Advanced Materials and Processing Branch

Currently available power storage systems, such as those used to supply power to microelectronic devices, typically consist of a single centralized canister and a series of wires to supply electrical power to where it is needed in a circuit. As the size of electrical circuits and components become smaller, there exists a need for a distributed power system to reduce Joule heating, wiring, and to allow autonomous operation of the various functions performed by the circuit. Our research is being conducted to develop a bio-nanobattery using ferritins reconstituted with both an iron core (Fe-ferritin) and a cobalt core (Co-ferritin). Both Co-ferritin and Fe-ferritin were synthesized and characterized as candidates for the bio-nanobattery. The reducing capability was determined as well as the half-cell electrical potentials, indicating an electrical output of nearly 0.5 V for the battery cell. Ferritins having other metallic cores are also being investigated, in order to increase the overall electrical output. Two dimensional ferritin arrays were also produced on various substrates, demonstrating the necessary building blocks for the bio-nanobattery. The bio-nanobattery will play a key role in moving to a distributed power storage system for electronic applications.

In a postetch treatment, chloride salts are used to greatly enhance and stabilize the photoluminescence (PL) from a porous silicon (PS) surface. We compare the enhancement and stabilization induced by solutions of the strong acid HCl (H++Cl-), saturated NaCl (in MeOH, where Me denotes methyl), and a tetrabutylammonium perchlorate [TBAP(Cl-)] solution. The extent and duration of the stabilization process and its dependence on the chloride-ion concentration, the identity of the cation, and the solvent composition are outlined and contrasted to strongly quenching NaF (Na++F-) and NaOH (Na++OH-) treatments. Treatment with HCl is found to produce the most efficient enhancement of the PL signal. The H+- and Cl--ion concentrations in solution are critical as the stability of the strong HCl-induced enhancement of the nitrogen-laser-induced luminescence from the PS surface depends, as well, on the presence of methanol. PS surfaces treated in an HCl/H2O solution display a strongly enhanced in situ luminescence, which decays rapidly in an ex situ environment without treatment in ultrahigh-purity (UHP) methanol. Samples treated in an HCl(H2O)/MeOH solution (greater than 2M) maintain their enhancement for extended periods. Chloride-ion stabilization appears independent of the method of preparing the PS structure, implying that chloride salt treatment largely stabilizes the surface structure of the luminescent PS. Scanning electron micrographs demonstrate the profound change that accompanies the HCl treatment of the PS surface. Energy dispersive spectroscopy reveals chloride incorporation into the PS surface at strongly photoluminescent regions. Raman scattering demonstrates that the PL is correlated with the creation of amorphous structural regions. In conjunction with detailed quantum-chemical modeling, in which we examine the derivatization of the PS surface, time-dependent histograms obtained for the HCl-treated systems indicate that the resulting luminescence, initiated through the pumping of the HCl-modified surface, displays the manifestation of a significant surface interaction. It is suggested that this interaction might result in the formation of both chlorosilanones and chlorosilylenes, the latter of which are formed in either a photochemically induced or chloride-catalyzed conversion of the silanone. The modification of the PS surface appears to facilitate the formation of a photoluminescing ``blue-green'' precursor state as well as a ``deep red'' emitter, both of which appear to be associated, at least in part, with surface-bound silylene isomers. The importance of these results to sensor development is considered.