Silicon-Immobilized Ferrocenyl Monolayers for All-Solid Molecular Charge Storage and Logic
Compared with metalloporphyrins, Fc is a much smaller molecule (average diameter of tetraphenylporphyrin and Fc are about 18 and 6.6 Å, respectively), and consequently is immobilized on silicon with a higher surface coverage, which gives rise to higher charge densities. Indeed, the surface coverages reached for high-quality ferrocenyl monolayers are in the range of (2.0–5.0) ×10-10 mol cm-2. This does not only allow for an extremely fast electron communication between the electroactive groups , but also yields charge densities in the range of 20–50 mC cm-2. These values are thus much higher than those measured for Si/SiO2 capacitors currently used in Dynamic Random Access Memories (5–10 mC cm-2).
Very recently, we also demonstrated that tailor-made micrometer-sized patterns of such redox-active monolayers could behave as light-activated molecular memory cells operating at low voltages with unprecedented capacitance performances . The characteristics of this stimuli-responsive device are of great scientific interest for data-processing applications, such as redox-based Boolean logic gates . In our system, the switching of the capacitance upon light irradiation that is observed only at a certain electrical potential constitutes the principle of all-solid two-input AND logic gate without the need of chemical inputs in solution. Such performances can be ascribed to the judicious combination between a photoswitchable conducting/insulating silicon substrate and high-quality microstamped redox-active assemblies.
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 Fabre, B.; Li, Y.; Scheres, L.; Pujari, S. P.; Zuilhof, H. Angew. Chem. Int. Ed. 2013, 52, 12024-12027.