TY - JOUR
T1 - Solid ammonia charging by low-energy electrons
AU - Sagi, Roey
AU - Akerman, Michelle
AU - Ramakrishnan, Sujith
AU - Asscher, Micha
N1 - Publisher Copyright:
© 2021 American Chemical Society. All rights reserved.
PY - 2021/2/25
Y1 - 2021/2/25
N2 - The interaction of condensed matter with low-energy electrons is relevant to a broad range of research fields as this interaction is directly associated with radiation chemistry. When discussing ammonia-containing solids, this interaction is presumed to have an important role in the formation of nitrogen-bearing prebiotic molecules detected in laboratory studies in the attempt to mimic cold extraterrestrial environments exposed to ionizing radiation. In a model study, we demonstrate that ammonia ices grown on a metallic substrate under ultrahigh vacuum (UHV) conditions can transport and accumulate electrons, mostly at surface sites near the ammonia/vacuum interface, forming a nanocapacitor-like structure. Amorphous and crystalline ammonia ices were grown at temperatures in the range of 3085 K. Their charging characteristics reveal a strong morphology, temperature, thickness, and electron-beam flux dependence. This was investigated in situ and noninvasively by continuous contact potential difference (CPD) measurements conducted with a Kelvin probe. Discharge upon annealing leads to an estimate of thermal trapping energetics. Weakly bound electrons are released as a result of the ammonia layers reorganization during the collapse and densification of the porous structure and its crystallization, whereas the more stable electrons are released only during desorption of multilayer ammonia molecules. Charging with subsequent discharge upon annealing can thus be utilized for investigating morphology and phase transitions of molecular solids.
AB - The interaction of condensed matter with low-energy electrons is relevant to a broad range of research fields as this interaction is directly associated with radiation chemistry. When discussing ammonia-containing solids, this interaction is presumed to have an important role in the formation of nitrogen-bearing prebiotic molecules detected in laboratory studies in the attempt to mimic cold extraterrestrial environments exposed to ionizing radiation. In a model study, we demonstrate that ammonia ices grown on a metallic substrate under ultrahigh vacuum (UHV) conditions can transport and accumulate electrons, mostly at surface sites near the ammonia/vacuum interface, forming a nanocapacitor-like structure. Amorphous and crystalline ammonia ices were grown at temperatures in the range of 3085 K. Their charging characteristics reveal a strong morphology, temperature, thickness, and electron-beam flux dependence. This was investigated in situ and noninvasively by continuous contact potential difference (CPD) measurements conducted with a Kelvin probe. Discharge upon annealing leads to an estimate of thermal trapping energetics. Weakly bound electrons are released as a result of the ammonia layers reorganization during the collapse and densification of the porous structure and its crystallization, whereas the more stable electrons are released only during desorption of multilayer ammonia molecules. Charging with subsequent discharge upon annealing can thus be utilized for investigating morphology and phase transitions of molecular solids.
UR - http://www.scopus.com/inward/record.url?scp=85101803335&partnerID=8YFLogxK
U2 - 10.1021/acs.jpcc.0c09658
DO - 10.1021/acs.jpcc.0c09658
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AN - SCOPUS:85101803335
SN - 1932-7447
VL - 125
SP - 3845
EP - 3858
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 7
ER -