Group of Nanomaterials and Microsystems, Physics Department, Universitat Autònoma de Barcelona, Barcelona, 08193 - Bellaterra, Spain.
Phys Chem Chem Phys. 2018 Dec 5;20(47):29989-29995. doi: 10.1039/c8cp06264a.
Physical vapour deposition has emerged as the technique to obtain glasses of unbeatable stability. However, vapour deposited glasses exhibit a different transformation mechanism to ordinary glasses produced from liquid. Vapour deposited glasses of different thermodynamic stability, from ultrastable to those similar to ordinary glasses, transform into the liquid state via front propagation starting at the most mobile surfaces/interfaces, at least for the first stages of the transformation, eventually dynamiting the high thermal stability achieved for some of these glasses. A previous study showed that it was possible to avoid this transformation front by capping the films with a higher Tg material. We show here fast calorimetry measurements on TPD and IMC vapour deposited glasses capped respectively with TCTA and TPD. This capped configuration is very effective in suppressing the heterogeneous transformation of the stable glasses into the supercooled liquid and shifts the devitrification temperature to much higher values, where the bulk homogeneous mechanism becomes active. This approach may be useful to further study the bulk glass transition in thin films.
物理气相沉积已成为获得稳定性无与伦比的玻璃的技术。然而，气相沉积玻璃表现出与从液体中生产的普通玻璃不同的转变机制。具有不同热力学稳定性的气相沉积玻璃，从超稳定到类似于普通玻璃的玻璃，通过从最易移动的表面/界面开始的前沿传播转变为液态，至少在转变的最初阶段是如此，最终会破坏这些玻璃中一些玻璃所达到的高热稳定性。先前的研究表明，通过用 Tg 更高的材料对薄膜进行封顶，可以避免这种转变前沿。我们在这里展示了对分别用 TCTA 和 TPD 封顶的 TPD 和 IMC 气相沉积玻璃的快速量热法测量。这种封顶结构在抑制稳定玻璃向过冷液体的非均相转变方面非常有效，并将析晶温度提高到更高的值，在该值下，体相均匀机制变得活跃。这种方法可能有助于进一步研究薄膜中的体玻璃转变。
