UC Berkeley

Van der Waals solids are a class of materials made up of loosely-bound, molecularly-thin layers. These layers can be readily detached from one another due to their weak interlayer van der Waals bonds, giving the materials their name. In 2004, the isolation of graphene, a single-atom-thick layer of carbon, from graphite, a bulk van der Waals material, prompted a surge of research interest in the nearly two-dimensional layers making up these materials. Their mechanical strength, stability in ambient conditions, flexibility, and near-transparency are intriguing for the production of flexible electronics. Meanwhile, their ultimate thinness opens an avenue for exploring extreme physics, offering the possibility of new kinds of devices, and making these materials intriguing to researchers in the short term. Graphene, the most famous, is a conductor. However, some van der Waals materials are semiconductors, which are necessary to produce electronic switches and light-emitting diodes (LEDs), while other van der Waals materials are insulators. There is considerable potential in combining these different van der Waals materials to produce so-called heterostructures, which can re-create existing functionality, such as light emission, or produce new devices with unique capabilities.

The difficulty of manipulating atomically-thin semiconductors has prevented them from achieving commercial application. Existing processes for manipulating van der Waals semiconductors do not offer control over the shape or size of the single-layer features produced.

By interrogating the role of stamp mechanics in the success of producing single layers, this thesis develops a method that enables the creation of van der Waals heterostructure arrays. After an introduction to the current state of the art in scalable manufacture of van der Waals monolayers and its tradeoffs in Chapter 1, Chapter 2 demonstrates a new process for creating patterned arrays of semiconducting monolayers from a bulk source. In order to measure the effectiveness of the method, this work introduces yield metrics relevant to nanomanufacturing of 2D material patterns. To further understand the role of the stamp in the process of exfoliation, Chapter 3 presents a finite element model bridging macroscale and nanoscale physics to understand the interaction between van der Waals layers and an elastic stamp. The results from this model carry implications for nanomanufacturing process design.

Chapter 4 then concludes with discussion of the usefulness and limitations of the methods developed in this work, and considers future directions that will enable high-yield mass production of van der Waals heterostructures.