2, Ecole Polytechnique Fédérale de Lausanne, Lausanne, , Switzerland
The ability to precisely control and combine the composition, size, shape and conformation of nanoscale building blocks represents a major challenge in current fabrication processes. Solution-based fabrication methods are particularly attractive due to their scalability, low cost, and mild operating conditions. While a high degree of size and shape control has been achieved during the last decades for the synthesis of nanoscale colloidal particles, the next challenge is to establish the knowledge and tools required to build arbitrarily designed hybrid 3D architectures with a high degree of placement control and material combination. In this respect, a promising strategy is to control solution-based growth at the nanoscale using scanning probes in liquid.
Our research focuses on the direct writing of functional metallic nanostructures using an electrochemical Atomic Force Microscope (AFM) as a nano-electrode in aqueous solutions containing metal salts, localizing electrochemical deposition in a 3D printing fashion. Our approach is to survey and control the phase formation and growth at the liquid/solid interface in electrodeposition with the AFM tip.
We investigate favourable parameters for local nucleation and growth, both numerically and experimentally. From the numerical point of view, we consider the physics of electrochemical and mass transport processes under DC and AC conditions. We match the deposition dynamics with the in-situ topography profiles of Cu-based structures as they grow (from 2D lines to 3D rods). As a first conclusion, we highlight the main parameters that define the writing resolution in 3 dimensions.
As an example of a functional metal structure, we fabricate a Cu plasmonic nanoantenna. The performance of the antenna is linked to the metal quality through plasmon damping effects. Reciprocally, we exploit the antenna performance as to understand how do the local electrochemical conditions affect the crystalline quality of the growth antenna.
Ultimately, this technique can be extended to different materials and morphologies, such as semiconducting and chiral structures. Moreover, scaling up the process is possible by means of mass parallelization. As such we envision this 3D-printing technique to be both useful for the manufacturing and rapid prototyping of novel light-matter nanodevices, as well as consider this a viable technique for large scale fabrication.