Adaptive and active optics grant the ability to correct for aberrations, focus and zoom factors changes, and compensate for environmental conditions. Hugely important in physical optics such as high resolution imaging and ground-based astronomy. Presented here is an adaptable lens and mirror technology capable of a full range of focal lengths and shapes. Using transparent oxides and the joule heating effect, local temperature changes can be induced to cause material expansion in a predefined shape based on the thermal distribution. By creating a constriction in the conductive layer adding resistance to the material and creating a localised heating element on the order of millimetres and below in scale. Actively changing the optical systems can be realised on the millisecond timescale additionally allowing an almost arbitrary lens shape as well as variable focal length. Similar effects can be exploited to create a deformable mirror where the active layer is a metallic reflector, such as aluminium or silver, and this layer is used to deliver heat using the same effects. Using this localised heating, focal lengths from infinity to a few centimetres can be achieved through highly expansive substrates and minimal heating and energy usage.
A multitude of such elements can be constructed in such a way to provide a micro-lens array of different focal lengths allowing a field of view with simultaneous focusing on several objects at once for imaging applications. These elements can also be combined over a larger area to create astronomy grade deformable mirrors. The heated areas can be freely designed to any desired shape such as space filling hexagons and create an unconventional adaptive optics systems with advantages over conventional systems.
The capability to actively control the formation of Surface Plasmon Polaritons (SPPs) by means of temperature changes is one of the base working principles for active plasmonic devices, sensors and imaging systems. In order to exploit this idea, it is necessary to have a very in-depth knowledge of the changes induced by heating in the optical properties of plasmonic materials in real operational conditions. Previous studies have tracked the influence of temperature on plasmonic materials’ refractive indices, but data are usually acquired with large temperature steps (≈ 100°C - 300°C), and don’t always focus on extracting a precise relationship between optical constants and temperature in non-ideal environments, assuming the a very high purity of the materials involved and a controlled atmosphere. This research aims to fill the gap in the existing literature by means of a systematic approach, involving both a temperature-controlled Surface Plasmon Resonance (SPR) acquisition setup capable of 1◦C steps and a computational approach to fit data and explain changes in the optical properties. To verify the influence of temperature changes on the localisation of the electric field itself, Finite Element Method (FEM) simulations using COMSOL Multiphysics are conducted. These simulations highlight the differences in systems at different temperatures in terms of electromagnetic field distribution.
Here, we apply a novel technique involving Joule-assisted active plasmonics to enhance the sensitivity of the well-established surface plasmon resonance (SPR) method. Typically, SPR curves are generated from an angularly resolved scan of the reflected light beam from a metal thin film – dielectric interface. Due to the sensitivity of Surface Plasmon Polaritons (SPPs), and confinement to the vicinity of the interface, they are an important utility in a variety of applications. In this work, a modified setup involving a heated active plasmonic bridge allows insight into the metal surface characteristics not seen through classical Attenuated Total Reflection (ATR) measurements. Here, a constriction in the metal acts as a microscale bridge which is heated, via the Joule effect, and whose temperature follows the cycle of an alternating current. Employing a lock-in amplifier, referenced to the applied sine wave, enables detection of the reflected light now modulated by the alternating current resulting in a change in the optical constants. This dynamic technique is more sensitive than the conventional ATR technique and hence is capable of detecting metal composition, surface chemistry, and morphology above the active plasmonic element. This has opened the door to enhance already highly sensitive SPR devices currently on the market. In this study, we focus on the phase relationship between the Joule heating of an active plasmonic device and demonstrate that the laser spot alignment is of crucial importance to reach optimal sensitivity.
The advancement of super-resolution techniques is essential to the progress of cell and molecular biology. This work presents an overview of the fundamentals and development of Plasmonic Electronically Addressable super-Resolution (PEAR) as a novel super-resolution technique. PEAR aims to improve on limitations faced by currently established methods. PEAR uses an active plasmonic element which is modulated by passing an electric current through the nanostructure, this modulated electric current causes changes in the electrical near field at the modulation frequency. Using a homodyne detection scheme, with the modulation frequency as a reference, sub-diffraction limit spatial information can be transferred into the far field. Recording changes in the modulated light levels allows an image of a sample’s surface to be constructed. PEAR offers a unique advantage over established methods. It ties the spatial resolution of the resulting image to the physical size of the active plasmonic element which, in its simplest, form consists of a constriction in a silver thin film, allowing tuning and de-tuning of the plasmonic resonance when heated. Passing an alternating current through the nanostructure causes changes to the surface plasmon resonance condition. Hence, modulating the electric near field localized to the vicinity of the active plasmonic element experiencing Joule heating. While these changes are of the order of a few percent relative to the overall light levels, the encoded modulation allows the use of a lock-in amplifier to extract changes in the light level at the modulation frequency far below the noise floor. As fluorescent material interacts with this modulated electric near-field it will transfer local information into the far-field, which can be collected using standard optics. As the modulation is highly localized to the active plasmonic element, only the area of fluorescent material directly interacting with the active plasmonic element out-couples the light encoded with the modulation frequency. This directly connects the resolution of the imaging technique to the geometry of the active plasmonic element. By scanning a fluorescent sample over the active plasmonic element in a raster fashion, a map of the localized information is compiled to form an image of the sample’s surface. The PEAR method provides a non-destructive, bio-compatible imaging method which is operational in air, with ease of scalability into multi-channel acquisition in order to reduce acquisition time while maintaining signal to noise ratio. Combining these advantages with the ability to tie the resolution to the physical size of the active plasmonic element makes the PEAR imaging method unique among other imaging technologies at the forefront of super-resolution imaging.
Carbon nanotubes, and more specifically single walled carbon nanotubes (SWNTs), possess unusual properties which are valuable for nanotechnology and other fields of materials science and technology, owing to their extraordinary thermal, electrical, and in particular mechanical properties. Most of the desirable mechanical properties, including a high tensile strength, result from the covalent sp2-bonds formed between individual carbon atoms. However, SWNTs are much softer in their radial compared to their axial direction, which results in a reversible elastic deformation of the cross section when applying sufficiently strong hydrostatic pressures. This article provides further evidence, via time dependent Raman spectroscopy, that a stable deformed state exists as a result of van-der-Waals-interactions within individual tubes and specifically that these tubes can fully recover from this deformed state on surprisingly long time scales on the order of tens of minutes. In order to distinguish inter-tube from intra-tube effects, all experiments have been performed with densely packed, vertically aligned, free-standing SWNT arrays in comparison to individual, de-bundled SWNTs. These insights lead to far reaching conclusions regarding the mechanical properties and binding energies of the found stable state and, via a detailed analysis of D-mode, enable the distinction of fully reversible deformations from defect induced states.1
Radial deformation phenomena of carbon nanotubes (CNTs) are attracting increased attention because even minimal changes of the CNT's cross section can result in significant changes of their electronic and optical properties. It is therefore important to have the ability to sensitively probe and characterize this radial deformation. High pressure Raman spectroscopy offers a general and powerful method to study such effects in SWNTs. In this experimental work, we focus in particular on one theoretically predicted Raman vibrational mode, the so-called "Squash Mode" (SM), named after its vibrational mode pattern, which has an E2g symmetry representation and exists at shifts below the radial breathing mode (RBM) region. The Squash mode was predicted to be more sensitive to environmental changes than the RBM.
Here we report on a detailed, experimental detection of SMs of aligned SWNT arrays with peaks as close as 18 cm-1 to the laser excitation energy. Furthermore, we investigate how the SM of aligned CNT arrays reacts when exposed to a high pressure environment of up to 9 GPa. The results confirm the theoretical predictions regarding the angular and polarization dependent variations of the SM's intensity with respect to their excitation. Furthermore, clear Raman upshifts of SM under pressures of up to 9 GPa are presented. The relative changes of these upshifts, and hence the sensitivity, are much higher than that of RBMs because of larger radial displacement of some of the participating carbon atoms during the SM vibration.
These novel ultra-sensitive Raman SM shifts of SWNTs provide enhanced sensitivity and demonstrate new opportunities for nano-optical sensors applications.
Is it possible to design a dedicated nanostructure on which all surface features contribute entirely to energy harvesting within a solar cell? This is an important challenge in the light that the efficiency of the solar cell technology utilised has a direct impact on the required land-use and also on reaching grid parity. Here, we take a unique approach and present an analytically derived optimum solution to the problem: a nanoscale metal topography, capable of significantly improving the efficiency of solid state solar cells via excitation of surface plasmon polaritons (SPPs). The presented structure is designed to achieve broadband excitation of SPPs through the highest possible density of desired k-vectors at the interface. This leads to high weighted absorption enhancements (>130%) and unprecedented improvements (>30%) of solar cell external quantum efficiencies over the entire harvestable range.
Several recent studies have described the use of infrared (IR) nanoimaging for non-invasive chemical discrimination of subcellular features and intracellular exogenous agents. In this work we outline a number of improvements in both quantitative IR nanoimage analysis and optical system improvements which enable recovery of nanoscale subcellular chemical localization with improved chemical precision. Additionally, we demonstrate how a combination of IR absorption nanoimaging and topographic data can produce subcellular chemical density and complexity maps, which can illustrate several cellular features of interest, including the label free localization of nuclei for both healthy and cancerous cell lines with sub 40nm accuracy. As many cell processes related to disease are governed by the position and dynamics of subcellular features, we present the ability to map biochemical inhomogeneity of cancer cells at nanoscale resolution as a means to explore the subcellular biomechanics underlying carcinogenesis.
This study reports on the use of surface enhanced Raman scattering (SERS) as a non-destructive tool for detection and localisation of Porphyrin-Gold nanoparticles (GNP) conjugates at the subcellular level. Conjugates of the hydrophobic photosensitizer meso-Tetraphenylporphyrin (TPP) and GNPs were synthesized. The TPP-GNPs were characterized by by ultraviolet—visible absorption spectroscopy, fluorescence spectroscopy and transmission electron microscopy. TPPGNPs with a mean diameter of 12 nm were introduced into SW480 human colon adenocarcinoma cells. Single point SERS was applied in conjunction with fluorescence microscopy to localize the exogenous materials within the cells. Our results indicate that the TPP-GNP nanomaterials are distributed within cells in the cytoplasm. Overall our results indicate that Raman spectroscopy has the potential to be a high-throughput tool to localise nanoparticles in the subcellular environment.
Photodynamic therapy (PDT) is an emerging technique for the treatment of cancerous and non-cancerous conditions.
Gold nanoparticles (GNPs) possess unique physical and chemical properties which allow them to act as multifunctional
agents in nanomedicine. GNP- photosensitizer conjugates have attracted increasing attention in drug delivery for
photodynamic cancer therapy. In the present investigation, we prepared covalent conjugates of the photosensitizer
Toluidine Blue O (TBO) and thiol protected GNPs. The suitability of TBO- GNPs conjugates for in vitro PDT was
assayed using the SW480 Human colon adenocarcinoma cell line. Our results suggest that gold nanoparticle conjugates
are an excellent vehicle for delivery of photosensitizer agents in the photodynamic therapy of cultured tumour cells.
At present there is considerable global concern in relation to environmental issues and future energy supplies, for
instance climate change (global warming) and the rapid depletion of fossil fuel resources. This trepidation has initiated a
more critical investigation into alternative and renewable sources of power such as geothermal, biomass, hydropower,
wind and solar energy. The immense dependence on electrical power in today's society has prompted the manufacturing
of devices such as photovoltaic (PV) cells to help alleviate and replace current electrical demands of the power grid. The
most popular and commercially available PV cells are silicon solar cells which have to date the greatest efficiencies for
PV cells. The drawback however is that the manufacturing of these cells is complex and costly due to the expense and
difficulty of producing and processing pure silicon. One relatively inexpensive alternative to silicon PV cells that we
are currently studying are dye-sensitised solar cells (DSSC or Grätzel Cells). DSSC are biomimetic solar cells which are
based on the process of photosynthesis. The SFI Strategic Research Centre for Solar Energy Conversion is a research
cluster based in Ireland formed with the express intention of bringing together industry and academia to produce
renewable energy solutions. Our specific research area is in DSSC and their electrical properties. We are currently
developing testing equipment for arrays of DSSC and developing optoelectronic models which todescribe the
performance and behaviour of DSSCs.
With growing energy and environmental concerns due to fossil fuel depletion and global warming there is an increasing
attention being attracted by alternative and/or renewable sources of power such as biomass, hydropower, geothermal,
wind and solar energy. In today's society there is a vast and in many cases not fully appreciated dependence on
electrical power for everyday life and therefore devices such as PV cells are of enormous importance. The more widely
used and commercially available silicon (semiconductor) based cells currently have the greatest efficiencies, however the
manufacturing of these cells is complex and costly due to the cost and difficulty of producing and processing pure
silicon. One new direction being explored is the development of dye-sensitised solar cells (DSSC). The SFI Strategic
Research Centre for Solar Energy Conversion is a new research cluster based in Ireland, formed with the express
intention of bringing together industry and academia to produce renewable energy solutions. Our specific area of
research is in biomimetic dye sensitised solar cells and their electrical properties. We are currently working to develop
test equipment, and optoelectronic models describing the performance and behaviors of dye-sensitised solar cells
(Grätzel Cells). In this paper we describe some of the background to our work and also some of our initial experimental
results. Based on these results we intend to characterise the
opto-electrical properties and bulk characteristics of simple
dye-sensitised solar cells and then to proceed to test new cell compositions.
KEYWORDS: Dye sensitized solar cells, Electrodes, Solar cells, Nanoparticles, Scanning electron microscopy, Transparent conductors, Biomimetics, Semiconductors, Electron transport, Titanium dioxide
The temporal response of a biomimetic dye-sensitized solar cell (DSSC) is critically linked to the intensity of the
incident light. When a DSSC is partially illuminated and the incoming light is of low intensity, the response time
of the cell is prolonged dramatically. In this report, the major components of the DSSC are investigated to find
the source and to provide a model of the driving mechanisms behind this delay. For low light level conditions,
only deep traps states of the TiO2 layer participate in electron transport resulting in a slow temporal response.
Increasing the illumination level thus increases the conductivity of the TiO2 electrode by filling these trap states
and increases the response time. This study shows a strong correlation between the light intensity, active area
and excitation wavelength on the temporal response time of a DSSC.
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