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The project was supported by the European Research Council (ERC) under the European Union Horizon 2020 Research and Innovation Program (Grant Agreement No. 819346). Optical trapping of small particles typically requires the use of high NA microscope objectives. Photonic metasurfaces are an attractive alternative to create strongly focused beams for optical trapping applications in an integrated platform. Here, we report on the design, fabrication, and characterization of optical metasurfaces with a numerical aperture up to 1.2 and trapping stiffness greater than 400 pN/μm/W. We demonstrate that these metasurfaces perform as well as microscope objectives with the same numerical aperture. We systematically analyze the impact of the metasurface dimension on the trapping performance and show efficient trapping with metasurfaces with an area as small as 0.001 mm2. Finally, we demonstrate the versatility of the platform by designing metasurfaces able to create multisite optical tweezers for the trapping of extended objects. Publisher PDF

The project was supported by the European Research Council (ERC) under the European Union Horizon 2020 research and innovation program (Grant Agreement No. 819346). Here we demonstrate the two-tier manipulation of holographic information using frequency-selective metasurfaces. Our results show that these devices can diffract light efficiently at designed frequency and environmental conditions. By changing the frequency and refractive index of the surrounding environment, the metasurfaces produce two different holographic images. We anticipate that these environmental dependent, frequency-selective metasurfaces will have practical applications in holographic encryption and sensing. Publisher PDF

The authors gratefully acknowledge the support by the College of Engineering Research Center under the Deanship of Scientific Research of King Khalid University, Saudi Arabia. (Grant No. 98) Self-aligned silicon micro-nano structured electron field emitter arrays were fabricated using pulsed krypton fluoride (KrF) excimer laser crystallization (ELC) of hydrogenated amorphous thin silicon films (a-Si:H) on metal coated backplane samples. We investigate the effect of laser processing parameters on the growth of micro-nano conical structures on the surface of the thin silicon films. Randomly oriented conical structures as high as 1 µm were fabricated using laser pulse frequency of 100 Hz and sample stage scanning speed of 0.25 mm/sec. Best field emission (FE) results were measured from samples with the highest surface features with FE currents in the order of 10−6 A and low turn-on emission threshold of ∼14 V/µm. Light emission from the prototype demonstrators was tested using bespoke driver electronics and planar anodes coated with indium tin-oxide (ITO) and medium voltage FE phosphors, to exemplify their usage for future flat panel display technologies. Postprint

Hydrogenated amorphous thin silicon films (a-Si:H) deposited on metal coated glass substrates were investigated to analyze the effect of a novel processing technique called Laser Assisted M...

Herein, we used a photosensitizing agent and red organic light-emitting diodes (OLEDs) against two strains of Leishmania amazonensis amastigotes, including a drug-resistant line. OLEDs are promising wearable light sources for photodynamic therapy of cutaneous leishmaniasis.

Bacterial infection and the growth of antibiotic resistance is a serious problem that leads to patient suffering, death and increased costs of healthcare. To address this problem, we propose using flexible organic light-emitting diodes (OLEDs) as light sources for photodynamic therapy (PDT) to kill bacteria. PDT involves the use of light and a photosensitizer to generate reactive oxygen species that kill neighbouring cells. We have developed flexible top-emitting OLEDs with the ability to tune the emission peak from 669 to 737 nm to match the photosensitizer, together with high irradiance, low driving voltage, long operational lifetime and adequate shelf-life. These features enable OLEDs to be the ideal candidate for ambulatory PDT light sources. A detailed study of OLED–PDT for killing Staphylococcus aureus was performed. The results show that our OLEDs in combination with the photosensitizer methylene blue, can kill more than 99% of bacteria. This indicates a huge potential for using OLEDs to treat bacterial infections. Flexible OLED technology is becoming increasingly mature and is ready to open new directions in antimicrobial photodynamic therapy. An international team led by Prof Ifor Samuel from University of St Andrews, UK presents a comprehensive study to show that flexible organic light-emitting diodes (OLEDs) are ideal light sources to be used in photodynamic therapy to kill bacteria. They design the OLED device structure to enable large area, high uniformity, low driving voltage, long operational lifetime, adequate shelf-life and colour tunability and address all the requirements of photodynamic therapy. Actual biological experiments show killing rates of more than 99% for S. aureus bacteria. The approach clearly demonstrates the huge potential of OLEDs for treatment of bacterial infections and future wearable healthcare devices.

Petrogal Brasil S.A., through the project “Sustainable biotechnological alternatives to increase the oil recovery factor of carbonate reservoirs” under the management of Instituto de Petróleo e Gás – ISPG and the National Agency of Petroleum, Natural Gas and Biofuels (ANP) provided financial support and grants to PJLG, PFA, ICFS, and ALBP, IDWS, Conselho Nacional de Desenvolvimento Cientifico e Tecnologico -CNPq provided a grant to LSF, and SP had financial support and grant from the Scottish Funding Council Global Challenges Research Fund. Oil recovery is a challenge and microbial enhanced oil recovery is an option. We theorized that the use of produced water (PW) with photo-stimulation could influence both production and viscosity of Xanthan gum. This study aimed at the evaluation of the effect of photo-stimulation by λ630 ± 1 ηm LED light on the biosynthesis of Xanthan gum produced by Xanthomonas campestris IBSBF 2103 strain reusing PW of the oil industry. We assessed the effect of photo-stimulation by LED light (λ630 nm) on the biosynthesis of Xanthan gum produced by X. campestris in medium containing produced water. Different energy densities applied during the microbial growth phase were tested. The highest production was achieved when using 12 J/cm2 LED light (p

OLEDs are attractive and distinctive light sources because of they are very thin, emit over an area and can be flexible. These features also make them very interesting for medical applications as compact, lightweight sources can enable ambulatory treatment. In photodynamic therapy (PDT), light in combination with a photosensitiser leads to the generation of reactive oxygen species that can kill nearby cells. We report the development of improved OLEDs for PDT. In particular, we show their use for antimicrobial PDT i.e. for killing bacteria, parasites and fungi in vitro.

Funding: NSF grant 1545852 (OISE:PIRE-SOMBRERO)/CONACyT 251992. Organic light emitting diodes (OLEDs) are very attractive light sources because they are large area emitters and, can in principle, deposited on flexible substrates. These features make them suitable for ambulatory photodynamic therapy (PDT), in fact there are a few reports of in vitro or in vivo OLED based PDT studies for cancer or microbial inhibition but to our best knowledge, none against yeasts. Yeast infections are a significant health risk, especially in low income countries with limited medical facilities. In this work, OLED-based antimicrobial PDT (aPDT), using methylene blue (MB) as photosensitizer (PS), is studied to inactivate opportunistic yeast of four Candida strains of two species: Candida albicans and Candida tropicalis. Before aPDT experiments, fluconazole-resistance was evaluated for all strains, showing that both strains of C. tropicalis were resistant and both strains of C. albicans were sensitive to it. We found that is useful for aPDT and that 3 repetitive irradiations work better than a single dose while keeping the total fluence constant, and that this result applies whether or not the strains are resistant to fluconazole. Postprint

Although the radiative transport theory is widely used in various biomedical, ocean, and atmospheric optic problems, there are few light transport problems that can be solved analytically. Therefore, Monte Carlo (MC) numerical simulations are used in most practical applications. In this study, light transport problems in continuously absorbing and discretely scattering media for pencil-like incident beams were considered theoretically using the single scattering approximation. Strict and closed-form analytical solutions to these problems were derived and compared with МС numerical results. Two sets of probabilistic parameters for the MC algorithm were explored. The first was the classical set for media with continuous absorption and smooth scattering, while the second was the newly substantiated set for media with continuous absorption and discrete scattering corresponding to the analytical medium's model. It was shown that if the same model was used in MC simulations and the analytical approach, all of the results were identical. A divergence up to 10% between the obtained analytics and MC results in the case of continuous absorption and smooth scattering was observed. Postprint

Funding: UK Engineering and Physical Sciences Research Council (Grant Number(s): EP/L015110/1). Antimicrobial photodynamic therapy (APDT) has been studied as a non-invasive therapy for treating cutaneous leishmaniasis to overcome challenges with current treatment, such as toxicity, resistance and need for in-patient hospital treatment. Organic light-emitting diodes (OLEDs) have emerged as an attractive technology that can provide wearable light-emitting materials that are conformable to human skin. This makes OLEDs ideal candidates for APDT by light-bandages for ambulatory care. In this work, we successfully develop suitable OLEDs to match the absorbance of three photosensitizers: methylene blue, new methylene blue, and 1,9-dimethyl-methylene blue to inactivate two Leishmania species in vitro: Leishmania major and Leishmania amazonensis. Parasites are treated either by LED (20 mWcm-2) or OLED (6.5 mWcm-2) at increasing photosensitizer concentrations at a radiant exposure of 50 Jcm-2. 1,9-Dimethyl-methylene blue is the most potent photosensitizer, killing both strains at nanomolar concentrations. We also explore the effect of different intensities from the OLEDs (0.7, 1.5, and 6.5 mWcm-2) and show that effective killing of Leishmania occurs even at very low intensity. These findings demonstrate the great potential of OLEDs as a new approach for ambulatory treatment of cutaneous leishmaniasis by APDT. Publisher PDF

Noise in the differential two-channel scheme of a classic laser Doppler flowmetry (LDF) instrument was studied. Formation of false spectral components in the output signal due to beating of electrical signals in the differential amplifier was found out. The improved block-diagram of the flowmeter was developed allowing to reduce the noise.

We investigate the carrier dynamics of thin films of black silicon, amorphous hydrogenated silicon which under laser annealing forms a microstructured surface with extremely high broadband optical absorption. We use Raman spectroscopy to determine the degree of crystallinity of the annealed surfaces, and investigate the dependence on crystallinity and fabrication method of the photoconductivity. Time-resolved THz spectroscopy is used to determine the evolution of the carrier scattering time and confinement of carriers on the picosecond time scale. We conclude that a fabrication method with high energy leading edge of the annealing laser results in black silicon with the largest photon-to-electron conversion efficiency, largest mobility, and longest carrier lifetime.

Energy efficient Wavelength Division Multiplexing (WDM) is the key to satisfying the future bandwidth requirements of datacentres. As the silicon photonics platform is regarded the only technology able to meet the required power and cost efficiency levels, the development of silicon photonics compatible narrow linewidth lasers is now crucial. We discuss the requirements for such laser systems and report the experimental demonstration of a compact uncooled external-cavity mW-class laser architecture with a tunable Si Photonic Crystal resonant reflector, suitable for direct Frequency Modulation. Postprint

This work was partially funded by the EPSRC, Scottish Enterprise, and the European Research Council under the Starting Grant 337508. We report the experimental demonstration of an alternative design of external-cavity hybrid lasers consisting of a III-V Semiconductor Optical Amplifier with fiber reflector and a Photonic Crystal (PhC) based resonant reflector on SOI. The Silicon reflector comprises a polymer (SU8) bus waveguide vertically coupled to a PhC cavity and provides a wavelength-selective optical feedback to the laser cavity. This device exhibits milliwatt-level output power and sidemode suppression ratio of more than 25 dB. Publisher PDF

Hydrogenated amorphous thin silicon films (a-Si:H) deposited using Plasma Enhanced Chemical Vapor Deposition (PECVD) on metal coated glass substrates were investigated to determine the effect of Aluminium Induced Crystallization (AIC) on their Electron Field Emission (FE) properties. Pre and post-surface characterization of the processed AIC-PECVD thin silicon films showed increased surface roughness and the presence of uniformly spaced “islandlike” micro/nano crystallites on the surface of both chromium (Cr) and molybdenum (Mo) backplane samples. Best FE results were obtained from a-Si:H sputtered with a thin layer of aluminum (Al) on top and isothermally annealed at 350 °C. FE currents were measured upto above 10−6 A at emission thresholds of 35–60 V/μm. FE results of the AIC-PECVD thin silicon films were found to be particularly dependent on backplane material and independent of the annealing temperature. Diode configuration field emission measurements have been conducted using an ANODE plate coated with indium tin-oxide (ITO) and phosphor to observe the light emission.

Black silicon is produced by laser annealing of a-Si:H films. During annealing, silicon microstructures are formed on the surface. We use time-resolved terahertz spectroscopy to study the photoconductivity dynamics in black silicon. We find that when a copper film is deposited on top of the a-Si:H layer prior to laser annealing, the carrier lifetime of black silicon is significantly reduced.

A series of hydrogenated amorphous silicon films have been deposited using plasma enhanced chemical vapour deposition (PECVD) and hot-wire chemical vapour deposition (HWCVD) techniques. The total concentration of bonded hydrogen in the films was varied between 3% and 18% as determined by hydrogen effusion measurements. Fourier transform infra-red (FTIR) spectra of the PECVD and HWCVD samples exhibit strong absorption peaks that correspond to Si–H bend and stretch modes, and Si–H2 stretch modes. A quantitative fit of the FTIR peak areas to the hydrogen effusion concentrations reveals that there is reasonable agreement between the required proportionality constants in PECVD and HWCVD material for the Si–H bend and stretch modes. The uncertainty error for the FTIR proportionality constants is consistently greater for the HWCVD data set, however, which may indicate that the effective dynamical charge of the Si–H dipoles is perturbed in the HWCVD material by bonded impurities that are sourced from the tungsten wire.

Electron Field Emission (FE) properties of various laser annealed thin silicon films on different substrates were investigated. HWCVD microcrystalline and PECVD amorphous silicon films were irradiated with Nd : YAG and XeCl Excimer lasers at varying energy densities. Encouraging FE results were mainly from XeCl Excimer laser processed PECVD and HWCVD films on metal backplanes. FE measurements were complemented by the study of film surface morphology. Geometric field enhancement factors from surface measurements and Fowler-Nordheim Theory (FNT) were compared. FE properties of the films were also found to be particularly influenced by the backplane material.

Thin silicon film samples were deposited using HWCVD and PECVD techniques to study the influence of laser annealing on their optical and electronic properties. Samples were annealed in air using a XeCl excimer and Nd:Yag lasers. Excimer laser annealing (ELA) at 50 to 222 mJ/cm 2 increased conductivity in PECVD films by 2 to 3 orders of magnitude and in HWCVD films by 1 to 2 orders of magnitude. ELA was also seen to decrease the optical gap in PECVD films by 0.5 eV and HWCVD films by 0.15 eV. Silicon–oxygen bond content was higher in as-deposited HWCVD films than PECVD films. Hydrogen content (at.%) in PECVD films was higher than HWCVD for higher H dilution ratios. A Nd:Yag laser 3-beam interference pattern was used to produce a periodic array of crystals in both PECVD and HWCVD films.

Hot-wire chemical-vapor-disposition (CVD) thin silicon films are studied by means of dark conductivity, FTIR, hydrogen evolution, and SEM surface characterization. Three types of metastability are observed: (1) long term irreversible degradation due to oxidization processes on the film surface, (2) reversible degradation determined by uncontrolled water and/or oxygen adsorption, and (3) a fast field-switching effect in the film bulk. We propose that this effect is associated with the morphology changes during film growth and an electrical field induced by adsorbed atmospheric components on the film surface. It is found that metastable processes close to the film surface are stronger than in the bulk.

Infrared spectroscopic data are correlated here together with conductivity results, transient photoconductivity measurements and fundamental absorption data in an attempt to understand the physical processes involved in the growth of tungsten hot-wire deposited hydrogenated amorphous silicon. Film surface growth processes initially involve diffusing thermally dissociated radicals, with a subsequent additional contribution from evaporated silicon species. We show how changing processes at the heated wire surface, surrounded by silane gas, affect the electronic and structural properties of the hydrogenated amorphous silicon produced. Depth profiling by chemical etching reveals substantial variations in the level of contamination and in the electronic structure throughout the film.

The diffusion of a chromium bottom contact has been studied through thin 10-nm amorphous silicon film. The concentration of the diffused impurity has been analyzed by an X-ray photon spectroscopy technique and the diffusion coefficient was estimated. Diffusion annealing was carried out in vacuum (10−6 mTorr), the temperature was kept at 400°C, and the annealing time was varied from 0 to 300 min. The authors propose that diffusion of chromium in thin hydrogenated amorphous film is limited by silicide formation at the metal-silicon interface.

Artificial biomimetic substrates provide useful models for studying cell adhesion, signaling, and differentiation. This article describes biological interactions with a new type of tunable, micro-nanotextured silicon substrate, generated by irradiation of a hydrogenated amorphous silicon film with a large beam, excimer laser (248 nm). In this study, we demonstrate that BV-2 microglial cells can sense differences in laser processed silicon surface topology over the range of 30 nm to 2 μm, where they undergo marked morphogenic changes with increasing feature size. The cells adopt a more elongated shape in the presence of the modified surface structure and exhibit increased levels of actin-rich microdomains, suggesting enhanced adhesion. The excimer laser modification of hydrogenated amorphous silicon to generate micro-nanostructures realizes large area benefits as well as providing a biomaterial where the external and internal structure can be altered and tuned for various applications. © 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 99A: 135–140, 2011.

The ultrafast photoconductivity dynamics of black silicon is measured by time-resolved terahertz spectroscopy. Black silicon is produced by laser annealing of an a-Si:H film. We show that the decay time of the photoconductivity depends on the annealing method and fluence used in the production process.

We present experimental and theoretical work on excimer laser microstructuring of hydrogenated amorphous silicon (a-Si∶H) films on molybdenum coated glass substrates, in the form of sharp and conical poly-Si spikes, for electron field emission applications.

SU8 Negative photoresist is finding high demand in applications such as MEMS sensors and waveguides. The possibility of photolithographic patterning and high physical and dielectric properties are attracting ever more users among workers in the electronics industry and increasingly in biomedical applications. In our work we employ an original method of exposing of SU8 and create high aspect ratio structures on glass and other substrates. Dry plasma etching results of negative epoxy-based photoresist by Inductively Coupled Plasma system using gases O2 and CF4 are presented.

The hydrogenated amorphous silicon (a-Si:H) films on molybdenum coated glass substrates were microstructured by irradiating the films using KrF excimer laser with a slope beam profile. By varying the laser processing parameters i.e., the laser pulse energy, the number of laser pulses and the laser energy distribution along the sample scan directions, the homogeneous, high density, and conical polycrystalline silicon features can be fabricated on the thin film surfaces. The electron field emission measurement results show that this kind of laser processed a- Si:H films possess good field emission characteristics with a low turn on electric field of less than 15 V/�� m and a larger saturation emission current. The diode configured field emission display devices have been demonstrated by using the laser irradiated a- Si:H films as the electron cold cathode emitters.

Thin silicon films deposited using the Hot-Wire Chemical Vapor Deposition (HWCVD) technique are studied here for the effect of XeCl excimer laser crystallization on their structural, optoelectronic, and electron field emission properties. Excimer Laser Annealing (ELA) of the silicon thin films indicated increased dark conductivity and reduced optical gap. Encouraging Field Emission (FE) results were obtained from XeCl excimer laser processed HWCVD films on Cr, V, Mo, and Ti backplanes. Geometric field enhancement factors from surface measurements and Fowler-Nordheim Theory (FNT) were compared. FE thresholds were also found to be particularly influenced by the backplane material.

Films deposited by the Hot Wire CVD method were studied by means of dark conductivity, FTIR, Hydrogen Evolution, SEM and AFM surface characterization. Three types of metastability were observed: a) long term irreversible degradation due to oxidization processes on the film surface, b) reversible degradation determined by uncontrolled water adsorption, c) fast field switching effect in the film bulk.Oxygen and hydrogen content and its bonding configurations have been analyzed by hydrogen evolution and infrared spectroscopy methods on the films deposited on glass substrates and silicon wafers subsequently. It has been found that metastable processes close to the film surface are stronger than in the bulk. The switching effect is the fast increase of charge carrier density observed on bottom chromium contacts under a condition of air admittance. We propose this effect is associated with morphology changes during film growth and electrical field induced by adsorbed atmospheric components on the film surface.

Terahertz generation has been achieved from a photoconductive switch based on hydrogenated nanocrystalline silicon (nc-Si:H), gated by a femtosecond laser. The nc-Si:H samples were produced by a hot wire chemical vapour deposition process, a process with low production costs owing to its higher growth rate and manufacturing simplicity. Although promising ultrafast carrier dynamics of nc-Si have been previously demonstrated, this is the first report on THz generation from a nc-Si:H material.