Purified graphite surface and vacancy states: undercoordination-induced quantum trap depression and lone pi-electron polarization

TL;DR

This paper introduces a straightforward method to purify graphite surface and vacancy states using angle-resolved XPS, confirming theoretical predictions about bond shortening, local strain, and electron polarization effects.

Contribution

It provides experimental validation of BOLS theory and elucidates how undercoordination induces quantum trap depression and electron polarization in graphite.

Findings

Shorter atomic bonds induce local strain and quantum potential depression.

Polarization of unpaired pi-electrons leads to high protrusions and Dirac EF states.

Quantum trap depression causes splitting of XPS C 1s states.

Abstract

We present a simple approach for purifying graphite surface and vacancy states using an angle-resolved x-ray photoelectron residual spectroscopy (XPS). Complementing the discoveries of Ugeda et al [Phys Rev Lett 104, 096804 (2010)], outcomes conform the BOLS theory [Sun, Prog Solid State Chem 35, 1-159 (2007)] expectation and the recent findings that the shorter and stronger bonds between undercoordinated atoms induce local strain and quantum potential depression with an association of local densification of energy and core electrons. The shorter atomic distance and the densely and deeply trapped bonding and core charges polarize in turn the unpaired pi-electrons nearby vacancy, giving rise to the high protrusions and the Dirac EF states as observed. The quantum trap depression and the screening due to the polarized EF states split the crystal potential and hence the extra XPRS C 1s states.