We report a facile method to grow multi-sectional TiO2 nanotube arrays consisting of alternating bamboo-shaped and smooth-walled nanotube sections by anodization.Two key factors are necessary for obtaining these morphologies.First,in order to avoid possible disruptions between the conjoint sections of the nanotube,the distribution of hydrogen ions is suggested not to be fiercely disturbed when switching from the first to the second stage.Second,to avoid the disruption of the nanotube at the joint which results from the disparity in diameters between sections,the direct current voltage is set to be the maximum of the square wave voltage.These newly developed TiO2 nanotube arrays are expected to have potential applications in solar cells,drug release and delivery systems.
LI ShiQi,YIN JianBo & ZHANG GengMin Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics,Peking University,Beijing 100871,China
The hierarchical structure and mechanical property of shell nacre are experimentally investigated from the new aspects of chemical stability and chemistry-mechanics coupling. Through chemical deproteinization or demineralization methods together with characterization techniques at micro/nano scales,it is found that the nacre of abalone,haliotis discus hannai,contains a hierarchical structure stacked with irregular aragonite platelets and interplatelet organic matrix thin layers. Yet the aragonite platelet itself is a nanocomposite consisting of nanoparticles and intraplatelet organic matrix framework. The mean diameter of the nanoparticles and the distribution of framework are quite different for different platelets. Though the interplatelet and in-traplatelet organic matrix can be both decomposed by sodium hydroxide solution,the chemical stability of individual aragonite platelets is much higher than that of the microstructure stacked with them. Further,macroscopic bending test or nanoindentation experiment is performed on the micro/nanostructure of nacre after sodium hydroxide treatment. It is found that the Young's modulus of both the stacked microstructure and nanocomposite platelet reduced. The reduction of the microstructure is more remark than that of the platelet. Therefore the chemical-mechanical stability of the nanocomposite platelet itself is much higher than that of the stacked microstructure of nacre.
SUN JinMei & GUO WanLin Institute of Nanoscience,Nanjing University of Aeronautics and Astronautics,Nanjing 210016,China
In this paper,configuration parameters of the waveguide are altered independently or simultaneously to control the cutoff frequencies of the guided band.The independent control range of the upper and lower cutoff frequencies is 55.0% and 63.9% of the photonic band gap(PBG),respectively.The regulating range of the simultaneous tuning can be as large as 28.6% in terms of the PBG,or 240% in terms of the bandwidth.This tuning cutoff frequency method provides an efficient way to tailor the guided band and further tune the optical properties of PhCWs.
