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Field regulation of single-molecule conductivity by a charged surface atom


Electrical transport through molecules has been much studied since it was proposed1 that individual molecules might behave like basic electronic devices, and intriguing single-molecule electronic effects have been demonstrated2,3. But because transport properties are sensitive to structural variations on the atomic scale4,5,6,7, further progress calls for detailed knowledge of how the functional properties of molecules depend on structural features. The characterization of two-terminal structures has become increasingly robust and reproducible8,9,10,11,12, and for some systems detailed structural characterization of molecules on electrodes or insulators is available13,14,15,16,17. Here we present scanning tunnelling microscopy observations and classical electrostatic and quantum mechanical modelling results that show that the electrostatic field emanating from a fixed point charge regulates the conductivity of nearby substrate-bound molecules. We find that the onset of molecular conduction is shifted by changing the charge state of a silicon surface atom, or by varying the spatial relationship between the molecule and that charged centre. Because the shifting results in conductivity changes of substantial magnitude, these effects are easily observed at room temperature.

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Figure 1: Visualization of the electrostatic potential emanating from a point source.
Figure 2: Absence of charge field effects on low-doped silicon.
Figure 3: Reversible modification of dangling bonds.
Figure 4: Orbitals and charge densities near a dangling bond.
Figure 5: Change in electronic properties with distance from the dangling bond.


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We have benefited from discussions with G. Kirczenow, G. Lopinski, S. Datta, H. Guo and R. Feenstra and from the technical expertise of M. Cloutier and D. Moffatt. Funding has been provided by iCORE, the NRC, the NSERC, CFI, the University of Alberta and CIAR. We are grateful for access to WestGrid and the Center of Excellence in Integrated Nanotools (University of Alberta) computational facilities.

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Correspondence to Robert A. Wolkow.

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Piva, P., DiLabio, G., Pitters, J. et al. Field regulation of single-molecule conductivity by a charged surface atom. Nature 435, 658–661 (2005).

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