Epsilon-near-zero metamaterials for optoelectronic applications

Metamaterials;Optoelectronics

Li, Xin ; Di Falco, Andrea ; Di Falco, Andrea

University:University of St Andrews

Department:Physics & Astronomy (School of)

关键词: Metamaterials;    Optoelectronics;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/18938/XinLiPhDThesis.pdf?sequence=2&isAllowed=y

来源: DR-NTU

【 摘 要 】

My PhD is focused on the design, fabrication and optoelectronic applications of epsilon-near-zero(ENZ) metamaterials (MMs), which have vanishing real part of the permittivity andsupport fascinating optical effects, including light squeezing, sub-wavelength imaging, enhanceddirective emission and enhanced non-resonant optical nonlinearity. Different approaches havebeen developed to realise ENZ media, such as tuning the modal dispersion in narrow plasmonicchannels, exploiting the natural dispersion of transparent conductive oxides and creating compositestructures with metals and dielectrics. As a platform with exotic physical properties, ENZ mediaalso exhibit enormous potentials in combination with tunability and various nanofeatures in thephotonic and plasmonic regimes.This thesis demonstrates two approaches to achieve the ENZ condition. One method is to stackmetal (Ag) and dielectric (SiO2) layers periodically at sub-wavelength scales. The resulting materialbehaves as an effective medium with an average permittivity close to zero, and we show thatthis ENZ medium can enhance the emission of quantum dots. This approach generally requiresnanofabrication techniques developed for flat and rigid substrates, for example, the electron beamevaporation, which are not always applicable to micro- and macroscopic devices with arbitraryshapes. To surpass these limitations, we design and experimentally demonstrate an optical freestanding and low-loss ENZ membrane in the visible range, by layering polymer (SU-8) and Agnano-layers. Additionally, we propose a method to introduce both flexibility and electrical tunabilityinto ENZ media by replacing the metal layer with a 2D material, graphene, in the multilayer model.The other way to obtain an ENZ response is using natural materials which operate in proximityof their plasma frequency, typically here the indium tin oxide (ITO) at the near-infraredrange. The ITO thin films are deposited using radio frequency magnetron sputtering, and theirpermittivities are manipulated via controlling fabrication parameters. We succeed in sweeping thezero-permittivity frequency of ITO media by controlling the gas recipe and deposition temperatureduring the sputtering process. To obtain specific optical responses, the ENZ ITO thin films aredesigned to be combined with different photonic features, including nanoantenna on microsphereand nanohelix, associated with a direct fabrication approach based on electron beam induceddeposition (EBID).Furthermore, this thesis extends the research range by realising the photonic trimming ofquantum emitters via various metallic nanofeatures fabricated directly using EBID method. Webelieve that the interaction of ENZ MMs with EBID approach offers an opportunity to create hybridENZ platforms for optoelectronic applications.