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Results of phase formation, resistivity (r), and thermo-electric power (S), are reported on Y1-xCaxBa2Cu2.7Co0.3O7 compounds with x = 0.1 and 0.2. Pristine compound i.e. without Co or Ca substitution crystallizes in orthorhombic structure with space group P/mmm. Cu-site Co substituted compound i.e. YBa2Cu2.7Co0.3O7 is tetragonal. With simultaneous doping of Ca at Y site in Co substituted compound i.e. Y1-xCaxBa2Cu2.7Co0.3O7 the tetragonal nature still remains. r(T) measurements showed superconducting transition temperature (Tc) to decrease from 90K (YBa2Cu3O7) to 33 K for YBa2Cu2.7Co0.3O7 which with further Ca substitution increases from 33K to 53K (Y0.9 Ca0.1Ba2Cu2.7Co0.3O7) and 67 K for Y0.8 Ca0.2Ba2Cu2.7Co0.3O7. Tc decreases first with Cu-site Co substitution by hole-filling and later recovers by simultaneous hole creation by Y site Ca substitution. Room temperature thermoelectric power S(300 K), which is an indirect measure of mobile carriers shows the decrease of carriers with Co doping and creation by Ca substitution. Our results demonstrate the hole filling by Co substitution is compensated by simultaneous Ca substitution., 10 pages of TEXT and Figs

TiO2 and Co-doped TiO2 (CTO) thin films deposited at various oxygen partial pressures by pulsed laser deposition exhibit room temperature ferromagnetism (RTFM) independent of their phase. Films deposited at 0.1 mTorr oxygen partial pressure show a complete rutile phase confirmed from glancing angle x-ray diffraction and Raman spectroscopy. At the highest oxygen partial pressure, i.e. 300 mTorr, although the TiO2 film shows a complete anatase phase, a small peak corresponding to the rutile phase along with the anatase phase is identified in the case of CTO film. An increase in O to Ti/(Ti+Co) ratio with increase in oxygen partial pressure is observed from Rutherford backscattering spectroscopy. It is revealed from x-ray photoelectron spectroscopy (XPS) that oxygen vacancies are found to be higher in the CTO film than TiO2, while the valency of cobalt remains in the +2 state. Therefore, the CTO film deposited at 300 mTorr does not show a complete anatase phase unlike the TiO2 film deposited at the same partial pressure. We conclude that RTFM in both films is not due to impurities/contaminants, as confirmed from XPS depth profiling and cross-sectional transmission electron microscopy (TEM), but due to oxygen vacancies. The magnitude of moment, however, depends not only on the phase of TiO2 but also on the crystallinity of the films.

This study reports on the layer thickness dependent effect of swift heavy ion irradiation (SHI) in W/Ni multilayer structures (MLS) having bilayer compositions of [W(25 A)/Ni(25 A)], [W(40 A)/Ni(40 A)] and [W(34 A)/Ni(57 A)] of 10-bilayers. These were grown on [1 0 0]-silicon using ion-beam sputtering. The pristine MLS were subjected to 120 MeV Au9+ ion irradiation up to a fluence of 1 × 1014 ions cm−2. Structural characterization of pristine and irradiated MLS was carried out employing wide-angle x-ray diffraction (WAXD), x-ray reflectivity (XRR) and cross-sectional transmission electron microscopy (X-TEM). The XRR studies reveal a decreasing trend in the SHI-induced interface roughness of MLS with thicker Ni layers. This effect is vividly clear in the WAXD and X-TEM studies. The X-TEM studies reveal thickness dependent microstructural changes in the MLS. The MLS with thinner bilayers undergo intra-layer microstructure changes from textured to nano-crystalline on irradiation whereas the MLS with thicker bilayers remain intact although the irradiation fluence is the same. This effect has been cross-verified, beyond all doubts, by studying the SHI irradiation effect on a MLS having a composite bilayer structure of [W(50 A)/Ni(50 A)]5BL/W(25 A)/Ni(25 A)]5BL]/Si grown over each other. The observed nano-crystallization has been attributed to thermal spike caused by large electronic energy deposition. Our analysis clearly reveals that the effect of SHI strongly depends on the layer thickness of the multilayers.

The formation of Ar bubbles in Al has been investigated by using depth-resolved positron annihilation spectroscopy and transmission electron microscopy. Due to Ar bubble formation, the Doppler-broadening S parameter decreases, while the W parameter increases compared to the reference unimplanted Al sample. The effect of Ar ion fluence and annealing temperature on these parameters has been investigated. The presence of Ar at near-surface region has been confirmed by Rutherford backscattering spectroscopy. Transmission electron microscopy also shows that the Ar bubbles are in solid state with fcc structure after annealing at 870 K. The average diameter and lattice parameter of these solid Ar bubbles are estimated to be about 4±1 nm and 0.495±0.005 nm, respectively.

Synthesis of gold and silver nanoparticles at room temperature using a polydimethylsiloxane (PDMS) microreactor has been reported. The reactions have been performed using aqueous metal salt solutions and borohydride reducing agent with tri-sodium citrate as the capping agent. Effect of concentration of reducing agent on the optical properties of the nanoparticles has been investigated. The nanoparticles were characterised by UV-Vis absorption spectroscopy and transmission electron microscopy. The UV-Vis absorption spectra show a blue shift in the spectra with increasing concentration of the reducing agent, which indicates reduction in the size with increased amount of the reducing agent. The sizes of the nanoparticles are uniformly smaller in the microreactor synthesis as compared to those in the conventional batch synthesis, under similar reaction conditions. The microreactor synthesis is very fast and improves the monodispersity with excellent reproducibility.

Fe/Al multilayer thin films with an overall atomic concentration ratio of Fe:Al=1:2 have been prepared by ion-beam sputtering. Phase formation and microstructural evolution with thermal annealing have been studied by x-ray reflectivity, cross-sectional transmission electron microscopy, dc magnetization, and conversion electron Mossbauer spectroscopy. These studies show that although the starting composition is Al rich, the intermixing of Fe and Al at the interfaces leads to the formation of a magnetic Fe3Al-like region at the interface. Thus, the magnetic contribution in the as-deposited multilayer structure (MLS) is not only from pure Fe but also from an Fe3Al-like region formed at the interface. On annealing the MLS, a stable nonmagnetic MLS consisting of intermetallic B2 Fe50Al50 separated by thin Al layers is formed. Further annealing only induces better ordering of Fe50Al50 and does not destroy the MLS.

The recently reported structure of the long period modulated phase of (1−x)NaNbO3–xCaTiO3, with x=0.16, has been revisited using transmission electron microscopic studies. It is shown that the dominant phase in the morphotropic phase boundary region of this mixed system is incommensurately modulated in the [001] direction with an approximate unit cell size of 2ap×2ap×24ap, where ap is the pseudoperovskite cell parameter.

Low-temperature x-ray diffraction, low-temperature transmission electron microscopy (TEM) and dielectric permittivity studies have been carried out on Sr1−xCaxTiO3 (x = 0.30 and 0.40) ceramics across its antiferroelectric phase transition. TEM has been performed for its structural and microstructural characterizations. Together with the occurrence of the usual structural modulation along [001] of the P 21212 (and Pbnm), which gives rise to the Pbcm phase, clear evidences of the occurrence of a new phase, appearing as a result of structural modulation along the [110]-type direction of the Pbnm, has also been found. The temperature dependent dielectric permittivity data appears to indicate the paraelectric nature of the new phase. The coexistence of this new phase with the Pbcm phase has been attributed to Δ-point instability, which is equally probable along any of the [100]-type directions of the basic perovskite structure. It appears that irrespective of the existing perovskite distortion, which results in P 21212 for x = 0.3 and Pbnm for x = 0.4; the Δ-point instability follows the cubic symmetry of the very basic perovskite.

Effects of oxygenation on the structural and dielectric properties of Sr1−xCaxTiO3 (0.20⩽x⩽0.40) ceramics, prepared through solid-state reaction, have been studied employing x-ray diffraction, transmission electron microscopy, and temperature dependent dielectric permittivity measurements. It has been found that oxygenation has drastic effects on the ceramics’ dielectric properties, but their crystal structure remains least affected. The effect of oxygenation on the sharpening of the first order antiferroelectric phase transition has been studied.

The microfluidic approach emerges as a new and promising technology for the synthesis of nanomaterials. A microreactor allows a variety of reaction conditions to be quickly scanned without consuming large amounts of raw material. In this study, we investigated the synthesis of water soluble 1-thioglycerol-capped Mn-doped ZnS nanocrystalline semiconductor nanoparticles (TG-capped ZnS:Mn) via a microfluidic approach. This is the first report for the successful doping of Mn in a ZnS semiconductor at room temperature as well as at 80 °C using a microreactor. Transmission electron microscopy and x-ray diffraction analysis show that the average particle size of Mn-doped ZnS nanoparticles is ∼3.0 nm with a zinc-blende structure. Photoluminescence, x-ray photoelectron spectroscopy, atomic absorption spectroscopy and electron paramagnetic resonance studies were carried out to confirm that the Mn(2+) dopants are present in the ZnS nanoparticles.

The electronic structure of BaPbO3 and Ba2PbO4 was investigated using photoemission, x-ray diffraction (XRD) and tight binding linear muffin tin orbital (TB-LMTO) band structure techniques. BaPbO3 is a base material for all Pb based superconductors. Rietveld analysis of the XRD data suggested that BaPbO3 is an orthorhombically distorted perovskite with Imma space group and Ba2PbO4 possesses tetragonal structure with I4/mmm space group. LMTO calculations indicated an insulating ground state for Ba2PbO4 with a band gap of 1.3 eV and a metallic ground state for BaPbO3. Ultraviolet photoemission results agree well with the LMTO calculations. The Pb–O1–Pb bond angle in the basal plane is a key parameter in deciding the electronic structure of these compounds. The Pb 4f and O 1s core levels of BaPbO3 exhibited asymmetry on the high binding energy side of the peak, indicating that both Pb and O contribute to the density of states at the Fermi edge. The core levels of Ba2PbO4 did not exhibit asymmetry. Core level asymmetry can be used to probe the local density of states at EF.

The effect of 120 MeV Au9+ ion irradiation and thermal annealing on [W(25 A)∕Ni(25 A)]×10 multilayers, grown on float-glass and silicon substrates, has been studied. Wide-angle x-ray diffraction studies of pristine, as well as irradiated W/Ni multilayers, show deterioration of the superlattice structure, but x-ray reflectivity (XRR) studies reveal a nearly unaffected multilayer structure. Analysis of the XRR data using “Parratt’s formalism” does show a significant increase of W/Ni interface roughness. The observed differences in wide-angle and low-angle scattering results of the irradiated W/Ni multilayers suggest significant difference in the interlayer and intralayer mixing induced by swift heavy ion irradiation. XRR results also reveal the fluence dependence of layer densification. Plane, as well as cross-sectional transmission electron microscopy, carried out in imaging and diffraction modes very clearly shows that at higher fluence the intralayer microstructure becomes nanocrystalline (1–2 nm) and at...

The space groups of Sr1−xCaxTiO3 in the composition range 0.20≤x≤0.30 have been investigated using powder x-ray diffraction (XRD) and electron diffraction techniques. Electron diffraction has been used in selected area diffraction (SAD), convergent beam electron diffraction (CBED) and micro-diffraction modes to record zero-order Laue zone (ZOLZ) and higher-order Laue zone (HOLZ) patterns. For the 0.20≤x≤0.30 composition range there is still controversy regarding the correct space group: P 21/m, Pnma, Imma or I4/mcm. By invoking Rietveld refinement, detailed analysis of CBED patterns containing A2-type GM-lines and comparison between simulated ZOLZ/FOLZ and experimentally observed SAD patterns, we have established that for Sr1−xCaxTiO3 (0.20≤x≤0.30) two types of phase coexist at room temperature. These are the Pnma and P 21212 orthorhombic phases, coexisting with volume fractions of about 40% and 60% respectively.

We report the structural and optical properties of Au nanoparticles embedded in a silica matrix synthesized by atom beam co-sputtering. The presence of surface plasmon resonant absorption indicates the formation of Au nanoparticles. Transmission electron microscopy (TEM) studies show the presence of Au nanoparticles with an average size ranging from ~1.8 to 5.4 nm with narrow size distributions depending on the relative areas of Au and SiO2. We discuss the process of nucleation and growth of Au nanoparticles in the nanocomposite films formed by co-sputtering. The present method of nanoparticle synthesis is compared with other ion beam based techniques such as ion implantation and ion beam mixing. Preliminary experiments for the detection of human ovarian cancer cells using these Au nanoparticles are described.

The variation of electrical resistivity rho with temperature T for the decagonal phase of the Al72Mn22 has been measured in the temperature range 300-680 K. The rho -T variation exhibits two main characteristics. One relates to the negative slope in sharp contrast to the corresponding crystalline phase. Evidence and arguments have been advanced to show that the effective transport mechanism in the temperature region studied is thermally activated hopping. The other observed characteristic relates to the possible fine structure in the rho -T curve, which may be expected to reflect the expected fine structure in the density of states of the quasicrystalline phase.

A 1% Pt/CeO2 catalyst prepared by the solution combustion method shows a higher catalytic activity for CO oxidation by O2 compared to Pt metal particles. At least six hydrogen atoms are taken up per Pt at −25 °C. The structure of 1% Pt/CeO2 catalyst has been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. Rietveld refinement shows that Pt ions are incorporated into the CeO2 matrix in the form of Ce1-xPtxO2-δ solid solution. A decrease in oxygen content in 1% Pt/CeO2 is seen in relation to pure CeO2. TEM studies show that Pt is dispersed as atoms or ions and only a small amount as Pt metal particles. The Pt(4f) core level region in XPS shows that Pt is present mostly in the Pt2+ ionic state on CeO2 surface. FTIR of 1% Pt/CeO2 shows a strongly adsorbed CO peak at 2082 cm-1 corresponding to oxidized Pt. These structural studies show that Pt ions in the catalyst are substituted for Ce4+...