Atomically defined tips in scanning probe microscopy - McGill Physics

AbstractIn this work we describe ultra-high vacuum fabrication of a nanoscale systemthat reveals Coulomb blockade at room temperature and its characterizationby single-electron sensitive electrostatic force microscopy (e-EFM). The systemconsists of Au nanoparticles separated from an Fe(001) back electrode by a crystallineultra-thin NaCl film. Due to the small size of the nanoparticles (3.5 nm high),the Coulomb blockade can be observed at room temperature. An atomic forcemicroscopy (AFM) cantilever is used as a movable gate to charge individual nanoparticlesvia single-electron tunneling from the back electrode. At the same timethe tunneling is detected by measuring frequency shift and damping of the oscillatingcantilever. The e-EFM technique can overcome limitations of other characterizationmethods based on lithographic fabrication. So far, however, it hasbeen successfully used only at low-temperatures. In this work, we extend thee-EFM technique to room temperature by carefully tuning the sample design andfabrication relative to the cantilever response to achieve maximum sensitivity.To grow atomically defined tunnel barriers we investigate the morphologyof MgO and NaCl ultra-thin films on Fe(001) surfaces by non-contact-AFM andlow energy electron diffraction (LEED). First, we demonstrate that the quality ofMgO films, typically grown in ultra-high vacuum (UHV) by electron-beam evaporation,can be improved by using reactive deposition method that gives full controlover the gaseous species existing in the evaporated beam. Second, we investigatethe effects of temperature and oxygen presence on the growth of NaClon Fe(001). As a result, we develop a protocol to grow NaCl films on the Fe(001)-p(1×1)O surface in a layer-by-layer mode, yielding atomically flat films with 40-60nm wide terraces (on a 12 ML thick film) and with far fewer defects than the MgOfilms.Using the NaCl film as a tunnel barrier that can be easily adjusted by modifyingthe film thickness we characterize single-electron charging at room temperatureof individual Au nanoparticles formed after thermal evaporation onto a 6i