Partially reduced graphite oxide as an electrode material for electrochemical double-layer capacitors

Partially reduced graphite oxide was prepared from graphite oxide by using synthetic graphite as precursor. The reduction of graphite oxide with a layer distance of 0.57?nm resulted in a reduction of the layer distance depending on the degree of reduction. Simultaneously the amount of oxygen functionalities in the graphite oxide was reduced, which was corroborated by elemental analysis and EDX. The electrochemical activation of the partially reduced graphite oxide was investigated for tetraethylammonium tetrafluoroborate in acetonitrile and in propylene carbonate. The activation potential depends significantly on the degree of reduction, that is, on the graphene-layer distance and on the solvent used. The activation potential decreased with increasing layer distance for both positive and negative activation. The resulting capacitance after activation was found to be affected by the layer distance, the oxygen functionalities and the used electrolyte. For a layer distance of 0.43?nm and with acetonitrile as the solvent, a differential capacitance of 220?Fg(-1) was achieved for the discharge of the positive electrode near the open-circuit potential and 195?Fg(-1) in a symmetric full-cell assembly.     

Structural characterization of epitaxial Cr(x)Mo(1-x) alloy thin films

To develop a model system containing regularly spaced misfit dislocations for studies of the radiation resistance of nanoscale defects, epitaxial thin films of Cr, Mo, and Cr(x)Mo(1-x) alloys were deposited on MgO(001) by molecular beam epitaxy. Film compositions were chosen to vary the lattice mismatch with MgO. The film structure was investigated by x-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS) and scanning transmission electron microscopy (STEM). Epitaxial films with reasonably high crystalline quality and abrupt interfaces were achieved at a relatively low deposition temperature, as confirmed by STEM. However, it was found by XRD and RBS in the channeling geometry that increasing the Mo content of the CrMo alloy films degraded the crystalline quality, despite the improved lattice match with MgO. XRD rocking curve data indicated that regions of different crystalline order may be present within the films with higher Mo content. This is tentatively ascribed to spinodal decomposition into Cr-rich and Mo-rich regions, as predicted by the Cr(x)Mo(1-x) phase diagram.     

Toward low-loss photonic crystal waveguides in InP/InGaAsP heterostructures

Line-defect photonic crystal waveguides exhibit severe propagation losses if they are implemented in semiconductor heterostructures with a weak refractive index contrast. We present, for what we believe is the first time, experimental structures for which we have evidence that fabrication imperfections are not the limiting factor in terms of propagation losses. We demonstrate a loss figure of 335±5 dB/cm, which is an improvement by a factor of about 2 with respect to state-of-the-art values. Simulations show that even lower losses can be obtained with different waveguide geometries. In other words, the dominant loss mechanism is related to the waveguide design, and losses are not expected to decrease upon further optimization of the fabrication process.     

Thickness shear mode resonators (“mass-sensitive devices”) in bioanalysis

A short overview of function and experimental set-ups of acoustic wave devices is given which, in contrast to other bioanalysis techniques, are based on a mechanical transduction mechanism. The most frequently used device is the thickness shear mode resonator (TSMR), which in the last few years was intensively employed in biosensor applications. TSMR biosensor studies in the field of nucleic acid interaction, adsorption of proteins to surfaces and immunosensing are reviewed. A main point concerns the interpretation of the sensor response not only in terms of mass loading, which underestimates the capabilities of these devices.     

HBr or not HBr? That is the question: crystal structure of 6‐hydroxy‐1,4‐diazepane‐1,4‐diium dibromide redetermined

Liu et al. [Chin. J. Struct. Chem. (1996). 15 , 371–373] reported the structure of 6‐hydroxy‐1,4‐diazepane di(hydrogen bromide), C₅H₁₂N₂O·2HBr, which was interpreted in terms of neutral diazepane and HBr molecules. We found, however, ample evidence that the formation of an organic salt, consisting of a diammonium cation and two bromide anions, is more plausible. This interpretation is also in agreement with thermogravimetric analysis and with the observed solution behaviour. The crystal structure of 6‐hydroxy‐1,4‐diazepane‐1,4‐diium dibromide, C₅H₁₄N₂O²⁺·2Br^?, measured at 142 K, crystallized in the orthorhombic space group P2₁2₁2₁. The structure displays O—H…Br and N—H…Br hydrogen bonding. Contact distances are given. A search in the Cambridge Structural Database for the singly‐bonded H—Br moiety revealed a total of 69 structures. The question, whether these structures really include HBr as neutral molecules or rather Br^? anions and a protonated substrate such as an amine, is addressed.     

Syntheses d'aryltetrahydropyrannyl ethers

Tetrahydropyranylation of methoxyphenols by acidic catalysis gives a mixture of C-and/or O-tetrahydropyranylated derivatives. It appears that the electron-donating group and the acidic strength of the catalyst play an important influence in directing such reactions. The synthesis of aryl tetrahydropyranyl ethers 9 has been developed involving the Mitsunobu reaction between substituted 2-carbonyl phenols and tetrahydropyranol derivatives.     

A study of thermal and mechanical effects on materials induced by pulsed laser drilling

Holes drilled in metals and silicon using different short-pulse lasers (copper vapour, Nd : YLF and titanium: sapphire) were characterized under optical and electron microscopy. The aim was to analyze and compare the thermal and mechanical effects on materials induced by laser drilling with a wide range of pulse widths (50 ns to 200 fs) and power densities (10⁸ W/cm² to 10¹⁵ W/cm²).Heat affected structural zones around micro-holes drilled in cold-rolled copper were revealed by analyzing ion-polished hole sections in the scanning electron microscope using electron channelling contrast. The heat affected zones were found to have a maximum width of 5 m to 10 m, independent of the duration of the pulses. Mechanically and thermally induced deformations and slip phenomena, including prismatic punching, were observed in laser-drilled molybdenum monocrystals. The dislocation arrangement which developed during laser drilling of silicon monocrystals was visualized by transmission electron microscopy.The microscopic studies showed that for percussion drilling in the high fluence range characterized by high ablation rates of a few micrometres per pulse the use of shorter pulses (_H < 50 ns) did not lead to any appreciable reduction in the melt component, material re-deposition or thermal load on the wall of the hole. In addition, the increasing mechanical loads on the material due to the higher pressure in the drill channel becomes a limiting factor for the precision of the processing.