Alternative method for the representation of microstructures in polycrystalline materials
Composite Raman intensity-distribution map on a polycrystalline CuInSe2 thin film. © HZB
EBSD orientation-distribution map from the same identical specimen position.
© HZB
Also Raman microspectroscopy in an optical microscope provides the means to determine local crystal orientations of polycrystalline materials over large sample areas. This method can be used alternatively to electron backscatter diffraction in a scanning electron microscope. It was shown by a team from Helmholtz-Zentrum Berlin and the Federal Institute for Materials Research and Testing (BAM) that both characterization techniques result in similar orientation distribution maps on areas of several hundreds of square micrometers.
Most solid materials are of polycrystalline nature. In which way the individual grains are oriented in the material can be relevant for its functional properties. In order to determine the corresponding orientation distributions on large specimen areas, generally, a scanning electron microscope is employed. The specimen surface needs to be prepared, before it can be probed under vacuum by an electron beam and analyzed using electron backscatter diffraction (EBSD).
It has now been shown by a team at HZB headed by Dr. Daniel Abou-Ras, together with Dr. Thomas Schmid from BAM, that equivalent orientation distribution maps can be obtained also by means of Raman microspectroscopy. This method needs only an optical microscopy setup, no time-consuming specimen preparation, and can also be conducted under ambient conditions.
The scientists used CuInSe2 thin films as a model system for their study. They showed that the experimental Raman intensities correspond well with the theoretical intensities calculated by using the local orientations from the EBSD map. “The sample area was scanned by a laser beam using step sizes of 200 nanometers. For such measurement conditions, the sample environment needs to be controlled carefully and kept stable for several hours,” explains Dr. Abou-Ras.
The application of Raman microspectroscopy for orientation distribution analysis is possible in principle for all polycrystalline materials, whether they are inorganic or organic, as long as they are Raman active.
The report has been published in Scientific Reports:
Orientation-distribution mapping of polycrystalline materials by Raman microspectroscopy, Norbert Schäfer, Sergiu Levcenco, Daniel Abou-Ras,Thomas Schmid, Doi: 10.1038/srep18410
- Perovskite solar cells from Germany are competing with China's PV technology - HZB 2025 Technology Transfer AwardPhotovoltaics is the leading technology in the transition to clean energy. However, traditional silicon-based solar technology has reached its efficiency limit. Therefore, a HZB-team has developed a perovskite-based multi-junction cell architecture. For this, Kevin J. Prince and Siddhartha Garud received the Helmholtz-Zentrum Berlin's (HZB) Technology Transfer Prize of 5,000 euros.
- Novel technique shines light on next-gen nanomaterials: how MXenes truly workResearchers have for the first time measured the true properties of individual MXene flakes — an exciting new nanomaterial with potential for better batteries, flexible electronics, and clean energy devices. By using a novel light-based technique called spectroscopic micro-ellipsometry, they discovered how MXenes behave at the single-flake level, revealing changes in conductivity and optical response that were previously hidden when studying only stacked layers. This breakthrough provides the fundamental knowledge and tools needed to design smarter, more efficient technologies powered by MXenes.
- Shedding light on insulators: how light pulses unfreeze electronsMetal oxides are abundant in nature and central to technologies such as photocatalysis and photovoltaics. Yet, many suffer from poor electrical conduction, caused by strong repulsion between electrons in neighboring metal atoms. Researchers at HZB and partner institutions have shown that light pulses can temporarily weaken these repulsive forces, lowering the energy required for electrons mobility, inducing a metal-like behavior. This discovery offers a new way to manipulate material properties with light, with high potential to more efficient light-based devices.