Effect of electron-beam treatment of sensor glass substrates for SPR devices on their metrological characteristics

Electron-beam treatment the glass substrates for sensitive elements of SPR devices causes almost two-fold narrowing their refractometric characteristics from 0.867 down to 0.453 deg. The angular shift was also changed, which made the measuring range wider by 0.37 deg. The sensitivity of SPR devices increased by 1.7 times from 1.425 up to 2.396 deg–1 as a consequence of lowering the energy expenses during propagation of surface plasmons along the boundary “metal–air”. The reason for this lowering is related to higher surface uniformity of the gold metal film, its higher density as well as lower nano-roughness of the glass surface and the thickness of heterointerface “gold–air”. In this case, the dispersion value for unevenness heights on the surface relatively to the base line was lowered from ±18 down to ±5 nm, mean-square roughness was three-fold reduced from 4.67 down to 1.64 nm, and the thickness of heterointerface gold–air was lowered from 3.26 down to 1.37 nm. It was ascertained using X-ray reflectometry that the film density increased from 17.2 up to 19.3 g/cm3 and reached the value typical for the bulk gold. It provided the changes in the refraction index and extinction coefficient of the gold film, which was ascertained using the ellipsometric method. Thus, the performed analysis of refractometric characteristics showed that electron-beam treatment the glass substrates of sensitive elements for SPR devices is able to efficiently enhance their sensitivity and to widen the range of measured resonance SPR angles.