Role Of Convection Flow On The Pattern Formation In The Drying Process Of Colloidal Suspension

We study the macroscopic drying patterns of aqueous suspensions of colloidal silica spheres. It was found that convection strength can influence pattern formation. Uniformed films are obtained at weaker convection strength. In addition, we make clear that it is not reasonable to discuss individually the effect of temperature and humidity on the colloid self-assembly. The physical mechanism is that these factors have relationship with the evaporation rate, which can affect the convection strength.

Influence Of Gravity On Structure Of Colloidal Crystal Using Simulated Microgravity

Liquid mixtures of water and deuterium oxide as the liquid phase, were used to match the density of charged colloidal particles. Kossel diffraction method was used to detect the crystal structures. The experiments under the density-matched (g=0) and unmatched (g=1) conditions are compared to examine the influence of gravity on the crystal structures formed by self-assembly of 110 nm (in diameter) polystyrene microspheres. The result shows that die gravity tends to make the lattice constants of colloidal crystals smaller at lower positions, which indicates that the effect of gravity should be taken into account in the study of the colloidal crystals.

Fabrication of conductive metallized nanostructures from self-assembled amphiphilic triblock copolymer templates: Nanospheres, nanowires, nanorings

Various metallized nanostructures (such as rings, wires with controllable lengths, spheres) have been successfully fabricated by coating metallic nanolayers onto soft nanotemplates through simple electroless methods. In particular, bimetallic nanostructures have been obtained by using simple methods. The multiple functional polymeric nanostructures, were obtained through the self-assembly of polystyrene/poly(4-vinyl pyridine) triblock copolymer (P4VP-b-PS-b-P4VP) in selective media by changing the common solvent properties. By combining field emission scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) characterization, it was confirmed that polymer/metal and bimetallic (Au@Ag) core-shell nanostructures could be achieved by chemical metal deposition method.

Electrochemical detection of DNA immobilized on gold colloid particles modified self-assembled monolayer electrode with silver nanoparticle label

The target DNA was immobilized successfully on gold colloid particles associated with a cysteamine monolayer on gold electrode surface. Self-assembly of colloidal An onto a cysteamine modified gold electrode can enlarge the electrode surface area and enhance greatly the amount of immobilized single stranded DNA (ssDNA). The electrontransfer processes of [Fe(CN)(6)](4)-/[Fe(CN)(6)](3-) on the gold surface were blocked due to the procedures of the target DNA immobilization, which was investigated by impedance spectroscopy. Then single stranded target DNA immobilized on the gold electrode hybridized with the silver nanoparticle-oligonucleotide DNA probe, followed by the release of the silver metal atoms anchored on the hybrids by oxidative metal dissolution, and the indirect determination of the released solubilized Ag-1 ions by anodic stripping voltammetry (ASV) at a carbon fiber microelectrode. The results show that this method has good correlation for DNA detection in the range of 10-800 pmol/1 and allows the detection level as low as 5 pmol/1 of the target oligonucleotides.

Multilayer assemblies of colloidal ZnS doped with silver and polyelectrolytes based on electrostatic interaction

Multilayer assemblies of silver doped ZnS colloid and polycation were fabricated by a self-assembly technique exploiting electrostatic interaction. UV/Vis spectra showed the uniform deposition process and X-ray photoemission spectroscopy (XPS) confirmed the coexistence of silver. It was found that the emission spectra of the silver doped ZnS colloid red-shifted to 528 nm comparing with undoped ZnS colloid. However, the most important finding was that the luminescence intensity of doped ZnS assembled in films was much stronger than that of undoped ZnS in films and that of doped ZnS in the spin-casting film. The mechanism of the enhancement luminescence was discussed. (C) 1998 Elsevier Science S.A. All rights reserved.

Micro- and macro-tribological study on a self-assembled dual-layer film

A novel self-assembled dual-layer film as apotential excellent lubricant for micromachines was successfully prepared on single-crystal silicon substrate by chemical adsorption of stearic acid (STA) molecules on self-assembled monolayer of 3-aminopropyltri

Electrochemical, spectroscopic and SPM evidence for the controlled formation of self-assembled monolayers and organised multilayers of ferrocenyl alkyl thiols on Au(111)

Organised multilayers were formed from the controlled self-assembly of ferrocene alkyl thiols on Au(111) surfaces. The control was accomplished by increasing the concentration of the thiol solutions used for the assembly. Cyclic voltammetry, ellipsometry, scanning probe microscopy (STM and AFM) and in situ FTIR spectroscopy were used to probe the differences between mono- and multilayers of the same compounds. Electrochemical desorption studies confirmed that the multilayer structure is attached to the surface via one monolayer. The electrochemical behaviour of the multilayers indicated the presence of more than one controlling factor during the oxidation step, whereas the reduction was kinetically controlled which contrasts with the behaviour of monolayers, which exhibit kinetic control for the oxidation and reduction steps. Conventional and imaging ellipsometry confirmed that multilayers with well-defined increments in thickness could be produced. However, STM indicated that at the monolayer stage, the thiols used promote the mobility of Au atoms on the surface. It is very likely that the multilayer structure is held together through hydrogen bonding. To the best of out knowledge, this is the first example of a controlled one-step growth of multilayers of ferrocenyl alkyl thiols using self-assembly techniques.

带电胶体粒子结晶过程的实验研究

利用带电单分散聚苯乙烯胶体粒子,通过自组装机理,制备了体积百分比为4·8%的具有多晶结构的胶体晶体,并用Kossel衍射技术和紫外可见分光光度计分别对晶体的生长过程进行了监测.通过对Kossel的图像分析检测不同阶段相应的晶格结构,发现胶体结晶过程晶体结构演变顺序为由液态—随机层结构—堆无序结构—面心立方孪晶结构到面心立方结构.定量地确定了结晶过程中晶体不同晶面的晶面间距和晶体的晶格常数,通过紫外可见分光光度计测量的晶体透射谱图,计算得到111晶面的晶面间距和晶体的晶格常数,与用Kossel衍射技术得到的结果相一致,还发现随样品放置时间的延长,衰减峰变窄和加深,并向短波方向移动,对应着晶体的晶格常数减小的现象.

Self-organized hexagonal ordering of quantum dot arrays

We report a structure of (In, Ga)As/GaAs quantum dots which are vertically correlated and laterally aligned in a hexagonal way thus forming three-dimensionally ordered arrays. The growth pathway is based on a mechanism of self-assembly by strain-mediated multilayer vertical stacking on a planar GaAs(100) substrate, rather than molecular-beam epitaxy on a prepatterned substrate. The strain energy of lateral island-island interaction is minimum for the arrangement of hexagonal ordering. However, realization of hexagonal ordering not only depends on a complicated trade-off between lateral and vertical island-island interaction but is also related to a delicate and narrow growth kinetics window.

Micro-mould method for self-assembling three-dimensional opal photonic crystals

By vertical sedimentation, silica micro-spheres were grown in different shapes of concave micro-zones which were etched on a (100) p-silicon substrate. The following were found: this method can effectively raise the quality of films by avoiding cracks; the geometry of the micro-zones affects the sediment of the film; regular hexagons and triangles best facilitate the growth of photonic crystals. This method is practical for its ability to fabricate self-assembly photonic crystals in previously designed small areas.

Symmetry in the diagonal self-assembled InAs quantum wire arrays on InP substrate

Diagonal self-assembled InAs quantum wire (QWR) arrays with the stacked InAs/In0.52Al0.48As structure are grown on InP substrates, which are (001)-oriented and misoriented by 6degrees towards the [100] direction. Both the molecular beam epitaxy (MBE) and migration enhanced epitaxy (MEE) techniques are employed. Transmission electron microscopy reveals that whether a diagonal InAs QWR array of the stacked InAs/InAlAs is symmetrical about the growth direction or not depends on the growth method as well as substrate orientation. Asymmetry in the diagonal MEE-grown InAs QWR array can be ascribed to the influence of surface reconstruction on upward migration of adatoms during the self-assembly of the InAs quantum wires.

Two-dimensional ordering of self-assembled InxGal-xAs quantum dots grown on GaAs(311)B surfaces

Two-dimensional (2D) ordering of self-assembled InxGa1-xAs quantum dots (QDs) fabricated on GaAs(311)B surface by molecular beam epitaxy (MBE) are reported. The QDs are aligned into rows deferring from the direction of the misorientation of the substrate, and strongly dependent on the mole In content x of InxGa1-xAs solid solution. The ordering alignment deteriorates significantly as the In content is increased to above 0.5. The 2D ordering can be described as a centered rectangular unit mesh with the two sides parallel to [01 (1) over bar] and [(2) over bar 33], respectively. Their relative arrangement seems to be determined by a combination of the strongly repulsive elastic interaction between neighbouring islands and the minimization of the strain energy of the whole system. The ordering also helps to improve the size homogeneity of the InGaAs islands. Photoluminescence (PL) result demonstrates that QDs grown on (311)B have the narrowest linewidth and the strongest integrated intensity, compared to those grown on (100) and other high-index planes under the same condition. (C) 1999 Elsevier Science B.V. All rights reserved.

Two-dimensional ordering of self-assembled InxGa1-xAs quantum dots grown on GaAs(311)B surfaces

The two-dimensional (2D) ordering of self-assembled InxGa1-xAs quantum dots (QDs) fabricated on GaAs(3 1 1)B surface by molecular beam epitaxy (MBE) are reported. The QDs are aligned into rows differing from the direction of the misorientation of the substrate, and strongly dependent on the mole In content x of InxGa1-As-x solid solution. The ordering alignment deteriorates significantly as the In content is increased to above 0.5. The 2D ordering can be described as a centered rectangular unit mesh with the two sides parallel to [0 1 (1) over bar] and [(2) over bar 3 3], respectively. Their relative arrangement seems to be determined by a combination of the strongly repulsive elastic interaction between the neighboring islands and the minimization of the strain energy of the whole system. The ordering also helps to improve the size homogeneity of the InGaAs islands. The photoluminescence (PL) result demonstrates that QDs grown on (3 1 1)B have the narrowest linewidth and the strongest integrated intensity, compared to those on (1 0 0) and other high-index planes under the same condition. (C) 1999 Elsevier Science B.V. All rights reserved.

Structural and optical characteristics of self-organized InAs quantum dots grown on GaAs (3 1 1)A substrates

Structural and optical investigations of InAs QDs grown on GaAs (3 1 1)A by molecular beam epitaxy (MBE) were reported. InAs/GaAs (3 1 1)A QDs with nonconventional, faceted, arrowhead-like shapes aligned in the [ - 2 3 3] direction have been disclosed by AFM image. Low defect and dislocation density on the QDs interfaces were indicated by the linear dependence of photoluminescence (PL) intensity on the excitation power. The fast red shift of PL energy and the monotonic decrease of FWHM with increasing temperature were observed and explained by carriers being thermally activated to the energy barrier produced by the wetting layer and then retrapped and recombined in energetically low-lying QDs states. (C) 1999 Elsevier Science B.V. All rights reserved.

Symmetry in the diagonal self-assembled InAs quantum wire arrays on InP substrate

Diagonal self-assembled InAs quantum wire (QWR) arrays with the stacked InAs/In0.52Al0.48As structure are grown on InP substrates, which are (001)-oriented and misoriented by 6degrees towards the [100] direction. Both the molecular beam epitaxy (MBE) and migration enhanced epitaxy (MEE) techniques are employed. Transmission electron microscopy reveals that whether a diagonal InAs QWR array of the stacked InAs/InAlAs is symmetrical about the growth direction or not depends on the growth method as well as substrate orientation. Asymmetry in the diagonal MEE-grown InAs QWR array can be ascribed to the influence of surface reconstruction on upward migration of adatoms during the self-assembly of the InAs quantum wires.