Going Organic - Electronically

Organic molecules could shape the future of electronics, say Weizmann Institute scientists who have recently placed common semiconductor-based devices, for the first time ever, under these molecules" control.

The inclusion of organic molecules in electronics would provide an extensive range of possibilities. However, attempts to do so have been impeded by "pinholes" - small defects in the layers of organic molecules used in semiconductor research. Pinholes are very difficult to detect and yet radically sway conductance. Scientists were unable to determine whether electric current measurements resulted from the passage of the current through these pinholes or through the organic molecule itself.

Ayelet Vilan, a graduate student working with Prof. David Cahen of the Weizmann Institute's Materials and Interfaces Department, decided to skirt the problem. Using newly synthesized organic molecules, she constructed a one-molecule-thick layer that is so thin the electric current generally passes by the molecules without interacting with them. The problem of assessing whether the current passed via an organic molecule or via a pinhole was thus eliminated. This enabled the accurate analysis of these molecules" effect on the semiconductor.

The scientists also found that changing the organic molecules used in the monolayer led to a predictable change in electrical characteristics  meaning that they could control the semiconductor's properties.

To work with the very fragile monolayers, Vilan developed a new method for preparing semiconductor devices. The technique is founded on a widely used semiconductor device (diode), which is comprised of a semiconductor (called GaAs) connected to a metal. She inserted the organic monolayer between these two components. Since it was essential to ensure that the monolayer would not be crushed, Vilan, building on the findings of Ellen Moons, one of Cahen's former students, used a thin gold leaf as the metal sheet and gently floated it onto the monolayer.

The study, published in Nature, introduces a feasible way to incorporate organic molecules into electronic devices. "But mainly," says Vilan, "it provides new insights into the emerging field of molecular electronics. So little is known about the interactions that occur between organic molecules and the electric conductors we normally use. This approach may provide a basis for designing novel types of semiconductor-based devices, from improvements in relatively simple applications, such as solar cells, to new computer chips."

Prof. David Cahen's research is supported by the Fusfeld Research Fund, Pennsylvania.