Synthesis and isolation of {110}-faceted gold bipyramids and rhombic dodecahedra

Two {110}-faceted gold nanostructures--rhombic dodecahedra and obtuse triangular bipyramids--have been synthesized via a Ag-assisted, seed-mediated growth method. The combination of a Cl(-)-containing surfactant with a low concentration of Ag(+) plays a role in the stabilization of the {110} facets. To the best of our knowledge, this is the first reported synthesis of a {110}-faceted bipyramid structure.     

Mössbauer study of Fe in 3C-SiC following 57Mn implantation

Our investigations on substitutional and interstitial Fe in the group IV semiconductors, from ⁵⁷Fe Mössbauer measurements following ⁵⁷Mn implantation, have been continued with investigations in 3C-SiC. Mössbauer spectra were collected after implantation and measurement at temperatures from 300 to 905 K. Following comparison with Mössbauer parameters for Fe in Si, diamond and Ge, four Fe species are identified: two due to Fe in tetrahedral interstitial sites surrounded, respectively, by four C atoms (Fe_i.C) or four Si atoms (Fe_i,Si) and two to Fe in (or close to) defect free or implantation damaged substitutional sites. An annealing stage at 300–500 K is evident. Above 600 K the Fe_i,Si fraction decreases markedly, reaching close to zero intensity at 905 K. This is accompanied by a corresponding increase in the Fe_i,C fraction.     

Thermal optimization of 1.55 μm OP-VECSEL with hybrid metal–metamorphic mirror for single-mode high power operation

We report on the thermal design and the characterization of InP-based 1.55 μm wavelength large diameter (～100 μm) optically pumped vertical external cavity surface emitting lasers (OP-VECSELs). The device is thermally optimized for high power ( > 70 mW) room-temperature (RT) continuous-wave (CW) single-mode operation. Efficient bottom heat dissipation in the 1/2-VCSEL chip is obtained thanks to the use of a hybrid metal– metamorphic GaAs/AlAs mirror integrated to the InP-based active region, and to subsequent soldering on a SiC substrate. A single-mode output power of 77mW is obtained under CW-RT laser operation, limited by the pump power. Moreover thermal simulations and characterizations of the 1/2-VCSEL chip show that even higher power could be obtained at higher pumping levels, using a CVD diamond substrate.     

Effectiveness of ultrasound for the destruction of Mycobacterium sp. strain (6PY1)

Ultrasound is widely used to disinfect drinking water and wastewater due to its strong physical and chemical effects on microorganisms. The aim of this study was to investigate the effect of ultrasound on the destruction of Mycobacterium strain 6PY1. Ultrasound waves (20 kHz or 612 kHz) were used to treat aqueous suspensions of Mycobacterium at different volumes, initial bacterial concentrations, and power densities. At the same power density and the same exposure time, sonication at high frequency resulted in a lower destruction of Mycobacterium sp. 6PY1 (35.5%) than sonication at low frequency (93%). The percentage of removal was not significantly affected by the volume of the irradiated suspension (150–300 ml) or the initial cell concentration (2.15 × 10⁻³–1.4 × 10⁻² mg protein L⁻¹). At low frequency, the removal percentage of Mycobacterium sp. 6PY1 increased with increasing the power density, with a constant level reached after a certain power density. At high frequency, the removal percentage of Mycobacterium sp. 6PY1 increased with increasing the power density. The mechanism of cell killing was investigated by examining the effects of OH radical scavengers such as sodium carbonate. At high frequency the presence of sodium carbonate suppressed the removal process. However, at low frequency the removal process was not affected, thus indicating that OH radicals have a negligible role in this case. The latter result was supported by ten time’s H₂O₂ production at high frequency greater than that at low frequency.     

Observation of spin-lattice relaxations of dilute Fe3+ in MgO by Mössbauer spectroscopy

We present a method to describe the temperature dependence of emission Mössbauer spectra showing slow spin-lattice relaxations of Fe^3?+? in MgO single crystals, obtained after implantation of ⁵⁷Mn at ISOLDE/CERN. The analysis is based on the Blume-Tjon model for the line-shape of relaxing paramagnetic sextets with the spin relaxation rate, τ ^???1 as a parameter. The temperature dependent spin relaxation rate of Fe^3?+? in MgO is found to increase to ~10⁸ s^???1 at 647 K by assuming a relaxation rate of τ ^???1?< 10⁶ s^???1 at 77 K. The results are in accordance with those obtained by electron paramagnetic resonance spectroscopy demonstrating the possibility of retrieving spin-lattice relaxation rates of dilute Fe^3?+? from emission Mössbauer spectroscopy of Mn/Fe-implanted oxides.     

Post-Modification of Copolymers Obtained by ATRP for an Application in Heterogeneous Asymmetric Salen Catalysis

Copolymers are valuable supports for obtaining heterogeneous catalysts that allow their recycling and therefore substantial savings, particularly in the field of asymmetric catalysis. This contribution reports the use of two comonomers: Azido-3-propylmethacrylate (AZMA) bearing a reactive azide function was associated with 2-methoxyethyl methacrylate (MEMA), used as a spacer, for the ATRP synthesis of copolymers, and then post-functionalized with a propargyl chromium salen complex. The controlled homopolymerization of MEMA by ATRP was firstly described and proved to be more controlled in molar mass than that of AZMA for conversions up to 63%. The ATRP copolymerization of both monomers made it possible to control the molar masses and the composition, with nevertheless a slight increase in the dispersity (from 1.05 to 1.3) when the incorporation ratio of AZMA increased from 10 to 50 mol%. These copolymers were post-functionalized with chromium salen units by click chemistry and their activity was evaluated in the asymmetric ring opening of cyclohexene oxide with trimethylsilyl azide. At an equal catalytic ratio, a significant increase in enantioselectivity was obtained by using the copolymer containing the largest part of salen units, probably allowing, in this case, the more favorable bimetallic activation of both the engaged nucleophile and electrophile. Moreover, the catalytic polymer was recovered by simple filtration and re-engaged in subsequent catalytic runs, up to seven times, without loss of activity or selectivity.     

Electrochemical Nano-Roughening of Gold Microstructured Electrodes for Enhanced Sensing in Biofluids**

A key challenge for sensor miniaturization is to create electrodes with smaller footprints, while maintaining or increasing sensitivity. In this work, the electroactive surface of gold electrodes was enhanced 30-fold by wrinkling followed by chronoamperometric (CA) pulsing. Electron microscopy showed increased surface roughness in response to an increased number of CA pulses. The nanoroughened electrodes also showed excellent fouling resistance when submerged in solutions containing bovine serum albumin. The nanoroughened electrodes were used for electrochemical detection of Cu²⁺ in tap water and of glucose in human blood plasma. In the latter case, the nanoroughened electrodes allowed highly sensitive enzyme-free sensing of glucose, with responses comparable to those of two commercial enzyme-based sensors. We anticipate that this methodology to fabricate nanostructured electrodes can accelerate the development of simple, cost-effective, and high sensitivity electrochemical platforms.