Field emission regime of a scanning tunnelling microscope: studies of Er/W(110) Er silicide surfaces

Scanning field-emission microscopy (SFEM) remains an underutilized yet powerful technique in scanning probe microscopy [1]. This regime of scanning tunneling microscopy (STM) offers unique advantages over conventional STM by enabling elemental-specific contrast resolution at the nanoscale.

In SFEM mode, the metallic tip is retracted further from the sample than in typical STM, up to hundreds of nanometers, fully suppressing tunneling. A negative potential applied between the tip and sample generates primary electrons through field emission. SFEM provides access to elemental composition via absorbed current imaging—a level of specificity unattainable in the tunneling regime. Emitted electrons also represent a new electronic system analyzed in the macroscopic environment via an electron analyzer, enabling secondary electron imaging and spectroscopy [2].

We present interactions of Er-silicide nanostructures on Si(111) [3] and Er-/Fe-W(110) surfaces, with complementary STM and STS results. These surfaces provide a platform to explore the SFEM, creating a contrast based on intrinsic material properties not available from topological analysis. We show absorbed current and energy-filtered imaging alongside spectroscopy to refine low-energy electron analysis, demonstrating material-specific imaging beyond STM capabilities.

[1] J. J. Sáenz et al., Appl. Phys. Lett. 65, 3022 (1994)

[3] D. A. Zanin et al., Proc. R. Soc. A 472, 20160475 (2016)

[4] C. Woffinden et al., Phys. Rev. B 79, 245406 (2009)