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L. Seetha Lakshmi V Sridharan DV Natarajan V Sankara Sastry T S Radhakrishnan 《Pramana》2002,58(5-6):1019-1026
Mn site is substituted with closed shell ions (Al, Ga, Ti, Zr and a certain combination of Zr and Al) and also with Fe and
Ru ions carrying the magnetic moment (S=5/2 and 2 respectively) at a fixed concentration of 5 at %. Substitution did not change either the crystal symmetry or the
oxygen stoichiometry. All substituents were found to suppress both the metal-insulator and ferromagnetic transition temperatures
(T
p(ρ) and T
C, respectively) to varied extents. Two main contributions identified for the suppression are the lattice disorder arising
due to difference in the ionic radii between the substituent (r
M) and the Mn3+ ion (r
Mn
3+) and in the case of the substituents carrying a magnetic moment, the type of magnetic coupling between the substituent and
that of the neighboring Mn ion. 相似文献
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A. Lunk P. Bachem P. Scheible L. Ulrich 《Applied Physics A: Materials Science & Processing》2001,72(5):557-564
The development of in situ diagnostics of the most important species and reactions in the plasma and/or on the surface during
thin-film growth is one of the current topics in plasma-enhanced vapor deposition. In situ thin film diagnostic methods which
could be used in plasma processing are restricted due to the presence of electrons and ions. The advantages and disadvantages
of different applicable methods will be discussed. The spectroscopic in situ control of boron nitride film growth is presented
as an example of surface modification in low-temperature, low-pressure plasma processing. The growth of cubic and hexagonal
boron nitride is observed by polarized infrared reflection spectroscopy in absorption and ellipsometric configurations as
well as by single-wavelength ellipsometry in the visible spectral range. Modeling of the experimental results gives detailed
information on growth conditions and internal stress of the films.
Received: 8 August 2000 / Accepted: 12 December 2000 / Published online: 3 April 2001 相似文献
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Separation and Characterization of Chloro-aquo-hydroxo-oxo-osmates(IV) As a result of the acidic hydrolysis of hexachloroosmate(IV), OsCl62?, and/or the careful reduction of osmium tetroxide with iron(II) sulfate in hydrochloric acid products have been obtained which have been separated by column chromatography using diethylaminoethyl cellulose. On the basis of the analytically determined Os:Cl ratios, the ionic charges that could be deduced from the elution behaviour, and the absorption spectra the products have been characterized as the monomers OsCl5(H2O)?, cis-OsCl4(OH)(H2O)?, fac-OsCl3(OH)2(H2O)? and mer-OsCl3(OH)(H2O)2, the O-bridged dimers Cl5Os? O? OsCl54?, cis-(H2O)Cl4Os? O? OsCl4(H2O)2?and fac-(H2O)(OH)Cl3Os? O? OsCl3(OH)(H2O)2? and the hydrogen bridges forming OH-bridged dimers shown in “Inhaltsübersicht”. 相似文献
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G. Lehmann P. Hess S. Weissmantel G. Reisse P. Scheible A. Lunk 《Applied Physics A: Materials Science & Processing》2002,74(1):41-45
Cubic boron nitride (c-BN) films of 200–420 nm thickness and high phase purity were deposited on silicon (100) substrates
by ion-assisted pulsed laser deposition (IA PLD)from a boron nitride target using a KrF-excimer laser, and by plasma-enhanced
physical vapor deposition (PE PVD)with a hollow-cathode arc evaporation device. In order to improve the c-BNfilm adhesion,
hexagonal boron nitride (h-BN) films with 25–50 nm thickness were used as buffer layers. The density and Young’s modulus of
the c-BNfilms were obtained by investigating the dispersion of surface acoustic waves. In data analysis a two-layer model
was applied in order to take the influence of the h-BNlayer into consideration. The values for the density vary from 2.95±0.25 g/cm3to 3.35±0.3 g/cm3, and those for the Young’s modulus from 420±40 GPa to 505±30 GPa. The results are compared with literature values reported
for nanocrystalline films, polycrystalline disks and single crystal c-BN.
Received: 26 March 2001 / Accepted: 29 March 2001 / Published online: 25 July 2001 相似文献
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We present a new generation of nano‐electromechanical systems (NEMS), which are realized by doping the semiconductor base material. In contrast to the traditional approach these doped NEMS (D‐NEMS) do not require a metallization layer. This makes them far lighter and hence increases resonance frequency and quality factor. Additionally, D‐NEMS can be tuned from the conductive state into an insulating one. This will enable a host of new device designs, like mechanically tunable pin‐junctions and nanomechanical single electron switches. We demonstrate D‐NEMS fabrication and operation from the intrinsic, to the light, and to the heavy regime of doping. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Zusammenfassung Der Bildungsmechanismus von asymmetrischen Zelluloseazetatmembranen, die zur Wasserentsalzung nach dem Prinzip der umgekehrten Osmose geeignet sind, wird untersucht. Die wichtigsten Herstellungsparameter wie Zusammensetzung der Membranlösung, Fällungstemperatur, Anlaßzeit- und Anlaßtemperatur werden diskutiert und interpretiert. Es wird davon ausgegangen, daß die eigentliche Bildung der Membran auf einer Fällungsreaktion aus einem Mehrkomponentensystem mit Mischungslücke beruht und die asymmetrische Struktur auf die Kinetik der Fällung aus einer stark übersättigten Lösung zurückzuführen ist. Hierzu wird das Mischungsdiagramm des Systems Zelluloseazetat-Aceton-Formamid-Wasser aufgenommen. Die Membranen werden nach Literaturvorschrift hergestellt, ihre Transporteigenschaften in Filtrationsversuchen mit einer l-gew.%igen NaCl-Lösung bei 100 atm hydrostatischem Druck bestimmt und ihre Struktur röntgenologisch und elektronenmikroskopisch untersucht.
Die vorliegende Arbeit wurde am Institut für Physikalische Chemie der T. H. Aachen unter der Leitung von Prof.U. Franck angefertigt. Wir danken Herrn Prof.Franck für seine Anregungen und die Förderung dieser Arbeit. Herrn Dr.Spei und Herrn Dr.Burchard danken wir für die Anfertigung der Röntgen-bzw. der Elektronenmikroskopaufnahmen. 相似文献
Summary The formation mechanism of asymmetric cellulose acetate membranes, which are suited for reverse osmosis desalination, is studied. The main parameters in the membrane preparation technique, i.e., the casting solution composition, the wash bath temperature, and the annealing time and temperature, are discussed and rationalized. The actual membrane formation is interpreted as precipitation of the polymer from a multicomponent system which is only partially miscible. The observed asymmetric membrane structure is related to the kinetics of precipitation from supersaturated solutions. The phase diagram of the system cellulose acetate-acetone-formamide-water is presented. Membranes are made according to a recipe given in the literature. Their transport properties are determined in filtration tests with a 1% sodium chloride solution at an applied hydrostatic pressure of 100 atm. X-ray diffraction and electron microscopy are used to study their structures.
Die vorliegende Arbeit wurde am Institut für Physikalische Chemie der T. H. Aachen unter der Leitung von Prof.U. Franck angefertigt. Wir danken Herrn Prof.Franck für seine Anregungen und die Förderung dieser Arbeit. Herrn Dr.Spei und Herrn Dr.Burchard danken wir für die Anfertigung der Röntgen-bzw. der Elektronenmikroskopaufnahmen. 相似文献
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