Impact of PHI XPS instruments on scientific discovery

This is the time to look back on the year 2022 – to see the impact of PHI’s various XPS instruments - VersaProbe, Quantera, and Quantes on discoveries and scientific advancements.

In 2022 more than 4400 scientific research using PHI XPS instrument were published, including journal articles, book chapters, etc. Out of these studies, 99 were published in high-impact journals such as Nature and Science.

One of the highest cited papers (24 citations in a year) was published in the Journal of Colloid and Interface Science.1 Our customers studied N-doped carbon fiber embedded with magnetic CoNi alloy particles producing high electromagnetic wave absorption properties. The group used the PHI VersaProbe instrument to perform the surface characterization of the material.

To completely understand the link between functions and structure, multi-technique characterization of materials utilizing complementary to XPS techniques, such as UPS on the same instrument, such as PHI VersaProbe and PHI Genesis, becomes essential.

A study (published in Nature Communications) done by researchers at the University of Electronic Science and Technology of China investigated the modification of top and bottom interfaces of Ta3N5 thin film photoanode using n-type In:GaN and p-type Mg:GaN.2 The group used the PHI VersaProbe instrument for obtaining detailed composition of layers using XPS, and the detailed band structure was using UPS (Figure 1). This work demonstrated the crucial role of interface engineering for thin film-based photoanode in achieving efficient PEC water splitting.

Figure 1: (a) UPS spectrum of Mg:GaN deposited on Nb substrate. (b)  UPS spectrum of In:GaN deposited on Nb substrate. (c)  Schematic diagram of band structure for In:GaN/Ta3N5/Mg:GaN film determined from UPS and UV–vis absorption measurements

Full electronic structure can be obtained by combining UPS with Low Energy Inverse Photoelectron Spectroscopy (LEIPS). In the study published in Nature, researchers studied 2D-carbon material with a conjugated carbon network forming a unique topology and having anisotropic properties in-plane.3 This material also exhibited moderate bandgap and conductivity in comparison to graphene, implying that the material can have applications in the semiconductor field. The electronic structure was constructed using UPS, and LEIPS experiments were carried out on the PHI VersaProbe instrument. (Figure 2)

Figure 2: Electronic band structure of the monolayer qHP C60 nanosheets measured by the UPS and LEIPS experiments. Eg represents the gap energy; ECB represents the energy difference between CBM and EF ; and EVB represents the energy difference between VBM and EF .

Understanding the chemical composition of the solid electrolyte interphase (SEI) formed at the interface between the electrode and an electrolyte is crucial for developing reliable batteries. XPS instruments with in-situ capabilities have become more and more utilized in studies of battery materials. In a recent paper published in Nature Communications by our customers at Oxford University, XPS measurements during lithium plating on the surface of a Li6PS5Cl solid-state electrolyte pellet using an electron beam are presented.4 They investigated a current density-mediated evolution of the interphase formed between Li metal and LPSCl sulfide solid electrolyte during electrochemical plating using an in situ XPS. A grounded and Li-backed SE surface as exposed to an electron beam. The negatively charged surface formed facilitates the migration of Li+ ions, eventually leading to the plating of metallic Li on the SE surface. The electron beam current was adjusted to modulate the electron flux incident at the SE surface, hence tuning the virtual electrode plating current. Figure 3 shows the evolution of core-level Li 1s, S 2p and P 2p XPS spectra and quantification during the virtual electrode plating process at the LPSCl surface at three different currents as a function of the charge passed.

Figure 3. XPS measurements to study SEI evolution during virtual electrode plating at SE surface.

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© 2023 Physical Electronics, Inc. (PHI) All Rights Reserved.