Memristor-based LSTM neuromorphic circuits for offshore wind turbine blade fault detection

The UK offshore wind industry is rapidly growing to meet CO2 emission targets. However, the main drawback of the offshore environment is the increased cost of maintenance. Artificial Neural Networks (ANN) show great potential to reduce this cost. Long Short-Term Memory (LSTM) is a form of Recurrent Neural Network (RNN) that shows promising results in solving time series-based problems, making them ideally suited for wind turbine condition monitoring. A dedicated circuit for a LSTM-based ANN that uses memristors will allow for more power efficient and faster computation, whilst being able to overcome the von Neumann bottleneck

Hybrid FIB milling strategy for the fabrication of plasmonic nanostructures on semiconductor substrates

The optical properties of plasmonic semiconductor devices fabricated by focused ion beam (FIB) milling deteriorate because of the amorphisation of the semiconductor substrate. This study explores the effects of combining traditional 30 kV FIB milling with 5 kV FIB patterning to minimise the semiconductor damage and at the same time maintain high spatial resolution. The use of reduced acceleration voltages is shown to reduce the damage from higher energy ions on the example of fabrication of plasmonic crystals on semiconductor substrates leading to 7-fold increase in transmission. This effect is important for focused-ion beam fabrication of plasmonic structures integrated with photodetectors, light-emitting diodes and semiconductor lasers

Long-Range and High-Efficiency Plasmon-Assisted Förster Resonance Energy Transfer

The development of a long-range and efficient Förster resonance energy transfer (FRET) process is essential for its application in key enabling optoelectronic and sensing technologies. Via controlling the delocalization of the donor’s electric field and Purcell enhancements, we experimentally demonstrate long-range and high-efficiency Förster resonance energy transfer using a plasmonic nanogap formed between a silver nanoparticle and an extended silver film. Our measurements show that the FRET range can be extended to over 200 nm while keeping the FRET efficiency over 0.38, achieving an efficiency enhancement factor of ∼108 with respect to a homogeneous environment. Reducing Purcell enhancements by removing the extended silver film increases the FRET efficiency to 0.55, at the expense of the FRET rate. We support our experimental findings with numerical calculations based on three-dimensional finite difference time-domain calculations and treat the donor and acceptor as classical dipoles. Our enhanced FRET range and efficiency structures provide a powerful strategy to develop novel optoelectronic devices and long-range FRET imaging and sensing systems

Stark Effect Control of the Scattering Properties of Plasmonic Nanogaps Containing an Organic Semiconductor

The development of actively tunable plas-monic nanostructures enables real-time reconfigurable and on demand enhancement of optical signals. This is an essential requirement for a wide range of applications such as sensing and nanophotonic devices, for which electrically driven tunability is required. By modifying the transition energies of a material via the application of an electric field, the Stark effect offers a reliable and practical approach to achieve such tunability. In this work, we report on the use of the Stark effect to control the scattering response of a plasmonic nanogap formed between a silver nanoparticle and an extended silver film separated by a thin layer of the organic semiconductor PQT-12. The plasmonic response of such nano-scattering sources follows the quadratic stark shift. Additionally, our approach allows to experimentally determine the polarizability of the semiconductor material embedded in the nanogap region, offering a new approach to probe the excitonic properties of extremely thin semi-conducting materials such as 2D materials under applied external electric field with nanoscale resolution

Plasmons Enhancing Sub-Bandgap Photoconductivity in TiO<inf>2</inf> Nanoparticles Film

The coupling between sub-bandgap defect states and surface plasmon resonances in Au nanoparticles and its effects on the photoconductivity performance of TiO2 are investigated in both the ultraviolet (UV) and visible spectrum. Incorporating a 2 nm gold nanoparticle layer in the photodetector device architecture creates additional trapping pathways, resulting in a faster current decay under UV illumination and a significant enhancement in the visible photocurrent of TiO2, with an 8-fold enhancement of the defects-related photocurrent. We show that hot electron injection (HEI) and plasmonic resonance energy transfer (PRET) jointly contribute to the observed photoconductivity enhancement. In addition to shedding light on the below-band-edge photoconductivity of TiO2, our work provides insight into new methods to probe and examine the surface defects of metal oxide semiconductors using plasmonic resonances

Probing the molecular orientation of a single conjugated polymer via nano-gap SERS

Determining the molecular orientation at the single molecule level is of key importance for a wide range of applications ranging from molecular electronic devices to biomedical applications. In this work surface-enhanced Raman scattering (SERS) was used to probe the light-emitting conjugated polymer F8-PFB at the single molecule level using nanoparticles on an extended metallic film nanogap. The directional field enhancement of the nanogap combined with density functional theory (DFT) calculations was used to determine the orientation of the molecule. This analysis revealed that the spin-coated conjugated polymer preferentially aligns its molecular chains parallel to the metallic substrate. The integration of this approach in nanofabrication and synthesis will have a profound impact on different fields ranging from molecular electronic devices to biomedical applications

Optically-programmable nonlinear photonic component for dielectric-loaded plasmonic circuitry

We demonstrate both experimentally and numerically a compact and efficient, optically tuneable plasmonic component utilizing a surface plasmon polariton ring resonator with nonlinearity based on trans-cis isomerization in a polymer material. We observe more than 3-fold change between high and low transmission states of the device at milliwatt control powers (?100 W/cm2 by intensity), with the performance limited by switching speed of the material. Such plasmonic components can be employed in optically programmable and reconfigurable integrated photonic circuitry

Magnetic Mode Coupling in Hyperbolic Bowtie Meta-Antennas

Hyperbolic metaparticles have emerged as the next step in metamaterial applications, providing tunable electromagnetic properties on demand. However, coupling of optical modes in hyperbolic meta-antennas has not been explored. Here, we present in detail the magnetic and electric dipolar modes supported by a hyperbolic bowtie meta-antenna and clearly demonstrate the existence of two magnetic coupling regimes in such hyperbolic systems. The coupling nature is shown to depend on the interplay of the magnetic dipole moments, controlled by the meta-antenna effective permittivity and nanogap size. In parallel, the meta-antenna effective permittivity offers fine control over the electrical field spatial distribution. Our work highlights new coupling mechanisms between hyperbolic systems that have not been reported before, with a detailed study of the magnetic coupling nature, as a function of the structural parameters of the hyperbolic meta-antenna, which opens the route toward a range of applications from magnetic nanolight sources to chiral quantum optics and quantum interfaces

NIR-quantum dots in biomedical imaging and their future

Fluorescence imaging has gathered interest over the recent years for its real-time response and high sensitivity. Developing probes for this modality has proven to be a challenge. Quantum dots (QDs) are colloidal nanoparticles that possess unique optical and electronic properties due to quantum confinement effects, whose excellent optical properties make them ideal for fluorescence imaging of biological systems. By selectively controlling the synthetic methodologies it is possible to obtain QDs that emit in the first (650–950 nm) and second (1000–1400 nm) near infra-red (NIR) windows, allowing for superior imaging properties. Despite the excellent optical properties and biocompatibility shown by some NIR QDs, there are still some challenges to overcome to enable there use in clinical applications. In this review, we discuss the latest advances in the application of NIR QDs in preclinical settings, together with the synthetic approaches and material developments that make NIR QDs promising for future biomedical applications