Reversibly Thermoswitchable Two-Dimensional Periodic Gratings Prepared from Tethered Poly(N-isopropylacrylamide) on Silicon Surfaces

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• 作者：Jem-Kun Chen ; Jing-Hong Wang ; Chih-Chia Cheng ; Jia-Yaw Chang
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2013
• 出版时间：April 24, 2013
• 年：2013
• 卷：5
• 期：8
• 页码：2959-2966
• 全文大小：497K
• 年卷期：v.5,no.8(April 24, 2013)
• ISSN：1944-8252

文摘

In this study we used atom transfer radical polymerization to graft poly(N-isopropylacrylamide) (PNIPAAm) onto flat Si substrates. We then applied very large-scale integration and reactive ion etching sequentially to generate 200-nm-scale hole arrays of tethered PNIPAAm as two-dimensional periodic concave gratings (2DPCGs) on the Si surfaces. The hole array structures of tethered PNIPAAm could be created and erased reversibly at 25 and 40 掳C, respectively, leading to significant changes in the effective refractive index (n_eff). The values of n_eff of the 2DPCGs were related to the depth of their holes generated after etching for various times, resulting in a color change from blue to red that could be observed by the naked eye at incident angles of 10鈥?0掳. Moreover, we used effective-medium theory to calculate the filling factors of air inside the 2DPCGs to verify the structural changes of the tethered PNIPAAm. Such designed 2DPCGs of thermorespective hydrogel films have potential applications in temperature-responsive optical devices [e.g., as antireflection structured surfaces (ARSs)] that operate at both visible and near-infrared wavelengths.

Keywords:

PNIPAAm brush; two-dimensional periodic grating; refractive index