The method of total internal reflection ellipsometry for thin film characterisation and sensing

Recently developed method of Total Internal Reflection Ellipsometry (TIRE) represents a very successful combination of the spectroscopic ellipsometry instrumentation with the Kretchmann type Surface Plasmon Resonance (SPR) geometry of the experiment. The modelling shows much higher sensitivity of the TIRE method to small changes in optical parameters (thickness and refractive index) of thin films, as compared to both traditional external reflection ellipsometry and SPR. Considering another advantage of performing the measurements in media of different optical density (and even opaque media), TIRE becomes very convenient for different sensing applications in both gaseous and liquid media, as well as for thin film characterisation. This work presents examples of applications of the TIRE method for the study of DNA hybridization and the registration of low molecular weight toxins. (C) 2007 Elsevier B.V. All rights reserved

Ellipsometry study of ultra thin layers of evaporated gold

Optical properties of ultra thin (from 1 to 40 nm) films of gold evaporated on glass; and silicon were studied with the method of spectroscopic ellipsometry in both external and internal reflection configurations as well as with the UV-visible absorption spectroscopy. The results obtained showed a gradual shift of the plasmon peak from 580 nm for 1 nm thick films to more than 1000 nm for thick (40 nm) gold films. Such phenomenon can be interpreted in terms of quantum confinement of surface plasmons in gold islands. The threshold of the metal-dielectric transition was found at the film thickness between 4 and 5 nm. Thiolation of the surface of glass has resulted in a slight decrease in the effective thickness of gold layer and respective smaller blue shift of n(lambda) and k(lambda) dispersion curves, however no dramatic changes were observed in the film morphology

Organic films for nanoelectronics and sensing applications

Films of polyallylamine hydrochloride (PAA) and polysteresulfonate sodium salt (PSS) were formulated using the polyelectrolyte self-assembly technique. Electrical measurements show that there is no presence of counter ions and films are electrically stable. Responses of composite films of PAA/(indicator/PAA) (Enzyme/PAA) deposited on suitably treated glass substrates to heavy metals and pesticides are found to be selective from their optical absorption spectra

The model of alkylphenol micelles bound to respective antibodies on the solid surface

The model of binding of micelles of nonylphenol molecules to respective antibodies immobilized on the solid surface is proposed. The actual dimensions of micelles obtained from AFM measurements were used in modelling and allowed to predict the shape of the micelle. An account of non-spherical shape of micelles and their simultaneous binding to several antibodies allows estimation of the micelle binding energy

Ellipsometric study of the adsorption of bovine serum albumin into porous silicon

The method of spectroscopic ellipsometry has been applied to study in situ the adsorption of bovine serum albumin (BSA). The porosity and amount of adsorbed BSA were determined by fitting the ellipsometric data to the Bruggeman effective medium approximation model. The presence of intermediate adsorbed layers of polyelectrolytes was found to increase protein adsorption

Study of electroluminescence in porous silicon for sensing applications

Electroluminescence (EL) of porous silicon (PS) samples was studied at anodic polarisation using neutral electrolyte contact. SEM and AFM morphology study of PS revealed its complex structure comprising features with micrometre and tens of nanometre dimensions. The observed features of EL, including its degradation during anodisation, were discussed in terms of a phenomenological model of a chemically modified silicon surface. The adsorption of polyelectrolytes polyallylamine (PAA) and polysterylsulphonate (PSS) demonstrated sufficient improvement of EL stability. The effect of adsorption of protein bovine serum albumin (BSA) on EL quenching was studied

Characterization of ZnSe nanocrystals grown by vapor phase epitaxy

This paper reports the application of scanning electron microscopy, x-ray diffraction, and photoluminescence techniques for characterization of ZnSe nanocrystals grown on GaAs (100) substrate from the vapor phase. The applied characterization techniques show the evidence for coexistence of two sets of nanocrystals with rather different characteristic sizes. In addition, the lowest energy levels of spherically shaped nanocrystals are calculated in the framework of the effective-mass approximation and compared with photoluminescence data

Interaction of volatile organic vapours with azo-calix 4 -resorcinarene and poly(9-vinylcarbazole) thin films using SPR measurements

Thin films of azo-calix[4]resorcinarene (AZO) and poly(9-vinylcarbazole) (PVK) have been deposited by the method of spin coating and are studied for the optical detection of volatile organic vapour molecules. Both types of films were exposed to a range of concentrations of the vapours of benzene, toluene, n-hexane, m-xylene, and 1-butanol, and films' interaction with the above molecules was monitored using surface plasmon resonance (SPR) method. The films optical parameters change as a result of such interaction; these changes were determined from the theoretical data fitting of the measured SPR curves. The reflection intensity was also monitored as a function of time at a fixed angle of incidence near the reflectivity minima of the SPR curves. Mechanism of interaction with the studied vapour molecules is discussed in terms of capillary condensation of the vapour molecules inside the nanoporous matrix of PVK and AZO films. The films' responsivity is found to correlate with the solubility of AZO and PVK molecules in the above solvents. (C) 2007 Elsevier B.V All rights reserved