Abstract
Understanding nanoscale molecular order within organic electronic materials is a crucial factor in building better organic electronic devices. At present, techniques capable of imaging molecular order within a polymer are limited in resolution, accuracy, and accessibility. In this work, presented are secondary electron (SE) spectroscopy and secondary electron hyperspectral imaging, which make an exciting alternative approach to probing molecular ordering in poly(3‐hexylthiophene) (P3HT) with scanning electron microscope‐enabled resolution. It is demonstrated that the crystalline content of a P3HT film is reflected by its SE energy spectrum, both empirically and through correlation with nano‐Fourier‐transform infrared spectroscopy, an innovative technique for exploring nanoscale chemistry. The origin of SE spectral features is investigated using both experimental and modeling approaches, and it is found that the different electronic properties of amorphous and crystalline P3HT result in SE emission with different energy distributions. This effect is exploited by acquiring hyperspectral SE images of different P3HT films to explore localized molecular orientation. Machine learning techniques are used to accurately identify and map the crystalline content of the film, demonstrating the power of an exciting characterization technique.
Highlights
A growing body of recent work has established the modern field of secondary electron (SE) energy spectroscopy.[1,2,3,4,5] This technique in the scanning electron microscope (SEM) has enabled fresh, exciting insights in to the properties of polymeric, organic, and biological materials by exploiting the relationship between the emitted SE energy distribution and various material properties
The semicrystalline film was processed from highly regioregular P3HT using a high-boiling point solvent and subsequently treated with a thermal anneal
We demonstrated that specific spectral features correlate with crystalline content in the film, through both empirical study of experimental spectra and from a theoretical standpoint with a Monte Carlo modeling technique
Summary
A growing body of recent work has established the modern field of secondary electron (SE) energy spectroscopy.[1,2,3,4,5] This technique in the scanning electron microscope (SEM) has enabled fresh, exciting insights in to the properties of polymeric, organic, and biological materials by exploiting the relationship between the emitted SE energy distribution and various material properties. Delivering fully on the potential of SEHI, as a characterization technique, requires a robust understanding of the nature of SE spectra and the ability to link spectral features with specific sample properties. Developing these links is a complex task. Peaks in the SE spectrum have been linked with the energy levels of conduction band minima in graphite[7,8] as well as the nanoscale bonding structure in organic materials.[9] The effect of sample doping on the spectrum shape is well documented.[10,11] building a deeper understanding of the origin of SE spectral features will unlock new analytical capabilities, for example in using a sample’s SE spectrum to probe and map its electronic or chemical properties directly. We demonstrate SEHI as a robust, analytical microscopy technique that can dramatically expand the capabilities of the modern-day SEM
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