Deposition of indigo thin films by Langmuir-Schaefer technique

Abstract

The main purpose of this thesis is to explore an opportunity to create a conductive thin film on the substrate for organic semiconductors with non-amphiphilic molecules of indigo by Langmuir-Schaefer deposition.

The hypothesis of this study was that high surface pressure of a Langmuir film of indigo leaded to an ordered Langmuir-Schaefer film. To do the experiment, Indigo powders were dissolved in a chloroform solvent and stirred at room temperature. The substrates of glass and SiO$_2$ for deposition were silanized to imitate a dielectric layer between a gate and a semiconducting film. After Langmuir-Schaefer deposition, the samples were mainly characterized by ultraviolet–visible spectroscopy (UV-Vis) and atomic force microscopy (AFM).

In UV-Vis characterization, the max absorption peak of the indigo film on the glass substrate was red-shifted to 670 nm from 600 nm of indigo solution due to the hydrogen bond between indigo molecules. The max absorption peak of an indigo film was red-shifted as decreasing surface pressure of Langmuir film and/or the number of deposition cycles. The AFM characterization revealed that the thickness of indigo thin film was around 5nm. It was also found that aggregates of indigo covered the surfaces of the samples and calculated root-mean-square surface roughness lay in between 2.6 to 18 nm.

In sum, this study showed that Langmuir-Schaefer deposition succeeded in creating an indigo thin film, and low surface pressure of a Langmuir film consisting of non-amphiphilic molecules of indigo has a positive impact to have an ordered Langmuir-Schaefer film.