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I. C. Robin,C. Tavares,J. Rothman,G. Feuillet,A. H. El-Shaer,A. Bakin,A. Waag,Le Si Dang 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5
The structural and the spectroscopic properties of a 2-inch ZnO epilayer grown by using molecular beam epitaxy are investigated. A 500-nm-thick substrate was grown on c-sappire by using a MgO buffer. In spite of the high dislocation density in the epilayer, temperature-dependent photoluminescence measurements show only a small decrease in the luminescence intensity between 4 K and 300 K. Time-resolved photoluminescence measurements reveal a decay time independent of temperature. Cathodoluminescence presents an inhomogeneous emission on a micrometric scale: a stronger emission is measured in small nanometric areas. A tentative explanation of this behavior is proposed.
Studies of N-Doped p-ZnO Layers Grown on c-Sapphire by Radical Source Molecular Beam Epitaxy
S. V. Ivanov,A. El-Shaer,M. Al-Suleiman,A. Bakin,A. Waag,O. G. Lyublinskaya,N. M. Shmidt,S. B. Listoshin,R. N. Kyutt,V. V. Ratnikov,A. Ya. Terentyev,B. Ya. Ber,T. A. Komissarova,L. I. Ryabova,D. R. Kh 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5
We report on the fabrication of p-type ZnO:N layers using radical-source molecular beam epitaxy and post-growth annealing of the samples. Plasma-activated oxygen and nitrogen fluxes are supplied via a single plasma cell. The combination of low growth temperature (350 − 400 ℃), slightly O-rich conditions, and post-growth annealing in the range of 650 − 800 ℃ results in efficient nitrogen pdoping with Hall hole concentration 3 × 1017 cm−3. The details of the structural and the electrical characterizations of the films are discussed. We report on the fabrication of p-type ZnO:N layers using radical-source molecular beam epitaxy and post-growth annealing of the samples. Plasma-activated oxygen and nitrogen fluxes are supplied via a single plasma cell. The combination of low growth temperature (350 − 400 ℃), slightly O-rich conditions, and post-growth annealing in the range of 650 − 800 ℃ results in efficient nitrogen pdoping with Hall hole concentration 3 × 1017 cm−3. The details of the structural and the electrical characterizations of the films are discussed.
Powder Metallurgy for Light Weight and Ultra-Light Weight Materials
Kieback, B.,Stephani, G.,Weiβgarber, T.,Schubert, T.,Waag, U.,Bohm, A.,Anderson, O.,Gohler, H.,Reinfried, M. The Korean Powder Metallurgy Institute 2003 한국분말재료학회지 (KPMI) Vol.10 No.6
As in other areas of materials technology, the tendency towards light weight constructions becomes more and more important also for powder metallurgy. The development is mainly driven by the automotive industry looking for mass reduction of vehicles as a major factor for fuel economy. Powder metallurgy has to offer a number of interesting areas including the development of sintered materials of light metals. PM aluminium alloys with improved properties are on the way to replace ferrous pars. For high temperature applications in the engine, titanium aluminide based materials offer a great potential, e.g. for exhaust valves. The PM route using elemental powders and reactions sintering is considered to be a cost effective way for net shape parts production. Furthermore it is expected that lower costs for titanium raw materials coming from metallurgical activities will offer new chances for sintered parts with titanium alloys. The field of cellular metals expands with the hollow sphere technique, that can provide materials of many metals and alloys with a great flexibility in structure modifications. These structures are expected to be used in improving the safety (crash absoption) and noise reduction in cars in the near future and offer great potential for many other applications.
Microscopic Origin of the Near-Band-Edge Emission in Aqueous Chemically-Grown ZnO Nanorods
C. Bekeny,T. Voss,B. Hilker,J. Gutowski,R. Hauschild,H. Kalt,B. Postels,A. Bakin,A. Waag 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5
The microscopic origin of the near-band-edge emission in low-temperature aqueous chemicallygrown ZnO nanorods is analyzed. For the as-grown nanorods, a broad and almost featureless main emission band at 3.366 eV is observed due the presence of a high donor and defect density. After the nanorods have been annealed at 800 ℃ for 1 hour in an oxygen atmosphere, a remarkable reduction of the linewidth of the near-band-edge emission from 10 meV to 4 meV is observed. Sharp and distinguishable excitonic transitions are visible. Time-resolved photoluminescence measurements show very fast recombination times of 11 ps for the as-grown sample while the radiative recombination time increases to 80 ps after the sample is annealed in oxygen atmosphere.