The Effect of Chromium on the Microstructure and Transparency of Diamond-like Carbon Films

At a Glance

Metadata	Details
Publication Date	2025-04-06
Journal	Processes
Authors	Vilius Dovydaitis, Mindaugas Milieška, Johnny Chimborazo, Enrico Gnecco, Liutauras Marcinauskas
Institutions	Kaunas University of Technology, Lithuanian Energy Institute
Citations	2
Analysis	Full AI Review Included

Technical Documentation & Analysis: Cr-DLC Films

This document analyzes the research on Chromium-doped Diamond-Like Carbon (Cr-DLC) films, focusing on microstructure and transparency, and connects the findings to the advanced material solutions offered by 6CCVD.

Executive Summary

Material Focus: The study successfully synthesized Cr-doped Diamond-Like Carbon (Cr-DLC) films on silicon and glass substrates using DC Magnetron Sputtering (DCMS).
Doping Effect: Increasing the Cr concentration from 7.4 at.% to 13.1 at.% resulted in a corresponding increase in oxygen contamination, reaching up to 51.0 at.%.
Structural Changes: Raman spectroscopy confirmed that higher Cr content promoted graphitization, increasing the sp² C=C bond fraction and shifting the G peak to higher wavenumbers.
Surface Quality: The average surface roughness (Ra) was minimized to 1.63 nm at an optimal Cr concentration of 9.2 at.%.
Optical Performance: Increased graphitization reduced optical transmittance at 500 nm from 57% (low Cr) down to 38% (high Cr).
Infrared Recovery: High oxygen content in the Cr-DLC films was found to compensate for sp³ C-C site loss, allowing the films to maintain transmittance values greater than 70% in the infrared wavelength range.
Core Value Proposition: This research highlights the critical need for precise material control (doping, purity, structure) to tune optical and tribological properties, a core strength of 6CCVD’s MPCVD diamond technology.

Technical Specifications

Extracted data points detailing the material properties and deposition parameters from the research.

Parameter	Value	Unit	Context
Cr Concentration Range	7.4 to 13.1	at.%	Measured in Cr-DLC films
Oxygen Concentration Range	34.6 to 51.0	at.%	Increased with rising Cr content
Film Thickness	220 to 250	nm	As-deposited films
Minimum Average Roughness (Ra)	1.63	nm	Achieved at 9.2 at.% Cr concentration
Minimum Root Mean Square Roughness (Rq)	2.07	nm	Achieved at 9.2 at.% Cr concentration
Optical Transmittance (500 nm)	38 to 57	%	Decreased with increasing Cr content
Infrared Transmittance	> 70	%	Maintained due to high oxygen content
G Peak Dispersion (D_G) Reduction	0.206 to 0.109	cm^-1/nm	Direct evidence of enhanced graphitic clustering
Deposition Method	DC Magnetron Sputtering	N/A	Used for film synthesis
Deposition Pressure (Ar)	2 to 3	Pa	Process parameter
Graphite Target Current	1.5	A	Process parameter
Chromium Target Current	0.5	A	Process parameter

Key Methodologies

The following outlines the primary steps and techniques used in the synthesis and characterization of the Cr-DLC films:

Substrate Preparation: Films were deposited onto Silicon (100) and glass substrates positioned 60 mm from the magnetrons.
Target Materials: High-purity targets were used: 99.99% pure Chromium and 99.9% pure Graphite (3-inch diameter discs).
Deposition Process: Direct Current Magnetron Sputtering (DCMS) was employed using Argon gas at a pressure of 2-3 Pa.
Recipe Parameters: Synthesis lasted 10 minutes, with target currents set at 1.5 A (Graphite) and 0.5 A (Chromium).
Elemental Analysis: Energy-Dispersive X-ray Spectroscopy (EDS) was used to determine the concentration of Cr, O, and C.
Structural Analysis: Multiwavelength Micro-Raman Spectroscopy (using 458 nm, 514 nm, and 633 nm lasers) was performed to analyze the bonding structure (ID/IG ratio, AD/AG ratio, G peak position, and FWHM) and sp²/sp³ content.
Surface Morphology: Atomic Force Microscopy (AFM) was utilized to measure surface roughness (Ra and Rq).
Optical Characterization: UV-VIS-NIR Spectrophotometry measured optical transmittance across the 400 nm to 1300 nm wavelength range.

6CCVD Solutions & Capabilities

This research demonstrates the challenges of tuning carbon film properties through doping and managing structural defects (sp² clustering). 6CCVD provides high-purity, highly controlled MPCVD diamond materials that offer superior performance baselines for optical and tribological applications, enabling researchers to bypass the limitations inherent in DLC films.

Applicable Materials & Services	Research Requirement/Challenge Addressed	6CCVD Technical Advantage
Optical Grade Single Crystal Diamond (SCD)	Need for extremely high sp³ content and transparency (DLC films suffer from graphitization).	SCD offers the highest intrinsic sp³ purity (>99.999%), ensuring maximum transparency and minimal defects for demanding optical applications (e.g., UV-VIS-IR windows).
High-Quality Polycrystalline Diamond (PCD)	Requirement for large-area coatings with excellent mechanical and thermal properties.	6CCVD offers PCD plates/wafers up to 125 mm in diameter, significantly exceeding typical lab-scale DLC deposition limits.
Precision Thickness Control	Need for thin films (paper used 220-250 nm) for specific optical interference or thermal management.	We provide precise thickness control for SCD and PCD films ranging from 0.1 µm up to 500 µm, allowing for exact engineering specifications.
Ultra-Low Roughness Polishing	Requirement for smooth surfaces (paper achieved Ra ~1.6 nm) for optical clarity and low friction.	6CCVD guarantees superior surface finish: Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, minimizing light scattering and enhancing tribological performance.
Boron-Doped Diamond (BDD)	Need for tunable electrical properties (the paper used Cr for structural modification).	BDD provides highly tunable electrical conductivity, ideal for electrochemical sensors, electrodes, and active electronic components, offering a robust alternative to metal-doped carbon films.
Custom Metalization Services	Integration of films into devices requiring specific contacts (e.g., Ti/Pt/Au contacts mentioned in related literature).	In-house metalization capabilities include Au, Pt, Pd, Ti, W, and Cu, ensuring robust, low-resistance interfaces for device integration.

Engineering Support

The complexity of tuning the sp²/sp³ ratio and managing defects, as demonstrated in this study, requires deep material science expertise. 6CCVD’s in-house PhD team specializes in optimizing MPCVD growth parameters to deliver materials with specific structural, optical, and electrical properties for similar Advanced Optical Coating and Tribological projects.

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

View Original Abstract

Cr-doped diamond-like carbon (DLC) films were formed on silicon and glass substrates by magnetron sputtering (MS). The surface morphology, elemental composition, bonding structure, and transparency of the as-deposited films were analyzed by atomic force microscopy (AFM), the energy-dispersive X-ray spectroscopy (EDS), multiwavelength micro-Raman spectrometer, and UV-VIS-NIR spectrophotometer. The study revealed that the oxygen concentration in the Cr-DLC films increased as the Cr content increased. The surface roughness of the films was slightly reduced when the Cr content was ~9.2 at.%, and further increase in the Cr content up to 13.1 at.% stimulated the growth of the highest-roughness Cr-DLC films. The micro-Raman analysis showed that the G peak position shifted to a higher wavenumber, and the sp² bond fraction increased as the Cr concentration in the DLC films rose. The optical transmittance of the Cr-DLC films was reduced by up to 30% compared to DLC coatings due to the increased graphitization process caused by chromium addition.

Tech Support

Original Source

DOI: https://doi.org/10.3390/pr13041098

References

2014 - History of diamond-like carbon films—From first experiments to worldwide applications [Crossref]
2014 - 60 years of DLC coatings: Historical highlights and technical review of cathodic arc processes to synthesize various DLC types, and their evolution for indus-trial applications [Crossref]
2023 - Doping effects on the tribological performance of diamond-like carbon coatings: A review [Crossref]
2022 - Diamond-like Carbon Films for Tribological Modification of Rubber [Crossref]
2020 - Tribomechanical properties of hard Cr-doped DLC coatings deposited by low-frequency HiPIMS [Crossref]
2016 - Tribology International Nanomechanical and nanotribological behavior of ultra-thin silicon-doped diamond-like carbon films [Crossref]
2011 - Synthesis, characterization and properties of the DLC films with low Cr concentration doping by a hybrid linear ion beam system [Crossref]