Scientia Iranica
Volume:17 Issue: 1, 2010

Precise positioning of nanoclusters through manipulation in the presence of other clusters is one of the main challenging tasks in nanoclusters assembly. Currently, the size of clusters which are used as building blocks is decreasing to a few nanometers. As a result, the particle nature of the matter has a crucial role in manipulator/cluster/substrate interactions. In order to understand and predict the behavior of nanoclusters during the positioning process, it is, therefore, essential to have a deep insight into the aforementioned nanoscale interactions. In this research, 2-D molecular dynamics simulations are used to investigate such behaviors. Performing the planar simulations can provide a rather satisfactory qualitative instrument for our aim while the computation time is considerably decreased in comparison with 3-D simulations. The system considered here is made up of a tip, two clusters and a substrate. The main focus here is on metallic nanoclusters. In order to study the behavior of the above system which is made up of di erent transition metals, Nose-Hoover dynamics and Sutton-Chen interatomic potential are used. Furthermore, the e ect of the material characteristics, tip form and manipulation scheme on the success of the process are examined. Such qualitative simulation studies can pave the pathway towards certain nanopositioning scenarios when considering di erent working conditions before consuming largescale computation time or high experimental expenses.

The comparative study of Active Screen Plasma Nitriding (ASPN) treatment of two Finemet-type alloys with the compositions of Fe73:5Si13:5B9Nb3Cu1 and Fe77Si11B9Nb2:4Cu0:6 was investigated in di erent temperatures ranging from 410C to 560C. Di erential Scanning Calorimetry (DSC), X-Ray Di ractometery (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), electrical resistivity, microhardness measurements and magnetic characterization by a Vibrating Sample Magnetometer (VSM) were utilized to characterize the treated samples. The comparison of the DSC data for the alloys suggested that the smaller amount of Nb as a growth inhibitor shifted the crystallization temperatures towards lower temperatures. Thus, the crystalline volume fraction and grain size in each temperature for Fe77Si11B9Nb2:4Cu0:6 alloy increased compared to Fe73:5Si13:5B9Nb3Cu1 alloy. The size of iron nitrides on the surface of the ribbons with the lower Si content was larger. The electrical resistivity for the annealed and nitrided Fe77Si11B9Nb2:4Cu0:6 alloy was lower compared to the annealed and nitrided Fe73:5Si13:5B9Nb3Cu1 alloy, due to the larger grain size and lower Si content of Fe(Si) phase in Fe77Si11B9Nb2:4Cu0:6 alloy. The VSM results showed that the maximum saturation magnetization and coercivity at 440C were obtained in Fe77Si11B9Nb2:4Cu0:6 alloy after nitriding under 75% H2 and 75% N2 gas mixture, respectively.

In this paper, we try to explain the origin of the anomalous elastic behavior of nanometersized DNA molecules, which has been observed in all-atom molecular dynamic simulations [A.K. Mazur, Biophys. J. 2006]. It is shown that this anomalous behavior is a consequence of nonlocal interactions between DNA base pairs and the intrinsic curvature of DNA. A nonlocal harmonic elastic rod model is proposed, which can successfully describe the elastic behavior of short DNA molecules.

In the present work, characterization of the surface trenches and vacancies with Amplitude Modulation AFM (AM-AFM) using Molecular Dynamics (MD) is simulated and the e ects of the tip shape on the resulting images are investigated. The simulated system includes a recently developed gold coated AFM probe which interacts with a sample including a surface trench or a single-atom vacancy. In order to examine the behavior of the above system, including di erent transition metals, a Molecular Dynamics (MD) simulation with Sutton-Chen (SC) interatomic potential is used. Special attention is dedicated to the study of tip geometry e ects such as the tip apex radius, the tip cone angle, the probe tilt angle, the tip apex atoms number, and the tip axis direction with respect to the FCC lattice structure on the resulting images.

In order to ensure better elastomer/functionalized Multi-Walled Carbon Nanotube (MWCNT) compatibility and to enhance the dispersion, a series of ionic liquids has been tested in regard to an improved interaction between elastomer and functionalized carbon nanotubes. We found that in the presence of especially one ionic liquid, namely, 1-butyl-1-methylpyrrolidinium tetra uoroborate, for the hydrogenated nitrile elastomer, used as basic polymer, a 1.83 fold increase of elongation at break was achieved with only  7 wt% ionic liquid loading. At this low concentration of ionic liquid the sample can be stretched up to 508% without mechanical failure. The use of this ionic liquid additionally results in high tensile strength (21.4 MPa) at low concentration (< 7 wt %) of ionic liquid. Energy-dispersive X-ray spectrometric scanning electron microscopy con rmed the homogeneous distribution of ionic liquids among nitrile elastomer chains by showing uniform signal belonging to uorine in ionic liquid, when the diffusion process of ionic liquid into nanocomposites was long enough (> 48 h) during the ionic liquid absorption measurements. Transmission electron microscopic images confirmed the good dispersion of the MWCNT along with the exfoliated structure of the CNTs in the rubber matrix.

The aim of this research is to prepare superparamagnetic polyurethane microspheres using SPIONs. Theophylline was used as a drug and the various stoichiometric ratios of isocyanate/polyol were studied to assess their application as a targeting delivery system. Magnetic polyurethane microspheres containing superparamagnetic iron oxide nanoparticles loaded with theophylline were prepared by the water in oil in water emulsion technique. The ratio of hexamethylenediisocyanate and polyol ("-polycaprolactone and starch) was modi ed and the release of theophylline was determined for a period of 20 days. These microspheres were characterized by TEM, SEM, FTIR and magnetometry. The microscopy images show the morphological shape of the superparamagnetic microspheres with an average size of 5 m. The FTIR and the magnetometry confirmed the presence of superparamagnetic nanoparticles in the microspheres. The release of theophylline was studied and dosed by UV spectrophotometer. With the use of PCL with a low molecular weight or in the presence of starch in the structure of polyurethane, the burst effect of drug is decreased. Finally, a SEM study showed an important degradation of the microspheres after the release process. The use of starch as a polyol caused significant improvement in burst effect of the superparamagnetic polyurethane microspheres.

In this study, a dislocation-based model is presented for investigating the evolution of microstructure and mechanical properties of thin lms during a wide range of straining. The model is applied to the High Pressure Torsion (HPT) process of thin nickel disks that provides valuable information on the evolution of material parameters during deformation. The model considers a free surface theory for thin films and can explain the size effect phenomenon in agreement with previous reported trends in literature.

In this research the morphology and mechanical properties of PAN/MWNTs nano bers are studied. The electrospinning process is used to produce ber at micro and nano scale. The dispersion of MWNTs in polymer solution is the key factor to obtain desirable properties in the nal product. Thus, the dispersion condition is investigated using SEM images. The morphological study of ber mats show that by increasing the amount of MWNTs in the polymer from 0 to 1 wt%, the surface roughness of bers is increased. Increasing the percentage of MWNTs in ber improves the tensile stress at maximum load for about 114% and modulus for about 40%.

Thick lms of calcinated and non calcinated nanobioglass(NBG)-titania nanocomposite coatings were prepared on stainless steel substrates using an alkoxide sol-gel process. The prepared lms were characterized by TEM, SEM, EDS, XRD and other methods. The composite lms obtained from calcinated NBG particles were compared to the lms obtained from non calcinated NBG particles. Here, we present a comparative study on the mechanical and adhesion properties of two types of lm (TiO2- calcinated NBG and TiO2-non calcinated NBG). The prepared thick lms were smooth and free of macro cracking, fracture or aking. The grain size of these lms was uniform and its nano scale con rmed using a TEM microscope. Adhesion tests were carried out according to the ASTM-D-3359-97 standard. The results showed that both calcinated and non calcinated NBG-titania lms have very good adhesion properties. The hardness of the prepared lms (TiO2-calcinated NBG and TiO2-non calcinated NBG) was compared by using a micro hardness test method. The results veri ed that the presence of calcinated NBG particles in a NBG-titania composite gradually enhanced the mechanical data of the prepared lms.

In this paper we describe a facile method for the synthesis of Cu2O nanoparticles by reduction of Fehling's solution, using glucose as reducing agent. Copper sulfate is used as a precursor with potassium sodium tartarate in an alkaline media to produce Fehling's solution. The precipitation of Cu2O nanoparticles from this solution in the presence of glucose was controlled by addition of SLES or Triton-X 100 as surfactants. The reactions have been carried out at 60C with high repeatability. The puri cation process of the Cu2O product does not require expensive methods, since a solid product is obtained from a reaction in liquid phase. The resulting Cu2O nanoparticles were characterized by X-Ray Di raction (XRD), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray spectroscopy (EDX), Transmission Electron Microscopy (TEM) and Fourier-transform infrared (FTIR) spectroscopy.