Metalloporphyrins as molecular precursors of electroactive hybrids: A characterization of their actual electronic states on Si(100) and (111) by AFM and XPS

Metalloporphyrins bound to silicon wafers exhibit a redox behaviour useful for information storage and resist the conditions of temperature required for processing real devices. An XPS and AFM study has been undertaken to evidence and understand the electronic states of different free bases and metalloporphyrins on Si(100) and (111). Both carbosilane (RC–Si) and alkoxysilane (RO–Si) bonds have been produced via thermal and electrochemical routes. In the resulting hybrids XPS has revealed, for the first time, that porphyrins exist as two distinct species on silicon. The behaviour of Co, Cu and Zn(II) porphyrinates has been evidenced, and a strategy to improve the molecular coverage by use of an organic spacer has been also proposed. The results will assist in the choice of suitable candidates for molecular electronics.