AVS 49th International Symposium
    Nanometer Structures Tuesday Sessions
       Session NS+EL-TuA

Paper NS+EL-TuA9
Growth and Properties of Si Compatible Nanostructures: Si Quantum Dots Grown on CaF@sub 2@/Si Films

Tuesday, November 5, 2002, 4:40 pm, Room C-207

Session: Quantum Dots
Presenter: A. Klust, University of Washington
Authors: A. Klust, University of Washington
A.A. Bostwick, University of Washington
T. Ohta, University of Washington
Q. Yu, University of Washington
M.A. Olmstead, University of Washington
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Si/CaF@sub 2@ is a promising candidate for epitaxial semiconductor/insulator heterostructures for optoelectronic applications because of the low lattice mismatch (0.5%) and large band gap difference (12.4 eV for CaF@sub 2@ vs. 1.1 eV for Si). In addition, the strongly dissimilar ionic/covalent bonding character in the system CaF@sub 2@/Si allows it to serves as a model system both to study heteroepitaxy of two dissimilar materials and to study the influence of bonding character and electronic structure on scanning probe microscopy. Here, we present an investigation of ultra-thin (1-3 molecular layers) CaF@sub 2@ films and Si quantum dots grown on these films using both non-contact atomic force microscopy (ncAFM) and scanning tunneling microscopy (STM). On the one hand, the extremely large band-gap of CaF@sub 2@ makes STM measurements difficult; stable imaging is not possible for films thicker than 3-4 molecular layers. On the other hand, STM gives complementary information to that obtained with ncAFM. For instance, scanning tunneling spectroscopy is used to characterize the electronic properties of single Si QD. Furthermore, the contrast during STM imaging of the CaF@sub 2@ films depends strongly on the polarity of the bias voltage and the film thickness. Non-contact AFM is used to clarify this behavior to separate electronic and topographic contributions to the STM images. Atomically-resolved ncAFM images of the CaF/Si interface layer will be shown and compared with similar published data obtained from bulk CaF@sub 2@(111) crystals.@footnote 1@ The atomic structure of the CaF/Si interface layer is practically identical to the surface structure of bulk CaF@sub 2@(111), while the electronic structure differs. We discuss the influence of the different electronic structure on atomic resolution ncAFM. @FootnoteText@ @footnote 1@A. S. Foster, C. Barth, A. L. Shluger, and M. Reichling, Phys. Rev. Lett. 86 (2001) 2373.