- Title
- A prototype permanent magnet solenoidal ioniser for the Newcastle scanning helium microscope
- Creator
- Martens, Joel
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2020
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The nascent field of scanning helium microscopy has seen increasingly rapid development in recent years. The technique utilises a beam of neutral, thermal energy helium atoms, forming an image based on variations in the reflected partial pressure as the sample surface is rastered through the beam. The low energy (5 – 100 meV) helium atoms are an ideal surface probe due to being completely inert, strictly surface sensitive and possessing a de Broglie wavelength of the order Ångstroms. While the properties of neutral helium are advantageous as a probe particle, the high ionisation energy presents a challenge for detection at the levels required in the microscope application. The difficulty of focusing a neutral helium beam has meant that the majority of the prototype helium microscopes employ a simple pinhole aperture to define the probe beam, sacrificing a large amount of the flux. As a result of the focusing method and the low sensitivity of available helium detectors, the signal levels achievable in the current generation of helium microscopes is the limiting factor preventing progress towards higher resolutions and faster imaging times. A class of electron ionisers, known as solenoidal ionisers, has been developed in the last decade for the well-established field of helium atom scattering. These ionisers demonstrate drastically increased sensitivities to helium (of the order of 1 A/mbar) in comparison with existing practice. Solenoidal ionisers use large electromagnetic solenoids to contain a long, dense population of electrons coaxial to the helium beam. While the sensitivities achieved far surpass previous electron ionisation techniques, the large solenoids require complex precision manufacturing to produce, including integrated cooling systems to manage the heat generated by the high currents applied (tens to hundreds of Amps). The research presented in this thesis describes the design, modelling and ultimate realisation of a desktop scale solenoidal ioniser that replaces the electromagnetic solenoid with a rare-earth permanent magnet assembly. The use of a permanent magnet greatly reduces the complexity of the required manufacturing as well as eliminating the power consumption and cooling requirements. The prototype ioniser has demonstrated a sensitivity to helium comparable to its larger electromagnetic counterparts as well as a rapid temporal response, making it an ideal candidate for implementation as a scanning helium microscope detector.
- Subject
- helium; microscope; solenoidal; ioniser; permanent magnet
- Identifier
- http://hdl.handle.net/1959.13/1422721
- Identifier
- uon:37871
- Rights
- Copyright 2020 Joel Martens
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 10 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 511 KB | Adobe Acrobat PDF | View Details Download |