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    Synthesis and Characterization of Chemically Etched Nanostructured Silicon

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    Type
    Thesis
    Authors
    Mughal, Asad Jahangir
    Advisors
    Chaieb, Saharoui cc
    Committee members
    Bakr, Osman cc
    Ooi, Boon S. cc
    Program
    Mechanical Engineering
    KAUST Department
    Physical Science and Engineering (PSE) Division
    Date
    2012-05
    Embargo End Date
    2013-05-30
    Permanent link to this record
    http://hdl.handle.net/10754/222131
    
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    Access Restrictions
    At the time of archiving, the student author of this thesis opted to temporarily restrict access to it. The full text of this thesis became available to the public after the expiration of the embargo on 2013-05-30.
    Abstract
    Silicon is an essential element in today’s modern world. Nanostructured Si is a more recently studied variant, which has currently garnered much attention. When its spatial dimensions are confined below a certain limit, its optical properties change dramatically. It transforms from an indirect bandgap material that does not absorb or emit light efficiently into one which can emit visible light at room temperatures. Although much work has been conducted in understanding the properties of nanostructured Si, in particular porous Si surfaces, a clear understanding of the origin of photoluminescence has not yet been produced. Typical synthesis approaches used to produce nanostructured Si, in particular porous Si and nanocrystalline Si have involved complex preparations used at high temperatures, pressures, or currents. The purpose of this thesis is to develop an easier synthesis approach to produce nanostructured Si as well as arrive at a clearer understanding of the origin of photoluminescence in these systems. We used a simple chemical etching technique followed by sonication to produce nanostructured Si suspensions. The etching process involved producing pores on the surface of a Si substrate in a solution containing hydrofluoric acid and an oxidant. Nanocrystalline Si as well as nanoscale amorphous porous Si suspensions were successfully synthesized using this process. We probed into the phase, composition, and origin of photoluminescence in these materials, through the use of several characterization techniques. TEM and SEM were used to determine morphology and phase. FT-IR and XPS were employed to study chemical compositions, and steady state and time resolved optical spectroscopy techniques were applied to resolve their photoluminescent properties. Our work has revealed that the type of oxidant utilized during etching had a significant impact on the final product. When using nitric acid as the oxidant, we formed nanocrystalline Si suspensions composed of particles with a crystal structure different than the common polymorph of Si. These particles emitted UV to blue wavelengths. Iron(III) chloride was also employed as an oxidant, and it created amorphous Si nanostructures from a bulk crystalline Si source. These suspensions showed ultra-bright visible photoluminescence, which could be tuned through engineering the surface.
    Citation
    Mughal, A. J. (2012). Synthesis and Characterization of Chemically Etched Nanostructured Silicon. KAUST Research Repository. https://doi.org/10.25781/KAUST-FB33Z
    DOI
    10.25781/KAUST-FB33Z
    ae974a485f413a2113503eed53cd6c53
    10.25781/KAUST-FB33Z
    Scopus Count
    Collections
    MS Theses; Physical Science and Engineering (PSE) Division; Mechanical Engineering Program

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