Exfoliated graphene ligands stabilizing copper cations

Exfoliated graphene ligands were prepared by heating exfoliated graphene sheets in ammonia gas at 1023 K. The functional groups of the functionalized exfoliated graphene ligands were mainly pyridine on the edges of the vacancy defects. Copper cations were coordinated with the ligands. Even after being heated at 773 K, coordinated copper did not show severe agglomeration. On the other hand, copper supported on exfoliated graphene sheets prepared by the conventional method agglomerated and ca. 20 nm of copper oxide was formed. This difference clearly shows that exfoliated graphene ligands stabilized copper cations.     

Imaging the structure, symmetry, and surface-inhibited rotation of polyoxometalate ions on graphene oxide

Atomic-resolution imaging of discrete [γ-SiW10O36]8- lacunary Keggin ions dispersed onto monolayer graphene oxide (GO) films by low voltage aberration corrected transmission electron microscopy is described. Under low electron beam dose, individual anions remain stationary for long enough that a variety of projections can be observed and structural information extracted with ca. ± 0.03 nm precision. Unambiguous assignment of the orientation of individual ions with respect to the point symmetry elements can be determined. The C2v symmetry [γ-SiW10O36]8- ion was imaged along its 2-fold C2 axis or orthogonally with respect to one of two nonequivalent mirror planes (i.e., σv). Continued electron beam exposure of a second ion imaged orthogonal to σv causes it to translate and/or rotate in an inhibited fashion so that the ion can be viewed in different relative orientations. The inhibited surface motion of the anion, which is in response to H-bonding-type interactions, reveals an important new property for GO in that it demonstrably behaves as a chemically modified (i.e., rather than chemically neutral) surface in electron microscopy. This behavior indicates that GO has more in common with substrates used in imaging techniques such as atomic force microscopy and scanning tunneling microscopy, and this clearly sets it apart from other support films used in transmission electron microscopy.     

Effect of cold working and ageing treatment on ductility of an Al-6.0% Zn-2.6% Mg alloy at 4.2 to 293 K

The effect of cold-working and ageing (CA) treatment on the ductility of an Al-Zn-Mg alloy was investigated at temperatures from 4.2 to 293 K. The ductility was improved by the CA treatment at 4.2, 77, 196 and 293 K. It was found that both the fracture strain and the reduction of area vary linearly with the area fraction of transgranular fracture. The improvement of ductility was thought to be due to the shape of the grain boundary, the formation of a subboundary and the scattering precipitate size in grains by which both the ledge- and the dimple-formation type intergranular fractures are difficult to occur. The increase of intergranular fracture with decreasing temperature is attributed to the increase of the difference between flow stresses in PFZ and in the matrix, the brittleness of grain boundary precipitates themselves, and the incoherent interface between grain boundary precipitates and the matrix. An intergranular fracture mechanism in the CA specimen is proposed.     

Catalytic Activity of Mesoporous Silica for Synthesis of Methyl N-Phenyl Carbamate from Dimethyl Carbonate and Aniline

Mesoporous silica MCM-41, especially an Al-containing one, showed high catalytic activity for synthesis of methyl N-phenyl carbamate from dimethyl carbonate and aniline at 363-383 K. It was easily separated from the product solution, and the catalyst was able to be used repeatedly.     

Flux change in type II superconductors induced by moving dislocations

The mixed state of a type II superconductor has been studied in the presence of moving dislocations. It is found that when dislocations move during plastic deformation there is a change in A.C. permeability which is reversible, with the mobile dislocations supplying the driving force for the transition. Such a transition has been observed in various lead based alloys, independent of the grain size, degree of homogeneity or heat-treatment.     

Accuracy evaluation in parameter prediction of analogue circuits using nonlinear oscillation methods

A methodology for predicting the specifications of a continuous-time biquad filter is presented. The predictions are made from a reduced set of measurements on the circuit reconfigured as a relaxation oscillator. The filter, based on operational transconductance amplifiers, has been designed in a CMOS 0.35 mum process. Technological process variation is considered as the main cause of deviation in the circuit behaviour. The work focuses on evaluation of prediction accuracy using non-parametric statistics     

Dynamics of carbon nanotube growth from fullerenes

The growth of double-walled carbon nanotubes from peapods was studied. The transformation was monitored by the decrease of fullerene Raman lines, the growth of inner tube Raman lines, and the development of X-ray diffraction patterns. A visual check of the growth process by HRTEM provided additional information. From the difference in time constants for the bleaching of fullerene Raman lines and for the growth of nanotube Raman lines, the existence of an intermediate phase was concluded that was eventually observed in X-ray diffraction and HRTEM. Time constants for the growth of large diameter inner tubes were up to a factor two larger than for small diameter inner tubes. The results fully support the fullerene coalescence growth model triggered by Stone-Wales transformations.