Formation of PbSe Nanocrystals: A Growth toward Nanocubes

In this paper we report an electron microscopic observation of crystal shape development when PbSe nanocrystals were synthesized using a dynamic injection technique at different temperatures in the presence of oleic acid. A two-step evolution mechanism was proposed, indicating that the shape evolution of PbSe nanocrystals is dependent on the growth time, whereas the crystalline size can be tuned by varying the growth temperature under the studied conditions. It also implies that a higher growth rate in the 〈111 〉 direction compared to that in the 〈100 〉 direction results in the formation of nanocubes. Lead chalcogenides are inspiring semiconductors with a narrow band gap. Size- and shape-controlled nanocrystals (NCs) of this family have demonstrated unique properties1-5 and can potentially be employed in numerous applications, such as near-IR luminescence6 and thermoelectric devices.7,8 To produce monodisperse NCs of lead chalcogenides with high quality and tunable size and shape, it is significant to understand their NC formation process. Since the growth of PbS9,10 and PbTe NCs11 has been investigated previously, similar exploration on PbS

Synthesis and magnetic properties of CoPt–poly(methylmethacrylate) nanostructured composite material

We have prepared nanometer-sized CoPt particles dispersed in a poly~methyl methacrylate~PMMA!matrix, as a novel nanostructured magnetic plastic, through a soft chemical processing route. In this work, CoPt nanoparticles were successfully synthesized from a solution phase reduction system in the presence of capping ligands and stabilizing agents at high temperature. The CoPt nanoparticles were annealed at 400 °C for 3 h, and were subsequently re-dispersed inmethylmethacrylate~monomer! . The polymerization was induced by a UV source and the hardness of final product was adjusted by varying the amount of monomeric cross-link agent. Annealed bare CoPt nanoparticles as a ‘‘core’’ material and CoPt–PMMA composite material were characterized by using energy dispersive spectroscopy, transmission electron microscopy, and x-ray diffraction, indicating that we are able to prepare CoPt nanoparticles with 10 nm in diameter ~after annealing by employing this high temperature colloidal processing method. Magnetic investigation of this CoPt–PMMA material indicates an intrinsic coercivity of 300 Oe at 300 K and 1665 Oe at 5 K

Synthesis and magnetic properties of CoPt–poly(methylmethacrylate) nanostructured composite material

We have prepared nanometer-sized CoPt particles dispersed in a poly~methyl methacrylate~PMMA!matrix, as a novel nanostructured magnetic plastic, through a soft chemical processing route. In this work, CoPt nanoparticles were successfully synthesized from a solution phase reduction system in the presence of capping ligands and stabilizing agents at high temperature. The CoPt nanoparticles were annealed at 400 °C for 3 h, and were subsequently re-dispersed inmethylmethacrylate~monomer! . The polymerization was induced by a UV source and the hardness of final product was adjusted by varying the amount of monomeric cross-link agent. Annealed bare CoPt nanoparticles as a ‘‘core’’ material and CoPt–PMMA composite material were characterized by using energy dispersive spectroscopy, transmission electron microscopy, and x-ray diffraction, indicating that we are able to prepare CoPt nanoparticles with 10 nm in diameter ~after annealing by employing this high temperature colloidal processing method. Magnetic investigation of this CoPt–PMMA material indicates an intrinsic coercivity of 300 Oe at 300 K and 1665 Oe at 5 K

Comparative study on phase development of lead titanate powders

Abstract Ž . Ultrafine lead titanate PbTiO powders in tetragonal form have been successfully prepared via two processing routes, 3 Ž . Ž . namely, conventional coprecipitation CPC and microemulsion-refined coprecipitation MCP . The formation process of lead titanate from the resulting precursors was monitored using techniques such as thermal analyses, FTIR spectroscopy, Raman scattering spectroscopy and X-ray diffraction for the phase identification. It was found that the microemulsion-refined processing route led to a lower formation temperature for lead titanate than that observed in the conventional coprecipitation route, and there is no detectable pyrochlore phase during the formation of PbTiO in the former case. The 3 two PbTiO powders have also been comparatively studied in particle morphology and specific surface areas. It indicates 3 that the microemulsion-refined coprecipitation is the technique that results in the formation of the finer powder of lead titanate than the conventional coprecipitation does in the present work.

The Roles of Buyang Huanwu Decoction in Anti-Inflammation, Antioxidation and Regulation of Lipid Metabolism in Rats with Myocardial Ischemia

Buyang Huanwu Decoction (BYHWD) is a well-known Chinese medicine formula. Recent studies have reported that BYHWD can be used to treat ischemic heart disease. This study investigated the potential mechanism underlying the roles of BYHWD in alleviating the myocardial ischemia induced by isoproterenol (ISO) in rats. Different doses of BYHWD (25.68, 12.84 and 6.42 g kg−1) were lavaged to rats, respectively. Then the expression of the cluster of differentiation 40 (CD40) in the mononuclear cells was measured using flow cytometry, and the expressions of CD40 and its ligand (CD40L) in myocardial tissues were determined by western blotting. The serum biochemical values of superoxide dismutase (SOD) activity, the malondialdehyde (MDA) level and the free fatty acid (FFA) content were measured. The results showed that the SOD activities of BYHWD groups were significantly higher than that of the ISO group, while the MDA levels and FFA contents of all BYHWD groups were lower than that of the ISO group. BYHWD could decrease the expression of CD40 in the mononuclear cells and the CD40 and CD40L expressions in myocardial tissues. Our data suggest that the roles of BYHWD are not only related to its antioxidative action and regulation of lipid metabolisms, but also to the inhibition of inflammatory pathway by the decreased CD40 and CD40L expressions in rats with myocardial ischemia

Pt 3 Co Concave Nanocubes: Synthesis, Formation Understanding, and Enhanced Catalytic Activity toward Hydrogenation of Styrene

We report a facile synthesis route to prepare high‐quality Pt 3 Co nanocubes with a concave structure, and further demonstrate that these concave Pt 3 Co nanocubes are terminated with high‐index crystal facets. The success of this preparation is highly dependent on an appropriate nucleation process with a successively anisotropic overgrowth and a preservation of the resultant high‐index planes by control binding of oleyl‐amine/oleic acid with a fine‐tuned composition. Using a hydrogenation of styrene as a model reaction, these Pt 3 Co concave nanocubes as a new class of nanocatalysts with more open structure and active atomic sites located on their high‐index crystallographic planes exhibit an enhanced catalytic activity in comparison with low‐indexed surface terminated Pt 3 Co nanocubes in similar size. Anisotropic overgrowth : Pt 3 Co concave nanocubes bounded by high‐index facets were prepared with a facile wet‐chemical method. The formation process for such concave nanostructures was systematically studied, and a plausible mechanism was proposed. These nanocrystals can be used as advanced nanocatalysts, showing high activity and reusability toward hydrogenation of styrene (see figure).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102689/1/chem_201301724_sm_miscellaneous_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/102689/2/1753_ftp.pd

Self-assembly of FePt nanoparticles into nanorings

The application of nanoparticles as quantum dots in nanoelectronics demands their arrangement in ordered arrays. Shape controlled self-assembly is a challenge due to the difficulties of obtaining proper self-assembling parameters, such as solvent concentration, organic ligands, and nanoparticle size. In this article, hard magnetic FePt nanoparticles were synthesized using a combination approach of reduction and thermal decomposition. The nanoparticles are about 4.5 nm and appeared as truncated octahedral enclosed by the {100} and {111} crystal facets of fcc structure. The nanoparticles are of hexagonal close packing and orient randomly in the self-assembly nanoarrays. By diluting the solution for large-area self-assembly, monolayer, submonolayer, and multilayer nanorings of FePt nanoparticles were formed. The nanoring formation is determined by hydrodynamics, surface effects, and interaction between the FePt nanoparticles and substrates

Nanocontact Disorder in Nanoelectronics for Modulation of Light and Gas Sensitivities

To fabricate reliable nanoelectronics, whether by top-down or bottom-up processes, it is necessary to study the electrical properties of nanocontacts. The effect of nanocontact disorder on device properties has been discussed but not quantitatively studied. Here, by carefully analyzing the temperature dependence of device electrical characteristics and by inspecting them with a microscope, we investigated the Schottky contact and Mott\u27s variable-range-hopping resistances connected in parallel in the nanocontact. To interpret these parallel resistances, we proposed a model of Ti/TiOx in the interface between the metal electrodes and nanowires. The hopping resistance as well as the nanocontact disorder dominated the total device resistance for high-resistance devices, especially at low temperatures. Furthermore, we introduced nanocontact disorder to modulate the light and gas responsivities of the device; unexpectedly, it multiplied the sensitivities compared with the intrinsic sensitivity of the nanowires. Our results improve the collective understanding of electrical contacts to low-dimensional semiconductor devices and will aid performance optimization in future nanoelectronics

High-performance non-Fermi-liquid metallic thermoelectric materials

Searching for high-performance thermoelectric (TE) materials in the paradigm of narrow-bandgap semiconductors has lasted for nearly 70 years and is obviously hampered by a bottleneck of research now. Here we report on the discovery of a few metallic compounds, TiFexCu2x-1Sb and TiFe1.33Sb, showing the thermopower exceeding many TE semiconductors and the dimensionless figure of merits comparable with the state-of-the-art TE materials. A quasi-linear temperature (T) dependence of electrical resistivity in 2 K - 700 K and the logarithmic T-dependent electronic specific heat at low temperature are also observed to coexist with the high thermopower, highlighting the strong intercoupling of the non-Fermi-liquid (NFL) quantum critical behavior of electrons with TE transports. Electronic structure analysis reveals the existence of fluctuating Fe-eg-related local magnetic moments, Fe-Fe antiferromagnetic (AFM) interaction at the nearest 4c-4d sites, and two-fold degenerate eg orbitals antiferromagnetically coupled with the dual-type itinerant electrons close to the Fermi level, all of which infer to a competition between the AFM ordering and Kondo-like spin compensation as well as a parallel two-channel Kondo effect. These effects are both strongly meditated by the structural disorder due to the random filling of Fe/Cu at the equivalent 4c/4d sites of the Heusler crystal lattice. The magnetic susceptibility deviates from ideal antiferromagnetism but can be fitted well by x(T) = 1/({\theta} + BT{\alpha}), seemingly being consistent with the quantum critical scenario of strong local correlation as discussed before. Our work not only breaks the dilemma that the promising TE materials should be heavily-doped semiconductors, but also demonstrates the correlation among high TE performance, NFL quantum criticality, and magnetic fluctuation, which opens up new directions for future research.Comment: 19 pages with 6 figure

Photoinduced electrooptics in the In2O3 nanocrystals incorporated into PMMA matrixes

We have observed an appearance of clear morphological structure in composites containing In2O3 nanocrystals (NCs) incorporated into polymethyl methacrylite (PMMA) matrices under optical treatment by a polarized femtosecond laser. The initial photoinduced treatment was carried out using a Ti:sapphire femtosecond laser emitting 140 fs p-polarized light at a maximum spectral wavelength 775 nm with pulse repetition 1 kHz. It was found that the average morphological radius is varied maximally only during illumination at liquid helium temperature (T = 4.2 K). The morphological average mean radius is strictly dependent on the sizes of incorporated In2O3 NCs. Afterwards we measured the linear electrooptic effect at cw He–Ne laser wavelength 633 nm during simultaneous treatment by 1060 and 530 nm coherent beams of a Nd–YAG picosecond laser. We have established that a decrease of the average morphological mean radius favours an increase of the optically poled linear electrooptic coefficient. The diameters of In2O3 NCs were evaluated using transmission electron microscopy (TEM) and light-scattering techniques, whereas the NC sizes and morphological average mean radius of formed nanocomposites were estimated by atomic force microscopy (AFM). A relationship between the diameter of the NC, composite morphological mean average radius and effective linear electrooptic coefficient was established.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58122/2/cm7_1_016204.pd