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Controllable Wrinkle Configurations by Soft Micro-Patterns to Enhance the Stretchability of Si Ribbons Yin Huang and Xue Feng* October 21, 2014 *Email: fengxue@tsinghua.edu.cn Background Stretchable Silicon Ribbons (D.Y. Khang, science ,et al., 2006) (Sun, et al., Nature, 2006) (c)Release prestrain (a) periodic activated patterns by UV light (b)Transfer printing Si ribbons (X. Feng, et al., ACS Nano, 2011) Wavy PZT nanoribbons Chemically controlled wrinkles Fabrication of wavy Si ribbons on a micro-patterned substrate Fabrication Process Silicon mold with rectangular punches using RIE technology; PDMS（10: 1）with rectangular punches of Wp and Wd 30-200 m and thickness 10 m; Si ribbons：Fabricated on SOI wafers，with widths 50m and thickness 200nm. (Huang Y., et al., Soft Matter., 2014) ‘Popup’ means the wrinkles are only in contact with the tops of the punches; ‘pop-down’ means the wrinkles are in contact with the bottoms of the punches. Experimental Results (Popup wrinkles) Uniform, periodic ‘pop-up’ wrinkles with almost the same wavelengths and amplitudes; The wavelengths are defined by the period of the punches (the sum of the width and spacing ); The punches for ‘pop-up’ wrinkles have larger widths and smaller spacings. Fabrication of wavy Si ribbons on a micro-patterned substrate Fabrication of wavy Si ribbons on a micro-patterned substrate Experimental Results (Pop-down wrinkles) Uniform, periodic ‘pop-up’ wrinkles with almost the same wavelengths and amplitudes; The wavelengths are defined by the period of the punches (the sum of the width and spacing ); The punches for ‘pop-down’ wrinkles have smaller widths and larger spacings. The configuration is totally determined by the geometry of the micro-patterns. Mechanical models Mechanical models for two buckling modes Silicon ribbon is modeled as an elastic nonlinear von Karman beam. （a）The ribbon thickness is much smaller than any other characteristic length； （b）The strain in Si ribbon is negligibly small