TY - JOUR
T1 - Large work function reduction by adsorption of a molecule with a negative electron affinity
T2 - Pyridine on ZnO (101̄0)
AU - Hofmann, Oliver T.
AU - Deinert, Jan Christoph
AU - Xu, Yong
AU - Rinke, Patrick
AU - Stähler, Julia
AU - Wolf, Martin
AU - Scheffler, Matthias
PY - 2013/11/7
Y1 - 2013/11/7
N2 - Using thermal desorption and photoelectron spectroscopy to study the adsorption of pyridine on ZnO(101̄0), we find that the work function is significantly reduced from 4.5 eV for the bare ZnO surface to 1.6 eV for one monolayer of adsorbed pyridine. Further insight into the interface morphology and binding mechanism is obtained using density functional theory. Although semilocal density functional theory provides unsatisfactory total work functions, excellent agreement of the work function changes is achieved for all coverages. In a closed monolayer, pyridine is found to bind to every second surface Zn atom. The strong polarity of the Zn-pyridine bond and the molecular dipole moment act cooperatively, leading to the observed strong work function reduction. Based on simple alignment considerations, we illustrate that even larger work function modifications should be achievable using molecules with negative electron affinity. We expect the application of such molecules to significantly reduce the electron injection barriers at ZnO/organic heterostructures.
AB - Using thermal desorption and photoelectron spectroscopy to study the adsorption of pyridine on ZnO(101̄0), we find that the work function is significantly reduced from 4.5 eV for the bare ZnO surface to 1.6 eV for one monolayer of adsorbed pyridine. Further insight into the interface morphology and binding mechanism is obtained using density functional theory. Although semilocal density functional theory provides unsatisfactory total work functions, excellent agreement of the work function changes is achieved for all coverages. In a closed monolayer, pyridine is found to bind to every second surface Zn atom. The strong polarity of the Zn-pyridine bond and the molecular dipole moment act cooperatively, leading to the observed strong work function reduction. Based on simple alignment considerations, we illustrate that even larger work function modifications should be achievable using molecules with negative electron affinity. We expect the application of such molecules to significantly reduce the electron injection barriers at ZnO/organic heterostructures.
UR - http://www.scopus.com/inward/record.url?scp=84903362831&partnerID=8YFLogxK
U2 - 10.1063/1.4827017
DO - 10.1063/1.4827017
M3 - Article
AN - SCOPUS:84903362831
SN - 0021-9606
VL - 139
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
IS - 17
M1 - 174701
ER -