Light‐Activated Electroactive Molecule‐Based Memory Microcells Confined on a Silicon Surface

Abstract

Among the existing charge-storage devices of modern computers, the dynamic random access memory (DRAM) provides the most interesting opportunity of integrating redoxactive molecular components.[1] The capacitance density of todays DRAM storage cell is on the order of 50-100 fF mm À2(5-10 mF cm À2 ) with a benchmark cell size below the squaremicrometer range. In this context, ferrocene (Fc) and metalcomplexed porphyrins have been explored as the most promising memory elements, because they show, both in solution and confined on surfaces, one to several perfectly reversible and stable one-electron redox reactions within an attractive potential window, that is, 0.0 to 1.0 V vs. a saturated calomel electrode (SCE). Therefore, the functionalization of technologically relevant conducting surfaces, such as oxidefree, hydrogen-terminated silicon (H-Si), with high-quality Fc-terminated [2][3][4][5][6][7][8] and metal-complexed porphyrin-terminated [9][10][11][12] monolayers has been demonstrated to be a powerful bottom-up approach for the fabrication of electrically addressable charge-storage devices with low-power consumption. Compared with metalloporphyrins, Fc is a much smaller molecule (average diameter of tetraphenylporphyrin and Fc are about 18 and 6.6 , 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 À10 mol cm À2 . This does not only allow for an extremely fast electron communication between the electroactive groups, [5] but also yields charge densities in the range of 20-50 mC cm À2

High-Density Modification of H-Terminated Si(111) Surfaces Using Short-Chain Alkynes

“…Oxide-free covalent modification of the Si surface therefore holds great promise in improving the performance of silicon-based semiconductors through electrical and chemical passivation. , Furthermore, oxide-free modified Si surfaces offer the added possibility to fine-tune semiconductor behavior by coupling organic molecules to the surface, giving rise to e.g. bottom-up molecular electronics. ,, Moreover, stable, covalently modified oxide-free Si surfaces have many applications in the immobilization and detection of biomolecules, − offer a platform on which fundamental physical and chemical processes such as electron transfer and reactivity can be studied, and are useful in molecular catalysis …”