Since 2004, graphene attracts intensive attention from scientists and engineers all over the world. During the last decades, the research relates to graphene and other 2 dimensional (2D) materials are rapidly increasing. Approximately, ten thousand journal papers have been published after the discovery of graphene in relative topics widely spread. On the other hand, the simple graphene properties research is nearly completed. Researchers turn their attention to other 2D materials or Van der Waals heterostructures. By increasing the liberty and knowledge of 2D materials, the Van der Waals heterostructures can start to build something on this 2D wander land. In this thesis the Van der Waals heterostructures is based on graphene and some other well known 2D materials such as hexagonal boron nitride (hBN) to study fundamental physics and possible applications in near future. In this thesis, three published papers which are related to Van der Waals heterostructures have been included. The electronic properties of encapsulated graphene on different 2D crystals have been investigated by the capacitance spectroscopy. Several 2D crystals have been tested as a substrate such as MoS2, WS2, mica, LiNbO3…etc. The quality of encapsulated device is correlates the interface self-cleaning. Follow with the fundamental physics study employed by a simple Van der Waals heterostructure. Graphene and hBN is lattice aligned within 2 degrees in difference and creates a new superlattice structure which just like moire pattern happens while two similar patterns overlapped. The basic electronic properties do not vary at near Dirac point. Away from the first generation Dirac point, the superlattice structure affects the band structure in higher carrier concentration. In this paper, aligned graphene-hBN capacitors have been demonstrated to discover more fine details of these many-body interactions in this superlattice structure. The final part is related to twist controlled graphene-graphene resonance tunneling transistors. A Van der Waals heterostructure is constructed by two aligned graphene stripes with a thin layer of hBN as a spacer. The electrons are tunneled from one stripe to another graphene stripe while a bias voltage applied. The resonance tunneling is occurred when two graphene flakes are aligned at certain bias voltage. In this paper, we contribute the resonance tunneling to momentum conservation of tunnelling electrons. Theory simulation is highly agreed with our experiment results.

As the family of two−dimensional(2D) materials has grown, two−dimensional heterostructure devices have emerged as great alternatives to replace conventional electronic materials and enable new functionality such as flexible and bendable electronics. The fabrication and performance of these devices depend critically on the understanding and ability to manipulate the mechanical interplay between the stacked materials. In this dissertation, we investigate adhesive interactions and determine the shear modulus of heterostructure devices made from Molybdenum Disulfide (MoS2). MoS2 has been attracting attention recently due to its semiconductor nature (having a direct band gap of 1.9 eV) along with its exceptional mechanical strength and flexibility. As the first step of our research, we suspended MoS2 flakes grown through chemical vapor deposition (CVD) over substrates made of metal (gold, titanium, chromium), semiconductor (germanium, silicon), insulator (silicon oxide), and semi-metal (graphite). Then, by creating pressure differences across the membrane, we forced MoS2 to bulge upward until we observe separation from the surface of the substrates. We demonstrated that MoS2 on graphite has the highest work of separation within the tested surface materials. Furthermore, we measured considerable adhesion hysteresis between the work of separation and the work of adhesion. We proposed that surface roughness and chemical interactions play a role in surface adhesion and separation of 2D materials. These experiments are critical to guiding the future design of electrical and mechanical devices based on 2D materials. Next, we measured the effective shear modulus of MoS2/few−layer graphene (FLG) heterostructures by employing a blister test. Again, by introducing a pressure differential across the suspended MoS2 membrane over the FLG substrate, the MoS2/FLG heterostructure peeled off from the silicon oxide surface once the critical pressure is exceeded. Incorporating a modified free energy model and Hencky’s axisymmetric membrane solution, we determine the average effective shear modulus of the heterostructure. This is the first experimental measurement of the shear modulus of heterostructure devices using a blister test and this platform can be extended to determine the shear modulus of other 2D heterostructures as well. / 2024-05-24T00:00:00Z