Researchers create circuits that operate at ‘hundreds of terahertz’

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Circuits that are said to operate at hundreds of terahertz have been designed and fabricated by researchers at the National University of Singapore. The team says its work has the potential to revolutionise high speed electronics, nanoscale optoelectronics and nonlinear optics.

The development is based on a new physical process called quantum plasmonic tunnelling. Current photonic elements are large, but operate at frequencies of 100THz, while current nanoelectronic devices are much smaller, making it difficult to combine the properties of both. According to researchers, it has long been known that light can interact with certain metals and can be captured in the form of plasmons – ultra fast oscillations of electrons that can be manipulated at the nanoscale. Quantum plasmon modes have been predicted to occur at atomic scales and have been difficult to investigate. In its study, the research team demonstrated that quantum plasmonics is possible at scales that are useful for real applications, then fabricated an element of a molecular electronic circuit using two plasmonic resonators. These structures, which can capture light in the form of plasmons, are bridged by a single molecule thick layer that switches on the quantum plasmonic tunnelling effects, enabling the circuits to operate at terahertz frequencies. The work was led by Assistant Professor Christian Nijhuis from the National University of Singapore's Faculty of Science and Dr Bai Ping and Dr Michel Bosman from A*STAR. Dr Bosman used advanced electron microscopy techniques to visualise and measure the optoelectronic properties of these structures at nanometre resolution. The measurements revealed the existence of the quantum plasmon mode and that its speed could be controlled by varying the molecular properties of the devices. By performing quantum corrected simulations, Dr Bai confirmed that quantum plasmonic properties could be controlled in the molecular electronic devices at high frequencies. Asst Prof Nijhuis said: "We are excited by the new findings. Our team is the first to observe the quantum plasmonic tunneling effects directly. This is also the first time that a research team has demonstrated theoretically and experimentally that very fast switching at optical frequencies are possible in molecular electronic devices." The researchers will now address the integration of these devices into real electronic circuits.