Sub-micron structuring/texturing of diamond-like carbon-coated replication masters with a femtosecond laser
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-02-01 |
| Journal | Applied Physics A |
| Authors | Aleksandra Michalek, Shaojun Qi, Afif Batal, Pavel Penchev, Hanshan Dong |
| Institutions | Coventry (United Kingdom), Manufacturing Technology Centre (United Kingdom) |
| Citations | 17 |
| Analysis | Full AI Review Included |
Technical Documentation: Sub-micron Structuring of Carbon Coatings for Replication Masters
Section titled âTechnical Documentation: Sub-micron Structuring of Carbon Coatings for Replication MastersâThis document analyzes the research paper âSub-micron structuring/texturing of diamond-like carbon-coated replication masters with a femtosecond laserâ to provide technical insights and connect the findings directly to 6CCVDâs advanced MPCVD diamond material solutions.
Executive Summary
Section titled âExecutive SummaryâThe research successfully demonstrated the feasibility of using femtosecond (fs) laser processing to create functional sub-micron textures on Diamond-Like Carbon (DLC) coatings, suitable for high-durability replication masters.
- Process Validation: Highly uniform Laser-Induced Periodic Surface Structures (LIPSS) were generated on thin DLC films (2-5 ”m) using optimized fs laser parameters (Fluence 58-130 mJ/cm2, ppstotal 28-47).
- Structural Change: fs laser irradiation induced the formation of a thin graphitized (sp2-rich) surface layer, confirmed by Raman spectroscopy, without causing long-range crystallization in the bulk DLC.
- Hardness Reduction: The graphitization resulted in a significant reduction in hardness, dropping from 22 GPa (as-received) to a range of 6-10 GPa (structured).
- Tribological Retention: Despite the structural changes, the Coefficient of Friction (CoF) remained largely unchanged (~0.12), preserving the critical lubricating properties required for injection moulding masters.
- Durability: The structured DLC coating retained a hardness level approximately three times greater than the underlying 316L stainless steel substrate, confirming its suitability for durable, functionalized replication tools.
- Geometric Achievement: The resulting LIPSS exhibited a periodicity of 700-800 nm and a ripple height of 200 nm, demonstrating precise sub-micron feature control.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the research regarding material properties, processing parameters, and resulting characteristics:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| DLC Film Thickness | 2-5 | ”m | Deposited via PACVD |
| As-Received Hardness | 22 (HV 2500) | GPa | Before laser treatment |
| Structured Hardness Range | 6 to 10 | GPa | After fs laser treatment (Samples S1-S4) |
| Substrate Material | 316L | Stainless Steel | 2.5 mm thick replication master base |
| As-Received Surface Roughness (Ra) | 0.05 | ”m | Initial surface quality |
| Laser Wavelength (λ) | 1030 | nm | fs Ytterbium-doped fiber laser source |
| Pulse Duration | 310 | fs | Ultrashort pulse regime |
| Optimized Fluence Range (F) | 58-130 | mJ/cm2 | Required for uniform LIPSS |
| Total Pulses per Spot (ppstotal) | 28-47 | - | Optimized for large area structuring |
| LIPSS Periodicity (Î) | 700-800 | nm | Low Spatial Frequency LIPSS (LSFL) |
| LIPSS Ripple Height | 200 | nm | Average height of structured features |
| Coefficient of Friction (CoF) | ~0.12 | - | Measured against 16 GPa Alumina ball |
| G Peak Shift (As-Received to Structured) | 1509 to 1590 | cm-1 | Indicative of surface graphitization |
Key Methodologies
Section titled âKey MethodologiesâThe experiment focused on optimizing fs laser parameters for large-area structuring of DLC coatings and characterizing the resulting structural and mechanical changes.
- Material Preparation: Thin DLC films (2-5 ”m) were deposited onto 316L stainless steel substrates using Plasma-Assisted Chemical Vapour Deposition (PACVD).
- Laser Setup: A femtosecond ytterbium-doped fiber laser (λ = 1030 nm, pulse duration 310 fs) was focused to a 40 ”m spot diameter (d) using a 100 mm telecentric lens.
- Structuring Strategy: A fixed hatch distance (h) of 3 ”m was used. LIPSS uniformity was controlled by varying scanning speed (v) and frequency (f) to achieve optimized fluence (F) and total pulses per spot (ppstotal).
- Topographical Analysis: Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) were used to assess LIPSS uniformity and geometry. Periodicity was quantified using 2D Fast Fourier Transformation (2D FFT).
- Structural Analysis:
- Raman spectroscopy (633 nm source) was used to analyze the sp2/sp3 bonding ratio via the I(D)/I(G) peak intensity ratio, confirming surface graphitization.
- Glancing Angle X-ray Diffraction (GAXRD, Cobalt source) was used to check for long-range crystallization within the DLC bulk.
- Mechanical and Tribological Testing:
- Hardness was measured via nanoindentation (400 nm depth control) to assess the impact of the laser-induced graphitized layer.
- Coefficient of Friction (CoF) and wear resistance were measured using a ball-on-plate tribometer under dry conditions against a hard alumina ball (16 GPa).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research successfully demonstrated functional surface texturing on DLC, but the resulting material suffered a significant 55-73% reduction in hardness due to graphitization. 6CCVD provides superior MPCVD diamond materials that offer inherent diamond properties (high hardness, low friction) on a robust, non-amorphous platform, enabling advanced structuring with minimal property degradation.
Applicable Materials
Section titled âApplicable MaterialsâFor researchers and engineers seeking to replicate or extend this work using materials that maintain maximum hardness and thermal stability during laser processing, 6CCVD recommends:
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Optical Grade Polycrystalline Diamond (PCD):
- Advantage: PCD offers extreme hardness (up to 100 GPa) and high thermal stability, making it highly resistant to the graphitization observed in amorphous DLC during high-intensity laser treatment.
- Application: Ideal for high-volume, high-wear replication masters where maintaining structural integrity and low friction over millions of cycles is critical. We offer PCD wafers up to 125mm diameter.
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High-Purity Single Crystal Diamond (SCD):
- Advantage: SCD provides the highest possible hardness and thermal conductivity. Its highly ordered lattice structure is inherently more stable than DLC, ensuring that fs laser structuring results in precise feature creation without bulk material modification.
- Application: Perfect for micro-optics, high-precision micro-injection molds, or applications requiring Ra < 1 nm surface quality prior to structuring.
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Boron-Doped Diamond (BDD):
- Advantage: If the LIPSS structuring is intended for electrochemical or sensing applications (as LIPSS are known for antibacterial and biological responses), BDD provides a conductive, robust diamond platform.
Customization Potential
Section titled âCustomization Potentialâ6CCVDâs in-house capabilities directly address the needs of advanced micro-structuring projects like those detailed in the paper, offering control over geometry, surface finish, and integration.
| Research Requirement | 6CCVD Capability | Technical Advantage |
|---|---|---|
| Substrate/Coating Thickness | SCD/PCD layers from 0.1 ”m up to 500 ”m. Substrates up to 10 mm. | Precise control over mechanical backing and thermal management for high-power laser processing. |
| Large Area Structuring | PCD plates/wafers up to 125mm diameter. | Enables industrial scaling of replication masters far beyond typical research dimensions. |
| Surface Quality | SCD Polishing: Ra < 1 nm. Inch-size PCD Polishing: Ra < 5 nm. | Provides an atomically smooth starting surface, superior to the 0.05 ”m Ra of the DLC used, ensuring higher fidelity in subsequent laser texturing. |
| Integration/Assembly | Custom Metalization (Au, Pt, Pd, Ti, W, Cu) and Laser Cutting. | Allows for precise integration of diamond masters into complex mold tooling or for creating electrical contacts for BDD applications. |
Engineering Support
Section titled âEngineering SupportâThe study highlights the sensitivity of carbon materials to fs laser parameters. 6CCVDâs in-house PhD team specializes in the material science of CVD diamond and can provide crucial support for similar projects:
- Material Selection: We assist in selecting the optimal SCD or PCD grade to maximize resistance to laser-induced graphitization and thermal stress.
- Process Optimization: Consultation on how the superior thermal properties of MPCVD diamond can mitigate heat dissipation issues, leading to cleaner, more precise LIPSS generation compared to DLC.
- Application Design: Expert guidance for designing custom diamond components for high-impact injection moulding or micro-replication projects where low CoF and high durability are paramount.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.