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• SEMPA
• UHV STM

Scanning Electron Microscopy with Polarization Analysis (SEMPA)

SEMPA schematic

Scanning Electron Microscopy with Polarization Analysis [EPG Pub# 555] is a technique that we have developed for looking at very small magnetic structures.

SEMPA images the magnetization by measuring the spin polarization of secondary electrons emitted in a scanning electron microscope. The secondary electron spin polarization is directly related to the magnetization of the sample. SEMPA therefore produces a direct image of the magnitude and the direction of the magnetization in the region probed by the incident electron beam.

SEMPA has several unique capabilities that set it apart from other magnetic imaging techniques: First, unlike most other techniques which image the magnetic field, SEMPA measures the magnitude and direction of the magnetization directly. Second, SEMPA has the high spatial resolution (about 10 nm), long working distance, and large depth of field characteristic of scanning electron microscopes. Third, SEMPA measurements of the magnetization are intrinsically independent of the topography, but the magnetic and topographic maps are measured simultaneously. This feature allows investigations of the correlations between magnetic and topographic structures. And finally, SEMPA is a relatively surface sensitive technique, because of the small (~1 nm) secondary electron escape depth. This makes SEMPA especially well suited for in situ studies of thin film and surface magnetization.

Currently, two SEMPA instruments are available in the Electron Physics Group. Both are also scanning Auger microprobes which allow us to obtain compositional maps of specimens as well as SEMPA images. Both instruments also use the same compact electron spin polarization analyzers [EPG Pub# 513] that were developed at NIST.

JEOL JAMP-30

PHI 670

One apparatus (a JEOL JAMP-30) has 60 nm spatial SEMPA resolution and has been modified with the addition of thin film evaporators and a Reflection High Energy Electron Diffraction (RHEED) system in order to do in situ measurements of thin film and multilayer magnetism.


The other SEMPA apparatus (a PHI 670) has a high brightness field emission cathode which enables it to image magnetic microstructures with 10 nm spatial resolution.


Online: August 1995
Last Updated: July 2007