A low-damage plasma surface modification method of stacked graphene bilayers for configurable wettability and electrical properties

Abstract

In this work, we study surface functionalization effects of artificially stacked graphene bilayers (ASGBs) to control its wetting properties via low-damage plasma. The ASGBs were prepared on a SiO 2 /Si substrate by stacking two monolayer graphene, which was grown by chemical vapor deposition. As a result, the low-damage plasma functionalization of ASGBs could hold both the key characteristics of surface functionalization and electrical transport properties of graphene sheets. To characterize ASGBs, Raman and x-ray photoelectron spectroscopy (XPS) were used to determine the degree of defect formation and functionalization. Meanwhile, the degree of the wettability of the ASGBs surface was determined by optical contact angle (CA) measurements. Based on experimental results, the compositional ratio of C-OH+COOH was found to increase 67% based on the analysis of XPS spectra after low-damage plasma treatment. This treatment effect can also be found with 75.3% decrease in the CA of water droplet on graphene. In addition, we found that the ratio of 2D/(D+G′) in Raman spectra shows strong correlation to the measured CA; it can be a reliable indicator of ASGBs surface wettability modification. This work showed that we obtained a higher degree functionalization of ASGBs without degrading the under-layer structure of ASGBs due to the moderate low-damage plasma treatment. The presented process technique of controllable wettability through low-damage plasma treatment can be employed for potential application in graphene-based sensors/devices.

Investigation of Plasma-Assisted Functionalization of Graphitic Materials for Epoxy Composites

“…Indeed, it has already been proved that surface oxygen functionalities provide polar centers to attract water molecules and enhance the surface hydrophilicity, thus lowering the water contact angle (WCA) values while surface C−H bonds contribute to the carbon hydrophobicity and higher WCA values [41]. He et al [42] showed that a correlation existed between the intensity of the C-O/OH component of the C 1s peak in X-ray Photoelectron Spectroscopy (XPS) analysis of graphitic filler and observed water contact angle; similar conclusions have been reached by Lin et al [43]. Based on this, the potential impact of the plasma treatment can be easily assessed by contact angle (CA) measurements providing a simple and time-effective tool to evaluate the presence of functional groups containing oxygen on the filler surface.…”

Hybrid GaAsSb/GaAs Heterostructure Core–Shell Nanowire/Graphene and Photodetector Applications

“…The peaks at ∼284, ∼285.5, 287.9, and ∼289 eV represent dominant sp 2 hybridized C−C bond, sp 3 hybridized C−C bond, a carbonyl group (CO) and a carboxyl group (COOH), respectively. 41,43,44 The small contributions of O 2 functional groups (CO and COOH) are most likely related to PMMA residue induced during transfer that confirm the superior quality of the pristine monolayer graphene on SiO 2 /p-Si(111). 43,44 This was corroborated from the Raman spectra and AFM data.…”

“…A reduction in I 2D /I G observed in these two samples relative to the rest of the plasma-treated samples is attributed to the dominance of O 2 -related functional groups on the graphene surface. 40,41 Next, O 2 plasma treatment-induced modifications in surface morphology and conductivity of the graphene surface were evaluated using an atomic force microscope and a conductive atomic force microscope. AFM surface topography image of the pristine graphene shows the wrinkle-free smooth surface of graphene on SiO 2 /p-Si(111) with a measured RMS roughness of ∼0.35 nm (Figure 4a), which is increased in the plasmatreated sample (1 W, 45 s) to an RMS roughness of ∼0.67 nm (Figure 4c).…”

“…These changes in XPS spectra can be correlated to the increased intensity of the Raman D peak and a concomitant reduction in Raman 2D peak intensity that is attributed to the suppression of C−C bonds and honeycomb lattice induced functional groups, namely, C−O and COOH. 39,41,45,46 The C−O and COOH groups have been reported 28,41 to be the key functional groups to enhance the wettability of graphene and hence would enable reshaping of the Ga droplet by varying the contact angle to the desired one. Hence, plasma treatment of the graphene surface, even at this low power and short duration, can impact nucleation center density and orientation of the grown NWs.…”

Surface Wettability Tuning of Acrylic Resin Photoresist and Its Aging Performance

“…Plasma treatment is a powerful way to achieve hydrophilic or hydrophobic properties for polymer surfaces. The plasma atmospheres [ 15 ] to achieve hydrophilic property include O 2 [ 16 , 17 , 18 ], N 2 [ 19 ], Cl 2 [ 20 ], Ar [ 21 , 22 ], Ar/O 2 [ 23 ], Ar/N 2 [ 23 ], and O 2 /H 2 [ 24 ], while the atmospheres for hydrophobic treatment include CF 4 [ 25 ], SF 6 [ 26 ], and Ar/SF 6 [ 23 ]. Among these atmospheres, oxygen plasma is more frequently used to form hydrophilic polymer surfaces to achieve increased wettability [ 27 ] and enhanced adhesion [ 28 ] used in microfluidic devices [ 1 , 15 ], biological fields [ 29 ], and so on.…”