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Nanostructured materials plated with metallic layer is a unique category within material science which explores numerous phenomena such as localized surface plasmon resonance (LSPR). Free metal electrons oscillations resonating with the visible excitation photons give strongly enhanced electric field in the nanostructure vicinity. This phenomenon is strongly utilized for ultrasensitive, fingerprint selective, fast analysis and an economical technique known as SERS i.e. surface-enhanced Raman spectroscopy. This paper is predominantly focused on fabrication and optimisation of the SERS substrates consisting of randomly oriented nanowires. The fabrication methodology includes fabrication of Si or ZnO nanowires on a wafer or optical fibre substrates utilizing 'Vapour- liquid-solid (VLS)' method within 'low-pressure chemical vapour deposition (LPCVD)' reactor or 'Chemical vapour deposition (CVD)'. SERS substrates’ optimization includes nano- structuring, and Ag metal plating by sputtering. The particularity of these specific silicon nanowires (SiNWs) is in their flexibility i.e. a possibility to shrink in bundles upon liquid immersion offering additional SERS signal enhancement. The morphological characteristics and the influence of sputtering are described by the fractal dimension and lacunar analysis. Finally, SERS substrates were characterized utilizing 4-mercaptophenylboronic acid (4-MPBA) as the test molecule. The laboratory substrates compared with the commercially available substrates showed excellent characteristics.

A new method for enhancing the Raman scattering signal has emerged recently, based on dielectric enhancement. Especially promising is the dielectric method based on microspheres and photonic nanojet – a narrow highly concentrated beam of light on the shadow side of the irradiated microsphere. The formation of the photonic nanojet is presented through Generalized Lorenz-Mie theory (GLMT), together with important properties and applications. Simulation images of the photonic nanojet are shown, both as solutions of GLMT equations, and numerical simulations. Furthermore, the photonic nanojet is presented as Raman scattering enhancement method different substrates (bulk, film on bulk, etc.) with microspheres and microspheres with a stem. The variation of the incident beam position is discussed, where raw enhancement reaches highest value (5.7x) for 0.50 NA objective, when the incident beam was focused 9 μm below the top of the 5-μm microsphere. Moreover, the combined dielectric enhancement with metallic surface-enhanced Raman scattering (SERS) is presented, together with future plans.

The key for successful and fast health recovery is in early disease detection and adequate treatment. The early and accurate detection method of unwanted processes in a living organism requires low molecules number detection and ‘specificity’ in order to accurately distinguish similar species. Surface-enhanced Raman spectroscopy (SERS) offers not only ultrasensitive molecular detection, but also a unique ‘fingerprint’ of the specific molecule, which finds applications from diagnostic to analytical chemistry and environmental monitoring. Fibre-optics based SERS probes are a step towards the solution. They preserve ultra- sensitivity and selectivity of common lab- substrates and offer fast, cost-effective, minimally invasive, real-time, in situ and in vivo monitoring especially suitable for out of lab environment. This work shows preliminary results of the fabrication methodology for fibre-optics based sensors which includes fabrication of silicon and zinc-oxide nanowires on silica fibre. Such sensor has shown Rhodamine 6G concentration detection limit of 10-9 M. Furthermore, we have demonstrated Raman signal enhancement with dielectric microspheres which is a step before the technology transfer to SERS substrates.

International audience

International audience

We show the reverse cross-relaxation process parameter can be calculated by fitting the slow decaying fluorescence tails emitted when pump level is almost depopulated. We also show more precise measure requires high pump intensity.

Silicon nanomaterials, known as one of the most important types of nanomaterials, feature a number of unique merits, such as excellent electronic/mechanical/optical properties, huge surface-to-volume ratios, and facile surface modification [1]. Fast development of silicon nanomaterials with well-defined structures and required functionalities has vastly promoted the advancement of silicon nanotechnology. Structuring surface and bulk of (poly)crystalline silicon on diff erent length scales can signifi cantly alter its properties and improve the performance of opto-electronic devices and sensors based on silicon. Diff erent dominant feature scales are responsible for modifi cation of some of electronic and optical properties of silicon. We present several chemical methods for easy structuring of silicon on nano and micro-scales, based on both electroless and anodic etching of silicon in hydrofl uoric acid based etchants, and chemical anisotropic etching of silicon in basic environments. We show how successive micro and nano structuring creates hierarchical silicon surfaces, which can be used to simultaneously exploit the advantages of both structuring feature length scales. We present some fi nal results of application of silicon nano structuring in development of SERS substrates [2] and silicon/organic heterojunctions for IR light sensing [3]. [1] G.F. Grom, D.J. Lockwood, J.P. McCaff rey, H.J. Labbe, P.M. Fauchet, B. White, J. Diener, D. Kovalev, F. Koch, L. Tsybeskov, Nature 407 (2000) 358 [2] L. Mikac, M. Ivanda, V. Đerek and M. Gotić, J. Raman Spectr. (2016). Doi: 10.1002- jrs.4911 [3] V. Đerek, E. D. Głowacki, M. Sytnyk, W. Heiss, M. Marciuš, M. Ristić, M. Ivanda, and N. S. Sariciftci, Appl. Phys. Lett. 107 (2015) 083302.

Surface enhanced Raman spectroscopy is an important technique for detection of wide number of analytes. Today, there is a growing need for the development of stable, sensitive, reproducible and portable SERS-active substrates for use in different fields. Some of the most extensively used SERS substrates are metal colloids. However, the use of the colloid solutions for SERS deals with important issues, like stability and reproducibility. Other popular types of substrates are rough or nanoporous surfaces, such as porous silicon, coated with noble metals. Porous silicon (pSi) is a semiconducting material typically obtained by electrochemical etching in hydrofluoric acid (HF). Due to its high surface-to-volume ratio pSi is an interesting material for photonic and sensing devices, drug delivery systems as well as for use in SERS. In this paper, attempts are made to prepare a stable and uniform noble metal colloidal solution as well as solid substrate using porous silicon (pSi) with deposited silver and gold nanostructures. SERS substrates obtained by different methods are evaluated for SERS efficiency using methylene blue and rhodamine 6G (R6G) at 514.5 and 633 nm. The prepared substrates showed good stability and reproducibility. For some substrates the concentrations detected were below nanomolar range.

This paper reports on the work done on photodarkening by our consortium. Particular emphasis is given to mitigate and measure photondarkening in high-quality Al-silicate fibers with high doping concentration.

Mitigation of photodarkening in Yb-doped lasers based on Al-silicate fibers

We investigated photodarkening loss evolution and its reduction in Yb3+ doped aluminosilicate fibers utilizing 633 nm light irradiation. We demonstrate the final photobleaching value is intensity dependent, but the percentage of photodarkening reduction does not depend on dopant concentrations for settled bleaching intensity. We also show that the defects generated during the initial photodakening process have lower energy and can be effectively bleached by 633 nm photons while defects generated during photodarkening loss saturation cannot be bleached by low energy photons © (2013) COPYRIGHT Society of Photo- Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Photodarkening in optical fibres and photo-induced defects