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Two-dimensional carbon nanowalls (CNWs) were prepared by microwave plasma-enhanced chemical-vapor deposition and scanning electron microscopy was used to observe their morphologies. The Raman observations of different sample orientations and polarizations show that CNWs are well crystallized. Micro-Raman scattering measurements were also carried out with different excitation laser lines (325, 488, 514, 532, and 633 nm). The D band shows a very strong shift of 46.19 cm-1/eV with excitation laser energy and this has been explained by the double resonance effect. The decreasing intensity ratios ID/IG and ID′/IG with increasing laser excitation energy were detected and discussed. [ABSTRACT FROM AUTHOR]

Raman spectroscopic studies of graphene have attracted much interest. The G-band Raman intensity of a single layer graphene on Si substrate with 300 nm SiO2 capping layer is surprisingly strong and is comparable to that of bulk graphite. To explain this Raman intensity anomaly, we show that in addition to the interference due to multiple reflection of the incident laser, the multiple reflection of the Raman signal inside the graphene layer must be also accounted for. Further studies of the role of SiO2 layer in the enhancement Raman signal of graphene are carried out and an enhancement factor of ∼30 is achievable, which is very significant for the Raman studies. Finally, we discuss the potential application of this enhancement effect on other ultrathin films and nanoflakes and a general selection criterion of capping layer and substrate is given. [ABSTRACT FROM AUTHOR]

Orientation dependent electron phonon (EP) coupling on single wurtzite CdS nanowires with average diameter of 60 nm has been studied using polarized Raman spectroscopy. The Raman spectra of nanowires are compared with those of bulk ribbon. Different from the bulk sample, the EP coupling of the nanowires is polarized along the longitudinal axis of wire and the diametral coupling strength exhibits a minimum due to the finite size effect of the Fröhlich potential. These results show that the highly anisotropic geometry of CdS nanowires is a dominant factor in determining the anisotropy of EP coupling. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) and Raman spectroscopies of CdSe/ZnS core/shell quantum dots (QDs) were studied under hydrostatic pressure (0–160 kbars) at room temperature. Two phase transitions, at 69 and 79 kbars, respectively, were observed, which correspond to wurtzite-rocksalt and rocksalt-cinnabar structural transformations. The full width at half maximum of PL peaks was found to decrease anomalously approximately 30% with pressure. These experimental data show significant difference between the CdSe/ZnS core/shell QDs and simple bare CdSe QDs or bulk CdSe, implying the ZnS shell plays a dominant role in structural stability and electronic state of such system. [ABSTRACT FROM AUTHOR]

Laser peening has an extensive application in traditional manufacturing industry. However, in additive manufacturing, the initial stresses on the parts often reduce the effects of laser peening and make it hard to achieve a desirable residual stress distribution. In this investigation, the interaction of initial residual stress and laser peening-induced stress was studied through numerical simulation and experimental tests. A finite element model (FEM) model was built to predict the stress distribution on laser-deposited sample, and its changed state is affected by laser peening. The microstructure and mechanical properties were also characterized experimentally. The result turned out that the thermal-induced tensile residual stress in laser-deposited sample can affect the laser peening result in both horizontal and longitudinal directions. Some mechanical properties of the LAMed sample were changed after LSP treatment. The hardness on the surface and 1-mm depth have been increased by 7% and 22%, respectively, and the yield strength was increased by 16%, while there is no significant change in the tensile strength and elongation rate. [ABSTRACT FROM AUTHOR]

Resonant Raman spectroscopy studies of (Mn, Co)-codoped ZnO films were carried out using the 325 nm laser as the excitation source. The mixed mode character of the longitudinal optical (LO) phonon reveals that the resonant Raman spectra of the films can be used to test the c-axis orientation degree of their crystallite grains. The ratio of integrated Raman intensities between the 2LO to LO changes as a function of annealing temperatures, which reaches maximum at about 800 °C and demonstrates the variation of electron-LO phonon coupling in the films. These can provide helpful information for the fabrication of ZnO based functional films and for the development of their future applications. [ABSTRACT FROM AUTHOR]

In this letter, we show how high-resolution scanning tunneling microscopy (STM) imaging can be used to reveal that certain edges of micromechanically exfoliated single layer graphene crystals on silicon oxide follow either zigzag or armchair orientation. Using the cleavage technique, graphene flakes are obtained that very often show terminating edges seemingly following the crystallographic directions of the underlying honeycomb lattice. Performing atomic resolution STM-imaging on such flakes, we were able to directly prove this assumption. Raman imaging carried out on the same flakes further validated our findings. [ABSTRACT FROM AUTHOR]

We demonstrate a reproducible layer engineering technique for multilayer graphene through controllable oxidation via a SiO2 capping layer. The oxidation method is able to reduce the thickness of few layer graphene to a single layer, as determined by a combination of contrast and Raman spectroscopies. We have also studied the electrical transport properties of graphene sheets with different thicknesses by focusing on their minimum conductivity. The average minimum conductivity of single layer graphene was found to be 0.3×4e2/h, while that of multilayer graphene consisting of n layers is approximately 1.2×4e2/h for n=2, 2.4×4e2/h for n=3, and 4ne2/h for n>3. The results suggest that the substrate plays an important role in determining the transport properties of thin graphene sheets with n<3, while its influence is relatively small in thicker graphene sheets. [ABSTRACT FROM AUTHOR]

Wear resistant composite layers were fabricated on 38CrMoAl steel by laser processing with NiCr/Cr3C2-CeO2 powders with addition of MoS or WS . The composite layers were heat treated at 150 and 300°C (MoS2), and 300 and 600°C (WS2). Microstructure, phases, microhardness, wear behaviour at room temperature and crack behaviour under loading of the laser processed and heat treated layers were investigated. Results indicate that undissolved MoS2 or WS2 were observed in all the layers. Heat treatment changed the microstructure and phases of all the laser processed layers. When the original majority phase of the laser processed layer was martensite, volume fraction of retained austenite increased after heat treatment; while when the original majority phase was austenite, volume fraction of retained austenite decreased after heat treatment. Full width at half maximum (FWHM) of martensite peaks in the laser processed layer with addition of 20 wt.% MoS2 decreased with heat treatment temperatures, indicating reduced defects in the heat treated layers. Laser processed layers with addition of 10 wt.% MoS2, 10 wt.% or 20 wt.% WS2 without heat treatment showed the best wear resistance while that with addition of 20 wt.% MoS2 showed the best wear resistance after heat treatment at 300°C. The wear mechanism of all the layers is abrasive, adhesive and oxidative wear, accompanied by the formation and removal of oxide film and sulphide containing tribofilms. The oxide film and sulphide lubricating phases formed on the worn surface during sliding wear play an important role in reducing friction and wear loss. Un-dissolved MoS2/WS2 and crack behaviour in case of loading is closely related to the microstructure of the pressed matrix. [ABSTRACT FROM AUTHOR]

The role of sulphuric acid (H2SO4) in fabrication graphene oxide besides as intercalant has not been well addressed. In this work, Raman spectroscopy is used to monitor structural evolution in chemical vapor deposition (CVD) graphene chemically oxidized by dilute H2SO4. From the analysis of Raman spectra of oxidized graphene, we propose that oxidation first initiates at preexisting defects, and vacancy-like defects are formed. Following is the radial growth of the vacancy, and oxidation pits appear in graphene. This assumption is further confirmed by atomic force microscope measurement. It is also found that with increase of amounts of defects, G peak is blue shift, and this is explained by defect and hole doping effect. Hole doping in graphene is much stronger at hexagon regions near the oxidation pits. This work helps in understanding the role of H2SO4 in fabrication graphene oxide as oxidizer as well as helps in obtaining structure information of graphene oxide. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Solid solution has been considered as an effective approach to advanced thermoelectrics. However, the benefit from the decrease in lattice thermal conductivity induced by the impurity scattering will be compensated by the reduction in carrier mobility, therefore suppressing the maximum figure of merit (zT). We demonstrate the characteristics of the fundamental properties, including the lattice thermal conductivity and carrier mobility, of undoped PbSe1−xSx solid solutions (0 < x < 1) at room temperature, which provide an efficient way to evaluate the maximum zT of the materials with optimum doping. The lattice thermal conductivity is found to decrease significantly after adding a small amount of PbSe into PbS matrix up to the composition of PbSe0.7S0.3 when the carrier mobility remains virtually unchanged, indicating the beneficial effect of impurity scattering to improve the thermoelectric performance. [ABSTRACT FROM AUTHOR]

Thin film polymer solar cells have been fabricated using regioregular poly(3-hexylthiophene) (P3HT) within [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction active layer. The influence of the thermal annealing temperature and the time duration on the performance of P3HT/PCBM bulk heterojunction solar cells based on different thickness of active layers has been investigated. The results demonstrate that thermal annealing is a thermally activated kinetic process. The effect is almost the same for high temperature annealing for a short time and low temperature annealing for a long time at a temperature greater than the glass temperature of P3HT. The device with a thicker active layer requires a higher temperature or a longer time annealing treatment to achieve the optimised phase separation for efficient charge separation and transport and thereby leads to optimal performance. The device with a thinner active layer requires a lower temperature or a shorter time annealing treatment to achieve the optimal performance. [ABSTRACT FROM AUTHOR]

To evaluate the efficacy and safety of leflunomide in the treatment of proliferative lupus nephritis, a prospective multi-centre observational study was conducted. Patients with biopsy proven proliferative lupus nephritis were assigned to receive either leflunomide or cyclophosphamide with concomitant prednisone. Leflunomide was given orally with a loading dose of 1 mg/kg/day for 3 days followed by 30 mg/day. Intravenous cyclophosphamide was administered monthly at a dose of 0.5 g/m2 of body-surface area. A total of 110 patients were enrolled, 70 in the leflunomide group and 40 in the cyclophosphamide group. The complete remission rate in the leflunomide group was 21% and partial remission rate 52%, as compared with 18% and 55%, respectively, in the cyclophosphamide group. Renal parameters and systemic lupus erythematosus disease activity index improved significantly and similarly in both groups. Serum creatinine decreased or stabilized in both treatment groups. No significant difference was noted with respect to clinical outcome between groups. Repeat biopsy also showed a significant reduction of active lesions in kidney pathology after 6 months of leflunomide treatment. Major adverse events, similar in both treatment groups, included infection, alopecia and hypertension. Leflunomide, compared with cyclophosphamide, in combination with prednisone was effective in the induction therapy of proliferative lupus nephritis and was generally well-tolerated. [ABSTRACT FROM AUTHOR]

Summary: This paper provides the length–weight relationships for six fish species collected from the Anning River, one of the biggest tributaries of the Yalong River in China. A total of 1096 specimens belonging to six fish species were analyzed. Among them, the length–weight relationships for 4 fish species are first‐time reports for FishBase and new maximum lengths of one fish species is also reported. [ABSTRACT FROM AUTHOR]

The carrier dynamics of Bi2Te3 is studied using the femtosecond pump-probe technique. Three distinct processes, including free carrier absorption, band filling, and electron-hole recombination, are found to contribute to the reflectivity changes. The two-temperature model is used to describe the intraband energy relaxation process of carriers, and the Drude contribution well explains the intensity dependence of the peak values of the nonoscillatory component in the reflectivity signal. The combined effects of free carrier absorption and band filling result in a reflection minimum at about 2 ps after laser excitation. The nonzero background signal increases linearly with the pump fluence, which is attributed to the electron-hole recombination. Finally, our results provide an illustration of investigating the carrier dynamics in semiconductors from the ultrafast reflectivity spectra. [ABSTRACT FROM AUTHOR]