Silicon Carbide possesses a combination of properties that make it ideal for use in electronics. Its high values of electric breakdown field, melting point and saturated electron drift velocity have attracted the attention of the semiconductor community. Although the interest in β-SiC/Si devices has intensified in recent years [1-2], little focus has been given to the study of nano-thin film devices. Monocrystalline nano-thin β-SiC films have been reproducibly grown on Si (100) by Gas Source Molecular Beam Epitaxy (GSMBE). Auger Electron Spectroscopy and Reflection High Energy Electron Diffraction characterization have confirmed a growth consistent of β-SiC/Si. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) characterization has determined film thicknesses of 30nm. These nano-films have been used in the fabrication of Metal-Semiconductor-Metal (MSM) devices formed from aluminum Schottky contacts. Under electrical characterization, these MSM devices have exhibited unique properties in that the dominant conduction path does not occur at the β-SiC/Si interface [3] as previously reported, but within the entire β-SiC layer. It is proposed that the device is isolated from the Silicon substrate and due to the nano-thin β-SiC films used in this work the differentiation between surface and ‘bulk’ is not clear. Results obtained through chemical experimentation have indicated that conduction is largely dependent on the surface condition of the device. This suggests the possibility for nano-thin, surface-like, β-SiC films to be used in chemical agent sensors.

In this work we explore the uniqueness of solution combustion synthesis (SCS) technique to produce luminescent nanostructured materials with metastable phases. We synthesized Gd2O3:Eu with the high-temperature phase and induced phase transformation toward the room temperature phase to investigate the effects of structural transformation on the luminescent properties. SCS is based on exothermic redox reactions that undergo self-sustaining combustion, yielding powders composed of agglomerates of nanocrystals with typical dimensions of tens of nanometers. Synthesis of materials through SCS occurs in conditions far from thermodynamic equilibrium and, due to the high temperatures achieved during combustion, metastable crystallographic phases can be formed. Eu-doped Gd2O3 was obtained with base-centered monoclinic structure and average nanocrystal size of 35 nm as determined by Debye-Scherre analysis. Phase transformation to the cubic structure was induced by isothermal annealing at 1000 oC for up to 152 hrs and followed by x-ray diffraction (XRD). Luminescence excitation and emission spectra were obtained as a function of annealing time. The transformation from monoclinic to cubic structure was followed by the behavior of the (111) monoclinic/(222) cubic intensity ratio. The ratio value for the as-prepared material is 6, decreasing fast to 3 after 5 hrs. annealing, and reaching a value of 0.1 after 152 hrs. Concomitant to the structural transformation, nanocrystal size was followed for both crystalline phases. The average nanocrystal size for the cubic phase increases from 27 to 47 nm from 1 to 152 hrs., respectively. On the other hand, nanocrystals with the monoclinic phase remained with a constant size around 38 nm. Overall, variation in size is small due to the low connectivity among nanocrystals resulting from the low isostatic pressure employed to prepare the pellets, together with the non-uniform shape of the agglomerates. Photoluminescence excitation spectra are dominated by a broad centered near 278 nm and assigned to the O2-Eu3+ charge transfer band. Photoluminescence emission results present the 5D0-7FJ (with J = 0-4) transitions of Eu3+ ions. The behavior of these bands was investigated as a function of annealing time and subsequently related to the structural changes.

Combinatorial gradient-controlled sputter deposition has been employed to produce a library of 100 separate thin films with a wide range of Mg-Al alloy compositions. We have successfully isolated the â (Mg17Al12) phase in polycrystalline films for investigation. The presence of the â phase has been found to be desirable for increasing corrosion resistance; however, in structural components under tensile loading and/or at elevated temperatures, the â phase precipitates undergo coarsening which induces poor creep behavior in several common alloys. We have also synthesized amorphous Mg-Al and mixed-phase compositions as identified by X-ray diffraction measurements. Details of the growth procedure as well as structural and compositional characterization are presented.

The batch-foaming behavior of multiphase polymer blends and block copolymers was systematically investigated using carbon dioxide as a blowing agent. Three different polymer systems were evaluated: (i) nanostructured triblock terpolymers, (ii) microstructured polymer blends, and (iii) nanostructured polymer blends. In order to obtain nanostructured blends, immis-cible blends of poly(2,6-dimethyl-1,4-phenylene ether)/poly(styrene-co-acrylonitrile) (PPE/SAN) were melt-compatibilised via polystyrene-b-polybutadiene-b-poly(methyl methacry-late) triblock terpolymers. Due to the specific interaction between the respective components, a nanostructured interphase between PPE and SAN was observed. With regard to neat block co-polymers, the self-assembly of solvent-cast SBM triblock terpolymers was exploited in order to produce nanostructured morphologies. In each case, the resulting foam morphology was charac-terized by evaluating the foam density as well as the cell size. Combined with the multiphase structure of the non-foamed material and its thermal as well as physical behavior, relationships between the foaming characteristics and the cellular morphology were established. As an exam-ple for the foaming results, submicro-cellular structures were observed by foaming nanostruc-tured polymer blends, while the cell walls still revealed the nanostructured morphology. In con-trast, batch-foaming of neat triblock terpolymers led to the formation of microcellular foams; however, as highlighted by scanning electron microscopy, the cell walls did undergo some fur-ther expansion and formed additional nano-sized cells. In the light of these results, new routes for preparing cellular polymers are derived by systematically exploiting the multiphase charac-teristics of polymer blends and block copolymers.

We describe the dynamics of the synthesis of gold nanoparticles by glow discharge in aqueous solutions. Initial [AuCl4]− concentration and the voltage applied between the electrodes were varied. Reduction rates were calculated from changes in concentration of [AuCl4]− vs. discharge time. A pulsed power supply was used to generate discharges in the aqueous solutions. The morphology of the nanoparticles obtained was observed by transmission electron microscopy (TEM). [AuCl4]− was reduced by H radicals or electrons generated by the discharge. Dendrite-shaped nanoparticles ∼150 nm in size were formed after discharge for 1 min. The pH of the solution decreased gradually with increasing discharge time. The decrease in pH led to dissolution of gold nanoparticles. The reduction and dissolution rates increased proportionately with the applied voltage. The size of gold nanoparticles decreased during discharge and was 20 nm after discharge for 45 min. When the reduction rate lowered as a result of dissolution, anisotropic nanoparticles were formed and continued to grow in the solution.

A white cast iron of composition Fe81C14Si5 can be cast into a nanostructure with network morphology by a fluxing technique. The conventional morphology of white cast iron, which is brittle, is eutectic. The mechanical behavior of network white cast iron is attractive. Hardness tests indicate that its average hardness value is ∼770 HV. The indentations made during hardness tests have no cracks. A stylus surface profiler was employed to study the surface profile at and near the indentations. The studies indicate that there are severe plastic flows, but without cracks.

Although chemical vapor deposited mullite (3Al2O3•2SiO2) environmental barrier coatings have shown promise in protecting Si-based substrates for gas-turbine applications, there is concern that the silica content within the mullite coating itself might be susceptible to hot-corrosion and recession during long term exposure to corrosive atmospheres. There is thus a strong motivation to substantially reduce or even virtually eliminate the silica from the surface of the mullite coatings that are in direct contact with atmospheres containing corrosive oxides and steam. Functionally graded mullite (3Al2O3•2SiO2) coatings have been grown for Si-based substrates and the composition has been tailored in these coatings, with the Al/Si ratio being stoichiometric (∼ 3) at the coating/substrate interface for coefficient of thermal expansion (CTE) match, and increasing monotonically towards the outer coating surface. These functionally graded coatings have some of the highest Al-rich mullite reported to date at the coating surface. At these extremely high Al/Si ratios, mullite structure breaks down and the formation of a nano-sized high-alumina rich phase occurs. High-resolution transmission electron microscopy has been used to characterize the structure and composition of high alumina mullite and will be discussed.

A molecular model is proposed for the dynamics of polymer chains in dilute polymer solutions containing well-dispersed spherical particles. In the presence of short range energetic affinity between the monomers and filler surface, the equilibrium structure of the adsorbed polymer layer is determined by a scaling theory. The viscoelastic response of the suspension is studied by a Maxwell model. It is shown that the solid-like properties of polymer nanocomposites in low frequency regimes could be attributed to the slowdown of the relaxation process of polymer chains. This process is controlled by the monomer-particle frictional interactions, density of the adsorbed polymer chains on the particles surface (controlled by monomer-particle adsorption energy), and volume fraction of the interfacial layer which can be enhanced by reduction of filler size or increasing the filler concentration.

Energies for symmetric tilt grain boundaries in pure Al and in Al with substitutional Pb defects at coincident sites along the grain boundaries were calculated using a modified embedded atom method potential and density functional theory. The agreement between the analytic potential, the first principles calculations and experiment is reasonably good for the pure system. For the Al-Pb system both the analytic potential and first principles calculations predict that Pb segregation to the interface is energetically preferred compared to the dilute solution. The application of a disclination structural unit model to calculating grain boundary energies over the entire range of tilt angles is also explained.

Thermoplastic polyolefin (TPO) contained 30 wt.% PP and 70 wt.% SEBS-g-MA, and its nanocomposites reinforced with 0.3 -1.5 wt.% organoclay (OMMT; Cloisite 30B) by a two-step melt mixing followed by injection molding. The microstructure and mechanical behavior of the TPO/OMMT nanocomposites were investigated. X-ray diffraction measurements revealed the absence of basal diffracting peak of OMMT in TPO/OMMT, suggesting formation of intercalated/exfoliated nanocomposites. Tensile tests showed that the stiffness, yield strength and tensile strength of TPO can be enhanced by adding low loading levels of OMMT. Thus, OMMT can reinforce TPO due to their large aspect ratios. Moreover, there was no reduction in the impact strength of the TPO/OMMT nanocomposites associated with the clay additions.

Current polyamide 11 and 12 are lacking in fire retardancy and high strength/high heat resistance characteristics for fabricated parts that are required for performance driven applications. The introduction of selected nanoparticles such as carbon nanofibers (CNFs), combined with a conventional intumescent flame retardant (FR) additive into the polyamide 11/polyamide 12 (PA11/PA12) by melt processing conditions has resulted in a family of intumescent polyamide nanocomposites. These intumescent PA11 and PA12 nanocomposites exhibit enhanced polymer performance characteristics, i.e., fire retardancy, high strength, and high heat resistance and are expected to expand the market opportunities for resin manufacturers. The overall objective of this research is to develop improved PA11 and PA12 polymers with enhanced flame retardancy, thermal, and mechanical properties for selective laser sintering (SLS) rapid manufacturing. Arkema RILSAN® PA11 polymer was examined with CNFs and Clairant Exolit® OP 1230 intumescent FR additive. They were used to create a family of FR intumescent PA11-CNF nanocomposites. Transmission electron microscopy (TEM) was used to determine the degree of CNFs and intumescent FR additive dispersion in PA11. Injection molded specimens were fabricated for material properties measurements. Thermal stability of these polymer nanocomposites (PNs) was examined by TGA. Flammability and thermal properties of these PNs were obtained using the cone calorimeter, UL 94 test method, and heat deflection temperature.

The purpose of this work is to examine the dielectric, electrical and thermo-mechanical properties of multi-walled carbon nanotubes (MWCNT) filled polypropylene nanocomposites formed by melt-mixing. To that aim dielectric relaxation spectroscopy (DRS) and dymamic mechanical analysis (DTMA) were employed. The results are discussed in terms of nucleating action of MWCNT and interfacial polymer-filler interactions. Special attention is paid to percolation aspects by both ac conductivity measurements for the samples which are above the percolation threshold and permittivity measurements for the samples which are below percolation threshold.

A new method of Si3N4/TiN nanocomposite powders through reaction at low temperatures was proposed and tested. The reduction of titanium chloride and silicon chloride by sodium was conducted in liquid ammonia at the temperature range of −40°C∼−50°C, and titanium nitride and silicon nitride nanopowders were obtained. Based on these reactions, in-situ coating and co-precipitation were conducted. The TiN nano-particles deposited on the surface of Si3N4 particles as the nuclei in the in-situ coating and in the co-precipitation two or more source of ions were reduced uniformly in the liquid ammonia. Si3N4/TiN nanocomposite powders were prepared by the both routes and were characterized with X-ray diffraction, transmission electron microscopy. The effects of in-situ and the particle size on the morphology of the composite were discussed.

(1-x)SiO2/(x)TiO2 composite micro/nano scale fibers with various compositions were successfully prepared by electrospinning their sol-gel precursors of titanium(IV) isopropoxide(TiP), and tetraethyl orthosilicate(TEOS), followed by calcinations. Any gelator or binder was not used in this direct preparation process for composite fibers. The surface morphology and structure of sintered composite fibers were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and Fourier transform infrared (FT-IR). The crystallization behavior and surface morphology of the as-spun fibers were largely influenced by the calcination temperature and the content of TiO2. The photocatalytic activity of SiO2/TiO2 composite fibers was examined by UV-DRS spectra. The experiments demonstrated that the MB in aqueous solution was successfully photodegraded using SiO2/TiO2 composite nanofibers under UV-visible light irradiation.

Phase transitions in stacked GeTe/SnTe and Ge2Se3/SnTe thin layers for potential phase-change memory applications have been investigated by X-ray diffraction using a two-dimensional area detector system. The as-deposited underlying GeTe or Ge2Se3 layer is amorphous, whereas the top SnTe layer is crystalline. In the GeTe/SnTe stack, the crystallization of GeTe phase occurs near 170°C, and upon further heating, the GeTe phase disappears, followed by the formation of rocksalt-structured GexSn1−xTe solid solution. In the Ge2Se3/SnTe stack, the phase transition starts with the separation of a SnSe phase due to the migration of Sn ions into the Ge2Se3 layer. SnSe is believed to facilitate the crystallization of Ge2Se3-SnTe solid solution at ∼360°C, which is much lower than the crystallization temperature of Ge2Se3, therefore consuming less power during the phase transition.

Due to the increasing prevalence of resistance of bacteria to antibiotics and antiseptic methods, new strategies to prevent colonization of biomaterials are needed. Due to its high antimicrobial activity and relatively low toxicity to human cells, we are evaluating silver (Ag) releasing plasma polymers as a strategy to prevent bacterial colonization. Such Ag/plasma polymer nanocomposite materials, consisting of nano-scaled metal clusters embedded within a plasma-polymer matrix can be deposited using a mixed, plasma polymerization /sputtering process. For example, Ag containing plasma polymer nanocomposites are deposited employing an Ag cathode, an appropriate monomer to yield the desired material properties of the matrix (biocompatibility) and an asymmetric reactor design. The focus of this paper is a new development at Empa: a multi-functional Ag/amino-hydrocarbon (Ag/a-C:H:N) nanocomposite that can enhance cell growth and simultaneously prevent bacterial colonization at surfaces. Ag/a-C:H:N coatings containing 4.0% Ag have been demonstrated to reduce bacterial adhesion of E. coli by up to 95%, as compared to an external polyester fabric control in a static assay. Likewise, these coatings demonstrated a bacterial toxic effect both at the surface and in the surrounding media due to the release of Ag ions. XPS characterization of various nanocomposites has shown that the Ag quantity and matrix characteristics of the films can be tailored to specific requirements by altering deposition parameters such as power input, pressure and gas feed ratio. Although the surface chemistry has been characterized, open questions remain to the amount and the kinetics of the release of Ag and the subsequent effect on bacteria and cells. Since Ag release profiles will ultimately determine the antimicrobial efficacy of the coatings, as well as duration of the effect, these dosing issues must be quantified and clarified. Ag release kinetics of the various Ag/a-C:H:N as measured by atomic absorption spectroscopy has been evaluated and the relationships to biological assays, including bacterial and cellular adhesion are clarified. A range of Ag/a-C:H:N coatings having various Ag content are tested in two biological assays, bacterial toxicity and cytoxicity. Bacterial growth tests using the pathogen, P. aeruginosa wild type (PAO1), were performed according to the method of Tiller et al. The method is based on the bacterial deposition from aerosols, thus, it mimics bacterial exposure through airways such as intubation tubes. Secondly, cytotoxicity assays of the nanocomposites has been performed using a murine fibroblast cell line 3T3 testing protocol, and the proliferation of the cultures was measured taking the DNA amount per well as an index (Bruinink 2001). We will answer questions regarding what is the fundamental Ag content and Ag release profile under static bacterial testing environments which allow a maximum bacterial-toxic effect with a minimum amount of Ag.

This study presents the mechanical and electrical properties (including elastic modulus, yield strength and electrical resistance) of PDMS/CNTs nanocomposites. The elastic modulus and yield strength were determined from tensile tests. In addition, a high resistance meter was used to measure the electrical resistances of the PDMS/CNTs nanocomposites. The test specimens of nanocomposites were manufactured using the thermoforming method. There were two recipes used during the thermoforming process: 100 °C for 1 hour, and 150 °C for 15 minutes. The mixtures of PDMS and CNTs were stirred by ultrasonic instrument to prevent polymerization. A feeler gap was used to define the thickness of the specimens. Therefore, the thickness could be controlled within the range of ∼100 μm. Four different kinds of specimens were investigated, including pure PDMS, 1.0 wt%, 2.0 wt% and 4.0 wt% CNTs polymeric composites. As for the l00°C recipe, the elastic modulus of pure PDMS, 1.0 wt%, 2.0 wt%, and 4.0 wt% CNTs were 1.05MPa, 1.17MPa, 1.10MPa and 1.35MPa, respectively. A for the l50°C recipe, the elastic modulus of pure PDMS, 1.0 wt%, 2.0 wt% and 4.0 wt% CNTs were 1.32MPa, 1.42MPa, 1.43MPa, and 1.54MPa. The differences of electrical resistance of PDMS/CNTs nanocomposites at two different conditions and the microstructures composed of the mixtures are also described in this article.

The optical properties of amorphous and crystalline silicon nanoparticles are studied. By tuning the power of the non-thermal plasma reactor, the structure of the particles is adjusted from amorphous to crystalline nanoparticles. The microstructure is studied using transmission electron microscopy, X-ray diffraction, and Raman vibrational spectroscopy. The photoluminescence quantum yields of crystalline nanoparticle samples are consistently higher than those of amorphous nanoparticles.

To realize ceramic/polymer nanocomposites for polymer waveguides, PMMA-coated Ta2O5 nanoparticles are synthesized as core/shell particles. Therefor a gas-phase process is used: the Karlsruhe Microwave Plasma Process. The organic coating is supposed to reduce the agglomeration of the ceramic cores and should facilitate the incorporation into the polymer resin. TEM investigations of the nanoparticles exhibit crystalline and amorphous Ta2O5 with sizes around 3 to 6 nm, confirmed by electron diffraction. Although the polymer coating is not visible in TEM imaging, electron energy loss spectroscopy (EELS) exhibits a significant C-edge, proofing the organic coating. The Ta2O5/PMMA nanoparticles are incorporated with different weight fractions to a maximum of 1 wt% by a dissolver stirrer into PMMA resin. The optical properties (refractive index, transmission) are determined as a function of the nanoparticle content. Compared to the pure polymer, the refractive index of the modified composite, measured at 633 nm, is increased by 0.001 and 0.004 at 0.1 wt% and 0.7 wt%, respectively. A similar tendency is observed at 1550 nm. The transmission in the near infrared (NIR) is similar to that of PMMA up to a content of 0.3 wt%. At higher nanoparticle contents transmission is reduced. The reduction in transmission is due to the presence of agglomerates larger then 1/10 of the applied wavelength, confirmed by TEM. The concept of incorporating inorganic/organic hybrid nanoparticles with intrinsic high refractive index in polymer matrices is very promising. A suitable effect in refractive index for application of ceramic nanoparticle/polymer nanocomposites as polymer waveguides could be observed even with low particle concentration.

Mesoporous silicas functionalized with aminopropyl groups were synthesized by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyl triethoxysilane (APTES) and characterized by nitrogen adsorption-desorption measurements. The pore volume drastically decreased from about 900 mm3/g for the unfunctionalized mesoporous silica to about 300 mm3/g for the aminopropyl-functionalized mesoporous silica (1.65 mmol-NH2/g). This result was explained in terms of the surface density of the aminopropyl groups in the pore.