Graduation Year

2012

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Physics

Major Professor

Pritish Mukherjee

Co-Major Professor

Sarath Witanachchi

Keywords

calcium cobalt oxide, microwave, nanoparticle, spray pyrolysis, thermoelectric, zinc oxide

Abstract

Nanoparticle and nanoparticulate films have been grown by a unique approach combining a microwave and nebulized droplets where the concentration and thus the resulting particle size can be controlled. The goal of such a scalable approach was to achieve it with the least number of steps, and without using expensive high purity chemicals or the precautions necessary to work with such chemicals. This approach was developed as a result of first using a laser unsuccessfully to achieve the desired films and particles. Some problems with the laser approach for growing desired films were solved by substituting the higher energy microwave for the laser. Additionally, several materials were first attempted to be grown with the laser and the microwave, and what was learned as result of failures was implemented to successfully demonstrate the technique.

The microwave system was characterized by using direct temperature measurements and models. Where possible, the temperature of deposition was determined using thermocouples. In the region of the waveguide, the elemental spectral lines were measured, and the temperature was calculated from measured spectral peaks. From the determined temperature, a diffusion calculation modeled the rate of heat transfer to the nebulized droplets. The result of the diffusion calculations explained the reason for the failure of the laser technique, and success for the microwave technique for simple chemistries.

The microwave assisted spray pyrolysis (MPAS) technique was used to grow ZnO nanoparticles of varying size. The properties of the different size particles was measured by optical spectroscopy and magnetic measurements and was correlated to the defects created.

The MPAS technique was used to grow films of Ca3Co4O9 containing varying sizes of nanoparticulates. The resistivity, Seebeck coefficient, and the power factor (PF) measured in the temperature range of 300-700 K for films grown by MPAS process with varying concentrations of calcium and cobalt chlorides are presented. Films with larger nanoparticles showed a trend toward higher PFs than those with smaller nanoparticles. Films with PFs as high as 220 μW/mK 2 were observed in films containing larger nanoparticles.

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