Academic literature on the topic 'CdO Nanoparticle'

In this work, CdS and ZnS semiconducting colloid nanoparticles coated with organic shell, containing either SO[3-] or NH[2+] groups, were deposited as thin films using the technique of electrostatic self-assembly. The films produced were characterized with UV-vis spectroscopy and spectroscopic ellipsometry - for optical properties; atomic force microscopy (AFM) - for morphology study; mercury probe - for electrical characterisation; and photon counter - for electroluminescence study. UV-vis spectra show a substantial blue shift of the main absorption band of both CdS and ZnS, either in the form of solutions or films, with respect to the bulk materials. The calculation of nanoparticles' radii yields the value of about 1.8 nm for both CdS and ZnS.The fitting of standard ellipsometry data gave the thicknesses (d) of nanoparticle layers of around 5 nm for both CdS and ZnS which corresponds well to the size of particles evaluated from UV-vis spectral data if an additional thickness of the organic shell is taken into account. The values of refractive index (n) and extinction coefficient (k) obtained were about 2.28 and 0.7 at 633 nm wavelength, for both CdS and ZnS.Using total internal reflection (TIRE), the process of alternative deposition of poly-allylamine hydrochloride (PAH) and CdS (or ZnS) layers could be monitored in-situ. The dynamic scan shows that the adsorption kinetic of the first layer of PAH or nanoparticles was slower than that of the next layer. The fitting of TIRE spectra gavethicknesses of about 7 nm and 12 nm for CdS and ZnS, respectively. It supports the suggestion of the formation of three-dimensional aggregates of semiconductor nanoparticles intercalated with polyelectrolyte. AFM images show the formation of large aggregates of nanoparticles, about 40-50 nm, for the films deposited from original colloid solutions, while smaller aggregates, about 12-20 nm, were obtained if the colloid solutions were diluted. Current-voltage (I-V) and capacitance-frequency (C-f) measurements of polyelectrolyte/nanoparticles (CdS or ZnS) films suggest the tunnelling behaviour in the films while capacitance- voltage (C-V) and conductance-voltage (G-V) measurements suggest that these nanoparticles are conductive. The electroluminescence was detected in sandwich structures of (PAH/CdS/PAH)[N] using a photon counting detector, but not in the case of ZnS films.

This project involves the investigation of a.c. and d.c. electrical characterisations and low-frequency noise properties of Langmuir-Blodgett (LB) films in metal-insulator-semiconductor (MIS) structure. Two types of insulating films based on hybrid organic-inorganic materials sandwiched between metal and semiconductor were fabricated. The original insulating films (untreated) were 40 layers Y-type LB films of Cd-salt stearic acid (CdSt[2]). The second type of insulating films were formed after the treatment of CdSt[2] films with H[2]S gas over a period of 12 hours at room temperature to grow CdS nanoparticles within the stearic acid matrix (treated). The capacitance-voltage (C-V) measurement of CdSt[2] LB films exhibit significant dependence on the measurement frequency in the accumulation region due to high d.c. leakage currents. By embedding CdS nanoparticles into the stearic acid matrix, less frequency dependent C-V curves were obtained. The problem in determining the true insulator capacitance due to frequency dispersion was overcome by using the Yang's model. The corresponding dielectric constant of LB films of CdSt[2] was found to be 2.3 and increased to 5.1 when embedded with CdS nanoparticles. The results from the dielectric loss measurement show that both devices agree well with Goswami and Goswami model. By incorporating CdS nanoparticles in the stearic acid matrix, the dielectric loss was found to increase which could be due to electrons being trapped by the CdS nanoparticles. A large current density was observed in the untreated devices at room temperature giving evidence of a leaky dielectric. The analysis of the temperature dependent I-V characteristics shown that current is independent of temperature, similar to the results published by several researchers which explained the current conduction mechanism in term of electron hopping and tunnelling through each bilayer of the LB films. In contrast, by embedding the CdS nanoparticles in the stearic acid matrix the currents have reduced by one-order of magnitude. The temperature dependence of the I-V characteristics showed the dependence of current on the device temperature at low electric field densities whilst less temperature dependence was observed at higher electric field density. Further investigation into the carrier transport mechanism, has found that the Poole-Frenkel effect was the dominant mechanism in the treated devices. A low frequency noise measurement setup has been designed and validated. The results of low-frequency noise measurement reported here are new. 1 / f noise was the only low-frequency noise observed in treated and untreated devices for frequencies up to 1kHz. The current noise spectral density S[I](f), was found to fit well with themodified Hooge's empirical model; [mathematical formula] where C, /, and f are noisemagnitude, current and frequency respectively. The exponential values of gamma and beta were found to lie within the acceptable ranges of 0.7 < gamma < 1.4 and 1 < beta < 3 respectively. The current noise power spectral density (PSD) at several fixed bias current was found to be dependent on the bias current with the PSDs for treated devices found to be approximately two-orders of magnitude higher. These results show that low-frequency noise measurement can be used to probe into the microstructure of the electron devices. It is believed that by embedding the CdS nanoparticles into the stearic acid matrix, electron trapping centres have been created which result in different current conduction behaviour from the untreated LB films of cadmium stearate.

The area of nanotechnology encompasses the synthesis of nanoscale materials, the understanding and the utilization of their physicochemical and optoelectronic properties, and the organization of nanoscale structures into predefined superstructures. The development of biologically inspired experimental processes for the synthesis of nanoparticles is evolving into an important branch of nanotechnology. Nanotechnology has recently emerged as an elementary division of science and technology that investigates and regulates the interaction at cell level between synthetic and biological materials with the help of nanoparticles. A wide range clean, nontoxic and eco-friendly synthesis of nanoparticles is an important aspect of current nanotechnology. Microbial synthesis of nanoparticles is a Green chemistry approach that interconnects nanotechnology and microbial biotechnology. Microorganisms play an important role in the eco-friendly synthesis of metal nanoparticles. This study illustrates the synthesis of CdS nanoparticles using the bactetia of Enterobacteriaceae ( Escherichia coli PTCC 1533 and Klebsiella pneumonia PTCC 1053) after 96 h of incubation at room temperature (30ºc) and pH 9. The morphology of the samples was analyzed using Scanning electron microscopy(SEM). The size of CdS nanoparticles in aqueous solution has been calculated using UV–Vis spectroscopy, XRD, FTIR, EDS and SEM measurements. The nanoparticles are found to be polydisperse in the size range 5–200 nm. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/34903

This dissertation contains four chapters with advances relevant to the fields of nanoparticle synthesis and nanoparticle self-assembly: a review of nanoparticle self-assembly, or “colloidal polymers”; dumbbell heterostructured nanorod synthesis; dipolar matchstick heterostructured nanorod synthesis; and self-assembly of dipolar matchsticks to form colloidal polymers. These chapters are followed by appendices containing supporting data for chapters two through four. The first chapter is a review summarizing current research involving the 1-D assembly of nanocrystals to form “colloidal polymers.” One of the major goals of materials chemistry is to synthesize hierarchical materials with precise controlled particle ordering covering all length scales of interest (termed, the “bottom up” approach). Recent advances in the synthesis of inorganic colloids have enabled the construction of complex morphologies for particles in the range of 1 – 100 nm. The next level of structural order is to control the structure of assemblies formed from these materials. Linear nanoparticle assemblies are particularly challenging to achieve due to the need to impart functionality to colloids such that (typically) only two sites are active per particle. An emerging idea in the literature which addresses this challenge is to consider linear assemblies of inorganic nanoparticles as colloidal analogs to traditional polymers. This conceptual framework has enabled the formation of linear assemblies having controlled composition (to form segmented and statistical copolymers), architecture (linear, branched, cyclic), and degree of polymerization (chain length). However, this emerging field of synthesizing colloidal polymers has not yet been reviewed in terms of methods to control fundamental polymer parameters. Therefore, linear nanoparticle assembly is reviewed in chapter 1 by applying concepts from traditional polymer science to nanoparticle assembly. The emphasis of chapter 1 is on controlling degree of polymerization, architecture, and composition for colloidal polymers, and seminal examples are highlighted which control these parameters. The second chapter is centered on a novel methodology to install ferromagnetic cobalt domains onto core@shell, “CdSe@CdS” nanorods. While the structures synthesized in this work were novel, the key advance from this work was the development of a methodology to separate nanorod activation from deposition of ferromagnetic cobalt domains onto semiconductor nanorods. As synthesized CdSe@CdS nanorods are passivated with strongly binding phosphonic acid ligands, and these ligands prevent direct deposition of many materials (such as cobalt). Synthetic methods must therefore modify nanorod surfaces prior to deposition of additional nanoparticle domains (tips). Previous synthetic methods for the deposition of magnetic domains onto nanorod termini typically combined activation of nanorod termini and metal deposition into a single synthetic step. While these previous reports were successful in achieving tipped nanorods, the coupling of these two reactions required matching the kinetics of nanorod activation and decomposition/reduction of metal precursors in order to achieve the desired heterostructure morphology. However, the presence of ligands used for nanorod activation can also affect the rate of metal precursor decomposition/reduction and the propensity of the metal to form free nanoparticles through homogeneous nucleation. Thus, simultaneous nanorod activation and metal deposition hinders modification of these syntheses to obtain differing heterostructured morphologies. In the work presented in chapter 2, we chemically activate nanorod termini towards cobalt deposition in a separate chemical step from deposition of metallic cobalt nanoparticle domains. First, reductive platinum deposition conditions were utilized to activate nanorod termini towards the deposition of cobalt domains, which were deposited in a subsequent reaction step. Then, the kinetics of nanorod activation during platinum deposition were tracked, and the platinum-tipped nanorod morphologies were correlated with the results of subsequent cobalt deposition reactions. Ultimately, controlled placement of cobalt domains onto one or both nanorod termini was demonstrated based on the degree of activation during platinum deposition. Cobalt nanoparticle tips were then selectively oxidized to form CoₓOy-tipped nanorods, which were a novel class of p-n type nanomaterials achieved over a total of five synthetic steps. Relevant supporting details for the synthesis of these dumbbell tipped nanorods are provided in Appendix A. The third chapter describes the synthesis of CoNP-tipped nanorods with a single, strongly dipolar, ferromagnetic CoNP-tip per nanorod. The key synthetic advance was the ability to activate a single terminus per nanorod without activation of lateral nanorod facets, which was vital in achieving these larger, dipolar, cobalt tips (rather than lateral decoration of cobalt onto nanorod lateral facets). These dipolar “matchstick” CoNP-tipped nanorods then spontaneously formed linear assemblies carrying nanorod side chains as pendant functionality. Activation of CdSe@CdS nanorods was found to occur through the deposition of small (< 2 nm) PtNP-tips which were not readily observable by standard characterization techniques. The finding that small (< 2 nm) PtNP-tips altered nanorod reactivity towards cobalt deposition emphasized the effect of subtle changes to nanorod surface chemistry. Relevant supporting details for the synthesis of these dipolar matchstick tipped nanorods are provided in appendix B. The fourth chapter is centered on the self-assembly of dipolar matchstick cobalt-tipped nanorods to form colloidal (co)polymers reminiscent of traditional bottlebrush polymers, with controlled composition and phase behavior on carbon surfaces. Similar to earlier findings in traditional polymer science, nanorod side chain length was found to significantly impact surface assembly of these colloidal analogs of bottlebrush copolymers, which provided a useful parameter for affecting surface wetting and phase behavior of nanoparticle thin films. This work was also the first demonstration of colloidal copolymers from the dipolar assembly of magnetic nanoparticles, where both segmented and statistical copolymer compositions were achieved. We then demonstrated, for the first time, that a colloidal copolymer with segmented composition can form a mesoscopic phase separated morphology which is similar to that observed for traditional block copolymers. This key advance opens the possibility of controlling structural ordering over still longer length scales by the development of methods to control phase separated morphologies in a manner similar to traditional block copolymers. Relevant supporting details for the synthesis and assembly of these colloidal bottlebrush polymers are provided in appendix C.