Featured Research

from universities, journals, and other organizations

Watching crystals grow provides clues to making smoother, defect-free thin films

Date:
January 24, 2010
Source:
Cornell University
Summary:
To make thin films for semiconductors in electronic devices, layers of atoms must be grown in neat, crystalline sheets. But while some materials grow smooth crystals, others tend to develop bumps and defects -- a serious problem for thin-film manufacturing. Physicists shed new light on how atoms arrange themselves into thin films.

Conventional theory says when films are being formed at the atomic scale, atoms land on top of each other and form mounds or "islands" and feel an energetic "pull" from other atoms that prevents them from hopping off the island's edges and crystallizing into smooth sheets. The result is rough spots on the thin films used to produce semiconductors. Cornell University-led researchers eliminated this pull by shortening the bonds between their particles. But they still saw particles hesitate at the island's edges. In this image, green particles are the ones that encounter a step edge or corner barrier. The orange particle encounters smaller barriers as it moves from site to site. The #1 indicates the bond being broken. The #2 indicates the bond that is forming. Near a step edge or corner the atoms do not have a new neighbor to form a bond with (so no #2 particle). This is what sets up the barrier.
Credit: Rajesh Ganapathy, Sharon Gerbode, Mark Buckley, and Itai Cohen

To make thin films for semiconductors in electronic devices, layers of atoms must be grown in neat, crystalline sheets. But while some materials grow smooth crystals, others tend to develop bumps and defects -- a serious problem for thin-film manufacturing.

Related Articles


In the online edition of the journal Science (Jan. 22, 2010), Cornell researchers shed new light on how atoms arrange themselves into thin films. Led by assistant professor of physics Itai Cohen, they recreated conditions of layer-by-layer crystalline growth using particles much bigger than atoms, but still small enough that they behave like atoms.

"These particles are big and slow enough that you can see what's going on in real time," explained graduate student Mark Buckley. Using an optical microscope, the scientists could watch exactly what their "atoms" -- actually, micron-sized silica particles suspended in fluid -- did as they crystallized. What's more, they were able to manipulate single particles one at a time and test conditions that lead to smooth crystal growth. In doing so, they discovered that the random darting motion of the particles is a key factor that affects how the crystals grow.

A major challenge to growing thin films with atoms is that the atoms often form mounds, rather than crystallizing into thin sheets. This happens because as atoms are deposited onto a substrate, they initially form small crystals, called islands. When more atoms are dumped on top of these crystals, the atoms tend to stay atop the islands, rather than hopping off the edges -- as though there were a barrier on the crystals' edges. This creates the pesky rough spots, "and it's game over" for a perfect thin film, Cohen said.

Conventional theory says that atoms that land on top of islands feel an energetic "pull" from other atoms that keeps them from rolling off. In their colloidal system, the researchers eliminated this pull by shortening the bonds between their particles. But they still saw that their particles hesitated at the islands' edges.

Further analysis using optical tweezers that manipulated individual particles allowed the researchers to measure just how long it took for particles to move off the crystal islands. Because the particles were suspended in a fluid, they were knocked about in what's called Brownian motion, which is like a random walk.

As the particles moved and diffused from one area to another, the researchers noted that the distance a particle had to travel to "fall" off an island's edge was three times farther than moving laterally from one site on the island to another.

And because the particles had to go this distance in a Brownian fashion, it took them nine times longer to complete this "fall." This difference in time explained why the researchers still saw a barrier at their island edges.

Atoms on a crystalline film move in a manner similar to Brownian particles, since the vibrations of the underlying crystal, called phonons, tend to jostle them about. The researchers surmised that in addition to the bonding between the atoms, this random motion may also contribute to the barrier at the crystals' edges, and hence the roughness in the crystal film.

"If the principles we have uncovered can be applied to the atomic scale, scientists will be able to better control the growth of thin films used to manufacture electronic components for our computers and cell phones," Cohen said.

The paper's co-authors are former postdoctoral associate Rajesh Ganapathy, now a faculty member at the Jawaharlal Nehru Centre for Advanced Scientific Research in Bangalore, India, and Sharon Gerbode and Mark Buckley, both graduate students.

The work was funded by King Abdullah University of Science and Technology, the Cornell Center for Materials Research, the National Science Foundation and the Cornell Nanoscale Science and Technology Facility.


Story Source:

The above story is based on materials provided by Cornell University. Note: Materials may be edited for content and length.


Cite This Page:

Cornell University. "Watching crystals grow provides clues to making smoother, defect-free thin films." ScienceDaily. ScienceDaily, 24 January 2010. <www.sciencedaily.com/releases/2010/01/100121141057.htm>.
Cornell University. (2010, January 24). Watching crystals grow provides clues to making smoother, defect-free thin films. ScienceDaily. Retrieved October 31, 2014 from www.sciencedaily.com/releases/2010/01/100121141057.htm
Cornell University. "Watching crystals grow provides clues to making smoother, defect-free thin films." ScienceDaily. www.sciencedaily.com/releases/2010/01/100121141057.htm (accessed October 31, 2014).

Share This



More Matter & Energy News

Friday, October 31, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

EU, Russia, Ukraine Seal Breakthrough Gas Accord

EU, Russia, Ukraine Seal Breakthrough Gas Accord

AFP (Oct. 31, 2014) Russia agrees to resume gas deliveries to war-torn Ukraine through the winter in an EU-brokered, multi-billion dollar deal signed by the three parties in Brussels. Duration: 01:10 Video provided by AFP
Powered by NewsLook.com
Relief After “gas War” Is Averted

Relief After “gas War” Is Averted

Reuters - Business Video Online (Oct. 31, 2014) A gas war between Russia and Ukraine has been averted. But as Hayley Platt reports a deal was only reached after Kiev's western creditors agreed to partly funding the deal. Video provided by Reuters
Powered by NewsLook.com
Jaguar Land Rover Opens $800 Million Factory in Britain

Jaguar Land Rover Opens $800 Million Factory in Britain

AFP (Oct. 30, 2014) British luxury car manufacturer Jaguar Land Rover opened a $800 million engine manufacturing centre in western England, creating 1,400 jobs. Duration: 00:45 Video provided by AFP
Powered by NewsLook.com
SkyCruiser Concept Claims to Solve Problem With Flying Cars

SkyCruiser Concept Claims to Solve Problem With Flying Cars

Buzz60 (Oct. 30, 2014) A start-up company called Krossblade says its SkyCruiser concept flying car solves the problem with most flying car concepts. Mara Montalbano (@maramontalbano) explains. Video provided by Buzz60
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