Research Program
Nanoscale Materials

Project #
NM4

Participating Faculty:             Esther R. Angert, Carl A. Batt

NBTC Students/Postdocs:     Soazig Delamarre, Yajaira Sierra, Sandra Saldana

Other Students/Postdocs:     Leonardo Maestri

Objectives

• Investigate optical properties of nanoparticle arrays
• Create nanoparticle array structures as catalysts for nanofiber/nanowire growth
• Construct novel recombinant S-layer truncation/fusion proteins and investigate their reassembly, surface-affinity and biotemplating properties

Methods
Optical properties of nanoparticle arrays

      We investigated the optical properties of two-dimensional nanoparticle arrays biotemplated using S-layers. These experiments were initially performed on gold nanoparticle arrays formed on HPI-layers, but may eventually be extended to include the characterization of nanoparticle arrays patterned onto other types of S-layers displaying a variety of different lattice parameters.

Nanoparticle array structures as catalysts for nanofiber/nanowire growth

      The nanoparticle arrays obtained using the above approaches were then subjected to plasma-enhanced chemical vapor deposition (PECVD) processes to synthesize the nanofiber/tube and nanowire arrays. We collaborated closely with Michael Simpson (Oakridge National Laboratories, ORNL) and used facilities in the Center for Nanoscale Material Science at ORNL. In addition we have explored the use of S-layers as etch resists in collaboration with Oxford Instruments.

Cloning and expression of S-layers

      Using native and recombinant S-layer proteins (derived from the gene sbpA in Bacillus sphaericus, as described in our progress report), we studied their surface interaction and reassembly characteristics on various solid substrates in more detail. Pattered substrates used for our surface-interaction and reassembly studies will be fabricated using the advanced electron-beam lithography systems.

Summary
Two-dimensional surface layer (S-layer) protein lattices isolated from the bacterium Deinococcus radiodurans and the acidothermophilic archaeon Sulfolobus acidocaldarius were used to biotemplate the formation of self-assembled, ordered arrays of gold nanoparticles and water-soluble CdSe/ZnS core/shell quantum dots. Transmission electron microscopy (TEM) studies revealed that use of the two different S-layers resulted in the fabrication of nanostructured arrays displaying different interparticle spacings and nanoparticle properties. These results demonstrate that it is possible to exploit the physico-chemical/structural diversity of S-layer scaffolds to tune the morphological patterning of metallic and semiconductor nanoparticle arrays (Figure 1).

      These S-layers have been used to demonstrate on a preliminary basis their ability to serve both as scaffolds for the growth of semiconductor structures and as ultra-high resolution etch resist materials. In both cases similar approaches have been used and are based upon our expansive foundation in understanding how to assemble S-layers on the surface and to then use them to create ordered arrays. The first test was carried out in conjunction with Mike Simpson at ORNL where carbon nanofibers were grown from nickel catalyst particles held in place by the S-layers (Figure 2). In the second test, gold nanoparticles biotemplated on the S-layers were used as a nanoetch mask in a SiCl₄ inductively-coupled plasma (ICP) etch process. This plasma etch process resulted in the successful formation of silicon nanopillars ~100 nm high and ~30 nm wide at the base.  This work was carried out in collaboration with Oxford Scientific (Figure 3).

Accomplishments