Scanning tunneling microscopy in the field-emission regime: Formation of a two-dimensional electron cascade

Wolfgang S M Werner,Hugo Cabrera,Alessandra Bellissimo,Ilona Müllerová,Oguzhan Gürlü,Gabriele Bertolini,Martin Oral,Jiří Zelinka,Tomáš Radlička

doi:10.1063/1.5128300

Abstract

The signal generation mechanism of the scanning field-emission microscope has been investigated via model calculations combining deterministic trajectory calculations in the field surrounding the field-emission tip in vacuum, with Monte Carlo simulations of the electron transport inside the solid. This model gives rise to a two-dimensional electron cascade. Individual trajectories of detected backscattered electrons consist of repeated segments of travel in vacuum followed by a re-entry into the solid and re-emission into vacuum after being elastically or inelastically scattered. These so-called electron bouncing events also create secondary electrons at macroscopic distances away from the primary impact position. The signal reaching the detector is made up of elastically and inelastically backscattered primary electrons created near the impact position under the tip and those secondary electrons created far away from it.

Highlights

An essential improvement is obtained when electron trajectories in vacuum are described in a deterministic way,7 while the transport inside the solid is modeled in a stochastic manner.8 The latter part comprises multiple elastic and inelastic scattering as well as the generation of the cascade of secondary electrons and their escape over the
The results show a salient difference of the signal generation mechanism with respect to conventional secondary electron microscopy: the formation of a two-dimensional electron cascade, which propagates along the surface in the field between the electron source, the sample, and the detector
The current model does not account for the details of the field emission process at the tip and assumes the latter to behave as a pointlike source emitting electrons only from the very center of the tip apex

Summary

Introduction

An essential improvement is obtained when electron trajectories in vacuum are described in a deterministic way,7 while the transport inside the solid is modeled in a stochastic manner.8 The latter part comprises multiple elastic and inelastic scattering as well as the generation of the cascade of secondary electrons and their escape over the. The signal reaching the detector is made up of elastically and inelastically backscattered primary electrons created near the impact position under the tip and those secondary electrons created far away from it.

Results

Conclusion