Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Transparent metal films for smart phone, tablet and TV displays

16.12.2015

A new material that is both highly transparent and electrically conductive could make large screen displays, smart windows and even touch screens and solar cells more affordable and efficient, according to the Penn State materials scientists and engineers who discovered it.

Indium tin oxide, the transparent conductor that is currently used for more than 90 percent of the display market, has been the dominant material for the past 60 years. However, in the last decade, the price of indium has increased dramatically. Displays and touchscreen modules have become a main cost driver in smartphones and tablets, making up close to 40 percent of the cost.


This is a figure showing the crystal structure of strontium vanadate (orange) and calcium vanadate (blue). The red dots are oxygen atoms arranged in 8 octohedra surrounding a single strontium or calcium atom. Vanadium atoms can be seen inside each octahedron.

Credit: Lei Zhang, Penn State

While memory chips and processors get cheaper, displays get more expensive from generation to generation. Manufacturers have searched for a possible ITO replacement, but until now, nothing has matched ITO's combination of optical transparency, electrical conductivity and ease of fabrication.

A team led by Roman Engel-Herbert, assistant professor of materials science and engineering, reports today (Dec 15) online in Nature Materials a new design strategy that approaches the problem from a different angle. The researchers use thin -- 10 nanometer -- films of an unusual class of materials called correlated metals in which the electrons flow like a liquid.

While in most conventional metals, such as copper, gold, aluminum or silver, electrons flow like a gas, in correlated metals, such as strontium vanadate and calcium vanadate, they move like a liquid. According to the researchers, this electron flow produces high optical transparency along with high metal-like conductivity.

"We are trying to make metals transparent by changing the effective mass of their electrons," Engel-Herbert said. "We are doing this by choosing materials in which the electrostatic interaction between negatively charged electrons is very large compared to their kinetic energy. As a result of this strong electron correlation effect, electrons 'feel' each other and behave like a liquid rather than a gas of non-interacting particles. This electron liquid is still highly conductive, but when you shine light on it, it becomes less reflective, thus much more transparent."

To better understand how they achieved this fine balance between transparency and conductivity, Engel-Herbert and his team turned to a materials theory expert, Professor Karin Rabe of Rutgers University.

"We realized that we needed her help to put a number on how 'liquid' this electron liquid in strontium vanadate is," Engel-Herbert said.

Rabe helped the Penn State team put together all the theoretical and mathematical puzzle pieces they needed to build transparent conductors in the form of a correlated metal. Now that they understand the essential mechanism behind their discovery, the Penn State researchers are confident they will find many other correlated metals that behave like strontium vanadate and calcium vanadate.

Lei Zhang, lead author on the Nature Materials paper and a graduate student in Engel-Herbert's group, was the first to recognize what they had discovered.

"I came from Silicon Valley where I worked for two years as an engineer before I joined the group," said Zhang. "I was aware that there were many companies trying hard to optimize those ITO materials and looking for other possible replacements, but they had been studied for many decades and there just wasn't much room for improvement. When we made the electrical measurements on our correlated metals, I knew we had something that looked really good compared to standard ITO."

Currently indium costs around $750 per kilogram, whereas strontium vanadate and calcium vanadate are made from elements with orders of magnitude higher abundance in the earth's crust. Vanadium sells for around $25 a kilogram, less than 5 percent of the cost of indium, while strontium is even cheaper than vanadium.

"Our correlated metals work really well compared to ITO," said Engel-Herbert. "Now, the question is how to implement these new materials into a large-scale manufacturing process. From what we understand right now, there is no reason that strontium vanadate could not replace ITO in the same equipment currently used in industry."

Along with display technologies, Engel-Herbert and his group are excited about combining their new materials with a very promising type of solar cell that uses a class of materials called organic perovskites. Developed only within the last half dozen years, these materials outperform commercial silicon solar cells but require an inexpensive transparent conductor. Strontium vanadate, also a perovskite, has a compatible structure that makes this an interesting possibility for future inexpensive, high-efficiency solar cells.

Engel-Herbert and Zhang have applied for a patent on their technology.

###

Along with Zhang and Engel-Herbert, Hai-Tian Zhang, Craig Eaton, Yuanxia Zheng and Matthew Brahlek, all students or postdoctoral Fellows in Engel-Herbert's group, worked on this paper, "Correlated metals as transparent conductors." Others from Penn State and the Materials Research Institute on this project were Moses Chan, Evan Pugh professor of physics, and his postdoctoral Fellow, Weiwei Zhao; and Venkatraman Gopalan, professor of materials science and engineering and his student Lu Guo.

With Rabe was her student Yuanjun Zhou from Rutgers University. Anna Barnes, Hamna Haneef and associate professor Nikolas Podraza of Univesity of Toledo also worked on this project.

The Office of Naval Research, the National Science Foundation and the Department of Energy funded this work. Fabrication of the correlated metals was performed at the Materials Research Institute in the laboratory facilities of Penn State's Millennium Science Complex.

Media Contact

A'ndrea Elyse Messer
aem1@psu.edu
814-865-9481

 @penn_state

http://live.psu.edu 

A'ndrea Elyse Messer | EurekAlert!

More articles from Materials Sciences:

nachricht Epoxy compound gets a graphene bump
14.11.2018 | Rice University

nachricht Automated adhesive film placement and stringer integration for aircraft manufacture
15.11.2018 | Fraunhofer IFAM

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: UNH scientists help provide first-ever views of elusive energy explosion

Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving "magnetic reconnection"--the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion--in the Earth's magnetotail, the magnetic environment that trails behind the planet.

Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can...

Im Focus: A Chip with Blood Vessels

Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.

Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...

Im Focus: A Leap Into Quantum Technology

Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.

In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...

Im Focus: Research icebreaker Polarstern begins the Antarctic season

What does it look like below the ice shelf of the calved massive iceberg A68?

On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.

Im Focus: Penn engineers develop ultrathin, ultralight 'nanocardboard'

When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure

Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

“3rd Conference on Laser Polishing – LaP 2018” Attracts International Experts and Users

09.11.2018 | Event News

On the brain’s ability to find the right direction

06.11.2018 | Event News

European Space Talks: Weltraumschrott – eine Gefahr für die Gesellschaft?

23.10.2018 | Event News

 
Latest News

Purdue cancer identity technology makes it easier to find a tumor's 'address'

16.11.2018 | Health and Medicine

Good preparation is half the digestion

16.11.2018 | Life Sciences

Microscope measures muscle weakness

16.11.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>