Use of a hexapod in diffraction measurements of substrate-supported crystals of organic semiconductors

Lin Yang,Hoichang Yang

doi:10.1107/s0909049509037911

Abstract

Thin films of organic semiconductor prepared on substrates generally contain crystals that have one common crystal plane parallel to the substrate but random in-plane orientations. In diffraction measurements of these structures, it is often required to anchor the X-ray beam on a fixed spot on the sample, such as an optically visible crystallite or island. Here, a hexapod is used in place of a traditional multi-circle diffractometer to perform area-detector-based diffraction measurements on an actual device that contains 6,13-bis(triisopropyl-silyethynyl)-pentacene (TIPS-pentacene) crystals. The hexapod allows for sample rotations about any user-defined rotation center. Two types of complex sample motions have been programmed to characterize the structure of the TIPS-pentacene crystal: an in-plane powder average has been performed at a fixed grazing-incident angle to determine the lattice parameters of the crystal; then the in-plane component of the scattering vector was continuously rotated in transmission geometry to determine the local crystal orientation.

Highlights

There has been a growing interest in developing organic semiconductor materials for applications such as organic fieldeffect transistors (OFETs), organic light-emitting diodes and organic photovoltaic devices (Dimitrakopoulos & Malenfant, 2002)
An important step in the development of these materials is to determine the crystalline structure of the material within the device and understand how it is correlated to the device performance. Since these devices are often fabricated on a flat substrate, the crystal structure can be characterized by grazing-incidence X-ray diffraction (GID) measurements
GID measurements that utilized area detectors have utilized X-ray beams that are focused in the direction of the sample normal to reduce the beam footprint on the sample (Yang, 2005), so as to achieve angular resolution comparable to those in point detector-based measurements

Summary

Introduction

There has been a growing interest in developing organic semiconductor materials for applications such as organic fieldeffect transistors (OFETs), organic light-emitting diodes and organic photovoltaic devices (Dimitrakopoulos & Malenfant, 2002). An important step in the development of these materials is to determine the crystalline structure of the material within the device and understand how it is correlated to the device performance. Since these devices are often fabricated on a flat substrate, the crystal structure can be characterized by grazing-incidence X-ray diffraction (GID) measurements. While GID measurements on substrate-supported organic semiconductors have been traditionally carried out using point detectors GID measurements that utilized area detectors have utilized X-ray beams that are focused in the direction of the sample normal to reduce the beam footprint on the sample (Yang, 2005), so as to achieve angular resolution comparable to those in point detector-based measurements

Methods

Results

Conclusion