This document has been archived.

Skip To Content
NSF Logo Search GraphicGuide To Programs GraphicImage Library GraphicSite Map GraphicHelp GraphicPrivacy Policy Graphic
OLPA Header Graphic
 
     
 

NSF Press Release

 


NSF PR 03-31 - March 20, 2003

Media contact:

 David Hart

 (703) 292-8070

 dhart@nsf.gov

Program contact:

 Charalabos C. Doumanidis

 (703) 292-7088

 cdoumani@nsf.gov

New Measurements Show Silicon Nanospheres Rank Among Hardest Known Materials

two silicon nanoparticles
Two silicon nanoparticles with approximately 70-nm radii imaged by transmission electron microscopy (TEM) by Chris Perrey in Professor Barry Carter's research group at the University of Minnesota. Similar particles and much smaller were evaluated mechanically by graduate student Bill Mook in Professor William Gerberich's group. The nanosphere on the left is relatively defect free while the one at the right has a "nanotwin" from left to right. Defect-free nanospheres were found to be much harder than bulk silicon. (The inserts are electron diffraction patterns to determine crystallographic orientation.)
Credit: C. Perrey, C.B. Carter, University of Minnesota
Select image for larger version
(Size: 44KB) , or download a high-resolution TIFF version of image (851KB)

12-nm diameter silicon nanosphere
A 12-nm diameter silicon nanosphere, deformed by 2.3 nanometers in an atomistic simulation conducted by Mike Baskes of Los Alamos National Laboratory. At the top and the bottom the atoms are transformed into an amorphous state with no dislocations detected. Such simulations supported the hardness results measured experimentally by Bill Gerberich's team at Minnesota.
Credit: M.I. Baskes, Los Alamos National Laboratory
Select image for larger version
(Size: 166KB) , or download a high-resolution TIFF version of image (687KB)

Larger versions (Total Size: 640KB) of all images from this document

 Note About Images

ARLINGTON, Va. -- University of Minnesota researchers have made the first-ever hardness measurements on individual silicon nanospheres and shown that the nanospheres' hardness falls between the conventional hardness of sapphire and diamond, which are among the hardest known materials. Being able to measure such nanoparticle properties may eventually help scientists design low-cost superhard materials from these nanoscale building blocks.

Up to four times harder than typical silicon -- a principal ingredient of computer chips, glass and sand -- the nanospheres demonstrate that other materials at the nanoscale, including sapphire, may also have vastly improved mechanical properties. The researchers' results were published online March 18 by the Journal of the Mechanics and Physics of Solids and will appear in June 2003 issue. The work is supported by the National Science Foundation (NSF), the independent federal agency that supports basic research in all fields of science and engineering.

"These results give us two reasons to be excited," said William Gerberich, chemical engineering and materials science professor at Minnesota and lead author on the paper along with his graduate student William Mook. "We can now look at the properties of these building blocks, and from there, we can begin to design superhard materials. In addition, we've now achieved a way to conduct experiments on a nanoscale particle and perform atom-by-atom supercomputer simulations on a similarly sized particle."

Such nanospheres might find early applications in rugged components of micro-electromechanical systems (MEMS), according to Gerberich. To produce a small gear, for example, the shape could be etched into a silicon wafer and filled with a composite including silicon carbide or silicon nitride nanospheres. The surrounding silicon could then be selectively etched away.

To make the measurements, the research team first devised a method for producing defect-free silicon nanospheres in which the silicon spheres condensed out of a stream of silicon tetrachloride vapor onto a sapphire surface. (Defects in the spheres reduce the hardness by acting as sites for flow or fracture.) The hardness was measured by squeezing individual particles between a diamond-tipped probe and the sapphire.

The smaller the sphere, the harder it was. The spheres tested ranged in size from 100 nanometers to 40 nanometers in diameter, and the corresponding hardness ranged from 20 gigapascals up to 50 gigapascals for the smallest nanospheres. For comparison, stainless steel has a hardness of 1 gigapascal, sapphire of about 40 gigapascals, and diamond of around 90 gigapascals. Bulk silicon averages about 12 gigapascals.

"People have never had these perfect, defect-free spheres to test before," Gerberich said. "You can compare the silicon nanospheres to materials such as nitrides and carbides, which typically have hardness values in the range of 30 to 40 gigapascals." The research team will study silicon carbide nanospheres next, but they'll need two diamond surfaces for the experiments, since squeezing a silicon carbide nanosphere would likely drill a hole into sapphire.

"This is the first time that a measurement of mechanical, rather than electromagnetic, properties of nanoparticles has been made, which we can now compare to the results of simulations," Gerberich said. "Mechanical properties of materials at this scale are much more difficult to simulate than electromagnetic properties."

A silicon sphere with a 40-nanometer diameter has approximately 40 million atoms. The spheres examined by the Minnesota researchers were composed of 5 million to 600 million atoms. Because materials science algorithms can simulate this number of atoms on supercomputers, the Minnesota team worked with Michael Baskes of Los Alamos National Laboratory to conduct some preliminary simulations, which corresponded well with the experimental findings.

"Better designs for these sorts of nanocomposites will be based on a better understanding of what goes into them," Gerberich said. "These measurements make it possible to pursue a bottom-up approach to materials design from a mechanical perspective."

-NSF-

Journal of the Mechanics and Physics of Solids: http://www.sciencedirect.com/science/journal/00225096

Principal Investigator: William Gerberich, 612-625-8548, wgerb@tc.umn.edu

NSF is an independent federal agency that supports fundamental research and education across all fields of science and engineering, with an annual budget of nearly $5 billion. NSF funds reach all 50 states through grants to nearly 2,000 universities and institutions. Each year, NSF receives about 30,000 competitive requests for funding, and makes about 10,000 new funding awards. NSF also awards over $200 million in professional and service contracts yearly.

Receive official NSF news electronically through the e-mail delivery system, NSFnews. To subscribe, send an e-mail message to join-nsfnews@lists.nsf.gov. In the body of the message, type "subscribe nsfnews" and then type your name. (Ex.: "subscribe nsfnews John Smith")

Useful Web Sites:
NSF Home Page: http://www.nsf.gov
News Highlights: http://www.nsf.gov/home/news.html
Newsroom: http://www.nsf.gov/od/lpa/news/media/start.htm
Science Statistics: http://www.nsf.gov/sbe/srs/stats.htm
Awards Searches: http://www.fastlane.nsf.gov/a6/A6Start.htm

 

 
 
     
 

 
National Science Foundation
Office of Legislative and Public Affairs
4201 Wilson Boulevard
Arlington, Virginia 22230, USA
Tel: 703-292-8070
FIRS: 800-877-8339 | TDD: 703-292-5090
 

NSF Logo Graphic