The Influence of Preparation Conditions on the Structural Properties and Hardness of Diamond-Like Carbon Films, Prepared by Plasma Source Ion Implantation
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-04-06 |
| Journal | Coatings |
| Authors | R. Hatada, S. Flege, Muhammad Naeem Ashraf, Arne Timmermann, Christoph Schmid |
| Institutions | Technical University of Darmstadt |
| Citations | 21 |
| Analysis | Full AI Review Included |
Technical Analysis & Product Alignment: Diamond-Like Carbon Film Properties via PSII
Section titled âTechnical Analysis & Product Alignment: Diamond-Like Carbon Film Properties via PSIIâExecutive Summary
Section titled âExecutive SummaryâThis documentation analyzes the research into tuning the structural and tribological properties of hydrogenated Diamond-Like Carbon (a-C:H, DLC) films prepared via unassisted Plasma Source Ion Implantation (PSII). The findings establish crucial correlations between key deposition parameters (voltage, pressure, Ar addition, holder type) and resulting material performance.
- Core Achievement: Demonstrated production of high-hardness DLC films (up to 22.4 GPa) and ultra-low friction coefficients (down to 0.049) using PSII without an external plasma source, simplifying potential scale-up.
- Structural Correlation: Counterintuitively, films exhibiting lower sp2 content (indicating more diamond-like character) showed both a higher hydrogen content (above 30 at.%) and a higher mechanical hardness (above 14 GPa).
- Process Variables: The use of DC voltage, higher gas pressure, argon addition, and a specialized grid-type holder promoted structural changes indicative of graphitization (higher I(D)/I(G) ratio and G peak position).
- Material Focus: Ethylene (C2H4) was used as the hydrocarbon precursor, selected for its high hydrogen richness, enabling effective investigation of hydrogen incorporation effects.
- Tribological Performance: Most samples achieved friction coefficients below 0.1, with the lowest values generally corresponding to films with the highest hydrogen and highest sp3 content, necessary for the lubricious tribolayer formation.
- 6CCVD Context: While the paper focuses on DLC, 6CCVD specializes in high-purity, high-performance SCD/PCD materials, which serve as superior alternatives or highly stable substrates for advanced coating techniques like PSII, particularly for applications requiring intrinsic hardness > 80 GPa.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Highest Hardness Achieved | 22.4 | GPa | Measured via Nanoindentation (Berkovich indenter) |
| Lowest Friction Coefficient | 0.049 | None | Steady-state value determined by Ball-on-Disk test (WC ball, 1 N) |
| Typical Hardness Range (a-C:H) | 10-20 | GPa | Standard range for hydrogenated DLC films |
| Film Thickness Range | 100-700 | nm | Resulting from 45-150 minute deposition runs |
| DC Sample Bias Voltage | -1.5 to -2.5 | kV | Used for preparation of highest hardness films |
| Pulsed Sample Bias Voltage | -10 to -18 | kV | Pulse length: 40 ”s; Repetition Rate: 250 Hz |
| Hydrogen Content Range | 22.7 - > 30 | at.% | Estimated empirically via Raman log(N/S) ratio |
| Process Pressure Range | 0.65, 0.7, 0.8 | Pa | Controlled process environment |
| Ethylene (C2H4) Flow Rate | 6 | sccm | Hydrocarbon precursor gas |
| Argon (Ar) Additive Flow Rate | 0.3 or 0.6 | sccm | Used for enhanced dissociation/sputtering effects |
| Raman G-Peak Position Range | 1510 to 1570 | cm-1 | Indicator of sp2 bonding and structural properties |
Key Methodologies
Section titled âKey MethodologiesâThe Diamond-Like Carbon films were synthesized using a custom, unassisted Plasma Source Ion Implantation (PSII) setup. The methodology focused on correlating input electrical and gas parameters with output structural (Raman) and mechanical (Hardness, Friction) characteristics.
- PSII System Configuration: Films were deposited using a high voltage applied directly to the sample holder to ignite the plasma (unassisted discharge).
- Substrates: 10 mm x 10 mm2 silicon wafer pieces.
- Process Gases: Ethylene (C2H4) was used as the precursor (6 sccm flow). Argon (Ar) was added in some experiments at flows of 0.3 sccm or 0.6 sccm.
- Voltage Application: Two voltage regimes were tested:
- Direct Current (DC): -1.5, -2.0, or -2.5 kV.
- Pulsed High Voltage: -10, -15, or -18 kV (40 ”s pulse length, 250 Hz repetition rate).
- Holder Variation: Experiments utilized two sample holder types: a 100 mm diameter plate-type (filled symbols in figures) and a 92 mm diameter grid-type (open symbols in figures).
- Structural Analysis (Raman Spectroscopy): A 633 nm laser was used to measure I(D)/I(G) ratio and Full Width at Half Maximum of the G peak (FWHM(G)), which correlate to the sp3/sp2 bonding ratio and hydrogen content (log(N/S) ratio).
- Mechanical Testing (Nanoindentation): Hardness was determined using a Berkovich diamond indenter and the continuous stiffness measurement (CSM) technique, evaluating data at 10% of the film thickness (100-700 nm) to avoid substrate influence.
- Tribological Testing (Ball-on-Disk): Friction coefficient was measured using a tungsten carbide (WC) ball (6 mm diameter) under a 1 N load at room temperature and 25% relative humidity.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research demonstrates the fine control necessary to engineer carbon materials for tribological and mechanical performance. While the study focuses on DLC films, 6CCVDâs MPCVD Diamond provides the foundational, high-purity, and structurally superior materials essential for replicating, optimizing, and extending this type of advanced engineering application.
Applicable Materials
Section titled âApplicable MaterialsâThe key insight from the paper is that enhanced hardness requires optimal carbon bonding (sp3 structure). 6CCVD offers materials that intrinsically possess superior sp3 bonding and performance characteristics compared to amorphous DLC.
| 6CCVD Material Recommendation | Material Properties & Application Fit |
|---|---|
| Electronic Grade Single Crystal Diamond (SCD) | Superior Replacement for High-Hardness DLC: SCD boasts intrinsic hardness > 80 GPa and is essentially hydrogen-free, overcoming the 22.4 GPa limit found in this DLC study. Ideal for ultra-wear resistance, high thermal conductivity (> 2000 W/mK), and extreme environment sensors/windows. |
| Optical Grade SCD Wafers | High-Purity Substrates: Perfect for replicating plasma deposition studies where substrate quality is paramount. Thicknesses are precisely controlled from 0.1 ”m up to 500 ”m, allowing for precise integration into optical or electronic devices. |
| Polycrystalline Diamond (PCD) Wafers | Large-Area Scalability: Since the paper mentions the importance of scale-up for PSII, our PCD wafers (available up to 125 mm diameter) provide large, robust, and mechanically stable surfaces for large-batch DLC coating processes or tool fabrication. |
| Boron-Doped Diamond (BDD) | Conductive Substrates: If the experimental setup requires a highly conductive substrate for optimized charge dispersion during PSII processing (especially high voltage pulsing), 6CCVD BDD materials offer excellent electrical properties combined with diamondâs mechanical stability. |
Customization Potential
Section titled âCustomization PotentialâThe experimental setup relied on highly specific mechanical components (sample holders, metal contacts). 6CCVDâs engineering capabilities ensure seamless integration of our diamond materials into proprietary deposition apparatus.
- Custom Dimensions: We offer laser cutting and shaping services to create non-standard geometries or grid patterns similar to the specialized holders used in this PSII research, ensuring optimal plasma contact and deposition uniformity for large wafers (up to 125mm PCD).
- Precision Thickness Control: We can supply PCD and SCD substrates up to 10 mm thick, providing the mechanical integrity needed for demanding ion implantation processes, or ultra-thin SCD layers (0.1 ”m) for integrated device layers.
- Integrated Metalization: The deposition process often requires precise electrical contacts. 6CCVD offers in-house custom metalization using common electrode materials (Ti, W, Au, Pt, Pd, Cu) directly onto the diamond surface, ready for vacuum chamber integration.
- Polishing Standards: For optimal tribological performance, surface smoothness is critical. We guarantee polishing to Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, ensuring that tribology experiments start with an exceptionally smooth base layer, minimizing surface morphology effects observed in the studyâs rougher pulsed samples.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team provides authoritative technical consultation. We understand the complex interplay between processing parameters (like voltage/pressure variation in PSII) and resulting diamond properties (sp3 fraction, friction coefficient, hardness). We can assist clients moving from thin film research (like this DLC study) to full-scale engineering applications requiring high-purity Single Crystal Diamond.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Diamond-like carbon (DLC) films were prepared from a hydrocarbon precursor gas by plasma source ion implantation (PSII), in which the plasma generation and the film deposition were coupled; i.e., the plasma was generated by the applied voltage and no additional plasma source was used. Several experimental parameters of the PSII process were varied, including the sample bias (high voltage, DC or pulsed), gas pressure, sample holder type and addition of argon in the plasma gas. The influence of the deposition conditions on the carbon bonding and the hydrogen content of the films was then determined using Raman spectroscopy. Nanoindentation was used to determine the hardness of the samples, and a ball-on-disk test to investigate the friction coefficient. Results suggest that films with a lower sp2 content have both a higher hydrogen content and a higher hardness. This counterintuitive finding demonstrated that the carbon bonding is more important to hardness than the reported hydrogen concentration. The highest hardness obtained was 22.4 GPa. With the exception of a few films prepared using a pulsed voltage, all conditions gave DLC films having similarly low friction coefficients, down to 0.049.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
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- 2001 - Differentiating the tribological performance of hydrogenated and hydrogen-free DLC coatings [Crossref]
- 2012 - Properties of hydrogenated DLC films as prepared by a combined method of plasma source ion implantation and unbalanced magnetron sputtering [Crossref]
- 2001 - The role of hydrogen in tribological properties of diamond-like carbon films [Crossref]
- 2018 - Anode layer source plasma-assisted hybrid deposition and characterization of diamond-like carbon coatings deposited on flexible substrates [Crossref]