No abstract

It is demonstrated that nuclear resonance reflectivity from isotopic multilayers can be used as a sensitive technique to study self-diffusion of a Mössbauer isotope ͑ 57 Fe in the present case͒. In the case of isotopic multilayers, in which alternate layers have the same chemical composition and differ only in the abundance of 57 Fe, nuclear resonance scattering causes x-ray scattering contrast between adjacent layers, resulting in the appearance of Bragg peaks corresponding to the bilayer periodicity. Diffusion of 57 Fe across the isotopic interface results in a decrease in the scattering contrast and thus a decrease in the intensity of the Bragg peak, making it possible to measure diffusion lengths of the order of 0.1 nm in chemically homogeneous films. The technique has been used to study self-diffusion of Fe in amorphous FeZr and nanocrystalline FeN alloys. In a-FeZr, measurements yield activation energy for Fe diffusion E = 0.42± 0.05 eV and the pre-exponent factor D 0 = exp͑−39± 1͒ m 2 / s. In nanocrystalline Fe 60 N 40 , variation in diffusivity due to structural relaxation at temperatures as low as 393 K could be observed. Measurements in the structurally relaxed state yield E = 0.8± 0.2 eV and D 0 = exp͑−28± 4͒ m 2 /s.

No abstract

The effect of Radio Frequency (RF) power on the properties of magnetron sputtered Al doped ZnO thin films and the related sensor properties are investigated. A series of 2 wt% Al doped ZnO; Zn0.98Al0.02O (AZO) thin films prepared with magnetron sputtering at different RF powers, are examined. The structural results reveal a good adhesive nature of thin films with quartz substrates as well as increasing thickness of the films with raising RF power. Besides, the increasing RF power is found to improve the crystallinity and grains growth as confirmed by X-ray diffraction. On the other hand, the optical transmittance is significantly influenced by the RF power, where the transparency values achieved are higher than 82% for all the AZO thin films and the estimated optical band gap energy is found to decrease with RF power due to an increase in the crystallite size as well as the film thickness. In addition, the defect induced luminescence at low temperature (77 K) and room temperature (300 K) was studied through photoluminescence spectroscopy, it is found that the defect density of electronic states of Al 3+ ion found to increase with increase of RF power due to the increase in the thickness of the film and the crystallite size. The gas sensing behavior of AZO films was studied for NO2 at 350 °C. The AZO film shows good response towards NO2 gas and also a good relationship between the response and the NO2 concentration, which is modeled using an empirical formula. The sensing mechanism of NO2 is discussed.

No abstract