The single molecular orientation switching of the Tb@C82 endohedral metallofullerene has been studied by using low-temperature ultrahigh vacuum (UHV) scanning tunneling microscopy (STM). An octanethiol self-assembled monolayer (SAM) was introduced between Tb@C82 and the Au111 substrate to control the thermal rotational states of Tb@C82. Scanning tunneling spectroscopy (STS) of Tb@C82 on an octanethiol SAM at 13 K demonstrated hysteresis including negative differential conductance (NDC). This observed hysteresis and NDC is interpreted in terms of a switching of the Tb@C82 molecular orientation caused by the interaction between its electric dipole moment and an external electric field.
Coulomb staircases in double-barrier tunneling junctions consisting of a scanning-probe-vacuum-gapalkanethiol-protected Au nanoparticle/Au ͑111͒ electrode have been measured as a function of the set point current of scanning tunneling spectroscopy. The tunneling resistances of the scanning probe-Au core of a nanoparticle ͑R 1 ͒ and the Au core-Au ͑111͒ electrode ͑R 2 ͒ are evaluated by fitting a theoretical Coulomb staircase into the experimental tunneling current-voltage characteristics measured by scanning tunneling spectroscopy. When a vacuum gap exists between the scanning probe and alkanethiol Au nanoparticles, R 1 is inversely proportional to the set point current. On the contrary, in the case of R 1 Ͻ R 2 , the top of the tip of the scanning probe tends to penetrate the octanethiol-protecting molecule of an Au nanoparticle. R 2 is found to be independent of the set point current, and R 2 of octanethiol-and hexanethiol-protected Au nanoparticles are evaluated as 7.6 G⍀ ± 10% and 460 M⍀ ± 10%, respectively.
We report a simple and high yield method for fabricating multiple nanogaps simultaneously by an electroless gold plating technique using electroless gold plating solution which consists of common medical liquid of iodine tincture and L(+)-ascorbic acid (vitamin C). The distance between the gold electrodes (33nm in average) on the SiO2∕Si substrate was decreased by selective deposition of gold onto the surface of the gold electrodes. By electroless gold plating, we fabricated nanogaps below 5nm in width with a 41% process yield. We also demonstrated the Coulomb blockade effect in octanethiol(C8)-protected Au nanoparticles by using such a fabricated nanogap.
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