UCLA

Graphene is one of the most amazing materials every discovered. It is the first stable two-dimensional crystal ever studied and has broadly impacted a myriad of fields ranging from physical science to engineering. Science has made such great advancements due to graphene that its discovery earned Nobel recognition in 2010. Initially isolated from bulk graphite using cellophane tape, its use in macroscale applications requires methods to produce it in high quality and on a very large scale. This synthetic problem is the basis for this thesis whereby the scalable synthesis and application of graphene is demonstrated utilizing chemical vapor deposition (CVD).

Mono-carbon containing methane gas is the most utilized carbon precursor for the CVD growth of graphene. To study the effects of other hydrocarbon precursor gases, graphene was grown by chemical vapor deposition from methane, ethane, and propane on copper foils. The larger molecules were found to more readily produce bilayer and multilayer graphene, due to a higher carbon concentration and different decomposition processes. Single- and bilayer graphene was grown with good selectivity in a simple, single-precursor process by varying the pressure of ethane from 250 to 1000 mTorr as characterized by Raman spectroscopy. The bilayer graphene is AB-stacked as shown by selected area electron diffraction analysis.

Vertically oriented structures of conductors and semiconductors, especially single crystals, are of great technological importance due to their directional and rapid charge carrier transport yet there does not exist a facile way to produce them. Here, we report a facile, solution-based "bottom-up" route for producing highly oriented, single crystalline, vertical arrays of conjugated molecules that exhibit uniform morphological and crystallographic orientations by employing a layer of graphene as a guiding substrate. Using an oligoaniline as model, we demonstrate that this method is highly versatile, allows for precision growth and deposition of crystals by first patterning the growth graphene substrates, and allows for the anisotropic transport of charged carriers to efficiently reach a conductivity of 12.3 S/cm along the vertical axis, the highest reported to date for an aniline oligomer. Large-area devices where current from individual crystals can be collectively harnessed are demonstrated, illustrating its promise for both micro- and macro-scopic device applications.

The transfer of large sheets of graphene is desired for a variety of applications including electronics and membrane technology. Currently, CVD grown graphene is isolated from a growth catalyst by use of polymer-assisted transfer. The underlying growth catalyst is etched away while the polymer acts as a support for transfer to arbitrary substrates before it is removed chemically and by high temperature annealing. While transferring graphene onto rigid substrates that can survive post-processing high temperature anneals is possible, the same is not true for plastic and flexible substrates. The use of the polymer may lead to unwanted contamination and damaged graphene films. We demonstrate a way to transfer very large sheets of graphene tailored for thickness onto flexible and porous membranes supports for use in size selective filtration. We utilize optimized

concentrations of ammonium persulfate to etch graphene grown on Cu-Ni alloys to produce polymer-free graphene film that can be transferred onto arbitrary substrates.