Available online at www.sciencedirect.com

17 (2008) 1613–1621www.elsevier.com/locate/diamond

Diamond & Related Materials

Thick DLC films deposited by PECVD on the internal surface ofcylindrical substrates

D. Lusk a,⁎, M. Gore a, W. Boardman b, T. Casserly b, K. Boinapally b, M. Oppus b, D. Upadhyaya b,A. Tudhope b, M. Gupta b, Y. Cao b, S. Lapp c

a Sub-One Europe Ltd., 1 Berry Street, Aberdeen, Scotland, AB25 1HF, UKb Sub-One Technology, 4464 Willow Rd., Bldg. 103, Pleasanton, CA, 94588, United States

c University of West of Scotland, Thin Film Centre, Paisley, PA1 2BE, UK

Available online 26 January 2008

Abstract

A new and exciting technique for performing DLC deposition on the inside of cylindrical substrates, in particular pipes, will be described.Using the hollow cathode effect (HCE), a high density plasma can be generated within such cylindrical substrates by using Plasma EnhancedChemical Vapor Deposition (PECVD). As the pipe itself is the vacuum chamber, such high density plasmas can be maintained by usingasymmetric bipolar direct current (DC) pulsed power. Very high deposition rates can thus be achieved of the order of 1 μm/min. The coatingthickness can be tailored for a specific application and is typically from 5–70 μm. A hydrocarbon precursor (C2H2) is used to deposit thick DLCfilms which are inert and have a high corrosion resistance. Adhesion to the metallic substrate is improved by adding silicon to the DLC layer.These films also have excellent erosion and wear resistant properties and the process can be optimized depending on what film properties are mostvital for whatever application the coating is required for. Corrosion and wear resistance are also improved by having a pure DLC layer on top ofthe deposited structure. The actual process and deposition system will be described in detail as well as how the technology works and how suchhigh density plasmas can be maintained for various lengths and diameters of pipe. Testing of such novel DLC films was done by varioustechniques and results will be shown of hardness, adhesion, layer thickness, wear and corrosion resistance. A vast number of applications cangreatly benefit from this novel process, on both a large and small scale. Examples of such applications would be industrial piping, offshoredrilling, chemical delivery systems, gun barrels and medical devices.© 2008 Elsevier B.V. All rights reserved.

Keywords: Diamond-like carbon; Corrosion; Chemical vapour deposition; Wear

1. Introduction

Numerous deposition techniques for applying a protectivecoating to the inside of cylindrical substrates, such as pipes, havebeen studied elsewhere [1–5]. Most common techniques suchas electroplating, painting or spraying (thermal, arc and highvelocity Oxy-Fuel) are considered for this application. Typicallythese involve specialised materials such as tungsten carbide andmost require further finishing of the coating surface to obtain auseful smoothness and finish. These traditional coating methodswere primarily developed to coat exterior or exposed surfacesand often have limited effectiveness when applied to coating

⁎ Corresponding author.E-mail address: dlusk@sub-one.com (D. Lusk).

0925-9635/$ - see front matter © 2008 Elsevier B.V. All rights reserved.doi:10.1016/j.diamond.2008.01.051

internal surfaces outside of a limited size range. In addition,many of the raw materials or process by products can be toxic orenvironmentally unfriendly.

This paper will present in detail, a unique process for de-positing extremely hard, smooth, corrosion and erosion resistantfilms on the interior surface of metallic components such as pipesand tubes through a hollow cathode plasma immersion ionprocessing (HCPIIP) method. This technique utilises the hollowcathode effect (HCE) to generate and maintain an extremely highdensity plasma inside the part to be coated which can be used toform coatings and films through a plasma enhanced chemicalvapour deposition (PECVD) process in the presence of certainprecursor gases.

By using carbon containing precursors, such as acetylene,extremely hard diamond-like carbon (DLC) films can be formed

Fig. 1. Diagram of process set up [17].

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on the inside of the component. As has been surveyed elsewhere,DLC films have unique combinations of high hardness, lowfriction, electrical insulation, chemical inertness, biologicalcompatibility, smoothness and resistance to wear [6–12]. Theunique properties of these films have attracted great interest in alarge number of industries including oil and gas, automotive,aerospace, medical, military and paper. Most of the depositiontechniques for producing DLC films are slow [13–16],≪1 μm/h, have limited capability or effectiveness in coating internal orunexposed surfaces, and produce high residual stresses in thefilm so limiting the practical coating thickness to a few μmwhich has limited the rate of commercial adoption for thesecoatings. In the case of piping and tubing, which typicallytransmit a potentially corrosive chemical down their internalarea, the attractive properties of DLC coatings can be used toreduce corrosion, wear and abrasion on the inside of the part toincrease useful lifetimes. In addition, the inherent smoothnessand low coefficient of friction properties of DLC films could beof benefit in reducing line losses as liquids and slurries flowthrough a coated tube.

An important advantage of the described PECVD process isthe ability to introduce different precursor materials during thecoating process and thus change the film composition or introducemultiple layer films during growth. This allows formation ofadhesion layers at the coating interface to promote strong bondingof the film, or multiple layer structures to enhance specificproperties of the film.

This article will give an overview of the vacuum depositionsystem and the technology which goes behind the deposition ofthese films. A detailed analysis of the characterization andtesting of the described DLC films will be given as well as anoverview of the range of properties that can be achieved. TheresultingDLC films are unique in that they are formed on interiorsurfaces, but more interestingly these films can be grown at ratesapproaching 1 μm/min to a total thickness of around 75 μm. Thenarrow dark space sheath intrinsic to hollow cathode dischargespromotes outstanding conformal coverage making the processsuitable for coating threads or other complex internal profiles.

Finally some detailed information on potential applications willbe reviewed to describe potential commercial benefits of thecoating.

2. Experimental

A novel hollow cathode plasma immersion ion processing(HCPIIP) deposition method has been developed with theintention of depositing thick, hard DLC films on the inside ofmetallic components. This method uses the hollow cathode effect(HCE) to generate an extremely high density plasma within thepipe itself. Maintaining a hollow cathode discharge within thecomponent is important for rapid growth of thick DLC basedfilms. The critical parameters for maintaining such a discharge arethe internal diameter of the part and the operating pressure.

Fig. 1 shows a schematic of the deposition system. Fromthe main gas source system, process and precursor gases areintroduced into the entrance head. The gas then travels down thepipe where it is ionized quickly and deposition takes place. Atthe exit head, a high vacuum pump and throttle valve are used tocontrol operating pressure and pump away any by products. Thepipe or component is a critical element of the plasma electricalcircuit, serving as the negatively biased cathode with respect topositively biased anodes, located at the entrance and exit heads.The anodes are electrically isolated from the cathode to be coatedby insulating spacers. The cathode bias plays an important rolein improving the stress, density and adhesion of the films byion bombardment energy. Under suitable vacuum conditions, abipolar asymmetric DC pulse is used to maintain a high densityplasma inside the component. Energetic positive ion bombard-ment is controlled by the magnitude of the applied voltage andby the pressure. Gas flow and pumping speed are varied suchthat the pressure inside the component provides a regime where ahollow cathode discharge can be maintained under the appliedcomponent voltage. This pressure is such that the electronmean free path is adjusted to the pipe diameter, which cause highenergy electrons to oscillate across the opposing cathodewalls resulting in multiple ionizing collisions and a high density

Fig. 3. Pressure versus diameter for (a) large and (b) small diameter tubes [19,20].

Table 1Typical deposition parameters

Chamber (part) pressure 100 mTorrDC voltage 100 V–10 kVDeposition rate 1 μm/minAr gas flow 200 sccmTMS gas flow 20–120 sccmC2H2 gas flow 100–300 sccm

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plasma being maintained [17]. As DLC films are insulative,short pulses (b30 μs) are used to dissipate any positive chargebuild up on the coating surface. This charge is compensatedwhen the plasma sheath collapses during the off cycle. Adjustingthe duty cycle of the DCwaveform can allow good control of thefilm uniformity and thus allows the gas to replenish during theoff cycle. A high density plasma promotes high deposition ratesand also allows some influence over the residual stress state andbonding state of the applied film.

Film adhesion is promoted through use of a high biasvoltage, which can result in ion implantation below the surfaceof the film, along with suitable precursors introduced at the startof a deposition cycle. Also, in-situ sputtering with argon and/ornitrogen can be used to clean and heat the component surfaceprior to coating. Typical deposition parameters are shown inTable 1.

This technique can be used to investigate a number ofdifferent aspect (length/diameter) ratios. High aspect ratio pipescan be coated with higher flows and low duty cycles [17]. InTable 1, for certain deposition parameters a range of values hasbeen shown. The reason for this is that these values can changebased upon the size of the part that is being coated. Currently anaspect ratio of 24/1 is possible. Fig. 2 shows examples of DLCcoated parts of different aspect ratio [18].

Coating pipes with different aspect ratio places importance oncontrolling critical scaling parameters to maintain an operatingregime suitable for the hollow cathode effect. Figs. 3(a) and 3(b)

Fig. 2. DLC coating on internal surfaces of pipes of various aspect ratios [18].

show the pressure required to generate a hollow cathode plasmafor large and small diameter tubes. The data shown in thesefigures was generated from Ref. [19] (for Fig. 3(a)) and fromRef. [20] (for Fig. 3(b)) using constant∼pressure×diameter. Ascan be seen, the data from the two references do not matchexactly, however this is due to the fact that a hollow cathodedischarge can be maintained over a wide pressure range for agiven spacing, although it may lose plasma density. More detailsabout the deposition process can be found in Ref. [17].

One of the key aspects of this process is the pendulummotion of hot electrons between the cathode walls which helpsto maintain the high density plasma. Also Langmuir probemeasurements from a hollow cathode plasma have shown thatan ion density of 2 coating thickness to a few 1012 cm−3 ispossible which is considerably higher than a standard pulsedDC plasma which shows a typical ion density of 1 coatingthickness to a few 1010 cm−3. It is also possible to achieve aconformal coating which exhibits low stress allowing thickfilms to be deposited in the region of 70 μm.

3. Results and discussion

Multilayer DLC coatings deposited using the describedtechnique were analyzed by various methods to depict the rangeof properties obtained from the resulting films. Specifically thehardness, scratch adhesion, corrosion, thickness and erosionproperties of the coating are described herein.

Fig. 5. SEM cross-section of ∼40 μm film on SS304 substrate.

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3.1. Film and layer thickness

The technique used for determining the thickness is theCalotest system which is manufactured by CSM Instruments[21]. Typically a tungsten carbide ball of a known diameter(∼20 mm) is used with diamond slurry to wear through the filmsurface until the substrate has been reached by the ball. The filmis then put under an optical microscope where geometry is usedto measure the coating thickness by comparing the relativediameter of the exposed surface layers to the known diameter ofthe ball.

Fig. 4 shows an optical microscopy image of a Calotestcrater in a typical multilayer DLC deposition on a 2”diameter by12” long 304 grade stainless steel tube. Using a silicon andhydrocarbon precursor, an initial layer of SiC is deposited uponthe bare stainless steel substrate. This SiC adhesion layer is usedto achieve a good chemical bond with the substrate which thenallows a thick stack of DLC dominant films to be deposited ontop of the adhesion layer. In this case, a high silicon doped DLClayer, DLC cap layer, low Si doped DLC layer and a final DLCcap layer are deposited on top of the adhesion layer to make upthe full DLC based film [18]. The structure shown in Fig. 4 has atotal thickness of ∼19 μm.

Fig. 5 shows a SEM cross-section of similar multilayercoating structure with a total thickness of 40 μm deposited bythe PECVD. The total deposition time to grow such a structurewas 100 min. In the SEM cameo image, the color is related tothe EDX data. Areas that are warmer colors have higher averageZ-number compositions. The brightest (warmest) region in theimage is of the steel substrate. The darkest regions are pure Cand layers of intermediate warmth are SiC/C mixed layers,which are deposited using a mixture of 2 gas precursors. Theseare a Si based precursor mixed with a hydrocarbon precursor.The image shows the excellent step coverage obtained overdefects on the steel pipe.

The described multilayer coating is deposited at a tempera-ture of ∼200 °C and when the coating relaxes back to roomtemperature, there is no sign of any cracking or breaking up ofthe film. The multilayer structure helps to reduce stress,improve corrosion and prevent crack propagation.

Fig. 4. Image from optical microscope of film after calotest [18].

3.2. Stress

Single layer DLC films were deposited on Si wafer substrateusing the system described in Fig. 1. Acetylene gas was used asthe carbon source. A platform was made to conform with theshape of the pipe, so that the flat Si substrates could sit hori-zontally inside the part and be coated. The stress of 3 differentsamples with 3 different coating thickness was analysed using aDektak profilometer, where the curvature was measured beforeand after coating. The Stoney equation was then used to calculatestress. Table 2 below shows the stress results found.

As can be seen, a very low stress film has been deposited bythis novel technique. There is no real difference observed in termsof thickness variation with stress. For most well-known depo-sition techniques, to get DLC to adhere to a metallic substrate, afilm of a few μm thick is the limitation before degradation appearsdue to high residual stresses in the film [22,23]. As a continuationof this stress result, it will be of interest to extend this investigationfurther to much thicker DLC films and see at what maximumthickness the DLC film will still be adhered to the substrate. DLCfilms of 20 μm and above are extremely difficult to deposit butthis technique can easily do this and also, a DLC based coating ofup to 70 μm has been deposited using this technique with varioushydrocarbon precursor combinations.

3.3. Fracture behaviour and erosion

The coating fracture behaviour under a Vickers indenter loadis shown in Fig. 6 [18].

Fig. 6(a) shows a top view SEM image of a 5 N indent andFig. 6(b) is a cross-section of the indent area after FIB. Theabove indent is formed by an initial plastic deformation of thesubstrate. Cracks form within the coating at some initial load

Table 2Stress results for 3 different DLC samples with varying thickness

Deposition Time (min) Layer thickness (μm) Stress (GPa)

2 0.67 0.516 2.83 0.5510 5.77 0.46

Fig. 6. (a) Top view of 5 N indent and (b) SEM cross-section of indent after FIB [18].

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and when increasing the load to its maximum, crack growthtakes place. Upon unloading of the tip, propagation of crackscan be seen at stress concentration points due to sharp indenteredges and finally delamination occurs within the layered struc-ture. Most importantly, the cross-sectional image shows thebenefits of a layered structure where deflection points arepresent within the structure for any crack propagation [18].

Multilayered films provide increased protection from ero-sion, additionally a harder substrate and thicker films provideenhanced erosion protection as shown in Fig. 7.

Here a gas jet erosion test is used to fire 50 μm diameterAl2O3 particles onto the surface of the coating at normal inci-dence for 10 min. The coating is then removed from the rig andinspected for potential damage. On the left side of Fig. 7 is amultilayer coating deposited on a 13Cr substrate where thehardness of the coating is 15 GPa and total coating thickness of23 μm. As can be seen, there is a slight color change to thesurface of the coating but no evidence of the abrasive breakingthrough the surface. Also shown in Fig. 7 is another multilayercoating which is deposited on 316 stainless steel. This coatinghas a hardness of 12 GPa and total thickness of 70 μm. This

Fig. 7. Gas jet e

coating is also showing no penetration of the surface with thistest. This clearly shows that the coating has excellent erosionresistant properties and for various substrate materials and filmproperties.

3.4. Hardness/wear

When depositing filmswith the objective of them having highcorrosion and erosion resistant properties, then the hardness andwear testing of these films is necessary. Table 3 shows generalproperties for hardness and wear that are found from these DLCfilms.

From Table 3 it is clear that a layer of DLC–Si on bare steelsubstrate greatly increases the hardness as expected. For theDLC–Si, the COFmeasured by tribometry is extremely low. Thewear coefficient is measured using a linear reciprocating weartribometer per ASTM G133, typically a 5 mm WC ball is usedwith an applied load of 5 N, and the wear track volume can thenbe measured from an optical profiler. The wear coefficient k isdefined as k=(volume of material removed (mm3) / (load inNewtons)× (length of wear track in meters). The value of wear

rosion test.

Table 3Hardness and wear properties for bare and coated substrate

Filmthickness(μm)

Young's Modulus(GPa)

Hardness(GPa)

COF Wearcoefficientmm3/Nm

DLC–Si Substrate DLC–Si Substrate DLC–Si DLC–Si

25 μm 184 193 22.7 2 0.02 4.72E−07

Fig. 8. Bare 13Cr and coated 13Cr substrates after corrosion test.

1618 D. Lusk et al. / Diamond & Related Materials 17 (2008) 1613–1621

coefficient confirms the excellent mechanical and adhesionproperties of the film.

A more detailed analysis of the wear resistance of the coatingusing different liquid based media, including media containinghighly abrasive particles such as titanium oxide (paint) and silica(drill mud), has also been carried out. Table 4 details informationabout the various media used and values for the COF andwear rate.

As shown in Table 4 various different media have beenlooked at where the choice of what liquids to use was down torelevant applications for this coating within industry. The dif-ferences between the uncoated and coated substrate are clearlyevident. In all cases excellent COF and wear rate have beendemonstrated which further confirms the excellent wear proper-ties of the coating and also indicates how versatile the coatingis to different environments which opens up a huge number ofapplications.

3.5. Corrosion

The chemical inertness of DLC films makes them veryattractive for corrosion prevention applications. The thinness ofthe coatings has limited their ability to function as good barrierfilms in many cases. Also, DLC films are known to have someweakness in the presence of moisture unless carefully structuredfor exposure to that environment [24]. Some examples of thecorrosion testing methods that were done to test the corrosiveproperties will be described. Fig. 8 shows a test which was doneinvolving a bare 13Cr substrate and a coated 13Cr substrate.

Fig. 8(a) shows the bare 13Cr substrate which was exposedto a drop of 15% HCL at room temperature. It can be seenclearly how quickly and extensively damage occurs to the baresubstrate when exposed to this solution. In contrast, Fig. 8(b) isa coated 13Cr substrate which was submerged in HCL for 65 h.What is evident from that test is that there is no damage to the

Table 4Wear resistant properties using various liquid based media

Substrate Media COF Wear coefficient mm3/Nm

1020 carbon steel Drill mud 0.04 6.55E−07Crude oil 0.03 2.65E−07Latex paint 0.03 1.40E−07Tap water 0.16 8.10E−07

316 stainless steel Drill mud 0.02 1.20E−06Crude oil 0.05 1.45E−07Latex paint 0.1 8.40E−07Tap water 0.09 4.05E−07

Uncoated steel Dry 0.4–0.6 NE−04

film after being placed in such a highly corrosive environment.The undamaged coating confirms both the good adhesion to thesubstrate and also the pinhole free nature of these films.

A more strenuous test of the film was conducted using a hotHCL solution with a coating on carbon steel (CS) 1020. Fig. 9shows the experimental set up for this test and Fig. 10 shows thecoating before and after this test and the test conditions.

From Fig. 10, the degradation of the uncoated CS1020substrate can clearly be seen in the top left hand section of Fig. 10whereby the pipewall has been completely penetrated under theseconditions. However with the DLC coating applied, no damageis seen on the coating after this test. Although the film is notextremely hard, the very good scratch adhesion properties arebeing confirmed by this test and also the pinhole free natureof them.

Another very aggressive corrosion test which the coating hasbeen subjected to was a sweet autoclave. In this test the com-ponent is exposed to a three layer corrosive media consisting of awater based, organic based and gaseous layer at elevatedtemperature and pressure. Fig. 11 shows the film before and aftera very aggressive test in which salt water brine was used for theaqueous phase and the gas phase had a very aggressive mixtureincluding both H2S and CO2. This test is well known within theoil and gas industry as a good measure of the ability of surfacecoatings to resist corrosion.

Looking at the before and after test images, it is evident therewere no indications of film delamination or penetration of thefilm surface. Also, on the after image on the bottom right of thefigure, attack of the uncoated SS304 substrate can be seen andthere has been no penetration of the corrosive chemicals to theinterface of the film to substrate.

The corrosion results shown here are clearly demonstratingthe extremely good corrosion resistant properties of the coating.

Fig. 9. Experimental set up for hot HCL test.

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A key element in the outstanding corrosion protection offeredby the described films is the ability to form very thick, barrierlike films of the DLC material. Also, by using some wideranging corrosion tests, it opens up different applications wherethis coating can be used. Relevant applications will be discussedin the next section.

4. Applications

The film properties achievable through the described PECVDprocess are quite unique, particularly on internal surfaces, andmany applications can be envisioned where these properties

Fig. 10. Coating before and after hot HC

could improve the useful service life or enhance the performanceof industrial components. Potential applications include auto-motive, military, medical, aerospace, oil and gas and pulp andpaper and many of these have been examined to various levels.Some examples of applications are for the military, the mostobvious application is in gun barrels, in both a small and largescale. For the small scale, especially in sandy environments,there is a need to use arms without oils to stop jamming of guns.On the larger scale there is a need to replace Cr plating for largecalibre guns used on ships, tanks and in the artillery [25].

For the medical industry there is a need for corrosion re-sistance on the inside of valves and tubes where good adhesion

L test and details of test conditions.

Fig. 11. Coating before and after sour autoclave test and details of test conditions.

1620 D. Lusk et al. / Diamond & Related Materials 17 (2008) 1613–1621

and smoothness is required. Also, implants for internal jointswould need to be coated since these can corrode inside thehuman body and as DLC is chemically inert this would beadvantageous for that [25].

For the pulp and paper industry, there is a need to replaceexpensive alloys which are used for corrosion resistance, withcheaper coated alloy steels. In the pulp mill, there are a largenumber of pipes and valves which carry corrosive materialwhere a coating on the inside of these parts would increase thelifetime of the parts and be cost effective [25].

In geothermal systems, pipes are used to bring hot water fromthe ground and heat exchangers. Lower frictional losses meanshigher transfer rates and obviously in oil and gas you haveoffshore drilling and gas delivery systems which would benefitfrom this technology [25].

Further advancing the technology for extended geometryapplications, such as transmission pipelines, will involve bothfurther scaling of the process to accommodate the greater lengthsand diameters associated with these applications as well as con-figuring the process to allow for on-site coating of seams, joints andrepairs. Experiments and modelling to allow further scale-up are inprogress and prototype in-situ coating concepts are being explored.

5. Conclusions

Anovel hollow cathode processingmethod has been describedwhich can deposit thick DLC based multilayer coatings on theinternal surfaces of cylindrical substrates. Details of the depo-sition system and technology have been shown with the actualpart itself acting as the vacuum chamber and the cathode. Inaddition to the ability to coat internally, the process is capable ofgrowing DLC based films to thickness in excess of 50 μm atgrowth rates approaching 1 μm/min. These parameters are quiteunusual in the current understanding of processing routes forDLCfilms and expand the scope and range of potential for commercialapplications. A description of amultilayerDLC coatingwhich hasbeen deposited using this technology has been described and the

most relevant testing procedures have been discussed in detailwhich demonstrate the unique combinations of high hardness,corrosion resistance and wear resistance, all with very goodadhesion to the metallic substrate. Well adhered surface layers ofthis type offer a new way to protect internal surfaces and cavitiesincluding the inside of pipes. An extensive list of applications hasbeen shown where corrosion and erosion problems have existedand it has been shown that many different industries can benefitgreatly from this process.

Acknowledgement

The authors express their gratitude to Shiela Yeh of Chevronfor performing hot HCL test and fruitful discussion on corrosionbehaviour of materials.

References

[1] H. Wesemeyer, H. Veltrop, US patent 5026466, “Method and device forcoating cavities of objects,” June 1991.

[2] W.F. Henshaw, J.R. White, A. Niiler, US patent 4407712, “Hollow cathodedischarge source of metal vapor,” October 1983.

[3] R.P. Fetherston,M.M. Shamim, J.R. Conrad, US patent 5988103, “Apparatusfor plasma source ion implantation and deposition for cylindrical subtrates”Nov 1999.

[4] S. Eidelman, US Patent 6787194, “Method and apparatus for pulseddetonation coating of internal surfaces of small diameter tubes and the like”Sep 2004.

[5] S.D. Knowles, D.J. Senor, S.V. Forbes, R.N. Johnson, G.W. Hollenberg,US Patent 6866886, “Method of coating the interior surface of a hollowobject with a diffusion coating” March 2005.

[6] J. Robertson, Materials Science and Engineering R 37 (2002) 129.[7] J. Robertson, Progress in Solid State Chemistry 21 (4) (1991) 199.[8] J. Roberston, Surface and Coatings Technology 50 (3) (1992) 185.[9] J. Robertson, Advances in Physics 35 (4) (1986) 317.[10] D.R. McKenzie, Reports on Progress in Physics 59 (1996) 1611.[11] P.D. Maguire, J.A. McLaughlin, T.I.T. Okpalugo, P. Lemoine, P.

Papakonstantinou, E.T. McAdams, M. Needham, A.A. Ogwu, M. Ball,G.A. Abbas, Diamond and Related Materials 14 (8) (2005) 1277.

[12] P. Lemoine, J.F. Zhao, J.P. Quinn, A.A. Ogwu, J.A. McLaughlin, P. Maguire,F. McGinnity, X. Shi, Wear 244 (1–2) (2000) 79.

1621D. Lusk et al. / Diamond & Related Materials 17 (2008) 1613–1621

[13] K.Y. Li, Z.F. Zhou, C.Y. Chan, I. Bello, C.S. Lee, S.T. Lee, Diamond andRelated Materials 10 (9–10) (2001) 1855.

[14] K. Kuramoto, Y. Domoto, H. Hirano, S. Kiyama, S. Tsuda, AppliedSurface Science 113–114 (1997) 227.

[15] S.J. Yu, Z.F. Ding, J. Xu, J.L. Zhang, T.C. Ma, Thin Solid Films 390 (1–2)(2001) 98.

[16] H. Kim, D.H. Jung, B. Park, K.C. Yoo, J.J. Lee, J.H. Joo, Surface andCoatings Technology 193 (1–3) (2005) 255.

[17] Boardman et al., “Method and System for Coating Internal Surfaces ofPrefabricated Process Piping in the Field”, US Patent Application, Pub.No. US 2006/0011468 A1.

[18] T. Casserly, K. Boinapally, M. Oppus, D. Upadhyaya, B. Boardman, A.Tudhope, Investigation of DLC–Si film deposited inside a 304SS pipeusing a novel hollow cathode plasma immersion ion processing method,

Proceedings of the Society of Vacuum Coaters Annual TechnicalConference (2007).

[19] T. Kalber, T. Jung, Surface & Coatings Technology 98 (Jan 1998) 1116.[20] L. Bardos, H. Barankova, Surface & Coatings Technology 146–147 (Sep–

Oct 2001) 463.[21] CSM Instruments SA, Rue de la Gare 4, Galileo Center, CH-2034 Peseux,

Switzerland.[22] D. Sheeja, B.K. Tay, L. Yin, S.P. Lau, Surface & Coatings Technology

154 (2002) 289–293.[23] O.R. Monteiro, J.Z. Ager III, D.H. Lee, R. Yu-Lo, K.C. Walter, M. Natasi,

Journal of Applied Physics 88 (5) (2000) 2395–2399.[24] M. Suzuki, A. Tanaka, T. Ohana, W. Zhang, Diamond and Related Materials

13 (2004) 1464.[25] Sub-One Technology Technical Report, 2004.