Jacqueline Labra Muñoz
Master student in the Electrical Engineering Department,
Faculty of Physical and Mathematical Science,
University of Chile. (Advisor: Prof. Dr. Diana Dulić)
Research in Nanoscience and Nanotechnology has become one of priority research topics worldwide. In particular fabrication and characterization of nanodevices allow us to explore the fundamental electronic, magnetic and mechanical properties of different systems, including bio-material. The protein networks include ferritin molecules with different iron content (20 – 800 iron atoms per ferritin molecule) and ferritin molecules with gold nanoparticles inside the cavity. We found that ferritin networks present a switching behavior by applying a range of +/- 8V, which is not reproducible and is unstable in time (e.g. by measuring 6 current-voltage cycles). From scanning tunneling microscope (STM) measurements, we stablished that single ferritin molecule (with 20 and 800 iron atoms) presents almost not conduction; the same behavior was found in the case of ferritin with gold content. Both type of measurements were performed in air, at room temperature, in a probe station. We conclude the conduction mechanism is determined mostly by the presence of multiple ferritin molecules (a network) and it is not related with the content inside the cavity of the ferritin molecules. In terms of the inorganic nanoparticles, we measured iron and iron-nickel nanoparticles, covered with an oxide shell of the associated metal. We recorded the current vs. voltage cycles at room temperature, in vacuum. We found that on average, bigger NPs are more conductive than smaller nanoparticles; and that if the density of NPs is higher, the probability of having several connected in parallel increases, and therefore also the current increases. We also measured the current-voltage cycles while increasing the temperature; starting from 20 K until 300 K, in vacuum, in the same probe station and using liquid helium to reach and maintain the low temperature. We found that the current-voltage cycles recorded at low temperature (20 K) had a shape consistent with a modified Coulomb blockade model (including off-set charges) for both type of nanoparticles. However, by studying the temperature dependence of the resistance, we obtained that only in big iron NPs the resistance had strong temperature dependence, i.e., the resistance decreases by 2-3 orders of magnitude while the temperature increases. In the case of iron-nickel nanoparticles the temperature dependence of the resistance was weaker than expected, which is not consistent with Coulomb blockade model. Therefore, we have shown that the modified Coulomb blockade model is consistent with the results obtained for the big iron nanoparticles, but iron- nickel NPs require other model to explain the transport mechanism.