Structural features in amine terminated monolayers on oxide baring substrates – counter anion position and possible chirality

Amine terminated monolayers on oxide baring substrates are widely used for various applications in micro and optoelectronics. In this work we have concentrated on structural surface features which have a major impact either on silicon work function (WF) by using ammoniumpropyl-triethoxysilane chloride surface derivatizing agent, or on ITO surface chirality by using chiral tyrosine terminated triethoxysilane. For the first case, the change obtained in the WF was mainly due to the amine terminated group which changes the surface dipole. Subtle tunability can be obtained by altering the counter anions from chloride to iodide, due to the ionic dipole between the ammonium moiety and the halide counter anions. The change in the WF and the electron affinity were measured by contact potential difference technique and supported theoretically by DFT calculations. Moreover, some light was shed on the structure of the layer and the position of the anion, influencing the ionic dipole created through the layer. Chiral amine monolayers on ITO were obtained by using D-tyrosine terminated triethoxysilanes. The ability of the chiral layer to induce its chirality was tested on a-priori achiral liquid crystals (LC) such as MBBA (methoxybenzylidene butylaniline). It was found that the chiral substrate partially deracemized the adjacent LC. Owing to the now reduced (chiral) symmetry of this substrate, the LC director undergoes a rotation, which was probed optically using the nematic electroclinic effect (ECE) measurements. These results confirmed the chirality induction of a chiral amine terminated monolayer on the LC.