Experimental Investigation of Laser Parameters Dependence of Surface Graphitization in Nanosecond Laser Ablation of Nanocrystalline Diamond
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2025-03-26 |
| Journal | Micromachines |
| Authors | Huixin Yuan, Chunyu Zhang, Chengwei Song, Zhibing He, Li Guo |
| Institutions | China Academy of Engineering Physics |
| Citations | 2 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This study experimentally optimized nanosecond (ns) laser ablation parameters for inducing controlled surface graphitization on Nanocrystalline Diamond (NCD) films, aiming to enhance surface performance for engineering applications.
- Core Value Proposition: Achieved maximum graphitization (highest IG/ID ratio) and minimized surface roughness (Sa = 744 nm) on NCD surfaces through precise control of dynamic laser parameters.
- Material Transformation: The ns laser induces rapid thermal excitation, causing the structural transformation of sp3-hybridized diamond carbon into conductive sp2-hybridized graphite.
- Optimal Linear Scanning Recipe: The single-factor optimized parameters for linear scanning were determined to be 25 mW laser power, 0.1 mm/s scanning speed, and 0.2 mm defocus level.
- Scanning Speed Effect: A moderate speed (0.1 mm/s) provided the best balance, ensuring sufficient thermal energy for phase transformation while minimizing ablation loss and debris formation.
- Optimal Surface Texturing: For complete surface coverage, a scanning interval of 6 µm yielded the highest graphitization degree and the smoothest surface morphology (Sa = 744 nm).
- Mechanism Insight: The optimization process successfully mitigated issues related to excessive local overheating (which causes evaporation/damage) and insufficient energy deposition (which prevents complete transformation).
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Material | Nanocrystalline Diamond (NCD) | N/A | Synthesized via Hot-Filament CVD (HF-CVD) |
| Sample Size | 2 x 2 x 1 | mm | NCD sample dimensions |
| Laser Type | Nanosecond Pulsed YAG | N/A | Light source for ablation |
| Wavelength | 532 | nm | Green light excitation source |
| Pulse Duration | 5 | ns | Laser pulse length |
| Repetition Rate | 1 | kHz | Laser pulse frequency |
| Laser Power Range | 15-35 (Interval 5) | mW | Parameter range investigated |
| Scanning Speed Range | 0.05-0.25 (Interval 0.05) | mm/s | Parameter range investigated |
| Defocus Range | 0-0.4 (Interval 0.1) | mm | Parameter range investigated |
| Scanning Interval Range | 0-12 (Interval 2) | µm | Parameter range investigated for surface scanning |
| Optimal Laser Power | 25 | mW | Yields highest IG/ID ratio |
| Optimal Scanning Speed | 0.1 | mm/s | Yields highest IG/ID ratio |
| Optimal Defocus Level | 0.2 | mm | Yields highest IG/ID ratio |
| Optimal Scanning Interval | 6 | µm | Yields highest IG/ID ratio and minimum roughness |
| Minimum Surface Roughness (Sa) | 744 | nm | Achieved at 6 µm scanning interval |
| Raman Excitation Source | 532 | nm | Used for characterizing graphitization |
| Diamond Peak (Raman) | 1332 | cm-1 | Characteristic sp3 vibration mode |
| G Peak (Raman) | ~1580 | cm-1 | Characteristic sp2 (graphite) vibration mode |
Key Methodologies
Section titled “Key Methodologies”The experimental investigation utilized a systematic single-factor approach to optimize the nanosecond laser ablation process on NCD samples:
- NCD Sample Preparation: Nanocrystalline diamond films were synthesized using Hot-Filament Chemical Vapor Deposition (HF-CVD) following standardized heteroepitaxial protocols.
- Laser Setup and Control: A nanosecond pulsed YAG laser (532 nm, 5 ns, 1 kHz) was used. A Glan prism regulated the laser power output with 1 mW precision.
- Linear Scanning Optimization (Speed and Power):
- Laser power was varied from 15 mW to 35 mW (at 0 mm defocus).
- Scanning speed was varied from 0.05 mm/s to 0.25 mm/s (at 25 mW power, 0 mm defocus).
- The optimal speed (0.1 mm/s) and power (25 mW) were selected based on the highest IG/ID ratio and minimal surface debris/splattering.
- Defocus Level Optimization:
- The defocus level was varied from 0 mm (focused) to 0.4 mm, using the optimal speed (0.1 mm/s) and power (25 mW).
- Defocusing reduced energy density, and 0.2 mm was found to maximize the graphitized layer area.
- Surface Scanning Optimization (Interval):
- The scanning interval (overlap) was varied from 0 µm to 12 µm, utilizing the optimal linear parameters (25 mW, 0.1 mm/s, 0.2 mm defocus).
- The optimal interval (6 µm) was selected based on the highest IG/ID ratio and the lowest surface roughness (Sa).
- Characterization:
- Morphology: Scanning Electron Microscopy (SEM) was used to observe microgrooves, deposited layers, LIPSS (Laser-Induced Periodic Surface Structures), and debris.
- Graphitization Degree: Raman spectroscopy (532 nm excitation) was employed. The degree of graphitization was quantified using the integrated intensity ratio of the G peak (graphite, IG) and the D peak (disorder/amorphous carbon, ID).
- Roughness: White light interferometry was used to measure the arithmetic mean height deviation (Sa).
Commercial Applications
Section titled “Commercial Applications”The controlled surface graphitization of NCD creates a highly functional composite surface layer (diamond substrate with a conductive, lubricious graphite coating), enabling applications in demanding engineering fields:
- Tribology and Wear Resistance: The graphite layer provides self-lubrication and a low friction coefficient, significantly improving the wear performance of NCD coatings and tools.
- High-Precision Machining Tools: Laser texturing allows for the fabrication of specific microstructures (microgrooves) on diamond cutting tools, enhancing chip evacuation and reducing friction during ultra-precision cutting.
- Advanced Electrode Materials: The formation of a highly conductive graphite layer on the insulating diamond surface enables the use of NCD in high-performance electrochemical electrodes and sensors.
- Microelectromechanical Systems (MEMS): The ability to precisely pattern conductive graphite structures on diamond substrates is crucial for fabricating robust, high-performance MEMS components operating in harsh environments.
- Optics and Infrared Absorption: Surface texturing, including LIPSS formation observed in this study, can be utilized to modify the infrared absorption properties of diamond films.
View Original Abstract
Nanocrystalline diamond (NCD) is regarded as a highly promising composite engineering material owing to its superior mechanical properties. Surface texturing significantly enhances the surface performance of NCD. Given the unique inherent combination of hardness and brittleness in NCD, laser ablation emerges as a critical method for fabricating surface microstructures. However, the research on laser-induced surface texturing of NCD remains limited. This study experimentally investigated the characteristics of nanosecond laser-ablation-induced graphitization in NCD and provided an in-depth analysis of the laser ablation mechanism, aiming to guide the optimization of NCD surface microtexture manufacturing. Specifically, we conducted systematic nanosecond pulse laser ablation experiments on NCD samples and utilized Raman spectroscopy to qualitatively characterize the graphitization within microgrooves and across the entire ablated surface. The effects of the laser scanning speed, power, defocus level, and scanning interval on the graphitization extent and morphological characteristics were systematically investigated, identifying the single-factor optimal parameter set for maximizing graphitization. Through single-factor experimental analysis, the findings of this study provide foundational data for subsequent multivariate-coupled optimization and offer theoretical support for enhancing the surface properties of NCD through microtexturing via laser ablation.
Tech Support
Section titled “Tech Support”Original Source
Section titled “Original Source”References
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