TY - JOUR
T1 - Energy-level alignment of a single molecule on ultrathin insulating film
AU - Imai-Imada, Miyabi
AU - Imada, Hiroshi
AU - Miwa, Kuniyuki
AU - Jung, Jaehoon
AU - Shimizu, Tomoko
AU - Kawai, Maki
AU - Kim, Yousoo
PY - 2018/11/15
Y1 - 2018/11/15
N2 - Elucidation of the energy-level alignment mechanism at a molecule/insulator/metal interface is a key to understanding the molecular and interfacial phenomena. Herein, we provide a detailed investigation into the electronic structures of a free-base phthalocyanine on NaCl films of various thicknesses using scanning tunneling microscopy/spectroscopy (STM/STS). The energy of the ionization and the affinity levels of the molecule were deduced from the STS spectra, and we determined their dependence on the NaCl-film thickness, which can be explained based on three effects: a voltage drop within the NaCl films, the degree of electric-field screening around the molecule, and a variation in the work function of the substrates. We further found that the energy levels relative to the vacuum level are independent of the work function of the substrate, and that the size of the energy gap increases with the thickness. Our results suggest that it is possible to predict the energy levels at the interfaces based on the energy levels of the molecules in a gas phase, the work function of the substrate, and the thickness of the insulating films.
AB - Elucidation of the energy-level alignment mechanism at a molecule/insulator/metal interface is a key to understanding the molecular and interfacial phenomena. Herein, we provide a detailed investigation into the electronic structures of a free-base phthalocyanine on NaCl films of various thicknesses using scanning tunneling microscopy/spectroscopy (STM/STS). The energy of the ionization and the affinity levels of the molecule were deduced from the STS spectra, and we determined their dependence on the NaCl-film thickness, which can be explained based on three effects: a voltage drop within the NaCl films, the degree of electric-field screening around the molecule, and a variation in the work function of the substrates. We further found that the energy levels relative to the vacuum level are independent of the work function of the substrate, and that the size of the energy gap increases with the thickness. Our results suggest that it is possible to predict the energy levels at the interfaces based on the energy levels of the molecules in a gas phase, the work function of the substrate, and the thickness of the insulating films.
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U2 - 10.1103/PhysRevB.98.201403
DO - 10.1103/PhysRevB.98.201403
M3 - Article
AN - SCOPUS:85056637026
VL - 98
JO - Physical Review B-Condensed Matter
JF - Physical Review B-Condensed Matter
SN - 2469-9950
IS - 20
M1 - 201403
ER -