Scientists at Tohoku University in Sendai and Kyoto University, both in Japan, report in the January issue of Nature Materials on their study of the plastic deformation of silicon wafers. They suggest that shaped wafers may find use as mirrors in an improved solar cell system and as lenses for x-ray optics.To produce the lenses and mirrors with focal distances of 30, 40, 50 and 100 mm, the researchers heated 0.3- to 0.4-mm-thick (111) silicon wafers to temperatures of approximately 1380 °C in a hydrogen atmosphere and subjected them to 5-MPa of pressure using a graphite die. X-ray diffraction measurements indicated that the curvature of the (111) lattice plane was in close agreement with that of the crystal surface.Potential applications include a high-efficiency photovoltaic setup in which the shaped silicon would act as a concave mirror, focusing solar radiation onto a conventional solar cell, while generating electricity itself from photons it absorbed. Calculations also suggest that a concave spheroidal x-ray monochromator constructed of shaped silicon would have a receiving angle 2000 times as large as that of a flat lithium-fluoride monochromator with approximately the same FWHM of the Bragg peak.
Photosensitizers