Electron-electron Interactions and Optical Properties of Two-dimensional Nanocrystals Description Title: Electron-electron Interactions and Optical Properties of Two-dimensional Nanocrystals Authors: Szulakowska, Ludmila Date: Abstract: This thesis presents a theory of electron-electron interaction effects and optical properties of nanostructures of two-dimensional 2D honeycomb crystals - graphene and transition metal dichalcogenides TMDC. Graphene, a semimetallic hexagonal lattice of carbon atoms can be described by a massless Dirac fermion model, with the conduction band CB and valence band VB touching in the corners of a hexagonal Brillouin zone, valleys K and -K. TMDC crystals sites host either a transition metal atom or a chalcogen dimer, which opens the energy gap and allows for describing their low-energy nature with massive Dirac fermion mDf model. For TMDCs it is possible to excite carriers in each valley with oppositely circularly polarised light, which offers promising prospects for devices based on electrons valley index, i. The dimensionality of 2D crystals can be further reduced to form quantum dots QDs - nanostructures con ned in all dimensions. This thesis first discusses hexagonal graphene QDs, which exhibit energy gap oscillation as a function of size, due to the edge type: zigzag or armchair.
Synthesis and doping modification of ultrathin WSe2/WS2 heterostructure
Excitonic Structure in Atomically-Thin Transition Metal Dichalcogenides | Academic Commons
Dominik Kufer. Monday, June 13, ICFO Auditorium In the last decade, two-dimensional 2D materials have attracted attention both in the nascent field of flexible nanotechnology as well as in more conventional semiconductor technol-ogies. Within the rapidly expanding portfolio of 2D materials, the group of semiconducting transition metal dichalcogenides TMDCs has emerged as an intriguing candidate for various optoelectronic applications.
Two-dimensional 2D transition metal dichalcogenides TMDCs have been considered as promising candidates for next generation nanoelectronics. On the other hand, the crystalline structures of TMDCs are enriched by a variety of intrinsic defects, including vacancies, adatoms, grain boundaries, and substitutional impurities. Customized design and engineering of the interfaces and defects provides an effective way to modulate the properties of TMDCs and finally enhance the device performance. Herein, we summarize and highlight recent advances and state-of-the-art investigations on the interface and defect engineering of TMDCs and their corresponding applications in electronic and optoelectronic devices. Subsequently, different types of structural defects in TMDCs are introduced.
Covalent organic frameworks COFs are porous crystalline extended structures comprised of molecular building blocks and stitched together through directional covalent bonds. This allows for the design and construction of 2D and 3D framework structures with atomic precision. In his dissertation, Christian Diercks has devised protocols for pre- and post synthetic functionalization of such frameworks to tailor them for electronic applications as electrocatalysts, heterojunctions, and solid state conductors. In particular, he has funcitonalized layered 2D COFs with cobalt porphyrin active sites for the electrocatalytic reduction of carbon dioxide into value-added carbon products. To optimize the performance of these catalysts he investigated structural parameters pore size and number of active sites , electronic parameters framework conductivity, overpotential , as well as the influence of the morphology of the catalyst.