Abstract: This paper presents a study on monitoring the native oxide growth on silicon micro-pillars. It also presents a comparison between the rates of oxide growth on pillars fabricated using the reactive ion etching (RIE) approach and the metal assisted chemical etching (MACE) approach. The native oxide growth is monitored using photoluminescence (PL) measurements. PL measurements showed that native silicon oxide grows at a higher rate on MACE pillars compared to RIE pillars. SEM images showed that the MACE pillars exhibit a porous outer layer while the RIE pillars show a dense outer layer. It is concluded that the porosity of the pillars enhances the native oxide growth.
Abstract: Quantum dots of CdSe, CdS and ZnS QDs were prepared by chemical reaction and used to fabricate organic quantum dot hybrid junction device. QD-LEDs were fabricated using layers of ITO/TPD: PMMA/CdSe/Alq3, ITO/TPD: PMMA/CdS/Alq3 and ITO/TPD: PMMA/ZnS/Alq3 devices which prepared by phase segregation method. The hybrid white light emitting devices consists, of three-layers deposited successively on the ITO glass substrate; the first layer was of N, N’-bis (3-methylphenyl)-N, N’-bis (phenyl) benzidine (TPD) polymer mixed with polymethyl methacrylate (PMMA) polymers. The second layer was QDs while the third layer was tris (8-hydroxyquinoline) aluminium (Alq3). The results of the optical properties show that the prepared QDs were nanocrystalline with defects formation. The calculated of energy gaps from photoluminescence (PL) spectrometer were 2.38, 2.69 and 3.64 eV for CdSe, CdS and ZnS respectively. The generated white light has acceptable efficiency using confinement effect which makes the energy gap larger, so that the direction of the light sites are toward the center of white light color. The hybrid junction devices (EL devices) were characterized by room temperature PL and electroluminescence (EL). Current-voltage (I–V) characteristics indicate that the output current is good compared to the few voltages ( 8-10.3 V) used which gives acceptable results to get a generation of white light. The EL spectrum reveals a broad emission band covering the range from 350 - 700 nm. The emissions causing this white luminescence were identified depending on the chromaticity coordinates (CIE 1931). The correlated color temperature (CCT) was found to be about 6250, 5310 and 5227K respectively. Fabrication of EL-devices from semiconductors material (CdSe, CdS and ZnS QDs) with hole injection organic polymer (TPD) and electron injection from organic molecules (Alq3) was effective in white light generation
Abstract: Using the method of molecular dynamics, FCC Ni nanowires containing hydrogen atoms in octahedral and tetrahedral pores are investigated in the course of high-speed uniaxial tensile loading along the direction <001>. The feature of structural transformations in Ni nanowires containing hydrogen is appearance on the stage of plastic deformation globular (spherical) formations consisting of hydrogen atoms
Abstract: Recently, many studies on the production of graphite/graphene reinforced aluminum-matrix composites using different fabrication methods, such as powder or semi-powder method, have been performed. However, cast aluminum/graphite or aluminum/graphene composites have not been widely investigated and the research on this production method mainly focuses on 3D graphite particle reinforcements. In this study, the use of a 2D graphene structure, i.e. graphene nanoplatelets (GNPs), in the production of cast Al/GNP composites is investigated. Graphene nanoplatelets reinforced cast aluminum matrix composites were produced using aluminum alloy as matrix material and different graphene nanoplatelets contents. Specimens were cast into a heated rectangular steel mold, the temperature of which was 100°C. All specimens underwent tensile and bending tests as well as hardness measurements and microstructural investigation. Ultimate Tensile Strength (UTS) was considerably increased, simultaneously with a slight decrease of elongation at break, in the case of 0.1 wt% graphene nanoplatelets addition. Regarding bending performance, a slight increase was observed as well. The flexural behavior for 0.1 wt% graphene nanoplatelets addition was exactly the same with the matrix material. The graphene nanoplatelets content found to affect both the surface and the chemical composition of the interdendritic region. After 0.1 wt%, further increase of the wt% graphene nanoplatelets content lead to formation of aluminum carbides (Al4C3) at the grain boundaries, with a consequent drop on the mechanical performance of the Al/GNPs composite.
Abstract: In present scenario, nanocomposites are playing an imperative role in most of the industrial application due to their outstanding performances with good mechanical properties. The aim of this research is to study the effect of tool rotational speed and traverse speed on micro structural and hardness properties of fabricated surface nanocomposites of Al-Al2O3. By varying tool rotational and traverse speed at a constant volume percentage the surface nanocomposites were produced by applying one pass of friction stir processing. A clear view of material flow and defect characterization in the stir zone were studied. Optimum condition of tool rotational speed of 1120 rpm and tool traverse speed of 16 mm/min was obtained to produce a defect free surface nanocomposite. Microstructure observations were carried out through optical microscope and micro hardness test were conducted by using Vickers micro hardness tester. From the phase volume fraction analysis, it was observed that the Al2O3 nanoparticles were well dispersed in the stir zone. It was found that, the tool speed and traverse speed had a significant impact on microstructure properties as well as mechanical properties of the fabricated surface nanocomposite. From the final results it was found that a mixture of dynamically restored ultra fine grins with a mean size of ~80 nm and the average micro hardness value of 130HV were achieved through a fabricated aluminium Al2O3 nanocomposite.