Laser-Induced Graphitisation of Diamond Under 30 fs Laser Pulse Irradiation

TL;DR

This study investigates how ultrashort 30 fs laser pulses induce graphitisation in CVD diamond, revealing a critical fluence threshold that significantly affects the transformation depth and chemical composition.

Contribution

It provides new insights into the fluence-dependent graphitisation process and chemical changes in diamond under ultrashort laser irradiation.

Findings

Graphitisation occurs below 3.9 J/cm2 fluence, forming crystalline sp2 carbon.

A three-fold increase in graphitised depth occurs near the critical fluence.

C=O groups form below the threshold and gradually cleave with increased fluence.

Abstract

The degree of laser-induced graphitisation from a sp3-bonded to a sp2-bonded carbon fraction in a single crystal chemical vapour deposited (CVD) diamond under a varying fluence of an ultrashort pulsed laser (30 fs, 800 nm, 1 kHz) irradiation has been studied. The tetrahedral CVD sp3-phase was found to transition to primarily an sp2-aromatic crystalline graphitic fraction below the critical fluence of 3.9 J/cm2, above which predominantly an amorphous carbon was formed. A fractional increase of fluence from 3.3 J/cm2 to 3.9 J/cm2 (~ 20 %) resulted in a substantial (~ three-fold) increased depth of the sp2-graphitised areas owing to the non-linear interactions associated with an fs-laser irradiation. Additionally, formation of C=O carbonyl group was observed below the critical threshold fluence; the C=O cleavage occurred gradually with the increase of irradiation fluence of 30 fs laser light. The implications for these findings on enhancement of fs-driven processing of diamond are discussed.