Summer 1995

Cockroach Pheromones
By Susan Chien

    Cornell scientists have identified the exact molecular shapes of the pheromones used by the brownbanded cockroach and the longhorn beetle to attract potential mates. Although the chemical composition and the two-dimensional structure of the cockroach pheromone were determined in previous studies, not until now have researches finally uncovered the stereochemistry, or three-dimensional structure, of the pheromone.

    Pheromones, which carry messages between members of the same species, can often reveal a great deal about the behavior of the species. This new knowledge about the exact nature of the molecules that carry messages gives more insight into the signals that nature uses to help members of the same species communicate with one another.

    In efforts to identify the stereochemistry of the pheromones, the scientists used a new synthetic method to produce stereoisomers. A number of these stereoisomers were produced and then each was compared to the original structure of the pheromone until a match was found.

    These latest studies could be used to develop chemical traps for such insects. The female brownbanded cockroach produces less than one-billionth of a gram of the pheromone, so only very small amounts of the chemical are needed to lure insects into traps. Cornell professor of chemistry Jerrold Meinwald, who directed the study, said that this new information provides the chemical basis for bio-rational pest control and spares the environment by substantially reducing the use of pesticides and other harmful chemicals.

    "This approach to pest control is based on understanding using the species' own communication system. It is not toxic, not dangerous, and will not affect other species," Meinwald said.

    Conventional methods to battle pest problems, such as heavy use of insecticides, often magnify the problem. Insecticides often kill everything within site, including natural predators that help control the population of the pest. Such events can often result in an explosion in the pest population.

    Brownbanded cockroaches are found in the United States and in select tropical areas around the world, while the longhorn beetle primarily resides in Japan. Recently, Japan set aside land and planted a forest of cedars in an effort to promote economic growth. But the longhorn beetle, which feeds on cedars, experienced a population explosion. These studies offer hope that the cedars may be saved and the beetle population reduced with biological control measures.

    The new knowledge of the stereochemistry of the pheromone is the last piece of the puzzle. Last fall, the individual chemical composition of the cockroach pheromone used to attract mates was identified. These studies helped scientists determine which chemicals the male cockroach responds to. The pheromone was separated into its individual components through gas chromatography, and response by the insect's antennae to each chemical was monitored. The insect's antennae, (its olfactory senses), produces small electrical charges in the presence of certain chemicals. The receptors show very high levels of sensitivity, with the ability to respond to the presence of a small number of molecules. With an electroantennographic detector to record these electrical charges, the insect's sensitivity to certain chemicals was determined.

    Researchers at North Carolina State University, Forest Products Research Institute, and the Fuji Flavor Company also contributed to the studies. The results of these latest studies appeared in the February issue of Proceedings of the National Academy of Sciences.

Electron Traps: Quantum Boxes
Vishal Jain

    Imagine a laser that could operate without any power-a perpetual machine of sorts. Such a laser may become a reality due to the work of researchers at the National Nanofabrication Facility (NNF) at Cornell, a gray windowless cube that juts out of Phillips Hall on the engineering quad.

    The NNF is one of the few labs in the nation that has the equipment capable of creating devices measured in nanometers; it also contains some of the cleanest air in the world since the lab's equipment requires less than a hundred dust particles per cubic-meter of air to operate. Many of the devices in the lab are e-beam machines that can focus an electron-beam as small as 20 nanometers in diameter.

Above: An array of quantum boxes

Each box is between 100-200 nm wide

    Professor L.F. Eastman has been leading researchers Jason D. Reed, Yu-Pei Chen, William J. Schaff and Eric Tantarelli in an effort to use the e-beam machines at the NNF to create quantum "boxes" and "wires" which are in effect, containment devices for electrons. If perfected, the quantum box has the potential to become the key component in a powerless or extremely low-power laser.

    In the first step of a long process to make the boxes, a layer of gallium arsenide is placed on a substrate. Then, a layer of indium gallium arsenide is placed on top of the gallium arsenide to serve as the material for the quantum box. A cap of gallium arsenide is layered onto indium gallium arsenide and finally, a resist is applied as the upper layer. The resist is the canvas for the electron beam, which draws a pattern on the resist by chemically changing the resist molecules it touches.

    After the pattern has been drawn on the resist, the entire wafer is exposed to a plasma of highly reactive chloride ions. These ions eat away at the portions of the resist that have been affected by the electron beam and "burn" their way through the entire wafer. In the end, the desired structures are left on the resist because they were protected from the plasma by the resist not touched by the electron beam.

    Quantum boxes could be a replacement for the quantum wells used in today's lasers. The quantum wells contain electrons that are limited from movement in one dimension. This means that their movement in the other two directions is random and does not contribute energy to the laser, which makes the laser draw a threshold current to operate. A quantum box can contain the movement of electrons in all three dimensions so that all the electron's energy will contribute to a laser's operation.

    "There's only one energy that an electron can have in that box, and every single carrier can participate in contributing energy to lasing wavelength," said Jason Reed. It is possible that a laser made using quantum boxes could operate without any threshold current. Even if some current is required, it is likely to be on the order of a nanoamp, which is much less than the current required to operate today's lasers.

    Another advantage of quantum box lasers is that they can be turned on and off faster than conventional lasers. Supplying a large threshold current to a laser takes time and slows the speed with which the laser can be turned on and off. A quantum box laser will draw a smaller threshold current and could be turned on or off two or three times as fast as today's lasers. This would dramatically increase the speed at which bits could be sent over today's fiber optic cables.

    There are still obstacles to overcome in creating quantum boxes good enough to be used in a laser. The surfaces of the boxes are often contaminated in the process, and remedying this would require an extremely expensive, perfect vacuum environment in which to work. In addition, all the boxes to be used in a laser must be exactly the same dimensions so that all the electrons will contribute to the lasing. One laser can require an array of millions of quantum boxes, making it difficult to ensure that all the boxes in the laser are uniform.

    Overcoming these problems will be a challenge because of the difficulties involved in manufacturing objects on a nanometer scale. However, if successful, this research will allow unparalleled control of electrons in lasers.