PEAR: A super-resolution imaging technique throughactive plasmonics

The research conducted here firstly develops an active plasmonic element capable of local electric near-field modulation at a known frequency. The element is then used as a core part of PEAR, Plasmonically Electronically Addressable super-Resolution, a new diffraction-limit-breaking imaging technology. PEAR has been proven to work as an imaging technology with proof-of-concept images within this thesis. Key advantages of PEAR are that it is a completely deterministic method, has strong multi-channel capabilities, and its resolution is tied to the physical size of the active plasmonic emitter. Active plasmonic elements can allow external control of a Surface Plasmon Polariton (SPP), which is a highly spatially confined electric field formed on a metal dielectric interface. Confinement, in this case, is perpendicular to the interface and the SPP propagates along it. The active plasmonic element can modulate the intensity of this local electric field in a spatially confined area in the vicinity of this element. The modulation is caused by an electric current heating a metal constriction causing changes in the electrical permittivity. The active plasmonic element is investigated through fully featured simulations using Finite-Difference Time-Domain (FDTD) and Finite Element method (FEM) techniques. These characterise and optimise the modulation that the element uses. In this body of work Atomic Force Microscope (AFM) lithography was used to shape arbitrary nanostructures. Simulations were hence validated through experiments. Super-resolution techniques are an integral part of modern science especially the bio-medical field. Improvements to these imaging technologies are hugely impactful towards understanding key biological processes which leads to advances in medicine. The imaging technology developed here uses the active plasmonic element described, to out-couple near-field information into the far-field since information beyond the diffraction-limit cannot be resolved in the far-field. Hence, lock-in amplification is used with the frequency modulation on the plasmonic element, as a reference, to spatially map the source of the sub-diffraction limited data. Due to the evanescent character of SPPs (approximately 100 nm) the sample must be close to the active plasmonic element. The ability to modulate a particular emitter with a unique frequency means multiple elements can be used simultaneously, even within the same sub-wavelength area. Building a large array of the active plasmonic elements makes this imaging method truly groundbreaking because it is completely deterministic, while still having vast multi-channel capabilities. A dual element 'array' is demonstrated experimentally. A scalable mass fabrication design is shown along with intermediate designs for arrays of less than 100 elements. Proof of concept images for this method are demonstrated and compared to a complimentary imaging method.