AVS 46th International Symposium
    Magnetic Interfaces and Nanostructures Technical Group Thursday Sessions
       Session MI+NS-ThA

Paper MI+NS-ThA7
Scanning-aperture Photo-emission Microscope for Magnetic Imaging

Thursday, October 28, 1999, 4:00 pm, Room 618/619

Session: Magnetic Imaging
Presenter: G.M. McClelland, IBM Almaden Research Center
Authors: G.M. McClelland, IBM Almaden Research Center
C.T. Rettner, IBM Almaden Research Center
Correspondent: Click to Email
We have demonstrated a new technique for magnetic imaging that is ultimately capable of spatial resolution better than 5 nm. In our instrument, photoemission is excited by a laser focused to a 10-micron spot. A scanning aperture above the magnetic surface allows only electrons from a small selected region to reach the electron detector. The magnetization in this region is determined from the dependence of photoemission on the circular polarization of the laser. Images of 10-nm-thick Co-Pt multilayer thin films on sapphire have been obtained. From a cesiated film, a high quantum efficiency of 0.002 was observed from 458 nm laser light. Circular dichroism of +/- 2 % is recorded by alternating the circular polarization of the light while scanning. The tip distance above the surface is maintained by advancing the tip until 1-nA tunneling to a positive sample is observed, then withdrawing 15 nm and switching polarity to detect photoemission through the tip. The resolution we observe agrees well with the 35-nm-sized aperture in the gold tip. From the observed noise, we project that there is enough signal to image at 5 nm resolution if a small enough aperture can be fabricated. Recent calculations show that image forces on the electron from the aperture walls act to make the effective aperture even smaller than the physical diameter. The insensitivity of the instrument to varying magnetic fields should make it ideal for time dependent magnetization measurements in an applied field.