My research focused on the growth and characterisation of topological insulators in both bulk crystal and nano forms. The growth methods used were a modified Bridgman technique for the bulk crystals, whilst the nano materials were grown using a chemical vapour deposition technique. For characterisation the following techniques were employed:
- Scanning electron microscopy
- Transmission electron microscopy
- Energy dispersive x-ray analysis
- Atomic force microscopy
- X-ray photoelectron spectroscopy
- X-ray Laue diffraction
- Powder x-ray diffraction
- SQUID magnetometry
- Muon spectroscopy
Thesis: Topological Insulators: A Study of Bulk Crystalline and Nanomaterials
A new class of materials, TIs and TCIs, have been shown to exhibit ex-otic surface state properties that are protected by mirror or time-reversal symmetry. It is expected that the surface states will be easier to detect if the SAVR of the material increases. We report the experimental procedures to obtain high quality crystal boules of the TCI, Sn1-xInxTe, for 0 < x < 0. 45, from which nanowires and microcrystals can be produced by the VLS growth technique. Detailed characterisation measurements of the bulk crystals, the superconducting properties as well as characterisation of the nanowires and microcrystals produced are presented. We also present optimised growth procedures to obtain high quality bulk crystals of the TCIs Pb1-xSnxTe and Pb1-xSnxSe, and nanowires from the bulk crystals, also using a VLS growth mechanism. Nanowires of Pb1-xSnxTe have been produced with a Sn composition of x = 0.25, at which a transition from trivial to non-trivial insulator is reported. The results obtained on the growth of nanomaterials of Pb1-xSnxSe are also described. Detailed characterisation of the bulk crystals and the nano materials through x-ray diraction, microscopy techniques and EDX analysis are presented. Sb2Te3 is also a topological insulator which, under certain con ditions, becomes superconducting. The growth methods and characterisation of Sb2Te3 crystal boules are discussed. The methods used to convert bulk samples of Sb2Te3 into nanomaterials and 2D layers on graphene are also presented. Investigating nanometer and micron sized materials thought to exhibit topological surface properties can present a challenge, as clean surfaces are a pre-requisite for band structure measurements when using nano-ARPES or laser-ARPES in UHV. We present the ndings of an XPS study where various cleaning methods have been employed to reduce the surface contamination and preserve the surface quality for surface sensitive measurements. Microcrystals of SnTe were treated with atomic hydrogen, argon sputtering, annealing, as well as a combination of treatments. The samples were characterised using SEM, both before and afte treatment. It was found that atomic hydrogen cleaning with an anneal cycle (200 C) gave the best clean surface results.
Topological Insulators: A Study of Bulk Crystalline and Nanomaterials (PDF of Thesis, 130 MB).
I completed my bachelors in physics at the University of Liverpool followed by a Postgraduate Certificate in Educational Studies at the University of Birmingham. I then went on to complete my masters at the University of Warwick. During my time at Liverpool, I was co-managing director of Havaa Laugh Ltd where we specialised in event management and advertising.
At Warwick during my MSc, I carried out research in the fabrication and characterisation of graphene in the surface science group under the supervision of Dr. Gavin Bell and Dr. Neil Wilson. Graphene was grown using ultra-high vacuum and chemical vapour deposition techniques. After my MSc, I spent a year in the Netherlands, at the University of Leiden working in the condensed matter physics group focusing on atomic and molecular conductors.
In Oct 2012 I joined the Superconductivity and Magnetism group under the supervision of Prof. Geetha Balakrishnan and Dr. Neil Wilson for my PhD, where my research focuses on the growth and characterisation of Topological Insulators. My Phd was sucessfully completed in July 2016.
Further information on my MSc project and my PhD work can be found on my webpage by clicking the following link: www.mohammedsaghir.co.uk