Reducing dislocation defect levels via sub-melt nanosecond pulsed-laser induced densification of diamond

TL;DR

This study demonstrates that nanosecond pulsed-laser annealing effectively relaxes dislocation-related strain in synthetic diamond by densifying and reorganizing near-surface defect networks, improving material quality for advanced applications.

Contribution

It provides quantitative evidence that sub-melt PLA reduces dislocation defects and strain in diamond, a novel approach for defect repair without damaging the material.

Findings

Significant reduction in surface roughness and void volume after PLA.

Narrowing of Raman spectral features indicating strain relaxation.

Smoother strain fields confirmed by STEM-GPA analysis.

Abstract

Dislocations and polishing-induced defect networks in synthetic diamond generate local strain fields that broaden Raman features and limit optical, thermal, and electronic performance. Sub-melt laser annealing has emerged as a route to repair near-surface defects without graphitization, yet quantitative evidence of densification, defect depletion, and property recovery remains limited. Here, we show that nanosecond pulsed-laser annealing (PLA) can relax dislocation-associated strain in single-crystal CVD diamond by compacting and reorganizing the damaged near-surface region. Single- and two-pulse PLA were applied, and structural evolution was quantified using co-registered ISO 25178 white-light interferometry, depth-resolved Raman spectroscopy, and cross-sectional STEM with geometric phase analysis (GPA). Across a 5x6 grid(n = 30), responsive regions show large reductions in local slope (Sdq 45-65%), developed area (Sdr 60-90%), height spread (Sp, Sz 30-65%), void volume (Vv 57-60%), and roughness amplitude (Sa, Sq 48-57%), consistent with densification of ~4-6.5 nm. Raman profiling reveals narrowing of the diamond line and improved spectral uniformity to depths of ~2-3 {\mu}m, indicating relaxation of dislocation-mediated strain beyond the compaction layer. STEM-GPA strain maps confirm smoother strain fields, reduced hotspots, and redistribution of localized strain concentrations after PLA. These results show that sub-melt PLA reduces dislocation-driven strain by compacting surface-connected free volume and reorganizing defect networks. The approach provides a scalable path to upgrade industrial-grade diamond including homoepitaxial, heteroepitaxial, and polycrystalline CVD to low-defect, device-ready surfaces relevant to high-power electronics, photonics, and quantum substrates.