Zainovia Lockman

Size dependent ferromagnetism in cerium oxide (CeO2) nanostructures independent of oxygen vacancies

Nanosized cerium oxide (CeO2) powders of different sizes were synthesized through homogeneous precipitation. Ferromagnetism was observed only in sub-20 nm powders. Ferromagnetic transition temperatures above room temperature and saturation magnetization values of 0.023 μB per CeO2 formula unit were measured. Chemical analysis of the powders showed that trace ferromagnetic impurities could not be responsible for the magnetic signals. Carefully controlled coulometric cyclic annealing studies combined with photoluminescence measurements showed that oxygen vacancies do not mediate the ferromagnetism in the samples.

Fast-rate formation of TiO2 nanotube arrays in an organic bath and their applications in photocatalysis.

In this work, 18.5 microm titanium oxide (TiO(2)) nanotube arrays were formed by the anodization of titanium (Ti) foil in ethylene glycol containing 1 wt% water and 5 wt% fluoride for 60 min at 60 V. The fast growth rate of the nanotube arrays at 308 nm min(-1) was achieved due to the excess fluoride content and the limited amount of water in ethylene glycol used for anodization. Limited water content and excess fluoride in ethylene glycol inhibited the formation of a thick barrier layer by increasing the dissolution rate at the bottom of the nanotubes. This eased the transport of titanium, fluorine and oxygen ions, and allowed the nanotubes to grow deep into the titanium foil. At the same time, the neutral condition offered a protective environment along the tube wall and pore mouth, which minimized lateral and top dissolution. Results from x-ray photoelectron spectra revealed that the TiO(2) nanotubes prepared in ethylene glycol contained Ti, oxygen (O) and carbon (C) after annealing. The photocatalytic activity of the nanotube arrays produced was evaluated by monitoring the degradation of methyl orange. Results indicate that a nanotube with an average diameter of 140 nm and an optimal tube length of 18.5 microm with a thin tube wall (20 nm) is the optimum structure required to achieve high photocatalytic reaction. In addition, the existence of carbon, high degree of anatase crystallinity, smooth wall and absence of fluorine enhanced the photocatalytic activity of the sample.

Structural and Morphology of ZnO Nanorods Synthesized Using ZnO Seeded Growth Hydrothermal Method and Its Properties as UV Sensing

In this study, zinc oxide (ZnO) nanorod arrays were synthesized using a simple hydrothermal reaction on ZnO seeds/n-silicon substrate. Several parameters were studied, including the heat-treatment temperature to produce ZnO seeds, zinc nitrate concentration, pH of hydrothermal reaction solution, and hydrothermal reaction time. The optimum heat-treatment temperature to produce uniform nanosized ZnO seeds was 400°C. The nanorod dimensions depended on the hydrothermal reaction parameters. The optimum hydrothermal reaction parameters to produce blunt tip-like nanorods (770 nm long and 80 nm in top diameter) were 0.1 M zinc nitrate, pH 7, and 4 h of growth duration. Phase analysis studies showed that all ZnO nanorods exhibited a strong (002) peak. Thus, the ZnO nanorods grew in a c-axis preferred orientation. A strong ultraviolet (UV) emission peak was observed for ZnO nanorods grown under optimized parameters with a low, deep-level emission peak, which indicated high optical property and crystallinity of the nanorods. The produced ZnO nanorods were also tested for their UV-sensing properties. All samples responded to UV light but with different sensing characteristics. Such different responses could be attributed to the high surface-to-volume ratio of the nanorods that correlated with the final ZnO nanorods morphology formed at different synthesis parameters. The sample grown using optimum synthesis parameters showed the highest responsivity of 0.024 A/W for UV light at 375 nm under a 3 V bias.

Effects of Postdeposition Annealing in Argon Ambient on Metallorganic Decomposed CeO2 Gate Spin Coated on Silicon

Cerium oxide (CeO 2 ) solution was prepared by cerium(III) acetylacetonate hydrate, methanol, and acetic acid as the starting materials via the metallorganic decomposition (MOD) method. Postdeposition annealing was performed onto the MOD-derived CeO 2 films deposited onto n-type Si substrates at different temperatures (600, 800, and 1000°C) under the flow of argon gas. A slow cooling rate was then accomplished for samples to cool down to room temperature. Four orientations [(111), (200), (220), and (311)] of CeO 2 films were revealed by X-ray diffraction analysis as well as α-Ce 2 O 3 and cerium silicate (Ce 2 Si 2 O 7 ). Epitaxial-like behavior was shown in the sample annealed at 600°C due to the (200)-oriented CeO 2 film, and the dominance of this plane ceased with the increase in annealing temperature. A negative voltage shift was observed in all of the samples, indicating that positive oxide charges were trapped in the oxide as a result of the presence of oxygen vacancies. An interface trap density was extracted from the capacitance-voltage measurement, and it was related to the current density-voltage characteristics of the investigated samples. The lowest density was perceived by the sample annealed at 1000°C due to the increment in the Ce 2 Si 2 O 7 layer, reduction in total interface trap density, and effective oxide charge.

Effect of Postdeposition Annealing in Oxygen Ambient on Gallium-Nitride-Based MOS Capacitors With Cerium Oxide Gate

This paper presents the effects of postdeposition annealing temperatures (400, 600, 800, and 1000°C) in oxygen ambient on the metal-organic decomposed CeO₂ films spin coated on an n-type GaN substrate. The compositions, structures, and morphologies of these samples are revealed by X-ray diffraction (XRD), field-emission scanning electron microscopy, and an atomic force microscope. XRD analysis discloses the presence of CeO₂ films, α-Ce₂O₃, and an interfacial layer of β-Ga₂O₃. The formation of α-Ce₂O₃ is due to the phase transformation of CeO₂, whereas the β-Ga₂O₃ interfacial layer is formed due to the inward diffusion of the released oxygen from CeO₂ reacting with decomposed GaN. These characterization results are then correlated with the metal-oxide-semiconductor characteristics of the CeO₂ gate annealed at different temperatures. It has been demonstrated that oxide annealed at 1000°C shows the lowest semiconductor-oxide interface-trap density, effective oxide charge, and the highest dielectric breakdown field.

The rapid growth of 3 µm long titania nanotubes by anodization of titanium in a neutral electrochemical bath

The length of titania nanotubes formed by anodization of 0.1 mm thick titanium foil was found to be a strong function of the pH of the electrolyte. The longest nanotubes were formed by using an electrolyte consisting of 1 M Na(2)SO(4) plus 5 wt% NH(4)F with pH 7. At this pH, after 30 min of anodization, 3 microm length nanotubular titania arrays with top diameters of approximately 50 nm and bottom diameters of 100 nm were produced. No acid was added to this electrolyte. The formation of titania nanotubes in neutral pH systems was therefore successful due to the excess NH(4)F in the electrolyte which increases the chemical dissolution process at the metal/oxide interface. Since the pH of the electrolyte at the top part of the nanotubes is kept very high, the dissolution of the nanotubes at the surface is minimal. However, the amount is adequate to remove the initial barrier layer, forming a rather well-defined nanoporous structure. All anodized foils were weakly crystalline and the transformation to anatase phase was achieved by heat treatment at temperatures from 200 to 500 degrees C for 1 h in air. Annealing at temperatures above 500 degrees C induce rutile phase formation and annealing at higher temperatures accelerates the diffusion of Ti(4+) leading to excessive growth and the nanotubular structure diminishes.

MOS Characteristics of Metallorganic-Decomposed CeO2 Spin-Coated on GaN

Metallorganic-decomposed CeO 2 has been successfully spin-coated on an n-type GaN substrate. The effect of postdeposition annealing temperature (400-1000°C) on the electrical characteristics of a CeO 2 /GaN-based metal oxide semiconductor (MOS) structure has been investigated. It has been identified that the sample annealed at the highest temperature demonstrated the highest dielectric breakdown field. The parameters that contributed to this observation have been discussed in detail in this article.

Electrical Properties of Pulsed Laser Deposited Y2O3 Gate Oxide on 4H-SiC

Yttrium oxide (Y 2 0 3 ) has been successfully deposited on n-type 4H-SiC substrates using pulsed laser deposition. The effects of postdeposition annealing temperature (400, 500, and 600°C) on the electrical properties of the Y 2 O 3 gate oxide have been studied in comparison with the as-deposited sample. The sample annealed at 600°C possessed the highest dielectric breakdown field of ∼6.5 MV cm -1 at 10- 6 A cm -2 , resulting from the lowest interface trap density and total interface trap density. The Fowler-Nordheim tunneling mechanism has been investigated on all samples and the highest value of barrier height extracted between the semiconductor and oxide conduction band edges was 2.67 eV.

Electroless Deposition of Ferromagnetic Cobalt Nanoparticles in Propylene Glycol

Ferromagnetic Co nanoparticles with diameters of about 40-400 nm are synthesized by electroless deposition in boiling propylene glycol. The Co particle size is decreased to a certain degree by varying the concentration of starting materials and by adding nucleating agents. The electrochemical behavior of propylene glycol is investigated by in situ measurements of mixed potential to understand the formation of Co nanoparticles in polyol systems. The mixed potential decreases with an increase in temperature and in the presence of NaOH, which suggests the faster decomposition of propylene glycol. It also shifts abruptly to a more negative value when nucleating agents are added. This indicates that nucleating agents catalyze both the oxidation reaction of propylene glycol and the reduction reaction of Co(II) species, as well as aid in the formation of Co nanoparticles as heterogeneous nucleation sites.

Effects of Post-Deposition Annealing on CeO2 Gate Prepared by Metal-Organic Decomposition (MOD) Method on 4H-SiC

Electrical properties of MOD-derived CeO2 film deposited on n-type 4H-SiC have been investigated. Post-deposition annealing of the oxide was performed in argon ambient for 15 minutes at 600, 800, and 1000°C in order to optimize the oxide properties. Spin-on coating was then used to deposit the annealed oxide onto the substrate. Results indicated that the effective oxide charge and slow trap density increased as temperature increased. Negative effective oxide charges were revealed in all annealed oxides. The lowest leakage current and interface trap density was obtained in the sample annealed in the highest temperature.