Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Chemists advance organic semiconductor processing

28.06.2007
Work with innovative materials improves understanding, design of plastic electronics

Any machinist will tell you that a little grease goes a long way toward making a tool work better. And that may soon hold true for plastic electronics as well.

Carnegie Mellon University chemists have found that grease can make some innovative plastics vastly better electrical conductors. This discovery, published June 25 in Advanced Materials (www3.interscience.wiley.com/cgi-bin/fulltext/114282726/PDFSTART), outlines a chemical process that could become widely adopted to produce the next generation of tiny switches for transistors in radio frequency identification tags, flexible screen displays, and debit or key cards.

“This research brings us closer to developing organic semiconductors with electrical and physical properties far superior to those that exist today,” said principal investigator Richard D. McCullough, professor of chemistry and dean of the Mellon College of Science at Carnegie Mellon. “We were surprised and amazed with our findings.” The new process involves adding a little grease in two ways, say the investigators. The first step involves chemically combining an inherently conducting polymer (ICP) with a grease-like chemical. The second step involves depositing this hybrid material — called a block copolymer — onto a greased platform.

On the surface layer of a transistor, ICPs make good electrical conductors that provide the switch element for a transistor to turn on and off. But ICPs are by nature brittle. To counter this brittleness, scientists chemically link ICPs with grease-like, elastic polymers to make block copolymers.

“These block copolymers are very promising for creating future materials, such as lightweight, thin composite films for ebook readers that you could roll up like today’s newspapers,” said Genevieve Sauvé, a research associate who conducted the latest research under conditions similar to a commercial production setting.

While they provide much-needed flexibility, elastic polymers insulate rather than conduct electricity. Block copolymers that contain grease-like polymers are less effective electrical conductors than pure ICPs. Yet in the right processing setting, the opposite can hold true, the Carnegie Mellon scientists now report. It just depends how you treat a transistor’s silicon dioxide base layer.

As part of the current study, the Carnegie Mellon team tested four block copolymers, each with a different ratio of insulating elastic polymer to conducting polymer. When they applied thin films of these different polymers to untreated silicon dioxide, they found the greater the overall amount of insulating polymer in the final film, the worse that film performed in conducting an electric charge. The result is a flexible switch layer that doesn’t work very well.

But when the scientists pretreated the transistor’s silicon dioxide platform with OTS-8 — a chemical that creates a grease-like coating — they found that transistors incorporating any of the four block copolymers conducted an electric charge with remarkable ease, even when the insulating polymer constituted more than half of the applied block copolymer.

“Something amazing is happening at the molecular interface between our block copolymer and the OTS-8-treated surface so the block copolymers self-assemble with great precision,” Sauvé said. “In fact, we think that the grease-like, insulating polymer in the material and the grease-coated surface both somehow exert important effects in driving this self-assembly.”

Block copolymers with up to 57 percent insulating polymer performed 10 times better on OTS-8-treated surfaces than they did on untreated surfaces, according to the investigators. More importantly, the block copolymers were nearly equal in their performance to ICPs alone on treated surfaces, according to McCullough.

“This is the first report that copolymers are good organic semiconductors,” McCullough said. “These results mean that we could soon design devices that are both flexible and highly functional.”

OTS-8 appears to help the block copolymers assemble into nanowires that are much more highly organized than those that self-assemble on untreated silicon dioxide, according to Sauvé. (See available images)

The Carnegie Mellon team used block copolymers containing ICPs called regioregular polythiophenes (rr-P3HTs), which were initially described by McCullough in 1992. In subsequent research, McCullough’s laboratory has developed cost-efficient methods to produce rr-P3HTs so they can be put into solution and sprayed onto surfaces using ink-jet printing. McCullough has also shown that rr-3PHTs can be modified to attach to different surfaces. By chemically linking rr-P3HTs with other elastic polymers, McCullough’s group has also produced conductive plastics with a range of physical properties that could suit different device applications.

The insulating, elastic polymer used in this latest work is poly(methylacrylate), or PMA. Sauvé is using this system to evaluate nanowire assembly and conductive properties of block copolymers made with polymers other than PMA. These additional polymers are being developed by research scientist Mihaela Iovu in McCullough’s lab.

Eventually, Sauvé says, polymer chemists could replace a silicon dioxide base with a flexible plastic so consumers could roll up plastic displays.

Lauren Ward | EurekAlert!
Further information:
http://www.plextronics.com
http://www.chem.cmu.edu/groups/mccullough/research/block_copolymers/index.html

More articles from Materials Sciences:

nachricht New design improves performance of flexible wearable electronics
23.06.2017 | North Carolina State University

nachricht Plant inspiration could lead to flexible electronics
22.06.2017 | American Chemical Society

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Quantum thermometer or optical refrigerator?

23.06.2017 | Physics and Astronomy

A 100-year-old physics problem has been solved at EPFL

23.06.2017 | Physics and Astronomy

Equipping form with function

23.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>