We present a cross-sectional scanning-tunneling microscopy investigation of the shape, size, and composition of InAs quantum dots in a GaAs matrix, grown by molecular beam epitaxy at low growth rate. From the dimensional analysis we conclude that the investigated quantum dots have an average height of 5 nm, a square base of 18 nm oriented along ͓010͔ and ͓100͔ and the shape of a truncated pyramid. From outward relaxation and lattice constant profiles we conclude that the dots consist of an InGaAs alloy and that the indium concentration increases linearly in the growth direction. Our results justify the predictions obtained from previous photocurrent measurements on similar structures and the used theoretical model.
The concept of a high-luminance light source based on luminescent conversion of LED light and optical concentration in a transparent phosphor is explained. Experiments on a realized light source show that a luminous flux of 8500 lm and a luminance of 500 cd/mm2 can be attained using 56 pump LEDs at 330 W electrical input power. The measurement results are compared to optical simulations, showing that the experimental optical efficiency is slightly lower than expected. The present status enables applications like mid-segment digital projection using LED technology, whereas the concept is scalable to higher fluxes.
Recent demonstrations have shown that near-field optical recording with a solid immersion lens in a conventional actuator is a strong candidate for optical storage beyond Blu-ray Disc. All results published so far were obtained with so-called first-surface configurations, in which the data layer is not protected by a cover-layer. In this paper we demonstrate a next step towards creating a system suitable for a commercial product with removable discs. First results are presented for read-out of discs with a few µm protective polymer cover-layer and a solid immersion lens with NA=1.45 and λ=405 nm.
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