Large-scale Fabrication of 2D Materials by Chemical Vapor Deposition

The family of 2D materials comprises a vast range of few-atom thick materials held together by van der Waals interactions that have a diverse set of material properties. While these materials are interesting in their own right, the most exciting aspect of their research is the ability to combine this vast range of materials - without the lattice mismatch constraints of conventional 3D materials - into atomically engineered, artificial 3D crystals that pave the way for new physics, and subsequently, for new applications. 2D materials are expected to disrupt a number of industries in the future, such as electronics, displays, energy, and catalysis.

The key bottleneck for commercial implementation is in large-scale synthesis and subsequent fabrication of high quality devices. Chemical vapor deposition is considered to be the most economically feasible synthesis method to this end. In the case of graphene, for which synthesis and transfer methods have been established, the key bottleneck is in cost reduction and device integration without significant degradation of material properties.

In the case of the other 2D materials, the key bottleneck is in the absence of reliable and scalable methods for synthesis. This thesis aims to address some of the challenges associated with materials fabrication in order to lay the groundwork for commercial implementation of 2D materials. To improve graphene implementation in electronic applications, copper catalyst foils were engineered to reduce surface roughness, wrinkles, and polycrystallinity in the resulting graphene layer; in the process, monocrystalline copper foils with a post-process surface roughness below 10 nm - an order of magnitude lower than current commercial foils - were achieved.

A new transfer technique was also developed as a route towards vertical integration of device fabrication process steps. To realize large-scale and economical graphene production, significant reductions in graphene production cost were achieved through efficient space utilization in a commercial chemical vapor deposition reactor, allowing for a 30x improvement in throughput.

A large-scale, non-destructive transfer process for DIY-application of graphene films onto arbitrary substrates was also developed through the use of commercially available polymer films and solvents. Finally, a novel in-situ process monitoring tool was developed to complement large-scale graphene production, which was used here to troubleshoot and optimize processes to enable reproducible and high quality graphene synthesis.

To address the challenge of synthesizing the vast library of 2D materials, a universal platform for 2D materials synthesis via CVD-like conditions was invented, and was used to synthesize more than 26 different compounds - some well-known and others never-before isolated - to demonstrate its universality.

The discovery of this general growth method calls for a perspective shift from the conventional 2D materials growth model inherited from graphene synthesis on copper, and provides an instructional guide for rapidly synthesizing prospective new 2D materials, paving the way for accelerated progress in the field in coming years.