Featured Research

from universities, journals, and other organizations

Researchers find new way to prevent cracking in nanoparticle films

Date:
October 15, 2012
Source:
University of Pennsylvania
Summary:
Making uniform coatings is a common engineering challenge, and, when working at the nanoscale, even the tiniest cracks or defects can be a big problem. New research has shown a new way of avoiding such cracks when depositing thin films of nanoparticles.

Nanoparticle films crack at certain thicknesses (left). By adding layers of thinner films, cracking can be avoided (right).
Credit: Image courtesy of University of Pennsylvania

Making uniform coatings is a common engineering challenge, and, when working at the nanoscale, even the tiniest cracks or defects can be a big problem. New research from University of Pennsylvania engineers has shown a new way of avoiding such cracks when depositing thin films of nanoparticles.

The research was led by graduate student Jacob Prosser and assistant professor Daeyeon Lee, both of the Department of Chemical and Biomolecular Engineering in Penn's School of Engineering and Applied Science. Graduate student Teresa Brugarolas and undergraduate student Steven Lee, also of Chemical and Biomolecular Engineering, and professor Adam Nolte of the Rose-Hulman Institute of Technology participated in the research.

Their work was published in the journal Nano Letters.

To generate a nanoparticle film, the desired particles are suspended in a suitable liquid, which is then thinly and evenly spread over the surface through a variety of physical methods. The liquid is then allowed to evaporate, but, as it dries, the film can crack like mud in the sun.

"One method for preventing cracking is modifying the suspension's chemistry by putting binding additives in there," Prosser said. "But that is essentially adding a new material to the film, which may ruin its properties."

This dilemma is highlighted in the case of electrodes, the contact points in many electrical devices that transfer electricity. High-end devices, like certain types of solar cells, have electrodes composed of nanoparticle films that conduct electrons, but cracks in the films act as insulators. Adding a binder to the films would only compound the problem.

"These binders are usually polymers, which are insulators themselves," Lee said. "If you use them, you're not going to get the targeted property, the conductivity, that you want."

Engineers can prevent cracks with alternative drying methods, but these involve ultra-high temperatures or pressures and thus expensive and complicated equipment. A cheap and efficient method for preventing cracks would be a boon for any number of industrial processes.

The ubiquity of cracking in this context, however, means that researchers know the "critical cracking thickness" for many materials. The breakthrough came when Prosser tried making a film thinner than this threshold, then stacking them together to make a composite of the desired thickness.

"I was thinking about how, in the painting of buildings and homes, multiple coats are used," Prosser said. "One reason for that is to avoid cracking and peeling. I thought it could work for these films as well, so I gave it a try."

"This is one of those things where, once you figure it out," Lee said, "it's so obvious, but somehow this method has evaded everyone all these years."

One reason this approach may have remained untried is that it is counterintuitive that it should work at all.

The method the researchers used to make the films is known as "spin-coating." A precise amount of the nanoparticle suspension -- in this case, silica spheres in water -- is spread over the target surface. The surface is then rapidly spun, causing centrifugal acceleration to thin the suspension over the surface in a uniform layer. The suspension then dries with continued rotation, causing the water to evaporate and leaving the silica spheres behind in a compacted arrangement.

But to make a second layer over this first, another drop of liquid suspension would need to be placed on the dried nanoparticles, something that would normally wash them away. However, the researchers were surprised when the dried layers remained intact after the process was repeated 13 times; the exact mechanism by which they remained stable is something of a mystery.

"We believe that the nanoparticles are staying on the surface," Lee said, "because covalent bonds are being formed between them even though we're not exposing them to high temperatures. The inspiration for that hypothesis came from our colleague Rob Carpick. His recent Nature paper was all about how silica-silica surfaces form bonds at room temperature; we think this will work with other kinds of metal oxides."

Future research will be necessary to pin down this mechanism and apply it to new types of nanoparticles.

The research was supported by the National Science Foundation and the Penn Materials Research Science and Engineering Center.


Story Source:

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


Journal Reference:

  1. Jacob H. Prosser, Teresa Brugarolas, Steven Lee, Adam J. Nolte, Daeyeon Lee. Avoiding Cracks in Nanoparticle Films. Nano Letters, 2012; 12 (10): 5287 DOI: 10.1021/nl302555k

Cite This Page:

University of Pennsylvania. "Researchers find new way to prevent cracking in nanoparticle films." ScienceDaily. ScienceDaily, 15 October 2012. <www.sciencedaily.com/releases/2012/10/121015132549.htm>.
University of Pennsylvania. (2012, October 15). Researchers find new way to prevent cracking in nanoparticle films. ScienceDaily. Retrieved July 24, 2014 from www.sciencedaily.com/releases/2012/10/121015132549.htm
University of Pennsylvania. "Researchers find new way to prevent cracking in nanoparticle films." ScienceDaily. www.sciencedaily.com/releases/2012/10/121015132549.htm (accessed July 24, 2014).

Share This




More Matter & Energy News

Thursday, July 24, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Creative Makeovers for Ugly Cellphone Towers

Creative Makeovers for Ugly Cellphone Towers

AP (July 24, 2014) Mobile phone companies and communities across the country are going to new lengths to disguise those unsightly cellphone towers. From a church bell tower to a flagpole, even a pencil, some towers are trying to make a point. (July 24) Video provided by AP
Powered by NewsLook.com
Algonquin Power Goes Activist on Its Target Gas Natural

Algonquin Power Goes Activist on Its Target Gas Natural

TheStreet (July 23, 2014) When The Deal's Amanda Levin exclusively reported that Gas Natural had been talking to potential suitors, the Ohio company responded with a flat denial, claiming its board had not talked to anyone about a possible sale. Lo and behold, Canadian utility Algonquin Power and Utilities not only had approached the company, but it did it three times. Its last offer was for $13 per share as Gas Natural's was trading at a 60-day moving average of about $12.50 per share. Now Algonquin, which has a 4.9% stake in Gas Natural, has taken its case to shareholders, calling on them to back its proposals or, possibly, a change in the target's board. Video provided by TheStreet
Powered by NewsLook.com
Robot Parking Valet Creates Stress-Free Travel

Robot Parking Valet Creates Stress-Free Travel

AP (July 23, 2014) 'Ray' the robotic parking valet at Dusseldorf Airport in Germany lets travelers to avoid the hassle of finding a parking spot before heading to the check-in desk. (July 23) Video provided by AP
Powered by NewsLook.com
Boeing Ups Outlook on 52% Profit Jump

Boeing Ups Outlook on 52% Profit Jump

Reuters - Business Video Online (July 23, 2014) Commercial aircraft deliveries rose seven percent at Boeing, prompting the aerospace company to boost full-year profit guidance- though quarterly revenues missed analyst estimates. Bobbi Rebell reports. Video provided by Reuters
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:
from the past week

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