Huaqiao University Team Uncovers New Friction Damage Mechanism In Single-Crystal Diamond
Sep 12, 2026
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Huaqiao University Team Uncovers New Friction Damage Mechanism in Single-Crystal Diamond, Advancing 4th-Generation Semiconductor Processing
Single-crystal diamond (SCD) is widely recognized as a core material for the fourth generation of semiconductors, thanks to its exceptional electron mobility, ultra-high thermal conductivity, ultra-wide bandgap and extreme hardness. It holds tremendous application potential in high-power devices, high-frequency sensors, thermal management and advanced optics. Before industrial deployment, however, SCD typically requires precision surface processing to achieve required geometries, dimensional accuracy and surface integrity. Deformation, fracture and phase transformation during processing have long been critical bottlenecks limiting yield and machining precision.
Recently, the research team led by Professors Xu Xipeng and Huang Hui at Huaqiao University conducted a systematic study on friction-induced damage in single-crystal diamond. Their findings, titled Formation mechanism of friction-induced directional tree-like microcracks in single-crystal diamond, have been published in the authoritative international journal International Journal of Mechanical Sciences. The study reveals for the first time the formation mechanism of friction-induced directional tree-like microcracks, providing a new theoretical basis for efficient, low-damage processing of single-crystal diamond.
01 First Observation: Directional Tree-Like Microcracks Induced by Friction
In friction sliding experiments between single-crystal diamond and quartz glass, the research team observed a distinctive tree-like microcrack morphology with clear directional characteristics. This morphology has rarely been reported under conventional friction sliding conditions, and differs both from the grid-like cracks commonly seen in mechanical processing and the periodic textures produced by laser processing.
Microcrack initiation is concentrated near wear scars and propagates along specific crystallographic directions. As friction time increases, the diamond surface follows a clear morphological evolution sequence:
- ▸ Initial stage: Wear scar forms and gradually deepens
- ▸ Middle stage: Fine cracks emerge around the wear scar
- ▸ Late stage: Cracks continue to propagate, forming extensive tree-like microcracks
Experimental data shows that surface roughness Sa rises from an initial 0.9 nm to 36.7 nm, 112.4 nm and 141.1 nm after 60, 90 and 120 minutes of friction respectively, with damage increasing significantly over time.
02 Interfacial Discharge: Key Clue to the Damage Mechanism
To identify the origin of tree-like microcracks, the team observed luminescence at the friction interface and performed analysis using optical emission spectroscopy.
During friction, the interface exhibited continuous luminescence accompanied by intermittent intense flashes. Characteristic peaks associated with gas discharge in air were detected in the spectrum, indicating that gas ionization and discharge may occur in the micro-gaps at the friction interface.
⚠️ Key Finding
Optical emission spectroscopy reflects the optical emission of the gas phase at the interface and cannot directly prove dielectric breakdown inside the diamond. Nevertheless, the gas discharge phenomenon is a critical link in the complete evidence chain of "interfacial discharge – local electrothermal damage", providing a core clue for deducing the damage mechanism.
Further electrostatic finite element simulations show that wear scars and interfacial micro-gaps produced by friction cause significant local electric field enhancement. In the representative model presented in the paper, the maximum normalized electric field at the corrugated interface reaches 2.24 times that of a flat interface. Greater surface roughness further amplifies the local maximum electric field and makes discharge more likely to occur.
03 Damage Mechanism: Coupling of Electric Field Enhancement and Crystallographic Anisotropy
Combining experimental characterization, electric field simulation and molecular dynamics calculations, the team proposed the formation mechanism of friction-induced tree-like microcracks in single-crystal diamond:
During continuous friction, charge accumulates at the interface due to triboelectrification. The geometry near the wear scar further amplifies the local electric field, causing interfacial discharge to occur preferentially in the scar region. Repeated charge accumulation and discharge creates a series of discharge points along the wear scar, providing preferential sites for microcrack initiation.
Meanwhile, Raman spectroscopy and TEM/EELS characterization reveal the presence of amorphous carbon, graphitized carbon, lattice distortion, brittle fracture features and residual compressive stress around the microcracks, confirming significant local structural transformation in the crack region.
Molecular dynamics simulations further explain the directional nature of the cracks. Under transient thermal loading, the diamond (001) surface undergoes anisotropic amorphization: structural disorder along the <100> direction is more pronounced than along the <110> direction, and the amorphous layer formed along <100> is thicker. This crystallographic anisotropy directly promotes crack propagation along specific directions, ultimately forming the tree-like morphology.
04 Industry Implications for SCD Precision Machining
The core value of this research lies in breaking through the traditional processing theory framework that only considers mechanical and thermal effects. For the first time, triboelectrification and interfacial electrical effects are incorporated into the analysis of processing damage in single-crystal diamond.
The findings suggest that in high-speed friction processing of SCD, the impact of triboelectrification and related electrical effects on surface damage must be fully considered in addition to conventional mechanical loading and thermal effects. This conclusion has important guiding significance for parameter optimization and equipment design of mainstream diamond processing technologies such as wire saw cutting, grinding and polishing.
The paper also notes that the electric field strength and transient local temperature during actual friction cannot yet be quantitatively characterized, and the influence of factors such as sliding speed, load, ambient humidity and grounding conditions on damage requires further in-depth investigation.
★ Summary
The Huaqiao University team has systematically elucidated the formation mechanism of friction-induced tree-like microcracks in single-crystal diamond, revealing the complete action chain of "local electric field enhancement – interfacial discharge – local electrothermal damage – crystallographic anisotropic propagation".
As a fourth-generation semiconductor material, the industrialization of single-crystal diamond is highly dependent on breakthroughs in precision processing technology. This research not only enriches the theoretical system of diamond tribology and processing damage, but also provides important theoretical support for the development of low-damage processing techniques and specialized equipment.
Disclaimer
This article is an interpretation of academic research results, compiled from publicly published papers for industry reference and communication only. It does not constitute any technical, investment or operational decision-making basis. The research conclusions stated herein represent only the views of the original paper authors. We make no express or implied warranties regarding the accuracy or completeness of the data. Please indicate the source when reprinting.
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