163 research outputs found
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
ΠΠΊΡΠΏΠ΅ΡΠΈΠΌΠ΅Π½ΡΠ°Π»ΡΠ½Π°Ρ Π°Π²ΡΠΎΠΌΠ°ΡΠΈΠ·ΠΈΡΠΎΠ²Π°Π½Π½Π°Ρ ΡΠΈΡΡΠ΅ΠΌΠ° Π³ΠΈΠ΄ΡΠΎΠΌΠ΅ΡΠ΅ΠΎΡΠΎΠ»ΠΎΠ³ΠΈΡΠ΅ΡΠΊΠΈΡ ΠΈΠ·ΠΌΠ΅ΡΠ΅Π½ΠΈΠΉ ΠΈ ΠΎΠ±ΡΠ°Π±ΠΎΡΠΊΠΈ Π΄Π°Π½Π½ΡΡ Π΄Π»Ρ Π±Π΅ΡΠ΅Π³ΠΎΠ²ΡΡ ΡΡΠ°Π½ΡΠΈΠΉ
Π Π°Π·ΡΠ°Π±ΠΎΡΠ°Π½ Π΄Π΅ΠΉΡΡΠ²ΡΡΡΠΈΠΉ ΠΌΠ°ΠΊΠ΅Ρ Π°Π²ΡΠΎΠΌΠ°ΡΠΈΠ·ΠΈΡΠΎΠ²Π°Π½Π½ΠΎΠΉ ΡΠΈΡΡΠ΅ΠΌΡ ΠΏΡΠΈΠ±ΡΠ΅ΠΆΠ½ΡΡ
Π³ΠΈΠ΄ΡΠΎΠΌΠ΅ΡΠ΅ΠΎΡΠΎΠ»ΠΎΠ³ΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΈΠ·ΠΌΠ΅ΡΠ΅Π½ΠΈΠΉ Π΄Π»Ρ ΠΌΠΎΡΡΠΊΠΎΠΉ ΡΠ΅ΡΠΈ ΠΠΎΡΠ³ΠΈΠ΄ΡΠΎΠΌΠ΅ΡΠ° Π£ΠΊΡΠ°ΠΈΠ½Ρ. Π ΡΠ΅ΡΠ΅Π½ΠΈΠ΅ 2000 β 2004 Π³Π³. ΠΏΡΠΎΠ²Π΅Π΄Π΅Π½Ρ ΠΈΡΠΏΡΡΠ°Π½ΠΈΡ ΠΈ ΠΎΠΏΡΡΠ½Π°Ρ ΡΠΊΡΠΏΠ»ΡΠ°ΡΠ°ΡΠΈΡ ΠΌΠ΅ΡΠ΅ΠΎΡΠΎΠ»ΠΎΠ³ΠΈΡΠ΅ΡΠΊΠΈΡ
(Π²Π΅ΡΠ΅Ρ, ΡΠ΅ΠΌΠΏΠ΅ΡΠ°ΡΡΡΠ° Π²ΠΎΠ·Π΄ΡΡ
Π°, Π°ΡΠΌΠΎΡΡΠ΅ΡΠ½ΠΎΠ΅ Π΄Π°Π²Π»Π΅Π½ΠΈΠ΅) ΠΈ Π³ΠΈΠ΄ΡΠΎΠ»ΠΎΠ³ΠΈΡΠ΅ΡΠΊΠΈΡ
(ΡΡΠΎΠ²Π΅Π½Ρ, ΡΠ΅ΠΌΠΏΠ΅ΡΠ°ΡΡΡΠ° ΠΈ ΡΠΎΠ»Π΅Π½ΠΎΡΡΡ Π²ΠΎΠ΄Ρ) ΠΈΠ·ΠΌΠ΅ΡΠΈΡΠ΅Π»ΡΠ½ΡΡ
Π±Π»ΠΎΠΊΠΎΠ², ΡΡΡΠ°Π½ΠΎΠ²Π»Π΅Π½Π½ΡΡ
Π² ΡΡΠ°Π½Π΄Π°ΡΡΠ½ΡΡ
ΡΡΠ»ΠΎΠ²ΠΈΡΡ
ΠΌΠΎΡΡΠΊΠΎΠΉ ΡΡΠ°Π½ΡΠΈΠΈ Β«Π‘Π΅Π²Π°ΡΡΠΎΠΏΠΎΠ»ΡΒ». ΠΡΠΈΠ²ΠΎΠ΄ΡΡΡΡ Π΄Π°Π½Π½ΡΠ΅ ΠΎ ΡΡΡΡΠΊΡΡΡΠ΅, ΠΎΡΠ½ΠΎΠ²Π½ΡΡ
ΡΠ΅Ρ
Π½ΠΎΠ»ΠΎΠ³ΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΏΡΠΈΠ½ΡΠΈΠΏΠ°Ρ
Π°Π²ΡΠΎΠΌΠ°ΡΠΈΠ·ΠΈΡΠΎΠ²Π°Π½Π½ΠΎΠΉ ΡΠΈΡΡΠ΅ΠΌΡ ΠΈ Π½Π΅ΠΊΠΎΡΠΎΡΡΠ΅ ΡΠ΅Π·ΡΠ»ΡΡΠ°ΡΡ ΠΊΠ²Π°Π·ΠΈΠ½Π΅ΠΏΡΠ΅ΡΡΠ²Π½ΡΡ
ΠΌΠ΅ΡΠ΅ΠΎΡΠΎΠ»ΠΎΠ³ΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΈ Π³ΠΈΠ΄ΡΠΎΠ»ΠΎΠ³ΠΈΡΠ΅ΡΠΊΠΈΡ
ΠΈΠ·ΠΌΠ΅ΡΠ΅Π½ΠΈΠΉ.Developed is functioning model of automated system of coastal hydrometeorological measurements for the marine net of State Hydrometeorological Institution of Ukraine. In 2000 β 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 βSevastopolβ were held. Data on structure, general technological principles of the automated system and some results of quazi-continuous meteorological and hydrological measurements is presented
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