Synthesis of Colloidal Mn2+:ZnO Quantum Dots and High-TC Ferromagnetic Nanocrystalline Thin Films

We report the synthesis of colloidal Mn2+-doped ZnO (Mn2+:ZnO) quantum dots and the preparation of room-temperature ferromagnetic nanocrystalline thin films. Mn2+:ZnO nanocrystals were prepared by a hydrolysis and condensation reaction in DMSO under atmospheric conditions. Synthesis was monitored by electronic absorption and electron paramagnetic resonance (EPR) spectroscopies. Zn(OAc)2 was found to strongly inhibit oxidation of Mn2+ by O2, allowing the synthesis of Mn2+:ZnO to be performed aerobically. Mn2+ ions were removed from the surfaces of as-prepared nanocrystals using dodecylamine to yield high-quality internally doped Mn2+:ZnO colloids of nearly spherical shape and uniform diameter (6.1 +/- 0.7 nm). Simulations of the highly resolved X- and Q-band nanocrystal EPR spectra, combined with quantitative analysis of magnetic susceptibilities, confirmed that the manganese is substitutionally incorporated into the ZnO nanocrystals as Mn2+ with very homogeneous speciation, differing from bulk Mn2+:ZnO only in the magnitude of D-strain. Robust ferromagnetism was observed in spin-coated thin films of the nanocrystals, with 300 K saturation moments as large as 1.35 Bohr magneton/Mn2+ and TC > 350 K. A distinct ferromagnetic resonance signal was observed in the EPR spectra of the ferromagnetic films. The occurrence of ferromagnetism in Mn2+:ZnO and its dependence on synthetic variables are discussed in the context of these and previous theoretical and experimental results.Comment: To be published in the Journal of the American Chemical Society Web on July 14, 2004 (http://dx.doi.org/10.1021/ja048427j

Structure and Stability of the Iodide Elpasolite, Cs2AgBiI6

Iodide elpasolites (or double perovskites, A2B'B"I6, B' = M+, B" = M3+) are predicted to be promising alternatives to lead-based perovskite semiconductors for photovoltaic and optoelectronic applications, but no iodide elpasolite has ever been definitively prepared or structurally characterized. Iodide elpasolites are widely predicted to be unstable due to favorable decomposition to the competing A3B2I9 (B = M3+) phase. Here, we report the results of synchrotron XRD and X-ray total scattering measurements on putative Cs2AgBiI6 nanocrystals made via anion exchange from parent Cs2AgBiBr6 nanocrystals. Rietveld refinement of XRD and PDF data shows that these nanocrystals indeed exhibit a tetragonal (I4-m) elpasolite structure, making them the first example of a structurally characterized iodide elpasolite. A series of experiments probing structural relaxation and the effects of surface ligation or grain size all point to the critical role of surface free energy in stabilizing the iodide elpasolite phase in these nanocrystals.Comment: 7 figures, 1 scheme, plus supporting information fil

Экспериментальная автоматизированная система гидрометеорологических измерений и обработки данных для береговых станций

Разработан действующий макет автоматизированной системы прибрежных гидрометеорологических измерений для морской сети Госгидромета Украины. В течение 2000 – 2004 гг. проведены испытания и опытная эксплуатация метеорологических (ветер, температура воздуха, атмосферное давление) и гидрологических (уровень, температура и соленость воды) измерительных блоков, установленных в стандартных условиях морской станции «Севастополь». Приводятся данные о структуре, основных технологических принципах автоматизированной системы и некоторые результаты квазинепрерывных метеорологических и гидрологических измерений.Developed is functioning model of automated system of coastal hydrometeorological measurements for the marine net of State Hydrometeorological Institution of Ukraine. In 2000 – 2004 the tests and experimental exploitation of meteorological (wind, atmospheric temperature, atmospheric pressure) and hydrological (water level, temperature and salinity) measuring blocks installed in standard conditions of marine station “Sevastopol” were held. Data on structure, general technological principles of the automated system and some results of quazi-continuous meteorological and hydrological measurements is presented