We report on zinc oxide thin films grown by atomic layer deposition at a low temperature, which is compatible with a low thermal budget required for some novel electronic devices. By selecting appropriate precursors and process parameters, we were able to obtain films with controllable electrical parameters, from heavily $n$ -type to the resistive ones. Optimization of the growth process together with the low temperature deposition led to ZnO thin films, in which no defect-related photoluminescence bands are observed. Such films show anticorrelation between mobility and free-electron concentration, which indicates that low $n$ electron concentration is a result of lower number of defects rather than the self-compensation effect.

In this paper, we discuss an impact of thin titanium dioxide (TiO₂) coatings on refractive index (RI) sensitivity and biofunctionalization of long-period gratings (LPGs). The TiO₂ overlays on the LPG surfaces have been obtained using atomic layer deposition (ALD) method. This method allows for a deposition of conformal, thickness-controlled, with well-defined optical properties, and high-RI thin films which are highly desired for optical fiber sensors. It has been found that for LPGs working at a dispersion turning point of higher order cladding modes only tens of nanometers of TiO₂ overlay thickness allow to obtain cladding mode transition effect, and thus significant improvement of RI sensitivity. When the TiO₂ overlay thickness reaches 70 nm, it is possible to obtain RI sensitivity exceeding 6200 nm/RIU in RI range where label-free sensors operate. Moreover, LPGs with TiO₂-enhanced RI sensitivity have shown improved sensitivity to bacteria endotoxin (E. coli B lipopolysaccharide) detection, when TiO₂ surface is functionalized with endotoxin binding protein (adhesin) of T4 bacteriophage.