The II–I Phase Transition Behavior of Butene-1 Copolymers with Hydroxyl Groups

The crystallization and II–I phase transition of functionalized polybutene-1 with hydroxyl groups were investigated by differential scanning calorimetry. The results show that the incorporated hydroxyl groups increase the nucleation density but decrease the growth rate in melt crystallization. Interestingly, for the generated tetragonal form II, the presence of polar hydroxyl groups can effectively accelerate the phase transition into the thermodynamically stable modification of trigonal form I, especially with stepwise annealing and high incorporation. Using stepwise annealing, II–I phase transition was enhanced by an additional nucleation step performed at a relatively low temperature, and the optimal nucleation temperature to obtain the maximum transition degree was ‒10 °C, which is independent from the content of hydroxyl groups. Furthermore, the accelerating effect of hydroxyl groups on the II–I transition kinetics can be increased by reducing the crystallization temperature when preparing form II crystallites. These results provide a potential molecular design approach for developing polybutene-1 materials.

Preparation and Characterization of Hollow Zinc Oxide Nanofibers and Investigation of Its Photocatalytic Properties

Hollow inorganic nanofibers have great potential application in the field of photocatalysis due to their special three-dimensional structure. In our work, we have fabricated ZnO hollow nanofibers (ZnO-HNF) by simple single-spinneret electrospinning of polyacrylonitrile (PAN)/zinc acetate precursor solution, followed by stepwise annealing at 300–500 °C. The results show that long and continuous ZnO-HNF with shell consisting of uniform compacted ZnO nanoparticles are successfully fabricated, and the shell thickness is approximately 30 nm. The formation mechanism of ZnO-HNF is speculated to be consequence of the different rate of mass diffusion during the annealing process (Kirkendall effect). The prepared Zn-HNF exhibits good performance in photocatalysis. The photocatalytic removal efficiency of Rhodamine B (RhB) under ultraviolet light irradiation can reach 94.08% in 1 hour, and the removal efficiency of Cr(VI) is 94.49% in 2 hours. This work provides new ideas for the development of ZnO in the field of photocatalysis, and provides new possibilities for more types of subsequent photocatalytic materials.

Strengthening of Al and Al-Mg alloy wires by melt inoculation with Al/MgB2 nanocomposite

This study hinges on the feasibility of strengthening Al and Al-Mg wires by adding Al nanocomposite pellets containing MgB2 nanoparticles into the melt upon fabrication. These MgB2 nanoparticles were obtained by fragmentation using a high-energy ball mill, and were, afterward, mechanically alloyed with pure aluminum. The resulting MgB2/Al nanocomposite pellets were sintered at 260°C to be subsequently added into molten aluminum and an Al-Mg alloy melt. Cold rolling intercalated with stepwise annealing allowed the fabrication of 1 mm diameter wires with a final area reduction of 96%. Mechanical and physical properties of the treated wire specimens were compared to those of similarly processed pure aluminum wire. The ultimate tensile strength of the treated wires increased approximately double fold with respect to untreated wires at the expense of some loss in electrical conductivity.

Dependence of open circuit voltage in a-Si:H and μc-Si:H solar cells on defect density in absorber layer varied by 2 MeV electron bombardment

Theoretically predicted values of the open circuit voltage (VOC) for a-Si:H or μc-Si:H based solar cells are substantially higher than the values achieved in of state-of-the-art devices. Fundamentally, open circuit voltage is determined by generation-recombination kinetics, where recombination is often controlled by the defect density in the absorber layer of a solar cell. The latter aspect is the focus of the paper. The relation between the VOC and the bulk recombination in the absorber layer is addressed in experiment by varying the defect density. The absorber layer defect density (spin density, NS, monitored with ESR) in a-Si:H and μc-Si:H solar cells was varied over two orders of magnitude using a 2 MeV electron bombardment and successive stepwise annealing. The results of the electron bombardment experiment are analyzed with respect to the illumination intensity dependency of the VOC, measured for the same set of a-Si:H and μc-Si:H solar cells. We find that the VOC of a-Si:H solar cells is not limited by defects in the bulk of the absorber layer, even at relatively high defect density up to 3–5 × 1016 cm−3 and, therefore, other limiting mechanisms have to be identified to improve voltage in these devices. In contrast, μc-Si:H solar cells show nearly classical VOC–NS relation. The bulk defect density in μc-Si:H absorber layer is thus likely the key limiting factor for VOC in these devices at present status of material quality (NS of 3–7 × 1015 cm−3). Further optimization of μc-Si:H in terms of bulk defect density is highly relevant for VOC improvement in solar cells.

Ni nanocrystals on HOPG(0001): A scanning tunnelling microscope study

The growth mode of small Ni clusters evaporated in UHV on HOPG has been investigated by scanning tunnelling microscopy. The size, the size distribution, and the shape of the clusters have been evaluated for different evaporation conditions and annealing temperatures. The total coverage of the surface strongly depends on the evaporation rate and time, whereas the influence of these parameters is low on the cluster size. Subsequent stepwise annealing has been performed. This results in a reduction of the total amount of the Ni clusters accompanied by a decreasing in the overall coverage of the surface. The diameter of the clusters appears to be less influenced by the annealing than is their height. Besides this, the cluster shape is strongly influenced, changing to a quasi-hexagonal geometry after the first annealing step, indicating single-crystal formation. Finally, a reproducible methodology for picking up individual clusters is reported Parts of this work have been presented as oral or poster presentations in several national and international conferences (Meeting of the Physical Society of Japan 2011 and 2012, 6th International Symposium on Surface Science 2012, and ImagineNano 2013)..