@inproceedings{14864,
  author       = {Stöllner, Andrea and Lenton, Isaac C and Muller, Caroline J and Waitukaitis, Scott R},
  booktitle    = {EGU General Assembly 2023},
  location     = {Vienna, Austria & Virtual},
  publisher    = {European Geosciences Union},
  title        = {{Measuring spontaneous charging of single aerosol particles}},
  doi          = {10.5194/egusphere-egu23-6166},
  year         = {2023},
}

@article{13197,
  abstract     = {Nominally identical materials exchange net electric charge during contact through a mechanism that is still debated. ‘Mosaic models’, in which surfaces are presumed to consist of a random patchwork of microscopic donor/acceptor sites, offer an appealing explanation for this phenomenon. However, recent experiments have shown that global differences persist even between same-material samples, which the standard mosaic framework does not account for. Here, we expand the mosaic framework by incorporating global differences in the densities of donor/acceptor sites. We develop
an analytical model, backed by numerical simulations, that smoothly connects the global and deterministic charge transfer of different materials to the local and stochastic mosaic picture normally associated with identical materials. Going further, we extend our model to explain the effect of contact asymmetries during sliding, providing a plausible explanation for reversal of charging sign that has been observed experimentally.},
  author       = {Grosjean, Galien M and Waitukaitis, Scott R},
  issn         = {2475-9953},
  journal      = {Physical Review Materials},
  keywords     = {Physics and Astronomy (miscellaneous), General Materials Science},
  number       = {6},
  publisher    = {American Physical Society},
  title        = {{Asymmetries in triboelectric charging: Generalizing mosaic models to different-material samples and sliding contacts}},
  doi          = {10.1103/physrevmaterials.7.065601},
  volume       = {7},
  year         = {2023},
}

@article{12697,
  abstract     = {Models for same-material contact electrification in granular media often rely on a local charge-driving parameter whose spatial variations lead to a stochastic origin for charge exchange. Measuring the charge transfer from individual granular spheres after contacts with substrates of the same material, we find instead a “global” charging behavior, coherent over the sample’s whole surface. Cleaning and baking samples fully resets charging magnitude and direction, which indicates the underlying global parameter is not intrinsic to the material, but acquired from its history. Charging behavior is randomly and irreversibly affected by changes in relative humidity, hinting at a mechanism where adsorbates, in particular, water, are fundamental to the charge-transfer process.},
  author       = {Grosjean, Galien M and Waitukaitis, Scott R},
  issn         = {1079-7114},
  journal      = {Physical Review Letters},
  keywords     = {General Physics, Electrostatics, Triboelectricity, Soft Matter, Acoustic Levitation, Granular Materials},
  number       = {9},
  publisher    = {American Physical Society},
  title        = {{Single-collision statistics reveal a global mechanism driven by sample history for contact electrification in granular media}},
  doi          = {10.1103/physrevlett.130.098202},
  volume       = {130},
  year         = {2023},
}

@article{12789,
  abstract     = {Experiments have shown that charge distributions of granular materials are non-Gaussian, with broad tails that indicate many particles with high charge. This observation has consequences for the behavior of granular materials in many settings, and may bear relevance to the underlying charge transfer mechanism. However, there is the unaddressed possibility that broad tails arise due to experimental uncertainties, as determining the shapes of tails is nontrivial. Here we show that measurement uncertainties can indeed account for most of the tail broadening previously observed. The clue that reveals this is that distributions are sensitive to the electric field at which they are measured; ones measured at low (high) fields have larger (smaller) tails. Accounting for sources of uncertainty, we reproduce this broadening in silico. Finally, we use our results to back out the true charge distribution without broadening, which we find is still non-Guassian, though with substantially different behavior at the tails and indicating significantly fewer highly charged particles. These results have implications in many natural settings where electrostatic interactions, especially among highly charged particles, strongly affect granular behavior.},
  author       = {Mujica, Nicolás and Waitukaitis, Scott R},
  issn         = {2470-0053},
  journal      = {Physical Review E},
  number       = {3},
  publisher    = {American Physical Society},
  title        = {{Accurate determination of the shapes of granular charge distributions}},
  doi          = {10.1103/PhysRevE.107.034901},
  volume       = {107},
  year         = {2023},
}

@article{12109,
  abstract     = {Kelvin probe force microscopy (KPFM) is a powerful tool for studying contact electrification (CE) at the nanoscale, but converting KPFM voltage maps to charge density maps is nontrivial due to long-range forces and complex system geometry. Here we present a strategy using finite-element method (FEM) simulations to determine the Green's function of the KPFM probe/insulator/ground system, which allows us to quantitatively extract surface charge. Testing our approach with synthetic data, we find that accounting for the atomic force microscope (AFM) tip, cone, and cantilever is necessary to recover a known input and that existing methods lead to gross miscalculation or even the incorrect sign of the underlying charge. Applying it to experimental data, we demonstrate its capacity to extract realistic surface charge densities and fine details from contact-charged surfaces. Our method gives a straightforward recipe to convert qualitative KPFM voltage data into quantitative charge data over a range of experimental conditions, enabling quantitative CE at the nanoscale.},
  author       = {Pertl, Felix and Sobarzo Ponce, Juan Carlos A and Shafeek, Lubuna B and Cramer, Tobias and Waitukaitis, Scott R},
  issn         = {2475-9953},
  journal      = {Physical Review Materials},
  number       = {12},
  publisher    = {American Physical Society},
  title        = {{Quantifying nanoscale charge density features of contact-charged surfaces with an FEM/KPFM-hybrid approach}},
  doi          = {10.1103/PhysRevMaterials.6.125605},
  volume       = {6},
  year         = {2022},
}