BEGIN:VCALENDAR VERSION:2.0 PRODID:-//132.216.98.100//NONSGML kigkonsult.se iCalcreator 2.20.4// BEGIN:VEVENT UID:20260611T103336EDT-6860eDXN8V@132.216.98.100 DTSTAMP:20260611T143336Z DESCRIPTION:Abstract\n\nThis thesis presents contributions to the understan ding of the fundamental properties of van der Waals materials\, motivated by the long-term goal of developing methods to tune and control the physic al properties of van der Waals materials. In the first part of this thesis \, a method to alkali dope graphene on-chip in an inert glovebox environme nt is presented\, enabling an electron density of 4 x 1014 cm-2 to be achi eved. The method is suitable for charge transport and optical spectroscopy measurements at ultra-high charge carrier density. In our experiments\, c esium vapour inside a cavity promotes cesium atom adsorption and ionizatio n at the graphene surface\, doping the graphene to ultra-high density leve ls. At the electron density of 4 x 1014 cm-2\, a drop in room temperature mobility to 140 cm2/Vs is recorded\, in accord with the effective mass inc rease. Once doped\, graphene can be hermetically sealed to protect against oxidation from the ambient environment\, enabling experimental manipulati on outside the glovebox environment. This method is substantively more fac ile than state-of-the-art ultra-high vacuum doping methods. In heavily dop ed graphene\, a large magnetoresistance at low temperature\, T = 1.3K\, is attributed to electron density fluctuations. Temperature dependent weak l ocalization reveals the prevalence of trigonal warping\, in accord with hi gh electron density. Non-resonant Raman scattering at a 785 nm pump wavele ngth independently confirms the high electron density achieved via the dyn amic contribution to the Raman G-band shift.\n\nThe second part of the the sis presents the experimental characterization of several electronic prope rties of franckeite\, a naturally occurring sulfosalt mineral with a van d er Waals superlattice structure composed of alternating incommensurate two -dimensional layers: pseudo-tetragonal PbS and hexagonal SnS2 layers. Expe rimental observations of the franckeite atomic structure\, using state-of- the-art high-angle annular dark-field (HAADF) scanning transmission electr on microscopy (STEM) and atom probe tomography (APT) are presented. Angle- resolved photoemission spectroscopy (ARPES) measurements of the band struc ture reveal an anisotropic two-valley valence band with in-plane effective mass values\, 19.1 and 1.6 m0. Optical reflection hyperspectra of exfolia ted franckeite is used to determine the direct optical band-gap at Eg = 1. 9 - 2.0 eV. Thermoelectric measurements of exfoliated franckeite flakes re veal a Seebeck coefficient of S= +45 uV/K and verify the intrinsic carrier s to be p-type.\n DTSTART:20231013T160000Z DTEND:20231013T180000Z LOCATION:Room 603\, McConnell Engineering Building\, CA\, QC\, Montreal\, H 3A 0E9\, 3480 rue University SUMMARY:PhD defence of Ayse Melis Aygar – High density\, on-chip\, alkali d oping of graphene and the characterization of the electronic structure of franckeite URL:https://www.mcgill.ca/ece/channels/event/phd-defence-ayse-melis-aygar-h igh-density-chip-alkali-doping-graphene-and-characterization-351764 END:VEVENT END:VCALENDAR