The surface morphology of molecular-beam-epitaxy-grown GaAs(001) has been investigated using in situ scanning tunneling microscopy and reflection high-energy electron diffraction. Films grown on nominally flat substrates at very slow growth rates display a multilevel system of terraces elongated along [11̄0], suggesting an edge energy anisotropy of the order of 10:1 and a preference for sticking at B-type steps.

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Cooperating robots have the potential to achieve tasks more quickly and with a higher probability of success than a single robot acting alone. This paper describes a system of miniature mobile robots and the algorithms used to demonstrate cooperative plume tracking and source localization. The robots share sensor information, but individually decide a course of action based on their estimate of the plume eld. This algorithm was implemented on a group of miniature mobile robots capable of measuring temperature plumes. Experimental results are presented for a representative test run. We also describe a 'next-generation' miniature mobile robot under development that occupies only 0.25 cubic inches in volume.

Chemiresistorsare fabricatedfrom materialsthat changetheir electricalresistancewhen exposedto certain chemical species.Composites of soluble polymers with metallic particles have shown remarkable sensitivity to many volatile organic chemicals, depending on the ability of the rmalyte molecules to swell the polymer matrix. These sensors can be made extremely small (< 100 square microns), operate at ambient temperatures, and require almost no power to read-out. However, the chemiresistor itself is only a part of a more complex sensor system that delivers chemical information to a user who can act on the information. We present the design, fabrication and performance of a chemiresistor array chip with four different chemiresistor materials, heaters and a temperature sensor. We also show the design and fabrication of an integrated chemiresistor array, where the electronics to read-out the chemiresistors is on the same chip with the electrodes for the chemiresistors. The circuit was designed to perform several fi,mctions to make the sensor data more usefi,d. This low-power, integrated chemiresistor array is small enough to be deployed on a Sandia-developed microrobot platform.

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