Direct Observation of Electron Trapping States in SiO2 by Constant-Final-State Photoelectron Yield Spectroscopy: Insights into the Electron-Transfer Model of Contact Electrification
Abstract
Understanding electrostatic charging of silicon dioxide (SiO2) is important for electrostatic control in a wide range of applications. Contact electrification (CE) is a major source of such charging, and electron transfer is considered one of its leading mechanisms. Several electron-transfer models have been proposed to explain CE; however, the density of states (DOS) involved in electron transfer has not been experimentally characterized. Determining this DOS is therefore essential for understanding the charging mechanism. However, measuring the DOS of insulating materials such as SiO2 remains challenging: photoemission spectroscopy, the standard technique for probing the DOS of materials, is unsuitable for highly insulating materials because sample charging during measurement can cause spectral distortion or even complete signal loss. Here, we directly and quantitatively determined the in-gap DOS of amorphous SiO2 using constant-final-state photoelectron yield spectroscopy (CFS-YS). Weak occupied states were observed within the band gap, and their marked increase after electron injection revealed that electron-trapping states are distributed over a broad energy range. Vacuum annealing markedly altered the in-gap DOS and electron-trapping behavior. The observed changes suggest a role for surface adsorbates, including water, in the charging behavior of SiO2. Charging simulations based on the experimentally measured in-gap DOS approximately reproduced the previously reported charging behavior and showed that the accumulated charge was concentrated near the surface. These findings indicate that in-gap states distributed over a broad energy range mediate electron transfer during CE and highlight the importance of considering experimentally determined DOS when evaluating proposed electron-transfer models.
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BibTeX
@misc{shibuya2026direct,
title = {{Direct Observation of Electron Trapping States in SiO$_2$ by Constant-Final-State Photoelectron Yield Spectroscopy: Insights into the Electron-Transfer Model of Contact Electrification}},
author = {Renjiro Shibuya and Manato Tateno and Runa Hoshikawa and Tomohiro Ishibashi and Hirohiko Fukagawa and Hisao Ishii},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.39748},
eprint = {2610.39748},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.39748},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Direct Observation of Electron Trapping States in SiO_2 by Constant-Final-State Photoelectron Yield Spectroscopy: Insights into the Electron-Transfer Model of Contact Electrification
AU - Renjiro Shibuya
AU - Manato Tateno
AU - Runa Hoshikawa
AU - Tomohiro Ishibashi
AU - Hirohiko Fukagawa
AU - Hisao Ishii
PY - 2026
DA - 2026/10/29
PB - arXiv
DO - 10.48550/arxiv.2610.39748
UR - https://arxiv.org/abs/2610.39748
AB - Understanding electrostatic charging of silicon dioxide (SiO_2) is important for electrostatic control in a wide range of applications. Contact electrification (CE) is a major source of such charging, and electron transfer is considered one of its leading mechanisms. Several electron-transfer models have been proposed to explain CE; however, the density of states (DOS) involved in electron transfer has not been experimentally characterized. Determining this DOS is therefore essential for understanding the charging mechanism. However, measuring the DOS of insulating materials such as SiO_2 remains challenging: photoemission spectroscopy, the standard technique for probing the DOS of materials, is unsuitable for highly insulating materials because sample charging during measurement can cause spectral distortion or even complete signal loss. Here, we directly and quantitatively determined the in-gap DOS of amorphous SiO_2 using constant-final-state photoelectron yield spectroscopy (CFS-YS). Weak occupied states were observed within the band gap, and their marked increase after electron injection revealed that electron-trapping states are distributed over a broad energy range. Vacuum annealing markedly altered the in-gap DOS and electron-trapping behavior. The observed changes suggest a role for surface adsorbates, including water, in the charging behavior of SiO_2. Charging simulations based on the experimentally measured in-gap DOS approximately reproduced the previously reported charging behavior and showed that the accumulated charge was concentrated near the surface. These findings indicate that in-gap states distributed over a broad energy range mediate electron transfer during CE and highlight the importance of considering experimentally determined DOS when evaluating proposed electron-transfer models.
ER -