Nano research could impact flexible electronic devices

ScienceDaily (Jan. 12, 2012) — A discovery by a research team at North Dakota State University, Fargo, and the National Institute of Standards and Technology (NIST), shows that the flexibility and durability of carbon nanotube films and coatings are intimately linked to their electronic properties. The research could one day impact flexible electronic devices such as solar cells and wearable sensors. The research also provided a promising young high school student the chance to work in the lab with world-class scientists, jumpstarting her potential scientific career.

The NDSU/NIST research team, led by Erik Hobbie, Ph.D., is working to determine why thin films made from metallic single-wall carbon nanotubes are superior for potential applications that demand both electronic performance and mechanical durability. "One simple reason is that the metallic nanotubes tend to transport charge more easily when they touch each other," said Hobbie. "But another less obvious reason has to do with how much the films can flex without changing their structure at very small scales."

Results from the study are published in ACS Nano.

The team includes NDSU graduate student John M. Harris; postdoctoral researcher Ganjigunte R. Swathi Iyer; Anna K. Bernhardt, North Dakota Governor's School attendee; and NIST researchers Ji Yeon Huh, Steven D. Hudson and Jeffrey A. Fagan.

There is great interest in using carbon nanotube films and coatings as flexible transparent electrodes in electronic devices such as solar cells. "Our research demonstrates that the flexibility and durability of these films are intimately linked to their electronic properties," said Hobbie. "This is a very new idea, so hopefully, it will generate a new series of studies and questions focused on the exact origins and consequences of this effect."

Such research could potentially result in material that reduces solar cell costs, and leads to the ability to use them in clothing or foldable electronics. Electronic devices currently on the market that require transparent electrodes, like touch screens and solar cells, typically use indium tin oxide, an increasingly expensive material. "It is also very brittle," said Hobbie, "implying that it cannot be used in devices that require mechanical flexibility like wearable or foldable electronics."

Single-wall carbon nanotubes show significant promise as transparent conductive coatings with outstanding electronic, mechanical and optical properties. "A particularly attractive feature of these films is that the physical properties can be tuned through the addition or subtraction of a relatively small number of nanotubes," said Hobbie. "Thin films made from such materials hold tremendous potential for flexible electronics applications, including the replacement of indium tin oxide in liquid crystal displays and photovoltaic devices."

Thin films made from metallic single-wall carbon nanotubes show better durability as flexible transparent conductive coatings, which the researchers attribute to a combination of superior mechanical performance and higher interfacial conductivity. The research team found significant differences in the electronic manifestations of thin-film wrinkling, depending on the electronic type of the nanotubes, and examined the underlying mechanisms.

The results of this study suggest that the metallic films make better flexible transparent conductive coatings; they have higher conductivity and are more durable. "Our results are relevant to a number of ongoing efforts in transparent conducting films and flexible electronic devices," said Hobbie.

The research was supported by the National Science Foundation through CMMI-0969155 and the U.S. Department of Energy through DE-FB36-08GO88160.

The opportunity to work on such research was new to Anna Bernhardt, a high school junior from a town of 1,000 people in western North Dakota. She was among 66 of the most academically driven high school sophomores and juniors who attended a six-week intensive summer residential program on the NDSU campus for scholastically motivated students in the state.

Students receive concentrated instruction from 40 NDSU faculty through discussion groups, labs, field trips and other activities. The state of North Dakota funds the cost of participation for North Dakota students who are accepted into the program. It's available free to public school students, while private and homeschool students selected for the program can make arrangements to attend for free through their local public school district.

While it is unusual for a young student to be involved in nanotechnology research at this level, it presented an opportunity for everyone involved. Bernhardt prepared single-wall carbon nanotube samples and participated in testing of the samples. "The experience of working in a research setting has helped me to decide that I would love to do more research in the future," said the young scientist. "The biggest benefit of working in the lab was getting a taste of the true research experience. Without North Dakota's Governor's School, I would never have been able to have this experience and surely wouldn't be so certain that I would like to do more research in the future."

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted from materials provided by North Dakota State University, via Newswise.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

John M. Harris, Ganjigunte R. Swathi Iyer, Anna K. Bernhardt, Ji Yeon Huh, Steven D. Hudson, Jeffrey A. Fagan, Erik K. Hobbie. Electronic Durability of Flexible Transparent Films from Type-Specific Single-Wall Carbon Nanotubes. ACS Nano, 2011; 111220100417004 DOI: 10.1021/nn204383t

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Highly efficient method for creating flexible, transparent electrodes developed

ScienceDaily (Nov. 22, 2011) — As the market for liquid crystal displays and other electronics continues to drive up the price of indium -- the material used to make the indium tin oxide (ITO) transparent electrodes in these devices -- scientists have been searching for a less costly and more dynamic alternative, particularly for use in future flexible electronics.

Besides its high price, ITO has several drawbacks. It's brittle, making it impractical for use in flexible displays and solar cells, and there is a lack of availability of indium, which is found primarily in Asia. Further, the production of ITO films is relatively inefficient.

Now, researchers at UCLA report in the journal ACS Nano that they have developed a unique method for producing transparent electrodes that uses silver nanowires in combination with other nanomaterials. The new electrodes are flexible and highly conductive and overcome the limitations associated with ITO.

For some time, silver nanowire (AgNW) networks have been seen as promising candidates to replace ITO because they are flexible and each wire is highly conductive. But complicated treatments have often been required to fuse crossed AgNWs to achieve low resistance and good substrate adhesion. To address this, the UCLA researchers demonstrated that by fusing AgNWs with metal-oxide nanoparticles and organic polymers, they could efficiently produce highly transparent conductors.

The team of researchers represents a collaboration between the department of materials science and engineering at the UCLA Henry Samueli School of Engineering and Applied Science; the department of chemistry and biochemistry in the UCLA College of Letters and Science; and the California NanoSystems Institute (CNSI) at UCLA.

The team was led by Yang Yang, a professor of materials science and engineering, and Paul Weiss, director of the CNSI and a professor of materials science and engineering and of chemistry and biochemistry.

"In this work, we demonstrate a simple and effective solution method to achieve highly conductive AgNW composite films with excellent optical transparency and mechanical properties," said Yang who also directs the Nano Renewable Energy Center at the CNSI. "This is by far the best solution: a processed, transparent electrode that is compatible with a wide variety of substrate choices."

Scientists can easily spray a surface with the nanowires to make a transparent mat, but the challenge is to make the silver nanowires adhere to the surface more securely without the use of extreme temperatures (200° C) or high pressures, steps that make the nanomaterials less compatible with the sensitive organic materials typically used to make flexible electronics.

To meet this challenge, Rui Zhu, the paper's first author, developed a low-temperature method to make high-performance transparent electrodes from silver nanowires using spray coating of a unique combination of nanomaterials.

First, researchers sprayed a solution of commercially available silver nanowires onto a surface. They then treated the nanowires with a solution of titanium dioxide nanoparticles to create a hybrid film. As the film dries, capillary forces pull the nanowires together, improving the film's conductivity. The scientists then coated the film with a layer of conductive polymer to increase the wires' adhesion to the surface.

The AgNW composite meshes are highly conductive, with excellent optical transparency and mechanical properties. The research team also built solar cells using the new electrodes and found that their performance was comparable to that of solar cells made with indium tin oxide.

The research received support from the Office of Naval Research and the Kavli Foundation.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted from materials provided by University of California - Los Angeles. The original article was written by Jennifer Marcus.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Rui Zhu, Choong-Heui Chung, Kitty C. Cha, Wenbing Yang, Yue Bing Zheng, Huanping Zhou, Tze-Bin Song, Chun-Chao Chen, Paul S. Weiss, Gang Li, Yang Yang. Fused Silver Nanowires with Metal Oxide Nanoparticles and Organic Polymers for Highly Transparent Conductors. ACS Nano, 2011; : 111104125342002 DOI: 10.1021/nn203576v

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Flexible electronics hold promise for consumer applications

ScienceDaily (Sep. 6, 2011) — New research from Wake Forest University has advanced the field of plastic-based flexible electronics by developing, for the first time, an extremely large molecule that is stable, possesses excellent electrical properties, and inexpensive to produce.

The technology, developed by Oana Jurchescu, assistant professor of physics at Wake Forest, her graduate students Katelyn Goetz and Jeremy Ward, and interdisciplinary collaborators from Stanford University, Imperial College (London), University of Kentucky and Appalachian State University, eventually may turn scientific wonders -- including artificial skin, smart bandages, flexible displays, smart windshields, wearable electronics and electronic wallpapers -- into everyday realities.

Jurchescu says plastic or organic semiconductors, produced in large volume using roll-to-roll processing, inkjet printing or spray deposition, represent the "electronics everywhere" trend of the future.

In the current consumer market, however, the word "electronic" is generally associated with the word "expensive." This is largely because products such as televisions, computers and cell phones are based on silicon, which is costly to produce. Organic electronics, however, build on carbon-based (plastic) materials, which offer not only ease of manufacturing and low cost, but also lightweight and mechanical flexibility, says Jurchescu.

The team recently published its manuscript in Advanced Materials.

Prior researchers predicted that larger carbon frameworks would have properties superior to their smaller counterparts, but until now there has not been an effective route to make these larger frameworks stable and soluble enough for study.

"To accelerate the use of these technologies, we need to improve our understanding of how they work," Jurchescu says. "The devices we study (field-effect transistors) are the fundamental building blocks in all modern-based electronics. Our findings shed light on the effect of the structure of the molecules on their electrical performance, and pave the way towards a design of improved materials for high-performance, low-cost, plastic-based electronics."

Jurchescu's lab is part of the physics department and the Center for Nanotechnology and Molecular Materials.

The team studied new organic semiconductor materials amenable to transistor applications and explored their structure-property relationships. Organic semiconductors are a type of plastic material characterized by a specific structure that makes them conductive. In modern electronics, a circuit uses transistors to control the current between various regions of the circuit.

The results of the published research may lead to significant technological improvements as the performance of the transistor determines the switching speed, contrast details, and other key properties of the display.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Wake Forest University. The original article was written by Kim McGrath.

Journal Reference:

Katelyn P. Goetz, Zhong Li, Jeremy W. Ward, Cortney Bougher, Jonathan Rivnay, Jeremy Smith, Brad R. Conrad, Sean R. Parkin, Thomas D. Anthopoulos, Alberto Salleo, John E. Anthony, Oana D. Jurchescu. Effect of Acene Length on Electronic Properties in 5-, 6-, and 7-Ringed Heteroacenes. Advanced Materials, 2011; 23 (32): 3698 DOI: 10.1002/adma.201101619

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here