AVS 71 Session CA+AS+SS-WeM: Chemical Analysis and Imaging at Interfaces Oral Session

Aqueous solution-vapor interfaces govern important phenomena in the environment and atmosphere, including the uptake and release of trace gases by aerosols and CO₂ sequestration by the oceans. A detailed understanding of these processes requires the investigation of liquid-vapor interfaces with chemical sensitivity and interface specificity. [1] This talk will discuss opportunities and challenges for investigations of liquid-vapor interfaces using X-ray photoelectron spectroscopy and describe recent experiments that have focused on the propensity of certain ions and the role of surfactants at the liquid-vapor interface.[2-4] The talk will also discuss the utilization of photoelectron angular distributions for the investigation of the depth of solvation of surfactants at the interface. [5-7]

[1] R. Dupuy, et al, J. Chem. Phys. 154, 060901 (2021).

[2] S. Gholami, et al., Environmental Science: Atmospheres 5, 291-299 (2025).

[3] C. Richter, et al., Phys. Chem. Chem. Phys. 26, 27292-27300 (2024).

[4] T. Buttersack, et al., Nat. Commun. 15, 8987 (2024).

[5] R. Dupuy, et al., Phys. Chem. Chem. Phys. 24, 4796-4808 (2022).

[6] R. Dupuy, et al., Acc. Chem. Res. 56, 215-223 (2023).

Synchrotron based X-ray spectroscopic techniques offers unique characterization of energy, catalysis and chemical process in regards to the functionality, complexity of material architecture and chemistry. In the operando soft X-ray spectroscopy study of interfacial phenomena, it has been found that the microstructure and composition of materials as well as the microstructure evolution process have a great influence on performances in a variety of fields, such as the energy conversion and energy storage materials in the chemical and catalytic processes. This presentation will show how to best use the X-ray spectroscopy characterization techniques, including X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) to investigate the real interfacial reaction mechanism during the operation. The experimental results show how operando soft X-ray spectra uncover the phase conversion, chemical and structure change of solid/liquid and solid/gas interfaces in real time, thus further enhance the understanding of real reaction mechanism.

Ambient Pressure X-ray Photoelectron Spectroscopy (APXPS) has established itself as a go-to technique to study heterogeneous and complex material systems under reaction environments. Multimodal approaches, which correlate information from two or more complementary techniques, are currently one of the forefronts of the APXPS development. In the past years, Advanced Light Source contributed one such setup: a combined Ambient Pressure PhotoEmission and grazing incidence X-ray Scattering (APPEXS) instrument commissioned and operated at beamline 11.0.2 The combination of the two in-situ techniques allows correlating structural and chemical information, which is critical for describing processes that transform materials in both these domains.

For example, by using APPEXS, we studied dynamics of the exsolution process of catalyst metallic nanoparticles [1], arrays of patterned nano-objects under reaction conditions [2], chemistry of ligands capping nanoparticles [3], discovered transformation of bimetallic nanoparticles during hydrogen storage process [4], and investigated CO₂ reduction catalyst under operating conditions [5]. Future developments of the technique and applications to a wider variety of scientific problems will be discussed.

[1] H. Kersell et al., Faraday discussions 236, 141-156 (2022)

[2] H. Kersell et al., Synchrotron Radiation News 35 (3), 61-66 (2022)

[3] M. Jaugstetter et al., ACS Nano 19, 1, 418–426 (2024)

[4] L.P. Matte et al., ACS Nano 19, 10, 10312–10322 (2025)

[5] G.Z. Girotto et al., arXiv preprint arXiv:2504.00350 (2025)

Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is a versatile technique for 2D and 3D analysis of surfaces. During the acquisition process, secondary ions are desorbed from the sample using one or more primary ion beams. These secondary ions are used to acquire a full mass spectrum at each voxel. Typically, a single acquisition mode is used when acquiring data, optimized for one specific potential aspect of the (unknown) sample. This becomes problematic when the number of acquisitions is constrained by the amount of sample available or the instrument time available. In the acquisition multiplexing approach, multiple acquisition modes, each of which is optimized for a specific performance aspect, are utilized during the acquisition process, resulting in multiple co-located datasets. Each of these acquired datasets may be analyzed individually in the traditional manner, or via algorithmic techniques such as Multivariate Statistical Analysis (MVSA) or Machine Learning (ML). Additionally, by taking advantage of the dataset’s co-location property, it is possible to analyze all of the acquired data at once, finding aspects of the sample which span the data spectrally, spatially, and across acquisition modes.

We have applied this approach to vary numerous performance parameters of ToF-SIMS instruments, such as the primary ion beam current, the primary ion species, the focus of the beam, etc. Subsequently, analysis routines optimized for the parameter that was varied were applied to the datasets to make full use of the resulting data. One example is acquiring datasets using different primary ion beam currents, and then generating a High Dynamic Range (HDR) like dataset. High primary ion currents result in intense peaks which may saturate the detector signal. At the same time, low intensity signals are noisy at low primary ion currents. Another parameter which we varied is whether to optimize the primary beam for high mass resolution (and lower spatial resolution), or high spatial resolution (and lower mass resolution). This results in two datasets with fully complementary information. These may then be analyzed using machine learning based image fusion to generate a single high mass high spatial resolution dataset.

Characterising and controlling surface electronic and quantum states is an almost ubiquitous challenge for electronic and quantum technologies. The diamond material system is a particular example, where bulk states can be created with extreme purity but surface states, chemical and physical, are not yet well controlled or even understood.

In this presentation I will detail our efforts to analyse the diamond surface, with a variety of vacuum science techniques and theoretical analyses, and reveal some of the chemical challenges being faced in passivating and functionalizing this surface. I will show evidence that these surfaces remain significantly disruptive for quantum devices and present recent efforts in the development of high performance hydrogen terminated diamond transistors. Finally, I will forecast the remaining challenges and next steps for improving the surface science of this important quantum electronic material.