Nano-Mesoscopic Interface: Hybrid Devices


Gianfranco Cerofolini STMicroelectronics

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The continuous size reduction associated with the development of microelectronics will, sooner or later, face the need of manipulating single molecules, addressing and contacting them to wanted regions of the device. Although the manipulation of individual molecules is already possible using the scanning tunneling microscope and their functional characterization is usually achieved for thiol-terminated molecules grafted to gold electrodes, both the process (individual management by scanning tunnel microscopy) and material (gold) are, however, incompatible with the integrated-circuit (IC) technology. Batch processing requires that the molecules are addressed to (photolithographically predefined) regions by a difference of chemical potentials. In turn, that requires a control of the chemical terminations of the surfaces of the most important IC films. Among them, the unique single crystalline surface is that of the silicon substrate, which makes it the most serious candidate for the growth of ordered functional films. Of the several producible orientations of silicon, the (100) surface is that with the largest applications. In usual technological cases, the (100) surface of silicon is hydrogen-terminated (immediately after aqueous HF etching) or covered by oxo terminations (after the formation of the native oxide). Although neither one nor the other has the necessary chemical and crystalline order required to be a seed for the deposition of molecular devices, they can, however, be used to prepare clean silicon surfaces with 2 × 1 reconstruction or hydrogen-terminated silicon surfaces with 2 × 1 or 1 × 1 reconstruction. Alkenes or alkynes can be used to functionalize the silicon via cycloaddition to the clean 2 × 1-reconstructed surface or via hydrosilation on the hydrogen-terminated surfaces.