Molecular structures tunneling

Section 5 is on one particular molecule, p-benzene dithiol. This is one of the most commonly studied molecules in molecular electronic transport junctions [7] (although it is also one of the most problematic). Section 6 discusses a separate measurement, inelastic electron tunneling spectroscopy [8, 9] (IETS). This can be quite accurate because it can be done on single molecules at low temperatures. It occurs because of small perturbations on the coherent transport, but it can be very indicative of such issues as the geometrical arrangement in the molecular transport junction, and pathways for electron transport through the molecular structure. 

Electron Tunneling in Artificial Organized Molecular Structures... 

The control parameters in STM experiments are the bias voltage and the tunneling current. The results of an experiment are the shape and the dimensions of atomic or molecular structures on the surface, and their apparent height compared to the surface environment. Generally, it has been found that apparent heights are not uniquely determined by a set of control parameters. The shape and dimensions of atomic structures are thus... 

M.A. Kozhushner, V.S. Polyanskii, I.I. Oleynik, Tunneling and resonant conductance in one-dimensional molecular structures, Chem. Phys. 319 (2005) 368. 

Fig. 3. PET takes place in a variety of environments. An electron may tunnel between reactants randomly dispersed in solid materials or in frozen media. In organized assemblies, the donor and acceptor molecules can be arranged in the medium in a variety of ways, depending on the molecular structures and charges of the reactants as well as the molecular structure of the environment The representation shown in this figure is only suggestive of the many possible arrangements...

Fourier-transform infrared FTIR to the tip by the strong electrostatic field, and then ionized by electrons tunneling from the gas atoms into the tip. These ions, accelerated along radial trajectories by Coulomb repulsion, map out the variations in the electric field strength across the surface with atomic resolution, showing the surface topography. Broad-band IRAS experiments are performed and the IR adsorption Molecular structure... 

Fig. 4.11 Scanning tunneling micrographs of hexa-tertiarybutyl decacyclene adsorbed on the Cu(llO) surface. Figures (a) and (b) show the molecular structure which is chiral because the three blades of the propeUer-Kke structure are rotated out of the plane of the molecule, (c) The adsorbed molecules are imaged as six bright spots arising from the six i-butyl groups and the two enantiomers tend to aggregate into bimolecular rows of like chirality, (d) Removal of the molecules reveals the formation of chiral holes in the rows of the Cu(llO) surface. The adsorbed molecules imprint their chirality into the achiral Cu(l 10) surface. Reprinted with permission from [40]. Copyright 2001 American Physical Society...

Stoddart and co-workers have developed molecular switch tunnel junctions [172] based on a [2]rotaxane, sandwiched between silicon and metallic electrodes. The rotaxane bears a cyclophane that shuttles along the molecular string toward the electrode and back again driven by an electrochemical translation. They used electrochemical measurements at various temperatures [173] to quantify the switching process of molecules not only in solution, but also in self-assembled monolayers and in a polymer electrolyte gel. Independent of the environment (solution, self-assembled monolayer or solid-state polymer gel), but also of the molecular structure - rotaxane or catenane - a single and generic switching mechanism is observed for all bistable molecules [173]. 

Figure 2.8 Three examples of small redox molecules for which in situ STM and single-molecule in situ STS have been recorded. Molecular structures and tunneling current-overpotential correlations are shown, (a) Two osmium polypyridine complexes on a Pt(lll) electrode surface and tunneling current-overpotential correlations at different bias voltages [55]. (b) Hexanethiol 4,4 -substi-tuted viologen (6V6) and 6-p-tetrathiafulvalene...

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