Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Physics

Supervisor

Prof. Giovanni Fanchini

Abstract

Deposition techniques for the fabrication of metal nanostructures influence their morphological properties, which in turn control their optical behavior. Here, copper nanoparticles (np-Cu’s) were grown using a deposition system that was specifically set up during this work, and is based on a radio frequency (RF) sputtering source that can operate at high temperature and under bias voltage. The effect of deposition conditions (RF power, chamber pressure and substrate bias voltage) on RF sputtered np-Cu’s using RF sputtering has been studied. The study included a comparison between the morphological and optical properties of as-grown np-Cu’s and thermally treated samples. The characterization of np-Cu’s is carried out by atomic force microscopy, UV-visible transmission spectrophotometry, scanning electron microscopy and scanning near field optical microscopy (SNOM) techniques. The results of the experiment showed that the combined effects of low RF power (25 W – 75 W), high chamber pressure (17 Pa – 23 Pa) and substrate DC bias voltage (300 V – 400 V) are required for obtaining dispersed np-Cu’s. Under these conditions, copper nanoparticles grow by aggregation of initial island nuclei due to a reduction in sputtering rate. Significantly, higher dispersed np-Cu’s are obtained when a set of samples grown at 25 W and 33 W RF power is subjected to thermal treatment in an oxygen-free glove box. Optical properties of np-Cu’s show improvement in the visible region (535nm – 580 nm) related to transmission enhancement in as-deposited samples and plasmonic enhancement in thermally treated ones. Furthermore, an approach to determine the position of the np-Cu induced scattered wave was explored using SNOM (x, z) measurements. In bare np-Cu’s the path length of the scattered wave is further from the np surface, measured orthogonally. We demonstrated experimentally a method that uses an SiO2 thin film as a spacer to broaden the scattered wave up to 500 nm from the np-Cu/SiO2 composite surface. The study provides an improved insight that helps to understand the physical mechanisms that may hinder the expected performance in plasmonic solar cells. With these results, the potential of incorporating np-Cu’s in plasmonic thin film solar cell structures looks very promising.


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