Atomic structure and spin polarization at the apex of tips used in spin-polarized scanning tunneling microscopy

Abstract

To analyze spin-polarized scanning tunneling microscopy (STM) studies quantitatively, we evaluated the atomic structure and spin polarization at the apex of Cr/W and Fe/W tips using field ion microscopy (FIM) and field-emitted electron polarimetry, respectively. The patchwork-patterned H2-FIM images of the Cr/W tip indicated partially developed Cr planes, and the spin polarization at the surface was 10 ± 3% at room temperature. H2-FIM images of the Fe/W tip indicate the crystalline order of Fe layers on the W tip, and its spin polarization was 41 ± 2%. These first results allow us to quantify the spin polarization in spin-dependent STM measurements.