This feature article describes the progress realized over the past half century in the field of surface-bound gradient structures created on or from soft materials (oligomers and/or polymers), or those enabling the study of the behavior of soft materials. By highlighting our work in the field and accounting for the contribution of other groups, we emphasize the exceptional versatility of gradient assemblies in facilitating fast screening of physicochemical phenomena, acting as "recording media" for monitoring a process, and playing a key role in the design and fabrication of surface-bound molecular and macromolecular motors capable of directing a transport phenomenon.

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.

We report on preparing assemblies of gold nanoparticles with continuous gradients in number density on flat silica-covered substrates. The methodology consists of (i) first forming a one-dimensional molecular gradient of amino groups (−NH2) on the substrate by vapor deposition of amine-terminated silane molecules, followed by (ii) attachment of gold nanoparticles to −NH2 functional groups by immersing the substrate in a colloidal gold solution. Experiments using atomic force microscopy reveal that the number density of nanoparticles on the substrate varies continuously as a function of the position on the substrate. Near-edge X-ray absorption fine structure studies confirm that the nanoparticle number density gradient is closely correlated with the concentration gradient of −NH2 groups anchored to the substrate. We demonstrate that the number density of nanoparticles within the gradient and the length of the gradient can be tuned by controlling the vapor diffusion of silane molecules. In addition we show that this simple methodology can be further extended to create double gradients, thus producing “a valley in nanoparticle concentration”.