Size Dependence of Nanoscale Wear of Silicon Carbide

At a Glance

Metadata	Details
Publication Date	2016-12-20
Journal	ACS Applied Materials & Interfaces
Authors	Chaiyapat Tangpatjaroen, David S. Grierson, Steven Shannon, Joseph E. Jakes, Izabela Szlufarska
Institutions	University of Wisconsin–Madison, North Carolina State University
Citations	26
Analysis	Full AI Review Included

Size Dependence of Nanoscale Wear in SiC: Analysis and Diamond Solutions

This document analyzes the research detailing the size-dependent wear mechanisms of Silicon Carbide (SiC) at the nanoscale. It connects the findings, particularly the critical role of ultra-hard, precisely shaped diamond counter-surfaces, to the manufacturing capabilities and materials provided by 6CCVD, a leading supplier of Microwave Plasma Chemical Vapor Deposition (MPCVD) diamond materials.

Executive Summary

This research reveals a critical transition in the tribological behavior of Single Crystal Silicon Carbide (sc-SiC) and Nanocrystalline Silicon Carbide (nc-SiC) at the nanoscale, directly impacting the design of Micro/Nanoelectromechanical Systems (MEMS/NEMS).

Size-Dependent Wear Reversal: At macro/micro scales (using tips with R ≈ 370 nm), SiC exhibits expected high wear resistance proportional to its superior hardness (37 GPa). However, at the nanoscale (using tips with R ≈ 20 nm), SiC surprisingly demonstrates lower wear resistance than softer silicon (Si) and silicon oxide (SiOx).
Mechanism Transition: This reversal is driven by a switch in the dominant wear mechanism: from plowing (governed by bulk hardness) at large contacts to adhesive wear/interfacial shear (governed by surface chemistry and shear strength) at small contacts.
High Interfacial Shear Strength: The study confirmed that sc-SiC possesses a significantly higher interfacial shear strength (210 ± 48 MPa) compared to Si (72 ± 15 MPa), making it prone to atomic-level removal under low loads.
Diamond Tooling Requirement: The investigation fundamentally relies on ultra-precise diamond counter-surfaces, utilizing both single-crystal diamond (SCD) nanoindenter tips and nanocrystalline diamond (PCD/NCD) AFM tips for accurate, single-asperity testing.
Implication for 6CCVD: These findings emphasize the necessity of high-quality, geometrically precise MPCVD diamond tips and coatings for accurate nanoscale tribology and the development of next-generation, friction-optimized NEMS devices.

Technical Specifications

The following key material and experimental parameters were extracted from the study, highlighting the extreme conditions and material properties under investigation.

Parameter	Value	Unit	Context
sc-SiC Hardness	37 ± 1	GPa	Single Crystal 4H-SiC (0001) wafer average.
nc-SiC Hardness	26 ± 2	GPa	Nanocrystalline 3C-SiC film average.
Si Hardness	12.6 ± 0.2	GPa	Single Crystal Si (100) average.
sc-SiC Elastic Modulus	397 ± 8.5	GPa	Measured via Oliver-Pharr method.
nc-SiC Film Thickness	500	nm	As-deposited, CVD grown film.
Nanoindenter Tip Radius (R_tip)	370	nm	Single Crystal Berkovich Diamond tip (Large Contact).
AFM Tip Radius Range (R_tip)	11 to 27	nm	Nanocrystalline Diamond tips (Small Contact).
Nanoindenter Load Range	50 to 2000	µN	Wear dominated by Plowing mechanism.
AFM Load Range	120 nN to 3.5 µN	nN/µN	Wear dominated by Interfacial Shear mechanism.
Interfacial Shear Strength (sc-SiC)	210 ± 48	MPa	Highest measured shear strength; cause of high nanoscale wear.
Surface Roughness (sc-SiC R_q)	0.19 ± 0.08	nm	Measured over 0.09 µm² area post-polishing/ion milling.
Test Environment	< 3 ± 3	%	Relative Humidity (Dry Nitrogen atmosphere).

Key Methodologies

The experiment relied on precise MPCVD diamond probes and rigorous surface preparation to isolate nanoscale wear mechanisms in a controlled, dry environment.

Material Growth and Preparation:
- Single-crystal 4H-SiC (0001) wafers (CREE®) and nanocrystalline 3C-SiC thin films (CVD grown, {111} texture) were utilized.
- sc-SiC samples were mechanically polished using diamond papers down to 0.1 µm grit, followed by ultrasonic cleaning and final ion milling (1 kV, 20 minutes) to achieve R_q ≈ 0.2 nm.
- nc-SiC films were solely prepared by ion milling to R_q ≈ 0.3 nm.
- Reference Si wafers were prepared with both thin and thick (~16 nm) native oxide layers.
Macro/Micro Scratch Test (Plowing Regime):
- A Hysitron TI 950 TriboIndenter was used with a Single Crystal Diamond Berkovich tip (R ≈ 370 nm).
- Six parallel scratches were formed under varying normal loads (50 µN to 2 mN).
- Each scratch consisted of 500 reciprocal cycles (3 µm length) conducted in a dry nitrogen environment.
Nanoscale Scratch Test (Interfacial Shear Regime):
- A Multimode 8 AFM was used with Nanocrystalline Diamond AFM tips (R ≈ 11-27 nm).
- Seven parallel scratches were formed under loads ranging from 120 nN to 3.5 µN.
- Each scratch consisted of 2,400 reciprocal cycles (3 µm length).
Wearless Regime Friction Measurement:
- Friction vs. load curves were measured using a nanocrystalline diamond AFM tip (R ≈ 20 nm equivalent), with loads varied up to 120 nN, ensuring no permanent deformation.
- Interfacial shear strength (τ) was calculated by fitting the data to the Maugis-Dugdale model using the Carpick-Ogletree-Salmeron (COS) equation.
Characterization:
- Hardness and elastic modulus were measured by nanoindentation (Oliver-Pharr method).
- Wear depth and volume were measured post-test via AFM imaging, supplemented by Focused Ion Beam (FIB) cross-sectioning for maximum accuracy.

6CCVD Solutions & Capabilities

This study underscores the critical relationship between material properties (Hardness, Shear Strength) and contact geometry (Tip Radius) in ultra-hard materials like SiC and diamond. 6CCVD provides the necessary high-purity MPCVD diamond materials and specialized fabrication services required to replicate this research, optimize next-generation tribological systems, and scale NEMS/MEMS production.

Applicable Materials & Components	Research Requirement & Context	6CCVD Solution & Value Proposition
Single Crystal Diamond (SCD) Material	Required for stable, high-precision nanoindenter tips (R ≈ 370 nm) and substrates for high-frequency NEMS resonators.	Optical Grade SCD Wafers: We supply high-purity SCD plates (0.1 µm to 500 µm thick, Ra < 1 nm polished) suitable for fabricating the most durable and dimensionally accurate single-crystal diamond tooling and device components.
Nanocrystalline Diamond (PCD) / NCD	Required for nanoscale AFM tips (R ≈ 11-27 nm) used in interfacial shear studies, proving superior stability to Si tips.	Custom PCD Plates & Films: 6CCVD provides MPCVD PCD plates up to 125 mm in diameter, perfect for advanced, large-format tribological studies or the mass fabrication of NCD tips/coatings used in scanning probe applications.
Boron-Doped Diamond (BDD)	Future MEMS/NEMS devices replacing SiC require high hardness plus superior electrical conductivity, often in harsh (high temp, nuclear) environments.	Heavy Boron Doped Diamond (BDD): BDD offers exceptional mechanical hardness combined with tunable conductivity, making it an ideal candidate material to exceed SiC performance in tribologically sensitive, electrically active MEMS for nuclear or high-temperature applications.
Surface Finish & Metrology	SiC samples required ultra-low surface roughness (R_q < 0.3 nm) for reliable nanoscale testing.	Precision Polishing Service: Our capability ensures ultra-flat surfaces (SCD R_a < 1 nm; inch-size PCD R_a < 5 nm), mandatory for research into interfacial shear and adhesion where surface chemistry and roughness are primary variables.
Device Integration & Customization	Integration of hard coatings into devices (e.g., SiC coatings reducing adhesion in Si-based MEMS, as cited).	Custom Metalization and Etching: We offer in-house metalization (Au, Pt, Pd, Ti, W, Cu) and precise laser cutting services to achieve complex geometries and robust electrical contacts, simplifying the integration of diamond into high-performance microstructures.

Engineering Support

The observed nanoscale wear phenomena—where hardness is decoupled from wear resistance—highlights the need for advanced material design. 6CCVD’s in-house PhD team provides consultative support to engineers and researchers focused on designing tribologically optimized components for MEMS/NEMS applications, leveraging the unique mechanical, thermal, and chemical properties of MPCVD diamond.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Nanoscale, single-asperity wear of single-crystal silicon carbide (sc-SiC) and nanocrystalline silicon carbide (nc-SiC) is investigated using single-crystal diamond nanoindenter tips and nanocrystalline diamond atomic force microscopy (AFM) tips under dry conditions, and the wear behavior is compared to that of single-crystal silicon with both thin and thick native oxide layers. We discovered a transition in the relative wear resistance of the SiC samples compared to that of Si as a function of contact size. With larger nanoindenter tips (tip radius ≈ 370 nm), the wear resistances of both sc-SiC and nc-SiC are higher than that of Si. This result is expected from the Archard’s equation because SiC is harder than Si. However, with the smaller AFM tips (tip radius ≈ 20 nm), the wear resistances of sc-SiC and nc-SiC are lower than that of Si, despite the fact that the contact pressures are comparable to those applied with the nanoindenter tips, and the plastic zones are well-developed in both sets of wear experiments. We attribute the decrease in the relative wear resistance of SiC compared to that of Si to a transition from a wear regime dominated by the materials’ resistance to plastic deformation (i.e., hardness) to a regime dominated by the materials’ resistance to interfacial shear. This conclusion is supported by our AFM studies of wearless friction, which reveal that the interfacial shear strength of SiC is higher than that of Si. The contributions of surface roughness and surface chemistry to differences in interfacial shear strength are also discussed.

Tech Support

Original Source

DOI: https://doi.org/10.1021/acsami.6b13283

References

2008 - Tribology on the Small Scale: A Bottom Up Approach to Friction, Lubrication, and Wear