Deposition optimization of DLC based coatings

for industrial applications

A.Stoica, V.Buršíková, T.Novotný, J.Čupera, T.Gardelka, R.Žemlička

Masaryk University, Brno

What is DLC?

DLC is an acronym for diamond-like carbon and the name commonly accepted for hard carbon coatings which have similar mechanical optical, electrical and chemical properties to natural diamond, but which do not have a dominant crystalline lattice structure. They are amorphous and consist of mixture of sp3 and sp2 carbon structures with sp2 bonded graphite-like clusters embedded in an amorphous sp3 -bonded carbon matrix. Generally they contain significant quantities of hydrogen.

The amorphous carbons family

C.Casiraghi, J.Robertson, A.C.Ferrari, Materials Today, 10, 1-2 (2007) 44.

One of the biggest hurdles in the amorphous carbon and DLC literature is understanding what exactly is referred to with these generic terms. Unfortunately, unlike carbon nanotubes, there are no simple indexes to easily classify these materials. Often films with completely different properties are called by the same name and vice versa.

DLC diamond-like carbon

diamond graphite

C C

H H

H

H H

H

sp3 CH3 group

C C

H H

H

C C

H

sp3 CH2 group

C C

C C

C

H H

C

sp3 CH group

Ternary phase diagram of amorphous carbons

Depending on the sp3 content and H content, DLC can be classified as: ta-C, which does not contain H and has a C-C sp3 content greater than 60%; PLCH if the H content is greater than 40 at.% and sp3 content is up to 70%; DLCH if H is 20-40 at.%; GLCH if H is below 20 at.% and the sp3 content is lower than 20%. In ta-C:H, the sp3 content can reach 70% while the H content is 25-35% and the C-C sp3 content is much greater than in PLCH.DLCH has a lower sp3 content than ta-C:H, for a given H content.

diamond

graphite hydrocarbons

C.Casiraghi, J.Robertson, A.C.Ferrari, Materials Today, 10, 1-2 (2007) 44.

DLC map

To identify which of the forms is on a particular sample, the fraction of hydrogen and the fraction of sp3 bonded carbon atoms (not graphite) must be measured. Knowing those two numbers enables a user to plot the "location" of the sample on the VDI-map. The closer to the upper left corner that a material plots, the better (and more) pure is the DLC. The authorative German VDI 2840 standards report affirms the superiority of ta-C. Dilutions with hydrogen and graphitic carbon degrade the DLC.

In 2006 the Association of German Engineers, VDI, the largest engineering association in Western Europe issued an authoritative report VDI_2840 in order to clarity the existing multiplicity of confusing terms and trade names.

Amorphous carbon films (diamond-like carbon films / DLC)

hydrogen-free hydrogenated

modified modified

with metal

with metal

with non-metal

sp2 sp3 sp2 sp2 or sp3 sp3 sp2 sp2

Hydrogen- free

amorphous carbon

film

Tetrahedral hydrogen-

free amorphous

carbon film

Metal- containing hydrogen-

free amorphous

carbon film

Hydrogenated amorphous

carbon film

Tetrahedral hydrogenated amorphous

carbon film

Metal- containing

hydrogenated amorphous

carbon film

Modified hydrogenated amorphous

carbon film

a-C ta-C a-C:Me a-C:H ta-C:H a-C:H:Me a-C:H:X

Me = W, Ti, … and X = Si, O, N, F, B, …

The Fraunhofer-IST chart

The mechanical properties of various elemental carbon materials

Material Form Density [g/cm3]

Covalent bonds

Young’s modulus

[GPa]

Hardness [GPa]

C60 Films ~1.7 Almost all sp2 ? ~0.2

C fibers Fibers 1.7 – 1.9 Almost all sp2 200 – 600 ?

Graphite Bulk ~2 100 % sp2 10 0.2 – 2

CNT Films <2? Almost all sp2 0.013 ?

a-C Films ~2.2 sp2-rich 100 – 200 10 – 20

a-C:H Films ~2.2 Intermediate 100 – 300 10 – 30

ta-C Films 3 – 3.2 sp3-rich 300 – 500 50 – 80

Diamond Bulk, films ~3.5 100 % sp3 1000 100

C. Donnet, A. Erdemir, Tribology of Diamond-Like Carbon Films Fundamentals and Applications, Springer Science + Business Media LLC, New York NY, 2008

What is pure DLC made of?

The diamond known from jewelry has carbon atoms arranged in 3-dimensional cubic lattices. In lonsdaleite the lattice would be hexagonal, like cells in a beehive. In DLC the cobbles are not crystalline; they are amorphous because they are made from random alternations between cubic and hexagonal lattices. The cobbles have no long-range order and so they have no fracture planes along which to break. The result is a very, very strong material.

http://en.wikipedia.org/wiki/File:Ta_C_structure.jpg

What can it do?

In short, diamond-like carbon (DLC) can coat things and make them last forever.

Properties depend mainly on composition. Product development is a severely proprietary business.

DLC is harder than natural diamond and slicker than Teflon. That combination gets more horsepower from engines, longer lifetimes from mechanical parts that rotate and slide, survival of fragile optics in hostile environments, and it saves lives by making better medical options available.

Final in vivo tests of coronary practice are made on pigs, not monkeys.

DLC for data and beer storage

Corrosion protective coatings. Continuous coverage with no pinholes, even for 1.2 nm Thick. Carbon film thickness on disk and sliders, magnetic spacing, and fly height vary with storage density (for longitudinal recording). For perpendicular recording, a given carbon thickness allows a much greater storage density, up to 1 Tbit/in2.

Hard disk architecture

DLC for data and beer storage

Near-field data storage technology uses a solid immersion lens (SIL). CDs and DVDs use a metallic reflective layer (in black) sandwiched between a substrate (in green) and a lacquer surface. Highly flat Polycarbonate disks. Transparent, protective coating, without melting the PC. Use C2H2 as precursor, not CH4, for high deposition rate. Stress a problem.

(a) Current optical data storage technology, using far-field optics. (b) Because SIL provides high spatial resolution, the spot size of laser beam through the SIL can be smaller than diffraction

limit in air, and the density of the associated optical data storage can be increased.

DLC for data and beer storage

Keep CO2 in, O2 out. Fizzy drinks, green tea, wine… a-C:H is bio-compatible Coating deposited on inside of PET bottle must be dense, transparent, deposited in 3 s, without melting the PET, and not peel off. Minimize heat load – maximize deposition rate. Use C2H2 as precursor, not CH4, for high deposition rates.

PET has a finite gas permeability that can limit the shelf life of some food and drink products. The addition of a gas impermeable coating on the inside wall of a standard PET bottle is necessary in order to minimize the permeation of CO2, O2, and H2O.

Diamond coatings of Diamond-like Carbon

Reduce friction and wear.

Can be deposited on almost anything that can be put in a vacuum.

Are made without toxic byproducts or harmful waste.

Are certified for use in food processing.

Diamond coatings make items last forever (almost).

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Applications of DLC film

Tooling components, such as endmills, drill bits, dies and molds. DLC is also used in the engines of modern supersport motorcycles, racecars and vehicles. Cutting edges of tools for the high-speed, dry shaping of difficult exposed surfaces of wood and aluminum (automobile dashboards). Multi-bladed razors used for wet shaving have the edges coated with hydrogen-free DLC.

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Application Razor blades

Some forms have been certified in the EU for food service and find extensive uses in the high-speed actions involved in processing novelty foods such as "chips" and in guiding material flows in packaging foodstuffs with plastic wraps. DLC is used to keep razor blade tips sharp. Extremely high deposition rate required.

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Diesel Engine Injectors

Low friction surfaces for Car parts. Handling an injection pressure in the range of 2,000 bar would not have been possible without the use of DLC coatings. Cam shaft surfaces.

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Deposition methods for a-C:H

RF PECVD 13.6 MHz Reactive sputtering (RF, magnetron, unbalanced..Ar + C2H2) Ion beam (C2H2 + Ar) High density plasmas in PECVD: – ECR (microwave) – Inductively coupled plasma (ICP) (RF) – Electron Cyclotron Wave Resonance (ECWR), RF

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RF PECVD

a-C:H properties depend on ion energy, thus DC self-bias voltage. Simplicity, high deposition rate. Deposition rate depends on source gas. RF power varies both Vbias and deposition current. Max hardness ~20 GPa, due to neutrals.

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What we do… we mix…

The properties of amorphous carbon can be tailored by varying the deposition parameters. The goal of our work is to investigate the tribological and mechanical properties and the surface quality of deposited amorphous carbon and doped amorphous carbon with varying deposition parameters.

CH4

H2

D2

HMDSO

N2

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What we do… optimization

Deuterated DLC films exhibit a higher hardness and elastic modulus. The nitrogen addition decreases the hardness and elastic modulus and leads to a beneficial reduction in the compressive stress of the films. The deposition rate decreases with increasing nitrogen source fraction. The surface energy decreased as the Si content of the SiO(x) incorporated DLC films increased. The compressive stress in the films was reduced, the film fracture toughness was improved and the deposition rate increased.

a-C:H

D

SiOx N

3

Key points

Despite the advantage that this name sounds good, it has the significant disadvantage that a whole class of materials with properties ranging between diamond, graphite and polymers is covered by the same name.

A solution for widespread industrial application should be based on measurement equipment that is easily accessible in usual analytical laboratories.

It is necessary to develop a classification, scientifically correct, which can be easily checked with easily acceptable methods.

DLC may be totally different from DLC

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Best Ion MicroGraph

TITLE: Artificial Nano “T4 Bacteriophage” Description: “T4 Bacteriophage” is a virus like the robot in the living body. Artificial nano “T4 Bacteriophage” was fabricated by Focused-Ion-Beam (FIB) CVD on Si surface. Size of the artificial nano “T4 Bacteriophage” is about ten times as large as the real virus. It is made of Diamond-like Carbon. It is likely to begin to walk in the nano space!! Magnification: 25,000X Instrument: SII NanoTechnology Inc. / SMI2050MS2 Submitted by: Reo Kometani & Shinji Matsui (University of Hyogo)

The 49th International Conference on Electron, Ion and Photon Beam Technology and Nanofabrication Bizarre/Beautiful Micrograph Contest, EIPBN Orlando 2005 1

Thank you for your attention!

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