From synchrotron to home laboratory with a 9 keV high intensity HAXPES-Lab
In the laboratory, led by Professor Atsushi Ogura, the objective is to improve the performance of solar cells and electronics devices based on semiconductor nanotechnology. In October 2018, a significant improvement in material characterization capability was achieved when the Scienta Omicron HAXPES-Lab system was installed. The HAXPES-Lab is a home laboratory-type hard X-ray photoelectron spectroscopy (HAXPES) system with the key components: monochromator, high energy analyzer and a 9 keV X-ray source, the Excillum MetalJet D2+.
The non-destructive technique of HAXPES opens up a window to the bulk, as the technique can characterize the element-specific chemical states sub surface of materials, e.g. at buried interfaces or in the bulk. Previously, 9 keV photoemission had only been possible at synchrotron beamlines but with the introduction of the HAXPES-Lab system experiments in the home laboratory became possible.
“By introducing home-lab HAXPES, continuous measurements for 24 hours a day, 365 days a year became possible. Previously, we were always limited by the available beam time and suffered from long waiting times. But with the HAXPES-Lab we could measure many samples with much faster turnaround from sample preparation, measurement and analysis to refined experiments. This allowed us to significantly accelerate our research and the result was a remarkable improvement in scientific output.”
Professor Atsushi Ogura
The use of buried interfaces instead of surface layers could be a solution for improving the stability, quality and e.g. to push the performance of materials, such as electronic devices. The drawback is that the layer stack becomes more complex, and the interfaces between the layers become very important. For this reason, methods like Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD) are used to evaluate the physical structure of the interface between different materials. However, the interface chemistry affects the device performance and needs to be evaluated as well.
“The HAXPES-Lab provides a compact and high-performance home-lab equipment enabling 24/7 access with results far beyond our expectations.”
To illustrate the performance and capability of HAXPES-Lab, Figure 1 shows the comparison of SPring-8 and home-lab measurement of a SiO2/Si structure. The sample has a 30-nm-thick SiO2 film grown on a Si substrate by thermal oxidation. The peaks in the vicinity of 1839 eV and 1843 eV are attributed to Si-Si and Si-O bonds, respectively. Both measurements in Figure 1 shows a clear signal originating from the Si-Si chemical state even though it is buried under 30 nm of SiO2. Using a standard XPS tool with an Al or Mg source it would have been virtually impossible to detect this Si-Si feature. In addition, it is noted that the results from SPring-8 and HAXPES-Lab are almost identical.
