# Subnanometer Thick Native sp2 Carbon on Oxidized Diamond Surfaces

## TL;DR

This paper uses angle-resolved XPS to study the chemical composition of the top few nanometers of diamond surfaces terminated with oxygen or hydrogen.

## Contribution

The study introduces a novel method using angle-resolved XPS to determine the thickness and chemical composition of the sp2 carbon layer on oxidized diamond surfaces.

## Key findings

- The sp2 carbon layer on oxygen-terminated diamond is 0.3 ± 0.1 nm thick.
- Oxygen is primarily bonded to the sp2 carbon layer rather than the sp3 diamond core.
- Angle-resolved XPS successfully identified sp2, ether, hydroxyl, carbonyl, and C–H groups on diamond surfaces.

## Abstract

Oxygen-terminated diamond has a wide breadth of applications,
which
include stabilizing near-surface color centers, semiconductor devices,
and biological sensors. Despite the vast literature on characterizing
functionalization groups on diamond, the chemical composition of the
shallowest portion of the surface (<1 nm) is challenging to probe
with conventional techniques like XPS and FTIR. In this work, we demonstrate
the use of angle-resolved XPS to probe the first ten nanometers of
both oxygen and hydrogen terminated (100) single-crystalline diamond
grown via chemical vapor deposition (CVD). With the use of consistent
peak-fitting methods, the peak identities and relative peak binding
energies were identified for sp2 carbon, ether, hydroxyl,
carbonyl, and C–H groups for both of these diamond surface
terminations. For the oxygen-terminated sample, we also quantified
the thickness of the sp2 carbon layer situated on top of
the bulk sp3 diamond bonded carbon to be 0.3 ± 0.1
nm, based on the analysis of the Auger electron spectra and D-parameter
calculations. These results indicate that the majority of the oxygen
is bonded to the sp2 carbon layer on the diamond, and not
directly to the sp3 diamond bonded carbon.