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Dissertations / Theses on the topic 'Molecular Charge'

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Published: 6 September 2023

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1

Renfrow, Steven N. (Steven Neal). "Charge State Distributions in Molecular Dissociation." Thesis, University of North Texas, 1998. https://digital.library.unt.edu/ark:/67531/metadc278340/.

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2

Smith, P. E. "Charge calculations in molecular mechanics." Thesis, University of Liverpool, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233873.

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3

Latt, Kyaw Zin. "Manipulation of Molecular Charge Density Waves and Molecular Transport Systems." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1557418915977344.

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4

Tylleman, Benoît. "Molecular engineering of anthradithiophenes for charge transport." Doctoral thesis, Universite Libre de Bruxelles, 2012. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209650.

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L’électronique organique est un nouveau domaine de recherche qui combine les propriétés électriques de l’électronique avec les propriétés mécanique des matériaux organiques. De nouvelles applications telles que des écrans flexibles, de l’éclairage de surface ou des cellules photovoltaïques flexibles, qui ne sont pas possible avec l’électronique basée sur le silicium, sont envisagées. Les semi-conducteurs organiques sont les matériaux clés de ces dispositifs électroniques. Pour le design moléculaire, deux paramètres doivent être optimisés :l’énergie de réorganisation qui doit être minimisée et l’intégrale de transfert qui doit être maximisée. Avec un noyau aromatique rigide et étendu, les acènes linéaires tels que le pentacène et les anthradithiophènes (ADT) possèdent des énergies de réorganisation parmi les plus petites. Quant à l’intégrale de transfert, son intensité va dépendre de l’arrangement moléculaire qui ne peut malheureusement pas encore être prédit. Divers substituents peuvent être introduit sur le noyau aromatique afin de moduler l’arrangement moléculaire et ainsi maximiser l’intégrale de transfert.

Durant cette thèse, nous nous sommes intéressés à l’amélioration du transport de charge des anthradithiophènes par design moléculaire. Deux approches ont été envisagées :l’approche moléculaire et l’approche macromoléculaire. L’approche moléculaire se base sur les travaux de Takimiya sur les naphtodithiophènes. Dans ces travaux, il est montré que la mobilité de charge est supérieure lorsque l’isomère anti est utilisé plutôt que l’isomère syn. Les anthradithiophènes sont généralement utilisés en tant que mélange d’isomères syn et anti ;ceci est une conséquence de la voie de synthèse utilisée. Il est raisonnable de penser qu’utiliser des ADT isomériquement purs donnera des mobilités de charge plus élevées, à l’instar des naphtodithiophènes. Le premier objectif de cette thèse est donc de développer une méthodologie permettant d’obtenir des ADT isomériquement purs. L’approche macromoléculaire est basée sur les travaux théoriques d’Antoine Van Vooren sur le couplage électronique via pont éthylène (non conjugué). Selon ces calculs, le couplage électronique entre deux noyaux aromatiques est plus important lorsqu’ils sont reliés par un pont éthylène que lorsqu’ils sont indépendants. Le second objectif de cette thèse est de développer une méthodologie qui permet d’attacher deux ADTs via a pont éthylène.

Une stratégie de synthèse menant à l’anti-ADT a été développée. La quantité d’anti-ADT disponible via cette méthodologie est assez faible. Par conséquent, une autre méthodologie a été développée. En fonctionnalisant un des intermédiaires de réaction, il est possible de séparer les deux isomères et ainsi d’obtenir de plus grandes quantités d’anti-ADT et de syn-ADT. Les spectres d’absorption UV-vis du mélange et des différents isomères ont été comparés. Des études sur des dispositifs électroniques utilisant des ADT isomériquement purs sont en cours.

Une stratégie de synthèse menant à l’ADT ponté a été développée. Dans cette stratégie, le pont éthylène est synthétisé en premier et les entités anthradithiophènes générées dans un deuxième temps. L’ADT ponté a été obtenu à l’état de traces, détectées uniquement par spectrométrie de masse. Des efforts synthétique supplémentaire sont nécessaire afin d’obtenir l’ADT ponté dans des quantités suffisantes pour fabriquer des dispositifs électroniques. La fabrication de dispositifs électroniques est une étape cruciale dans la détermination de l’impact du pont sur la mobilité de charge.


Doctorat en Sciences
info:eu-repo/semantics/nonPublished

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5

Ghassemizadeh, Reyhaneh [Verfasser], and Michael [Akademischer Betreuer] Walter. "Ab initio study on molecular charge transport and conformational analysis of organic molecules." Freiburg : Universität, 2019. http://d-nb.info/1190560429/34.

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6

Goryaynov, Alexander G. "Molecular Size and Charge Effects on Nucleocytoplasmic Transport Studied By Single-Molecule Microscopy." Bowling Green State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1357278635.

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7

Bennett, M. A. "Charge exchange between light ions." Thesis, University of Newcastle Upon Tyne, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355835.

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8

Hudson, B. D. "Charge calculations : Theory and applications." Thesis, University of Liverpool, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372697.

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9

Fonari, Alexandr. "Theoretical description of charge-transport and charge-generation parameters in single-component and bimolecular charge-transfer organic semiconductors." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54323.

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In this dissertation, we employ a number of computational methods, including Ab Initio, Density Functional Theory, and Molecular Dynamics simulations to investigate key microscopic parameters that govern charge-transport and charge-generation in single-component and bimolecular charge-transfer organic semiconductors. First, electronic (transfer integrals, bandwidths, effective masses) and electron-phonon couplings of single-component organic semiconductors are discussed. In particular, we evaluate microscopic charge-transport parameters in a series of nonlinear acenes with extended pi-conjugated cores. Our studies suggest that high charge-carrier mobilities are expected in these materials, since large electronic couplings are obtained and the formation of self-localized polarons due to local and nonlocal electron-phonon couplings is unlikely. Next, we evaluate charge detrapping due to interaction with intra-molecular crystal vibrations in order to explain changes in experimentally measured electric conductivity generated by pulse excitations in the IR region of a photoresistor based on pentacene/C60 thin film. Here, we directly relate the nonlocal electron-phonon coupling constants with variations in photoconductivity. In terms of charge-generation from an excited manifold, we evaluate the modulation of the state couplings between singlet and triplet excited states due to crystal vibrations, in order to understand the effect of lattice vibrations on singlet fission in tetracene crystal. We find that the state coupling between localized singlet and correlated triplet states is much more strongly affected by the dynamical disorder due to lattice vibrations than the coupling between the charge-transfer singlet and triplet states. Next, the impact of Hartree-Fock exchange in the description of transport properties in crystalline organic semiconductors is discussed. Depending on the nature of the electronic coupling, transfer integrals and bandwidths can show a significant increase as a function of the amount of the Hartree-Fock exchange included in the functional. Similar trend is observed for lattice relaxation energy. It is also shown that the ratio between electronic coupling and lattice relaxation energy is practically independent of the amount of the Hartree-Fock exchange, making this quantity a good candidate for incorporation into tight-binding transport models. We also demonstrate that it is possible to find an amount of the Hartree-Fock exchange that recovers (quasi-particle) band structure obtained from a highly accurate G0W0 approach. Finally, a microscopic understanding of a phase transition in charge-carrier mobility from temperature independent to thermally activated in stilbene-tetrafluoro-tetracyanoquinodimethane crystal is provided.
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10

Stires, John C. "Charge transfer complexes in molecular electronics : approaching metallic conduction /." Diss., Connect to a 24 p. preview or request complete full text in PDF formate. Access restricted to UC campuses, 2007. http://wwwlib.umi.com/cr/ucsd/fullcit?p3250672.

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11

Sánchez-Carrera, Roel S. "Theoretical characterization of charge transport in organic molecular crystals." Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26579.

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In this thesis, a first-principles methodology to investigate the impact of electron-phonon interactions on the charge-carrier mobilities in organic molecular crystals has been developed. Well-known organic materials such as oligoacene and oligothienoacene derivatives were studied in detail. The nature of the intramolecular vibronic coupling in oligoacenes and oligothienoacenes was studied using an approach that combines high-resolution gas-phase photo-electron spectroscopy measurements with first-principles quantum-mechanical calculations. The electron interactions with optical phonons in oligoacene single crystals were investigated using both density functional theory and empirical force field methods. The low-frequency optical modes are found to play a significant role in dictating the temperature dependence of the charge-transport properties in the oligoacene crystals. The microscopic charge-transport parameters in the pentathienoacene, 1,4-diiodobenzene, and 2,6-diiodo-dithieno[3,2-b:2',3'-d]thiophene crystals were also investigated. It was found that the intrinsic charge transport properties in the pentathienoacene crystal might be higher than that in two benchmark high-mobility organic crystals, i.e., pentacene and sexithienyl. For 1,4-diiodobenzene crystal, a detailed quantum-mechanical study indicated that its high mobility is primarily associated with the iodine atoms. In the 2,6-diiododithieno[3,2-b:2',3'-d]thiophene crystal, the main source of electronic interactions were found along the π-stacking direction. For negatively charged carriers, the halogen-functionalized molecular crystals show a very large polaron binding energy, which suggests significantly low charge-transport mobility for electrons.
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12

Lin, Lili. "Theoretical Modeling of Intra- and Inter-molecular Charge Transport." Doctoral thesis, KTH, Teoretisk kemi och biologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-94103.

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This thesis focuses on theoretical study of charge transportproperties in molecular systems. The understanding of the transportprocess and mechanism in molecular systems is essential forthe design of new functional molecular materials and molecularelectronic devices. The molecular junctions and organic molecularcrystals have been used as the model systems to highlight the usefulnessof theoretical modelling. A molecular junction is a system that consists ofone or several molecules sandwiched between two electrodes.The charge transport in molecular junctions is a very complex processthat is affected by the interaction between molecules and electrodes,the surroundings, as well as electron-electron (e-e) andelectron-phonon (e-p) couplings. When the molecule-electrode couplingis strong, the transport process can be very quick. If the e-p couplingis weak, the inelastic tunneling has only negligible contributions to thetotal current and the elastic electron tunneling plays the dominant role.Furthermore, the hopping process becomes dominant in the case of strong e-pcoupling, for which the geometric relaxation of the molecule needsto be considered. In this thesis, we have examined these three kinds oftransport processes separately. The first studied system is a molecular junction consisting of aromaticallycoupled bimolecules. Its elastic electron tunneling property is simulatedusing Green's functional theory at density functional theory level.The dependence of the conductance of bimolecular junctions on the vertical distances,horizontal distances and the tilt angles has been systematically studied. Theinelastic electron tunneling spectra (IETS) of molecular junctions have beencalculated for several systems that were experimentally measured with conflictingresults and controversial assignments. Our calculations provide the reliableassignments for the experimental spectra and revealed unprecedented detailsabout the molecular conformations within the junctions under different conditions.It demonstrates that a combined theoretical and experimental IETS study is capableof accurately determining the structure of a single molecule inside the junction.The hopping process is a dominant charge transfer process in organic molecularcrystals. We have studied the charge transport ability of four kinds of n-typeorganic semiconductor materials to find out the related structure-to-propertyrelationship. It is done by adopting the quantum charge transfer rate equationcombined with the random walk approach.
QC 20120515
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13

Alavi, Ali. "Molecular-dynamics studies of thin films and charge-transfer." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358367.

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14

Martin, Lee. "Structures and properties of magnetic molecular charge transfer salts." Thesis, University College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300630.

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15

Perera, Uduwanage Gayani E. "STM Investigation of Charge-Transfer and Spintronic Molecular Systems." Ohio University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1300141817.

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16

Sánchez-Carrera, Roel S. "Theoretical characterization of charge transport in organic molecular crystals." Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26579.

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Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2009.
Committee Chair: Brédas, Jean-Luc; Committee Member: Kippelen, Bernard; Committee Member: Marder, Seth; Committee Member: Sherrill, David; Committee Member: Whetten, Robert. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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17

Mozafari, Elham. "A Theoretical Study of Charge Transport in Molecular Crystals." Licentiate thesis, Linköpings universitet, Beräkningsfysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-88111.

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The main objective of this thesis is to provide a deeper understanding of the charge transport phenomena occuring in molecular crystals. The focus is on the stability and the dynamics of the polaron as the charge carrier. To achieve this goal, a series of numerical calculations are performed using the semi-emprical "Holstien-Peierls" model. The model considers both intra- (Holstein) and inter- (Peierls) molecular interactions, in particular the electron-phonon interactions. First, the stability of the polaron in an ordered two dimensional molecular lattice with an excess charge is studied using Resilient backPropagation, RPROP, algorithm. The stability is defined by the "polaron formation energy". This formation energy is obtained for a wide range of parameter sets including both intra- and inter-molecular electron-phonon coupling strengths and their vibrational frequencies, transfer intergral and electric field. We found that the polaron formation energies lying in the range of 50-100 meV are more interesting for our studies. The second step to cover is the dynamical behaviour of the polaron. Using the stable polaron solutions acheived in the first step, an electric field is applied as an external force, pushing the charge to move. We observed that the polaron remains stable and moves with a constant velocity for only a limited range of parameter sets. Finally, the impact of disorder and temperature on the charge dynamics is considered. Adding disorder to the system will result in a more restricted parameter set space for which the polaron is dynamically stable and mobile. Temperature is included in the Newtonian equations of motion via a random force. We observed that the polaron remains localized and moves with a diffusive behaviour up to a certain temperature. If the temperature increases to values above this critical temperature, the localized polaron becomes delocalized. All this research work is coded in MATLAB software , allowing us to run the calculations, test and validate our results.
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18

Canola, Sofia <1989&gt. "Modeling charge and energy transfer in organic molecular materials." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amsdottorato.unibo.it/8131/1/Canola_Sofia_tesi.pdf.

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The understanding of nanoscale physics, chemistry and biology still poses unanswered questions such as how the optical and electrical properties of materials evolve from those of individual molecules, and organic semiconductors fall in this class of materials. The main processes occurring in such systems are both charge and energy transfer, responsible for the practical operation of electronic devices. Therefore, an understanding at a fundamental level of the electronic properties of the involved molecules can help the optimization of each process, for a better global performance of the material. My three years PhD activity was developed along two major lines of research: charge and energy transport, both based on the computational investigation of intramolecular properties and intermolecular interactions. Strictly related to energy transport are the optical properties of condensed phase materials and how they evolve from those of isolated molecular components. The charge transport properties were investigated for several organic molecular crystals showing semiconducting behavior, whose experimental crystal structure and charge mobilities are available. As the same interactions that drive the transport of charge play also a role in determining the optical properties and the energy transport in molecular aggregates, in my research activity I investigated such processes as well. In this regard, I took into account a dimer of perylene-bisimide, with the aim of elucidating the role of charge transfer states and their effect on optoelectronic properties. Additionally, to assess the propagation of excited states in a molecular material a kinetic constant is required, similarly to charge transport, but the expression in this case includes the overlap between the absorption spectrum of the acceptor and the emission spectrum of the donor. To this end I also developed a code devoted to the simulation of linear absorption and emission spectra of an isolated molecule, starting from computed quantum mechanical properties.
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19

Rubio, Pons Oscar. "Charge-transfer excitations and phtophysical properties of molecular building blocks." Doctoral thesis, KTH, Teoretisk kemi (stängd 20110512), 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-184.

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This thesis reports a state-of-the-art theoretical study of photophysical properties of organic charge-transfer aromatic molecules. These molecules are building blocks of molecular functional materials used in modern photonics technology and play essential roles in chemistry and biology in general. A good understanding of these systems is thus important. The theoretical results for permanent dipole moments of some substituted benzenes have been obtained using the coupled cluster singles and doubles (CCSD) method. The performance of density functional theory (DFT) for the geometry and electronic properties has been compared with that of traditional ab initio methods, such as Hartree-Fock, second-order Möller Plesset perturbation theory (MP2), CCSD and CCSD(T). Limitations of the DFT methods for charge transfer molecules have been demonstrated. The multi-configuration self-consistent field (MCSCF) method has been applied to understand properties of the triplet states of benzene derivatives by studying their phosphorescence with the inclusion of contributions from vibronic coupling. It has also been employed to calculate the photophysics of the thioxanthone molecule containing three benzene rings in combination with the CASPT2 method, resolving a long-standing problem concerning the possible stable conformations of the molecule. With knowledge of the building blocks a series of porphyrin derivatives with exceptionally large two-photon absorption cross sections were designed, and proposed for use in bioimaging applications. The static and dynamic properties of a few zinc and platinum organometallic compounds, being possible candidates for optical limiting devices, have also investigated.
QC 20101011
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20

Rubio, Pons Óscar. "Charge-transfer excitations and photophysical properties of molecular building blocks /." Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-184.

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21

Peckus, Domantas. "Ultrafast exciton and charge carrier dynamics in nanostructured molecular layers." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2013~D_20131220_150447-81409.

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Due to their unique properties organic semiconductors may be used for various applications in organic optoelectronic devices: light emitting devices, lasers, field-effect transistors, photovoltaic cells and etc. Despite high perspectives of organic semiconductors they are still upstaged by their inorganic counterparts. Development of organic electronics requires better understanding of electrooptical properties of organic semiconductors and relationships between their structure and functions. The main goal of this thesis is a detailed investigation of ultrafast exciton and charge carrier processes in pure organic semiconductors and their blends with fullerene derivatives. Investigated organic or silicon organic semiconductors were poly-di-n-hexylsilane (PDHS), polyfluorenes F8BT and PSF-BT, merocyanine MD376. C60 fullerene and its derivative PCBM were used in blends. Ultrafast transient absorption, fluorescence, and integral mode photocurrent measurements were used for investigations. The investigation of PDHS nanocomposites revealed that PDHS incorporation into nanopores can be used for improvement of fluorescence properties. Formation of intramolecular charge transfer state was proposed for PSF-BT neat films. Charge transfer scheme of the formation of long-lived charge pair state in PSF-BT/PCBM blend was presented. The charge pair and free charge carrier generation scheme in merocyanine blends with fullerene derivatives were discussed in detail. Analysis of measurement... [to full text]
Dėl savo unikalių savybių organiniai puslaidininkiai gali būti plačiai pritaikyti įvairiuose optoelektroniniuose prietaisuose: organiniuose šviestukuose, organiniuose lazeriuose, organiniuose tranzistoriuose ir organiniuose šviesos elementuose. Visi šie pritaikymai yra galimi dėl organinių molekulių laidumo. Nepaisant didelių organinių puslaidininkių perspektyvų, jie vis dar yra nukonkuruojami neorganinių puslaidininkių. Pagrindinis šių tezių tikslas yra detaliai ištirti eksitonų ir krūvininkų dinamikos procesus grynuose organiniuose puslaidininkiuose ir jų mišiniuose su fulereno dariniais. Buvo matuoti organiniai ir silicio organiniai puslaidininkiai: poli-di-n-heksilsilanas (PDHS), polifluoreno dariniai F8BT ir PSF-BT, merocianinas MD376. Mišiniuose naudoti fulerenai buvo C60 ir jo darinys PCBM. Tyrimams buvo naudoti ultraspartūs skirtuminės sugerties, fluorescencijos ir integralinės fotosrovės matavimai. PDHS tyrimai atskleidė, kad neorganinės matricos sumažina nespindulinį relaksacijos kanalą. PDHS nanokompozitai gali būti naudojami polimero fluorescencijos savybių: stabilumo, kvantinio našumo pagerinimui. Polifluorenų F8BT ir PSF-BT grynų plėvelių tyrimų metu nustatyti eksitonų-eksitonų anihiliacijos ir eksitonų migracijos skirtumai. Vidumolekulinės krūvio pernašos būsenos formavimasis buvo pasiūlytas PSF-BT grynoms plėvelėms. Pristatyta ilgi gyvuojančių krūvininkų porų formavimosi schema PSF-BT/PCBM mišiniuose. Krūvio pernašos būsenų formavimasis buvo ištirtas... [toliau žr. visą tekstą]
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22

Fornari, Rocco P. "Modelling charge and exciton transport in polymeric and molecular systems." Thesis, University of Warwick, 2018. http://wrap.warwick.ac.uk/110784/.

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In this thesis some fundamental aspects of charge transport and exciton dynamics in organic semiconductors are explored from a theoretical and computational point of view. After a brief review of the field of organic electronics, the theoretical methods most commonly used to describe exciton dynamics and charge transport are summarised, with an emphasis on the specific methods employed in this thesis (chapter 1). A very general kinetic rate of hopping between electronic states in the incoherent regime is then derived (chapter 2). This rate contains the most commonly used rates (Miller-Abrahams, Marcus, Marcus-Levich-Jortner) as special cases. The excitonic couplings between molecules determine the properties of excited states in biological and artificial molecular aggregates. A large number of excitonic couplings in these systems are computed (chapters 3 and 4) including both the Coulombic and the short-range (non-Coulombic) contributions as well as the thermal fluctuation of the coupling (dynamic disorder). The effect of thermal fluctuations in crystalline materials is found to be important when evaluating exciton dynamics (chapter 3). The short-range component of the coupling needs to be included when the interacting molecules are in close contact (chapter 3). The characteristics of charge transport in disordered polymers depend in principle on many parameters. With the aim of accounting for the complicated nature of these materials, a very general charge transport model is presented here (chapter 5). A detailed electronic structure with variable localization of the electronic states is obtained from a simple model Hamiltonian depending on just a few parameters. Using the hopping rate derived in chapter 2, the charge mobility along disordered polymer chains is computed. The proposed model includes features of both variable range hopping (VRH) and mobility edge (ME) models, but it starts from fewer assumptions. Donor-acceptor copolymers have a narrower transport band which in principle should result in lower mobility. Instead, the narrower band is found to enhance mobility if the other parameters are kept constant. By exploring the large parameter space of this model, the temperature dependence of mobility is found to follow a universal Arrhenius behaviour in agreement with experimental data (chapter 6). The activation energy for transport depends only on the effective electronic disorder of the polymer chain. When the 3D structure of the polymer chains and the role of inter-chain hopping are also considered (chapter 7), the mobility is found to be linearly dependent on the persistence length. The activation energy is found to depend only on the electronic disorder and not on chain rigidity.
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23

Meneau, Aurélie Yvette Béatrice. "Charge transport physics of high-mobility, solution-crystallised molecular semiconductors." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708741.

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24

Forster, Christine. "Aspects of charge exchange in ion-atom collisions." Thesis, Durham University, 1990. http://etheses.dur.ac.uk/6189/.

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The straight line semi-classical Impact Parameter method has been modified for use with classical trajectories. Ion-atom collisions have been modelled using wavefunctions expanded in terms of atomic basis states which were centred on either the target or projectile ions. Total and differential charge exchange cross-sections are presented for (^4)He(^++) and (^4)He(^+) collisions within the centre of mass energy range 0.21 kev < E(_em) < 2.5 keV. Results using curved and straight line paths are compared with data from other authors. Significant trajectory effects were found at the lower energies in the range. The curved trajectory results were lower than those from the straight line model and also lower than previous calculations carried out. At higher energies in the range there was good agreement between straight line and curved trajectory models and previous work. Differential cross-sections were found to be sensitive to the trajectories employed, and comparisons have been made with previous work. Total, state specific and differential cross- sections for charge exchange are presented for Be(^++) and H collisions using a five state basis, within the centre of mass energy range 0.111 keV < E(_em) < 0.4444 keV. There was reasonable agreement between the straight line results and previous work. There were significant trajectory effects for all the final charge transfer states. Results are presented for low-energy collisions between positively charged muons and atomic hydrogen. An eight state basis has been used. Direct excitation cross sections for n = 2 atomic states and charge transfer cross sections to Is and n = 2 have been calculated. The effect on the cross sections of using different internuclear potentials has been examined. Trajectory effects were small for charge transfer to Is but were more pronounced in the direct excitation and charge exchange cross- sections to n = 2. These results have been compared to those obtained for curved trajectory H(^+) and H collisions at the same relative velocity, to assess the validity of velocity scaling. It was found that velocity scaling was reliable for charge transfer to Is and for total electron capture cross-sections. However, it was progressively inaccurate for direct excitation and for electron capture into excited states for µ(^+) impact energies of less than 300 eV. These results are discussed and suggestions for further work are made.
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25

Murphy, John Gerard. "Charge changing and ionising collisions between positive ions." Thesis, Queen's University Belfast, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239212.

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26

Padgett, R. "Merged beam measurements of mutual neutralization with molecular ions." Thesis, University of Newcastle Upon Tyne, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242357.

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27

Hirata, Narukuni. "Molecular control of charge recombination dynamics in dye sensitised solar cells." Thesis, Imperial College London, 2006. http://hdl.handle.net/10044/1/7846.

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28

Leung, Anthony Yat-Wah. "Molecular dynamics study of shaped charge penetration and crystal structure properties." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610707.

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29

Keighley, Simon David. "Label-free detection of nucleic acids by their intrinsic molecular charge." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612387.

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Di, Motta Simone <1985&gt. "Structure-Property Relationships and Charge Transport Modeling of Organic Molecular Materials." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4573/1/dimotta_simone_tesi.pdf.

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From the perspective of a new-generation opto-electronic technology based on organic semiconductors, a major objective is to achieve a deep and detailed knowledge of the structure-property relationships, in order to optimize the electronic, optical, and charge transport properties by tuning the chemical-physical characteristics of the compounds. The purpose of this dissertation is to contribute to such understanding, through suitable theoretical and computational studies. Precisely, the structural, electronic, optical, and charge transport characteristics of several promising organic materials recently synthesized are investigated by means of an integrated approach encompassing quantum-chemical calculations, molecular dynamics and kinetic Monte Carlo simulations. Particular care is addressed to the rationalization of optical and charge transport properties in terms of both intra- and intermolecular features. Moreover, a considerable part of this project involves the development of a home-made set of procedures and parts of software code required to assist the modeling of charge transport properties in the framework of the non-adiabatic hopping mechanism applied to organic crystalline materials. As a first part of my investigations, I mainly discuss the optical, electronic, and structural properties of several core-extended rylene derivatives, which can be regarded to as model compounds for graphene nanoribbons. Two families have been studied, consisting in bay-linked perylene bisimide oligomers and N-annulated rylenes. Beside rylene derivatives, my studies also concerned electronic and spectroscopic properties of tetracene diimides, quinoidal oligothiophenes, and oxygen doped picene. As an example of device application, I studied the structural characteristics governing the efficiency of resistive molecular memories based on a derivative of benzoquinone. Finally, as a second part of my investigations, I concentrate on the charge transport properties of perylene bisimides derivatives. Precisely, a comprehensive study of the structural and thermal effects on the charge transport of several core-twisted chlorinated and fluoro-alkylated perylene bisimide n-type semiconductors is presented.
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31

Di, Motta Simone <1985&gt. "Structure-Property Relationships and Charge Transport Modeling of Organic Molecular Materials." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amsdottorato.unibo.it/4573/.

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From the perspective of a new-generation opto-electronic technology based on organic semiconductors, a major objective is to achieve a deep and detailed knowledge of the structure-property relationships, in order to optimize the electronic, optical, and charge transport properties by tuning the chemical-physical characteristics of the compounds. The purpose of this dissertation is to contribute to such understanding, through suitable theoretical and computational studies. Precisely, the structural, electronic, optical, and charge transport characteristics of several promising organic materials recently synthesized are investigated by means of an integrated approach encompassing quantum-chemical calculations, molecular dynamics and kinetic Monte Carlo simulations. Particular care is addressed to the rationalization of optical and charge transport properties in terms of both intra- and intermolecular features. Moreover, a considerable part of this project involves the development of a home-made set of procedures and parts of software code required to assist the modeling of charge transport properties in the framework of the non-adiabatic hopping mechanism applied to organic crystalline materials. As a first part of my investigations, I mainly discuss the optical, electronic, and structural properties of several core-extended rylene derivatives, which can be regarded to as model compounds for graphene nanoribbons. Two families have been studied, consisting in bay-linked perylene bisimide oligomers and N-annulated rylenes. Beside rylene derivatives, my studies also concerned electronic and spectroscopic properties of tetracene diimides, quinoidal oligothiophenes, and oxygen doped picene. As an example of device application, I studied the structural characteristics governing the efficiency of resistive molecular memories based on a derivative of benzoquinone. Finally, as a second part of my investigations, I concentrate on the charge transport properties of perylene bisimides derivatives. Precisely, a comprehensive study of the structural and thermal effects on the charge transport of several core-twisted chlorinated and fluoro-alkylated perylene bisimide n-type semiconductors is presented.
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32

Coomber, Andrew Treeve. "Magnetic and electrical properties of low dimensional molecular solids." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387616.

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33

Cowen, M. C. "Space charge effects in ion sources for quadrupole mass spectrometers." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337960.

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34

Bonnet, Marie-Laure, Vincent Robert, Masahisa Tsuchiizu, Yukiko Omori, and Yoshikazu Suzumura. "Intramolecular charge ordering in the multi molecular orbital system (TTM-TTP)I3." American Institute of Physics, 2010. http://hdl.handle.net/2237/14165.

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35

Deschler, Felix. "How molecular doping affects the charge separation process in polymer-fullerene blends." Diss., lmu, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-153170.

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36

Ravi, Sankar Ashwin. "Molecular weight effects of PBT-6 polymeric semiconductor on charge carrier mobility." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50414.

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Organic π-conjugated Donor-Acceptor copolymers are emerging as potential candidate materials for organic field effect transistor (OFET) and organic photovoltaic (OPV) applications. The electron-deficient benzothiadiazole group coupled with an electron-rich oligothiophene to form donor-acceptor copolymers has attracted significant attention. These low optical band gap materials absorb photons in the range of 400-800 nm and exhibit good thermal stability. In particular, poly(benzothiadiazole-sexithiophene) (PBT6) exhibits excellent performance in optoelectronic devices and high thermal stability. Here, we present the chemical synthesis and characterization of the polymer, PBT6. Three samples of PBT-6 with differing molecular weights in the range of Mn 18000-45000 Da were synthesized. Each polymer was characterized with respect to its photophysical, thermal properties and field-effected mobility was determined. Devices were prepared by drop-casting polymer solutions in 1,2-dichlorobenzene (DCB) onto an OFET (bottom gate/bottom contact) substrate and the devices were used to examine the charge transport properties of each polymer system. The optimal solvent to be used for processing technique was determined and surface techniques using OTS-8 and OTS-18 were compared through contact angle measurements. The measured charge carrier mobilities were in the range of 0.45-0.6 cm² / V.s. Polymer films prepared via drop-casting and which were thermal annealed exhibit mobilities as high as 0.825 cm² / V.s. This work examines the effect of molecular weight on the charge carrier transport properties and demonstrates the correlation of performance with molecular ordering. Drop-casted films of PBT-6 exhibit highly ordered crystalline lamellar structure with high degree of π- π stacking with edge-on orientation on the substrate. The longer conjugation lengths promote intrachain charge transfer. This high degree of molecular ordering in high MW samples of PBT6 improves the interchain and intrachain charge transfer leading to enhanced mobilities. The increased molecular weight (MW) facilitates in forming more uniform thin films which is vital in processing and application of polymer thin film technologies. These results and observations clearly demonstrate the potential of PBT-6 as a semiconducting material for Optoelectronic devices.
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Bruque, Nicolas Alexander. "High throughput ab initio modeling of charge transport for bio-molecular-electronics." Diss., [Riverside, Calif.] : University of California, Riverside, 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3359891.

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Thesis (Ph. D.)--University of California, Riverside, 2009.
Includes abstract. Title from first page of PDF file (viewed March 12, 2010). Available via ProQuest Digital Dissertations. Includes bibliographical references (p. 117-136). Also issued in print.
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38

Jalkh, Joanna. "Engineering of functionalized monolayers for molecular electronics." Thesis, Rennes 1, 2015. http://www.theses.fr/2015REN1S153.

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La modification des surfaces revêt un intérêt primordial dans de nombreux champs d'applications de la chimie, comme la chimie analytique et l'électronique moléculaire. Ce travail a porté sur l'étude de différentes monocouches liées de façon covalente à des surfaces conductrices (principalement le carbone) et préparées à partir de l'électroréduction de sels d'aryldiazonium. Ces monocouches organiques ont été fonctionnalisées avec des groupements terminaux électroactifs différents, et l'on s'est intéressé aux propriétés de transfert de charge (au sens large) des couches résultantes. Tout d'abord des couches portant un système redox simple à base de ferrocène ont été étudiées dans différents milieux organiques conventionnels et en milieu liquides ioniques. L'effet de l'éloignement du système redox vis-à-vis de la surface a été également analysé en variant la longueur du pont ancrant. Dans un second temps, les monocouches organiques ont été fonctionnalisées par des unités tétrathiafulvalène (TTF). Les TTF sont des molécules (donneur d'électrons) connues pour former des complexes à transfert de charge avec le tétracyanoquinodiméthane (TCNQ), accepteur d'électrons. La formation de complexes à transfert de charge entre des TTF immobilisées dans la monocouche et des dérivés TCNQ a été étudiée et modulée selon l'éloignement du TTF vis-à-vis de la surface (variation de la longueur du lien ancrant) et en fonction de la force de l'accepteur. Enfin, des monocouches avec des groupements terminaux de type fluorène ou spirobifluorène (SBF) ont été préparées. Le comportement bloquant vis-à-vis-du transfert d'électron a été étudié par microscopie électrochimique (SECM) en présence de deux médiateurs redox différents et la conductivité des couches a été évaluée par CP-AFM (microscopie à force atomique – mesure de courants locaux). Il est montré que les propriétés de transfert/transport de charges sont influencées par l'encombrement stérique associé au fluorène ou au SBF (variation de la substitution). Ces monocouches organiques stables, bien organisées apparaissent très prometteuses comme composants dans des dispositifs d'électronique moléculaire
Surface modification is of paramount importance in many fields of chemistry like analytical chemistry and molecular electronics. This work deals with the study of different monolayers covalently bound on conducting (mainly carbon) surfaces, and produced from the electroreduction of aryldiazonium salts. By introducing electroactive components in the resulting monolayers, the different studies in this work mainly focused on charge-transfer properties (in a large sense). First, monolayers bearing simple redox-active ferrocenyl terminal groups were investigated. The electrochemical behavior of these monolayers was analyzed in different conventional organic media and in ionic liquids (RTILs) and by varying the length of the bridging unit between the surface and the ferrocene groups. Second, redox-active tetrathiafulvalene (TTF) molecules were used to functionalize the monolayers. TTF molecules are well-known donor molecules able to form charge-transfer complexes with tetracyanoquinodimethane (TCNQ) as an electron-acceptor. The formation of charge-transfer complexes between immobilized TTF and TCNQ derivatives was studied and modulated by varying the chain length of the bridging unit between the TTF donor and the surface and by varying the electron-withdrawing ability of the TCNQ acceptors. Third, monolayers with fluorene and spirobifluorene (SBF) terminal groups were prepared. The blocking behavior towards electron transfer was studied by electrochemical microscopy (SECM) with two redox mediators and the conductivity of the layers was investigated by CP-AFM (Conducting Probe-Atomic Force Microscopy). Effects due to the steric hindrance of the fluorene or SBF derivatives were evidenced. Such stable, organized and organic monolayers seem to be promising candidates for molecular electronic devices
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39

Lindsay, Bernard Gregory. "State selected studies of some charge transfer and dissociative ionization collisions." Thesis, Queen's University Belfast, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317102.

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40

Fernández, Torrente Isabel [Verfasser]. "Local spectroscopy of bi-molecular self-assemblies : screening, charge transfer, and magnetism at the molecular scale / Isabel Fernández Torrente." Berlin : Freie Universität Berlin, 2008. http://d-nb.info/1023169959/34.

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41

Taboada-Serrano, Patricia Larisse. "Colloidal Interactions in Aquatic Environments: Effect of Charge Heterogeneity and Charge Asymmetry." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7521.

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The classical theory of colloids and surface science has universally been applied in modeling and calculations involving solid-liquid interfaces encountered in natural and engineered environments. However, several discrepancies between the observed behavior of charged solid-liquid interfaces and predictions by classical theory have been reported in the past decades. The hypothesis that the mean-field, pseudo-one-component approximation adopted within the framework of the classical theory is responsible for the differences observed is tested in this work via the application of modeling and experimental techniques at a molecular level. Silica and silicon nitride are selected as model charged solid surfaces, and mixtures of symmetric and asymmetric indifferent and non-indifferent electrolytes are used as liquid phases. Canonical Monte Carlo simulations (CMC) of the electrical double layer (EDL) structure of a discretely charged planar silica surface, embedded in solutions of indifferent electrolytes, reveal the presence of a size exclusion effect that is enhanced at larger values of surface charge densities. That effect translates into an unexpected behavior of the interaction forces between a charged planar surface and a spherical particle. CMC simulations of the electrostatic interactions and calculations of the EDL force between a spherical particle and a planar surface, similarly charged, reveal the presence of two attractive force components: a depletion effect almost at contact and a long-range attractive force of electrostatic origin due to ion-ion correlation effects. Those two-force components result from the consideration of discreteness of charge in the interaction of solid-liquid interfaces, and they contradict the classical theory predictions of electrostatic repulsive interaction between similarly charged surfaces. Direct interaction force measurements between a charged planar surface and a colloidal particle, performed by atomic force microscopy (AFM), reveal that, when indifferent and non-indifferent electrolytes are present in solution, surface charge modification occurs in addition to the effects on the EDL behavior reported for indifferent electrolytes. Non-uniformity and even heterogeneity of surface charge are detected due to the action of non-indifferent, asymmetric electrolytes. The phenomena observed explain the differences between the classical theory predictions and the experimental observations reported in the open literature, validating the hypothesis of this work.
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42

Siriwong, Khatcharin. "A combined quantum mechanics and molecular dynamics study of charge transfer in DNA." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972057528.

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43

Kaun, Chao-Cheng 1969. "First-principles study of charge transport in molecular wires and field effect devices." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=84269.

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In this work, we present theoretical analysis of charge transport at the molecular scale. We use a state-of-the-art theoretical tool to investigate a number of key issues of molecular electronics, paying particular attention to quantitative comparison with experimental data which have been confirmed by different labs. Our analysis allows us not only to understand the data, but also to make quantitative predictions.
We have calculated the length dependence of resistance for molecular wires, including oligophenylene thiol and alkanethiol molecules. Our results are in excellent agreement with the corresponding measured data. Our analysis provides a good understanding of charge conduction mechanism in these molecular wires. This is the first time in molecular conduction research that a parameter-free modeling agrees so well with real data. We have also studied the conformational dependence of current of a biphenyldithiol molecule in terms of the dihedral angle variations. The charge current can be tuned by this parameter, and the ratio of tuning can be as large as several hundred fold. A physical picture emerges from our analysis.
We have investigated the momentum filtering effect due to molecule orbitals. This study allows us to understand why some incoming Bloch states can conduct through the molecule, while others cannot. By adding different end-groups to the molecule, we found that conduction channels can be varied. We have also studied the gate potential control of electric current. The gate voltage shifts the resonance state of the molecule thereby inducing a current modulation. We found that the gating efficiency strongly depends on the geometry of the gate electrode. The current through a biphenyl dimethanethiol molecule is found to be switchable by applying gate voltages, and the on/off current ratio can be substantial.
Finally, using carbon nanotubes with substitutional nitrogen, we clearly demonstrate that conventional equilibrium conductance analysis was not enough to describe the whole transport features in molecular devices. A nitrogen doped zigzag nanotube showed that even a single atom substitution has increased the current flow and, for small radii tubes, narrowed the current gap. Periodical substitution makes zigzag semiconducting tubes metallic, a prediction which has been confirmed by a subsequent experiment. For an armchair metallic nanotube, doping with a single impurity reduces current. The physics of these behaviours has been addressed.
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44

Döring, Robin Carl [Verfasser]. "Charge-transfer dynamics in molecular donor-acceptor systems and heterostructures / Robin Carl Döring." Gießen : Universitätsbibliothek, 2018. http://d-nb.info/116655855X/34.

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45

Döring, Robin [Verfasser]. "Charge-transfer dynamics in molecular donor-acceptor systems and heterostructures / Robin Carl Döring." Gießen : Universitätsbibliothek, 2018. http://d-nb.info/116655855X/34.

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46

Ganeshalingam, Sashikesh. "Charge transfer of Rydberg hydrogen molecules and atoms at doped silicon surfaces." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:9f1f6bb6-47a0-47f6-ad55-52f416d08815.

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The work of this thesis focuses on the interaction of high Rydberg states of hydrogen molecules and atoms with various doped Si semiconductor surfaces with the results compared with those obtained with an atomically flat gold surface. The major part of the thesis was carried out using para-H₂ molecular Rydberg states with principal quantum number n = 17 - 21 and core rotational quantum number N⁺ = 2. Subsequently, this study was continued using H atomic Rydberg states with principal quantum number n = 29 - 34. The high Rydberg states have been produced using two-step laser excitation. For close Rydberg surface separation (< 6 n² a.u.), the Rydberg states may be ionized due to an attractive surface potential experienced by the Rydberg electron, and the remaining ion core may be detected by applying an external electric field. An efficient ion detectability method is introduced to compare the many surface ionization profiles quantitatively. The p-type doped Si surfaces enhance the detected ion-signal more than the n-type doped Si surfaces due to the presence of widely distributed positive dopant charge fields in the p-type doped Si surfaces. As the dopant density increases, the area sampled by the resultant ions becomes effectively more neutral, and the decay rate of the potential from the surface dopant charge with distance from the surface becomes more rapid. Therefore, the minimum ionization distance is also reduced with increasing dopant density. It is found that the detected ion-signal decreases with increasing dopant density of both p- and n- type doped Si surfaces. The higher-n Rydberg states have shown higher ion detectability than that of lower-n Rydberg states and this variation also becomes smaller when increasing the dopant density. Experiments involving H2 Rydberg molecules incident on various doped Si surfaces in the presence of a Stark field at the point of excitation are also presented here. The surface ionization profiles produced via both electron and ion detection schemes are measured by changing the Stark polarization. Positive surface dopant charges oppose production of backscattered electrons and negative surface dopant charges enhance the electron-signal. For the electron detection scheme, lightly doped n-type Si surfaces show higher detectability but in the case of p-type Si surfaces the more heavily doped Si surfaces give a higher detected signal. This different behaviour of the detected ion or electron signal implies a different production mechanism. Theoretical trajectory simulations were also carried out based on a new 2D surface potential model. The results qualitatively agree with the experimental results and explain the changes of the surface ionization profiles between the various dopant types and dopant densities of the Si surfaces.
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47

Jarmusik, Keith Edward. "An Improved Model for Interpreting Molecular Scale Electrostatic Interactions." Case Western Reserve University School of Graduate Studies / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1275666964.

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48

Melnyk, Anton [Verfasser]. "Relating chemical structure and molecular packing to charge transport in conjugated polymers / Anton Melnyk." Mainz : Universitätsbibliothek Mainz, 2017. http://d-nb.info/1133214800/34.

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49

Pingel, Patrick. "Morphology, charge transport properties, and molecular doping of thiophene-based organic semiconducting thin films." Phd thesis, Universität Potsdam, 2013. http://opus.kobv.de/ubp/volltexte/2014/6980/.

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Organic semiconductors combine the benefits of organic materials, i.e., low-cost production, mechanical flexibility, lightweight, and robustness, with the fundamental semiconductor properties light absorption, emission, and electrical conductivity. This class of material has several advantages over conventional inorganic semiconductors that have led, for instance, to the commercialization of organic light-emitting diodes which can nowadays be found in the displays of TVs and smartphones. Moreover, organic semiconductors will possibly lead to new electronic applications which rely on the unique mechanical and electrical properties of these materials. In order to push the development and the success of organic semiconductors forward, it is essential to understand the fundamental processes in these materials. This thesis concentrates on understanding how the charge transport in thiophene-based semiconductor layers depends on the layer morphology and how the charge transport properties can be intentionally modified by doping these layers with a strong electron acceptor. By means of optical spectroscopy, the layer morphologies of poly(3-hexylthiophene), P3HT, P3HT-fullerene bulk heterojunction blends, and oligomeric polyquaterthiophene, oligo-PQT-12, are studied as a function of temperature, molecular weight, and processing conditions. The analyses rely on the decomposition of the absorption contributions from the ordered and the disordered parts of the layers. The ordered-phase spectra are analyzed using Spano’s model. It is figured out that the fraction of aggregated chains and the interconnectivity of these domains is fundamental to a high charge carrier mobility. In P3HT layers, such structures can be grown with high-molecular weight, long P3HT chains. Low and medium molecular weight P3HT layers do also contain a significant amount of chain aggregates with high intragrain mobility; however, intergranular connectivity and, therefore, efficient macroscopic charge transport are absent. In P3HT-fullerene blend layers, a highly crystalline morphology that favors the hole transport and the solar cell efficiency can be induced by annealing procedures and the choice of a high-boiling point processing solvent. Based on scanning near-field and polarization optical microscopy, the morphology of oligo-PQT-12 layers is found to be highly crystalline which explains the rather high field-effect mobility in this material as compared to low molecular weight polythiophene fractions. On the other hand, crystalline dislocations and grain boundaries are identified which clearly limit the charge carrier mobility in oligo-PQT-12 layers. The charge transport properties of organic semiconductors can be widely tuned by molecular doping. Indeed, molecular doping is a key to highly efficient organic light-emitting diodes and solar cells. Despite this vital role, it is still not understood how mobile charge carriers are induced into the bulk semiconductor upon the doping process. This thesis contains a detailed study of the doping mechanism and the electrical properties of P3HT layers which have been p-doped by the strong molecular acceptor tetrafluorotetracyanoquinodimethane, F4TCNQ. The density of doping-induced mobile holes, their mobility, and the electrical conductivity are characterized in a broad range of acceptor concentrations. A long-standing debate on the nature of the charge transfer between P3HT and F4TCNQ is resolved by showing that almost every F4TCNQ acceptor undergoes a full-electron charge transfer with a P3HT site. However, only 5% of these charge transfer pairs can dissociate and induce a mobile hole into P3HT which contributes electrical conduction. Moreover, it is shown that the left-behind F4TCNQ ions broaden the density-of-states distribution for the doping-induced mobile holes, which is due to the longrange Coulomb attraction in the low-permittivity organic semiconductors.
Organische Halbleiter kombinieren die molekulare Vielfalt und Anpassbarkeit, die mechanische Flexibilität und die preisgünstige Herstellung und Verarbeitung von Kunststoffen mit fundamentalen Halbleitereigenschaften wie Lichtabsorption und -emission und elektrischer Leitfähigkeit. Unlängst finden organische Leuchtdioden Anwendung in den Displays von TV-Geräten und Smartphones. Für die weitere Entwicklung und den Erfolg organischer Halbleiter ist das Verständnis derer physikalischer Grundlagen unabdingbar. Ein für viele Bauteile fundamentaler Prozess ist der Transport von Ladungsträgern in der organischen Schicht. Die Ladungstransporteigenschaften werden maßgeblich durch die Struktur dieser Schicht bestimmt, z.B. durch den Grad der molekularen Ordnung, die molekulare Verbindung von kristallinen Domänen und durch Defekte der molekularen Packung. Mittels optischer Spektroskopie werden in dieser Arbeit die temperatur-, molekulargewichts- und lösemittelabhängigen Struktureigenschaften poly- und oligothiophenbasierter Schichten untersucht. Dabei basiert die Analyse der Absorptionsspektren auf der Zerlegung in die spezifischen Anteile geordneten und ungeordneten Materials. Es wird gezeigt, dass sich hohe Ladungsträgerbeweglichkeiten dann erreichen lassen, wenn der Anteil der geordneten Bereiche und deren molekulare Verbindung in den Schichten möglichst hoch und die energetische Unordnung in diesen Bereichen möglichst klein ist. Der Ladungstransport in organischen Halbleitern kann außerdem gezielt beeinflusst werden, indem die Ladungsträgerdichte und die elektrische Leitfähigkeit durch molekulares Dotieren, d.h. durch das Einbringen von Elektronenakzeptoren oder -donatoren, eingestellt werden. Obwohl der Einsatz dotierter Schichten essentiell für effiziente Leuchtdioden und Solarzellen ist, ist der Mechanismus, der zur Erzeugung freier Ladungsträger im organischen Halbleiter führt, derzeit unverstanden. In dieser Arbeit wird der Ladungstransfer zwischen dem prototypischen Elektronendonator P3HT und dem Akzeptor F4TCNQ untersucht. Es wird gezeigt, dass, entgegen verbreiteter Vorstellungen, fast alle F4TCNQ-Akzeptoren einen ganzzahligen Ladungstransfer mit P3HT eingehen, aber nur 5% dieser Paare dissoziieren und einen beweglichen Ladungsträger erzeugen, der zur elektrischen Leitfähigkeit beiträgt. Weiterhin wird gezeigt, dass die zurückgelassenen F4TCNQ-Akzeptorionen Fallenzustände für die beweglichen Ladungsträger darstellen und so die Ladungsträgerbeweglichkeit in P3HT bei schwacher Dotierung absinkt. Die elektrischen Kenngrößen Ladungsträgerkonzentration, Beweglichkeit und Leitfähigkeit von F4TCNQ-dotierten P3HT-Schichten werden in dieser Arbeit erstmals in weiten Bereichen verschiedener Akzeptorkonzentrationen untersucht.
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50

Ide, Julien. "Modeling of charge transport processes in supra-molecular architectures and at organic-organic interfaces." Thesis, Bordeaux 1, 2011. http://www.theses.fr/2011BOR14366/document.

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Abstract:
L’optimisation de cellules solaires organiques repose sur l’amélioration de différents paramètres électroniques et structuraux. En particulier, les processus de séparation et de transport de charge doivent être optimisés pour obtenir des rendements élevés. Les processus de séparation de charge dans ces dispositifs s’effectuent aux interfaces donneur/accepteur suite à un décalage entre les niveaux électroniques de ces deux matériaux. Suivant leur nature, des interactions aux interfaces peuvent conduire à l’apparition d’un dipôle pouvant favoriser ou défavoriser la génération de charges libres ; toutefois, l’origine de ce dipôle d’interface est très mal connue. Ainsi, la première partie de cette thèse s’est attaché à une meilleure compréhension de l’origine de ce dipôle en appliquant une approche théorique multi-échelle sur un système D/A typique : l’interface pentacène/C60. L’amélioration des cellules solaires organiques repose également sur l’augmentation des longueurs de diffusion d’exciton et de la mobilité des porteurs de charge dans les couches actives. Ainsi, l’extension de l’ordre structural au sein d’une hétérojonction constituée de deux cristaux liquides colonnaires électroniquement complémentaires pourrait aider à améliorer ces paramètres. En deuxième partie, nous avons donc analysé l’impact du désordre structural présent au sein d’un auto-assemblage monodimensionnel de perylène diimide sur les paramètres électroniques gouvernant le transport de charge en couplant des calculs de dynamique moléculaire à des calculs de chimie quantique. Les mobilités des porteurs de charge ont été estimées en simulant des mesures de mobilité en temps de vol calculées dans le cadre du formalisme de Marcus puis comparées à l’expérience. Des résultats préliminaires issus de simulations de dynamique moléculaire sur une hétérojonction entre deux cristaux liquides électroniquement complémentaire récemment synthétisés ont été reportés en dernière partie
The development of efficient organic solar cells relies on the optimization of different correlated electronic and structural parameters. In particular, efficient charge separation and charge transport processes are essential to get high conversion yields. The charge separation processes in these devices occur at the donor/acceptor interfaces due to the energetic mismatch between the electronic structures of the two materials. Depending on the nature of these materials, interfacial interactions may lead to the appearance of a significant dipole that can help or disadvantage the generation of free charges. However, the origin of this interface dipole is still unclear. Thus, the first part of this thesis presents a multiscale theoretical approach to address the origin of the interface dipole at a prototypical D/A interface: the pentacene/C60 interface. Improving of the conversion efficiency of organic solar cells also relies on the increase of both the exciton diffusion length and of the charge carrier mobilities. For this purpose, a possible route is to expand the structural order inside the heterojunction via the self-organization of two electronically complementary columnar liquid crystals. This point is investigated in the second part of this thesis. First, we address the impact of the structural disorder on the electronic parameters mediating the charge transport properties in a one-dimensional self-assembly of perylene diimides by coupling molecular dynamics simulations to quantum-chemical calculations. The charge carrier mobilities are evaluated by means of time-of-flight numerical simulations in the framework of the Marcus formalism and compared to the experience. Then, we present preliminary results issued from atomistic molecular dynamics simulations on the heterojunction between two recently synthesized electronically complementary discotic liquid crystals
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