Surface plasmons resonance spectroscopy and its application to sensor devices : a novel approach with the combination of X-ray spectroscopy

Almost 100 years ago, R. W. Wood observed strong, angular dependent variations in the intensity of light that was reflected from an optical metal grating. This effect was due to the interaction of light with a fundamental excitation of a metal-dielectric interface. This excitation is characterised by a charge density oscillation in the metal, which is accompanied by an electromagnetic field that extends in both media. Since the energy is confined to the vicinity of the metal surface, and the conduction electrons of a metal can be treated as plasma, this excitation is called the surface plasmons resonance.
For quite a long period of time, not much progress was made in this field until the availability of new theoretical and experimental techniques triggered growing interest in the optics of metallic thin film.
In this work, a self made surface plasmons resonance set-up was constructed using the Kretschmann's configuration. Using the self made device, diverse static measurements were carried out to verify the credibility of the sensor.
The bulk behavior of polymers has been investigated extensively since the discovery of their (commercial) value in many applications during the 1940s. Thus, nowadays the relation between molecular structure and macroscopic behaviour is fairly well understood.
However, since molecular interactions always show changes in thicknesses and refractive indices, by combining the device with x-ray spectroscopy would guarantee the independent monitoring of thickness and electron density variation during such interactions. In this way the self made device was then adapted to our home x-ray device and simultaneous measurements of SPR and x-ray reflectivity were also carried out on a polymer film.
Using both devices simultaneously we studied the diffusion of gold colloids through a thin layer of polymer initiated by an external perturbation, heat. By varying the temperature of the sample stepwise from 150°C to 200°C, a vertical distribution of gold colloids within the polymer was created. This vertically induced electron density variation was recorded independently using the x-ray reflectivity device after each annealing step. Simultaneously the optical changes brought about by the vertically induced electron density were also recorded using the SPR sensor device. By simulating the results obtained from the x-ray reflectivity and the subsequent calculation of the electron density within the polymer layer, we could later verify the responds recorded by the SPR response.
Finally colloids with a diameter greater than the thickness of the polymer film were also brought onto the surface of the polymer layer and the sample also annealed from 150°C to 220°C. Although this time there was no diffusion of the colloids into the polymer, the submerged part of the colloids into the polymer also created an electron density variation within the polymer layer. This was later modelled and simulated. This generated electron density variation as a result of this submersion of the colloids into the polymer was later seen to be responsible for the characteristic movement of the SPR response towards higher angles.
The simultaneous study of a dynamic process using both spectroscopic processes has never been made up till date.