Binding Energies of Charged Particles on Dielectric Surfaces in Liquid Nitrogen

TL;DR

This work presents a noninvasive electro-optic Kerr-effect method to quantify the effective binding energies $E_b$ of charged particles on dielectric surfaces in liquids by applying controlled electric fields and monitoring Kerr-induced ellipticity. The approach is demonstrated with ions/electrons on dTPB-coated and uncoated PMMA immersed in liquid nitrogen, yielding a consistent binding energy scale of about $0.12~\mathrm{meV}$ for a 3 Å separation and identifying a desorption threshold near $E_{\mathrm{eff}} \approx 4$ kV/cm. The technique relies on a detailed Kerr analysis, including fringe-field corrections and RC effects in the HV circuitry, and uses a sigmoidal fit to extract surface interaction parameters. The method provides a general framework for probing charge–surface interactions in liquid environments, with potential impact on detector technologies and the control of electric-field-induced systematic effects in cryogenic systems.

Abstract

A new approach for determining the binding energies of charged particles, such as ions and electrons, on dielectric surfaces in cryogenic liquids is introduced. The experimental technique outlined in this paper is employed to observe the buildup of charged particles on nonconductive surfaces using the electro-optic Kerr effect. The initial results of binding energy measurements on surfaces of deuterated tetraphenyl butadiene (dTPB)-coated and uncoated polymethyl methacrylate (PMMA) in liquid nitrogen are presented. Under these conditions, the ions or electrons displayed binding energies of less than 1 meV. Although these findings were obtained in liquid nitrogen, the methodology is not limited to cryogenic liquids and is applicable to a wide variety of fluids, with no essential dependence on temperature.

Figures (11)

• Figure 1: Schematic of the cryostat used to measure ion binding energies. The central region of the cryostat is shown, including the electrode assembly and two PMMA inserts with a narrow optical access gap for the laser beam. Note that the LHe container and the capillary were not used in the experiments described in this paper. The figure is adapted from Fig. 6 of Ref. Korsch2024
• Figure 2: Photograph of the experimental cryostat. Visible components include the high-voltage leads, liquid-helium fill lines, pump ports, cesium source, lead shielding blocks, and optical access through quartz windows.
• Figure 3: The optics setup for the measurement of binding energy of ions and electrons on dielectric surfaces. The figure is adapted from Fig. 7 of Ref. Korsch2024.
• Figure 4: A block diagram of the electric circuitry connected to the HV electrodes. See text for details. The figure is adapted from Fig. 8 of Ref. Korsch2024.
• Figure 5: Voltage drop signal measured across the measurement resistor, $R_m^{-}$. A sinusoidal driving waveform of frequency of 400 mHz was applied to the HV${-}$ supply.