Stress and charge transfer in uniaxially strained CVD graphene

Abstract

Mechanical properties of graphene prepared by chemical vapor deposition (CVD) are not easily comparable to the properties of nearly perfect graphene prepared by mechanical cleavage. In this work, we attempt to investigate the mechanical performance of CVD graphene (simply supported or embedded in polymer matrix), transferred by two different techniques, under uniaxial loading with simultaneous in-situ monitoring by Raman microspectroscopy. The level of charge transfer doping and strain is assessed using the vector analysis modified for uniaxial strain. The strain distribution across the samples varies significantly, owing to the growth and transfer process, which induces wrinkles and faults in the CVD graphene.In simply supported specimens, the stress transfer efficiency is generally very low and the changes in Raman spectra are dominated by variations in the charge transfer originating from the realignment of the domains on the substrate upon the application of strain. In contrast, samples covered with an additional polymer layer exhibit an improved stress transfer efficiency, and the alterations of charge doping levels are negligible. In fully embedded specimens, the variations in stress transfer efficiencies are caused by the size of the effective graphene domains defined by cracks, folds and/or wrinkles.

Wrinkled Few-Layer Graphene as Highly Efficient Load Bearer

“…PMMA as well as on SU-8. 13 On the other hand, in the present case, the graphene conforms well on the substrate without the presence of delaminated areas. This can be deduced by the fact that the polymer is also wrinkled along with the graphene as a unified system (figure 1).…”

“…15 Even though the dimensions of those islands can be modified to some extent depending on the transfer method, 13 the delaminated wrinkles which cause a sincere drop in the interfacial stress transfer are present on different kinds of polymers as PET 14 , PMMA as well as on SU-8. 13 On the other hand, in the present case, the graphene conforms well on the substrate without the presence of delaminated areas. This can be deduced by the fact that the polymer is also wrinkled along with the graphene as a unified system (figure 1).…”

Enhancing the adhesion of graphene to polymer substrates by controlled defect formation

“…For exfoliated graphene/ PMMA systems the maximum values recorded are in the range of 55-60 cm -1 /% for the 2D peak and ~25cm -1 /% for the mean value of the G peak [99]. For corresponding CVD graphene/ PMMA systems the above values represent upper limits often difficult to attain due to the inherent morphological defects of the CVD-grown graphene [19,34,100]. In this context, strain rate maps extracted for both loading and unloading cycles can actually be considered as an indirect adhesion indicators, since the measured Raman variations shifts of Pos(2D) and Pos(G) are related with the "true" strain transferred from the matrix to the inclusion.…”

Synthesis and Characterization of Graphene/ITO Nanoparticle Hybrid Transparent Conducting Electrode

“…Electron/hole doping or n -type/ p -type doping in graphene introduced a red/blueshift in the Raman spectrum, and the magnitude of the shift and relative 2D band intensity with respect to undoped graphene depended on the dopant concentration [ 56 ]. Graphene subjected to tensile/compressive strain also strongly affected the red/blueshift of the Raman spectrum owing to the elongation of the C–C bond [ 2 , 10 , 57 ]. The redshift Raman spectrum in the ITO nanoparticle-decorated graphene revealed that the ITO nanoparticles introduced an n-type doping effect with lattice distortion on the graphene.…”