This proposal aims to tackle important issues in a research field known as 'plasmonics', based on the optics of tiny 'lumps' of metal. These have great potential for many applications relevant to our daily lives, with the promise of significant impact on related sciences, industry (and therefore the economy) and the well-being of our society.
Optics is one of the most ancient sciences, but also one of the most important today. The science of optics has been 'shrinking'. Historically, significant optical phenomena were only noticeable at the macroscale length, which are normally larger than one millimetre (so are distinguishable to the human eye). Today many optoelectronic devices have basic elements at the microscale length (1 micrometre is one thousandth of a millimetre), such as the light-emitting elements in most TV screens, computers and mobile phone displays and the core diameter of optical fibres. Scientists are now studying optics at even smaller lengths, the nanometre scale (1 nanometre is one billionth of a metre. Compared with a metre, a nanometre being the head of a pencil compared with the Earth), termed nano-optics. This proposal aims to tackle some key issues in one very important branch of nano-optics, namely plasmonics, which studies the optical properties of tiny metal 'lumps' approximately a few tens to hundreds of nanometres in diameter (so-called nanoparticles). Metal nanoparticles can exhibit a range of extraordinary optical properties not seen in the bulk material. For example, when two metal nanoparticles are placed very close to each other, leaving only a tiny gap (a few nanometres or less), which can be hundreds of times smaller than the smallest focal spots achievable with a state-of-the-art modern optical microscope. Furthermore, the power of the light inside the nano-gap can be millions of times stronger than that of the incident light. Such an extreme concentration and enhancement of light is at the heart of the research field of plasmonics, central to many very important applications in a wide range of aspects that will have an impact on society, such as energy generation, imaging, data storage, computing, sensing, health, security and defence, to name a few.
However, some key issues concerning how light interacts with metals at such close distances remain unsolved. Classical theories that have been so successful in explaining almost every optical phenomenon in our daily life, have encountered difficulty when trying to properly explain the optics inside nanometre and sub-nanometre scale junctions. At such close distances, quantum mechanical effects and some other peculiar effects called "nonlocality" play significant roles. Although some important new theories have been developed recently, there is an urgent need to validate them by rigorous experiment.
This proposal aims to provide a systematic investigation of how light behaves when squeezed between extremely small gaps. We will create robust junctions that are stable even at distances smaller than one nanometre, through a range of advanced technologies, including using atomically-thin two-dimensional materials, such as graphene. We will even create a tuneable gap at the sub-nanometre-scale distance, an extremely challenging task (imagine that the gap is only a few atoms wide!) but significantly important. This will provide an unprecedented detailed investigation to crack the secret of how light behaves at the deepest level of a nano-world. The proposed research will lead to the development of a number of technologies that are hugely important to our society, such as developing ultrasensitive molecular sensors (which can be used for the detection of tiny amounts of substances, even single molecules, e.g., chemical and biological contaminants in food, viruses in blood for early disease diagnosis, drugs, and explosives etc) and novel optoelectronic industry.
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