Increasing charge mobility in single molecular organic crystals

March 21, 2005

LOS ANGELES, CA -- Flexible displays that can be folded up in your pocket? More accurate biological and chemical sensors? Biocompatible electronics? In research that may help determine the best materials for a wide range of future electronics applications, a scientist from the U.S. Department of Energy's Brookhaven National Laboratory will report on the intrinsic electronic properties of molecular organic crystals at the March 2005 meeting of the American Physical Society. Brookhaven materials scientist Vladimir Butko will describe the experimental techniques and key findings on Monday, March 21, at 3:42 p.m. in room 152 of the Los Angeles Convention Center.

Organic materials are particularly attractive for potential applications such as flexible displays, or so-called "electronic paper," because they are inherently flexible. "Imagine a computer screen that you could crumple or fold like a sheet of plastic film," Butko says. Yet for this and any other electronics application, the materials must also be able to carry an electric current.

"These organic materials, by themselves, have almost no charge carriers -- electrons or "holes" [the absence of electrons] -- to carry current," Butko says. "They act as insulators. But if we inject charge carriers, we can sometimes create organic devices such as field-effect transistors [FETs], through which charge will flow."

To find out which materials have the best potential for carrying current, Butko has been studying single crystals of molecular organic materials such as pentacene and rubrene. Though these crystals themselves may not have direct applications, they provide the simplest form in which to study the materials' intrinsic electronic properties -- unaffected by factors that might play a role in larger samples such as polycrystalline thin films.

The key, says Butko, is to know whether the injected charge carriers will have a high mobility or stay localized. The most stringent test of localization is to cool such a device to very low temperatures: somewhat close to absolute zero, which is approximately -273 degrees Celsius. At these low temperatures the mobility edge can be probed without the complication of thermal activation -- a process that assists charge carrier transport in semiconductors due to large thermal energy at high temperatures. The studies were done using a physical properties measurement system (PPMS) and electrometers at the Los Alamos National Laboratory.

In his talk, Butko will present first evidence for low-temperature, quasi-temperature-independent transport of injected charge in a crystalline organic FET. "These materials, which also have the highest charge mobility at room temperature among organic FETs, can be most useful for electronic applications," Butko says.

Once scientists identify the best crystals, they will use thin-film methods to test their applicability for electronic devices from e-paper to large-format display screens.
-end-
This research was done in collaboration with Arthur Ramirez, David Lang and Xiaoliu Chi from Bell Laboratories, and Jason Lashley from Los Alamos National Laboratory, and was funded in part by the Office of Basic Energy Sciences within the U.S. Department of Energy's Office of Science.

One of the ten national laboratories overseen and funded primarily by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization. Visit Brookhaven Lab's electronic newsroom for links, news archives, graphics, and more: http://www.bnl.gov/newsroom

Note to local editors: Vladimir Butko lives in Sound Beach, New York.

DOE/Brookhaven National Laboratory

Related Crystals Articles from Brightsurf:

A new method to measure optical absorption in semiconductor crystals
Tohoku University researchers have revealed more details about omnidirectional photoluminescence (ODPL) spectroscopy - a method for probing semiconducting crystals with light to detect defects and impurities.

Fat crystals trigger chronic inflammation
A congenital disorder of the fat metabolism can apparently cause chronic hyperreaction of the immune system.

First ever observation of 'time crystals' interacting
For the first time ever, scientists have witnessed the interaction of a new phase of matter known as 'time crystals'.

'Blinking" crystals may convert CO2 into fuels
Imagine tiny crystals that ''blink'' like fireflies and can convert carbon dioxide, a key cause of climate change, into fuels.

Laser takes pictures of electrons in crystals
Microscopes of visible light allow to see tiny objects as living cells and their interior.

Rubies on sapphire: Recipe for making crystals in flux
The effect of the holding temperature and solubility curve of rubies was elucidated, for Al2O3:Cr in MoO3 from 1050 to 1200.

Transparency discovered in crystals with ultrahigh piezoelectricity
Use of an AC rather than a DC electric field can improve the piezoelectric response of a crystal.

New photonic liquid crystals could lead to next-generation displays
A new technique to change the structure of liquid crystals could lead to the development of fast-responding liquid crystals suitable for next generation displays -- 3D, augmented and virtual reality -- and advanced photonic applications such as mirrorless lasers, bio-sensors and fast/slow light generation, according to an international team of researchers from Penn State, the Air Force Research Laboratory and the National Sun Yat-sen University, Taiwan.

The secret behind crystals that shrink when heated
Scientists at Brookhaven Lab have new experimental evidence and a predictive theory that solves a long-standing materials science mystery: why certain crystalline materials shrink when heated.

Engineered protein crystals make cells magnetic
If scientists could give living cells magnetic properties, they could perhaps manipulate cellular activities with external magnetic fields.

Read More: Crystals News and Crystals Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.