dominant bandgap emission at 310 nm, along with several higher-energy emissions due to impurity phases.In conclusion, well-defined [ZnSe](DETA) 0.5 nanobelts have been synthesized successfully by tuning the composition of a ternary solution made of DETA, hydrazine hydrate, and deionized water. We find that an appropriate amount of hydrazine hydrate is essential for the formation of elegant [ZnSe](DETA) 0.5 nanobelts. While the optical properties of the nanobelts are not changed significantly, the ability to make these II-VI-based hybrid semiconductor nanostructure microparticles into nanocrystals with uniform shape and size is one step further towards the miniaturization of devices. In addition, surface modification or combination with other materials may introduce new phenomena and properties into this system with remarkable quantum size effects and expand their potential for applications in advanced semiconductor devices. ExperimentalAll chemicals were of analytical grade and used as received without further purification. In a typical procedure, ZnSO 4 ·7H 2 O (0.05 mmol) and Na 2 SeO 3 (0.05 mmol) were added into a mixed solution (35 mL) with a volume ratio of V N 2 H 4 ·H 2 O /V DETA /V H 2 O = 5:14:16 under stirring. The mixed solution was then transferred into a Teflon-lined autoclave (with a filling ratio of 80 %). The autoclave was closed and kept at 180°C for 12 h, and then cooled to room temperature naturally. The white floccules formed after the reaction were washed with distilled water and absolute ethanol, and dried under vacuum at 80°C for 6 h.XRD patterns of the products were obtained on a Japan Rigaku DMax-cA rotation anode X-ray diffractometer equipped with graphite monochromatized Cu Ka radiation (k = 1.54178 Å). TEM images were acquired on a Hitachi Model H-800 instrument at an accelerating voltage of 200 kV. UV-vis spectra were recorded on a Shimadzu UV-240 spectrophotometer at room temperature. PL spectra were measured on a Fluorolog3-TAU-P instrument at room temperature.
We report on the generation of assemblies comprising number density gradients of nanoparticles in two (2D) and three (3D) dimensions. These structures are fabricated by creating a surface-bound organic template which directs the spatial arrangement of gold nanoparticles. The 2D template is made of amine-terminated organosilane with a concentration gradient along the solid substrate. The 3D matrix comprises surface-anchored poly(acryl amide), whose molecular weight changes gradually on the specimen. In both cases, the composite is assembled at low pH, where the positively charged-NH + 3 groups within the organic scaffold attract negatively charged gold nanoparticles. We use a battery of experimental tools to determine the number density of particles along the gradient substrate and in the case of 3D structures also their spatial distribution. For 2D gradient assemblies, we show that gold nanoparticle coverage on the surface decreases gradually as the concentration of substrate-bound aminosilane decreases. The number of particles in the polymer brush/particle hybrid is found to increase with increasing polymer molecular weight. We show that for a given grafting density of polymer brush, larger particles predominantly stay near the brush-air interface. In contrast, smaller nanoparticles penetrate deeper into the polymer brush, thus forming a 3D structure. Finally, we discuss possible applications of these nanoparticle gradient assemblies.
A three‐step approach to tailor cell adhesion via surface‐grafted polymer gradients is shown in this image from the work of Genzer and co‐workers on p. 2802. Surface‐anchored polymer assemblies with gradients in polymer molecular weight and/or grafting density are first employed to tailor adsorption of the protein, which in turn governs the number density as well as the extent of spreading of osteoblastic cells. Increasing the surface coverage of the polymer results in a decrease in the amount of protein adsorbed, which causes a decrease in the number of cells adhered and a change in cell morphology.
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