How Good Are the Performances of Graphene and Boron Nitride Against the Wear of Copper?
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2021-02-28 |
| Journal | Materials |
| Authors | Min Kang, Hai Woong Park, Arnaud Caron |
| Institutions | Korea University of Technology and Education |
| Citations | 4 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled āExecutive SummaryāThis study investigates the tribological performance of monolayer Graphene (Gr) and Hexagonal Boron Nitride (BN) coatings on copper (Cu) substrates against wear induced by a stiff diamond AFM tip, focusing on the critical trade-off between friction and wear protection.
- Wear Retardation: Both Gr and BN significantly retard the onset of plastic deformation (plowing) of the underlying copper substrate, acting as effective load supports.
- Superior Wear Protection: BN provides superior wear resistance compared to Gr. The critical normal force (Fny) required to initiate plowing is 3066 nN for BN/Cu, 1507 nN for Gr/Cu, and 989 nN for bare annealed Cu.
- Mechanism of Protection: The enhanced load-bearing capacity of BN is attributed to its higher out-of-plane stiffness compared to Graphene, which makes it more resistant to being stamped into the soft Cu substrate.
- Friction Trade-off: This stiffness comes at a cost: in the wear-less regime, BN exhibits a higher friction coefficient (Āµ ā 0.20) than Graphene (Āµ ā 0.11).
- Friction Mechanism: Wear-less friction for coated Cu is governed by the puckering mechanism of the 2D material (folding ahead of the indenter), while wear at high loads is governed by plastic plowing of the underlying Cu substrate.
- Wear Depth Reduction: BN reduced the mean wear depth (Ī“w) to 9 nm, significantly better than Graphene (16 nm) and bare annealed Copper (30 nm).
Technical Specifications
Section titled āTechnical Specificationsā| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Material | Copper (Cu) | - | Cold-rolled, annealed at 1300 K |
| Coating Thickness | Monolayer | - | Graphene and Hexagonal Boron Nitride (h-BN) |
| Tip Material | Diamond | - | Stiff, coated AFM cantilever (CDT-NCLR) |
| Tip Radius (R) | 10 | nm | Estimated size of diamond nanocrystallites |
| Copper Shear Strength (Ļ) | 6.32 | GPa | Fitted JKR model for bare Cu (low load) |
| Copper Hardness (H) | 4.7 | GPa | Calculated at plowing onset (1.54 nm penetration depth) |
| Bare Cu Critical Normal Force (Fny) | 989 | nN | Onset of plowing |
| Graphene/Cu Critical Normal Force (Fny) | 1507 | nN | Onset of plowing (52% increase over bare Cu) |
| BN/Cu Critical Normal Force (Fny) | 3066 | nN | Onset of plowing (210% increase over bare Cu) |
| Graphene Friction Coefficient (Āµ) | 0.112 | - | Wear-less (puckering) regime |
| BN Friction Coefficient (Āµ) | 0.1989 | - | Wear-less (puckering) regime |
| Bare Cu Mean Wear Depth (Ī“w) | 30 | nm | After tribological testing (Fn up to 6930 nN) |
| Graphene/Cu Mean Wear Depth (Ī“w) | 16 | nm | After tribological testing |
| BN/Cu Mean Wear Depth (Ī“w) | 9 | nm | After tribological testing |
Key Methodologies
Section titled āKey MethodologiesāThe tribological performance was assessed using Friction Force Microscopy (FFM) under controlled environmental conditions (T = 293 K, RH = 40%).
- Sample Preparation:
- Monolayer Graphene and h-BN were grown on cold-rolled copper foil using Chemical Vapor Deposition (CVD).
- A bare copper control sample was prepared by annealing the foil at 1300 K in an Ar/H2 mixture.
- Chemical Verification:
- X-ray Photoelectron Spectroscopy (XPS) confirmed the presence and quality of the coatings (e.g., C1s peak for sp2 graphene bonds, B1s/N1s peaks for BN).
- AFM Setup and Calibration:
- A stiff diamond-coated AFM cantilever (NanoSensors CDT-NCLR) was used.
- Cantilever stiffnesses (Cn and Cl) were calculated using geometrical beam theory and resonance frequency measurements.
- Photodiode sensitivity (S) was calibrated on a noncompliant nanocrystalline diamond film.
- Tribological Testing Protocol:
- The AFM tip performed repeated reciprocal sliding over a fixed 2.5 x 2.5 Āµm2 area within a single copper grain.
- Sliding velocity (vs) was 20 Āµm/s.
- Normal force (Fn) was incrementally increased across 14 steps, ranging from 15 nN up to 6930 nN.
- Data Analysis:
- Topographical images were used to track the evolution of the roughness parameter (Rq) and identify the onset of wear (Fny).
- Friction force (<Ff>) was calculated from the difference between forward and backward lateral deflection signals.
- Low-load friction data was fitted using the Johnson-Kendall-Roberts (JKR) model for bare Cu (shearing) and linear models for coated Cu (puckering).
- Post-test noncontact AFM was used to measure the final mean wear depth (Ī“w) by analyzing the height distribution of the worn area.
Commercial Applications
Section titled āCommercial ApplicationsāThe findings regarding the superior wear protection of BN and the low friction of Gr are highly relevant for miniaturized systems requiring robust, ultra-thin tribological layers.
- Micro- and Nano-Electromechanical Systems (MEMS/NEMS): Utilizing monolayer BN as a high-performance, load-bearing coating for critical moving parts (e.g., micro-actuators, micro-switches) to prevent stiction and wear without compromising device geometry.
- High-Density Data Storage: Applying Graphene as an ultra-low friction solid lubricant in hard disk drives or other storage devices where minimizing friction and energy dissipation is paramount.
- Flexible Electronics and Wearable Devices: Integrating 2D material coatings onto flexible copper interconnects or contacts to enhance durability and reliability under repeated mechanical stress and sliding motion.
- Miniaturized Electrical Contacts: Employing BN coatings to protect copper contacts in micro-connectors from abrasive wear and plastic deformation, ensuring long-term electrical stability and mechanical integrity.
- Advanced Composite Coatings: Developing multi-layer 2D material systems where the out-of-plane stiffness can be engineered (e.g., Gr/BN stacks) to achieve an optimal balance between low friction (Graphene characteristic) and high wear resistance (BN characteristic).
View Original Abstract
We investigate the copper-wear-protective effects of graphene and boron nitride in single asperity sliding contact with a stiff diamond-coated atomic force microscopy (AFM)-tip. We find that both graphene and boron nitride retard the onset of wear of copper. The retardment of wear is larger with boron nitride than with graphene, which we explain based on their respective out-of-plane stiffnesses. The wear protective effect of boron nitride comes, however, at a price. The out-of-plane stiffness of two-dimensional materials also determines their friction coefficient in a wear-less friction regime. In this regime, a higher out-of-plane stiffness results in larger friction forces.
Tech Support
Section titled āTech SupportāOriginal Source
Section titled āOriginal SourceāReferences
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