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dc.contributorDepartment of Applied Physicsen_US
dc.contributor.advisorLau, S. P. (AP)en_US
dc.creatorKam, Tsz Yau-
dc.identifier.urihttps://theses.lib.polyu.edu.hk/handle/200/11733-
dc.languageEnglishen_US
dc.publisherHong Kong Polytechnic Universityen_US
dc.rightsAll rights reserveden_US
dc.titleSynthesis and characterization of ultrathin black phosphorusen_US
dcterms.abstractTwo-dimensional materials attract much attention from material scientists due to their unique physical and optical properties. Graphene and transition metal dichalcogenides are examples of widely studied 2D materials. Black Phosphorus (BP), namely phosphorene, is an emerging candidate in this field. It has a thickness-dependent energy bandgap ranging from 0.3 eV to 2.0 eV in bulk to monolayer and high carrier mobility, making it an excellent choice for optoelectronics applications. Furthermore, the unique A17 orthorhombic crystal structure of BP with weak interlayer van der Waals force also provides the anisotropic behaviour in BP along with the zigzag (ZZ) and armchair (AC) directions. This anisotropy makes it a great thermoelectric and piezoelectric candidate. In this study, BP crystals were synthesized by the chemical vapour transportation method. Red phosphorus, tin, and iodine were used as precursors and heated in a vacuum-sealed quartz tube to produce BP. It was then mechanically exfoliated for characterization. Small Raman shift in bulk and exfoliated BP was observed, and anisotropy polarised Raman was measured. Single crystal quality and high purity of BP were confirmed by selected area electron diffraction and energy dispersive x-ray in the transmission electron microscope observation.en_US
dcterms.abstractMolecular beam epitaxy BP synthesis was attempted by using GaP source and mica substrate with a fast cooling after growth. Raman spectroscopy, atomic force microscopy, and x-ray diffraction characterized the large area thin film uniformity and crystalline structure.en_US
dcterms.abstractThe strain-induced electrical conductance of BP in ZZ and AC orientations was also investigated. Conductance (G) of 4.43μS and 1.01 μS were observed in the AC and ZZ directions, with a ratio Gac/Gzz of 4.4 without strain. Conductance along ZZ and AC were also measured with applied 0 -1.4% uniaxial strain in either ZZ or AC direction. In most cases, the conductance drops exponentially to about 20% of the original value at 1.4% strain except the conductance of ZZ orientation when applying strain in the same direction, which is half of its original. Results suggested that the unique conductance behaviour in ZZ direction with uniaxial ZZ strain could be attributed to the spatial preference transition of electrical conductance in BP.en_US
dcterms.extentxii, 87 pages : color illustrationsen_US
dcterms.isPartOfPolyU Electronic Thesesen_US
dcterms.issued2022en_US
dcterms.educationalLevelM.Phil.en_US
dcterms.educationalLevelAll Masteren_US
dcterms.LCSHTwo-dimensional materialsen_US
dcterms.LCSHPhosphorusen_US
dcterms.LCSHHong Kong Polytechnic University -- Dissertationsen_US
dcterms.accessRightsopen accessen_US

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Please use this identifier to cite or link to this item: https://theses.lib.polyu.edu.hk/handle/200/11733