Journal of Nano Research Vol. 11

Abstract: In this work, we report the directed self organization of multilayer thin film devices with colloidal nanoparticles through Layer-by-Layer (LbL) technique [1]. Self-organization of nanoparticles into assemblies to create novel nanostructures is getting increasing research attention in microelectronics, medical, energy and environmental applications. Directed self-organization of nanoparticles [2] into multilayer thin films were achieved by LbL growth through the interaction of oppositely charged of colloidal nanoparticles on substrates of any kind and shapes. Multilayer thin film devices were fabricated using multilayers of gold (conducting) nanoparticles separated by a dielectric nanoparticulate layer of zinc sulphide. The thin films obtained have been studied extensively and the changes in surface morphology, the optical absorption characteristics, thickness, uniformity, adhesion, and conduction behavior are reported. Current voltage (I-V) characteristics of multilayer devices with an increasing number of deposition cycles show an initial current blockade until an onset voltage value, which increases linearly upon the additional layers stacked in devices [3]. A conductive behavior of the device was observed upon exceeding the onset voltage. Moreover, I-V behavior showed that the conduction onset voltage increases linearly depending on the numbers of layers in the final device controlled by the deposition cycles. Systematic I-V characteristics in the forward and reverse biased conditions demonstrated rectifying behaviors in the onset of conduction voltage which makes these films attractive for future electronic device applications.

Abstract: In this paper, we apply a new simple method to specify how a given finite group is matured or unmatured introduced by Shinsaku Fujita. Then, the all integer-valued characters of the fullerene C80 and Tert-Butyl Alcohol are verified.

Abstract: Self-diffusion in magnetron sputtered nanocrystalline Fe films was investigated by neutron reflectometry on [natFe(10 nm)/57Fe(5 nm)]20 isotope multilayers between 310 and 510°C. The determined diffusivities corresponding to diffusion length between 0.8 – 2.1 nm are time dependent and decrease by more than two orders of magnitude during isothermal annealing. This behaviour can be attributed due to the annihilation of frozen-in point defects, formed during sputtering. For very long annealing times of more than 8 days the diffusivities above 400°C are in good accordance with the volume diffusivities on single crystals given in the literature. However, at temperatures below 400°C the diffusivities are higher than extrapolated literature data, indicating that defect annihilation is still an ongoing process. Furthermore, a comparison of diffusivities obtained for nanocrystalline Fe films prepared by magnetron sputtering and ion beam sputtering, respectively, is presented and discussed.

Abstract: We report a theoretical model to describe the spatiotemporal dynamics of a new system consisting of sul…de ions di¤using into an organic gel containing mercaptoethanol-capped cadmium ions. The product, cadmium sul…de, exhibits a faint yellow transparent propagating front starting at the gel-outer electrolyte interface. When subjected to UV light, this system reveals ‡uorescing CdS nuclei localized spatially in a narrow region (constant width), called pulse, that leads the front and propagates down the tube. The reported model is based on reaction-di¤usion equations coupled to dynamical competitive particle growth. The resulting evolution equations were solved numerically and the results are shown.

Abstract: Zinc oxide (ZnO) has found many important applications such as optoelectronic devices, sensors and varistors. The challenging part however is synthesizing ZnO nanoparticles and its utilisation as EM detectors. Sol-gel and self-combustion techniques were chosen in this study due to the ability to produce single phase and nano-size samples. The starting mixture consists of 10 grams of zinc (II) nitrate, Zn(NO3)2.6H2O salt which was dissolved in 50 mL of nitric acid, HNO3.The solution was stirred at 250 rpm continuously for 1 day. The mixture was then gradually heated for every 15 minutes until it combusted at 110oC for the self-combustion technique. For the sol-gel technique, the dissolved mixture was heated at 40oC, 50oC, 60oC and 70oC until the gelatine was formed. After the drying process, the as-prepared samples were annealed at 100oC and 200 oC for 1 hour for each technique. Characterizations were performed by using X-Ray Diffraction (XRD), Raman Spectra and Scanning Electron Microscopy (SEM).The XRD analysis showed a major peak of [101] plane at 2Ө for the self-combustion technique and the sol-gel technique. Raman results for the samples prepared via sol-gel and self-combustion techniques had shown the major peak of ZnO that is located at the Raman shifts of 437.67 cm-1. Using the Scherrer equation, single crystal nano particle of ZnO was successfully obtained in the range of 38.49 nm to 50.70 nm for the sample prepared via the sol gel technique. By the self-combustion technique, the average dimension of the as-prepared sample is in the range of 34-49 nm. Further heat treatment resulted in a major change of the Raman shift corresponding to the single phase ZnO nano particles. The best samples were used as electromagnetic (EM) detectors. The EM detectors are polymer based composite which were prepared using a casting technique.

Abstract: Nowadays, different production methods of nanoparticles have been developed. Among novel wet-chemical processes, the Chemical Bath Deposition (CBD) method is used to synthesize nanoparticles more easily than the other method. In this investigation, titanium dioxide (TiO2) nanoparticles were synthesized by the Chemical Bath Deposition (CBD) method. Tetraisopropyl titanate (C12H28O4Ti), sodium hydroxide (NaOH) and ethanol were used as initial materials. Appropriate solvents were used for preparation of samples. CBD process was carried out at 50°C for 90 min and the obtained materials washed and then dried at room temperature for 48 hrs. For determining particle size and evaluation of morphological characteristics, X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used. The TEM observation indicated that the average particles size of powder is about 10-30 nm and the shape of product is semi-spherical shape. The final results present that the CBD method is more suitable than the other process because of it showing a low processing cost and fine powders.

Abstract: Microwave irradiation is a novel method to accelerate the preparation of inorganic nanoparticles as well as various nanostructures such as nanotubes, nanorods, and nanowires. In this research, silver (Ag) nanostructures with various morphologies were prepared via a rapid microwave-assisted technique. The spherical and polygonal Ag nanoparticles were synthesized in the presence of Polyvinilpyroliden (PVP) as stabilizing agent. Ethylene glycol (EG) serves as a solvent. The silver nanoparticles were produced by Continuous and Discontinuous Wave irradiation. The obtained materials were characterized by UV-visible and transmission electron microscopy (TEM). The results present that the size of nanoparticles increase in continuous irradiation. In this process, the morphology of product is polygonal. In the discontinuous process the colloidal particle size is smaller than that obtained from the continuous process. Furthermore, the Ag nanoparticles have spherical shapes. The final data show that microwave processing has unique advantages over conventional heating processes.

Abstract: A key factor for the efficiency in nanostructured devices is charge transport. Despite considerable attention to this subject, the precise nature of transport processes in these systems has remained unresolved. To understand the microscopic aspects of carrier dynamics, we suggest a method for the calculation of correlation functions. They can be expressed as the Fourier transform of a kernel containing the frequency-dependent conductivity (). We present results for the velocity correlation functions , the mean square deviation of position R2 = <[R(t)-R(o)]2> and the diffusion coefficient D = (R2/t) in materials, like TiO2, ZnO, Si, for which a Drude-Lorentz description or its generalizations applies with a good agreement with experiments. We find that D = 0, indicating absence of diffusion at long times, except in the Drude case (o = 0). For small times t/ < 1, however, diffusion can occur even when o 0, within a limited region of size increasing with the value of o. The quantum mechanical extension of this method allows applications for the nanodiffusion in nanostructured, porous and cellular materials, as for biological, medical and nanopiezotronic devices.

Abstract: W-25%Cu nanocomposite was produced via a thermochemical co-precipitation procedure. Copper nitrate and sodium tungstate salts were used as Cu and W containing precursors respectively. Aqueous solutions of these salts were reacted under controlled pH condition prepared by ammonia addition and the resulting precipitates were then calcined at 450oC and hydrogen reduced at 800oC. The products of each step were characterized by XRD and Electron Microscope. Using a basic medium with a pH of 13 which caused the formation of complex Cu(NH3)42+ was found to provide suitable condition for precipitation of nanosized composite powders. Cu2WO4(OH)2 and CuWO4.2H2O as raw precipitates, CuWO4-x , CuO, and WO3 as calcined powders, and W-Cu reduced composite powders, all were seen to keep nanosize dimensions through high temperature treatments of fabrication. Sintering of the reduced powders at the temperature of 1150oC led in a density of about 98% theoretical density.