Papers by Author: Sujira Promnimit

Abstract: Hexagonal ZnO nanocrystals were synthesized through a hydrothermal route under mild conditions (growth temperature of 90°C at atmospheric pressure). Pre-synthesized ZnO nanoparticles were used to serve as nucleation sites for the growth of the nanocrystals. The growth of ZnO nanorods was found to be surface independent. The dimensions of the hexagonal ZnO nanocrystals were observed to be dependent on the concentration of the reactants used (sources of Zn2+ and OH-ions), pH of the growth bath and also on the duration of crystal growth. The average diameter and height of the ZnO nanocrystals was found to be directly proportional to the concentration of the reactants as well as hydrolysis time. The orientation of the nanocrystals was found to be dependent upon the seeding method employed. Hexagonal single crystals of a wide range of dimensions and aspect ratios could be successfully synthesized through a control of growth parameters.

Abstract: In this work, we report sensing of Zn2+ ions using chitosan capped colloidal gold nanoparticles in aqueous media. The chitosan capping not just acted as an electro-static stabilizer to the colloidal gold nanoparticles, but also could bind to Zn2+ ions if present in the solution. However, the Zn2+ ions chelation to the chitosan capping decreased the stability of the colloidal gold hence shifted the surface plasmon peak to higher wavelengths. The extent of this red shift was found to be dependent on the concentration of the Zn2+ ions and therefore the presence of Zn2+ ions could be determined both qualitatively and quantitatively by analyzing the optical spectra of the chitosan capped gold nanoparticles. The sensing capability was also affected by the size of the nanoparticles, which could be tuned by adjusting the molar ratio of the reducing agent and the gold salt to the desired levels. Optical characteristics showed satisfactory results in estimating the amount of Zn2+ ions in water. This is thus a promising method for on the spot assessment of heavy metal ion concentrations in water.

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.