Title: "CVD of Graphene: 2D Crystal Growth Model, Grain Size Control, and Scalable Transfer via Mechanical Delamination"
Name of the Student: Mr. Suman Kumar Mandal
Degree Registered: Ph.D. Engineering 
Advisor: Prof. Srinivasan Raghavan, CeNSE
Date: 10th October 2025, Friday - Time: 3:30 PM
Venue: ONLINE: https://shorturl.at/4xYib

Abstract

The synthesis of large-area two-dimensional (2D) materials via chemical vapor deposition (CVD) 
has garnered significant attention due to their potential in diverse applications. The deposition 
of these materials from the vapor phase occurs by the nucleation of atomically thin crystalline 
layers and the subsequent motion of the edges or steps that bound the nuclei. Most theories of 
crystal growth that address the motion of atomic steps were developed before the more recent 
advent of 2D materials. They typically fall into two buckets. One, based on the Burton-Cabrera-Frank
 (B.C.F.) theory that envisions growth through attachment of atoms to a thermally rough edge. 
A second approach is based on the so-called 1D nucleation mechanism, which suggests growth via 
nucleation and propagation of atomic rows along smooth edges.

As summarized in this thesis, they have shortcomings. To address these deficiencies and 
build upon their ideas, a comprehensive analytical framework has been developed to 
investigate the growth kinetics of 2D materials. Graphene grown on copper serves as 
the model experimental system. To the best of our knowledge, the development of a theory 
and its application to 2D growth to test validity has not been done before. For atomically 
thin graphene edges, a two-step growth mechanism involving double-kink nucleation at 
crystal edges followed by subsequent attachment of additional units to these features 
is proposed. As in the B.C.F. and other subsequent theories, a structure of the edge is 
first arrived at and modelled in terms of a kink density. The differences between the 
previous models and the one proposed in this thesis are highlighted, along with 
physico-chemical parameter regimes in which they converge. Based on the interplay 
at these edges with the growth ambient, four distinct growth modes were 
identified: mono-nuclear, poly-nuclear row-by-row, poly-nuclear multi-row, 
and dendritic modes that depend on crystal morphology, size, supersaturation, 
and substrate chemistry. All three main aspects of 2D growth, growth velocity, 
saturation nucleation density,  and coverage with time, are predicted. It is also 
shown that using this model, 2D growth can be used as a probe to determine surface 
supersaturation, a parameter that is not otherwise available.

Leveraging this mechanistic understanding, this thesis demonstrates the ability to 
control graphene grain size through supersaturation modulation, achieving a 
two-order-of-magnitude tunability. Additionally, the critical role of trace oxygen
 impurities in the copper substrate is discussed, which is found to significantly
 impact the morphology of graphene single crystals and the grain size in the 
full-coverage polycrystalline film. Understanding and modelling the growth mechanism 
of 2D edges is crucial as it directly influences grain size, a critical parameter 
determining the suitability of 2D materials for specific applications. For instance, 
large graphene grains are advantageous for electronics and impermeable barrier applications, 
while smaller grains are preferred for chemical sensors.

Finally, to bridge the gap between synthesis and practical applications, a scalable 
mechanical delamination method has been developed to transfer graphene films from copper
 to a target polymer substrate. This method overcomes the limitations of the conventional
 wet-transfer technique, resulting in large-area, defect-free, and affordable transferred 
graphene. The delaminated graphene exhibits state-of-the-art moisture impermeability of
 2.7x10-3 grams/m2/day over a large area of 1-inch2, demonstrating its potential for 
ultra-high moisture barrier applications.

In summary, this thesis provides a foundational understanding of the growth kinetics 
of 2D materials, enabling precise control over their grain size for specific applications. 
Moreover, the development of an efficient transfer method brings us closer to realizing 
the full potential of CVD-grown graphene in various technological domains.