Force interaction between a W tip and Si(111) investigated under ultrahigh vacuum conditions
2000 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 62, no 20, 13680-13686 p.Article in journal (Refereed) Published
The force on a W tip has been measured in ultrahigh vacuum during approach and indentation against Si(111). The maximum separation where we detect an attractive force is 5 Å, which is within the range where wave-function overlap should occur. Calculating the van der Waals force using the sphere-flat geometry and a radius of 150 Å that we determine by scanning electron microscopy overestimates the force, while a cone-shaped tip apex is consistent with our results. After contact we observe discontinuous steps in the force curve in agreement with molecular-dynamics simulations. The stiffness of the junction increases during the first 5 Å after contact and stabilizes at ~25 N/m, which is approximately a factor of 3 lower than estimated from classical elasticity theory. The maximum adhesive force is ~5 nN. We also present a model that relates the dynamic behavior of the force-feedback controller to the formation of a connective neck over the tip-surface gap.
Place, publisher, year, edition, pages
2000. Vol. 62, no 20, 13680-13686 p.
Engineering and Technology
IdentifiersURN: urn:nbn:se:liu:diva-47541DOI: 10.1103/PhysRevB.62.13680OAI: oai:DiVA.org:liu-47541DiVA: diva2:268437