Applications of Diamond-like Carbon Coatings E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 755

Veröffentlichungsjahr: 2025

Beschreibung

An incisive guide to diamond-like carbon (DLC) coatings and their contemporary applications

In Applications of Diamond-like Carbon Coatings, distinguished researcher Dr. Abdul Wasy Zia delivers an insightful and up-to-date discussion of the latest advancements in new and non-conventional applications of diamond-like carbon (DLC) coatings. The editor explains the transformation of typical topics into advanced applications of DLC, including tribology for future transportation solutions, green lubrication, invasive implants, MEMS, optical devices, and more.

The book also details advanced and contemporary trends in DLC coatings, like material informatics involving artificial intelligence and machine learning, and new, net-zero applications, including energy storage batteries. Readers will also find:

• A thorough introduction to applications of DLC coatings in mechanics, transportation, medicine, and electrical and optical device manufacture
• Comprehensive explorations of emerging trends in DLC coatings, including green energy, data-centric approaches, textile and plastics, and carbon circularity from DLC coated products
• Practical discussions of how small and medium industries can design and develop DLC coatings for broad engineering applications
• Complete treatments of the benefits and opportunities presented by DLC coating applications

Perfect for postgraduate students and researchers with an interest in DLC coatings, Applications of Diamond-like Carbon Coatings will also benefit scholars and instructors in academia, technical managers, scientists, engineers, and corporate research and development professionals with backgrounds in chemistry, materials science, polymer chemistry, and physical chemistry.

Leseprobe

Table of Contents

Cover

Table of Contents

Title Page

Copyright

List of Contributors

Preface

Section I: Diamond-like Carbon Coatings

Chapter 1: Introduction of Diamond-like Carbon Coatings

1.1 Introduction

1.2 DLC Coatings for Mechanical and Transportation Applications

1.3 DLC Coatings for Medical Applications

1.4 DLC Coatings for Electrical and Optical Devices

1.5 DLC Coatings for Optical Applications

1.6 Emerging Applications of DLC Coatings

1.7 Limitations of DLC Coatings

1.8 Q-Carbon as a Superior Coating Material

1.9 Summary

References

Chapter 2: Deposition Methods of Diamond-like Carbon Coatings

2.1 Introduction

2.2 Classification of Carbon Coatings

2.3 Deposition Methods

2.4 Deposition Mechanisms

2.5 Influence of Deposition Parameters

2.6 Properties and Analysis Methods

2.7 Applications

2.8 Conclusions

References

Chapter 3: Properties of Diamond-like Carbon Coatings

3.1 Introduction to Diamond-like Carbon Coating

3.2 General Categorization of DLC Coatings

3.3 Preparation of DLC Coatings

3.4 Characterization Techniques of DLC Coatings

3.5 Properties of DLC Coatings

3.6 Improving the Properties of DLC Coatings

3.7 Applications and Uses of DLC Coatings

3.8 Summary and Future Outlook

References

Section II: Diamond-like Carbon Coatings for Mechanical and Transportation Applications

Chapter 4: Diamond-like Carbon Coatings for Tools and Molds

4.1 Introduction

4.2 Hot Forging Die Tool Failure Mechanisms

4.3 Surface Treatments in Die Tools and Molds

4.4 Deposition of DLC Coatings

4.5 Structural Properties of DLC Coatings

4.6 Mechanical and Tribological Properties of DLC Coatings

4.7 Applications of DLC Coatings in Die Tools and Molds

4.8 Challenges and Future Perspective of DLC Coatings

References

Chapter 5: Diamond-like Carbon Coatings for Solid Lubrication: Production Techniques, Properties, and Applications

5.1 Introduction

5.2 Classifications of DLC Coatings

5.3 Deposition Methods of DLC Coatings

5.4 Tribology of DLC Coatings

5.5 Modification of DLC Coatings for Reduced Wear and Friction

5.6 Applications of DLC Coatings

5.7 Summary and Future Directions

References

Chapter 6: Diamond-like Carbon Coatings and Green Lubricants

6.1 Introduction

6.2 DLC Coatings in Sustainable Tribology: Navigating Green Engineering Concepts

6.3 Role and Importance of Doping Elements on DLC Lubricating Properties

6.4 Interactions of DLC Coatings with Green Additives

6.5 Lubrication Behavior of DLC Coatings with Base Lubricants

6.6 Conclusion

Acknowledgements

References

Section III: Diamond-like Carbon Coatings for Medical Applications

Chapter 7: Diamond-like Carbon Coatings for Artificial Implants

7.1 Introduction

7.2 Requirements for DLC Coatings When Employed to Artificial Implants

7.3 Application for Load-bearing Implants

7.4 Application for Dental Implants and Braces/Retainers

7.5 Concluding Remarks

References

Chapter 8: Diamond-like Carbon Coatings for Orthopedic Implants and Surgical Tools

8.1 Introduction

8.2 Orthopedic Substrates and DLC Coating Techniques

8.3 Carbon Coatings as Part of Multilayer Systems or as a Base for Doping

8.4 Properties of DLC Coatings and Their Use in Orthopedics and Surgical Instruments

8.5 Examples of Applications of Carbon Coatings in Orthopedics and on Surgical Instruments

8.6 Conclusion

References

Section IV: Diamond-like Carbon Coatings for Electrical and Optical Devices

Chapter 9: Diamond-like Carbon Coatings for Electric Storage Batteries

9.1 Introduction

9.2 Applications of DLC Coatings in Secondary Batteries

9.3 Conclusions and Future Research

References

Chapter 10: DLC Coatings for Optical and Optoelectronic Applications

10.1 Introduction

10.2 Production and Characterization Methods

10.3 Optical and Optoelectronic Properties

10.4 Effect of Production Methods/Parameters on DLC Film Properties

10.5 DLC Films in Optical and Optoelectronic Applications

10.6 Conclusion

References

Section V: Emerging Applications of Diamond-like Carbon Coatings

Chapter 11: Diamond-like Carbon Coatings for Polymers and Textiles

11.1 Introduction

11.2 Polymer Substrates and Techniques for Developing DLC Coatings on Them

11.3 Properties of DLC Coatings for Which They Find Application in Polymer Modification

11.4 Application Areas for Carbon Coatings for Polymers and Textiles

11.5 Conclusion

References

Chapter 12: Diamond-like Carbon Coating Applications in MEMS

12.1 Introduction

12.2 Mechanical Properties of DLC Coatings

12.3 DLC Applications for Sensors

12.4 DLC Applications for Nanoactuators

12.5 Industrial Processing

12.6 Applications of DLC Coatings Structural Integrity

12.7 DLC Applications for MEMS Tribology

12.8 DLC Coatings System and Performance

12.9 Conclusion

References

Chapter 13: Data-centric Process, Property, and Performance of Carbon Coatings

13.1 Introduction

13.2 Data-centric Manufacturing Process of Carbon Coatings

13.3 Data-centric Virtual Synthesis and Structural Design of Carbon Coatings

13.4 Understanding the Properties of Carbon Coatings With Data-centric Approaches

13.5 Data-centric Performance Assessment of Carbon Coatings

13.6 Applications of Carbon Coating in Enhancing the Heat Transfer Processes

13.7 Conclusion

References

Chapter 14: Circularity and Techno-economic Analysis of Carbon-coated Products

14.1 Introduction

14.2 Potential Reprocessing Methods for Carbon De-coating

14.3 Decision Matrix of Carbon De-coating Methods

14.4 Technical Analysis of Carbon De-coating Methods

14.5 Economic Analysis of Carbon De-coating Methods

14.6 Case Study – Carbon De-coating from Cutting Tools

14.7 Conclusion

References

Index

End User License Agreement

List of Tables

Chapter 1

Table 1.1 Important physical characteristics of carbon materials currently in ...

Chapter 2

Table 2.1 A summary of deposition methods associated with DLC films.

Table 2.2 Properties of different carbon materials.

Table 2.3 Practical applications of protective DLC films.

Chapter 3

Table 3.1 List of thermal conductivity of five different carbon films.

Table 3.2 List of elements incorporated into DLC coatings and their biological...

Table 3.3 Electrical properties of Al-Si-DLC-Al before and after irradiation o...

Table 3.4 Properties of DLC films deposited by ion beam deposition technique.

Table 3.5 Friction coefficients of a-C:H and a-C type coatings prepared by pul...

Table 3.6 Results of wear tests for coated and uncoated sample.

Table 3.7 Hardness and modulus values of samples deposited at room temperature...

Chapter 4

Table 4.1 Overview of various DLC coating techniques, benefits, and limitation...

Chapter 6

Table 6.1 Effect of different nanoparticles on the coefficient of friction red...

Chapter 7

Table 7.1 Requirements for coatings applied to artificial implants.

Table 7.2 Summary of literature findings on DLC coatings employed for load-bea...

Chapter 10

Table 10.1 Deposition techniques used for the production of DLC films.

Table 10.2 Common methods used for the characterization of DLC films.

Table 10.3 Refractive index and/or bandgap energy of DLC-based thin films.

Chapter 12

Table 12.1 Tensile strength of ta-C as a function of specimen dimensions [27] /...

Table 12.2 Friction and wear properties of DLC. Reproduced from [15] / with per...

Chapter 13

Table 13.1 Maximum equivalent stresses during loading and relaxation at the fat...

Chapter 14

Table 14.1 Decision matrix of the de-coating methods.

Guide

Cover

Table of Contents

Title Page

Copyright

List of Contributors

Preface

Begin Reading

Index

End User License Agreement

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Applications of Diamond-like Carbon Coatings

Edited by Abdul Wasy Zia

Institute of Mechanical Process and Energy Engineering (IMPEE), School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, United Kingdom

Copyright © 2025 by JW-Wiley.

All rights reserved, including rights for text and data mining and training of artificial intelligence technologies or similar technologies.

Published by John Wiley & Sons, Inc., Hoboken, New Jersey.

Published simultaneously in Canada.

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Library of Congress Cataloging-in-Publication Data

Names: Zia, Abdul Wasy, editor.

Title: Applications of diamond-like carbon coatings / edited by Abdul Wasy Zia.

Description: Hoboken, New Jersey : John Wiley & Sons Inc., [2025] | Includes bibliographical references and index.

Identifiers: LCCN 2024047186 | ISBN 9781394189113 (hardback) | ISBN 9781394189120 (adobe pdf) | ISBN 9781394189137 (epub)

Subjects: LCSH: Diamond thin films. | Protective coatings.

Classification: LCC TP873.5.D5 A77 2025 | DDC 667/.9--dc23/eng/20250224

LC record available at https://lccn.loc.gov/2024047186

Cover Image: ©Springer Nature

Cover Design: WILEY

List of Contributors

Raies Abdullah

School of Materials Science and Engineering

Jiangsu University

Zhenjiang

China

Farooq Ahmad

School of Materials Science and Engineering

Jiangsu University

Zhenjiang

China

Muhammad Shahid Arshad

Laboratory for Tribology and Interface Nanotechnology

University of Ljubljana

Ljubljana

Slovenia

Department for Nanostructured Materials

K7

Jožef Stefan Institute

Ljubljana

Slovenia

Muhammad Asim

School of Professional Education & Executive Development

The Hong Kong Polytechnic University

Kowloon

Hong Kong

Naim Aslan

Faculty of Engineering

Department of Metallurgical and Materials Engineering

Munzur University

Tunceli

Turkiye

Rare Earth Elements Application and Research Center

Munzur University

Tunceli

Turkiye

Muhammad Abdul Basit

Department of Materials Science and Engineering

Institute of Space Technology

Islamabad

Pakistan

Muhammad Umar Farooq

The Sargent Centre for Process Systems Engineering

Department of Chemical Engineering

University College London

London

UK

Nawal Haider

Department of Materials Science and Engineering

Institute of Space Technology

Islamabad

Pakistan

Muhammad Ihsan-Ul-Haq

Energy Storage and Distributed Resources Division

Lawrence Berkeley National Laboratory

Berkeley, CA

USA

Interdisciplinary Research Center for Sustainable Energy Systems (IRC-SES)

King Fahd University of Petroleum and Minerals

Dhahran

Saudi Arabia

Materials Science and Engineering Department

King Fahd University of Petroleum and Minerals

Dhahran

Saudi Arabia

Muhammad Ikhlaq

School of Engineering

Newcastle University

Newcastle upon Tyne

UK

Dyson Institute of Engineering and Technology

Malmesbury

UK

Hafiz Mahmood Ilahi

Department of Mechanical Engineering

City University of Hong Kong

Hong Kong SAR

China

Ashmal James

Institute of Mechanical Process and Energy Engineering (IMPEE)

School of Engineering and Physical Sciences

Heriot-Watt University

Edinburgh

UK

Krzysztof Jastrzębski

Division of Biomedical Engineering and Functional Materials

Institute of Material Science and Engineering

Lodz University of Technology

Lodz

Poland

Naveen Joshi

Department of Materials Science and Engineering

Centennial Campus

North Carolina State University

Raleigh, NC

USA

Witold Kaczorowski

Division of Biomedical Engineering and Functional Materials

Institute of Material Science and Engineering

Lodz University of Technology

Lodz

Poland

Pranay Kalakonda

Department of Materials Science and Engineering

North Carolina State University

Raleigh, NC

USA

Sarmad Ali Khan

Department of Industrial and Manufacturing Engineering

University of Engineering and Technology

Lahore

Pakistan

Mümin Mehmet Koç

Department of Medical Services and Techniques

School of Medical Service

Kırklareli University

Kırklareli

Turkiye

Department of Physics

Faculty of Science and Art

Kırklareli University

Kırklareli

Turkiye

Deepak Kumar

Department of Mechanical Engineering

Carnegie Mellon University

Pittsburgh, PA

USA

Department of Materials Design and Innovation

University at Buffalo

New York, NY

USA

Max Marian

Department of Mechanical and Metallurgical Engineering

School of Engineering

Pontificia Universidad Católica de Chile

Macul

Región Metropolitana

Chile

Institute of Machine Design and Tribology (IMKT)

Leibniz University Hannover

Garbsen

Germany

Jamile Mohammadi Moradian

School of Materials Science and Engineering

Jiangsu University

Zhenjiang

China

Irfan Nadeem

Laboratory for Tribology and Interface Nanotechnology

University of Ljubljana

Ljubljana

Slovenia

Jagdish Narayan

Department of Materials Science and Engineering

Centennial Campus

North Carolina State University

Raleigh, NC

USA

Roger J. Narayan

Department of Materials Science and Engineering

Centennial Campus

North Carolina State University

Raleigh, NC

USA

Joint Department of Biomedical Engineering

Centennial Campus

North Carolina State University and UNC Chapel Hill

Raleigh, NC

USA

Piotr Niedzielski

Division of Biomedical Engineering and Functional Materials

Institute of Material Science and Engineering

Lodz University of Technology

Lodz

Poland

Marko Polajnar

Laboratory for Tribology and Interface Nanotechnology

University of Ljubljana

Ljubljana

Slovenia

Himanshu Rai

Department of Control Engineering

Faculty of Electrical Engineering

Czech Technical University in Prague

Prague

Czech Republic

Mudassar Rauf

School of Mechanical and Electrical Engineering

Wenzhou University

Wenzhou

China

Benedict Rothammer

Engineering Design

Friedrich-Alexander-Universität Erlangen-Nuremberg (FAU)

Erlangen

Germany

Virendra Pratap Singh

Department of Mechanical Engineering

IES College of Technology

Bhopal

India

Muhammad Usman

Department of Mechanical Engineering

City University of Hong Kong

Hong Kong SAR

China

Ramsha Zafar

Department of Materials Science and Engineering

Institute of Space Technology

Islamabad

Pakistan

Abdul Wasy Zia

Institute of Mechanical Process and Energy Engineering (IMPEE)

School of Engineering and Physical Sciences

Heriot-Watt University

Edinburgh

UK

Preface

Carbon coatings were reported in 1954 and exhibit graphite-like behaviors since diamond-like carbon (DLC) coatings were reported around 1970. DLC coatings grasped rapid recognition in the industry and were widely adopted for mechanical applications as DLC coatings exhibit high hardness, lower friction coefficient, and excellent antiwear properties. DLC coatings have progressed through a range of deposition techniques like physical vapor deposition, plasma-enhanced chemical vapor deposition, etc.; coating architectures such as monolayer, multilayer, doped; nanocrystalline, amorphous, or granular morphologies; and have been used for a wider range of industrial applications including automotive, mechanical components and cutting tools, healthcare products, renewable energy, computing and electronics, plastics, textiles sectors, etc.

This book presents current advancements in the applications of DLC coatings. Thirty-three subject experts have contributed 14 chapters to this book, which presents 5 major sections on DLC coatings. The first section introduces DLC coatings, details on deposition methods, and their properties. The second section presents DLC applications for mechanical and transportation with emphasis at tools and molds, solid lubricants, and green tribology. The third section presents DLC applications for medical sector such as artificial implants and surgical tools. The fourth section presents DLC applications in electrical and optical devices such as energy storage batteries and optoelectronic products. New DLC markets are emerging with industrial transformation. Therefore, the last section presents new trends in DLC applications such as DLC coatings for polymer and textiles, micro-electromechanical systems. The last two chapters highlight the significance of the data-centric process–property–performance relationship of DLC coatings and the circularity of DLC-coated products back to cradle-to-cradle product life cycle after the de-coating process in aspiration of a circular economy for green and sustainable ecology.

The book contents are suitable for new researchers in DLC to subject experts and would be a useful source for teaching, research, policymaking, and industrial audiences associated with DLC coatings.

Editor

Abdul Wasy Zia, PhD

Edinburgh

Section IDiamond-like Carbon Coatings

Chapter 1Introduction of Diamond-like Carbon Coatings

Naveen Joshi1, Jagdish Narayan1, Roger J. Narayan1,2

1 Department of Materials Science and Engineering, Centennial Campus, North Carolina State University, Raleigh, NC, USA

2 Joint Department of Biomedical Engineering, Centennial Campus, North Carolina State University, Raleigh, NC, USA

Contents

1.1 Introduction

1.2 DLC Coatings for Mechanical and Transportation Applications

1.2.1 DLC Coatings for Lubricants

1.2.2 DLC Coatings for Pipelines, Tubes, and Molds

1.3 DLC Coatings for Medical Applications

1.3.1 DLC Coatings for Orthopedics

1.3.2 DLC Coatings for Antimicrobial Performance

1.3.3 DLC Coatings for Cardiovascular Implants

1.4 DLC Coatings for Electrical and Optical Devices

1.4.1 DLC Coatings for MEMS

1.4.2 DLC Coatings for Nonvolatile Storage, Low-K Dielectrics, and Field Emitters

1.5 DLC Coatings for Optical Applications

1.6 Emerging Applications of DLC Coatings

1.6.1 DLC Coatings for Energy Storage Applications

1.6.2 DLC Coatings for Polymers and Textiles

1.6.3 Optimizing DLC Coatings Through the Utilization of Artificial Intelligence Tools

1.7 Limitations of DLC Coatings

1.8 Q-Carbon as a Superior Coating Material

1.9 Summary

1.1 Introduction

Carbon materials have attracted immense attention due to their exceptional mechanical strength and unique functionalities [1]. Among carbon materials, diamond-like carbon (DLC) has been extensively examined for its versatile structure and multifunctional capabilities [2]. The term DLC is generally utilized to define a type of carbon-based materials containing a mixture of (graphitic) sp2- and (diamond) sp3-hybridized phases. DLC can contain 0–50% hydrogen atoms depending on the deposition methods employed [3]. However, the DLC coatings can be formed without hydrogen incorporation. Narayan et al. showed the formation of hydrogen-free DLC films with high sp3 bonding and superior mechanical properties by pulsed laser deposition (PLD) [4]. The ternary phase diagram of DLC structures, as proposed by Robertson, is shown in Figure 1.1 [5]. Regions designated as a-C, ta-C, and a-C:H refer to pure carbon, tetrahedral amorphous carbon, and hydrogenated carbon with the corresponding extent of hydrogenation, respectively. Due to the variable fractions of sp2- and sp3-hybridized states, DLC structures show excellent mechanical strength, resistance to wear, resistance to corrosion, reduced friction coefficient, and unique functional properties [2, 4]. Thus, DLC materials have been a popular choice of coating materials for applications in mechanical and transportation industries, biomedical implants and devices, storage devices, and optical products. Some of the significant properties of different classes of carbon materials are summarized in Table 1.1 [6].

Figure 1.1 Ternary phase diagram that describes various parameters of DLC materials.

Source: Reproduced from [6] / with permission of ELSEVIER.

Table 1.1 Important physical characteristics of carbon materials currently in use.

Source: Reproduced from [6] / with permission of ELSEVIER.

Mass density (g cm

−3

)

Hydrogen content (at. %)

Number density (1 cm

−3

)

Hard/soft

Diamond

3.51

–

0

0.29

Superhard

Graphite

2.25

–

0

0.19

Soft

ta-C

3.2

–

1

0.27

Superhard

a-C:H

2.3

11

0.21

Hard

Polystyrene

1.05

50

0.16

Soft

Several approaches have been developed for processing DLC films, such as both chemical vapor deposition (CVD) and physical vapor deposition (PVD) techniques. Among PVD techniques, ion beam deposition, PLD, and magnetron sputtering are widely explored for the deposition of DLC films [7]. Ion beam deposition facilitates the deposition of high-quality coatings at near-room temperature. However, the deposition rate is too low; the substrates require complex manipulation methods for uniform deposition, limiting the practical application of this approach [8]. Sputtering is employed as another popular technique to deposit DLC films with variable sp2 content. Even so, the low ion energies associated with sputter deposition result in the poor mechanical strength of the coatings, making them unsuitable for high-strength applications [9]. On the other hand, PLD yields smooth DLC coatings with high sp3 content, but it has not yet been developed for the large-scale manufacturing of DLC, and it is often challenging to produce uniform coatings using this technique [10]. Among the CVD techniques, the plasma-enhanced chemical vapor deposition (PECVD) process has been commonly utilized for the growth of DLC films with high uniformity, conformal coverage, and reasonable deposition rates [11]. The PECVD also enables the growth of strain-free and adherent DLC coatings with high levels of mechanical strength and resistance to wear and corrosion [11–13]. Thus, it is highly preferred for the large-scale manufacturing of DLC coatings. A schematic showing the PECVD chamber used in the growth of DLC films is provided in Figure 1.2 [13].

Figure 1.2 Schematic showing the PECVD instrument utilized for the deposition of the DLC films [13] / John Wiley & Sons/CC BY 4.0.

DLC structures are doped with several elements and compounds to improve their functionality [14]. Metals and semiconductors such as Mo, Cu, Cr, Ag, Ti, Ni, Al, W, and Si and compounds such as ZnO and W2C have been reported to have doped to improve the performance of DLC coatings [13–17]. Among them, silicon (Si) is highly preferred as a dopant material, as it is known to reduce the internal stresses in the coating, enhance the adhesion of the coating to the underlying substrate, and improve the thermal stability of DLC structures [13, 18, 19]. Si-incorporated DLC (Si-DLC) is also shown to have a low friction coefficient, improved resistance to wear, and improved resistance to corrosion [18]. In addition, Yang et al. noted that Si-DLC coatings are biocompatible and inhibit microbial activity, expounding their applications to implantable medical devices [13]. This chapter gives an overview of several doped and undoped DLC coatings and their applications in mechanical and transportation, biomedical devices, electrical devices, and optical products. The limitations of DLC coatings are discussed briefly, and quenched carbon (Q-carbon) is introduced as an emerging, superior alternative for coating materials that are currently in use.

1.2 DLC Coatings for Mechanical and Transportation Applications

The unique combination of high hardness, reduced friction coefficient, resistance to wear, and resistance to corrosion in DLC materials have made them an unambiguous choice for protective coatings in the mechanical and transportation industry [2, 6]. Since their discovery in the 1950s, DLC coatings were first investigated for their unique scratch resistance properties [20]. In 1973, Aisenberg and Chabot reported that the cutting characteristics of paper cutting blades may be significantly improved by coating them with DLC films [21]. The wear tests revealed that the coefficient of friction is reduced on the coated blades. Since then, DLC coatings have been commonly used to enhance the performance of machines and mechanical tools. Moreover, due to their sophisticated structural properties, gears, bearings, and the inside of the automotive engines are coated with DLC to reduce wear, reduce friction, and the need for lubrication. Thus, it helps improve fuel efficiency and reduce the maintenance costs of the vehicle [22]. Some of these structural applications of DLC coatings are discussed in this section.

1.2.1 DLC Coatings for Lubricants

DLC is a popular choice of coating for mechanical and transportation applications, as it is a material that is able to provide high resistance to corrosion, low friction, and high hardness under dry sliding conditions with a coefficient friction as low as 0.01–0.5 based on the environmental conditions the DLC coating is subjected to [5, 23]. For instance, hydrogenated coatings perform better in an inert environment. In contrast, hydrogen-free DLC is preferred in humid environments where a friction coefficient as low as 0.1 can be achieved for an extended period [5, 24]. The variation of the coefficient of friction with relative humidity for hydrogenated and nonhydrogenated DLC coatings is shown in Figure 1.3 [25]. Another class of DLC coatings, which is referred to as near-frictionless carbon, is associated with the lowest possible friction coefficient of any known material (~0.005) due to the passivation of the contact surface achieved by hydrogenated carbon atoms in DLC [25–27]. As such, the hydrogen content and chemical bonding in the coatings have a significant impact on the coefficient of friction. However, fabricating a single type of DLC to achieve low friction in both dry and humid environments is quite challenging. To address this issue, a new class of DLC coatings called diamond-like nanocomposite (DLN) coatings was developed [28, 29]. The structure of DLN materials consists of two amorphous interpenetrating networks with minimal bonding between them. Mutual stabilization within these networks reduces the coating residual stress, improves adhesion, and inhibits graphitic carbon growth at elevated temperatures [25, 28–30]. Furthermore, DLN provides a low friction coefficient and can adapt to dry and humid environments, expounding the mechanical applications of DLC coatings [25, 29].

Figure 1.3 Changes in frictional coefficient with relative humidity for a-C:H and ta-C coatings.

Source: Reproduced from [25] / with permission of IOP Publishing.

1.2.2 DLC Coatings for Pipelines, Tubes, and Molds

In addition to a low coefficient of friction, DLC coatings show low wear rates ranging from 10−7 to 10−9 mm3 Nm−1 [31]. However, specific test conditions (e.g. temperature, relative humidity, and dopant materials) are known to influence the wear properties of DLC coatings. For instance, the water vapor condensed on the contact zone in humid conditions can inhibit the dry lubricating effect of DLC and prevent the formation of transferred layers, leading to an increase in wear [31, 32]. Similarly, working temperature has a significant impact on the wear rates of DLC coatings. Gharam et al. have shown that the wear rate increases from a value of 0.5 × 10−5 mm3 Nm−1 to a value of 8.5 × 10−5 mm3 Nm−1 from room temperature to 100 °C and then gradually decreases to 400 °C [33]. Thus, several strategies, such as element doping, surface implantation, and surface thermal treatments, have been employed to overcome these challenges. Among them, doping is found to be a promising technique to enhance the mechanical and transportation properties of DLC [34]. DLC structures have been doped with various elements such as N, Mo, Cu, Cr, Ag, Ti, Ni, Al, W, and Si and various compounds such as W2C and Mo2C [14–18, 34]. One of the studies showed that co-doping DLC structures with Ti and Ni significantly reduced the internal stresses in the film, improving the durability of the coatings [35]. In another study, Wei et al. have shown that the metal interlayers of Cr, Ti, and Al in DLC led to a significant enhancement in the adhesion of these coatings by stabilizing the sp2 clusters and thus decreasing the graphitization in the DLC structures [36]. Damasceno et al. observed a similar effect in the incorporation of Si into DLC [18]. Additionally, Kim and Lee’s work showed that Si-DLC films resulted in a significant reduction in wear rate and a reduction in friction coefficient, leading to improved tribological properties in the film [37]. Figure 1.4 shows the variation of wear rate in Si-DLC films with varied concentrations of Si [38]. The sample with the highest Si content showed a significant reduction in the wear rate as well as an increase in the elastic modulus of the film. In addition, co-doping N/Si and O/Si in DLC was shown to elevate the thermostability of these structures [39]. Furthermore, Si prefers to create sp3 bonding within DLC, increasing the sp3/sp2 ratio in the films. The increase in the sp3 content in the films stabilizes the DLC structure, enhancing the strength of these coatings [40]. Thus, Si has been a popular choice of dopant materials to enhance the multifunctional capabilities of DLC coatings for mechanical applications [18, 19, 37–40].

Figure 1.4 (i) 3D and (ii) 2D morphologies and profiles of wear rates for Si-DLC films with varied concentrations of silicon.

Source: Reproduced from [38] / with permission of ELSEVIER.

1.3 DLC Coatings for Medical Applications

DLC is one of the oldest and most popular forms of carbon-based materials to be employed for biomedical applications [41]. In the 1990s, Thomson et al. reported that DLC coatings are biocompatible [42]. Since then, they have been widely studied for various biomedical applications due to their versatile properties. In addition to biocompatibility, DLC materials exhibit high resistance to corrosion, improved tribological properties, antimicrobial activity, and anti-inflammatory action, making them an ideal choice for biomedical implants and devices [43]. DLC films can be deposited on several types of substrates at relatively low deposition temperatures; this characteristic makes this class of carbon-based materials technologically and commercially important. Thus, it has been a popular choice of coating for orthopedic, cardiovascular, and dental implants [41–43].

1.3.1 DLC Coatings for Orthopedics

The life of prosthetic joints is severely shortened due to their tendency to wear and corrosion over time [44]. Therefore, DLC coatings have attracted interest in orthopedic applications because of their low friction coefficient, improved resistance to wear and corrosion, and biocompatibility [43]. In one of the studies, it was demonstrated that the DLC-coated femoral head Ti-6Al-4V alloy showed enhanced wear resistance as compared to the wear rate of uncoated stainless steel, alumina, titanium, and zirconia implants [45]. In another study, Tiainen et al. demonstrated that the wear rate of DLC-coated metal-polyethylene hip joints was reduced by 106 times smaller than that of metal-polyethylene joints or metal-metal joints [46]. Dowling group reported improved biocompatibility in DLC-coated hip joints with high sp3 content, achieved by doping DLC with Si [47]. Similarly, Sheeja et al. showed that the corrosion resistance and hardness of Co-Cr-Mo alloy (orthopedic implant material) was significantly increased by coating it with Si-DLC [48]. In another study performed by Mitura and others, DLC-coated orthopedic screws showed no signs of corrosion or inflammation even after 52 weeks [49]. On the contrary, there are also reports on the failure of DLC-coated orthopedic implants. DLC-coated knee joint implants showed excessive wear and spallation when paired with ultrahigh molecular weight polyethylene [50]. In a similar study, Taeger et al. found that the DLC-coated Ti-6Al-V femoral head failed faster than the alumina femoral head, indicating a need for the development of a biomaterial with enhanced functionalities having superior wear, toughness, and adhesion [51].

1.3.2 DLC Coatings for Antimicrobial Performance

Microbial biofilms are ubiquitously increasing the risk of medical device infection [52]. As such, treatment related to medical device infections often requires the removal and replacement of devices, increasing healthcare costs and mortality [52]. DLC coating acts as a simple yet powerful antimicrobial layer by preventing the adhesion of microbes to the surface of the implants [46]. Yang et al. demonstrated that oxygen plasma-treated Si-DLC is hydrophilic, exhibits a lower negative zeta potential value, and showed antifungal behavior against Candida albicans (Figure 1.5) [13]. In another study, Robertson and others reported that Ge-doped DLC significantly reduced the formation of Pseudomonas aeruginosa biofilms on SS316 substrates [53]. Bociaga et al. opine that the antimicrobial response of Si-DLC is promising but needs further investigation [54]. A recent report on the antibiofilm characteristics of prosthetic meshes coated with several metal-containing DLC thin films showed significant antimicrobial activity against five microbial species. They propose that modified DLC coatings are a suitable choice of biomedical coatings because of their biocompatibility, mechanical strength, and antimicrobial activity [55].

Figure 1.5 The water contact angle values for (a) Si-DLC, (b) oxygen plasma-treated Si-DLC (O-Si-DLC), (c) fluorine-terminated Si-DLC (F-Si-DLC), and (d) zeta potential values of Si-DLC, O-Si-DLC, and F-Si-DLC coatings versus the electrolyte solution pH values [13] / John Wiley & Sons/CC BY 4.0.

1.3.3 DLC Coatings for Cardiovascular Implants

One of the primary requirements of a cardiovascular implant is that it should not activate plasma enzymes in order to prevent thrombosis. As such, early studies on DLC-coated heart implants showed a tendency to prevent platelet activation and coagulation of blood [56]. Cheng et al. have reported improved hemocompatibility in Ti-doped DLC due to its hydrophobicity and smooth surface [57]. In another study, researchers have shown that incorporating Si into DLC improves endothelial cell attachment while reducing the adhesion of platelets at the same time [58]. They showed that the results were even better when Si-DLC films were treated with fluorine. All these findings showed that functionalized DLC coatings may be utilized for cardiovascular devices such as stents and heart valves. In addition, Gutensohn et al. showed that DLC-coated stents were resistant to corrosion, while noncoated stents released metal ions into the human plasma within four days of implantation [59]. In another study, Choi and others have shown that catheters coated with silver-doped DLC were highly effective in preventing bacterial infection while preventing the adhesion of platelets [60]. They believe that a greater focus should be placed on employing DLC coatings on cardiovascular devices owing to their multifunctional capabilities.

1.4 DLC Coatings for Electrical and Optical Devices

Due to their unconventional and excellent photoelectronic performance, broadband transparency, and ease of synthesis, DLC materials are among the emerging coating materials for electrical and optical devices [61]. The optical bandgap of DLC materials is governed by the amount and the size of sp2 graphitic clusters because the sp2 structure has one π bond [62]. As such, the bandgap value of DLC may be suitably tuned by controlling the sp2/sp3 content in the films. Similarly, the electrical conductivity of DLC structures may be increased by several orders of magnitude by increasing the sp2 content and through the incorporation of metals within the films [61, 63]. Due to this precise manipulation of their optical and electrical functionalities, DLC materials are being evaluated for their applications in devices such as micro-electromechanical systems (MEMS), batteries, field emitters, and antireflective coatings in infrared (IR) devices [61].

1.4.1 DLC Coatings for MEMS

MEMS technology consists of miniaturized devices, including electronic and mechanical components grown through microfabrication techniques [25]. It is widely explored as a feasible option to automate devices for various applications [7, 25]. Owing to their tunable electronic properties and the ability for wafer-scale integration of electric circuits, Si-based materials are a popular choice for the MEMS devices currently in use [25]. However, the fabrication of Si microelectronic systems is not economical and requires state-of-the-art facilities to ensure their proper growth and integration of circuits. Moreover, the poor mechanical strength and low fracture toughness of Si make this process even more challenging [64]. This phenomenon has led to the search for new and efficient material systems for use in MEMS. As such, polymers (e.g. polymethylmethacrylate and polydimethylsiloxane) are being explored due to their suitability [7, 25]. Among the prospective candidates for MEMS devices, diamond and DLC are the most promising due to their unusual mechanical properties and tunable electrical and optical properties that are otherwise not possible in Si-based materials [25]. Due to their very high tensile and fracture strength, Young’s modulus, increased resistance to wear, and reduced coefficient of friction, DLC coatings are deemed suitable for high-frequency MEMS applications. In addition, the low coefficient of thermal expansion and very high thermal conductivity of DLC make them suitable candidates for packaging devices and thermal actuators that require efficient heat dissipation [25]. Moreover, the chemical inertness, mechanical strength, biocompatibility, and hydrophobicity of DLC make them a popular choice for coating materials for applications in bio-MEMS, such as biosensing and implantable medical devices [65]. Thus, DLC can be exploited as a promising structural material to provide unique features that are otherwise not possible with the existing materials and also as a coating material in order to enhance the functional properties of MEMS devices [25].

1.4.2 DLC Coatings for Nonvolatile Storage, Low-K Dielectrics, and Field Emitters

The tunable electrical properties achieved by controlling the sp2-hybridized states in DLC structures have enabled their applications in nonvolatile storage devices [7, 62]. As such, the high density of electronic trap states in DLC that are otherwise detrimental for electronic devices is being explored to create nonvolatile digital information storage devices [66]. Gerstner et al. observed a reduction in resistance as well as an increase in the capacitance of DLC structures after a negative bias was applied. They showed that the effects are reversible after the application of a positive bias [67]. They describe a two-state conduction mechanism where electron hopping and Pool–Frenkel conduction were observed in the high resistance states and low resistance states, respectively. Memory devices with high retention times as high as one year were designed by defining the binary states corresponding to the low and high resistance states. Another promising application of DLC coatings is its potential use as a low-K material that can be used for back end of the line circuits to upgrade their performance [61, 68]. Even though the dielectric constant of DLC materials is significantly higher (5.6) than SiO2 (4.0) that is currently used, Grill et al. have shown that the dielectric constant of DLC can be modified to lower values (2.7–3.8) than SiO2 by controlling the deposition conditions [68]. Furthermore, the outstanding mechanical properties, good adhesion, and high thermal stability of DLC coatings make them futuristic candidates for low-K dielectrics [25, 61]. Since the 1990s, DLC coatings have been considered for field emitter applications and have been shown to enhance the field emission performance of traditional Spindt-type emission tips [69]. Oh et al. have shown that the nitrogen-incorporated DLC coatings reduced the turn-on voltage by 45% and simultaneously increased the emission current (from a value of 160 µA to a value of 1520 µA) [70]. Furthermore, the functionalization of the DLC-coated tips by plasma etching in hydrogen and oxygen also demonstrated a significant reduction in threshold voltage and an increase in the emission current [71]. More recently, the Narayan Research Group has shown that the field emission properties of Q-carbon (a new allotrope of carbon) outweigh the performance of DLC-coated filed emitters with a turn-on electric field as low as ~2.38 V µm−1 and a substantial emission current density of ~33 µA cm−2, which was associated with (a) the sp2/sp3 mixture in Q-carbon and (b) a large local field enhancement because of the unique diamond tetrahedral microstructure and the local geometry that is absent in DLC coatings [72]. Figure 1.6 illustrates the temporal evolution of field emission in DLC coatings, revealing a notable decline in both the total emission current and the emitting area over a three-hour period [73].

Figure 1.6 The emission images obtained from the patterned DLC coating: (a) initial image and (b) image after three hours.

Source: Reprinted with permission from Ref. [73].

1.5 DLC Coatings for Optical Applications

DLC is one of the most popular antireflective coatings for IR optics that are made from ZnSe, ZnS, or Ge because of its IR transparency [74]. DLC coatings are also utilized to protect ZnS IR windows when it is used with a GeC intermediate layer [75]. He et al. have demonstrated that DLC protective coatings can enhance durability and also improve the functionalities of organic photoconductors [76]. The antiwear properties and low deposition temperatures of DLC coatings make them suitable for protection against abrasion caused by polycarbonate sunglasses. Thermal imaging systems use DLC coatings as a barrier against deterioration of the surface of Al mirrors [76]. In addition to their uses as protective optical coatings, DLC is also being explored for the fabrication of optical components [61]. Soares et al. have demonstrated the facile patterning of DLC with hard masks, such as SiO2 and Al, by etching in oxygen plasma [77]. In conjunction with IR transparency, this expands the applications of DLC coatings for the recording of IR diffractive optical components that exhibit excellent pattern quality and precise surface control. DLC coatings are also being explored as candidates for photovoltaic applications. A high optical absorption coefficient obtained by increasing the sp3 fraction in DLC structures was exploited for absorbing a significant amount of solar energy [78]. As such, a photovoltaic effect was observed in Si-DLC coatings, where the reverse current rose by three orders of magnitude on exposure of the structures to AM1 light (when compared to the undoped DLC coatings) [78].

1.6 Emerging Applications of DLC Coatings

DLC materials have been the number one choice of coatings for cutting tools, automotive parts, and biomedical implants due to their outstanding strength as well as resistance to corrosion. In this regard, efforts involving DLC coatings have mostly focused on enhancing their mechanical properties in the recent past. However, due to their multifunctional capabilities and extended product life, DLC coatings are being explored for various applications such as energy storage, innovative smart textiles, and polymers [6, 7]. In addition, recent advancements in machine learning and materials informatics have revolutionized data-driven materials development and viable manufacturing of technologically and commercially important materials with enhanced performance and durability. This approach has enabled the virtual optimization of DLC coatings to improve their structural and functional properties by saving cost and energy resources [7]. Thus, materials informatics has a strong potential to aid the sustainable production of DLC coatings by uplifting their capabilities [79].

1.6.1 DLC Coatings for Energy Storage Applications

Carbon materials are given significant attention for energy storage applications because of their structural and electrochemical stability, electrical conductivity, and durability [80]. Among them, DLC is being explored for use in Li-ion batteries (LIBs) due to its lithium-ion trapping characteristics and electronic conductivity [81]. The electrical properties of DLC can be suitably tuned by modifying the deposition conditions, post-processing treatments, and concentration of the doping elements. Due to their superior structural stability, DLC coatings are known to resist the dendrite growth in LIB and provide a three-dimensional conducting environment for Li+ ions [81]. As such, Cho et al. have demonstrated the increased capacity of up to 50 cycles in DLC-coated cathodes, whereas uncoated cathodes failed after 7 cycles [82]. In another study, Zhang et al. showed that the cyclic efficiency associated with lithium electrodes increased by up to 60% after 50 cycles when coated with DLC [83]. Figure 1.7 presents a comparative analysis of the cyclic performance of as-fabricated and laser-annealed carbon-based electrodes with varying sp2 content, indicating enhanced capacity in the laser-annealed electrodes [84]. DLC coatings have also been shown to lower the contact resistance of current collectors, enhancing the performance of LiFePO4