Large-Area, Periodic, Hexagonal Wrinkles on Nanocrystalline Graphitic Film

Sinusoidal wrinkles develop in compressively stressed film as a means to release stored elastic energy. Here, a simple way to fabricate large-area, periodic, hexagonal wrinkled pattern on nanocrystalline graphitic films grown on c-plane sapphire (<50 nm thick) by the spontaneous delamination-buckling of the as-grown film during cooling is reported. According to the continuum mechanics calculation, strain-relief pattern adopting the hexagonal wrinkled pattern has a lower elastic energy than that of the telephone cord wrinkle at thickness regime below 50 nm. A high-fidelity transfer method is developed to transfer the hexagonal wrinkled films onto arbitrary substrates. Nanoindentation studies show that hexagonal wrinkle film engineered this way may act as shock absorber. The hexagonal wrinkled carbon film is able to selectively promote the differentiation of human mesenchymal stem cell toward the osteogenic lineage in the absence of osteogenic inducing medium. A unique hexagonal wrinkled pattern is generated on nanocrystalline graphitic films grown on polished c-plane sapphire substrate via a simple delamination-buckling process. The dimensional features of the wrinkles can be manipulated by adjusting the thickness of deposited films. In addition, a high-fidelity dry transfer method for transfer of wrinkled films onto arbitrary substrates is developed for further applications.