Organic Materials & Devices, Institute of Polymer Materials, Department of Materials Science, University of Erlangen-Nürnberg, Erlangen, Germany.
Langmuir. 2012 Oct 2;28(39):13900-4. doi: 10.1021/la3027978. Epub 2012 Sep 19.
In this work, we compared the kinetics of monolayer self-assembly long-chained carboxylic acids and phosphonic acids on thin aluminum oxide surfaces and investigated their dielectric properties in capacitors and low-voltage organic thin-film transistors. Phosphonic acid anchor groups tend to substitute carboxylic acid molecules on aluminum oxide surfaces and thus allow the formation of mixed or fully exchanged monolayers. With different alkyl chain substituents (n-alkyl or fluorinated alkyl chains), the exchange reaction can be monitored as a function of time by static contact angle measurements. The threshold voltage in α,α'-dihexyl-sexithiophene thin-film transistors composed of such mixed layer dielectrics correlates with the exchange progress and can be tuned from negative to positive values or vice versa depending on the dipole moment of the alkyl chain substituents. The change in the dipole moment with increasing exchange time also shifts the capacitance of these devices. The rate constants for exchange reactions determined by the time-dependent shift of static contact angle, threshold voltage, and capacitance exhibit virtually the same value thus proving the exchange kinetics to be highly controllable. In general, the exchange approach is a powerful tool in interface engineering, displaying a great potential for tailoring of device characteristics.
在这项工作中，我们比较了长链羧酸和膦酸在薄氧化铝表面上的单层自组装动力学，并研究了它们在电容器和低压有机薄膜晶体管中的介电性能。膦酸锚定基团倾向于取代氧化铝表面上的羧酸分子，从而允许形成混合或完全交换的单层。通过不同的烷基链取代基（正烷基或全氟烷基链），可以通过静态接触角测量来监测交换反应随时间的进展。由这种混合层电介质组成的α,α'-二己基-六噻吩薄膜晶体管的阈值电压与交换进展相关，并且可以根据烷基链取代基的偶极矩从负值调至正值或反之亦然。随着交换时间的增加，偶极矩的变化也会改变这些器件的电容。通过静态接触角、阈值电压和电容的时变位移确定的交换反应速率常数实际上具有相同的值，从而证明交换动力学具有高度可控性。一般来说，交换方法是界面工程中的有力工具，在调整器件特性方面显示出巨大的潜力。
