Effects of Substrate Bias Voltage on Structure of Diamond-Like Carbon Films on AISI 316L Stainless Steel - A Molecular Dynamics Simulation Study
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-08-30 |
| Journal | Materials |
| Authors | Ngoc-Tu Do, VanâHai Dinh, Le Van Lich, Hong-Hue Dang-Thi, TrongâGiang Nguyen |
| Institutions | Hanoi University of Industry, Hanoi University of Science and Technology |
| Citations | 9 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study utilized Molecular Dynamics (MD) simulations to investigate the growth and structural properties of Diamond-Like Carbon (DLC) films deposited on AISI 316L stainless steel substrates under varying substrate bias voltages (Vs).
- Optimal Bias Voltage: A substrate bias voltage of 120 V was identified as optimal, resulting in a highly compact DLC film structure with a smooth surface morphology.
- Peak sp3 Content: The highest overall sp3 hybridization fraction, crucial for hardness and density, reached 48.5% at the 120 V bias.
- Parabolic Dependence: The sp3 fraction exhibited a parabolic dependence on Vs (0 V to 300 V), increasing up to 120 V and subsequently decreasing, consistent with experimental findings.
- Structural Degradation: Low (0 V) and excessively high (300 V) bias voltages led to looser, rougher film structures due to insufficient energy for densification (0 V) or structural damage from intense bombardment (300 V).
- Growth Mechanism: The bias voltage controls the incident C atom energy, balancing subplantation (densification and sp2-to-sp3 transformation) against the breaking of formed sp3 bonds.
- Interface Formation: The deposition process involved four stages: C-atom diffusion, island formation, substrate-atom diffusion (forming a transition layer), and stable growth.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Optimal Substrate Bias (Vs) | 120 | V | Yields highest sp3 fraction and compact structure. |
| Peak sp3 Hybridization | 48.5 | % | Overall fraction achieved at 120 V Vs. |
| Incident Kinetic Energy | 15 | eV/atom | Energy of deposited C atoms in the simulation. |
| Substrate Composition (Fe:Cr:Ni) | 69.6:18.1:12.3 | Mole Fraction % | Model of AISI 316L stainless steel. |
| Substrate Dimensions | 36 x 36 x 15.6 | A | Dimensions of the MD simulation cell. |
| Simulation Time Step | 1.0 | fs | Molecular Dynamics calculation step. |
| First RDF Peak (C-C) | 1.54 | A | Corresponds to the first nearest neighbor distance in DLC. |
| Second RDF Peak (C-C) | 2.54 | A | Corresponds to the second nearest neighbor distance in DLC. |
| Transition Layer sp3 Content (0 V) | Low | % | Difficult to form sp3 bonds due to mixing of Fe, Cr, Ni, and C atoms. |
| Activation Barrier (sp2-sp3) | 0.33 | eV/atom | Theoretical energy required for graphite-diamond interconversion. |
Key Methodologies
Section titled âKey MethodologiesâThe growth process of DLC film on AISI 316L was simulated using the Molecular Dynamics (MD) method implemented in the LAMMPS code.
- Substrate Modeling: The AISI 316L substrate (Fe:Cr:Ni) was constructed with a face-centered cubic (FCC) structure and divided into three regions: a fixed zone (bottom layer), a constant temperature zone (maintained at 300 K), and a relaxed zone (top layers).
- Interatomic Potentials: A hybrid potential scheme was employed to describe all pairwise interactions:
- Substrate (Fe-Cr-Ni): Embedded-Atom Method (EAM) potential.
- Film (C-C): Tersoff potential.
- Film-Substrate (C-Ni): Morse potential (parameters fitted to previous studies).
- Film-Substrate (Fe-C, Cr-C): Tersoff/ZBL potential.
- Deposition Parameters: 3000 C atoms were incident perpendicularly onto the substrate surface. The incident kinetic energy was fixed at 15 eV/atom, simulating magnetron sputtering conditions.
- Bias Voltage Simulation: Substrate bias voltage (Vs, ranging from 0 V to 300 V) was simulated by applying an equivalent electric field perpendicular to the substrate surface during deposition.
- Structural Characterization: Film structure was analyzed using the Radial Distribution Function (RDF) to confirm amorphous characteristics and short-range order similar to diamond. The sp3/sp2 hybridization ratio was calculated along the film thickness and as an overall percentage.
Commercial Applications
Section titled âCommercial ApplicationsâThe ability to precisely control the sp3/sp2 ratio and film density via substrate bias voltage makes this DLC deposition technology highly relevant for applications requiring tailored surface properties.
- Biomedical Implants:
- Coating orthopedic implants (e.g., AISI 316L) to enhance biocompatibility.
- Preventing corrosion and the release of toxic metal ions (Cr, Ni, Mo) when the metal is placed in the body (e.g., coronary stents).
- Energy and Electrochemical Devices:
- Protective coatings for bipolar plates in Polymer Electrolyte Membrane Fuel Cells (PEMFCs).
- Tuning the sp3/sp2 ratio to balance high corrosion resistance with sufficient electrical conductivity (resistivity range 1012 to 1016 Ωcm).
- Industrial Tooling and Wear Resistance:
- Protective coatings for cutting tools and molds (e.g., precision glass components).
- High sp3 fraction films enhance hardness and wear resistance in demanding industrial environments.
- Tribological Systems:
- Applications requiring low friction and high wear resistance in moving mechanical assemblies.
View Original Abstract
With the recent significant advances in micro- and nanoscale fabrication techniques, deposition of diamond-like carbon films on stainless steel substrates has been experimentally achieved. However, the underlying mechanism for the formation of film microstructures has remained elusive. In this study, the growth processes of diamond-like carbon films on AISI 316L substrate are studied via the molecular dynamics method. Effects of substrate bias voltage on the structure properties and sp3 hybridization ratio are investigated. A diamond-like carbon film with a compact structure and smooth surface is obtained at 120 V bias voltage. Looser structures with high surface roughness are observed in films deposited under bias voltages of 0 V or 300 V. In addition, sp3 fraction increases with increasing substrate bias voltage from 0 V to 120 V, while an opposite trend is obtained when the bias voltage is further increased from 120 V to 300 V. The highest magnitude of sp3 fraction was about 48.5% at 120 V bias voltage. The dependence of sp3 fraction in carbon films on the substrate bias voltage achieves a high consistency within the experiment results. The mechanism for the dependence of diamond-like carbon structures on the substrate bias voltage is discussed as well.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
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