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Surface Structure of Single-Crystal Hexagonal Ice

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Surface Structure of Single-Crystal Hexagonal Ice Surface Structure of Single-Crystal Hexagonal Ice A senior honors thesis for the Department of Chemistry Alexandra Brumberg Tufts University, 2016 1 ii TABLE OF CONTENTS Table of Figures........................................................................................................................................... v 1 Introduction ......................................................................................................................................... 1 2 Theory .................................................................................................................................................. 3 2.1 Properties of Ice ............................................................................................................................ 3 2.1.1 Structure of Hexagonal Ice ................................................................................................... 3 2.1.2 Thermodynamic Growth ....................................................................................................... 5 2.1.3 Wulff Construction ............................................................................................................... 5 2.2 D2O Ice .......................................................................................................................................... 6 2.3 Differential Interference Contrast Microscopy ............................................................................. 7 2.3.1 Nomarski Prism..................................................................................................................... 8 3 Experimental ....................................................................................................................................... 9 3.1 Single-Crystal Growth Procedure ................................................................................................. 9 3.1.1 Modified Bridgman Apparatus ............................................................................................. 9 3.1.2 Crucible Design................................................................................................................... 10 3.1.3 Purification and Preparation ................................................................................................ 11 3.1.4 Growth Termination ............................................................................................................ 12 3.1.5 Computer Controls .............................................................................................................. 12 3.1.6 Adjusting the Shelf Temperature ........................................................................................ 13 3.1.7 Probe Analysis .................................................................................................................... 13 3.2 Crystal Characterization .............................................................................................................. 14 3.2.1 Rigsby Stage ....................................................................................................................... 15 3.2.2 Saw Fixture ......................................................................................................................... 15 3.2.3 Microtoming ....................................................................................................................... 17 3.2.4 Formvar Etching ................................................................................................................. 17 3.2.5 Full Procedure ..................................................................................................................... 18 4 Results ................................................................................................................................................ 20 4.1 Face Stability at the Ice-Water Interface ..................................................................................... 20 4.1.1 Face Stability ...................................................................................................................... 20 4.1.2 Boule Orientation ................................................................................................................ 23 4.2 Producing Desired Ice Faces ....................................................................................................... 23 4.2.1 Identifying the c-Axis ......................................................................................................... 23 4.2.2 Determination of 휽 and 휶 ................................................................................................... 24 4.2.3 Selected Face Rotation Angles ........................................................................................... 25 iii 4.3 Atypical Etch Pits ....................................................................................................................... 25 4.3.1 High Index Faces ................................................................................................................ 25 4.3.2 Basal Face Irregularities ...................................................................................................... 27 4.4 D2O Ice Growth .......................................................................................................................... 28 4.4.1 Procedural Modifications .................................................................................................... 28 4.4.2 Probe Analysis .................................................................................................................... 28 4.4.3 D2O Etching ........................................................................................................................ 31 4.5 Contrast Microscopy ................................................................................................................... 32 4.5.1 Step Edges on the Prism Faces ........................................................................................... 33 4.5.2 Construction of the Microscope .......................................................................................... 34 5 Conclusion ......................................................................................................................................... 36 6 Acknowledgements ........................................................................................................................... 36 7 References .......................................................................................................................................... 37 iv TABLE OF FIGURES Figure 1. The hexagonal structure of ice Ih. (a) Location of the three a-axes and the c-axis. ...................... 3 Figure 2. Molecular representation of the three main faces of ice Ih. The atoms and bonds highlighted in red are those that are at the surface. (a) is the basal face, while (b) and (c) are typically represented as the primary prism and secondary prism faces, respectively. (Images taken from Ref. 17). ............................... 4 Figure 3. Separation of ordinary and extraordinary components of a beam passing through a Wollaston prism. (Image taken from Ref. 34.) ............................................................................................................... 8 Figure 4. Separation of ordinary and extraordinary components of a beam passing through a Nomarski prism. (Image taken from Ref. 34.) ............................................................................................................... 8 Figure 5. A cut-away of the modified Bridgman apparatus. The crucible progresses downward through the machine; growth occurs at the shelf. (Image taken from Ref. 11.) ............................................................... 9 Figure 6. Crucible shape. ........................................................................................................................... 10 Figure 7. Vacuum line used for degassing. ................................................................................................ 11 Figure 8. The c-axis tilt 휃 and a-axis roll 훼. .............................................................................................. 14 Figure 9. A demonstration of how multiple domains can easily be spotted within the crossed polarizers. Each shaded area corresponds to a separate domain; this boule does not have a particular dominant domain. .................................................................................................................................................................... 15 Figure 10. Extinction events that occur with the c-axis oriented (a) vertically and (b) horizontally. ........ 15 Figure 11. Laboratory axes X, Y, and Z, as related to the saw fixture and sample mount. ....................... 16 Figure 12. The rotation mount along (a) X and (b) Z. ............................................................................... 16 Figure 13. Example of the excessive striations present on an ice surface after microtoming with an old razor blade. .................................................................................................................................................. 17 Figure 14. Visualization of how the hexagonal structure of ice gives way to etch pit shape. Etch pits can be simulated by embedding a hexagonal prism in the surface and then removing it to leave behind a negative imprint. .......................................................................................................................................................
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