Chemical Vapor Deposition Growth and Characterization of Low-Dimensional Materials

Abstract
Access to electronic and excitonic phenomena in low-dimensional materials depends critically on the ability to control how their nanoscale structures are formed and organized.  This thesis explores chemical vapor deposition as a means of engineering such conditions, with emphasis on how controlled synthesis enables emergent physical behavior in onedimensional carbon nanotubes and two-dimensional transition metal dichalcogenides.  
The first part investigates boron-doped ultrasmall carbon nanotubes grown inside the interconnected channels of ZSM-5 zeolite. The confined geometry stabilizes subnanometer carbon structures that are difficult to access in free-standing form. By optimizing the highpressure CVD process and introducing boron during growth, a highly filled ultrasmall nanotube network was obtained. Structural and compositional characterization supports the formation of mixed confined nanotube motifs with effective boron incorporation. The resulting samples show superconducting-like signatures across magnetic, transport, pointcontact spectroscopic, and thermodynamic measurements, suggesting that  confinement and in situ doping provide a route to electronic states beyond those typically available in conventional carbon nanotube systems.  
The second part develops spatially confined salt-assisted CVD for the growth of submillimeter-scale monolayer WS2 and WSe2 crystals. These large monolayers provide the material basis for assembling WSe2/WS2 heterostructures with well-defined overlap regions, enabling strong-field optical measurements of interlayer exciton dynamics. Under a strong inplane THz field, bright intralayer excitons are driven from WSe2 to WS2, with the transfer efficiency collapsing onto a universal scaling governed by the exciton Keldysh parameter.  Together with quantum-mechanical simulations, this behavior supports a Floquet-assisted tunneling mechanism and shows that exciton populations in van der Waals heterostructures can be actively redistributed on ultrafast timescales.
Taken together, this thesis establishes controlled CVD growth as the materials basis for probing the electronic and excitonic responses studied here.