Department of Physics, Washington University in St Louis, MO 63130, USA.
Nanotechnology. 2010 Apr 16;21(15):155601. doi: 10.1088/0957-4484/21/15/155601. Epub 2010 Mar 19.
We show here that the morphological pathway of spontaneous dewetting of ultrathin Ag films on SiO2 under nanosecond laser melting is dependent on film thickness. For films with thickness h of 2 nm < or = h < or = 9.5 nm, the morphology during the intermediate stages of dewetting consisted of bicontinuous structures. For films with 11.5 nm < or = h < or = 20 nm, the intermediate stages consisted of regularly sized holes. Measurement of the characteristic length scales for different stages of dewetting as a function of film thickness showed a systematic increase, which is consistent with the spinodal dewetting instability over the entire thickness range investigated. This change in morphology with thickness is consistent with observations made previously for polymer films (Sharma and Khanna 1998 Phys. Rev. Lett. 81 3463-6; Seemann et al 2001 J. Phys.: Condens. Matter 13 4925-38). Based on the behavior of free energy curvature that incorporates intermolecular forces, we have estimated the morphological transition thickness for the intermolecular forces for Ag on SiO2. The theory predictions agree well with observations for Ag. These results show that it is possible to form a variety of complex Ag nanomorphologies in a consistent manner, which could be useful in optical applications of Ag surfaces, such as in surface enhanced Raman sensing.
我们在这里展示了在纳秒激光熔化下，SiO2 上的超薄 Ag 薄膜自发去湿的形态途径取决于薄膜厚度。对于厚度为 2nm<h<9.5nm 的薄膜，去湿的中间阶段的形态由双连续结构组成。对于 11.5nm<h<20nm 的薄膜，中间阶段由规则尺寸的孔组成。对不同去湿阶段的特征长度尺度随薄膜厚度的变化进行测量，结果显示出系统的增加，这与整个研究厚度范围内的旋节线不稳定性一致。这种形态随厚度的变化与以前对聚合物薄膜的观察结果一致（Sharma 和 Khanna 1998 Phys. Rev. Lett. 81 3463-6; Seemann 等人，2001 J. Phys.：Condens. Matter 13 4925-38）。基于包含分子间力的自由能曲率的行为，我们估算了 Ag 在 SiO2 上的分子间力的形态转变厚度。理论预测与 Ag 的观察结果非常吻合。这些结果表明，以一致的方式形成各种复杂的 Ag 纳米形态是可能的，这在 Ag 表面的光学应用中可能是有用的，例如在表面增强拉曼传感中。
