Magnetically confined laser-induced breakdown spectroscopy was investigated by studying the optical emission from laser-induced plasma plumes expanding across an external transverse magnetic field. KrF excimer laser pulses with a pulse duration of 23 ns and a wavelength of 248 nm were used to produce plasmas from Al, Cu, and Co targets. Various optical emission lines obtained from Al and Cu targets show an obvious enhancement in the intensity of optical emission when a magnetic field of ϳ0.8 T is applied, while the optical emission lines from Co targets show a decrease in the optical emission intensity. The enhancement factors of optical emission lines were measured to be around 2 for the Al and Mn ͑impurity͒ lines from Al targets, and 6-8 for Cu lines from Cu targets. Temporal evolution of the optical emission lines from the Al samples shows a maximum enhancement in emission intensity at time delays of 8 -20 s after the incident laser pulse, while from the Cu targets it shows a continuous enhancement at time delays of 3 -20 s after the pulse. The enhancement in the optical emission from the Al and Cu plasmas was presumably due to the increase in the effective plasma density as a result of magnetic confinement. The decrease in the emission intensity from the Co plasmas was suggested to be due to the decrease of effective plasma density as a result of the magnetic force.

No abstract

We report both a facile, scalable method to prepare reduced graphene oxide hydrogels through the electrodeposition of graphene oxide and its use as an electrode for high-performance supercapacitors. Such systems exhibited specific capacitances of 147 and 223 F g(-1) at a current density of 10 A g(-1) when using H2SO4 and H2SO4 + hydroquinone redox electrolytes, respectively.

Wavelength-matched vibrational excitations of ethylene ͑C 2 H 4 ͒ molecules using a tunable carbon dioxide ͑CO 2 ͒ laser were employed to significantly enhance the chemical vapor deposition ͑CVD͒ of diamond in open air using a precursor gas mixture of C 2 H 4 , acetylene ͑C 2 H 2 ͒, and oxygen ͑O 2 ͒. The CH 2 -wag vibration mode ͑ 7 ͒ of the C 2 H 4 molecules was selected to achieve the resonant excitation in the CVD process. Both laser wavelengths of 10.591 and 10.532 m were applied to the CVD processes to compare the C 2 H 4 excitations and diamond depositions. Compared with 10.591 m produced by common CO 2 lasers, the laser wavelength of 10.532 m is much more effective to excite the C 2 H 4 molecules through the CH 2 -wag mode. Under the laser irradiation with a power of 800 W and a wavelength of 10.532 m, the grain size in the deposited diamond films was increased by 400% and the film thickness was increased by 300%. The quality of the diamond crystals was also significantly enhanced.

We compare the superconducting phase-diagram under high magnetic fields (up to H = 45 T) of Fe1+ySe0.4Te0.6 single crystals originally grown by the Bridgman-Stockbarger (BRST) technique, which were annealed to display narrow superconducting transitions and the optimal transition temperature Tc 14 K, with the diagram for samples of similar stoichiometry grown by the travelingsolvent floating-zone technique as well as with the phase-diagram reported for crystals grown by a self-flux method. We find that the so-annealed samples tend to display higher ratios Hc2/Tc, particularly for fields applied along the inter-planar direction, where the upper critical field Hc2(T ) exhibits a pronounced downward curvature followed by saturation at lower temperatures T . This last observation is consistent with previous studies indicating that this system is Pauli limited. An analysis of our Hc2(T ) data using a multiband theory suggests the emergence of the Fulde-Ferrel-Larkin-Ovchnikov state at low temperatures. A detailed structural x-ray analysis, reveals no impurity phases but an appreciable degree of mosaicity in as-grown BRST single-crystals which remains unaffected by the annealing process. Energy-dispersive x-ray analysis showed that the annealed samples have a more homogeneous stoichiometric distribution of both Fe and Se with virtually the same content of interstitial Fe as the non-annealed ones. Thus, we conclude that the excess of Fe, in contrast to structural disorder, contributes to decrease the superconducting upper-critical fields of this series. Finally, a scaling analysis of the fluctuation conductivity in the superconducting critical regime, suggests that the superconducting fluctuations have a two-dimensional character in this system.

Vibrational resonant excitation of ethylene ͑C 2 H 4 ͒ molecules using a carbon dioxide laser was employed to promote reactions in precursors of ethylene, acetylene ͑C 2 H 2 ͒, and oxygen to enhance diamond deposition. One of the vibrational modes ͑CH 2 wag mode, v 7 ͒ of the C 2 H 4 molecules was selected to achieve the resonant excitation in the reactions. Optical emission spectroscopy was used to study the effects of laser resonant excitation on the reactions for diamond deposition. The optical emissions of CH and C 2 species were enhanced with the laser excitation, indicating that there are more active species generated in the reactions. Thicknesses and grain sizes of the deposited films were increased correspondingly. Temperature calculations from the line set in the R-branch of CH emission spectra indicated that a nonthermal process is involved in the enhanced diamond deposition.

No abstract

No abstract