Indium oxide (In 2 O 3 ) has been used widely for ultra-sensitive toxic gas (such as NO 2 1 and NH 3 2 ) detectors, transparent conductors, 3 solar cells, and optoelectronic devices. 4 It is anticipated that low-dimensional In 2 O 3 may exhibit some unique properties, including novel optical behaviors. 5,6 Although various types of In 2 O 3 , including 2D (i.e., thin films) 7,8 and 1D (i.e., nanowires) 9-11 structures, have been extensively prepared and investigated, few reports were concentrated on In 2 O 3 quantum dots (0D). 12,13 Synthesis and study of high-quality and monodisperse In 2 O 3 nanocrystals (NCs) as 0D quantum-confined materials are still essential and significant. In this communication, we report our synthesis of single-crystal, quasi-monodisperse In 2 O 3 NCs, as well as the optical observation from these NCs.All of the chemicals were used as received from Aldrich without further purification. In a typical experiment, 0.40 mmol of indium acetate (99.99%), 0.55 mL of oleylamine (70%), and 0.60 mL of oleic acid (90%) were combined with 7.0 mL of hexadecane (>99%) in a three-neck flask equipped with a condenser. The system was vacuumed at room temperature and at 110°C for a while, respectively, to form a clear light-green solution. At 110°C , 1.45 mmol of trimethylamine N-oxide (TMNO, 98%) was subsequently introduced into this vigorously stirred hot mixture under an argon stream. The temperature of this system was then increased to 120°C, where it remained for 1 h under agitation and argon protection. The color of the solution gradually turned lightyellow. The temperature was further increased to 290°C at a rate of 10°C/min for an additional 35 min reflux. The mixture was clear-brown during the first 5 min at 290°C, and subsequently changed to a yellow turbid slurry during the following 25 min, and finally turned clear again. These colloids were cooled to room temperature by quickly removing the heating source, and then isolated by adding a sufficient amount of ethanol and separating with centrifugation. The yielded precipitate was redispersed in hexane followed by centrifugation to remove the very small amount of insoluble aggregates. The morphology and phase structure were evaluated using a transmission electron microscope (TEM) (JEOL 2010) and an X-ray diffractometer (XRD) (Philips X-pert system), respectively. We realized that the ratio of oleic acid and oleylamine was a key factor to form In 2 O 3 NCs. Oleic acid without oleylamine and TMNO would not result in any NCs; if TMNO with oleic acid were introduced into the reaction without oleylamine, only indium hydroxide would form according to the results of our XRD analyses; whereas a high content of oleylamine without oleic acid and TMNO would make the NCs rapidly grow and aggregate. We also realized that the TMNO acts as not only a sole oxidizing agent. In addition, it was determined that the reaction temperature is another important parameter which affects the morphology and size of In 2 O 3 NCs. The lower the reaction temperature, the sma...
Perovskite YFe0.5Cr0.5O3 exhibits magnetization reversal at low applied fields due to the competition between the single ion magnetic anisotropy and the antisymmetric Dzyaloshinsky–Moriya interaction. Below a compensation temperature (Tcomp), a tunable bipolar switching of magnetization is demonstrated by changing the magnitude of the field while keeping it in the same direction. The present compound also displays both normal and inverse magnetocaloric effects above and below 260 K, respectively. These phenomena coexisting in a single magnetic system can be tuned in a predictable manner and have potential applications in electromagnetic devices.
We have studied the growth of thin cerium films on Pt(111) with x-ray photoemission spectroscopy (XPS) and low-energy electron diffraction. No ordered structures were observed for the Ce films immediately after room-temperature deposition. After heat treatment to 770 K, ordered Ce-Pt compounds were formed. For films with initial coverages greater than 3.5 ML, a hexagonal pattern with periodicity nearly twice that of Pt(111) appeared after annealing. For this 1.96X1.96 structure, the periodicity is close to that of the compound CePt&, the XPS data show a stoichiometry of CePt2 23 and the observed Ce valence is 3.07. For films having initial coverages from 0.9 to 1.8 ML, a 1.94X 1.94 pattern with small satellites around the main spots appeared; the Ce valence is 3.11 and the stoichiometry is CePt3. Between 2.1 and 3.2 ML, a 1.96X 1.96 pattern with a superimposed 1.96X 1.96 net rotated by 30' was observed with valence around 3.09. Studies of the take-off angle dependence of the emission indicate that the valence has the same value near the surface as in the bulk. We have also performed CO and Oz adsorption studies and found extremely low sticking coefficients for these molecules on the 1.96X1.96 CePt2 p3 surface. Since these well-characterized single-crystal Ce compound films are highly suitable for photoemission experiments and adsorption studies, we have attempted to formulate empirical rules for predicting which compound species will be generated by similar means.Nd/Cu(111), Yb/Cu(100), Sm/Cu (111) and Eu/Pd (111), where ordered compound(s) were observed and/or identified after annealing. In this work, we attempt to grow single-crystal cerium intermetallics by evaporating clean cerium films onto clean Pt(111) substrates and annealing in situ. We use low-energy electron diff'raction (LEED) to determine structure and XPS (with varying take-off angle) to determine surface and bulk stoichiometry and valence. (The Ce 3d core level is used to measure the valence. ) Our major objective is to learn how to grow clean, well-characterized single-crystal Ce intermetallics for use in future heavy-fermion photoemis-
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