Thin-Film Morphology

DeLongchamp, D. A. Fischer, E. K. Lin, M. Heeney, I. McCulloch and M. F. Toney, Significant dependence of morphology and charge carrier mobility on substrate surface chemistry in high performance polythiophene semiconductor films. Appl. Rhys. Lett., 90, 062117 (2007). Copyright 2007, American Institute of Physics 

Alternating copolymers of thieno[2,3-6]thiophene and 4,4 -dialkyl-2,2 -bithiophene, referred to as pBTCT [poly(Bithiophene-crossconjugated thiophene)] were also designed and synthesized (Table 17.1,8) [52]. The most stable backbone conformation for these polymers requires that, where possible, the sulfurs in adjacent backbone units arrange in an anti configuration in order to maximize the spatial separation 

Polymer Comonomer Comonomer HOMO energy level Saturated charge carrier mobility (cm s )  

A regioregular homopolymer of 3-nonylthieno[3,2-Z ]thiophene was also prepared (Table 17.1, 10) however the molecular weight was low and no evidence of thermal transitions was observed by DSC [51]. Charge transport characteristics were not reported. The homopolymer of 3,6-dimethoxythieno[3,2-f ]thiophene [53] and copolymers of 3,4-dialkoxythieno[2,3-f ]thiophene [54] have recently been reported as a possible alternative to the conducting polymer ethylenedioxythiophene (PEDOT). Co-polymers of thieno[3,2-Z ]thiophene [55-57] and thieno[2,3-f ]thiophene [58] with 9,9-dialkyl fluorene have also been reported for both transistor and OLED applications. In the case of the thieno[3,2-b]thiophene copolymer, the polymer exhibited thermotropic liquid crystalline behavior with a nematic phase at high temperature [59]. p-Type field effect mobilities in transistor devices were on the order of 1 x 10 cm V s . Although the value is on the low side of acceptable performance, a comparison to the well-studied 

6-11) can be obtained varying experimental parameters. Such a complexity arises 

6 Electronic Structure and Energy Transfer in Solid a-Sexithienyl 

The early stages of growth involve nucleation and formation of islands (Fig. 

Fi urc 6-12. Model for the calculation of the van der Waals potential experienced by a single Tg molecule on a Tg ordered surface. Each molecule is modeled as a chain of 6 polarizable spherical units, and the surface as 8-layer slab, each layer containing 266 molecules (only part of the cluster is shown). The model is based on X-ray diffraction and dielectric constant experimental data. The two configurations used for evaluating the corrugation of the surface potential are shown. Adapted with permission from Ref. [48]. 

---

Giasson S, Israelaohvili J N and Yoshizawa H 1997 Thin film morphology and tribology study of mayonnaise J. Food Sc/. 62 640-4... 

Choi, S. Y. Mamak, M. Coombs, N. Chopra, N. Ozin, G. A. 2004. Thermally stable two-dimensional hexagonal mesoporous nanocrystalline anatase, meso-nc-Ti02 Bulk and crack-free thin film morphologies. Adv. Fund. Mater. 14 335-344. 

Fig. 5 Schematic cross-sections of thin film morphologies of the topographic pattern grown by a graphoepitaxy method. A micropattern with different lamellar domain orientation is shown, a Surface-parallel lamellae, typical of film thickness t greater than the natural equilibrium period Lq. b Surface-perpendicular lamellae, typical of film thickness t less than L0. (adapted from [41])...

An alternative route to prepare well-defined block copolymers is first to prepare the homopolymers with functional groups and then to connect them by noncovalent interactions [92-99], A systematic 4x4 library of block copolymers based on PSt and PEG connected by an asymmetrical octahedral (itXterpyridine) ruthenium complex at the block junction was reported [78], Moreover, the thin film morphology of this library was investigated. 

Fig. 37. Theoretical predictions for thin film morphology of a phase-separating polymer mixture. Case I yA where yA and yB are the surface tensions of components A and B, respectively, and yAB is the interfacial tension. Case II yA

Fig. 26 Snapshots of DDFT calculations, modeling a thin supported film of A3B12A3 cylinder-forming block copolymer in a 128 x 32 x 26 bit volume. Crops of the middle layer, visualizing the reorientation of cylinders via the transient PL phase are shown after (a) 56,000, (b) 57,200, (c) 58,400, and (d) 59,600 time steps. The thin film morphology is shown by the isodensity surface of A component for a threshold value of 6a = 0.33. Reprinted from [111], with permission. Copyright 2006 American Chemical Society...

In a large part of what we have discussed above, we considered binary polymer mixtures. However, the situation is somewhat different, if instead of polymer blends, thin films of block copolymers are investigated. Due to the molecular connectivity of the different blocks, the inherent length scale is now determined by the size of the molecules. Early experiments focussed on the thin film morphology in symmetric diblock copolymers, where surface interactions tend to orient the block copolymer lamellae parallel to the boundary surfaces. In contrast to most bulk specimens, the planar interfaces lead to the formation... 

Messier R, Yehoda J E (1985) Geometry of thin-film morphology. J Appl Phys 58 3739-3746... 

Figure 16-37. Top normalized absorption (left) and emission (middle) spectra and PL-decay curves (right) of Ooct-OPV5-CN" in (A) solution, (B) as-deposited film, (C) annealed film (160 °C, 5 min), and (D) single crystal. Bottom polarized-light micrographs of the two thin-film morphologies scale bar 100 pm.

Figure 16-41. Electrical characteristics for single-layer lTO/Ooct-OPV5/Al devices with an as-deposited (O) or annealed (120 C, 5 min active layer. Inset luminance as a function of cell current for both thin-film morphologies.

Fig. 13 SEM images of BC 16 and BC 30. a,b Surface of bulk samples after solvent vapour annealing (SVA). c,d Thin film morphologies after spin coating from chloroform followed by SVA. e,f Thin film morphologies after spin coating from chlorobenzene. Bright domains are ascribed to PPerAcr and dark domains to P3HT. Scale bar is 200 nm in all pictures...

Lim, E. et al., Thin-film morphologies and solution-processable field-effect transistor... 

Abstract We review thin-film morphologies of hybrid liquid-crystalline/amorphous block copolymers. The microphase separation of the blocks and the smectic hquid crystalline ordering within one of the blocks are treated systematically in terms of the interaction parameters. The competition of the tandem interactions in terms of length scales and of surface anchoring can be used advantageously to control the orientation of block interfaces for nanopatterning. 

Muller-Buschbaum, P., Bauer, E., Wimnicke, O., Stamm, M. The control of thin film morphology by the interplay of dewetting, phase separation and microphase separation. J. Phys. Condensed Matter 17(9), S363-S386 (2005)... 

---