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1

Rectification in donor-acceptor molecular junctions  

International Nuclear Information System (INIS)

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

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

Molecular rectification in triangularly shaped graphene nanoribbons.  

Science.gov (United States)

We present a theoretical study of electron transport in tailored zigzag graphene nanoribbons (ZGNRs) with triangular structure using density functional theory together with the nonequilibrium Green's function formalism. We find significant rectification with a favorite electron transfer direction from the vertex to the right edge. The triangular ZGNR connecting to the electrode with one thiol group at each terminal shows an average rectification ratio of 8.4 over the bias range from -1.0 to 1.0 V. This asymmetric electron transport property originates from nearly zero band gap of triangular ZGNR under negative bias, whereas a band gap opens under positive bias. When the molecule is connected to the electrode by multithiol groups, the current is enhanced due to strong interfacial coupling; however, the rectification ratio decreases. The simulation results indicate that the unique electronic states of triangular ZGNR are responsible for rectification, rather than the asymmetric anchoring groups. PMID:23081769

Liu, Hongmei; Wang, Hongbo; Zhao, Jianwei; Kiguchi, Manabu

2013-02-15

4

Terahertz rectification by periodic two-dimensional electron plasma  

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-06-24

5

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

2008-09-17

6

Rectification in one--dimensional electronic systems  

CERN Document Server

Asymmetric current--voltage ($I(V)$) curves, known as the diode or ratchet effect, in one--dimensional electronic conductors can have their origin from scattering off a single asymmetric impurity in the system. We investigate this effect in the framework of the Tomonaga--Luttinger model for electrons with spin. We show that electron interactions strongly enhance the ratchet effect and lead to a pronounced current rectification even if the impurity potential is weak. For strongly interacting electrons and not too small voltages, the ratchet current, $I_r = [I(V)+I(-V)]/2$, measuring the asymmetry in the current--voltage curve, has a power--law dependence on the voltage with a negative exponent, $I_r \\sim V^{-|z|}$, leading to a bump in the current--voltage curve.

Braunecker, B; Marston, J B; Braunecker, Bernd

2005-01-01

7

Molecular rectification of thiol-linked Au|PTCDI-[CH2]n|Au junctions  

Science.gov (United States)

The electronic transport properties of the PTCDI-[CH2]n(0?n?6) molecular junctions with different molecular lengths are theoretically investigated via the first-principles density functional theory (DFT) and non-equilibrium Green's function (NEGF) method. Our results show that the transport properties depend on molecular lengths. The equilibrium conductance of the probed systems decreases exponentially with the increasing number n of the CH2 unit. With n?1, the rectifying effect has been found. In the n=6 case, a significant rectification ratio of 72.6 is achieved at the bias of ±2.1 V in our probed voltage range. The rectification effect arises from asymmetric molecular structures. Our results suggest these molecules have great potential application in the molecular-scale device.

Zheng, Ganhong; Dai, Zhenxiang; Zhang, Yanyan; Dong, Yuqin; Ma, Yongqing; Li, Guang

2012-08-01

8

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

2011-08-18

9

Effect of geometrical torsion on the rectification properties of diblock conjugated molecular diodes  

Science.gov (United States)

We model several Au/conjugated molecule/Au junctions in the presence of molecular geometrical torsions. A rectification ratio of around 10 in the twisty diphenyldipyrimidinyl system is obtained, which is in good agreement with experiment. Deeper insight into the rectification mechanism of the conjugated molecular diodes is presented on the basis of simulations in a set of simpler but similar junctions. The rectification effect (the ratio) is significantly improved with increasing the molecular twist, while the conductance is reduced accordingly. Our results suggest that the rectification can be enhanced by the geometrical-torsion-induced reduction in the conjugation length of organic molecules.

Cui, Bin; Zhao, Wenkai; Wang, Hui; Zhao, Jingfen; Zhao, He; Li, Dongmei; Jiang, Xiaohui; Zhao, Peng; Liu, Desheng

2014-08-01

10

Molecular junctions in the Coulomb blockade regime: rectification and nesting  

CERN Document Server

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

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

2006-01-01

11

Charge transport and rectification in molecular junctions formed with carbon-based electrodes.  

Science.gov (United States)

Molecular junctions formed using the scanning-tunneling-microscope-based break-junction technique (STM-BJ) have provided unique insight into charge transport at the nanoscale. In most prior work, the same metal, typically Au, Pt, or Ag, is used for both tip and substrate. For such noble metal electrodes, the density of electronic states is approximately constant within a narrow energy window relevant to charge transport. Here, we form molecular junctions using the STM-BJ technique, with an Au metal tip and a microfabricated graphite substrate, and measure the conductance of a series of graphite/amine-terminated oligophenyl/Au molecular junctions. The remarkable mechanical strength of graphite and the single-crystal properties of our substrates allow measurements over few thousand junctions without any change in the surface properties. We show that conductance decays exponentially with molecular backbone length with a decay constant that is essentially the same as that for measurements with two Au electrodes. More importantly, despite the inherent symmetry of the oligophenylamines, we observe rectification in these junctions. State-of-art ab initio conductance calculations are in good agreement with experiment, and explain the rectification. We show that the highly energy-dependent graphite density of states contributes variations in transmission that, when coupled with an asymmetric voltage drop across the junction, leads to the observed rectification. Together, our measurements and calculations show how functionality may emerge from hybrid molecular-scale devices purposefully designed with different electrodes beyond the so-called "wide band limit," opening up the possibility of assembling molecular junctions with dissimilar electrodes using layered 2D materials. PMID:25024198

Kim, Taekyeong; Liu, Zhen-Fei; Lee, Chulho; Neaton, Jeffrey B; Venkataraman, Latha

2014-07-29

12

Stretch or contraction induced inversion of rectification in diblock molecular junctions.  

Science.gov (United States)

Based on ab initio theory and nonequilibrium Green's function method, the effect of stretch or contraction on the rectification in diblock co-oligomer molecular diodes is investigated theoretically. Interestingly, an inversion of rectifying direction induced by stretching or contracting the molecular junctions, which is closely related to the number of the pyrimidinyl-phenyl units, is proposed. The analysis of the molecular projected self-consistent Hamiltonian and the evolution of the frontier molecular orbitals as well as transmission coefficients under external biases gives an inside view of the observed results. It reveals that the asymmetric molecular level shift and asymmetric evolution of orbital wave functions under biases are competitive mechanisms for rectification. The stretching or contracting induced inversion of the rectification is due to the conversion of the dominant mechanism. This work suggests a feasible technique to manipulate the rectification performance in molecular diodes by use of the mechanically controllable method. PMID:24028125

Zhang, Guang-Ping; Hu, Gui-Chao; Song, Yang; Xie, Zhen; Wang, Chuan-Kui

2013-09-01

13

Stretch or contraction induced inversion of rectification in diblock molecular junctions  

Science.gov (United States)

Based on ab initio theory and nonequilibrium Green's function method, the effect of stretch or contraction on the rectification in diblock co-oligomer molecular diodes is investigated theoretically. Interestingly, an inversion of rectifying direction induced by stretching or contracting the molecular junctions, which is closely related to the number of the pyrimidinyl-phenyl units, is proposed. The analysis of the molecular projected self-consistent Hamiltonian and the evolution of the frontier molecular orbitals as well as transmission coefficients under external biases gives an inside view of the observed results. It reveals that the asymmetric molecular level shift and asymmetric evolution of orbital wave functions under biases are competitive mechanisms for rectification. The stretching or contracting induced inversion of the rectification is due to the conversion of the dominant mechanism. This work suggests a feasible technique to manipulate the rectification performance in molecular diodes by use of the mechanically controllable method.

Zhang, Guang-Ping; Hu, Gui-Chao; Song, Yang; Xie, Zhen; Wang, Chuan-Kui

2013-09-01

14

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

International Nuclear Information System (INIS)

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

15

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

Energy Technology Data Exchange (ETDEWEB)

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

Shanmugam, S. [Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036 (India); Viswanathan, B. [Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036 (India)], E-mail: bvnathan@iitm.ac.in; Varadarajan, T.K. [Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036 (India)

2008-12-20

16

Terahertz radiation by optical rectification in a hydrogen-bonded organic molecular ferroelectric crystal, 2-phenylmalondialdehyde  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Terahertz radiation by optical rectification has been observed at room temperature in a hydrogen-bonded organic molecular ferroelectric crystal, 2-phenyl malondialdehyde (PhMDA). The radiated electromagnetic wave consisted of a single-cycle terahertz pulse with a temporal width of $\\sim$ 0.5 ps. The terahertz radiation amplitude divided by the sample thickness in PhMDA was nearly equivalent to that in a typical terahertz wave emitter ZnTe. This is attributable to a long cohe...

Guan, W.; Kida, N.; Sotome, M.; Kinoshita, Y.; Takeda, R.; Inoue, A.; Horiuchi, S.; Okamoto, H.

2014-01-01

17

Molecular mechanism of rectification at identified electrical synapses in the Drosophila giant fiber system.  

Science.gov (United States)

Electrical synapses are neuronal gap junctions that mediate fast transmission in many neural circuits. The structural proteins of gap junctions are the products of two multigene families. Connexins are unique to chordates; innexins/pannexins encode gap-junction proteins in prechordates and chordates. A concentric array of six protein subunits constitutes a hemichannel; electrical synapses result from the docking of hemichannels in pre- and postsynaptic neurons. Some electrical synapses are bidirectional; others are rectifying junctions that preferentially transmit depolarizing current anterogradely. The phenomenon of rectification was first described five decades ago, but the molecular mechanism has not been elucidated. Here, we demonstrate that putative rectifying electrical synapses in the Drosophila Giant Fiber System are assembled from two products of the innexin gene shaking-B. Shaking-B(Neural+16) is required presynaptically in the Giant Fiber to couple this cell to its postsynaptic targets that express Shaking-B(Lethal). When expressed in vitro in neighboring cells, Shaking-B(Neural+16) and Shaking-B(Lethal) form heterotypic channels that are asymmetrically gated by voltage and exhibit classical rectification. These data provide the most definitive evidence to date that rectification is achieved by differential regulation of the pre- and postsynaptic elements of structurally asymmetric junctions. PMID:19084406

Phelan, Pauline; Goulding, L Ann; Tam, Jennifer L Y; Allen, Marcus J; Dawber, Rebecca J; Davies, Jane A; Bacon, Jonathan P

2008-12-23

18

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

19

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

CERN Document Server

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

Li, Yunyun; Marchesoni, Fabio; Li, Baowen

2014-01-01

20

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

International Nuclear Information System (INIS)

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

 
 
 
 
21

Terahertz radiation by optical rectification in a hydrogen-bonded organic molecular ferroelectric crystal, 2-phenylmalondialdehyde  

Science.gov (United States)

Terahertz radiation by optical rectification has been observed at room temperature in a hydrogen-bonded organic molecular ferroelectric crystal, 2-phenyl malondialdehyde (PhMDA). The radiated electromagnetic wave consisted of a single-cycle terahertz pulse with a temporal width of ˜0.5 ps. The terahertz radiation amplitude divided by the sample thickness in PhMDA was nearly equivalent to that in a typical terahertz wave emitter ZnTe. This is attributable to a long coherence length in the range of 130-800 µm for the terahertz radiation from PhMDA. We also discussed the possibility of PhMDA as a terahertz wave emitter in terms of the phase-matching condition.

Guan, Wenguang; Kida, Noriaki; Sotome, Masato; Kinoshita, Yuto; Takeda, Ryotaro; Inoue, Akito; Horiuchi, Sachio; Okamoto, Hiroshi

2014-09-01

22

Dependence of electronic rectification in carbon nanocone devices upon electrode materials  

International Nuclear Information System (INIS)

Very recently, we found that single-walled carbon nanocones (SWCNCs) of tens of atoms can serve as rectifiers if Au electrodes are applied (Ming et al 2012 Appl. Phys. Lett. 100 063119). In this paper, the dependence of rectification effects on different electrode materials (Au, Cu, Ag, Li, Be, Pd and Pt) is systematically investigated by density functional theory and non-equilibrium Green's function, showing that materials with lower energy bonded with the SWCNC possess better rectification effects. The rectification mechanism is revealed, including the fact that the contact distance between the tip of the SWCNC and the electrode is also an important factor for rectification effects.

23

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

2008-09-17

24

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

25

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

26

Tuning electrochemical rectification via quantum dot assemblies.  

Science.gov (United States)

A novel approach to tuning electrochemical rectification using 2D assemblies of quantum dots (QDs) is presented. Asymmetric enhancement of the oxidation and reduction currents in the presence of the Fe(CN)(6)(3-/4-) redox couple is observed upon adsorption of QDs at thiol-modified Au electrodes. The extent of the electrochemical rectification is dependent on the average QD size. A molecular blocking layer is generated by self-assembling 11-mercaptoundecanoic acid (MUA) and an ultrathin film of poly(diallyldimethylammonium chloride) (PDADMAC) on the electrode. The polycationic film allows the electrostatic adsorption of 3-mercaptopropionic acid (MPA)-stabilized CdTe QDs, generating 2D assemblies with approximately 0.4% coverage. The QD adsorption activates a fast charge transfer across the blocking layer in which the reduction process is more strongly enhanced than the oxidation reaction. The partial electrochemical rectification is rationalized in terms of the relative position of the valence (VB) and conduction band (CB) edges with respect to the redox Fermi energy (?(redox)). Quantitative analysis of the exchange current density obtained from electrochemical impedance spectroscopy demonstrates that the enhancement of charge transport across the molecular barrier is strongly dependent on the position of the QD valence band edge relative to ?(redox). The average electron tunneling rate constant through the QD assemblies is estimated on the basis of the Gerischer model for electron transfer. PMID:21050000

Kissling, Gabriela P; Bünzli, Christa; Fermín, David J

2010-12-01

27

Electron tunneling in molecular junctions  

Science.gov (United States)

This thesis describes approximately four years of fundamental research in the field of molecular electronics. Data are obtained on nanoscopic metal---molecule---metal junctions using conducting-probe atomic force microscopy (CP-AFM). The CP-AFM method involves a conductive AFM probe that is brought into contact with a molecular monolayer that has been self-assembled on a conductive substrate. Tunneling currents are measured to describe charge transport through a small number of molecules. While there are many architectures for creating such molecular tunnel junctions, CP-AFM offers a quick and simple route to formation of nanoscale junctions void of pinholes, with the ability to change contact metals, and measure and control junction compression. Four experiments are highlighted in this manuscript as contributions to the field. The first deals with effects of the type of connection between electrode and molecule (i.e., either a chemical bond or a physical contact), electrode work function, and applied bias. The breadth of this experiment focuses on a series of alkanethiol and alkanedithiol monolayers of varying length in order to characterize both the length dependence and the extrapolated contact resistance. These parameters are then used in the context of conventional theory to extract transmission coefficients relating to tunneling transport through different contacts and as the result of different metals. The second experiment focuses on issues of reproducibility in CP-AFM measurements by performing measurements on Au/decanethiol/Au junctions under a variety of experimental conditions. The third experiment focuses on current rectification (asymmetry with applied voltage) of decanethiol junctions in comparison to a perfluorinated analogue (SHC2H4C 8F17). Alkanethiol monolayers are known to create surface dipoles that decrease the work function of the substrate that they are deposited upon. The opposite shift and rectification direction occurs for the perfluorinated analogue, indicating a correlation of the surface dipole and observed asymmetry. Finally, applied load is varied in the fourth experiment similar to nanoindentation. Measurements are performed on alkanethiols other than decanethiol, with various loading rates and maximum applied loads. The data are modeled using conventional contact mechanics to estimate film modulus and plastic deformation.

Engelkes, Vincent Bernard

28

Measurement and understanding of single-molecule break junction rectification caused by asymmetric contacts.  

Science.gov (United States)

The contact effects of single-molecule break junctions on rectification behaviors were experimentally explored by a systematic control of anchoring groups of 1,4-disubstituted benzene molecular junctions. Single-molecule conductance and I-V characteristic measurements reveal a strong correlation between rectifying effects and the asymmetry in contacts. Analysis using energy band models and I-V calculations suggested that the rectification behavior is mainly caused by asymmetric coupling strengths at the two contact interfaces. Fitting of the rectification ratio by a modified Simmons model we developed suggests asymmetry in potential drop across the asymmetric anchoring groups as the mechanism of rectifying I-V behavior. This study provides direct experimental evidence and sheds light on the mechanisms of rectification behavior induced simply by contact asymmetry, which serves as an aid to interpret future single-molecule electronic behavior involved with asymmetric contact conformation. PMID:25106605

Wang, Kun; Zhou, Jianfeng; Hamill, Joseph M; Xu, Bingqian

2014-08-01

29

Measurement and understanding of single-molecule break junction rectification caused by asymmetric contacts  

Science.gov (United States)

The contact effects of single-molecule break junctions on rectification behaviors were experimentally explored by a systematic control of anchoring groups of 1,4-disubstituted benzene molecular junctions. Single-molecule conductance and I-V characteristic measurements reveal a strong correlation between rectifying effects and the asymmetry in contacts. Analysis using energy band models and I-V calculations suggested that the rectification behavior is mainly caused by asymmetric coupling strengths at the two contact interfaces. Fitting of the rectification ratio by a modified Simmons model we developed suggests asymmetry in potential drop across the asymmetric anchoring groups as the mechanism of rectifying I-V behavior. This study provides direct experimental evidence and sheds light on the mechanisms of rectification behavior induced simply by contact asymmetry, which serves as an aid to interpret future single-molecule electronic behavior involved with asymmetric contact conformation.

Wang, Kun; Zhou, Jianfeng; Hamill, Joseph M.; Xu, Bingqian

2014-08-01

30

Communication: Thermal rectification in liquids by manipulating the solid-liquid interface  

Science.gov (United States)

Thermal rectification, the origin of which lies in modifying the thermal resistance in a nonlinear manner, could significantly improve the thermal management of a wide range of nano-devices (both electronic and thermoelectric), thereby improving their efficiencies. Since rectification requires a material to be inhomogeneous, it has been typically associated with solids. However, the structure of solids is relatively difficult to manipulate, which makes the tuning of thermal rectification devices challenging. Since liquids are more amenable to tuning, this could open up new applications for thermal rectification. We use molecular dynamics simulations to demonstrate thermal rectification using liquid water. This is accomplished by creating an inhomogeneous water phase, either by changing the morphology of the surface in contact with the liquid or by imposing an arbitrary external force, which in practice could be through an electric or magnetic field. Our system consists of a bulk fluid that is confined in a reservoir that is bounded by two walls, one hot and the other cold. The interfacial (Kapitza) thermal resistance at the solid-fluid interface and the density gradient of the bulk fluid both influence the magnitude of the thermal rectification. However, we find that the role of the interfacial resistance is more prominent than the application of an external force on the bulk fluid.

Murad, Sohail; Puri, Ishwar K.

2012-08-01

31

Thermal Rectification In Asymmetric Graphene Ribbons  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this paper, heat flux in graphene nano ribbons has been studied by using molecular dynamics simulations. It is found that the heat flux runs preferentially along the direction of decreasing width, which demonstrates significant thermal rectification effect in the asymmetric graphene ribbons. The dependence of rectification ratio on the vertex angle and the length are also discussed. Compared to the carbon nanotube based one-dimensional thermal rectifier, graphene nano rib...

Yang, Nuo; Zhang, Gang; Li, Baowen

2009-01-01

32

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

Science.gov (United States)

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

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

2011-10-25

33

Thermal Rectification in Bulk Material Through Unusual Behavior of Electron Thermal Conductivity of Al-Cu-Fe Icosahedral Quasicrystal  

Science.gov (United States)

In this study, a new thermal rectifier working at high temperatures above 300 K was developed using Al61.5Cu26.5Fe12 icosahedral quasicrystal and Ag2Te. The thermal conductivity of Al61.5Cu26.5Fe12 increased drastically with temperature and, at 1000 K, reached a value nine times larger than that at 300 K. The thermal conductivity of Ag2Te showed a sudden decrease at around 400 K, and the thermal conductivity at 423 K became 60% smaller than that at 300 K. By making a composite consisting of Al61.5Cu26.5Fe12 icosahedral quasicrystal and Ag2Te, we succeeded in obtaining a large thermal rectification ratio (TRR) of |J large|/|J small| = 1.63 using two heat reservoirs maintained at T H = 543 K and T L = 300 K. The obtained TRR value is the largest among those ever reported for bulk thermal rectifiers.

Nakayama, Ryu-suke; Takeuchi, Tsunehiro

2014-05-01

34

Electronic Properties of a Phenylacetylene Molecular Junction with Dithiocarboxylate Anchoring Group  

International Nuclear Information System (INIS)

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

35

A gate controlled conjugated single molecule diode: Its rectification could be reversed  

Science.gov (United States)

A gate controlled Au/diphenyldipyrimidinyl/Au single molecule diode is simulated by a tight-binding Hamiltonian combined with Green's Function and transport methods. After calculating a number of electronic transport characteristics under various gate voltages, a clear modulation by gate is got and when the positive voltage is high enough, the rectification could be reversed. This is advisable for the designing and building future molecular logic devices and integrated circuits.

Zhang, Qun

2014-10-01

36

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

International Nuclear Information System (INIS)

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

37

Kinetic theory for electron transmission through a molecular wire  

International Nuclear Information System (INIS)

A theoretical description of electron transmission through a molecular wire embedded in between two leads is carried out using the density matrix method. Accounting for the Coulomb repulsion among the transferred electrons nonlinear kinetic equations for the reduced single-electron distributions are derived. The respective transfer rates contain contributions from different transmission channels which are characterized by the number of excess electrons present in the wire in the course of the charge transmission. Special attention is focused on the study of single-electron transmission. It is shown that a direct lead-lead (elastic) transmission as well as a transmission including the population of intermediate wire states (inelastic transmission) becomes possible if the electron to be transferred moves through a wire without a further excess charge. The probability to find a molecule in such an 'empty' wire state follows from a relation between the rates of incoming and outgoing lead-molecule/molecule-lead charge transfer. In turn, they are responsible for the formation of the inelastic component of the current. Thus, it could be demonstrated that the inelastic charge transmission not only determines the inelastic part of the current but is able to control the elastic component as well. Moreover, the inelastic transmission may result in a specific kinetic rectification effect

38

Unexpected large thermal rectification in asymmetric grain boundary of graphene  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have investigated the lattice thermal transport across the asymmetric tilt grain boundary between armchair and zigzag graphene by nonequilibrium molecular dynamics (NEMD). We have observed significant temperature drop and ultra-low temperature-dependent thermal boundary resistance. More importantly, we find an unexpected thermal rectification phenomenon. The thermal conductivity and Kapitza conductance is direction-dependent. The effect of thermal rectification could be a...

Cao, Hai-yuan; Xiang, Hongjun; Gong, Xin-gao

2011-01-01

39

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.)

40

Unconventional molecule-resolved current rectification in diamondoid–fullerene hybrids  

Science.gov (United States)

The unimolecular rectifier is a fundamental building block of molecular electronics. Rectification in single molecules can arise from electron transfer between molecular orbitals displaying asymmetric spatial charge distributions, akin to p–n junction diodes in semiconductors. Here we report a novel all-hydrocarbon molecular rectifier consisting of a diamantane–C60 conjugate. By linking both sp3 (diamondoid) and sp2 (fullerene) carbon allotropes, this hybrid molecule opposingly pairs negative and positive electron affinities. The single-molecule conductances of self-assembled domains on Au(111), probed by low-temperature scanning tunnelling microscopy and spectroscopy, reveal a large rectifying response of the molecular constructs. This specific electronic behaviour is postulated to originate from the electrostatic repulsion of diamantane–C60 molecules due to positively charged terminal hydrogen atoms on the diamondoid interacting with the top electrode (scanning tip) at various bias voltages. Density functional theory computations scrutinize the electronic and vibrational spectroscopic fingerprints of this unique molecular structure and corroborate the unconventional rectification mechanism.

Randel, Jason C.; Niestemski, Francis C.; Botello-Mendez, Andrés R.; Mar, Warren; Ndabashimiye, Georges; Melinte, Sorin; Dahl, Jeremy E. P.; Carlson, Robert M. K.; Butova, Ekaterina D.; Fokin, Andrey A.; Schreiner, Peter R.; Charlier, Jean-Christophe; Manoharan, Hari C.

2014-09-01

 
 
 
 
41

Unconventional molecule-resolved current rectification in diamondoid–fullerene hybrids  

Science.gov (United States)

The unimolecular rectifier is a fundamental building block of molecular electronics. Rectification in single molecules can arise from electron transfer between molecular orbitals displaying asymmetric spatial charge distributions, akin to p–n junction diodes in semiconductors. Here we report a novel all-hydrocarbon molecular rectifier consisting of a diamantane–C60 conjugate. By linking both sp3 (diamondoid) and sp2 (fullerene) carbon allotropes, this hybrid molecule opposingly pairs negative and positive electron affinities. The single-molecule conductances of self-assembled domains on Au(111), probed by low-temperature scanning tunnelling microscopy and spectroscopy, reveal a large rectifying response of the molecular constructs. This specific electronic behaviour is postulated to originate from the electrostatic repulsion of diamantane–C60 molecules due to positively charged terminal hydrogen atoms on the diamondoid interacting with the top electrode (scanning tip) at various bias voltages. Density functional theory computations scrutinize the electronic and vibrational spectroscopic fingerprints of this unique molecular structure and corroborate the unconventional rectification mechanism. PMID:25202942

Randel, Jason C.; Niestemski, Francis C.; Botello-Mendez, Andrés R.; Mar, Warren; Ndabashimiye, Georges; Melinte, Sorin; Dahl, Jeremy E. P.; Carlson, Robert M. K.; Butova, Ekaterina D.; Fokin, Andrey A.; Schreiner, Peter R.; Charlier, Jean-Christophe; Manoharan, Hari C.

2014-01-01

42

Basic Devices For Molecular Electronics  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract: 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. It is easier to build electronic circuits using molecules since they are small and their properties can be tuned. Molecular electronics has some advantages over other technologies for implementing logic circuits. The size of molecules is at least 1nm and at most 100nm. This leads to less area and power dissipation. Considering this novel technology, molecules are used as the active components of the circuit, for transporting electric charge. In this paper, a half adder cell based on molecular electronics is presented. The area occupied by this kind of half 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.

Laxmi N. Pawar

2014-03-01

43

Magnetically Induced Thermal Rectification  

CERN Document Server

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

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

2006-01-01

44

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

45

Electron scattering by molecular oxygen  

Energy Technology Data Exchange (ETDEWEB)

Collisions of electrons with molecules is one of the fundamental processes which occur both in atomic and molecular physics and also in chemistry. These collisions are vital in determining the energy balance and transport properties of electrons in gases and plasmas at low temperatures. There are many important applications for the basic understanding of these collision processes. For example, the study of planetary atmospheres and the interstellar medium involves electron collisions with both molecules and molecular ions. In particular, two of the major cooling mechanisms of electrons in the Earth's ionosphere are (i) the fine structure changing transitions of oxygen atoms by electron impact and (ii) the resonant electron-impact vibrational excitation of N{sub 2}. Other applications include magnetohydrodynamic power generation and laser physics. A molecule, by definition, will contain more than one nucleus and consequently the effect of nuclear motion in the molecule leads to many extra processes in electron scattering by molecules which cannot occur in electron-atom scattering. As for atoms, both elastic and inelastic scattering occur, but in the case of inelastic electron scattering by molecules, the target molecule is excited to a different state by the process. The excitation may be one, or some combination, of rotational, vibrational and electronic transitions. Other reactions which may occur include dissociation of the molecule into its constituent atoms or ionisation. Another difficulty arises when considering the interactions between the electron and the molecule, This interaction, which considerably complicates the calculation, is non-spherical and various methods have been developed over the years to represent this interaction. This thesis considers electron scattering by molecular oxygen in the low energy range i.e. 0-15eV. These collisions are of considerable interest in atmospheric physics and chemistry where the electron impact excitation of O{sub 2} has great importance. Another reason why oxygen is an interesting and unusual molecule to study is the open-shell nature of the target which has {sup 3}{sigma}{sub g}{sup -} as its ground electronic state.

Duddy, P.E

1999-03-01

46

Rectifying properties of oligo(phenylene ethynylene) heterometallic molecular junctions: molecular length and side group effects.  

Science.gov (United States)

The rectifying properties of ?,?-dithiol terminated oligo(phenylene ethynylene) molecules sandwiched between heterometallic electrodes, including the molecular length and side group effects, are theoretically investigated using the fully self-consistent nonequilibrium Green's function method combined with density functional theory. The results show nonlinear variation with changes in molecule length: when the molecule becomes longer, the current decreases at first and then increases while the rectification shifts in the opposite direction. This stems from the change in molecular eigenstates and the coupling between the molecule and electrodes caused by different molecular lengths. The rectifying behavior of heterometallic molecular junctions can be attributed to the asymmetric molecule-electrode contacts, which lead to asymmetric electronic tunneling spectra, molecular eigenvalues, molecular orbitals, and potential drop at reversed equivalent bias voltages. Our results provide a fundamental understanding of the rectification of heterometallic molecular junction, and a prediction of rectifiers with different rectification properties from those in the experiment, using electrodes with reduced sizes. PMID:25220880

Fu, Xiao-Xiao; Zhang, Rui-Qin; Zhang, Guang-Ping; Li, Zong-Liang

2014-01-01

47

Rectifying Properties of Oligo(Phenylene Ethynylene) Heterometallic Molecular Junctions: Molecular Length and Side Group Effects  

Science.gov (United States)

The rectifying properties of ?,?-dithiol terminated oligo(phenylene ethynylene) molecules sandwiched between heterometallic electrodes, including the molecular length and side group effects, are theoretically investigated using the fully self-consistent nonequilibrium Green's function method combined with density functional theory. The results show nonlinear variation with changes in molecule length: when the molecule becomes longer, the current decreases at first and then increases while the rectification shifts in the opposite direction. This stems from the change in molecular eigenstates and the coupling between the molecule and electrodes caused by different molecular lengths. The rectifying behavior of heterometallic molecular junctions can be attributed to the asymmetric molecule-electrode contacts, which lead to asymmetric electronic tunneling spectra, molecular eigenvalues, molecular orbitals, and potential drop at reversed equivalent bias voltages. Our results provide a fundamental understanding of the rectification of heterometallic molecular junction, and a prediction of rectifiers with different rectification properties from those in the experiment, using electrodes with reduced sizes. PMID:25220880

Fu, Xiao-Xiao; Zhang, Rui-Qin; Zhang, Guang-Ping; Li, Zong-Liang

2014-01-01

48

Unexpected large thermal rectification in asymmetric grain boundary of graphene  

Science.gov (United States)

We have investigated the lattice thermal transport across the asymmetric tilt grain boundary between armchair and zigzag graphene by nonequilibrium molecular dynamics (NEMD). We have observed significant temperature drop and ultra-low temperature-dependent thermal boundary resistance. More importantly, we find an unexpected thermal rectification phenomenon. The thermal conductivity and Kapitza conductance is direction-dependent. The effect of thermal rectification could be amplified by increasing the difference of temperature imposed on two sides. Our results propose a promising kind of thermal rectifier and phonon diodes based on polycrystalline graphene without delicate manipulation of the atomic structure.

Cao, Hai-Yuan; Xiang, Hongjun; Gong, Xin-Gao

2012-10-01

49

Inelastic electron transport through molecular junctions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Currently, molecular tunnel junctions are recognized as important active elements of various nanodevices. This gives a strong motivation to study physical mechanisms controlling electron transport through molecules. Electron motion through a molecular bridge is always somewhat affected by the environment, and the interactions with the invironment could change the energy of the traveling electron. Under certain conditions these inelastic effects may significantly modify elect...

Zimbovskaya, Natalya A.

2013-01-01

50

Theoretical background for inward rectification.  

Science.gov (United States)

Theoretical background has been reviewed for inward rectification due to a potassium current termed IRK. The Eyring rate theory in which the thermodynamic rate coefficient for chemical reactants (channels and ions in this case) can be described in terms of energy barriers for potassium ions can mimic not only the polarity and degree of rectification but also the voltage-dependence of the barium-induced IRK block. The model predicts that the blocking site locates 30-70% depth from the outer margin of the IRK channel. PMID:10819495

Tanaka, A; Tokimasa, T

1999-12-01

51

Molecular Programming Pseudo-code Representation to Molecular Electronics  

CERN Document Server

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

Pradhan, Manas Ranjan

2010-01-01

52

Electron spectroscopy and molecular structure  

International Nuclear Information System (INIS)

Electron spectroscopy can now be applied to solids, liquids and gases. Some fields of research require ultrahigh vacuum conditions, in particular those directly concerned with surface phenomena on the monolayer level. Liquids have just recently been subject to studies and several improvements and extensions of this technique can be done. Much advance has lately been achieved in the case of gases, where the pressure range presently is 10-5-1 torr. Signal-to-background ratios for core lines can be approximately 1000:1 and the resolution has been increased to the extent that vibrational fine structures of 1s levels in some small molecules have been observed. These improvements are based on the monochromatization of the exciting AlK? radiation. Under such conditions the background is furthermore so much reduced that shake-up structures are more generally accessible for closer studies. ESCA shifts are also much easier to resolve and to measure with higher precision, around 0.02 eV. The photoionization dynamics including atomic and molecular relaxations has been investigated, both experimentally and theoretically. In the valence electron region improvements in energy resolution and in the application of the intensity model based on the MO-LCAO approximation greatly facilitate the assignments of the valence orbitals. Accumulation of empirical evidences gathered from series of similar chemical species and also better methods of calculation, both ab initio and semiempirical, have gradually resulted in a much better understanding of the molecular orbital description. The experience of the latest ESCA instrument with monochromatization has motivated an attempt to design an optimized apparatus according to the general principles of this prototype. A considerable gain in intensity can be made at an improved resolution set by the inherent diffraction pattern of the focussing spherical quartz crystals. (author)

53

Molecular electronics from principles to practice  

CERN Document Server

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

54

Electronic transport properties of molecular junctions based on the direct binding of aromatic ring to electrodes  

International Nuclear Information System (INIS)

Highlights: • Transport properties of molecular junction having direct binding of aromatic ring to electrode have been investigated. • The conductance of junction with sp-type electrode is higher than that of junction with sd-type electrode. • The rectifying mechanism critically depends on the nature of benzene–electrode coupling. • The p–n junction-like can be obtained even without heteroatom doping. • The negative differential resistance effect was observed for the case of sp-type electrode. - Abstract: We have used the non-equilibrium Green’s function in combination with the density functional theory to investigate the quantum transport properties of the molecular junctions including a terminated benzene ring directly coupled to surface of metal electrodes (physisorption). The other side of molecule was connected to electrode via thiolate bond (chemisorption). Two different electrodes have been studied, namely Cu and Al. Rectification and negative differential resistance behavior have been observed. We found that the electron transport mechanism is affected by the nature of benzene–electrode coupling. In other words, the transport mechanism depends on the nature of metallic electrode. Changing from sp- to sd-metallic electrode, the molecular junction changes from the Schottky to p–n junction-like diode. The transmission spectra, projected density of state, molecular projected self-consistent Hamiltonian, transmission eigenchannel, and Muliken population have been analyzed for explanation of electronic transport properties. Understanding the transport mechanism in junction having direct coupling of ?-conjugate to electrode will be useful to design the future molecular devices

55

Electron transmission through molecules and molecular interfaces  

CERN Document Server

Electron transmission through molecules and molecular interfaces has been a subject of intensive research due to recent interest in electron transfer phenomena underlying the operation of the scanning tunneling microscope (STM) on one hand, and in the transmission properties of molecular bridges between conducting leads on the other. In these processes the traditional molecular view of electron transfer between donor and acceptor species give rise to a novel view of the molecule as a current carrying conductor, and observables such as electron transfer rates and yields are replaced by the conductivities, or more generally by current-voltage relationships, in molecular junctions. In this paper I review the current knowledge and understanding of this field, with particular emphasis on theoretical issues. Different approaches to computing the conduction properties of molecules and molecular assemblies are reviewed, and the relationships between them are discussed. Following a detailed discussion of static juncti...

Nitzan, A

2001-01-01

56

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

57

Electrons in molecules from basic principles to molecular electronics  

CERN Document Server

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

Launay, Jean-Pierre

2014-01-01

58

Electron transport through molecular junctions  

International Nuclear Information System (INIS)

functional theory which presently is often used to analyze important characteristics of molecules and molecular clusters. Finally, we discuss some kinds of nanoelectronic devices built using molecules and similar systems such as carbon nanotubes, various nanowires and quantum dots.

59

Probing molecular chirality via electronic transport  

International Nuclear Information System (INIS)

We investigate electronic molecular transport in several conjugated organic oligomers by means of ab initio calculations and nonequilibrium Green's functions method. We demonstrate that the I-V characteristics of these molecules constitute a direct manifestation of their degree of molecular chirality, which is calculated using group theory and depends exclusively on the atomic positions. This result shows that electronic current through these specific molecules is strongly correlated with their geometrical degree of chirality.

60

Computer simulation of electron transfer in molecular electronic devices  

Energy Technology Data Exchange (ETDEWEB)

The study of electron transfer through individual molecules bound to metal electrodes has become important due to the potential application in molecular electronic devices. Since the electronic and atomic motions in these molecules influence each other, they need to be treated self-consistently. We have used self-consistent quantum chemistry molecular dynamics calculations to discuss some of the issues related to electron transfer through a spatially symmetric [9,10-bis((2'-para-mercaptophenyl)-ethinyl)-anthracene] and an asymmetric [1,4-bis((2'-para-mercaptophenyl)-ethinyl)-2-acetyl-amino-5-nitro-benzene] molecule bound to metal electrodes. Specifically addressed are the effects of voltage inversion on electron transfer between electrodes through both molecules. Our results show an electron transfer behaviour that reproduces the spatial symmetry of the molecules in agreement with experimental current-voltage data. The change in time of electron density and dimerisation at specific atomic sites is also discussed.

Correia, Helena M.G. [Departamento de Fisica, Universidade do Minho, Campus de Gualtar, 4710-057 Braga (Portugal); Ramos, Marta M.D. [Departamento de Fisica, Universidade do Minho, Campus de Gualtar, 4710-057 Braga (Portugal)]. E-mail: marta@fisica.uminho.pt

2005-12-15

 
 
 
 
61

Spin-excited states and rectification in an organic spin rectifier  

Science.gov (United States)

Spin-excited states in an asymmetric magnetic organic co-oligomer diode are investigated theoretically. The results demonstrate that the structural asymmetry of the co-oligomer is modulated by the spin-excited states, which is embodied in the wave functions of the eigenstates as well as the spin density wave. By calculating the transport property, a robust spin-current rectification concomitant with a charge-current rectification is observed in all spin-excited states. However, the current through the diode is suppressed distinctly by the spin-excited states, while the rectification ratios may be reduced or enhanced depending on the bias and the excited spins. The intrinsic mechanism is analyzed from the spin-dependent transmission combined with the change of molecular eigenstates under bias. Finally, the temperature-induced spin excitation is simulated. Significant rectification behavior is obtained even at room temperature.

Zuo, Meng-Ying; Hu, Gui-Chao; Li, Ying; Ren, Jun-Feng; Wang, Chuan-Kui

2014-08-01

62

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

Science.gov (United States)

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

Wu, Xiangli

1995-01-01

63

Electron spectroscopy of exploding fast molecular ions  

International Nuclear Information System (INIS)

Auger electrons emitted from atomic (C+-, N+-, O+)- and molecular (N+2-, CP+)-projectiles (ca. 80keV A-1) excited under single collision conditions in thin gaseous targets (N2, CO2)have been measured. The dominant lines in the observed spectra can be attributed to the decay of Li- and Be-like configurations using intermediate coupling Dirac-Fock calculations. Molecular projectiles (N+2 and CO+) loose their binding electrons in the collisions and the molecular fragments explode via Coulomb repulsion, imposing their kinematics on the deexcitation radiation. This results in the additional kinematic line broadening in the Auger electron energy spectra. It can be well separated from all other contributions to the total linewidth by comparing the spectra of atomic and molecular projectiles of equivalent velocity. (Auth.)

64

Molecular ferroelectrics: where electronics meet biology.  

Science.gov (United States)

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. PMID:24018952

Li, Jiangyu; Liu, Yuanming; Zhang, Yanhang; Cai, Hong-Ling; Xiong, Ren-Gen

2013-12-28

65

Separation processes, I: Azeotropic rectification  

Directory of Open Access Journals (Sweden)

Full Text Available In a series of two articles, the problems of azeotrope separation (part I and the design of separation units (part II were analyzed. The basic definition and equations of vapour-liquid equilibria for ideal and non-ideal systems, the importance of the activity coefficient calculation necessary for the analysis of non-ideal equilibrium systems, as well as theoretical aspects of azeotrope rectification and the determination of the optimal third component (modifier or azeotrope agent are presented in the first part.

Milojevi? Svetomir

2005-01-01

66

Thermoelectric effect in molecular electronics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Paulsson, M.; Datta, S.

2003-01-01

67

Electron transport in asymmetric biphenyl molecular junctions: effects of conformation and molecule-electrode distance  

Science.gov (United States)

On the basis of ab-initio calculations, we predict the effect of conformation and molecule-electrode distance on transport properties of asymmetric molecular junctions for different electrode materials M (M = Au, Ag, Cu, and Pt). The asymmetry in these junctions is created by connecting one end of the biphenyl molecule to conjugated double thiol (model A) and single thiol (model B) groups, while the other end to Cu atom. A variety of phenomena viz. rectification, negative differential resistance (NDR), switching has been observed that can be controlled by tailoring the interface state properties through molecular conformation and molecule-electrode distance for various M. These properties are further analyzed by calculating transmission spectra, molecular orbitals, and orbital energy. It is found that Cu electrode shows significantly enhanced rectifying performance with change in torsion angles, as well as with increase in molecule-electrode distances than Au and Ag electrodes. Moreover, Pt electrode manifests distinctive multifunctional behavior combining switch, diode, and NDR. Thus, the Pt electrode is suggested to be a good potential candidate for a novel multifunctional electronic device. Our findings are compared with available experimental and theoretical results. Supplementary material in the form of one pdf file available from the Journal web page at http://http//dx.doi.org/10.1140/epjb/e2014-50133-2

Parashar, Sweta; Srivastava, Pankaj; Pattanaik, Manisha; Jain, Sandeep Kumar

2014-09-01

68

Effect of nanopore geometry on ion current rectification  

International Nuclear Information System (INIS)

We present the results of systematic studies of ion current rectification performed on artificial asymmetric nanopores with different geometries and dimensions. The nanopores are fabricated by the ion track etching method using surfactant-doped alkaline solutions. By varying the alkali concentration in the etchant and the etching time, control over the pore profile and dimensions is achieved. The pore geometry is characterized in detail using field-emission scanning electron microscopy. The dependence of the ion current rectification ratio on the pore length, tip diameter, and the degree of pore taper is analysed. The experimental data are compared to the calculations based on the Poisson-Nernst-Planck equations. A strong effect of the tip geometry on the diode-like behaviour is confirmed.

69

Effect of nanopore geometry on ion current rectification  

Energy Technology Data Exchange (ETDEWEB)

We present the results of systematic studies of ion current rectification performed on artificial asymmetric nanopores with different geometries and dimensions. The nanopores are fabricated by the ion track etching method using surfactant-doped alkaline solutions. By varying the alkali concentration in the etchant and the etching time, control over the pore profile and dimensions is achieved. The pore geometry is characterized in detail using field-emission scanning electron microscopy. The dependence of the ion current rectification ratio on the pore length, tip diameter, and the degree of pore taper is analysed. The experimental data are compared to the calculations based on the Poisson-Nernst-Planck equations. A strong effect of the tip geometry on the diode-like behaviour is confirmed.

Apel, Pavel Yu; Blonskaya, Irina V; Orelovitch, Oleg L [Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Joliot-Curie str. 6, 141980 Dubna (Russian Federation); Ramirez, Patricio [Departament de Fisica Aplicada, Universitat Politecnica de Valencia, Camino de Vera s/n, E-46022 Valencia (Spain); Sartowska, Bozena A, E-mail: apel@nrmail.jinr.ru [Institute of Nuclear Chemistry and Technology, Dorodna str. 16, 03-195, Warsaw (Poland)

2011-04-29

70

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

71

Molecular Electronics : Synthesis of Organic Molecules for Nanoscale Electronics  

DEFF Research Database (Denmark)

This thesis includes the synthesis and characterisation of organic compounds designed for molecular electronics. The synthesised organic molecules are mainly based on two motifs, the obigo(phenyleneethynylenes) (OPE)s and tetrathiafulvalene (TTF) as shown below. These two scaffolds (OPE and TTF) are chemically merged together to form cruciform-like structures that are an essential part of the thesis. The cruciform molecules were subjected to molecular conductance measurements to explore their capability towards single-crystal field-effect transistors (Part 1), molecular wires, and single electron transistors (Part 2). The synthetic protocols rely on stepwise Sonogashira coupling reactions. Conductivity studies on various OPE-based molecular wires reveal that mere OPE compounds have a higher electrical resistance compared to the cruciform based wires (up to 9 times higher). The most spectacular result, however, was obtained by a study of a single molecular transistor. The investigated OPE5-TTF compound was captured in a three-terminal experiment, whereby manipulation of the molecule’s electronic spin was possible in different charge states. Thus, we demonstrated how the cruciform molecules could be potential candidates for future molecular electronics Synthesis of a new donor-acceptor chromophore based on a benzoquinone- TTF motif (QuinoneDTF) is also described herein (Part 2). Reaction of this molecule with acid induces a colour change from purple to orange. The purple colour can be restored by addition of base. If the QuinoneDTF chromophore was implemented into a molecular device, it could be possible to switch the conductance through the device by pH alternation.

Jennum, Karsten Stein

2013-01-01

72

Computational Nanotechnology Molecular Electronics, Materials and Machines  

Science.gov (United States)

This presentation covers research being performed on computational nanotechnology, carbon nanotubes and fullerenes at the NASA Ames Research Center. Topics cover include: nanomechanics of nanomaterials, nanotubes and composite materials, molecular electronics with nanotube junctions, kinky chemistry, and nanotechnology for solid-state quantum computers using fullerenes.

Srivastava, Deepak; Biegel, Bryan A. (Technical Monitor)

2002-01-01

73

Electronic continuum model for molecular dynamics simulations  

Science.gov (United States)

A simple model for accounting for electronic polarization in molecular dynamics (MD) simulations is discussed. In this model, called molecular dynamics electronic continuum (MDEC), the electronic polarization is treated explicitly in terms of the electronic continuum (EC) approximation, while the nuclear dynamics is described with a fixed-charge force field. In such a force-field all atomic charges are scaled to reflect the screening effect by the electronic continuum. The MDEC model is rather similar but not equivalent to the standard nonpolarizable force-fields; the differences are discussed. Of our particular interest is the calculation of the electrostatic part of solvation energy using standard nonpolarizable MD simulations. In a low-dielectric environment, such as protein, the standard MD approach produces qualitatively wrong results. The difficulty is in mistreatment of the electronic polarizability. We show how the results can be much improved using the MDEC approach. We also show how the dielectric constant of the medium obtained in a MD simulation with nonpolarizable force-field is related to the static (total) dielectric constant, which includes both the nuclear and electronic relaxation effects. Using the MDEC model, we discuss recent calculations of dielectric constants of alcohols and alkanes, and show that the MDEC results are comparable with those obtained with the polarizable Drude oscillator model. The applicability of the method to calculations of dielectric properties of proteins is discussed.

Leontyev, I. V.; Stuchebrukhov, A. A.

2009-02-01

74

Radiative thermal rectification using superconducting materials  

Science.gov (United States)

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

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

2014-03-01

75

Radiative thermal rectification using superconducting materials  

International Nuclear Information System (INIS)

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

76

Exploiting plasmon-induced hot electrons in molecular electronic devices.  

Science.gov (United States)

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. PMID:23550717

Conklin, David; Nanayakkara, Sanjini; Park, Tae-Hong; Lagadec, Marie F; Stecher, Joshua T; Chen, Xi; Therien, Michael J; Bonnell, Dawn A

2013-05-28

77

Nanostructured organic-inorganic photodiodes with high rectification ratio.  

Science.gov (United States)

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?°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. PMID:21730664

Karan, Santanu; Mallik, Biswanath

2008-12-10

78

Towards reproducible, scalable lateral molecular electronic devices  

Science.gov (United States)

An approach to reproducibly fabricate molecular electronic devices is presented. Lateral nanometer-scale gaps with high yield are formed in Au/Pd nanowires by a combination of electromigration and Joule-heating-induced thermomechanical stress. The resulting nanogap devices are used to measure the electrical properties of small numbers of two different molecular species with different end-groups, namely 1,4-butane dithiol and 1,5-diamino-2-methylpentane. Fluctuations in the current reveal that in the case of the dithiol molecule devices, individual molecules conduct intermittently, with the fluctuations becoming more pronounced at larger biases.

Durkan, Colm; Zhang, Qian

2014-08-01

79

Electronically diabatic quantum dynamics of molecular desorption  

Science.gov (United States)

The photodesorption of a diatomic from a metal surface, following absorption of visible or UV light, involves electronic transitions of the desorbing species coupled to the lattice vibrations and electron-hole excitations of the substrate. We present a general treatment of these phenomena, based on the Liouville-Von Neuman equation for the density operator, and a stochastic theory of localized perturbations in an extended system. The Hamiltonian of the extended molecular system is divided into a term for the localized primary degrees of freedom (DFs) affected by the desorption, coupled to secondary DFs that acts as a time-evolving bath. A self-consistent field treatment gives an effective (non-Hermitian) Hamiltonian for the primary DFs that accounts for energy fluctuation and dissipation in terms of the properties of adsorbate and substrate. A diabatic electronic representation is used to eliminate momentum couplings between adsorbate electronic states. The bath dynamics is studied for lattice vibrations and for electronic excitations. Electron-hole excitations of the substrate are considered for intraband and interband transitions. The assumption of Brownian motion leads to expressions for the dissipative potentials in terms of the time-correlation functions of lattice displacements and of electron density fluctuations. The dissipation depends on time, allowing for time-dependent substrate temperatures and generalizing the Langevin description. Dissipation contributes to the time evolution of both ground and excited electronic states of the desorbing species. The model is discussed for the special case of Ni(001)(ads)CO.

Bekši?, Dario; Micha, David A.

1995-09-01

80

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

 
 
 
 
81

Tuning molecular orbitals in molecular electronics and spintronics.  

Science.gov (United States)

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. PMID:19769353

Kim, Woo Youn; Kim, Kwang S

2010-01-19

82

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

83

Modelling of inelastic effects in molecular electronics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 des...

Jauho, A. P.

2005-01-01

84

Proceedings of the molecular electronic devices workshop  

Science.gov (United States)

Switching at the molecular level is discussed in several papers. The Bell Laboratories' workers developed the concept of 'smart molecules' where eight bit data processing could be carried out via optical methods. F. L. Carter's discussion of both conformational switching and electron tunnelling at the molecular level envisions either soliton propagation in conjugated linear polymers or metal-like conduction in (SN)x as modes of communication with the switching elements. An experimental example of fast switching in thin films of CuTCNQ is provided. The section on materials and microfabrication includes D. Sandman's (GTE) generalized approach to organic pi-donor-acceptor systems and K. Ulmer's (Genex) speculation on the engineered biological assembly of molecular ultracircuits. The first step toward the biological assembly of an electronic device is discussed in two related papers in which Ag metal was selectively deposited on a polylysine substrate. Two serious problem areas that might be anticipated are considered by D. K. Ferry (quantum effects in arrays of devices) and C. S. Guenzer ('soft' errors). That nature has, of course, numerous practical examples of 'molecular' switching which is evident from, among others, the two stimulating papers of L. L. Shipman (ANL) on the photosynthesis process and from a paper of S. R. Hameroff and R. Watts (U. of Arizona) on microtubules. They developed a micro-computer model of the ubiquitous microtubules that strongly suggests that considerable information processing occurs in the alpha, beta tubulin helical structure.

Carter, F. L.

1981-10-01

85

High rectification ratios of Fe-porphyrin molecules on Au facets  

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-09-14

86

High rectification ratios of Fe–porphyrin molecules on Au facets  

International Nuclear Information System (INIS)

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

87

Scan-rate-dependent ion current rectification and rectification inversion in charged conical nanopores.  

Science.gov (United States)

Herein we report a theoretical study of diode-like behavior of negatively charged (e.g., glass or silica) nanopores at different potential scan rates (1-1000 V·s(-1)). Finite element simulations were used to determine current-voltage characteristics of conical nanopores at various electrolyte concentrations. This study demonstrates that significant changes in rectification behavior can be observed at high scan rates because the mass transport of ionic species appears sluggish on the time scale of the voltage scan. In particular, it explains the influence of the potential scan rate on the nanopore rectifying properties in the cases of classical rectification, rectification inversion, and the "transition" rectification domain where the rectification direction in the nanopore could be modulated according to the applied scan rate. PMID:21851111

Momotenko, Dmitry; Girault, Hubert H

2011-09-21

88

Thermal conductance and rectification of asymmetric tilt grain boundary in graphene  

CERN Document Server

We have investigated the lattice thermal transport across the asymmetry tilt grain boundary between armchair and zigzag grains by using nonequilibrium molecular dynamics (NEMD). We have observed significant temperature drop and ultralow temperature-dependent thermal boundary resistance. Importantly, we find an unexpected thermal rectification phenomenon, i.e, the thermal conductivity and Kapitza conductance is asymmetric with respect to the thermal transport direction. And the effect of thermal rectification could be amplified by increasing the difference of temperature imposed on two sides. Our results propose a new promising kind of thermal rectifier and phonon diodes from polycrystalline graphene without delicate manupulation of the atomic structures.

Cao, Hai-Yuan; Gong, Xin-Gao

2011-01-01

89

Interfacial thermal resistance and thermal rectification between suspended and encased single layer graphene  

Science.gov (United States)

With molecular dynamics simulations, we systematically investigate interfacial thermal resistance between suspended and encased single layer graphene. Combining with lattice dynamics analysis, we demonstrate that induced by substrate coupling which serves as perturbation, the long wavelength flexural phonon mode in the encased graphene is significantly suppressed when compared with that in the suspended graphene. Therefore, at the interface between suspended and encased graphene, in-plane phonon modes can transmit well, whereas low frequency flexural phonon modes are reflected, leading to this nontrivial interfacial thermal resistance. The impacts of coupling strength, temperature, and size of the system on this type of interfacial thermal resistance are explored. More interesting, we find that thermal rectification can be realized in this inhomogeneous encased graphene structures with a thermal rectification efficiency of 40% at 50 K temperature difference. Our study provides insight to better understand thermal transport in two-dimensional materials and promising structures for practical thermal rectification devices.

Xu, Wen; Zhang, Gang; Li, Baowen

2014-10-01

90

Towards molecular electronics: electron transport through single molecules  

International Nuclear Information System (INIS)

Full text: Molecular electronics, a new emerging science area in the field of nanotechnology, is seen as a potential replacement for silicon device-technology in the next decade. To enable such a technology, an essential initial requirement is a detailed understanding of the electrical conduction properties of molecules placed between metal electrodes. We recently investigated the electrical conduction of single molecules using first-principle quantum mechanical calculations based on the density functional theory and non-equilibrium Green's function techniques. We demonstrate that each molecule has its own distinct current-voltage characteristic, determined by the positions of the molecular energy levels and the degree of electrode-molecule coupling. We show that the calculated attenuation factors of molecular wires made of polyene dithiol, polyphenyl dithiol and alkane dithiol agree with experimental data. Furthermore we reveal that photo isomerization of azobenzene can be utilized as an electrical molecular switch and that bipyridine dithiol, in the presence of a gate electrode, can function as a single-molecule field-effect transistor. Different experimental techniques that help to elucidate the conduction properties of single molecules will be discussed

91

Modeling ion sensing in molecular electronics  

International Nuclear Information System (INIS)

We examine the ability of molecules to sense ions by measuring the change in molecular conductance in the presence of such charged species. The detection of protons (H+), alkali metal cations (M+), calcium ions (Ca2+), and hydronium ions (H3O+) is considered. Density functional theory (DFT) is used within the Keldysh non-equilibrium Green's function framework (NEGF) to model electron transport properties of quinolinedithiol (QDT, C9H7NS2), bridging Al electrodes. The geometry of the transport region is relaxed with DFT. The transport properties of the device are modeled with NEGF-DFT to determine if this device can distinguish among the M+ + QDT species containing monovalent cations, where M+ = H+, Li+, Na+, or K+. Because of the asymmetry of QDT in between the two electrodes, both positive and negative biases are considered. The electron transmission function and conductance properties are simulated for electrode biases in the range from ?0.5?V to 0.5?V at increments of 0.1 V. Scattering state analysis is used to determine the molecular orbitals that are the main contributors to the peaks in the transmission function near the Fermi level of the electrodes, and current-voltage relationships are obtained. The results show that QDT can be used as a proton detector by measuring transport through it and can conceivably act as a pH sensor in solutions. In addition, QDT may be able to distinguish among different monovalent species. This work suggests an approach to design modern molecular electronic conductance sensors with high sensitivity and specificity using well-established quantum chemistry

92

Modeling ion sensing in molecular electronics  

Energy Technology Data Exchange (ETDEWEB)

We examine the ability of molecules to sense ions by measuring the change in molecular conductance in the presence of such charged species. The detection of protons (H{sup +}), alkali metal cations (M{sup +}), calcium ions (Ca{sup 2+}), and hydronium ions (H{sub 3}O{sup +}) is considered. Density functional theory (DFT) is used within the Keldysh non-equilibrium Green's function framework (NEGF) to model electron transport properties of quinolinedithiol (QDT, C{sub 9}H{sub 7}NS{sub 2}), bridging Al electrodes. The geometry of the transport region is relaxed with DFT. The transport properties of the device are modeled with NEGF-DFT to determine if this device can distinguish among the M{sup +} + QDT species containing monovalent cations, where M{sup +} = H{sup +}, Li{sup +}, Na{sup +}, or K{sup +}. Because of the asymmetry of QDT in between the two electrodes, both positive and negative biases are considered. The electron transmission function and conductance properties are simulated for electrode biases in the range from ?0.5?V to 0.5?V at increments of 0.1 V. Scattering state analysis is used to determine the molecular orbitals that are the main contributors to the peaks in the transmission function near the Fermi level of the electrodes, and current-voltage relationships are obtained. The results show that QDT can be used as a proton detector by measuring transport through it and can conceivably act as a pH sensor in solutions. In addition, QDT may be able to distinguish among different monovalent species. This work suggests an approach to design modern molecular electronic conductance sensors with high sensitivity and specificity using well-established quantum chemistry.

Chen, Caroline J.; Smeu, Manuel, E-mail: manuel.smeu@northwestern.edu; Ratner, Mark A., E-mail: ratner@northwestern.edu [Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208 (United States)

2014-02-07

93

Modeling ion sensing in molecular electronics  

Science.gov (United States)

We examine the ability of molecules to sense ions by measuring the change in molecular conductance in the presence of such charged species. The detection of protons (H+), alkali metal cations (M+), calcium ions (Ca2+), and hydronium ions (H3O+) is considered. Density functional theory (DFT) is used within the Keldysh non-equilibrium Green's function framework (NEGF) to model electron transport properties of quinolinedithiol (QDT, C9H7NS2), bridging Al electrodes. The geometry of the transport region is relaxed with DFT. The transport properties of the device are modeled with NEGF-DFT to determine if this device can distinguish among the M+ + QDT species containing monovalent cations, where M+ = H+, Li+, Na+, or K+. Because of the asymmetry of QDT in between the two electrodes, both positive and negative biases are considered. The electron transmission function and conductance properties are simulated for electrode biases in the range from -0.5 V to 0.5 V at increments of 0.1 V. Scattering state analysis is used to determine the molecular orbitals that are the main contributors to the peaks in the transmission function near the Fermi level of the electrodes, and current-voltage relationships are obtained. The results show that QDT can be used as a proton detector by measuring transport through it and can conceivably act as a pH sensor in solutions. In addition, QDT may be able to distinguish among different monovalent species. This work suggests an approach to design modern molecular electronic conductance sensors with high sensitivity and specificity using well-established quantum chemistry.

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

2014-02-01

94

Characterization of Hybrid Electronic Materials for Molecular Based Device Electronics  

Science.gov (United States)

Nanoscale device development, as an exercise in electronic materials fabrication, comes down to essentially one of two approaches---``top-down'' or ``bottom-up.'' In the former, the drive is to retain the macroscopic properties of the materials involved while shrinking toward ever diminishing device geometries. The latter approach attempts to control individual molecules and/or quantum-level structures, during the course of fabrication, in order to ultimately realize device functionality. This bottom-up design and control of molecular assemblies has united device engineers and scientists in testing new combinations of materials, both organic and inorganic. As a result, an entirely new class of nanoscale electronic structures and devices has emerged to create the field of hybrid electronic materials or HEMs^1. HEMs have shown promise as the basis for exciting device applications ranging from quantum computing to unique drug delivery methods. Although theoretical proposals of unimolecular transport began as early as the 1970s, it has been within the last decade in particular that research has yielded significant results in terms of nanoscale electronic applications for HEMs^2. However, many unresolved fundamental issues of electronic materials remain in this field. It is for this reason that in this talk, I will discuss a selection of HEM components (e.g.- self-assembled monolayers of n-alkanethiols, porphyrin molecules), their characterization, and their propensity for future nanoelectronic device development. 1. James R. Heath and Mark A. Ratner, Physics Today, May 2003; 43-49. 2. Mark A. Reed and Takhee Lee (Eds.), ``Molecular Nanoelectronics,'' American Scientific Publishers, Stevenson Ranch, CA, 2003.

Daniels-Race, Theda

2008-03-01

95

Modelling of inelastic effects in molecular electronics  

Energy Technology Data Exchange (ETDEWEB)

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.

Jauho, Antti-Pekka [MIC - Department of Micro and Nanotechnology NanoDTU, Technical University of Denmark, Bldg. 345East, Oersteds Plads, DK-2800 Kgs. Lyngby (Denmark)

2006-04-01

96

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

97

Projected quasiparticle theory for molecular electronic structure.  

Science.gov (United States)

We derive and implement symmetry-projected Hartree-Fock-Bogoliubov (HFB) equations and apply them to the molecular electronic structure problem. All symmetries (particle number, spin, spatial, and complex conjugation) are deliberately broken and restored in a self-consistent variation-after-projection approach. We show that the resulting method yields a comprehensive black-box treatment of static correlations with effective one-electron (mean-field) computational cost. The ensuing wave function is of multireference character and permeates the entire Hilbert space of the problem. The energy expression is different from regular HFB theory but remains a functional of an independent quasiparticle density matrix. All reduced density matrices are expressible as an integration of transition density matrices over a gauge grid. We present several proof-of-principle examples demonstrating the compelling power of projected quasiparticle theory for quantum chemistry. PMID:21974513

Scuseria, Gustavo E; Jiménez-Hoyos, Carlos A; Henderson, Thomas M; Samanta, Kousik; Ellis, Jason K

2011-09-28

98

Flexible molecular-scale electronic devices.  

Science.gov (United States)

Flexible materials and devices could be exploited in light-emitting diodes, electronic circuits, memory devices, sensors, displays, solar cells and bioelectronic devices. Nanoscale elements such as thin films, nanowires, nanotubes and nanoparticles can also be incorporated into the active films of mechanically flexible devices. Large-area devices containing extremely thin films of molecular materials represent the ultimate scaling of flexible devices based on organic materials, but the influence of bending and twisting on the electrical and mechanical stability of such devices has never been examined. Here, we report the fabrication and characterization of two-terminal electronic devices based on self-assembled monolayers of alkyl or aromatic thiol molecules on flexible substrates. We find that the charge transport characteristics of the devices remain stable under severe bending conditions (radius ? 1 mm) and a large number of repetitive bending cycles (?1,000). The devices also remain reliable in various bending configurations, including twisted and helical structures. PMID:22659606

Park, Sungjun; Wang, Gunuk; Cho, Byungjin; Kim, Yonghun; Song, Sunghoon; Ji, Yongsung; Yoon, Myung-Han; Lee, Takhee

2012-07-01

99

Electron dynamics in molecular interactions principles and applications  

CERN Document Server

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

Hagelberg, Frank

2013-01-01

100

Electron-pair excitations and the molecular Coulomb continuum  

Energy Technology Data Exchange (ETDEWEB)

Electron-pair excitations in the molecular hydrogen continuum are described by quantizing rotations of the momentum plane of the electron pair about 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.

Colgan, James [Los Alamos National Laboratory

2009-01-01

 
 
 
 
101

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

International Nuclear Information System (INIS)

Silicon oxide (SiOx) thin film was deposited onto fluorine-doped tin oxide (FTO) and silicon wafer substrate by the reduction of an aqueous solution containing ammonium hexafluorosilicate, dimethylamine borane and cetyltrimethylammonium bromide (CTAB). Characterization of the films by X-ray photoelectron spectroscopic depth profile and infrared spectroscopy proved that the addition of CTAB into the film enhanced the aggregation of silica particles and the growth rate. The SiOx films (resistivity: 3.2 x 108 ? cm) remarkably improved the rectification properties of FTO/SiOx/poly(3,4-ethylenedioxythiophene) derivative diodes. A rectification mechanism based on conduction of electron and ions was investigated.

102

Electron transfer through rigid organic molecular wires enhanced by electronic and electron–vibration coupling  

Science.gov (United States)

Electron transfer (ET) is a fundamental process in a wide range of biological systems, photovoltaics and molecular electronics. Therefore to understand the relationship between molecular structure and ET properties is of prime importance. For this purpose, photoinduced ET has been studied extensively using donor–bridge–acceptor molecules, in which ?-conjugated molecular wires are employed as bridges. Here, we demonstrate that carbon-bridged oligo-p-phenylenevinylene (COPV), which is both rigid and flat, shows an 840-fold increase in the ET rate compared with the equivalent flexible molecular bridges. A 120-fold rate enhancement is explained in terms of enhanced electronic coupling between the electron donor and the electron acceptor because of effective conjugation through the COPVs. The remainder of the rate enhancement is explained by inelastic electron tunnelling through COPV caused by electron–vibration coupling, unprecedented for organic molecular wires in solution at room temperature. This type of nonlinear effect demonstrates the versatility and potential practical utility of COPVs in molecular device applications.

Sukegawa, Junpei; Schubert, Christina; Zhu, Xiaozhang; Tsuji, Hayato; Guldi, Dirk M.; Nakamura, Eiichi

2014-10-01

103

Electron transfer through rigid organic molecular wires enhanced by electronic and electron-vibration coupling.  

Science.gov (United States)

Electron transfer (ET) is a fundamental process in a wide range of biological systems, photovoltaics and molecular electronics. Therefore to understand the relationship between molecular structure and ET properties is of prime importance. For this purpose, photoinduced ET has been studied extensively using donor-bridge-acceptor molecules, in which ?-conjugated molecular wires are employed as bridges. Here, we demonstrate that carbon-bridged oligo-p-phenylenevinylene (COPV), which is both rigid and flat, shows an 840-fold increase in the ET rate compared with the equivalent flexible molecular bridges. A 120-fold rate enhancement is explained in terms of enhanced electronic coupling between the electron donor and the electron acceptor because of effective conjugation through the COPVs. The remainder of the rate enhancement is explained by inelastic electron tunnelling through COPV caused by electron-vibration coupling, unprecedented for organic molecular wires in solution at room temperature. This type of nonlinear effect demonstrates the versatility and potential practical utility of COPVs in molecular device applications. PMID:25242485

Sukegawa, Junpei; Schubert, Christina; Zhu, Xiaozhang; Tsuji, Hayato; Guldi, Dirk M; Nakamura, Eiichi

2014-10-01

104

Time rectification system for in-beam TOF-PET  

International Nuclear Information System (INIS)

A time rectification system for a In-Beam TOF-PET was described.It consists of a pair of BaF2(?40 mm x 45 mm) crystals coupled to Philips photomultipliers XP2020Q and a time coincidence electronic system using standard NIM modules. The best coincidence timing resolution of the system for pairs of 511 keV gamma rays is 576 ps. Some factors affecting the time resolution were primarily discussed, such as the types of photomultiplier tubes (PMT), the model of signal readout, the effects of different discriminators and timing amplifiers. The experiment results show that the signal read from the PMT dynode can get the optimum resolution; the PMT types, especially the rise time and electronic transmit time greatly affect the system performance. The shorter the rise time and electronic transmit time for the PMTs is, the better the timing performance is. The system timing performance is also related to the electronic combination. (authors)

105

Safety of electronic molecular resonance adenoidectomy.  

Science.gov (United States)

Adenoidectomy is one of the most frequent operations in children. In order to reduce hospital stay costs, today, this procedure is performed as day surgery. Even though adenoidectomy is not considered risky, some minor complications may occur, the most important being bleeding (0.5-8% incidence). The surgical technique used can influence considerably postoperative pain and time to recovery. This aspect is essential in the management of day surgery patients, for whom the need of safe and rapid maneuvers associated with early recovery determines the choice of the surgical procedure. Recently, we developed a surgical technique based on the use of an electronic molecular resonance tool associated with bendable suction electrocautery. This study was carried out on 600 patients, divided into two groups, the first undergoing ablation using the molecular resonance tool and the second undergoing curette adenoidectomy. The two groups were homogeneous for age, sex, surgical indications, and grade of adenoid hypertrophy. The following parameters were considered: duration of surgery, importance of intraoperative bleeding, time to cicatrization, incidence of bleeding complications. Duration of surgery and intra- and postoperative bleeding were much lower in the first group than in the group undergoing traditional adenoidectomy. In addition, rhinopharyngeal complete cicatrization, defined as absolute absence of pseudomembrane, was much quicker in the first group, as assessed by postoperative endoscopy. Another major advantage offered by the molecular resonance tool is the accuracy of surgery performed under visual control in a practically bloodless field. To sum up, this method, thanks to its technical features and safety, is particularly indicated in children and in patients with coagulation disorders. PMID:15533564

Tarantino, V; D'Agostino, R; Melagrana, A; Porcu, A; Stura, M; Vallarino, R; Calevo, M G

2004-12-01

106

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

107

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

Directory of Open Access Journals (Sweden)

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

Shin-ya Koshihara

2012-07-01

108

Molecular and electronic structure of Tröger's bases  

Science.gov (United States)

The equilibrium conformations of Tröger's base and two new analogues were investigated at the MP2/6-31G(d, p) ab initio level of theory. The electronic structure of these rigid yet sharply folded molecules was investigated by means of their spectroscopic properties. The 13C-NMR chemical shifts, calculated by the CSGT (continuous set of gauge transformations) formalism with the HF-B3LYP/6-311+G(2d, p) hybrid functional model, were fairly consistent with NMR observations. The He(I) photoelectron spectra were measured and interpreted by means of ab initio many-body OVGF (outer valence Green's function) calculations. The theoretical results satisfactorily reproduced the energies and splittings of the uppermost bands, associated with the two nitrogen lone pair orbitals and the phenyl ? orbitals. Electron transmission spectroscopy, with the support of calculated ?? virtual orbital energies, was employed to characterize the empty molecular levels. The 2,3,8,9-tetramethoxy analogue of Tröger's base exhibits a complex conformational situation. Whereas its NMR spectrum indicates a predominance of trans- trans arrangements of the two o-dimethoxy groups in CDCl 3 solution, its photoelectron spectrum should be interpreted in terms of a mixture of the trans- trans and twisted conformers in the gas phase.

Galasso, V.; Jones, D.; Modelli, A.

2003-03-01

109

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

2011-09-21

110

Molecular Self-assembly for Organic Electronics  

Science.gov (United States)

Self-assembled thin films of novel organic molecules hold the promise of emerging technologies and applications ranging from sensors for biological applications to organic electronics and more efficient organic photovoltaics. Self-assembled monolayers (SAMs) form as a result of a delicate balance between competing molecule-substrate and intermolecular interactions. To control such self-assembly processes, it is mandatory to understand how this balance reflects onto the SAM's final structure. Here we present an ultra-high vacuum scanning tunneling microscopy (STM) study of the self-assembly of novel pentacene derivatives and functionalized fullerenes (F-C60) on metal surfaces. Pentacene is known to exhibit large carrier mobility and has been studied extensively as a semiconductor in organic thin film devices. However, it is subject to facile photo-oxidation that limits device lifetime. We recently synthesized novel pentacene derivatives that show a dramatically increased resistance to photo-oxidation. We identified 6,13-dichloropentacene as a promising candidate for organic electronics. On the compact surface of gold, 6,13-dichloropentacene forms self-assembled domains with various high symmetry orientations. The quality of the SAM is seem to dramatically improve when the 6,13-dichloropentacene are deposited on the (788) vicinal surface of gold where the presence of parallel atomic steps will select only one of the possible SAM orientations due to the molecule-step interaction. Thus we observe the formation of very large self-assembled 6,13-dichloropentacene monolayers with perfect single domain orientation. We have also studied the self-assembly of C60 functionalized with alkyl chains of various lengths (F-C60) on Ag(111). We find that as a function of the alkyl chain length various structures are forming, ranging from zigzag like to linear arrays of C60 fullerene cages. The symmetry and unit cell size of the F-C60 SAMs is dictated by the alkyl-surface and the intermolecular interactions. These results show that C60 molecules can be assembled in 2D and non-compact molecular arrays with a surface density controllable via appropriate chemical functionalization. Those structures show promise as candidates for selfassembled molecular junctions.

Wang, Jun; Kaur, Irvinder; Diaconescu, Bogdan; Jazdzyk, Mikael; Miller, Glen P.; Pohl, Karsten

2009-10-01

111

Distance Dependence of the Electronic Contact of a Molecular Wire  

Science.gov (United States)

The central molecular wire of a so-called Reactive Lander molecule is brought in electronic contact with an atomic scale metallic nanostructure by manipulation with the STM tip. Several stable conformations are obtained in a controlled way, in accordance with calculations. An additional contribution to the tunneling current is observed at the end of the molecular board, reflecting the electronic interaction between the molecular wire and the nanostructure. The characteristic intensity of this electronic contact for different conformations is discussed by means of the vertical interatomic distance between the molecular wire and the metal atoms.

Grill, L.; Moresco, F.; Jiang, P.; Stojkovic, S.; Gourdon, A.; Joachim, C.; Rieder, K.-H.

2005-09-01

112

Noise rectification in quasigeostrophic forced turbulence  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

1998-01-01

113

Quality of approximate electron densities and internal consistency of molecular alignment algorithms in molecular quantum similarity.  

Science.gov (United States)

The calculation of molecular quantum similarity measures using the molecular electron density requires the electron density and molecular alignment between two molecules. To obtain meaningful quantum similarity matrices, the electron density should be calculated efficiently and accurately and the alignment should be internally consistent. The internal consistency of the alignment for a series of molecules is investigated through distance geometry concepts. The calculation of the quantum similarity matrix requires the calculation of a quadratic number of similarity integrals, and a scheme to obtain these efficiently is developed. Both the alignment procedure and the ASA method for approximate molecular electron densities are tested for a set of steroid molecules. PMID:12870913

Bultinck, Patrick; Carbó-Dorca, Ramon; Van Alsenoy, Christian

2003-01-01

114

Predicted Rectification and Negative Differential Spin Seebeck Effect at Magnetic Interfaces  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study the nonequilibrium Seebeck spin transport across metal-magnetic insulator interfaces. The conjugate-converted thermal-spin transport is assisted by the exchange interaction at the interface, between conduction electrons in the metal lead and localized spins in the insulating magnet lead. We predict the rectification and negative differential spin Seebeck effect and resolve their microscopic mechanism, as a consequence of the strongly-fluctuated electronic density of...

Ren, Jie

2013-01-01

115

Estimates of electron capture cross sections for excited molecular states  

International Nuclear Information System (INIS)

The reciprocity between radiative electron attachment and photodetachment serves to justify the use of a one-electron theory of photodetachment to estimate the likelihood of interactions between a free electron and various excited molecular states. Results indicate a strong dependence of interaction likelihood on the electronic state of the molecule and imply that the electron capture cross sections for excited molecules could be significantly different than those for ground state molecules. 4 figs

116

Current rectification by asymmetric molecules: An ab initio study  

CERN Document Server

We study current rectification effect in an asymmetric molecule HOOC-C$_6$H$_4$-(CH$_2$)$_n$ sandwiched between two Aluminum electrodes using an {\\sl ab initio} nonequilibrium Green function method. The conductance of the system decreases exponentially with the increasing number $n$ of CH$_2$. The phenomenon of current rectification is observed such that a very small current appears at negative bias and a sharp negative differential resistance at a critical positive bias when $n\\ge 2$. The rectification effect arises from the asymmetric structure of the molecule and the molecule-electrode couplings. A significant rectification ratio of $\\sim$38 can be achieved when $n=5$.

Zhou, Y; Xu, Y; Zeng, Z Y; Zhou, Yan-hong; Zheng, Xiao-hong; Xu, Ying; Zeng, Zhao Yang

2006-01-01

117

A New Full Adder Cell for Molecular Electronics  

Directory of Open Access Journals (Sweden)

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

Keivan Navi

2012-01-01

118

Molecular Modeling and Multiscaling Issues for Electronic Material Applications  

CERN Document Server

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

Yuen, Matthew; Fan, Haibo

2012-01-01

119

A molecular shift register based on electron transfer  

Science.gov (United States)

An electronic shift-register memory at the molecular level is described. The memory elements are based on a chain of electron-transfer molecules and the information is shifted by photoinduced electron-transfer reactions. This device integrates designed electronic molecules onto a very large scale integrated (silicon microelectronic) substrate, providing an example of a 'molecular electronic device' that could actually be made. The design requirements for such a device and possible synthetic strategies are discussed. Devices along these lines should have lower energy usage and enhanced storage density.

Hopfield, J. J.; Onuchic, Josenelson; Beratan, David N.

1988-01-01

120

Encyclopedia of molecular biology [electronic resource  

International Nuclear Information System (INIS)

Focusing on the fundamentals of molecular biology and encompassing all aspects of the expression of genetic information, this encyclopedia will become the first point of reference for both newcomers and established professionals in molecular biology needing to learn about any particular aspect of the field.

 
 
 
 
121

Concatenation of reversible electronic energy transfer and photoinduced electron transfer to control a molecular piston.  

Science.gov (United States)

Reversible electronic energy transfer and photoinduced electron transfer conspire in the light-driven dethreading of a molecular piston, showing the potential of combining these processes in supramolecular systems. PMID:22428161

Scarpantonio, Luca; Tron, Arnaud; Destribats, Carole; Godard, Pascale; McClenaghan, Nathan D

2012-04-25

122

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

123

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

124

Using molecular similarity to construct accurate semiempirical electron structure theories  

CERN Document Server

A methodology is developed for building semiempirical exchange-correlation functionals for large molecules. The method uses molecular similarity by assuming that data collected for a molecular subsystem in various environments, such as for an aldehyde functional group in different molecules and electrostatic fields, contains the information needed to describe it in other similar environments. The method uses a data set of highly accurate calculations on a molecular subsystem to map the subsystem two-electron density onto its one-electron density. The two-electron density, and therefore the exchange-correlation functional, of a large molecule is approximated from the predicted two-electron densities of overlapping molecular subsystems. The method is demonstrated on two simple model systems: full inclusion of correlation on minimal-basis hydrogen chains and MP2 on substituted aldehydes.

Janesko, B G; Janesko, Benjamin G.; Yaron, David

2003-01-01

125

Precision Rectification of Airborne SAR Image  

DEFF Research Database (Denmark)

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

Dall, JØrgen; Zhang, Zhe

1997-01-01

126

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

127

Rectification of niobium and tantalum pentachlorides in packed columns  

International Nuclear Information System (INIS)

Experimentally determined are mass transfer characteristics of the packed column - the height of the transfer units at rectification separation of mixtures of niobium and tantalum pentachlorides. Experimental data on corrosion resistance and rectification kinetics confirmed the expediency of the use of packed columns for separation and purification of niobium and tantalum pentachlorides

128

Photoelectrochemical solar conversion systems molecular and electronic aspects  

CERN Document Server

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

Munoz, Andres G

2012-01-01

129

Electron and molecular ion collisions relevant to divertor plasma  

International Nuclear Information System (INIS)

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

130

Projectile electron loss with a molecular hydrogen target  

International Nuclear Information System (INIS)

We examine the effect of a molecular hydrogen target, as contrasted with an atomic target, on one-electron-projectile electron loss within the framework of the plane-wave Born approximation. Two different approaches are explored: (1) the use of an approximate molecular wave function due to Weinbaum, and (2) the use of a modified form factor for the two atoms in the H2 molecule. The resulting cross-section expressions are compared with experimental cross sections for electron loss by various one-electron projectiles. We find that for a projectile atomic number larger than 5, molecular effects are negligible in total cross sections and then the electron-loss cross section per molecule is just equal to twice the total cross section per atom

131

Molecular orbital theory and its application to electron spectroscopy  

International Nuclear Information System (INIS)

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

132

Electron propagator theory approach to ab initio calculations of electron transfer rate and molecular conductance  

Science.gov (United States)

The ab initio theoretical approach to calculations of molecular electron transfer rate and molecular junction conductance is presented. The implemented approach is founded on Landauer formalism coupled to electron propagator theory (Green-Keldysh functions formalism) of solving the Dyson equation for molecular junction. The electron transfer rate calculation algorithm implementing quantum chemistry computational software output is proposed. The conductance through a single molecular orbital is found to be equal to a quantum of conductance, 2e2/h. The existence of the maximal value of electron transfer rate through a single molecular orbital is proposed, (?2/4h)?L?RF, whose order-of-magnitude estimate is 1011-1013 s-1.

Kletsov, Aleksey A.

2014-09-01

133

The electron momentum distribution of molecular hydrogen  

International Nuclear Information System (INIS)

The (e,2e) cross section for electron impact ionization of the hydrogen molecule has been measured with a precision of a few percent at 400 eV incident energy. The experimental values are compared to predictions based upon a broad range of theoretical wavefunctions. Discrepancies between theory and experiment are similar to those found when comparing experimental and theoretical Compton profiles. (orig.)

134

Energy Transformation in Molecular Electronic Systems  

Energy Technology Data Exchange (ETDEWEB)

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

Kasha, Michael

1999-05-17

135

Molecular frame Auger electron energy spectrum from N2  

Science.gov (United States)

Here we present the first angle-resolved, non-resonant (normal) Auger spectra for impulsively aligned nitrogen molecules. We have measured the angular pattern of Auger electron emission following K-shell photoionization by 1.1 keV photons from the Linac Coherent Light Source (LCLS). Using strong-field-induced molecular alignment to make molecular frame measurements is equally effective for both repulsive and quasi-bound final states. The capability to resolve Auger emission angular distributions in the molecular frame of reference provides a new tool for spectral assignments in congested Auger electron spectra that takes advantage of the symmetries of the final diction states. Based on our experimental results and theoretical predictions, we propose the assignment of the spectral features in the Auger electron spectrum.

Cryan, J. P.; Glownia, J. M.; Andreasson, J.; Belkacem, A.; Berrah, N.; Blaga, C. I.; Bostedt, C.; Bozek, J.; Cherepkov, N. A.; DiMauro, L. F.; Fang, L.; Gessner, O.; Gühr, M.; Hajdu, J.; Hertlein, M. P.; Hoener, M.; Kornilov, O.; Marangos, J. P.; March, A. M.; McFarland, B. K.; Merdji, H.; Messerschmidt, M.; Petrovi?, V. S.; Raman, C.; Ray, D.; Reis, D. A.; Semenov, S. K.; Trigo, M.; White, J. L.; White, W.; Young, L.; Bucksbaum, P. H.; Coffee, R. N.

2012-03-01

136

Room Temperature Molecular Single-Electron Transistor  

CERN Document Server

A room temperature single-electron transistor based on the single cluster molecule has been demonstrated for the first time. Scanning tunneling microscope tip was used to study the transport via single carboran cluster molecules 1,7-(CH$_3$)$_2$-1,2-C$_2$B$_{10}$H$_9$Tl(OCOCF$_3$)$_2$ incorporated into the Langmuir-Blodgett monolayer of the stearic acid. DC I-V curves at 300 K showed well pronounced Coulomb staircase, and the current could be controlled by a lithographically fabricated gold gate electrode.

Soldatov, E S; Trifonov, A S; Gubin, S P; Kolesov, V V; Presnov, D E; Iakovenko, S A; Khomutov, G B; Korotkov, A N

1996-01-01

137

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

Science.gov (United States)

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

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

2014-02-25

138

Electron-Phonon Correlation Effects in Molecular Transistors  

CERN Document Server

The effects of electron-phonon interactions in molecular transistors are studied analytically in the Kondo regime. We show that a Holstein electron-phonon coupling can explain the weak gate voltage dependence of the Kondo temperature observed experimentally in some of these devices. A molecular center-of-mass mode opens a new channel for charge and spin fluctuations and in the antiadabatic limit the latter are described by an asymmetric two-channel Kondo model. Below the Kondo temperature the system develops a dynamical Jahn-Teller distortion and a low energy peak emerges in the phonon spectral density that could be observed in Raman microscopy experiments.

Balseiro, C A; Grempel, D R

2006-01-01

139

Thomas double scattering in electron capture from oriented molecular hydrogen  

International Nuclear Information System (INIS)

Electron capture from hydrogen molecules by protons is treated using the second-order Born approximation. Differential cross sections in an adiabatic-nuclei approximation for specific molecular orientations and for an equally weighted averaging over all orientations are presented for incident energies of 2.5 and 10 MeV. A Hartree-Fock molecular wave function and linearized-propagator approximation are employed to evaluate the amplitude. An approximate factoring of the amplitude into double scattering and diffraction (arising from the two target nuclei) components is shown to give a poor description of high-velocity molecular capture

140

Inelastic electron tunneling spectroscopy in molecular junctions: Peaks and dips  

CERN Document Server

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

 
 
 
 
141

Peculiarities of electron excitations decay in ion-molecular crystals  

International Nuclear Information System (INIS)

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

142

A new parametrizable model of molecular electronic structure  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A new electronic structure model is developed in which the ground state energy of a molecular system is given by a Hartree-Fock-like expression with parametrized one- and two-electron integrals over an extended (minimal + polarization) set of orthogonalized atom-centered basis functions, the variational equations being solved formally within the minimal basis but the effect of polarization functions being included in the spirit of second-order perturbation theory. It is desi...

Laikov, Dimitri N.

2011-01-01

143

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

144

The Molecular Electronic Device and the Biochip Computer: Present Status  

Science.gov (United States)

The idea that a single molecule might function as a self-contained electronic device has been of interest for some time. However, a fully integrated version--the biochip or the biocomputer, in which both production and assembly of molecular electronic components is achieved through biotechnology--is a relatively new concept that is currently attracting attention both within the scientific community and among the general public. In the present article we draw together some of the approaches being considered for the construction of such devices and delineate the revolutionary nature of the current proposals for molecular electronic devices (MEDs) and biochip computers (BCCs). With the silicon semiconductor industry already in place and in view of the continuing successes of the lithographic process it seems appropriate to ask why the highly speculative MED or BCC has engendered such interest. In some respects the answer is paradigmatic as much as it is real. It is perhaps best stated as the promise of the realm of the molecular. Thus it is envisioned that devices will be constructed by assembly of individual molecular electronic components into arrays, thereby engineering from small upward rather than large downward as do current lithographic techniques. An important corollary of the construction technique is that the functional elements of such an array would be individual molecules rather than macroscopic ensembles. These two aspects of the MED/BCC--assembly of molecular arrays and individually accessible functional molecular units--are truly revolutionary. Both require scientific breakthroughs and the necessary principles, quite apart from the technology, remain essentially unknown. It is concluded that the advent of the MED/BCC still lies well before us. The twin criteria of utilization of individual molecules as functional elements and the assembly of such elements remains as elusive as ever. Biology engineers structures on the molecular scale but biomolecules do not seem to be imbued with useful electronic properties. Molecular beam epitaxy and thin-film techniques produce electronic devices but they ``engineer down'' and are currently unable to generate individual molecular units. The potential of the MED/BCC field is matched only by the obstacles that must be surmounted for its realization.

Haddon, R. C.; Lamola, A. A.

1985-04-01

145

Dynamic rectification in a thermal diode based on fluid-solid interfaces: Contrasting behavior of soft materials and fluids  

Science.gov (United States)

We have used molecular dynamics simulations to demonstrate that significant rectification is possible in nano-devices by manipulating solid-fluid interfaces between a thin solid wall and a soft material. In addition, the nature of the rectification is opposite to that for a solid wall and a simpler polar fluid (e.g., water). This thus opens the possibilities of reversing the direction of rectification in a nano-device which could lead to more precise control of heat transfer rates. Our simulations also show that surface modifications of the type introduced here can lead to over six fold increase in heat transfer rates in nano-devices. Dissipating heat from increasingly miniaturized semi-conductors of the future will become increasingly important since size limitations are often dictated by heat dissipation rates. These results also point to some other exciting practical applications. If the outside wall of a house were made hydrophilic, during hot summer days when the intent is to reduce heat transfer from the ambient (Ta > Tin), a small polar fluid like water could be introduced between the two walls. During nights, in order to cool the house (when Tin > Ta) water could be replaced by a less volatile soft material to enhance heat transfer. Thus, the same wall would demonstrate significant rectification in both cases but with different fluids.

Murad, Sohail; Puri, Ishwar K.

2014-05-01

146

Computational Nanotechnology of Molecular Materials, Electronics and Machines  

Science.gov (United States)

This viewgraph presentation covers carbon nanotubes, their characteristics, and their potential future applications. The presentation include predictions on the development of nanostructures and their applications, the thermal characteristics of carbon nanotubes, mechano-chemical effects upon carbon nanotubes, molecular electronics, and models for possible future nanostructure devices. The presentation also proposes a neural model for signal processing.

Srivastava, D.; Biegel, Bryan A. (Technical Monitor)

2002-01-01

147

The Electron-Pair Repulsion Model for Molecular Geometry  

Science.gov (United States)

Describes how the electron-pair repulsion model qualitatively explains the size and shape of molecular orbitals. Briefly discusses trigonal bipyramidal molecules, three-center bonds, and transition elements. Describes cluster compounds and finishes with a discussion of the exceptions to the model and effects of ligand-ligand repulsions. (RR)

Gillespie, R. J.

1970-01-01

148

Exploring coherent transport through ?-stacked systems for molecular electronic devices  

DEFF Research Database (Denmark)

Understanding electron transport across ?-stacked systems can help to elucidate the role of intermolecular tunneling in molecular junctions and potentially with the design of high-efficiency molecular devices. Here we show how conjugation length and substituent groups influence the electron transport and thermoelectric response in the ?-stacked structures by investigating five representative stacked molecular junctions. We found that a ?-stacked system of two substituted anthracenes exhibits good thermopower and a high power factor, suggesting that increased conjugation can enhance the thermoelectric response. The fully eclipsed structure of quinhydrone exhibits a high power factor at the minimum energy structure and could thus be a better candidate in a thermoelectric device compared with the other ?-stacked systems considered.

Li, Qian; Solomon, Gemma

2014-01-01

149

Electron energy-loss spectra in molecular fluorine  

Science.gov (United States)

Electron energy-loss spectra in molecular fluorine, for energy losses from 0 to 17.0 eV, have been taken at incident electron energies of 30, 50, and 90 eV and scattering angles from 5 to 140 deg. Features in the spectra above 11.5 eV energy loss agree well with the assignments recently made from optical spectroscopy. Excitations of many of the eleven repulsive valence excited electronic states are observed and their location correlates reasonably well with recent theoretical results. Several of these excitations have been observed for the first time and four features, for which there are no identifications, appear in the spectra.

Nishimura, H.; Cartwright, D. C.; Trajmar, S.

1979-01-01

150

Theory and Application of Dissociative Electron Capture in Molecular Identification  

CERN Document Server

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

151

Electron induced ionization and dissociation of molecular ions  

Science.gov (United States)

The present study is devoted to the quantitative investigation of electron-induced ionization and dissociation reactions of molecular ions using a novel experimental technique developed in our lab.These reactions are of importance in plasmas where step-wise ionization and dissociation reactions can occur at appreciable rates and thus strongly influence the plasma properties. We have extended studies for the case of electron-induced dissociation reactions of molecular ions from the mere measurement of cross section functions to the simultaneous determination of the kinetic energy distribution (KED) of the product ions formed and the corresponding cross section q. This allows us to obtain three-dimensional plots of the single differential cross section dq/dW versus incident electron energy E and product ion kinetic energy W.

Matt, Sara; David, Rainer; Stamatovic, Aleksander; Scheier, Paul; Maerk, Tilmann

1999-10-01

152

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

Science.gov (United States)

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. PMID:23824018

Ge, Ling; Bernasconi, Leonardo; Hunt, Patricia

2013-08-21

153

Analytical techniques for characterization of organic molecular assemblies in molecular electronics devices  

International Nuclear Information System (INIS)

The analytical techniques used for the physical characterization of organic molecular electronic-based devices are surveyed and discussed. These protocols include methods that are used to probe molecular assemblies such as single wavelength ellipsometry, water contact angle goniometry, cyclic voltammetry, infrared spectroscopy, and X-ray photoelectron spectroscopy, and methods used to measure charge transport properties of devices such as scanning tunneling microscopy, and inelastic electron tunneling spectroscopy. Examples from our laboratory and the literature are given for each of these analytical techniques

154

Analytical techniques for characterization of organic molecular assemblies in molecular electronics devices  

Energy Technology Data Exchange (ETDEWEB)

The analytical techniques used for the physical characterization of organic molecular electronic-based devices are surveyed and discussed. These protocols include methods that are used to probe molecular assemblies such as single wavelength ellipsometry, water contact angle goniometry, cyclic voltammetry, infrared spectroscopy, and X-ray photoelectron spectroscopy, and methods used to measure charge transport properties of devices such as scanning tunneling microscopy, and inelastic electron tunneling spectroscopy. Examples from our laboratory and the literature are given for each of these analytical techniques.

James, Dustin K. [Department of Chemistry and Smalley Institute for Nanoscale Science and Technology, MS 222, Rice University, 6100 Main Street, Houston, TX 77005 (United States)]. E-mail: dustin@rice.edu; Tour, James M. [Department of Chemistry and Smalley Institute for Nanoscale Science and Technology, MS 222, Rice University, 6100 Main Street, Houston, TX 77005 (United States)]. E-mail: tour@rice.edu

2006-05-24

155

Research ZVS Synchronous Rectification of Resonant Converter  

Directory of Open Access Journals (Sweden)

Full Text Available In order to expand the application of synchronous rectification, the technology using ZVS synchronous rectifier is studied which is based on the IPT resonant converter. By using its own resonant characteristic, a novel control method that AC-DC section of the resonant converter works in ZVS SR state is proposed in this study. First of all, the ZVS working operation of SR is analyzed and equivalent circuits for each operation mode are also given. On that basis, the novel control method is proposed. Then, according to the differential equations of equivalent circuit, the state space model is established. In order to make full-bridge SR network of the secondary circuit work in ZVS state, the ZVS operating point can be obtained by solving the fixed point function which is based on the state space model and stroboscopic mapping method. Moreover, operating principle of control circuit for ZVS SR is also presented. Finally, experimental results verify the effectiveness of control method proposed in this study.

Xiao Kui Li

2014-01-01

156

A new parametrizable model of molecular electronic structure  

CERN Document Server

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

Laikov, Dimitri N

2011-01-01

157

Laser induced - tunneling, electron diffraction and molecular orbital imaging  

International Nuclear Information System (INIS)

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

158

New directions in electron paramagnetic resonance spectroscopy on molecular nanomagnets.  

Science.gov (United States)

Recent developments and results in the area of electron paramagnetic resonance (EPR) in molecular nanomagnetism are reviewed. Emphasis is placed on unconventional measurement methods, such as frequency-domain magnetic resonance spectroscopy, interferometer-based Fourier-transform, terahertz spectroscopy, and terahertz time-domain spectroscopy. In addition, different methods to investigate EPR by monitoring the change in magnetization or magnetic torque in the presence of microwave radiation are discussed. Finally, an overview is given of application of pulse EPR in investigations of molecular nanomagnets. PMID:22076082

van Slageren, J

2012-01-01

159

Transient Molecular-Ion Formation in Rydberg-Electron Capture  

International Nuclear Information System (INIS)

Resonance structure has been observed in total cross sections for the capture of an electron from a Rydberg-state atom by a singly charged projectile with speed vion comparable to the Bohr velocity ve of the target electron. Prominent peaks in the data at reduced velocities v=vion/ve=0.8 and 0.5 result from two distinct capture mechanisms in which the target electron passes once or three times, respectively, through the midplane between the nuclei. The three-swap peak at v=0.5 marks the high-velocity limit of molecular-ion formation in which the electron is shared between the two charge centers. This result illustrates that new paradigms for collision dynamics may emerge when reactions are examined at or near the correspondence principle limit

160

Transient Molecular-Ion Formation in Rydberg-Electron Capture  

Energy Technology Data Exchange (ETDEWEB)

Resonance structure has been observed in total cross sections for the capture of an electron from a Rydberg-state atom by a singly charged projectile with speed {ital v}{sub ion} comparable to the Bohr velocity {ital v}{sub {ital e}} of the target electron. Prominent peaks in the data at reduced velocities {ital {tilde v}}={ital v}{sub ion}/{ital v}{sub {ital e}}=0.8 and 0.5 result from two distinct capture mechanisms in which the target electron passes once or three times, respectively, through the midplane between the nuclei. The three-swap peak at {ital {tilde v}}=0.5 marks the high-velocity limit of molecular-ion formation in which the electron is shared between the two charge centers. This result illustrates that new paradigms for collision dynamics may emerge when reactions are examined at or near the correspondence principle limit.

MacAdam, K.B.; Day, J.C.; Aguilar, J.C.; Homan, D.M.; MacKellar, A.D.; Cavagnero, N.J. [University of Kentucky, Lexington, Kentucky 40506-0055 (United States)

1995-08-28

 
 
 
 
161

Special issue on ultrafast electron and molecular dynamics  

Science.gov (United States)

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

Martin, Fernando; Hishikawa, Akiyoshi; Vrakking, Marc

2014-06-01

162

Electronic shift register memory based on molecular electron-transfer reactions  

Science.gov (United States)

The design of a shift register memory at the molecular level is described in detail. The memory elements are based on a chain of electron-transfer molecules incorporated on a very large scale integrated (VLSI) substrate, and the information is shifted by photoinduced electron-transfer reactions. The design requirements for such a system are discussed, and several realistic strategies for synthesizing these systems are presented. The immediate advantage of such a hybrid molecular/VLSI device would arise from the possible information storage density. The prospect of considerable savings of energy per bit processed also exists. This molecular shift register memory element design solves the conceptual problems associated with integrating molecular size components with larger (micron) size features on a chip.

Hopfield, J. J.; Onuchic, Jose Nelson; Beratan, David N.

1989-01-01

163

Electronic kinetics of molecular nitrogen and molecular oxygen in high-latitude lower thermosphere and mesosphere  

Directory of Open Access Journals (Sweden)

Full Text Available Total quenching rate coefficients of Herzberg states of molecular oxygen and three triplet states of molecular nitrogen in the collisions with O2 and N2 molecules are calculated on the basis of quantum-chemical approximations. The calculated rate coefficients of electronic quenching of O2* and N2* molecules show a good agreement with available experimental data. An influence of collisional processes on vibrational populations of electronically excited N2 and O2 molecules is studied for the altitudes of high-latitude lower thermosphere and mesosphere during auroral electron precipitation. It is indicated that molecular collisions of metastable nitrogen N2(A3?u* with O2 molecules are principal mechanism in electronic excitation of both Herzberg states c1?u&minus, A'3?u, A3?u+ and high vibrational levels of singlet states a1?g and b1?g+ of molecular oxygen O2 at these altitudes.

A. S. Kirillov

2010-01-01

164

Electronic kinetics of molecular nitrogen and molecular oxygen in high-latitude lower thermosphere and mesosphere  

Energy Technology Data Exchange (ETDEWEB)

Total quenching rate coefficients of Herzberg states of molecular oxygen and three triplet states of molecular nitrogen in the collisions with O{sub 2} and N{sub 2} molecules are calculated on the basis of quantum-chemical approximations. The calculated rate coefficients of electronic quenching of O{sub 2}{sup *} and N{sub 2}{sup *} molecules show a good agreement with available experimental data. An influence of collisional processes on vibrational populations of electronically excited N{sub 2} and O{sub 2} molecules is studied for the altitudes of high-latitude lower thermosphere and mesosphere during auroral electron precipitation. It is indicated that molecular collisions of metastable nitrogen N{sub 2}(A{sup 3}{sigma}{sub u}{sup +}) with O{sub 2} molecules are principal mechanism in electronic excitation of both Herzberg states c{sup 1}{sigma}{sub u}{sup -}, A'{sup 3}{delta}{sub u}, A{sup 3}{sigma}{sub u}{sup +} and high vibrational levels of singlet states a{sup 1}{delta}{sub g} and b{sup 1}{sigma}{sub g}{sup +} of molecular oxygen O{sub 2} at these altitudes. (orig.)

Kirillov, A.S. [Russian Academy of Sciences, Apatity (Russian Federation). Polar Geophysical Inst. of the Kola Science Centre

2010-07-01

165

Determination of hydrogen and electron densities in interstellar molecular clouds  

International Nuclear Information System (INIS)

The moleular hydrogen densities is six interstellar molecular clouds have been determined from the spectral data for 12CO and 13CO using the radiative transfer model with large scale velocity gradient. The results indicate that in the central part of the cloud the density of H2 decreases exponentially with the distance from the centre. This is physically realistic, as a finite value of hydrogen density at the centre is obtained. The electron density near the centre of the Orion A cloud has been determined from the spectral data for HCN. For other clouds considered by us the electron densities appear to be too low to affect the spectral intensity. (author)

166

Electron densities and the excitation of CN in molecular clouds  

Science.gov (United States)

In molecular clouds of modest density and relatively high fractional ionization, the rotational excitation of CN is controlled by a competition among electron impact, neutral impact and the interaction with the cosmic background radiation. The degree of excitation can be measured through optical absorption lines and millimeter-wave emission lines. The available, accurate data on CN in diffuse and translucent molecular clouds are assembled and used to determine electron densities. The derived values, n(e) = roughly 0.02 - 0.5/cu cm, imply modest neutral densities, which generally agree well with determinations by other techniques. The absorption- and emission-line measurements of CN both exclude densities higher than n(H2) = roughly 10 exp 3.5/cu cm on scales varying from 0.001 to 60 arcsec in these clouds.

Black, John H.; Van Dishoeck, Ewine F.

1991-01-01

167

Thermal rectification in nonmetallic solid junctions: Effect of Kapitza resistance  

Science.gov (United States)

Based on Fourier's law for heat conduction, we investigate the asymmetric heat flow in two segment rods of nonmetallic materials. Specifically, we study the effect of the Kapitza resistance at the boundary of the segments on the thermal rectification. To understand basic features of the rectification, we first develop analytical calculation for the heat currents in an ideal rod of a macroscopic length. Explicitly, this is made by assuming that the thermal conductivity of each constituent has a power-law dependence on temperature and also assuming the continuity of temperature at the boundary. Then, we introduce the temperature jump at the boundary due to the Kapitza resistance and show that this effect on the thermal rectification becomes significant as the length of the rod decreases typically to submillimeters. In particular, we find that the temperature jump yields a finite rectification even when no asymmetry is predicted in the heat currents from the continuity of temperature at the junction. The obtained results have an important implication for the analysis of the thermal rectification of a rod consisting of semiconductors Ge and Si.

Tamura, Shin-ichiro; Ogawa, Kazuo

2012-10-01

168

Pressure shifts and electron scattering in atomic and molecular gases  

International Nuclear Information System (INIS)

In this work, the authors focus on one aspect of Rydberg electron scattering, namely number density effects in molecular gases. The recent study of Rydberg states of CH3I and C6H6 perturbed by H2 is the first attempt to investigate number density effects of a molecular perturber on Rydberg electrons. Highly excited Rydberg states, because of their ''large orbital'' nature, are very sensitive to the surrounding medium. Photoabsorption or photoionization spectra of CH3I have also been measured as a function of perturber pressure in 11 different binary gas mixtures consisting of CH3I and each one of eleven different gaseous perturbers. Five of the perturbers were rare gases (He, Ne, Ar, Kr, Xe) and six were non-dipolar molecules (H2, CH4, N2, C2H6, C3H8). The goal of this work is to underline similarities and differences between atomic and molecular perturbers. The authors first list some results of the molecular study

169

The molecular and electronic structure of Li5B4  

International Nuclear Information System (INIS)

Based on a molecular structure characterized earlier, a molecular orbital calculation was made on Li5B4. The electronic structure of Li5B4 thus calculated shows (1) a partial electron charge transfer of about 0.35 eu from a five-lithium-atom cluster (at an energy level E') to a four-boron-atom cluster (also at E') is necessary to stabilize the Li5B4 molecular structure and (2) the stabilization energy based on the electrostatic interaction using a multipole expansion amounts to 2 eV per four-boron-atom unit or equivalent to 1.06 kcal (gm B)-1. From the experimental fact that the Li5B4 compound alloy is a metallic conductor, the remaining 0.65 eu charges in the five-lithium-atom cluster at E' are assumed to delocalize and to become 'free' electrons. This delocalization yields an additional energy of 1.70 kcal (gm B)-1. The calculated total stabilization energy is therefore 2.76 kcal (gm B)-1 compared with the experimental value of 2.2 +- 0.2 kcal (gm B)-1. (Auth.)

170

Nonlinear optical rectification in semiparabolic quantum wells with an applied electric field  

International Nuclear Information System (INIS)

The optical rectification (OR) in a semiparabolic quantum well with an applied electric field has been theoretically investigated. The electronic states in a semiparabolic quantum well with an applied electric field are calculated exactly, within the envelope function and the displaced harmonic oscillator approach. Numerical results are presented for the typical Al x Ga1- x As/GaAs quantum well. These results show that the applied electric field and the confining potential frequency of the semiparabolic quantum well have a great influence on the OR coefficient. Moreover, the OR coefficient also depends sensitively on the relaxation rate of the semiparabolic quantum well system

171

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

DEFF Research Database (Denmark)

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

DiCarlo, L.; M. Marcus, C.

2003-01-01

172

Effects of molecular orientation on electron-transfer collisions  

International Nuclear Information System (INIS)

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

173

Measuring Electronic Properties of Topological Defects in Molecular Graphene  

Science.gov (United States)

With the development of artificial ``molecular'' graphene, it is possible to create a two-dimensional electron system very similar to graphene by assembling molecules in the appropriate geometry on surface states using a scanning tunneling microscope (STM) tip. Using this same system, we recreate many lattice defects that occur naturally in graphene. Such defects have a significant effect on the electronic and transport properties of natural graphene, and are thus of notable interest in the development of nanoelectronics. In particular, we study rotational grain boundaries, which are formed by the rotation of a region of graphene with respect to the rest of the lattice. These include the Stone-Wales defect, the simplest with two adjacent carbon sites rotated by 90 degrees, as well as a common larger topological defect recently identified as the flower defect. Using STM, we examine the electronic properties of these defects in molecular graphene, paying particular attention to the emergence of new states close to the Dirac point and the quasiparticle scattering. These geometries are also studied in hole- and electron-doped variants.

Camp, Charlie; Rastawicki, Dominik; Gomes, Kenjiro; Ko, Wonhee; Mar, Warren; Rue Thian, Ming; Niestemski, Francis; Contryman, Alex; Gonzalez, Carolina; Manoharan, Hari

2012-02-01

174

Rectification and flux reversals for vortices interacting with triangular traps  

International Nuclear Information System (INIS)

We simulate vortices in superconductors interacting with two-dimensional arrays of triangular traps. We find that, upon application of an ac drive, a net dc flow can occur which shows current reversals with increasing ac drive amplitude for certain vortex densities, in agreement with recent experiments and theoretical predictions. We identify the vortex dynamics responsible for the different rectification regimes. We also predict the occurrence of a novel transverse rectification effect in which a dc flow appears that is transverse to the direction of the applied ac drive

175

Consideration of enhancement of thermal rectification using metamaterial models  

Science.gov (United States)

We present a systematic study to highlight some of the fundamental physics that governs metamaterial based electromagnetic thermal rectifiers. In such thermal rectifiers, the rectification arises from the alignment or misalignment of surface resonances in the forward or reverse scenarios, whereas the bulk states of metamaterials do not contribute to rectification. Therefore, we show that one can understand the behavior of such rectifiers by examining the relative excitation strength of the surface and bulk resonances. We verify such an understanding by accounting for the dependence of the contrast ratio on various parameters that define the dielectric response of the metamaterials.

Iizuka, Hideo; Fan, Shanhui

2014-11-01

176

Molecule-electrode interfaces in molecular electronic devices.  

Science.gov (United States)

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. PMID:23571285

Jia, Chuancheng; Guo, Xuefeng

2013-07-01

177

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

178

Electron collisions and internal excitation in stored molecular ion beams  

International Nuclear Information System (INIS)

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

179

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

Science.gov (United States)

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

Sue, Chi-Hau

180

Molecular x-ray- and electron-scattering intensities  

International Nuclear Information System (INIS)

Various results concerning molecular x-ray- and electron-scattering intensities are presented. (i) Directional elastic intensities for H2 and N2 are calculated and a qualitative explanation for the results is given. (ii) The differences between the usual elastic intensities for x-ray and electron scattering from nonvibrating but freely rotating diatomic molecules, and the fully elastic intensities for scattering from the J = 0 state are examined for H2 and N2. The usual elastic intensities are rigorously shown to be greater than the fully elastic ones and the differences are correctly mimicked by the independent-atom model. (iii) Polarization functions are found to be important in the restricted-Hartree-Fock description of the total and elastic intensities. A counterintuitive ordering of basis-set effects on one- and two-electron properties is found and explained in the case of H2. (iv) It is shown that, in two-electron systems, a quantity closely related to the Coulson-Neilson Coulomb hole function can be extracted from experimental x-ray-scattering intensities. Both these quantities are displayed for H2. (v) An analogous procedure in the many-electron case is shown to yield the intracular projection of the statistical pair-correlation density

 
 
 
 
181

Electron transport through catechol-functionalized molecular rods  

International Nuclear Information System (INIS)

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

182

Vibrational excitations in molecular layers probed by ballistic electron microscopy  

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-10-28

183

Theory of electron transfer and molecular state in DNA  

Science.gov (United States)

In this thesis, a mechanism for long-range electron transfer in DNA and a systematic search for high conductance DNA are developed. DNA is well known for containing the genetic code of all living species. On the other hand, there are some experimental indications that DNA can mediate effectively long-range electron transfer leading to the concept of chemistry at a distance. This can be important for DNA damage and healing. In the first part of the thesis, a possible mechanism for long-range electron transfer is introduced. The weak distance dependent electron transfer was experimentally observed using transition metal intercalators for donor and acceptor. In our model calculations, the transfer is mediated by the molecular analogue of a Kondo bound state well known from solid state physics of mixed-valence rare-earth compounds. We believe this is quite realistic, since localized d orbitals of the transition metal ions could function as an Anderson impurity embedded in a reservoir of rather delocalized molecular orbitals of the intercalator ligands and DNA pi orbitals. The effective Anderson model is solved with a physically intuitive variational ansatz as well as with the essentially exact DMRG method. The electronic transition matrix element, which is important because it contains the donor-acceptor distance dependence, is obtained with the Mulliken-Hush algorithm as well as from Born-Oppenheimer potential energy surfaces. Our possible explanation of long-range electron transfer is put in context to other more conventional mechanisms which also could lead to similar behavior. Another important issue of DNA is its possible use for nano-technology. Although DNA's mechanical properties are excellent, the question whether it can be conducting and be used for nano-wires is highly controversial. Experimentally, DNA shows conducting, semi-conducting and insulating properties. Motivated by these wide ranging experimental results on the conductivity of DNA, we have embarked on a theoretical effort to ascertain what conditions might induce such remarkable behavior. We use a combination of an ab initio density functional theory method and a parameterized Huckel-Slater-Koster model. Our focus here is to examine whether any likely DNA structures or environments can yield reduced activation gaps to conduction or enhanced electronic overlaps. In particular, we study a hypothetical stretched ribbon structure, A-, and B-form DNA, and the effects of counterions and humidity. Unlike solids, DNA and other molecules are considered soft condensed matter. Hence, we study the influence of vibrations upon the electronic structure of DNA. We calculate parameters for charge transfer rates between adjacent bases. We find good agreement between our estimated rates and recent experimental data assuming that torsional vibrations limit the charge transfer most significantly.

Endres, Robert Gunter

2002-09-01

184

Electronic and magnetic structure of vivianite: cluster molecular orbital calculations  

Science.gov (United States)

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

Grodzicki, M.; Amthauer, G.

185

Storage ring experiments on electron-molecular-ion interactions  

Science.gov (United States)

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

Wolf, Andreas

2013-07-01

186

Terahertz pulse generation via optical rectification in photonic crystal microcavities  

CERN Document Server

Using a 3D fully-vectorial nonlinear time-domain analysis we numerically investigate the generation of terahertz radiation by pumping a photonic crystal microcavity out of resonance. High quality factors and a quadratic susceptibility lead to few-cycle terahertz pulses via optical rectification. Material dispersion as well as linear and nonlinear anisotropy is fully accounted for.

Falco, A D; Assanto, G; Falco, Andrea Di; Conti, Claudio; Assanto, Gaetano

2005-01-01

187

Probing ultrafast electronic and molecular dynamics with free-electron lasers  

Science.gov (United States)

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

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

2014-06-01

188

Molecular Electronics: Insight from First-Principles Transport Simulations  

DEFF Research Database (Denmark)

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

Paulsson, Magnus; Frederiksen, Thomas

2010-01-01

189

Dissociative electron attachment in nonplanar chlorocarbons with ?*/?*-coupled molecular orbitals  

Science.gov (United States)

Total absolute cross sections for the dissociative electron attachment (DEA) process are reported for a series of nonplanar ethylenic and phenylic compounds monosubstituted with (CH2)nCl groups, where n=1-4. Coupling between the local ?* molecular orbitals provided by the unsaturated moieties and the ?* (C-Cl) orbital is thus examined as a function of the separation of these groups. In particular, the coupling is viewed from the perspective of the interacting temporary negative ions formed by short lived occupation of these orbitals and their decay into the DEA channel. A theoretical treatment of ``remote'' bond breaking, presented elsewhere, satisfactorily accounts for DEA in the chloroethylenic compounds presented here and emphasizes not only the delocalization of the coupled anionic wave functions but the importance of their relative phases. The dependence of the cross sections on the vertical attachment energies, measured by electron transmission spectroscopy, is also explored and compared to that found previously in chlorinated alkanes.

Aflatooni, K.; Gallup, G. A.; Burrow, P. D.

2010-03-01

190

Photoelectron spectroscopy via electronic spectroscopy of molecular ions  

International Nuclear Information System (INIS)

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

191

Imaging ultrafast molecular dynamics with laser-induced electron diffraction.  

Science.gov (United States)

Establishing the structure of molecules and solids has always had an essential role in physics, chemistry and biology. The methods of choice are X-ray and electron diffraction, which are routinely used to determine atomic positions with sub-ångström spatial resolution. Although both methods are currently limited to probing dynamics on timescales longer than a picosecond, the recent development of femtosecond sources of X-ray pulses and electron beams suggests that they might soon be capable of taking ultrafast snapshots of biological molecules and condensed-phase systems undergoing structural changes. The past decade has also witnessed the emergence of an alternative imaging approach based on laser-ionized bursts of coherent electron wave packets that self-interrogate the parent molecular structure. Here we show that this phenomenon can indeed be exploited for laser-induced electron diffraction (LIED), to image molecular structures with sub-ångström precision and exposure times of a few femtoseconds. We apply the method to oxygen and nitrogen molecules, which on strong-field ionization at three mid-infrared wavelengths (1.7, 2.0 and 2.3??m) emit photoelectrons with a momentum distribution from which we extract diffraction patterns. The long wavelength is essential for achieving atomic-scale spatial resolution, and the wavelength variation is equivalent to taking snapshots at different times. We show that the method has the sensitivity to measure a 0.1?Å displacement in the oxygen bond length occurring in a time interval of ?5?fs, which establishes LIED as a promising approach for the imaging of gas-phase molecules with unprecedented spatio-temporal resolution. PMID:22398558

Blaga, Cosmin I; Xu, Junliang; DiChiara, Anthony D; Sistrunk, Emily; Zhang, Kaikai; Agostini, Pierre; Miller, Terry A; DiMauro, Louis F; Lin, C D

2012-03-01

192

Fragmentation of molecular ions in slow electron collisions  

International Nuclear Information System (INIS)

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

193

Fragmentation of molecular ions in slow electron collisions  

Energy Technology Data Exchange (ETDEWEB)

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

Novotny, Steffen

2008-06-25

194

Theoretical study of nanostructures and molecular electronic systems  

Science.gov (United States)

Research studies on systems with reduced size and dimensionality have attracted great attention for the past two decades. This is mainly driven by industrial development, which demands the fabrication of new, small, well-controlled devices as well as the desire to understand quantum effects which manifest in these small structures. In this thesis we theoretically investigate quantum coherent transport properties of nano structures in the form of molecular electronic systems. Our approach is based on Landauer-Buttiker transport theory. However, the details of the method depend on the interaction complexity. We have carried out detailed analysis on finite length carbon nanotubes based magnetic tunnel junction using tight binding atomic model and Green's function approach. This device shows clear spin valve effect even when contacted with the same ferro-magnetic material with a long spin scattering length. In addition to this, transport at the atomic level is highly affected by the molecular states resulting in conductance oscillation of finite size arm-chair carbon nanotube as a function of its length. When short carbon nanotubes are weakly contacted to external leads, they act as quantum dots with strong interaction at the molecular scale. To analyse these systems, we have developed a many-body wave function formalism which include spin degeneracy. This approach clearly shows the strong dependence of the device electronic response on the number of electrons already inside the tube. Finally, we have carried out ab initio analysis based on Density Functional Theory within Local Density Approximations to investigate the current-voltage (I-V) characteristics of various gold nanowires. Our results demonstrate that transport properties of these systems crucially depend on the electronic properties of the scattering region, the leads, and most importantly the interaction of the scattering region with the leads. For ideal, clean Au contacts, the theoretical results indicate a linear I-V behavior. However, when sulfur impurities exist at the contact junction, nonlinear I-V curves emerge due to a tunnelling barrier established in the presence of the S atom. The most striking observation is that even a single S atom can cause a qualitative change of the I-V curve from linear to nonlinear. Our theoretical results were compared to experimental data, qualitative and sometimes quantitative understanding of the experiments are obtained.

Mehrez, Hatem

195

Mapping molecular motions leading to charge delocalization with ultrabright electrons.  

Science.gov (United States)

Ultrafast processes can now be studied with the combined atomic spatial resolution of diffraction methods and the temporal resolution of femtosecond optical spectroscopy by using femtosecond pulses of electrons or hard X-rays as structural probes. However, it is challenging to apply these methods to organic materials, which have weak scattering centres, thermal lability, and poor heat conduction. These characteristics mean that the source needs to be extremely bright to enable us to obtain high-quality diffraction data before cumulative heating effects from the laser excitation either degrade the sample or mask the structural dynamics. Here we show that a recently developed, ultrabright femtosecond electron source makes it possible to monitor the molecular motions in the organic salt (EDO-TTF)2PF6 as it undergoes its photo-induced insulator-to-metal phase transition. After the ultrafast laser excitation, we record time-delayed diffraction patterns that allow us to identify hundreds of Bragg reflections with which to map the structural evolution of the system. The data and supporting model calculations indicate the formation of a transient intermediate structure in the early stage of charge delocalization (less than five picoseconds), and reveal that the molecular motions driving its formation are distinct from those that, assisted by thermal relaxation, convert the system into a metallic state on the hundred-picosecond timescale. These findings establish the potential of ultrabright femtosecond electron sources for probing the primary processes governing structural dynamics with atomic resolution in labile systems relevant to chemistry and biology. PMID:23598343

Gao, Meng; Lu, Cheng; Jean-Ruel, Hubert; Liu, Lai Chung; Marx, Alexander; Onda, Ken; Koshihara, Shin-Ya; Nakano, Yoshiaki; Shao, Xiangfeng; Hiramatsu, Takaaki; Saito, Gunzi; Yamochi, Hideki; Cooney, Ryan R; Moriena, Gustavo; Sciaini, Germán; Miller, R J Dwayne

2013-04-18

196

Quantitative exploration of electron transfer in a single noncovalent supramolecular assembly.  

Science.gov (United States)

Electron transfer through a noncovalent interaction bears essential relevance to the functions of bottom-up supramolecular assembly. However, rather little knowledge regarding such phenomena at the single-molecule level is currently available. Herein we report the direct quantification of electron-transfer processes for a single noncovalently linked porphyrin-fullerene dyad. Facilitated electron transfer via a charge-transfer interaction in-between was successfully measured by utilizing a fullerene molecular tip. The rectification property of the supramolecular assembly was determined and quantitatively assessed. The present study opens up a way to explore quantitatively the rich electronic properties of supramolecules at the single-molecule level. PMID:23534478

Bui, Phuc T; Nishino, Tomoaki; Yamamoto, Yojiro; Shiigi, Hiroshi

2013-04-10

197

Electron-Impact Dissociation of Hydrocarbon Molecular Ions  

International Nuclear Information System (INIS)

Absolute cross-sections for electron-impact dissociation of CHx+(x = 1, 2, 3) producing CHy+ (y = 0, 1, 2) fragment ions were measured in the 3-100 eV range using a crossed electron-ion beams technique with total uncertainties of about 11% near the cross-section peaks. For CH+ dissociation, although the measured energy dependence agrees well with two sets of storage ring measurements, the magnitude of the present results lies about 15%-25% lower at the cross-section peak near 40 eV. For dissociation of CH2+, the cross-sections are nearly identical for energies above 15 eV, but they are dramatically different at lower energies. The CH+ channel exhibits a strong peak rising from an observed threshold of about 6 eV; the C+ channel is relatively flat down to the lowest measured energy. For dissociation of CH3+ and CD3+, good agreement is found with other results reported for the CH+ fragment, but some differences are found for the CD2+ and C+ fragments. A pilot study has also been undertaken to assess the feasibility of applying a molecular dynamics approach to treat the full range of electron-hydrocarbon dissociation processes, especially for energies above a few eV, in order to provide an overarching theoretical model that can be readily applied. Comparison with the experimental data for CH+ shows favourable agreement. (author)

198

Electron tunneling in molecular solids. An orbital overlap model  

International Nuclear Information System (INIS)

The long-range transfer processes (range, R approx. 20-50 A) of excess electrons produced by radiolysis of molecular solids are analyzed in terms of an orbital overlap model. A united atom approximation makes possible the separation of angular and radial factors. The angular dependence is used to treat the effect of the relative orientation of donor and acceptor molecules on the transfer rate; variations of up to a factor of approx. 1000 are predicted. A distinction is drawn between reactions of electrons with scavengers (or transfer between additives), where the significant overlap is localized around donor and acceptor sites, and recombination with a cation produced by the radiolysis, where the overlap is largely spread out over the intervening volume. In the former case, interference due to nodes in the wave functions is significant, while in the latter, various powers of R appear in the preexponential factor. The role of the Franck--Condon principle in determining the effective barrier height is discussed. Electronic interaction is also important in determining transfer rates for different donors and acceptors. 3 figures, 2 tables

199

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

Science.gov (United States)

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

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

2010-07-27

200

Molecular model for aqueous ferrous--ferric electron transfer  

Energy Technology Data Exchange (ETDEWEB)

We present a molecular model for studying the prototypical ferric--ferrous electron transfer process in liquid water, and we discuss its structural implications. Treatment of the nonequilibrium dynamics will be the subject of future work. The elementary constituents in the model are classical water molecules, classical ferric ions (i.e., Fe/sup 3 +/ particles), and a quantal electron. Pair potentials and pseudopotentials describing the interactions between these constituents are presented. These interactions lead to ligand structures of the ferric and ferrous ions that are in good agreement with those observed in nature. The validity of the tight binding model is examined. With umbrella sampling, we have computed the diabatic free energy of activation for electron transfer. The number obtained, roughly 20 kcal/mol, is in reasonable accord with the aqueous ferric--ferrous transfer activation energy of about 15 to 20 kcal/mol estimated from experiment. The Marcus relation for intersecting parabolic diabatic free energy surfaces is found to be quantitatively accurate in our model. Due to its significance to future dynamical studies, we have computed the tunnel splitting for our model in the absence of water molecules. Its value is about 1 k/sub B/ T at room temperature for ferrous--ferric separations around 5.5 A. This indicates that the dynamics of the electron transfer are complex involving both classical adiabatic dynamics and quantal nonadiabatic transitions. The dynamics may also be complicated due to glassy behavior of tightly bound ligand water molecules. We discuss this glassy behavior and also describe contributions to the solvation energetics from water molecules in different solvation shells. Finally, the energetics associated with truncating long ranged forces is discussed and analyzed.

Kuharski, R.A.; Bader, J.S.; Chandler, D.; Sprik, M.; Klein, M.L.; Impey, R.W.

1988-09-01

 
 
 
 
201

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

202

Dihydroazulene: from controlling photochromism to molecular electronics devices.  

Science.gov (United States)

Recent synthetic advances allowing large-scale preparation and systematic functionalization of the dihydroazulene (DHA)-vinylheptafulvene (VHF) photo-/thermoswitch have enabled detailed studies on how to tune optical and switching properties and have paved the way for using this system as a functional unit in molecular electronics and materials chemistry. Since discovery of its photochromism in the 1980'ies, numerous examples of DHA-VHF systems have been developed, allowing multimode switching, fluorescence-control and fine tuning of absorbance and VHF half-lives, giving insights into the mechanism of the switching event. Here, we present an overview of the properties of the DHA-VHF system, together with some selected synthetic procedures which have paved the way for its development. PMID:25175333

Broman, Søren Lindbæk; Nielsen, Mogens Brøndsted

2014-10-21

203

Rectification of the OPAL Cold Neutron Source Cryogenic System  

International Nuclear Information System (INIS)

The Cold Neutron Source (CNS) at ANSTO's OPAL Reactor had experienced repeated outages since 2009 due to failures in the cryogenic system. An extensive root cause analysis was initiated in May 2012, led by an ANSTO team that also involved knowledgeable external experts. At the conclusion of the investigation, a set of recommendations was released to address the identified contributing causes. A rectification program was established to implement the solutions. Cryogenic operation of the CNS, providing end users with cold neutrons, successfully returned to service in July 2013. Thanks to the unique stand-by operation mode of the CNS, irradiation activities at the reactor, as well as thermal neutron availability, had not been affected during the year-long investigation/rectification process. Some technical and operational aspects of the investigation, testing and engineering modifications are discussed in this presentation

204

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

205

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)

206

Ionic fragmentation channels in electron collisions of small molecular ions  

Energy Technology Data Exchange (ETDEWEB)

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

Hoffmann, Jens

2009-01-28

207

The coherence length in molecular and electron beam diffraction  

International Nuclear Information System (INIS)

The trouble with the 'coherence length' in electron and molecular beam diffraction is that the concept of a transfer width introduced by PARK et al. although essentially correct has often been misinterpreted, while the concept of the so-called 'coherence length', found in text books, is in many cases not correct. This lecture will start by recognizing that the diffraction patterns of electrons and molecules are exclusively the result of the interference of each particle with itself. In the case of a perfect surface grating the broadening of the diffractive peaks is the consequence of instrument imperfections. It will be argued that the problem is in fact a visibility problem, i.e., how much information can be extracted from the diffraction pattern in spite of the perturbing effect of the instrument. The main conclusion is that information about periodic structures much larger than the familiar 1O0 A length are present in diffraction patterns but that this information can be extracted by deconvoluting for the instrumental effects. (orig.)

208

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.)

209

Goal-oriented rectification of camera-based document images.  

Science.gov (United States)

Document digitization with either flatbed scanners or camera-based systems results in document images which often suffer from warping and perspective distortions that deteriorate the performance of current OCR approaches. In this paper, we present a goal-oriented rectification methodology to compensate for undesirable document image distortions aiming to improve the OCR result. Our approach relies upon a coarse-to-fine strategy. First, a coarse rectification is accomplished with the aid of a computationally low cost transformation which addresses the projection of a curved surface to a 2-D rectangular area. The projection of the curved surface on the plane is guided only by the textual content's appearance in the document image while incorporating a transformation which does not depend on specific model primitives or camera setup parameters. Second, pose normalization is applied on the word level aiming to restore all the local distortions of the document image. Experimental results on various document images with a variety of distortions demonstrate the robustness and effectiveness of the proposed rectification methodology using a consistent evaluation methodology that encounters OCR accuracy and a newly introduced measure using a semi-automatic procedure. PMID:20876019

Stamatopoulos, Nikolaos; Gatos, Basilis; Pratikakis, Ioannis; Perantonis, Stavros J

2011-04-01

210

Calibration and rectification research for fish-eye lens application  

Science.gov (United States)

The purpose of this paper aims to promote the application of fish-eye lens. Accurate parameters calibration and effective distortion rectification of an imaging device is of utmost importance in machine vision. Fish-eye lens produces a hemispherical field of view of an environment, which appears definite significant since its advantage of panoramic sight with a single compact visual scene. But fish-eye lens image has an unavoidable inherent severe distortion. The precise optical center is the precondition for other parameters calibration and distortion correction. Therefore, three different optical center calibration methods have been researched for diverse applications. Support Vector Machine (SVM) and Spherical Equidistance Projection Algorithm (SEPA) are integrated to replace traditional rectification methods. SVM is a machine learning method based on the theory of statistics, which have good capabilities of imitating, regression and classification. In this research, SVM provides a mapping table between the fish-eye image and the standard image for human eyes. Two novel training models have been designed. SEPA has been applied to promote the rectification effect of the edge of fish-eye lens image. The validity and effectiveness of our achievements are demonstrated by processing the real images.

Feng, Weijia; Zhang, Baofeng; Cao, Zuoliang; Zong, Xiaoning; Röning, Juha

2011-01-01

211

Origin of rectification in boron nitride heterojunctions to silicon.  

Science.gov (United States)

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

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

2013-04-10

212

Reconciling expressions for terahertz generation by bulk optical rectification  

Science.gov (United States)

Over the last 15 years, many groups have analyzed terahertz generation by optical rectification and subsequently many different expressions are present in the literature. The theory has been developed for the (100), (110), (111) and more recently the (112) crystal faces and compared to experimental results. A recent paper by Hargreaves, Radhanpura and Lewis (HRL) deals with optical rectification in zinc blende crystals for arbitrary excitation conditions. The current paper analyzes expressions from the literature to reconcile any differences. In most cases, we have found that the generalized theory reproduces the results published in previous papers with some phase shift in azimuthal angle. However, these phase shifts not only differ between papers but also, within the one paper, between different crystal orientations. As notations tend to differ between papers, the need for a generalized and agreed definition of co-ordinates and angles becomes apparent. Identifying where these corrections originate is made more difficult with some of the papers missing explicit definitions of co-ordinate systems and azimuthal angles. It has been found that the differences originate from the definition of the azimuthal angle and direction of rotation. With these differences reconciled, the general theory is able to reproduce the azimuthal angle dependence of terahertz generation by optical rectification.

Bleasdale, C. S.; Lewis, R. A.

2010-06-01

213

Detection of resonances in electron--molecule scattering using a modulated supersonic molecular beam  

International Nuclear Information System (INIS)

Resonance spectra are presented for electron-molecule scattering using supersonic molecular beams. The supersonic beam is crossed at right angles by an electron beam. Results for N2 and CO are presented

214

Separation and purification of niobium and tantalum by rectification of their pentafluorides  

International Nuclear Information System (INIS)

Main statistic parameters of the process of rectification separation of niobium and tantalum in the form of their pentafluorides and pentachlorides are calculated. Comparison of the data obtained shows that niobium pentafluoride rectification efficiency is 5 time less according to the value of interstage flow than the rectification of their pentachlorides. To illustrate the possibilities of rectification separation and purification of niobium and tantalum pentafluorides a number of experiments have been carried out. Experiments have grounded that the use of high-efficiency rectification coulomus is necessary for the fine separation of pentafluoride data and for their purification from a number of impurities. Behaviour of impurities during rectification purification of pentafluorides is in correlation with the data on liquid-vapor phase equilibria in studied systems of pentafluorides-impurity (TiF4, AlF3, WF6, WOF4, MoOF4, MoF6)

215

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

216

Micro- and Nanostructured Materials for Active Devices and Molecular Electronics  

Energy Technology Data Exchange (ETDEWEB)

Traditional single layer barrier coatings are not adequate in preventing degradation of the performance of organic molecular electronic and other active devices. Most advanced devices used in display technology now consist of micro and nanostructured small molecule, polymer and inorganic coatings with thin high reactive group 1A metals. This includes organic electronics such as organic light emitting devices (OLED). The lifetimes of these devices rapidly degrades when they are exposed to atmospheric oxygen and water vapor. Thin film photovoltaics and batteries are also susceptible to degradation by moisture and oxygen. Using in-line coating techniques we apply a composite nanostructured inorganic/polymer thin film barrier that restricts moisture and oxygen permeation to undetectable levels using conventional permeation test equipment. We describe permeation mechanisms for this encapsulation coating and flat panel display and other device applications. Permeation through the multilayer barrier coating is defect and pore limited and can be described by Knudsen diffusion involving a long and tortuous path. Device lifetime is also enhanced by the long lag times required to reach the steady state flux regime. Permeation rates in the range of 10-6 cc,g/m2/d have been achieved and OLED device lifetimes. The structure is robust, yet flexible. The resulting device performance and lifetimes will also be described. The barrier film can be capped with a thin film of transparent conductive oxide yielding an engineered nanostructured device for next generation, rugged, lightweight or flexible displays. This enables, for the first time, thin film encapsulation of emissive organic displays.

Martin, Peter M.; Graff, Gordon L.; Gross, Mark E.; Burrows, Paul E.; Bennett, Wendy D.; Mast, Eric S.; Hall, Michael G.; Bonham, Charles C.; Zumhoff, Mac R.; Williford, Rick E.

2003-10-01

217

Rectification induced in N2AA-doped armchair graphene nanoribbon device  

Science.gov (United States)

By using non-equilibrium Green function formalism in combination with density functional theory, we investigated the electronic transport properties of armchair graphene nanoribbon devices in which one lead is undoped and the other is N2AA-doped with two quasi-adjacent substitutional nitrogen atoms incorporating pairs of neighboring carbon atoms in the same sublattice A. Two kinds of N2AA-doped style are considered, for N dopants substitute the center or the edge carbon atoms. Our results show that the rectification behavior with a large rectifying ratio can be found in these devices and the rectifying characteristics can be modulated by changing the width of graphene nanoribbons or the position of the N2AA dopant. The mechanisms are revealed to explain the rectifying behaviors.

Chen, Tong; Li, Xiao-Fei; Wang, Ling-Ling; Luo, Kai-Wu; Xu, Liang

2014-07-01

218

Quantum mechanical simulations of polymers for molecular electronics and photonics  

International Nuclear Information System (INIS)

Ab initio quantum mechanical studies can play an important role in obtaining a detailed understanding of the electronic structure of existing materials, and in predicting the properties of new ones. In this article the authors give a general outline of their research activity in two areas dealing with new materials, specifically, conducting polymers and polymers with non-linear optical properties. The authors present the strategy followed for the study of these molecular systems, and an overview of their findings concerning the structure of the prototypical conducting polymer, i.e. pure and doped polyacetylene (PA). They focused attention on vibrational spectra and infrared and Raman intensities. The results of self-consistent-field (SCF) calculations on charged soliton-like molecules are consistent with experimental observation. In particular, they show that the theoretically established accidental mutual exclusion of infrared and Raman bands invalidates the requirement formulated on the basis of the interpretation of experimental data, that defects in PA must have local C/sub 2h/ symmetry. These conclusions are derived from extensive calculations for which supercomputer performance was imperative and carried out on the parallel supercomputer assembled at IBM-Kingston as a loosely coupled array of processors (LCAP). The authors briefly describe this computer system which has proven to be ideally suited to the methods of ab initio quantum chemistry

219

Electronic structure of the N4+ molecular ion  

International Nuclear Information System (INIS)

The N4+ ion is an important species in the chemistry of the atmosphere. Here N4+ has been studied theoretically using the methods of ab initio molecular quantum mechanics. There is considerable complexity involved in the theoretical study of N4+ due to (a) the fact that N2+ has two low-lying electronic states, X 2?/sub g/+ and A 2Pi/sub u/ and the order of these is reversed within the Hartree--Fock approximation and (b) there are six low-lying electronic states of N4+. Results are first presented at the self-consistent-field (SCF) level of theory using a double zeta (DZ) basis set N(9s 5p/4s 2p). Both Koopmans' theorem and direct positive ion calculations in both D/sub 2h/ (rectangle) and C/sub 2v/ (regular trapezoid) symmetry suggest only a single (out of six) substantially bound electronic state, the 2B/sub 2u/(D/sub 2h/) or 2A1(C/sub 2v/) state. Because the D/sub 2h/ SCF wave function necessitates a compromise description of the N2+N2+ asymptote, the predicted dissociation energy is artificially large, although in reasonable agreement with experiment. Polarization functions were added to the basis set and all three geometrical parameters examined to locate the C/sub 2v/ equilibrium structure, which lies 19.9 kcal below the dissociation limit N2+N2+N2+(2?/sub g/+). Similar theoretical methods were applied to the T-shape geometry, with the constrained equilibrium structure bound by 24.2 kcal. The linear conformation represents the absolute minimum on the N4+ potential energy surface, lying 30.4 kcal below N2+N2+. The latter dissociation energy agrees well with the experimental value of approx.26 kcal. In studying the linear 2?+ state, the surprising result was found that the 2?/sub g/+ restricted Hartree--Fock wave function is unstable with respect to the removal of the g/u element of symmetry

220

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

CERN Document Server

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

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

2001-01-01

 
 
 
 
221

A COMPARISON OF ELECTRONIC SPUTTERING INDUCED BY MOLECULAR AND ATOMIC IONS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Fast 12C2 molecular ions have been produced in the Uppsala tandem accelerator and used in an electronic sputtering experiment designed to compare sputtering yields produced by molecular and atomic primary ions of 0.49 cm/ns. Positive secondary ions of biomolecules sputtered with molecular primary ions are studied for the first time. The experiments show that "vicinage effects" due to sputtering with molecular primary ions vary in strength with the secondary ion species. It is however also dem...

Hedin, A.; Ha?kansson, P.; Sundqvist, B.; Johnson, R.

1989-01-01

222

Tuning the electron transport of molecular junctions by chemically functionalizing anchoring groups: First-principles study  

Science.gov (United States)

In this first-principles study, we present density-functional calculations of the electronic structures and electron transport properties of organic molecular junctions with several anchoring groups containing atoms with different electronegativities, i.e., benzenediboronate (BDB), benzenedicarboxylate (BDC), and dinitrobenzene (DNB) molecular junctions sandwiched between two Cu(110) electrodes. The electronic-structure calculations exhibit a significant difference in the density of states not only at the anchoring groups but also at the aromatic rings of the molecular junctions, suggesting that the electron transport is specific for each system. Our transport calculations show that the BDB and DNB molecular junctions have finite electron transmissions at the zero-bias limit while the BDC molecular junction has a negligible electron transmission. Moreover, for the BDB and DNB systems, the electron transmission channels around the Fermi energy reveal fingerprint features, which provide specific functionalities for the molecular junctions. Therefore, our theoretical results demonstrate the possibility to precisely tune the electron transport properties of molecular junctions by engineering the anchoring groups at the single-atom level.

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

2012-06-01

223

Rectification properties of conically shaped nanopores: consequences of miniaturization.  

Science.gov (United States)

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. PMID:24002326

Pietschmann, J-F; Wolfram, M-T; Burger, M; Trautmann, C; Nguyen, G; Pevarnik, M; Bayer, V; Siwy, Z

2013-10-21

224

Rectification of aerial images using piecewise linear transformation  

Science.gov (United States)

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

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

2014-02-01

225

Exploring Higher-Lying Electronic States of a Molecular Switch by Coherent Triggered-Exchange 2D Electronic Spectroscopy  

Directory of Open Access Journals (Sweden)

Full Text Available We use pump-repump-probe transient absorption spectroscopy to investigate the role of higher-lying electronic states in the photochemistry of a molecular switch. Moreover, replacing the pump pulse by a pulse-shaper-generated phase-stable double pulse, triggered-exchange two-dimensional (TE2D electronic spectroscopy is established in the visible regime.

Nuernberger P.

2013-03-01

226

Exploring Higher-Lying Electronic States of a Molecular Switch by Coherent Triggered-Exchange 2D Electronic Spectroscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We use pump-repump-probe transient absorption spectroscopy to investigate the role of higher-lying electronic states in the photochemistry of a molecular switch. Moreover, replacing the pump pulse by a pulse-shaper-generated phase-stable double pulse, triggered-exchange two-dimensional (TE2D) electronic spectroscopy is established in the visible regime.

Nuernberger P.; Buback J.; Kullmann M.; Ruetzel S.; Brixner T.

2013-01-01

227

Silicon nanowires and silicon/molecular interfaces for nanoscale electronics  

Science.gov (United States)

This thesis describes the utilization of silicon nanowires and molecular films towards the realization of nanoscale electronics. The key enabling technology is the method in which the silicon nanowires are produced---the superlattice nanowire pattern transfer (SNAP) method. The SNAP method allows for the simultaneous formation and alignment of metal or semiconducting nanowires using a template-mediated approach. High-performance n- and p-type silicon nanowire field-effect transistors (FETs) were demonstrated. These FETs exhibited consistent performance and strong performance metrics such as high on/off ratios, high on-currents, high mobilities and low subthreshold swings. Due to the nanowire's large surface-area-to-volume ratio, surface states were shown to dominate performance, especially for the n-type FETs. Reducing the number of surface states improved performance significantly. N- and p-type silicon nanowire FETs were integrated into complementary symmetry (CS) logic circuits. This required the development of a pattern doping technique that allowed for spatial control of doped regions. The inverter circuit was fabricated and tested. A gain of ˜ 5 was consistently measured from 7 working inverter circuits. This demonstration provided the foundation for the eventual fabrication and characterization of the other Boolean logic functions. A methodology was developed that optimizes the design of high-performance logic circuits constructed from Si NW p- and n-type FETs. Circuit performance can be predicted from individual fabricated NW FETs before prototype circuits are manufactured, resulting in a faster and more efficient design process. These results suggest design options for fabricating high performance NW circuits, which can then be implemented experimentally. The effectiveness of this methodology is shown by optimizing the gain of Si NW complementary symmetry inverter from an initially measured value of 8 to a gain of 45. Lastly, methods to covalently attach electronically interesting molecules via microcontact printing onto gold and silicon substrates were developed. In these studies, the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction was used to form the covalent attachment. It was observed that the reaction would proceed readily by replacing the Cu catalyst in the stamp ink by a Cu coating on the stamp directly. This reaction proceeded quickly on both azide-terminated monolayers on Au and Si(111) substrates.

Sheriff, Bonnie Ann

228

Dihydroazulene Photochromism:Synthesis, Molecular Electronics and Hammett Correlations  

DEFF Research Database (Denmark)

This thesis describes the development of a versatile synthetic protocol for preparation of a large selection of dihydroazulenes (DHAs) with both electron withdrawing and donating groups. By UV-Vis and NMR spectroscopies and even in a single-molecule junction, their ability to undergo a light-induced ring-opening reaction to vinylheptafulvenes (VHFs) and a thermally induced back-reaction (VHF ? DHA) were studied in detail. The first chapter briefly introduces photoswitches with focus, in particular, on the most well-known photoswitches. Then, the synthesis and properties of the DHA/VHF system will be discussed in detail. The second chapter describes the design and synthesis of DHA/VHFs intended for use in molecular electronics and their solution and single-molecule junction switching properties. By the expansion of the recently reported procedure for functionalization of this system by Suzuki cross-coupling reactions, systems with either one or two “molecular alligator clips” were prepared. These were studied in solution by UV-Vis absorption spectroscopy and in a single-molecule junction, the latter by the group of Danilov and Kubatkin at the Chalmers University of Technology. A single-molecule device was prepared in which reversible switching between states of conductance could be accomplished by either light/heat or light/bias. The third chapter describes the synthesis of a large number of donor and/or acceptor functionalized DHA/VHFs and the systematic dependence of the rate of the thermally induced back-reaction (VHF ? DHA), studied by UV-Vis absorption spectroscopy. In seven different model systems, the rate of back-reaction was found to obey a Hammett correlation when plotting ln(k) against the appropriate ?-values. These plots were used to estimate the ?-value of substituents which have not yet been determined such as heteroaromatics (furan, thiophene, and 1,2,3-triazole) and alkynes (triisopropylsilylethyne, trimethylsilyl- 1,3-butadiyne, and 1,3-butadiyne). It was also shown that the absorption maximum of the VHF and the rate of back-reaction can be conveniently fine-tuned by these donor or acceptor groups. The fourth chapter describes the synthesis and study of a VHF containing two sites for ring-closure in an attempt to overcome the problem of the VHF taking an unreactive conformation which was speculated to cause the relatively slow back-reaction (VHF ? DHA). The study showed that the rate of back-reaction was increased with close to a factor of 2 which is only the statistical improvement of having two possible sites for back-reaction as supposed to just one. The fifth chapter describes, in short, my contributions to an additional seven papers published. Figure 1. Structure of proposed transition state (TS) for the thermally induced ring-closure (VHF ? DHA). This strongly polarized TS is responsible for substituent-dependency of this reaction (left). Reversible switching between the states of the DHA/VHF trapped in a silver nano-gap (right).

Broman, SØren Lindbæk

2013-01-01

229

Digital image processing for the rectification of television camera distortions.  

Science.gov (United States)

All television systems introduce distortions into the imagery they record which influence the results of quantitative photometric and geometric measurements. Digital computer techniques provide a powerful approach to the calibration and rectification of these systematic effects. Nonlinear as well as linear problems can be attacked with flexibility and precision. Methods which have been developed and applied for the removal of structured system noises and the correction of photometric, geometric, and resolution distortions in vidicon systems are briefly described. Examples are given of results derived primarily from the Mariner Mars 1969 television experiment.

Rindfleisch, T. C.

1971-01-01

230

Study of rectification at the metal-cadmium telluride contact  

International Nuclear Information System (INIS)

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

231

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

232

First-principles study of the electron transport through conjugated molecular wires with different carbon backbones  

Science.gov (United States)

The nonequilibrium Green's function approach in combination with density-functional theory is used to perform ab initio quantum-mechanical calculations of the electron transport properties of polyacetylene, polythiophene, poly(phenylene vinylene), poly(p-phenylene ethynylene), and poly(p-phenylene) molecules sandwiched between two gold electrodes. The results demonstrate that the conjugation path has a profound effect on the electron transport property of the molecular wires. Among the five molecular wires, polyacetylene is the most conductive one. The conductivities of the five molecular wires decrease with an order of polyacetylene > polythiophene > poly(phenylene vinylene) > poly(p-phenylene ethynylene) > poly(p-phenylene). The conductivities of polyacetylene and polythiophene are much higher than those of poly(phenylene vinylene), poly(p-phenylene ethynylene), and poly(p-phenylene). The difference of electron transport behaviors of these molecular wires are analyzed in terms of the electronic structures, the transmission spectra, and the spatial distributions of molecular orbitals.

Yao, Jinhuan; Li, Yanwei; Zou, Zhengguang; Wang, Hongbo; Shen, Yufang

2012-03-01

233

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

Science.gov (United States)

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

Margulis, Vl A.; Muryumin, E. E.; Gaiduk, E. A.

2013-10-01

234

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

International Nuclear Information System (INIS)

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

235

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

International Nuclear Information System (INIS)

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

236

Stereo Calibration and Rectification for Omnidirectional Multi-camera Systems  

Directory of Open Access Journals (Sweden)

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

Yanchang Wang

2012-10-01

237

Secondary-electron-production cross sections for electron-impact ionization of molecular nitrogen  

International Nuclear Information System (INIS)

Measurements of the double-differential cross section (DDCS), as a function of the ejected energy, angle, and primary energy for electron-impact ionization of molecular nitrogen are reported at incident energies of 200, 500, 1000, and 2000 eV. The ejection angle was varied from 300 to 1500 in steps of 150. The cross sections were obtained by use of a crossed-beam apparatus with an effusive gas source and a pulsed electron beam. Scattered and ejected electrons were energy analyzed by time-of-flight analysis from below 2 eV to the primary energy. The relative measurements were placed on an absolute scale by matching the experimental elastic differential cross sections to absolute measurements at each primary energy. Comparisons of the DDCS with previous reported values revealed significant differences. The DDCS were fitted to a Legendre polynomial expansion as a function of the ejection angle. Platzman plot analysis was carried out on the energy distributions determined from the fit coefficients. The total ionization cross sections at these primary energies were deduced from this plot. An autoionization feature at 2.3 eV was observed for the first time in measurements of this nature and has been assigned as due to a Rydberg state converging to the B 2?/sub u/+ ionic state which decays to the X 2?/sub g/+ ground state of N2+. An analysis of the autoionization lines observed in the present work in the range 0.4--2.5 eV is also presented

238

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 results obtained show an interrelation between the floating process, the optimum geometry, and the presence of an external field. Cases involving the Le Chatelier principle are discussed, and an in...

Simon I Rabasseda, Si?lvia; Duran I Portas, Miquel

1997-01-01

239

EPICEA: Probing High-Energy Electron Emission In The Molecular Frame  

Science.gov (United States)

Electron emission provides an excellent opportunity to probe the electronic structure and the chemical reactivity of materials. For molecules, the most natural way is describing it in the molecular frame. Recently, using the upgraded version of the EPICEA coincidence setup available at PLEIADES beamline at SOLEIL (France), we were able to measure the electron emission in the molecular frame for kinetic energies up to several hundreds of eV. At these high energies the de Broglie wavelength is comparable to or smaller than the inter-nuclear distance, the possibility of observing the intramolecular electron diffraction thus being opened.

Liu, Xiao-Jing; Nicolas, Christophe; Robert, Emmanuel; Miron, Catalin

2014-04-01

240

Electron loss from multiply protonated lysozyme ions in high energy collisions with molecular oxygen.  

Science.gov (United States)

We report on the electron loss from multiply protonated lysozyme ions Lys-Hn(n)+ (n = 7 - 17) and the concomitant formation of Lys-Hn(n+1)+. in high-energy collisions with molecular oxygen (laboratory kinetic energy = 50 x n keV). The cross section for electron loss increases with the charge state of the precursor from n = 7 to n = 11 and then remains constant when n increases further. The absolute size of the cross section ranges from 100 to 200 A2. The electron loss is modeled as an electron transfer process between lysozyme cations and molecular oxygen. PMID:11506221

Hvelplund, P; Nielsen, S B; Sørensen, M; Andersen, J U; Jørgensen, T J

2001-08-01

 
 
 
 
241

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

CERN Document Server

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

242

Recent progress in atomic and molecular collisions and the interface with electronic structure theory  

International Nuclear Information System (INIS)

Some examples of areas in atomic and molecular collisions where there has been recent progress - in theory, in computations, or in experimental work - are discussed, and the new needs from electronic structure theory are stressed. 76 references, 2 tables

243

Resonant electron heating and molecular phonon cooling in single C$_{60}$ junctions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study heating and heat dissipation of a single \\c60 molecule in the junction of a scanning tunneling microscope (STM) by measuring the electron current required to thermally decompose the fullerene cage. The power for decomposition varies with electron energy and reflects the molecular resonance structure. When the STM tip contacts the fullerene the molecule can sustain much larger currents. Transport simulations explain these effects by molecular heating due to resonant ...

Schulze, G.; Franke, K. J.; Gagliardi, A.; Romano, G.; Lin, C. S.; Da Rosa, A.; Niehaus, T. A.; Frauenheim, Th; Di Carlo, A.; Pecchia, A.; Pascual, J. I.

2008-01-01

244

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

Science.gov (United States)

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

Mandado, Marcos; Ramos-Berdullas, Nicolás

2014-06-30

245

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.)

246

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

International Nuclear Information System (INIS)

The angular distribution of Auger electrons emitted in the decay of molecular K-shell vacancies created by photoabsorption is predicted to be a direct probe of the anisotropy of molecular photoabsorption. The sigma?? discrete absorption of the sigma?sigma f-wave shape resonance in N2 and CO are given as examples

247

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

International Nuclear Information System (INIS)

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

248

Adventures in molecular electronics: how to attach wires to molecules  

Science.gov (United States)

Films of both methoxy-terminated alkanethiols and a molecular wire candidate on Au{1 1 1} substrates were exposed to a variety of transition and alkali earth metals (Al, Au, Ag, Ca, Cr, Fe, Cu, Mg, Ti). The results show that aggressively reacting metals, such as Ti, destroy the organic monolayer and metals of intermediate reactivity, e.g. Cu, react at the termini and also penetrate the monolayer and react with the substrate. The results of these investigations provide a basis by which future construction of molecular devices based on desired chemical reactivity may proceed.

Haynie, B. C.; Walker, A. V.; Tighe, T. B.; Allara, D. L.; Winograd, N.

2003-01-01

249

Adventures in molecular electronics: how to attach wires to molecules  

Energy Technology Data Exchange (ETDEWEB)

Films of both methoxy-terminated alkanethiols and a molecular wire candidate on Au{l_brace}1 1 1{r_brace} substrates were exposed to a variety of transition and alkali earth metals (Al, Au, Ag, Ca, Cr, Fe, Cu, Mg, Ti). The results show that aggressively reacting metals, such as Ti, destroy the organic monolayer and metals of intermediate reactivity, e.g. Cu, react at the termini and also penetrate the monolayer and react with the substrate. The results of these investigations provide a basis by which future construction of molecular devices based on desired chemical reactivity may proceed.

Haynie, B.C.; Walker, A.V.; Tighe, T.B.; Allara, D.L.; Winograd, N

2003-01-15

250

Adventures in molecular electronics: how to attach wires to molecules  

International Nuclear Information System (INIS)

Films of both methoxy-terminated alkanethiols and a molecular wire candidate on Au{1 1 1} substrates were exposed to a variety of transition and alkali earth metals (Al, Au, Ag, Ca, Cr, Fe, Cu, Mg, Ti). The results show that aggressively reacting metals, such as Ti, destroy the organic monolayer and metals of intermediate reactivity, e.g. Cu, react at the termini and also penetrate the monolayer and react with the substrate. The results of these investigations provide a basis by which future construction of molecular devices based on desired chemical reactivity may proceed

251

Free-electron laser induced processes in thin molecular ice.  

Science.gov (United States)

Intermolecular reactions in and on icy films on silicate and carbonaceous grains constitute a major route for the formation of new molecular constituents in interstellar molecular clouds. In more diffuse regions and in protoplanetary discs, energetic radiation can trigger reaction routes far from thermal equilibrium. As an analog of interstellar ice-covered dust grains, highly-oriented pyrolytic graphite (HOPG) covered with D2O, NO, and H atoms is irradiated by ultrashort XUV pulses and the desorbing ionic and neutral products are analysed. The yields of several products show a nonlinear intensity dependence and thus enable the elucidation of reaction dynamics by two-pulse correlated desorption. PMID:25302398

Siemer, Björn; Roling, Sebastian; Frigge, Robert; Hoger, Tim; Mitzner, Rolf; Zacharias, Helmut

2014-01-01

252

High rectification and photovoltaic effect in oxide nano-junctions  

Science.gov (United States)

Polar oxide-based heterostructures composed of ferroelectric PbZr0.2Ti0.8O3 and hole-doped La0.8Sr0.2MnO3 ultrathin epitaxial films were fabricated on Nb:SrTiO3 substrates to check the viability of all oxide-based photovoltaic (PV) nano-junctions. We observed clear diode-like behavior, yielding a rectification ratio up to ˜ 1000. This large enhancement could be attributed to the presence of an ultrathin ferroelectric layer (<10 nm) that greatly contributed to the improved PV performance by promoting carrier separation, as compared with oxide junctions without the ferroelectric layer. Therefore, our results provide useful information for developing highly efficient ferroelectric oxide-based PV devices.

Choi, T.; Jiang, L.; Lee, S.; Egami, T.; Lee, H. N.

2012-09-01

253

Maximal rectification ratios for bi-segment thermal rectifiers  

CERN Document Server

We study bi-segment thermal rectifiers whose forward heat fluxes are greater than reverse counterparts. Presently, a shortcoming of thermal rectifiers is that the rectification ratio, namely the forward flux divided by the reverse flux, remains too small for practical applications. In this study, we have managed to discover and theoretically derive the ultimate limit of such ratios, which are validated by numerical simulations, experiments, and micro-scale Hamiltonian-oscillator analyses. For rectifiers whose thermal conductivities are linear with the temperature, this limit is simply a numerical value of 3. For those whose conductivities are nonlinear with temperatures, the maxima equal $\\kappa_{max}/\\kappa_{min}$, where the two extremes denote values of the solid segment materials that can be possibly found or fabricated within a reasonable temperature range on earth. Recommendations for manufacturing high-ratio rectifiers are also given with examples.

Shih, Tien-Mo; Guo, Ziquan; Liu, Guangcao; Merlitz, Holger; Pagni, Patrick J; Chen, Zhong

2014-01-01

254

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

255

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

256

Molecular double core-hole electron spectroscopy for chemical analysis  

CERN Document Server

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

257

Porphyrins as Molecular Electronic Components of Functional Devices  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Jurow, Matthew; Schuckman, Amanda E.; Batteas, James D.; Drain, Charles Michael

2010-01-01

258

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

1995-01-01

259

Molecular dynamics simulations of the Ag+ or Na+ cation with an excess electron in bulk water  

International Nuclear Information System (INIS)

The properties of an excess electron interacting with a monovalent cation in bulk water are studied by molecular dynamics simulations. Sodium and silver cations are chosen as prototypical cases because of their very different redox properties. In both cases, mixed quantum classical molecular dynamics simulations reproduce the experimental UV-Vis spectra. In the case of silver, we observe a highly polarized neutral atom, corresponding to a dipolar excitonic state. For sodium a contact cation/electron pair is observed. Free energy curves along the cation electron coordinate are calculated using quantum Umbrella Sampling technique. The relative stability of the different chemical species is discussed

260

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

 
 
 
 
261

Investigation of the molecular conformations of ethanol using electron momentum spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

The valence electronic structure and momentum-space electron density distributions of ethanol have been investigated with our newly constructed high-resolution electron momentum spectrometer. The measurements are compared to thermally averaged simulations based on Kohn-Sham (B3LYP) orbital densities as well as one-particle Green's function calculations of ionization spectra and Dyson orbital densities, assuming Boltzmann's statistical distribution of the molecular structure over the two energy minima defining the anti and gauche conformers. One-electron ionization energies and momentum distributions in the outer-valence region were found to be highly dependent upon the molecular conformation. Calculated momentum distributions indeed very sensitively reflect the distortions and topological changes that molecular orbitals undergo due to the internal rotation of the hydroxyl group, and thereby exhibit variations which can be traced experimentally. The B3LYP model Kohn-Sham orbital densities are overall in good agreement with the experimental distributions, and closely resemble benchmark ADC(3) Dyson orbital densities. Both approaches fail to quantitatively reproduce the experimental momentum distributions characterizing the highest occupied molecular orbital. Since electron momentum spectroscopy measurements at various electron impact energies indicate that the plane wave impulse approximation is valid, this discrepancy between theory and experiment is tentatively ascribed to thermal disorder, i.e. large-amplitude and thermally induced dynamical distortions of the molecular structure in the gas phase.

Ning, C G; Luo, Z H; Huang, Y R; Liu, K; Zhang, S F; Deng, J K [Department of Physics and Key Laboratory of Atomic and Molecular NanoSciences of MOE, Tsinghua University, Beijing 100084 (China); Hajgato, B; Morini, F; Deleuze, M S [Research Group of Theoretical Chemistry, Department SBG, Hasselt University, Agoralaan Gebouw D, B-3590 Diepenbeek (Belgium)], E-mail: ningcg@tsinghua.edu.cn, E-mail: djk-dmp@tsinghua.edu.cn, E-mail: michael.deleuze@uhasselt.be

2008-09-14

262

High throughput ab initio modeling of charge transport for bio-molecular-electronics  

Science.gov (United States)

Self-assembled nanostructures, composed of inorganic and organic materials, have multiple applications in the fields of engineering and nanotechnology. Experimental research using nanoscaled materials, such as semiconductor/metallic nanocrystals, nanowires (NW), and carbon nanotube (CNT)-molecular systems have potential applications in next generation nano electronic devices. Many of these molecular systems exhibit electronic device functionality. However, experimental analytical techniques to determine how the chemistry and geometry affects electron transport through these devices does not yet exist. Using theory and modeling, one can approximate the chemistry and geometry at the atomic level and also determine how the chemistry and geometry governs electron current. Nanoelectronic devices however, contain several thousand atoms which makes quantum modeling difficult. Popular atomistic modeling approaches are capable of handling small molecular systems, which are of scientific interest, but have little engineering value. The lack of large scale modeling tools has left the scientific and engineering community with a limited ability to understand, explore, and design complex systems of engineering interest. To address these issues, I have developed a high performance general quantum charge transport model based on the non-equilibrium Green function (NEGF) formalism using density functional theory (DFT) as implemented in the FIREBALL software. FIREBALL is a quantum molecular dynamics code which has demonstrated the ability to model large molecular systems. This dissertation project of integrating NEGF into FIREBALL provides researchers with a modeling tool capable of simulating charge current in large inorganic/organic systems. To provide theoretical support for experimental efforts, this project focused on CNT-molecular systems, which includes the discovery of a CNT-molecular resonant tunneling diode (RTD) for electronic circuit applications. This research also answers basic scientific questions regarding how the geometry and chemistry of CNT-molecular systems affects electron transport.

Bruque, Nicolas Alexander

263

Electronic structure and molecular orientation of a Zn-tetra-phenyl porphyrin multilayer on Si(111)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The electronic properties and the molecular orientation of Zn-tetraphenyl-porphyrin films deposited on Si(111) have been investigated using synchrotron radiation. For the first time we have revealed and assigned the fine structures in the electronic spectra related to the HOMOs and LUMOs states. This is particularly important in order to understand the orbital interactions, the bond formation and the evolution of the electronic properties with oxidation or reduction of the p...

Cudia, C. Castellarin; Vilmercati, P.; Larciprete, R.; Cepek, C.; Zampieri, G.; Sangaletti, L.; Pagliara, S.; Verdini, A.; Cossaro, A.; Floreano, L.; Morgante, A.; Petaccia, L.; Lizzit, S.; Battocchio, C.; Polzonetti, G.

2005-01-01

264

Fabrication of Nanowire Arrays for Molecular Electronics and Chemical Sensing  

Science.gov (United States)

The recently developed technique of superlattice nanowire pattern transfer (SNAP) allows for the fabrication of arrays of nanowires at wire diameter, regularity, aspect ratio, and pitch that exceeds that of currently available techniques [1]. These arrays have potential applications in the fabrication of ultra-dense nanoscale circuits including FET based logic, molecular memory, and chemical sensing with commensurate constraints on nanowire geometry, conductivity, and chemical reactivity. For example, room temperature transport measurements of semiconducting wires show both Ohmic conductivity as well as a pronounced gating response. This enables the construction of a multiplexer with geometric scaling, effectively bridging the macroscopic and mesoscopic size regimes with a scalable architecture. Similar applications for molecular memory and chemical sensing will also be discussed. This work supported by the DARPA Moletronics Program, the Semiconductor Research Corporation, and MARCO Center funding. [1] N. Melosh, et al., Science 300, 112 (2003).

Johnston-Halperin, Ezekiel; Beckman, R.; Melosh, N.; Luo, Y.; Green, J. E.; Boukai, A.; Heath, J. R.

2004-03-01

265

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

266

Theory of laser-induced electron transport through molecular gases  

International Nuclear Information System (INIS)

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

267

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

268

CN excitation and electron densities in diffuse molecular clouds  

CERN Document Server

Utilising previous work by the authors on the spin-coupled rotational cross-sections for electron-CN collisions, data for the associated rate coefficients is 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 (IOS) approximation. The dominant hyperfine transitions are those with $\\Delta N=\\Delta j= \\Delta F=1$. For dipole-allowed transitions, electron-impact rates are shown to exceed those for excitation of CN by para-H$_2$($j=0$) 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 (CMB) 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...

Harrison, Stephen; Tennyson, Jonathan

2013-01-01

269

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

270

Rectification of acetylcholine-elicited currents in PC12 pheochromocytoma cells.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The current-voltage (I-V) relationship for acetylcholine-elicited currents in the rat pheochromocytoma cell line PC12 is nonlinear. Two voltage-dependent processes that could account for the whole-cell current rectification were examined, receptor channel gating and single receptor channel permeation. We found that both factors are involved in the rectification of the whole-cell currents. The voltage dependence of channel gating determines the shape of the I-V curve at negative potentials. Th...

Ifune, C. K.; Steinbach, J. H.

1990-01-01

271

A parity function for studying the molecular electronic structure  

DEFF Research Database (Denmark)

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

Schmider, Hartmut

1996-01-01

272

Regularizing the molecular potential in electronic structure calculations. II. Many-body methods.  

Science.gov (United States)

In Paper I of this series [F. A. Bischoff, "Regularizing the molecular potential in electronic structure calculations. I. SCF methods," J. Chem. Phys. 141, 184105 (2014)] a regularized molecular Hamilton operator for electronic structure calculations was derived and its properties in SCF calculations were studied. The regularization was achieved using a correlation factor that models the electron-nuclear cusp. In the present study we extend the regularization to correlated methods, in particular the exact solution of the two-electron problem, as well as second-order many body perturbation theory. The nuclear and electronic correlation factors lead to computations with a smaller memory footprint because the singularities are removed from the working equations, which allows coarser grid resolution while maintaining the precision. Numerical examples are given. PMID:25399131

Bischoff, Florian A

2014-11-14

273

Rectification of the EMG is an unnecessary and inappropriate step in the calculation of Corticomuscular coherence.  

Science.gov (United States)

Corticomuscular coherence (CMC) estimation is a frequency domain method used to detect a linear coupling between rhythmic activity recorded from sensorimotor cortex (EEG or MEG) and the electromyogram (EMG) of active muscles. In motor neuroscience, rectification of the surface EMG is a common pre-processing step prior to calculating CMC, intended to maximize information about action potential timing, whilst suppressing information relating to motor unit action potential (MUAP) shape. Rectification is believed to produce a general shift in the EMG spectrum towards lower frequencies, including those around the mean motor unit discharge rate. However, there are no published data to support the claim that EMG rectification enhances the detection of CMC. Furthermore, performing coherence analysis after the non-linear procedure of rectification, which results in a significant distortion of the EMG spectrum, is considered fundamentally flawed in engineering and digital signal processing. We calculated CMC between sensorimotor cortex EEG and EMG of two hand muscles during a key grip task in 14 healthy subjects. CMC calculated using unrectified and rectified EMG was compared. The use of rectified EMG did not enhance the detection of CMC, nor was there any evidence that MUAP shape information had an adverse effect on the CMC estimation. EMG rectification had inconsistent effects on the power and coherence spectra and obscured the detection of CMC in some cases. We also provide a comprehensive theoretical analysis, which, along with our empirical data, demonstrates that rectification is neither necessary nor appropriate in the calculation of CMC. PMID:22120690

McClelland, Verity M; Cvetkovic, Zoran; Mills, Kerry R

2012-03-30

274

Electronic transport through tape-porphyrin molecular bridges  

International Nuclear Information System (INIS)

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

275

The Smeagol method for spin- and molecular-electronics  

CERN Document Server

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

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

2005-01-01

276

Electron transport through heterocyclic molecule: ab initio molecular orbital theory  

International Nuclear Information System (INIS)

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

277

The emission continuum of electron excited molecular hydrogen  

International Nuclear Information System (INIS)

Photo-excitation of hydrogen molecule from the X1?+g state to the B1?+u, C1?+u, and D1?u states and subsequent emission to the dissociation continuum is the primary destruction mechanism of H2 in interstellar clouds. The authors have recently calculated continuum emission profiles of B1?+u - X1?+g, C1?u - X1?+g, B' 1?+u - X1 ?+g, and D1?u - X1?+g transitions of H2. Synthetic spectra based on the calculated profiles are in excellent agreement with high-resolution electron-impact induced emission spectra obtained at 100 eV. An improved intensity calibration standard and dissociation yields of the Lyman and Werner continuua produced by both electron and photon impact excitation will be presented

278

Applications of the Information Theory to Problems of Molecular Electronic Structure and Chemical Reactivity  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract: Recent studies on applications of the information theoretic concepts to molecular systems are reviewed. This survey covers the information theory basis of the Hirshfeld partitioning of molecular electron densities, its generalization to many electron probabilities, the local information distance analysis of molecular charge distributions, the charge transfer descriptors of the donor-acceptor reactive systems, the elements of a “thermodynamic” description of molecular charge displacements, both “vertical” (between molecular fragments for the fixed overall density and “horizontal” (involving different molecular densities, with the entropic representation description provided by the information theory. The average uncertainty measures of bond multiplicities in molecular “communication” systems are also briefly summarized. After an overview of alternative indicators of the information distance (entropy deficiency, missing information between probability distributions the properties of the “stockholder” densities, which minimize the entropy deficiency relative to the promolecule reference, are summarized. In particular, the surprisal analysis of molecular densities is advocated as an attractive information-theoretic tool in the electronic structure theory, supplementary to the familiar density difference diagrams. The subsystem information density equalization rules satisfied by the Hirshfeld molecular fragments are emphasized: the local values of alternative information distance densities of subsystems are equal to the corresponding global value, characterizing the molecule as a whole. These local measures of the information content are semi-quantitatively related to the molecular density difference function. In the density functional theory the effective external potentials of molecular fragments are defined, for which the subsystem densities are the ground-state densities. The nature of the energetic and “entropic” equilibrium conditions is reexamined and the entropy representation forces driving the charge transfer in molecular systems are introduced. The latter combine the familiar Fukui functions of subsystems with the information densities, the entropy representation “intensive” conjugates of the subsystem electron densities, and are shown to exactly vanish for the “stockholder” charge distribution. The proportionality relations between charge response characteristics of reactants, e.g., the Fukui functions, are derived. They are shown to follow from the minimum entropy deficiency principles formulated in terms of both the subsystems electron densities and Fukui functions, respectively.

Roman F. Nalewajski

2002-04-01

279

Electron spectra and structure of atomic and molecular clusters  

International Nuclear Information System (INIS)

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

280

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

Science.gov (United States)

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(+). PMID:23944679

Khemiri, Noura; Dardouri, Riadh; Oujia, Brahim; Gadéa, Florent Xavier

2013-09-12

 
 
 
 
281

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

International Nuclear Information System (INIS)

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

282

Electronic and magnetic structure of LaSr-2×4 manganese oxide molecular sieve nanowires.  

Science.gov (United States)

In this study we combine scanning transmission electron microscopy, electron energy loss spectroscopy and electron magnetic circular dichroism to get new insights into the electronic and magnetic structure of LaSr-2×4 manganese oxide molecular sieve nanowires integrated on a silicon substrate. These nanowires exhibit ferromagnetism with strongly enhanced Curie temperature (T c >500 K), and we show that the new crystallographic structure of these LaSr-2×4 nanowires involves spin orbital coupling and a mixed-valence Mn3+/Mn4+, which is a must for ferromagnetic ordering to appear, in line with the standard double exchange explanation. PMID:24735528

Gazquez, Jaume; Carretero-Genevrier, Adrián; Gich, Martí; Mestres, Narcís; Varela, María

2014-06-01

283

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

Science.gov (United States)

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 [14]. The results show similar trends to available experimental data.

Pisarra, M.; Sindona, A.; Riccardi, P.

2011-05-01

284

Coupled electron-phonon transport from molecular dynamics with quantum baths  

International Nuclear Information System (INIS)

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

285

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

2009-01-14

286

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

2009-01-01

287

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

288

Monte Carlo approach to the spatial deposition of energy by electrons in molecular hydrogen  

Science.gov (United States)

The Monte Carlo (MC) and continuous slowdown approximation (CSDA) approaches to the spatial deposition of energy by electrons are compared using the same detailed atomic cross section (DACS). It is found that the CSDA method overestimates the amount of energy that is deposited near the end of the path for electrons above a few hundred electron volts. The MC results are in approximate agreement with experimental data in such a way as to be relatively independent of the actual gas used. Our MC results are extended to obtain the three-dimensional deposition of energy by sub-keV electrons in molecular hydrogen.

Heaps, M. G.; Green, A. E. S.

1974-01-01

289

Chirally Sensitive Electron-Induced Molecular Breakup and the Vester-Ulbricht Hypothesis  

Science.gov (United States)

We have studied dissociative electron attachment in sub-eV collisions between longitudinally polarized electrons and chiral bromocamphor molecules. For a given target enantiomer, the dissociative Br anion production depends on the helicity of the incident electrons, with an asymmetry that depends on the electron energy and is of order 3×10-4. The existence of chiral sensitivity in a well-defined molecular breakup reaction demonstrates the viability of the Vester-Ulbrict hypothesis, namely, that the longitudinal polarization of cosmic beta radiation was responsible for the origins of biological homochirality.

Dreiling, J. M.; Gay, T. J.

2014-09-01

290

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

International Nuclear Information System (INIS)

Polaron theory of tunneling through a molecular quantum dot (MQD) with strong electron-vibron interactions and attractive electron-electron correlations is developed. The dot is modeled as a d-fold-degenerate energy level weakly coupled to the leads. The effective attractive interaction between polarons in the dot results in a 'switching' phenomenon in the current-voltage characteristics when d>2, in agreement with the results for the phenomenological negative-U model. The degenerate MQD with strong electron-vibron coupling has two stable current states in a certain interval of the bias voltage below some critical temperature

291

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

International Nuclear Information System (INIS)

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.

292

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

293

Molecular electron affinities and the calculation of the temperature dependence of the electron-capture detector response.  

Science.gov (United States)

The use of the electron-capture detector (ECD) to measure molecular electron affinities and kinetic parameters for reactions of thermal electrons is reviewed. The advances of the past decade are emphasized and include the multistate electron-capture detector model and the use of semi-empirical self-consistent field quantum mechanical calculations and half wave reduction potential values to support gas phase experimental results. A procedure for the evaluation of the adiabatic electron affinities of the main group elements and the homonuclear diatomic molecules is presented. Potential excited states are identified for the magnetron (MGN) values for quinones, thermal charge transfer (TCT) values for CS2, C6F6, SF6 and photoelectron spectroscopy (PES) values for O2, NO, nitromethane, and the nucleic acids. Literature electron affinities are then evaluated. The temperature dependence of the electron-capture detector can be calculated using values for kinetic rate constants and electron affinities to optimize response and temperature sensitivity in analytical procedures. The temperature dependence for adenine, guanine, thymine and cytosine are predicted for reactions with thermal electrons. Using the recent advances, the new adiabatic electron affinities are: all in electron volts (eV), 4-F-benzaldehyde (0.57 +/- 0.05) and acetophenones (APs) 4-F-AP (0.52 +/- 0.05); 2-CF3-AP (0.79 +/- 0.05); 3-CF3-AP (0.79 +/- 0.05); 4-CF3-AP (0.89 +/- 0.05); 3-CI-AP (0.67 +/- 0.05); and 4-Cl-AP (0.64 +/- 0.05). The adiabatic electron affinities of chloro and fluorobenzenes range from 0.17 to 1.15 eV and 0.13 to 0.86 eV. PMID:15214661

Chen, E C M; Chen, E S

2004-05-28

294

Electronic structure investigations in conductance across porphyrin-fullerene molecular junctions  

Science.gov (United States)

ab-initio density functional electronic structure calculations have been performed on a weakly interacting porphyrin-fullerene molecular junction. The goal of the study was to investigate the conductance trend across the porphyrin-fullerene molecular junction. We demonstrate that the conductance is dependent on the "X" group (X=H, F, OH) present on the donor porphyrin derivative. The porphyrin-fullerene junction with fluorine substituted in the porphyrin has the largest conductance.

Kashid, Vikas; Salunke, H. G.; Shah, Vaishali

2013-02-01

295

High-conductive organometallic molecular wires with delocalized electron systems strongly coupled to metal electrodes.  

Science.gov (United States)

Besides active, functional molecular building blocks such as diodes or switches, passive components, for example, molecular wires, are required to realize molecular-scale electronics. Incorporating metal centers in the molecular backbone enables the molecular energy levels to be tuned in respect to the Fermi energy of the electrodes. Furthermore, by using more than one metal center and sp-bridging ligands, a strongly delocalized electron system is formed between these metallic "dopants", facilitating transport along the molecular backbone. Here, we study the influence of molecule-metal coupling on charge transport of dinuclear X(PP)2FeC4Fe(PP)2X molecular wires (PP = Et2PCH2CH2PEt2); X = CN (1), NCS (2), NCSe (3), C4SnMe3 (4), and C2SnMe3 (5) under ultrahigh vacuum and variable temperature conditions. In contrast to 1, which showed unstable junctions at very low conductance (8.1 × 10(-7) G0), 4 formed a Au-C4FeC4FeC4-Au junction 4' after SnMe3 extrusion, which revealed a conductance of 8.9 × 10(-3) G0, 3 orders of magnitude higher than for 2 (7.9 × 10(-6) G0) and 2 orders of magnitude higher than for 3 (3.8 × 10(-4) G0). Density functional theory (DFT) confirmed the experimental trend in the conductance for the various anchoring motifs. The strong hybridization of molecular and metal states found in the C-Au coupling case enables the delocalized electronic system of the organometallic Fe2 backbone to be extended over the molecule-metal interfaces to the metal electrodes to establish high-conductive molecular wires. PMID:25233125

Schwarz, Florian; Kastlunger, Georg; Lissel, Franziska; Riel, Heike; Venkatesan, Koushik; Berke, Heinz; Stadler, Robert; Lörtscher, Emanuel

2014-10-01

296

Shapes of leading tunnelling trajectories for single-electron molecular ionization  

CERN Document Server

Based on the geometrical approach to tunnelling by P.D. Hislop and I.M. Sigal [Memoir. AMS 78, No. 399 (1989)], we introduce the concept of a leading tunnelling trajectory. It is then proven that leading tunnelling trajectories for single active electron models of molecular tunnelling ionization (i.e., theories where a molecular potential is modelled by a single-electron multi-centre potential) are linear in the case of short range interactions and ``almost'' linear in the case of long range interactions. The results are presented on both the formal and physically intuitive levels. Physical implications of the proven statements are discussed.

Bondar, Denys I; Ivanov, Misha Yu

2010-01-01

297

Distant electron tunneling controlled by external fields in molecular nano structures  

International Nuclear Information System (INIS)

The influence of stochastic, periodic, and magnetic fields on a long-range electron tunneling in donor - bridge - acceptor and electrode - molecular wire - electrode structures is studied theoretically. The description of a bridge-mediated electron tunneling between donor and acceptor groups is shown to be possible via the introduction of effective transfer rates. The principal distinction in the dependence of low-temperature elastic and inelastic tunnel currents mediated by a molecular wire with bridging paramagnetic ions on an applied magnetic field is considered. The appearance of the field-induced inversion and suppression effects is widely discussed

298

Shapes of leading tunnelling trajectories for single-electron molecular ionization  

Energy Technology Data Exchange (ETDEWEB)

Based on the geometrical approach to tunnelling by Hislop and Sigal (1989 Mem. AMS 78 No 399), we introduce the concept of a leading tunnelling trajectory. It is then proven that leading tunnelling trajectories for single-active-electron models of molecular tunnelling ionization (i.e. theories where a molecular potential is modelled by a single-electron multi-centre potential) are linear in the case of short-range interactions and 'almost' linear in the case of long-range interactions. The results are presented on both the formal and physically intuitive levels. Physical implications of the obtained results are discussed.

Bondar, Denys I; Liu Wingki, E-mail: dbondar@princeton.edu, E-mail: wkliu@uwaterloo.ca [Department of Physics and Astronomy, Guelph-Waterloo Physics Institute, University of Waterloo, Waterloo, Ontario N2 L 3G1 (Canada)

2011-07-08

299

Participation of Low Molecular Weight Electron Carriers in Oxidative Protein Folding  

Directory of Open Access Journals (Sweden)

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

József Mandl

2009-03-01

300

Electron induced conformational changes of imine-based molecular switches on a Au(111) surface  

Energy Technology Data Exchange (ETDEWEB)

Organic molecules exhibiting controllable reversible transitions between isomeric states on surfaces promise an enormous potential in the field of molecular electronics. The reversible cis-trans isomerization of azobenzene-like molecules is often hindered by a strong interaction of the nitrogen lone-pair electrons of the di-azo bridge (-N=N-) with the substrate. In order to improve the isomerization capabilities, the di-azo bridge is substituted by an imine-group (-N=CH-). Here, we use low-temperature scanning tunneling microscopy to investigate a sub-monolayer of the newly designed imine-based molecular switch NPCI on a Au(111) surface. Its carboxylic termination mediates the formation of hydrogen-bonded dimers, which align in rows along the herringbone reconstruction. We were able to induce reversible conformational changes with the tunneling electrons from the STM tip and determine its efficiency as a function of electron energy.

Lotze, Christian; Pascual, Jose Ignacio [Inst. f. Experimentalphysik, Freie Universitaet Berlin (Germany); Luo, Ying; Haag, Rainer [Inst. f. Organische Chemie, Freie Universitaet Berlin (Germany)

2010-07-01

 
 
 
 
301

Electronic structure of the Magnesium hydride molecular ion  

CERN Document Server

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

302

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.

303

Electronic structure of the magnesium hydride molecular ion  

Science.gov (United States)

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.

Aymar, M.; Guérout, R.; Sahlaoui, M.; Dulieu, O.

2009-08-01

304

Electronic structure of the magnesium hydride molecular ion  

Energy Technology Data Exchange (ETDEWEB)

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{sup +} 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{sup +} as a function of the interatomic distance. This study represents the first step towards the modelling of collisions between trapped cold Mg{sup +} ions and H{sub 2} molecules.

Aymar, M; Guerout, R; Sahlaoui, M; Dulieu, O, E-mail: mireille.aymar@lac.u-psud.f, E-mail: romain.guerout@lac.u-psud.f, E-mail: m-sahlaoui@mail.univ-tlemcen.d, E-mail: olivier.dulieu@lac.u-psud.f [Laboratoire Aime Cotton, CNRS, Bat. 505, Univ. Paris-Sud, F-91405 Orsay, Cedex (France)

2009-08-14

305

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

306

A study of the inelastic scattering of fast electrons from molecular hydrogen  

International Nuclear Information System (INIS)

Inelastic scattering of fast electrons from the electronic ground state of H2 is investigated in the context of the first Born approximation plus exchange a la Ochkur. Excited molecular states of singlet symmetry have been obtained in terms of rather extended C.I. wavefunctions. Generalized oscillator strength, differential and total cross section values for final states of ?sub(g,u) and PIsub(g,u) symmetry have been evaluated and are discussed. (author)

307

Molecular electronic level alignment at weakly coupled organic film/metal interfaces.  

Science.gov (United States)

Electronic level alignment at interfaces of molecular materials with inorganic semiconductors and metals controls many interfacial phenomena. How the intrinsic properties of the interacting systems define the electronic structure of their interface remains one of the most important problems in molecular electronics and nanotechnology that can be solved through a combination of surface science experimental techniques and theoretical modeling. In this article, we address this fundamental problem through experimental and computational studies of molecular electronic level alignment of thin films of C6F6 on noble metal surfaces. The unoccupied electronic structure of C6F6 is characterized with single molecule resolution using low-temperature scanning tunneling microscopy-based constant-current distance-voltage spectroscopy. The experiments are performed on several noble metal surfaces with different work functions and distinct surface-normal projected band structures. In parallel, the electronic structures of the quantum wells (QWs) formed by the lowest unoccupied molecular orbital state of the C6F6 monolayer and multilayer films and their alignment with respect to the vacuum level of the metallic substrates are calculated by solving the Schrödinger equation for a semiempirical one-dimensional (1D) potential of the combined system using input from density functional theory. Our analysis shows that the level alignment for C6F6 molecules bound through weak van der Waals interactions to noble metal surfaces is primarily defined by the image potential of metal, the electron affinity of the molecule, and the molecule surface distance. We expect the same factors to determine the interfacial electronic structure for a broad range of molecule/metal interfaces. PMID:25303040

Zhao, Jin; Feng, Min; Dougherty, Daniel Barker; Sun, Hao; Petek, Hrvoje

2014-10-28

308

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Pistolesi, Fabio

2009-01-01

309

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)

310

Electronic structure and magnetic anisotropy for nickel-based molecular magnets  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Recent magnetic measurements on tetra-nickel molecular magnets [Ni(hmp)(ROH)Cl]$_4$, where R=CH$_3$, CH$_2$CH$_3$, or (CH$_2$)$_2$C(CH$_3$)$_3$ and hmp$^-$ is the monoanion of 2-hydroxymethylpyridine, revealed a strong exchange bias prior to the external magnetic field reversal as well as anomalies in electron paramagnetic resonance peaks at low temperatures. To understand the exchange bias and observed anomalies, we calculate the electronic structure and magnetic properties...

Park, Kyungwha; Yang, En-che; Hendrickson, David N.

2004-01-01

311

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

International Nuclear Information System (INIS)

The emission cross sections for the characteristic x radiation accompanying the capture of an electron by C6+ and O8+ nuclei in molecular hydrogen at a collision energy E0 = 0.6--8 keV/amu have been measured. It is shown that the electron is captured in a state of the C5+ and O7+ ions with large principal quantum numbers. This occurs when the population of states with different orbital moments is approximately uniform

312

Molecular electronics at metal/semiconductor junctions. Si inversion by sub-nanometer molecular films.  

Science.gov (United States)

Electronic transport across n-Si-alkyl monolayer/Hg junctions is, at reverse and low forward bias, independent of alkyl chain length from 18 down to 1 or 2 carbons! This and further recent results indicate that electron transport is minority, rather than majority carrier dominated, occurs via generation and recombination, rather than (the earlier assumed) thermionic emission, and, as such, is rather insensitive to interface properties. The (m)ethyl results show that binding organic molecules directly to semiconductors provides semiconductor/metal interface control options, not accessible otherwise. PMID:19438192

Yaffe, Omer; Scheres, Luc; Puniredd, Sreenivasa Reddy; Stein, Nir; Biller, Ariel; Lavan, Rotem Har; Shpaisman, Hagay; Zuilhof, Han; Haick, Hossam; Cahen, David; Vilan, Ayelet

2009-06-01

313

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

314

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

CERN Document Server

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

315

Assessment of a nanoparticle bridge platform for molecular electronics measurements.  

Science.gov (United States)

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. PMID:20890018

Jafri, S H M; Blom, T; Leifer, K; Strømme, M; Löfås, H; Grigoriev, A; Ahuja, R; Welch, K

2010-10-29

316

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

Energy Technology Data Exchange (ETDEWEB)

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

Krantz, Claude

2009-10-28

317

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

International Nuclear Information System (INIS)

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

318

Electron-molecular cation reactive collisions: from channel mixing to competitive processes  

International Nuclear Information System (INIS)

The competition between dissociative recombination, vibrational excitation, and dissociative excitation of molecular cations in electron-impact collisions is discussed within the formalism of the Multichannel Quantum Defect Theory. Illustrative results are given for the HD+/HD and CO+/CO systems.

319

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

CERN Document Server

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

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

2006-01-01

320

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.

2006-01-01

 
 
 
 
321

Electronic Structure of Covalently Linked Zinc Bacteriochlorin Molecular Arrays: Insights into Molecular Design for NIR Light Harvesting.  

Science.gov (United States)

Pigment-based molecular arrays, especially those based on porphyrins, have been extensively studied as viable components of artificial light harvesting devices. Unlike porphyrins, bacteriochlorins absorb strongly in the NIR, yet little is known of the applicability of covalently linked bacteriochlorin-based arrays in this arena. To lay the foundation for future studies of excited state properties of such arrays, we present a systematic study of the ground state electronic structure of zinc bacteriochlorin (ZnBC) molecular arrays with various linkers and linker attachment sites (meso vs ?) employing density functional theory in combination with the energy-based fragmentation (EBF) method, and the EBF with molecular orbitals (EBF-MO) method. We find that the level of steric hindrance between the ZnBC and the linker is directly correlated with the amount of ground sate electronic interactions between the ZnBCs. Low steric hindrance between the ZnBC and the linker found in alkyne-linked arrays results in strongly interacting arrays that are characterized by a decrease in the HOMO-LUMO energy gaps, large orbital energy dispersion in the frontier region, and low ZnBC-linker rotational barriers. In contrast, sterically hindered linkers, such as aryl-based linkers, result in weakly interacting arrays characterized by increased orbital energy degeneracy in the frontier region and high ZnBC-linker rotational barriers. For all linkers studied, the level of steric hindrance decreases when the ZnBCs are linked at the ? position. Hence, ZnBC arrays that exhibit strong, weak, or intermediate ground-state electronic interactions can be realized by adjusting the level of steric hindrance with a judicious choice of the linker type and linker attachment site. Such tuning may be essential for design of light harvesting arrays with desired spectral properties. PMID:25237715

Shrestha, Kushal; González-Delgado, Jessica M; Blew, James H; Jakubikova, Elena

2014-10-23

322

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

323

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

324

Electronic Correlations in Oligo-acene and -thiophene Organic Molecular Crystals  

CERN Document Server

From first principles calculations we determine the Coulomb interaction between two holes on oligo-acene and -thiophene molecules in a crystal, as a function of the oligomer length. The relaxation of the molecular geometry in the presence of holes is found to be small. In contrast, the electronic polarization of the molecules that surround the charged oligomer, reduces the bare Coulomb repulsion between the holes by approximately a factor of two. In all cases the effective hole-hole repulsion is much larger than the calculated valence bandwidth, which implies that at high doping levels the properties of these organic semiconductors are determined by electron-electron correlations.

Brocks, G; Morpurgo, A F; Brocks, Geert; Brink, Jeroen van den; Morpurgo, Alberto F.

2004-01-01

325

Electronic structure and molecular orientation of a Zn-tetra-phenyl porphyrin multilayer on Si(111)  

CERN Document Server

The electronic properties and the molecular orientation of Zn-tetraphenyl-porphyrin films deposited on Si(111) have been investigated using synchrotron radiation. For the first time we have revealed and assigned the fine structures in the electronic spectra related to the HOMOs and LUMOs states. This is particularly important in order to understand the orbital interactions, the bond formation and the evolution of the electronic properties with oxidation or reduction of the porphyrins in supramolecular donor-acceptor complexes used in photovoltaic devices.

Cudia, C C; Larciprete, R; Cepek, C; Zampieri, G; Sangaletti, L; Pagliara, S; Verdini, A; Cossaro, A; Floreano, L; Morgante, A; Petaccia, L; Lizzit, S; Battocchio, C; Polzonetti, G; Goldoni, A

2005-01-01

326

Angular distributions of molecular Auger electrons: The case of C 1s Auger emission in CO  

Science.gov (United States)

The results of a study of the Auger-electron photoelectron angular correlations in the case of the C 1s ionization of the CO molecule are presented and compared with theoretical calculations in the Hartree-Fock approximation based on the two-step model. The measurements have been performed at two photon energies, 305 and 318eV , respectively, and at three angles of photoelectron emission relative to the light polarization vector: namely, 0°, 30°, and 60°. A general agreement is found between theory and experiment for the coincidence angular distributions and the relative magnitudes of the Auger-electron photoelectron angular correlations. However, both experiment and theory show that the Auger-electron photoelectron angular correlations are not sufficiently sensitive to the details of the Auger-electron wave function to allow a “complete” Auger experiment in molecules. On the other hand, our calculations demonstrate that the Auger-electron angular distribution measured in the molecular frame is very sensitive to the individual contributions of different partial waves of the Auger electron. Therefore we conclude that the complete experiment for the Auger decay in molecules can be realized only measuring the Auger-electron angular distributions in the molecular frame.

Semenov, S. K.; Kuznetsov, V. V.; Cherepkov, N. A.; Bolognesi, P.; Feyer, V.; Lahmam-Bennani, A.; Casagrande, M. E. Staicu; Avaldi, L.

2007-03-01

327

Angular distributions of molecular Auger electrons: The case of C 1s Auger emission in CO  

International Nuclear Information System (INIS)

The results of a study of the Auger-electron-photoelectron angular correlations in the case of the C 1s ionization of the CO molecule are presented and compared with theoretical calculations in the Hartree-Fock approximation based on the two-step model. The measurements have been performed at two photon energies, 305 and 318 eV, respectively, and at three angles of photoelectron emission relative to the light polarization vector: namely, 0 degree sign , 30 degree sign , and 60 degree sign . A general agreement is found between theory and experiment for the coincidence angular distributions and the relative magnitudes of the Auger-electron-photoelectron angular correlations. However, both experiment and theory show that the Auger-electron-photoelectron angular correlations are not sufficiently sensitive to the details of the Auger-electron wave function to allow a 'complete' Auger experiment in molecules. On the other hand, our calculations demonstrate that the Auger-electron angular distribution measured in the molecular frame is very sensitive to the individual contributions of different partial waves of the Auger electron. Therefore we conclude that the complete experiment for the Auger decay in molecules can be realized only measuring the Auger-electron angular distributions in the molecular frame

328

Recent Advances in Photoinduced Electron Transfer Processes of Fullerene-Based Molecular Assemblies and Nanocomposites  

Directory of Open Access Journals (Sweden)

Full Text Available Photosensitized electron-transfer processes of fullerenes hybridized with electron donating or other electron accepting molecules have been surveyed in this review on the basis of the recent results reported mainly from our laboratories. Fullerenes act as photo-sensitizing electron acceptors with respect to a wide variety of electron donors; in addition, fullerenes in the ground state also act as good electron acceptors in the presence of light-absorbing electron donors such as porphyrins. With single-wall carbon nanotubes (SWCNTs, the photoexcited fullerenes act as electron acceptor. In the case of triple fullerene/porphyrin/SWCNT architectures, the photoexcited porphyrins act as electron donors toward the fullerene and SWCNT. These mechanisms are rationalized with the molecular orbital considerations performed for these huge supramolecules. For the confirmation of the electron transfer processes, transient absorption methods have been used, in addition to time-resolved fluorescence spectral measurements. The kinetic data obtained in solution are found to be quite useful to predict the efficiencies of photovoltaic cells.

Osamu Ito

2012-05-01

329

Monte Carlo simulation of energy deposition by low-energy electrons in molecular hydrogen  

Science.gov (United States)

A set of detailed atomic cross sections has been used to obtain the spatial deposition of energy by 1-20-eV electrons in molecular hydrogen by a Monte Carlo simulation of the actual trajectories. The energy deposition curve (energy per distance traversed) is quite peaked in the forward direction about the entry point for electrons with energies above the threshold of the electronic states, but the peak decreases and broadens noticeably as the electron energy decreases below 10 eV (threshold for the lowest excitable electronic state of H2). The curve also assumes a very symmetrical shape for energies below 10 eV, indicating the increasing importance of elastic collisions in determining the shape of the curve, although not the mode of energy deposition.

Heaps, M. G.; Furman, D. R.; Green, A. E. S.

1975-01-01

330

Internal waves and rectification in a linearly stratified fluid  

Science.gov (United States)

Laboratory experiments were performed in a 13-m diameter rotating tank equipped with a continuous shelf break geometry and a central piston-like plunger. The fluid density was linearly stratified. The amplitude and period of the plunger, the rotation rate of the platform and the stratification are the parameters of the problem. The density fluctuations at six stations above and at mid-depth of the slope, along with dye visualization of the flow, were recorded. A limited set of experiments showed that a barotropic periodical forcing generated a first mode baroclinic wave which initially appears at the slope and propagates offshore. The likely presence of internal energy rays either slightly above, or immediately along the slope, is in agreement with previous analytical, laboratory and selected oceanic observations. In the former case, the stratification was such that the slope flow at mid-depth was supercritical while in the latter case, slope flow at mid-depth was critical. Rotation tended to decrease the amplitude of the generated internal wave. Also, non-linear processes were likely to act upon these waves for their normalized amplitude tended to decrease as the forcing increased (for similar forcing period, rotation rate and stratification). After the internal wave reflected from the plunger reaches the slope, there is a complex non-stationary regime with an occurrence of internal wave breaking in the vicinity of the slope. Thus there was an appearance of localized patches of turbulence and mixing. These events appeared both in dye visualization and in density fluctuations records. The subsequent mixing, or else the combined effect of topographical rectification and mixing, led to the appearance of a distinct Lagrangian transport, localized in the first few centimeters above the slope and oriented so as to leave the shallow waters on the right of its displacement.

Pérenne, Nicolas; Renouard, Dominique P.

331

Fabrication and electrical characterization of carbon-based molecular electronic junctions  

Science.gov (United States)

Contact mode atomic force microscopy (AFM) was used to intentionally scratch a monolayer deposited on a pyrolyzed photoresist film (PPF). The force was set to completely remove the monolayer but not to damage the underlying PPF surface. A line profile determined across the scratch with tapping mode AFM permitted determination of the monolayer thickness from the depth of the scratch. Carbon/molecule/metal molecular junctions were fabricated by metal deposition of titanium or copper onto monolayers of biphenyl (BP), and nitrobiphenyl (NBP), and multilayers of NBP covalently bonded to sp2 carbon substrates. The electronic behavior of Ti junctions was extremely dependent on residual gas pressure during e-beam deposition, due to the formation of a disordered Ti oxyhydroxide deposit. Carbon/molecule/Cu molecular electronic junctions were fabricated by metal deposition of copper onto films of various thicknesses of fluorene (FL), biphenyl (BP) and nitrobiphenyl (NBP) covalently bonded to flat, graphitic carbon. A "crossed wire" junction configuration provided high device yield and good junction reproducibility. Current/voltage characteristics were investigated for 72 junctions with various molecular structures and thicknesses, and at several temperatures. The strong effects of molecular structure and thickness on junction conductance and current density indicate molecular control of electronic properties. The current/voltage curves for all cases studied were nearly symmetric, scan rate independent, repeatable at least thousands of cycles, and exhibited negligible hysteresis. For junctions made with BP, FL, and NBP monolayers, the conductance varied by a factor of 40 at low voltage. Junctions made with NBP showed a decrease in conductivity of a factor of 1300 when the molecular layer thicknesses increased from 1.6 to 4.5 nm. The slope of ln(i) vs layer thickness for both BP and NBP was weakly dependent on applied voltage, and ranged from 0.16 to 0.24 A-1. These attenuation factors are similar to those observed for similar molecular layers on modified electrodes used to discern electrochemical kinetics. Plots of ln(i) vs V1/2 were linear above + 0.01V and over 2 to 4 orders of magnitude of the current. All junctions studied showed weak temperature dependence in the range of approximately 325 to 214 K, implying activation barriers in the range of 0.06 to 0.08 eV. The carbon/molecule/copper junction structure provides a robust, reproducible platform for investigations of the dependence of electron transport in molecular junctions on both molecular structure and temperature. (Abstract shortened by UMI.)

Anariba-Bardales, Franklin E.

332

Device for measuring the total cross-section (TCS) of electron scattering and the experimental electron-molecular nitrogen TCS at intermediate energy  

International Nuclear Information System (INIS)

The authors present a device designed for the absolute measurement of total electron-atom and electron-molecule cross section at intermediate energy. The experimental total cross sections for electron scattering form nitrogen molecular in the energy range 500-2600 eV are also given

333

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)

334

Phonon effects in molecular conduction junctions  

Science.gov (United States)

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

Nitzan, Abraham

2005-03-01

335

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

International Nuclear Information System (INIS)

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

336

pH-regulated ionic current rectification in conical nanopores functionalized with polyelectrolyte brushes.  

Science.gov (United States)

Mimicking biological ion channels capable of pH-regulated ionic transport, synthetic nanopores functionalized with pH-tunable polyelectrolyte (PE) brushes have been considered as versatile tools for active transport control of ions, fluids, and bioparticles on the nanoscale. The ionic current rectification (ICR) phenomenon through a conical nanopore functionalized with PE brushes whose charge highly depends upon the local solution properties (i.e., pH and background salt concentration) is studied theoretically for the first time. The results show that the rectification magnitude, as well as the preferential rectification direction, is sensitive to the pH stimulus. The bulk concentration of the background salt can also significantly influence the charge of the PE brushes and accordingly affect the ICR phenomenon. The obtained results provide an insightful understanding of the pH-regulated ICR and guidelines for designing nanopores functionalized with PE brushes for pH-tunable applications. PMID:24358472

Zeng, Zhenping; Ai, Ye; Qian, Shizhi

2014-02-14

337

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

338

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

Directory of Open Access Journals (Sweden)

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

RicardoOLouro

2014-06-01

339

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

Science.gov (United States)

Dissimilatory metal reducing organisms play key roles in the biogeochemical cycle of metals as well as in the durability of submerged and buried metallic structures. The molecular mechanisms that support electron transfer across the microbe-metal interface in these organisms remain poorly explored. It is known that outer membrane proteins, in particular multiheme cytochromes, are essential for this type of metabolism, being responsible for direct and indirect, via electron shuttles, interaction with the insoluble electron acceptors. Soluble electron shuttles such as flavins, phenazines, and humic acids are known to enhance extracellular electron transfer. In this work, this phenomenon was explored. All known outer membrane decaheme cytochromes from Shewanella oneidensis MR-1 with known metal terminal reductase activity and a undecaheme cytochrome from Shewanella sp. HRCR-6 were expressed and purified. Their interactions with soluble electron shuttles were studied using stopped-flow kinetics, NMR spectroscopy, and molecular simulations. The results show that despite the structural similarities, expected from the available structural data and sequence homology, the detailed characteristics of their interactions with soluble electron shuttles are different. MtrC and OmcA appear to interact with a variety of different electron shuttles in the close vicinity of some of their hemes, and with affinities that are biologically relevant for the concentrations typical found in the medium for this type of compounds. All data support a view of a distant interaction between the hemes of MtrF and the electron shuttles. For UndA a clear structural characterization was achieved for the interaction with AQDS a humic acid analog. These results provide guidance for future work of the manipulation of these proteins toward modulation of their role in metal attachment and reduction. PMID:25018753

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

2014-01-01

340

Dynamic admittance of carbon nanotube-based molecular electronic devices and their equivalent electric circuit  

International Nuclear Information System (INIS)

We use first-principles quantum mechanics to simulate the transient electrical response through carbon nanotube-based conductors under time-dependent bias voltages. The dynamic admittance and time-dependent charge distribution are reported and analyzed. We find that the electrical response of these two-terminal molecular devices can be mapped onto an equivalent classical electric circuit and that the switching time of these end-on carbon nanotube devices is only a few femtoseconds. This result is confirmed by studying the electric response of a simple two-site model device and is thus generalized to other two-terminal molecular electronic devices.

 
 
 
 
341

Carbon-fiber tips for scanning probe microscopes and molecular electronics experiments  

Science.gov (United States)

We fabricate and characterize carbon-fiber tips for their use in combined scanning tunneling and force microscopy based on piezoelectric quartz tuning fork force sensors. An electrochemical fabrication procedure to etch the tips is used to yield reproducible sub-100-nm apex. We also study electron transport through single-molecule junctions formed by a single octanethiol molecule bonded by the thiol anchoring group to a gold electrode and linked to a carbon tip by the methyl group. We observe the presence of conductance plateaus during the stretching of the molecular bridge, which is the signature of the formation of a molecular junction.

Rubio-Bollinger, Gabino; Castellanos-Gomez, Andres; Bilan, Stefan; Zotti, Linda A.; Arroyo, Carlos R.; Agraït, Nicolás; Cuevas, Juan Carlos

2012-05-01

342

Charge-transport properties of prototype molecular materials for organic electronics based on graphene nanoribbons.  

Science.gov (United States)

The semiconducting properties of molecular material prototypes for graphene nanoribbons are rationalized by quantum-chemical calculations. The present contribution focuses on the hole transport properties of circum(oligo)acenes and compares the intrinsic efficiency of these materials for charge transport in the hopping regime with respect to the (oligo)acenes parent compounds. The results at the molecular scale predict significantly higher mobilities in circum(oligo)acenes mainly due to lower electron-phonon coupling. The importance of non-covalent intermolecular interactions is also highlighted; the description of the dimeric nanostructures expected in thin films devices needs the inclusion of dispersion forces. PMID:19421532

Sancho-García, J C; Pérez-Jiménez, A J

2009-04-21

343

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.

344

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

345

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

CERN Document Server

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

Mazzola, Guglielmo; Sorella, Sandro

2014-01-01

346

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

347

Investigation of size and electronic effects on Kapitza conductance with non-equilibrium molecular dynamics  

Science.gov (United States)

In nanosystems, the thermal resistance between materials typically dominates the overall resistance. While size effects on thermal conductivity are well documented, size effects on thermal boundary conductance have only been speculated. In response, we characterize the relationship between interfacial resistance and material dimension using molecular dynamics. We find that the interfacial resistance increases linearly with inverse system length but is insensitive to cross-sectional area. Also, from the temperature-dependence of interfacial resistance, we conclude that contributions of short-wavelength phonons dominate. Lastly, by coupling the molecular dynamics to a two-temperature model, we show that electron-mediated transport has little effect on thermal resistance.

Jones, R. E.; Duda, J. C.; Zhou, X. W.; Kimmer, C. J.; Hopkins, P. E.

2013-05-01

348

When electrons meet molecular ions and what happens next: dissociative recombination from interstellar molecular clouds to internal combustion engines.  

Science.gov (United States)

The interaction of matter with its environment is the driving force behind the evolution of 99% of the observed matter in the universe. The majority of the visible universe exists in a state of weak ionization, the so called fourth state of matter: plasma. Plasmas are ubiquitous, from those occurring naturally; interstellar molecular clouds, cometary comae, circumstellar shells, to those which are anthropic in origin; flames, combustion engines and fusion reactors. The evolution of these plasmas is driven by the interaction of the plasma constituents, the ions, and the electrons. One of the most important subsets of these reactions is electron-molecular ion recombination. This process is significant for two very important reasons. It is an ionization reducing reaction, removing two ionised species and producing neutral products. Furthermore, these products may themselves be reactive radical species which can then further drive the evolution of the plasma. The rate at which the electron reacts with the ion depends on many parameters, for examples the collision energy, the internal energy of the ion, and the structure of the ion itself. Measuring these properties together with the manner in which the system breaks up is therefore critical if the evolution of the environment is to be understood at all. Several techniques have been developed to study just such reactions to obtain the necessary information on the parameters. In this paper the focus will be on one the most recently developed of these, the Ion Storage Ring, together with the detection tools and techniques used to extract the necessary information from the reaction. PMID:18618616

Thomas, Richard D

2008-01-01

349

Ion current rectification inversion in conic nanopores: nonequilibrium ion transport biased by ion selectivity and spatial asymmetry.  

Science.gov (United States)

We show both theoretically and experimentally that the ion-selectivity of a conic nanopore, as defined by a normalized density of the surface charge, significantly affects ion current rectification across the pore. For weakly selective negatively charged pores, intra-pore ion transport controls the current and internal ion enrichment/depletion at positive/reverse biased voltage (current enters/leaves through the tip, respectively), which is responsible for current rectification. For strongly selective negatively charged pores under positive bias, the current can be reduced by external field focusing and concentration depletion at the tip at low ionic strengths and high voltages, respectively. These external phenomena produce a rectification inversion for highly selective pores at high (low) voltage (ionic strength). With an asymptotic analysis of the intra-pore and external ion transport, we derive simple scaling laws to quantitatively capture empirical and numerical data for ion current rectification and rectification inversion of conic nanopores. PMID:23387614

Yan, Yu; Wang, Lin; Xue, Jianming; Chang, Hsueh-Chia

2013-01-28

350

Block of inward rectification by intracellular H+ in immature oocytes of the starfish Mediaster aequalis  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Intracellular pH was recorded in immature starfish oocytes using pH- sensitive microelectrodes, and inwardly rectifying potassium currents were measured under voltage clamp. When the intracellular pH was lowered using acetate-buffered artificial sea water from the normal value of 7.09 to 5.9, inward rectification was completely blocked. The relationship between inward rectification and internal pH between 7.09 and 5.9 could be fit by a titration curve for the binding of three H ions to a site...

1982-01-01

351

Fabrication of tunnel junction-based molecular electronics and spintronics devices  

International Nuclear Information System (INIS)

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

352

Modulations of electronic tunneling rates through flexible molecular bridges by a dissipative superexchange mechanism  

International Nuclear Information System (INIS)

Long-range coherent electron transfer between a donor and an acceptor is often assisted by intermediate molecular bridge, via the superexchange tunneling mechanism. The effect of electronic-nuclear coupling intensity on the tunneling rate and mechanism is analyzed using a generalized spin-boson model, in which the two level system, representing the donor and the acceptor is coupled to a dissipative nuclear bath only indirectly, via additional N bridge sites. A Langevin-Schroedinger equation, based on a mean field approximation, is applied in order to study the corresponding many-body dynamics, and the results are supported by numerically exact calculations for a single nuclear bridge mode. At zero temperature and when the electron tunneling is slower than the nuclear motion, the main effect of electronic-nuclear coupling is the dissipation of electronic energy at the bridge into nuclear vibrations. At small coupling intensities, the electronic tunneling rate increases due to this dissipative mechanism, but as the coupling intensity increases the tunneling into the acceptor is suppressed and efficient dissipation leads to electronic trapping (solvation) at the bridge. This analysis agrees with numerous experimental and theoretical studies, emphasizing the importance of the nuclear bridge conformation and the bridge flexibility in controlling the electron transfer rate in donor-bridge-acceptor systems

353

Electron-vibration effects on the thermoelectric efficiency of molecular junctions  

Science.gov (United States)

The thermoelectric properties of a molecular junction model, appropriate for large molecules such as fullerenes, are studied within a nonequilibrium adiabatic approach in the linear regime at room temperature. A self-consistent calculation is implemented for electron and phonon thermal conductance showing that both increase with the inclusion of the electron-vibration coupling. Moreover, we show that the deviations from the Wiedemann-Franz law are progressively reduced upon increasing the interaction between electronic and vibrational degrees of freedom. Consequently, the junction thermoelectric efficiency is substantially reduced by the electron-vibration coupling. Even so, we find that, for realistic parameters values, the thermoelectric figure of merit can still have peaks of the order of unity.

Perroni, C. A.; Ninno, D.; Cataudella, V.

2014-09-01

354

Generation of excess charge carriers in molecularly doped polymers by electron-beam irradiation  

International Nuclear Information System (INIS)

The processes of generation and transport of excess charge carriers in molecularly doped polycarbonate and polystyrene were experimentally studied at room temperature. The polymers were ionized by 7- and 50-keV electrons. The radiation-chemical yield of free ions was determined by means of the universal method based on the combination of the time-of-flight technique in two carrier generation modes (surface and bulk generation) with the measurement of nonsteady-state conductivity. It was shown that the radiation-chemical yield of free ions under irradiation by 7-keV electrons is almost the same as that in the case of 50-keV electrons, despite the substantially different values of the linear energy transfer for these electrons

355

Energy spreading and angular distribution of a beam of electrons in molecular hydrogen  

Science.gov (United States)

A Monte Carlo approach is used to obtain the energy spreading and angular distribution of initially monoenergetic and monodirectional beams of electron incident on a gas of molecular hydrogen. Several beams of primary electrons and the resultant secondaries are degraded in a step-by-step procedure which utilizes a detailed set of cross sections, together with reasonable approximations for the creation of secondary electrons. Particular attention is paid to the initial angular distribution of secondary electrons. An analytic function which characterizes current experimental differential cross-section data is used to provide realistic inputs into our calculations. The results for energy distribution as a function of distance and angular distribution at selected energies and distances are illustrated.

Heaps, M. G.; Green, A. E. S.

1975-01-01

356

Complete chemical transformation of a molecular film by subexcitation electrons (<3 eV).  

Science.gov (United States)

The potential of slow electrons to act as a soft tool to control a chemical reaction in the condensed phase is demonstrated. By setting the energy of a well defined electron beam to values below 3 eV, the surface of a thin film of 1,2-C(2)F(4)C(l2) molecules can completely be transformed into molecular chlorine (and by-products, possibly perfluorinated polymers). At higher energies (>6 eV) some equilibrium state between product and educt composition can be achieved, however, accompanied by a gradual overall degradation of the film. The effect of complete transformation is based on both the selectivity and particular energy dependence of the initial step of the reaction which is dissociative electron attachment to C(2)F(4)C(l2), but also the fact that the initial molecule is efficiently decomposed by subexcitation electrons while the product C(l2) is virtually unaffected. PMID:14683298

Balog, Richard; Illenberger, Eugen

2003-11-21

357

Desorption induced by electronic transitions (DIET) of neutral fragments from chemisorbed biological molecular systems  

Science.gov (United States)

Low-energy electron stimulated desorption of neutral fragments from oligomers chemisorbed onto a gold surface is investigated within the 1-30 eV range. The oligonucleotides are anchored to the surface via a sulfur-bound technique similar to the procedure used in molecular self-assemblies. We show that under electron impact the dissociation of DNA bases occurs, leading to the production of CN, OCN and/or H 2NCN neutral species, which are the most intense observable yields. The incident electron energy dependence of these desorbed neutral species exhibits typical signatures of dissociative electron attachment initiated by the formation of shape and core-excited resonances below 20 eV, whereas usually non-resonant processes (i.e. dipolar dissociation or dissociative ionization) become predominant above 20 eV.

Abdoul-Carime, H.; Dugal, P. C.; Sanche, L.

2000-04-01

358

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

Science.gov (United States)

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

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

2013-02-13

359

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

International Nuclear Information System (INIS)

Highlights: • We simulate electron dynamics in polyene and polyyne bridged molecular wires. • Time-dependent configuration interaction method has been employed. • A multireference configuration interaction singles approach is proposed. • We investigate the role of symmetry and localization of the initial state. • Introduction of a sodium cluster at the acceptor end leads to electron trapping. - Abstract: In this study we present methodological developments of the time-dependent configuration interaction (TDCI) method for ab initio electron dynamics in donor–bridge–acceptor systems. Especially, we investigate the role of valence electron correlation, the scheme for selecting the determinantal basis, and the computational effort. Our test systems are molecules of the type Li–(C2)n–CN, Li–(C2H2)n–CN, and Na9–(C2H2)2–CN. In this way, this study is intended as a step towards rigorous description of charge transfer in molecular wires attached to metal surfaces or nanoparticles using a many-electron wavefunction. Also, a multi-reference configuration interaction singles approach is suggested as a good compromise between computational effort and accuracy

360

Wave packet evolution approach to ionization of hydrogen molecular ion by fast electrons  

CERN Document Server

The multiply differential cross section of the ionization of hydrogen molecular ion by fast electron impact is calculated by a direct approach, which involves the reduction of the initial 6D Schr\\"{o}dinger equation to a 3D evolution problem followed by the modeling of the wave packet dynamics. This approach avoids the use of stationary Coulomb two-centre functions of the continuous spectrum of the ejected electron which demands cumbersome calculations. The results obtained, after verification of the procedure in the case atomic hydrogen, reveal interesting mechanisms in the case of small scattering angles.

Serov, V V; Joulakian, B B; Vinitsky, S I; Serov, Vladislav V.; Derbov, Vladimir L.; Joulakian, Boghos B.; Vinitsky, Sergue I.

2000-01-01

 
 
 
 
361

An ab initio molecular orbital study of the electron affinity of boron clusters  

Science.gov (United States)

The electron affinities of boron clusters were studied using ab initio molecular orbital methods to discuss the phenomenon of clustered boron anions emitted during sputtering. Calculations were performed at the MP4(SDQ)/CBSB5 level. The calculated electron affinities of B, B 2, and B 3 were found to be 0.214, 3.66, and 3.20 eV, respectively. These values are qualitatively consistent with the experimental data of sputtering yield of B -, B 2-, and B 3-.

Takeuchi, T.; Yamamoto, M.; Kiuchi, M.

1999-06-01

362

An ab initio molecular orbital study of the electron affinity of boron clusters  

Energy Technology Data Exchange (ETDEWEB)

The electron affinities of boron clusters were studied using ab initio molecular orbital methods to discuss the phenomenon of clustered boron anions emitted during sputtering. Calculations were performed at the MP4(SDQ)/CBSB5 level. The calculated electron affinities of B, B{sub 2}, and B{sub 3} were found to be 0.214, 3.66, and 3.20 eV, respectively. These values are qualitatively consistent with the experimental data of sputtering yield of B{sup -}, B{sub 2}{sup -}, and B{sub 3}{sup -}.

Takeuchi, T.; Yamamoto, M.; Kiuchi, M. E-mail: dd160@onri.go.jp

1999-06-01

363

An ab initio molecular orbital study of the electron affinity of boron clusters  

International Nuclear Information System (INIS)

The electron affinities of boron clusters were studied using ab initio molecular orbital methods to discuss the phenomenon of clustered boron anions emitted during sputtering. Calculations were performed at the MP4(SDQ)/CBSB5 level. The calculated electron affinities of B, B2, and B3 were found to be 0.214, 3.66, and 3.20 eV, respectively. These values are qualitatively consistent with the experimental data of sputtering yield of B-, B2-, and B3-

364

Electron, ion and atomic beams interaction with solid high-molecular dielectrics  

International Nuclear Information System (INIS)

A mathematical model was constructed and numerical investigation performed of the interaction between intense electron, ion and atomic beams and solid high-molecular dielectrics under various boundary conditions. The model is based on equations of the mechanics of continuum, electrodynamics and kinetics, describing the accumulation and relaxation of space charge and shock-wave processes, as well as the evolution of electric field in the sample. A semi-empirical procedure is proposed for the calculation of energy deposition by electron beam in a target in the presence of a non-uniform electric field. (author). 4 figs., 2 refs

365

Imaging molecular structures by electron diffraction using an intense few-cycle pulse.  

Science.gov (United States)

As an intense few-cycle pulse interacts with an atomic or molecular target, its strong oscillating field may first pull electrons out of the target and subsequently drive them back to scatter on the target. The scattering may occur only a few times or even once during the interaction. This unique property of few-cycle pulses enables one to image ultrafast transient structures of matter by the means of pulse-driven electron diffraction. We demonstrated this phenomenon with K(+)(2) via three-dimensional calculations of the time-dependent Schro dinger equation. PMID:15783814

Hu, S X; Collins, L A

2005-02-25

366

Electronic Transport Properties of an Anthraquinone-Based Molecular Switch with Carbon Nanotube Electrodes  

International Nuclear Information System (INIS)

Based on the nonequilibrium Green's function method and density functional theory calculations, we theoretically investigate the electronic transport properties of an anthraquinone-based molecular switch with carbon nanotube electrodes. The molecules that comprise the switch can convert between reduced hydroquinone (HQ) and oxidized anthraquinne (AQ) states via redox reactions. Our results show that the on-off ratio is increased one order of magnitude when compared to the case of gold electrodes. Moreover, an obvious negative differential resistance behavior at much low bias (0.07 V) is observed in the HQ form. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

367

Resonant Ion Pair Formation in Electron Collisions with Ground State Molecular Ions  

International Nuclear Information System (INIS)

Resonant ion pair formation from collisions of electrons with ground state diatomic molecular ions has been observed and absolute cross sections measured. The cross section for HD+ is characterized by an abrupt threshold at 1.9thinspthinspeV and 14 resolved peaks in the range of energies 0?E?14 eV . The dominant mechanism responsible for the structures appears to be resonant capture and stabilization, modified by two-channel quantum interference. Data on HF+ show structure correlated with photoionization of HF and with dissociative recombination of electrons with this ion. copyright 1999 The American Physical Society

368

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

2013-05-01

369

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

CERN Document Server

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

Sharoyan, E G

2005-01-01

370

X-ray incoherent scattering factor for molecular nitrogen as determined by high energy electron scattering  

International Nuclear Information System (INIS)

A beam of high energy electrons, 25 keV, was scattered off an effusive gas jet of molecular nitrogen, and the energy loss spectrum from 0 to 800 eV was measured for scattering angles ranging from 0.30 to 2.00. The energy loss spectra were converted to relative generalized oscillator strength (GOS) distributions and Bethe sum rule normalized to an absolute intensity scale. The x-ray incoherent scattering factor, S(K), as a function of momentum transfer, K, was determined by the use of the S(-1,K) GOS sum rule and compared with the predictions of theory. The effect of electron correlation on S(K) was determined by comparison of the experiment with molecular near Hartree-Fock calculations. Results from an extensive CI calculation were found to be in agreement with their experimental results, but proposed scaling of the CI theory appears to be incorrect

371

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

Directory of Open Access Journals (Sweden)

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

Hassan Safouhi

2004-02-01

372

Electronic sputtering of large organic molecules and its application in bio molecular mass spectrometry  

International Nuclear Information System (INIS)

This is a review of research which has its origin in the discovery of Plasma Desorption Mass Spectrometry (PDMS). Two main fields of research have developed, namely fundamental studies of the ejection process at fast ion impact and studies of applications of the new mass spectrometric technique. In this review the emphasis will be on the process of electronic sputtering of organic solids but also applications of this process in bio molecular mass spectrometry will be discussed. (author)

373

Interface engineering for organic electronics : manufacturing of hybrid inorganic-organic molecular crystal devices  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Organic semiconductors are at the basis of Organic Electronics. Objective of this dissertation is “to fabricate high-quality organic molecular single-crystal devices”, to explore the intrinsic properties of organic semiconductors. To achieve this, the in situ fabrication of complete field-effect transistors by direct deposition of metal contacts and oxide gate dielectrics on the surface of free-standing pentacene single-crystals at room temperature (with the ‘quasi-dynamic stencil de...

Veen, Peter Jan

2011-01-01

374

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

375

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

Science.gov (United States)

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 Markovian 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 mechanisms, coherent dynamics, and inelastic transport, in the overall charge current. This is done by studying two model variants: The first admits inelastic electron transmission only, while the second one allows for both coherent and incoherent pathways.

Simine, Lena; Segal, Dvira

2013-06-01

376

Experiments on Interactions of Electrons with Molecular Ions in Fusion and Astrophysical Plasmas  

International Nuclear Information System (INIS)

Through beam-beam experiments at the Multicharged Ion Research Facility (MIRF) at Oak Ridge National Laboratory (ORNL) and at the CRYRING heavy ion storage ring at Stockholm University, we are seeking to formulate a more complete picture of electron-impact dissociation of molecular ions. These inelastic collisions play important roles in many low temperature plasmas such as in divertors of fusion devices and in astrophysical environments. An electron-ion crossed beams experiment at ORNL investigates the dissociative excitation and dissociative ionization of molecular ions from a few eV up to 100 eV. Measurements on dissociative recombination (DR) experiments are made at CRYRING, where chemical branching fractions and fragmentation dynamics are studied. Taking advantage of a 250-kV acceleration platform at the MIRF, a merged electron-ion beams energy loss apparatus is employed to study DR down to zero energy. Recent results on the dissociation of molecular ions of importance in fusion and astrophysics are presented

377

Application of resonant X-ray emissions for molecular/electronic structure analysis of boron nitrides  

Energy Technology Data Exchange (ETDEWEB)

We describe the application of resonant X-ray emissions for molecular/electronic structure analysis of boron nitrides using quasimonochromatic undulator radiation at the Photon Factory. Prominent resonant X-ray emissions due to B1s-B2p{pi}{sup *}-B1s{sup -1} transitions were observed in w-BN composed of four-fold boron atoms and in h-BN composed of three-fold boron atoms, when the photon energy of the incident undulator beams coincided with the B1s-B2p{pi}{sup *} absorption energy. However, no resonance was observed in c-BN composed of four-fold boron atoms. The resonant X-ray emission reflects the electronic structure of unoccupied molecular orbitals which strongly depend on the conformations of the boron atoms. These findings confirm that resonant X-ray emissions can be useful indices for molecular and electronic structure analysis of boron nitrides. (orig.) With 005 figs., 13 refs.

Muramatsu, Y. [NTT, Tokyo (Japan). Integrated Inf. and Energy Syst. Labs.; Kouzuki, H.; Kaneyoshi, T.; Motoyama, M. [Hyogo Prefectural Institute of Industrial Research, 3-1-12 Yukihira-cho, Suma-ku, Kobe 654 (Japan); Agui, A.; Shin, S. [The Institute for Solid State Physics, The University of Tokyo, 3-2-1 Midori-cho, Tanashi-shi, Tokyo 188 (Japan); Kato, H. [Photon Factory, National Laboratory for High Energy Physics, 1-1 Oho, Tsukuba-shi, Ibaraki 305 (Japan); Kawai, J. [Department of Materials Science and Engineering, Kyoto University, Yoshidahoncho, Sakyo-ku, Kyoto 606-01 (Japan)

1997-08-01

378

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)

379

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2007-06-15

380

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

International Nuclear Information System (INIS)

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

 
 
 
 
381

Molecular and electronic structure of the peptide subunit of Geobacter sulfurreducens conductive pili from first principles.  

Science.gov (United States)

The respiration of metal oxides by the bacterium Geobacter sulfurreducens requires the assembly of a small peptide (the GS pilin) into conductive filaments termed pili. We gained insights into the contribution of the GS pilin to the pilus conductivity by developing a homology model and performing molecular dynamics simulations of the pilin peptide in vacuo and in solution. The results were consistent with a predominantly helical peptide containing the conserved ?-helix region required for pilin assembly but carrying a short carboxy-terminal random-coiled segment rather than the large globular head of other bacterial pilins. The electronic structure of the pilin was also explored from first principles and revealed a biphasic charge distribution along the pilin and a low electronic HOMO-LUMO gap, even in a wet environment. The low electronic band gap was the result of strong electrostatic fields generated by the alignment of the peptide bond dipoles in the pilin's ?-helix and by charges from ions in solution and amino acids in the protein. The electronic structure also revealed some level of orbital delocalization in regions of the pilin containing aromatic amino acids and in spatial regions of high resonance where the HOMO and LUMO states are, which could provide an optimal environment for the hopping of electrons under thermal fluctuations. Hence, the structural and electronic features of the pilin revealed in these studies support the notion of a pilin peptide environment optimized for electron conduction. PMID:22779741

Feliciano, Gustavo T; da Silva, Antonio J R; Reguera, Gemma; Artacho, Emilio

2012-08-01

382

Nonequilibrium Molecular Dynamics Simulation of Interacting Many Electrons Scattered by Lattice Vibrations  

Science.gov (United States)

We propose a new model suitable for a nonequilibrium molecular dynamics (MD) simulation of electrical conductors in both linear- and nonlinear-response regimes. The model consists of classical electrons and atoms. The atoms compose a lattice vibration system. The electrons are scattered by electron--electron and electron--atom interactions. Since the scattering cross section is physically more important than the functional form of a scattering potential, we propose to devise the electron--atom interaction potential in such a way that its scattering cross section agrees with that of quantum--mechanical one. To illustrate advantages of the proposed model, we perform a nonequilibrium MD simulation assuming a doped semiconductor at room or higher temperature. In the linear response regime, we confirm Ohm's law, the dispersion relations and the fluctuation--dissipation relation. Furthermore, we obtain reasonable dependence of the electrical conductivity on temperature, despite the fact that our model is a classical model. In the nonlinear response regime, we find that the response of the current to the electric field becomes strongly nonlinear, and the electron temperature rises nonlinearly as a function of the Joule heat.

Lee, Fan; Yuge, Tatsuro; Shimizu, Akira

2012-06-01

383

Exploring electronic transport in molecular junctions by conducting atomic force microscopy.  

Science.gov (United States)

Measuring the electronic transport properties of single molecules and molecular nanostructuresis an interesting and challenging new frontier from both a fundamental as well as technologicalperspective. Conducting atomic force microscopy (C-AFM) represents an attractive line of approachgiven its ability to position a sharp electrical probe with nanometer-scale precision and a controllednano-Newton-range force. Moreover, the combination of AFM imaging and C-AFM electrical characterizationenables investigation of the relationship between structure and function in molecular architectures.The aim of the present review is twofold: (1) to introduce the C-AFM method, alongside a discussionof experimental practices, capabilities and limitations, and (2) to provide an overview of the applicationof C-AFM to different types of molecular systems. These include alkane-based and oligomer-based self-assembledmonolayers, molecular crystals, conducting polymer films, molecular wires (e.g. carbon nanotubes),and electrically active biomolecules. We will also discuss C-AFM approaches that allow single moleculemeasurements as well as other recent developments. PMID:23636678

Mativetsky, Jeffrey M; Palma, Matteo; Samorì, Paolo

2008-01-01

384

WebProp: Web interface for ab initio calculation of molecular one-electron properties.  

Science.gov (United States)

This note describes the features and implementation issues of WebProp, a web-based interface for evaluating ab initio quality one-electron properties. The interface code is written in HTML and Python, while the backend is handled using Python and our indigenously developed code INDPROP for property evaluation. A novel feature of this setup is that it provides a simple interface for computing first principle one-electron properties of small to medium sized molecules. To facilitate computation of otherwise expensive calculations on large molecular systems, we employ the Molecular Tailoring Approach (MTA) developed in our laboratory to obtain the density matrix (DM). This DM is then employed for computing the one-electron properties of these systems. The backend transparently handles jobs submitted by the user and runs them either on a single machine or over a grid of compute nodes. The results of the calculations, which include the summary and the files necessary for visualization of one-electron properties, are e-mailed to the user. The user can either directly use the data or visualize it using visualization tools such as UNIVIS-2000 or Drishti. PMID:17654647

Ganesh, V; Kavathekar, Ritwik; Rahalkar, Anuja; Gadre, Shridhar R

2008-02-01

385

The electronic absorption spectra of some acyl azides. Molecular orbital treatment  

Science.gov (United States)

The electronic absorption spectra of benzoyl azide and its derivatives: p-methyl, p-methoxy, p-chloro and p-nitrobenzoyl azide were investigated in different solvents. The observed spectra differ basically from the electronic spectra of aryl azides or alkyl azides. Four intense ?-? * transitions were observed in the accessible UV region of the spectrum of each of the studied compounds. The contribution of charge transfer configurations to the observed transitions is rather weak. Shift of band maximum with solvent polarity is minute. On the other hand, band intensity is highly dependent on the solvent used. The observed transitions are delocalized rather than localized ones as in the case with aryl and alkyl azides. The attachment of the C dbnd O group to the azide group in acyl azides has a significant effect on the electronic structure of the molecule. The arrangements as well as energies of the molecular orbitals are different in acyl azides from those in aryl azides. The first electronic transition in phenyl azide is at 276 nm, whereas that of bezoyle azide is at 251 nm. Ab initio molecular orbital calculations using both RHF/6-311G* and B3LYP/6-31+G * levels were carried out on the ground states of the studied compounds. The wave functions of the excited states were calculated using the CIS and the AM1-CI procedures.

Abu-Eittah, Rafie H.; Mohamed, Adel A.; Farag, A. M.; Al Omar, Ahmed M.

2008-06-01

386

Control of molecular organization and energy level alignment by an electronically nanopatterned boron nitride template.  

Science.gov (United States)

Suitable templates to steer the formation of nanostructure arrays on surfaces are indispensable in nanoscience. Recently, atomically thin sp(2)-bonded layers such as graphene or boron nitride (BN) grown on metal supports have attracted considerable interest due to their potential geometric corrugation guiding the positioning of atoms, metallic clusters or molecules. Here, we demonstrate three specific functions of a geometrically smooth, but electronically corrugated, sp(2)/metal interface, namely, BN/Cu(111), qualifying it as a unique nanoscale template. As functional adsorbates we employed free-base porphine (2H-P), a prototype tetrapyrrole compound, and tetracyanoquinodimethane (TCNQ), a well-known electron acceptor. (i) The electronic moirons of the BN/Cu(111) interface trap both 2H-P and TCNQ, steering self-organized growth of arrays with extended molecular assemblies. (ii) We report an effective decoupling of the trapped molecules from the underlying metal support by the BN, which allows for a direct visualization of frontier orbitals by scanning tunneling microscopy (STM). (iii) The lateral molecular positioning in the superstructured surface determines the energetic level alignment; i.e., the energy of the frontier orbitals, and the electronic gap are tunable. PMID:24328081

Joshi, Sushobhan; Bischoff, Felix; Koitz, Ralph; Ecija, David; Seufert, Knud; Seitsonen, Ari Paavo; Hutter, Jürg; Diller, Katharina; Urgel, José I; Sachdev, Hermann; Barth, Johannes V; Auwärter, Willi

2014-01-28

387

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

388

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

389

Reaction dynamics of a molecular switch unveiled by coherent two-dimensional electronic spectroscopy.  

Science.gov (United States)

Coherent two-dimensional electronic spectroscopy is usually employed on molecular species with fixed geometric configuration. Here we present two-dimensional Fourier-transform electronic spectra of dissolved 6,8-dinitro-1',3',3'-trimethylspiro[2H-1-benzopyran-2,2'-indoline] (6,8-dinitro-BIPS), a photochromic system present in two ring-open forms differing in the cis/trans configuration of a double bond, which both undergo a photoinduced ring closure. The two-dimensional spectra, recorded with 20 fs pump pulses centered at 605 nm and a supercontinuum probe covering the complete visible spectral range, allow for a detailed analysis of the photophysics and photochemistry of the two isomers and directly reveal that cis/trans isomerization among them does not play a major role. This experiment demonstrates the potential of two-dimensional electronic spectroscopy for reactive processes. PMID:21809866

Kullmann, Martin; Ruetzel, Stefan; Buback, Johannes; Nuernberger, Patrick; Brixner, Tobias

2011-08-24

390

Attosecond Precision Pump-Probe Experiments: Visualizing Molecular and Electronic Dynamics  

Science.gov (United States)

A series of time-resolved experiments is reported with the goal (i) to map, completely characterize and finally to control femtosecond nuclear motion in simple molecules, (ii) to generate and observe ultra-fast electronic wave-packets and, (iii) to study correlated sub-fs few-electron dynamics in strong-field multiple ionization. For that purpose, we have developed a unique combination of a `reaction microscope' spectrometer (with an integrated Li-MOT target) imaging the complete many-particle final-state momentum space and a pump-probe setup providing two 7 fs, ca. 0.1 PW/cm**2 pulses at variable delays between 0 and 3300 fs, reaching absolute and relative precisions as good as 70 as and 1 as, respectively. (i) Via Coulomb explosion imaging we reconstruct the time-dependent probability density of the dissociating, rotating and vibrating nuclear wave-packets in the most fundamental molecular systems, the hydrogen and deuterium molecular ions. We observe the `collapse' and `revival' of their vibrational wave packets, investigate their composition via Fourier analysis, show novel routes to directly visualize field modified potential curves yielding a complete characterization of the field-induced ultra-fast molecular dynamics and, most recently, study the formation of hydrogen molecular ions in laser-induced fragmentation of methane. A one attosecond relative accuracy is demonstrated mapping the vibrational motion in the neutral deuterium molecule and the corresponding excitation mechanism is identified by determination of the absolute quantum phase of the motion. (ii) Using a Li-MOT target as an effective one-electron target we have coherently populated and observed fast electronic wave packets in low-lying states. (iii) For multiple ionization of atoms recoil-ion momentum distributions allow us to distinguish different ionization pathways and to reveal first time information on few-electron emission. For Ne we observe signatures of highly correlated recollision-induced three- and four-electron processes measured to occur on a 500 as time scale.

Ullrich, Joachim

2008-05-01

391

Odd-Even Effect in Molecular Electronic Transport via an Aromatic Ring.  

Science.gov (United States)

A distinct odd-even effect on the electrical properties, induced by monolayers of alkyl-phenyl molecules directly bound to Si(111), is reported. Monomers of H2C?CH-(CH2)n-phenyl, with n = 2-5, were adsorbed onto Si-H and formed high-quality monolayers with a binding density of 50-60% Si(111) surface atoms. Molecular dynamics simulations suggest that the binding proximity is close enough to allow efficient ?-? interactions and therefore distinctly different packing and ring orientations for monomers with odd or even numbers of methylenes in their alkyl spacers. The odd-even alternation in molecular tilt was experimentally confirmed by contact angle, ellipsometry, FT-IR, and XPS with a close quantitative match to the simulation results. The orientations of both the ring plane and the long axis of the alkyl spacer are more perpendicular to the substrate plane for molecules with an even number of methylenes than for those with an odd number of methylenes. Interestingly, those with an even number conduct better than the effectively thinner monolayers of the molecules with the odd number of methylenes. We attribute this to a change in the orientation of the electron density on the aromatic rings with respect to the shortest tunneling path, which increases the barrier for electron transport through the odd monolayers. The high sensitivity of molecular charge transport to the orientation of an aromatic moiety might be relevant to better control over the electronic properties of interfaces in organic electronics. PMID:25338192

Toledano, Tal; Sazan, Haim; Mukhopadhyay, Sabyasachi; Alon, Hadas; Lerman, Keti; Bendikov, Tatyana; Major, Dan T; Sukenik, Chaim N; Vilan, Ayelet; Cahen, David

2014-11-18

392

Resonanant enhancement of molecular excitation intensity in inelastic electron scattering spectrum owing to interaction with plasmons in metallic nanoshell  

CERN Document Server

A quantum-mechanical model to calculate the electron energy-loss spectra (EELS) for the system of a closely located metallic nanoshell and a molecule has been developed. At the resonance between the molecular excitation and plasmon modes in the nanoshell, which can be provided by a proper choice of the ratio of the inner and outer nanoshell radii, the cross-section of inelastic electron scattering at the molecular excitation energy is shown to grow significantly, because the molecular transition borrows the oscillator strength from a plasmon. The enhancement of the inelastic electron scattering by the molecule makes it possible to observe molecular transitions with an electron microscope. The dependences of the EEL spectra on the relative arrangement of the molecule and the nanoshell, the ratio between the inner and outer nanoshell radii, and the scattering angle are plotted and analyzed.

Goliney, I Yu

2014-01-01

393

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

Energy Technology Data Exchange (ETDEWEB)

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

Comes, Ryan; Liu Hongxue; Lu Jiwei [Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Gu, Man [Department of Physics, University of Virginia, Charlottesville, Virginia 22904 (United States); Khokhlov, Mikhail; Wolf, Stuart A. [Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Guilford College, Greensboro, North Carolina 27410 (United States)

2013-01-14

394

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

International Nuclear Information System (INIS)

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

395

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

International Nuclear Information System (INIS)

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)

396

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

Science.gov (United States)

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. PMID:20957235

Ziessel, Raymond; Harriman, Anthony

2011-01-14

397

Electronic States of Single-Component Molecular Conductors [M(tmdt)2  

Science.gov (United States)

The electronic states of isostructural single-component molecular conductors [M(tmdt)2] (M = Ni, Au, and Cu) are theoretically studied. By considering fragments of molecular orbitals as basis functions, we construct a multiorbital model common for the three materials. The tight-binding parameters are estimated from results of first-principles band calculations, leading to a systematic view of their electronic structures. We find that the interplay between a p?-type orbital (L) on each of the two ligands and a pd?-type orbital (M?) centered on the metal site plays a crucial role: their energy difference controls the electronic states near the Fermi energy. For the magnetic materials (M = Au and Cu), we take into account Coulomb interactions on different orbitals, i.e., we consider the multiorbital Hubbard model. Its ground-state properties are calculated within mean-field approximation where various types of magnetic structures with different orbital natures are found. An explanation for the experimental results in [Cu(tmdt)2] is provided: The quasi-degeneracy of the two types of orbitals leads to a dual state where localized M? spins appear, and L sites show a nonmagnetic state owing to dimerization. On the other hand, [Au(tmdt)2] locates in the subtle region in terms of the degree of orbital mixing. We propose possible scenarios for its puzzling antiferromagnetic phase transition, involving the M? orbital in contrast to previous discussions mostly concentrating on the L sector.

Seo, Hitoshi; Ishibashi, Shoji; Otsuka, Yuichi; Fukuyama, Hidetoshi; Terakura, Kiyoyuki

2013-05-01

398

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

Science.gov (United States)

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

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

399

Correlative super-resolution fluorescence and electron microscopy of the nuclear pore complex with molecular resolution.  

Science.gov (United States)

Here, we combine super-resolution fluorescence localization microscopy with scanning electron microscopy to map the position of proteins of nuclear pore complexes in isolated Xenopus laevis oocyte nuclear envelopes with molecular resolution in both imaging modes. We use the periodic molecular structure of the nuclear pore complex to superimpose direct stochastic optical reconstruction microscopy images with a precision of nuclear pore complex proteins by standard immunocytochemistry with primary and secondary antibodies and reveal that the nuclear pore complex is composed of eight gp210 (also known as NUP210) protein homodimers. In addition, we find subpopulations of nuclear pore complexes with ninefold symmetry, which are found occasionally among the more typical eightfold symmetrical structures. PMID:25146397

Löschberger, Anna; Franke, Christian; Krohne, Georg; van de Linde, Sebastian; Sauer, Markus

2014-10-15

400

Effects of relative orientation of the molecules on electron transport in molecular devices  

CERN Document Server

Effects of relative orientation of the molecules on electron transport in molecular devices are studied by non-equilibrium Green's function method based on density functional theory. In particular, two molecular devices, with the planer Au$_{7}$ and Ag$_{3}$ clusters sandwiched between the Al(100) electrodes are studied. In each device, two typical configurations with the clusters parallel and vertical to the electrodes are considered. It is found that the relative orientation affects the transport properties of these two devices completely differently. In the Al(100)-Au$_7$-Al(100) device, the conductance and the current of the parallel configuration are much larger than those in the vertical configuration, while in the Al(100)-Ag$_{3}$-Al(100) device, an opposite conclusion is obtained.

Zhou, Y H; Xu, Y; Zeng, Z Y; Zeng, Z; Zhou, Yan-Hong; Zheng, Xiao-Hong; Xu, Ying; Zeng, Zhao Yang; Zeng, Zhi

2006-01-01

 
 
 
 
401

Effects of Contact Atomic Structure on Electronic Transport in Molecular Junction  

International Nuclear Information System (INIS)

Based on nonequilibrium Green's function and first-principles calculations, we investigate the change in molecular conductance caused by different adsorption sites with the presence of additional Au atom around the metal-molecule contact in the system that benzene sandwiched between two Au(111) leads. The motivation is the variable situations that may arise in break junction experiments. Numerical results show that the enhancement of conductance induced by the presence of additional Au is dependent on the adsorption sites of anchoring atom. When molecule is located on top site with the presence of additional Au atoms, it can increase molecular conductance remarkably and present negative differential resistance under applied bias which cannot be found in bridge and hollow sites. Furthermore, the effects of different distance between additional Au and sulfur atoms in these three adsor