Controlling the spin orientation of photoexcited electrons by symmetry breaking

We study reflection of optically spin-oriented hot electrons as a means to probe the semiconductor crystal symmetry and its intimate relation with the spin-orbit coupling. The symmetry breaking by reflection manifests itself by tipping the net-spin vector of the photoexcited electrons out of the light propagation direction. The tipping angle and the pointing direction of the net-spin vector are set by the crystal-induced spin precession, momentum alignment and spin-momentum correlation of the initial photoexcited electron population. We examine non-magnetic semiconductor heterostructures and semiconductor/ferromagnet systems and show the unique signatures of these effects.Comment: 4 pages, 3 figures, resubmitte

Spin relaxation in low-dimensional systems

We review some of the newest findings on the spin dynamics of carriers and excitons in GaAs/GaAlAs quantum wells. In intrinsic wells, where the optical properties are dominated by excitonic effects, we show that exciton-exciton interaction produces a breaking of the spin degeneracy in two-dimensional semiconductors. In doped wells, the two spin components of an optically created two-dimensional electron gas are well described by Fermi-Dirac distributions with a common temperature but different chemical potentials. The rate of the spin depolarization of the electron gas is found to be independent of the mean electron kinetic energy but accelerated by thermal spreading of the carriers.Comment: 1 PDF file, 13 eps figures, Proceedings of the 1998 International Workshop on Nanophysics and Electronics (NPE-98)- Lecce (Italy

Obtaining formaldehyde on a new catalytic system

Formaldehyde is widely used in many fields of industry. The increase in the need for formaldehyde led to an increase in scientific research, the purpose of which is to obtain the greatest yield of the product (formaldehyde) with minimal costs for raw materials, catalyst and its regeneration, energy carriers, etc. At industrial plants for the production of formaldehyde by oxidative dehydrogenation of methanol on the silver on pumice catalyst, the process temperature is maintained at 600 ° C. The process of obtaining formaldehyde by oxidation of methanol with air oxygen at the combination of catalysts "silver" and "silver on pumice" in the temperature range of 250–450 °C is investigated. The results showed the possibility of practical application of the combined catalyst. Chemical and technological parameters of the process with the use of a new catalyst are slightly lower than production indicators, however, the temperature of the pilot process is 2 times lower - this will reduce not only the energy costs, but also increase the life of the catalyst and the cost of its regeneration