University of Twente Student Theses


Investigation into the transport properties of isolated FePt nanoparticles using STM

Groen, Maarten (2011) Investigation into the transport properties of isolated FePt nanoparticles using STM.

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Abstract:Using single, hard-magnetic clusters at the nanoscale may be an important step towards higher bit densities and improved performance for next-generation data storage systems. In light of this application, this project investigates the electron transport properties of ~3 nm FePt nanoparticles using STM spectroscopy, focusing on single-electron tunneling (Coulomb blockade) behavior and spin-dependent transport (TMR measurements). The deposition of single, isolated nanoparticles on surfaces is studied and achieved through control of nanoparticle dispersion concentration and submergence time of adhesive substrates in this dispersion. The results are verified by STM topographic and spectroscopic measurements. For single-electron experiments highly conductive gold surfaces were fabricated, while for TMR experiments Co/Al2O3 and LSMO surfaces were fabricated as ferromagnetic substrates. Particle immobilization on gold substrates is achieved using 1,9-nonanedithiol selfassembled monolayers, as demonstrated by STM topographic imaging. For Co/Al2O3 and LSMO substrates a ~3 nm poly(ethyleneimine) polymer film is used as adhesion layer. On this material anchoring is found to not be strong enough to allow STM measurements, and strong tip degradation is observed. Using the dithiol adhesion layer on flame-annealed gold, the Coulomb blockade is reproducibly observed in STM I-V spectroscopy at low temperature (T ≈ 40 K). The Coulomb staircase is used to derive a Coulomb charging energy of ~0.15 eV ( =ˆ ~1.1 aF total capacitance) for one nanoparticle. The onset of Coulomb blockade is also made visible in room temperature measurements.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:35 chemistry
Programme:Nanotechnology MSc (60028)
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