Dunnill, Charles W. H. (2008) Synthesis, characterisation and properties of tantalum based inorganic nanofibres. PhD thesis. http://theses.gla.ac.uk/173/ Copyright and moral rights for this thesis are retained by the author A copy can be downloaded for personal non-commercial research or study, without prior permission or charge This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the Author The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the Author When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given Glasgow Theses Service http://theses.gla.ac.uk/ [email protected] SYNTHESIS, CHARACTERISATION AND PROPERTIES OF TANTALUM BASED INORGANIC NANOFIBRES A thesis submitted to the University of Glasgow for the degree of Doctor of Philosophy By Charles W. H. Dunnill MSci School of Chemistry University of Glasgow December 2007 © Charles W. H. Dunnill. December 2007 Abstract This thesis describes the synthesis and characterisation of 1-dimensional nanometric phases using simple preparative reactions and a variety of characterisation methods. Comparison of properties between the bulk and nanomorphology has played a large part and is a common theme throughout. High aspect ratio tantalum disulfide, TaS 2 nanofibres were prepared from a 1:2 stoichiometric mixture of elemental powders in a one-step synthesis utilising silica ampoules. A surface assisted growth phenomena was investigated and found to significantly increase the yield, both in quality and quantity. The resulting nanofibres were seen to retain and indeed enhance some of the bulk properties, e.g. a 50 fold increase in observed superconducting transition temperature. Changing the stoichiometry of the reactants to 1:3, produced tantalum trisulfide nanofibres. Tantalum trisulfide is of interest as it has pseudo 1-dimensional crystal structure and properties in the bulk. TEM and SAED have shown that the TaS 3 unit cell is oriented with the b direction parallel to the long axis of the nanofibres, indicating the potential for the transfer of the low dimensional properties of the bulk material into the nanophase morphology. (Low dimensional properties of bulk TaS3 result from chains of tantalum atoms propagating along the b direction of the unit cell). Although the structure of the TaS 3 remains illusive the preliminary investigations show these nanofibres to be metallic along their lengths, potentially leading to many applications in nanoscale electrical devices. The concept of pseudomorphic change from the disulfide nanomaterials into more functional materials such as Ta 3N5 and Ta 2O5 was investigated. Nanofibres were initially formed and can reversibly be inter-converted between the three different nanometric phases (TaS 2, Ta 3N5 and Ta 2O5) using simple solid-gas reaction, without significant loss of nanofibrous morphology. Further this series of reactions shows potential for the formation of i other related and potentially applicable nanometric phases such as TaN, TaO 2 and TaON as well as opening the door to countless other analogous systems. ii Quotes “These nanotubes are so amazing that they may be useful to everybody” Nobel laureate R. Smalley Nanotechnology “will bring revolutionary changes to all branches of industry, beginning with the production of antibiotics and ending with new weapons” E. Drexler "Nanotechnology is the base technology of an industrial revolution in the 21st century. Those who control nanotechnology will lead the industry" Michiharu Nakamura, Executive VP at Hitachi iii Acknowledgements Many people have been instrumental in the facilitation of the project. Firstly I’d like to thank Professor Duncan Gregory whose supervision has kept me on track throughout the project. Secondly I’d like to thank all the past and present lab members from both institutions; Nottingham and Glasgow, who have been there for support and made my time in the lab memorable. I would like to thank all the technical support, again from both institutions, be it workshop staff or technicians who have helped me find build or repair equipment. I would also like to thank: Hannah Edwards and Paul Brown from the University of Nottingham and Ian MacLaren from the University of Glasgow, who have helped out with the TEM, as well as Nikki Weston from the University of Nottingham who has helped out with SEM and Jim Gallagher from the University of Glasgow who has been there for support with the primary SEM used in the project. A nanofibre based project like this is nothing without the ability to image the structures, so TEM and SEM have played an important role in the characterisation of some of the nanofibrous materials discussed. Philip Moriarty and Andrew Stannard from the University of Nottingham are also thanked for their time in the attempts to gain understanding of the electrical behaviour of the nanowires. iv Contents Abstract……………………………………………………………………………...…..….i Quotes…………………………………………………………………………………........iii Acknowledgements………………………………………….………………………...……iv Contents………………………………………………………………………………......…v Glossary of Abbreviations……………………………………………………………..……ix List of Tables…………………………….………………………………………..….……..x List of Figures…………………………………………………………………………….…xii Chapter 1: General Introduction and Theory ......................................................................... 1 1.1 Introduction............................................................................................................ 1 1.1.1 Current Uses of Nanotechnology .................................................................... 3 1.1.2 Inorganic Compounds Known to Form Nanofibres ......................................... 6 1.1.3 Conventional Definitions for Inorganic Nanofibres......................................... 7 1.2 Basic Crystallography............................................................................................. 7 1.2.1 Unit Cells, Crystal Systems and the Bravais Lattice ........................................ 7 1.2.2 Point Groups................................................................................................... 9 1.2.3 Space Groups.................................................................................................. 9 1.2.4 Miller Indices ............................................................................................... 10 1.2.5 Bragg’s Law................................................................................................. 12 1.3 Charge-Density-Waves......................................................................................... 13 1.3.1 Formation of Charge-Density-Waves............................................................ 14 1.3.2 Conduction in Charge-Density-Wave Systems.............................................. 15 1.3.3 Measurable Properties of Charge-Density-Wave Systems ............................. 16 1.4 Magnetic Materials............................................................................................... 16 1.4.1 Types of Magnetic Material.......................................................................... 20 1.4.2 Paramagnetic Materials................................................................................. 20 1.4.3 Ferromagnetic Materials............................................................................... 22 1.4.4 Superconducting Materials............................................................................ 23 1.5 MX 2 Compounds (Bulk)....................................................................................... 25 1.5.1 Tantalum Disulfide....................................................................................... 26 1.5.2 Properties of TaS 2 ......................................................................................... 27 1.6 MX 3 Compounds.................................................................................................. 30 1.6.1 Tantalum Trisulfide ...................................................................................... 30 1.7 Oxides.................................................................................................................. 32 1.8 Tantalum Oxide.................................................................................................... 32 1.9 Nitrides ................................................................................................................ 33 1.10 Tantalum Nitride .................................................................................................. 33 1.11 Inorganic Nanofibre Research............................................................................... 34 1.11.1 MX 2 Compounds Nanofibres ........................................................................ 35 1.11.1.1 Tungsten Disulfide Nanofibres................................................................. 36 1.11.1.2 Molybdenum Disulfide Nanofibres .......................................................... 36 1.11.1.3 Niobium Disulfide Nanofibres ................................................................. 37 1.11.1.4 Tantalum Disulfide Nanofibres ................................................................ 38 1.11.1.5 Niobium Diselenide Nanofibres ............................................................... 39 1.11.1.6 Molibdenum Diselenide and Tungsten Diselenide Nanofibres.................. 40 1.11.1.7 Other Disulfide Nanofibres