Bessel beam fabrication of graphitic micro electrodes in diamond using laser bursts

TL;DR

This study demonstrates that using pulsed Bessel beams in burst mode laser writing enables the fabrication of highly conductive graphitic microelectrodes in diamond, with lower resistivity achieved through heat accumulation and optimized burst features.

Contribution

It introduces a novel laser fabrication method using burst mode Bessel beams to produce more conductive graphitic microelectrodes in diamond, surpassing traditional single-pulse techniques.

Findings

Burst mode enhances electrode conductivity via heat accumulation.

Longest burst durations yield the lowest resistivity in electrodes.

Microelectrodes with resistivity around 0.01 Ω·cm are achievable.

Abstract

We present the fabrication of conductive graphitic microelectrodes in diamond by using pulsed Bessel beams in the burst mode laser writing regime. The graphitic wires are created in the bulk of a 500 {\mu}m thick monocrystalline HPHT diamond (with (100) orientation) perpendicular to the sample surface, without beam scanning or sample translation. In particular, the role of different burst features in the resistivity of such electrodes is investigated for two very different sub-pulse durations namely 200 fs and 10 ps, together with the role of thermal annealing. Micro-Raman spectroscopy is implemented to investigate the laser-induced crystalline modification, and the results obtained by using two different laser repetition rates, namely 20 Hz and 200 kHz, are compared. A comparison of the micro-Raman spectra and of the resistivity of the electrodes fabricated respectively with 10 ps single pulses and with bursts (of sub-pulses) of similar total duration has also been made, and we show that the burst mode writing regime allows to fabricate more conductive micro electrodes, thanks to the heat accumulation process leading to stronger graphitization. Moreover, the microfabrication of diamond by means of the longest available bursts (~ 46.7 ps duration) featured by 32 sub-pulses of 200 fs duration, with intra-burst time delay of 1.5 ps (sub-THz bursts), leads to graphitic wires with the lowest resistivity values obtained in this work, especially at low repetition rate such as 20 Hz. Indeed, micro electrodes with resistivity on the order of 0.01 {\Omega} cm can be fabricated by Bessel beams in the burst mode regime even when the bursts are constituted by femtosecond laser sub-pulses, in contrast with the results of the standard writing regime with single fs pulses typically leading to less conductive micro electrodes.