Impact of post-growth thermal annealing and environmental exposure on the unintentional doping of CVD graphene films

Abstract

The effect of vacuum annealing followed by exposure to oxygen and water vapor on the unintentional doping of CVD-grown graphene was investigated. CVD graphene samples were cycled between room temperature and 500 °C in vacuum while in situ Raman measurements were recorded. During the heating and cooling cycle, a hysteresis in the Raman response due to the desorption of p-dopants was observed. Upon exposure to O2 gas or air, a blue shift in the Raman response with respect to the as grown film was observed which was due to increased adsorption of p-dopants on the sample. Experiments showed that a combination of water vapor and oxygen is more effective in p-doping the samples than just oxygen and that the doping effects are reversible in both cases. Electrical measurements performed on back-gated field effect graphene devices indicate that shifts in the Dirac point correlate well to the shifts in the Raman peak positions as well as changes found in XPS and Kelvin Probe measurements, verifying the changes in doping of the graphene.

Formation of Air Stable Graphene p–n–p Junctions Using an Amine‐Containing Polymer Coating

“…The samples were then annealed in an inert environment at 200 °C overnight to remove any species that might be chemically and/or physically adsorbed on the graphene during the transfer process. [ 31 ] Lithography and plasma etching were used to defi ne a channel; the source and drain contacts (50 nm Au deposited through E-beam evaporation)…”

“…Chemical vapor deposition (CVD) graphene fi lms are intrinsically p-doped due to the presence of chemical groups bounded and/or physically absorbed to graphene during the transfer process. [ 31 ] A heat treatment process under an inert atmosphere has been typically employed on CVD graphene fi lms to remove the unintentional dopants in order to fully reveal the effect of intentional dopants. [ 31 ] Both graphene FET devices and control graphene samples were heated up to 200 °C under an inert atmosphere and held up to 180 min to allow for desorption of atmospheric p-dopants bonded to the sample, prior to PEIE deposition.…”

“…[ 31 ] A heat treatment process under an inert atmosphere has been typically employed on CVD graphene fi lms to remove the unintentional dopants in order to fully reveal the effect of intentional dopants. [ 31 ] Both graphene FET devices and control graphene samples were heated up to 200 °C under an inert atmosphere and held up to 180 min to allow for desorption of atmospheric p-dopants bonded to the sample, prior to PEIE deposition. It is believed that PEIE fi lm can function as an encapsulating layer to limit any p-doping by exposure to air.…”

Epitaxial Graphene and Graphene–Based Devices Studied by Electrical Scanning Probe Microscopy

“…Exposure to atmospheric environment may significantly alter the electronic properties of graphene and functionality of graphene-based devices due to an additional extrinsic doping [67][68][69], where such common species as water vapor, oxygen, nitrogen and carbon oxides and hydrocarbons act as p-dopants, see e.g., [70][71][72][73][74][75][76][77]. However, high reactivity and instability of many of these dopants make their practical application rather limited [70].…”

Effect of annealing on Raman spectra of monolayer graphene samples gradually disordered by ion irradiation

“…Many works were devoted to the annealing of mono-and multi-layered graphene films. However, in most of previous papers, annealing was used for pristine, non-irradiated graphene as a procedure for overcoming unintentional doping and removal of polymer residues, which remain after wet graphene transfer to the substrate or after photolithography used in the device processing [10][11][12][13][14] . In a few papers, the procedure of annealing was employed to samples preliminary irradiated with ions 15,16 , plasma 17 and UV light 18 .…”