Epitaxial Al₂O₃(0001)/Cu(111) Template Development for CVD Graphene Growth

Abstract

Chemical vapor deposition (CVD) is widely considered to be the most economically viable method to produce graphene for high-end applications. However, this deposition technique typically yields undesired grain boundaries in the graphene crystals, which drastically increases the sheet resistance of the layer. These grain boundaries are mostly caused by the polycrystalline nature of the catalytic template that is commonly used. Therefore, to prevent the presence of grain boundaries in graphene crystals, it is crucial to develop a large scale, single-crystalline template. In this paper, we demonstrate the deposition of a single-crystalline Cu(111) film on top of a 2″ sapphire wafer. The crystalline quality of the Cu(111) templates is optimized by controlled modification of the sapphire surface termination and by tuning the Cu deposition conditions. Moreover, we find that the Cu layer transforms into an untwinned single-crystalline Cu(111) structure after annealing at typical graphene growth temperatures. This allows for the growth of high-quality graphene by the CVD technique. The findings presented in this paper are an important step forward in the production of wafer scale, single-crystalline graphene.

Single-Layer Graphene Synthesis on a Al2O3(0001)/Cu(111) Template Using Chemical Vapor Deposition

“…40 The reduction is followed by graphene growth at the same temperature through the addition of the methane (CH 4 ) precursor for 30 min, without altering the H 2 and Ar flows. Next, the reactor chamber was cooled down to room temperature at a cooling rate of 10…”

Single orientation graphene synthesized on iridium thin films grown by molecular beam epitaxy

“…These observations of angular and curved edges are similar to what has been reported for insufficiently annealed pulsed laser deposited iridium films containing the twinned domains 24 and also for graphene grown on Cu(111) on sapphire prior to annealing. 27 The domain size of the Ir islands as observed in the NC-AFM images lie between 10 nm and 100 nm, while in-plane domain size retrieved from XRD investigations is $14 nm. This difference can be understood from the fact that XRD experiments provide representative information about the whole sample, while AFM measurements give the local information about the probed area, which is 500 nm  500 nm in this case.…”

“…We believe this to be a signature of dewetting of the iridium film arising from the rapid temperature changes during the CVD growth of graphene. Large dewetting features of $50 lm size have been observed by SEM on high-temperature annealed films of Cu(111) grown on sapphire 27 and Ir(111) grown on YSZ/Si(111). 25 The dewetting of the films could be avoided by an additional acid cleaning of sapphire in the former case, and use of thicker YSZ buffer layer on Si(111) in the latter case.…”

“…Sapphire crystals are widely used as substrates to grow metal films due to their high thermal and chemical stabilities, necessary for withstanding the harsh conditions of the CVD process required for the synthesis of high-quality graphene. [27][28][29][30] Single crystal iridium(111) films can be deposited by pulsed laser deposition (PLD) 24 and metal-organic CVD 31 on (0001) sapphire single crystals. Deposition of epitaxial iridium films on other orientations of sapphire was also reported by using the method of metal-organic CVD and an epitaxial relationship between different orientations a) Electronic mail: arti.pandey@desy.de b)…”

Large-area borophene sheets on sacrificial Cu(111) films promoted by recrystallization from subsurface boron

“…Graphene has also been successfully grown on Cu buffer films deposited on sapphire. 27,28 This Cu buffer were subsequently 'sacrificed' by dissolving it in FeCl 3 solution, leaving a free-standing graphene film that then can be repositioned on any supporting substrate of choice; moreover, sapphire substrates were reused multiple times. 29 Our objective was to achieve similar results with borophene, and this is the main result of this work.…”