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

At a Glance

Metadata	Details
Publication Date	2025-05-15
Journal	Crystals
Authors	Hassan Zhairabany, Hesam Khaksar, Edgars Vanags, Krišjānis Šmits, Anatolijs Šarakovskis
Institutions	Kaunas University of Technology, University of Latvia
Citations	1
Analysis	Full AI Review Included

Technical Analysis & Documentation: Molybdenum-Doped Diamond-like Carbon Films

Executive Summary

This analysis reviews the synthesis and characterization of Molybdenum-doped Diamond-like Carbon (Mo-DLC) films, focusing on their structural, mechanical, and tribological properties relevant to high-performance micro- and nano-devices.

Material and Method: Non-hydrogenated DLC and Mo-DLC films were deposited on Si (100) wafers using DC magnetron sputtering.
Key Control Variables: Molybdenum concentration (1.2 at.% to 10.3 at.%) and synthesis temperature (180 °C to 235 °C) were the primary factors investigated.
Microstructural Impact: Increased Mo content promotes graphitization, leading to a reduction in the desirable sp³ site fraction and a corresponding decrease in nanohardness (up to 21%).
Mechanical Performance: Maximum nanohardness achieved was 8.4 GPa (Mo-DLC5 film deposited at 180 °C), significantly lower than intrinsic diamond.
Tribological Control: The lowest nano-friction coefficient (CoF = 0.029) was achieved at the highest temperature (235 °C) and lowest Mo concentration (1.2 at.%), demonstrating extreme sensitivity to deposition conditions.
Application Relevance: The findings are critical for tailoring film performance in demanding applications like MEMS production, micro-gearboxes, and micro-turbines, where nanoscale friction control is paramount.

Technical Specifications

The following hard data points were extracted from the research, detailing the material performance under varying synthesis conditions.

Parameter	Value	Unit	Context
Mo Concentration Range	1.2 to 10.3	at.%	Controlled by slit opening
Synthesis Temperature Range	180 to 235	°C	Controlled by target-substrate distance
Film Thickness Range	150 to 210	nm	Determined by SEM cross-section
Nanohardness (H) Max	8.24 ± 0.35	GPa	Mo-DLC5 (180 °C deposition)
Young’s Modulus (E) Max	83.66 ± 7.88	GPa	Mo-DLC5 (180 °C deposition)
H/E Ratio (Max)	0.134 ± 0.002	N/A	Mo-DLC4 (225 °C deposition)
Friction Coefficient (CoF) Min	0.029	N/A	Mo-DLC1 (235 °C, 1.2 at.% Mo)
Friction Coefficient (CoF) Max	0.21	N/A	Mo-DLC5 (180 °C deposition)
Oxygen Content (Max)	20.4 ± 2.4	at.%	Mo-DLC5 (180 °C deposition)
Surface Roughness (RMS) Min	1.9	nm	Mo-DLC1 (235 °C deposition)

Key Methodologies

The Mo-DLC films were synthesized and characterized using the following procedures:

Deposition Technique: DC magnetron sputtering was employed using flat graphite and molybdenum (99.95% purity) targets.
Substrate Preparation: Films were deposited onto cleaned Si (100) wafers.
Vacuum and Gas Flow: The chamber was evacuated to a base pressure of ~0.01 Pa, then filled with Argon to a working pressure of ~3 Pa.
Target Power Control: Graphite target current was fixed at 1.5 A; Molybdenum target current was fixed at 0.25 A.
Mo Concentration Control: Molybdenum content was varied by adjusting the slit opening above the Mo target from 4 mm to 16 mm.
Temperature Control: Substrate temperature was controlled indirectly by varying the target-substrate distance (4 cm, 6 cm, 8 cm), resulting in synthesis temperatures between 180 °C and 235 °C.
Structural and Chemical Analysis: Films were characterized using Energy Dispersive X-ray Spectroscopy (EDX), X-ray Photoelectron Spectroscopy (XPS), and Raman Spectroscopy (to determine sp³/sp² ratios).
Mechanical and Tribological Testing: Nanohardness and Young’s Modulus were measured via nanoindentation (CSM technique). Nano-friction coefficient was measured using Atomic Force Microscopy (AFM) with a PPP-LFMR-10 probe (tip radius < 7 nm).

6CCVD Solutions & Capabilities

The research highlights the challenges of achieving stable, high-performance mechanical and tribological properties in DLC films due to sensitivity to temperature, dopant concentration, and resulting sp³/sp² ratio instability. For applications requiring the ultimate in hardness, wear resistance, and predictable nanoscale friction control (such as MEMS, micro-turbines, and high-precision optics), 6CCVD’s MPCVD diamond materials offer superior, intrinsic performance.

Research Requirement/Challenge	6CCVD Solution & Material Recommendation	Technical Advantage
Ultimate Hardness & Wear Resistance	Single Crystal Diamond (SCD) Plates	SCD offers intrinsic hardness (~100 GPa) and Young’s Modulus (~1000 GPa), far exceeding the 8.4 GPa maximum achieved by Mo-DLC, providing unmatched durability for high-stress nano-devices.
Large-Area High-Performance Coatings	Polycrystalline Diamond (PCD) Wafers	6CCVD provides custom PCD plates/wafers up to 125mm in diameter, enabling scalable production of micro-devices that require large-area diamond integration.
Precise sp³ Bonding Control	High-Purity MPCVD Diamond	Unlike DLC, where the sp³/sp² ratio is unstable and highly sensitive to deposition temperature (180 °C to 235 °C), 6CCVD guarantees diamond purity with >99.99% sp³ content, ensuring stable mechanical properties regardless of minor thermal fluctuations.
Ultra-Low Friction Surface Finish	Precision Polishing Services	The paper achieved RMS roughness down to 1.9 nm. 6CCVD offers state-of-the-art polishing, guaranteeing surface roughness Ra < 1nm for SCD and Ra < 5nm for inch-size PCD, minimizing adhesion and friction forces critical at the nanoscale.
Custom Integration & Electrical Contacts	In-House Metalization Capabilities	For integrating diamond into micro-systems (e.g., sensors or contacts), 6CCVD offers custom metal stacks including Ti, Pt, Au, Pd, W, and Cu deposited directly onto the diamond surface.
Doping for Functionality (e.g., Electrochemistry)	Boron-Doped Diamond (BDD)	For electrochemical or sensing applications, 6CCVD supplies BDD films and substrates, offering superior stability and conductivity compared to metal-doped carbon films.

6CCVD’s MPCVD diamond provides a robust, high-ppurity alternative to DLC, eliminating the microstructural instability and low hardness limitations observed in the Mo-DLC system. Our materials are engineered for predictable performance in extreme environments.

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

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

Original Source

DOI: https://doi.org/10.3390/cryst15050463

References

2016 - Influence of the silicon and oxygen content on the properties of non-hydrogenated amorphous carbon coatings [Crossref]
2016 - Effect of structure and deposition technology on tribological properties of DLC coatings alloyed with VIA group metals [Crossref]
2018 - Magnetron-sputtered copper/diamond-like carbon composite thin films with super anti-corrosion properties [Crossref]
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]
2016 - Iron, nitrogen and silicon doped diamond like carbon (DLC) thin films: A comparative study [Crossref]
2013 - Diamond like carbon coatings for potential application in biological implants—A review [Crossref]
2022 - Effect of deposition temperature on the microstructure and tribological properties of Si-DLC coatings prepared by PECVD [Crossref]
2023 - Microstructure, magnetic properties and corrosion resistance of Co-DLC nanocomposite film controlled by substrate temperature [Crossref]
2015 - RSM base study of the effect of deposition temperature and hydrogen flow on the wear behavior of DLC films [Crossref]
2020 - Influence of deposition temperature on the structure, optical and electrical properties of a-C films by DCMS [Crossref]