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6CCVD Research

Structural, Mechanical, and Tribological Properties of Molybdenum-Doped Diamond-like Carbon Films

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2025-05-15
JournalCrystals
AuthorsHassan Zhairabany, Hesam Khaksar, Edgars Vanags, Kriťjānis Šmits, Anatolijs Šarakovskis
InstitutionsJagiellonian University, University of Latvia
Citations1
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research investigates the synthesis and performance tuning of Molybdenum-doped Diamond-like Carbon (Mo-DLC) films via DC magnetron sputtering, focusing on the critical influence of Mo concentration and deposition temperature on nanoscale properties.

  • Optimal Friction Performance: The lowest friction coefficient (CoF) of 0.029 was achieved in the Mo-DLC1 film (1.2 at.% Mo) deposited at the highest temperature (235 °C). This low friction is crucial for nano-device functionality.
  • Temperature-Hardness Trade-off: Reducing the synthesis temperature from 235 °C to 180 °C significantly enhanced the nanohardness (up to 8.24 GPa) and sp3 bond fraction, but resulted in a severe degradation of tribological performance, increasing the CoF up to seven times (to 0.21).
  • Graphitization Mechanism: Increasing Mo concentration (up to 10.3 at.%) promotes the graphitization of the DLC matrix, lowering the sp3 site fraction and reducing nanohardness by up to 21% (down to 6.32 GPa).
  • Oxygen Incorporation: High oxygen content (up to 20.4 at.% at 180 °C) was observed, particularly at lower deposition temperatures and higher Mo concentrations, contributing to reduced hardness and elasticity.
  • Tailoring Properties: The study confirms that controlling Mo content and substrate temperature provides a viable pathway for tailoring the sp3/sp2 ratio, nanohardness, and nano-friction coefficient for specific micro- and nano-device applications.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Deposition MethodDC Magnetron SputteringN/ASynthesis technique
Substrate MaterialSi (100) wafersN/AFilm base
Working Pressure~3PaArgon atmosphere
Target Current (Graphite)1.5AFixed parameter
Target Current (Mo)0.25AFixed parameter
Deposition Temperature Range180 to 235°CControlled by target-substrate distance (4 cm to 8 cm)
Film Thickness Range150 to 210nmMeasured via SEM cross-section
Mo Concentration Range1.2 to 10.3at.%Measured via EDX
Oxygen Concentration Range6.5 to 20.4at.%Measured via EDX (Highest in Mo-DLC5 at 180 °C)
Nanohardness Range (H)6.32 to 8.24GPaMeasured via Nanoindenter
Young’s Modulus Range (E)49.22 to 83.66GPaMeasured via Nanoindenter
Lowest Friction Coefficient (CoF)0.029N/AMo-DLC1 (1.2 at.% Mo, 235 °C)
Highest Friction Coefficient (CoF)0.21N/AMo-DLC5 (6.6 at.% Mo, 180 °C)
Lowest RMS Roughness (RRMS)1.9nmMo-DLC1
G Peak Position Range1566.1 to 1576.8cm-1Raman Spectroscopy data
sp3 C-C Content (XPS)29 to 35%Measured after 75 s etching time

Key Methodologies

Section titled “Key Methodologies”

The Mo-DLC films were synthesized using DC magnetron sputtering, with properties controlled primarily by target-substrate distance and Mo flux.

  1. Substrate and Chamber Setup: Si (100) wafers were used as substrates. The chamber was evacuated to a base pressure of ~0.01 Pa, then filled with Argon to a working pressure of ~3 Pa.
  2. Target Configuration: Two 3-inch targets (Graphite, 99.95% purity Molybdenum) were used. Target currents were fixed (1.5 A for C, 0.25 A for Mo).
  3. Mo Concentration Control: A shield with a slit mount was used above the Mo target. Mo concentration (1.2 at.% to 10.3 at.%) was controlled by varying the slit opening width (4 mm to 16 mm).
  4. Temperature Control: Substrate temperature (180 °C to 235 °C) was controlled by varying the target-substrate distance (4 cm, 6 cm, 8 cm). Deposition duration was fixed at 10 minutes for all films.
  5. Microstructural Analysis:
    • Composition: Energy Dispersive X-ray Spectroscopy (EDX) determined elemental composition and mapping.
    • Bonding: X-ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy determined sp3/sp2 ratios and Mo-C/Mo-O bonding states.
  6. Mechanical and Tribological Testing:
    • Hardness/Modulus: Nanoindentation (MTS Agilent G200) using Continuous Stiffness Measurement (CSM) determined nanohardness (H) and Young’s modulus (E).
    • Friction/Roughness: Atomic Force Microscopy (AFM) measured surface roughness (Ra, RRMS) and nano-friction force (used to calculate CoF) under loads ranging from 10 nN to 45 nN.

Commercial Applications

Section titled “Commercial Applications”

The ability to precisely tune the hardness and friction coefficient of Mo-DLC films makes them highly valuable for advanced engineering sectors, particularly those involving micro-scale moving parts.

  • Micro-Electro-Mechanical Systems (MEMS): Essential for reducing friction and wear in critical components like micro-gearboxes, micro-turbines, and micro-actuators, where surface forces dominate bulk properties.
  • Precision Machining and Tooling: Used as protective coatings for cutting tools, molds, and dies, leveraging high hardness (up to 8.4 GPa) and wear resistance.
  • Automotive and Aerospace: Application in high-performance engine components, fuel injection systems, and satellite mechanisms requiring stable, low-friction coatings across operational temperature ranges.
  • Biomedical Devices: Mo-DLC films offer enhanced biocompatibility and mechanical stability for use in orthopedic implants and cardiovascular stents, where low wear rates are mandatory.
  • Data Storage Devices: Potential use in hard disk drives (HDD) and magnetic storage media to protect read/write heads and platters due to their low friction and high density.
View Original Abstract

Non-hydrogenated diamond-like carbon (DLC) films and molybdenum-doped diamond-like carbon (Mo-DLC) films were deposited by direct current magnetron sputtering. The formation was carried out on Si (100) wafers. The influence of molybdenum concentration and deposition temperature on the surface morphology, chemical composition, type of chemical bonds, friction force at nanoscale, and nanohardness of the DLC coatings were investigated by atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and nanoindenter, respectively. The concentration of molybdenum in the films varies from 1.2 at.% to 10.3 at.%. The increase in molybdenum content promotes the graphitization of DLC films, lowering the sp3 site fraction and increasing the oxygen content, which contributes to the reduction in nanohardness (by 21%) of the DLC films. The decrease in the synthesis temperature from 235 °C to 180 °C enhanced the oxygen amount up to 20.4 at.%. The sp3 site fraction and nanohardness of the Mo-DLC films were enhanced with the reduction in the deposition temperature. The film deposited at a substrate temperature of 235 °C exhibited the lowest friction coefficient (CoF) of 0.03, where its molybdenum concentration was 1.2 at.%. The decline in the synthesis temperature increased the CoF of the Mo-DLC films up to seven times.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2016 - Influence of the silicon and oxygen content on the properties of non-hydrogenated amorphous carbon coatings [Crossref]
  2. 2016 - Effect of structure and deposition technology on tribological properties of DLC coatings alloyed with VIA group metals [Crossref]
  3. 2018 - Magnetron-sputtered copper/diamond-like carbon composite thin films with super anti-corrosion properties [Crossref]
  4. 2020 - The formation of the “rod-like wear debris” and tribological properties of Ag-doped diamond-like carbon films fabricated by a high-power pulsed plasma vapor deposition technique [Crossref]
  5. 2016 - Iron, nitrogen and silicon doped diamond like carbon (DLC) thin films: A comparative study [Crossref]
  6. 2013 - Diamond like carbon coatings for potential application in biological implants—A review [Crossref]
  7. 2022 - Effect of deposition temperature on the microstructure and tribological properties of Si-DLC coatings prepared by PECVD [Crossref]
  8. 2023 - Microstructure, magnetic properties and corrosion resistance of Co-DLC nanocomposite film controlled by substrate temperature [Crossref]
  9. 2015 - RSM base study of the effect of deposition temperature and hydrogen flow on the wear behavior of DLC films [Crossref]
  10. 2020 - Influence of deposition temperature on the structure, optical and electrical properties of a-C films by DCMS [Crossref]

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