Polarization Raman Imaging of Organic Monolayer Islands for Crystal Orientation Analysis.

Toki Moriyama,Masatoshi Kitamura,Takayuki Umakoshi,Prabhat Verma,Yoshiaki Hattori,Koki Taguchi

doi:10.1021/acsomega.0c06313

Toki Moriyama, Masatoshi Kitamura + Show 4 more

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https://doi.org/10.1021/acsomega.0c06313

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Abstract

An organic semiconductor film made of diphenyl derivative dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DPh-DNTT) has high carrier mobility. However, this mobility may be greatly affected by the crystal orientation of the DPh-DNTT’s first layer. Polarization Raman microscopy is widely used to quantitatively analyze the molecular orientation, and thus holds great potential as a powerful tool to investigate the crystal orientation of monolayer DPh-DNTT with high spatial resolution. In this study, we demonstrate polarization Raman imaging of monolayer DPh-DNTT islands for crystal orientation analysis. We found that the DPh-DNTT sample indicated a strong dependence of the Raman intensity on the incident polarization direction. Based on the polarization dependence, we developed an analytical method of determining the crystal orientation of the monolayer DPh-DNTT islands and experimentally confirmed that our technique was highly effective at imaging the islands’ crystal orientation with a spatial resolution of a few hundred nanometers.

Highlights

Thin-film organic semiconductors have been widely studied for their high applicability originating from their lightweight, flexibility, and low processing cost
With the advancement of organic electronics, the development of organic semiconducting materials has garnered significant attention, among which dinaphtho[2,3-b:2′,3′-f ]thieno[3,2-b]thiophene (DNTT) is one of the most promising because of its high stability in air conditions and high carrier mobility.[4−6] In DNTT-based Organic field-effect transistors (OFETs), a thin DNTT film as a channel layer is usually deposited on a substrate with a gate insulator via vacuum evaporation, and carrier transport occurs within a few nanometers of the film from the film/gate interface.[7]
We fabricated the monolayer DPh-DNTT islands in two different shapes, i.e., round and cruciform, which were controlled by the substrate temperature during the deposition as well as prior substrate treatments

Summary

Introduction

Thin-film organic semiconductors have been widely studied for their high applicability originating from their lightweight, flexibility, and low processing cost. To investigate the crystal orientation of thin films, X-ray diffraction[14−20] and low-energy electron diffraction[21−23] are the common techniques. They usually offer spatially averaged information, making it difficult to understand the spatial variation of the crystal orientation

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