Rational route to fabrication of uni-dimensional surface gradients presenting stochastic and periodic arrangement of nanoparticles

Nanostructure gradients exhibiting graded variation in a nanostructure geometric variable carry high promise as tool for parallel and high-throughput optimization of a range of on-chip devices and functional interfaces. The capabilities to fabricate nanostructure gradients, with desired size and slope, while preserving scalability and operational flexibility is however limited. In this direction, we demonstrate a simple and flexible approach to prepare nanostructure gradients, subjecting a functionalized chip for the adsorption of nanoparticles or ions from aqueous media, with varying durations of exposure along the length of the chip. The configuration is similar to dip-coating, however, with the solution front moving relative to a stationary substrate. The flow rate, dimension of the chamber, and the functional layers are shown as simple handles to achieve the desired gradient morphology. Gradients with stochastic as well as periodic organization of nanoparticle assemblies are demon-strated through the choice of different functional layers underneath the nanoparticle layer, viz. aminosilane monolayers, cross-linked plasma polymer and copolymer templates. The approach paves way to rationally designed gradients, benefitting from the significant flexibility in the choice of operational conditions, without specific constraints on the size of the substrates that can be used.