Three-dimensional atomic scale analysis of nanostructured materials

The 3-dimensional atom probe (3DAP) has been used to provide atomic-scale microcharacterisation of a number of nanostructured materials. Grain boundary segregation has been investigated in electrodeposited nanocrystalline nickel and Ni-P. In the nanocrystalline nickel, there was no observable grain boundary segregation in the as-deposited condition. After annealing, carbon and sulphur contamination was found at the boundary of an abnormally-grown grain. In the as-deposited Ni-P alloy, only limited grain boundary segregation of P is seen, but annealing produces significant segregation and the formation of Ni₃P precipitates at grain boundaries. The phase chemistry in a melt-spun amorphous Fe-Si-Cu-Nb-B-Al (FINEMET-type) alloy has also been studied, and the hetereogeneous nucleation of Fe-Si nanocrystals at Cu precipitates shown conclusively. It is found that at early stages of crystallisation, there is only limited partitioning of the Si between the nanocrystals and the amorphous matrix. Atom probe studies of thin layered films have historically been limited by specimen preparation problems, but recent advances have now yielded data on metallic multilayer films. This has allowed atomic-scale measurements of interface chemistry in these films for the first time.     

Structural, compositional, thermal resistant and hydro-oleophobic properties of fluorine based block-co-polymer films on quartz substrates by wet chemical process

Crack free and smooth surfaces of poly [4,5-difluoro 2,2-bis (trifluoromethyl)-(1,3 dioxole)-co-tetrafluoroethylene] (TFE-co-TFD) thin films have been deposited by wet chemical dip coating technique on polished quartz and glass slide substrates. The deposited films have been subjected to annealing at different temperatures ranging from 100 to 500 °C for 1 h in argon atmosphere. The elemental composition of the as-deposited (xerogel) thin film as well as film annealed at 400 °C was measured by X-ray photoelectron spectroscopy and observed that there was no change in the composition of the film. X-ray diffraction pattern revealed the amorphous behaviour of both as-deposited and film annealed at 400 °C. Surface morphology and elemental composition of the films have been examined by employing scanning electron microscopy attached with energy dispersive X-ray analyser, respectively. It was found that as the annealing temperature increased from 100 to 400 °C, nano-hemisphere-like structures have been grown, which in turn has shown increase in the water contact angle from 122^o to 148^o and oil (peanut) contact angle from 85° to 96°. No change in the water contact angle (122°) has been observed when the films deposited at room temperature were heated in air from 30 to 80 °C as well as exposed to steam for 8 days for 8 h/day indicating thermal stability of the film.     

Tuning diagonal components of static linear and first nonlinear polarizabilities of doped quantum dots by Gaussian white noise

We investigate the modulation of diagonal components of static linear (α_xx, α_yy) and first nonlinear (β_xxx, β_yyy) polarizabilities of quantum dots by Gaussian white noise. Quantum dot is doped with impurity represented by a Gaussian potential and repulsive in nature. The study reveals the importance of mode of application of noise (additive/multiplicative) on the polarizability components. The doped system is further exposed to a static external electric field of given intensity. As important observation we have found that the strength of additive noise becomes unable to influence the polarizability components. However, the multiplicative noise influences them conspicuously and gives rise to additional interesting features. Multiplicative noise even enhances the magnitude of the polarizability components immensely. The present investigation deems importance in view of the fact that noise seriously affects the optical properties of doped quantum dot devices.     

Surface morphology and step fluctuations on Ag nanowires

Silver nanowires fabricated using a wet-chemical synthesis have been characterized in UHV using scanning tunneling microscopy. The nanowires have a faceted structure with a high density of steps at the facet boundaries. Monolayer height steps are easily imaged, and have measurable temporal fluctuations at room temperature. Measurement of the step time correlation functions shows that the steps fluctuate via periphery diffusion, with a hopping time constant of 0.10-0.24 s. The symmetry of islands on the facets and the quantitative step characteristics are both consistent with (1 0 0) oriented facets, in agreement with previous TEM characterization.     

Preparation and characterization of polymer coated superparamagnetic magnetite nanoparticle agglomerates

In order to produce magnetic microparticles (agglomerates), magnetite (Fe₃O₄) particles were synthesized using coprecipitation of FeSO₄·7H₂O and FeCl₃·6H₂O with the presence of poly(methacrylic acid) (PMAA) in aqueous solution.. Transmission electron microscopy (TEM), X-ray diffraction, and vibrating sample magnetometry (VSM) methods were used to characterize the PMAA coated superparamagnetic agglomerates. The influences of various processing parameters such as the process temperature, PMAA content, and the addition of surfactant on the agglomerate size and size distribution of produced magnetic microparticles were investigated. The particle size and size distribution characteristics, (the volume weighted mean size (D[4,3], surface weighted mean size D[3,2], the geometric standard deviation, and span value) of the magnetic agglomerates were determined using the laser diffraction technique. The PMAA coated magnetic agglomerates with surface weighted mean sizes ranging from 1.5 to 3 μm were produced successfully.     

NMR property of sodalite loaded with potassium

²⁷Al NMR property of potassium-loaded sodalite, which shows antiferromagnetic transition around 70 K, is reported. Monotonic narrow spectrum above 70 K is broadened below 70 K. The broadened spectrum is analyzed with an assumption that the broadening is given by dipolar field from magnetic moment in the cage of sodalite. Two Gaussian functions are used for fitting. Widths of each component proportionally scale each other. The ratio between the Gaussian widths of each component of the narrower and the broader components is 15±3.     

Preparation and photocatalytic property of α-Fe2O3 hollow core/shell hierarchical nanostructures

We report the preparation of a novel kind of α-Fe₂O₃ hollow core/shell hierarchical nanostructures self-assembled by nanosheets. A green precursor powder is first prepared using nontoxic and inexpensive FeCl₃ and urea in ethylene glycol by a surfactant-free solvothermal method at 160 °C for 15 h. The α-Fe₂O₃ hollow core/shell hierarchical nanostructures are obtained by the thermal treatment of the green precursor powder. The as-prepared α-Fe₂O₃ hollow core/shell hierarchical nanostructures are porous, and exhibit a good photocatalytic activity for the degradation of phenol. The samples are characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).     

Thermoluminescence studies of bismuth doped BaxCa1−xS nanostructures

Bismuth doped Ba_1−xCa_xS:Bi (x=0-1) nanocrystallities have been prepared by the solid state reaction method and characterized by XRD and TEM. X-ray diffraction analysis shows the formation of the compounds in cubic structure at room temperature. Only partial replacement of Ba is possible and we found that Ba_0.5Ca_0.5S:Bi could not be prepared due to the difference between ionic radii of barium and calcium. Thermoluminescence studies of these samples after exposure to UV radiation have been carried out. The TL glow curve of Ba_xCa_1−xS:Bi has been found to be a simple structure with a single peak at 405, 428 and 503 K for x=1, 0.8 and 0, respectively. The kinetic parameters at various heating rates namely activation energy (E), order of kinetics (b) and frequency factor (s) of the Ba_1−xCa_xS:Bi (x=0.2) (0.4 mol%) sample have been determined using Chen’s method. The deconvolution of curve was done using the GCD function suggested by Kitis. The effect of different heating rates and different amount of dose has also been discussed.     

Synthesis of a magnetically separable composite photocatalyst with high photocatalytic activity under sunlight

A novel magnetically separable composite photocatalyst (N-doped titania-coated γ-Fe₂O₃ magnetic activated carbon) was prepared. It consists of N-doped titania, activated carbon and γ-Fe₂O₃. The whole processes were carried out under low temperature. The prepared sample was characterized by XRD, DRS, SEM, BET and vibrating sample magnetometer (VSM). The photocatalytic activity was determined by degradation of Reactive Brilliant Red X-3B in an aqueous solution under solar irradiation. Results showed that this as-prepared composite photocatalyst exhibited much higher photocatalytic activity than Degussa P25. Furthermore, the photocatalyst can be separated easily by an external magnetic field. Thus, the photocatalyst can be recycled without mass losing, and the degradation percent of X-3B decreased less than 2% after six cycles.     

Self-assembly of Sb2O3 nanowires into microspheres: Synthesis and characterization

Sb₂O₃ nanowires with diameters of ∼233 nm and microspheres assembled by these nanowires were successfully synthesized by a simple poly-(vinylpyrrolidone) (PVP) assisted hydrothermal method. The morphologies, nano/microstructures and optical properties of the as-grown nanowires and microspheres were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-vis diffuse reflection spectrum. It has been found that the experimental parameters, such as mineralizers, played crucial roles in the morphological control of Sb₂O₃ nanowires. The possible growth mechanism of microspheres has been proposed.