Article

Impact of PHI Auger instruments on scientific discovery

The cornerstone of scientific progress, comprehension, and communication lies in high-quality research publications. In this review, we examine the role of the Physical Electronics Auger Electron Spectroscopy (AES) instrument in facilitating scientific advancements in 2022.

Over 800 scholar publications, including peer-reviewed articles and book chapters, have been published in 2022 using PHI AES instruments, many of which were published in high-impact journals.

PHI AES instruments were used to study a large range of materials for applications of high technological and research importance – high temperature anti-corrosion coatings¹, carbide-free steels², structural steel^3-4, lunar geology⁵, area selective ALD⁶, environmental remediation⁷, and fuel cells⁸.

One paper published in the last year of impressive scientific merit utilized a PHI AES instrument to study proton exchange membrane (PEM) fuel cells⁸. The study, published in Energy Conversion and Management by researchers at KTH Royal Institute of Technology and Sandvik Materials Technology, shows how these fuel cells offer a promising supplement to battery electric vehicles in their crucial replacement of the internal combustion engine. Improvement to bipolar plates (BPPs) within PEM fuel cells could reduce cost and increase power density.

AES was used to better understand the dissolution process leading to corrosion of the BPPs.  Figure 1 shows SEM images, AES spectra and AES depth profiles of the BPPs surfaces at end of life. Compared to the pristine plate, the anode under H₂ starvation conditions shows an absence of Fe and Ni in the carbon coated area as seen in the orange trace of the survey spectrum (Figure 1d, middle, orange trace). Additionally, the sputter depth profile depicted in Figure 1d (right) reveals a constant Cr content (represented by the blue trace), whereas the profile of the pristine plate (Figure 1a, right) displays a decreased Cr content in the surface proximity area. This observation suggests that the staining has dissolved until a stable Cr concentration has been achieved.

Figure 1: Surface analysis (SEM [left], AES [middle], and AES sputter depth profiling [right]) of stains and the surrounding carbon-coated area on C-coated 316L bipolar plates. (a) Pristine plate. (d) Anode plate (carbon-coated 316L) in the presence of hydrogen starvation.

AES played a critical role in understanding the corrosion mechanism of these BPPs. The high spatial resolution (<5 nm on modern systems) imaging combined with elemental quantification and precise depth profiling enable these corrosion mechanism studies which contribute to the development of a highly stable alternative to the fossil fuel powered internal combustion engine.

Another esteemed paper published in 2022 in Chemistry of Materials by Yarbrough and coworkers⁶ at Stanford utilized a PHI AES instrument to study area selective atomic layer deposition (AS-ALD), a way of manufacturing thin films on the nanoscale with angstrom level control of thickness. In this work, AES was used to determine the selectivity of the ALD process.

Figure 2: (a) SEM image of copper/SiO2 patterned substrate before Al ALD. (b) AES elemental mapping of Al on the copper/SiO2 pattern after 30 cycles of Al ALD. (C) Elemental linescans of copper/SiO2 pattern by AES after 30 cycles of Al ALD. Linescans are offset for ease of viewing.

Figure 2 shows the results of AES analysis of the AS-ALD substrate. Figure 2b shows an AES elemental map of Al showing deposition only in the selected areas, and a corresponding lack of Al in the non-deposition areas. The line scan extracted from across this area (Figure 2c) further demonstrates successful selectivity- high Al and Cu intensity regions correspond to low Si and vice versa. The high spatial resolution imaging capabilities of the PHI AES instrument allow for characterization of such deposition regions on the nanoscale.

Physical Electronics takes pride in the significant contributions made by its PHI AES systems towards attaining noteworthy scientific accomplishments in the past year. For more information on the research referred to in this article, please refer to the citations provided below.

1. https://doi.org/10.1016/j.surfcoat.2022.128503
2. https://doi.org/10.1016/j.msea.2022.143525
3. https://doi.org/10.1016/j.elecom.2022.107265
4. https://doi.org/10.1016/j.nme.2022.101139
5. https://dx.doi.org/10.46770/AS.2022.014
6. https://doi.org/10.1021/acs.chemmater.2c00513
7. https://doi.org/10.1021/acsearthspacechem.1c00413
8. https://doi.org/10.1016/j.enconman.2021.115153