Size Effect in Electron Paramagnetic Resonance Spectra of Impurity Centers in Diamond Nanoparticles

TL;DR

This study investigates how reducing the size of diamond nanoparticles affects their electron paramagnetic resonance spectra, revealing a transition from hyperfine structure to structureless signals as particles become very small.

Contribution

It provides experimental evidence of size-dependent changes in EPR spectra of diamond nanoparticles, highlighting the delocalization of surface electron spins and suppression of hyperfine interactions at nanoscale.

Findings

Hyperfine patterns diminish with decreasing particle size

Emergence of new structureless signals in small particles

Surface electron spins become delocalized over the entire nanoparticle

Abstract

The evolution of the polycrystalline pattern of electron paramagnetic resonance (EPR) spectra of intrinsic and induced paramagnetic centers in an ensemble of submicrometer diamond particles on diminishing average particle size is considered. Recent experimental data unambiguously demonstrate consistent reduction and then zeroing of typical hyperfine pattern from P1 centers on approaching a certain particle size and below it. These changes are accompanied by appearance and strengthening of new structureless signals. In small particles the electron wave function of a surface paramagnetic center is delocalized over the whole nanoparticle. In result the electron spin "experiences" the average field of all surrounding nuclei, which is zero. At the same time, the paramagnetic centers localized in the bulk of a nanoparticle are also cut off the hyperfine interaction due to the electron spin diffusion. Thus, upon the nanodiamond particle size decreases the hyperfine related features of the polycrystalline EPR spectrum become weaker and the spectrum appear to be structureless.