WorldWideScience
1

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

DEFF Research Database (Denmark)

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

Kuznetsov, A.M.; Ulstrup, Jens

2002-01-01

2

Tuning rectification in single-molecular diodes.  

Science.gov (United States)

We demonstrate a new method of achieving rectification in single molecule devices using the high-bias properties of gold-carbon bonds. Our design for molecular rectifiers uses a symmetric, conjugated molecular backbone with a single methylsulfide group linking one end to a gold electrode and a covalent gold-carbon bond at the other end. The gold-carbon bond results in a hybrid gold-molecule "gateway" state pinned close to the Fermi level of one electrode. Through nonequilibrium transport calculations, we show that the energy of this state shifts drastically with applied bias, resulting in rectification at surprisingly low voltages. We use this concept to design and synthesize a family of diodes and demonstrate through single-molecule current-voltage measurements that the rectification ratio can be predictably and efficiently tuned. This result constitutes the first experimental demonstration of a rationally tunable system of single-molecule rectifiers. More generally, the results demonstrate that the high-bias properties of "gateway" states can be used to provide additional functionality to molecular electronic systems. PMID:24274757

Batra, Arunabh; Darancet, Pierre; Chen, Qishui; Meisner, Jeffrey S; Widawsky, Jonathan R; Neaton, Jeffrey B; Nuckolls, Colin; Venkataraman, Latha

2013-01-01

3

Reversible rectification in sub-monolayer molecular heterojunctions  

Science.gov (United States)

Pentacene and C60 are archetypal molecules for optically active acceptor-donor heterojunctions and have been used as the active materials in bilayer solar cells. We will discuss UHV STM and STS measurements on these bi-molecular films deposited sequentially to form heterojunctions on Cu(111). It is observed that rectification can be detected at the single-junction limit, and that the direction of rectification flips in accordance with the polarity of the heterojunction. The morphology of heterolayers will also be discussed. It is found that the density of a Pn monolayer can be affected by choice of growth conditions, and in turn can affect the overall morphology of the heterolayer and the rectification behavior of the heterojunctions. We will also briefly discuss progress towards probing the photophysical behavior of these systems. The correlation of atomic-scale structure and electronic behavior at the single-junction limit has important implications for applications of such heterojunctions, such as solar cells or OLEDs.

Smerdon, Joe; Giebink, Chris; Bode, Matthias; Guisinger, Nathan; Guest, Jeffrey

2011-03-01

4

Rectification Mechanism in Di-Block Oligomer Molecular Diodes  

CERN Document Server

We investigated a mechanism of rectification in di-block oligomer diode molecules that have recently been synthesized and showed a pronounced asymmetry in the measured I-V spectrum. The observed rectification effect is due to the resonant nature of electron transfer in the system and localization properties of bound state wave functions of resonant states of the tunneling electron interacting with asymmetric molecule in an electric field. The asymmetry of the tunneling wave function is enhanced or weakened depending on the polarity of applied bias. The conceptually new theoretical approach, the Green's function theory of sub-barrier scattering, is able to provide a physically transparent explanation of this rectification effect based on the concept of the bound state spectrum of a tunneling electron. The theory predicts the characteristic features of the I-V spectrum in qualitative agreement with experiment.

Oleynik, I I; Posvyanskii, V S; Yu, L

2005-01-01

5

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

Science.gov (United States)

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

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

2014-07-29

6

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

OpenAIRE

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

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

2014-01-01

7

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

CERN Document Server

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.

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

2014-01-01

8

Thermal rectification of electrons in hybrid normal metal-superconductor nanojunctions  

Energy Technology Data Exchange (ETDEWEB)

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.

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

9

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

International Nuclear Information System (INIS)

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

10

Electronic transport properties of phenylacetylene molecular junctions  

International Nuclear Information System (INIS)

Electronic transport properties of a kind of phenylacetylene compound— (4-mercaptophenyl)-phenylacetylene are calculated by the first-principles method in the framework of density functional theory and the nonequilibrium Green's function formalism. The molecular junction shows an obvious rectifying behaviour at a bias voltage larger than 1.0 V. The rectification effect is attributed to the asymmetry of the interface contacts. Moreover, at a bias voltage larger than 2.0 V, which is not referred to in a relevant experiment [Fang L, Park J Y, Ma H, Jen A K Y and Salmeron M 2007 Langmuir 23 11522], we find a negative differential resistance phenomenon. The negative differential resistance effect may originate from the change of the delocalization degree of the molecular orbitals induced by the bias. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

11

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

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 ...

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

1998-01-01

12

Current rectification by mediating electroactive polymers  

Energy Technology Data Exchange (ETDEWEB)

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 Fe{sup 2+/3+} and on the Fe(CN){sub 6}{sup 3-/4-} redox couples in solution that prove the proposed mechanisms of electrochemical rectification.

Ybarra, Gabriel; Moina, Carlos [Centro de Investigacion sobre Electrodeposicion y Procesos Superficiales, Instituto Nacional de Tecnologia Industrial, CC 157, (1650) San Martin (Argentina); Florit, M. Ines [INIFTA, Facultad de Ciencias Exactas, UNLP, Suc. 4, CC 16, (1900) La Plata (Argentina); Posadas, Dionisio [INIFTA, Facultad de Ciencias Exactas, UNLP, Suc. 4, CC 16, (1900) La Plata (Argentina)], E-mail: dposadas@inifta.unlp.edu.ar

2008-04-20

13

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

Science.gov (United States)

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

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

2011-10-25

14

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

Science.gov (United States)

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

Zhang, Qun

2014-10-01

15

Towards graphyne molecular electronics  

Science.gov (United States)

?-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.

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

2015-02-01

16

Towards graphyne molecular electronics.  

Science.gov (United States)

?-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. PMID:25699991

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

2015-01-01

17

Molecular electronics under the microscope  

Science.gov (United States)

The field of molecular electronics has developed significantly as experimental techniques to study charge transport through single molecules have become more reliable. Three Articles in this issue highlight how chemists can now better understand and control electronic properties at the molecular level.

2015-03-01

18

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

Energy Technology Data Exchange (ETDEWEB)

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

Min, Y., E-mail: minshiyi@gmail.com [School of Science, Nantong University, Nantong, Jiangsu, 226007 (China); Fang, J.H.; Zhong, C.G. [School of Science, Nantong University, Nantong, Jiangsu, 226007 (China); Yao, K.L. [School of Physics, Huazhong University of Science and Technology, Wuhan, 430074 (China)

2012-05-07

19

Electron transport through molecular junctions  

Science.gov (United States)

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.

Zimbovskaya, Natalya A.; Pederson, Mark R.

2011-12-01

20

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 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.

21

Kinetic theory for electron transmission through a molecular wire  

International Nuclear Information System (INIS)

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

22

Unconventional molecule-resolved current rectification in diamondoid-fullerene hybrids.  

Science.gov (United States)

The unimolecular rectifier is a fundamental building block of molecular electronics. Rectification in single molecules can arise from electron transfer between molecular orbitals displaying asymmetric spatial charge distributions, akin to p-n junction diodes in semiconductors. Here we report a novel all-hydrocarbon molecular rectifier consisting of a diamantane-C60 conjugate. By linking both sp(3) (diamondoid) and sp(2) (fullerene) carbon allotropes, this hybrid molecule opposingly pairs negative and positive electron affinities. The single-molecule conductances of self-assembled domains on Au(111), probed by low-temperature scanning tunnelling microscopy and spectroscopy, reveal a large rectifying response of the molecular constructs. This specific electronic behaviour is postulated to originate from the electrostatic repulsion of diamantane-C60 molecules due to positively charged terminal hydrogen atoms on the diamondoid interacting with the top electrode (scanning tip) at various bias voltages. Density functional theory computations scrutinize the electronic and vibrational spectroscopic fingerprints of this unique molecular structure and corroborate the unconventional rectification mechanism. PMID:25202942

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

2014-01-01

23

Electrical gating and rectification in graphene three-terminal junctions  

International Nuclear Information System (INIS)

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.

24

Electrical gating and rectification in graphene three-terminal junctions  

Energy Technology Data Exchange (ETDEWEB)

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.

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

25

Dipole-mediated rectification of intramolecular photoinduced charge separation and charge recombination.  

Science.gov (United States)

Controlling charge transfer at a molecular scale is critical for efficient light harvesting, energy conversion, and nanoelectronics. Dipole-polarization electrets, the electrostatic analogue of magnets, provide a means for "steering" electron transduction via the local electric fields generated by their permanent electric dipoles. Here, we describe the first demonstration of the utility of anthranilamides, moieties with ordered dipoles, for controlling intramolecular charge transfer. Donor-acceptor dyads, each containing a single anthranilamide moiety, distinctly rectify both the forward photoinduced electron transfer and the subsequent charge recombination. Changes in the observed charge-transfer kinetics as a function of media polarity were consistent with the anticipated effects of the anthranilamide molecular dipoles on the rectification. The regioselectivity of electron transfer and the molecular dynamics of the dyads further modulated the observed kinetics, particularly for charge recombination. These findings reveal the underlying complexity of dipole-induced effects on electron transfer and demonstrate unexplored paradigms for molecular rectifiers. PMID:25162490

Bao, Duoduo; Upadhyayula, Srigokul; Larsen, Jillian M; Xia, Bing; Georgieva, Boriana; Nuñez, Vicente; Espinoza, Eli M; Hartman, Joshua D; Wurch, Michelle; Chang, Andy; Lin, Chung-Kuang; Larkin, Jason; Vasquez, Krystal; Beran, Gregory J O; Vullev, Valentine I

2014-09-17

26

Electron transport and redox reactions in carbon-based molecular electronic junctions.  

Science.gov (United States)

A unique molecular junction design is described, consisting of a molecular mono- or multilayer oriented between a conducting carbon substrate and a metallic top contact. The sp2 hybridized graphitic carbon substrate (pyrolyzed photoresist film, PPF) is flat on the scale of the molecular dimensions, and the molecular layer is bonded to the substrate via diazonium ion reduction to yield a strong, conjugated C-C bond. Molecular junctions were completed by electron-beam deposition of copper, titanium oxide, or aluminium oxide followed by a final conducting layer of gold. Vibrational spectroscopy and XPS of completed junctions showed minimal damage to the molecular layer by metal deposition, although some electron transfer to the molecular layer resulted in partial reduction in some cases. Device yield was high (>80%), and the standard deviations of junction electronic properties such as low voltage resistance were typically in the range of 10-20%. The resistance of PPF/molecule/Cu/Au junctions exhibited a strong dependence on the structure and thickness of the molecular layer, ranging from 0.13 ohms cm2 for a nitrobiphenyl monolayer, to 4.46 ohms cm2 for a biphenyl monolayer, and 160 ohms cm2 for a 4.3 nm thick nitrobiphenyl multilayer. Junctions containing titanium or aluminium oxide had dramatically lower conductance than their PPF/molecule/Cu counterparts, with aluminium oxide junctions exhibiting essentially insulating behavior. However, in situ Raman spectroscopy of PPF/nitroazobenzene/AlO(x)/Au junctions with partially transparent metal contacts revealed that redox reactions occurred under bias, with nitroazobenzene (NAB) reduction occurring when the PPF was biased negative relative to the Au. Similar redox reactions were observed in PPF/NAB/TiO(x)/Au molecular junctions, but they were accompanied by major effects on electronic behavior, such as rectification and persistent conductance switching. Such switching was evident following polarization of PPF/molecule/TiO2/Au junctions by positive or negative potential pulses, and the resulting conductance changes persisted for several minutes at room temperature. The "memory" effect implied by these observations is attributed to a combination of the molecular layer and the TiO2 properties, namely metastable "trapping" of electrons in the TiO2 when the Au is negatively biased. PMID:16738711

McCreery, Richard L; Wu, Jing; Kalakodimi, Rajendra Prasad

2006-06-14

27

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

International Nuclear Information System (INIS)

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

28

Dirac Electrons in Molecular Solids  

Energy Technology Data Exchange (ETDEWEB)

Electrons in solids are characterized by the energy bands, which indicate that electrons are considered to be 'elementary particles' with specific effective masses and g-factors reflecting features of each solid. There are cases where these particles obey dispersion relationship similar to those of Dirac electrons. Examples include graphite and bismuth both of which are known for many years, together with graphene, a single layer of graphite, recently addressed intensively after its realization. Another recent example is a molecular solid, {alpha}-ET{sub 2}I{sub 3}, which is described by an equation similar to Weyl equation with massless Dirac cones but the coordinate axis is tilted because of the location of cones at off-symmetry points. Orbital susceptibility of such Dirac electrons in graphite and bismuth has been known to have striking features not present in ordinary band electrons but resulting from the inter-band matrix elements of magnetic field. Results of theoretical studies on not only orbital susceptibility but also Hall effect of such Dirac electrons in molecular solids with tilting are introduced in this paper.

Fukuyama, Hidetoshi [Faculty of Science and Research Institute for Science and Technology Tokyo University of Science, Tokyo 162-8601 (Japan); Kobayashi, Akito [Institute for Advanced Research, Nagoya University, Nagoya 464-8602 (Japan); Suzumura, Yoshikazu, E-mail: fukuyama@rs.kagu.tus.ac.jp [Department of Physics, Nagoya University, Nagoya 464-8602 (Japan)

2011-07-20

29

Graphitic silicon nitride: a metal-free ferromagnet with charge and spin current rectification.  

Science.gov (United States)

As a first example, herein we show that g-Si(4)N(3) is expected to act as a metal-free ferromagnet featuring both charge and spin current rectification simultaneously. Such rectification is crucial for envisioning devices that contain both logic and memory functionality on a single chip. The spin coherent quantum-transport calculations on g-Si(4)N(3) reveal that the chosen system is a unique molecular spin filter, the current-voltage characteristics of which is asymmetric in nature, which can create a perfect background for synchronous charge and spin current rectification. To shed light on this highly unusual in-silico observation, we have meticulously inspected the bias-dependent modulation of the spin-polarized eigenstates. The results indicate that, whereas only the localized 2p orbitals of the outer-ring (OR) Si atoms participate in the transmission process in the positive bias, both OR Si and N atoms contribute in the reverse bias. Furthermore, we have evaluated the spin-polarized electron-transfer rate in the tunneling regime, and the results demonstrate that the transfer rates are unequal in the positive and negative bias range, leading to the possible realization of a simultaneous logic-memory device. PMID:25044228

Sen, Sabyasachi; Chakrabarti, Swapan

2014-09-15

30

Fullerene Derived Molecular Electronic Devices  

Science.gov (United States)

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 grapheme sheet, more complex joints require other mechanisms. In this work we explore structural and electronic properties of complex 3-point junctions of carbon nanotubes using a generalized tight-binding molecular-dynamics scheme.

Menon, Madhu; Srivastava, Deepak; Saini, Subbash

1998-01-01

31

Carbon Nanotubes: Molecular Electronic Components  

Science.gov (United States)

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.

Srivastava, Deepak; Saini, Subhash; Menon, Madhu

1997-01-01

32

Carbon Nanotube Based Molecular Electronics  

Science.gov (United States)

Carbon nanotubes and the nanotube heterojunctions have recently emerged as excellent candidates for nanoscale molecular electronic device components. Experimental measurements on the conductivity, rectifying behavior and conductivity-chirality correlation have also been made. While quasi-one dimensional simple heterojunctions between nanotubes with different electronic behavior can be generated by introduction of a pair of heptagon-pentagon defects in an otherwise all hexagon graphene sheet. Other complex 3- and 4-point junctions may require other mechanisms. Structural stability as well as local electronic density of states of various nanotube junctions are investigated using a generalized tight-binding molecular dynamics (GDBMD) scheme that incorporates non-orthogonality of the orbitals. The junctions investigated include straight and small angle heterojunctions of various chiralities and diameters; as well as more complex 'T' and 'Y' junctions which do not always obey the usual pentagon-heptagon pair rule. The study of local density of states (LDOS) reveal many interesting features, most prominent among them being the defect-induced states in the gap. The proposed three and four pointjunctions are one of the smallest possible tunnel junctions made entirely of carbon atoms. Furthermore the electronic behavior of the nanotube based device components can be taylored by doping with group III-V elements such as B and N, and BN nanotubes as a wide band gap semiconductor has also been realized in experiments. Structural properties of heteroatomic nanotubes comprising C, B and N will be discussed.

Srivastava, Deepak; Saini, Subhash; Menon, Madhu

1998-01-01

33

Overview of Nanotechnology: Molecular Electronics  

Science.gov (United States)

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

34

Electronic continuum model for molecular dynamics simulations  

OpenAIRE

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...

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

2009-01-01

35

Electron spectroscopy and molecular structure  

International Nuclear Information System (INIS)

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

36

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

International Nuclear Information System (INIS)

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

37

Organic-based molecular switches for molecular electronics  

Science.gov (United States)

In a general sense, molecular electronics (ME) is the branch of nanotechnology which studies the application of molecular building blocks for the fabrication of electronic components. Among the different types of molecules, organic compounds have been revealed as promising candidates for ME, due to the easy access, great structural diversity and suitable electronic and mechanical properties. Thanks to these useful capabilities, organic molecules have been used to emulate electronic devices at the nanoscopic scale. In this feature article, we present the diverse strategies used to develop organic switches towards ME with special attention to non-volatile systems.

Fuentes, Noelia; Martín-Lasanta, Ana; Álvarez de Cienfuegos, Luis; Ribagorda, Maria; Parra, Andres; Cuerva, Juan M.

2011-10-01

38

Unimolecular electronic rectifiers  

Science.gov (United States)

The fabrication of a unimolecular rectifier is the first step toward the fabrication of nanoscale unimolecular electronic circuit elements. For instance, a nanoscale current transistor will enable the future molecular computer to be much denser, smaller, and faster than present computers, provided that the size of each element (rectifier, resistor, transistor) is small (3-10 nm) and the speed of electron transfer through the element is fast (expected direction and some rectification in the reverse direction are analyzed and discussed. Thu through-film electrical conductivity of Langmuir-Blodgett monolayer films of 1 was studied as a function of temperature. The current is usually smaller at low temperature, but rectification was observed between 370 K and 105 K, with a rectification ratio as large at 105 K as at room temperature. Unimolecular electrical rectification by monolayers of molecule 1 is unequivocally confirmed. The sandwich ``Al | LB monolayer of 1 | Al'' is the smallest rectifier in the world. The details of the fabrication of the sandwich, the instrumentation, as well as the electrical circuit are described. The core-level N1s XPS spectrum reveals the three expected N valence states. The valence-level XPS spectrum can be correlated with theory. Pressure/area isotherms, film transfer, and rectification of five analogs of the molecule were studied, but no rectification was observed on these systems. Pressure/area isotherms of four cholesterol derivatives and a fullerene derivative are reported. Preliminary work on a molecular transistor is also reported. Future work on low-temperature measurements with an improved sandwich structure, and on a molecular transistor is proposed.

Chen, Bo

39

Electrons in molecules from basic principles to molecular electronics  

CERN Document Server

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

Launay, Jean-Pierre

2014-01-01

40

Spin-excited states and rectification in an organic spin rectifier  

Science.gov (United States)

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

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

2014-08-01

41

Towards Mono-Molecular Electronics  

OpenAIRE

The use of single molecules as active components in electronic devices is presently considered a potential alternative to semiconductor-based nano-scale electronics since it directly provides precisely-defined nano-scale components for electronic devices which eventually allows for simple processing and devicefabrication. In this thesis the self-assembly and electron transport properties of conjugated molecules are investigated by means of scanning tunneling microscopy (STM) and spectrosco...

Ja?ckel, Frank

2005-01-01

42

Electron transport through molecular bridge systems  

OpenAIRE

Electron transport characteristics are investigated through some molecular chains attached to two non-superconducting electrodes by the use of Green's function method. Here we do parametric calculations based on the tight-binding formulation to characterize the electron transport through such bridge systems. The transport properties are significantly influenced by (a) the length of the molecular chain and (b) the molecule-to-electrodes coupling strength and here we focus are...

Maiti, Santanu K.

2009-01-01

43

Femtosecond electron diffraction: making the molecular movie  

Science.gov (United States)

The ability to watch atoms move in real time - to directly observe transition states - has been referred to as "making the molecular movie". Femtosecond electron diffraction is ideally suited for this purpose since it records the atomic structure of the sample with sub-Angstrom spatial resolution and femtosecond temporal resolution. Many-body simulations of ultrashort electron pulse propagation dynamics allowed the development of sources for femtosecond electron pulses with sufficient number density to perform near single shot structure determinations, a requirement for studies of irreversible processes. We have obtained atomic level views of melting of thin films of aluminum and gold under strongly driven conditions. The results are consistent with a thermally driven phase transition and the observed time scales reflect the different electron-phonon coupling constants for these metals. Recent technical advances in electron gun design have further improved the temporal resolution of femtosecond electron diffraction. New electron pulse characterization techniques use direct laser-electron interaction and electron-electron interaction to determine the temporal overlap of the pump and probe pulses as well as the time resolution of the system. These advances have made femtosecond electron diffraction capable of observing transition states in molecular systems. The camera for "making the molecular movie" is now in hand.

Hebeisen, Christoph T.; Dwyer, Jason R.; Jordan, Robert E.; Harb, Maher; Ernstorfer, Ralph; Miller, R. J. D.

2005-09-01

44

Electron screening in molecular fusion reactions  

International Nuclear Information System (INIS)

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

45

Thermoelectric effect in molecular electronics  

OpenAIRE

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

Paulsson, M.; Datta, S.

2003-01-01

46

Electron transport in molecular systems  

International Nuclear Information System (INIS)

Large-scale quantum electronic structure calculations coupled with nonequilibrium Green function theory are employed for determining quantum conductance on practical length scales. The combination of state-of-the-art quantum mechanical methods, efficient numerical algorithms, and high performance computing allows for realistic evaluation of properties at length scales that are routinely reached experimentally. Two illustrations of the method are presented. First, quantum chemical calculations using up to 104 basis functions are used to investigate the amphoteric doping of carbon nanotubes by encapsulation of organic molecules. As a second example, we investigate the electron transport properties of a Si/organic molecule/Si junction using a numerically optimized basis

47

Progress in molecular precursors for electronic materials  

Energy Technology Data Exchange (ETDEWEB)

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

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

1996-09-01

48

Molecular electronics. It's all about contacts.  

Science.gov (United States)

A key requirement in molecular electronics studies is the ability to measure the conductivity of a single molecule. But as Hipps explains in his Perspective, such measurements are often more about contacts than about molecular conductivity. Depending on the experimental setup, DNA behaves like a semiconductor, insulator, or metal. Cui et al. have designed a method that overcomes some of these problems, opening the door to systematic, reliable, and reproducible studies of the molecule-contact interface. PMID:11641487

Hipps, K W

2001-10-19

49

Transient Dynamics in Molecular Junctions: Coherent Bichromophoric Molecular Electron Pumps  

CERN Document Server

The possibility of using single molecule junctions as electron pumps for energy conversion and storage is considered. It is argued that the small dimensions of these systems enable to make use of unique intra-molecular quantum coherences in order to pump electrons between two leads and to overcome relaxation processes which tend to suppress the pumping efficiency. In particular, we demonstrate that a selective transient excitation of one chromophore in a bi-chromophoric donor-bridge-acceptor molecular junction model yields currents which transfer charge (electron and holes) unevenly to the two leads in the absence of a bias potential. The utility of this mechanism for charge pumping in steady state conditions is proposed.

Volkovich, Roie

2010-01-01

50

Ion current rectification and rectification inversion in conical nanopores: a perm-selective view  

OpenAIRE

Ionic transport in charged conical nanopores is known to give rise to ion current rectification. The present study shows that the rectification direction can be inverted when using electrolyte solutions at very low ionic strengths. To elucidate these phenomena, electroneutral conical nanopores containing a perm-selective region at the tip have been investigated and shown to behave like classical charged nanopores. An analytical model is proposed to account for these rectification processes.

Momotenko, Dmitry; Cortes Salazar, Fernando; Josserand, Jacques; Liu, Shujuan; Shoa, Yuanuha; Girault, Hubert

2011-01-01

51

Molecular Dissociation Induced by Electron Collisions  

Science.gov (United States)

Free electrons can efficiently break molecules or molecular ions in low-energy collisions by the processes of dissociative recombination or attachment. These processes make slow electrons efficient chemical agents in many environments. For dissociative recombination, in particular, studies of the underlying reaction paths and mechanisms have become possible on a uniquely elementary level in recent years both for theory and experiment. On the experimental side, collisions can be prepared at resolved collision energies down to the meV (10 Kelvin) level, increasingly gaining control also over the initial molecular quantum level, and individual events are detected and kinematically analyzed by fast-beam coincidence fragment imaging. Experiments are reported from the ion cooler ring TSR in Heidelberg. Stored beams of molecular ions cooled in their external and internal degrees of freedom are collinearly merged with intense and cold electron beams from cryogenic GaAs photocathodes, recently shown to yield fast cooling of the center-of-mass motion also for heavy and correspondingly slow molecular ion beams. To reconstruct the molecular fragmentation events multiparticle imaging can now be used systematically with collision energies set a wide range, especially aiming at specific electron capture resonances. Thus, for CF^+ it is found that the electronic state of the C fragment (^3P or ^1D) switches resonantly when the collision energy is changed by only a small fraction. As a new powerful tool, an energy-sensitive multi-strip surface-barrier detector (EMU) has been set up to measure with near-unity efficiency the masses of all fragments together with their hit positions in high-multiplicity events. Among many uses, this device allows internal molecular excitations to be derived for individual chemical channels in polyatomic fragmentation. New results will be presented in particular on the breakup of the hydronium ion (D3O^+).

Wolf, Andreas

2009-05-01

52

Molecular Electronics : Synthesis of Organic Molecules for Nanoscale Electronics  

DEFF Research Database (Denmark)

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

Jennum, Karsten Stein

2013-01-01

53

Nanostructured organic inorganic photodiodes with high rectification ratio  

Science.gov (United States)

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

Karan, Santanu; Mallik, Biswanath

2008-12-01

54

Computational Nanotechnology Molecular Electronics, Materials and Machines  

Science.gov (United States)

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

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

2002-01-01

55

DNA and microfluidics: Building molecular electronics systems  

Energy Technology Data Exchange (ETDEWEB)

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

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

2006-05-24

56

DNA and microfluidics: Building molecular electronics systems  

International Nuclear Information System (INIS)

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

57

Towards reproducible, scalable lateral molecular electronic devices  

Energy Technology Data Exchange (ETDEWEB)

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

Durkan, Colm, E-mail: cd229@eng.cam.ac.uk; Zhang, Qian [Nanoscience Centre, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA (United Kingdom)

2014-08-25

58

Towards reproducible, scalable lateral molecular electronic devices  

International Nuclear Information System (INIS)

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

59

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

60

Electronic ferroelectricity in molecular organic crystals  

Science.gov (United States)

Electronic ferroelectricity in molecular organic crystals is reviewed from a theoretical perspective. In particular, we focus on the charge-driven-type electronic ferroelectricity where electronic charge order without inversion symmetry induces a spontaneous electric polarization in quarter-filling systems. Two necessary conditions to realize this type of ferroelectricity are the dimer-type lattice structure and alternate electronic charge alignments. Some prototypical organic compounds are introduced. In particular, ?-type BEDT-TTF organic salts, which are termed the dimer-Mott insulating systems, are focused on. Recent developments in the theoretical researches for dielectric and magnetodielectric properties, a collective dipole excitation and a possibility of superconductivity induced by polar charge fluctuation are reviewed. Some perspectives are presented.

Ishihara, Sumio

2014-12-01

61

Fullerene-derived molecular electronic devices  

Science.gov (United States)

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.

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

1998-08-01

62

Georeferencing CAMS data: Polynomial rectification and beyond  

Science.gov (United States)

The Calibrated Airborne Multispectral Scanner (CAMS) is a sensor used in the commercial remote sensing program at NASA Stennis Space Center. In geographic applications of the CAMS data, accurate geometric rectification is essential for the analysis of the remotely sensed data and for the integration of the data into Geographic Information Systems (GIS). The commonly used rectification techniques such as the polynomial transformation and ortho rectification have been very successful in the field of remote sensing and GIS for most remote sensing data such as Landsat imagery, SPOT imagery and aerial photos. However, due to the geometric nature of the airborne line scanner which has high spatial frequency distortions, the polynomial model and the ortho rectification technique in current commercial software packages such as Erdas Imagine are not adequate for obtaining sufficient geometric accuracy. In this research, the geometric nature, especially the major distortions, of the CAMS data has been described. An analytical step-by-step geometric preprocessing has been utilized to deal with the potential high frequency distortions of the CAMS data. A generic sensor-independent photogrammetric model has been developed for the ortho-rectification of the CAMS data. Three generalized kernel classes and directional elliptical basis have been formulated into a rectification model of summation of multisurface functions, which is a significant extension to the traditional radial basis functions. The preprocessing mechanism has been fully incorporated into the polynomial, the triangle-based finite element analysis as well as the summation of multisurface functions. While the multisurface functions and the finite element analysis have the characteristics of localization, piecewise logic has been applied to the polynomial and photogrammetric methods, which can produce significant accuracy improvement over the global approach. A software module has been implemented with full integration of data preprocessing and rectification techniques under Erdas Imagine development environment. The final root mean square (RMS) errors for the test CAMS data are about two pixels which are compatible with the random RMS errors existed in the reference map coordinates.

Yang, Xinghe

63

Length-Dependence of Electron Transfer in Conjugated Molecular Wires  

Science.gov (United States)

The electron transfer (ET) properties of ?-electron conjugated molecular wires consisting of polyene chain, [>C=CVDA decreases exponentially with increase in the length of the molecular wire. However, in contrast with the rigid ?-bonded molecular wires, the decay constant, ?, for the conjugated systems exhibits three different regimes over the calculated length. This is attributed to the delocalized nature of the electrons along molecular length that facilitates retention of the electron coupling even at large separations between the donor and acceptor centers.

Karna, Shashi; Mallick, Govind; Pandey, Ravindra

2007-03-01

64

Thermal conductance and rectification of asymmetric tilt grain boundary in graphene  

CERN Document Server

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

Cao, Hai-Yuan; Gong, Xin-Gao

2011-01-01

65

Triazatriangulene as binding group for molecular electronics  

DEFF Research Database (Denmark)

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).

Wei, Zhongming; Wang, Xintai

2014-01-01

66

Molecular wires: tuning of electron transport  

OpenAIRE

Electron transport characteristics through molecular wires are studied by using the Green's function formalism. Parametric calculations are performed based on the tight-binding model to investigate the transport properties through the wires. The transport characteristics are significantly influenced by (a) the interference effects, (b) chemical substituent group, (c) molecule-to-electrode coupling strength and (d) the gate voltage, and, here we focus our results in these asp...

Maiti, Santanu K.

2009-01-01

67

Terahertz Radiation from Phase Matched Optical Rectification in Magnetized Plasmas and Crystals  

Science.gov (United States)

Nonlinear optics in a crystal is described by an expansion of the electronic polarization in powers of the electric field. The second order term in the expansion leads to several frequency conversion effects including optical rectification. Optical rectification of a laser pulse leads to the generation of terahertz radiation when the laser pulse length is on the order of 1 picosecond. We discuss an experiment underway at the Naval Research Laboratory utilizing a phase matched optical rectification process to efficiently generate terahertz radiation in GaSe and other crystals. We also discuss the analogous process in a magnetized plasma, and show that phase matching can be achieved by tuning the laser pulse length, plasma density, and magnetic field strength. Particle-in-cell simulations suggest that relativistic terahertz pulses can be generated in a plasma.

Gordon, Daniel; Sprangle, Phillip; Ting, Antonio; Kapetanakos, Christos; Alexeev, Ilya; Briscoe, Eldridge

2004-11-01

68

Towards molecular electronics: electron transport through single molecules  

International Nuclear Information System (INIS)

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

69

Modeling ion sensing in molecular electronics  

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-02-07

70

Electron dynamics in molecular interactions principles and applications  

CERN Document Server

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

Hagelberg, Frank

2013-01-01

71

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

Science.gov (United States)

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

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

2014-10-01

72

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

Science.gov (United States)

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

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

2014-10-01

73

Projected quasiparticle theory for molecular electronic structure.  

Science.gov (United States)

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

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

2011-09-28

74

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 isotopo> , 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)

75

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

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

Okazaki, N

2003-01-01

76

Discontinuous approximate molecular electronic wave-functions  

International Nuclear Information System (INIS)

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

77

Radiative thermal rectification using superconducting materials  

Energy Technology Data Exchange (ETDEWEB)

Thermal rectification can be defined as an asymmetry in the heat flux when the temperature difference between two interacting thermal reservoirs is reversed. In this Letter, we present a far-field radiative thermal rectifier based on high-temperature superconducting materials with a rectification ratio up to 80%. This value is among the highest reported in literature. Two configurations are examined: a superconductor (Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8}) exchanging heat with (1) a black body and (2) another superconductor, YBa{sub 2}Cu{sub 3}O{sub 7} in this case. The first configuration shows a higher maximal rectification ratio. Besides, we show that the two-superconductor rectifier exhibits different rectification regimes depending on the choice of the reference temperature, i.e., the temperature of the thermostat. Presented results might be useful for energy conversion devices, efficient cryogenic radiative insulators engineering, and thermal logical circuits’ development.

Nefzaoui, Elyes, E-mail: elyes.nefzaoui@univ-poitiers.fr; Joulain, Karl, E-mail: karl.joulain@univ-poitiers.fr; Drevillon, Jérémie; Ezzahri, Younès [Institut Pprime, Université de Poitiers-CNRS-ENSMA, 2, Rue Pierre Brousse, Bâtiment B25, TSA 41105, 86073 Poitiers Cedex 9 (France)

2014-03-10

78

pH-Reversed ionic current rectification displayed by conically shaped nanochannel without any modification  

Science.gov (United States)

Ion current through a nascent nanochannel with conically shaped geometry in PET (polyethylene terephthalate) membrane sandwiched between two same buffer solutions at pH ion current rectification, as expected for nanochannels with a positive surface charge, if voltages beyond +/-2V range were scanned. We reasoned that the current rectification engendered by the positive surface charge of a conical nanochannel was due to further protonation of the hydrogen bonded hydrogel layer or neutral carboxylic acid inside the nanochannel. Therefore, our results enrich the knowledge about nanochannel technology and indicate that a nanofluidic diode based on pH-reversed ion current rectification through a conical nanochannel can be achieved without any modification of the PET membrane.Ion current through a nascent nanochannel with conically shaped geometry in PET (polyethylene terephthalate) membrane sandwiched between two same buffer solutions at pH ion current rectification, as expected for nanochannels with a positive surface charge, if voltages beyond +/-2V range were scanned. We reasoned that the current rectification engendered by the positive surface charge of a conical nanochannel was due to further protonation of the hydrogen bonded hydrogel layer or neutral carboxylic acid inside the nanochannel. Therefore, our results enrich the knowledge about nanochannel technology and indicate that a nanofluidic diode based on pH-reversed ion current rectification through a conical nanochannel can be achieved without any modification of the PET membrane. Electronic supplementary information (ESI) available: SEM images of multi-tracked nanochannel fabricated from a surfactant-protected one-step etching method. See DOI: 10.1039/c1nr10434a

Guo, Zhijun; Wang, Jiahai; Ren, Jiangtao; Wang, Erkang

2011-09-01

79

Langmuir-Blodgett Films a unique tool for molecular electronics  

CERN Document Server

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

Hussain, Syed Arshad

2009-01-01

80

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

Directory of Open Access Journals (Sweden)

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

Shin-ya Koshihara

2012-07-01

81

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

OpenAIRE

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...

Ren, Jie; Zhu, Jian-xin; Gubernatis, James E.; Wang, Chen; Li, Baowen

2011-01-01

82

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 i 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)

83

Brownian motors: current fluctuations and rectification efficiency  

CERN Document Server

With this work we investigate an often neglected aspect of Brownian motor transport: The r\\^{o}le of fluctuations of the noise-induced current and its consequences for the efficiency of rectifying noise. In doing so, we consider a Brownian inertial motor that is driven by an unbiased monochromatic, time-periodic force and thermal noise. Typically, we find that the asymptotic, time- and noise-averaged transport velocities are small, possessing rather broad velocity fluctuations. This implies a corresponding poor performance for the rectification power. However, for tailored profiles of the ratchet potential and appropriate drive parameters, we can identify a drastic enhancement of the rectification efficiency. This regime is marked by persistent, uni-directional motion of the Brownian motor with few back-turns, only. The corresponding asymmetric velocity distribution is then rather narrow, with a support that predominantly favors only one sign for the velocity.

Machura, L; Talkner, P; Luczka, J; Marchesoni, F; Hänggi, P

2004-01-01

84

Thermal rectification in nonlinear quantum circuits  

OpenAIRE

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 ...

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

2009-01-01

85

Metric rectification of curved document images.  

Science.gov (United States)

In this paper, we propose a metric rectification method to restore an image from a single camera-captured document image. The core idea is to construct an isometric image mesh by exploiting the geometry of page surface and camera. Our method uses a general cylindrical surface (GCS) to model the curved page shape. Under a few proper assumptions, the printed horizontal text lines are shown to be line convergent symmetric. This property is then used to constrain the estimation of various model parameters under perspective projection. We also introduce a paraperspective projection to approximate the nonlinear perspective projection. A set of close-form formulas is thus derived for the estimate of GCS directrix and document aspect ratio. Our method provides a straightforward framework for image metric rectification. It is insensitive to camera positions, viewing angles, and the shapes of document pages. To evaluate the proposed method, we implemented comprehensive experiments on both synthetic and real-captured images. The results demonstrate the efficiency of our method. We also carried out a comparative experiment on the public CBDAR2007 data set. The experimental results show that our method outperforms the state-of-the-art methods in terms of OCR accuracy and rectification errors. PMID:21808093

Meng, Gaofeng; Pan, Chunhong; Xiang, Shiming; Duan, Jiangyong; Zheng, Nanning

2012-04-01

86

Formation of metastable electronic states in polysilylene molecular wire.  

Czech Academy of Sciences Publication Activity Database

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

Nešp?rek, Stanislav

87

Molecular Self-assembly for Organic Electronics  

Science.gov (United States)

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

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

2009-10-01

88

Sufficient conditions for thermal rectification in graded materials  

OpenAIRE

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 wi...

Pereira, Emmanuel

2011-01-01

89

Dissociative recombination of molecular ions with electrons  

Science.gov (United States)

An overview is presented for the present state of the art of laboratory measurements of the dissociative recombination of molecular ions with electrons. Most work has focussed on obtaining rates and their temperature dependence, as these are of primary interest for model calculations of ionospheres. A comparison of data obtained using the microwave afterglow method, the flowing afterglow technique, and the merged beam technique shows that generally the agreement is quite good, but there are some serious discrepancies, especially in the case of H(3+) recombination, that need to be resolved. Results of some earlier experimental work need to be reexamined in the light of more recent developments. Such cases are pointed out and a compilation of rate coefficients that have withstood scrutiny is presented. Recent advances in experimental methods, such as the use of laser-in-duced fluorescence, make it possible to identify some neutral products of dissociative recombination. What has been done so far and what results one might expect from future work are briefly reviewed.

Johnsen, Rainer

1990-01-01

90

Electron beam irradiation effect on nanostructured molecular sieve catalysts  

Energy Technology Data Exchange (ETDEWEB)

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.

Yuan Zhongyong; Zhou Wuzong; Parvulescu, Viorica; Su Baolian E-mail: bao-lian.su@fundp.ac.be

2003-06-01

91

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.

92

Molecular modeling and multiscaling issues for electronic material applications  

CERN Document Server

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 ...

Iwamoto, Nancy; Yuen, Matthew; Fan, Haibo

93

Contactless electronic transport in a bio-molecular junction  

Energy Technology Data Exchange (ETDEWEB)

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.

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

94

Electron Interference in Molecular Circular Polarization Attosecond XUV Photoionization  

Directory of Open Access Journals (Sweden)

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.

Kai-Jun Yuan

2015-01-01

95

A New Full Adder Cell for Molecular Electronics  

Directory of Open Access Journals (Sweden)

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

Keivan Navi

2012-01-01

96

A New Full Adder Cell for Molecular Electronics  

CERN Document Server

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

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

2012-01-01

97

Electron transfer in pendant-group and molecularly doped polymers  

Science.gov (United States)

Utilizing the molecular-ion model previously constructed to describe photoemission and ultraviolet absorption in pendant-group polymers, we derive an expression for the probability of electron transfer between a molecular ion and a neutral molecular species embedded in a frequency-dependent dielectric medium described by the (nonlocal) longitudinal dielectric response function ?(q-->,?). The medium is taken to exhibit three branches of its longitudinal polarization excitation spectrum defined by ?(q-->,?(q-->))=0: a low-frequency branch corresponding to intermolecular motions, an infrared branch corresponding to molecular vibrational modes, and a high-frequency branch corresponding to valence-electron excitations. In addition, the linear coupling of the electron to the intramolecular modes of the initial and final molecular ions is incorporated into the model. The electron-transfer probability is evaluated as a function of the spacing, R, between the molecular-ion sites and the energy difference between the intitial and final molecular-ion states. Utilizing parameters in ?(q-->,?) typical of pendant-group polymers (e.g., polystyrene, polyvinylpyridine) or the matrices utilized in molecularly doped polymers films (e.g., polycarbonates), we find that the electron-transfer process is activated and that the low-frequency dielectric relaxations characteristic of these polymers create this activation. Explicit expressions for the activation energies are derived and evaluated numerically for poly(2-vinylypyridine): a material for which a model of ?(q-->,?) is available in the literature. The valence-electron excitations do not influence the electron-transfer activation energies, but both the intramolecular and longitudinal-polarization vibrational modes increase these activation energies above the values predicted using the low-frequency relaxations alone. The energies, ??n, of many of these vibrational modes are, however, larger than thermal energies, kT. Consequently, the predicted electron-transfer activation energies are smaller than those given by traditional semiclassical models of electron transfer. Moreover, these activation energies also depend explicitly on the spacing, R, between the two sites. This R dependence is evaluated for both classical and quantum-mechanical models of the change densities on the molecular ions. Our analysis predicts, therefore, the complete spacing and temperature dependence of the electron-transfer probabilities as functions of the intramolecular molecular-ion vibrational frequencies and electron-vibration coupling constants, and of the frequency and spatial dependence of the dielectric response of the medium in which these ions are embedded. This prediction permits the identification of scaling laws relating both the activation energies and electron-transfer prefactors to molecular and dielectric observables: an identification which provides valuable guidance in the molecular design of efficient electronic transport media.

Duke, C. B.; Meyer, R. J.

1981-03-01

98

Precision Rectification of Airborne SAR Image  

DEFF Research Database (Denmark)

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

Dall, JØrgen; Liao, M.

1997-01-01

99

Microwave power engineering generation, transmission, rectification  

CERN Document Server

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

Okress, Ernest C

1968-01-01

100

Recycled Noise Rectification: A Dumb Maxwell's Daemon  

CERN Document Server

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

Borromeo, M; Marchesoni, F

2006-01-01

101

Electron-Phonon Correlation Effects in Molecular Transistors  

OpenAIRE

The interplay of electron-electron and electron-phonon interactions is studied analytically in the Kondo regime. A Holstein electron-phonon coupling is shown to produce a weakening of the gate voltage dependence of the Kondo temperature and may explain the observed anomalies in some of these devices. A molecular center-of-mass mode opens a new channel for charge and spin fluctuations and in the antiadabatic limit the latter are described by an asymmetric two-channel Kondo mo...

Balseiro, C. A.; Cornaglia, P. S.; Grempel, D. R.

2006-01-01

102

Electronic transport through oligopeptide chains: An artificial prototype of a molecular diode  

Science.gov (United States)

Using an effective tight-binding model, together with a transfer matrix technique, we investigate the electronic transport through an oligopeptide chain composed by two amino acid pairs alanine-lysine (Ala-Lys) and threonine-alanine (Thr-Ala), respectively, sandwiched between two platinum electrodes. Our results show that factors such as the oligopeptide chain length and the possible combinations between the amino acids residues are crucial to the diode-like profile of the current-voltage (I-V) characteristics, whose asymmetric curves were analyzed using the inverted rectification ratio (IRR).

Oliveira, J. I. N.; Albuquerque, E. L.; Fulco, U. L.; Mauriz, P. W.; Sarmento, R. G.

2014-09-01

103

Using molecular similarity to construct accurate semiempirical electron structure theories  

CERN Document Server

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

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

2003-01-01

104

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

105

Electron and molecular ion collisions relevant to divertor plasma  

International Nuclear Information System (INIS)

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

106

Molecular Basis for Directional Electron Transfer*  

OpenAIRE

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

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

2010-01-01

107

Instructional Approach to Molecular Electronic Structure Theory  

Science.gov (United States)

Describes a graduate quantum mechanics projects in which students write a computer program that performs ab initio calculations on the electronic structure of a simple molecule. Theoretical potential energy curves are produced. (MLH)

Dykstra, Clifford E.; Schaefer, Henry F.

1977-01-01

108

Molecular interfaces for plasmonic hot electron photovoltaics  

Science.gov (United States)

The use of self-assembled monolayers (SAMs) to improve and tailor the photovoltaic performance of plasmonic hot-electron Schottky solar cells is presented. SAMs allow the simultaneous control of open-circuit voltage, hot-electron injection and short-circuit current. To that end, a plurality of molecule structural parameters can be adjusted: SAM molecule's length can be adjusted to control plasmonic hot electron injection. Modifying SAMs dipole moment allows for a precise tuning of the open-circuit voltage. The functionalization of the SAM can also be selected to modify short-circuit current. This allows the simultaneous achievement of high open-circuit voltages (0.56 V) and fill-factors (0.58), IPCE above 5% at the plasmon resonance and maximum power-conversion efficiencies of 0.11%, record for this class of devices.The use of self-assembled monolayers (SAMs) to improve and tailor the photovoltaic performance of plasmonic hot-electron Schottky solar cells is presented. SAMs allow the simultaneous control of open-circuit voltage, hot-electron injection and short-circuit current. To that end, a plurality of molecule structural parameters can be adjusted: SAM molecule's length can be adjusted to control plasmonic hot electron injection. Modifying SAMs dipole moment allows for a precise tuning of the open-circuit voltage. The functionalization of the SAM can also be selected to modify short-circuit current. This allows the simultaneous achievement of high open-circuit voltages (0.56 V) and fill-factors (0.58), IPCE above 5% at the plasmon resonance and maximum power-conversion efficiencies of 0.11%, record for this class of devices. Electronic supplementary information (ESI) available: Contact-potential differentiometry measurements, FTIR characterization, performance statistics and gold devices. See DOI: 10.1039/c4nr06356b

Pelayo García de Arquer, F.; Mihi, Agustín; Konstantatos, Gerasimos

2015-01-01

109

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

OpenAIRE

We investigate the orientation dependence of molecular high-order harmonic generation (HHG) both numerically and analytically. We show that the molecular recollision electronic wave packets (REWPs) in the HHG are closely related to the ionization potential as well as the particular orbital from which it ionized. As a result, the spectral amplitude of the molecular REWP can be significantly different from its reference atom (i.e., with the same ionization potential as the mol...

Chen, Yanjun; Li, Yan; Yang, Shiping; Liu, Jie

2008-01-01

110

Rectification of light refraction in curved waveguide arrays  

OpenAIRE

An 'optical ratchet' for discretized light in photonic lattices, which enables to observe rectification of light refraction at any input beam conditions, is theoretically presented, and a possible experimental implementation based on periodically-curved zigzag waveguide arrays is proposed.

Longhi, S.

2010-01-01

111

Digital image transformation and rectification of spacecraft and radar images  

Science.gov (United States)

Digital image transformation and rectification can be described in three categories: (1) digital rectification of spacecraft pictures on workable stereoplotters; (2) digital correction of radar image geometry; and (3) digital reconstruction of shaded relief maps and perspective views including stereograms. Digital rectification can make high-oblique pictures workable on stereoplotters that would otherwise not accommodate such extreme tilt angles. It also enables panoramic line-scan geometry to be used to compile contour maps with photogrammetric plotters. Rectifications were digitally processed on both Viking Orbiter and Lander pictures of Mars as well as radar images taken by various radar systems. By merging digital terrain data with image data, perspective and three-dimensional views of Olympus Mons and Tithonium Chasma, also of Mars, are reconstructed through digital image processing. ?? 1985.

Wu, S.S.C.

1985-01-01

112

Molecular Surface Mesh Generation by Filtering Electron Density Map  

OpenAIRE

Bioinformatics applied to macromolecules are now widely spread and in continuous expansion. In this context, representing external molecular surface such as the Van der Waals Surface or the Solvent Excluded Surface can be useful for several applications. We propose a fast and parameterizable algorithm giving good visual quality meshes representing molecular surfaces. It is obtained by isosurfacing a filtered electron density map. The density map is the result of the maximum of Gaussian functi...

Joachim Giard; Macq, Beno Amp T.

2010-01-01

113

Current rectification by asymmetric molecules: An ab initio study  

OpenAIRE

We study current rectification effect in an asymmetric molecule HOOC-C$_6$H$_4$-(CH$_2$)$_n$ sandwiched between two Aluminum electrodes using an {\\sl ab initio} nonequilibrium Green function method. The conductance of the system decreases exponentially with the increasing number $n$ of CH$_2$. The phenomenon of current rectification is observed such that a very small current appears at negative bias and a sharp negative differential resistance at a critical positive bias whe...

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

2006-01-01

114

Energy Transformation in Molecular Electronic Systems  

Energy Technology Data Exchange (ETDEWEB)

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

Kasha, Michael

1999-05-17

115

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

116

Electron Momentum Spectroscopy of 1???Butene: A Theoretical Analysis Using Molecular Dynamics and Molecular Quantum Similarity  

OpenAIRE

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 a...

Shojaei, S. H. Reza; Vandenbussche, Jelle; Deleuze, M. S.; Bultinck, Patrick

2013-01-01

117

Room Temperature Molecular Single-Electron Transistor  

CERN Document Server

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

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

1996-01-01

118

Room Temperature Molecular Single-Electron Transistor  

OpenAIRE

A room temperature single-electron transistor based on the single cluster molecule has been demonstrated for the first time. Scanning tunneling microscope tip was used to study the transport via single carboran cluster molecule 1,7-(CH_3)_2-1,2-C_2B_{10}H_9Tl(OCOCF_3)_2 incorporated into the Langmuir-Blodgett monolayer of the stearic acid. DC I-V curves at 300 K showed well pronounced Coulomb staircase, and the current could be controlled by a lithographically fabricated gol...

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

1996-01-01

119

Molecular modeling of electron trapping in polymer insulators  

Science.gov (United States)

The presence of space charge in the polymeric insulation of high-voltage cables is correlated with electric breakdown. There is a vast literature concerned with the experimental characterization of space charge and with phenomenological models of space charge formation and discharge. However, a direct link between molecular properties, space charge formation and eventual breakdown has still to be established. In this paper, we suggest a new scheme that constitutes a first step in linking microscopic defects to the formation of space charge. Although our goal is to understand the role of defects at the molecular level in electron trapping and the formation of space charge in polyethylene, we start by considering a "model" material; the wax tridecane (n-C13H28). It is clear that both physical (e.g., conformational defects) and chemical defects (e.g., broken bonds) may be present in insulating materials and may both trap electrons. In the present paper, we focus on the role of physical defects. Our analysis suggests that by defining the defect energy in terms of the molecular electron affinity, a relationship is established between the electron trap and the molecular properties of the material. The electron affinity and its variation with wax molecule conformation have been calculated using density functional theory (DFT, as implemented in the code DMol). By performing molecular-dynamics simulations of amorphous waxes, we are able to determine likely conformational defects, and by using ab initio methods estimate the trapping energies. Conformational defects in these waxy materials are predicted to produce shallow traps with energies below 0.3 eV. These results are used to estimate the energy, number, and residence times of electrons in conformational traps in polyethylene.

Meunier, M.; Quirke, N.

2000-07-01

120

Assembling molecular electronic junctions one molecule at a time.  

Science.gov (United States)

Diffusion of metal atoms onto a molecular monolayer attached to a conducting surface permits electronic contact to the molecules with minimal heat transfer or structural disturbance. Surface-mediated metal deposition (SDMD) involves contact between "cold" diffusing metal atoms and molecules, due to shielding of the molecules from direct exposure to metal vapor. Measurement of the current through the molecular layer during metal diffusion permits observation of molecular conductance for junctions containing as few as one molecule. Discrete conductance steps were observed for 1-10 molecules within a monolayer during a single deposition run, corresponding to "recruitment" of additional molecules as the contact area between the diffusing Au layer and molecules increases. For alkane monolayers, the molecular conductance measured with SDMD exhibited an exponential dependence on molecular length with a decay constant (?) of 0.90 per CH(2) group, comparable to that observed by other techniques. Molecular conductance values were determined for three azobenzene molecules, and correlated with the offset between the molecular HOMO and the contact Fermi level, as expected for hole-mediated tunneling. Current-voltage curves were obtained during metal deposition showed no change in shape for junctions containing 1, 2, and 10 molecules, implying minimal intermolecular interactions as single molecule devices transitioned into several molecules devices. SDMD represents a "soft" metal deposition method capable of providing single molecule conductance values, then providing quantitative comparisons to molecular junctions containing 10(6) to 10(10) molecules. PMID:21995487

Bonifas, Andrew P; McCreery, Richard L

2011-11-01

121

Molecular orbital theory of ballistic electron transport through molecules  

Science.gov (United States)

Electron transport through molecules occurs, for instance, in STM imaging and in conductance measurements on molecular electronic devices (MEDs). To model these phenomena, we use a non-Hermitian model Hamiltonian [1] for the description of open systems that exchange current density with their environment. We derive qualitative, molecular-orbital-based rules relating molecular structure and conductance. We show how side groups attached to molecular conductors [2] can completely suppress the conductance. We discuss interference effects in aromatic molecules [3] that can also inhibit electron transport. Rules are developed [1] for the prediction of Fano resonances. All these phenomena are explained with a molecular orbital theory [1,4] for molecules attached to macroscopic reservoirs. [1] F. Goyer, M. Ernzerhof, and M. Zhuang, JCP 126, 144104 (2007); M. Ernzerhof, JCP 127, 204709 (2007). [2] M. Ernzerhof, M. Zhuang, and P. Rocheleau, JCP 123, 134704 (2005); G. C. Solomon, D Q. Andrews, R P. Van Duyne, and M A. Ratner, JACS 130, 7788 (2008). [3] M. Ernzerhof, H. Bahmann, F. Goyer, M. Zhuang, and P. Rocheleau, JCTC 2, 1291 (2006); G. C. Solomon, D. Q. Andrews, R. P. Van Duyne, and M. A. Ratner, JCP 129, 054701 (2008). [4] B.T. Pickup, P.W. Fowler, CPL 459, 198 (2008); P. Rocheleau and M. Ernzerhof, JCP, submitted.

Ernzerhof, Matthias; Rocheleau, Philippe; Goyer, Francois

2009-03-01

122

Self assembled monolayers on silicon for molecular electronics  

International Nuclear Information System (INIS)

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

123

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

124

Electron energy-loss spectra in molecular fluorine  

Science.gov (United States)

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

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

1979-01-01

125

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

DEFF Research Database (Denmark)

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

Li, Qian; Solomon, Gemma

2014-01-01

126

On electric-quadrupole and magnetic-dipole contributions to optical rectification in isotropic media near optical resonance  

OpenAIRE

Abstract A molecular theory of resonant optical rectification via the second-order electric-dipole polarizability related to magnetic-dipole and electric-quadrupole interaction of an electromagnetic radiation with atoms and molecules of an isotropic medium is presented. The magnetic-dipole and electric-quadrupole contributions to Dc electric-dipole polarization can be produced by arbitrarily polarized light which has to be at resonance with a molecule. Th...

Zawodny, Roman

2007-01-01

127

Electron impact ionization and dissociation of molecular ions  

International Nuclear Information System (INIS)

Using a NIER type electron impact ion source in combination with a double focusing, two sector field, mass spectrometer of reversed geometry different methods have been used to elucidate the energetics, kinetics and dynamics of the interaction of electrons with various molecules and molecular ions. The first part of the present work deals with electron impact ionization studies concerning ionization cross sections and appearance energies of multiply-charged C70Z+ ions, z=1-6. From the measured appearance energies ionization energies have been deduced and their dependence on the charge state agrees well with theoretical predictions. For singly and doubly charged Cnz+, n = 52-70, relative activation energies for C2 evaporation have been derived from measured appearance energies by using finite heat bath theory. The main part of this thesis deals with dissociative ionization of fullerenes. We have studied in detail spontaneous and electron induced decay reactions. From measured peak shapes of the fragment ions we have deduced kinetic energy release distributions (KERD), the mean kinetic energy release (KER), and in a further step the activation energy of the decaying molecular system. To study also electron induced ionization and dissociation of mass selected ions we have constructed a high performance electron gun which has been mounted between the magnetic and the electrostatic sector field. It turned out that the atic sector field. It turned out that the (KER) of electron induced decay reactions is higher than the corresponding value for the spontaneous decay in accordance with RRKM theory. (author)

128

Electron induced ionization and dissociation of molecular ions  

Science.gov (United States)

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

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

1999-10-01

129

Chiral molecular films as electron polarizers and polarization modulators  

Science.gov (United States)

Recent experiments on electron scattering through molecular films have shown that chiral molecules can be efficient sources of polarized electrons even in the absence of heavy nuclei as source of a strong spin-orbit interaction. We show that self-assembled monolayers (SAMs) of chiral molecules are strong electron polarizers due to the high-density effect of the monolayers and explicitly compute the scattering amplitude off a helical molecular model of carbon atoms. Longitudinal polarization is shown to be the signature of chiral scattering. For elastic scattering, we find that at least double-scattering events must take place for longitudinal polarization to arise. We predict energy windows for strong polarization, determined by the energy dependences of spin-orbit strength and multiple scattering probability. An incoherent mechanism for polarization amplification is proposed, that increases the polarization linearly with the number of helix turns, consistent with recent experiments on DNA SAMs.

Medina, Ernesto; López, Floralba; Ratner, Mark A.; Mujica, Vladimiro

2012-07-01

130

Theory and Application of Dissociative Electron Capture in Molecular Identification  

CERN Document Server

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

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

2006-01-01

131

Chiral molecular films as electron polarizers and polarization modulators  

CERN Document Server

Recent experiments on electron scattering through molecular films have shown that chiral molecules can be efficient sources of polarized electrons even in the absence of heavy nuclei as source of a strong spin-orbit interaction. We show that self-assembled monolayers (SAMs) of chiral molecules are strong electron polarizers due to the high density effect of the monolayers and explicitly compute the scattering amplitude off a helical molecular model of carbon atoms. Longitudinal polarization is shown to be the signature of chiral scattering. For elastic scattering, we find that at least double scattering events must take place for longitudinal polarization to arise. We predict energy windows for strong polarization, determined by the energy dependences of spin-orbit strength and multiple scattering probability. An incoherent mechanism for polarization amplification is proposed, that increases the polarization linearly with the number of helix turns, consistent with recent experiments on DNA SAMs.

Medina, Ernesto; Ratner, Mark; Mujica, Vladimiro

2012-01-01

132

Research ZCS Synchronous Rectification of Resonant Converter  

Directory of Open Access Journals (Sweden)

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.

Xiao Kui Li

2014-01-01

133

Research ZVS Synchronous Rectification of Resonant Converter  

Directory of Open Access Journals (Sweden)

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

Xiao Kui Li

2014-01-01

134

A Landsat Digital Image Rectification System  

Science.gov (United States)

DIRS is a Digital Image Rectification System for the geometric correction of Landsat Multispectral Scanner digital image data. DIRS removes spatial distortions from the data and brings it into conformance with the Universal Transverse Mercator (UTM) map projection. Scene data in the form of landmarks or Ground Control Points (GCPs) are used to drive the geometric correction algorithms. The system offers extensive capabilities for 'shade printing' to aid in the determination of GCPs. Affine, two dimensional least squares polynominal and spacecraft attitude modeling techniques for geometric mapping are provided. Entire scenes or selected quadralaterals may be rectified. Resampling through nearest neighbor or cubic convolution at user designated intervals is available. The output products are in the form of digital tape in band interleaved, single band or CCT format in a rotated UTM projection. The system was designed and implemented on large scale IBM 360 computers with at least 300-500K bytes of memory for user application programs and five nine track tapes plus direct access storage.

Van Wie, P.; Stein, M.

1976-01-01

135

Electronic transmission of three-terminal pyrene molecular bridge  

International Nuclear Information System (INIS)

This paper investigates theoretically the electronic transmission spectra of the three terminal pyrene molecular bridge and the quantum current distribution on each bond by the tight-binding model based on nonequilibrium Green's function and the quantum current density approach, in which one ? molecular orbital is taken into account per carbon atom when the energy levels and HOMO-LUMO gap are obtained. The transmission spectra show that the electronic transmission of the three terminal pyrene molecular bridge depends obviously on the incident electronic energy and the pyrene eigenenergy. The symmetrical and oscillation properties of the transmission spectra are illustrated. A novel plus-minus energy switching function is found. The quantum current distribution shows that the loop currents inside the pyrene are induced, and some bond currents are much larger than the input and the output currents. The reasons why the loop currents and the larger bond currents are induced are the phase difference of the atomic orbits and the degeneracy of the molecular orbits. The calculations illustrate that the quantum current distributions are in good agreement with Kirchhoff quantum current conservation law. (general)

136

A new parametrizable model of molecular electronic structure  

CERN Document Server

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

Laikov, Dimitri N

2011-01-01

137

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.

138

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

OpenAIRE

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...

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

2014-01-01

139

Rigorous theory of molecular orientational nonlinear optics  

Directory of Open Access Journals (Sweden)

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.

Chong Hoon Kwak

2015-01-01

140

Rigorous theory of molecular orientational nonlinear optics  

Science.gov (United States)

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.

Kwak, Chong Hoon; Kim, Gun Yeup

2015-01-01

141

Special issue on ultrafast electron and molecular dynamics  

Science.gov (United States)

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

Martin, Fernando; Hishikawa, Akiyoshi; Vrakking, Marc

2014-06-01

142

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

Directory of Open Access Journals (Sweden)

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

A. S. Kirillov

2010-01-01

143

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-07-01

144

Asymmetric propagation of electronic wave function through molecular bonding and anti-bonding states  

OpenAIRE

Electron transport through molecular bridge shows novel quantum features. Propogation of electronic wave function through molecular bridge is completely different than individual atomic bridge employed between two contacts. In case of molecular bridge electronic wave propagators interfere and effect conduction through molecular bonding and anti-bonding states.In the present work i showed through simple calculation that interference of electronic wave propagators cause asymme...

Imran, Muhammad

2011-01-01

145

Rapid characterizing of ferromagnetic materials using spin rectification  

Science.gov (United States)

Spin rectification is a powerful tool for dc electric detections of spin dynamics and electromagnetic waves. Technically, elaborately designed on-chip microwave devices are needed in order to realize that effect. In this letter, we propose a rapid characterizing approach based on spin rectification. By directly sending dynamic current into ferromagnetic films with stripe shape, resonant dc voltages can be detected along the longitudinal or transversal directions. As an example, Fe (010) films with precise crystalline structure and magnetic parameters were used to testify the reliability of such method. We investigated not only the dynamic parameters and the precise anisotropy constants of the Fe crystals but also the principle of spin rectification in this method.

Fan, Xiaolong; Wang, Wei; Wang, Yutian; Zhou, Hengan; Rao, Jinwei; Zhao, Xiaobing; Gao, Cunxu; Gui, Y. S.; Hu, C.-M.; Xue, Desheng

2014-12-01

146

Molecular structure of cyclododecane, C 12H 24, as determined by electron diffraction and molecular mechanics  

Science.gov (United States)

The molecular structure of cyclododecane has been studied at 120°C using gas phase electron diffraction assisted by molecular mechanics calculations. Two models suggested earlier by X-ray data have been tested. Electron diffraction data are compatible with a D4 model while the D2d model can be rejected, in agreement with molecular mechanics calculations which favor the first model by 10.5 kcal mol -1 over the second. For a model with D4 symmetry the experimental results give average bond lengths ( rg), independent bond and torsion angles (? ?) with estimated uncertainties of 3?. C?C 1.540(1) Å, C?H 1.114(3) Å, ? H?C?H 104.2(18)°, ? C1?C2?C3 115.0(7)°, ? (C1?C2?C3?C4) 159.5(12)°.

Atavin, E. G.; Mastryukov, V. S.; Allinger, N. L.; Almenningen, A.; Seip, R.

1989-09-01

147

Ab Initio Molecular Dynamics on the Electronic Boltzmann Equilibrium Distribution  

CERN Document Server

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.

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

2010-01-01

148

Candidate molecular ions for an electron electric dipole moment experiment  

International Nuclear Information System (INIS)

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

149

Molecular Surface Mesh Generation by Filtering Electron Density Map  

Directory of Open Access Journals (Sweden)

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

Joachim Giard

2010-01-01

150

Nonequilibrium electron charging in carbon-nanotube-based molecular bridges  

OpenAIRE

We evidence the importance of electron charging under nonequilibrium conditions for carbon-nanotube-based molecular bridges, using a self-consistent Green's function method with an extended Huckel Hamiltonian and a three-dimensional Poisson solver. Our analysis demonstrates that such feature is highly dependent on the chirality of the carbon nanotube as well as on the type of the contact metal, conditioning in a nongeneralized way the system's conduction mechanism. Based on ...

Deretzis, Ioannis; La Magna, Antonino

2007-01-01

151

Coherent electron emission for dissociative ionization of molecular hydrogen by electron impact  

Energy Technology Data Exchange (ETDEWEB)

The single ionization of hydrogen molecules is studied theoretically as a function of the molecular alignment. Within the framework of the two-effective center model, multiple differential cross sections as a function of both electron momenta in the final channel of the reaction, and the internuclear orientation, are computed for both non-dissociative and dissociative final H{sup +}{sub 2} states. Preliminary results show that the interference pattern arising from the two-center character of the molecular target changes strongly with the final state of the residual molecular ion.

Fojon, O A; Stia, C R; Rivarola, R D, E-mail: ofojon@fceia.unr.edu.ar [Instituto de Fisica Rosario, CONICET and Universidad Nacional de Rosario, Av. Pellegrini 250, 2000 Rosario (Argentina)

2011-04-01

152

Coherent electron emission for dissociative ionization of molecular hydrogen by electron impact  

International Nuclear Information System (INIS)

The single ionization of hydrogen molecules is studied theoretically as a function of the molecular alignment. Within the framework of the two-effective center model, multiple differential cross sections as a function of both electron momenta in the final channel of the reaction, and the internuclear orientation, are computed for both non-dissociative and dissociative final H+2 states. Preliminary results show that the interference pattern arising from the two-center character of the molecular target changes strongly with the final state of the residual molecular ion.

153

Pressure shifts and electron scattering in atomic and molecular gases  

International Nuclear Information System (INIS)

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

154

Two-dimensional electronic spectroscopy of molecular aggregates.  

Science.gov (United States)

The properties of molecular aggregates, coupled clusters of small molecules, are often challenging to unravel because of their inherent complexity and disordered environments. Their structure-function relationships are often far from obvious. However, their ability to efficiently channel excitation energy over remarkable distances, as is the case in photosynthetic light harvesting, is a compelling motivation to investigate them. Understanding and subsequently mimicking the processes in photosynthesis, for example, will set the stage for considerable advances in using light harvesting to fuel renewable energy technologies. Two-dimensional (2D) electronic spectroscopy is emerging as a nonlinear optical technique that provides significant insight into the interactions and dynamics of complex molecular systems. In addition to spectrally resolving excitation and emission energies over significant bandwidths with femtosecond resolution, this technique has already enabled discoveries about the structure and dynamics of photosynthetic light-harvesting complexes and other aggregates. Multiple capabilities unique to 2D electronic spectroscopy enable such findings. For example, the spectral resolution of excitation and emission combined with the ability to eliminate the effects of static disorder can reveal the homogeneous line width of a transition and the different dynamic contributions to it. Two dimensional spectroscopy is also sensitive to electronic coherence and has been employed to identify and characterize coherent excitation energy transfer dynamics in photosynthetic systems and conjugated polymers. The presence of cross-peaks, signals for which excitation and emission occur at different wavelengths, provides multiple forms of information. First, it allows the identification of states in congested spectra and reveals correlations between them. Second, we can track excitation energy flow from origin to terminus through multiple channels simultaneously. Finally, 2D electronic spectroscopy is uniquely sensitive to intermolecular electronic coupling through the sign and amplitude of the cross-peaks. This feature makes it possible to reveal spatial molecular configurations by probing electronic transitions. Another means of "resolving" these angstrom-scale arrangements is to manipulate the probing laser pulse polarizations. In this way, we can isolate and modulate specific processes in order to retrieve structural information. In this Account, we demonstrate these capabilities through a close collaboration between experiments and modeling on isolated photosynthetic pigment-protein complexes and also on J-aggregates. Each of the probed systems we describe offers insights that have both increased the utility of 2D electronic spectroscopy and led to discoveries about the molecular aggregates' dynamics and underlying structure. PMID:19691358

Ginsberg, Naomi S; Cheng, Yuan-Chung; Fleming, Graham R

2009-09-15

155

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

DEFF Research Database (Denmark)

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

Larade, Brian; Taylor, Jeremy Philip

2001-01-01

156

Mechanism of Enhanced Rectification in Unimolecular Borromean Ring Devices  

CERN Document Server

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

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

2006-01-01

157

Bounds for the rectification efficiency of solar radiation  

Science.gov (United States)

Efficiency bounds for the rectification (AC to DC conversion) efficiency of non-coherent broadband radiation are derived, motivated by determining a basic limit for solar rectifying antennas. The limit is shown to be 2/? for a single full-wave rectifier. We also derive the increase in rectification efficiency that is possible by cascading multiple rectifiers. The approach for deriving the broadband limit follows from an analysis of sinusoidal signals of random phase. This analysis is also germane for harvesting ambient radio-frequency radiation from multiple uncorrelated sources.

Mashaal, Heylal; Gordon, Jeffrey M.

2013-09-01

158

Modulations to molecular high order harmonic generation by electron de Broglie wave  

OpenAIRE

We present a new theory that the molecular high order harmonic generation in an intense laser field is determined by molecular internal symmetry and momentum distribution of the tunneling-ionized electron. The molecular internal symmetry determines the quantum interference form of the returning electron inside the molecule. The electron momentum distribution determines the relative interference strength of each individual electron de Broglie wave. All individual electron de ...

Chen, J.; Chen, Y. J.; Fan, J.; Liu, J.; Chen, S. G.; He, X. T.

2008-01-01

159

Intermolecular thermoelectric-like effects in molecular nano electronic systems  

International Nuclear Information System (INIS)

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

160

Growth, modification and integration of carbon nanotubes into molecular electronics  

Science.gov (United States)

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

Moscatello, Jason P.

161

Geometric rectification of radar imagery using digital elevation models  

Science.gov (United States)

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

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

1983-01-01

162

Ion Current Rectification Behavior at Novel Borosilicate Glass Capillaries.  

Czech Academy of Sciences Publication Activity Database

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

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

163

Electron collisions and internal excitation in stored molecular ion beams  

Energy Technology Data Exchange (ETDEWEB)

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

Buhr, H.

2006-07-26

164

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.)

165

Long-distance photoinitiated electron transfer through polyene molecular wires  

International Nuclear Information System (INIS)

Long-chain polyenes can be used as molecular wires to facilitate electron transfer between a photo-excited donor and an acceptor in an artificial photosynthetic system. The authors present data here on two Zn-porphyrin-polyene-anthraquinone molecules possessing either 5 or 9 all trans double bonds between the donor and acceptor, 1 and 2. The center-to-center distances between the porphyrin and the quinone in these relatively rigid molecules are 25 angstrom for 1 and 35 angstrom for 2. Selective picosecond laser excitation of the Zn-porphyrin and 1 and 2 results in the very rapid transfer of an electron to the anthraquinone in <2 ps and 10 ps, respectively. The resultant radical ion pairs recombine with ? = 10 ps for 1 and ? = 25 ps for 2. The electron transfer rates remain remarkably rapid over these long distances. The involvement of polyene radical cations in the mechanism of the radical ion pair recombination reaction is clear from the transient absorption spectra of 1 and 2, which show strong absorbances in the near-infrared. The strong electronic coupling between the Zn-porphyrin n the anthraquinone provided by low-lying states of the polyene make it possible to transfer an electron rapidly over very long distances

166

Semiclassical theory of electronically nonadiabatic transitions in molecular collision processes  

Science.gov (United States)

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

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

1979-01-01

167

Electron transport through catechol-functionalized molecular rods  

International Nuclear Information System (INIS)

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

168

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.

169

Vibrational excitations in molecular layers probed by ballistic electron microscopy  

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-10-28

170

Fast Electron Repulsion Integrals for Molecular Coulomb Sturmians  

DEFF Research Database (Denmark)

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

Avery, James Emil

2013-01-01

171

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)

172

Probing ultrafast electronic and molecular dynamics with free-electron lasers  

Science.gov (United States)

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

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

2014-06-01

173

Electronic structure of the lithium molecular anion, Li-2  

International Nuclear Information System (INIS)

Calculations have been performed on the electronic structure and potential energy curves for the Li-2 anion using CI wavefunctions optimized for the ground and excited molecular states. The ground 2?+ /sub u/ state of Li-2 lies below the X 1?+ /sub g/ state of Li2 and can be treated using standard variational methods. The excited states of Li-2 are, in general, resonant states and are unstable with respect to autoionization. These states, however, are of interest in low-energy e + Li2 dissociative attachment and vibrational excitation processes. Our calculated electronic affinity for Li2 is 0.42 eV, in good agreement with previous theoretical studies. In contrast with the H2 system, we find a rich spectrum of low-lying resonant states for Li-2

174

Rotational excitation of molecular nitrogen by electron impact  

International Nuclear Information System (INIS)

Collision cross sections for rotational excitation processes of a molecular nitrogen by electron impact are calculated at the energy range of 0.01 to 3 eV. It is shown that integrated cross sections for rotationally inelastic scattering are noticeably enhanced by the short range interaction between the scattered electron and the target nitrogen molecule at the impact energy as low as 0.08 eV. At the energy region of the well-known ?g resonance, it is confirmed that the cross section for the rotational excitation of j = 0 to j' = 4 becomes larger than that for j = 0 to j' = 2 by more than the ratio of statistical weight (2j' + 1) of the final rotational state j'. An explanation to this fact is given by analysing the expression of the integrated cross section. (author)

175

Radiative lifetimes of excited electronic states in molecular ions  

International Nuclear Information System (INIS)

Radiative lifetimes of excited electronic states of several molecular ions have been measured using a technique which permits the mass selective storage of ions for periods of many ms. This technique is used to record radiative lifetimes ranging from 60 ns to approx. 10 ?s. The use of a radiofrequency quadrupole ion trap to confne the ions reduces the problem of space charge induced spatial dissipation of ions and permits the selective excitation of electronic states. Using this technique, careful measurements of the B2?+/sub u/ state of N+2 and the A2Pi states of N+2 and CO+ have been made. The results obtained are in good agreement with previous studies. The analysis of the radiative lifetime for the CH+ and CD+ A1Pi(?' = 0) state results in a value significantly larger than earlier determinations. The new results are used to make revised estimates of interstellar abundances of CH+

176

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.)

177

Electron-Phonon Interactions in C_28-derived Molecular Solids  

Science.gov (United States)

We have investigated molecular solids made from various small close-shell fullerenes to determine their structural and electronic properties in their pristine and doped forms. Binding energies, band structure, and electron-phonon coupling were calculated using the ab initio SIESTA [1] code. We find a C_28H4 solid that binds weakly and exhibits many of the salient features of solid C_60. The electron-phonon interaction potential is over twice as large as that of C_60. Our calculations show that endohedral doping of the C_28H4 solid produces an electronic structure similar to that of the alkal-doped fullerides which is suggestive of high superconducting transition temperatures T_c. In keeping with simple estimates of Tc carried out in the literature (e.g. [2]), one obtains T_c( Na@ C_28 H_4)? 6T_c( K_3 C_60)? 116K. *Supported by NSF DMR 99-76550 and DOE DEFG-96-ER45439. [1] J. Soler et. al, J. Phys.: Condens. Matter 14, 2745 (2002). [2] N. Breda et. al, Phys. Rev. B 62, 130 (2000).

Romero, Nichols A.; Kim, Jeongnim; Martin, Richard M.

2004-03-01

178

Fragmentation of molecular ions in slow electron collisions  

Energy Technology Data Exchange (ETDEWEB)

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

Novotny, Steffen

2008-06-25

179

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

Science.gov (United States)

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

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

2010-07-27

180

Design of a Molecular Memory Device: The Electron Transfer Shift Register Memory  

Science.gov (United States)

A molecular shift register memory at the molecular level is described. The memory elements consist of molecules can exit in either an oxidized or reduced state and the bits are shifted between the cells with photoinduced electron transfer reactions.

Beratan, D.

1993-01-01

181

Theoretical modeling of electronic transport in molecular devices  

Science.gov (United States)

In this thesis a novel approach for simulating electronic transport in nanoscale structures is introduced. We consider an open quantum system (the electrons of structure) accelerated by an external electromotive force and dissipating energy through inelastic scattering with a heat bath (phonons) acting on the electrons. This method can be regarded as a quantum-mechanical extension of the semi-classical Boltzmann transport equation. We use periodic boundary conditions and employ Density Functional Theory to recast the many-particle problem in an effective single-particle mean-field problem. By explicitly treating the dissipation in the electrodes, the behavior of the potential is an outcome of our method, at variance with the scattering approaches based on the Landauer formalism. We study the self-consistent steady-state solution, analyzing the out-of-equilibrium electron distribution, the electrical characteristics, the behavior of the self-consistent potential and the density of states of the system. We apply the method to the study of electronic transport in several molecular devices, consisting of small organic molecules or atomic wires sandwiched between gold surfaces. For gold wires we recover the experimental evidence that transport in short wires is ballistic, independent of the length of the wire and with conductance of one quantum. In benzene-1,4-dithiol we find that the delocalization of the frontier orbitals of the molecule is responsible for the high value of conductance and that, by inserting methylene groups to decouple the sulfur atoms from the carbon ring, the current is reduced, in agreement with the experimental measurements. We study the effect a geometrical distortion in a molecular device, namely the relative rotation of the carbon rings in a biphenyl-4,4'-dithiol molecule. We find that the reduced coupling between pi orbitals of the rings induced by the rotation leads to a reduction of the conductance and that this behavior is captured by a simple two level model. Finally the transport properties of alkanethiol monolayers are analyzed by means of the local density of states at the Fermi energy: we find an exponential dependence of the current on the length of the chain, in quantitative agreement with the corresponding experiments.

Piccinin, Simone

182

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

International Nuclear Information System (INIS)

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

183

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)

184

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

International Nuclear Information System (INIS)

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

185

Rectification of the OPAL Cold Neutron Source Cryogenic System  

International Nuclear Information System (INIS)

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

186

Epipolar image rectification through geometric algorithms with unknown parameters  

Science.gov (United States)

Image processing in photogrammetry is commonly used for scene reconstruction. Although two-dimensional applications can be solved using isolated images, reconstruction of three-dimensional scenes usually requires the use of multiple images simultaneously. Epipolar image rectification is a common technique for this purpose. It typically requires internal orientation parameters and, therefore, knowledge of camera calibration and relative orientation parameters between images. A reparameterization of the fundamental matrix through a completely geometric algorithm of seven parameters that enables the epipolar image rectification of a photogrammetric stereo pair without introducing any orientation parameters and without premarking ground control points is presented. The algorithm enables the generation of different stereoscopic models with a single photogrammetric pair from unknown cameras, scanned from a book, or frames from video sequences. Stereoscopic models with no parallaxes have been obtained with a standard deviation of <0.5 pixels.

Herráez, José; Denia, José Luis; Navarro, Pablo; Rodríguez, Jaime; Teresa Martín, M.

2013-10-01

187

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

International Nuclear Information System (INIS)

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

188

Effect of triangular vacancy defect on thermal conductivity and thermal rectification in graphene nanoribbons  

Energy Technology Data Exchange (ETDEWEB)

We investigate the thermal transport properties of armchair graphene nanoribbons (AGNRs) possessing various sizes of triangular vacancy defect within a temperature range of 200–600 K by using classical molecular dynamics simulation. The results show that the thermal conductivities of the graphene nanoribbons decrease with increasing sizes of triangular vacancy defects in both directions across the whole temperature range tested, and the presence of the defect can decrease the thermal conductivity by more than 40% as the number of removed cluster atoms is increased to 25 (1.56% for vacancy concentration) owing to the effect of phonon–defect scattering. In the meantime, we find the thermal conductivity of defective graphene nanoribbons is insensitive to the temperature change at higher vacancy concentrations. Furthermore, the dependence of temperatures and various sizes of triangular vacancy defect for the thermal rectification ration are also detected. This work implies a possible route to achieve thermal rectifier for 2D materials by defect engineering.

Yang, Ping, E-mail: yangpingdm@ujs.edu.cn [Laboratory of Advanced Manufacturing and Reliability for MEMS/NEMS/OEDS, Jiangsu University, Zhenjiang 212013 (China); Li, Xialong; Zhao, Yanfan [Laboratory of Advanced Manufacturing and Reliability for MEMS/NEMS/OEDS, Jiangsu University, Zhenjiang 212013 (China); Yang, Haiying [School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013 (China); Wang, Shuting, E-mail: wangst@mail.hust.edu.cn [School of Mechanical Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China)

2013-11-01

189

Determination of differential cross sections for electron-impact excitation of electronic states of molecular oxygen  

Energy Technology Data Exchange (ETDEWEB)

The development and initial results of a method for the determination of differential cross sections for electron scattering by molecular oxygen are described. The method has been incorporated into an existing package of computer programs which, given spectroscopic factors, dissociation energies and an energy-loss spectrum for electron-impact excitation, determine the differential cross sections for each electronic state relative to that of the elastic peak. Enhancements of the original code were made to deal with particular aspects of electron scattering from O{sub 2}, such as the overlap of vibrational levels of the ground state with transitions to excited states, and transitions to levels close to and above the dissocation energy in the Herzberg and Schumann-Runge continua. The utility of the code is specifically demonstrated for the ''6-eV states'' of O{sub 2}, where we report absolute differential cross sections for their excitation by 15-eV electrons. In addition an integral cross section, derived from the differential cross section measurements, is also reported for this excitation process and compared against available theoretical results. The present differential and integral cross sections for excitation of the ''6-eV states'' of O{sub 2} are the first to be reported in the literature for electron-impact energies below 20 eV. (c) 2000 The American Physical Society.

Campbell, L. [Physics Department, Flinders University of South Australia, G.P.O. Box 2100, Adelaide, South Australia, 5001, (Australia); Green, M. A. [Physics Department, Flinders University of South Australia, G.P.O. Box 2100, Adelaide, South Australia, 5001, (Australia); Brunger, M. J. [Physics Department, Flinders University of South Australia, G.P.O. Box 2100, Adelaide, South Australia, 5001, (Australia); Teubner, P. J. O. [Physics Department, Flinders University of South Australia, G.P.O. Box 2100, Adelaide, South Australia, 5001, (Australia); Cartwright, D. C. [Theoretical Divisions, B285, Los Alamos National Laboratories, Los Alamos, New Mexico 87545 (United States)

2000-02-01

190

The effect of asymmetrical electrode on the transport properties of molecular devices  

International Nuclear Information System (INIS)

By applying nonequilibrium Green's functions in combination with the density functional theory, we have investigated the electronic transport properties of molecular devices consisting of the carbon atomic chain coupling with symmetry and asymmetry Au electrodes. The asymmetry Au electrodes systems display good rectifying behavior. The main origin of this phenomenon is that a molecular core coupling with asymmetry electrodes can generate two asymmetrical Schottky barriers at both extended molecule regions. This rectification is also explained by the calculated transmission spectrum and the spatial distribution of the LUMO and HOMO states

191

Rectification of License Plate Images Based on HT and Projection  

OpenAIRE

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

Jingsong Tao; Hao Feng,; Qingxin Zhu; Hongyao Deng

2013-01-01

192

Suppression of rectification at metal-Mott-insulator interfaces  

OpenAIRE

Charge transport through metal-Mott-insulator interfaces is studied and compared with that through metal-band-insulator interfaces. For band insulators, rectification has been known to occur owing to a Schottky barrier, which is produced by the work-function difference. For Mott insulators, however, qualitatively different current-voltage characteristics are obtained. Theoretically, we use the one-dimensional Hubbard model for a Mott insulator and attach to it the tight-bind...

Yonemitsu, Kenji; Maeshima, Nobuya; Hasegawa, Tatsuo

2007-01-01

193

Fullerene-based Anchoring Groups for Molecular Electronics  

DEFF Research Database (Denmark)

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

Martin, Christian A.; Ding, Dapeng

2008-01-01

194

Probing flexible conformations in molecular junctions by inelastic electron tunneling spectroscopy  

Directory of Open Access Journals (Sweden)

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.

Mingsen Deng

2015-01-01

195

Probing flexible conformations in molecular junctions by inelastic electron tunneling spectroscopy  

Science.gov (United States)

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.

Deng, Mingsen; Ye, Gui; Cai, Shaohong; Sun, Guangyu; Jiang, Jun

2015-01-01

196

Controllable thermal rectification realized in binary phase change composites.  

Science.gov (United States)

Phase transition is a natural phenomenon happened around our daily life, represented by the process from ice to water. While melting and solidifying at a certain temperature, a high heat of fusion is accompanied, classified as the latent heat. Phase change material (PCM) has been widely applied to store and release large amount of energy attributed to the distinctive thermal behavior. Here, with the help of nanoporous materials, we introduce a general strategy to achieve the binary eicosane/PEG4000 stuffed reduced graphene oxide aerogels, which has two ends with different melting points. It's successfully demonstrated this binary PCM composites exhibits thermal rectification characteristic. Partial phase transitions within porous networks instantaneously result in one end of the thermal conductivity saltation at a critical temperature, and therefore switch on or off the thermal rectification with the coefficient up to 1.23. This value can be further raised by adjusting the loading content of PCM. The uniqueness of this device lies in its performance as a normal thermal conductor at low temperature, only exhibiting rectification phenomenon when temperature is higher than a critical value. The stated technology has broad applications for thermal energy control in macroscopic scale such as energy-efficiency building or nanodevice thermal management. PMID:25748640

Chen, Renjie; Cui, Yalong; Tian, He; Yao, Ruimin; Liu, Zhenpu; Shu, Yi; Li, Cheng; Yang, Yi; Ren, Tianling; Zhang, Gang; Zou, Ruqiang

2015-01-01

197

Controllable Thermal Rectification Realized in Binary Phase Change Composites  

Science.gov (United States)

Phase transition is a natural phenomenon happened around our daily life, represented by the process from ice to water. While melting and solidifying at a certain temperature, a high heat of fusion is accompanied, classified as the latent heat. Phase change material (PCM) has been widely applied to store and release large amount of energy attributed to the distinctive thermal behavior. Here, with the help of nanoporous materials, we introduce a general strategy to achieve the binary eicosane/PEG4000 stuffed reduced graphene oxide aerogels, which has two ends with different melting points. It's successfully demonstrated this binary PCM composites exhibits thermal rectification characteristic. Partial phase transitions within porous networks instantaneously result in one end of the thermal conductivity saltation at a critical temperature, and therefore switch on or off the thermal rectification with the coefficient up to 1.23. This value can be further raised by adjusting the loading content of PCM. The uniqueness of this device lies in its performance as a normal thermal conductor at low temperature, only exhibiting rectification phenomenon when temperature is higher than a critical value. The stated technology has broad applications for thermal energy control in macroscopic scale such as energy-efficiency building or nanodevice thermal management.

Chen, Renjie; Cui, Yalong; Tian, He; Yao, Ruimin; Liu, Zhenpu; Shu, Yi; Li, Cheng; Yang, Yi; Ren, Tianling; Zhang, Gang; Zou, Ruqiang

2015-03-01

198

Joint estimation of epipolar geometry and rectification parameters using point correspondences for stereoscopic TV sequences  

OpenAIRE

An optimal stereo sequence needs to be rectified in order to avoid vertical disparities and similar image distortions. However, due to imperfect stereo rigs, vertical disparities occur mainly due to a mechanical misalignment of the cameras. Several rectification methods are known, most of them are based on a strong calibration. However, calibration data is often not provided, such that the rectification needs to be done based on point correspondences. In this paper, we propose a rectification...

Zilly, F.; Mu?ller, M.; Kauff, P.; Eisert, P.

2010-01-01

199

Picometer-Scale Electronic Control of Molecular Dynamics Inside a Single Molecule  

Science.gov (United States)

Tunneling electrons from a low-temperature (5 kelvin) scanning tunneling microscope were used to control, through resonant electronic excitation, the molecular dynamics of an individual biphenyl molecule adsorbed on a silicon(100) surface. Different reversible molecular movements were selectively activated by tuning the electron energy and by selecting precise locations for the excitation inside the molecule. Both the spatial selectivity and energy dependence of the electronic control are supported by spectroscopic measurements with the scanning tunneling microscope. These experiments demonstrate the feasibility of controlling the molecular dynamics of a single molecule through the localization of the electronic excitation inside the molecule.

Lastapis, M.; Martin, M.; Riedel, D.; Hellner, L.; Comtet, G.; Dujardin, G.

2005-05-01

200

Vibration-induced inelastic effects in the electron transport through multisite molecular bridges  

OpenAIRE

We theoretically analyzed inelastic effects in the electron transport through molecular junctions originating from electron-vibron interactions. The molecular bridge was simulated by a periodic chain of identical interacting hydrogen-like atoms providing a set of energy states for the electron tunneling. To avoid difficulties inevitably arising when advanced computational techniques are employed to study inelastic electron transport through multilevel bridges, we propose and...

Zimbovskaya, Natalya A.; Kuklja, Maija M.

2009-01-01

201

Molecular dynamics simulation of electron trapping in the sapphire lattice  

International Nuclear Information System (INIS)

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 mode. Dynamical aspects are studied here by performing Molecular Dynamics simulations. We show that an excess electron introduced into the sapphire lattice (? -Al2O3) can be trapped only at a limited number of sites. The energy gained by allowing the electron to localize in these sites is of the order of 4-5 eV, in good agreement with the results of the space charge model. Displacements of the neighboring ions due to the implanted charge are shown to be localized in a small region of about 5 A. Detrapping is observed at 250 K. The ionic displacements turn out to play an important role in modifying the potential landscape by lowering, in a dynamical way, the barriers that cause localization at low temperature. (author). 18 refs, 7 figs, 2 tabs

202

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)

203

Ionic fragmentation channels in electron collisions of small molecular ions  

Energy Technology Data Exchange (ETDEWEB)

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

Hoffmann, Jens

2009-01-28

204

Atomic spectral methods for molecular electronic structure calculations  

International Nuclear Information System (INIS)

Theoretical methods are reported for ab initio calculations of the adiabatic (Born-Oppenheimer) electronic wave functions and potential energy surfaces of molecules and other atomic aggregates. An outer product of complete sets of atomic eigenstates familiar from perturbation-theoretical treatments of long-range interactions is employed as a representational basis without prior enforcement of aggregate wave function antisymmetry. The nature and attributes of this atomic spectral-product basis are indicated, completeness proofs for representation of antisymmetric states provided, convergence of Schroedinger eigenstates in the basis established, and strategies for computational implemention of the theory described. A diabaticlike Hamiltonian matrix representative is obtained, which is additive in atomic-energy and pairwise-atomic interaction-energy matrices, providing a basis for molecular calculations in terms of the (Coulombic) interactions of the atomic constituents. The spectral-product basis is shown to contain the totally antisymmetric irreducible representation of the symmetric group of aggregate electron coordinate permutations once and only once, but to also span other (non-Pauli) symmetric group representations known to contain unphysical discrete states and associated continua in which the physically significant Schroedinger eigenstates are generally embedded. These unphysical representations are avoided by isolating the physical block of the Hamiltonian matrthe physical block of the Hamiltonian matrix with a unitary transformation obtained from the metric matrix of the explicitly antisymmetrized spectral-product basis. A formal proof of convergence is given in the limit of spectral closure to wave functions and energy surfaces obtained employing conventional prior antisymmetrization, but determined without repeated calculations of Hamiltonian matrix elements as integrals over explicitly antisymmetric aggregate basis states. Computational implementations of the theory employ efficient recursive methods which avoid explicit construction the metric matrix and do not require storage of the full Hamiltonian matrix to isolate the antisymmetric subspace of the spectral-product representation. Calculations of the lowest-lying singlet and triplet electronic states of the covalent electron pair bond (H2) illustrate the various theorems devised and demonstrate the degree of convergence achieved to values obtained employing conventional prior antisymmetrization. Concluding remarks place the atomic spectral-product development in the context of currently employed approaches for ab initio construction of adiabatic electronic eigenfunctions and potential energy surfaces, provide comparisons with earlier related approaches, and indicate prospects for more general applications of the method

205

Rectification induced in N2AA-doped armchair graphene nanoribbon device  

International Nuclear Information System (INIS)

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

206

Nonlocal tunnel magnetoresistance and thermal rectification effect in a nanoscale three-terminal junction.  

Science.gov (United States)

We investigate thermally driven electronic transport through a quantum dot (QD) coupled to two ferromagnetic leads and one normal-metallic lead. The effect of spin accumulation and temperature bias on the tunnel magnetoresistance (TMR) is examined. We obtain a nonlocal negative TMR, which also exhibits a rectification effect as a function of the QD level modulated by a gate voltage. For a negative QD level, the TMR is zero, and the TMR is negative for a positive QD level. This effect arises from the interplay of the spin accumulation and thermoelectric transport, which detects the sign reversal of spin accumulation in the QD. In addition, our system can also be used as a spin current generator. PMID:23148042

Ying, Yibo; Jin, Guojun

2012-12-12

207

Nonlocal tunnel magnetoresistance and thermal rectification effect in a nanoscale three-terminal junction  

International Nuclear Information System (INIS)

We investigate thermally driven electronic transport through a quantum dot (QD) coupled to two ferromagnetic leads and one normal-metallic lead. The effect of spin accumulation and temperature bias on the tunnel magnetoresistance (TMR) is examined. We obtain a nonlocal negative TMR, which also exhibits a rectification effect as a function of the QD level modulated by a gate voltage. For a negative QD level, the TMR is zero, and the TMR is negative for a positive QD level. This effect arises from the interplay of the spin accumulation and thermoelectric transport, which detects the sign reversal of spin accumulation in the QD. In addition, our system can also be used as a spin current generator.

208

Probing flexibility in porphyrin-based molecular wires using double electron electron resonance.  

Science.gov (United States)

A series of butadiyne-linked zinc porphyrin oligomers, with one, two, three, and four porphyrin units and lengths of up to 75 A, have been spin-labeled at both ends with stable nitroxide TEMPO radicals. The pulsed EPR technique of double electron electron resonance (DEER) was used to probe the distribution of intramolecular end-to-end distances, under a range of conditions. DEER measurements were carried out at 50 K in two types of dilute solution glasses: deutero-toluene (with 10% deutero-pyridine) and deutero-o-terphenyl (with 5% 4-benzyl pyridine). The complexes of the porphyrin oligomers with monodentate ligands (pyridine or 4-benzyl pyridine) principally adopt linear conformations. Nonlinear conformations are less populated in the lower glass-transition temperature solvent. When the oligomers bind star-shaped multidentate ligands, they are forced to bend into nonlinear geometries, and the experimental end-to-end distances for these complexes match those from molecular mechanics calculations. Our results show that porphyrin-based molecular wires are shape-persistent, and yet that their shapes can deformed by binding to multivalent ligands. Self-assembled ladder-shaped 2:2 complexes were also investigated to illustrate the scope of DEER measurements for providing structural information on synthetic noncovalent nanostructures. PMID:19736940

Lovett, Janet E; Hoffmann, Markus; Cnossen, Arjen; Shutter, Alexander T J; Hogben, Hannah J; Warren, John E; Pascu, Sofia I; Kay, Christopher W M; Timmel, Christiane R; Anderson, Harry L

2009-09-30

209

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

Science.gov (United States)

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.

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

2015-03-01

210

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

Science.gov (United States)

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

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

2015-03-01

211

Quantum mechanical simulations of polymers for molecular electronics and photonics  

International Nuclear Information System (INIS)

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

212

Testing accelerometer rectification error caused by multidimensional composite inputs with double turntable centrifuge  

Science.gov (United States)

Rectification error is a critical characteristic of inertial accelerometers. Accelerometers working in operational situations are stimulated by composite inputs, including constant acceleration and vibration, from multiple directions. However, traditional methods for evaluating rectification error only use one-dimensional vibration. In this paper, a double turntable centrifuge (DTC) was utilized to produce the constant acceleration and vibration simultaneously and we tested the rectification error due to the composite accelerations. At first, we deduced the expression of the rectification error with the output of the DTC and a static model of the single-axis pendulous accelerometer under test. Theoretical investigation and analysis were carried out in accordance with the rectification error model. Then a detailed experimental procedure and testing results were described. We measured the rectification error with various constant accelerations at different frequencies and amplitudes of the vibration. The experimental results showed the distinguished characteristics of the rectification error caused by the composite accelerations. The linear relation between the constant acceleration and the rectification error was proved. The experimental procedure and results presented in this context can be referenced for the investigation of the characteristics of accelerometer with multiple inputs.

Guan, W.; Meng, X. F.; Dong, X. M.

2014-12-01

213

Anisotropic scattered data interpolation for pushbroom image rectification.  

Science.gov (United States)

This paper deals with fast and accurate visualization of pushbroom image data from airborne and spaceborne platforms. A pushbroom sensor acquires images in a line-scanning fashion, and this results in scattered input data that need to be resampled onto a uniform grid for geometrically correct visualization. To this end, we model the anisotropic spatial dependence structure caused by the acquisition process. Several methods for scattered data interpolation are then adapted to handle the induced anisotropic metric and compared for the pushbroom image rectification problem. A trick that exploits the semiordered line structure of pushbroom data to improve the computational complexity several orders of magnitude is also presented. PMID:24733010

Ringaby, Erik; Friman, Ola; Forssén, Per-Erik; Opsahl, Thomas Olsvik; Haavardsholm, Trym Vegard; Kåsen, Ingebjørg

2014-05-01

214

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

215

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.

216

Quantum Computing Using Pulse-Based Electron-Nuclear Double Resonance (endor):. Molecular Spin-Qubits  

Science.gov (United States)

Electrons with the spin quantum number 1/2, as physical qubits, have naturally been anticipated for implementing quantum computing and information processing (QC/QIP). Recently, electron spin-qubit systems in organic molecular frames have emerged as a hybrid spin-qubit system along with a nuclear spin-1/2 qubit. Among promising candidates for QC/QIP from the materials science side, the reasons for why electron spin-qubits such as molecular spin systems, i.e., unpaired electron spins in molecular frames, have potentialities for serving for QC/QIP will be given in the lecture (Chapter), emphasizing what their advantages or disadvantages are entertained and what technical and intrinsic issues should be dealt with for the implementation of molecular-spin quantum computers in terms of currently available spin manipulation technology such as pulse-based electron-nuclear double resonance (pulsed or pulse ENDOR) devoted to QC/QIP. Firstly, a general introduction and introductory remarks to pulsed ENDOR spectroscopy as electron-nuclear spin manipulation technology is given. Super dense coding (SDC) experiments by the use of pulsed ENDOR are also introduced to understand differentiating QC ENDOR from QC NMR based on modern nuclear spin technology. Direct observation of the spinor inherent in an electron spin, detected for the first time, will be shown in connection with the entanglement of an electron-nuclear hybrid system. Novel microwave spin manipulation technology enabling us to deal with genuine electron-electron spin-qubit systems in the molecular frame will be introduced, illustrating, from the synthetic strategy of matter spin-qubits, a key-role of the molecular design of g-tensor/hyperfine-(A-)tensor molecular engineering for QC/QIP. Finally, important technological achievements of recently-emerging CD ELDOR (Coherent-Dual ELectron-electron DOuble Resonance) spin technology enabling us to manipulate electron spin-qubits are described.

Sato, Kazuo; Nakazawa, Shigeki; Rahimi, Robabeh D.; Nishida, Shinsuke; Ise, Tomoaki; Shimoi, Daisuke; Toyota, Kazuo; Morita, Yasushi; Kitagawa, Masahiro; Carl, Parick; Höfner, Peter; Takui, Takeji

2009-06-01

217

Dihydroazulene Photochromism:Synthesis, Molecular Electronics and Hammett Correlations  

DEFF Research Database (Denmark)

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

Broman, SØren Lindbæk

2013-01-01

218

Self-assembled and electrochemically deposited mono/multilayers for molecular electronics applications  

International Nuclear Information System (INIS)

For the development of molecular electronics, it is desirable to investigate characteristics of organic molecules with electronic device functionalities. In near future, such molecular devices could be integrated with silicon to prepare hybrid nanoelectronic devices. In this paper, we review work done in our laboratory on study of characteristics of some functional molecules. For these studies molecular mono and multilayers have been deposited on silicon surface by self-assembly and electrochemical deposition techniques. Both commercially available and specially designed and synthesized molecules have been utilized for these investigations. We demonstrate dielectric layers, memory, switching, rectifier and negative differential resistance devices based on molecular mono and multilayers.

219

Rectification effects in superconductors with magnetic pinning centers  

International Nuclear Information System (INIS)

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

220

Stereo Calibration and Rectification for Omnidirectional Multi-camera Systems  

Directory of Open Access Journals (Sweden)

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

Yanchang Wang

2012-10-01

221

Analysis of secondary-electron emission in beam-foil experiments with molecular ions  

International Nuclear Information System (INIS)

We analyze the possibility of large oscillatory wake effects in secondary-electron emission induced by molecular ions, which were proposed in previous interpretations of results derived from beam-foil experiments. We show that theoretical expectations are in disagreement with the description of such oscillatory effects in terms of wake phenomena. Our analysis of various experimental evidences suggests a different origin for the effect. We propose a simple explanation for the molecular effect in secondary-electron emission, which is based on previous knowledge of electron emission from solid targets, and of molecular effects in the energy loss of ion clusters in solid foils

222

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

International Nuclear Information System (INIS)

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

223

Manipulation of large molecules by low-temperature STM: model systems for molecular electronics  

Energy Technology Data Exchange (ETDEWEB)

The ability of the low-temperature scanning tunneling microscope to manipulate atoms and to build nanostructures with atomic precision can be extended to the manipulation of larger molecules and to selectively modify their internal degrees of freedom. Manipulation experiments on individual molecules show an exciting diversity of physical, chemical, and electronic phenomena. They permit a deeper insight into the quantum electronics of molecular systems and provide important information on the conformational and mechanical properties of single complex molecules. In this article, recent experiments on specially designed molecules will be reviewed, which investigate model systems interesting for the developing of molecular electronics. Starting from the realization of the principle of a molecular switch, going through the possibility of recording the small intramolecular changes inside a complex molecule during its movement, toward the study of the electronic contact between a single molecular wire and a metallic nanoelectrode.

Moresco, Francesca [Institut fuer Experimentalphysik, Freie Universitaet Berlin, Arnimallee 14, D-14195 Berlin (Germany)]. E-mail: moresco@physik.fu-berlin.de

2004-10-01

224

Manipulation of large molecules by low-temperature STM: model systems for molecular electronics  

International Nuclear Information System (INIS)

The ability of the low-temperature scanning tunneling microscope to manipulate atoms and to build nanostructures with atomic precision can be extended to the manipulation of larger molecules and to selectively modify their internal degrees of freedom. Manipulation experiments on individual molecules show an exciting diversity of physical, chemical, and electronic phenomena. They permit a deeper insight into the quantum electronics of molecular systems and provide important information on the conformational and mechanical properties of single complex molecules. In this article, recent experiments on specially designed molecules will be reviewed, which investigate model systems interesting for the developing of molecular electronics. Starting from the realization of the principle of a molecular switch, going through the possibility of recording the small intramolecular changes inside a complex molecule during its movement, toward the study of the electronic contact between a single molecular wire and a metallic nanoelectrode

225

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

OpenAIRE

The electronic states of isostructural single-component molecular conductors [M(tmdt)2] (M= Ni, Au, and Cu) are theoretically studied. By considering fragments of molecular orbitals as basis functions, we construct a multiorbital model common for the three materials. The tight-binding parameters are estimated from results of first-principles band calculations, leading to a systematic view of their electronic structures. We find that the interplay between a p\\pi-type orbital ...

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

2013-01-01

226

Ab initio analysis of electron-phonon coupling in molecular devices  

OpenAIRE

We report first principles analysis of electron-phonon coupling in molecular devices under external bias voltage and during current flow. Our theory and computational framework are based carrying out density functional theory within the Keldysh nonequilibrium Green's function formalism. We analyze which molecular vibrational modes are most relevant to charge transport under nonequilibrium conditions. For a molecular tunnel junction of a 1,4-benzenedithiolate molecule contact...

Sergueev, N.; Roubtsov, D.; Guo, Hong

2005-01-01

227

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

OpenAIRE

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

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

1997-01-01

228

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

Science.gov (United States)

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

Balestro, Franck

2013-03-01

229

Polaron effects on nonlinear optical rectification in asymmetrical Gaussian potential quantum wells with applied electric fields  

International Nuclear Information System (INIS)

Polaron effects on nonlinear optical rectification in asymmetrical Gaussian potential quantum wells are studied by the effective mass approximation and the perturbation theory. The numerical results show that nonlinear optical rectification coefficients are strongly dependent on the barrier hight V0 of the Gaussian potential quantum wells, the range L of the confinement potential and the electric field F. Besides, the numerical results show that no matter how V0, L and F change, taking into consideration polaron effects, the optical rectification coefficients ?0(2) get greatly enhanced.

230

Polaron effects on nonlinear optical rectification in asymmetrical Gaussian potential quantum wells with applied electric fields  

Energy Technology Data Exchange (ETDEWEB)

Polaron effects on nonlinear optical rectification in asymmetrical Gaussian potential quantum wells are studied by the effective mass approximation and the perturbation theory. The numerical results show that nonlinear optical rectification coefficients are strongly dependent on the barrier hight V{sub 0} of the Gaussian potential quantum wells, the range L of the confinement potential and the electric field F. Besides, the numerical results show that no matter how V{sub 0}, L and F change, taking into consideration polaron effects, the optical rectification coefficients ?{sub 0}{sup (2)} get greatly enhanced.

Wu, Jinghe [Department of Physics, Henan Institute of Education, Zhengzhou 450046 (China); Guo, Kangxian, E-mail: axguo@sohu.com [Department of Physics, College of Physics and Electronic Engineering, Guangzhou University, Guangzhou 510006 (China); Liu, Guanghui [Department of Physics, College of Physics and Electronic Engineering, Guangzhou University, Guangzhou 510006 (China)

2014-08-01

231

Quantum Entanglement and Electron Correlation in Molecular Systems  

OpenAIRE

We study the relation between quantum entanglement and electron correlation in quantum chemistry calculations. We prove that the Hartree-Fock (HF) wave function does not violate Bell's inequality, thus is not entangled while the configuration interaction (CI) wave function is entangled since it violates Bell's inequality. Entanglement is related to electron correlation and might be used as an alternative measure of the electron correlation in quantum chemistry calculations. ...

Wang, Hefeng; Kais, Sabre

2007-01-01

232

Modelling of boron isotope separation by chemical exchange rectification process  

International Nuclear Information System (INIS)

This paper deals with modelling and simulation of boron isotope separation by chemical exchange rectification between BF3 and the complex anisole BF3. The relationship between separation factor and reaction equilibrium constant was studied and an expression for the temperature dependence of separation factor in the An BF3-BF3 system was given, on the basis of material balance, chemical equilibrium, separation factor and summation equation, the mathematical model of boron isotope was established. In addition, effects of temperature and reflux ratio on separation process were analyzed, the results showed if the concentration of 10B product rose from 19% to 99% at room temperature and pressure, the minimum number of theoretical plates of enriching stage should achieve 200, the minimum number of theoretical plates of dilute stage should achieve 127, and the optimum reflux ratio was about 160. (authors)

233

Voltage rectification in two-dimensional Josephson junction arrays  

International Nuclear Information System (INIS)

We study numerically the directed motion of vortices (antivortices) under an applied ac bias in two-dimensional Josephson junction arrays (JJA) with an asymmetrically modulated periodic vortex pinning potential. We find that the ratchet effect in large 2D JJA can be obtained using the RSJ model for the overdamped vortex dynamics. The rectification effect shows a strong dependence on vortex density as well as an inversion of the vortex flow direction with the ac amplitude, for a wide range of magnetic field around f = 1/2 (f being the vortex density). Our results are in good agreement with very recent experiments by D.E. Shalom and H. Pastoriza [D.E. Shalom, H. Pastoriza, Phys. Rev. Lett. 94 (2005) 177001

234

CONCURRENT FAULT RECTIFICATION (CFR ARCHITECTURE FOR MOTION ANALYSIS COMPUTING ARRAYS  

Directory of Open Access Journals (Sweden)

Full Text Available This paper develops a novel Concurrent Fault Rectification (CFR architecture for Motion Analysis Computing Arrays (MACA. Any single fault in each Processing Element (PE in an MACA can be effectively detected and corrected using the concept of Dual-Remnant codes i.e., Remnant and Proportionate (RP code. A Good Example is the H.264 video compression standard, also known as MPEG-4 Advanced Video Coding application. It uses a context-based adaptive method to speed up the multiple reference frames Motion Analysis by avoiding 76%–96% unnecessary reference frames computation. A large PE array accelerates the computation speed especially in High Resolution devices such as HDTV(High Definition Television.The Visual Quality and Peak Signal-to-Noise Ratio (PSNR at a given bit rate are influenced if a fault occurred in MA process.

S. Vasanth Vigneshwaran

2013-10-01

235

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

International Nuclear Information System (INIS)

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

236

Electrochemical current rectification-a novel signal amplification strategy for highly sensitive and selective aptamer-based biosensor.  

Science.gov (United States)

Electrochemical aptamer-based (E-AB) sensors represent an emerging class of recently developed sensors. However, numerous of these sensors are limited by a low surface density of electrode-bound redox-oligonucleotides which are used as probe. Here we propose to use the concept of electrochemical current rectification (ECR) for the enhancement of the redox signal of E-AB sensors. Commonly, the probe-DNA performs a change in conformation during target binding and enables a nonrecurring charge transfer between redox-tag and electrode. In our system, the redox-tag of the probe-DNA is continuously replenished by solution-phase redox molecules. A unidirectional electron transfer from electrode via surface-linked redox-tag to the solution-phase redox molecules arises that efficiently amplifies the current response. Using this robust and straight-forward strategy, the developed sensor showed a substantial signal amplification and consequently improved sensitivity with a calculated detection limit of 114nM for ATP, which was improved by one order of magnitude compared with the amplification-free detection and superior to other previous detection results using enzymes or nanomaterials-based signal amplification. To the best of our knowledge, this is the first demonstration of an aptamer-based electrochemical biosensor involving electrochemical rectification, which can be presumably transferred to other biomedical sensor systems. PMID:25460883

Feng, Lingyan; Sivanesan, Arumugam; Lyu, Zhaozi; Offenhäusser, Andreas; Mayer, Dirk

2015-04-15

237

Determination of Rectification Corrections for Semi Gantry Crane Rail Axes in the Local 3D Coordinate System  

Science.gov (United States)

Electronic tacheometers are currently the standard instruments used in geodetic work, including also geodetic engineering measurements. The main advantage connected with this equipment is among others high accuracy of the measurement and thus high accuracy of the final determinations represented for example by the points' coordinates. One of many applications of the tacheometers is the measurement of crane rail axes. This measurement is based on polar method and it allows to get the spatial coordinates of points in 3D local system. The standard technology of measurement of crane rail axes and development of its calculations' results is well-known and widely presented in the subject literature. At the same time new methods of observations results evaluation are developing. Some new proposals for the development of measurement results were already presented in (Kami?ski, 2013). This paper is a generalisation of the paper quoted above. The authors developed the concept which was presented there by a proposal for determining rectification corrections for semi gantry crane rail axes. To carried out the task, the parametric method with conditions on parameters was used. Moreover the practical tests on simulated measurement results were conducted. The results obtained from alignment confirmed the theoretical assumptions. Despite the fact that analyses were carried out only on the simulated data, it is already possible to say that presented method for determination of rectification corrections for crane rail axes can be used for development of the observations from real measurement.

Filipiak, Daria; Kami?ski, Waldemar

2015-02-01

238

Rectification in substituted atomic wires: a theoretical insight.  

Science.gov (United States)

Recently, there have been discussions that the giant diode property found experimentally in diblock molecular junctions could be enhanced by the many-body electron correlation effect beyond the mean field theory. In addition, the effect of electron-phonon scattering on an electric current through the diode molecule, measured by inelastic tunneling spectroscopy (IETS), was found to be symmetric with respect to the voltage sign change even though the current is asymmetric. The reason for this behavior is a matter of speculation. In order to clarify whether or not this feature is limited to organic molecules in the off-resonant tunneling region, we discuss the current asymmetry effect on IETS in the resonant region. We introduced heterogeneous atoms into an atomic wire and found that IETS becomes asymmetric in this substituted atomic wire case. Our conclusion gives the other example of intrinsic differences between organic molecules and metallic wires. While the contribution of electron-phonon scattering to IETS is not affected by the current asymmetry in the former case, it is affected in the latter case. The importance of the contribution of the electron-hole excitation to phonon damping in bringing about the current asymmetry effect in IETS in the latter case is discussed. PMID:22466527

Asai, Yoshihiro

2012-04-25

239

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

240

Interference effects in single ionization of molecular hydrogen by electron impact  

International Nuclear Information System (INIS)

A recently developed molecular three-continuum approximation is employed to compute differential cross sections for the ionization of hydrogen molecules by electron impact. Within the framework of this approximation, the chosen final electronic wavefunction takes into account the molecular character of the target as well as the correlate motion between the aggregates in the final channel of the reaction. Fivefold-differential cross sections as a function of both the electron momenta in the final state and the molecular orientation are studied for different kinematical arrangements. Interference structures coming from the two-centre geometry of the molecule are predicted in this case. Integrated cross sections over all molecular orientations are also calculated. It is shown that interference patterns remain, even for this case. (letter to the editor)

241

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

CERN Document Server

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.

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

1997-01-01

242

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

CERN Document Server

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.

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

2004-01-01

243

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-06-28

244

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

International Nuclear Information System (INIS)

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

245

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

Science.gov (United States)

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

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

2006-05-01

246

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

Science.gov (United States)

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

Bruque, Nicolas Alexander

2009-12-01

247

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

International Nuclear Information System (INIS)

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

248

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

International Nuclear Information System (INIS)

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

249

Laser-assisted electron diffraction for femtosecond molecular imaging  

Energy Technology Data Exchange (ETDEWEB)

We report the observation of laser-assisted electron diffraction (LAED) through the collision of 1 keV electrons with gas-phase CCl{sub 4} molecules in a femtosecond near-infrared laser field. In the angular distribution of the scattered electrons with the energy shifts of ±??, we observed clear diffraction patterns which reflect the geometrical structure of the molecules at the moment of laser irradiation. Our results demonstrate that ultrafast nuclear dynamics of molecules can be probed by LAED with the high temporal (<10 fs) and spatial (?0.01 Å) resolutions.

Morimoto, Yuya; Kanya, Reika [Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Yamanouchi, Kaoru, E-mail: kaoru@chem.s.u-tokyo.ac.jp [Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); NANOQUINE, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)

2014-02-14

250

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

251

Renormalization of Molecular Electronic Levels at Metal-Molecule Interfaces  

CERN Document Server

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

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

2006-01-01

252

Rectification of acetylcholine-elicited currents in PC12 pheochromocytoma cells.  

OpenAIRE

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

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

1990-01-01

253

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

OpenAIRE

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 polye...

Nguyen, Nam-trung; Lam, Yee-cheong; Ho, Soon-seng; Low, Cassandra Lee-ngo

2008-01-01

254

Molecular double core-hole electron spectroscopy for chemical analysis  

CERN Document Server

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

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

2010-01-01

255

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1996-02-01

256

Dynamical properties of single-electron devices and molecular magnets  

OpenAIRE

This doctoral dissertation consists of theoretical studies of a number of nanometer-scale structures. In papers [1]-[5], the emphasis is on tiny devices based on conducting materials, i.e., metals and doped semiconductors. Depending on the feature size, geometry, and the electronic density of states, charging effects and quantization of single-electron states may occur. These properties can be utilized to control charge and electric current with the precision of fractions of the electroni...

Pohjola, Teemu

2001-01-01

257

Influences of molecular weight on curing effect of epoxy resin irradiated by electron beam  

International Nuclear Information System (INIS)

The influences of molecular weight on electron beam (EB) curing in epoxy resins were studied. The rate of radiation reaction in epoxy resin systems decreases with the increasing molecular weight. Under the low radiation dose, the curing thickness and curing degree is small for samples with high molecular weight. The effect of molecular weight decreases with the increasing radiation dose. The glass transition temperature (Tg) and the storage modulus (E') are under the control of curing degree in samples, and the molecular weight will play a role on the samples with similar curing degree. After heat treatment, the Tg and E' of epoxy resins cured by radiation will increase. The molecular weight is directly associated with effect of heat treatment

258

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

Science.gov (United States)

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

Bischoff, Florian A

2014-11-14

259

Trimer effects in fragment molecular orbital-linear combination of molecular orbitals calculation of one-electron orbitals for biomolecules  

Science.gov (United States)

The fragment molecular orbital (FMO)-linear combination of molecular orbitals (LCMO) method incorporates as an efficient post-process calculation of one-electron orbitals of the whole system after the FMO total energy calculation. A straightforward way to increase the accuracy is inclusion of the trimer effect. Here, we derive a comprehensive formulation called the FMO3-LCMO method. To keep the computational costs of the trimer term low enough, we use a matrix-size reduction technique. We evaluated the accuracy and efficiency of the FMO3-LCMO scheme in model biological systems (alanine oligomer and chignolin). The results show that delocalized electronic orbitals with covalent and hydrogen bonds are better described at the trimer level, and the FMO3-LCMO method is applicable to quantitative evaluations of a wide range of frontier orbitals in large biosystems.

Kobori, Tomoki; Sodeyama, Keitaro; Otsuka, Takao; Tateyama, Yoshitaka; Tsuneyuki, Shinji

2013-09-01

260

Molecular and Electronic Structure of n-Alkyl Cyanobiphenyl Nematogens  

Energy Technology Data Exchange (ETDEWEB)

First principle electronic structure calculations (ab-initio and density functional) were performed on a series of substituted cyanobiphenyls to examine the structural and electronic properties as a function of the alkyl tail length and changes in torsion angle about the central bond connecting the rings. We find good agreement between our results and previous electronic structure studies for the optimized torsion angle between phenyls in the cyanobiphenyls, and changes in dipole moment for the cyanobiphenyls. We also find the torsion angle and rotational barriers in cyanobiphenyls to be similar to that in simple biphenyl. However, we find large discrepancies with the recent density functional calculations that reported a much smaller torsion angle in the syanobiphenyls.

Risser, Steven M.(TEXAS A and M UNIVERSITY); Ferris, Kim F.(BATTELLE (PACIFIC NW LAB))

2001-12-01

261

Through-space conjugated molecular wire comprising three ?-electron systems.  

Science.gov (United States)

A [2.2]paracyclophane-based through-space conjugated oligomer comprising three ?-electron systems was designed and synthesized. The arrangement of three ?-conjugated systems in an appropriate order according to the energy band gap resulted in efficient unidirectional photoexcited energy transfer by the Förster mechanism. The energy transfer efficiency and rate constants were estimated to be >0.999 and >10(12) s(-1), respectively. The key point for the efficient energy transfer is the orientation of the transition dipole moments. The time-dependent density functional theory (TD-DFT) studies revealed the transition dipole moments of each stacked ?-electron system; each dipole moment was located on the long axis of each stacked ?-electron system. This alignment of the dipole moments is favorable for fluorescence resonance energy transfer (FRET). PMID:25056560

Morisaki, Yasuhiro; Kawakami, Naoya; Shibata, Shotaro; Chujo, Yoshiki

2014-10-01

262

Molecular shock response of explosives: electronic absorption spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-01-01

263

Electron transfer statistics and thermal fluctuations in molecular junctions.  

Science.gov (United States)

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. PMID:25725711

Goswami, Himangshu Prabal; Harbola, Upendra

2015-02-28

264

Recombination of molecular helium ions at high electron temperatures  

International Nuclear Information System (INIS)

Measurements were performed of the rate of decay of anafterglow plasma from a constant current discharge in He at pressure 25 mm Hg st. and electron concentration n/sub e/0.4=(en-dash1.4)x1011 cm-3. The value of n/sub e/ in the afterglow was measured in terms of the decay of the discharge current at a constant intensity E of the longitudinal electric field; the electron temperature T/sub e/ in the afterglow was calculated in terms of the field intensity E and varied within (5--12)x1030K. The dependence of the recombination coefficient ? on T/sub e/ in the range (5--12)x1030K is approximated by the relation ?0.8=0.2(center-dot)=10-8(T/sub e//104K)/sup() -3.0plus-or-minus0.5/ cm3/s. The value of ? does not depend on the electron concentration. The measures values of ? are significantly higher than can be anticipated on the basis of an extrapolation of existing experimental data on the literature for T/sub e/ in the region 300-1500 K. This is explained by a possible increased role played by dissociative recombination of He+2 ions at high electron temperatures

265

Implementation of the analytical energy gradient method in the nuclear and electronic molecular orbital theory  

International Nuclear Information System (INIS)

In order to optimize the average geometries of molecular systems using the nuclear and electronic molecular orbital theory (NEMO), we have deducted the expression for calculating the analytical gradient of the energy in the Hartree-Fock theory, for any kind quantum specie. The implementation was done within the computational package APMO (Any-Particle Molecular Orbital) and in order to verify the correct implementation of the method, we have calculated the model molecules H2, HF and H2O, with numerical and analytical methods. With the use of analytical derivatives within of the OMME formalism, we will have a more efficient calculation of the nuclear-electronic structure of molecular systems with the APMO package.

266

Coupled electron-phonon transport from molecular dynamics with quantum baths  

Science.gov (United States)

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

Lü, J. T.; Wang, Jian-Sheng

2009-01-01

267

Coupled electron-phonon transport from molecular dynamics with quantum baths  

International Nuclear Information System (INIS)

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

268

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

Science.gov (United States)

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

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

2014-06-01

269

Electronic excitation induced amorphization in titanate pyrochlores: an ab initio molecular dynamics study.  

Science.gov (United States)

The response of titanate pyrochlores (A2Ti2O7, A = Y, Gd and Sm) to electronic excitation is investigated utilizing an ab initio molecular dynamics method. All the titanate pyrochlores are found to undergo a crystalline-to-amorphous structural transition under a low concentration of electronic excitations. The transition temperature at which structural amorphization starts to occur depends on the concentration of electronic excitations. During the structural transition, O2-like molecules are formed, and this anion disorder further drives cation disorder that leads to an amorphous state. This study provides new insights into the mechanisms of amorphization in titanate pyrochlores under laser, electron and ion irradiations. PMID:25660219

Xiao, H Y; Weber, W J; Zhang, Y; Zu, X T; Li, S

2015-01-01

270

Probing a molecular electronic transition by two-colour sum-frequency generation spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

We demonstrate that a new emerging technique, two-colour sum-frequency generation (SFG) spectroscopy, can be used to probe the molecular electronic properties of self-assembled monolayers (SAMs). In the CH spectral range (2800-3200 cm{sup -1}), we show that the sum-frequency generation signal of a porphyrin alkanethiol derivative adsorbed on Pt(1 1 1) reaches a maximum intensity at {approx}435 nm SFG wavelength. This wavelength corresponds to the porphyrin moiety specific {pi}-{pi}* molecular electronic transition which is called the Soret or B band. This resonant behaviour is not observed for 1-dodecanethiol SAMs, which are devoid of molecular electronic transition in the investigated visible spectral range.

Humbert, C.; Dreesen, L.; Nihonyanagi, S.; Masuda, T.; Kondo, T.; Mani, A.A.; Uosaki, K.; Thiry, P.A.; Peremans, A

2003-05-15

271

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

Science.gov (United States)

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

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

2010-08-24

272

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

OpenAIRE

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 orientati...

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

2006-01-01

273

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

OpenAIRE

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 trans...

Kai Sotthewes; Victor Geskin; René Heimbuch; Avijit Kumar; Zandvliet, Harold J. W.

2014-01-01

274

Electron Transfer Dynamics in Efficient Molecular Solar Cells  

Energy Technology Data Exchange (ETDEWEB)

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.

Meyer, Gerald John

2014-10-01

275

Electron induced dissociation of H2 and CO2: molecular frame (e, 2e) spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

Collisions of energetic electrons with molecules that induce chemical and physical reactions are of fundamental importance for a range of areas from plasma physics to radiation damage in living tissue. The study of dissociative ionization of molecules where the molecular ion is fragmenting can provide detailed insight into the molecular reaction dynamics. In this work experiments were performed for H{sub 2} and CO{sub 2} at low collision energy (E{sub 0}=54.5 eV). A Reaction Microscope was used to measure the momentum vectors of all charged particles emerging from the collision. While for fast electron impact ionization can be well understood as a pure binary collision of the projectile and the target electron, at low energy the ionic potential and, therefore, the molecular structure and its alignment relative to the projectile beam can strongly influence the electron emission pattern. This was demonstrated recently in non-perturbative calculations. Therefore, an important aspect of our measurement is the determination of the molecular axis alignment during the collision. This was realized by detecting the momentum vector of an ionic fragment resulting from the post-collision dissociation of the molecular ion. Fully differential cross sections as well as their interpretation are delivered.

Ren, Xueguang; Pflueger, Thomas; Xu, Shenyue; Senftleben, Arne; Dorn, Alexander; Ullrich, Joachim [Max-Planck-Institut fuer Kernphysik, 69117 Heidelberg (Germany)

2011-07-01

276

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

Science.gov (United States)

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

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

2014-10-01

277

Electron transport through heterocyclic molecule: ab initio molecular orbital theory  

International Nuclear Information System (INIS)

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

278

Electronic transport through tape-porphyrin molecular bridges  

Energy Technology Data Exchange (ETDEWEB)

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

Tagami, Katsunori; Tsukada, Masaru

2004-10-01

279

Multiple scattering approach to elastic electron collisions with molecular clusters  

International Nuclear Information System (INIS)

We revisit our multiple-scattering method to treat low-energy elastic electron collisions with (H2O)2. Calculations are performed for different geometries of the water dimer with different dipole moments. The effect of the dipole moment of the cluster is analysed. The elastic cross sections are compared to R-matrix results. Good agreement is found above 1 eV for all geometries. The results confirm the validity of the technique.

280

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1988-01-01

281

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

282

Fully Differential Molecular-Frame Measurements for the Electron-Impact Dissociative Ionization of H2  

Science.gov (United States)

We present fully differential state-resolved experimental data for the dissociative ionization of molecular hydrogen induced through electron impact. Molecular-frame ionization cross sections are derived for transitions from the X1?g+ molecular ground state to the 1s?g, 2p?u, 2s?g, and 2p?u states of H2+. For transitions to the 2s?g and 2p?u states, a strong orientation dependence in the cross sections is revealed, with “side-on” preferred to “end-on” collisions and a propensity for the fragment proton to emerge along the normal to the scattering plane.

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

2010-01-01

283

An apparatus to investigate the fragmentation of molecular dications by electron impact  

International Nuclear Information System (INIS)

An experimental setup to study the fragmentation of molecular dications formed via inner shell ionization by electron impact is described. The main components of the setup are a cylindrical mirror analyzer, CMA, used to detect the Auger electrons, which mark the molecular site where the ionization occurred and select the state of the dication, and a time of flight mass spectrometer, TOF-MS, used to detect the parent doubly charged ion or its fragments. The fragmentation is studied via Auger electron-ion and Auger electron-ion-ion coincidence experiments. The results of the measurements used to characterize the spectrometer are presented and discussed. Then the potentialities of the setup are described via selected examples of its applications

284

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

Energy Technology Data Exchange (ETDEWEB)

The molecular donor 9,9-ethane-1,2-diylidene-bis(N-methyl-9,10-dihydroacridine) (NMA) has been synthesized, and its electronic properties were characterized at interfaces to metals with photoelectron spectroscopy. Here a decrease of the sample work function is observed that becomes larger with increasing molecular coverage and clearly exceeds values that would be expected for metal surface electron ''push back'' alone, confirming the electron donating nature of NMA. For tris(8-hydroxyquinoline)aluminum (Alq{sub 3}) deposited on top of a NMA-modified Au(111) surface, the electron injection barrier (EIB) is reduced by 0.25 eV compared to that on pristine Au(111). Furthermore, the EIB reduction depends linearly on {theta} of the donor-modified Au(111) surface, adjustable by NMA pre-coverage. Comparisons are also given to the stronger donor MV0.

Broeker, Benjamin; Blum, Ralf-Peter; Heimel, Georg; Frisch, Johannes; Rabe, Juergen P.; Koch, Norbert [Institut fuer Physik, Humboldt-Universitaet zu Berlin (Germany); Beverina, Luca [Department of Materials Science and INSTM, State University of Milano-Bicocca (Italy); Hofmann, Oliver T.; Zojer, Egbert [Institute of Solid State Physics, Graz University of Technology (Austria); Vollmer, Antje [Helmholtz-Zentrum Berlin, Bessy II, Berlin (Germany)

2010-07-01

285

Participation of Low Molecular Weight Electron Carriers in Oxidative Protein Folding  

Directory of Open Access Journals (Sweden)

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

József Mandl

2009-03-01

286

Electronic structure and magnetic anisotropy for nickel-based molecular magnets  

OpenAIRE

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

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

2004-01-01

287

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

OpenAIRE

Understanding the properties of hydrated electrons, which were first observed using pulse radiolysis of water in 1962, is crucial because they are key species in many radiation chemistry processes. Although time-resolved spectroscopic studies and molecular simulations have shown that an electron in water (prepared, for example, by water photoionization) relaxes quickly to a localized, cavity-like structure similar to 2.5 angstrom in radius, this picture has recently been questioned. In anothe...

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

2012-01-01

288

Rotational Cooling of HD+ Molecular Ions by Superelastic Collisions with Electrons  

OpenAIRE

Merging an HD+ beam with velocity matched electrons in a heavy ion storage ring we observed rapid cooling of the rotational excitations of the HD+ ions by superelastic collisions (SEC) with the electrons. The cooling process is well described using theoretical SEC rate coefficients obtained by combining the molecular R-matrix approach with the adiabatic nuclei rotation approximation. We verify the Delta J=-2 SEC rate coefficients, which are predicted to be dominant as opposed to the Delta J=-...

Shafir, D.; Novotny, S.; Buhr, H.; Altevogt, S.; Faure, A.; Grieser, M.; Harvey, A. G.; Heber, O.; Hoffmann, J.; Kreckel, H.; Lammich, L.; Nevo, I.; Pedersen, H. B.; Rubinstein, H.; Schneider, I. F.

2009-01-01

289

Cluster molecular orbital description of the electronic structures of mixed-valence iron oxides and silicates  

Science.gov (United States)

A molecular orbital description, based on spin-unrestricted X??-scattered wave calculations, is given for the electronic structures of mixed valence iron oxides and silicates. The cluster calculations show that electron hopping and optical intervalence charge-transger result from weak FeFe bonding across shared edges of FeO6 coordination polyhedra. In agreement with Zener's double exchange model, FeFe bonding is found to stabilize ferromagnetic coupling between Fe2+ and Fe3+ cations. ?? 1986.

Sherman, D.M.

1986-01-01

290

A measurement of the momentum transfer cross-section of electrons in molecular oxygen  

International Nuclear Information System (INIS)

The only data on the momentum transfer cross-section of electrons in molecular oxygen, in the energy range 0-10eV, is that derived from transport coefficients. This paper describes a method applicable to any gas, to obtain a more direct measurement. First order diffusion theory is used to find a relationship between the gas pressure and the current arriving at a collector when electrons diffuse through a field free space. (Auth.)

291

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

OpenAIRE

Dissimilatory metal reducing organisms play key roles in the biogeochemical cycle of metals as well as in the durability of submerged and buried metallic structures. The molecular mechanisms that support electron transfer across the microbe-metal interface in these organisms remain poorly explored. It is known that outer membrane proteins, in particular multiheme cytochromes, are essential for this type of metabolism, being responsible for direct and indirect, via electron shuttles, interacti...

RicardoOLouro

2014-01-01

292

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

Science.gov (United States)

Electronic level alignment at interfaces of molecular materials with inorganic semiconductors and metals controls many interfacial phenomena. How the intrinsic properties of the interacting systems define the electronic structure of their interface remains one of the most important problems in molecular electronics and nanotechnology that can be solved through a combination of surface science experimental techniques and theoretical modeling. In this article, we address this fundamental problem through experimental and computational studies of molecular electronic level alignment of thin films of C(6)F(6) on noble metal surfaces. The unoccupied electronic structure of C(6)F(6) 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 C(6)F(6) 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 C(6)F(6) molecules bound through weak van der Waals interactions to noble metal surfaces is primarily defined by the image potential of metal, the electron affinity of the molecule, and the molecule surface distance. We expect the same factors to determine the interfacial electronic structure for a broad range of molecule/metal interfaces. PMID:25303040

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

2014-10-28

293

Cooperative electron-phonon interaction in molecular chains  

OpenAIRE

Using a controlled analytic treatment, we derive a model that generically describes cooperative strong electron-phonon interaction (EPI) in one-band and two-band Jahn-Teller (JT) systems. The model involves a {\\em next-nearest-neighbor} hopping and a nearest-neighbor repulsion. Rings with odd number of sites (o-rings) belong to a different universality class compared to rings with even number (e-rings). The e-rings, upon tuning repulsion, undergo a dramatic discontinuous tra...

Yarlagadda, Sudhakar

2007-01-01

294

Electron cooling through resonant collisions with H2+ molecular ion  

International Nuclear Information System (INIS)

Electron cooling in H2+ through resonant capture leading to (i) vibrational excitation and (ii) vibrational dissociation of H2+ has been studied within the scope of Born-Oppenheimer approximation, using Feshbach's projection operator technique. Results are presented for (i) cross-sections for certain specific vibrational transitions (v sub(i) ? v sub(f)), and for (ii) total cross-sections for vibrational dissociation. Variations in the rotational inelasticity effects as obtained for different types of vibrational excitations are discussed. (author)

295

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

CERN Document Server

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

Le Pimpec, F; Laurent, Jean Michel

2001-01-01

296

Exploring electronic transport properties of AlN nanoribbon molecular device - A first-principles investigation  

Science.gov (United States)

The novel AlN nanoribbon molecular device is investigated using density functional theory for different voltage bias. The electronic transport properties of AlN nanoribbon are discussed in terms of device density of states, electron density, transmission spectrum and transmission pathways. It is evident that increasing the bias voltage leads to transition of electrons from the valence band to the conduction band across AlN nanoribbon. The electron density is found to be more along nitrogen sites. The transmission increases with the increase in bias voltage. The transmission can be fine-tuned at different energy intervals by varying the bias potential. The transmission pathways provide the insight for transmission of electrons along AlN nanoribbon. Mostly, the transmission is observed along the top and bottom regions of AlN nanoribbon. The results of the present work will give a clear picture to improve the electronic transport property along AlN nanoribbon.

Chandiramouli, R.

2015-01-01

297

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

298

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

CERN Document Server

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...

Walczak, K

2006-01-01

299

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

Directory of Open Access Journals (Sweden)

Full Text Available Dynamics of photoinduced phase transitions in molecular conductors are reviewed from the perspective of interplay between correlated electrons and phonons. (1 The charge-transfer complex TTF-CA shows a transition from a neutral paraelectric phase to an ionic ferroelectric phase. Lattice phonons promote this photoinduced transition by preparing short-range lattice dimerization as a precursor. Molecular vibrations stabilize the neutral phase so that the ionic phase, when realized, possesses a large ionicity and the Mott character; (2 The organic salts ?-(BEDT-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.

Kenji Yonemitsu

2012-01-01

300

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.)

301

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

Energy Technology Data Exchange (ETDEWEB)

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

Krantz, Claude

2009-10-28

302

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)

303

Electron diffraction study of molybdenum pentafluoride trimeric molecular structure  

International Nuclear Information System (INIS)

Using the gas electron diffraction method the structure of trimeric molecules of molybdenum pentafluoride has been studied. It is established that the (MoF5)3 molecule has a configuration of the Dsub(3h) symmetry and is characterized by the following parameters: rsub(a)(Mo-Fsub(Eh)=rsub(a)(Mo-Fsub(a)=1.814 (6), lsub(a)(Mo-Fsub(Eh))=lsub(a)(Mo-Fsub(a))=0.049 (12), rsub(a)(Mo-Fsub(M))=2.012 (10), lsub(a)(Mo-Fsub(M))=0.066 (19) A and angles Fsub(M)MoFsub(M)=79.4 (1.1), Fsub(Eh)MoFsub(Eh)=100.5 (2, 1), Fsub(a)MoFsub(a)=160.1 (1, 0) deg. From analysis of spectroscopic and electrodiffraction data the (MoF5)3 molecule vibration frequencies have been evaluated

304

Molecular Imaging Using X-Ray Free-Electron Lasers  

Science.gov (United States)

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.

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

2013-04-01

305

Combinatorial optimization of a molecular glass photoresist system for electron beam lithography.  

Science.gov (United States)

Electron beam lithography is a powerful technique for the production of nanostructures but pattern quality depends on numerous interacting process variables. Orthogonal gradients of resist composition, baking temperatures, and development time as well as dose variations inside writing fields are used to prepare ternary combinatorial libraries for an efficient stepwise optimization of a molecular glass negative tone resist system. PMID:22009688

Bauer, Wolfgang-Andreas C; Neuber, Christian; Ober, Christopher K; Schmidt, Hans-Werner

2011-12-01

306

Molecular effects in ion-electron emission from clean metal surfaces  

International Nuclear Information System (INIS)

The authors have measured electron emission yields from clean Al, Cu and Ag under 2-50 keV H+, D+, H2+ impact. It is found that molecular ion yields are lower than twice the yield of atomic ions. No isotope effects are observed for equal-velocity ions. (Auth.)

307

Structure, Dynamics, and Reactivity of Hydrated Electrons by Ab Initio Molecular Dynamics.  

Czech Academy of Sciences Publication Activity Database

Ro?. 45, ?. 1 (2012), s. 23-32. ISSN 0001-4842 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: 20.833, year: 2012

Maršálek, Ond?ej; Uhlig, Frank; Vandevondele, J.; Jungwirth, Pavel

2012-01-01

308

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

Directory of Open Access Journals (Sweden)

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

Galovi? Slobodanka P.

2006-01-01

309

Molecular mapping by low-energy-loss energy-filtered transmission electron microscopy imaging.  

Science.gov (United States)

Structure-function relationships in supramolecular systems depend on the spatial distribution of molecules, ions, and particles within complex arrays. Imaging the spatial distribution of molecular components within nanostructured solids is the objective of many recent techniques, and a powerful tool is electron spectroscopy imaging in the transmission electron microscope (ESI-TEM) in the low-energy-loss range, 0-80 eV. This technique was applied to particulate and thin film samples of dielectric polymers and inorganic compounds, providing excellent distinction between areas occupied by various macromolecules and particles. Domains differentiated by small changes in molecular composition and minor differences in elemental contents are clearly shown. Slight changes in the molecules produce intensity variations in molecular spectra that are in turn expressed in sets of low-energy-loss images, using the standard energy-filtered transmission electron microscopy (EFTEM) procedures. The molecular map resolution is in the nanometer range and very close to the bright-field resolution achieved for the same sample, in the same instrument. Moreover, contrast is excellent, even though sample exposure to the electron beam is minimal. PMID:19222212

Linares, Elisângela M; Leite, Carlos A P; Valadares, Leonardo F; Silva, Cristiane A; Rezende, Camila A; Galembeck, Fernando

2009-03-15

310

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

International Nuclear Information System (INIS)

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

311

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

International Nuclear Information System (INIS)

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

312

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

CERN Document Server

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

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

2006-01-01

313

Electronic polarization in solids probed by dissociation of fast molecular ions  

International Nuclear Information System (INIS)

The interpretation of molecular ion interaction with solid through conventional stopping power theories is criticised. Comparison of experimental data to simulation of proton velocity distribution after 11.2 MeV OH+ dissociation in carbon foils supports this criticism. A different description of the average potential around a moving ion in solid due to electronic polarization is given. The polarization of the Fermi sea of electrons is described by the Coulomb distortion of the single electron wave function due to scattering on the moving ion. The use of such potential for the simulation of experiments agrees favourably with the measured data. (orig.)

314

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

CERN Document Server

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

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

2004-01-01

315

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

OpenAIRE

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

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

2006-01-01

316

Theoretical study of characteristics of a molecular single-electron transistor  

International Nuclear Information System (INIS)

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

317

A critical study of the molecular coulombic barriermodel (MCBM) for multiple electron capture  

International Nuclear Information System (INIS)

Multiple electron capture by highly charged ions in collision with rare gas targets is experimentally investigated. Differential cross sections are measured for specific processes in which both the number of electrons lost by the target and captured by the projectile are determined. This set of data is compared with the predictions of the Molecular Coulombic Barrier Model. The good predictive quality of this model is confirmed but deficiencies are pinpointed which are attributed to the neglect of ''simultaneous'' electron transfers as well as to the intrinsic static character of the model. (orig.)

318

Critical study of the molecular Coulombic barrier model for multiple electron capture by highly charged ions  

International Nuclear Information System (INIS)

Multiple electron capture by highly charged ions in collision with rare gas targets is experimentally investigated. Differential cross sections are measured for specific processes in which both the number of electrons lost by the target and captured by the projectile are determined. This set of data is compared with the predictions of the molecular Coulombic barrier model. The good predictive quality of this model is confirmed but deficiencies are pinpointed which are attributed to the neglect of 'simultaneous' electron transfers as well as to the intrinsic static character of the model. (author)

319

Auger-electron spectra formation under solid surface bombardment by diatomic molecular beams  

International Nuclear Information System (INIS)

The calculation of the characteristic Auger-electron spectrum, emitted under solid surface bombardment by accelerated diatomic molecular ion beams, has been performed. Non-additivity of such spectra, realized in both the shift and broadening of the characteristic peak, observed under monoatomic ion bombardment has been exhibited. The shift and broadening values have been shown to be defined by three parameters: the molecular beam velocity, the corresponding vacancy lifetime and the screening parameter. The possibility of the relative contribution estimation of symmetrical and asymmetrical collisions into the given peak formation has been discussed. In addition the connection between the proton charge state inside the metal and the characteristics of Auger-electron spectra, observed under molecular beam bombardment, have been considered. (author)

320

Full two-electron calculations of antiproton collisions with molecular hydrogen  

DEFF Research Database (Denmark)

Total cross sections for single ionization and excitation of molecular hydrogen by antiproton impact are presented over a wide range of impact energies from 1 keV to 6.5 MeV. A nonperturbative time-dependent close-coupling method is applied to fully treat the correlated dynamics of the electrons. Good agreement is obtained between the present calculations and experimental measurements of single-ionization cross sections at high energies, whereas some discrepancies with the experiment are found around the maximum. The importance of the molecular geometry and a full two-electron description is demonstrated. The present findings provide benchmark results which might be useful for the development of molecular models.

Lühr, Armin Christian; Saenz, Alejandro

2010-01-01

321

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

Science.gov (United States)

Here, we combine super-resolution fluorescence localization microscopy with scanning electron microscopy to map the position of proteins of nuclear pore complexes in isolated Xenopus laevis oocyte nuclear envelopes with molecular resolution in both imaging modes. We use the periodic molecular structure of the nuclear pore complex to superimpose direct stochastic optical reconstruction microscopy images with a precision of <20?nm on electron micrographs. The correlative images demonstrate quantitative molecular labeling and localization of nuclear pore complex proteins by standard immunocytochemistry with primary and secondary antibodies and reveal that the nuclear pore complex is composed of eight gp210 (also known as NUP210) protein homodimers. In addition, we find subpopulations of nuclear pore complexes with ninefold symmetry, which are found occasionally among the more typical eightfold symmetrical structures. PMID:25146397

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

2014-10-15

322

He2+ molecular ions in helium glow discharges: the effect of bulk electron temperature  

International Nuclear Information System (INIS)

He2+ molecular ions may be present in a concentration comparable to that of atomic ions in dc helium glow discharges operated at medium pressures (several tens of millibars). We use hybrid discharge simulations to study in a self-consistent way the creation, transport and loss processes of both atomic and molecular ionic species and the role of molecular ions in the self-sustainment of the discharges. In the pressure range where recombination processes are significant, the temperature of the cold (bulk, trapped) electrons is expected to strongly influence the discharge properties. In order to clarify these effects we investigate the influence of cold electron temperature (used as an input parameter) on the results of the simulations based on a hybrid model

323

Carbon Nanotube Based Molecular Electronics and Motors: A View from Classical and Quantum Dynamics Simulations  

Science.gov (United States)

The tubular forms of fullerenes popularly known as carbon nanotubes are experimentally produced as single-, multiwall, and rope configurations. The nanotubes and nanoropes have shown to exhibit unusual mechanical and electronic properties. The single wall nanotubes exhibit both semiconducting and metallic behavior. In short undefected lengths they are the known strongest fibers which are unbreakable even when bent in half. Grown in ropes their tensile strength is approximately 100 times greater than steel at only one sixth the weight. Employing large scale classical and quantum molecular dynamics simulations we will explore the use of carbon nanotubes and carbon nanotube junctions in 2-, 3-, and 4-point molecular electronic device components, dynamic strength characterization for compressive, bending and torsional strains, and chemical functionalization for possible use in a nanoscale molecular motor. The above is an unclassified material produced for non-competitive basic research in the nanotechnology area.

Srivastava, Deepak; Saini, Subhash (Technical Monitor)

1998-01-01

324

Electronic structure of covalently linked zinc bacteriochlorin molecular arrays: insights into molecular design for NIR light harvesting.  

Science.gov (United States)

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

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

2014-10-23

325

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

Directory of Open Access Journals (Sweden)

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

Osamu Ito

2012-05-01

326

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)

327

Yield enhancement of molecular ions with MeV ion-induced electronic excitation  

International Nuclear Information System (INIS)

We performed secondary ion mass spectrometry for arginine thin films in the incident energy range from 10 keV to 2 MeV, in which electronic energy loss in the surface region increases with energy and exceeds the nuclear energy loss. The yield of protonated arginine increased with incident energy, and at 2 MeV it was approximately two orders of magnitude larger than at 10 keV, where the nuclear collision process is dominant. It was found that the molecular ion desorption is enhanced by the electronic excitation induced in the near-surface region. In addition, the yield ratios of the fragment ions to the protonated arginine decreased with incident energy, which indicates that the nuclear energy deposition significantly affects molecular fragmentation. These results demonstrate a soft desorption and ionization of biomolecules by the MeV ion-induced electronic excitation

328

Yield enhancement of molecular ions with MeV ion-induced electronic excitation  

Science.gov (United States)

We performed secondary ion mass spectrometry for arginine thin films in the incident energy range from 10 keV to 2 MeV, in which electronic energy loss in the surface region increases with energy and exceeds the nuclear energy loss. The yield of protonated arginine increased with incident energy, and at 2 MeV it was approximately two orders of magnitude larger than at 10 keV, where the nuclear collision process is dominant. It was found that the molecular ion desorption is enhanced by the electronic excitation induced in the near-surface region. In addition, the yield ratios of the fragment ions to the protonated arginine decreased with incident energy, which indicates that the nuclear energy deposition significantly affects molecular fragmentation. These results demonstrate a soft desorption and ionization of biomolecules by the MeV ion-induced electronic excitation.

Nakata, Y.; Honda, Y.; Ninomiya, S.; Seki, T.; Aoki, T.; Matsuo, J.

2008-12-01

329

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

Science.gov (United States)

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.

Ba?c?, A.; Hoggan, P. E.

2015-02-01

330

Ab initio molecular dynamics simulation study of dissociative electron attachment to dialanine conformers.  

Science.gov (United States)

Dissociative electron attachment (DEA) processes of six low-lying conformers (1-6) of dialanine in the gas phase are investigated by using ab initio molecular dynamics simulations. The incoming electron is captured and primarily occupies the virtual molecular orbital ?*, which is followed by the different dissociation processes. The electron attachments to conformers 1 and 2 having the stronger N-H···N and O-H···O intramolecular hydrogen bonds do not lead to fragmentations, but two different backbone bonds are broken in the DEAs to conformers 3 (or 4) and 6, respectively. It is interesting that the hydrogen abstraction of -NH from the terminal methyl group -CH3 is found in the roaming dissociation of the temporary anion of conformer 3. The present simulations enable us to have more insights into the peptide backbone bond breaks in the DEA process and demonstrate a promising way toward understanding of the radiation damages of complicated biological system. PMID:25679256

Feng, Wen-Ling; Tian, Shan Xi

2015-03-12

331

Multimer Radical Ions and Electron/Hole Localization in Polyatomic Molecular Liquids: A critical review  

CERN Document Server

While ionization of some polyatomic molecular liquids (such as water and aliphatic alcohols) yields so-called "solvated electrons" in which the excess electron density is localized in the interstices between the solvent molecules, most organic and inorganic liquids yield radical anions and cations in which the electron and spin densities reside on the solvent molecule or, more commonly, a group of such molecules. The resulting multimer ions have many unusual properties, such as high rates of diffusive hopping. The "solvated electron" can be regarded as a variant of a multimer radical anion in which the charge, while perturbing the solvent molecules, mainly resides in the space between these molecules. We give several examples of less known modes for electron localization in liquids that yield multimer radical anions (such as C6F6, benzene, acetonitrile, carbon disulfide and dioxide, etc.) and holes localization in liquids that yield multimer radical cations (such as cycloalkanes). Current understanding of the...

Shkrob, I A; Sauer, Myran C.; Shkrob, Ilya A.

2004-01-01

332

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

Science.gov (United States)

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

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

2012-04-01

333

Electron Compton scattering from methane and inelastic electron scattering from molecular nitrogen at variable impact energy and scattering angle  

International Nuclear Information System (INIS)

Full text: Neutron scattering has been used in the past to measure Compton profiles of atomic motion. However, it was recently found that similar information could be obtained from electron scattering experiments. In that work, 15-30keV electrons were scattered at 44.3 deg by a solid formvar sample. In the present work we have observed Compton profiles of the nuclei in a gas phase species (CH4) using high-momentum-transfer quasi-elastic electron scattering. With an impact energy of 1995 eV and 100 deg scattering angle, we observe the quasi-elastic electron scattering spectrum for methane shown in the figure. The peak profiles reflect the quantum mechanical zero point motion of each nucleus, convoluted with the instrumental energy width ( ? 0.6eV fwhm). Detailed peak area analysis reveals an anomalously low relative area for the hydrogen peak, which provides evidence for quantum entanglement of the protons (this effect has also been observed in neutron scattering experiments). The N 1s ? ?* transition of molecular nitrogen has been studied over the ranges 2-30 deg scattering angle and 150-1300eV final electron energy. Results are compared with recently published theoretical calculations by Michelin et al

334

Improved electron ionization ion source for the detection of supersonic molecular beams  

Science.gov (United States)

An improved electron ionization (EI) ion source is described, based on the modification of a Brink-type EI ion source through the addition of a second cage with a fine mesh outside the ion chamber. The added outer cage shields the inner ion cage (ionization zone) against the penetration of the filament and electron repeller potentials, and thus results in the provision of ions with narrower ion energy distribution, hence improved ion-beam quality. The closer to zero electrical field inside the ion cage enables improved filtration (rejection) of ions that are produced from vacuum background compounds, based on difference in ion energies of beam and background species. The improved background ion filtration and ion-beam quality resulted in 2.6 times higher mass spectrometric ion signal, combined with 6.4 times better signal to noise ratio, in comparison with the same ion source having a single cage. The dual cage ion source further provides a smaller or no reduction of the electron emission current upon lowering the electron energy for achieving softer EI and/or electron attachment ionization. It also improves the long-term mass spectral and signal reproducibility and enables fast, automated change of the electron energy. Consequently, the dual cage EI ion source is especially effective for use with gas chromatography mass spectrometry with supersonic molecular beams (SMB), liquid chromatography mass spectrometry with SMB, ion guns with SMB, and any other experimental systems with SMB or nonthermal molecular beams.

Amirav, Aviv; Fialkov, Alexander; Gordin, Alexander

2002-08-01

335

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

OpenAIRE

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

1982-01-01

336

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.

337

[Non-linear rectification of sensor based on immune genetic Algorithm].  

Science.gov (United States)

A non-linear rectification based on immune genetic algorithm (IGA) is proposed in this paper, for the shortcoming of the non-linearity rectification. This algorithm introducing the biologic immune mechanism into the genetic algorithm can restrain the disadvantages that the poor precision, slow convergence speed and early maturity of the genetic algorithm. Computer simulations indicated that the algorithm not only keeps population diversity, but also increases the convergent speed, precision and the stability greatly. The results have shown the correctness and effectiveness of the method. PMID:25508412

Lu, Lirong; Zhou, Jinyang; Niu, Xiaodong

2014-08-01

338

Rectification cleaning AsCl3 from the admixture of oxygen  

Directory of Open Access Journals (Sweden)

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.

Maznitska O. V.

2008-06-01

339

Tuning electron transport through a single molecular junction by bridge modification  

International Nuclear Information System (INIS)

The possibility of controlling electron transport in a single molecular junction represents the ultimate goal of molecular electronics. Here, we report that the modification of bridging group makes it possible to improve the performance and obtain new functions in a single cross-conjugated molecular junction, designed from a recently synthesized bipolar molecule bithiophene naphthalene diimide. Our first principles results show that the bipolar characteristic remains after the molecule was modified and sandwiched between two metal electrodes. Rectifying is the intrinsic characteristic of the molecular junction and its performance can be enhanced by replacing the saturated bridging group with an unsaturated group. A further improvement of the rectifying and a robust negative differential resistance (NDR) behavior can be achieved by the modification of unsaturated bridge. It is revealed that the modification can induce a deviation angle about 4° between the donor and the acceptor ?-conjugations, making it possible to enhance the communication between the two ? systems. Meanwhile, the low energy frontier orbitals of the junction can move close to the Fermi level and encounter in energy at certain biases, thus a transport channel with a considerable transmission can be formed near the Fermi level only at a narrow bias regime, resulting in the improvement of rectifying and the robust NDR behavior. This finding could be useful for the design of single molecular devices.

340

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

Directory of Open Access Journals (Sweden)

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

RicardoOLouro

2014-06-01

341

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

Science.gov (United States)

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

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

2014-01-01

342

Superatom spectroscopy and the electronic state correlation between elements and isoelectronic molecular counterparts.  

Science.gov (United States)

Detailed in the present investigation are results pertaining to the photoelectron spectroscopy of negatively charged atomic ions and their isoelectronic molecular counterparts. Experiments utilizing the photoelectron imaging technique are performed on the negative ions of the group 10 noble metal block (i.e. Ni-, Pd-, and Pt-) of the periodic table at a photon energy of 2.33 eV (532 nm). The accessible electronic transitions, term energies, and orbital angular momentum components of the bound electronic states in the atom are then compared with photoelectron images collected for isoelectronic early transition metal heterogeneous diatomic molecules, M-X- (M = Ti,Zr,W; X = O or C). A superposition principle connecting the spectroscopy between the atomic and molecular species is observed, wherein the electronic structure of the diatomic is observed to mimic that present in the isoelectronic atom. The molecular ions studied in this work, TiO-, ZrO-, and WC- can then be interpreted as possessing superatomic electronic structures reminiscent of the isoelectronic elements appearing on the periodic table, thereby quantifying the superatom concept. PMID:20080555

Peppernick, Samuel J; Gunaratne, K D Dasitha; Castleman, A W

2010-01-19

343

Accessible information from molecular-scale volumes in electronic systems: Fundamental physical limits  

Science.gov (United States)

We consider fundamental limits on accessible information from molecular-scale volumes in electronic systems. Our approach is based on a quantitative measure-the volume accessible information-which we define as the Shannon mutual information associated with the best possible quantum measurement that can access a system through a specified readout volume. Specifically, we obtain a general expression for an upper bound on the volume accessible information that depends only on the manner in which information is encoded in electron states and specification of the readout volume. This bound is obtained within a tight-binding framework for simplicity and compatibility with atomistic descriptions of molecular-scale electronic systems. As an illustration, we study the volume accessible information bound for measurements accessing finite segments of long polyparaphenylene (PPP) molecules with binary information encoded in the states of electrons in the lowest unoccupied molecular orbital band. Evaluation of this bound reveals severe limits on the amount of information accessible from measurements on short PPP chain segments, where the state distinguishability required for reliable information extraction is diminished.

Anderson, Neal G.

2006-02-01

344

Destruction of Ar+2 molecular ions by electron collisions in a plasma  

International Nuclear Information System (INIS)

A spectroscopic study of the Ar2+ molecular ion destruction by plasma electrons has been 2 made. The rate constant of the process has been measured over a wide electron temperature range from room temperature to Te?2 eV typical of a self-sustained gas discharge. Below 0.4 eV the values obtained agree with the published data on the magnitude and temperature variation of the coefficient of the Ar2+ dissociative recombination with electrons. In the range Te=0.5-2 eV, the molecular ion destruction rate was found to have considerably increased with increasing temperature due to the onset of collisional dissociation by plasma electrons. A comparison of calculated with experimental values of the dissociation rate constants measured at various argon pressures suggests a nonequilibrium population distribution, Ar2+ (v), over the vibrational levels v. This opens up a possibility of investigating the still poorly explored processes of vibrational relaxation of molecular ions in a plasma by fairly simple spectroscopic means. 24 refs., 7 figs., 2 tabs

345

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

Science.gov (United States)

We fabricate and characterize carbon-fiber tips for their use in combined scanning tunneling and force microscopy based on piezoelectric quartz tuning fork force sensors. An electrochemical fabrication procedure to etch the tips is used to yield reproducible sub-100-nm apex. We also study electron transport through single-molecule junctions formed by a single octanethiol molecule bonded by the thiol anchoring group to a gold electrode and linked to a carbon tip by the methyl group. We observe the presence of conductance plateaus during the stretching of the molecular bridge, which is the signature of the formation of a molecular junction. PMID:22587692

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

2012-01-01

346

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

International Nuclear Information System (INIS)

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

347

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

Science.gov (United States)

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

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

2011-02-01

348

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

International Nuclear Information System (INIS)

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

349

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-02-15

350

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

CERN Document Server

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

Mazzola, Guglielmo; Sorella, Sandro

2014-01-01

351

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2007-03-01

352

Probing flexibility in porphyrin-based molecular wires using double electron electron resonance.  

OpenAIRE

A series of butadiyne-linked zinc porphyrin oligomers, with one, two, three, and four porphyrin units and lengths of up to 75 A, have been spin-labeled at both ends with stable nitroxide TEMPO radicals. The pulsed EPR technique of double electron electron resonance (DEER) was used to probe the distribution of intramolecular end-to-end distances, under a range of conditions. DEER measurements were carried out at 50 K in two types of dilute solution glasses: deutero-toluene (with 10% deutero-py...

Lovett, Je; Hoffmann, M.; Cnossen, A.; Shutter, At; Hogben, Hj; Warren, Je; Pascu, Si; Kay, Cw; Timmel, Cr; Anderson, Hl

2009-01-01

353

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

Science.gov (United States)

The work in this dissertation consists of a two-part study concerning molecular-based electronics and atomic layer deposition (ALD). As conventional "top-down" silicon-based technology approaches its expected physical and technical limits, researchers have paid considerable attention to "bottom-up" approaches including molecular-based electronics that self assembles molecular components and ALD techniques that deposit thin films with atomic layer control. Reliable fabrication of molecular-based devices and a lack of understanding of the conduction mechanisms through individual molecules still remain critical issues in molecular-based electronics. Nanoparticle/molecule(s)/nanoparticle assemblies of "dimers" and "trimers", consisting of two and three nanoparticles bridged by oligomeric ethynylene phenylene molecules (OPEs), respectively, are successfully synthesized by coworkers and applied to contact nanogap electrodes (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.

Na, Jeong-Seok

354

Ab initio molecular dynamics simulation of electronic energy dissipation: HCl/Al(111)  

Energy Technology Data Exchange (ETDEWEB)

The scattering of vibrationally excited HCl molecules from Au(111) has been studied experimentally and interpreted in view of electronically nonadiabatic processes. We present ab initio molecular dynamics simulations of the scattering of highly vibrationally excited HCl molecules at Al(111). The time-dependent Kohn-Sham equations are integrated numerically for the electrons, and the positions of the ions follow Ehrenfest dynamics. The electronic excitation along the trajectory is obtained from comparison of the time-dependent electronic structure with the electronic ground state at the respective frozen-in ionic positions. Reducing numerical expenses, the simulations are carried through for mass-scaled systems. Under the assumption of linear friction, the dissipation is extrapolated to the physical masses of the ions. For not vibrating HCl molecules we obtain only a faint energy transfer into electron-hole pairs. Electronic energy dissipation is significant for a strongly vibrating HCl molecule in front of Al(111). Different geometries with either the H-or Cl-atom pointing towards the surface are compared. We note that electronic friction has turned out not to be enhanced for a situation where the H-atom points towards the surface and oscillates in the charge density tail of the metal.

Grotemeyer, Michael; Pehlke, Eckhard [Institut fuer Theoretische Physik und Astrophysik, Universitaet Kiel (Germany)

2010-07-01

355

Atomic and Molecular Photoelectron and Auger Electron SpectroscopyStudies Using Synchrotron Radiation  

Energy Technology Data Exchange (ETDEWEB)

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

Southworth, Stephen H.

1982-01-01

356

The Impact of Direct Ionization by Beam Electrons on the Electron Kinetics of the Beam Discharge Plasma in Molecular Hydrogen  

Science.gov (United States)

In a recent paper the stationary beam plasma discharge in partially dissociated hydrogen was investigated where the electron component was described by the Boltzmann equation for a mixture of atomic and molecular hydrogen and the main heavy charged and neutral particles by balance equations. It was assumed that, via the quasilinear beam plasma interaction, the electron beam produces only the turbulent electric field whilst an additional production of plasma electrons due to direct ionization by the beam and thus a direct influence on the balances of charge carriers were neglected. Now the additional production of plasma electrons due to direct ionization by the beam is studied on the basis of a generalized Boltzmann equation but for the simpler model of a purely molecular hydrogen plasma. For experimentally obtainable values of the turbulence energy density, beam energy, beam ionization degree and electron life time the calculation of the electron energy distribution function and of the direct beam contribution to the electron particle balance shows a marked influence of the direct beam ionization with increasing degree of beam ionization.Translated AbstractDer Einfluß der durch Strahlelektronen verursachten Direktionisation auf die Elektronenkinetik des Strahl-Entladungsplasmas in molekularem WasserstoffIn einer kürzlich erschienenen Arbeit wurde das stationäre Strahl-Entladungsplasma in teilweise dissoziiertem Wasserstoff, untersucht, wobei die Elektronenkomponente durch die Boltzmann-Gleichung für ein Gemisch von atomarem und molekularem Wasserstoff und die wesentlichen schweren geladenen und neutralen Teilchen durch Bilanzgleichungen beschrieben wurden. Hierbei wurde angenommen, daß der Elektronenstrahl vermittels der quasilinearen Strahl Plasma-Wechselwirkung nur das turbulente elektrische Feld erzeugt, während eine zusätzliche Erzeugung von Plasmaelektronen infolge direkter Ionisation durch den Strahl und somit ein direkter Einfluß auf die Bilanzen der geladenen Teilchen vernachlässigt wurde. Im folgenden wird die zusätzliche Erzeugung von Plasmaelektronen infolge direkter Strahlionisation auf der Grundlage einer verallgemeinerten Boltzmann-Gleichung jedoch für das einfachere Modell des rein molekularen Wasserstoffplasmas untersucht. Für experimentell realisierbare Werte der Turbulenzenergiedichte, der Strahlenergie, des Strahlionisierungsgrades und der Lebensdauer der Elektronen zeigt die Berechnung der Elektronenenergieverteilungsfunktion und des direkten Strahlbeitrages zur Elektronen-Teilchenbilanz einen ausgeprägten Einfluß der direkten Strahlionisation mit anwachsendem Strahlionisierungsgrad.

Winkler, R.; Wilhelm, J.; Krasheninnikov, S. I.

357

Electronically nonadiabatic dynamics in complex molecular systems: an efficient and accurate semiclassical solution.  

Science.gov (United States)

Chemical reaction dynamics is always a central theme in chemistry research. In many important chemical processes, reaction dynamics is electronically nonadiabatic, i.e., dynamics involves coupled multiple electronic states. We demonstrate in this paper that a semiclassical (SC) treatment based on an initial value representation methodology and a classical mapping formalism for the electronic degrees of freedom is now able to provide a rigorous and practical solution to electronically nonadiabatic dynamics in complex molecular systems. The key component of this treatment is to incorporate a correlated importance sampling protocol in nonadiabatic SC calculations, which results in a speedup factor of 100 or more in comparison with that using the standard sampling approach. This is illustrated by application to a two-state model coupled with up to 10 nuclear bath modes for a benchmark nonadiabatic excitation energy transfer problem. This work provides great opportunities for the effectively theoretical investigations on reaction mechanisms in complex molecular systems, in which electronically nonadiabatic dynamics plays an importance role. PMID:23799272

Tao, Guohua

2013-07-18

358

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

Energy Technology Data Exchange (ETDEWEB)

Highlights: • We simulate electron dynamics in polyene and polyyne bridged molecular wires. • Time-dependent configuration interaction method has been employed. • A multireference configuration interaction singles approach is proposed. • We investigate the role of symmetry and localization of the initial state. • Introduction of a sodium cluster at the acceptor end leads to electron trapping. - Abstract: In this study we present methodological developments of the time-dependent configuration interaction (TDCI) method for ab initio electron dynamics in donor–bridge–acceptor systems. Especially, we investigate the role of valence electron correlation, the scheme for selecting the determinantal basis, and the computational effort. Our test systems are molecules of the type Li–(C{sub 2}){sub n}–CN, Li–(C{sub 2}H{sub 2}){sub n}–CN, and Na{sub 9}–(C{sub 2}H{sub 2}){sub 2}–CN. In this way, this study is intended as a step towards rigorous description of charge transfer in molecular wires attached to metal surfaces or nanoparticles using a many-electron wavefunction. Also, a multi-reference configuration interaction singles approach is suggested as a good compromise between computational effort and accuracy.

Ramakrishnan, Raghunathan, E-mail: rama@mytum.de; Raghunathan, Shampa; Nest, Mathias

2013-07-11

359

Design and Simulation of Molecular Nonvolatile Single-Electron Resistive Switches  

CERN Document Server

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

Simonian, Nikita; Likharev, Konstantin K

2012-01-01

360

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

Energy Technology Data Exchange (ETDEWEB)

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

Bochicchio, Roberto C., E-mail: rboc@df.uba.ar [Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and IFIBA, CONICET, Ciudad Universitaria, 1428 Buenos Aires (Argentina); Miranda-Quintana, Ramón A. [Laboratory of Computational and Theoretical Chemistry, Faculty of Chemistry, University of Havana, Zapata e G y Mazón, 10400 Havana (Cuba); Rial, Diego [Departamento de Matemática, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and IMAS, CONICET, Ciudad Universitaria, 1428 Buenos Aires (Argentina)

2013-11-21

361

Electron-beam-cured adhesives based on low-molecular-weight carboxylated butadiene-nitrile rubber  

International Nuclear Information System (INIS)

Effects of a series of organic and inorganic additives on the initial sticking and autohesion dynamics of electron-beam-cured adhesives for adhesive tapes, based on low-molecular-weight carboxylated butadiene-acrylonitrile rubber, were examined. Radiation curing of the compositions on polyvinyl chloride surface was conducted in air under 500 keV electron beam irradiation with absorbed doses up to 700 kGy. A sensitizing effect was observed upon introduction of trimethylol propane triacrylate in amounts of 1 wt.% to the reaction mixture

362

Search for the electron's electric dipole moment with a cold molecular beam of ThO  

Science.gov (United States)

We describe a method for an improved search for the electric dipole moment (EDM) of the electron, using a cold molecular beam of thorium monoxide (ThO). We identify the metastable H state in ThO as being highly sensitive to the CP-violating EDM of the electron. ThO in a beam is shown to have excellent properties for rejection of systematic errors and for efficient state preparation and detection. We report on recent progress in the production of cold ThO molecules and measurement of the lifetime of the H state.

Vutha, Amar C.; Baker, O. Keith; Campbell, Wesley C.; Demille, David; Doyle, John M.; Gabrielse, Gerald; Gurevich, Yulia V.; Jansen, Maarten A. H. M.

2008-05-01

363

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

International Nuclear Information System (INIS)

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

364

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

Energy Technology Data Exchange (ETDEWEB)

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

Zong, W.; Dunn, G.H.; Djuric, N.; Greene, C.H.; Neau, A. [JILA and Department of Physics, University of Colorado and National Institute of Standards and Technology, Boulder, Colorado 80309-0440 (United States); Zong, W.; Larsson, M.; Al-Khalili, A.; Neau, A.; Derkatch, A.M.; Vikor, L.; Shi, W.; Rosen, S. [Department of Molecular Physics, Stockholm University, Box 6730 S-113 85 Stockholm (Sweden); Le Padellec, A. [Universite Catholique de Louvain, Institut de Physique, Chemin du cyclotron, 2-B1348 Louvain-la-Neuve (Belgium); Danared, H.; af Ugglas, M. [Manne Siegbahn Laboratory, S-104 05 Stockholm (Sweden)

1999-08-01

365

Rotational cooling of HD+ molecular ions by superelastic collisions with electrons.  

Science.gov (United States)

Merging an HD+ beam with velocity matched electrons in a heavy ion storage ring we observed rapid cooling of the rotational excitations of the HD+ ions by superelastic collisions (SEC) with the electrons. The cooling process is well described using theoretical SEC rate coefficients obtained by combining the molecular R-matrix approach with the adiabatic nuclei rotation approximation. We verify the DeltaJ=-2 SEC rate coefficients, which are predicted to be dominant as opposed to the DeltaJ=-1 rates and to amount to (1-2)x10;{-6} cm;{3} s;{-1} for initial angular momentum states with J< or =7, to within 30%. PMID:19658863

Shafir, D; Novotny, S; Buhr, H; Altevogt, S; Faure, A; Grieser, M; Harvey, A G; Heber, O; Hoffmann, J; Kreckel, H; Lammich, L; Nevo, I; Pedersen, H B; Rubinstein, H; Schneider, I F; Schwalm, D; Tennyson, J; Wolf, A; Zajfman, D

2009-06-01

366

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

International Nuclear Information System (INIS)

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

367

Non-dissociative single ionization of molecular hydrogen by electron and positron impact  

International Nuclear Information System (INIS)

We present experimental results for impact ionization of molecular hydrogen by electrons and positrons for the range of impact energies from threshold to about 2 keV (0.4- 2 keV for e-). Our electron data agree with the most recent one measured by others. When we compare our positron results to earlier published single ionization cross sections we find significant differences for impact energies from threshold to about 100 eV with the new cross sections being substantially smaller. In the present study an effort has been made to discriminate against false signals caused by positronium formation and other effects. (author)

368

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

CERN Document Server

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

Schaefer III, Henry F

2012-01-01

369

Molecular-Atomic Transition in the Deuterium Hugoniot with Coupled Electron Ion Monte Carlo  

CERN Document Server

We have performed accurate simulations of the Deuterium Hugoniot using Coupled Electron Ion Monte Carlo (CEIMC). Using highly accurate quantum Monte Carlo methods for the electrons, we study the region of maximum compression along the principal Hugoniot, where the system undergoes a continuous transition from a molecular fluid to a monatomic fluid. We include all relevant physical corrections so that a direct comparison to experiment can be made. Around 50 GPa we found a maximum compression of 4.85, roughly 10% larger than previous theoretical predictions and experimental data but still compatible with the latter because of their large uncertainty.

Tubman, Norm M; Pierleoni, Carlo; Holzmann, Markus; Ceperley, David M

2014-01-01

370

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

International Nuclear Information System (INIS)

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

371

Length dependence of electron transport through molecular wires--a first principles perspective.  

Science.gov (United States)

One-dimensional wires constitute a fundamental building block in nanoscale electronics. However, truly one-dimensional metallic wires do not exist due to Peierls distortion. Molecular wires come close to being stable one-dimensional wires, but are typically semiconductors, with charge transport occurring via tunneling or thermally-activated hopping. In this review, we discuss electron transport through molecular wires, from a theoretical, quantum mechanical perspective based on first principles. We focus specifically on the off-resonant tunneling regime, applicable to shorter molecular wires (theory are discussed, starting with the computational workhorse - density functional theory (DFT), and moving on to many-electron GW methods as well as GW-inspired DFT + Sigma calculations. These different levels of theory are applied in two major computational frameworks - complex band structure (CBS) calculations to estimate the tunneling decay constant, beta, and Landauer-Buttiker transport calculations that consider explicitly the effects of contact geometry, and compute the transmission spectra directly. In general, for the same level of theory, the Landauer-Buttiker calculations give more quantitative values of beta than the CBS calculations. However, the CBS calculations have a long history and are particularly useful for quick estimates of beta. Comparing different levels of theory, it is clear that GW and DFT + Sigma calculations give significantly improved agreement with experiment compared to DFT, especially for the conductance values. Quantitative agreement can also be obtained for the Seebeck coefficient - another independent probe of electron transport. This excellent agreement provides confirmative evidence of off-resonant tunneling in the systems under investigation. Calculations show that the tunneling decay constant beta is a robust quantity that does not depend on details of the contact geometry, provided that the same contact geometry is used for all molecular lengths considered. However, because conductance is sensitive to contact geometry, values of beta obtained by considering conductance values where the contact geometry is changing with the molecular junction length can be quite different. Experimentally measured values of beta in general compare well with beta obtained using DFT + Sigma and GW transport calculations, while discrepancies can be attributed to changes in the experimental contact geometries with molecular length. This review also summarizes experimental and theoretical efforts towards finding perfect molecular wires with high conductance and small beta values. PMID:25407785

Khoo, Khoong Hong; Chen, Yifeng; Li, Suchun; Quek, Su Ying

2015-01-01

372

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

CERN Document Server

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

Sharoyan, E G

2005-01-01

373

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

CERN Document Server

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.

Lühmann, Dirk-Sören; Sengstock, Klaus

2015-01-01

374

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

CERN Document Server

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

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

2004-01-01

375

Structural and electronic properties of pentacene molecule and molecular pentacene solid  

CERN Document Server

The structural and electronic properties of a single pentacene molecule and a pentacene molecular crystal, an organic semiconductor, are examined by a first-principles method based on the generalized gradient approximation of density functional theory. Calculations were carried out for a triclinic unit cell containing two pentacene molecules. The bandwidths of the valence and conduction bands which determine the charge migration mechanism are found to depend strongly on the crystallographic direction. Along the triclinic reciprocal lattice vectors A and B which are orientated approximately perpendicular to the molecular axes the maximal valence (conduction) band width amounts to only 75 (59) meV, even smaller values are obtained for the C direction parallel to molecular axes even less. Along the stacking directions A+B and A-B, however, the maximal valence (conduction) band width is found to reach 145 (260) meV. The value for the conduction band width is larger than estimates for the polaron binding energy bu...

Endres, R G; Yang, L H; Witte, G; Woll, C; Woll, Ch.

2002-01-01

376

Electron-molecular vibration coupling effect on the Raman spectrum of organic charge transfer salts  

Science.gov (United States)

Vibrational spectra of dimerized and tetramerized radical clusters have been calculated to understand the features of electron-molecular vibration (EMV) coupling effects for the charge ordered system (CO). The calculated spectra show that the totally in-phase Raman band, which is usually used as a measure of the molecular ionicity, approaches to the frequency corresponding to the average molecular ionicity in the cluster, with increasing the EMV coupling constant. On the other hand, when large charge disproportionation (CD) presents, vibronic bands show steep shift for small variation of the CD ratio. These results suggest that concerning to the normal modes with a large EMV coupling constant, we should focus on the frequency of the vibronic bands instead of the totally in-phase mode to discuss the charge distribution. Key words. Charge ordering charge disproportionation Raman spectroscopy vibrational spectroscopy

Yamamoto, Kaoru; Yakushi, Kyuya

2004-04-01

377

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

OpenAIRE

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...

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

2001-01-01

378

A new apparatus for the study of electron impact fragmentation of molecular clusters  

OpenAIRE

This paper reports on the development of a new experiment for the study of electron-impact induced dissociation and fragmentation of molecular clusters and biomolecules and other species solvated in water clusters. The purpose is to look at clusters that are of interest to biophysics, atmospheric physics, and other fields. The experiment consists of a differentially pumped vacuum system, with an expansion chamber to generate a pulsed supersonic beam of clusters, and a collision...

Barrett, Gerard; Burgt, Peter J. M.

2008-01-01

379

Krylov Subspace Method for Molecular Dynamics Simulation based on Large-Scale Electronic Structure Theory  

CERN Document Server

For large scale electronic structure calculation, the Krylov subspace method is introduced to calculate the one-body density matrix. Its arithmetic structure is studied for its validation. Molecular dynamics simulation of Si(001) surface reconstruction is examined as an example, and the results reproduce the essential mechanism of asymmetric surface dimer. An appropriate choice of controlling parameters is discussed for the efficient and practical calculation.

Takayama, R; Fujiwara, T; Takayama, Ryu; Hoshi, Takeo; Fujiwara, Takeo

2004-01-01

380

On Measuring the Electron Electric Dipole Moment in Trapped Molecular Ions  

OpenAIRE

Trapped diatomic molecular ions could prove to be a sensitive probe for a permanent electron electric dipole moment (eEDM). We propose to use a ground or metastable $^3\\Delta_1$ level, due to its high polarizability and large EDM enhancement factor. Ions allow for simple trapping and long interrogation times, but require a time-varying electric bias field in order to probe the eEDM. We discuss experimental design as well as challenges in performing a precision spectroscopic ...

Leanhardt, Aaron E.; Bohn, John L.; Loh, Huanqian; Maletinsky, Patrick; Meyer, Edmund R.; Sinclair, Laura C.; Stutz, Russell P.; Cornell, Eric A.

2010-01-01

381

The diabatic picture of electron transfer, reaction barriers and molecular dynamics  

OpenAIRE

Diabatic states have a long history in chemistry, beginning with early valence bond pictures of molecular bonding and extending through the construction of model potential energy surfaces to the modern proliferation of methods for computing these elusive states. In this review, we summarize the basic principles that define the diabatic basis and demonstrate how they can be applied in the specific context of constrained density functional theory. Using illustrative examples from electron trans...

Voorhis, Troy; Kowalczyk, Timothy Daniel; Kaduk, Benjamin J.; Wang, Lee-ping; Cheng, Chiao-lun; Wu, Qin

2009-01-01

382

A study of the deactivation of electronically excited radicals during collisions with atomic and molecular gases  

Science.gov (United States)

The deactivation of electronically excited CN and NH radicals and NO molecules during collisions with atomic (He, Ne, and Ar) and molecular (N2, H2, CO, and CH) gases is investigated experimentally. The deactivation rate constants and collision cross-sections are determined using the fluorescence quenching method. The results of the study can be used in analyzing the processes occurring in chemical gas lasers and in the upper atmospheric layers of the earth and other planets.

Tereshchenko, E. N.; Dodonova, N. Ia.

383

Superatom spectroscopy and the electronic state correlation between elements and isoelectronic molecular counterparts  

OpenAIRE

Detailed in the present investigation are results pertaining to the photoelectron spectroscopy of negatively charged atomic ions and their isoelectronic molecular counterparts. Experiments utilizing the photoelectron imaging technique are performed on the negative ions of the group 10 noble metal block (i.e. Ni-, Pd-, and Pt-) of the periodic table at a photon energy of 2.33 eV (532 nm). The accessible electronic transitions, term energies, and orbital angular momentum components of the bou...

Peppernick, Samuel J.; Gunaratne, K. D. Dasitha; Castleman, A. W.

2009-01-01

384

Using Markov models to simulate electron spin resonance spectra from molecular dynamics trajectories  

OpenAIRE

Simulating electron spin resonance (ESR) spectra directly from molecular dynamics simulations of a spin labeled protein necessitates a large number (hundreds or thousands) of relatively long (hundreds of ns) trajectories. To meet this challenge, we explore the possibility of constructing accurate stochastic models of the spin label dynamics from atomistic trajectories. A systematic, two-step procedure, based on the probabilistic framework of hidden Markov models, is developed to build a discr...

Sezer, Deniz; Freed, Jack H.; Roux, Benoi?t

2008-01-01

385

Dimer Model for Electronic and Molecular Systems and the Intermediate Phase  

CERN Document Server

We introduce a lattice model of dimers with directional interactions as a paradigm of molecular fluids or strongly correlated Cooper pairs in electronic systems. The model supports an intermediate phase that is common to both systems. There are two different ideal glasses having no moblity since they possess zero entropy. A pairing parameter is introduced to study the geometrical distribution of holes in various phases.

Semerianov, F

2004-01-01

386

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

Science.gov (United States)

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.

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

2014-12-01

387

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

International Nuclear Information System (INIS)

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

388

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

Energy Technology Data Exchange (ETDEWEB)

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

Bannister, Mark E [ORNL; Aliabadi, Habib [ORNL; Bahati Musafiri, Eric [ORNL; Fogle, Mark R. [Oak Ridge National Laboratory (ORNL); Krstic, Predrag S [ORNL; Vane, C Randy [ORNL; Ehlerding, A. [Stockholm University, Stockholm, Sweden; Geppert, W. [Stockholm University, Stockholm, Sweden; Hellberg, F. [Stockholm University, Stockholm, Sweden; Zhaunerchyk, Vitali [Stockholm University, Stockholm, Sweden; Larsson, Mats [Stockholm University, Stockholm, Sweden; Thomas, Richard D [ORNL

2007-01-01

389

Electronically excited molecular nitrogen and molecular oxygen in the high-latitude upper atmosphere  

Directory of Open Access Journals (Sweden)

Full Text Available Relative vibrational populations of triplet B3?g, W3?,sub>u, B'3?u? states of N2 and the b1?g+ state of O2 are calculated for different altitudes of the high-latitude upper atmosphere during auroral electron precipitation. It is shown that collisional processes cause a wavelength shift in the distribution of relative intensities for 1PG ?v=3 sequence of N2. The calculation of relative populations for vibrational levels v=1–5 of the b1?g+ state in the auroral ionosphere has not given an agreement with experimental results. Preliminary estimation of the contribution of the reaction O2++NO to the production of O2(b1?g+ on the basis of a quantum-chemical approximation does not allow for an explanation of the observable vibrational population of the b1?g+ state in the aurora.

A. S. Kirillov

2008-05-01

390

Rectification in synthetic conical nanopores: a one-dimensional Poisson-Nernst-Planck model.  

Science.gov (United States)

Ion transport in biological and synthetic nanochannels is characterized by phenomena such as ion current fluctuations and rectification. Recently, it has been demonstrated that nanofabricated synthetic pores can mimic transport properties of biological ion channels [P. Yu. Apel, Nucl. Instrum Methods Phys. Res. B 184, 337 (2001); Z. Siwy, Europhys. Lett. 60, 349 (2002)]. Here, the ion current rectification is studied within a reduced one-dimensional (1D) Poisson-Nernst-Planck (PNP) model of synthetic nanopores. A conical channel of a few nm to a few hundred nm in diameter, and of a few mum long is considered in the limit where the channel length considerably exceeds the Debye screening length. The rigid channel wall is assumed to be weakly charged. A one-dimensional reduction of the three-dimensional problem in terms of corresponding entropic effects is put forward. The ion transport is described by the nonequilibrium steady-state solution of the 1D Poisson-Nernst-Planck system within a singular perturbation treatment. An analytic formula for the approximate rectification current in the lowest order perturbation theory is derived. A detailed comparison between numerical results and the singular perturbation theory is presented. The crucial importance of the asymmetry in the potential jumps at the pore ends on the rectification effect is demonstrated. This so constructed 1D theory is shown to describe well the experimental data in the regime of small-to-moderate electric currents. PMID:18517353

Kosi?ska, I D; Goychuk, I; Kostur, M; Schmid, G; Hänggi, P

2008-03-01

391

Photo-electron momentum distribution and electron localization studies from laser-induced atomic and molecular dissociations  

Science.gov (United States)

The broad objective of ultrafast strong-field studies is to be able to measure and control atomic and molecular dynamics on a femtosecond timescale. This thesis work has two major themes: (1) Study of high-energy photoelectron distributions from atomic targets. (2) Electron localization control in atomic and molecular reactions using shaped laser pulses. The first section focuses on the study of photoelectron diffraction patterns of simple atomic targets to understand the target structure. We measure the full vector momentum spectra of high energy photoelectrons from atomic targets (Xe, Ar and Kr) generated by intense laser pulses. The target dependence of the angular distribution of the highest energy photoelectrons as predicted by Quantitative Rescattering Theory (QRS) is explored. More recent developments show target structure information can be retrieved from photoelectrons over a range of energies, from 4Up up to 10Up, independent of the peak intensity at which the photoelectron spectra have been measured. Controlling the fragmentation pathways by manipulating the pulse shape is another major theme of ultrafast science today. In the second section we study the asymmetry of electron (and ion) emission from atoms (and molecules) by interaction with asymmetric pulses formed by the superposition of two colors (800 & 400 nm). Xe electron momentum spectra obtained as a function of the two-color phase exhibit a pronounced asymmetry. Using QRS theory we can analyze this asymmetric yield of the high energy photoelectrons to determine accurately the laser peak intensity and the absolute phase of the two-color electric field. This can be used as a standard pulse calibration method for all two-color studies. Experiments showing strong left-right asymmetry in D+ ion yield from D2 molecules using two-color pulses is also investigated. The asymmetry effect is found to be very ion-energy dependent.

Ray, Dipanwita

392

Novel silicon metal-oxide semiconductor devices for molecular sensing and hot electron spectroscopy  

Science.gov (United States)

This dissertation describes results from a novel hybrid molecular/metal-oxide-semiconductor field effect transistor (MOSFET). The device consists of a buried channel silicon-on-insulator MOSFET with a molecular monolayer attached to its surface. The device is made using a 2 mum minimum gate length, silicon MOSFET process developed in Arizona State University. A hybrid molecular/MOSFET structure that is sensitive to the presence of a molecular monolayer on its surface was fabricated and characterized. The device was fabricated from a silicon-on-insulator (SOI) substrate. A substrate voltage was used to invert the buried Si:SiO 2 interface in this device. This allowed the top surface of the silicon to be free of any insulating layers, apart from a thin native oxide that forms on exposure to air. The buried inversion layer was less than 40 nm away from the exposed surface, and the threshold voltage of the device was strongly influenced by the surface potential. Measurements of the drain current as a function of substrate voltage can be accurately reproduced from numerical simulation by treating the charge at the native oxide interface as a fitting parameter. A large shift in the threshold voltage occurring after attachment of the molecular monolayer was observed, which was explained by molecular protonation of the native oxide. A split gate SOI device structure was also developed and fabricated to improve the sensitivity of the hybrid molecular/MOSFET. Because of its very small size, the nano-scale hybrid device will be susceptible to hot carrier effects. Numerical simulation of a 100nm x 100nm split gate device showed high electron velocity at the drain end of the channel. A novel scanning probe technique is suggested as a way of measuring the hot electron distribution in the channel of the split gate structure. This structure is also suitable for hot electron spectroscopy in ultra short channel MOSFETs because it resembles a conventional MOSFET and its inversion channel is close to the ambient and therefore accessible with the tip of a scanning probe microscope.

Yang, Jinman

393

Quantum transport in molecular electronic devices described with complex source and sink potentials  

Science.gov (United States)

We present a non-Hermitian model Hamiltonian containing complex potentials [1,2] that is devised to study ballistic transport in molecular electronic devices (MEDs). The complex potentials replace semi-infinite contacts and act as source and sink of probability current density. This approach is rigorous in the sense that the exact wave function is recovered in the interior of the MED. We employ this technique to calculate the conductance through certain prototypical MEDs [3]. We also extend this method [4] such that we can go beyond the one- electron picture by constructing two-electron states explicitly. We present results for simple model system described by Hubbard-type Hamiltonians. The impact of electron correlation effects on the molecular conductance is discussed. [1] F. Goyer, M. Ernzerhof, M. Zhuang, JCP, 126, 144104 (2007). [2] M. Ernzerhof, JCP, to appear nov. 2007. [3] M. Ernzerhof, H. Bahmann, F. Goyer, M. Zhuang, P. Rocheleau, J. Chem. Theory Comput., 2, 1291 (2006); M. Ernzerhof, M. Zhuang, P. Rocheleau, JCP, 123, 134704 (2005). [4] A. Goker, F. Goyer, M. Ernzerhof, work in pogress.

Goyer, Francois; Goker, Ali; Ernzerhof, Matthias

2008-03-01

394

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

Science.gov (United States)

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

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

2014-01-28

395

Recent Experimental Studies of Electron-Impact Excitation of Atomic and Molecular Ions  

International Nuclear Information System (INIS)

This paper reviews the most recent experimental studies of absolute cross sections for electron-impact excitation of atomic and dissociative excitation of molecular ions. Experimental studies of such processes have been carried out for more than 40 years. Much of the discussion is oriented to the work involving the author; however an effort will be made to include other results. In discussing electron impact excitation of atomic ions we will examine primarily transitions in which dielectronic resonaces play a dominant role, and measurements which can be used to benchmark results of theoretical calculations. Of particular interest, partially motivated by fusion efforts and partially by plasma etching and deposition, are investigations of dissociative excitation of light hydrocarbon ions. Methods employing colliding beams of electrons and ions, either in crossed or merged beams configurations are emphasized

396

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

International Nuclear Information System (INIS)

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

397

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

International Nuclear Information System (INIS)

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

398

Molecular states of correlated electrons in a quantum dot. Theory and inelastic light scattering experiments  

International Nuclear Information System (INIS)

Complete text of publication follows. The paradigm of few-electron complexes in semiconductor quantum dots relies on the 'particle-in-a-box' idea that the lowest-energy orbitals are filled according to Pauli's exclusion principle. If Coulomb repulsion is sufficiently strong to overcome the kinetic energy cost of localization, a different scenario is predicted: a 'Wigner' molecule forms, made of electrons frozen in space according to a geometrical pattern. In this talk I will provide evidence of correlated molecular behaviour in dots populated by two, three, and four electrons, which is based on inelastic light scattering measurements combined with configuration-interaction calculations. Our spectroscopy measures the neutral few-body excitations of the electron molecule, which are either vibrations of the electrons around their relative equilibrium positions - fixed by Coulomb interaction - or rigid-body rotations. We find that spectra of low-lying excitations associated with changes of the relative-motion wave function - the analogues of the vibration modes of a conventional molecule - do not depend on the rotational state represented by the angular momentum. In the case of a molecular dimer, we observe the fundamental breathing mode. For three electrons, we see the emergence of a fully spin-polarized state, which is the simplest possible realization of Stoner ferromagnetism. This work is done in collaboration with V. Pellegrini, A. Pinczuk, E. Molinari, G. Goldoni, Lni, A. Pinczuk, E. Molinari, G. Goldoni, L. N. Pfeiffer, B. S. Dennis, K. W. West, A. Gamucci, S. Kalliakos, C. P. Garcia, A. Singha, and it is supported by Projects MIUR-PRIN no. 2008H9ZAZR, CINECA-ISCRA-B FERMIFEW, and Fondazione Cassa di Risparmio di Modena COLDandFEW.

399

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

CERN Document Server

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

Goliney, I Yu

2014-01-01

400

Single molecule electronics: increasing dynamic range and switching speed using cross-conjugated species.  

Science.gov (United States)

Molecular electronics is partly driven by the goal of producing active electronic elements that rival the performance of their solid-state counterparts, but on a much smaller size scale. We investigate what constitutes an ideal switch or molecular device, and how it can be designed, by analyzing transmission plots. The interference features in cross-conjugated molecules provide a large dynamic range in electron transmission probability, opening a new area for addressing electronic functionality in molecules. This large dynamic range is accessible through changes in electron density alone, enabling fast and stable switching. Using cross-conjugated molecules, we show how the width, depth, and energetic location of the interference features can be controlled. In an example of a single molecule transistor, we calculate a change in conductance of 8 orders of magnitude with an applied gate voltage. Using multiple interference features, we propose and calculate the current/voltage behavior of a molecular rectifier with a rectification ratio of >150,000. We calculate a purely electronic negative differential resistance behavior, suggesting that the large dynamic range in electron transmission probability caused by quantum interference could be exploited in future electronic devices. PMID:19053415

Andrews, David Q; Solomon, Gemma C; Van Duyne, Richard P; Ratner, Mark A

2008-12-24

401

Application of ring-polymer molecular dynamics to electronically nonadiabatic excess electron dynamics in water clusters: Importance of nuclear quantum effects  

Science.gov (United States)

The ring-polymer molecular dynamics (RPMD) method was applied to the real-time excess electron dynamics in water clusters within a one-electron pseudo-potential model, where the excess electron motion is described with the grid-based wave function while nuclear motions of water are described with RPMD. We have simulated electronically non-adiabatic relaxation dynamics associated with s ? p excitation of an excess electron in the (H2O)50- water anion cluster. We compared the RPMD results to the corresponding results obtained from classical MD simulations. It was found that nuclear quantum effects are playing a very important role in determining nonadiabatic relaxation time.

Yoshikawa, Takehiro; Takayanagi, Toshiyuki

2013-03-01

402

Demonstrations for the effect of composite electric fields of molecular ions on the motion of secondary electrons due to ion irradiation  

Energy Technology Data Exchange (ETDEWEB)

The present simulation demonstrates the energy loss of each individual secondary electron due to the composite electric field formed from molecular ions. Both of the secondary electron and molecular ions are produced from an incident ion impact ionization process. The initial conditions of the secondary electron under which this electron is trapped near the trajectory are found for a proton and a carbon ion.

Moribayashi, Kengo, E-mail: moribayashi.kengo@jaea.go.jp

2013-11-01

403

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

OpenAIRE

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...

2011-01-01

404

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

International Nuclear Information System (INIS)

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

405

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-01-14

406

Molecular dissociation in accelerator mass spectrometry for trace impurity characterization in electronic materials  

International Nuclear Information System (INIS)

There is a present need to characterize trace elements in electronic materials at impurity levels of sub parts-per-billion. The authors are developing such an instrument for stable trace element analysis of electronic materials using accelerator mass spectrometry (AMS). While AMS has been applied to radioisotope determinations with sensitivities as great as 1 part in 1015, existing AMS instruments are not designed for stable element analysis and can not adequately perform these measurements without extensive modifications. The authors are developing an instrument with an ultra-low sample-contamination UHV sputter ion source which injects mass-analyzed negative secondary ions from the sample into a 3 MV tandem accelerator. During acceleration, electrons are stripped from the ions. For charge states greater than 2+, molecular species dissociate and only atomic ions are expected to survive. Momentum/ charge and energy/charge discrimination, followed by velocity and total energy detection, provide unambiguous elemental identification with a sensitivity of 1 part-per-trillion (5 x 1010 atoms/cm3). The authors report the first computer automated, molecular interference free mass scan

407

Electron-impact dissociative ionization of the molecular ion HDO+: A global view  

Science.gov (United States)

We present a combined experimental and theoretical study of the fragmentation of HDO2+ molecular ions produced by electron-impact ionization of HDO+ in the collision energy range 20-2500 eV. Experimental absolute partial inclusive cross sections for the production of OD+,OH+, and O+ are reported and compared successfully to theoretical predictions. Ab initio methods are used to calculate the electron-impact ionization cross sections of the cationic ground state and first excited state leading to the first seven dicationic states. Dissociation probabilities of each channel are obtained by performing classical molecular dynamics on fitted dicationic potential energy surfaces. The predictive character of the theoretical modeling allows us to estimate that the nonmeasured dissociation channel giving a neutral oxygen atom contributes to 30% of the total ionization cross section. The isotopic ratio OD+/OH+ deduced from the experiment is (3.1±0.2) on average, constant in the 30-2500 eV energy range. The calculated isotopic ratio is found to be strongly dependent on the vibrational excitation of the target. Good agreement with the experimental value is obtained for a vibrational excitation corresponding to a temperature of about 2500 K, which is compatible with typical characteristics of electron cyclotron resonance (ECR) ion sources.

Defrance, P.; Jureta, J.; Lecointre, J.; Giglio, E.; Gervais, B.; Dal Cappello, C.; Ruiz-Lopez, M.; Charpentier, I.; Hervieux, P.-A.

2014-10-01

408

Electron capture and loss processes in heavy ion and molecular ion collisions with solids  

International Nuclear Information System (INIS)

Angular (theta) and velocity (v /SUB e/ ) distributions of convoy electrons have been measured with monoatomic and molecular projectile ions (H+, D+, H2+, D2+, H3+, He+, He++ at 1.7 MeV/U and U+44, Ti+14 at 1.4 MeV/U) as a function of the projectile dwell time t /SUB D/ in carbon foils (2 to 50 ?g/cm2). The spectra with light projectiles from carbon foils are compared with those of gaseous CH4 targets. For the light and molecular projectiles the shapes and yield of convoy electrons depend strongly on the dwell time. A narrow, strongly theta-dependent contribution at v /SUB e/ = v /SUB p/ can be distinguished from a theta-independent part at v /SUB e/ 2+ at v /SUB e/ = v /SUB p/ and under zero degrees is found to be more than about 20 times as large as is expected from the contribution of loss electrons in last layer collisions

409

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

Science.gov (United States)

Electronic energy transfer (EET) plays a critical role in many biological processes and is used by nature to direct energy to a site where chemical reactions need to be initiated. Such EET can occur over large distances and can involve many individual molecules of identical, similar or disparate chemical identity. Advances in spectroscopy and data processing have allowed the rates of EET to be measured on extremely fast timescales such that improved mechanistic insight becomes feasible. At the same time, highly sophisticated synthetic operations have been devised that facilitate the isolation and purification of elaborate multi-component molecular arrays. A key feature of these arrays concerns the logical positioning of individual units in a way that favours directed EET along the molecular axis or along some other preferred pathway. The availability of these novel molecular materials allows close examination of popular theoretical models and paves the way for the development of advanced molecular sensors, artificial light harvesters, fluorescent labels and sensitizers. Of particular interest is the spectacular growth in the application of boron dipyrromethene dyes as basic reagents in such artificial photon collectors and these compounds have dominated the market in recent years because of their synthetic versatility and valuable photophysical properties. In this article, recent developments in the field are highlighted in terms of synthesis and subsequent spectroscopic exploration. PMID:20957235

Ziessel, Raymond; Harriman, Anthony

2011-01-14

410

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

Science.gov (United States)

Electron energy-loss spectroscopy and electron-ion coincidence techniques were used to determine the total generalized oscillator strength distribution (GOSD) of molecular hydrogen (H2) under 200 eV incident electron energy at a scattering angle of 6 degree. Ionic GOSDs were obtained for each formed ion at each energy-loss value and were determined by scattered electron-ion coincidence measurements. The total and partial ionic GOSDs of H2 were compared with the OOSDs from the experimental results of both photon and fast-electron impacts. We observed auto-ionization induced by excitation to the optically forbidden Q 1 1?+ g (1) state near 28 eV. Additionally, the non-ionic GOSD, defined as the difference between the total GOSD and the total ionic GOSD, was determined. From the non-ionic GOSD, neutral dissociation from excitation to the forbidden Q 1 1?+ g (1) state near 28 eV and the Q 2 series near 35 eV were identified.

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

2014-04-01

411

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

International Nuclear Information System (INIS)

Electron energy-loss spectroscopy and electron-ion coincidence techniques were used to determine the total generalized oscillator strength distribution (GOSD) of molecular hydrogen (H2) under 200 eV incident electron energy at a scattering angle of 6 degrees. Ionic GOSDs were obtained for each formed ion at each energy-loss value and were determined by scattered electron-ion coincidence measurements. The total and partial ionic GOSDs of H2 were compared with the Optical Oscillation Strength Distributions (OOSDs) from the experimental results of both photon and fast-electron impacts. We observed auto-ionization induced by excitation to the optically forbidden Q11?g+(1) state near 28 eV. Additionally, the non-ionic GOSD, defined as the difference between the total GOSD and the total ionic GOSD, was determined. From the non-ionic GOSD, neutral dissociation from excitation to the forbidden Q11?g+(1) state near 28 eV and the Q2 series near 35 eV were identified. (authors)

412

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

Science.gov (United States)

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

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

413

New Materials, Methods, and Molecules for Microelectronic and Molecular Electronic Devices  

Science.gov (United States)

This dissertation reports a variety of new methods and materials for the fabrication of electronic devices. Particular emphasis is placed on low-cost, solution based methods for flexible electronic device fabrication, and new substrates and molecules for molecular electronic tunnel junctions. Chapter 2 reports a low-cost, solution based method for depositing patterned metal circuitry onto a variety of flexible polymer substrates. Microcontact printing an aluminum (III) porphyrin complex activates selected areas of an oxidized polymer substrate to electroless copper metallization. Chapter 3 reports a new transparent conductive electrode for use in optoelectronic devices. A highly conductive, transparent silver nanowire network is embedded at the surface of an optical adhesive, which can be applied to a variety of rigid and flexible polymer substrates. Chapter 4 describes a new approach to the self-assembly of mesoscale components into two-dimensional arrays. Unlike most previously reported self-assembly motifs, this method is completely dry; eliminating solvent makes this method compatible with the assembly of electronic components. Chapter 5 describes a new class of self-assembled monolayer (SAM) on gold formed from dihexadecyldithiophosphinic acid ((C16) 2DTPA) adsorbate molecules. The binding and structure (C16) 2DTPA SAMs is dependent upon the roughness and morphology of the underlying gold substrate. Chapter 6 investigates the influence of chain length on the binding and structure of dialkyl-DTPA SAMs on smooth, template-stripped (TS) gold. Binding of the DTPA head group is independent of the length of the alkyl chain, while the structure of the organic layer has a counter-intuitive dependence: As the length of the alkyl chain increases, these SAMs become more disordered and liquid-like. Chapter 7 describes the fabrication of ultra smooth gold substrates using chemical mechanical polishing (CMP). These substrates are smooth, uniform, and prove to be ideal candidates for bottom electrodes within SAM-based molecular electronic tunnel junctions. Chapter 8 investigates the charge transport properties of new diphenyldithiophosphinic acid (Ph 2DTPA) SAMs on TS gold within metal-SAM//Ga2O3/EGaIn molecular tunnel junctions. A computational investigation provides insight into the electronic structure of the junction.

Miller, Michael Stephen

414

A CPU/GPU collaborative approach to high-speed remote sensing image rectification based on RFM  

Science.gov (United States)

Image rectification is a common task in remote sensing application and usually time-consuming for large-size images. Based on the characteristics of the Rational Functional Model (RFM)-based rectification process, this paper proposes a novel CPU/GPU collaborative approach to high-speed rectification of remote sensing images. Three performance optimization strategies are presented in detail, including maximizing device occupancy, improving memory access efficiency and increasing instruction throughput. Experimental results using SPOT-5 and ZiYuan-3 (ZY3) remote sensing images show that the proposed method can achieve the processing speed up to 8GB/min, which significantly exceeds that of common commercial software. Real-time remote sensing image rectification can be expected with further optimized algorithm and more efficient I/O operation.

Sun, Yiwei; Liu, Bin; Sun, Xiliang; Wan, Wenhui; Di, Kaichang; Liu, Zhaoqin

2014-05-01

415

The dependence of the electronic conductivity of carbon molecular sieve electrodes on their charging states.  

Science.gov (United States)

The dependence of the electronic conductivity of activated carbon electrodes on their potential in electrolyte solutions was examined. Kapton polymer films underwent carbonization (1000 degrees C), followed by a mild oxidation process (CO(2) at 900 degrees C) for various periods of time, to obtain carbons of different pore structures. A specially designed cell was assembled in order to measure the conductivity of carbon electrodes at different potentials in solutions. When the carbon electrodes possessed molecular sieving properties, a remarkable dependence of their conductivity on their charging state was observed. Aqueous electrolyte solutions containing ions of different sizes were used in order to demonstrate this phenomenon. As the average pore size of the activated carbons was larger, their molecular sieving ability was lower, and the dependence of their conductivity on their charging state regained its classical form. This behavior is discussed herein. PMID:16599523

Pollak, Elad; Genish, Isaschar; Salitra, Gregory; Soffer, Abraham; Klein, Lior; Aurbach, Doron

2006-04-13

416

Measuring the electron electric dipole moment using a cold molecular beam  

Science.gov (United States)

A test of theories beyond the standard model is in progress using a cold beam of thorium monoxide (ThO) to improve the experimental limit on the electric dipole moment of the electron (eEDM). Improvements are expected on the current experimental eEDM limit because of the large internal electric field of polarized ThO, the long lifetime and magnetic field insensitivity of the metastable H state used in the experiment, the powerful systematic error canceling provided by the H state ?-doublet structure, and the high-flux, well collimated molecular beam provided by a buffer gas-cooled beam source. We detail the progress of this experiment, including the development of techniques to produce the ThO emission source, cool and collimate the molecular beam, and create stable electric and magnetic field configurations.

Petrik, Elizabeth; Campbell, Wesley; Gurevich, Yulia; Hess, Paul; Hutzler, Nicholas; Kirilov, Emil; Parsons, Maxwell; Spaun, Benjamin; Vutha, Amar; Demille, David; Gabrielse, Gerald; Doyle, John

2010-03-01

417

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

CERN Document Server

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

Strong, A E

1997-01-01

418

Electronic and transport properties of azobenzene monolayer junctions as molecular switches  

CERN Document Server

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

Wang, Yan

2012-01-01

419

Non-adiabatic quantum molecular dynamics: ionization of many-electron systems  

International Nuclear Information System (INIS)

We propose a novel method to describe realistically ionization processes with absorbing boundary conditions in basis expansion within the formalism of so-called non-adiabatic quantum molecular dynamics. This theory couples self-consistently a classical description of the nuclei with a quantum-mechanical treatment of the electrons in atomic many-body systems. In this paper, we extend the formalism by introducing absorbing boundary conditions via an imaginary potential. It is shown how this potential can be constructed in time-dependent density functional theory in basis expansion. The approach is first tested on the hydrogen atom and the pre-aligned hydrogen molecular ion H2+ in intense laser fields where reference calculations are available. It is then applied to study the ionization of non-aligned H2+ and H2. Striking differences in the orientation dependence between both molecules are found. Surprisingly, enhanced ionization is predicted for perpendicularly aligned molecules

420

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

421

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

Science.gov (United States)

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

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

2014-06-14

422

Effects of Contact Atomic Structure on Electronic Transport in Molecular Junction  

International Nuclear Information System (INIS)

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

423

Theoretical estimation of the electron molecular vibration coupling in several organic donor molecules  

Science.gov (United States)

The electron-molecular vibration (EMV) coupling constants and the accompanying vibronic energy values of five kinds of organic donor molecules (TTF +1, TTP +1, TTPY +1, TOF +1 and TSF +1) are crucial ingredients of metallic organic salts, and have been theoretically estimated in order to systematically investigate their dependencies on the molecular structures. The effect of the replacement of sulfur atoms in TTF +1 with oxygen and selenium atoms (TOF +1 and TSF +1) has been paid particular attention. It has been found that the EMV coupling constant decreases in the order of TOF +1>TTF +1>TSF +1>TTP +1>TTPY +1. That is, the smaller coupling constants appear in the larger-sized molecule with heavier atoms.

Taniguchi, M.; Misaki, Y.; Tanaka, K.

2000-03-01

424

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

International Nuclear Information System (INIS)

The structures of molecular crystal surfaces were investigated for the first time by the use of low-energy electron diffraction (LEED). The experimental results from a variety of molecular crystals were examined and compared as a first step towards understanding the properties of these surfaces on a microscopic level. The method of sample preparation employed, vapor deposition onto metal single-crystal substrates at low temperatures in ultrahigh vacuum, allowed concurrent study of the structures of adsorbed monolayers on metal surfaces and of the growth processes of molecular films on metal substrates. The systems investigated were ice, ammonia, naphthalene, benzene, the n-paraffins (C3 to C8), cyclohexane, trioxane, acetic acid, propionic acid, methanol, and methylamine adsorbed and condensed on both Pt(111) and Ag(111) surfaces. Electron-beam-induced damage of the molecular surfaces was observed after electron exposures of 10-4 A sec cm-2 at 20 eV. Aromatic molecular crystal samples were more resistant to damage than samples of saturated molecules. The quality and orientation of the grown molecular crystal films were influenced by substrate preparation and growth conditions. Forty ordered monolayer structures were observed. 110 figures, 22 tables, 162 references

425

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

International Nuclear Information System (INIS)

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

426

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

International Nuclear Information System (INIS)

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

427

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

Directory of Open Access Journals (Sweden)

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

Deniz Türkpençe

2013-06-01

428

Molecular scale shock response: electronic absorption spectroscopy of laser shocked explosives  

Science.gov (United States)

Single shot spectroscopies are being employed to answer questions fundamental to shock initiation of explosives. The goals are to: 1) determine the extent to which electronic excitations are, or are not, involved in shock induced reactions, 2) test the multiphonon up-pumping hypothesis in explosives, and 3) provide data on the initial evolution of temperature and chemistry following the shock loading of explosives on scales amenable to comparison to molecular dynamics simulations. The data presented in this talk are focused on answering the first question. Recent experimental results measuring the time history of ultraviolet/visible absorption spectroscopy of laser shocked explosive thin films and single crystals will be discussed.

McGrane, Shawn; Whitley, Von; Moore, David; Bolme, Cindy; Eakins, Daniel

2009-06-01

429

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

OpenAIRE

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

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

1999-01-01

430

On Measuring the Electron Electric Dipole Moment in Trapped Molecular Ions  

CERN Document Server

Trapped diatomic molecular ions could prove to be a sensitive probe for a permanent electron electric dipole moment (eEDM). We propose to use a ground or metastable $^3\\Delta_1$ level, due to its high polarizability and large EDM enhancement factor. Ions allow for simple trapping and long interrogation times, but require a time-varying electric bias field in order to probe the eEDM. We discuss experimental design as well as challenges in performing a precision spectroscopic measurement in rapidly time-varying electric fields.

Leanhardt, Aaron E; Loh, Huanqian; Maletinsky, Patrick; Meyer, Edmund R; Sinclair, Laura C; Stutz, Russell P; Cornell, Eric A

2010-01-01

431

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

Science.gov (United States)

Based on the nonequilibrium Green's function method and density functional theory calculations, we theoretically investigate the electronic