A solution-based synthesis route was developed to produce large quantities of MgO nanorods. Hydrated basic magnesium chloride, which has needle-like crystal structure, was used as a precursor. A subsequent two-step transformation process with magnesium hydroxide as an intermediate product was used to preserve the morphology of the precursor to yield magnesium oxide nanorods. Scanning electron microscopy, powder X-ray diffraction and energy dispersive X-ray spectroscopy show that the products are very pure (>95%) crystalline MgO nanorods with diameters from 40 nm to 200 nm and lengths 10 microns or longer. High-resolution transmission electron microscopy and electron diffraction further reveal that these MgO nanorods are single crystals and that the rod axis is along the <110> crystal direction. A model for the structural transformation from hydrated basic magnesium chloride to magnesium oxide has been developed and compared to our experimental results. This solution-based process can be easily scaled-up, and is a low-cost source of pure magnesium oxide nanorods needed in many industrial applications, for example, as reinforcing agents in matrix composites and as flux-pinning centers in high-TC superconductors.

Molecular beam deposition (MB) of thin film metal oxide is prospective for application in gas sensor technology due to the well-controlled oxide molecular fluxes during creation of multi-oxide structures with improved characteristics. However, the MB process leads to some oxygen deficiency in the oxide. Further application of the MB technology (and, in general, the e-beam oxide deposition in vacuum) for processing of sensor structures needs the control and correction of the oxygen stoichiometry by adding in-situ atomic oxygen to the growing material or via the thin film oxidation after deposition.

Thin films (50 to 500 nm) of SnOx and TiOx were deposited on SiO2/(001)Si substrates at 100°C by MB from SnO2 and TiO2 sources. The film stoichiometry in the as-deposited state and after annealing in vacuum and in oxygen is characterized by XRD, TEM and RBS. Oxygen annealing transformed the strongly non-stoichiometric SnO (Romarchite) in the as-deposited state to Cassiterite, SnO2. Structure transformations in the TiO2 films during annealing are also discussed.

Tungsten oxide is a material of significant interest for applications in several areas. It can, for example, be used as the electrochromic film in smart windows. Tungsten trioxide nanoparticles were produced using an advanced gas evaporation unit in which the tungsten was oxidized in low pressure ambient air. The tungsten trioxide particles were formed via vapor condensation and were deposited by gas deposition technique to avoid coagulation effects. The average size of the primary particles was around 5 nm, depending on the heating power and the pressure. The particles exhibited a body centred cubic structure. The impedance spectrum of particle deposits showed resonance and negative capacitance effects. The correlation between fabrication conditions, structure and impedance spectrum is discussed.

Various properties of particles can be altered by coating them with a layer of different chemical composition. Yttrium iron garnet (YIG) particles has been coated with silica for control of their sintering, corrosion resistance, and stabilization of magnetic properties. This silica cover was obtained by hydrolysis of tetraethylorthosilicate (TEOS) in 2-propanol. This material was characterized by transmission (TEM) electron microscopy, (XEDS) X-ray energy-dispersive spectrometry, (XPS) X-ray photoemission spectroscopy and (VSM) vibrating sample magnetometry. YIG was heterocoagulated by silica as indicated by TEM micrographies. XPS measurements indicated that only binding energy for silicon and oxygen was found on the silica shell, which confirms that the YIG was covered. The values of the saturation magnetization differ from the heterocoagulated system to well-crystallized YIG.

Nanocrystalline ITO powders have been prepared by a hydroxide coprecipitation method. Through the variation of aging time after precipitation, we have characterized the size, morphology and the structure of the precipitates. It was found that the precipitates are in the state of InOOH at first. Further aging up to 48 h changed it to In(OH)3 structure. After calcinations of the precipitates, rhombohedral nanocrystalline ITO powder with spherical shape was produced from InOOH structured precipitates, while cubic nanocrystalline ITO powder was produced from In(OH)3. Fraction of the rhombohedral ITO powder decreased as the aging time increased. The particle size of the cubic ITO increased with aging time but that of rhombohedral ITO (∼15 nm) was almost invariant.

Mono-dispersed TiO2 ultrafme particles with diameters 40-400nm were obtained from aqueous TiOCl2 solution with 0.67M Ti4+ concentration prepared diluting TiCl4 by homogeneous precipitation process in the ranges of 17-230°C. With the spontaneous hydrolysis of TiOCl2, which means the natural decrease of pH value in the aqueous solution, all mono-dispersed precipitates were crystallized with the anatase or rutile TiO2 phase. TiO2 precipitate with the pure rutile phase was fully formed at the temperatures below 65 °C, not involving the evaporation of H2O, and above 155 °C, which were available by suppressing it. TiO2 precipitate with rutile phase including a small amount of the anatase phase started to be formed in the intermediate temperatures above 70 °C showing the full formation of the anatase above 95 °C under the free evaporation of H2O. However, in the case of completely suppressing H2O evaporation at the temperatures above 70°C, TiO2 precipitate with anatase phase was fully transformed into the precipitate with the rutile phase by the vapor pressure of H2O. Therefore, the formation of TiO2 precipitates with the rutile phase around room temperature would be caused due to the existence of the capillary pressure between the agglomerated needle-shaped particles or the ultrafme clusters, together with the slow reaction rate.

In superparamagnetic materials, the change of the direction of the magnetization is not associated with the movement of Bloch walls, but with thermal fluctuation of the magnetization vector. Therefore, the resonance frequency of the Bloch walls is no longer limiting the maximum frequency for applications. The limit found in superparamagnetic materials is given by the frequency of electron spin resonance. This behavior was verified for spinelle type ferrites made of ceramic or polymer coated oxide nanoparticles produced by the microwave plasma process. By selecting the composition of the spinelle type ferrites the energy of magnetic anisotropy controlling the susceptibility and the maximum frequency for applications can be adjusted. Superparamagnetic materials have their frequency limit beyond 2 GHz. Coating of the particles reduces dipole – dipole interaction destroying superparamagnetism. Even when the susceptibility is in the order of magnitude of today's commercial ferrites, the saturation magnetization is found to be smaller than the theoretically expected value. This phenomenon is partly clarified by soft X-ray magnetic circular dichroism (SXMCD) measurements, showing a significant orbital magnetic moment anti arallel to the direction of the spin moment. Additionally, it was found that the amount of Fe2+ ions is possibly larger than expected by thermodynamic data of bulk materials.

Here we report the synthesis of organically passivated nanoparticles of gold, chromium and nickel. The routes involve the reduction of a metal precursor in various Lewis base solvents, which appear to affect the final nanoparticle morphology. The preparation of highly monodispersed samples can lead to the potential for further manipulation of dots into ordered 2D and 3D arrays. These colloidal thin films and crystals have potential application in magnetic data storage devices.

In an attempt to both prepare nanocrystalline bismuth and understand the fundamental chemistry behind the formation of this potentially interesting material, we have examined the reduction of BiCl3 in the presence of strongly coordinating solvents and ligands. These studies have resulted in the formation of bismuth powders with approximate average particle sizes of between 20 and 40 nm which exhibit large size distributions. The simultaneous reduction of both gold and bismuth precursors, done in an attempt to better control the final particle size, instead produces Au2Bi of comparable dimensions. There is no evidence that the ligands utilized in either of these systems remain bound to the final product. These nanocrystalline powders have been characterized through XRD and TEM, and full details of the synthesis are presented.

A new strategy for stabilizing inorganic nanoparticles in nonpolar solutions is described. Resorcinarenes 1-3 were synthesized and evaluated as surfactants because of their large concave headgroups with multiple contact sites. Au nanoparticles ranging from 3-20 nm in diameter were generated in the vapor phase and dispersed into dilute hydrocarbon solutions of 1-3, where they were stabilized for up to several months. Chemisorption is most likely mediated by multiple Au-O interactions, as indicated by several control experiments and by surface-enhanced Raman spectroscopy. The resorcinarenes were readily displaced by dodecanethiol, which resulted in the precipitation of particles >5 nm as determined by absorption spectroscopy and transmission electron microscopy. This suggests that the mobility of the resorcinarene tailgroups are important for maintaining the larger nanoparticles in a dispersed state. Resorcinarene surfactants with stronger chemisorptive properties are currently being explored.

Highly oriented proteins with characteristic nanometer dimensions are used as a template for the synthesis and support of metallic nanoparticles. Following a bottom-up approach, noble metal particles in the nanometer size range were obtained by the reduction of the corresponding metal salts in the presence of the protein assemblies. The catalytic activity of the protein-supported particles was determined by hydrogenation reactions.

Ion-implantation and thermal-processing methods have been used to form nanophase magnetic precipitates of metallic cobalt that are embedded in the near-surface region of single crystals of Al2O3. The Co precipitates are isolated, single-crystal particles that are crystallographically oriented with respect to the host Al2O3 lattice. Embedded nanophase Co precipitates were formed by the implantation of Co+ at an energy of 140 keV and a dose of 8 × 1016 ions/cm2 followed by annealing in a reducing atmosphere. The implanted/annealed Co depth profile, particle size distributions and shapes, and the orientational relationship between the nanophase precipitates and the host crystal lattice were determined using RBS/channeling, transmission electron microscopy, and x-ray diffraction. Magneto-optical effects arising from Co precipitates formed in the near-surface region of Al2O3 were observed and characterized using magnetic circular dichroism. Magnetic properties of the Co-particle/host nanocomposites were investigated in the temperature range of 77 to 295 K in applied fields of up to 10 kG using a superconducting quantum interference device (SQUID) magnetometer. Implantation of the Co particles by Pt or Xe ions produced a large anisotropic increase in their coercivity. Accordingly, these magnetic nanoparticle systems may be of interest for magnetic data storage applications. Details of the magnetic properties of the Co/Al2O3 nanocomposites including their retentivity, coercivity, saturation field, and magnetic anisotropy are presented.

By means of integral temperature dependent conductance measurements, the effective capacitance of ligand stabilized nanoparticles, arranged in dense packings or networks, can be deduced from the activation energy of the charge transport, for which the use of the Landauer formula is proposed. According to this, the barrier resistance in ligand stabilized nanoparticle arrangements depends predominantly on the inter particle spacing rather than on the chemical composition of the molecules. Comparison with data of the single molecule resistance determined by local probe techniques or by theoretical methods shows remarkable aggreement.

This paper describes a procedure based on the Tollens' process for preparing crystalline nanoparticles of silver with well-controlled, uniform sizes. The starting reagents are similar to those commonly used for electroless deposition of silver and are commercially available from the Peacock Laboratories (Philadelphia, PA). Only under appropriate conditions, mixing of these reagents was able to generate stable dispersions of silver colloids, rather than thin films of silver coated on surfaces of objects immersed in the solution (including the inner surface of the container). We have demonstrated the capability and feasibility of this method by forming stable dispersions of highly monodispersed, single crystalline colloids of silver with dimensions in the range of 20-50 nm.

Alloys, with six different compositions in the system Mg-Ca-Zn were produced by melt spinning. The aging behavior of alloys was investigated by measuring the changes in microhardness after isochronal aging and the microstructure was analyzed by means of Transmission Electron Microscopy(TEM), Energy Dispersive X-ray Spectrometry (EDS), Scanning Transmission Electron Microscopy (STEM) and Scanning Electron Microscopy (SEM). All six compositions in the as-solidified condition show a difference in microstructure between the wheel contact side (zone A) and the free surface side (zone B) as a result of the differences in the solidification rate across the ribbons. One of the alloys was chosen to be more deeply investigated in this work as it exhibited grain boundary films and presented the highest peak hardness among the low Ca alloys. The comparison between the two microstructural zones in this alloy can aid in understanding of the phase transformation steps during cooling with a model which is proposed here.

SmxFe100−x samples with x = 7.6, 10.5 and 12.5 were prepared by high energy ball-milling and subsequent annealing at various temperature Ta, 600 < Ta < 1200 °C. Rietveld analysis coupled to Curie temperature measurements and M6ssbauer spectroscopy revealed for 600 < Ta < 900 °C an hexagonal phase P6/mmm derived from TbCu7 with stoichiometry SmFe9. At Ta > 900 °C, the ordered R3m Sm2Fe17 structure is obtained so that SmFe9 appears as the out-of-equilibrium precursor of Sm2Fe17. The Curie temperature and hyperfine field augmentation found for SmFe9 results from an increase of the interatomic distance in the Fe-Fe dumbbell, responsible for a reduction of the negative exchange interaction.

Al-Sm and Al-Y-Fe alloys with a high number density of nanocrystalline fcc-Al homogeneously dispersed within the amorphous matrix have been synthesized by devitrifying the precursor metallic glasses produced by rapid solidification. The kinetics of metallic glass formation and the development of the nanostructure during devitrification are discussed in terms of the rate limiting mechanism. The glass transition temperature of the two metallic glasses has been successfully assessed with the application of the modulated-temperature differential scanning calorimetry (DDSC). In addition, the formation of quenched-in nuclei was investigated by a comparison study on the cold-rolled and melt-spun Al92Sm8 amorphous samples. Furthermore, the enhancement of the particle density of the fcc-Al nanocrystals in the amorphous matrix after devitrification has been demonstrated by the incorporation of nanosize Pb particles.

Gold-coated iron core-shell structure and Au/Fe/Au onion-like nanoparticles synthesized using reverse micelles were characterized by transmission electron microscopy (TEM). The average nanoparticle size of the core-shell structure is about 8 nm, with about 6 nm diameter core and 2 nm shell. The gold shell structure can be resolved from both high resolution electron microscopy (HREM) image and energy dispersive X-ray spectrum (EDS). Even though the gold and iron electron diffraction rings overlap a little bit, they can still be identified due to the slight mismatch of the diffraction rings. The Au/Fe/Au onion-like nanoparticles were also observed. The nanoparticles were formed with about 6 nm diameter gold core, 1 nm iron interlayer and 2 nm gold shell. The shell structure coated on the core appeared unhomogeneous, however, in both cases the iron core and interlayer iron shell stay air-stable.

Pyridine solutions of CdSe nanocrystals were solution-deposited in the fabrication of thin film transistors (TFTs). A peak mobility of 1 cm2V−1s−1 and an ON/OFF ratio of 3×104 were observed for TFTs processed at 350 °C. The nanocrystals acted as a precursor to the bulk material, coalescing to form a semiconductor thin film when heated at plastic-compatible temperatures. Single crystalline regions several hundred times the size of the original semiconductor nanocrystals were observed for films processed at 350 °C. We also report a process for direct liquid phase deposition and patterning of nanoparticle inks at sub-micron resolutions by elastomeric embossing and AFM nanospotting. These results suggest that microelectronic devices produced from nanoparticle-based inks can enjoy the processing advantages usually associated with organic materials while retaining the performance advantages typically associated with inorganic materials.

This paper reports the study of semiconducting oxides to develop gas sensors in thick-film form for use in atmospheric pollutant monitoring devices. The investigation was achieved with the following steps: selection of the suitable oxides and of their most appropriate processing method to obtain nano-sized powders, fabrication using screen-printing technology of thick-film sensors from these powders, and electrical measurements in laboratory and in the field. Chemical routes such as sol-gel techniques and thermal decomposition of heteronuclear complexes have been used to prepare nano-sized powders of n-type (TiO2) and p-type (LaFeO3 and SmFeO3) semiconducting oxides. Thick-film gas sensors have been produced by screen-printing technology. Pastes have been prepared and printed on laser precut 96% alumina substrates, each 2×2 mm element being provided with a heater, comb-type Au contacts and a Pt-100 resistor for controlling the operating temperature. The firing of the films has been performed in conditions able to keep grain size at nanometer level. Electrical responses to some major polluting gases (CO, NO, NO2 and O3) have been tested in laboratory and in the field, and compared with results of the analytical techniques approved by the international standards.