Gas phase controlled deposition of high quality large-area graphene films

Abstract

A gas phase controlled graphene synthesis resembling a CVD process that does not critically depend on cooling rates is reported. The controllable catalytic CVD permits high quality large-area graphene formation with deft control over the thickness from monolayers to thick graphitic structures at temperatures as low as 750 1C.Graphene has attracted enormous attention because of its exciting structural and electrical properties. 1 Extremely high mobilities 2 and a tunable band gap 3 make graphene potentially useful for innovative approaches to electronics 4 and sensing. 5 For these applications a scalable and reproducible method for graphene production is required. Mechanical exfoliation of graphite 6 and decomposition 7 of SiC surfaces upon thermal treatment have been the main sources for graphene, with limitations in quality and scalability. Solution-phase 8 and solvothermal syntheses of graphene 9 were a major improvement for processing, however for device fabrication, a reproducible method such as CVD yielding high quality films of controlled thickness is desirable. Recently, the formation of graphene under CVD-like conditions on Ir, 10a Ru, 10b Ni 11 and Cu 12 surfaces has been reported. Nevertheless, these processes are not conventional CVD since they rely on precipitation of carbon upon cooling and require high-quality substrates, elevated temperatures (B1000 1C) and accurate control over cooling rates.Here, we introduce a CVD process which produces high quality graphene with tunable thickness on Ni surfaces. We have synthesised large-area graphene films (41 cm 2 ) in a simple tubular CVD reactor using ethyne (acetylene) as precursor under varying CVD parameters. The nickel substrates were prepared by E-beam evaporation (Edwards Auto500) of Ni (200 nm) on thermally-grown silicon dioxide (300 nm). The substrates were introduced in a tube furnace heated to temperatures between 650 1C and 1000 1C. After reduction by a mixture of hydrogen and argon (1 : 1) for 5 min, Ar was shut off and acetylene was introduced, keeping the overall pressure between 0.5 and 5 Torr for various dwell times. The flow rate was nominally 60 sccm for acetylene and 180 sccm for hydrogen or argon, unless otherwise specified. The substrates were then cooled under nitrogen flow with rates exceeding 15 1C s À1 or as slow as 0.15 1C s À1 . For reference, bare SiO 2 substrates were also placed in the CVD chamber. A Zeiss Ultra FE SEM with an EDX detector was used for imaging the graphene layers directly on the substrates. Aberration-corrected HRTEM was carried out using an Oxford-JEOL JEM2200MCO FEGTEM/STEM fitted with two CEOS C s aberration correctors, operated at 80 kV. The samples for HRTEM were prepared by directly peeling off the carbon deposit from the substrate with a formvar film which then was deposited onto a TEM grid. Raman spectra were taken with a Jobin-Yvon Labram Raman spectrometer using an excitation wavelength of 633 nm, with a probe size of 2 mm. Typically, five Raman spectra were taken on each sample to confirm homogeneit...

A study of the key parameters, including the crucial role of H2 for uniform graphene growth on Ni foil

“…Kumar et al [25] gives an interpretation of the catalytic role of the support (a thin Ni film), identifying the two phases of hetero-epitaxial and homo-epitaxial carbon layer deposition. They demonstrated the absence of catalyst segregation in the formation of graphene layers, based on the consideration that the solubility of carbon in Ni is less than 1% at 950 • C.…”

“…The literature on this theme can essentially be divided between (i) those in which graphene films were prepared on nickel films [23,4,[24][25][26][27][28][29][30] (sputtered or evaporated on substrate), mostly for microelectronic applications, and (ii) those using nickel foils [31][32][33] to obtain very large areas of graphene with which to make transparent electrodes; these could be used as a in substitute for ITO in flat panel displays, liquid crystal displays, touch panels, solar cells and EMI shielding. Each of the papers written supplies a contribution to the interpretation of the reaction mechanism.…”

“…Since the first successful fabrication of graphene by cleavage, three major methods for the fabrication of single-and multi-layer graphene have been investigated. These methods include micromechanical cleavage [1] chemical exfoliation of graphite [8,9], and chemical vapor deposition (CVD) of hydrocarbons on a substrate surface [10][11][12][13][14][15][16][17][18][19][20][21][22][23]4,[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. Among them, the latter (CVD growth) is considered to be of the most promising due to its capability of producing large-area deposition, the lack of intense mechanical and/or chemical treatments and its flexibility.…”

The effect of downstream plasma treatments on graphene surfaces

“…Two different cases formed the focus of this investigation. In the first case a few layer graphene sample that was grown on a Ni substrate (growth details Kumar et al [57]) was transferred onto a SiO 2 substrate without the use of polymer support. The sample underwent annealing in forming gas (Ar:H 2 , 9:1) for 10 hours at 900 ˚C.…”

Controlled synthesis of transition metal dichalcogenide thin films for electronic applications

“…However, they are not readily compatible with standard microprocessing techniques; and the films produced from individual flakes display inferior electronic properties to those obtained by mechanical exfoliation [27]. Chemical vapour deposition (CVD) is a versatile, cost effective and industry compatible technique, which has greatly advanced graphene research in recent years by making high quality films readily available [28,29]. Similar methods can be used for the production of TMD films, and several routes to the production of MoS 2 thin films have recently been outlined.…”