Foresight Nanotech Institute Logo

« Go Back

You are viewing
Foresight Archives

Image of nano

Nanostructures in Nature and Technology

R. Stanley Williams*

Hewlett-Packard Labs,
Palo Alto, CA 94304 USA

This is an abstract for a presentation given at the
Ninth Foresight Conference on Molecular Nanotechnology.
There will be a link from here to the full article when it is available on the web.


Magnetotactic bacteria utilize strings of magnetite nanocrystals as an aid to navigation. These 'nanodevices' have been fabricated on the earth for roughly two billion years, and we may have even seen similar nanodevices fabricated on Mars. The very existence of these 'natural' nanostructures raises questions about how they were made and why they appear to be so stable against Ostwald ripening. If thermodynamically stable nanodevices can be fabricated by bacteria, then we should be able to learn from them how to fabricate 'quantum dot' and wire structures for use in man-made devices.

I explore the possibilities and limitations of utilizing the energetics of surfaces and interfaces, as well as the symmetry relation between overlayer and substrate, to devise self-assembled epitaxial nanostructures. First, I examine the well-studied system of coherently strained Ge islands grown on Si (001), and develop a thermodynamic model for the growth and evolution of the nanocrystals. This model generalizes the zero-temperature energetic picture of Shchukin et al. [1] by including the principle of detailed balance for different sized nanocrystals into the expression for the free energy of the island ensemble [2]. Next, I demonstrate that the classes of Ge nanocrystals that form can be modified dramatically via the presence of a surfactant. Finally, I show how to grow regular arrays of uniformly sized epitaxial nanowires on a surface by combining this thermodynamic understanding with the basic crystal symmetries of the ovelayer and substrate as a constraint on the system.

  1. V. A. Shchukin, N. N. Ledentsov, P. S. Kop'ev and D. Bimberg, Phys. Rev. Lett. 75 (1995) 2968.
  2. R. S. Williams, G. Medeiros-Ribeiro, T. I. Kamins, and D. A. A. Ohlberg, Acc. Chem. Res. 32 (1999) 425.

*Corresponding Address:
R. Stanley Williams Hewlett-Packard Labs 1501 Page Mill Road, MS 1L-14, Palo Alto, CA 94304 USA


Foresight Programs


Home About Foresight Blog News & Events Roadmap About Nanotechnology Resources Facebook Contact Privacy Policy

Foresight materials on the Web are ©1986–2018 Foresight Institute. All rights reserved. Legal Notices.

Web site developed by Stephan Spencer and Netconcepts; maintained by James B. Lewis Enterprises.