Efremov Mikhail Yu
Materials Science Center, University of Wisconsin - Madison, Madison, Wisconsin 53706, USA.
Rev Sci Instrum. 2014 Dec;85(12):123901. doi: 10.1063/1.4902565.
Ellipsometry is one of the standard methods for observation of glass transition in thin polymer films. This work proposes that sensitivity of the method to surface morphology can complicate manifestation of the transition in a few nm thick samples. Two possible mechanisms of free surface roughening in the vicinity of glass transition are discussed: roughening due to lateral heterogeneity and roughening associated with thermal capillary waves. Both mechanisms imply an onset of surface roughness in the glass transition temperature range, which affects the experimental data in a way that shifts apparent glass transition temperature. Effective medium approximation models are used to introduce surface roughness into optical calculations. The results of the optical modeling for a 5 nm thick polystyrene film on silicon are presented.
椭圆偏振测量法是观察聚合物薄膜玻璃化转变的标准方法之一。这项工作表明，该方法对表面形态的敏感性会使几纳米厚样品中转变的表现变得复杂。讨论了玻璃化转变附近自由表面粗糙度增加的两种可能机制：由于横向不均匀性导致的粗糙度增加以及与热毛细波相关的粗糙度增加。这两种机制都意味着在玻璃化转变温度范围内表面粗糙度开始增加，这会以某种方式影响实验数据，从而使表观玻璃化转变温度发生偏移。使用有效介质近似模型将表面粗糙度引入光学计算中。给出了硅上5纳米厚聚苯乙烯薄膜的光学建模结果。
