Iva Šarić

The effect of thermal treatment of radiation-induced EPR signals of different polymorphic forms of trehalose.

Electron paramagnetic resonance (EPR) signals induced by γ-radiation in different polymorphic forms of trehalose were studied with dosimetry applications in view. Dose response of trehalose in terms of the concentration of induced paramagnetic centers was studied in the dose range from 0.5 to 50 kGy. The dependences of the dose responses of anhydrous β-crystalline trehalose (TRE(β)) and glassy trehalose (TRE(g)) on dose are linear up to 15 kGy, whereas the linearity of the dependence for trehalose dihydrate (TRE(h)) is limited to about 10 kGy. At doses above 15 kGy, the dependences get saturated for all three forms. The relative radiation sensitivities pointed to the following order of decreasing concentrations of radiation-induced paramagnetic centers in the forms: TRE(g)>TRE(β)>TRE(h). The results showed that at all three trehalose polymorphic forms are suitable for dosimetry, especially for retrospective dose measurements. Also, thermal stability and decay kinetics of the EPR signals of the different forms of trehalose were studied in isothermal annealing experiments. The kinetic parameters, which had been derived by fitting the Arrhenius function to the measured decay rate constants, indicated that the fading of the EPR signals varied from one polymorphic form of trehalose to another. This emphasizes the impact of the molecular packing in the vicinity of the radiation-induced paramagnetic centers on their stability.

Ta2N3 nanocrystals grown in Al2O3 thin layers

Tantalum nitride nanoparticles (NPs) and cubic bixbyite-type Ta2N3 nanocrystals (NCs) were grown in (Ta–N+Al2O3)/Al2O3 periodic multilayers (MLs) after thermal treatment. The MLs were prepared by magnetron deposition at room temperature and characterized using grazing incidence small-angle X-ray scattering (GISAXS), X-ray reflectivity (XRR), grazing incidence X-ray diffraction (GIXRD), secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS). We found amorphous tantalum nitride NPs at 600–800 °C, with a high degree of ordering along the surface normal and short-range ordering within the layers containing tantalum (metallic layers). At an even higher annealing temperature of 900 °C the NPs crystallize in the rare and relatively unexplored Ta2N3 phase. However, the environment, morphology and spatial ordering of the NCs depend on the thickness of the metallic layers. For 12 nm thick metallic layers, the Ta2N3 NCs have an average diameter of 6 nm and they are confined and short-range ordered within the metallic layers. When the metallic layers are thinner, the NCs grow over 20 nm in diameter, show no spatial ordering, while the periodic structure of the ML was completely destroyed. The results presented here demonstrate a self-assembly process of tantalum nitride NPs, the morphological properties of which depend on the preparation conditions. This can be used as a generic procedure to realize highly tunable and designable optical properties of thin films containing transition-metal nitride nanocrystals.