Multilayer graphene deposited by a filtered cathodic vacuum arc (2018)

Graphene is a single layer of sp2 bonded carbon atoms; it was first practically isolated from graphite in 2004 via mechanical exfoliation and has since attracted much attention due to its remarkable properties. However, to replace existing materials in electronic and other devices, efficient methods are needed to synthesize high quality graphene directly on a range of substrates, including thermally sensitive surfaces. Although there are several methods capable of producing graphene; each technique has weaknesses, which limit their applicability. <br><br>This thesis demonstrated, for the first time, that it is possible to energetically deposit graphene films onto copper foil using physical vapour deposition (PVD) in a filtered cathodic vacuum arc (FCVA) deposition system. Raman spectroscopy and transmission electron microscopy (TEM) revealed that the graphene films were of uniform thickness of ~10 layers and that these can be deposited at moderate temperatures of 750 °C. The resulting films, which can be prepared at high deposition rates, were comparable in quality to graphene films grown at 1050 °C using conventional chemical vapour deposition (CVD). This difference in growth temperature is attributed to dynamic annealing which occurs as film grows from the energetic carbon flux present in FCVA.<br><br>The effect of processing gasses during the growth of FCVA deposited carbon films on copper foil was explored. It was shown that neither the presence of hydrogen or methane had a favourable influence on the growth of FCVA deposited graphene, with both leading to increased defects through ion bombardment. The growth of graphene by CVD requires the removal of the native oxide layer on the copper substrate aided by the presence of hydrogen gas. It was found that the energetic C+ ions in FCVA remove the oxide layer by sputtering without the need for any hydrogen gas. <br><br>This thesis also explored the deposition of graphene on other substrates. In the case of nickel substrates, it was found that graphene films can also be prepared at moderate substrate temperatures. Much higher carbon doses were required to produce graphene films on nickel due to the solubility of carbon in this substrate. This indicates that the growth mode differs between substrates as observed in CVD grown graphene. The films deposited onto nickel were also found not to be uniform in thickness, demonstrating that the grain structure of the nickel substrate influenced the growth of graphene layers.<br><br>The growth of a film by CVD is dependent on a reaction between the substrate and the processing gas. In PVD, a film can be energetically deposited onto almost any type of substrate. Hence, the possibility of depositing graphene onto hexagonal boron nitride (BN), yttrium stabilised zirconia (YSZ) and silicon carbide (SiC) was explored. It was found that carbon films deposited at 750 oC on BN adopted a graphene microstructure. However, no evidence of graphene was found when films were deposited at 750 oC on YSC and SiC.<br><br>Interest in the properties of junctions between semiconductor materials and carbon allotropes is growing. Carbon films with high sp2 fractions were energetically deposited onto copper template-layers. These copper template-layers were subsequently sacrificially etched to leave carbon films supported directly on either silicon or silica. On silicon, ordered growth was inhibited by the formation of copper silicide. However, on silica, large areas of ~ 10 graphene layers were formed with orientation parallel to the substrate. Both the copper template-layers and the carbon films were energetically deposited in the same FCVA deposition system. The energetic deposition process provides dense, high quality <111> copper and conditions suitable for producing graphene layers at lower growth temperatures than those required for conventional CVD grown graphene.