Raman Study of the Diamond to Graphite Transition Induced by the Single Femtosecond Laser Pulse on the (111) Face

At a Glance

Metadata	Details
Publication Date	2022-12-29
Journal	Nanomaterials
Authors	А.А. Khomich, V. V. Kononenko, Oleg S. Kudryavtsev, E.V. Zavedeev, А. В. Хомич
Institutions	Prokhorov General Physics Institute, Institute of Radio-Engineering and Electronics
Citations	20
Analysis	Full AI Review Included

Technical Documentation & Analysis: Femtosecond Laser Graphitization of Diamond (111)

This document analyzes the research paper “Raman Study of the Diamond to Graphite Transition Induced by the Single Femtosecond Laser Pulse on the (111) Face” to provide technical specifications and highlight how 6CCVD’s advanced MPCVD diamond materials and services directly support and enable the replication and scaling of this critical research.

Executive Summary

The following points summarize the core findings and the value proposition for engineers and scientists utilizing 6CCVD materials for ultrafast laser processing:

Optimal Orientation: The study confirms that the (111) crystal face of Single Crystal Diamond (SCD) is the optimal orientation for femtosecond (fs) laser-induced graphitization, minimizing stress and maximizing the structural perfection of the resulting sp² phase.
Highly Oriented Graphite (HOG) Production: High-quality HOG layers were successfully produced using a single 120 fs, 266 nm UV pulse, demonstrating a pathway for creating ordered conductive regions within a dielectric diamond matrix.
Optimal Fluence Identified: Maximum structural perfection (HOG) was achieved at a narrow laser fluence window of 4-6 J/cm², significantly above the 1.81 J/cm² graphitization threshold.
Three Graphitization Regimes: The research clearly delineated three regimes based on fluence: nonablative surface graphitization (10 nm to 70 nm depth), customary ablative graphitization (saturation), and bulk graphitization (initiated above 8-10 J/cm², penetrating ~1 µm).
Material Quality: The resulting HOG exhibited excellent structural quality, characterized by a narrow G-band FWHM of 20-30 cm^-1 and a low I_D/I_G ratio of 0.20-0.25.
6CCVD Relevance: 6CCVD provides the necessary high-purity, low-nitrogen Optical Grade SCD (111) substrates, polished to Ra < 1 nm, required to replicate and scale this precise surface modification technique for advanced carbon composite electronics and photonics applications.

Technical Specifications

The following table extracts key quantitative data and parameters from the study, focusing on the material properties and laser processing conditions.

Parameter	Value	Unit	Context
Substrate Material	Natural Type IIa SCD	N/A	Low nitrogen concentration (< 10¹⁷ cm^-3)
Crystal Orientation	(111)	N/A	Used for minimal stress graphitization
Laser Wavelength	266	nm	3rd harmonic Ti:sapphire (UV)
Pulse Duration (FWHM)	120	fs	Ultrafast processing regime
Gaussian Beam Radius (w_g)	2.21	µm	Calculated at 1/e level
Graphitization Threshold (F_th)	1.81	J/cm²	Onset of surface graphitization
Optimal Fluence for HOG	4 - 6	J/cm²	Achieves maximum structural perfection
Bulk Graphitization Threshold	8 - 10	J/cm²	Initiates transformation in the crystal bulk
Maximum Graphite Thickness	~200	nm	Estimated via Raman attenuation method
Ablated Crater Depth (Max)	~100	nm	Measured after oxidation (surface regime)
Bulk Excited Volume Depth	~1	µm	Depth of optical field penetration
HOG Quality (G-band FWHM)	20 - 30	cm^-1	Indicates high structural order
HOG Quality (I_D/I_G Ratio)	0.20 - 0.25	N/A	Corresponds to nanocrystallite size L_a ~50-60 nm

Key Methodologies

The experiment relied on precise material selection and controlled ultrafast laser parameters coupled with high-resolution spectroscopic analysis.

Material Selection: A natural Type IIa Single Crystal Diamond (SCD) with a mechanically cleaved (111) face was used, characterized by extremely low nitrogen concentration (< 10¹⁷ cm^-3) and minimal impurity-defect bands.
Ultrafast Laser Setup: A single pulse from the 3rd harmonic of a Ti:sapphire laser (266 nm wavelength) with a 120 fs pulse duration was employed to induce non-thermal, dense electron-hole plasma-driven phase transition.
Fluence Range: Pulse energy was varied dynamically from the graphitization threshold (0.3 µJ) up to 10 µJ, resulting in a fluence range of F ≈ 1-45 J/cm² at the spot center.
Ablation Measurement: Crater depths were measured using white light interferometry and atomic force microscopy after annealing the sample in air at 600 °C to completely remove the sp² phase, ensuring accurate measurement of the ablated diamond volume.
Structural Characterization: Confocal Raman spectroscopy (473 nm excitation) was used to analyze the sp² phase structure (D, G, D’ bands) and estimate the thickness of the graphitized layer based on the attenuation of the diamond line intensity.

6CCVD Solutions & Capabilities

The successful replication and industrial scaling of femtosecond laser graphitization for advanced diamond electronics require highly controlled, high-purity diamond substrates. 6CCVD is uniquely positioned to supply the necessary materials and engineering support.

Applicable Materials

To replicate the high-quality HOG formation demonstrated in this study, researchers require substrates that match or exceed the purity and crystalline perfection of the natural Type IIa diamond used.

Optical Grade Single Crystal Diamond (SCD): Recommended material. Our SCD is grown via MPCVD, offering superior purity and precise crystallographic orientation control compared to natural diamond.
- Purity: We guarantee low-nitrogen SCD, ensuring the material background does not interfere with the laser-induced sp² phase formation or subsequent electronic properties.
- Orientation: We supply wafers precisely oriented to the (111) face, which the research confirms is critical for minimizing strain and achieving highly ordered graphitic structures.

Customization Potential

The study highlights the need for precise surface quality and the potential for integrating these conductive regions into devices. 6CCVD’s custom capabilities directly address these requirements:

Research Requirement	6CCVD Custom Capability	Technical Advantage
Ultra-Smooth Surface Finish	Precision Polishing (Ra < 1 nm)	Essential for minimizing surface defects that could disrupt the nonablative graphitization regime (F < 4 J/cm²) and ensuring uniform laser absorption.
Scaling Device Footprints	Custom Dimensions (Plates up to 125 mm)	Enables the transition from micron-scale research spots to large-area device fabrication using Polycrystalline Diamond (PCD) or large SCD wafers.
Integration of Electrodes/Contacts	In-House Metalization (Au, Pt, Ti, W, Cu)	We offer custom metal stacks (e.g., Ti/Pt/Au) deposited directly onto the diamond surface, facilitating the integration of the laser-written HOG regions into functional electronic or sensor devices.
Deep Processing/Bulk Studies	Substrate Thickness Control (up to 10 mm)	For studies extending into the bulk graphitization regime (exciting volumes up to 1 µm deep), we provide substrates up to 10 mm thick, ensuring mechanical stability and sufficient material depth.

Engineering Support

The complex interplay between laser fluence, crystal orientation, and resulting sp² structure requires expert guidance.

6CCVD’s in-house PhD team specializes in MPCVD diamond growth and post-processing techniques. We offer consultation on material selection, surface preparation, and orientation control for similar Femtosecond Laser Processing and Carbon Composite Development projects.
We assist researchers in defining optimal specifications for SCD or PCD substrates tailored to specific graphitization regimes (e.g., maximizing nonablative surface HOG formation vs. deep bulk modification).

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

View Original Abstract

The use of the ultrafast pulse is the current trend in laser processing many materials, including diamonds. Recently, the orientation of the irradiated crystal face was shown to play a crucial role in the diamond to graphite transition process. Here, we develop this approach and explore the nanostructure of the sp2 phase, and the structural perfection of the graphite produced. The single pulse of the third harmonic of a Ti:sapphire laser (100 fs, 266 nm) was used to study the process of producing highly oriented graphite (HOG) layers on the (111) surface of a diamond monocrystal. The laser fluence dependence on ablated crater depth was analyzed, and three different regimes of laser-induced diamond graphitization are discussed, namely: nonablative graphitization, customary ablative graphitization, and bulk graphitization. The structure of the graphitized material was investigated by confocal Raman spectroscopy. A clear correlation was found between laser ablation regimes and sp2 phase structure. The main types of structural defects that disrupt the HOG formation both at low and high laser fluencies were determined by Raman spectroscopy. The patterns revealed give optimal laser fluence for the production of perfect graphite spots on the diamond surface.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano13010162

References

2021 - Femtosecond laser micromachining of diamond: Current research status, applications and challenges [Crossref]
2019 - Femtosecond laser written photonic and microfluidic circuits in diamond [Crossref]
2002 - Inducing and probing non-thermal transitions in semiconductors using femtosecond laser pulses [Crossref]
2018 - Multistep transition of diamond to warm dense matter state revealed by femtosecond X-ray diffraction [Crossref]
2018 - Q-carbon harder than diamond [Crossref]
2014 - Raman investigation of femtosecond laser-induced graphitic columns in single-crystal diamond [Crossref]
2016 - Structural transformation of monocrystalline diamond driven by ultrashort laser pulses [Crossref]
2017 - Diamond graphitization by laser-writing for all-carbon detector applications [Crossref]
2022 - Laser-induced graphitisation of diamond under 30 fs laser pulse irradiation [Crossref]
2018 - The influence of the ionization regime on femtosecond laser beam machining mono-crystalline diamond [Crossref]