Abstract
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 demonstrated 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.
Highlights
Nanoscale devices and interfaces that take advantage of unique op tical, electronic and surface behaviour of engineered nanostructures have been leveraged across a range of applications including sensors, data storage, self-cleaning interfaces, energy storage or harvesting, and bio interfaces
The volume change can be operationally controlled by both flow rate and the size of the vial (Fig. 1b) providing large flexibility in the choice of the exposure rates, irrespective of the dimension of the sample (Fig. 1c)
The configuration further ensures that the chamber remains closed throughout the process, which is helpful to reduce impact of evaporation
Summary
Nanoscale devices and interfaces that take advantage of unique op tical, electronic and surface behaviour of engineered nanostructures have been leveraged across a range of applications including sensors, data storage, self-cleaning interfaces, energy storage or harvesting, and bio interfaces In all these cases, the geometric attribute that delivers the optimal functionality is identified by systematic investigations that map the impact of multiple geometry variables and drawing robust correla tion between nanostructure and functionality. The task is simplified by resorting to combinatorial approaches that rely on simultaneous and parallel execution of multiple experiments at one time Prominent examples in this direction includes microarrays that spatially separate the variables into addressable regions, and spatial gradients, that continuously vary a certain variable as a function of distance on a surface. Spatial gradients on the other hand are better disposed for a graded change in the variable investigated
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