One of the most interesting features of fullerene C60 molecules is their flexible functionality depending on the form of inter-C60 bonds in a film. Therefore, ability to control the formation and annihilation of inter-C60 bond with single molecular precision is certainly useful for active nanodevices. Here, we present methodology and application of controlled inter-C60 chemical reactions using a tip of scanning tunneling microscope (STM).
For the experiments, we used C60 films formed on the Si(111)√3×√3R30°-Ag and on the highly oriented pyrolitic graphite surfaces. We can intentionally induce polymerization or depolymerization reactions at room temperature by changing a polarity of bias voltage applied to the C60 film. At negative bias condition, C60 molecules were efficiently reacted with each other via [2+2] cycloaddition reaction beneath a tip. In contrast, the created [2+2] cycloadducts tend to dissociate into monomers by applying positive bias voltage. Magnitude of bias voltage is important for controlling the spatial precision and the area of the above STM-tip-induced chemical reactions. The spatial distribution of the created [2+2] cycloadducts beneath a tip becomes smaller as decreasing the magnitude of negative bias voltage. Similar tendency was observed for positive bias voltages to induce dissociation reaction. By setting the appropriate polarity and magnitude of the bias voltage, we created single [2+2] cycloadduct and dissociated it beneath the STM tip. We demonstrated rewritable data storage with ultra-high density using an STM-tip. Bits information was recorded by the two distinct states of molecules with and without inter-C60 bonds. In this demonstration, an array of bits with a density of 200 Tbit / inch2 was realized and manipulated using a C60 film as a recording media.
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