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Dissertations / Theses on the topic 'Molecular electronics'
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1
Rajagopal, Senthil Arun. "SINGLE MOLECULE ELECTRONICS AND NANOFABRICATION OF MOLECULAR ELECTRONIC DEVICES." Miami University / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=miami1155330219.
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Jäckel, Frank. "Self assembly and electronic properties of conjugated molecules: towards mono molecular electronics." [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=975579010.
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Peters, Ben. "Switchable molecular electronics." Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.497070.
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Qian, Xiaofeng. "Electronic structure and transport in molecular and nanoscale electronics." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44783.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008.Includes bibliographical references (p. 239-256).
Two approaches based on first-principles method are developed to qualitatively and quantitatively study electronic structure and phase-coherent transport in molecular and nanoscale electronics, where both quantum mechanical nature of electrons and dimensionality of systems play the critical roles in their electronic, magnetic and optical properties. Our first approach is based on Green's function method with ab initio quasiatomic orbitals within Landauer formalism. To efficiently and accurately apply Green's function method, we develop a minimal basis-set of quasiatomic orbitals from plane-wave density functional theory (DFT) results. This minimal basis-set resembles quasi-angular momentum characteristics in solid state systems and it further validates Slater's original idea of linear combinations of atomic orbitals. Based on their ab initio tight-binding matrices, the accuracy, efficiency and stability of our scheme are demonstrated by various examples, including band structure, Fermi surface, Mülliken charge, bond order, and quasiatomic-orbitals-projected band structure and quasiatomic-orbitals-projected Fermi surface. Remarkably these quasiatomic orbitals reveal the symmetry and chemical bonding nature of different molecular, surface and solid systems. With this minimal basis-set, quantum conductance and density of states of coherent electron transport are calculated by Green's function method in the Landauer formalism. Several molecular and nanoscale systems are investigated including atomic wires, benzene dithiolate, phenalenyl dithiolate and carbon nanotube with and without different types of defects.
(cont.) Conductance eigenchannel decomposition, phase-encoded conductance eigenchannel visualization, and local current mapping are applied to achieve deeper understandings of electron transport mechanism, including spin dependence, dimensionality dependence, defect dependence, and quantum loop current induced by time-reversal symmetry breaking. Our second approach naturally arises due to the fact that electron transport is an excited state process. Time-dependent density functional theory (TDDFT) is a fundamental approach to account for dynamical correlations of wave functions and correct band gap in DFT. In our second approach, we mainly focus on the mathematical formulation and algorithm development of TDDFT with ultrasoft pseudopotentials and projector augmented wave method. Calculated optical absorption spectrum gives correct positions and shapes of excitation peaks compared to experimental results and other TDDFT results with norm-conserving pseudopotentials. Our method is further applied to study Fermi electron transmission through benzene dithiolate molecular junction sandwiched by two gold chains. It is first verified that group velocity of Fermi electron in the gold chain obtained by TDDFT agrees with that from band structure theory. Then under rigid band and zero bias approximations, a tiny Fermi electron wave packet from the chain is injected into the molecular junction. Transmission coefficient evaluated after the scattering process is around 5%. This is in agreement with the result from Green's function method. The two methods also show similar characteristic propagation channel. This nice agreement verifies that Green's function approach based on DFT reaches the TDDFT result without dynamical electron correlations in the linear response region.
(cont.) With further development, our quasiatomic orbitals can serve as a minimal basis-set to combine non-equilibrium Green's function and TDDFT together with GW quasi-particle corrections. The unified method will provide a more accurate and efficient way to explore various molecular and nanoscale electronic devices such as chemical sensor, electromechanical device, magnetic memory, and optical electronics.
by Xiaofeng Qian.
Ph.D.
5
Larade, Brian. "Theory of molecular electronics." Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=38496.
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One of the central problems of molecular electronics is to understand electron conduction properties when a functional molecule is interfaced with external electrodes and put under external bias and gate potentials. These properties are influenced by the molecule-electrode interaction as well as by the structure of the functional region of the device. In this thesis, we investigate from first-principles the transport properties of a number of molecular-scale systems, and try to relate the observed features to both the atomic and electronic structure.We start with a detailed analysis of transport through carbon atomic wires, and find that the equilibrium conductance is sensitive to charge transfer doping, and that the I-V characteristics exhibit negative differential resistance at high bias due to a shift of conduction channels relative to the states of the electrodes.
Using a Sc3N C80 metallofullerene device, we address several general questions about quantum transport through molecular systems and provide strong evidence that transport in such molecular devices is mediated by molecular electronic states which have been renormalized by the device environment.
The possibility of inducing nuclear dynamics in single-molecule Au-C 60-Au transistors via inelastic, resonance-mediated tunneling current is examined using a method based on the combination of a theory of current-triggered dynamics[1] and our nonequilibrium Green's function approach of computing electron transport properties.
We investigate several single molecule field-effect transistors consisting of conjugated molecules in contact with metallic electrodes. The source-drain current is found to be sensitive to the external gate potential and the molecular structure; with modulations of the current as large as several thousand fold.
Given a proposed operation principle, we obtain quantitative results on the rectification properties for an organic molecule rectifying diode. The I-V characteristic shows clear rectification behavior, and is explained from the simple picture of shifting of molecular levels due to substituents and an externally applied bias voltage.
Finally, we report a formulation combining density functional theory with the Keldysh nonequilibrium Green's function, for calculating quantum mechanical forces under external bias and during electron transport. We present an example force calculation consisting of a single atom point contact.
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Ryno, Sean Michael. "Molecular-scale understanding of electronic polarization in organic molecular crystals." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53919.
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Organic electronic materials, possessing conjugated π-systems, are extensively used as the active layers in organic electronic devices, where they are responsible for charge transport. In this dissertation, we employ a combination of quantum-mechanical and molecular- mechanics methods to provide insight into how molecular structure, orientation, packing, and local molecular environment influence the energetic landscape experienced by an excess charge in these organic electronic materials. We begin with an overview of charge transport in organic electronic materials with a focus on electronic polarization while discussing recent models, followed by a review of the computational methods employed throughout our investigations.
We provide a bottom-up approach to the problem of describing electronic polarization by first laying the framework of our model and comparing calculated properties of bulk materials to available experimental data and previously proposed models. We then explore the effects of changing the electronic structure of our systems though perfluorination, and investigate the effects of modifying the crystalline packing through the addition of bulky functional groups while investigating how the non-bonded interactions between molecular neighbors change in different packing motifs.
As interfaces are common in organic electronics and important processes such as charge transport and charge separation occur at these interfaces, we model organic-vacuum and organic-organic interfaces to determine the effect changing the environment from bulk to interface has on the electronic polarization. We first investigate the effects of removing polarizable medium adjacent to the charge carrier and then, by modeling a realistic organic- organic interface in a model solar cell, probe the environment of each molecular site at the interface to gain a more complete understanding of the complex energetic landscape. Finally, we conclude with a study of the non-bonded interactions in linear oligoacene dimers, model π-conjugated materials, to assess the impact of dimer configuration and acene length on the intermolecular interaction energy, and highlight the importance of dispersion and charge penetration to these systems.
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Li, Elise Yu-Tzu. "Electronic structure and quantum conductance of molecular and nano electronics." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/65270.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 129-137).
This thesis is dedicated to the application of a large-scale first-principles approach to study the electronic structure and quantum conductance of realistic nanomaterials. Three systems are studied using Landauer formalism, Green's function technique and maximally localized Wannier functions. The main focus of this thesis lies on clarifying the effect of chemical modifications on electron transport at the nanoscale, as well as on predicting and designing new type of molecular and nanoelectronic devices. In the first study, we suggest and investigate a quantum interference effect in the porphyrin family molecules. We show that the transmission through a porphyrin molecule at or near the Fermi level varies by orders of magnitude following hydrogen tautomerization. The switching behavior identified in porphyrins implies new application directions in single molecular devices and molecular-size memory elements. Moving on from single molecules to a larger scale, we study the effect of chemical functionalizations to the transport properties of carbon nanotubes. We propose several covalent functionalization schemes for carbon nanotubes which display switchable on/off conductance in metallic tubes. The switching action is achieved by reversible control of bond-cleavage chemistry in [1+2] cycloadditions, via the 8p 3 8s p 2 rehybridization it induces; this leads to remarkable changes of conductance even at very low degrees of functionalization. Several strategies for real-time control on the conductance of carbon nanotubes are then proposed. Such designer functional groups would allow for the first time direct control of the electrical properties of metallic carbon nanotubes, with extensive applications in nanoscale devices. In the last part of the thesis we address the issue of low electrical conductivity observed in carbon nanotube networks. We characterize intertube tunneling between carbon nanotube junctions with or without a covalent linker, and explore the possibility of improving intertube coupling and enhance electrical tunneling by transition metal adsorptions on CNT surfaces. The strong hybridization between transition metal d orbitals with the CNT [pi] orbitals serves as an excellent electrical bridge for a broken carbon nanotube junction. The binding and coupling between a transition metal atom and sandwiching nanotubes can be even stronger in case of nitrogendoped carbon nanotubes. Our studies suggest a more effective strategy than the current cross-linking methods used in carbon nanotube networks.
by Elise Yu-Tzu Li.
Ph.D.
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Wiles, Alan Andrew. "Redox active molecules with molecular electronics and synthetic applications." Thesis, University of Glasgow, 2013. http://theses.gla.ac.uk/4878/.
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Redox active molecules are ubiquitous to nature and have properties that make them coveted targets for applications in areas of synthesis as well as for the development of materials. This thesis describes the synthesis and characterisation of several flavin donor-acceptor dyads designed around an oligothiophene donor backbone and a flavin acceptor moiety. These show potential applications as optoelectronic materials. It also describes the synthesis of a ferrocene-flavin tetracyanobutadiene super-acceptor compound which showed preliminary evidence of non-linear-optic effects. Finally, a novel method was developed to investigate the redox umpolung activated reactions of vinylferrocene. The vinyl group of vinylferrocene was activated by polarity inversion of ferrocene to ferrocenium and was able to undergo Diels-Alder cycloadditions with cyclobutadiene and furan, as well as, Markovnikov addition of thiols. These reactions were then used to explore the use of vinylferrocene as a redox auxiliary and as a redox active tag in polymers and have the potential to be used in nanoparticles as well as biological systems.
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Ruttkowski, Eike. "Device development for molecular electronics /." Göttingen : Sierke, 2007. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=016480628&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Vezzoli, Andrea. "Environmental effects in molecular electronics." Thesis, University of Liverpool, 2015. http://livrepository.liverpool.ac.uk/2031980/.
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Researchers have looked at the possibility of using single molecules as functional building blocks in electronics circuits since the 1970s. The field of molecular electronics, despite its experimental and theoretical challenges, has continued to grow incessantly from a simple scientific curiosity to an emerging field with hundreds of publications per year. Thanks to the development of scanning probe microscopy a variety of techniques currently used to characterise the electrical properties of single molecules has been developed, and molecular systems mimicking the behaviour of traditional electronic components, such as transistors or rectifiers, have been prepared. Despite the obvious fact that supramolecular interactions must play a role in the charge transfer process, only a small number of reports on the subject have been published. In this thesis a set of molecular wires with an oligothiophene central unit, sandwiched between two insulating chains, has been used to probe the effect of such interactions on molecular conductance using several scanning tunnelling microscopy techniques. It has been found that the side-chain length has little effect on molecular conductance, but the presence of water in the surrounding environment triggers an increase in conductance and a switch in the behaviour from activationless to thermally-activated. Furthermore, upon exposure to electron-withdrawing small molecules, these oligothiophene molecular wires form charge transfer complexes, with conductance enhanced by a factor up to 100. Measurements performed in UHV confirmed the observed behaviour, and theoretical calculations were performed to explain it in the coherent tunnelling regime. A gateway state arising from coupling of the molecular backbone to the sulfur contacts accounts for the observed shallow decay of conductance with length, while shifting of transport resonances upon interaction with water and the appearance of interference features upon charge transfer complexation explained the temperature dependence and the conductance enhancement, with experimental observation closely matched by DFT calculations.
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SONEDDA, STEFANO. "Integrated Electronics for Molecular Biosensing." Doctoral thesis, Università degli Studi di Cagliari, 2021. http://hdl.handle.net/11584/310631.
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This thesis, Integrated electronics for molecular biosensing, focuses on different approaches to sense the presence and activity of a specific analyte by using integrated electronic platforms. The aim of the first platform is to detect the enzyme telomerase. Telomerase causes the elongation of telomeres, which are part of the chromosomes, and determines the lifespan of cells. Telomerase expression is a marker of malignity in tumoral cells and its evaluation can be exploited for early diagnosis of many types of cancer cells. To detect the telomerase enzyme, a CMOS (complementary metal-oxide semiconductor) biosensor based on CMFET (Charge-Modulated Field Effect Transistor) able to measure kinetics of DNA replication and telomerase reaction was developed. The sensor can be functionalized by immobilizing single strands of DNA that contain the telomeric sequence, used as probes. If telomerase is present, the probes will be elongated by the enzyme and the charge on the sensing area will change, which reflects in a variation of the output current or voltage. The chip includes three different readout schemes (voltage, current- and time-based), each of which has different measuring ranges and operating conditions. The measured data is then digitized, stored, and can be sent off-chip through SPI (Serial Peripheral Interface) protocol. A total of 1024 biosensors have been integrated in a single chip with a size of 10x10 mm2. Each sensor can be independently addressed and functionalized by an electrochemical procedure using an integrated potentiostat, thus requiring no external equipment. Although the sensors have been tailored and optimized to perform telomerase detection, the sensing areas can be functionalized to be used with different analytes. This feature turns the chip into a complete bioassay platform.
The second part of this work rises from the idea that bacteria, like Escherichia coli, can detect analytes in solution even at extremely low concentrations and change their movement through a process called chemotaxis, to move towards chemical gradients in the solution. E. coli moves by rotating its flagella either clockwise (for random tumbles) or counterclockwise (for straight runs, when it senses a chemical it is attracted to). Therefore, observing bacteria flagellar rotation can give enough information on the presence of a specific analyte in the solution. To electronically detect bacteria movement, an active surface covered in electrodes has been designed. By measuring the impedance between each pair of electrodes through an integrated LIA (lock-in amplifier), it is possible to know how a single bacterium is moving. By that, the presence or absence of the analyte can be deduced, thus effectively turning bacteria into chemical sensors.
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Georgiev, Vihar Petkov. "Electronic structure/function relationships in metal nanowires : components for molecular electronics." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:594d870f-feef-474b-98e9-5f09505908a3.
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The dramatic expansion of the electronics industry over the past 40 years has been based on the progressive reduction in size of the silicon-based semiconductor components of integrated circuits. The miniaturisation of semi-conductor circuits cannot, however, continue indefinitely, and we are rapidly approaching the stage where quantum effects will prevent further dramatic improvements in computer performance using existing technology. As a result, the field of molecular electronics, which seeks to identify and develop much smaller molecular analogues of the transistors that make up integrated circuits, has expanded rapidly over the past few years. Recent studies suggested that extended metal atom chains (EMAC) may have many potential applications in molecular electronics, but it is clear that this potential can only be realised if we establish a link between the fundamental electronic properties of these systems and the transport of electrons. For this reason the ultimate goal of this thesis is to relate the electronic structure of extended metal chains to their electron transport properties. We address the problem using non-equilibrium Green’s function, in conjugation with density functional theory. In the results sections of this thesis we present calculations on tricobalt, trichromium and trinickel chains. Our data suggested that in the trimetal chains, the dominant electron transport channel is the σ manifold, while the π systems establish the contact with the electrodes. The implication of this is that even when the highly polarized π channels are strongly rehybridised by the applied electric field, current flow is not affected. In the trichromium systems we find that the distortion of the chain away from the symmetric equilibrium structure does not perturb the current flow but rather enhances it. Our rather counter intuitive conclusion is therefore that ‘broken wires’ (highly unsymmetric) are more efficient conductors than their symmetric counterparts. We have performed calculation on longer penta- and heptacobalt structures chains to establish the extent to which longer structures attenuate the conductance. Our calculations show significant oscillations of the conductance due to development of a one-dimensional band structure about the Fermi level. The evolution of the electron transport properties in cobalt chains with different length is a complex one, but it is clear that narrowing the band gap in longer chains makes it increasingly likely that the Fermi level will be in resonance with one or more of the orbitals of the extended metal atom chain.
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Samorí, Paolo. "Self-assembly of conjugated (macro)molecules nanostructures for molecular electronics /." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=962281530.
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Jenny, Nicolas [Verfasser]. "Synthesis of New Functional Molecules for Molecular Electronics / Nicolas Jenny." München : Verlag Dr. Hut, 2012. http://d-nb.info/1026652278/34.
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Peiris, Malwattage Chandramalika Rukmali. "Covalently linked molecule–electrode contacts toward robust molecular-electronics circuits." Thesis, Curtin University, 2020. http://hdl.handle.net/20.500.11937/84186.
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The use of molecules as active components in electronic devices is a trend in current electronics and a potential alternative to the semiconductor-based nanoelectronics. This thesis provides a step forward in terms of potential chemistries for molecular electronics on silicon. Different molecule-electrode contacts were investigated at the macro and nano-scale using electrochemical techniques and single-molecule circuits. The work also explored the potential of silicon oxide layers as alternative materials in molecular electronics, as both a static and dynamic material.
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Chiu, Po-Wen. "Towards carbon nanotube based molecular electronics." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=969392451.
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Inkpen, Michael Stephen. "Branched organometallic complexes for molecular electronics." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/39379.
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To date, investigations concerning single or small groups of molecules for molecular electronics have largely focussed upon the transfer of electrons from donor to acceptor (electrodes or redox centres), through a single molecular pathway (bridging ligand or linear structure). Herein is described the synthesis and electrochemical properties of some branched and macrocyclic compounds containing {FeCp 2 } and {Ru(dppe) 2 } centres, with phenylene ethynylene backbones and pyridyl-termini for surface binding (Chapters 2 and 5 , respectively). Such systems provide two well-defined molecular pathways for electron transfer, facilitating the study of quantum interference effects and other phenomena resulting from concurrent, and ultimately convergent, electron transport. In addition, the large-scale 'oxidative purification' of 1,1?-diiodoferrocene ( 1 ) is presented (Chapter 2) , its usefulness as a starting material being further enhanced by an investigation into the optimisation of its (typically low-moderate yielding) reactions with terminal alkynes under Sonogashira cross-coupling conditions (Chapter 3) . As part of this study, attempts to synthesise 1,1?-bis[(4-thioacetylphenyl)ethynyl]ferrocene from 1 and 4-ethynylphenylthioacetate unexpectedly produced a cyclic trimer (15) of the latter. This observation afforded an explanation as to why the Fc?C?C?C6H4?SAc motif may not be formed using this approach, and resulted in the realisation of a new route to ?-phenylthioketones in general. The linear complex Ru(dppe)2(C?C?C5H4N)2 (17) has also been prepared - a synthesis complicated by the bifunctional nature of the 4-ethynylpyridine ligand (Chapter 4). It is hoped that future conductance studies of this and extended structures will complement recent work by others on analogous complexes with isonitrile and thiolate-termini. Experiences with protecting the pyridyl nitrogen of 4-ethynylpyridine, and the moderate success of employing N-methyl-4- ethynylpyridinium triflate (19) as a ligand, are detailed. Finally, 'mixed-valence' complexes of the type [{M(L) n}2(?-BL)] (?-BL = bridging ligand) are discussed and evaluated in light of recently observed correlations between their measured ?E1/20 values (the difference between sequential redox events, ?E1/20 = E20 - E10) and IR triple bond frequencies of analogous {M(L) n}?R (R = C?O, ?C?N?C?C?Ph) complexes (a indicator of electron density at {M(L) n}) (Chapter 6). Trends in individual contributions to the free energy of comproportionation are explored for complexes of the type [{M(L) n}2(?-C?C?C?C)].
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Zhu, Jingyuan. "Solution processable nanostructures for molecular electronics." Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/30923.
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In molecular electronics, the building material (traditionally elemental semiconductor) is replaced by single molecules or a nanoscale collection of molecules. Key to molecular electronics is the ability to precisely embed molecules into a nano device/structure and to manipulate large numbers of functional devices so they can be built in parallel, with each nano-device precisely located on the electrodes. In this work, the assembly of organic and inorganic nanostructures dispersed in aqueous solutions has been controlled via chemical functionalisation. By combining this bottom-up assembly strategy with traditional top-down lithographic apporaches, the properties of these nanostructures have been investigated via a range of different techniques. The high degree of control on the molecular design through chemical synthesis and the scalability by self-assembly make this approach of interest in the field of molecular electronics. In this regard, this dissertation presents a solution-based assembly method for producing molecular transport junctions employing metallic single-walled carbon nanotubes as nanoelectrodes. On solid substrates, electrical and electronic properties have been investigated by Conducting Atomic Force Microscopy (C-AFM). Furthermore, different strategies for asymmetric junction formation have been explored towards the development of a potential nanoscale Schottky diode. Moreover, various patterning techniques based on shadow evaporation and AFM probe scratching have been investigated for the assembly of 1-D nanostructures. Nanostructures dispersed in solution were organised onto surfaces by means of dielectrophoretic assembly, and their electronic properties was then measured by the means of a probing station. In addition to the aforementioned organic nanostructures, we also report on the dispersion of boron nitride nanotubes (BNNT) by DNA wrapping, followed by the formation of nano-hybrids of boron nitride nanotubes and carbon nanotubes. Previously, researchers have adopted BNNT as a 2D dielectric layer. The work inspires me to adopt boron nitride nanotubes as 1D dielectric materials. The techniques developed in this thesis are of interest for fundamental studies of electron transport in molecules and nanostructures. Addtionally, the approaches developed in this work may facilitate the advancement of new technologies for electronics, including, but not limited to, future circuits based on single-wall carbon/boron nitride nanotubes with specific functionality.
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Wilson, Lucy Elizabeth. "Cyclic organometallic complexes for molecular electronics." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/57037.
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Interest in molecular scale electronics systems originates from the intention to miniaturise and harness the potential of electron scale electronic transfer phenomena. Current physical investigations have focused on producing and measuring systems with single molecular pathways and/or containing simple redox-active centres. Herein is described the synthesis linear, branched and cyclic {Ru(dppe)2} and {FeCp2} containing systems to enable the study of quantum interference effects and the resulting phenomena from multi-electronic pathways. In Chapter 3, a new methodology has been developed and utilised to synthesise a range of novel 1’,1’’’-biferrocene containing systems. The versatility of this method has produced an array of linear 1’,1’’’-biferrocene containing molecular wires with varying gold binding groups to allow comparison of charge through different binding groups and orientations. The multi-valency of these systems has been probed by electrochemistry, spectroelectrochemistry and DFT to classify all these systems as on the Class II/III border. The synthetic and design considerations to organometallic system are discussed, including several different routes to the cyclisation of covalently bonded conjugated systems. These results, highlight the importance of intramolecular cyclisation routes for these and result in four different cyclic products being reported. The linear, branched and cyclic {Ru(dppe)2} containing systems that resulted from these investigations will enable the study of conductance effects resulting from multiple electronic pathways and redox activity and the linear, asymmetric and symmetric cyclic ferrocene systems will complement these studies with increased redox activity and interference effects. The cyclic, branched and linear systems and have been evaluated and compared for their charge transfer properties through; electrochemistry, IR spectroscopy, spectroelectrochemistry and DFT enabling the classification of the mixed valent species and discussion of through bond and through space communication within the branched and cyclic systems.
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Wirtz, René. "DNA-based self-assembling molecular electronics." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615788.
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Unge, Mikael. "Molecular Electronics : A Theoretical Study of Electronic Structure of Bulk and Interfaces." Doctoral thesis, Linköpings universitet, Beräkningsfysik, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-6938.
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This thesis deals with theoretical studies of the electronic structure of molecules used in the context of molecular electronics. Both studies with model Hamiltonians and first principle calculations have been performed. The materials studied include molecular crystals of pentacene and DNA, which are used as active material in field-effect transistors and as tentative molecular wires, respectively. The molecular magnet compound TCNE and surface modification by means of chemisorption of TDAE on gold are also studied. Molecular crystals of pentacene are reported to have the highest field-effect mobility values for organic thin film field-effect transistors. The conduction process in field-effect transistors applications occurs in a single layer of the molecular crystal. Hence, in studies of transport properties molecular crystals of pentacene can be considered as a two dimensional system. An open question of these system is if the charge transport is bandlike or if as a result of disorder is a hopping process. We address this question in two of the included papers, paper I and paper II. The conducting properties of DNA are of interest for a broad scientific community. Biologist for understanding of oxidatively damaged DNA and physicist and the electronics community for use as a molecular wire. Some reports on the subject classifies DNA as a conductor while other report insulating behavior. The outcome of the investigations are heavily dependent on the type of DNA being studied, clearly there is a big difference between the natural and more or less random sequence in, e.g., λ-DNA and the highly ordered syntethic poly(G)-poly(C) DNA. It has been suggested that long-range correlation would yield delocalized states, i.e., bandlike transport, in natural DNA, especially in the human chromosome 22. In paper III we show that this is not the case. In general our results show that DNA containing an approximately equal amount of the four basis is an insulator in a static picture. An emerging research field is spintronics. In spintronic devices the spin of the charge carrier is as important as the charge. One can envision a device where spin alone is the carrier of information. In realizing spintronic devices, materials that are both magnetic and semiconducting are needed. Systems that exhibit both these properties are organic-based magnets. In paper IV the electronic structure of the molecular magnet compound TCNE is studied, both experimentally and theoretically. The injection of carriers from metal contacts to organic semiconductors is central to the performance of organic based devices. The interface between the metal contact and the organic material has been pointed out to be one of the device parameters that most significantly influences the device performance. This relates to the process of injection of charge carriers in to the organic material. In some contact and organic material combinations the energy barrier for charge injection can be very high. The barrier can be reduced by modify the interface dipole, this is achieved by a monolayer of adsorbed molecules at the interface. The molecule TDAE chemisorbed on gold is studied in paper V.
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Unge, Mikael. "Molecular electronics : a theoretical study of electronic structure of bulk and interfaces /." Linköping : Univ, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-6938.
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Peacock, Darren. "Parallelized multigrid applied to modeling molecular electronics." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101160.
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This thesis begins with a review on the topic of molecular electronics. The purpose of this review is to motivate the need for good theory to understand and predict molecular electronics behaviour. At present the most promising theoretical formalism for dealing with this problem is a combination of density functional theory and nonequilibrium Green's functions (NEGF-DFT). This formalism is especially attractive because it is an ab-initio technique, meaning that it is completely from first principles and does not require any empirical parameters. An implementation of this formalism has been developed by the research group of Hong Guo and is presented and explained here. A few other implementations which are similar but differ in some ways are also discussed briefly to highlight their various advantages and disadvantages.One of the difficulties of ab-initio calculations is that they can be extremely costly in terms of the computing time and memory that they require. For this reason, in addition to using appropriate approximations, sophisticated numerical analysis tech niques need to be used. One of the bottlenecks in the NEGF-DFT method is solving the Poisson equation on a large real space grid. For studying systems incorporating a gate voltage it is required to be able to solve this problem with nonperiodic boundary conditions. In order to do this a technique called multigrid is used. This thesis examines the multigrid technique and develops an efficient implementation for the purpose of use in the NEGF-DFT formalism. For large systems, where it is necessary to use especially large real space grids, it is desirable to run simulations on parallel computing clusters to handle the memory requirements and make the code run faster. For this reason a parallel implementation of multigrid is developed and tested for performance. The multigrid tool is incorporated into the NEGF-DFT formalism and tested to ensure that it is properly implemented. A few calculations are made on a benzenedithiol system with gold leads to show the effect of an applied gate voltage.
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Plank, Natalie O. V. "Functionalisation of carbon nanotubes for molecular electronics." Thesis, University of Edinburgh, 2005. http://hdl.handle.net/1842/12783.
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Carbon nanotubes (CNTs) have been chemically functionalised for electronic device applications using plasma exposure processes. Two areas of CNT device have been investigated. Firstly the conversion of the inherent p=type field effect behaviour of the CNTs to n-type field effects behaviour and secondly to control the positioning of CNTs on a substrate. To convert CNTs from p-type to n-type semiconductors, the chemically unreactive CNTs have been functionalised by exposure to fluorinated plasmas, both CF4 and SF6. Further functionalisation with 1,2-diaminoethane was then employed on functionalised CNTs exposed to a CF4 plasma at low bias conditions, the purpose of the amine molecule is to donate electrons to the CNTs. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy have confirmed both the presence of fluorine and nitrogen on the CNT surface as well as the structural integrity of the CNTs. The functionalisation mechanism was seen to depend on the ionic current density and the fluorine plasma during the initial fluorine exposure stages. Electronic characterisation of the plasma fluorinated and the 1,2-diaminoethane functionalised CNTs in backgated geometry was then applied with randomly distributed CNTs on gold electrodes. The fluorinated CNTs have exhibited p-type field dependent behaviour in air, whilst the aminated CNTs have begun to show indication of n-type field dependent behaviour. The second process used molecular stamping of 2-thiolpyridine using poly(dimethylsiloxane) (PDMS) stamps; a method which allows applications for both pristine and functionalised CNTs. Molecular stamping of 2-thiolpyridine using poly(dimethylsiloxane) (PDMS) stamping techniques, have been developed to self-assemble CNTs over a substrate and onto predefined electrode structures. By optimising the concentration of 2-thiolpyridine in ethanol and using a dilute suspension of CNTs in 1,2-dichloroethane, CNTs could be self-assembled using two similar fabrication processes. The molecular stamping experiments have confirmed that altering the order of the steps within the fabrication process, to have CNTs on top of electrodes or underneath electrodes, can control the field dependent qualities of devices in a limited gate voltage range. The limiting factor to device reproducibility is the ability to produce homogeneous CNT solutions. With control over the CNT chirality and suspension it is predicted the molecular stamping methods would be a fast and reliable process for high yield CNT devices.
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Catarelli, Samantha. "Contact and medium effects on molecular electronics." Thesis, University of Liverpool, 2014. http://livrepository.liverpool.ac.uk/2009448/.
Full textAbstract:
The initial aim of this project was to form a single-pot molecular spintronics technique. To achieve such a goal an understanding of the effect of measurement environment, and the of the metal-molecule contact are important. While the gold-thiol system has been well studied, little work has been done on the ferromagnetic contacts needed for molecular spintronics. It was therefore necessary to measure not only different metals but also different molecular anchors to work towards the best possible combination. A broadening of the understanding of the effect of the metal contact was initially performed by using PM-IRRAS to investigate molecular monolayers formed on Ni through potential assisted assembly. Co was also investigated as a possible metal for molecular spintronics. As a means of achieving a single-pot molecular spintronics setup deposition of Co from ionic liquids was investigated, although this was unsuccessful. Although a single-pot molecular spintronic system was ruled out for the time being, when used in tandem with an ionic liquid environment, Co allowed for successful single molecule conductance measurements. Furthermore these measurements showed similar conductance values to the analogous Au systems. The potential of the ionic liquid environment in molecular electronics was investigated in depth. Through the use of single molecule conductance measurements and electrochemical measurements ionic liquids were seen to be an exciting opportunity for molecular electronics. Ionic liquids extend the abilities of molecular electronics compared to more traditional environments. Furthermore the characteristics of ionic liquids can be exploited to allow desirable molecular traits to be witnessed. For example when viologen containing molecules were previously investigated in aqueous electrolytes an off-on switching was seen, whereas in ionic liquids analogous molecules showed off-on-off switching, likely as a result of the ionic liquid locking the ring conformation. This project has shown that when performing molecular electronics measurements both the environment and the metal-molecule contact are important. These findings are important to note because it means that when forming a molecular electronic system the entire junction should be carefully considered, rather than just the molecular backbone. Through careful choice of the entire molecular electronic junction a system rivaling those of traditional electronics may be formed.
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Chappell, Sarah. "Transition metal terpyridine complexes for molecular electronics." Thesis, University of Liverpool, 2014. http://livrepository.liverpool.ac.uk/2011084/.
Full textAbstract:
Currently there is a huge amount of interest in the synthesis and electrical characterisation of single molecules that have the potential for use in electronic devices. In order for this technology to move forward it is necessary to gain insights into structure-property relationships at the nanoscale, as well as a basic understanding of the charge transport through various molecular architectures. It has previously been demonstrated that the electrical properties of redox active single molecules can be investigated as a function of potential. This thesis investigates the single molecule conductance properties of molecules incorporating a transition metal centre. The research presented in this thesis investigates two major studies. The first is a study into the electrochemical and conductance properties of a variety of transition metal based complexes. Initial electrochemical and conductance investigations of a series of pyterpy transition metal complexes showed a similar conductance for all the series, this was investigated in two different environments. The ligand was then varied and several ruthenium complexes were investigated, to investigate the anchoring group effect and to examine the length and conductance relationship. The data presented here demonstrates a higher conductance for methyl sulphide anchoring group than the pyridyl anchoring group. The data presented showed a low dependence on molecular length, suggesting a hopping transport mechanism. The conductance behaviour of two [M(pyterpy)2](PF6)2 complexes were investigated as a function of potential in an ionic liquid medium. The data presented exhibited an increase in conductance as the redox potential was reached. The second study investigated the conductance behaviour of two 6-porphyrin nanorings. This is the first conductance study on these porphyrin based complexes. The study investigated a ‘complete’ and ‘broken’ nanoring and showed a smaller than expected difference in conductance between them. This preliminary study has allowed for the development of the structure to investigate possible quantum interference effects.
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Jalkh, Joanna. "Engineering of functionalized monolayers for molecular electronics." Thesis, Rennes 1, 2015. http://www.theses.fr/2015REN1S153.
Full textAbstract:
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 moléculaireSurface 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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Kulisic, Niksa. "Heteroacenes as potential materials for molecular electronics." Doctoral thesis, Università degli studi di Trieste, 2010. http://hdl.handle.net/10077/3609.
Full textAbstract:
2008/2009In this thesis, different strategies for obtaining azaacenes suitable for solution-based processing techniques have been investigated and developed. The first synthetic approach involved the condensation of commercially available compounds which include the diamines 2,3-diaminobenzene, 2,3-diaminonaphtalene and 2,3-diaminophenazine and the bromoanilic acid and embelin. This synthetic route yielded a series of dihydroazaacenes with 5 and 7 fused aromatic rings. The low overall solubility of this azaacenes did not permit an extensive characterization of the compounds. A second synthetic approach was developed to investigate both C-N exchange and lateral expansion of the π-conjugation. Through this approach a tetraazaoctacene derivative was obtained and characterized. However it lacked of solubility necessary for being compatible with solution-processing techniques. A third strategy was based on the introduction of solubilizing groups on such extended tetraazaoctacene core. While the di-substitution did not render the azaoctacene soluble in neutral media, tetra-substitution yielded a derivative with enhanced solubility in neutral solvent.
1981
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DIMONTE, ALICE. "Nanogap structures for molecular electronics and biosensing." Doctoral thesis, Politecnico di Torino, 2013. http://hdl.handle.net/11583/2506146.
Full textAbstract:
Molecular transport characterization is an active part of the research field in nanotechnology. In this interesting branch the self-assembly approach is highly exploited; it consists in spontaneous formation of highly ordered monolayers
on various substrate surfaces. Self-assembled monolayers (SAMs) have found their applications in various areas, such as nanoelectronics, surface engineering, biosensing, etc. An important area in biosensing is the electrochemical detection, that enables sensing of dierent biomarkers with an important role, for many dierent applications in biomedical diagnostics or in monitoring of biological systems. Various test structures have been developed in order to carry out characterizations of self-assembled molecules, and numerous reports have been published in the past several years on the transport characteristics.
This thesis' purpose is the single protein biomolecular sensing, that could become the starting point for monitoring drugs, developing clean energy systems,
realizing bio-opto-electronic transistors... The possibility to cover so many fields is related to the kind of proteins, molecules, bioelements that will be inserted inside sensors. Biomolecular sensing has to be thought in order to reach a result with the better compromise between instrumentation versatility and measurements precision. The main underlying idea is to use single molecules as active elements in nano-devices. As a consequence, the proper realization of a molecule-electrode contact is a crucial issue. What is needed by author is something versatile, precize, cheap, at single molecule level and able to record measurements in few time in order to do statistical characterizations. The final goal of this work is a platform system adapt for both industry and research field.
Electrical nanogap devices are the main character of this work. They have proven good performances as element for detecting small quantities of biomolecules, allowing direct transduction of biomolecular signals into useful
electrical ones such as resistance/impedance, capacitance/dielectric, or field effect. Nanogaps are now one of the most busy area of research in the nanotechnology world. Moreover, these structures do not require feedback to maintain the mutual arrangement (comparing with conducting tip AFM) and are less
stochastic with respect to electrochemical cells. Several techniques can be applied to nanogap fabrication: mechanically broken or positioned junctions, nano-scale lithography by Synchrotron radiation sources, electrochemical deposition and etching, and electromigration. None of these techniques is presently able to give precise control as to thefinal gap size. In this thesis the electromigration approach has been choosen, because of several useful characteristics. It is cost eective, because of the relatively low complexity of the required equipment. It can be embedded into a lab-on-chip
system, thus exploiting the possibility to tailor the gap formation process by means of a digital loop control system. To this end, it just requires a conventional microchip fabrication process. It allows the parallelization with a smart packaging through which it is possible to produce more probes at the same time and perform many measurements in contemporary. The employment of nanogaps, as an instrumentation for the molecular charac-
terization, has also some issues that have to be considered in order to obtain useful measurements. To characterize molecules the leakedge must be not higher than some pA to avoid the noise overcome the signal. Nanogap platform is perfect for molecular electronics. The experiments have been developed in dry way, as a consequence the solutions were evaporated before the measurement starting. This brought several problems cause biochemical analysis requires liquid solution in order to avoid an untimely death of the bio-elements tha has to be characterized. Considering a future developement, an improvement is necessary in terms of a system able to work with salty solutions without damaging the microchip's probes. Therefore it is a necessary a set-up allowing the anchorage
of a microfluidic part. At the same time it is necessary to keep in mind that the presence of a new system has to not overcome the molecule signal, maintaining the leakedge under some tens of pA.
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RATTALINO, ISMAEL. "Nanogap electrodes for molecular electronics and biosensing." Doctoral thesis, Politecnico di Torino, 2014. http://hdl.handle.net/11583/2574160.
Full textAbstract:
Singlemolecule experiments have been attracting interest since they can pave the way towards the realization of new molecular devices and biosensors. Molecular electronics could be an alternative to classical electronics to overcome the technologic dimensional limit of CMOS technology. On the other hand, biosensor downscaling can open to new detection techniques that are impossible at the conventional dimensional scale. Nowadays, single molecule experiments are mainly based on scanning probe techniques to manipulate and characterize
molecules at the nanoscale. Although these techniques have revealed effective tools, real applications are restricted by problems of miniaturization, cost, integration and portability.
Nanogap electrodes are an emerging new probing tool for single molecule experiments that can serve a function equivalent to classical probing systems, but guaranteing the integration and portability required in real applications. For these reasons, nanogap electrodes are the object of this thesis, from the fabrication to their employment in molecular electronics and biosensing.
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Carroll, Richard Lloyd. "Studies of the Structural and Electronic Properties of Self-Assembled Monolayers ? Towards Molecular Electronics." NCSU, 2001. http://www.lib.ncsu.edu/theses/available/etd-20010709-120336.
Full textAbstract:
The field of Molecular Electronics (ME) is growing at a rapid pace. The study of materials that have utility at the level of several, or single, molecules is exciting becausethe development of these sorts of systems offers a pathway to potentially avoid the perils of continually shrinking Silicon-based fabrication. This work examines the state of the art in fabrication techniques for semiconductor systems, then examines current examples of ME to be found in the academic literature. This review is designed to plumb the depths of a few important demonstrations, as opposed to a broad overview of the entire body of work. Further, scanning probe lithography techniques are demonstrated that allow for the study of small ensembles of interesting molecules in isolation. By utilizing these techniques, the structural and electronic properties of molecules can be studied, with a focus towards determining the likely utility of a particular species in a ME framework. Experimental study of redox-active self-assembled monolayer (SAM) films shows that under specific conditions, some films display a negative differential resistance (NDR) response that has possible utility in the development of ME devices. Ferrocene- and galvinol-terminated SAMs both show NDR at room temperature. A possible mechanism for the NDR behavior is believed to be resonant tunneling through low-lying, accessible redox-states in the molecule.
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Franco, Pujante Carlos. "Organic free radicals for molecular electronics and spintronics." Doctoral thesis, Universitat Autònoma de Barcelona, 2016. http://hdl.handle.net/10803/399515.
Full textAbstract:
La presente tesis doctoral se centra en el campo de la electrónica molecular, en particular se ocupa del desarrollo de nuevos dispositivos moleculares y del estudio de los fenómenos de transferencias electrónica asociados a ellos. Las propiedad de los policloro trifenilmetil radicales (PTM) han sido utilizadas en este trabajo para investigar los diferentes mecanismos de transferencia de carga asociados a varios sistemas en los cuales los PTM están involucrados.
En la primera parte de la tesis se ha descrito el estudio de los procesos de transferencia de carga a través de dos diferentes familias de hilos moleculares, una de vinilo tiofene y la otra de oligo-p-fenilenos vinilenos fusionado conectados a dos moléculas de PTM las cuales actúan como dadores y aceptores de electrones en sistemas de valencia mixta D-B-A. Estos sistemas han sido completamente caracterizados por diferentes técnicas espectroscópicas en sus diferentes estados de oxidación: neutro, de valencia mixta y oxidada. Además, los mecanismos para la transferencia electrónica intermolecular a través de estos hilos moleculares han sido elucidados.
En la segunda parte de la tesis ha sido reportada la síntesis de una familia de derivados de PTM con grupos tiol conectados al PTM a través de un cadena alquílica de diferentes longitudes, capaces de formar monocapas auotensambladas (SAM) sobre substratos de oro. Asimismo, se ha estudiado los mecanismos de transferencia electrónica a través de las SAMs de PTM en sus diferentes estados de oxidación, contactadas estas por el electrodo de eutéctico galio-indio y por el microscopio de efecto túnel.
Para finalizar, en la última parte de la tesis, se ha reportado el estudio de las propiedades magnéticas y eléctricas de dos derivados de PTM en break-juction unimoleculares de oro y HOPG. Interesante fue el hecho de que en las break-juction unimoleculares de oro, se detectó un pico Kondo lo que indica que el momento magnético del radical PTM interactúa con los electrones de conducción.The present Doctoral Thesis is framed in the field of molecular electronics, specifically is focused on the development of new molecular electronic devices and on the study of the electron transfer phenomena associated to them. We exploit the properties of polychloro thriphenylmethyl radical (PTM) molecules to explore the charge transfer mechanisms involved in many different systems containing PTM derivatives. In the first part of the Thesis, we have described the study of the charge transfer process through two different families of molecular wires, oligo vinylene-thiophne (nTV) and fused oligo-p-phenylene vinylene (nCOPV), connecting two PTM moieties acting as electron donor/acceptor in mixed valence systems D-B-A. These systems were fully characterized by different spectroscopic techniques in their neutral, mixed valence and oxidized states. The mechanism for the intramolecular charge transfer through these wires was elucidated. In the second part of Thesis we have reported the synthesis of a family of PTM derivatives containing a thiol terminal group connected to the PTM through an alkyl chain with different length, able to form self-assembled monolayers (SAM) on gold substrates. We have studied the charge transport mechanisms through PTM SAMs contacted by eutectic gallium-indium electrode and scanning tunneling microcopy, in their different redox states. Finally, in last part of the thesis we have reported the study of the electric and magnetic properties of two PTM derivatives in gold and HOPG single molecule break-junctions. On gold PTM break-junctions, a Kondo peak was detected indicating that the localized magnetic moment of PTM radical interacts with conducting electrons.
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Prasongkit, Jariyanee. "Molecular Electronics : Insight from Ab-Initio Transport Simulations." Doctoral thesis, Uppsala universitet, Materialteori, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-160474.
Full textAbstract:
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 (DFT). We apply the method to study the electronic transport properties of two-probe systems consisting of molecules or atomic wires sandwiched between leads. A few molecular electronic devices are characterized; namely, conducting molecular wires, molecular switches and molecular recognition sensors. The considered applications are interconnection of different nanoelectronic units with cumulene molecular wires; adding switching functionality to the molecular connectors by applying stress to the CNT-cumulene-CNT junction or by introducing phthalocyanine unit; sensing of individual nucleotides, e.g., for DNA sequencing applications. The obtained results provide useful insights into the electron transport properties of molecules. Several interesting and significant features are analyzed and explained in particular such as, level pinning, negative differential resistance, interfering of conducting channels etc.
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Atkins, Karen Jane. "Asymmetrically substituted donor-acceptor heterocycles for molecular electronics." Thesis, University of the West of England, Bristol, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277901.
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Truong, Tran N. B. "Molecular design for controlling morphology in organic electronics." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120904.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 140-158).
Chapter 1 gives an introduction to the structure, operation mechanism, performance parameters, and challenges of organic photovoltaic devices. We also discuss some strategies to improve the performance of photovoltaics, with an emphasis on morphology control in polymer bulk-heterojunction devices. Chapter 2 describes the synthesis of a class of polymer additives for bulk-heterojunction (BHJ) solar cells based on an extended triptycene-containing unit. The incorporation of these additives on BHJ photovoltaic devices based on PTB7 and PC71BM leads to an increase in power conversion efficiencies of 10-20%. We also found that the additives produce more consistent performance in devices, minimizing variation from processing conditions. Chapter 3 presents a modular synthetic route to access functionalized 2,5-di(thiophen-2- y1)- 1-H-arylpyrroles (SNS) from readily available starting materials. We demonstrated the use of this building block in the synthesis of conjugated polymers with high thermal stability and solubility. Characterization of the polymers reveals a correlation between molecular packing and charge carrier mobility. Chapter 4 discusses strategies to enhance conjugation in organic electronic materials, using 2,5-di(thiophenyl)-N-arylpyrrole (SNS) as a model system. The first section describes synthetic routes to access a novel polycyclic heteroaromatic building block via intramolecular cyclization reactions. The second section explores the electrochemical properties of SNS units for the opportunity to enhance conjugation via electrochemical methods.
by Tran N. B. Truong.
Ph. D.
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Marx, Eike. "Self-assembly of CdSe nanocrystals for molecular electronics." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616244.
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Nguyen, Trung Hieu, and Trung Hieu Nguyen. "Controlling Molecular Orientation with Applications to Organic Electronics." Thesis, The University of Arizona, 2017. http://hdl.handle.net/10150/624108.
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The design of organic electronic devices is heavily dependent upon the orientation of the molecular solid which influences the direction that charge carriers are able to traverse across the π-system. In this work, thin films of copper phthalocyanine (CuPc) were deposited using thermal deposition over SiO2 and CuI both substrates having demonstrated the ability to confer different orientations onto thermally evaporated CuPc. A variety of scattering and spectroscopic techniques were utilized to characterize the electronic, chemical, and crystalline structures of CuPc to determine the effects that the substrates have over these structures when the molecule's
self-assembly is altered. The findings in this study will be integrated into future works as reference points and control studies in order to draw meaningful and direct connections between MPcs that have differing electron affinity, transition metal cores, and functional groups as well as multi-layers of various MPcs within unique heterojunctions.
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Trasobares, Sánchez Jorge. "High frequency electronics on nanodot molecular junctions : interaction between molecules, ions and waves." Thesis, Lille 1, 2015. http://www.theses.fr/2015LIL10168/document.
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Une combinaison entre l’assemblage de monocouches au sommet de nano-cristaux d’or et la microscopie à sonde locale permet d’explorer l’interaction entre les molécules actives et son milieu, mais aussi démontrer expérimentalement une diode moléculaire peut travailler à haute fréquence. La fabrication des nanocristaux d’or par lithographie électronique rapide nous a permis leur caractérisation par des techniques nécessitant des surfaces millimétrique, mais également par des techniques en champ proche. La détection electrochimique d’un petit nombre de molécules par nanocrystal prévoit d’intéressantes recherches futures sur l’attache et la détection de molécules uniques sur la nano-particule d’or. D’un côté, cette étude confirme une théorie récente: les effets coopératifs entre les molécules ont un effet d’asymétrie sur « la courbe d’histogramme de conductance ». D’un autre côté, des théories d’électrochimie ont été utilisées pour investiguer les effets d’interaction entre molécules avec groupe redox et l’écart-type de l’énergie moléculaire. Cette étude nous a permis d’extraire des gammes d’énergie de couplage entre molécules, un premier pas vers une estimation quantitative expérimentale de ce paramètre clé pour les applications en électronique organique. A l’aide d’un AFM couplé à un système de mesure en hyperfréquences, nous mesurons les propriétés électroniques à l’échelle nanométrique. Nous prouvons une diode moléculaire à 18 GHz avec un ratio de redressement de 12 dB (facteur 4) à cette fréquence. Des petites capacitances, dans la gamme de l’aF ont en particulier permis d’observer ce comportement à hautes fréquencesAn attractive combination of self-assembled monolayers on top of “Au” single crystal Nanoparticles (AuNp) and Scanning Probe Microscopies permits to explore the interaction between active molecules in the junction, as well as with the media. At the same time, we demonstrate the experimental proof of a molecular rectifying diode working at gigahertz frequency. Device fabrication by fast e-beam lithography allows their characterization by techniques that may need millimeter scale surfaces as well as by near field Scanning Probe Microscopies. Detection of a little number of molecules per AuNP promises interesting future research in the challenge of grafting and detecting single molecules per nanoparticle. On the one hand, this investigation confirms a recent theoretical prediction that cooperative effects between molecules may have an effect on the asymmetry of the conductance histogram line shape. On the other hand, established electrochemical theories are exploited to investigate similar factors such as interaction between redox molecules and the modification of the energy level of molecular orbitals. This study permits extracting a range of coupling energies between molecules that may be a first step towards the quantitative experimental estimation of this key parameter in molecular electronics. Thanks to an AFM connected to Network analyzer, we characterize a molecular diode operating at high frequency to 18 GHz with a rectification ratio of 12 dB (factor 4) at this frequency. Small capacitances in the order of few aF permit to see this behavior at high frequencies
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Whitehead, Roger James. "Highly conducting molecular crystals." Thesis, University of Nottingham, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329892.
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Harzmann, Gero [Verfasser]. "Novel Tailor-Made Externally Triggerable Single- Molecular Switches for Molecular Electronics / Gero Harzmann." München : Verlag Dr. Hut, 2016. http://d-nb.info/1097817806/34.
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Van, Niekerk Philip Charl. "A Cryogenic CMOS-based Control System for Testing Superconductor Electronics." Thesis, Link to the online version, 2008. http://hdl.handle.net/10019/1338.
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Zhang, Lei, and 张磊. "First principles transport study of molecular device." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B50899557.
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This thesis discusses DC and AC transport properties of molecular devices from first principles. For dc bias, based on the non-equilibrium Green’s function (NEGF) technique coupled with the density functional theory (DFT), the dc current density distribution of a molecular device Al-C60-Al is numerically investigated from first principles. Due to the presence of non-local pseudo-potential, the conventional definition of current density is not suitable to describe the correct current density profile inside the molecular device. By using the new definition of current density which includes the contribution due to the nonlocal potential, our numerical results show that the new definition of current density J(r) conserves the current. In addition, the current obtained from the current density calculated inside the molecular device equals to that calculated from the Landauer-Büttiker formula. When the external bias is time dependent, a theoretical formalism to study the time dependent transport behavior of molecular device from first principles is proposed based on the non-equilibrium Green’s function (NEGF) and time dependent density functional theory (TDDFT). For the purpose of numerical implementation on molecular devices, a computational tractable numerical scheme is discussed in detail. The transient current of two molecular devices Al-1,4-dimethylbenzene-Al and Al-Benenze-Al are numerically studied from first principles. To overcome the computational complexity due to the memory term, a fast algorithm has been employed to speed up the calculation and CPU time has been reduced from the scaling N^3to N^2 log(_2^2)(N) for the step like pulse, where N is the number of time step in the time evolution of Green’s function.published_or_final_version
Physics
Doctoral
Doctor of Philosophy
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Ma, Yuefei. "Analysis of programmable molecular electronic systems." Texas A&M University, 2003. http://hdl.handle.net/1969.1/5997.
Full textAbstract:
The continuing scaling down in size of microelectronics devices has motivated
the development of molecular electronic devices, often called moletronics, which use
molecules to function as electronic devices. One of the moletronics is the programmable
molecular array. In this device, disordered arrays of metallic islands are interlinked by
molecules. It is addressed by a small number of input/output leads located on the
periphery of the device.
In this dissertation, a thorough investigation of the programmable molecular
array is performed. First, theoretical calculations for single molecules are carried out.
The effect of bias voltage on the electron transmission through the molecule is reported.
Next, electrical measurements are conducted on programmable molecular arrays.
Negative differential resistance and memory phenomena are found. The electrical
characteristics of the programmable molecular array populated with different molecules
indicate that the metallic islands contribute to the above phenomena. The electrical conductance through the metallic islands is investigated, and conformational change of
the metallic islands under bias is reported.
Furthermore, a scenario is proposed to use molecular vibronics and electrostatic
potential to transport and process signals inside the programmable molecular array.
Simulated results are presented.
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Bonifas, Andrew Paul. "Spectroscopy, Fabrication, and Electronic Characterization of Molecular Electronic Devices." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1305653420.
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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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Jiang, Jun. "A Quantum Chemical View of Molecular and Nano-Electronics." Doctoral thesis, Stockholm : Biotechnology, Kungliga tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4335.
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Chin, S. N. "Induced 1D hole gases and molecular electronics with nanogaps." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597607.
Full textAbstract:
This thesis comprises two distinct pieces of work. The first piece involved the fabrication and study of induced one-dimensional hole gas. The second is based on molecular electronics and consisted of the development of nanogaps and measurements of nanocrystals and molecules using the gaps. GaAs/AlGaAs heterostructure was used to create the 1D hole gas. A 2D hole gas can be induced at the GaAs/AlGaAs interface by applying a negative voltage to a surface gate. Changing the gate voltage changes the density of the holes in the 2D system. At low densities, interaction effects become more prominent. The effective mass of holes is about eight times that of electrons in GaAs. Therefore holes are much more sensitive to interaction effects and may exhibit interesting behaviours not seen in electron systems. Unfortunately the quality of wafers were not good enough. Although induced 1D hole devices have been fabricated, they could not give us new insight into physics. For the molecular electronics project a technique was developed to fabricate nanogaps of size 5 nm. These gaps have been used to study molecules and nanocrystals. Both single-particle energy levels and Coulomb charging effects are important in affecting the tunnelling spectra of the nanocrystal devices. Measurements on molecular devices have proved less successful. The molecular systems are very complex, and hold great potential for device applications. The nanogaps developed can be used to measure various nano-elements, the only requirement on the elements being the ability to self-assemble a monolayer on gold surface, which is the way nano-elements are incorporated into the gaps.
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Musumeci, Chiara. "Supramolecular electronics : from molecular wires to (semi)conducting materials." Phd thesis, Université de Strasbourg, 2014. http://tel.archives-ouvertes.fr/tel-01038014.
Full textAbstract:
Supramolecular electronics aims to construct and investigate the optoelectronic properties of tailored supramolecular nanoarchitectures. The aim of this thesis is to get control over the organization of organic molecular systems and correlate their structure with the electrical properties, with particular attention at the nanoscale properties. The exploited strategies require a focused molecular design, the balancing of intermolecular and interfacial interactions, a control on the kinetics of the processes and possibly the exploitation of external forces. The presented results showed that understanding the local properties of a material on a nanoscale basis is a huge fundamental challenge to bring solutions to both scientific and technological issues, since in electronic devices the performances are strongly dependent on the order at the supramolecular level.
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Szablewski, M. "Multi-functional D-#pi#-A materials for molecular electronics." Thesis, Cranfield University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305322.
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Wang, Lixin. "Ferrocene-based molecular electronics and nanomanufacturing of palladium nanowires." College Park, Md. : University of Maryland, 2007. http://hdl.handle.net/1903/7757.
Full textAbstract:
Thesis (Ph. D.)--University of Maryland, College Park, 2007.Thesis research directed by: Dept. of Chemistry and Biochemistry. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.