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This work reports an optimal way to fabricate strontium hexaferrite with porous-reticulated structure using a variation of the replication technique and taking two different precursors, one obtained from the coprecipitation and the other from the ceramic method. Changes made to the original replication technique include the addition of Arabic gum as binder, and the addition of ethylene glycol to form the ceramic sludge. In addition, some parameters such as the relation between solid material and liquid phase, the quantity of binder and the heat treatment were varied to obtain high quality magnetic foams. Two polymeric sponges were used as patterns, one with average pore size of 300 μm diameter and the other with 1100 μm. The characterization of the samples included the analysis of the structure and phase purity, the magnetic properties, the remanence properties, magnetic interactions and the microstructural characteristics. Results indicate that both, the powder precursors and the polymeric pattern play an important role in the configuration of the foam structure and this configuration has an important influence on the dipolar interactions which tend to demagnetize the samples. In addition, it was analyzed the behavior between the minimum value of the δ M curves and the hysteresis properties.

We have investigated 3C-SiC layers grown on silicon and on poli-Si in order to realize test MEMS structures. The strain of the films were investigated by the fabrication of cantilevers, beams, springs and we successfully fabricated a Double-Ended-Tuning-Fork double clamped SiC resonator on the film, with perfectly aligned actuation electrode.

In this work we report on the growth of cubic silicon carbide using CBr4and silane as precursors at different C3H8/CBr4flow ratios. The layers were deposited on 2’’ (001) Si wafers by means of the VPE technique in a horizontal cold-wall reactor with induction heating. The growths were performed at atmospheric pressure, in H2atmosphere and involved several steps: Si thermal etching; carburisation; epitaxial growth. Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were performed to observe the film morphology and defects and correlate them with the gas phase composition. Results show that the addition of CBr4to the standard SiH4and C3H8precursor can change the crystalline nature and the morphology of the grown SiC.

β-SiC/SiO2 core-shell NWs have been synthesized on patterned silicon wafers in a CVD system, using carbon oxide as single precursor and nickel nitrate as catalytic element, in nitrogen or argon atmosphere at 1100°C. The coaxial structure and the crystallinity of the NW core are examined by (scanning) transmission electron microscopy. The patterning of the substrate allows to grow NWs in selected areas only, as imaged by SEM. Cathodoluminescence (CL) panchromatic images of the same areas point out that the light emitted under electron excitation is localized only in the area covered with NWs. The room-temperature CL spectrum has three different components peaked at 2.45 eV, related to the 3C-SiC near-band-edge emission, and at 2.75 and 3.75 eV, that are induced by the triplet and singlet states of oxygen-deficiency centers ODC(II) in silicon dioxide shell.

-SiC and -SiC/SiO2 core-shell nanowires (NWs) grown on silicon substrates by three different processes, based on the use of i) carbon monoxide, ii) silane with propane and iii) carbon tetrachloride precursors, are analysed by structural and optical techniques. Spectroscopic cathodoluminescence studies show a luminescence enhancement in core-shell structures, ascribed to an effective role of the shell as both carrier injecting barrier and passivation layer. In NWs grown using CCl4 precursor, a peculiar luminescence with dominant red component at about 2 eV has been detected and ascribed to point defects related to an unintentional oxygen incorporation.

3C-SiC films were grown on Si by VPE using CBr4 as the carbon source, at temperatures ranging between 1100 to 1250°C. XRD, TEM, AFM, and SEM results indicate that the epitaxy proceeds as a 3D growth of uncoalesced islands at low temperature, whereas a continuous layer with hillocks on top is obtained above 1200°C. The shape and faceting of the islands are analyzed by AFM, showing (311) preferred facets.

The growth of 3C-SiC on (001) silicon substrates by means of vapor phase epitaxy is described. The growth mechanisms are discussed with the aid of structural and morphological characterizations performed by X-ray diffraction, transmission electron microscopy, and atomic force microscopy. Raman spectroscopy was used to study the residual stress. A large shift of Raman peaks with respect to the expected values for the bulk is observed and explained by the relaxation of Raman selection rules due to lattice defects. The stress and stress gradients through the film thickness are observed and studied on micrometer-sized structures such as membranes and cantilevers. Local Raman peak fluctuations are observed on millimeter-sized membranes, while cantilevers show different degrees of curling depending on film thickness.

A comparative study of the morphology of 3C-SiC films prepared with different C:Si ratios is presented. The silane precursor controls the growth rate at all values of C:Si ratio but combined of observations using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) indicates that the C:Si ratio is critical in determining the grain size and at values of C:Si close to 1 texturing and faceting become evident. Makyoh Topography reveals various surface defects, a slight mesoscale roughness and bending of the epiwafers.

Cubic SiC layers grown by VPE on n-type, p-type or semi-insulating Si substrates have been characterized as regards the formation of voids in the Si substrate, namely pyramidal voids and micropipes. The former have been detected in n-type substrates, the latter in p-type and semi-insulating substrates. The total empty volume of the pyramidal voids is higher than that of the micropipes suggesting that the probability of Si out-diffusion is higher in the n-type Si substrates. The results are discussed in terms of the influence of the Fermi level on the diffusivity of the Si atoms and their out-diffusion from the substrate.

The binary oxide AlVO4 is being proposed as a new gas sensor material. An X-ray investigation, IR spectrum analysis, resistivity and a calculation of the electronic structure of this compound have been carried out in order to determine its structural, absorptive and sensor properties. The fragment [Al3V3O23]18− is the chain chosen to study the electronic properties of AlVO4 in the framework of the frontier orbital theory and the interaction between molecules has been described by the Molecular Electrostatic Potential (MEP). The vibration analysis and the simulated infrared spectrum (IR) were calculated for the unit [Al3V3O23]18− and a comparative analysis with the experimental spectrum of AlVO4 is also presented.

In recent years several ferroelectric thin films have been studied at microwave frequencies; lead zirconate titanate (PZT) and barium-strontium titanate (BST) has been widely investigated. However, the microwave dielectric properties of strontium-bismuth tantalate (SBT) have not yet been investigated so widely [1]. The purpose of this work is the microwave characterization of the dielectric properties of an SBT thin film biased at different DC voltages. The dielectric properties of SBT make it a good material for the production of FERAM memories. Microwave characterizations may show other properties that could promote the SBT as good candidate for capacitors to be employed also in microwave circuits (e.g. resonators and filters). In this work a study of high frequency dielectric properties has been performed and equivalent circuit model has been used to correct the measurements.

AlVO4 thin films were prepared by infrared Nd:YAG pulsed laser deposition on two different substrates (polycrystalline Al2O3 and monocrystalline MgO). The distance between the target-substrate (30 mm) and the partial oxygen pressure (0.14 mbar) during the deposition process were chosen taking into account the previous experiences with other oxides. The substrate temperature was varied between 300 and 600 °C finding an optimum at about 400 °C. At higher temperatures, the vanadium seems to evaporate from substrate surface with a strong change of stoichiometry. Preferential growth of AlVO4 films in the direction (022), were grown on MgO substrates. A very high sensitivity of these films to a flux of NO2 gas is also shown.

A simple method for preparing polycrystalline bulk PbFe12O19 hexaferrite has been developed. Ceramic samples were prepared using the ceramic method, and any lead deficiency can be compensated by a correct X-ray diffraction analysis by the Rietveld refinement method and a further addition of PbO. Adequate sintering conditions are necessary to obtain the single-phase compound.

Ferroelectric thin films have been investigated intensely by many researchers over the past decade, but some important phenomena that influence the electrical properties have been overlooked. This work addresses the lead enrichment, which is observed on the surface of lead zirconate titanate films. The XPS compositional profiles of PZT films prepared using different thermal treatments are presented and correlated with the preparation conditions. The segregation profiles are explained in terms of a simple oxidation model that induces the diffusion of lead to the surface. The ionic diffusion also induces self-polarisation, commonly seen in ferroelectric films. The implications on the electrical properties of ferroelectric films, particularly, imprint of the polarisation state, are also discussed.

AlVO4 is a relatively new sensor material derived from V2O5/Al2O3 mixtures to selectively detect NO and NO2 gases. Previous studies carried out in order to determine its structural, absorptive and sensory properties indicate that the AlVO4 is not the only single phase. This work deals with the synthesis of the compound by the ceramic and the nitrate decomposition methods, and by the sol gel route. The Rietveld refinement of the compound was carried out in order to determine its crystal structure. Single phase of AlVO4 was successfully obtained via the nitrate decomposition and the sol gel methods. Thereafter, films prepared by the sol gel route were deposited on alumina and Si/SiO2/Pt substrates and characterized by SEM and X-ray diffraction. The electric characterization of the AlVO4 on alumina substrate film is also presented.

Magnetic and Mo ssbauer measurements have been performed on polycrystalline samples of Ga substituted M-type hexagonal ferrites having compositions PbFe12−xGa x O19 (0 9 are paramagnetic at all temperatures. The magnetic moments of the non substituted Fe3+ ions in the spin-up predominant sublattice do not have the same temperature dependence, because of the presence of non magnetic Ga3+ ions in the neighbouring lattice sites. For x 3, the faster decline of the saturation magnetisation can be attributed to the onset of non collinear magnetic order.

PbFe12O19 hexaferrite thin films with a high degree of orientation in the perpendicular direction have been deposited by pulsed laser ablation on 1×1-cm2 (0001) sapphire substrate at 700°C under 3.0 mbar partial pressure of high purity oxygen. The anisotropic character of the films was demonstrated by a remanence ratio of 86% in the perpendicular direction in contrast with to 20% in the parallel direction to the film plane. The X-ray diffraction analysis confirmed this orientation, showing only the (0001) lines of PbFe12O19 compound. The hexagonal lattice parameters determined were a=5.885 A and c=23.066 A. Moderate values of coercive field (2.5 kOe) and saturation magnetisation (165 emu/cm3) were obtained.

Pulsed laser ablation deposition has been used to grow polycrystalline PbFe 12 O 19 thin films with high coercivity on Si/SiO 2 substrates. The influence of the substrate temperature (550–775°C) and the oxygen pressure (1.0–3.0 mbar) on the magnetic properties during the deposition is reported. The crystallisation of PbFe 12 O 19 thin films occurs in the temperature range of 600–750°C, which is somewhat lower than that for the Sr and Ba hexaferrites, which crystallise in the range of 750–850°C. M-type lead hexaferrite films with high saturation magnetisation (280 emu/cm 3 ) and high coercive field (3.8 kOe) were grown using a substrate temperature of 700°C and a pressure of 3.0 mbar of oxygen. These films were observed to be isotropic, with an M r / M s ratio of ∼0.5.

Magnetic and Mossbauer measurements have been performed on polycrystalline substituted M-type hexagonal ferrites of compositions PbFe12−xScxO19 (x = 0, 0.5, 1, 1.5) and PbFe12−xInxO19 (x = 0, 1, 2). The substitution of the Fe3+ by Sc3+ and In3+ ions perturbs the axial magnetic order giving rise to angled magnetic structures. From the values of the quadrupole splitting of the Fe57 14.4 keV level, measured above and below the Curie temperatures, the angle between the magnetic moment of the Fe3+ ions in various sublattices and the hexagonal c-axis have been deduced. At 77 K the measured angles do not exceed 20° and depending on x are different for different sublattices. The dependence of x on the saturation magnetisation at 0 K, expressed in Bohr magnetons, differs markedly in Sc and In containing compounds, partly due to the different substitution probability of iron in the spin up and spin down sublattices, and also due to the different spin canting angles.

A new method has been developed to grow nickel-catalysed SiC nanowires on silicon, by a chemical reaction involving carbon tetrachloride as a single precursor. This produces long crystalline 3C–SiC nanowires with axis, as verified by transmission electron microscopy. A broad optical emission centred at about 2 eV is detected by cathodoluminescence spectroscopy. The Gaussian component at about 2.2 eV corresponds to the indirect 3C–SiC band gap emission, while the dominant red emission is related to oxygen incorporation.

The melt spinning of a NdFeB alloy of stoichiometric composition was investigated under various ambient gas pressures, from atmospheric pressure, 100 kPa (760 Torr) to vacuum, 0.13 Pa (10 −3 Torr). Gas pockets were observed on the roll contact surface of ribbons produced at pressures close to atmospheric, whilst a reduction in pressure, to 50 kPa (380 Torr) caused the disappearance of the gas pockets. The absence of the gas pockets led to more consistent magnetic properties for the nanocrystalline ribbon.

PbFe 12 O 19 powders were obtained by thermal decomposition of hydroxide–carbonate coprecipitated salts and metal–organic precursors at 920°C. Significant microstructural differences have been found between both specimens. The MOD powder comprised submicronic particles of remarkably high coercivity (5 kOe), and the magnetization mechanism was dominated by coherent rotation. In contrast, the coercivity for chemically coprecipitated powders was very poor (1.6 kOe), when compared with Ba- and Sr-compounds prepared following the same method, a behavior associated with excessive grain growth. Cell parameters, microstructure, Curie temperature, hysteretic properties, anisotropy field and the saturation magnetization as a function of the temperature in the interval 77–300 K are reported.

The variation of the tetragonal distortion (c/a) with particle size of Pb(Zr, Ti)O3 nanoparticle thin films prepared by the sol–gel technique is reported. The tetragonal distortion of the unit cell, which is related to the spontaneous polarization, decreases exponentially with size and vanishes at 16 nm. This distortion was correlated with the used additive in the preparation processing and crystallization temperature of the films, and the existence of a critical grain size for the ferroelectric phase transition was observed. The phase transition was monitored by X-ray diffraction, scanning electron microscopy, and electrical measurements.

In the present work the metallorganic decomposition technique has been applied to grow high-coercivity isotropic polycrystalline BaFe 12 O 19 thin films on ZrO 2 /Si substrates. The influence of several growth parameters on the magnetic properties, such as the film thickness, the annealing temperature (500–850°C) and the atmosphere during thermal treatments (oxygen and air), is reported. Barium hexaferrite formation starts at 600°C, the reaction being completed within relatively short times; above 700°C, a beneficial effect of an O 2 atmosphere on i H c was found. In these films particles tend to behave as single domain in the thermically demagnetized state.

The effects of mechanical grinding on the magnetic and structural properties and on the phase formation of Dy-Fe-(B, C) alloys have been studied. X-ray diffraction, Mossbauer spectroscopy and thermomagnetic analysis show that there is a decomposition of the Dy 2 Fe 14 (B, C) phase accompanied by the formation of α-Fe. In addition, for boron rich alloys magnetic phases which are revealed in the TMA curves disappear during the measurement. The magnetic measurements showed a gradual fall in coercivity at longer grinding times. The magnetisation falls initially and then rises, due to the amorphisation and decomposition of the original phases and the formation of the α-Fe.

The effect of temperature and atmosphere during the crystallization process on electrical and reliability characteristics of ferroelectric capacitors, obtained by sol-gel deposition of lead zirconate titanate films, have been examined for non-volatile memory applications. Films with good ferroelectric properties were achieved after 600 and 650 °C, 1 hour crystallization in a O2 atmosphere: a remanent polarization of about 20 μC/cm2 and a coercive field of 125 kV/cm was obtained with a durability factor better than 108 cycles. The results point out that in 5/48 lead zirconate/titanate films, where a morphotropic phase boundary exists, fatigue more likely results from a stress relief process than from charge migration.

A scanning friction force microscope has been used to study the surfaces of lead zirconate titanate thin films prepared by sol-gel and pulsed laser ablation. As well as mapping the topography of the films the friction force has proven to be a sensitive tool which can be used to detect compositional changes. Although the laser deposited films had some larger defects up to 500 nm, the grains had a smooth texture (roughness = 2–5 nm). Sol-gel films had grain sizes of the order of 150 nm and roughness of 20–50 nm. Zirconium rich films also had “rosettes” approximately 1 μm in diameter and raised 200 nm above the surrounding matrix. The technique was sensitive enough to discern chemical differences at the grain boundaries and between the “rosettes” and the matrix.

The structural and magnetic properties of deformed powders of M-type Baferrite, obtained by mechanical grinding, have been investigated using X-ray diffraction, Mossbauer spectroscopy, thermomagnetic analysis, and magnetic measurements. The rapid decrease in the magnetization after short grinding times in air is attributed to the formation of a phase which is paramagnetic at room temperature but at 150 K the phase behaves like a spin-glass, with antiferromagnetic short-range order. From Mossbauer spectra this phase has at least five non-equivalent sites of iron with hyperfine interaction field values Hrf(77 K): H1=38.69; H2=37.01; H3=36.14; H4= 34.31 and H5=30.96 MA/m, and a magnetic moment μFe = 2.1μB. At longer grinding times the deformed BaFe12O19 samples were found to be thermodynamically unstable and decomposed partially into α-Fe2O3 and Fe3O4.

A W-type hexagonal ferrite of composition Sr(ZnLi 0.5 Fe 0.5 )Fe 16 O 27 has been prepared by ceramic technique using ball milling followed by heat treatment at 1100, 1200 and 1320°C for different times. The samples were examined by thermomagnetic analysis, X-ray diffraction, magnetic and Mossbauer measurements. W-type single-phase compounds were obtained by heating the samples at 1320°C but only polyphase material was obtained after heating to 1100 and 1200°C. The samples treated at 1320°C for 5 h had the best intrinsic magnetic properties: σ s = 89 ± 1 emu⧸g, H A = 13.8 kOe and T C = 432°C. The Mossbauer spectra give evidence of a magnetic order, in agreement with a hypothesis of selective occupation by Zn 2+ and Li + cations of the tetrahedral and octahedral spin-down sublattices, respectively.

Scanning force and friction microscopy (SFFM) has, for the first time, been applied to investigate the morphology and phase structure of Pb(Zr, Ti)O3 ferroelectric thin films, deposited by sol-gel. The topographic characterization (roughness 20–50 nm, grain size 150–500 nm) reveals the presence of clusters of grains (rosettes) in zirconium rich films. The friction measurements show that the rosettes and the surrounding material are composed of different phases. Quantitative comparisons of the friction forces are performed.

One of the perspective directions in using positive temperature coefficient (PTC) thermistors is their application in surface heater in various electronic devices and integrated circuits. The special interest in this connection makes possible fabrication of thin film structures on the basis of materials with PTCR. In the given work a result of the investigation of Y–BaTiO 3 thin films has been presented. Thin films have been deposited by RF-sputtering technique. Films had thickness of 1.5–2 μm. Subsequent annealing was carried out to obtain polycrystalline films of a single phase. The temperature dependence of resistance of films has been investigated. The increase of the resistance were observed in the temperature range 50–80°C. The jump of the resistance in field of phase transition was 70%.

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.