Institut für Festkörperphysik, Technische Universität Graz, Graz, Austria.
Chemphyschem. 2013 Aug 5;14(11):2554-9. doi: 10.1002/cphc.201300227. Epub 2013 May 27.
The order in molecular monolayers is a crucial aspect for their technological application. However, the preparation of defined monolayers by spin-coating is a challenge, since the involved processes are far from thermodynamic equilibrium. In the work reported herein, the dynamic formation of dioctyl-benzothienobenzothiophene monolayers is explored as a function of temperature by using X-ray scattering techniques and atomic force microscopy. Starting with a disordered monolayer after the spin-coating process, post-deposition self-reassembly at room temperature transforms the initially amorphous layer into a well-ordered bilayer structure with a molecular herringbone packing, whereas at elevated temperature the formation of crystalline islands occurs. At the temperature of the liquid-crystalline crystal-smectic transition, rewetting of the surface follows resulting in a complete homogeneous monolayer. By subsequent controlled cooling to room temperature, cooling-rate-dependent kinetics is observed; at rapid cooling, a stable monolayer is preserved at room temperature, whereas slow cooling causes bilayer structures. Increasing the understanding and control of monolayer formation is of high relevance for achieving ordered functional monolayers with defined two-dimensional packing, for future applications in the field of organic electronics.
分子单层的有序性是其技术应用的关键方面。然而，通过旋涂法制备具有明确结构的单层是一个挑战，因为所涉及的过程远非热力学平衡。在本文所报道的工作中，通过使用 X 射线散射技术和原子力显微镜，研究了二辛基苯并噻吩并苯并噻吩单层在温度下的动态形成过程。从旋涂过程后的无序单层开始，在室温下的沉积后自组装将初始非晶层转变为具有分子人字形堆积的有序双层结构，而在升高的温度下则会形成结晶岛。在向列-近晶相转变的温度下，表面重新润湿，从而形成完全均匀的单层。通过随后的受控冷却至室温，可以观察到冷却速率相关的动力学；在快速冷却时，在室温下可以保持稳定的单层，而缓慢冷却会导致双层结构。增加对单层形成的理解和控制对于实现具有明确二维堆积的有序功能单层具有重要意义，这对于有机电子学领域的未来应用具有重要意义。
