Materials Science

Layered Films Make the Grade

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Science  03 Aug 2001:
Vol. 293, Issue 5531, pp. 763
DOI: 10.1126/science.293.5531.763c

Graded semiconductor films, in which the band gap changes through the thickness of film, have numerous potential applications in devices such as photodetectors, waveguides, and bipolar transistors, but their preparation often requires numerous advanced fabrication steps. Mamedov et al. show how layer-by-layer solution growth of colloidal nanoparticles, in which alternating layers of polyelectrolytes immobilize each layer, can be used to build up graded semiconductor films. In this case, they assembled CdTe particles in bilayer stacks, starting with nanoparticles emitting in the green and increasing in size to those emitting in the yellow, orange, and finally red (each color layer was typically five to ten bilayers thick). Although the gradation achieved is not as fine as that possible with vacuum epitaxy methods, the layers are still well below optical wavelengths, thus suggesting applications such as polarizability or refractive index tuning. — PDS

J. Am. Chem. Soc. 10.1021/ja015857q.

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