Kadashchuk A, Schols S, Heremans P, Skryshevski Yu, Piryatinski Yu, Beinik I, Teichert C, Hernandez-Sosa G, Sitter H, Andreev A, Frank P, Winkler A
IMEC v.z.w., SOLO-PME, Kapeldreef 75, B-3001 Leuven, Belgium.
J Chem Phys. 2009 Feb 28;130(8):084901. doi: 10.1063/1.3073883.
A comparative study of steady-state and time-resolved photoluminescence of para-sexiphenyl (PSP) films grown by organic molecular beam epitaxy (OMBE) and hot wall epitaxy (HWE) under comparable conditions is presented. Using different template substrates [mica(001) and KCl(001) surfaces] as well as different OMBE growth conditions has enabled us to vary greatly the morphology of the PSP crystallites while keeping their chemical structure virtually untouched. We prove that the broad redshifted emission band has a structure-related origin rather than being due to monomolecular oxidative defects. We conclude that the growth conditions and type of template substrate impacts substantially on the film morphology (measured by atomic force microscopy) and emission properties of the PSP films. The relative intensity of the defect emission band observed in the delayed spectra was found to correlate with the structural quality of PSP crystallites. In particular, the defect emission has been found to be drastically suppressed when (i) a KCl template substrate was used instead of mica in HWE-grown films, and (ii) in the OMBE-grown films dominated by growth mounds composed of upright standing molecules as opposed to the films consisting of crystallites formed by molecules lying parallel to the substrate.
本文展示了在可比条件下，对通过有机分子束外延（OMBE）和热壁外延（HWE）生长的对六苯基（PSP）薄膜的稳态和时间分辨光致发光进行的比较研究。使用不同的模板衬底（云母(001)和KCl(001)表面）以及不同的OMBE生长条件，使我们能够在基本保持其化学结构不变的情况下，极大地改变PSP微晶的形态。我们证明，宽的红移发射带起源于与结构相关的因素，而非单分子氧化缺陷。我们得出结论，生长条件和模板衬底的类型对PSP薄膜的形态（通过原子力显微镜测量）和发射特性有重大影响。在延迟光谱中观察到的缺陷发射带的相对强度与PSP微晶的结构质量相关。特别地，已发现当（i）在HWE生长的薄膜中使用KCl模板衬底而非云母，以及（ii）在由直立分子组成的生长丘主导的OMBE生长薄膜中，与由平行于衬底的分子形成的微晶组成的薄膜相比，缺陷发射被显著抑制。
