Oxidation Kinetics of Nano Crystalline Tin Oxide Conductive Thin Films

Tin oxide was the first transparent conductor to have achieved significant commercialization. SnO2 is an n-type semiconductor with an optical band gap of about 3.6 eV in poly crystalline form. One of the main reasons for the wide use is its rather desirable characteristic of having both, high optical transmittance and high electrical conductivity. Under optimum deposition conditions, tin oxide crystallizes in the tetragonal (rutile) structure. In this study, nano crystalline thin oxide conductive thin films has been manufactured by thermal evaporation techniques onto steel substrates using metallic tin targets and oxidation kinetics have been studied after D.C. plasma oxidation by using XRD (X-Ray Diffraction). The activation energy of SnO and SnO2 from Sn phase transformations has also been studied.

Development of Nano-Structured Aluminum Surfaces by LSM

Aluminum is one of most common metals in all advanced and modern scientific and technological applications including electrical, electronic, chemical, engineering, energy and medical fields. The performance of aluminum alloys determines to large extent the quality and economic status of the different processes. Aluminum surface structure determine its performance where nano sized grains and layer can improve aluminum properties and performance. In this work, the improvement of aluminum surface structure and formation of nano structured surface grains by laser surface melting (LSM) using Nd-YAG laser under argon atmosphere was investigated. Different power and scanning speed were applied. The physical and chemical properties of the produced surfaces were examined. SEM, EDX and XRD analyses were performed and were correlated to hardness results. Corrosion resistance of the treated surface was investigated to evaluate their performance in aggressive media and chemical and medical applications. From the obtained data it can be concluded that Nd-YAG laser surface melting of aluminum results in formation of 750 micron nano-structured surface layer. Adjustment of LSM parameters could produce 100 nm grains or less. The obtained results showed also that LSM under argon can eliminate the formation of Al2O3 surface layer which may deteriorates the performance in certain applications. Surface layer rich in AlN is formed upon LSM. It was concluded also that corrosion resistance of the treated aluminum surfaces was improved to large extent by LSM.

Characterization of Nano- and Micro-Filled Resin Composites Used as Dental Restorative Materials

Adhesively-bonded resin composites have the advantage of conserving sound tooth structure with the potential for tooth reinforcement, while at the same time providing an aesthetically acceptable restoration. However, no composite material has been able to meet both the functional needs of posterior restorations and the superior aesthetics required for anterior restoration. In an attempt to develop a dental resin composite that had the mechanical strength of hybrid composite materials and the superior polish and gloss retention associated with microfilled materials, nanofilled resin composites have been introduced in the market. Although nanofillers are the most popular fillers utilized in current visible light-activated dental resin composites and are claimed to be the solution for the most challenging material limitations as a universal restorative material, the mechanisms by which these fillers influence the resin composite properties are not well explained. In this study, some physical and mechanical properties of a nanofilled resin composite containing 60 vol. % zirconia and silica fillers were evaluated and compared to those of a microhybrid resin composite of the same composition. The nanofilled resin composite was found to have equivalent polymerization shrinkage and depth of cure to the microhybrid material but a slightly lower degree of conversion and density. Regarding mechanical behaviour, although the nanocomposite was found to exhibit significantly higher wear resistance, and equivalent flexural strength, its indentation modulus and nanohardness were slightly lower. Field-emission scanning electron microscopy (FE-SEM) analysis was conducted in order to evaluate the microstructure and to obtain a better understanding of the effect of the nanofillers on the behaviour of the nanocomposite.

Characterization and In-Vitro Assessment of Nano-Hydroxyapatite Prepared by Polymeric Route

Hydroxyapatite is the most used calcium phosphate in implant production. In this study a novel method for the preparation of nano-hydroxyapatite is described. A mixture of calcium chloride and potassium hydrogen phosphate were introduced to the urea-formaldehyde resin during formation. The obtained resin was precalcined at 450°C to get rid of the organic materials. The prepared powder was characterized using XRD, thermal analysis (DTA, TG), FT-IR, TEM and SEM supplemented with EDAX. In particular, the results of XRD show that the powder produced at 900°C was wholly formed of nano-hydroxyapatite. TEM reveals that nano-hydroxyapatite particles have spherical shape and their size was less than 50 nm in width. SEM confirms the fine nature of the produced powder. The dielectric constant increases with increasing temperature and decreases with increasing frequencies. The dielectric loss shows a relaxation peak, which shifts to the higher frequency region with increasing temperature, conforming to a Debye-type relaxation process. In-vitro results show that fine grains of acicular hydroxyapatite were formed by immersing disc in simulated body fluid solution (SBF) proving the apatite formation onto the surface. Future work recommends incorporation of the prepared nano-sized hydroxyapatite into biocompatible polymer for tissue engineering applications.

The Effect of Pressure on the Microstructural Behavior on SnO2 Thin Films Deposited by RF Sputtering

Tin oxide has multiple technological applications including Li-ion batteries, gas sensors, optoelectronic devices, transparent conductors and solar cells. In this study tin dioxide (SnO2) thin films were deposited on glass substrates by RF sputtering process in the oxygen (O2) and argon (Ar) plasma medium. The deposition of the thin SnO2 films was carried out by RF sputtering from SnO2 targets. Before deposition the system was evacuated to 10−4 torr vacuum level and backfilled with Ar. The deposition of the nano structured thin SnO2 films have been performed at different gas pressures. The deposition of the SnO2 was both carried out at different pure argon gas pressures and argon/oxygen mediums with varying oxygen partial pressures. The effect of argon and argon/oxygen partial gas pressures on the grain structure and film thickness were analyzed in the resultant thin films. The deposited thin films both on glass and stainless steel substrates were characterized with scanning electron microscopy (SEM), X-ray diffractometry equipped with multi purpose attachment. The grain size of the deposited layer was determined by X-ray analysis. The Atomic Force Microscopy (AFM) technique was also conducted on the some selected coatings to reveal grain structure and growth behaviors.

Fabrication and Properties of Nylon-6/Layered Silicate Nanocomposites by Melt Blending

Polymer/clay nanocomposites currently attract immense interest from both research and industrial communities. By dispersing at the molecular level a tiny amount of clay within a polymeric matrix, a wide range of properties can be significantly improved. The efficiency of the clay (layered silicate) in improving the properties of the polymer materials is primarily determined by the degree of its dispersion in the polymer matrix. To promote the molecular and stable dispersion of the clay layers, the clays should be organically-modified with onium salts. In this work, nylon-6 nanocomposites based on two types of commercial organoclays were prepared by melt blending via single-screw extrusion. The good dispersion of clay in the nylon-6 nanocomposites was confirmed by X-ray diffraction and transmission electron microscopy. The influence of the dispersed nano-clay fillers on the thermal and mechanical properties of the resulting nanocomposites was characterized using thermogravimetric analysis and nanoindentation.

Effect of Nanostructured Thermal Spray Coatings on Fatigue Behavior of Low-Carbon Steel

Nanostructured and conventional titania (TiO2) coatings were thermally sprayed using air plasma spray (APS) and high velocity oxy-fuel (HVOF) processes. The fatigue and mechanical properties of these coatings were investigated. The fatigue strength of coatings deposited onto low-carbon steel showed that the nanostructured titania coated specimens exhibited significantly higher fatigue strength compared to the conventionally sprayed titania. SEM analysis of fracture surfaces revealed valuable information regarding the influence of these coatings on the performance of the coated component. Analysis of surface deformation around Vickers indentations was carried out. This investigation gives new understanding to the nature of fatigue and deformation of these coatings.

Novel Multifunctional Composites by Functionally Dispersed Carbon Nanotubes Throughout the Matrix of Carbon/Carbon Composites

Recently, increasing demands for smarter and smaller products calls for the development of multifunctional composites. These materials are used not only as structural materials but also satisfy the needs for additional functionalities such as thermal, electrical, magnetic, optical, chemical, biological, etc. In this research, a novel carbon nanotubes dispersion approach leads to a new generation of multifunctional composites with additionally novel thermal functionality, we called it heat-directed functionality. These distinctive composites have unique capability which can conduct the majority of the transferred heat by conduction to the preferred area or direction of the thermal structure. This unique heat-directed property can be attained by varying the in-plane thermal conductivity. Varying the in-plane thermal conductivity of the composites functionally is achieved by dispersing highly heat-conductive materials such as carbon nanotubes throughout the matrix functionally, not uniformly. Therefore, in this research three phase carbon/carbon composites have been fabricated with functionally dispersed carbon nanotubes throughout the carbon matrix of continuously plain woven carbon fiber fabrics in order to attain this useful property. The fabricated heat-directed carbon/carbon composites have been examined experimentally and numerically. The in-situ full-field infrared measurements and finite element analysis of the designed composites showed that the heat transfer direction can be substantially controlled by just functionally dispersed a few percentages of carbon nanotubes through the matrix of traditional long carbon fiber-reinforced carbon matrix composites. This exceptional property can play a significant performance improvement in heat transfer process along the in-plane of the materials as well as helping to decrease the heating up of the Earth, global warming, due to the escaped heat of many engineering applications. In other words, the efficient heat energy management or heat energy saving via using the introduced multifunctional carbon/carbon composites with heat-directed functionality can significantly help with both sides of the equation of efficient energy consumption and friendly-environment applications.

Transmission Coefficients for Tunneling of Electrons and Holes in Biased Ga1−xAlxAs–GaAs–Ga1−xAlxAs Triple Barriers Semiconductor Heterostructures

In this work we calculate the transmission coefficients for tunneling of electrons and holes through biased triple barriers (double-wells) semiconductor heterostructures (TBSH’s), composed of Ga1−xAlxAs–GaAs–Ga1−xAlxAs with x = 0.45. The calculations are based on the effective mass theory that employs the spatial effective masses and the temperature dependent of the material parameters that constitute the heterostructure. The transverse motions of carriers are also considered. In the analysis the Airy’s function formalism is taken into account. It is found that, the resonant transmission energies for both electrons and holes are decreased by enhancing the applied voltage. Also, the total resonant transmission energies for the tunneling carriers are deviated toward higher energies, as the temperature is increased. Therefore, these devices should be operated at low temperatures. Furthermore, the present work shows a discrepancy in resonant transmission energies with those reported ones, due to ignoring the effect of temperature.

Measurement of DNA Hybridization by Nano-Deformation of Microcantilever in CMOS Biosensor

A 1 cm × 1 cm biosensor chip for analyzing DNA hybridization is developed by CMOS process. The sensor chip has 6 measurement regions, each region with 3 pairs of parallel microcantilever of 125 × 60 × 0.75μm. The microcantilever is a 4-layer structure composed of an immobilized surface layer, a top insulation layer, an embedded piezoresistive layer, and a bottom insulation layer to measure the nano-deformation induced by the surface-assemble monolayer of alkanethiols on Au. By the Langmuir adsorption model, the estimated adsorption rate of the ssDNA is 0.005sec−1. The design has intrinsic sensitivity needed in biochemical applications such as detecting nucleotide polymorphism and single base mutation to sequence DNA. The capability of in-situ, multipoint measurement promise many frontiers to be explored.