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We report transport of electron-hole complexes in semiconductor quantum wells under applied electric fields. Negatively charged excitons ([X.sup.-]), created by laser excitation of a high electron mobility transistor, are observed to drift upon applying a voltage between the source and drain. In contrast, neutral excitons do not drift under similar conditions. The [X.sup.-] mobility is found to be as high as 6.5 X [10.sup.4] [cm.sup.2] [V.sup.-1] [s.sup.-1]. The results demonstrate that [X.sup.-] exists as a free particle in the best-quality samples and suggest that light emission from opto-electronic devices can be manipulated through exciton drift under applied electric fields., The exciton, the bound state resulting from the Coulomb attraction of an optically excited electron-hole pair, is often described as the semiconductor analog of the hydrogen atom. In 1958, Lampert [...]

The use of bottom-up approaches to construct patterned surfaces for technological applications is appealing, but to date is applicable to only relatively small areas (-10 square micrometers). We constructed highly periodic patterns at macroscopic length scales, in the range of square millimeters, by combining self-assembly of disk-like porphyrin dyes with physical dewetting phenomena. The patterns consisted of equidistant 5-nanometer-wide lines spaced 0.5 to 1 micrometers apart, forming single porphyrin stacks containing millions of molecules, and were formed spontaneously upon drop-casting a solution of the molecules onto a mica surface. On glass, thicker lines are formed, which can be used to align liquid crystals in large domains of square millimeter size. [ABSTRACT FROM AUTHOR]