A surge in the developments in nanoscience in recent years has opened the door to new possibilities in the field of semiconductors, in particular the fabrication of high quality semiconductor nanocrystals. These materials are important to the semiconductor photovoltaics and photo induced water splitting devices. The aim of this thesis is to advance understanding regarding the band edge energy level (Eedge) alignment of as-fabricated nanoscale semiconductors (such as quantum dots, QDs) through 'hot injection' methodologies, as well as investigation of the chemical reaction mechanisms behind this synthetic approach. Eedge evolution of binary and ternary cadmium chalcogenide QDs were studied electrochemically, employing an ultramicroelectrode. It was found that, with change in particle size or composition, variations in the band gap were mainly attributed to changes in the conduction Eedge; a non-linear conduction Eedge bowing phenomenon also revealed when tuning the composition of alloyed QDs. A radical reaction during the phosphine-free QDs synthetic approach was detected through NMR, FTIR. and mass spectroscopy, which further led to studies of the chemical reaction mechanism of formation of quaternary CuZnSnS(Se4) (CZTS, CZTSe) and binary iron chalcogenide nanocrystals. By employing a modified electrode approach, Eedge of as-prepared quaternary CZTS(Se) and binary ion chalcogenide nanocrystals were also determined. It was discovered that the conductivity of CZTSe is three orders of magnitude higher than the CZTS nanocrystals; the detection of metallic copper (formed in the precursor preparation step) and different oxidative power of S and Se species, are found to be the reasons behind the- difference in charge transport ability. The scientific contributions reported in this thesis add precious value to the picture of energy level distribution of semiconductors, and the chemical mechanism study provides guidance for scale up production and new material synthesis, which are crucial factors in the fabrication of electrochemical semiconductor devices.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:619262 |
| Date | January 2013 |
| Creators | Hou, Bo |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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