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Title: Forces at the nanoscale : interactions in atomic force microscopy and dielectrophoresis
Author: Sweetman, Adam
ISNI:       0000 0004 2689 1075
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2010
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Interactions at the nanoscale are governed almost exclusively by electromagnetic forces, but the interplay between different scaling laws produces a vast array of behaviours. We investigate radically different systems spanning almost three orders of magnitude of length scales, and use a variety of experimental techniques to determine the forces present in each regime, and the interplay between them. An important prototypical surface in SPM science has been the Si(100) surface, which due to it’s unstable buckling and complex electronic structure has fostered considerable debate in the surface science community. We have used small amplitude, high sensitivity combined qPlus STM/AFM to investigate tip -- sample interactions on the Si(100) surface at low-temperature in UHV, with a focus on the chemical, and electronic properties of the system and how these are modified by the probe. We present the first atomic resolution combined force/tunnel current results on the surface and show that great care must be taken in interpreting either pure AFM or pure STM data. We also examine tip -- sample interactions on arrays of thiol passivated spin-cast nanoparticles in both UHV and ambient conditions and show for the first time how minor modifications to the experimental parameters can radically alter the data collected, most likely due to the thiol -- surface -- tip interaction. We also present SKPM and voltage spectroscopy of the same samples and show the importance of electrostatic interactions in correct height determination of these network arrays, in parallel with the caution that must be maintained in interpreting CPD data. A key mechanism for the manipulation of meso-scale objects in solution is Dielelectrophoresis, which offers strong material and size specificity and a high degree of spatial control. In the final experimental chapter we investigate the effect of inhomogenous electric fields on nanoparticles in aqueous solution, and reveal how previously uninvestigated electrochemical effects can become important even at high frequencies, and may offer a new and exciting route for the control of self organised nanowires in solution.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics