(6dp) Engineering Peptides to Build Inorganic Materials

My overall research interests lie in chemical self assembly of nanomaterials from the atom up and directing assembly of nanomaterials at various length scales. My PhD (with John G. Ekerdt at UT Austin) focused on understanding surface reactions that lead to nanocrystal formation in chemical vapor deposition and controlling reaction kinetics to spatially direct the self assembly of nanocrystals. My postdoctoral fellowship (NRC-NIST Postdoctoral Fellow with Wen-li Wu and Eric K. Lin) is serving to bridge this PhD expertise to solution based nanocrystal synthesis and assembly of nanomaterials. Currently I am gaining expertise with neutron and x-ray scattering techniques and working with engineered peptides as related to the studies proposed below.

Proposed and Current Studies: Engineering peptides to build inorganic materials

Molecular biology has progressed to the point where previously rare materials (i.e., specialty proteins, peptides, enzymes, etc.) are now readily available and can be prepared through automated synthesis in the laboratory at the gram level. This availability allows one to exploit the efficiency of biological systems to elegantly create materials. Directed evolution and phage display techniques have long been used to identify peptides that interact with inorganic materials such as metals and semiconductors [1, 2]. More recently, peptide sequences have been identified that mediate the formation of nanomaterials from ions in solution through biomineralization [3]. The potential to create complex structures from the atom up using biomolecules is interesting for technological applications and helps provide insights into mechanisms of how biological macromolecules and inorganics interact. Many problems can be addressed through study of engineered peptides that build inorganic materials; specifically I am interested in:

Peptide-ion interactions. Metal ion complexation and coordination with peptides in vivo is critical in many biological processes. Biomimetic photosynthetic structures and myriad human health issues such as Alzheimer's disease require an improved understanding of peptide-ion interactions.

Macromolecular chemistry in proteins. Macromolecules are known to control their local chemical environment, allowing access to seemingly unfavorable reaction pathways. Engineered peptides offer model systems to control and understand these effects in larger macromolecular systems.

Fundamentals of biomineralization. The exact mechanism of peptide-mediated nanostructure formation is unclear at present [2]. Conventionally there has been strong interest in biomineralization proteins that reduce ions in solution and build complex, hierarchical inorganic materials such as bone, teeth, and shells. Applying new techniques and capabilities to biomineralization processes can contribute to answering many of the outstanding questions in this area and in newer areas such as implant bio-integration.

Postdoctoral work: Applying x-ray and neutron scattering techniques to nanomaterial synthesis and nanomaterial assembly

My NRC Fellowship at NIST is focused on obtaining expertise working with biomolecules and using neutron and x-ray scattering to study nanomaterial synthesis in solution. Neutron scattering is especially helpful because contrast matching techniques allow study of structure and dynamics of only the polymer or peptides participating in nucleation and growth processes. Currently, I am applying x-ray and neutron scattering techniques to study (1) how image charges affect polyelectrolyte adsorption in systems with widely different relative dielectric properties and (2) how peptides mediate nucleation of nanoparticles in solution. This work is providing the necessary tools and experience to link my PhD expertise in controlling nanomaterial assembly with the proposed studies using engineered peptides.

PhD work: Directed nucleation and growth of nanomaterials in chemical vapor deposition

Surface chemistry governs the self assembly of nanostructures on surfaces in chemical vapor deposition (CVD) processes, such as the assembly of nanocrystals on oxide surfaces for flash memory applications. The initial sub-monolayer of atoms on a surface exhibits unexpected, unique reactive pathways for different oxide surfaces [4-7]. Nanocrystal assembly, which is governed by these surface reactions, is then studied on patterned substrates to direct self assembly of nanocrystals [8, 9]. Directed nucleation and growth of nanocrystals is examined within macroscopic (~100 μm) to nanoscopic (20 nm) features [10, 11]. Below a critical size, nanocrystal formation is sharply affected; however, we found that nanocrystals (singlets, doublets, and triplets) can form even in the smallest 20 nm features through judicious choice of reaction conditions. To extend this level of understanding and control to solution based nanomaterials systems, the new tools and techniques I am learning during my postdoc are required.

Aside from the thesis work described above, I also investigated the growth of Si nanowires by the vapor-liquid-solid (VLS) method [12], investigated surface chemistry of dielectrics with non-linear optical techniques [13], developed a combinatorial approach to screen nanostructure growth conditions [14], and fabricated core-shell nanocrystals for chemical and electrical stability [15].

References

1. Whaley, S.R., et al., Selection of peptides with semiconductor binding specificity for directed nanocrystal assembly. Nature, 2000. 405(6787): p. 665-668.

2. Sarikaya, M., et al., Molecular biomimetics: nanotechnology through biology. Nature Materials, 2003. 2(9): p. 577-585.

3. Naik, R.R., et al., Biomimetic synthesis and patterning of silver nanoparticles. Nature Materials, 2002. 1(3): p. 169-172.

4. Zhu, J.H., W.T. Leach, S.K. Stanl3y, J.G. Ekerdt, X.M. Yan. Growth of high-density Si nanoparticles on Si3N4 and SiO2 thin films by hot-wire chemical vapor deposition. Journal of Applied Physics, 2002. 92(8): p. 4695-4698.

5. Stanl3y, S.K. and J.G. Ekerdt, Surface reactions in chemical vapor deposition of metals and silicon alloys. Surface Science Reports, 2007. Invited Review (In Prep.).

6. Stanl3y, S.K., S.S. Coffee, and J.G. Ekerdt, Interactions of germanium atoms with silica surfaces. Applied Surface Science, 2005. 252(4): p. 878-882.

7. Stanl3y, S.K. and J.G. Ekerdt. Interactions of Ge atoms with hi-k oxide dielectric surfaces. Materials Research Society Symposium Proceedings 879E, Paper Z3.23 (2005).

8. Stanl3y, S.K., et al., Surface reactions and kinetically-driven patterning scheme for selective deposition of Si and Ge nanoparticle arrays on HfO2. Surface Science, 2006. 600(5): p. L54-L57.

9. Stanl3y, S.K., et al., Ge interactions on HfO2 surfaces and kinetically driven patterning of Ge nanocrystals on HfO2. Journal of Vacuum Science & Technology A, 2006. 24(1): p. 78-83.

10. Stanl3y, S.K., S.S. Coffee, and J.G. Ekerdt. Directed self assembly of nanocrystals within macroscopic to nanoscopic features. Materials Research Society Symposium Proceedings 901E, Paper 0901-Ra19-03.1 (2006).

11. Coffee, S.S., S.K. Stanl3y, and J.G. Ekerdt, Directed nucleation of ordered nanoparticle arrays on amorphous surfaces. Journal of Vacuum Science & Technology B, 2006. 24(4): p. 1913-1917.

12. N.N. Kulkarni, J. Bae, C.K. Shih, S.K. Stanl3y, S.S. Coffee, J.G. Ekerdt.., Low-threshold field emission from cesiated silicon nanowires. Applied Physics Letters, 2005. 87(21): p. 3.

13. R. Carriles, J. Kwon, Y.Q. An, S.K. Stanl3y, J.G. Ekerdt, M.C. Downer, J. Price, A.C. Diebold.., Optical characterization of process-dependent charging in hafnium oxide structures. Journal of Vacuum Science & Technology B, 2006. 24(4): p. 2160-2168.

14. Stanl3y, S.K. and J.G. Ekerdt. Combinatorial studies for high density Si and Ge nanoparticle arrays. Materials Research Society Symposium Proceedings 933E, Paper 0933-G05-11 (2006).

15. Stanl3y, S.K. and J.G. Ekerdt. Core-shell Ge nanoparticles on oxide surfaces for enhanced interface stability. Materials Research Society Symposium Proceedings 933E, Paper 0933-G02-07 (2006).