[Show abstract][Hide abstract] ABSTRACT: In this work, we demonstrate a new strategy to create WZ-GaN/3C-SiC heterostructure nanowires, which feature controllable morphologies. The latter is realized by exploiting the stacking faults in 3C-SiC as preferential nucleation sites for the growth of WZ-GaN. Initially, cubic SiC nanowires with an average diameter of ~100 nm, which display periodic stacking fault sections, are synthesized in a CVD process to serve as the core of the heterostructure. Subsequently, hexagonal wurtzite-type GaN shells with different shapes are grown on the surface of 3C-SiC wire core. In this context it is possible to obtain two types of WZ-GaN/3C-SiC heterostructure nanowires by means of carefully controlling the corresponding CVD reactions. Here, the stacking faults, initially formed in 3C-SiC nanowires, play a key role in guiding the epitaxial growth of WZ-GaN as they represent surface areas of the 3C-SiC nanowires that feature a higher surface energy. A dedicated structural analysis of the interfacial region by means of high-resolution transmission electron microscopy (HRTEM) revealed that the disordering of the atom arrangements in the SiC defect area promote a lattice-matching with respect to the WZ-GaN phase, which results in a preferential nucleation. All WZ-GaN crystal domains exhibit an epitaxial growth on 3C-SiC featuring a crystallographic relationship of [1-210]WZ-GaN //[01-1]3C-SiC, (0001)WZ-GaN//(111)3C-SiC and dWZ-GaN(0001)≈2d3C-SiC(111). The approach to utilize structural defects of a nanowire core to induce a preferential nucleation of foreign shells generally opens up a number of opportunities for the epitaxial growth of a wide range of semiconductor nanostructures which are otherwise impossible to acquire. Consequently, this concept possesses tremendous potential for the applications of semiconductor heterostructures in various fields such as optics, electrics, electronics and photocatalysis for energy harvesting and environment processing.
[Show abstract][Hide abstract] ABSTRACT: Open-celled silicon carbide (SiC) foam has been proven of a promising underwater acoustic absorption
material. However, further improvement of its sound absorption capacity especially at low frequency is
restricted by the acoustic impedance mismatch between the foam material and the water surrounding it.
How to tailor the existing SiC foam in order to achieve an optimized impedance match is a key issue. In this
work, the underwater acoustic absorption performance of open-celled SiC foam is studied by both analytical and experimental methods. First, based on Zwikker–Kosten’s theory, the modified Johnson–Allard
(J–A) model is proposed to analytically predict the absorption performance of liquid-saturated SiC foam.
Then three approaches including (i) backing the test samples by a 30-mm-thick air cavity, (ii) enclosing a
certain amount of water and (iii) filling the samples with silicon oil are proposed to improve the underwater sound absorption performance of SiC foam. The underwater acoustic absorbency of the silicon
oil filled SiC foam is significantly improved, especially in the low frequency band. A sound absorption
coefficient near unity is achieved by this manner over a significant portion of the investigated frequency
range, eg. 750–4000 Hz. The foam partially filled with water also shows enhanced sound absorbency at
low frequency, but the foams backed by air gap and saturated fully by water display degraded sound
Colloids and Surfaces A Physicochemical and Engineering Aspects 10/2015; 482:568-574. DOI:10.1016/j.colsurfa.2015.06.046 · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Highly porous activated carbon prepared from sunflower seed hull (SSH), an abundant agriculture byproduct, was demonstrated as low-cost and efficient adsorbent for Cr(VI) removal. The porous carbon can be micropore or mesopore dominant depending on the impregnation ratio of the ZnCl2 activating reagent and SSH. The micropore dominant samples exhibited superior Cr(VI) adsorption capacity as compared to the samples with higher percentage of mesopore volume. It was interesting to note that the optimum pH for Cr(VI) removal in higher concentration solutions was lower as more H+ ions were required to produce an appropriate amount of the easily absorbable HCrO4− ions. However, hexavalent chromium was reduced to trivalent chromium in solution at pH ≤ 2.0, which reduced the overall removal rate of the total chromium. The adsorption behaviors of Cr(VI) on SSH activated carbons can be well described by Langmuir isotherm model and pseudo-second-order kinetic model, implying that the adsorption occurred through monolayer formation on the surface of adsorbents via chemical interactions.
Journal of Environmental Chemical Engineering 03/2015; 3(2). DOI:10.1016/j.jece.2015.02.025
[Show abstract][Hide abstract] ABSTRACT: We report transport studies on (Bi,Sb)2Te3 topological insulator thin films
with tunable electronic band structure. We find a doping and temperature regime
in which the Hall coefficient is negative indicative of electron-type carriers,
whereas the Seebeck coefficient is positive indicative of hole-type carriers.
This sign anomaly is due to the distinct transport behaviors of the bulk and
surface states: the surface Dirac fermions dominate magnetoelectric transport
while the thermoelectric effect is mainly determined by the bulk states. These
findings may inspire new ideas for designing topological insulator-based high
efficiency thermoelectric devices.
Physical Review B 02/2015; 91(7). DOI:10.1103/PhysRevB.91.075431 · 3.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Silicon carbide (SiC) foam prepared by polymer pyrolysis combined with molten silicon reactive infiltration (MRI) process was experimentally studied for the first time regarding its underwater acoustic absorption coefficient (α) mainly over low and middle frequency range (200–4000 Hz). The relationship between α and the pore structure of SiC foam including pore size (d) and foam thickness (t) was studied. The results indicated that α increased with the decrease of pore size from 3 to 1 mm in most frequencies measured. α also increased with sample thickness at both low and medium frequency, but in general it was more sensitive to pore size than to sample thickness. The existing models built for air-filled porous material under atmospheric circumstance were not valid to describe the underwater acoustic absorption behavior of SiC foam materials.
Colloids and Surfaces A Physicochemical and Engineering Aspects 02/2015; 471. DOI:10.1016/j.colsurfa.2015.01.091 · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The objective of this study was to investigate the possibility of silicon carbide (SiC) foam as an alternative material for porous hydroxyapatite (HA). The characters of two materials were evaluated and compared by a series of in vitro biological tests. The result of the morphology showed that SiC foam provided beneficial structure for cell migration. On the level of primary-osteoblasts proliferation measured by MTT assay and cell cycle analysis showed that the proliferation rate increased in the early stage on HA but in the advanced stage on SiC foam. There was no significant difference between the two materials on the level of cell differentiation detected by alkaline phosphatase (ALP) assay and real-time PCR. All of the results indicated that SiC foam was comparable to HA in terms of biocompatibility and bone conductivity.
Journal of Hard Tissue Biology 01/2015; 24(1):37-42. DOI:10.2485/jhtb.24.37 · 0.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: It is crucial for the studies of the transport properties and quantum effects related to Dirac surface states of three-dimensional topological insulators (3D TIs) to be able to simultaneously tune the chemical potentials of both top and bottom surfaces of a 3D TI thin film. We have realized this in molecular beam epitaxy-grown thin films of 3D TIs, as well as magnetic 3D TIs, by fabricating dual-gate structures on them. The films could be tuned between n-type and p-type by each gate alone. Combined application of two gates can reduce the carrier density of a TI film to a much lower level than with only one of them and enhance the film resistance by 10000 %, implying that Fermi level is tuned very close to the Dirac points of both top and bottom surface states without crossing any bulk band. The result promises applications of 3D TIs in field effect devices.
[Show abstract][Hide abstract] ABSTRACT: The interplay between topological protection and broken time reversal symmetry in topological insulators may lead to highly unconventional magnetoresistance behaviour that can find unique applications in magnetic sensing and data storage. However, the magnetoresistance of topological insulators with spontaneously broken time reversal symmetry is still poorly understood. In this work, we investigate the transport properties of a ferromagnetic topological insulator thin film fabricated into a field effect transistor device. We observe a complex evolution of gate-tuned magnetoresistance, which is positive when the Fermi level lies close to the Dirac point but becomes negative at higher energies. This trend is opposite to that expected from the Berry phase picture, but is intimately correlated with the gate-tuned magnetic order. The underlying physics is the competition between the topology-induced weak antilocalization and magnetism-induced negative magnetoresistance. The simultaneous electrical control of magnetic order and magnetoresistance facilitates future topological insulator based spintronic devices.
[Show abstract][Hide abstract] ABSTRACT: ZnO–Al2O3–B2O3–SiO2 (ZABS) glass powder was used as interlayer to join alumina ceramics. The effect of joining temperature on the microstructure and strength of joints was investigated. The results showed that the ZABS glass can react with alumina substrate to form a layer of ZnAl2O4 at Al2O3/glass interface. Bending test exhibited that low joining temperature (1150 °C) led to low joint strength due to the formation of pores in the interlayer, originated by high viscosity of the glass. High joining temperature (1250 °C) also resulted in low joint strength, because of large CTE (coefficient of thermal expansion) mismatch between amorphous interlayer and alumina substrate. Therefore, only when the joining temperature was appropriate (1200 °C), defect-free interface and high joint strength can be obtained. The optimum joint strength reached 285 MPa, which was the same as the base material strength.
Journal of Materials Science and Technology -Shenyang- 09/2014; 30(9). DOI:10.1016/j.jmst.2014.01.011 · 1.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Alumina, metalized with Ti by magnetron sputtering, has been successfully bonded to a Kovar alloy using Ag-5 wt% Pd filler. The effects of Ti content on the interfacial microstructure and mechanical properties were investigated. The results showed that a reaction layer was formed at the alumina/filler interface. Microanalysis indentified the reaction products to be titanium oxide and Pd Ti compounds. The thickness of the reaction layer and the residual filler layer played determinable roles on the joint strength. The maximum four-point flexural strength of the brazed joints at room temperature reached as high as 177.3 MPa when the thickness of Ti layer was 3 mu m.
Ceramics International 05/2014; 40(4):5699-5705. DOI:10.1016/j.ceramint.2013.11.008 · 2.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: AuCl3 loaded structured catalysts were prepared on SiC foam supported with pre-coated activated carbon layers. The catalytic properties of the structured catalysts towards hydrochlorination of acetylene were tested in a fixed-bed reactor with the AuCl3 loaded on activated carbon pellets as a reference. For isopyknic catalysts, the structured catalyst with only one fifth of the Au amount as that was used on the reference catalyst exhibited even a little higher acetylene conversion and much better stability than the latter no matter what the gas hourly space velocities of acetylene were used. The results indicated that the more homogeneous distribution of AuCl3 particles and better heat transfer along the fixed-bed reactor originated from the low pressure drop and high thermal conductivity of the SiC foam supported structured catalysts might be able to account for their improved efficiency and stability. It is believed that these novel structured C/Au catalysts can be potentially applied in VCM industrialization in view of their greatly reduced cost and much prolonged life.
Journal of Materials Science and Technology -Shenyang- 05/2014; 30(5). DOI:10.1016/j.jmst.2014.01.013 · 1.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Heterostructure based interface engineering has been proved an effective
method for finding new superconducting systems and raising superconductivity
transition temperature (TC). In previous work on one unit-cell (UC) thick FeSe
films on SrTiO3 (STO) substrate, a superconducting-like energy gap as large as
20 meV, was revealed by in situ scanning tunneling microscopy/spectroscopy
(STM/STS). Angle resolved photoemission spectroscopy (ARPES) further revealed a
nearly isotropic gap of above 15 meV, which closes at a temperature of ~ 65 K.
If this transition is indeed the superconducting transition, then the 1-UC FeSe
represents the thinnest high TC superconductor discovered so far. However, up
to date direct transport measurement of the 1-UC FeSe films has not been
reported, mainly because growth of large scale 1-UC FeSe films is challenging
and the 1-UC FeSe films are too thin to survive in atmosphere. In this work, we
successfully prepared 1-UC FeSe films on insulating STO substrates with
non-superconducting FeTe protection layers. By direct transport and magnetic
measurements, we provide definitive evidence for high temperature
superconductivity in the 1-UC FeSe films with an onset TC above 40 K and a
extremely large critical current density JC ~ 1.7*106 A/cm2 at 2 K. Our work
may pave the way to enhancing and tailoring superconductivity by interface
Chinese Physics Letters 11/2013; 31(1). DOI:10.1088/0256-307X/31/1/017401 · 0.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Highly accessible porous ZSM-5 coating with high loading and high adherence was successfully grown on SIC foam support using a two-step coating and steam-assisted crystallization process. The zeolite precursor gel pre-coated on the SiC foam surface and existed in the upper mixed coating layer functioned as a binder to firmly bond the SiC support and the pre-coated zeolite crystals with the formation of a dense ZSM-5 transition layer. The high porosity was achieved from the pre-coated zeolite crystals. The ZSM-5/SiC foam composite catalyst prepared by the proposed method showed higher propylene selectivity and propylene to ethylene (P/E) ratio, lower C-1-C-4 saturated hydrocarbons and aromatics and as well as higher stability in comparison to that prepared by conventional in situ hydrothermal process in methanol to propylene reaction. (c) 2013 Elsevier Inc. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: We report the discovery of a new diluted magnetic semiconductor, Li(Zn,Mn)P,
in which charge and spin are introduced independently via lithium
off-stoichiometry and the isovalent substitution of Mn2+ for Zn2+,
respectively. Isostructural to (Ga,Mn)As, Li(Zn,Mn)P was found to be a p-type
ferromagnetic semiconductor with excess Lithium providing charge doping. First
principles calculations indicate that excess Li is favored to partially occupy
the Zn site, leading to hole doping. Ferromagnetism is mediated in
semiconducting samples of relative low mobile carriers with a small coercive
force, indicating an easy spin flip.
Physical Review B 08/2013; 88(8). DOI:10.1103/PhysRevB.88.081203 · 3.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Different semiconductive SiC foam supports were prepared by varying the sintering temperature and atmosphere, and with or without alkaline solution treatment and high temperature oxidation following a macromolecule pyrogenation combined with reaction bonding method. Nano-TiO2 particles were immobilized onto these SiC foam supports by a composite sol–gel method. The phase, surface morphology, the type of conduction and the photocatalytic activity of the TiO2–SiC composite photocatalysts were studied. The TiO2 coated on p-type Si-free SiC support showed the highest photocatalytic efficiency in degradation of 4-aminobenzenesulfonic acid (4-ABS) in aqueous solution as compared to that coated on n-type SiC support and p-type SiC supports with residual Si or SiO2 on the surface. The result showed that the TiO2 coatings immobilized on p-type semiconductive SiC foam supports exhibited obviously higher photocatalytic activity in comparison to that coated on n-type SiC foam support. The p–n heterojunctions formed between the p-type SiC supports and n-type TiO2 coatings might be able to account for the better charge separation and transfer as well as the photocatalytic activity of the TiO2–SiC composite photocatalyst.
Journal of Materials Science and Technology -Shenyang- 08/2013; 19(11):1074–1078. DOI:10.1016/j.jmst.2013.08.021 · 1.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The novel SiC foam valve tray was made of thin slices of SiC foam material with a high specific surface area. Hydrodynamic performances of the novel SiC foam valve tray were studied with air-water system at atmospheric pressure. These performance parameters included pressure drop, entrainment, weeping and clear liquid height. The mass transfer efficiency of the SiC foam valve tray was measured in laboratory plate column. Compared with the F1 float valve tray, the dry pressure drop was decreased about 25%, the entrainment rate was about 70% lower at high gas load, the weeping was much better, and the mass transfer efficiency was far higher. Thus, the overall performance of the novel SiC foam valve tray was better than that of F1 float valve tray.
Chinese Journal of Chemical Engineering 08/2013; 21(8):821–826. DOI:10.1016/S1004-9541(13)60552-2 · 1.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Structured TiO2–SiC photocatalysts were prepared by coating TiO2 nanoparticles on Si incorporated SiC foam supports, and their photocatalytic activities toward degradation of organic contaminant under UV light irradiation were evaluated by taking 4-aminobenzenesulfonic acid (4-ABS) as a model contaminant. In comparison to SiC foam support and TiO2 nanoparticles the TiO2–SiC photocatalysts exhibited significantly enhanced photocatalytic performance. The effects of coating thickness of TiO2 and pore sizes of the SiC foam supports on the photocatalytic activities were studied. A synergistic photocatalytic effect between the p-type semiconductive SiC foam supports and the n-type TiO2 coating was proposed to account for this enhanced photocatalytic properties.
[Show abstract][Hide abstract] ABSTRACT: Foam party: A new method is reported for the immobilization of carbon nanotubes (CNTs) onto silicon carbide foam to afford a CNT/SiC monolith catalyst for sustainable chemistry applications. The as-synthesized monolith displayed good stability and high catalytic performance in the oxidative dehydrogenation (ODH) of 1-butene into butadiene.
[Show abstract][Hide abstract] ABSTRACT: A CaO–Al2O3–SiO2 (CAS)‐based glass interlayer was developed for joining of porous alumina membrane tubes with dense alumina in this work. The results indicated that the interfacial microstructure of the joint was highly sensitive to the quench rate from the joining temperature, which rendered crystallization of CaTiSiO5 at a fast quench rate but CaAl2Si2O8 at a slow quench rate due to the interfacial reaction between the CAS glass interlayer and the substrate. An extra crystallization treatment during quench, i.e., dwelling at 800°C–900°C for 2 h, produced a multiphase interlayer consisting of LiAlSi2O6, CaTiSiO5, and CaAl2Si2O8. All joints were evaluated by the thermal shock test. The results showed that the LiAlSi2O6‐containing joint interlayer had much lower thermal shock resistance than those without LiAlSi2O6.
Journal of the American Ceramic Society 06/2013; 96(6). DOI:10.1111/jace.12310 · 2.61 Impact Factor