3D-Hydrogen Analysis of Ferromagnetic Microstructures in Proton Irradiated Graphite

TL;DR

This study uses 3D hydrogen microscopy to analyze hydrogen distribution in proton-irradiated graphite, revealing confined hydrogen peaks and lateral diffusion, which may influence magnetic properties.

Contribution

It provides the first detailed 3D hydrogen distribution analysis in proton-irradiated graphite, linking hydrogen localization to magnetic order mechanisms.

Findings

Hydrogen is confined within the end of range in irradiated graphite.

No evidence of diffusion broadening along the c-axis.

Lateral hydrogen diffusion accounts for missing hydrogen in microspot regions.

Abstract

Recently, magnetic order in highly oriented pyrolytic graphite (HOPG) induced by proton broad- and microbeam irradiation was discovered. Theoretical models propose that hydrogen could play a major role in the magnetism mechanism. We analysed the hydrogen distribution of pristine as well as irradiated HOPG samples, which were implanted to micrometer-sized spots as well as extended areas with various doses of 2.25 MeV protons at the Leipzig microprobe LIPSION. For this we used the sensitive 3D hydrogen microscopy system at the Munich microprobe SNAKE. The background hydrogen level in pristine HOPG is determined to be less than 0.3 at-ppm. About 4.8e15 H-atoms/cm^2 are observed in the near-surface region (4 um depth resolution). The depth profiles of the implants show hydrogen located within a confined peak at the end of range, in agreement with SRIM Monte Carlo simulations, and no evidence of diffusion broadening along the c-axis. At sample with microspots, up to 40 at-% of the implanted hydrogen is not detected, providing support for lateral hydrogen diffusion.