Argonne National Laboratory Center for Nanoscale Materials U.S. Department of Energy

Developing Smarter STM Tips

Scanning tunneling microscopy tips

X-ray nanotomography surface rendering of a smart scanning tunneling microscope tip. The platinum-iridium tip (red) has been coated with a SiO2 insulating layer (green). Image obtained using the CNM's Hard X-Ray Nanoprobe beamline at Sector 26 of the Advanced Photon Source.

Scientists from the Center for Nanoscale Materials X-Ray Microscopy and Electronic & Magnetic Materials & Devices groups, in collaboration with Argonne's Electron Microscopy Center and X-Ray Science Division, have used CNM's Hard X-Ray Nanoprobe to obtain for the first time an important three-dimensional view of insulator-coated smart tips that in the future can be utilized in synchrotron X-ray scanning tunneling microscopy (SXSTM).

The team used X-ray nanotomography technology available at the Hard X-Ray Nanoprobe to study the buried interface between the platinum-iridium tip and the insulating film in order to understand the structural and transport properties of the insulating coatings. The ability to see the internal structure of these coatings with X-ray nanotomography at a voxel resolution of 30 nm has helped to better understand the coating process, which in turn will guarantee exceptionally performing tips for SXSTM research.

One of today's great challenges is to develop techniques that enable the study of novel materials at nanometer length scales with electronic, chemical, and magnetic contrast. The combination of scanning tunneling microscopy with synchrotron X-rays has the potential to meet this goal. While the scanning probe provides the high spatial resolution, photoabsorption of X-rays yields chemical and magnetic contrast. However, in order to take full advantage of the method's potential, novel insulator-coated tips with ultrasmall conducting apexes have to be developed. The insulating layer smartly minimizes the background signal otherwise detected by the sidewall of the tip.

V. Rose, T. Y. Chien, J. Hiller, D. Rosenmann, and R. P. Winarski, " X-ray nanotomography of SiO2-coated Pt90Ir10 tips with sub-micron conducting apex," Applied Physics Letters, 99, 173102 (2011)

January 2012

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