Direct Growth of Highly Conductive Large‐Area Stretchable Graphene.

What is it about?

The direct synthesis of inherently defect-free, large-area graphene on flexible substrates is a key technology for soft electronic devices. In the present work, in situ plasma-assisted thermal chemical vapor deposition is implemented in order to synthesize 4 in. diameter high-quality graphene directly on 10 nm thick Ti-buffered substrates at 100 °C. The in situ synthesized monolayer graphene displays outstanding stretching properties coupled with low sheet resistance. Further improved mechanical and electronic performances are achieved by the in situ multi-stacking of graphene. The four-layered graphene multi-stack is shown to display an ultralow resistance of ≈6 Ω sq−1, which is consistently maintained during the harsh repeat stretching tests and is assisted by self-p-doping under ambient conditions. Graphene-field effect transistors fabricated on polydimethylsiloxane substrates reveal an unprecedented hole mobility of ≈21 000 cm2 V−1 s−1 at a gate voltage of −4 V, irrespective of the channel length, which is consistently maintained during the repeat stretching test of 5000 cycles at 140% parallel strain. The leading edge of soft electronics research is driving toward the realization of large-area and stretchable transparent electrodes and devices that integrate with each other into delicate soft displays, sensors, or energy harvesters.[1-12] In particular, graphene satisfies most of the critical requirements for flexible electrode and device applications and has attracted significant attention.[13-15] However, the high operation temperature of at least 1000 °C required for the large-area growth of graphene by conventional chemical vapor deposition (CVD) process hinders the widespread application of graphene-based electrodes and devices. Moreover, the conventional two-step process consisting of high-temperature CVD-based growth of graphene on metallic substrates and its subsequent transfer onto flexible substrates inevitably generates wrinkles, ripples, and metallic residues that significantly lower the graphene quality.[16-21] Even the most recent and advanced CVD-based graphene growth technique demonstrates that the synthesis of large-area graphene via industrially friendly and versatile CVD is challenging.

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Why is it important?

The present authors have previously proposed a possible transfer-free CVD-based graphene growth technology by combining the direct current sputtering of a Ti-buffer layer onto the substrate with subsequent CVD growth of graphene on the Ti [22]. The results of post-synthesis analysis and density functional theory (DFT) calculation, the strong Ti–C interaction was proven to generate the required carbon seeds on the Ti and to facilitate the thermodynamically driven spontaneous growth of a graphene monolayer at 150 °C.

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