Electron tunneling transport

The electron transport properties described earlier markedly differ when the particles are organized on the substrate. When particles are isolated on the substrate, the well-known Coulomb blockade behavior is observed. When particles are arranged in a close-packed hexagonal network, the electron tunneling transport between two adjacent particles competes with that of particle-substrate. This is enhanced when the number of layers made of particles increases and they form a FCC structure. Then ohmic behavior dominates, with the number of neighbor particles increasing. In the FCC structure, a direct electron tunneling process from the tip to the substrate occurs via an electrical percolation process. Hence a micro-crystal made of nanoparticles acts as a metal. 

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. 

Nakamura H, Yamashita K, Rocha AR, Sanvito S (2008) Efficient ab initio method for inelastic transport in nanoscale devices analysis of inelastic electron tunneling spectroscopy. Phys Rev B 78(23) 235418-235420... 

Troisi A, Ratner MA (2006) Molecular transport junctions propensity rules for inelastic electron tunneling spectra. Nano Lett 6(8) 1784-1788... 

Keywords Charge transport Electrochemical molecular junctions Electron tunnelling Electron hopping Molecular electronics Photoactive molecular junctions... 

Apart from the more conventional transport measurements of molecular junctions at constant bias voltage, alkane(di)thiols-based molecular junctions were also characterized by transition voltage spectroscopy [258, 259], AC voltage modulation [260], and inelastic electron tunneling spectroscopies [261],... 

The observed dependence of the rate of electron tunneling on the orientation of the reacting particles suggests that orientation of porphyrin rings can perhaps serve as an instrument regulating the rate of electron transport during photosynthesis. 

In all cases there is a need for the rapid transfer of electrons in a controlled direction. It is to be expected that ligands will have mobile, conjugated electronic systems to allow electrons to be transported away rapidly from the metal centre to avoid recombination with the positive hole. In addition to movement of electrons through the binding system, the possibility of electron tunnelling must be considered. 

The key phenomenon revealing the most of the underlying physics is transport, where the effects of interactions play a crucial role. The processes of electron tunneling from grain to grain that govern electron transfer, are... 

Fig. 3. The possible design of systems for PET across membranes (a) — electron tunneling in S // — // A system (b) — carrier-mediated transport in S // A, // A2 system (c) — sensitizer-mediated transport in D // S // A system...

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