Experimental Parametric Investigation of Nanosecond Laser-Induced Surface Graphitization of Nano-Crystalline Diamond

At a Glance

Metadata	Details
Publication Date	2024-06-03
Journal	Materials
Authors	Huixin Yuan, Liang Zhao, Junjie Zhang
Institutions	Harbin Institute of Technology
Citations	4
Analysis	Full AI Review Included

Technical Documentation & Analysis: Nanosecond Laser Graphitization of NCD

Executive Summary

This documentation analyzes the experimental investigation into nanosecond laser-induced graphitization of Nano-Crystalline Diamond (NCD), a critical pretreatment method for enhancing the machinability of ultra-hard diamond components.

Core Challenge Addressed: Overcoming the exceptional hardness and brittleness of NCD to achieve ultrahigh surface quality via subsequent grinding and polishing.
Mechanism: Nanosecond pulsed laser ablation induces rapid thermal excitation, causing the sp³-hybridized diamond lattice to transform into softer sp²-hybridized graphite, facilitating material removal.
Optimal Parameters Identified: Maximum graphitization with minimal surface cracking (brittle fracture) was achieved using a laser power of 25 mW and a pulse repetition rate of 1000 Hz (1 kHz).
Achieved Result: Optimized linear scanning produced V-shaped microgrooves with a depth of approximately 5 µm, exhibiting uniform sidewall textures and a high graphitization degree (I_G/I_D ratio of 2.26).
6CCVD Value Proposition: 6CCVD provides the high-quality, large-area Polycrystalline Diamond (PCD) and specialized NCD films necessary to scale this laser pretreatment process for industrial applications, ensuring superior material consistency and customizable dimensions up to 125mm.

Technical Specifications

Parameter	Value	Unit	Context
Material Investigated	Nano-Crystalline Diamond (NCD)	N/A	CVD prepared bulk sample
NCD Grain Size Range	50-100	nm	Material property
NCD Hardness	99	GPa	Intrinsic material property
Laser Type	Nanosecond Pulsed YAG	N/A	Used for ablation/graphitization
Laser Wavelength	532	nm	Green light regime
Laser Pulse Width	5	ns	Short interaction time
Optimal Laser Power (Point Scan)	25	mW	Maximized graphitization (I_G/I_D)
Optimal Pulse Repetition Rate	1000	Hz	Minimizing brittle cracks/fractures
Optimal Scanning Speed (Linear)	0.01	mm/s	Microgroove fabrication
Ablation Threshold (Calculated)	3.3	J/cm²	Determined for 5.6 µm spot radius
Optimal Microgroove Depth	~5	µm	Achieved using optimized linear parameters
Maximum Graphitization Ratio	2.26	N/A	I_G/I_D ratio (Linear Scan, 25 mW, 1 kHz)
Graphitization Temperature	> 700	°C	Required for sp³ to sp² transition
Diamond Raman Peak	1332	cm^-1	Characteristic sp³ vibration mode
Graphite G Peak	1580	cm^-1	Characteristic sp² vibration mode

Key Methodologies

The experimental investigation utilized systematic single-variable controlled experiments focusing on laser power and pulse repetition rate to optimize NCD graphitization.

Material Preparation: Bulk NCD samples (2 mm x 2 mm x 1 mm) were prepared via Chemical Vapor Deposition (CVD), characterized by a high hardness (99 GPa) and fine grain size (50-100 nm).
Laser Setup: A nanosecond pulsed YAG laser (532 nm, 5 ns pulse width) was used in a constant temperature (20 °C) and dust-free workshop environment.
Beam Control: The laser beam profile was shaped using a diaphragm, and power was precisely adjusted via a granular prism (accuracy of 0.1 mW).
Ablation Modes: Experiments were conducted in two modes:
- Point Scanning: Used to determine optimal power and repetition rate for microhole formation and graphitization characteristics.
- Linear Scanning: Used to fabricate microgrooves using optimized parameters (25 mW, 1000 Hz, 0.01 mm/s).
Morphological Characterization: Scanning Electron Microscopy (SEM) was used to analyze surface morphology, requiring a thin layer of Au film (~5 nm) to enhance conductivity for imaging.
Graphitization Characterization: Raman Spectroscopy (532 nm wavelength) was employed to detect the phase transformation, quantifying the degree of graphitization using the ratio of the Graphite G peak intensity (I_G) to the Disordered D peak intensity (I_D).

6CCVD Solutions & Capabilities

The research demonstrates a viable pathway for enhancing the machinability of NCD through precise laser pretreatment. 6CCVD is uniquely positioned to supply the high-quality CVD diamond materials and customization services required to scale this research into industrial processes.

Applicable Materials

The study utilized Nano-Crystalline Diamond (NCD), which falls within the fine-grain Polycrystalline Diamond (PCD) spectrum. 6CCVD offers materials optimized for this application:

Optical Grade PCD: Ideal for replicating and extending this research. Our PCD films offer superior uniformity and controlled grain sizes, ensuring consistent graphitization behavior across large areas.
Custom NCD/UCD Films: For highly specialized applications requiring grain sizes precisely in the 50-100 nm range, 6CCVD can engineer custom Ultra-Nanocrystalline Diamond (UCD) or NCD films via MPCVD.
SCD Substrates: While the paper focused on NCD, 6CCVD can supply high-purity Single Crystal Diamond (SCD) substrates (up to 500 µm thick) for comparative studies on laser-induced graphitization mechanisms.

Customization Potential for Scaling

The successful implementation of this pretreatment method requires large, highly uniform diamond plates, which 6CCVD specializes in providing:

Requirement from Paper	6CCVD Capability	Technical Advantage
Small Sample Size (2x2 mm)	Custom Dimensions up to 125mm	Enables industrial scaling of laser pretreatment for large components (e.g., optical windows, heat spreaders).
Bulk Material (1 mm thick)	Substrates up to 10 mm thick	Provides robust material for high-power applications or deep microgroove fabrication.
Need for High Surface Integrity	Ultra-Low Roughness Polishing	We offer polishing down to Ra < 5nm for inch-size PCD, ensuring the post-graphitization surface meets stringent requirements.
Potential for Device Integration	Custom Metalization Services	If the graphitized layer is used as an electrode or contact, 6CCVD offers in-house deposition of Au, Pt, Pd, Ti, W, and Cu films.

Engineering Support

The research highlights the extreme sensitivity of graphitization to processing parameters (e.g., 25 mW power and 1000 Hz repetition rate are optimal, while 1500 Hz causes severe cracking).

Parameter Optimization: 6CCVD’s in-house PhD team specializes in MPCVD growth and post-processing of diamond materials. We offer consultation services to assist engineers and researchers in selecting the optimal diamond grade (grain size, purity) and pre-treatment parameters for similar Enhanced Diamond Machinability projects.
Material Consistency: We guarantee the density (3.52 g/cm³) and hardness (99 GPa) consistency required for reliable laser ablation thresholds (3.3 J/cm²) across large batches of material.
Global Logistics: We ensure reliable, global delivery of custom diamond materials (DDU default, DDP available) to keep your research timeline on track.

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

View Original Abstract

While nano-crystalline diamond (NCD) is a promising engineering composite material for its unique mechanical properties, achieving the ultrahigh surface quality of NCD-based components through conventional grinding and polishing is challenging due to its exceptional hardness and brittleness. In the present work, we experimentally investigate the nanosecond laser ablation-induced graphitization characteristics of NCD, which provides a critical pretreatment method of NCD for realizing its superlative surface finish. Specifically, systematic experimental investigations of the nanosecond pulsed laser ablation of NCD are carried out, in which the characteristics of graphitization are qualitatively characterized by the Raman spectroscopy detection of the ablated area of the microhole and microgroove. Subsequently, the influence of laser processing parameters on the degree and morphological characteristics of graphitization is evaluated based on experimental data and related interpretation, from which optimized parameters for maximizing the graphitization of NCD are then identified. The findings reported in the current work provide guidance for promoting the machinability of NCD via laser irradiation-induced surface modification.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma17112704

References

2020 - Indentation hardness of diamond single crystals, nanopolycrystal, and nanotwinned diamonds: A critical review [Crossref]
2020 - Shock Response of Full Density Nanopolycrystalline Diamond [Crossref]
2013 - Observation of higher stiffness in nanopolycrystal diamond than monocrystal diamond [Crossref]
2016 - Optical properties of ultrapure nano-polycrystalline diamond [Crossref]
2018 - Recent advances in diamond power semiconductor devices [Crossref]
2021 - Plastic Deformation and Strengthening Mechanisms of Nanopolycrystalline Diamond [Crossref]
2022 - Micro-scale abrasion investigations of single-crystal diamonds using nano-polycrystalline diamond wheels [Crossref]
2010 - Precision and micro CVD diamond-coated grinding tools [Crossref]
2022 - Polishing of polycrystalline diamond using synergies between chemical and mechanical inputs: A review of mechanisms and processes [Crossref]
2016 - Synthesis and characterization of microcrystalline diamond to ultrananocrystalline diamond films via Hot Filament Chemical Vapor Deposition for scaling to large area applications [Crossref]