Conductive graphitic wires generation in diamond by means of pulsed Bessel beam micromachining

At a Glance

Metadata	Details
Publication Date	2023-01-01
Journal	EPJ Web of Conferences
Authors	Akhil Kuriakose, Andrea Chiappini, Belén Sotillo, Adam Britel, Pietro Aprà
Institutions	University of Insubria, Istituto di Fotonica e Nanotecnologie
Analysis	Full AI Review Included

Technical Documentation & Analysis: 3D Conductive Graphitic Wires in CVD Diamond

Executive Summary

This research successfully demonstrates the fabrication of highly conductive, three-dimensional graphitic microelectrodes within synthetic Single Crystal Diamond (SCD) using advanced ultrafast laser micromachining techniques.

Core Achievement: Generation of transverse graphitic microelectrodes in 500 µm thick SCD using pulsed Bessel beams (BB) without requiring sample translation.
Material & Method: High-quality monocrystalline CVD diamond was modified in-bulk using a 790 nm Ti:Sapphire laser system, shaped into a Bessel beam with a 3 µm core size.
Record Conductivity: Achieved a low electrical resistivity of 0.04 Ω cm, confirmed to be one of the lowest values reported in the literature for laser-micromachined diamond structures, and the lowest using Bessel beams.
Optimization Insight: Optimal conductivity was achieved using longer pulse durations (10 ps) compared to femtosecond pulses (200 fs), favoring better diamond-to-graphite transformation.
Critical Applications: The resulting conductive structures are essential for next-generation diamond-based detectors, microfluidic chips, and integrated photonic circuits requiring integrated electric field sources or current collection.
6CCVD Relevance: 6CCVD specializes in providing the high-purity, custom-oriented SCD substrates (up to 500 µm thickness) required to replicate and scale this advanced fabrication process.

Technical Specifications

The following hard data points were extracted from the research detailing the material properties and optimal fabrication parameters:

Parameter	Value	Unit	Context
Substrate Material	Monocrystalline CVD Diamond	N/A	Synthetic SCD
Substrate Thickness Used	500	µm	Sample dimension (0.5 mm)
Optimal Electrical Resistivity	0.04	Ω cm	Achieved using 10 ps pulses
Optimal Pulse Duration	10	ps	Favored better conductivity
Optimal Pulse Energy	6	µJ	Used for best IV measurement
Laser Wavelength	790	nm	Ti:Sapphire amplified system
Bessel Beam Core Size	3	µm	Transverse dimension
Bessel Beam Non-Diffracting Length	700	µm	Optimized to cross sample thickness
Crystal Orientations Tested	(100) and (110)	N/A	Affects morphology and conductivity
Number of Pulses (Example)	9000	N/A	Used for 5 µJ, 200 fs fabrication (Fig 1)

Key Methodologies

The fabrication of in-bulk graphitic microelectrodes relied on precise control over the Bessel beam profile and laser parameters:

Material Selection: Monocrystalline CVD diamond samples (5 mm x 5 mm x 0.5 mm) with specific crystal orientations ((100) and (110)) were utilized.
Laser Source: A 20-Hz Ti:Sapphire amplified laser system delivering 40 fs transform-limited pulses at 790 nm was employed, with pulse duration tunable up to the ps regime.
Beam Shaping: A conical lens (axicon) was used to reshape the Gaussian input beam into a finite energy Bessel beam (BB).
Focal Optimization: A telescopic system demagnified the BB to achieve a 3 µm core size and a 700 µm non-diffracting length, ensuring the focal length crossed the entire 500 µm sample thickness.
Micromachining Regime: Fabrication was performed in a multiple shot regime (up to 9000 pulses) with the laser pulses injected orthogonally to the sample surface, eliminating the need for sample translation along the beam propagation direction.
Parameter Tuning: Pulse duration was varied from 200 fs up to 10 ps, and pulse energy was varied (e.g., 5 µJ to 6 µJ) to optimize the diamond-to-graphite conversion.
Characterization: Micro-Raman spectroscopy confirmed the crystalline structure modification, and electrical characterization was performed via Current-Voltage (IV) measurements using a 2-probe configuration.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-specification diamond materials and custom engineering services required to replicate, scale, and advance this research into commercial applications such as high-energy particle detectors and integrated photonics.

Applicable Materials

To achieve the high-quality graphitization and low resistivity demonstrated, the research requires high-purity, low-defect SCD material.

Optical Grade SCD (Single Crystal Diamond): This material is essential for minimizing scattering and absorption during the ultrafast laser process. 6CCVD provides SCD wafers with thicknesses ranging from 0.1 µm up to 500 µm, perfectly matching the 500 µm thickness used in this study.
Custom Crystal Orientation: The study highlights the importance of crystal orientation ((100) vs. (110)) on microstructure morphology. 6CCVD offers custom-oriented SCD substrates to optimize the graphitization process for specific device geometries.

Customization Potential

6CCVD’s in-house capabilities directly address the needs of advanced diamond device fabrication:

Requirement from Research	6CCVD Capability	Benefit to Customer
Substrate Dimensions	Plates/wafers up to 125 mm (PCD) and custom SCD sizes.	Enables scaling from R&D samples (5x5 mm) to production-scale devices.
Thickness Control	SCD thickness control from 0.1 µm to 500 µm.	Provides precise material thickness matching the 500 µm requirement for through-wafer graphitization.
Surface Quality	Polishing to Ra < 1 nm (SCD).	Ensures optimal optical coupling and minimizes surface defects prior to laser processing.
Integrated Electrodes	Internal metalization capability (Au, Pt, Pd, Ti, W, Cu).	While the paper focused on graphitic electrodes, 6CCVD can deposit contact pads (e.g., Ti/Pt/Au) onto the diamond surface for robust electrical interfacing and packaging.
Logistics	Global shipping (DDU default, DDP available).	Ensures rapid and reliable delivery of sensitive materials worldwide.

Engineering Support

6CCVD’s in-house PhD team offers expert consultation for projects involving advanced diamond processing. We can assist engineers and scientists in selecting the optimal diamond grade, orientation, and surface preparation required for complex laser micromachining applications, including:

Optimizing material selection for high-energy particle detectors.
Designing substrates for integrated photonic circuits utilizing graphitic waveguides or electrodes.
Consulting on the necessary material specifications (e.g., nitrogen concentration, defect density) to achieve reproducible, high-conductivity graphitization results.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

We present the fabrication of transverse graphitic microelectrodes in a 500 μm thick synthetic diamond bulk by means of pulsed Bessel beams. By suitably placing the elongated focal length of the Bessel beam across the entire sample, the graphitic wires grow from the bottom surface up to the top during multiple shot irradiation. The morphology of the microstructures generated and the micro-Raman spectra are studied as a function of the laser parameters and the diamond crystal orientation. We show the possibility to generate high conductivity microelectrodes, which are crucial for the application of electric fields or current transport/collection in various chips and detectors.

Tech Support

Original Source

DOI: https://doi.org/10.1051/epjconf/202328705016