Conductivity measurement of individual SnS nanoparticles by Peak Force AFM
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Conductivity measurement of individual SnS nanoparticles by Peak Force AFM C. Prastani1, A. Vetushka2, M. Hývl2, A. Fejfar2, M. Nanu3, D. Nanu3, R. E. I. Schropp4, and J. K. Rath1 1
Utrecht University, Faculty of Science, Debye Institute for Nanomaterials Science-Physics of
Devices, High Tech Campus 5, 5656 AE Eindhoven, The Netherlands 2
Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnicka 10, 162 53
Praha 6, Czech Republic 3
Thin Film Factory B.V., Hemma Oddastrjitte 5, 8927 AA Leeuwarden, The Netherlands
4
Energy Research Center of the Netherlands (ECN), Solar Energy, High Tech Campus Building 5, p-057 (WAY), 5656 AE Eindhoven, The Netherlands. Eindhoven University of Technology (TU/e), Department of Applied Physics, Plasma & Materials Processing, P.O. Box 513, 5600 MB Eindhoven, The Netherlands ABSTRACT Peak Force Atomic Force Microscope is a new technique to characterize fragile materials such as nanoparticles with high accuracy with only one measurement. Unlike the tapping mode AFM, Peak Force AFM operates at a frequency below the resonant frequency of the cantilever. This allows for a direct control of the forces and avoids lateral forces that may damage the sample as in contact mode AFM. Furthermore, the performance characteristics of Peak Force AFM are suitable to work also in Tunneling AFM (TUNA) mode, enabling the study of the electrical properties of materials. In this work SnS nanoparticles capped with tri-n-octylphosphine oxide (TOPO) have been characterized. By means of Peak Force AFM it is possible to measure simultaneously topography and current maps of nanoparticles, yielding information about the shape, size and the conductivity of even a single nanoparticle. The topography map clearly showed single nanoparticles with a size less than 5 nm and spherical shape. In the conductivity map it is possible to discern the same nanoparticles, the correlation with the topography map is evident. This confirms the conduction (though not calibrated) of SnS nanoparticles. This type of measurements has been repeated many times in order to check the reproducibility of this technique. Moreover, the same nanoparticles have been measured also by Torsional Resonant TUNA AFM in order to compare it with Peak Force AFM. By means of TR-TUNA it was possible to measure the topography of SnS nanoparticles capped with TOPO but not the current. Besides, the resolution of the topography map acquired by TR-TUNA AFM is inferior to Peak Force AFM. From this comparison it has been found that the conductivity of nanoparticles, even if they are capped with TOPO, can be measured by Peak Force AFM, a result that thus far has been difficult to achieve by other types of AFM. INTRODUCTION
Nanoparticles have shown great potential to improve the performance of electronic device. They can be used in many biomedical applications [1-2], lithium ion batteries [3-4] and solar cells [5-6]. In the last ten years the research has been focused on the development of new synthesis of nanoparticles in order to improve
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