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Abstract Formation of energetic species at the surface of aqueous microdroplets, including abundant hydroxyl radicals, oxidation products, and ionized N2and O2gas, has been previously attributed to the high electric field at the droplet surface. Here, evidence for a new mechanism for electronic excitation involving electron emission from negatively charged water droplets is shown. Droplet evaporation can lead to the emission of ions and droplet fission, but unlike positively charged droplets, negatively charged droplets can also shed charge by electron emission. With nanoelectrospray, no anions or negatively charged droplets are produced with a positive electrospray potential. In contrast, abundant O2+•and H3O+(H2O) are formed with negative electrospray. When toluene vapor is introduced with negative electrospray, abundant toluene radical cations and fragments are produced. Both O2+•and toluene radical cations are produced with pneumatic nebulization. The electrons produced from evaporating negatively charged droplets can be accelerated by an external electric field in electrospray, or by the field generated between droplets with opposite polarities produced by pneumatic nebulization. This electron emission/ionization mechanism leads to electronic excitation >10 eV, and it may explain some of the surprising chemistries that were previously attributed to the high intrinsic electric field at the surface of aqueous droplets.
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This content will become publicly available on January 21, 2026
Influence of hydrogen and oxygen surface termination on the mechanism of sub-bandgap photoelectron emission from diamond(111) into vacuum and into water
Wide-bandgap semiconductors have unique electron emission properties by virtue of having high-lying conduction bands. Among these, diamond stands out because of its chemical stability, allowing it to serve as a solid-state electron source in vacuum and non-vacuum environments, including water. However, the underlying mechanisms of electron emission are not well understood. Here, we report investigations of the mechanisms of electron emission from H-terminated and oxidized surfaces of single-crystal boron-doped diamond(111) in vacuum and in water using both sub-bandgap (4.75 eV and 3.05 eV) and above-bandgap (21.2 eV) excitation. Energy-resolved photoemission spectra in vacuum using different incident photon energies reveal two distinct energy distributions, reflecting different emission pathways. While oxidation greatly reduces electron emission into vacuum using both sub-bandgap and above-bandgap sources, facile electron emission into water persists on the oxidized samples using sub-bandgap excitation and is directly observed through transient optical absorption measurements using sub-bandgap excitation. Low-energy inverse photoemission spectroscopy shows that oxidation leads to broad distribution of surface states throughout the diamond bandgap. Our studies highlight
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- Award ID(s):
- 1904106
- PAR ID:
- 10569306
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Diamond and Related Materials
- Edition / Version:
- 1.0
- Volume:
- 153
- Issue:
- C
- ISSN:
- 0925-9635
- Page Range / eLocation ID:
- 112011
- Subject(s) / Keyword(s):
- Single crystal diamond Electron affinity Surface termination Solvated electrons Photoelectron emission Low-energy Inverse Photemission Spectroscopy
- Format(s):
- Medium: X Size: 2MB Other: pdf
- Size(s):
- 2MB
- Sponsoring Org:
- National Science Foundation
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