2:15 PM - 2:30 PM
▼ [6p-A504-5] Coverage Dependence of Energy Levels in Organic Monolayer
Keywords:inverse photoemission spectroscopy, ultraviolet photoemission spectroscopy, polarization effect
It is reported that the ionization energy (IE) and electron affinity (EA) of organic materials in the solid phase depend on the molecular orientation and mixing ratio of two molecules having different quadrupole moments. In this presentation, we will demonstrate that IE and EA also depend on the surface coverage of an organic molecule below 1 monolayer (ML).
In the earlier studies, only IE is measured by using ultraviolet photoemission spectroscopy (UPS) and discussed alongside theoretical studies. Here, we also precisely examine the EA to elucidate the mechanism based on the experimental data by using low-energy inverse photoemission spectroscopy (LEIPS) which enable us to directly measure the unoccupied states with the precision of 0.1 eV.
For the molecules, copper phthalocyanine (CuPc) and copper hexadecafluoro-phthalocyanine (F16CuPc) were chosen since the molecules have a similar structure but possess a permanent quadrupole moment with the opposite direction. To obtain films with flat-lying orientation, we used a highly oriented pyrolytic graphite (HOPG) surface as a substrate.
Then we use the polarization effect in solid to explain the behaviour obtained from the experiment. The polarization effect can be divided into the dynamic interaction D, approximated by charge-induced dipole interaction, and the static interaction S, approximated by charge-permanent quadrupole interaction. From the experiment we we can conclude that the shift of EA and IE in the sub-monolayer region is predominately contributed by S.
In the earlier studies, only IE is measured by using ultraviolet photoemission spectroscopy (UPS) and discussed alongside theoretical studies. Here, we also precisely examine the EA to elucidate the mechanism based on the experimental data by using low-energy inverse photoemission spectroscopy (LEIPS) which enable us to directly measure the unoccupied states with the precision of 0.1 eV.
For the molecules, copper phthalocyanine (CuPc) and copper hexadecafluoro-phthalocyanine (F16CuPc) were chosen since the molecules have a similar structure but possess a permanent quadrupole moment with the opposite direction. To obtain films with flat-lying orientation, we used a highly oriented pyrolytic graphite (HOPG) surface as a substrate.
Then we use the polarization effect in solid to explain the behaviour obtained from the experiment. The polarization effect can be divided into the dynamic interaction D, approximated by charge-induced dipole interaction, and the static interaction S, approximated by charge-permanent quadrupole interaction. From the experiment we we can conclude that the shift of EA and IE in the sub-monolayer region is predominately contributed by S.