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(In1−xDyx)2O3 (x = 0, 0.05, 0.10) nanoparticles with a particle size of 15–22 nm were obtained by an auto-combustion method. The powder x-ray diffraction (XRD), Raman and x-ray absorption near edge spectral (XANES) analysis revealed a cubic bixbyite structure (space group Ia-3). The presence of Dy3+ ions in the In2O3 host lattice was confirmed from XPS data. The high-resolution transition electron microscopic (HRTEM) and XANES revealed the single phase (solid solution) nature of the nanoparticles. The optical band gap was found to increase from 3.57 eV to 3.64 eV by doping Dy into the In2O3 lattice. Photoluminescence spectra shows emission in the yellow region probably due to oxygen related vacancies. A weak ferromagnetic property was seen for Dy-doped In2O3 at room temperature, while pure In2O3 is diamagnetic. It seems that Dy:In2O3 is not a suitable␣system to consider for dilute magnetic semiconductors in spintronic devices.

Structural, optical and surface properties of epitaxially grown 2D GaN nanowall network using Molecular Beam Epitaxy have been compared to those of non-epitaxially grown single-crystalline 1D GaN nanowires using Chemical Vapour Deposition. The kinetics of growth mechanisms and formed morphology are shown to significantly influence the respective band structures and consequently their luminescence properties. X-ray diffraction and Raman spectroscopy reveal that the epitaxial 2D nanowall network experiences a hydrostatic strain in addition to a compressive strain, whereas non-epitaxial 1D nanowires possess a morphology-dependent tensile/compressive strain and a negligible hydrostatic strain. Slightly blue-shifted photoluminescence emission from both these nanostructures is markedly enhanced compared to that from an epilayer. The epitaxial nanowall network exhibits the highest enhancement in the band edge emission among them. X-ray photoelectron spectroscopy spectra show shifts in the valence band features and in the hybridization of shallow core levels. Using the XRD, Raman, PL and XPS data, a variation in the band structure of these differently kinetically formed GaN nanostructures is also sketched.

For spintronic devices, the room temperature ferromagnetism in dilute semiconductors is essential. We report here the successful preparation of (In1−xGdx)2O3 [x = 0, 0.05, 0.10] by auto-combustion method. The powder XRD and SAED data confirmed the formation of single-phase cubic bixbyite In2O3. The particles are in the range of 18–22 nm size. Raman spectra showed doping of Gd3+ ions in the In2O3 lattice. The 3+ valence state of In and Gd was confirmed from XPS and XAS techniques. The magnetic hysteresis loop and EPR spectra showed the weak ferromagnetism in (In0.90Gdn0.10)2O3, while the pure In2O3 is diamagnetic and (In0.95Gdn0.05)2O3 is paramagnetic. To our knowledge, it is the first study to report the RTFM in Gd-doped In2O3 nanoparticles.

Nitride alloys are considered potential candidates as photoelectrodes for photoelectrochemical water splitting. Here we show an In0.25Ga0.75N layer activated by indium nitride quantum dots as efficient photoanode for photoelectrochemical hydrogen generation by water splitting when directly grown on cheap silicon (111) substrates. Photocurrent measurements show more than five times enhancement by the indium nitride quantum dots compared to a bare In0.25Ga0.75N-on-silicon photoanode. The maximum incident photon-to-current conversion efficiency is 44% at 550 nm at 0.4 V, the applied-bias photon-to-current efficiency is 4.1% and the hydrogen and oxygen generation rates are 75 µmol h−1 cm−2 and 33 µmol h−1 cm−2 at 0.2 V under 100 mW cm−2 white light illumination. Nitride based photoelectrodes are promising candidates for photoelectrochemical water splitting and hydrogen generation but suffer from quick degradation. Here the authors show indium gallium nitride activated by InN quantum dots on silicon which can be used as stable photoanode for efficient water splitting.

Surface nitridation of the c-sapphire substrate is used to improve the optical and structural quality of a GaN nanowall network film grown by plasma assisted molecular beam epitaxy. The nitridation results in the formation of a thin AlN layer on the sapphire surface. Several in-situ and ex-situ characterization are complementarily used to probe the changes in epitaxial growth, band edge emission and strain in the films. The GaN nanowall network layer formed on the pre-nitrided substrate shows a two order higher intensity of band edge luminescence than that of a GaN epilayer, demonstrating its potential for light-emission applications. Open image in new window

The amount of dopant concentration, alongwith the choice of dopant, is one of the most conducive factor for the favourable outcome for light driven activities of a material. The present paper reports on the synthesis of zinc oxide nanorods doped with different concentrations of copper (Cu–ZnO) by simple, low-cost mechanical assisted thermal decomposition process. The as synthesized samples were tested for visible light driven photo-electrochemical (PEC) and photocatalytic activities on various hazardous dyes using methylene blue (MB), methyl orange and mixed green dye (methyl thymol blue + methylene blue). The study helped us to reveal that highest degradation efficiency was achieved for Cu concentration of 5% in ZnO on MB (91.1% degradation in 40 min). Compared to pure ZnO, the photoactivity of 5% Cu–ZnO composites shows higher photodegradation of dyes. Moreover, the photocatalytic results were found consistent with PEC studies which showed maximum current generation of +9.4 mA for 5% Cu–ZnO (carried out under dark and illumination condition). The mechanism for this enhanced photoactivity has been proposed based on the relationship established between oxygen vacancies and defects generation in the material due to different doping concentrations that directly influence its photocatalytic efficiency.

A new ternary nitride, CoMoN2, was prepared in the nanosize regime of 9.0 ± 2.0 nm, by nitridation of the precursor intermetallic nitride Co3Mo3N. XRD–Rietveld analysis revealed the presence of 0.60 (±0.02) mass % of Co impurity phase. The calculated space groups of CoMoN2 and Co are P6 3 /mmc and Fm-3m, respectively. The N atoms lie at the interstitial sites and the 12 calculated nitrogen sites indicate the presence of a layered structure. The XPS studies indicated the presence of the nitride and surface oxynitride/oxide phases. CoMoN2 is an interstitial nitride with Co and Mo in the zero oxidation state. The room temperature susceptibility is estimated after subtracting the ferromagnetic contribution from cobalt and found to be 2.7 × 10−4 emu g−1 Oe−1, indicating the Pauli-paramagnetic nature. The ferromagnetic exchange interactions between the Co atoms in CoMoN2 are reduced due to the presence of Mo and N in the crystal lattice. The hysteresis loop shift 19 Oe is attributed to the demagnetizing dipolar fields created in the soft CoMoN2 phase by the hard Co phase.

In the present study, two approaches have been used for enhancing the hydrogenation properties of Pd. In the first approach, metal thin film (Cu, Ag) has been deposited over Pd and hydrogenation properties of bimetal layer Cu (thin film)/Pd(thin film) and Ag(thin film)/Pd(thin film) have been studied. In the second approach, Ag metal nanoparticles have been deposited over Pd and hydrogenation properties of Ag (nanoparticle)/Pd (thin film) have been studied and compared with Ag(thin film)/Pd(thin film) bimetal layer system. The observed hydrogen sensing response is stable and reversible over a number of hydrogen loading and deloading cycles in both bimetallic systems. Alloying between Ag and Pd is suppressed in case of Ag(nanoparticle)/Pd(thin film) bimetallic layer on annealing as compared to Ag (thin film)/Pd(thin film).

In this work, polysorbate surfactants with same functional groups but with varying molecular masses (Tween-80, Tween-40 and Tween-20) in different concentrations (0.1% to 20% w/w) were used to study the effect of the length of the surfactant chain on the luminescence of the entrapped TOPO-capped CdSe nanocrystals. Various phospholipids with different functional headgroups such as ethylene glycol (-PEG) and amine (-NH2) were used to improve biocompatibility and provide sites for bioconjugation respectively. It is understood that that the hydrophobic ends of the surfactant binds with the water repelling groups of the cap layer, thus modifying the CdSe cap layer and making it soluble in aqueous media. It was observed that the PL emission intensity of CdSe increases with increase in concentration of Tween-series surfactant unlike in the case of thiol-coated CdSe nanoparticles. However, higher PL intensity was obtained in the case of stoichiometric CdSe with Tween-40 corresponding to 20% w/w. The efficient PL sustainability of water-soluble CdSe QD's can be attributed to the simpler chain structure of Tween-40 surfactant resulting in better passivation of the micelle.

Zinc oxide (ZnO) and Ni-doped zinc oxide (ZnO:Ni) films are prepared by atom beam sputtering with an intent of growing transparent conducting oxide (TCO) material and understanding its physical properties. The crystalline phases of the films are identified by the grazing angle X-ray diffraction (GAXRD) technique. Thicknesses of the films are measured by ellipsometry. Chemical states of the elements present in the films are investigated by X-ray photoelectron spectroscopy (XPS), which indicates the presence of Ni in the ZnO environment in a divalent state. Average transmission across the ZnO:Ni film was determined to be ∼83% in the visible region, which is less than that (∼90%) of undoped ZnO films. The resistivity measured by van der Pauw technique of the ZnO:Ni film (∼9×10-3 Ω cm) is two orders of magnitude smaller as compared to its undoped counterpart (1 Ω cm). For ZnO:Ni film an average carrier concentration of ∼1.4×1019 cm-3 was observed by Hall measurements. Two important mechanisms reported in the literature viz. influence of d–d transition bands and electron scattering from crystallites/grains are discussed as the possible causes for the increase in conductivity on Ni doping in ZnO.

Homogenous Ag–Au alloy nanoparticles having an average size of 12 ± 2 nm were successfully prepared by the exploding wire technique comprising of a wire–plate system and using 12 V batteries. The X-ray photoelectron spectroscopy data reveal the formation of alloy nanoparticles with Ag80-Au20 composition, which agrees with the absorption data, obtained using UV-Visible spectroscopy. XPS also reveals a thin metal-oxide shell on the metallic alloy core. These alloy nanoparticles show visible fluorescence emission that was compared with the observed fluorescence from pure Ag nanoparticles. A mechanism for the observed fluorescence is also provided.

In this work, the role of conducting [poly (p-phenylinevinylene) (PPV)] and nonconducting (polystyrene) polymers on the properties of their respective composites with CdSe quantum dots of varied sizes has been investigated. The emission and structural properties of polymer–CdSe composites are found to be dependent on the crystallite size and morphology of CdSe nanocrystallites. Smaller CdSe quantum dots (size, ∼5 nm) ensures efficient charge transfer process across polymer–CdSe interface as evident by almost complete quenching of photoluminescence (PL) emission as compared to larger CdSe quantum dots (size, ∼7 nm). Presence of residual trioctylphosphine (TOP)/ tri-n-octylphosphine-oxide (TOPO) species and agglomeration of particles act as a hindrance for quenching of emission and hence charge transfer for larger CdSe nanocrystallites. Emission studies indicated an increased conjugation length for PPV polymers in different solvents (toluene, pyridine) and in solid state. Nonconducting polymer polystyrene shows charge transfer across polymer–CdSe interface as well. However, polystyrene polymer has a shorter chain length, which ensures maximum coverage on the surface of CdSe nanocrystallites and provides better photostability to CdSe QDs within the polymer matrix as compared to that for PPV–CdSe nanocomposites.

Homogenous nano structured CeO2 films have been prepared by a sol-gel process using different mole ratios of citric acid as additive. XPS studies clearly illustrate an increase in Ce3+ proportion upon the use of higher citric acid content for the deposition of films. The crystallite sizes in the films lie in the nanorange. Photoluminescence emission in the films is attributed to various defects resulting from crystallization. Lowest transparency, high Ce3+ content and optimum sized crystallites in CeO2 (1:1.5) films have led to its highest PL characteristics. Ce3+ chemical state is the major contributor to the PL activity of these films. The SEM micrographs show a reduced level of CeO2 agglomeration in the films deposited using higher citric acid contents. A comparison of different properties of CeO2 films deposited using citric acid and CeO2–TiO2 films has also been made.

Ag is adsorbed in ultra-high vacuum on to the (7x7) reconstructed Si(111) surface with submonolayer coverage control with a deposition rate of 3-3 x 1012 atoms/cm2/sec. The initial stages of growth and intermediate equilibrium phase formation are determined by using low energy electron diffraction (LEED) and X-ray photoelectron diffraction (XPD) for structural information, and auger electron spectroscopy (AES) and electron energy loss spectroscopy (EELS) for composition and interaction analyses. Room temperature (RT) adsorption results in the nearly epitaxial (1 x 1) surface phase growth in the simultaneous multi-layer growth mode. The quenching of the dangling bond states during adsorption is observed by monitoring thep-character of the Si LVV auger peak. For depositions carried out at high temperatures (HT), several plateaus in the auger uptake curve with the (√3 x √3)-R30° LEED structures are formed. It is observed that a minimum coverage of 0–33 monolayer (ML) is required for the formation of the (√3 x √3) phase and this phase causes the reappearance of thep-electron-related states that were quenched by 1.0 ML adsorption at RT. However the (√3 x √3) is observed for higher coverages (0.66 and 1.0 ML) also. The polar angle anisotropy of Si(2p) emission in XPD indicates the rearrangement of substrate Si atoms for the formation of the (√3 x √3) phase. The EELS data also shows relevant changes due to adsorption of Ag at RT and upon annealing. The results suggest the importance of controlled deposition parameters, the lack of which may have kept the determination of the nature and coverage of the (√3 x √3) surface phase unresolved in literature.

We present here a report on a role of initial nitridation of Si(111) surface on GaN nanorod growth. High quality wurtzite GaN nanorods are grown by Molecular Beam Epitaxy on bare Si(111)-7x7, crystalline and amorphous silicon nitride at 750oC, under nitrogen rich conditions. Using in-situ reflection high energy electron diffraction and ex-situ X-ray photoelectron spectroscopy, field emission scanning electron microscopy and photoluminescence, the structural and chemical properties are monitored. In the first part of the study, we have optimized the conditions of the N2* RF plasma, for formation of crystalline and amorphous silicon nitride on Si(111)-7x7 surface. While in the second part, GaN nanorods are grown on clean and these modified Si(111) substrates. Anisotropic spots are observed by RHEED for GaN grown on clean Si and on the amorphous silicon nitride, while circular, sharp and intense RHEED spots have been observed for GaN grown on crystalline Si3N4. FESEM results show nanorod growth in all the three different conditions. However, GaN nanorods grown on crystalline Si3N4 surface are observed to be self aligned and oriented along direction, while those grown on amorphous silicon nitride and bare Si(111) surfaces show great disorder increasing, respectively. Overall, the results clearly demonstrate that high quality of dense and self aligned c-oriented GaN nanorods can be formed on Si(111) surface by modifying it by appropriate nitridation.

Of late, high index Si surfaces like, (5 5 12) are being explored for the formation of 1D nanostructures in the form of nanowires or chains. The surface topography of Si (5 5 12) presents an unique template for the growth of 1D nanostructures. In this paper we report the adsorption-desorption studies of Sb onto (2×1) reconstructed surface of Si (5 5 12). Motivated by our earlier studies of adsorption/desorption of Sb on low index surfaces (001) and (111), studying the interaction on high index surface like (5 5 12) is found to be interesting. The experiments have been performed in UHV with in-situ growth and probed by using AES, LEED and EELS techniques. The uptake curve shows initially a simultaneous multilayer growth of Sb up to 4 ML and then at 20 ML the entire Si surface is covered by Sb. The LEED patterns show a disorder during growth at RT above 1 ML. EELS studies at 250 eV, primary beam energy show that as the adsorption proceeds the features of bulk Sb start appearing above 4ML coverage. However, the bulk Sb features are not complete until a high enough coverage of Sb (˜20ML) which suggests the existence of the primary rows up to a higher coverage. Annealing studies have also been performed on the RT adsorbed system, to study the residual thermal desorption characteristics. Annealing the system to about 7900C results in Si (337) facets at a low coverage of 0.2 ML. The anisotropy in the LEED spots suggests an ordered Sb adsorption along (1 10) and a local disorder in the (665 ) direction. Thus we provide evidence for the formation of a zig-zag 1D-nanowire of Sb grown on the (5 5 12). The new phase is also accompanied by forming a dangling bond state at 3 eV in EELS.

The adsorption of Sb on the high index Si (5 5 12) has been studied at higher substrate temperature (HT) (800°C), using in situ surface characterization techniques like Auger Electron Spectroscopy (AES), Low Energy Electron Diffraction (LEED), and Electron Energy Loss Spectroscopy (EELS). The surface morphology of this high index Si (5 5 12) surface has row like trenches along (110) direction. We have performed the study of Sb adsorption and desorption on the Si (5 5 12) substrate held at different temperatures. The different pathways adopted during adsorption and desorption have suggested the dominant role of kinetics I forming various surface phases on the Si (5 5 12) substrate. The adsorption at room temperature resulted in the formation of (225) surface phase, while the adsorption at 680°C resulted in the (337) phase. The sequential thermal desorption of the room temperature and high temperature adsorbed surface resulted in the formation of (337) phases at 800°C, with anisotropic growth along one direction. While the adsorption at 800°C resulted in the formation of anisotropic (337) like phases, the further increase in the coverage formed a 2x Si (225) phase. Annealing this 2x Si (225) phase again resulted in the formation of anisotropic (337) phase. Thus formation of interface by controlling the growth kinetics can result in the formation of various tailored structures with desired properties.

CdSexTe1-x nanoparticles (with different stoichiometry ratio x) dispersed in silicon dioxide films have been grown by magnetron sputtering technique followed by thermal annealing. Effect of thermal annealing conditions on the structural, compositional, optical and electronic properties of nanoparticles has been studied using GAXRD, XPS, TEM, and spectroscopic ellipsometry techniques. A structural transformation in the nanoparticle core mediated purely by surface layer effects in the case of CdTe and a spontaneous self-organization of nanoparticles into nanorods in the case of CdSe via fractal growth has been observed. Preliminary observations from the ellipsometry measurements carried out on some of these nanoparticle films shows a blue shift of absorption edge.

Molecular films of amino propyl triethoxy silane (APTES) attached with cinnamoyl moieties were deposited on indium tin oxide (ITO) coated glass and quartz substrates by self-assembly technique. The deposition of the monolayer films resulted in a large change in the wettability of the substrates. X-ray photoelectron spectroscopy (XPS) and UV-spectroscopy were used to study the structure and properties of the grown films. The molecular assembly was photodimerized by irradiating it with a linearly polarized UV-light. Thus created polymer-solid interface has been shown to produce good, stable planar orientation of ferroelectric liquid crystal mixtures. The electro-optical and switching properties of the ferroelectric liquid crystal cells have been investigated and found to be quite similar to those prepared in conventional manner.

The effect of deposition rate and substrate temperature on the electrical resistivity (ρ), temperature coefficient of resistance (TCR) and thermolelectric power (TEP) of palladium films, in the thickness range 2 to 25 nm, is found to be marked. Higher rates of deposition and substrate temperatures are found to result in larger grains and hence changes in transport properties. The Fuchs-Sondheimer theory is used to explain the size effect in palladium films while the Mayadas-Shatzkes and Meyer relations are employed to study these effects onρ, TCR and TEP.

Mesures de la resistivite electrique de couches minces de manganese d'epaisseurs comprises entre 10 et 80 nm a trois temperatures 77, 300 et 465 K

Etude experimentale. Couches preparees par evaporation. Mesure de la resistance de la couche en courant alternatif pour des frequences comprises entre 100 Hz et 1 MHz