Atomic Layer Deposition of Ultrathin Crystalline Epitaxial Films of V2O5.

Ultrathin epitaxial films (10-90 nm thick) of V2O5 have been grown on c-Al2O3 by atomic layer deposition using vanadyl acetylacetonate as the vanadium precursor along with oxygen plasma. Various process parameters have been optimized for the purpose, and excellent crystalline films could be obtained below 200 °C, without the need for post-heat treatment. With a moderate temperature window, the process yields a growth rate of 0.45 Å/cycle. The films have been characterized by electron microscopy, atomic force microscopy, Raman spectroscopy, and other means. The films exhibit a (001) preferred orientation with respect to c-Al2O3 and undergo compressive strain at the initial few monolayer growth to adjust epitaxially with the substrate. Heterojunction diodes based on TiO2(p)-(n)V2O5 as well as a humidity sensor have been fabricated using the V2O5 films.

Atomic Layer Deposition of p-Type Epitaxial Thin Films of Undoped and N-Doped Anatase TiO2.

Employing atomic layer deposition, we have grown p-type epitaxial undoped and N-doped anatase TiO2(001) thin films on c-axis Al2O3 substrate. From X-ray diffraction and transmission electron microscopy studies, crystallographic relationships between the film and the substrate are found to be (001)TiO2//(0001)Al2O3 and [1̅10]TiO2//[011̅0]Al2O3. N-doping in TiO2 thin films enhances the hole concentration and mobility. The optical band gap of anatase TiO2 (3.23 eV) decreases to 3.07 eV upon N-doping. The epitaxial films exhibit room-temperature ferromagnetism and photoresponse. A TiO2-based homojunction diode was fabricated with rectification from the p-n junction formed between N-doped p-TiO2 and n-TiO2.

Surface plasmon resonance of Ag nanoparticles embedded in partially oxidized amorphous Si matrix.

Nanocomposite films containing Ag nanoparticles embedded in partially oxidized amorphous Si matrix were deposited on silica glass substrates by co-sputtering of Ag and Si with 1.5 keV neutral Ar atoms. The Ag content and thickness of the nanocomposite films was determined by Rutherford backscattering spectrometry. Optical absorption studies revealed the presence of surface plasmon resonance (SPR) indicating the formation of Ag nanoparticles in the as-deposited films. The position, width and strength of SPR have been found to be strongly dependent on the Ag content of the films. For annealing in oxidizing atmosphere, a significant red shift in the SPR along with a drastic reduction in the resonant absorption has been observed. The amount of red shift has been found to be dependent on the Ag content of the films. Transmission electron microscopy was used to study the size distribution, shape and crystal structure of Ag nanoparticles in the nanocomposite films. TEM analysis of annealed sample revealed the formation of silver oxide nanoshells surrounding Ag nanoparticles.

MeV gold ion induced sputtered nanoparticles from gold nanostructures: dependence of incident flux and temperature.

The high-energy and heavy-ion induced sputtered particles from nanostructures under various conditions can result in variety of size distributions. 1.5 MeV Au2+ ions induced sputtering from isolated gold nanostructures deposited on silicon substrate have been studied as a function of incident ion flux (dose rate) and the sputter particle catcher at low temperature. At higher fluxes, a bimodal distribution of the sputtered particles has been observed. Cross-sectional transmission electron microscopy and Rutherford backscattering spectrometry measurements showed that the sputter particle size distribution depends on morphology at surface and interfaces. The results for the size distribution from a catcher at low temperature showed the less agglomeration of ejected clusters on the catcher grids, resulting in the lower-disperse size distribution.

Observation of a universal aggregation mechanism and a possible phase transition in Au sputtered by swift heavy ions.

Two exponents delta for the size distribution of n-atom clusters, Y(n) approximately n{-delta}, have been found in Au clusters sputtered from embedded Au nanoparticles under swift heavy ion irradiation. For small clusters, below 12.5 nm in size, delta has been found to be 3/2, which can be rationalized as occurring from a steady state aggregation process with size independent aggregation. For larger clusters, a delta value of 7/2 is suggested, which might come from a dynamical transition to another steady state where aggregation and evaporation rates are size dependent. In the present case, the observed decay exponents do not support any possibility of a thermodynamic liquid-gas-type phase transition taking place, resulting in cluster formation.

Green synthesis of highly stabilized nanocrystalline silver particles by a non-pathogenic and agriculturally important fungus T. asperellum.

A controlled and up-scalable biosynthetic route to nanocrystalline silver particles with well-defined morphology using cell-free aqueous filtrate of a non-pathogenic and commercially viable biocontrol agent Trichoderma asperellum is being reported for the first time. A transparent solution of the cell-free filtrate of Trichoderma asperellum containing 1 mM AgNO(3) turns progressively dark brown within 5 d of incubation at 25 °C. The kinetics of the reaction was studied using UV-vis spectroscopy. An intense surface plasmon resonance band at ∼410 nm in the UV-vis spectrum clearly reveals the formation of silver nanoparticles. The size of the silver particles using TEM and XRD studies is found to be in the range 13-18 nm. These nanoparticles are found to be highly stable and even after prolonged storage for over 6 months they do not show significant aggregation. A plausible mechanism behind the formation of silver nanoparticles and their stabilization via capping has been investigated using FTIR and surface-enhanced resonance Raman spectroscopy.

Flux dependent MeV self-ion-induced effects on Au nanostructures: dramatic mass transport and nanosilicide formation.

We report a direct observation of dramatic mass transport due to 1.5 MeV Au(2+) ion impact on isolated Au nanostructures of average size ≈7.6 nm and height ≈6.9 nm that are deposited on Si(111) substrate under high flux (3.2 × 10(10)-6.3 × 10(12) ions cm(-2) s(-1)) conditions. The mass transport from nanostructures was 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 redistribution. The mass transport is explained on the basis of thermal effects and the creation of rapid diffusion paths in the nanoscale regime during the course of ion irradiation. The unusual mass transport is found to be associated with the formation of gold silicide nano-alloys at subsurfaces. The complexity of the ion-nanostructure interaction process is discussed with a direct observation of melting (in the form of spherical fragments on the surface) phenomena. Transmission electron microscopy, scanning transmission electron microscopy, and Rutherford backscattering spectroscopy methods have been used.

Interfacial deposition of Ag on Au seeds leading to AucoreAgshell in organic media.

A seed mediated procedure for the synthesis of hydrophobic Au(core)Ag(shell) nanoparticles in toluene is demonstrated. The reaction proceeds by way of the interfacial reduction of silver ions by 3-pentadecylphenol followed by their deposition on hydrophobized Au nanoparticles. Such a hitherto unreported interfacial seeded growth reaction leads to the formation of phase pure Au(core)Ag(shell) nanoparticles that retain the hydrophobicity of the seed particles and remain stable in toluene. Such core-shell structures are however not formed in the aqueous phase. The core-shell architecture was verified using TEM analysis and the formation process was studied by recording the UV-vis spectra of the organic phase nanoparticles as a function of time. TEM kinetics also showed gradual increase in the silver layer thickness. Conclusive evidence was however obtained on examination of the HRTEM images of the products formed. Elemental analysis using X-ray photoelectron spectroscopy of the Au(core)Ag(shell) nanostructure revealed the presence of metallic silver. Moreover changing the surface capping of the Au seed does not affect the formation of the Au(core)Ag(shell) nanostructure.