High Quality Monolayer Graphene Synthesized by Resistive Heating Cold Wall Chemical Vapor Deposition

摘要

The growth of graphene using resistive-heating cold-wall chemical vapor deposition (CVD) is demonstrated. This technique is 100 times faster and 99% lower cost than standard CVD. A study of Raman spectroscopy, atomic force microscopy, scanning electron micro­scopy, and electrical magneto-transport measurements shows that cold-wall CVD graphene is of comparable quality to natural graphene. Finally, the first transparent flexible graphene capacitive touch-sensor is demonstrated. Chemical vapor deposition (CVD) of monolayer graphene on copper1, 2 has emerged as one of the most competitive growth methods for securing the industrial exploitation of graphene, due to its compatibility with Si and roll-to-roll technologies.3 Recently, there has been tremendous progress in controlling the morphology,4-6 functionalization,7-10 and growth of heterostructures of intrinsic and doped graphene.11 However, the low-throughput and the very high production cost for high-quality CVD graphene are central challenges for the industrial exploitation of this material.12, 13 The most common CVD approach is to use a hot-wall system where Cu foils are heated at temperatures ≈1000 °C in a quartz tube furnace through which the precursor hydrocarbon gas flows. The long processing time, that can take a few hours, limits the throughput of graphene by this method. At the same time the typical cost of graphene produced in this way is in excess of 1 cm−2, whereas its retail price ranges from 4.57 cm−2 to 21 cm−2 (see the Supporting Information). Therefore, a way forward to increase the throughput and reduce the production cost is to grow graphene in a cold wall CVD system which heats selectively only the Cu foils. Few types of cold wall CVD have been investigated so far for the growth of graphene3, 14-19 such as magnetic induction heating CVD,14 rapid thermal annealing CVD using halogen lamp heating,15, 16 Joule heating CVD,17, 18 and resistively heated stage CVD.19 Of all these methods, the resistively heated stage CVD approach allows for faster, more efficient heating and cooling, shorter growth time, and less gas consumption. This method provides a more uniform substrate heating, it reduces the chemical reactions which can take place in the gas phase at high temperature known to contaminate graphene and it allows for very fast cooling rates, which have been shown to enhance the quality of graphene grown by CVD on copper foil.20 Furthermore, this type of cold-wall CVD system is found in manufacturing plants of the semiconductor industries. Most importantly we show that with this method truly high quality monolayer graphene can be reproducibly grown. To date, virtually nothing is known on the growth mechanism of monolayer graphene by cold-wall CVD, as well as on its quality and suitability for flexible electronic applications. Therefore, understanding the growth and properties of graphene obtained with cold-wall CVD is imperative to enable the exploitation of this material and facilitate the birth of novel graphene-based applications. Here we report a completely new mechanism for the growth of graphene by resistively heated stage cold-wall CVD which is markedly different from the growth mechanism of graphene in a hot-wall CVD. Through a combined study of Raman spectroscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM) we elucidate the early stage formation of graphene by monitoring the transition from disordered carbon adsorbed on Cu to graphene. We also demonstrate for the first time (1) high-throughput production, (2) ultralow cost, and (3) high quality monolayer graphene grown on Cu foils by resistively heated stage cold-wall CVD. Our technique merges short deposition time (approximately few minutes) with high-efficiency heating of a cold-wall CVD system, resulting in ≈99% reduction in graphene production cost. The Raman spectra of our graphene films shows a low defect related peak and in devices with an area of 5600 μm2 fabricated o