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Theses Doctoral

Optical Studies of Excitonic Effects at Two-Dimensional Nanostructure Interfaces

Ajayi, Obafunso

Atomically thin two-dimensional nanomaterials such as graphene and transition metal dichalcogenides (TMDCs) have seen a rapid growth of exploration since the isolation of monolayer graphene. These materials provide a rich field of study for physics and optoelectronics applications. Many applications seek to combine a two dimensional (2D) material with another nanomaterial, either another two dimensional material or a zero (0D) or one dimensional (1D) material. The work in this thesis explores the consequences of these interactions from 0D to 2D. We begin in Chapter 2 with a study of energy transfer at 0D-2D interfaces with quantum dots and graphene. In our work we seek to maximize the rate of energy transfer by reducing the distance between the materials. We observe an interplay with the distance-dependence and surface effects from our halogen terminated quantum dots that affect our observed energy transfer. In Chapter 3 we study supercapacitance in composite graphene oxide- carbon nanotube electrodes. At this 2D-1D interface we observe a compounding effect between graphene oxide and carbon nanotubes. Carbon nanotubes increase the accessible surface area of the supercapacitors and improve conductivity by forming a conductive pathway through electrodes. In Chapter 4 we investigate effective means of improving sample quality in TMDCs and discover the importance of the monolayer interface. We observe a drastic improvement in photoluminescence when encapsulating our TMDCs with Boron Nitride. We measure spectral linewidths approaching the intrinsic limit due to this 2D-2D interface. We also effectively reduce excess charge and thus the trion-exciton ratio in our samples through substrate surface passivation. In Chapter 5 we briefly discuss our investigations on chemical doping, heterostructures and interlayer decoupling in ReS₂. We observe an increase in intensity for p-doped MoS₂ samples. We investigated the charge transfer exciton previously identified in heterostructures. Spectral observation of this interlayer exciton remained elusive in our work but provided the motivation for our work in Chapter 4. We also discuss our preliminary results on interlayer decoupling in ReS₂.


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More About This Work

Academic Units
Mechanical Engineering
Thesis Advisors
Hone, James C.
Ph.D., Columbia University
Published Here
January 17, 2017