Highly ordered, honeycomb-like iron oxide (hematite) films were fabricated by double-step anodic oxidation of iron foil. The honeycomb structure obtained by double step anodization was found to be more effective in producing a large area film with homogeneous pore distribution compared to nanotubes fabricated by the conventional single-step anodic oxidation process. To prevent agglomeration of the hematite film during the annealing process, a thin alumina layer was deposited on the hematite film surface by atomic layer deposition. With this alumina shielding and subsequent removal by alkaline treatment, one-dimensional (1-D) hematite nanostructure was preserved perfectly after annealing at 550 C. This highly ordered 1-D nanostructure film showed much enhanced photoelectrochemical cell performances relative to hematite films with low degrees of ordering.
A new fabrication process of a vertically aligned ferroelectric perovskite PbTiO 3 nanowire array on Ti substrate is presented. Polycrystalline TiO 2 nanotubes are first fabricated by anodic oxidation of Ti foil and then treated hydrothermally in a lead acetate solution to obtain single-crystalline nanowires. This nanotube-to-nanowire transformation on conducting substrate could be described by a swelling-and-rupture mechanism, in which individually well-developed nanotubes are swollen and broken along the friction planes because of difference in the directions of expansion force. Nanowires with a uniform diameter of ca. 40 nm and a length of 10 μm show single-crystalline nature over the entire length of nanowires and ultrahigh density corresponding to ca. 0.22 Tb inch -2 . The ferroelectric property of individual PbTiO 3 nanowires and whole area of nanowire arrays has been demonstrated by piezo-response force microscopy.
A new synthetic method is reported for depositing BaTiO(3) nanowire film on conducting glass. First, a TiO(2) particle thin film is prepared by spray coating, and then transformed to single crystalline BaTiO(3) nanowires grown on the conducting glass by hydrothermal treatment using TiO(2) particles as seeds of nanowire growth. The BaTiO(3) nanowires are 50-100 nm in diameter and have a film thickness of 4 µm. The capacitance of the BaTiO(3) one-dimensional (1D) nanowire array film was found to be 4.5 times higher than that of the nanoparticle film by measuring the impedance. The piezoelectric property of an individual BaTiO(3) nanowire was also demonstrated by piezoforce microscopy.
The positive bias temperature instability (PBTI) characteristics of the n-channel metal-oxide-semiconductor field emission transistors which had different kinds of high-k dielectric gate oxides were studied with the different stress-relaxation times. The degradation in the threshold voltage followed a power-law on the stress times. In particular, we found that their PBTI behaviors were closely related to the structural phase of the high-k dielectric gate oxide. In an amorphous gate oxide, the negative charges were trapped into the stress-induced defects of which energy level was so deep that the trapped charges were de-trapped slowly. Meanwhile, in a crystalline gate oxide, the negative charges were trapped mostly in the pre-existing defects in the crystallized films during early stage of the stress time and de-trapped quickly due to the shallow energy level of the defects.
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