2025 Theses Doctoral

Moving beyond scotch tape: scalable, research-grade graphene by oxygen-free chemical vapor deposition

Amontree, Jacob Maxwell

Graphene grown by chemical vapor deposition (CVD) on metal surfaces has become a leading contender for producing large-area films, suitable for industrial-scale technologies. Unlike conventional exfoliation techniques, which yield only tiny flakes of graphene from graphite, CVD enables the fabrication of high-quality graphene sheets. In the CVD graphene community, there has been a lack of reproducibility in both synthesis and transfer. These struggles point to hidden variable and a misunderstanding of the fundamental kinetics of the CVD process. This has led to doubts about whether CVD-Gr can match the intrinsic quality of exfoliated graphene (Ex-Gr), which is still considered the benchmark for pristine performance. In this thesis, trace oxygen is identified as the primary culprit preventing the realization of reproducibility in graphene synthesis.

By designing a CVD-Gr reactor with the principal goal of reducing oxygen below the part-per-million (ppm)-level, oxygen-free CVD (OF-CVD) graphene with intrinsic quality can be obtained. Various material characterization techniques are utilized to showcase the ultra-high graphene quality such as: atomic force microscopy (AFM), scanning tunneling microscopy (STM), Raman spectroscopy, and electrical transport measurements. Furthermore, a dry-transfer method is adopted to construct a graphite-gated device demonstrating the first occurrence of fully-quantized fractional quantum hall states in CVD-Gr. Forced oxide intercalation during the aforementioned dry-transfer method is shown to cause extrinsic damage, preventing the resulting graphene from being scalable.

To combat this issue, a metal-assisted procedure allows graphene exfoliation from a metal growth catalyst to be facil- itated via direct nickel (Ni) evaporation. By starting the process with pristine graphene along with careful tuning of deposition and transfer parameters, no further damage is introduced into the graphene film as shown by the utter lack of D-peak. The transferred films exhibit atomically flat surfaces—almost indistinguishable from the surrounding SiO₂ surface. Ni-assisted transfer also produce graphene domains nearly free of both strain and doping, rivaling performance ob- served in suspended mechanically exfoliated graphene flakes. A dual-graphite-gated device utilizing Ni-transferred graphene exhibit intrinsic transport in the form of: ultra-low residual carrier fluctuations, full-quantization of two and four-flux composite fermion (CF) states, and disorder broadening at limits only seen with state-of-the-art mechanically exfoliated graphene devices.

Finally, a magic-angle twisted bilayer graphene structure is assembled to demonstrate the potential for scalable device fabrication in the twistronics community. The electrochemical performance of graphene-based biosensors is often constrained by structural disorder and surface contamination introduced during synthesis and transfer. This study examines the influence of growth atmosphere on the electrochemical behavior of CVD-Gr, with a focus on oxygen-free (OF-CVD) conditions. Graphene films synthesized without trace oxygen exhibit markedly improved charge transfer properties compared to commercial and conventional-CVD counterparts.

Using both outer- and inner-sphere redox probes—such as ferrocenecarboxylic acid and reduced nicotinamide-adenine dinucleotide (NADH)—key metrics including heterogeneous electron transfer kinetics, charge-transfer resistance, and redox peak stability are evaluated. OF-CVD graphene demonstrates high electron transfer rates, reduced interfacial impedance, and exceptional analytical selectivity across a wide dynamic range. Microelectrode architectures fabricated from these films further suppress non-faradaic currents, enhancing sensitivity and enabling detection at nanomolar concentrations. These improvements are attributed to the reduced defect density, monolayer uniformity, and chemical inertness of the graphene surface. Collectively, the findings highlight the critical role of synthesis conditions in determining electrochemical performance and establish oxygen-free CVD graphene as a promising platform for sensitive, reproducible biosensing in both conventional and extreme environments.