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1

Mechanisms of molecular electronic rectification through electronic levels with strong vibrational coupling  

DEFF Research Database (Denmark)

We present a new view and an analytical formalism of electron flow through a donor-acceptor molecule inserted between a pair of metal electrodes. The donor and acceptor levels are strongly coupled to an environmental nuclear continuum. The formalism applies to molecular donor-acceptor systems both in vacuum or air, and in aqueous solution under electrochemical potential control. Multifarious patterns of rectified electron flow from the negatively to the positively biased electrode arise. The electronic interaction between the donor and acceptor fragments, mutually and with the electrodes, can be weak, corresponding to the fully diabatic limit. The rectification process then reduces to a sequence of vibrationally relaxed single-electron transfer steps. In the limits where the interactions are strong, denoted as the partially and fully adiabatic limits, the character of the rectification process is different, and electron flow proceeds coherently, without vibrational relaxation. In still another class of mechanisms the electronic level broadening of either donor or acceptor from the adjacent electrode is so strong that it is comparable to the vibrational broadening. The process then reduces to a three-level transition similar to STM of large redox molecules. Recent data for rectification in hexadecyl-quinolinium tricyanodimethanide monolayers by Metzger and co-workers [J. Am. Chem. Soc. 119, 10455 (1997); Acc. Chem. Res. 32, 950 (1999)], are discussed in terms of the reported views and formalism.

Kuznetsov, A.M.; Ulstrup, Jens

2002-01-01

2

Rectification in donor-acceptor molecular junctions  

Energy Technology Data Exchange (ETDEWEB)

We perform density functional theory (DFT) calculations on molecular junctions consisting of a single molecule between two Au(111) electrodes. The molecules consist of an alkane or aryl bridge connecting acceptor, donor or thiol endgroups in various combinations. The molecular geometries are optimized and wavefunctions and eigenstates of the junction calculated using the DFT method, and then the electron transport properties for the junction are calculated within the non-equilibrium Green's function (NEGF) formalism. The current-voltage or i(V) characteristics for the various molecules are then compared. Rectification is observed for these molecules, particularly for the donor-bridge-acceptor case where the bridge is an alkane, with rectification being in the same direction as the original findings of Aviram and Ratner (1974 Chem. Phys. Lett. 29 277-83), at least for relatively large negative and positive applied bias. However, at smaller bias rectification is in the opposite direction and is attributed to the lowest unoccupied orbital associated with the acceptor group.

Ford, M J; Hoft, R C; McDonagh, A M; Cortie, M B [Institute for Nanoscale Technology, University of Technology, Sydney, PO Box 123, Broadway, NSW 2007 (Australia)], E-mail: mike.ford@uts.edu.au

2008-09-17

3

Rectification in donor-acceptor molecular junctions.  

Science.gov (United States)

We perform density functional theory (DFT) calculations on molecular junctions consisting of a single molecule between two Au(111) electrodes. The molecules consist of an alkane or aryl bridge connecting acceptor, donor or thiol endgroups in various combinations. The molecular geometries are optimized and wavefunctions and eigenstates of the junction calculated using the DFT method, and then the electron transport properties for the junction are calculated within the non-equilibrium Green's function (NEGF) formalism. The current-voltage or i(V) characteristics for the various molecules are then compared. Rectification is observed for these molecules, particularly for the donor-bridge-acceptor case where the bridge is an alkane, with rectification being in the same direction as the original findings of Aviram and Ratner (1974 Chem. Phys. Lett. 29 277-83), at least for relatively large negative and positive applied bias. However, at smaller bias rectification is in the opposite direction and is attributed to the lowest unoccupied orbital associated with the acceptor group. PMID:21694413

Ford, M J; Hoft, R C; McDonagh, A M; Cortie, M B

2008-08-26

4

Rectification in donor-acceptor molecular junctions.  

UK PubMed Central (United Kingdom)

We perform density functional theory (DFT) calculations on molecular junctions consisting of a single molecule between two Au(111) electrodes. The molecules consist of an alkane or aryl bridge connecting acceptor, donor or thiol endgroups in various combinations. The molecular geometries are optimized and wavefunctions and eigenstates of the junction calculated using the DFT method, and then the electron transport properties for the junction are calculated within the non-equilibrium Green's function (NEGF) formalism. The current-voltage or i(V) characteristics for the various molecules are then compared. Rectification is observed for these molecules, particularly for the donor-bridge-acceptor case where the bridge is an alkane, with rectification being in the same direction as the original findings of Aviram and Ratner (1974 Chem. Phys. Lett. 29 277-83), at least for relatively large negative and positive applied bias. However, at smaller bias rectification is in the opposite direction and is attributed to the lowest unoccupied orbital associated with the acceptor group.

Ford MJ; Hoft RC; McDonagh AM; Cortie MB

2008-09-01

5

Rectification of displacement currents in an adiabatic electron pump  

CERN Document Server

Rectification of ac displacement currents generated by periodic variation of two independent gate voltages of a quantum dot can lead to a dc voltage linear in the frequency. The presence of this rectified displacement current could account for the magnetic field symmetry observed in a recent measurement on an adiabatic quantum electron pump by Switkes et al. [Science 283, 1905 (1999)].

Brouwer, P W

2001-01-01

6

First-principles study of rectification in bis-2-(5-ethynylthienyl)ethyne molecular junctions.  

Science.gov (United States)

Using density functional theory (DFT) combined with the first-principles nonequilibrium Green's function (NEGF), we investigated the electron-transport properties and rectifying behaviors of several molecular junctions based on the bis-2-(5-ethynylthienyl)ethyne (BETE) molecule. To examine the roles of different rectification factors, asymmetric electrode-molecule contacts and donor-acceptor substituent groups were introduced into the BETE-based molecular junction. The asymmetric current-voltage characteristics were obtained for the molecular junctions containing asymmetric contacts and donor-acceptor groups. In our models, the computed rectification ratios show that the mode of electrode-molecule contacts plays a crucial role in rectification and that the rectifying effect is not enhanced significantly by introducing the additional donor-acceptor components for the molecular rectifier with asymmetric electrode-molecule contacts. The current-voltage characteristics and rectifying behaviors are discussed in terms of transmission spectra, molecular projected self-consistent Hamiltonian (MPSH) states, and energy levels of MPSH states. PMID:21718049

Yuan, Shundong; Wang, Shiyan; Mei, Qunbo; Ling, Qidan; Wang, Lianhui; Huang, Wei

2011-07-27

7

First-principles study of rectification in bis-2-(5-ethynylthienyl)ethyne molecular junctions.  

UK PubMed Central (United Kingdom)

Using density functional theory (DFT) combined with the first-principles nonequilibrium Green's function (NEGF), we investigated the electron-transport properties and rectifying behaviors of several molecular junctions based on the bis-2-(5-ethynylthienyl)ethyne (BETE) molecule. To examine the roles of different rectification factors, asymmetric electrode-molecule contacts and donor-acceptor substituent groups were introduced into the BETE-based molecular junction. The asymmetric current-voltage characteristics were obtained for the molecular junctions containing asymmetric contacts and donor-acceptor groups. In our models, the computed rectification ratios show that the mode of electrode-molecule contacts plays a crucial role in rectification and that the rectifying effect is not enhanced significantly by introducing the additional donor-acceptor components for the molecular rectifier with asymmetric electrode-molecule contacts. The current-voltage characteristics and rectifying behaviors are discussed in terms of transmission spectra, molecular projected self-consistent Hamiltonian (MPSH) states, and energy levels of MPSH states.

Yuan S; Wang S; Mei Q; Ling Q; Wang L; Huang W

2011-08-01

8

Inverse rectification in donor-acceptor molecular heterojunctions.  

UK PubMed Central (United Kingdom)

The transport properties of a junction consisting of small donor-acceptor molecules bound to Au electrodes are studied and understood in terms of its hybrid donor-acceptor-electrode interfaces. A newly synthesized donor-acceptor molecule consisting of a bithiophene donor and a naphthalenediimide acceptor separated by a conjugated phenylacetylene bridge and a nonconjugated end group shows rectification in the reverse polarization, behavior opposite to that observed in mesoscopic p-n junctions. Solution-based spectroscopic measurements demonstrate that the molecule retains many of its original constituent properties, suggesting a weak hybridization between the wave functions of the donor and acceptor moieties, even in the presence of a conjugated bridge. Differential conductance measurements for biases as high as 1.5 V are reported and indicate a large asymmetry in the orbital contributions to transport arising from disproportionate electronic coupling at anode-donor and acceptor-cathode interfaces. A semi-empirical single Lorentzian coherent transport model, developed from experimental data and density functional theory based calculations, is found to explain the inverse rectification.

Yee SK; Sun J; Darancet P; Tilley TD; Majumdar A; Neaton JB; Segalman RA

2011-11-01

9

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

10

Spin current and rectification in one-dimensional electronic systems  

CERN Multimedia

Spin and charge currents can be generated by an ac voltage through a one-channel quantum wire with strong electron interactions in a static uniform magnetic field. In a certain range of low voltages, the spin current can grow as a negative power of the voltage bias as the voltage decreases. The spin current expressed in units of hbar/2 per second can become much larger than the charge current in units of the electron charge per second. The system requires neither spin-polarized particle injection nor time-dependent magnetic fields.

Braunecker, B; Braunecker, Bernd

2006-01-01

11

Microwave Rectification at the Boundary between Two-Dimensional Electron Systems  

CERN Multimedia

Rectification of microwave radiation (20-40 GHz) by a line boundary between two two-dimensional metals on a silicon surface was observed 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 $n_1 \\approx n_2$. 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 in this system.

Hoxha, I; Zimbovskaya, N A; Sarachik, M P; Klapwijk, T M

2001-01-01

12

Theory of Rectification in Tour Wires: The Role of Electrode Coupling  

DEFF Research Database (Denmark)

We report first-principles studies of electronic transport and rectification in molecular wires attached to gold electrodes. Our ab initio calculation gives an accurate description of the voltage drop as well as the broadening and alignment of the molecular levels in the metal-molecule-metal complex. We find that the operation range and rectification in such strongly chemisorbed molecules is limited by the width of the transmission resonances and their proximity to the Fermi level.

Taylor, Jeremy Philip; Brandbyge, Mads

2002-01-01

13

A theoretical view of unimolecular rectification  

International Nuclear Information System (INIS)

The concept of single molecule rectifiers proposed in a theoretical work by Aviram and Ratner in 1974 was the starting point of the now vibrant field of molecular electronics. In the meantime, a built-in asymmetry in the conductance of molecular junctions has been reported at the experimental level. In this contribution, we present a theoretical comparison of three different types of unimolecular rectifiers: (i) systems where the donor and acceptor parts of the molecules are taken from charge-transfer salt components; (ii) zwitterionic systems and (iii) tour wires with nitro substituents. We conduct an analysis of the rectification mechanism in these three different types of asymmetric molecules on the basis of parameterized quantum chemical models as well as with a full non-equilibrium Green's function-density functional theory (NEGF-DFT) treatment of the current-voltage characteristics of the respective metal-molecule-metal junctions. We put a particular emphasis on the prediction of rectification ratios (RRs), which are crucial for the assessment of the technological usefulness of single molecule junctions as diodes. We also compare our results with values reported in the literature for other types of molecular rectification, where the essential asymmetry is not induced by the structure of the molecule alone but either by a difference in the electronic coupling of the molecule to the two electrodes or by attaching alkyl chains of different lengths to the central molecular moiety.

2008-09-17

14

A theoretical view of unimolecular rectification  

Energy Technology Data Exchange (ETDEWEB)

The concept of single molecule rectifiers proposed in a theoretical work by Aviram and Ratner in 1974 was the starting point of the now vibrant field of molecular electronics. In the meantime, a built-in asymmetry in the conductance of molecular junctions has been reported at the experimental level. In this contribution, we present a theoretical comparison of three different types of unimolecular rectifiers: (i) systems where the donor and acceptor parts of the molecules are taken from charge-transfer salt components; (ii) zwitterionic systems and (iii) tour wires with nitro substituents. We conduct an analysis of the rectification mechanism in these three different types of asymmetric molecules on the basis of parameterized quantum chemical models as well as with a full non-equilibrium Green's function-density functional theory (NEGF-DFT) treatment of the current-voltage characteristics of the respective metal-molecule-metal junctions. We put a particular emphasis on the prediction of rectification ratios (RRs), which are crucial for the assessment of the technological usefulness of single molecule junctions as diodes. We also compare our results with values reported in the literature for other types of molecular rectification, where the essential asymmetry is not induced by the structure of the molecule alone but either by a difference in the electronic coupling of the molecule to the two electrodes or by attaching alkyl chains of different lengths to the central molecular moiety.

Stadler, R; Geskin, V; Cornil, J [Laboratory for Chemistry of Novel Materials, University of Mons-Hainaut, Place du Parc 20, B-7000 Mons (Belgium)], E-mail: r.stadler@averell.umh.ac.be

2008-09-17

15

A theoretical view of unimolecular rectification.  

Science.gov (United States)

The concept of single molecule rectifiers proposed in a theoretical work by Aviram and Ratner in 1974 was the starting point of the now vibrant field of molecular electronics. In the meantime, a built-in asymmetry in the conductance of molecular junctions has been reported at the experimental level. In this contribution, we present a theoretical comparison of three different types of unimolecular rectifiers: (i) systems where the donor and acceptor parts of the molecules are taken from charge-transfer salt components; (ii) zwitterionic systems and (iii) tour wires with nitro substituents. We conduct an analysis of the rectification mechanism in these three different types of asymmetric molecules on the basis of parameterized quantum chemical models as well as with a full non-equilibrium Green's function-density functional theory (NEGF-DFT) treatment of the current-voltage characteristics of the respective metal-molecule-metal junctions. We put a particular emphasis on the prediction of rectification ratios (RRs), which are crucial for the assessment of the technological usefulness of single molecule junctions as diodes. We also compare our results with values reported in the literature for other types of molecular rectification, where the essential asymmetry is not induced by the structure of the molecule alone but either by a difference in the electronic coupling of the molecule to the two electrodes or by attaching alkyl chains of different lengths to the central molecular moiety. PMID:21694412

Stadler, R; Geskin, V; Cornil, J

2008-08-26

16

Thermal rectification in mass-graded nanotubes: a model approach in the framework of reverse non-equilibrium molecular dynamics simulations  

International Nuclear Information System (INIS)

The thermal rectification in nanotubes with a mass gradient is studied by reverse non-equilibrium molecular dynamics simulations. We predict a preferred heat flow from light to heavy atoms which differs from the preferential direction in one-dimensional monoatomic systems. This behavior of nanotubes is explained by anharmonicities caused by transverse motions which are stronger at the low-mass end. The present simulations show an enhanced rectification with increasing tube length, diameter and mass gradient. Implications of the present findings for applied topics are mentioned concisely.

2010-02-19

17

Rectification Properties of Carbon Nanotube ''Y-Junctions''  

Energy Technology Data Exchange (ETDEWEB)

Quantum conductivity of single-wall carbon nanotube Y-junctions is calculated. The current versus voltage characteristics of these junctions show asymmetry and rectification, in agreement with recent experimental results. Furthermore, rectification is found to be independent of the angle between the branches of these junctions, indicating this to be an intrinsic property of symmetric Y-junctions. The implications for the Y-junction to function as a nanoscale molecular electronic switch are investigated.

Andriotis, Antonis N.; Menon, Madhu; Srivastava, Deepak; Chernozatonskii, Leonid

2001-08-06

18

Rectification in Luttinger liquids  

CERN Multimedia

We investigate the rectification of an ac bias in Luttinger liquids in the presence of an asymmetric potential (the ratchet effect). We show that strong repulsive electron interaction enhances the ratchet current in comparison with Fermi liquid systems, and the I-V curve is strongly asymmetric in the low-voltage regime even for a weak asymmetric potential. At higher voltages the ratchet current exhibits an oscillatory voltage dependence.

Feldman, D E; Vinokur, V M

2004-01-01

19

Rectification in Symmetric Conjugated Molecules with Asymmetric Linkers  

Science.gov (United States)

Demonstrating single-molecule rectification is an important step towards the realization of molecule-based electronic devices. Most molecules put forward as potential rectifiers employ asymmetric molecular backbones. In contrast, we show that we can create rectifying junctions by designing asymmetry only into the linker groups used to bond the molecule to metal electrodes. Our molecules consist of a conjugated backbone terminated with methylsulfide on one end and methyl-trimethyltin on the other. These molecules couple to Au electrodes through an Au-SMe donor acceptor bond, which serves as the electronically weak link, and a Au-C covalent bond, which is created in-situ after the SnMe3 cleaves off [1]. We create thousands of molecular junctions using a modified STM setup in a solution of molecules, measure their current-voltage (IV) characteristics and create averaged IV curves. We find that asymmetrically terminated molecules show non-linear IV curves with significant rectification, while molecules terminated symmetrically with either SMe or SnMe3 do not show substantial rectification. We also find that the rectification direction is dependent on molecular orientation in the junction. [1] Chen, W., et al., J. Am. Chem. Soc., 2011. 133(43): p. 17160-17163

Batra, Arunabh; Meisner, Jeffrey S.; Widawsky, Jonathan R.; Huisman, Eek; Nuckolls, Colin; Venkataraman, Latha

2012-02-01

20

Length dependence of carbon-doped BN nanowires: A-D Rectification and a route to potential molecular devices  

Science.gov (United States)

Based on the first-principles approach, electronic transport properties of different lengths of carbon-doped boron-nitrogen nanowires, capped with two thiols as end groups connected to Au electrodes surfaces, are investigated. The results show that rectifying performance and negative differential resistance (NDR) behaviors can be enhanced obviously by increasing the length. Analysis of Mülliken population, transmission spectra, evolutions of frontier orbitals and molecular projected self-consistent Hamiltonian of molecular orbital indicate that electronic transmission strength, charge transfer and distributions of molecular states change are the intrinsic origin of these rectifying performances and NDR behaviors.

Qiu, M.; Liew, K. M.

2013-02-01

 
 
 
 
21

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

22

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

23

Molecular Electronics on Silicon?  

Science.gov (United States)

Developing molecular electronics on silicon has various advantages as a hybrid technology, utilizing the extensive infrastructure of the integrated chip industry, as well as better chemical bonding and elimination of undesirable metal-induced gap states. In addition, there can be new physics from the silicon band-edge. For instance, we anticipate a novel resonant tunneling diode that exhibits a negative differential resistance (NDR) at positive (negative) substrate bias when the molecular levels slip past the band-edge of p(n)-doped silicon. Atomistic simulation of silicon is much harder than metals, requiring attention to its bulk bandstructure, band-bending, reconstruction and surface states. In the first part of my talk, I will discuss the basic physics of nonequilibrium transport through various molecular wires, understandable in terms of the contact Fermi energy, molecular levels, their broadenings and the electrostatic potential profile. We simulate molecular conduction by self-consistently combining an electronic structure calculation (semi-empirical or ab-initio) with a quantum transport calculation (Keldysh nonequilibrium Green's function formalism), that can yield current-voltage (I-V) characteristics for various devices (molecules, nanotubes, quantum point contacts etc.) with no adjustable parameters [1]. In this context, I will discuss the performance limits of molecular transistor action, gated electrostatically as well as conformationally [2]. Finally, I will describe the modeling issues and the physics of molecular NDR on silicon [3], for which there now is experimental support (Mark Hersam group, Northwestern University). [1] P. S. Damle, A. W. Ghosh and S. Datta, Phys. Rev. B 64, 201403(R), 2001. [2] A. W. Ghosh, T. Rakshit and S. Datta, cond-mat/0212166. [3] T. Rakshit, G-C. Liang, A. W. Ghosh and S. Datta, cond-mat/0305695.

Ghosh, Avik

2004-03-01

24

Thermal rectification in asymmetric U-shaped graphene flakes  

Science.gov (United States)

In this paper, we study the thermal rectification in asymmetric U-shaped graphene flakes by nonequilibrium molecular dynamics simulations. The graphene flakes are composed of a beam and two asymmetric arms. It is found that the heat flux runs preferentially from the wide arm to the narrow arm, which indicates a strong rectification effect. The dependence of the rectification ratio upon the heat flux, the length and the width of the beam and the two arms is studied. It shows that the two asymmetric arms play the central role in thermal rectification and a proper design is needed to obtain the maximum rectification ratio. The result suggests a possible route to manage the heat dissipation in U-shaped graphene based nanoelectronic devices that have recently been fabricated.

Cheh, Jigger; Zhao, Hong

2012-06-01

25

Molecular Determinants of Electrical Rectification of Single Channel Conductance in Gap Junctions Formed by Connexins 26 and 32  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The fully open state of heterotypic gap junction channels formed by pairing cells expressing connexin 32 (Cx32) with those expressing connexin 26 (Cx26) rectifies in a way that cannot be predicted from the current–voltage (I–V) relation of either homotypic channel. Using a molecular genetic analysis...

Oh, Seunghoon; Rubin, Joshua B.; Bennett, Michael V.L.; Verselis, Vytas K.; Bargiello, Thaddeus A.

26

Electronic communication through molecular bridges.  

UK PubMed Central (United Kingdom)

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.

Herrmann C; Elmisz J

2013-10-01

27

Spin-filtering and rectification effects in a Z-shaped boron nitride nanoribbon junction.  

Science.gov (United States)

A Z-shaped junction constructed by a few-nanometer-long armchair-edged boron nitride nanoribbon (ABNNR) sandwiched between two semi-infinite zigzag-edged BNNR electrodes with different hydrogen-passivated edge treatment is proposed, and its spin-dependent electronic transport is studied by ab initio calculations. It is found that a short ABNNR exhibits metallic behavior and can be used as a conduction channel. Interestingly, the spin-filtering and rectification effects exist in the junctions without any edge passivation or with boron-edge passivation. The analysis on the projected density of states and spatial distribution of molecular projected self-consistent Hamiltonian eigenstates gives an insight into the observed results for the system. Our results suggest that a BNNR-based nanodevices with spin-filtering and rectification effects may be synthesized from an hexagonal boron nitride sheet by properly tailoring and edge passivation. PMID:23343291

Wan, Haiqing; Zhou, Benhu; Liao, Wenhu; Zhou, Guanghui

2013-01-21

28

Spin-filtering and rectification effects in a Z-shaped boron nitride nanoribbon junction.  

UK PubMed Central (United Kingdom)

A Z-shaped junction constructed by a few-nanometer-long armchair-edged boron nitride nanoribbon (ABNNR) sandwiched between two semi-infinite zigzag-edged BNNR electrodes with different hydrogen-passivated edge treatment is proposed, and its spin-dependent electronic transport is studied by ab initio calculations. It is found that a short ABNNR exhibits metallic behavior and can be used as a conduction channel. Interestingly, the spin-filtering and rectification effects exist in the junctions without any edge passivation or with boron-edge passivation. The analysis on the projected density of states and spatial distribution of molecular projected self-consistent Hamiltonian eigenstates gives an insight into the observed results for the system. Our results suggest that a BNNR-based nanodevices with spin-filtering and rectification effects may be synthesized from an hexagonal boron nitride sheet by properly tailoring and edge passivation.

Wan H; Zhou B; Liao W; Zhou G

2013-01-01

29

Electrode materials for biphenyl-based rectification devices.  

UK PubMed Central (United Kingdom)

An ab initio approach was utilized to explore the electronic transport properties of 4'-thiolate-biphenyl-4-dithiocarboxylate (TBDT) sandwiched between two electrodes made of various materials X (X?=?Cu, Ag, and Au). Analysis of current-voltage (I-V) characteristics, rectification performance, transmission functions, and the projected density of states (PDOS) under various external voltage biases showed that the transport properties of these constructed systems are markedly impacted by the choice of electrode materials. Further, Cu electrodes yield the best rectifying behavior, followed by Ag and then Au electrodes. Interestingly, the rectification effects can be tuned by changing the torsion angle between the two phenyl rings, as well as by stretching the contact distances between the end group and the electrodes. For Cu, the maximum rectifying ratio increases by 37 % as the contact distance changes from 1.7 Å to 1.9 Å. This is due to an increase in coupling strength asymmetry between the molecule and the electrodes. Our findings are compared with the results reported for other systems. The present calculations are helpful not only for predicting the optimal electrode material for practical applications but also for achieving better control over rectifying performance in molecular devices.

Parashar S; Srivastava P; Pattanaik M

2013-08-01

30

Electron scattering on molecular hydrogen  

International Nuclear Information System (INIS)

The author considers scattering phenomena which occur when a beam of electrons interacts with a molecular hydrogen gas of low density. Depending on the energy loss of the scattered electrons one can distinguish elastic scattering, excitation and (auto)ionization of the H2-molecule. The latter processes may also lead to dissociation. These processes are investigated in four experiments in increasing detail. (Auth.)

1980-01-01

31

Image rectification for stereoscopic visualization.  

UK PubMed Central (United Kingdom)

This paper proposes an approach to rectifying two images of the same scene captured by cameras at general positions so that the results form a stereo pair that satisfies the constraints of the stereoscopic visualization platforms. This is unlike conventional image rectification research that primarily focuses on making stereo matching easier but pays little attention to 3D viewing. The novel derivation of the rectification algorithm also has an intuitive physical meaning that is not available from conventional approaches. Practical issues related to wide-baseline rectification and operation range of the proposed method are analyzed. Both simulated and real data experiments are used to assess the performance of the proposed algorithm.

Zhou J; Li B

2008-11-01

32

RENEWED APPROACH FOR IMAGE RECTIFICATION  

Directory of Open Access Journals (Sweden)

Full Text Available This paper proposed a new method for image rectification ,it is the process by which the pairs of stereo images of same solid scene taken from different viewpoints in order to produce a pair of “matched epipolar projections” and become parallel to the x-axis of image. A stereo rectified images are helpful for matching algorithms.It restricts that each line parallel to x-axis.The stereo rectification is not unique and actually lead to undesirable distortions. To overcome the drawback of the relative distortion between left image and right image an epipolar line rectification technique is used for point detection and reduce the distortion by minimized the camera rotation angle at each step.By comparative experiments show that the algorithm has an accuracy where other methods fail, namely when the epipolar lines are far from horizontal. Keywords--- Rectification, stereovision, epipolar, distortion, camera rotation.

Sahil Bansal

2011-01-01

33

Molecular electronics in silico  

Energy Technology Data Exchange (ETDEWEB)

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 10{sup 15} cm{sup -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{sup -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 10{sup 12} cm{sup -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 10{sup 11} cm{sup -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. (orig.)

Cerofolini, G.F. [STMicroelectronics, Agrate Brianza (Italy); Romano, E. [University of Milano-Bicocca, Department of Materials Science, Milano (Italy); CNISM, Milano (Italy)

2008-05-15

34

Silicon-based molecular electronics  

CERN Document Server

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 tunneling diode (RTD) that shows negative differential resistance (NDR) when the molecular levels are driven by an STM potential into the semiconducting band-gap. The peaks appear for positive bias on a p-doped and negative for an n-doped substrate. Charging in these devices is compromised by the RTD action, allowing possible identification of several molecular highest occupied (HOMO) and lowest unoccupied (LUMO) levels. Recent experiments by Hersam et al. [1] support our theoretical predictions.

Rakshit, T; Ghosh, A W; Datta, S

2003-01-01

35

EDITORIAL: Focus on Molecular Electronics FOCUS ON MOLECULAR ELECTRONICS  

Science.gov (United States)

The notion 'molecular electronics' has been used more frequently since the 1970s and summarizes a series of physical phenomena and ideas for their application in connection with organic molecules, oligomers, polymers, organic aggregates and solids. The properties studied in this field were connected to optical and electrical phenomena, such as optical absorption, fluorescence, nonlinear optics, energy transport, charge transfer, electrical conductance, and electron and nuclear spin-resonance. The final goal was and is to build devices which can compete or surpass some aspects of inorganic semiconductor devices. For example, on the basis of organic molecules there exist rectifiers, transistors, molecular wires, organic light emitting diodes, elements for photovoltaics, and displays. With respect to applications, one aspect of the organic materials is their broad variability and the lower effort and costs for their processability. The step from microstructures to the investigation of nanostructures is a big challenge also in this field and has lead to what nowadays is called molecular electronics in its narrow sense. In this field the subjects of the studies are often single molecules, e.g. single molecule optical spectroscopy, electrical conductance, i.e. charge transport through a single molecule, the influence of vibrational degrees of freedom, etc. A challenge here is to provide the techniques for addressing in a reproducible way the molecular scale. In another approach small molecular ensembles are studied in order to avoid artefacts from particular contact situations. The recent development of the field is presented in [1 8]. In this Focus Issue we present new results in the field of 'molecular electronics', both in its broad and specialized sense. One of the basic questions is the distribution of the energy levels responsible for optical absorption on the one hand and for the transport of charge on the other. A still unanswered question is whether the Wannier exciton model applies in which the excitation is distributed over several molecules or whether a good description is given by the Frenkel exciton model with the electron and the whole being localized at the same molecular unit. In organic semiconductors the charge transport usually occurs on the basis of holes because of the presence of many defects giving rise to a localization of the electrons. It is therefore a challenge to produce materials with both positive and negative mobile charge carriers. In the 1990s V M Agranovich introduced the idea of hybrid excitons, i.e. of nanostructured materials consisting of both organic and inorganic semiconductors. At the interface between the organic and inorganic parts new excitons can appear, being a superposition of both Frenkel and Wannier excitons and having both the high oscillator strength of the Frenkel and the large optical nonlinearity of the Wannier exciton. The problem is to find optimum combinations of the organic and inorganic parts to enable the hybrid structure concept to work. Micro-cavities also play an important role in the investigation of organic materials resulting in a new state (polariton) as the superposition of a photon and an exciton because of the large exciton photon interaction. A similar excitation arises because of the interaction between plasmons and photons. A special geometrical shape of a nano-cavity increases the interaction between the electromagnetic radiation and a dipole sitting in the cavity. The interaction between vibronic degrees of freedom and electronic excitations plays an important role for various phenomena such as nonlinear processes, the question of coherence, information on the shape of a potential hypersurface, etc. With the help of femtosecond laser pulses, detailed information on such vibrations can be obtained. Also of great importance is the investigation of the energy transfer in artificial light-harvesting systems, e.g. in dendrimers. Finally the combination of experimental and theoretical investigations allows for a comparison of the spectra of two molecules wi

Scheer, Elke; Reineker, Peter

2008-06-01

36

Image rectification for stereoscopic visualization.  

Science.gov (United States)

This paper proposes an approach to rectifying two images of the same scene captured by cameras at general positions so that the results form a stereo pair that satisfies the constraints of the stereoscopic visualization platforms. This is unlike conventional image rectification research that primarily focuses on making stereo matching easier but pays little attention to 3D viewing. The novel derivation of the rectification algorithm also has an intuitive physical meaning that is not available from conventional approaches. Practical issues related to wide-baseline rectification and operation range of the proposed method are analyzed. Both simulated and real data experiments are used to assess the performance of the proposed algorithm. PMID:18978849

Zhou, Jin; Li, Baoxin

2008-11-01

37

Delayed Rectification and Anomalous Rectification in Frog's Skeletal Muscle Membrane  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Delayed rectification was elicited in frog's skeletal muscles bathed in choline-Ringer's solution, in normal Ringer's solution with tetrodotoxin, in 40 mM Na2SO4 solution with tetrodotoxin, and even in 40 mM K2SO4 solution when the membrane had been previously hyperpolarized. However, after a susta...

Nakajima, Shigehiro; Iwasaki, Shizuko; Obata, Kunihiko

38

Thermal rectification in quantum graded mass systems  

CERN Document Server

We show the existence of thermal rectification in the graded mass quantum chain of harmonic oscillators with self-consistent reservoirs. Our analytical study allows us to identify the ingredients leading to the effect. The presence of rectification in this effective, simple model (representing graded mass materials, systems that may be constructed in practice) indicates that rectification in graded mass quantum systems may be an ubiquitous phenomenon. Moreover, as the classical version of this model does not present rectification, our results show that, here, rectification is a direct result of the quantum statistics.

Pereira, Emmanuel

2010-01-01

39

Overview of Nanotechnology: Molecular Electronics  

Science.gov (United States)

This overview of nanotechnology is presented by the NaMCATE project. Nanoelectronics "consists of nanoscale switches, diodes and transistors made of nanoparticles, carbon nanotubes and organic molecules." Energy band structures of solid state materials and basic concepts of quantum mechanics are discussed in this module. This lesson provides two learning activities on Chemical Bonds of Molecular Electronics and Conductive Polymers and Measurements of Semiconductor Bandgap Using Optical Absorption. Additionally, a powerpoint presentation is included.Users must create a free login in order to view the material.

2011-09-22

40

Molecular electronics from principles to practice  

CERN Multimedia

This consistent and comprehensive text is unique in providing an informed insight into molecular electronics by contrasting the prospects for molecular scale electronics with the continuing development of the inorganic semiconductor industry. Providing a wealth of information on the subject from background material to possible applications, Molecular Electronics contains all the need to know information in one easily accessible place. Speculation about future developments has also been included to give the whole picture of this increasingly popular and important topic.

Petty, Michael C

2008-01-01

 
 
 
 
41

Molecular Programming Pseudo-code Representation to Molecular Electronics  

CERN Multimedia

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

42

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.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. Electronic supplementary information (ESI) available: Experimental details on synthesis of polymer PVP-Bn, optical methods, 1H-NMR spectra, details on pH and ionic strength studies, and examples of current actuation with several different nanopores. See DOI: 10.1039/c3nr02105j

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

2013-09-01

43

The role of contacts in molecular electronics  

CERN Document Server

Molecular electronic devices are the upmost destiny of the miniaturization trend of electronic components. Although not yet reproducible on large scale, molecular devices are since recently subject of intense studies both experimentally and theoretically, which agree in pointing out the extreme sensitivity of such devices on the nature and quality of the contacts. This chapter intends to provide a general theoretical framework for modelling electronic transport at the molecular scale by describing the implementation of a hybrid method based on Green function theory and density functional algorithms. In order to show the presence of contact-dependent features in the molecular conductance, we discuss three archetypal molecular devices, which are intended to focus on the importance of the different sub-parts of a molecular two-terminal setup.

Cuniberti, G; Gutíerrez, R

2002-01-01

44

Atomic Electron Populations by Molecular Orbital Theory.  

Science.gov (United States)

The detailed distribution of electrons in molecules can be broken down into atomic orbital populations if an atomic orbital basis is used for a molecular orbital wave function (LCAO). A total assignment of all electrons in a molecule to atomic orbitals (a...

W. J. Hehre R. F. Stewart J. A. Pople

1968-01-01

45

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.).

1996-01-01

46

Molecular ferroelectrics: where electronics meet biology.  

UK PubMed Central (United Kingdom)

In the last several years, we have witnessed significant advances in molecular ferroelectrics, with the ferroelectric properties of molecular crystals approaching those of barium titanate. In addition, ferroelectricity has been observed in biological systems, filling an important missing link in bioelectric phenomena. In this perspective, we will present short historical notes on ferroelectrics, followed by an overview of the fundamentals of ferroelectricity. The latest developments in molecular ferroelectrics and biological ferroelectricity will then be highlighted, and their implications and potential applications will be discussed. We close by noting molecular ferroelectric as an exciting frontier between electronics and biology, and a number of challenges ahead are also described.

Li J; Liu Y; Zhang Y; Cai HL; Xiong RG

2013-09-01

47

Nanostructured organic-inorganic photodiodes with high rectification ratio  

International Nuclear Information System (INIS)

[en] High quality organic-inorganic heterojunction photodiodes based on nanostructured copper (II) phthalocyanine (CuPc) and intrinsic zinc oxide (i-ZnO) have been fabricated. The i-ZnO thin films/layers were grown by RF magnetron sputtering on clean indium tin oxide (ITO) coated glass substrates. These films have been characterized by optical absorption and field emission scanning electron microscopy (FESEM). CuPc thin films deposited at room temperature on i-ZnO have exhibited a change in their surface morphology with the post-deposition annealing temperature under normal atmosphere. The electrical dark conductivity and the photoconductivity of ITO/i-ZnO/CuPc/Au sandwich structures have been measured under various photoexcitation intensities using a xenon light source. The devices have shown excellent reproducibility of their electrical characteristics and high rectification ratios. The highest rectification ratio is nearly 831 calculated above the threshold voltage at room temperature for the sample annealed at 250 deg. C (i.e. Pc 250). The effects of the annealing temperature of CuPc on the surface morphology, rectification ratio, and optical properties have been discussed.

2008-12-10

48

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

49

Thermoelectric effect in molecular electronics  

CERN Multimedia

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 understood and controversial even though it is a central factor in determining the nature of conduction (n- or p-type). We also note that the thermoelectric voltage measured over Guanine molecules with an STM by Poler et al., indicate conduction through the HOMO level, i.e., p-type conduction.

Paulsson, M

2003-01-01

50

Mechanically controllable break junctions for molecular electronics.  

UK PubMed Central (United Kingdom)

A mechanically controllable break junction (MCBJ) represents a fundamental technique for the investigation of molecular electronic junctions, especially for the study of the electronic properties of single molecules. With unique advantages, the MCBJ technique has provided substantial insight into charge transport processes in molecules. In this review, the techniques for sample fabrication, operation and the various applications of MCBJs are introduced and the history, challenges and future of MCBJs are discussed.

Xiang D; Jeong H; Lee T; Mayer D

2013-09-01

51

The electronic structure of condensed molecular systems  

Energy Technology Data Exchange (ETDEWEB)

We have reviewed some of the basic properties of the electronic structure of condensed molecular systems. For the rare-gas solids, we concentrated our discussion on changes in the ground- and excited-state crystal-atomic wave functions as calculated with an approximate theoretical method. Compression of these wave functions leads to a softening of the equation of state at high densities, which seems to account for much of the total many-body effects. This compression is a true many-body effect and cannot be easily decomposable into a sum of 3-body and higher terms. We reviewed the electronic properties of four molecular systems, each manifesting different behavior at high densities. Because of a general lack of theory of the electronic structure of molecular solids, we restricted ourselves to a descriptive account. Solid oxygen, for instance, seems to exhibit the beginnings of covalent bonding between the ..pi..* orbitals on adjacent molecules in its epsilon phase. It was a combination of optical-absorption data and infrared and Raman spectroscopy that led to these conclusions. Iodine is unique in that it becomes metallic as a molecular crystal at pressures easily obtainable experimentally. It is interesting that the x-ray data, which indicates a transition to a monatomic lattice at 21 GPa, and the Moessbauer spectra, which implies that molecular character is retained to 30 GPa, are in such disagreement. The next system discussed, solid acetylene, is a nice example of high-pressure polymerization and study of this system should shed light on the polymerization of more complicated systems. Finally, we briefly discussed the predicted dissociation of solid molecular nitrogen at high pressures. Here, theory has made a prediction and experiment has disproven it. Molecular systems show a diverse range of behavior in electronic structures at high pressures, from metallization to chemistry; theory is lagging. 68 refs., 10 figs.

LeSar, R.A.

1988-01-01

52

Powerless Logical Gates Based on Molecular Electronics  

Directory of Open Access Journals (Sweden)

Full Text Available In this study, a new AND gate as well as a new OR gate based on Molecular electronics are proposed. Then, these gates are extended to n-input gates which have decreased the number of required elements and they have been designed as modify as possible. The main advantage of these designs is the fact that they are powerless.

M.B. Nasrollahnejad; M.M. Madani; S. Arabi Nowdeh; S. Ghasemi

2013-01-01

53

DNA and microfluidics: Building molecular electronics systems  

Energy Technology Data Exchange (ETDEWEB)

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.

Ye Yun [Chemical Sensors Group, Department of Chemical and Physical Sciences, University of Toronto at Mississauga, 3359 Mississauga Road North, Mississauga, Ont., L5L 1C6 (Canada); Chen Lu [Chemical Sensors Group, Department of Chemical and Physical Sciences, University of Toronto at Mississauga, 3359 Mississauga Road North, Mississauga, Ont., L5L 1C6 (Canada); Liu Xuezhu [Chemical Sensors Group, Department of Chemical and Physical Sciences, University of Toronto at Mississauga, 3359 Mississauga Road North, Mississauga, Ont., L5L 1C6 (Canada); Krull, Ulrich J. [Chemical Sensors Group, Department of Chemical and Physical Sciences, University of Toronto at Mississauga, 3359 Mississauga Road North, Mississauga, Ont., L5L 1C6 (Canada)]. E-mail: ukrull@utm.utoronto.ca

2006-05-24

54

Exploiting plasmon-induced hot electrons in molecular electronic devices.  

UK PubMed Central (United Kingdom)

Plasmonic nanostructures can induce a number of interesting responses in devices. Here we show that hot electrons can be extracted from plasmonic particles and directed into a molecular electronic device, which represents a new mechanism of transfer from light to electronic transport. To isolate this phenomenon from alternative and sometimes simultaneous mechanisms of plasmon-exciton interactions, we designed a family of hybrid nanostructure devices consisting of Au nanoparticles and optoelectronically functional porphyin molecules that enable precise control of electronic and optical properties. Temperature- and wavelength-dependent transport measurements are analyzed in the context of optical absorption spectra of the molecules, the Au particle arrays, and the devices. Enhanced photocurrent associated with exciton generation in the molecule is distinguished from enhancements due to plasmon interactions. Mechanisms of plasmon-induced current are examined, and it is found that hot electron generation can be distinguished from other possibilities.

Conklin D; Nanayakkara S; Park TH; Lagadec MF; Stecher JT; Chen X; Therien MJ; Bonnell DA

2013-05-01

55

Electron localization following attosecond molecular photoionization.  

UK PubMed Central (United Kingdom)

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 has become possible only with the recent development of isolated attosecond (10(-18)-s) laser pulses. Such pulses have been used to investigate atomic photoexcitation and photoionization and electron dynamics in solids, and in molecules could help explore the prompt charge redistribution and localization that accompany photoexcitation processes. In recent work, the dissociative ionization of H(2) and D(2) was monitored on femtosecond timescales and controlled using few-cycle near-infrared laser pulses. Here we report a molecular attosecond pump-probe experiment based on that work: H(2) and D(2) are dissociatively ionized by a sequence comprising an isolated attosecond ultraviolet pulse and an intense few-cycle infrared pulse, and a localization of the electronic charge distribution within the molecule is measured that depends-with attosecond time resolution-on the delay between the pump and probe pulses. The localization occurs by means of two mechanisms, where the infrared laser influences the photoionization or the dissociation of the molecular ion. In the first case, charge localization arises from quantum mechanical interference involving autoionizing states and the laser-altered wavefunction of the departing electron. In the second case, charge localization arises owing to laser-driven population transfer between different electronic states of the molecular ion. These results establish attosecond pump-probe strategies as a powerful tool for investigating the complex molecular dynamics that result from the coupling between electronic and nuclear motions beyond the usual Born-Oppenheimer approximation.

Sansone G; Kelkensberg F; Pérez-Torres JF; Morales F; Kling MF; Siu W; Ghafur O; Johnsson P; Swoboda M; Benedetti E; Ferrari F; Lépine F; Sanz-Vicario JL; Zherebtsov S; Znakovskaya I; L'huillier A; Ivanov MY; Nisoli M; Martín F; Vrakking MJ

2010-06-01

56

Nanofluidic diode based on branched alumina nanochannels with tunable ionic rectification.  

Science.gov (United States)

In this work, the synthetic alumina nanochannels with bi-, tri-, and tetra-branched geometry structures exhibited ionic current rectifications with nonlinear I-V curves. Such diode performance of the branched alumina nanochannel is mainly dependent on the cooperative asymmetry of the branched structure and the surface-charge distribution on inner walls. By regulating the geometry, electrolyte pH, and solution concentration, the tunable ionic rectification properties are effectively obtained including both the rectification ratios and the rectifying direction that were deduced from the converted ion selectivity. This nanofluidic diode may open up a new opportunity for the application of the complex nanofluidic devices in contrast to previously reported channels to provide molecular analysis, controlled mass transport, drug release, and various logic gate operations. PMID:23844847

Kong, Yan; Fan, Xia; Zhang, MingHui; Hou, Xu; Liu, ZhaoYue; Zhai, Jin; Jiang, Lei

2013-07-23

57

Nanofluidic diode based on branched alumina nanochannels with tunable ionic rectification.  

UK PubMed Central (United Kingdom)

In this work, the synthetic alumina nanochannels with bi-, tri-, and tetra-branched geometry structures exhibited ionic current rectifications with nonlinear I-V curves. Such diode performance of the branched alumina nanochannel is mainly dependent on the cooperative asymmetry of the branched structure and the surface-charge distribution on inner walls. By regulating the geometry, electrolyte pH, and solution concentration, the tunable ionic rectification properties are effectively obtained including both the rectification ratios and the rectifying direction that were deduced from the converted ion selectivity. This nanofluidic diode may open up a new opportunity for the application of the complex nanofluidic devices in contrast to previously reported channels to provide molecular analysis, controlled mass transport, drug release, and various logic gate operations.

Kong Y; Fan X; Zhang M; Hou X; Liu Z; Zhai J; Jiang L

2013-08-01

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 F2, 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 F2 using EELS and have been able to resolve most of these questions

1985-01-01

59

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

60

Surface microscopic structure and electrochemical rectification of a branched alkanethiol self-assembled monolayer.  

Science.gov (United States)

The tert-butanethiol self-assembled monolayers (SAMs) on Au(111) surfaces were prepared from various solvents and investigated by a combination of scanning tunneling microscopy (STM) and electrochemistry in aqueous environments. High-resolution STM images reveal a (radical(7) x radical(7))R19 degrees surface lattice structure, in contrast with the conventional lattice (radical(3) x radical(3))R30 degrees structure for straight-chain alkanethiol SAMs. Interestingly, such a branched monolayer shows electrochemical rectification toward redox probes. We suggest that electrochemical rectification could be a general characteristic of short-chain branched alkanthiol SAMs, and originate in localized electronic effects. PMID:16471649

Chi, Qijin; Zhang, Jingdong; Ulstrup, Jens

2006-01-26

 
 
 
 
61

Surface microscopic structure and electrochemical rectification of a branched alkanethiol self-assembled monolayer.  

UK PubMed Central (United Kingdom)

The tert-butanethiol self-assembled monolayers (SAMs) on Au(111) surfaces were prepared from various solvents and investigated by a combination of scanning tunneling microscopy (STM) and electrochemistry in aqueous environments. High-resolution STM images reveal a (radical(7) x radical(7))R19 degrees surface lattice structure, in contrast with the conventional lattice (radical(3) x radical(3))R30 degrees structure for straight-chain alkanethiol SAMs. Interestingly, such a branched monolayer shows electrochemical rectification toward redox probes. We suggest that electrochemical rectification could be a general characteristic of short-chain branched alkanthiol SAMs, and originate in localized electronic effects.

Chi Q; Zhang J; Ulstrup J

2006-01-01

62

Current Rectification and Seebeck Coefficient of Serially Coupled Double Quantum Dots  

Science.gov (United States)

The transport properties of serially coupled quantum dots (SCQDs) embedded in a matrix connected to metallic electrodes are theoretically studied in the linear and nonlinear regimes. The current rectification and negative differential conductance of SCQDs under the Pauli spin blockade condition are attributed to the combination of bias-direction dependent probability weight and off-resonant energy levels yielded by the applied bias across the junctions. We observe the spin-polarization current rectification under the Zeeman effect. The maximum spin-polarization current occurs in the forward bias regime. Such behavior is different from the charge current rectification. Finally, the Seebeck coefficient (S) of SCQDs is calculated and analyzed in the cases without and with electron phonon interactions. The application of SCQDs as a temperature detector is discussed on the basis of the nonlinear behavior of S with respect to temperature difference across the junction.

Tseng, Yen-Chun; Kuo, David M.-T.

2013-01-01

63

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

2013-05-23

64

Modelling of inelastic effects in molecular electronics  

CERN Document Server

Ab initio modeling of molecular electronics is nowadays routinely performed by combining the Density Functional Theory (DFT) and Nonequilibrium Green function (NEGF) techniques. This method has its roots in the current formula given by Meir and Wingreen, and we discuss some applications and accompanying pitfalls and restrictions of this approach. Quite recently papers have begun to appear where inelastic effects are considered, and we illustrate these new developments by describing our own work on transport in atomic gold wires.

Jauho, A P

2005-01-01

65

Electron energy degradation in molecular hydrogen  

International Nuclear Information System (INIS)

The degradation and the subexcitation spectra were calculated in dilute molecular hydrogen produced by monoenergetic source electrons with energies of 2 and 10 keV. The cross-section data of Gerhart were re-examined and refined. A new code for computation of degradation spectra is discussed, and sensitivity of the results to variation in the input data is examined. A previously discovered scaling of the yield of ions is also examined for this case

1976-01-01

66

Tuning molecular orbitals in molecular electronics and spintronics.  

UK PubMed Central (United Kingdom)

With the advance of nanotechnology, a variety of molecules, from single atoms to large-scale structures such as graphene or carbon nanotubes, have been investigated for possible use as molecular devices. Molecular orbitals (MOs) are a key ingredient in determining the transport properties of molecules, because they contain all the quantum mechanical information of molecular electronic structures and offer spatial conduction channels for electron transport. Therefore, the delicate modulation of the MOs enables us to tune the performance of electron transport through the molecule. Electric and magnetic fields are powerful and readily accessible means for that purpose. In this Account, we describe the effects of external fields on molecular electronic and spintronic devices. Quantum transport through a molecule that connects source and drain electrodes depends strongly on the alignment of molecular energy levels with respect to the chemical potentials at both electrodes. This dependence results from the energy levels being exploited in resonant tunneling processes when the molecule is weakly coupled to the electrodes in the molecular junction. Molecular energy levels can be shifted by the Stark effect of an external electric field. For a molecule with no permanent dipole moment, the polarizability is the primary factor determining the energy shift of each MO, according to the second-order Stark effect; more polarizable MOs undergo a larger energy shift. Interestingly, even a small shift may lead to a completely nontrivial result. For example, we show a magnetic on-off switching phenomenon of a molecule controlled by an electric field. If a molecule has a nonmagnetic ground state but a highly polarizable magnetic excited state with an energy slightly above the ground state, the magnetic excited state can have lower energy than the ground state under a sufficiently strong electric field. A magnetic field is normally used to control spin orientation in a ferromagnetic system. Here we show that the magnetic field can also be used to control MOs. A graphene nanoribbon with zig-zag-shaped edges (ZGNR) has a ferromagnetic spin ordering along the edges, and the spin states have unique orbital symmetries. Both spin polarizations and orbital symmetries can simultaneously be controlled by means of an external magnetic field. The ZGNR spin-valve devices incorporating this effect are predicted to show an extreme enhancement (compared with conventional devices) of magnetoresistance due to the double spin-filtering process. In such a system, spins are filtered not only by spin matching-mismatching between both electrodes as in normal spin-valve devices, but also by the orbital symmetry matching-mismatching. Thus, a new type of magnetoresistance, and with extremely large values, so-called super-magnetoresistance (distinct from the conventional tunneling or giant magnetoresistance), is available with this method. MOs are at the heart of understanding and tuning transport properties in molecular systems. Therefore, investigating the effects of external fields on MOs is important not only for understanding fundamental quantum phenomena in molecular devices but also for practical applications in the development of interactive devices.

Kim WY; Kim KS

2010-01-01

67

Molecular rectification with identical metal electrodes at low temperatures Thin film deposition; Gold; Molecular electronics; Langmuir- Blodgett; Au/LB/Au structures; Fabrication  

CERN Multimedia

A gold deposition technique for the fabrication of Au/LB/Au structures has been developed. The kinetic energy of evaporated gold atoms is reduced by scattering the gold atoms from argon gas. Moreover, the samples are cooled down below 173K (-100 deg C) to avoid the diffusion of gold atoms into the LB films and to fabricate electrically continuous thin gold electrodes (This technique has since been used in fabrication of Au/LB/Au structures even with monolayer LB films (Metzger, et al. (2001)). To measure the current-voltage characteristics of the Au/LB/Au structures at liquid helium temperatures, new junction geometries have been explored. To avoid the direct contact of the Gallium-Indium eutectic onto the LB films, which is the cause of the breakdown of the junction at lower temperatures, a cross electrode junction geometry is used. The problem of poor Langmuir-Blodgett film deposition at the penumbra region of the base electrode is avoided by covering the penumbra region with an insulating omega-tricosenoic...

Okazaki, N

2003-01-01

68

Modelling of inelastic effects in molecular electronics  

International Nuclear Information System (INIS)

Ab initio modeling of molecular electronics is nowadays routinely performed by combining the Density Functional Theory (DFT) and Nonequilibrium Green function (NEGF) techniques. This method has its roots in the current formula given by Meir and Wingreen, and we discuss some applications and accompanying pitfalls and restrictions of this approach. Quite recently papers have begun to appear where inelastic effects are discussed, treated with models where the parameters are determined via ab initio methods, and we illustrate these new developments by describing our own work on transport in atomic gold wires.

2006-04-01

69

Electron-pair excitations and the molecular Coulomb continuum  

International Nuclear Information System (INIS)

Electron-pair excitations in the molecular hydrogen continuum are described by quantizing rotations of the momentum plane of the electron pair about by the pair's relative momentum. A helium-like description of the molecular pi.Joto 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.

2009-01-01

70

Energy transformation in molecular electronic systems  

International Nuclear Information System (INIS)

Our new optical pumping spectroscopy (steady state, and double-laser pulse) allows the production and study of the unstable rare tautomer in its ground and excited states, including picosecond dynamic studies. Molecules under study here included 7-azaindole (model for biological purines), 3-hydroxyflavone (model for plant flavones), lumichrome, and other heterocyclics. New detailed molecular mechanisms for proton transfer are derived, especially with catalytic assisting molecules. A new proton-transfer laser of extraordinary efficiency has become a side dividend, possibly worth of industrial development. The excited and highly reactive singlet molecular oxygen species 1?/sub g/) has proven to be ubiquitous in chemical peroxide systems and in physically excited sensitizer-oxygen systems. Hyperbaric oxygen mechanisms in biology probably involve singlet oxygen. We have undertaken a spectroscopic study of tris - dibenzoylmethane chelates of Al, Gd, Eu, and Yb trivalent ions. These chelates offer a variety of electronic behaviors, from Z-effects on ?-electron spin-orbital coupling (Al, Gd) to Weissman intramolecular energy transfer to 4f mestable levels (Eu, Gd). Elegant new spectroscopic resolution at 77K permits separation of tautomeric, parasitic self-absorption, dissociation, and cage effects to be resolved. 18 refs., 4 figs

1985-01-01

71

Energy transformation in molecular electronic systems  

Science.gov (United States)

Our new optical pumping spectroscopy allows the production and study of the unstable rate tautomer in its ground and excited states, including picosecond dynamic studies. Molecules under study here included 7-azaindole 3-hydroxyflavone, lumichrome, and other heterocyclics. New detailed molecular mechanisms for proton transfer are derived, especially with catalytic assisting molecules. A new proton-transfer laser of extraordinary efficiency has become a side dividend, possibly worthy of industrial development. The excited and highly reactive singlet molecular oxygen species (1) DELTA sub g has proven to be ubiquitous in chemical peroxide systems and in physically excited sensitizer-oxygen systems. Hyperbaric oxygen mechanisms in biology probably involve singlet oxygen. We have undertaken a spectroscopic study of trisdibenzoylmethane chelates of Al, Gd, Eu, and Yb trivalent ions. These chelates offer a variety of electronic behaviors, from Z-effects on (PI)--electron spin-orbital coupling (Al, Gd) to Weissman intramolecular energy transfer to 4f mestable levels (Eu, Gd). Elegant new spectroscopic resolution at 77K permits separation of tautomeric, parasitic self-absorption, dissociation, and cage effects to be resolved.

Kasha, M.

1985-07-01

72

Energy transformation in molecular electronic systems  

Energy Technology Data Exchange (ETDEWEB)

Our new optical pumping spectroscopy (steady state, and double-laser pulse) allows the production and study of the unstable rare tautomer in its ground and excited states, including picosecond dynamic studies. Molecules under study here included 7-azaindole (model for biological purines), 3-hydroxyflavone (model for plant flavones), lumichrome, and other heterocyclics. New detailed molecular mechanisms for proton transfer are derived, especially with catalytic assisting molecules. A new proton-transfer laser of extraordinary efficiency has become a side dividend, possibly worth of industrial development. The excited and highly reactive singlet molecular oxygen species /sup 1/..delta../sub g/) has proven to be ubiquitous in chemical peroxide systems and in physically excited sensitizer-oxygen systems. Hyperbaric oxygen mechanisms in biology probably involve singlet oxygen. We have undertaken a spectroscopic study of tris - dibenzoylmethane chelates of Al, Gd, Eu, and Yb trivalent ions. These chelates offer a variety of electronic behaviors, from Z-effects on ..pi..-electron spin-orbital coupling (Al, Gd) to Weissman intramolecular energy transfer to 4f mestable levels (Eu, Gd). Elegant new spectroscopic resolution at 77K permits separation of tautomeric, parasitic self-absorption, dissociation, and cage effects to be resolved. 18 refs., 4 figs.

Kasha, M.

1985-07-25

73

Discontinuous approximate molecular electronic wave-functions  

International Nuclear Information System (INIS)

Following Kohn, Schlosser and Marcus and Weare and Parr an energy functional is defined for a molecular problem which is stationary in the neighborhood of the exact solution and permits the use of trial functions that are discontinuous. The functional differs from the functional of the standard Rayleigh--Ritz method in the replacement of the usual kinetic energy operators circumflex T(?) with operators circumflex T'(?) = circumflex T(?) + circumflex I(?) generates contributions from surfaces of nonsmooth behavior. If one uses the nabla PSI . nabla PSI way of writing the usual kinetic energy contributions, one must add surface integrals of the product of the average of nabla PSI and the change of PSI across surfaces of discontinuity. Various calculations are carried out for the hydrogen molecule-ion and the hydrogen molecule. It is shown that ab initio calculations on molecules can be carried out quite generally with a basis of atomic orbitals exactly obeying the zero-differential overlap (ZDO) condition, and a firm basis is thereby provided for theories of molecular electronic structure invoking the ZDO aoproximation. It is demonstrated that a valence bond theory employing orbitals exactly obeying ZDO can provide an adequate account of chemical bonding, and several suggestions are made regarding molecular orbital methods

1977-01-01

74

Photovoltaic and Rectification Currents in Quantum Dots  

CERN Multimedia

We investigate theoretically and experimentally the statistical properties of dc current through an open quantum dot subject to ac excitation of a shape-defining gate. The symmetries of rectification current and photovoltaic current with respect to applied magnetic field are examined. Theory and experiment are found to be in good agreement throughout a broad range of frequency and ac power, ranging from adiabatic to nonadiabatic regimes.

Vavilov, M G; Marcus, C M

2004-01-01

75

Can azulene-like molecules function as substitution-free molecular rectifiers?  

Science.gov (United States)

The feasibility of employing azulene-like molecules as a new type of high performance substitution-free molecular rectifier has been explored using NEGF-DFT calculation. The electronic transport behaviors of metal-molecule-metal junctions consisting of various azulene-like dithiol molecules are investigated, which reveals that the azulene-like molecules exhibit high conductance and bias-dependent rectification effects. Among all the substitution-free azulene-like structures, cyclohepta[b]cyclopenta[g]naphthalene exhibits the highest rectification ratio, revealing that the all fused aromatic ring structure and an appropriate separation between the pentagon and heptagon rings are essential for achieving both high conductance and high rectification ratio. The rectification ratio can be increased by substituting the pentagon ring with electron-withdrawing group and/or the heptagon ring with electron donating groups. Further increase of the rectification ratio may also be obtained by lithium adsorption on the pentagon ring. This work reveals that azulene-like molecules may be used as a new class of highly conductive unimolecular rectifiers. PMID:21822508

Zhou, Kai-Ge; Zhang, Yong-Hui; Wang, Le-Jia; Xie, Ke-Feng; Xiong, Yu-Qing; Zhang, Hao-Li; Wang, Cheng-Wei

2011-08-05

76

Can azulene-like molecules function as substitution-free molecular rectifiers?  

UK PubMed Central (United Kingdom)

The feasibility of employing azulene-like molecules as a new type of high performance substitution-free molecular rectifier has been explored using NEGF-DFT calculation. The electronic transport behaviors of metal-molecule-metal junctions consisting of various azulene-like dithiol molecules are investigated, which reveals that the azulene-like molecules exhibit high conductance and bias-dependent rectification effects. Among all the substitution-free azulene-like structures, cyclohepta[b]cyclopenta[g]naphthalene exhibits the highest rectification ratio, revealing that the all fused aromatic ring structure and an appropriate separation between the pentagon and heptagon rings are essential for achieving both high conductance and high rectification ratio. The rectification ratio can be increased by substituting the pentagon ring with electron-withdrawing group and/or the heptagon ring with electron donating groups. Further increase of the rectification ratio may also be obtained by lithium adsorption on the pentagon ring. This work reveals that azulene-like molecules may be used as a new class of highly conductive unimolecular rectifiers.

Zhou KG; Zhang YH; Wang LJ; Xie KF; Xiong YQ; Zhang HL; Wang CW

2011-09-01

77

Regions of continuous rectification in systems divided into distillation regions  

Energy Technology Data Exchange (ETDEWEB)

The authors present the mechanisms of formation of regions of continuous clear rectification in three-component azeotropic systems of any complexity divided into distillation regions. The limitations of the process for all types of clear rectification have been determined. They have noted the phenomena of intersection of sets in which the rectification process develops as a function of the type of the specified separation. The phenomenon of transfer through the separating manifold of distillation has been pointed out.

Balashov, M.I.; Grishunin, A.V.; Serafimov, L.A.

1985-07-01

78

Molecular electronics in pinnae of Mimosa pudica.  

UK PubMed Central (United Kingdom)

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.

Volkov AG; Foster JC; Markin VS

2010-07-01

79

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

80

Langmuir-Blodgett Films a unique tool for molecular electronics  

CERN Multimedia

Molecular electronics is a new, exciting and interdisciplinary field of research. The main concern of the subject is to exploit the organic materials in electronic and optoelectronic devices. On the other hand Langmuir-Blodgett (LB) film deposition technique is one of the best among few methods used to manipulate materials in molecular level. In this article LB film preparation technique has been discussed briefly with an emphasize of its application towards molecular electronics.

Hussain, Syed Arshad

2009-01-01

 
 
 
 
81

Chemical transformations during rectification of products of hydroformylation of propylene  

Energy Technology Data Exchange (ETDEWEB)

The occurrence of reactions related to losses of the target products, aldehydes and alcohols, was established in continuous rectification of the products of hydroformylation of propylene. The sections of the zone of primary occurrence of the reactions of aldol condensation, formation of acetals, and esterification of butyl alcohols with butyric acids were determined in the rectification column. It was shown that with increase in temperature in the rectification column still the degree of aldehyde and alcohol conversion in the overall rectification system decreases with respect to aldol condensation and acetal formation, while increasing with respect to alcohol esterification.

Kuz' mina, L.S.; Maiorova, L.V.; Kharisov, M.A.

1988-09-10

82

Electron and molecular dynamics: Penning ionization and molecular charge transport  

Science.gov (United States)

An understanding of fundamental reaction dynamics is an important problem in chemistry. In this work, experimental and theoretical methods are combined to study the dynamics of fundamental chemical reactions. Molecular collision and dissociation dynamics are explored with the Penning ionization of amides, while charge transfer reactions are examined with charge transport in organic thin film devices. Mass spectra from the Penning ionization of formamide by He*, Ne*, and Ar* were measured using molecular beam experiments. When compared to 70eV electron ionization spectra, the He* and Ne* spectra show higher yields of fragments resulting from C--N and C--H bond cleavage, while the Ar* spectrum only shows the molecular ion, H-atom elimination, and decarbonylation. The differences in yields and observed fragments are attributed to the differences in the dynamics of the two ionization methods. Fragmentation in the Ar* spectrum was analyzed using quantum chemistry and RRKM calculations. Calculated yields for the Ar* spectrum are in excellent agreement with experiment and show that 15% and 50% of the yields for decarbonylation and H-atom elimination respectively are attributed to tunneling. The effects of defects, traps, and electrostatic interactions on charge transport in imperfect organic field effect transistors were studied using course-grained Monte Carlo simulations with explicit introduction of defect and traps. The simulations show that electrostatic interactions dramatically affect the field and carrier concentration dependence of charge transport in the presence of a significant number of defects. The simulations also show that while charge transport decreases linearly as a function of neutral defect concentration, it is roughly unaffected by charged defect concentration. In addition, the trap concentration dependence on charge transport is shown to be sensitive to the distribution of trap sites. Finally, density functional theory calculations were used to study how charge localization affects the orbital energies of positively charged bithiophene clusters. These calculations show that the charge delocalizes over at least seven molecules, is more likely to localize on "tilted" molecules due to polarization effects, and affects molecules anisotropically. These results suggest that models for charge transport in organic semiconductors should be modified to account for charge delocalization and intermolecular interactions.

Madison, Tamika Arlene

83

Recycled Noise Rectification: A Dumb Maxwell's Daemon  

CERN Document Server

The one dimensional motion of a massless Brownian particle on a symmetric periodic substrate can be rectified by re-injecting its driving noise through a realistic recycling procedure. If the recycled noise is multiplicatively coupled to the substrate, the ensuing feed-back system works like a passive Maxwell's daemon, capable of inducing a net current that depends on both the delay and the autocorrelation times of the noise signals. Extensive numerical simulations show that the underlying rectification mechanism is a resonant nonlinear effect: The observed currents can be optimized for an appropriate choice of the recycling parameters with immediate application to the design of nanodevices for particle transport.

Borromeo, M; Marchesoni, F

2006-01-01

84

Molecular transport junctions: Current from electronic excitations in the leads  

CERN Multimedia

Using a model comprising a 2-level bridge connecting free electron reservoirs we show that coupling of a molecular bridge to electron-hole excitations in the leads can markedly effect the source-drain current through a molecular junction.In some cases, e.g. molecules that exhibit strong charge transfer transitions, the contribution from electron-hole excitations can exceed the Landauer elastic current and dominate the observed conduction.

Galperin, M; Ratner, M A; Galperin, Michael; Nitzan, Abraham; Ratner, Mark A.

2006-01-01

85

Time-dependent degradation spectrum of electrons in molecular nitrogen  

Energy Technology Data Exchange (ETDEWEB)

The time-dependent electron energy distribution functions in molecular are calculated when a source of primary electrons with energy 1 keV acts on the gas. The actual forms of the cross sections for the elementary electron processes are used. The relaxation resulting from excitation of the gas by pulses of electrons and the approach to steady state when a constant source of primary electrons in turned on are treated. The rates at which energy goes into ionization and excitation of the different sate of molecular N{sub 2} are calculated as functions of time. 25 refs., 8 figs.

Konovalov, V.P.; Skorik, M.A.; Son, E.E. [Moscow Physicotechnical Institute (Russian Federation)

1992-06-01

86

A New Full Adder Cell for Molecular Electronics  

CERN Multimedia

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.

Ghasemi, Mehdi; Navi, Keivan; 10.5121/vlsic.2011.2401

2012-01-01

87

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

Energy Technology Data Exchange (ETDEWEB)

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 C{sub 60} 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.

Gagliardi, Alessio; Frauenheim, Thomas; Niehaus, Thomas A [Bremen Center for Computational Materials Science, University of Bremen, D-28359 Bremen (Germany); Romano, Giuseppe; Pecchia, Alessandro; Di Carlo, Aldo [CNR-INFM Department of Electronics Engineering, University of Rome ' Tor Vergata' , Via del Politecnico 1, 00133 Rome (Italy)], E-mail: gagliard@bccms.uni-bremen.de, E-mail: Gagliardi@Ing.uniroma2.it

2008-06-15

88

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.

2008-01-01

89

Dissociation of Xe2+ molecular ions by electrons in plasma  

International Nuclear Information System (INIS)

Destruction of Xe2+ molecular ions by electrons in He-Xe plasma is investigated in the electron temperature range Te 0.03-2eV. The rate constant for the Xe2+ ions dissociation by electrons is measured for the first time. This process appears to be more effective than the dissociative recombination at electron temperatures Te>1eV. (author).

1991-01-01

90

Rectification of Uncalibrated Images for Stereo Vision  

Directory of Open Access Journals (Sweden)

Full Text Available 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 distance of all of the correspondent points to the corresponding epipolar line, then obtain the system equations, through solving system of equations, thus get the rectifying transformation matrix and rectify the stereo image pairs. Experiments show that, the size of the rectified images change not so seriously, the vertical disparity is eliminated, so the subsequent stereo correspondence can be fulfilled on the horizontal scan line of the rectified images completely.

HAN Huiyan; HAN Xie; Yang Fengbao

2013-01-01

91

Image Rectification Using Affine Epipolar Geometric Constraint  

Directory of Open Access Journals (Sweden)

Full Text Available To rapidly and accurately search the corresponding points along scan-lines, rectification of stereo pairs are performed so that corresponding epipolar lines are parallel to the horizontal scan-lines and the difference in vertical direction is zero. In this paper, the method to rectify image pairs could be divided into three steps including projective transformation, affine transformation and shearing transformation. The projective transformation matrix is computed under the affine epipolar geometry constraint, and the values of unknown parameters are searched by an algorithm which does not require the relative matrix be positive definite. In this paper, an optimization function is presented to remove the difference in vertical direction and an algorithm is developed to estimate initial values of some parameters such as scale weights and vertical offset.

Liansheng Sui; Jiulong Zhang; Duwu Cui

2009-01-01

92

Optimal control of a periodic rectification process  

Energy Technology Data Exchange (ETDEWEB)

The authors propose a control procedure based on the principle of maximum values, to avoid the rigidity of differential equation approaches that lead to the acceptance of various dubious ''givens.'' The mathematical model proposed has the advantage of reducing the number of calculations required by transforming the initial system to a smaller dimensional system, through the use of ''quasistationary'' values. The system of differential equations is divided into beginning and basic intervals, which are unequal. Periodic rectification is based on so-called slow components in some equations and fast components in others. The proposed method can be used to calculate optimal control of a process for separating a three-component mixture, reducing the time required for the operation by 60%. 6 references, 4 figures.

Kafarov, V.V.; Vetokhin, V.N.; Rozhkov, A.M.

1982-12-01

93

Photoelectrochemical solar conversion systems molecular and electronic aspects  

CERN Multimedia

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

94

Molecular Spintronics Spin-Dependent Electron Transport in Molecular Wires  

CERN Multimedia

We present a theoretical study of spin-dependent transport through molecular wires bridging ferromagnetic metal nanocontacts. We extend to magnetic systems a recently proposed model that provides a em quantitative explanation of the conductance measurements of Reed et al. on Au break-junctions bridged by self-assembled molecular monolayers (SAMs) of 1,4-benzene-dithiolate (BDT) molecules. Based on our calculations, we predict that spin-valve behavior should be observable in nickel break-junctions bridged by SAM's formed from BDT. We also consider spin transport in systems consisting of a clean ferromagnetic nickel STM tip and SAMs of benzene-thiol molecules on gold and nickel substrates. We find that spin-valve behavior should be possible for the Ni substrate. For the case where the substrate is gold, we show that it should be possible to inject a highly spin-polarized current into the substrate.

Emberly, E; Emberly, Eldon; Kirczenow, George

2002-01-01

95

Fitting molecular fragments into electron density  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A number of techniques for the location of small and medium-sized model fragments in experimentally phased electron-density maps are explored. The application of one of these techniques to automated model building is discussed.

Cowtan, Kevin

96

Electron dopable molecular wires based on the extended viologens.  

Science.gov (United States)

Facile electron transfer in molecules with one dimension greatly exceeding the other two is essential in the development of new molecular electronic devices as these molecules can serve as so-called molecular wires. In this communication the electrochemical behavior of a series of molecules with multiple extended viologen moieties has been studied. We show that the electron transfer in the shortest wire is due to reduction of two identical communicating pyridinium moieties leading to a full charge delocalization, whereas the electron transfer in molecules with n? 2 is due to reduction of initially non-communicating centers. This was confirmed by digital simulation of cyclic voltammograms. All studied molecules accept reversibly at least four and up to ten electrons without any long-term chemical changes, which is a prerequisite for their future application. Chemical stability of these molecules after multiple electron transfer was confirmed by in situ UV-Vis spectroelectrochemical detection. PMID:21566835

Kolivoška, Viliam; Gál, Miroslav; Pospíšil, Lubomír; Valášek, Michal; Hromadová, Magdaléna

2011-05-13

97

Electron dopable molecular wires based on the extended viologens.  

UK PubMed Central (United Kingdom)

Facile electron transfer in molecules with one dimension greatly exceeding the other two is essential in the development of new molecular electronic devices as these molecules can serve as so-called molecular wires. In this communication the electrochemical behavior of a series of molecules with multiple extended viologen moieties has been studied. We show that the electron transfer in the shortest wire is due to reduction of two identical communicating pyridinium moieties leading to a full charge delocalization, whereas the electron transfer in molecules with n? 2 is due to reduction of initially non-communicating centers. This was confirmed by digital simulation of cyclic voltammograms. All studied molecules accept reversibly at least four and up to ten electrons without any long-term chemical changes, which is a prerequisite for their future application. Chemical stability of these molecules after multiple electron transfer was confirmed by in situ UV-Vis spectroelectrochemical detection.

Kolivoška V; Gál M; Pospíšil L; Valášek M; Hromadová M

2011-06-01

98

Self-assembled nanogaps for molecular electronics  

Energy Technology Data Exchange (ETDEWEB)

A nanogap for molecular devices was realized using solution-based self-assembly. Gold nanorods were assembled to gold nanoparticle-coated conducting SnO{sub 2}:Sb nanowires via thiol end-capped oligo(phenylenevinylene)s (OPVs). The molecular gap was easily created by the rigid molecule itself during self-assembly and the gap length was determined by the molecule length. The gold nanorods and gold nanoparticles, respectively covalently bonded at the two ends of the molecule, had very small dimensions, e.g. a width of {approx}20 nm, and hence were expected to minimize the screening effect. The ultra-long conducting SnO{sub 2}:Sb nanowires provided the bridge to connect one of the electrodes of the molecular device (gold nanoparticle) to the external circuit. The tip of the atomic force microscope (AFM) was contacted onto the other electrode (gold nanorod) for the electrical measurement of the OPV device. The conductance measurement confirmed that the self-assembly of the molecules and the subsequent self-assembly of the gold nanorods was a feasible method for the fabrication of the nanogap of the molecular devices.

Tang Qingxin; Tong Yanhong; Jain, Titoo; Hassenkam, Tue; Moth-Poulsen, Kasper; Bjoernholm, Thomas [Nano-Science Center and Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100, Copenhagen (Denmark); Wan Qing [School of Physics and Microelectronics, Hunan University, Changsha 410082 (China)], E-mail: tb@nano.ku.dk

2009-06-17

99

Self-assembled nanogaps for molecular electronics  

DEFF Research Database (Denmark)

A nanogap for molecular devices was realized using solution-based self-assembly. Gold nanorods were assembled to gold nanoparticle-coated conducting SnO2:Sb nanowires via thiol end-capped oligo(phenylenevinylene)s (OPVs). The molecular gap was easily created by the rigid molecule itself during self-assembly and the gap length was determined by the molecule length. The gold nanorods and gold nanoparticles, respectively covalently bonded at the two ends of the molecule, had very small dimensions, e. g. a width of similar to 20 nm, and hence were expected to minimize the screening effect. The ultra-long conducting SnO2:Sb nanowires provided the bridge to connect one of the electrodes of the molecular device (gold nanoparticle) to the external circuit. The tip of the atomic force microscope (AFM) was contacted onto the other electrode (gold nanorod) for the electrical measurement of the OPV device. The conductance measurement confirmed that the self-assembly of the molecules and the subsequent self-assembly of the gold nanorods was a feasible method for the fabrication of the nanogap of the molecular devices.

Tang, Qingxin; Tong, Yanhong

2009-01-01

100

Self-assembled nanogaps for molecular electronics  

International Nuclear Information System (INIS)

A nanogap for molecular devices was realized using solution-based self-assembly. Gold nanorods were assembled to gold nanoparticle-coated conducting SnO2:Sb nanowires via thiol end-capped oligo(phenylenevinylene)s (OPVs). The molecular gap was easily created by the rigid molecule itself during self-assembly and the gap length was determined by the molecule length. The gold nanorods and gold nanoparticles, respectively covalently bonded at the two ends of the molecule, had very small dimensions, e.g. a width of ?20 nm, and hence were expected to minimize the screening effect. The ultra-long conducting SnO2:Sb nanowires provided the bridge to connect one of the electrodes of the molecular device (gold nanoparticle) to the external circuit. The tip of the atomic force microscope (AFM) was contacted onto the other electrode (gold nanorod) for the electrical measurement of the OPV device. The conductance measurement confirmed that the self-assembly of the molecules and the subsequent self-assembly of the gold nanorods was a feasible method for the fabrication of the nanogap of the molecular devices.

2009-06-17

 
 
 
 
101

Ion-pair formation in electron recombination with molecular ions  

International Nuclear Information System (INIS)

By studying ion-pair formation in electron recombination with molecular ions, fundamental knowledge on the molecular dynamics can be obtained. In order to study these types of reactions, both the electron recombination as well as the dynamics all the way to the asymptotic limits must be well described. We have used the wave packet technique to study ion-pair formation in electron recombination with HeH+, HD+, H3+ and HF+. We here discuss what will determine the general shape of the ion-pair cross section, the threshold effects, possible interference effects as well as the ratio of the cross sections of ion-pair formation to dissociative recombination.

2007-01-01

102

Theory of nonlinear electromagnetic rectification in a BCS superconductor  

International Nuclear Information System (INIS)

Within the framework of the BCS pairing approximation, a theory of nonlinear electromagnetic rectification in a Cooper-paired jellium is established. It is pointed out that the electromagnetic rectification phenomenon, inevitably present as the many-body system's reaction in a second-harmonic generation process, is of special interest in a superconductor where induced dc currents flow without resistance. Based on a density-matrix approach the nonlinear response tensor is derived and discussed. The importance of nonlocality for the rectification process in centrosymmetric media is stressed. A simple expression for the response tensor is derived in the limit in which the nonlocal pairing effects are included to lowest order. It is demonstrated that electromagnetic rectification occurs only when the nonlinear response has a diamagnetic part. By considering the electromagnetic-rectification phenomenon as a nonlinear-dynamical Meissner effect, the relation to the linear Meissner effect is emphasized. A qualitative discussion of the rectification process at a superconductor-vacuum interface is undertaken. An integrodifferential equation describing, on the basis of the semiclassical infinite-barrier model, the diamagnetic screening of the nonlinear dc magnetic field is set up and discussed

1990-10-01

103

Theory of nonlinear electromagnetic rectification in a BCS superconductor  

Energy Technology Data Exchange (ETDEWEB)

Within the framework of the BCS pairing approximation, a theory of nonlinear electromagnetic rectification in a Cooper-paired jellium is established. It is pointed out that the electromagnetic rectification phenomenon, inevitably present as the many-body system's reaction in a second-harmonic generation process, is of special interest in a superconductor where induced dc currents flow without resistance. Based on a density-matrix approach the nonlinear response tensor is derived and discussed. The importance of nonlocality for the rectification process in centrosymmetric media is stressed. A simple expression for the response tensor is derived in the limit in which the nonlocal pairing effects are included to lowest order. It is demonstrated that electromagnetic rectification occurs only when the nonlinear response has a diamagnetic part. By considering the electromagnetic-rectification phenomenon as a nonlinear-dynamical Meissner effect, the relation to the linear Meissner effect is emphasized. A qualitative discussion of the rectification process at a superconductor-vacuum interface is undertaken. An integrodifferential equation describing, on the basis of the semiclassical infinite-barrier model, the diamagnetic screening of the nonlinear dc magnetic field is set up and discussed.

Keller, O. (Institute of Physics, University of Aalborg, Pontoppidanstraede 103, DK-9220 Aalborg Ost (Denmark))

1990-10-01

104

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

105

Electronic conduction in a model three-terminal molecular transistor.  

UK PubMed Central (United Kingdom)

The electronic conduction of a novel, three-terminal molecular architecture, analogous to a heterojunction bipolar transistor, is studied. In this architecture, two diode arms consisting of donor-acceptor molecular wires fuse through a ring, while a gate modulating wire is a pi-conjugated wire. The calculated results show the enhancement or depletion mode of a transistor on applying a gate field along the positive or negative direction. A small gate field is required to switch on the current in the proposed architecture. The changes in the electronic conduction can be attributed to the intrinsic dipolar molecular architecture in terms of the evolution of molecular wavefunctions, specifically the one associated with the terphenyl group of the modulating wire in the presence of the gate field.

He H; Pandey R; Karna SP

2008-12-01

106

Electronic conduction in a model three-terminal molecular transistor  

Science.gov (United States)

The electronic conduction of a novel, three-terminal molecular architecture, analogous to a heterojunction bipolar transistor, is studied. In this architecture, two diode arms consisting of donor-acceptor molecular wires fuse through a ring, while a gate modulating wire is a ?-conjugated wire. The calculated results show the enhancement or depletion mode of a transistor on applying a gate field along the positive or negative direction. A small gate field is required to switch on the current in the proposed architecture. The changes in the electronic conduction can be attributed to the intrinsic dipolar molecular architecture in terms of the evolution of molecular wavefunctions, specifically the one associated with the terphenyl group of the modulating wire in the presence of the gate field.

He, Haiying; Pandey, Ravindra; Karna, Shashi P.

2008-12-01

107

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

UK PubMed Central (United Kingdom)

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.

Vilozny B; Wollenberg AL; Actis P; Hwang D; Singaram B; Pourmand N

2013-10-01

108

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

2013-08-12

109

Molecular and electronic structure of ?-valerothiolactone.  

UK PubMed Central (United Kingdom)

The crystal structure of the six-member heterocyclic ?-valerothiolactone (1-thiocycloalkan-2-one) compound has been determined by X-ray diffraction at low temperature, revealing that its skeleton adopts a half-chair conformation. The conformation around the thioester group is almost planar with an anti orientation of the C=O double bond with respect the S-C single bond [C(2)-S(1)-C(6)-O(1) = 176.26(8)°]. The skeletal parameters, especially valence angles [?C5-C6-S = 121.19(6)°, ?O=C6-C5 = 122.25(8)°, ?C6-S-C2 = 106.80(4)°], differ from those typically found in acyclic thioester compounds, symptomatic of the presence of strain effects. The conventional ring strain energy was determined to be 7.5 kcal/mol at the MP2/6-311++G(d,p) level of calculation within the hyperhomodesmotic model approximation. Moreover, the valence electronic structure was investigated by HeI photoelectron spectroscopy assisted by quantum chemical calculations at the OVGF/6-311++G(d,p) level of theory. The first three bands at 9.35, 9.50, and 11.53 eV denote ionizations related with the n(S), n(O), and ?(C=O) orbitals, respectively, demonstrating the importance of the -SC(O)- group in the outermost electronic properties.

Dugarte NY; Erben MF; Boese R; Ge MF; Yao L; Della Védova CO

2010-12-01

110

Ultrafast Molecular Imaging by Laser Induced Electron Diffraction  

CERN Document Server

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

111

Molecular and electronic structure of electroactive self-assembled monolayers.  

UK PubMed Central (United Kingdom)

Self-assembled monolayers (SAMs) containing electroactive functional groups are excellent model systems for the formation of electronic devices by self-assembly. In particular ferrocene-terminated alkanethiol SAMs have been extensively studied in the past. However, there are still open questions related with their electronic structure including the influence of the ferrocene group in the SAM-induced work function changes of the underlying metal. We have thus carried out a thorough experimental and theoretical investigation in order to determine the molecular and electronic structure of ferrocene-terminated alkanethiol SAMs on Au surfaces. In agreement with previous studies we found that the Fc-containing alkanethiol molecules adsorb forming a thiolate bond with the Au surface with a molecular geometry 30° tilted with respect to the surface normal. Measured surface coverages indicate the formation of a compact monolayer. We found for the first time that the ferrocene group has little influence on the observed work function decrease which is largely determined by the alkanethiol. Furthermore, the ferrocene moiety lies 14 Å above the metal surface covalently bonded to the alkanethiol SAM and its HOMO is located at -1.6 eV below the Fermi level. Our results provide new valuable insight into the molecular and electronic structure of electroactive SAMs which are of fundamental importance in the field of molecular electronics.

Méndez De Leo LP; de la Llave E; Scherlis D; Williams FJ

2013-03-01

112

Inelastic electron tunneling spectroscopy in molecular junctions: Peaks and dips  

CERN Multimedia

We study inelastic electron tunneling through a molecular junction using the non-equilibrium Green function (NEGF) formalism. The effect of the mutual influence between the phonon and the electron subsystems on the electron tunneling process is considered within a general self-consistent scheme. Results of this calculation are compared to those obtained from the simpler Born approximation and the simplest perturbation theory approaches, and some shortcomings of the latter are pointed out. The self-consistent calculation allows also for evaluating other related quantities such as the power loss during electron conduction. Regarding the inelastic spectrum, two types of inelastic contributions are discussed. Features associated with real and virtual energy transfer to phonons are usually observed in the second derivative of the current I with respect to the voltage when plotted against the latter. Signatures of resonant tunneling driven by an intermediate molecular ion appear as peaks in the first derivative d(c...

Galperin, M; Nitzan, A; Galperin, Michael; Ratner, Mark A.; Nitzan, Abraham

2004-01-01

113

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

114

Electron-nuclear corellations for photoinduced dynamics in molecular dimers  

Science.gov (United States)

Ultrafast photoinduced dynamics of electronic excitation in molecular dimers is drastically affected by dynamic reorganization of of inter- and intra- molecular nuclear configuration modelled by quantized nuclear degree of freedom [1]. The dynamics of the electronic population and nuclear coherence is analyzed with help of both numerical solution of the chain of coupled differential equations for mean coordinate, population inversion, electronic-vibrational correlation etc.[2] and by propagating the Gaussian wavepackets in relevant adiabatic potentials. Intriguing results were obtained in the approximation of small energy difference and small change of nuclear equilibrium configuration for excited electronic states. In the limiting case of resonance between electronic states energy difference and frequency of the nuclear mode these results have been justified by comparison to exactly solvable Jaynes-Cummings model. It has been found that the photoinduced processes in dimer are arranged according to their time scales:(i) fast scale of nuclear motion,(ii) intermediate scale of dynamical redistribution of electronic population between excited states as well as growth and dynamics of electronic -nuclear correlation,(iii) slow scale of electronic population approaching to the quasiequilibrium distribution, decay of electronic-nuclear correlation, and diminishing the amplitude of mean coordinate oscillations, accompanied by essential growth of the nuclear coordinate dispersion associated with the overall nuclear wavepacket width. Demonstrated quantum-relaxational features of photoinduced vibronic dinamical processess in molecular dimers are obtained by simple method, applicable to large biological systems with many degrees of freedom. [1] J. A. Cina, D. S. Kilin, T. S. Humble, J. Chem. Phys. (2003) in press. [2] O. V. Prezhdo, J. Chem. Phys. 117, 2995 (2002).

Kilin, Dmitri S.; Pereversev, Yuryi V.; Prezhdo, Oleg V.

2003-03-01

115

Molecular dynamics simulation of electronically excited polyatomic molecules  

International Nuclear Information System (INIS)

A computer simulation method is proposed for MD study of the photoinduced intramolecular dynamics in polyatomic molecules electronically excited by ultrashort laser pulses. An efficient, partially analytical procedure for calculation of the absorption (emission) spectra is developed and used for determination of molecular potentials in accordance with the experimental supersonic jets spectra. (author). 21 refs, 4 figs, 1 tab.

1993-01-01

116

Self assembled monolayers on silicon for molecular electronics  

Energy Technology Data Exchange (ETDEWEB)

We present an overview of various aspects of the self-assembly of organic monolayers on silicon substrates for molecular electronics applications. Different chemical strategies employed for grafting the self-assembled monolayers (SAMs) of alkanes having different chain lengths on native oxide of Si or on bare Si have been reviewed. The utility of different characterization techniques in determination of the thickness, molecular ordering and orientation, surface coverage, growth kinetics and chemical composition of the SAMs has been discussed by choosing appropriate examples. The metal counterelectrodes are an integral part of SAMs for measuring their electrical properties as well as using them for molecular electronic devices. A brief discussion on the variety of options available for the deposition of metal counterelectrodes, that is, soft metal contacts, vapor deposition and soft lithography, has been presented. Various theoretical models, namely, tunneling (direct and Fowler-Nordheim), thermionic emission, Poole-Frenkel emission and hopping conduction, used for explaining the electronic transport in dielectric SAMs have been outlined and, some experimental data on alkane SAMs have been analyzed using these models. It has been found that short alkyl chains show excellent agreement with tunneling models; while more experimental data on long alkyl chains are required to understand their transport mechanism(s). Finally, the concepts and realization of various molecular electronic components, that is, diodes, resonant tunnel diodes, memories and transistors, based on appropriate architecture of SAMs comprising of alkyl chains ({sigma}- molecule) and conjugated molecules ({pi}-molecule) have been presented.

Aswal, D.K. [Institut d' Electronique, Microelectronique et Nanotechnologie - CNRS ' Molecular Nanostructures and Devices' group BP60069, avenue Poincare, F-59652 cedex, Villeneuve d' Ascq (France) and Technical Physics and Prototype Engineering Division, Bhabha Atomic Research Center, Trombay, Mumbai 400 085 (India)]. E-mail: dkaswal@yahoo.com; Lenfant, S. [Institut d' Electronique, Microelectronique et Nanotechnologie - CNRS ' Molecular Nanostructures and Devices' group BP60069, avenue Poincare, F-59652 cedex, Villeneuve d' Ascq (France); Guerin, D. [Institut d' Electronique, Microelectronique et Nanotechnologie - CNRS ' Molecular Nanostructures and Devices' group BP60069, avenue Poincare, F-59652 cedex, Villeneuve d' Ascq (France); Yakhmi, J.V. [Technical Physics and Prototype Engineering Division, Bhabha Atomic Research Center, Trombay, Mumbai 400 085 (India); Vuillaume, D. [Institut d' Electronique, Microelectronique et Nanotechnologie - CNRS ' Molecular Nanostructures and Devices' group BP60069, avenue Poincare, F-59652 cedex, Villeneuve d' Ascq (France)

2006-05-24

117

Bias effects on the electronic spectrum of a molecular bridge.  

Science.gov (United States)

In this paper the effect of bias and geometric symmetry breaking on the electronic spectrum of a model molecular system is studied. Geometric symmetry breaking can either enhance the dissipative effect of the bias, where spectral peaks are disabled, or enable new excitations that are absent under zero bias conditions. The spectral analysis is performed on a simple model system by solving for the electronic response to an instantaneously impulsive perturbation in the dipole approximation. The dynamical response is extracted from the electronic equations of motion as expressed by the Keldysh formalism. This expression provides for the accurate treatment of the electronic structure of a bulk-coupled system at the chosen model Hamiltonian electronic structure level. PMID:21303153

Phillips, Heidi; Prociuk, Alexander; Dunietz, Barry D

2011-02-01

118

Bias effects on the electronic spectrum of a molecular bridge.  

UK PubMed Central (United Kingdom)

In this paper the effect of bias and geometric symmetry breaking on the electronic spectrum of a model molecular system is studied. Geometric symmetry breaking can either enhance the dissipative effect of the bias, where spectral peaks are disabled, or enable new excitations that are absent under zero bias conditions. The spectral analysis is performed on a simple model system by solving for the electronic response to an instantaneously impulsive perturbation in the dipole approximation. The dynamical response is extracted from the electronic equations of motion as expressed by the Keldysh formalism. This expression provides for the accurate treatment of the electronic structure of a bulk-coupled system at the chosen model Hamiltonian electronic structure level.

Phillips H; Prociuk A; Dunietz BD

2011-02-01

119

Linking electronic and molecular structure: insight into aqueous chloride solvation.  

UK PubMed Central (United Kingdom)

Aqueous chloride solutions are ubiquitous and diverse; systems include sea water, atmospheric droplets, geological processes and biological organisms. However, despite considerable effort, a complete microscopic model of the hydration shell, and local electronic structure of the aqueous chloride ion and its dynamics has not been established. In this work we employ ab initio molecular dynamics to study an aqueous chloride solution. In particular, local solvation events and the electronic structure around the chloride ion are interrogated. We employ the Effective Molecular Orbital (EMO) method which partitions the electronic structure into solute and solvent components while maintaining a rigorous quantum mechanical description of both. Movement of the chloride highest occupied molecular orbital (HOMO) energy within the valence band of water is revealed. The chloride ion has little impact on the average water electronic structure, however, locally the electronic effect of the chloride ion is significant. With the Hofmeister series in mind we find that the electronic effect of the chloride ion extends beyond the first solvation shell, but not beyond the edge of the second solvation shell. The chloride ion sits near the centre of the Hofmeister series because of an essential degeneracy between water-water and water-Cl H-bonding and because of a strong similarity in the water and chloride electronic structure. The chloride ion prefers to be symmetrically solvated by six H-bonding water molecules, however, the chloride HOMO energy and the coordination number oscillate in response to local fluctuations driven by the dynamics of the bulk water. A combined structural and electronic analysis has led to a distinction between two types of water molecule within the first solvation shell, those that H-bond to the chloride ion, and those that remain local (i.e. within the first solvation shell) but which H-bond to other water molecules. There are indications that these exhibit different dynamics with respect to residence times and rotational vs. translational motion.

Ge L; Bernasconi L; Hunt P

2013-08-01

120

Theory and Application of Dissociative Electron Capture in Molecular Identification  

CERN Multimedia

The coupling of an electron monochromator (EM) to a mass spectrometer (MS) has created a new analytical technique, EM-MS, for the investigation of electrophilic compounds. This method provides a powerful tool for molecular identification of compounds contained in complex matrices, such as environmental samples. EM-MS expands the application and selectivity of traditional MS through the inclusion of a new dimension in the space of molecular characteristics--the electron resonance energy spectrum. However, before this tool can realize its full potential, it will be necessary to create a library of resonance energy scans from standards of the molecules for which EM-MS offers a practical means of detection. Here, an approach supplementing direct measurement with chemical inference and quantum scattering theory is presented to demonstrate the feasibility of directly calculating resonance energy spectra. This approach makes use of the symmetry of the transition-matrix element of the captured electron to discriminat...

Havey, C D; Jones, T; Voorhees, K J; Laramee, J A; Cody, R B; Clougherty, D P; Eberhart, Mark; Voorhees, Kent J.; Laramee, James A.; Cody, Robert B.; Clougherty, Dennis P.

2006-01-01

 
 
 
 
121

Molecular design for novel radiation resist decomposable by electron detachment  

International Nuclear Information System (INIS)

[en] Molecular structures that can be dissociated into two fragments in cryogenic solid by electron detachment have been investigated for constructing high-resolution radiation resists that are free from blur due to the migration of secondary electrons. Within examined molecules that are known to be dissociative by electron detachment in liquids, only the radical cations of (C6H5)2(OH)C-CH(OH)C6H5 and [(CH3C6H5)(C6H5)(OH)C-]2 dissociate into benzyl-type radicals and cations. A polymer containing these molecules at the center of the skeleton can be used as a resist with high sensitivity and high spatial resolution, since the exposure of ionizing radiation causes stepwise reduction of the molecular weight by direct ionization.

2008-09-01

122

Chiral molecular films as electron polarizers and polarization modulators  

CERN Document Server

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. Longitudinal polarization is shown to be the signature of chiral scattering. For elastic scattering, we find that at least double scattering events must take place for longitudinal polarization to arise. We predict energy windows for strong polarization, determined by the energy dependences of spin-orbit strength and multiple scattering probability. An incoherent mechanism for polarization amplification is proposed, that increases the polarization linearly with the number of helix turns, consistent with recent experiments on DNA SAMs.

Medina, Ernesto; Ratner, Mark; Mujica, Vladimiro

2012-01-01

123

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

124

Low-energy electron-collision processes in molecular chlorine  

International Nuclear Information System (INIS)

The results of close-coupling calculations using the complex Kohn variational method are reported for a variety of low-energy electron-collision processes involving molecular chlorine. We report cross sections for elastic scattering and momentum transfer, as well as dissociative excitation of the five lowest electronically excited states (1,3?u, 1,3?g, 3?u+) which are formed by promoting an occupied valence electron into an antibonding (5?u) orbital. We also report cross sections for the excitation of the lowest bound optically allowed states in Cl2. The cross sections, especially at very low energies, are found to depend sensitively on both target polarization and a proper balance of correlation effects in the N- and (N+1)-electron systems. Comparison is made between the results of this study and the limited body of experimental results available for this system

1994-01-01

125

Peculiarities of electron decay excitation in ionic-molecular crystals  

International Nuclear Information System (INIS)

Peculiarities of chemical and energetic structure of ionic-molecular crystals (IMC) are causing by number of electron excitation decay features in compare with alkali halogen crystals. These features are as follows: both the electrons and the holes simultaneously can been captured and localized on anion and cation complexes; intramolecular forces arising in the result of charge capture can conduct to decay of anion and cation complexes; products of anion and cation complexes decay could participating in following reactions for new products formation. All these processes and products of electron excitation decay exert strong influence on optical, magnetic and electrical performances of IMC. Knowledge of ways and mechanisms of electron excitation in IMC can allow to radiation stability control of crystals with help of impurities, participating in different channels of solid state reactions

1999-01-01

126

Control of electron transport through Fano resonances in molecular wires  

CERN Document Server

Using a first principles approach, we study the electron transport properties of two molecules of length 2.5nm which are the building blocks for a new class of molecular wires containing fluorenone units. We show that the presence of side groups attached to these units leads to Fano resonances close to the Fermi energy. As a consequence electron transport through the molecule can be controlled either by chemically modifying the side group, or by changing the conformation of the side group. This sensitivity, which is not present in Breit-Wigner resonances, opens up new possibilities for novel single-molecule sensors.

Papadopoulos, T; Lambert, C; Papadopoulos, Theodoros; Grace, Iain; Lambert, Colin

2006-01-01

127

Control of electron transport through Fano resonances in molecular wires  

Science.gov (United States)

Using a first principles approach, we study the electron transport properties of two molecules of length 2.5nm , which are the building blocks for a new class of molecular wires containing fluorenone units. We show that the presence of side groups attached to these units leads to Fano resonances close to the Fermi energy. As a consequence electron transport through the molecule can be controlled either by chemically modifying the side group, or by changing the conformation of the side group. This sensitivity, which is not present in Breit-Wigner resonances, opens up new possibilities for novel single-molecule sensors.

Papadopoulos, T. A.; Grace, I. M.; Lambert, C. J.

2006-11-01

128

Stereo rectification of calibrated image pairs based on geometric transformation  

Directory of Open Access Journals (Sweden)

Full Text Available The objective of stereo rectification is to make the corresponding epipolar lines of image pairs be parallel to the horizontal direction, so that the efficiency of stereo matching is improved as the corresponding points stay in the same horizontal lines of both images. In this paper?a simple and convenient rectification method of calibrated image pairs based on geometric transformation is proposed, which can avoid the complicated calculation of many previous algorithms such as based on epipolar lines, based on fundamental matrix or directly depend on corresponding points. This method is divided into two steps including coordinate system transformation and re-projection of image points. Firstly, we establish two virtual cameras with parallel optical axis by coordinate system transformation based on the pose relationship of the two cameras from calibration result. Secondly, we re-project the points of the original image onto new image planes of the virtual cameras through geometrical method, and then realized the stereo rectification. Experiments of real stereo image pairs show that the proposed method is able to realize the rectification of stereo image pairs accurately and efficiently.

Huihuang Su; Bingwei He

2011-01-01

129

Resonance emission studies of solutions: Molecular dynamics and electronic dephasing  

Energy Technology Data Exchange (ETDEWEB)

The ability to generate intense UV laser frequencies has allowed the study of a range of important chemical species via spontaneous resonance Raman scattering. These include biological chromophores as well as small molecules of fundamental chemical significance. Here we demonstrate how the UV excited spontaneous resonance emission of small photodissociative molecules is a detailed molecular probe of the changes in the solute-solvent potential due to electronic excitation of the solute. With the aid of molecular dynamics simulations the analysis of resonance emission lineshapes, intensities and polarization reveals the fate of the isolated molecule photodissociation dynamics in solutions (baths) as well as providing a molecular description of the optical dephasing processes in the systems studied. These include methyl iodide and carbon disulfide in argon, methane, sulfur hexafluoride and carbon dioxide. Results will also be presented for these chromophores in critical regions and liquid solutions.

Ziegler, L.D.; Fan, R.; Kalbfleisch, T.S. [Boston Univ., Boston, MA (United States)

1995-12-01

130

Molecular Surface Mesh Generation by Filtering Electron Density Map  

Directory of Open Access Journals (Sweden)

Full Text Available Bioinformatics applied to macromolecules are now widely spread and in continuous expansion. In this context, representing external molecular surface such as the Van der Waals Surface or the Solvent Excluded Surface can be useful for several applications. We propose a fast and parameterizable algorithm giving good visual quality meshes representing molecular surfaces. It is obtained by isosurfacing a filtered electron density map. The density map is the result of the maximum of Gaussian functions placed around atom centers. This map is filtered by an ideal low-pass filter applied on the Fourier Transform of the density map. Applying the marching cubes algorithm on the inverse transform provides a mesh representation of the molecular surface.

Joachim Giard; Benoît Macq

2010-01-01

131

Ultrafast electron diffraction: oriented molecular structures in space and time.  

UK PubMed Central (United Kingdom)

The technique of ultrafast electron diffraction allows direct measurement of changes which occur in the molecular structures of isolated molecules upon excitation by femtosecond laser pulses. The vectorial nature of the molecule-radiation interaction also ensures that the orientation of the transient populations created by the laser excitation is not isotropic. Here, we examine the influence on electron diffraction measurements--on the femtosecond and picosecond timescales--of this induced initial anisotropy and subsequent inertial (collision-free) molecular reorientation, accounting for the geometry and dynamics of a laser-induced reaction (dissociation). The orientations of both the residual ground-state population and the excited- or product-state populations evolve in time, with different characteristic rotational dephasing and recurrence times due to differing moments of inertia. This purely orientational evolution imposes a corresponding evolution on the electron scattering pattern, which we show may be similar to evolution due to intrinsic structural changes in the molecule, and thus potentially subject to misinterpretation. The contribution of each internuclear separation is shown to depend on its orientation in the molecular frame relative to the transition dipole for the photoexcitation; thus not only bond lengths, but also bond angles leave a characteristic imprint on the diffraction. Of particular note is the fact that the influence of anisotropy persists at all times, producing distinct differences between the asymptotic "static" diffraction image and the predictions of isotropic diffraction theory.

Baskin JS; Zewail AH

2005-11-01

132

Designs for molecular circuits that use electronic coherence.  

UK PubMed Central (United Kingdom)

The mounting evidence of recent years regarding long-lived coherent dynamics of electronic excitations in several light-harvesting antenna proteins suggests the possibility of realizing and exploiting light-initiated quantum dynamics in synthetic molecular devices based on electronic energy transfer. Inspired by the field of molecular logic, we focus this discussion on the prospect of using quantum coherence to control the direction of energy flow in a molecular circuit. As a prototype system we consider a circuit consisting of three chromophores that deliver energy to two trap chromophores. Our aim is to control to which trap the energy is more likely to be delivered. This is achieved by switching one of the circuit chromophores ON and OFF from the system, such that the direction of energy flow substantially changes from the ON and OFF states of the circuit. We find that quantum coherence can allow a significant ability to direct energy transfer in the circuit. However, when realistic levels of noise are added, quantum coherence only slightly improves the ability to direct electronic energy in comparison to a classical hopping mechanism.

Fassioli F; Oblinsky DG; Scholes GD

2013-01-01

133

Single-Electron Molecular Transistors on the Base of Various Types of Cluster Molecules.  

Science.gov (United States)

Effect of single-electron tunneling in double-junction tunnel system based on single molecule was investigated. Molecular single-electron transistor was demonstrated. The comparison of measured characteristics with the similar characteristics of molecular...

E. S. Soldatov A. S. Trifonov S. P. Gubin V. V. Khanin G. B. Khomutov

1999-01-01

134

Electron momentum spectroscopy of 1-butene: a theoretical analysis using molecular dynamics and molecular quantum similarity.  

Science.gov (United States)

The results of experimental studies of the valence electronic structure of 1-butene by means of electron momentum spectroscopy (EMS) have been reinterpreted on the basis of molecular dynamical simulations in conjunction with the classical MM3 force field. The computed atomic trajectories demonstrate the importance of thermally induced nuclear dynamics in the electronic neutral ground state, in the form of significant deviations from stationary points on the potential energy surface and considerable variations of the C-C-C-C dihedral angle. These motions are found to have a considerable influence on the computed spectral bands and outer-valence electron momentum distributions. Euclidean distances between spherically averaged electron momentum densities confirm that thermally induced nuclear motions need to be fully taken into account for a consistent interpretation of the results of EMS experiments on conformationally flexible molecules. PMID:23902590

Shojaei, S H Reza; Vandenbussche, Jelle; Deleuze, Michael S; Bultinck, Patrick

2013-08-22

135

Electron momentum spectroscopy of 1-butene: a theoretical analysis using molecular dynamics and molecular quantum similarity.  

UK PubMed Central (United Kingdom)

The results of experimental studies of the valence electronic structure of 1-butene by means of electron momentum spectroscopy (EMS) have been reinterpreted on the basis of molecular dynamical simulations in conjunction with the classical MM3 force field. The computed atomic trajectories demonstrate the importance of thermally induced nuclear dynamics in the electronic neutral ground state, in the form of significant deviations from stationary points on the potential energy surface and considerable variations of the C-C-C-C dihedral angle. These motions are found to have a considerable influence on the computed spectral bands and outer-valence electron momentum distributions. Euclidean distances between spherically averaged electron momentum densities confirm that thermally induced nuclear motions need to be fully taken into account for a consistent interpretation of the results of EMS experiments on conformationally flexible molecules.

Shojaei SH; Vandenbussche J; Deleuze MS; Bultinck P

2013-09-01

136

Magnon-mediated thermal rectification with forward-bias and breakdown temperatures  

Science.gov (United States)

In an ideal model, a thermal rectifier is the thermal equivalent of the electrical diode. A device which leads a greater heat flow in one direction than another one. Currently used bulk and molecular mechanisms which can potentially result in thermal rectifying behavior have not evidenced that the rectification factor can reach one order of magnitude, which is an arbitrary limit required to deem the effect useful for engineered systems. Here, we have succeeded in building thermal diodes with thermal rectification factors up to 1.62 under 29 K temperature bias. Devices manipulate heat via the activation and deactivation of magnons in magnetic materials at room temperature through the Curie temperature. Furthermore, this factor can be enhanced further by improving the magnetic properties in the material and by increasing the thermal bias. In addition, thermal diodes present a well-defined breakdown as well as forward temperatures which control accurately the on state of the device. This approach paves the way to pursuit the one order limit at room temperature in a simple way and opens a new route towards the next generation of thermal devices.

Martínez-Flores, J. J.; Licea-Jimenez, L.; Perez Garcia, S. A.; Alvarez-Quintana, J.

2013-09-01

137

Intermolecular thermoelectric-like effects in molecular nano electronic systems  

International Nuclear Information System (INIS)

[en] Intramolecular thermoelectric-like coefficients are introduced and computed of a single molecule nano electronic system. Values of the electronic Intramolecular thermoelectric-like coefficients are calculated based on the density and energy transfers between different parts of the molecule using quantum theory of atoms in molecule. Since, Joule and Peltier heating are even (symmetrical) and odd (antisymmetric) functions of the external bias, it is possible to divide Intramolecular thermoelectric-like coefficients into two components, symmetrical and antisymmetrical Intramolecular thermoelectric-like coefficients, which describe the intramolecular Joule-like and Peltier-like effects, respectively. In addition, a semiclassical temperature model is presented to describe intramolecular temperature mapping (intramolecular energy distributions) in molecular nano electronic systems.

2012-01-01

138

Machine Learning of Molecular Electronic Properties in Chemical Compound Space  

CERN Multimedia

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 a data base of \\textit{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 ML model is based on a deep multi-task artificial neural network, exploiting underlying correlations between various molecular properties. The input is identical to \\emph{ab initio} methods, \\emph{i.e.} nucle...

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

2013-01-01

139

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.

Larade, Brian; Taylor, Jeremy Philip

2001-01-01

140

Two-dimensional electronic spectroscopy of molecular excitons.  

Science.gov (United States)

Understanding of the nuclear and electronic structure and dynamics of molecular systems has advanced considerably through probing the nonlinear response of molecules to sequences of pulsed electromagnetic fields. The ability to control various degrees of freedom of the excitation pulses-such as duration, sequence, frequency, polarization, and shape-has led to a variety of time-resolved spectroscopic methods. The various techniques that researchers use are commonly classified by their dimensionality, which refers to the number of independently variable time delays between the pulsed fields that induce the signal. Though pico- and femtosecond time-resolved spectroscopies of electronic transitions have come of age, only recently have researchers been able to perform two-dimensional electronic spectroscopy (2D-ES) in the visible frequency regime and correlate transition frequencies that evolve in different time intervals. The two-dimensional correlation plots and their temporal evolution allow one to access spectral information that is not exposed directly in other one-dimensional nonlinear methods. In this Account, we summarize our studies of a series of increasingly complex molecular chromophores. We examine noninteracting dye molecules, a monomer-dimer equilibrium of a prototypical dye molecule, and finally a supramolecular assembly of electronically coupled absorbers. By tracing vibronic signal modulations, differentiating line-broadening mechanisms, analyzing distinctly different relaxation dynamics, determining electronic coupling strengths, and directly following excitation energy transfer pathways, we illustrate how two-dimensional electronic spectroscopy can image physical phenomena that underlie the optical response of a particular system. Although 2D-ES is far from being a "turn-key" method, we expect that experimental progress and potential commercialization of instrumentation will make 2D-ES accessible to a much broader scientific audience, analogous to the development of multidimensional NMR and 2D-IR. PMID:19673525

Milota, Franz; Sperling, Jaroslaw; Nemeth, Alexandra; Mancal, Tomás; Kauffmann, Harald F

2009-09-15

 
 
 
 
141

Electron Degradation and Yields of Initial Products: 4. Subexcitation Electrons in Molecular Oxygen.  

Science.gov (United States)

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-dep...

M. A. Ishii M. Kimura M. Inokuti K. Kowari

1988-01-01

142

Fulleropyrrolidine end-capped molecular wires for molecular electronics--synthesis, spectroscopic, electrochemical, and theoretical characterization  

DEFF Research Database (Denmark)

In continuation of previous studies showing promising metal-molecule contact properties a variety of C(60) end-capped "molecular wires" for molecular electronics were prepared by variants of the Prato 1,3-dipolar cycloaddition reaction. Either benzene or fluorene was chosen as the central wire, and synthetic protocols for derivatives terminated with one or two fullero[c]pyrrolidine "electrode anchoring" groups were developed. An aryl-substituted aziridine could in some cases be employed directly as the azomethine ylide precursor for the Prato reaction without the need of having an electron-withdrawing ester group present. The effect of extending the p-system of the central wire from 1,4-phenylenediamine to 2,7-fluorenediamine was investigated by absorption, fluorescence, and electrochemical methods. The central wire and the C(60) end-groups were found not to electronically communicate in the ground state. However, the fluorescence of C(60) was quenched by charge transfer from the wire to C(60). Quantum chemical calculations predict and explain the collapse of coherent electronic transmission through one of the fulleropyrrolidine-terminated molecular wires.

SØrensen, Jakob Kryger; Fock, Jeppe

2011-01-01

143

The Impact of Molecular Polarization on the Electronic Properties of Molecular Semiconductors  

CERN Multimedia

The ground state of a carrier in a molecular semiconductor is studied using a model hamiltonian in which the itinerant charge is treated in the tight binding approximation and is coupled, through charge-dipole interaction terms to a quantum field of Frenkel-excitons representing the surrounding, polarizable molecules. We demonstrate that, in the presence of static or thermal disorder, this "electronic polaron" problem can be mapped onto an Anderson model with correlated diagonal and non-diagonal disorder. Some conclusions are drawn on the role of molecular polarization on the dynamics of an extra charge in acenes.

Bussac, M N; Zuppiroli, L

2003-01-01

144

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

145

Molecule-electrode interfaces in molecular electronic devices.  

UK PubMed Central (United Kingdom)

Understanding charge transport of single molecules or a small collection of molecules sandwiched between electrodes is of fundamental importance for molecular electronics. This requires the fabrication of reliable devices, which depend on several factors including the testbed architectures used, the molecule number and defect density being tested, and the nature of the molecule-electrode interface. On the basis of significant progresses achieved in both experiments and theory over the past decade, in this tutorial review, we focus on new insights into the influence of the nature of the molecule-electrode interface, the most critical issue hindering the development of reliable devices, on the conducting properties of molecules. We summarize the strategies developed for controlling the interfacial properties and how the coupling strength between the molecules and the electrodes modulates the device properties. These analyses should be valuable for deeply understanding the relationship between the contact interface and the charge transport mechanism, which is of crucial importance for the development of molecular electronics, organic electronics, nanoelectronics, and other interface-related optoelectronic devices.

Jia C; Guo X

2013-07-01

146

Rectification behavior of PATP self-assembled on ZnO microrod arrays.  

UK PubMed Central (United Kingdom)

A rectifying hybrid junction was fabricated by the self-assembly of 4-aminothiophenol (PATP) on well-aligned ZnO microrod arrays. Good rectification behavior was obtained from the device of Al/ZnO/PATP/Al. The electron transport at the ZnO/PATP interface was investigated systematically by experimental observation and theoretical simulation. X-ray photoelectron spectroscopy (XPS) analysis confirmed the strong binding between PATP and ZnO via S-Zn bonds. The effective energy barrier and ideality factor of the rectifying diode were estimated by the current-voltage (I-V) measurement and thermionic emission theory. The molecule dipole effect on work function was studied through energy band theory. Theoretical calculation results based on density functional theory (DFT) also indicated a significant dipole, caused by the anchoring effect of PATP, resulting in the changes of surface electronic characteristics of ZnO.

Fang S; Xu C; Jin Z; Sheng F; Shi Z; Wang Y; Zhu G

2013-04-01

147

Enhanced electron-capture and charge variation of molecular ions  

International Nuclear Information System (INIS)

The following question is asked: For molecular ions moving within a stopping medium, its atomic-ion components separating under the influence of their mutual repulsion, how do the charges of the atomic ions vary with the dept of penetration? To address this question, the author considers a diatomic, homonuclear molecular ion whose center of mass moves with velocity V in a solid. He can describe this molecular ion as a pair of atomic ions having equal nuclear charges, Z, each carrying a number, N(x), of electrons which are bound to their respective centers of force. Let the displacement of nuclear charge Z1 relative to nuclear charge Z2 be described by the internuclear separation R. For a depth of penetration into the solid, x, the internuclear separation, R(x) = R(t), will be determined by the Coulomb explosion between the interacting charges, q1 = q2 = q(x), where q(x) = Z-N(x). The relative motion of the ion pair may be neglected so that each atomic ion moves with the velocity of the center of mass; i.e., V1 = V2 = V. For the present, he restricts consideration to molecular ions whose internuclear axes are aligned parallel with the direction of the beam. 4 refs., 1 fig.

1989-01-01

148

Electron transport in nanotube--molecular wire hybrids  

CERN Multimedia

We study contact effects on electron transport across a molecular wire sandwiched between two semi-infinite (carbon) nanotube leads as a model for nanoelectrodes. Employing the Landauer scattering matrix approach we find that the conductance is very sensitive to parameters such as the coupling strength and geometry of the contact. The conductance exhibits markedly different behavior in the two limiting scenarios of single contact and multiple contacts between the molecular wire and the nanotube interfacial atoms. In contrast to a single contact the multiple-contact configuration acts as a filter selecting single transport channels. It exhibits a scaling law for the conductance as a function of coupling strength and tube diameter. We also observe an unusual narrow-to-broad-to-narrow behavior of conductance resonances upon decreasing the coupling.

Fagas, G; Richter, K

2001-01-01

149

Vibrational excitations in molecular layers probed by ballistic electron microscopy  

International Nuclear Information System (INIS)

[en] 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

150

Stretched exponential relaxation in molecular and electronic glasses  

International Nuclear Information System (INIS)

Stretched exponential relaxation, exp[-(t/?)?], fits many relaxation processes in disordered and quenched electronic and molecular systems, but it is widely believed that this function has no microscopic basis, especially in the case of molecular relaxation. For electronic relaxation the appearance of the stretched exponential is often described in the context of dispersive transport, where ? is treated as an adjustable parameter, but in almost all cases it is generally assumed that no microscopic meaning can be assigned to 0g, a glass transition temperature. We show that for molecular relaxation ?(Tg) can be understood, providing that one separates extrinsic and intrinsic effects, and that the intrinsic effects are dominated by two magic numbers, ?SR=3/5 for short-range forces, and ?K=3/7 for long-range Coulomb forces, as originally observed by Kohlrausch for the decay of residual charge on a Leyden jar. Our mathematical model treats relaxation kinetics using the Lifshitz-Kac-Luttinger diffusion to traps depletion model in a configuration space of effective dimensionality, the latter being determined using axiomatic set theory and Phillips-Thorpe constraint theory. The experiments discussed include ns neutron scattering experiments, particularly those based on neutron spin echoes which measure S(Q, t) directly, and the traditional linear response measurements which span the range from ?s to s, as collected and analysed phenomenologically by Angell, Ngai, Boehmer and others. The electronic materials discussed include a-Si:H, granular C60, semiconductor nanocrystallites, charge density waves in TaS3, spin glasses, and vortex glasses in high-temperature semiconductors. The molecular materials discussed include polymers, network glasses, electrolytes and alcohols, Van der Waals supercooled liquids and glasses, orientational glasses, water, fused salts, and heme proteins. In the intrinsic cases the theory of ?(Tg) is often accurate to 2%, which is often better than the quoted experimental accuracies ?5%. The extrinsic cases are identified by explicit structural signatures which are discussed at length. The discussion also includes recent molecular dynamical simulations for metallic glasses, spin glasses, quasicrystals and polymers which have achieved the intermediate relaxed Kohlrausch state and which have obtained values of ? in excellent agreement with the prediction of the microscopic theory. (author)

1996-01-01

151

Increasing thermal rectification: Effects of long-range interactions.  

UK PubMed Central (United Kingdom)

In this paper, we study the effects of the interparticle interaction range on heat flow. We show that, by increasing the interaction range, we may amplify the thermal conductivity and even change the regime of heat transport. More importantly, considering a crucial problem of phononics, namely, the search of a suitable thermal diode, we investigate the range effects in some graded systems in which thermal rectification is a ubiquitous phenomenon. In such graded models, we show that long-range interactions may significatively increase the rectification power and may avoid its decay with the system size, thus solving relevant problems of the usual proposals of rectifiers. Our results indicate that graded materials are genuine candidates for the actual fabrication of thermal diodes.

Pereira E; Avila RR

2013-09-01

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

Rectification of License Plate Images Based on HT and Projection  

Directory of Open Access Journals (Sweden)

Full Text Available It is crucial to segment characters correctly and improve rate of correct character recognition when processing automobile license plates corrections. In this paper, two algorithms are proposed to obtain the horizontal tilt and vertical shear angles. The transformation matrix for images rectification is given and the subpixel issue is solved. Some experiments were done to test the algorithms. Experimental results show that the algorithm is robust, flexible and effective.

Hongyao Deng; Qingxin Zhu; Jingsong Tao; Hao Feng

2013-01-01

154

Thermal rectification in similar and dissimilar metal contacts  

Energy Technology Data Exchange (ETDEWEB)

An investigation was conducted to verify experimentally the existence of thermal rectification and to determine the effect of surface roughness and material type. Four pairs of test specimens were evaluated: one with a smooth Nickel 200 surface in contact with a rough Nickel 200 surface, one with a smooth Stainless Steel 304 surface in contact with a rough Stainless Steel 304 surface, one with a smooth Nickel 200 surface in contact with a rough Stainless Steel 304 surface, and finally, one with a smooth Stainless Steel 304 surface in contact with a rough Nickel 200 surface. The thermal contact conductance was measured for heat flow from both the smooth to rough and rough to smooth configurations for all four parts. The results indicate that thermal rectification is a function of surface characteristics, material type, and heat flow direction. For similar materials in contact, some thermal rectification was observed with heat flow from the rough surface to the smooth surface resulting in a higher value of contact conductance. For dissimilar materials, the thermal contact conductance was highest when the heat flow was from the Stainless Steel 304 to Nickel 200. In these cases, the surface roughness was shown to be of secondary importance.

Stevenson, P.F.; Peterson, G.P.; Fletcher, L.S. (Texas A and M Univ., College Station (USA))

1991-02-01

155

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

2013-03-22

156

Origin of rectification in boron nitride heterojunctions to silicon.  

UK PubMed Central (United Kingdom)

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.

Teii K; Hori T; Mizusako Y; Matsumoto S

2013-04-01

157

Designing bistable [2]rotaxanes for molecular electronic devices.  

UK PubMed Central (United Kingdom)

The development of molecular electronic components has been accelerated by the promise of increased circuit densities and reduced power consumption. Bistable rotaxanes have been assembled into nanowire crossbar devices, where they may be switched between low- and high-conductivity states, forming the basis for a molecular memory. These memory devices have been scaled to densities of 10(11) bits cm(-2), the 2020 node for memory of the International Technology Roadmap for Semiconductors. Investigations of the kinetics and thermodynamics associated with the electromechanical switching processes of several bistable [2]rotaxane derivatives in solution, self-assembled monolayers on gold, polymer electrolyte gels and in molecular switch tunnel junction devices are consistent with a single, universal switching mechanism whose speed is dependent largely on the environment, as well as on the structure of the switching molecule. X-ray reflectometry studies of the bistable rotaxanes assembled into Langmuir monolayers also lend support to an oxidatively driven mechanical switching process. Structural information obtained from Fourier transform reflection absorption infrared spectroscopy of rotaxane monolayers taken before and after evaporation of a Ti top electrode confirmed that the functionality responsible for switching is not affected by the metal deposition process. All the considerable experimental data, taken together with detailed computational work, support the hypothesis that the tunnelling current hysteresis, which forms the basis of memory operation, is a direct result of the electromechanical switching of the bistable rotaxanes.

Dichtel WR; Heath JR; Stoddart JF

2007-06-01

158

Designing bistable [2]rotaxanes for molecular electronic devices.  

Science.gov (United States)

The development of molecular electronic components has been accelerated by the promise of increased circuit densities and reduced power consumption. Bistable rotaxanes have been assembled into nanowire crossbar devices, where they may be switched between low- and high-conductivity states, forming the basis for a molecular memory. These memory devices have been scaled to densities of 10(11) bits cm(-2), the 2020 node for memory of the International Technology Roadmap for Semiconductors. Investigations of the kinetics and thermodynamics associated with the electromechanical switching processes of several bistable [2]rotaxane derivatives in solution, self-assembled monolayers on gold, polymer electrolyte gels and in molecular switch tunnel junction devices are consistent with a single, universal switching mechanism whose speed is dependent largely on the environment, as well as on the structure of the switching molecule. X-ray reflectometry studies of the bistable rotaxanes assembled into Langmuir monolayers also lend support to an oxidatively driven mechanical switching process. Structural information obtained from Fourier transform reflection absorption infrared spectroscopy of rotaxane monolayers taken before and after evaporation of a Ti top electrode confirmed that the functionality responsible for switching is not affected by the metal deposition process. All the considerable experimental data, taken together with detailed computational work, support the hypothesis that the tunnelling current hysteresis, which forms the basis of memory operation, is a direct result of the electromechanical switching of the bistable rotaxanes. PMID:17430812

Dichtel, William R; Heath, James R; Stoddart, J Fraser

2007-06-15

159

Ballistic switching and rectification in single wall carbon nanotube Y junctions  

Energy Technology Data Exchange (ETDEWEB)

Transport properties of various semiconducting zig-zag carbon nanotube Y junctions are studied for the investigations of rectification and switching. Our results indicate that such junctions, when symmetric, can support both ballistic rectification and/or the ballistic switching operating modes. Although structural symmetry of the Y junction is found to be a necessary condition for rectification, it may not be sufficient in all cases.

Andriotis, Antonis N.; Menon, Madhu; Srivastava, Deepak; Chernozatonskii, Leonid

2001-07-09

160

Electronic stopping power from ab-initio Ehrenfest molecular dynamics  

Science.gov (United States)

Many materials are exposed to particle radiation: Metal walls of nuclear reactors in fission systems are subject to ion bombardment. Solar cells and semiconductor components in satellites are damaged by ions from cosmic rays. In order to achieve high radiation tolerance, it is essential to comprehend the interaction of fast projectiles with the ionic and electronic system of the target at a fundamental level. Based on the real-time propagation of time-dependent Kohn-Sham equations we developed a highly parallel plane-wave implementation of non-adiabatic Ehrenfest molecular dynamics, overcoming the adiabatic Born-Oppenheimer approximation. Thanks to the excellent scalability of our explicit integration scheme on supercomputers, it allows for the parameter-free computation of electronic stopping with hundreds of atoms in the calculation. We summarize our approach with some attention to important computational details. The influence of different charge states of H, He, and Li projectiles penetrating an Al target will be outlined. While we find good agreement with experiment up to the maximum of electronic stopping, deviations for high velocities are discussed in the light of the theoretical framework and off-channeling effects. Prepared by LLNL under Contract DE-AC52-07NA27344.

Schleife, Andre; Kanai, Yosuke; Correa, Alfredo

2013-03-01

 
 
 
 
161

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

162

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

163

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

International Nuclear Information System (INIS)

[en] Electron slowing-down processes in molecular oxygen gas in the subexcitation domain (below the 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 the previously studied cases of N2 and CO2, O2 has the special features in its inelastic cross sections of (i) strong delta-function-like peaks in the vibrational excitation cross section below 1.3 eV and (ii) very low energy thresholds of electronic excitation channels. These features provide a stringent test for 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

1989-03-15

164

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 the 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 the previously studied cases of N/sub 2/ and CO/sub 2/, O/sub 2/ has the special features in its inelastic cross sections of (i) strong delta-function-like peaks in the vibrational excitation cross section below 1.3 eV and (ii) very low energy thresholds of electronic excitation channels. These features provide a stringent test for 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.

Ishii, M.A.; Kimura, M.; Inokuti, M.; Kowari, K.

1989-03-15

165

Preparation and rectification function of multilayer oxide p-i-n junction  

Science.gov (United States)

The all perovskite oxide p-i-n junctions formed by integrating semiconducting p-type (hole-doped) manganite (La,Sr)MnO3 (LSMO) and metallic n-type (electron-doped) cuprate superconductor (La,Ce)2CuO4, in between, the ferroelectric (Ba,Sr)TiO3 (BST) (which is in n-type semiconducting [1]) is sandwiched as the depletion barrier layer (i). It is shown that the perfect interfaces of the integrated layers is the most important factor to determine the rectification function of such p-i-n junction. For the typical p-i-n junction with depletion layer BST~20 nm, under the bias case, the forward current density is in 10-1A cm-2 order. The built-in field is estimated to be ~1.7 V, the depolarization field is ~1.4 V, and the reverse broken field is ~-3.3 V.

Xia, F. J.; Fu, Y. J.; Xu, B.; Zhu, B. Y.; Qiu, X. G.; Cao, L. X.; Yuan, J.; Wu, H.; Li, J. J.; Jin, A. Z.; Wang, Y. M.; Li, F. H.; Liu, B. T.; Xie, Z.; Zhao, B. R.

2012-12-01

166

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)

2012-01-01

167

Fullerene-based Anchoring Groups for Molecular Electronics  

DEFF Research Database (Denmark)

We present results on a new fullerene-based anchoring group for molecular electronics. Using lithographic mechanically controllable break junctions in vacuum we have determined the conductance and stability of single-molecule junctions of 1,4-bis(fullero[c]pyrrolidin-1-yl)benzene. The compound can be self-assembled from solution and has a low-bias conductance of 3 × 10-4 G0. Compared to 1,4-benzenedithiol the fullerene-anchored molecule exhibits a considerably lower conductance spread. In addition, the signature of the new compound in histograms is more significant than that of 1,4-benzenediamine, probably owing to a more stable adsorption motif. Statistical analyses of the breaking of the junctions confirm the stability of the fullerene-gold bond.

Martin, Christian A.; Ding, Dapeng

2008-01-01

168

The diversity of electron-transport behaviors of molecular junctions: correlation with the electron-transport pathway.  

Science.gov (United States)

We report the electron-transport behaviors of a number of molecular junctions composed of pi-conjugated molecular wires. From calculations performed by using density functional theory (DFT) combined with the non-equilibrium Green's function (NEGF) method, we found that the length-conductivity relations are diverse, depending on the particular molecular structures. The results reveal that the conductance-length dependence follows an exponential law for many conjugated molecules with a single channel, such as oligothiophene, oligopyrrole and oligophenylene. Therefore, a quantitative relation between the energy gap (E(g))(infinity) of the molecular wire and the attenuation factor beta can be defined. However, when the molecular wires have multichannels, the decay of conductance does not follow the exponential relation. For example, the conductance of porphyrin-based oligomers and fused thiophene decays almost linearly. The diversity of electron-transport behaviors of molecular junctions is directly dominated by the electron-transport pathway. PMID:20379983

Liu, Hongmei; Yu, Cui; Gao, Nengyue; Zhao, Jianwei

2010-06-21

169

The diversity of electron-transport behaviors of molecular junctions: correlation with the electron-transport pathway.  

UK PubMed Central (United Kingdom)

We report the electron-transport behaviors of a number of molecular junctions composed of pi-conjugated molecular wires. From calculations performed by using density functional theory (DFT) combined with the non-equilibrium Green's function (NEGF) method, we found that the length-conductivity relations are diverse, depending on the particular molecular structures. The results reveal that the conductance-length dependence follows an exponential law for many conjugated molecules with a single channel, such as oligothiophene, oligopyrrole and oligophenylene. Therefore, a quantitative relation between the energy gap (E(g))(infinity) of the molecular wire and the attenuation factor beta can be defined. However, when the molecular wires have multichannels, the decay of conductance does not follow the exponential relation. For example, the conductance of porphyrin-based oligomers and fused thiophene decays almost linearly. The diversity of electron-transport behaviors of molecular junctions is directly dominated by the electron-transport pathway.

Liu H; Yu C; Gao N; Zhao J

2010-06-01

170

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

171

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 N2+ and the fist positive system of N2 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 Ou+-- x1?g+ system of Au2 and the A2?--- 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 Ao=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 H2, have been measured. Also in this work, the deexcitation of the B3?+(0+u), v'=14 level of I2 after pulsed laser excitation has been studied. The quenching cross sections by collisions with I2, H2, CO2 and CH4 have been determin-ed. (Author)

1989-01-01

172

Rectification properties of conically shaped nanopores: consequences of miniaturization.  

UK PubMed Central (United Kingdom)

Nanopores attracted a great deal of scientific interest as templates for biological sensors as well as model systems to understand transport phenomena at the nanoscale. The experimental and theoretical analysis of nanopores has been so far focused on understanding the effect of the pore opening diameter on ionic transport. In this article we present systematic studies on the dependence of ion transport properties on the pore length. Particular attention was given to the effect of ion current rectification exhibited in conically shaped nanopores with homogeneous surface charges. We found that reducing the length of conically shaped nanopores significantly lowered their ability to rectify ion current. However, rectification properties of short pores can be enhanced by tailoring the surface charge and the shape of the narrow opening. Furthermore we analyzed the relationship of the rectification behavior and ion selectivity for different pore lengths. All simulations were performed using MsSimPore, a software package for solving the Poisson-Nernst-Planck (PNP) equations. It is based on a novel finite element solver and allows for simulations up to surface charge densities of -2 e per nm(2). MsSimPore is based on 1D reduction of the PNP model, but allows for a direct treatment of the pore with bulk electrolyte reservoirs, a feature which was previously used in higher dimensional models only. MsSimPore includes these reservoirs in the calculations, a property especially important for short pores, where the ionic concentrations and the electric potential vary strongly inside the pore as well as in the regions next to the pore entrance.

Pietschmann JF; Wolfram MT; Burger M; Trautmann C; Nguyen G; Pevarnik M; Bayer V; Siwy Z

2013-10-01

173

Cascade units for neon isotope production by rectification  

Science.gov (United States)

The basics of neon isotope separation by the distillation method at T = 28 K are discussed. The required numbers of transfer units at the top and bottom column sections are calculated for different loads. The experimental characteristics of packed rectification columns are presented and examples of the cascade are discussed. A configuration for a cryogenic circuit based on a high-pressure throttle neon cycle with intermediate nitrogen cooling is presented. The necessity for and the technical feasibility of creating a driver pressure difference between the columns for different stages are demonstrated.

Bondarenko, V. L.; Simonenko, Yu. M.; Diachenko, O. V.; Matveyev, E. V.

2013-05-01

174

Mechanism of rectification in inward-rectifier K+ channels.  

UK PubMed Central (United Kingdom)

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 approximately 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 block by both types of alkylamines increases with chain length. Mutation D172N in the second transmembrane segment reduces the channel's affinity significantly for long bis-amines, but only slightly for short ones (or for mono-amines of any length), whereas a double COOH-terminal mutation (E224G and E299S) moderately reduces the affinity for all bis-amines. The apparent valence of channel block increases from approximately 2 for short amines to saturate at approximately 5 for long bis-amines or at approximately 4 for long mono-amines. On the basis of these and other observations, we propose that to block the channel pore one amine group in all alkylamines tested binds near the same internal locus formed by the COOH terminus, while the other amine group of bis-amines, or the alkyl tail of mono-amines, "crawls" toward residue D172 and "pushes" up to 4 or 5 K+ ions outwardly across the narrow K+ selectivity filter. The strong voltage dependence of channel block therefore reflects the movement of charges carried across the transmembrane electrical field primarily by K+ ions, not by the amine molecule itself, as K+ ions and the amine blocker displace each other during block and unblock of the pore. This simple displacement model readily accounts for the classical observation that, at a given concentration of intracellular K+, rectification is apparently related to the difference between the membrane potential and the equilibrium potential for K+ ions rather than to the membrane potential itself.

Guo D; Ramu Y; Klem AM; Lu Z

2003-04-01

175

Mechanism of rectification in inward-rectifier K+ channels.  

Science.gov (United States)

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 approximately 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 block by both types of alkylamines increases with chain length. Mutation D172N in the second transmembrane segment reduces the channel's affinity significantly for long bis-amines, but only slightly for short ones (or for mono-amines of any length), whereas a double COOH-terminal mutation (E224G and E299S) moderately reduces the affinity for all bis-amines. The apparent valence of channel block increases from approximately 2 for short amines to saturate at approximately 5 for long bis-amines or at approximately 4 for long mono-amines. On the basis of these and other observations, we propose that to block the channel pore one amine group in all alkylamines tested binds near the same internal locus formed by the COOH terminus, while the other amine group of bis-amines, or the alkyl tail of mono-amines, "crawls" toward residue D172 and "pushes" up to 4 or 5 K+ ions outwardly across the narrow K+ selectivity filter. The strong voltage dependence of channel block therefore reflects the movement of charges carried across the transmembrane electrical field primarily by K+ ions, not by the amine molecule itself, as K+ ions and the amine blocker displace each other during block and unblock of the pore. This simple displacement model readily accounts for the classical observation that, at a given concentration of intracellular K+, rectification is apparently related to the difference between the membrane potential and the equilibrium potential for K+ ions rather than to the membrane potential itself. PMID:12642596

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

2003-03-17

176

The effect of functional group in changing of electron transport characteristics of molecular wires  

International Nuclear Information System (INIS)

[en] Using green's function based on tight-binding model, we have investigated transport properties of molecular systems which are sandwiched between two semi-infinite leads, in presence of functional group. Our results demonstrate that the transport properties can be influenced by the host molecular system, number of functional groups, the location where they are connected to molecular system. Thus these molecular wires can act as an electronic molecular sensor.

2012-01-01

177

Single-Image Rectification Technique in Forensic Science.  

UK PubMed Central (United Kingdom)

Many researchers have been working in Spain to document the communal graves of those assassinated during the Spanish Civil War. This article shows the results obtained with two low-cost photogrammetric techniques for the basic documentation of forensic studies. These low-cost techniques are based on single-image rectification and the correction of the original photo displacement due to the projection and perspective distortions introduced by the lens of the camera. The capability of image rectification is tested in an excavation in the village of Loma de Montija (Burgos, Spain). The results of both techniques are compared with the more accurate data obtained from a laser scanner system RIEGL LMS-Z390i to evaluate the error in the lengths. The first technique uses a camera situated on a triangle-shaped pole at a height of 5 m and the second positions the camera over the grave using a linearly actuated device. The first technique shows measurement errors less than 6%, whereas the second shows greater errors (between 8% and 14%) owing to the positioning of the carbon-fiber cross on an uneven surface.

González-Jorge H; Puente I; Eguía P; Arias P

2013-02-01

178

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; Xiaojin Gong; Ying Lin; Jilin Liu

2012-01-01

179

Batch distillation employing cyclic rectification and stripping operations.  

UK PubMed Central (United Kingdom)

Several strategies have been proposed to increase the operating efficiency of batch distillation. In this study, conventional batch rectification and inverted batch stripping are used cyclically to promote high product flow rates for a binary fractionation. Process controls are implemented to maintain constant product purity specifications by varying the slope of the operating line. While rectifying, the light component is removed as distillate, concentrating the heavy component in the reboiler. As a result, the distillate rate decreases with time. The column is then changed from rectification to stripping modes, and the heavy component is removed as bottoms product, concentrating the light component in the distillate drum. This causes the bottoms rate to diminish with time, and the column is once again converted back to rectifying mode. Cyclic operation, transitioning from batch rectifying to stripping back to rectifying, continues until all of the initial charge is fractionated or is combined with a new charge. The fractionation of ethanol and 1-propanol using the proposed operating strategy is shown to provide several advantages including energy and time savings when compared to conventional batch or inverted batch distillation alone.

Flodman HR; Timm DC

2012-05-01

180

Tuning electron transport through molecular junctions by chemical modification of the molecular core: First-principles study  

Science.gov (United States)

The unique versatility of the electronic structures of organic molecules can be potentially utilized to engineer single-molecular electronic devices with specific functionalities. Here, we report on how the electronic structures and the transport properties of molecular junctions containing a ?-conjugated terephthalic acid molecule in a scanning tunneling microscopy (STM) configuration can be tuned by modifying their chemical composition at a single-atom level. More specifically, this strategy implies (i) to change the molecular core through a chemical functionalization process and (ii) to modify the chemical nature of the STM-tip-apex atom. In this respect, our first-principles calculations of the electronic structures and the corresponding electron transport reveal that by the insertion and increase of the number of N atoms in the six-membered benzenelike aromatic ring, the electron transmission at the Fermi level increases. However, the calculated electron transmission at the Fermi level does not depend significantly on the specific position of the N atom in the aromatic ring. Nevertheless, when the tip-apex atom is changed from Cu to W, the electron transmission of the molecular junction significantly changes in an energy range above the Fermi level.

Tsukamoto, Shigeru; Caciuc, Vasile; Atodiresei, Nicolae; Blügel, Stefan

2013-09-01

 
 
 
 
181

A quantum molecular similarity analysis of changes in molecular electron density caused by basis set flotation and electric field application  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quantum molecular similarity (QMS) techniques are used to assess the response of the electron density of various small molecules to application of a static, uniform electric field. Likewise, QMS is used to analyze the changes in electron density generated by the process of floating a basis set. The ...

Simon i Rabasseda, Sílvia; Duran i Portas, Miquel

182

New formula for dependence of molecular electronic energy on internuclear distance  

Energy Technology Data Exchange (ETDEWEB)

We formulate an integral virial theorem which connects the change in the molecular electronic energy during finite changes in the size of the nuclear core (in the case of a diatomic molecule, during finite changes of the internuclear distance) with a matrix element of the kinetic electronic energy operator and with an overlap integral between wave functions. Our results can be used to calculate the dependence of the molecular electronic energy on the internuclear distance, as well as to check the quality of, and to improve, the approximate electronic wave functions. The theory is illustrated by the simplest example of the approximate MO LCAO wave function for the hydrogen molecular ion.

Rebane, T.K.

1988-05-01

183

Electron degradation and yields on initial products. II. Subexcitation electrons in molecular nitrogen  

International Nuclear Information System (INIS)

[en] Subexcitation electrons lose their kinetic energy through vibrational excitation, rotational excitation, and elastic collisions in molecular gases. Initial yields of vibrationally and rotationally excited states of nitrogen molecules are calculated by using the Spencer--Fano equation (SFE) and its simplification, the continuous-slowing-down approximation (CSDA), both in time-independent and time-dependent representations. One focus of the present study is a close comparison of the CSDA with the rigorous treatment of the SFE in the subexcitation domain. The present result reveals for the first time distinct energy regions in which either vibrational excitation or rotational excitation dominates. This recognition explains the different time dependence of the yields of vibrational and rotational excitation

1988-12-15

184

Electron degradation and yields on initial products. II. Subexcitation electrons in molecular nitrogen  

Energy Technology Data Exchange (ETDEWEB)

Subexcitation electrons lose their kinetic energy through vibrational excitation, rotational excitation, and elastic collisions in molecular gases. Initial yields of vibrationally and rotationally excited states of nitrogen molecules are calculated by using the Spencer--Fano equation (SFE) and its simplification, the continuous-slowing-down approximation (CSDA), both in time-independent and time-dependent representations. One focus of the present study is a close comparison of the CSDA with the rigorous treatment of the SFE in the subexcitation domain. The present result reveals for the first time distinct energy regions in which either vibrational excitation or rotational excitation dominates. This recognition explains the different time dependence of the yields of vibrational and rotational excitation.

Kowari, K.; Kimura, M.; Inokuti, M.

1988-12-15

185

Development of an electron-temperature-dependent interatomic potential for molecular dynamics simulation of tungsten under electronic excitation  

International Nuclear Information System (INIS)

[en] Irradiation of a metal by lasers or swift heavy ions causes the electrons to become excited. In the vicinity of the excitation, an electronic temperature is established within a thermalization time of 10-100 fs, as a result of electron-electron collisions. For short times, corresponding to less than 1 ps after excitation, the resulting electronic temperature may be orders of magnitude higher than the lattice temperature. During this short time, atoms in the metal experience modified interatomic forces as a result of the excited electrons. These forces can lead to ultrafast nonthermal phenomena such as melting, ablation, laser-induced phase transitions, and modified vibrational properties. We develop an electron-temperature-dependent empirical interatomic potential for tungsten that can be used to model such phenomena using classical molecular dynamics simulations. Finite-temperature density functional theory calculations at high electronic temperatures are used to parametrize the model potential

2008-12-01

186

Vortex rectification effects in films with periodic asymmetric pinning  

CERN Document Server

We study the transport of vortices excited by an ac current in an Al film with an array of nanoengineered asymmetric antidots. The vortex response to the ac current is investigated by detailed measurements of the voltage output as a function of ac current amplitude, magnetic field and temperature. The measurements revealed pronounced voltage rectification effects which are mainly characterized by the two critical depinning forces of the asymmetric potential. The shape of the net dc voltage as a function of the excitation amplitude indicates that our vortex ratchet behaves in a way very different from standard overdamped models. Rather, as demonstrated by the observed output signal, the repinning force, necessary to stop vortex motion, is considerably smaller than the depinning force, resembling the behavior of the so-called inertia ratchets. Calculations based on an underdamped ratchet model provide a very good fit to the experimental data.

De van Vondel, J; Zhu, B Y; Morelle, M; Moshchalkov, V V

2005-01-01

187

Inadequacies in De Broglie's Theory: rectifications, verifications, and applications  

Science.gov (United States)

The proposed paper calls attention towards the unobserved mathematical and conceptual inadequacies persisting in the wave-particle duality and matter wave's concepts, given by Louis de Broglie. Matter wave's frequency and phase velocity expressions, shown to be inappropriate, are the consequences of these inadequate concepts. The rectifications in these concepts are presented through the corrected implementation of analogy between light waves and matter waves and thus modified frequency and phase velocity expressions are introduced. The proposed expressions are free from all the inadequacies and negations, contrary to that confronted by de Broglie's proposed expressions. Mathematical proofs for the proposed modified frequency and phase velocity expression are also presented. A novel General Quantum Mechanical Wave Equation is proposed involving the modified phase velocity expression, which itself can precisely derive out Schrodinger's and Dirac's Equation.

Chauhan, Himanshu; Sinha, R. K.

2013-10-01

188

Molecular Spintronics: Theory of Spin-Dependent Electron Transport in Fe/BDT/Fe Molecular Wire Systems  

Science.gov (United States)

Metal/Molecule/Metal junction systems forming molecular wires are currently the focus of intense study. Recently, spin-dependent electron transport in molecular wires with magnetic Ni electrodes has been studied theoretically, and spin-valve effects have been predicted.* Here we explore theoretically another magnetic molecular wire system, namely, ferromagnetic Fe nano-contacts bridged with 1,4-benzene-dithiolate (BDT). We estimate the essential structural and electronic parameters for this system based on ab initio density functional calculations (DFT) for some simple model systems involving thiol groups and Fe clusters as well as semi-empirical considerations and the known electronic structure of bulk Fe. We then use Lippmann-Schwinger and Green's function techniques together with the Landauer formalism to study spin-dependent transport. *E. G. Emberly and G. Kirczenow, Chem. Phys. 281, 311 (2002); R. Pati, L. Senapati, P.M. Ajayan and S.K. Nayak, Phys. Rev. B68, 100407 (2003).

Dalgleish, Hugh; Kirczenow, George

2004-03-01

189

Electronic transport in fullerene C20 bridge assisted by molecular vibrations.  

Science.gov (United States)

The effect of molecular vibrations on electronic transport is investigated with the smallest fullerene C20 bridge, utilizing the Keldysh nonequilibrium Green's function techniques combined with the tight-binding molecular-dynamics method. Large discontinuous steps appear in the differential conductance when the applied bias voltage matches particular vibrational energies. The magnitude of the step is found to vary considerably with the vibrational mode and to depend on the local electronic states besides the strength of electron-vibration coupling. On the basis of this finding, a novel way to control the molecular motion by adjusting the gate voltage is proposed. PMID:16090961

Yamamoto, Takahiro; Watanabe, Kazuyuki; Watanabe, Satoshi

2005-08-02

190

All-carbon sp-sp2 hybrid structures: Geometrical properties, current rectification, and current amplification  

Science.gov (United States)

All-carbon sp-sp2 hybrid structures comprised of a zigzag-edged trigonal graphene (ZTG)and carbon chains are proposed and constructed as nanojunctions. It has been found that such simple hybrid structures possess very intriguing propertiesapp:addword:intriguing. The high-performance rectifying behaviors similar to macroscopic p-n junction diodes, such as a nearly linear positive-bias I-V curve (metallic behavior), a very small leakage current under negative bias (insulating behavior), a rather low threshold voltage, and a large bias region contributed to a rectification, can be predicted. And also, a transistor can be built by such a hybrid structure, which can show an extremely high current amplification. This is because a sp-hybrid carbon chain has a special electronic structure which can limit the electronic resonant tunneling of the ZTG to a unique and favorable situation. These results suggest that these hybrid structures might promise importantly potential applications for developing nano-scale integrated circuits.

Zhang, Zhenhua; Zhang, Junjun; Kwong, Gordon; Li, Ji; Fan, Zhiqiang; Deng, Xiaoqing; Tang, Guiping

2013-01-01

191

All-carbon sp-sp(2) hybrid structures: Geometrical properties, current rectification, and current amplification.  

Science.gov (United States)

All-carbon sp-sp(2) hybrid structures comprised of a zigzag-edged trigonal graphene (ZTG)and carbon chains are proposed and constructed as nanojunctions. It has been found that such simple hybrid structures possess very intriguing propertiesapp:addword:intriguing. The high-performance rectifying behaviors similar to macroscopic p-n junction diodes, such as a nearly linear positive-bias I-V curve (metallic behavior), a very small leakage current under negative bias (insulating behavior), a rather low threshold voltage, and a large bias region contributed to a rectification, can be predicted. And also, a transistor can be built by such a hybrid structure, which can show an extremely high current amplification. This is because a sp-hybrid carbon chain has a special electronic structure which can limit the electronic resonant tunneling of the ZTG to a unique and favorable situation. These results suggest that these hybrid structures might promise importantly potential applications for developing nano-scale integrated circuits. PMID:23999318

Zhang, Zhenhua; Zhang, Junjun; Kwong, Gordon; Li, Ji; Fan, Zhiqiang; Deng, Xiaoqing; Tang, Guiping

2013-09-01

192

Electron spin resonance study on lignin molecular mobility  

International Nuclear Information System (INIS)

[en] 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

193

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

194

The role of geometry in nanoscale rectennas for rectification and energy conversion  

Science.gov (United States)

We have previously presented a method for optical rectification that has been demonstrated both theoretically and experimentally and can be used for the development of a practical rectification and energy conversion device for the electromagnetic spectrum including the visible portion. This technique for optical frequency rectification is based, not on conventional material or temperature asymmetry as used in MIM or Schottky diodes, but on a purely geometric property of the antenna tip or other sharp edges that may be incorporated on patch antennas. This "tip" or edge in conjunction with a collector anode providing connection to the external circuit constitutes a tunnel junction. Because such devices act as both the absorber of the incident radiation and the rectifier, they are referred to as "rectennas." Using current nanofabrication techniques and the selective Atomic Layer Deposition (ALD) process, junctions of 1 nm can be fabricated, which allow for rectification of frequencies up to the blue portion of the spectrum (see Section 2).

Miskovsky, N. M.; Cutler, P. H.; Mayer, A.; Willis, B. G.; Zimmerman, D. T.; Weisel, G. J.; Chen, James M.; Sullivan, T. E.; Lerner, P. B.

2013-09-01

195

New insights into molecular structure and dynamics using soft x-ray electron spectroscopy  

International Nuclear Information System (INIS)

[en] The combination of high-resolution electron energy analyzers and 3rd generation synchrotron radiation sources opens up possibilities to study molecular inner-shell photo- and Auger electron emission in a new level of detail. Even weak molecular perturbations of the energy levels and angular emission patterns can be studied. In this report, some examples of such studies are given based on recent experiments at the Advanced Light Source, using a Scienta SES-200 electron spectrometer. Examples of carbon 1s photoemission of ethyne, sulphur 2p photoemission of carbonyl sulphide, and resonant Auger electron emission of carbon dioxide are presented

2000-02-14

196

Laboratory distillation and rectification of oil mixtures. Laboratornaya peregonka i rektifikatsiya neftyanykh smesey  

Energy Technology Data Exchange (ETDEWEB)

The basic methods for studying the fractional composition and methods for breaking down complex mixtures are examined. Different methods for distillation and rectification and the devices for implementing them are described. An evaluation is given of the effectiveness of laboratory rectification methods for determining the properties and composition of petroleum products and the potential content of light petroleum products in the oils. The results are presented of original experimental studies.

Manovyan, A.K.; Khachaturyan, D.A.; Lozin, V.V.

1984-01-01

197

Molecular vibrations-induced quantum beats in two-dimensional electronic spectroscopy  

CERN Multimedia

Quantum beats in nonlinear spectroscopy of molecular aggregates are often attributed to electronic phenomena of excitonic systems, while nuclear degrees of freedom are commonly included into models as overdamped oscillations of bath constituents responsible for dephasing. However, molecular systems are coupled to various high-frequency molecular vibrations, which can cause the spectral beats hardly distinguishable from those created by purely electronic coherences. Models containing damped, undamped and overdamped vibrational modes coupled to an electronic molecular transition are discussed in this paper in context of linear absorption and two-dimensional electronic spectroscopy. Analysis of different types of bath models demonstrates how do vibrations map onto two-dimensional spectra and how the damping strength of the coherent vibrational modes can be resolved from spectroscopic signals.

Butkus, Vytautas; Abramavicius, Darius

2012-01-01

198

An Electronically Non-Adiabatic Generalization of Ring Polymer Molecular Dynamics  

CERN Multimedia

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

199

Application of the Schwinger variational principle to electron-molecular ion scattering  

International Nuclear Information System (INIS)

The authors present some preliminary results of the application of the Schwinger variational principle to electron-molecular ion scattering. The results of this application to e-H2+ scattering in the static-exchange approximation are encouraging. (Auth.)

1979-06-16

200

Computer simulation of electron induced molecular radiation damage  

International Nuclear Information System (INIS)

The decay of DNA-bound Auger electron emitters causes strongly localized high-LET effects in the immediate surrounding of the radionuclide. For 125I, the most prominent Auger emitter in radiation biology, electron spectra of individual decays are generated by Monte Carlo simulation. The interaction of these electrons with the DNA as well as with the nearest surrounding is simulated. The use of simple assumptions allows the modelling of radiation damages like single and double strand breaks. In this paper, some selected results of these simulations are presented; in particular, the high-LET character of the Auger electrons is emphasized. (orig.).

1996-01-01

 
 
 
 
201

Observation of molecular frame (e,2e) cross section using an electron-electron-fragment ion triple coincidence apparatus  

Energy Technology Data Exchange (ETDEWEB)

An apparatus for electron-electron-fragment ion triple coincidence experiments has been developed to examine binary (e,2e) scattering reaction in the molecular frame. In the axial recoil limit of fragmentation of the residual ion, measurements of vector correlations among the three charged particles are equivalent to (e,2e) experiments with fixed-in-space molecules. Details and performance of the apparatus are reported, together with preliminary result of collision dynamics study on ionisation-excitation processes of fixed-in-space H{sub 2} molecules. We believe that this is the first observation of molecular frame (e,2e) cross sections.

Takahashi, M. [Institute for Molecular Science, Okazaki 444 8585 (Japan) and Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980 8577 (Japan)]. E-mail: masahiko@ims.ac.jp; Watanabe, N. [Institute for Molecular Science, Okazaki 444 8585 (Japan); Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980 8577 (Japan); Khajuria, Y. [Institute for Molecular Science, Okazaki 444 8585 (Japan); Nakayama, K. [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980 8577 (Japan); Udagawa, Y. [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980 8577 (Japan); Eland, J.H.D. [Physical and Theoretical Chemistry Laboratory, Oxford University, Oxford OX13QZ (United Kingdom)

2004-12-01

202

Observation of molecular frame (e,2e) cross section using an electron-electron-fragment ion triple coincidence apparatus  

International Nuclear Information System (INIS)

[en] An apparatus for electron-electron-fragment ion triple coincidence experiments has been developed to examine binary (e,2e) scattering reaction in the molecular frame. In the axial recoil limit of fragmentation of the residual ion, measurements of vector correlations among the three charged particles are equivalent to (e,2e) experiments with fixed-in-space molecules. Details and performance of the apparatus are reported, together with preliminary result of collision dynamics study on ionisation-excitation processes of fixed-in-space H2 molecules. We believe that this is the first observation of molecular frame (e,2e) cross sections

2004-01-01

203

Electron irradiation reduction of the molecular weight of nitrocellulose  

International Nuclear Information System (INIS)

A process is described for obtaining low molecular weight products. Nitrocellulose is subjected to a dose of ionising radiations of around 1.0 to 50 megarads at ambient temperature, in the presence of a humidifying agent

1975-12-01

204

Energy Transformation in Molecular Electronic Systems. Progress Report.  

Science.gov (United States)

Intramolecular Porton Transfer: Amplified spontaneous emission and laser action has been discovered in 3-hydroxyflavone. Proton transfer is also being studied in flavins (lumichrome) and DNA purines (adenine and guanine). Singlet Molecular Oxygen Studies:...

M. Kasha

1984-01-01

205

Coherent electron-phonon coupling and polaron-like transport in molecular wires  

CERN Multimedia

We present a technique to calculate the transport properties through one-dimensional models of molecular wires. The calculations include inelastic electron scattering due to electron-lattice interaction. The coupling between the electron and the lattice is crucial to determine the transport properties in one-dimensional systems subject to Peierls transition since it drives the transition itself. The electron-phonon coupling is treated as a quantum coherent process, in the sense that no random dephasing due to electron-phonon interactions is introduced in the scattering wave functions. We show that charge carrier injection, even in the tunneling regime, induces lattice distortions localized around the tunneling electron. The transport in the molecular wire is due to polaron-like propagation. We show typical examples of the lattice distortions induced by charge injection into the wire. In the tunneling regime, the electron transmission is strongly enhanced in comparison with the case of elastic scattering throu...

Ness, H; Fisher, A J

2001-01-01

206

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

Energy Technology Data Exchange (ETDEWEB)

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..--> pi.. discrete absorption of the sigma..-->..sigma f-wave shape resonance in N/sub 2/ and CO are given as examples.

Dill, D.; Swanson, J.R.; Wallace, S.; Dehmer, J.L.

1980-10-27

207

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.).

1988-01-01

208

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

209

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

210

On the relation between electronic structure and molecular dynamics  

International Nuclear Information System (INIS)

A formalism is developed for relating dynamic observables of collision processes to the electronic structure of the colliding species. Expressions are derived for functional derivatives of dynamic observables with respect to the full electronic wavefunction for the case of indistinguishable collision partners as well as for nonidentical partners. For wavefunctions described by orbitals, the formalism is extended to relate dynamic observables to electronic orbitals and orbital coefficients. The formalism is illustrated with the simple example of H+D and H+H elastic scattering cross sections at energies between 0.5 and 5.0 eV. Regions of the wavefunction which have particularly strong influence on the cross sections are identified by the functional derivatives. The manner in which the dynamics enters into the sensitivity is discussed. Particle indistinguishability is seen to influence the sensitivity of the collision to electronic structure

1990-09-15

211

Observation of electrical switching, reverse rectification and hysteresis in nanostructured organic-organic heterojunction.  

UK PubMed Central (United Kingdom)

Nanostructured organic-organic (O-O) heterojunction was fabricated by using the thin films of a hole transporting material, copper phthalocyanine (CuPc) and an electron transporting material, copper hexadecafluoro-phthalocyanine (F16CuPc). The nanostructured thin films were characterized by optical absorption spectra, FESEM, AFM, X-ray diffraction, etc. Grain size of CuPc and F16CuPc on the substrate surface was different. XRD analysis shows that the crystallinity of the double layer films/heterojunction decreases as compared to the single layer film. The heterojunction sandwich structure ITO/F16CuPc/CuPc/Al, in the present study has shown a good diode like current-voltage (I-V) characteristics with reverse rectifying characteristics. In addition, electrical switching and hysteresis phenomena have also been observed in both sides of the voltage polarities. Interestingly, the single layer sandwich structure of the type ITO/CuPc/Al and ITO/F16CuPc/Al did not show any noticeable electrical switching and hysteresis in I-V characteristics as compared to double layer heterostructure. The reverse rectification has been explained on the basis of band bending due to the accumulation of charge carriers near the junction and the electrical switching has been explained considering the charge carriers trapping and detrapping at the O-O interface.

Chowdhury A; Biswas B; Bera RN; Mallik B

2013-01-01

212

Ab initio analysis of electron-phonon coupling in molecular devices  

CERN Document Server

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

213

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

Energy Technology Data Exchange (ETDEWEB)

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.

Lucchese, R.R.; McKoy, V.

1981-08-01

214

Distinctive character of electronic and vibrational coherences in disordered molecular aggregates  

CERN Multimedia

Coherent dynamics of coupled molecules are effectively characterized by the two-dimensional (2D) electronic coherent spectroscopy. Depending on the coupling between electronic and vibrational states, oscillating signals of purely electronic, purely vibrational or mixed origin can be observed. Even in the "mixed" molecular systems two types of coherent beats having either electronic or vibrational character can be distinguished by analyzing oscillation Fourier maps, constructed from time-resolved 2D spectra. The amplitude of the beatings with the electronic character is heavily affected by the energetic disorder and consequently electronic coherences are quickly dephased. Beatings with the vibrational character depend weakly on the disorder, assuring their long-time survival. We show that detailed modeling of 2D spectroscopy signals of molecular aggregates providesdirect information on the origin of the coherent beatings.

Butkus, Vytautas; Abramavicius, Darius; Valkunas, Leonas

2013-01-01

215

Post-complementary metal-oxide-semiconductor vertical and molecular transistors: A platform for molecular electronics  

Science.gov (United States)

We demonstrate two types of post-complementary vertical-metal-insulator tunneling transistor in which a self-assembled monolayer is coupled to the channel of one of them. It is found that the properties of the molecular device are better than those of similar transistors in which these molecules are absent. The molecular transistor exhibits higher currents than the non-molecular device and shows negligible leakage currents, with clear features which are attributed to the properties of the molecules.

Mentovich, Elad D.; Richter, Shachar

2011-07-01

216

In situ superexchange electron transfer through a single molecule: a rectifying effect.  

Science.gov (United States)

An increasingly comprehensive body of literature is being devoted to single-molecule bridge-mediated electronic nanojunctions, prompted by their prospective applications in molecular electronics and single-molecule analysis. These junctions may operate in gas phase or electrolyte solution (in situ). For biomolecules, the latter is much closer to their native environment. Convenient target molecules are aromatic molecules, peptides, oligonucleotides, transition metal complexes, and, broadly, molecules with repetitive units, for which the conducting orbitals are energetically well below electronic levels of the solvent. A key feature for these junctions is rectification in the current-voltage relation. A common view is that asymmetric molecules or asymmetric links to the electrodes are needed to acquire rectification. However, as we show here, this requirement could be different in situ, where a structurally symmetric system can provide rectification because of the Debye screening of the electric field in the nanogap if the screening length is smaller than the bridge length. The Galvani potentials of each electrode can be varied independently and lead to a transistor effect. We explore this behavior for the superexchange mechanism of electron transport, appropriate for a wide class of molecules. We also include the effect of conformational fluctuations on the lowest unoccupied molecular orbital (LUMO) energy levels; that gives rise to non-Arrhenius temperature dependence of the conductance, affected by the molecule length. Our study offers an analytical formula for the current-voltage characteristics that demonstrates all these features. A detailed physical interpretation of the results is given with a discussion of reported experimental data. PMID:16641101

Kornyshev, Alexei A; Kuznetsov, Alexander M; Ulstrup, Jens

2006-04-25

217

In situ superexchange electron transfer through a single molecule: a rectifying effect.  

UK PubMed Central (United Kingdom)

An increasingly comprehensive body of literature is being devoted to single-molecule bridge-mediated electronic nanojunctions, prompted by their prospective applications in molecular electronics and single-molecule analysis. These junctions may operate in gas phase or electrolyte solution (in situ). For biomolecules, the latter is much closer to their native environment. Convenient target molecules are aromatic molecules, peptides, oligonucleotides, transition metal complexes, and, broadly, molecules with repetitive units, for which the conducting orbitals are energetically well below electronic levels of the solvent. A key feature for these junctions is rectification in the current-voltage relation. A common view is that asymmetric molecules or asymmetric links to the electrodes are needed to acquire rectification. However, as we show here, this requirement could be different in situ, where a structurally symmetric system can provide rectification because of the Debye screening of the electric field in the nanogap if the screening length is smaller than the bridge length. The Galvani potentials of each electrode can be varied independently and lead to a transistor effect. We explore this behavior for the superexchange mechanism of electron transport, appropriate for a wide class of molecules. We also include the effect of conformational fluctuations on the lowest unoccupied molecular orbital (LUMO) energy levels; that gives rise to non-Arrhenius temperature dependence of the conductance, affected by the molecule length. Our study offers an analytical formula for the current-voltage characteristics that demonstrates all these features. A detailed physical interpretation of the results is given with a discussion of reported experimental data.

Kornyshev AA; Kuznetsov AM; Ulstrup J

2006-05-01

218

Study of rectification at the metal-cadmium telluride contact  

International Nuclear Information System (INIS)

[en] 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[fr] Ce travail a eu pour objet la determination de la hauteur de la barriere de potentiel du contact entre divers metaux et du telluride de cadmium de type N ou P. Selon le traitement de surface du semiconducteur: rodage, polissage ou decapage chimique dans une solution de brome-methanol, des differences de l'ordre de 0,1 eV apparaissent sur la valeur de la hauteur de la barriere qui est toujours inferieure a 0,9 - 1,0 eV. Dans tous les cas, les resultats ne peuvent etre simplement expliques par la theorie de Schottky

1981-01-01

219

Energy transformation in molecular electronic systems. Progress report  

Energy Technology Data Exchange (ETDEWEB)

Intramolecular Porton Transfer: Amplified spontaneous emission and laser action has been discovered in 3-hydroxyflavone. Proton transfer is also being studied in flavins (lumichrome) and DNA purines (adenine and guanine). Singlet Molecular Oxygen Studies: Excited-state studies are underway. (DLC)

Kasha, M.

1984-01-01

220

Application of quantum chemistry to nanotechnology: electron and spin transport in molecular devices.  

UK PubMed Central (United Kingdom)

Rapid progress of nanotechnology requires developing novel theoretical methods to explain complicated experimental results and predict new functions of nanodevices. Thus, for the last decade, one of the challenging works of quantum chemistry is to understand the electron and spin transport phenomena in molecular devices. This critical review provides an extensive survey of on-going research and its current status in molecular electronics with the focus on theoretical applications to diverse types of devices along with a brief introduction of theoretical methods and its practical implementation scheme. The topics cover diverse molecular devices such as molecular wires, rectifiers, field effect transistors, electrical and optical switching devices, nanosensors, spin-valve devices, negative differential resistance devices and inelastic electron tunnelling spectroscopy. The limitations of the presented method and the possible approaches to overcome the limitations are addressed (183 references).

Kim WY; Choi YC; Min SK; Cho Y; Kim KS

2009-08-01

 
 
 
 
221

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

International Nuclear Information System (INIS)

[en] 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

222

Molecular-frame angular distribution of normal and resonant Auger electrons  

Energy Technology Data Exchange (ETDEWEB)

Molecular-frame angular distributions (MFADs) of resonant and non-resonant ('normal') Auger electrons were determined using angle-resolved electron-ion coincidence spectroscopy. Here, we concentrate on the MFADs of normal N2 KVV Auger electrons. We conclude that their MFADs are independent of both photon energy and light polarization direction, thus confirming that the two-step model is a good approximation. All threshold and shape-resonance phenomena can be attributed to the absorption process and are irrelevant for the Auger decay in the molecular frame. Distinct differences in the MFADs are found as a function of the Auger final state.

Rolles, D; Pesic, Z D; Dumitriu, I; Berrah, N [Physics Department, Western Michigan University, Kalamazoo, Michigan 49008 (United States); Pruemper, G; Fukuzawa, H; Liu, X-J; Ueda, K [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan); Harries, J, E-mail: Daniel.Rolles@asg.mpg.d [Japan Synchrotron Radiation Research Institute, Sayo-gun, Hyogo 679-5198 (Japan)

2010-02-01

223

Molecular-frame angular distribution of normal and resonant Auger electrons  

International Nuclear Information System (INIS)

Molecular-frame angular distributions (MFADs) of resonant and non-resonant (normal) Auger electrons were determined using angle-resolved electron-ion coincidence spectroscopy. Here, we concentrate on the MFADs of normal N2 KVV Auger electrons. We conclude that their MFADs are independent of both photon energy and light polarization direction, thus confirming that the two-step model is a good approximation. All threshold and shape-resonance phenomena can be attributed to the absorption process and are irrelevant for the Auger decay in the molecular frame. Distinct differences in the MFADs are found as a function of the Auger final state.

2010-02-01

224

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

225

Mechanisms of spontaneous two-electron emission from core-excited states of molecular CO.  

Science.gov (United States)

We demonstrate that the observation of slow electrons emitted in the decay of molecular core-excited states can be a sensitive probe of the double Auger processes, and that in combination with electron-electron coincidence spectroscopy, it can provide clear insight into the mechanisms involved. The present study identifies all cascade Auger paths from the C1s-to-Rydberg states in CO to final states of CO2+. One pathway includes the first directly identified case of molecular level-to-level autoionization of a cation and shows remarkable selectivity for a specific final state. PMID:18999827

Kaneyasu, T; Hikosaka, Y; Lablanquie, P; Penent, F; Andric, L; Gamblin, G; Eland, J H D; Tamenori, Y; Matsushita, T; Shigemasa, E

2008-10-29

226

Mechanisms of Spontaneous Two-Electron Emission from Core-Excited States of Molecular CO  

International Nuclear Information System (INIS)

[en] We demonstrate that the observation of slow electrons emitted in the decay of molecular core-excited states can be a sensitive probe of the double Auger processes, and that in combination with electron-electron coincidence spectroscopy, it can provide clear insight into the mechanisms involved. The present study identifies all cascade Auger paths from the C1s-to-Rydberg states in CO to final states of CO2+. One pathway includes the first directly identified case of molecular level-to-level autoionization of a cation and shows remarkable selectivity for a specific final state

2008-10-31

227

Reactions of ground-state and electronically excited sodium atoms with methyl bromide and molecular chlorine  

Energy Technology Data Exchange (ETDEWEB)

The reactions of ground- and excited-state Na atoms with methyl bromide (CH{sub 3}Br) and chlorine (Cl{sub 2}) have been studied by using the crossed molecular beams method. For both reactions, the cross sections increase with increasing electronic energy. The product recoil energies change little with increasing Na electronic energy, implying that the product internal energies increase substantially. For Na + CH{sub 3}Br, the steric angle of acceptance opens with increasing electronic energy.

Weiss, P.S.; Mestdagh, J.M.; Schmidt, H.; Covinsky, M.H.; Lee, Y.T. (Lawrence Berkeley Lab., CA (United States))

1991-04-18

228

Reactions of ground-state and electronically excited sodium atoms with methyl bromide and molecular chlorine  

International Nuclear Information System (INIS)

The reactions of ground- and excited-state Na atoms with methyl bromide (CH3Br) and chlorine (Cl2) have been studied by using the crossed molecular beams method. For both reactions, the cross sections increase with increasing electronic energy. The product recoil energies change little with increasing Na electronic energy, implying that the product internal energies increase substantially. For Na + CH3Br, the steric angle of acceptance opens with increasing electronic energy.

1991-01-01

229

Molecular control of electron and hole transfer processes: Theory and applications  

Energy Technology Data Exchange (ETDEWEB)

Recent decades have seen remarkable advances in microscopic understanding of electron transfer (ET) processes in widely ranging contexts, including solid-state, liquid solution, and complex biological assemblies. The primary goal of this chapter is to report recent advances in the modeling, calculation, and analysis of electronic coupling in complex molecular aggregates, thereby allowing an assessment of current progress toward the goal of molecular-level control and design. The control of electron transfer kinetics (i.e., enhancing desired processes, while inhibiting others) involves, of course, system energetics (especially activation and reorganization energies) as well as electronic coupling, which is most directly relevant only after the system has reached the appropriate point (or region) along the reaction coordinate. Nevertheless, to focus the discussion in this chapter, the authors will consider such energetics, and the associated molecular and solvent coordinates which control then, only to the extent that they bear on the analysis of the electronic coupling. In the following sections they first discuss the formulation of basic ET models, including the definition of initial and final states, the role of orbitals and 1-particle models in a many-electron context, the utility of various effective Hamiltonians, and the role of vibronic as well as purely electronic effects. With these theoretical tools in hand, they then examine very recent applications to complex molecular systems using the techniques of computational quantum chemistry, followed by detailed analysis of the numerical results. They then conclude with some comments regarding the current ``state of the art`` and remaining challenges.

Newton, M.D. [Brookhaven National Lab., Upton, NY (United States). Dept. of Chemistry; Cave, R.J. [Harvey Mudd Coll., Claremont, CA (United States). Dept. of Chemistry

1996-02-01

230

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

231

Sub-10-nanometre metallic gaps for use in molecular electronics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis presents the development of a selective-etch fabrication process to create sub-10 nanometre metallic gaps and the subsequent use of the gaps to study the electronics of nanocrystals and molecules. A complete picture of the success of the process required both examination by scanning elec...

Curtis, Kellye Suzanne

232

Electron diffraction study of molecular structure of uranium halides  

International Nuclear Information System (INIS)

Using the high-temperature gas electron diffraction method, uranium tetrahalides UX4 (X=F-I), and uranium trichloride and triiodide are studied. Some methodical peculiarities are discussed and the results of studies of the structure of uranium halides are discussed. The frequencies of vibration spectrum and strength constants are estimated. 25 refs.; 2 figs.; 2 tabs

1990-01-01

233

CN excitation and electron densities in diffuse molecular clouds  

Science.gov (United States)

Utilizing previous work by the authors on the spin-coupled rotational cross-sections for electron-CN collisions, data for the associated rate coefficients are presented. Data on rotational, fine-structure and hyperfine-structure transition involving rotational levels up to N = 20 are computed for temperatures in the range 10-1000 K. Rates are calculated by combining Born-corrected R-matrix calculations with the infinite-order-sudden approximation. The dominant hyperfine transitions are those with ?N = ?j = ?F = 1. For dipole-allowed transitions, electron-impact rates are shown to exceed those for excitation of CN by para-H2(j = 0) by five orders of magnitude. The role of electron collisions in the excitation of CN in diffuse clouds, where local excitation competes with the cosmic microwave background photons, is considered. Radiative transfer calculations are performed and the results compared to observations. These comparisons suggest that electron density lies in the range n(e) ˜ 0.01-0.06 cm-3 for typical physical conditions present in diffuse clouds.

Harrison, Stephen; Faure, Alexandre; Tennyson, Jonathan

2013-11-01

234

Electron-nuclear correlations for photo-induced dynamics in molecular dimers  

Science.gov (United States)

Ultrafast photoinduced dynamics of electronic excitation in molecular dimers is drastically affected by the dynamic reorganization of inter- and intra- molecular nuclear configuration modeled by a quantized nuclear degree of freedom [Cina et al., J. Chem Phys. 118, 46 (2003)]. The dynamics of the electronic population and nuclear coherence is analyzed by solving the chain of coupled differential equations for population inversion, electron-vibrational correlation, etc. [Prezhdo, Pereverzev, J. Chem. Phys. 113, 6557 (2000)]. Intriguing results are obtained in the approximation of a small change of the nuclear equilibrium upon photoexcitation. In the limiting case of resonance between the electronic energy gap and the frequency of the nuclear mode these results are justified by comparison to the exactly solvable Jaynes-Cummings model. It is found that the photoinduced processes in the model dimer are arranged according to their time scales: (i) Fast scale of nuclear motion, (ii) intermediate scale of dynamical redistribution of electronic population between excited states as well as growth and dynamics of electron-nuclear correlation, (iii) slow scale of electronic population approach to the quasi-equilibrium distribution, decay of electron-nuclear correlation, and decrease of the amplitude of mean coordinate oscillation. The latter processes are accompanied by a noticeable growth of the nuclear coordinate dispersion associated with the overall nuclear wave packet width. The demonstrated quantum relaxation features of the photoinduced vibronic dynamics in molecular dimers are obtained by a simple method, applicable to systems with many degrees of freedom.

Kilin, Dmitri S.; Pereversev, Yuri V.; Prezhdo, Oleg V.

2004-06-01

235

Electron transport through heterocyclic molecule: ab initio molecular orbital theory  

Energy Technology Data Exchange (ETDEWEB)

We have calculated the electron transport properties of molecule wires by an ab initio molecule orbital theory on the basis of the first-principles density functional theory (DFT) and the non-equilibrium Green function (NEGF) technique. The wires are made of heterocyclic molecule (furan, thiophene, and pyrrole, shown in first figure), in contact with the atomic scale Au electrodes. The results of our calculation reveal: (1) the furan has a much high conductance in contrast to the others and (2) the heteroatom can significantly affect the transport property by changing electronic structure of the heterocyclic molecule. We find the step-like I-V feature qualitative agreement with the experimental findings.

Cheng, W.W.; Liao, Y.X.; Chen, H.; Note, R.; Mizuseki, H.; Kawazoe, Y

2004-06-14

236

Vibrational mode mediated electron transport in molecular transistors  

Science.gov (United States)

We investigate the steady-state electronic transport through a suspended dimer molecule coupled to leads. When strongly coupled to a vibrational mode, the electron transport is enhanced at the phonon resonant frequency and higher-order resonances. The temperature and bias determines the nature of the phonon-assisted resonances, with clear absorption and emission peaks. The strong coupling also induces a Frank-Condon-like blockade, suppressing the current between the resonances. We compare an analytical polaron transformation method to two exact numerical methods: the Hierarchy equations of motion and an exact diagonalization in the Fock basis. In the steady-state, our two numerical results are an exact match and qualitatively reflect the main features of the polaron treatment. Our results also indicate the possibility of compensating the current decrease due to the thermal environment.

Santamore, Deborah; Lambert, Neill; Nori, Franco

2013-03-01

237

The Smeagol method for spin- and molecular-electronics  

CERN Multimedia

{\\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

238

Electron diffraction study of molecular structure of uranium triiodide  

International Nuclear Information System (INIS)

Structure of UI3 molecules is studied by gaseous electron diffraction method. The obtained structural parameter values (R(UI)=2.88, R(II)=3.98 A) correspond to efficient pyromidal configuration of UI3 molecules with the valence angle value ?(IUI)=88.0 deg. Decrease of interatomic distances values in UI3 molecule in transition to gaseous phase is due to molecule depolymerization and may testify to uranium-iodine bond covalent character

1990-01-01

239

A low-loss hybrid rectification technique for piezoelectric energy harvesting  

Science.gov (United States)

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.

Schlichting, A. D.; Fink, E.; Garcia, E.

2013-09-01

240

Molecular gas electron distribution function with space and time variation  

Energy Technology Data Exchange (ETDEWEB)

The desire for improved control over electric discharge phenomena in a wide variety of scientific, technological, manufacturing, and waste processing activities spurs the development of non-equilibrium, non-uniform, and time dependent models. This paper addresses the situation of a slightly ionized, uniform gas with a space and time varying electric field, and in which inelastic collisions occur. The purpose here is to present a reasonably consistent, and reasonably accessible analytical result for the electron kinetics in a gas discharge regime of technological interest. This paper will be structured as follows. First, the analytical result for the logarithmic derivative in energy of the electron distribution function is state. Then, a discussion of the derivation is given. Examples of the solution are shown for an idealized nitrogen-like gas where a uniform electric field ramps in time between static conditions, and then for sinusoidal behavior. Further examples show the effect of a static electric field that decays exponentially with distance. Finally, the combined effect of field gradients in space and time is demonstrated by mapping out the average electron energy in the model gas for a field with sinusoidal temporal variation and exponential spatial decay.

Garcia, M.

1995-05-01

 
 
 
 
241

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

International Nuclear Information System (INIS)

[en] Electron excitation and emission phenomena, due to Na+ 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.

2011-05-01

242

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

243

Molecular-Frame Angular Distributions of Resonant CO:C(1s) Auger Electrons  

International Nuclear Information System (INIS)

The molecular-frame angular distributions of resonantly excited CO:C(1s)??* Auger electrons were determined using angle-resolved electron-ion coincidence spectroscopy in combination with a novel transformation procedure. Our new methodology yields full three-dimensional electron angular distributions with high energy resolution from the measurement of electrons at only two angles. The experimentally determined distributions are well reproduced by calculations performed in a simple one-center approximation, allowing an unambiguous identification of several overlapping Auger lines.

2008-12-31

244

Molecular-frame angular distributions of resonant CO:C(1s) Auger electrons.  

Science.gov (United States)

The molecular-frame angular distributions of resonantly excited CO:C(1s) --> pi* Auger electrons were determined using angle-resolved electron-ion coincidence spectroscopy in combination with a novel transformation procedure. Our new methodology yields full three-dimensional electron angular distributions with high energy resolution from the measurement of electrons at only two angles. The experimentally determined distributions are well reproduced by calculations performed in a simple one-center approximation, allowing an unambiguous identification of several overlapping Auger lines. PMID:19437639

Rolles, D; Prümper, G; Fukuzawa, H; Liu, X J; Pesi?, Z D; Fink, R F; Grum-Grzhimailo, A N; Dumitriu, I; Berrah, N; Ueda, K

2008-12-31

245

Reorganization energy of electron transfer processes in ionic fluids: a molecular Debye-Huckel approach.  

UK PubMed Central (United Kingdom)

The reorganization energy of electron transfer processes in ionic fluids is studied under the linear response approximation using a molecule Debye-Hückel theory. Reorganization energies of some model reactants of electron transfer reactions in molten salts are obtained from molecular simulations and a molecule Debye-Hückel approach. Good agreements between simulation results and the results from our theoretical calculations using the same model Hamiltonian are found. Applications of our theory to electron transfer reactions in room temperature ionic liquids further demonstrate that our theoretical approach presents a reliable and accurate methodology for the estimation of reorganization energies of electron transfer reactions in ionic fluids.

Xiao T; Song X

2013-03-01

246

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

247

Coupled electron-phonon transport from molecular dynamics with quantum baths.  

UK PubMed Central (United Kingdom)

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.

Lü JT; Wang JS

2009-01-01

248

Coupled electron-phonon transport from molecular dynamics with quantum baths  

Energy Technology Data Exchange (ETDEWEB)

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.

Lue, J T; Wang Jiansheng [Center for Computational Science and Engineering and Department of Physics, National University of Singapore, Singapore 117542 (Singapore)

2009-01-14

249

Coupled electron-phonon transport from molecular dynamics with quantum baths.  

Science.gov (United States)

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. PMID:21813980

Lü, J T; Wang, Jian-Sheng

2008-12-09

250

Ab initio investigation of electronic properties of the magnesium hydride molecular ion.  

UK PubMed Central (United Kingdom)

In this work, adiabatic potential energy curves, spectroscopic constants, dipole moments, and vibrational levels for numerous electronic states of magnesium hydride molecular ion (MgH(+)) are computed. These properties are determined by the use of an ab initio method involving a nonempirical pseudopotential for the magnesium core (Mg), the core polarization potential (CPP), the l-dependent cutoff functions and the full valence configuration interaction (FCI). The molecular ion is thus treated as a two-electron system. Our calculations on the MgH(+) molecular ion extend previous theoretical works to numerous electronic excited states in the various symmetries. A good agreement with the available theoretical and experimental works is obtained for the spectroscopic constants, the adiabatic potential energy curves, and the dipole moments for the lowest states of MgH(+).

Khemiri N; Dardouri R; Oujia B; Gadéa FX

2013-09-01

251

Microscopic theory of single-electron tunneling through molecular-assembled metallic nanoparticles  

CERN Multimedia

We present a microscopic theory of single-electron tunneling through metallic nanoparticles connected to the electrodes through molecular bridges. It combines the theory of electron transport through molecular junctions with the description of the charging dynamics on the nanoparticles. We apply the theory to study single-electron tunneling through a gold nanoparticle connected to the gold electrodes through two representative benzene-based molecules. We calculate the background charge on the nanoparticle induced by the charge transfer between the nanoparticle and linker molecules, the capacitance and resistance of molecular junction using a first-principles based Non-Equilibrium Green's Function theory. We demonstrate the variety of transport characteristics that can be achieved through ``engineering'' of the metal-molecule interaction.

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

2003-01-01

252

Ab-initio Investigation of Electronic Properties of the Magnesium Hydride Molecular Ion.  

UK PubMed Central (United Kingdom)

In this work, adiabatic potential energy curves, spectroscopic constants, dipole moments and vibrational levels for numerous electronic states of magnesium hydride molecular ion (MgH+) are computed. These properties are determined by the use of an ab-initio method involving a non-empirical pseudo-potential for the magnesium core (Mg), the core polarization potential (CPP), the l-dependent cut-off functions and the full valence configuration interaction (FCI). The molecular ion is thus treated as a two-electron system. Our calculations on the MgH+ molecular ion extend previous theoretical works to numerous electronic excited states in the various symmetries. A good agreement with the available theoretical and experimental works is obtained for the spectroscopic constants, the adiabatic potential energy curves and the dipole moments for the lowest states of MgH+.

Khémiri N; Dardouri R; Oujia B; Gadea FX

2013-08-01

253

Electronic and transport properties of a molecular junction with asymmetric contacts.  

UK PubMed Central (United Kingdom)

Asymmetric molecular junctions have been shown experimentally to exhibit a dual-conductance transport property with a pulse-like current-voltage characteristic, by Reed and co-workers. Using a recently developed first-principles integrated piecewise thermal equilibrium current calculation method and a gold-benzene-1-olate-4-thiolate-gold model molecular junction, this unusual transport property has been reproduced. Analysis of the electrostatics and the electronic structure reveals that the high-current state results from subtle bias induced charge transfer at the electrode-molecule contacts that raises molecular orbital energies and enhances the current-contributing molecular density of states and the probabilities of resonance tunneling of conduction electrons from one electrode to another.

Tsai MH; Lu TH

2010-02-01

254

Electron attachment processes of molecular clusters involving slow electrons and high-Rydberg rare gas atoms  

International Nuclear Information System (INIS)

[en] High-Rydberg rare gas atoms or slow electrons were allowed to collide with gas-phase clusters of hydrogen cyanide, ethylene oxide and so forth. Novel cluster anions were found to be produced as a result of electron attachment to the clusters by use of a mass-spectroscopic technique. The mechanism of the electron attachment was discussed in terms of the size-distributions of the cluster anions and their isotopic effect

1989-01-01

255

Intermixing in Cu/Co: molecular dynamics simulations and Auger electron spectroscopy depth profiling  

CERN Multimedia

The ion-bombardment induced evolution of intermixing is studied by molecular dynamics simulations and by Auger electron spectroscopy depth profiling analysis (AESD) in Cu/Co multilayer. It has been shown that from AESD we can derive the low-energy mixing rate and which can be compared with the simulated values obtained by molecular dynamics (MD) simulations. The overall agreement is reasonably good hence MD can hopefuly be used to estimate the rate of intermixing in various interface systems.

Süle, P

2006-01-01

256

Possibility of removing heavy impurities from ethyl alcohol by rectification under reduced pressure  

Energy Technology Data Exchange (ETDEWEB)

This paper develops a method of gas-chromatographic determination of trace amounts of higher alcohols in ethyl alcohol and examines the possibility of removing these impurities from ethyl alcohol by rectification under reduced pressure. The Tsvet-102 chromatograph with a flame-ionization detector was used in development of a method for gas-chromatographic analysis of ethyl alcohol. The experimental results show that good separation of the impurities is achieved in the capillary column where the impurities were separated. The relative retention volumes of the components are given. The best separation is achieved at 50 mm pressure. At this pressure the content of higher alcohols in ethyl alcohol is lowered by rectification from 1.5.10/sup -1/ to 5.10/sup -4/ vol. %. Thus, rectification of ethyl alcohol under reduced pressure is an effective method of removing heavy impurities from ethyl alcohol.

Zuereva, V.I.; Elliev, Y.E.

1986-01-10

257

Virtual camera rectification with geometrical approach on single-lens stereovision using a biprism  

Science.gov (United States)

We propose a geometrical approach for virtual camera rectification on uncalibrated single-lens stereovision using a biprism. This system is also called a virtual stereovision system, as the image captured can be divided into two which are equivalent to two images captured using two cameras with different perspectives. The proposed method is divided into two parts. The first part is to compute the projection transformation matrix of two virtual cameras based on a unique geometrical ray sketching, which can accurately recover the extrinsic parameters, and the second part is to compute the rectification transformation matrix, which is applied on the images captured using the system. As the geometrical analysis eliminates the complex calibration process and rectification reduces the correspondence searching to one-dimensional, this method provides a simple stereo matching technique for this system. Experimental results are presented to show the effectiveness of the approach.

Lim, Kah Bin; Wang, Daolei; Kee, Wei Loon

2012-04-01

258

Separation of pyridine bases by combining simple rectification and azeotropic distillation with water - Part II  

Energy Technology Data Exchange (ETDEWEB)

Separation of the lutidine fraction and isolation of all 4 of its main components from bituminous coal tar using simple rectification and azeotropic distillation with water are discussed. Experiments are described using lutidine fraction distilled from coal tar carbolic oil in an AUTODEST HMS 1000 automatic distilling apparatus. Detailed composition of bases, lutidine fraction and concentrates of isomeric dimethylpyridines is given in tabular form. Results, given in graphs, show that separation was clearer with azeotropic distillation than with simple rectification, e.g. 77% concentrates of 3,6-dimethyl pyridine, 3- and 4-methyl pyridine were obtained from the azeotropes of the 3-picoline fraction, but azeotropic distillation is felt to have no great advantage, since yield is relatively low. The most efficient method is to separate pyridine bases by distillation, then to separate the fractions thus obtained by simple rectification or azeotropic distillation with water. 7 refs.

Vymetal, J.

1987-06-01

259

Empirical study of nonlinearity tensor dominating THz generation in barium borate crystal through optical rectification  

Science.gov (United States)

The optical rectification is an important optical method to generate the THz wave. However, there is a lack of knowledge about the properties of the nonlinearity tensor which governs the optical rectification process. In this work, we demonstrate that some key information of the nonlinearity tensor of barium borate (BBO) crystal could be revealed by 2-dimensional time-domain spectroscopic measurements. The experimental results indicate that d 22 of the nonlinearity tensor coefficients of BBO crystal plays negligible role during the THz generation by optical rectification. At the same time, a proportional relationship among three other nonzero nonlinearity tensor coefficients, i.e., d 33, d 31, and d 15, could be obtained empirically. It is worth noting that our method is also applicable to similar nonlinearity study in THz region of other types of crystals.

Zhang, Y.; Zheng, Y.; Xu, S.; Liu, W.

2011-06-01

260

Collective vortex rectification effects in films with a periodic pinning array  

CERN Document Server

The vortex ratchet effect has been studied in Al films patterned with square arrays of submicron antidots. We have investigated the transport properties of two sets of samples: (i) asymmetrical antidots where vortices are driven by an unbiased ac current, and (ii) symmetrical antidots where in addition to the ac drive a dc bias was used. For each sample, the rectified (dc) voltage is measured as a function of drive amplitude and frequency, magnetic field, and temperature. As unambiguously shown by our data, the voltage rectification in the asymmetric antidots is induced by the intrinsic asymmetry in the pinning potential created by the antidots, whereas the rectification in the symmetric antidots is induced by the dc bias. In addition, the experiments reveal interesting collective phenomena in the vortex ratchet effect. At fields below the first matching field ($H_1$), the dc voltage--ac drive characteristics present two rectification peaks, which is interpreted as an interplay between the one-dimensional mot...

De Souza-Silva, C C; Zhu, B Y; Morelle, M; Moshchalkov, V V; Silva, Clecio C. de Souza

2005-01-01

 
 
 
 
261

Alternative electron flows (water-water cycle and cyclic electron flow around PSI) in photosynthesis: molecular mechanisms and physiological functions.  

UK PubMed Central (United Kingdom)

An electron flow in addition to the major electron sinks in C(3) plants [both photosynthetic carbon reduction (PCR) and photorespiratory carbon oxidation (PCO) cycles] is termed an alternative electron flow (AEF) and functions in the chloroplasts of leaves. The water-water cycle (WWC; Mehler-ascorbate peroxidase pathway) and cyclic electron flow around PSI (CEF-PSI) have been studied as the main AEFs in chloroplasts and are proposed to play a physiologically important role in both the regulation of photosynthesis and the alleviation of photoinhibition. In the present review, I discuss the molecular mechanisms of both AEFs and their functions in vivo. To determine their physiological function, accurate measurement of the electron flux of AEFs in vivo are required. Methods to assay electron flux in CEF-PSI have been developed recently and their problematic points are discussed. The common physiological function of both the WWC and CEF-PSI is the supply of ATP to drive net CO(2) assimilation. The requirement for ATP depends on the activities of both PCR and PCO cycles, and changes in both WWC and CEF-PSI were compared with the data obtained in intact leaves. Furthermore, the fact that CEF-PSI cannot function independently has been demonstrated. I propose a model for the regulation of CEF-PSI by WWC, in which WWC is indispensable as an electron sink for the expression of CEF-PSI activity.

Miyake C

2010-12-01

262

Electron impact dissociation of H2+ using variationally adjusted LCAO-type molecular orbitals  

International Nuclear Information System (INIS)

[en] Electron impact dissociation of the H2+ ion through 1sigmasub(g)?1sigmasub(u) electronic excitation has been considered using the Born approximation. The molecular wavefunctions have been constructed by a linear combination of variationally adjusted atomic orbitals. The cross sections are found to be significantly higher than those obtained by Peek using exact (Born-Oppenheimer) wavefunctions for H2+. This brings out the limitation of the LCAO prescription for constructing molecular orbitals, since the wavefunctions used are 'good' in that they predict the energy values very satisfactorily. (Auth.)

1976-01-01

263

Effects of molecular gases on Xe electroluminescence and electron resonance trapping  

Energy Technology Data Exchange (ETDEWEB)

Xenon electroluminescence (EL) has been studied in the presence of small amounts of molecular gases and some results are reported. A theoretical model, which explains the EL in terms of a peak in the electron energy distribution near the energy of subexcitative resonance of 7.77 eV (electron resonance trapping), was developed to take into account the effects of a molecular gas present at low concentrations. The results obtained with air, at concentrations lower than 10/sup 3/ p.p.m., seem to fit well the developed model.

De' Munari, G.M.; Gabba, L.; Giusiano, F.; Mambriani, G. (Parma Univ. (Italy). Ist. di Fisica)

1984-06-01

264

The roles of electronic and nuclear stopping in the desorption valine negative molecular ions  

Energy Technology Data Exchange (ETDEWEB)

The yield of valine negative molecular ions has been measured as a function of Xe/sup +/, Kr/sup +/, and Ar/sup +/ primary ion velocity. The electronic and nuclear stopping powers are comparable in magnitude and opposite in slope in the experimental velocity region. The yield data are explained in terms of electronic stopping power alone, with no contribution from nuclear stopping power within the experimental error. Low molecular weight atomic species are found to be best described by a nuclear stopping power related process. 18 refs., 3 figs.

Hunt, J.E.; Salehpour, M.; Fishel, D.L.; Tou, J.C.

1988-01-01

265

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

266

Studies of isotopic effects in the excited electronic states of molecular systems  

International Nuclear Information System (INIS)

Rare gas halogen (RGH) lasers serve as convenient tools for a range of photophysical processes which exhibit isotope effects. This document summarizes progress in the production of molecular systems in their electronic excited states with the aid of RGH lasers, and the various isotopic effects one can study under these conditions. We conclude that the basic physical mechanisms involved in the isotopically sensitive characteristics of excited molecular electronic states are sufficiently selective to be useful in both the detection and separation of many atomic materials.

1982-01-01

267

Studies of isotropic effects in the excited electronic states of molecular systems  

Science.gov (United States)

Rare gas halogen (RGH) lasers serve as convenient tools for a range of photophysical processes which exhibit isotope effects. Progress in the production of molecular systems in their electronic excited states with the aid of RGH lasers, and the various isotopic effects one can study under these conditions is summarized. It is concluded that the basic physical mechanisms involved in the isotopically sensitive characteristics of excited molecular electronic states are sufficiently selective to be useful in both the detection and separation of many atomic materials.

268

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: AnIV[FeII(CN)6].xH2O (An = Th, U, Np, Pu); AmIII[FeIII(CN)6].xH2O; Pu III[CoIII(CN)6].xH2O and K(H?)AnIII[FeII(CN)6].xH2O (An = Pu, Am). The metal oxidation states have been obtained thanks to the ?CN, stretching vibration and to the actinide LIII absorption edge studies. As Prussian Blue, the AnIV[FeII(CN)6].xH2O (An = Np, Pu) are class II of Robin and Day compounds. X-ray Diffraction has shown besides that these complexes crystallize in the P63/m space group, as the isomorphic LaKFe(CN)6.4H2O complex used as structural model. The EXAFS oscillations at the iron K edge and at the An LIII 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 cyanoferrates is comparable to the one of lanthanides. However, the actinides typical behavior towards the lanthanides is brought to the fore by the AnIV versus LnIII 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

269

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

270

Electron-nuclear correlations for photo-induced dynamics in molecular dimers  

CERN Document Server

Ultrafast photoinduced dynamics of electronic excitation in molecular dimers is drastically affected by the dynamic reorganization of inter- and intra- molecular nuclear configuration modeled by a quantized nuclear degree of freedom [Cina et. al, J. Chem Phys. {118}, 46 (2003)]. The dynamics of the electronic population and nuclear coherence is analyzed by solving the chain of coupled differential equations for %mean coordinate, population inversion, electron-vibrational correlation, etc. [Prezhdo, Pereverzev, J. Chem. Phys. {113} 6557 (2000)]. Intriguing results are obtained in the approximation of a small change of the nuclear equilibrium upon photoexcitation. In the limiting case of resonance between the electronic energy gap and the frequency of the nuclear mode these results are justified by comparison to the exactly solvable Jaynes-Cummings model. It is found that the photoinduced processes in the model dimer are arranged according to their time scales: (i) fast scale of nuclear motion, (ii) intermediat...

Kilin, D S; Prezhdo, O V; Kilin, Dmitri S.; Pereversev, Yuri V.; Prezhdo, Oleg V.

2004-01-01

271

Electronic structure of the magnesium hydride molecular ion  

International Nuclear Information System (INIS)

In this paper, using a standard quantum chemistry approach based on pseudopotentials for atomic core representation, Gaussian basis sets and effective core polarization potentials, we investigate the electronic properties of the MgH+ ion. We first determine potential energy curves for several states using different basis sets and discuss their predicted accuracy by comparing our values of the well depths and position with other available results. We then calculate permanent and transition dipole moments for several transitions. Finally, for the first time, we calculate the static dipole polarizability of MgH+ as a function of the interatomic distance. This study represents the first step towards the modelling of collisions between trapped cold Mg+ ions and H2 molecules.

2009-08-14

272

Molecular imaging using X-ray free-electron lasers.  

UK PubMed Central (United Kingdom)

The opening of hard X-ray free-electron laser facilities, such as the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory in the United States, has ushered in a new era in structural determination. With X-ray pulse durations down to 10 fs or shorter, and up to 10(13) transversely coherent photons per pulse in a narrow spectral bandwidth, focused irradiances of 10(18) to 10(21) W cm(-2) or higher can be produced at X-ray energies ranging from 500 eV to 10 keV. New techniques for determining the structure of systems that cannot be crystallized and for studying the time-resolved behavior of irreversible reactions at femtosecond timescales are now available.

Barty A; Küpper J; Chapman HN

2013-01-01

273

Electronic structure of the Magnesium hydride molecular ion  

CERN Multimedia

In this paper, using a standard quantum chemistry approach based on pseudopotentials for atomic core representation, Gaussian basis sets, and effective core polarization potentials, we investigate the electronic properties of the MgH$^+$ ion. We first determine potential energy curves for several states using different basis sets and discuss their predicted accuracy by comparing our values of the well depths and position with other available results. We then calculate permanent and transition dipole moments for several transitions. Finally for the first time, we calculate the static dipole polarizability of MgH$^+$ as function of the interatomic distance. This study represents the first step towards the modeling of collisions between trapped cold Mg$^+$ ions and H$_2$ molecules.

Aymar, Mireille; Sahlaoui, Mohamed; Dulieu, Olivier

2009-01-01

274

Atomic and molecular photoelectron and Auger-electron-spectroscopy studies using synchrotron radiation  

International Nuclear Information System (INIS)

Electron spectroscopy, combined with synchrotron radiation, was used to measure the angular distributions of photoelectrons and Auger electrons from atoms and molecules as functions of photon energy. The branching ratios and partial cross sections were also measured in certain cases. By comparison with theoretical calculations, the experimental results are interpreted in terms of the characteristic electronic structure and ionization dynamics of the atomic or molecular sample. The time structure of the synchrotron radiation source was used to record time-of-flight (TOF) spectra of the ejected electrons. The double-angle-TOF method for the measurement of photoelectron angular distributions is discussed. This technique offers the advantages of increased electron collection efficiency and the elimination of certain systematic errors. An electron spectroscopy study of inner-shell photoexcitation and ionization of Xe, photoelectron angular distributions from H2 and D2, and photoionization cross sections and photoelectron asymmetries of the valence orbitals of NO are reported

1982-01-01

275

Electron Stimulated Molecular Desorption of a NEG St 707 at Room Temperature  

CERN Multimedia

Electron stimulated molecular desorption (ESD) from a NEG St 707 (SAES GettersTM) sample after conditioning and after saturation with isotopic carbon monoxide2,13C18O, has been studied on a laboratory setup. Measurements were performed using an electron beam of 300 eV kinetic energy, with an average electron intensity of 1.6 1015 electrons s-1. The electrons were impinging on the 15 cm2 target surface at perpendicular incidence. It is found that the desorption yields h (molecules/electron) of the characteristic gases in an UHV system (hydrogen, methane, water, carbon monoxide, carbon dioxide) for a fully activated NEG as well as for a NEG fully saturated with 13C18O are lower than for OFHC copper baked at 120oC. A small fraction only of the gas which is required to saturate the getter surface can be re-desorbed and thus appears to be accessible to ESD.

Le Pimpec, F; Laurent, Jean Michel

2001-01-01

276

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

277

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

Directory of Open Access Journals (Sweden)

Full Text Available 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.

Henryk Chojnacki

2003-01-01

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

Non-adiabatic molecular Hamiltonian Canonical transformation coupling electronic and vibrational motions  

CERN Multimedia

The coupling of electronic and vibrational motion is studied by two canonical transformations namely normal coordinate transformation and momentum transformation on molecular Hamiltonian. It is shown that by these transformations we can pass from crude approximation to adiabatic approximation and then to non-adiabatic (diabatic) Hamiltonian. This leads to renormalized fermions and renormalized diabatic phonons. Simple calculations on $H_{2}$, $HD$, and $D_{2}$ systems are performed and compared with previous approaches. Problem of electronic quasi-degeneracy is discussed.

Hubac, I; Polasek, M; Urbán, J; Mach, P P; Masik, J; Leszczynski, J; Hubac, Ivan; Babinec, Peter; Polasek, Martin; Urban, Jan; Mach, Pavel; Masik, Jozef; Leszczynski, Jerzy

1998-01-01

280

Improved limit on the mass of the electron antineutrino from the beta decay of molecular tritium  

International Nuclear Information System (INIS)

Based on a study of the shape of the beta spectrum of free molecular tritium, a new upper limit of 13.4 eV (95% confidence level) is reported on the mass of the electron antineutrino. This result appears to be inconsistent with the reported value for the mass of 26(5) eV. The electron neutrino is evidently not massive enough to close the universe by itself. (author) 2 tabs., 1 fig., 21 refs.

1992-01-01

 
 
 
 
281

Improved limit on the mass of electron neutrino from the beta decay of molecular tritium  

International Nuclear Information System (INIS)

We report a new upper limit of 13.4 eV (95% confidence level) on the mass of the electron antineutrino from a study of the shape of the beta spectrum of free molecular tritium. This result appears to be inconsistent with a reported value for the mass of 26(5) eV. The electron neutrino is evidently not massive enough to close the universe by itself.

1990-01-01

282

Drying of ethyl alcohol by extractive rectification and choosing a fractionating agent  

Energy Technology Data Exchange (ETDEWEB)

Ethyl alcohol can be dried by extractive rectification with monoethylene glycol more efficiently than with the triethylene glycol used industrially. The extractive rectification of ethyl alcohol does not require stabilization of the column with the distillate of dried alcohol, which can only worsen the process characteristics. The required reflux ratio is generated as a result of absorption of ethyl alcohol vapor by the extractant. To reduce the water content of ethyl alcohol from 6 to 0.5 wt. % with a yield not less than 70% the rectifying section of the column must have not less than six theoretical plates.

Sobolev, A.S.; Borisov, A.V.; Raskina, M.G. Chesnokov, B.B.

1987-11-10

283

Quantum dynamics of electron-nuclear correlations in photo-excited molecular dimers  

Science.gov (United States)

Ultrafast photoinduced dynamics of electronic excitation in molecular dimers is affected by the dynamic reorganization of inter- and intra- molecular nuclear configuration modeled by quantized nuclear degree of freedom [Cina et. al, J. Chem Phys. 118, 46 (2003)]. The quantum dynamics of electronic-nuclear excitation in a model dimer is analyzed in the limit of small nuclear reorganization for excited electronic states. The relaxational behavior of mean coordinate, population inversion, electronic-vibrational correlation etc. are obtained by means of the reduced description [Prezhdo, J. Chem. Phys. 117, 2995 (2002)], that is potentially applicable to large biological systems. Despite of absence of the heat bath the system is approaching the quasi-equilibrium state, due to the destructive interference of the wavefunction coefficients. The correlation between electronic and vibrational subsystems rises, oscillates, and relaxes similar to the population inversion. The averages and dispersions of electronic and vibrational operators oscillate in a complementary fashion. This work is being developing towards description of the exciton transfer and femtosecond optical experiments in molecular systems.

Kilin, Dmitri S.; Pereverzev, Yuri V.; Prezhdo, Oleg V.

2003-05-01

284

Detection of electronic and vibrational coherences in molecular systems by 2D electronic photon echo spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

Two-dimensional optical photon echo spectra are simulated for model systems which exhibit vibrational, electronic and a combination of electronic and vibrational coherent dynamics. The coherent motion manifests itself as periodic beatings of the spectrum cross-peak intensity with the population time. The intensity modulations are compared to evolution of the excited-state population and coordinate expectation value. The advantageous capabilities of the technique as well as possible difficulties in spectra interpretations are outlined. Possibilities for distinguishing electronic and vibrational coherences are discussed.

Egorova, Dassia [Department of Chemistry, Technical University of Munich, D-85747 Garching (Germany)], E-mail: egorova@ch.tum.de

2008-05-23

285

Assessment of a nanoparticle bridge platform for molecular electronics measurements  

Energy Technology Data Exchange (ETDEWEB)

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.

Jafri, S H M; Blom, T; Leifer, K [Division for Electron Microscopy and Nanoengineering, Department of Engineering Sciences, Angstroem Laboratory, Uppsala University, Box 534, SE-75121 Uppsala (Sweden); Stroemme, M; Welch, K [Division for Nanotechnology and Functional Materials, Department of Engineering Sciences, Angstroem Laboratory, Uppsala University, Box 534, SE-75121 Uppsala (Sweden); Loefaas, H; Grigoriev, A; Ahuja, R, E-mail: Klaus.Leifer@angstrom.uu.se, E-mail: Ken.Welch@angstrom.uu.se [Department of Physics and Astronomy, Uppsala University, BOX 516, SE-75120 Uppsala (Sweden)

2010-10-29

286

Theory of Photoinduced Phase Transitions in Molecular Conductors: Interplay Between Correlated Electrons, Lattice Phonons and Molecular Vibrations  

Directory of Open Access Journals (Sweden)

Full Text Available Dynamics of photoinduced phase transitions in molecular conductors are reviewed from the perspective of interplay between correlated electrons and phonons. (1) The charge-transfer complex TTF-CA shows a transition from a neutral paraelectric phase to an ionic ferroelectric phase. Lattice phonons promote this photoinduced transition by preparing short-range lattice dimerization as a precursor. Molecular vibrations stabilize the neutral phase so that the ionic phase, when realized, possesses a large ionicity and the Mott character; (2) The organic salts ?-(BEDT-TTF)2RbZn(SCN)4 and ?-(BEDT-TTF)2I3 show transitions from a charge-ordered insulator to a metal. Lattice phonons make this photoinduced transition hard for the former salt only. Molecular vibrations interfere with intermolecular transfers of correlated electrons at an early stage; (3) The organic salt ?-(d-BEDT-TTF)2Cu[N(CN)2]Br shows a transition from a Mott insulator to a metal. Lattice phonons modulating intradimer transfer integrals enable photoexcitation-energy-dependent transition pathways through weakening of effective interaction and through introduction of carriers.

Kenji Yonemitsu

2012-01-01

287

Restrained-ensemble molecular dynamics simulations based on distance histograms from double electron-electron resonance spectroscopy.  

UK PubMed Central (United Kingdom)

DEER (double electron-electron resonance) spectroscopy is a powerful pulsed ESR (electron spin resonance) technique allowing the determination of spin-spin distance histograms between site-directed nitroxide label sites on a protein in their native environment. However, incorporating ESR/DEER data in structural refinement is challenging because the information from the large number of distance histograms is complex and highly coupled. Here, a novel restrained-ensemble molecular dynamics simulation method is developed to incorporate the information from multiple ESR/DEER distance histograms simultaneously. Illustrative tests on three coupled spin-labels inserted in T4 lysozyme show that the method efficiently imposes the experimental distance distribution in this system. Different rotameric states of the ?1 and ?2 dihedrals in the spin-labels are also explored by restrained ensemble simulations. Using this method, it is hoped that experimental restraints from ESR/DEER experiments can be used to refine structural properties of biological systems.

Roux B; Islam SM

2013-05-01

288

Effect of electron overheating on the tunneling current of a molecular transistor  

Science.gov (United States)

The effect of overheating of the electron subsystem on the Coulomb blockade in a structure (molecular transistor) based on a metal cluster containing a finite number of atoms has been theoretically studied. The electron energy spectrum in such quantum grains of cylindrical and spherical shape has been calculated. An increase in the electron subsystem temperature in the cluster leads to vanishing of the current gap and pronounced smoothening of the quantum and Coulomb steps on the current-voltage characteristic of the structure, in agreement with experimental observations.

Pogosov, V. V.; Vasyutin, E. V.; Babich, A. V.

2007-09-01

289

Reviewprobing protein electron transfer mechanisms from the molecular to the cellular length scales.  

UK PubMed Central (United Kingdom)

The mechanisms of bridge-mediated electron transfer (ET) reactions vary from coherent deep tunneling to thermally activated hopping. This short review focuses on some developments in the study of protein ET mechanisms at the molecular and at the cellular levels. It explains experimental and theoretical work on the influence of electronic-energy and electronic-coupling fluctuations on ET rates and on the switch from the tunneling to the hopping regimes. It also describes recent work on extracellular ET, in particular on bacterial nanowires which support ET over micron length scales. Future directions in these research areas are discussed. © 2012 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 100: 82-92, 2013.

Skourtis SS

2013-04-01

290

Guiding electron emissions by excess negative charges in multiply charged molecular anions.  

UK PubMed Central (United Kingdom)

Using photoelectron imaging, we show the effects of excess negative charges on the directions of outgoing electrons in multiply charged anions. Photoemissions are observed to occur either in a perpendicular or parallel direction, depending on the molecular configurations and origins of the detached electrons. Detachment of the ? electrons from biphenyl-disulfonate dianions is shown to occur in a perpendicular direction due to the Coulomb repulsion from the two terminal charges, whereas detachment from the sulfonate groups in linear aliphatic disulfonates occurs in parallel directions.

Ning CG; Dau PD; Wang LS

2010-12-01

291

Guiding electron emissions by excess negative charges in multiply charged molecular anions.  

Science.gov (United States)

Using photoelectron imaging, we show the effects of excess negative charges on the directions of outgoing electrons in multiply charged anions. Photoemissions are observed to occur either in a perpendicular or parallel direction, depending on the molecular configurations and origins of the detached electrons. Detachment of the ? electrons from biphenyl-disulfonate dianions is shown to occur in a perpendicular direction due to the Coulomb repulsion from the two terminal charges, whereas detachment from the sulfonate groups in linear aliphatic disulfonates occurs in parallel directions. PMID:21231651

Ning, Chuan-Gang; Dau, Phuong Diem; Wang, Lai-Sheng

2010-12-22

292

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

293

Kinetics of electron-molecular processes on the semiconductor film surface  

International Nuclear Information System (INIS)

One possible type of kinetics of electron-molecular processes on the semiconductor-film surface is analysed. The expressions for chemisorption time constant tsub(i0) and transition time tsub(t) from chemisorption of one type of the particles to chemisorption of the other one give a very good description of the experimental results

1985-01-01

294

Influence of the electron-phonon iinteraction on phonon heat conduction in a molecular nanowire  

Directory of Open Access Journals (Sweden)

Full Text Available A model for phonon heat conduction in a molecular nanowire is developed. The calculation takes into account modification of the acoustic phonon dispersion relation due to the electron-phonon interaction. The results obtained are compared with models based upon a simpler, Callaway formula.

Galovi? Slobodanka P.; ?evizovi? D.; Zekovi? S.; Ivi? Z.

2006-01-01

295

Simulation of electron conduction in a prototypical three-terminal molecular transistor  

Science.gov (United States)

In a single molecule, electronic charge can be modulated either by electrical field or by chemical effects, thereby opening up the possibility of their use as active elements in electronic devices. In this talk, we present the results of a theoretical study on the electronic conduction of a novel, three-terminal molecular architecture, analogous to a heterojunction bipolar transistor. In this architecture, two diode arms consisting of donor-acceptor molecular wires fuse through a ring, while a gate modulating wire is a ?-conjugated wire. The calculated results show the enhancement or depletion mode of a transistor by applying a gate field along the positive or negative direction. A small gate field is required to switch on the current in the proposed architecture. The changes in the electronic conduction can be attributed to the intrinsic dipolar molecular architecture in terms of the evolution of molecular wavefunctions, specifically the one associated with the terphenyl group of the modulating wire in the presence of the gate field.

He, Haiying; Pandey, Ravindra; Karna, Shashi

2009-03-01

296

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-...

Salvador Sedano, Pedro; Fradera i Llinàs, Xavier; Duran i Portas, Miquel

297

Development of a room temperature molecular electronics: Direct vs indirect metal complex synthesis  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis discusses the possibility of using molecular units as electronic devices as well as the synthesis of a number of such prototypes. This thesis also serves as a comparison between ‘direct’ (complexes as ligands/complexes as metals) and ‘indirect’ (on-complex) synthesis as a method of metal...

Cleary, Laura

298

Contact geometry and electronic transport properties of Ag-benzene-Ag molecular junctions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The contact geometry and the electronic transport properties of Ag-benzene-Ag molecular junctions have been investigated by using first-principles quantum transport simulations. Our calculations show that a moderate benzene-silver interaction can be achieved when benzene is adsorbed on the Ag(111) s...

SANVITO, STEFANO

299

Structure, dynamics, and reactivity of hydrated electrons by ab initio molecular dynamics.  

UK PubMed Central (United Kingdom)

Understanding the properties of hydrated electrons, which were first observed using pulse radiolysis of water in 1962, is crucial because they are key species in many radiation chemistry processes. Although time-resolved spectroscopic studies and molecular simulations have shown that an electron in water (prepared, for example, by water photoionization) relaxes quickly to a localized, cavity-like structure ?2.5 Å in radius, this picture has recently been questioned. In another experimental approach, negatively charged water clusters of increasing size were studied with photoelectron and IR spectroscopies. Although small water clusters can bind an excess electron, their character is very different from bulk hydrated species. As data on electron binding in liquid water have become directly accessible experimentally, the cluster-to-bulk extrapolations have become a topic of lively debate. Quantum electronic structure calculations addressing experimental measurables have, until recently, been largely limited to small clusters; extended systems were approached mainly with pseudopotential calculations combining a classical description of water with a quantum mechanical treatment of the excess electron. In this Account, we discuss our investigations of electrons solvated in water by means of ab initio molecular dynamics simulations. This approach, applied to a model system of a negatively charged cluster of 32 water molecules, allows us to characterize structural, dynamical, and reactive aspects of the hydrated electron using all of the system's valence electrons. We show that under ambient conditions, the electron localizes into a cavity close to the surface of the liquid cluster. This cavity is, however, more flexible and accessible to water molecules than an analogous area around negatively charged ions. The dynamical process of electron attachment to a neutral water cluster is strongly temperature dependent. Under ambient conditions, the electron relaxes in the liquid cluster and becomes indistinguishable from an equilibrated, solvated electron on a picosecond time scale. In contrast, for solid, cryogenic systems, the electron only partially localizes outside of the cluster, being trapped in a metastable, weakly bound "cushion-like" state. Strongly bound states under cryogenic conditions could only be prepared by cooling equilibrated, liquid, negatively charged clusters. These calculations allow us to rationalize how different isomers of electrons in cryogenic clusters can be observed experimentally. Our results also bring into question the direct extrapolation of properties of cryogenic, negatively charged water clusters to those of electrons in the bulk liquid. Ab initio molecular dynamics represents a unique computational tool for investigating the reactivity of the solvated electron in water. As a prototype, the electron-proton reaction was followed in the 32-water cluster. In accord with experiment, the molecular mechanism is a proton transfer process that is not diffusion limited, but rather controlled by a proton-induced deformation of the excess electron's solvent shell. We demonstrate the necessary ingredients of a successful density functional methodology for the hydrated electron that avoids potential pitfalls, such as self-interaction error, insufficient basis set, or lack of dispersion interactions. We also benchmark the density functional theory methods and outline the path to faithful ab initio simulations of dynamics and reactivity of electrons solvated in extended aqueous systems.

Marsalek O; Uhlig F; VandeVondele J; Jungwirth P

2012-01-01

300

Structure, dynamics, and reactivity of hydrated electrons by ab initio molecular dynamics.  

Science.gov (United States)

Understanding the properties of hydrated electrons, which were first observed using pulse radiolysis of water in 1962, is crucial because they are key species in many radiation chemistry processes. Although time-resolved spectroscopic studies and molecular simulations have shown that an electron in water (prepared, for example, by water photoionization) relaxes quickly to a localized, cavity-like structure ?2.5 Å in radius, this picture has recently been questioned. In another experimental approach, negatively charged water clusters of increasing size were studied with photoelectron and IR spectroscopies. Although small water clusters can bind an excess electron, their character is very different from bulk hydrated species. As data on electron binding in liquid water have become directly accessible experimentally, the cluster-to-bulk extrapolations have become a topic of lively debate. Quantum electronic structure calculations addressing experimental measurables have, until recently, been largely limited to small clusters; extended systems were approached mainly with pseudopotential calculations combining a classical description of water with a quantum mechanical treatment of the excess electron. In this Account, we discuss our investigations of electrons solvated in water by means of ab initio molecular dynamics simulations. This approach, applied to a model system of a negatively charged cluster of 32 water molecules, allows us to characterize structural, dynamical, and reactive aspects of the hydrated electron using all of the system's valence electrons. We show that under ambient conditions, the electron localizes into a cavity close to the surface of the liquid cluster. This cavity is, however, more flexible and accessible to water molecules than an analogous area around negatively charged ions. The dynamical process of electron attachment to a neutral water cluster is strongly temperature dependent. Under ambient conditions, the electron relaxes in the liquid cluster and becomes indistinguishable from an equilibrated, solvated electron on a picosecond time scale. In contrast, for solid, cryogenic systems, the electron only partially localizes outside of the cluster, being trapped in a metastable, weakly bound "cushion-like" state. Strongly bound states under cryogenic conditions could only be prepared by cooling equilibrated, liquid, negatively charged clusters. These calculations allow us to rationalize how different isomers of electrons in cryogenic clusters can be observed experimentally. Our results also bring into question the direct extrapolation of properties of cryogenic, negatively charged water clusters to those of electrons in the bulk liquid. Ab initio molecular dynamics represents a unique computational tool for investigating the reactivity of the solvated electron in water. As a prototype, the electron-proton reaction was followed in the 32-water cluster. In accord with experiment, the molecular mechanism is a proton transfer process that is not diffusion limited, but rather controlled by a proton-induced deformation of the excess electron's solvent shell. We demonstrate the necessary ingredients of a successful density functional methodology for the hydrated electron that avoids potential pitfalls, such as self-interaction error, insufficient basis set, or lack of dispersion interactions. We also benchmark the density functional theory methods and outline the path to faithful ab initio simulations of dynamics and reactivity of electrons solvated in extended aqueous systems. PMID:21899274

Marsalek, Ondrej; Uhlig, Frank; VandeVondele, Joost; Jungwirth, Pavel

2011-09-07

 
 
 
 
301

Path-integral simulations with fermionic and bosonic reservoirs: Transport and dissipation in molecular electronic junctions  

CERN Document Server

We expand iterative numerically-exact influence functional path-integral tools and present a method capable of following the nonequilibrium time evolution of subsystems coupled to multiple bosonic and fermionic reservoirs simultaneously. Using this method, we study the real-time dynamics of charge transfer and vibrational mode excitation in an electron conducting molecular junction. We focus on nonequilibrium vibrational effects, particularly, the development of vibrational instability in a current-rectifying junction. Our simulations are performed by assuming large molecular vibrational anharmonicity (or low temperature). This allows us to truncate the molecular vibrational mode to include only a two-state system. Exact numerical results are compared to perturbative Master equation calculations demonstrating an excellent agreement in the weak electron-phonon coupling regime. Significant deviations take place only at strong coupling. Our simulations allow us to quantify the contribution of different transport...

Simine, Lena

2013-01-01

302

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

303

Ab initio analysis of electron-phonon coupling in molecular devices.  

Science.gov (United States)

We report a 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 on carrying out density functional theory within the Keldysh nonequilibrium Green's function formalism. Using a molecular tunnel junction of a 1,4-benzenedithiolate molecule contacted by two aluminum leads as an example, we analyze which molecular vibrational modes are most relevant to charge transport under nonequilibrium conditions. We find that the low-lying modes are 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. PMID:16241682

Sergueev, N; Roubtsov, D; Guo, Hong

2005-09-29

304

Full two-electron calculations of antiproton collisions with molecular hydrogen  

DEFF Research Database (Denmark)

Total cross sections for single ionization and excitation of molecular hydrogen by antiproton impact are presented over a wide range of impact energies from 1 keV to 6.5 MeV. A nonperturbative 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 experiment are found around the maximum. The importance of the molecular geometry and a full two-electron description is demonstrated. The present findings provide benchmark results which might be useful for the development of molecular models.

Lühr, Armin Christian; Saenz, Alejandro

2010-01-01

305

Phasing electron diffraction data by molecular replacement: strategy for structure determination and refinement.  

UK PubMed Central (United Kingdom)

Electron crystallography is arguably the only electron cryomicroscopy (cryo EM) technique able to deliver atomic resolution data (better then 3 Å) for membrane proteins embedded in a membrane. The progress in hardware improvements and sample preparation for diffraction analysis resulted in a number of recent examples where increasingly higher resolutions were achieved. Other chapters in this book detail the improvements in hardware and delve into the intricate art of sample preparation for microscopy and electron diffraction data collection and processing. In this chapter, we describe in detail the protocols for molecular replacement for electron diffraction studies. The use of a search model for phasing electron diffraction data essentially eliminates the need of acquiring image data rendering it immune to aberrations from drift and charging effects that effectively lower the attainable resolution.

Wisedchaisri G; Gonen T

2013-01-01

306

Challenges to computational quantum chemistry from contemporary advances in polyatomic molecular electronic spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

Molecular electronic spectroscopy featuring intramolecular proton transfer and twisted intramolecular charge transfer poses a whole new range of problems for computational quantum chemistry. The development of the four-level laser based on the intramolecular proton-transfer focuses on the subtleties of the interaction of the singlet and triplet electronic state manifolds of the two different tautomeric species. Examples are given of the sensitive variation of proton-transfer fluorescence with chemical substitution. A competing excitation channel is shown to exist when internal molecular torsion couples with sudden polarization to yield a twisted intramolecular charge transfer configuration. In such systems, three competing fluorescences can be observed. Several electronic puzzles are presented that can provide fertile territory for quantum chemical computations. 6 figs., 2 tabs.

Kasha, M. (Florida State Univ., Tallahassee (United States)); Parthenopoulos, D. (Philip Morris Europe Research and Development, Neuchatel (Switzerland)); Dellinger, B. (Univ. of Dayton, OH (United States))

1993-01-01

307

Photoelectron and electron momentum spectroscopy of tetrahydrofuran from a molecular dynamical perspective.  

Science.gov (United States)

The results of experimental studies of the valence electronic structure of tetrahydrofuran employing He I photoelectron spectroscopy as well as Electron Momentum Spectroscopy (EMS) have been reinterpreted on the basis of Molecular Dynamical simulations employing the classical MM3 force field and large-scale quantum mechanical simulations employing Born-Oppenheimer Molecular Dynamics in conjunction with the dispersion corrected ?B97XD exchange-correlation functional. Analysis of the produced atomic trajectories demonstrates the importance of thermal deviations from the lowest energy path for pseudorotation, in the form of considerable variations of the ring-puckering amplitude. These deviations are found to have a significant influence on several outer-valence electron momentum distributions, as well as on the He I photoelectron spectrum. PMID:23387306

Shojaei, S H Reza; Morini, Filippo; Deleuze, Michael S

2013-02-20

308

Photoelectron and electron momentum spectroscopy of tetrahydrofuran from a molecular dynamical perspective.  

UK PubMed Central (United Kingdom)

The results of experimental studies of the valence electronic structure of tetrahydrofuran employing He I photoelectron spectroscopy as well as Electron Momentum Spectroscopy (EMS) have been reinterpreted on the basis of Molecular Dynamical simulations employing the classical MM3 force field and large-scale quantum mechanical simulations employing Born-Oppenheimer Molecular Dynamics in conjunction with the dispersion corrected ?B97XD exchange-correlation functional. Analysis of the produced atomic trajectories demonstrates the importance of thermal deviations from the lowest energy path for pseudorotation, in the form of considerable variations of the ring-puckering amplitude. These deviations are found to have a significant influence on several outer-valence electron momentum distributions, as well as on the He I photoelectron spectrum.

Shojaei SH; Morini F; Deleuze MS

2013-03-01

309

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

310

Photoinduced intra- and intermolecular electron transfer in solutions and in solid organized molecular assemblies.  

UK PubMed Central (United Kingdom)

The present paper highlights results of a systematic study of photoinduced electron transfer, where the fundamental aspects of the photochemistry occurring in solutions and in artificially or self-assembled molecular systems are combined and compared. In photochemical electron transfer (ET) reactions in solutions the electron donor, D, and acceptor, A, have to be or to diffuse to a short distance, which requires a high concentration of quencher molecules and/or long lifetimes of the excited donor or acceptor, which cannot always be arranged. The problem can partly be avoided by linking the donor and acceptor moieties covalently by a single bond, molecular chain or chains, or rigid bridge, forming D-A dyads. The covalent combination of porphyrin or phthalocyanine donors with an efficient electron acceptor, e.g. fullerene, has a two-fold effect on the electron transfer properties. Firstly, the electronic systems of the D-A pair result in a formation of an exciplex intermediate upon excitation both in solutions and in solid phases. The formation of the exciplex accelerates the ET rate, which was found to be as fast as >10(12) s(-1). Secondly, the total reorganization energy can be as small as 0.3 eV, even in polar solvents, which allows nanosecond lifetimes for the charge separated (CS) state. Molecular assemblies can form solid heterogeneous, but organized systems, e.g. molecular layers. This results in more complex charge separation and recombination dynamics. A distinct feature of the ET in organized assemblies is intermolecular interactions, which open a possibility for a charge migration both in the acceptor and in the donor layers, after the primary intramolecular exciplex formation and charge separation in the D-A dyad. The intramolecular ET is fast (35 ps) and efficient, but the formed interlayer CS states have lifetimes in microsecond or even second time domain. This is an important result considering possible applications.

Lemmetyinen H; Tkachenko NV; Efimov A; Niemi M

2011-01-01

311

Photoinduced intra- and intermolecular electron transfer in solutions and in solid organized molecular assemblies.  

Science.gov (United States)

The present paper highlights results of a systematic study of photoinduced electron transfer, where the fundamental aspects of the photochemistry occurring in solutions and in artificially or self-assembled molecular systems are combined and compared. In photochemical electron transfer (ET) reactions in solutions the electron donor, D, and acceptor, A, have to be or to diffuse to a short distance, which requires a high concentration of quencher molecules and/or long lifetimes of the excited donor or acceptor, which cannot always be arranged. The problem can partly be avoided by linking the donor and acceptor moieties covalently by a single bond, molecular chain or chains, or rigid bridge, forming D-A dyads. The covalent combination of porphyrin or phthalocyanine donors with an efficient electron acceptor, e.g. fullerene, has a two-fold effect on the electron transfer properties. Firstly, the electronic systems of the D-A pair result in a formation of an exciplex intermediate upon excitation both in solutions and in solid phases. The formation of the exciplex accelerates the ET rate, which was found to be as fast as >10(12) s(-1). Secondly, the total reorganization energy can be as small as 0.3 eV, even in polar solvents, which allows nanosecond lifetimes for the charge separated (CS) state. Molecular assemblies can form solid heterogeneous, but organized systems, e.g. molecular layers. This results in more complex charge separation and recombination dynamics. A distinct feature of the ET in organized assemblies is intermolecular interactions, which open a possibility for a charge migration both in the acceptor and in the donor layers, after the primary intramolecular exciplex formation and charge separation in the D-A dyad. The intramolecular ET is fast (35 ps) and efficient, but the formed interlayer CS states have lifetimes in microsecond or even second time domain. This is an important result considering possible applications. PMID:21031207

Lemmetyinen, Helge; Tkachenko, Nikolai V; Efimov, Alexander; Niemi, Marja

2010-10-29

312

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

Energy Technology Data Exchange (ETDEWEB)

Auger electron emission following the excitation of molecular (CO/sub 2//sup +/ and N/sub 2//sup +/) and atomic ions (C/sup +/ and N/sup +/) 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.

Schneider, D.; Kanter, E.P.; Zabransky, B.J.

1983-01-01

313

Atomic spectral-product representations of molecular electronic structure: metric matrices and atomic-product composition of molecular eigenfunctions.  

UK PubMed Central (United Kingdom)

Recent progress is reported in development of ab initio computational methods for the electronic structures of molecules employing the many-electron eigenstates of constituent atoms in spectral-product forms. The approach provides a universal atomic-product description of the electronic structure of matter as an alternative to more commonly employed valence-bond- or molecular-orbital-based representations. The Hamiltonian matrix in this representation is seen to comprise a sum over atomic energies and a pairwise sum over Coulombic interaction terms that depend only on the separations of the individual atomic pairs. Overall electron antisymmetry can be enforced by unitary transformation when appropriate, rather than as a possibly encumbering or unnecessary global constraint. The matrix representative of the antisymmetrizer in the spectral-product basis, which is equivalent to the metric matrix of the corresponding explicitly antisymmetric basis, provides the required transformation to antisymmetric or linearly independent states after Hamiltonian evaluation. Particular attention is focused in the present report on properties of the metric matrix and on the atomic-product compositions of molecular eigenstates as described in the spectral-product representations. Illustrative calculations are reported for simple but prototypically important diatomic (H(2), CH) and triatomic (H(3), CH(2)) molecules employing algorithms and computer codes devised recently for this purpose. This particular implementation of the approach combines Slater-orbital-based one- and two-electron integral evaluations, valence-bond constructions of standard tableau functions and matrices, and transformations to atomic eigenstate-product representations. The calculated metric matrices and corresponding potential energy surfaces obtained in this way elucidate a number of aspects of the spectral-product development, including the nature of closure in the representation, the general redundancy or linear dependence of its explicitly antisymmetrized form, the convergence of the apparently disparate atomic-product and explicitly antisymmetrized atomic-product forms to a common invariant subspace, and the nature of a chemical bonding descriptor provided by the atomic-product compositions of molecular eigenstates. Concluding remarks indicate additional studies in progress and the prognosis for performing atomic spectral-product calculations more generally and efficiently.

Ben-Nun M; Mills JD; Hinde RJ; Winstead CL; Boatz JA; Gallup GA; Langhoff PW

2009-07-01

314

Beyond frontier molecular orbital theory: a systematic electron transfer model (ETM) for polar bimolecular organic reactions.  

UK PubMed Central (United Kingdom)

Polar bimolecular reactions often begin as charge-transfer complexes and may proceed with a high degree of electron transfer character. Frontier molecular orbital (FMO) theory is predicated in part on this concept. We have developed an electron transfer model (ETM) in which we systematically transfer one electron between reactants and then use density functional methods to model the resultant radical or radical ion intermediates. Sites of higher reactivity are revealed by a composite spin density map (SDM) of odd electron character on the electron density surface, assuming that a new two-electron bond would occur preferentially at these sites. ETM correctly predicts regio- and stereoselectivity for a broad array of reactions, including Diels-Alder, dipolar and ketene cycloadditions, Birch reduction, many types of nucleophilic additions, and electrophilic addition to aromatic rings and polyenes. Conformational analysis of radical ions is often necessary to predict reaction stereochemistry. The electronic and geometric changes due to one-electron oxidation or reduction parallel the reaction coordinate for electrophilic or nucleophilic addition, respectively. The effect is more dramatic for one-electron reduction.

Cahill KJ; Johnson RP

2013-03-01

315

Recovery of high purity sulfuric acid from the waste acid in toluene nitration process by rectification.  

UK PubMed Central (United Kingdom)

Waste sulfuric acid is a byproduct generated from numerous industrial chemical processes. It is essential to remove the impurities and recover the sulfuric acid from the waste acid. In this study the rectification method was introduced to recover high purity sulfuric acid from the waste acid generated in toluene nitration process by using rectification column. The waste acid quality before and after rectification were evaluated using UV-Vis spectroscopy, GC/MS, HPLC and other physical and chemical analysis. It was shown that five nitro aromatic compounds in the waste acid were substantially removed and high purity sulfuric acid was also recovered in the rectification process at the same time. The COD was removed by 94% and the chrominance was reduced from 1000° to 1°. The recovered sulfuric acid with the concentration reaching 98.2 wt% had a comparable quality with commercial sulfuric acid and could be recycled back into the toluene nitration process, which could avoid waste of resources and reduce the environmental impact and pollution.

Song K; Meng Q; Shu F; Ye Z

2013-01-01

316

Automatic quality control of oil rectification products. Avtomatizirovannoye upravleniye kachestvom produktov rektifikatsii nyefti  

Energy Technology Data Exchange (ETDEWEB)

This work is devoted to automatic control of the quality of products of vacuum distillation of oil at oil refining plants, and is based on a large amount of factual material, modern scientific concepts, research methods, mathematical apparatus and computer theory, ensuring a high quality of rectification products.

Ovezov, B.B.

1980-01-01

317

High purification of boron tribromide by periodic rectification in emulsification mode  

International Nuclear Information System (INIS)

A high purification of boron tribromide by periodic rectification in flooding mode is carried out. The product is obtained with the metal content of 1?10-7-1?10-8 wt % and organic substances content of not more than 1?10-5 wt. % which meets the demands of fiber optics.

1990-01-01

318

Dynamic 3D Scene Depth Reconstruction via Optical Flow Field Rectification  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this paper, we propose a depth propagation scheme based on optical flow field rectification towards more accurate depth reconstruction. In depth reconstruction, the occlusions and low-textural regions easily result in optical flow field errors, which lead ambiguous depth value or holes without de...

Yang, You; Liu, Qiong; Ji, Rongrong; Gao, Yue

319

High-pressure rectification and absorption using the Mellapak packed column  

Energy Technology Data Exchange (ETDEWEB)

High-pressure rectification and absorption are most commonly applied in the petrochemical and oil or gas-processing industries. The common separating columns are equipped with plates. The performance of packed columns at higher pressures was investigated and compared with the performance of Pall rings and plates. Possible applications are discussed for the example of two commercial columns.

Spiegel, L.; Bomio, P.

1987-02-01

320

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

 
 
 
 
321

Electronic structure/function relationships in metal nanowires: components for molecular electronics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The dramatic expansion of the electronics industry over the past 40 years has been based on the progressive reduction in size of the silicon-based semiconductor components of integrated circuits. The miniaturisation of semi-conductor circuits cannot, however, continue indefinitely, and we are rap...

Georgiev, Vihar Petkov; John, McGrady

322

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

323

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

324

Nanoscale assembly for molecular electronics and in situ characterization during atomic layer deposition  

Science.gov (United States)

The work in this dissertation consists of a two-part study concerning molecular-based electronics and atomic layer deposition (ALD). As conventional "top-down" silicon-based technology approaches its expected physical and technical limits, researchers have paid considerable attention to "bottom-up" approaches including molecular-based electronics that self assembles molecular components and ALD techniques that deposit thin films with atomic layer control. Reliable fabrication of molecular-based devices and a lack of understanding of the conduction mechanisms through individual molecules still remain critical issues in molecular-based electronics. Nanoparticle/molecule(s)/nanoparticle assemblies of "dimers" and "trimers", consisting of two and three nanoparticles bridged by oligomeric ethynylene phenylene molecules (OPEs), respectively, are successfully synthesized by coworkers and applied to contact nanogap electrodes (molecular transistor is also demonstrated with trimers trapped across nanogap electrodes. The source-drain current is modulated within a factor of 2 with a gate bias voltage of -2 to +2 V. A subthreshold slope of ˜110 mV/decade is obtained. Finally, we report on both fundamental understanding and application of atomic layer deposition. First, in situ analysis tools such as quartz crystal microbalance and electrical conductance measurements are combined to reveal direct links between surface reactions, charge transfer, and dopant incorporation during ZnO and ZnO:Al ALD. Second, the ability of ALD to form uniform and conformal coating onto complex nanostructures is explored to improve the ambient stability of single molecules/nanoparticle assemblies using Al2O3 ALD as an encapsulation layer. In addition, the ability to shield the surface polarity of ZnO nanostructures using Al 2O3 + ZnO ALD, leading to hierarchical morphology evolution from one-dimensional ZnO nanorods to three-dimensional ZnO nanosheets with branched nanorods during hydrothermal growth is investigated.

Na, Jeong-Seok

325

Atomic and Molecular Photoelectron and Auger Electron SpectroscopyStudies Using Synchrotron Radiation  

Energy Technology Data Exchange (ETDEWEB)

Electron spectroscopy, combined with synchrotron radiation, was used to measure the angular distributions of photoelectrons and Auger electrons from atoms and molecules as functions of photon energy. The branching ratios and partial cross sections were a 130 measured in certain cases. By comparison with theoretical calculations, the experimental results are interpreted in terms of the characteristic electronic structure and ionization dynamics of the atomic or molecular sample. The time structure of the synchrotron radiation source was used to record time-of-flight (TOF) spectra o f the ejected electrons. The ''a double-angle-TOF'' method for the measurement of photoelectron angular distributions is discussed. This technique offers the advantages of increased electron collect ion efficiency and the elimination of certain systematic errors. Several results were obtained for Xe using photon energies in the range hv {approx_equal} 60-190 eV, where excitation and ionization of the inner-subshell 4d electrons dominates. The 4d asymmetry parameter {beta} exhibits strong oscillations with energy, in agreement with several theoretical calculations. As predicted, the 5p asymmetry parameter was observed to deviate strongly from that calculated using the independent-electron model, due to intershell correlation with the 4d electrons.

Southworth, Stephen H.

1982-01-01

326

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

327

First-principles study of the electronic transport properties of the anthraquinone-based molecular switch  

Energy Technology Data Exchange (ETDEWEB)

By applying non-equilibrium Green's function (NEGF) formalism combined with first-principles density functional theory (DFT), we have investigated the electronic transport properties of the anthraquinone-based molecular switch. The molecule that comprises the switch can be converted between the hydroquinone (HQ) and anthraquinone (AQ) forms via redox reactions. The transmission spectra of these two forms are remarkably distinctive. Our results show that the current through the HQ form is significantly larger than that through the AQ form, which suggests that this system has attractive potential application in future molecular switch technology.

Zhao, P., E-mail: ss_zhaop@ujn.edu.c [School of Science, University of Jinan, Jinan 250022 (China); Liu, D.S. [School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China); Department of Physics, Jining University, Qufu 273155 (China); Wang, P.J.; Zhang, Z. [School of Science, University of Jinan, Jinan 250022 (China); Fang, C.F.; Ji, G.M. [School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China)

2011-02-15

328

First-principles study of the electronic transport properties of the anthraquinone-based molecular switch  

International Nuclear Information System (INIS)

By applying non-equilibrium Green's function (NEGF) formalism combined with first-principles density functional theory (DFT), we have investigated the electronic transport properties of the anthraquinone-based molecular switch. The molecule that comprises the switch can be converted between the hydroquinone (HQ) and anthraquinone (AQ) forms via redox reactions. The transmission spectra of these two forms are remarkably distinctive. Our results show that the current through the HQ form is significantly larger than that through the AQ form, which suggests that this system has attractive potential application in future molecular switch technology.

2011-02-15

329

First-principles study of the electronic transport properties of the anthraquinone-based molecular switch  

Science.gov (United States)

By applying non-equilibrium Green’s function (NEGF) formalism combined with first-principles density functional theory (DFT), we have investigated the electronic transport properties of the anthraquinone-based molecular switch. The molecule that comprises the switch can be converted between the hydroquinone (HQ) and anthraquinone (AQ) forms via redox reactions. The transmission spectra of these two forms are remarkably distinctive. Our results show that the current through the HQ form is significantly larger than that through the AQ form, which suggests that this system has attractive potential application in future molecular switch technology.

Zhao, P.; Liu, D. S.; Wang, P. J.; Zhang, Z.; Fang, C. F.; Ji, G. M.

2011-02-01

330

The molecular structure of trimethylphosphine-boron triiodide as studied by gas-phase electron diffraction  

International Nuclear Information System (INIS)

The molecular structure of trimethylphosphine-boron triiodide (CH3)3P.BI3 has been determined by means of gas-electron diffraction. The molecular parameters and their uncertainties were r sub(g)(B-I) = 2.233 +- 0.003 A, r sub(g)(P-B) = 1.947 +- 0.011 A, r sub(g)(C-P) = 1.809 +- 0.003 A, r sub(g)(C-H) = 1.094 +- 0.008 A, 0, and 0. The gaseous molecule was rigid with respect to the rotational vibration around the P-B bond. (author)

1982-01-01

331

Measurements of secondary electron cross sections by the pulsed electron beam time-of-flight method. I. Molecular nitrogen  

International Nuclear Information System (INIS)

The secondary electron cross sections for gaseous molecular nitrogen are reported at ejection angles of 30, 45, 60, 75, 90, 105, 120, 135 and 1500, for the energy range 1.5 eV to 20 eV and incident electron energy of 1 keV. The pulsed electron beam time-of-flight methd was employed. The results were placed on an absolute scale by normalization to the elastic scattering. They were compared, where possible, with those reported by Opal, Beaty, and Peterson (OBP). The agreement is somewhat better when the OBP data are divided by 0.53 + 0.47 sintheta as suggested by Rudd and DuBois. Fits of our data by Legendre-polynomial expansions are used to estimate the low-energy portion of the cross-section, dsigma/dE. This work suggests that existing experimental cross sections for secondary electron ejection as a function of angle and ejected energy may be no better known than +-40%, especially in the low energy region. 7 references, 14 figures, 2 tables.

1983-01-01

332

Rectification of the current in alpha-hemolysin pore depends on the cation type: the alkali series probed by MD simulations and experiments  

Science.gov (United States)

A striking feature of the alpha-hemolysin channel—a prime candidate for biotechnological applications—is the dependence of its ionic conductance on the magnitude and direction of the applied bias. Through a combination of lipid bilayer single-channel recording and molecular dynamics (MD) simulations, we characterized the current-voltage relationship of alpha-hemolysin for all alkali chloride salts at neutral pH. The rectification of the ionic current was found to depend on the type of cations and increase from Li+ to Cs+. Analysis of the MD trajectories yielded a simple quantitative model that related the ionic current to the electrostatic potential, the concentration and effective mobility of ions in the channel. MD simulations reveal that the major contribution to the current asymmetry and rectification properties originates from the cationic contribution to the current that is significantly reduced in a cationic dependent way when the membrane polarity is reversed. The variation of chloride current was found to be less important. We report that the differential affinity of cations for the charged residues positioned at the channel’s end modulates the number of ions inside the channel stem thus affecting the current properties. Through direct comparison of simulation and experiment, this study evaluates the accuracy of the MD method for prediction of the asymmetric, voltage dependent conductances of a membrane channel.

Bhattacharya, Swati; Muzard, L.; Payet, L.; Mathe, Jerome; Bockelmann, Ulrich; Aksimentiev, Aleksei; Viasnoff, Virgile

2011-01-01

333

The exact molecular wavefunction as a product of an electronic and a nuclear wavefunction.  

UK PubMed Central (United Kingdom)

The Born-Oppenheimer approximation is a basic approximation in molecular science. In this approximation, the total molecular wavefunction is written as a product of an electronic and a nuclear wavefunction. Hunter [Int. J. Quantum Chem. 9, 237 (1975)] has argued that the exact total wavefunction can also be factorized as such a product. In the present work, a variational principle is introduced which shows explicitly that the total wavefunction can be exactly written as such a product. To this end, a different electronic Hamiltonian has to be defined. The Schro?dinger equation for the electronic wavefunction follows from the variational ansatz and is presented. As in the Born-Oppenheimer approximation, the nuclear motion is shown to proceed in a potential which is the electronic energy. In contrast to the Born-Oppenheimer approximation, the separation of the center of mass can be carried out exactly. The electronic Hamiltonian and the equation of motion of the nuclei resulting after the exact separation of the center of mass motion are explicitly given. A simple exactly solvable model is used to illustrate some aspects of the theory.

Cederbaum LS

2013-06-01

334

New light on molecular and materials complexity: 4D electron imaging.  

Science.gov (United States)

In this Perspective, 4D electron imaging is highlighted, after introducing some concepts, with an overview of selected applications that span chemical reactions, molecular interfaces, phase transitions, and nano(micro)mechanical systems. With the added dimension of time in microscopy, diffraction, and electron-energy-loss spectroscopy, the focus is on direct visualization of structural dynamics with atomic and nanoscale resolution in the four dimensions of space and time. This contribution provides an expose of emerging developments and an outlook on future applications in materials and biological sciences. PMID:20000855

Shorokhov, Dmitry; Zewail, Ahmed H

2009-12-23

335

New light on molecular and materials complexity: 4D electron imaging.  

UK PubMed Central (United Kingdom)

In this Perspective, 4D electron imaging is highlighted, after introducing some concepts, with an overview of selected applications that span chemical reactions, molecular interfaces, phase transitions, and nano(micro)mechanical systems. With the added dimension of time in microscopy, diffraction, and electron-energy-loss spectroscopy, the focus is on direct visualization of structural dynamics with atomic and nanoscale resolution in the four dimensions of space and time. This contribution provides an expose of emerging developments and an outlook on future applications in materials and biological sciences.

Shorokhov D; Zewail AH

2009-12-01

336

X radiation accompanying electron capture by oxygen and carbon nuclei in molecular hydrogen  

Energy Technology Data Exchange (ETDEWEB)

The emission cross sections for the characteristic x radiation accompanying the capture of an electron by C/sup 6 +/ and O/sup 8 +/ nuclei in molecular hydrogen at a collision energy E/sub 0/ = 0.6--8 keV/amu have been measured. It is shown that the electron is captured in a state of the C/sup 5 +/ and O/sup 7 +/ ions with large principal quantum numbers. This occurs when the population of states with different orbital moments is approximately uniform.

Afrosimov, V.V.; Basalaev, A.A.; Gordeev, Y.S.; Donets, E.D.; Zinov' ev, A.N.; Ovchinnikov, S.Y.; Panov, M.N.

1981-09-20

337

Non Franck-Condon effects in the molecular electronic excitation of O2 and CO  

International Nuclear Information System (INIS)

Franck-Condon envelopes in electron energy loss spectra recorded for the X1?+ ? B1?+ and X+?g-?B'3?u- transitions in CO and O2 show a pronounced variation with scattering angle. This behavior is in sharp contrast with the results standard formulations confirmed by all previous studies of electron impact and optically induced molecular excitation. Underlying mechanisms revealed by a theoretical investigation employing multi reference configuration interaction suggest that such phenomena may be much more general than previously assumed

1992-01-01

338

On the path length of an excess electron interacted with optical phonons in a molecular chain  

Energy Technology Data Exchange (ETDEWEB)

We show that in a molecular chain with dispersionless phonons at zero temperature, a 'quasistationary' moving soliton state of an excess electron is possible. As the soliton velocity vanishes, the path length of the excess electron exponentially tends to infinity. It is demonstrated that in the presence of dispersion, when the soliton initial velocity exceeds the maximum group velocity of the chain, the soliton slows down until it reaches the maximum group velocity and then moves stationarily at this maximum group velocity. A conclusion is made of the fallacy of some works were the existence of moving polarons in a dispersionless medium is considered infeasible.

Lakhno, V.D. [Institute of Mathematical Problems of Biology, Russian Academy of Sciences, Pushchino, Moscow Region 142290 (Russian Federation)], E-mail: lak@impb.psn.ru

2008-08-25

339

On the path length of an excess electron interacted with optical phonons in a molecular chain  

International Nuclear Information System (INIS)

We show that in a molecular chain with dispersionless phonons at zero temperature, a 'quasistationary' moving soliton state of an excess electron is possible. As the soliton velocity vanishes, the path length of the excess electron exponentially tends to infinity. It is demonstrated that in the presence of dispersion, when the soliton initial velocity exceeds the maximum group velocity of the chain, the soliton slows down until it reaches the maximum group velocity and then moves stationarily at this maximum group velocity. A conclusion is made of the fallacy of some works were the existence of moving polarons in a dispersionless medium is considered infeasible.

2008-08-25

340

Non-Equilibrium Dynamics of Correlated Electron Transfer in Molecular Chains  

CERN Document Server

The relaxation dynamics of correlated electron transport (ET) along molecular chains is studied based on a substantially improved numerically exact path integral Monte Carlo (PIMC) approach. As archetypical model we consider a Hubbard chain containing two interacting electrons coupled to a bosonic bath. For this generalization of the ubiquitous spin-boson model, the intricate interdependence of correlations and dissipation leads to non-Boltzmann thermal equilibrium distributions for many-body states. By mapping the multi-particle dynamics onto an isomorphic single particle motion this phenomenon is shown to be sensitive to the particle statistics and due to its robustness allows for new control schemes in designed quantum aggregates.

Mühlbacher, L; Komnik, A

2005-01-01

 
 
 
 
341

Electronic structure calculations with two-component molecular spinors and relativistic effective core potentials  

International Nuclear Information System (INIS)

We have been developing computational methods to calculate electronic structures of molecules using relativistic effective core potentials with spin-orbit terms. Since spin-orbit interactions are contained in the Hamiltonian employed to derive one electron wavefunctions, orbitals in the present method become two-component spinors confirmining the double group symmetry. Starting from the HF method using two-component molecular spinors, the present scheme has been extended to relativistic MP2 and CI methods. These two-component methods are especially useful to study the interplay between spin-orbit and correlation effects on molecular structures and properties. Results calculated by the present methods are available for many diatomic molecules and a few polyatomic systems.

1996-01-01

342

Electronic structure calculations with two-component molecular spinors and relativistic effective core potentials  

Energy Technology Data Exchange (ETDEWEB)

We have been developing computational methods to calculate electronic structures of molecules using relativistic effective core potentials with spin-orbit terms. Since spin-orbit interactions are contained in the Hamiltonian employed to derive one electron wavefunctions, orbitals in the present method become two-component spinors confirmining the double group symmetry. Starting from the HF method using two-component molecular spinors, the present scheme has been extended to relativistic MP2 and CI methods. These two-component methods are especially useful to study the interplay between spin-orbit and correlation effects on molecular structures and properties. Results calculated by the present methods are available for many diatomic molecules and a few polyatomic systems.

Lee, Yoon Sup [KAIST, Taejon (Korea, Republic of)

1996-12-31

343

The two dimensional Hubbard model: a theoretical tool for molecular electronics  

International Nuclear Information System (INIS)

When speaking about molecular electronics, the obvious question which occurs is how does one study it theoretically. The simplest theoretical model suitable for application in molecular electronics is the two dimensional Hubbard model. The aim of the present paper is to introduce this model, and give some examples of the systems which it can describe. After a short mathematically oriented discussion, it will be shown how to calculate the electrical conductivity of a particular planar system: a rectangular lattice with mutually independent conductivities along the two axes,but without using the 2D Hamiltonian. This system could find applications in high Tc studies. It will finally be shown that the electrical conductivity of graphene can be determined not by using the full formalism of the 2D Hubbard model, but by a slight reformulation of the Hamiltonian of the 1D Hubbard model.

2010-11-01

344

The soliton capture of conversion electrons from an atom attached to a molecular chain  

Energy Technology Data Exchange (ETDEWEB)

It was known that Auger effect of rearrangement of the electronic shell is accompanied by the ejection of an electron from an atomic envelope and that two alternatives are possible: internal conversion is achieved by interaction with the photon emitted from the nucleus, or transfer of excitation to the electron by the nucleus is achieved in the absence of any radiation, i.e., the transfer is realized with zero total momentum. In this paper, the authors investigate the special case for an atom attached to a molecular chain, which posseses a localized form of excitation, i.e., the soliton. The solitons from a potential well for electrons, in which the electrons become trapped rather than being able to escape into free space. That process of capturing electrons by crystal excitation is not so rare if the excitations are nonlocalized. It is important to estimate the probability of transition of electons from the K atomic shell in both cases, i.e., with and without interaction of electrons with photons. Here, is used the theory of internal conversion without relativistic effects. 11 refs.

Ajazij, H.; Shemsidini, Z.; Stepancic, B.; Zakula, R.B.

1987-01-01

345

Damage clusters in molecular-ion-bombarded gold, observed by transmission electron microscopy  

International Nuclear Information System (INIS)

[en] Stereo electron microscopy of gold bombarded at room temperature with atomic and molecular ions shows that the nature of damage clusters is sensitive to the density of deposited energy. Both the total number of defects and their distribution in space show that vacancy loops are formed preferentially at high density of deposited energy and interstitial loops at low density. Calculations indicate that the limiting density corresponds to approximately 10-2 point defects per atom. (Auth.)

1976-01-01

346

Transmission electron microscopy investigations of defects in molecular beam epitaxy-grown oxide films  

Energy Technology Data Exchange (ETDEWEB)

With a view to increasing the superconductive transition temperature of thin films of La{sub 2}CuO{sub 4} grown by molecular beam epitaxy, films were grown on substrates of lattice parameters such that the film-substrate misfit became small and tensile, or compressive. The microstructure of these films was investigated using transmission electron microscopy and qualitative correlations with physical properties suggested. (orig.)

Williams, E.J. [IBM Research Lab., Rueschlikon (Switzerland). IBM Research Div.]|[Departement de Physique de la Matiere Condensee, Universite de Geneve, CH-1211, Geneve (Switzerland); Daridon, A. [IBM Research Lab., Rueschlikon (Switzerland). IBM Research Div.]|[Institute of Inorganic Chemistry, University of Bern, CH-3012, Bern (Switzerland); Arrouy, F.; Locquet, J.-P.; Maechler, E. [IBM Research Lab., Rueschlikon (Switzerland). IBM Research Div.; Perret, J.; Jaccard, Y. [IBM Research Lab., Rueschlikon (Switzerland). IBM Research Div.]|[Institut de Physique, Universite de Neuchatel, CH-2000, Neuchatel (Switzerland); Siegenthaler, H. [Institute of Inorganic Chemistry, University of Bern, CH-3012, Bern (Switzerland); Martinoli, P. [Institut de Physique, Universite de Neuchatel, CH-2000, Neuchatel (Switzerland); Fischer, Oe. [Departement de Physique de la Matiere Condensee, Universite de Geneve, CH-1211, Geneve (Switzerland)

1997-04-01

347

Applications of the Schwinger variational principle to electron-molecule collisions and molecular photoionization  

International Nuclear Information System (INIS)

In this article we present a detailed overview of our studies of molecular photoionization and electron-molecule collisions in which we have used Schwinger-like variational principles and several important extensions of these principles. The various variational functionals and formulations, the interrelationships between these formulations, and a detailed discussion of the numerical and computational procedures which have been used in applications are presented. (orig.)

1986-01-01

348

Applications of the Schwinger variational principle to electron-molecule collisions and molecular photoionization  

Energy Technology Data Exchange (ETDEWEB)

In this article we present a detailed overview of our studies of molecular photoionization and electron-molecule collisions in which we have used Schwinger-like variational principles and several important extensions of these principles. The various variational functionals and formulations, the interrelationships between these formulations, and a detailed discussion of the numerical and computational procedures which have been used in applications are presented. (orig.).

Lucchese, R.R.; Takatsuka, Kazuo; McCoy, V.

1986-01-01

349

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

CERN Multimedia

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

350

On the distance dependence of electron transfer through molecular bridges and wires  

CERN Multimedia

The dependence of electron transfer rates and yields in bridged molecular systems on the bridge length, and the dependence of the zero-bias conduction of molecular wires on wire length are discussed. Both phenomena are controlled by tunneling across the molecular bridge and are consequently expected to show exponential decrease with bridge length that is indeed often observed. Deviations from this exponential dependence for long bridges, in particular a crossover to a very weak dependence on bridge length were recently observed experimentally and discussed theoretically in terms of thermal relaxation and dephasing on the bridge. Here we discuss two other factors that potentially affect the bridge length dependence of these phenomena. First, in experiments initiated by an initial preparation of a non-stationary "donor" state the initial energy is not well defined. A small contribution from initially populated eigenstates that are of mostly bridge-level character may dominate transmission for long bridges, resu...

Skourtis, S; Skourtis, Spiros; Nitzan, Abraham

2002-01-01

351

Low-energy Electron collisions with O$_2$: Test of Molecular R-matrix without Diagonalization  

CERN Document Server

Electron collisions with O$_2$ at scattering energies below 1 eV are studied in the fixed-nuclei approximation for a range of internuclear separations using the ab initio molecular R-matrix method. The $^2\\Pi_g$ scattering eigenphases and quantum defects are calculated. The parameters of the resonance and the energy of the bound negative ion are then extracted. Different models of the target that employ molecular orbitals calculated for the neutral target are compared with models based on anionic orbitals. A model using a basis of anionic molecular orbitals yields physically correct results in good agreement with experiment. An alternative method of calculation of the R-matrix is tested, where instead of performing a single complete diagonalization of the Hamiltonian matrix in the inner region, the system of linear equations is solved individually for every scattering energy. This approach is designed to handle problems where diagonalization of an extremely large Hamiltonian is numerically too demanding.

Tarana, Michal

2013-01-01

352

Molecular solution approach to synthesize electronic quality Cu2ZnSnS4 thin films.  

UK PubMed Central (United Kingdom)

Successful implementation of molecular solution processing from a homogeneous and stable precursor would provide an alternative, robust approach to process multinary compounds compared with physical vapor deposition. Targeting deposition of chemically clear, high quality crystalline films requires specific molecular structure design and solvent selection. Hydrazine (N2H4) serves as a unique and powerful medium, particularly to incorporate selected metallic elements and chalcogens into a stable solution as metal chalcogenide complexes (MCC). However, not all the elements and compounds can be easily dissolved. In this manuscript, we demonstrate a paradigm to incorporate previously insoluble transitional-metal elements into molecular solution as metal-atom hydrazine/hydrazine derivative complexes (MHHD), as exemplified by dissolving of the zinc constituent as Zn(NH2NHCOO)2(N2H4)2. Investigation into the evolution of molecular structure reveals the hidden roadmap to significantly enrich the variety of building blocks for soluble molecule design. The new category of molecular structures not only set up a prototype to incorporate other elements of interest but also points the direction for other compatible solvent selection. As demonstrated from the molecular precursor combining Sn-/Cu-MCC and Zn-MHHD, an ultrathin film of copper zinc tin sulfide (CZTS) was deposited. Characterization of a transistor based on the CZTS channel layer shows electronic properties comparable to CuInSe2, confirming the robustness of this molecular solution processing and the prospect of earth abundant CZTS for next generation photovoltaic materials. This paradigm potentially outlines a universal pathway, from individual molecular design using selected chelated ligands and combination of building blocks in a simple and stable solution to fundamentally change the way multinary compounds are processed.

Yang W; Duan HS; Cha KC; Hsu CJ; Hsu WC; Zhou H; Bob B; Yang Y

2013-05-01

353

Molecular solution approach to synthesize electronic quality Cu2ZnSnS4 thin films.  

Science.gov (United States)

Successful implementation of molecular solution processing from a homogeneous and stable precursor would provide an alternative, robust approach to process multinary compounds compared with physical vapor deposition. Targeting deposition of chemically clear, high quality crystalline films requires specific molecular structure design and solvent selection. Hydrazine (N2H4) serves as a unique and powerful medium, particularly to incorporate selected metallic elements and chalcogens into a stable solution as metal chalcogenide complexes (MCC). However, not all the elements and compounds can be easily dissolved. In this manuscript, we demonstrate a paradigm to incorporate previously insoluble transitional-metal elements into molecular solution as metal-atom hydrazine/hydrazine derivative complexes (MHHD), as exemplified by dissolving of the zinc constituent as Zn(NH2NHCOO)2(N2H4)2. Investigation into the evolution of molecular structure reveals the hidden roadmap to significantly enrich the variety of building blocks for soluble molecule design. The new category of molecular structures not only set up a prototype to incorporate other elements of interest but also points the direction for other compatible solvent selection. As demonstrated from the molecular precursor combining Sn-/Cu-MCC and Zn-MHHD, an ultrathin film of copper zinc tin sulfide (CZTS) was deposited. Characterization of a transistor based on the CZTS channel layer shows electronic properties comparable to CuInSe2, confirming the robustness of this molecular solution processing and the prospect of earth abundant CZTS for next generation photovoltaic materials. This paradigm potentially outlines a universal pathway, from individual molecular design using selected chelated ligands and combination of building blocks in a simple and stable solution to fundamentally change the way multinary compounds are processed. PMID:23581974

Yang, Wenbing; Duan, Hsin-Sheng; Cha, Kitty C; Hsu, Chia-Jung; Hsu, Wan-Ching; Zhou, Huanping; Bob, Brion; Yang, Yang

2013-04-30

354

An analytical procedure to evaluate electronic integrals for molecular quantum mechanical calculations  

International Nuclear Information System (INIS)

Full text: We propose an alternative methodology for the calculation of electronic integrals, through an analytical function based on the generalized Gaussian function (q Gaussian), where a single q Gaussian replaces the usual linear combination of Gaussian functions for different basis set. Moreover, the integrals become analytical functions of the interatomic distances. Therefore, when estimating certain quantities such as molecular energy, g Gaussian avoid new calculations of the integrals: they are simply another value of the corresponding function. The procedure proposed here is particularly advantageous, when compared with the usual one, because it reduces drastically the number of two-electronic integrals used in the construction of the Fock matrix, enabling the use of the quantum mechanics in the description of macro-molecular systems. This advantage increases when the size of the molecular systems become larger and more complex. While in the usual approach CPU time increases with n4, in the one proposed here the CPU time scales linearly with n. This catastrophic dependence of the rank the Hamiltonian or Fock matrix with n4 two-electron integrals is a severe bottleneck for petaFLOPS computing time. Its is important to emphasize that this methodology is equally applicable to systems of any sizes, including biomolecules, solid materials and solutions, within the HF, post-HF and DFT theories. (author)

2004-01-01

355

An analytic approach to 2D electronic PE spectra of molecular systems  

Energy Technology Data Exchange (ETDEWEB)

Graphical abstract: The three-pulse photon echo (3P-PE) spectra of finite molecular systems using direct calculation from electronic Hamiltonians allows peak classification from 3P-PE spectra dynamics. Display Omitted Highlights: {yields} RWA approach to electronic photon echo. {yields} A straightforward calculation of 2D electronic spectrograms in finite molecular systems. {yields} Importance of population time dynamics in relation to inter-site coherent coupling. - Abstract: The three-pulse photon echo (3P-PE) spectra of finite molecular systems and simplified line broadening models is presented. The Fourier picture of a heterodyne detected three-pulse rephasing PE signal in the {delta}-pulse limit of the external field is derived in analytic form. The method includes contributions of one and two-excitonic states and allows direct calculation of Fourier PE spectrogram from corresponding Hamiltonian. As an illustration, the proposed treatment is applied to simple systems, e.g. 2-site two-level system (TLS) and n-site TLS model of photosynthetic unit. The importance of relation between Fourier picture of 3P-PE dynamics (corresponding to nonzero population time, T) and coherent inter-state coupling is emphasized.

Szoecs, V., E-mail: szocs@fns.uniba.sk [Institute of Chemistry, Comenius University, Mlynska dolina CH2, 842 15 Bratislava (Slovakia)

2011-05-26

356

An analytic approach to 2D electronic PE spectra of molecular systems  

International Nuclear Information System (INIS)

Graphical abstract: The three-pulse photon echo (3P-PE) spectra of finite molecular systems using direct calculation from electronic Hamiltonians allows peak classification from 3P-PE spectra dynamics. Display Omitted Highlights: ? RWA approach to electronic photon echo. ? A straightforward calculation of 2D electronic spectrograms in finite molecular systems. ? Importance of population time dynamics in relation to inter-site coherent coupling. - Abstract: The three-pulse photon echo (3P-PE) spectra of finite molecular systems and simplified line broadening models is presented. The Fourier picture of a heterodyne detected three-pulse rephasing PE signal in the ?-pulse limit of the external field is derived in analytic form. The method includes contributions of one and two-excitonic states and allows direct calculation of Fourier PE spectrogram from corresponding Hamiltonian. As an illustration, the proposed treatment is applied to simple systems, e.g. 2-site two-level system (TLS) and n-site TLS model of photosynthetic unit. The importance of relation between Fourier picture of 3P-PE dynamics (corresponding to nonzero population time, T) and coherent inter-state coupling is emphasized.

2011-05-26

357

Activationless charge transport across 4.5 to 22 nm in molecular electronic junctions.  

UK PubMed Central (United Kingdom)

In this work, we bridge the gap between short-range tunneling in molecular junctions and activated hopping in bulk organic films, and greatly extend the distance range of charge transport in molecular electronic devices. Three distinct transport mechanisms were observed for 4.5-22-nm-thick oligo(thiophene) layers between carbon contacts, with tunneling operative when d?< 8 nm, activated hopping when d > 16 nm for high temperatures and low bias, and a third mechanism consistent with field-induced ionization of highest occupied molecular orbitals or interface states to generate charge carriers when d = 8-22 nm. Transport in the 8-22-nm range is weakly temperature dependent, with a field-dependent activation barrier that becomes negligible at moderate bias. We thus report here a unique, activationless transport mechanism, operative over 8-22-nm distances without involving hopping, which severely limits carrier mobility and device lifetime in organic semiconductors. Charge transport in molecular electronic junctions can thus be effective for transport distances significantly greater than the 1-5 nm associated with quantum-mechanical tunneling.

Yan H; Bergren AJ; McCreery R; Della Rocca ML; Martin P; Lafarge P; Lacroix JC

2013-04-01

358

Modeling molecular acidity with electronic properties and Hammett constants for substituted benzoic acids.  

UK PubMed Central (United Kingdom)

Molecular acidity is an important physiochemical property essential in many fields of molecular studies, but an efficient and reliable computational approach to make accurate predictions is still missing. In this work, based on our previous studies to use gas phase electronic properties such as molecular electrostatic potential and valence natural atomic orbitals of the acidic atom and leaving proton, we demonstrate here that different approaches can be employed to tackle this problem. To that end, we employ 196 singly, doubly, and triply substituted benzoic acids for the study. We show that two different approaches are possible, one focusing on the carboxyl group through its localized electronic properties and the other on the substituting groups via Hammett constants and their additivity rule. Our present results clearly exhibit that with the linear models built from the singly substituted species, one can accurately predict the pK(a) values for the doubly and triply substituted species with both of these two approaches. The predictions from these approaches are consistent with each other and agree well with the experimental data. These intrinsically different approaches are the two manifestations of the same molecular acidity property, both valid and complementary to each other.

Huang Y; Liu L; Liu W; Liu S; Liu S

2011-12-01

359

Modeling molecular acidity with electronic properties and Hammett constants for substituted benzoic acids.  

Science.gov (United States)

Molecular acidity is an important physiochemical property essential in many fields of molecular studies, but an efficient and reliable computational approach to make accurate predictions is still missing. In this work, based on our previous studies to use gas phase electronic properties such as molecular electrostatic potential and valence natural atomic orbitals of the acidic atom and leaving proton, we demonstrate here that different approaches can be employed to tackle this problem. To that end, we employ 196 singly, doubly, and triply substituted benzoic acids for the study. We show that two different approaches are possible, one focusing on the carboxyl group through its localized electronic properties and the other on the substituting groups via Hammett constants and their additivity rule. Our present results clearly exhibit that with the linear models built from the singly substituted species, one can accurately predict the pK(a) values for the doubly and triply substituted species with both of these two approaches. The predictions from these approaches are consistent with each other and agree well with the experimental data. These intrinsically different approaches are the two manifestations of the same molecular acidity property, both valid and complementary to each other. PMID:22082252

Huang, Ying; Liu, Lianghong; Liu, Wanhui; Liu, Shaogang; Liu, Shubin

2011-12-02

360

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

Science.gov (United States)

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.

C. Preferencial, Kala; P. Aruna, Priya; John Thiruvadigal, D.

2013-05-01

 
 
 
 
361

Helical polyacetylene-a conductive material for self-contained molecular electronic device use  

International Nuclear Information System (INIS)

We describe mono-substituted helical poly(phenyl)acetylene, a structural variation of polyacetylene that may overcome its problem: the lack of chemical stability. Helical polyacetylene shows an intrinsic stiff rod structure, which can be enhanced by the choice of suitable side groups. The structure looks like a narrow spiral with a conjugated electron system, covered by attached side groups spiralling in the opposite sense. We consider this unique material as a prototype for molecular electronic device use. It provides the electronic function, mechanical packaging and electrical insulation through a variety of side groups and exhibits useful self-assembly properties. We provide evidence that such materials, in many variations, show the expected overall structure, can be synthesized through living polymerization (which is necessary for the fabrication of monomers by monomer controlled structures), do show enhanced chemical stability, are amenable to self-assembly, may be deposited in an oriented fashion and do show electrical conductivity.

2008-12-17

362

Molecular-frame photoelectron and electron-frame photoion angular distributions and their interrelation  

Energy Technology Data Exchange (ETDEWEB)

General expressions for molecular frame photoelectron angular distributions (MFPAD) and the angular distributions of the recoil fragments relative to the electron emission direction, called 'the electron frame photoion angular distribution' (EFPAD), are analysed within the dipole approximation. We describe the projection methods as a tool to extract the maximum amount of information about MFPAD and EFPAD recorded by photoelectron-photoion coincidence momentum spectroscopy, using the N 1s photoionization of NO at 412 eV as a specific example. Via a simulation of an experiment on EFPAD with electron detection in only two directions, we demonstrate the usefulness of the EFPAD and how to obtain full information on the EFPAD and MFPAD from such a restricted measurement of the EFPAD.

Liu, X-J [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan); Lucchese, R R [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan); Grum-Grzhimailo, A N [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan); Morishita, Y [National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8568, Japan (Japan); Saito, N [National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8568, Japan (Japan); Pruemper, G [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan); Ueda, K [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan)

2007-02-14

363

Molecular-frame photoelectron and electron-frame photoion angular distributions and their interrelation  

International Nuclear Information System (INIS)

General expressions for molecular frame photoelectron angular distributions (MFPAD) and the angular distributions of the recoil fragments relative to the electron emission direction, called 'the electron frame photoion angular distribution' (EFPAD), are analysed within the dipole approximation. We describe the projection methods as a tool to extract the maximum amount of information about MFPAD and EFPAD recorded by photoelectron-photoion coincidence momentum spectroscopy, using the N 1s photoionization of NO at 412 eV as a specific example. Via a simulation of an experiment on EFPAD with electron detection in only two directions, we demonstrate the usefulness of the EFPAD and how to obtain full information on the EFPAD and MFPAD from such a restricted measurement of the EFPAD.

2007-02-14

364

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

International Nuclear Information System (INIS)

[en] 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

365

Molecular orbital view of the electronic coupling between two metal nanoparticles  

Energy Technology Data Exchange (ETDEWEB)

The electronic coupling between metal nanoparticles is responsible for intriguing new phenomena observed when the particles are near touching contact, which is exemplified by recent investigations of nanoparticle dimers. However, little is known about the role of the molecular orbitals of the nanoparticle dimers. The expectation is that the physics and chemistry of the system must be reflected in the orbitals that control the bonding at touching contact. This expectation is borne out in the present investigation in which we present a comprehensive theoretical study based on density-functional theory of the electronic coupling between two silver nanoparticles. We explain our findings by studying the molecular orbitals of the dimers as a function of the separation and relative orientation between the nanoparticles. We show that as the nanoparticles approach each other a bond-forming step takes place, and that the strength of the hybridization is a key element to determine various properties of the system. We find that the relative orientation between the nanoparticles plays an important role in determining the strength of the coupling which can be visualized by the spatial distribution of the highest occupied molecular orbitals. Moreover, the strength of the coupling will in turn determine the ease of their transition to the nonlinear dielectric-response regime. This effect allows for the tunability of the electronic coupling and magnetic moment of the dimer. Our findings are essential for understanding and tailoring desired physical and chemical properties of closely aggregated nanoparticles relevant for applications such as surface-enhanced Raman scattering and quantum transport in molecular devices.

Troparevsky, Claudia [University of Tennessee, Knoxville (UTK); Zhao, Ke [University of Tennessee, Knoxville (UTK); Xiao, Di [ORNL; Eguiluz, Adolfo G [ORNL; Zhang, Zhenyu [ORNL

2010-01-01

366

Molecular orbital view of the electronic coupling between two metal nanoparticles  

Science.gov (United States)

The electronic coupling between metal nanoparticles is responsible for intriguing new phenomena observed when the particles are near touching contact, which is exemplified by recent investigations of nanoparticle dimers. However, little is known about the role of the molecular orbitals of the nanoparticle dimers. The expectation is that the physics and chemistry of the system must be reflected in the orbitals that control the bonding at touching contact. This expectation is borne out in the present investigation in which we present a comprehensive theoretical study based on density-functional theory of the electronic coupling between two silver nanoparticles. We explain our findings by studying the molecular orbitals of the dimers as a function of the separation and relative orientation between the nanoparticles. We show that as the nanoparticles approach each other a bond-forming step takes place, and that the strength of the hybridization is a key element to determine various properties of the system. We find that the relative orientation between the nanoparticles plays an important role in determining the strength of the coupling which can be visualized by the spatial distribution of the highest occupied molecular orbitals. Moreover, the strength of the coupling will in turn determine the ease of their transition to the nonlinear dielectric-response regime. This effect allows for the tunability of the electronic coupling and magnetic moment of the dimer. Our findings are essential for understanding and tailoring desired physical and chemical properties of closely aggregated nanoparticles relevant for applications such as surface-enhanced Raman scattering and quantum transport in molecular devices.

Troparevsky, M. Claudia; Zhao, Ke; Xiao, Di; Eguiluz, Adolfo G.; Zhang, Zhenyu

2010-07-01

367

Extremely low-loss rectification methodology for low-power vibration energy harvesters  

Science.gov (United States)

Because of its promise for the generation of wireless systems, energy harvesting technology using smart materials is the focus of significant reported effort. Various techniques and methodologies for increasing power extraction have been tested. One of the key issues with the existing techniques is the use of diodes in the harvesting circuits with a typical voltage drop of 0.7 V. Since most of the smart materials, and other transducers, do not produce large voltage outputs, this voltage drop becomes significant in most applications. Hence, there is a need for designing a rectification method that can convert AC to DC with minimal losses. This paper describes a new mechanical rectification scheme, designed using reed switches, in a full-bridge configuration that shows the capability of working with signals from millivolts to a few hundred volts with extremely low losses. The methodology has been tested for piezoelectric energy harvesters undergoing mechanical excitation.

Tiwari, R.; Ryoo, K.; Schlichting, A.; Garcia, E.

2013-06-01

368

Seebeck rectification enabled by intrinsic thermoelectrical coupling in magnetic tunneling junctions.  

UK PubMed Central (United Kingdom)

An intrinsic thermoelectric coupling effect in the linear response regime of magnetic tunneling junctions (MTJ) is reported. In the dc response, it leads to a nonlinear correction to Ohm's law. Dynamically, it enables a novel Seebeck rectification and second harmonic generation, which apply for a broad frequency range and can be magnetically controlled. A phenomenological model on the footing of the Onsager reciprocal relation and the principle of energy conservation explains very well the experimental results obtained from both dc and frequency-dependent transport measurements performed up to GHz frequencies. Our work refines previous understanding of magnetotransport and microwave rectification in MTJs. It forms a new foundation for utilizing spin caloritronics in high-frequency applications.

Zhang ZH; Gui YS; Fu L; Fan XL; Cao JW; Xue DS; Freitas PP; Houssameddine D; Hemour S; Wu K; Hu CM

2012-07-01

369

Rectification-adapted snake for complex-boundary segmentation in noisy images  

Science.gov (United States)

In this paper, a contour-fitness improved adaptive snake, namely, edge-conducted rectification-adapted snake (ECRA-snake) is proposed for segmenting complex-boundary objects in the noisy image. The ECRA-snake includes a main ingredient called edge-conducted evolution (ECE), where the adaptations of model coefficients can accommodate ECE itself to the characteristics of salient edges for better curve fitting in tracking. Following ECE, a direction-induced rectification evolution (DIRE) will correct boundary-unmatched snake fragments by handling the initial direction and the tensile-force weighting of unqualified snaxels in this snake re-evolution. Simulation results demonstrate that the proposed ECRA-snake can obtain better object-boundary coincidence than the Gradient Vector Flow (GVF) model in segmenting the complex-boundary object from noisy images.

Chan, Din-Yuen; Hsu, Roy C.; Wu, Pang-Hao; Liu, Cheng-Ting

2013-03-01

370

Concentration-gradient-dependent ion current rectification in charged conical nanopores.  

UK PubMed Central (United Kingdom)

Ion current rectification (ICR) in negatively charged conical nanopores is shown to be controlled by the electrolyte concentration gradient depending on the direction of ion diffusion. The degree of ICR is enhanced with the increasing forward concentration difference. An unusual rectification inversion is observed when the concentration gradient is reversely applied. A numerical simulation based on the coupled Poisson and Nernst-Planck (PNP) equations is proposed to solve the ion distribution and ionic flux in the charged and structurally asymmetric nanofluidic channel with diffusive ion flow. Simulation results qualitatively describe the diffusion-induced ICR behavior in conical nanopores suggested by the experimental data. The concentration-gradient-dependent ICR enhancement and inversion is attributed to the cooperation and competition between geometry-induced asymmetric ion transport and the diffusive ion flow. The present study improves our understanding of the ICR in asymmetric nanofluidic channels associated with the ion concentration difference and provides insight into the rectifying biological ion channels.

Cao L; Guo W; Wang Y; Jiang L

2012-01-01

371

Regeneration of spent extractant TBP-diluent by rectification with water vapor  

International Nuclear Information System (INIS)

Laboratory investigations of regeneration of irradiated and so disturbed industrial extractant (30 % TBP in organic solvent) by distillation with superheating water vapor in the periodic mode are carried out. It is shown that distilled extractant recovers fully its hydrodynamic and extraction-reextraction properties. Residue of the rectification is 3-7 % of starting volume and contents practically only TBP. One-stage rectification carrying out with superheated water vapor under rarefaction or with saturated water vapor under atmospheric pressure maintains withdrawal of all extractant and approves to use any solvent. Two-stage method permits to separate the extractant for tributylphosphate and diluent with purification of either of them when boiling temperature of diluent is by 50-70 deg lower of tributylphosphate one

2002-01-01

372

A 0.5-?m-thick polycrystalline silicon Schottky diode with rectification ratio of 106  

International Nuclear Information System (INIS)

Polycrystalline Si films, 0.5-?m thick, were obtained as a result of metal-induced growth by sputtering from a Si target on 25 nm thick Ni prelayers at 525 deg. C. Silicon grew heteroepitaxially on the NiSi2 layer formed due to the reaction between the sputtered Si atoms and Ni. Schottky diodes were fabricated on the Si films by deposition of a Schottky metal on the front surface of the film while Ni disilicide provided an intimate ohmic contact at the back. A Pd/n-Si diode using an n-Si film annealed for 2 h at 700 deg. C in forming gas demonstrated a rectification ratio of 106, while an as-deposited p-Si film provided an Al/p-Si diode with rectification of five orders of magnitude. Schottky barrier properties are briefly discussed.

2002-02-25

373

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

374

Dithiocarbamate Anchoring in Molecular Wire Junctions: A First Principles Study  

CERN Document Server

Recent experimental realization [J. Am. Chem. Soc., 127 (2005) 7328] of various dithiocarbamate self assembly on gold surface opens the possibility for use of dithiocarbamate linkers to anchor molecular wires to gold electrodes. In this paper, we explore this hypothesis computationally. We computed the electron transport properties of 4,4'-bipyridine (BP), 4,4'-bipyridinium-1,1'-bis(carbodithioate) (BPBC), 4-(4'-pyridyl)-peridium-1-carbodithioate (BPC) molecule junctions based on the density functional theory and non-equilibrium Green's functions. We demonstrated that the stronger molecule-electrode coupling associated with the conjugated dithiocarbamate linker broadens transmission resonances near the Fermi energy. The broadening effect along with the extension of the $\\pi$ conjugation from the molecule to the gold electrodes lead to enhanced electrical conductance for BPBC molecule. The conductance enhancement factor is as large as 25 at applied voltage bias 1.0 V. Rectification behavior is predicted for BP...

Li, Z; Li, Zhenyu

2006-01-01

375

Azeotropic Rectification of a Mixture of Silicon Tetrachloride with Trimethylchlorosilane in the Presence of Acetonitrile.  

Science.gov (United States)

Batch and continuous units are described for separating binary azeotropes consisting of SiCl4 plus acetonitrile(CH3CN) (b.p. 49.1C) and (CH3)3SiCl and CH3CN (b.p. 56.5C). The 1st unit consists principally of 3 rectification columns. In the 1st, the low-bo...

T. P. Korablina Y. K. Molokanov M. V. Barinova

1969-01-01

376

Kinetic method of simulation of the multicomponent rectification process of hydrogen isotopes  

International Nuclear Information System (INIS)

Alternative kinetic method for calculation of the rectification process is represented. In accordance with that the system of differential equations of mass transfer via every mixture component is solved. Mass output coefficients needed for mass transfer coefficients determination are calculated using empirical dependences. Equations of the heat distribution correcting the inner flows in column are solved taking into account the evolution of heat due to tritium decay whereof affects on general separation efficiency at high concentrations

2002-01-01

377

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

378

Low temperature rectification for the separation of 85-Kr and 133-Xe from nuclear facilities  

International Nuclear Information System (INIS)

[en] Waste gas from reprocessing plants contains such a large amount of Kr 85 that a separation should be undertaken. Laybold-Heraeus, in collaboration with GfK in Karlsruhe, are at present building an experimental plant to demonstrate Kr 85 separation, first with synthetic gases, by means of low temperature rectification. This process, at the end of a long gas purification line, within which radioactive aerosols and I 129 are also separated, is described. (author)

1978-03-29

379

Effect of thermal rectification on colors of Eucalyptus Saligna and Pinus caribaea Woods  

Directory of Open Access Journals (Sweden)

Full Text Available Eucalyptus saligna and Pinus caribaea var. hondurensis woods underwent a variety of thermal rectification treatments (from 120ºC to 180ºC) to evaluate the effect of heating on their colorimetric properties. The following color parameters were measured: lightness (L), a* coordinate (green-red coordinate), b* coordinate (blue-yellow coordinate), saturation (C), and tonality angle (H). This study demonstrates that thermal rectification can be regarded as a tool for adding value to wood through color modification by heating. Results also suggest that thermal rectification might be a tool for homogenizing wood tonality and reddish color between species. Both tested species have shown very distinct colorimetric behaviors as a function of thermal treatments. The conifer was more resistant to thermal darkening than the hardwood while exposed to temperatures below 160ºC. The green-red coordinate (a*) and the tonality angle (H) tended to be homogenized for both species, as they decreased in eucalyptus, and increased in pinus, as a function of heating. The effect of wood heating on the blue-yellow coordinate (b*), saturation (C), and tonality angle (H) was likely to be opposite between both tested species.

Ana Lúcia Piedade Sodero Martins Pincelli; Luiz Fernando de Moura; José Otávio Brito

2012-01-01

380

Effect of thermal rectification on colors of Eucalyptus Saligna and Pinus caribaea Woods  

Scientific Electronic Library Online (English)

Full Text Available Abstract in english Eucalyptus saligna and Pinus caribaea var. hondurensis woods underwent a variety of thermal rectification treatments (from 120ºC to 180ºC) to evaluate the effect of heating on their colorimetric properties. The following color parameters were measured: lightness (L), a* coordinate (green-red coordinate), b* coordinate (blue-yellow coordinate), saturation (C), and tonality angle (H). This study demonstrates that thermal rectification can be regarded as a tool for adding (more) value to wood through color modification by heating. Results also suggest that thermal rectification might be a tool for homogenizing wood tonality and reddish color between species. Both tested species have shown very distinct colorimetric behaviors as a function of thermal treatments. The conifer was more resistant to thermal darkening than the hardwood while exposed to temperatures below 160ºC. The green-red coordinate (a*) and the tonality angle (H) tended to be homogenized for both species, as they decreased in eucalyptus, and increased in pinus, as a function of heating. The effect of wood heating on the blue-yellow coordinate (b*), saturation (C), and tonality angle (H) was likely to be opposite between both tested species.

Sodero Martins Pincelli, Ana Lúcia Piedade; de Moura, Luiz Fernando; Brito, José Otávio

2012-01-01

 
 
 
 
381

Determining molecular structures and conformations directly from electron diffraction using a genetic algorithm.  

UK PubMed Central (United Kingdom)

A global optimization strategy, based upon application of a genetic algorithm (GA), is demonstrated as an approach for determining the structures of molecules possessing significant conformational flexibility directly from gas-phase electron diffraction data. In contrast to the common approach to molecular structure determination, based on trial-and-error assessment of structures available from quantum chemical calculations, the GA approach described here does not require expensive quantum mechanical calculations or manual searching of the potential energy surface of the sample molecule, relying instead upon simple comparison between the experimental and calculated diffraction pattern derived from a proposed trial molecular structure. Structures as complex as all-trans retinal and p-coumaric acid, both important chromophores in photosensing processes, may be determined by this approach. In the examples presented here, we find that the GA approach can determine the correct conformation of a flexible molecule described by 11 independent torsion angles. We also demonstrate applications to samples comprising a mixture of two distinct molecular conformations. With these results we conclude that applications of this approach are very promising in elucidating the structures of large molecules directly from electron diffraction data.

Habershon S; Zewail AH

2006-02-01

382

Analysis of the electronic contribution to the molecular vibrational magnetic moment  

Energy Technology Data Exchange (ETDEWEB)

The electron current contributions g{sub zz,el}{sup vib} and g{sub zz,el}{sup rot} to the vibrational and rotational g-factors of the H{sub 3}{sup +} molecule are calculated by the gauge-invariant atomic orbital method. The electron current contribution to the vibrational g-factor is shown to consist of two parts of opposite signs: the negative one, corresponding to the motion of the electron shell caused by the rotational motion of the nuclei along small circles with the angular frequency of the degenerate vibration, and the positive one, corresponding to the electron motion caused by a deformation wave running around the molecular contour in the opposite direction. The absolute value of the first part increases, and that of the second one decreases, with an increase of the effective charge {zeta} of 1s atomic orbitals. In contrast to the definitely negative value g{sub zz,el}{sup rot}, the electronic contribution to the vibrational g-factor g{sub zz,el}{sup vib} changes its sign as the effective charges {zeta} of atomic orbitals increase; it is positive when {zeta} < 1.26, and negative when {zeta} < 1.26. For {zeta} = 1.07, it was found that g{sub zz,el}{sup rot} = -0.0198 (which agrees with the calculations of other authors) and g{sub zz,el}{sup vib} = +0.095. 8 refs., 3 figs., 3 tabs.

Braun, P.A.; Volodicheva, M.I.; Rebane, T.K. [St. Petersburg State Univ. (Russian Federation)

1995-03-01

383

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

384

Electron transfer in dye-sensitised semiconductors modified with molecular cobalt catalysts: photoreduction of aqueous protons.  

UK PubMed Central (United Kingdom)

A visible-light driven H(2) evolution system comprising of a Ru(II) dye (RuP) and Co(III) proton reduction catalysts (CoP) immobilised on TiO(2) nanoparticles and mesoporous films is presented. The heterogeneous system evolves H(2) efficiently during visible-light irradiation in a pH-neutral aqueous solution at 25 °C in the presence of a hole scavenger. Photodegradation of the self-assembled system occurs at the ligand framework of CoP, which can be readily repaired by addition of fresh ligand, resulting in turnover numbers above 300 mol H(2) (mol CoP)(-1) and above 200,000 mol H(2) (mol?TiO(2) nanoparticles)(-1) in water. Our studies support that a molecular Co species, rather than metallic Co or a Co-oxide precipitate, is responsible for H(2) formation on TiO(2). Electron transfer in this system was studied by transient absorption spectroscopy and time-correlated single photon counting techniques. Essentially quantitative electron injection takes place from RuP into TiO(2) in approximately 180 ps. Thereby, upon dye regeneration by the sacrificial electron donor, a long-lived TiO(2) conduction band electron is formed with a half-lifetime of approximately 0.8 s. Electron transfer from the TiO(2) conduction band to the CoP catalysts occurs quantitatively on a 10 ?s timescale and is about a hundred times faster than charge-recombination with the oxidised RuP. This study provides a benchmark for future investigations in photocatalytic fuel generation with molecular catalysts integrated in semiconductors.

Lakadamyali F; Reynal A; Kato M; Durrant JR; Reisner E

2012-11-01

385

Electron transfer in dye-sensitised semiconductors modified with molecular cobalt catalysts: photoreduction of aqueous protons.  

Science.gov (United States)

A visible-light driven H(2) evolution system comprising of a Ru(II) dye (RuP) and Co(III) proton reduction catalysts (CoP) immobilised on TiO(2) nanoparticles and mesoporous films is presented. The heterogeneous system evolves H(2) efficiently during visible-light irradiation in a pH-neutral aqueous solution at 25 °C in the presence of a hole scavenger. Photodegradation of the self-assembled system occurs at the ligand framework of CoP, which can be readily repaired by addition of fresh ligand, resulting in turnover numbers above 300 mol H(2) (mol CoP)(-1) and above 200,000 mol H(2) (mol?TiO(2) nanoparticles)(-1) in water. Our studies support that a molecular Co species, rather than metallic Co or a Co-oxide precipitate, is responsible for H(2) formation on TiO(2). Electron transfer in this system was studied by transient absorption spectroscopy and time-correlated single photon counting techniques. Essentially quantitative electron injection takes place from RuP into TiO(2) in approximately 180 ps. Thereby, upon dye regeneration by the sacrificial electron donor, a long-lived TiO(2) conduction band electron is formed with a half-lifetime of approximately 0.8 s. Electron transfer from the TiO(2) conduction band to the CoP catalysts occurs quantitatively on a 10 ?s timescale and is about a hundred times faster than charge-recombination with the oxidised RuP. This study provides a benchmark for future investigations in photocatalytic fuel generation with molecular catalysts integrated in semiconductors. PMID:23033059

Lakadamyali, Fezile; Reynal, Anna; Kato, Masaru; Durrant, James R; Reisner, Erwin

2012-10-02

386

Tailoring electronic states of a single molecule using adamantane-based molecular tripods.  

UK PubMed Central (United Kingdom)

Adsorption structures and electronic states of molecular tripods, having a Br atom (BATT) and a ferrocene derivative (Ferrocene-ATT) at the head part of the adamantane-based trithiolate, adsorbed on Au(111) have been investigated using low temperature scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). We found that BATT and Ferrocene-ATT form self-assembled monolayers (SAMs), and their orderings are identical to one another, which suggests that the adsorption structure of adamantane-based molecular tripods is independent of the type of functional substituent attached to the head part. The electronic states originated from the ferrocene group were confirmed in the STS spectrum of Ferrocene-ATT whereas those are absent in the BATT spectrum. We note that the ferrocene part has few interactions with the Au substrate owing not only to the upright geometry of Ferrocene-ATT but also to the insulative properties of the adamantane base. The STS mapping revealed the spatial distribution of the electronic state of Ferrocene-ATT.

Katano S; Kim Y; Kitagawa T; Kawai M

2013-09-01

387

Long-range interfacial electron transfer of metalloproteins based on molecular wiring assemblies.  

Science.gov (United States)

We address some physical features associated with long-range interfacial electron transfer (ET) of metalloproteins in both electrochemical and electrochemical scanning tunneling microscopy (ECSTM) configurations, which offer a brief foundation for understanding of the ET mechanisms. These features are illustrated experimentally by new developments of two systems with the blue copper protein azurin and enzyme nitrite reductase as model metalloproteins. Azurin and nitrite reductase were assembled on Au(111) surfaces by molecular wiring to establish effective electronic coupling between the redox centers in the proteins and the electrode surface for ET and biological electrocatalysis. With such assemblies, interfacial ET proceeds through chemically defined and well oriented sites and parallels biological ET. In the case of azurin, the ET properties can be characterized comprehensively and even down to the single-molecule level with direct observation of redox-gated electron tunnelling resonance. Molecular wiring using a pi-conjugated thiol is suitable for assembling monolayers of the enzyme with catalytic activity well-retained. The catalytic mechanism involves multiple-ET steps including both intramolecular and interfacial processes. Interestingly, ET appears to exhibit a substrate-gated pattern observed preliminarily in both voltammetry and ECSTM. PMID:16512372

Chi, Qijin; Zhang, Jingdong; Jensen, Palle S; Christensen, Hans E M; Ulstrup, Jens

2006-01-01

388

Cross section for production of excited hydrogen atoms following dissociative excitation of molecular hydrogen by electron impact  

International Nuclear Information System (INIS)

[en] For the purpose of investigating molecular hydrogen present in plasmas, the production cross section of excited hydrogen atoms due to dissociative excitation of molecular hydrogen by electron collisions has been estimated from the emission cross sections of Lyman and Balmer lines. (author)

1990-01-01

389

Artificial light-harvesting antennae: electronic energy transfer by way of molecular funnels.  

UK PubMed Central (United Kingdom)

Electronic energy transfer (EET) plays a critical role in many biological processes and is used by nature to direct energy to a site where chemical reactions need to be initiated. Such EET can occur over large distances and can involve many individual molecules of identical, similar or disparate chemical identity. Advances in spectroscopy and data processing have allowed the rates of EET to be measured on extremely fast timescales such that improved mechanistic insight becomes feasible. At the same time, highly sophisticated synthetic operations have been devised that facilitate the isolation and purification of elaborate multi-component molecular arrays. A key feature of these arrays concerns the logical positioning of individual units in a way that favours directed EET along the molecular axis or along some other preferred pathway. The availability of these novel molecular materials allows close examination of popular theoretical models and paves the way for the development of advanced molecular sensors, artificial light harvesters, fluorescent labels and sensitizers. Of particular interest is the spectacular growth in the application of boron dipyrromethene dyes as basic reagents in such artificial photon collectors and these compounds have dominated the market in recent years because of their synthetic versatility and valuable photophysical properties. In this article, recent developments in the field are highlighted in terms of synthesis and subsequent spectroscopic exploration.

Ziessel R; Harriman A

2011-01-01

390

Self-assembling monolayers of helical oligopeptides with applications in molecular electronics  

CERN Multimedia

prepared. Transformation of the two (Trt)Cys residues of the resin-bound peptide to the intramolecular disulphide by iodine was achieved in acetonitrile but not in DMF. CD suggested that the conformation of this peptide was a mixture of helix and random coil. Films of the peptide-disulphide and the peptide-dithiol adsorbed from protic solvents were characterised as multilayers by ellipsometry. However CV and ellipsometry showed that a monolayer was successfully prepared from acetonitrile. Future targets for improving and extending this method to form monolayers of linked disulphides are presented. The aim of this project was to develop a generic method of preparing a 'molecular architecture' containing functional groups on a surface at predetermined relative positions several nm apart. This would be of great utility in molecular electronics, chemical sensors and other fields. It was proposed that such an architecture could be prepared on gold using linked, helical oligopeptides that contained the components o...

Strong, A E

1997-01-01

391

Intramolecular electronic interactions in conjugated ferrocene-pi-extended-tetrathiafulvalene donor-pi-donor molecular hybrids  

Science.gov (United States)

The synthesis of new hybrid ferrocene and pi-extended tetrathiafulvalene (TTF) donor(1)-pi-donor(2) molecular assemblies 16a-c has been carried out by a Wittig-Horner reaction of the respective phosphonate esters 15a-c with 2-(2-ferrocenylvinyl)-9, 10-anthraquinone (18) prepared by olefination of ferrocenecarboxaldehyde (14) and the anthraquinone phosphonium salt 17. Electrochemical studies show that the D(1)-pi-D(2) (D = donor) molecular assemblies 16a-c essentially retain the redox characteristics of both ferrocene and the pi-extended TTF components and the effects of solvent, temperature, scan rate, and working electrode are significant. Most importantly, pronounced intramolecular electronic interactions between the two donor moieties were observed by cyclic voltammetry and Osteryoung square wave voltammetry in both the ground and charged states. Semiempirical calculations support the electrochemical observations. PMID:11149856

Liu; Perez; Martin; Echegoyen

2000-12-29

392

Intramolecular electronic interactions in conjugated ferrocene-pi-extended-tetrathiafulvalene donor-pi-donor molecular hybrids  

UK PubMed Central (United Kingdom)

The synthesis of new hybrid ferrocene and pi-extended tetrathiafulvalene (TTF) donor(1)-pi-donor(2) molecular assemblies 16a-c has been carried out by a Wittig-Horner reaction of the respective phosphonate esters 15a-c with 2-(2-ferrocenylvinyl)-9, 10-anthraquinone (18) prepared by olefination of ferrocenecarboxaldehyde (14) and the anthraquinone phosphonium salt 17. Electrochemical studies show that the D(1)-pi-D(2) (D = donor) molecular assemblies 16a-c essentially retain the redox characteristics of both ferrocene and the pi-extended TTF components and the effects of solvent, temperature, scan rate, and working electrode are significant. Most importantly, pronounced intramolecular electronic interactions between the two donor moieties were observed by cyclic voltammetry and Osteryoung square wave voltammetry in both the ground and charged states. Semiempirical calculations support the electrochemical observations.

Liu SG; Perez I I; Martin N; Echegoyen L

2000-12-01

393

Impact of derivatization on electron transmission through dithienylethene-based photoswitches in molecular junctions.  

UK PubMed Central (United Kingdom)

We report a combined Non-Equilibrium Green's Function - Density Functional Theory study of molecular junctions made of photochromic diarylethenes between gold electrodes. The impact of derivatization of the molecule on the transmission spectrum is assessed by introducing: (i) substituents on the diarylethene core; and (ii) linker substituents between the gold surface and the diarylethene. We illustrate that substituents on the core shift considerably the HOMO/LUMO level energies in gas phase but do not change the I-V characteristics of the molecular junctions; this behaviour has been rationalized by establishing links between the transmission spectrum and interfacial electronic reorganization upon chemisorption. In contrast, the different linker substituents under study modulate the conductivity of the junction by changing the degree of orbital hybridization with the metallic electrodes and the degree of orbital polarization.

Van Dyck C; Geskin V; Kronemeijer AJ; de Leeuw DM; Cornil J

2013-03-01

394

Impact of derivatization on electron transmission through dithienylethene-based photoswitches in molecular junctions.  

Science.gov (United States)

We report a combined Non-Equilibrium Green's Function - Density Functional Theory study of molecular junctions made of photochromic diarylethenes between gold electrodes. The impact of derivatization of the molecule on the transmission spectrum is assessed by introducing: (i) substituents on the diarylethene core; and (ii) linker substituents between the gold surface and the diarylethene. We illustrate that substituents on the core shift considerably the HOMO/LUMO level energies in gas phase but do not change the I-V characteristics of the molecular junctions; this behaviour has been rationalized by establishing links between the transmission spectrum and interfacial electronic reorganization upon chemisorption. In contrast, the different linker substituents under study modulate the conductivity of the junction by changing the degree of orbital hybridization with the metallic electrodes and the degree of orbital polarization. PMID:23416894

Van Dyck, Colin; Geskin, Victor; Kronemeijer, Auke J; de Leeuw, Dago M; Cornil, Jérôme

2013-03-28

395

Molecular structure of trimethylphosphine-boron triiodide as studied by gas-phase electron diffraction  

Energy Technology Data Exchange (ETDEWEB)

The molecular structure of trimethylphosphine-boron triiodide (CH/sub 3/)/sub 3/P.BI/sub 3/ has been determined by means of gas-electron diffraction. The molecular parameters and their uncertainties were r sub(g)(B-I) = 2.233 +- 0.003 A, r sub(g)(P-B) = 1.947 +- 0.011 A, r sub(g)(C-P) = 1.809 +- 0.003 A, r sub(g)(C-H) = 1.094 +- 0.008 A,

Iijima, Kinya; Koshimizu, Eiichi; Shibata, Shuzo (Shizuoka Univ. (Japan). Faculty of Science)

1982-08-01

396

Molecular geometry and predissociation times in the A1A'' electronic state of HCN and DCN  

International Nuclear Information System (INIS)

Merging of the vibrational structures of the A and B electronic states of HCN and DCN into a single A1A'' state, and new measurements of rotational fine structure between 1600 and 1950 A, have made it possible to attempt refinement of the molecular geometry in the A state; an attempt based on rotational constants of HCN, DCN, D13CN and DC15N will be described. The estimated A-state lifetimes of the DCN's and their variations with vibrational quantum numbers are presented. These lifetimes range from 120 to 0.4 ps. 2 references

1985-01-01

397

A molecular switch and electronic circuit modulate catalase activity in catalase-peroxidases.  

UK PubMed Central (United Kingdom)

The catalase reaction of catalase-peroxidases involves catalase-specific features built into a peroxidase core. An arginine, 20 A from the active-site heme, acts as a molecular switch moving between two conformations, one that activates heme oxidation and one that activates oxoferryl heme reduction by H(2)O(2), facilitating the catalatic pathway in a peroxidase. The influence of the arginine is imparted to the heme through its association with or dissociation from a tyrosinate that modulates reactivity through a Met-Tyr-Trp crosslinked adduct and a pi electron interaction of the heme with the adduct Trp.

Carpena X; Wiseman B; Deemagarn T; Singh R; Switala J; Ivancich A; Fita I; Loewen PC

2005-12-01

398

A molecular switch and electronic circuit modulate catalase activity in catalase-peroxidases.  

Science.gov (United States)

The catalase reaction of catalase-peroxidases involves catalase-specific features built into a peroxidase core. An arginine, 20 A from the active-site heme, acts as a molecular switch moving between two conformations, one that activates heme oxidation and one that activates oxoferryl heme reduction by H(2)O(2), facilitating the catalatic pathway in a peroxidase. The influence of the arginine is imparted to the heme through its association with or dissociation from a tyrosinate that modulates reactivity through a Met-Tyr-Trp crosslinked adduct and a pi electron interaction of the heme with the adduct Trp. PMID:16211084

Carpena, Xavier; Wiseman, Ben; Deemagarn, Taweewat; Singh, Rahul; Switala, Jacek; Ivancich, Anabella; Fita, Ignacio; Loewen, Peter C

2005-12-01

399

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

Energy Technology Data Exchange (ETDEWEB)

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.

Zhang Yujuan; Wang Cong [LCP, Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China); Zhang Ping [LCP, Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China); Center for Applied Physics and Technology, Peking University, Beijing 100871 (China)

2012-11-15

400

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; Azmi Gençten

2013-01-01

 
 
 
 
401

Limit on electron neutrino mass from observation of the beta decay of molecular tritium  

Energy Technology Data Exchange (ETDEWEB)

We report the most sensitive upper limit set on the mass of the electron antineutrino. The upper limit of 9.4 eV (95% confidence level) was obtained from a study of the shape of the beta decay spectrum of free molecular tritium. Achieving such a level of sensitivity required precise determinations of all processes that modify the shape of the observed spectrum. This result is in clear disagreement with a reported value for the mass of 26(5) eV. 30 refs., 3 figs., 2 tabs.

Wilkerson, J.F.; Bowles, T.J.; Friar, J.L.; Robertson, R.G.H.; Stephenson, G.J. Jr.; Wark, D.L. (Los Alamos National Lab., NM (USA)); Knapp, D.A. (Lawrence Livermore National Lab., CA (USA))

1990-01-01

402

Molecular fingerprints in the electronic properties of crystalline organic semiconductors : From experiment to theory  

DEFF Research Database (Denmark)

By comparing photoemission spectroscopy with a non-perturbative dynamical mean field theory extension to many-body ab initio calculations, we show in the prominent case of pentacene crystals that an excellent agreement with experiment for the bandwidth, dispersion and lifetime of the hole carrier bands can be achieved in organic semiconductors provided that one properly accounts for the coupling to molecular vibrational modes and the presence of disorder. Our findings rationalize the growing experimental evidence that even the best band structure theories based on a many-body treatment of electronic interactions cannot reproduce the experimental photoemission data in this important class of materials.

Ciuchi, S.; Hatch, R.C.

2012-01-01

403

Ab initio study of isomerism in molecular ions Li2AB+ with 10 valence electrons  

International Nuclear Information System (INIS)

Ab initio calculations of surfaces of Li2AB+ molecular ion potential energy with biatomic anions AB- with 10 valence electrons have been made in the framework of approximations MP2/6-31G1/HF/6-31G*+ZPE(HF/6-31G*) and MP4SDTQ/631G*//MP2/6-31G*+ZPE(MP2/6-31G*). Influence of electron correlation on the accuracy of calculations of their structural and vibrational characteristics is studied. The following most favourable structures have been found: linear for Li2BO+, Li2CN+, and bent one for Li2BS+, with cations coordinated at different anion atoms; onium one for AlOLi2+, AlSLi2+, SiNLi2+ and SiPLi2+ with both cations at electronegative atom of anion

1997-01-01

404

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

Energy Technology Data Exchange (ETDEWEB)

We present an experimental study on 500-3000 eV energy electron irradiation of ammonia ice at 20 K. While molecular nitrogen and diazene (N{sub 2}H{sub 2}) were detected during post-irradiation thermal desorption no appreciable traces of hydrazine (N{sub 2}H{sub 4}) 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: Black-Right-Pointing-Pointer Experimental study on 500-3000 eV electron irradiation of ammonia ice at 20 K. Black-Right-Pointing-Pointer Observation of nitrogen and diazene during post-irradiation thermal desorption. Black-Right-Pointing-Pointer No appreciable traces of hydrazine (N{sub 2}H{sub 4}).

Barberio, M., E-mail: marianna.barberio@fis.unical.it [Dipartimento di Fisica, Universita della Calabria, Ponte Bucci Cubo 31 C, Rende (Italy); Barone, P., E-mail: pasquale.barone@fis.unical.it [Dipartimento di Fisica, Universita della Calabria, Ponte Bucci Cubo 31 C, Rende (Italy); Vasta, R., E-mail: vasta@fis.unical.it [Dipartimento di Fisica, Universita della Calabria, Ponte Bucci Cubo 31 C, Rende (Italy); Istituto di Scienze Neurologiche-Centro Nazionale delle Ricerche-Germaneto, 88100, Catanzaro (Italy); Manico, G., E-mail: gmanico@dmfci.unict.it [Dipartimento di Fisica e Astronomia, Universita di Catania, Via Santa Sofia 64, Catania (Italy); Xu, F., E-mail: fang.xu@fis.unical.it [Dipartimento di Fisica, Universita della Calabria, Ponte Bucci Cubo 31 C, Rende (Italy)

2012-06-01

405

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

406

The McClelland approximation and the distribution of ?-electron molecular orbital energy levels  

Directory of Open Access Journals (Sweden)

Full Text Available The total ?-electron energy E of a conjugated hydrocarbon with n carbon atoms and m carbon–carbon bonds can be approximately calculated by means of the McClelland formula E = g SQRT(2mr), where g is an empirical ?tting constant, g ? 0.9. It was claimed that the good quality of the McClelland approximation is a consequence of the fact that the ?-electron molecular orbital energy levels are distributed in a nearly uniform manner. It will now be shown that the McClelland approximation does not depend on the nature of the distribution of energy levels, i.e., that it is compatible with a large variety of such distributions.

IVAN GUTMAN

2007-01-01

407

Hilbert-space partitioning of the molecular one-electron density matrix with orthogonal projectors  

CERN Document Server

A double-atom partitioning of the molecular one-electron density matrix is used to describe atoms and bonds. All calculations are performed in Hilbert space. The concept of atomic weight functions (familiar from Hirshfeld analysis of the electron density) is extended to atomic weight matrices. These are constructed to be orthogonal projection operators on atomic subspaces, which has significant advantages in the interpretation of the bond contributions. In close analogy to the iterative Hirshfeld procedure, self-consistency is built in at the level of atomic charges and occupancies. The method is applied to a test set of about 67 molecules, representing various types of chemical binding. A close correlation is observed between the atomic charges and the Hirshfeld-I atomic charges.

Vanfleteren, Diederik; Bultinck, Patrick; Ayers, Paul W; Waroquier, Michel; 10.1063/1.3521493

2011-01-01

408

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

409

Electronic structure and magnetic properties of a molecular octanuclear chromium-based ring.  

UK PubMed Central (United Kingdom)

A comprehensive study of electronic and magnetic properties of Cr8F8Piv16 (HPiv = pivalic acid, trimethyl acetic acid) molecular ring is presented. The total, local and orbital projected density of states are calculated by the first principle density functional theory calculations using the package SIESTA. The original molecule has been approximated by replacing the pivallic groups by H atoms (hydrogen saturation). Electron density, deformation density, electrostatic potential and spin density maps are analyzed and compared with experiment for the first time. Magnetic properties are investigated in detail. Magnetic moments are calculated using two different approaches: the Mulliken one and integration of muffin-tin sphere with a given radius. Different magnetic configurations (ferromagnetic, antiferromagnetic and many more with randomly distributed spins up and down) are considered to extract exchange interaction parameter J and check the stability of its estimate.

Slusarski T; Brzostowski B; Tomecka D; Kamieniarz G

2011-10-01

410

Electronic structure and magnetic properties of a molecular octanuclear chromium-based ring.  

Science.gov (United States)

A comprehensive study of electronic and magnetic properties of Cr8F8Piv16 (HPiv = pivalic acid, trimethyl acetic acid) molecular ring is presented. The total, local and orbital projected density of states are calculated by the first principle density functional theory calculations using the package SIESTA. The original molecule has been approximated by replacing the pivallic groups by H atoms (hydrogen saturation). Electron density, deformation density, electrostatic potential and spin density maps are analyzed and compared with experiment for the first time. Magnetic properties are investigated in detail. Magnetic moments are calculated using two different approaches: the Mulliken one and integration of muffin-tin sphere with a given radius. Different magnetic configurations (ferromagnetic, antiferromagnetic and many more with randomly distributed spins up and down) are considered to extract exchange interaction parameter J and check the stability of its estimate. PMID:22400306

Slusarski, T; Brzostowski, B; Tomecka, D; Kamieniarz, G

2011-10-01

411

Differential cross section for molecular ionization by electron impact in the adiabatic approximation  

Energy Technology Data Exchange (ETDEWEB)

Molecular ionization by electron impact is examined in the Born-Oppenheimer approximation where the rotational and vibrational motions of the nuclei are considered separable. Expressions for the differential cross section, applicable to an exact treatment of the adiabatic electronic wave functions, are derived in terms of a momentum-transferred summation for three levels of experimental resolution, spatially unpolarized, spatially unpolarized and rotationally unresolved, and spatially unpolarized and rotationally and vibrationally unresolved. Several possible advantages of a momentum-transferred summation relative to a partial-wave summation are discussed. Most importantly, the expected relatively rapid convergence of the momentum-transferred summation effectively reduces the number of transition matrix elements which must be calculated. Additionally, the momentum-transferred summation involves an ''incoherent'' summation which, in general, is more easily computed. Lastly, we present explicit expressions for the transition probabilities in the plane-wave and distorted-wave Born approximations.

Zurales, R.W.; Lucchese, R.R.

1987-04-01

412

A molecular mechanism of the energetic coupling of a sequence of electron transfer reactions to endergonic reactions.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A molecular mechanism of the energetic coupling of a sequence of electron transfer reactions to endergonic reactions is proposed and discussed from a physical point of view. The scheme represents a synthesis of concepts of electron transfer by tunneling and the conformational and chemiosmotic aspect...

Cartling, B; Ehrenberg, A

413

Calculation of the electronic stopping cross-sections of compounds for low energy protons by using molecular orbitals  

Energy Technology Data Exchange (ETDEWEB)

The modified Firsov model has been applied to the calculation of the electronic stopping cross-section of compounds for low energy protons by using molecular orbitals. We used the Symmetry Adapted Linear Combination of Atomic Orbitals representation of molecular orbitals, instead of Floating Spherical Gaussian Orbitals. We used Gaussian and Slater type orbitals as a basis set of atomic orbitals. By applying this method, the electronic stopping cross-sections of compounds have been calculated by considering compounds as a whole, without separating core and bond orbitals of compounds and the concept of molecular fragments.

Tufan, Mustafa Cagatay [European Commission, Joint Research Centre, Institute for Transuranium Elements, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany) and Ondokuz Mayis University, Faculty of Arts and Sciences, Physics Department, 55139 Samsun (Turkey)]. E-mail: Mustafa.tufan@cec.eu.int; Guemues, Hasan [Ondokuz Mayis University, Faculty of Arts and Sciences, Physics Department, 55139 Samsun (Turkey); Kabadayi, Onder [Giresun University, Faculty of Arts and Sciences, Physics Department, 28100 Giresun (Turkey)

2007-03-15

414

Calculation of the electronic stopping cross-sections of compounds for low energy protons by using molecular orbitals  

International Nuclear Information System (INIS)

[en] The modified Firsov model has been applied to the calculation of the electronic stopping cross-section of compounds for low energy protons by using molecular orbitals. We used the Symmetry Adapted Linear Combination of Atomic Orbitals representation of molecular orbitals, instead of Floating Spherical Gaussian Orbitals. We used Gaussian and Slater type orbitals as a basis set of atomic orbitals. By applying this method, the electronic stopping cross-sections of compounds have been calculated by considering compounds as a whole, without separating core and bond orbitals of compounds and the concept of molecular fragments

2007-01-01

415

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 (C3 to C8), 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

416

Visualization and interpretation of attosecond electron dynamics in laser-driven hydrogen molecular ion using Bohmian trajectories.  

Science.gov (United States)

We analyze the attosecond electron dynamics in hydrogen molecular ion driven by an external intense laser field using the Bohmian trajectories. To this end, we employ a one-dimensional model of the molecular ion in which the motion of the protons is frozen. The Bohmian trajectories clearly visualize the electron transfer between the two protons in the field and, in particular, confirm the recently predicted attosecond transient localization of the electron at one of the p