Angle-Resolved Nanosphere Lithography:  Manipulation of Nanoparticle Size, Shape, and Interparticle Spacing

Abstract

This work presents a novel approach to fine-tuning the size, shape, and interparticle spacing of nanoparticles fabricated by nanosphere lithography (NSL). This approach, termed angle-resolved nanosphere lithography (AR NSL), is a variant of NSL that yields vastly different, and increasingly flexible, nanostructures. This is accomplished by controlling the angle, θ, between the surface normal of the sample assembly and the propagation vector of the material deposition beam. Comparison of experimental results to simulated nanoparticle array geometries generated using an analytical model show excellent qualitative agreement. Using AR NSL, we have demonstrated that it is possible to reduce in-plane nanoparticle dimensions by a factor of 4. This important result shows that it will be possible to achieve fabrication of nanoparticles with precision control of their dimensions in a size regime comparable with the industry standard electron beam lithography. AR NSL provides a massively parallel, rather than serial, nanoparticle fabrication method. One limitation of the AR NSL technique is the inability to pattern an entire substrate with a single nanoparticle geometry without control of the mask domain orientation. While the presence of multiple domains in any given colloidal crystal mask complicates the fabrication of large-area homogeneous nanoparticle arrays, this quality is, in fact, useful in laboratory scale experiments requiring a diverse set of nanostructure features on a single sample. The precision tuning of nanoparticle size, shape, and spacing that can be achieved in a massively parallel, materials/substrate general, and inexpensive fashion using AR NSL is likely to have significant impact on the fields of surface-enhanced spectroscopy, near field optical microscopy, nanoscopic object manipulation, and chemical/biological sensing.

Controlled Evaluation of Silver Nanoparticle Dissolution Using Atomic Force Microscopy

“…Assessing the potential risk of the release of AgNPs to the environment requires that exposure be accounted for in addition to toxicity. 2,28 Not only must realistic concentrations of AgNPs be predicted for various environmental compartments, but the most likely forms of nanosilver in those compartments must also be determined. In order to fully account for exposure risks, much more data is needed about the release, transport, and fate of AgNPs in the environment.…”

“…Modeling efforts by Nowack and coworkers, on the other hand, only considered nanosilver in their risk assessments, either neglecting silver dissolution or assuming that dissolved silver was eliminated from the system. 28,29 Mueller and Nowack ignored all environmental transformations, including dissolution, aggregation, and sedimentation. 28 Gottschalk et al attempted to account for the effects of dissolution and sedimentation on AgNP fate, but they disregarded any other environmental transformations.…”

“…28,29 Mueller and Nowack ignored all environmental transformations, including dissolution, aggregation, and sedimentation. 28 Gottschalk et al attempted to account for the effects of dissolution and sedimentation on AgNP fate, but they disregarded any other environmental transformations. 29 The authors admitted that they were forced to make these assumptions due to the lack of reliable data, which highlights the need for studies on the environmental transformations of AgNPs.…”

“…93 Even more control over lateral dimensions, interparticle spacing, and particle shape can be achieved by varying the angle of the substrate relative to the direction of the material deposition beam. 86,99 Particle morphology can also be controlled by additional processing of the particle array. For example, truncated tetrahedral particles have been converted into hemispherical particles by electrochemical and thermal processing.…”

“…27 NSL facilitates control over size, shape, and interparticle spacing for a number of different materials and substrates. [28][29][30][31] In this study, the dissolution rates of NSLproduced AgNPs were quantified by atomic force microscopy (AFM), which gave a detailed description of changes in particle size and shape as a function of time and NaCl concentration.…”