Anisotropic Wrinkles of Graphene on Metal and Semiconductor Surfaces
Kwok, Kam Sang
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Graphene is a single layer of carbon with exceptional physical properties and chemical stability. The electronic band structure and chemical reactivity of graphene can be modified and enhanced by distorting the carbon-carbon bonds. Strained graphene exhibits different electrical, chemical and wetting properties from that flat graphene. However, controlling anisotropic wrinkles of graphene still remains challenging. Here we propose new methods to create tensile strain in graphene on metal and semiconductor surfaces. Nanoscale and random graphene wrinkles were generated by the mismatch of thermal expansions of a bilayer. The bilayer comprised of aluminum (Al) or silicon (Si) and polymethyl methacrylate (PMMA) film, and graphene was then transferred on top of the bilayer. Random wrinkles were formed by heating the composite above the glass transition temperature of PMMA, due to the coefficient of thermal expansion of PMMA was greater than the Al and Si. In the end, strain in graphene was confirmed and quantified by the Raman spectra. To control anisotropic wrinkles of graphene, two techniques were explored. The first technique applied polydimethylsiloxane (PDMS) molds on the surface of the composite during the heating process. The second patterned the Si (by photolithography and plasma etching prior transferring graphene. Both techniques generated few microns of wrinkles. We anticipated that both techniques would modify the chemical and electrical properties of graphene selectively. lectively.