Fabrication and characterization of thermally oxidized TiO2 thin films on Si(100) substrates

Mixed phase TiO2 is known to have better photocatalytic property as the resulting grain boundaries and interfaces between substrate, anatase and rutile phases play a crucial role in transferring/trapping photogenerated electrons. Here we have grown three different thicknesses (10 nm, 30 nm and 50 nm) of Ti thin films on Si(100) substrate in a sputter coater. Thermal oxidation in air at 600 °C for 1 h leads to the formation of mixed phase TiO2 thin films. Surface morphology and crystalline quality of thin film are discussed using XRD, SEM and TEM results. Moiré fringes resulting from interfacial strain have been discussed using lattice resolved HRTEM images

Effect of halogen addition to monolayer protected gold nanoparticles

The effects of N-halosuccinimide and halogen addition to monolayer protected gold nanoparticles (Au NPs) dispersed in organic media are described. Contrary to the expectation that nanoparticles dispersed in organic media are stable against aggregation, N-iodosuccinimide addition induced aggregation of octadecylamine capped gold nanoparticles in chloroform or toluene. It was observed that even KI and CuI addition could bring about the aggregation though they are very sparingly soluble in organic solvents. It was also found that even molecular iodine could bring about the above mentioned aggregation. Interestingly, when CuI is used the aggregated structures readily convert to very thin flat nanostructures upon exposure to an electron beam or UV irradiation. In fact when the aggregation is induced by the addition of KI or N-iodosuccinamide we do not see the flattening of the aggregated structures exemplifying the important role of Cu ions in making these flat structures

Flux dependent MeV self-ion- induced effects on Au nanostructures: Dramatic mass transport and nano-silicide formation

We report a direct observation of dramatic mass transport due to 1.5 MeV Au2+ ion impact on isolated Au nanostructures of an average size 7.6 nm and a height 6.9 nm that are deposited on Si (111) substrate under high flux (3.2x10^10 to 6.3x10^12 ions cm-2 s-1) conditions. The mass transport from nanostructures found to extend up to a distance of about 60 nm into the substrate, much beyond their size. This forward mass transport is compared with the recoil implantation profiles using SRIM simulation. The observed anomalies with theory and simulations are discussed. At a given energy, the incident flux plays a major role in mass transport and its re-distribution. The mass transport is explained on the basis of thermal effects and creation of rapid diffusion paths at nano-scale regime during the course of ion irradiation. The unusual mass transport is found to be associated with the formation of gold silicide nanoalloys at sub-surfaces. The complexity of the ion-nanostructure interaction process has been discussed with a direct observation of melting (in the form of spherical fragments on the surface) phenomena. The transmission electron microscopy, scanning transmission electron microscopy and Rutherford backscattering spectroscopy methods have been used.Comment: 16 pages, 6 Figure

Environment-mediated structure, surface redox activity and reactivity of ceria nanoparticles

Nanomaterials, with potential application as bio-medicinal agents, exploit the chemical properties of a solid, with the ability to be transported (like a molecule) to a variety of bodily compartments. However, the chemical environment can change significantly the structure and hence properties of a nanomaterial. Accordingly, its surface reactivity is critically dependent upon the nature of the (biological) environment in which it resides. Here, we use Molecular Dynamics (MD) simulation, Density Functional Theory (DFT) and aberration corrected TEM to predict and rationalise differences in structure and hence surface reactivity of ceria nanoparticles in different environments. In particular we calculate reactivity 'fingerprints' for unreduced and reduced ceria nanoparticles immersed in water and in vacuum. Our simulations predict higher activities of ceria nanoparticles, towards oxygen release, when immersed in water because the water quenches the coordinative unsaturation of surface ions. Conversely, in vacuum, surface ions relax into the body of the nanoparticle to relieve coordinative unsaturation, which increases the energy barriers associated with oxygen release. Our simulations also reveal that reduced ceria nanoparticles are more active towards surface oxygen release compared to unreduced nanoceria. In parallel, experiment is used to explore the activities of ceria nanoparticles that have suffered a change in environment. In particular, we compare the ability of ceria nanoparticles, in an aqueous environment, to scavenge superoxide radicals compared to the same batch of nanoparticles, which have first been dried and then rehydrated. The latter show a distinct reduction in activity, which we correlate to a change in the redox chemistry associated with moving between different environments. The reactivity of ceria nanoparticles is therefore not only environment dependent, but is also influenced by the transport pathway or history required to reach the particular environment in which its reactivity is to be exploited. © 2013 The Royal Society of Chemistry

Fabrication and characterization of thermally oxidized TiO2 thin films on Si(100) substrates

732-736Mixed phase TiO2 is known to have better photocatalytic property as the resulting grain boundaries and interfaces between substrate, anatase and rutile phases play a crucial role in transferring/trapping photogenerated electrons. Here we have grown three different thicknesses (10 nm, 30 nm and 50 nm) of Ti thin films on Si(100) substrate in a sputter coater. Thermal oxidation in air at 600 °C for 1 h leads to the formation of mixed phase TiO2 thin films. Surface morphology and crystalline quality of thin film are discussed using XRD, SEM and TEM results. Moiré fringes resulting from interfacial strain have been discussed using lattice resolved HRTEM images

Low-energy ion beam synthesis of ag endotaxial nanostructures in silicon

Coherently, embedded metal nanostructures (endotaxial) are known to have potential applications concerning the areas of plasmonics, optoelectronics and thermoelectronics. Incorporating appropriate concentrations of metal atoms into crystalline silicon is critical for these applications. Therefore, choosing proper dose of low-energy ions, instead of depositing thin film as a source of metal atoms, helps in avoiding surplus concentration of metal atoms that diffuses into the silicon crystal. In this work, 30 keV silver negative ions are implanted into a SiO (x) /Si(100) at two different fluences: 1 x 10(15) and 2.5 x 10(15) Ag- ions/cm(2). Later, the samples are annealed at 700 A degrees C for 1 h in Ar atmosphere. Embedded silver nanostructures have been characterized using planar and cross-sectional TEM (XTEM) analysis. Planar TEM analysis shows the formation of mostly rectangular silver nanostructures following the fourfold symmetry of the substrate. XTEM analysis confirms the formation of prism-shaped silver nanostructures embedded inside crystalline silicon. Endotaxial nature of the embedded crystals has been discussed using selected area electron diffraction analysis.UGC-DAE CSR, KC Collaborative Research Project UGC-DAE-CSR-KC/CRS/15/IOP/MS/01/0669/0670/075

Environment-Mediated Structure, Surface Redox Activity And Reactivity Of Ceria Nanoparticles

Nanomaterials, with potential application as bio-medicinal agents, exploit the chemical properties of a solid, with the ability to be transported (like a molecule) to a variety of bodily compartments. However, the chemical environment can change significantly the structure and hence properties of a nanomaterial. Accordingly, its surface reactivity is critically dependent upon the nature of the (biological) environment in which it resides. Here, we use Molecular Dynamics (MD) simulation, Density Functional Theory (DFT) and aberration corrected TEM to predict and rationalise differences in structure and hence surface reactivity of ceria nanoparticles in different environments. In particular we calculate reactivity \u27fingerprints\u27 for unreduced and reduced ceria nanoparticles immersed in water and in vacuum. Our simulations predict higher activities of ceria nanoparticles, towards oxygen release, when immersed in water because the water quenches the coordinative unsaturation of surface ions. Conversely, in vacuum, surface ions relax into the body of the nanoparticle to relieve coordinative unsaturation, which increases the energy barriers associated with oxygen release. Our simulations also reveal that reduced ceria nanoparticles are more active towards surface oxygen release compared to unreduced nanoceria. In parallel, experiment is used to explore the activities of ceria nanoparticles that have suffered a change in environment. In particular, we compare the ability of ceria nanoparticles, in an aqueous environment, to scavenge superoxide radicals compared to the same batch of nanoparticles, which have first been dried and then rehydrated. The latter show a distinct reduction in activity, which we correlate to a change in the redox chemistry associated with moving between different environments. The reactivity of ceria nanoparticles is therefore not only environment dependent, but is also influenced by the transport pathway or history required to reach the particular environment in which its reactivity is to be exploited. © 2013 The Royal Society of Chemistry

Morphology And Surface Analysis Of Pure And Doped Cuboidal Ceria Nanoparticles

Cuboidal nanoparticles of ceria are examined by high resolution imaging and analysis to explore their local morphology of faces, edges, and corners. Synthesized with and without Sm doping using a hydrothermal process, we find a high fraction of particles enclosed by {100} facets, which are normally energy-penalized compared to octahedral {111} facets. Electron tomography conducted at high magnification with lattice resolved imaging is combined with electron energy loss spectroscopy revealing oxidation states of Ce ions. It is found that extended {100} faces exist predominantly without local nanofaceting, except for {111} corner caps and subfacets on {110} edges. Reduced Ce is found on all {100} surfaces, while Sm doping does not lower the reduced Ce concentration. Molecular dynamics simulations are used to complement the microscopy, including the formation of {111} subfacets on {110} edges, formation of a {111} corner facet, and also the fact that reduced Ce ions prefer low coordinated positions like steps and corners along with more active {100} faces. © 2013 American Chemical Society

Cationic Surface Reconstructions On Cerium Oxide Nanocrystals: An Aberration-Corrected Hrtem Study

The analysis of cell-specific mRNA expression is a promising new method for the identification of body fluids. A number of mRNA markers have been identified for the forensically most relevant body fluids: blood, saliva, semen, vaginal secretions, and menstrual blood. Apart from a significant improvement in specificity compared to conventional protein-based methods, other important advantages of body fluid identification by mRNA profiling include the possibility of simultaneously isolating RNA and DNA from the same piece of stain and the ability to multiplex numerous RNA markers for the identification of one or several body fluids. RNA profiling can be incorporated into current DNA analysis pipelines. © 2012 Springer Science+Business Media, LLC