Para-sexiphenyl thin films grown by hot wall epitaxy on KCl(001) substrates

Abstract

Here, we use atomic force microscopy (AFM) to study the morphology and growth kinetics of para-sexiphenyl layers deposited by hot wall epitaxy on crystalline KCl(001) substrates. It is shown that the growth process is quite complex and can be divided preliminarily into two steps. The initial growth stage is characterized by the formation of long needlelike crystallites built of “lying” molecules and oriented mainly into the ⟨110⟩ directions in accordance with the substrate’s fourfold symmetry. If the coverage increases, terraced crystalline mounds composed of monolayers of upright standing molecules start to develop between the needles. The mound formation is due to repeated two-dimensional nucleation of para-sexiphenyl molecules. By means of phase imaging in the AFM tapping mode, it could be further demonstrated that both needlelike crystallites and flat terraced mounds grow directly on the substrate surface, i.e., there is no wetting layer formed during the deposition of para-sexiphenyl on KCl(001).

Temperature dependent growth morphologies of parahexaphenyl on SiO2 supported exfoliated graphene

“…Regular patterns of 6P needles on crystalline substrates have also been found on KCl (100), 6,17 phlogopite and muscovite mica. 1,8,39 However, these substrates are of minor technological relevance compared to graphene which has great potential to serve as mechanically flexible and transparent electrode material in organic electronics.…”

“…6P growth at 280-333 K The 6P films grown at temperatures below 360 K turned out to be homogeneous across the whole graphene flakes and can, therefore, be well characterized by 5 Â 5 lm 2 images. 16,17,33 In the following and throughout this text, islands consisting of upright standing molecules will be termed "islands" and objects composed from flat lying molecules will be termed "needles." 1, a series of AFM topography images showing the 6P film morphologies evolving for substrate temperatures from 280 to 333 K is presented.…”

“…8,9 Controlling the thin film growth is a key feature for successful technological implementation of organic semiconductors. 3,[15][16][17] The use of graphene (Gr) as substrate for organic semiconductors is of special significance because it bears potential to replace the transparent indium tin oxide (ITO) as electrode material in organic optoelectronics. 5,10 The molecular orientation with respect to the substrate surface can be tuned by changing the substrate properties.…”

Self‐organization of Nanostructures in Inorganic and Organic Semiconductor Systems

“…It should be noted here that growth of the same molecule results on a variety of substrates in self-organized nanostructure arrays. On Al(111) 6P forms crystallites that arrange star-like in 6 different directions [35,4] whereas on KCl(001) [36] and TiO 2 (110) [37] needle-like crystallites with lengths of several 100 nm till some lm arrange along the substrates' close-packed directions. For the latter case it could be shown that not only the interplay with the substrate geometry determines pattern symmetry but also the change in growth temperature significantly influences structure, size, and shape of the resulting nanostructures.…”

Nucleation and growth of thin films of rod-like conjugated molecules

“…This is also observed in experiments. When the coexistence of structures formed from flat lying and upright standing molecules is observed, the first ones are often responsible for nucleating the latter [83,84].…”