Department of Experimental Physics, Institute for Physics and Astronomy, University of Potsdam, Karl-Liebknecht Strasse 24/25, 14476 Potsdam, Germany.
ACS Appl Mater Interfaces. 2013 Aug 28;5(16):7743-7. doi: 10.1021/am400682w. Epub 2013 Aug 13.
The interface between thin films of metal and polymer materials play a significant role in modern flexible microelectronics viz., metal contacts on polymer substrates, printed electronics and prosthetic devices. The major emphasis in metal-polymer interface is on studying how the externally applied stress in the polymer substrate leads to the deformation and cracks in metal film and vice versa. Usually, the deformation process involves strains varying over large lateral dimensions because of excessive stress at local imperfections. Here we show that the seemingly random phenomena at macroscopic scales can be rendered rather controllable at submicrometer length scales. Recently, we have created a metal-polymer interface system with strains varying over periods of several hundred nanometers. This was achieved by exploiting the formation of surface relief grating (SRG) within the azobenzene containing photosensitive polymer film upon irradiation with light interference pattern. Up to a thickness of 60 nm, the adsorbed metal film adapts neatly to the forming relief, until it ultimately ruptures into an array of stripes by formation of highly regular and uniform cracks along the maxima and minima of the polymer topography. This surprising phenomenon has far-reaching implications. This is the first time a direct probe is available to estimate the forces emerging in SRG formation in glassy polymers. Furthermore, crack formation in thin metal films can be studied literally in slow motion, which could lead to substantial improvements in the design process of flexible electronics. Finally, cracks are produced uniformly and at high density, contrary to common sense. This could offer new strategies for precise nanofabrication procedures mechanical in character.
金属薄膜与聚合物材料之间的界面在现代柔性微电子学中起着重要的作用，例如聚合物衬底上的金属接触、印刷电子和假肢设备。金属-聚合物界面的主要重点是研究聚合物衬底上施加的外部应力如何导致金属薄膜的变形和裂纹，反之亦然。通常，由于局部缺陷处的应力过大，变形过程涉及到很大的横向尺寸变化的应变。在这里，我们表明在宏观尺度上看似随机的现象可以在亚微米长度尺度上变得相当可控。最近，我们通过利用含有偶氮苯的光敏聚合物膜在光干涉图案照射下形成表面浮雕光栅 (SRG) ，创建了一个应变在几百纳米周期变化的金属-聚合物界面系统。在吸附金属膜的厚度达到 60nm 之前，它可以很好地适应形成的浮雕，直到它最终通过在聚合物形貌的最大值和最小值处形成高度规则和均匀的裂纹而破裂成一系列条纹。这一惊人的现象具有深远的意义。这是第一次可以直接探测到玻璃状聚合物中 SRG 形成产生的力。此外，在薄金属薄膜中可以进行裂纹形成的慢动作研究，这可能会极大地改进柔性电子产品的设计过程。最后，与常识相反，裂纹以均匀和高密度的方式产生。这可能为具有机械特性的精确纳米制造工艺提供新的策略。
