A facile chemical approach to enhance the photoluminescence of poly(2-methoxy-5-propyloxy-sulfonate-1,4-phenylenevinylene) (MPS-PPV) by alternately incorporating the rigid p-phenylenevinylene comonomer units into the conjugated backbone is reported. In dilute aqueous solution the resulting anionic conjugated copolymer, poly[(2-methoxy-5-propyloxysulfonate-1,4- phenylenevinylene)-alt-(1,4-phenylenevinylene)] (CO-MPS-PPV), has a fluorescence quantum yield of 51.6%, about an order of magnitude higher than that of the homopolymer. Because of their amphiphilic nature, CO-MPS-PPV chains self-organize into micelle-like aggregates in water. The structure changes of the aggregates can be perceived through monitoring photoluminescence spectra at different solvent compositions and pH values. The fluorescence of the conjugated copolymer solution is highly sensitive to the cationic surfactant, and emission can be drastically quenched to about 5% of original intensity in the presence of extremely low concentration (26 μmol/L) of dodecyltrimethylammonium bromide. Such behavior is totally different from its homopolymer counterpart, whose emission is increased by the same surfactant. Water-soluble conjugated polymers with tunable hydrophobic/hydrophilic characteristics afford the diversity of these fluorescence sensory materials. CO-MPS-PPV is also an ideal material for electroluminescence application. The ionic conductivity of CO-MPS-PPV leads to a nearly balanced hole and electron injection from ITO and metal electrodes to the active layer. A light-emitting device fabricated from a composite of CO-MPS-PPV and ionic conducting polyurethane distinguishes from conventional LED by fetching performances like lower turn-on voltage (2 V), light emission under both forward and reverse bias (dual electroluminescence), and fast on/off kinetics (less than 80 ms) under ambient conditions. © 2006 American Chemical Society.

Gu Zhen;Zhang Yang;Shen Qun-Dong;Bao Yong-Jun;Wang Mu

Macromolecules

2006

We report in this paper the electric properties of nanostructured copper filament arrays self-organized by a novel electrochemical method. Due to the spontaneous oscillation of the concentration field of [Cu ²⁺ ] in front of the growing interface, crystallites of copper and cuprous oxide appear alternately on the filaments of the electrodeposits. A conducting atomic force microscope (CAFM) and current imaging tunnelling spectroscopy (CITS) were used to characterize the electric properties of the nanostructured copper filaments. By applying a constant voltage across the conducting probe of the CAFM and the sample, an electric current mapping is achieved, in which alternating low and high current regions correspond exactly to the periodic nanostructures on the filaments. The profile of the electric current along the structured filament has been analysed, and no noticeable potential drop has been observed. A typical linear I-V curve for a metal and nonlinear I-V curve for a semiconductor were collected in the high and low current regions respectively. These results suggest that despite the periodic distribution of Cu 2 O crystallites on the deposited filament, there should exist a metallic core of copper crystallites inside the filament. This type of structured metal-semiconductor filament might have potential application. © 2006 IOP Publishing Ltd.

Wu Zhe;Bao Yong-Jun;Wang Mu;Peng Ru-Wen;Hao Xi-Ping;Ming Nai-Ben;Yu Guang-Wei;Fleury Vincent

Journal of Physics Condensed Matter

2006

Polycrystalline ferroelectric SrBi 4 Ti 4 O 15 thin films were prepared on Pt-coated silicon substrates by pulsed laser deposition. Structures of the films were analyzed by x-ray diffraction, atomic force microscopy (AFM) and scanning electron microscopy. At an applied field of 275 kV/cm, the films showed good hysteresis loops with remnant polarization (P r ), saturated polarization (P s ) and coercive field (E c ) of 3.11 μC/cm ² , 7.81 μC/cm ² and 68 kV/cm, respectively. At 120 kV/cm switching pulse field, fatigue tests were carried out systematically by varying the switching pulsewidth with a fixed duty cycle and with a fixed switching period, respectively. A gradual increase followed by an abrupt increase of the fatigue rate was observed with the increase of the switching pulsewidth. Field-induced defect diffusion was used to explain the results. © 2002 American Institute of Physics.

Zhang Shan-Tao;Yang Bin;Chen Yan-Feng;Liu Zhi-Guo;Yin Xiao-Bo;Wang Yuan;Wang Mu;Ming Nai-Ben

Journal of Applied Physics

2002

We report in this article a mechanism to form regularly zigzag branch of CsCl crystallites on a flat glass substrate, in which the crystallographic orientation rotates continuously, and a pattern with long-range order on tens of micrometer scale is generated. Atomic force microscopy (AFM) indicates that this unusual crystallization behavior is associated with successive nucleation at the concave edge of crystallite facet and glass substrate, where interfacial tension underneath the nucleus is asymmetric. We suggest that these observations reveal a new lateral growth mode, and may help to understand a class of long-range ordering effect in crystallization. © 2007 Elsevier B.V. All rights reserved.

Pan Wei;Mao Y. W.;Shu D. J.;Ma G. B.;Wang Mu;Peng R. W.;Hao X. P.;Ming N. B.

Journal of Crystal Growth

2007

Heteroepitaxial thin film growth may start by nucleating three-dimensional (3D) or two-dimensional (2D) islands on foreign substrate. Depending on the interfacial energies, heteroepitaxial growth can be categorized into three modes: Frank-van der Merwe (FM), Stranski-Krastanow (SK), and Volmer-Weber (VW). In this lecture, we concentrate on the detail process of horizontal extension of a crystalline island on foreign substrate via successive nucleation at the concave corner of the crystal facet and the foreign substrate. It is demonstrated that due to the difference of surface tensions at the concave corner, once a nucleus appears at the corner, the crystallographic orientation of the nucleus is spontaneously twisted. By successive nucleation at the concave corner, the crystalline layer develops laterally, with its crystallographic orientation continuously rotated. Such a previously untouched effect could be the physical origin to form a few regular spatial patterns in the interfacial growth. A theory is developed, which provides a criterion to observe such an effect in the nucleation-mediated lateral growth. © 2007 American Institute of Physics.

Wang Mu;Shu Dajun;Peng Ruwen;Ming Naiben

Aip Conference Proceedings

2007

Wang Mu;Wildburg G.;Van Esch J. H.;Bennema P.;Nolte R. J M;Ringsdorf H.

Physical Review Letters

1994

Formation of periodic nanostructures on Cu/Cu 2 O films was demonstrated using electrodeposition. It was observed that the periodicity could be tuned from 100 nm to a few hundred nanometers by changing the self-organized growth conditions. Oscillating current/voltage was measured during the formation of the structured film. The dependence of the oscillations on the pH of electrolyte and the applied electric current across the electrodes was also investigated. A theoretical model was proposed to describe the oscillatory behavior of the coupling in electrodeposition.

Wang Yuan;Cao Yu;Wang Mu;Zhong Sheng;Zhang Ming-Zhe;Feng Yan;Peng Ru-Wen;Hao Xi-Ping;Ming Nai-Ben

Physical Review E Statistical Nonlinear and Soft Matter Physics

2004

In this paper, we investigate transmission of electromagnetic wave through aperiodic dielectric multilayers. A generic feature shown is that the mirror symmetry in the system can induce the resonant transmission, which originates from the positional correlations (for example, presence of dimers) in the system. Furthermore, the resonant transmission can be manipulated at a specific wavelength by tuning aperiodic structures with internal symmetry. The theoretical results are experimentally proved in the optical observation of aperiodic SiO2/TiO2 multilayers with internal symmetry. We expect that this feature may have potential applications in optoelectric devices such as the wavelength division multiplexing system.

Peng R. W.;Liu Y. M.;Huang X. Q.;Qiu F.;Wang Mu;Hu A.;Jiang S. S.;Feng D.;Ouyang L. Z.;Zou J.

Physical Review B Condensed Matter and Materials Physics

2004

We report in this letter the fabrication of unique single-crystalline silver filaments with periodic, pearl-chain-like structures by electrodeposition without using any templates, surfactants, and additives. Fourier transform infrared spectroscopy, infrared focus-plane-array imaging, and numerical simulations demonstrate that the excited surface waves may sustain on the silver "pearl chains" in midinfrared range. Based on the propagation features of surface waves on the silver filaments, we suggest that such a structure can be applied for light transmission in midinfrared range. © 2009 American Institute of Physics.

Wu Zhe;Li Hong-Min;Xiong Xiang;Ma Guo-Bin;Wang Mu;Peng Ru-Wen;Ming Nai-Ben

Applied Physics Letters

2009

Zhang Z. J.;Peng R. W.;Wang Z.;Gao F.;Sun W. H.;Wang Q. J.;Wang Mu;Huang X. R.

Applied Physics Letters

2009