Title : Applying an external bias in XPS as a means to obtain additional information about materials
Abstract:
In conventional spectral acquisition, differential charging is compensated by a low‑energy electron flood gun (neutralizer). Although differences in nanoparticle synthesis and, consequently, in their electronic structure are significant, this approach does not provide a complete picture of the interaction between the nanoparticle core and its carbonaceous shell. Applying a positive bias shifts photoelectron peaks from metallic regions toward higher binding energies by the full magnitude of the bias. In poorly conducting regions, the shift is smaller and determined by sample morphology and charge‑dissipation pathways. Using this approach, we revealed the presence of multiple phases in an Ag–La nanoparticle system. When a positive bias is applied together with the electron flood, peaks from metallic regions again shift by the bias, whereas peaks from poorly conducting regions remain nearly unchanged due to partial neutralization of positive charge. This produces a contrast opposite to the previous case; nevertheless, both modes of controlled differential charging exhibit the same underlying effect—an “electronic chromatography,” i.e., separation of spectral components along the binding‑energy axis according to local conductivity and electrostatic potential. Here, XPS is employed to visualize a p–n junction in a silicon detector under various biasing con-figurations. In the classical configuration, applying a bias yields little contrast because the sample is a single‑material system and differential charging develops predominantly along the depth. In contrast, an alternative wiring scheme combined with an arbitrary‑waveform bias enables tracking of transient processes and differentiation of signals from the p‑ and n‑type regions. Mapping the binding‑energy position of Si 2p shows polarity‑dependent peak shifts. Beyond straightforward visualization, this approach provides access to the dynamics of p–n‑junction operation, because the binding‑energy scale now carries a time component. This, in particular, makes it possible to delineate intrinsic (i) regions in neutron detectors. Thus, we demonstrate the potential to extract additional electrophysical information that is useful for local device characterization and failure analysis.
