Scherwitzl Boris, Resel Roland, Winkler Adolf
Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria.
J Chem Phys. 2014 May 14;140(18):184705. doi: 10.1063/1.4875096.
Organic dyes have recently been discovered as promising semiconducting materials, attributable to the formation of hydrogen bonds. In this work, the adsorption and desorption behavior, as well as thin film growth was studied in detail for indigo molecules on silicon dioxide with different substrate treatments. The material was evaporated onto the substrate by means of physical vapor deposition under ultra-high vacuum conditions and was subsequently studied by Thermal Desorption Spectroscopy (TDS), Auger Electron Spectroscopy, X-Ray Diffraction, and Atomic Force Microscopy. TDS revealed initially adsorbed molecules to be strongly bonded on a sputter cleaned surface. After further deposition a formation of dimers is suggested, which de-stabilizes the bonding mechanism to the substrate and leads to a weakly bonded adsorbate. The dimers are highly mobile on the surface until they get incorporated into energetically favourable three-dimensional islands in a dewetting process. The stronger bonding of molecules within those islands could be shown by a higher desorption temperature. On a carbon contaminated surface no strongly bonded molecules appeared initially, weakly bonded monomers rather rearrange into islands at a surface coverage that is equivalent to one third of a monolayer of flat-lying molecules. The sticking coefficient was found to be unity on both substrates. The desorption energies from carbon covered silicon dioxide calculated to 1.67 ± 0.05 eV for multilayer desorption from the islands and 0.84 ± 0.05 eV for monolayer desorption. Corresponding values for desorption from a sputter cleaned surface are 1.53 ± 0.05 eV for multilayer and 0.83 ± 0.05 eV for monolayer desorption.
有机染料最近被发现是很有前景的半导体材料，这归因于氢键的形成。在这项工作中，详细研究了经不同衬底处理的二氧化硅上靛蓝分子的吸附和解吸行为以及薄膜生长情况。该材料在超高真空条件下通过物理气相沉积蒸发到衬底上，随后通过热脱附光谱法（TDS）、俄歇电子能谱、X射线衍射和原子力显微镜进行研究。TDS显示，最初吸附的分子在溅射清洁的表面上牢固结合。进一步沉积后，表明形成了二聚体，这使与衬底的键合机制不稳定，并导致吸附质的弱键合。二聚体在表面上具有很高的迁移率，直到它们在去湿过程中融入能量有利的三维岛中。这些岛中分子更强的键合可以通过更高的脱附温度来表明。在受碳污染的表面上，最初没有出现强键合的分子，弱键合的单体而是在表面覆盖率相当于平躺分子单层的三分之一时重新排列成岛。发现两种衬底上的 sticking 系数均为 1。从碳覆盖的二氧化硅上解吸的能量，对于从岛中多层解吸计算为 1.67±0.05 eV，对于单层解吸为 0.84±0.05 eV。从溅射清洁表面解吸的相应值，多层解吸为 1.53±0.05 eV，单层解吸为 0.83±0.05 eV。
