Analysis of femtosecond laser surface patterning on bulk single-crystalline diamond

Abstract

Preliminary work is reported on 2-D and 3-D microstructures written directly with a Yb:YAG 1026 nm femtosecond (fs) laser on bulk chemical vapour deposition (CVD) single-crystalline diamond. Smooth graphitic lines and other structures were written on the surface of a CVD diamond sample with a thickness of 0.7 mm under low laser fluences. This capability opens up the opportunity for making electronic devices and micro-electromechanical structures on diamond substrates. The fabrication process was optimised through testing a range of laser energies at a 100 kHz repetition rate with sub-500 fs pulses. These graphitic lines and structures have been characterised using optical microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy. Using these analysis techniques, the formation of sp 2 and sp 3 bonds is explored and the ratio between sp 2 and sp 3 bonds after fs laser patterning is quantified. We present the early findings from this study and characterise the relationship between the graphitic line formation and the different fs laser exposure conditions.

Femtosecond laser micromachining of diamond: Current research status, applications and challenges

“…The acid-scrub involves cleaning the samples in a solution of sulphuric (H 2 SO 4 ), perchloric and nitric (HNO 3 ) acids (mixed at 5:3:1 wt.% ratios) and heated to 200 °C to remove the graphitized layer formed on the machined surface [35]. Likewise, an aqua regia, a mixture of HNO 3 and hydrochloric acids (at 1:3 wt.% ratios) can be employed to boil the samples at 120 °C for 2 hrs [107]. Following the acid cleaning process, the samples are rinsed in a de-ionised water and dried with a compressed nitrogen gas [107].…”

“…Likewise, an aqua regia, a mixture of HNO 3 and hydrochloric acids (at 1:3 wt.% ratios) can be employed to boil the samples at 120 °C for 2 hrs [107]. Following the acid cleaning process, the samples are rinsed in a de-ionised water and dried with a compressed nitrogen gas [107].…”

Femtosecond laser-induced microstructures on diamond for microfluidic sensing device applications

“…The root mean square (RMS) roughness of the substrate without fs-laser irradiation was 4.9 nm. 6 In comparison, the RMS roughness of irradiated area was 64.3 6 10.8 nm in the microfluidic channels. The increased roughness was due to the formation of the graphitic clusters by the laser-induced plasma.…”

“…However, little progress on in vivo biocompatible devices has been reported, for the extreme hardness of diamond increases the difficulties in fabrication of nano/micrometer structures on its surface. 6 Previously, surface modification on diamond substrates was performed by focused ion beam (FIB) technology, but it required a longer time (up to hours) to complete the entire fabrication process. 7 Reactive ion etching (RIE) has been offered as an alternative method with an inefficient etching rate of $10 lm h À1 on the diamond surface.…”

“…Before the fs-laser irradiation, the diamond was subjected to the process of removing surface contaminations. 6 After finishing surface cleaning process, the diamond substrate was fixed on a flat glass slide for insertion into the fs-inscription system. After fs-laser irradiation, the diamond substrate was characterized by SEM, Raman spectroscopy and AFM, after being subjected to the following further cleaning process: (1) immersion in acetone/isopropanol ultrasonic bath (room temperature, 30 min/ 30 min) to remove organic contamination; (2) boiling in aqua regia (70 C, 2 h) to remove metallic contamination; (3) boiling in 95% H 2 SO 4 þ 36% HNO 3 (9:1, 100 C, 8 h) to partially remove the graphitic layer generated by the fslaser.…”