@article{21765,
  abstract     = {Dielectric particles of the same material exchange electrical charge during collisions or sliding contacts, yet the underlying charge-exchange mechanism is still not understood. The fact that particles can become highly charged as a result of this effect has significant consequences for many settings, both in nature and industry, such as thunderstorms, volcanic eruptions, particle aggregation during meteorite and planet formation, and the clogging of industrial granular systems. Toward understanding these systems, great efforts have been made to develop precise in situ measurements for particle charge, e.g., to determine ensemble charge distributions or measure exchange during individual contacts. Here, we present experimental results concerning the particle size scaling of the stationary-state charge distributions of oxide particles in the sub-millimeter range. We measure the charge distributions for large ensembles of monodisperse ZrO2:SiO2 composite spheres, ranging from 172 to 545µ⁢m in diameter. These distributions are non-Gaussian and collapse to a single master curve when plotted as functions of the surface charge density Σ=𝑞/4⁢𝜋⁢𝑅2. X-ray fluorescence and atomic force microscopy measurements show that the differences in the measured charge distributions are not due to variations in chemical composition or surface roughness, but rather to size alone. Our findings provide constraints on microscopic models for charge exchange, namely that they should lead to steady-state distributions that are non-Gaussian and scale in a specific way with particle size.},
  author       = {Lara, Macarena and Flores, Marcos and Castillo, Gustavo and Tassara, Santiago and Waitukaitis, Scott R and Mujica, Nicolás},
  issn         = {2475-9953},
  journal      = {Physical Review Materials},
  number       = {4},
  publisher    = {American Physical Society},
  title        = {{Particle size scaling of non-Gaussian granular charge distributions}},
  doi          = {10.1103/qw6t-xqdw},
  volume       = {10},
  year         = {2026},
}

@article{17476,
  abstract     = {Lead halide perovskites have recently been reported to demonstrate an exceptionally high nonlinear (Kerr) refractive index n2 of up to 10−8cm2/W in CH3⁢NH3⁢PbBr3. Other researchers, however, observe different, substantially more conservative numbers. In order to resolve this disagreement, the nonlinear Kerr index of a bulk sample of lead halide perovskite was measured directly by means of an interferometer. This approach has many advantages as compared to the more standard z-scan technique. In particular, this method allows studying the induced changes to the refractive index in a time-resolved manner, thus enabling to separate the different contributions to 𝑛2. The extracted 𝑛2 values for CsPbBr3 and MAPbBr3 at 𝜆≈1µ⁢m are 𝑛2=+2.1×10−14cm2/W and 𝑛2=+6×10−15cm2/W, respectively. Hence, these values are substantially lower than what has been indicated in most of the previous reports, implying the latter one should be regarded with great care.},
  author       = {Lorenc, Dusan and Zhumekenov, Ayan and Bakr, Osman M. and Alpichshev, Zhanybek},
  issn         = {2475-9953},
  journal      = {Physical Review Materials},
  number       = {8},
  publisher    = {American Physical Society},
  title        = {{No extraordinary χ(3) in lead-halide perovskites: Placing an upper bound on Kerr nonlinearity by means of time-resolved interferometry}},
  doi          = {10.1103/PhysRevMaterials.8.085403},
  volume       = {8},
  year         = {2024},
}

@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},
}