Browsing by Author "Barth, Clemens"

Now showing 1 - 4 of 4
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    Chemical Identification of Ions in Doped NaCl by Scanning Force Microscopy
    (American Physical Society (APS), 2009) Foster, Adam S.; Barth, Clemens; Henry, Claude R.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of Science
    A quantitative comparison between experiment and theory is presented, which shows that all ions of the Suzuki structure on (001) surfaces of Mg2+ or Cd2+ doped NaCl crystals can be identified despite the tip-surface distance, differences in impurity chemistry, and surface termination. The identification can be used to calibrate the potential of the tip's last atom, and it is proposed to use these surfaces for better characterization of deposited nano-objects.
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    Defect mediated manipulation of nanoclusters on an insulator
    (Nature Publishing Group, 2013) Hynninen, Teemu; Cabailh, Gregory; Foster, Adam S.; Barth, Clemens; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of Science
    With modern scanning probe microscopes, it is possible to manipulate surface structures even at the atomic level. However, manipulation of nanoscale objects such as clusters is often more relevant and also more challenging due to the complicated interactions between the surface, cluster and apparatus. We demonstrate the manipulation of nanometer scale gold clusters on the NaCl(001) surface with a non-contact atomic force microscope, and show that the movement of clusters is in certain cases constrained to specific crystallographic directions. First principles calculations explain this kinetic anisotropy as the result of the cluster attaching to surface defects: cation vacancies allow the clusters to bond in such a way that they only move in one direction. Constraining the movement of clusters could be exploited in the construction of nanostructures or nanomechanical devices, and the manipulation signatures may also be used for identifying cluster-defect complexes.
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    Imaging the real shape of nanoclusters in scanning force microscopy
    (AIP Publishing, 2008) Pakarinen, Olli H.; Barth, Clemens; Foster, Adam S.; Henry, Claude R.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of Science
    A quantitative comparison between experiment and theory is given for the constant height mode imaging of metal nanoclusters in dynamic scanning force microscopy. We explain the fundamental mechanisms in the contrast formation with the help of the system Pd/MgO(001). The comparison shows that the shape and size of nanoclusters are precisely imaged due to the sharpness of the tip’s last nanometer. This quantitative comparison proves our previously proposed model for the contrast formation.
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    Role of tip structure and surface relaxation in atomic resolution dynamic force microscopy: CaF2(111) as a reference surface
    (American Physical Society (APS), 2002) Foster, Adam S.; Barth, Clemens; Shluger, Alexander L.; Nieminen, Risto M.; Reichling, Michael; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of Science
    By combining experimental dynamic scanning force microscope (SFM) images of the CaF2(111) surface with an extensive theoretical modeling, we demonstrate that the two different contrast patterns obtained reproducibly on this surface can be clearly explained in terms of the change of the sign of the electrostatic potential at the tip end. We also present direct theoretical simulations of experimental dynamic SFM images of an ionic surface at different tip-surface distances. Experimental results demonstrate a qualitative transformation of the image pattern, which is fully reproduced by the theoretical modeling and is related to the character of tip-induced displacements of the surface atoms. The modeling of the image transformation upon a systematic reduction of the tip-surface distance with ionic tips allows an estimate of the tip-surface distance present in experiment, where 0.28–0.40 nm is found to be optimal for stable imaging with well-defined atomic contrast. We also compare the modeling with ionic tips to results for a pure silicon tip. This comparison demonstrates that a silicon tip can yield only one type of image contrast and that the tip-surface interaction is not strong enough to explain the image contrast observed experimentally. The proposed interpretation of two types of images for the CaF2(111) surface can also be used to determine the chemical identity of imaged features on other surfaces with similar structure.