Making His Mark on Light
Read it, roll it, recycle it. A newspaper? No, we are talking War and Peace — Leo Tolstoy's 1,400-page masterpiece, as thin as a few sheets of paper but actually made of plastic.
This electronic book is not available in local stores — yet — but the sophisticated new technology such a display device would rely on, organic light-emitting diodes, or OLEDs, is already on the market. Some cell phones, digital cameras and automobiles that have displays that use OLED technology are just entering the marketplace.
OLEDs promise to revolutionize the flat-panel display industry with vivid new displays that have a wider viewing angle and are thinner, brighter, sharper and more colorful and flexible than current liquid crystal displays (LCDs).
As the technology improves, ultra-thin plastic displays for outdoor advertising, computer monitors, greeting cards, personal digital assistants (PDAs) and other portable devices, plus optical circuits, medical diagnostics and electronic books, will begin to appear.
"We are now just seeing the first generation of OLEDs — future generations will be even better, and OLED displays will be everywhere," says Tobin Marks, the Vladimir N. Ipatieff Professor of Catalytic Chemistry and professor of materials science and engineering.
Unlike LCDs, OLEDs are self-luminous and do not require backlighting, making them much more energy efficient than LCDs. A typical OLED structure consists of multiple thin layers of organic materials sandwiched between a transparent anode and a metallic cathode. When an electric charge is applied, the organic material quickly lights up. A low voltage is enough to produce a very bright light.
Working with theorist Mark Ratner (G69), Charles E. and Emma H. Morrison Professor in Chemistry, and physicist Pulak Dutta, professor of physics and astronomy, Marks has been studying how electricity is injected into plastic, flows through the material and is turned into light. His experiments resulted in organic molecules self-assembling one layer at a time into a thin plastic film — the basis for his OLED technology.
"The idea is to rationally design and synthesize completely new structures that self-assemble and generate the desired functions, such as rich color and viewing angle," says Marks. "This requires the molecules to interact with each other and organize themselves in certain ways."
The kinds of self-assembling "smart molecules" that Marks and his group are making also could be used to produce organic transistors. Instead of being carved out of silicon, transistor structures would be printed much like newspapers are printed, but with organic molecules as the "ink" and plastic as the "paper."
One application would be radio frequency identification tags to be used for labeling items in a store or tracking them in a factory. "You could walk up to a cash register at the grocery store," says Marks, "and it would automatically sense what each item costs and whether or not it has passed its expiration date — all in one step."
Marks also is studying hard (inorganic) materials that have very unusual properties, such as being transparent and also electrically conductive. Current transparent conductors, used in television screens and energy-efficient windows, are nowhere near optimal.
"Transparent conductors go hand in hand with OLEDs — if we can make better transparent conductors, we can make better OLEDs," says Marks. The next generation of solar energy cells is also going to require far better transparent conductors as well, he adds.
Organic light-emitting diodes, transparent conductors, organic transistors — these are more than enough to keep any chemist busy, but Marks readily embraces all these challenges, in addition to his catalysis research.
"Tobin's work is marked by amazing originality and diversity as well as an appreciation of important fundamental and practical problems that must be solved," says Fred Basolo, Morrison Professor Emeritus of Chemistry and department chair when Marks joined Northwestern. "He is not afraid to pioneer new areas or to question established dogmas. For these reasons alone, his work has had enormous impact." — M.F.