TEM is a versatile tool to study materials and devices down to the atomic scale. Far from simply being a very good microscope, the TEM can be considered as an in-house beam line, where imaging, diffraction, spectroscopy, and many other techniques can be combined to provide a comprehensive view of the sample unrivaled by any other facilities. The goal of the NORTEM infrastructure is to make these techniques available to the Norwegian research community. Below are some highlights from recent years.
Studies of crystal structure
Using the high resolution capabilities of the FEI Titan, atomic scale details of the crystal structure of materials can be studied. Here, the interface between a Zn2GeO4 nanocrystal and the surrounding ZnO is studied, to further understand the how embedded nanostructures can enhance the light harvesting properties of photovoltaic devices.
Image licensed under CC-BY 3.0.
Imaging of defects
The properties of materials can be significantly altered by defects in the perfect crystal lattice. Identifying these and understanding their formation and evolution is of central importance when tailoring materials' properties to the desired performance. In this example, the formation of stacking faults and their interaction with implanted nitrogen in ZnO was studied.
Image ©2019 American Chemical Society. Reproduced with permission.
Monochromated Electron Energy Loss Spectroscopy (EELS) gives us access to 'a synchrotron in the TEM', allowing the unique combination of both high spatial resolution and spectroscopy in the IR to X-ray range. In this example, the Burstein-Moss shift and conduction band plasmons in Ga-doped ZnO were investigated, demonstrating that the charge carrier density in semiconductors can be measured with nanometer resolution.
Image ©2018 American Physical Society. Reproduced with permission.
In catalytic and electrochemical applications, control of the composition and microstructure of the catalysts and electrodes is crucial. Here STEM imaging and chemical analysis by EDS were used to verify the structure and composition of ~20 nm active Ni particles in a protonic membrane reformer for production of high purity hydrogen.
Image ©2017 Springer Nature. Reproduced with permission.
Mapping of fields
In addition to spectroscopy, imaging, and diffraction, several techniques can be used to measure and image intrinsic electric and magnetic fields in the sample. In this work in-line electron holography was performed using the JEOL 2100F to investigate the electrostatic potential across BaZrO3 grain boundaries. These measurements were successfully compared with models taking detailed compositional and structural information as input.
Image ©2019 the PCCP Owner Societies. Reproduced with permission.
Nanoscale chemical states
Using core loss EELS, chemical binding information can be obtained down to the atomic scale. In this example, EELS was used to uncover clustering of nitrogen in a ZnO-GaN alloy, and to identify the covalent N-N bonding characteristic of molecular nitrogen, thereby demonstrating the formation of bubbles of nitrogen gas in the sample.
Image licensed under CC-BY 3.0.