Production and characterization of carbon-based nanomaterials : single- and double-layer graphene for high-pressure Raman spectroscopy

University essay from Luleå tekniska universitet/Maskinteknik/Physics

Abstract: Graphene is a novel carbon nanomaterial and a great promise fornanotechnology applications in a near future, thanks to its outstandingmechanical and electronic properties. Less than 4 Angstroms (Å) in thickness, mono-crystal graphene flakes can reach tens of millimeters in their biggest dimension, making it a 2-dimensional crystal. This one-atom-thick sheet of pure sp² carbon displays Young modulus reaching 1TPa, a theoretical hardness higher than diamond, and is also a close-to-perfect (ballistic) conductor for heat and charge carriers. This dazzling array of exceptional properties makes graphene a state-of-the-art candidate for a list of applications in nanoscale electronic devices, bio-nanotechnologies, and advanced materials.Raman spectroscopy constitutes a non-destructive and time-efficient technique that probes many properties: the samples quality, thickness, doping. Most importantly, Resonance Raman Spectroscopy allows determination of the number of layers of graphene flakes (Single-Layer Graphene SLG, Double-Layer Graphene DLG, N-Layer Graphene NLG). A high-pressure study of graphene species by in-situ Resonance Raman Spectroscopy will provide a direct probing of the sp² carbon-carbon bond strength when SLG is studied, and the inter-planar interaction in the case of DLG. For an optimal comparative study, SLG and DLG graphene flakes need to be probed at High-Pressure without a supporting substrate.For this purpose, this thesis aims at the synthesis of high-quality grapheneflakes in a reliable and reproducible manner. The second goal of the thesisis to extensively characterize these samples at ambient conditions, and torealize their transfer into a high-pressure device called Diamond Anvil-Cell(DAC) to prepare the in-situ experiments. Graphene samples are prepared using a mechanical exfoliation method, which was optimized to reach the fast and reproducible production of high-quality flakes, whose size can reach up to 20µm in their biggest dimension. Graphene samples provided by ourcollaborators are also investigated.The characterization confirms the production of high-quality supportedsamples (low or no D-band in the Raman spectra), and though transfer of thesamples into the DAC is so far unsuccessful, a slight change in the materials used (from Cu-based grids to Au grids) should make the transfer possible and open the path to High-Pressure measurements for both types of samples.We have also proposed an innovative method to produce graphene fromnano-lithographically patterned NanoPillars by mechanical exfoliation. Albeit unsuccessful as we first expected it, the cleavage, as showed by SEM,provokes a peeling of the pillars' superior layers, accordingly to theexpected mechanism. These efforts open the way to a new promising route forthe synthesis of large area graphene-based nanostructures.