Self-organization of Fe clusters on mesoporous TiO2templates

Surface distortion of Fe dot-decorated TiO2 nanotubular templates using time-of-flight grazing incidence small angle scattering

Physical properties of nanoclusters, nanostructures and self-assembled nanodots, which in turn are concomitantly dependent upon the morphological properties, can be modulated for functional purposes. Here, in this article, magnetic nanodots of Fe on semiconductor TiO₂ nanotubes (TNTs) are investigated with time-of-flight grazing incidence small-angle neutron scattering (TOF-GISANS) as a function of wavelength, chosen from a set of three TNT templates with different correlation lengths. The results are found corroborating with the localized scanning electron microscopy (SEM) images. As we probe the inside and the near-surface region of the Fe-dotted TNTs with respect to their homogeneity, surface distortion and long-range order using TOF-GISANS, gradual aberrations at the top of the near-surface region are identified. Magnetization measurements as a function of temperature and field do not show a typical ferromagnetic behavior but rather a supermagnetic one that is expected from a nonhomogeneous distribution of Fe–dots in the intertubular crevasses.

Tailoring morphology, structure and photoluminescence properties of anodic TiO2nanotubes

TiO2nanotube (TNT) structures were grown perpendicular to fluorine-doped tin-oxide-coated glass substrates by anodic oxidation of titanium films. The morphology, crystal structure and optical properties of the TNTs were shown to be dependent on the thickness of the titanium film, which acts as an electrode in electrochemical anodization. Field emission scanning electron microscopy measurements revealed that an increase in titanium thickness from 1.5 to 2.7 µm caused a considerable increase in both inner diameter and tube length, which in turn increases the porosity and the physical surface of the TNTs per unit area. Grazing-incidence small-angle scattering was used to infer the statistical lateral ordering of the TNTs over macroscopic length scales. X-ray diffraction data show an increase in the texture coefficient for the (004) plane as well as theI004/I101intensity ratio with titanium film thickness. All these factors lead to a significant improvement in the photoluminescence intensity from titania nanotubes, which is about five times more than from titania nanoporous materials under similar circumstances.

Morphology of Fe nanolayers with Pt overlayers on low-temperature annealing

Agglomeration or dewetting is technologically important in the microelectronics industry as it is one of the methods of producing arrays of nanosized metal clusters. This report investigates the grain morphology evolution due to low-temperature annealing (473 K) in Fe layers with Pt overlayers. X-ray diffuse scattering and grazing-incidence small-angle X-ray scattering (GISAXS) have been used to access different correlation lengths and correlate them with grain sizes from transmission electron microscopy. Overall, the GISAXS data indicate that the nanoparticles or nanoclusters in the samples appear as bimodal distributions. It is shown that, for an Fe layer with vertical grain sizes of 5 and 11 nm, irrespective of cluster size, there is no signature of agglomeration between the Fe and Pt layers even with very long annealing times (3000 min). The vertical grain sizes are mediated by the film thickness. Furthermore, an alternating variation with grain sizes of 4 and 7 nm is achieved by Al doping, but without a restriction on the Fe layer thickness. Even in this case, the agglomeration process is seen to remain unaffected by annealing for the same time durations, but only for the larger sized nanoclusters. The smaller ones are seen to grow in size, with increased correlation lengths for the maximum annealing time owing to higher surface energy.

GISAXS and TOF-GISANS studies on surface and depth morphology of self-organized TiO2nanotube arrays: model anode material in Li-ion batteries

Self-organized anodic titania (TiO2) nanotube arrays are an interesting model anode material for use in Li-ion batteries owing to their excellent rate capability, their cycling stability and their enhanced safety compared to graphite. A composite material where carbothermally treated conductive TiO2nanotubes are used as support for a thin silicon film has been shown to have the additional advantage of high lithium storage capacity. This article presents a detailed comparison of the structure, surface and bulk morphology of self-organized conductive TiO2nanotube arrays, with and without silicon coating, using a combination of X-ray diffraction, X-ray reflectivity, grazing-incidence small-angle X-ray scattering (GISAXS) and time-of-flight grazing-incidence small-angle neutron scattering (TOF-GISANS) techniques. X-ray diffraction shows that the nanotubes crystallize in the anatase structure with a preferred (004) orientation. GISAXS and TOF-GISANS are used to study the morphology of the nanotube arrays, delivering values for the inner nanotube radius and intertubular distances with high statistical relevance because of the large probed volume. The analyses reveal the distinct signatures of a prominent lateral correlation of the TiO2nanotubes of ∼94 nm and a nanotube radius of ∼46 nm. The porosity averaged over the entire film using TOF-GISANS is 46%. The inner nanotube radius is reduced to half (∼23 nm) through the silicon coating, but the prominent lateral structure is preserved. Such in-depth morphological investigations over large sample volumes are useful towards development of more efficient battery electrode morphologies.