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beta-SiC nanowires were synthesized on different monocrystalline substrates: Si (001), Si (111), 3C-SiC (001), 4H-SiC (0001), 6H-SiC (0001). The SIC nanowire growth was carried out using a Chemical Vapor Deposition method, with silane and propane diluted in hydrogen (3%) as precursors. The deposition was performed at atmospheric pressure and at 1100 degrees C, after dewetting of the Ni catalyst, which had been previously evaporated onto the substrate, to induce 1D growth according to a VLS process. The crystal structure of the nanowires, as determined by X-ray diffraction and High Resolution Transmission Electron Microscopy, corresponds to 3C-SiC polytype growing along a < 111 > direction, irrespective of the substrate. The occurrence of (111) stacking faults was observed, partly reduced for samples grown on 3C-SiC substrate. The growth on (111) substrate allowed to achieve a good vertical alignment of the nanowires, as investigated by Scanning Electron Microscopy. High Angle Annular Dark Field imaging and Energy Dispersive X-Ray spectroscopy were performed to study the catalyst particle on top of the wires and showed the formation of a nickel-silicon alloy.

Cubic silicon carbide nanowires (-SiC or 3C-SiC NW) have been grown by Vapour Phase Epitaxy on (001) silicon substrates patterned by conventional photolithography and on Micro Electro Mechanical Systems (MEMS, e.g. cantilevers, springs, bridges) fabricated on (001) Silicon On Insulator (SOI) wafers. The NW morphology was investigated by scanning electron microscopy, showing that the nanowires grew selectively where a nickel thin layer was previously deposited, thanks to its catalytic action. High resolution transmission electron microscopy studies showed that the NWs are predominantly 3C polytype with growth axis and stacking defects on (111) planes.

To assess deformation issues in the vapor phase epitaxy of 3C-SiC on (0 0 1) and (1 1 1) Si substrates, we investigated different pre-growth (carburisation) procedures, adding various amount of SiH4 to C3H8. The mechanical deformation of the samples was measured by quantitative Makyoh topography, through which 3D deformation maps of the entire wafers were obtained. X-ray diffraction was used to check the crystal quality of the layers and, in transmission geometry, to assess whether the observed deformation was plastic or elastic. Residual stress of the deposited 3C-SiC layers was investigated across the entire wafer substrates by using Raman spectroscopy and values between 0.5 and 1 GPa were found. It was observed that, for a given carburisation procedure, the crystalline orientation of the Si substrates plays an important role in the substrate curvature (convex and concave). The addition of SiH4 during carburisation ramp leads to increased deformation for SiC/Si (0 0 1), while decreased deformation for SiC/Si (1 1 1).

Single crystals of Zn l-x Mn x Cr 2 0 4 have been grown by the chemical vapour transport (CVT) technique using chlorine as the transport agent. The zinc chromite grew with little difficulty. The presence of manganese chromite liquid caused the ampoules to crack when the crystals rich in manganese were grown. In addition, when the spinels were grown with nominal starting compositions x > 0.5, the condensation of MnCI 2 caused the crystals grown to be depleted in manganese. A thermodynamic study of the closed tube system has been done in order to determine the most favourable conditions for growth and calculate the ranges of temperature and chlorine pressure most suitable to avoid the segregation of manganese. Single crystals of different compositions were analyzed by X-ray diffractometric methods. Magnetic susceptibility measurements suggest a spin-glass-like behaviour which is explained by the existence of a cluster-glass state.

Single crystals of Zn1−xMnxCr2O4, where x=0–1, were grown by the chemical vapour transport (CVT) technique using chlorine as the transport agent. A thermodynamic study of both systems, (ZnCr2O4 + MnCr2O4-Cl2 and Zn1−xMnxCr2O4-Cl2, was done in order to investigate the effect of spurious species, i.e. MnCl2(liq), on the transport of the mixed spinel, and structural investigations using X-ray diffraction were carried out. Susceptibility measurements as a function of temperature from 2–300 K for the different compositions are reported, and the magnetic phase diagram was determined as a function of composition and temperature.

Since the introduction of carbon nanotubes in 1992, the study of one-dimesional nanomaterials, which includes metallic, magnetic, semiconducting and oxide compounds, has attracted considerable interest, especially as regards nanowires (NW), nanobelts and nanorods [Kolasinski, 2006]. The main interests of this research are in the realization of nanoelectronic devices (e.g. nano field-effect transistors), nano-electromechanical systems, and nano-sensors exploiting high selectivity and compatibility with biological systems. Nanostructures may present very different characteristic and novel properties with respect to the corresponding bulk material, and they have important physical and chemical properties, in particular large specific surface/volume ratio and quantum size effects, which permit many applications such as nanoscale devices, sensors and scanning probes not possible with standard structures. Silicon carbide (SiC) has gained importance as both a coating and a structural material for Micro Electro Mechanical Systems (MEMS) (Sarro, 2000; Mehregany et al, 2000). SiC is a wide bandgap semiconductor used for high temperature, high power applications and radiation–hard environments. The high Si-C bond energy confers a high Young’s modulus and hence mechanical toughness and high fracture strength (Li and Bhushan, 1999); moreover, it is chemically inert to the most corrosive and erosive chemicals and is biocompatible (Willander et al. 2006; Casady and Johnson 1996; Yakimova et al. 2007). More than 100 polytypes of SiC exist but the SiC cubic phase (3C-SiC) has drawn particular attention because it can be deposited on Si (Marshall et al. 1973). The combination of these distinctive physical, chemical and mechanical properties of SiC and the possibility to synthesize SiC NW make this material an excellent candidate for the design and fabrication of nanodevices. Surface functionalization introduces specific chemical functional groups onto a surface, in order to tailor its properties to specific needs. Functionalization of NW is nowadays a burgeoning field of activity, and motivates researchers involved in nanotechnology and related activities: defining a specific molecule/NW interface, suitable for selective bonding to a chosen chemical species, is a key step of the development of nano-objects tuned by the physical and chemical properties of molecules, and may have notable application in sensing and biosensing.

The Dy 2 Fe 14 B 1- x C x (0 ⩽ x ⩽ 1) alloys have been studied in order to understand the main differences in the phase formation between the carbides and borides. The amorphous alloys were prepared by melt spinning and the recrystallisation was studied by differential thermal analysis, X-ray diffraction and Mossbauer spectroscopy. The results reveal some interesting features about the crystallisation mechanism of these amorphous alloys.

The crystal structures of RbTiOAsO4, KTiO(Po.58,AS0.42)O4, RbTiOPO4 and (Rbo.465,Ko.535)TiOPO4, all of which are orthorhombic (space group Pna2~) and isostructural with KTiOPO4, have been determined from single-crystal X-ray diffraction data and refined to R factors between 0.027 and 0.040. The results are used for an analysis of structural trends in crystals of the KTiOPO4 family by comparison of the room-temperature structures with that proposed for the high-temperature prototypic phase (space group Pnan).

The main steps of the phase formation processes which take place in samples of W-type hexaferrites containing cadmium, prepared by chemical coprecipitation, have been analysed. The processes were followed by Mossbauer spectroscopy, powder X-ray diffraction, thermomagnetic analysis and magnetic measurements. For samples heated in the temperature range 1000–1100°C, the phase formation processes are the same as those verified for the other zinc, nickel, cobalt W-type compounds: forTh=1000°C the only phases present are SrFe12O19 (M-type ferrite) and CdFe2O4 (spinel ferrite); in contrast, forTh>1100°C, the solid state reaction between the M-type and the spinel phases does not take place and the spinel phase decomposes, leading to the formation of α-Fe2O3.

The Fe80–xCrxSi10B10 amorphous alloy system has been investigated for values of x between 0 and 14. The substitution of Cr for Fe caused a decrease in the Curie temperature, T C , of the alloy. Low-temperature annealing was found to increase T C by up to 16°C. Magnetic measurements were also performed on selected alloys. This series of alloys, which have T C markedly below the crystallisation temperature, have potential to be used in magnetic temperature sensors.

Crystallographic properties of several single crystals of ternary ABC2 (A = Cu, Ag; B = In, Ga; C = Te, Se) compounds, of Cd1−xMnxTe (0.5 ≤ x ≤ 0.66), of quaternary and pentenary (CuIn1−xGaxSe2(1−yTe2y with x = 0, 0.7, 1 and y = 0.135, 0.65, 0.4) solid solutions have been determined by single crystal X-ray diffraction. Many chalcopyrite compounds and alloys show thermal polymorphism involving order-disorder phase transitions, and the structure changes are characterized by a first order transition from ordered tetragonal chalcopyrite to the completely disordered zinc-blende and/or wurtzite structures. All the single crystals were grown by chemical vapour phase transport in a close tube using iodine as the transport agent. The phases observed in growing ternary compounds depend on the temperature used during the growth process. For the multinary solid solutions the situation appears to be more complex: in fact, together with the expected phases some altogether unexpected ones were detected, confirming the idea that the growth process of these compounds is dependent not only on temperature but also on parameters involving the composition and growth kinetics.

Polycrystalline Pb(Ti 0.48 Zr 0.52 )O 3 films were deposited by laser ablation onto glass slides using a Nd:YAG laser. Film thicknesses of 4–8 μm were grown. X-ray diffraction indicated that a heat treatment at 450°C for 6 h is sufficient to recrystallize the perovskite. Scanning electron microscopy reveals that, after this heat treatment, a dense film is obtained with the desired composition.

Pb 1− x Sn x Te single crystals have been grown by a vertical Bridgman method. They have typical Hall mobilities and carrier concentration values of 10 3 cm 2 /V · s and 10 18 cm -3 , respectively, and change from p- to n-type as the Sn content increases. The ingots were single crystal with a subgrain structure that has a misorientation no higher than 2′. The segregation of Sn has been determined and it suggests that there is a convective flow in the liquid.

The effects of ambient gas type and pressure on the surface quality of melt spun Fe 73.5 Si 13.5 B 9 Cu 1 Nb 3 soft magnetic alloy ribbons has been studied and the influence of surface roughness on the coercivity, H c , of these ultra-soft magnetic materials determined. The coercivity of ribbons heat treated to developed minimum H c increased as a function of ambient chamber pressure, P amb .

PbFe 12 − x Me x O 19 , Me = Sc, In (0 ⩽ x ⩽ 3), hexaferrites have been characterised by vibrational sample magnetometry and Mossbauer spectroscopy in the temperature range 77–800 K. For both series, the saturation magnetisation and the Curie temperature showed a rapid fall with the substitutions. It was also established that In and Sc ions enter the pseudohexahedral sublattice b with the same probability as for other lattice sites.

Silicon carbide nanowires have been synthesized by carbothermal reduction, from carbon monoxide and single crystal silicon. Transmission electron microscopy and cathodoluminescence studies confirm the growth of a cubic β-SiC core, coated with an amorphous oxide shell. Planar defects, as stacking faults and rotational twins, are present on (1 1 1) planes. The formation of short thick rods or long thin wires, depending on the growth temperature and time, is discussed.

Wafer bending is a serious problem that affects the growth of cubic silicon carbide on silicon. Thermal and lattice mismatch are often cited as the causes of stress in this system, but they alone cannot account for severe wafer warp seen in many cases. This work proposes diffusion-induced stress as a new mechanism that can explain the extreme degree of bending observed.

Thin films of doped semiconducting barium-strontium titanate (Ba,Sr)TiO3 are prepared by pulsed laser ablation. It is shown that the crystal structure, morphology, and electrical properties of (Ba,Sr)TiO3 thin films are determined primarily by the actual ablation conditions. The ablation regimes of deposition permitting preparation of uniform polycrystalline thin films with a composition close to that of the target and with grain sizes larger than 0.1 μm are established. These samples have a positive temperature coefficient of resistance in the phase transition region. The change in the resistivity can be as much as 100%.

A modified Bridgman method with a high temperature gradient was used to grow Hg 1− x Mn x Te single crystals from Te-rich solution. Magnetic susceptibility experiments were performed in the temperature range from 80 to 300 K. Raman scattering measurements, carried out at room temperature, revealed two peaks characteristic of the pure HgTe spectrum at 118 cm −1 and 138 cm −1 and a third weaker peak at 256 cm −1 .

The growth, crystal structure and powder second-harmonic generation (SHG) of crystals of K0.84(Ti0.92, Nb0.08)OPO4 (KTNP) is reported. The crystal structure of KTNP, orthorhombic, space group Pna21 (C92v), a=12.815(4), b=6.413(2) and c=10.597 A, has been refined to R=0.034. The incorporation of 8% Nb mostly on the Ti(1) site is shown to be self-compensated electrically by the creation of vacancies on the K+ sites. The powder SHG from a KTNP sample has been measured and compared with that from a similar stoichiometric KTiOPO4 sample. The results are discussed with reference to the small differences between the crystal structures of KTNP and KTP.

This work describes the application of two different test structures to execute broadband microwave measurements of the dielectric constant of ceramic thin films. Coplanar waveguide probes and vector network analyzer were used to measure the dielectric constant versus frequency of thin films of lead zirconate titanate and zirconium titanate, fabricated by sol gel methods. One-step lithography was used to produce planar metal-insulator-metal and interdigitated capacitor test patterns. The two test structures are compared for zirconium titanate films. The metal-insulator-metal method has been applied also to a lead zirconate titanate film and to show the capability of computing the dielectric tunability. (C) 2007 Elsevier Ltd. All rights reserved.

This work describes the growth of 3C-SiC on silicon by vapour phase epitaxy. The carburisation, a key step to nucleating SiC on silicon is treated in detail. The carburisation layer, characterised by X ray diffraction, and transmission electron microscopy, was found to be smooth, epitaxial and monocrystalline on the substrate. Chemical analysis by XPS shows that the layer is Si rich and that residues of the precursors remain on the surface.

For the compounds formed by barium hexaferrite particles embedded in a silica xerogel matrix, the analysis of the structural evolution and magnetic properties under thermal treatment was carried out by X-ray diffraction (XRD), Rietveld refinement and vibrating sample magnetometry (VSM). A variation of the Rietveld refinement method is used to calculate the amorphous and crystalline content in these composites by assuming an initial crystalline model with the same composition as the materials to be modeled.

M-type lead hexaferrites (PbFe12O19) have been prepared using sol-gel methods. Lead and iron precursors were dissolved in butoxyethanol and stabilised with acetylacetone to produce a sol with good wetting and surface coating characteristics. Powder samples were investigated to optimise conditions for the growth of thin films. The «spin on» technique was used to provide homogeneous films. X-ray diffraction and thermomagnetic analysis vibrating sample magnetometry have been performed to assess phase distribution and transformation. The results show that the hexaferrite phase can be crystallised above 700 °C and that for the first indication that this phase is metastable in air below 650 °C.

Alloys with composition Fe73.5Cu1Nb3Si22.5−xBx, where x=6 and 9, have been studied from the as-cast state, through various stages of crystallization, in annealing range of 300–650 °C, by the technique of ferromagnetic resonance (FMR). The annealing was performed isothermally at preset temperatures to produce nanocrystalline structures in an amorphous matrix. Both the nanocrystalline structures and the surrounding amorphous matrix are ferromagnetic, and will therefore contribute to the FMR spectra. The spectral features, resonance field, intensity, and linewidth have been used to characterize the structurally related changes in the sample during the crystallization process. The major changes in the spectra are observed to occur in the region of the crystallization peak in the differential thermal analysis curves for these samples. The FMR spectra exhibit a complex in-plane angular variation, which is understood in terms of preferential orientation of the magnetization vector in the direction of the ribbon,...

Stabilization of the unipolar state via the formation of inhomogeneous impurity distribution in crystal bulk is considered. Possible growth of crystals with stable characteristics is demonstrated on triglycine sulfate (TGS) crystals with a regular inhomogeneous impurity distribution. The properties of TGS crystals with an inhomogeneous distribution of chromium ions grown above and below the Curie temperature T C are studied. Inhomogeneous TGS crystals of three types are obtained: type-I crystals with a smooth variation of the concentration gradient along the growth direction, type-II crystals with a periodic layer variation of the impurity concentration, and type-III crystals with a sawtooth-like variation of the impurity concentration along the sample length. The TGS crystals with the regular inhomogeneous impurity distribution in the ferroelectric phase are characterized by higher values of the internal bias field E b , unipolarity coefficient k, and pyroelectric coefficient γ than the inhomogeneous crystals in the paraelectric phase and the crystals with the statistic impurity distribution grown by the conventional method.

It is often assumed that evaporation causes lead and bismuth depletion at the surface of ferroelectric films. However, this is in contrast with evidence that shows surface enrichment of Pb and Bi. A segregation mechanism that is analogous to the diffusion processes observed during the oxidation of metals is described. The presence of an electrochemical potential is discussed, together with the implications on the electrical properties of ferroelectric films.

Pb(Ti0.48Zr0.52)O3 films produced by pulsed laser ablation deposition have been locally examined for their homogeneity and thickness through a comparative use of Raman and infrared spectroscopy. Raman scattering intensity appears to be an oscillating function of the position of the point under measurements. The observed oscillations were explained by light interference effects in the film and used to obtain the thickness profile and the refractive index dispersion of the film. The intensity distribution in Raman spectra across the film differs from that of the target. This difference is larger at the center than near the edge of the film.

A simple model to study the SrTiO 3 perovskite phase formation as a function of the growth parameters by pulsed laser ablation deposition technique has been reported. This model takes into account mainly the equilibrium between the oxygen density and the density characteristic of the pulsed laser deposition (PLD) system. From the critical oxygen concentration of 0.6 for the SrTiO 3 phase, the experimental parameters such as chamber partial pressure and substrate temperature were tailored according to model by adjusting the optimum growth conditions. The critical experimental parameters during the growth were determined: 0.1 mbar of the oxygen pressure and 750 °C of the substrate temperature.

A simple model to investigate the formation of the oxide phase during the growth of ternary oxides films by laser ablation deposition has been proposed. Since the crystallinity properties of the oxide films are subject to the oxygen stoichiometry, the model is based on the balance between the density of the oxygen and a characteristic density of the system, δ =3 N 0 / L 0 3 , in order to scale the optimal target–substrate distance, L 0 . The interaction plume–laser is not considered. The model was applied for growing PbFe 12 O 19 hexaferrite thin film, and it shows that the theoretical conditions found are near to the optimal ones for the film growth. According to the model, for a fixed oxygen pressure of 1.0 mbar and a substrate temperature of 700 °C, a target–substrate distance, L 0 ≈3.1 cm, corresponding to a critical density of oxygen, n g =2.74×10 15 cm −3 , has been determined. The films show a high degree of c -axis orientation, high crystallographic quality and a proper stoichiometry.

Species of batflies of bats from Amazonas and Pará, Brazil are reported. Eleven species of Streblidae and three of Nycteribiidae were found on nine species of bats, belonging to seven genera. Pseudostrebla greenwelli Wenzel, 1996, Trichobius affinis Wenzel, 1976, Trichobius silvicolae Wenzel, 1976, and Hershkovitzia inaequalis Theodor, 1967 were collected for the first time in Brazil. Strebla consocia Wenzel, 1966, Strebla galindoi Wenzel, 1966, Trichobius dugesioides phyllostomus Guerrero, 1998, and Trichobius joblingi Wenzel, 1966 are new records for state of Amazonas. Noctiliostrebla maai Wenzel, 1966, Basilia dubia Guimarães & D'Andretta, 1956, and Basilia ferruginea Miranda Ribeiro, 1903 are new records for state of Pará.

The transport of material from target to substrate has been monitored in the pulsed laser deposition of Pb(Ti0.48Zr0.52)O3 films on p‐doped Si(100) using two in situ diagnostics, namely plume fluorescence spectroscopy and plume ion mass spectrometry. The as‐grown PZT films are specular, with thicknesses which decrease from 350 to 250 nm on a radius 5 mm from the center and show a dielectric hysteresis with typical remanent polarizations and coercive fields of 0.2 μC/cm2 and 124 kV/cm, respectively. The analysis of the plume fluorescence emission and ionic yield indicates that oxidation of the ablated material occurs during transport from target to substrate and that, in order to grow ferroelectric thin films, the substrate should be located in the region of the plume where the relative concentrations of metal oxides and clusters increase.