Light enhancement in surface-enhanced raman scattering at oblique incidence

Surface enhanced Raman scattering (SERS) measurements have been carried out at different focusing conditions using objective lenses of different numerical apertures. The experimentally observed dependence of SERS intensity of thiophenol-coated Ag nano-islands shows a close-to-linear scaling with the collection aperture. The linear relationship breaks down for large numerical apertures, which suggests that the scattering is anisotropic. Numerical simulations of realistically shaped Ag nano-islands were carried out, and the spatial distribution of hot-spots has been revealed at different heights near the nano-islands. Local field enhancements of up to 100 times were estimated. The simulation also suggests an explanation for the anisotropy in the scattering observed for larger numerical aperture objectives. This appears to be due to a reduction in the local field enhancement as the electric field vector component in the plane of the shallow metal islands reduces at larger angles of incidence

Photoluminescence from voids created by femtosecond-laser pulses inside cubic-BN

Photoluminescence (PL) from femtosecond-laser-modified regions inside cubic-boron nitride (c-BN) was measured under UV and visible light excitation. Bright PL at the red spectral range was observed, with a typical excited state lifetime of ∼4  ns. Sharp emission lines are consistent with PL of intrinsic vibronic defects linked to the nitrogen vacancy formation (via Frenkel pair) observed earlier in high-energy electron-irradiated and ion-implanted c-BN. These, formerly known as the radiation centers, RC1, RC2, and RC3, have been identified at the locus of the voids formed by a single femtosecond-laser pulse. The method is promising to engineer color centers in c-BN for photonic applications

Toxic substance mechanisms : contemporary topics in chemical and drug research

We propose a novel substrate for SERS bio-sensing composed of an hexagonal array of gold nanorods embedded in an anodically-oxidized alumina substrate, reaching a surface field enhancement up to 220 times

Surface-enhanced Raman scattering sensor based on laser nano-textured surfaces

Nano-textured surfaces of dielectric materials were prepared by laser ablation using femtosecond laser pulses. The ripples with periods 170-270 nm were prepared on several substrates: SiC, Al2O3, GaP, glass and synthetic diamond. Gold and silver coated surfaces were used to detect surface enhanced Raman scattering (SERS) of chemically and physically adsorbed molecules of thyophenol and rhodamine. Polarization sensitivity of ripple sensors was measured for irradiation by linearly polarized light. The limit of detection of SERS substrate was found one order of magnitude higher as compared with commercial Klarite and Solas substrates

Analysis of defects patterned by femtosecond pulses inside KBr and SiO2 glass

Colour centres in KBr and defects in silica glass were formed by focused femtosecond laser pulses. It is shown that under simple laser exposure, KBr develops a similar colouration as that achieved with electron and ion bombardment or high-energy X-ray irradiation. The three-dimensional (3D) character of direct laser writing in the volume of KBr allows a new level of control in the spatial arrangement of colour centres and defects. Five different colour centres were identified in KBr through the absorption spectrum; they have different charge and vacancy distribution configurations. The densities of the V- and F-centres were estimated to be 3.9 × 1019 and 3.4 × 1019 cm−3 using Smakula’s formula. In silica, a high density of paramagnetic E′ centres ~1.9 × 1020 cm−3 was determined by quantitative electron spin resonance spectroscopy. Birefringence due to colour centres and laser-induced defects was measured using Stokes polarimetry. In the case of colour centres in KBr, retardation in excess of 0.05 (Formula presented.) was determined throughout the visible spectrum from 400 to 800 nm. The use of polariscopy for analysis of high-pressure and high-temperature phase formation induced by 3D laser structuring is discussed

Statistically quantified measurement of an Alzheimer's marker by surface-enhanced Raman scattering

Fibrillar forms of the Amyloid- (A) protein have been implicated in the early stages of Alzheimer's disease (AD), however there are no standardised assays for soluble A oligomer biomarkers that provide the best indication of the disease progression [1,2]. As a step towards a fast and label-free method for testing different AD biomarkers, we have combined laser nano-textured substrates with a SERS mapping technique and validated it using soluble A-40 oligomers [3-5]. The nano-textured SERS substrates provide fast (&5min), label-free spectra associated with soluble A-40 oligomers down to a concentration of 10 nM. Statistical analysis of the spectral intensities mapped over the substrate surface shows a quantitative correlation with the oligomer concentration