Journal of Nano Research Vol. 10

Abstract: As the size of a free-standing crystal approaches a few tens of nanometers, the image force experienced by a dislocation can exceed the Peierls force. This will lead to dislocations leaving the nanocrystal without the application of an external stress and thus making it dislocation free. In this investigation a finite element methodology is developed for the calculation of the critical size at which a free-standing crystal becomes edge dislocation free. A simple edge dislocation is simulated using Finite Element Method (FEM) by feeding-in the appropriate stress-free strain in an idealized domains corresponding to the introduction of an extra half-plane of atoms. The image force experienced by the edge dislocation is calculated as the gradient of the plot of the energy of the system as a function of the position of the simulated dislocation. In nanocrystals, due to the proximity of multiple surfaces, the net image force due to multiple images has to be calculated. Additionally, surface or/and domain deformations have to be taken into account in nanocrystals; which can drastically alter the image force. For the crystal to become dislocation free, the minimum image force experienced by the dislocation, has to exceed the Peierls force. Minimum image force values calculated from the FEM models are compared with the Peierls stress values obtained from literature to determine the critical domain size at which crystal becomes edge dislocation free.

Abstract: This study employs a direct-synthesis method to produce titania (TiO2)/water nanofluid, which is a working fluid involved in the electrophoretic deposition (EPD) of nanophotocatalytic films. In general, using organic solvents and water as the bulk liquids in EPD produces environmental pollution and defective films due to the electrolysis of water. To mitigate water electrolysis, the fabrication method proposed in this study adds an anionic dispersant to the TiO2/water nanofluid. The anionic dispersant changes the surface charge of TiO2 nanoparticles to facilitate their deposition on the anode. For low voltage EPD processes, this method effectively improves defective nanophotocatalytic films. These defects are caused by bubbles from the water electrolysis, as the volume of oxygen produced at the anode amounts to half of the hydrogen produced at the cathode. The objective of this study is to propose empirical equations describing the relationship between film thickness and electric parameters.

Abstract: Zinc hot-dip galvanizing is one of the most effective methods for the corrosion protection of ferrous substrates. However, the failure of zinc coatings is possible when exposed to harsh environments for rather long periods. The application of a thin diamond like carbon (DLC) film on the top of the zinc coating might be a promising method for promoting their corrosion resistance. In the present work, a DLC thin film was deposited on zinc galvanized coatings by Plasma Enhanced Chemical Vapor Deposition. The as-formed film was composed of nanostructured and amorphous areas. The electron diffraction patterns acquired from the nanograins correspond to carbon phases with d-spacing ranging from diamond to graphite. Additionally, after 18 days of exposure in a simulated marine atmosphere, the DLC coated samples were proven to be more resistant than the naked galvanized coatings indicating its potential to improve the corrosion resistance of galvanized ferrous materials.

Abstract: In this paper, the electronic eigenstates and energy spectra of a two-dimensional system formed by three concentric, coupled, semiconductor quantum rings with a perpendicular magnetic field in the presence and the absence of a single ionized hydrogenic donor impurity are studied. It is found that the magnetic field localizes the electron wave function in the inner rings. The effects of hydrogenic donor on the electronic structure of concentric triple quantum rings are investigated in the both on- and off-center configurations. It is shown that as the donor moves away from the center of the system, the ground state energy decreases monotonically, the degeneracy is lifted and the gap between the energy levels increases. Also, the binding energy of donor impurity increases with increasing magnetic field.

Abstract: Quaternary semiconductor alloys based on GaSb are suitable for thermo-photo voltaic cell applications as they have low and adjustable band-gap. However, they exhibit phase separation which destroys band-gap uniformity. In this work, GalnAsSb thin films grown on GaSb vicinal substrates were studied by Transmission Electron Microscopy, in order to determine the influence of the growth parameters on phase separation. It was found that the coatings exhibit two types of compositional modulation, one parallel and the other forming an angle with the substrate plane.

Abstract: Surface enhanced Raman spectroscopy (SERS) is a promising molecular imaging modality capable of simultaneously detecting multiple molecular biomarkers. With the biocompatibility and functionalizability of Au, Au-nanoparticle based Raman tags possess the potential for in vivo SERS cancer biomarker detection. Here, we report the large scale synthesis of a new type of Au nanoparticles, Porous Hollow Au Nanoparticles (PHAuNPs), and demonstrate their potential application as SERS imaging tags. PHAuNPs feature a sub-20 nm porous shell and a 50 nm void core. Such unique morphology enables them to strongly absorb and scatter near infrared lights due to the surface plasmon resonant effect of Au. This makes them particularly suitable for in vivo applications, where NIR wavelengths are considered as a ‘clear window’ for deeper penetration of light. The construction and characterization of PHAuNP-based Raman nanotag, including attachment of Raman dye, pegylation and their stability, are described. Cytotoxicity of Raman nanotags are tested using the radioactive [3H]thymidine incorporation method. The results show that pegylated Raman nanotags are stable and non-toxic and can potentially be used for in vivo applications.