Transparent, Conductive Coatings Produced
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The selected area diffraction patterns (SAD) of the iron nanoparticles revealed the presence of bcc iron and a cubic spinel structure similar to γ-Fe2O3 and Fe3O4. Further examination with x-ray photoelectron spectroscopy showed that the oxidation state of iron was Fe3+, clearly identifying the oxide shell as γ-Fe2O3. With the use of convergent-beam electron diffraction, the scientists obtained single crystal electron diffraction patterns and identified the epitaxial relationship between the iron core and the oxide shell. When analyzing the thickness fringes observed in HRTEM images, the scientists estimated the thickness of the oxide layer as 4.2 nm. The investigators observed a continuous change in the orientation of adjacent iron {100} and {110} facets, and bending of the {111} oxide fringes. As a result, they estimated a compressive strain of 3% due to the mismatch on the {100} facets. They suggest that this compression reduced the oxide lattice spacing in the iron surface and therefore improved the passive characteristics of the oxide layer. The analysis of the images obtained also showed that γ-Fe2O3 layers grew epitaxially on the iron surface. The researchers quantified the growth rate by using the Caberra-Mott theory of oxidation of metal. They report that the rate of oxidation is initially very fast but decreases considerably after the oxide shell is 3 nm thick, at room temperature conditions. For a 4-nm layer, the growth temperature is about 420 K, which the researchers considered consistent with their experimental estimations. Following the assumptions taken in the application of this theory, the researchers suggest that the small size of the particles contribute to the growth of an epitaxial layer. SIARI S. SOSA
Silicon Analogue of Spiropentadiene is Isolated Disilenes, Si=Si double bonded compounds, are commonly hard to isolate because they are unstable. As reported in the October 20 issue of Science, a group of researchers at Tohoku University, Japan,
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has synthesized and isolated a stable disilene, tetrakis[tri(tert-butyldimethylsilyl) silyl]spiropentasiladiene (compound 2), which is a silicon analogue of spiropentadiene (compound 1). As an original Si cluster (Si21), compound 2 has very attractive features, according to the researchers. Electrons are delocalized over the whole cluster through spiroconjugation, which is very sensitive to the twisting of substituents at Si=Si bonds. Therefore, the spiroconjugation can be tuned by the substituents. The researchers projected these features can be used for optoelectronic devices. In their research, chemistry professor Mitsuo Kira and his colleagues established that the reaction of [tris(tert-butyldimethylsilyl)silyl]dibromochlorosilane with potassium graphite at −78°C gives two products, one of which is compound 2. Crystallization from hexane gives compound 2, an oxygen- and moisturesensitive dark red crystal, in 3.5% yield. Contrary to compound 1, which decomposes at −100°C, spiropentasiladiene does not evolve to decomposition/degradation befor
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