Featured Research

from universities, journals, and other organizations

Nanoscale Materials Grow With The Flow

Date:
February 22, 2009
Source:
DOE/Ames Laboratory
Summary:
Scientists have shown that nanoscale, uniform lead islands on silicon are spontaneously and quickly created by unusually mobile atoms. The discovery of the "liquid-like" nanogrowth mechanism is promising for nanotechnology applications, which require fast, consistent, and efficient material growth for industrial-scale production.

A single lead-on-silicon island (orange) grown over a substrate step. The island includes both 5-layer (stable) and 4-layer (unstable) heights and shows different nucleation as a function of layer height. An additional small amount of lead was added to test how new islands nucleate on top (the white “blobs”). The 4-layer height has many small islands while the 5-layer height has only a few large, fractal islands. Although the island is a single island with two connected parts, the two parts behave as if they are separate and each has different “reactivity.”
Credit: Image courtesy of DOE/Ames Laboratory

Imagine unloading a pile of bricks onto the ground and watching the bricks assemble themselves into a level, straight wall in only a few minutes. While merely a fantasy for builders in the everyday world, these types of self-assembled structures are a reality for those who build materials in the nanoworld.

Michael C. Tringides, a senior physicist at the U.S. Department of Energy's Ames Laboratory, has shown that nanoscale "straight wall" lead islands on silicon are spontaneously and quickly created by unusually mobile atoms.

Several years ago, Tringides' research group was the first to observe that lead atoms deposited on a silicon surface at low temperatures self-organize into uniform-height island nanostructures. The laws of quantum mechanics – specifically, Quantum Size Effects – determine why lead atoms stack up to create uniform islands while other nanostructure systems organize into islands that vary in height.

How the lead-on-silicon islands organized into uniform-height islands remained a mystery until Tringides' team made the surprising discovery that when lead atoms move along the surface of a silicon substrate, the lead atoms exhibit a liquid-like motion instead of the typical random-type diffusion observed in other systems. The liquid-like motion of atoms was observed using scanning tunneling microscopy at Ames Lab and low energy electron microscopy performed by collaborators in Hong Kong.

"One big surprise was that the atoms were moving a lot at such a low temperature: 150 degrees Kelvin or minus 123 degrees Celsius," said Tringides. "The other surprise was that the atoms weren't moving randomly like individual atoms as we would expect. In this particular case, it seemed like the whole layer of lead atoms was moving like a liquid.

Fluid-like motion of the lead atoms explains why the layer moves so easily and forms uniform islands so quickly.

"When applying nanotechnology, it's very important to be able to make nanostructures of the same dimension using a method that others can easily replicate," said Tringides. "And, it's important that the growth process is fast."

Tringides' work succeeds in terms of uniformity and speed. The lead islands self-organize on silicon in only two to three minutes. Also, better understanding of how the lead islands grow will help researchers see if other systems show the same liquid-like behavior at low temperatures.

With such promising findings in hand, Tringides' team, which includes associate scientist Myron Hupalo and graduate students Steven Binz and Jizhou Chen, further investigated the possible use of these unusual lead islands on silicon as templates to study typical atomic processes, such as adsorption, nucleation and atom bonding. These processes are important in the study of reactivity and catalysis.

During those experiments, Tringides' group made another unexpected discovery. Normally atomic processes depend on an element's chemical nature, but the group found that when it came to lead islands, quantum mechanics had another surprise in store: The atomic processes depend dramatically on whether the island height is odd or even rather than its chemical nature. Tringides' group made this intriguing observation in a large lead island that had formed over a step on the original silicon surface. The top of the large island was flat as expected.

"But, the part of the island sitting on the higher terrace of silicon was four layers high, and the other part of the island sitting on the lower terrace was five layers," said Tringides.

The group studied nucleation on this unusual island by adding a very small amount of lead to its surface, creating many new small islands on top of the large island. Examination revealed that the density of the new islands was 60 times higher on the four-layer part of the island than on the five-layer part even though the two parts of the island were connected, suggesting that atom bonding is easier on the four-layer islands.

"The island was made up of the same element, lead, throughout," said Tringides. "So, we would expect the two parts of the island to communicate with each other, and atoms should be able to easily move from left to right and right to left among both halves of the island, so the density of the new small islands should have been the same in both parts."

Instead, the two halves of the island behaved like two separate islands. The four-layer section of the island has similar characteristics to independent four-layer islands, and the five-layer section behaved like other five-layer islands.

"For the purpose of growing materials, the two-part island indicates that we may not have to change the element to create variation in material properties," said Tringides. "Instead, we may be able to just change the height of the island."

"This is promising because it's easier to change the geometry of an island than to go out and find a new, exotic material," he added.

Tringides plans further experiments using gas adsorption to test the relationship between material reactivity and island height.

The Department of Energy's Office of Science, Basic Energy Sciences Office funded the work.


Story Source:

The above story is based on materials provided by DOE/Ames Laboratory. Note: Materials may be edited for content and length.


Cite This Page:

DOE/Ames Laboratory. "Nanoscale Materials Grow With The Flow." ScienceDaily. ScienceDaily, 22 February 2009. <www.sciencedaily.com/releases/2009/02/090212132322.htm>.
DOE/Ames Laboratory. (2009, February 22). Nanoscale Materials Grow With The Flow. ScienceDaily. Retrieved October 20, 2014 from www.sciencedaily.com/releases/2009/02/090212132322.htm
DOE/Ames Laboratory. "Nanoscale Materials Grow With The Flow." ScienceDaily. www.sciencedaily.com/releases/2009/02/090212132322.htm (accessed October 20, 2014).

Share This



More Matter & Energy News

Monday, October 20, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Gulfstream G500, G600 Unveiling

Gulfstream G500, G600 Unveiling

Flying (Oct. 20, 2014) Watch Gulfstream's public launch of the G500 and G600 at their headquarters in Savannah, Ga., along with a surprise unveiling of the G500, which taxied up under its own power. Video provided by Flying
Powered by NewsLook.com
Japanese Scientists Unveil Floating 3D Projection

Japanese Scientists Unveil Floating 3D Projection

Reuters - Innovations Video Online (Oct. 20, 2014) Scientists in Tokyo have demonstrated what they say is the world's first 3D projection that floats in mid air. A laser that fires a pulse up to a thousand times a second superheats molecules in the air, creating a spark which can be guided to certain points in the air to shape what the human eye perceives as an image. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Hey, Doc! Sewage, Beer and Food Scraps Can Power Chevrolet’s Bi-Fuel Impala

Hey, Doc! Sewage, Beer and Food Scraps Can Power Chevrolet’s Bi-Fuel Impala

3BL Media (Oct. 20, 2014) Hey, Doc! Sewage, Beer and Food Scraps Can Power Chevrolet’s Bi-fuel Impala Video provided by 3BL
Powered by NewsLook.com
What We Know About Microsoft's Rumored Smartwatch

What We Know About Microsoft's Rumored Smartwatch

Newsy (Oct. 20, 2014) Microsoft will reportedly release a smartwatch that works across different mobile platforms, has a two-day battery life and tracks heart rate. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins