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Sample records for molecular electronic rectification

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

    DEFF Research Database (Denmark)

    Kuznetsov, A.M.; Ulstrup, Jens

    2002-01-01

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

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

    DEFF Research Database (Denmark)

    Kuznetsov, A.M.; Ulstrup, Jens

    2002-01-01

    We present a new view and an analytical formalism of electron flow through a donor-acceptor molecule inserted between a pair of metal electrodes. The donor and acceptor levels are strongly coupled to an environmental nuclear continuum. The formalism applies to molecular donor-acceptor systems both in vacuum or air, and in aqueous solution under electrochemical potential control. Multifarious patterns of rectified electron flow from the negatively to the positively biased electrode arise. The ele...

  3. Terahertz rectification by periodic two-dimensional electron plasma

    Energy Technology Data Exchange (ETDEWEB)

    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

    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.

  4. Current rectification by simple molecular quantum dots: an ab-initio study

    CERN Document Server

    Larade, B

    2003-01-01

    We calculate a current rectification by molecules containing a conjugated molecular group sandwiched between two saturated (insulating) molecular groups of different length (molecular quantum dot) using an ab-initio non-equilibrium Green's function method. In particular, we study S-(CH2)m-C10H6-(CH2)n-S dithiol with Naphthalene as a conjugated central group. The rectification current ratio ~35 has been observed at m = 2 and n = 10, due to resonant tunneling through the molecular orbital (MO) closest to the electrode Fermi level (lowest unoccupied MO in the present case). The rectification is limited by interference of other conducting orbitals, but can be improved by e.g. adding an electron withdrawing group to the naphthalene.

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

    Science.gov (United States)

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

    2012-08-01

    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.

  6. Current rectification by simple molecular quantum dots: an ab-initio study

    OpenAIRE

    Larade, B.; Bratkovsky, A. M.

    2003-01-01

    We calculate a current rectification by molecules containing a conjugated molecular group sandwiched between two saturated (insulating) molecular groups of different length (molecular quantum dot) using an ab-initio non-equilibrium Green's function method. In particular, we study S-(CH2)m-C10H6-(CH2)n-S dithiol with Naphthalene as a conjugated central group. The rectification current ratio ~35 has been observed at m = 2 and n = 10, due to resonant tunneling through the molec...

  7. Transverse rectification in density-modulated two-dimensional electron gases

    OpenAIRE

    Ganczarczyk, A.; Rojek, S.; Quindeau, A.; Geller, M.; Hucht, A.; Notthoff, C.; Reuter, D; Wieck, A. D.; König, J.; Lorke, A.

    2008-01-01

    We demonstrate tunable transverse rectification in a density-modulated two-dimensional electron gas (2DEG). The density modulation is induced by two surface gates, running in parallel along a narrow stripe of 2DEG. A transverse voltage in the direction of the density modulation is observed, i.e. perpendicular to the applied source-drain voltage. The polarity of the transverse voltage is independent of the polarity of the source-drain voltage, demonstrating rectification in t...

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

    CERN Document Server

    Li, Yunyun; Marchesoni, Fabio; Li, Baowen

    2014-01-01

    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.

  9. Rectification of electronic heat current by a hybrid thermal diode

    OpenAIRE

    Martínez-Pérez, M. J.; Fornieri, A.; Giazotto, F.

    2014-01-01

    We report the realization of an ultra-efficient low-temperature hybrid heat current rectifier, thermal counterpart of the well-known electric diode. Our design is based on a tunnel junction between two different elements: a normal metal and a superconducting island. Electronic heat current asymmetry in the structure arises from large mismatch between the thermal properties of these two. We demonstrate experimentally temperature differences exceeding $60$ mK between the forwa...

  10. Molecular Electronics

    DEFF Research Database (Denmark)

    Jennum, Karsten Stein

    2013-01-01

    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 ca...

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

    CERN Document Server

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

    2014-01-01

    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 coherence length in the range of 130 $\\sim$ 800 $\\mu$m 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.

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

    OpenAIRE

    Taylor, Jeremy Philip; Brandbyge, Mads; Stokbro, Kurt

    2002-01-01

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

  13. Thermal rectification of electrons in hybrid normal metal-superconductor nanojunctions

    Energy Technology Data Exchange (ETDEWEB)

    Giazotto, F., E-mail: giazotto@sns.it [NEST, Instituto Nanoscienze-CNR and Scuola Normale Superiore, I-56127 Pisa (Italy); Bergeret, F. S., E-mail: sebastian-bergeret@ehu.es [Centro de Física de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU, Manuel de Lardizabal 4, E-20018 San Sebastián (Spain); Donostia International Physics Center (DIPC), Manuel de Lardizabal 5, E-20018 San Sebastián (Spain)

    2013-12-09

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

  14. Electronic properties of organic monolayers and molecular devices

    Indian Academy of Sciences (India)

    D Vuillaume; S Lenfant; D Guerin; C Delerue; C Petit; G Salace

    2006-07-01

    We review some of our recent experimental results on charge transport in organic nanostructures such as self-assembled monolayer and monolayers of organic semiconductors. We describe a molecular rectifying junction made from a sequential self-assembly on silicon. These devices exhibit a marked current–voltage rectification behavior due to resonant transport between the Si conduction band and the molecule highest occupied molecular orbital of the molecule. We discuss the role of metal Fermi level pinning in the current–voltage behavior of these molecular junctions. We also discuss some recent insights on the inelastic electron tunneling behavior of Si/alkyl chain/metal junctions.

  15. Theoretical limits on the threshold for the response of long cells to weak extremely low frequency electric fields due to ionic and molecular flux rectification.

    OpenAIRE

    Weaver, J C; Vaughan, T E; Adair, R K; Astumian, R D

    1998-01-01

    Understanding exposure thresholds for the response of biological systems to extremely low frequency (ELF) electric and magnetic fields is a fundamental problem of long-standing interest. We consider a two-state model for voltage-gated channels in the membrane of an isolated elongated cell (Lcell = 1 mm; rcell = 25 micron) and use a previously described process of ionic and molecular flux rectification to set lower bounds for a threshold exposure. A key assumption is that it is the ability of ...

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

    International Nuclear Information System (INIS)

    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

  17. Rectification in Y-junctions of Luttinger liquid wires

    OpenAIRE

    Wang, Chenjie; Feldman, D. E.

    2010-01-01

    We investigate rectification of a low-frequency ac bias in Y-junctions of one-channel Luttinger liquid wires with repulsive electron interaction. Rectification emerges due to three scatterers in the wires. We find that it is possible to achieve a higher rectification current in a Y-junction than in a single wire with an asymmetric scatterer at the same interaction strength and voltage bias. The rectification effect is the strongest in the absence of the time-reversal symmetr...

  18. Current rectification by mediating electroactive polymers

    International Nuclear Information System (INIS)

    In this work we briefly review the theoretical basis for the electrochemical rectification in mediated redox reactions at redox polymer modified electrodes. Electrochemical rectification may have two distinct origins. It is either caused by a slow kinetics of the reaction between the external redox couple and the mediator or it is originated by a slow electronic transport within the film under an unfavorable thermodynamic condition. We show experimental results for the redox mediation reaction of poly(o-aminophenol) (POAP) on the Fe2+/3+ and on the Fe(CN)63-/4- redox couples in solution that prove the proposed mechanisms of electrochemical rectification

  19. Molecular motor efficiency is maximized in the presence of both power-stroke and rectification through feedback

    Science.gov (United States)

    Schmitt, R. K.; Parrondo, J. M. R.; Linke, H.; Johansson, J.

    2015-06-01

    We present a model for a feedback-controlled ratchet consisting of a Brownian particle and a moving, finite barrier that is shifted by an external agent depending on the position of the particle. By modifying the value of a single parameter of the feedback protocol, the model can act either as a pure rectifier, a power-stroke (PS) motor, or a combination of both. Interestingly, in certain situations the motor reaches a maximum efficiency for an intermediate value of that parameter, i.e., for a combination of the information ratchet and the PS mechanisms. We relate our results to the biological motors kinesin, myosin II, and myosin V, finding that these motors operate in a regime of length scales and forces where the efficiency is maximized for a combination of rectification and PS mechanisms.

  20. Towards graphyne molecular electronics

    Science.gov (United States)

    Li, Zhihai; Smeu, Manuel; Rives, Arnaud; Maraval, Valérie; Chauvin, Remi; Ratner, Mark A.; Borguet, Eric

    2015-02-01

    ?-Graphyne, a carbon-expanded version of graphene (‘carbo-graphene’) that was recently evidenced as an alternative zero-gap semiconductor, remains a theoretical material. Nevertheless, using specific synthesis methods, molecular units of ?-graphyne (‘carbo-benzene’ macrocycles) can be inserted between two anilinyl (4-NH2-C6H4)-anchoring groups that allow these fragments to form molecular junctions between gold electrodes. Here, electrical measurements by the scanning tunnelling microscopy (STM) break junction technique and electron transport calculations are carried out on such a carbo-benzene, providing unprecedented single molecule conductance values: 106?nS through a 1.94-nm N-N distance, essentially 10 times the conductance of a shorter nanographenic hexabenzocoronene analogue. Deleting a C4 edge of the rigid C18 carbo-benzene circuit results in a flexible ‘carbo-butadiene’ molecule that has a conductance 40 times lower. Furthermore, carbo-benzene junctions exhibit field-effect transistor behaviour when an electrochemical gate potential is applied, opening the way for device applications. All the results are interpreted on the basis of theoretical calculations.

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

    Science.gov (United States)

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

    2011-10-25

    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

  2. Electron transport through molecular junctions

    Science.gov (United States)

    Zimbovskaya, Natalya A.; Pederson, Mark R.

    2011-12-01

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

  3. Electron transport through molecular junctions

    International Nuclear Information System (INIS)

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

  4. Molecular electronic junction transport

    DEFF Research Database (Denmark)

    Solomon, Gemma C.; Herrmann, Carmen; Ratner, Mark

    2012-01-01

    Whenasinglemolecule,oracollectionofmolecules,isplacedbetween two electrodes and voltage is applied, one has a molecular transport junction. We discuss such junctions, their properties, their description, and some of their applications. The discussion is qualitative rather than quantitative, and focuses on mechanism, structure/function relations, regimes and mechanisms of transport, some molecular regularities, and some substantial challenges facing the field. Because there are many regimes and m...

  5. Theoretical limits on the threshold for the response of long cells to weak extremely low frequency electric fields due to ionic and molecular flux rectification.

    Science.gov (United States)

    Weaver, J C; Vaughan, T E; Adair, R K; Astumian, R D

    1998-11-01

    Understanding exposure thresholds for the response of biological systems to extremely low frequency (ELF) electric and magnetic fields is a fundamental problem of long-standing interest. We consider a two-state model for voltage-gated channels in the membrane of an isolated elongated cell (Lcell = 1 mm; rcell = 25 micron) and use a previously described process of ionic and molecular flux rectification to set lower bounds for a threshold exposure. A key assumption is that it is the ability of weak physical fields to alter biochemistry that is limiting, not the ability of a small number of molecules to alter biological systems. Moreover, molecular shot noise, not thermal voltage noise, is the basis of threshold estimates. Models with and without stochastic resonance are used, with a long exposure time, texp = 10(4) s. We also determined the dependence of the threshold on the basal transport rate. By considering both spherical and elongated cells, we find that the lowest bound for the threshold is Emin approximately 9 x 10(-3) V m-1 (9 x 10(-5) V cm-1). Using a conservative value for the loop radius rloop = 0.3 m for induced current, the corresponding lower bound in the human body for a magnetic field exposure is Bmin approximately 6 x 10(-4) T (6 G). Unless large, organized, and electrically amplifying multicellular systems such as the ampullae of Lorenzini of elasmobranch fish are involved, these results strongly suggest that the biophysical mechanism of voltage-gated macromolecules in the membranes of cells can be ruled out as a basis of possible effects of weak ELF electric and magnetic fields in humans. PMID:9788920

  6. 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.)

  7. Single-molecule diodes with high rectification ratios through environmental control

    Science.gov (United States)

    Capozzi, Brian; Xia, Jianlong; Adak, Olgun; Dell, Emma J.; Liu, Zhen-Fei; Taylor, Jeffrey C.; Neaton, Jeffrey B.; Campos, Luis M.; Venkataraman, Latha

    2015-06-01

    Molecular electronics aims to miniaturize electronic devices by using subnanometre-scale active components. A single-molecule diode, a circuit element that directs current flow, was first proposed more than 40?years ago and consisted of an asymmetric molecule comprising a donor-bridge-acceptor architecture to mimic a semiconductor p-n junction. Several single-molecule diodes have since been realized in junctions featuring asymmetric molecular backbones, molecule-electrode linkers or electrode materials. Despite these advances, molecular diodes have had limited potential for applications due to their low conductance, low rectification ratios, extreme sensitivity to the junction structure and high operating voltages. Here, we demonstrate a powerful approach to induce current rectification in symmetric single-molecule junctions using two electrodes of the same metal, but breaking symmetry by exposing considerably different electrode areas to an ionic solution. This allows us to control the junction's electrostatic environment in an asymmetric fashion by simply changing the bias polarity. With this method, we reliably and reproducibly achieve rectification ratios in excess of 200 at voltages as low as 370?mV using a symmetric oligomer of thiophene-1,1-dioxide. By taking advantage of the changes in the junction environment induced by the presence of an ionic solution, this method provides a general route for tuning nonlinear nanoscale device phenomena, which could potentially be applied in systems beyond single-molecule junctions.

  8. Unexpected large thermal rectification in asymmetric grain boundary of graphene

    OpenAIRE

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

    2011-01-01

    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...

  9. Giant Thermal Rectification from Polyethylene Nanofiber Thermal Diodes

    OpenAIRE

    ZHANG, Teng; Luo, Tengfei

    2015-01-01

    The realization of phononic computing is held hostage by the lack of high performance thermal devices. Here we show through theoretical analysis and molecular dynamics simulations that unprecedented thermal rectification factors (as large as 1.20) can be achieved utilizing the phase dependent thermal conductivity of polyethylene nanofibers. More importantly, such high thermal rectifications only need very small temperature differences (< 20 oC) across the device, which is a ...

  10. Silicon-based molecular electronics

    CERN Document Server

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

    2003-01-01

    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.

  11. Molecular electronic-structure theory

    CERN Document Server

    Helgaker, Trygve; Olsen, Jeppe

    2014-01-01

    Ab initio quantum chemistry has emerged as an important tool in chemical research and is appliced to a wide variety of problems in chemistry and molecular physics. Recent developments of computational methods have enabled previously intractable chemical problems to be solved using rigorous quantum-mechanical methods. This is the first comprehensive, up-to-date and technical work to cover all the important aspects of modern molecular electronic-structure theory. Topics covered in the book include: * Second quantization with spin adaptation * Gaussian basis sets and molecular-integral evaluati

  12. Nanotechnology Review: Molecular Electronics to Molecular Motors

    Science.gov (United States)

    Srivastava, Deepak; Saini, Subhash (Technical Monitor)

    1998-01-01

    Reviewing the status of current approaches and future projections, as already published in scientific journals and books, the talk will summarize the direction in which computational and experimental nanotechnologies are progressing. Examples of nanotechnological approaches to the concepts of design and simulation of carbon nanotube based molecular electronic and mechanical devices will be presented. The concepts of nanotube based gears and motors will be discussed. The above is a non-technical review talk which covers long term precompetitive basic research in already published material that has been presented before many US scientific meeting audiences.

  13. Electrical gating and rectification in graphene three-terminal junctions

    Energy Technology Data Exchange (ETDEWEB)

    Händel, B. [FG Nanotechnologie, Institut für Mikro- und Nanotechnologien MacroNano and Institut für Mikro- und Nanoelektronik, Postfach 100565, 98684 Ilmenau (Germany); FG Festkörperelektronik, Institut für Mikro- und Nanotechnologien MacroNano and Institut für Mikro- und Nanoelektronik, Technische Universität Ilmenau, Postfach 100565, 98684 Ilmenau (Germany); Hähnlein, B. [FG Nanotechnologie, Institut für Mikro- und Nanotechnologien MacroNano and Institut für Mikro- und Nanoelektronik, Postfach 100565, 98684 Ilmenau (Germany); Göckeritz, R. [FG Nanostrukturierte Materialien, Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, Von-Danckelmann-Platz 3, 06120 Halle (Saale) (Germany); Schwierz, F. [FG Festkörperelektronik, Institut für Mikro- und Nanotechnologien MacroNano and Institut für Mikro- und Nanoelektronik, Technische Universität Ilmenau, Postfach 100565, 98684 Ilmenau (Germany); Pezoldt, J., E-mail: joerg.pezoldt@tu-ilmenau.de [FG Nanotechnologie, Institut für Mikro- und Nanotechnologien MacroNano and Institut für Mikro- und Nanoelektronik, Postfach 100565, 98684 Ilmenau (Germany)

    2014-02-01

    Graphene was grown on semiinsulating silicon carbide at 1800 °C and atmospheric argon pressure. The all carbon T- and Y-shape three terminal junction devices were fabricated using electron beam lithography. All devices featured the negative rectification effect. The exact properties of the devices like the curvature of the output voltage response can be tuned by changing the branch width in the T- and Y-shape devices. Beside the rectification a switching behavior is demonstrated with the same three terminal junctions.

  14. Carbon Nanotubes: Molecular Electronic Components

    Science.gov (United States)

    Srivastava, Deepak; Saini, Subhash; Menon, Madhu

    1997-01-01

    The carbon Nanotube junctions have recently emerged as excellent candidates for use as the building blocks in the formation of nanoscale molecular electronic networks. While the simple joint of two dissimilar tubes can be generated by the introduction of a pair of heptagon-pentagon defects in an otherwise perfect hexagonal graphene sheet, more complex joints require other mechanisms. In this work we explore structural characteristics of complex 3-point junctions of carbon nanotubes using a generalized tight-binding molecular-dynamics scheme. The study of pi-electron local densities of states (LDOS) of these junctions reveal many interesting features, most prominent among them being the defect-induced states in the gap.

  15. Electronic continuum model for molecular dynamics simulations

    OpenAIRE

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

    2009-01-01

    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 rathe...

  16. Electron and Phonon Transport in Molecular Junctions

    DEFF Research Database (Denmark)

    Li, Qian

    2015-01-01

    Molecular electronics provide the possibility to investigate electron and phonon transport at the smallest imaginable scale, where quantum effects can be investigated and exploited directly in the design. In this thesis, we study both electron transport and phonon transport in molecular junctions. The system we are interested in here are ?-stacked molecules connected with two semi-infinite leads. ?-stacked aromatic rings, connected via ?-? electronic coupling, provides a rather soft mechanical b...

  17. Computer simulation of electron transfer in molecular electronic devices

    OpenAIRE

    Correia, Helena M. G.; Ramos, Marta M. D.

    2005-01-01

    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-mercaptophen...

  18. Giant Thermal Rectification from Polyethylene Nanofiber Thermal Diodes

    CERN Document Server

    Zhang, Teng

    2015-01-01

    The realization of phononic computing is held hostage by the lack of high performance thermal devices. Here we show through theoretical analysis and molecular dynamics simulations that unprecedented thermal rectification factors (as large as 1.20) can be achieved utilizing the phase dependent thermal conductivity of polyethylene nanofibers. More importantly, such high thermal rectifications only need very small temperature differences (< 20 oC) across the device, which is a significant advantage over other thermal diodes which need temperature biases on the order of the operating temperature. Taking this into consideration, we show that the dimensionless temperature-scaled rectification factors of the polymer nanofiber diodes range from 12 to 25 - much larger than other thermal diodes (< 8). The polymer nanofiber thermal diode consists of a crystalline portion whose thermal conductivity is highly phase-sensitive and a cross-linked portion which has a stable phase. Nanoscale size effect can be utilized t...

  19. Electron transport through dipyrimidinyl-diphenyl diblock molecular wire: protonation effect

    CERN Document Server

    Li, Z

    2006-01-01

    Recently, rectifying direction inversion has been observed in dipyrimidinyl-diphenyl (PMPH) diblock molecular wire [J. Am. Chem. Soc. (2005) 127, 10456], and a protonation mechanism was suggested to explain this interesting phenomena. In this paper, we study the protonation effect on transport properties of PMPH molecule by first principles calculations. No significant rectification is found for the pristine diblock molecular wire. Protonation leads to conductance enhancement and rectification. However, for all considered junctions with rectifying effect, the preferential current directions are samely from dipyrimidinyl side to diphenyl side. Effect of molecule-electrode anchoring geometry is studied, and it is not responsible for the discrepancy between experiment and theory.

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

    Science.gov (United States)

    Lan, Tran Nguyen

    2014-01-01

    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.

  1. Electrons in molecules from basic principles to molecular electronics

    CERN Document Server

    Launay, Jean-Pierre

    2014-01-01

    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, ...

  2. Valve-Less Rectification Pumps.

    Czech Academy of Sciences Publication Activity Database

    Tesa?, Václav

    Heidelberg : Springer Science+Business Media, LLC, 2008 - (Dongqing, L.), s. 2131-2139 ISBN 978-0-387-48998-8 R&D Projects: GA ?R GA101/07/1499 Institutional research plan: CEZ:AV0Z20760514 Keywords : microfluidics * pumps * fluidic rectification Subject RIV: BK - Fluid Dynamics http://www.springer.com/engineering/book/978-0-387-49000-7

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

    Science.gov (United States)

    Wu, Xiangli

    1995-01-01

    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.

  4. Radar image registration and rectification

    Science.gov (United States)

    Naraghi, M.; Stromberg, W. D.

    1983-01-01

    Two techniques for radar image registration and rectification are presented. In the registration method, a general 2-D polynomial transform is defined to accomplish the geometric mapping from one image into the other. The degree and coefficients of the polynomial are obtained using an a priori found tiepoint data set. In the second part of the paper, a rectification procedure is developed that models the distortion present in the radar image in terms of the radar sensor's platform parameters and the topographic variations of the imaged scene. This model, the ephemeris data and the digital topographic data are then used in rectifying the radar image. The two techniques are then used in registering and rectifying two examples of radar imagery. Each method is discussed as to its benefits, shortcomings and registration accuracy.

  5. Progress in molecular precursors for electronic materials

    Energy Technology Data Exchange (ETDEWEB)

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

    1996-09-01

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

  6. Spin-excited states and rectification in an organic spin rectifier

    Science.gov (United States)

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

    2014-08-01

    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.

  7. Projected Quasiparticle Theory for Molecular Electronic Structure

    OpenAIRE

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

    2011-01-01

    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 strong correlations with effective one-electron (mean-field) computational cost. The e...

  8. Desactivation of tritium waters by rectification methods

    International Nuclear Information System (INIS)

    Results of experiments into the basic rectification processes dedicated to tritium separation from reactor, technological and waste waters are presented. Coefficients of separation for rectification of water (1.028), ammonia (1.05), azeotrope H2O - HTO - HNO3 (1.098) and D2O - DTO - DNO3 (1.039) are performed. Operating schemes of tritium separating units are reviewed

  9. Single-Component Molecular Metals for Molecular Electronics

    Science.gov (United States)

    Tanaka, Hisashi; Tokumoto, Madoka; Kobayashi, Hayao; Kobayashi, Akiko

    2004-03-01

    Many organic conductors consist of more than one component, i.e. donor molecules and acceptor molecules, to form charge transfer complexes. In most single-component molecular conductors, "doping" process is necessary to create charge carriers. Both of them require complex or multiple processes for preparation and therefore are not suitable for application as conducting wires or leads in molecular electronics. Therefore, intrinsic single-component molecular metals would be more desirable as molecular wires, in terms of processibility. Recently we have reported that [Ni(tmdt)2] (tmdt=trimethylenetetrathiafulvalenedithiolate) is a new three-dimensional synthetic metallic crystal composed of single-component molecules[1]. The neutral [Ni(tmdt)2] crystal shows a conductivity as high as 400 S/cm at room temperature, and stays metallic down to 0.6 K. Moreover, de Haas-van Alphen oscillations, consistent with the three-dimensional Fermi surface, were observed using AFM micro cantilever[2]. In this presentation, we will report the anisotropy in the electrical conductivity of [Ni(tmdt)2] single crystal, compared with that of three-dimensional molecular stacking. In particular, the difference between single crystal conduction and polycrystalline conduction, as well as a processibility study as wiring material, will be presented. [1] H. Tanaka et al., Science 291, 197 (2001) [2] H. Tanaka et al. to be published.

  10. 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

  11. Wave rectification in plasma sheaths surrounding electric field antennas

    Science.gov (United States)

    Boehm, M. H.; Carlson, C. W.; Mcfadden, J. P.; Clemmons, J. H.; Ergun, R. E.; Mozer, F. S.

    1994-01-01

    Combined measurements of Langmuir or broadband whistler wave intensity and lower-frequency electric field waveforms, all at 10-microsecond time resolution, were made on several recent sounding rockets in the auroral ionosphere. It is found that Langmuir and whistler waves are partically rectified in the plasma sheaths surrounding the payload and the spheres used as antennas. This sheath rectification occurs whenever the high frequency (HF) potential across the sheath becomes of the same order as the electron temperature or higher, for wave frequencies near or above the ion plasma frequency. This rectification can introduce false low-frequency waves into measurements of electric field spectra when strong high-frequency waves are present. Second harmonic signals are also generated, although at much lower levels. The effect occurs in many different plasma conditions, primarily producing false waves at frequencies that are low enough for the antenna coupling to the plasma to be resistive.

  12. Fullerene-derived molecular electronic devices

    Science.gov (United States)

    Menon, M.; Srivastava, D.; Saini, S.

    1998-08-01

    The carbon nanotube junctions have recently emerged as excellent candidates for use as the building blocks in the formation of nanoscale electronic devices. While the simple joint of two dissimilar tubes can be generated by the introduction of a pair of heptagon-pentagon defects in an otherwise perfect hexagonal graphene sheet, more complex joints require other mechanisms. In this work we explore structural and electronic properties of complex three-point junctions of carbon nanotubes using a generalized tight-binding molecular-dynamics scheme.

  13. Secondary electron emission with molecular projectiles

    International Nuclear Information System (INIS)

    The authors present results for the secondary electron emission (SEE) from thin foil targets, induced by both molecular ions and their atomic constituents as projectiles. The Sternglass theory for kinetic SEE states a proportionality between ? and the electronic stopping power, Se, which has been verified in various experiments. With comparing secondary electron (SE) yields induced by molecular projectiles to those induced by monoatomic projectiles, it is therefore possible to test models for the energy loss of molecular or cluster projectiles. Since the atomic constituents of the molecule are repelled from each other due to Coulomb explosion (superimposed by multiple scattering) while traversing the solid, it is interesting to measure the residual mutual influence on SEE and Se with increasing internuclear separation. This can only be achieved with thin foils, where (as in the present case) the SE-yields from the exit surface can be measured separately. The authors measured the SE-yields from the entrance (?B) and exit (?F) surfaces of thin C- and Al-foils (150 to 1,000 angstrom) with CO+, C+ and O+ (15 to 85 keV/u) and H2+ and H+ (0.3 to 1.2 MeV/u). The molecular effect defined as the ratio R(?) between the yields induced by molecular projectiles and the sum of those induced by their atomic constituents was calculated. The energy dependence of R(?) can be well represented by the calculated energy loss ratio of di-proton-clusters by Brandt. This supports Brandt's model for the energy loss of clusters

  14. Triazatriangulene as binding group for molecular electronics

    DEFF Research Database (Denmark)

    Wei, Zhongming; Wang, Xintai

    2014-01-01

    The triazatriangulene (TATA) ring system was investigated as a binding group for tunnel junctions of molecular wires on gold surfaces. Self-assembled monolayers (SAMs) of TATA platforms with three different lengths of phenylene wires were fabricated, and their electrical conductance was recorded by both conducting probe-atomic force microscopy (CP-AFM) and scanning tunneling microscopy (STM). Similar measurements were performed for phenylene SAMs with thiol anchoring groups as references. It was found that, despite the presence of a sp3 hybridized carbon atom in the conduction path, the TATA platform displays a contact resistance only slightly larger than the thiols. This surprising finding has not been reported before and was analyzed by theoretical computations of the transmission functions of the TATA anchored molecular wires. The relatively low contact resistance of the TATA platform along with its high stability and directionality make this binding group very attractive for molecular electronic measurements and devices. (Figure Presented).

  15. Electron and Phonon Transport in Molecular Junctions

    DEFF Research Database (Denmark)

    Li, Qian

    2015-01-01

    Molecular electronics provide the possibility to investigate electron and phonon transport at the smallest imaginable scale, where quantum effects can be investigated and exploited directly in the design. In this thesis, we study both electron transport and phonon transport in molecular junctions. The system we are interested in here are ?-stacked molecules connected with two semi-infinite leads. ?-stacked aromatic rings, connected via ?-? electronic coupling, provides a rather soft mechanical bridge while maintaining high electronic conductivity. We investigate electron transport and the thermoelectric response of five representative ?-stacked systems. We find that the transmission and power factor are both enhanced by increasing the conjugation length or adding substituent groups. The local transmission shows that several extra paths are added by cyano groups, which increases the total transmission at the Fermi energy. We propose and analyze a way of using ?   stacking to design molecular junctions to control heat transport. We develop a simple model system to identify optimal parameter regimes and then use density functional theory (DFT) to extract model parameters for a number of specific ?-stacked systems. It is found that the proposed mechanism can indeed signicantly reduce the phonon conductance but also increase it depending on the specific molecules and stackings used. Furthermore, we study how a molecule's conformation influence phonon transport by mechanically compressing an alkane chain in the junction with graphene leads, using DFT combined with scattering matrix approach. We find that the thermal conductance of the compressed junction drops by half in comparison to the extended junction, making it possible to turn on and o the heat current. The reduced thermal conductance in the compressed junction mainly stems from a large suppression of the transmission coefficients of the longitudinal and the in-plane transverse channels of the leads. Finally, we return and investigate phonon transport through ?-stacked molecules connected to graphene leads including all modes of the system using DFT method. It is found that the thermal conductance of ?-stacked systems can be reduced by 95%, compared with that in a single-molecule junction. Phonon transmission of ?-stacked systems is reduced dramatically in the whole frequency range and the left transmission mainly remains below 5 THz.

  16. Characterization of Hybrid Electronic Materials for Molecular Based Device Electronics

    Science.gov (United States)

    Daniels-Race, Theda

    2008-03-01

    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.

  17. Angular distribution of molecular auger electrons

    Science.gov (United States)

    Lehmann, J.; Bonhoff, K.; Bonhoff, S.; Lohmann, B.; Blum, K.

    1997-02-01

    We present a general theory for the angular distribution of molecular Auger electrons that can be applied to both diatomic and polyatomic molecules. The Auger process is described in the two-step model. By choosing a convenient parameterization we obtain a formula for the angular distribution which clearly separates the effects of the two steps. The geometry and dynamics of the primary ionization are described by a set of order parameters. The information available on the dynamics of the Auger transition is contained in a set of anisotropy parameters, which have been calculated for HF and H2O.

  18. Projected quasiparticle theory for molecular electronic structure.

    Science.gov (United States)

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

    2011-09-28

    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

  19. Electron Impact Dissociation of Molecular Ions

    International Nuclear Information System (INIS)

    Electron impact experiments were performed by means of our crossed electron-ion beam set-up. Singly and/or multiply charged ions that results from molecular ion fragmentation are detected individually. Cross-sections for their production are determined from their respective thresholds up to 2.5 keV. The animated crossed beams method is applied to measure: - Absolute inclusive cross sections for electron impact dissociation to individual ionic fragments from the energy threshold up to 2.5 keV. - The contributions from the different reaction channels are separated: single ionization (SI), dissociative excitation (DE) and dissociative ionization (DI). - Kinetic energy release distributions (KERD) of the fragment ions are determined at selected incident electron energies. It allows determination of groups of electronically excited states that contribute to the process considered. - Energy threshold determination allows identification of target initial ground and excited states. 1. Monohydride ions: HeH+, NH+, OH+, and isotopologues XD+: For HeH+, experimental results are available for the production of He+ and He2+. They were analysed taking into account the vibrational population measured in a separate charge transfer experiment (paper in preparation). 2. Polyhydride ions: NH2+, NH3+, OH2+ , OH3+ and isotopologues (unpublished). 3. Hydro(deutero)-carbon ions: C2D3+, C2D4+ and isotopologues C2D3H+, C2D2H2+ (unpublished). Experimental results have been obtained for C2D3+ and C2D4+. The collected data were analysed in detail. 4. Others: C2+ (unpublished). The full analysis of data for electron impact dissociation of C2+ yielding the C+ fragment was performed. These data now need to be published. N2H+, in progress. D3+, D2H+. Dissociation of H3+isotopologues have recently discussed comprehensively, especially as regards isotope effects in the fragmentation. (author)

  20. Energy transformation in molecular electronic systems

    International Nuclear Information System (INIS)

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

  1. Thermal conductance and rectification of asymmetric tilt grain boundary in graphene

    CERN Document Server

    Cao, Hai-Yuan; Gong, Xin-Gao

    2011-01-01

    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.

  2. Theory of Vibrationally Inelastic Electron Transport through Molecular Bridges

    OpenAIRE

    Cizek, Martin; Thoss, Michael; Domcke, Wolfgang

    2003-01-01

    Vibrationally inelastic electron transport through a molecular bridge that is connected to two leads is investigated. The study is based on a generic model of vibrational excitation in resonant transmission of electrons through a molecular junction. Employing methods from electron-molecule scattering theory, the transmittance through the molecular bridge can be evaluated numerically exactly. The current through the junction is obtained approximately using a Landauer-type for...

  3. Langmuir-Blodgett Films a unique tool for molecular electronics

    CERN Document Server

    Hussain, Syed Arshad

    2009-01-01

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

  4. Thermoelectric transport with electron-phonon coupling and electron-electron interaction in molecular junctions

    OpenAIRE

    Ren, Jie; Zhu, Jian-Xin; Gubernatis, James E.; Chen WANG; LI, Baowen

    2011-01-01

    Within the framework of nonequilibrium Green's functions, we investigate the thermoelectric transport in a single molecular junction with electron-phonon and electron-electron interactions. By transforming into a displaced phonon basis, we are able to deal with these interactions non-perturbatively. Then, by invoking the weak tunneling limit, we are able to calculate the thermoelectricity. Results show that at low temperatures, resonances of the thermoelectric figure of meri...

  5. Electroosmotic flow rectification in conical nanopores

    Science.gov (United States)

    Laohakunakorn, Nadanai; Keyser, Ulrich F.

    2015-07-01

    Recent experimental work has suggested that electroosmotic flows (EOFs) through conical nanopores exhibit rectification in the opposite sense to the well-studied effect of ionic current rectification. A positive bias voltage generates large EOF and small current, while negative voltages generate small EOF and large current. Here we systematically investigate this effect using finite-element simulations. We find that inside the pore, the electric field and salt concentration are inversely correlated, which leads to the inverse relationship between the magnitudes of EOF and current. Rectification occurs when the pore is driven into states characterized by different salt concentrations depending on the sign of the voltage. The mechanism responsible for this behaviour is concentration polarization, which requires the pore to exhibit the properties of permselectivity and asymmetry.

  6. Electroosmotic flow rectification in conical nanopores

    CERN Document Server

    Laohakunakorn, Nadanai

    2015-01-01

    Recent experimental work has suggested that electroosmotic flows (EOF) through conical nanopores exhibit rectification in the opposite sense to the well-studied effect of ionic current rectification. A positive bias voltage generates large EOF and small current, while negative voltages generate small EOF and large current. Here we systematically investigate this effect using finite-element simulations. We find that inside the pore, the electric field and salt concentration are inversely correlated, which leads to the inverse relationship between the magnitudes of EOF and current. Rectification occurs when the pore is driven into states characterized by different salt concentrations depending on the sign of the voltage. The mechanism responsible for this behaviour is concentration polarization, which requires the pore to exhibit the properties of permselectivity and asymmetry.

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

    CERN Document Server

    Okazaki, N

    2003-01-01

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

  8. Electron Impact Dissociation of Molecular Ions

    International Nuclear Information System (INIS)

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

  9. Purification of benzene by extractive rectification

    Energy Technology Data Exchange (ETDEWEB)

    Smoroda, A.I.; Ovsii, A.N.; Kashaba, I.F.; Belitskii, A.N.; Beizer, V.N.; Iliev, V.V.; Pirozhkov, G.P.

    1978-01-01

    Benzene is a very important product, affecting the development of the organic synthesis industry, especially in the production of plastics and synthetic fibers. As a result, the production of benzene is constantly increasing. There is a simultaneous increase in the demands made on its quality. The results from removal of saturated hydrocarbon impurities from benzene by extractive rectification under industrial conditions at the Yasinovka Coke Works are given. The extractive rectification unit was shown to be practical and efficient in operation. The resulting benzene meets the present and expected user requirements.

  10. Thermal rectification in nonlinear quantum circuits

    DEFF Research Database (Denmark)

    Ruokola, T.; Ojanen, T.

    2009-01-01

    We present a theoretical study of radiative heat transport in nonlinear solid-state quantum circuits. We give a detailed account of heat rectification effects, i.e., the asymmetry of heat current with respect to a reversal of the thermal gradient, in a system consisting of two reservoirs at finite temperatures coupled through a nonlinear resonator. We suggest an experimentally feasible superconducting circuit employing the Josephson nonlinearity to realize a controllable low-temperature heat rectifier with a maximal asymmetry of the order of 10%. We also discover a parameter regime where the rectification changes sign as a function of temperature.

  11. Formation of metastable electronic states in polysilylene molecular wire.

    Czech Academy of Sciences Publication Activity Database

    Nešp?rek, Stanislav

    Dresden : MaxPlanckInstitut für Physik komplexer Systeme, 2004. s. C-45. [International Workshop on Advances in Molecular Electronics: From Molecular Materials to Single Molecule Devices.. 23.02.2004-27.02.2004, Dresden] R&D Projects: GA MŠk OC D14.30 Keywords : polysilylene * molecular wire * metastable states Subject RIV: BM - Solid Matter Physics ; Magnetism

  12. Langmuir-Blodgett Films a unique tool for molecular electronics

    OpenAIRE

    Hussain, Syed Arshad

    2009-01-01

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

  13. Anomalous rectification in horizontal cells.

    Science.gov (United States)

    Werblin, F S

    1975-01-01

    1. The electrical properties of horizontal cells in the mudpuppy in light and dark were measured with a pair of micropipettes separated by about 1 mum with low coupling resistance so that no bridge circuitry was required. 2. All horizontal cells studied showed significant anomalous rectification: the current-voltage characteristic for about 60 per cent of the cells studied had a slope resistance of about 20-30 M omega at the dark potential level; the slope resistance increased by about 15% for each 10 mV depolarization and decreased by about 15% for each 10 mV hyperpolarization. The remaining 40% of the horizontal cells showed a higher input resistance at corresponding potential levels but had similar rectifying properties. 3. The increase in resistance with depolrization developed with a time course of about 1/2 sec when steady steps of outward current were passed across the membrane, but the time course for resistance decrease with hyperpolarization was much shorter for steady inward current steps. In about half the horizontal cells there was a transient decrease in resistance lasting about 100 msec immediately following the outward current steps superimposed upon the slower sustained resistance increase. 4. The normal 20-30 mV hyperpolarizing light response was associated with little or no change in input resistance. However, if the membrane potential was held at the dark potential level with extrinsic current, thereby eliminating the potential-dependent resistance change, a light-elicited resistance increase of about 10 M omega was measured. 5. The time-dependent change in membrane resistance elicited by polarizing steps of current obscured the reversal potential for the response. However, when the reversal potential was measured at short times following polarization of the membrane, before the time-dependent resistance change developed, it was estimated at between +15 and +50 m V. 6. The results suggest that the horizontal cell response is mediated by a light-elicited resistance increase at the synaptic membrane which is obscured by a potential- and time-dependent resistance decrease at another part of the membrane. PMID:1133775

  14. Electron beam irradiation effect on nanostructured molecular sieve catalysts

    International Nuclear Information System (INIS)

    Electron impact can induce chemical changes on particle surfaces of zeolites and molecular sieve catalysts. Some experimental observations of electron irradiation effect on molecular sieve catalysts are presented, e.g., electron-beam-induced growth of bare silver nanowires from zeolite crystallites, formation of vesicles in calcium phosphate, migration of microdomains in iron-oxide doped mesoporous silicas, structural transformation from mesostructured MCM-41 to microporous ZSM-5, etc. The formation mechanisms of the surface structures are discussed

  15. A Quantum Chemical View of Molecular and Nano-Electronics

    OpenAIRE

    Jiang, Jun

    2007-01-01

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

  16. Electron Interference in Molecular Circular Polarization Attosecond XUV Photoionization

    Directory of Open Access Journals (Sweden)

    Kai-Jun Yuan

    2015-01-01

    Full Text Available Two-center electron interference in molecular attosecond photoionization processes is investigated from numerical solutions of time-dependent Schrödinger equations. Both symmetric H\\(_2^+\\ and nonsymmetric HHe\\(^{2+}\\ one electron diatomic systems are ionized by intense attosecond circularly polarized XUV laser pulses. Photoionization of these molecular ions shows signature of interference with double peaks (minima in molecular attosecond photoelectron energy spectra (MAPES at critical angles \\(\\vartheta_c\\ between the molecular \\(\\textbf{R}\\ axis and the photoelectron momentum \\(\\textbf{p}\\. The interferences are shown to be a function of the symmetry of electronic states and the interference patterns are sensitive to the molecular orientation and pulse polarization. Such sensitivity offers possibility for imaging of molecular structure and orbitals.

  17. A New Full Adder Cell for Molecular Electronics

    Directory of Open Access Journals (Sweden)

    Keivan Navi

    2012-01-01

    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.

  18. A New Full Adder Cell for Molecular Electronics

    Directory of Open Access Journals (Sweden)

    Mehdi Ghasemi

    2011-09-01

    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.

  19. A New Full Adder Cell for Molecular Electronics

    CERN Document Server

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

    2012-01-01

    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.

  20. Contactless electronic transport in a bio-molecular junction

    Energy Technology Data Exchange (ETDEWEB)

    Hossain, Faruque M., E-mail: fhossain@unimelb.edu.au; Al-Dirini, Feras; Skafidas, Efstratios [Department of Electrical and Electronic Engineering, The University of Melbourne, Parkville 3010 (Australia); Center for Neural Engineering (CfNE), The University of Melbourne, Parkville 3010 (Australia)

    2014-07-28

    Molecular electronics hold promise for next generation ultra-low power, nano-scale integrated electronics. The main challenge in molecular electronics is to make a reliable interface between molecules and metal electrodes. Interfacing metals and molecules detrimentally affects the characteristics of nano-scale molecular electronic devices. It is therefore essential to investigate alternative arrangements such as contact-less tunneling gaps wherever such configurations are feasible. We conduct ab initio density functional theory and non-equilibrium Green's functions calculations to investigate the transport properties of a biocompatible glycine molecular junction. By analyzing the localized molecular orbital energy distributions and transmission probabilities in the transport-gap, we find a glycine molecule confined between two gold electrodes, without making a contact, is energetically stable and possesses high tunneling current resembling an excellent ohmic-like interface.

  1. Contactless electronic transport in a bio-molecular junction

    International Nuclear Information System (INIS)

    Molecular electronics hold promise for next generation ultra-low power, nano-scale integrated electronics. The main challenge in molecular electronics is to make a reliable interface between molecules and metal electrodes. Interfacing metals and molecules detrimentally affects the characteristics of nano-scale molecular electronic devices. It is therefore essential to investigate alternative arrangements such as contact-less tunneling gaps wherever such configurations are feasible. We conduct ab initio density functional theory and non-equilibrium Green's functions calculations to investigate the transport properties of a biocompatible glycine molecular junction. By analyzing the localized molecular orbital energy distributions and transmission probabilities in the transport-gap, we find a glycine molecule confined between two gold electrodes, without making a contact, is energetically stable and possesses high tunneling current resembling an excellent ohmic-like interface.

  2. Molecular modeling and multiscaling issues for electronic material applications

    CERN Document Server

    Iwamoto, Nancy; Yuen, Matthew; Fan, Haibo

    Volume 1 : 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 ...

  3. A molecular shift register based on electron transfer.

    Science.gov (United States)

    Hopfield, J J; Onuchic, J N; Beratan, D N

    1988-08-12

    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. PMID:17829175

  4. Spin-dependent rectification in the C59N molecule

    Indian Academy of Sciences (India)

    Mahvash Arabi Darehdor; Nasser Shahtahmasebi

    2013-02-01

    Coherent spin-dependent electron transport is investigated in three conditions: (1) a C60 molecule is connected to two ferromagnetic (FM) electrodes symmetrically, (2) a C59N molecule is connected to two FM electrodes symmetrically and (3) a C59N molecule is connected to two FM electrodes asymmetrically. This work is based on a single-band tight-binding model Hamiltonian and the Green’s function approach with the Landauer–Buttiker formalism. Electrodes used in this study are semi-infinite FM electrodes with finite cross-section. Obvious rectification effect is observed in the C59 N molecule which is connected to the FM electrodes asymmetrically. This effect is more in the P alignment of FM electrodes than in AP alignment of FM electrodes. This study indicates that the rectification behaviour is due to the asymmetry in molecule and junctions. Also in this investigation tunnel magnetoresistance (TMR) is calculated for these molecules. Asymmetry is observed in TMR of C59N which is coupled to the electrodes asymmetrically due to asymmetric junctions, but TMR of C60 is symmetric.

  5. Predicted Rectification and Negative Differential Spin Seebeck Effect at Magnetic Interfaces

    OpenAIRE

    Ren, Jie

    2013-01-01

    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...

  6. Using molecular similarity to construct accurate semiempirical electron structure theories

    CERN Document Server

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

    2003-01-01

    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.

  7. Theory of Vibrationally Inelastic Electron Transport through Molecular Bridges

    CERN Document Server

    Cizek, M; Domcke, W; Cizek, Martin; Thoss, Michael; Domcke, Wolfgang

    2003-01-01

    Vibrationally inelastic electron transport through a molecular bridge that is connected to two leads is investigated. The study is based on a generic model of vibrational excitation in resonant transmission of electrons through a molecular junction. Employing methods from electron-molecule scattering theory, the transmittance through the molecular bridge can be evaluated numerically exactly. The current through the junction is obtained approximately using a Landauer-type formula. Considering different parameter regimes, which include both the case of a molecular bridge that is weakly coupled to the leads, resulting in narrow resonance structures, and the opposite case of a broad resonance caused by strong interaction with the leads, we investigate the characteristic effects of coherent and dissipative vibrational motion on the electron transport. Furthermore, the validity of widely used approximations such as the wide-band approximation and the restriction to elastic transport mechanisms is investigated in so...

  8. Photoelectrochemical solar conversion systems molecular and electronic aspects

    CERN Document Server

    Munoz, Andres G

    2012-01-01

    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

  9. Site-directed deep electronic tunneling through a molecular network

    International Nuclear Information System (INIS)

    Electronic tunneling in a complex molecular network of N(>2) donor/acceptor sites, connected by molecular bridges, is analyzed. The 'deep' tunneling dynamics is formulated using a recursive perturbation expansion, yielding a McConnell-type reduced N-level model Hamiltonian. Applications to models of molecular junctions demonstrate that the donor-bridge contact parameters can be tuned in order to control the tunneling dynamics and particularly to direct the tunneling pathway to either one of the various acceptors

  10. Rectification of the Channelrhodopsin Early Conductance

    Science.gov (United States)

    Gradmann, Dietrich; Berndt, André; Schneider, Franziska; Hegemann, Peter

    2011-01-01

    We analyzed the nonlinear current-voltage relationships of the early conducting state of channelrhodopsin-2 expressed in Xenopus oocytes and human embryonic kidney cells with respect to changes of the electrochemical gradients of H+, Na+/K+, and Ca2+/Mg2+. Several models were tested for wild-type ChR2 and mutations at positions E90, E123, H134, and T159. Voltage-gating was excluded as cause for the nonlinearity. However, a general enzyme kinetic model with one predominant binding site yielded good fits throughout. The empty site with an apparent charge number of about ?0.3 and strong external cation binding causes some inward rectification of the uniport function. Additional inward rectification is due to asymmetric competition from outside between the transported ion species. Significant improvement of the fits was achieved by introducing an elastic voltage-divider formed by the voltage-sensitive barriers. PMID:21889442

  11. Research ZCS Synchronous Rectification of Resonant Converter

    OpenAIRE

    Xiao Kui Li

    2014-01-01

    In this study, the application of ZCS synchronous rectification for the IPT resonant converter is researched. A novel control method that AC-DC section of the resonant converter works in ZCS SR state is proposed by using the characteristic of resonant tank current. First, the ZCS working operation of SR is presented, analyzed and equivalent circuits for each operation mode are also given, respectively. Then, the novel control method of ZCS SR for resonant convert...

  12. Rectification Efficiency of Two Harmonically Coupled Particles

    Science.gov (United States)

    Sun, Lian-Xiu

    2009-04-01

    Transportation properties of two harmonically coupled particles moving in a Bashing or rocking ratchet potential are investigated in terms of Langevin simulation. The efficiency for rectification of non-equilibrium fluctuation is calculated by using a new definition. The results show that both the average current and efficiency of two coupled particles in the flashing ratchet are larger than that of a single particle and these quantities are non-monotonous functions of the potential remaining time.

  13. Rectification Efficiency of Two Harmonically Coupled Particles

    International Nuclear Information System (INIS)

    Transportation properties of two harmonically coupled particles moving in a Bashing or rocking ratchet potential are investigated in terms of Langevin simulation. The efficiency for rectification of non-equilibrium fluctuation is calculated by using a new definition. The results show that both the average current and efficiency of two coupled particles in the flashing ratchet are larger than that of a single particle and these quantities are non-monotonous functions of the potential remaining time

  14. Thermal rectification in nonlinear quantum circuits

    DEFF Research Database (Denmark)

    Ruokola, T.; Ojanen, T.; Jauho, Antti-Pekka

    2009-01-01

    We present a theoretical study of radiative heat transport in nonlinear solid-state quantum circuits. We give a detailed account of heat rectification effects, i.e., the asymmetry of heat current with respect to a reversal of the thermal gradient, in a system consisting of two reservoirs at finite temperatures coupled through a nonlinear resonator. We suggest an experimentally feasible superconducting circuit employing the Josephson nonlinearity to realize a controllable low-temperature heat rec...

  15. Noise rectification in quasigeostrophic forced turbulence

    CERN Document Server

    Alvarez, A; Tintore, J; Alvarez, Alberto; Hernandez-Garcia, Emilio; Tintore, Joaquin

    1998-01-01

    We study the appearance of large scale mean motion sustained by stochastic forcing on a rotating fluid (in the quasigeostrophic approximation) flowing over topography. As in other noise rectification phenomena, the effect requires nonlinearity and absence of detailed balance to occur. By application of an analytical coarse graining procedure we identify the physical mechanism producing such effect: It is a forcing coming from the small scales that manifests in a change in the effective viscosity operator and in the effective noise statistical properties.

  16. Noise rectification in quasigeostrophic forced turbulence

    OpenAIRE

    Álvarez, Alberto; Hernández-García, Emilio; Tintoré, Joaquín

    1998-01-01

    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...

  17. Thermal rectification in nonlinear quantum circuits

    OpenAIRE

    Ruokola, T.; Ojanen, T.; Jauho, Antti-Pekka

    2009-01-01

    We present a theoretical study of radiative heat transport in nonlinear solid-state quantum circuits. We give a detailed account of heat rectification effects, i.e. the asymmetry of heat current with respect to a reversal of the thermal gradient, in a system consisting of two reservoirs at finite temperatures coupled through a nonlinear resonator. We suggest an experimentally feasible superconducting circuit employing the Josephson nonlinearity to realize a controllable low ...

  18. 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)

  19. Molecular Spintronics Spin-Dependent Electron Transport in Molecular Wires

    CERN Document Server

    Emberly, E; Emberly, Eldon; Kirczenow, George

    2002-01-01

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

  20. EXPERIMENTAL AND THEORETICAL RESULTS OF RECTIFICATION MEASUREMENTS IN AN STM

    OpenAIRE

    Cutler, P.; Feuchtwang, T.; Huang, Z.; Tsong, T.; Nguyen, H.; A. Lucas; Sullivan, T.

    1987-01-01

    Recent measurements of dc current-voltage characteristics of Scanning Tunneling Microscope junctions have confirmed their expected high rectification property. We have exploited this property to study rectification at infrared frequencies. A laser beam of linearly polarized light is focused on an STM junction and the resulting dc bias induced across the junction by the alternating, asymmetrical tunnel current is detected. Results have been obtained that exhibit rectification for W-Si, W-Ni, a...

  1. Thermal rectification properties of multiple-quantum-dot junctions

    OpenAIRE

    Kuo, David M. -T.; Chang, Yia-chung

    2010-01-01

    It is illustrated that semiconductor quantum dots (QDs) embedded into an insulating matrix connected with metallic electrodes and some vacuum space can lead to significant thermal rectification effect. A multilevel Anderson model is used to investigate the thermal rectification properties of the multiple-QD junction. The charge and heat currents in the tunneling process are calculated via the Keldysh Green's function technique. We show that pronounced thermal rectification a...

  2. Controlling molecular fragmentation using low energy electrons

    International Nuclear Information System (INIS)

    We show that functional group dependence exists in dissociative attachment of electrons to molecules and this leads to site and bond selectivity in fragmenting organic molecules at the N-H, O-H and C-H sites using electron energy as a control parameter. This phenomenon is investigated further by measuring the momentum distribution of hydride ions using the newly developed ion momentum imaging technique. We find that while the electron attachment at the O-site leads to a two-body fragmentation, attachment at the C-site leads to few-body fragmentation. Several new phenomena like 'bond orientation dependent electron attachment' and direct screening of one part of the molecule by another part to the incoming electron are unravelled in the very rich momentum distribution data of the hydride ions that we have obtained at various resonances

  3. Quantum computing using molecular electronic and vibrational states

    International Nuclear Information System (INIS)

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

  4. Self-assembled nanogaps for molecular electronics

    DEFF Research Database (Denmark)

    Tang, Qingxin; Tong, Yanhong; Jain, Titoo; Hassenkam, Tue; Wan, Qing; Moth-Poulsen, Kasper; Bjørnholm, Thomas

    2009-01-01

    A nanogap for molecular devices was realized using solution-based self-assembly. Gold nanorods were assembled to gold nanoparticle-coated conducting SnO2:Sb nanowires via thiol end-capped oligo(phenylenevinylene)s (OPVs). The molecular gap was easily created by the rigid molecule itself during self-assembly and the gap length was determined by the molecule length. The gold nanorods and gold nanoparticles, respectively covalently bonded at the two ends of the molecule, had very small dimensions, ...

  5. Molecular dynamics simulations of electron irradiated PVDF nanofibers

    Science.gov (United States)

    Miao, Jiayuan; Bhatta, Ram; Kisielowski, Christian; Lolla, Dinesh; Reneker, Darrell; Tsige, Mesfin; Taylor, Philip

    2014-03-01

    High-resolution, aberration corrected transmission electron microscopy was used to observe morphological changes and segmental motion of electrospun poly(vinylidene fluoride) nanofibers in an 80 kilovolt electron beam. Atomic and molecular scale high-resolution images of fibers were made with an aberration corrected electron microscope. Chemical and morphological changes, which include the breaking of the fiber, loss of fluorine atoms and cross-linking of chains, caused by the high-energy electron beam were observed. We present the results of molecular dynamics (MD) simulations of such atomic and molecular level observations. The calculational models include the influence of chain scission, chain recoiling, and torsional defects on the morphology of a nanofiber. The effects of the loss of fluorine atoms and the applied tension on the morphology of the fibers were also investigated. Work supported by the Petroleum Research Fund of the American Chemical Society.

  6. Two-electron processes in molecular collisions

    International Nuclear Information System (INIS)

    Orientation effects are reported for the ionization plus excitation of H2 by electron bombardment. The yield of H+-fragment ions as a function of angle relative to the beam direction are reported for angles from 18deg to 90deg and collision energies of 408, 545, and 1089 eV. Comparisons are made between experiment and theoretical predictions based on dipole interactions between projectile and target electrons. (orig.)

  7. Special issue on ultrafast electron and molecular dynamics

    Science.gov (United States)

    Hishikawa, Akiyoshi; Martin, Fernando; Vrakking, Marc

    2013-07-01

    Your invitation to submit. Journal of Physics. B: Atomic Molecular and Optical Physics (JPhysB) is delighted to announce a forthcoming special issue on ultrafast electron and molecular dynamics to appear in 2014, and invites you to submit a paper. Within the last decade, a number of novel approaches have emerged, both experimental and theoretical, that allow the investigation of (time-resolved) molecular dynamics in novel ways not anticipated before. Experimentally, the introduction of novel light sources such as high-harmonic generation 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. Along the way, particular types of molecular dynamics, such as dynamics around conical intersections, have gained an increased prominence, sparked by an emerging realization about the essential role that this dynamics plays in relaxation pathways in important bio-molecular systems. 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. 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 some of the most important developments in the field, while at the same time indicating how studies of (time-resolved) molecular dynamics are likely to evolve in the coming years. You are invited to submit your article by 1 December 2013.

  8. Towards molecular electronics with scalable nanopore junctions

    Science.gov (United States)

    Neuhausen, Alex; Goldhaber-Gordon, David; Chidsey, Chris

    2010-03-01

    We have fabricated and measured nanoscale molecular junctions. Each device consists of a shallow pore in an oxide layer, with a self-assembled monolayer (SAM) on a gold surface at the bottom. The use of a conductive polymer as a top-contact avoids previously noted issues of metal diffusion into contacted SAMs. Larger pores are more likely to contain monolayer defects and dislocations, thus nanometer-scale control over the pore size allows us to investigate transport through the SAM as a function of defect density. The planar geometry and use of robust materials in the device allows for additional molecular synthesis after monolayer formation. For example, we use ``click'' chemistry to alter the functionality of SAMs of azide-terminated alkanethiols. The use of mixed monolayers to substantially dilute the number of conducting molecules in a 50-nanometer diameter pore allows us to observe few to single-molecule transport behavior.

  9. Laser induced electron diffraction: a tool for molecular orbital imaging

    CERN Document Server

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

    2012-01-01

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

  10. Triazatriangulene as binding group for molecular electronics

    DEFF Research Database (Denmark)

    Wei, Zhongming; Wang, Xintai; Borges, Anders; Santella, Marco; Li, Tao; Sørensen, Jakob Kryger; Vanin, Marco; Hu, Wenping; Liu, Yunqi; Ulstrup, Jens; Solomon, Gemma C.; Chi, Qijin; Bjørnholm, Thomas; Nørgaard, Kasper; Laursen, Bo Wegge

    2014-01-01

    The triazatriangulene (TATA) ring system was investigated as a binding group for tunnel junctions of molecular wires on gold surfaces. Self-assembled monolayers (SAMs) of TATA platforms with three different lengths of phenylene wires were fabricated, and their electrical conductance was recorded by both conducting probe-atomic force microscopy (CP-AFM) and scanning tunneling microscopy (STM). Similar measurements were performed for phenylene SAMs with thiol anchoring groups as references. It was...

  11. Ultrafast Molecular Imaging by Laser Induced Electron Diffraction

    OpenAIRE

    Peters, Michel; Nguyen-Dang, Tung; Cornaggia, Christian; Saugout, Sébastien; Charron, Eric; Keller, Arne; Atabek, Osman

    2010-01-01

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

  12. Inelastic electron tunneling spectroscopy of molecular transport junctions

    Energy Technology Data Exchange (ETDEWEB)

    Song, Hyunwook [Kyung Hee University, Yongin (Korea, Republic of); Lee, Takhee [Seoul National University, Seoul (Korea, Republic of); Reed, Mark [Yale University, New Haven, CT (United States)

    2014-05-15

    Inelastic electron tunneling spectroscopy (IETS) has become a premier analytical tool in the investigation of nano scale and molecular junctions. The IETS spectrum provides invaluable information about the structure, bonding, and orientation of component molecules in the junctions. One of the major advantages of IETS is its sensitivity and resolution at the level of single molecules. This review discusses how IETS is used to study molecular transport junctions and presents an overview of recent experimental studies.

  13. Ballistic thermal rectification in nanoscale three-terminal junctions

    OpenAIRE

    Zhang, Lifa; Wang, Jian-Sheng; LI, Baowen

    2010-01-01

    We study ballistic thermal transport in three-terminal atomic nanojunctions by the nonequilibrium Green's function method. We find that there is ballistic thermal rectification in asymmetric three-terminal structures because of the incoherent phonon scattering from the control terminal. With spin-phonon interaction, we also find the ballistic thermal rectification even in symmetric three-terminal paramagnetic structures.

  14. Ultrafast Molecular Imaging by Laser Induced Electron Diffraction

    CERN Document Server

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

    2010-01-01

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

  15. Energy Transformation in Molecular Electronic Systems

    Energy Technology Data Exchange (ETDEWEB)

    Kasha, Michael

    1999-05-17

    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.

  16. 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

  17. Research ZVS Synchronous Rectification of Resonant Converter

    OpenAIRE

    Xiao Kui Li

    2014-01-01

    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 prop...

  18. Microwave power engineering generation, transmission, rectification

    CERN Document Server

    Okress, Ernest C

    1968-01-01

    Microwave Power Engineering, Volume 1: Generation, Transmission, Rectification considers the components, systems, and applications and the prevailing limitations of the microwave power technology. This book contains four chapters and begins with an introduction to the basic concept and developments of microwave power technology. The second chapter deals with the development of the main classes of high-power microwave and optical frequency power generators, such as magnetrons, crossed-field amplifiers, klystrons, beam plasma amplifiers, crossed-field noise sources, triodes, lasers. The third

  19. 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

  20. The molecular electronic device and the biochip computer: present status.

    OpenAIRE

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

    1985-01-01

    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 bei...

  1. Quantum information analysis of electronic states at different molecular structures

    OpenAIRE

    Barcza, G; Legeza, Ö.; Marti, K.H.; Reiher, M.

    2010-01-01

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

  2. Molecular dynamics simulation of electronically excited polyatomic molecules

    International Nuclear Information System (INIS)

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

  3. Excitation of solid electron by proton and hydrogen molecular ions

    International Nuclear Information System (INIS)

    An electric stopping power of solid for hydrogen molecular ion (H2+, H3+) and ion cluster (2H+, 3H+) which lost the bounded electron from the former, were estimated and compared with the value of proton. The spacial distribution of the bounded electron of hydrogen molecular ions such as H2+ and H3+ was assumed by the molecular orbital on the basis of gauss function. In calculating the electric stopping power, a conduction electron is modelled on the free electron gas model and an exitation of bounded electron on the wave packet model. In any cases, the excitation of electron is described by the dielectric function. An effective charge Zeff, the index of the amount of stopping power S, is defined as Zeff = (s/sp)2/1 where Sp represents the stopping power for proton running with the same velocity in the same solid. This effective charge is a useful physical parameter to arrange the stopping power data, because it shows the practical charge number of the injection ion with bounded electron to be reduced to the point charge. The effective charges of H2+ and He+ in low energy field are different depend on the orientations when they transmitted through the carbon film. The effective charge of H2+ was less than 1 if the molecular axis was parallel to the running direction. In high energy field, the dependence of orientation was not observed. The differences of effective charges of H3+ passing through the carbon, aluminium and krypton gas were about 0.2, the small value indicating the small dependence of value on the materials. (S.Y.)

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

    DEFF Research Database (Denmark)

    Li, Qian; Solomon, Gemma

    2014-01-01

    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.

  5. Gold nanoparticle assisted assembly of a heme protein for enhancement of long-range interfacial electron transfer

    DEFF Research Database (Denmark)

    Jensen, Palle Skovhus; Chi, Qijin; Grumsen, Flemming Bjerg; Abad, J.M.; Horsewell, Andy; Schiffrin, D.J.; Ulstrup, Jens

    2007-01-01

    Interfacial electron transfer (ET) of biological macromolecules such as metalloproteins is the key process in bioelectrochemistry, enzymatic electrocatalysis, artificial ET chains, single-molecule electronic amplification and rectification, and other phenomena associated with the area of bioelectronics. A key challenge in molecular bioelectronics is to improve the efficiency of long-range charge transfer. The present work shows that this can be achieved by nanoparticle (NP) assisted assembly of ...

  6. Theory and Application of Dissociative Electron Capture in Molecular Identification

    CERN Document Server

    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

    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...

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

    DEFF Research Database (Denmark)

    Sørensen, Jakob Kryger; Fock, Jeppe; Pedersen, Anders Holmen; Petersen, Asger B; Jennum, Karsten; Bechgaard, Klaus; Kilså, Kristine; Geskin, Victor; Cornil, Jérôme; Bjørnholm, Thomas; Nielsen, Mogens Brøndsted

    2011-01-01

    In continuation of previous studies showing promising metal-molecule contact properties a variety of C(60) end-capped "molecular wires" for molecular electronics were prepared by variants of the Prato 1,3-dipolar cycloaddition reaction. Either benzene or fluorene was chosen as the central wire, and synthetic protocols for derivatives terminated with one or two fullero[c]pyrrolidine "electrode anchoring" groups were developed. An aryl-substituted aziridine could in some cases be employed directly...

  8. Effect of interfacial coupling on rectification in organic spin rectifiers

    Science.gov (United States)

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

    2015-07-01

    The effect of interfacial coupling on rectification in an organic co-oligomer spin diode is investigated theoretically by considering spin-independent and spin-resolved couplings respectively. In the case of spin-independent coupling, an optimal interfacial coupling strength with a significant enhanced rectification ratio is found, whose value depends on the structural asymmetry of the molecule. In the case of spin-resolved coupling, we found that only the variation of the interfacial coupling with specific spin is effective to modulate the rectification, which is due to the spin-filtering property of the central asymmetric magnetic molecule. A transition of the spin-current rectification between parallel spin-current rectification and antiparallel spin-current rectification may be observed with the variation of the spin-resolved interfacial coupling. The interfacial effect on rectification is further analyzed from the spin-dependent transmission spectrum at different biases. Project supported by the National Natural Science Foundation of China (Grant No. 1374195), the Natural Science Foundation of Shandong Province, China (Grant No. ZR2014AM017), and the Excellent Young Scholars Research Fund of Shandong Normal University, China.

  9. Bonding in Molecular Crystals from the Local Electronic Pressure Viewpoint

    CERN Document Server

    Tsirelson, Vladimir G; Tokatly, Ilya V

    2015-01-01

    The spatial distribution of the internal pressure of an electron fluid, which spontaneously arises at the formation of a molecule or a crystal, is linked to the main features of chemical bonding in molecular crystals. The local pressure is approximately expressed in terms of the experimental electron density and its derivatives using the density functional formalism and is applied to identify the bonding features in benzene, formamide and chromium hexacarbonyl. We established how the spatial regions of compression and stretching of the electron fluid in these solids reflect the typical features of chemical bonds of different types. Thus, the internal electronic pressure can serve as a bonding descriptor, which has a clear physical meaning and reveals the specific features of variety of the chemical bonds expressing them in terms of the electron density.

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

    DEFF Research Database (Denmark)

    Larade, Brian; Taylor, Jeremy Philip; Zheng, Q. R.; Mehrez, Hatem; Pomorski, Pawel; Guo, Hong

    2001-01-01

    We address several general questions about quantum transport through molecular systems by an ab initio analysis of a scandium-nitrogen doped C-80 metallofullerene device. Charge transfer from the Sc3N is found to drastically change the current-voltage characteristics: the current through the Sc3N @ C-80 device is double that through a bare C-80 device. We provide strong evidence that transport in such molecular devices is mediated by molecular electronic states which have been renormalized by th...

  11. Electron impact study of molecular ions of some benzyl derivatives

    International Nuclear Information System (INIS)

    The ionization energies at threshold and values of higher energy levels for the molecular ions of benzyl alcohol, benzyl amine and benzyl cyanide are reported using electron impact technique. The first ionization energy values are found to be 8.26 eV (benzyl alcohol), 8.49 eV(benzyl amine)and 9.32 eV (benzyl cyanide). Some of the reported higher energy levels for the molecular ions are tentatively explained. The differences in the relative abundances for the main fragment ions are discussed and attributed to the effect of the different substituents - OH, -NH2 and -CN groups

  12. III - V semiconductor structures for biosensor and molecular electronics applications

    Energy Technology Data Exchange (ETDEWEB)

    Luber, S.M.

    2007-01-15

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

  13. Digital deformation model for fisheye image rectification.

    Science.gov (United States)

    Hou, Wenguang; Ding, Mingyue; Qin, Nannan; Lai, Xudong

    2012-09-24

    Fisheye lens can provide a wide view over 180°. It then has prominence advantages in three dimensional reconstruction and machine vision applications. However, the serious deformation in the image limits fisheye lens's usage. To overcome this obstacle, a new rectification method named DDM (Digital Deformation Model) is developed based on two dimensional perspective transformation. DDM is a type of digital grid representation of the deformation of each pixel on CCD chip which is built by interpolating the difference between the actual image coordinate and pseudo-ideal coordinate of each mark on a control panel. This method obtains the pseudo-ideal coordinate according to two dimensional perspective transformation by setting four mark's deformations on image. The main advantages are that this method does not rely on the optical principle of fisheye lens and has relatively less computation. In applications, equivalent pinhole images can be obtained after correcting fisheye lens images using DDM. PMID:23037373

  14. Interplay between electron-electron and electron-vibration interactions on the thermoelectric properties of molecular junctions

    OpenAIRE

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

    2014-01-01

    The linear thermoelectric properties of molecular junctions are theoretically studied close to room temperature within a model including electron-electron and electron-vibration interactions on the molecule. A nonequilibrium adiabatic approach is generalized to include large Coulomb repulsion through a self-consistent procedure and applied to the investigation of large molecules, such as fullerenes, within the Coulomb blockade regime. The focus is on the phonon thermal condu...

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

    Science.gov (United States)

    Murad, Sohail; Puri, Ishwar K.

    2014-05-01

    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.

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

    Directory of Open Access Journals (Sweden)

    A. S. Kirillov

    2010-01-01

    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.

  17. Molecular electronics an introduction to theory and experiment

    CERN Document Server

    Cuevas, Juan Carlos

    2010-01-01

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

  18. Electron densities and the excitation of CN in molecular clouds

    Science.gov (United States)

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

    1991-01-01

    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.

  19. Ab Initio Molecular Dynamics on the Electronic Boltzmann Equilibrium Distribution

    CERN Document Server

    Alonso, J L; Echenique, P; Polo, V; Rubio, A; Zueco, D

    2010-01-01

    We prove that for a combined system of classical and quantum particles, it is possible to write a dynamics for the classical particles that incorporates in a natural way the Boltzmann equilibrium population for the quantum subsystem. In addition, these molecular dynamics do not need to assume that the electrons immediately follow the nuclear motion (in contrast to any adiabatic approach), and do not present problems in the presence of crossing points between different potential energy surfaces (conical intersections or spin-crossings). A practical application of this molecular dynamics to study the effect of temperature in molecular systems presenting (nearly) degenerate states -- such as the avoided crossing in the ring-closure process of ozone -- is presented.

  20. Sufficient conditions for thermal rectification in general graded materials.

    Science.gov (United States)

    Pereira, Emmanuel

    2011-03-01

    We address a fundamental problem for the advance of phononics: the search of a feasible thermal diode. We establish sufficient conditions for the existence of thermal rectification in general graded materials. By starting from simple assumptions satisfied by the usual anharmonic models that describe heat conduction in solids, we derive an expression for the rectification. The analytical formula shows how to increase the rectification, and the conditions to avoid its decay with the system size, a problem present in the recurrent model of diodes given by the sequential coupling of two or three different parts. Moreover, for these graded systems, we show that the regimes of nondecaying rectification and of normal conductivity do not overlap. Our results indicate the graded systems as optimal materials for a thermal diode, the basic component of several devices of phononics. PMID:21517453

  1. Ab Initio Molecular Dynamics on the Electronic Boltzmann Equilibrium Distribution

    OpenAIRE

    Alonso J.L.; Castro A.; Echenique P.; Polo V.; Rubio A.; Zueco D.

    2010-01-01

    We prove that for a combined system of classical and quantum particles, it is possible to write a dynamics for the classical particles that incorporates in a natural way the Boltzmann equilibrium population for the quantum subsystem. In addition, these molecular dynamics do not need to assume that the electrons immediately follow the nuclear motion (in contrast to any adiabatic approach), and do not present problems in the presence of crossing points between different potent...

  2. Electron dopable molecular wires based on the extended viologens.

    Czech Academy of Sciences Publication Activity Database

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

    2011-01-01

    Ro?. 13, ?. 23 (2011), s. 11422-11429. ISSN 1463-9076 R&D Projects: GA ?R GA203/08/1157; GA ?R GA203/09/0705; GA AV ?R IAA400400802; GA MŠk(CZ) MEB041006 Institutional research plan: CEZ:AV0Z40400503; CEZ:AV0Z40550506 Keywords : electron transfer * spectroelectrochemistry * molecular wires Subject RIV: CG - Electrochemistry Impact factor: 3.573, year: 2011

  3. Fast Electron Repulsion Integrals for Molecular Coulomb Sturmians

    DEFF Research Database (Denmark)

    Avery, James Emil

    2013-01-01

    A new method is presented for calculating interelectron repulsion integrals for molecular Coulomb Sturmian basis sets. This makes use of an expansion of densities in terms of 2k-Sturmians, and the interelectron repulsion integrals are then calculated by a method based on the theory of hyperspherical harmonics. A rudimentary software library has been implemented and preliminary benchmarks indicate very good performance: On average 40 ns, or approximately 80 clock cycles, per electron repulsion in...

  4. Molecular Dynamics Simulation of Electron Trapping in the Sapphire Lattice

    OpenAIRE

    Rambaut, C.; Oh, K.H.; Jaffrezic, H.; Kohanoff, J.; Fayeulle, S.

    1995-01-01

    Energy storage and release in dielectric materials can be described on the basis of the charge trapping mechanism. Most phenomenological aspects have been recently rationalized in terms of the space charge model~\\cite{blaise,blaise1}. Dynamical aspects are studied here by performing Molecular Dynamics simulations. We show that an excess electron introduced into the sapphire lattice (\\alumina) can be trapped only at a limited number of sites. The energy gained by allowing the...

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

    DEFF Research Database (Denmark)

    Larade, Brian; Taylor, Jeremy Philip

    2001-01-01

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

  6. Rigorous theory of molecular orientational nonlinear optics

    Directory of Open Access Journals (Sweden)

    Chong Hoon Kwak

    2015-01-01

    Full Text Available Classical statistical mechanics of the molecular optics theory proposed by Buckingham [A. D. Buckingham and J. A. Pople, Proc. Phys. Soc. A 68, 905 (1955] has been extended to describe the field induced molecular orientational polarization effects on nonlinear optics. In this paper, we present the generalized molecular orientational nonlinear optical processes (MONLO through the calculation of the classical orientational averaging using the Boltzmann type time-averaged orientational interaction energy in the randomly oriented molecular system under the influence of applied electric fields. The focal points of the calculation are (1 the derivation of rigorous tensorial components of the effective molecular hyperpolarizabilities, (2 the molecular orientational polarizations and the electronic polarizations including the well-known third-order dc polarization, dc electric field induced Kerr effect (dc Kerr effect, optical Kerr effect (OKE, dc electric field induced second harmonic generation (EFISH, degenerate four wave mixing (DFWM and third harmonic generation (THG. We also present some of the new predictive MONLO processes. For second-order MONLO, second-order optical rectification (SOR, Pockels effect and difference frequency generation (DFG are described in terms of the anisotropic coefficients of first hyperpolarizability. And, for third-order MONLO, third-order optical rectification (TOR, dc electric field induced difference frequency generation (EFIDFG and pump-probe transmission are presented.

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

    Science.gov (United States)

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

    2013-09-01

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

  8. Machine Learning of Molecular Electronic Properties in Chemical Compound Space

    CERN Document Server

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

    2013-01-01

    The combination of modern scientific computing with electronic structure theory can lead to an unprecedented amount of data amenable to intelligent data analysis for the identification of meaningful, novel, and predictive structure-property relationships. Such relationships enable high-throughput screening for relevant properties in an exponentially growing pool of virtual compounds that are synthetically accessible. Here, we present a machine learning (ML) model, trained on a data base of \\textit{ab initio} calculation results for thousands of organic molecules, that simultaneously predicts multiple electronic ground- and excited-state properties. The properties include atomization energy, polarizability, frontier orbital eigenvalues, ionization potential, electron affinity, and excitation energies. The ML model is based on a deep multi-task artificial neural network, exploiting underlying correlations between various molecular properties. The input is identical to \\emph{ab initio} methods, \\emph{i.e.} nucle...

  9. Collision processes of electrons with molecular hydrogen ions

    International Nuclear Information System (INIS)

    Collision processes of electrons with trapped ions of mass numbers 1, 2, 3, 5, 7, 10, 14 and 20 are investigated in the concentric electron-beam device. Trapping characteristics are measured and lead to the conclusion that all the ions in the trap are hydrogenic. Cross section functions for the electron impact dissociation of H2+, H3+ and H5+ are measured. the shape of the H2+ dissociation function indicates that the molecular ions are trapped for a sufficiently long time for vibrational decay to upsilon = 0 to occur. There is good agreement between the present low energy H3+ dissociation data and previous work. Dissociation cross sections for H5+ and the temperature dependence of the e-H5+ recombination rate are measured. The latter is in good agreement with previous room temperature data and facilitates the prediction of the recombination rate in the Jovian ionosphere. (author)

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

    DEFF Research Database (Denmark)

    SØrensen, Jakob Kryger; Fock, Jeppe

    2011-01-01

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

  11. Molecular Electronic Angular Motion Transducer Broad Band Self-Noise

    Directory of Open Access Journals (Sweden)

    Dmitry Zaitsev

    2015-11-01

    Full Text Available Modern molecular electronic transfer (MET angular motion sensors combine high technical characteristics with low cost. Self-noise is one of the key characteristics which determine applications for MET sensors. However, until the present there has not been a model describing the sensor noise in the complete operating frequency range. The present work reports the results of an experimental study of the self-noise level of such sensors in the frequency range of 0.01–200 Hz. Based on the experimental data, a theoretical model is developed. According to the model, self-noise is conditioned by thermal hydrodynamic fluctuations of the operating fluid flow in the frequency range of 0.01–2 Hz. At the frequency range of 2–100 Hz, the noise power spectral density has a specific inversely proportional dependence of the power spectral density on the frequency that could be attributed to convective processes. In the high frequency range of 100–200 Hz, the noise is conditioned by the voltage noise of the electronics module input stage operational amplifiers and is heavily reliant to the sensor electrical impedance. The presented results allow a deeper understanding of the molecular electronic sensor noise nature to suggest the ways to reduce it.

  12. 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.)

  13. Fast Electron Repulsion Integrals for Molecular Coulomb Sturmians

    DEFF Research Database (Denmark)

    Avery, James Emil

    2013-01-01

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

  14. Vibrational excitations in molecular layers probed by ballistic electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    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

    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.

  15. Ab initio molecular dynamics on the electronic Boltzmann equilibrium distribution

    International Nuclear Information System (INIS)

    We prove that for a combined system of classical and quantum particles, it is possible to describe a dynamics for the classical particles that incorporates in a natural way the Boltzmann equilibrium population for the quantum subsystem. In addition, these molecular dynamics (MD) do not need to assume that the electrons immediately follow the nuclear motion (in contrast to any adiabatic approach) and do not present problems in the presence of crossing points between different potential energy surfaces (conical intersections or spin-crossings). A practical application of this MD to the study of the effect of temperature on molecular systems presenting (nearly) degenerate states-such as the avoided crossing in the ring-closure process of ozone-is presented.

  16. Research ZVS Synchronous Rectification of Resonant Converter

    Directory of Open Access Journals (Sweden)

    Xiao Kui Li

    2014-01-01

    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.

  17. Research ZCS Synchronous Rectification of Resonant Converter

    Directory of Open Access Journals (Sweden)

    Xiao Kui Li

    2014-01-01

    Full Text Available In this study, the application of ZCS synchronous rectification for the IPT resonant converter is researched. A novel control method that AC-DC section of the resonant converter works in ZCS SR state is proposed by using the characteristic of resonant tank current. First, the ZCS working operation of SR is presented, analyzed and equivalent circuits for each operation mode are also given, respectively. Then, the novel control method of ZCS SR for resonant converter is proposed. According to the ZCS working operation of SR and the differential equations of equivalent circuit, a steady-state mathematical model of the circuit is established. On that basis, the calculation method for ZCS operating point of SR is deduced by solving the fixed point function about resonant tank current. Moreover, the specific flow chart for calculating ZCS operating point of SR and the steady-state waveforms of each state variable is also presented and operating principle of control circuit for ZCS SR is described in detail. Finally, experimental results verify the effectiveness of control method proposed in this study.

  18. Detection and Rectification of Distorted Fingerprints.

    Science.gov (United States)

    Xuanbin Si; Jianjiang Feng; Jie Zhou; Yuxuan Luo

    2015-03-01

    Elastic distortion of fingerprints is one of the major causes for false non-match. While this problem affects all fingerprint recognition applications, it is especially dangerous in negative recognition applications, such as watchlist and deduplication applications. In such applications, malicious users may purposely distort their fingerprints to evade identification. In this paper, we proposed novel algorithms to detect and rectify skin distortion based on a single fingerprint image. Distortion detection is viewed as a two-class classification problem, for which the registered ridge orientation map and period map of a fingerprint are used as the feature vector and a SVM classifier is trained to perform the classification task. Distortion rectification (or equivalently distortion field estimation) is viewed as a regression problem, where the input is a distorted fingerprint and the output is the distortion field. To solve this problem, a database (called reference database) of various distorted reference fingerprints and corresponding distortion fields is built in the offline stage, and then in the online stage, the nearest neighbor of the input fingerprint is found in the reference database and the corresponding distortion field is used to transform the input fingerprint into a normal one. Promising results have been obtained on three databases containing many distorted fingerprints, namely FVC2004 DB1, Tsinghua Distorted Fingerprint database, and the NIST SD27 latent fingerprint database. PMID:26353261

  19. Electronic and magnetic structure of vivianite: cluster molecular orbital calculations

    Science.gov (United States)

    Grodzicki, M.; Amthauer, G.

    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.

  20. Fullerene-based Anchoring Groups for Molecular Electronics

    DEFF Research Database (Denmark)

    Martin, Christian A.; Ding, Dapeng; Sørensen, Jakob Kryger; Bjørnholm, Thomas; van Ruitenbeek, Jan M.; van der Zant, Herre

    2008-01-01

    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 additi...

  1. Modulation of rectification and negative differential resistance in graphene nanoribbon by nitrogen doping

    International Nuclear Information System (INIS)

    By applying the nonequilibrium Green's function formalism combined with density functional theory, we have investigated the electronic transport properties of two nitrogen-doped armchair graphene nanoribbon-based junctions M1 and M2. In the left part of M1 and M2, nitrogen atoms are doped at two edges of the nanoribbon. In the right part, nitrogen atoms are doped at one edge and at the center for M1 and M2, respectively. Obvious rectifying and negative differential resistance behaviors are found, which are strongly dependent on the doping position. The maximum rectification and peak-to-valley ratios are up to the order of 104 in M2.

  2. Probing ultrafast electronic and molecular dynamics with free-electron lasers

    International Nuclear Information System (INIS)

    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. (review article)

  3. Molecular Electronics: Insight from First-Principles Transport Simulations

    DEFF Research Database (Denmark)

    Paulsson, Magnus; Frederiksen, Thomas

    2010-01-01

    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.

  4. Electronic structure calculations on molecular photo-FET.

    Czech Academy of Sciences Publication Activity Database

    Kratochvílová, Irena; Pavelka, Mat?j; Nešp?rek, Stanislav; Sworakowski, J.; Záliš, Stanislav

    Leiden : Bell Academic Publishers, 2006 - (Simos, T.; Maroulis, G.), s. 1547-1549 ISBN 978-90-04-15542-8. ISSN 1573-4196. - (Lecture Ser. Computer and Computational Sci.. 7b). [International Conference on Computational Methods in Science and Engineering. Chania (GR), 27.10.2006-01.11.2006] R&D Projects: GA MŠk OC 137; GA AV ?R KAN401770651; GA AV ?R 1ET400400413; GA MŠk OC 139 Institutional research plan: CEZ:AV0Z10100520; CEZ:AV0Z40400503; CEZ:AV0Z40500505 Keywords : molecular electronics * photochromic molecules * electronic structure * DFT calculations Subject RIV: BM - Solid Matter Physics ; Magnetism

  5. Laser-induced currents along molecular wire junctions

    CERN Document Server

    Franco, Ignacio; Brumer, Paul

    2008-01-01

    The treatment of the previous paper is extended to molecular wires. Specifically, the effect of electron-vibrational interactions on the electronic transport induced by femtosecond $\\omega+2\\omega$ laser fields along unbiased molecular nanojunctions is investigated. For this, the photoinduced vibronic dynamics of trans-polyacetylene oligomers coupled to macroscopic metallic leads is followed in a mean-field mixed quantum-classical approximation. A reduced description of the dynamics is obtained by introducing projective lead-molecule couplings and deriving an effective Schr\\"odinger equation satisfied by the orbitals in the molecular region. Two possible rectification mechanisms are identified and investigated. The first one relies on near-resonance photon-absorption and is shown to be fragile to the ultrafast electronic decoherence processes introduced by the wire's vibrations. The second one employs the dynamic Stark effect and is demonstrated to be highly efficient and robust to electron-vibrational intera...

  6. Fragmentation of molecular ions in slow electron collisions

    Energy Technology Data Exchange (ETDEWEB)

    Novotny, Steffen

    2008-06-25

    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.)

  7. 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.)

  8. Fabrication of Micro-Gap Electrodes for Molecular Electronics

    Science.gov (United States)

    Edura, Tomohiko; Mizuno, Jun; Tsutsui, Ken; Saito, Mikiko; Tokuda, Masahide; Onozato, Harumasa; Koizumi, Toshiko; Wada, Yasuo; Haemori, Masamitsu; Koinuma, Hideomi

    Recently, organic molecular electrical devices such as molecular thin film transistors have received considerable attentions as possible candidates for next generation electrical and optical devices. This paper reports fabricating technologies of flat metallic electrodes on insulating substrates with micro-gap separation. The key technologies of fabricating the planar type electrodes are liftoff method by the combination of bi-layer photoresist with overhang profile and electron beam evaporation of thin metal (Ti and Au) films and SiO2-CMP (Chemical Mechanical Polishing) method of CVD (Chemical Vapor Deposition) deposited TEOS (Tetraethoxysilane) - SiO2 layer. The raggedness of the electrode/insulator interface and the electrode surface on the micro-gap electrodes were less than 3 nm. The isolation characteristics of fabricated electrodes were in the order of 1013 ohm at room temperature, which is enough for analyzing electronic properties of organic thin film devices. Finally, pentacene FET characteristics are discussed fabricated on the micro-gap flat electrodes. The mobility of this FET was 0.015cm2/Vs, which was almost on the order of the previous results. These results suggest that high performance organic thin film transistors would be realized on these advanced electrode structures.

  9. Mechanism of Enhanced Rectification in Unimolecular Borromean Ring Devices

    CERN Document Server

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

    2006-01-01

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

  10. Machine learning of molecular electronic properties in chemical compound space

    International Nuclear Information System (INIS)

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

  11. Machine learning of molecular electronic properties in chemical compound space

    Science.gov (United States)

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

    2013-09-01

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

  12. Molecular orbital calculations of two-electron states for P donor solid-state spin qubits

    OpenAIRE

    Kettle, L. M.; Goan, Hsi-Sheng; Smith, Sean C.

    2005-01-01

    We theoretically study the Hilbert space structure of two neighbouring P donor electrons in silicon-based quantum computer architectures. To use electron spins as qubits, a crucial condition is the isolation of the electron spins from their environment, including the electronic orbital degrees of freedom. We provide detailed electronic structure calculations of both the single donor electron wave function and the two-electron pair wave function. We adopted a molecular orbita...

  13. Electronic transport of molecular nanowires by considering of electron hopping energy between the second neighbors

    Directory of Open Access Journals (Sweden)

    H Rabani

    2015-07-01

    Full Text Available In this paper, we study the electronic conductance of molecular nanowires by considering the electron hopping between the first and second neighbors with the help Green’s function method at the tight-binding approach. We investigate three types of structures including linear uniform and periodic chains as well as poly(p-phenylene molecule which are embedded between two semi-infinite metallic leads. The results show that in the second neighbor approximation, the resonance, anti-resonance and Fano phenomena occur in the conductance spectra of these structures. Moreover, a new gap is observed at edge of the lead energy band wich its width depends on the value of the electron hopping energy between the second neighbors. In the systems including intrinsic gap, this hopping energy shifts the gap in the energy spectra.

  14. Probing flexible conformations in molecular junctions by inelastic electron tunneling spectroscopy

    Directory of Open Access Journals (Sweden)

    Mingsen Deng

    2015-01-01

    Full Text Available The probe of flexible molecular conformation is crucial for the electric application of molecular systems. We have developed a theoretical procedure to analyze the couplings of molecular local vibrations with the electron transportation process, which enables us to evaluate the structural fingerprints of some vibrational modes in the inelastic electron tunneling spectroscopy (IETS. Based on a model molecule of Bis-(4-mercaptophenyl-ether with a flexible center angle, we have revealed and validated a simple mathematical relationship between IETS signals and molecular angles. Our results might open a route to quantitatively measure key geometrical parameters of molecular junctions, which helps to achieve precise control of molecular devices.

  15. Spin Polarized Electron Transport in a Magnetically Coupled Molecular Wire

    Science.gov (United States)

    Senapati, L.

    2005-03-01

    Nanostructured materials present new opportunities for spintronics and for coherent applications such as quantum information processing. In order to make progress in these areas, new materials that are optimized for spin transfer are required. We will present theoretical studies of electronic structure and transport in magnetically coupled bridging molecules that reveal how coherent spin transport between nanostructures may be enhanced by suitable molecular design. We will present a study on a bridge consisting of two molecules coupled by a vanadium atom and sandwiched by two magnetic contacts (Ni) at both ends. Our first-principles density functional calculations suggest that by controlling the spin of the vanadium atom, one can control the spin polarized transport through the magnetically coupled molecules. The ground state of the magnetically coupled molecular bridge when sandwiched between similar magnetic cluster contacts at both ends (e.g. magnetic clusters such as Ni), prefers anti-parallel to parallel spin configurations. Control of the vanadium spin could be implemented by magnetic STM tips. The large difference in resistance between the two spin configuration states of such a system could be used to make GMR like devices.

  16. Molecularly imprinted polymers as recognition materials for electronic tongues.

    Science.gov (United States)

    Huynh, Tan-Phat; Kutner, Wlodzimierz

    2015-12-15

    For over three decades now, molecularly imprinted polymers (MIPs) have successfully been used for selective chemical sensing because the shape and size of their imprinted molecular cavities perfectly matched those of the target analyte molecules. Moreover, orientation of recognizing sites of these cavities corresponded to those of the binding sites of the template molecules. In contrast, electronic tongue (e-tongue) is usually an array of low-affinity recognition units. Its selectivity is based on recognition pattern or multivariate analysis. Merging these two sensing devices led to a synergetic hybrid sensor, an MIP based e-tongue. Fabrication of these e-tongues permitted simultaneous sensing and discriminating several analytes in complex solutions of many components so that these arrays compensated for limitation in cross-reactivity of MIPs. Apparently, analytical signals generated by MIP-based e-tongues, compared to those of ordinary sensor arrays, were more reliable where a unique pattern or 'fingerprint' for each analyte was generated. Additionally, several transduction platforms (from spectroscopic to electrochemical) engaged in constructing MIP-based e-tongues, found their broad and flexible applications. The present review critically evaluates achievements in recent developments of the MIP based e-tongues for chemosensing. PMID:26233642

  17. A scheme for automatic text rectification in real scene images

    Science.gov (United States)

    Wang, Baokang; Liu, Changsong; Ding, Xiaoqing

    2015-03-01

    Digital camera is gradually replacing traditional flat-bed scanner as the main access to obtain text information for its usability, cheapness and high-resolution, there has been a large amount of research done on camera-based text understanding. Unfortunately, arbitrary position of camera lens related to text area can frequently cause perspective distortion which most OCR systems at present cannot manage, thus creating demand for automatic text rectification. Current rectification-related research mainly focused on document images, distortion of natural scene text is seldom considered. In this paper, a scheme for automatic text rectification in natural scene images is proposed. It relies on geometric information extracted from characters themselves as well as their surroundings. For the first step, linear segments are extracted from interested region, and a J-Linkage based clustering is performed followed by some customized refinement to estimate primary vanishing point(VP)s. To achieve a more comprehensive VP estimation, second stage would be performed by inspecting the internal structure of characters which involves analysis on pixels and connected components of text lines. Finally VPs are verified and used to implement perspective rectification. Experiments demonstrate increase of recognition rate and improvement compared with some related algorithms.

  18. RECTIFICATION OF BORIC ACID IN NUCLEAR TOWER PLANTS

    Directory of Open Access Journals (Sweden)

    Kazimierz Brodowicz

    1979-01-01

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

  19. Ion Current Rectification Behavior at Novel Borosilicate Glass Capillaries.

    Czech Academy of Sciences Publication Activity Database

    Silver, Barry Richard; Holub, Karel; Mare?ek, Vladimír

    Ústí nad Labem : BEST servis, 2012 - (Navrátil, T.; Fojta, M.), s. 120-124 ISBN 978-80-905221-0-7. [Moderní elektrochemické metody /32./. Jet?ichovice (CZ), 21.05.2012-25.05.2012] Institutional support: RVO:61388955 Keywords : ion * rectification * impedance Subject RIV: CG - Electrochemistry

  20. Transmission electron microscopy and the molecular structure of icosahedral viruses.

    Science.gov (United States)

    San Martín, Carmen

    2015-09-01

    The field of structural virology developed in parallel with methodological advances in X-ray crystallography and cryo-electron microscopy. At the end of the 1970s, crystallography yielded the first high resolution structure of an icosahedral virus, the T=3 tomato bushy stunt virus at 2.9Å. It took longer to reach near-atomic resolution in three-dimensional virus maps derived from electron microscopy data, but this was finally achieved, with the solution of complex icosahedral capsids such as the T=25 human adenovirus at ?3.5Å. Both techniques now work hand-in-hand to determine those aspects of virus assembly and biology that remain unclear. This review examines the trajectory followed by EM imaging techniques in showing the molecular structure of icosahedral viruses, from the first two-dimensional negative staining images of capsids to the latest sophisticated techniques that provide high resolution three-dimensional data, or snapshots of the conformational changes necessary to complete the infectious cycle. PMID:26072114

  1. Ionic fragmentation channels in electron collisions of small molecular ions

    Energy Technology Data Exchange (ETDEWEB)

    Hoffmann, Jens

    2009-01-28

    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.)

  2. 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)

  3. 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.)

  4. Molecular rectifying diodes from self-assembly on silicon

    CERN Document Server

    Lenfant, S; Delerue, C; Allan, G

    2003-01-01

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

  5. Rectification And Revival Of Muslim World

    Directory of Open Access Journals (Sweden)

    M azram

    2012-01-01

    Full Text Available The present doldrums position and state of decadence, internal differences, external aggression (geographical and ideological, lack of self-confidence and dependence, illiteracy, political instability, economic disaster, lack of knowledge and wisdom, back benchers in science and technology, education, medicine, trade and business, banking system and defensive incapability of Muslim Ummah prompted me to write this article.  Although most of the Muslim nations got their independence because of their dedicated struggle and historic events and incidents but the old masters remained active for a remote control over the Muslim Ummah.  Their intellectuals and scholars, individually as well as collectively, have propagated and advised their leadership, the tactics and approaches by which Muslim Ummah can again be enslaved.  Writings of S.P. Huntington and F. Fukuyama are clear examples.  They are actively gearing the international institutions so cleverly that Muslim Ummah does not even realize their ill motives and objectives.  They brought their leadership in a confronting position with Muslim Ummah and hence threatening the world peace.  This situation prompted us to look at our principal sources of inspiration, which are, the Qur’an, Sunnah of the Prophet (SAW, and examples of the “enlightened Caliphs” and see if we could work out a seminal guidelines for our rectification  and revival.  We have gathered together some of these impressions; these are all tentative, nothing final about them, but these are here nonetheless. ABSTRAK: Kehadiran situasi kebelungguan dan  keruntuhan, perbezaan dalaman, pencerobohan luar (geografi dan ideologi, kurang keyakinan diri dan pergantungan, buta huruf, ketidakstabilan politik, bencana ekonomi, kekurangan ilmu dan hikmah, ketinggalan dalam sains dan teknologi, pendidikan, perubatan, perdagangan dan perniagaan, sistem perbankan dan ketidakupayaan pertahanan umat Islam mendorong saya untuk menulis artikel ini. Walaupun kebanyakan negara-negara Islam mendapat kemerdekaan mereka kerana perjuangan mereka yang berdedikasi dan peristiwa dan kejadian yang bersejarah tetapi sejarah orang lama yang kekal aktif untuk mengawal kedudukan umat Islam. Keintelektuallan mereka, secara individu dan secara berkumpulan, telah dikembangkan melalui nasihat kepimpinan mereka, taktik dan pendekatan yang Muslim Ummah sekali lagi boleh diperhambakan. Karya SP Huntington dan F. Fukuyama adalah contoh yang jelas. Mereka secara aktif menggerakkan institusi antarabangsa sehingga umat Islam tidak menyedari motif tersirat dan objektif mereka. Mereka telah membawa kepimpinan mereka dalam kedudukan yang dihadapi dengan umat Islam dan dengan itu mengancam keamanan dunia. Keadaan ini mendorong kita untuk melihat sumber-sumber inspirasi utama, iaitu al-Quran, Sunnah Nabi (SAW, dan contoh-contoh "Khalifah pencerahan" dan lihat jika kita boleh merumuskan satu garis panduan pembetulan dan pemulihan. Kami telah berkumpul bersama untuk mengawal perasaan, ini semua tentatif, walau bagaimanapun tiada apa-apa jua yang muktamad tentang mereka.KEYWORDS: SWT (subhana wa taala; pbuh (peace and blessings be upon him; ra (radiallahu anha/u

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

    Science.gov (United States)

    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

    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

  7. Interference-induced thermoelectric switching and heat rectification in quantum Hall junctions

    Science.gov (United States)

    Vannucci, Luca; Ronetti, Flavio; Dolcetto, Giacomo; Carrega, Matteo; Sassetti, Maura

    2015-08-01

    Interference represents one of the most striking manifestations of quantum physics in low-dimensional systems. Despite evidence of quantum interference in charge transport having been known for a long time, signatures of interference-induced thermal properties have been reported only recently, paving the way for the phase-coherent manipulation of heat in mesoscopic devices. In this work we show that anomalous thermoelectric properties and efficient heat rectification can be achieved by exploiting the phase-coherent edge states of quantum Hall systems. By considering a tunneling geometry with multiple quantum point contacts, we demonstrate that the interference paths effectively break the electron-hole symmetry, allowing for a thermoelectric charge current flowing either from hot to cold or vice versa, depending on the details of the tunnel junction. Correspondingly, an interference-induced heat current is predicted, and we are able to explain these results in terms of an intuitive physical picture. Moreover, we show that heat rectification can be achieved by coupling two quantum Hall systems with different filling factors, and that this effect can be enhanced by exploiting the interference properties of the tunnel junction.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-01-01

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

  9. Electronic properties of single-molecule junction: Effect of the molecular distortion

    International Nuclear Information System (INIS)

    For a model system consisting of a benzenedithio (BDT) molecule sandwiched between two Au plates, the electronic properties as a function of different BDT geometry are investigated using density functional theory. The distorted BDT structures are got through stretching the electrode distance. The corresponding electronic properties, including the spatial distribution of the frontier orbits, the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital levels and density of states at the Fermi energy are determined. It reveals that the molecular distortion essentially determines electronic structures. The result should be beneficial to understand the stress-dependent or structure-dependent transport mechanism of electrons of the BDT junction.

  10. Theoretical study of molecular vibrations in electron momentum spectroscopy experiments on furan: An analytical versus a molecular dynamical approach

    International Nuclear Information System (INIS)

    The influence of thermally induced nuclear dynamics (molecular vibrations) in the initial electronic ground state on the valence orbital momentum profiles of furan has been theoretically investigated using two different approaches. The first of these approaches employs the principles of Born-Oppenheimer molecular dynamics, whereas the so-called harmonic analytical quantum mechanical approach resorts to an analytical decomposition of contributions arising from quantized harmonic vibrational eigenstates. In spite of their intrinsic differences, the two approaches enable consistent insights into the electron momentum distributions inferred from new measurements employing electron momentum spectroscopy and an electron impact energy of 1.2 keV. Both approaches point out in particular an appreciable influence of a few specific molecular vibrations of A1 symmetry on the 9a1 momentum profile, which can be unravelled from considerations on the symmetry characteristics of orbitals and their energy spacing

  11. Theoretical study of molecular vibrations in electron momentum spectroscopy experiments on furan: an analytical versus a molecular dynamical approach.

    Science.gov (United States)

    Morini, Filippo; Deleuze, Michael S; Watanabe, Noboru; Takahashi, Masahiko

    2015-03-01

    The influence of thermally induced nuclear dynamics (molecular vibrations) in the initial electronic ground state on the valence orbital momentum profiles of furan has been theoretically investigated using two different approaches. The first of these approaches employs the principles of Born-Oppenheimer molecular dynamics, whereas the so-called harmonic analytical quantum mechanical approach resorts to an analytical decomposition of contributions arising from quantized harmonic vibrational eigenstates. In spite of their intrinsic differences, the two approaches enable consistent insights into the electron momentum distributions inferred from new measurements employing electron momentum spectroscopy and an electron impact energy of 1.2 keV. Both approaches point out in particular an appreciable influence of a few specific molecular vibrations of A1 symmetry on the 9a1 momentum profile, which can be unravelled from considerations on the symmetry characteristics of orbitals and their energy spacing. PMID:25747082

  12. Micro- and Nanostructured Materials for Active Devices and Molecular Electronics

    Energy Technology Data Exchange (ETDEWEB)

    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

    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.

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

    CERN Document Server

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

    2001-01-01

    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...

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

    Directory of Open Access Journals (Sweden)

    Nuernberger P.

    2013-03-01

    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.

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

    OpenAIRE

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

    2013-01-01

    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.

  16. Maximal rectification ratios for idealized bi-segment thermal rectifiers

    Science.gov (United States)

    Shih, Tien-Mo; Gao, Zhaojing; Guo, Ziquan; Merlitz, Holger; Pagni, Patrick J.; Chen, Zhong

    2015-08-01

    Thermal rectifiers whose forward heat fluxes are greater than reverse counterparts have been extensively studied. Here we have discovered, idealized, and derived the ultimate limit of such rectification ratios, which are partially 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 ?max/?min, where two extremes denote values of the solid segment materials that can be possibly found or fabricated within a reasonable temperature range. Recommendations for manufacturing high-ratio rectifiers are also given with examples. Under idealized assumptions, these proposed rectification limits cannot be defied by any bi-segment thermal rectifiers.

  17. Terahertz generation by optical rectification in uniaxial birefringent crystals

    OpenAIRE

    Rowley, J D; Wahlstrand, J. K.; Zawilski, K. T.; Schunemann, P. G.; Giles, N. C.; Bristow, A. D.

    2012-01-01

    The angular dependence of terahertz (THz) emission from birefringent crystals can differ significantly from that of cubic crystals. Here we consider optical rectification in uniaxial birefringent materials, such as chalcopyrite crystals. The analysis is verified in (110)-cut ZnGeP_2 and compared to (zincblende) GaP. Although the crystals share the same nonzero second-order tensor elements, the birefringence in chalcopyrite crystals cause the pump pulse polarization to evolve...

  18. Efficient Video Rectification and Stabilisation for Cell-Phones

    OpenAIRE

    Ringaby, Erik; Forssén, Per-Erik

    2012-01-01

    This article presents a method for rectifying and stabilising video from cell-phones with rolling shutter (RS) cameras. Due to size constraints, cell-phone cameras have constant, or near constant focal length, making them an ideal application for calibrated projective geometry. In contrast to previous RS rectification attempts that model distortions in the image plane, we model the 3D rotation of the camera. We parameterise the camera rotation as a continuous curve, with knots distributed acr...

  19. Decontamination of nitric acid by distillation or rectification

    International Nuclear Information System (INIS)

    The undesirable active and non-active components were removed from the simulated solution of nitric acid formed in the course of the absorption of NOx liberated during the vitrification of liquid medium-level nuclear power plant waste. Decontamination factor values of 5 for both 137Cs and Na and the reduction of the content of inactive salts below the limits required by the State standard for technical nitric acid were attained by rectification. (author) 1 tab., 4 figs., 5 refs

  20. Dihydroazulene Photochromism:Synthesis, Molecular Electronics and Hammett Correlations

    DEFF Research Database (Denmark)

    Broman, SØren Lindbæk

    2013-01-01

    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).

  1. DC Rectification of Microwaves in YIG/Pt/Py Trilayers

    Science.gov (United States)

    Sklenar, Joseph; Ketterson, John; Jungfleisch, Matthias; Jiang, Wanjun; Zhang, Wei; Pearson, John; Hoffmann, Axel; Yang, Qinghui; Wen, Qiye; Zhang, Huaiwu

    2015-03-01

    The DC voltage arising from the rectification of microwaves passing through a ferromagnet/spin Hall metal bilayer structure at ferromagnetic resonance is a powerful tool in understanding spin-orbit torques from spin Hall effects. Rectification mechanisms such as anisotropic magnetoresistance of the ferromagnetic or spin Hall magnetoresistance of the spin Hall metal can contribute depending on whether the ferromagnet is conductive or insulating. For both types of ferromagnets, spin pumping acting in concert with the inverse spin Hall effect can also generate additional DC voltages. We have studied rectification in a trilayer system of YIG/Pt/Py under conditions where both ferromagnets are simultaneously excited. By tipping the DC magnetic field out of the sample plane we can make the resonances of both ferromagnet materials degenerate. In this simultaneous resonance regime we observe an enhancement in the voltage of the YIG lineshape coming at the expense of the Py signal. Furthermore, at arbitrarily tipped out-of-plane tipping angles we observe asymmetries of the Py signal under field reversal. We compare this observation with the behavior of Py/Pt bilayer samples. This work was supported by DOE, Office of Science, Materials Science and Engineering Division.

  2. Unified framework for automatic image stitching and rectification

    Science.gov (United States)

    An, Jaehyun; Kim, Beom Su; Koo, Hyung Il; Cho, Nam Ik

    2015-05-01

    Conventional image stitching methods were developed under the assumption or condition that (1) the optical center of a camera is fixed (fixed-optical-center case) or (2) the camera captures a plane target (plane-target case). Hence, users should know or test which condition is more appropriate for the given set of images and then select a right algorithm or try multiple stitching algorithms. We propose a unified framework for the image stitching and rectification problem, which can handle both cases in the same framework. To be precise, we model each camera pose with six parameters (three for the rotation and three for the translation) and develop a cost function that reflects the registration errors on a reference plane. The designed cost function is effectively minimized via the Levenberg-Marquardt algorithm. For the given set of images, when it is found that the relative camera motions between the images are large, the proposed method performs rectification of images and then composition using the rectified images; otherwise, the algorithm simply builds a visually pleasing result by selecting a viewpoint. Experimental results on synthetic and real images show that our method successfully performs stitching and metric rectification.

  3. Goal-oriented rectification of camera-based document images.

    Science.gov (United States)

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

    2011-04-01

    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

  4. Rectification induced in N{sub 2}{sup AA}-doped armchair graphene nanoribbon device

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Tong; Wang, Ling-Ling, E-mail: llwang@hnu.edu.cn; Luo, Kai-Wu; Xu, Liang [School of Physics and Microelectronic and Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, Hunan University, Changsha 410082 (China); Li, Xiao-Fei, E-mail: xfli@hnu.edu.cn [School of Physics and Microelectronic and Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, Hunan University, Changsha 410082 (China); Department of Electrical and Information Engineering, University of Electronic Science and Technology of China, Chengdu 610054 (China)

    2014-07-07

    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 N{sub 2}{sup AA}-doped with two quasi-adjacent substitutional nitrogen atoms incorporating pairs of neighboring carbon atoms in the same sublattice A. Two kinds of N{sub 2}{sup AA}-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 N{sub 2}{sup AA} dopant. The mechanisms are revealed to explain the rectifying behaviors.

  5. Molecular orbital calculations of two-electron states for P donor solid-state spin qubits

    CERN Document Server

    Kettle, L M; Smith, S C; Goan, Hsi-Sheng; Smith, Sean C.

    2005-01-01

    We theoretically study the Hilbert space structure of two neighbouring P donor electrons in silicon-based quantum computer architectures. To use electron spins as qubits, a crucial condition is the isolation of the electron spins from their environment, including the electronic orbital degrees of freedom. We provide detailed electronic structure calculations of both the single donor electron wave function and the two-electron pair wave function. We adopted a molecular orbital method for the two-electron problem, forming a basis with the calculated single donor electron orbitals. Our two-electron basis contains many singlet and triplet orbital excited states, in addition to the two simple ground state singlet and triplet orbitals usually used in the Heitler-London approximation to describe the two-electron donor pair wave function. We determined the excitation spectrum of the two-donor system, and study its dependence on strain, lattice position and inter donor separation. This allows us to determine how isola...

  6. Electron spin resonance study on lignin molecular mobility

    International Nuclear Information System (INIS)

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

  7. Distinctive character of electronic and vibrational coherences in disordered molecular aggregates

    OpenAIRE

    Butkus, Vytautas; Zigmantas, Donatas; Abramavicius, Darius; Valkunas, Leonas

    2013-01-01

    Coherent dynamics of coupled molecules are effectively characterized by the two-dimensional (2D) electronic coherent spectroscopy. Depending on the coupling between electronic and vibrational states, oscillating signals of purely electronic, purely vibrational or mixed origin can be observed. Even in the "mixed" molecular systems two types of coherent beats having either electronic or vibrational character can be distinguished by analyzing oscillation Fourier maps, construct...

  8. Modelling the effect of structure and base sequence on DNA molecular electronics

    OpenAIRE

    Ramos, Marta M. D.; Correia, Helena M. G.

    2008-01-01

    DNA is a material that has the potential to be used in nanoelectronic devices as an active component. However, the electronic properties of DNA responsible for its conducting behaviour remain controversial. Here we use a self-consistent quantum molecular dynamics method to study the effect of DNA structure and base sequence on the energy involved when electrons are added or removed from isolated molecules and the transfer of the injected charge along de molecular axis when an electric field i...

  9. Efficient electronic structure calculation for molecular ionization dynamics at high x-ray intensity

    OpenAIRE

    Hao, Yajiang; Inhester, Ludger; Hanasaki, Kota; Son, Sang-Kil; Santra, Robin

    2015-01-01

    We present the implementation of an electronic-structure approach dedicated to ionization dynamics of molecules interacting with x-ray free-electron laser (XFEL) pulses. In our scheme, molecular orbitals for molecular core-hole states are represented by linear combination of numerical atomic orbitals that are solutions of corresponding atomic core-hole states. We demonstrate that our scheme efficiently calculates all possible multiple-hole configurations of molecules formed ...

  10. 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.)

  11. Multi-electron coincidence spectroscopy: double photoionization from molecular inner-shell orbitals

    International Nuclear Information System (INIS)

    We have studied double photoionization from molecular inner-shell orbitals and investigated the properties of the resultant double core-hole states in molecules, by multi-electron coincidence spectroscopy with a magnetic bottle electron spectrometer. A brief summary of our previous studies is presented

  12. First principles study of the electron transport through cis -polyacetylene based molecular wires

    Science.gov (United States)

    Yao, Jinhuan; Li, Yanwei; Zou, Zhengguang; Yang, Jianwen; Yin, Zhoulan

    2011-10-01

    The electron transport properties of cis-polyacetylene and cis-polyacetylene based molecular wires (oligo(cyclopentadiene), oligo(pyrrole), and oligo(furan)) have been studied theoretically using a combination of density-functional theory and non-equilibrium Green?s functions method. The results demonstrate that the introduction of bridging group X (X=CH 2, NH, and O) in cis-polyacetylene has a profound effect on the electron transport behavior of the molecules. The conductance of the four molecular wires decreases in the order of polyacetylene>oligo(cyclopentadiene)>oligo(furan)>oligo(pyrrole). In particular, the conductances of oligo(furan) and oligo(pyrrole) are much lower than those of polyacetylene and oligo(cyclopentadiene). The mechanism of this difference of electron transport properties of these four molecular systems is analyzed in terms of their geometric structures, electronic structures, transmission spectra, and spatial distribution of frontier orbitals. It is found that the energy levels of frontier molecular orbitals and the evolution of spatial distribution of frontier molecular orbitals with the applied bias are the essential reason for generating this difference of electron transport behaviors of the four molecular systems.

  13. Tunneling of electrons via rotor-stator molecular interfaces: combined ab initio and model study

    CERN Document Server

    Petreska, Irina; Pejov, Ljupco; Kocarev, Ljupco

    2015-01-01

    Tunneling of electrons through rotor-stator anthracene aldehyde molecular interfaces is studied with a combined ab initio and model approach. Molecular electronic structure calculated from first principles is utilized to model different shapes of tunneling barriers. Together with a rectangular barrier, we also consider a sinusoidal shape that captures the effects of the molecular internal structure more realistically. Quasiclassical approach with the Simmons' formula for current density is implemented. Special attention is paid on conformational dependence of the tunneling current. Our results confirm that the presence of the side aldehyde group enhances the interesting electronic properties of the pure anthracene molecule, making it a bistable system with geometry dependent transport properties. We also investigate the transition voltage and we show that confirmation dependent field emission could be observed in these molecular interfaces at realistically low voltages. The present study accompanies our previ...

  14. Rectification of nanopores in aprotic solvents - transport properties of nanopores with surface dipoles

    Science.gov (United States)

    Plett, Timothy; Shi, Wenqing; Zeng, Yuhan; Mann, William; Vlassiouk, Ivan; Baker, Lane A.; Siwy, Zuzanna S.

    2015-11-01

    Nanopores have become a model system to understand transport properties at the nanoscale. We report experiments and modeling of ionic current in aprotic solvents with different dipole moments through conically shaped nanopores in a polycarbonate film and through glass nanopipettes. We focus on solutions of the salt LiClO4, which is of great importance in modeling lithium based batteries. Results presented suggest ion current rectification observed results from two effects: (i) adsorption of Li+ ions to the pore walls, and (ii) a finite dipole moment rendered by adsorbed solvent molecules. Properties of surfaces in various solvents were probed by means of scanning ion conductance microscopy, which confirmed existence of an effectively positive surface potential in aprotic solvents with high dipole moments.Nanopores have become a model system to understand transport properties at the nanoscale. We report experiments and modeling of ionic current in aprotic solvents with different dipole moments through conically shaped nanopores in a polycarbonate film and through glass nanopipettes. We focus on solutions of the salt LiClO4, which is of great importance in modeling lithium based batteries. Results presented suggest ion current rectification observed results from two effects: (i) adsorption of Li+ ions to the pore walls, and (ii) a finite dipole moment rendered by adsorbed solvent molecules. Properties of surfaces in various solvents were probed by means of scanning ion conductance microscopy, which confirmed existence of an effectively positive surface potential in aprotic solvents with high dipole moments. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06340j

  15. Measuring relative barrier heights in molecular electronic junctions with transition voltage spectroscopy.

    Science.gov (United States)

    Beebe, Jeremy M; Kim, BongSoo; Frisbie, C Daniel; Kushmerick, James G

    2008-05-01

    Though molecular devices exhibiting potentially useful electrical behavior have been demonstrated, a deep understanding of the factors that influence charge transport in molecular electronic junctions has yet to be fully realized. Recent work has shown that a mechanistic transition occurs from direct tunneling to field emission in molecular electronic devices. The magnitude of the voltage required to enact this transition is molecule-specific, and thus measurement of the transition voltage constitutes a form of spectroscopy. Here we determine that the transition voltage for a series of alkanethiol molecules is invariant with molecular length, while the transition voltage of a conjugated molecule depends directly on the manner in which the conjugation pathway has been extended. Finally, by examining the transition voltage as a function of contact metal, we show that this technique can be used to determine the dominant charge carrier for a given molecular junction. PMID:19206478

  16. Symmetry of "molecular" configurations of interacting electrons in a quantum dot in strong magnetic fields

    CERN Document Server

    Imamura, H; Aoki, H; Imamura, Hiroshi; Maksym, Peter A.; Aoki, Hideo

    1997-01-01

    A molecular description for magic-number configurations of interacting electrons in a quantum dot in high magnetic fields developed by one of the authors has been elaborated for four, five and six electron dots. For four electrons, the magic spin-singlet states are found to alternate between two different resonating valence bond (RVB)-like states. For the five-electron spin-polarized case, the molecular description is shown to work for the known phenomenon of magic-number sequences that correspond to both the N-fold symmetric ring configuration and a $(N-1)$-fold symmetric one with a center electron. A six-electron dot is shown here to have an additional feature in which inclusion of quantum mechanical mixing between classical configurations, which are deformed and degenerate, restores the N-fold symmetry and reproduces the ground-state energy accurately.

  17. Optically induced transport through semiconductor-based molecular electronics

    International Nuclear Information System (INIS)

    A tight binding model is used to investigate photoinduced tunneling current through a molecular bridge coupled to two semiconductor electrodes. A quantum master equation is developed within a non-Markovian theory based on second-order perturbation theory with respect to the molecule-semiconductor electrode coupling. The spectral functions are generated using a one dimensional alternating bond model, and the coupling between the molecule and the electrodes is expressed through a corresponding correlation function. Since the molecular bridge orbitals are inside the bandgap between the conduction and valence bands, charge carrier tunneling is inhibited in the dark. Subject to the dipole interaction with the laser field, virtual molecular states are generated via the absorption and emission of photons, and new tunneling channels open. Interesting phenomena arising from memory are noted. Such a phenomenon could serve as a switch

  18. Cascade units for neon isotopes production by rectification method

    International Nuclear Information System (INIS)

    Basics of neon separation into isotopes by distillation method at T = 28 K are discussed. The required numbers of transfer units of the top and bottom column sections at different loads are calculated. The experimental characteristics of packed rectification columns are presented and examples of the cascade outlined. A scheme of cryogenic circuit based on the high-pressure throttle neon cycle with intermediate nitrogen cooling is presented. The necessity and the technical ability to create the driving difference of pressures between columns of various stages demonstrated.

  19. Application and rectification of the blowing air measuring system

    International Nuclear Information System (INIS)

    This article introduces application of the blowing air measuring in the Pilot Plant, briefly introduces the rectification of measuring parameters of pulsed extraction column. measuring liquid level of stank which contains two phase medium, the blowing air measuring system of mixer-settler, supervising liquid float, alarm of high level, supervising exinanition signals, measuring liquid level in the hot cells, easily crystallized blowing air system. Through the experience of cold-test and thermal-test, it showed that this measuring method was accuracy and reliable in application, meanwhile maintained conveniently. (authors)

  20. 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

  1. MOLECULAR EFFECTS IN THE SECONDARY ELECTRON EMISSION FROM ENTRANCE AND EXIT SURFACES OF THIN SOLID FOILS

    OpenAIRE

    Kroneberger, K.; Rothard, H.; Burkhard, M.; Kemmler, J.; Koschar, P.; Heil, O.; Biedermann, C; Lencinas, S.; Keller, N.; Lorenzen, P.; Hofmann, D; Clouvas, A.; E. Veje; Groeneveld, K.

    1989-01-01

    We present results of the secondary electron emission coefficient ? from thin foi1 targets (2 to 25µg/cm2), for which we measured the secondary electron yields in backward (?b) as well as in forward (?f) direction separately, using both molecular ions and their atomic constituents as projectiles at 0.1 to 1.2MeV/u. The results are compared with monte carlo calculations of the electronic stopping power Se of molecular projectiles and with a modell for Se of clusters of Brandt et al. They show ...

  2. Mechanical modulation of single-electron tunneling through molecular-assembled metallic nanoparticles

    CERN Document Server

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

    2004-01-01

    We present a microscopic study of single-electron tunneling in nanomechanical double-barrier tunneling junctions formed using a vibrating scanning nanoprobe and a metallic nanoparticle connected to a metallic substrate through a molecular bridge. We analyze the motion of single electrons on and off the nanoparticle through the tunneling current, the displacement current and the charging-induced electrostatic force on the vibrating nanoprobe. We demonstrate the mechanical single-electron turnstile effect by applying the theory to a gold nanoparticle connected to the gold substrate through alkane dithiol molecular bridge and probed by a vibrating platinum tip.

  3. Investigation of the molecular conformations of ethanol using electron momentum spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    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

    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.

  4. Investigation of the molecular conformations of ethanol using electron momentum spectroscopy

    International Nuclear Information System (INIS)

    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

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

    Science.gov (United States)

    Bruque, Nicolas Alexander

    2009-12-01

    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.

  6. Self-Assembled Molecular Rafts at Liquid|Liquid Interfaces for Four-Electron Oxygen Reduction

    OpenAIRE

    Olaya, Astrid Johana; Schaming, Delphine Henriette; Brevet, Pierre-François Marie; Nagatani, Hirohisa; Zimmermann, Tomas; Vanicek, Jiri; Xu, Hai-jun; Gros, Claude P.; Barbe, Jean-Michel; Girault, Hubert

    2012-01-01

    The self-assembly of the oppositely charged watersoluble porphyrins, cobalt tetramethylpyridinium porphyrin (CoTMPyP4+) and cobalt tetrasulphonatophenyl porphyrin (CoTPPS4?), at the interface with an organic solvent to form molecular “rafts”, provides an excellent catalyst to perform the interfacial four-electron reduction of oxygen by lipophilic electron donors such as tetrathiafulvalene (TTF). The catalytic activity and selectivity of the self-assembled catalyst toward the four-electron pat...

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

    International Nuclear Information System (INIS)

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

  8. Intense Electron Beams from GaAs Photocathodes as a Tool for Molecular and Atomic Physics

    OpenAIRE

    Krantz, Claude

    2009-01-01

    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 stable cathode lifetimes of 24 h or more. ...

  9. Renormalization of Molecular Electronic Levels at Metal-Molecule Interfaces

    CERN Document Server

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

    2006-01-01

    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.

  10. Semiclassical initial value representation for electronically nonadiabatic molecular dynamics

    International Nuclear Information System (INIS)

    The semiclassical initial value representation (SC-IVR), which has recently seen a great deal of interest for treating nuclear dynamics on a single potential energy surface, is generalized to be able to describe electronically nonadiabatic (i.e., multisurface) processes. The essential idea is a quantization of the classical electron-nuclear Hamiltonian of Meyer and Miller [J. Chem. Phys. 70, 3214 (1979)] within the SC-IVR methodology. Application of the approach to a series of test problems suggested by Tully shows it to provide a good description of electronically nonadiabatic dynamics for a variety of situations. copyright 1997 American Institute of Physics

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1996-02-01

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

  12. Molecular double core-hole electron spectroscopy for chemical analysis

    CERN Document Server

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

    2010-01-01

    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 ...

  13. Secondary-emission electron gun for high pressure molecular lasers

    International Nuclear Information System (INIS)

    A new type of high voltage, large area electron gun is described. Ions are generated in a low pressure ion source, extracted by a grid, and accelerated by a -130-kV continuously biased electrode. By secondary emission, these ions produce electrons which are accelerated toward the grid. They go through the ion source and an electron window (15x5 cm). Electron-beam density profiles display a good uniformity. The current density, limited only by the available power for the discharge, reaches presently 1 mA/cm2. The advantages of this gun over others are moderate vacuum requirements and capability for both low current cw and high current pulsed beams with easy control at ground potential and small energy requirement

  14. Molecular double core-hole electron spectroscopy for chemical analysis

    OpenAIRE

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

    2010-01-01

    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 an...

  15. Recent advances in molecular electronics based on carbon nanotubes.

    Science.gov (United States)

    Bourgoin, Jean-Philippe; Campidelli, Stéphane; Chenevier, Pascale; Derycke, Vincent; Filoramo, Arianna; Goffman, Marcelo F

    2010-01-01

    Carbon nanotubes (CNTs) have exceptional physical properties that make them one of the most promising building blocks for future nanotechnologies. They may in particular play an important role in the development of innovative electronic devices in the fields of flexible electronics, ultra-high sensitivity sensors, high frequency electronics, opto-electronics, energy sources and nano-electromechanical systems (NEMS). Proofs of concept of several high performance devices already exist, usually at the single device level, but there remain many serious scientific issues to be solved before the viability of such routes can be evaluated. In particular, the main concern regards the controlled synthesis and positioning of nanotubes. In our opinion, truly innovative use of these nano-objects will come from: (i) the combination of some of their complementary physical properties, such as combining their electrical and mechanical properties, (ii) the combination of their properties with additional benefits coming from other molecules grafted on the nanotubes, and (iii) the use of chemically- or bio-directed self-assembly processes to allow the efficient combination of several devices into functional arrays or circuits. In this article, we outline the main issues concerning the development of carbon nanotubes based electronics applications and review our recent results in the field. PMID:21137718

  16. A Quantum of Solace: molecular electronics of benzodiazepines

    Science.gov (United States)

    Turin, Luca; Horsfield, Andrew; Stoneham, Marshall

    2011-03-01

    Benzodiazepines and related drugs modulate the activity of GABA-A receptors, the main inhibitory receptor of the central nervous system. The prevailing view is that these drugs bind at the interface between two receptor subunits and allosterically modulate the response to GABA. In this talk I shall present evidence that benzodiazepines work instead by facilitating electron transport from the cytoplasm to a crucial redox-sensitive group in the gamma subunit. If this idea is correct, benzodiazepines should not only be regarded as keys fitting into a lock, but also as one-electron chemical field-effect transistors fitting into an electronic circuit. Supported by DARPA Grant N66001-10-1-4062.

  17. Molecular structure determination of cyclooctane by Ab Initio and electron diffraction methods in the gas phase

    International Nuclear Information System (INIS)

    The determination of the molecular structure of molecules is of fundamental importance in chemistry. X-rays and electron diffraction methods constitute in important tools for the elucidation of the molecular structure of systems in the solid state and gas phase, respectively. The use of quantum mechanical molecular orbital ab initio methods offer an alternative for conformational analysis studies. Comparison between theoretical results and those obtained experimentally in the gas phase can make a significant contribution for an unambiguous determination of the geometrical parameters. In this article the determination for an unambiguous determination of the geometrical parameters. In this article the determination of the molecular structure of the cyclooctane molecule by electron diffraction in the gas phase an initio calculations will be addressed, providing an example of a comparative analysis of theoretical and experimental predictions. (author)

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

    International Nuclear Information System (INIS)

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

  19. Electron transfer statistics and thermal fluctuations in molecular junctions

    International Nuclear Information System (INIS)

    We derive analytical expressions for probability distribution function (PDF) for electron transport in a simple model of quantum junction in presence of thermal fluctuations. Our approach is based on the large deviation theory combined with the generating function method. For large number of electrons transferred, the PDF is found to decay exponentially in the tails with different rates due to applied bias. This asymmetry in the PDF is related to the fluctuation theorem. Statistics of fluctuations are analyzed in terms of the Fano factor. Thermal fluctuations play a quantitative role in determining the statistics of electron transfer; they tend to suppress the average current while enhancing the fluctuations in particle transfer. This gives rise to both bunching and antibunching phenomena as determined by the Fano factor. The thermal fluctuations and shot noise compete with each other and determine the net (effective) statistics of particle transfer. Exact analytical expression is obtained for delay time distribution. The optimal values of the delay time between successive electron transfers can be lowered below the corresponding shot noise values by tuning the thermal effects

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

    Science.gov (United States)

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

    2013-09-12

    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

  1. NATO Advanced Study Institute on Electronic Structure of Polymers and Molecular Crystals

    CERN Document Server

    Ladik, János

    1975-01-01

    The NATO Advanced Study Institute on "Electronic Structure of Polymers and Molecular Crystals" was held at the Facultes Universi­ taires de Namur (F.U.N.) from September 1st till September 14th, 1974. We wish to express our appreciation to the NATO Scientific Affairs Division whose generous support made this Institute possible and to the Facultes Universitaires de Namur and the Societe Chimique de Belgique which provided fellowships and travel grants to a number of students. This volume contains the main lectures about the basic principles of the field and about different recent developments of the theory of the electronic structure of polymers and molecular crystals. The school started with the presentation of the basic SCF-LCAO theory of the electronic structure of periodic polymers and molecular crystals (contributions by Ladik, Andre & Delhalle) showing how a combination of quantum chemical and solid state physical methods can provide band structures for these systems. The numerical aspects of these ...

  2. NATO Advanced Research Workshop on Vectorization of Advanced Methods for Molecular Electronic Structure

    CERN Document Server

    1984-01-01

    That there have been remarkable advances in the field of molecular electronic structure during the last decade is clear not only to those working in the field but also to anyone else who has used quantum chemical results to guide their own investiga­ tions. The progress in calculating the electronic structures of molecules has occurred through the truly ingenious theoretical and methodological developments that have made computationally tractable the underlying physics of electron distributions around a collection of nuclei. At the same time there has been consider­ able benefit from the great advances in computer technology. The growing sophistication, declining costs and increasing accessibi­ lity of computers have let theorists apply their methods to prob­ lems in virtually all areas of molecular science. Consequently, each year witnesses calculations on larger molecules than in the year before and calculations with greater accuracy and more com­ plete information on molecular properties. We can surel...

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

    DEFF Research Database (Denmark)

    Lu, Jing Tao; Wang, J. S.

    2009-01-01

    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.

  4. Enhancing rectification of a nano-swimmer system by multi-layered asymmetric barriers

    Science.gov (United States)

    Chen, Yen-Fu; Xiao, Song; Chen, Hsuan-Yi; Sheng, Yu-Jane; Tsao, Heng-Kwong

    2015-10-01

    The rectification of nano-swimmers in two chambers separated by a strip of funnel gates is explored by dissipative particle dynamics simulations. According to the trajectories of active colloids across the funnel zone, two rectification mechanisms are identified: geometry-assisted diffusion and trap-hindered diffusion. In general, geometry-assisted diffusion dominates at a small active force (Fa) and run time (?) while trap-hindered diffusion governs at a large Fa and ?. The rectification ratio is affected by the funnel shape and various geometries are considered: open/closed triangular, circular and rectangular funnels. The rectification ratio of open funnels is always greater than that of closed funnels. Moreover, the open circular funnel has the best performance while the triangular one has the worst. Rectification can be enhanced as the number of funnel layers is increased. It is found that the rectification ratio of self-propelled colloids can be dramatically augmented by triple-layered funnels to be as high as 30. Our simulation study offers an efficient approach for rectification enhancement.

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

    OpenAIRE

    Tarana, Michal; Chris H. Greene

    2013-01-01

    Electron collisions with O$_2$ at scattering energies below 1 eV are studied in the fixed-nuclei approximation for a range of internuclear separations using the ab initio molecular R-matrix method. The $^2\\Pi_g$ scattering eigenphases and quantum defects are calculated. The parameters of the resonance and the energy of the bound negative ion are then extracted. Different models of the target that employ molecular orbitals calculated for the neutral target are compared with m...

  6. Molecular volume and electronic and vibrational polarizibilities for amorphous LaAlO3

    International Nuclear Information System (INIS)

    Grazing incidence x-ray reflectivity measurements are used to determine the density of sputter-deposited LaAlO3 and anodized LaAl films. Together with refractive index and dielectric constant measurements, it is demonstrated that a coherent picture emerges explaining the low dielectric constant of the amorphous films (?13) as compared to the single-crystal value (?26). The importance of molecular volume dependence of the electronic and vibrational molecular polarizabilities is underlined

  7. Electron Transfer Dynamics in Efficient Molecular Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Meyer, Gerald John

    2014-10-01

    This research provided new mechanistic insights into surface mediated photochemical processes relevant to solar energy conversion. In this past three years our research has focused on oxidation photo-redox chemistry and on the role surface electric fields play on basic spectroscopic properties of molecular-semiconductor interfaces. Although this research as purely fundamental science, the results and their interpretation have relevance to applications in dye sensitized and photogalvanic solar cells as well as in the storage of solar energy in the form of chemical bonds.

  8. A parity function for studying the molecular electronic structure

    DEFF Research Database (Denmark)

    Schmider, Hartmut

    1996-01-01

    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.

  9. Electronic and magnetic properties of silicon supported organometallic molecular wires: a density functional theory (DFT) study

    Science.gov (United States)

    Liu, Xia; Tan, Yingzi; Li, Xiuling; Wu, Xiaojun; Pei, Yong

    2015-08-01

    The electronic and magnetic properties of transition metal (TM = Sc, Ti, V, Cr and Mn) atom incorporated single and double one-dimensional (1D) styrene molecular wires confined on the hydrogen-terminated Si(100) surface are explored for the first time by means of spin-polarized density functional theory, denoted as Si-[TM(styrene)]. It is unveiled that TM atoms bind asymmetrically to the adjacent phenyl rings, which leads to novel electronic and magnetic properties in stark contrast to the well-studied gas phase TM-benzene molecular wires. Si-[Mn(styrene)]? and Si-[Cr(styrene)]? single molecular wires (SMWs) are a ferromagnetic semiconductor and half metal, respectively. Creation of H-atom defects on the silicon surface can introduce an impurity metallic band, which leads to novel half-metallic magnetism of a Si-[Mn(styrene)]? system. Moreover, double molecular wires (DMWs) containing two identical or hetero SMWs are theoretically designed. The [Mn(styrene)]?-[Cr(styrene)]? DMW exhibits half-metallic magnetism where the spin-up and spin-down channels are contributed by two single molecular wires. Finally, we demonstrate that introducing a TM-defect may significantly affect the electronic structure and magnetic properties of molecular wires. These studies provide new insights into the structure and properties of surface supported 1-D sandwiched molecular wires and may inspire the future experimental synthesis of substrate confined organometallic sandwiched molecular wires.The electronic and magnetic properties of transition metal (TM = Sc, Ti, V, Cr and Mn) atom incorporated single and double one-dimensional (1D) styrene molecular wires confined on the hydrogen-terminated Si(100) surface are explored for the first time by means of spin-polarized density functional theory, denoted as Si-[TM(styrene)]. It is unveiled that TM atoms bind asymmetrically to the adjacent phenyl rings, which leads to novel electronic and magnetic properties in stark contrast to the well-studied gas phase TM-benzene molecular wires. Si-[Mn(styrene)]? and Si-[Cr(styrene)]? single molecular wires (SMWs) are a ferromagnetic semiconductor and half metal, respectively. Creation of H-atom defects on the silicon surface can introduce an impurity metallic band, which leads to novel half-metallic magnetism of a Si-[Mn(styrene)]? system. Moreover, double molecular wires (DMWs) containing two identical or hetero SMWs are theoretically designed. The [Mn(styrene)]?-[Cr(styrene)]? DMW exhibits half-metallic magnetism where the spin-up and spin-down channels are contributed by two single molecular wires. Finally, we demonstrate that introducing a TM-defect may significantly affect the electronic structure and magnetic properties of molecular wires. These studies provide new insights into the structure and properties of surface supported 1-D sandwiched molecular wires and may inspire the future experimental synthesis of substrate confined organometallic sandwiched molecular wires. Electronic supplementary information (ESI) available: The geometric structure, and the energy band structure of Sc-, Ti- and [V(styrene)]? SMWs and DMWs on the H-Si(100) surface. See DOI: 10.1039/c5nr02608c

  10. Molecular-scale imaging of unstained deoxyribonucleic acid fibers by phase transmission electron microscopy

    International Nuclear Information System (INIS)

    The molecular structure of deoxyribonucleic acid (DNA) fibers was observed by a phase reconstruction method called three-dimensional Fourier filtering using a 200 kV transmission electron microscope. The characteristic helical structure and the spacing of adjacent base pairs of DNA were partially resolved due to an improved signal-to-noise ratio and resolution enhancement by the phase reconstruction although the molecular structure was damaged by the electron beam irradiation. In the spherical aberration-free phase images, the arrangements of single atom-sized spots forming sinusoidal curves were sometimes observed, which seem to be the contrast originating in the sulfur atoms along the main chains

  11. Shapes of leading tunnelling trajectories for single-electron molecular ionization

    CERN Document Server

    Bondar, Denys I; Ivanov, Misha Yu

    2010-01-01

    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.

  12. Effects of molecular gases on Xe electroluminescence and electron resonance trapping

    Energy Technology Data Exchange (ETDEWEB)

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

    1984-06-01

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

  13. Effects of molecular gases on Xe electroluminescence and electron resonance trapping

    International Nuclear Information System (INIS)

    Xenon electroluminescence (EL) has been studied in the presence of small amounts of molecular gases and some results are reported. A theoretical model, which explains the EL in terms of a peak in the electron energy distribution near the enrgy of subexcitative resonance at 7.77 eV (electron resonance trapping), was developed to take into account the effects of a molecular gas present at low concentrations. The results obtained with air, at concentrations lower than 103 p.p.m., seem to fit well the developed model

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1988-01-01

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

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

    International Nuclear Information System (INIS)

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

  16. Electronic absorption spectra and nonlinear optical properties of CO2 molecular aggregates: A quantum chemical study

    Indian Academy of Sciences (India)

    Tarun K Mandal; Sudipta Dutta; Swapan K Pati

    2009-09-01

    We have investigated the structural aspects of several carbon dioxide molecular aggregates and their spectroscopic and nonlinear optical properties within the quantum chemical theory framework. We find that, although the single carbon dioxide molecule prefers to be in a linear geometry, the puckering of angles occur in oligomers because of the intermolecular interactions. The resulting dipole moments reflect in the electronic excitation spectra of the molecular assemblies. The observation of significant nonlinear optical properties suggests the potential application of the dense carbon dioxide phases in opto-electronic devices.

  17. Tuning intermetallic electronic coupling in polyruthenium systems via molecular architecture

    Indian Academy of Sciences (India)

    Sandeep Ghumaan; Goutam Kumar Lahiri

    2006-11-01

    A large number of polynuclear ruthenium complexes encompassing selective combinations of spacer (bridging ligand, BL) and ancillary (AL) functionalities have been designed. The extent of intermetallic electronic communication in mixed-valent states and the efficacy of the ligand frameworks towards the tuning of coupling processes have been scrutinised via structural, spectroelectrochemical, EPR, magnetic and theoretical investigations. Moreover, the sensitive oxidation state features in the complexes of non-innocent quinonoid bridging moieties have also been addressed.

  18. Dihydroazulene Photochromism:Synthesis, Molecular Electronics and Hammett Correlations

    DEFF Research Database (Denmark)

    Broman, Søren Lindbæk

    2013-01-01

    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 particul...

  19. Assessment of delocalized and localized molecular orbitals through electron momentum spectroscopy

    International Nuclear Information System (INIS)

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

  20. Effect of torsion angle on electronic transport through different anchoring groups in molecular junction

    International Nuclear Information System (INIS)

    By applying nonequilibrium Green's function formalism combined with first-principles density functional theory, we investigate effect of torsion angle on electronic transport properties of 4,4'-biphenyl molecule connected with different anchoring groups (dithiocarboxylate and thiol group) to Au(111) electrodes. The influence of the HOMO-LUMO gaps and the spatial distributions of molecular orbitals on the quantum transport through the molecular device are discussed. Theoretical results show that the torsion angle plays important role in conducting behavior of molecular devices. By changing the torsion angle between two phenyl rings, namely changing the magnitude of the intermolecular coupling effect, a different transport behavior can be observed in these two systems.

  1. Dissipative Effects in the Electronic Transport through DNA Molecular Wires

    CERN Document Server

    Gutíerrez, R; Cuniberti, G

    2005-01-01

    We investigate the influence of a dissipative environment which effectively comprises the effects of counterions and hydration shells, on the transport properties of short \\DNA wires. Their electronic structure is captured by a tight-binding model which is embedded in a bath consisting of a collection of harmonic oscillators. Without coupling to the bath a temperature independent gap opens in the electronic spectrum. Upon allowing for electron-bath interaction the gap becomes temperature dependent. It increases with temperature in the weak-coupling limit to the bath degrees of freedom. In the strong-coupling regime a bath-induced {\\it pseudo-gap} is formed. As a result, a crossover from tunneling to activated behavior in the low-voltage region of the $I$-$V$ characteristics is observed with increasing temperature. The temperature dependence of the transmission near the Fermi energy, $t(E_{\\rm F})$, manifests an Arrhenius-like behavior in agreement with recent transport experiments. Moreover, $t(E_{\\rm F})$ sh...

  2. Participation of Low Molecular Weight Electron Carriers in Oxidative Protein Folding

    Directory of Open Access Journals (Sweden)

    József Mandl

    2009-03-01

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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

    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)

  4. Molecular structure and electronic structure of 2-pyridine-carbaldehyde thiosemicarbazone

    Energy Technology Data Exchange (ETDEWEB)

    Biyushkin, V.N.; Chumakov, Yu.M.; Samus' , N.M.; Baka, I.D.

    1987-07-01

    In a continuation of research into the relationship between the molecular structure, electronic structure, and antitumor activity of the thiosemicarbazones of ..cap alpha..-(N)-heterocyclic aldehydes an x-ray crystallographic investigation of 2-pyridinecarbaldehyde thiosemicarbazone monohydrate was undertaken, and the electronic structure of the thiosemicarbazone molecule was calculated by a quantum-chemical method. The compound exhibits clearly defined activity against sarcoma 180.

  5. 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)

  6. Calculation of low-energy electron dissociative attachment of molecular hydrogen for plasma applications

    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 ? and J of the target molecules and for electron temperature in the range 0-30 000 K. (author)

  7. Molecular Electronic Level Alignment at Weakly Coupled Organic Film/Metal Interfaces

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-10-28

    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.

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

    DEFF Research Database (Denmark)

    Lu, Jing Tao; Wang, J. S.

    2009-01-01

    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) appr...

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

    Directory of Open Access Journals (Sweden)

    Kenji Yonemitsu

    2012-01-01

    Full Text Available Dynamics of photoinduced phase transitions in molecular conductors are reviewed from the perspective of interplay between correlated electrons and phonons. (1 The charge-transfer complex TTF-CA shows a transition from a neutral paraelectric phase to an ionic ferroelectric phase. Lattice phonons promote this photoinduced transition by preparing short-range lattice dimerization as a precursor. Molecular vibrations stabilize the neutral phase so that the ionic phase, when realized, possesses a large ionicity and the Mott character; (2 The organic salts ?-(BEDT-TTF2RbZn(SCN4 and ?-(BEDT-TTF2I3 show transitions from a charge-ordered insulator to a metal. Lattice phonons make this photoinduced transition hard for the former salt only. Molecular vibrations interfere with intermolecular transfers of correlated electrons at an early stage; (3 The organic salt ?-(d-BEDT-TTF2Cu[N(CN2]Br shows a transition from a Mott insulator to a metal. Lattice phonons modulating intradimer transfer integrals enable photoexcitation-energy-dependent transition pathways through weakening of effective interaction and through introduction of carriers.

  10. 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

  11. Interaction of hydrogen molecular ions with thin foils. I. Convoy electrons

    International Nuclear Information System (INIS)

    Doubly differential electron spectra from thin carbon foils (2 to 20 ?g/cm2) bombarded with 0.8 MeV/amu H+, H2+, H3+, and 3He+ ion beams have been measured in the angular range 150 to 300. A predominant group of electrons whose velocities are centered about the ion velocity (convoy electrons) is observed even at these large angles, for thinner foils with molecular ions H2+ and H3+. The yield of convoy electrons for H3+ is always larger than that for H2+ and both yields are strongly dependent on foil thickness. Our results for H2+ and H3+ are consistent with the model that the electron loss process is the dominant mechanism for producing convoy electrons

  12. Maximal rectification ratios for bi-segment thermal rectifiers

    CERN Document Server

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

    2014-01-01

    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.

  13. Terahertz generation by optical rectification in uniaxial birefringent crystals

    CERN Document Server

    Rowley, J D; Zawilski, K T; Schunemann, P G; Giles, N C; Bristow, A D

    2012-01-01

    The angular dependence of terahertz (THz) emission from birefringent crystals can differ significantly from that of cubic crystals. Here we consider optical rectification in uniaxial birefringent materials, such as chalcopyrite crystals. The analysis is verified in a (110)-cut ZnGeP2 and compared to (zincblende) GaP. Although the structures share the same nonzero second-order tensor elements, birefringence causes the pump pulse polarization to evolve as it propagates through the crystal, resulting in a drastically different angular dependence in chalcopyrite crystals. The analysis is extended to predict the response from {012}- and (114)-cut chalcopyrite crystals, revealing an increase in the maximum emission in comparison to (110)-cut crystals.

  14. Light-induced self-assembly of active rectification devices

    CERN Document Server

    Stenhammar, J; Marenduzzo, D; Cates, M E

    2015-01-01

    Self-propelled colloidal objects, such as motile bacteria or synthetic microswimmers, have microscopically irreversible individual dynamics - a feature they share with all living systems. The incoherent behaviour of individual swimmers can then be harnessed (or "rectified") by microfluidic devices that create systematic motions impossible in equilibrium. Examples include flow of rotor particles round a circuit, steady rotation of a gear wheel in a bacterial bath, and pumping of bacteria between chambers by "funnel gates". Here we present a computational proof-of-concept study, showing that such active rectification devices might be created directly from an unstructured "primordial soup" of motile particles, solely by using spatially modulated illumination to control their local propulsion speed. Alongside both microscopic irreversibility and speed modulation, our mechanism requires spatial symmetry breaking, such as a chevron light pattern, and strong interactions between particles, such as volume exclusion c...

  15. DC/DC converter with improved rectification for higher efficiency

    Energy Technology Data Exchange (ETDEWEB)

    Maisel, Peter; Saliternig, Martin [Continental AG, Nuernberg (Germany)

    2010-07-01

    High-power dc-dc converters are an important element of the electrical system of electric vehicles and hybrid electric vehicles. These complex modular components provide the link between the high-voltage level used for the powertrain and the low-voltage bus for the lighting system, engine management and auxiliary needs in the vehicle. The essential requirements for all converters are high efficiency, compact size, lightweight and reliability. A very popular method to increase the efficiency is the synchronous rectification. Parasitic inductances in the commutation circuit and reverse recovery effects can produce a ringing with voltage overshoots at the diodes and the transistors. These spikes can cause higher average power dissipation in the seminconductors and higher EMI (electromagnetic interference).

  16. Metal–semiconductor nanojunctions and their rectification characteristics

    Indian Academy of Sciences (India)

    Anindita Bose; Kuntal Chatterjee; Dipankar Chakravorty

    2009-06-01

    Junctions of silver–copper oxide and silver–zinc oxide, respectively were prepared within the pores of diameters, 20 nm, in anodic aluminium oxide membranes. Voltage–current characteristics were measured over the temperature range 373–573 K which showed rectification behaviour. Using the standard equation the difference between the work functions of the metal and the semiconductor was calculated. This showed a variation with the temperature of measurement. This is explained as arising due to the effect of pressure generated as a result of thermal expansion of the metallic phases concerned between the electrodes. This is consistent with the theoretical prediction of Fermi level shifting of the semiconductor within the bandgap as a function of pressure.

  17. Terahertz generation by optical rectification in uniaxial birefringent crystals

    Science.gov (United States)

    Rowley, J. D.; Wahlstrand, J. K.; Zawilski, K. T.; Schunemann, P. G.; Giles, N. C.; Bristow, A. D.

    2012-07-01

    The angular dependence of terahertz (THz) emission from birefringent crystals can differ significantly from that of cubic crystals. Here we consider optical rectification in uniaxial birefringent materials, such as chalcopyrite crystals. The analysis is verified in (110)-cut ZnGeP_2 and compared to (zincblende) GaP. Although the crystals share the same nonzero second-order tensor elements, the birefringence in chalcopyrite crystals cause the pump pulse polarization to evolve as it propagates through the crystal, resulting in a drastically different angular dependence in chalcopyrite crystals. The analysis is extended to {012}- and {114}-cut chalcopyrite crystals and predicts more efficient conversion for the {114} crystal cut over the {012}- and {110}-cuts.

  18. Holstein-Hubbard model approach to electronic conduction through molecular quantum dots

    CERN Document Server

    Walczak, K

    2006-01-01

    Here we study the nonlinear transport properties of a molecular device in which electron-electron and electron-phonon interactions are present. The considered device is composed of vibrating molecular bridge weakly connected to two metallic electrodes. Molecule itself is treated as a quantum dot with discrete energy levels, while its connection to the electrodes is described within the wide-band approximation. Nonperturbative computational scheme, used in this work, is based on the Green's function theory within the framework of mapping technique (GFT-MT). This method transforms the many-body electron-phonon interaction problem into a one-body multi-channel single-electron scattering problem with occupation of particular quasi-levels calculated in a self-consistent way. It is shown that transport in the presence of phonons is mediated via polaron propagation, while the combined effect of electron-electron and electron-phonon coupling is to reduce the current flowing through the device and to induce the negati...

  19. Non-radiative relaxation and rectification behavior of metal/semiconductor tetrapod heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Kanta Haldar, Krishna; Kundu, Simanta; Patra, Amitava, E-mail: msap@iacs.res.in [Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032 (India)

    2014-02-10

    The metal-semiconductor hetero-structures have recently emerged as functional materials for their potential applications in the areas of photonic, optoelectronic, and other fields. Here, we discuss the structural characterization of Au/CdSe tetrapod hetero-structures by using high-resolution transmission electron microscope, high angle annular dark field-scanning transmission electron microscopic, and X-ray diffraction. The blue shifting of the plasmonic band and red shifting of the excitonic band suggest a strong surface plasmon-exciton interaction between Au and CdSe in Au/CdSe tetrapod heterostructure. A significant photoluminescence quenching (83.4%) of CdSe nanorod (NR) is observed in the presence of Au nanoparticle in Au/CdSe tetrapod heterostructure. The radiative and nonradiative decay rates of CdSe nanorods are found to be modified in Au/CdSe tetrapod structures and the nonradiative rate changes from 1.91?×?10{sup 7}?s{sup ?1} to 9.33?×?10{sup 9}?s{sup ?1} for CdSe NR to Au/CdSe tetrapod structure, respectively. Current-voltage characteristics of Au/CdSe heterostructure exhibit the rectification property with a threshold voltage of about 0.85?V and the rectifying ratio is 140 which can open up avenues for developing challenging devices.

  20. Non-radiative relaxation and rectification behavior of metal/semiconductor tetrapod heterostructures

    International Nuclear Information System (INIS)

    The metal-semiconductor hetero-structures have recently emerged as functional materials for their potential applications in the areas of photonic, optoelectronic, and other fields. Here, we discuss the structural characterization of Au/CdSe tetrapod hetero-structures by using high-resolution transmission electron microscope, high angle annular dark field-scanning transmission electron microscopic, and X-ray diffraction. The blue shifting of the plasmonic band and red shifting of the excitonic band suggest a strong surface plasmon-exciton interaction between Au and CdSe in Au/CdSe tetrapod heterostructure. A significant photoluminescence quenching (83.4%) of CdSe nanorod (NR) is observed in the presence of Au nanoparticle in Au/CdSe tetrapod heterostructure. The radiative and nonradiative decay rates of CdSe nanorods are found to be modified in Au/CdSe tetrapod structures and the nonradiative rate changes from 1.91?×?107?s?1 to 9.33?×?109?s?1 for CdSe NR to Au/CdSe tetrapod structure, respectively. Current-voltage characteristics of Au/CdSe heterostructure exhibit the rectification property with a threshold voltage of about 0.85?V and the rectifying ratio is 140 which can open up avenues for developing challenging devices

  1. Ion current rectification, limiting and overlimiting conductances in nanopores.

    Science.gov (United States)

    van Oeffelen, Liesbeth; Van Roy, Willem; Idrissi, Hosni; Charlier, Daniel; Lagae, Liesbet; Borghs, Gustaaf

    2015-01-01

    Previous reports on Poisson-Nernst-Planck (PNP) simulations of solid-state nanopores have focused on steady state behaviour under simplified boundary conditions. These are Neumann boundary conditions for the voltage at the pore walls, and in some cases also Donnan equilibrium boundary conditions for concentrations and voltages at both entrances of the nanopore. In this paper, we report time-dependent and steady state PNP simulations under less restrictive boundary conditions, including Neumann boundary conditions applied throughout the membrane relatively far away from the nanopore. We simulated ion currents through cylindrical and conical nanopores with several surface charge configurations, studying the spatial and temporal dependence of the currents contributed by each ion species. This revealed that, due to slow co-diffusion of oppositely charged ions, steady state is generally not reached in simulations or in practice. Furthermore, it is shown that ion concentration polarization is responsible for the observed limiting conductances and ion current rectification in nanopores with asymmetric surface charges or shapes. Hence, after more than a decade of collective research attempting to understand the nature of ion current rectification in solid-state nanopores, a relatively intuitive model is retrieved. Moreover, we measured and simulated current-voltage characteristics of rectifying silicon nitride nanopores presenting overlimiting conductances. The similarity between measurement and simulation shows that overlimiting conductances can result from the increased conductance of the electric double-layer at the membrane surface at the depletion side due to voltage-induced polarization charges. The MATLAB source code of the simulation software is available via the website http://micr.vub.ac.be. PMID:25978328

  2. 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.)

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

    Energy Technology Data Exchange (ETDEWEB)

    Krantz, Claude

    2009-10-28

    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.)

  4. Molecular and electronic structure of actinide hexa-cyanoferrates

    International Nuclear Information System (INIS)

    The goal of this work is to improve our knowledge on the actinide-ligand bond properties. To this end, the hexacyanoferrate entities have been used as pre-organized ligand. We have synthesized, using mild chemistry, the following series of complexes: AnIV[FeII(CN)6].xH2O (An = Th, U, Np, Pu); AmIII[FeIII(CN)6].xH2O; Pu III[CoIII(CN)6].xH2O and K(H?)AnIII[FeII(CN)6].xH2O (An = Pu, Am). The metal oxidation states have been obtained thanks to the ?CN, stretching vibration and to the actinide LIII absorption edge studies. As Prussian Blue, the AnIV[FeII(CN)6].xH2O (An = Np, Pu) are class II of Robin and Day compounds. X-ray Diffraction has shown besides that these complexes crystallize in the P63/m space group, as the isomorphic LaKFe(CN)6.4H2O complex used as structural model. The EXAFS oscillations at the iron K edge and at the An LIII edge allowed to determine the An-N, An-O, Fe-C and Fe-N distances. The display of the multiple scattering paths for both edges explains the actinide contribution absence at the iron edge, whereas the iron signature is present at the actinide edge. We have shown that the actinide coordination sphere in actinides hexa-cyanoferrates is comparable to the one of lanthanides. However, the actinides typical behavior towards the lanthanides is brought to the fore by the AnIV versus LnIII ions presence in this family of complexes. Contrarily to the 4f electrons, the 5f electrons influence the electronic properties of the compounds of this family. However, the gap between the An-N and Ln-N distances towards the corresponding metals ionic radii do not show any covalence bond evolution between the actinide and lanthanide series. (author)

  5. Molecular Imaging Using X-Ray Free-Electron Lasers

    Science.gov (United States)

    Barty, Anton; Küpper, Jochen; Chapman, Henry N.

    2013-04-01

    The opening of hard X-ray free-electron laser facilities, such as the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory in the United States, has ushered in a new era in structural determination. With X-ray pulse durations down to 10 fs or shorter, and up to 1013 transversely coherent photons per pulse in a narrow spectral bandwidth, focused irradiances of 1018 to 1021 W cm-2 or higher can be produced at X-ray energies ranging from 500 eV to 10 keV. New techniques for determining the structure of systems that cannot be crystallized and for studying the time-resolved behavior of irreversible reactions at femtosecond timescales are now available.

  6. Molecular isotopic effects on coupled electronic and nuclear fluxes

    International Nuclear Information System (INIS)

    A full quantum treatment shows that coupled electronic and nuclear fluxes exhibit a strong sensitivity to a small mass change in a vibrating molecule. This has been exemplified with the existing isotopes of H2+ as well as few fictitious ones. We find that the fluxes undergo a significant change as one goes from one isotope of reduced mass ? to another. Other well-defined observables are likewise affected. It turns out that as a general rule, the heavier the isotope, the larger the flux, the smaller the dispersion, and the longer the revival period. While we were able to confirm analytically that the time at the first turning point scales as ?(?) and that the revival period changes linearly with ?, the mechanism of other observables remains subtle as the result of quantum interference highlighted by the pronounced difference observed on the dispersion pattern.

  7. Electrons in Cold Water Clusters: An ab Initio Molecular Dynamics Study of Localization and Metastable States.

    Czech Academy of Sciences Publication Activity Database

    Maršálek, Ond?ej; Uhlig, F.; Jungwirth, Pavel

    2010-01-01

    Ro?. 114, ?. 48 (2010), s. 20489-20495. ISSN 1932-7447 R&D Projects: GA ?R GA203/08/0114; GA MŠk LC512 Institutional research plan: CEZ:AV0Z40550506 Keywords : solvated electron * water clusters * ab initio molecular dynamics Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 4.520, year: 2010

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

    CERN Document Server

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

    2006-01-01

    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...

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

    Science.gov (United States)

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

  10. Computer Simulations of Molecular Electronic Devices in Vacuum and in Organic Solvents

    Science.gov (United States)

    Wang, Huachuan

    The main aim of this dissertation is to study the structure and dynamics of molecular electronic devices in vacuum and in solvent environment, with special focus on the mechanical properties and cross-section geometries of the break-junction down to the atomic level. The problem statement relies on how to overcome the limitations of observations from experiments, to interpret and reduce the gap between experiential measurements and theoretical studies. In order to reach this goal, a molecular system involving gold nano-electrodes, organic dithiol molecules and a driving-spring model has been built based on the experimental set-up of the break junction (BJ) technique. This technique can be classified as the mechanical controllable break junction (MCBJ) and scanning tunneling / atomic force microscope break junction (STM/AFM-BJ). We then generated self-assembled monolayers and molecular junctions by combining grand-canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulation. These approaches allow us to calibrate the structure and dynamics of molecular junctions under multiple environmental factors simultaneously. In the final stage, conductance calculations are performed using the density functional theory (DFT) in combination with the Green's function techniques. The intermediate molecular junction structures could be used to perform electronic transport calculations to eventually close the force-structure-conductance loop.

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

    International Nuclear Information System (INIS)

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

  12. Secondary electron emission from Au by medium energy atomic and molecular ions

    CERN Document Server

    Itoh, A; Obata, F; Hamamoto, Y; Yogo, A

    2002-01-01

    Number distributions of secondary electrons emitted from a Au metal surface have been measured for atomic and molecular ions of H sup + , He sup + , C sup + , N sup + , O sup + , H sup + sub 2 , H sup + sub 3 , HeH sup + , CO sup + and O sup + sub 2 in the energy range 0.3-2.0 MeV. The emission statistics obtained are described fairly well by a Polya function. The Polya parameter b, determining the distribution shape, is found to decrease monotonously with increasing emission yield gamma, revealing a surprising relationship of b gamma approx 1 over the different projectile species and impact energies. This finding supports certainly the electron cascading model. Also we find a strong negative molecular effect for heavier molecular ions, showing a significant reduction of gamma compared to the estimated values using constituent atomic projectile data.

  13. Secondary electron emission from Au by medium energy atomic and molecular ions

    International Nuclear Information System (INIS)

    Number distributions of secondary electrons emitted from a Au metal surface have been measured for atomic and molecular ions of H+, He+, C+, N+, O+, H+2, H+3, HeH+, CO+ and O+2 in the energy range 0.3-2.0 MeV. The emission statistics obtained are described fairly well by a Polya function. The Polya parameter b, determining the distribution shape, is found to decrease monotonously with increasing emission yield ?, revealing a surprising relationship of b??1 over the different projectile species and impact energies. This finding supports certainly the electron cascading model. Also we find a strong negative molecular effect for heavier molecular ions, showing a significant reduction of ? compared to the estimated values using constituent atomic projectile data

  14. Structural influences on thermal rectification of one-dimensional mass-graded lattices

    International Nuclear Information System (INIS)

    In this work, we perform a systematic analysis of various structural parameters that have an influence on the thermal rectification effect and the negative differential thermal resistance present in a one-dimensional anharmonic lattice with a mass gradient. After determining the optimal number of thermostated oscillators to enhance the rectification effect we determined that, for a random perturbation to the mass profile, rectification is enhanced, whereas negative differential thermal resistance is diminished. When a cubic term is included in the interaction potential thermal rectification is reduced, an effect more evident for large mass gradients. All results are obtained for larger system sizes than those so far considered for the present problem, thus revealing a complex interplay between the magnitude of the mass gradient and system size that is far from trivial and remains to be fully understood. (paper)

  15. Generation of Narrowband Tunable THz-Radiation via Optical Rectification in Periodically Poled Materials

    OpenAIRE

    Torosyan, G.; Nerkararyan, K.; Avetisyan, Y.; Beigang, R.

    2003-01-01

    The generation of tunableTHz-radiation via optical rectification offs-pulses in periodically poled nonlinearmaterials is reported and its applicationfor biomedical sensing using THz-senorsbased on planar wave guides is discussed indetail.

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

    CERN Document Server

    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

    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.

  17. Molecular dynamics simulations of ions in electron plasmas at strong coupling

    International Nuclear Information System (INIS)

    Molecular dynamic (MD) computer simulations are used to investigate the stopping of heavy ions in strongly coupled electron plasmas. Our results show, that in this regime collisions between the electrons as well as non-linear screening effects yield at low ion velocities a dependence of the stopping power on the ion charge Z which scales like Z1.43 instead of the usual Z2 ln(const/Z)-scaling for weak coupling. This is connected with an enhanced local density of electrons around a highly charged, slow ion. (orig.)

  18. Improvement of rectification effects in diffuser/nozzle structures with viscoelastic fluids

    OpenAIRE

    Nguyen, Nam-Trung; Lam, Yee-Cheong; Ho, Soon-Seng; Low, Cassandra Lee-Ngo

    2008-01-01

    This paper reports the improvement of rectification effects in diffuser?nozzle structures with viscoelastic fluids. Since rectification in a diffuser?nozzle structure with Newtonian fluids is caused by inertial effects, micropumps based on this concept require a relatively high Reynolds numbers and high pumping frequencies. In applications with relatively low Reynolds numbers, anisotropic behavior can be achieved with viscoelastic effects. In our investigations, a solution of dilute polyethyl...

  19. Inward rectification of a potassium channel in cardiac ventricular cells depends on internal magnesium ions.

    OpenAIRE

    Vandenberg, C A

    1987-01-01

    The mechanism of rectification of the inwardly rectifying potassium channel was examined with single-channel recording techniques in isolated ventricular myocytes from adult guinea pig heart. Inward, or anomalous, rectification describes the property that potassium (K) current can enter the cell at potentials negative to the potassium equilibrium potential, EK, more readily than it can leave the cell at positive potentials. Voltage ramps applied to single inward rectifier channels in cell-att...

  20. Toward optimizing the electronic structure and properties of large-area molecular junctions

    International Nuclear Information System (INIS)

    Full text: Large area molecular electronic junctions that contain ensembles of >1012 molecules sandwiched between two conducting contacts are complex devices with many possible molecule-contact configurations. Several different types of molecules (e.g., nitroazobenzene, biphenyl, nitrobiphenyl, fluorene) and contacts (e.g., pyrolyzed photo resist films or PPF, C, Au, Ag, Cu) have been employed in the construction of these devices. In these devices, often the molecular layer is covalently bonded to one of the electrodes and physisorbed on the other. Electronic structure modeling is very important for understanding the behaviour of these complex systems. We investigate the covalent bonding of molecules to Au (111), Ag (111), Cu (111), Cu (001), Cu (011), and graphene electrodes, and employ advanced concepts, such as binding energy, bond order, DOS, molecular orbital energy level and spatial distribution, to analyze the efficiency of electronic interaction. The physisorption of molecules to metal surfaces is also explored, e.g. nitrobenzene/Cu system. For calculation of the current-voltage dependence and understanding of electron transport, we intend to employ the tandem of ab initio electronic structure methods and non-equilibrium Green functions technique. (author)

  1. VUV diagnostic of electron impact processes in low temperature molecular hydrogen plasma

    CERN Document Server

    Komppula, J

    2015-01-01

    Novel methods for diagnostics of molecular hydrogen plasma processes, such as ionization, production of high vibrational levels, dissociation of molecules via excitation to singlet and triplet states and production of metastable states, are presented for molecular hydrogen plasmas in corona equilibrium. The methods are based on comparison of rate coefficients of plasma processes and optical emission spectroscopy of lowest singlet and triplet transitions, i.e. Lyman-band ($B^1\\Sigma^+_u \\rightarrow X^1\\Sigma^+_g$) and molecular continuum ($a^3\\Sigma^+_g \\rightarrow b^3\\Sigma^+_u$), of the hydrogen molecule in VUV wavelength range. Comparison of rate coefficients of spin-allowed and/or spin-forbidden excitations reduces the uncertainty caused by the non-equilibrium distributions of electron energy and molecular vibrational level, which are typically known poorly in plasma sources. The described methods are applied to estimate the rates of various plasma processes in a filament arc discharge.

  2. VUV diagnostics of electron impact processes in low temperature molecular hydrogen plasma

    Science.gov (United States)

    Komppula, J.; Tarvainen, O.

    2015-08-01

    Novel methods for diagnostics of molecular hydrogen plasma processes, such as ionization, production of high vibrational levels, dissociation of molecules via excitation to singlet and triplet states and production of metastable states, are presented for molecular hydrogen plasmas in corona equilibrium. The methods are based on comparison of rate coefficients of plasma processes and optical emission spectroscopy of lowest singlet and triplet transitions, i.e. Lyman band ({{B}1}?\\text{u}+\\to {{X}1}?\\text{g}+ ) and molecular continuum ({{a}3}?\\text{g}+\\to {{b}3}?\\text{u}+ ), of the hydrogen molecule in the VUV wavelength range. Comparison of rate coefficients of spin-allowed and/or spin-forbidden excitations reduces the uncertainty caused by the non-equilibrium distributions of electron energy and molecular vibrational level, which are typically known poorly in plasma sources. The described methods are applied to estimate the rates of various plasma processes in a filament arc discharge.

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

    Science.gov (United States)

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

    2013-03-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Lundberg, D. P.; Kaita, R.; Majeski, R. M.; Stotler, D. P.

    2010-06-28

    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.

  5. Benchmark values for molecular two-electron integrals arising from the Dirac equation.

    Science.gov (United States)

    Ba?c?, A; Hoggan, P E

    2015-02-01

    The two-center two-electron Coulomb and hybrid integrals arising in relativistic and nonrelativistic ab initio calculations on molecules are evaluated. Compact, arbitrarily accurate expressions are obtained. They are expressed through molecular auxiliary functions and evaluated with the numerical Global-adaptive method for arbitrary values of parameters in the noninteger Slater-type orbitals. Highly accurate benchmark values are presented for these integrals. The convergence properties of new molecular auxiliary functions are investigated. The comparison for two-center two-electron integrals is made with results obtained from single center expansions by translation of the wave function to a single center with integer principal quantum numbers and results obtained from the Cuba numerical integration algorithm, respectively. The procedures discussed in this work are capable of yielding highly accurate two-center two-electron integrals for all ranges of orbital parameters. PMID:25768632

  6. 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

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

    International Nuclear Information System (INIS)

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

  8. Secondary electron emission from solid molecular hydrogen under the bombardment by high-energy charged particles

    International Nuclear Information System (INIS)

    The theory has been developed of secondary electron emission from solid molecular hydrogen occurring under the bombardment by high-energy charged particles. The solution of equation of low-energy secondary electrons transfer to the surface, fitting the needed boundary conditions, is found by the methods of transport linear theory. The expression is obtained for flux density of electrons escaping from the surface of the material. The value of the surface potential barrier is calculated at the environment-vacuum interface. It is shown that the expression for the angular and energy distributions of the electrons which escaped from the target comprises two summands. The first summand corresponds to the particles, multiply scattered on hydrogen molecules, the second one corresponds to electrons, which escaped from the material unscattered

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

    Science.gov (United States)

    Ben-Nun, M; Mills, J D; Hinde, R J; Winstead, C L; Boatz, J A; Gallup, G A; Langhoff, P W

    2009-07-01

    Recent progress is reported in development of ab initio computational methods for the electronic structures of molecules employing the many-electron eigenstates of constituent atoms in spectral-product forms. The approach provides a universal atomic-product description of the electronic structure of matter as an alternative to more commonly employed valence-bond- or molecular-orbital-based representations. The Hamiltonian matrix in this representation is seen to comprise a sum over atomic energies and a pairwise sum over Coulombic interaction terms that depend only on the separations of the individual atomic pairs. Overall electron antisymmetry can be enforced by unitary transformation when appropriate, rather than as a possibly encumbering or unnecessary global constraint. The matrix representative of the antisymmetrizer in the spectral-product basis, which is equivalent to the metric matrix of the corresponding explicitly antisymmetric basis, provides the required transformation to antisymmetric or linearly independent states after Hamiltonian evaluation. Particular attention is focused in the present report on properties of the metric matrix and on the atomic-product compositions of molecular eigenstates as described in the spectral-product representations. Illustrative calculations are reported for simple but prototypically important diatomic (H(2), CH) and triatomic (H(3), CH(2)) molecules employing algorithms and computer codes devised recently for this purpose. This particular implementation of the approach combines Slater-orbital-based one- and two-electron integral evaluations, valence-bond constructions of standard tableau functions and matrices, and transformations to atomic eigenstate-product representations. The calculated metric matrices and corresponding potential energy surfaces obtained in this way elucidate a number of aspects of the spectral-product development, including the nature of closure in the representation, the general redundancy or linear dependence of its explicitly antisymmetrized form, the convergence of the apparently disparate atomic-product and explicitly antisymmetrized atomic-product forms to a common invariant subspace, and the nature of a chemical bonding descriptor provided by the atomic-product compositions of molecular eigenstates. Concluding remarks indicate additional studies in progress and the prognosis for performing atomic spectral-product calculations more generally and efficiently. PMID:19552480

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

    Science.gov (United States)

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

    2011-01-14

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

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

    International Nuclear Information System (INIS)

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

  12. The influence of finite lifetime of electronic states on the vibrational structure of molecular electronic spectra

    International Nuclear Information System (INIS)

    A general theory describing the effect of finite lifetime of electronic states on the vibrational structure of electronic spectra is developed. A proper description of the decay of the excited state involved in the transition is achieved by summing the perturbation series for the T matrix to infinte order in the interaction responsible for the decay. An effective non-hermitian Hamiltonian is obtained which describes the vibrational motion in the short-lived electronic state. The finite lifetime influences the spectra in a different way, depending whether the short-lived state is the final or the initial state of the electronic transition. In the former case the spectrum given by an incoherent superposition of lorentzian lines, while in the latter case there are interferences between the vibrational levels of the short-lived electronic state which modify the vibrational structure in a characteristic manner. The theory is applied to various spectra of CO and N2 involving the excitation of K-shell electrons. (Auth.)

  13. Well-ordered monolayers of alkali-doped coronene and picene: Molecular arrangements and electronic structures

    International Nuclear Information System (INIS)

    Adsorptions of alkali metals (such as K and Li) on monolayers of coronene and picene realize the formation of ordered phases, which serve as well-defined model systems for metal-intercalated aromatic superconductors. Upon alkali-doping of the monolayers of coronene and picene, scanning tunneling microscopy and X-ray absorption spectroscopy revealed the rearrangement of the entire molecular layer. The K-induced reconstruction of both monolayers resulted in the formation of a structure with a herringbone-like arrangement of molecules, suggesting the intercalation of alkali metals between molecular planes. Upon reconstruction, a shift in both the vacuum level and core levels of coronene was observed as a result of a charge transfer from alkali metals to coronene. In addition, a new density of states near the Fermi level was formed in both the doped coronene and the doped picene monolayers. This characteristic electronic feature of the ordered monolayer has been also reported in the multilayer picene films, ensuring that the present monolayer can model the properties of the metal-intercalated aromatic hydrocarbons. It is suggested that the electronic structure near the Fermi level is sensitive to the molecular arrangement, and that both the strict control and determinations of the molecular structure in the doped phase should be important for the determination of the electronic structure of these materials

  14. 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)

  15. Well-ordered monolayers of alkali-doped coronene and picene: Molecular arrangements and electronic structures

    Energy Technology Data Exchange (ETDEWEB)

    Yano, M.; Endo, M.; Hasegawa, Y.; Okada, R.; Yamada, Y., E-mail: yamada@bk.tsukuba.ac.jp; Sasaki, M. [Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan)

    2014-07-21

    Adsorptions of alkali metals (such as K and Li) on monolayers of coronene and picene realize the formation of ordered phases, which serve as well-defined model systems for metal-intercalated aromatic superconductors. Upon alkali-doping of the monolayers of coronene and picene, scanning tunneling microscopy and X-ray absorption spectroscopy revealed the rearrangement of the entire molecular layer. The K-induced reconstruction of both monolayers resulted in the formation of a structure with a herringbone-like arrangement of molecules, suggesting the intercalation of alkali metals between molecular planes. Upon reconstruction, a shift in both the vacuum level and core levels of coronene was observed as a result of a charge transfer from alkali metals to coronene. In addition, a new density of states near the Fermi level was formed in both the doped coronene and the doped picene monolayers. This characteristic electronic feature of the ordered monolayer has been also reported in the multilayer picene films, ensuring that the present monolayer can model the properties of the metal-intercalated aromatic hydrocarbons. It is suggested that the electronic structure near the Fermi level is sensitive to the molecular arrangement, and that both the strict control and determinations of the molecular structure in the doped phase should be important for the determination of the electronic structure of these materials.

  16. Spectroscopic mapping and selective electronic tuning of molecular orbitals in phosphorescent organometallic complexes – a new strategy for OLED materials

    OpenAIRE

    Ewen, Pascal R; Sanning, Jan; Koch, Tobias; Doltsinis, Nikos L; Strassert, Cristian A.; Wegner, Daniel

    2014-01-01

    The improvement of molecular electronic devices such as organic light-emitting diodes requires fundamental knowledge about the structural and electronic properties of the employed molecules as well as their interactions with neighboring molecules or interfaces. We show that highly resolved scanning tunneling microscopy (STM) and spectroscopy (STS) are powerful tools to correlate the electronic properties of phosphorescent complexes (i.e., triplet emitters) with their molecular structure as we...

  17. Modelling the effect of structure and base sequence on DNA molecular electronics

    International Nuclear Information System (INIS)

    DNA is a material that has the potential to be used in nanoelectronic devices as an active component. However, the electronic properties of DNA responsible for its conducting behaviour remain controversial. Here we use a self-consistent quantum molecular dynamics method to study the effect of DNA structure and base sequence on the energy involved when electrons are added or removed from isolated molecules and the transfer of the injected charge along the molecular axis when an electric field is applied. Our results show that the addition or removal of an electron from DNA molecules is most exothermic for poly(dC)-poly(dG) in its B-form and poly(dA)-poly(dT) in its A-form, and least exothermic in its Z-form. Additionally, when an electric field is applied to a charged DNA molecule along its axis, there is electron transfer through the molecule, regardless of the number and sign of the injected charge, the molecular structure and the base sequence. Results from these simulations provide useful information that is hard to obtain from experiments and needs to be considered for further modelling aiming to improve charge transport efficiency in nanoelectronic devices based on DNA

  18. In vivo demonstration of injectable microstimulators based on charge-balanced rectification of epidermically applied currents

    Science.gov (United States)

    Ivorra, Antoni; Becerra-Fajardo, Laura; Castellví, Quim

    2015-12-01

    Objective. It is possible to develop implantable microstimulators whose actuation principle is based on rectification of high-frequency (HF) current bursts supplied through skin electrodes. This has been demonstrated previously by means of devices consisting of a single diode. However, previous single diode devices caused dc currents which made them impractical for clinical applications. Here flexible thread-like stimulation implants which perform charge balance are demonstrated in vivo. Approach. The implants weigh 40.5 mg and they consist of a 3 cm long tubular silicone body with a diameter of 1 mm, two electrodes at opposite ends, and, within the central section of the body, an electronic circuit made up of a diode, two capacitors, and a resistor. In the present study, each implant was percutaneously introduced through a 14 G catheter into either the gastrocnemius muscle or the cranial tibial muscle of a rabbit hindlimb. Then stimulation was performed by delivering HF bursts (amplitude development of minimally invasive implantable devices for neuroprostheses based on electrical stimulation. The proposed methodology is intended to relieving such bottleneck. In terms of mass, thinness, and flexibility, the demonstrated implants appear to be unprecedented among the intramuscular stimulation implants ever assayed in vertebrates.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2007-03-01

    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.

  20. Controlling spin-polarized electron transport through a molecule: The role of molecular conformation

    Science.gov (United States)

    Senapati, L.; Pati, R.; Erwin, S. C.

    2007-07-01

    We investigate theoretically the spin-polarized electron transport through a complex organic molecule coupled to magnetic contacts. Our focus is on how low-energy deformations of the molecule affect the current-voltage characteristics and the magnetotransport of this molecular-scale device. We find that fairly modest deformations, costing only a few tens of meVs, can substantially change the tunneling current—by factors of 2 or more. Such deformations have still larger impact on the magnetoresistance, with small changes in molecular conformation even leading to changes in the sign of the magnetoresistance.

  1. Self-assembled molecular rafts at liquid|liquid interfaces for four-electron oxygen reduction.

    Science.gov (United States)

    Olaya, Astrid J; Schaming, Delphine; Brevet, Pierre-Francois; Nagatani, Hirohisa; Zimmermann, Tomas; Vanicek, Jiri; Xu, Hai-Jun; Gros, Claude P; Barbe, Jean-Michel; Girault, Hubert H

    2012-01-11

    The self-assembly of the oppositely charged water-soluble porphyrins, cobalt tetramethylpyridinium porphyrin (CoTMPyP(4+)) and cobalt tetrasulphonatophenyl porphyrin (CoTPPS(4-)), at the interface with an organic solvent to form molecular "rafts", provides an excellent catalyst to perform the interfacial four-electron reduction of oxygen by lipophilic electron donors such as tetrathiafulvalene (TTF). The catalytic activity and selectivity of the self-assembled catalyst toward the four-electron pathway was found to be as good as that of the Pacman type cofacial cobalt porphyrins. The assembly has been characterized by UV-visible spectroscopy, Surface Second Harmonic Generation, and Scanning Electron Microscopy. Density functional theory calculations confirm the possibility of formation of the catalytic CoTMPyP(4+)/ CoTPPS(4-) complex and its capability to bind oxygen. PMID:22107335

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

    International Nuclear Information System (INIS)

    A Monte Carlo approach is used to obtain the energy spreading and angular distribution of initially monoenergetic and monodirectional beams of electrons 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

  3. Effects of intense femtosecond pumping on ultrafast electronic-vibrational dynamics in molecular systems with relaxation.

    Science.gov (United States)

    Egorova, Dassia; Gelin, Maxim F; Thoss, Michael; Wang, Haobin; Domcke, Wolfgang

    2008-12-01

    We investigate the influence of strong femtosecond optical pulses on the ultrafast dynamics of molecular systems. The study is based on a series of generic molecular models of increasing complexity, which incorporate multiple and mutually coupled electronic states, electronic-vibrational interaction, and vibrational relaxation. The influence of vibrational relaxation is treated using multilevel Redfield theory. Comparisons to benchmark results of the multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) method demonstrate the validity of the field-free implementation of Redfield theory employed in this work for weak system-bath interaction. The calculated electronic population and vibrational wave-packet dynamics demonstrate the intricate interplay of strong-field excitation, laser-induced Rabi oscillations, electronic interaction, vibronic coupling, and dissipation. In particular, we show that the interaction with a strong laser pulse may result in pronounced coherent vibrational motion in a dissipative system, even for laser pulses that are longer than the vibrational period. Furthermore, vibrational relaxation in combination with strong laser pulse excitation can lead to revivals of the electronic population after the excitation pulse is over. PMID:19063557

  4. Quantum chemistry the development of ab initio methods in molecular electronic structure theory

    CERN Document Server

    Schaefer III, Henry F

    2004-01-01

    This guide is guaranteed to prove of keen interest to the broad spectrum of experimental chemists who use electronic structure theory to assist in the interpretation of their laboratory findings. A list of 150 landmark papers in ab initio molecular electronic structure methods, it features the first page of each paper (which usually encompasses the abstract and introduction). Its primary focus is methodology, rather than the examination of particular chemical problems, and the selected papers either present new and important methods or illustrate the effectiveness of existing methods in predi

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

    CERN Document Server

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

    2000-01-01

    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.

  6. Molecular solution approach to synthesize electronic quality Cu2ZnSnS4 thin films.

    Science.gov (United States)

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

    2013-05-01

    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

  7. Diffractive imaging of a molecular rotational wavepacket with femtosecond Megaelectronvolt electron pulses

    CERN Document Server

    Yang, Jie; Vecchione, Theodore; Robinson, Matthew S; Li, Renkai; Hartmann, Nick; Shen, Xiaozhe; Coffee, Ryan; Corbett, Jeff; Fry, Alan; Gaffney, Kelly; Gorkhover, Tais; Hast, Carsten; Jobe, Keith; Makasyuk, Igor; Reid, Alexander; Robinson, Joseph; Vetter, Sharon; Wang, Fenglin; Weathersby, Stephen; Yoneda, Charles; Centurion, Martin; Wang, Xijie

    2015-01-01

    Imaging changes in molecular geometries on their natural femtosecond timescale with sub-Angstrom spatial precision is one of the critical challenges in the chemical sciences, since the nuclear geometry changes determine the molecular reactivity. For photoexcited molecules, the nuclear dynamics determine the photoenergy conversion path and efficiency. We performed a gas-phase electron diffraction experiment using Megaelectronvolt (MeV) electrons, where we captured the rotational wavepacket dynamics of nonadiabatically laser-aligned nitrogen molecules. We achieved an unprecedented combination of 100 fs root-mean-squared (RMS) temporal resolution and sub-Angstrom (0.76 {\\AA}) spatial resolution that makes it possible to resolve the position of the nuclei within the molecule. In addition, the diffraction patterns reveal the angular distribution of the molecules, which changes from prolate (aligned) to oblate (anti-aligned) in 300 fs. Our results demonstrate a significant and promising step towards making atomical...

  8. Electronic structure of the molecular switch tetra-tert-butyl-azobenzene adsorbed on Ag(111)

    Energy Technology Data Exchange (ETDEWEB)

    Tegeder, P.; Hagen, S.; Leyssner, F.; Wolf, M. [Freie Universitaet Berlin, Fachbereich Physik, Berlin (Germany); Peters, M.V.; Hecht, S. [Max-Planck-Institut fuer Kohlenforschung, Muelheim an der Ruhr (Germany); Klamroth, T.; Saalfrank, P. [Universitaet Potsdam, Theoretische Chemie, Institut fuer Chemie, Potsdam-Golm (Germany)

    2007-08-15

    Occupied and unoccupied electronic states in tetra-tert-butyl-azobenzene (TBA) absorbed on Ag(111) have been investigated by one-photon and two-photon photoemission spectroscopy. These measurements allow the quantitative determination of energetic positions of the highest occupied (HOMO) and the lowest unoccupied molecular orbital (LUMO) as well as the n=1 image potential state. The assignment of the electronic states are supported by quantum chemical calculations. Experimentally a HOMO-LUMO gap of 2.85 eV is observed, whereas the gap obtained from the calculated molecular orbital energies is 0.92 eV larger. This discrepancy can be explained by image charge screening. Furthermore, two unoccupied final states located 0.18 and 0.43 eV above the vacuum level, respectively, have been identified. (orig.)

  9. Systematics in a measurement of the electron's electric dipole moment using trapped molecular ions

    Science.gov (United States)

    Grau, Matt; Cossel, Kevin; Cairncross, William; Gresh, Dan; Zhou, Yan; Ye, Jun; Cornell, Eric

    2015-05-01

    A precision measurement of the electron's electric dipole moment (EDM) has important implications for physics beyond the Standard Model. Trapped molecular ions offer high sensitivity in such an experiment because of the large effective electric fields and long coherence times that are possible. Our experiment uses Ramsey spectroscopy of HfF+ ions in a linear RF trap with rotating bias fields, achieving coherence times beyond 1 second for 1000 trapped ions. Compared to other electron EDM experiments that use molecular beams, we will be sensitive to a different class of systematic errors. In this work we investigate systematic errors arising from all fields involved in the experiment, including the trapping and polarizing electric fields, magnetic field gradients, and motional effects such as geometric phases. This work was supported by NIST and NSF.

  10. A quantum simulator for molecules: Imaging molecular orbitals and electronic dynamics with ultracold atoms

    CERN Document Server

    Lühmann, Dirk-Sören; Sengstock, Klaus

    2015-01-01

    In the recent years, ultracold atoms in optical lattices have proven their great value as quantum simulators for studying strongly-correlated phases and complex phenomena in solid-state systems. Here we reveal their potential as quantum simulators for molecular physics and propose a technique to image the three-dimensional molecular orbitals with high resolution. The outstanding tunability of ultracold atoms in terms of potential and interaction offer fully-adjustable model systems for gaining deep insight into the electronic structure of molecules. We study the orbitals of an artificial benzene molecule and discuss the effect of tunable interactions in its conjugated pi electron system with special regard to localization and spin order. The dynamical timescale of ultracold atom simulators are on the order milliseconds which allow for the time-resolved monitoring of a broad range of dynamical processes. As an example, we compute the hole dynamics in the conjugated pi system of the artificial benzene molecule.

  11. Macroscopic quantum coherence in a single molecular magnet and Kondo effect of electron transport

    International Nuclear Information System (INIS)

    We report a Kondo-effect study of electron transport through a quantum dot with embedded biaxial single-molecule magnet based on slave boson mean-field theory and non-equilibrium Green-function technique. It is found the macroscopic quantum coherence of molecule-magnet results in the Kondo peak split of differential conductance due to interaction between electron and molecular magnet. It is also demonstrated that both the peak height and position can be controlled by the sweeping magnetic field and polarization of ferromagnetic electrodes. The characteristic peak split may be used to identify the macroscopic quantum coherence and develop molecule devices. -- Highlights: ? Splits of Kondo peak are induced by the single molecular magnet. ? Kondo effect can be controlled by magnetic field and its sweeping speed in our model. ? The suppression and broadening of Kondo peaks is also observed with increase of temperature. ? The peaks height and position is sensitive to polarization of the electrode.

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

    CERN Document Server

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

    2009-01-01

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

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

    CERN Document Server

    Tarana, Michal

    2013-01-01

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

  14. Heavy-Core Staffanes : A Computational Study of Their Fundamental Properties of Interest for Molecular Electronics

    OpenAIRE

    Sandström, Niclas

    2007-01-01

    The basic building blocks in molecular electronics often correspond to conjugated molecules. A compound class consisting of rigid rod-like staffane molecules with the heavier Group 14 elements Si, Ge, Sn and Pb at their bridgehead positions has now been investigated. Herein these oligomers are called heavy-core or Si-, Ge-, Sn- or Pb-core staffanes. These compounds benefit from interaction through their bicyclo[1.1.1]pentane monomer units. Quantum chemical calculations were performed to probe...

  15. Light Quasiparticles Dominate Electronic Transport in Molecular Crystal Field-Effect Transistors

    OpenAIRE

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

    2007-01-01

    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* comparable to free electron mass. Furthermore, the m* values inferred from our experiments are in agreement with those determin...

  16. Quantum mechanical study of molecular switches : electronic structure, kinetics and dynamical aspects

    OpenAIRE

    Doki?, Jadranka

    2009-01-01

    Molecular photoswitches are attracting much attention lately mostly because of their possible applications in nano technology, and their role in biology. One of the widely studied representatives of photochromic molecules is azobenzene (AB). With light, by a static electric field, or with tunneling electrons this specie can be "switched" from the flat and energetically more stable trans form, into the compact cis form. The back reaction can be induced optically or thermally. Quantum chemic...

  17. Electron Paramagnetic Resonance Linewidths and Lineshapes for the Molecular Magnets Fe8 and Mn12

    OpenAIRE

    Park, Kyungwha; Novotny, M. A.; Dalal, N. S.; Hill, S.; Rikvold, P. A.

    2001-01-01

    We study theoretically Electron Paramagentic Resonance (EPR) linewidths for single crystals of the molecular magnets Fe$_8$ and Mn$_{12}$ as functions of energy eigenstates $M_s$, frequency, and temperature when a magnetic field along the easy axis is swept at fixed excitation frequency. This work was motivated by recent EPR experiments. To calculate the linewidths, we use density-matrix equations, including dipolar interactions and distributions of the uniaxial anisotropy p...

  18. The effect of molecular mobility on electronic transport in carbon nanotube-polymer composites and networks

    International Nuclear Information System (INIS)

    A multiscale modeling approach to the prediction of electrical conductivity in carbon nanotube (CNT)–polymer composite materials is developed, which takes into account thermally activated molecular mobility of the matrix and the CNTs. On molecular level, a tight-binding density functional theory and non-equilibrium Green's function method are used to calculate the static electron transmission function in the contact between two metallic carbon nanotubes that corresponds to electron transport at 0?K. For higher temperatures, the statistical distribution of effective contact resistances is considered that originates from thermal fluctuations of intermolecular distances caused by molecular mobility of carbon nanotube and the polymer matrix. Based on this distribution and using effective medium theory, the temperature dependence of macroscopic electrical resistivity for CNT-polymer composites and CNT mats is calculated. The predicted data indicate that the electrical conductivity of the CNT-polymer composites increases linearly with temperature above 50?K, which is in a quantitative agreement with the experiments. Our model predicts a slight nonlinearity in temperature dependence of electric conductivity at low temperatures for percolated composites with small CNT loading. The model also explains the effect of glass transition and other molecular relaxation processes in the polymer matrix on the composite electrical conductivity. The developed multiscale approach integrates the atomistic charge transport mechanisms in percolated CNT-polymer composites with the macroscopic response and thus enables direct comparison of the prediction with the measurements of macroscopic material properties

  19. The effect of molecular mobility on electronic transport in carbon nanotube-polymer composites and networks

    Science.gov (United States)

    Shenogin, Sergei; Lee, Jonghoon; Voevodin, Andrey A.; Roy, Ajit K.

    2014-12-01

    A multiscale modeling approach to the prediction of electrical conductivity in carbon nanotube (CNT)-polymer composite materials is developed, which takes into account thermally activated molecular mobility of the matrix and the CNTs. On molecular level, a tight-binding density functional theory and non-equilibrium Green's function method are used to calculate the static electron transmission function in the contact between two metallic carbon nanotubes that corresponds to electron transport at 0 K. For higher temperatures, the statistical distribution of effective contact resistances is considered that originates from thermal fluctuations of intermolecular distances caused by molecular mobility of carbon nanotube and the polymer matrix. Based on this distribution and using effective medium theory, the temperature dependence of macroscopic electrical resistivity for CNT-polymer composites and CNT mats is calculated. The predicted data indicate that the electrical conductivity of the CNT-polymer composites increases linearly with temperature above 50 K, which is in a quantitative agreement with the experiments. Our model predicts a slight nonlinearity in temperature dependence of electric conductivity at low temperatures for percolated composites with small CNT loading. The model also explains the effect of glass transition and other molecular relaxation processes in the polymer matrix on the composite electrical conductivity. The developed multiscale approach integrates the atomistic charge transport mechanisms in percolated CNT-polymer composites with the macroscopic response and thus enables direct comparison of the prediction with the measurements of macroscopic material properties.

  20. The effect of molecular mobility on electronic transport in carbon nanotube-polymer composites and networks

    Energy Technology Data Exchange (ETDEWEB)

    Shenogin, Sergei, E-mail: sergei.shenogin.ctr.ru@us.af.mil [Air Force Research Laboratory, Materials and Manufacturing Directorate, 2941 Hobson Way, Wright-Patterson Air Force Base, Ohio 45433 (United States); University of Dayton Research Institute, 300 College Park, Dayton, Ohio 45469 (United States); Lee, Jonghoon [Air Force Research Laboratory, Materials and Manufacturing Directorate, 2941 Hobson Way, Wright-Patterson Air Force Base, Ohio 45433 (United States); UTC, Inc., 1270 N Fairfield Rd, Dayton, Ohio 45432 (United States); Voevodin, Andrey A.; Roy, Ajit K. [Air Force Research Laboratory, Materials and Manufacturing Directorate, 2941 Hobson Way, Wright-Patterson Air Force Base, Ohio 45433 (United States)

    2014-12-21

    A multiscale modeling approach to the prediction of electrical conductivity in carbon nanotube (CNT)–polymer composite materials is developed, which takes into account thermally activated molecular mobility of the matrix and the CNTs. On molecular level, a tight-binding density functional theory and non-equilibrium Green's function method are used to calculate the static electron transmission function in the contact between two metallic carbon nanotubes that corresponds to electron transport at 0?K. For higher temperatures, the statistical distribution of effective contact resistances is considered that originates from thermal fluctuations of intermolecular distances caused by molecular mobility of carbon nanotube and the polymer matrix. Based on this distribution and using effective medium theory, the temperature dependence of macroscopic electrical resistivity for CNT-polymer composites and CNT mats is calculated. The predicted data indicate that the electrical conductivity of the CNT-polymer composites increases linearly with temperature above 50?K, which is in a quantitative agreement with the experiments. Our model predicts a slight nonlinearity in temperature dependence of electric conductivity at low temperatures for percolated composites with small CNT loading. The model also explains the effect of glass transition and other molecular relaxation processes in the polymer matrix on the composite electrical conductivity. The developed multiscale approach integrates the atomistic charge transport mechanisms in percolated CNT-polymer composites with the macroscopic response and thus enables direct comparison of the prediction with the measurements of macroscopic material properties.

  1. Theoretical Study of Molecular and Electronic Structures of 51 Knot Systems: Two?Layered ONIOM Calculations

    Scientific Electronic Library Online (English)

    Aguinaldo R. de, Souza; Nelson H., Morgon.

    2015-05-01

    Full Text Available In this study we examine the electronic and molecular structures of the [51 knot···(PF6)10]+ pentafoil knot system and report calculated interaction energies that result from halides (X = F, Cl, Br, and I) localized at the center of the [51 knot···(PF6)9]X molecular structure. The equilibrium geomet [...] ries were fully optimized at the ONIOM(M06/6-31G(2d,p):PM6) level of theory, starting from an initial geometry for the pentafoil knot obtained from experimental X-ray data. The molecular systems were divided into two layers, for which the M06/6-31G(2d,p) level of theory was used to describe the high layer ([C4H6]5X- structure) and the PM6 semiempirical method was employed for the low layer. The calculated electronic energies show that the interaction between the fluorine anion and the pentafoil knot produces the most stable structure, whereas an unfavorable interaction is observed for iodide due to the diffuse character of its electronic cloud. Using basis set superposition error (BSSE) correction techniques, the observed values of the interaction are -0.201 hartrees for the fluoride ion and -0.100 hartrees for iodide.

  2. Low-voltage electron microscopy of polymer and organic molecular thin films

    International Nuclear Information System (INIS)

    We have demonstrated the capabilities of a novel low-voltage electron microscope (LVEM) for imaging polymer and organic molecular thin films. The LVEM can operate in transmission electron microscopy, scanning transmission electron microscopy, scanning electron microscopy, and electron diffraction modes. The microscope operates at a nominal accelerating voltage of 5 kV and fits on a tabletop. A detailed discussion of the electron-sample interaction processes is presented, and the mean free path for total electron scattering was calculated to be 15 nm for organic samples at 5 kV. The total end point dose for the destruction of crystallinity at 5 kV was estimated at 5x10-4 and 3.5x10-2 C/cm2 for polyethylene and pentacene, respectively. These values are significantly lower than those measured at voltages greater than 100 kV. A defocus series of colloidal gold particles allowed us to estimate the experimental contrast transfer function of the microscope. Images taken of several organic materials have shown high contrast for low atomic number elements and a resolution of 2.5 nm. The materials studied here include thin films of the organic semiconductor pentacene, triblock copolymer films, single-molecule dendrimers, electrospun polymer fibers and gold nanoparticles

  3. Carbon Electrode-Molecule Junctions: A Reliable Platform for Molecular Electronics.

    Science.gov (United States)

    Jia, Chuancheng; Ma, Bangjun; Xin, Na; Guo, Xuefeng

    2015-09-15

    The development of reliable approaches to integrate individual or a small collection of molecules into electrical nanocircuits, often termed "molecular electronics", is currently a research focus because it can not only overcome the increasing difficulties and fundamental limitations of miniaturization of current silicon-based electronic devices, but can also enable us to probe and understand the intrinsic properties of materials at the atomic- and/or molecular-length scale. This development might also lead to direct observation of novel effects and fundamental discovery of physical phenomena that are not accessible by traditional materials or approaches. Therefore, researchers from a variety of backgrounds have been devoting great effort to this objective, which has started to move beyond simple descriptions of charge transport and branch out in different directions, reflecting the interdisciplinarity. This Account exemplifies our ongoing interest and great effort in developing efficient lithographic methodologies capable of creating molecular electronic devices through the combination of top-down micro/nanofabrication with bottom-up molecular assembly. These devices use nanogapped carbon nanomaterials (such as single-walled carbon nanotubes (SWCNTs) and graphene), with a particular focus on graphene, as point contacts formed by electron beam lithography and precise oxygen plasma etching. Through robust amide linkages, functional molecular bridges terminated with diamine moieties are covalently wired into the carboxylic acid-functionalized nanogaps to form stable carbon electrode-molecule junctions with desired functionalities. At the macroscopic level, to improve the contact interface between electrodes and organic semiconductors and lower Schottky barriers, we used SWCNTs and graphene as efficient electrodes to explore the intrinsic properties of organic thin films, and then build functional high-performance organic nanotransistors with ultrahigh responsivities. At the molecular level, to form robust covalent bonds between electrodes and molecules and improve device stability, we developed a reliable system to immobilize individual molecules within a nanoscale gap of either SWCNTs or graphene through covalent amide bond formation, thus affording two classes of carbon electrode-molecule single-molecule junctions. One unique feature of these devices is the fact that they contain only one or two molecules as conductive elements, thus forming the basis for building new classes of chemo/biosensors with ultrahigh sensitivity. We have used these approaches to reveal the dependence of the charge transport of individual metallo-DNA duplexes on ?-stacking integrity, and fabricate molecular devices capable of realizing label-free, real-time electrical detection of biological interactions at the single-event level, or switching their molecular conductance upon exposure to external stimuli, such as ion, pH, and light. These investigations highlight the unique advantages and importance of these universal methodologies to produce functional carbon electrode-molecule junctions in current and future researches toward the development of practical molecular devices, thus offering a reliable platform for molecular electronics and the promise of a new generation of multifunctional integrated circuits and sensors. PMID:26190024

  4. A low-loss hybrid rectification technique for piezoelectric energy harvesting

    International Nuclear Information System (INIS)

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

  5. Oxidation of Electron Donor-Substituted Verdazyls: Building Blocks for Molecular Switches.

    Science.gov (United States)

    Haller, Benjamin C; Chambers, Dallas; Cheng, Ran; Chemistruck, Victoria; Hom, Timothy F; Li, Zhengzheng; Nguyen, Jeffrey; Ichimura, Andrew; Brook, David J R

    2015-10-29

    Species that can undergo changes in electronic configuration as a result of an external stimulus such as pH or solvent polarity can play an important role in sensors, conducting polymers, and molecular switches. One way to achieve such structures is to couple two redox-active fragments, where the redox activity of one of them is strongly dependent upon environment. We report on two new verdazyls, one subsituted with a di-tert-butyl phenol group and the other with a dimethylaminophenyl group, that have the potential for such behavior upon oxidation. Oxidation of both verdazyls with copper(II) triflate in acetonitrile gives diamagnetic verdazylium ions characterized by NMR and UV-vis spectroscopies. Deprotonation of the phenol-verdazylium results in electron transfer and a switch from a singlet state to a paramagnetic triplet diradical identified by electron spin resonance. The dimethylaminoverdazylium 9 has a diamagnetic ground state, in line with predictions from simple empirical methods and supported by density functional theory calculations. These results indicate that verdazyls may complement nitroxides as spin carriers in the design of organic molecular electronics. PMID:26451688

  6. Secondary ion and electron yield measurements for surfaces bombarded with large molecular ions

    International Nuclear Information System (INIS)

    Secondary-ion and secondary-electron emission yields from surfaces bombarded with large molecular ions have been measured in a tandem time-of-flight mass spectrometer. The primary ions were produced by matrix-assisted laser desorption/ionization and ranged in mass from about 6000 to 110 000 u, and in energy from 5 to 25 keV. The yields were measured for surfaces of stainless steel and CsI in modest vacuum conditions. Electron and ion emission were observed for incident velocities as low as 3.5 km/s (0.06 eV/u). For a given energy, the yields decrease rapidly with increasing mass in the low mass range, but for large incident projectiles at 25 keV (or higher), the efficiency of secondary ion production is more or less constant near unity. The efficiency of secondary electron production continues to decrease slowly with increasing mass, but remains >?30% throughout the mass range typically encountered in mass spectrometry of proteins (i.e. molecular weight 0.1 eV/u). For high velocities, the yield of electrons and ions is significantly higher for a CsI surface compared to stainless steel, but for velocities corresponding to

  7. Relation between molecular electrostatic potential, several electronic properties and antibacterial activity of some synthetic furane derivatives

    Science.gov (United States)

    Monasterios, Melina; Avendaño, Milagros; Amaro, María Isabel; Infante, Wilson; Charris, Jaime

    2006-10-01

    The present work reports the preliminary evaluation of the antibacterial activity, molecular electrostatic potential (MEP) determination and relevant electronic properties for their behavior as one electron acceptor, of a serial of compounds, active and inactive analogues, derived form furan, that were previously synthesized within our investigation group, with the purpose of establishing the existence of a valid correlation between their antibacterial activity and those electrostatic and electronic properties. According to the balance between the positive and negative areas in combination with the size of the MEP's area it was determined that these derivatives exhibit activity against Gram-positive and Gram-negative bacteria or only against Gram-positive ones. We found no valid correlation between the single point energy, the energy associated to the lowest unoccupied molecular orbital (LUMO); LUMO's density, nucleophilic susceptibility, Log P and the dipole moment, with the experimental activity determined for them. This could be because this is an homologous serial where the properties derived from the electronic distribution just change between those molecules that have a nitro group (active) in contrast with those wherein this group is absent (inactive).

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

    Na, Jeong-Seok

    The work in this dissertation consists of a two-part study concerning molecular-based electronics and atomic layer deposition (ALD). As conventional "top-down" silicon-based technology approaches its expected physical and technical limits, researchers have paid considerable attention to "bottom-up" approaches including molecular-based electronics that self assembles molecular components and ALD techniques that deposit thin films with atomic layer control. Reliable fabrication of molecular-based devices and a lack of understanding of the conduction mechanisms through individual molecules still remain critical issues in molecular-based electronics. Nanoparticle/molecule(s)/nanoparticle assemblies of "dimers" and "trimers", consisting of two and three nanoparticles bridged by oligomeric ethynylene phenylene molecules (OPEs), respectively, are successfully synthesized by coworkers and applied to contact nanogap electrodes (slope at ˜1.5 V, indicating the transition from direct tunneling to Fowler-Nordheim tunneling. Monitoring of the conductance is also performed in real-time during trapping as well as during other modification and exposure sequences after trapping over short-term and long-term time scales. The real-time monitoring of conductance through dimer structures during trapping offers immediate detection of a specific fault which is ascribed to a loss of active molecules and fusing of the nanoparticles in the junction occurring mostly at a high applied voltage (?3 VAC). After successful trapping, the sample exposure to air reveals a small rapid decrease in current, followed by a slower exponential increase, and eventual current saturation. This work also reports on the dependence of electron transport on molecular length (2 to 4.7 nm) and structure (linear-type in dimers and Y-type in trimers). The extracted electronic decay constant of ˜0.12 A-1 and effective contact resistance of ˜4 MO indicate a strong electronic coupling between the chain ends, facilitating electron transport over long distances. A three terminal molecular transistor is also demonstrated with trimers trapped across nanogap electrodes. The source-drain current is modulated within a factor of 2 with a gate bias voltage of -2 to +2 V. A subthreshold slope of ˜110 mV/decade is obtained. Finally, we report on both fundamental understanding and application of atomic layer deposition. First, in situ analysis tools such as quartz crystal microbalance and electrical conductance measurements are combined to reveal direct links between surface reactions, charge transfer, and dopant incorporation during ZnO and ZnO:Al ALD. Second, the ability of ALD to form uniform and conformal coating onto complex nanostructures is explored to improve the ambient stability of single molecules/nanoparticle assemblies using Al2O3 ALD as an encapsulation layer. In addition, the ability to shield the surface polarity of ZnO nanostructures using Al 2O3 + ZnO ALD, leading to hierarchical morphology evolution from one-dimensional ZnO nanorods to three-dimensional ZnO nanosheets with branched nanorods during hydrothermal growth is investigated.

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

    International Nuclear Information System (INIS)

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

  11. Molecular structure and free energy landscape for electron transport in the decahaem cytochrome MtrF.

    Science.gov (United States)

    Breuer, Marian; Zarzycki, Piotr; Shi, Liang; Clarke, Thomas A; Edwards, Marcus J; Butt, Julea N; Richardson, David J; Fredrickson, James K; Zachara, John M; Blumberger, Jochen; Rosso, Kevin M

    2012-12-01

    The free energy profile for electron flow through the bacterial decahaem cytochrome MtrF has been computed using thermodynamic integration and classical molecular dynamics. The extensive calculations on two versions of the structure help to validate the method and results, because differences in the profiles can be related to differences in the charged amino acids local to specific haem groups. First estimates of reorganization free energies ? yield a range consistent with expectations for partially solvent-exposed cofactors, and reveal an activation energy range surmountable for electron flow. Future work will aim at increasing the accuracy of ? with polarizable forcefield dynamics and quantum chemical energy gap calculations, as well as quantum chemical computation of electronic coupling matrix elements. PMID:23176454

  12. Atomic and molecular complex resonances from real eigenvalues using standard (hermitian) electronic structure calculations

    CERN Document Server

    Landau, Arie; Kaprálová-Ž?ánská, Petra Ruth; Moiseyev, Nimrod

    2015-01-01

    Complex eigenvalues, resonances, play an important role in large variety of fields in physics and chemistry. For example, in cold molecular collision experiments and electron scattering experiments, autoionizing and pre-dissociative metastable resonances are generated. However, the computation of complex resonance eigenvalues is difficult, since it requires severe modifications of standard electronic structure codes and methods. Here we show how resonance eigenvalues, positions and widths, can be calculated using the standard, widely used, electronic-structure packages. Our method enables the calculations of the complex resonance eigenvalues by using analytical continuation procedures (such as Pad\\'{e}). The key point in our approach is the existence of narrow analytical passages from the real axis to the complex energy plane. In fact, the existence of these analytical passages relies on using finite basis sets. These passages become narrower as the basis set becomes more complete, whereas in the exact limit,...

  13. Ultrafast Photoinduced Symmetry-Breaking Charge Separation and Electron Sharing in Perylenediimide Molecular Triangles.

    Science.gov (United States)

    Wu, Yilei; Young, Ryan M; Frasconi, Marco; Schneebeli, Severin T; Spenst, Peter; Gardner, Daniel M; Brown, Kristen E; Würthner, Frank; Stoddart, J Fraser; Wasielewski, Michael R

    2015-10-21

    We report on a visible-light-absorbing chiral molecular triangle composed of three covalently linked 1,6,7,12-tetra(phenoxy)perylene-3,4:9,10-bis(dicarboximide) (PDI) units. The rigid triangular architecture reduces the electronic coupling between the PDIs, so ultrafast symmetry-breaking charge separation is kinetically favored over intramolecular excimer formation, as revealed by femtosecond transient absorption spectroscopy. Photoexcitation of the PDI triangle dissolved in CH2Cl2 gives PDI(+•)-PDI(-•) in ?CS = 12.0 ± 0.2 ps. Fast subsequent intramolecular electron/hole hopping can equilibrate the six possible energetically degenerate ion-pair states, as suggested by electron paramagnetic resonance/electron-nuclear double resonance spectroscopy, which shows that one-electron reduction of the PDI triangle results in complete electron sharing among the three PDIs. Charge recombination of PDI(+•)-PDI(-•) to the ground state occurs in ?CR = 1.12 ± 0.01 ns with no evidence of triplet excited state formation. PMID:26418462

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

    CERN Document Server

    Goliney, I Yu

    2014-01-01

    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.

  15. Influence of low-symmetry distortions on electron transport through metal atom chains: when is a molecular wire really "broken"?

    OpenAIRE

    2011-01-01

    In the field of molecular electronics, an intimate link between the delocalization of molecular orbitals and their ability to support current flow is often assumed. Delocalization, in turn, is generally regarded as being synonymous with structural symmetry, for example, in the lengths of the bonds along a molecular wire. In this work, we use density functional theory in combination with nonequilibrium Green's functions to show that precisely the opposite is true in the extended metal atom cha...

  16. Research on geometric rectification of the Large FOV Linear Array Whiskbroom Image

    Science.gov (United States)

    Liu, Dia; Liu, Hui-tong; Dong, Hao; Liu, Xiao-bo

    2015-08-01

    To solve the geometric distortion problem of large FOV linear array whiskbroom image, a model of multi center central projection collinearity equation was founded considering its whiskbroom and linear CCD imaging feature, and the principle of distortion was analyzed. Based on the rectification method with POS, we introduced the angular position sensor data of the servo system, and restored the geometric imaging process exactly. An indirect rectification scheme aiming at linear array imaging with best scanline searching method was adopted, matrixes for calculating the exterior orientation elements was redesigned. We improved two iterative algorithms for this device, and did comparison and analysis. The rectification for the images of airborne imaging experiment showed ideal effect.

  17. Radiative Thermal Rectification between SiC and SiO2

    CERN Document Server

    Joulain, Karl; Drevillon, Jérémie; Rousseau, Benoit; Meneses, Domingos De Sousa

    2015-01-01

    By means of fluctuationnal electrodynamics, we calculate radiative heat flux between two planar materials respectively made of SiC and SiO2. More specifically, we focus on a first (direct) situation where one of the two materials (for example SiC) is at ambient temperature whereas the second material is at a higher one, then we study a second (reverse) situation where the material temperatures are inverted. When the two fluxes corresponding to the two situations are different, the materials are said to exhibit a thermal rectification, a property with potential applications in thermal regulation. Rectification variations with temperature and separation distance are here reported. Calculations are performed using material optical data experimentally determined by Fourier transform emission spectrometry of heated materials between ambient temperature (around 300 K) and 1480 K. It is shown that rectification is much more important in the near-field domain, i.e. at separation distances smaller than the thermal wav...

  18. Nano-fabrication of molecular electronic junctions by targeted modification of metal-molecule bonds

    Science.gov (United States)

    Jafri, S. Hassan M.; Löfås, Henrik; Blom, Tobias; Wallner, Andreas; Grigoriev, Anton; Ahuja, Rajeev; Ottosson, Henrik; Leifer, Klaus

    2015-09-01

    Reproducibility, stability and the coupling between electrical and molecular properties are central challenges in the field of molecular electronics. The field not only needs devices that fulfill these criteria but they also need to be up-scalable to application size. In this work, few-molecule based electronics devices with reproducible electrical characteristics are demonstrated. Our previously reported 5?nm gold nanoparticles (AuNP) coated with ?-triphenylmethyl (trityl) protected 1,8-octanedithiol molecules are trapped in between sub-20?nm gap spacing gold nanoelectrodes forming AuNP-molecule network. When the trityl groups are removed, reproducible devices and stable Au-thiol junctions are established on both ends of the alkane segment. The resistance of more than 50 devices is reduced by orders of magnitude as well as a reduction of the spread in the resistance histogram is observed. By density functional theory calculations the orders of magnitude decrease in resistance can be explained and supported by TEM observations thus indicating that the resistance changes and strongly improved resistance spread are related to the establishment of reproducible and stable metal-molecule bonds. The same experimental sequence is carried out using 1,6-hexanedithiol functionalized AuNPs. The average resistances as a function of molecular length, demonstrated herein, are comparable to the one found in single molecule devices.

  19. Molecular potentials and wave function mapping by high-resolution electron spectroscopy and ab initio calculations

    Energy Technology Data Exchange (ETDEWEB)

    Kimberg, Victor, E-mail: victor.kimberg@pks.mpi.de [Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Straße 38, 01187 Dresden (Germany); Miron, Catalin, E-mail: miron@synchrotron-soleil.fr [Synchrotron SOLEIL, l’Orme des Merisiers, Saint-Aubin, BP 48, FR-91192 Gif-sur-Yvette Cedex (France)

    2014-08-15

    Highlights: • Some studies related to the vibrational wave functions mapping phenomenon are reviewed. • The core-excited vibrational wave functions were mapped using dissociative and bound final states. • High-resolution experimental data is accompanied by ab initio calculations. • The mapping phenomenon allows one to extract constants of the molecular potentials. • The mapping techniques are general and can be applied for the study of many systems. - Abstract: The recent development of high brightness 3{sup rd} generation soft X-ray sources and high energy resolution electron spectrometers made it possible to accurately trace quantum phenomena associated to the vibrational dynamics in core-excited molecules. The present paper reviews the recent results on mapping of vibrational wave functions and molecular potentials based on electron spectroscopy. We discuss and compare the mapping phenomena in various systems, stressing the advantages of the resonant X-ray scattering for studying of the nuclear dynamics and spectroscopic constants of small molecules. The experimental results discussed in the paper are most often accompanied by state-of-the-art ab initio calculations allowing for a deeper understanding of the quantum effects. Besides its fundamental interest, the vibrational wave function mapping is shown to be useful for the analysis of core- and valence-excited molecular states based on the reflection principle.

  20. Molecular potentials and wave function mapping by high-resolution electron spectroscopy and ab initio calculations

    International Nuclear Information System (INIS)

    Highlights: • Some studies related to the vibrational wave functions mapping phenomenon are reviewed. • The core-excited vibrational wave functions were mapped using dissociative and bound final states. • High-resolution experimental data is accompanied by ab initio calculations. • The mapping phenomenon allows one to extract constants of the molecular potentials. • The mapping techniques are general and can be applied for the study of many systems. - Abstract: The recent development of high brightness 3rd generation soft X-ray sources and high energy resolution electron spectrometers made it possible to accurately trace quantum phenomena associated to the vibrational dynamics in core-excited molecules. The present paper reviews the recent results on mapping of vibrational wave functions and molecular potentials based on electron spectroscopy. We discuss and compare the mapping phenomena in various systems, stressing the advantages of the resonant X-ray scattering for studying of the nuclear dynamics and spectroscopic constants of small molecules. The experimental results discussed in the paper are most often accompanied by state-of-the-art ab initio calculations allowing for a deeper understanding of the quantum effects. Besides its fundamental interest, the vibrational wave function mapping is shown to be useful for the analysis of core- and valence-excited molecular states based on the reflection principle

  1. Dithiocarbamate Anchoring in Molecular Wire Junctions: A First Principles Study

    CERN Document Server

    Li, Z; Li, Zhenyu

    2006-01-01

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

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

    International Nuclear Information System (INIS)

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

  3. Excitons and excess electrons in nanometer size molecular polyoxotitanate clusters: electronic spectra, exciton dynamics, and surface states.

    Science.gov (United States)

    Bao, Jianhua; Yu, Zhihao; Gundlach, Lars; Benedict, Jason B; Coppens, Philip; Chen, Hung Cheng; Miller, John R; Piotrowiak, Piotr

    2013-04-25

    The behavior of excitons and excess electrons in the confined space of a molecular polyoxotitanate cluster Ti17(?4-O)4(?3-O)16(?2-O)4(OPr(i))20 (in short Ti17) was studied using femtosecond pump-probe transient absorption, pulse radiolysis, and fluorescence spectroscopy. Due to pronounced quantum size effects, the electronic spectra of the exciton, Ti17*, and the excess electron carrying radical anion, Ti17(•-), are blue-shifted in comparison with bulk TiO2 and have maxima at 1.91 and 1.24 eV, respectively. The 0.7 eV difference in the position of the absorption maxima of Ti17* and Ti17(•-) indicates the presence of strong Coulomb interaction between the conduction band electron and the valence band hole in the ?1 nm diameter cluster. Ground state Raman spectra and the vibronic structure of the fluorescence spectrum point to the importance of the interfacial ligand modes in the stabilization and localization of the fully relaxed exciton. Four pentacoordinate Ti sites near the surface of the cluster appear to play a special role in this regard. Solvent polarity has only a minor influence on the spectral behavior of Ti17*. Exciton recombination in Ti17 is faster than in anatase nanoparticles or mesoporous films. The kinetics exhibits three components, ranging from less than 1 ps to 100 ps, which are tentatively assigned to the geminate recombination within the core of the cluster and to the decay of the surface stabilized charge transfer exciton. A persistent long-lived component with ? > 300 ps may indicate the involvement of intraband dark states, i.e., triplet excitons (3)Ti17*. PMID:23113586

  4. Effects of contrast improvement on high voltage rectification type of x-ray diagnostic apparatus

    International Nuclear Information System (INIS)

    The purpose of this study was to analyze the effect on the selectivity on of high-voltage rectification device that measured the performance of the grid, and the contrast improvement ability (K factor) by measuring the scattered radiation content of the transmitted X-rays. The scattered radiation generated when the X-ray flux comes from the diagnostic X-ray generator that passes through an object. Targeting four different rectifications of X-ray generators, the mean value of the tube voltage and the tube current was measured in order to maximize the accuracy of the generating power dose within the same exposure condition. Using fluorescence meter, the content of the scattered rays that are transmitted through the acrylic was measured depending on the grid usage. When grid is not used, the content of the scattered rays was the lowest (34.158%) with the single-phase rectifier, was increased with the inverter rectifier (37.043%) and the three-phase 24-peak rectification method (37.447%). The difference of the scattered radiation content of each device was significant from the lowest 0.404% to the highest 3.289% while using 8:1 grid, the content of the scattered ray was the lowest with the single content of the scattered ray was the lowest with the single-phase rectifier (18.258%), was increased with the rectifier (25.502%) and the 24-peaks rectification (24.217%). Furthermore, there was difference up to content 7.244% to the lowest content 1.285% within three-phase 24-peaks rectification, inverter rectifications, and single-phase rectifier depending on the selectivity of the grid. Drawn from the statistical analysis, there was a similar relationship between the contrast improvement factor and the K factor. As a result, the grid selectivity and the contrast were increased within the single-phase rectifier rather than the constant voltage rectifier

  5. Molecular physics

    CERN Document Server

    Williams, Dudley

    2013-01-01

    Methods of Experimental Physics, Volume 3: Molecular Physics focuses on molecular theory, spectroscopy, resonance, molecular beams, and electric and thermodynamic properties. The manuscript first considers the origins of molecular theory, molecular physics, and molecular spectroscopy, as well as microwave spectroscopy, electronic spectra, and Raman effect. The text then ponders on diffraction methods of molecular structure determination and resonance studies. Topics include techniques of electron, neutron, and x-ray diffraction and nuclear magnetic, nuclear quadropole, and electron spin reson

  6. Density functional theory studies on molecular structure, vibrational spectra and electronic properties of cyanuric acid

    Science.gov (United States)

    Prabhaharan, M.; Prabakaran, A. R.; Srinivasan, S.; Gunasekaran, S.

    2015-03-01

    The present work has been carried out a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of cyanuric acid. The FT-IR (100-4000 cm-1) and FT-Raman spectra (400-4000 cm-1) of cyanuric acid were recorded. In DFT methods, Becke's three parameter exchange-functional (B3) combined with gradient-corrected correlation functional of Lee, Yang and Parr (LYP) by implementing the split-valence polarized 6-31G(d,p) and 6-31++G(d,p) basis sets have been considered for the computation of the molecular structure optimization, vibrational frequencies, thermodynamic properties and energies of the optimized structures. The density functional theory (DFT) result complements the experimental findings. The electronic properties, such as HOMO-LUMO energies and molecular electrostatic potential (MESP) are also performed. Mulliken population analysis on atomic charges is also calculated. The first order hyperpolarizability (?total) of this molecular system and related properties (?, ? and ??) are calculated using DFT/B3LYP/6-31G (d,p) and B3LYP/6-311++G(d,p) methods. The thermodynamic functions (heat capacity, entropy and enthalpy) from spectroscopic data by statistical methods were also obtained for the range of temperature 50-1000 K.

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

    Science.gov (United States)

    Ziessel, Raymond; Harriman, Anthony

    2011-01-14

    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

  8. Rectification cleaning AsCl3 from the admixture of oxygen

    Directory of Open Access Journals (Sweden)

    Maznitska O. V.

    2008-06-01

    Full Text Available The process of the rectification cleaning of three-chlorous arsenic from the admixtures of products of his hydrolysis in the atmosphere of chlorous hydrogen has been considered in the article. Dependence of coefficient of relative volatility a three-chlorous arsenic from his concentration in muriatic solution is explored. The conduct of coefficient of relative volatility with concentrations of HCl and AsCl3 is compared. Saving of equalization of balance and equalization of working curve of column at such conduct of process of rectification is shown.

  9. Size dependence rectification performances induced by boron and nitrogen co-doping in rhombic graphene nanoribbons

    International Nuclear Information System (INIS)

    Rectification performances of rhombic graphene nanoribbons coupled to gold electrodes through thiolate bonds with left and right vertical carbon atoms substituted by one nitrogen or boron atom are analyzed by performing theoretical calculations using a self-consistent ab initio approach that combines the density functional theory with the non-equilibrium Green's function formalism. Increasing the size of graphene nanoribbon markedly improves the rectification effect because of the asymmetric potential profile distribution in rhombic graphene for polarization near the boron and nitrogen atoms.

  10. Spin rectification in thermally driven XXZ spin chain via the spin-Seebeck effect

    OpenAIRE

    Thingna, Juzar; Wang, Jian-Sheng

    2013-01-01

    We study the phenomenon of spin-current rectification in a one-dimensional XXZ spin chain in the presence of a thermal drive. In our model a pure spin current is generated by a temperature difference between two harmonic heat baths which in turn creates a spin voltage via the spin-Seebeck effect. Along with a local spin-current operator definition and the nonequilibrium modified Redfield solution we study the spin-rectification ratio as a function of system size and external...

  11. Tuning the Electronic Structure of Graphene by Molecular Dopants: Impact of the Substrate.

    Science.gov (United States)

    Christodoulou, Christos; Giannakopoulos, Angelos; Ligorio, Giovanni; Oehzelt, Martin; Timpel, Melanie; Niederhausen, Jens; Pasquali, Luca; Giglia, Angelo; Parvez, Khaled; Müllen, Klaus; Beljonne, David; Koch, Norbert; Nardi, Marco V

    2015-09-01

    A combination of ultraviolet and X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and first principle calculations was used to study the electronic structure at the interface between the strong molecular acceptor 1,3,4,5,7,8-hexafluorotetracyano-naphthoquinodimethane (F6TCNNQ) and a graphene layer supported on either a quartz or a copper substrate. We find evidence for fundamentally different charge redistribution mechanisms in the two ternary systems, as a consequence of the insulating versus metallic character of the substrates. While electron transfer occurs exclusively from graphene to F6TCNNQ on the quartz support (p-doping of graphene), the Cu substrate electron reservoir induces an additional electron density flow to graphene decorated with the acceptor monolayer. Remarkably, graphene on Cu is n-doped and remains n-doped upon F6TCNNQ deposition. On both substrates, the work function of graphene increases substantially with a F6TCNNQ monolayer atop, the effect being more pronounced (?1.3 eV) on Cu compared to quartz (?1.0 eV) because of the larger electrostatic potential drop associated with the long-distance graphene-mediated Cu-F6TCNNQ electron transfer. We thus provide a means to realize high work function surfaces for both p- and n-type doped graphene. PMID:26280572

  12. Electronic and transport properties of azobenzene monolayer junctions as molecular switches

    CERN Document Server

    Wang, Yan

    2012-01-01

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

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

    CERN Document Server

    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

    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.

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

    CERN Document Server

    Strong, A E

    1997-01-01

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

  15. A morphological study of molecularly imprinted polymers using the scanning electron microscope

    International Nuclear Information System (INIS)

    Molecular imprinting is an emerging technique for producing polymers with applications in affinity-based separation, in biomimetic sensors, in catalysis, etc. This variety of uses relies upon the production of polymers with different affinities, specificities, sensitivities and loading capacities. Research into the development of molecular imprinted polymers (MIPs) with new or improved morphologies - which involves modification of the polymerisation process - is therefore underway. This paper reports a comparative study of non-covalent MIPs synthesised by 'bulk' polymerisation using digoxin as template. These were synthesised under different conditions, i.e., changing the functional monomers employed (methacrylic acid or 2-vinylpyridine), the porogens (acetonitrile or dichloromethane) used, and by altering the volume of the latter. The polymerisation process was allowed to proceed either under UV light or in a thermostat-controlled waterbath. The surface morphology (was determined by scanning electron microscopy) and the ability of the different polymers to selectively rebind the template was then evaluated

  16. A morphological study of molecularly imprinted polymers using the scanning electron microscope

    Energy Technology Data Exchange (ETDEWEB)

    Paniagua Gonzalez, Gema [Departamento de Ciencias Analiticas, Facultad de Ciencias, Universidad Nacional de Educacion a Distancia (UNED), 28040 Madrid (Spain)]. E-mail: gpaniagua@pas.uned.es; Fernandez Hernando, Pilar [Departamento de Ciencias Analiticas, Facultad de Ciencias, Universidad Nacional de Educacion a Distancia (UNED), 28040 Madrid (Spain); Durand Alegria, J.S. [Departamento de Ciencias Analiticas, Facultad de Ciencias, Universidad Nacional de Educacion a Distancia (UNED), 28040 Madrid (Spain)

    2006-01-31

    Molecular imprinting is an emerging technique for producing polymers with applications in affinity-based separation, in biomimetic sensors, in catalysis, etc. This variety of uses relies upon the production of polymers with different affinities, specificities, sensitivities and loading capacities. Research into the development of molecular imprinted polymers (MIPs) with new or improved morphologies - which involves modification of the polymerisation process - is therefore underway. This paper reports a comparative study of non-covalent MIPs synthesised by 'bulk' polymerisation using digoxin as template. These were synthesised under different conditions, i.e., changing the functional monomers employed (methacrylic acid or 2-vinylpyridine), the porogens (acetonitrile or dichloromethane) used, and by altering the volume of the latter. The polymerisation process was allowed to proceed either under UV light or in a thermostat-controlled waterbath. The surface morphology (was determined by scanning electron microscopy) and the ability of the different polymers to selectively rebind the template was then evaluated.

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

    CERN Document Server

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

    2009-01-01

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

  18. Quantum Effects in Nanoantennas and Their Applications in Tunability, Mixing, and Rectification

    KAUST Repository

    Chen, Pai-Yen

    2015-08-04

    It has been recently shown that optical nanoantennas made of single or paired metallic nanoparticles can efficiently couple the propagating light into and from deeply subwavelength volumes. The strong light-matter interaction mediated by surface plasmons in metallic nanostructures allows for localizing optical fields to a subdiffraction-limited region, thereby enhancing emission of nanoemitters and offering the flexible control of nanofocused radiation. Here we theoretically study the nanodipole antennas with submicroscopic gaps, i.e. a few nanometers, for which there exists linear and high-order nonlinear quantum conductivities due to the photon-assisted tunneling effect. Noticeably, these quantum conductivities induced at the nanogap are enhanced by several orders of magnitude, due to the strongly localized optical fields associated with the plasmonic resonance.In this talk, we will show that by tailoring the geometry of nanoantennas and the quantum well structure, a quantum nanodipole antenna with a gap size of few nanometers can induce linear, high-order quantum conductivities that are considerably enhanced by the surface plasmon resonance. We envisage here a number of intriguing nanophotonic applications of these quantum nanoantennas, including (i) modulatable and switchable radiators and metamaterials, with electronic and all-optical tuning (which is related to the two photon absorption), (ii) optical rectification for detection and energy harvesting of infrared and visible light, which are related to the relevant second-order quantum conductivity, (iii) harmonic sensing for the work function and the optical index of nanoparticle, e.g. DNA and molecules, loaded inside the nanogap, and (iv) high harmonic generation and wave mixing with nonlinear quantum conductivities.

  19. Electronic transport and vibrational modes in the smallest molecular bridge: H2 in Pt nanocontacts

    OpenAIRE

    Garcia, Yamila; Palacios, J. J.; Fabian, E. San; Verges, J. A.; Perez-Jimenez, A. J.; Louis, E

    2003-01-01

    We present a state-of-the-art first-principles analysis of electronic transport in a Pt nanocontact in the presence of H2 which has been recently reported by Smit et al. in Nature 419, 906 (2002). Our results indicate that at the last stages of the breaking of the Pt nanocontact two basic forms of bridge involving H can appear. Our claim is, in contrast to Smit et al.'s, that the main conductance histogram peak at G approx 2e^2/h is not due to molecular H2, but to a complex ...

  20. Electron Localization in Molecular Fragmentation of H2 by Carrier-Envelope Phase Stabilized Laser Pulses

    Science.gov (United States)

    Kremer, Manuel; Fischer, Bettina; Feuerstein, Bernold; de Jesus, Vitor L. B.; Sharma, Vandana; Hofrichter, Christian; Rudenko, Artem; Thumm, Uwe; Schröter, Claus Dieter; Moshammer, Robert; Ullrich, Joachim

    2009-11-01

    Fully differential data for H2 dissociation in ultrashort (6 fs, 760 nm), linearly polarized, intense (0.44PW/cm2) laser pulses with a stabilized carrier-envelope phase (CEP) were recorded with a reaction microscope. Depending on the CEP, the molecular orientation, and the kinetic energy release (KER), we find asymmetric proton emission at low KERs (0-3 eV), basically predicted by Roudnev and Esry, and much stronger than reported by Kling et al. Wave packet propagation calculations reproduce the salient features and discard, together with the observed KER-independent electron asymmetry, the first ionization step to be the reason for the asymmetric proton emission.

  1. Electron Localization in Molecular Fragmentation of H2 by Carrier-Envelope Phase Stabilized Laser Pulses

    International Nuclear Information System (INIS)

    Fully differential data for H2 dissociation in ultrashort (6 fs, 760 nm), linearly polarized, intense (0.44 PW/cm2) laser pulses with a stabilized carrier-envelope phase (CEP) were recorded with a reaction microscope. Depending on the CEP, the molecular orientation, and the kinetic energy release (KER), we find asymmetric proton emission at low KERs (0-3 eV), basically predicted by Roudnev and Esry, and much stronger than reported by Kling et al. Wave packet propagation calculations reproduce the salient features and discard, together with the observed KER-independent electron asymmetry, the first ionization step to be the reason for the asymmetric proton emission.

  2. Influence of molecular conformations on the electronic structure of organic charge transfer salts

    OpenAIRE

    Guterding, Daniel; Valenti, Roser; Jeschke, Harald O.

    2015-01-01

    We report ab-initio calculations for the electronic structure of organic charge transfer salts $\\kappa$-(ET)$_2$Cu[N(CN)$_2$]Br, $\\kappa$-(ET)$_2$Cu[N(CN)$_2$]I, $\\kappa^{\\prime \\prime}$-(ET)$_2$Cu[N(CN)$_2$]Cl and $\\kappa$-(ET)$_2$Cu$_2$(CN)$_3$. These materials show an ordering of the relative orientation of terminal ethylene groups in the BEDT-TTF molecules at finite temperature and our calculations correctly predict the experimentally observed ground state molecular c...

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

    CERN Document Server

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

    2011-01-01

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

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

    CERN Document Server

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

    2011-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-11-26

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

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

    Energy Technology Data Exchange (ETDEWEB)

    1994-06-01

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

  7. Focus: Two-dimensional electron-electron double resonance and molecular motions: The challenge of higher frequencies

    Science.gov (United States)

    Franck, John M.; Chandrasekaran, Siddarth; Dzikovski, Boris; Dunnam, Curt R.; Freed, Jack H.

    2015-06-01

    The development, applications, and current challenges of the pulsed ESR technique of two-dimensional Electron-Electron Double Resonance (2D ELDOR) are described. This is a three-pulse technique akin to 2D Exchange Nuclear Magnetic Resonance, but involving electron spins, usually in the form of spin-probes or spin-labels. As a result, it required the extension to much higher frequencies, i.e., microwaves, and much faster time scales, with ?/2 pulses in the 2-3 ns range. It has proven very useful for studying molecular dynamics in complex fluids, and spectral results can be explained by fitting theoretical models (also described) that provide a detailed analysis of the molecular dynamics and structure. We discuss concepts that also appear in other forms of 2D spectroscopy but emphasize the unique advantages and difficulties that are intrinsic to ESR. Advantages include the ability to tune the resonance frequency, in order to probe different motional ranges, while challenges include the high ratio of the detection dead time vs. the relaxation times. We review several important 2D ELDOR studies of molecular dynamics. (1) The results from a spin probe dissolved in a liquid crystal are followed throughout the isotropic ? nematic ? liquid-like smectic ? solid-like smectic ? crystalline phases as the temperature is reduced and are interpreted in terms of the slowly relaxing local structure model. Here, the labeled molecule is undergoing overall motion in the macroscopically aligned sample, as well as responding to local site fluctuations. (2) Several examples involving model phospholipid membranes are provided, including the dynamic structural characterization of the boundary lipid that coats a transmembrane peptide dimer. Additionally, subtle differences can be elicited for the phospholipid membrane phases: liquid disordered, liquid ordered, and gel, and the subtle effects upon the membrane, of antigen cross-linking of receptors on the surface of plasma membrane, vesicles can be observed. These 2D ELDOR experiments are performed as a function of mixing time, Tm, i.e., the time between the second and third ?/2 pulses, which provides a third dimension. In fact, a fourth dimension may be added by varying the ESR frequency/magnetic field combination. Therefore, (3) it is shown how continuous-wave multifrequency ESR studies enable the decomposition of complex dynamics of, e.g., proteins by virtue of their respective time scales. These studies motivate our current efforts that are directed to extend 2D ELDOR to higher frequencies, 95 GHz in particular (from 9 and 17 GHz), in order to enable multi-frequency 2D ELDOR. This required the development of quasi-optical methods for performing the mm-wave experiments, which are summarized. We demonstrate state-of-the-art 95 GHz 2D ELDOR spectroscopy through its ability to resolve the two signals from a spin probe dissolved in both the lipid phase and the coexisting aqueous phase. As current 95 GHz experiments are restricted by limited spectral coverage of the ?/2 pulse, as well as the very short T2 relaxation times of the electron spins, we discuss how these limitations are being addressed.

  8. Focus: Two-dimensional electron-electron double resonance and molecular motions: The challenge of higher frequencies

    International Nuclear Information System (INIS)

    The development, applications, and current challenges of the pulsed ESR technique of two-dimensional Electron-Electron Double Resonance (2D ELDOR) are described. This is a three-pulse technique akin to 2D Exchange Nuclear Magnetic Resonance, but involving electron spins, usually in the form of spin-probes or spin-labels. As a result, it required the extension to much higher frequencies, i.e., microwaves, and much faster time scales, with ?/2 pulses in the 2-3 ns range. It has proven very useful for studying molecular dynamics in complex fluids, and spectral results can be explained by fitting theoretical models (also described) that provide a detailed analysis of the molecular dynamics and structure. We discuss concepts that also appear in other forms of 2D spectroscopy but emphasize the unique advantages and difficulties that are intrinsic to ESR. Advantages include the ability to tune the resonance frequency, in order to probe different motional ranges, while challenges include the high ratio of the detection dead time vs. the relaxation times. We review several important 2D ELDOR studies of molecular dynamics. (1) The results from a spin probe dissolved in a liquid crystal are followed throughout the isotropic ? nematic ? liquid-like smectic ? solid-like smectic ? crystalline phases as the temperature is reduced and are interpreted in terms of the slowly relaxing local structure model. Here, the labeled molecule is undergoing overall motion in the macroscopically aligned sample, as well as responding to local site fluctuations. (2) Several examples involving model phospholipid membranes are provided, including the dynamic structural characterization of the boundary lipid that coats a transmembrane peptide dimer. Additionally, subtle differences can be elicited for the phospholipid membrane phases: liquid disordered, liquid ordered, and gel, and the subtle effects upon the membrane, of antigen cross-linking of receptors on the surface of plasma membrane, vesicles can be observed. These 2D ELDOR experiments are performed as a function of mixing time, Tm, i.e., the time between the second and third ?/2 pulses, which provides a third dimension. In fact, a fourth dimension may be added by varying the ESR frequency/magnetic field combination. Therefore, (3) it is shown how continuous-wave multifrequency ESR studies enable the decomposition of complex dynamics of, e.g., proteins by virtue of their respective time scales. These studies motivate our current efforts that are directed to extend 2D ELDOR to higher frequencies, 95 GHz in particular (from 9 and 17 GHz), in order to enable multi-frequency 2D ELDOR. This required the development of quasi-optical methods for performing the mm-wave experiments, which are summarized. We demonstrate state-of-the-art 95 GHz 2D ELDOR spectroscopy through its ability to resolve the two signals from a spin probe dissolved in both the lipid phase and the coexisting aqueous phase. As current 95 GHz experiments are restricted by limited spectral coverage of the ?/2 pulse, as well as the very short T2 relaxation times of the electron spins, we discuss how these limitations are being addressed

  9. Ultrafast XUV spectroscopy: Unveiling the nature of electronic couplings in molecular dynamics

    Science.gov (United States)

    Timmers, Henry Robert

    Molecules are traditionally treated quantum mechanically using the Born-Oppenheimer formalism. In this formalism, different electronic states of the molecule are treated independently. However, most photo-initiated phenomena occurring in nature are driven by the couplings between different electronic states in both isolated molecules and molecular aggregates, and therefore occur beyond the Born-Oppenheimer formalism. These couplings are relevant in reactions relating to the perception of vision in the human eye, the oxidative damage and repair of DNA, the harvesting of light in photosynthesis, and the transfer of charge across large chains of molecules. While these reaction dynamics have traditionally been studied with visible and ultraviolet spectroscopy, attosecond XUV pulses formed through the process of high harmonic generation form a perfect tool for probing coupled electronic dynamics in molecules. In this thesis, I will present our work in using ultrafast, XUV spectroscopy to study these dynamics in molecules of increasing complexity. We begin by probing the relaxation dynamics of superexcited states in diatomic O 2. These states can relax via two types of electronic couplings, either through autoionization or neutral dissociation. We find that our pump-probe scheme can disentangle the two relaxation mechanisms and independently measure their contributing lifetimes. Next, we present our work in observing a coherent electron hole wavepacket initiated by the ionization of polyatomic CO 2 near a conical intersection. The electron-nuclear couplings near the conical intersection drive the electron hole between different orbital configurations. We find that we can not only measure the lifetime of quantum coherence in the electron hole wavepacket, but also control its evolution with a strong, infrared probing field. Finally, we propose an experiment to observe the migration of an electron hole across iodobenzene on the few-femtosecond timescale. We present experimental modifications made to the high harmonic generation set-up in order to probe this ultrafast and elusive charge migration. These results demonstrate the potential of ultrafast, XUV spectroscopy in probing the inner-workings of electronic couplings occurring in nature.

  10. Quantum molecular dynamics study on energy transfer to the secondary electron in surface collision process of an ion

    Energy Technology Data Exchange (ETDEWEB)

    Shibahara, M [Department of Mechanical Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); Satake, S; Taniguchi, J [Department of Applied Electronics, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, 278-8510 (Japan)], E-mail: siba@mech.eng.osaka-u.ac.jp

    2008-03-15

    In the present study the quantum molecular dynamics method was applied to an energy transfer problem to an electron during ionic surface collision process in order to elucidate how energy of ionic collision transfers to the emitted electrons. Effects of various physical parameters, such as the collision velocity and interaction strength between the observed electron and the classical particles on the energy transfer to the electron were investigated by the quantum molecular dynamics method when the potassium ion was collided with the surface so as to elucidate the energy path to the electron and the predominant factor of energy transfer to the electron. Effects of potential energy between the ion and the electron and that between the surface molecule and the electron on the electronic energy transfer were shown in the present paper. The energy transfer to the observed secondary electron through the potential energy term between the ion and the electron was much dependent on the ion collision energy although the energy increase to the observed secondary electron was not monotonous through the potential energy between the ion and surface molecules with the change of the ion collision energy.

  11. Quantum molecular dynamics study on energy transfer to the secondary electron in surface collision process of an ion

    International Nuclear Information System (INIS)

    In the present study the quantum molecular dynamics method was applied to an energy transfer problem to an electron during ionic surface collision process in order to elucidate how energy of ionic collision transfers to the emitted electrons. Effects of various physical parameters, such as the collision velocity and interaction strength between the observed electron and the classical particles on the energy transfer to the electron were investigated by the quantum molecular dynamics method when the potassium ion was collided with the surface so as to elucidate the energy path to the electron and the predominant factor of energy transfer to the electron. Effects of potential energy between the ion and the electron and that between the surface molecule and the electron on the electronic energy transfer were shown in the present paper. The energy transfer to the observed secondary electron through the potential energy term between the ion and the electron was much dependent on the ion collision energy although the energy increase to the observed secondary electron was not monotonous through the potential energy between the ion and surface molecules with the change of the ion collision energy

  12. Mimicking the electron transfer chain in photosystem II with a molecular triad thermodynamically capable of water oxidation

    OpenAIRE

    Megiatto, Jackson D.; Antoniuk-Pablant, Antaeres; Sherman, Benjamin D.; Kodis, Gerdenis; Gervaldo, Miguel; Moore, Thomas A.; Moore, Ana L.; Gust, Devens

    2012-01-01

    In the photosynthetic photosystem II, electrons are transferred from the manganese-containing oxygen evolving complex (OEC) to the oxidized primary electron-donor chlorophyll P680•+ by a proton-coupled electron transfer process involving a tyrosine-histidine pair. Proton transfer from the tyrosine phenolic group to a histidine nitrogen positions the redox potential of the tyrosine between those of P680•+ and the OEC. We report the synthesis and time-resolved spectroscopic study of a molecular...

  13. Effects of electron-phonon interaction on thermal and electrical transport through molecular nano-conductors

    Directory of Open Access Journals (Sweden)

    Jing-Tao Lü

    2015-05-01

    Full Text Available The topic of this review is the effects of electron-phonon interaction (EPI on the transport properties of molecular nano-conductors. A nano-conductor connects to two electron leads and two phonon leads, possibly at different temperatures or chemical potentials. The EPI appears only in the nano-conductor. We focus on its effects on charge and energy transport. We introduce three approaches. For weak EPI, we use the nonequilibrium Green’s function method to treat it perturbatively. We derive the expressions for the charge and heat currents. For weak system-lead couplings, we use the quantum master equation approach. In both cases, we use a simple single level model to study the effects of EPI on the system’s thermoelectric transport properties. It is also interesting to look at the effect of currents on the dynamics of the phonon system. For this, we derive a semi-classical generalized Langevin equation to describe the nano-conductor’s atomic dynamics, taking the nonequilibrium electron system, as well as the rest of the atomic degrees of freedom as effective baths. We show simple applications of this approach to the problem of energy transfer between electrons and phonons.

  14. Calculation of the spectrum of quasiparticle electron excitations in organic molecular semiconductors

    Science.gov (United States)

    Tikhonov, E. V.; Uspenskii, Yu. A.; Khokhlov, D. R.

    2015-06-01

    A quasiparticle electronic spectrum belongs to the characteristics of nanoobjects that are most important for applications. The following methods of calculating the electronic spectrum are analyzed: the Kohn-Sham equations of the density functional theory (DFT), the hybrid functional method, the GW approximation, and the Lehmann approximation used in the spectral representation of one-electron Green's function. The results of these approaches are compared with the data of photoemission measurements of benzene, PTCDA, and phthalocyanine (CuPc, H2Pc, FePc, PtPc) molecules, which are typical representatives of organic molecular semiconductors (OMS). This comparison demonstrates that the Kohn-Sham equations of DFT incorrectly reproduce the electronic spectrum of OMS. The hybrid functional method correctly describes the spectrum of the valence and conduction bands; however, the HOMO-LUMO gap width is significantly underestimated. The correct gap width is obtained in both the GW approximation and the Lehmann approach, and the total energy in this approach can be calculated in the local density approximation of DFT.

  15. Effects of electron-phonon interaction on thermal and electrical transport through molecular nano-conductors

    Science.gov (United States)

    Lü, Jing-Tao; Zhou, Hangbo; Jiang, Jin-Wu; Wang, Jian-Sheng

    2015-05-01

    The topic of this review is the effects of electron-phonon interaction (EPI) on the transport properties of molecular nano-conductors. A nano-conductor connects to two electron leads and two phonon leads, possibly at different temperatures or chemical potentials. The EPI appears only in the nano-conductor. We focus on its effects on charge and energy transport. We introduce three approaches. For weak EPI, we use the nonequilibrium Green's function method to treat it perturbatively. We derive the expressions for the charge and heat currents. For weak system-lead couplings, we use the quantum master equation approach. In both cases, we use a simple single level model to study the effects of EPI on the system's thermoelectric transport properties. It is also interesting to look at the effect of currents on the dynamics of the phonon system. For this, we derive a semi-classical generalized Langevin equation to describe the nano-conductor's atomic dynamics, taking the nonequilibrium electron system, as well as the rest of the atomic degrees of freedom as effective baths. We show simple applications of this approach to the problem of energy transfer between electrons and phonons.

  16. On the dissociative electron attachment as a potential source of molecular hydrogen in irradiated liquid water

    International Nuclear Information System (INIS)

    In the radiolysis of liquid water, different mechanisms for the formation of molecular hydrogen (H2) are involved at different times after the initial energy disposition. It has been suggested that the contributions of the eaq- + eaq-, H + eaq- and H + H reactions between hydrated electrons (eaq-) and hydrogen atoms in the spurs are not sufficient to account for all of the observed H2 yield (0.45 molecules/100 eV) on the microsecond time scale. Addressing the question of the origin of an unscavengeable H2 yield of 0.15 molecules/100 eV produced before spur expansion, we suggest that the dissociative capture of the so-called vibrationally-relaxing electrons by H2O molecules is a possible pathway for the formation of part of the initial H2 yield. Comparison of recent dissociative-electron-attachment H--anion yield-distribution measurements from amorphous H2O films with the energy spectrum of vibrationally-relaxing electrons in irradiated liquid water, calculated by Monte Carlo simulations, plays in favor of this hypothesis. (author)

  17. Exploring the vibrational fingerprint of the electronic excitation energy via molecular dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Deyne, Andy Van Yperen-De; Pauwels, Ewald; Ghysels, An; Waroquier, Michel; Van Speybroeck, Veronique; Hemelsoet, Karen, E-mail: karen.hemelsoet@ugent.be [Center for Molecular Modeling (CMM), Ghent University, Technologiepark 903, 9052 Zwijnaarde (Belgium); De Meyer, Thierry [Center for Molecular Modeling (CMM), Ghent University, Technologiepark 903, 9052 Zwijnaarde (Belgium); Department of Textiles, Ghent University, Technologiepark 907, 9052 Zwijnaarde (Belgium); De Clerck, Karen [Department of Textiles, Ghent University, Technologiepark 907, 9052 Zwijnaarde (Belgium)

    2014-04-07

    A Fourier-based method is presented to relate changes of the molecular structure during a molecular dynamics simulation with fluctuations in the electronic excitation energy. The method implies sampling of the ground state potential energy surface. Subsequently, the power spectrum of the velocities is compared with the power spectrum of the excitation energy computed using time-dependent density functional theory. Peaks in both spectra are compared, and motions exhibiting a linear or quadratic behavior can be distinguished. The quadratically active motions are mainly responsible for the changes in the excitation energy and hence cause shifts between the dynamic and static values of the spectral property. Moreover, information about the potential energy surface of various excited states can be obtained. The procedure is illustrated with three case studies. The first electronic excitation is explored in detail and dominant vibrational motions responsible for changes in the excitation energy are identified for ethylene, biphenyl, and hexamethylbenzene. The proposed method is also extended to other low-energy excitations. Finally, the vibrational fingerprint of the excitation energy of a more complex molecule, in particular the azo dye ethyl orange in a water environment, is analyzed.

  18. Molecular beam deposition and characterization of thin organic films on metals for applications in organic electronics

    Energy Technology Data Exchange (ETDEWEB)

    Witte, G.; Woell, C. [Physikalische Chemie I, Ruhr-Universitaet Bochum, 44780 Bochum (Germany)

    2008-03-15

    The deposition of organic thin films on metal substrates using molecular beam deposition will be reviewed with a special emphasis on molecules which exhibit high charge carrier mobilities and are thus suited to be used as organic semiconductors (OSCs), namely pentacene, rubrene and perylene. Special emphasis will be on aspects of organic molecular beam deposition (OMBD) relevant for the device performance in organic field effect transistors (OFETs), in particular with regard to avoiding or minimizing structural defects at support/OSC interfaces. In addition, another aspect governing - and often limiting - charge injection at electrodes into an OSC, electronic level alignment at molecule/metal interfaces, are discussed in the context of recent accurate ab-initio electronic structure calculations. Finally, we present a novel experimental approach to determine charge transport properties of defect-free, nm-sized OSCs where extrinsic contributions to e.g. charge carrier mobilities can be strictly excluded, thus opening the way towards the determination of true intrinsic OSC properties. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. Molecular structure, vibrational, electronic and thermal properties of 4-vinylcyclohexene by quantum chemical calculations

    Science.gov (United States)

    Nagabalasubramanian, P. B.; Periandy, S.; Karabacak, Mehmet; Govindarajan, M.

    2015-06-01

    The solid phase FT-IR and FT-Raman spectra of 4-vinylcyclohexene (abbreviated as 4-VCH) have been recorded in the region 4000-100 cm-1. The optimized molecular geometry and vibrational frequencies of the fundamental modes of 4-VCH have been precisely assigned and analyzed with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) method at 6-311++G(d,p) level basis set. The theoretical frequencies were properly scaled and compared with experimentally obtained FT-IR and FT-Raman spectra. Also, the effect due the substitution of vinyl group on the ring vibrational frequencies was analyzed and a detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated total energy distribution (TED). The time dependent DFT (TD-DFT) method was employed to predict its electronic properties, such as electronic transitions by UV-Visible analysis, HOMO and LUMO energies, molecular electrostatic potential (MEP) and various global reactivity and selectivity descriptors (chemical hardness, chemical potential, softness, electrophilicity index). Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Atomic charges obtained by Mulliken population analysis and NBO analysis are compared. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures are also calculated.

  20. A bifurcated molecular pentad capable of sequential electronic energy transfer and intramolecular charge transfer.

    Science.gov (United States)

    Harriman, Anthony; Stachelek, Patrycja; Sutter, Alexandra; Ziessel, Raymond

    2015-10-21

    An extended molecular array, comprising three distinct types of chromophores and two additional redox-active subunits, that harvests photons over most of the visible spectral range has been synthesized and characterised. The array exhibits a rich variety of electrochemical waves when examined by cyclic voltammetry but assignment can be made on the basis of control compounds and molecular orbital calculations. Stepwise electronic energy transfer occurs along the molecular axis, corresponding to a gradient of excitation energies, to populate the lowest-energy excited state of the ultimate acceptor. The latter species, which absorbs and emits in the far-red region, enters into light-induced charge transfer with a terminal amine group. The array is relatively stable under illumination with white light but degrades slowly via a series of well-defined steps, the first of which is autocatalytic. One of the main attributes of this system is the capability to harvest an unusually high fraction of sunlight while providing protection against exposure to UV light. PMID:26381219

  1. Electrochemical gate-controlled electron transport of redox-active single perylene bisimide molecular junctions

    Science.gov (United States)

    Li, C.; Mishchenko, A.; Li, Z.; Pobelov, I.; Wandlowski, Th; Li, X. Q.; Würthner, F.; Bagrets, A.; Evers, F.

    2008-09-01

    We report a scanning tunneling microscopy (STM) experiment in an electrochemical environment which studies a prototype molecular switch. The target molecules were perylene tetracarboxylic acid bisimides modified with pyridine (P-PBI) and methylthiol (T-PBI) linker groups and with bulky tert-butyl-phenoxy substituents in the bay area. At a fixed bias voltage, we can control the transport current through a symmetric molecular wire Au|P-PBI(T-PBI)|Au by variation of the electrochemical 'gate' potential. The current increases by up to two orders of magnitude. The conductances of the P-PBI junctions are typically a factor 3 larger than those of T-PBI. A theoretical analysis explains this effect as a consequence of shifting the lowest unoccupied perylene level (LUMO) in or out of the bias window when tuning the electrochemical gate potential VG. The difference in on/off ratios reflects the variation of hybridization of the LUMO with the electrode states with the anchor groups. IT-ES(T) curves of asymmetric molecular junctions formed between a bare Au STM tip and a T-PBI (P-PBI) modified Au(111) electrode in an aqueous electrolyte exhibit a pronounced maximum in the tunneling current at -0.740, which is close to the formal potential of the surface-confined molecules. The experimental data were explained by a sequential two-step electron transfer process.

  2. Electrochemical gate-controlled electron transport of redox-active single perylene bisimide molecular junctions

    International Nuclear Information System (INIS)

    We report a scanning tunneling microscopy (STM) experiment in an electrochemical environment which studies a prototype molecular switch. The target molecules were perylene tetracarboxylic acid bisimides modified with pyridine (P-PBI) and methylthiol (T-PBI) linker groups and with bulky tert-butyl-phenoxy substituents in the bay area. At a fixed bias voltage, we can control the transport current through a symmetric molecular wire Au|P-PBI(T-PBI)|Au by variation of the electrochemical 'gate' potential. The current increases by up to two orders of magnitude. The conductances of the P-PBI junctions are typically a factor 3 larger than those of T-PBI. A theoretical analysis explains this effect as a consequence of shifting the lowest unoccupied perylene level (LUMO) in or out of the bias window when tuning the electrochemical gate potential VG. The difference in on/off ratios reflects the variation of hybridization of the LUMO with the electrode states with the anchor groups. IT-ES(T) curves of asymmetric molecular junctions formed between a bare Au STM tip and a T-PBI (P-PBI) modified Au(111) electrode in an aqueous electrolyte exhibit a pronounced maximum in the tunneling current at -0.740, which is close to the formal potential of the surface-confined molecules. The experimental data were explained by a sequential two-step electron transfer process

  3. Research Update: Molecular electronics: The single-molecule switch and transistor

    Energy Technology Data Exchange (ETDEWEB)

    Sotthewes, Kai; Heimbuch, René, E-mail: r.heimbuch@utwente.nl; Kumar, Avijit; Zandvliet, Harold J. W. [Physics of Interfaces and Nanomaterials, MESA Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede (Netherlands); Geskin, Victor [Service de Chimie des Materiaux Nouveaux, University of Mons, Mons (Belgium)

    2014-01-01

    In order to design and realize single-molecule devices it is essential to have a good understanding of the properties of an individual molecule. For electronic applications, the most important property of a molecule is its conductance. Here we show how a single octanethiol molecule can be connected to macroscopic leads and how the transport properties of the molecule can be measured. Based on this knowledge we have realized two single-molecule devices: a molecular switch and a molecular transistor. The switch can be opened and closed at will by carefully adjusting the separation between the electrical contacts and the voltage drop across the contacts. This single-molecular switch operates in a broad temperature range from cryogenic temperatures all the way up to room temperature. Via mechanical gating, i.e., compressing or stretching of the octanethiol molecule, by varying the contact's interspace, we are able to systematically adjust the conductance of the electrode-octanethiol-electrode junction. This two-terminal single-molecule transistor is very robust, but the amplification factor is rather limited.

  4. Research Update: Molecular electronics: The single-molecule switch and transistor

    Directory of Open Access Journals (Sweden)

    Kai Sotthewes

    2014-01-01

    Full Text Available In order to design and realize single-molecule devices it is essential to have a good understanding of the properties of an individual molecule. For electronic applications, the most important property of a molecule is its conductance. Here we show how a single octanethiol molecule can be connected to macroscopic leads and how the transport properties of the molecule can be measured. Based on this knowledge we have realized two single-molecule devices: a molecular switch and a molecular transistor. The switch can be opened and closed at will by carefully adjusting the separation between the electrical contacts and the voltage drop across the contacts. This single-molecular switch operates in a broad temperature range from cryogenic temperatures all the way up to room temperature. Via mechanical gating, i.e., compressing or stretching of the octanethiol molecule, by varying the contact's interspace, we are able to systematically adjust the conductance of the electrode-octanethiol-electrode junction. This two-terminal single-molecule transistor is very robust, but the amplification factor is rather limited.

  5. Electron ionization LC-MS with supersonic molecular beams-the new concept, benefits and applications.

    Science.gov (United States)

    Seemann, Boaz; Alon, Tal; Tsizin, Svetlana; Fialkov, Alexander B; Amirav, Aviv

    2015-11-01

    A new type of electron ionization LC-MS with supersonic molecular beams (EI-LC-MS with SMB) is described. This system and its operational methods are based on pneumatic spray formation of the LC liquid flow in a heated spray vaporization chamber, full sample thermal vaporization and subsequent electron ionization of vibrationally cold molecules in supersonic molecular beams. The vaporized sample compounds are transferred into a supersonic nozzle via a flow restrictor capillary. Consequently, while the pneumatic spray is formed and vaporized at above atmospheric pressure the supersonic nozzle backing pressure is about 0.15?Bar for the formation of supersonic molecular beams with vibrationally cold sample molecules without cluster formation with the solvent vapor. The sample compounds are ionized in a fly-though EI ion source as vibrationally cold molecules in the SMB, resulting in 'Cold EI' (EI of vibrationally cold molecules) mass spectra that exhibit the standard EI fragments combined with enhanced molecular ions. We evaluated the EI-LC-MS with SMB system and demonstrated its effectiveness in NIST library sample identification which is complemented with the availability of enhanced molecular ions. The EI-LC-MS with SMB system is characterized by linear response of five orders of magnitude and uniform compound independent response including for non-polar compounds. This feature improves sample quantitation that can be approximated without compound specific calibration. Cold EI, like EI, is free from ion suppression and/or enhancement effects (that plague ESI and/or APCI) which facilitate faster LC separation because full separation is not essential. The absence of ion suppression effects enables the exploration of fast flow injection MS-MS as an alternative to lengthy LC-MS analysis. These features are demonstrated in a few examples, and the analysis of the main ingredients of Cannabis on a few Cannabis flower extracts is demonstrated. Finally, the advantages of EI-LC-MS with SMB are listed and discussed. Copyright © 2015 John Wiley & Sons, Ltd. PMID:26505770

  6. A multiscale simulation technique for molecular electronics: design of a directed self-assembled molecular n-bit shift register memory device

    International Nuclear Information System (INIS)

    A general method useful in molecular electronics design is developed that integrates modelling on the nano-scale (using quantum-chemical software) and on the micro-scale (using finite-element methods). It is applied to the design of an n-bit shift register memory that could conceivably be built using accessible technologies. To achieve this, the entire complex structure of the device would be built to atomic precision using feedback-controlled lithography to provide atomic-level control of silicon devices, controlled wet-chemical synthesis of molecular insulating pillars above the silicon, and controlled wet-chemical self-assembly of modular molecular devices to these pillars that connect to external metal electrodes (leads). The shift register consists of n connected cells that read data from an input electrode, pass it sequentially between the cells under the control of two external clock electrodes, and deliver it finally to an output device. The proposed cells are trimeric oligoporphyrin units whose internal states are manipulated to provide functionality, covalently connected to other cells via dipeptide linkages. Signals from the clock electrodes are conveyed by oligoporphyrin molecular wires, and ?-oxo porphyrin insulating columns are used as the supporting pillars. The developed multiscale modelling technique is applied to determine the characteristics of this molecular device, with in particular utilization of the inverted region for molecular electron-transfer processes shown to facilitate latching and control using exceptionally low energy costs per logic operation compared to standard CMOS shift register technology. (paper)

  7. A multiscale simulation technique for molecular electronics: design of a directed self-assembled molecular n-bit shift register memory device.

    Science.gov (United States)

    Lambropoulos, Nicholas A; Reimers, Jeffrey R; Crossley, Maxwell J; Hush, Noel S; Silverbrook, Kia

    2013-12-20

    A general method useful in molecular electronics design is developed that integrates modelling on the nano-scale (using quantum-chemical software) and on the micro-scale (using finite-element methods). It is applied to the design of an n-bit shift register memory that could conceivably be built using accessible technologies. To achieve this, the entire complex structure of the device would be built to atomic precision using feedback-controlled lithography to provide atomic-level control of silicon devices, controlled wet-chemical synthesis of molecular insulating pillars above the silicon, and controlled wet-chemical self-assembly of modular molecular devices to these pillars that connect to external metal electrodes (leads). The shift register consists of n connected cells that read data from an input electrode, pass it sequentially between the cells under the control of two external clock electrodes, and deliver it finally to an output device. The proposed cells are trimeric oligoporphyrin units whose internal states are manipulated to provide functionality, covalently connected to other cells via dipeptide linkages. Signals from the clock electrodes are conveyed by oligoporphyrin molecular wires, and ?-oxo porphyrin insulating columns are used as the supporting pillars. The developed multiscale modelling technique is applied to determine the characteristics of this molecular device, with in particular utilization of the inverted region for molecular electron-transfer processes shown to facilitate latching and control using exceptionally low energy costs per logic operation compared to standard CMOS shift register technology. PMID:24270608

  8. Long-Range Electron Effects upon Irradiation of Molecular Solids and Polymers

    International Nuclear Information System (INIS)

    Long-range electron effects are responsible for specific localization and selectivity of the radiation-induced chemical transformations occurring in molecular solids and polymers, when the classic diffusion mobility is essentially restricted. In particullar, understanding of the effects of this kind may be of key significance for establishing new ways to control the radiation sensitivity of macromolecules and organized polymeric systems, nanomaterials and biopolymers. This talk will present an overview of model studies of the long-range electron effects with the characteristic scale from several angstroms to ten nanometers. The following aspects of the problem will be analyzed: (1) Positive hole delocalization in ionized molecules. This phenomenon has been demonstrated experimentally and confirmed by quantum chemical calculations for a number of various-type molecules (alkanes, conjugated polyenes, bifunctional compounds). The effective delocalization length was found to be up to 2 nm (or even larger). The role of this effect in site-selective radiation chemistry will be discussed in the frame of concepts of distributed reactivity and 'switching' between delocalized and localized states. (2) Trap-to-trap positive hole and electron migration between isolated molecules or functional groups. The characteristic distance for this process was estimated to be 2 to 4 nm. Special impact will be made on the possible role of this process in selection of specific isomers or conformers upon irradiation of complex systems and macromolecules. (3) The effects of long-range scavenging of low-energy secondary electrons in polymers and organized polymeric systems. As revealed by model experiments, the radius of electron capture in solid polymers may be in the range of 1 to 10 nm. Possible implications of scavenging effects for controlling the radiation chemistry of polymers and organized polymeric systems will be considered

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

    Science.gov (United States)

    Last, Isidore; Jortner, Joshua

    2004-11-01

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

  10. High harmonic spectroscopy of electron localization in the hydrogen molecular ion

    International Nuclear Information System (INIS)

    Interaction of a laser pulse with a centrally symmetric medium, such as an isotropic gas of atoms, leads to the generation of harmonic emission which contains exclusively odd harmonics of the incident field. This result is the consequence of both the central symmetry of the medium and the temporal symmetry of the oscillating electric field, E(t+?/?l)=?E(t), where ?l is the laser frequency. In the case of oriented heteronuclear molecules, the spatial symmetry no longer holds and both odd and even harmonics become allowed. Here we show, by solving the time-dependent Schrödinger equation for H2+, D2+, and T2+, that even-order harmonic generation is also possible for sufficiently long infrared (IR) laser pulses in homonuclear molecules. The appearance of even harmonics is a signature of the coupled electron-nuclear dynamics and reflects field-induced electron localization initiated by the strong laser field, which breaks the spatial symmetry in the system. The analysis of even harmonics generated by pulses of different durations might therefore provide information on correlated electron-nuclear dynamics and charge migration in more complex un-oriented molecular ensembles. (paper)

  11. Modification of microstructures and physical properties of ultra high molecular weight polyethylene by electron beam irradiation

    International Nuclear Information System (INIS)

    An ultra high molecular weight polyethylene was irradiated with the electron beam at dose levels ranging from 100 kGy to 1MGy. The microstructures of the irradiated samples were characterized by FTIR, gel fraction measurement, DSC and small and wide angle X ray scattering. For the mechanical properties, a static tensile test and creep experiment were also performed. The cross-linking and the crystal morphology changes were the main microstructural changes to influence the mechanical properties. It was found that 250 kGy appeared to the optimal dose level to induce cross-links in the amorphous area and recrystalliztion in the crystal lamellae. At doses above 250 kGy, the electron beam penetrates into the crystal domains, resulting in cross-links in the crystal domains and reduction in the crystal size and crystallinity. The static mechanical properties (modulus, strength) and the creep resistance were enhanced by the electron beam irradiation. The stiffness rather correlated with the degree of cross-links, while the strength with the crystal morphology. (author)

  12. Modification of microstructures and physical properties of ultra high molecular weight polyethylene by electron beam irradiation

    International Nuclear Information System (INIS)

    An ultra high molecular weight polyethylene was irradiated with the electron beam at dose levels ranging from 100kGY to 1MGy. The microstructures of the irradiated samples were characterized by FTIR, gel fraction measurement, DSC and small and wide angle X-ray scattering. For the mechanical properties, a static tensile test and creep experiment were also performed. The cross-linking and the crystal morphology changes were the main microstructural changes to influence the mechanical properties. It was found that 250kGy appeared to the optimal dose level to induce cross-links in the amorphous area and recrystalliztion in the crystal lamellae. At doses above 250 kGy, the electron beam penetrates into the crystal domains, resulting in cross-links in the crystal domains and reduction in the crystal size and crystallinity. The static mechanical properties (modulus, strength) and the creep resistance were enhanced by the electron beam irradiation. The stiffness rather correlated with the degree of cross-links, while the strength with the crystal morphology. (author)

  13. Solvated electrons at elevated temperatures in different alcohols: Temperature and molecular structure effects

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Yu [Department of Nuclear Engineering and Management, Graduate School of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); Lin, Mingzhang [Nuclear Science and Engineering Directorate, Japan Atomic Energy Agency, 2-4 Shirakata-Shirane, Tokai, Naka, Ibaraki 319-1195 (Japan); Katsumura, Yosuke, E-mail: katsu@n.t.u-tokyo.ac.j [Department of Nuclear Engineering and Management, Graduate School of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); Nuclear Professional School, Graduate School of Engineering, University of Tokyo, 2-22 Shirakata-Shirane, Tokai, Naka, Ibaraki 319-1188 (Japan); Fu, Haiying; Muroya, Yusa [Nuclear Professional School, Graduate School of Engineering, University of Tokyo, 2-22 Shirakata-Shirane, Tokai, Naka, Ibaraki 319-1188 (Japan)

    2010-12-15

    The absorption spectra of solvated electrons in pentanol, hexanol and octanol are measured from 22 to 200, 22 to 175 and 50 to150 {sup o}C, respectively, at a fixed pressure of 15 MPa, using nanosecond pulse radiolysis technique. The results show that the peak positions of the absorption spectra have a red-shift (shift to longer wavelengths) as temperature increases, similar to water and other alcohols. Including the above mentioned data, a compilation of currently available experimental data on the energy of absorption maximum (E{sub max}) of solvated electrons changed with temperature in monohydric alcohols, diols and triol is presented. E{sub max} of solvated electron is larger in those alcohols that have more OH groups at all the temperatures. The molecular structure effect, including OH numbers, OH position and carbon chain length, is investigated. For the primary alcohols with same OH group number and position, the temperature coefficient increases with increase in chain length. For the alcohols with same chain length and OH numbers, temperature coefficient is larger for the symmetric alcohols than the asymmetric ones.

  14. Molecular Ornstein-Zernike approach to the solvent effects on solute electronic structures in solution

    Science.gov (United States)

    Yoshida, Norio; Kato, Shigeki

    2000-09-01

    A new approach to ab initio electronic structure calculations of solute molecules in solution is presented. Combined with the molecular Ornstein-Zernike (MOZ) integral equation theory for polyatomic liquids, solute electronic wave function and solvent distribution around a solute are determined in a self-consistent manner. The hypernetted chain approximation is employed for solving the MOZ equation. In order to describe the short-range solute-solvent interactions, the effective potential operating solute electron is placed on a solute molecule, which is determined by a least-squares fitting to ab initio exchange repulsion/charge transfer energies. The present method, referred to as the MOZ self-consistent-field (SCF) method, is applied to a solute H2O molecule in water solvent. The solvent shift for the vertical excitation to the n?* state of H2CO in aqueous solution is also examined. The results obtained by the MOZ-SCF calculations are compared with those by the reference interaction site model-SCF theory and the polarizable continuum model.

  15. Solvated electrons at elevated temperatures in different alcohols: Temperature and molecular structure effects

    International Nuclear Information System (INIS)

    The absorption spectra of solvated electrons in pentanol, hexanol and octanol are measured from 22 to 200, 22 to 175 and 50 to150 oC, respectively, at a fixed pressure of 15 MPa, using nanosecond pulse radiolysis technique. The results show that the peak positions of the absorption spectra have a red-shift (shift to longer wavelengths) as temperature increases, similar to water and other alcohols. Including the above mentioned data, a compilation of currently available experimental data on the energy of absorption maximum (Emax) of solvated electrons changed with temperature in monohydric alcohols, diols and triol is presented. Emax of solvated electron is larger in those alcohols that have more OH groups at all the temperatures. The molecular structure effect, including OH numbers, OH position and carbon chain length, is investigated. For the primary alcohols with same OH group number and position, the temperature coefficient increases with increase in chain length. For the alcohols with same chain length and OH numbers, temperature coefficient is larger for the symmetric alcohols than the asymmetric ones.

  16. A method for the direct measurement of electronic site populations in a molecular aggregate using two-dimensional electronic-vibrational spectroscopy

    Science.gov (United States)

    Lewis, Nicholas H. C.; Dong, Hui; Oliver, Thomas A. A.; Fleming, Graham R.

    2015-09-01

    Two dimensional electronic spectroscopy has proved to be a valuable experimental technique to reveal electronic excitation dynamics in photosynthetic pigment-protein complexes, nanoscale semiconductors, organic photovoltaic materials, and many other types of systems. It does not, however, provide direct information concerning the spatial structure and dynamics of excitons. 2D infrared spectroscopy has become a widely used tool for studying structural dynamics but is incapable of directly providing information concerning electronic excited states. 2D electronic-vibrational (2DEV) spectroscopy provides a link between these domains, directly connecting the electronic excitation with the vibrational structure of the system under study. In this work, we derive response functions for the 2DEV spectrum of a molecular dimer and propose a method by which 2DEV spectra could be used to directly measure the electronic site populations as a function of time following the initial electronic excitation. We present results from the response function simulations which show that our proposed approach is substantially valid. This method provides, to our knowledge, the first direct experimental method for measuring the electronic excited state dynamics in the spatial domain, on the molecular scale.

  17. An Electronic Structure Approach to Charge Transfer and Transport in Molecular Building Blocks for Organic Optoelectronics

    Science.gov (United States)

    Hendrickson, Heidi Phillips

    A fundamental understanding of charge separation in organic materials is necessary for the rational design of optoelectronic devices suited for renewable energy applications and requires a combination of theoretical, computational, and experimental methods. Density functional theory (DFT) and time-dependent (TD)DFT are cost effective ab-initio approaches for calculating fundamental properties of large molecular systems, however conventional DFT methods have been known to fail in accurately characterizing frontier orbital gaps and charge transfer states in molecular systems. In this dissertation, these shortcomings are addressed by implementing an optimally-tuned range-separated hybrid (OT-RSH) functional approach within DFT and TDDFT. The first part of this thesis presents the way in which RSH-DFT addresses the shortcomings in conventional DFT. Environmentally-corrected RSH-DFT frontier orbital energies are shown to correspond to thin film measurements for a set of organic semiconducting molecules. Likewise, the improved RSH-TDDFT description of charge transfer excitations is benchmarked using a model ethene dimer and silsesquioxane molecules. In the second part of this thesis, RSH-DFT is applied to chromophore-functionalized silsesquioxanes, which are currently investigated as candidates for building blocks in optoelectronic applications. RSH-DFT provides insight into the nature of absorptive and emissive states in silsesquioxanes. While absorption primarily involves transitions localized on one chromophore, charge transfer between chromophores and between chromophore and silsesquioxane cage have been identified. The RSH-DFT approach, including a protocol accounting for complex environmental effects on charge transfer energies, was tested and validated against experimental measurements. The third part of this thesis addresses quantum transport through nano-scale junctions. The ability to quantify a molecular junction via spectroscopic methods is crucial to their technological design and development. Time dependent perturbation theory, employed by non-equilibrium Green's function formalism, is utilized to study the effect of quantum coherences on electron transport and the effect of symmetry breaking on the electronic spectra of model molecular junctions. The fourth part of this thesis presents the design of a physical chemistry course based on a pedagogical approach called Writing-to-Teach. The nature of inaccuracies expressed in student-generated explanations of quantum chemistry topics, and the ability of a peer review process to engage these inaccuracies, is explored within this context.

  18. Molecular double slit and Young-type electron interference in ionization

    International Nuclear Information System (INIS)

    We provide a brief review of the electron spectroscopic investigation of fast ion-atom collision. Particularly we focus on the investigation of the collisions involving homo-nuclear diatomic molecules. It has been demonstrated that coherent electron emission from the two identical atomic centers can be visualized as a emission from a molecular double slit. The fast charged particle impact ionization and double differential electron emission spectrum then can be used not only to explore more about the ionization mechanisms but also the Young type electron interference. Although such a mechanism was predicted earlier, by Cohen and Fano in 1966, but it took about 40 years to have a clear experimental confirmation. Since then it has been an active field of research worldwide. The fast ion beams from Pelletron accelerator, with velocity about 10% of velocity of light, and the slower ions at intermediate velocity obtained from an ECR based ion-accelerator at TIFR are used for some of these studies. The brief overview includes mainly our experimental results over last several years on the derivation of the interference induced oscillations in the electron spectrum. The use of forward backward asymmetry in electron emission spectrum is an innovative and unambiguous way to study the interference. In addition, the double frequency component of the oscillation is also observed and has been explained in terms of a double scattering mechanism i.e. including the second order effect in the Born series for scattering amplitude. Clear differences in the results for and those for O2 and N2 are explained in terms of ab-initio theoretical models based on the linear combination of atomic orbitals for the target and the distortion of the initial and final states due to the moving Coulomb field of highly charged projectiles. The comparison between fast heavy ions and fast electrons as projectiles are also investigated regarding the structure of the interference oscillations. This is mainly a brief review of our own contribution in this field of research. The work of other international groups are also referred to some extent. (author)

  19. Correlation between energy deposition and molecular damage from Auger electrons: A case study of ultra-low energy (5–18 eV) electron interactions with DNA

    International Nuclear Information System (INIS)

    Purpose: The present study introduces a new method to establish a direct correlation between biologically related physical parameters (i.e., stopping and damaging cross sections, respectively) for an Auger-electron emitting radionuclide decaying within a target molecule (e.g., DNA), so as to evaluate the efficacy of the radionuclide at the molecular level. These parameters can be applied to the dosimetry of Auger electrons and the quantification of their biological effects, which are the main criteria to assess the therapeutic efficacy of Auger-electron emitting radionuclides. Methods: Absorbed dose and stopping cross section for the Auger electrons of 5–18 eV emitted by125I within DNA were determined by developing a nanodosimetric model. The molecular damages induced by these Auger electrons were investigated by measuring damaging cross section, including that for the formation of DNA single- and double-strand breaks. Nanoscale films of pure plasmid DNA were prepared via the freeze-drying technique and subsequently irradiated with low-energy electrons at various fluences. The damaging cross sections were determined by employing a molecular survival model to the measured exposure–response curves for induction of DNA strand breaks. Results: For a single decay of125I within DNA, the Auger electrons of 5–18 eV deposit the energies of 12.1 and 9.1 eV within a 4.2-nm3 volume of a hydrated or dry DNA, which results in the absorbed doses of 270 and 210 kGy, respectively. DNA bases have a major contribution to the deposited energies. Ten-electronvolt and high linear energy transfer 100-eV electrons have a similar cross section for the formation of DNA double-strand break, while 100-eV electrons are twice as efficient as 10 eV in the induction of single-strand break. Conclusions: Ultra-low-energy electrons (<18 eV) substantially contribute to the absorbed dose and to the molecular damage from Auger-electron emitting radionuclides; hence, they should be considered in the dosimetry calculation of such radionuclides. Moreover, absorbed dose is not an appropriate physical parameter for nanodosimetry. Instead, stopping cross section, which describes the probability of energy deposition in a target molecule can be an appropriate nanodosimetric parameter. The stopping cross section is correlated with a damaging cross section (e.g., cross section for the double-strand break formation) to quantify the number of each specific lesion in a target molecule for each nuclear decay of a single Auger-electron emitting radionuclide

  20. Excitation and charge transfer in He+ + H collisions. A molecular approach including two-electron translation factors

    International Nuclear Information System (INIS)

    In a previous paper we have pointed out that the common-translation-factor (CTF) method is the only one which, at present, and within the framework of the molecular model of atomic collisions, can be shown to be both convergent and computationally fast, even for many-electron systems. In this Communication we check that this second statement is correct, presenting, for the first time, a molecular calculation involving two-electron translation factors, for He+ + H collisions. A careful study of the sensitivity of the calculated cross sections to the choice of the CTF is performed, and conclusions on that sensitivity are drawn, for several types of processes

  1. Excitation and charge transfer in He/sup +/ + H collisions. A molecular approach including two-electron translation factors

    Energy Technology Data Exchange (ETDEWEB)

    Errea, L.F.; Mendez, L.; Riera, A.

    1983-06-01

    In a previous paper we have pointed out that the common-translation-factor (CTF) method is the only one which, at present, and within the framework of the molecular model of atomic collisions, can be shown to be both convergent and computationally fast, even for many-electron systems. In this Communication we check that this second statement is correct, presenting, for the first time, a molecular calculation involving two-electron translation factors, for He/sup +/ + H collisions. A careful study of the sensitivity of the calculated cross sections to the choice of the CTF is performed, and conclusions on that sensitivity are drawn, for several types of processes.

  2. A molecular symmetry analysis of the electronic states and transition dipole moments for molecules with two torsional degrees of freedom

    International Nuclear Information System (INIS)

    We present a molecular symmetry analysis of electronic states and transition dipole moments for molecules which undergo large amplitude intramolecular torsions. The method is based on the correlation between the point group of the molecule at highly symmetric configurations and the molecular symmetry group. As an example, we determine the global irreducible representations of the electronic states and transition dipole moments for the quinodimethane derivative 2-[4-(cyclopenta-2,4-dien-1-ylidene)cyclohexa-2,5-dien-1-ylidene]-2H-1, 3-dioxole for which two torsional degrees of freedom can be activated upon photo-excitation and construct the resulting symmetry adapted transition dipole functions

  3. Electron microscopy investigation of interface between carbon fiber and ultra high molecular weight polyethylene

    Energy Technology Data Exchange (ETDEWEB)

    Stepashkin, A.A.; Chukov, D.I., E-mail: dil_chukov@yahoo.com; Gorshenkov, M.V.; Tcherdyntsev, V.V.; Kaloshkin, S.D.

    2014-02-15

    Highlights: • Effect of the carbon fibers surface treatments on the adhesive interactions in UHMWPE composites was studied. • Air oxidation of carbon filler ensures most significant increase in adhesion interaction in UHMWPE based composites. • Nanosized UHMWPE fibers with 20–40 nm in diameter and with 6–10 ?m in length, was observed on the surface of carbon fibers. -- Abstract: Scanning electron microscopy was used to investigate the surface of initial and modified high-strength and high-modulus carbon fibers as well as interfaces in the ultra high molecular weight polyethylene, filled with above-mentioned fibers. Effect of the fibers surface modifying method on the adhesive interactions in composites was studied. It was observed that interaction of matrix with a modified surface of fibers results in a formation of bonds with strength higher than the yield strength of the polymer. It results in a formation of long nanosized polymer wires at tensile fracture of composites.

  4. Electronic transport and vibrational modes in the smallest molecular bridge: H2 in Pt nanocontacts

    CERN Document Server

    García, Y; Fabian, E S; Vergés, J A; Pérez-Jiménez, A J; Louis, E; Garcia, Yamila

    2003-01-01

    We present a state-of-the-art first-principles analysis of electronic transport in a Pt nanocontact in the presence of H2 which has been recently reported by Smit et al. in Nature 419, 906 (2002). Our results indicate that at the last stages of the breaking of the Pt nanocontact two basic forms of bridge involving H can appear. Our claim is, in contrast to Smit et al.'s, that the main conductance histogram peak at G approx 2e^2/h is not due to molecular H2, but to a complex Pt2H2 where the H2 molecule dissociates. A first-principles vibrational analysis that compares favorably with the experimental one also supports our claim .

  5. Electronic structure calculations and molecular dynamics simulations with linear system-size scaling

    CERN Document Server

    Mauri, F; Francesco Mauri; Giulia Galli

    1994-01-01

    We present a method for total energy minimizations and molecular dynamics simulations based either on tight-binding or on Kohn-Sham hamiltonians. The method leads to an algorithm whose computational cost scales linearly with the system size. The key features of our approach are (i) an orbital formulation with single particle wavefunctions constrained to be localized in given regions of space, and (ii) an energy functional which does not require either explicit orthogonalization of the electronic orbitals, or inversion of an overlap matrix. The foundations and accuracy of the approach and the performances of the algorithm are discussed, and illustrated with several numerical examples including Kohn-Sham hamiltonians. In particular we present calculations with tight-binding hamiltonians for diamond, graphite, a carbon linear chain and liquid carbon at low pressure. Even for a complex case such as liquid carbon - a disordered metallic system with differently coordinated atoms - the agreement between standard dia...

  6. A micro seismometer based on molecular electronic transducer technology for planetary exploration

    International Nuclear Information System (INIS)

    This letter describes an implementation of micromachined seismometer based on molecular electronic transducer (MET) technology. As opposed to a solid inertial mass, MET seismometer senses the movement of liquid electrolyte relative to fixed electrodes. The employment of micro-electro-mechanical systems techniques reduces the internal size of the sensing cell to 1?m and improves the reproducibility of the device. For operating bias of 600 mV, a sensitivity of 809 V/(m/s2) was measured under acceleration of 400?g(g?9.81m/s2) at 0.32 Hz. A ?115 dB (relative to (m/s2)/?(Hz)) noise level at 1 Hz was achieved. This work develops an alternative paradigm of seismic sensing device with small size, high sensitivity, low noise floor, high shock tolerance, and independence of installation angle, which is promising for next generation seismometers for planetary exploration.

  7. Progress towards a measurement of the electron electric dipole moment with trapped molecular ions

    Science.gov (United States)

    Cairncross, Will; Cossel, Kevin; Grau, Matt; Gresh, Dan; Ye, Jun; Cornell, Eric

    2014-05-01

    Trapped molecular ions are well suited to searches for the electric dipole moment of the electron (eEDM) due to the long coherence times possible. The current experiment at JILA focuses on the metastable 3?1 level of HfF+ in a Paul trap with additional rotating electric and magnetic bias fields. We have demonstrated the ability to state-selectively transfer population to the desired 3?1 J = 1 state in the ion trap and to efficiently read-out the population in single spin states using photodissociation. Using these techniques, we performed Stark spectroscopy of the eEDM measurement states and made an absolute determination of the magnetic g-factors of the mF = +/- 3 / 2 Zeeman sub-levels. Finally, we have demonstrated eEDM-sensitive Ramsey spectroscopy in a rotating bias field with 100 ms coherence time and four detected ion counts on average per experimental cycle.

  8. Fabrication of a Few-Layer Graphene Electrodes for Molecular Electronics Devices

    Directory of Open Access Journals (Sweden)

    Holovchenko A.

    2014-08-01

    Full Text Available We report on thefabrication of a molecular transistor based on a single molecule trapped in a few-layergraphene nanogap. The device is pre-patterned with He-ion beam milling oroxygen plasma etching prior to nanogap formation. Pre-patterning helps tolocalize the gap, and to make it narrower, so that only a few or a singlemolecule can be trapped in it. The nanogap is formed by an electroburning techniqueat room temperature. In order to test the functionality of the device wedeposited diamino-terphenyl molecules in the nanogap. Three-terminal electricalmeasurements showed an increase of the current after deposition, and a gatevoltage dependence at low temperatures. Hence, pre-patterned few-layer graphenejunctions can be used for electron transport measurements through a terphenylmolecule with a future prospective towards more complex molecularconfigurations.

  9. Electron microscopy investigation of interface between carbon fiber and ultra high molecular weight polyethylene

    International Nuclear Information System (INIS)

    Highlights: • Effect of the carbon fibers surface treatments on the adhesive interactions in UHMWPE composites was studied. • Air oxidation of carbon filler ensures most significant increase in adhesion interaction in UHMWPE based composites. • Nanosized UHMWPE fibers with 20–40 nm in diameter and with 6–10 ?m in length, was observed on the surface of carbon fibers. -- Abstract: Scanning electron microscopy was used to investigate the surface of initial and modified high-strength and high-modulus carbon fibers as well as interfaces in the ultra high molecular weight polyethylene, filled with above-mentioned fibers. Effect of the fibers surface modifying method on the adhesive interactions in composites was studied. It was observed that interaction of matrix with a modified surface of fibers results in a formation of bonds with strength higher than the yield strength of the polymer. It results in a formation of long nanosized polymer wires at tensile fracture of composites

  10. Surface free energy of ultra-high molecular weight polyethylene modified by electron and gamma irradiation

    International Nuclear Information System (INIS)

    Surface free energy of biocompatible polymers is important factor which affects the surface properties such as wetting, adhesion and biocompatibility. In the present work, the change in the surface free energy of ultra-high molecular weight polyethylene (UHMWPE) samples, which is produced by electron beam and gamma ray irradiation were, investigated. Mechanism of the changes in surface free energy induced by irradiations of doses ranging from 25 to 500 kGy was studied. FTIR technique was applied for sample analysis. Contact angle measurements showed that wettability and surface free energy of samples have increased with increasing the irradiation dose, where the values of droplet contact angle of the samples decrease gradually with increasing the radiation dose. The increase in the wettability and surface free energy of the irradiated samples are attributed to formation of hydrophilic groups on the polymer surface by the oxidation, which apparently occurs by exposure of irradiated samples to the air.

  11. Surface free energy of ultra-high molecular weight polyethylene modified by electron and gamma irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Abdul-Kader, A.M., E-mail: tawwab@itme.edu.pl [Physics Department, Faculty of Science, Helwan University, Ain Helwan, Cairo (Egypt); Turos, A. [Institute of Electronic Materials Technology, 01-919 Warsaw, ul. Wolczynska 133 (Poland); Soltan Institute of Nuclear Studies, 05-400 Swierk/Otwock (Poland); Radwan, R.M. [Radiation Physics Department, National Center for Radiation Research and Technology (NCRRT), Atomic Energy Authority (AEA), P.O. Box 29, Nasr City, Cairo (Egypt); Kelany, A.M. [Physics Department, Faculty of Science, Helwan University, Ain Helwan, Cairo (Egypt)

    2009-06-15

    Surface free energy of biocompatible polymers is important factor which affects the surface properties such as wetting, adhesion and biocompatibility. In the present work, the change in the surface free energy of ultra-high molecular weight polyethylene (UHMWPE) samples, which is produced by electron beam and gamma ray irradiation were, investigated. Mechanism of the changes in surface free energy induced by irradiations of doses ranging from 25 to 500 kGy was studied. FTIR technique was applied for sample analysis. Contact angle measurements showed that wettability and surface free energy of samples have increased with increasing the irradiation dose, where the values of droplet contact angle of the samples decrease gradually with increasing the radiation dose. The increase in the wettability and surface free energy of the irradiated samples are attributed to formation of hydrophilic groups on the polymer surface by the oxidation, which apparently occurs by exposure of irradiated samples to the air.

  12. Molecular modeling of interactions in electronic nose sensors for environmental monitoring

    Science.gov (United States)

    Shevade, A. V.; Ryan, M. A.; Homer, M. L.; Manfreda, A. M.; Yen, S. -P. S.; Zhou, H.; Manatt, K.

    2002-01-01

    We report a study aimed at understanding analyte interactions with sensors made from polymer-carbon black composite films. The sensors are used in an Electronic Nose (ENose) which is used for monitoring the breathing air quality in human habitats. The model mimics the experimental conditions of the composite film deposition and formation and was developed using molecular modeling and simulation tools. The Dreiding 2.21 Force Field was used for the polymer and analyte molecules while graphite parameters were assigned to the carbon black atoms. The polymer considered for this work is methyl vinyl ether / maleic acid copolymer. The target analytes include both inorganic (NH3) and organic (methanol) types of compound. Results indicate different composite-analyte interaction behavior.

  13. Efficient preconditioning of the electronic structure problem in large scale ab initio molecular dynamics simulations

    Science.gov (United States)

    Schiffmann, Florian; VandeVondele, Joost

    2015-06-01

    We present an improved preconditioning scheme for electronic structure calculations based on the orbital transformation method. First, a preconditioner is developed which includes information from the full Kohn-Sham matrix but avoids computationally demanding diagonalisation steps in its construction. This reduces the computational cost of its construction, eliminating a bottleneck in large scale simulations, while maintaining rapid convergence. In addition, a modified form of Hotelling's iterative inversion is introduced to replace the exact inversion of the preconditioner matrix. This method is highly effective during molecular dynamics (MD), as the solution obtained in earlier MD steps is a suitable initial guess. Filtering small elements during sparse matrix multiplication leads to linear scaling inversion, while retaining robustness, already for relatively small systems. For system sizes ranging from a few hundred to a few thousand atoms, which are typical for many practical applications, the improvements to the algorithm lead to a 2-5 fold speedup per MD step.

  14. HDL surface lipids mediate CETP binding as revealed by electron microscopy and molecular dynamics simulation

    Science.gov (United States)

    Zhang, Meng; Charles, River; Tong, Huimin; Zhang, Lei; Patel, Mili; Wang, Francis; Rames, Matthew J.; Ren, Amy; Rye, Kerry-Anne; Qiu, Xiayang; Johns, Douglas G.; Charles, M. Arthur; Ren, Gang

    2015-03-01

    Cholesteryl ester transfer protein (CETP) mediates the transfer of cholesterol esters (CE) from atheroprotective high-density lipoproteins (HDL) to atherogenic low-density lipoproteins (LDL). CETP inhibition has been regarded as a promising strategy for increasing HDL levels and subsequently reducing the risk of cardiovascular diseases (CVD). Although the crystal structure of CETP is known, little is known regarding how CETP binds to HDL. Here, we investigated how various HDL-like particles interact with CETP by electron microscopy and molecular dynamics simulations. Results showed that CETP binds to HDL via hydrophobic interactions rather than protein-protein interactions. The HDL surface lipid curvature generates a hydrophobic environment, leading to CETP hydrophobic distal end interaction. This interaction is independent of other HDL components, such as apolipoproteins, cholesteryl esters and triglycerides. Thus, disrupting these hydrophobic interactions could be a new therapeutic strategy for attenuating the interaction of CETP with HDL.

  15. Exploring the Tilt-Angle Dependence of electron tunneling across Molecular junction of Self-Assembled Alkanethiols

    DEFF Research Database (Denmark)

    Frederiksen, Thomas; Munuera, C.

    2009-01-01

    Electronic transport mechanisms in molecular junctions are investigated by a combination of first-principles calculations and current?voltage measurements of several well-characterized structures. We study self-assembled layers of alkanethiols grown on Au(111) and form tunnel junctions by contacting the molecular layers with the tip of a conductive force microscope. Measurements done under low-load conditions permit us to obtain reliable tilt-angle and molecular length dependencies of the low-bias conductance through the alkanethiol layers. The observed dependence on tilt-angle is stronger for the longer molecular chains. Our calculations confirm the observed trends and explain them as a result of two mechanisms, namely, a previously proposed intermolecular tunneling enhancement as well as a hitherto overlooked tilt-dependent molecular gate effect.

  16. Changes of molecular mass of humus acids and their systems of polyconjugation upon peat modification by flow of fast electrons

    International Nuclear Information System (INIS)

    It has been studied that while treating peat humus acids in a moist state with the flow of electrons one can observe along with an absorbed dose an increase of averaged molecular masses, high-molecular fractions share, decrease of low-molecular constituent share and insignificant reduction of samples poly-dispersion ability, thus testifying to the polymerization process run. By the ESR-spectroscopy method it has been shown that peat humus acid radiation modification is accompanied by the formation of new structures of polyconjugation (authors)

  17. Hildebrand and Hansen solubility parameters from molecular dynamics with applications to electronic nose polymer sensors.

    Science.gov (United States)

    Belmares, M; Blanco, M; Goddard, W A; Ross, R B; Caldwell, G; Chou, S-H; Pham, J; Olofson, P M; Thomas, Cristina

    2004-11-30

    We introduce the Cohesive Energy Density (CED) method, a multiple sampling Molecular Dynamics computer simulation procedure that may offer higher consistency in the estimation of Hildebrand and Hansen solubility parameters. The use of a multiple sampling technique, combined with a simple but consistent molecular force field and quantum mechanically determined atomic charges, allows for the precise determination of solubility parameters in a systematic way (sigma = 0.4 hildebrands). The CED method yields first-principles Hildebrand parameter predictions in good agreement with experiment [root-mean-square (rms) = 1.1 hildebrands]. We apply the CED method to model the Caltech electronic nose, an array of 20 polymer sensors. Sensors are built with conducting leads connected through thin-film polymers loaded with carbon black. Odorant detection relies on a change in electric resistivity of the polymer film as function of the amount of swelling caused by the odorant compound. The amount of swelling depends upon the chemical composition of the polymer and the odorant molecule. The pattern is unique, and unambiguously identifies the compound. Experimentally determined changes in relative resistivity of seven polymer sensors upon exposure to 24 solvent vapors were modeled with the CED estimated Hansen solubility components. Predictions of polymer sensor responses result in Pearson R2 coefficients between 0.82 and 0.99. PMID:15389751

  18. Effect of contact interface configuration on electronic transport in (C20)2-based molecular junctions

    International Nuclear Information System (INIS)

    Using first-principles calculations, we study the electronic transport properties in Au-(C20)2-Au molecular junctions with different contact interface configurations: point contact and bond contact. We observe that the transmission through the bond contact is considerably higher than that of point contact. Furthermore, the I–V characteristics are rather different. For the bond contact, we get a metallic behavior followed by a varistor-type behavior. While as for the point contact, the current increases very slowly in a nonlinear way and is one order of magnitude smaller than that of bond contact. We attribute these obvious differences to the distinct contact configurations. -- Highlights: ? The I–V properties of (C20)2 molecular devices are affected by contact configuration. ? As for the bond contact, metallic behavior in the low bias is observed. ? Varistor-type behavior and nonlinear I–V characteristic in the high bias are found. ? As for the point contact, the Landauer conductance greatly decreases. ? The current is one order of magnitude smaller than that of bond contact.

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

    Energy Technology Data Exchange (ETDEWEB)

    Johnsson, P; Rouzee, A; Siu, W; Huismans, Y; Vrakking, M J J [FOM Institute for Atomic and Molecular Physics (AMOLF), Science Park 113, 1098 XG Amsterdam (Netherlands); Lepine, F [Universite Lyon 1, CNRS, LASIM, UMR 5579, 43 bvd. du 11 novembre 1918, F-69622 Villeurbanne (France); Marchenko, T [Laboratoire d' Optique Applique, ENSTA/Ecole Polytechnique, Chemin de la Huniere, 91761 Palaiseau (France); Duesterer, S; Tavella, F; Stojanovic, N; Azima, A; Treusch, R [Hamburger Synchrotronstrahlungslabor (HASYLAB) at Deutsches Elektronen-Synchrotron (DESY) Notkestrasse 85, D-22607 Hamburg (Germany); Kling, M F [Max-Planck Institut fuer Quantenoptik, Hans-Kopfermann Strasse 1, D-85748 Garching (Germany)], E-mail: per.johnsson@fysik.lth.se

    2009-07-14

    High flux extreme ultraviolet (XUV) sources like the free electron laser (FEL) in Hamburg (FLASH) offer the possibility of diffractive imaging of small objects. Irrespective of whether the diffraction is based on the detection of photons or photoelectrons, it is required that the measurement is done in the reference frame of the molecule meaning that, for a sample of several molecules, it is necessary to pre-align the molecules in the sample. As a step towards performing molecular frame diffraction experiments, we report experiments on field-free molecular alignment performed at FLASH. The impulsive alignment induced by a 100 fs near-infrared laser pulse in a rotationally cold CO{sub 2} sample is characterized by ionizing and dissociating the molecules with a time-delayed XUV-FEL pulse. The time-dependent angular distributions of ionic fragments measured by a velocity map imaging spectrometer exhibit rapid changes associated with the induced rotational dynamics. The experimental results show hints of a dissociation process that depends nonlinearly on the XUV intensity.

  20. Cone-Like Rectification Properties of cGMP-Gated Channels in Transmutated Retinal Photoreceptors of Nocturnal Geckoes

    Science.gov (United States)

    Giacomoni, Chiara

    2014-01-01

    Photoreceptors of nocturnal geckoes are scotopic, with rod-shaped outer segments, and sensitivities to light similar to the one of retinal rods from other species of lower vertebrates. However, these cells are not rods, but they originated from cones of ancestral diurnal geckoes with pure-cone retinas, after being forced to adapt to a nocturnal behavior. Several interesting adaptations of these rod-like cones have been studied to date; molecular biology and functional studies confirmed that several proteins of the phototransductive cascade display structural and functional properties that indicate their origin from cones rather than from rods. In this paper, we investigate, with whole cell voltage clamp in the photoreceptor detached outer segment preparation, the voltage rectification properties of cGMP-gated channels in three species, Gekko gecko, Tarentola mauritanica, and Hemidactylus frenatus. We show that the current-voltage properties in the physiological voltage range are reminiscent of the ones of cGMP-gated channels from cones rather than from rods of other cold-blooded vertebrates. The origin and the relevance of the mechanisms investigated are discussed. PMID:25506076

  1. The spectral function and the nature of motion of a conduction electron in orientationally disordered molecular cryocrystal

    International Nuclear Information System (INIS)

    The spectral function of an excess particle (electron, hole) which moves in a molecular cryocrystal without long-range orientational order is obtained. Assuming that the angle correlations decay exponentially (in time and space) it is shown that the spectral function changes abruptly with disordering appears. Thus, the particle movement transforms from coherent to incoherent (diffusive). This behavior is in qualitative agreement with the recent ?SR studies of electron mobility in ?-N2

  2. Advances in the MQDT approach of electron/molecular cation reactive collisions: High precision extensive calculations for applications

    Directory of Open Access Journals (Sweden)

    Motapon O.

    2015-01-01

    Full Text Available Recent advances in the stepwise multichannel quantum defect theory approach of electron/molecular cation reactive collisions have been applied to perform computations of cross sections and rate coefficients for dissociative recombination and electron-impact ro-vibrational transitions of H2+, BeH+ and their deuterated isotopomers. At very low energy, rovibronic interactions play a significant role in the dynamics, whereas at high energy, the dissociative excitation strongly competes with all other reactive processes.

  3. Synthesis and Studies of Sulfur-Containing Heterocyclic Molecules for Molecular Electronics

    DEFF Research Database (Denmark)

    Mazzanti, Virginia

    2014-01-01

    This work describes the synthesis and studies of sulfur containing ? conjugated heterocycles, which are considered interesting motifs in the field of molecular electronics. The first project, which is covered in Chapter 1, concerns the functionalization of tetracycle dibenzo[bc,fg][1,4]dithiapentalene (DDP). Attempts to prepare the S-O analog are also discussed. Chapter 2, focuses upon the studies performed on DDP and other sulfur containing ? conjugated organic molecules. Organic Field Effect Transistor devices were fabricated and their performances were evaluated. Chapter 3 entails the synthesis of dimeric structures of redox active system tetrathiafulvalene (TTF). Molecules with different conjugation pathways bridging two TTFs were synthesized and studied using CV and DPV in order to probe the electronic interaction between these two redox units. The last aspect of this thesis, which is presented in Chapter 4, deals with the incorporation of two TTF units into acetylenic scaffolds to generate greater redox active cyclic systems. Improvements of a previously reported macrocycle synthesis and development of asymmetric macrocyclic systems incorporating two TTF moieties were achieved. The instability issue of synthetic intermediates bearing free acetylenes was overcome employing a new strategy. This involved the end–capping of the acetylenic functionality with triphenylphosphine gold motif producing stable organometallic complexes, which could be subsequently used in Sonogashira cross coupling reactions to construct such macrocycles.

  4. Electronic redistribution around oxygen atoms in silicate melts by ab initio molecular dynamics simulation

    CERN Document Server

    Vuilleumier, R; Guillot, B

    2011-01-01

    The structure around oxygen atoms of four silicate liquids (silica, rhyolite, a model basalt and enstatite) is evaluated by ab initio molecular dynamics simulation. Thanks to the use of maximally localized Wannier orbitals to represent the electronic ground state of the simulated system, one is able to quantify the redistribution of electronic density around oxygen atoms as a function of the cationic environment and melt composition. It is shown that the structure of the melt in the immediate vicinity of the oxygen atoms modulates the distribution of the Wannier orbitals associated with oxygen atoms. In particular the evaluation of the distances between the oxygen-core and the orbital Wannier centers and their evolution with the nature of the cation indicates that the Al-O bond in silicate melts is certainly less covalent than the Si-O bond while for the series Mg-O, Ca-O, Na-O and K-O the covalent character of the M-O bond diminishes rapidly to the benefit of the ionic character. Furthermore it is found that...

  5. EDF: Computing electron number probability distribution functions in real space from molecular wave functions

    Science.gov (United States)

    Francisco, E.; Pendás, A. Martín; Blanco, M. A.

    2008-04-01

    Given an N-electron molecule and an exhaustive partition of the real space ( R) into m arbitrary regions ?,?,…,? ( ?i=1m?=R), the edf program computes all the probabilities P(n,n,…,n) of having exactly n electrons in ?, n electrons in ?,…, and n electrons ( n+n+⋯+n=N) in ?. Each ? may correspond to a single basin (atomic domain) or several such basins (functional group). In the later case, each atomic domain must belong to a single ?. The program can manage both single- and multi-determinant wave functions which are read in from an aimpac-like wave function description ( .wfn) file (T.A. Keith et al., The AIMPAC95 programs, http://www.chemistry.mcmaster.ca/aimpac, 1995). For multi-determinantal wave functions a generalization of the original .wfn file has been introduced. The new format is completely backwards compatible, adding to the previous structure a description of the configuration interaction (CI) coefficients and the determinants of correlated wave functions. Besides the .wfn file, edf only needs the overlap integrals over all the atomic domains between the molecular orbitals (MO). After the P(n,n,…,n) probabilities are computed, edf obtains from them several magnitudes relevant to chemical bonding theory, such as average electronic populations and localization/delocalization indices. Regarding spin, edf may be used in two ways: with or without a splitting of the P(n,n,…,n) probabilities into ? and ? spin components. Program summaryProgram title: edf Catalogue identifier: AEAJ_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEAJ_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 5387 No. of bytes in distributed program, including test data, etc.: 52 381 Distribution format: tar.gz Programming language: Fortran 77 Computer: 2.80 GHz Intel Pentium IV CPU Operating system: GNU/Linux RAM: 55 992 KB Word size: 32 bits Classification: 2.7 External routines: Netlib Nature of problem: Let us have an N-electron molecule and define an exhaustive partition of the physical space into m three-dimensional regions. The edf program computes the probabilities P(n,n,…,n)?P({n}) of all possible allocations of n electrons to ?, n electrons to ?,…, and n electrons to ?,{n} being integers. Solution method: Let us assume that the N-electron molecular wave function, ?(1,N), is a linear combination of M Slater determinants, ?(1,N)=?rMC?(1,N). Calling S?rs the overlap matrix over the 3D region ? between the (real) molecular spin-orbitals (MSO) in ?(?1r,…?Nr) and the MSOs in ?,(?1s,…,?Ns), edf finds all the P({n})'s by solving the linear system ?{n}{?kmtkn}P({n})=?r,sMCCdet[?kmtS?rs], where t=1 and t,…,t are arbitrary real numbers. Restrictions: The number of {n} sets grows very fast with m and N, so that the dimension of the linear system (1) soon becomes very large. Moreover, the computer time required to obtain the determinants in the second member of Eq. (1) scales quadratically with M. These two facts limit the applicability of the method to relatively small molecules. Unusual features: Most of the real variables are of precision real*16. Running time: 0.030, 2.010, and 0.620 seconds for Test examples 1, 2, and 3, respectively. References: [1] A. Martín Pendás, E. Francisco, M.A. Blanco, Faraday Discuss. 135 (2007) 423-438. [2] A. Martín Pendás, E. Francisco, M.A. Blanco, J. Phys. Chem. A 111 (2007) 1084-1090. [3] A. Martín Pendás, E. Francisco, M.A. Blanco, Phys. Chem. Chem. Phys. 9 (2007) 1087-1092. [4] E. Francisco, A. Martín Pendás, M.A. Blanco, J. Chem. Phys. 126 (2007) 094102. [5] A. Martín Pendás, E. Francisco, M.A. Blanco, C. Gatti, Chemistry: A European Journal 113 (2007) 9362-9371.

  6. On the molecular and electronic structure of matrine-type alkaloids

    International Nuclear Information System (INIS)

    A systematic study of the molecular and electronic structure of the eight possible members in the trans-matrine series and of two dehydro-derivatives, sophocarpine and sophoramine, has been performed. According to density functional theory (DFT) calculations these alkaloids exhibit a variety of form and junction of the four six-membered rings and all but sophocarpine have a strong preference for one conformation. Sophocarpine is predicted to have a marked conformational flexibility at the lactamic nitrogen and to exist as a mixture of two nearly isoenergetic conformers (C/D-trans and -cis) in the gas phase or solution. The theoretical predictions are consistent with the available X-ray experimental results as well as IR and NMR evidence. The absolute configuration of the preferred conformer of each compound has been established theoretically and corroborated with the specific optical rotation calculated at the sodium D line. The conformational equilibrium of sophocarpine has also been supported by this physical property. The computed gas-phase proton affinity of matrines indicates a basicity comparable to that of other polycyclic proton sponges. The lowest-energy electronic transitions have been characterized by time-dependent DFT calculations as mainly due to excitations spanning the frontier orbitals ?(NCO), n(O), n(Naminic), and ?*(CO). The electronic structures have also been studied by measuring and calculating significant features of the NMR and photoelectron spectra. In particular, a representative set of NMR chemical shifts and nuclear spin-spin coupling constants, obtained with DFT formalisms, compares favourably with experiment. Notably, the stereoelectronic hyperconjugative effects on ??(Heq/Hax) and ?1 J(CHeq/CHax) of the >N-CO- groups is correctly accounted for by the theoretical results. Based on ab initio outer valence Green's function calculations, a reliable description of the uppermost bands in the photoelectron spectra has been advanced. The splitting and sequence of the ionization energies reflect a complex interaction of the n and ? chromophores

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

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

    2013-06-01

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

  9. Development of low temperature rectification for Kr-85 separation in a reprocessing plant

    International Nuclear Information System (INIS)

    The history of the development of low temperature rectification for removing krypton 85 from the waste gas is briefly described. Experience gained by the Karlsruhe Nuclear Research Centre in this period compared to processes developed elsewhere (low temperature washing with fluorine/chlorine hydrocarbon R12, low temperature adsorption in fixed beds) are used to make decisions for the large Wackersdorf reprocessing plant. The KfK reference process contains the preseparation or combustion of O2 and NOx by reduction with hydrogen on a precious metal catalyst, the adsorptive removal of H2O and CO2, and the subsequent low temperature rectification for separating N2,Xe and Kr. A proposal is made based on experience and the desirable boundary conditions for the Wackersdorf reprocessing plant are given. In the comparison of variants of the process, with and without oxygen, the former is given preference. (RB)

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

    Science.gov (United States)

    Jalikop, Shreyas; Hilgenfeldt, Sascha

    2011-11-01

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

  11. Spectroscopic mapping and selective electronic tuning of molecular orbitals in phosphorescent organometallic complexes – a new strategy for OLED materials

    Science.gov (United States)

    Ewen, Pascal R; Sanning, Jan; Koch, Tobias; Doltsinis, Nikos L

    2014-01-01

    Summary The improvement of molecular electronic devices such as organic light-emitting diodes requires fundamental knowledge about the structural and electronic properties of the employed molecules as well as their interactions with neighboring molecules or interfaces. We show that highly resolved scanning tunneling microscopy (STM) and spectroscopy (STS) are powerful tools to correlate the electronic properties of phosphorescent complexes (i.e., triplet emitters) with their molecular structure as well as the local environment around a single molecule. We used spectroscopic mapping to visualize several occupied and unoccupied molecular frontier orbitals of Pt(II) complexes adsorbed on Au(111). The analysis showed that the molecules exhibit a peculiar localized strong hybridization that leads to partial depopulation of a dz² orbital, while the ligand orbitals are almost unchanged. We further found that substitution of functional groups at well-defined positions can alter specific molecular orbitals without influencing the others. The results open a path toward the tailored design of electronic and optical properties of triplet emitters by smart ligand substitution, which may improve the performance of future OLED devices. PMID:25551053

  12. Local-field effects in current transport through molecular electronic devices: Current density profiles and local non-equilibrium electron distributions

    CERN Document Server

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

    2004-01-01

    We analyze non-equilibrium current transport in molecular electronic devices, using as an example devices formed by two terphenyl dithiol molecules attached to gold electrodes. Using a first-principles based self-consistent matrix Green's function method, we show that the spatially resolved current density profiles and local electrochemical potential drops provide valuable information regarding the local field effect on molecular transport, which depend on the internal structure of the molecules and cannot be obtained from measuring the current- and conductance-voltage characteristics alone.

  13. Molecular projectile effects for kinetic electron emission from carbon- and metal-surfaces bombarded by slow hydrogen ions

    International Nuclear Information System (INIS)

    Total yields for kinetic electron emission (KE) have been determined for impact of hydrogen monomer-, dimer- and trimer-ions (impact energy <10 keV) on atomically clean surfaces of carbon-fiber inforced graphite used as first-wall armour in magnetic fusion devices. The data are compared with KE yields for impact of same projectile ions on atomically clean highly oriented pyrolytic graphite and polycrystalline gold. We discuss KE yields for the different targets if bombarded by equally fast molecular and atomic ions in view to 'projectile molecular effects' (different yields per proton for equally fast atomic and molecular ions), which are expected from calculated electronic projectile energy losses in these target materials

  14. Molecular projectile effects for kinetic electron emission from carbon- and metal-surfaces bombarded by slow hydrogen ions

    CERN Document Server

    Cernusca, S; Aumayr, F; Diez-Muino, R; Juaristi, J I

    2003-01-01

    Total yields for kinetic electron emission (KE) have been determined for impact of hydrogen monomer-, dimer- and trimer-ions (impact energy <10 keV) on atomically clean surfaces of carbon-fiber inforced graphite used as first-wall armour in magnetic fusion devices. The data are compared with KE yields for impact of same projectile ions on atomically clean highly oriented pyrolytic graphite and polycrystalline gold. We discuss KE yields for the different targets if bombarded by equally fast molecular and atomic ions in view to 'projectile molecular effects' (different yields per proton for equally fast atomic and molecular ions), which are expected from calculated electronic projectile energy losses in these target materials.

  15. Nonlinear heat transport in mesoscopic conductors: Rectification, Peltier effect and Wiedemann-Franz law

    OpenAIRE

    Lopez, Rosa; Sanchez, David

    2013-01-01

    We investigate nonlinear heat properties in mesoscopic conductors using a scattering theory of transport. Our approach is based on a leading-order expansion in both the electrical and thermal driving forces. Beyond linear response, the transport coefficients are functions of the nonequilibrium screening potential that builds up in the system due to interactions. Within a mean-field approximation, we self-consistently calculate the heat rectification properties of a quantum d...

  16. Dynamic 3D Scene Depth Reconstruction via Optical Flow Field Rectification

    OpenAIRE

    Yang, You; Liu, Qiong; Ji, Rongrong; GAO, YUE

    2012-01-01

    In this paper, we propose a depth propagation scheme based on optical flow field rectification towards more accurate depth reconstruction. In depth reconstruction, the occlusions and low-textural regions easily result in optical flow field errors, which lead ambiguous depth value or holes without depth in the obtained depth map. In this work, a scheme is proposed to improve the precision of depth propagation and the quality of depth reconstruction for dynamic scene. The proposed scheme first ...

  17. Wideband THz Time Domain Spectroscopy based on Optical Rectification and Electro-Optic Sampling

    OpenAIRE

    Tomasino, A; Parisi, A.; Stivala, S.; Livreri, P.; Cino, A. C.; A. C. Busacca; Peccianti, M.; Morandotti, R.

    2013-01-01

    We present an analytical model describing the full electromagnetic propagation in a THz time-domain spectroscopy (THz-TDS) system, from the THz pulses via Optical Rectification to the detection via Electro Optic-Sampling. While several investigations deal singularly with the many elements that constitute a THz-TDS, in our work we pay particular attention to the modelling of the time-frequency behaviour of all the stages which compose the experimental set-up. Therefore, our model considers the...

  18. Design of high power rectification power supply based on digital control

    International Nuclear Information System (INIS)

    For typical high power rectification power supply, a design based on digital control is introduced. The feasibility and superiority of the digital control scheme were verified through the design and experimental results of the filament power supply for high current ion source of NBI. The application of digital control scheme, making the filament power supply design is more intelligent and simple, as related applications provide a reference. (authors)

  19. Rectification and diffusion of self-propelled particles in a two-dimensional corrugated channel

    OpenAIRE

    Ai, Bao-Quan; Chen, Qiu-yan; He, Ya-feng; Li, Feng-guo; Zhong, Wei-Rong

    2014-01-01

    Rectification and diffusion of non-interacting self-propelled particles is numerically investigated in a two-dimensional corrugated channel. From numerical simulations, we obtain the average velocity and the effective diffusion coefficient. It is found that the self-propelled particles can be rectified by the self-propelled velocity. There exist optimal values of the parameters (the self-propelled velocity, the translational diffusion constant, and the height of the potentia...

  20. THz generation by optical rectification and competition with other nonlinear processes

    OpenAIRE

    Zhao, Zhen-Yu; Hameau, Sophie; Tignon, Jérôme

    2006-01-01

    We present a study of the competition between tera-hertz (THz) generation by optical rectification in ZnTe crystals, two-photon absorption, second harmonic generation and free-carrier absorption. The two-photon nonlinear absorption coefficient, second harmonic generation efficiency and free-carrier absorption coefficient in the THz range are measured independently. The incident pump field is shown to be depleted by two-photon absorption and the THz radiation is shown to be reduced, upon focu...

  1. Terahertz wave generation via optical rectification from multiferroic BiFeO3

    OpenAIRE

    Talbayev, D.; Lee, Seongsu; Cheong, S.-W.; A.J. Taylor

    2008-01-01

    We detected broadband coherent terahertz (THz) emission from multiferroic BiFeO3 after illuminating a high-quality bulk single ferroelectric domain crystal with a ~100 fs optical pulse. The dependence of the emitted THz waveform on the energy and polarization of the optical pulse is consistent with the optical rectification mechanism of THz emission. The THz emission provides a sensitive probe of the electric polarization state of BiFeO3, enabling applications in ferroelectr...

  2. Reconstruction of two-dimensional molecular structure with laser-induced electron diffraction from laser-aligned polyatomic molecules

    Science.gov (United States)

    Yu, Chao; Wei, Hui; Wang, Xu; Le, Anh-Thu; Lu, Ruifeng; Lin, C. D.

    2015-10-01

    Imaging the transient process of molecules has been a basic way to investigate photochemical reactions and dynamics. Based on laser-induced electron diffraction and partial one-dimensional molecular alignment, here we provide two effective methods for reconstructing two-dimensional structure of polyatomic molecules. We demonstrate that electron diffraction images in both scattering angles and broadband energy can be utilized to retrieve complementary structure information, including positions of light atoms. With picometre spatial resolution and the inherent femtosecond temporal resolution of lasers, laser-induced electron diffraction method offers significant opportunities for probing atomic motion in a large molecule in a typical pump-probe measurement.

  3. Efficient inverted polymer solar cells with thermal-evaporated and solution-processed small molecular electron extraction layer

    Science.gov (United States)

    Sun, Fu-Zhou; Shi, Ai-Li; Xu, Zai-Quan; Wei, Huai-Xin; Li, Yan-Qing; Lee, Shuit-Tong; Tang, Jian-Xin

    2013-04-01

    Efficient inverted polymer solar cell is reported upon by integrating with a small molecular 1,3,5-tri(phenyl-2-benzimi-dazolyl)-benzene (TPBi) electron extraction layer (EEL) at low processing temperature with thermal-evaporation and solution-process, resulting in the power conversion efficiencies of 3.70% and 3.47%, respectively. The potential of TPBi as an efficient EEL is associated with its suitable electronic energy level for electron extraction and hole blocking from the active layer to the indium tin oxide cathode.

  4. Molecular dynamics simulation of electron-ion temperature relaxation in dense hydrogen: A scheme of truncated Coulomb potential

    Science.gov (United States)

    Ma, Qian; Dai, Jiayu; Kang, Dongdong; Zhao, Zengxiu; Yuan, Jianmin; Zhao, Xueqing

    2014-12-01

    Molecular dynamics (MD) simulations are performed to investigate the temperature relaxation between electrons and ions in a fully ionized, dense hydrogen plasma. We used HM (J. P. Hansen and I. R. McDonald) potential and introduced a truncated Coulomb interaction, which can avoid Coulomb catastrophe by choosing an appropriate cutting radius. The calculated results are compared with those from theoretical models (LS, GMS, BPS), whose applicability is also discussed. The effect of the interaction between ions and electrons on the temperature relaxation process is also investigated in the strong collision region. Finally, we discuss the effect of exchange interaction of electrons to the temperature relaxation.

  5. Controlling Electronic Structures by Irradiation in Single-walled SiC Nanotubes: A First-Principles Molecular Dynamics Study

    International Nuclear Information System (INIS)

    Using first principles molecular dynamics simulations, the displacement threshold energy and defect configurations are determined in SiC nanotubes. The simulation results reveal that a rich variety of defect structures (vacancies, Stone-Wales defects, and antisite defects) are formed with threshold energies of from 11 to 64 eV. The threshold energy shows an anisotropic behavior and exhibits a dramatic decrease with decreasing tube diameter. The electronic structure can be altered by the defects formed by irradiation, which suggests that the electron irradiation may be a way to use defect engineering to tailor electronic properties of SiC nanotubes

  6. Controlling electronic structures by irradiation in single-walled SiC nanotubes: a first-principles molecular dynamics study

    International Nuclear Information System (INIS)

    Using first-principles molecular dynamics simulations, the displacement threshold energy and defect configurations are determined in SiC nanotubes. The simulation results reveal that a rich variety of defect structures (vacancies, Stone-Wales defects and antisite defects) are formed with threshold energies from 11 to 64 eV. The threshold energy shows an anisotropic behavior and exhibits a dramatic decrease with decreasing tube diameter. The electronic structure can be altered by the defects formed by irradiation, which suggests that the electron irradiation may be a way to use defect engineering to tailor electronic properties of SiC nanotubes.

  7. Thermal rectification and thermal resistive phase cross over in exponential mass graded materials

    Science.gov (United States)

    Shah, T. N.; Gajjar, P. N.

    2013-12-01

    Concept of the functional graded materials (FGMs) has been explored by considering exponential mass variation along the chain of anharmonic oscillators in the study of heat transport at low dimensions. This exponential distribution of mass along the space invokes the diffusion of phonons transport which results to temperature gradient, asymmetric heat flow, thermal rectification and cross over between positive differential thermal resistance (PDTR) and negative differential thermal resistance (NDTR) in one-dimensional (1D) exponential mass graded chain. The temperature dependence thermal rectification achieved is 4-74% and also predicted that the thermal rectification can be controlled by tuning the higher and lower average temperature limits of two thermal reservoirs. It is also seen that in FGMs, the thermal conductivity does not change drastically against the average temperature of two heat baths. The cross over between PDTR and NDTR can be tuned either by mass ratio of one dimensional (1D) exponential mass graded anharmonic chain and/or by temperature difference between two heat baths. The figure of merit of the 1D structure can also be tuned by mass gradient, the higher mass gradient material will work as the potential candidate for better thermoelectric material.

  8. Laser Activated Electron Tunneling Based Mass Spectrometric Imaging of Molecular Architectures of Mouse Brain Revealing Regional Specific Lipids.

    Science.gov (United States)

    Huang, Lulu; Tang, Xuemei; Zhang, Wenyang; Jiang, Ruowei; Zhong, Hongying

    2016-01-01

    A comprehensive description of overall brain architecture at the molecular level is essential for understanding behavioral and cognitive processes in health and diseases. Although fluorescent labeling of target proteins has been successfully established to visualize a brain connectome, the molecular basis for diverse neurophysiological phenomena remains largely unknown. Here we report a brain-wide, molecular-level, and microscale imaging of endogenous metabolites, in particular, lipids of mouse brain by using laser activated electron tunneling (LAET) and mass spectrometry. In this approach, atomic electron emission along with finely tuned laser beam size provides high resolution that can be down to the sub-micrometer level to display spatial distribution of lipids in mouse brain slices. Electron-directed soft ionization has been achieved through exothermal capture of tunneling photoelectrons as well as unpaired electron-initiated chemical bond cleavages. Regionally specific lipids including saturated, mono-unsaturated, and poly-unsaturated fatty acids as well as other lipids, which may be implicated in neurological signaling pathways, have been discovered by using this laser activated electron tunneling based mass spectrometric imaging (LAET-MSI) technique. PMID:26613184

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

    International Nuclear Information System (INIS)

    The aim of this project was to develop a generic method of preparing a 'molecular architecture' containing functional groups on a surface at predetermined relative positions several nm apart. This would be of great utility in molecular electronics, chemical sensors and other fields. It was proposed that such an architecture could be prepared on gold using linked, helical oligopeptides that contained the components of interest and sulphur functions able to form monolayers on gold by the self-assembly technique. Towards this ultimate aim Self-Assembled Monolayers (SAMs) of monomeric oligopeptides (13-17 residues) were prepared and characterised. Peptides containing three Met residues spaced in the sequence so that their side-chains lay on the same side of the helix were shown by circular dichroism (CD) to be strongly helical in organic solvents. Their self-assembled films on gold were characterised by Reflection-Absorption Infrared Spectroscopy (RAIRS) which showed the peptides adsorbed with the helix axes parallel to the surface, the orientation expected for self-assembly. However the surface coverage measured by cyclic voltammetry (CV) of the peptides' ferrocenyl derivatives on gold electrodes were less than expected for monolayers. Comparison of the films of ferrocenyl derivatives of Met and Cys showed that the thiolate bound more strongly than the thioether. Accordingly an oligopeptide containing two Cys residues at i, i+3, designed to be 310-helical, was prepared. Transformation of the two (Trt)Cys residues of the resin-bound peptide to the intramolecular disulphide by iodine was achieved in acetonitrile but not in DMF. CD suggested that the conformation of this peptide was a mixture of helix and random coil. Films of the peptide-disulphide and the peptide-dithiol adsorbed from protic solvents were characterised as multilayers by ellipsometry. However CV and ellipsometry showed that a monolayer was successfully prepared from acetonitrile. Future targets for improving and extending this method to form monolayers of linked disulphides are presented. (author)

  10. Communication: Electronic and transport properties of molecular junctions under a finite bias: A dual mean field approach

    International Nuclear Information System (INIS)

    We show that when a molecular junction is under an external bias, its properties cannot be uniquely determined by the total electron density in the same manner as the density functional theory for ground state properties. In order to correctly incorporate bias-induced nonequilibrium effects, we present a dual mean field (DMF) approach. The key idea is that the total electron density together with the density of current-carrying electrons are sufficient to determine the properties of the system. Two mean fields, one for current-carrying electrons and the other one for equilibrium electrons can then be derived. Calculations for a graphene nanoribbon junction show that compared with the commonly used ab initio transport theory, the DMF approach could significantly reduce the electric current at low biases due to the non-equilibrium corrections to the mean field potential in the scattering region

  11. Communication: Electronic and transport properties of molecular junctions under a finite bias: A dual mean field approach

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Shuanglong; Feng, Yuan Ping [Department of Physics and Graphene Research Centre, National University of Singapore, 2 Science Drive 3, Singapore 117542 (Singapore); Zhang, Chun, E-mail: phyzc@nus.edu.sg [Department of Physics and Graphene Research Centre, National University of Singapore, 2 Science Drive 3, Singapore 117542 (Singapore); Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543 (Singapore)

    2013-11-21

    We show that when a molecular junction is under an external bias, its properties cannot be uniquely determined by the total electron density in the same manner as the density functional theory for ground state properties. In order to correctly incorporate bias-induced nonequilibrium effects, we present a dual mean field (DMF) approach. The key idea is that the total electron density together with the density of current-carrying electrons are sufficient to determine the properties of the system. Two mean fields, one for current-carrying electrons and the other one for equilibrium electrons can then be derived. Calculations for a graphene nanoribbon junction show that compared with the commonly used ab initio transport theory, the DMF approach could significantly reduce the electric current at low biases due to the non-equilibrium corrections to the mean field potential in the scattering region.

  12. Radio-sensibility study of pseudo cereals by means of molecular markers and electronic microscopy

    International Nuclear Information System (INIS)

    With the purpose of observing the radio sensibility in two species of pseudo cereals group (Amaranthus hypochondria cus and Chenopodium berlandieri subsp. nuttalliae), germplasm of 4 amaranth genotypes was irradiated (A-21-0-10, Mixquic-09, M-2 and M-6) and 4 huauzontle genotypes (H-18, H-19, H-10 and red Chia) in the Gamma Irradiator of the ININ in a dose range of 50 to 500 Gy with intervals each 50 Gy and a treatment witness without irradiating. The evaluation of the material was carried out in three stages: 1) the pheno logy and morphology was evaluated during the plants development in each treatment under greenhouse conditions; 2) the radio sensibility was evaluated at molecular level by means of molecular markers type Ssr (Simple Sequence Repeats); and 3) the irradiated seeds were analyzed by under vacuum electronic microscopy. According to the results, the pheno logy phases were ahead in lower doses to 250 Gy for amaranth and higher doses to 150 Gy for huauzontle, there being a morphological variation in leaves and cob. The morphological variables were favored in dose from 50 to 200 Gy for amaranth, while in huauzontle the morphology presented more response variation to the radiation. In the DNA, the 21 Ssr were 100% polymorphic in amaranth and 97% polymorphic in huauzontle, being one of the more polymorphic the QCA0005 in amaranth and QCA0005 in huauzontle. The generated dendrograms showed greater similarity between Mixquic-09 and M-2 (amaranth) and between H-19 and H-10 (huauzontle). While by treatments, in amaranth the dose of 500 Gy presented most polymorphic difference and in huauzontle was the dose of 200 Gy. The under vacuum electronic microscopy did not show differences in the seed structure while the elemental analysis showed the presence of carbon, oxygen, aluminum, sulfur and calcium as the most common elements and in more concentration carbon and oxygen. For A. hypochondria cus the dose DL50 (median lethal dose) was between 50 and 100 Gy and for C. berlandieri subsp. nuttalliae was between 250 and 300 Gy, ranges that are recommended as good for future works of genetic improvement. (Author)

  13. A Molecular Electronic Transducer based Low-Frequency Accelerometer with Electrolyte Droplet Sensing Body

    Science.gov (United States)

    Liang, Mengbing

    "Sensor Decade" has been labeled on the first decade of the 21st century. Similar to the revolution of micro-computer in 1980s, sensor R&D developed rapidly during the past 20 years. Hard workings were mainly made to minimize the size of devices with optimal the performance. Efforts to develop the small size devices are mainly concentrated around Micro-electro-mechanical-system (MEMS) technology. MEMS accelerometers are widely published and used in consumer electronics, such as smart phones, gaming consoles, anti-shake camera and vibration detectors. This study represents liquid-state low frequency micro-accelerometer based on molecular electronic transducer (MET), in which inertial mass is not the only but also the conversion of mechanical movement to electric current signal is the main utilization of the ionic liquid. With silicon-based planar micro-fabrication, the device uses a sub-micron liter electrolyte droplet sealed in oil as the sensing body and a MET electrode arrangement which is the anode-cathode-cathode-anode (ACCA) in parallel as the read-out sensing part. In order to sensing the movement of ionic liquid, an imposed electric potential was applied between the anode and the cathode. The electrode reaction, I3-- + 2e-- ? 3I --, occurs around the cathode which is reverse at the anodes. Obviously, the current magnitude varies with the concentration of ionic liquid, which will be effected by the movement of liquid droplet as the inertial mass. With such structure, the promising performance of the MET device design is to achieve 10.8 V/G (G=9.81 m/s2) sensitivity at 20 Hz with the bandwidth from 1 Hz to 50 Hz, and a low noise floor of 100 microg/sqrt(Hz) at 20 Hz.

  14. Molecular electronics using diazonium-derived adlayers on carbon with Cu top contacts: critical analysis of metal oxides and filaments

    International Nuclear Information System (INIS)

    Evaporation of Cu metal onto thin (less than 5 nm) molecular layers bonded to conductive carbon substrates results in electronic junctions with an ensemble of molecules sandwiched between two conductors. The resulting devices have previously been characterized through analysis of current density-voltage (j-V) curves for several different molecular layers and as a function of layer thickness. The approach represents an 'ensemble' rather than 'single molecule' technique, in which the electronic response represents that of a large number of molecules (106-1012) in parallel as well as the conducting contacts contained in the molecular junction. In this paper, we extend a more detailed investigation of two critical issues: the possibility of conduction by metal filaments, and the potential role of top contact oxidation contributing to the electronic properties of the junctions. The results show that the conductance of the junctions can be modulated by changes in the deposition environment, but that the changes are not related to Cu oxide in the top contact. Based on these results, we propose that the conditions during top contact deposition change the way in which the molecules contact the metal, leading to differences in the effective junction area. Finally, through systematic studies using variation of the temperature, we show that metal filament conduction is distinct from that observed for the molecular junctions and that if the current observed experimentally passed through nanoscopic metal filaments the Joule heating would lead to rapid melting. For a series of junctions with structurally related aromatic molecules (including biphenyl, nitrobiphenyl, fluorene, and nitroazobenzene), the electron transfer mechanism is briefly investigated using area-independent analysis methods. It is shown that field emission and/or transport through bands formed by the molecular layer is likely, based on the weak temperature dependence of junction conductance

  15. Self-consistent GW calculations of electronic transport in thiol- and amine-linked molecular junctions

    DEFF Research Database (Denmark)

    Strange, M.; Rostgaard, Carsten

    2011-01-01

    The electronic conductance of a benzene molecule connected to gold electrodes via thiol, thiolate, or amino anchoring groups is calculated using nonequilibrium Green functions in combination with the fully self-consistent GW approximation for exchange and correlation. The calculated conductance of benzenedithiol and benzenediamine is one-fifth that predicted by standard density functional theory (DFT), in very good agreement with experiments. In contrast, the widely studied benzenedithiolate structure is found to have a significantly higher conductance due to the unsaturated sulfur bonds. These findings suggest that more complex gold-thiolate structures where the thiolate anchors are chemically passivated by Au adatoms are responsible for the measured conductance. Analysis of the energy level alignment obtained with DFT, Hartree-Fock, and GW reveals the importance of self-interaction corrections (exchange) on the molecule and dynamical screening at the metal-molecule interface. The main effect of the GW self-energy is to renormalize the level positions; however, its influence on the shape of molecular resonances also affects the conductance. Non-self-consistent G(0)W(0) calculations, starting from either DFT or Hartree-Fock, yield conductance values within 50% of the self-consistent GW results.

  16. Scanning electron microscopy and molecular dynamics of surfaces of growing and ablating hexagonal ice crystals

    Directory of Open Access Journals (Sweden)

    W. C. Pfalzgraff

    2009-10-01

    Full Text Available Optical properties of cirrus ice clouds play an important role in regulating Earth's radiative balance. It has been hypothesized that the surfaces of cirrus ice crystals may be characterized by mesoscopic (micrometer-scale texturing, or roughness, in order to explain discrepancies between theoretical and observed light-scattering properties. Here, we present the first clearly resolved observations of surfaces of hexagonal ice crystals, using variable-pressure scanning electron microscopy. During growth conditions, the ice surface develops trans-prismatic strands, separated from one another by distances of 5–10 ?m. These strands become more pronounced during ablation, and exhibit a wider range of separations. Under re-growth conditions, faceting is re-established initially at prismatic edges. Molecular dynamics studies of a free-standing ice Ih nanocolumn showed no trans-prismatic strands at the atomistic level, suggesting that these strands originate at a spatial scale greater than 10 nm. The observed surface roughness could be used to construct more realistic representations of cirrus clouds in climate models, and constrain theories of ice crystal growth and ablation.

  17. Molecular weight distribution of electron and ?-ray irradiated PEEK measured by very high temperature GPC

    International Nuclear Information System (INIS)

    Poly(ether ether ketone)(PEEK) films were irradiated with electron beam in air and in helium. Gel fractions of the PEEK samples were determined as the ratio of the weight of insoluble fraction/total weigh by extracting the samples with 1-chloronaphthalene (1-CN) at 260degC. While unirradiated PEEK samples were dissolved in 1-CN completely, PEEK samples highly (10 - 50 MGy) irradiated in air were almost insoluble in the solvent. The weight-average molecular weight Mw of soluble fractions of the samples were measured by very high temperature gel permeation chromatography (VHTGPC): it was found that the Mw decreases with increasing dose. On the other hand, PEEK samples irradiated in helium gave gel fractions at lower doses (0 - 5 MGy) than in air. The PEEK films were also irradiated with 60Co ?-rays in the dose range, i.e. from 0 to 5 MGy. The ?-irradiated PEEK samples were completely dissolved in 1-CN at 260degC. Their Mw measured by VHTGPC decreases with increasing dose. (author)

  18. NATO Advanced Study Institute on Lower-Dimensional Systems and Molecular Electronics

    CERN Document Server

    Day, Peter; Papavassiliou, George

    1990-01-01

    This volume represents the written account of the NATO Advanced Study Institute "Lower-Dimensional Systems and Molecular Electronics" held at Hotel Spetses, Spetses Island, Greece from 12 June to 23 June 1989. The goal of the Institute was to demonstrate the breadth of chemical and physical knowledge that has been acquired in the last 20 years in inorganic and organic crystals, polymers, and thin films, which exhibit phenomena of reduced dimensionality. The interest in these systems started in the late 1960's with lower-dimensional inorganic conductors, in the early 1970's with quasi-one-dimensional crystalline organic conductors. which by 1979 led to the first organic superconductors, and, in 1977, to the fITSt conducting polymers. The study of monolayer films (Langmuir-Blodgett films) had progressed since the 1930's, but reached a great upsurge in . the early 1980's. The pursuit of non-linear optical phenomena became increasingly popular in the early 1980's, as the attention turned from inorganic crystals t...

  19. Modulation of direct electron transfer of cytochrome c by use of a molecularly imprinted thin film.

    Science.gov (United States)

    Bosserdt, Maria; Gajovic-Eichelman, Nenad; Scheller, Frieder W

    2013-08-01

    We describe the preparation of a molecularly imprinted polymer film (MIP) on top of a self-assembled monolayer (SAM) of mercaptoundecanoic acid (MUA) on gold, where the template cytochrome c (cyt c) participates in direct electron transfer (DET) with the underlying electrode. To enable DET, a non-conductive polymer film is electrodeposited from an aqueous solution of scopoletin and cyt c on to the surface of a gold electrode previously modified with MUA. The electroactive surface concentration of cyt c was 0.5 pmol cm(-2). In the absence of the MUA layer, no cyt c DET was observed and the pseudo-peroxidatic activity of the scopoletin-entrapped protein, assessed via oxidation of Ampliflu red in the presence of hydrogen peroxide, was only 30% of that for the MIP on MUA. This result indicates that electrostatic adsorption of cyt c by the MUA-SAM substantially increases the surface concentration of cyt c during the electrodeposition step, and is a prerequisite for the productive orientation required for DET. After template removal by treatment with sulfuric acid, rebinding of cyt c to the MUA-MIP-modified electrode occurred with an affinity constant of 100,000 mol(-1) L, a value three times higher than that determined by use of fluorescence titration for the interaction between scopoletin and cyt c in solution. The DET of cyt c in the presence of myoglobin, lysozyme, and bovine serum albumin (BSA) reveals that the MIP layer suppresses the effect of competing proteins. PMID:23660694

  20. A micro seismometer based on molecular electronic transducer technology for planetary exploration

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Hai; Tang, Rui [School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287 (United States); Carande, Bryce; Oiler, Jonathan [School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287 (United States); Zaitsev, Dmitri; Agafonov, Vadim [Center of Molecular Electronics, Moscow Institute of Physics and Technology, Moscow (Russian Federation); Yu, Hongyu [School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287 (United States); School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287 (United States)

    2013-05-13

    This letter describes an implementation of micromachined seismometer based on molecular electronic transducer (MET) technology. As opposed to a solid inertial mass, MET seismometer senses the movement of liquid electrolyte relative to fixed electrodes. The employment of micro-electro-mechanical systems techniques reduces the internal size of the sensing cell to 1{mu}m and improves the reproducibility of the device. For operating bias of 600 mV, a sensitivity of 809 V/(m/s{sup 2}) was measured under acceleration of 400{mu}g(g{identical_to}9.81m/s{sup 2}) at 0.32 Hz. A -115 dB (relative to (m/s{sup 2})/{radical}(Hz)) noise level at 1 Hz was achieved. This work develops an alternative paradigm of seismic sensing device with small size, high sensitivity, low noise floor, high shock tolerance, and independence of installation angle, which is promising for next generation seismometers for planetary exploration.

  1. Moving solvated electrons with light: Nonadiabatic mixed quantum/classical molecular dynamics simulations of the relocalization of photoexcited solvated electrons in tetrahydrofuran (THF)

    International Nuclear Information System (INIS)

    Motivated by recent ultrafast spectroscopic experiments [Martini et al., Science 293, 462 (2001)], which suggest that photoexcited solvated electrons in tetrahydrofuran (THF) can relocalize (that is, return to equilibrium in solvent cavities far from where they started), we performed a series of nonequilibrium, nonadiabatic, mixed quantum/classical molecular dynamics simulations that mimic one-photon excitation of the THF-solvated electron. We find that as photoexcited THF-solvated electrons relax to their ground states either by continuous mixing from the excited state or via nonadiabatic transitions, ?30% of them relocalize into cavities that can be over 1 nm away from where they originated, in close agreement with the experiments. A detailed investigation shows that the ability of excited THF-solvated electrons to undergo photoinduced relocalization stems from the existence of preexisting cavity traps that are an intrinsic part of the structure of liquid THF. This explains why solvated electrons can undergo photoinduced relocalization in solvents like THF but not in solvents like water, which lack the preexisting traps necessary to stabilize the excited electron in other places in the fluid. We also find that even when they do not ultimately relocalize, photoexcited solvated electrons in THF temporarily visit other sites in the fluid, explaining why the photoexcitation of THF-solvated electrons is so efficient at promoting recombination with nearby scavengers. Overall, our study shows that the defining characteristic of a liquid that permits the photoassisted relocalization of solvated electrons is the existence of nascent cavities that are attractive to an excess electron; we propose that other such liquids can be found from classical computer simulations or neutron diffraction experiments

  2. Probing molecular-level organizational structure and electronic decoupling of tartaric acid domains supported on Ag(111)

    Energy Technology Data Exchange (ETDEWEB)

    Santagata, N M [Department of Chemistry, North Carolina State University, Raleigh, NC 27695-7518 (United States); Lakhani, A M; DeWitt, D J; Luo, P; Pearl, T P [Department of Physics, North Carolina State University, Raleigh, NC 27695-7518 (United States)], E-mail: tppearl@ncsu.edu

    2008-03-15

    Mechanisms of adsorption and organization of organic molecules on metallic surfaces play a significant role in the growth of chemically and electronically tuned monolayer thin films. Intercommunication between functional groups for individual adsorbates can serve as the primary driving force for monolayer crystallinity as well as electronic structure, especially in the limit of weak interaction between the adsorbate and substrate. In this article we discuss the submonolayer ordering of a chiral molecule, tartaric acid (C{sub 4}H{sub 6}O{sub 6}), weakly bound to an achiral metal surface, Ag(111), as studied with low temperature scanning tunneling microscopy (STM) and differential conductance imaging. Molecularly resolved images of enantiomerically pure (R,R)- and (S,S)-tartaric acid domains on Ag(111) are presented and the role of intermolecular hydrogen bonding in stereospecific domain and superlattice formation is addressed. Additionally, we consider films formed from the deposition of a racemic mixture of tartaric acid enantiomers. Lastly we present differential conductance mapping of tartaric acid molecular domains that highlights an intrinsic decoupling of molecular film electronic states with respect to the metallic lattice. While the chiral expression that drives the formation of enantiomeric domains does not induce stereospecific conductance, we demonstrate electronic differentiation of submonolayer organic domains from the Ag(111) surface.

  3. Effect of electron beam radiation on the structure and mechanical properties of ultra high molecular weight polyethylene fibers

    International Nuclear Information System (INIS)

    Ultra high molecular weight polyethylene fibers have been crosslinked by electron beam. The structure and mechanical properties of them have been investigated in different irradiation atmospheres. The obtained results show that the gel content and crosslinking density increase with the increase of dose, the swelling ratio and average molecular weight of crosslinked net decrease with the increase of dose, the tensile strength and failure elongation decrease with the increase of dose, the tensile modulus increases with the increase of dose. When the samples are irradiated in air, vacuum and acetylene atmospheres, the effect of irradiation in acetylene atmosphere is best

  4. Multiphoton Ionization as a clock to Reveal Molecular Dynamics with Intense Short X-ray Free Electron Laser Pulses

    CERN Document Server

    Fang, L; Murphy, B; Tarantelli, F; Kukk, E; Cryan, J P; Glownia, M; Bucksbaum, P H; Coffee, R N; Chen, M; Buth, C; Berrah, N

    2013-01-01

    We investigate molecular dynamics of multiple ionization in N2 through multiple core-level photoabsorption and subsequent Auger decay processes induced by intense, short X-ray free electron laser pulses. The timing dynamics of the photoabsorption and dissociation processes is mapped onto the kinetic energy of the fragments. Measurements of the latter allow us to map out the average internuclear separation for every molecular photoionization sequence step and obtain the average time interval between the photoabsorption events. Using multiphoton ionization as a tool of multiple-pulse pump-probe scheme, we demonstrate the modi?cation of the ionization dynamics as we vary the x-ray laser pulse duration.

  5. Electronic devices and circuits

    CERN Document Server

    Pridham, Gordon John

    1968-01-01

    Electronic Devices and Circuits, Volume 1 deals with the design and applications of electronic devices and circuits such as passive components, diodes, triodes and transistors, rectification and power supplies, amplifying circuits, electronic instruments, and oscillators. These topics are supported with introductory network theory and physics. This volume is comprised of nine chapters and begins by explaining the operation of resistive, inductive, and capacitive elements in direct and alternating current circuits. The theory for some of the expressions quoted in later chapters is presented. Th

  6. Properties of sizeable [n]cycloparaphenylenes as molecular models of single-wall carbon nanotubes elucidated by Raman spectroscopy: structural and electron-transfer responses under mechanical stress.

    Science.gov (United States)

    Peña Alvarez, Miriam; Mayorga Burrezo, Paula; Kertesz, Miklos; Iwamoto, Takahiro; Yamago, Shigeru; Xia, Jianlong; Jasti, Ramesh; López Navarrete, Juan T; Taravillo, Mercedes; Baonza, Valentín G; Casado, Juan

    2014-07-01

    [n]Cycloparaphenylenes behave as molecular templates of "perfectly chemically defined" single-wall carbon nanotubes. These [n]CPP molecules have electronic, mechanical, and chemical properties in size correspondence with their giant congeners. Under mechanical stress, they form charge-transfer salts, or complexes with fullerene, by one-electron concave-convex electron transfer. PMID:24838669

  7. Oxidation of ultra high molecular weigh polyethylene irradiated with low energy electron beams and subsequent graft polymerization of MMA

    International Nuclear Information System (INIS)

    The ultra high molecular weight polyethylene (UHMWPE) samples with different thickness were irradiated with different low energy electron beams and energy dependent surface treatment was investigated. The change of the melting temperature and crystallinity of samples were measured by using DSC and the radical yields were also determined by ESR. The graft polymerization of MMA onto UHMWPE was investigated and it was found that peroxyl radical from oxides would play a role as an initiator. The treatment with 80 keV electron beams showed that the reaction would start from the surface. (Author)

  8. Theoretical studies of triple differential cross section for (e, 2e) reaction of molecular hydrogen by electron

    International Nuclear Information System (INIS)

    The momentum-space molecular distorted-wave approximation (MDWBA) model is developed, which transform the multiple center problem of molecules in coordinate space to a single center problem in momentum space. In the MDWBA model, the incident, the scattered, and the ejected electron wave functions are obtained from solving the Lippmann-Schwinger Equations. Using this approach, the triple differential cross sections for electron-impact ionization of hydrogen molecule in the coplanar asymmetric geometry at incident energies of 100 eV are calculated, and compared with the existing experimental and theoretical data. From the comparison, the present calculations are giving an overall good representation of the experimental data. (authors)

  9. Optical rectification at visible frequency in biased bilayer graphene

    Science.gov (United States)

    Hipolito, F.; Pereira, Vitor M.

    2015-03-01

    The second order response of the electrical current to an electromagnetic field is analyzed within the framework of non-equilibrium many-body perturbation theory for the case of a two-dimensional electronic system such as graphene and its bilayer. The absence of inversion symmetry in a biased graphene bilayer allows a finite DC response in second order to an AC electromagnetic wave. The induced DC current is evaluated for biased bilayer at finite temperature, and its tunability is analyzed as a function of electron density, which can be experimentally varied by means of a global gate voltage applied to the sample. Both intrinsic and photon drag microscopic processes are considered, as they contribute on similar footing to the photocurrent in general. However, the dependencies of these two contributions on the polarization state of the incident light are different, which allows the manipulation of the relative contribution of intrinsic versus photon drag contributions by tuning the experimental parameters. For example, the photocurrent emerging from circularly polarized light stems entirely from photon drag, as the circular photogalvanic effect is forbidden by the C3 rotation symmetry of the honeycomb lattice.

  10. Structure impact on the thermal and electronic properties of bismuth telluride by ab-initio and molecular dynamics calculations

    International Nuclear Information System (INIS)

    We use molecular dynamics and ab-initio methods to predict the thermal and electronic properties of new materials with high figures of merit. The simulated systems are bulk bismuth tellurides with antisite and vacancy defects. Optimizations of the materials under investigation are performed by the SIESTA code for subsequent calculations of force constants, electronic properties, and Seebeck coefficients. The prediction of the thermal conductivity is made by Non-Equilibrium Molecular Dynamics (NEMD) using the LAMMPS code. The thermal conductivity of bulk bismuth telluride with different stoichiometry and with a number of substitution defects is calculated. We have found that the thermal conductivity can be decreased by 60% by introducing vacancy defects. The calculated thermal conductivities for the different structures are compared with the available experimental and theoretical results.

  11. Detection of atomic and molecular mega-electron-volt projectiles using an x-ray charged coupled device camera

    Science.gov (United States)

    Chabot, M.; Martinet, G.; Béroff, K.; Pino, T.; Bouneau, S.; Genolini, B.; Grave, X.; Nguyen, K.; le Gailliard, C.; Rosier, P.; Féraud, G.; Friha, H.; Villier, B.

    2011-10-01

    We show that an x-ray charge coupled device (CCD) may be used as a particle detector for atomic and molecular mega-electron-volt (MeV) projectiles of around a few hundred keV per atomic mass unit. For atomic species, spectroscopic properties in kinetic energy measurements (i.e., linearity and energy resolution) are found to be close to those currently obtained with implanted or surface barrier silicon particle detectors. For molecular species, in order to increase the maximum kinetic energy detection limit, we propose to put a thin foil in front of the CCD. This foil breaks up the molecules into atoms and spreads the charges over many CCD pixels and therefore avoiding saturation effects. This opens new perspectives in high velocity molecular dissociation studies with accelerator facilities.

  12. Detection of atomic and molecular mega-electron-volt projectiles using an x-ray charged coupled device camera

    International Nuclear Information System (INIS)

    We show that an x-ray charge coupled device (CCD) may be used as a particle detector for atomic and molecular mega-electron-volt (MeV) projectiles of around a few hundred keV per atomic mass unit. For atomic species, spectroscopic properties in kinetic energy measurements (i.e., linearity and energy resolution) are found to be close to those currently obtained with implanted or surface barrier silicon particle detectors. For molecular species, in order to increase the maximum kinetic energy detection limit, we propose to put a thin foil in front of the CCD. This foil breaks up the molecules into atoms and spreads the charges over many CCD pixels and therefore avoiding saturation effects. This opens new perspectives in high velocity molecular dissociation studies with accelerator facilities.

  13. The accuracy of molecular bond lengths computed by multireference electronic structure methods

    International Nuclear Information System (INIS)

    We compare experimental Re values with computed Re values for 20 molecules using three multireference electronic structure methods, MCSCF, MR-SDCI, and MR-AQCC. Three correlation-consistent orbital basis sets are used, along with complete basis set extrapolations, for all of the molecules. These data complement those computed previously with single-reference methods. Several trends are observed. The SCF Re values tend to be shorter than the experimental values, and the MCSCF values tend to be longer than the experimental values. We attribute these trends to the ionic contamination of the SCF wave function and to the corresponding systematic distortion of the potential energy curve. For the individual bonds, the MR-SDCI Re values tend to be shorter than the MR-AQCC values, which in turn tend to be shorter than the MCSCF values. Compared to the previous single-reference results, the MCSCF values are roughly comparable to the MP4 and CCSD methods, which are more accurate than might be expected due to the fact that these MCSCF wave functions include no extra-valence electron correlation effects. This suggests that static valence correlation effects, such as near-degeneracies and the ability to dissociate correctly to neutral fragments, play an important role in determining the shape of the potential energy surface, even near equilibrium structures. The MR-SDCI and MR-AQCC methods predict Re values with an accuracy comparable to, or better than, the best single-reference methods (MP4, CCSD, and CCSD(T)), despite the fact that triple and higher excitations into the extra-valence orbital space are included in the single-reference methods but are absent in the multireference wave functions. The computed Re values using the multireference methods tend to be smooth and monotonic with basis set improvement. The molecular structures are optimized using analytic energy gradients, and the timings for these calculations show the practical advantage of using variational wave functions for which the Hellmann-Feynman theorem can be exploited

  14. Topology and stability of conjugated hidrocarbons. The dependence of total p-electron energy on molecular topology

    Directory of Open Access Journals (Sweden)

    IVAN GUTMAN

    2005-03-01

    Full Text Available In spite of the fact that research on the mathematical properties of the total p-electron energy E (as computed by means of the Hückel molecular orbital approximation started already in the 1940s, many results in this area have been obtained also in the newest times. In 1978 this author published in this journal a review on E. The present article is another review on E, summarizing the progress in the theory of E, achieved since then.

  15. Dependence of the total p-electron energy on a large number of non-bonding molecular orbitals

    Directory of Open Access Journals (Sweden)

    NATASA CMILJANOVIC

    2004-10-01

    Full Text Available Using a recently developed method for computing the effect of non-bonding molecular orbitals (NBMOs on the total p-electron energy (E, it was found that the dependence of E on the number n0 of NBMOs is almost perfectly linear. We now show that this regularity remains valid for very large values of n0, in particular, to hold up to n0 = 20.

  16. Dependence of the total p-electron energy on a large number of non-bonding molecular orbitals

    OpenAIRE

    NATASA CMILJANOVIC; SVETLANA MILOSAVLJEVIC; SLAVKO RADENKOVIC; DRAGAN STEVANOVIC; IVAN GUTMAN

    2004-01-01

    Using a recently developed method for computing the effect of non-bonding molecular orbitals (NBMOs) on the total p-electron energy (E), it was found that the dependence of E on the number n0 of NBMOs is almost perfectly linear. We now show that this regularity remains valid for very large values of n0, in particular, to hold up to n0 = 20.

  17. On the Phase Shift of Reflection High Energy Electron Diffraction Intensity Oscillations during Ge(001) Homoepitaxy by Molecular Beam Epitaxy

    OpenAIRE

    McCamy, James W.; Shin, Byungha; Leonard, John P.; Aziz, Michael

    2007-01-01

    We have conducted a systematic investigation of the phase shift of the Reflection High Energy Electron Diffraction (RHEED) intensity oscillations during homoepitaxy of Ge(001) by molecular beam epitaxy for a wide range of diffraction conditions. Our results show that for small incidence angles with a beam azimuth several degrees away from the crystallographic symmetry direction, the phase is independent of incidence angle; however, it starts to shift once the incidence angle is high enough t...

  18. Basis set construction for molecular electronic structure theory: Natural orbital and Gauss-Slater basis for smooth pseudpotentials

    OpenAIRE

    Petruzielo, Frank R.; Toulouse, Julien; Umrigar, C. J.

    2010-01-01

    A simple yet general method for constructing basis sets for molecular electronic structure calculations is presented. These basis sets consist of atomic natural orbitals from a multi-configurational self-consistent field calculation supplemented with primitive functions, chosen such that the asymptotics are appropriate for the potential of the system. Primitives are optimized for the homonuclear diatomic molecule to produce a balanced basis set. Two general features that fac...

  19. Molecular simulations of outersphere reorganization energies for intramolecular electron and hole transfer in polar solvents

    International Nuclear Information System (INIS)

    Outersphere reorganization energies (?) for intramolecular electron transfer (ET) and hole transfer are studied in anion- and cation-radical forms of complex organic substrates (biphenylyl-spacer-naphtyl) in polar solvents simulated by means of the nonpolarizable models of water and 1,2-dichloroethane. The earlier elaborated molecular/continuum approach (the MD/FRCM, J. Chem. Phys., 119 (2003) 8024) is used; this method provides a physically relevant background for separating inertial and inertialess polarization responses within a nonpolarizable MD simulation (the SPC water model). Quantum-chemical calculations of solute charge distributions were performed with semiempirical (AM1) and second ab initio (HF/6-31G(d,p)) approximations. Ab initio charges give lower ?-values and are preferable, probably, because of including the effect of the SCRF polarization of the diabatic ET states. Standard Lennard-Jones and charge parameters implemented in MD runs were not specially fitted for reproducing ET effects. The difference in values for a cation and an anion originating from the same parent structure was specially investigated. As shown earlier, this effect, nonlinear in its nature, proved to be extremely large when a model dipolar two-site system was studied. For the present ET structures representing real chemical substrates it has reduced to a plausible value of 6-8 kcal/mol. The study of the temperature dependence of ? comprises a first MD simulation of this problem and its slope was found to be in accord with an experimental observation for an anionic species. Calculations of absolute ?-values for the hole transfer in 1,2-dichloroethane are the first MD simulations of reorganization energies in experimentally studied reactions. Computed values of ?-s are higher than the experimental data. The effect of this magnitude could be eliminated by proper tuning the solvent parameters

  20. Structural and electronic properties of organo-halide hybrid perovskites from ab initio molecular dynamics.

    Science.gov (United States)

    Quarti, Claudio; Mosconi, Edoardo; De Angelis, Filippo

    2015-04-14

    The last two years have seen the unprecedentedly rapid emergence of a new class of solar cells, based on hybrid organic-inorganic halide perovskites. The success of this class of materials is due to their outstanding photoelectrochemical properties coupled to their low cost, mainly solution-based, fabrication techniques. Solution processed materials are however often characterized by an inherent flexible structure, which is hardly mapped into a single local minimum energy structure. In this perspective, we report on the interplay between structural and electronic properties of hybrid lead iodide perovskites investigated using ab initio molecular dynamics (AIMD) simulations, which allow the dynamical simulation of disordered systems at finite temperature. We compare the prototypical MAPbI3 (MA = methylammonium) perovskite in its cubic and tetragonal structure with the trigonal phase of FAPbI3 (FA = formamidinium), investigating different starting arrangements of the organic cations. Despite the relatively short time scale amenable to AIMD, typically a few tens of ps, this analysis demonstrates the sizable structural flexibility of this class of materials, showing that the instantaneous structure could significantly differ from the time and thermal averaged structure. We also highlight the importance of the organic-inorganic interactions in determining the fluxional properties of this class of materials. A peculiar spatial localization of the valence and conduction band edges is also found, with a dynamics in the range of 0.1 ps, which is associated with the positional dynamics of the organic cations within the cubo-octahedral perovskite cage. This asymmetry in the spatial localization of the band edges is expected to ease exciton dissociation and assist the initial stages of charge separation, possibly constituting one of the key factors for the impressive photovoltaic performances of hybrid lead-iodide perovskites. PMID:25766785