Type I-type II transition of self-assembled In0.55Al0.45As/Al0.5Ga0.5As quantum dots

The photoluminescence (PL) of In0.55Al0.45As/Al0.5Ga0.5As self-assembled quantum dots has been measured at 15 and 80 K under hydrostatic pressure. The lateral size of the dots ranges from 7 to 62 nm. The emissions from the dots with 26, 52 and 62 nm size have a blue shift under pressure, indicating that these quantum dots have the normal type-I structure with lowest conduction band at the Gamma -valley. However, the PL peak of dots with 7 nm diameter moves to lower energy with increasing pressure. It is a typical character for the X-related transition. Then these small dots have a type-II structure with the X-valley as the lowest conduction level. An envelope-function calculation confirms that the Gamma -like exciton transition energy will rise above the X-like transition energy in the In0.55Al0.45As/Al0.5Ga0.5As structure if the dot size is small enough.

Synthesis of nickel(II) complexes of alpha-isoxazolylazo-beta-diketones and their absorption of spin-coating films and thermal properties for HD-DVD-R

Three kinds of new nickel(II) complexes of alpha-isoxazolylazo-beta-diketones with blue-violet light absorption were synthesized. Their structures were postulated based on elemental analysis, MS and FT-IR spectra. Smooth films on K9 glass substrates were prepared using the spin-coating method. The absorption properties and thermal stability of these complexes were discussed. The static optical recording test for high density digital versatile disc-recordable (HD-DVD-R) system was also studied. (c) 2005 Elsevier B.V. All rights reserved.

Aluminium doping induced enhancement of p-d coupling in ZnO

Valence-band type Auger lines in Al doped and undoped ZnO were comparatively studied with the corresponding core level x-ray photoelectron spectrography (XPS) spectra as references. Then the shift trend of energy levels in the valence band was that p and p-s-d states move upwards but e and p-d states downwards with increasing Al concentration. The decreased energy of the Zn 3d state is larger than the increased energy of the 0 2p state, indicating the lowering of total energy. This may indicate that Al doping could induce the enhancement of p-d coupling in ZnO, which originates from stronger Al-O hybridization. The shifts of these states and the mechanism were confirmed by valence band XPS spectra and 0 K-edge x-ray absorption spectrography (XAS) spectra. Finally, some previously reported phenomena are explained based on the Al doping induced enhancement of p-d coupling.

Type I-type II transition of self-assembled In0.55Al0.45As/Al0.5Ga0.5As quantum dots

The photoluminescence (PL) of In0.55Al0.45As/Al0.5Ga0.5As self-assembled quantum dots has been measured at 15 and 80 K under hydrostatic pressure. The lateral size of the dots ranges from 7 to 62 nm. The emissions from the dots with 26, 52 and 62 nm size have a blue shift under pressure, indicating that these quantum dots have the normal type-I structure with lowest conduction band at the Gamma -valley. However, the PL peak of dots with 7 nm diameter moves to lower energy with increasing pressure. It is a typical character for the X-related transition. Then these small dots have a type-II structure with the X-valley as the lowest conduction level. An envelope-function calculation confirms that the Gamma -like exciton transition energy will rise above the X-like transition energy in the In0.55Al0.45As/Al0.5Ga0.5As structure if the dot size is small enough.

Construction of 2-D directional filter bank by cascading checkerboard-shaped filter pair and CMFB

In this paper, we propose a new approach to construct a 2-dimensional (2-D) directional filter bank (DFB) by cascading a 2-D nonseparable checkerboard-shaped filter pair and 2-D separable cosine modulated filter bank (CMFB). Similar to diagonal subbands in 2-D separable wavelets, most of the subbands in 2-D separable CMFBs, tensor products of two 1-D CMFBs, are poor in directional selectivity due to the fact that the frequency supports of most of the subband filters are concentrated along two different directions. To improve the directional selectivity, we propose a new DFB to realize the subband decomposition. First, a checkerboard-shaped filter pair is used to decompose an input image into two images containing different directional information of the original image. Next, a 2-D separable CMFB is applied to each of the two images for directional decomposition. The new DFB is easy in design and has merits: low redundancy ratio and fine directional-frequency tiling. As its application, the BLS-GSM algorithm for image denoising is extended to use the new DFBs. Experimental results show that the proposed DFB achieves better denoising performance than the methods using other DFBs for images of abundant textures. (C) 2008 Elsevier B.V. All rights reserved.

Theoretical study of p-d hybridization in Co perovskite

The real-space recursion method and unrestricted Hartree-Fock approximation have been applied to calculate the density of states of various Co perovskite, CeCoO3, SrCoO3 and Sr1-xCexCoO3. We have studied the magnetically ordered states of these Co perovskites in an enlarged double cell, and find its various magnetic structures due to the occupancy of 3d band and its interaction with neighboring Co ions. In this study, we have studied the p-d hybridization of the three Co perovskites, we find t(2g) electrons are localized and the flat e(g) band is responsible for the itinerant behavior, and although the rare earth elements itself contribute little to the DOS at the Fermi energy, the DOS at Fermi energy and the magnetic moment changed consequently because of different valence of Co ions in these compounds and p-d hybridization effect is very important. (C) 2009 Elsevier B.V. All rights reserved.

Restudy on the wave functions of Gamma(nS) states in the light-front quark model and the radiative decays of Gamma(nS) -> eta(b) + gamma

The light-front quark model has been applied to calculate the transition matrix elements of heavy hadron decays. However, it is noted that using the traditional wave functions of the light-front quark model given in the literature, the theoretically determined decay constants of the Gamma(nS) obviously contradict the data. This implies that the wave functions must be modified. Keeping the orthogonality among the nS states and fitting their decay constants, we obtain a series of the wave functions for Gamma(nS). Based on these wave functions and by analogy with the hydrogen atom, we suggest a modified analytical form for the Gamma(nS) wave functions. Using the modified wave functions, the obtained decay constants are close to the experimental data. Then we calculate the rates of radiative decays of Gamma(nS) -> eta(b) + gamma. Our predictions are consistent with the experimental data on decays Gamma(3S) -> eta(b) + gamma within the theoretical and experimental errors.

Ultrathin-film growth of para-sexiphenyl (II): Formation of large-size domain and continuous thin film

The large-size domain and continuous para-sexiphenyl (p-6P) ultrathin film was fabricated successfully on silicon dioxide (SiO2) substrate and investigated by atomic force microscopy and selected area electron diffraction. At the optimal substrate temperature of 180 degrees C, the first-layer film exhibits the mode of layer growth, and the domain size approaches 100 mu m(2). Its saturated island density (0.018 mu m(-2)) is much smaller than that of the second-layer film (0.088 mu m(-2)), which begins to show the Volmer-Weber growth mode.

Hydrothermal Synthesis, Structures, and Luminescent Properties of Seven d(10) Metal-Organic Frameworks Based on 9,9-Dipropylfluorene-2,7-Dicarboxylic Acid (H(2)DFDA)

A series of Zn(II) and Cd(II) metal-organic frameworks, namely, [Zn(DFDA)] (1), [Cd(DFDA)(C2H5OH)] (2), [Zn-2(DFDA)(2)(L-1)(2)](2) center dot 3H(2)O (3), [Cd-2(DFDA)(2)(L-1)(2)] (4), [Zn(DFDA)(L-2)] (5), [Cd(DFDA)(L-2)(DMF)] (6), and [Zn(DFDA)(L-3)] (7) (where DFDA = 9,9-dipropylfluorene-2,7-dicarboxylate anion, L-1 = 1,4-bis(imidazol-1-ylmethyl)benzene, L-2 = 1,1'-(1,4-butanediyl) bis(imidazole), L-3 = 2,2'-bipyridine) have been synthesized under hydrothermal conditions and structurally characterized. Compound 1 exhibits a three-dimensional (3D framework containing one-dimensional (1D) Zn(II)-O clusters, with (4(8).6(7)) topology. Compound 2 contains hydrophobic channels built from infinite 1D Cd(II)-O clusters, with (4(8).5(4).6(3)) topology.

Synthesis and self-assembly of poly(ethylene oxide)-b-poly(2-hydroxyethyl methacrylate)

Poly(ethylene oxide)-b-poly(2-hydroxyethyl methacrylate) (PEO-b-PHEMA) was synthesized by successive atom transfer radical polymerization (ATRP) of 2-hydroxyethyl methacrylate(HEMA) monomer using PEO-Br macroinitiator as initiator, CuBr/CuBr2 and 2,2.-bipyridyl (bpy) as catalyst and ligand. IR, H-1 NMR, and GPC analysis indicate that PEO-b-PHEMA block copolymer with low polydispersity index (M-w/M-n approximate to 1.1) has been formed. Self-assembly of this double hydrophilic block copolymer in the selective solvent and water was also studied. Owing to the high hydrophilic nature of the PEO and PHEMA blocks, this double hydrophilic block copolymer cannot disperse well in water. So block copolymer was modified by part esterification of PEO-b-PHEMA with acetic anhydride, which increased the hydrophobic group of the PHEMA block. The TEM results show that this block copolymer spontaneously form well-defined micelles in water.

The study of synthesis of poly(ethylene oxide)-b-poly(N,N-dimethylacrylamide) by atom transfer radical polymerization and self-assembly in selective solvents

Poly( ethylene oxide)-b-poly(N, N-dimethylacrylamide) (PEO-b-PDMA) was synthesized by successive atom transfer radical polymerization (ATRP) of N, N-dimethylacrylamide (DMA) monomer using PEO-Br macro initiators as initiator, CuBr and 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazamacrocyclotetra decane (Me-6[14] aneN(4)) as catalyst and ligand. PEO-Br macroinitiator was synthesized by esterification of PEO with 2-bromoisobutyryl bromide. GPC and H-1 NMR studies show that the plot of ln([DMA](0)/[ DMA]) against the reaction time is linear, and the molecular weight of the resulting PDMA increased linearly with the conversion. Within 3 h, the polymerization can reach almost 60% of conversion. PEO-b-PDMA copolymer with low polydispersity index (M-w/M-n approximate to 1.1) is obtained. Self-assembly of PEO-b-PDMA in selective solvents is also studied. It could self-assemble into micelles in methanol/acetone (1/10, v/v) solution. TEM analyses of the PEO-b-PDMA micelles with narrow size distribution revealed that their size and shape depend much on the copolymer composition.

Aggregation behavior of amphiphilic D-pi-A molecules bearing recognition group

Aggregation behavior of two amphiphilic D-pi -A molecules bearing barbituric acid as both recogniton group and electron-drawing substituent, 5-(4-dodecyl oxybenzylidene)-(1H, 3H)-2,4,6-pyrimidine trione (PB12) and 5-(4-N,N-didodecyl aminobenzylidene)-(1H,3H)-2,4,6-pyrimidine trione (AB(12)) was studied by UV-visible, fluorescence, and surface voltaic spectroscopies (SPS). The experimental results indicate that PB12 tends to form J-aggregate and AB(12) tends to form H-aggregate under increasing concentration. An intramolecular twisted charge transfer (TICT) emission around 500 nm is observed when J-aggregate is formed between PB12 molecules, and an excimer emission around 600 nm is observed when H-aggregate is formed between AB(12) molecules.