# The Effects of Surface Spin Polarization on Copper Oxidation by Triplet Oxygen

## TL;DR

This paper shows that surface spin polarization can speed up copper oxidation by favoring the formation of CuO over Cu2O.

## Contribution

The study demonstrates that spin-polarized surfaces accelerate copper oxidation through preferential CuO formation.

## Key findings

- Spin-polarized surfaces show faster copper oxide formation compared to nonpolarized regions.
- CuO forms preferentially over Cu2O on spin-polarized surfaces.
- CuO oxidation propagates from the edges of copper films toward the center.

## Abstract

The process of copper oxidation has been thoroughly studied
for
many years, yielding a significant understanding of its kinetics and
chemistry. However, the possible roles of surface spin polarization
in important issues such as oxidation rates have not been widely explored
despite the triplet nature of molecular oxygen. Here, we investigate
the spin-dependent oxidation of copper films by triplet O2, exploiting engineered ferromagnetic substrates to impose controlled
surface spin polarization. Three sample architectures that enable
comparison between spin-polarized and nonpolarized surfaces were implemented
to enable direct comparison between regions of varying spin polarization
on the same sample. Combining various surface-sensitive techniques,
including atomic force microscopy, Kelvin probe force microscopy,
ellipsometry, and magneto-optical Kerr effect, we followed oxide growth
kinetics and electronic property changes over time scales from minutes
to weeks. Our results demonstrate that spin-polarized surfaces exhibit
a significant acceleration in copper oxide formation compared with
less polarized regions. The difference appears to be driven by a preference
toward the formation of cupric oxide (CuO), the second oxidation state
of copper, over cuprous oxide (Cu2O), the first oxidation
state. We suggest that the results are related to the different magnetic
properties of each oxide. Our data also reveal that the CuO oxidation
phase propagates from the Cu film edges toward the center of the sample.
These findings provide direct evidence of the surface-spin influence
on metal oxidation kinetics and support the notion that spin polarization
can induce a lower activation energy barrier for electron transfer
between metal to triplet O2. Beyond advancing the fundamental
understanding of corrosion chemistry, this spin-dependent control
of surface reactivity opens potential avenues for tailored catalyst
design, spintronic device stability, and corrosion mitigation strategies.