How to measure work functions from aqueous solutions

The recent application of concepts from condensed-matter physics to photoelectron spectroscopy (PES) of volatile, liquid-phase systems has enabled the measurement of electronic energetics of liquids on an absolute scale. Particularly, vertical ionization energies, VIEs, of liquid water and aqueous solutions, both in the bulk and at associated interfaces, can now be routinely determined. These IEs are referenced to the local vacuum level, which is the appropriate quantity for condensed matter with associated surfaces, including liquids. Here, we connect this newly accessible energy level to another important surface property, namely, the solution work function, e$\Phi_{liq}$. We lay out the prerequisites for and unique challenges of determining e$\Phi$ of aqueous solutions and liquids in general. We demonstrate - for a model aqueous solution with a tetra-n-butylammonium iodide (TBAI) surfactant solute - that concentration-dependent work functions, associated with the surface dipoles generated by the segregated interfacial layer of TBA$^+$ and I$^-$ions, can be accurately measured under controlled conditions. We detail the nature of surface potentials, uniquely tied to the nature of the flowing-liquid sample, which must be eliminated or quantified to enable such measurements. This allows us to refer measured spectra of aqueous solutions to the Fermi level and quantitatively assign surfactant concentration-dependent spectral shifts to competing work function and electronic-structure effects, the latter determining, e.g., (electro)chemical reactivity. We describe the extension of liquid-jet PES to quantitatively access concentration-dependent surface descriptors that have so far been restricted to solid-phase measurements. These studies thus mark the beginning of a new era in the characterization of the interfacial electronic structure of aqueous solutions and liquids more generally.Comment: Main manuscript: 26 pages, 7 figures. Supporting information: 5 pages, 5 figure

How to measure work functions from aqueous solutions

The recent application of concepts from condensed-matter physics to photoelectron spectroscopy (PES) of volatile, liquid-phase systems has enabled the measurement of electronic energetics of liquids on an absolute scale. Particularly, vertical ionization energies, VIEs, of liquid water and aqueous solutions, both in the bulk and at associated interfaces, can now be accurately, precisely, and routinely determined. These IEs are referenced to the local vacuum level, which is the appropriate quantity for condensed matter with associated surfaces, including liquids. In this work, we connect this newly accessible energy level to another important surface property, namely, the solution work function, $eΦ_{liq}$. We lay out the prerequisites for and unique challenges of determining $eΦ$ of aqueous solutions and liquids in general. We demonstrate – for a model aqueous solution with a tetra-n-butylammonium iodide (TBAI) surfactant solute – that concentration-dependent work functions, associated with the surface dipoles generated by the segregated interfacial layer of TBA$^+$ and I$^−$ ions, can be accurately measured under controlled conditions. We detail the nature of surface potentials, uniquely tied to the nature of the flowing-liquid sample, which must be eliminated or quantified to enable such measurements. This allows us to refer aqueous-phase spectra to the Fermi level and to quantitatively assign surfactant-concentration-dependent spectral shifts to competing work function and electronic-structure effects, where the latter are typically associated with solute–solvent interactions in the bulk of the solution which determine, e.g., chemical reactivity. The present work describes the extension of liquid-jet PES to quantitatively access concentration-dependent surface descriptors that have so far been restricted to solid-phase measurements. Correspondingly, these studies mark the beginning of a new era in the characterization of the interfacial electronic structure of aqueous solutions and liquids more generally

Photoelectron Spectroscopy from a Liquid Flatjet - data

Data set pertaining to the article "Photoelectron spectroscopy from a liquid flatjet", published in J. Chem. Phys. 158, 234202 (2023). Files with extension .h5 are hdf5-files structured according to the NeXus standard v2020.10, see https://www.nexusformat.org/ https://fairmat-experimental.github.io/nexus-fairmat-proposal/50433d9039b3f33299bab338998acb5335cd8951/mpes-structure.html NeXus data files can be opened with any software capable of opening hdf5-structured files. The following viewers are adapted to the specifics of the NeXus data format: * nexpy (distributed with python) * https://h5web.panosc.eu/h5wasm (web-based NeXus viewer maintained by the European Photon and Neutron Open Science Cloud-consortium) Additionally, some properties of our liquid jet sample environment are described by extensions to standard NeXus explained in a notes-section in each file. In each NeXus file-entry, two types of spectra are shown: 1. Sweep-averaged spectra, integrated over the non-dispersive coordinate of our detector ('data'). 2. As-measured data ('raw'). Files with extension .txt are tab-separated ascii-files. The following files are provided: Measured spectra underlying the articles' figures: Figure2NEXUS.h5 Figure3NEXUS.h5 Figure4NEXUS.h5 Figure5NEXUS.h5 Figure6NEXUS.h5 Figure7NEXUS.h5 Numeric representation of the results shown in graphical form: 'Figure 6.txt'. In case you have any questions regarding this data set please contact: Uwe Hergenhahn, [email protected] .Funding acknowledgements: Deutsche Forschungsgemeinschaft (Wi 1327/5-1), Max-Water initiative of the Max-Planck-Gesellschaft, JSPS KAKENHI Grant No. JP20K15229

Photoelectron spectroscopy from a liquid flatjet

We demonstrate liquid-jet photoelectron spectroscopy from a flatjet formed by the impingement of two micron-sized cylindrical jets of different aqueous solutions. Flatjets provide flexible experimental templates enabling unique liquid-phase experiments that would not be possible using single cylindrical liquid jets. One such possibility is to generate two co-flowing liquid-jet sheets with a common interface in vacuum, with each surface facing the vacuum being representative of one of the solutions, allowing face-sensitive detection by photoelectron spectroscopy. The impingement of two cylindrical jets also enables the application of different bias potentials to each jet with the principal possibility to generate a potential gradient between the two solution phases. This is shown for the case of a flatjet composed of a sodium iodide aqueous solution and neat liquid water. The implications of asymmetric biasing for flatjet photoelectron spectroscopy are discussed. The first photoemission spectra for a sandwich-type flatjet comprised of a water layer encapsulated by two outer layers of an organic solvent (toluene) are also shown