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A Concept for Molecular Addressing by Means of Far-reaching Electromagnetic Interactions in the Visible
摘要： A pronounced concentration dependence of the time constant of fluorescence decay was found, disproving Strickler-Berg’s equation restricting molecular light emission to a local process. Thus, interactions were found significantly extending to more than 100 nm and make such systems promising for interfaces between molecular dots or more complex molecular arrangements and conventional macroscopic electronics.
关键词： Interfaces,Fluorescence,Strickler-Berg-equation,Molecular electronics
更新于2025-09-23 15:23:52
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Long-Range Activationless Photostimulated Charge Transport in Symmetric Molecular Junctions
摘要： Molecular electronic junctions consisting of nitroazobenzene oligomers covalently bonded to a conducting carbon surface using an established 'all-carbon' device design were illuminated with UV?vis light through a partially transparent top electrode. Monitoring junction conductance with a DC bias imposed permitted observation of photocurrents while varying the incident wavelength, intensity, molecular layer thickness, and temperature. The photocurrent spectrum tracked the in situ absorption spectrum of nitroazobenzene, increased linearly with light intensity, and depended exponentially on applied bias. The electronic characteristics of the photocurrent differed dramatically from those of the same device in the dark, with orders of magnitude higher conductance and very weak attenuation with molecular layer thickness (β = 0.14 nm?1 for thickness above 5 nm). The temperature dependence of the photocurrent was opposite that of the dark current, with a 35% decrease in conductance between 80 and 450 K, while the dark current increased by a factor of 4.5 over the same range. The photocurrent was similar to the dark current for thin molecular layers but greatly exceeded the dark current for low bias and thick molecular layers. We conclude that the light and dark mechanisms are additive, with photoexcited carriers transported without thermal activation for a thickness range of 5?10 nm. The inverse temperature dependence is likely due to scattering or recombination events, both of which increase with temperature and in turn decrease the photocurrent. Photostimulated resonant transport potentially widens the breadth of conceivable molecular electronic devices and may have immediate value for wavelength-specific photodetection.
关键词： charge transport,optoelectronics,photocurrent,molecular electronics,molecular orbital energy,tunneling barrier,HOMO?LUMO gap,photoinduced transport
更新于2025-09-23 15:22:29
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Electroburning of few-layer graphene flakes, epitaxial graphene, and turbostratic graphene discs in air and under vacuum
摘要： Graphene-based electrodes are very promising for molecular electronics and spintronics. Here we report a systematic characterization of the electroburning (EB) process, leading to the formation of nanometer-spaced gaps, on different types of few-layer graphene (namely mechanically exfoliated graphene on SiO2, graphene epitaxially grown on the C-face of SiC and turbostratic graphene discs deposited on SiO2) under air and vacuum conditions. The EB process is found to depend on both the graphene type and on the ambient conditions. For the mechanically exfoliated graphene, performing EB under vacuum leads to a higher yield of nanometer-gap formation than working in air. Conversely, for graphene on SiC the EB process is not successful under vacuum. Finally, the EB is possible with turbostratic graphene discs only after the creation of a constriction in the sample using lithographic patterning.
关键词： graphene,graphene based electrodes,molecular electronics,molecular spintronics
更新于2025-09-23 15:22:29
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Surface enhanced Raman scattering on molecule junction
摘要： Surface enhanced Raman scattering (SERS) is a powerful tool to study a small number of molecules adsorbed on metal surface. Recently, SERS is utilized to investigate the atomic structure of the molecule junction, which is a key component of molecular electronic devices. It is because the molecule is trapped between nano gap electrodes, and strong enhanced ?eld is formed in the gap. The Raman signal from the molecule in the molecular junction is selectively observed. The SERS was ?rst studied for the molecule junction, where small number of molecules bridge metal electrodes. Currently, the SERS of the single molecule junction is also reported. In this review, we discuss the history of the SERS of the molecule junction, and application of SERS to the molecule junction. Structural change induced by the application of the voltage across the junction and the chemical reaction on the single molecule junction have been reported with SERS.
关键词： Surface enhance Raman scattering,Molecular electronics,Single molecular junction
更新于2025-09-23 15:21:21
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Controlling and Observing of Sharp-Valleyed Quantum Interference Effect in Single Molecular Junctions
摘要： The ability to control the quantum interference (QI) effect in single molecular junctions is attractive in the application of molecular electronics. Herein we report that the QI effect of meta-benzene based molecule with dihydrobenzo[b]thiophene as the anchoring group (meta-BT) can be controlled by manipulating the electrode potential of the junctions in electrolyte while the redox state of the molecule does not change. More than two orders of magnitude conductance change is observed for meta-BT ranging from < 10-6.0 G0 to 10-3.3 G0 with varying the electrode potential, while the upper value is even larger than the conductance of para-BT (para-benzene based molecule with anchoring group of dihydrobenzo[b]thiophene). This phenomenon is attributed to the shifting of energy level alignment between the molecule and electrodes under electrode potential control. Calculation is carried out to predict the transmission function of single molecular junction and the work function of Au surface in the presence of the molecule, and good agreement is found between theory and experiments, both showing sharp-valley featured destructive QI effect for the meta-BT. The present work demonstrates that the QI effect can be tuned through electrochemical gating without change of molecular redox states, which provides a feasible way towards realization of effective molecular switches.
关键词： molecular electronics,single molecular junctions,electrochemical gating,conductance,quantum interference
更新于2025-09-23 15:21:01
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Unraveling Doping Capability of Conjugated Polymers for Strategic Manipulation of Electric Dipole Layer toward Efficient Charge Collection in Perovskite Solar Cells
摘要： Developing electrical organic conductors is challenging because of the difficulties involved in generating free charge carriers through chemical doping. To devise a novel doping platform, the doping capabilities of four designed conjugated polymers (CPs) are quantitatively characterized using an AC Hall-effect device. The resulting carrier density is related to the degree of electronic coupling between the CP repeating unit and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), and doped PIDF-BT provides an outstanding electrical conductivity, exceeding 210 S cm?1, mainly due to the doping-assisted facile carrier generation and relatively fast carrier mobility. In addition, it is noted that a slight increment in the electron-withdrawing ability of the repeating unit in each CP diminishes electronic coupling with F4-TCNQ, and severely deteriorates the doping efficiency including the alteration of operating doping mechanism for the CPs. Furthermore, when PIDF-BT with high doping capability is applied to the hole transporting layer, with F4-TCNQ as the interfacial doping layer at the interface with perovskite, the power conversion efficiency of the perovskite solar cell improves significantly, from 17.4% to over 20%, owing to the ameliorated charge-collection efficiency. X-ray photoelectron spectroscopy and Kelvin probe analyses verify that the improved solar cell performance originates from the increase in the built-in potential because of the generation of electric dipole layer.
关键词： conjugated polymers,conducting polymers,doping,molecular electronics,solar cells
更新于2025-09-23 15:21:01
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Nanoscale junctions for single molecule electronics fabricated using bilayer nanoimprint lithography combined with feedback controlled electromigration
摘要： Nanoscale Junctions for Single Molecule Electronics Fabricated using Bilayer Nanoimprint Lithography combined with Feedback Controlled Electromigration. Nanoimprint lithography (NIL) is a fast, simple and high throughput technique that allows fabrication of structures with nanometre precision features at low cost. We present an advanced bilayer nanoimprint lithography approach to fabricate four terminal nanojunction devices for use in single molecule electronic studies. In the first part of this work, we demonstrate a NIL lift-off process using a bilayer resist technique that negates problems associated with metal side-wall tearing during lift-off. In addition to precise nanoscale feature replication, we show that it is possible to imprint micron-sized features while still maintaining a bilayer structure enabling an undercut resist structure to be formed. This is accomplished by choosing suitable imprint parameters as well as residual layer etching depth and development time. We then use a feedback controlled electromigration procedure, to produce room-temperature stable nanogap electrodes with sizes below 2 nm. This approach facilitates the integration of molecules in stable, solid-state molecular electronic devices as demonstrated by incorporating benzenethiol as molecular bridges between the electrodes and characterizing its electronics properties through current-voltage measurements. The observation of molecular transport signatures, showing current suppression in the I-V behaviour at low voltage, which is then lifted at high voltage, signifying on- and off-resonant transport through molecular levels as a function of voltage, is confirmed in repeated I-V sweeps. The large conductance, symmetry of the I-V sweep and small value of the voltage minimum in Transition Voltage Spectroscopy indicates the bridging of the two benzenethiol molecules is by π–stacking.
关键词： electromigration,transition voltage spectroscopy,nanoimprint,lithography,benzenethiol,bilayer resist,molecular bridge,molecular electronics
更新于2025-09-16 10:30:52
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Scenarios of local spectral property and multifunctional spin selecting for a triple quantum dot molecule: How do the bonding and antibonding orbitals contribute to the spin currents?
摘要： Molecular electronic device is considered as a promising candidate for next generation electronic component, where the basic challenge involves understanding the charge and spin transports through molecular objects. In this paper, with the help of the sophisticated numerical renormalization group technique, we study theoretically the spin selective transport in a parallel triple quantum dot molecular device pierced by a local magnetic field along z axis. Based on simplified parameters of real molecular system, we find such device acts as a multi-functional spin selector when the inter-molecule tunneling couplings are asymmetric, including two 100% polarized spin-up summits, and one 100% spin-down summit in the linear conductance. We show in detail the local density of states for the bonding and anti-boding orbitals, and attribute the spin selection to the orbital polarized Coulomb blockade effect. We demonstrate our numerical results are consistent with those estimated by the analytical techniques, including the Friedel sum rule and the energy level crossings of the isolated orbitals.
关键词： Coulomb blockade effect,Multifunctional spin selector,Triple quantum dot molecule,Numerical renormalization group technique,Molecular electronics device
更新于2025-09-12 10:27:22
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Orbital Control of Long Range Transport in Conjugated and Metal-Centered Molecular Electronic Junctions
摘要： Large area molecular junctions consisting of covalently bonded molecular layers between conducting carbon electrodes were compared for Co and Ru complexes as well as nitroazobenzene and anthraquinone, in order to investigate the effect of molecular structure and orbital energies on electronic behavior. A wide range of molecular layer thickness (d) from 1.5-28 nm was examined, and revealed three distinct transport regimes in attenuation plots of current density (J) vs thickness. For d < 5 nm, the four molecular structures had comparable current densities and thickness dependence despite significant differences in orbital energies, consistent with coherent tunneling and strong electronic coupling between the molecules and contacts. For d > 12 nm, transport depends on electric field rather than bias, with the slope of ln J vs d near zero when plotted at constant electric field. At low temperature (T < 150 K), transport is nearly activationless and likely occurs by sequential tunneling and/or field induced ionization. For d =5-10 nm, transport correlates with the energy gap between the highest occupied and lowest unoccupied molecular orbitals, and ln J is linear with the square root of the bias or electric field. Such linearity occurs for all three transport regimes, and is consistent with energy barrier lowering by the applied electric field. The results clearly indicate a strong dependence of charge transport on molecular orbital energies provided d> 5 nm, with a variation of seven orders of magnitude of J for different molecules and d=10 nm. The results provide insights into charge transport mechanisms as well as a basis for rational design of molecular electronic devices.
关键词： molecular electronics,molecular junction,charge transport,multistep tunneling
更新于2025-09-10 09:29:36
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Reference Module in Chemistry, Molecular Sciences and Chemical Engineering || Switching Behavior of Tripodal Molecules on Au(111) Studied With STM
摘要： The electric conductance is one of the fundamental properties of a molecular junction and of highest importance with regard to future applications of molecular electronics. It is well-known that the molecular functionality in a junction can drastically deviate from the functionality in the gas phase. Therefore, in order to properly design a molecular circuit, the overall system has to be considered including the electrodes and the coupling between the molecule and the leads. Besides the molecular core structure, the chemical design of the molecule has to take into account the anchoring groups that form the contact to the metal electrodes. Ideally, the anchoring groups fulfill several requirements. Most importantly, they make the molecule adsorb in a well-defined geometry on the designated substrate, and they allow for sufficient charge transport across the molecular core. In addition to suitable anchoring groups, the coupling to the electrodes can be controlled by the overall design of the molecule. In particular, a tripodal arrangement of the molecular foot structure ensures a well-defined adsorption geometry and allows for a functional group protruding from the surface by design. These three-dimensional molecules are exceptionally suited for contacting experiments using scanning probe techniques as they circumvent the experimental inconvenience when picking up a two-dimensional molecule typically implying irreversibility due to plastic deformations. In contrast to flat-lying, two-dimensional molecules electrons can be injected in well-defined configuration. One drawback with regard to scanning probe techniques is the limited access to the foot structure.
关键词： anchoring groups,STM,molecular electronics,tripodal molecules,conductance
更新于2025-09-10 09:29:36