Ultrafast imaging of photoelectron packets generated from graphite surface

TL;DR

This paper introduces a novel ultrafast imaging technique to observe the evolution of photoelectron packets from graphite, revealing detailed dynamics of electron emission, acceleration, and surface charge interactions.

Contribution

It presents a new electron projection imaging method to study ultrafast photoelectron dynamics and surface charge effects near graphite surfaces.

Findings

Photoelectron emission from graphite originates from thermionic emission.

Electrons undergo adiabatic acceleration and cooling before expansion.

Surface charge dipole layers form with high sheet density.

Abstract

We present an electron projection imaging method to study the ultrafast evolution of photoelectron density distribution and transient fields near the surface. The dynamical profile of the photoelectrons from graphite reveals an origin of a thermionic emission, followed by an adiabatic process leading to electron acceleration and cooling before a freely expanding cloud is established. The hot electron emission is found to couple with a surface charge dipole layer formation, with a sheet density several orders of magnitude higher than that of the vacuum emitted cloud.