Nano-scale surface interactions Studied by TEM-SPM

Rynno Lohmus 1Donats Erts 2Ants Lohmus 1Hakan Olin 3Ilmar Kink 1Justin D. Holmes 4

1. Institute of Physics, University of Tartu, Riia str. 142, Tartu 51014, Estonia
2. Institute of Chemical Physics, Riga LV-1586, Latvia
3. Chalmers University of Technology, Physics and Engineering Physics (CTH), Göteborg 41296, Sweden
4. Cork University College, Department of Chemistry, Cork, Ireland

Abstract

Scanning probe microscope (SPM) in combination with transmission electron microscope (TEM), so called TEM-SPM , was used for adhesion and force interaction studies of metallic and semiconducting nanowires and nanocontacts. TEM-SPM is an attractive combined tool for direct investigation of the structure, electronic properties, and interactions in atomic scale. In TEM-SPM the size and shape of the tip and sample, as well as the size of contact area and the type of interaction (elastic/plastic), are observed directly.
In short, our TEM-SPM consists of a piezo tube which is used for fine motion, and of a geared stepping motor for rough z-motion. For force measurements we used an AFM cantilever. The force was measured by direct measurement of the displacement of the AFM tip. The TEM-SPM was inserted into a Philips CM200 field emission gun TEM. TEM-SPM was used to investigate force interactions between two gold samples and mechanical properties and force interactions of Si and Ge nanowires.
When approaching gold coated AFM tip to sharp Au tip an anomalous high value of the jump-to-contact distance was found. We ascribe this to an enhanced surface diffusion of gold atoms towards the tip-sample gap due to the van der Waals forces, leading to an avalanche situation where the gap is quickly filled until the ordinary jump-to-contact distance. Neck formation was observed in the gap between two nanocontacts during the jump to contact. It showed up when the gap between two gold nanoasperities was decreased below 1 nm.
The contact radius at zero applied loads were measured and compared with adhesion theories. The results were in the Maugis transition region, between the limiting cases of the Derjaguin-Müller-Toporov (DMT) and the Johnson-Kendall-Roberts (JKR) models.
Nanowire of diameter less than 1 nm was created in the gap between two Au nanocontacts by lateral AFM tip movement. The rupture force of Au nanowire was 9 nm, which corresponds to about 1 nN per atom.

Presentation: invited oral at E-MRS Fall Meeting 2003, Symposium F, by Rynno Lohmus
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-15 10:45
Revised:   2009-06-08 12:55
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