Epitaxy of Ge nanowires grown from biotemplated Au nanoparticle catalysts.

Semiconductor nanowires (NWs) are being actively investigated due to their unique functional properties which result from their quasi-one-dimensional structure. However, control over the crystallographic growth direction, diameter, location, and morphology of high-density NWs is essential to achieve the desirable properties and to integrate these NWs into miniaturized devices. This article presents evidence for the suitability of a biological templated catalyst approach to achieve high-density, epitaxial growth of NWs via the vapor-liquid-solid (VLS) mechanism. Bacterial surface-layer protein lattices from Deinococcus radiodurans were adsorbed onto germanium substrates of (111), (110), and (100) crystallographic orientations and used to template gold nanoparticles (AuNPs) of different diameters. Orientation-controlled growth of GeNWs was achieved from very small size (5-20 nm) biotemplated AuNP catalysts on all of the substrates studied. Biotemplated GeNWs exhibited improved morphologies, higher densities (NW/microm(2)), and more uniform length as compared to GeNWs grown from nontemplated AuNPs on the substrate surfaces. The results offer an integrated overview of the interplay of parameters such as catalyst size, catalyst density, substrate crystallographic orientation, and the presence of the protein template in determining the morphology and growth direction of GeNWs. A comparison between templated and nontemplated growth provides additional insight into the mechanism of VLS growth of biotemplated NWs.

Entropically driven self-assembly of Lysinibacillus sphaericus S-layer proteins analyzed under various environmental conditions.

S-Layer proteins are an example of bionanostructures that can be exploited in nanofabrication. In addition to their ordered structure, the ability to self-assembly is a key feature that makes them a promising technological tool. Here, in vitro self-assembly kinetics of SpbA was investigated, and found that it occurs at a rate that is dependent on temperature, its concentration, and the concentration of calcium ions and sodium chloride. The activation enthalpy (120.81 kJ . mol(-1)) and entropy (129.34 J . mol(-1) . K(-1)) obtained infers that the incorporation of monomers incurs in a net loss of hydrophobic surface. By understanding how the protein monomers drive the self-assembly at different conditions, the rational optimization of this process was feasible.

Vertical growth of Ge nanowires from biotemplated Au nanoparticle catalysts.

Semiconductor nanowires are being actively investigated because of their unique physical properties and potential applications in nanoelectronics and optoelectronic devices. However, current hurdles for device integration include the lack of control over the orientation, location, and packing density of nanowires. This communication presents for the first time the use of a unique, bottom-up approach for the catalyzed growth of semiconductor nanowires via biological templating. High-density, vertically oriented growth of Ge nanowires with monodispersed diameters and spacings was achieved through patterning of very small sized (5-20 nm) Au nanoparticles using bacterial surface-layer proteins as a template. We envision the applicability of this biotemplating approach to a variety of nanowires and substrate materials.