Atomically thin 2D Materials and Heterostructures: Preparation, Characterization, and Applications

Atomically thin two-dimensional (2D) materials and heterostructures have emerged as a frontier in materials science, offering unique physical properties and unprecedented potential for technological applications. These materials, such as graphene, transition metal dichalcogenides (TMDs), and hexagonal boron nitride (hBN), exhibit exceptional electronic, optical, and mechanical characteristics due to their reduced dimensionality and strong quantum confinement effects. As research progresses, the disassembling and reassembling the 2D materials to realize these heterostructures is still a hot and ongoing research. Ensuring clean interfaces and high-quality materials is crucial to access these novel properties.

After a brief introduction and literature review, Chapter 3 introduces different novel approaches to the stacking of different 2D materials and the fabrication of heterostructures with tailored properties, enabling the exploration of novel phenomena such as phase change investigation of PdSe₂ and the memcapacitive and memresistive effects of stacked nanosheets of PdSe₂. These heterostructures are pivotal for advancing nanoelectronics, photonics, and phase transition devices. A simple polymer-free graphene transfer technique is introduced that improves the quality of transferred graphene.

Chapter 4 of the dissertation investigates the behaviour of various excitons such as free exciton, bound exciton along with defect states in a partially encapsulated GaSe by varying the GaSe thickness and temperature (4 to 295 K). This further expands our understanding of excitons and deep defects in 2D GaSe. This knowledge is crucial for the future use of GaSe in nano-optoelectronics, particularly when it comes to manipulating its optical properties.

Finally, chapter 5 investigates the structural evolution and correlated optical properties of the various alloys between PdSe₂ and PdTe₂ with different Te fractions. we have observed several phase transitions using Raman spectroscopy, and transitions from PdSe₂ ambipolar transport characteristics to n-type in PdSe_1.8Te_0.2, and subsequently to p-type in PdSe_1.5Te_0.5 as Te doping increases.