and CmDn''+) which play a particular role in the plasma studies are systematically investigated in our laboratory. Previous results were published for the methane series (CDn''+, n=1-4), for C2D+ and C2D2+. See number of references in the list here below. Experimental results have been obtained for C2D3+ and C2D4+. The collected data need to be analyzed in detail in order to determine separately the contributions of dissociative excitation and ionization, as well as the associated energy thresholds and KERDs. The standard procedure will be applied to put these data in a form which is suitable for plasma modelling applications. 4. Others: C2+ (unpublished). The full analysis of data for electron impact dissociation of C2+ yielding the C+ fragment was performed. These data now need to be published. 5. Nitrogen: NH+, ND+ and N2+. Dissociation of the nitrogen hydride has recently been made available to the community. In addition, dissociation of N2+was published earlier. ''Electron impact dissociation and ionization of NH+: formation of N+ and N2+'' J. Lecointre, J.J. Jureta and P. Defrance, J. Phys. B: At. Mol. Opt. Phys. 43 (2010) 105202. ''Electron impact dissociation of ND+: formation of D+'' J. Lecointre, D.S. Belic, S. Cherkani-Hassani and P. Defrance, Eur. Phys. J. D 61 (2011) in press. ''Electron Impact dissociation and ionisation of N2+'' E.M. Bahati, J.J. Jureta, D.S. Belic, H. Cherkani-Hassani, M.O. Abdellahi and P. Defrance, J. Phys. B: At. Mol. Opt. Phys. 34 (2001) 2963. (author)

2012-08-01

72

Polarization-modulated rectification at ferroelectric surfaces.  

Science.gov (United States)

By correlating room temperature conductive atomic force microscopy with low temperature electrostatic force microscopy images of the same sample region, we demonstrate that nanoscale electric conduction between a sharp tip and the surface of ferroelectric HoMnO3 is intrinsically modulated by the polarization of ferroelectric domains. Conductance spectra reveal that the electric conduction is described by polarization-induced Schottky-like rectification at low bias, but dominated by a space-charge limited conduction mechanism at high bias. Our observation demonstrates visualization of ferroelectric domain structure by electric conduction, which may be used for nondestructive readout of nanoscale ferroelectric memories and/or ferroelectric sensors. PMID:20867135

Wu, Weida; Guest, J R; Horibe, Y; Park, S; Choi, T; Cheong, S-W; Bode, M

2010-05-28

73

Polarization-modulated rectification at ferroelectric surfaces.  

Energy Technology Data Exchange (ETDEWEB)

By correlating room temperature conductive atomic force microscopy with low temperature electrostatic force microscopy images of the same sample region, we demonstrate that nanoscale electric conduction between a sharp tip and the surface of ferroelectric HoMnO{sub 3} is intrinsically modulated by the polarization of ferroelectric domains. Conductance spectra reveal that the electric conduction is described by polarization-induced Schottky-like rectification at low bias, but dominated by a space-charge limited conduction mechanism at high bias. Our observation demonstrates visualization of ferroelectric domain structure by electric conduction, which may be used for nondestructive readout of nanoscale ferroelectric memories and/or ferroelectric sensors.

Wu, W.; Guest, J. R.; Horibe, Y.; Park, S.; Choi, T.; Cheong, S.-W.; Bode, M.; Center for Nanoscale Materials; Rutgers Univ.; Chung-Ang Univ.

2010-05-28

74

Precision Rectification of Airborne SAR Image  

DEFF Research Database (Denmark)

A simple and direct procedure for the rectification of a certain class of airborne SAR data is presented. The relief displacements of SAR data are effectively removed by means of a digital elevation model and the image is transformed to the ground coordinate system. SAR data from the Danish EMISAR([7]) is used. The EMISAR produces data with a geometrical resolution of 2.0 meters. The corrected image is tested against photogrammetric control measurements and an accuracy better than 0.5 pixel corresponding to 0.75 meters is obtained. The results indicate promising possibilities for the application of SAR data in the difficult process of map revision and updating.

Dall, Jørgen; Liao, M.

1997-01-01

75

Molecular Slater Integrals for Electronic Energy Calculations.  

Science.gov (United States)

The algorithms for computing molecular integrals with Slater functions implemented in the SMILES package for molecular calculations have been thoroughly analyzed regarding the accuracy and computational cost for high quantum numbers and in a wide range of...

G. Ramirez I. Ema J. Fernandez Rico R. Lopez

2010-01-01

76

A Quantum Chemical View of Molecular and Nano-Electronics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This dissertation presents a generalized quantum chemical approach for electron transport in molecular electronic devices based on Green's function scattering theory. It allows to describe both elastic and inelastic electron transport processes at first principles levels of theory, and to treat devices with metal electrodes either chemically or physically bonded to the molecules on equal footing. Special attention has been paid to understand the molecular length dependence of current-voltage ...

Jiang, Jun

2007-01-01

77

Chiral molecular films as electron polarizers and polarization modulators  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Recent experiments on electron scattering through molecular films have shown that chiral molecules can be efficient sources of polarized electrons even in the absence of heavy nuclei as source of a strong spin-orbit interaction. We show that self-assembled monolayers (SAMs) of chiral molecules are strong electron polarizers due to the high density effect of the monolayers and explicitly compute the scattering amplitude off a helical molecular model of carbon atoms. Longitudi...

Medina, Ernesto; Lo?pez, Floralba; Ratner, Mark; Mujica, Vladimiro

2012-01-01

78

Molecular Modeling and Multiscaling Issues for Electronic Material Applications  

CERN Document Server

Molecular Modeling and Multiscaling Issues for Electronic Material Applications provides a snapshot on the progression of molecular modeling in the electronics industry and how molecular modeling is currently being used to understand material performance to solve relevant issues in this field. This book is intended to introduce the reader to the evolving role of molecular modeling, especially seen through the eyes of the IEEE community involved in material modeling for electronic applications.  Part I presents  the role that quantum mechanics can play in performance prediction, such as properties dependent upon electronic structure, but also shows examples how molecular models may be used in performance diagnostics, especially when chemistry is part of the performance issue.  Part II gives examples of large-scale atomistic methods in material failure and shows several examples of transitioning between grain boundary simulations (on the atomistic level)and large-scale models including an example of the use ...

Yuen, Matthew; Fan, Haibo

2012-01-01

79

A New Full Adder Cell for Molecular Electronics  

Directory of Open Access Journals (Sweden)

Full Text Available Due to high power consumption and difficulties with minimizing the CMOS transistor size, molecular electronics has been introduced as an emerging technology. Further, there have been noticeable advances in fabrication of molecular wires and switches and also molecular diodes can be used for designing different logic circuits. Considering this novel technology, we use molecules as the active components of the circuit, for transporting electric charge. In this paper, a full adder cell based on molecular electronics is presented. This full adder is consisted of resonant tunneling diodes and transistors which are implemented via molecular electronics. The area occupied by this kind of full adder would be much times smaller than the conventional designs and it can be used as the building block of more complex molecular arithmetic circuits.

Keivan Navi

2012-01-01

80

Molecular dynamics simulations of the interactions of excited electrons  

International Nuclear Information System (INIS)

In this paper the processes of electron-electron interaction taking place in a highly excited electron gas are analyzed on the basis of molecular dynamics simulations. The time evolution of the system is described by using either classic mechanics or a quantum mechanical representation. New aspects of the collective behavior of the particles are born out by the simulations

1989-12-02

 
 
 
 
81

Molecular Electronics : A Theoretical Study of Electronic Structure of Bulk and Interfaces  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis deals with theoretical studies of the electronic structure of molecules used in the context of molecular electronics. Both studies with model Hamiltonians and first principle calculations have been performed. The materials studied include molecular crystals of pentacene and DNA, which are used as active material in field-effect transistors and as tentative molecular wires, respectively. The molecular magnet compound TCNE and surface modification by means of chemisorption of TDAE o...

Unge, Mikael

2006-01-01

82

Effects of cetyltrimethylammonium bromide on redox deposition and rectification properties of silicon oxide thin film  

Energy Technology Data Exchange (ETDEWEB)

Silicon oxide (SiO{sub x}) thin film was deposited onto fluorine-doped tin oxide (FTO) and silicon wafer substrate by the reduction of an aqueous solution containing ammonium hexafluorosilicate, dimethylamine borane and cetyltrimethylammonium bromide (CTAB). Characterization of the films by X-ray photoelectron spectroscopic depth profile and infrared spectroscopy proved that the addition of CTAB into the film enhanced the aggregation of silica particles and the growth rate. The SiO{sub x} films (resistivity: 3.2 x 10{sup 8} {Omega} cm) remarkably improved the rectification properties of FTO/SiO{sub x}/poly(3,4-ethylenedioxythiophene) derivative diodes. A rectification mechanism based on conduction of electron and ions was investigated.

Chigane, Masaya, E-mail: chigane@omtri.city.osaka.j [Department of Electronic Materials, Osaka Municipal Technical Research Institute, 1-6-50, Morinomiya, Joto-ku, Osaka 536-8553 (Japan); Izaki, Masanobu [Department of Production Systems Engineering, Toyohashi University of Technology, 1-1, Hibarigaoka, Tempaku-cho, Toyohashi-shi, Aichi 441-8580 (Japan); Watanabe, Mitsuru [Department of Electronic Materials, Osaka Municipal Technical Research Institute, 1-6-50, Morinomiya, Joto-ku, Osaka 536-8553 (Japan); Yamaguchi, Ippei [Graduate School of Engineering, Doshisha University, Kyotanabe, Kyoto 610-0321 (Japan); Shinagawa, Tsutomu; Ishikawa, Masami [Department of Electronic Materials, Osaka Municipal Technical Research Institute, 1-6-50, Morinomiya, Joto-ku, Osaka 536-8553 (Japan)

2009-04-02

83

Molecular tips for scanning tunneling microscopy: intermolecular electron tunneling for single-molecule recognition and electronics.  

Science.gov (United States)

This paper reviews the development of molecular tips for scanning tunneling microscopy (STM). Molecular tips offer many advantages: first is their ability to perform chemically selective imaging because of chemical interactions between the sample and the molecular tip, thus improving a major drawback of conventional STM. Rational design of the molecular tip allows sophisticated chemical recognition; e.g., chiral recognition and selective visualization of atomic defects in carbon nanotubes. Another advantage is that they provide a unique method to quantify electron transfer between single molecules. Understanding such electron transfer is mandatory for the realization of molecular electronics. PMID:24420248

Nishino, Tomoaki

2014-01-01

84

Polarization-modulated rectification at ferroelectric surfaces  

Science.gov (United States)

By correlating room temperature conductive atomic force microscopy (c-AFM) with low temperature electrostatic force microscopy (EFM) images taken at different temperatures but the same location, we demonstrate that nanoscale electric conduction between a sharp tip and the surface of ferroelectric HoMnO3 is intrinsically modulated by the polarization of ferroelectric domains. Conductance spectra reveal that the electric conduction is described by polarization-induced Schottky-like rectification at low bias, but dominated by a space-charge limited conduction mechanism at high bias. Our observation demonstrates visualization ferroelectric domain structure by electric conduction, which may be used for non-destructive read-out of nanoscale ferroelectric memories or sensors.

Wu, Weida; Horibe, Y.; Park, S.; Choi, T.; Cheong, S.-W.; Kim, S. B.; Guest, J. R.; Bode, M.

2010-03-01

85

Mechanism of Rectification in Inward-rectifier K+ Channels  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Rectification in inward-rectifier K+ channels is caused by the binding of intracellular cations to their inner pore. The extreme sharpness of this rectification reflects strong voltage dependence (apparent valence is ?5) of channel block by long polyamines. To understand the mechanism by which polyamines cause rectification, we examined IRK1 (Kir2.1) block by a series of bis-alkyl-amines (bis-amines) and mono-alkyl-amines (mono-amines) of varying length. The apparent affinity of channel blo...

Guo, Donglin; Ramu, Yajamana; Klem, Angela M.; Lu, Zhe

2003-01-01

86

Electron-phonon scattering in molecular electronics: from inelastic electron tunnelling spectroscopy to heating effects  

International Nuclear Information System (INIS)

In this paper, we investigate dissipation in molecular electronic devices. Dissipation is a crucial quantity which determines the stability and heating of the junction. Moreover, several experimental techniques which use inelastically scattered electrons as probes to investigate the geometry in the junction are becoming fundamental in the field. In order to describe such physical effects, a non-equilibrium Green's function (NEGF) method was implemented to include scattering events between electrons and molecular vibrations in current simulations. It is well known that the final heating of the molecule depends also on the ability of the molecule to relax vibrational quanta into the contact reservoirs. A semi-classical rate equation has been implemented and integrated within the NEGF formalism to include this relaxation. The model is based on two quantities: (i) the rate of emission of phonons in the junction by electron-phonon scattering and (ii) a microscopic approach for the computation of the phonon decay rate, accounting for the dynamical coupling between the vibrational modes localized on the molecule and the contact phonons. The method is applied to investigate inelastic electron tunnelling spectroscopy (IETS) signals in CO molecules on Cu(110) substrates as well as dissipation in C60 molecules on Cu(110) and Si(100) surfaces. It is found that the mechanisms of energy relaxation are highly mode-specific and depend crucially on the lead electronic structure and junction geometry

2008-06-01

87

Molecular Basis for Directional Electron Transfer*  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Biological macromolecules involved in electron transfer reactions display chains of closely packed redox cofactors when long distances must be bridged. This is a consequence of the need to maintain a rate of transfer compatible with metabolic activity in the framework of the exponential decay of electron tunneling with distance. In this work intermolecular electron transfer was studied in kinetic experiments performed with the small tetraheme cytochrome from Shewanella oneidensis MR-1 and fro...

Paquete, Catarina M.; Saraiva, Ivo H.; Calc?ada, Eduardo; Louro, Ricardo O.

2010-01-01

88

Photoelectrochemical solar conversion systems molecular and electronic aspects  

CERN Document Server

Providing new insights into the molecular and electronic processes involved in the conversion of sunlight into chemical products, Photoelectrochemical Solar Conversion Systems: Molecular and Electronic Aspects begins with an historical overview and a survey of recent developments in the electrochemistry of semiconductors and spectroscopic techniques. It then provides a comprehensive introduction to the science of conversion cells, reviews current issues and potential directions, and covers a wide range of materials from organic to inorganic cells.Employing a tutorial organization with balanced

Munoz, Andres G

2012-01-01

89

Hole-electron quantum tunnelling interferences through a molecular junction  

Science.gov (United States)

The Configuration Interaction Elastic Scattering Quantum Chemistry (CI-ESQC) method is used to calculate the many-body electronic transmission coefficient through a molecular junction in a coherent superposition of hole and electron tunnelling processes. Independent hole and electron destructive interferences are still existing and with a net zero of transmission at the interference energy locations. But in the molecule electronic gap, CI-ESQC leads to a destructive interference with a non zero of transmission between hole and electron processes. This explains the non zero of transmission destructive interference recently observed at the Fermi level in the molecule electronic gap.

Portais, Mathilde; Joachim, Christian

2014-01-01

90

Ultrafast molecular imaging by laser-induced electron diffraction  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We address the feasibility of imaging geometric and orbital structures of a polyatomic molecule on an attosecond time scale using the laser-induced electron diffraction (LIED) technique. We present numerical results for the highest molecular orbitals of the CO(2) molecule excited by a near-infrared few-cycle laser pulse. The molecular geometry (bond lengths) is determined within 3% of accuracy from a diffraction pattern which also reflects the nodal properties of the initial molecular orbital...

Peters, Michel; Nguyen-dang, Tung; Cornaggia, Christian; Saugout, Se?bastien; Charron, Eric; Keller, Arne; Atabek, Osman

2011-01-01

91

Electron and molecular ion collisions relevant to divertor plasma  

International Nuclear Information System (INIS)

We introduce the concept of the multi-channel quantum defect theory (MQDT) and show the outline of the MQDT newly extended to include the dissociative states. We investigate some molecular processes relevant to the divertor plasma by using the MQDT: the dissociative recombination, dissociative excitation, and rotation-vibrational transition in the hydrogen molecular ion and electron collisions. (author)

2005-02-01

92

Molecular orbital theory and its application to electron spectroscopy  

International Nuclear Information System (INIS)

The electron spectroscopy developed remarkably in recent years has provided much information on elemental compositions and electronic states of the surface layer. Molecular orbital theories frequently used in analyses of the photoelectron spectra are reviewed. The DV-X? method in which numerical bases are used for estimating the molecular potential in the Hartree-Fock-Slater equation is in excellent agreement with the observations. Example calculations of molecular orbital energies and density of states by this method are presented. Usefulness of the method in other fields is also indicated. (author)

1978-01-01

93

Using circumacenes to improve organic electronics and molecular electronics: design clues  

International Nuclear Information System (INIS)

Theoretical modeling is used here to ascertain the potential use of circumacenes to improve the transport parameters of ?-conjugated materials acting as: (i) the layered molecular constituent for organic electronic devices; and (ii) the molecular component of gold-molecule-gold nanobridges for molecular electronic device use. It is concluded that, to a first approximation, the molecular length or, alternatively, the HOMO-LUMO gap (HOMO: highest occupied molecular orbital; LUMO: lowest unoccupied molecular orbital) can be used to relate the two transport regimes usually found in these two fields, thus serving as a key design parameter for guaranteeing good performance of circumanthracene for both regimes. It is also clearly established that going beyond this simple relationship requires knowledge of the detailed molecule-contact geometry of the molecular nanobridge, and how its tremendous impact on the binding strength and the conductance prevents blind extrapolation of results obtained for molecular nanobridges built by means of different experimental set-ups.

2009-11-25

94

Molecular Structure and Dynamics Probed by Rydberg Electrons  

Science.gov (United States)

Probing molecular structure as a chemical reaction unfolds has been a long standing goal in chemical physics. Most spectroscopic and diffraction techniques work well when the molecule is cold and thus vibrational motion is minimized. Yet, in order to initiate a chemical reaction, a large amount of energy has to be pumped into the molecule. Therefore, most well-established techniques are generally inapplicable to studying ultrafast molecular transformations except for highly favorable cases. In our research we demonstrated that Rydberg electrons are very sensitive to the molecular structure. Photoionization of the molecule out of Rydberg states reveals a purely electronic spectrum not encumbered by vibrational motion. Thus, the technique is largely insensitive to the vibrations of the molecule. As an example of using Rydberg electrons as a probe for molecular structure we report on the isomerizations of cyclohexadiene and quadricyclane on an ultrafast time scale.

Rudakov, Fedor; Weber, Peter

2010-03-01

95

Quantum computing using molecular electronic and vibrational states  

International Nuclear Information System (INIS)

We numerically constructed elementary phase-correct global quantum gates by using molecular electronic and vibrational states to encode two qubits and implement the Deutsch-Jozsa algorithm. The calculations were based on optimal control theory (OCT). The molecular species we chose were Na2 and Li2. The electronic X1?g+ and A1?u+ states were taken as two orthonormalized energy levels of the electronic qubit. The vibrational qubits were those involved in these electronic states. The time duration of the optimized pulses with high fidelity was typically 500-900 fs, which reflects the wavepacket dynamics in electronically ground and excited states. When implementing the Deutsch-Jozsa algorithm by combining these elementary gates, we obtained a maximum probability 83.12% for Li2 molecule, which indicates that the electronic-vibrational qubits are worse than the vibrational-vibrational and the vibrational-rotational qubits reported so far

2008-01-22

96

Electron localization following attosecond molecular photoionization  

Digital Repository Infrastructure Vision for European Research (DRIVER)

For the past several decades, we have been able to directly probe the motion of atoms that is associated with chemical transformations and which occurs on the femtosecond (10(-15)-s) timescale. However, studying the inner workings of atoms and molecules on the electronic timescale(1-4) has become possible only with the recent development of isolated attosecond (10(-18)-s) laser pulses(5). Such pulses have been used to investigate atomic photoexcitation and photoionization(6,7) and electron dy...

2010-01-01

97

Sensors | Special Issue : Molecular Sensing and Molecular Electronics  

... Yoke Khin Yap Department of Physics, Michigan Technological University, 118 Fisher Hall, 1400 Townsend Drive, Houghton, Michigan, 49931-1295, USA Website: http://phy.mtu.edu/yap/ E-Mail: ykyap@mtu.edu Phone: +1 906 4872900 Fax: +1 906 4872933 Interests: nanotubes; graphene; nanosheets; nanowires; quantum dots; quantum electronics, biological sensing;... Yoke Khin YapDr. Dongyan ZhangGuest Editors Submission Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research ...

98

Carbohydrate-actuated nanofluidic diode: switchable current rectification in a nanopipette.  

Science.gov (United States)

Nanofluidic structures share many properties with ligand-gated ion channels. However, actuating ion conductance in artificial systems is a challenge. We have designed a system that uses a carbohydrate-responsive polymer to modulate ion conductance in a quartz nanopipette. The cationic polymer, a poly(vinylpyridine) quaternized with benzylboronic acid groups, undergoes a transition from swollen to collapsed upon binding to monosaccharides. As a result, the current rectification in nanopipettes can be reversibly switched depending on the concentration of monosaccharides. Such molecular actuation of nanofluidic conductance may be used in novel sensors and drug delivery systems. PMID:23934399

Vilozny, Boaz; Wollenberg, Alexander L; Actis, Paolo; Hwang, Daniel; Singaram, Bakthan; Pourmand, Nader

2013-10-01

99

Mechanism of Rectification in Tunneling Junctions Based on Molecules with Asymmetric Potential Drops  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This paper proposes a mechanism for the rectification of current by self-assembled monolayers (SAMs) of alkanethiolates with Fc head groups (SC\\(_{11}\\)Fc) in SAM-based tunneling junctions with ultra-flat Ag bottom electrodes and liquid metal (Ga\\(_2\\)O\\(_3\\)/EGaIn) top electrodes. A systematic physical-organic study based on statistically large numbers of data (N = 300?1000) reached the conclusion that only one energetically accessible molecular orbital (the HOMO of the Fc) is necessary t...

2010-01-01

100

Molecular electronics in junctions with energy disorder  

Energy Technology Data Exchange (ETDEWEB)

We investigate transport through molecular wires whose energy levels are affected by environmental fluctuations. We assume that the relevant fluctuations are so slow that they, within a tight-binding description, can be described by disordered, Gaussian distributed onsite energies. For long wires, we find that the corresponding current distribution can be rather broad even for a small energy variance. Moreover, we analyse with a Floquet master equation the interplay of laser excitations and static disorder. Then the disorder leads to spatial asymmetries such that the laser driving can induce a ratchet current.

Kaiser, Franz J; Haenggi, Peter; Kohler, Sigmund [Theoretische Physik I, Institut fuer Physik der Universitaet Augsburg, Universitaetsstrasse 1, 86135 Augsburg (Germany)], E-mail: franz.josef.kaiser@physik.uni-augsburg.de

2008-06-15

 
 
 
 
101

Molecular electronics in junctions with energy disorder  

International Nuclear Information System (INIS)

We investigate transport through molecular wires whose energy levels are affected by environmental fluctuations. We assume that the relevant fluctuations are so slow that they, within a tight-binding description, can be described by disordered, Gaussian distributed onsite energies. For long wires, we find that the corresponding current distribution can be rather broad even for a small energy variance. Moreover, we analyse with a Floquet master equation the interplay of laser excitations and static disorder. Then the disorder leads to spatial asymmetries such that the laser driving can induce a ratchet current

2008-06-01

102

Laser induced electron diffraction: a tool for molecular orbital imaging  

CERN Document Server

We explore the laser-induced ionization dynamics of N2 and CO2 molecules subjected to a few-cycle, linearly polarized, 800\\,nm laser pulse using effective two-dimensional single active electron time-dependent quantum simulations. We show that the electron recollision process taking place after an initial tunnel ionization stage results in quantum interference patterns in the energy resolved photo-electron signals. If the molecule is initially aligned perpendicular to the field polarization, the position and relative heights of the associated fringes can be related to the molecular geometrical and orbital structure, using a simple inversion algorithm which takes into account the symmetry of the initial molecular orbital from which the ionized electron is produced. We show that it is possible to extract inter-atomic distances in the molecule from an averaged photon-electron signal with an accuracy of a few percents.

Peters, Michel; Charron, Eric; Keller, Arne; Atabek, Osman

2012-01-01

103

Energy Transformation in Molecular Electronic Systems  

Energy Technology Data Exchange (ETDEWEB)

This laboratory has developed many new ideas and methods in the electronic spectroscopy of molecules. This report covers the contract period 1993-1995. A number of the projects were completed in 1996, and those papers are included in the report. The DOE contract was terminated at the end of 1995 owing to a reorganizational change eliminating nationally the projects under the Office of Health and Environmental Research, U. S. Department of Energy.

Kasha, Michael

1999-05-17

104

Electron-phonon interactions in single octanedithiol molecular junctions.  

Science.gov (United States)

We study the charge transport properties and electron-phonon interactions in single molecule junctions, each consisting of an octanedithiol molecule covalently bound to two electrodes. Conductance measurements over a wide temperature range establish tunneling as the dominant charge transport process. Inelastic electron tunneling spectroscopy performed on individual molecular junctions provides a chemical signature of the molecule and allows electron-phonon interaction induced changes in the conductance to be explored. By fitting the conductance changes in the molecular junction using a simple model for inelastic transport, it is possible to estimate the phonon damping rates in the molecule. Finally, changes in the inelastic spectra are examined in relation to conductance switching events in the junction to demonstrate how changes in the configuration of the molecule or contact geometry can affect the conductance of the molecular junction. PMID:20553018

Hihath, Joshua; Bruot, Christopher; Tao, Nongjian

2010-07-27

105

Intramolecular Electron Transfer in Phenoxylate and Catecholate based Molecular Systems  

Digital Repository Infrastructure Vision for European Research (DRIVER)

La Tesi "Intramolecular Electron Transfer in Phenoxylate and Catecholate Based Molecular Systems" es situa entre el camp de la química inorgànica i la química física. L'objectiu principal és l'estudi dels diversos mecanismes de transferència electrònica intramolecular (TEI), degut al seu interès en camps emergents com l'electrònica molecular. Els complexes de valència-mixte (VM) formats per un lligand orgànic electro-actiu i un ió metàl·lic amb almenys dos estats d'oxida...

2008-01-01

106

Intramolecular electron transfer in phenoxylate and catecholate based molecular systems/  

Digital Repository Infrastructure Vision for European Research (DRIVER)

La Tesi "Intramolecular Electron Transfer in Phenoxylate and Catecholate Based Molecular Systems" es situa entre el camp de la química inorgànica i la química física. L'objectiu principal és l'estudi dels diversos mecanismes de transferència electrònica intramolecular (TEI), degut al seu interès en camps emergents com l'electrònica molecular. Els complexes de valència-mixte (VM) formats per un lligand orgànic electro-actiu i un ió metàl·lic amb almenys dos estats d'oxida...

2009-01-01

107

Imaging femtosecond molecular orbitals and attosecond electron wavepackets  

International Nuclear Information System (INIS)

Full text: Single-electron molecular orbital wave functions are mathematical constructs that are used to describe the multi-electron wave function of molecules. The highest lying orbitals are of particular interest since they are responsible for the chemical properties of molecules. To observe them change as molecular bonds are formed and broken is to observe the essence of chemistry. Yet single orbitals are difficult to observe experimentally - until now impossible on the time scale of chemical reactions. We show that the full 3-dimensional structure of a single orbital can be imaged using a seemingly unlikely technique - high harmonic generation from aligned molecules using intense femtosecond laser pulses. We show how the projection of a molecular orbital is obtained for each molecular alignment from its broadband harmonic spectrum. Measuring the harmonics for a series of molecular alignments leads to a tomographic reconstruction of the single orbital wave function. As an experimental example, we reconstruct the highest occupied molecular orbital of N2. The same process, using a 5 fs laser pulse, can reveal attosecond electronic wavepacket motion in atoms. The wavepacket is created as a superposition of electronic states. Tunnel ionization occurs from the highest state, yet xuv emission is from the interaction of the continuum electron wavefunction with all coherent states that make up the wavepacket. A simple Schroedinger calculation shows that the harmonic emission from such a wavepacket contains a series of minima that are related to the wavepacket motion. Since the returning electron wavefunction is chirped in time, different harmonic frequencies correspond to different instants of time. This is like a streak camera with a range of about 1 fs. By changing the pump-probe delay, the structure in the spectra move, reflecting the motion of the bound-state wavepacket. (author)

2005-01-09

108

Ultrafast Molecular Imaging by Laser Induced Electron Diffraction  

CERN Multimedia

We address the feasibility of imaging geometric and orbital structure of a polyatomic molecule on an attosecond time-scale using the Laser Induced Electron Diffraction, LIED, technique [T. Zuo \\textit{et al.}, Chem. Phys. Lett. \\textbf{259}, 313 (1996)]. We present numerical results obtained for the CO$_2$ molecule using a single active electron model. The molecular geometry (bond-lengths) is determined within 3% of accuracy from a diffraction pattern which also reflects the nodal properties of the initial molecular orbital. Robustness of the structure determination is discussed with respect to vibrational and rotational motions with a complete interpretation of the laser-induced mechanisms.

Peters, Michel; Cornaggia, Christian; Saugout, Sébastien; Charron, Eric; Keller, Arne; Atabek, Osman

2010-01-01

109

Two dimensional molecular electronics spectroscopy for molecular fingerprinting, DNA sequencing, and cancerous DNA recognition.  

Science.gov (United States)

Laser-driven molecular spectroscopy of low spatial resolution is widely used, while electronic current-driven molecular spectroscopy of atomic scale resolution has been limited because currents provide only minimal information. However, electron transmission of a graphene nanoribbon on which a molecule is adsorbed shows molecular fingerprints of Fano resonances, i.e., characteristic features of frontier orbitals and conformations of physisorbed molecules. Utilizing these resonance profiles, here we demonstrate two-dimensional molecular electronics spectroscopy (2D MES). The differential conductance with respect to bias and gate voltages not only distinguishes different types of nucleobases for DNA sequencing but also recognizes methylated nucleobases which could be related to cancerous cell growth. This 2D MES could open an exciting field to recognize single molecule signatures at atomic resolution. The advantages of the 2D MES over the one-dimensional (1D) current analysis can be comparable to those of 2D NMR over 1D NMR analysis. PMID:24446806

Rajan, Arunkumar Chitteth; Rezapour, Mohammad Reza; Yun, Jeonghun; Cho, Yeonchoo; Cho, Woo Jong; Min, Seung Kyu; Lee, Geunsik; Kim, Kwang S

2014-02-25

110

Ultrafast molecular imaging by laser-induced electron diffraction  

International Nuclear Information System (INIS)

We address the feasibility of imaging geometric and orbital structures of a polyatomic molecule on an attosecond time scale using the laser-induced electron diffraction (LIED) technique. We present numerical results for the highest molecular orbitals of the CO2 molecule excited by a near-infrared few-cycle laser pulse. The molecular geometry (bond lengths) is determined within 3% of accuracy from a diffraction pattern which also reflects the nodal properties of the initial molecular orbital. Robustness of the structure determination is discussed with respect to vibrational and rotational motions with a complete interpretation of the laser-induced mechanisms.

2011-05-01

111

Electron diffraction determination of molecular constants of uranium hexachloride  

International Nuclear Information System (INIS)

The estimates of molecular constants of uranium hexachloride available in literature are mainly based on the data for the condensed phase. The recommended values essentially differ from each other. Thus, different authors recommend the R3(UCl) values of 246 pm and 250 pm. In recent years, the authors have carried out systematic electron diffraction studies of the molecular structure of uranium chlorides. They have shown by mass-spectrometric analysis of the UCl6 evaporation products that below 375 K the vapor contains only of monomer molecules (>99%). This permits the determination of molecular constants of uranium hexachloride in the gas phase on the basis of the available procedures

1993-11-01

112

Peculiarities of electron excitations decay in ion-molecular crystals  

International Nuclear Information System (INIS)

Ionic-molecular crystals (IMC) have wide application in various optical devices. Its are using in capacity of solid state dosimetric materials and isolators. Peculiarities of chemical and energetic states of IMC lead to following number of features of electron excitation decay in comparison with alkaline-halogen crystals: - both an electrons and a holes simultaneously could be captured and localized either on anion or on cation complexes; - in-molecular forces arising in result of charge capture could conduct to decay of anion or cation complex; - decay products od anion or cation complex could participate in following reaction of new products formation. All these processes and new products of electron excitation decay exert strong effect on optical, magnetic and electrical characteristics of IMC. Knowledge of way and mechanisms of electron excitation decay in IMC could allow to control of radiation stability of crystals with help of impurities participating in different channels of solid state reactions

1996-09-19

113

High-Order Harmonic Generation and Molecular Orbital Tomography: Characteristics of Molecular Recollision Electronic Wave Packets  

CERN Multimedia

We investigate the orientation dependence of molecular high-order harmonic generation (HHG) both numerically and analytically. We show that the molecular recollision electronic wave packets (REWPs) in the HHG are closely related to the ionization potential as well as the particular orbital from which it ionized. As a result, the spectral amplitude of the molecular REWP can be significantly different from its reference atom (i.e., with the same ionization potential as the molecule under study) in some energy regions due to the interference between the atomic cores of the molecules. This finding is important for molecular orbital tomography using HHG[Nature \\textbf{432}, 867(2004)].

Chen, Yanjun; Yang, Shiping; Liu, Jie

2008-01-01

114

Photocurrent, Rectification, and Magnetic Field Symmetry of Induced Current Through Quantum Dots  

DEFF Research Database (Denmark)

We report mesoscopic dc current generation in an open chaotic quantum dot with ac excitation applied to one of the shape-defining gates. For excitation frequencies large compared to the inverse dwell time of electrons in the dot (i.e., GHz), we find mesoscopic fluctuations of induced current that are fully asymmetric in the applied perpendicular magnetic field, as predicted by recent theory. Conductance, measured simultaneously, is found to be symmetric in field. In the adiabatic (i.e., MHz) regime, in contrast, the induced current is always symmetric in field, suggesting its origin is mesoscopic rectification.

DiCarlo, L.; M. Marcus, C.

2003-01-01

115

Charge, density and electron temperature in a molecular ultracold plasma  

CERN Document Server

A Rydberg gas of NO entrained in a supersonic molecular beam releases electrons as it evolves to form an ultracold plasma. The size of this signal, compared with that extracted by the subsequent application of a pulsed electric field, determines the absolute magnitude of the plasma charge. This information, combined with the number density of ions, supports a simple thermochemical model that explains the evolution of the plasma to an ultracold electron temperature.

Rennick, C J; Ortega-Arroyo, J; Godin, P J; Grant, E R

2009-01-01

116

Imaging the molecular dynamics of dissociative electron attachment to water  

Energy Technology Data Exchange (ETDEWEB)

Momentum imaging experiments on dissociative electron attachment to the water molecule are combined with ab initio theoretical calculations of the angular dependence of the quantum mechanical amplitude for electron attachment to provide a detailed picture of the molecular dynamics of dissociation attachment via the two lowest energy Feshbach resonances. The combination of momentum imaging experiments and theory can reveal dissociation dynamics for which the axial recoil approximation breaks down and thus provides a powerful reaction microscope for DEA to polyatomics.

Adaniya, Hidihito; Rudek, B.; Osipov, Timur; Haxton, Dan; Weber, Thorsten; Rescigno, Thomas N.; McCurdy, C.W.; Belkacem, Ali

2009-10-19

117

Molecular Transport Junctions: Propensity Rules for Inelastic Electron Tunneling Spectra  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We develop a series of propensity rules for interpreting Inelastic Electron Tunneling (IET) spectra of single-molecule transport junctions. IETS has no selection rules, such as those seen in optical, infrared and Raman spectra, because IETS features arise not from the field-dipole interaction characterizing these other spectroscopies, but from vibronic modification of the electronic levels. Expansion of the Landauer-Imry formula in Taylor series in molecular normal coordinat...

Troisi, Alessandro; Ratner, Mark A.

2006-01-01

118

Mechanism of Enhanced Rectification in Unimolecular Borromean Ring Devices  

CERN Multimedia

We have studied charge transport through individual Borromean Ring complexes, both with and without anchor groups, in gated double barrier tunneling junctions (DBTJs) formed using the electrical breakjunction technique on gold nanowires. While common single molecule device characteristics can be observed with either form of the Borromean Rings, the complexes with anchor groups show strong rectification of conduction in a relatively high percentage of samples. We present our data along with a simple model underlining the mechanism by which the arrangement and composition of the weakly bonding anchor groups attached to the electroactive element may promote a device configuration resulting in rectification.

Scott, G D; Peters, A J; Cantrill, S J; Stoddart, J F; Jiang, H W

2006-01-01

119

Quantum information analysis of electronic states at different molecular structures  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have studied transition metal clusters from a quantum information theory perspective using the density-matrix renormalization group (DMRG) method. We demonstrate the competition between entanglement and interaction localization. We also discuss the application of the configuration interaction based dynamically extended active space procedure which significantly reduces the effective system size and accelerates the speed of convergence for complicated molecular electronic ...

Barcza, G.; Legeza, O?; Marti, K. H.; Reiher, M.

2010-01-01

120

Candidate molecular ions for an electron electric dipole moment experiment  

Science.gov (United States)

This paper is a theoretical work in support of a newly proposed experiment [R. Stutz and E. Cornell, Bull. Am. Soc. Phys. 89, 76 (2004)] that promises greater sensitivity to measurements of the electron’s electric dipole moment (EDM) based on the trapping of molecular ions. Such an experiment requires the choice of a suitable molecule that is both experimentally feasible and possesses an expectation of a reasonable EDM signal. We find that the molecular ions PtH+ and HfH+ are both suitable candidates in their low-lying ?3 states. In particular, we anticipate that the effective electric fields generated inside these molecules are approximately 73 and -17GV/cm , respectively. As a byproduct of this discussion, we also explain how to make estimates of the size of the effective electric field acting in a molecule, using commercially available nonrelativistic molecular structure software.

Meyer, Edmund R.; Bohn, John L.; Deskevich, Michael P.

2006-06-01

 
 
 
 
121

The information content of electron flow through adsorbed molecular monolayers.  

Science.gov (United States)

We point to the ability of noncontact measurements of electron transport via self-assembled monolayers to provide chemical, A-resolved information about the underlying molecule. A conceptual framework is presented to model a current flow of soft electrons through a molecular monolayer to a substrate and explore the information content of this and other emerging noncontact measurements. A numerical scheme is developed where advantage is taken of the split-operator formalism to propagate the incident electronic wave function over a suitable periodic potential energy surface representing the self-assembled monolayer. The (experimentally observable) potential difference introduced by the transmitted electrons is extracted from the time-averaged electron density using the Poisson equation of classical electrostatics. PMID:20025336

Sherratt, Paul A J; Cohen, Hagai; Seideman, Tamar

2009-12-21

122

Effect of molecular desorption on the electronic properties of self-assembled polarizable molecular monolayers.  

Science.gov (United States)

We investigated the interfacial electronic properties of self-assembled monolayers (SAM)-modified Au metal surface at elevated temperatures. We observed that the work functions of the Au metal surfaces modified with SAMs changed differently under elevated-temperature conditions based on the type of SAMs categorized by three different features based on chemical anchoring group, molecular backbone structure, and the direction of the dipole moment. The temperature-dependent work function of the SAM-modified Au metal could be explained in terms of the molecular binding energy and the thermal stability of the SAMs, which were investigated with thermal desorption spectroscopic measurements and were explained with molecular modeling. Our study will aid in understanding the electronic properties at the interface between SAMs and metals in organic electronic devices if an annealing treatment is applied. PMID:24491327

Wang, Gunuk; Jeong, Hyunhak; Ku, Jamin; Na, Seok-In; Kang, Hungu; Ito, Eisuke; Jang, Yun Hee; Noh, Jaegeun; Lee, Takhee

2014-04-01

123

A new parametrizable model of molecular electronic structure  

CERN Document Server

A new electronic structure model is developed in which the ground state energy of a molecular system is given by a Hartree-Fock-like expression with parametrized one- and two-electron integrals over an extended (minimal + polarization) set of orthogonalized atom-centered basis functions, the variational equations being solved formally within the minimal basis but the effect of polarization functions being included in the spirit of second-order perturbation theory. It is designed to yield good dipole polarizabilities and improved intermolecular potentials with dispersion terms. The molecular integrals include up to three-center one-electron and two-center two-electron terms, all in simple analytical forms. A method to extract the effective one-electron Hamiltonian of nonlocal-exchange Kohn-Sham theory from the coupled-cluster one-electron density matrix is designed and used to get its matrix representation in a molecule-intrinsic minimal basis as an input to the paramtrization procedure -- making a direct link...

Laikov, Dimitri N

2011-01-01

124

Rectification of boric acid in nuclear power plants  

International Nuclear Information System (INIS)

Some experimental results of rectification of aqueous solution of boric acid, in the range of parameters used in nuclear power plants are presented. The values of plate efficiency have been obtained experimentally. The concentration distribution has been calculated in case of 3 plate column. Some data concerning the thermodynamic equilibrium of the system have been added. (author)

1979-01-01

125

Geometric rectification of radar imagery using digital elevation models  

Science.gov (United States)

Geologic analysis of radar imagery requires accurate spatial rectification to allow rock type discrimination and meaningful exploitation of multisensor data files. A procedure is described which removes distortions produced by most sources including the heretofore elusive problem of terrain induced effects. Rectified imagery is presented which displays geologic features not apparent in the distorted data.

Naraghi, M.; Stromberg, W.; Daily, M.

1983-01-01

126

RECTIFICATION OF BORIC ACID IN NUCLEAR TOWER PLANTS  

Directory of Open Access Journals (Sweden)

Full Text Available The paper presents some experimental results of rectification of aqueous solution of boric acid, in the range of parameters used in nuclear power planta, She values of plate efficiency has been obtained experimentally. The concentration distribution has been calculates in case of 3 plate column. Some data concerning the thermodynamic equilibrium of the system have been added.

Kazimierz Brodowicz

1979-01-01

127

Fullerenes, carbon nanotubes, and graphene for molecular electronics.  

Science.gov (United States)

With the constant growing complexity of electronic devices, the top-down approach used with silicon based technology is facing both technological and physical challenges. Carbon based nanomaterials are good candidates to be used in the construction of electronic circuitry using a bottom-up approach, because they have semiconductor properties and dimensions within the required physical limit to establish electrical connections. The unique electronic properties of fullerenes for example, have allowed the construction of molecular rectifiers and transistors that can operate with more than two logical states. Carbon nanotubes have shown their potential to be used in the construction of molecular wires and FET transistors that can operate in the THz frequency range. On the other hand, graphene is not only the most promising material for replacing ITO in the construction of transparent electrodes but it has also shown quantum Hall effect and conductance properties that depend on the edges or chemical doping. The purpose of this review is to present recent developments on the utilization carbon nanomaterials in molecular electronics. PMID:21894583

Pinzón, Julio R; Villalta-Cerdas, Adrián; Echegoyen, Luis

2012-01-01

128

Laser induced - tunneling, electron diffraction and molecular orbital imaging  

International Nuclear Information System (INIS)

Full text: Multiphoton ionization in the tunneling limit is similar to tunneling in a scanning tunneling microscope. In both cases an electron wave packet tunnels from a bound (or valence) state to the continuum. I will show that multiphoton ionization provides a route to extend tunneling spectroscopy to the interior of transparent solids. Rotating the laser polarization is the analogue of scanning the STM tip - a means of measuring the crystal symmetry of a solid. In gas phase molecules the momentum spectrum of individual electrons can be measured. I will show that, as we rotate the molecule with respect to the laser polarization, the photoelectron spectrum samples a filter projection of the momentum wave function (the molecular analogue to the band structure) of the ionizing orbital. Some electrons created during multiphoton ionization re-collide with their parent ion. I will show that they diffract, revealing the scattering potential of the ion - the molecular structure. The electron can also interfere with the initial orbital from which it separated, creating attosecond XUV pulses or pulse trains. The amplitude and phase of the radiation contains all information needed to re-construct the image of the orbital (just as a sheared optical interferometer can fully characterize an optical pulse). Strong field methods provide an extensive range of new tools to apply to atomic, molecular and solid-state problems. (author)

2008-07-02

129

Electron collision processes in atomic and molecular physics  

International Nuclear Information System (INIS)

Interaction of electro-magnetic radiation with atoms, molecules and cluster constitutes a major field of research in physical, chemical and biological sciences in recent years. Progress in atomic molecular and optical physics has made a significant impact on mankind in the 21st century. Most of the technological growth, such as electronic communications, computers etc., are due to significant developments in atomic and quantum physics. This conference provides an opportunity for students, researchers and teachers to interact with other scientists of high repute and fame and helps to abreast of the latest developments and advancements in the fields of Atomic, Molecular and Optical Physics. Papers relevant to INIS are indexed separately

2013-01-01

130

Theoretical descriptions of electron transport through single molecules: Developing design tools for molecular electronic devices  

Science.gov (United States)

There are vast numbers of organic compounds that could be considered for use in molecular electronics. Hence there is a need for efficient and economical screening tools. Here we develop theoretical methods to describe electron transport through individual molecules, the ultimate goal of which is to establish design tools for molecular electronic devices. To successfully screen a compound for its use as a device component requires a proper representation of the quantum mechanics of electron transmission. In this work we report the development of tools for the description of electron transmission that are: Charge self-consistent, valid in the presence of a finite applied potential field and (in some cases) explicitly time-dependent. In addition, the tools can be extended to any molecular system, including biosystems, because they are free of restrictive parameterizations. Two approaches are explored: (1) correlation of substituent parameter values (sigma), (commonly found in organic chemistry textbooks) to properties associated with electron transport, (2) explicit tracking of the time evolution of the wave function of a nonstationary electron. In (1) we demonstrate that the a correlate strongly with features of the charge migration process, establishing them as useful indicators of electronic properties. In (2) we employ a time-dependent description of electron transport through molecular junctions. To date, the great majority of theoretical treatments of electron transport in molecular junctions have been of the time-independent variety. Time dependence, however, is critical to such properties as switching speeds in binary computer components and alternating current conductance, so we explored methods based on time-dependent quantum mechanics. A molecular junction is modeled as a single molecule sandwiched between two clusters of close-packed metal atoms or other donor and acceptor groups. The time dependence of electron transport is investigated by initially localizing an electron on the donor and following the time development of the corresponding non-stationary wavefunction of the time-independent Hamiltonian. We demonstrate that the time-dependent treatment of electron transport predicts physically intuitive results, while providing insights not available from time-independent methods.

Carroll, Natalie R.

131

III - V semiconductor structures for biosensor and molecular electronics applications  

Energy Technology Data Exchange (ETDEWEB)

The present work reports on the employment of III-V semiconductor structures to biosensor and molecular electronics applications. In the first part a sensor based on a surface-near two dimensional electron gas for a use in biological environment is studied. Such a two dimensional electron gas inherently forms in a molecular beam epitaxy (MBE) grown, doped aluminum gallium arsenide - gallium arsenide (AlGaAs-GaAs) heterostructure. Due to the intrinsic instability of GaAs in aqueous solutions the device is passivated by deposition of a monolayer of 4'-substituted mercaptobiphenyl molecules. The influence of these molecules which bind to the GaAs via a sulfur group is investigated by Kelvin probe measurements in air. They reveal a dependence of GaAs electron affinity on the intrinsic molecular dipole moment of the mercaptobiphenyls. Furthermore, transient surface photovoltage measurements are presented which demonstrate an additional influence of mercaptobiphenyl chemisorption on surface carrier recombination rates. As a next step, the influence of pH-value and salt concentration upon the sensor device is discussed based on the results obtained from sensor conductance measurements in physiological solutions. A dependence of the device surface potential on both parameters due to surface charging is deduced. Model calculations applying Poisson-Boltzmann theory reveal as possible surface charging mechanisms either the adsorption of OH- ions on the surface, or the dissociation of OH groups in surface oxides. A comparison between simulation settings and physical device properties indicate the OH- adsorption as the most probable mechanism. In the second part of the present study the suitability of MBE grown III-V semiconductor structures for molecular electronics applications is examined. In doing so, a method to fabricate nanometer separated, coplanar, metallic electrodes based on the cleavage of a supporting AlGaAs-GaAs heterostructure is presented. This is followed by a thorough topographical and electrical characterization of fabricated devices which includes the electrostatic trapping of single gold nanoclusters between the electrodes. A first application to molecular electronics is presented by conductance measurements on a molecular layer of oligophenylenvinylene derivatives. Simulations on model molecules applying extended Hueckel theory and the nonequilibrium Greens function formalism reveal a good qualitative agreement between theory and experiment. Furthermore, promising extensions to the present fabrication method are discussed. These include the processing and characterization of broken T-shaped electrodes suitable for measurements on single molecules, and the transition to pure semiconductor electrodes based on indium arsenide. (orig.)

Luber, S.M.

2007-01-15

132

Special issue on ultrafast electron and molecular dynamics  

Science.gov (United States)

In the last few years, the advent of novel experimental and theoretical approaches has made possible the investigation of (time-resolved) molecular dynamics in ways not anticipated before. Experimentally, the introduction of novel light sources such as high-harmonic generation (HHG) and XUV/x-ray free electron lasers, and the emergence of novel detection strategies, such as time-resolved electron/x-ray diffraction and the fully coincident detection of electrons and fragment ions in reaction microscopes, has significantly expanded the arsenal of available techniques, and has taken studies of molecular dynamics into new domains of spectroscopic, spatial and temporal resolution, the latter including first explorations into the attosecond domain, thus opening completely new avenues for imaging electronic and nuclear dynamics in molecules. Along the way, particular types of molecular dynamics, e.g., dynamics around conical intersections, have gained an increased prominence, sparked by the realization of the essential role that this dynamics plays in relaxation pathways in important bio-molecular systems. In the short term, this will allow one to uncover and control the dynamics of elementary chemical processes such as, e.g., ultrafast charge migration, proton transfer, isomerization or multiple ionization, and to address new key questions about the role of attosecond coherent electron dynamics in chemical reactivity. The progress on the theoretical side has been no less impressive. Novel generations of supercomputers and a series of novel computational strategies have allowed nearly exact calculations in small molecules, as well as highly successful approximate calculations in large, polyatomic molecules, including biomolecules. Frequent and intensive collaborations involving both theory and experiment have been essential for the progress that has been accomplished. The special issue 'Ultrafast electron and molecular dynamics' seeks to provide an overview of the current developments, as well as new concepts that are emerging in this field when studying molecular dynamics at attosecond or few-femtosecond time-scales. It also aims at indicating how such studies are likely to evolve in the coming years. In this context, the present special issue contains contributions from recognized experts on HHG, free electron lasers, attosecond and femtosecond pump–probe spectroscopy, electron and x-ray diffraction methods, photoionization and theoretical methods specially designed for the analysis of experiments in this field. Seven review articles report on the present status of some selected topics, namely, table-top and free-electron lasers operating in the XUV and x-ray wavelength regimes to investigate ultrafast molecular dynamics, imaging methods to visualize electron and nuclear dynamics, nonlinear optics applications, and recent theoretical developments. These and other topics are covered by 32 research papers, in which new exciting results show the path for future developments in this field.

Martin, Fernando; Hishikawa, Akiyoshi; Vrakking, Marc

2014-06-01

133

Molecular electronics an introduction to theory and experiment  

CERN Document Server

This book provides a comprehensive overview of the rapidly developing field of molecular electronics. It focuses on our present understanding of the electrical conduction in single-molecule circuits and provides a thorough introduction to the experimental techniques and theoretical concepts. It will also constitute as the first textbook-like introduction to both the experiment and theory of electronic transport through single atoms and molecules. In this sense, this publication will prove invaluable to both researchers and students interested in the field of nanoelectronics and nanoscience in

Cuevas, Juan Carlos

2010-01-01

134

Molecular Transport Junctions: Propensity Rules for Inelastic Electron Tunneling Spectra  

CERN Document Server

We develop a series of propensity rules for interpreting Inelastic Electron Tunneling (IET) spectra of single-molecule transport junctions. IETS has no selection rules, such as those seen in optical, infrared and Raman spectra, because IETS features arise not from the field-dipole interaction characterizing these other spectroscopies, but from vibronic modification of the electronic levels. Expansion of the Landauer-Imry formula in Taylor series in molecular normal coordinates gives a convenient, accurate perturbation-type formula for calculating both frequency and intensity of the IETS spectrum. Expansion in a Dyson-like form permits derivation of propensity rules, both symmetry-based and pathway-deduced, allowing correlation of structure and coupling geometry with the IETS spectrum. These propensity rules work very well for the calculated spectrum of four typical molecular bridges.

Troisi, A; Troisi, Alessandro; Ratner, Mark A.

2006-01-01

135

Candidate molecular ions for an electron electric dipole moment experiment  

International Nuclear Information System (INIS)

This paper is a theoretical work in support of a newly proposed experiment [R. Stutz and E. Cornell, Bull. Am. Soc. Phys. 89, 76 (2004)] that promises greater sensitivity to measurements of the electron's electric dipole moment (EDM) based on the trapping of molecular ions. Such an experiment requires the choice of a suitable molecule that is both experimentally feasible and possesses an expectation of a reasonable EDM signal. We find that the molecular ions PtH+ and HfH+ are both suitable candidates in their low-lying 3? states. In particular, we anticipate that the effective electric fields generated inside these molecules are approximately 73 and -17 GV/cm, respectively. As a byproduct of this discussion, we also explain how to make estimates of the size of the effective electric field acting in a molecule, using commercially available nonrelativistic molecular structure software

2006-06-01

136

Elastic and Inelastic Electron Tunneling in Molecular Devices  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A theoretical framework for calculating electron transport through molecular junctions is presented. It is based on scattering theory using a Green's function formalism. The model can take both elastic and inelastic scattering into account and treats chemical and physical bonds on equal footing. It is shown that it is quite reliable with respect to the choice of functional and basis set. Applications concerning both elastic and inelastic transport are presented, though the emphasis is on the ...

Kula, Mathias

2006-01-01

137

Ab initio analysis of vibrational eigenmodes in molecular electronic systems  

Science.gov (United States)

Resent research focussed on gaining qualitative understanding of transport phenomena in molecular-scale systems indicates the significance of electron-molecular (e-mv) vibration interactions in molecules. From the theoretical point of view, calculation of the eigenmodes of molecular vibrations and the coupling parameters of an e-mv interaction Hamiltonian is of the high interest. Using DFT method within the Keldysh nonequilibrium Green's function formalism we calculate the eigenfrequencies ?_? of the center-of-mass and the radial breathing vibrational modes of C_60 molecule sandwiched in between two Al electrodes. Using this technique we studied these vibrational modes in the presence of bias and gate voltages applied to the device. We found that the nonzero gate voltage strongly changes the electronic DOS near the device Fermi level and thus has the considerable effect on the molecule vibrational spectrum. Small variations in bias voltage applied to the electrodes seem not to change the vibrational eigenfrequencies significantly. Finally, we discuss whether these modes are important in calculation of the inelastic corrections to the current flowing through the molecular-scale devices.

Sergueev, Nikolai; Roubtsov, Dan; Guo, Hong

2004-03-01

138

Renormalized molecular levels in a Sc3N@C-80 molecular electronic device  

DEFF Research Database (Denmark)

We address several general questions about quantum transport through molecular systems by an ab initio analysis of a scandium-nitrogen doped C-80 metallofullerene device. Charge transfer from the Sc3N is found to drastically change the current-voltage characteristics: the current through the Sc3N @ C-80 device is double that through a bare C-80 device. We provide strong evidence that transport in such molecular devices is mediated by molecular electronic states which have been renormalized by the device environment, such as the electrodes and external bias V-b. The renormalized molecular levels and main transmission features shift in energy corresponding to half the applied bias voltage. This is also consistent with our finding that the voltage drops by V-b/2 at each molecule/electrode contact.

Taylor, Jeremy Philip

2001-01-01

139

Effects of molecular orientation on electron-transfer collisions  

International Nuclear Information System (INIS)

K+ ions have been detected from the intersection of a beam of K atoms (5-30 eV) with beams of various simple molecules, such as CH3Br and CF3Br, which had been oriented prior to the collision. Production of ions in the collision is found to be highly dependent on orientation. The effect is most pronounced near threshold (?5 eV) and almost disappears at higher (30 eV) energies. Attack at the reactive halogen end produces the most ions, regardless of the polarity of that end. For each molecule, the reactive end seems to have the lower threshold energy. These observations may be a result of the electron being transferred to a specific end of the molecule, but the experiments measure only the net result of an electron transfer followed by the separation of the ions. Whether or not electron jump per se depends on orientation is still an open question, but the authors are able to qualitatively interpret the experimental results as being due to interactions between the ions as they separate in the exit channel. Most of the negative molecular ions dissociate, ejecting a halogen X- in the direction of the (oriented) molecular axis. If the X end is oriented away from the incoming K atom, the ejected X- will travel in the same direction as the K+, making the electron more likely to return to the K+ ion and reducing the K+ signal in this unfavorable orientation

1991-10-17

140

Spin and molecular electronics in atomically generated orbital landscapes  

Science.gov (United States)

Ab initio computational methods for electronic transport in nanoscaled systems are an invaluable tool for the design of quantum devices. We have developed a flexible and efficient algorithm for evaluating I-V characteristics of atomic junctions, which integrates the nonequilibrium Green’s function method with density functional theory. This is currently implemented in the package SMEAGOL. The heart of SMEAGOL is our scheme for constructing the surface Green’s functions describing the current-voltage probes. It consists of a direct summation of both open and closed scattering channels together with a regularization procedure of the Hamiltonian and provides great improvements over standard recursive methods. In particular it allows us to tackle material systems with complicated electronic structures, such as magnetic transition metals. Here we present a detailed description of SMEAGOL together with an extensive range of applications relevant for the two burgeoning fields of spin and molecular electronics.

Rocha, A. R.; García-Suárez, V. M.; Bailey, S.; Lambert, C.; Ferrer, J.; Sanvito, S.

2006-02-01

 
 
 
 
141

Poly(3-hexylthiophene)/multiwalled carbon hybrid coaxial nanotubes: nanoscale rectification and photovoltaic characteristics.  

Science.gov (United States)

We fabricate hybrid coaxial nanotubes (NTs) of multiwalled carbon nanotubes (MWCNTs) coated with light-emitting poly(3-hexylthiophene) (P3HT). The p-type P3HT material with a thickness of approximately 20 nm is electrochemically deposited onto the surface of the MWCNT. The formation of hybrid coaxial NTs of the P3HT/MWCNT is confirmed by a transmission electron microscope, FT-IR, and Raman spectra. The optical and structural properties of the hybrid NTs are characterized using ultraviolet and visible absorption, Raman, and photoluminescence (PL) spectra where, it is shown that the PL intensity of the P3HT materials decreases after the hybridization with the MWCNTs. The current-voltage (I-V) characteristics of the outer P3HT single NT show the semiconducting behavior, while ohmic behavior is observed for the inner single MWCNT. The I-V characteristics of the hybrid junction between the outer P3HT NT and the inner MWCNT, for the hybrid single NT, exhibit the characteristics of a diode (i.e., rectification), whose efficiency is clearly enhanced with light irradiation. The rectification effect of the hybrid single NT has been analyzed in terms of charge tunneling models. The quasi-photovoltaic effect is also observed at low bias for the P3HT/MWCNT hybrid single NT. PMID:20533839

Kim, Kihyun; Shin, Ji Won; Lee, Yong Baek; Cho, Mi Yeon; Lee, Suk Ho; Park, Dong Hyuk; Jang, Dong Kyu; Lee, Cheol Jin; Joo, Jinsoo

2010-07-27

142

Fine tuning of the electronic structure of ?-conjugated molecules for molecular electronics  

International Nuclear Information System (INIS)

Molecular components with their inherent scalability are expected to be promising supplements for nanoscale electronic devices. Here we report on how to specifically tune the electronic structure of chemisorbed molecules and thus to gain control of molecular transport properties. The electronic structure of our prototype ?-conjugated carboxylic acid anchored on the Cu(110) surface is modified systematically by inserting nitrogen atoms in a six-membered aromatic ring, a carboxylic functional group at the aromatic ring or both. Depending on the specific nature of the substituent, the relative position of the occupied or unoccupied electronic states with respect to the Fermi level can be specifically controlled and thus the transport properties of the studied molecular systems are modified intentionally, as proven by our scanning tunneling spectroscopy measurements. On the basis of the insight gained by our systematic experiment and first-principles calculations we are also able to predict the specific molecular character (? or ?) of the orbitals involved in the transport process of a carboxylate-Cu(110) system, depending on the functionalization pattern employed.

2011-04-08

143

Fine tuning of the electronic structure of ?-conjugated molecules for molecular electronics.  

Science.gov (United States)

Molecular components with their inherent scalability are expected to be promising supplements for nanoscale electronic devices. Here we report on how to specifically tune the electronic structure of chemisorbed molecules and thus to gain control of molecular transport properties. The electronic structure of our prototype ?-conjugated carboxylic acid anchored on the Cu(110) surface is modified systematically by inserting nitrogen atoms in a six-membered aromatic ring, a carboxylic functional group at the aromatic ring or both. Depending on the specific nature of the substituent, the relative position of the occupied or unoccupied electronic states with respect to the Fermi level can be specifically controlled and thus the transport properties of the studied molecular systems are modified intentionally, as proven by our scanning tunneling spectroscopy measurements. On the basis of the insight gained by our systematic experiment and first-principles calculations we are also able to predict the specific molecular character (? or ?) of the orbitals involved in the transport process of a carboxylate-Cu(110) system, depending on the functionalization pattern employed. PMID:21346307

Caciuc, V; Lennartz, M C; Atodiresei, N; Karthäuser, S; Blügel, S

2011-04-01

144

Fine tuning of the electronic structure of {pi}-conjugated molecules for molecular electronics  

Energy Technology Data Exchange (ETDEWEB)

Molecular components with their inherent scalability are expected to be promising supplements for nanoscale electronic devices. Here we report on how to specifically tune the electronic structure of chemisorbed molecules and thus to gain control of molecular transport properties. The electronic structure of our prototype {pi}-conjugated carboxylic acid anchored on the Cu(110) surface is modified systematically by inserting nitrogen atoms in a six-membered aromatic ring, a carboxylic functional group at the aromatic ring or both. Depending on the specific nature of the substituent, the relative position of the occupied or unoccupied electronic states with respect to the Fermi level can be specifically controlled and thus the transport properties of the studied molecular systems are modified intentionally, as proven by our scanning tunneling spectroscopy measurements. On the basis of the insight gained by our systematic experiment and first-principles calculations we are also able to predict the specific molecular character ({sigma} or {pi}) of the orbitals involved in the transport process of a carboxylate-Cu(110) system, depending on the functionalization pattern employed.

Caciuc, V; Lennartz, M C; Atodiresei, N; Karthaeuser, S; Bluegel, S, E-mail: n.atodiresei@fz-juelich.de, E-mail: s.karthaeuser@fz-juelich.de [Peter Gruenberg Institut, Institute for Advanced Simulation and JARA, Forschungszentrum Juelich GmbH, D-52425 Juelich (Germany)

2011-04-08

145

Growth, modification and integration of carbon nanotubes into molecular electronics  

Science.gov (United States)

Molecules are the smallest possible elements for electronic devices, with active elements for such devices typically a few Angstroms in footprint area. Owing to the possibility of producing ultra-high density devices, tremendous effort has been invested in producing electronic junctions by using various types of molecules. The major issues for molecular electronics include (1) developing an effective scheme to connect molecules with the present micro- and nano-technology, (2) increasing the lifetime and stabilities of the devices, and (3) increasing their performance in comparison to the state-of-the-art devices. In this work, we attempt to use carbon nanotubes (CNTs) as the interconnecting nanoelectrodes between molecules and microelectrodes. The ultimate goal is to use two individual CNTs to sandwich molecules in a cross-bar configuration while having these CNTs connected with microelectrodes such that the junction displays the electronic character of the molecule chosen. We have successfully developed an effective scheme to connect molecules with CNTs, which is scalable to arrays of molecular electronic devices. To realize this far reaching goal, the following technical topics have been investigated. (1) Synthesis of multi-walled carbon nanotubes (MWCNTs) by thermal chemical vapor deposition (T-CVD) and plasma-enhanced chemical vapor deposition (PECVD) techniques (Chapter 3). We have evaluated the potential use of tubular and bamboo-like MWCNTs grown by T-CVD and PE-CVD in terms of their structural properties. (2) Horizontal dispersion of MWCNTs with and without surfactants, and the integration of MWCNTs to microelectrodes using deposition by dielectrophoresis (DEP) (Chapter 4). We have systematically studied the use of surfactant molecules to disperse and horizontally align MWCNTs on substrates. In addition, DEP is shown to produce impurityfree placement of MWCNTs, forming connections between microelectrodes. We demonstrate the deposition density is tunable by both AC field strength and AC field frequency. (3) Etching of MWCNTs for the impurity-free nanoelectrodes (Chapter 5). We show that the residual Ni catalyst on MWCNTs can be removed by acid etching; the tip removal and collapsing of tubes into pyramids enhances the stability of field emission from the tube arrays. The acid-etching process can be used to functionalize the MWCNTs, which was used to make our initial CNT-nanoelectrode glucose sensors. Finally, lessons learned trying to perform spectroscopic analysis of the functionalized MWCNTs were vital for designing our final devices. (4) Molecular junction design and electrochemical synthesis of biphenyl molecules on carbon microelectrodes for all-carbon molecular devices (Chapter 6). Utilizing the experience gained on the work done so far, our final device design is described. We demonstrate the capability of preparing patterned glassy carbon films to serve as the bottom electrode in the new geometry. However, the molecular switching behavior of biphenyl was not observed by scanning tunneling microscopy (STM), mercury drop or fabricated glassy carbon/biphenyl/MWCNT junctions. Either the density of these molecules is not optimum for effective integration of devices using MWCNTs as the nanoelectrodes, or an electroactive contaminant was reduced instead of the ionic biphenyl species. (5) Self-assembly of octadecanethiol (ODT) molecules on gold microelectrodes for functional molecular devices (Chapter 7). We have realized an effective scheme to produce Au/ODT/MWCNT junctions by spanning MWCNTs across ODT-functionalized microelectrodes. A percentage of the resulting junctions retain the expected character of an ODT monolayer. While the process is not yet optimized, our successful junctions show that molecular electronic devices can be fabricated using simple processes such as photolithography, self-assembled monolayers and dielectrophoresis.

Moscatello, Jason P.

146

Intense laser effects on nonlinear optical absorption and optical rectification in single quantum wells under applied electric and magnetic field  

Energy Technology Data Exchange (ETDEWEB)

In this work the effects of intense laser on the electron-related nonlinear optical absorption and nonlinear optical rectification in GaAs-Ga{sub 1-x}Al{sub x}As quantum wells are studied under, applied electric and magnetic field. The electric field is applied along the growth direction of the quantum well whereas the magnetic field has been considered to be in-plane. The calculations were performed within the density matrix formalism with the use of the effective mass and parabolic band approximations. The intense laser effects are included through the Floquet method, by modifying the confining potential associated to the heterostructure. Results are presented for the nonlinear optical absorption, the nonlinear optical rectification and the resonant peak of these two optical processes. Several configurations of the dimensions of the quantum well, the applied electric and magnetic fields, and the incident intense laser radiation have been considered. The outcome of the calculation suggests that the nonlinear optical absorption and optical rectification are non-monotonic functions of the dimensions of the heterostructure and of the external perturbations considered in this work.

Duque, C.A., E-mail: cduque_echeverri@yahoo.es [Instituto de Fisica, Universidad de Antioquia, AA 1226 Medellin (Colombia); Kasapoglu, E. [Department of Physics, Cumhuriyet University, 58140 Sivas (Turkey); Sakiroglu, S. [Dokuz Eyluel University, Physics Department, 35160 Buca, Izmir (Turkey); Sari, H. [Department of Physics, Cumhuriyet University, 58140 Sivas (Turkey); Soekmen, I. [Dokuz Eyluel University, Physics Department, 35160 Buca, Izmir (Turkey)

2011-01-01

147

Inelastic Electron Tunneling Spectroscopy in Molecular Electronic Devices from First-Principles  

Science.gov (United States)

In this thesis, we present the first-principle calculations of inelastic electron tunneling spectroscopy(IETS) in single molecular break junctions. In a two-probe electrode-molecule-electrode setup, density functional theory(DFT) is used for the construction of the Hamiltonian and the Keldysh non-equilibrium Green's function(NEGF) technique will be employed for determining the electron density in non-equilibrium system conditions. Total energy functional, atomic forces and Hessian matrix can be obtained in the DFT-NEGF formalism and self-consistent Born approximation(SCBA) is used to integrate the molecular vibrations (phonons) into the framework once the phonon spectra and eigenvectors are calculated from the dynamic matrix. Geometry optimization schemes will also be discussed as an indispensable part of the formalism as the equilibrium condition is crucial to correctly calculate the phonon properties of the system. To overcome the numerical difficulties, especially the large computational time demand of the electron-phonon coupling problem, we develop a numerical approximation for the electron self-energy due to phonons and the error is controlled within numerical precision. Besides, a direct IETS second order I-V derivative expression is derived to reduce the error of numerical differentiation under reasonable assumptions. These two approximations greatly reduce the computation requirement and make the calculation feasible within current numerical capability. As the application of the DFT-NEGF-SCBA formalism, we calculate the IETS of the gold-octanedithiol(ODT) molecular junction. The I-V curve, conductance and IETS from ab-inito calculations are compared directly to experiments. A microscopic understanding of the electron-phonon coupling mechanism in the molecular tunneling junctions is explained in this example. In addition, comparisons of the hydrogen-dissociative and hydrogen-non-dissociative ODT junctions as well as the different charge transfer behaviors are presented to show the effects of thiol formation in the ODT molecular junction.

Ji, Tao

148

Heat Flow in Classical and Quantum Systems and Thermal Rectification  

CERN Document Server

The understanding of the underlying dynamical mechanisms which determine the macroscopic laws of heat conduction is a long standing task of non-equilibrium statistical mechanics. A better understanding of the mechanism of heat conduction may lead to potentially interesting applications based on the possibility to control the heat flow. Indeed, different models of thermal rectifiers has been recently proposed in which heat can flow preferentially in one direction. Although these models are far away from a prototype realization, the underlying mechanisms are of very general nature and, as such, are suitable of improvement and may eventually lead to real applications. We briefly discuss the problem of heat transport in classical and quantum systems and its relation to the chaoticity of the dynamics. We then study the phenomenon of thermal rectification and briefly discuss the different types of microscopic mechanisms that lead to the rectification of heat flow.

Casati, Giulio

2007-01-01

149

Electron collisions and internal excitation in stored molecular ion beams  

Energy Technology Data Exchange (ETDEWEB)

In storage ring experiments the role, which the initial internal excitation of a molecular ion can play in electron collisions, and the effect of these collisions on the internal excitation are investigated. Dissociative recombination (DR) and inelastic and super-elastic collisions are studied in the system of He{sup +}{sub 2}. The DR rate coefficient at low energies depends strongly on the initial vibrational excitation in this system. Therefore changes in the DR rate coefficient are a very sensitive probe for changes in the vibrational excitation in He{sup +}{sub 2}, which is used to investigate the effects of collisions with electrons and residual gas species. The low-energy DR of HD{sup +} is rich with resonances from the indirect DR process, when certain initial rotational levels in the molecular ion are coupled to levels in neutral Rydberg states lying below the ion state. Using new procedures for high-resolution electron-ion collision spectroscopy developed here, these resonances in the DR cross section can be measured with high energy sensitivity. This allows a detailed comparison with results of a MQDT calculation in an effort to assign some or all of the resonances to certain intermediate Rydberg levels. (orig.)

Buhr, H.

2006-07-26

150

Electron collisions and internal excitation in stored molecular ion beams  

International Nuclear Information System (INIS)

In storage ring experiments the role, which the initial internal excitation of a molecular ion can play in electron collisions, and the effect of these collisions on the internal excitation are investigated. Dissociative recombination (DR) and inelastic and super-elastic collisions are studied in the system of He+2. The DR rate coefficient at low energies depends strongly on the initial vibrational excitation in this system. Therefore changes in the DR rate coefficient are a very sensitive probe for changes in the vibrational excitation in He+2, which is used to investigate the effects of collisions with electrons and residual gas species. The low-energy DR of HD+ is rich with resonances from the indirect DR process, when certain initial rotational levels in the molecular ion are coupled to levels in neutral Rydberg states lying below the ion state. Using new procedures for high-resolution electron-ion collision spectroscopy developed here, these resonances in the DR cross section can be measured with high energy sensitivity. This allows a detailed comparison with results of a MQDT calculation in an effort to assign some or all of the resonances to certain intermediate Rydberg levels. (orig.)

2006-01-01

151

Molecular order affecting electron transport through ssDNA  

International Nuclear Information System (INIS)

DNA is considered to be the ideal model for studies of electron transport in molecule/conductor systems due to its stability, easily controlled structure and the presumed electrical properties. Scanning tunnelling microscope (STM) studies of single-stranded DNA bound to Au (1 1 1) or Au nanodots with a thiol linker were carried out under ambient conditions. The results show that the electron transfer between the STM tip and the gold is governed by the serial resistance of the oligomer strands and a water film. Electron transfer properties also depend on the alignment of the DNA strands. Measurements show that well-ordered parallel arrangement of the molecules protruding from flat crystalline surfaces is favourable for electron transport compared with unordered arrangements of molecules on spherical nanodots. Nanodots are good candidates for effective charge production by absorption of light allowing chemical reactions to happen at the dots, which can be used for storing the light energy. Understanding electron transport through molecular structures is of crucial importance for the development of such novel photovoltaic devices.

2009-07-01

152

Selection of thermodynamically optimal distribution patterns during rectification  

Energy Technology Data Exchange (ETDEWEB)

Under consideration is the selection of distribution patterns during rectification of multicomponent mixtures on a thermadynamic basis to minimize the work of separation. Analysis of double and triple-column fractionators on a thermodynamic basis shows no contradiction with economic indices. Analysis of the distribution patterns also confirmed the principle of dichotomous distribution the 50:50 rule. From the thermodynamic point of view the greater the efficiency of the fractionating, the more closely this maxim is approached.

Maykov, V.P.; Lagutina, I.S.

1981-01-01

153

Thermal rectification effects of multiple semiconductor quantum dot junctions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Based on the multiple energy level Anderson model, this study theoretically examines the thermoelectric effects of semiconductor quantum dots (QDs) in the nonlinear response regime. The charge and heat currents in the sequential tunneling process are calculated by using the Keldysh Green's function technique. Results show that the thermal rectification effect can be observed in a multiple QD junction system, whereas the tunneling rate, size fluctuation, and location distribu...

Kuo, David M. T.

2010-01-01

154

Vibrational excitations in molecular layers probed by ballistic electron microscopy  

Energy Technology Data Exchange (ETDEWEB)

We demonstrate the information on molecular vibrational modes via the second derivative (d{sup 2}I{sub B}/dV{sup 2}) of the ballistic electron emission spectroscopy (BEES) current. The proposed method does not create huge fields as in the case of conventional derivative spectroscopy and maintains a zero bias across the device. BEES studies carried out on three different types of large polycyclic aromatic hydrocarbon (PAH) molecular layers show that the d{sup 2}I{sub B}/dV{sup 2} spectra consist of uniformly spaced peaks corresponding to vibronic excitations. The peak spacing is found to be identical for molecules within the same PAH family though the BEES onset voltage varies for different molecules. In addition, injection into a particular orbital appears to correspond to a specific vibrational mode as the manifestation of the symmetry principle.

Kajen, Rasanayagam Sivasayan; Chandrasekhar, Natarajan [Institute of Materials Research and Engineering, 3 Research Link, 117602 (Singapore); Feng Xinliang; Muellen, Klaus [Max-Planck-Institut fuer Polymerforschung, Postfach 3148, D-55021 Mainz (Germany); Su Haibin, E-mail: n-chandra@imre.a-star.edu.sg, E-mail: muellen@mpip-mainz.mpg.de, E-mail: hbsu@ntu.edu.sg [Division of Materials Science, Nanyang Technological University, 50 Nanyang Avenue, 639798 (Singapore)

2011-10-28

155

Vibrational excitations in molecular layers probed by ballistic electron microscopy  

International Nuclear Information System (INIS)

We demonstrate the information on molecular vibrational modes via the second derivative (d2IB/dV2) of the ballistic electron emission spectroscopy (BEES) current. The proposed method does not create huge fields as in the case of conventional derivative spectroscopy and maintains a zero bias across the device. BEES studies carried out on three different types of large polycyclic aromatic hydrocarbon (PAH) molecular layers show that the d2IB/dV2 spectra consist of uniformly spaced peaks corresponding to vibronic excitations. The peak spacing is found to be identical for molecules within the same PAH family though the BEES onset voltage varies for different molecules. In addition, injection into a particular orbital appears to correspond to a specific vibrational mode as the manifestation of the symmetry principle.

2011-10-28

156

Fast Electron Repulsion Integrals for Molecular Coulomb Sturmians  

DEFF Research Database (Denmark)

A new method is presented for calculating interelectron repulsion integrals for molecular Coulomb Sturmian basis sets. This makes use of an expansion of densities in terms of $2k$-Sturmians, and the interelectron repulsion integrals are then calculated by a method based on the theory of hyperspherical harmonics. A rudimentary software library has been implemented and preliminary benchmarks indicate very good performance: On average 40ns, or approximately 80 clock cycles, per electron repulsion integral. This makes molecular Coulomb Sturmians competitive with Gaussian type orbitals in terms of speed, and is three to four orders of magnitude faster than methods based on expanding the exponential type orbitals in Gaussians. A full software library will be made available during August 2013.

Avery, James Emil

2013-01-01

157

Quantum information analysis of electronic states at different molecular structures  

CERN Multimedia

We have studied transition metal clusters from a quantum information theory perspective using the density-matrix renormalization group (DMRG) method. We demonstrate the competition between entanglement and interaction localization. We also discuss the application of the configuration interaction based dynamically extended active space procedure which significantly reduces the effective system size and accelerates the speed of convergence for complicated molecular electronic structures to a great extent. Our results indicate the importance of taking entanglement among molecular orbitals into account in order to devise an optimal orbital ordering and carry out efficient calculations on transition metal clusters. We propose a recipe to perform DMRG calculations in a black-box fashion and we point out the connections of our work to other tensor network state approaches.

Barcza, G; Marti, K H; Reiher, M

2010-01-01

158

Electron transport through catechol-functionalized molecular rods  

International Nuclear Information System (INIS)

The charge transport properties of a catechol-type dithiol-terminated oligo-phenylene-ethynylene was investigated by cyclic voltammetry (CV) and by the scanning tunnelling microscopy break junction technique (STM-BJ). Single molecule charge transport experiments demonstrated the existence of high and low conductance regions. The junction conductance is rather weakly dependent on the redox state of the bridging molecule. However, a distinct dependence of junction formation probability and of relative stretching distances of the catechol- and quinone-type molecular junctions is observed. Substitution of the central catechol ring with alkoxy-moieties and the combination with a topological analysis of possible ?-electron pathways through the respective molecular skeletons lead to a working hypothesis, which could rationalize the experimentally observed conductance characteristics of the redox-active nanojunctions

2013-11-01

159

Semiclassical theory of electronically nonadiabatic transitions in molecular collision processes  

Science.gov (United States)

An introductory account of the semiclassical theory of the S-matrix for molecular collision processes is presented, with special emphasis on electronically nonadiabatic transitions. This theory is based on the incorporation of classical mechanics with quantum superposition, and in practice makes use of the analytic continuation of classical mechanics into the complex space of time domain. The relevant concepts of molecular scattering theory and related dynamical models are described and the formalism is developed and illustrated with simple examples - collinear collision of the A+BC type. The theory is then extended to include the effects of laser-induced nonadiabatic transitions. Two bound continuum processes collisional ionization and collision-induced emission also amenable to the same general semiclassical treatment are discussed.

Lam, K. S.; George, T. F.

1979-01-01

160

From Molecular Meccano to Nano-Functional Materials for Molecular Electronics Applications  

Science.gov (United States)

Mechanically interlocked molecules (MIMs), such as bistable catenanes and rotaxanes, have found technological applications in fields as disparate as those involving molecular switches and machines, nanoelectromechanical systems (NEMS), and molecular electronic devices. All these multifarious applications of MIMs require that the synthesis of these molecular components be straightforward and efficient. Furthermore, the elaboration of the structural features of MIMs into metal-organic frameworks (MOFs) provides a way of bringing MIMs from solution into solid state in a systematic and hierarchical manner. This dissertation describes successful attempts in realizing such concepts. The pi-electron deficient tetracationic cyclophane, namely cyclobis(paraquat-p-phenylene) (CBQPT4+), which is a key component in the MIMs for molecular electronics applications, now can be synthesized by a new "template-trading" protocol. The time taken to synthesize CBPQT4+ has been halved as a result of using a pH-responsive derivative of 1,5-diaminonaphthalene to displace the template employed during its synthesis, instead of the time-consuming and energy-wasteful liquid-liquid extraction. By utilizing the considerable sophistication of organic synthesis methods, a series of rigid organic dicarboxylic acids containing crown ethers and [2]catenanes moieties are designed and synthesized. These novel dicarboxylic crown ethers not only retain the characteristics of their parent crown ethers since they can bind cationic guests and serve as templates for making MIMs, but they also present coordination sites to connect with secondary building units (SBUs) in MOFs, in which the organic linkers act as "edges" that bridge the metal centers which in turn act as "vertices". This strategy allows the "bottom-up" construction of crystalline MOFs, whose bulk properties in the solid state can be designed and predicted by the characteristics of the molecular building blocks and superstructures. The resulting MOF-1001 and MOF-1002, which adopt the primitive cubic structure, are capable of docking paraquat cation guests within the crown ethers inside in a stereoelectronically controlled fashion, a behavior similar to enzymes binding incoming substrates. And MOF-1030, which is synthesized from an exceptionally long [2]catenane organic strut, is a three-dimensional MOF structure with vast openness, allowing MIMs-based prototypical molecular switches to be anchored at precise locations and with uniform relative orientations throughout the framework as a whole. These studies not only represent efficient approaches to the preparation of MOFs with complex functionalities, but also set the stage for the development of next-generation nano-functional materials for molecular electronics applications.

Sue, Chi-Hau

 
 
 
 
161

Origin of rectification in boron nitride heterojunctions to silicon.  

Science.gov (United States)

Cubic and hexagonal boron nitride (cBN and hBN) heterojunctions to n-type Si are fabricated under low-energy ion bombardment by inductively coupled plasma-enhanced chemical vapor deposition using the chemistry of fluorine. The sp2-bonded BN/Si heterojunction shows no rectification, while the cBN/sp2BN/Si heterojunction has rectification properties analogue to typical p-n junction diodes despite a large thickness (?130 nm) of the sp2BN interlayer. The current-voltage characteristics at temperatures up to 573 K are governed by thermal excitation of carriers, and mostly described with the ideal diode equation and the Frenkel-Poole emission model at low and high bias voltages, respectively. The rectification in the cBN/sp2BN/Si heterojunction is caused by a bias-dependent change in the barrier height for holes arising from stronger p-type conduction in the cBN layer and enhanced with the thick sp2BN interlayer for impeding the reverse current flow at defect levels mainly associated with grain boundaries. PMID:23521160

Teii, Kungen; Hori, Takuro; Mizusako, Yusei; Matsumoto, Seiichiro

2013-04-10

162

Molecular Dynamics Simulations of Shocks Including Electronic Heat Conduction and Electron-Phonon Coupling  

Science.gov (United States)

Shocks are often simulated using the classical molecular dynamics (MD) method in which the electrons are not included explicitly and the interatomic interaction is described by an effective potential. As a result, the fast electronic heat conduction in metals and the coupling between the lattice vibrations and the electronic degrees of freedom can not be represented. Under conditions of steep temperature gradients that can form near the shock front, however, the electronic heat conduction can play an important part in redistribution of the thermal energy in the shocked target. We present the first atomistic simulation of a shock propagation including the electronic heat conduction and electron-phonon coupling. The computational model is based on the two-temperature model (TTM) that describes the time evolution of the lattice and electron temperatures by two coupled non-linear differential equations. In the combined TTM-MD method, MD substitutes the TTM equation for the lattice temperature. Simulations are performed with both MD and TTM-MD models for an EAM Al target shocked at 300 kbar. The target includes a tilt grain boundary, which provides a region where shock heating is more pronounced and, therefore, the effect of the electronic heat conduction is expected to be more important. We find that the differences between the predictions of the MD and TTM-MD simulations are significantly smaller as compared to the hydrodynamics calculations performed at similar conditions with and without electronic heat conduction.

Ivanov, Dmitriy S.; Zhigilei, Leonid V.; Bringa, Eduardo M.; de Koning, Maurice; Remington, Bruce A.; Caturla, Maria Jose; Pollaine, Stephen M.

2004-07-01

163

Storage ring experiments on electron-molecular-ion interactions  

Science.gov (United States)

Merged-beams collision experiments between electrons and molecular ions at the Test Storage Ring (TSR) in Heidelberg are presented. The paper gives an overview of results and literature from this work, focusing on recent developments of the experimental tools and resulting data. These include in particular the internal product energies in the dissociative recombination of polyatomic cations and the atomic final states in the dissociative recombination of diatomic cations. In addition, an outlook to dissociative recombination experiments at the upcoming cryogenic electrostatic storage ring CSR is given.

Wolf, Andreas

2013-07-01

164

Understanding Cellulose Through Molecular Simulation and Electron Tomography  

Energy Technology Data Exchange (ETDEWEB)

High-resolution cellulose crystal structures have been determined from diffraction experiments using large diameter microfibrils as the sample material. However, cellulose microfibrils in plants are much smaller in diameter, and are more difficult to directly examine experimentally. Molecular dynamics simulation combined with quantum chemical calculations can help to elucidate the structure and dynamics of small diameter cellulose microfibrils. These simulation techniques also aid in the interpretation of electron tomography volumetric structural data from maize cell walls, where pretreatment with dilute acid or ammonia reveals microfibril geometry.

Matthews, J.

2013-01-01

165

Electronic and magnetic structure of vivianite: cluster molecular orbital calculations  

Science.gov (United States)

The electronic and magnetic structure of the octahydrophosphate vivianite, Fe3(PO4)2.8H2O, has been investigated by cluster molecular orbital calculations in local spin density approximation. Optical and Mössbauer spectra are well reproduced by the calculations, and the differences between the two iron sites can be correlated with differences in the geometrical structure of the first coordination sphere. The spin structure within the crystallographic ac plane is derived and explained on the basis of different superexchange pathways via edges of the phosphate tetrahedra. The calculations demonstrate that quite large clusters (up to 118 atoms) are necessary to arrive at reliable results.

Grodzicki, M.; Amthauer, G.

166

Molecular Electronics: Insight from First-Principles Transport Simulations  

DEFF Research Database (Denmark)

Conduction properties of nanoscale contacts can be studied using first-principles simulations. Such calculations give insight into details behind the conductance that is not readily available in experiments. For example, we may learn how the bonding conditions of a molecule to the electrodes affect the electronic transport. Here we describe key computational ingredients and discuss these in relation to simulations for scanning tunneling microscopy (STM) experiments with C-60 molecules where the experimental geometry is well characterized. We then show how molecular dynamics simulations may be combined with transport calculations to study more irregular situations, such as the evolution of a nanoscale contact with the mechanically controllable break-junction technique. Finally we discuss calculations of inelastic electron tunnelling spectroscopy as a characterization technique that reveals information about the atomic arrangement and transport channels.

Paulsson, Magnus; Frederiksen, Thomas

2010-01-01

167

Photoelectron spectroscopy via electronic spectroscopy of molecular ions  

International Nuclear Information System (INIS)

In this work, a new aspect of the correlation between optical and photoelectron spectra is discussed on the basis of which the first ionization potentials of condensed-ring aromatics can be estimated from certain features in the electronic spectra of their positive ions. Furthermore, it is noticed that the first IP's are very sensitive to molecular size as the latter's inclusion in the regression formulas improves the results considerably. Once the first ionization potential for a molecule is determined, its higher IP's may be computed if the lower-energy electronic bands for its cation are known. This procedure is especially useful for such systems whose uv photoelectron spectra are unknown. (author). 11 refs, 10 figs, 1 tab

1990-10-01

168

Probing ultrafast electronic and molecular dynamics with free-electron lasers  

Science.gov (United States)

Molecular dynamics is an active area of research, focusing on revealing fundamental information on molecular structures and photon–molecule interaction and with broad impacts in chemical and biological sciences. Experimental investigation of molecular dynamics has been advanced by the development of new light sources and techniques, deepening our understanding of natural processes and enabling possible control and modification of chemical and biomolecular processes. Free-electron lasers (FELs) deliver unprecedented intense and short photon pulses in the vacuum ultraviolet and x-ray spectral ranges, opening a new era for the study of electronic and nuclear dynamics in molecules. This review focuses on recent molecular dynamics investigations using FELs. We present recent work concerning dynamics of molecular interaction with FELs using an intrinsic clock within a single x-ray pulse as well as using an external clock in a pump–probe scheme. We review the latest developments on correlated and coincident spectroscopy in FEL-based research and recent results revealing photo-induced interaction dynamics using these techniques. We also describe new instrumentations to conduct x-ray pump–x-ray probe experiments with spectroscopy and imaging detectors.

Fang, L.; Osipov, T.; Murphy, B. F.; Rudenko, A.; Rolles, D.; Petrovic, V. S.; Bostedt, C.; Bozek, J. D.; Bucksbaum, P. H.; Berrah, N.

2014-06-01

169

The role of optical rectification in the generation of terahertz radiation from GaBiAs  

International Nuclear Information System (INIS)

We report on a detailed study of the emission of terahertz-frequency electromagnetic radiation from layers of GaBiyAs1-y (0?y<0.04) grown by molecular beam epitaxy on (311)B and (001) GaAs substrates. We measure two orthogonally polarized components of the terahertz radiation emitted under excitation by ultrashort near-infrared laser pulses in both transmission and reflection geometries as a function of the crystal rotation about its surface normal as well as the effect of in-plane magnetic field and pump fluence on the terahertz emission. We conclude that the principal mechanism for terahertz generation is via optical rectification rather than transient currents.

2009-06-22

170

Fragmentation of molecular ions in slow electron collisions  

International Nuclear Information System (INIS)

The fragmentation of positively charged hydrogen molecular ions by the capture of slow electrons, the so called dissociative recombination (DR), has been investigated in storage ring experiments at the TSR, Heidelberg, where an unique twin-electron-beam arrangement was combined with high resolution fragment imaging detection. Provided with well directed cold electrons the fragmentation kinematics were measured down to meV collision energies where pronounced rovibrational Feshbach resonances appear in the DR cross section. For thermally excited HD+ the fragmentation angle and the kinetic energy release were studied at variable precisely controlled electron collision energies on a dense energy grid from 10 to 80 meV. The anisotropy described for the first time by Legendre polynomials higher 2nd order and the extracted rotational state contributions were found to vary on a likewise narrow energy scale as the rotationally averaged DR rate coefficient. Ro-vibrationally resolved DR experiments were performed on H2+ produced in distinct internal excitations by a novel ion source. Both the low-energy DR rate as well as the fragmentation dynamics at selected resonances were measured individually in the lowest two vibrational and first three excited rotational states. State-specific DR rates and angular dependences are reported. (orig.)

2008-01-01

171

Alternative Systems for Molecular Electronics: Functionalized Carboxylic Acids on Structured Surfaces  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Molecular electronics is recognized as a key candidate to succeed the silicon based technology as soon as the end of the semiconductor roadmap is reached. An important step towards the realization of molecular electronics is the combination of common CMOS devices and molecular elements to new systems.

Lennartz, Maria Christina

2010-01-01

172

The effect of spatial symmetry on the nonlinear optical rectification of lens-shaped quantum dots  

International Nuclear Information System (INIS)

The one-band k·p model, the compact density matrix approach and the iterative method are used to calculate the nonlinear optical rectification coefficient (ORC) of an electron confined in an asymmetric lens-shaped quantum dot (ALQD). Numerical results are presented for the typical GaAs ALQD. The effects of the size of the ALQD, the incident photon energy and the symmetry of the QD on the ORC are investigated. It is found that there is a scaling rule that connects the ORC to the size of the ALQD. Using this scaling rule, it is shown that the ORC increases, and its peak shifts to lower energies, with increasing dot size. Also, the ORC decreases with increasing mirror symmetry of the QD. (paper)

2012-06-01

173

Machine learning of molecular electronic properties in chemical compound space  

International Nuclear Information System (INIS)

The combination of modern scientific computing with electronic structure theory can lead to an unprecedented amount of data amenable to intelligent data analysis for the identification of meaningful, novel and predictive structure–property relationships. Such relationships enable high-throughput screening for relevant properties in an exponentially growing pool of virtual compounds that are synthetically accessible. Here, we present a machine learning model, trained on a database of ab initio calculation results for thousands of organic molecules, that simultaneously predicts multiple electronic ground- and excited-state properties. The properties include atomization energy, polarizability, frontier orbital eigenvalues, ionization potential, electron affinity and excitation energies. The machine learning model is based on a deep multi-task artificial neural network, exploiting the underlying correlations between various molecular properties. The input is identical to ab initio methods, i.e. nuclear charges and Cartesian coordinates of all atoms. For small organic molecules, the accuracy of such a ‘quantum machine’ is similar, and sometimes superior, to modern quantum-chemical methods—at negligible computational cost. (paper)

2013-09-01

174

Machine learning of molecular electronic properties in chemical compound space  

Science.gov (United States)

The combination of modern scientific computing with electronic structure theory can lead to an unprecedented amount of data amenable to intelligent data analysis for the identification of meaningful, novel and predictive structure-property relationships. Such relationships enable high-throughput screening for relevant properties in an exponentially growing pool of virtual compounds that are synthetically accessible. Here, we present a machine learning model, trained on a database of ab initio calculation results for thousands of organic molecules, that simultaneously predicts multiple electronic ground- and excited-state properties. The properties include atomization energy, polarizability, frontier orbital eigenvalues, ionization potential, electron affinity and excitation energies. The machine learning model is based on a deep multi-task artificial neural network, exploiting the underlying correlations between various molecular properties. The input is identical to ab initio methods, i.e. nuclear charges and Cartesian coordinates of all atoms. For small organic molecules, the accuracy of such a ‘quantum machine’ is similar, and sometimes superior, to modern quantum-chemical methods—at negligible computational cost.

Montavon, Grégoire; Rupp, Matthias; Gobre, Vivekanand; Vazquez-Mayagoitia, Alvaro; Hansen, Katja; Tkatchenko, Alexandre; Müller, Klaus-Robert; Anatole von Lilienfeld, O.

2013-09-01

175

Ab initio quantum mechanical/molecular mechanical simulation of electron transfer process: Fractional electron approach  

International Nuclear Information System (INIS)

Electron transfer (ET) reactions are one of the most important processes in chemistry and biology. Because of the quantum nature of the processes and the complicated roles of the solvent, theoretical study of ET processes is challenging. To simulate ET processes at the electronic level, we have developed an efficient density functional theory (DFT) quantum mechanical (QM)/molecular mechanical (MM) approach that uses the fractional number of electrons as the order parameter to calculate the redox free energy of ET reactions in solution. We applied this method to study the ET reactions of the aqueous metal complexes Fe(H2O)62+/3+ and Ru(H2O)62+/3+. The calculated oxidation potentials, 5.82 eV for Fe(II/III) and 5.14 eV for Ru(II/III), agree well with the experimental data, 5.50 and 4.96 eV, for iron and ruthenium, respectively. Furthermore, we have constructed the diabatic free energy surfaces from histogram analysis based on the molecular dynamics trajectories. The resulting reorganization energy and the diabatic activation energy also show good agreement with experimental data. Our calculations show that using the fractional number of electrons (FNE) as the order parameter in the thermodynamic integration process leads to efficient sampling and validate the ab initio QM/MM approach in the calculation of redox free energies

2008-03-28

176

Electron degradation and yields of initial products: IV, Subexcitation electrons in molecular oxygen  

Energy Technology Data Exchange (ETDEWEB)

Electron-slowing down processes in molecular oxygen gas in the subexcitation domain (below ionization threshold) are studied by using the Spencer-Fano (SF) equation and its simplification, the continuous-slowing-down approximation (CSDA), both in time-dependent and time-independent representations. Compared to N/sub 2/ and CO/sub 2/ previously studied, O/sub 2/ has special features in its inelastic cross sections, namely, strong delta-function-like peaks in the vibrational excitation cross section below 1.3 eV, and very low energy thresholds of electronic excitation channels. These features provide as a stringent test of the CSDA. Indeed, our results clearly show for the first time that the CSDA fails even qualitatively to reproduce the electron degradation spectrum given by the exact SF method over the whole energy regime studied. 7 refs., 10 figs., 1 tab.

Ishii, M.A.; Kimura, M.; Inokuti, M.; Kowari, Ken-ichi

1988-01-01

177

Rectification of aerial images using piecewise linear transformation  

Science.gov (United States)

Aerial images are widely used in various activities by providing visual records. This type of remotely sensed image is helpful in generating digital maps, managing ecology, monitoring crop growth and region surveying. Such images could provide insight into areas of interest that have lower altitude, particularly in regions where optical satellite imaging is prevented due to cloudiness. Aerial images captured using a non-metric cameras contain real details of the images as well as unexpected distortions. Distortions would affect the actual length, direction and shape of objects in the images. There are many sources that could cause distortions such as lens, earth curvature, topographic relief and the attitude of the aircraft that is used to carry the camera. These distortions occur differently, collectively and irregularly in the entire image. Image rectification is an essential image pre-processing step to eliminate or at least reduce the effect of distortions. In this paper, a non-parametric approach with piecewise linear transformation is investigated in rectifying distorted aerial images. The non-parametric approach requires a set of corresponding control points obtained from a reference image and a distorted image. The corresponding control points are then applied with piecewise linear transformation as geometric transformation. Piecewise linear transformation divides the image into regions by triangulation. Different linear transformations are employed separately to triangular regions instead of using a single transformation as the rectification model for the entire image. The result of rectification is evaluated using total root mean square error (RMSE). Experiments show that piecewise linear transformation could assist in improving the limitation of using global transformation to rectify images.

Liew, L. H.; Lee, B. Y.; Wang, Y. C.; Cheah, W. S.

2014-02-01

178

Rovibronic energy levels for triplet electronic states of molecular deuterium  

CERN Document Server

Optimal set of 1046 rovibronic energy levels for 35 triplet electronic states of $D_2$ has been obtained by means of statistical analysis of all available values of wavenumbers of rovibronic transitions studied in emission, absorption, laser and anticrossing spectroscopic experiments of various authors. We used new method of the analysis (Lavrov, Ryazanov, JETPLett., 2005), which does not need any a priory assumptions concerning molecular structure being based only on two fundamental principles: maximum likelihood and Rydberg-Ritz. The method provides the opportunity to obtain the estimation of experimental errors of the wavenumbers independent from those reported in original papers. From 3801 published wavenumber values 207 were excluded as blunders, wavenumber values of 122 from them were measured in our experiments. The remaining set of 3716 experimental data has been divided into 14 subsets of uniformly precise data having close to normal error distribution. Unknown shift between levels of ortho- and para...

Lavrov, B P

2007-01-01

179

Hydration effect on the electronic transport properties of oligomeric phenylene ethynylene molecular junctions  

International Nuclear Information System (INIS)

A first-principles computational method based on the hybrid density functional theory is developed to simulate the electronic transport properties of oligomeric phenylene ethynylene molecular junctions with H2O molecules accumulated in the vicinity as recently reported by Na et al. [Nanotechnology 18 424001 (2007)]. The numerical results show that the hydrogen bonds between the oxygen atoms of the oligomeric phenylene ethynylene molecule and H2O molecules result in the localisation of the molecular orbitals and lead to the lower transition peaks. The H2O molecular chains accumulated in the vicinity of the molecular junction can not only change the electronic structure of the molecular junctions, but also open additional electronic transport pathways. The obvious influence of H2O molecules on the electronic structure of the molecular junction and its electronic transport properties is thus demonstrated. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

2010-06-01

180

Study of rectification at the metal-cadmium telluride contact  

International Nuclear Information System (INIS)

The barrier heights at the contact between metals and N or P type cadmium telluride have been determined. Various surface treatments have been used for the semiconductor: lapping, polishing and etching in a bromine in methanol solution. Depending on these preparation differences of about 0.1 eV have been observed for the barrier height which in any case was no more than 0.9 - 1.0 eV. These results can not be explained by only considering the Schottky theory of rectification

1981-01-01

 
 
 
 
181

Three-dimensional mapping from stereo images with geometrical rectification  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this paper we present a method for mapping 3D unknown environments from stereo images. It is based on a dense disparity image obtained by a process of window correlation. To each image in the sequence a geometrical rectification process is applied, which is essential to remove the conical perspective of the images obtained with a photographic camera. This process corrects the errors in coordinates x and y to obtain a better matching for the map information. The mapping method is an applica...

Gallego Sa?nchez, Antonio Javier; Molina Carmona, Rafael; Villagra? Arnedo, Carlos

2006-01-01

182

Radical and non-radical carbazole derivatives formolecular electronics. Molecular Glasses and Liquid Crystals.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Molecular electronics is an emergent area of the new technologies related to the use of organic and biological materials in optoelectronic and electronic devices. Among the materials used in electronic applications, low molecular weight materials, or molecular materials, became of great interest in the last years, due to the advantages they present in front of the traditional polymeric materials, such as, easier synthesis, purification and characterization, and a better processability.The obj...

Castellanos Ortega, Sonia

2010-01-01

183

Molecular rectifying diodes from self-assembly on silicon  

CERN Multimedia

We demonstrate a molecular rectifying junction made from a sequential self-assembly on silicon. The device structure consists of only one conjugated (p) group and an alkyl spacer chain. We obtain rectification ratios up to 37 and threshold voltages for rectification between -0.3V and -0.9V. We show that rectification occurs from resonance through the highest occupied molecular orbital of the p-group in good agreement with our calculations and internal photoemission spectroscopy. This approach allows us to fabricate molecular rectifying diodes compatible with silicon nanotechnologies for future hybrid circuitries.

Lenfant, S; Delerue, C; Allan, G

2003-01-01

184

Ionic fragmentation channels in electron collisions of small molecular ions  

Energy Technology Data Exchange (ETDEWEB)

Dissociative Recombination (DR) is one of the most important loss processes of molecular ions in the interstellar medium (IM). Ion storage rings allow to investigate these processes under realistic conditions. At the Heidelberg test storage ring TSR a new detector system was installed within the present work in order to study the DR sub-process of ion pair formation (IPF). The new detector expands the existing electron target setup by the possibility to measure strongly deflected negative ionic fragments. At the TSR such measurements can be performed with a uniquely high energy resolution by independently merging two electron beams with the ion beam. In this work IPF of HD{sup +}, H{sub 3}{sup +} and HF{sup +} has been studied. In the case of HD{sup +} the result of the high resolution experiment shows quantum interferences. Analysis of the quantum oscillations leads to a new understanding of the reaction dynamics. For H{sub 3}{sup +} it was for the first time possible to distinguish different IPF channels and to detect quantum interferences in the data. Finally the IPF of HF{sup +} was investigated in an energy range, where in previous experiments no conclusive results could be obtained. (orig.)

Hoffmann, Jens

2009-01-28

185

Ionic fragmentation channels in electron collisions of small molecular ions  

International Nuclear Information System (INIS)

Dissociative Recombination (DR) is one of the most important loss processes of molecular ions in the interstellar medium (IM). Ion storage rings allow to investigate these processes under realistic conditions. At the Heidelberg test storage ring TSR a new detector system was installed within the present work in order to study the DR sub-process of ion pair formation (IPF). The new detector expands the existing electron target setup by the possibility to measure strongly deflected negative ionic fragments. At the TSR such measurements can be performed with a uniquely high energy resolution by independently merging two electron beams with the ion beam. In this work IPF of HD+, H3+ and HF+ has been studied. In the case of HD+ the result of the high resolution experiment shows quantum interferences. Analysis of the quantum oscillations leads to a new understanding of the reaction dynamics. For H3+ it was for the first time possible to distinguish different IPF channels and to detect quantum interferences in the data. Finally the IPF of HF+ was investigated in an energy range, where in previous experiments no conclusive results could be obtained. (orig.)

2009-01-01

186

Determination of molecular parameters by electron collisions and laser techniques  

International Nuclear Information System (INIS)

In this work a general procedure to study diatomic molecules in intermediate coupling scheme has been developed. This study allows to obtain expressions to calculate molecular line strengths and rotational transition intensities. These results are used in a numerical program to synthetize vibrational and rotational band spectra of any diatomic molecule. With this technique the experimental spectra of the first negative system of N_2"+ and the fist positive system of N_2 are reproduced theoretically and it is possible to deduce its electronic transition moments values by comparison. Also the method has been applied to compare the synthetized bands with the experimental spectra of the B O_u"+-- x"1?_g"+ system of Au_2 and the A"2?--- x "2? system of OH. From these comparison band intensities and electronic moments can be deduced. The branching ratio method to measure the relative spectral response in the 1100-1560 A"o=wavelength range of a vacuum uv monochromator has been used. Relative intensity of rotational lines with origine in a common upper vibrational-rotational level of Warner and Lyman systems of H_2, have been measured. Also in this work, the deexcitation of the B"3?"+(0"+_u), v'=14 level of I_2 after pulsed laser excitation has been studied. The quenching cross sections by collisions with I_2, H_2, CO_2 and CH_4 have been determin-ed. (Author)

1989-01-01

187

Large nonlinear optical rectification in atomic hexagonal layers with broken space inversion symmetry  

International Nuclear Information System (INIS)

Motivated by possible applications in optoelectronics, we consider nonlinear optical rectification (NOR) in two planar hexagonal lattice structures with broken space inversion symmetry—namely, in graphene epitaxially grown on a SiC substrate and in boronitrene (a monolayer of BN). For both structures, we calculate the second-order nonlinear optical susceptibility ?(2)(0;?, ? ?) relevant to the NOR effect and evaluate a bias voltage V0 appearing at the structure terminals under strong laser irradiation. We show that the reason for the ?(2)(0;?, ? ?) being nonvanishing in the examined structures is their sublattice (inversion) asymmetry combined with the trigonal symmetry of their ?-electron energy bands near the corners of the hexagonal Brillouin zone of those structures. In spite of being rather small, the trigonal warping of the energy bands involved is found to provide a remarkably large magnitude of the NOR susceptibility, reaching the order of 5 × 10?4 esu for the graphene/SiC overlayer system when the pump photon energy ?? approaches the bandgap energy EG (?0.26 eV) of the overlying graphene. For a graphene sample of a few microns length, irradiated by a normally incident laser beam with a relatively moderate power density of 10 kW cm?2, the corresponding optical rectification voltage V0 is estimated to be as large as several millivolts. Moreover, the sign of the voltage (i.e., its polarity) can be sharply reversed by sweeping the photon energy through the inter-?-band resonance condition ?? = EG. This frequency-controlled optical switching, if realized, will be a potent technique for graphene-based photonics and optoelectronics. (paper)

2013-10-01

188

Rectification effects in superconductors with magnetic pinning centers  

International Nuclear Information System (INIS)

We investigate the dynamics and pinning properties of vortices in superconducting Al films deposited on top of a close-packed array of Py microsized loops by electrical transport measurements. The micromagnets have an in-plane magnetic moment that can be set in different magnetic states by applying an external field parallel to the plane of the pattern. When the loops are set in the magnetic vortex-state, for which the stray field is the smallest, a weaker pinning in comparison with the polarized states (i.e. strong stray field) is observed. In addition, a clear influence of the chosen magnetic state of the Py rings on the dynamics of the vortex motion under an ac-excitations is obtained. When the magnetic elements are in the as-grown state a rectification signal which reverses sign when the field changes polarity is observed. In contrast to that, when the array of loops is magnetized the observed rectification effect is independent of the field polarity and can be reversed by reorienting the magnetization of the micromagnets

2008-04-01

189

Stereo Calibration and Rectification for Omnidirectional Multi-camera Systems  

Directory of Open Access Journals (Sweden)

Full Text Available Stereo vision has been studied for decades as a fundamental problem in the field of computer vision. In recent years, computer vision and image processing with a large field of view, especially using omnidirectional vision and panoramic images, has been receiving increasing attention. An important problem for stereo vision is calibration. Although various kinds of calibration methods for omnidirectional cameras are proposed, most of them are limited to calibrate catadioptric cameras or fish?eye cameras and cannot be applied directly to multi?camera systems. In this work, we propose an easy calibration method with closed?form initialization and iterative optimization for omnidirectional multi?camera systems. The method only requires image pairs of the 2D target plane in a few different views. A method based on the spherical camera model is also proposed for rectifying omnidirectional stereo pairs. Using real data captured by Ladybug3, we carry out some experiments, including stereo calibration, rectification and 3D reconstruction. Statistical analyses and comparisons of the experimental results are also presented. As the experimental results show, the calibration results are precise and the effect of rectification is promising.

Yanchang Wang

2012-10-01

190

Electron transfer across ?-helical peptides: Potential influence of molecular dynamics  

Science.gov (United States)

Three hydrophobic leucine-rich peptides Fc18L, Ac18L and 18LAc were prepared. These peptides are equipped with a cystein sulfhydryl group which enables the formation of thin films on gold surfaces. Using these peptides, two types of films of ?-helical peptides have been prepared, in which the redox-active peptide Fc18L is diluted by Ac18L ( SAM1) or by a mixture of Ac18L and 18LAc ( SAM2). In SAM1, the dipole moments of the peptides are aligned in the same direction, whereas in SAM2, they are opposite. Reflection absorption infrared spectroscopy (RAIRS) revealed that the peptides are more vertically oriented in SAM2 compared to those in SAM1. The interaction among the macroscopic helix dipoles gives tighter packing of the peptides in SAM2. Importantly, the electron transfer properties in the two films are significantly different, which is rationalized by differences in the molecular dynamics of the two films.

Mandal, Himadri S.; Kraatz, Heinz-Bernhard

2006-07-01

191

Electron transfer across ?-helical peptides: Potential influence of molecular dynamics  

International Nuclear Information System (INIS)

Three hydrophobic leucine-rich peptides Fc18L, Ac18L and 18LAc were prepared. These peptides are equipped with a cystein sulfhydryl group which enables the formation of thin films on gold surfaces. Using these peptides, two types of films of ?-helical peptides have been prepared, in which the redox-active peptide Fc18L is diluted by Ac18L (SAM1) or by a mixture of Ac18L and 18LAc (SAM2). In SAM1, the dipole moments of the peptides are aligned in the same direction, whereas in SAM2, they are opposite. Reflection absorption infrared spectroscopy (RAIRS) revealed that the peptides are more vertically oriented in SAM2 compared to those in SAM1. The interaction among the macroscopic helix dipoles gives tighter packing of the peptides in SAM2. Importantly, the electron transfer properties in the two films are significantly different, which is rationalized by differences in the molecular dynamics of the two films

2006-07-11

192

Inelastic Scattering of Low-Energy Electrons by Molecular Oxygen  

Science.gov (United States)

By means of a crossed-beam technique, we have measured electron energy loss spectra for gaseous phase molecular oxygen. The scattering angles of the measurements were from 12 through 156^circ, in 12^circ increments. A variety of electron impact energies in the range 5 through 50 eV were employed. The results of our measurements are differential cross sections for vibrational excitation, excitation of the states comprising the Schumann-Runge continuum, and excitation of the longest and second bands. Using these, we computed integrated cross sections. For the Schumann-Runge continuum, Franck-Condon region potential -energy curves were also obtained. The vibrational-excitation cross sections exhibit a resonance just below 10 eV impact. Additionally, their angular distributions possess pronounced P-wave character near this impact energy. Based on the available information regarding the O_sp{2}{-} ion, it seems the only candidate states of this ion which could be responsible are the A^2 Pi_{u}(v) and a^4 sum_sp{u}{-}(v) states; the latter seems more likely. Via computerized least-square analysis, the Schumann -Runge continuum spectra were decomposed into contributions from the 1^3Pi_{g}(v) and B^3sum_sp{u }{-}(v) states, and one unidentified excitation. Cross sections and linear Franck-Condon region potential-energy curves were obtained for the 1 ^3Pi_{g}(v) and B ^3sum_sp{u}{-}(v) states were obtained. While the origin of the unidentified excitation is unclear, it seems most likely a computational artifact resulting from some combination of a pertubation to the B^3sum_sp {u}{-}(v) state's potential -energy curve and a nonconstant moment for the X ^3sum_sp{g}{-}>=ts B^3sum_sp{u}{-}(v) transition. Finally, we have measured cross sections for excitation of the longest and second bands. Substantial D-wave character was apparent in the angular distributions for these cross sections. Additionally, the angular distributions indicate that both excitations are composite in nature, arising from the excitation of at least two electronic states. It is not possible to conclusively identify these states, but theoretical predictions, coupled with the notion of perturbations to the nearby B^3sum _sp{u}{-}(v) suggest that at least one of the states has ^3sum _sp{u}{-} symmetry.

Sweeney, Christopher John

1995-01-01

193

First-Principles Based Matrix-Green's Function Approach to Molecular Electronic Devices General Formalism  

CERN Multimedia

Transport in molecular electronic devices is different from that in semiconductor mesoscopic devices in two important aspects: (1) the effect of the electronic structure and (2) the effect of the interface to the external contact. A rigorous treatment of molecular electronic devices will require the inclusion of these effects in the context of an open system exchanging particle and energy with the external environment. This calls for combining the theory of quantum transport with the theory of electronic structure starting from the first-principles. We present a rigorous yet tractable matrix Green's function approach for studying transport in molecular electronic devices, based on the Non-Equilibrium Green's Function Formalism of quantum transport and the density-functional theory of electronic structure using local orbital basis sets. By separating the device rigorously into the molecular region and the contact region, we can take full advantage of the natural spatial locality associated with the metallic sc...

Xue, Y; Ratner, M A; Xue, Yongqiang; Datta, Supriyo; Ratner, Mark A.

2001-01-01

194

Efficient terahertz generation by optical rectification at 1035 nm.  

Science.gov (United States)

We demonstrate efficient generation of THz pulses by optical rectification of 1.03 um wavelength laser pulses in LiNbO3 using tilted pulse front excitation for velocity matching between the optical and THz fields. Pulse energies of 100 nJ with a spectral bandwidth of up to 2.5 THz were obtained at a pump energy of 400 uJ and 300 fs pulse duration. This conversion efficiency of 2.5x10(-4) was an order of magnitude higher than that obtained with collinear optical recitification in GaP, and far higher still than that measured using ZnTe in an optimized geometry. Using a simple model we demonstrate that two- and three-photon absorption strongly limit the THz generation efficiency at high pump fluences in ZnTe and GaP. PMID:19547531

Hoffmann, Matthias C; Yeh, Ka-Lo; Hebling, János; Nelson, Keith A

2007-09-01

195

Computational studies of shape rectification in directed self-assembly  

Science.gov (United States)

We use self-consistent field theory (SCFT) to study shape rectification in overlapped cylindrical and non-cylindrical prepatterns. Specifically, we examine the potential of directed self-assembly (DSA) of block copolymers to not only reduce critical dimensions relative to the template, but also repair defects in the guiding prepatterns and produce defectfree contact holes. In our study over a wide range of prepattern dimensions, we found that defects in the central minorblock domain arise with decreasing center-to-center distance of the prepattern. Increasing the minor-block fraction in the block copolymer was observed to remove some of the defects. We also studied the effect of adding homopolymer to the block copolymer melt and show how blends can successfully eliminate defects and increase the range of the process window relative to the neat diblock case without influencing domain properties such as the critical dimension and the hole-to-hole distance.

Iwama, Tatsuhiro; Laachi, Nabil; Delaney, Kris T.; Kim, Bongkeun; Fredrickson, Glenn H.

2014-03-01

196

Energy level alignment and electron transport through metal/organic contacts. From interfaces to molecular electronics  

Energy Technology Data Exchange (ETDEWEB)

A new calculational approach to describing metal/organic interfaces. A valuable step towards a better understanding of molecular electronics. Nominated as an outstanding contribution by the Autonomous University of Madrid. In recent years, ever more electronic devices have started to exploit the advantages of organic semiconductors. The work reported in this thesis focuses on analyzing theoretically the energy level alignment of different metal/organic interfaces, necessary to tailor devices with good performance. Traditional methods based on density functional theory (DFT), are not appropriate for analyzing them because they underestimate the organic energy gap and fail to correctly describe the van der Waals forces. Since the size of these systems prohibits the use of more accurate methods, corrections to those DFT drawbacks are desirable. In this work a combination of a standard DFT calculation with the inclusion of the charging energy (U) of the molecule, calculated from first principles, is presented. Regarding the dispersion forces, incorrect long range interaction is substituted by a van der Waals potential. With these corrections, the C60, benzene, pentacene, TTF and TCNQ/Au(111) interfaces are analyzed, both for single molecules and for a monolayer. The results validate the induced density of interface states model.

Abad, Enrique

2013-07-01

197

27 CFR 1.82 - Acquiring or receiving distilled spirits in bulk for redistillation, processing, rectification...  

Science.gov (United States)

...rectification, warehousing, or warehousing and bottling. 1.82 Section 1.82 Alcohol, Tobacco Products and Firearms ALCOHOL...Bottling of Distilled Spirits Bulk Sales and Bottling § 1.82 Acquiring or receiving distilled spirits in...

2009-04-01

198

How the geometric configuration and the surface charge distribution influence the ionic current rectification in nanopores  

International Nuclear Information System (INIS)

Asymmetrical properties of ion transport have been found in single conical nanopores and partly charged nano-channels. Recently, nanofluidic diodes based on this novel phenomenon have been fabricated. To generally understand the mechanism of the ionic current rectification, we study the ionic electric behaviours in several kinds of nanopores based on Poisson-Nernst-Planck equations. The calculated results show that for a partly charged nanopore, the geometry of the uncharged section, which might have been overlooked previously, has a substantial influence on current rectification. In addition, surface charge distribution is also an influential factor in current rectification. In particular, for a long homogeneously charged conical nanopore, the electrical and geometric properties of the section near the nanopore tip with a length of hundreds of nanometres are mainly responsible for the ionic current rectification. This result is consistent with the results of recent experiments on nanofluidic diodes

2007-11-21

199

How the geometric configuration and the surface charge distribution influence the ionic current rectification in nanopores  

Energy Technology Data Exchange (ETDEWEB)

Asymmetrical properties of ion transport have been found in single conical nanopores and partly charged nano-channels. Recently, nanofluidic diodes based on this novel phenomenon have been fabricated. To generally understand the mechanism of the ionic current rectification, we study the ionic electric behaviours in several kinds of nanopores based on Poisson-Nernst-Planck equations. The calculated results show that for a partly charged nanopore, the geometry of the uncharged section, which might have been overlooked previously, has a substantial influence on current rectification. In addition, surface charge distribution is also an influential factor in current rectification. In particular, for a long homogeneously charged conical nanopore, the electrical and geometric properties of the section near the nanopore tip with a length of hundreds of nanometres are mainly responsible for the ionic current rectification. This result is consistent with the results of recent experiments on nanofluidic diodes.

Wang Xinwei [State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871 (China); Xue Jianming [State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871 (China); Wang Lin [State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871 (China); Guo Wei [State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871 (China); Zhang Weiming [State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871 (China); Wang Yugang [State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871 (China); Liu Qi [Center for Microfluidics and Nanotechnology, Peking University, Beijing 100871 (China); Ji Hang [Center for Microfluidics and Nanotechnology, Peking University, Beijing 100871 (China); Ouyang Qi [Center for Microfluidics and Nanotechnology, Peking University, Beijing 100871 (China)

2007-11-21

200

Study on Industrial Rectification Process of Cadmium by Means of Radioactive Tracers.  

Science.gov (United States)

Methods of cadmium production and principles of a rectification technique used in Poland for rectifying cadmium materials obtained in zinc metallurgy have been reviewed. Studies on the separation of cadmium from zinc and on the behaviour of arsenic under ...

K. Akerman M. Brafman H. Fik M. Nowak K. Kruszewski

1964-01-01

 
 
 
 
201

Dissipative Effects in the Electronic Transport through DNA Molecular Wires  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We investigate the influence of a dissipative environment which effectively comprises the effects of counterions and hydration shells, on the transport properties of short DNA wires. Their electronic structure is captured by a tight-binding model which is embedded in a bath consisting of a collection of harmonic oscillators. Without coupling to the bath a temperature independent gap in the electronic spectrum opens in the electronic spectrum. Upon allowing for electron-bath interaction the ga...

Gutie?rrez, Rafael; Mandal, Sudeep; Cuniberti, Gianaurelio

2005-01-01

202

Electron spin resonance study on lignin molecular mobility  

International Nuclear Information System (INIS)

Molecular mobility of grinded wood lignin is studied in the wide temperature range using the recombination-kinetic method. Macroradicals formed during low-temperature ?-radiolysis of lignin, are used as a molecular probe. Analysis of curves of stage-by-stage heating of specimens confirms microheterogeneity of lignin

1981-01-01

203

Landauer Theory, Inelastic Scattering and Electron Transport in Molecular Wires  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this paper we address the topic of inelastic electron scattering in mesoscopic quantum transport. For systems where only elastic scattering is present, Landauer theory provides an adequate description of transport that relates the electronic current to single-particle transmission and reflection probabilities. A formalism proposed recently by Bonca and Trugman facilitates the calculation of the one-electron transmission and reflection probabilities for inelastic processes...

Emberly, Eldon G.; Kirczenow, George

1999-01-01

204

Dependence of molecular hydrogen formation in water on scavengers of the precursor to the hydrated electron  

Energy Technology Data Exchange (ETDEWEB)

Early studies on the radiolysis of water suggested a wide variety of precursors, and mechanisms, for the formation of the observed yield of molecular hydrogen. Molecular hydrogen yields have been measured in the {gamma} radiolysis of aqueous solutions with a wide variety of scavengers of the hydrated electron and its precursors. A decrease in molecular hydrogen yield with increasing scavenging capacity of the hydrated electron is found with all solutes. Scavengers with particularly high rate coefficients for reaction with the precursors to the hydrated electron compared to the hydrated electron, such as selenate and to a lesser extent molybdate, show a more rapid decrease in hydrogen yields with increasing scavenging capacity than is observed with the other solutes. The yield of molecular hydrogen is better parameterized by the scavenging capacity for the precursors to the hydrated electron than by the scavenging capacity for the hydrated electron. Good scavengers of precursors to the hydrated electrons do not exhibit a nonscavengable hydrogen yield in the high scavenging capacity limit. These results suggest that the previously accepted nonscavengable yield of molecular hydrogen is due to precursors of the hydrated electron and it can be lowered with appropriate scavengers.

Pastina, B. [Univ. of Notre Dame, IN (United States). Radiation Lab.]|[Commissariat a l`Energie Atomique, Gif sur Yvette (France); LaVerne, J.A.; Pimblott, S.M. [Univ. of Notre Dame, IN (United States). Radiation Lab.

1999-07-22

205

Dependence of molecular hydrogen formation in water on scavengers of the precursor to the hydrated electron  

International Nuclear Information System (INIS)

Early studies on the radiolysis of water suggested a wide variety of precursors, and mechanisms, for the formation of the observed yield of molecular hydrogen. Molecular hydrogen yields have been measured in the ? radiolysis of aqueous solutions with a wide variety of scavengers of the hydrated electron and its precursors. A decrease in molecular hydrogen yield with increasing scavenging capacity of the hydrated electron is found with all solutes. Scavengers with particularly high rate coefficients for reaction with the precursors to the hydrated electron compared to the hydrated electron, such as selenate and to a lesser extent molybdate, show a more rapid decrease in hydrogen yields with increasing scavenging capacity than is observed with the other solutes. The yield of molecular hydrogen is better parameterized by the scavenging capacity for the precursors to the hydrated electron than by the scavenging capacity for the hydrated electron. Good scavengers of precursors to the hydrated electrons do not exhibit a nonscavengable hydrogen yield in the high scavenging capacity limit. These results suggest that the previously accepted nonscavengable yield of molecular hydrogen is due to precursors of the hydrated electron and it can be lowered with appropriate scavengers

1999-07-22

206

Molecular Dynamics and Electron Density Studies of Siderophores and Peptides.  

Science.gov (United States)

The dissertation comprises three separate studies of siderophores and peptides. In the first of these studies the relative potential energies for a series of diastereomers of a siderophore neocoprogen I are evaluated with molecular mechanics force field methods. Charges on the hydroxamate moiety are determined with a synthetic model siderophore compound using valence population refinements, and alternatively, with the theoretical ab initio/ESP calculations. The single diastereomer found in the crystal structure is among four characterized by the low potential energy, while prevalence of Delta vs. Lambda configuration about the iron is found to be a property of the entire series. In the second study the crystal structure of a ferrichrome siderophore ferrirhodin is reported. The crystal structure conformation of the molecular backbone as well as the iron coordination geometry compare well with other ferrichrome structures. The differences between the acyl groups of ferrirubin and ferrirhodin are explored using the methods of molecular mechanics. The third study a 300 ps, 300 K, in vacuo molecular dynamics simulation of didemnin A and B yields distinct molecular conformers, which are different from the one found in the crystal structure or modeled in solution, using the Nuclear Overhauser Effect data. Evaluations of the relative potential energy are performed with short 10 ps simulations in solution. Didemnins are natural depsipeptides isolated from a Caribbean tunicate and characterized by particularly potent antiproliferative and immunomodulatory activity. Conformationally rigid and flexible regions of the molecule are described. A short review of the molecular mechanics methodology is given in the introduction.

Fidelis, Krzysztof Andrzej

1990-08-01

207

An Electronically Non-Adiabatic Generalization of Ring Polymer Molecular Dynamics  

CERN Document Server

In this thesis I generalize Ring Polymer Molecular Dynamics (RPMD) rate theory to electronically non-adiabatic systems, followed by application to two one-dimensional curve crossing models and a multidimensional spin-boson model.

Hele, Timothy J H

2013-01-01

208

On the variations of molecular rotational states due to electron impact transitions  

International Nuclear Information System (INIS)

The author propose a new approach (which is not based on adiabatic approximation) allowing to describe uniformly all know experimental data on the distribution of intensity in a fine structure of electron molecular spectra

1991-01-01

209

Kinetic description of a dynamically coupled free-electron- and molecular gas laser  

International Nuclear Information System (INIS)

The parametric interaction of longitudinal and transverse waves is studied for a system of a molecular medium and a relativistic electron beam. The system offers interesting possibilities for generation of coherent radiation. (Auth.)

1982-06-15

210

Analyzing the electric response of molecular conductors using "electron deformation" orbitals and occupied-virtual electron transfer.  

Science.gov (United States)

The concept of "electron deformation orbitals" (EDOs) is used to investigate the electric response of conducting metals and oligophenyl chains. These orbitals and their eigenvalues are obtained by diagonalization of the deformation density matrix (difference between the density matrices of the perturbed and unperturbed systems) and can be constructed as linear combinations of the unperturbed molecular orbitals within "frozen geometry" conditions. This form of the EDOs allows calculating the part of the electron deformation density associated to an effective electron transfer from occupied to virtual orbitals (valence to conduction band electron transfer in the band model of conductivity). It is found that the "electron deformation" orbitals pair off, displaying the same eigenvalue but opposite sign. Each pair represents an amount of accumulation/depletion of electron charge at different molecular regions. In the oligophenyl systems investigated only one pair contributes effectively to the charge flow between molecular ends, resulting from the promotion of electrons from occupied orbitals to close in energy virtual orbitals of appropriate symmetry and overlapping. Analysis of this pair along explains the differences in conductance of olygophenyl chains based on phenyl units. © 2014 Wiley Periodicals, Inc. PMID:24676839

Mandado, Marcos; Ramos-Berdullas, Nicolás

2014-06-30

211

Flexible Fitting of Atomic Structures into Electron Microscopy Maps Using Molecular Dynamics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A novel method to flexibly fit atomic structures into electron microscopy (EM) maps using molecular dynamics simulations is presented. The simulations incorporate the EM data as an external potential added to the molecular dynamics force field, allowing all internal features present in the EM map to be used in the fitting process, while the model remains fully flexible and stereochemically correct. The molecular dynamics flexible fitting (MDFF) method is validated for available crystal struct...

2008-01-01

212

Classical molecular dynamics simulation of the photoinduced electron transfer dynamics of plastocyanin.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Classical molecular dynamics simulations are used to investigate the nuclear motions associated with photoinduced electron transfer in plastocyanin. The blue copper protein is modeled using a molecular mechanics potential; potential parameters for the copper-protein interactions are determined using an x-ray crystallographic structure and absorption and resonance Raman spectra. Molecular dynamics simulations yield a variety of information about the ground (oxidized) and optically excited (cha...

Ungar, L. W.; Scherer, N. F.; Voth, G. A.

1997-01-01

213

Proceedings of the 2. Latin American Meeting on Atomic, Molecular and Electronic Collisions  

International Nuclear Information System (INIS)

Annals of the II Latin American Meeting on Atomic, Molecular and Electronic Collisions. Over than 50 people from Latin America participated on this meeting giving talks on different subjects (theoretical and experimental), related to atomic and molecular physics, as well as, nuclear physics. (A.C.A.S.)

1988-09-25

214

Angular distribution of molecular K-shell Auger electrons: Spectroscopy of photoabsorption anisotropy  

International Nuclear Information System (INIS)

The angular distribution of Auger electrons emitted in the decay of molecular K-shell vacancies created by photoabsorption is predicted to be a direct probe of the anisotropy of molecular photoabsorption. The sigma?? discrete absorption of the sigma?sigma f-wave shape resonance in N_2 and CO are given as examples

1980-10-27

215

Quantum Dynamical Approach to Electron Transfers in DNA-Molecular Nanowires  

International Nuclear Information System (INIS)

We numerically investigate electron transfers in nanowires which consist of deoxyribonucleic acid (DNA) molecules (up to five base pairs for double-strands and seven bases for single-strands) by quantum dynamical calculations. DNA molecules are applied to organic nanodevices and the performance depends on electronic transfer properties. Combining quantum chemical molecular-orbital calculations and stochastic mechanics, we provide an analyzing method of quantum dynamical electron motions. From one-electron wavefunctions or molecular orbitals, we calculate some dynamical properties, such as mean-square displacement and self-diffusion coefficients relating with electron mobility. Our calculation suggests that the electron transfers through the double-strands of GC base pairs while the electrons are localized in the double-strands of AT base pairs nor the single-strands of G bases

2007-04-01

216

Quantum Dynamical Approach to Electron Transfers in DNA-Molecular Nanowires  

Energy Technology Data Exchange (ETDEWEB)

We numerically investigate electron transfers in nanowires which consist of deoxyribonucleic acid (DNA) molecules (up to five base pairs for double-strands and seven bases for single-strands) by quantum dynamical calculations. DNA molecules are applied to organic nanodevices and the performance depends on electronic transfer properties. Combining quantum chemical molecular-orbital calculations and stochastic mechanics, we provide an analyzing method of quantum dynamical electron motions. From one-electron wavefunctions or molecular orbitals, we calculate some dynamical properties, such as mean-square displacement and self-diffusion coefficients relating with electron mobility. Our calculation suggests that the electron transfers through the double-strands of GC base pairs while the electrons are localized in the double-strands of AT base pairs nor the single-strands of G bases.

Sakamoto, S; Ohmachi, Y; Tomiya, M [Department of Materials and Life Science, Seikei University, Musashino, Tokyo 180-8633 (Japan)

2007-04-15

217

THz generation from InN films due to destructive interference between optical rectification and photocurrent surge  

International Nuclear Information System (INIS)

We have investigated the characteristics of THz generation including the dependence of the output power and polarization on the incident angle and pump polarization from two series of InN films grown by plasma-assisted molecular beam epitaxy (PAMBE) and metal organic chemical vapor deposition (MOCVD), respectively. Following the analyses of our results, we have attributed the mechanism of the THz generation from these InN samples to the destructive interference between optical rectification and photocurrent surge. Under the average intensity of 176 W cm?2 for the subpicosecond laser pulses at 782 nm, the THz output powers were measured to be as high as 2.4 µW from the 220 nm InN film, with the output frequencies spanning the band from 300 GHz to 2.5 THz

2010-01-01

218

Electronic read-out of a single nuclear spin using a molecular spin transistor  

Science.gov (United States)

Thanks to recent advances of nanofabrication techniques, molecular electronics devices can address today the ultimate probing of electronic transport flowing through a single molecule. Not only this electronic current can show signatures of the molecular quantum levels but it can also detect the magnetic state of the molecule. As a consequence, an entirely novel research field called molecular spintronics in which quantum magnetism of molecular systems can be interfaced to nanoelectronics is now emerging. One of the recent challenges of this field was to probe by this current, not the only spin state of an electron, but the state of a single nuclear spin. Such an achievement was experimentally unimaginable a few years ago. Indeed, the magnetic signal carried by a single nuclear spin is a thousand times less than that of a single electron spin ... Using a Single Molecular Magnet (TbPc2) as a molecular spin transistor in a three terminals configuration, the experiment consists in measuring the current changes when ones sweep the external magnetic field applied to the molecule. When the magnetic spin of the molecule changes its quantum state, a change of current is recorded. Because of the well-defined relationship that exists between the electron spin and nuclear spin carried by the nuclei of the Terbium atom, it is possible to perform the electronic read-out of the electronic spin state which, in turn give information on the state of a single nuclear spin. Application of this effect for quantum information manipulation and storage can be envisioned, as the observation of energy level lifetimes on the order of tens of seconds opens the way to coherent manipulations of a single nuclear spin.[4pt] Reference:[0pt] ``Electronic read-out of a single nuclear spin using a molecular spin transistor,'' R. Vincent, S. Klyatskaya, M. Ruben, W. Wernsdorfer, F. Balestro, Nature, Vol. 488, p.357, (2012).

Balestro, Franck

2013-03-01

219

Heat flux distribution and rectification of complex networks  

Energy Technology Data Exchange (ETDEWEB)

It was recently found that the heterogeneity of complex networks can enhance transport properties such as epidemic spreading, electric energy transfer, etc. A trivial deduction would be that the presence of hubs in complex networks can also accelerate the heat transfer although no concrete research has been done so far. In the present study, we have studied this problem and have found a surprising answer: the heterogeneity does not favor but prevents the heat transfer. We present a model to study heat conduction in complex networks and find that the network topology greatly affects the heat flux. The heat conduction decreases with the increase of heterogeneity of the network caused by both degree distribution and the clustering coefficient. Its underlying mechanism can be understood by using random matrix theory. Moreover, we also study the rectification effect and find that it is related to the degree difference of the network, and the distance between the source and the sink. These findings may have potential applications in real networks, such as nanotube/nanowire networks and biological networks.

Liu Zonghua [Institute of Theoretical Physics and Department of Physics, East China Normal University, Shanghai 200062 (China); Wu Xiang; Yang Huijie; Li Baowen [Department of Physics and Centre for Computational Science and Engineering, National University of Singapore, 117546 Singapore (Singapore); Gupte, Neelima [Department of Physics, Indian Institute of Technology, Madras, Chennai 600036 (India)], E-mail: zhliu@phy.ecnu.edu.cn, E-mail: phylibw@nus.edu.sg

2010-02-15

220

Heat flux distribution and rectification of complex networks  

International Nuclear Information System (INIS)

It was recently found that the heterogeneity of complex networks can enhance transport properties such as epidemic spreading, electric energy transfer, etc. A trivial deduction would be that the presence of hubs in complex networks can also accelerate the heat transfer although no concrete research has been done so far. In the present study, we have studied this problem and have found a surprising answer: the heterogeneity does not favor but prevents the heat transfer. We present a model to study heat conduction in complex networks and find that the network topology greatly affects the heat flux. The heat conduction decreases with the increase of heterogeneity of the network caused by both degree distribution and the clustering coefficient. Its underlying mechanism can be understood by using random matrix theory. Moreover, we also study the rectification effect and find that it is related to the degree difference of the network, and the distance between the source and the sink. These findings may have potential applications in real networks, such as nanotube/nanowire networks and biological networks.

2010-02-01

 
 
 
 
221

Molecular electronic junction transport : some pathways and some ideas  

DEFF Research Database (Denmark)

Whenasinglemolecule,oracollectionofmolecules,isplacedbetween two electrodes and voltage is applied, one has a molecular transport junction. We discuss such junctions, their properties, their description, and some of their applications. The discussion is qualitative rather than quantitative, and focuses on mechanism, structure/function relations, regimes and mechanisms of transport, some molecular regularities, and some substantial challenges facing the field. Because there are many regimes and mechanisms in transport junctions, we will discuss time scales, geometries, and inelastic scattering methods for trying to determine the properties of molecules within these junctions. Finally, we discuss some device applications, some outstanding problems, and some future directions.

Solomon, Gemma C.; Herrmann, Carmen

2012-01-01

222

Density-functional calculations of molecular electron affinities  

Directory of Open Access Journals (Sweden)

Full Text Available Electron affinities of twelve small molecules were calculated by density functional theory using two different functionals(B88-P86 and B3LYP combined with three different basis sets(6-31++G** ; 6-311++G** ; aug-cc-pVTZ. Outer valence Green?s function method is also employed for calculation of electron affinities of the molecules. The two most efficient approaches were found to be the combination of (1B88-P86 with 6-31++G** basis set and (2B3LYP with 6-31++G**. The two approaches were employed to calculate electron affinities of some medium size molecules.

Takahata Yuji

1999-01-01

223

Renormalization of Molecular Electronic Levels at Metal-Molecule Interfaces  

CERN Document Server

The electronic structure of benzene on graphite (0001) is computed using the GW approximation for the electron self-energy. The benzene quasiparticle energy gap is predicted to be 7.2 eV on graphite, substantially reduced from its calculated gas-phase value of 10.5 eV. This decrease is caused by a change in electronic correlation energy, an effect completely absent from the corresponding Kohn-Sham gap. For weakly-coupled molecules, this correlation energy change is seen to be well described by a surface polarization effect. A classical image potential model illustrates trends for other conjugated molecules on graphite.

Neaton, J B; Louie, S G; Hybertsen, Mark S.; Louie, Steven G.

2006-01-01

224

Laser-assisted electron diffraction for femtosecond molecular imaging  

Science.gov (United States)

We report the observation of laser-assisted electron diffraction (LAED) through the collision of 1 keV electrons with gas-phase CCl4 molecules in a femtosecond near-infrared laser field. In the angular distribution of the scattered electrons with the energy shifts of ±??, we observed clear diffraction patterns which reflect the geometrical structure of the molecules at the moment of laser irradiation. Our results demonstrate that ultrafast nuclear dynamics of molecules can be probed by LAED with the high temporal (<10 fs) and spatial (˜0.01 Å) resolutions.

Morimoto, Yuya; Kanya, Reika; Yamanouchi, Kaoru

2014-02-01

225

Ab initio analysis of electron-phonon coupling in molecular devices  

CERN Multimedia

We report first principles analysis of electron-phonon coupling in molecular devices under external bias voltage and during current flow. Our theory and computational framework are based carrying out density functional theory within the Keldysh nonequilibrium Green's function formalism. We analyze which molecular vibrational modes are most relevant to charge transport under nonequilibrium conditions. For a molecular tunnel junction of a 1,4-benzenedithiolate molecule contacted by two leads, the low-lying modes of the vibration are found to be most important. As a function of bias voltage, the electron-phonon coupling strength can change drastically while the vibrational spectrum changes at a few percent level.

Sergueev, N; Guo, H; Guo, Hong

2005-01-01

226

Iterative approach to the Schwinger variational principle applied to electron--molecular-ion collisions  

International Nuclear Information System (INIS)

We present a study of electron--molecular-ion collisions. The scattering equations are solved using an iterative approach to the Schwinger variational principle. These equations are formulated using the Coulomb Green's function to properly treat the long-range Coulomb tail of the molecular-ion potential. We apply this approach to electron--hydrogen-molecular-ion collisions in the static-exchange approximation. We obtain elastic differential cross sections, and also use the continuum states from these calculations to compute the photoionization cross section of the hydrogen molecule. The iterative method used here converged rapidly in all calculations performed

1981-01-01

227

Tight binding description of the electronic response of a molecular device to an applied voltage  

CERN Multimedia

We analyze the effect of an external electric field on the electronic structure of molecules which have been recently studied as molecular wires or diodes. We use a self-consistent tight binding technique which provides results in good agreement with ab initio calculations and which may be applied to a large number of molecules. The voltage dependence of the molecular levels is mainly linear with slopes intimately related to the electronic structure of the molecules. We emphasize that the response to the applied voltage is an important feature which governs the behavior of a molecular device.

Krzeminski, Christophe; Allan, Guy; 10.1021/jp011263y

2011-01-01

228

Molecular double core-hole electron spectroscopy for chemical analysis  

CERN Multimedia

We explore the potential of double core hole electron spectroscopy for chemical analysis in terms of x-ray two-photon photoelectron spectroscopy (XTPPS). The creation of deep single and double core vacancies induces significant reorganization of valence electrons. The corresponding relaxation energies and the interatomic relaxation energies are evaluated by CASSCF calculations. We propose a method how to experimentally extract these quantities by the measurement of single and double core-hole ionization potentials (IPs and DIPs). The influence of the chemical environment on these DIPs is also discussed for states with two holes at the same atomic site and states with two holes at two different atomic sites. Electron density difference between the ground and double core-hole states clearly shows the relaxations accompanying the double core-hole ionization. The effect is also compared with the sensitivity of single core hole ionization potentials (IPs) arising in single core hole electron spectroscopy. We have ...

Tashiro, Motomichi; Fukuzawa, Hironobu; Ueda, Kiyoshi; Buth, Christian; Kryzhevoi, Nikolai V; Cederbaum, Lorenz S

2010-01-01

229

Electronic shells or molecular orbitals : photoelectron spectra of Agn- clusters  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Photoelectron spectra of Ag - n clusters with n=1–21 recorded at different photon energies (hnu=4.025, 4.66, 5.0, and 6.424 eV) are presented. Various features in the spectra of Ag - 2–Ag - 9 can be assigned to electronic transitions predicted from quantum chemical ab initio calculations. While this comparison with the quantum chemical calculations yields a detailed and quantitative understanding of the electronic structure...

Handschuh, Haiko; Cha, Chia-yen; Bechthold, Paul S.; Gantefo?r, Gerd; Eberhardt, Wolfgang

1995-01-01

230

Porphyrins as Molecular Electronic Components of Functional Devices  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The proposal that molecules can perform electronic functions in devices such as diodes, rectifiers, wires, capacitors, or serve as functional materials for electronic or magnetic memory, has stimulated intense research across physics, chemistry, and engineering for over 35 years. Because biology uses porphyrins and metalloporphyrins as catalysts, small molecule transporters, electrical conduits, and energy transducers in photosynthesis, porphyrins are an obvious class of molecules to investig...

2010-01-01

231

Arylthio-substituted coronenes as tailored building blocks for molecular electronics.  

Science.gov (United States)

The electron transport through molecules in molecular devices is typically influenced by the nature of the interfaces with the contacting electrodes and by the interactions between neighbouring molecules. It is a major goal of molecular electronics to adjust the electronic function of a molecular device by tailoring the intrinsic molecular properties and the interfacial and intermolecular interactions. Here, we report on the tunability of the electronic properties of coronene derivatives, namely dodecakis(arylthio)coronenes (DATCs), which are found to exhibit a three-dimensional aromatic system. Scanning tunnelling microscopy (STM), spectroscopy (STS) and simulations based on the density functional theory (DFT) are employed to characterize the structural and electronic properties of these molecules deposited on Au(111) surfaces. It is shown that modifications of the peripheral aryl-groups allow us to specifically affect the self-assembly and the charge transport characteristics of the molecules. Molecular assemblies like supramolecular wires with highly delocalized orbitals and single molecules with molecular "quantum dot" characteristics are obtained in this way. PMID:22193370

Kowalzik, Peter; Atodiresei, Nicolae; Gingras, Marc; Caciuc, Vasile; Schnaebele, Nicolas; Raimundo, Jean-Manuel; Blügel, Stefan; Waser, Rainer; Karthäuser, Silvia

2012-02-01

232

Two-center interference effects on the electron capture process by alpha particles from molecular hydrogens  

Energy Technology Data Exchange (ETDEWEB)

The single-electron capture process in the collision of fast alpha particles with hydrogen molecules is treated using the first-order Born approximation with correct boundary conditions. The results are obtained by considering both the inter-nuclear and nuclear-electronic interactions and by employing a Hartree-Fock molecular wave function. Double differential cross sections are evaluated for the electron capture from a molecular target with a fixed orientation. In the fixed-nuclei approximation, the differential cross sections are calculated for an equally-weighted averaging over all molecular orientations. The interference patterns, due to the scattering from two atomic centers, are apparent in different forms both in the double differential cross sections and in the cross sections as a function of the angle between the molecular axis and the incident direction. Integrated cross sections are calculated and compared with other theoretical and experimental results.

Ghanbari-Adivi, E. [Physics Department and Isfahan Quantum-Optics Group (IQOG), University of Isfahan, Hezar Jerib Street, Isfahan 8174673441 (Iran, Islamic Republic of)], E-mail: ghanbari@phys.ui.ac.ir

2009-10-01

233

Measuring the Density of a Molecular Cluster Injector via Visible Emission from an Electron Beam  

International Nuclear Information System (INIS)

A method to measure the density distribution of a dense hydrogen gas jet is presented. A Mach 5.5 nozzle is cooled to 80K to form a flow capable of molecular cluster formation. A 250V, 10mA electron beam collides with the jet and produces H? emission that is viewed by a fast camera. The high density of the jet, several 1016cm-3, results in substantial electron depletion, which attenuates the H? emission. The attenuated emission measurement, combined with a simplified electron-molecule collision model, allows us to determine the molecular density profile via a simple iterative calculation.

2010-01-01

234

Measuring the Density of a Molecular Cluster Injector via Visible Emission from an Electron Beam  

Energy Technology Data Exchange (ETDEWEB)

A method to measure the density distribution of a dense hydrogen gas jet is pre- sented. A Mach 5.5 nozzle is cooled to 80K to form a flow capable of molecular cluster formation. A 250V, 10mA electron beam collides with the jet and produces H? emission that is viewed by a fast camera. The high density of the jet, several 1016cm?3, results in substantial electron depletion, which attenuates the H? emission. The attenuated emission measurement, combined with a simplified electron-molecule collision model, allows us to determine the molecular density profile via a simple iterative calculation.

D.P. Lundberg, R. Kaita, R. Majeski, and D.P. Stotler

2010-06-28

235

The Quantified NTO Analysis for the Electronic Excitations of Molecular Many-Body Systems  

CERN Multimedia

We show that the origin of electronic transitions of molecular many-body systems can be revealed by a quantified natural transition orbitals (QNTO) analysis and the electronic excitations of the total system can be mapped onto a standard orbitals set of a reference system. We further illustrate QNTO on molecular systems by studying the origin of electronic transitions of DNA moiety, thymine and thymidine. This QNTO analysis also allows us to assess the performance of various functionals used in time-dependent density functional response theory.

Li, Jian-Hao; Guo, Guang-Yu; Hayashi, Michitoshi

2011-01-01

236

Intra-molecular electron transfer and electric conductance via sequential hopping: Unified theoretical description  

International Nuclear Information System (INIS)

The relation between intra-molecular electron transfer in the donor-bridge-acceptor system and zero-bias conductance of the same bridge in the metal-molecule-metal junction is analyzed for the sequential hopping regime of both processes. The electron transfer rate and molecular conductance are expressed in terms of rates characterizing each individual step of electron motion. Based on the results obtained, we derive the analytical expression that relates these two quantities in the general case of the energy landscape governing hopping transport

2005-01-01

237

Probing localization and mobility of an excess electron in a-Si by quantum molecular dynamics  

International Nuclear Information System (INIS)

The behavior of an excess electron in a-Si is studied over a wide temperature range using the quantum-molecular-dynamics approach. The electron is found to be localized in a nearly spherical void of radius ?3 A, and is surrounded by a ring of eight Si atoms. The simulation results for the electron mobility are in good agreement with the time-of-flight measurements

1992-04-15

238

Simultaneous measurements of electronic conduction and Raman response in molecular junctions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Electronic conduction through single molecules is affected by the molecular electronic structure as well as by other information that is extremely difficult to assess, such as bonding geometry and chemical environment. The lack of an independent diagnostic technique has long hampered single-molecule conductance studies. We report simultaneous measurement of the conductance and the Raman spectra of nanoscale junctions used for single-molecule electronic experiments. Blinking ...

Ward, Daniel R.; Halas, Naomi J.; Ciszek, Jacob W.; Tour, James M.; Wu, Yanpeng; Nordlander, Peter; Natelson, Douglas

2008-01-01

239

Simulations of one- and two-electron systems by Bead-Fourier path integral molecular dynamics  

Science.gov (United States)

The Bead-Fourier path integral molecular dynamics technique introduced earlier [S. D. Ivanov, A. P. Lyubartsev, and A. Laaksonen, Phys. Rev. E 67 066710 (2003)] is applied for simulation of electrons in the simplest molecules: molecular hydrogen, helium atom, and their ions. Special attention is paid to the correct description of electrons in the core region of a nucleus. In an attempt to smooth the Coulomb potential at small distances, a recipe is suggested. The simulation results are in excellent agreement with the analytical solution for the ``harmonic helium atom'', as well as with the vibrational potential of the H2 molecule and He ionization energies. It is demonstrated, that the Bead-Fourier path integral molecular dynamics technique is able to provide the accuracy required for the description of electron structure and chemical bonds in cases when electron exchange effects need not be taken into account.

Ivanov, Sergei D.; Lyubartsev, Alexander P.

2005-07-01

240

Fully differential molecular-frame electron impact ionization measurements  

International Nuclear Information System (INIS)

(e,2e) measurements in the molecular frame using a new spectrometer are described. This work requires a triple coincidence experiment in which (e,2e+ion) events are detected. Preliminary results are presented for a nitrogen target, which illustrate the performance of the apparatus. The nitrogen data clearly shows that the (e,2e) cross section depends sensitively on the orientation of the molecule relative to the incident direction.

2010-02-01

 
 
 
 
241

Molecular wire-nanotube interfacial effects on electron transport  

CERN Document Server

We discuss the conductance of a molecular bridge between mesoscopic electrodes supporting low-dimensional transport and bearing an internal structure. As an example for such nanoelectrodes we assume semi-infinite (carbon) nanotubes. In the Landauer scattering matrix approach, we show that the conductance of this hybrid is very sensitive to the geometry of the contact unlike the usual behaviour in the presence of bulk electrodes.

Fagas, G; Richter, K

2002-01-01

242

Theory of laser-induced electron transport through molecular gases  

International Nuclear Information System (INIS)

Conditions are found for the growth of a current in an electron swarm in gaseous media in the presence of intense, monochromatic radiation. For transport to occur by free-free absorption, it is necessary for the medium to have left- or right-handed chirality (as in a sample of chiral molecules), such that the radiative-dipole rate of absorption by the swarm is unequal for electron velocities upsilon-arrow-right and -upsilon-arrow-right relative to the photon direction

1981-01-01

243

Molecular shock response of explosives: electronic absorption spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

Electronic absorption spectroscopy in the range 400-800 nm was coupled to ultrafast laser generated shocks to begin addressing the question of the extent to which electronic excitations are involved in shock induced reactions. Data are presented on shocked polymethylmethacrylate (PMMA) thin films and single crystal pentaerythritol tetranitrate (PETN). Shocked PMMA exhibited thin film interference effects from the shock front. Shocked PETN exhibited interference from the shock front as well as broadband increased absorption. Relation to shock initiation hypotheses and the need for time dependent absorption data (future experiments) is briefly discussed.

Mcgrne, Shawn D [Los Alamos National Laboratory; Moore, David S [Los Alamos National Laboratory; Whitley, Von H [Los Alamos National Laboratory; Bolme, Cindy A [Los Alamos National Laboratory; Eakins, Daniel E [Los Alamos National Laboratory

2009-01-01

244

A low-loss hybrid rectification technique for piezoelectric energy harvesting  

International Nuclear Information System (INIS)

Embedded systems have decreased in size and increased in capability; however, small-scale energy storage technologies still significantly limit these advances. Energy neutral operation using small-scale energy harvesting technologies would allow for longer device operation times and smaller energy storage masses. Vibration energy harvesting is an attractive method due to the prevalence of energy sources in many environments. Losses in efficiency due to AC–DC rectification and conditioning circuits limit its application. This work presents a low-loss hybrid rectification technique for piezoelectric vibration energy harvesting using magnetically actuated reed switches and a passive semiconductor full-bridge rectifier. This method shows the capability to have higher efficiency levels and the rectification of low-voltage harvesters without the need for active electrical components. A theoretical model shows that the hybrid rectification technique performance is highly dependent on the proximity delay and the hysteresis behavior of the reed switches. Experimental results validate the model and support the hypothesis of increased performance using the hybrid rectification technique. (paper)

2013-09-01

245

A parity function for studying the molecular electronic structure  

DEFF Research Database (Denmark)

Sections through the molecular Wigner function with zero momentum variable are shown to provide important information about the off-diagonal regions of the spinless one-particle reduced density matrix. Since these regions are characteristic for the bonding situation in molecules, the sections are qualitatively even more affected by the presence of chemical bonds than a complementary projection, the reciprocal form factor. In this paper we discuss, on the grounds of a variety of examples, how this rather simple function may aid the understanding of the chemical bond on a one-particle level. (C) 1996 American Institute of Physics.

Schmider, Hartmut

1996-01-01

246

The Smeagol method for spin- and molecular-electronics  

CERN Document Server

{\\it Ab initio} computational methods for electronic transport in nanoscaled systems are an invaluable tool for the design of quantum devices. We have developed a flexible and efficient algorithm for evaluating $I$-$V$ characteristics of atomic junctions, which integrates the non-equilibrium Green's function method with density functional theory. This is currently implemented in the package {\\it Smeagol}. The heart of {\\it Smeagol} is our novel scheme for constructing the surface Green's functions describing the current/voltage probes. It consists of a direct summation of both open and closed scattering channels together with a regularization procedure of the Hamiltonian, and provides great improvements over standard recursive methods. In particular it allows us to tackle material systems with complicated electronic structures, such as magnetic transition metals. Here we present a detailed description of {\\it Smeagol} together with an extensive range of applications relevant for the two burgeoning fields of s...

Rocha, A R; Bailey, S; Lambert, C J; Ferrer, J; Sanvito, S

2005-01-01

247

Electron spectra and structure of atomic and molecular clusters  

Energy Technology Data Exchange (ETDEWEB)

Changes in electronic structure that occur during the stepwise transition from gas phase monomers to large clusters which resemble the condensed phase were studied. This basic information on weakly bound clusters is critical to the understanding of such phenomena as nucleation, aerosol formation, catalysis, and gas-to-particle conversion, yet there exist almost no experimental data on neutral particle energy levels or binding energies as a function of cluster size. (GHT)

Dehmer, P.M.

1980-01-01

248

Electronic magnetic resonance in a series of antiferromagnetic molecular perovskites  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The magnetic properties of a series of ternary tetrathiafulvalenium (TTF+) salts incorporating, within a unique antiperovskite structure, a discrete halide (Y = Cl-, Br- or I-) in addition to an octahedral molybdenum halide cluster dianion Mo6X142- (with X = Cl or Br), are described. The preparation and structural chemistry of the materials of general formula (TTF+)3 (Mo6X142-)(Y-) are briefly recalled. The single-crystal electronic magnetic resonance is explored in details using an X-band ES...

1993-01-01

249

Machine Learning of Molecular Electronic Properties in Chemical Compound Space  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The combination of modern scientific computing with electronic structure theory can lead to an unprecedented amount of data amenable to intelligent data analysis for the identification of meaningful, novel, and predictive structure-property relationships. Such relationships enable high-throughput screening for relevant properties in an exponentially growing pool of virtual compounds that are synthetically accessible. Here, we present a machine learning (ML) model, trained on...

Montavon, Gre?goire; Rupp, Matthias; Gobre, Vivekanand; Vazquez-mayagoitia, Alvaro; Hansen, Katja; Tkatchenko, Alexandre; Mu?ller, Klaus-robert; Von Lilienfeld, O. Anatole

2013-01-01

250

Electronic transport through tape-porphyrin molecular bridges  

International Nuclear Information System (INIS)

We investigated theoretically how molecular conjugation affects current-voltage (I-V) curves through three types of oligoporphyrin molecules, i.e., the tape-porphyrin, the butadiyne-linked porphyrin, and the edge-fused porphyrin molecules. Among these, the tape-porphyrin molecule is found to be the most conductive due to its extremely small HOMO-LUMO energy gap. Furthermore, the I-V curves through this type of molecule are found to depend considerably on atomic sites to which electrodes are connected. In particular, as long as the applied bias is weak, the current is found to flow strongest when both electrodes are connected to the atomic sites referred to as meso sites. This feature is caused by the fact that the HOMO relevant to resonant tunneling has a higher charge density on the meso sites. These findings indicate that designing not only molecules but also contact structures is highly significant for realizing a desirable function in single molecular devices

2004-10-01

251

Electron degradation and yields of initial products. IX. Subexcitation electrons in a mixture of molecular oxygen and molecular nitrogen  

Science.gov (United States)

The behavior of subexcitation electrons in gaseous mixtures of O2 and N2 is studied by using the Spencer-Fano theory and its simplified continuous-slowing-down approximation. Because of its strong resonance around 2 eV, N2 is overwhelmingly dominant over O2 in energy-loss processes. Addition of N2 to O2, even a few percent, causes significant changes in some yields of O2. In particular, yields for electron attachment and rotational excitation for O2 show a strong nonlinearity as a function of composition, while all yields of N2 depend linearly on composition.

Ishii, M. A.; Kimura, Mineo; Inokuti, Mitio

1992-01-01

252

Molecular systems for ultrafast optical switching: Controlling electron transfer reactions with femtosecond laser pulses  

Energy Technology Data Exchange (ETDEWEB)

Rapid, reversible photoinduced electron transfer reactions are a class of photophysical phenomena that can be exploited to develop schemes for optical switching. Molecular electronic switches, wires, micro-sensors for chemical analysis, and opto-electronic components for use in optical computing are currently under active investigation. The principal advantages of using molecules in these applications are high component density, increased response speeds, and high energy efficiency. Since photoinduced electron transfer processes within molecules can take place on a picosecond time scale, it should be possible to produce efficient devices that respond very rapidly. Molecules that employ reversible electron transfer reactions for optical switching should possess both speed and photostability advantages over molecular switches based on photochemical changes in molecular structure. For this purpose the authors recently designed several molecular systems that display properties that may be exploited for optical switching. In this paper, two or more laser pulses are used to manipulate photochromic ion pairs that results from rapid reversible photoinduced electron transfer in complex donor-acceptor molecules.

Greenfield, S.R.; Gosztola, D.J.; Wasielewski, M.R.

1994-04-01

253

Effect of dielectric barrier on rectification, injection and transport properties of printed organic diodes  

International Nuclear Information System (INIS)

Rectification ratios of 105 were observed in printed organic copper/polytriarylamine (PTAA)/silver diodes with a thin insulating barrier layer at the copper/PTAA interface. To clarify the origin of the high rectification ratio in the diodes, the injection, transport and structure of the diodes with two different copper cathodes were examined using impedance spectroscopy and x-ray photoelectron spectroscopy (XPS). The impedance data confirm that the difference in diode performance arises from the copper/PTAA interface. The XPS measurements show that the copper surface in both diode structures is covered by a layer of Cu2O topped by an organic layer. The organic layer is thicker on one of the surfaces, which results in lower reverse currents and higher rectification ratios in the printed diodes. We suggest a model where a dipole at the dual insulating layer induces a shift in the semiconductor energy levels explaining the difference between the diodes with different cathodes.

2011-07-27

254

Effect of an electric field on the nonlinear optical rectification of a quantum ring  

Science.gov (United States)

We have studied the effects of an external electric field on the nonlinear optical rectification of a semiconductor quantum ring. An electric field applied in the ring plane destroys the rotational invariance. Calculations are performed by using the matrix diagonalization method and the compact density-matrix approach within the effective-mass approximation. The results indicate that an increase of electric field gives the red shift of the peak positions of nonlinear optical rectification. The roles of ring size and magnetic field strength as control parameters on this nonlinear property have been investigated. Our results show rich nonlinear optical rectification for quantum rings in the presence of electric fields, which effectively displays the signature of the Aharonov-Bohm oscillation.

Xie, Wenfang

2014-06-01

255

Coupled electron-phonon transport from molecular dynamics with quantum baths  

International Nuclear Information System (INIS)

Based on generalized quantum Langevin equations for the tight-binding wavefunction amplitudes and lattice displacements, electron and phonon quantum transport are obtained exactly using molecular dynamics (MD) in the ballistic regime. The electron-phonon interactions can be handled with a quasi-classical approximation. Both charge and energy transport and their interplay can be studied. We compare the MD results with those of a fully quantum mechanical nonequilibrium Green's function (NEGF) approach for the electron currents. We find a ballistic to diffusive transition of the electron conduction in one-dimensional chains as the chain length increases.

2009-01-14

256

Coupled electron-phonon transport from molecular dynamics with quantum baths  

DEFF Research Database (Denmark)

Based on generalized quantum Langevin equations for the tight-binding wavefunction amplitudes and lattice displacements, electron and phonon quantum transport are obtained exactly using molecular dynamics (MD) in the ballistic regime. The electron-phonon interactions can be handled with a quasi-classical approximation. Both charge and energy transport and their interplay can be studied. We compare the MD results with those of a fully quantum mechanical nonequilibrium Green's function (NEGF) approach for the electron currents. We find a ballistic to diffusive transition of the electron conduction in one-dimensional chains as the chain length increases.

Lu, Jing Tao; Wang, J. S.

2009-01-01

257

Rotational excitation of molecular ions by electron impact under interstellar conditions  

International Nuclear Information System (INIS)

A generalized expression for the rate coefficient for rotational excitation of molecular ions by electron impact under interstellar conditions has been obtained from the first order perturbation theory. The expression has been obtained by considering only the electron-dipole term of the interaction potential which is the most dominant term. The effect of short range and electron-quadrupole interactions has been assessed. The importance of electron-ion collisions in relation to H2-ion collisions in the interpretation of the spectral data obtained for ions from interstellar sources has also been assessed

1981-08-01

258

Molecular dynamics study of kinetic electron emission induced by slow sodium ions incident on gold surfaces  

Energy Technology Data Exchange (ETDEWEB)

Electron excitation and emission phenomena, due to Na{sup +} ion impact on Au (1 0 0) surfaces, are studied at incident projectile energies below the threshold for kinetic electron emission. The trajectories and velocities of the projectile and the target atoms are simulated with molecular dynamics. This information are used to calculate the energy loss by electronic stopping as a series of discrete events, localized in space and time, that are treated as sources of excitation energy. The diffusion of the energy deposited by the projectile into the solid is converted into electron yield as proposed by Duvenbeck and coworkers . The results show similar trends to available experimental data.

Pisarra, M., E-mail: michele.pisarra@fis.unical.i [Dipartimento di Fisica, Universita della Calabria and INFN, Gruppo Collegato di Cosenza via P. Bucci, Cubo 31C, 87036 Rende, Cosenza (Italy); Sindona, A.; Riccardi, P. [Dipartimento di Fisica, Universita della Calabria and INFN, Gruppo Collegato di Cosenza via P. Bucci, Cubo 31C, 87036 Rende, Cosenza (Italy)

2011-05-01

259

Inelastic electron tunneling spectroscopy of gold-benzenedithiol-gold junctions: accurate determination of molecular conformation.  

Science.gov (United States)

The gold-benzenedithiol-gold junction is the classic prototype of molecular electronics. However, even with the similar experimental setup, it has been difficult to reproduce the measured results because of the lack of basic information about the molecular confirmation inside the junction. We have performed systematic first principles study on the inelastic electron tunneling spectroscopy of this classic junction. By comparing the calculated spectra with four different experimental results, the most possible conformations of the molecule under different experimental conditions have been successfully determined. The relationship between the contact configuration and the resulted spectra is revealed. It demonstrates again that one should always combine the theoretical and experimental inelastic electron tunneling spectra to determine the molecular conformation in a junction. Our simulations have also suggested that in terms of the reproducibility and stability, the electromigrated nanogap technique is much better than the mechanically controllable break junction technique. PMID:21309567

Lin, Li-Li; Wang, Chuan-Kui; Luo, Yi

2011-03-22

260

Electron stimulation of internal torsion of a surface-mounted molecular rotor.  

Science.gov (United States)

A molecular rotor which includes a central rotator group was investigated by scanning tunneling microscopy at 4.9 K as it was grafted on a Cu(111) surface via its two terminal groups. Topographs with submolecular resolution revealed several distinct molecular conformations which we attribute to different angular orientations of the rotator and which are locally stable states according to density functional theory calculations. Time-resolved tunneling current spectra showed that the rotator undergoes a torsional motion around the molecular long axis as stimulated by tunneling electrons in a one-electron process with an excitation energy threshold of 355 meV. Calculations identified an intrinsic axial vibration mode of the rotator group at 370 meV as adsorbed on the surface, which we propose to be the channel for effectively converting the tunneling electron energy into the mechanical energy of the intramolecular torsion. PMID:20731465

Wang, Weihua; Shi, Xingqiang; Jin, Mochen; Minot, Christian; Van Hove, Michel A; Collin, Jean-Paul; Lin, Nian

2010-08-24

 
 
 
 
261

Molecular fragmentation by recombination with cold electrons studied with a mass sensitive imaging detector  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The recombination of a molecular cation with a low-energy electron, followed by fragmentation, is a fundamental reaction process in cold and dilute plasmas. For polyatomic ions, it can yield molecular fragments in ro-vibrationally excited states. The discrimination between decay channels with chemically different fragments and the measurement of their excitation energies pose an experimental challenge. This work discusses a new experimental scheme based on fast beam fragment imaging in a stor...

2010-01-01

262

Control of Rectification and Gating of Cloned KATP Channels by the Kir6.2 Subunit  

Digital Repository Infrastructure Vision for European Research (DRIVER)

KATP channels are a functional complex of sulphonylurea receptor (SUR1, SUR2) and inward rectifier K+ (Kir6.1, Kir6.2) channel subunits. We have studied the role of the putative pore forming subunit (Kir6.2) in regulation of rectification and gating of KATP channels generated by transfection of SUR1 and Kir6.2 cDNAs in COSm6 cells. In the absence of internal polyvalent cations, the current-voltage relationship is sigmoidal. Mg2+ or spermine4+ (spm) each induces a mild inward rectification....

1997-01-01

263

Interplay between molecular conformation and intermolecular interactions in conformational polymorphism: a molecular perspective from electronic calculations of tolfenamic acid.  

Science.gov (United States)

Tolfenamic acid exhibits conformational polymorphism. The molecules in its two commonly occurred crystal structures form similar hydrogen-bonded dimers but differ in conformation. The conformational variance was analyzed by electronic calculation methods with the aim to unravel intrinsic connection between the conformational flexibility and intermolecular interactions in the polymorphs. The study was conducted mainly by conceptual density functional theory (DFT) and natural bond orbital (NBO) analysis. It is found that the conformational polymorphism is resulted from the energy competition between intramolecular ?-conjugation and intermolecular hydrogen bonding. By adapting conformation that departs from being the most energetically stable, tolfenamic acid molecules can strengthen the intermolecular hydrogen-bonding interactions in the crystals. The study illustrates how the molecule's electronic properties are influenced by conformational variation and, inherently, how the intermolecular interactions become regulated. Moreover, understanding molecular interaction and crystal packing necessitates electronic structure calculation and analysis, which can be further facilitated by utilizing DFT and NBO concepts. PMID:21570454

Mattei, Alessandra; Li, Tonglei

2011-10-14

264

Theoretical study of the electronic structure of different states of the KRb+ molecular ion  

International Nuclear Information System (INIS)

Full text.The molecular activities in ultra-cold alkali atom trapping stimulate theoretical developments to compute relevant adiabatic potential curves, especially in the framework of the pseudopotential methods. For these methods the molecular ion KRb+ is treated as system with one active electron moving in a field of two ionic cores, where core valence electron interactions are presented by an effective potential. Potential energies have been calculated over a wide range of internuclear distance (5.0-60ao) for the lowest states of symmetry 2?, 2?, 2? and ? for the molecular ion KRb+. To avoid an over estimation of the dissociation energy the perturbative treatment is replaced by an l-dependent core-polarization potential of the Foucrault et al. For the one valence electron of the two considered atoms, we recalculated the polarization potential cut-off parameters rkl, and rRbl by taking l=0,1,2 and ri2=ri3. Molecular orbital for the molecular ion KRb+ were derived from Self Consistent Field calculations (SCF), and full valence Configuration Interaction (IC) calculations were performed. Extensive tables of energy values versus internuclear distance are displayed and molecular spectroscopic constants have been derived, for the first time, for the bound states with regular shape

2000-11-23

265

Electron degradation and yields of initial products. IX. Subexcitation electrons in a mixture of molecular oxygen and molecular nitrogen  

Energy Technology Data Exchange (ETDEWEB)

The behavior of subexcitation electrons in gaseous mixtures of O{sub 2} and N{sub 2} is studied by using the Spencer-Fano theory and its simplified continuous-slowing-down approximation. Because of its strong resonance around 2 eV, N{sub 2} is overwhelmingly dominant over O{sub 2} in energy-loss processes. Addition of N{sub 2} to O{sub 2}, even a few percent, causes significant changes in some yields of O{sub 2}. In particular, yields for electron attachment and rotational excitation for O{sub 2} show a strong nonlinearity as a function of composition, while all yields of N{sub 2} depend linearly on composition.

Ishii, M.A.; Kimura, M.; Inokuti, M. (Argonne National Laboratory, Argonne, Illinois 60439 (United States))

1992-01-01

266

Electronic mapping of molecular orbitals at the molecule-metal interface.  

Science.gov (United States)

The molecule-metal interface formed by pyridine-2,5-dicarboxylic acid chemically bonded to the Cu(110) surface is investigated by scanning tunneling microscopy and first-principles calculations. Our current-voltage spectroscopy studies reveal an electronic mapping of molecular orbitals as a function of tip position. By combining experimental and theoretical investigations, individual molecular orbitals are characterized by their energy and spatial distribution. The importance of adsorption geometries and conformational changes on the electron transport properties is highlighted. PMID:20867996

Lennartz, M C; Caciuc, V; Atodiresei, N; Karthäuser, S; Blügel, S

2010-08-01

267

Assessing molecular similarity from results of ab initio electronic structure calculations  

Energy Technology Data Exchange (ETDEWEB)

A new molecular similarity index, called the number of overlapping electrons (NOEL), is proposed. This similarity index can be computed very rapidly from the natural orbitals and their occupation numbers of the molecules under comparison. The low computational cost makes it possible to optimize the mutual orientation of molecules by maximizing NOEL. The magnitude of NOEL is related to the number of electrons in the molecular fragment common to both molecules. The new approach is illustrated on the examples of benzene, aniline, nitrobenzene, and 4-nitroaniline molecules and the acetate, isoxazole 3-oxide and isoxazole 5-oxide anions.

Cioslowski, J.; Fleischmann, E.D. (Florida State Univ., Tallahassee (USA))

1991-01-02

268

Accurate and robust molecular crystal modeling using fragment-based electronic structure methods.  

Science.gov (United States)

Accurately modeling molecular crystal polymorphism requires careful treatment of diverse intra- and intermolecular interactions which can be difficult to achieve without the use of high-level ab initio electronic structure techniques. Fragment-based methods like the hybrid many-body interaction QM/MM technique enable the application of accurate electronic structure models to chemically interesting molecular crystals. The theoretical underpinnings of this approach and the practical requirements for the QM and MM contributions are discussed. Benchmark results and representative applications to aspirin and oxalyl dihydrazide crystals are presented. PMID:24292635

Beran, Gregory J O; Wen, Shuhao; Nanda, Kaushik; Huang, Yuanhang; Heit, Yonaton

2014-01-01

269

Molecular and electronic structure of actinide hexa-cyanoferrates  

International Nuclear Information System (INIS)

The goal of this work is to improve our knowledge on the actinide-ligand bond properties. To this end, the hexacyanoferrate entities have been used as pre-organized ligand. We have synthesized, using mild chemistry, the following series of complexes: An"I"V[Fe"I"I(CN)_6].xH_2O (An = Th, U, Np, Pu); Am"I"I"I[Fe"I"I"I(CN)_6].xH_2O; Pu "I"I"I[Co"I"I"I(CN)_6].xH_2O and K(H?)An"I"I"I[Fe"I"I(CN)_6].xH_2O (An = Pu, Am). The metal oxidation states have been obtained thanks to the ?_C_N, stretching vibration and to the actinide L_I_I_I absorption edge studies. As Prussian Blue, the An"I"V[Fe"I"I(CN)_6].xH_2O (An = Np, Pu) are class II of Robin and Day compounds. X-ray Diffraction has shown besides that these complexes crystallize in the P6_3/m space group, as the isomorphic LaKFe(CN)_6.4H_2O complex used as structural model. The EXAFS oscillations at the iron K edge and at the An L_I_I_I edge allowed to determine the An-N, An-O, Fe-C and Fe-N distances. The display of the multiple scattering paths for both edges explains the actinide contribution absence at the iron edge, whereas the iron signature is present at the actinide edge. We have shown that the actinide coordination sphere in actinides hexa-cyanoferrates is comparable to the one of lanthanides. However, the actinides typical behavior towards the lanthanides is brought to the fore by the An"I"V versus Ln"I"I"I ions presence in this family of complexes. Contrarily to the 4f electrons, the 5f electrons influence the electronic properties of the compounds of this family. However, the gap between the An-N and Ln-N distances towards the corresponding metals ionic radii do not show any covalence bond evolution between the actinide and lanthanide series. (author)

2001-01-01

270

Assessment of delocalized and localized molecular orbitals through electron momentum spectroscopy  

Science.gov (United States)

Recently, there was a hot controversy about the concept of localized orbitals, which was triggered by Grushow's work titled “Is it time to retire the hybrid atomic orbital?” [J. Chem. Educ. 88, 860 (2011)]. To clarify the issue, we assess the delocalized and localized molecular orbitals from an experimental view using electron momentum spectroscopy. The delocalized and localized molecular orbitals based on various theoretical models for CH4, NH3, and H2O are compared with the experimental momentum distributions. Our results show that the delocalized molecular orbitals rather than the localized ones can give a direct interpretation of the experimental (e, 2e) results.

Liu, Yuan; Cheung, Ling-Fung; Ning, Chuan-Gang

2014-06-01

271

Electron transfer flavoprotein deficiency: Functional and molecular aspects.  

DEFF Research Database (Denmark)

Multiple acyl-CoA dehydrogenase deficiency (MADD) is a recessively inherited metabolic disorder that can be due to a deficiency of electron transfer flavoprotein (ETF) or its dehydrogenase (ETF-ubiquinone oxidoreductase). ETF is a mitochondrial matrix protein consisting of alpha- (30kDa) and beta- (28kDa) subunits encoded by the ETFA and ETFB genes, respectively. In the present study, we have analysed tissue samples from 16 unrelated patients with ETF deficiency, and we report the results of ETF activity, Western blot analysis and mutation analysis. The ETF assay provides a reliable diagnostic tool to confirm ETF deficiency in patients suspected to suffer from MADD. Activity ranged from less than 1 to 16% of controls with the most severely affected patients disclosing the lowest activity values. The majority of patients had mutations in the ETFA gene while only two of them harboured mutations in the ETFB gene. Nine novel disease-causing ETF mutations are reported.

Schiff, M; Froissart, R

2006-01-01

272

Triazole, benzotriazole, and naphthotriazole as copper corrosion inhibitors: I. Molecular electronic and adsorption properties.  

Science.gov (United States)

The gas-phase adsorption of 1,2,3-triazole, benzotriazole, and naphthotriazole-considered as corrosion inhibitors-on copper surfaces was studied and characterized using density functional theory (DFT) calculations. We find that the molecule-surface bond strength increases with increasing molecular size, thus following the sequence: triazolemolecular electronegativity and chemical hardness, which decrease monotonously as the molecular size increases. While the electronegativity of triazole is almost degenerate with the work function of Cu(111) surface, the electronegativity of larger acenotriazoles is smaller. The difference in electronegativity between the Cu(111) and the acenotriazoles thus increases with increasing the molecular size, which, together with decreasing the molecular hardness, results in larger molecule-to-metal electron charge transfer and stronger molecule-surface bonds. PMID:22076907

Kokalj, Anton; Kova?evi?, Nataša; Peljhan, Sebastijan; Finšgar, Matjaž; Lesar, Antonija; Milošev, Ingrid

2011-12-23

273

Neutral Molecular Dissociation of SiH4 and SiF4 by Electron Impact.  

Science.gov (United States)

Neutral molecular dissociation by electrons, i.e. the formation of neutral ground-state fragments resulting from electron impact on a molecule is a very important basic electron collision process. These processes are also important in a many applications, in particular in discharges and plasmas, where the dissociation fragments are often reactive radicals and trigger the subsequent plasma chemistry. We have been studying the electron- induced neutral molecular dissociation of various Si- compounds, in particular SiH4 and SiF4 leading to the formation of final-state-specific Si(1S), Si(1D), and Si (3P). We will present a comprehensive account of the absolute cross sections that we determined for these 3 final states for the 2 molecules as well as for the three Si-organic molecules TMS, HMDSO, and TEOS. Work supported by the US Department of Energy.

Abramzon, N.; Raynor, T.; Becker, K.; Martus, K.

2003-05-01

274

Participation of Low Molecular Weight Electron Carriers in Oxidative Protein Folding  

Directory of Open Access Journals (Sweden)

Full Text Available Oxidative protein folding is mediated by a proteinaceous electron relay system, in which the concerted action of protein disulfide isomerase and Ero1 delivers the electrons from thiol groups to the final acceptor. Oxygen appears to be the final oxidant in aerobic living organisms, although the existence of alternative electron acceptors, e.g. fumarate or nitrate, cannot be excluded. Whilst the protein components of the system are well-known, less attention has been turned to the role of low molecular weight electron carriers in the process. The function of ascorbate, tocopherol and vitamin K has been raised recently. In vitro and in vivo evidence suggests that these redox-active compounds can contribute to the functioning of oxidative folding. This review focuses on the participation of small molecular weight redox compounds in oxidative protein folding.

József Mandl

2009-03-01

275

Effect of basis set superposition error on the electron density of molecular complexes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The effect of basis set superposition error (BSSE) on molecular complexes is analyzed. The BSSE causes artificial delocalizations which modify the first order electron density. The mechanism of this effect is assessed for the hydrogen fluoride dimer with several basis sets. The BSSE-corrected first-order electron density is obtained using the chemical Hamiltonian approach versions of the Roothaan and Kohn-Sham equations. The corrected densities are compared to uncorrected densities based on t...

Salvador Sedano, Pedro; Fradera I Llina?s, Xavier; Duran I Portas, Miquel

2000-01-01

276

Describing the molecular mechanism of organic reactions by using topological analysis of electronic localization function  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Here, we provide an essay on the analysis of the reaction mechanism at the molecular level; in particular, the evolution of the electron pair, as it is provided by the ELF, is used to decribe the reaction pathway. Then, the reaction mechanism is determined by the topological changes of the ELF gradient field along a series of structural stability domains. From this analysis, concepts such as bond breaking/forming processes, formation/annihilation of lone pairs and other electron pair rearrang...

2011-01-01

277

Rate coefficients for low-energy electron dissociative attachment to molecular hydrogen  

Energy Technology Data Exchange (ETDEWEB)

Calculation of rate constants for dissociative electron attachment to molecular hydrogen is reported. The calculation is based on an improved nonlocal resonance model of Cizek, Horacek and Domcke which takes fully into account the nonlocality of the resonance dynamics and uses potentials with correct asymptotic forms. The rate constants are calculated for all quantum numbers v and J of the target molecules and for electron temperature in the range 0-30000 K. (author)

Horacek, J.; Houfek, K.; Cizek, M. [Charles University, Faculty of Mathematics and Physics, Prague (Czech Republic); Murakami, I.; Kato, T. [National Inst. for Fusion Science, Toki, Gifu (Japan)

2003-02-01

278

Rate coefficients for low-energy electron dissociative attachment to molecular hydrogen  

International Nuclear Information System (INIS)

Calculation of rate constants for dissociative electron attachment to molecular hydrogen is reported. The calculation is based on an improved nonlocal resonance model of Cizek, Horacek and Domcke which takes fully into account the nonlocality of the resonance dynamics and uses potentials with correct asymptotic forms. The rate constants are calculated for all quantum numbers v and J of the target molecules and for electron temperature in the range 0-30000 K. (author)

2003-01-01

279

Measurement of molecular motion in organic semiconductors by thermal diffuse electron scattering  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Many of the remarkable electrical and optical properties of organic semiconductors are governed by the interaction of electronic excitations with intra- and intermolecular vibrational modes. However, in specific systems this interaction is not understood in detail at a molecular level and this has been due, at least in part, to the lack of easy-to-use and widely available experimental probes of the structural dynamics. Here we demonstrate that thermal diffuse scattering in electron diffractio...

2013-01-01

280

Studies on Electronic Charge of the Hydrogen Bond Proton in Model Molecular Systems  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract: The population analysis of the hydrogen bond atoms was analyzed within the different basis sets for model molecular systems for the ground and low-lying excited electronic states. The Mulliken, Lőwdin and Hirshfeld methods were used in our investigations. It has been shown that normally the proton is transferred, however, in some excited electronic states the hydrogen atom displacement might be responsible for the tautomeric interconversion.

2003-01-01

 
 
 
 
281

An apparatus for measuring absolute electron scattering cross sections for molecular radicals  

International Nuclear Information System (INIS)

Electron collision cross sections for highly reactive CFx (x = 1–3) radicals are required to model technological plasmas. In spite of their importance to industry, experimental studies of electron interactions with CFx radicals are rarely reported in the literature. A new apparatus for measuring absolute elastic differential cross sections for molecular radicals is reported and a sample absolute cross section for the CF2 radical is presented to demonstrate the application of this experiment

2008-08-01

282

Tuning fulleride electronic structure and molecular ordering via variable layer index  

Science.gov (United States)

C60 fullerides are uniquely flexible molecular materials that exhibit a rich variety of behaviour, including superconductivity and magnetism in bulk compounds, novel electronic and orientational phases in thin films and quantum transport in a single-C60 transistor. The complexity of fulleride properties stems from the existence of many competing interactions, such as electron-electron correlations, electron-vibration coupling and intermolecular hopping. The exact role of each interaction is controversial owing to the difficulty of experimentally isolating the effects of a single interaction in the intricate fulleride materials. Here, we report a unique level of control of the material properties of KxC60 ultrathin films through well-controlled atomic layer indexing and accurate doping concentrations. Using scanning tunnelling microscope techniques, we observe a series of electronic and structural phase transitions as the fullerides evolve from two-dimensional monolayers to quasi-three-dimensional multilayers in the early stages of layer-by-layer growth. These results demonstrate the systematic evolution of fulleride electronic structure and molecular ordering with variable KxC60 film layer index, and provide essential information for the development of new molecular structures and devices.

Wang, Yayu; Yamachika, Ryan; Wachowiak, Andre; Grobis, Michael; Crommie, Michael F.

2008-03-01

283

Assessment of a nanoparticle bridge platform for molecular electronics measurements  

International Nuclear Information System (INIS)

A combination of electron beam lithography, photolithography and focused ion beam milling was used to create a nanogap platform, which was bridged by gold nanoparticles in order to make electrical measurements and assess the platform under ambient conditions. Non-functionalized electrodes were tested to determine the intrinsic response of the platform and it was found that creating devices in ambient conditions requires careful cleaning and awareness of the contributions contaminants may make to measurements. The platform was then used to make measurements on octanethiol (OT) and biphenyldithiol (BPDT) molecules by functionalizing the nanoelectrodes with the molecules prior to bridging the nanogap with nanoparticles. Measurements on OT show that it is possible to make measurements on relatively small numbers of molecules, but that a large variation in response can be expected when one of the metal-molecule junctions is physisorbed, which was partially explained by attachment of OT molecules to different sites on the surface of the Au electrode using a density functional theory calculation. On the other hand, when dealing with BPDT, high yields for device creation are very difficult to achieve under ambient conditions. Significant hysteresis in the I-V curves of BPDT was also observed, which was attributed primarily to voltage induced changes at the interface between the molecule and the metal.

2010-10-29

284

Molecular electronic density fitting using elementary Jacobi rotations under atomic shell approximation  

Science.gov (United States)

Fitted electron density functions constitute an important step in quantum similarity studies. This fact not only is presented in the published papers concerning quantum similarity measures (QSM), but also can be associated with the success of the developed fitting algorithms. As has been demonstrated in previous work, electronic density can be accurately fitted using the atomic shell approximation (ASA). This methodology expresses electron density functions as a linear combination of spherical functions, with the constraint that expansion coefficients must be positive definite, to preserve the statistical meaning of the density function as a probability distribution. Recently, an algorithm based on the elementary Jacobi rotations (EJR) technique was proven as an efficient electron density fitting procedure. In the preceding studies, the EJR algorithm was employed to fit atomic density functions, and subsequently molecular electron density was built in a promolecular way as a simple sum of atomic densities. Following previously established computational developments, in this paper the fitting methodology is applied to molecular systems. Although the promolecular approach is sufficiently accurate for quantum QSPR studies, some molecular properties, such as electrostatic potentials, cannot be described using such a level of approximation. The purpose of the present contribution is to demonstrate that using the promolecular ASA density function as the starting point, it is possible to fit ASA-type functions easily to the ab initio molecular electron density. A comparative study of promolecular and molecular ASA density functions for a large set of molecules using a fitted 6-311G atomic basis set is presented, and some application examples are also discussed. PMID:11045812

Amat; Carbo-Dorca

2000-09-01

285

Intense electron beams from GaAs photocathodes as a tool for molecular and atomic physics  

Energy Technology Data Exchange (ETDEWEB)

We present cesium-coated GaAs photocathodes as reliable sources of intense, quasi-monoenergetic electron beams in atomic and molecular physics experiments. In long-time operation of the Electron Target of the ion storage ring TSR in Heidelberg, cold electron beams could be realised at steadily improving intensity and reliability. Minimisation of processes degrading the quantum efficiency allowed to increase the extractable current to more than 1mA at usable cathode lifetimes of 24 h or more. The benefits of the cold electron beam with respect to its application to electron cooling and electron-ion recombination experiments are discussed. Benchmark experiments demonstrate the superior cooling force and energy resolution of the photoelectron beam compared to its thermionic counterparts. The long period of operation allowed to study the long-time behaviour of the GaAs samples during multiple usage cycles at the Electron Target and repeated in-vacuum surface cleaning by atomic hydrogen exposure. An electron emission spectroscopy setup has been implemented at the photocathode preparation chamber of the Electron Target. Among others, this new facility opened the way to a novel application of GaAs (Cs) photocathodes as robust, ultraviolet-driven electron emitters. Based on this principle, a prototype of an electron gun, designed for implementation at the HITRAP setup at GSI, has been built and taken into operation successfully. (orig.)

Krantz, Claude

2009-10-28

286

Reduction of the Glauber amplitude for electron impact rotational excitation of quadrupolar molecular ions  

International Nuclear Information System (INIS)

A reduction of the Glauber amplitude for the rotational excitation of pure quadrupolar molecular ions by electron impact is presented in a form suitable for numerical evaluation. The differential cross-section is expressed in terms of one dimensional integrals over impact parameter. (author)

1981-01-01

287

Electronic structure and correlations in pristine and potassium doped Cu-Phthalocyanine molecular crystals  

CERN Multimedia

We investigate the changes in the electronic structure of copper phthalocyanine (CuPc) crystals that is caused by intercalation with potassium. This is done by means of {\\it ab initio} LSDA and LSDA+U calculations of the electronic structure of these molecular crystals. Pristine CuPc is found to be an insulator with local magnetic moments and a Pc-derived valence band with a width of 0.32 eV. In the intercalated compound $\\rm K_2CuPc$ the additional electrons that are introduced by potassium are fully transferred to the $e_g$ states of the Pc-ring. A molecular low spin state results, preserving, however, the local magnetic moment on the copper ions. The degeneracy of the $e_g$ levels is split by a crystal field that quenches the orbital degeneracy and gives rise to a band splitting of 110 meV. Molecular electronic Coulomb interactions enhance this splitting in $\\rm K_2CuPc$ to a charge gap of 1.4 eV. The bandwidth of the conduction band is 0.56 eV, which is surprisingly large for a molecular solid. This is li...

Giovannetti, G; Van den Brink, J; Giovannetti, Gianluca; Brocks, Geert; Brink, Jeroen van den

2006-01-01

288

IR-MALDI OF LOW MOLECULAR WEIGHT COMPOUNDS USING A FREE ELECTRON LASER.  

Science.gov (United States)

Initial experiments on infrared matrix-assisted laser desorption/ionization mass spectrometry (IR-MALDI) using a free electron laser in the analysis of low-molecular-weight compounds are reported. Mass spectra from samples of ethylenediaminetetraacetic acid (EDTA), nitrilotriacet...

289

Progress towards the measurement of absolute elastic electron-molecular radical scattering cross sections  

International Nuclear Information System (INIS)

We report on our progress in developing a dedicated crossed beam apparatus, for the measurement of absolute cross sections for elastic scattering of electrons from molecular radicals. Features which are original to this apparatus will be highlighted, and a discussion of its current status and future developments provided

2007-10-01

290

Theoretical study of characteristics of a molecular single-electron transistor  

International Nuclear Information System (INIS)

A technique for the calculation of current-to-voltage curves and control curves of a molecular single-electron transistor with a discrete energy spectrum has been developed. The effective recursive methods for quick computation of the Gibbs canonical distribution of electrons between energy levels, as well as techniques for the fast calculation of the distribution function for a slow relaxation process have been found. Characteristics of the single-electron transistor in the cases of different types of molecule's energy spectrum, fast and slow energy relaxations have been compared

2004-10-01

291

Electronic structure of amorphous germanium disulfide via density functional molecular dynamics simulations  

CERN Document Server

Using density functional molecular dynamics simulations we study the electronic properties of glassy g-GeS$_2$. We compute the electronic density of states, which compares very well with XPS measurements, as well as the partial EDOS and the inverse participation ratio. We show the electronic contour plots corresponding to different structural environments, in order to determine the nature of the covalent bonds between the atoms. We finally study the local atomic charges, and analyze the impact of the local environment on the charge transfers between the atoms. The broken chemical order inherent to amorphous systems leads to locally charged zones when integrating the atomic charges up to nearest-neighbor distances.

Blaineau, S; Blaineau, Sebastien; Jund, Philippe

2004-01-01

292

Electronic structure and correlations in pristine and potassium doped Cu-Phthalocyanine molecular crystals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We investigate the changes in the electronic structure of copper phthalocyanine (CuPc) crystals that is caused by intercalation with potassium. This is done by means of {\\it ab initio} LSDA and LSDA+U calculations of the electronic structure of these molecular crystals. Pristine CuPc is found to be an insulator with local magnetic moments and a Pc-derived valence band with a width of 0.32 eV. In the intercalated compound $\\rm K_2CuPc$ the additional electrons that are introd...

Giovannetti, Gianluca; Brocks, Geert; Brink, Jeroen Den

2006-01-01

293

Electron irradiation effect on antimony doping of silicon grown by molecular-beam epitaxy  

International Nuclear Information System (INIS)

The effect of electron irradiation on the antimony doping levels in silicon molecular-beam epitaxy has been studied. For substrate temperatures in the 620--800 "0C range, electron irradiation enhances the doping efficiency significantly. Sharp, well-defined profiles, high doping levels (up to 3 x 10"1"9 cm"-"3) and high-quality epitaxial layers are obtained. Using a semiempirical model, a chart of the doping levels as a function of both the substrate temperature and antimony flux is developed. The influence of electron irradiation on the antimony adlayer is also discussed

1987-02-15

294

Toward sub-20 nm hybrid nanofabrication by combining the molecular ruler method and electron beam lithography  

Energy Technology Data Exchange (ETDEWEB)

It is of great interest and importance to develop new nanofabrication processes to fabricate sub-20 nm structures with sub-2 nm resolution for next-generation nanoelectronic devices. A combination of electron beam lithography (EBL) and a molecular ruler is one of the promising methods to make these fine structures. Here we successfully develop a hybrid method to fabricate sub-20 nm nanogap devices at the desired positions with a complex structure by developing a post-EBL process, which enabled us to avoid damaging the molecular ruler with the high-energy electron beam, and to fully utilize the EBL resolution. It was found that slight etching of the Ti adhesion layer of the parent metal (Pt) by ACT935J solution assisted the removal of molecular rulers, resulting in improved enhancement in the product yield (over 70%) of nanogap devices.

Li, C B; Hasegawa, T; Miyazaki, H; Odaka, S; Tsukagoshi, K; Aono, M [International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044 (Japan); Tanaka, H, E-mail: cbli.aa@gmail.com, E-mail: HASEGAWA.Tsuyoshi@nims.go.jp [Graduate School of Science and School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan)

2010-12-10

295

Measurement of molecular motion in organic semiconductors by thermal diffuse electron scattering.  

Science.gov (United States)

Many of the remarkable electrical and optical properties of organic semiconductors are governed by the interaction of electronic excitations with intra- and intermolecular vibrational modes. However, in specific systems this interaction is not understood in detail at a molecular level and this has been due, at least in part, to the lack of easy-to-use and widely available experimental probes of the structural dynamics. Here we demonstrate that thermal diffuse scattering in electron diffraction patterns from organic semiconductors, such as 6,13-bistriisopropyl-silylethynyl pentacene, allows the dominant lattice vibrational modes to be probed directly. The amplitude and direction of the dominant molecular motions were determined by comparison of the diffuse scattering with simulations and molecular dynamics calculations. Our widely applicable approach enables a much deeper understanding of the structural dynamics in a broad range of organic semiconductors. PMID:23892786

Eggeman, Alexander S; Illig, Steffen; Troisi, Alessandro; Sirringhaus, Henning; Midgley, Paul A

2013-11-01

296

Have we been here before? Inorganic precursors for collective electronic behaviour of molecular crystals  

Energy Technology Data Exchange (ETDEWEB)

The community focused on collective electronic properties of organic and metal-organic molecular crystals sometimes assumes that these are uniquely a consequence of the fact that the lattice is composed of molecular building blocks. However, quantum mechanics has a wider horizon and precursors for some of the phenomena currently occupying our field were observed and investigated a while ago in various inorganic lattices. We recall some of the latter, which serve to highlight what really is unique to the molecular solid state. We also recall a simplified classification scheme to correlate crystal structures and physical properties. Examples from magnetism include one- and two-dimensional ferromagnetism and complex magnetic lattice topologies; from electron transport we mention low-dimensional superconductors incorporating localized magnetic moments

Day, Peter, E-mail: profpday@msn.co

2010-06-01

297

Generation of radially polarized terahertz pulses via velocity-mismatched optical rectification.  

Science.gov (United States)

We demonstrate the generation of radially polarized terahertz pulses via optical rectification in a Cherenkov geometry exploiting velocity mismatch, contrary to the traditional approach for generating linearly polarized terahertz beams. A compact system is implemented using 001-cut ZnTe pumped by an ultrafast Yb-doped fiber amplifier. PMID:17356677

Chang, Guoqing; Divin, Charles J; Liu, Chi-Hung; Williamson, Steven L; Galvanauskas, Almantas; Norris, Theodore B

2007-02-15

298

Radiation-based near-field thermal rectification with phase transition materials  

Science.gov (United States)

The capability of manipulating heat flow has promising applications in thermal management and thermal circuits. In this Letter, we report strong thermal rectification effect based on the near-field thermal radiation between silicon dioxide (SiO2) and a phase transition material, vanadium dioxide (VO2), separated by nanometer vacuum gaps under the framework of fluctuational electrodynamics. Strong coupling of surface phonon polaritons between SiO2 and insulating VO2 leads to enhanced near-field radiative transfer, which on the other hand is suppressed when VO2 becomes metallic, resulting in thermal rectification. The rectification factor is close to 1 when vacuum gap is at 1 ?m and it increases to almost 2 at sub-20-nm gaps when emitter and receiver temperatures are set to 400 and 300 K, respectively. Replacing bulk SiO2 with a thin film of several nanometers, rectification factor of 3 can be achieved when the vacuum gap is around 100 nm.

Yang, Yue; Basu, Soumyadipta; Wang, Liping

2013-10-01

299

An image rectification method on image sequence of monocular motion vision  

Science.gov (United States)

Image rectification reduce the search space from 2-dimension to 1-dimension and improve the searching efficiency of stereo matching algorithm greatly. In this paper, a simple and convenient method, which fully considered image sequence of monocular motion vision, is proposed to rectify the calibrated image sequence. The method is based on coordinate system transformation, which can avoid the mass and complex computations, and the method rectifies image sequence (three images) at once, which is efficient in image sequence processing. In this method, the rectification is composed of several steps. Firstly, we establish a reference coordinate system by three movement position. The Z axis of the reference coordinate system o_XYZ is the normal vector of the plane which three positions located. The direction of X axis coincides with the baseline from position 2 to position 1. We set Y axis according to right-hand principle. Secondly, we set the x axis and z axis of reference image space coordinate system o_xyz coincides with the X axis and Z axis of the reference coordinate system, and the y axis is set to coincide with the line from position 2 to position 3. Finally, we deduce a homography matrix to realize the image rectification. Both image data and computer simulation data show that the method is an effective rectification method.

Li, Yunting; Zhang, Jun; Hu, Wenwen; Liu, Xiaomao; Tian, Jinwen

2013-10-01

300

Plasmons in nanoscale metal junctions: optical rectification and thermometry  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We use simultaneous electronic transport and optical characterization measurements to reveal new information about electronic and optical processes in nanoscale junctions fabricated by electromigration. Comparing electronic tunneling and photocurrents allows us to infer the optical frequency potential difference produced by the plasmon response of the junction. Together with the measured tunneling conductance, we can then determine the locally enhanced electric field within ...

Natelson, Douglas; Ward, Daniel R.; Hu?ser, Falco; Pauly, Fabian; Cuevas, Juan Carlos; Corley, David A.; Tour, James M.

2011-01-01

 
 
 
 
301

Efficient electronic coupling and improved stability with dithiocarbamate-based molecular junctions  

Science.gov (United States)

Molecular electronic devices require stable and highly conductive contacts between the metal electrodes and molecules. Thiols and amines are widely used to attach molecules to metals, but they form poor electrical contacts and lack the robustness required for device applications. Here, we demonstrate that dithiocarbamates provide superior electrical contact and thermal stability when compared to thiols on metals. Ultraviolet photoelectron spectroscopy and density functional theory show the presence of electronic states at 0.6 eV below the Fermi level of Au, which effectively reduce the charge injection barrier across the metal-molecule interface. Charge transport measurements across oligophenylene monolayers reveal that the conductance of terphenyl-dithiocarbamate junctions is two orders of magnitude higher than that of terphenyl-thiolate junctions. The stability and low contact resistance of dithiocarbamate-based molecular junctions represent a significant step towards the development of robust, organic-based electronic circuits.

von Wrochem, Florian; Gao, Deqing; Scholz, Frank; Nothofer, Heinz-Georg; Nelles, Gabriele; Wessels, Jurina M.

2010-08-01

302

Influence of inelastic electron-phonon interaction on the noise power through a molecular junction  

Science.gov (United States)

The effect of the inelastic electron-phonon interaction on the spin-dependent transport through a ferromagnetic/molecular structure as FM/trans-PA/FM model junction is numerically investigated. Based on a generalized Green's function formalism and also the mapping technique, which transforms the many-body electron-phonon interaction problem into a multi-channels single-electron scattering problem, we found that in the presence of the electron-phonon interaction, the currents are generally reduced and the step-like structure of the current-voltage characteristic are deformed. In addition, our results indicate that the main influence of the inclusion of the electron-phonon interaction is the reduction of the conductance gap of the molecule. Furthermore, it is shown that due to inelastic interactions, the noise power increase and the significant change occurs in the Fano factor.

Ketabi, S. A.; Ashhadi, M.

2013-09-01

303

Transient behaviour of electron exchange between a molecular wire and a metal electrode  

Energy Technology Data Exchange (ETDEWEB)

Highlights: > Modeling electron transfer rate to electrode from redox via mediated bridge of atoms. > Redox interaction of solvent modeled as classical harmonic oscillator bath. > Both transient and rate constants are calculated. > Negative differential resistance at high overpotential for thermal electron transfer. > Dependency on chain length is analysed. - Abstract: We consider electron exchange between a metal electrode and an attached molecular wire with a redox center at its end. A model Hamiltonian based on a tight-binding scheme is proposed, which contains the coupling of the redox system to the solvent. The corresponding Green's function is calculated exactly, and the time dependence is derived from its Fourier transform. For the case of photo-exited transfer we calculate current transients for a few representative cases. In addition, we calculate the rate of electron transfer for thermal electron transfer from the redox center to the electrode following a potential step.

Cruz, A.V.B., E-mail: bruno@imsc.res.in [Institute of Mathematical Sciences CIT Campus, Chennai 600113 (India); Mishra, A.K. [Institute of Mathematical Sciences CIT Campus, Chennai 600113 (India); Schmickler, W. [Institute of Theoretical Chemistry, Ulm University, D89069 Ulm (Germany)

2011-05-30

304

Molecular structure and internal rotation of (Z)-chloroacetaldehyde oxime by gas-phase electron diffraction  

Science.gov (United States)

The molecular structure of gaseous (Z)-chloroacetaldehyde oxime has been determined by gas-phase electron diffraction and molecular structure optimization has been carried out by molecular orbital calculations. The molecular skeleton is planar and the potential barrier height to internal rotation around the C?C bond ( V1) was estimated to be 2.7 kcal mol -1. The geometrical parameters obtained are: rg(?Cl)=1.789±0.001Å, rg(C?C)=1.513±0.003Å, rg(C?N)=1.284±0.001Å, rg(N?O)=1.416±0.001Å, ?CCCl=109.7±0.2°, ?CCN=124.9±0.3°, ?CNO=110.6±0.2°.

Iijima, Kinya; Hanamori, Toshiya; Sakaizumi, Takeshi; Ohashi, Osamu

1993-10-01

305

Phonon effects in molecular conduction junctions  

Science.gov (United States)

This talk will give an overview of our work on effects of electron-phonon coupling on molecular conduction, including dephasing, dissipation and heating, then describe some recent observations, interpretations and predictions on three phenomena involving phonons in molecular junctions: (a) Heat conduction and its rectification by molecular wires^1,2; (b) inelastic electron tunneling spectroscopy^3-5 and (c) phonon-induced multi-stability, hysteresis and negative differential resistance in molecular conduction.^6 ^1 D. Segal, A. Nitzan and P. Hä'nggi, J. Chem. Phys. 119, 6840-6855 (2003) ^2 D. Segal and A. Nitzan, cond-mat/0405472 ^3 M. Galperin, M. Ratner and A. Nitzan, J. Chem. Phys. 121, 11965-11979 (2004) ^4 M. Galperin, M. Ratner and A. Nitzan, Nano Lett., 4, 1605-1611 (2004) ^5 M. Galperin, A. Nitzan, M. A. Ratner and D. R. Stewart, to be published http://atto.tau.ac.il/˜nitzan/253.pdf ^6 M. Galperin, M. A.Ratner and A. Nitzan, Nano Letters, in press http://atto.tau.ac.il/˜nitzan/254.pdf

Nitzan, Abraham

2005-03-01

306

Molecular Computational Investigation of Electron Transfer Kinetics across Cytochrome-Iron Oxide Interfaces  

International Nuclear Information System (INIS)

The interface between electron transfer proteins such as cytochromes and solid phase mineral oxides is central to the activity of dissimilatory-metal reducing bacteria. A combination of potential-based molecular dynamics simulations and ab initio electronic structure calculations are used in the framework of Marcus' electron transfer theory to compute elementary electron transfer rates from a well-defined cytochrome model, namely the small tetraheme cytochrome (STC) from Shewanella oneidensis, to surfaces of the iron oxide mineral hematite (a-Fe2O3). Room temperature molecular dynamics simulations show that an isolated STC molecule favors surface attachment via direct contact of hemes I and IV at the poles of the elongated axis, with electron transfer distances as small as 9 Angstroms. The cytochrome remains attached to the mineral surface in the presence of water and shows limited surface diffusion at the interface. Ab initio electronic coupling matrix element (VAB) calculations of configurations excised from the molecular dynamics simulations reveal VAB values ranging from 1 to 20 cm-1, consistent with nonadiabaticity. Using these results, together with experimental data on the redox potential of hematite and hemes in relevant cytochromes and calculations of the reorganization energy from cluster models, we estimate the rate of electron transfer across this model interface to range from 1 to 1000 s-1 for the most exothermic driving force considered in this work, and from 0.01 to 20 s-1 for the most endothermic. This fairly large range of electron transfer rates highlights the sensitivity of the rate upon the electronic coupling matrix element, which is in turn dependent on the fluctuations of the heme configuration at the interface. We characterize this dependence using an idealized bis-imidazole heme to compute from first principles the VAB variation due to porphyrin ring orientation, electron transfer distance, and mineral surface termination. The electronic matrix element and consequently the rate of electron transfer are found to be sensitive to all parameters considered. This work indicates that biomolecularly similar solvent-exposed bis-histidine hemes in outer-membrane cytochromes such as MtrC or OmcA are likely to have an affinity for the oxide surface in water governing the approach and interfacial conformation and, if allowed sufficient conformational freedom, will achieve distances and configurations required for direct interfacial electron transfer.

2007-08-02

307

Time-dependent theoretical treatments of the dynamics of electrons and nuclei in molecular systems  

International Nuclear Information System (INIS)

An overview is presented of methods for time-dependent treatments of molecules as systems of electrons and nuclei. The theoretical details of these methods are reviewed and contrasted in the light of a recently developed time-dependent method called electron-nuclear dynamics. Electron-nuclear dynamics (END) is a formulation of the complete dynamics of electrons and nuclei of a molecular system that eliminates the necessity of constructing potential-energy surfaces. Because of its general formulation, it encompasses many aspects found in other formulations and can serve as a didactic device for clarifying many of the principles and approximations relevant in time-dependent treatments of molecular systems. The END equations are derived from the time-dependent variational principle applied to a chosen family of efficiently parametrized approximate state vectors. A detailed analysis of the END equations is given for the case of a single-determinantal state for the electrons and a classical treatment of the nuclei. The approach leads to a simple formulation of the fully nonlinear time-dependent Hartree-Fock theory including nuclear dynamics. The nonlinear END equations with the ab initio Coulomb Hamiltonian have been implemented at this level of theory in a computer program, ENDyne, and have been shown feasible for the study of small molecular systems. Implementation of the Austin Model 1 semiempirical Hamiltonian is discussed as a route to large molecular systems. The linearized END equations at this level of theory are shown to lead to the random-phase approximation for the coupled system of electrons and nuclei. The qualitative features of the general nonlinear solution are analyzed using the results of the linearized equations as a first approximation. Some specific applications of END are presented, and the comparison with experiment and other theoretical approaches is discussed

1994-07-01

308

Auger-electron emission following fast (MeV) molecular- and atomic-ion impact on thin C-foils  

International Nuclear Information System (INIS)

Auger electron emission following the excitation of molecular (CO"2"+ and N"2"+) and atomic ions (C"+ and N"+) in thin carbon foils has been measured at MeV impact energies. Relative Auger electron yields from molecular-ion impact have been compared to that from atomic ion impact at equal ion velocities

1983-08-02

309

Ionization Potential, Electron Affinity, Electronegativity, Hardness, and Electron Excitation Energy: Molecular Properties from Density Functional Theory Orbital Energies  

Energy Technology Data Exchange (ETDEWEB)

Representative atomic and molecular systems, including various inorganic and organic molecules with covalent and ionic bonds, have been studied by using density functional theory. The calculations were done with the commonly used exchange-correlation functional B3LYP followed by a comprehensive analysis of the calculated highest-occupied and lowest-unoccupied Kohn-Sham orbital (HOMO and LUMO) energies. The basis set dependence of the DFT results shows that the economical 6-31+G* basis set is generally sufficient for calculating the HOMO and LUMO energies (if the calculated LUMO energies are negative) for use in correlating with molecular properties. The directly calculated ionization potential (IP), electron affinity (EA), electronegativity (c), hardness (h), and first electron excitation energy (t) are all in good agreement with the available experimental data. A generally applicable linear correlation relationship exists between the calculated HOMO energies and the experimental/calculated IP's. We have also found satisfactory linear correlation relationships between the calculated LUMO energies and experimental/calculated EA's (for the bound anionic states), between the calculated average HOMO/LUMO energies and c values, between the calculated HOMO-LUMO energy gaps and h values, and between the calculated HOMO-LUMO energy gaps and experimental/calculated first excitation energies. By using these linear correlation relationships, the calculated HOMO and LUMO energies can be employed to semi-quantitatively estimate ionization potential, electron affinity, electronegativity, hardness, and first excitation energy.

Zhan, Chang-Guo; Nichols, Jeffrey A.; Dixon, David A.

2003-05-22

310

Quantum-information analysis of electronic states of different molecular structures  

International Nuclear Information System (INIS)

We have studied transition metal clusters from a quantum information theory perspective using the density-matrix renormalization group (DMRG) method. We demonstrate the competition between entanglement and interaction localization and discuss the application of the configuration interaction-based dynamically extended active space procedure, which significantly reduces the effective system size and accelerates the speed of convergence for complicated molecular electronic structures. Our results indicate the importance of taking entanglement among molecular orbitals into account in order to devise an optimal DMRG orbital ordering and carry out efficient calculations on transition metal clusters. Apart from these algorithmic observations, which lead to a recipe for black-box DMRG calculations, our work provides physical understanding of electron correlation in molecular and cluster structures in terms of entropy measures of relevance also to recent work on tensor-network representations of electronic states. We also identify those molecular orbitals which are highly entangled and discuss the consequences for chemical bonding and for the structural transition from an dioxygen binding copper cluster to an bis-oxygen-bridged system with broken O-O bond.

2011-01-01

311

Investigation of Terminal Group Effect on Electron Transport Through Open Molecular Structures  

International Nuclear Information System (INIS)

The effect of terminal groups on the electron transport through metal-molecule-metal system has been investigated using nonequilibrium Green's function (NEGF) formalism combined with extended Huckel theory (EHT). Au-molecule-Au junctions are constructed with borazine and BCN unit structure as core molecule and sulphur (S), oxygen (O), selenium (Se) and cyano-group (CN) as terminal groups. The electron transport characteristics of the borazine and BCN molecular systems are analyzed through the transmission spectra and the current-voltage curve. The results demonstrate that the terminal groups modifying the transport behaviors of these systems in a controlled way. Our result shows that, selenium is the best linker to couple borazine to Au electrode and oxygen is the best one to couple BCN to Au electrode. Furthermore, the results of borazine systems are compared with that of BCN molecular systems and are discussed. Simulation results show that the conductance through BCN molecular systems is four times larger than the borazine molecular systems. Negative differential resistance behavior is observed with borazine-CN system and the saturation feature appears in BCN systems. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

2013-05-15

312

Determination of the gas-phase molecular structure of bis(trimethylsilyl)sulphide by electron diffraction and molecular mechanics calculations  

Science.gov (United States)

The molecular structure of S(SiMe 3) 2 in the gas phase has been determined by electron diffraction, aided by molecular mechanics (MM2) calculations. The results of two refinements are reported. In the first, the SiMe 3 groups were assumed to have local C3 symmetry, while in the second all the S?Si distances, Si?C distances, and SSiC and CSiC angles were allowed to differ from one another, with the differences fixed at the values calculated by molecular mechanics. Allowing for the asymmetry of the SiMe 3 groups had a significant effect on some of the refined parameters, most notably the mean SSiC angle, which increased from 105.6(7) to 109.2(3)°, and the angle SiSSi, which increased from 104.0(5)° to 105.8(7)°. Other major parameters ( ra) obtained in the refinement with asymmetric SiMe 3 groups are r(Si?S)=215.4(1) pm and r(Si?C) (mean)=187.1(1) pm. The two SiMe 3 groups are twisted by 17.1(13) and 29.6(14)° from the position in which one Si?C bond of each group lies anti with respect to the further S?Si bond.

Anderson, David G.; Forsyth, George A.; Rankin, David W. H.

1990-04-01

313

Exploring the molecular mechanisms of electron shuttling across the microbe/metal space  

Science.gov (United States)

Dissimilatory metal reducing organisms play key roles in the biogeochemical cycle of metals as well as in the durability of submerged and buried metallic structures. The molecular mechanisms that support electron transfer across the microbe-metal interface in these organisms remain poorly explored. It is known that outer membrane proteins, in particular multiheme cytochromes, are essential for this type of metabolism, being responsible for direct and indirect, via electron shuttles, interaction with the insoluble electron acceptors. Soluble electron shuttles such as flavins, phenazines, and humic acids are known to enhance extracellular electron transfer. In this work, this phenomenon was explored. All known outer membrane decaheme cytochromes from Shewanella oneidensis MR-1 with known metal terminal reductase activity and a undecaheme cytochrome from Shewanella sp. HRCR-6 were expressed and purified. Their interactions with soluble electron shuttles were studied using stopped-flow kinetics, NMR spectroscopy, and molecular simulations. The results show that despite the structural similarities, expected from the available structural data and sequence homology, the detailed characteristics of their interactions with soluble electron shuttles are different. MtrC and OmcA appear to interact with a variety of different electron shuttles in the close vicinity of some of their hemes, and with affinities that are biologically relevant for the concentrations typical found in the medium for this type of compounds. All data support a view of a distant interaction between the hemes of MtrF and the electron shuttles. For UndA a clear structural characterization was achieved for the interaction with AQDS a humic acid analog. These results provide guidance for future work of the manipulation of these proteins toward modulation of their role in metal attachment and reduction.

Paquete, Catarina M.; Fonseca, Bruno M.; Cruz, Davide R.; Pereira, Tiago M.; Pacheco, Isabel; Soares, Claudio M.; Louro, Ricardo O.

2014-01-01

314

Light quasiparticles dominate electronic transport in molecular crystal field-effect transistors  

Energy Technology Data Exchange (ETDEWEB)

We report on an infrared spectroscopy study of mobile holes in the accumulation layer of organic field-effect transistors based on rubrene single crystals. Our data indicate that both transport and infrared properties of these transistors at room temperature are governed by light quasiparticles in molecular orbital bands with the effective masses m[small star, filled]comparable to free electron mass. Furthermore, the m[small star, filled]values inferred from our experiments are in agreement with those determined from band structure calculations. These findings reveal no evidence for prominent polaronic effects, which is at variance with the common beliefs of polaron formation in molecular solids.

Li, Z. Q.; Podzorov, V.; Sai, N.; Martin, Michael C.; Gershenson, M. E.; Di Ventra, M.; Basov, D. N.

2007-03-01

315

Molecular structure of molybdenum oxide tetrachloride studied by gas electron diffraction  

International Nuclear Information System (INIS)

The molecular structure of molybdenum oxide tetrachloride was determined to be a square pyramid by a sector-microphotometer method of gas electron diffraction. The following molecular parameters were obtained by a least-squares method: rsub(g)(Mo-Cl)=2.279+-0.003 A, rsub(g)(Mo-O)=1.658+-0.005A, and rsub(g)(Cl...Cl(s))=3.142+-0.008 A. The structure of gaseous MoOCl4 is similar to that of gaseous WOCl4. The infrared spectra of MoOCl4 were also measured in solutions. (auth.)

1975-01-01

316

Dependence of total ?-electron energy on the number of non-bonding molecular orbitals  

International Nuclear Information System (INIS)

In recent work [Gutman et al. (2004) Chem Phys Lett 383: 171] a method was developed by means of which the influence of non-bonding molecular orbitals (NBMOs) on the value of total ?-electron energy (E) can be separated from the multitude of other molecular-structure-dependent effects. We now extend this method and establish the relation between E and the number n 0 of NBMOs. It is shown that E (when computed within the HMO approximation, and expressed in the units of the HMO resonance integral ?) is a decreasing function of n 0, and that the dependence of E on n 0 is almost perfectly linear. (author)

2004-01-01

317

Unexpectedly high pressure for molecular dissociation in liquid hydrogen by a reliable electronic simulation  

CERN Document Server

The study of the high pressure phase diagram of hydrogen has continued with renewed effort for about one century as it remains a fundamental challenge for experimental and theoretical techniques. Here we employ an efficient molecular dynamics based on the quantum Monte Carlo method, which can describe accurately the electronic correlation and treat a large number of hydrogen atoms, allowing a realistic and reliable prediction of thermodynamic roperties. We find that the molecular liquid phase is unexpectedly stable and the transition towards a fully atomic liquid phase occurs at much higher pressure than previously believed. The old standing problem of low temperature atomization is, therefore, still far from experimental reach.

Mazzola, Guglielmo; Sorella, Sandro

2014-01-01

318

Direct observation of electron-transfer-induced conformational transformation (molecular actuation) in a bichromophoric electron donor.  

Science.gov (United States)

With the aid of laser-flash photolysis, the one-electron oxidation of conformationally mobile tetramethoxydibenzobicyclo[4.4.1]undecane (1), using photoexcited chloranil as an oxidant, allows us to show that extended 1(+•) undergoes a conformational transformation to ?-stacked folded 1(+•) on a microsecond time scale (? ? 1 ?s), which is at least six times longer than that found for the conformationally locked model compound. PMID:20491456

Shukla, Ruchi; Thakur, Khushabu; Chebny, Vincent J; Reid, Scott A; Rathore, Rajendra

2010-11-18

319

When electron transfer meets electron transport in redox-active molecular nanojunctions.  

Science.gov (United States)

A scanning electrochemical microscope (SECM) was used to arrange two microelectrodes face-to-face separated by a micrometric gap. Polyaniline (PANI) was deposited electrochemically from the SECM tip side until it bridged the two electrodes. The junctions obtained were characterized by following the current through the PANI as a function of its electrochemical potential measured versus a reference electrode acting as a gate electrode in a solid-state transistor. PANI nanojunctions showed conductances below 100 nS in the oxidized state, indicating control of the charge transport within the whole micrometric gap by a limited number of PANI wires. The SECM configuration makes it possible to observe in the same experiment and in the same current range the electron-transfer and electron-transport processes. These two phenomena are distinguished here and characterized by following the variation of the current with the bias voltage and the scan rate. The electron-transfer current changes with the scan rate, while the charge-transport current varies with the bias voltage. Finally, despite the initially micrometric gap, a junction where the conductance is controlled by a single oligoaniline strand is achieved. PMID:23331168

Janin, Marion; Ghilane, Jalal; Lacroix, Jean-Christophe

2013-02-13

320

Fabrication of tunnel junction-based molecular electronics and spintronics devices  

Energy Technology Data Exchange (ETDEWEB)

Tunnel junction-based molecular devices (TJMDs) are highly promising for realizing futuristic electronics and spintronics devices for advanced logic and memory operations. Under this approach, {approx}2.5 nm molecular device elements bridge across the {approx}2-nm thick insulator of a tunnel junction along the exposed side edge(s). This paper details the efforts and insights for producing a variety of TJMDs by resolving multiple device fabrication and characterization issues. This study specifically discusses (i) compatibility between tunnel junction test bed and molecular solutions, (ii) optimization of the exposed side edge profile and insulator thickness for enhancing the probability of molecular bridging, (iii) effect of fabrication process-induced mechanical stresses, and (iv) minimizing electrical bias-induced instability after the device fabrication. This research will benefit other researchers interested in producing TJMDs efficiently. TJMD approach offers an open platform to test virtually any combination of magnetic and nonmagnetic electrodes, and promising molecules such as single molecular magnets, porphyrin, DNA, and molecular complexes.

Tyagi, Pawan, E-mail: ptyagi@udc.edu [University of the District of Columbia, Department of Civil and Mechanical Engineering (United States)

2012-10-15

 
 
 
 
321

Design and Simulation of Molecular Nonvolatile Single-Electron Resistive Switches  

CERN Document Server

We have carried out a preliminary design and simulation of a single-electron resistive switch based on a system of two linear, parallel, electrostatically-coupled molecules: one implementing a single-electron transistor and another serving as a single-electron trap. To verify our design, we have performed a theoretical analysis of this "memristive" device, based on a combination of ab-initio calculations of the electronic structures of the molecules and the general theory of single-electron tunneling in systems with discrete energy spectra. Our results show that such molecular assemblies, with a length below 10 nm and a footprint area of about 5 nm$^2$, may combine sub-second switching times with multi-year retention times and high ($> 10^3$) ON/OFF current ratios, at room temperature. Moreover, Monte Carlo simulations of self-assembled monolayers (SAM) based on such molecular assemblies have shown that such monolayers may also be used as resistive switches, with comparable characteristics and, in addition, b...

Simonian, Nikita; Likharev, Konstantin K

2012-01-01

322

Determining contact potential barrier effects on electronic transport in single molecular junctions  

Science.gov (United States)

The authors introduced a simplified multiple-barrier model based on the widely accepted traditional tunneling model to describe the electron transport behaviors in single molecule junction systems. The contact potential barrier height ?c and the contact decay constant ?c were taken as the key indexes to represent certain contact conformations. By monitoring the dynamic changes of contact potential barriers corresponding to the mechanical extension of contact conformations with our newly developed Scanning Probe Microscope (SPM)-break junction technique and then fitting into the model, we established an in-depth and detailed understanding of the molecule-metal contact effects on electronic transport properties in single molecular junctions.

Zhou, Jianfeng; Xu, Bingqian

2011-07-01

323

Amplified spontaneous emission of a molecular nitrogen laser excited by an intense relativistic electron beam  

International Nuclear Information System (INIS)

Report of a study of the shape and length of the output pulse of a molecular nitrogen laser, excited by an intense relativistic electron beam, is described. The rate equations are computer solved, at first ignoring the spontaneous emission during the excitation process. Afterwards the rate equations are solved taking into account excitation functions of various shapes and lengths, related to electron-beam pulses of a few kA and a few nsec. Laser power output, energy, and peak-time, i.e., the time at which the gain reaches its saturated value, are given and discussed as functions of the intensity and rise time of the excitation functions

1975-01-01

324

Polarization effects in the elastic scattering of electrons by molecular hydrogen  

Energy Technology Data Exchange (ETDEWEB)

The elastic differential cross section of electrons from molecular hydrogen has been calculated in the independent-atom model using the Glauber approximation for both direct and exchange scattering amplitudes. Polarization effects have been considered through the modified Glauber amplitude for the direct scattering. For the exchange amplitude the result obtained by Franco and Halpern has been used. Numerical results for various incident electron energies have been carried out. The polarization contribution has been found to have negative effects in bringing the calculated results close to the experimental values.

Narasimham, V.L.; Ramachandran, A.S.; Warke, C.S.

1982-05-01

325

Cooling a vibrational mode coupled to a molecular single-electron transistor  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We consider a molecular single electron transistor coupled to a vibrational mode. For some values of the bias and gate voltage transport is possible only by absorption of one ore more phonons. The system acts then as a cooler for the mechanical mode at the condition that the electron temperature is lower than the phonon temperature. The final effective temperature of the vibrational mode depends strongly on the bias conditions and can be lower or higher of the reservoir in contact with the os...

Pistolesi, Fabio

2009-01-01

326

Communication: Reduced density matrices in molecular systems: Grand-canonical electron states  

International Nuclear Information System (INIS)

Grand-canonical like descriptions of many electron atomic and molecular open systems which are characterized by a non-integer number of electrons are presented. Their associated reduced density matrices (RDMs) are obtained by introducing the contracting mapping for this type of distributions. It is shown that there is loss of information when connecting RDMs of different order by partial contractions. The energy convexity property of these systems simplifies the description. Consequently, this formulation opens the possibility to a new look for chemical descriptors such as chemical potential and reactivity among others. Examples are presented to discuss the theoretical aspects of this work

2013-11-21

327

Enhancing electron transport in molecular wires by insertion of a ferrocene center.  

Science.gov (United States)

We have determined the conductance of alkane-linked ferrocene molecules with carboxylic acid anchoring groups using the STM break junction technique, and three sets of conductance values were found, i.e. high conductance (HC), medium conductance (MC) and low conductance (LC) values. The enhancing effect of the incorporated ferrocene on the electron transport in saturated alkane molecular wires is demonstrated by the increased conductance of the ferrocene molecules, attributed to the reduction of the tunneling barrier and the HOMO-LUMO gap induced by the insertion of ferrocene. Furthermore, the electron-withdrawing carbonyl group on the unconjugated backbone has little or no influence on single-molecule conductance. The current work provides a feasible approach for the design of high-performance molecular wires. PMID:24382483

Sun, Yan-Yan; Peng, Zheng-Lian; Hou, Rong; Liang, Jing-Hong; Zheng, Ju-Fang; Zhou, Xiao-Yi; Zhou, Xiao-Shun; Jin, Shan; Niu, Zhen-Jiang; Mao, Bing-Wei

2014-02-14

328

Molecular Three-Center Electronic Integrals Over Slater-Type Orbitals Evaluated Using Nonlinear Transformations  

Directory of Open Access Journals (Sweden)

Full Text Available Molecular three-center electronic integrals over Slater-type orbitals are required for ab initio and density functional theory (DFT molecular structure calculations. They occur in many millions of terms, even for small molecules and require rapid and accurate evaluation. In this work, we present a very efficient approach based on properties of Bessel and sine functions and on nonlinear transformations for accurate numerical evaluation of integrals under consideration. Numerical results are obtained for three-center nuclear and three-center two-electron Coulomb and hybrid integrals over Slater-type orbitals for HCN, C2H2, Zn3, BH3, and CH4 molecules. We also performed the same calculations using existing codes to show the accuracy of the new algorithm. The results obtained in this work illustrate the efficiency of the algorithm based on the SD approach, which will lead to a definitive suite of ab initio Slater software.

Hassan Safouhi

2004-02-01

329

High Temperature Molecular Magnetism Caused by pi-electrons: Copper Phthalocyanine Doped with Alkaline Metals  

CERN Multimedia

Electron spin resonance spectra of copper phthalocyanine doped with alkaline metals (AxCuPc) have been investigated. The temperature dependence of ESR spectra indicates the ferromagnetic behavior. The Curie-Weiss temperature varies from 30K to 115K depending on the stoichiometry x of samples. Some particles of polycrystalline samples were attracted to a weak magnet at temperature slightly higher than 77K. The observed magnetism is caused by unpaired pi-electrons of phthalocyanine anions on the Eg doubly degenerated molecular orbital. The observed ferromagnetism can be understood within the framework of the McConnell-2 model proposed for organic ferromagnetic charge-transfer complexes. The high-temperature magnetism in AxCuPc is considered to be a result of the Zener mechanism of double exchange between phthalocyanine molecular anions of different valence.

Sharoyan, E G

2005-01-01

330

One-electron atomic-molecular ions containing Lithium in a strong magnetic field  

CERN Document Server

The one-electron Li-containing Coulomb systems of atomic type $(li, e)$ and molecular type $(li, li, e)$, $(li, \\alpha, e)$ and $(li, p, e)$ are studied in the presence of a strong magnetic field $B \\leq 10^{7}$ a.u. in the non-relativistic framework. They are considered at the Born-Oppenheimer approximation of zero order (infinitely massive centers) within the parallel configuration (molecular axis parallel to the magnetic field). The variational and Lagrange-mesh methods are employed in complement to each other. It is demonstrated that the molecular systems ${\\rm LiH}^{3+}$, ${\\rm LiHe}^{4+}$ and ${\\rm Li}_{2}^{5+}$ can exist for sufficiently strong magnetic fields $B \\gtrsim 10^{4}$ a.u. and that ${\\rm Li}_{2}^{5+}$ can even be stable at magnetic fields typical of magnetars.

Pilón, H Olivares; Turbiner, A V; Vieyra, J C López

2009-01-01

331

Importance of electronic self-consistency in the TDDFT based treatment of nonadiabatic molecular dynamics  

CERN Document Server

A mixed quantum-classical approach to simulate the coupled dynamics of electrons and nuclei in nanoscale molecular systems is presented. The method relies on a second order expansion of the Lagrangian in time-dependent density functional theory (TDDFT) around a suitable reference density. We show that the inclusion of the second order term renders the method a self-consistent scheme and improves the calculated optical spectra of molecules by a proper treatment of the coupled response. In the application to ion-fullerene collisions, the inclusion of self-consistency is found to be crucial for a correct description of the charge transfer between projectile and target. For a model of the photoreceptor in retinal proteins, nonadiabatic molecular dynamics simulations are performed and reveal problems of TDDFT in the prediction of intra-molecular charge transfer excitations.

Niehaus, T A; Torralva, B; Frauenheim, T; Frauenheim, Th.

2004-01-01

332

Fully differential molecular-frame measurements for the electron-impact dissociative ionization of H2.  

Science.gov (United States)

We present fully differential state-resolved experimental data for the dissociative ionization of molecular hydrogen induced through electron impact. Molecular-frame ionization cross sections are derived for transitions from the X{1}Sigma{g}{+} molecular ground state to the 1ssigma{g}, 2psigma{u}, 2ssigma{g}, and 2ppi{u} states of H2+. For transitions to the 2ssigma{g} and 2ppi{u} states, a strong orientation dependence in the cross sections is revealed, with "side-on" preferred to "end-on" collisions and a propensity for the fragment proton to emerge along the normal to the scattering plane. PMID:20366592

Bellm, S; Lower, J; Weigold, E; Mueller, D W

2010-01-15

333

One-electron atomic-molecular ions containing lithium in a strong magnetic field  

International Nuclear Information System (INIS)

The one-electron lithium-containing Coulomb systems of atomic type Li2+ and molecular type Li5+2, LiHe4+ and LiH3+ are studied in the presence of a strong magnetic field B ? 107 au in a non-relativistic framework. They are considered at the Born-Oppenheimer approximation of zero order (infinitely massive centres) within the parallel configuration (molecular axis parallel to the magnetic field). The variational and Lagrange-mesh methods are employed, complementing each other. It is demonstrated that the molecular systems LiH3+, LiHe4+ and Li5+2 can exist for sufficiently strong magnetic fields B ?> 104 au and that Li5+2 can even be stable at magnetic fields typical of magnetars.

2010-03-28

334

Quantum Simulation of 2p-? Electronic Hamiltonian in Molecular Ethylene by Using an NMR Quantum Computer  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Classical simulation of a quantum system is a hard problem. It’s known that these problems can be solved efficiently by using quantum computers. This study demonstrates the simulation of the molecular Hamiltonian of 2p-? electrons of ethylene in order to calculate the ground state energy. The ground state energy is estimated by an iterative phase estimation algorithm. The ground state is prepared by the adiabatic state...

Deniz Türkpençe; Azmi Gençten

2013-01-01

335

Charge constrained density functional molecular dynamics for simulation of condensed phase electron transfer reactions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present a plane-wave basis set implementation of charge constrained density functional molecular dynamics (CDFT-MD) for simulation of electron transfer reactions in condensed phase systems. Following earlier work of Wu et al. Phys. Rev. A 72, 024502 (2005), the density functional is minimized under the constraint that the charge difference between donor and acceptor is equal to a given value. The classical ion dynamics is propagated on the Born-Oppenheimer surface of the ...

Oberhofer, H.; Blumberger, J.

2009-01-01

336

Full two-electron calculations of antiproton collisions with molecular hydrogen  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Total cross sections for single ionization and excitation of molecular hydrogen by antiproton impact are presented over a wide range of impact energy from 1 keV to 6.5 MeV. A nonpertubative time-dependent close-coupling method is applied to fully treat the correlated dynamics of the electrons. Good agreement is obtained between the present calculations and experimental measurements of single-ionization cross sections at high energies, whereas some discrepancies with the expe...

Lu?hr, Armin; Saenz, Alejandro

2009-01-01

337

Electronic structure and molecular orbital study of hole-transport material triphenylamine derivatives  

Energy Technology Data Exchange (ETDEWEB)

Recently, triphenylamine (TPA), 4,4'-bis(phenyl-m-tolylamino)biphenyl (TPD), 4,4'-bis(1-naphthylphenylamino)biphenyl (NPB) and their derivatives are widely used in the organic light-emitting diode (OLED) devices as a hole-transporting material (HTM) layer. We have optimized twenty different structures of HTM materials by using density functional theory (DFT), B3LYP/6-31G method. All these different structures contain mono-amine and diamine TPA derivatives. The energies of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) along with molecular orbitals for these HTMs are also determined. We have found that the central amine nitrogen atom and the phenyl ring, which is next to the central amine nitrogen atom, show significant contribution to the HOMO and LUMO, respectively. The sum of the calculated bond angles ({alpha}+{beta}+{gamma}) of the central amine nitrogen atom has been applied to describe the bonding and the energy difference for HOMO and LUMO in these TPA derivatives. Electronic structure calculations have been performed for these TPA derivatives. Again, the LCAO-MO patterns of HOMO and LUMO levels of these derivatives are used to investigate their electron density. A series of electron-transporting steps are predicted for these compounds employing these calculated results.

Wang, B.-C. [Department of Chemistry, Tamkang University, Tamsui 251, Taiwan (China)]. E-mail: bcw@mail.tku.edu.tw; Liao, H.-R. [Department of Chemistry, Tamkang University, Tamsui 251, Taiwan (China); Chang, J.-C. [Materials Research Laboratory, ITRI, Hsinchiu 310, Taiwan (China); Chen Likey [Materials Research Laboratory, ITRI, Hsinchiu 310, Taiwan (China); Yeh, J.-T. [Materials Research Laboratory, ITRI, Hsinchiu 310, Taiwan (China)

2007-06-15

338

Electronic structure and molecular orbital study of hole-transport material triphenylamine derivatives  

International Nuclear Information System (INIS)

Recently, triphenylamine (TPA), 4,4'-bis(phenyl-m-tolylamino)biphenyl (TPD), 4,4'-bis(1-naphthylphenylamino)biphenyl (NPB) and their derivatives are widely used in the organic light-emitting diode (OLED) devices as a hole-transporting material (HTM) layer. We have optimized twenty different structures of HTM materials by using density functional theory (DFT), B3LYP/6-31G method. All these different structures contain mono-amine and diamine TPA derivatives. The energies of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) along with molecular orbitals for these HTMs are also determined. We have found that the central amine nitrogen atom and the phenyl ring, which is next to the central amine nitrogen atom, show significant contribution to the HOMO and LUMO, respectively. The sum of the calculated bond angles (?+?+?) of the central amine nitrogen atom has been applied to describe the bonding and the energy difference for HOMO and LUMO in these TPA derivatives. Electronic structure calculations have been performed for these TPA derivatives. Again, the LCAO-MO patterns of HOMO and LUMO levels of these derivatives are used to investigate their electron density. A series of electron-transporting steps are predicted for these compounds employing these calculated results

2007-06-01

339

Darwin at the molecular scale: selection and variance in electron tunnelling proteins including cytochrome c oxidase  

Science.gov (United States)

Biological electron transfer is designed to connect catalytic clusters by chains of redox cofactors. A review of the characterized natural redox proteins with a critical eye for molecular scale measurement of variation and selection related to physiological function shows no statistically significant differences in the protein medium lying between cofactors engaged in physiologically beneficial or detrimental electron transfer. Instead, control of electron tunnelling over long distances relies overwhelmingly on less than 14?? spacing between the cofactors in a chain. Near catalytic clusters, shorter distances (commonly less than 7??) appear to be selected to generate tunnelling frequencies sufficiently high to scale the barriers of multi-electron, bond-forming/-breaking catalysis at physiological rates. We illustrate this behaviour in a tunnelling network analysis of cytochrome c oxidase. In order to surmount the large, thermally activated, adiabatic barriers in the 5–10?kcal?mol?1 range expected for H+ motion and O2 reduction at the binuclear centre of oxidase on the 103–105?s?1 time-scale of respiration, electron access with a tunnelling frequency of 109 or 1010?s?1 is required. This is provided by selecting closely placed redox centres, such as haem a (6.9??) or tyrosine (4.9??). A corollary is that more distantly placed redox centres, such as CuA, cannot rapidly scale the catalytic site barrier, but must send their electrons through more closely placed centres, avoiding direct short circuits that might circumvent proton pumping coupled to haems a to a3 electron transfer. The selection of distances and energetic barriers directs electron transfer from CuA to haem a rather than a3, without any need for delicate engineering of the protein medium to ‘hard wire’ electron transfer. Indeed, an examination of a large number of oxidoreductases provides no evidence of such naturally selected wiring of electron tunnelling pathways.

Moser, Christopher C; Page, Christopher C; Dutton, P. Leslie

2006-01-01

340

Effect of linear surface-charge non-uniformities on the electrokinetic ionic-current rectification in conical nanopores.  

Science.gov (United States)

The electrokinetic ionic-current rectification in a conical nanopore with linearly varying surface-charge distributions is studied theoretically by using a continuum model composed of a coupled system of the Nernst-Planck equations for the ionic-concentration field and the Poisson equation for the electric potential in the electrolyte solution. The numerical analysis includes the electrochemistry inside reservoirs connected to the nanopore, neglected in previous studies, and more precise accounts of the ionic current are provided. The surface-charge distribution, especially near the tip of the nanopore, significantly affects the ionic enrichment and depletion, which, in turn, influence the resulting ionic current and the rectification. It is shown that non-uniform surface-charge distribution can reverse the direction, or sense, of the rectification. Further insights into the ionic-current rectification are provided by discussing the intriguing details of the electric potential and ionic-concentration fields, leading to the rectification. Rationale for future studies on ionic-current rectification, associated with other non-uniform surface-charge distributions and electroosmotic convection for example, is discussed. PMID:18977486

Qian, Shizhi; Joo, Sang W; Ai, Ye; Cheney, Marcos A; Hou, Wensheng

2009-01-15

 
 
 
 
341

Hydrostatic pressure and temperature effects on nonlinear optical rectification in a lens shape InAs/GaAs quantum dot  

Energy Technology Data Exchange (ETDEWEB)

We have performed theoretical calculation of the nonlinear optical rectification in a lens shape InAs/GaAs quantum dot (0D). The combined effects of hydrostatic pressure and temperature on the nonlinear optical rectification in lens-shaped InAs QDs are studied under the compact density matrix formalism and the effective mass approximation. From our calculation, it is found that the subband energies and optical rectification susceptibility are quite sensitive to the applied hydrostatic pressure and temperature. The results show that the resonant peak of the optical rectification can be red-shifted or blue-shifted and their intensity also varied by external probes such as hydrostatic pressure and temperature. In addition, the oscillator strength is strongly affected by these parameters. - Highlights: Black-Right-Pointing-Pointer Theoretical calculation of the nonlinear optical rectification in a lens shape InAs/GaAs quantum dot was performed. Black-Right-Pointing-Pointer Optical rectification susceptibility is quite sensitive to the applied hydrostatic pressure and temperature. Black-Right-Pointing-Pointer The oscillator strength is strongly affected by the applied hydrostatic pressure and temperature.

Bouzaieene, L., E-mail: lotfi.bouzaiene@fsm.rnu.tn [Laboratoire de Micro-optoelectronique et Nanostructures, Departement de Physique, Faculte des Sciences de Monastir, Universite de Monastir (Tunisia); Ben Mahrsia, R.; Baira, M.; Sfaxi, L.; Maaref, H. [Laboratoire de Micro-optoelectronique et Nanostructures, Departement de Physique, Faculte des Sciences de Monastir, Universite de Monastir (Tunisia)

2013-03-15

342

Rectification of pulsatile stress on soft tissues: a mechanism for normal-pressure hydrocephalus  

Science.gov (United States)

Hydrocephalus is a pathological condition of the brain that occurs when cerebrospinal fluid (CSF) accumulates excessively in the brain cavities, resulting in compression of the brain parenchyma. Counter-intuitively, normal-pressure hydrocephalus (NPH) does not show elevated pressure differences across the compressed parenchyma. We investigate the effects of nonlinear tissue mechanics and periodic driving in this system. The latter is due to the cardiac cycle, which provides significant intracranial pressure and volume flow rate fluctuations. Nonlinear rectification of the periodic driving within a model of fluid flow in poroelastic material can lead to compression or expansion of the parenchyma, and this effect does not rely on changes in the mean intracranial pressure. The rectification effects can occur gradually over several days, in agreement with clinical studies of NPH.

Jalikop, Shreyas; Hilgenfeldt, Sascha

2011-11-01

343

Universal method for separating spin pumping from spin rectification voltage of ferromagnetic resonance.  

Science.gov (United States)

We develop a method for universally resolving the important issue of separating spin pumping from spin rectification signals in bilayer spintronics devices. This method is based on the characteristic distinction of spin pumping and spin rectification, as revealed in their different angular and field symmetries. It applies generally for analyzing charge voltages in bilayers induced by the ferromagnetic resonance (FMR), independent of FMR line shape. Hence, it solves the outstanding problem that device-specific microwave properties restrict the universal quantification of the spin Hall angle in bilayer devices via FMR experiments. Furthermore, it paves the way for directly measuring the nonlinear evolution of spin current generated by spin pumping. The spin Hall angle in a Py/Pt bilayer is thereby directly measured as 0.021±0.015 up to a large precession cone angle of about 20°. PMID:24313526

Bai, Lihui; Hyde, P; Gui, Y S; Hu, C-M; Vlaminck, V; Pearson, J E; Bader, S D; Hoffmann, A

2013-11-22

344

Research of distortion rectification method for large vision angle IR imaging system  

Science.gov (United States)

During the large visual angle IR image distortion rectification process there are some difficulties, first pick-up rectifying points is hard, second measuring and rectifying distortion are wasting time, third rectifying screen is difficult to make and it costs much. In order to overcome those disadvantages an IR imaging distortion rectification method, which using asterisk rectifying screen, is proposed. This method takes the image of a special made asterisk rectifying screen at first, then using SIFT operator to detect the real imaging positions of rectifying points in the image. Based on the real positions mean slope is used to compute theoretical imaging positions of those rectifying points. After that least square arithmetic is adopted to calculate the distortion parameters. The experiment result has shown that: the proposed method has the advantages of high precision, low cost, simple process and universal applicability.

Zhang, Xue-yuan; Ren, Zhen; Zhang, Zheng-hui; Sun, Guang-li

2013-09-01

345

Comparison research of algorithms about ortho-rectification for remote sensing image  

Science.gov (United States)

There are kinds of methods for ortho-rectification in application of remote sensing, including Collinearity Equation Model, Strict Geometric Model based on Affine Transformation, Improved Polynomial Model, Rational Function Model, Method based on Neural Network, and so on. But there is lack of system comparison between these methods. On the basis of detailing the algorithm of these methods above, advantages and drawbacks about these algorithms are summarized in this paper. Specific emphasis is the mathematical derivation and algorithm of RFM. Two kinds of algorithm based on neural network were taken in application of ortho-rectification. To compare accuracy and effective between the above methods, we also detailed the processing steps and make some experiments. The result shows that: in the condition of the same GCPs distribution, Rational Function Model that can reach sub pixel accuracy is the best of all from the viewpoint of precision, which can be used in practice in spite of its relatively slower speed.

Luan, Qingzu; Liu, Huiping; Wang, Xiaodong; Huang, Wenli; Zhou, Xiaoluo

2008-10-01

346

The electronic structure of the alkaline-earth-atom (Ca, Sr, Ba) hydride molecular ions  

International Nuclear Information System (INIS)

The main electronic properties, namely potential energy curves, permanent and transition dipole moments, static dipole polarizabilities, of the alkaline-earth hydride ion SrH+, as well as of CaH+ and BaH+ are computed through a full configuration interaction performed in a two-valence electronic configuration space build from a large Gaussian basis set. The doubly charged ionic core of the alkaline-earth atoms is modelled by an effective core potential including core polarization effects. Our study confirms that the properties of these series of molecular ions have very similar patterns, while it is predicted that the major electronic transition between the electronic ground state and the lowest excited state in BaH+ is significantly weaker than the one in CaH+ and SrH+. Such a study represents a first step towards the modelling of reactive collisions between cold and trapped alkaline-earth ions and H2, as well as for precision measurements based on overtone transitions using cold molecular ions.

2012-11-14

347

Optimized terahertz generation via optical rectification in ZnTe crystals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report on optimal control of the output energy of terahertz (THz) waves generated by optical rectification of femtosecond pulses in ZnTe crystals. An enhancement by a factor up to 2.4 is obtained with chirped pump pulses. The optimized THz wave also displays a spectral broadening. The influence of the optical pulse shaping on the pump pulse propagation, and consequently on the THz generation efficiency, is numerically investigated and discussed.

Vidal, Se?bastien; Je?ro?me, Degert; Tondusson, Marc; Freysz, Eric; Oberle, Jean

2013-01-01

348

Research on automatic optimization of ground control points in image geometric rectification based on Voronoi diagram  

Science.gov (United States)

With the development of remote sensing satellites, the data quantity of remote sensing image is increasing tremendously, which brings a huge workload to the image geometric rectification through manual ground control point (GCP) selections. GCP database is one of the effective methods to cut down manual operation. The GCP loaded from database is generally redundant, which may result in a rectification slowdown. How to automatically optimize these ground control points is a problem that should be resolved urgently. According to the basic theory of geometric rectification and the principle of GCP selection, this paper deeply comprehends some existing methods about automatic optimization of GCP, and puts forward a new method of automatic optimization of GCP based on voronoi diagram to filter ground control points from the overfull ones without manual subjectivity for better accuracy. The paper is organized as follows: First, it clarifies the basic theory of remote sensing image multinomial geometric rectification and the arithmetic of how to get the GCP error. Second, it particularly introduces the voronoi diagram including its origin, development and characteristics, especially the creating process. Third, considering the deficiencies of existing methods about automatic optimization of GCP, the paper presents the idea of applying voronoi diagram to filter GCP in order to complete automatic optimization. During this process, it advances the conception of single GCP's importance value based on voronoi diagram. Then by integrating the GCP error and GCP's importance value, the paper gives the theory and the flow of automatic optimization of GCPs as well. It also presents an example of the application of this method. In the conclusion, it points out the advantages of automatic optimization of GCP based on the voronoi diagram.

Li, Ying; Cheng, Bo

2009-10-01

349

Rectification of skeletal muscle ryanodine receptor mediated by FK506 binding protein.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The cytosolic receptor for immunosuppressant drugs, FK506 binding protein (FKBP12), maintains a tight association with ryanodine receptors of sarcoplasmic reticulum (SR) membrane in skeletal muscle. The interaction between FKBP12 and ryanodine receptors resulted in distinct rectification of the Ca release channel. The endogenous FKBP-bound Ca release channel conducted current unidirectionally from SR lumen to myoplasm; in the opposite direction, the channel deactivated with fast kinetics. The...

Ma, J.; Bhat, M. B.; Zhao, J.

1995-01-01

350

Electronic transport properties of carbon chains between Au and Ag electrodes: A first-principles study  

International Nuclear Information System (INIS)

We report first-principles calculations of the current-voltage characteristic and the conductance of carbon-based molecular wires with different length capped with sulfur ends between two metallic electrodes made of different metals. The optimized molecular structure of carbon chain in the junction is presented on the structure of polyyne. The conductance of the polyyne wires shows oscillatory behavior depending on the number of carbon atoms (triple bonds). Current rectification is found and rectification direction presents inversion with the odd and even number of carbon atoms. -- Highlights: ? Au and Ag as two asymmetric electrodes. ? Relaxed carbon chain structure is in the form of polyyne. ? Oscillatory conductance behavior with the number of carbon atoms. ? Current rectification of carbon chains in the asymmetric electrodes. ? Rectification inversion with the number of carbon atoms.

2011-09-26

351

Electron dynamics across molecular wires: A time-dependent configuration interaction study  

Science.gov (United States)

In this study we present methodological developments of the time-dependent configuration interaction (TDCI) method for ab initio electron dynamics in donor-bridge-acceptor systems. Especially, we investigate the role of valence electron correlation, the scheme for selecting the determinantal basis, and the computational effort. Our test systems are molecules of the type Li-(C2)n-CN, Li-(C2H2)n-CN, and Na9-(C2H2)2-CN. In this way, this study is intended as a step towards rigorous description of charge transfer in molecular wires attached to metal surfaces or nanoparticles using a many-electron wavefunction. Also, a multi-reference configuration interaction singles approach is suggested as a good compromise between computational effort and accuracy.

Ramakrishnan, Raghunathan; Raghunathan, Shampa; Nest, Mathias

2013-07-01

352

Electron scattering on centrosymmetric molecular dianions Pt(CN)42- and Pt(CN)62-  

International Nuclear Information System (INIS)

Electron scattering on stored Pt(CN)42- and Pt(CN)62- centrosymmetric molecular dianions has been performed at the electrostatic storage ring ELISA. The thresholds for production of neutral particles by electron bombardment were found to be 17.2 and 18.7 eV, respectively. The relatively high thresholds reflect the strong Coulomb repulsion in the incoming channel as well as a high energetic stability of the target electrons. A trianion resonance was identified with a positive energy of 17.0 eV for the Pt(CN)42- square-planar complex, while three trianion resonances were identified for the Pt(CN)62- octahedral complex with positive energies of 15.3, 18.1, and 20.1 eV

2004-11-12

353

Low and intermediate energy electron collisions with the C$_2^-$ molecular anion  

CERN Multimedia

Calculations are presented which use the molecular R-matrix with pseudo-states (MRMPS) method to treat electron impact electron detachment and electronic excitation of the carbon dimer anion. Resonances are found above the ionisation threshold of C$_2^-$ with $^1\\Sigma^+_g$, $^1\\Pi_g$ and $^3\\Pi_g$ symmetry. These are shape resonances trapped by the effect of an attractive polarisation potential competing with a repulsive Coulomb interaction. The $\\Pi_g$ resonances are found to give structure in the detachment cross section similar to that observed experimentally. Both excitation and detachment cross sections are found to be dominated by large impact parameter collisions whose contribution is modelled using the Born approximation.

Halmova, Gabriela; Tennyson, Jonathan

2008-01-01

354

Connections between molecular photoionization and electron-molecule scattering with emphasis on shape resonances  

International Nuclear Information System (INIS)

Most of our detailed information on the spectroscopy and dynamics of the electronic continuum of molecules is based on the complementary probes - photoionization and electron scattering. Though usually studied separately, it is most useful to appreciate the connections between these two processes since our understanding of one is often the key to interpreting or even generating new results in the other. We approach this subject in two steps. First, we very briefly outline the well-established connections, e.g., the Bethe-Born theory and comparisons of isoelectronic systems. Then we focus on a point of contact - the role of shape resonances in molecular photoionization and electron-molecule scattering - for which a substantial amount of new information has become available. Specific topics include mapping of resonances from the neutral (h? + molecule) to the negative ion (e + molecule) system, angular distributions, and interaction with vibration

1979-09-07

355

Rectification of SEMG as a tool to demonstrate synchronous motor unit activity during vibration.  

Science.gov (United States)

The use of surface electromyography (SEMG) in vibration studies is problematic since motion artifacts occupy the same frequency band with the SEMG signal containing information on synchronous motor unit activity. We hypothesize that using a harsher, 80-500 Hz band-pass filter and using rectification can help eliminate motion artifacts and provide a way to observe synchronous motor unit activity that is phase locked to vibration using SEMG recordings only. Multi Motor Unit (MMU) action potentials using intramuscular electrodes along with SEMG were recorded from the gastrocnemius medialis (GM) of six healthy male volunteers. Data were collected during whole body vibration, using vibration frequencies of 30 Hz, 35 Hz, 40 Hz or 50 Hz. A computer simulation was used to investigate the efficacy of filtering under different scenarios: with or without artifacts and/or motor unit synchronization. Our findings indicate that motor unit synchronization took place during WBV as verified by MMU recordings. A harsh filtering regimen along with rectification proved successful in demonstrating motor unit synchronization in SEMG recordings. Our findings were further supported by the results from the computer simulation, which indicated that filtering and rectification was efficient in discriminating motion artifacts from motor unit synchronization. We suggest that the proposed signal processing technique may provide a new methodology to evaluate the effects of vibration treatments using only SEMG. This is a major advantage, as this non-intrusive method is able to overcome movement artifacts and also indicate the synchronization of underlying motor units. PMID:23098913

Sebik, Oguz; Karacan, Ilhan; Cidem, Muharrem; Türker, Kemal S

2013-04-01

356

Effect of dielectric barrier on rectification, injection and transport properties of printed organic diodes  

Energy Technology Data Exchange (ETDEWEB)

Rectification ratios of 10{sup 5} were observed in printed organic copper/polytriarylamine (PTAA)/silver diodes with a thin insulating barrier layer at the copper/PTAA interface. To clarify the origin of the high rectification ratio in the diodes, the injection, transport and structure of the diodes with two different copper cathodes were examined using impedance spectroscopy and x-ray photoelectron spectroscopy (XPS). The impedance data confirm that the difference in diode performance arises from the copper/PTAA interface. The XPS measurements show that the copper surface in both diode structures is covered by a layer of Cu{sub 2}O topped by an organic layer. The organic layer is thicker on one of the surfaces, which results in lower reverse currents and higher rectification ratios in the printed diodes. We suggest a model where a dipole at the dual insulating layer induces a shift in the semiconductor energy levels explaining the difference between the diodes with different cathodes.

Lilja, K E; Heljo, P; Tuukkanen, S; Joutsenoja, T; Lupo, D [Tampere University of Technology, Department of Electronics, PO Box 692, FI-33101 Tampere (Finland); Majumdar, H S; Oesterbacka, R [Abo Akademi University, Department of Natural Science and Center for Functional Materials, Porthansgatan 3, FI-20500, Turku (Finland); Lahtonen, K; Valden, M, E-mail: kaisa.lilja@tut.fi [Tampere University of Technology, Surface Science Laboratory, PO Box 692, FI-33101 Tampere (Finland)

2011-07-27

357

Doubly excited states of molecular hydrogen by scattered electron-ion coincidence measurements  

Science.gov (United States)

Electron energy-loss spectroscopy and electron-ion coincidence techniques were used to determine the total generalized oscillator strength distribution (GOSD) of molecular hydrogen (H2) under 200 eV incident electron energy at a scattering angle of 6 degree. Ionic GOSDs were obtained for each formed ion at each energy-loss value and were determined by scattered electron-ion coincidence measurements. The total and partial ionic GOSDs of H2 were compared with the OOSDs from the experimental results of both photon and fast-electron impacts. We observed auto-ionization induced by excitation to the optically forbidden Q1 1?+g(1) state near 28 eV. Additionally, the non-ionic GOSD, defined as the difference between the total GOSD and the total ionic GOSD, was determined. From the non-ionic GOSD, neutral dissociation from excitation to the forbidden Q1 1?+g(1) state near 28 eV and the Q2 series near 35 eV were identified. Contribution to the Topical Issue "Electron and Positron Induced Processes", edited by Michael Brunger, Radu Campeanu, Masamitsu Hoshino, Oddur Ingólfsson, Paulo Limão-Vieira, Nigel Mason, Yasuyuki Nagashima and Hajime Tanuma.

Takahashi, Karin; Sakata, Yosuke; Hino, Yuta; Sakai, Yasuhiro

2014-04-01

358

Electron molecular beam epitaxy: Layer-by-layer growth of complex oxides via pulsed electron-beam deposition  

International Nuclear Information System (INIS)

Complex oxide epitaxial film growth is a rich and exciting field, owing to the wide variety of physical properties present in oxides. These properties include ferroelectricity, ferromagnetism, spin-polarization, and a variety of other correlated phenomena. Traditionally, high quality epitaxial oxide films have been grown via oxide molecular beam epitaxy or pulsed laser deposition. Here, we present the growth of high quality epitaxial films using an alternative approach, the pulsed electron-beam deposition technique. We demonstrate all three epitaxial growth modes in different oxide systems: Frank-van der Merwe (layer-by-layer); Stranski-Krastanov (layer-then-island); and Volmer-Weber (island). Analysis of film quality and morphology is presented and techniques to optimize the morphology of films are discussed.

2013-01-14

359

Molecular And Electronic Structures of Mononuclear Iron Complexes Using Strongly Electron-Donating Ligands And Their Oxidized Forms  

Energy Technology Data Exchange (ETDEWEB)

The ligand L{sup 2-} (H{sub 2}L = N,N'-dimethyl-N,N'-bis(3,5-di-t-butyl-2-hydroxybenzyl)-1,2-diaminoethane) has been employed for the synthesis of two mononuclear Fe{sup III} complexes, namely, [LFe({eta}{sup 2}-NO{sub 3})] and [LFeCl]. L{sup 2-} is comprised of four strongly electron-donating groups (two tert-amines and two phenolates) that increase the electron density at the coordinated ferric ions. This property should facilitate oxidation of the complexes, that is, stabilization of the oxidized species. The molecular structures in the solid state have been established by X-ray diffraction studies. [LFeCl] is five-coordinate in a square-pyramidal coordination environment with the ligand adopting a trans-conformation, while [LFe({eta}{sup 2}-NO{sub 3})] is six-coordinate in a distorted octahedral environment with the ligand in a {beta}-cis conformation. The electronic structures have been studied using magnetization, EPR, Mossbauer (with and without applied field), UV-vis-NIR, and X-ray absorption spectroscopies, which demonstrate highly anisotropic covalency from the strong {sigma}- and {pi}-donating phenolates. This analysis is supported by DFT calculations on [LFeCl]. The variations of the well-understood spectroscopic data in the solid state to the spectroscopic data in solution have been used to obtain insight in the molecular structure of the two complexes in solution. While the molecular structures of the solid states are retained in solutions of nonpolar aprotic solvents, there is, however, one common molecular structure in all protic polar solvents. The analysis of the LMCT transitions and the rhombicity E/D clearly establish that both compounds exhibit a {beta}-cis conformation in these protic polar solvents. These two open coordination sites, cis to each other, allow access for two potential ligands in close proximity. Electrochemical analysis establishes two reversible oxidation waves for [LFeCl] at +0.55 V and +0.93 V vs Fc{sup +}/Fc and one reversible oxidation wave at +0.59 V with an irreversible oxidation at +1.07 V vs Fc{sup +}/Fc for [LFe({eta}{sup 2}-NO{sub 3})]. The one- and the two-electron oxidations of [LFeCl] by chronoamperometry have been followed spectroscopically. The increase of a strong band centered at 420 nm indicates the formulation of [LFeCl]{sup +} as a Fe{sup III} monophenoxyl radical complex and of [LFeCl]{sup 2+} as a Fe{sup III} bisphenoxyl radical complex. These studies imply that the ligand L{sup 2-} is capable of providing a flexible coordination geometry with two binding sites for substrates and the allocation of two oxidation equivalents on the ligand.

Strautmann, J.B.H.; George, S.DeBeer; Bothe, E.; Bill, E.; Weyhermuller, T.; Stammler, A.; Bogge, H.; Glaser, T.

2009-05-26

360

Transmission of 0--15 eV monoenergetic electrons through thin-film molecular solids  

International Nuclear Information System (INIS)

The transmission coefficient for monoenergetic electrons (0.04 eV FWHM) passing through thin films (approx.100 A) of molecular solids is measured as a function of electron energy in the range 0--15 eV. The visibility of sharp maxima in the transmission spectra is enhanced by measuring the negative value of the second energy derivative of the transmitted current with respect to electron energy. In benzene, fluorobenzene, pyridine, benzaldehyde, furan, cyclohexene and 1,3- and 1,4-cyclohexadiene, the spectra exhibit from six to eight maxima, whereas in pyrrole and thiophene four structures are resolved. With the exception of the first two features in fluorobenzene and the first feature for the other solids investigated, all other maxima correlate within at least +- 0.5 eV with the gas-phase electronic transitions. This correlation is achieved by increasing the energy scale of the transmission spectra relative to the gas-phase electronic energy levels. These findings corroborate previous experiments on solid organic films by Hamill and co-workers who attributed peaks in the first energy derivative of the transmitted current to energy-loss events. It is shown that the transmission features can arise either from an increase in the overall transmission coefficient due to the production of inelastically scattered electrons or from the formation of an electron--exciton complex through the temporary capture of an injected excess electron by field of a Frenkel exciton. The first low-energy feature in each spectrum may possibly arise from an enhancement of vibrational excitation related to the energy dependence of the structure factor

1979-12-15

 
 
 
 
361

Optical rectification and field enhancement in a plasmonic nanogap  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Metal nanostructures act as powerful optical antennas1, 2 because collective modes of the electron fluid in the metal are excited when light strikes the surface of the nanostructure. These excitations, known as plasmons, can have evanescent electromagnetic fields that are orders of magnitude larger than the incident electromagnetic field. The largest field enhancements often occur in nanogaps between plasmonically active nanostructures3, 4, but it is extremely challenging to measure the field...

Ward, Daniel R.; Hu?ser, Falco; Pauly, Fabian; Cuevas, Juan Carlos; Natelson, Douglas

2010-01-01

362

A high molecular weight donor for electron injection interlayers on metal electrodes.  

Science.gov (United States)

The molecular donor 9,9'-ethane-1,2-diylidene-bis(N-methyl-9,10-dihydroacridine) (NMA) has been synthesized, and its electronic properties were characterized both in solution using cyclic voltammetry and optical absorption spectroscopy, and at interfaces to metals with photoelectron spectroscopy (PES). The optical energy gap of NMA in solution increases by 0.10 eV when the compound is doubly oxidized. On the basis of quantum-chemical calculations, this ipsochromic effect is rationalized by a change in geometry involving a severe torsion of the two acridinium moieties with respect to the central double bond, thus reducing conjugation upon oxidation. PES is reported for NMA deposited on Au(111), Ag(111), and Cu(111) single crystals. A decrease of the sample work function is observed that becomes larger with increasing molecular coverage and clearly exceeds values that would be expected for metal surface electron "push back" alone, confirming the electron donating nature of NMA. The growth mode of NMA on all three surfaces is almost layer-by-layer (Frank-van der Merwe). For tris(8-hydroxyquinoline)aluminum (Alq(3)) deposited on top of a NMA-modified Au(111) surface, the electron injection barrier (EIB) is reduced by 0.25 eV compared to that on pristine Au(111). Furthermore, the EIB reduction depends linearly on Phi of the donor-modified Au(111) surface, adjustable by NMA precoverage. This enables continuous tuning of the EIB in organic electronic devices, in order to optimize device efficiency and performance. PMID:19856371

Bröker, Benjamin; Blum, Ralf-Peter; Beverina, Luca; Hofmann, Oliver T; Sassi, Mauro; Ruffo, Riccardo; Pagani, Giorgio A; Heimel, Georg; Vollmer, Antje; Frisch, Johannes; Rabe, Jürgen P; Zojer, Egbert; Koch, Norbert

2009-12-01

363

Ab initio molecular dynamics study on the electron capture processes of protonated methane (CH5+).  

Science.gov (United States)

Electron capture dynamics of protonated methane (CH5(+)) have been investigated by means of a direct ab initio molecular dynamics (MD) method. First, the ground and two low-lying state structures of CH5 (+) with eclipsed Cs , staggered Cs and C2v symmetries were examined as initial geometries in the dynamics calculation. Next, the initial structures of CH5 (+) in the Franck-Condon (FC) region were generated by inclusion of zero point energy and then trajectories were run from the selected points on the assumption of vertical electron capture. Two competing reaction channels were observed: CH5 (+) + e (-)--> CH4 + H (I) and CH5 (+) + e (-) --> CH3 + H2 (II). Channel II occurred only from structures very close to the s- Cs geometry for which two protons with longer C-H distances are electronically equivalent in CH5 (+). These protons have the highest spin density as hydrogen atoms following vertical electron capture of CH5 (+) and are lost as H2. On the other hand, channel I was formed from a wide structural region of CH5 (+). The mechanism of the electron capture dynamics of CH5 is discussed on the basis of the theoretical results. PMID:18959386

Tachikawa, Hiroto; Orr-Ewing, Andrew J

2008-11-20

364

Electron-beam-induced changes in ultra-high-molecular weight polyethylene  

Science.gov (United States)

Post-irradiation studies have been carried out to elucidate the effects of electron beam irradiation on the structural, optical, dielectric and thermal properties of ultra-high-molecular weight polyethylene (UHMWPE) films. The modifications in the optical band gap, activation energy, oscillator strength, and transition dipole moment have been investigated as a function of electron radiation dose using UV-Vis absorption spectra of UHMWPE films. The spectral analysis showed a decrease in both the optical band gap and activation energy, whereas the oscillator strength and the transition dipole moment increased with the increase in electron radiation doses. Further, the dielectric measurements indicated a slight increase in the dielectric constant and the ac conductivity of the UHMWPE films upon electron irradiation. The thermal analysis carried out by differential scanning calorimeter and thermo-gravimetric analyzer revealed that the melting temperature, degree of crystallinity and thermal stability of the UHMWPE films increased, obviously, due to the predominant cross-linking following high doses of electron radiation.

Mathad, R. D.; Harish Kumar, H. G.; Sannakki, Basavaraj; Sanjeev, Ganesh; Sarma, K. S. S.; Francis, Sanju

365

Modification of Defect Structures in Graphene by Electron Irradiation: Ab Initio Molecular Dynamics Simulations  

Energy Technology Data Exchange (ETDEWEB)

Defects play an important role on the unique properties of the sp2-bonded materials, such as graphene. The creation and evolution of mono-vacancy, di-vacancy, Stone-Wales (SW) and grain boundaries (GBs) under irradiation in graphene are investigated using density functional theory and time-dependent density functional theory molecular dynamics simulations. It is of great interest to note that the patterns of these defects can be controlled through electron irradiation. The SW defects can be created by electron irradiation with energy of above the displacement threshold energy (Td, {approx}19 eV) and can be healed with an energy (14-18 eV) lower than Td. The transformation between four types of divacancies, V2(5-8-5), V2(555-777), V2(5555-6-7777), and V2(55-77) can be realized through bond rotation induced by electron irradiation. The migrations of divancancies, SW defects, and GBs can also be controlled by electron irradiation. Thus, electron irradiation can serve as an important tool to modify morphology in a controllable manner, and to tailor the physical properties of graphene.

Wang, Zhiguo; Zhou, Yungang; Bang, Junhyeok; Prange, Micah P.; Zhang, Shengbai; Gao, Fei

2012-08-02

366

Long-range electron tunnelling in oligo-porphyrin molecular wires.  

Science.gov (United States)

Short chains of porphyrin molecules can mediate electron transport over distances as long as 5-10 nm with low attenuation. This means that porphyrin-based molecular wires could be useful in nanoelectronic and photovoltaic devices, but the mechanisms responsible for charge transport in single oligo-porphyrin wires have not yet been established. Here, based on electrical measurements of single-molecule junctions, we show that the conductance of the oligo-porphyrin wires has a strong dependence on temperature, and a weak dependence on the length of the wire. Although it is widely accepted that such behaviour is a signature of a thermally assisted incoherent (hopping) mechanism, density functional theory calculations and an accompanying analytical model strongly suggest that the observed temperature and length dependence is consistent with phase-coherent tunnelling through the whole molecular junction. PMID:21804555

Sedghi, Gita; García-Suárez, Víctor M; Esdaile, Louisa J; Anderson, Harry L; Lambert, Colin J; Martín, Santiago; Bethell, Donald; Higgins, Simon J; Elliott, Martin; Bennett, Neil; Macdonald, J Emyr; Nichols, Richard J

2011-08-01

367

Ion source of molecular beam with ionization by electron beam in magnetic field  

International Nuclear Information System (INIS)

The high-efficiency ion source for a mass-spectrometer detector of molecular beams and their scattering products is described. The ion source is designed according to a scheme of impact ionization of a beam particle by a longitudinal electron beam in a magnetic field with a strength of up to 130 mT. The design of the source developed is very flexible and has no limitations for use in any experiments with molecular beams. An ionization efficiency of particles of an atomic helium beam of 10-3 ions/atom has been achieved. The useful signal-to-noise ratio in the detector chamber is 3x104 during detection of ions with the mass-to-charge ratio m/q = 4 amu

2006-01-01

368

Electron-correlated fragment-molecular-orbital calculations for biomolecular and nano systems.  

Science.gov (United States)

Recent developments in the fragment molecular orbital (FMO) method for theoretical formulation, implementation, and application to nano and biomolecular systems are reviewed. The FMO method has enabled ab initio quantum-mechanical calculations for large molecular systems such as protein-ligand complexes at a reasonable computational cost in a parallelized way. There have been a wealth of application outcomes from the FMO method in the fields of biochemistry, medicinal chemistry and nanotechnology, in which the electron correlation effects play vital roles. With the aid of the advances in high-performance computing, the FMO method promises larger, faster, and more accurate simulations of biomolecular and related systems, including the descriptions of dynamical behaviors in solvent environments. The current status and future prospects of the FMO scheme are addressed in these contexts. PMID:24740821

Tanaka, Shigenori; Mochizuki, Yuji; Komeiji, Yuto; Okiyama, Yoshio; Fukuzawa, Kaori

2014-06-14

369

Field-free molecular alignment probed by the free electron laser in Hamburg (FLASH)  

CERN Document Server

We report experiments on field-free molecular alignment performed at FLASH, the free electron laser (FEL) in Hamburg. The impulsive alignment induced by a 100 fs near-infrared laser pulse in a rotationally cold CO_2 sample is characterized by ionizing and dissociating the molecules with a time delayed extreme ultra-violet (XUV) FEL pulse. The time-dependent angular distributions of ionic fragments measured by a velocity map imaging spectrometer shows rapid changes associated with the induced rotational dynamics. The experimental results also show hints of a dissociation process that depends non-linearly on the XUV intensity. With samples of aligned molecules at FLASH, experiments using ultrashort XUV pulses become possible in the molecular frame, which will enable new insights into the understanding of molecules and their interactions.

Johnsson, P; Siu, W; Huismans, Y; Lepine, F; Marchenko, T; Düsterer, S; Tavella, F; Stojanovic, N; Azima, A; Treusch, R; Kling, M F; Vrakking, M J J

2009-01-01

370

Electronic and transport properties of azobenzene monolayer junctions as molecular switches  

CERN Document Server

We investigate from first-principles the change in transport properties of a two-dimensional azobenzene monolayer sandwiched between two Au electrodes that undergoes molecular switching. We focus on transport differences between a chemisorbed and physisorbed top monolayer-electrode contact. The conductance of the monolayer junction with a chemisorbed top contact is higher in \\textit{trans} configuration, in agreement with the previous theoretical predictions of one-dimensional single molecule junctions. However, with a physisorbed top contact, the "ON" state with larger conductance is associated with the \\textit{cis} configuration due to a reduced effective tunneling pathway by switching from \\textit{trans} to \\textit{cis}, which successfully explains recently experimental measurements of azobenzene monolayer junctions. A simple model is developed to explain electron transmission across subsystems in the molecular junction. We also discuss the effects of monolayer packing density, molecule tilt angle, and con...

Wang, Yan

2012-01-01

371

AC field induced quantum rectification effect in tunnel junctions  

CERN Multimedia

We study the appearance of directed current in tunnel junctions, quantum ratchet effect, in the presence of an external ac field f(t). The current is established in a one-dimensional discrete inhomogeneous "tight-binding model". By making use of a symmetry analysis we predict the right choice of f(t) and obtain the directed current as a difference between electron transmission coefficients in opposite directions, $\\Delta T = T^{LR}-T^{RL}$. Numerical simulations confirm the predictions of the symmetry analysis and moreover, show that the directed current can be drastically increased by a proper choice of frequency and amplitudes of the ac field f(t).

Fistul, M V; Flach, S

2003-01-01

372

Potential curves and spectroscopic study of the electronic states of the molecular ion LiCs+  

International Nuclear Information System (INIS)

Full text.Due to a very accurate high-resolution techniques and to the spectacular developments in ultracold alkali atom trapping developments which are at the root of photo association spectroscopy there has been a renewed interest on the spectroscopic study of alkali dimers. The existence of new experimental data on these species has stimulated theoretical approaches, necessary to provide predictions accurate enough to be useful for interpretation and evenly for guidance of experiments. With the aim of improving the accuracy of predictions we will perform a theoretical study of the electronic structure of the molecular ion LiCs+, using a method mainly in the way by which core-valence effects are taken into account. To investigate the electronic structure of LiCs+ we will use the package CIPSI (Configuration Interaction by Perturbation of a multiconfiguration wave function Selected Interactively) of the Laboratoire de Physique Quantique (Toulouse, France). The atoms Li and Cs will be treated through non-empirical effective one electron core potentials of Durand and Barthelat type. Molecular orbitals for LiCs+ will be derived from Self Consistent Field Calculations (SCF) and full valence Configuration Interaction (IC) calculations. A core-core interaction more elaborated than the usual approximation 1/R will be taken into account as the sum of an exponential repulsive term plus a long range dispersion term approximated by the well known London formula. Potential energy calculations will be performed for different molecular states, for numerous values of the inter-nuclear distance R in a wide range. Spectroscopic constants have been derived for the bound states with a regular shape A ro vibrational study have been performed for the ground states with a calculation of the rotational and centrifugal distortion constants. A calculation for the transition dipole moment and matrix elements have been done for the bound states

2004-05-26

373

Vibration rotation calculation of the electronic states of the molecular ion NaCs+  

International Nuclear Information System (INIS)

Full text.In the past ten years there has been a renewed interest on the spectroscopic study of alkali dimers because of the high resolution techniques and the spectacular developments in ultracold alkali atom trapping which are at the root of the photo association spectroscopy. The existence of new experimental data of these species has stimulated theoretical approaches, necessary to provide predictions accurate enough to be useful for interpretation and evenly for guidance of experiments. With the aim of improving the accuracy of predictions we will perform a theoretical study of the electronic structure of the molecular ion NaCs+, using a method mainly in the way by which core-valence effects are taken into account. To investigate the electronic structure of NaCs+ we will use the package CIPSI (Configuration Interaction by Perturbation of a multiconfiguration wave function Selected Interactively) of the Laboratoire de Physique Quantique (Toulouse, France). The atoms Na and Cs will be treated through non-empirical effective one electron core potentials of Durand and Barthelat type. Molecular orbitals for NaCs+ will be derived from Self Consistent field Calculations SCF) and full valence Configuration Interaction (IC) calculations. A core-core interaction more elaborated than the usual approximation 1/R will be taken into account as the sum of an exponential repulsive term plus a long range dispersion term approximated by the well known London formula. Potential energy calculations will be performed for different molecular states, for numerous values of the inter-nuclear distance R in a wide range. Spectroscopic constants will be derived for the bound states with a regular shape. A ro vibrational study have been performed for the ground states with a calculation of the rotational and centrifugal distortion constants. A calculation for the transition dipole moment and matrix elements have been done for the bound states. Determination of an RKR potentials of the bound states of the ion NaCs+ obtained from an ab initio calculation

2004-05-26

374

A study of electron impact excitation of molecular oxygen at a scattering angle of 180 deg  

International Nuclear Information System (INIS)

Excitation of molecular oxygen by electron impact has been observed at the backward scattering angle of 180 deg. . For these studies a new solenoid system with a conical geometry has been designed to implement the angle-changing technique. Energy loss spectra have been measured to deduce differential cross-sections for vibrational excitation of the X3?g- ground state and excitation of the a1?g state at 180 deg. . Excitation of the b1?g+ state has not been observed at 180 deg. in agreement with the theoretically predicted selection rule ?-??+ at that angle

2004-01-01

375

Theoretical studies of a nanoparticle bridge platform for molecular electronics measurements  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The main focus of this thesis is the theoretical investigations of a nanogap platform used for molecular electronics measurements under ambient conditions. The nanogap is about 20 nm wide, while the molecules investigated here (octanethiol(OT) and octanedithiol(ODT)) are about 1-1.5 nm long making it impossible to bridge the gap with one molecule. Two different approaches are investigated. In the first approach the electrodes of the nanogap are coated with a layer of OT molecules, and large g...

Lo?fa?s, Henrik

2011-01-01

376

Quantum Simulation of 2p-? Electronic Hamiltonian in Molecular Ethylene by Using an NMR Quantum Computer  

Directory of Open Access Journals (Sweden)

Full Text Available Classical simulation of a quantum system is a hard problem. It’s known that these problems can be solved efficiently by using quantum computers. This study demonstrates the simulation of the molecular Hamiltonian of 2p-? electrons of ethylene in order to calculate the ground state energy. The ground state energy is estimated by an iterative phase estimation algorithm. The ground state is prepared by the adiabatic state preparation and the implementation of the procedure is carried out by numerical simulation of two-qubit NMR quantum simulator. The readout scheme of the simulator is performed by extracting binary bits via NMR interferometer.

Deniz Türkpençe

2013-06-01

377

The electronic and optical properties of warm dense nitrous oxide using quantum molecular dynamics simulations  

International Nuclear Information System (INIS)

First-principles molecular-dynamics simulations based on density-functional theory have been used to study the electronic and optical properties of fluid nitrous oxide under extreme conditions. Systematic descriptions of pair-correlation function, atomic structure, and the charge density distribution are used to investigate the dissociation of fluid nitrous oxide. The electrical and optical properties are derived from the Kubo-Greenwood formula. It is found that the nonmetal-metal transition for fluid nitrous oxide can be directly associated to the dissociation and has significant influence on the optical properties of the fluid.

2012-11-01

378

Using model of united atom for evaluation of lifetime of negative molecular ions relatively electron autosplitting  

International Nuclear Information System (INIS)

The model, making it possible to evaluate the lifetimes of the form resonances for the low energy electrons scattering (from the thermal one up to several eV) on the multiatomic molecules, is proposed. The model parameters are determined by the concrete structural and experimental molecular characteristics. The results of the evaluation calculation of the negative ions lifetime of the different symmetry molecules of the diatomic halogens, parabenzoquinone, C60 fullerene, benzothiazoles, anthraquinone derivatives and benzene substitutes are presented. The obtained data show that the lifetimes prove to be sufficient for formation of the fragmentary ions, observed in the negative ions mass-spectra

2002-10-01

379

Charge transfer molecular complexes of arylidene anthranilic acid derivatives with ?-electron acceptors  

Science.gov (United States)

X-Benzylidenesanthranilic acid molecular complexes with ?-acceptors, tetracyanoethylene, 2,3-dichloro-5,6-dicyano- p-benzoquinone and chloranil, have been studied. The intramolecular hydrogen bonding that exists in such compounds greatly inhibits the transition of the nitrogen azomethine n-electrons. The formation constant values and molar extinction coefficients of the p-dimethyl-aminobenzylidenean-thranilic acid-DDQ CT complexes have been determined in CH 2Cl 2, C 2H 4Cl 2 and CHCl 3 in the temperature range 10-30°C. Such CT complexes are of strong n-? type.

El-Gyar, S. A.; Ibrahim, S. A.; El-Gahami, M. A.

1989-01-01

380

Characterization of molecular mobility in seed tissues: an electron paramagnetic resonance spin probe study.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The relationship between molecular mobility (tauR) of the polar spin probe 3-carboxy-proxyl and water content and temperature was established in pea axes by electron paramagnetic resonance (EPR) and saturation transfer EPR. At room temperature, tauR increased during drying from 10(-11) s at 2.0 g water/g dry weight to 10(-4) s in the dry state. At water contents below 0.07 g water/g dry weight, tauR remained constant upon further drying. At the glass transition temperature, tauR was constant ...

Buitink, J.; Hemminga, M. A.; Hoekstra, F. A.

1999-01-01

 
 
 
 
381

Studies of the surface structures of molecular crystals and of adsorbed molecular monolayers on the (111) crystal faces of platinum and silver by low-energy electron diffraction  

International Nuclear Information System (INIS)

The structures of molecular crystal surfaces were investigated for the first time by the use of low-energy electron diffraction (LEED). The experimental results from a variety of molecular crystals were examined and compared as a first step towards understanding the properties of these surfaces on a microscopic level. The method of sample preparation employed, vapor deposition onto metal single-crystal substrates at low temperatures in ultrahigh vacuum, allowed concurrent study of the structures of adsorbed monolayers on metal surfaces and of the growth processes of molecular films on metal substrates. The systems investigated were ice, ammonia, naphthalene, benzene, the n-paraffins (C_3 to C_8), cyclohexane, trioxane, acetic acid, propionic acid, methanol, and methylamine adsorbed and condensed on both Pt(111) and Ag(111) surfaces. Electron-beam-induced damage of the molecular surfaces was observed after electron exposures of 10"-"4 A sec cm"-"2 at 20 eV. Aromatic molecular crystal samples were more resistant to damage than samples of saturated molecules. The quality and orientation of the grown molecular crystal films were influenced by substrate preparation and growth conditions. Forty ordered monolayer structures were observed. 110 figures, 22 tables, 162 references

1977-01-01

382

Studies of the surface structures of molecular crystals and of adsorbed molecular monolayers on the (111) crystal faces of platinum and silver by low-energy electron diffraction  

Energy Technology Data Exchange (ETDEWEB)

The structures of molecular crystal surfaces were investigated for the first time by the use of low-energy electron diffraction (LEED). The experimental results from a variety of molecular crystals were examined and compared as a first step towards understanding the properties of these surfaces on a microscopic level. The method of sample preparation employed, vapor deposition onto metal single-crystal substrates at low temperatures in ultrahigh vacuum, allowed concurrent study of the structures of adsorbed monolayers on metal surfaces and of the growth processes of molecular films on metal substrates. The systems investigated were ice, ammonia, naphthalene, benzene, the n-paraffins (C/sub 3/ to C/sub 8/), cyclohexane, trioxane, acetic acid, propionic acid, methanol, and methylamine adsorbed and condensed on both Pt(111) and Ag(111) surfaces. Electron-beam-induced damage of the molecular surfaces was observed after electron exposures of 10/sup -4/ A sec cm/sup -2/ at 20 eV. Aromatic molecular crystal samples were more resistant to damage than samples of saturated molecules. The quality and orientation of the grown molecular crystal films were influenced by substrate preparation and growth conditions. Forty ordered monolayer structures were observed. 110 figures, 22 tables, 162 references.

Firment, L.E.

1977-01-01

383

Formation of molecular nitrogen and diazene by electron irradiation of solid ammonia  

International Nuclear Information System (INIS)

We present an experimental study on 500–3000 eV energy electron irradiation of ammonia ice at 20 K. While molecular nitrogen and diazene (N2H2) were detected during post-irradiation thermal desorption no appreciable traces of hydrazine (N2H4) were observed. We suggest that the recombination between adjacent nitrogen atoms and between neighboring NH radicals can be the main mechanism responsible for the formation of the observed molecules, whereas hydrazine formed by two amino radicals is probably in an excited state and decays into diazene and hydrogen. - Highlights: ? Experimental study on 500–3000 eV electron irradiation of ammonia ice at 20 K. ? Observation of nitrogen and diazene during post-irradiation thermal desorption. ? No appreciable traces of hydrazine (N2H4).

2012-06-01

384

Auger electrons--a nanoprobe for structural, molecular and cellular processes.  

Science.gov (United States)

This paper provides a brief review of recently published work on biophysical and biological aspects of Auger processes. Three specific questions have been considered. (1) Does charge neutralisation contribute to molecular damage such as DNA strand breaks? (2) How many DNA double strand breaks are produced by a single decay of DNA bound (125)I? (3) What is the correlation between number of gammaH2AX foci and number of double strand breaks (DSB)? The paper also gives preliminary reports on two new calculations: (a) calculation of the spectrum of Auger electrons released during decay of (124)I and (b) the use of Auger electrons in the decay of (125)I as a probing agent of novel DNA structures. PMID:17132671

Nikjoo, H; Girard, P; Charlton, D E; Hofer, K G; Laughton, C A

2006-01-01

385

High electron mobility in Ga(In)NAs films grown by molecular beam epitaxy  

Energy Technology Data Exchange (ETDEWEB)

We report the highest mobility values above 2000 cm{sup 2}/Vs in Si doped GaNAs film grown by molecular beam epitaxy. To understand the feature of the origin which limits the electron mobility in GaNAs, temperature dependences of mobility were measured for high mobility GaNAs and referential low mobility GaInNAs. Temperature dependent mobility for high mobility GaNAs is similar to the GaAs case, while that for low mobility GaInNAs shows large decrease in lower temperature region. The electron mobility of high quality GaNAs can be explained by intrinsic limiting factor of random alloy scattering and extrinsic factor of ionized impurity scattering.

Miyashita, Naoya; Ahsan, Nazmul; Monirul Islam, Muhammad; Okada, Yoshitaka [Research Center for Advanced Science and Technology (RCAST), The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904 (Japan); Inagaki, Makoto [Toyota Technological Institute, 2-12-1 Hisakata, Tempaku-ku, Nagoya 468-8511, Aichi (Japan); Yamaguchi, Masafumi [Research Center for Advanced Science and Technology (RCAST), The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904 (Japan); Toyota Technological Institute, 2-12-1 Hisakata, Tempaku-ku, Nagoya 468-8511, Aichi (Japan)

2012-11-26

386

Fabrication of dissimilar metal electrodes with nanometer interelectrode distance for molecular electronic device characterization  

Energy Technology Data Exchange (ETDEWEB)

We report a versatile process for the fabrication of dissimilar metal electrodes with a minimum interelectrode distance of less than 6 nm using electron beam lithography and liftoff pattern transfer. This technique provides a controllable and reproducible method for creating structures suited for the electrical characterization of asymmetric molecules for molecular electronics applications. Electrode structures employing pairs of Au electrodes and non-Au electrodes were fabricated in three different patterns. Parallel electrode structures 300 {mu}m long with interelectrode distances as low as 10 nm, 75 nm wide electrode pairs with interelectrode distances less than 6 nm, and a multiterminal electrode structure with reproducible interelectrode distances of 8 nm were realized using this technique. The processing issues associated with the fabrication of these structures are discussed along with the intended application of these devices. (c) 2000 American Vacuum Society.

Guillorn, Michael A. [Department of Electrical and Computer Engineering, University of Tennessee, Knoxville, Tennessee 37996 (United States); Carr, Dustin W. [Cornell Nanofabrication Facility, Cornell University, Ithaca, New York 14853 (United States); Tiberio, Richard C. [Cornell Nanofabrication Facility, Cornell University, Ithaca, New York 14853 (United States); Greenbaum, Elias [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Simpson, Michael L. [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

2000-05-01

387

Center for Molecular Electronics, University of Missouri, St. Louis. Environmental Assessment  

Energy Technology Data Exchange (ETDEWEB)

The Department of Energy (DOE) proposes to authorize the University of Missouri, St. Louis to proceed with the detailed design and construction of the proposed Center for Molecular Electronics. The proposed Center would consist of laboratories and offices housed in a three-story building on the University campus. The proposed modular laboratories would be adaptable for research activities principally related to physics, chemistry, and electrical engineering. Proposed research would include the development and application of thin-film materials, semi-conductors, electronic sensors and devices, and high-performance polymers. Specific research for the proposed Center has not yet been formulated, therefore, specific procedures for any particular process or study cannot be described at this time. The proposed construction site is an uncontaminated panel of land located on the University campus. This report contains information about the environmental assessment that was performed in accordance with this project.

1994-06-01

388

Diffusion and phase diagram of an electron-hole bilayer: A molecular dynamics study  

International Nuclear Information System (INIS)

Molecular dynamics simulations of a classical, symmetric electron-hole bilayer for various values of the coupling strength ? and interlayer separation distance d have been performed. We have analyzed the pair correlation functions, the static structure factor, and the diffusion coefficient in this study. As d is decreased, diffusion goes through a minimum and then increases very rapidly; its behavior at small d can be attributed to the formation of stable, weakly interacting electron-hole dipoles. We have constructed the phase diagram in the ?-d plane based on the amplitude of the main peak of the intralayer static structure factor and the diffusion coefficient. It is found that a solid phase is not possible for d less than about 0.5 for any ?, nor for ? less than about 100 for any d. Our phase diagram, obtained using a different methodology, is in good agreement with the one in the literature

2007-04-15

389

Molecular imaging with X-ray free electron lasers: dream or reality?  

CERN Document Server

X-ray Free Electron Lasers (XFEL) are revolutionary photons sources, whose ultrashort, brilliant pulses are expected to allow single molecule diffraction experiments providing structural information on the atomic length scale. This ultimate goal, however, is currently hampered by several challenging questions basically concerning sample damage, Coulomb explosion and the role of nonlinearity. By employing an original \\emph{ab-initio} approach, as well as exceptional resources of parallel computing, we address these issues showing that accurate XFEL-based single molecule imaging will be only possible with ultrashort pulses of half of femtosecond, due to significant radiation damage and the formation of preferred multi-soliton clusters which reshape the overall electronic density of the molecular system at the femtosecond scale.

Fratalocchi, Andrea

2010-01-01

390

Electronic Ferroelectricity in a Molecular Crystal with Large Polarization Directing Antiparallel to Ionic Displacement  

Science.gov (United States)

Ferroelectric polarization of 6.3?Ccm-2 is induced by the neutral-to-ionic transition, upon which nonpolar molecules of electron donor tetrathiafulvalene (TTF) and acceptor p-chloranil (CA) are incompletely ionized to ±0.60e and dimerized along the molecular stacking chain. We find that the ferroelectric properties are governed by intermolecular charge transfer rather than simple displacement of static point charge on molecules. The observed polarization and poling effect on the absolute structural configuration can be interpreted in terms of electronic ferroelectricity, which not only exhibits antiparallel polarity to the ionic displacement but also enhances the polarization more than 20 times that of the point-charge model.

Kobayashi, Kensuke; Horiuchi, Sachio; Kumai, Reiji; Kagawa, Fumitaka; Murakami, Youichi; Tokura, Yoshinori

2012-06-01

391

Electron spin resonance and photoluminescence in pyrolytic silicon nitride films irradiated with argon and molecular ions  

International Nuclear Information System (INIS)

The photoluminescence and electron spin resonance phenomena are studied at room temperature for pyrolytic silicon nitride films irradiated with argon ions or molecular nitrogen ions and annealed at temperatures in the range 500-1100oC. The absorption spectrum suggests that the broad photoluminescence band at 400-600 nm is due to electron transitions between the band tails. The low-dose irradiation with argon ions slightly reduces the photoluminescence intensity, whereas the high-dose irradiation followed by annealing at 800-900oC can induce a more than twofold increase in the intensity. At the same time, irradiation with nitrogen ions profoundly suppresses the integrated photoluminescence intensity that decreases by more than an order of magnitude. A correlation between the changes in the photoluminescence intensity and the amplitude of the ESR spectra on annealing of the silicon nitride films is observed.

2009-07-01

392

Absolute measurements of electron capture cross sections of C3+ from atomic and molecular hydrogen  

International Nuclear Information System (INIS)

Absolute measurements of single- and double-electron-capture cross sections by C3+ projectiles on atomic and molecular hydrogen targets were performed for projectile energies between 1.0 and 3.5 MeV for the single- and 1.0 and 2.0 MeV for the double-capture processes. The ?H/?H2 cross section ratios were measured using an absolutely calibrated tungsten-tube furnace for the production of atomic hydrogen. The single-capture data are compared with calculations based on the boundary-corrected first Born approximation, the eikonal approximation and a semiclassical model, presenting a good overall agreement. Calculations for the double capture using an analytical expression, obtained within the independent electron approximation and based on the same semiclassical model, give a reasonable qualitative description of the data. (author)

2000-02-14

393

Electronic processes in molecular dynamics simulations of nanoscale metal tips under electric fields  

CERN Document Server

Electronic effects play a crucial role in the temperature evolution of metal parts which have electric currents running through them. The increase in temperature due to resistive heating can cause the melting of metal nanoscale wires creating damage in electric circuits. Likewise, electric currents are also present in sharp features on metal surfaces exposed to high electric fields. The destruction of such tips can lead to vacuum arcs, supplying the neutral species to build up plasma over the surface. To follow the temperature evolution caused by electric currents in such a tip, we developed a new model, based on an existing molecular dynamics code, to include resistive heating and electronic thermal conduction. The results given by the new simulation model are in good agreement with analytical predictions. (C) 2011 Published by Elsevier B.V.

Parviainen, S; Djurabekova, F; Timko, H; 10.1016/j.commatsci.2011.02.010

2011-01-01

394

Memory effect in a molecular quantum dot with strong electron-vibron interaction  

Science.gov (United States)

The multi-polaron theory of tunnelling through a molecular quantum dot (MQD) is developed, which takes phonon side-bands and strong electron attractive correlations fully into account. The dot is modeled as a d-fold degenerate energy level weakly coupled to leads. The effective attractive interaction between tunnel carriers strongly coupled to vibrons in the molecule (polarons) results in a bistable current-voltage characteristic if d>2. This behavior is in agreement with the phenomenological negative-U model that we have studied earlier [1]. The degenerate MQD with strong electron-vibron coupling has two stable current states. This switching behavior vanishes above some critical temperature . [1] A.S.Alexandrov, A.M. Bratkovsky, and R.S.Williams, Phys. Rev. B (Jan 2003).

Bratkovsky, Alexander; Alexandrov, A. S.

2003-03-01

395

Broadband Velocity Modulation Spectroscopy of Molecular Ions for Use in the Jila Electron Edm Experiment  

Science.gov (United States)

The JILA electron electric dipole moment (eEDM) experiment will use a low-lying, metastable ^3?_1 state in trapped molecular ions of HfF^+ or ThF^+. Prior to this work, the low-lying states of these molecules had been investigated by PFI-ZEKE spectroscopy. However, there were no detailed studies of the electronic structure. The recently developed technique of frequency comb velocity modulation spectroscopy (VMS) provides broad-bandwidth, high-resolution, ion-sensitive spectroscopy, allowing the acquisition of 150 cm^{-1} of continuous spectra in 30 minutes over 1500 simultaneous channels. By supplementing this technique with cw-laser VMS, we have investigated the electronic structure of HfF^+ in the frequency range of 9950 to 14600 cm^{-1}, accurately fitting and assigning 16 rovibronic transitions involving 8 different electronic states including the X^1?^+ and a^3?_1 states. In addition, an observed ^3?_{0+} state with coupling to both the X and a states has been used in the actual eEDM experiment to coherently transfer population from the rovibronic ground state of HfF^+ to the eEDM science state. Furthermore, we report on current efforts of applying frequency comb VMS at 700 - 900 nm to the study of ThF^+, which has a lower energy ^3?_1 state and a greater effective electric field, and will provide increased sensitivity for a measurement of the eEDM. A. E. Leanhardt et. al., Journal of Molecular Spectroscopy 270, 1-25 (2011). B. J. Barker, I. O. Antonov, M. C. Heaven, K. A. Peterson, Journal of Chemical Physics 136, 104305 (2012). L. C. Sinclair, K. C. Cossel, T. Coffey, J. Ye, E. A. Cornell, Physical Review Letters 107, 093002 (2011). K.C. Cossel et. al., Chemical Physics Letters 546, 1-11 (2012).

Gresh, Daniel N.; Cossel, Kevin C.; Cornell, Eric A.; Ye, Jun

2013-06-01

396

On the comparison of efficiencies of dissociative recombination and dissociation by collisions of electrons with molecular ions  

International Nuclear Information System (INIS)

General relationships are obtained between the cross section of the dissociative recombination with the formation of highly-excited atoms and that of the dissociation by collisions of electrons with molecular ions. Some concrete calculations are carried out for H_2"+. The accuracy of the collisions with electrons is discussed

1986-01-01

397

Measurements of Energy Distribution of Molecular Ions and their Fragments Produced by Electron Impact with a New Spectroscopic Technique  

Science.gov (United States)

The energy distribution function of molecules and molecular fragments produced by electron impact is measured using a Delayed Extraction Time-Of- Flight (DETOF) spectroscopy. This new technique is able to measure energy distribution of ions from thermal energies up to a few electron volts.

Ferreira, Natalia; Sigaud, L.; de Jesus, V. L. B.; Rocha, A. B.; Shah, M. B.; Montenegro, E. C.

2012-11-01

398

Measurements of Energy Distribution of Molecular Ions and their Fragments Produced by Electron Impact with a New Spectroscopic Technique  

International Nuclear Information System (INIS)

The energy distribution function of molecules and molecular fragments produced by electron impact is measured using a Delayed Extraction Time-Of- Flight (DETOF) spectroscopy. This new technique is able to measure energy distribution of ions from thermal energies up to a few electron volts.

2012-11-05

399

Analytical evaluation of molecular electronic integrals using Poisson's equation: Exponential-type orbitals and atom pairs  

Science.gov (United States)

The integral bottleneck in evaluating molecular energies arises from the two-electron contributions. These are difficult and time-consuming to evaluate, especially over exponential type orbitals, used here to ensure the correct behavior of atomic orbitals. The two-center two-electron integrals are essential to describe atom pairs in molecules and distinguish those that are bound. In this work on analytical integration, it is shown that the two-center Coulomb integrals involved can be expressed as one-electron kinetic energy-like integrals. This is accomplished using the fact that the Coulomb operator is a Green's function of the Laplacian. The ensuing integrals may be further simplified by defining spectral forms for the one-electron potential satisfying Poisson's equation therein. A sum of overlap integrals with the atomic orbital energy eigenvalue as a factor is then obtained to give the Coulomb energy. This is most easily evaluated by direct integration. The orbitals involved in three and four center integrals are translated to two centers. This is discussed very briefly. The evaluation of exchange energy is a straightforward extension of this work. The summation coefficients in spectral forms are evaluated analytically from Gaunt coefficients. The Poisson method may be used to calculate Coulomb energy integrals efficiently. For a single processor, gains of CPU time for a given chemical accuracy exceed a factor of 4. This method lends itself to efficient evaluation on a parallel computer.

Absi, Noureddine; Hoggan, Philip

400

Genetics and molecular biology of the electron flow for sulfate respiration in Desulfovibrio  

Directory of Open Access Journals (Sweden)

Full Text Available Progress in the genetic manipulation of the Desulfovibrio strains has provided an opportunity to explore electron flow pathways during sulfate respiration. The function of hydrogen production and consumption during oxidation of organic acids with sulfate as electron acceptor prompted the formulation of the hydrogen cycling model by Odom and Peck (FEMS Microbiol. Lett. 12:47-50, 1981. Examination of this model by many laboratories has generated conflicting results. Recent application of molecular genetic tools for the exploration of the metabolism of Desulfovibrio vulgaris Hildenborough has provided several new datasets that might provide insights and constraints to the electron flow pathways. These datasets include 1 gene expression changes measured in microarrays for cells cultured with different electron donors and acceptors, 2 relative mRNA abundances for cultures grown with lactate plus sulfate, and 3 a random transposon mutant library selected on lactate plus sulfate medium. Studies of directed mutations eliminating apparent key components, the quinone-interacting membrane-bound oxidoreductase (Qmo complex, the Type 1 tetraheme cytochrome c3 (Tp1- c3, or the Type 1 cytochrome c3:menaquinone oxidoreductase (Qrc complex, suggest a greater flexibility in electron flow than previously considered. The new datasets revealed the absence of random transposons in the genes encoding an enzyme with homology to CO-induced membrane-bound hydrogenase. From this result, we infer that Coo-hydrogenase plays an important role in D. vulgaris Hildenborough growth on lactate plus sulfate. These observations along with those reported previously have been combined in a model showing dual pathways of electrons from the oxidation of both lactate and the intermediate pyruvate during sulfate respiration. Continuing genetic and biochemical analyses of key genes in Desulfovibrio strains will allow further clarification of a general model for sulfate respiration.

KimberlyL.Keller

2011-06-01

 
 
 
 
401

The effects of mixing molecular gases on plasma parameters in a system with a grid-controlled electron temperature  

International Nuclear Information System (INIS)

Plasma parameter variations as a function of a mixing ratio in an electron temperature control system using a grid are investigated. Under the grid, the electron temperature, as well as electron density, is a strong function of a mixing ratio. The electron temperature decreases with a mixing ratio of molecular gases (O2 and CF4), and the large inelastic cross section of molecular gas is the reason for the decrease in the electron temperature. When the length of sheath around the grid wires is comparable to the space between the grid wires, only 10% mixing of CF4 decreases the electron temperature to 0.8 eV in 10 mTorr Ar/CF4 plasma

2002-03-01

402

Few-electron molecular states and their transitions in a single InAs quantum dot molecule  

CERN Multimedia

We study electronic configurations in a single pair of vertically coupled self-assembled InAs quantum dots, holding just a few electrons. By comparing the experimental data of non-linear single-electron transport spectra in a magnetic field with many-body calculations, we identify the spin and orbital configurations to confirm the formation of molecular states by filling both the quantum mechanically coupled symmetric and anti-symmetric states. Filling of the anti-symmetric states is less favored with increasing magnetic field, and this leads to various magnetic field induced transitions in the molecular states.

Ota, T; Tarucha, S; Nakata, Y; Song, H Z; Miyazawa, T; Usuki, T; Takatsu, M; Yokoyama, N

2005-01-01

403

Single-electron capture by Ar2+ from atomic and molecular targets  

International Nuclear Information System (INIS)

Translational-energy spectra for state-selective single-electron capture by Ar2+ from atomic (He, Ne, Ar, Kr, Xe) and molecular (N2, O2, NO, N2O, NH3, CO2, CH4, C2H6, 1-C4H8, C6H6) target gases are recorded at 6 keV impact energy using a reversed-geometry double-focusing mass spectrometer. Spectra indicate the presence of excited states of Ar2+, the populations of which are controlled by varying the ionising electron energy Esub(e). For Ar2+-He at Esub(e) = 70 eV, capture from the first excited state of Ar2+ into the ground state AR+ is most intense, whereas at Esub(e) = 43 eV, ground state to ground state capture dominates. For Ar2+-rare-gas systems, relative cross sections are discussed in terms of calculated reaction windows. For molecular targets, dissociation is evident in many cases. (author)

1987-08-28

404

Fragmentation and electronic decay of vacuum-ultraviolet-excited resonant states of molecular CsCl  

International Nuclear Information System (INIS)

Electronic and nuclear relaxation of molecular CsCl following photoexcitation in the vacuum ultraviolet region is investigated. From the total ion yield and the Cs+ and Cl+ partial ion yield spectra covering the 8 - 22 eV photon energy range, a number of resonating excited states are identified. The fragmentation patterns of the excited and ionized CsCl molecules and also the Cs2Cl2 dimers are studied in detail from ion time-of-flight mass spectra recorded at and around the resonances. Molecular dissociation following the resonant excitation is discussed and an ionic model is applied to explain the observations, emphasizing some principal differences from other alkali chloride molecules (KCl). The valence photoelectron spectra are found to show strong enhancement and pronounced new structures at resonant photon energies. These effects are assigned to a 'cross-ionic' autoionization decay process and are found to be due to a lifetime-dependent interplay between the electronic and nuclear relaxation

2003-10-14

405

Rectification in Porphyrin/Fullerene Dyads on Au(111)*  

Science.gov (United States)

We present an ultrahigh vacuum scanning tunneling microscopy (UHV-STM) and scanning tunneling spectroscopy study of ex-situ self assembled supramolecular dyads, consisting of fulleropyrrolidines (PyC2C60) axially ligated to zinc(II) tetraphenylporphyrin (ZnTPP), self organized by axial ligation to a 4-aminothiophenol (4-ATP), self assembled monolayer on gold (111). By highly diluting the PyC2C60 solution, and subsequently annealing in vacuum, isolated dyads are obtained; these show both bias polarity-dependent apparent height in STM images, and highly rectifying behaviour in tunneling spectroscopy. First principles density functional theory calculations clarify the conformational and the electronic properties of the 4-ATP/ZnTPP/PyC2C60 system. The rectifying behavior is explained using a model based on the Aviram-Ratner mechanism. * Work supported by the CNR-INFM, by a NSF US-Italy Cooperative Research Program #OISE-0242579, by the SpiDME European project and by MIUR FIRB 2003 `SYNERGY' grant. Lab for Physical Sciences and in part by a NSF-MRSEC, DMR# 0520471.

Britti, Dominic; Phaneuf, Ray; Matino, Francesca; Arima, Valentina; Piacenza, Manuel; Della Sala, Fabio; Maruccio, Giuseppe; Del Sole, Roberta; Mele, Giuseppe; Vasapollo, Giuseppe; Cingolani, Roberto; Rinaldi, Ross

2008-03-01

406

Using a Molecular Modeling Program to Calculate Electron Paramagnetic Resonance Hyperfine Couplings in Semiquinone Anion Radicals  

Science.gov (United States)

This paper presents a laboratory exercise in computational chemistry in which molecular orbital theory is used to calculate hyperfine couplings in semiquinone anion radicals found by EPR spectroscopy. The exercise can be used in conjunction with a classic experiment described in Experiments in Physical Chemistry by Shoemaker, Garland, and Nibler, or it can be used as a stand-alone computational exercise. It is designed to be carried out using the program HyperChem for the personal computer, but other molecular modeling programs can be used. Because of the depth of this exercise, a preparatory analysis of the diatomic NO molecule is suggested. The student uses semiempirical molecular orbital calculation methods to optimize the geometry of the semiquinone anion and then performs a single point calculation on the optimized molecule while recording to a log file. The student then examines the log file to find the a and b electron populations for the H atom orbitals, from which the spin densities and finally hyperfine couplings are calculated. The results of the analysis, carried out using more than one semiempirical method, are compared with the experimental values to provide the student with an assessment of the accuracy of the calculation.

Haddy, Alice

2001-09-01

407

Theoretical prediction of the electronic states of the molecular ion KCs+  

International Nuclear Information System (INIS)

Full text.By using an ab initio calculation with the spin-orbit effect the potential energy has been calculated over a wide range of internuclear distance (5.0-60ao) for numerous electronic states of symmetry 2?+, 2?, 2? and ? for the molecular ion KCs+. To avoid an over estimation of the dissociation energy the perturbative treatment is replaced by an l-dependent core-polarization potential of the Foucrault et al. For the atoms K and Cs we used respectively the following Gaussian basis sets: (8s 7p 4d/ 7s 5p 2d) and (7s 6p 5d/ 8s 7p 6d). Core-valence effect, including core polarization and core-valence correlation are taken into consideration. Molecular orbital for the molecular ion KCs+ were derived from Self Consistent Field calculations (SCF), and full valence Configuration Interaction (IC) calculations were performed. By using a canonical functions approach a rovibrational study is done for calculating the eigenvalues Ev, the rotational constant Bv, the centrifugal distortion constant Dv (up to 120 vibrational levels) and the spectroscopic constants for eight bound states 2?+ and ?. Extensive tables of energy values versus internuclear distance are displayed at the following address http:lasim.univ-lyon1.fr/allouche/mcs.htm

2000-11-23

408

Note: Electrical detection and quantification of spin rectification effect enabled by shorted microstrip transmission line technique  

International Nuclear Information System (INIS)

We describe a shorted microstrip method for the sensitive quantification of Spin Rectification Effect (SRE). SRE for a Permalloy (Ni80Fe20) thin film strip sputtered onto SiO2 substrate is demonstrated. Our method obviates the need for simultaneous lithographic patterning of the sample and transmission line, therefore greatly simplifying the SRE measurement process. Such a shorted microstrip method can allow different contributions to SRE (anisotropic magnetoresistance, Hall effect, and anomalous Hall effect) to be simultaneously determined. Furthermore, SRE signals from unpatterned 50 nm thick Permalloy films of area dimensions 5 mm × 10 mm can even be detected

2014-02-01

409

Study of the second harmonic generation and optical rectification in a cBN crystal  

International Nuclear Information System (INIS)

Cubic boron nitride (cBN) - a kind of an artificial (synthetic) crystal with the band gap of ?6.3 eV, which has the zinc blende structure and the 4-bar 3m symmetry, is studied. The optical rectification is obtained and the second harmonic generation (SHG) is observed in the cBN crystal for the first time by using a 1064-nm Q-switched Nd:YAG laser. The green light at 532 nm from the cBN sample can be seen with a naked eye. (nonlinear optical phenomena)

2007-02-28

410

High conversion efficiency, high energy terahertz pulses by optical rectification in cryogenically cooled lithium niobate.  

Science.gov (United States)

We demonstrate highly efficient terahertz (THz) generation by optical rectification (OR) of near-optimum pump pulses centered at 1.03 ?m in cryogenically cooled lithium niobate. Using a close to optimal pulse duration of 680 fs and a pump energy of 1.2 mJ, we report conversion efficiencies above 3.8±0.4%, which is more than an order of magnitude higher than previously reported. The results confirm the advantage of using cryogenic cooling of the lithium niobate crystal that significantly reduces the THz absorption, enabling the scaling of THz pulse energies to the millijoule level via OR. PMID:23455302

Huang, Shu-Wei; Granados, Eduardo; Huang, Wenqian Ronny; Hong, Kyung-Han; Zapata, Luis E; Kärtner, Franz X

2013-03-01

411

THz generation via optical rectification from multiferroic BiFeO3  

Energy Technology Data Exchange (ETDEWEB)

We detected broadband coherent terahertz (THz) emission from multiferroic BiFeO{sub 3} after illuminating a high-quality bulk single ferroelectric domain crystal with a {approx}100 fs optical pulse. The dependence of the emitted THz waveform on the energy and polarization of the optical pulse is consistent with the optical rectification mechanism of THz emission. The THz emission provides a sensitive probe of the electric polarization state of BiFeO{sub 3}, enabling applications in ferroelectric memories and ferroelectric domain imaging. We also report room-temperature THz optical constants of BiFeO{sub 3}.

Talbayev, Diyar [Los Alamos National Laboratory; Taylor, Antoinette J [Los Alamos National Laboratory

2008-01-01

412

Note: electrical detection and quantification of Spin Rectification Effect enabled by shorted microstrip transmission line technique.  

Science.gov (United States)

We describe a shorted microstrip method for the sensitive quantification of Spin Rectification Effect (SRE). SRE for a Permalloy (Ni80Fe20) thin film strip sputtered onto SiO2 substrate is demonstrated. Our method obviates the need for simultaneous lithographic patterning of the sample and transmission line, therefore greatly simplifying the SRE measurement process. Such a shorted microstrip method can allow different contributions to SRE (anisotropic magnetoresistance, Hall effect, and anomalous Hall effect) to be simultaneously determined. Furthermore, SRE signals from unpatterned 50 nm thick Permalloy films of area dimensions 5 mm × 10 mm can even be detected. PMID:24593409

Soh, Wee Tee; Peng, Bin; Chai, Guozhi; Ong, C K

2014-02-01

413

Terahertz emission from yttrium barium copper oxide thin films via bulk electric quadrupole optical rectification  

International Nuclear Information System (INIS)

The authors describe here the first observation of terahertz emission from unbiased YBa_2Cu_3O_7_-_? (YBCO) thin films. These films are excited by 150 fs, 1.5 eV and 3.0 eV, optical pulses for a range of temperatures, T, 4 K < T < 300 K and for a range of oxygen doping from optimally-doped (? = 0) to insulating (? = 0.8). They demonstrate that this emission is generated by optical rectification due to the bulk electric quadrupole source term, comprising the first observation of such a source term in terahertz emission

1998-05-13

414

Electron and nuclear dynamics of molecular clusters in ultraintense laser fields. IV. Coulomb explosion of molecular heteroclusters.  

Science.gov (United States)

In this paper we present a theoretical and computational study of the temporal dynamics and energetics of Coulomb explosion of (CD4)(n) and (CH4)(n) (n=55-4213) molecular heteroclusters in ultraintense (I=10(16)-10(19) W cm(-2)) laser fields, addressing the manifestation of electron dynamics, together with nuclear energetic and kinematic effects on the heterocluster Coulomb instability. The manifestations of the coupling between electron and nuclear dynamics were explored by molecular dynamics simulations for these heteroclusters coupled to Gaussian laser fields (pulse width tau=25 fs), elucidating outer ionization dynamics, nanoplasma screening effects (being significant for Icharges and masses. Nonuniform heterocluster Coulomb explosion (eta >1) manifests an overrun effect of the light ions relative to the heavy ions, exhibiting the expansion of two spatially separated subclusters, with the light ions forming the outer subcluster at the outer edge of the spatial distribution. Important features of the energetics of heterocluster Coulomb explosion originate from energetic triggering effects of the driving of the light ions by the heavy ions (C(4+) for I=10(17)-10(18) W cm(-2) and C(6+) for I=10(19) W cm(-2)), as well as for kinematic effects. Based on the CVI assumption, scaling laws for the cluster size (radius R(0)) dependence of the energetics of uniform Coulomb explosion of heteroclusters (eta=1) were derived, with the size dependence of the average (E(j,av)) and maximal (E(j,M)) ion energies being E(j,av)=aR(0) (2) and E(j,M)=(5a/3)R(0) (2), as well as for the ion energy distributions P(E(j)) proportional to E(j) (1/2); E(j)1) result in an isotope effect, predicting the enhancement (by 9%-11%) of E(H,av) for Coulomb explosion of (C(4+)H(4) (+))(eta) (eta=3) relative to E(D,av) for Coulomb explosion of (C(4+)D(4) (+))(eta) (eta=1.5), with the isotope effect being determined by the ratio of the kinematic parameters for the pair of Coulomb exploding clusters. Kinematic effects for nonuniform explosion also result in a narrow isotope dependent energy distribution (of width DeltaE) of the light ions (with DeltaE/E(H,av) approximately 0.3 and DeltaE/E(D,av) approximately 0.4), with the distribution peaking at the high energy edge, in marked contrast with the uniform explosion case. Features of laser-heterocluster interactions were inferred from the analyses of the intensity dependent boundary radii (R(0))(I) and the corresponding average D+ ion energies (E(D,av))(I), which provide a measure for optimization of the cluster size at intensity I for the neutron yield from dd nuclear fusion driven by Coulomb explosion (NFDCE) of these heteroclusters. We infer on the advantage of deuterium containing heteronuclear clusters, e.g., (CD4)(n) in comparison to homonuclear clusters, e.g., (D2)(n/2), for dd NFDCE, where the highly charged heavy ions (e.g., C4+ or C6+) serve as energetic and kinematic triggers driving the D+ ions to a high (10-200 keV) energy domain. PMID:15511153

Last, Isidore; Jortner, Joshua

2004-11-01

415

Open-shell molecular electronic states from the parametric two-electron reduced-density-matrix method  

Science.gov (United States)

The parametric variational two-electron reduced-density-matrix (2-RDM) method, developed from an analysis of positivity (N-representability) constraints on the 2-RDM, is extended to treat both closed- and open-shell molecules in singlet, doublet, and triplet spin states. The parametric 2-RDM method can be viewed as using N-representability conditions to modify the 2-RDM from a configuration interaction singles-doubles wave function to make the energy size extensive while keeping the 2-RDM approximately N-representable [J. Kollmar, Chem. Phys. 125, 084108 (2006); A. E. DePrince and D. A. Mazziotti, Phys. Rev. A 76, 049903 (2007)]. Vertical excitation energies between triplet and singlet states are computed in a polarized valence triple-zeta basis set. In comparison to traditional single-reference wave function methods, the parametric 2-RDM method recovers a larger percentage of the multireference correlation in the singlet excited states, which improves the accuracy of the vertical excitation energies. Furthermore, we show that molecular geometry optimization within the parametric 2-RDM method can be efficiently performed through a Hellmann-Feynman-like relation for the energy gradient with respect to nuclear coordinates. Both the open-shell extension and the energy-gradient relation are applied to computing relative energies and barrier heights for the isomerization reaction HCN+HNC+. The computed 2-RDMs very nearly satisfy well known, necessary N-representability conditions.

Deprince, A. Eugene; Mazziotti, David A.

2009-04-01

416

Understanding the Electronic Structures of Some Molecular, Surface, and Solid State Systems  

Science.gov (United States)

The electronic structure of molecular, surface and solid state systems is studied using the extended Huckel (EH) method as well as ab initio and density functional theory (DFT) methods. The Ba_5Ga_6 phase contains nearly perfect octahedral Ga _6 clusters with one more skeletal electron pair (i.e. Ga_sp{6}{10- }) than predicted by the Wade-Mingos rules. Chapter 1 presents calculations showing that the octahedral cluster, either as isolated Ga_sp{6}{10 -} or in the extended Ba_5Ga _6 structure, is unstable with respect to Jahn-Teller distortion. There is room for hydrides in the Ba_5Ga_6 structure; Ba_5Ga_6 H_2 is an attractive formulation with a reasonable electronic structure. In Chapter 2 both cluster and extended slab models for the bare Si(001) surface and for acetylene chemisorbed on that surface are studied. Our calculations point to a buckled Si-Si dimer on the bare reconstructed surface. Acetylene adsorbs onto the dimer to form a four-membered disilacyclobutene ring without breaking the Si-Si bond. A likely pathway for the cycloaddition, via a pi-complex precursor and a biradical intermediate, is suggested. The nature of the intramolecular hydrogen-hydrogen interaction in iridium complexes (Ir-Hcdots H-N) is the subject of Chapter 3. This unusual, recently discovered HcdotsH interaction is found to be weakly attractive and primarily ionic in origin. It might also be realized intermolecularly, as shown by restricted Hartree-Fock/6-31G* computations. The bonding in the Cs_3Te _{22} phase, which contains both Te_8 rings and Te_6 nets, is studied. The focus is on the geometric and electronic features of this unique 2,3-connected Te _6 net. Both the linear and T-shaped Te geometries assumed by Te in this net are determined by their particular electron count. Both types of tellurium atoms are hypervalent. Several possible variations and distortions of this net are discussed. The discrete crown -shaped Te_8 units in the phase show normal covalent bonding and should occur in smaller molecular entities, too. According to our computations, Cs _3Te_{22} should be metallic. Two structurally related phases, CsTe _7 and Cs_2Te _{15}, are suggested.

Liu, Qiang

1995-01-01