- Title
- Imaging with atoms: aspects of scanning helium microscopy
- Creator
- Barr, Matthew Gordon
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2016
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Microscopy is an essential tool for the discovery, application and fabrication of new materials, structures and devices. However, there exists a range of systems that are traditionally challenging to image, such as transparent, weakly-bonded, insulating, very rough and magnetic samples. Furthermore, many of these systems (such as organic thin films, biological specimens and delicate adsorbate structures) suffer degradation under the energetic photons, electrons or ions of conventional microscopies. Neutral helium is the ideal probe of such surfaces, owing to its low mass, lack of net charge or spin, and short de Broglie wavelength. Moreover, the low kinetic energy of thermal helium atoms (of the order meV) means that these probe particles are unambiguously surface sensitive, scattering from the outermost electron corrugation of the sample. The advantages of helium atoms as a surface probe have already been demonstrated in the established technique of Helium Atom Scattering (HAS). Nevertheless, HAS is limited by its lack of spatial resolution, hence limiting its application to relatively simple, heterogeneous systems. The work presented in this thesis describes the realisation of a fundamentally new imaging technique based on HAS. This instrument, in which a fine beam of helium is rastered over a sample, operates in a similar configuration to a scanning electron microscope and hence is referred to as a Scanning Helium Microscope or SHeM. Chapter 1 examines the motivations for constructing a SHeM, and then provides an assessment of the technologies required to demonstrate proof of concept of the technique. In Chapter 2, an appropriate measure of image contrast is provided, alongside a detailed discussion of the potential mechanisms by which SHeM image contrast could be generated. Thereafter, a semi-empirical gas flow model of SHeM performance is outlined, providing an avenue towards the construction of a practicable instrument. Chapter 3 commences with a comprehensive description of the design, construction and characterisation of the first-generation SHeM. This prototype instrument was then used to image a range of systems, demonstrating contrast that arises predominantly from the surface topology of the sample. To address the primary weaknesses of the prototype instrument, a second-generation SHeM was then constructed, with an aim towards the observation of weaker, more exotic contrast mechanisms. The design, construction and characterisation of the second instrument is outlined in Chapter 4, whilst the subsequent contrast investigations are detailed in Chapter 5. Indeed, the work reported in Chapter 5 constitutes the first demonstration of contrast arising from the elemental composition of the sample under investigation by SHeM. Furthermore, this chemical contrast is shown to be inelastic in nature and apparent under the oxide or physisorbed layers present in ex situ prepared samples. Chapter 6 then comprises a discussion of the design pathways to the realisation of an improved, third-generation SHeM. These discussions are accompanied by a number of pilot studies and simulations, which show that a higher resolution, next-generation SHeM is readily achievable using current technology. Finally, Chapter 7 concludes with an outlook for the future development and application of scanning helium microscopy.
- Subject
- scanning helium microscope; SHeM; helium atom scattering; HAS; neutral atom microscope
- Identifier
- http://hdl.handle.net/1959.13/1312654
- Identifier
- uon:22446
- Rights
- Copyright 2016 Matthew Gordon Barr
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Abstract | 400 KB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Thesis | 12 MB | Adobe Acrobat PDF | View Details Download |