This project has earned different achievements that can be categorized into the following three categories: 1) theoretical and conceptual advances, 2) development of original methods and technologies, and 3) experimental achievements, as detailed below.
1) The theoretical advances include both analytical developments and numerical techniques. From a theoretical point of view, the most important achievements are a) The development of the theory for optical forces in the time domain and its utilization to demonstrate that both approaches proposed by Abraham and Minkowski for the optical momentum converge to the same value in the time domain. b) A better understanding of the concept of optical torque and its link to the multipoles supported by a nanostructure. This is central to rotary motions driven by optical fields and a profound consequence has been the discovery that a torque and the ensuing rotation can be caused not only by the spin angular momentum of light, but also by its orbital angular momentum. c) The study of van der Waals forces in confined geometries and the evidence of an equivalent for those dispersive forces to hot spots, as known in plasmonic systems.
2) Several original technological procedures have been developed for the fabrication of specific nanostructures. They include a) A recipe to stabilize nanostructures made in silver, which extends the range of plasmonic metals that can be used to produce strong optical fields in the visible spectrum. b) The stabilization of plasmonic electrodes with a very high geometrical (length/width) aspect ratio through an organic self-assembled monolayer that builds a solid link between substrate and structures, and can find applications in many other fields of nanotechnology. c) A particularly refined nanotechnology for the fabrication of optically-driven nanomotors, requiring over twenty different steps in the cleanroom and combining two of the main approaches to define nanostructures: lift-off and ion etching, as well as a collection of different dielectric and metallic materials. Remarkably, it reached a resolution better than 20 nm in the realized nanostructures, with an extremely high yield. Numerical techniques have also been developed, including d) The utilization of the surface integral equation technique to compute van der Waals forces caused by fluctuating dipoles in intricate geometries. e) The extensive use of machine learning for the generation of nanostructures with exceptional optical torques.
3) Important experimental achievements include a) The combination of optical forces with low frequency dielectrophoretic forces, enabling action at distance over different lengthscales. b) The detailed study of the relationship between an optically trap nanoparticle and its surrounding to explore a specific environment and its physico-chemical properties. c) The local polymerization and immobilization caused by an optically trapped plasmonic particle, providing another approach to manufacturing at the nanoscale in three dimensions. d) The realization of an optical nano-pump, as a disruptive concept that could find many applications where small amounts of chemicals must be delivered locally.
These results have been disseminated in very good peer-reviewed scientific journals and presented in many conferences, both live and on-line during the pandemic. The PI had been invited to numerous scientific conferences and seminars in universities to present the results of the project.
We also organized specific public events around the project, including the Swiss NanoConvention and a roundtable discussion between industry and academia on Innovation and manufacturing at the nanoscale. Key elements from Nanofactory were also introduced into the Microengineering curriculum at the Swiss Federal Institute of Technology Lausanne (EPFL), notably by increasing the number of credits devoted to nanotechnologies, sensing, manufacturing and optics during the third year of study, reaching approximately 200 students every year.
