The design of (bio)electronic devices relies on localized grafting at the micrometer or submicrometer scale. The existing approaches typically expose macroscopic areas of the substrate and perform the grafting locally, for instance, by light irradiation (photochemical), resulting in an expensive and long process. The developed alternative allows the local grafting of molecules by fine design of the surface properties of the substrate. The doped silicon is chosen as substrate due to its importance for integration in microelectronic devices.[1]
Doping was performed locally by implantation of phosphor (1021 cm-3) in an illustrative micrometric pattern. Atomic force microscopy (AFM) showed that electrografting of diazonium salts on HF-pretreated samples (which occurs at low cathodic potential) is effective mostly on doped zones, contrary to the electrografting of vinylic monomers (which occurs at highly cathodic potential) for which homogeneous grafting was observed [2]
The understanding of the differences between the electronic properties of the different areas of the doped silicon substrate requires high resolution X-ray photoemission spectroscopy with spatial resolution on the scale of the pattern of this illustrative device. This information was obtained by energy filtered X-ray photoelectron emission microscopy (XPEEM) and associated small area spectroscopy. [3] The XPEEM NanoESCA, installed at the Nanocharacterisation Centre of the CEA Leti-Minatec, can reach high spatial (100 nm) and energy (100 meV) resolutions by the use of high brilliant and monochromatic soft x-ray radiation at beam lines of the European Synchrotron Radiation Facility. [4] The high resolution spectra on the micrometric doped zone shows subtle changes in the core level binding energies which are not due to the shift in the Fermi level, since the microscope references the sample Fermi level.
References:
[1] S. Palacin et al., ChemPhysChem 2004, 5, 1468.
[2] J. Charlier et al., ChemPhysChem 2005, 6, 70.
[3] M. Escher et al., J. Phys.: Condens. Matter 17 (2005) S1329.
[4] O. Renault et al., Surf. Sci. (2007), to be published.
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