In order to image individual bits in hard disks or domains in magnetic materials, the silicon tip of an SFM (see glossary) must be made sensitive to the magnetic leakage fields emerging from such samples.

Construction of a complex ultra-high vacuum force microscope at Empa

Glossary: In 1986 the inventors of the scanning force microscope called their discovery the Atomic Force Microscope (AFM), a designation that is still common today. However, since it is possible to measure not only interatomic forces, but also forces of a different physical or chemical nature the instrument is also known today as a Scanning Force Microscope (SFM).

Work is now in progress at Empa aimed at considerably improving MFM tips using the equipment for thin film production and for characterization of magnetic materials available to researchers there. It will then be possible to achieve a lateral resolution of a few nanometers. One Empa researcher is concentrating on magnetic point contacts, while others are working on reliable magnetic storage devices and magnetic shape memory alloys.

Apart from the imaging of magnetic materials, the SFM is also used at Empa to characterize surfaces on the atomic scale. The Basel Institute of Physics achieved an important breakthrough with the development of a complex force microscope (UHVLTSFM) that operates in an ultra-high vacuum (UHV) and at low temperatures (only a few degrees above absolute zero). This was used in 2001 to measure the force between two individual atoms for the first time ever.The tip was positioned over a selected atom and then brought up close to it. The chemical link occurring between the foremost atom of the tip and the sample atom was then measured as a function of the distance between the two atoms. This provides the basis for manipulating material on an atomic scale with the SFM and combining nanostructures from individual atoms or molecules. Physicists and mechanical engineers are currently designing and building a complex UHV-LTSFM at Empa. It will be possible to use ultra-small cantilevers (ten times smaller than those used today) in this device, thereby enabling its sensitivity to be increased by a factor of 10.This ought to make it possible, for example, not only to image individual molecules but also to observe their oscillation states and to carry out further experiments vital for basic research.

Prof. Dr Hans Josef Hug, Empa, Überlandstr. 129, CH-8600 Dübendorf, Switzerland, Tel. +41 (0)44 823 41 25, E-mail: hans-josef.hug@empa.ch, www.empa.ch
www.SwissProbe.com

Funding and scientific support by:

• Empa internal research programmes
• NCCR Nanoscale Science (Basel University)
• SNF
• R’EQUIP
• Top Nano 21
• KTI

References:

• G. Binnig, C.F. Quate, C. Gerber, Phys. Rev. Lett. 56, 930 (1986).
• P. Kappenberger, H.J. Hug et al., Phys. Rev. Lett. 91, 267202/1 (2003).
• M.A. Lantz, H.J. Hug, et al., Science 291, 2580 (2001).