Sharp J S, Forrest J A
Department of Physics and Guelph-Waterloo Physics Institute, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada, N2L 3G1.
Phys Rev E Stat Nonlin Soft Matter Phys. 2003 Mar;67(3 Pt 1):031805. doi: 10.1103/PhysRevE.67.031805. Epub 2003 Mar 24.
We have performed dielectric loss measurements at 1 kHz on thin films of isotactic poly(methyl methacrylate). A key distinction of our studies is that the samples measured were supported films with one free surface rather than films that have metallic electrodes covering both surfaces. This unique sample geometry allows us to eliminate any effects due to evaporation of metal onto the top film surface and provides a unique opportunity to make direct comparisons between dielectric loss and glass transition measurements. Film thicknesses in the range from 6 microm to 7 nm were prepared on Al coated substrates. The dielectric loss peak and ellipsometric glass transition temperature of all films were measured. The dielectric loss was found to exhibit no discernible film thickness dependence in either the temperature of the maximum loss value or the shape of the loss curve. In contrast, the measured T(g) values were found to decrease with decreasing film thickness with a maximum shift of 10 K for a 7-nm film. Dielectric measurements were also made on Al coated films and these samples also showed no shift in the temperature of the loss peak. Finally, the T(g) measurements were also made on Si substrates. These values exhibited an increasing T(g) value with film thickness with a maximum increase of approximately 15 K being measured for a 7-nm film.
我们对全同立构聚（甲基丙烯酸甲酯）薄膜在1 kHz频率下进行了介电损耗测量。我们研究的一个关键区别在于，所测量的样品是具有一个自由表面的支撑薄膜，而非两面都覆盖有金属电极的薄膜。这种独特的样品几何形状使我们能够消除由于金属蒸发到薄膜顶面而产生的任何影响，并提供了一个在介电损耗和玻璃化转变测量之间进行直接比较的独特机会。在涂覆有铝的基板上制备了厚度范围从6微米到7纳米的薄膜。测量了所有薄膜的介电损耗峰和椭偏玻璃化转变温度。结果发现，介电损耗在最大损耗值的温度或损耗曲线的形状方面均未表现出明显的薄膜厚度依赖性。相比之下，测量得到的T(g)值随薄膜厚度的减小而降低，对于7纳米厚的薄膜，最大偏移为10 K。还对涂覆有铝的薄膜进行了介电测量，这些样品的损耗峰温度也没有偏移。最后，也在硅基板上进行了T(g)测量。这些值随薄膜厚度增加而呈现T(g)值升高的趋势，对于7纳米厚的薄膜，测量到的最大升高约为15 K。
