SPR-BASED SENSORS STUDIED BY ELECTRON-ENERGY-LOSS SPECTROSCOPY AND ATTENUATED TOTAL-REFLECTION

Electron energy loss spectroscopy (EELS) and attenuated total reflection (ATR) are employed to excite and study the surface plasmon of thin silver films. The films studied are used in surface plasmon resonance-(SPR-) based sensors, where the surface plasmon is excited using the evanescent wave from a light beam totally internally reflected from the base of a prism (Kretschmann configuration) and the resonance is observed as an attenuation of the reflected light intensity as the angle of incidence of the light in the prism is scanned. Such sensors exploit the high sensitivity of the surface plasmon frequency to the refractive index of layers of adsorbed molecules on the surface. The surface plasmon frequency, however, is also a sensitive function of the silver film preparation conditions which control the preferred crystallographic orientation and surface roughness of the silver. Surface roughness is known to strongly affect the surface plasmon frequency and there is much controversy concerning the influence of crystal orientation on the dispersion characteristics of the surface plasmon. The present work investigates the effect of varying the deposition temperature of the films on the surface plasmon characteristics (measured by EELS and ATR). The results are discussed in terms of the crystallographic orientation (studied by X-ray diffraction (XRD)) and the surface roughness (studied by scanning tunneling microscopy (STM)) of the films.