by Keyword: Conductance

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López-Martínez, Montserrat, Artés, Juan Manuel, Sarasso, Veronica, Carminati, Marco, Díez-Pérez, Ismael, Sanz, Fausto, Gorostiza, Pau, (2017). Differential electrochemical conductance imaging at the nanoscale Small 13, (36), 1700958

Electron transfer in proteins is essential in crucial biological processes. Although the fundamental aspects of biological electron transfer are well characterized, currently there are no experimental tools to determine the atomic-scale electronic pathways in redox proteins, and thus to fully understand their outstanding efficiency and environmental adaptability. This knowledge is also required to design and optimize biomolecular electronic devices. In order to measure the local conductance of an electrode surface immersed in an electrolyte, this study builds upon the current–potential spectroscopic capacity of electrochemical scanning tunneling microscopy, by adding an alternating current modulation technique. With this setup, spatially resolved, differential electrochemical conductance images under bipotentiostatic control are recorded. Differential electrochemical conductance imaging allows visualizing the reversible oxidation of an iron electrode in borate buffer and individual azurin proteins immobilized on atomically flat gold surfaces. In particular, this method reveals submolecular regions with high conductance within the protein. The direct observation of nanoscale conduction pathways in redox proteins and complexes enables important advances in biochemistry and bionanotechnology.

Keywords: Differential electrochemical conductance, ECSTM, Electron transport pathway, Iron passivation, Redox metalloproteins

Aragonès, Albert C., Darwish, Nadim, Im, JongOne, Lim, Boram, Choi, Jeongae, Koo, Sangho, Díez-Pérez, Ismael, (2015). Fine-tuning of single-molecule conductance by tweaking both electronic structure and conformation of side substituents Chemistry – A European Journal 21, (21), 7716-7720

Herein, we describe a method to fine-tune the conductivity of single-molecule wires by employing a combination of chemical composition and geometrical modifications of multiple phenyl side groups as conductance modulators embedded along the main axis of the electronic pathway. We have measured the single-molecule conductivity of a novel series of phenyl-substituted carotenoid wires whose conductivity can be tuned with high precision over an order of magnitude range by modulating both the electron-donating character of the phenyl substituent and its dihedral angle. It is demonstrated that the electronic communication between the phenyl side groups and the molecular wire is maximized when the phenyl groups are twisted closer to the plane of the conjugated molecular wire. These findings can be refined to a general technique for precisely tuning the conductivity of molecular wires.

Keywords: Carotenoids, Conductance, Self-assembly, Single-molecule studies, STM break junction

Darwish, Nadim., Aragonès, A. C., Darwish, T., Ciampi, S., Díez-Pérez, I., (2014). Multi-responsive photo- and chemo-electrical single-molecule switches Nano Letters 14, (12), 7064-7070

Incorporating molecular switches as the active components in nanoscale electrical devices represents a current challenge in molecular electronics. It demands key requirements that need to be simultaneously addressed including fast responses to external stimuli and stable attachment of the molecules to the electrodes while mimicking the operation of conventional electronic components. Here, we report a single-molecule switching device that responds electrically to optical and chemical stimuli. A light pointer or a chemical signal can rapidly and reversibly induce the isomerization of bifunctional spiropyran derivatives in the bulk reservoir and, consequently, switch the electrical conductivity of the single-molecule device between a low and a high level. The spiropyran derivatives employed are chemically functionalized such that they can respond in fast but practical time scales. The unique multistimuli response and the synthetic versatility to control the switching schemes of this single-molecule device suggest spiropyran derivatives as key candidates for molecular circuitry.

Keywords: Molecular Electronics, Multi-Responsive Molecular Switches, Photo- and Chemo-Switches Spiropyran, Single-Molecule Conductance, STM Break-Junction, Electronic equipment, Isomerization, Molecular electronics, Photochromism, Electrical conductivity, Electronic component, Molecular switches, Single-molecule conductances, Single-molecule devices, Spiropyran derivatives, Spiropyrans, STM Break-Junction, Molecules

Diez-Perez, Ismael, Hihath, Joshua, Hines, Thomas, Wang, Zhong-Sheng, Zhou, Gang, Mullen, Klaus, Tao, Nongjian, (2011). Controlling single-molecule conductance through lateral coupling of [pi] orbitals Nature Nanotechnology 6, (4), 226-231

In recent years, various single-molecule electronic components have been demonstrated(1). However, it remains difficult to predict accurately the conductance of a single molecule and to control the lateral coupling between the pi orbitals of the molecule and the orbitals of the electrodes attached to it. This lateral coupling is well known to cause broadening and shifting of the energy levels of the molecule; this, in turn, is expected to greatly modify the conductance of an electrodemolecule- electrode junction(2-6). Here, we demonstrate a new method, based on lateral coupling, to mechanically and reversibly control the conductance of a single-molecule junction by mechanically modulating the angle between a single pentaphenylene molecule bridged between two metal electrodes. Changing the angle of the molecule from a highly tilted state to an orientation nearly perpendicular to the electrodes changes the conductance by an order of magnitude, which is in qualitative agreement with theoretical models of molecular pi-orbital coupling to a metal electrode. The lateral coupling is also directly measured by applying a fast mechanical perturbation in the horizontal plane, thus ruling out changes in the contact geometry or molecular conformation as the source for the conductance change.

Keywords: Junction conductance, Electron-transport, Interface, Dependence, Mechanism, Length