De Yan

Nanoparticles and 3D sponge-like porous networks of manganese oxides and their microwave absorption properties.

Hydrohausmannite nanoparticles (approximately 10 nm) were prepared by the hydrothermal method at 100 degrees C for 72 h. Subsequent annealing was done in air at 400 degrees C and 800 degrees C for 10 h, Mn(3)O(4) nanoparticles (approximately 25 nm) and 3D Mn(2)O(3) porous networks were obtained, respectively. The products were characterized by XRD, TEM, SAED and FESEM. Time-dependent experiments were carried out to exhibit the formation process of the Mn(2)O(3) networks. Their microwave absorption properties were investigated by mixing the product and paraffin wax with 50 vol%. The Mn(3)O(4) nanoparticles possess excellent microwave absorbing properties with the minimum reflection loss of -27.1 dB at 3.1 GHz. In contrast, the Mn(2)O(3) networks show the weakest absorption of all samples. The absorption becomes weaker with the annealing time increasing at 800 degrees C. The attenuation of microwave can be attributed to dielectric loss and their absorption mechanism was discussed in detail.

Morphology-controlled synthesis, growth mechanism, optical and microwave absorption properties of ZnO nanocombs

ZnO nanocombs and nanorods with different morphologies have been successfully synthesized through a simple metal vapour deposition route at 600-750 degrees C using pure zinc powder or zinc and graphite powders as source materials. The structures and morphologies of the products were characterized in detail by using x-ray diffraction, scanning electron microscopy, transmission electron microscopy and laser Raman spectrometer. The morphologies of the products can be easily controlled by tuning the following four factors: reaction temperature, the distance between the source and the substrates, the kinds of substrates and the kinds of precursors. Possible growth mechanisms for the formation of ZnO nanostructures with different morphologies are discussed. Photoluminescence studies show that there are sharp UV and broad defect-related green emissions for all products. Relative intensity of the UV to defect-related green emissions decreases from ZnO nanorods to nanocombs. Microwave absorption properties of these nanocombs are also investigated. The value of the minimum reflection loss is -12 dB at 11 GHz for the ZnO nanocomb composite with a thickness of 2.5 mm.

Structure and photoluminescence property of Eu-doped SnO2 nanocrystalline powders fabricated by sol–gel calcination process

Eu-doped SnO2 nanocrystalline powders were fabricated by the sol–gel calcination process. The effect of Eu doping concentrations on the structure and photoluminescence properties of Eu-doped SnO2 nanocrystalline powders was investigated. X-ray diffraction patterns, Fourier transformation infrared spectrum, field emission scanning electron microscope and high-resolution transmission electron microscope are employed to investigate the morphology and the structure of Eu-doped SnO2 nanocrystalline powders. The samples display reddish-orange light and red light when excited at indirect and direct excitation, respectively. Meanwhile, PL spectra indicate that the quenching concentrations are different when the excitation wavelength alters. Based on the analysis of the PL spectra, it is believed that Eu3+ ions located at different sites in the SnO2 host are selectively excited.

Structure and Properties of Cobalt Disulfide Nanowire Arrays Fabricated by Electrodeposition

Highly ordered arrays of parallel cobalt disulfide nanowires with a diameter of about 40 nm and a length up to several tens of micrometers were synthesized by two electrical fields in an anodized aluminum oxide film. The cobalt disulfide nanowires have a cubic pyrite structure. In the study of electrochemical properties, it is found that the reaction of cobalt disulfide is an intercalation reaction in the range of 1.6-3.0 V, while a redox reaction in the range of 0.02-1.6 V is probable. The CoS 2 nanowires are ferromagnetic and the easy magnetization direction is along the nanowire axes.

One-pot synthesis of ZnS hollow spheres via a low-temperature, template-free hydrothermal route

ZnS hollow nanospheres with porous shells were successfully fabricated by a simple one-pot template-free hydrothermal route with the assistance of trolamine. The hollow nanospheres with a mean diameter of about 220 nm and the pore size of the porous shell of about 3.2 nm exhibit large BET surface areas of 129.9 m2 g−1. The formation of ZnS hollow nanospheres was definitely driven by the well-known Ostwald ripening process. The morphology of the product could be controlled by adjusting the volume of trolamine in the ternary solution, which could influence the nucleation density and rate of the growing region during the initial stage of reaction. As synthesized, highly defective nanocrystalline ZnS exhibits a very strong defect-related green emission, which may pertain to the emission enhancement of the unique geometrical morphology of ZnS hollow nanospheres with a porous shell. The observed green PL emission of the wurtzite-type ZnS nanomaterials could provide an interesting application in the development of novel luminescent devices.

Synthesis, Characterization, and Microwave Absorption Property of the SnO2Nanowire/Paraffin Composites

In this article, SnO2nanowires (NWs) have been prepared and their microwave absorption properties have been investigated in detail. Complex permittivity and permeability of the SnO2NWs/paraffin composites have been measured in a frequency range of 0.1–18 GHz, and the measured results are compared with that calculated from effective medium theory. The value of maximum reflection loss for the composites with 20 vol.% SnO2NWs is approximately −32.5 dB at 14 GHz with a thickness of 5.0 mm.In this article, SnO2nanowires (NWs) have been prepared and their microwave absorption properties have been investigated in detail. Complex permittivity and permeability of the SnO2NWs/paraffin composites have been measured in a frequency range of 0.1-18 GHz, and the measured results are compared with that calculated from effective medium theory. The value of maximum reflection loss for the composites with 20 vol.% SnO2NWs is approximately -32.5 dB at 14 GHz with a thickness of 5.0 mm.

Characterization of the single crystalline iron sulfide nanowire array synthesis by pulsed electrodeposition

Magnetic material Fe7S8 nanowire arrays have been successfully synthesized by pulsed electrodeposition in porous anodized aluminum oxide template. X-ray diffraction results show that the as-synthesized nanowires are single crystalline and have a highly preferential orientation. Scanning electron microscopy and transmission electron microscopy observations indicate that the ordered Fe7S8 nanowire arrays are uniform with a diameter of 50nm and length up to several tens of micrometers. The temperature variation of the magnetic properties has also been studied.

Morphology-Controlled Syntheses, Growth Mechanisms, and Optical Properties of ZnO Nanocombs/Nanotetrapods

Both ZnO nanocomb and nanotetrapod structures have been synthesized via a simple chemical vapor deposition process in a horizontal tube furnace. The morphology of the products is affected by the distance between the source material and the deposition substrate. The formation of nanocombs has been attributed to the self-catalysis effect of polar surface. The octahedral multiple-twin model is responsible for the formation of tetrapods and tripod-like arms at the end of nanowires. The evolutive process of them has been given out in detail and the results provided valuable models in understanding crystal growth mechanisms in nanometer building-blocks and to further grow net nanostructures. And their photoluminescence properties also have been discussed.

Structure and optical investigation of faceted hexagonal aluminum nitride nanotube arrays

Arrays of single-crystalline aluminum nitride nanotubes (AlNNTs) were successfully synthesized at 780 °C by a facile CVD method without templates or catalysts. Faceted hexagonal AlNNTs with diameters from tens to hundreds of nanometers were observed. 264 nm deep-ultraviolet emission associated with Al vacancies was detected by photoluminescence. Raman characterization indicates that the lattice of the AlNNTs is notably defective, and disorder-activated silent B1 (low) and B1 (high) were detected at 583.0 and 730.0 cm−1 respectively, which were allowed by the breakdown of the translational crystal symmetry. The redshift of E2 (high) Raman modes indicates that biaxial tensile stress exists in the samples.

Low-Temperature Hydrothermal Synthesis and Electrochemical Properties of Birnessit-Type Manganese Dioxide Nanosheets

Birnessite MnO2 nanosheets were synthesized by self-limiting deposition of KMnO4 in a facile low-temperature hydrothermal process. The MnO2 electrode exhibits a high specific capacitance of 169 F g-1 at a current density of 0.1 A g-1, good rate capability with a capacitance of 96 F g-1 even at a high current density of 5 A g-1, as well as excellent cycle stability with capacitance retention of 94% at 1 A g-1 after 1,000 cycles.