No abstract

No abstract

No abstract

Optical properties of high-frequency Au gratings with a fixed period (296.6 ± 0.5 nm) and a variable modulation depth are studied using measurements of spectral and angular dependence of transmission and reflection of polarized light in order to build the dispersion curves of excited optical modes and to identify their types. It was shown that in gratings with small modulation depth only propagating surface plasmon-polaritons (SPP) modes were observed. With increasing of modulation depth, the intensity of SPP decreases and localized plasmon (LP) resonance appears, which is more intense at small incident angles, and overlaps with the SPP modes. For grating with isolated grooves (nanowires), mostly LP resonance is observed. After additional deposition of gold onto grating with isolated grooves, the intensity of the SPP mode increases again, and the LP band maximum shifts to longer wavelengths.

The increase of the sensitivity of surface plasmon resonance (SPR) refractometers was studied experimentally by forming a periodic relief in the form of a grating with submicron period on the surface of the Au-coated chip. Periodic reliefs of different depths and spatial frequency were formed on the Au film surface using interference lithography and vacuum chalcogenide photoresists. Spatial frequencies of the grating were selected close to the conditions of Bragg reflection of plasmons for the working wavelength of the SPR refractometer and the used environment (solution of glycerol in water). It was found that the degree of refractometer sensitivity enhancement and the value of the interval of environment refractive index variation, Δn, in which this enhancement is observed, depend on the depth of the grating relief. By increasing the depth of relief from 13.5 ± 2 nm to 21.0 ± 2 nm, Δn decreased from 0.009 to 0.0031, whereas sensitivity increased from 110 deg./RIU (refractive index unit) for a standard chip up to 264 and 484 deg./RIU for the nanostructured chips, respectively. Finally, it was shown that the working range of the sensor can be adjusted to the refractive index of the studied environment by changing the spatial frequency of the grating, by modification of the chip surface or by rotation of the chip.

Stable surface functionalization is required in many applications such as in biosensing. For this purpose, hydrocarbon‐based plasma polymer films (PPFs) were investigated by controlling cross‐linking and film structure at the nanoscale, while functional groups were incorporated using a CO2/C2H4 low pressure plasma. In particular, an oxygen‐rich termination layer of 1 nm (top layer) was gradually deposited onto a more cross‐linked PPF (base layer) with varying thickness (<20 nm) yielding highly stable yet functional a‐C:H:O films as compared to conventional oxygen‐rich PPFs. Such stabilized nano‐layers provided a homogeneous functionalization of Au‐coated (flat) biochips as used for immunosensing as well as of nanostructured Au‐coated surfaces explored for enhanced biosensing. The used periodic grating coated by the highly stable a‐C:H:O nano‐layer can be adjusted to the required environmental refractive index range yielding a distinct sensitivity enhancement for biosensing.

No abstract

No abstract