Mechanical Robustness of Graphene on Flexible Transparent Substrates.

Moon H Kang,Matthew T Cole,Lizbeth O Prieto López,William I Milne,John A Williams,Ken Teo,Bingan Chen

doi:10.1021/acsami.6b06557

Moon H Kang, Matthew T Cole + Show 5 more

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https://doi.org/10.1021/acsami.6b06557

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Abstract

This study reports on a facile and widely applicable method of transferring chemical vapor deposited (CVD) graphene uniformly onto optically transparent and mechanically flexible substrates using commercially available, low-cost ultraviolet adhesive (UVA) and hot-press lamination (HPL). We report on the adhesion potential between the graphene and the substrate, and we compare these findings with those of the more commonly used cast polymer handler transfer processes. Graphene transferred with the two proposed methods showed lower surface energy and displayed a higher degree of adhesion (UVA: 4.40 ± 1.09 N/m, HPL: 0.60 ± 0.26 N/m) compared to equivalent CVD-graphene transferred using conventional poly(methyl methacrylate) (PMMA: 0.44 ± 0.06 N/m). The mechanical robustness of the transferred graphene was investigated by measuring the differential resistance as a function of bend angle and repeated bend-relax cycles across a range of bend radii. At a bend angle of 100° and a 2.5 mm bend radius, for both transfer techniques, the normalized resistance of graphene transferred on polyethylene terephthalate (PET) was around 80 times less than that of indium-tin oxide on PET. After 10(4) bend cycles, the resistance of the transferred graphene on PET using UVA and HPL was found to be, on average, around 25.5 and 8.1% higher than that of PMMA-transferred graphene, indicating that UVA- and HPL-transferred graphene are more strongly adhered compared to PMMA-transferred graphene. The robustness, in terms of maintained electrical performance upon mechanical fatigue, of the transferred graphene was around 60 times improved over ITO/PET upon many thousands of repeated bending stress cycles. On the basis of present production methods, the development of the next-generation of highly conformal, diverse form factor electronics, exploiting the emerging family of two-dimensional materials, necessitates the development of simple, low-cost, and mechanically robust transfer processes; the developed UVA and HPL approaches show significant potential and allow for large-area-compatible, near-room temperature transfer of graphene onto a diverse range of polymeric supports.

Highlights

The ever increasing demands on functionality from consumer electronics has highlighted the need for a wider class of mechanically flexible transparent conductors
Graphene transferred with the two proposed methods showed lower surface energy and displayed a higher degree of adhesion (UVA: 4.40 ± 1.09 N/m, hot-press lamination (HPL): 0.60 ± 0.26 N/m) compared to equivalent chemical vapor deposited (CVD)-graphene transferred using conventional poly(methyl methacrylate) (PMMA: 0.44 ± 0.06 N/m)
We have reported on two novel techniques for the transfer of CVD graphene onto flexible and transparent polymeric substrates via UV adhesive (UVA) and hot-press lamination (HPL)

Summary

■ INTRODUCTION

The ever increasing demands on functionality from consumer electronics has highlighted the need for a wider class of mechanically flexible transparent conductors. Bending readily encourages further delamination of already weakly adhered zones, thereby rapidly degrading over time and cycle number the sample’s mechanical robustness.[50] CVD synthesis results in the formation of a polycrystalline two-dimensional material with low, yet still unavoidable, vacancies and line defects, both of which likely further form during the transfer process Such defects tend to nucleate additional defects resulting in microcrack formation, between grains where the graphene is otherwise weakly bound to the substrate. Two-dimensional materials, and those with microcorrugations, have an extra degree of freedom in the Z direction allowing for effective lateral stress dissipation Another possible explanation for the superior robustness of graphene in the present mechanical studies is that the strong covalent bonds within the graphitic lattice accommodate significant strain prior to failure.[53] the average ΔR/R0 of UVA and HPL graphene were lower (0.53 and 0.65, respectively) than in the PMMA graphene case (0.71), which are consistent with our earlier bend-angle tests. It is probable that percolative networking effects and associated transport play a central role in the graphene systems ability to resist repeated strain cycles compared to ITO alternatives

■ CONCLUSIONS

Findings

■ REFERENCES