Browsing by Subject "Transmission electron microscopy tem"

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Open Access
Investigation of local structure effect and X-ray absorption characteristics (EXAFS) of Fe (Ti) K-edge on photocatalyst properties of SrTi (1-x)Fe xO (3-δ)
(2012) Ghaffari, M.; Liu, T.; Huang H.; Tan O.K.; Shannon, M.
In this study, the STF x photocatalyst powder was synthesized with a high temperature solid state reaction. The microstructures and surface of samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The electronic properties and local structure of the perovskite STF x (0 ≤ x ≤ 1) systems were probed by extended X-ray absorption fine structure (EXAFS) spectroscopy. The XPS results revealed that with increasing iron doping, the amount of Fe 3+ and Fe 4+ increased significantly. The X-ray absorption data are discussed in detail with respect to the Fe (Ti) K-edge. The substitution of iron by titanium increased the Ti (Fe)-O first shell disorder factors that can be explained by increasing the oxygen vacancies. Oxygen vacancies or defects act as electron traps, which could capture the photo induced electrons and thus could effectively inhibit the recombination of the photo induced electrons and holes. Moreover due to the substitution of Ti with Fe, lattice shrinkage was observed and the largest derivation from the Gaussian distribution in STF x was from those samples with x = 0.6 and x = 0.8. The substitution of iron by titanium increased the iron valence state, hence the formation of the Jahn-Teller Fe 4+ ion. With increasing iron dopant the [Ti(Fe)-O] ave decreased and bond length of [Ti-O] and the consequent [Ti-O-Ti] increased and this phenomenon affected the photocatalyst and photo degradation properties of material and also decreased its efficiency. © 2012 Elsevier B.V. All rights reserved.
Open Access
Preparation of Al 2O 3and AlN nanotubes by atomic layer deposition
(Cambridge University Press, 2012) Ozgit-Akgun, Çagla; Kayacı, Fatma; Dönmez, İnci; Çağatay, Engin; Uyar, Tamer; Bıyıklı, Necmi
Al 2O 3 and AlN nanotubes were fabricated by depositing conformal thin films via atomic layer deposition (ALD) on electrospun nylon 66 (PA66) nanofiber templates. Depositions were carried out at 200°C, using trimethylaluminum (TMAl), water (H 2O), and ammonia (NH 3) as the aluminum, oxygen, and nitrogen precursors, respectively. Deposition rates of Al 2O 3 and AlN at this temperature were ∼1.05 and 0.86 Å/cycle. After the depositions, Al 2O 3- and AlN-coated nanofibers were calcinated at 500°C for 2 h in order to remove organic components. Nanotubes were characterized by using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). AlN nanotubes were polycrystalline as determined by high resolution TEM (HR-TEM) and selected area electron diffraction (SAED). TEM images of all the samples reported in this study indicated uniform wall thicknesses. © 2012 Materials Research Society.
Open Access
Structural and phase evolution in mechanically alloyed calcium copper titanate dielectrics
(2013) Alizadeh, M.; Ardakani H.A.; Amini, R.; Ghazanfari, M.R.; Ghaffari, M.
Nanocrystalline calcium-copper-titanate (CCTO) dielectric powders were prepared by mechanical alloying. Phase transformations and structural evolution of the mechanically activated powders were investigated through the Rietveld refinement of the X-ray diffraction results. The crystallite size, lattice strain, and weight fraction of individual phases were estimated based on crystal structure refinement. Furthermore, the microstructural properties and thermal behavior of the milled powders were investigated by Transmission Electron Microscopy (TEM) and Differential Thermal Analysis (DTA), respectively. It was found that CCTO nanocrystals can be successfully synthesized after the amorphization of the initial crystalline materials. Semi-spherical nano-size particles were developed after sufficient milling time. Formation of an amorphous phase during the milling cycle was confirmed by the presence of the glass transition and crystallization peaks in the thermal analysis profiles. © 2012 Elsevier Ltd and Techna Group S.r.l.