Nanoimaging of Orientational Defects in Semiconducting Organic Films

Abstract

The development of defect analysis for inorganic semiconductors in the past century paved the way for the success story of today's electronics. By analogy, defect analysis plays a critical role in developing and improving devices based on organic molecular semiconductors. However, because of weak molecular interactions, absent in inorganic semiconductors, device-relevant thin organic films are susceptible to the formation of defects in the molecular orientation, which in turn have a profound impact on the performance in the optoelectronic applications. To address this problem, we broaden the applicability of scattering-type scanning near-field optical microscopy (s-SNOM) and utilize the light-induced anisotropic response of vibrational modes to reveal the defects in molecular orientation. We show that in the case of molecular islands with steep crystal facets only the scattered s-SNOM optical amplitude can be exploited to describe the molecular arrangement reliably, while the phase-based analysis leads to artifacts. The presented s-SNOM analysis of molecular defects can be universally applied to diverse topographies, even at the nanoscale.

Nanoscale Probing of the Supramolecular Assembly in a Two‐Component Gel by Near‐Field Infrared Spectroscopy

“…The interferometric recording of the scattered light provides infrared spectra at a spatial resolution approximately equivalent to that of the tip (20 nm) [21–28] . sSNOM has been used for the analysis of polymeric thin film surfaces, [24,29–35] imaging of cells, [36–40] viruses [41,42] and neurons [43] and the structural elucidation of protein fibrils [44–46] …”

Formation of Anti-Etching Nanopatterns in Field-Emission Scanning Probe Lithography on Calixarene Films

“…To investigate the unexpected negative tone phenomenon after wet development and the origin of patterns’ etching resistance, we employed nano-FTIR to analyze the chemical composition of products after FE-SPL and wet development. Nano-FTIR integrates IR spectroscopy and scattering-type near-field scanning microscopy (s-SNOM), enabling identification of material chemical properties at a sun-ten nanometer length scale. − We first demonstrate that the described nano-FTIR method can be employed to probe the chemical vibrational information of a 10 nm thick 4M1AC6 molecular film. Herein, we compare the near-field nano-FTIR spectra of this film used in the FE-SPL with the nano-FTIR spectra and the far-field HATR-FTIR spectra of a few-of-microns thick film.…”

Liquid Phase Exfoliation of Rubrene Single Crystals into Nanorods and Nanobelts

“…In infrared-scanning near-field optical microscopy (IR-SNOM) the scattered near-field amplitude and phase of light focused on a metal-coated AFM tip are measured. − It offers nanoscale spatial and spectral resolution and enables the assignment of the vibrational modes and molecular orientation of organic molecules in thin films and crystals. − Previously, we used IR-SNOM to investigate orthorhombic rubrene single crystals and to correlate the enhanced signal of certain vibrational modes with the orientation of the rubrene molecules . Here, we apply IR-SNOM to individual rubrene nanorods and nanobelts deposited on gold-coated silicon substrates to gain further information about the degree of order in these nanostructures.…”