Spherical submicrometer-sized titanium dioxide (TiO2 or titania) particles were prepared by the sol-gel method from hydrolysis and condensation of titanium butoxide Ti(OC4H9)4 using ammonia as a catalyst in ethanol/acetonitrile and annealing in air at 100°C. Subsequently, they were deposited onto silicon substrates, in order to form a monolayer of TiO2 particles. Then these samples were irradiated at room temperature with Si2+ ions at 4, 6 and 8 MeV, with fluences in the 2×1014-2×1015 Si/cm2 range, under an angle of 45° with respect to the sample surface. The titania particles were characterized by scanning electron microscopy to determine their size and shape before and after the ion irradiation. After the Si irradiation the spherical silica particles turned into ellipsoidal particles, as a result of the increase of the particle dimension perpendicular to the ion beam and the decrease in the direction parallel to the ion beam. This deformation effect increases monotonically with the ion fluence, and depends on the electronic energy loss of the impinging ion.

We present a new approach for modeling strongly anisotropic crystal and epitaxial growth using regularized, anisotropic Cahn-Hilliard-type equations as a model for the growth and coarsening of thin films. When the surface anisotropy is sufficiently strong, sharp corners form and unregularized anisotropic Cahn-Hilliard equations become ill-posed. Our models contain a high order Willmore regularization to remove the ill posedness at the corners. A key feature of our approach is the development of a new formulation in which the interface thickness is independent of crystallographic orientation. In our previous work, we have provided matched asymptotic analysis to show the convergence of our diffuse interface model to the analytical sharp interface model. In previous models there was no such convergence to sharp interface model when the Willmore energy was considered. We present 2D numerical results using an adaptive, nonlinear multigrid finite-difference method. In particular, we find excellent agreement between the computed shapes using the Cahn-Hilliard approach, with a finite but small Willmore regularization, with dynamical numerical simulations of a sharp interface model. The equilibrium shapes from our diffuse model are compared with an analytical sharp-interface theory recently developed by Spencer [1] at the corners, and there is excellent match. Away from the corners there is an excellent agreement between the diffuse model and the classical Wulff shape. Finally, in order to model the misfit and displacement strains, we add the elastic energy and corresponding forces to our diffuse model. We analyze numerically the effect of elastic stress on the corner regularization in terms of two parameters: one parameter that describes the relative strength of the elastic energy to surface energy and the second that characteristics the strength of the surface energy anisotropy. Adding elastic energy modifies the equilibrium shape and in particular affects the shape of the corners. We can predict different Qdot shapes, such as pyramids and domes, based on the strength of the elastic interactions.

The kinetics of formation of palladium nanoparticles with well-defined morphologies (rods, cubes, MTP icosahedra, bipyramids) was studied using a combination of TEM and dynamic light scattering (DLS). The present study was focused on the role of the concentration and the size of seeds on both the kinetics of growth and the morphology distribution. Results clearly emphasize the role of the seed concentration (and not the size) on the growth kinetics in agreement with a collision theory model.

It is determined that the interfacial strain due to lattice mismatch between the substrate (template) and the overgrown nanostructure has substantial influence on the final morphology and faceting of nanostructures. AlGaN and GaN nanostructures were grown on different substrates/templates, namely Sapphire, AlN/Sapphire, Al0.5Ga0.5N/Sapphire and GaN/Sapphire, where interfacial strain for overgrown nanostructures changes from compressive to tensile respectively. GaN nanostructures grown by metalorganic chemical vapor deposition (MOCVD) using identical growth parameters exhibit pyramidal morphologies under low or no mismatch strain, while highly strained structures with compressive strain evolve into prismatic shapes when grown in the c-crystallographic direction. In addition, it is shown that interfacial strain also affects the growth rate and alloy composition of ternary AlGaN nanostructures produced under identical conditions on different templates/substrates. AlGaN nanostructures grown under compressive strain show higher vertical and lower lateral growth rates when compared to those under tensile strain. Scanning electron microscopy, transmission electron microscopy and cathodoluminescene were used to characterize growth rates, shape and composition of the nanostructures. Observed variation in morphologies, growth rates and compositions are explained in terms of the strain dependency of adatom diffusion barriers on strained surfaces and Ehrlich-Schwoebel barriers across different crystallographic planes. Density functional (DFT) calculations were performed to determine the dependency of adatom diffusion on strained GaN and AlN surfaces.

In this study, cubic and spherical FePt clusters were created by inert gas condensation in an argon-helium dc sputter discharge under different flow and target power conditions. The plasma recipes for spherical and cubic clusters called for high He:Ar ratio, low target power and low He:Ar ratio, high target power, respectively. As expected, Langmuir probe measurements show the recipes led to larger ion density for the cubic case (2 × 108 cm−3 versus 6 × 106 cm−3 for spherical). We conclude that the larger density of argon ions increased the cluster-ion collision probability, heating the clusters in situ to promote atomic rearrangements and the formation of the ordered L10 crystal structure rather than the disordered fcc structure.

Recent results in the use of Zinc Oxide (ZnO) nano/submicron crystals in fields as diverse as sensors, UV lasers, solar cells, piezoelectric nanogenerators and light emitting devices have reinvigorated the interest of the scientific community in this material. To fully exploit the wide range of properties offered by ZnO, a good understanding of the crystal growth mechanism and related defects chemistry is necessary. However, a full picture of the interrelation between defects, processing and properties has not yet been completed, especially for the ZnO nanostructures that are now being synthesized. Furthermore, achieving good control in the shape of the crystal is also a very desirable feature based on the strong correlation there is between shape and properties in nanoscale materials. In this paper, the synthesis of ZnO nanostructures via two alternative aqueous solution methods - sonochemical and hydrothermal - will be presented, together with the influence that the addition of citric anions or variations in the concentration of the initial reactants have on the ZnO crystals shape. Foreseen applications might be in the field of sensors, transparent conductors and large area electronics possibly via ink-jet printing techniques or self-assembly methods.

Electromagnetic enhancement arising from plasmon resonance excitation plays a major role in surface-enhanced Raman spectroscopy (SERS), and as a result nanoparticle morphology can significantly affect SERS intensities. In this paper we have calculated these enhancements as well as extinction spectra using the discrete dipole approximation for a system consisting of a dimer of gold disks that is made using on-wire lithography. Including surface roughness in the calculations leads to SERS enhancements for the disks whose dependence on disk spacing and thickness is in agreement with experimental measurements, with a maximum enhancement when the thickness of the disk and the disk-disk gap are 100 nm and 32 nm, respectively. These results are in better agreement with experiments than earlier estimates based on flat surfaces.

Metallic clusters show excellent performance as catalysts because of their high surface-to-volume ratio. An inert-gas aggregation source is an experimental method by which clusters are produced. In such a method, cluster coalescence is one of growth modes of clusters. Bimetallic clusters also attract much attention of researchers because of their novel physical and chemical properties. At coalescence of two metallic clusters of different species, alloying or core-shell structuring tends to occur spontaneously. Resulting alloyed clusters or core-shell clusters will behave as unique catalysts. In this paper, morphological evolution of two metallic clusters of different elements at coalescence is investigated using molecular-dynamics simulation. All pair combinations of the elements Au, Ag, Pt, and Pd are considered. The interactions between such metallic atoms are calculated by using generic embedded-atom method (GEAM) potential. Two clusters of icosahedral structure are equilibrated at specified temperature beforehand. The two clusters are put close to each other, where the nearest two atoms belonging to the two clusters, respectively, start to interact with each other. After coalescence the original surfaces of the two clusters decrease, and the surface energy is transformed into the kinetic energy. Consequently, the temperature of the united cluster rises. If this temperature is higher than the melting temperature, melting and local alloying at the interface occur. If alloying spreads into the united cluster, an alloyed bimetallic cluster is synthesized. If melting occurs only in one of the two clusters, and the atoms in liquid phase gradually cover the surface of the other cluster, a core-shell cluster appears. The morphological evolutions in the two modes of coalescence are followed, and under what conditions each mode of coalescence occurs is discussed.

The results show that the surface energy and atom size of two clusters determine which mode is selected at coalescence.

Tin-dioxide (SnO2) ultra-small nanorods (UNR) have been successfully synthesized using the novel micellar technique. From transmission electron microscopy, the average diameter and length of the UNRs are estimated to be 1.3 nm and 5.0 nm, respectively. The crystal structure of the SnO2 UNRs was found to be tetragonal from the glazing incidence x-ray diffraction. The optical band gap estimated from the absorption spectrum is blue-shifted by 1 eV from that of bulk (3.64 eV). The photoluminescence spectrum shows two groups of peaks each with several fine peaks, one in the wavelength range of 270 – 370 nm and the other in the range of 380 – 500 nm which are due to the strong quantum confinement effect.

This paper describes an innovative and simple technique to synthesize anisotropic nanostructures of both lithium niobate (LiNbO3) and niobium oxide (Nb2O5). These materials were obtained using a solution-phase non-hydrolytic decomposition of LiNb(OPri)6 with or without the presence of Nb and Li-chlorides. The stability of LiCl is suggested as an explanation for the lack of LiNbO3 production in the chloride-based reaction. After 2 and 24 hours of reaction crystalline products of Nb2O5 and LiNbO3 are obtained without further thermal treatment. The products of both reactions contained a mixture of spherical and rod-like morphologies. Larger crystals of LiNbO3 and Nb2O5 were predominantly found to be anisotropic with aspect ratios of 7:1 and 3:1, respectively. These structures are believed to result from the natural anisotropy of the unit cell for these materials and from the use of triphenylphosphine oxide (TPPO) as a coordinating solvent. Our solution-phase synthesis is easily scaled-up as a one-pot procedure that offers a promising route to controlling crystal size and morphology. Details of the composition and the growth of our LiNbO3 and Nb2O5 nanostructures will be discussed in addition to the details of our experimental procedure.