The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Scanning Force Microscopy Simulations of Nanoparticles on Insulating Surfaces

Olli Pakarinen

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Information and Natural Sciences for public examination and debate in Auditorium E at Helsinki University of Technology (Espoo, Finland) on the 15th of February, 2008, at 13 o'clock.

Overview in PDF format (ISBN 978-951-22-9222-6)   [1588 KB]
Dissertation is also available in print (ISBN 978-951-22-9221-9)

Abstract

Scanning (atomic) force microscopy (SFM/AFM) is a surface science method capable of imaging surfaces with atomic resolution. SFM is a local probe method, closely related to other scanning probe microscopy methods like scanning tunneling microscopy (STM). Dynamic SFM studied in this thesis utilizes a very sharp tip at the end of an oscillating cantilever, and forms images of surfaces by measuring the tip-sample interaction while scanning very close (typically less than 1 nm) above the surface.

Computational work is typically needed for interpretation of experimental SFM results, as the output of the instrument depends strongly on the atomic structure of the tip apex, unknown in most experiments. Simulations also open a window to view the atomic scale processes which determine the outcome of the experiment, and can show new ways to optimise the use of SFM.

This dissertation presents computational simulations of scanning force microscopy, focusing on imaging nanoscale particles on insulating surfaces. Numerical methods to calculate the tip-sample interactions are developed. Simulations of atomic resolution contrast in SFM imaging are performed utilizing density functional theory as well as semiclassical methods. Larger scale simulations focusing on the tip convolution problem are made possible with the development of a numerical code calculating van der Waals interaction between arbitrarily shaped objects. The effect of humidity on particle-surface interaction is studied by development of another numerical code modeling the capillary forces.

The described work generates new understanding of image formation in SFM, and of the change of behavior of capillary forces at the nanoscale. A new application to utilize the constant height mode of SFM to greatly diminish the tip convolution effect is presented, and its success is explained with simulations.

This thesis consists of an overview and of the following 5 publications:

  1. A. S. Foster, O. H. Pakarinen, J. M. Airaksinen, J. D. Gale, and R. M. Nieminen, Simulating atomic force microscopy imaging of the ideal and defected TiO2 (110) surface, Physical Review B 68, 195410 (2003). © 2003 American Physical Society. By permission.
  2. O. H. Pakarinen, A. S. Foster, M. Paajanen, T. Kalinainen, J. Katainen, I. Makkonen, J. Lahtinen, and R. M. Nieminen, Towards an accurate description of the capillary force in nanoparticle-surface interactions, Modelling and Simulation in Materials Science and Engineering 13, 1175 (2005). © 2005 Institute of Physics Publishing. By permission.
  3. C. Barth, O. H. Pakarinen, A. S. Foster, and C. R. Henry, Imaging nanoclusters in the constant height mode of the dynamic SFM, Nanotechnology 17, S128 (2006). © 2006 Institute of Physics Publishing. By permission.
  4. O. H. Pakarinen, C. Barth, A. S. Foster, R. M. Nieminen, and C. R. Henry, High-resolution scanning force microscopy of gold nanoclusters on the KBr (001) surface, Physical Review B 73, 235428 (2006). © 2006 American Physical Society. By permission.
  5. Olli H. Pakarinen, Clemens Barth, Adam S. Foster, and Claude R. Henry, Imaging the real shape of nanoclusters in scanning force microscopy, Journal of Applied Physics 103, 054313 (2008). © 2008 American Institute of Physics. By permission.

Keywords: force microscopy, SFM, AFM, nc-AFM, DFM, nanoclusters

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© 2008 Helsinki University of Technology

Last update 2011-05-26