Growth of para-Hexaphenyl Thin Films on Flat, Atomically Clean versus Air-Passivated TiO2(110) Surfaces

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• 作者：Dominik Wrana ; Markus Kratzer ; Konrad Szajna ; Marek Nikiel ; Benedykt R. Jany ; Marcin Korzekwa ; Christian Teichert ; Franciszek Krok
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：July 23, 2015
• 年：2015
• 卷：119
• 期：29
• 页码：17004-17015
• 全文大小：906K
• ISSN：1932-7455

文摘

We report on para-hexaphenyl (6P) ultrathin film growth on freshly prepared and air-passivated atomically flat rutile titanium dioxide single-crystal (110) surfaces. The surface morphology of the developed structures has been investigated in situ and ex situ by means of various scanning probe techniques and electron microscopy. In situ 6P deposition results in the formation of a wetting layer of lying molecules coexisting with bunches of tens of micrometers long needles oriented along the TiO₂[11虆0] surface direction. The observed bunching of the 3鈥? nm high needles is explained in terms of anisotropic diffusion paths along and perpendicular to the needles. Air exposure of the as-prepared films induces the formation of small features at the cost of the 6P wetting layer, whereas the needles stay unchanged. In contrast, 6P deposition on already air-passivated TiO₂(110) yields the formation of dendritic islands, composed of roughly upright-standing molecules. No 6P wetting layer forms on the air-passivated surface. In addition to air exposure, we have checked the impact of surface modification via ion beam bombardment. Growth of 6P on gradient ion-beam-modified titanium dioxide substrates kept at either room or elevated temperature reveals that a slight surface roughening is sufficient to switch the film from lying molecular orientation to upright-standing orientation. However, surface stoichiometry severely influences film properties like size, density, and shape of the 6P islands.