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Van der Waals heterostructure is a highly versatile platform to unveil two-dimensional (2D) electron physics and to explore new device functionalities. In this dissertation, we present comprehensive experimental studies of van der Waals heterostructures considering the rotational control between different 2D layers. A hemispherical handle polymer stamp is introduced to improve 2D layer transfer, which allows rotational control when stacking 2D layers. To verify the accuracy of rotational control, we demonstrate a rotationally aligned double monolayer graphene using a sequential pick-up of two graphene layers, which originate from a single crystal domain, and compare it with Bernal stacked bilayer graphene using Raman spectroscopy, scanning probe microscopy (SPM), and electrical transport measurements under an applied transverse electric-field. We also demonstrate resonant tunneling in double bilayer graphene heterostructures using hexagonal boron nitride (hBN) as an interlayer dielectric, in which rotational alignment between the two bilayer graphene is the key ingredient for the device functionality. To further highlight the significance of highly accurate rotational alignment between different layers, we demonstrate tunable moiré crystals in small-twist-angle bilayer graphene. A comprehensive electron transport study is conducted, and the data are compared with SPM results. We observe transport gaps at ±8 electrons per moiré unit cell, along with a conductivity minimum at charge neutrality with twist angle less than 1°. In magnetic fields, we also observe the emergence of a Hofstadter butterfly in the energy spectrum, with four-fold degenerate Landau levels (LLs), and broken symmetry quantum Hall states at filling factors, ν = ±1, ±2, ±3. We demonstrate dual-gated tungsten diselenide (WSe₂) interlayer tunneling devices, consisting of two WSe₂ monolayers with controlled rotational alignment, and separated by a thin hBN tunnel barrier. In samples where the two WSe₂ have a 0° relative twist the tunneling current-voltage characteristics reveal resonant tunneling, manifested by negative differential resistance, which stem from energy and momentum conservation. Because WSe₂ possesses strong spin-orbit coupling which leads to coupled spin-valley degrees of freedom, controlling the angle between the two WSe₂ monolayers allows us to probe the conservation of spin-valley degree of freedom in tunneling.

The Polaroid Corporation, in May of 1983, introduced Polachrome CS color transparency film and a new process called the Autoprocess system. This system offers the convenience of obtaining instant color transparencies in about three minutes. The film has excellent projection and viewing characteristics. The product was designed to have its largest market with professional photographers. Polachrome's construction creates problems for the printer in that moire patterns occur during the separation process. This study gives a short background for both additive color screen films and dye layer films, and a comparison is made to help the reader understand the problems with scanning Polachrome film. When attempting to scan Polachorme CS film, moire patterns are produced because of the color filters which make up the film. The emphasis of this study was to determine which scanner controls could be used to remove the moire patterns. Polachrome CS film is based on the principle of an additive color screen theory. The film contains many layers, one layer consisting of red, green, and blue filters which either passes or stops light. When this filter layer is viewed by the scanning lens an interference pattern called moire is produced by the variables of screen ruling, unsharp masking controls, and the angle of the transparency on the scanning drum. The hypothesis states that Polachrome CS color transparency film can be scanned on the DC-300 B/L laser scanner, so that separations are free of all moire patterns with acceptable definition. Pre-testing was necessary to determine which variables of the scanning process had an effect on producing a moire pattern. The results of the pre-tests determined the final choice of variables, which were then tested together. Defocusing, unsharp masking (intensity and starting point), as well as the angle at which the transparency is mounted, were determined to be the major variables that cause a moire pattern when scanning Polachrome CS transparency film. From the combination of these variables a total of 48 proofs were generated for the visual experiment. The visual experiment had two parts, involving 30 viewers, viewing the 48 proofs. Part I dealt with a question relating to moire patterns and Part II dealt with a question relating to the definition of the image. Data was recorded and analyzed. The hypothesis, that separations can be generated free of moire patterns with acceptable definition, was proven by 16 percent of the proofs tested. This resulted in a set of recommendations given as guidelines to follow when Polachrome transparency film is electronically scanned on the DC-300 B/L laser scanner.