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Title: Development of High Aspect Ratio Nano-Focusing Si and Diamond Refractive X-ray optics using deep reactive ion etching
Author: Malik, Adnan Muhammad
ISNI:       0000 0004 2747 0280
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2013
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This thesis is devoted to the development of nano-focusing refractive optics for high energy X-rays using planar microelectronic technology. The availability of such optics is the key for the exploitation of high brilliance third and fourth generation X-ray sources. Advancements in the quality of optics available are commensurate with advancements in the fabrication technology. The fabrication process directly influences the quality and performance, so must be understood and controlled. In the first part of this thesis, the development of high aspect ratio Si kinoform lenses is examined. It is shown that control of the re-entrance angle is critical for successful fabrication; in fact, a large re-entrance angle can destroy the lens during the fabrication process. Through an etch study, it was found that as aspect ratio increases, control of the re-entrance angle becomes harder. To control the re-entrance angle for very high aspect ratios, a novel approach based on sacrificial structures was proposed and initial results presented. The second part is dedicated to an experimental study of refractive lenses made from diamond. Due to its low atomic number, relatively high density and very high thermal conductivity, diamond is one of the most desirable lens materials for refractive X-ray optics. However, due to its extreme hardness, it is very difficult to structure into a form suitable for X-ray lenses. To overcome this difficulty a Si moulding technique was used and focusing down to a 400 nm wide spot was achieved. Several obstacles were encountered and successfully overcome. The hardest obstacle was to obtain selective void-free filling in the Si moulds. Several methods were investigated. A method based on a sacrificial oxide layer and an Electrostatic Self-Assembly process was found to be the most useful. The approach discovered in this thesis is not limited to X-ray lenses, but can be applied to a wide variety of high aspect ratio MEMS requiring void-free diamond filling and smooth sidewalls.
Supervisor: Korsunsky, Alexander; Alianelli, Lucia; Chen, Yifang Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Nanomaterials ; Processing of advanced materials ; Silicon ; Materials engineering ; X-ray lens ; Nano-focusing ; CVD diamond ; Deep Reactive Ion Etching