Characterization of individual molecular adsorption geometries by atomic force microscopy: Cu-TCPP on rutile TiO2 (110).
Functionalized materials consisting of inorganic substrates with organic adsorbates play an increasing role in emerging technologies like molecular electronics or hybrid photovoltaics. For such applications, the adsorption geometry of the molecules under operating conditions, e.g., ambient temperature, is crucial because it influences the electronic properties of the interface, which in turn determine the device performance. So far detailed experimental characterization of adsorbates at room temperature has mainly been done using a combination of complementary methods like photoelectron spectroscopy together with scanning tunneling microscopy. However, this approach is limited to ensembles of adsorbates. In this paper, we show that the characterization of individual molecules at room temperature, comprising the determination of the adsorption configuration and the electrostatic interaction with the surface, can be achieved experimentally by atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). We demonstrate this by identifying two different adsorption configurations of isolated copper(ii) meso-tetra (4-carboxyphenyl) porphyrin (Cu-TCPP) on rutile TiO2 (110) in ultra-high vacuum. The local contact potential difference measured by KPFM indicates an interfacial dipole due to electron transfer from the Cu-TCPP to the TiO2. The experimental results are verified by state-of-the-art first principles calculations. We note that the improvement of the AFM resolution, achieved in this work, is crucial for such accurate calculations. Therefore, high resolution AFM at room temperature is promising for significantly promoting the understanding of molecular adsorption.
Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland.
Res
R
Jöhr
Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland.
Antoine
A
Hinaut
Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland.
Rémy
R
Pawlak
Physics Department, Shahid Beheshti University, G. C., Evin, 19839 Tehran, Iran.
Ali
A
Sadeghi
Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland.
Santanu
S
Saha
Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland.
Stefan
S
Goedecker
Department of Physics, Jagiellonian University, Lojasiewicza 11, 30-348 Krakow, Poland.
Bartosz
B
Such
Department of Physics, Jagiellonian University, Lojasiewicza 11, 30-348 Krakow, Poland.
Marek
M
Szymonski
Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland.
Ernst
E
Meyer
Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland.
Thilo
T
Glatzel