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1

Current rectification, switching, polarons, and defects in molecular electronic devices  

CERN Document Server

Devices for nano- and molecular size electronics are currently a focus of research aimed at an efficient current rectification and switching. A few generic molecular scale devices are reviewed here on the basis of first-principles and model approaches. Current rectification by (ballistic) molecular quantum dots can produce the rectification ratio ~100. Current switching due to conformational changes in the molecules is slow, on the order of a few kHz. Fast switching (~1THz) may be achieved, at least in principle, in a degenerate molecular quantum dot with strong coupling of electrons with vibrational excitations. We show that the mean-field approach fails to properly describe intrinsic molecular switching and present an exact solution to the problem. Defects in molecular films result in spurious peaks in conductance, apparent negative differential resistance, and may also lead to unusual temperature and bias dependence of current. The observed switching in many cases is_extrinsic_, caused by changes in molecu...

Bratkovsky, A M

2006-01-01

2

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

3

Terahertz rectification by periodic two-dimensional electron plasma  

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-06-24

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

Molecular junctions in the Coulomb blockade regime: rectification and nesting  

CERN Document Server

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

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

2006-01-01

6

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2008-12-20

7

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

International Nuclear Information System (INIS)

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

8

Interface states, negative differential resistance, and rectification in molecular junctions with transition-metal contacts  

Science.gov (United States)

We present a theory of nonlinear transport phenomena in molecular junctions where single thiolated organic molecules bridge transition metal nanocontacts whose densities of states have strong d orbital components near the Fermi level. At moderate bias, we find electron transmission between the contacts to be mediated by interface states within the molecular highest-occupied-molecular-orbital-lowest-unoccupied-molecular-orbital gap that arise from hybridization between the thiol-terminated ends of the molecules and the d orbitals of the transition metals. Because these interface states are localized mainly within the metal electrodes, we find their energies to accurately track the electrochemical potentials of the contacts when a variable bias is applied across the junction. We predict resonant enhancement and reduction of the interface state transmission as the applied bias is varied, resulting in negative differential resistance (NDR) in molecular junctions with Pd nanocontacts. We show that these nonlinear phenomena can be tailored by suitably choosing the nanocontact materials: If a Rh electrode is substituted for one Pd contact, we predict enhancement of these NDR effects. The same mechanism is also predicted to give rise to rectification in Pd/molecule/Au junctions. The dependences of the interface state resonances on the orientation of the metal interface, the adsorption site of the molecule, and the separation between the thiolated ends of the molecule and the metal contacts are also discussed.

Dalgleish, Hugh; Kirczenow, George

2006-06-01

9

Obvious variation of rectification behaviors induced by isomeric anchoring groups for dipyrimidinyl–diphenyl molecular junctions  

Energy Technology Data Exchange (ETDEWEB)

The rectifying properties modulated by isomeric anchoring groups of dipyrimidinyl–diphenyl co-oligomer diodes sandwiched between two gold electrodes are investigated using density functional theory combined with the nonequilibrium Green's function method. Our results show that the rectifying behaviors of the co-oligomer diode are significantly modulated by isomeric substitution of anchoring groups. When the isomeride nitrile end group is replaced by the isocyanide one, for symmetric arrangement of electrodes, the rectifying direction shows obvious inversion for the isocyanide–diblock–thiol junction, and the rectification ratio is obviously enhanced for the thiol–diblock–isocyanide junction. The influence on rectification induced by asymmetric electrodes is also discussed. The analysis of the transmission spectra and the molecular projected self-consistent Hamiltonian under various external bias voltages gives inside mechanisms of the observed results.

Song, Yang; Bao, De-Liang; Xie, Zhen; Zhang, Guang-Ping; Wang, Chuan-Kui, E-mail: ckwang@sdnu.edu.cn

2013-12-13

10

Spin current and rectification in one-dimensional electronic systems  

CERN Document Server

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

Braunecker, B; Braunecker, Bernd

2006-01-01

11

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

International Nuclear Information System (INIS)

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

12

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-03-15

13

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

Science.gov (United States)

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

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

2014-09-01

14

Anchoring Group Electronic Structure Engineering in Molecular Electronics  

CERN Document Server

Electron transport properties of conjugated molecular wires linked to gold electrodes through thiol or dithiocarboxylate anchoring groups are studied from first principles. The microscopic origin of the experimentally observed current amplification by the dithiocarboxylate anchoring groups is established. A new microscopic mechanism of rectification is predicted based upon electronic structure of asymmetrical anchoring groups. Our calculations show that electronic structure of anchoring groups accompanied by molecular orbital interaction picture can be used as a guiding principle to predict transport properties of molecular wire junctions.

Li, Z; Li, Zhenyu

2006-01-01

15

Electronic transport in molecular junctions  

Science.gov (United States)

A combined density functional theory and Green function method is used to study some basics and applications in the field of molecular electronics. We have investigated the effects of lateral interactions on the conductance of two molecules connected in parallel to semi-infinite leads. The system, modeled after a self-assembled monolayer, consists of benzylmercaptane molecules sandwiched between gold electrodes. We find that the conductance increases when intermolecular interaction comes into play. The source of this increase is the indirect interaction through the gold substrate rather than direct molecule-molecule interaction. As for applications, single-molecule spintronic switch and spin valve, rectifier and negative differential resistive (NDR) diode are proposed. Spintronic switch is constructed by a di-cobaltocene containing molecule. The anti-parallel (singlet) configuration blocks electron transport near the Fermi energy, while the spin parallel (triplet) configuration enables a much higher current. The energy difference between the anti-parallel and parallel states depends on the insulating spacer separating the two cobaltocenes, allowing switching through the application of a moderate magnetic field. In addition, single cobaltocene containing molecule can be used as a spin valve. Rectification of current through a single molecule with an intrinsic spatial asymmetry is studied. The molecule contains a cobaltocene moiety in order to take advantage of its relatively localized and high energy d states. A rectifier with large voltage range, high current density, and low threshold voltage can be realized. The evolution of molecular orbitals under both forward and reverse bias reveals the source of rectification being asymmetric potential drop. Our calculations demonstrate the plausibility of making excellent molecular diodes by using metallocenes, pointing to a fruitful class of molecules. Analogous to a quantum double dot system, we found that diblock structured molecules could also show NDR. We show that molecular level crossing in a molecular double dot (MDD) system containing cobaltocene and ferrocene leads to NDR and hysteresis. Time-dependent transport properties of molecular junctions under external perturbation of a short time pulse or an alternative bias is studied by solving Green function in the time domain, combined with electronic structure information coming from ab initio density functional calculations. We found that the short time response depends on lead structure, bias voltage and barrier heights both at molecule-lead contacts and within molecules. Under an alternative current (AC) mode, the electron flow either lags (capacitive response) or leads (inductive response) the bias signal. The critical frequency for this transition is characteristic of a junction, depending on factors such as electronic structure of the leads and capacitance of the contacts.

Liu, Rui

2006-01-01

16

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

17

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

DEFF Research Database (Denmark)

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

Taylor, Jeremy Philip; Brandbyge, Mads

2002-01-01

18

Molecular rectification in a metal-insulator-metal junction based on self-assembled monolayers.  

Science.gov (United States)

An electrical junction formed by mechanical contact between two self-assembled monolayers (SAMs)--a SAM formed from an dialkyl disulfide with a covalently linked tetracyanoquinodimethane group that is supported by silver (or gold) and a SAM formed from an alkanethiolate SAM that is supported by mercury-rectifies current. The precursor to the SAM on silver (or gold) was bis(20-(2-((2,5-cyclohexadiene-1,4-diylidene)dimalonitrile))decyl)) disulfide and that for the SAM on mercury was HS(CH(2))(n-1)CH(3) (n = 14, 16, 18). The electrical properties of the junctions were characterized by current-voltage measurements. The ratio of the conductivity of the junction in the forward bias (Hg cathodic) to that in the reverse bias (Hg anodic), at a potential of 1 V, was 9 +/- 2 when the SAM on mercury was derived from HS(CH(2))(15)CH(3). The ratio of the conductivity in the forward bias to that in the reverse bias increased with decreasing chain length of the alkanethiol used to form the SAM on mercury. These results demonstrate that a single redox center asymmetrically placed in a metal-insulator-metal junction can cause the rectification of current and indicate that a fixed dipole in the insulating region of a metal-insulator-metal junction is not required for rectification. PMID:12296740

Chabinyc, Michael L; Chen, Xiaoxi; Holmlin, R Erik; Jacobs, Heiko; Skulason, Hjalti; Frisbie, C Daniel; Mujica, Vladimiro; Ratner, Mark A; Rampi, Maria Anita; Whitesides, George M

2002-10-01

19

Effect of Protonation on the electronic properties of DNA base pairs: Applications for molecular electronics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Protonation of DNA basepairs is a reversible phenomenon which can be controlled by tuning the pH of the system. Under mild acidic conditions, the hydrogen bonding pattern of the DNA basepairs undergoes a change. We study the effect of protonation on the electronic properties of the DNA basepairs to probe for possible molecular electronics applications. We find that, under mild acidic pH conditions, the A:T basepair shows excellent rectification behaviour which is, however, a...

Mallajosyula, Sairam S.; Pati, Swapan K.

2007-01-01

20

Tuning electrochemical rectification via quantum dot assemblies.  

Science.gov (United States)

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

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

2010-12-01

 
 
 
 
21

Effect of proportion on rectification in organic co-oligomer spin rectifiers  

International Nuclear Information System (INIS)

The rectification behaviours in organic magnetic/nonmagnetic co-oligomer spin rectifiers are investigated theoretically. It is found that both the charge current and the spin current through the device are rectified at the same time. By adjusting the proportion between the magnetic and nonmagnetic components, the threshold voltage and the rectification ratio of the rectifier are modulated. A large rectification ratio is obtained when the two components are equal in length. The intrinsic mechanism is analysed in terms of the asymmetric localization of molecular orbitals under biases. The effect of molecular length on the rectification is also discussed. These results will be helpful in the future design of organic spin diodes. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

22

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

Science.gov (United States)

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

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

2014-08-01

23

Molecular electron affinities  

International Nuclear Information System (INIS)

Molecular electron affinities have historically been difficult quantities to measure accurately. These difficulties arise from differences in structure between the ion and neutral as well as the existence of excited negative ion states. To circumvent these problems, relative electron affinities were determined in this dissertation by studying equilibrium electron transfer reactions using a pulsed ion cyclotron resonance (ICR) spectrometer. Direct measurement of ion and neutral concentrations for reactions of the general type, A- + B = B- + A, allow calculation of the equilibrium constant and, therefore, the free energy change. The free energy difference is related to the difference in electron affinities between A and B. A relative electron affinity scale covering a range of about 45 kcal/mol was constructed with various substituted p-benzoquinones, nitrobenzenes, anhydrides, and benzophenones. To assign absolute electron affinities, various species with accurately known electron affinities are tied to the scale via ion-cyclotron double resonance bracketing techniques. After the relative scale is anchored to these species with well-known electron affinities, the scale is then used as a check on other electron affinity values as well as generating new electron affinity values. Many discrepancies were found between the electron affinities measured using the ICR technique and previous literature determinationsns

24

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

25

Electronic Properties of a Phenylacetylene Molecular Junction with Dithiocarboxylate Anchoring Group  

Science.gov (United States)

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

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

2013-01-01

26

Electronic Properties of a Phenylacetylene Molecular Junction with Dithiocarboxylate Anchoring Group  

International Nuclear Information System (INIS)

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

27

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

28

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

Science.gov (United States)

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

Nakayama, Ryu-suke; Takeuchi, Tsunehiro

2015-01-01

29

Molecular Electronic Test Structures  

Science.gov (United States)

We describe and show electrical measurements of a test vehicle to electrically characterize self-assembled monolayers comprised of candidate molecular electronic (ME) molecules. ME test structures (METS) are needed to reliably measure various molecules; to validate theoretical models and allow results to be confidently compared from lab to lab. A metal-1/molecule/metal-2 METS, based upon nanopores in suspended ultrathin SiO2 films, has been developed. A process flow is shown for these METS and an effective test protocol described. These methodologies ensure that the electrical results can be attributed to the molecules and not an artifact of the test structure itself. Current-voltage curves were obtained for devices with no molecules and for devices containing long-chain alkane-thiols. These two limits, a conducting short, and an insulating film in the nanopore, respectively, characterize the METS and allow the properties of conducting molecules of interest to be reliably measured. We will also report on how different top-metal deposition methods affect the final electrical performance of the METS.

Richter, C. A.; Suehle, J. S.; Edelstein, M. D.; Kirillov, O. K.; van Zee, R. D.

2002-03-01

30

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

31

Unconventional molecule-resolved current rectification in diamondoid–fullerene hybrids  

Science.gov (United States)

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

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

2014-01-01

32

Unconventional molecule-resolved current rectification in diamondoid–fullerene hybrids  

Science.gov (United States)

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

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

2014-09-01

33

Ionic Current Rectification Through Silica Nanopores  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Nanopores immersed in electrolytic solution and under the influence of an electric field can produce ionic current rectification, where ionic currents are higher for one voltage polarity than for the opposite polarity, resulting in an asymmetric current-voltage (I-V) curve. This behavior has been observed in polymer and silicon-based nanopores as well as in theoretically studied continuum models. By means of atomic level molecular dynamics (MD) simulations, we have performed a systematic inve...

Cruz-chu, Eduardo R.; Aksimentiev, Aleksei; Schulten, Klaus

2009-01-01

34

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.

35

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

36

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-05-25

37

Nonlinear Metal-Insulator-Metal (MIM) Nanoplasmonic Waveguides Based on Electron Tunneling for Optical Rectification and Frequency Generation  

Science.gov (United States)

Metal-Insulator-Metal (MIM) electron tunneling diodes have recently emerged as an attractive alternative to semiconductor photodiodes for THz and optical detection due to their fast response time and relative ease of fabrication. However, current antenna-coupled MIM diode detectors are still limited by poor responsivity and low detection bandwidth due to impedance mismatch between the diode and antenna, large RC time constant of lumped MIM junctions, and narrow bandwidth of traditional antenna designs. In this thesis we address these issues by considering traveling-wave MIM detector designs which exhibit enhanced responsivity and low impedance that can be more easily matched to planar antennas. We also propose new antenna geometries based on surface modification of traditional bowtie antennas that are capable of receiving ultra-wideband THz signals. The concept of traveling-wave MIM detectors is then extended to the investigation of nonlinear MIM nanoplasmonic waveguides for on-chip single-cycle THz pulse generation, frequency conversion, as well as plasmonic switching and modulation.

Lei, Xiaoqin

38

Electronic continuum model for molecular dynamics simulations  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

39

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)

40

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

 
 
 
 
41

Marcus theory application to the problem of electron transport in molecular devices  

CERN Document Server

A simple Marcus theory is used to study electron transport in molecular rectifier. The device is made of two metallic electrodes connected by a molecule, which contains acceptor and donor subunits, separated by insulating bridge. Both subunits are modeled as quantum dots with discrete energy levels, isolated by potential barrier and weakly coupled to both electrodes through tunnel junctions. Proposed method is applied to hemiquinone molecule and current-voltage characteristic is obtained at an arbitrary strength of the potential drop over the tunneling region. It is shown that rectification current depends on the position of the acceptor's LUMO and donor's HOMO levels with respect to the Fermi energy of the electrodes before bias is applied, and their shift due to the bias voltage.

Walczak, K

2003-01-01

42

Molecular electronics device modeling for system design.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have used the Breit-Wigner resonance formula to model a class of molecular electronics devices with the aim to establish an abstract model for a molecular electronic device that can be used in a general cross bar architecture of future nanoelectronic systems. We show that the molecular I-V curves can be characterized by a very small number of variables including the couplings between the contact and leads.

Lei, Ci; Pamunuwa, Dinesh B.; Bailey, Stephen; Lambert, Colin

2007-01-01

43

Thermal rectification at silicon/horizontally aligned carbon nanotube interfaces  

Science.gov (United States)

Non-equilibrium molecular dynamics simulations were performed to investigate the thermal rectification effect of a system composed of a 400 nm long horizontally aligned single-walled (10, 10) carbon nanotube (CNT) and Si substrate. By imposing a series of positive and negative heat currents across the interface, a thermal rectification effect was observed. The maximum thermal rectification is about 184% when the interfacial heat flux is 60 W/m, which is very promising for thermal rectifier applications. By phonon-related analysis, we found that for heat flowing from Si to CNT, the increase of the interfacial thermal conductance with heat flux is due to the better match of phonon density of states between CNT and Si substrate at broad moderate frequencies, while for heat flowing from CNT to Si, the low-frequency phonon modes excited at large heat fluxes dominate the interfacial heat transfer and such low-frequency phonon mode mechanism is responsible for the thermal rectification effect. Moreover, we proposed a simple yet very useful method to quantify the directional contributions of lattice vibrations to the total interfacial heat flux and we demonstrated that the out-of-plane lattice vibrations at the interface dominate the heat transfer across the silicon/horizontally aligned carbon nanotube interfaces.

Zhang, Xiaoliang; Hu, Ming; Tang, Dawei

2013-05-01

44

The role of contacts in molecular electronics  

CERN Document Server

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

Cuniberti, G; Gutíerrez, R

2002-01-01

45

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

46

Gap theory of rectification in ballistic three-terminal conductors  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We introduce a model for rectification in three-terminal ballistic conductors, where the central connecting node is modeled as a chaotic cavity. For bias voltages comparable to the Fermi energy, a strong nonlinearity is created by the opening of a gap in the transport window. Both noninteracting cavity electrons at arbitrary temperature as well as the hot electron regime are considered. Charging effects are treated within the transmission formalism using a self-consistent an...

Jordan, Andrew N.; Buttiker, Markus

2008-01-01

47

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

48

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

49

Molecular modeling of inelastic electron transport in molecular junctions  

Energy Technology Data Exchange (ETDEWEB)

A quantum chemical approach for the modeling of inelastic electron tunneling spectroscopy of molecular junctions based on scattering theory is presented. Within a harmonic approximation, the proposed method allows us to calculate the electron-vibration coupling strength analytically, which makes it applicable to many different systems. The calculated inelastic electron transport spectra are often in very good agreement with their experimental counterparts, allowing the revelation of detailed information about molecular conformations inside the junction, molecule-metal contact structures, and intermolecular interaction that is largely inaccessible experimentally.

Jiang Jun; Kula, Mathias; Luo Yi [Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, S-106 91 Stockholm (Sweden)], E-mail: luo@kth.se

2008-09-17

50

Molecular modeling of inelastic electron transport in molecular junctions  

Science.gov (United States)

A quantum chemical approach for the modeling of inelastic electron tunneling spectroscopy of molecular junctions based on scattering theory is presented. Within a harmonic approximation, the proposed method allows us to calculate the electron-vibration coupling strength analytically, which makes it applicable to many different systems. The calculated inelastic electron transport spectra are often in very good agreement with their experimental counterparts, allowing the revelation of detailed information about molecular conformations inside the junction, molecule-metal contact structures, and intermolecular interaction that is largely inaccessible experimentally.

Jiang, Jun; Kula, Mathias; Luo, Yi

2008-09-01

51

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

52

Dirac Electrons in Molecular Solids  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 a...

Fukuyama, Hidetoshi; Kobayashi, Akito; Suzumura, Yoshikazu

2011-01-01

53

Electron screening in molecular fusion reactions  

CERN Document Server

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 wavefunctions 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.

Shoppa, T D; Koonin, S E; Langanke, K; Seki, R

1995-01-01

54

First Principles Study of Molecular Electronic Devices  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Molecular electronics is an active research area for the future information technology. The fabrication of basic electronic elements with molecules as the core-operators has been made experimentally in the laboratory in recent years. However, the underlying electron or charge transport mechanisms for most devices are still under debate, Theoretical modelling based on the first-principles methods are expected to play an important role in this field. A generalized quantum chemical approach base...

Su, Wenyong

2006-01-01

55

Geometrical-induced rectification in two-dimensional ballistic nanodevices  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The paper demonstrates that a two-dimensional ballistic nanodevice in which the electron gas satisfies either the Schroodinger equation (as in quantum wells in common semiconductor heterostructures) or the Dirac equation (as in graphene) is able to rectify an electric signal if the device has a non-uniform cross section, for instance a taper configuration. No p-n junctions or dissimilar electrodes are necessary for rectification.

Dragoman, Daniela; Dragoman, Mircea

2012-01-01

56

Rectification in Tunneling Junctions: 2,2'-Bipyridyl-Terminated n-Alkanethiolates.  

Science.gov (United States)

Molecular rectification is a particularly attractive phenomenon to examine in studying structure-property relationships in charge transport across molecular junctions, since the tunneling currents across the same molecular junction are measured, with only a change in the sign of the bias, with the same electrodes, molecule(s), and contacts. This type of experiment minimizes the complexities arising from measurements of current densities at one polarity using replicate junctions. This paper describes a new organic molecular rectifier: a junction having the structure Ag(TS)/S(CH2)11-4-methyl-2,2'-bipyridyl//Ga2O3/EGaIn (Ag(TS): template-stripped silver substrate; EGaIn: eutectic gallium-indium alloy) which shows reproducible rectification with a mean r(+) = |J(+1.0 V)|/|J(-1.0 V)| = 85 ± 2. This system is important because rectification occurs at a polarity opposite to that of the analogous but much more extensively studied systems based on ferrocene. It establishes (again) that rectification is due to the SAM, and not to redox reactions involving the Ga2O3 film, and confirms that rectification is not related to the polarity in the junction. Comparisons among SAM-based junctions incorporating the Ga2O3/EGaIn top electrode and a variety of heterocyclic terminal groups indicate that the metal-free bipyridyl group, not other features of the junction, is responsible for the rectification. The paper also describes a structural and mechanistic hypothesis that suggests a partial rationalization of values of rectification available in the literature. PMID:25389953

Yoon, Hyo Jae; Liao, Kung-Ching; Lockett, Matthew R; Kwok, Sen Wai; Baghbanzadeh, Mostafa; Whitesides, George M

2014-12-10

57

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

58

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

Science.gov (United States)

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

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

2014-09-01

59

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

60

Intermolecular effect in molecular electronics.  

Science.gov (United States)

We investigate the effects of lateral interactions on the conductance of two molecules connected in parallel to semi-infinite leads. The method we use combines a Green function approach to quantum transport with density functional theory for the electronic properties. The system, modeled after a self-assembled monolayer, consists of benzylmercaptane molecules sandwiched between gold electrodes. We find that the conductance increases when intermolecular interaction comes into play. The source of this increase is the indirect interaction through the gold substrate rather than direct molecule-molecule interaction. A striking resonance is produced only 0.3 eV above the Fermi energy. PMID:15740279

Liu, Rui; Ke, San-Huang; Baranger, Harold U; Yang, Weitao

2005-01-22

 
 
 
 
61

Intermolecular Effect in Molecular Electronics  

CERN Document Server

We investigate the effects of lateral interactions on the conductance of two molecules connected in parallel to semi-infinite leads. The method we use combines a Green function approach to quantum transport with density functional theory for the electronic properties. The system, modeled after a self-assembled monolayer, consists of benzylmercaptane molecules sandwiched between gold electrodes. We find that the conductance increases when intermolecular interaction comes into play. The source of this increase is the indirect interaction through the gold substrate rather than direct molecule-molecule interaction. A striking resonance is produced only 0.3 eV above the Fermi energy.

Liu, R; Baranger, H U; Yang, W; Liu, Rui; Ke, San-Huang; Baranger, Harold U.; Yang, Weitao

2005-01-01

62

Electron Recombination with Small Molecular Ions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Brinne Roos, Johanna

2007-01-01

63

The electronic structure of condensed molecular systems  

Energy Technology Data Exchange (ETDEWEB)

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

LeSar, R.A.

1988-01-01

64

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

65

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

66

Scanning probe methods applied to molecular electronics  

Energy Technology Data Exchange (ETDEWEB)

Scanning probe methods on insulating films offer a rich toolbox to study electronic, structural and spin properties of individual molecules. This work discusses three issues in the field of molecular and organic electronics. An STM head to be operated in high magnetic fields has been designed and built up. The STM head is very compact and rigid relying on a robust coarse approach mechanism. This will facilitate investigations of the spin properties of individual molecules in the future. Combined STM/AFM studies revealed a reversible molecular switch based on two stable configurations of DBTH molecules on ultrathin NaCl films. AFM experiments visualize the molecular structure in both states. Our experiments allowed to unambiguously determine the pathway of the switch. Finally, tunneling into and out of the frontier molecular orbitals of pentacene molecules has been investigated on different insulating films. These experiments show that the local symmetry of initial and final electron wave function are decisive for the ratio between elastic and vibration-assisted tunneling. The results can be generalized to electron transport in organic materials.

Pavlicek, Niko

2013-08-01

67

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

68

Mechanical and Electronic Properties of Molecular Boxes  

Science.gov (United States)

The area of functional nanoscale porous molecular materials is still at an early formative stage. Recently, novel classes of cavity-containing materials assembled from discrete building blocks were synthesized, which offer possibilities for selective molecular separation and control over chemical processes like catalysis and sensing. We describe "molecular boxes" built from six-coordinate Re "cornerposts" interconnected with various "walls" built on links like pyrazine, bipyridine, and metal porphyrins. We have used interactively the first-principles density functional and the molecular dynamics approaches in analysis of Zn-porphyrin-based boxes, to gain insight on their mechanical conformation and stability, and electronic response to their chemical environment. In addition, we consider effects on structure and reactivity due to a functional element Mn-porphyrin, inserted within the box.

Miljacic, Ljubomir; Sarkisov, Lev; Snurr, Randall; Ellis, Donald

2004-03-01

69

Observation of molecular level behavior in molecular electronic junction device  

Science.gov (United States)

In this dissertation, I utilize AFM based scanning probe measurement and surface enhanced Raman scattering based vibrational spectroscopic analysis to directly characterize topographic, electronic, and chemical properties of molecules confined in the local area of M3 junction to elucidate the molecular level behavior of molecular junction electronic devices. In the introduction, the characterization of molecular electronic devices with different types of metal-molecule-metal (M3) structures based upon self-assembled monolayers (SAMs) is reviewed. A background of the characterization methods I use in this dissertation, conducting probe atomic force microscopy (cp-AFM) and surface enhanced Raman spectroscopy (SERS), is provided in chapter 1. Several attempts are performed to create the ideal top metal contacts on SAMs by metal vapor phase deposition in order to prevent the metal penetration inducing critical defects of the molecular electronic devices. The scanning probe microscopy (SPM), such as cp-AFM, contact mode (c-) AFM and non-contact mode (nc-) AFM, in ultra high vacuum conditions are utilized to study the process of the metal-SAM interface construction in terms of the correlation between the morphological and electrical properties including the metal nucleation and filament generation as a function of the functionalization of long-chain alkane thiolate SAMs on Au. In chapter 2, the nascent condensation process of vapor phase Al deposition on inert and reactive SAMs are studied by SPM. The results of top deposition, penetration, and filament generation of deposited Al are discussed and compared to the results previously observed by spectroscopic measurements. Cp-AFM was shown to provide new insights into Al filament formation which has not been observed by conventional spectroscopic analysis. Additionally, the electronic characteristics of individual Al filaments are measured. Chapter 3 reveals SPM characterization of Au deposition onto --COOH terminated SAMs utilized with strong surface dipole-dipole intermolecular interaction based on hydrogen bonding and ionic bonding potentially preventing the metal penetration. The observed results are discussed with kinetic paths of metal atoms on each SAM including temporal vacancies controlled by the intermolecular interactions in SAM upon the comparison with the spectroscopic results previously reported. The results in chapter 2 and 3 strongly suggests that AFM based characterization technique is powerful tool especially for detecting molecular-size local phenomena in vapor phase metal deposition process, especially, the electric short-circuit filaments growing through SAMs, which may induce critical misinterpretation of M3 junction device properties. In Chapter 4, an altered metal deposition process on inert SAM with using a buffer layer is performed to diminish the kinetic energy of impinging metal atoms. SPM characterization reveals an abrupt metal-SAM interface without any metal penetration. Examined electric characteristics also revealed typical non-resonant tunneling characteristics of long chain alkane thiolate SAMs. In chapter 5, the buffer layer assisted growth process is used to prepare a nano particles-SAM pristine interface on SAMs to control the metal-SAM interaction in order to study the fundamental issue of chemical enhancement mechanism of SERS. Identical Au nanoparticles-SAM-Au M3 structures with different Au-SAM interactions reveal a large discrepancy of enhancement factors of ˜100 attributed to the chemical interaction. In chapter 6, Raman spectroscopy of M3 junction is applied to the characterization of molecular electronics devices. A crossed nanowire junction (X-nWJ) device is employed for in-situ electronic-spectroscopic simultaneous characterization using Raman spectroscopy. A detailed study reveals the multi-probe capability of X-nWJ for in-situ Raman and in-elastic electron tunneling spectroscopy (IETS) as vibrational spectroscopies to diagnose molecular electronic devices. In chapter 7, aniline oligomer (OAn) based redox SAMs are characterized b

Maitani, Masato

70

Radiative thermal rectification using superconducting materials  

Science.gov (United States)

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

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

2014-03-01

71

Rectification of spin currents in spin chains  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study spin transport in nonitinerant one-dimensional quantum spin chains. Motivated by possible applications in spintronics, we consider rectification effects in both ferromagnetic and antiferromagnetic systems. We find that the crucial ingredients in designing a system that displays a nonzero rectification current are an anisotropy in the exchange interaction of the spin chain combined with an offset magnetic field. For both ferromagnetic and antiferromagnetic systems we...

Hoogdalem, Kevin A.; Loss, Daniel

2011-01-01

72

Optimal rectification by strongly coupled spins  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study heat transport in a pair of strongly coupled spins. In particular, we present a condition for optimal rectification, i.e., flow of heat in one direction and complete isolation in the opposite direction. We show that the strong-coupling formalism is necessary for correctly describing heat flow in a wide range of parameters, including moderate to low couplings. We present a situation in which the strong-coupling formalism predicts optimal rectification whereas the phe...

Werlang, T.; Marchiori, M. A.; Cornelio, M. F.; Valente, D.

2014-01-01

73

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.

74

High rectification ratios of Fe–porphyrin molecules on Au facets  

International Nuclear Information System (INIS)

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

75

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

76

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

77

Very large thermal rectification in bulk composites consisting partly of icosahedral quasicrystals  

Science.gov (United States)

The bulk thermal rectifiers usable at a high temperature above 300 K were developed by making full use of the unusual electron thermal conductivity of icosahedral quasicrystals. The unusual electron thermal conductivity was caused by a synergy effect of quasiperiodicity and by a narrow pseudogap at the Fermi level. The rectification ratio, defined by TRR = |{{{\\boldsymbol{J}} }large}|/|{{{\\boldsymbol{J}} }small}|, reached vary large values exceeding 2.0. This significant thermal rectification would lead to new practical applications for the heat management.

Takeuchi, Tsunehiro

2014-12-01

78

Probing electronic excitations in molecular conduction  

CERN Document Server

We identify experimental signatures in the current-voltage (I-V) characteristics of weakly contacted molecules directly arising from excitations in their many electron spectrum. We calculate transport properties using a multielectron master equation in the Fock space of an exact diagonalized model many-body Hamiltonian benchmarked for a prototypical molecule (benzene). Using this approach, we quantitatively explain various unique features of molecular conduction that are difficult to capture even qualitatively using standard one-electron self-consistent field (SCF) approaches.

Muralidharan, B; Pati, S K; Datta, S

2005-01-01

79

Secondary electron emission with molecular projectiles  

International Nuclear Information System (INIS)

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

80

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

 
 
 
 
81

Triazatriangulene as binding group for molecular electronics.  

Science.gov (United States)

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 sp(3) 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. PMID:25426950

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

2014-12-16

82

Electron capture by protons in molecular hydrogen  

International Nuclear Information System (INIS)

The electron-capture probability at large scattering angles has been calculated for proton-H2 collisions between 1 and 20 keV. The molecular approximation for the triatomic H3+ system is used. The transition probabilities are obtained in the impact-parameter approximation. The theoretical results reproduce the essential features of the low-energy experimental data of Lockwood and Everhart (Phys. Rev.; 125:567 (1962)). (author)

83

Reverse rectification behavior of NiPc (p-type)/F16CuPc (n-type) heterojunction  

Science.gov (United States)

In this paper we present reverse rectification behavior of an organic heterojunction comprising of nickel phthalocyanine (NiPc) and copper-hexadecafluroro-phthalocyanine (F16CuPc) grown by MBE. Using Kelvin Probe we found that charge is accumulated at both side of interface, electrons in F16CuPc and holes in NiPc. The thickness of charge accumulated at the interface is about 20 nm. Based on Kelvin Probe data, mechanism of reverse rectification is explained.

Kumar, Arvind; Samanta, Soumen; Singh, Ajay; Debnath, A. K.; Prasad, R.; Aswal, D. K.; Gupta, S. K.

2012-06-01

84

Thermal boundary conductance and thermal rectification in molecules.  

Science.gov (United States)

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

Leitner, David M

2013-10-24

85

Molecular Electronics: From Physics to Computing  

CERN Document Server

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

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

2005-01-01

86

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

87

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

88

Performance of reverse rectification heat transformer  

Energy Technology Data Exchange (ETDEWEB)

Many industrial processes produce abundant quantities of low-grade waste heat. This heat is generally in the form of polluted waste water at temperatures of 60{sup o}C to 100{sup o}C. They have no economic value and may incur additional costs to the process, since it may be necessary to cool these effluents before dispersing them into the environment. Upgrading this thermal energy could be done using a heat transformer. We propose the utilization of a new type of absorption heat transformer using ``reverse-rectification`` cycle. The machine is a combination of two constant pressure, multistage, gas-liquid columns: the rectification column acting as a separator and reverse-rectification column acting as a mixer. This paper presents the general working scheme of the heat transformer, results of simulation carried out with the working mixture water-ethylene glycol and an example of such a machine. (author)

Labidi, J. [APINA, San Sebastian (Spain); Jeday, M.R. [ISET, Gabes (Tunisia); Le Goff, P. [CNRS, LSGC, Nancy (France)

1997-08-01

89

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

90

Probing molecular electronics with mechanical break junctions  

Science.gov (United States)

We will report on experiments with single molecule junctions, performed with the mechanically controlled break-junction technique. A review is given on the capabilities of the technique and the results obtained so far. The importance of the molecular structure, the local environment, the contacts, and of the electronic polarizability will be elucidated. As a particular example, we will present an experiment with a molecule that was designed to form a single-molecule diode when contacted from two sides. The concept is closely related to Aviram-Ratner's Gedankenexperiment. Indeed, the IVs show a pronounced asymmetry, whereas a blind experiment with symmetric molecules resulted in symmetric IVs. A closer analysis of the data, involving theoretical models, suggests that the bias-dependent charge reconfiguration of the electronic structure is responsible for the diode-like characteristics.

Weber, Heiko

2006-03-01

91

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

92

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

93

Optimal rectification in the ultrastrong coupling regime.  

Science.gov (United States)

We study the effect of ultrastrong coupling on the transport of heat. In particular, we present a condition for optimal rectification, i.e., flow of heat in one direction and complete isolation in the opposite direction. We show that the strong-coupling formalism is necessary for correctly describing heat flow in a wide range of parameters, including moderate to low couplings. We present a situation in which the strong-coupling formalism predicts optimal rectification whereas the phenomenological approach predicts no heat flow in any direction, for the same parameter values. PMID:25019727

Werlang, T; Marchiori, M A; Cornelio, M F; Valente, D

2014-06-01

94

Thermal rectification in nonlinear quantum circuits  

DEFF Research Database (Denmark)

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

Ruokola, T.; Ojanen, T.

2009-01-01

95

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

96

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

97

Electron transport in atomic and molecular wires  

Science.gov (United States)

Molecular electronics involves constructing atomic and molecular junctions in which an atomic chain or a single molecule or small number of molecules are bridged between two electrodes, measuring and understanding the current-voltage response of such junctions. Contacts between the atoms or molecules and the electrodes greatly affect the current-voltage characteristics. Other challenges include how to determine the conductance of single molecules. This dissertation presents a study of single atomic/molecular conductance with modified Scanning Tunneling Microscope (STM) and Atomic Force Microscope (AFM). Firstly I describe an electron transport study of atomically-thin Au wires by (1) modulating the electrochemical potential and (2) anion adsorption onto the wire. The potential modulation induces a conductance change around 0.55G0 (G0 = 2e2/h) per V for a wire with conductance quantized near 1G0 in the absence of anion adsorption. However, in the presence of I- adsorption, the conductance changes as much as 1.5G0/V. Second, I present the work of determining single-molecule conductance of various molecules by repeatedly forming thousands of Au-molecule-Au junctions. The molecules tested have either S-atoms or N-atoms on both sides so that they can form Au-S or Au-N bonds chemically to ensure the good contacts. I have determined the tunneling decay constant (betaN) of the N-alkanedithiol molecules to be 1.0 +/- 0.1 per carbon atom and depends on the applied bias very weakly. The forces needed to break down the single N-alkanedithiol molecule junction and the 4,4' bipyridine molecule junction are 1.5 +/- 0.2nN and 0.8 +/- 0.2nN respectively, suggesting that the Au-Au bond broke in the alkanedithiol case while the Au-N bond broke in the 4,4' bipyridine case. I have determined the length and base-pair dependence of the DNA conductance. Electron transport through different base pair DNA molecules decreases exponentially with the number of "AT" base pairs inserted in the G-rich region but inversely proportional to the length of "GC" base pairs. A DNA molecule with mismatch was found to conduct less than its perfectly matched sequences.

Xu, Bingqian

98

Electron and molecular dynamics: Penning ionization and molecular charge transport  

Science.gov (United States)

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

Madison, Tamika Arlene

99

Reactions in molecular nanofilms induced by low energy electrons  

Digital Repository Infrastructure Vision for European Research (DRIVER)

5 Summary and Conclusions Reactions in molecular nanofilms of a few monolayers thickness induced by low energy electrons (0-20 eV) are studied by means of electron stimulated desorption (ESD) of fragment anions and by thermal desorption spectroscopy (TDS). In ESD fragment ions emitted into vacuum are recorded mass spectrometrically as function of the electron energy. In TDS the molecular film is irradiated by electrons at defined energy for a defined time. The irradiated film is then deso...

Orzol, Mario

2010-01-01

100

Molecular and electronic structure of Troeger's bases  

International Nuclear Information System (INIS)

The equilibrium conformations of Troeger's base and two new analogues were investigated at the MP2/6-31G(d, p) ab initio level of theory. The electronic structure of these rigid yet sharply folded molecules was investigated by means of their spectroscopic properties. The 13C-NMR chemical shifts, calculated by the CSGT (continuous set of gauge transformations) formalism with the HF-B3LYP/6-311+G(2d, p) hybrid functional model, were fairly consistent with NMR observations. The He(I) photoelectron spectra were measured and interpreted by means of ab initio many-body OVGF (outer valence Green's function) calculations. The theoretical results satisfactorily reproduced the energies and splittings of the uppermost bands, associated with the two nitrogen lone pair orbitals and the phenyl ? orbitals. Electron transmission spectroscopy, with the support of calculated ?* virtual orbital energies, was employed to characterize the empty molecular levels. The 2,3,8,9-tetramethoxy analogue of Troeger's base exhibits a complex conformational situation. Whereas its NMR spectrum indicates a predominance of trans-trans arrangements of the two o-dimethoxy groups in CDCl3 solution, its photoelectron spectrum should be interpreted in terms of a mixture of the trans-trans and twisted conformers in the gas phase

 
 
 
 
101

Rotational excitation of interstellar molecular ions by electrons  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Electrons are known to be efficient in rotationally exciting molecular ions in cold ionized media. Rotational effects have also been shown to affect the dissociative recombination (DR) process. Electron collisions are thus expected to play a significant role in the thermalization and dissociation dynamics of molecular ions, both in the laboratory and in space. Using the molecular R-matrix method combined with the Adiabatic-Nuclei-Rotation (ANR) approximation corrected for threshold and closed...

Faure, A.; Tennyson, J.; Kokoouline, V.; Greene, C. H.

2009-01-01

102

Rectification of the channelrhodopsin early conductance.  

Science.gov (United States)

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

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

2011-09-01

103

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

104

Shape dependent synthesis and field emission induced rectification in single ZnS nanocrystals.  

Science.gov (United States)

We report on the synthesis of shape controlled ZnS nanocrystals designed into nanodots, nanorods, and nanowires retaining the same diameter and crystallographic phase. We used UHV scanning tunneling microscopy and spectroscopy to study rectification behavior from single nanocrystals. The nanorod and nanowire show large tunneling current at the negative bias in comparison to the positive bias demonstrating current rectification, while the nanodot shows symmetric current-voltage behavior. We proposed a tunneling mechanism where direct tunneling is followed by resonant tunneling mechanism through ZnS nanocrystal at lower applied bias voltages. Stimulation of field emission in Fowler-Nordheim tunneling regime at higher negative bias voltages enables the rectification behavior from the ZnS nanorod or nanowire. Absence of rectification from the ZnS nanodot is associated with spherical shape where the field emission becomes less significant. Realizing functional electronic component from such shape dependent single ZnS nanocrystal may provide a means in realizing nanocrystal based miniaturized devices. PMID:24779471

Thupakula, Umamahesh; Dalui, Amit; Debangshi, Anupam; Bal, Jayanta K; Kumar, Gundam S; Acharya, Somobrata

2014-05-28

105

Molecular Electronics : Insight from Ab-Initio Transport Simulations  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis presents the theoretical studies of electronic transport in molecular electronic devices. Such devices have been proposed and investigated as a promising new approach that complements conventional silicon-based electronics. To design and fabricate future nanoelectronic devices, it is essential to understand the conduction mechanism at a molecular or atomic level. Our approach is based on the non-equilibrium Green's function method (NEGF) combined with density functional theory (DF...

Prasongkit, Jariyanee

2011-01-01

106

A Quantum Chemical View of Molecular and Nano-Electronics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Jiang, Jun

2007-01-01

107

Excitation and dissociation of molecular ions by electron impact. Decay of molecular Rydberg state  

International Nuclear Information System (INIS)

Processes of excitation, dissociation and dissociative recombination of molecular ions in high vibrational states in collisions with electrons are considered. The most important, in this case, transition mechanism related to the interaction of external electron and dipole moment of molecular ion is taken account of. Inner electrons of molecular ion don't participate in the transitions considered. It is shown that for weak coupled external electron such mechanism of electron energy exchange and nuclei movement results in the appearance of the effective process of autodissociation decay of the Rydberg states of a vibration-excited molecule

108

Thermal Rectification in the Nonequilibrium Quantum-Dot-System  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Quantum thermal transport in two-quantum-dot system with Dzyaloshinskii-Moriya interaction (DM interaction) has been studied. The sign of thermal rectification can be controlled through changing the energy splitting or the DM interaction strength. The anisotropic term in the system can also affect the sign of rectification. Compared with other proposals [Phys. Rev. B 80, 172301 (2009)], our model can offer larger rectification efficiency and show the potential application in...

Chen, T.; Wang, X. B.

2012-01-01

109

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

110

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

111

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

112

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

113

Photoelectrochemical solar conversion systems molecular and electronic aspects  

CERN Document Server

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

Munoz, Andres G

2012-01-01

114

Fabrication of multilayer edge molecular electronics and spintronics devices  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Advancement of molecular devices will critically depend on the approach to establish electrical connections to the functional molecule(s). We produced a molecular device strategy which is based on chemically attaching of molecules between the two magnetic/nonmagnetic metallic electrodes along the multilayer edge(s) of a prefabricated tunnel junction. Here, we present the fabrication methodology for producing these multilayer edge molecular electronics/spintronics devices (ME...

Tyagi, Pawan

2011-01-01

115

Ballistic thermal rectification in nanoscale three-terminal junctions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Zhang, Lifa; Wang, Jian-sheng; Li, Baowen

2010-01-01

116

Molecular Spintronics Spin-Dependent Electron Transport in Molecular Wires  

CERN Document Server

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

Emberly, E; Emberly, Eldon; Kirczenow, George

2002-01-01

117

Automated rectification and geocoding of SAR imagery  

Science.gov (United States)

An automated post-processing system has been developed for rectification and geocoding of SAR (Synthetic Aperture Radar) imagery. The system uses as input a raw uncorrected image from the operational SAR correlator, and produces as a standard output a rectified and geocoded product. The accurate geolocation of SAR image pixels is provided by a spatial transformation model which maps the slant range-azimuth SAR image pixels into their location on a prespecified map grid. This model predicts the geodetic location of each pixel by utilizing: the sensor platform position; a geoid model; the parameters of the data collection system and the processing parameters used in the SAR correlator. Based on their geodetic locations, the pixels are mapped by using the desired cartographic projection equations. This rectification and geocoding technique has been tested with Seasat and SIR-B images. The test results demonstrate absolute location uncertainty of less than 50 m and relative distortion (scale factor and skew) of less than 0.1 percent relative to local variations from the assumed geoid.

Kwok, R.; Curlander, J. C.

1987-01-01

118

Fragmentation of molecular ions in slow electron collisions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 a...

Novotny, Steffen

2008-01-01

119

Electron interference in molecular photoionization by attosecond laser pulses.  

Science.gov (United States)

Molecular photoionization by intense attosecond linearly and circularly polarized X-ray laser pulses is investigated from numerical solutions of time-dependent Schrödinger equations for the one-electron systems H2(+) and H3(++). Both momentum stripes and rings in photoelectron angular distributions are observed. The first with momentum intervals ?p(s)=2??/R, where R is the molecular internuclear distance, results from interference of the coherent continuum scattering electron wave packets, which is shown to be insensitive to the laser polarization and wavelength. Diffraction of the directly ionized electrons leads to the momentum rings defined by the angle theta(p(r)R=cos(-1)(2n?)/p(r)R between the electron momentum p(r) and the molecular internuclear R axis. These patterns are well described by multi-center interference models. Such complex patterns allow us to probe intermolecular structures. PMID:23589510

Yuan, Kai-Jun; Lu, Huizhong; Bandrauk, André D

2013-05-10

120

Self-assembled nanogaps for molecular electronics  

International Nuclear Information System (INIS)

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

 
 
 
 
121

Self-assembled nanogaps for molecular electronics  

DEFF Research Database (Denmark)

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

Tang, Qingxin; Tong, Yanhong

2009-01-01

122

Gate tunable nonlinear rectification effects in three-terminal graphene nanojunctions  

Science.gov (United States)

We report on a study of the room-temperature nonlinear charge transport properties of three-terminal junction devices made from graphene. We demonstrate that the graphene three terminal junction devices show a rectification characteristic, namely, when voltages VL = V and VR = -V are applied to the left and the right terminal in a push-pull configuration, the voltage output from the central terminal VC is finite and is scaled approximately with V2. The rectification coefficient can be effectively tuned by a gate voltage and shows a transport carrier polarity dependence. We further show that the nonlinear charge transport characteristics can be used to probe the electronic structure of graphene nanostructures and to study the thermoelectrical power of graphene. These results show that the graphene three-terminal junction devices could be used as novel building blocks for nanoelectronics and as novel devices for the study of the material properties of graphene on the nanoscale.

Zhu, R. J.; Huang, Y. Q.; Kang, N.; Xu, H. Q.

2014-04-01

123

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

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

2001-01-01

124

Molecular electronics in junctions with energy disorder  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Kaiser, Franz J.; Ha?nggi, Peter; Kohler, Sigmund

2008-01-01

125

Laser induced electron diffraction: a tool for molecular orbital imaging  

CERN Document Server

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

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

2012-01-01

126

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. PMID:25578026

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

2015-01-28

127

Electronic tunneling currents at optical frequencies  

Science.gov (United States)

Rectification characteristics of nonsuperconducting metal-barrier-metal junctions as deduced from electronic tunneling theory have been observed experimentally for optical frequency irradiation of the junction.

Faris, S. M.; Fan, B.; Gustafson, T. K.

1975-01-01

128

Molecular rectifying diodes from self-assembly on silicon  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Lenfant, Ste?phane; Krzeminski, Christophe; Delerue, Christophe; Allan, Guy; Vuillaume, Dominique

2003-01-01

129

Inelastic electron tunneling spectroscopy of molecular transport junctions  

Science.gov (United States)

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

Song, Hyunwook; Lee, Takhee; Reed, Mark

2014-05-01

130

Digital deformation model for fisheye image rectification.  

Science.gov (United States)

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

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

2012-09-24

131

Image Rectification Using Affine Epipolar Geometric Constraint  

Directory of Open Access Journals (Sweden)

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

Liansheng Sui

2009-02-01

132

Electronic Transport in Molecular Diode Heterojunctions  

Science.gov (United States)

Anode-donor, donor-acceptor, and acceptor-cathode interfaces dominate the performance of organic solar cells. However, within thin-film, bulk-heterojunction, or nanostructured morphologies, interfacial transport affects are not well understood. In order to better understand these interfaces, a simplified system consisting of a single, small, diode molecule covalently bound to electrodes (anode-end group-donor-bridge-acceptor-end group-cathode) is considered. The end groups and bridge moities can be interchanged using chemical synthesis technique to understand how these parameters affect electronic transport. Here, we report our findings on single-molecule diode measurements using a conducting atomic force microscope on four newly synthesized molecules consisting of bithiophene donors and naphthalene diimide acceptors with systematic interchange of two end groups and two bridge moities. We explain the electronic structure of these molecules using absorption and fluorescence spectrometry, cyclic voltammetry, and transition voltage spectrometry in conjunction with newly developed theory.

Yee, Shannon; Sun, Jibin; Darancet, Pierre; Tilley, T. Don; Neaton, Jeffrey; Segalman, Rachel A.

2010-03-01

133

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

134

Electron-Phonon Correlation Effects in Molecular Transistors  

CERN Document Server

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

Balseiro, C A; Grempel, D R

2006-01-01

135

Calibration-free sinusoidal rectification and uniform retinal irradiance in scanning light ophthalmoscopy.  

Science.gov (United States)

Sinusoidal rectification (i.e., desinusoiding) is necessary for scanning imaging systems and is typically achieved by calculating a rectification transform from a calibration image such as a regular grid. This approach is susceptible to error due to electronic or mechanical instability that can alter the phase of the imaging window with respect to the calibration transform. Here, we show a calibration-free rectification method implemented from live video of a scanning light ophthalmoscope (SLO) with or without adaptive optics (AO). This approach, which capitalizes on positional differences in the images obtained in the forward and backward scan directions, dynamically keeps the imaging window in phase with the motion of the sinusoidal resonant scanner, preventing errors from signal drift over time. A benefit of this approach is that it allows the light power across the field-of-view (FOV) to be modulated inversely to achieve uniform irradiance on the retina, a feature desirable for functional imaging methods and light safety in SLOs. PMID:25531615

Yang, Qiang; Yin, Lu; Nozato, Koji; Zhang, Jie; Saito, Kenichi; Merigan, William H; Williams, David R; Rossi, Ethan A

2015-01-01

136

Rectification of light refraction in curved waveguide arrays  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

137

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

Science.gov (United States)

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

Murad, Sohail; Puri, Ishwar K.

2014-05-01

138

Molecular ?(2) gratings via electron-beam lithography  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We show that the nonlinear optical activity of an organic molecule may be quenched by electron irradiation. Exploiting this effect, we inscribe periodic ?(2) patterns in the molecular films by means of a scanning electron microscope. The second harmonic diffraction efficiency of the resulting ?(2) gratings is measured. The relative intensity of the diffraction orders observed agrees with the expectations for a sheet of nonlinear dipoles with a periodic modulation. No linear diffraction is s...

Domi?nguez-jua?rez, Jorge Luis; Macovez, Roberto; Gonza?lez, Mari?a Ujue?; Martorell, Jordi

2010-01-01

139

Imaging the Molecular Dynamics of Dissociative Electron Attachment to Water  

Science.gov (United States)

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

Adaniya, H.; Rudek, B.; Osipov, T.; Haxton, D. J.; Weber, T.; Rescigno, T. N.; McCurdy, C. W.; Belkacem, A.

2009-12-01

140

Imaging the molecular dynamics of dissociative electron attachment to water  

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-10-19

 
 
 
 
141

Flux rectification in the quantum X X Z chain  

Science.gov (United States)

Thermal rectification is the phenomenon by which the flux of heat depends on the direction of the flow. It has attracted much interest in recent years due to the possibility of devising thermal diodes. In this paper, we consider the rectification phenomenon in the quantum XXZ chain subject to an inhomogeneous field. The chain is driven out of equilibrium by the contact at its boundaries with two different reservoirs, leading to a constant flow of magnetization from one bath to the other. The nonunitary dynamics of this system, which is modeled by a Lindblad master equation, is treated exactly for small sizes and numerically for larger ones. The functional dependence of the rectification coefficient on the model parameters (anisotropy, field amplitude, and out of equilibrium driving strength) is investigated in full detail. Close to the XX point and at small inhomogeneity and low driving, we have found an explicit expression for the rectification coefficient that is valid at all system sizes. In particular, it shows that the phenomenon of rectification persists even in the thermodynamic limit. Finally, we prove that in the case of the XX chain, there is no rectification.

Landi, Gabriel T.; Novais, E.; de Oliveira, Mário J.; Karevski, Dragi

2014-10-01

142

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Nijhuis, Christian A.; Reus, William F.; Whitesides, George M.

2010-01-01

143

Molecular design for novel radiation resist decomposable by electron detachment  

Energy Technology Data Exchange (ETDEWEB)

Molecular structures that can be dissociated into two fragments in cryogenic solid by electron detachment have been investigated for constructing high-resolution radiation resists that are free from blur due to the migration of secondary electrons. Within examined molecules that are known to be dissociative by electron detachment in liquids, only the radical cations of (C{sub 6}H{sub 5}){sub 2}(OH)C-CH(OH)C{sub 6}H{sub 5} and [(CH{sub 3}C{sub 6}H{sub 5})(C{sub 6}H{sub 5})(OH)C-]{sub 2} dissociate into benzyl-type radicals and cations. A polymer containing these molecules at the center of the skeleton can be used as a resist with high sensitivity and high spatial resolution, since the exposure of ionizing radiation causes stepwise reduction of the molecular weight by direct ionization.

Ichikawa, Tsuneki [Division of Materials Chemistry, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628 (Japan)], E-mail: tsuneki@eng.hokudai.ac.jp

2009-12-15

144

Molecular design for novel radiation resist decomposable by electron detachment  

International Nuclear Information System (INIS)

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

145

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

146

Fragmentation of Small Multi-Electron Molecular Ions in Cold Electron Collisions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The fragmentation of the small multi-electron molecular ions HF+, DF+ and D3O+ was investigated in slow electron collisions leading to dissociative recombination. Momentum spectroscopy of the collision products from stored beams of each ion species merged with an intense cold electron beam has been performed at the ion-storage ring TSR, Heidelberg, utilizing two different imaging detectors. For the first time, a rotationally and fine-structure resolved kinetic energy release spectrum of the D...

Stu?tzel, Julia

2010-01-01

147

Electron transport properties of single molecular junctions under mechanical modulations.  

Science.gov (United States)

Electron transport behaviors of single molecular junctions are very sensitive to the atomic scale molecule-metal electrode contact interfaces, which have been difficult to control. We used a modified scanning probe microscope-break junction technique (SPM-BJT) to control the dynamics of the contacts and simultaneously monitor both the conductance and force. First, by fitting the measured data into a modified multiple tunneling barrier model, the static contact resistances, corresponding to the different contact conformations of single alkanedithiol and alkanediamine molecular junctions, were identified. Second, the changes of contact decay constant were measured under mechanical extensions of the molecular junctions, which helped to classify the different single molecular conductance sets into specific microscopic conformations of the molecule-electrode contacts. Third, by monitoring the changes of force and contact decay constant with the mechanical extensions, the changes of conductance were found to be caused by the changes of contact bond length and by the atomic reorganizations near the contact bond. This study provides a new insight into the understanding of the influences of contact conformations, especially the effect of changes of dynamic contact conformation on electron transport through single molecular junctions. PMID:22466314

Zhou, Jianfeng; Guo, Cunlan; Xu, Bingqian

2012-04-25

148

Electron transport properties of single molecular junctions under mechanical modulations  

International Nuclear Information System (INIS)

Electron transport behaviors of single molecular junctions are very sensitive to the atomic scale molecule-metal electrode contact interfaces, which have been difficult to control. We used a modified scanning probe microscope-break junction technique (SPM-BJT) to control the dynamics of the contacts and simultaneously monitor both the conductance and force. First, by fitting the measured data into a modified multiple tunneling barrier model, the static contact resistances, corresponding to the different contact conformations of single alkanedithiol and alkanediamine molecular junctions, were identified. Second, the changes of contact decay constant were measured under mechanical extensions of the molecular junctions, which helped to classify the different single molecular conductance sets into specific microscopic conformations of the molecule-electrode contacts. Third, by monitoring the changes of force and contact decay constant with the mechanical extensions, the changes of conductance were found to be caused by the changes of contact bond length and by the atomic reorganizations near the contact bond. This study provides a new insight into the understanding of the influences of contact conformations, especially the effect of changes of dynamic contact conformation on electron transport through single molecular junctions. (paper)

149

Low Energy Elastic Electron Scattering from Molecular Targets  

Science.gov (United States)

An overview of recent activity between Cal State and Juiz de Fora (Expt) and CalTech and Campinas and U. F. Parana (Theory) regarding elastic electron scattering from Methanol, Ethanol, Butanol and Propanol and Water, Molecular Hydrogen and Molecular Nitrogen will be presented. The experimental data (using an aperture source of gas) were taken at energies of 1eV up to 100eV and the theory is the Multichannel Schwinger with Polarization effects included. In most cases agreement between theory and experiment is very good, considering these are large calculations.

Khakoo, Murtadha A.; Muse, John; Silva, Helen; Lopes, Cristina; McKoy, B. Vincent; Winstead, Carl; Lima, Marco A. P.; Bettega, Marcio

2008-05-01

150

Electron impact study of molecular ions of some benzyl derivatives  

International Nuclear Information System (INIS)

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

151

Excess electrons bound to molecular systems with a vanishing dipole but large molecular quadrupole.  

Science.gov (United States)

Electron attachment properties of covalent molecules and ion clusters with vanishing dipole moments but large quadrupoles are studied with coupled cluster ab initio methods. Selection of the molecules studied is driven by two goals, finding a paradigm quadrupole-bound anion and investigating whether there is a correlation between the magnitude of the molecular quadrupole and the vertical attachment energy. Out of all examined species, only the ion clusters and four of the covalent molecules are found to support bound anions. The shapes and spatial extents of the associated excess electron distributions are qualitatively and quantitatively characterized, respectively. Two of the four covalent systems are especially promising as paradigm systems because of advantageous trade-offs regarding the number of isomers and conformers as well as synthetic closeness to commercial sources. No correlation was found between the vertical attachment energy and molecular quadrupole in an analysis that included the newly identified bound anions, those molecules, which were found not to support bound anions, and succinonitrile, which had been studied before. Moreover, there is clearly no such thing as a "critical quadrupole moment". There are, however, very strong electron correlation effects involved in the binding of the excess electrons, and similar to succinonitrile, for five out of six anions identified here, the molecular quadrupole of the neutral itself is too weak to bind an excess electron, and electron correlation in the form of dynamic polarization is required to do so. PMID:24521465

Sommerfeld, Thomas; Dreux, Katelyn M; Joshi, Robin

2014-09-01

152

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

153

A generalized quantum chemical approach for elastic and inelastic electron transports in molecular electronics devices  

Science.gov (United States)

A generalized quantum chemical approach for electron transport in molecular devices is developed. It allows one to treat devices where the metal electrodes and the molecule are either chemically or physically bonded on equal footing. An extension to include the vibration motions of the molecule has also been implemented which has produced the inelastic electron-tunneling spectroscopy of molecular electronics devices with unprecedented accuracy. Important information about the structure of the molecule and of metal-molecule contacts that are not accessible in the experiment are revealed. The calculated current-voltage (I-V) characteristics of different molecular devices, including benzene-1,4-dithiolate, octanemonothiolate [H(CH2)8S], and octanedithiolate [S(CH2)8S] bonded to gold electrodes, are in very good agreement with experimental measurements.

Jiang, Jun; Kula, Mathias; Luo, Yi

2006-01-01

154

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

155

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

156

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

In a molecular semiconductor, the carrier is dressed with a polarization cloud that we treat as a quantum field of Frenkel excitons coupled to it. The consequences of the existence of this electronic polaron on the dynamics of an extra charge in a material like pentacene can thus be evaluated.

Bussac, M. N.; Picon, J. D.; Zuppiroli, L.

2003-01-01

157

Molecular interferometer to decode attosecond electron–nuclear dynamics  

Science.gov (United States)

Understanding the coupled electronic and nuclear dynamics in molecules by using pump–probe schemes requires not only the use of short enough laser pulses but also wavelengths and intensities that do not modify the intrinsic behavior of the system. In this respect, extreme UV pulses of few-femtosecond and attosecond durations have been recognized as the ideal tool because their short wavelengths ensure a negligible distortion of the molecular potential. In this work, we propose the use of two twin extreme UV pulses to create a molecular interferometer from direct and sequential two-photon ionization processes that leave the molecule in the same final state. We theoretically demonstrate that such a scheme allows for a complete identification of both electronic and nuclear phases in the wave packet generated by the pump pulse. We also show that although total ionization yields reveal entangled electronic and nuclear dynamics in the bound states, doubly differential yields (differential in both electronic and nuclear energies) exhibit in addition the dynamics of autoionization, i.e., of electron correlation in the ionization continuum. Visualization of such dynamics is possible by varying the time delay between the pump and the probe pulses. PMID:24591647

Palacios, Alicia; González-Castrillo, Alberto; Martín, Fernando

2014-01-01

158

Molecular interferometer to decode attosecond electron-nuclear dynamics.  

Science.gov (United States)

Understanding the coupled electronic and nuclear dynamics in molecules by using pump-probe schemes requires not only the use of short enough laser pulses but also wavelengths and intensities that do not modify the intrinsic behavior of the system. In this respect, extreme UV pulses of few-femtosecond and attosecond durations have been recognized as the ideal tool because their short wavelengths ensure a negligible distortion of the molecular potential. In this work, we propose the use of two twin extreme UV pulses to create a molecular interferometer from direct and sequential two-photon ionization processes that leave the molecule in the same final state. We theoretically demonstrate that such a scheme allows for a complete identification of both electronic and nuclear phases in the wave packet generated by the pump pulse. We also show that although total ionization yields reveal entangled electronic and nuclear dynamics in the bound states, doubly differential yields (differential in both electronic and nuclear energies) exhibit in addition the dynamics of autoionization, i.e., of electron correlation in the ionization continuum. Visualization of such dynamics is possible by varying the time delay between the pump and the probe pulses. PMID:24591647

Palacios, Alicia; González-Castrillo, Alberto; Martín, Fernando

2014-03-18

159

Determination of hydrogen and electron densities in interstellar molecular clouds  

International Nuclear Information System (INIS)

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

160

Bonding and Molecular Geometry without Orbitals- The Electron Domain Model  

Science.gov (United States)

An alternative to the conventional valence bond approach to bonding and geometry-the electron domain model-is presented. This approach avoids some of the problems with the standard approach and presents fewer difficulties for the student, while still providing a physical basis for the VSEPR model and a link to the valence bond model. The electron domain model also emphasizes the importance of the Pauli principle in understanding the chemical bond and molecular geometry. A letter from Derek W. Smith in our April 2000 issue addresses the above.

Gillespie, Ronald J.; Spencer, James N.; Moog, Richard S.

1996-07-01

 
 
 
 
161

Molecular electronics an introduction to theory and experiment  

CERN Document Server

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

Cuevas, Juan Carlos

2010-01-01

162

Electron densities and the excitation of CN in molecular clouds  

Science.gov (United States)

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

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

1991-01-01

163

Electronic emission spectroscopy of Group IV tetrachloro molecular ions  

International Nuclear Information System (INIS)

Two broad continuous bands are observed in the visible region following electron impact ionization of a He-seeded molecular beam of SiCl4 or GeCl4. By using tunable vacuum UV radiation from a synchrotron source to measure the threshold energy at which the fluorescence bands occur, it is shown that the bands are related to the initial formation of the C 2T2 state of the parent ion SiCl+4/GeCl+4. By comparison with photoelectron data, the bands are assigned to bound--free transitions in SiCl+4/GeCl+4 C 2T2--A 2T2 and X 2T1. The C state of CCl+4 does not fluoresce. The results are compared with the electronic emission spectra of the three tetrafluoro molecular ions

164

Electronic emission spectroscopy of Group IV tetrachloro molecular ions  

Science.gov (United States)

Two broad continuous bands are observed in the visible region following electron impact ionization of a He-seeded molecular beam of SiCl4 or GeCl4. By using tunable vacuum UV radiation from a synchrotron source to measure the threshold energy at which the fluorescence bands occur, it is shown that the bands are related to the initial formation of the C˜ 2T2 state of the parent ion SiCl+4/GeCl+4. By comparison with photoelectron data, the bands are assigned to bound-free transitions in SiCl+4/GeCl+4 C˜ 2T2-Ã 2T2 and X˜ 2T1. The C˜ state of CCl+4 does not fluoresce. The results are compared with the electronic emission spectra of the three tetrafluoro molecular ions.

Lambert, I. R.; Mason, S. M.; Tuckett, R. P.; Hopkirk, A.

1988-09-01

165

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.

166

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

DEFF Research Database (Denmark)

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

DiCarlo, L.; M. Marcus, C.

2003-01-01

167

Molecular Light Emission Induced by Inelastic Electron Tunneling  

Science.gov (United States)

Light emission from molecular layers has been induced by inelastically tunneling electrons in a tunneling junction. The fast quenching of molecular emission on metal surfaces was suppressed by use of the "transparent conductor" indium-tin-oxide for the junction electrodes. The emission measurements have been made in squeezable tunneling junctions as small as 10-9 square centimeters, coated with 9-10 dichloro-anthracene layers. At a bias of 2.5 to 3.5 volts, yields of 5000 photons per microcoulomb were observed. Evidence for the molecular origin of the emission is given. This method shows good prospects for use in the imaging of chromophores on surfaces with atomic resolution.

Flaxer, Eli; Sneh, Ofer; Cheshnovsky, Ori

1993-12-01

168

Rovibronic energy levels for triplet electronic states of molecular deuterium  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An optimal set of 1050 rovibronic energy levels for 35 triplet electronic states of $D_2$ has been obtained by means of a statistical analysis of all available wavenumbers of triplet-triplet rovibronic transitions studied in emission, absorption, laser and anticrossing spectroscopic experiments of various authors. We used a new method of the analysis (Lavrov, Ryazanov, JETP Letters, 2005), which does not need any \\it a priori \\rm assumptions concerning the molecular structur...

Lavrov, B. P.; Umrikhin, I. S.

2007-01-01

169

Molecular structure of bromotrichloromethane as determined by gas electron diffraction  

International Nuclear Information System (INIS)

The molecular structure of CBrCl3 has been determined by gas electron diffraction to be as follows: r sub(g)(C-Cl) = 1.7654(17) A, r sub(g)(C-Br) = 1.944(4) A, and 4(13)0. The mean amplitudes have been fixed at the calculated values in the data analysis. The result has been compared with the structures of related halomethanes. (author)

170

Ionic Fragmentation Channels in Electron Collisions of Small Molecular Ions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ion...

Hoffmann, Jens

2008-01-01

171

Electron collisions and internal excitation in stored molecular ion beams  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 He2+. 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...

Buhr, Henrik

2006-01-01

172

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

173

First-Principles Simulations of Inelastic Electron Tunneling Spectroscopy of Molecular Electronic Devices  

Science.gov (United States)

A generalized Green's function theory is developed to simulate the inelastic electron tunneling spectroscopy (IETS) of molecular junctions. It has been applied to a realistic molecular junction with an octanedithiolate embedded between two gold contacts in combination with the hybrid density functional theory calculations. The calculated spectra are in excellent agreement with recent experimental results. Strong temperature dependence of the experimental IETS spectra is also reproduced. It is shown that the IETS is extremely sensitive to the intra-molecular conformation and to the molecule-metal contact geometry.

Jiang, Jun; Kula, Mathias; Lu, Wei; Luo, Yi

2005-08-01

174

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

175

Inelastic electron tunneling spectroscopy in molecular junctions: peaks and dips.  

Science.gov (United States)

We study inelastic electron tunneling through a molecular junction using the nonequilibrium Green's function formalism. The effect of the mutual influence between the phonon and the electron subsystems on the electron tunneling process is considered within a general self-consistent scheme. Results of this calculation are compared to those obtained from the simpler Born approximation and the simplest perturbation theory approaches, and some shortcomings of the latter are pointed out. The self-consistent calculation allows also for evaluating other related quantities such as the power loss during electron conduction. Regarding the inelastic spectrum, two types of inelastic contributions are discussed. Features associated with real and virtual energy transfer to phonons are usually observed in the second derivative of the current I with respect to the voltage Phi when plotted against Phi. Signatures of resonant tunneling driven by an intermediate molecular ion appear as peaks in the first derivative dI/dPhi and may show phonon sidebands. The dependence of the observed vibrationally induced lineshapes on the junction characteristics, and the linewidth associated with these features are also discussed. PMID:15634159

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

2004-12-15

176

Machine Learning of Molecular Electronic Properties in Chemical Compound Space  

CERN Document Server

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

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

2013-01-01

177

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

Science.gov (United States)

In continuation of previous studies showing promising metal-molecule contact properties a variety of C(60) end-capped "molecular wires" for molecular electronics were prepared by variants of the Prato 1,3-dipolar cycloaddition reaction. Either benzene or fluorene was chosen as the central wire, and synthetic protocols for derivatives terminated with one or two fullero[c]pyrrolidine "electrode anchoring" groups were developed. An aryl-substituted aziridine could in some cases be employed directly as the azomethine ylide precursor for the Prato reaction without the need of having an electron-withdrawing ester group present. The effect of extending the ?-system of the central wire from 1,4-phenylenediamine to 2,7-fluorenediamine was investigated by absorption, fluorescence, and electrochemical methods. The central wire and the C(60) end-groups were found not to electronically communicate in the ground state. However, the fluorescence of C(60) was quenched by charge transfer from the wire to C(60). Quantum chemical calculations predict and explain the collapse of coherent electronic transmission through one of the fulleropyrrolidine-terminated molecular wires. PMID:21133403

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

2011-01-01

178

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

DEFF Research Database (Denmark)

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

SØrensen, Jakob Kryger; Fock, Jeppe

2011-01-01

179

Digital image transformation and rectification of spacecraft and radar images  

Science.gov (United States)

The application of digital processing techniques to spacecraft television pictures and radar images is discussed. The use of digital rectification to produce contour maps from spacecraft pictures is described; images with azimuth and elevation angles are converted into point-perspective frame pictures. The digital correction of the slant angle of radar images to ground scale is examined. The development of orthophoto and stereoscopic shaded relief maps from digital terrain and digital image data is analyzed. Digital image transformations and rectifications are utilized on Viking Orbiter and Lander pictures of Mars.

Wu, S. S. C.

1985-01-01

180

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

 
 
 
 
181

Rectification inversion in oxygen substituted graphyne-graphene-based heterojunctions.  

Science.gov (United States)

Current rectification is found in oxygen-substituted zigzag graphyne nanoribbon/hydrogen-terminated zigzag graphene nanoribbon heterostructure junctions, from the application of nonequilibrium Green's function formalism combined with density functional theory. This behavior could be tuned by varying the number and location of oxygen atoms in the zigzag graphyne nanoribbon parts, and the rectification direction could be reversed due to the parity limitation tunneling effect. Moreover, an obvious negative differential resistance behavior is found and may be explained by two different mechanisms. PMID:25516239

Zhao, Wen-Kai; Cui, Bin; Fang, Chang-Feng; Ji, Guo-Min; Zhao, Jing-Fen; Kong, Xiang-Ru; Zou, Dong-Qing; Jiang, Xiao-Hui; Li, Dong-Mei; Liu, De-Sheng

2015-02-01

182

Consideration of enhancement of thermal rectification using metamaterial models  

Science.gov (United States)

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

Iizuka, Hideo; Fan, Shanhui

2014-11-01

183

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

Science.gov (United States)

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

Sue, Chi-Hau

184

Ab initio molecular dynamics on the electronic Boltzmann equilibrium distribution  

Energy Technology Data Exchange (ETDEWEB)

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.

Alonso, J L; Echenique, P [Departamento de Fisica Teorica, Universidad de Zaragoza, Pedro Cerbuna 12, E-50009 Zaragoza (Spain); Castro, A; Polo, V [Institute for Biocomputation and Physics of Complex Systems (BIFI), University of Zaragoza, Mariano Esquillor s/n, E-50018 Zaragoza (Spain); Rubio, A [Nano-Bio Spectroscopy group and ETSF Scientific Development Centre, Departamento de Fisica de Materiales, Universidad del PaIs Vasco, Centro de Fisica de Materiales, CSIC-UPV/EHU-MPC and DIPC, E-20018 San Sebastian (Spain); Zueco, D, E-mail: dzueco@unizar.e [Instituto de Ciencia de Materiales de Aragon and Departamento de Fisica de la Materia Condensada, CSIC-Universidad de Zaragoza, E-50009 Zaragoza (Spain)

2010-08-15

185

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

186

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

187

Quantum information analysis of electronic states at different molecular structures  

CERN Document Server

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

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

2010-01-01

188

Molecular Electronics with Quantum-dot Cellular Automata  

Science.gov (United States)

We are investigating a way of using coupled quantum cells to construct digital computing elements. The Quantum-dot Cellular Automata (QCA) approach uses cells composed of a few "dots" among which electrons may tunnel. No tunneling occurs between cells. These ideas have been implemented in metallic and semiconductor systems, where one often considers the cells as artificial molecules. We are now investigating the possibilities of using actual molecules to implement this scheme. The potential advantages of a truly molecular approach are considerable: chemical self-assembly of units, high-temperature operation, remarkable packing densities. The QCA approach offers the advantages of supporting general-purpose computing, very low power dissipation, and true signal gain. Specific molecular implementations currently being explored will be discussed.

Lent, Craig S.

2000-03-01

189

Electronic correlations in oligo-thiophene molecular crystals  

Energy Technology Data Exchange (ETDEWEB)

The Coulomb interaction between two holes on oligo-thiophene molecules is studied systematically as a function of the oligomer length using first principles density function calculations. The effect of molecular geometry relaxation upon this interaction is found to be small. In contrast, electronic polarization of the molecules that surround the charged oligomer in the crystal lattice reduces the bare Coulomb repulsion between the holes by approximately a factor of 2. In all cases, the effective hole-hole repulsion is much larger than the valence band width, which means that at high doping levels, strong correlation effects should become important.

Brink, Jeroen van den [Institute-Lorentz for Theoretical Physics, Universiteit Leiden, P.O. Box 9506, 2300 RA Leiden (Netherlands)]. E-mail: brink@ilorentz.org; Brocks, Geert [Faculty of Applied Science and MESA Research Institute, University of Twente, P.O. Box 217, 7500 AE Enschede (Netherlands); Morpurgo, Alberto F. [Department of Applied Physics, Delft University of Technology, Delft (Netherlands)

2005-04-15

190

Molecular structure of bromotrichloromethane as determined by gas electron diffraction  

Energy Technology Data Exchange (ETDEWEB)

The molecular structure of CBrCl/sub 3/ has been determined by gas electron diffraction to be as follows: r sub(g)(C-Cl) = 1.765/sub 4/(1/sub 7/) A, r sub(g)(C-Br) = 1.944(4) A, and

Konaka, S.; Yamagata, K.; Kimura, M. (Hokkaido Univ., Sapporo (Japan). Faculty of Science)

1981-08-01

191

Models of Electrodes and Contacts in Molecular Electronics  

CERN Document Server

In an effort to bridge the difference in atomic structure between experiments and theoretical calculations in molecular electronics, and to explore quantum confinement effects in thin electrodes (leads), we report here, by using Au-benzenedithiol-Au as a model system, systematic investigations of different models for the leads and the lead-molecule contacts: leads with different cross sections, leads consisting of infinite surfaces, and surface leads with a local nanowire or atomic chain of different lengths. The method adopted is a non-equilibrium Green function method combined with density functional theory calculations for the electronic structure and transport, in which the leads and molecule are treated on the same footing. It is shown that leads with a small cross section will lead to large oscillations in the transmission function, T(E), which depend significantly on the lead structure (orientation) because of quantum waveguide effects. This oscillation slowly decays along with the increase of the lead...

Ke, S H; Yang, W; Ke, San-Huang; Baranger, Harold U.; Yang, Weitao

2005-01-01

192

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)

193

IV. Dissociative recombination of electrons and molecular ions  

International Nuclear Information System (INIS)

The present state of the theory of the dissociative recombination of electrons and molecular ions is reviewed and its shortcomings shown. The mechanisms of direct and indirect dissociative processes are described. Several approximative methods employing the analogy with the recombination of atomic ions and electrons are used for the determination of the dissociative recombination factor. Analyzing the derived formulae the temperature dependence of the dissociative recombination factor is determined and the results are compared with experimental data obtained by several authors. The energy levels of atoms created at the dissociative recombination of He2+, Ar2+, and O2+ ions are described. Methods of measuring the recombination factor are listed. The existing experimental data are summarized and the possible explanation of the observed variations is presented. An exhaustive list of references is given. (J.U.)

194

Molecular Electronics: Insight from First-Principles Transport Simulations  

DEFF Research Database (Denmark)

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

Paulsson, Magnus; Frederiksen, Thomas

2010-01-01

195

Attachment of very slow electrons to molecules and molecular clusters  

International Nuclear Information System (INIS)

Using a novel laser photoelectron attachment (LPA) method Klar et al. recently investigated free electron attachment processes with an effective resolution around 0.2 meV and demonstrated that the limiting E-1/2 dependence is only reached at very low energies (? 1 meV); moreover, they detected cusp-structure at onsets for vibrational excitation. In the present paper we describe efforts in this direction by applying the LPA method to studies of some molecular cluster systems. We performed experiments for the cluster targets SF6, CO2, N2O, O2 and a mixture of O2 with H2O and found three different types of behaviour for electron attachment near threshold. (author)

196

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

197

Fast electronic structure methods for strongly correlated molecular systems  

International Nuclear Information System (INIS)

A short review is given of newly developed fast electronic structure methods that are designed to treat molecular systems with strong electron correlations, such as diradicaloid molecules, for which standard electronic structure methods such as density functional theory are inadequate. These new local correlation methods are based on coupled cluster theory within a perfect pairing active space, containing either a linear or quadratic number of pair correlation amplitudes, to yield the perfect pairing (PP) and imperfect pairing (IP) models. This reduces the scaling of the coupled cluster iterations to no worse than cubic, relative to the sixth power dependence of the usual (untruncated) coupled cluster doubles model. A second order perturbation correction, PP(2), to treat the neglected (weaker) correlations is formulated for the PP model. To ensure minimal prefactors, in addition to favorable size-scaling, highly efficient implementations of PP, IP and PP(2) have been completed, using auxiliary basis expansions. This yields speedups of almost an order of magnitude over the best alternatives using 4-center 2-electron integrals. A short discussion of the scope of accessible chemical applications is given

198

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.)

199

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

Science.gov (United States)

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

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

2010-07-27

200

Synthesis of one-dimensional metal-containing insulated molecular wire with versatile properties directed toward molecular electronics materials.  

Science.gov (United States)

We report, herein, the design, synthesis, and properties of new materials directed toward molecular electronics. A transition metal-containing insulated molecular wire was synthesized through the coordination polymerization of a Ru(II) porphyrin with an insulated bridging ligand of well-defined structure. The wire displayed not only high linearity and rigidity, but also high intramolecular charge mobility. Owing to the unique properties of the coordination bond, the interconversion between the monomer and polymer states was realized under a carbon monoxide atmosphere or UV irradiation. The results demonstrated a high potential of the metal-containing insulated molecular wire for applications in molecular electronics. PMID:24428791

Masai, Hiroshi; Terao, Jun; Seki, Shu; Nakashima, Shigeto; Kiguchi, Manabu; Okoshi, Kento; Fujihara, Tetsuaki; Tsuji, Yasushi

2014-02-01

 
 
 
 
201

Electronic stopping power from ab-initio Ehrenfest molecular dynamics  

Science.gov (United States)

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

Schleife, Andre; Kanai, Yosuke; Correa, Alfredo

2013-03-01

202

Electron-Impact Dissociation of Hydrocarbon Molecular Ions  

International Nuclear Information System (INIS)

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

203

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Castellanos Ortega, Sonia

2010-01-01

204

Rovibronic energy levels for triplet electronic states of molecular deuterium  

CERN Document Server

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

Lavrov, B P

2007-01-01

205

Electronic damping of molecular motion at metal surfaces  

CERN Document Server

A method for the calculation of the damping rate due to electron-hole pair excitation for atomic and molecular motion at metal surfaces is presented. The theoretical basis is provided by Time Dependent Density Functional Theory (TDDFT) in the quasi-static limit and calculations are performed within a standard plane-wave, pseudopotential framework. The artificial periodicity introduced by using a super-cell geometry is removed to derive results for the motion of an isolated atom or molecule, rather than for the coherent motion of an ordered over-layer. The algorithm is implemented in parallel, distributed across both ${\\bf k}$ and ${\\bf g}$ space, and in a form compatible with the CASTEP code. Test results for the damping of the motion of hydrogen atoms above the Cu(111) surface are presented.

Trail, J R; Bird, D M

2009-01-01

206

Electron bombardment fragmentation of size selected molecular clusters  

International Nuclear Information System (INIS)

(CO2)n, (NO)n and (NH3)n clusters are generated in a supersonic molecular beam and size selected by scattering from an He beam. By measurements of angular dependent mass spectra, TOF distributions and the angular dependence of the scattered signal quantitative information on the fragmentation probability by electron impact is derived. The van der Waals systems (CO2)n and (NO)n appear only at masses which are simply multiples of the monomer mass. The preferred cluster ion is the monomer ion for all investigated cluster sizes with n=2 to 4. The fragment pattern for the quasi-hydrogen bonded (NH3)n-cluster shows, beside a large number of fragment masses, a preference for protonated ions. The results are explained in terms of simple models based on the structural change from the neutral to the ionized configuration and the fragmentation pattern of the monomer followed by ion-molecule reactions. (orig.)

207

High hopes: can molecular electronics realise its potential?  

Science.gov (United States)

Manipulating and controlling the self-organisation of small collections of molecules, as an alternative to investigating individual molecules, has motivated researchers bent on processing and storing information in molecular electronic devices (MEDs). Although numerous ingenious examples of single-molecule devices have provided fundamental insights into their molecular electronic properties, MEDs incorporating hundreds to thousands of molecules trapped between wires in two-dimensional arrays within crossbar architectures offer a glimmer of hope for molecular memory applications. In this critical review, we focus attention on the collective behaviour of switchable mechanically interlocked molecules (MIMs)--specifically, bistable rotaxanes and catenanes--which exhibit reset lifetimes between their ON and OFF states ranging from seconds in solution to hours in crossbar devices. When these switchable MIMs are introduced into high viscosity polymer matrices, or self-assembled as monolayers onto metal surfaces, both in the form of nanoparticles and flat electrodes, or organised as tightly packed islands of hundreds and thousands of molecules sandwiched between two electrodes, the thermodynamics which characterise their switching remain approximately constant while the kinetics associated with their reset follow an intuitively predictable trend--that is, fast when they are free in solution and sluggish when they are constrained within closely packed monolayers. The importance of seamless interactions and constant feedback between the makers, the measurers and the modellers in establishing the structure-property relationships in these integrated functioning systems cannot be stressed enough as rationalising the many different factors that impact device performance becomes more and more demanding. The choice of electrodes, as well as the self-organised superstructures of the monolayers of switchable MIMs employed in the molecular switch tunnel junctions (MSTJs) associated with the crossbars of these MEDs, have a profound influence on device operation and performance. It is now clear, after much investigation, that a distinction should be drawn between two types of switching that can be elicited from MSTJs. One affords small ON/OFF ratios and is a direct consequence of the switching in bistable MIMs that leads to a relatively small remnant molecular signature--an activated chemical process. The other leads to a very much larger signature and ON/OFF ratios resulting from physical or chemical changes in the electrodes themselves. Control experiments with various compounds, including degenerate catenanes and free dumbbells, which cannot and do not switch, are crucial in establishing the authenticity of the small ON/OFF ratios and remnant molecular signatures produced by bistable MIMs. Moreover, experiments conducted on monolayers in MSTJs of molecules designed to switch and molecules designed not to switch have been probed directly by spectroscopic and other means in support of MEDs that store information through switching collections of bistable MIMs contained in arrays of MSTJs. In the quest for the next generation of MEDs, it is likely that monolayers of bistable MIMs will be replaced by robust crystalline extended structures wherein the switchable components, derived from bistable MIMs, are organised precisely in a periodic manner. PMID:22648395

Coskun, Ali; Spruell, Jason M; Barin, Gokhan; Dichtel, William R; Flood, Amar H; Botros, Youssry Y; Stoddart, J Fraser

2012-07-21

208

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

International Nuclear Information System (INIS)

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

209

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

210

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

International Nuclear Information System (INIS)

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

211

Rectification of energy transport in nonlinear metamaterials via ratchets  

International Nuclear Information System (INIS)

The presence of discrete breathers (DBs) has already been described in nonlinear photonic materials, such as ferroelectrics and metamaterials (MMs) by the Klein–Gordon (K–G) approach. Rectification of energy transport in MMs in the presence of an appropriate external field is studied via symmetry breaking leading to directed energy transport or ratchet behaviour. Based on the earlier development of the K–G equation in a MM system with a split-ring resonator for antenna applications, a theoretical model for current density is worked out by symmetry analysis and its violation to characterize the ratchet effect. The time-averaged current shows interesting results against phase shift in the ac driver. These data are further related to various parameters, such as coupling and damping in the system. For MMs, this opens a new application for rectification using ratchets. (paper)

212

Rectification of the OPAL Cold Neutron Source Cryogenic System  

Energy Technology Data Exchange (ETDEWEB)

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.

Lu, Weijian [Australian Nuclear Science and Technology Organisation, Sydney (Australia)

2013-07-01

213

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

214

Rectification of thermal fluctuations in a chaotic cavity heat engine  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We investigate the rectification of thermal fluctuations in a mesoscopic on-chip heat engine. The engine consists of a hot chaotic cavity capacitively coupled to a cold cavity which rectifies the excess noise and generates a directed current. The fluctuation-induced directed current depends on the energy asymmetry of the transmissions of the contacts of the cold cavity to the leads and is proportional to the temperature difference. We discuss the maximal power output of the ...

Sothmann, Bjo?rn; Sa?nchez, Rafael; Jordan, Andrew N.; Bu?ttiker, Markus

2012-01-01

215

Suppression of rectification at metal-Mott-insulator interfaces  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

216

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)

217

Ionic fragmentation channels in electron collisions of small molecular ions  

International Nuclear Information System (INIS)

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

218

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

International Nuclear Information System (INIS)

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

219

Origin of rectification in boron nitride heterojunctions to silicon.  

Science.gov (United States)

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

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

2013-04-10

220

Reconciling expressions for terahertz generation by bulk optical rectification  

Science.gov (United States)

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

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

2010-06-01

 
 
 
 
221

Rectification of the EMG Signal Impairs the Identification of Oscillatory Input to the Muscle  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Rectification of EMG signals is a common processing step used when performing electroencephalographic–electromyographic (EEG–EMG) coherence and EMG–EMG coherence. It is well known, however, that EMG rectification alters the power spectrum of the recorded EMG signal (interference EMG). The purpose of this study was to determine whether rectification of the EMG signal influences the capability of capturing the oscillatory input to a single EMG signal and the common oscillations between tw...

Neto, Osmar Pinto; Christou, Evangelos A.

2010-01-01

222

Air-pressure tunable depletion width, rectification behavior, and charge conduction in oxide nanotubes.  

Science.gov (United States)

Metal-oxide nanotubes provide large surface areas and functionalizable surfaces for a variety of optical and electronic applications. Here we report air-tunable rectifying behavior, depletion width modulation, and two-dimensional (2D) charge conduction in hollow titanium-dioxide nanotubes. The metal contact forms a Schottky-diode in the nanotubes, and the rectification factor (on/off ratio) can be varied by more than 3 orders of magnitude (1-2 × 10(3)) as the air pressure is increased from 2 mTorr to atmospheric pressure. This behavior is explained using a change in depletion width of these thin nanotubes by adsorption of water vapor on both surfaces of a hollow nanotube, and the resulting formation of a metal-insulator-semiconductor (MIS) junction, which controls the 2D charge conduction properties in thin oxide nanotubes. PMID:25594471

Alivov, Yahya; Funke, Hans H; Singh, Vivek; Nagpal, Prashant

2015-02-01

223

THz Generation by Optical Rectification and Competition with Other Nonlinear Processes  

International Nuclear Information System (INIS)

We present a study of the competition between tera-hertz (THz) generation by optical rectification in (110) ZnTe crystals, two-photon absorption, second harmonic generation and free-carrier absorption. The two-photon nonlinear absorption coefficient, second harmonic generation efficiency and free-carrier absorption coefficient in the THz range are measured independently The incident pump field is shown to be depleted by two-photon absorption and the THz radiation is shown to be reduced, upon focusing, by free-carrier absorption. The reduction of the generated THz radiation upon tight focusing is explained, provided that one also takes into account diffraction effects from the sub-wavelength THz source. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

224

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

International Nuclear Information System (INIS)

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

225

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.

226

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

Energy Technology Data Exchange (ETDEWEB)

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 10{sup 4} in M2.

Zhao, P., E-mail: ss_zhaop@ujn.edu.cn [School of Physics and Technology, 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); Li, S.J. [School of Physics and Technology, University of Jinan, Jinan 250022 (China); Chen, G., E-mail: ss_cheng@ujn.edu.cn [School of Physics and Technology, University of Jinan, Jinan 250022 (China)

2013-06-17

227

Electronic structure of the N4+ molecular ion  

International Nuclear Information System (INIS)

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

228

Inelastic Scattering of Low-Energy Electrons by Molecular Oxygen  

Science.gov (United States)

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

Sweeney, Christopher John

1995-01-01

229

Contacting single molecules to metallic electrodes by scanning tunnelling microscope manipulation: model systems for molecular electronics  

International Nuclear Information System (INIS)

The electronic contact between a molecular wire and a metallic electrode will play an important role in future molecular electronics as its properties determine the conductivity of the molecule-metal system. Scanning tunnelling microscopy manipulation reveals various advantages for the investigation of electronic contacts at the atomic scale. In this review, several examples of molecular wire-electrode systems are presented, where single molecules are placed in contact in a controlled way. Changed chemical structures of the molecule and, on the other hand, different shapes and dimensions of electrodes lead to a variety of contact configurations. The contact can be characterized using the additional contribution to the tunnelling current, but also using the influence on the electronic states of the electrode and the molecule. The quality of the contact is discussed in terms of the vertical distance between the molecular wire and the metal atoms and of the chemical composition of the molecular end group

230

Rectification of aerial images using piecewise linear transformation  

Science.gov (United States)

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

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

2014-02-01

231

Simulation Aspects in the Study of Rectification of Satellite Scanner Data  

Science.gov (United States)

Complete sensor/platform modelling is derived and used for the generation of synthetic data and for rectification studies of satellite scanner data. All satellite position and sensor attitude parameters are recovered. Rectification accuracy improves marginally when using more than 25 control points, and is highly sensitive to errors in image point identification.

Mikhail, E. M.; Paderes, F. C., Jr.

1983-01-01

232

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

233

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. PMID:25554319

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

2014-12-01

234

Geometrical rectification of spin-scan images from Pioneer 11  

Science.gov (United States)

Images of Saturn received from Pioneer 11 suffer from geometrical distortions due to the curvilinear scan lines and the unequal sampling intervals in orthogonal directions, which are inherent in spin-scan imaging. In this paper geometrical image rectification by polynomial transformation based on control points is discussed. Factors that affect the accuracy of reconstruction are shown to include the spatial distribution and spatial density of control points, and the order of the polynomial distortion model. A computer implementation of the technique is described.

Strickland, R. N.; Burke, J. J.

1980-01-01

235

Silicon nanowires and silicon/molecular interfaces for nanoscale electronics  

Science.gov (United States)

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

Sheriff, Bonnie Ann

236

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

237

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.

238

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

Energy Technology Data Exchange (ETDEWEB)

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.

Gupta, S.K., E-mail: drgupta@barc.gov.in [Technical Physics and Prototype Engineering Division, Bhabha Atomic Research Centre, Mumbai 400085 (India); Koiry, S.P.; Chauhan, A.K.; Padma, N.; Aswal, D.K.; Yakhmi, J.V. [Technical Physics and Prototype Engineering Division, Bhabha Atomic Research Centre, Mumbai 400085 (India)

2009-10-30

239

Study on hydrodynamics and kinetics of cesium and rubidium rectification in filled column  

International Nuclear Information System (INIS)

Some hydrodynamic and mass exchange characteristics of cesium and rubidium rectification in field column are studied. For the experiments cesium with 2.4-3.2 weight % rubidium, rubidium with 0.3-0.7 % cesium and rubidium with 0.1-0.2 % cesium and 10-12 % potassium admixtures have been taken. The main hydraulic and mass exchange characteristics of the field column during cesium and rubidium rectification are determined. The rectification process of heavy alkaline metals does not have any principal differences from rectification of standard systems at moderate temperatures. During rectification of rubidium with an admixture of cesium the maximum separation degree can be achieved in the pressure range of 100-200 mm Hg

240

Enhanced electron attachment to laser-irradiated molecular hydrogen  

International Nuclear Information System (INIS)

Efficient H- formation in laser-irradiated hydrogen is reported. The electrons produced by laser photoionization are converted to negative ions via dissociative electron attachment. The observed H- signal is more than two orders of magnitude larger than the maximum possible H- signal that can be expected via electron attachment of high-vibrational states of the ground electronic state that may be indirectly populated. Dissociative electron attachment to superexcited states is proposed as a possible mechanism

 
 
 
 
241

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

International Nuclear Information System (INIS)

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

242

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

CERN Document Server

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

Butkus, Vytautas; Abramavicius, Darius

2012-01-01

243

Synthesis of Single Wall Carbon Nanotube Arrays and Their Application in Single Molecular electronics  

Science.gov (United States)

Molecular electronics utilize molecular as building blocks to fabricate electronic components. Due to the advantage of its size, molecular electronics has been an attractive candidate for future electronics for a long time. However, there are major challenges to be solved before single molecular electronic device could be used widely. One of these challenges is the lack of high yield, low cost fabrication technique. Carbon nanotubes are new materials with great electronic conductivity and small diameter, etc. They are great candidate for the electrode of single molecular electronic devices. A great effort of this thesis has been devoted into the chemical vapor deposition (CVD) synthesis of carbon nanotube, especially the surface aligned carbon nanotube array on miscut quartz surface. A state of art recipe to synthesize carbon nanotube array on quartz with promising cleanliness, density, alignment and nanotube length has been developed. Two novel fabrication processes were proposed and tested to fabricate electrode for single molecule electronic devices with carbon nanotube array. In addition, a fabrication process to create large amount of identical length of carbon nanotubes was introduced and studied.

Shan, Yuyao

244

Electronic and Molecular Surface Structures of Dye-Sensitized TiO2 Interfaces  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The dye-sensitized solar cell is a promising solar cell technology. In these systems the key process for light to electricity conversion is molecular in nature and is initiated in dye molecules adsorbed at a semiconducting surface. This thesis focuses on the electronic and molecular surface structure of the dye/TiO2 interface, and the experimental results were obtained from surface sensitive X-ray based electron spectroscopic methods. Two families of dyes, triarylamine based organic dyes and ...

Hahlin, Maria

2010-01-01

245

Alignment of beam-foil excited fast (MeV) molecular ions from defined electronic configuration  

International Nuclear Information System (INIS)

Collisions at MeV energies of molecular, heavy ions with gaseous and with solid matter are used to create highly excited and highly ionized collision partners. After the collision the molecular, heavy ions separate via Coulomb explosion. They impose their kinematics to both the molecular fragments and to the Auger electrons emitted from the excited fragments. The angular distribution of the Auger line-shape yields information on directional effects of specific configurations of the system. (author)

246

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

International Nuclear Information System (INIS)

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

247

Electron irradiation reduction of the molecular weight of nitrocellulose  

International Nuclear Information System (INIS)

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

248

Quantum Entanglement and Electron Correlation in Molecular Systems  

CERN Document Server

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. As an example we show the calculations of entanglement for the H$_2$ molecule and how it is related to electron correlation of the system, which is the difference between the exact and the HF energies.

Wang, H; Kais, Sabre; Wang, Hefeng

2007-01-01

249

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

CERN Document Server

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

Krzeminski, Christophe; Allan, Guy; 10.1021/jp011263y

2011-01-01

250

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

251

Quasi-null release of radioactive gases from nuclear power plants achieved by low temperature rectification  

International Nuclear Information System (INIS)

The conventional waste gas processing facilities of nuclear power stations cannot ensure complete retention of the activities contained in the waste gas. The residual activity is governed by Kr85 and C14 because of their long half-lives. Waste gas processing facilities with low temperature rectification make it possible to retain both Kr85 and the much smaller quantities of C14 which occurs mainly in the form of CO2. The CO2 is frozen out in the process of cooling the waste gas flow down to the rectification temperature, and the krypton is separated out in the rectification column together with xenon. (orig.)

252

Theoretical study of donor-spacer-acceptor structure molecule for use as stable molecular rectifier: geometric and electronic structures  

International Nuclear Information System (INIS)

Recently, molecular electronics has attracted much attention as a 'post-silicon technology' for future nanoscale electronic devices. One of the most important elements in molecular electronic devices is the realization of a unimolecular rectifier. In the present study, the geometric and electronic structure of the TTF-derivative (donor)-sigma-bond-TCNQ-derivative (acceptor), a leading candidate for a molecular rectifying device has been investigated theoretically using ab initio quantum mechanical calculations

253

Bending of conjugated molecular wires and its effect on electron conduction properties  

Science.gov (United States)

The electronic structure and electron transport properties of simple conjugated molecular wires like oligophenylene ethynylene (OPE) and oligophenylene vinylene (OPV) are studied under compression. If artificially confined to a given shorter length, the oligomers tend to bend and bending causes a loss in the overlap of the conjugated molecular orbitals. Theoretical modeling of electronic transport has been carried out for all undistorted and compressed OPE/OPV oligomers. OPV exists in step-like or V-like conformations and they have the same stability with very similar frontier molecular orbitals. The conductances of these molecular wires are calculated when inserted between two gold probes and the conductances for OPV are found to be comparable to OPE when the interfaces are same. The conductance decreases with bending due to the gradual loss in overlap of the molecular orbitals. It is also found that the conductances of the molecular wires decrease very strongly if the terminal sulfur atom is simultaneously bonded to hydrogen and a gold surface, thus reflecting the importance of the interface in determining the conductance in two-probe systems. From the conductance studies it may be concluded that if one or more benzene rings of OPE are rotated from coplanar conditions, the orthogonal molecular orbitals may completely block the electronic transport, rendering the molecule insulating.

Das, Bidisa

2010-10-01

254

Bending of conjugated molecular wires and its effect on electron conduction properties  

International Nuclear Information System (INIS)

The electronic structure and electron transport properties of simple conjugated molecular wires like oligophenylene ethynylene (OPE) and oligophenylene vinylene (OPV) are studied under compression. If artificially confined to a given shorter length, the oligomers tend to bend and bending causes a loss in the overlap of the conjugated molecular orbitals. Theoretical modeling of electronic transport has been carried out for all undistorted and compressed OPE/OPV oligomers. OPV exists in step-like or V-like conformations and they have the same stability with very similar frontier molecular orbitals. The conductances of these molecular wires are calculated when inserted between two gold probes and the conductances for OPV are found to be comparable to OPE when the interfaces are same. The conductance decreases with bending due to the gradual loss in overlap of the molecular orbitals. It is also found that the conductances of the molecular wires decrease very strongly if the terminal sulfur atom is simultaneously bonded to hydrogen and a gold surface, thus reflecting the importance of the interface in determining the conductance in two-probe systems. From the conductance studies it may be concluded that if one or more benzene rings of OPE are rotated from coplanar conditions, the orthogonal molecular orbitals may completely block the electronic transport, rendering the molecule insulating.

255

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

Science.gov (United States)

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

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

2012-02-01

256

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

257

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

258

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

CERN Document Server

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

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

2011-01-01

259

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)

260

Maximal rectification ratios for bi-segment thermal rectifiers  

CERN Document Server

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

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

2014-01-01

 
 
 
 
261

Intense terahertz pulses by four-wave rectification in air.  

Science.gov (United States)

We describe a new four-wave rectification method for the generation of intense, ultrafast terahertz (THz) pulses from gases. The fundamental and second-harmonic output of an amplified Ti:sapphire laser is focused to a peak intensity of ~5x10(14)W/cm (2) . Under these conditions, peak THz fields estimated at 2 kV/cm have been observed; the measured power spectrum peaks near 2 THz. Phase-dependent measurements show that this is a coherent process and is sensitive to the relative phases of the fundamental and second-harmonic pulses. Comparable THz signals have been observed from nitrogen and argon as well as from air. PMID:18066171

Cook, D J; Hochstrasser, R M

2000-08-15

262

Molecular dynamics study of electron-irradiation effects in single-walled carbon nanotubes  

International Nuclear Information System (INIS)

Molecular dynamics studies are carried out to investigate electron-irradiation effects in single-walled carbon nanotubes. We have proposed a simulation model which includes the interaction between a high-energy incident electron and a carbon atom, based on Monte Carlo method using the elastic-scattering cross section. The atomic level behavior of a single-walled carbon nanotube under electron irradiation is demonstrated in nanosecond time scale. The incident electron energy, tube diameter, and tube temperature dependences of electron-irradiation effects are studied with the simulation

263

Coherent charge transport through molecular wires: "Exciton blocking" and current from electronic excitations in the wire  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We consider exciton effects on current in molecular nanojunctions, using a model comprising a two two-level sites bridge connecting free electron reservoirs. Expanding the density operator in the many-electron eigenstates of the uncoupled sites, we obtain a 16X16 density matrix in the bridge subspace whose dynamics is governed by Liuoville equation that takes into account interactions on the bridge as well as electron injection and damping to and from the leads. Our consider...

Li, Guangqi; Fainberg, Boris D.; Nitzan, Abraham; Kohler, Sigmund; Ha?nggi, Peter

2009-01-01

264

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

265

A Quantum of Solace: molecular electronics of benzodiazepines  

Science.gov (United States)

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

Turin, Luca; Horsfield, Andrew; Stoneham, Marshall

2011-03-01

266

Laser-assisted electron diffraction for femtosecond molecular imaging  

International Nuclear Information System (INIS)

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

267

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

268

Molecular structure and conformational composition of methyl chloroacetate:An electron-diffraction and ab initio molecular orbital investigation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The molecular structure and conformational composition of methyl chloroacetate, H2ClCC(O)OCH3, have been determined by gas-phase electron-diffraction (GED), using results from ab initio molecular orbital calculations (HF, MP2 and MP3/6-311+G(d,p)) to obtain constraints on some of the structural parameters. The molecules exist in the gas-phase at 25 °C as a mixture of two stable conformers: syn with CCl eclipsing CO and gauche with CH approximately eclipsing CO. In both of these conformers OC...

Aarset, Kirsten; Boldermo, Kjell Gunnar; Hagen, Kolbjørn

2010-01-01

269

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

270

Effect of CO adsorption on the electron transport behavior of single Fe-porphyrin molecular wire  

Science.gov (United States)

The effect of CO adsorption on the electron transport behavior of single Fe-porphyrin molecular wire with sulfur end groups bonded to two gold (1 1 1) electrodes is investigated using nonequilibrium Green's function formalism combined with first-principles density functional theory. The current-voltage characteristics of the single Fe-porphyrin molecular wires with and without CO adsorption are calculated. The results demonstrate that Fe-porphyrin molecular wire shows a negative differential resistance (NDR) at 2.0 V. The molecular current through Fe-porphyrin is significantly reduced after CO adsorption. Such a significant difference indicates the potential application of Fe-porphyrin as a molecular sensor and/or a molecular switch. The molecular projected self-consistent Hamiltonian (MPSH) states and transmission coefficients of the single Fe-porphyrin molecular wires with and without CO adsorption are analyzed. It is found that the changes of the MPSH states of the single Fe-porphyrin molecular wires with and without CO adsorption lead to the switching behavior. Furthermore, the transmission coefficients of the single Fe-porphyrin molecular wires with and without CO adsorption under various external voltages are also investigated. The results show that the transmissions through the highest occupied MPSH and the lowest unoccupied MPSH states of the single Fe-porphyrin molecular wire are suppressed significantly at this external voltage of 2.0 V, which causes the NDR.

Li, Y. W.; Yin, Z. L.; Yao, J. H.; Deng, X. S.; Yang, C. L.

2010-11-01

271

Multiple-electron removal and molecular fragmentation of CO by fast F4+ impact  

Science.gov (United States)

Multiple-electron removal from and molecular fragmentation of carbon monoxide molecules caused by collisions with 1-MeV/amu F4+ ions were studied using the coincidence time-of-flight technique. In these collisions, multiple-electron removal of the target molecule is a dominant process. Cross sections for the different levels of ionization of the CO molecule during the collision were determined. The relative cross sections of ionization decrease with increasing number of electrons removed in a similar way as seen in atomic targets. This behavior is in agreement with a two-step mechanism, where first the molecule is ionized by a Franck-Condon ionization and then the molecular ion dissociates. Most of the highly charged intermediate states of the molecule dissociate rapidly. Only CO+ and CO2+ molecular ions have been seen to survive long enough to be detected as molecular ions. The relative cross sections for the different breakup channels were evaluated for collisions in which the molecule broke into two charged fragments as well as for collisions where only a single charged molecular ion or fragment were produced. The average charge state of each fragment resulting from COQ+-->Ci++Oj+ breakup increases with the number of electrons removed from the molecule approximately following the relationship i¯=j¯=Q/2 as long as K-shell electrons are not removed. This does not mean that the charge-state distribution is exactly symmetric, as, in general, removing electrons from the carbon fragment is slightly more likely than removing electrons from the oxygen due to the difference in binding energy. The cross sections for molecular breakup into a charged fragment and a neutral fragment drop rapidly with an increasing number of electrons removed.

Ben-Itzhak, I.; Ginther, S. G.; Carnes, K. D.

1993-04-01

272

Computational investigations of the electronic structure of molecular actinide compounds  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this PhD thesis the electronic structure of a range of actinide compounds has been investigated using density functional theory. The reason for using DFT instead of other methods is mainly due to the size of the compounds which makes multireference calculations prohibitively expensive, but also to make comparisons with previously calculated DFT results. The first chapter presents the basic concepts of electronic structure theory and the chemical properties of the actinides and lanthani...

Jonasson, L.

2009-01-01

273

Porphyrins as Molecular Electronic Components of Functional Devices  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2010-01-01

274

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

275

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

International Nuclear Information System (INIS)

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

276

Bioconjugation-induced ionic current rectification in aptamer-modified single cylindrical nanopores.  

Science.gov (United States)

Aptamer-protein conjugation inside a confined environment generates a non-homogeneous fixed charge distribution, leading to the emergence of ionic current rectification characteristics in single cylindrical nanopores. PMID:25627437

Ali, Mubarak; Nasir, Saima; Ensinger, Wolfgang

2015-02-10

277

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

278

Molden: a pre- and post-processing program for molecular and electronic structures.  

Science.gov (United States)

Molden is a software package for pre- and postprocessing of computational chemistry program data. Interfacing to the ab initio programs Games-US/UK and Gaussian and to the semi-empirical package MOPAC is provided. The emphasis is on computation and visualization of electronic and molecular properties but, e.g., reaction pathways can be simulated as well. Some molecular properties of interest are processed directly from the output of the computational chemistry programs, others are calculated in MOLDEN before display. The package features different options to display MOLecular electronic DENsity, each focusing on a different structural aspect: molecular orbitals, electron density, molecular minus atomic density and the Laplacian of the electron density. To display difference density, either the spherically averaged atomic density or the oriented ground state atomic density can be used for a number of standard basis sets. The quantum mechanical electrostatic potential or a distributed multiple expansion derived electrostatic potential can be calculated and atomic charges can be fitted to these potentials calculated on Connolly surface(s). Reaction pathways and molecular vibrations can be visualized. Input structures can be generated with a Z-matrix editor. A variety of graphics languages is supported: XWindows, postscript, VRML and Povray format. PMID:10721501

Schaftenaar, G; Noordik, J H

2000-02-01

279

Recent advances in molecular electronics based on carbon nanotubes.  

Science.gov (United States)

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

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

2010-01-01

280

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

Eucalyptus saligna and Pinus caribaea var. hondurensis woods underwent a variety of thermal rectification treatments (from 120ºC to 180ºC) to evaluate the effect of heating on their colorimetric properties. The following color parameters were measured: lightness (L), a* coordinate (green-red coordinate), b* coordinate (blue-yellow coordinate), saturation (C), and tonality angle (H). This study demonstrates that thermal rectification can be regarded as a tool for adding value to wood through...

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

2012-01-01

 
 
 
 
281

Size effects on thermal rectification in mass-graded anharmonic lattices  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this work we study the thermal rectification efficiency of a one-dimensional mass-graded anharmonic oscillator lattice at large system sizes. A modest increase in rectification is observed. When the magnitude of the mass gradient scales with the system size, the aforementioned effect increases substantially. This result can be unmistakeably attributed to an asymmetry in the local temperature profile obtained for the employed parameter values.

Romero-bastida, M.; Gonzalez-alarcon, Armando

2014-01-01

282

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Vandenberg, C. A.

1987-01-01

283

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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, {\\it et al.}, Nucl. Instr. Meth. B {\\bf 184}, 337 (2001); Z. Siwy, {\\it et al.}, Europhys. Lett. {\\bf 60}, 349 (2002)]. Here, the ion current rectification is studied within a reduced 1D Poisson-Nern...

Kosin?ska, I. D.; Goychuk, I.; Kostur, M.; Schmid, G.; Ha?nggi, P.

2007-01-01

284

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

285

Electronic energy loss of slow projectiles evaluated by molecular orbital theory  

International Nuclear Information System (INIS)

Based on the Firsov model of electronic excitations in slow atomic collisions, a method for calculations of the electronic energy loss is proposed. In this method, molecular orbital theory is employed in order to obtain the electronic excitation probability of a quasi-molecule between colliding atoms. By this method, the electronic stopping power has been calculated for the case of the Li-B and Li-Ta collision pairs. Using this calculated electronic stopping power, molecular dynamics simulations have been performed in order to analyze the energy loss observed in a recent experiment, in which 1-keV Li+ ions were scattered from a TaB2 (0 0 0 1) surface. These experimental observations are well explained by this theory

286

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

Science.gov (United States)

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

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

2004-06-01

287

Molecular and electronic structure of TiH2  

Science.gov (United States)

Ab initio electronic structure calculations using correlated wave functions have been performed to investigate the structure and energetics of TiH2 in its low-lying electronic states. Several triplet states have been found to lie very close to each other in energy (within 5 kcal/mol) and nearly 1 eV below the lowest singlet state. The lowest quintet states appear to be considerably higher in energy. The ground state of TiH2 is found to be bent 3B1 in C2v symmetry, with the 3A1 state lying only 1 kcal/mol higher in energy. The lowest singlet state, 1A1, is found to be slightly bent, but with a very flat potential energy surface. The Ti-H bond in all TiH2 electronic states is predicted to be strongly polarized Ti+H-. The use of state-averaged multiconfigurational self-consistent field wave functions is essential to obtain a consistent picture of all electronic states of interest.

Kudo, Takako; Gordon, Mark S.

1995-05-01

288

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

International Nuclear Information System (INIS)

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

289

Current hysteresis and memory effect in a molecular quantum dot with strong electron-vibron interaction  

CERN Document Server

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

Alexandrov, A S

2002-01-01

290

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

Science.gov (United States)

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

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

2014-09-01

291

Coupled electron-phonon transport from molecular dynamics with quantum baths  

DEFF Research Database (Denmark)

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

Lu, Jing Tao; Wang, J. S.

2009-01-01

292

The molecular structure of niobium pentachloride by quantum chemical calculations and gas electron diffraction  

Science.gov (United States)

The molecular structure of NbCl 5 was determined experimentally by gas electron diffraction and computationally by structure optimisation of D 3h models. The bond distances obtained by ab initio calculations with very large basis sets, relativistic effects included through the one-electron Douglas-Kroll method and all electrons correlated at the MP2 level and by gas electron diffraction are: (calc/exp) Nb-Cl ax=230.7/230.6(5) pm and Nb-Cl eq=227.0/227.5(4) pm.

Gove, S. K.; Gropen, O.; Fægri, K.; Haaland, A.; Martinsen, K.-G.; Strand, T. G.; Volden, H. V.; Swang, O.

1999-08-01

293

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

294

Charge Transfer, Energy-level ''Lineup'' and Transmission in Molecular Electronic Devices  

Science.gov (United States)

There has been strong interest and significant progress in measuring electron transport through single molecules, due to their potential use in future molecular nanotechnology. Such molecular electronic devices usually involve the adsorption of single or a small group of molecules onto two large metallic electrodes. Understanding the electronic property of such metal-molecule-metal systems at equilibrium therefore provides the starting point for understanding their property under nonzero bias. We present first-principle based calculation of some equilibrium properties of the molecular device formed by a phenyldithiolate molecule bridging two gold electrodes, i.e., charge transfer, energy-level ''lineup'' and transmission. In contrast to previous works, we have used local-spin-density-functional theory with a Gaussian-type orbital basis, which not only allows us to use established techniques in molecular electronic structure theory but also to rationalize the result of computation in terms of the familiar language of bonding and orbital interactions in chemistry. We show that significant charge transfer from the metal to the molecule occurs, involving mostly the end sulfur atoms and localized in the interfacial region. Such charge transfer increases the electrostatic potential in the molecule thus changing the energy level structure and the corresponding charge distribution within the molecule. The interaction between the resulting molecular orbitals and the surface metal states determines the lineup of molecular levels relative to the metal Fermi-level and the transmission through the molecule. Our work also points to the importance of interface ''engineering'' for controlling the charge transfer and therefore the energy-level ''lineup'' in molecular electronic devices.

Xue, Yongqiang; Datta, Supriyo; Ratner, Mark

2001-03-01

295

Electronic Transport in Fullerene C20 Bridge Assisted by Molecular Vibrations  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The effect of molecular vibrations on electronic transport is investigated with the smallest fullerene C20 bridge, utilizing the Keldysh nonequilibrium Green's function techniques combined with the tight-binding molecular-dynamics method. Large discontinuous steps appear in the differential conductance when the applied bias-voltage matches particular vibrational energies. The magnitude of the step is found to vary considerably with the vibrational mode and to depend on the l...

Yamamoto, Takahiro; Watanabe, Kazuyuki; Watanabe, Satoshi

2005-01-01

296

Imiging molecular dynamics of dissociative electron attachment to polyatomic molecules: ammonia, methane, and methanol  

Science.gov (United States)

Momentum imaging experiment is performed to study molecular dynamics of dissociative electron attachment(DEA) to the ammonia, methane, and methanol molecules for their well known resonances. The momentum spheres of the negative ion fragments, H^-,NH^-,NH2^- from ammonia, H^-,CH^-,CH2^- from methane, H^-,O^-,CH3O^- from methanol, show unique angular distribution in their respective resonances, indicating each resonance involves different molecular dynamics.

Adaniya, Hidehito; Slaughter, Daniel; Weber, Thorsten; Belkacem, Ali

2011-06-01

297

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Mendes, Mario Benjamin

2010-01-01

298

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

Science.gov (United States)

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

Chen, E C M; Chen, E S

2004-05-28

299

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

300

The Smeagol method for spin- and molecular-electronics  

CERN Document Server

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

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

2005-01-01

 
 
 
 
301

Molecular aspects of biological energy and electron transport: photosynthesis  

International Nuclear Information System (INIS)

Pulse radiolysis and flash photolysis have been applied to chemical systems involved in biological energy and electron transport processes. The processes of particular interest are those that take place in mitochondria (i.e. oxidative phosphorylation), in chloroplasts (i.e. photosynthesis) and in photo-receptors (i.e. vision). Pulse radiation techniques can be applied either to the intact biological membranes (see, for example, Witt, Quart. Rev. Biophys.; 4:365 (1971)), or to simple solutions of individual components of the various excitation and electron transport chains. The two approaches are complementary. In this paper a description is given of some data obtained from simple solutions which are helpful in interpreting information similarly gained from intact photosynthetic membranes, and hence in understanding certain aspects of photosynthesis. (author)

302

Electronic magnetic resonance in a series of antiferromagnetic molecular perovskites  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Coulon, C.; Livage, C.; Gonzalvez, L.; Boubekeur, K.; Batail, P.

1993-01-01

303

Electron spectra and structure of atomic and molecular clusters  

International Nuclear Information System (INIS)

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

304

Opto-Electronic Properties of Conjugated Molecular Wires:  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Conjugated polymers are of considerable current interest because of their semi-conducting and light-emitting properties. These properties, combined with their relatively low cost and good processability as compared to inorganic semiconductors, make them attractive candidates for application in plastic electronic devices. Conjugated polymers are being considered for application as the semi-conducting layer in low-cost field-effect transistors (FETs) for the fabrication of flexible or disposabl...

Grozema, F. C.

2003-01-01

305

Shapes of leading tunnelling trajectories for single-electron molecular ionization  

CERN Document Server

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

Bondar, Denys I; Ivanov, Misha Yu

2010-01-01

306

Linear momentum transfer effects in molecular dissociation produced by electron impact.  

Science.gov (United States)

In this study of molecular dissociation produced by electron impact, diatomic systems and polyatomic molecules are considered, and attention is given to the effects of thermal motion and of momentum transfer in the collision process. A procedure is described which makes it possible to 'construct' both the laboratory angular distribution and velocity distribution of the atomic fragments (or, alternatively, the time-of-flight distribution). The calculation assumes that s-wave electron scattering predominates, i.e., that excitation occurs near threshold. The computational procedure may also be reversed to allow construction of possible molecular models to fit given experimental angular and velocity distribution data.

Misakian, M.; Pearl, J. C.; Mumma, M. J.

1972-01-01

307

Measurement of electron transport properties of molecular junctions fabricated by electrochemical and mechanical methods  

Science.gov (United States)

We describe two methods to fabricate metal-molecule-metal junctions. The first method starts with a pair of electrodes separated with a molecular scale gap on an oxidized silicon substrate. These electrodes are fabricated by combining electron beam lithography and electrochemical deposition/etching. A molecular junction is formed when a molecule bridges the gap. This method can fabricate rather stable molecular junctions, however, the yield is low and the exact number of molecules in the junctions is uncertain. The second method forms a molecular junction by separating a scanning tunneling microscope tip from contact with a metal substrate in a solution containing sample molecules. This method, although is not device compatible, can create a large number of molecular junctions over a short period of time, which is ideal for statistical analysis.

Li, X. L.; He, H. X.; Xu, B. Q.; Xiao, X. Y.; Nagahara, L. A.; Amlani, I.; Tsui, R.; Tao, N. J.

2004-12-01

308

First-Principles Simulations of Inelastic Electron Tunneling Spectroscopyof Molecular Junctions  

CERN Document Server

A generalized Green's function theory is developed to simulate the inelastic electron tunneling spectroscopy (IETS) of molecular junctions. It has been applied to a realistic molecular junction with an octanedithiolate embedded between two gold contacts in combination with the hybrid density functional theory calculations. The calculated spectra are in excellent agreement with recent experimental results. Strong temperature dependence of the experimental IETS spectra is also reproduced. It is shown that the IETS is extremely sensitive to the intra-molecular conformation and to the molecule-metal contact geometry.

Jiang, J; Lu, W; Luo, Y; Jiang, Jun; Kula, Mathias; Lu, Wei; Luo, Yi

2005-01-01

309

Effect of Chemical Modifications on the Electronic Transport Properties of the Optical Molecular Switch  

Science.gov (United States)

Using first-principles density functional theory and nonequilibrium Green's function formalism, we investigate the effect of chemical modifications on the electronic transport properties of the dihydroazulene optical molecular switch. The molecule that comprises the switch can convert between the closed and the open forms upon photoexcitation. Theoretical results show that the chemical modifications play an important role in determining the switching behavior of such molecular device. This result reflects that the current ratio can be manipulated with the careful selection of the substituents and can provide fundamental guidelines for the design of functional molecular devices.

Xia, Cai-Juan; Liu, De-Sheng; Liu, Han-Chen; Zhang, Ying-Tang

2012-01-01

310

Assessment of delocalized and localized molecular orbitals through electron momentum spectroscopy  

Science.gov (United States)

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

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

2014-06-01

311

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

Science.gov (United States)

Nanostructured organic-organic (O-O) heterojunction was fabricated by using the thin films of a hole transporting material, copper phthalocyanine (CuPc) and an electron transporting material, copper hexadecafluoro-phthalocyanine (F16CuPc). The nanostructured thin films were characterized by optical absorption spectra, FESEM, AFM, X-ray diffraction, etc. Grain size of CuPc and F16CuPc on the substrate surface was different. XRD analysis shows that the crystallinity of the double layer films/heterojunction decreases as compared to the single layer film. The heterojunction sandwich structure ITO/F16CuPc/CuPc/Al, in the present study has shown a good diode like current-voltage (I-V) characteristics with reverse rectifying characteristics. In addition, electrical switching and hysteresis phenomena have also been observed in both sides of the voltage polarities. Interestingly, the single layer sandwich structure of the type ITO/CuPc/Al and ITO/F16CuPc/Al did not show any noticeable electrical switching and hysteresis in I-V characteristics as compared to double layer heterostructure. The reverse rectification has been explained on the basis of band bending due to the accumulation of charge carriers near the junction and the electrical switching has been explained considering the charge carriers trapping and detrapping at the O-O interface. PMID:23646732

Chowdhury, Avijit; Biswas, Bipul; Bera, Raghu Nath; Mallik, Biswanath

2013-01-01

312

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

313

Cooperative electron-phonon interaction in molecular chains  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

314

Electronic structure and magnetic anisotropy for nickel-based molecular magnets  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2004-01-01

315

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

316

The Electronic Structure of Organic Molecular Materials : Theoretical and Spectroscopic Investigations  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In the present thesis the electronic properties of two organic molecules were studied by means of density functional theory (DFT) in connection to their possible applications in organic photovoltaics and molecular spintronics respectively. The first analysed system is the C60 derivative PCBM extensively used in polymer solar cells for the charge separation process. Since fullerenes have been shown to undergo modifications as a result of light exposure, investigating their electronic structure...

Brumboiu, Iulia Emilia

2014-01-01

317

Low-energy collisions with atomic and molecular ions in a photocathode electron target  

Science.gov (United States)

Dielectronic recombination of highly charged atomic ions and dissociative recombination of molecular ions have been investigated using fast ion beams merged with cold intense electron beams (down to HF+) dissociative recombination with the cold electrons, producing n = 2 hydrogen atoms, was seen to occur for specific excited initial rotational levels. These levels were identified by their fragment energies down to about 4meV and it is envisaged to measure these energies with sub-meV accuracy.

Wolf, A.; Orlov, D. A.; Krantz, C.; Lestinsky, M.; Shornikov, A.; Novotný, O.; Stützel, J.; Buhr, H.; Mendes, M.; Petrignani, A.; Grieser, M.; Schippers, S.; Müller, A.; Ferro, F.; Lindroth, E.

2009-11-01

318

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

Directory of Open Access Journals (Sweden)

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

Henryk Chojnacki

2003-06-01

319

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

320

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2003-02-01

 
 
 
 
321

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

A double-atom partitioning of the molecular one-electron density matrix is used to describe atoms and bonds. All calculations are performed in Hilbert space. The concept of atomic weight functions (familiar from Hirshfeld analysis of the electron density) is extended to atomic weight matrices. These are constructed to be orthogonal projection operators on atomic subspaces, which has significant advantages in the interpretation of the bond contributions. In close analogy to t...

Vanfleteren, Diederik; Neck, Dimitri; Bultinck, Patrick; Ayers, Paul W.; Waroquier, Michel

2011-01-01

322

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

CERN Document Server

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

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

1998-01-01

323

Molecular electronics at Metal / Semiconductor Junctions Si inversion by Sub-nm Molecular Films  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Electronic transport across n-Si-alkyl monolayer/Hg junctions is, at reverse and low forward bias, independent of alkyl chain-length from 18 down to 1 or 2 carbons! This and further recent results indicate that electron transport is minority, rather than majority carrier-dominated, occurs via generation and recombination, rather than (the earlier assumed) thermionic emission and, as such is rather insensitive to interface properties. The (m)ethyl results show that binding or...

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

2009-01-01

324

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

325

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

326

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

International Nuclear Information System (INIS)

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

327

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

328

Electronic structure of the magnesium hydride molecular ion  

International Nuclear Information System (INIS)

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

329

Electronic structure of the magnesium hydride molecular ion  

Energy Technology Data Exchange (ETDEWEB)

In this paper, using a standard quantum chemistry approach based on pseudopotentials for atomic core representation, Gaussian basis sets and effective core polarization potentials, we investigate the electronic properties of the MgH{sup +} ion. We first determine potential energy curves for several states using different basis sets and discuss their predicted accuracy by comparing our values of the well depths and position with other available results. We then calculate permanent and transition dipole moments for several transitions. Finally, for the first time, we calculate the static dipole polarizability of MgH{sup +} as a function of the interatomic distance. This study represents the first step towards the modelling of collisions between trapped cold Mg{sup +} ions and H{sub 2} molecules.

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

2009-08-14

330

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

Energy Technology Data Exchange (ETDEWEB)

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

Maddern, T M [ARC Centre of Excellence for Antimatter-Matter Studies, SoCPES, Flinders University, Adelaide (Australia); Hargreaves, L R [ARC Centre of Excellence for Antimatter-Matter Studies, SoCPES, Flinders University, Adelaide (Australia); Buckman, S J [ARC Centre of Excellence for Antimatter-Matter Studies, RSPhysSE, Australian National University, Canberra (Australia); Brunger, M J [ARC Centre of Excellence for Antimatter-Matter Studies, SoCPES, Flinders University, Adelaide (Australia)

2007-10-15

331

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

332

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)

333

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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.

Motapon, O.; Tamo, F. O. W.; Backodissa, D.; Chakrabarti, K.; Mezei, J. Z.; Lique, F.; Schneider, I. F.; Tchang-brillet, L.; Tudorache, D.; Dulieu, O.; Bultel, A.; Tennyson, J.; Wolf, A.; Urbain, X.

2011-01-01

334

On the relationship between molecular state and single electron pictures in simple electrochemical junctions.  

Science.gov (United States)

We consider a molecular conduction junction that comprises a redox molecule bridging between metal electrodes, in the limit of weak coupling and high temperature where electron transport is dominated by Marcus electron transfer kinetics. We address the correspondence between the Marcus description in terms of nuclear potential energy surfaces associated with different charging states of the molecular bridge, and the single electron description commonly used in theories of molecular conduction. The relationship between the energy gap, reorganization energy and activation energy parameters of the Marcus theory and the corresponding energy parameters in the single electron description is elucidated. We point out that while transport in the normal Marcus regime involves activated (therefore relatively slow) transitions between at least two charging states of the molecular bridge, deep in the inverted regime only one of these states is locally stable and transitions into this state are activationless. The relatively slow rates that characterize the normal Marcus transport regime manifest themselves in the appearance of hysteresis in the system transport behavior as a function of gate or bias potentials for relatively slow scan rates of these potentials, but not bistability in the junction conduction behavior. We also consider the limit of fast solvent reorganization that may reflect the response of the electronic environment (electronic polarization of a solvent and of the metal electrodes) to the changing charging state of the bridge. In this limit, environmental reorganization appears as renormalization of the bridge electronic energy levels. We show that the effect of this reorganization on the junction conduction properties is not universal and depends on the particular bridge charging states that are involved in the conduction process. PMID:22847314

Migliore, Agostino; Schiff, Philip; Nitzan, Abraham

2012-10-28

335

Molecular structure of cycloheptene, C 7H 12, as determined by electron diffraction and molecular mechanics calculations  

Science.gov (United States)

The structure of cycloheptene has been investigated by gas-phase electron diffraction at 20°C and by molecular mechanics (MM2). The energetically less favorable conformer, the boat, is shown to be incompatible with experiment. The geometrical parameters of the chair conformer were found to be ( ra structure): C?C 1.343(8) Å, C2-C3 1.516(16) Å, C3-C4 (?C4-C5) 1.536(8) Å, C?H 1.108(7) Å; ? C?C?C 123.8(8)°, ?C4?C5?C6 113.9(24)°, ?H?C?H 107.9(36)°; flap angles ? 1 128.0(33)° and ? 2 120.2(44)°. The differences between the parameters calculated by molecular mechanics are all within the reported uncertainties.

Ermolaeva, L. I.; Mastryukov, V. S.; Allinger, N. L.; Almenningen, A.

1989-05-01

336

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

CERN Document Server

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

Simine, Lena

2013-01-01

337

Molecular Conduction through Adlayers: Cooperative Effects can Help or Hamper Electron Transport  

Energy Technology Data Exchange (ETDEWEB)

We use a one-electron, tight-binding model of a molecular adlayer sandwiched between two metal electrodes to explore how cooperative effects between molecular wires influence electron transport through the adlayer. When compared to an isolated molecular wire, an adlayer exhibits cooperative effects that generally enhance conduction away from an isolated wire s resonance and diminish conductance near such a resonance. We also find that the interwire distance (related to the adlayer density) is a key quantity. Substrate-mediated coupling induces most of the cooperative effects in dense adlayers, whereas direct, interwire coupling (if present) dominates in sparser adlayers. In this manner, cooperative effects through dense adlayers cannot be removed, suggesting an optimal adlayer density for maximizing conduction.

Reuter, Matthew G [ORNL; Seideman, Tamar [Northwestern University, Evanston; Ratner, Mark A. [Northwestern University, Evanston

2011-01-01

338

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

CERN Document Server

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

Blaineau, S; Blaineau, Sebastien; Jund, Philippe

2004-01-01

339

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2006-01-01

340

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 (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

2014-12-01

 
 
 
 
341

Assessment of a nanoparticle bridge platform for molecular electronics measurements  

International Nuclear Information System (INIS)

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

342

Recent advances in photoinduced electron transfer processes of fullerene-based molecular assemblies and nanocomposites.  

Science.gov (United States)

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. PMID:22592087

Ito, Osamu; D'Souza, Francis

2012-01-01

343

Detection of Inelastic Electron Transport Properties in Molecular Junctions by Internal Substitutions  

Science.gov (United States)

Doping and chemical substitutions for molecules is one of promising technique to control the I-V characteristic and engineering of molecular devices. In this presentation, we propose an idea of internal substations to detect ballistic and inelastic transport in molecular junctions. We adopt the benzene-dithiol as a template molecule and apply first principle transport calculations, which are based on nonequilibrium Green's function combined with density functional theory, to several internally substituted systems. The inelastic transport is treated within the conventional lowest order expansion (c-LOE) formalism. By comparison of substituted systems, we show systematic analyses of electron tunneling pathway for both ballistic and inelastic currents as well as electron-phonon couplings on bridge molecules. The correlation of inelastic electron tunneling spectroscopy (IETS) and Raman spectroscopy will be also discussed.

Nakamura, Hisao

2010-03-01

344

A low-loss hybrid rectification technique for piezoelectric energy harvesting  

International Nuclear Information System (INIS)

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

345

Magnetically driven high-frequency rectification in a cooperative system of magnetic tunnel junctions: Frequency dependence  

International Nuclear Information System (INIS)

The effect of magnetically driven high-frequency rectification in a polycrystalline La0.7Ca0.3MnO3 manganite has been measured at different frequencies of microwave radiation. The magnetic field dependence of a rectified voltage has a broad peak resembling an absorption line, whose shape and position are determined by the radiation frequency. The rectification effect in a polycrystalline manganite sample is related to a ramified network of magnetic tunnel junctions, which is formed by ferromagnetic conducting grains with insulator boundaries. The results of measurements are consistent with a model for the magneto-dependent rectification effect based on the interplay between a spin-polarized current through the tunnel junctions and magnetic resonance induced in the grains forming the junctions. - Research Highlights: ? Granular manganite works as a magnetic-field-driven microwave detector. ? The rectification effect occurs due to the interplay between a spin-polarized current and spin dynamics. ? Not all tunnel junctions contribute to the magnetically dependent rectification effect.

346

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

347

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

International Nuclear Information System (INIS)

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

348

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

Science.gov (United States)

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

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

2009-07-01

349

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

International Nuclear Information System (INIS)

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

350

Quantum-information analysis of electronic states of different molecular structures  

International Nuclear Information System (INIS)

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

351

Tuning electron transport through a single molecular junction by bridge modification  

Science.gov (United States)

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.

Li, Xiao-Fei; Qiu, Qi; Luo, Yi

2014-07-01

352

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.

353

Tuning electron transport through a single molecular junction by bridge modification  

Energy Technology Data Exchange (ETDEWEB)

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.

Li, Xiao-Fei, E-mail: xf.li@uestc.edu.cn; Qiu, Qi [School of Optoelectronic Information, University of Electronic Science and Technology of China, Chengdu, Sichuan 610054 (China); Luo, Yi [Division of Theoretical Chemistry and Biology, School of Biotechnology, KTH, Royal Institute of Technology, S-106 91 Stockholm (Sweden)

2014-07-07

354

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

355

Molecular view of an electron transfer process essential for iron-sulfur protein biogenesis.  

Science.gov (United States)

Biogenesis of iron-sulfur cluster proteins is a highly regulated process that requires complex protein machineries. In the cytosolic iron-sulfur protein assembly machinery, two human key proteins--NADPH-dependent diflavin oxidoreductase 1 (Ndor1) and anamorsin--form a stable complex in vivo that was proposed to provide electrons for assembling cytosolic iron-sulfur cluster proteins. The Ndor1-anamorsin interaction was also suggested to be implicated in the regulation of cell survival/death mechanisms. In the present work we unravel the molecular basis of recognition between Ndor1 and anamorsin and of the electron transfer process. This is based on the structural characterization of the two partner proteins, the investigation of the electron transfer process, and the identification of those protein regions involved in complex formation and those involved in electron transfer. We found that an unstructured region of anamorsin is essential for the formation of a specific and stable protein complex with Ndor1, whereas the C-terminal region of anamorsin, containing the [2Fe-2S] redox center, transiently interacts through complementary charged residues with the FMN-binding site region of Ndor1 to perform electron transfer. Our results propose a molecular model of the electron transfer process that is crucial for understanding the functional role of this interaction in human cells. PMID:23596212

Banci, Lucia; Bertini, Ivano; Calderone, Vito; Ciofi-Baffoni, Simone; Giachetti, Andrea; Jaiswal, Deepa; Mikolajczyk, Maciej; Piccioli, Mario; Winkelmann, Julia

2013-04-30

356

Molecular view of an electron transfer process essential for iron–sulfur protein biogenesis  

Science.gov (United States)

Biogenesis of iron–sulfur cluster proteins is a highly regulated process that requires complex protein machineries. In the cytosolic iron–sulfur protein assembly machinery, two human key proteins—NADPH-dependent diflavin oxidoreductase 1 (Ndor1) and anamorsin—form a stable complex in vivo that was proposed to provide electrons for assembling cytosolic iron–sulfur cluster proteins. The Ndor1–anamorsin interaction was also suggested to be implicated in the regulation of cell survival/death mechanisms. In the present work we unravel the molecular basis of recognition between Ndor1 and anamorsin and of the electron transfer process. This is based on the structural characterization of the two partner proteins, the investigation of the electron transfer process, and the identification of those protein regions involved in complex formation and those involved in electron transfer. We found that an unstructured region of anamorsin is essential for the formation of a specific and stable protein complex with Ndor1, whereas the C-terminal region of anamorsin, containing the [2Fe-2S] redox center, transiently interacts through complementary charged residues with the FMN-binding site region of Ndor1 to perform electron transfer. Our results propose a molecular model of the electron transfer process that is crucial for understanding the functional role of this interaction in human cells. PMID:23596212

Banci, Lucia; Bertini, Ivano; Calderone, Vito; Ciofi-Baffoni, Simone; Giachetti, Andrea; Jaiswal, Deepa; Mikolajczyk, Maciej; Piccioli, Mario; Winkelmann, Julia

2013-01-01

357

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

358

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2014-01-01

359

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

International Nuclear Information System (INIS)

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

360

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

 
 
 
 
361

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

362

Molecular-dynamic calculation of the relaxation of the electron energy distribution function in a plasma  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A molecular-dynamic (MD) code is used to calculate the temporal evolution of nonequilibrium electron distribution functions in plasmas. To the authors' knowledge, this is the first time that a molecular-dynamic code has been used to treat this problem using a macroscopic number of particles. The code belongs to the class of P3M (particle-particle-particle-mesh) codes. Since the equations solved by the MD code are fundamental, this approach avoids several assumptions that are inherent to alter...

David, N.; Hooker, Sm

2003-01-01

363

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 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

364

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

365

Inward rectification in the transverse tubular system of frog skeletal muscle studied with potentiometric dyes.  

Science.gov (United States)

The non-penetrating potentiometric dyes NK2367 and WW375 were used to investigate the effect of inward rectification on the weighted-average tubular membrane potential in single frog muscle fibres voltage clamped using a three-Vaseline-gap method. In 100 mM-K solution, when inward rectification was activated by hyperpolarization the steady-state amplitude of the transverse tubular system (T-system) optical signal was reduced, and its rise time was faster than that recorded for an equivalent depolarization. The voltage dependence of the optical attenuation followed that of inward rectification, increasing with increasing hyperpolarization. For a voltage-clamp step of -140 mV the optical attenuation was 0.72 which corresponds to a weighted-average T-system potential change of 100 mV. When inward rectification was blocked in a Cs, TEA solution the optical attenuation was also abolished. The voltage dependence of the block of the inward currents in solutions containing low concentrations of Cs was also reflected in the T-system optical signals. Our results were satisfactorily predicted by a radial cable model of the T-system, assuming the same specific inward rectifier conductance in surface and tubular membranes. This analysis predicts that the measured optical attenuation corresponds to a decrease in the tubular space constant, lambda T, from 120 micron under passive conditions to about 40 micron when inward rectification is fully, activated. The voltage dependence of inward rectification measured at the surface membrane was reasonably well predicted by assuming that the specific conductance obeyed a Boltzmann type of voltage dependence; the major effect of tubular decrements was to reduce the steepness of the total (surface + T-system) conductance-voltage relation. PMID:3873536

Ashcroft, F M; Heiny, J A; Vergara, J

1985-02-01

366

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

Science.gov (United States)

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

Thomas, Richard D

2008-01-01

367

Fabrication of tunnel junction-based molecular electronics and spintronics devices  

International Nuclear Information System (INIS)

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

368

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

369

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Shyng, S. -l; Ferrigni, T.; Nichols, C. G.

1997-01-01

370

Inward rectification in the transverse tubular system of frog skeletal muscle studied with potentiometric dyes.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The non-penetrating potentiometric dyes NK2367 and WW375 were used to investigate the effect of inward rectification on the weighted-average tubular membrane potential in single frog muscle fibres voltage clamped using a three-Vaseline-gap method. In 100 mM-K solution, when inward rectification was activated by hyperpolarization the steady-state amplitude of the transverse tubular system (T-system) optical signal was reduced, and its rise time was faster than that recorded for an equivalent d...

Ashcroft, Fm; Heiny, Ja; Vergara, J.

1985-01-01

371

Optical rectification and third harmonic generation of spherical quantum dots: Controlling via external factors  

Science.gov (United States)

In this paper simultaneous effects of pressure, temperature, external electric field and laser radiation on the optical rectification and third harmonic generation of a spherical quantum dot with parabolic confinement and dressed impurity are studied. By means of matrix diagonalization technique, energy eigenvalues and functions are evaluated and used to find the optical rectification coefficient and third harmonic generation of the system via density operator method. It is shown that these nonlinear optical quantities strongly depend on pressure, temperature, electric field, confinement frequency and dressing laser intensity. Obvious effects of these external factors propose new facilities with different effects to control nonlinear optical properties of such systems.

Vaseghi, B.; Sadri, M.; Rezaei, G.; Gharaati, A.

2015-01-01

372

Electron and gas temperature dependences of the dissociative recombination coefficient of molecular ions Ar{sub 2}{sup +} with electrons  

Energy Technology Data Exchange (ETDEWEB)

This paper presents the measured values of the total dissociative recombination coefficient of molecular Ar{sub 2}{sup +} ions with electrons {alpha}(Ar{sub 2}{sup +}) as a function of both electron and gas temperatures. The measured recombination coefficient can be expressed as {alpha}{sub Ar{sup 2+}} (T{sub e}, T{sub gas}) = (8.1 {+-} 0.5) x 10{sup -7} (T{sub e}/300 K){sup -0.64} (T{sub gas}/300 K) {sup -0.86}cm{sup 3}s{sup -1} in the temperature ranges 300 K {<=} T{sub e} {<=} 10 400 K and 300 K {<=} T{sub gas} {<=} 500 K.

Lukac, P; Mikus, O; Zabudla, Z; Trnovec, J [Experimental Physics Department, Faculty of Mathematics, Physics and Informatics, Comenius University, Mlynska dolina F2, 842 48 Bratislava (Slovakia); Morva, I; Morvova, M, E-mail: imrich.morva@fmph.uniba.sk [Department of Astronomy, Earth Sciences and Meteorology, Faculty of Mathematics, Physics and Informatics, Comenius University, Mlynska dolina F2, 842 48 Bratislava (Slovakia)

2011-10-15

373

Electron-vibration effects on the thermoelectric efficiency of molecular junctions  

Science.gov (United States)

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

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

2014-09-01

374

Storage, transport, release: heme versatility in nitrite reductase electron transfer studied by molecular dynamics simulations.  

Science.gov (United States)

Using molecular dynamics simulations of the thermodynamic integration type, we study the energetics and kinetics of electron transfer through the nitrite reductase enzyme of Sulfurospirillum deleyianum, Wolinella succinogenes and Campylobacter jejuni. In all of these five-heme proteins, the storage of an even number of electrons within a monomeric chain is thermodynamically favoured. Kinetically, two of these electrons are usually transferred almost simultaneously towards the active site. Although the free energy landscape for charge transfer varies significantly from organism to organism, the heme cofactor closest to the interface of a protein dimer always exhibits a particularly low free energy, suggesting that protein dimerization is functional. Interheme electron interaction effects do not play a significant role. PMID:25579411

Bauß, Anna; Koslowski, Thorsten

2015-01-28

375

Tuning electron transfer rates through molecular bridges in quantum dot sensitized oxides.  

Science.gov (United States)

Photoinduced electron transfer processes from semiconductor quantum dots (QDs) molecularly bridged to a mesoporous oxide phase are quantitatively surveyed using optical pump-terahertz probe spectroscopy. We control electron transfer rates in donor-bridge-acceptor systems by tuning the electronic coupling strength through the use of n-methylene (SH-[CH2]n-COOH) and n-phenylene (SH-[C6H4](n)-COOH) molecular bridges. Our results show that electron transfer occurs as a nonresonant quantum tunneling process with characteristic decay rates of ?(n) = 0.94 ± 0.08 and ?(n) = 1.25 per methylene and phenylene group, respectively, in quantitative agreement with reported conductance measurements through single molecules and self-assembled monolayers. For a given QD donor-oxide acceptor separation distance, the aromatic n-phenylene based bridges allow faster electron transfer processes when compared with n-methylene based ones. Implications of these results for QD sensitized solar cell design are discussed. PMID:24093529

Wang, Hai; McNellis, Erik R; Kinge, Sachin; Bonn, Mischa; Cánovas, Enrique

2013-11-13

376

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

International Nuclear Information System (INIS)

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

377

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

378

The external complex scaling method in prolate spheroidal coordinates for the electron impact ionization of molecular hydrogen  

International Nuclear Information System (INIS)

We calculated the multi-fold differential cross section of the single and double ionization of molecular hydrogen by electron impact by using the prolate spheroidal external complex scaling method for ejected electrons and Born expansion up to second term for scattered electron

379

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

380

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

 
 
 
 
381

Breaking a tetrahedral molecular ion with electrons: Study of NH4^+  

Science.gov (United States)

We apply a general theoretical model to study the dissociative recombination of the polyatomic ion NH4^+. The high symmetry of the molecule, represented by the tetrahedral group, leads to complex vibronic couplings responsible for dissociative recombination. By applying multi-channel quantum defect theory and using symmetry considerations, we treat the doubly and triply degenerate modes and electronic states of NH4^+ to calculate a theoretical cross section which agrees well with existing experimental data. This represents, to our knowledge, the first DR study for a molecular ion with triply degenerate electronic states and normal modes.

Douguet, Nicolas; Kokoouline, Viatcheslav; Orel, Ann

2012-06-01

382

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

383

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

384

Single Wall Bamboo Shaped Carbon Nanotube:. a Molecular Dynamics and Electronic Study  

Science.gov (United States)

Thermal stability and molecular electronic properties of a single walled, bamboo shaped carbon nanotube has been investigated. Molecular dynamics method is applied to investigate thermal stability, and electronic properties are calculated at the Extended Huckel level. Although bamboo shaped carbon nanotubes observed in experimental literature are multi-walled, it is shown that the suggested structural model in this work, which is single-walled, is also both thermodynamically and energetically stable. Bamboo shape of the model investigated is due to periodical coronene-like spacers. The resultant structure is compartmented, having geometrical aberrations in the vicinity of spacers. There is no degradation in the average coordination number. The geometrical aberrations in the vicinity of spacers is due to curvature induced by the pentagons of the resultant geometry.

Malcio?lu, Osman Bari?; Ta?ci, Emre; Erkoç, ?akir

385

The Electronic Structure of a Local Charge-Transfer-Induced Spin Transition Molecular Adsorbate  

Science.gov (United States)

The spin crossover phenomena has been identified in the [Fe(H2B(pz)2) bpy] where pz=(1-pyrazolyl)borate [Fe(H2B(pz)2) bpy], and but there is currently a lack of knowledge of the physical nature of this phenomena and the electronic structure of this organometallic compound has not been well characterized. We have investigated the interface electronic characteristics of molecular thin films of the metal-organic [Fe(H2B(pz)2) bpy] by ultraviolet photoelectron spectroscopy (UPS) and inverse photoemission (IPES). X-ray absorption spectroscopy (XAS) and Infrared spectroscopy (IR spectroscopy) were also used to study [Fe(H2B(pz)2) bpy]. The IPES results coincide with XAS, and the model calculations. The molecular vibrational modes have been identified from a comparison of the IR spectroscopy with model calculations.

Zhang, Xin; Wu, Ning; Zhang, Zhengzheng; Létard, Jean-François; Guillaume, François; Doudin, Bernard; Dowben, Peter

2011-03-01

386

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

387

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

Directory of Open Access Journals (Sweden)

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

Hassan Safouhi

2004-02-01

388

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

389

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

390

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

391

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

CERN Document Server

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

Tarana, Michal

2013-01-01

392

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

International Nuclear Information System (INIS)

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

393

Optimal values of rovibronic energy levels for triplet electronic states of molecular deuterium  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Optimal set of 1050 rovibronic energy levels for 35 triplet electronic states of $D_2$ has been obtained by means of a statistical analysis of all available wavenumbers of triplet-triplet rovibronic transitions studied in emission, absorption, laser and anticrossing spectroscopic experiments of various authors. We used a new method of the analysis (Lavrov, Ryazanov, JETP Letters, 2005), which does not need any \\it a priory \\rm assumptions concerning the molecular structure b...

Lavrov, B. P.; Umrikhin, I. S.

2008-01-01

394

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 h...

Brocks, Geert; Brink, Jeroen Den; Morpurgo, Alberto F.

2003-01-01

395

Investigations of the breakup dynamics of small molecular ions recombining with electrons  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Dissociative recombination is the process in which a molecular ion recombines with an electron and then fragments into neutral products. This process has been studied in many experiments over the years at the ion storage ring CRYRING at the Manne Siegbahn Laboratory, Stockholm University. In this thesis the experimental methods and data analysis procedures used to investigate dissociative recombination are presented together with the results for several diatomic and triatomic ions. Cross sect...

Hellberg, Fredrik

2005-01-01

396

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

Science.gov (United States)

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

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

2013-05-01

397

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

398

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

399

Lewis Structures Are Models for Predicting Molecular Structure, Not Electronic Structure  

Science.gov (United States)

This article argues against a close relationship between Lewis dot structures and electron structure obtained from quantum mechanical calculations. Lewis structures are a powerful tool for structure prediction, though they are classical models of bonding and do not predict electronic structure. The "best" Lewis structures are those that, when combined with the VSEPR model, allow the accurate prediction of molecular properties, such as polarity, bond length, bond angle, and bond strength. These structures are achieved by minimizing formal charges within the molecule, even if it requires an expanded octet on atoms beyond the second period. Lewis structures that show an expanded octet do not imply full d-orbital involvement in the bonding. They suggest that the presence of low-lying d-orbitals is important in producing observed molecular structures. Based on this work, the presence of electron density, not a large separation in charge, is responsible for the short bond lengths and large angles in species containing nonmetal atoms from beyond the second period. This result contradicts results obtained from natural population analysis, a method that attempts to derive Lewis structures from molecular orbital calculations.

Purser, Gordon H.

1999-07-01

400

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2007-06-15

 
 
 
 
401

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

International Nuclear Information System (INIS)

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

402

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

International Nuclear Information System (INIS)

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

403

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-05-26

404

Fabrication of reproducible, integration-compatible hybrid molecular/si electronics.  

Science.gov (United States)

Reproducible molecular junctions can be integrated within standard CMOS technology. Metal-molecule-semiconductor junctions are fabricated by direct Si-C binding of hexadecane or methyl-styrene onto oxide-free H-Si(111) surfaces, with the lateral size of the junctions defined by an etched SiO2 well and with evaporated Pb as the top contact. The current density, J, is highly reproducible with a standard deviation in log(J) of 0.2 over a junction diameter change from 3 to 100 ?m. Reproducibility over such a large range indicates that transport is truly across the molecules and does not result from artifacts like edge effects or defects in the molecular monolayer. Device fabrication is tested for two n-Si doping levels. With highly doped Si, transport is dominated by tunneling and reveals sharp conductance onsets at room temperature. Using the temperature dependence of current across medium-doped n-Si, the molecular tunneling barrier can be separated from the Si-Schottky one, which is a 0.47 eV, in agreement with the molecular-modified surface dipole and quite different from the bare Si-H junction. This indicates that Pb evaporation does not cause significant chemical changes to the molecules. The ability to manufacture reliable devices constitutes important progress toward possible future hybrid Si-based molecular electronics. PMID:25098545

Yu, Xi; Lovrin?i?, Robert; Kraynis, Olga; Man, Gabriel; Ely, Tal; Zohar, Arava; Toledano, Tal; Cahen, David; Vilan, Ayelet

2014-12-01

405

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

Science.gov (United States)

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

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

2008-02-01

406

Multiple mechanisms underlying rectification in retinal cyclic nucleotide-gated (CNGA1) channels.  

Science.gov (United States)

In cyclic nucleotide-gated (CNGA1) channels, in the presence of symmetrical ionic conditions, current-voltage (I-V) relationship depends, in a complex way, on the radius of permeating ion. It has been suggested that both the pore and S4 helix contribute to the observed rectification. In the present manuscript, using tail and gating current measurements from homotetrameric CNGA1 channels expressed in Xenopus oocytes, we clarify and quantify the role of the pore and of the S4 helix. We show that in symmetrical Rb(+) and Cs(+) single-channel current rectification dominates macroscopic currents while voltage-dependent gating becomes larger in symmetrical ethylammonium and dimethylammonium, where the open probability strongly depends on voltage. Isochronal tail currents analysis in dimethylammonium shows that at least two voltage-dependent transitions underlie the observed rectification. Only the first voltage-dependent transition is sensible to mutation of charge residues in the S4 helix. Moreover, analysis of tail and gating currents indicates that the number of elementary charges per channel moving across the membrane is less than 2, when they are about 12 in K(+) channels. These results indicate the existence of distinct mechanisms underlying rectification in CNG channels. A restricted motion of the S4 helix together with an inefficient coupling to the channel gate render CNGA1 channels poorly sensitive to voltage in the presence of physiological Na(+) and K(+). PMID:24400150

Arcangeletti, Manuel; Marchesi, Arin; Mazzolini, Monica; Torre, Vincent

2013-11-01

407

Dithiocarbamate Anchoring in Molecular Wire Junctions: A First Principles Study  

CERN Document Server

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

Li, Z; Li, Zhenyu

2006-01-01

408

High-resolution electron collision spectroscopy of the elementary second-row molecular ions  

International Nuclear Information System (INIS)

The fundamental molecules composed of atoms from the second row of the periodic table (C,N,O,F) have a rich structure of excited potential curves that can be probed at high energy resolution by observing fragmentation processes following collisions with quasi-monochromatic electrons. Experiments of this type are performed in merged electron and ion beams at the ion storage ring TSR in Heidelberg. Using a cold, photocathode-produced electron beam, experiments on the system CF+ yield rich structure in the collision energy dependence of both dissociative recombination and excitation. Moreover, the final atomic levels reached in the fragmentation can be observed, shedding light on their correlation to the collisionally populated excited molecular potentials

409

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

International Nuclear Information System (INIS)

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

410

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

Science.gov (United States)

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

Ullrich, Joachim

2008-05-01

411

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.

412

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

413

K-shell photoionization of N{sub 2}: Angular resolved molecular frame photoelectron - Auger electron coincidence spectra  

Energy Technology Data Exchange (ETDEWEB)

The possibility to separate Auger transitions to different repulsive doubly charged final ion states by measuring the photo- and the Auger -electrons in coincidence in the molecular frame is demonstrated.

Cherepkov, N A; Semenov, S K [State University of Aerospace Instrumentation, 190000 St. Petersburg (Russian Federation); Schoeffler, M S; Titze, J; Petridis, N; Jahnke, T; Cole, K; Schmidt, L Ph H; Czasch, A; Akoury, D; Jagutzki, O; Schmidt-Boecking, H [Institut fuer Kernphysik, University Frankfurt, Max-von-Laue-Str. 1, D-60438 Frankfurt Germany (Germany); McCurdy, W; Rescigno, T; Osipov, T; Lee, S; Prior, M H; Belkacem, A [Lawrence Berkeley National Lab., Berkeley CA 94720 (United States); Cocke, C L [Department of Physics, Kansas State University, Cardwell Hall, Manhattan KS 66506 (United States); Landers, A [Department of Physics, Auburn University Auburn AL 36849 (United States)

2009-11-01

414

Odd-even effect in molecular electronic transport via an aromatic ring.  

Science.gov (United States)

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

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

2014-11-18

415

Test-beds for molecular electronics: metal-molecules-metal junctions based on Hg electrodes.  

Science.gov (United States)

Junctions based on mesoscopic Hg electrodes are used to characterize the electrical properties of the organic molecules organized in self-assembled monolayers (SAMs). The junctions M-SAM//SAM-Hg are formed by one electrode based on metals (M) such as Hg, Ag, Au, covered by a SAM, and by a second electrode always formed by a Hg drop carrying also a SAM. The electrodes, brought together by using a micromanipulator, sandwich SAMs of different nature at the contact area (approximately = 0.7 microm2). The high versatility of the system allows a series of both electrical and electrochemical junctions to be assembled and characterized: (i) The compliant nature of the Hg electrodes allows incorporation into the junction and measurement of the electrical behavior of a large number of molecular systems and correlation of their electronic structure to the electrical behavior; (ii) by functionalizing both electrodes with SAMs exposing different functional groups, X and Y, it is possible to compare the rate of electron transfer through different X...Y molecular interactions; (iii) when the junction incorporates one of the electrode formed by a semitransparent film of Au, it allows electrical measurements under irradiation of the sandwiched SAMs. In this case the junction behaves as a photoswitch; iv) incorporation of redox centres with low lying, easily reachable energy levels, provides electron stations as indicated by the hopping mechanism dominating the current flow; (v) electrochemical junctions incorporating redox centres by both covalent and electrostatic interactions permit control of the potential of the electrodes with respect to that of the redox state by means of an external reference electrode. Both these junctions show an electrical behavior similar to that of conventional diodes, even though the mechanism generating the current flow is different. These systems, demonstrating high mechanical stability and reproducibility, easy assembly, and a wide variety of produced results, are convenient test-beds for molecular electronics and represent a useful complement to physics-based experimental methods. PMID:21137710

Simeone, Felice Carlo; Rampi, Maria Anita

2010-01-01

416

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

Science.gov (United States)

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

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

2013-04-25

417

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

Science.gov (United States)

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; Gu, Man; Khokhlov, Mikhail; Liu, Hongxue; Lu, Jiwei; Wolf, Stuart A.

2013-01-01

418

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

419

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

420

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

Science.gov (United States)

The present work has been carried out a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of cyanuric acid. The FT-IR (100-4000cm(-1)) and FT-Raman spectra (400-4000cm(-1)) of cyanuric acid were recorded. In DFT methods, Becke's three parameter exchange-functional (B3) combined with gradient-corrected correlation functional of Lee, Yang and Parr (LYP) by implementing the split-valence polarized 6-31G(d,p) and 6-31++G(d,p) basis sets have been considered for the computation of the molecular structure optimization, vibrational frequencies, thermodynamic properties and energies of the optimized structures. The density functional theory (DFT) result complements the experimental findings. The electronic properties, such as HOMO-LUMO energies and molecular electrostatic potential (MESP) are also performed. Mulliken population analysis on atomic charges is also calculated. The first order hyperpolarizability (?total) of this molecular system and related properties (?, ? and ??) are calculated using DFT/B3LYP/6-31G (d,p) and B3LYP/6-311++G(d,p) methods. The thermodynamic functions (heat capacity, entropy and enthalpy) from spectroscopic data by statistical methods were also obtained for the range of temperature 50-1000K. PMID:25544187

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

2015-03-01

 
 
 
 
421

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

422

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)

423

Analysis of the electronic contribution to the molecular vibrational magnetic moment  

International Nuclear Information System (INIS)

The electron current contributions gzz,elvib and gzz,elrot to the vibrational and rotational g-factors of the H3+ molecule are calculated by the gauge-invariant atomic orbital method. The electron current contribution to the vibrational g-factor is shown to consist of two parts of opposite signs: the negative one, corresponding to the motion of the electron shell caused by the rotational motion of the nuclei along small circles with the angular frequency of the degenerate vibration, and the positive one, corresponding to the electron motion caused by a deformation wave running around the molecular contour in the opposite direction. The absolute value of the first part increases, and that of the second one decreases, with an increase of the effective charge ? of 1s atomic orbitals. In contrast to the definitely negative value gzz,elrot, the electronic contribution to the vibrational g-factor gzz,elvib changes its sign as the effective charges ? of atomic orbitals increase; it is positive when ? zz,elrot = -0.0198 (which agrees with the calculations of other authors) and gzz,elvib = +0.095. 8 refs., 3 figs., 3 tabs

424

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)

425

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

426

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

CERN Document Server

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

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

2009-01-01