Stranski-Krastanov growth of small molecule crystallites

2 Stranski-Krastanov growth of small molecule crystallites 

During deposition, there will be an optimum substrate temperature (or possibly a series of temperatures as the deposition progresses) for the formation of high quality crystals, exclusion of water, and adjustment of the crystal phase. These parameters will not be exactly the same for each deposition setup, but some t q)ical starting points are presented in Appendix B and in the literature (see, for example, [40] and [65]). Some experimentation is required to determine the optimum thickness, rate, and substrate temperature for a given deposition and material system. 

The deposition rate has a clear effect on device performance, but there is some substantial disagreement in the literature on the optimum rates for each 

An interesting byproduct of Stranski-Krastanov growth is that polycrys-talline oligomeric semiconductors almost universally need to be bottom gated. The top surface is poorly ordered and exhibits performance orders of magnitude worse than the bottom surface. Many amorphous small molecules and most polymers can be operated with a top or bottom gate. 

Solution deposited small molecules experience many of the same organizational issues as soluble polymeric materials. Drying time and environment, interaction with the substrate, and the presence of topography and chemical states on the gate dielectric can all complicate proper crystallization. 

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