NAS Technical Memorandum 1021 1 1 

Diamondlke Carbon Protecive 

Coatings for Optical Wndows

Diane M. Swec andMichael J. Mirtch 

Lewis Research Center 

Cleveland, Ohio 

Prepad for the

1989 Technical Symposia on Aerospace Sensig

sponsred by The Interaionl Society for Optical Engierng 

Orlando, Florida, March 27-3 1, 198 

IlJASA-TH-1021 I?) DIABONDLIKE CAREON 

PBOTECTIVE COATIblCS FOR OPTICAL ZlIIDOClS 

(HASA. Lewis Research Center) 16 pCSCL 20E 

- 

18 9- 2 7506 

Unclas 

G3/74 10224122 
DIAMONDLIKE CARBON PROTECTIVE COATINGS FOR OPTICAL WINDOWS 

Diane M. Swec and Michael J. Mirtich 

National Aeronautics and Space Admini stration 

Lewis Research Center 

Cleveland, Ohio 44135 

SUMMARY 

Diamondlike carbon (DLC) films were deposited on infrared transmitting 

optical windows and were evaluated as protective coatings for these windows 

exposed to particle and rain erosion. The DLC films were deposited on zinc 

selenide (ZnSe) and zlnc sulfide (ZnS) by three different ion beam methods: 

(1) sputter deposition from a carbon target using an 8-cm argon ion source, 

(2) direct deposi tlon by a 30-cm hollow cathode ion source with hydrocarbon 

gas in argon, and (3) dual beam direct deposition by the 30-cm hollow cathode 

ion source and an 8-cm argon ion source. In an attempt to improve the adherence of the DLC films on ZnSe and ZnS, ion beam cleaning, ion implantation 

with helium and neon ions, or sputter deposition of a thin, ion beam intermediate coating was employed prior to deposition of the DLC film. The protection that the DLC films afforded the windows from Darticle and rain erosion 

was evaluated, along with the hydrogen content, adherence, intrinsic stress, 

and infrared transmittance of the films. Because of elevated stress levels 

the ion beam sputtered DLC films and in those ion beam deposited with butane 

films thicker than 0.1 pm and with good adherence on ZnS and ZnSe could not 

be generated. An intermediate coating of germanium successfully allowed the 

DLC films to remain adherent to the optical windows and caused only a negligible reduction in the specular transmittance of the ZnS and ZnSe at 10 pn. 

These DLC films did not protect the optical windows from simulated particle 

erosion; however, they did improve the performance of ZnS exposed to rain 

eros i on. 

n 

INTRODUCTION 

Infrared-transparent materials, such as zinc sulfide (ZnS) and zinc selenide (ZnSe), are those most often used as optical windows. However, these 

materials are soft and undergo serious degradation when subjected to severe 

particle-impacting environmental conditions (ref. 1). Therefore, attempts have 

been made to harden these window surfaces to protect them from sand or rain 

impact. 

Hard thin films may be used to maintain the optical integrity of infrared 

windows. The desired films must be adherent and durable such that they protect 

ZnS and ZnSe windows from particle and rain erosion as well as chemical attack. 

A low film-stress level Is also desirable so that a thick layer of these hard 

films can be deposited for maximum protection of the soft materials. One film 

with this potential Is &$amondlike carbon (DLC) (refs. 1 and 2). DLC films are 

transparent over a broad spectral range, resist chemical attack, and are moisture and abrasion resistant. 

Three different ion beam methods were used to deposit DLC films on fused 

silica (SiO2>, silicon (SI), ZnS, and ZnSe: 

carbon target by an 8-cm argon Ion source, (2) direct deposition by a 30-cm 

(1) sputter deposition from a 
hollow cathode ion source with hydrocarbon gas in argon (Ar), and (3) dual beam 

direct deposition by the 30-cm hollow cathode and an 8-cm argon ion source. 

To improve the adherence of the DLC films on ZnS and ZnSe, the following techniques were employed prior to deposition of the film: 

(2) ion implantation via "knock on" of thin carbon films by 100-keV nitrogen 

ions, (3) ion implantation with 100-keV neon and helium ions, and (4) thin, 

ion beam sputter-deposited intermediate coatings of germanium (Ge) or silicon. 

The DLC films were then evaluated for hydrogen content, adherence, intrinsic 

stress, infrared transmittance, and protection from particle and rain erosion. 

An erosion test employing a microsandblaster with 27-pm-diameter aluminum 

oxide (A12031 particles was developed to determine quantitative values of the 

protection that the diamondlike films afforded the window surfaces. After 

erosion an infrared (IR) spectrophotometer was used to indicate the change in 

specular transmittance between 2.5 and 50 pm. The DLC-coated windows were 

also subjected to water droplets at 180 m/sec for exposure times up to 15 min 

in a rain erosion facility at Wright Patterson Air Force Base. These samples 

were qualitatively evaluated by optically viewing the pitting, microcracks, 

and subsurface ring cracks that resulted from the erosion. The results of 

these studies are presented in this paper. 

(1) ion beam cleaning, 

APPARATUS AND PROCEDURE 

Diamondlike carbon films were ion beam sputter deposited from a pyrolytic 

graphite target by an 8-cm-diameter source (ref. 3). A 1000-eV argon ion beam 

was produced for sputter cleaning and deposition. 

was -1.0 mA/cm2 in the vicinity of the sputter target and substrates, which 

were located 20 cm downstream of the ion source. The ion source was operated 

with a hot filament neutralizer in a vacuum facility that maintained pressures 

of 2x10-5 torr during operation. In conjunction with this method, hydrogen 

gas was introduced in the vacuum chamber to evaluate its effect on these films. 

The introduction of hydrogen gas raised the background pressure to a range of 

7x10-5 to 10-4 torr. Films 0.1 pm thick were deposited on the various substrates. 

The ion beam current density 

A 30-cm-diameter ion source with its optics masked to 10 cm in diameter 

was used to directly deposit the DLC films (ref. 4). The ion source used 

argon gas in the hollow cathode located in the main discharge chamber, as well 

as in the neutralizer. Hydrocarbon gas was introduced through a manifold into 

the discharge chamber at a molar ratio of 0.28 CH4 or 0.10 C4H10 to argon. 

Typically, current densities were 1 mA/cm2 at a distance of 2.5 cm axially 

downstream of the grids, and argon ion energies ranged from 90 to 250 eV. 

It is believed that amorphous carbon films are produced under conditions 

where growth and sputtering occur simultaneously, therefore increased sputtering may decrease the number of graphite precursors incorporated in the films 

and hence improve the quality (ref. 4). An 8-cm ion source with a filament 

cathode was used during the dual beam deposition to direct a beam of 200- to 

600-eV argon ions at a current density of 25 pA/cm2 on the substrates while 

the DLC film was being deposited by the 30-cm source. 

The intrinsic stress of the DLC films was measured with a stress gauge, and 

an adherence tester was used to determine the adherence of the DLC films. The 

transmittance of the DLC films in the visible region was obtained with an integrating sphere, and the IR transmittance was measured with a spectrophotometer. 

2 
An erosion test was developed that used a sandblaster to give quantitative 

values to the protection that the DLC films afforded fused silica (ref. 5). 

The fused silica surfaces were exposed to 100-pm-diameter Si02 particles at 

27 m/sec, and then the protective quality of the film was characterized by the 

resulting change in specular transmittance by a neon-helium ellipsometer. The 

protection that the DLC films afforded the ZnS and ZnSe surfaces was quantitatively determined from another simulated particle erosion test (ref. 6). 

wlndow surfaces were eroded by exposing them to 27-pm-diameter A1203 particles 

with an estimated stream velocity of 335 m/sec in a microsandblaster. 

protective quality of the film was then characterized by the change in specular 

transmittance due to the particle erosion with an IR spectrophotometer between 

wavelengths of 2.5 and 50 pm. 

The 

The 

‘A facility at the Wright Patterson Air Force Base was employed to evaluate 

the rain erosion performance of the DLC films. The rain erosion facility consisted of a variable-speed rotating arm apparatus with speeds to 210 m/sec and 

a simulated rainfall of 7x10-4 cm/sec. The rotating arm apparatus employed 

a horizontally mounted, 8-ft double-arm propeller blade powered by a 400-hp 

motor. 

trolled water droplets were sprayed on the test specimens, which were mounted 

in the blade tips. 

A pipe ring containing hypodermic needles was positioned such that conRESULTS AND DISCUSSION 

Hydrogen Content 

Nuclear reaction and combustion analysis for hydrogen was performed on the 

The atomic ratio 

DLC films (ref. 7). This technique showed that DLC films made by the various 

deposition methods have very similar hydrogen depth profiles. 

of hydrogen to carbon (HK) was low at the film surface and rose to a constant 

value at a depth of 50 nm. Table I shows the hydrogen-to-carbon ratios measured one-half of the distance through the DLC films for the three different 

deposition methods. There is a variation in hydrogen content which depends on 

the method used to deposit the DLC film. DLC films made by single ion-beam 

deposition with CH4 had an H/C ratio of 0.91. Adding the energy of the second 

ion source (dual beam) reduced this ratio to 0.62. Thus, the second source 

removed some of the hydrogen. DLC films generated by the single source, but 

with C4H10, also had an H/C ratio of 0.62. The films generated by ion beam 

sputter deposition from a graphite target contained the least amount of hydrogen, an H/C ratio of 0.22. The addition of up to 35 percent hydrogen gas into 

the vacuum facility during sputter deposition doubled the hydrogen content 

of these films. 

Semiquantitative Infrared spectroscopy was also performed on these ion 

beam deposited films. The Integrated intensity of the C-H stretching band at 

about 3.4 pm indicated that the ratio of chemically bonded hydrogen to carbon 

was between 0.03 and 0.44 (ref. 7). The difference between the two hydrogen 

analysi s techniques indicates the presence of nonbonded hydrogen in the f i lms. 

3 
Intrinsic Stress 

The DLC films deposited on Si exhibited a compressive stress that varied 

depending on the deposition method, hydrocarbon gas, and energy of deposition. 

Figures 1 to 3 show the stress levels of 0.1-pm-thick DLC films made by the 

different ion beam deposition methods. Figure 1 is a plot of the compressive 

stress as a function of the H/Ar gas ratio for CH4 and C4H10 gases deposited 

at 110 eV by the single ion-beam source. The stress for each type of film was 

independent of the HlAr ratio, but was 2.5 times as large for the C4H10 films 

as it was for the CH4 films. Figure 2 shows that the stress in the CH4 single 

beam films can be reduced to values as low as 4x109 dynelcm2 by decreasing 

the deposition energy to 90 eV. Figure 3 shows the compressive stress for DLC 

films deposited by ion sputtering a graphite target (including those films made 

with the addition of hydrogen). The compressive stress was 1.6~1010 dynelcm2 

for a pure, sputter-deposited film and rose slightly to 2.3~10'0 dynelcm2 for 

a film with hydrogen addition. These stress levels are higher than those for 

films made by direct ion beam deposition, single or dual, with CH4. Table I 

lists the stress levels for the various DLC films. The data indicate that the 

film stress does not depend on the hydrogen content, but on other parameters 

such as deposition technique and conditions, and hydrocarbon gas. 

Adherence 

The adherence of the DLC films on fused silica was measured by following 

the procedure used by Mirtich (ref. 8). Films up to 1 pm thick, deposited 

by either single or dual beam systems with CH4, were at least as adherent as 

the maximum measurable adherence of the tester: namely, 2.8~106 N/d. These 

films were so adherent that, for some of the films, portions of the Si02 gave 

way with the film still intact. films made by the single ion-beam system with 

C4H10 began to spall once the thickness reached 0.15 pm, and the films that 

were sputter deposited from the graphite target began to spall at 0.2 pm 

thick, indicating an upper limit of the allowable thickness of these films. 

This was expected, since the stress levels of these two types of DLC films were 

greater than those made with CH4 in either the single or dual beam. 

In an attempt to improve the adherence of DLC films that were ion beam 

deposited on ZnS and ZnSe, four techniques were used prior to film deposition 

(ref. 9). Ion beam cleaning of the window materials was the first technique 

used, but was not sufficient, as it was with the Si02 or Si substrates, to 

allow the DLC films to remain adherent. The films had negligible adherence 

(<1.4x104 N/m2> and spa1 led almost immediately after deposition on both 

ZnS and ZnSe. The second technique involved ion implantation via "knock on" 

of thin carbon films on the surface of ZnS and ZnSe by 50 to 100 keV nitrogen 

ions. This technique also failed to allow the DLC films to remain adherent. 

In the third technique, the window surfaces were ion implanted with neon or 

helium at energies var ing between 50 and 100 keV and at doses from 0.5~10~~ 

to 2x1017 particleslcmj. These films spalled after a period of time. The 

fourth technique, which used a thin intermediate coating of germanium or silicon, successfully allowed the DLC films to remain adherent. Thin films of Ge 

or Si, 0.1 pm thick, were ion beam sputter deposited onto ZnS and ZnSe prior 

to deposition of DLC. The interface of Si looked good on deposit, but spalled 

as a function of time and/or thickness. Germanium films as thick as 0.4 pm 

4 
exhibited adherence equal to the strength of the substrate and showed no sign 

of deterioration even after 6 months. DLC films deposited on ZnS and ZnSe with 

an intermediate Ge coating of 0,,05 pm showed adherence values of 106 to 

1.4~106 N/m2, also equal to the strength of the substrate. 

sible to obtain the same adherence values of DLC-Ge films deposited on ZnS and 

ZnSe substrates that were first Implanted with 100-keV He ions at doses to 

2x1 017 part i cl eslcm2. 

It was also posA bonus of ion implantation was the improved physical hardness of the substrate, shown in figure 4 for ZnS. The Vickers hardness as a function of the 

applied load for unimplanted ZnS and ZnSe was compared with that for ZnS and ZnSe 

that were He ion implanted at 100 keV at a dose equal to 2x1017 particles/cm2. 

At the 5-g indentor load, the surface hardness for the implanted ZnS shows a 

dramatic 70 percent increase over the unimplanted ZnS. 

Transmittance 

The transmittance of the DLC films on fused silica in the visible region 

was obtained by using the Bowman technique (ref. 10). The DLC films obtained 

from the single ion-beam deposition method with CH4 have a spectral transmittance similar to those generated by the dual beam source, but the single beam 

films have lower transmittance values when they are greater than 0.12 pm 

thick. This is evident in figure 5, where the spectral transmittance is shown 

for DLC films, 0.15 pm thick, generated by both methods. The 0.15-pm-thick 

dual beam film has greater transmittance at all wavelengths when compared with 

the single beam film of the same thickness. The increased absorption most 

likely arises from the presence of systems of conjugated double bonds within 

the film, although the presence of oxygen could also play a role (ref. 11). 

Both the graphitic precursors and the oxygen would be expected to be reduced 

by the increased sputtering from the second source. A 0.05-pm-thick DLC 

film that was single ion-beam deposited from CH4 displays spectral transmittance values greater than 90 percent at wavelengths greater than 0.8 pm. 

Figure 5 also shows spectral data for a 0.17-pm-thick DLC film that was ion 

beam sputter deposited from a graphite target. 

only between 0.4 and 0.8 pm for this film, and it is very low compared with 

the DLC films that were direct deposited. The low transmittance of the sputtered film may be due to its low hydrogen content. 

The transmittance was measured 

The DLC films deposited on Si substrates acted as antireflective coatings, 

enhancing the infrared transmittance that was greatest at shorter wavelengths 

and that decreased wlth increasing wavelength. This antireflective property 

was observed for all of the DLC films deposited on Si, and therefore was independent of deposition method. 

A spectrophotometer was used to measure the IR transmittance of the DLC 

films deposited on the ZnS and ZnSe, substrates. The spectral transmittance of 

the window material did not change In the wavelength region of 2.5 to 25 pm 

for the ZnS and ZnSe substrates coated with 0-1-pm-thick DLC films. The use 

of an intermediate Ge film or ion Implantation also did not change the IR 

transmlttance of ZnS and ZnSe. FIgure 6 shows the specular IR transmittance 

of ZnS before and after Implantation with 100-keV He ions at a dose of 5~10~6 

particles/cd. The two traces fall on top of each other, indicating that 

there is no variation in the IR specular transmittance of ZnS after exposure to 

5 
100-keV He ions. The intermediate coating of Ge, which allows good DLC film 

adherence to ZnS and ZnSe, shows only small reductions in IR specular transmittance especially at larger wavelengths. This is shown in figure 7, where the IR 

specular transmittance of a ZnSe substrate coated with an intermediate layer of 

0.03 pm Ge and a 0.1-pm DLC film from the single beam with CH4 is presented 

along with the transmittance of an uncoated ZnSe substrate. Although the IR 

specular transmittance is reduced at shorter wavelengths, only a 1 percent loss 

occurs at 10 pm. This reduction could be eliminated by picking the proper 

DLC and Ge thicknesses to allow the combination to become an antireflective 

coati ng . 

Erosion Tests 

To determine the protection the DLC films afforded the ZnS and ZnSe, the 

surfaces were exposed to both 27-pm-diameter A1203 particles in a microsandblaster and water droplets at 180 m/sec for exposure times up to 15 min. 

Particle erosion. - The erosion protection that the various DLC films 

afforded fused silica was first evaluated to determine the best method of coating the optical windows. For this test, 2- by 2-cm Si02 samples were one-half 

coated with the DLC films and then placed in the sandblaster (refs. 5 and 12). 

Only half of the fused silica and half of the DLC film were then exposed to the 

Si02 particles for various periods of time. The specular transmittance data 

were normalized to eliminate the uncertainty in the various parameters of the 

particle erosion test, and are presented in a manner that eliminates the exposure time and highlights the protection afforded by the DLC films. Figure 8 

is the normalized specular transmittance after the erosion of uncoated fused 

silica and of fused silica coated with DLC films, 0.1 and 0.2 pm thick, made 

by the single ion beam with CH4. The unprotected fused silica has a slope 

of one. It is clear that the DLC films extend the erosion lifetime of the 

fused silica and that the 0.2-pm DLC film extends the lifetime more than the 

0.1-pm DLC film. 

0.1-pm films are presented in figure 9. The DLC films generated by ion beam 

sputter deposition and by either single or dual ion-beam deposition with CH4 protected the fused silica, and the protection appears to be independent of the 

deposition method. The ion beam sputter-deposited DLC films with the addition 

of hydrogen are also presented. These films eroded at a faster rate than the 

unprotected fused silica, thus making them less erosion resistant than the 

other DLC films. 

The protection of the different ion beam deposited DLC 

The ZnS and ZnSe substrates were one-half coated with the DLC films that 

were determined to give the best erosion protection to fused silica and were 

exposed to the A1203 particles in the microsandblaster (ref. 6). 

10 and 11 indicate the change in specular transmittance at 10 pm due to total 

erosion time for various surfaces of ZnS and ZnSe, respectively, coated with 

the DLC films. In both figures there is an envelope that portrays the erosion 

rate of the uncoated surfaces. This envelope is necessary because each ZnS and 

ZnSe substrate had a slightly different initial transmittance because the substrate thickness was not the same, although the erosion follows the same curve. 

The DLC films were 0.1 pm thick, and were either sputter deposited from a 

graphite target or direct deposited from the single ion-beam source with CH4. 

An intermediate layer of 0.03-pm Ge was used in all cases. Some of the ZnS 

and ZnSe surfaces were also first He ion implanted at 100 keV at doses of 

0.5~1017 and 2x1017 particles/cm2, and then coated with the DLC film from the 

Figures 

6 
single beam with CH4. 

ion implantation plus the DLC film afforded the ZnS and ZnSe surfaces any 

extension in particle erosion lifetime after exposure to the A1203 particles. 

Rain erosion. - Only ZnS surfaces were evaluated for rain erosion performance in the facility at Wright Patterson Air Force Base. The ZnS surfaces were 

first polished to a 20/10 finish, but many small pits remained in the surface 

which could not be removed by polishing. This was undesirable since these pits 

could be a source of crack propagation during the rain erosion testing. Zinc 

sulfide, DLC coated ZnS, and ZnS that was first implanted with 100-keV He ions 

at a dose to 2x1017 particles/cm2 and then coated with the DLC film were subjected to rain erosion. 

it was clear from optically viewing the ZnS surfaces exposed to the water droplets at 400 mph that there was a performance improvement in the ZnS surface 

that was ion implanted, coated with a 0.04-pm intermediate layer of Ge, and 

then coated with a O.l-pm DLC film from the single beam with CH4. In comparison with ZnS or even ZnS windows coated with a 0.1-pm-thick DLC film, the ion 

implantation plus the DLC coating decreased the number of new pits and delayed 

the start of subsurface ring fractures. This could be expected since the ion 

implantation improved the physical hardness (fig. 4) at the surface to a depth 

of -1.0 pm of the ZnS (ref. 9). 

transmittance between 2.5 and 25 pm for the ion-implanted and DLC-coated ZnS 

surface after it was exposed to rain erosion. 

As both figures indicate, neither the DLC films nor the 

Although no quantitative data will be presented herein, 

There also were no changes in the specular 

Since ion implantation of the ZnS window resulted in improved performance, 

a ZnS surface was implanted with He+ at 1 MeV to further increase the depth 

of surface physical hardness. However, during the rain erosion test of this 

ZnS surface (which was also coated with 0.1-pm DLC and 0.04-pm Gel, the ionimplanted surface layer delaminated from the ZnS substrate. 

CONCLUSIONS 

Three different ion beam methods were used to deposit diamondlike carbon 

(DLC) films on various substrates. 

ited DLC films was nearly one, while the ion beam sputter-deposited films had 

a relatively low HIC ratio even with the addition of hydrogen gas. The compressive stress exhibited by the DLC films did not depend on the hydrogen content, but on other parameters such as the deposition technique and conditions, 

and hydrocarbon gas. Elevated stress levels of DLC films that were ion beam 

deposited with C4H10 or ion beam sputter deposited from a graphite target 

indicated that thick films with good adherence on ZnS and ZnSe could not be 

generated. 

The hydrogen content of the ion beam deposhowever 

coating 

ited an 

Even though the DLC films on fused silica exhibited adherence as good as 

the maximum measurable adherence of the tester, these films were not as adherent on the ZnS and ZnSe substrates, Therefore, four techniques were used prior 

to the deposition of the DLC films to improve the adherence. Ion beam cleaning 

and ion imDlantation did not increase film adherence. Ion imolantation did, 

e 

exhi bate 

and 

, improve the physical hardness of the substrates. An intermedia 

of Ge successfully allowed the DLC films to remain adherent, and 

adherence equal to the strehgth of the substrate. This intermed 

Ge film caused a small reduction in the IR specular transmittance of ZnS 

ZnSe at shorter wavelengths, but only a 1 percent loss occurred at 10 pm 

7 
Since the DLC films deposited on Si acted as an antireflective coating, thereby 

enhancing the IR transmittance, this reduction could be eliminated by picking 

the proper combination of DLC and Ge thicknesses to produce an antireflective 

coating. 

Although ion implantation plus a DLC film did not protect the ZnS and ZnSe 

windows exposed to the simulated particle erosion, it did improve the performance of ZnS exposed to rain erosion. The ZnS windows that were He ion implanted 

and coated with DLC and an intermediate Ge layer had fewer new surface pits and 

a delayed start of subsurface ring cracks. Hardening the window surface itself 

by ion implantation, in addition to coating it with a thick stress-free 

diamondlike carbon film, might increase the lifetime of infrared transmitting 

windows and protect them from both rain and less severe particle erosion. 

REFERENCES 

1. Nadler, M.P.; Donovan, T.M.; and Green, A.K.: Thermal Annealing Study of 

Carbon Films Formed by the Plasma Decomposition of Hydrocarbons. Thin 

Solid Films, vol. 116, no. 1-3, June 22, 1984, pp. 241-247. 

2. Holland, L.; and Ojha, S.M.: Infrared Transparent and Amorphous Carbon 

Grown Under Ion Impact in a Butane Plasma. Thin Solid Films, vol. 48, 

no. 3, Feb. 1, 1978, pp. L21-L23. 

3. Banks, B.A.; and Rutledge, S.K.: Ion Beam Sputter Deposited Diamond-Like 

Fi lms . NASA TM-82873, 1982. 

4. Mirtich, M.J.; Swec, D.M.; and Angus, J.C.: Dual Ion Beam Deposition of 

Carbon Films With Diamondlike Properties. NASA TM-83743, 1984. 

5. Nir, D.: Mechanical Protection of DLC Films on Fused Silica Slides. NASA 

TM-87056, 1985. 

6. Swec, D.M.; Mirtich, M.J.; Nir, D.; and Banks, B.A.: Comparison of 

Protective Coatings for Infrared Transmitting Windows. J. Vac. Sci. 

Technol. A, vol. 4, no. 6, Nov.-Dec. 1986, pp. 3030-3031. 

7. Angus, J.C.; Stuitz, J.E.; Shiller, P.J.; McDonald, J.R.; Mirtich, M.J.; 

and Domitz, S.: Composition and Properties of the So-called "DiamondLike" Amorphous Carbon Films. Thin Solid Films, vol. 118, no. 3, Aug. 17, 

1984, pp. 311-320. 

8. Mirtich, M.J.: Adherence of Ion Beam Sputter Deposited Metal Films on 

H-13 Steel. J. Vac. Sci. Technol., vol. 18, no. 2, Mar. 1981, pp. 186-189. 

9. Mirtich, M.J.; Nir, D.; Swec, D.M.; and Banks, B.A.: The Use of- Intermediate Layers to Improve the Adherence of Diamondlike Carbon Films on ZnS 

and ZnSe. J. Vac. Sci. Technol. A, vol. 4, 1986, pp. 2680-2681. 

10. Bowman, R.L.; Mirtich, M.J.; and Weigand, A.J.: The Changes in Optical 

Properties of Various Transmitting Materials Due to Simulated Micrometeoroid Exposure. NASA TM X-52687, 1969. 

8 
11. Angus, J.C.; Mirtich, M.J.; and Wintucky, E.G.: Ion Beam Deposition of 

Amorphous Carbon Films Wlth Diamond Like Properties. 

Formation by Ion Implantation, S.T. Picraux and W.J. Choyke, eds., 

North-Holland, 1982, pp. 433-440. 

Metastable Materials 

Deposition 

method 

Single beam, CH4 

Dual beam, CH4 

Single beam, C4H10 

Graphite sputtering 

Graphite sputtering 

12. Mirtich, M.J.; Nir, D.; Swec, D.M.; and Banks, B.A.: Diamondlike Carbon 

Protective Coatings for IR Materials. NASA TM-87083, 1985. 

Stress, 

dyne/crn2 

0.9x10'0 

2.6 

.9 

1.6 

2.3 

TABLE I. - PROPERTIES OF DIAMONDLIKE CARBON FILMS 

DEPOSITED BY DIFFERENT ION BEAM 

DEPOSITION METHODS 

Hydrogen content, 

H/C 

0.91 

.62 

.62 

.22 

.53 

I + H2 addition I I I 

9 
N 

. 6 

g2- 

vi 

a 

v) 

W 

Li 

W 

v) 

W 

5 

8‘- 

O- 0 

3x9 

r, 

0 

80 100 120 140 160 

WAr, PERCENT 

Figure 1. - Compressive stress as function of WAr gas ratio for 

0.l-pmthick DLC films made with CH4 and C4H10 in the single ionbeam Swrm at 110 eV. 

3x1O1O 

r N 

6 t 

6 

9 

Li2 

W 

a L 35 PERCENT Hg -. 

27 PERCENT H27, 8. 

31 PERCENTH2- 

I -‘-la PERCENT H2 

10 

2( 

16 

N 

. € 

c u a.. 

12 vi 

a 

2 

ma 

a 

cn 

W 

2 

W 

u) 

W 

0 : 

4 

0 

09 

50 100 150 200 250 

DEPOSITION ENERGY, eV 

Figure 2. - Compressive stress as function of depositlon energy for 

, 0.l-pn-thick DLC films made with CH4 in the single ion-beam source. 

0 10 20 30 40 50 

LOAD, g 

Figure 4. - Vickers hardness as function of applied load for unimpianted 

ZnS, and for ZnS implanted with He ions, at 100 keV at a dose of 

2x1017 partides’cm2. 
IMPLANTED / 

DEPOSITION THICKNESS, 

METHOD )un 

0 SPWERED 0.17 

0 DUALBEAM. 

.I5 

A SINGLE BEAM, 

(344 

P CH4 .I5 

0 

.4 .8 .8 1 .o 1.2 1.4 

WAVELENGTH, pm 

Flgure 5. - Transmittance as function of wavelength for 

MC fllme made with CH4 in the single or dual lonbarn source, and DLC films made by sputter 

deposltkm of a Oraphlte taroel. 

1 i I I 

WAVELENGTH, pm 

Figure 6. - Specular bMwm dZn8 befom and after He ion implantation at 100 keV at a dose of 5x1Ol6 particles/cm2. 

11 
r 

UNCOATED ZnSe 

c 

WAVELENGTH, pn 

Figure 7. - Specular transmiltance of 0.1-p DLC film made with CH4 in the single beam with and without an intermediate layer of 0.03-pm Ge on the 

ZnSe substrate. 

I 

I 

1 .a 

0 

1 .a 

0 0.2-)lm-THICK DLC FILM 

0 0.1-V-THICK DLC FILM 

- UNCOATED FUSED SILICA 

/ -/ 

I I I I I 

.2 .4 .6 .8 1 .a 

NORMALIZED SPECULAR TRANSMRTANCE, 

UNCOATED FUSED SILICA 

Figure 8. - Normalized specular transmlltance of fused silica coated 

with DLC films, 0.1 and 0.2 pm thick, made with CH4 In the single 

Ion-beam source, and uncoated fused silica, both after exposure to 

100-p Si02 particles at 27 mlsec. 

8 

.8 P 

0 

0 SPLITTERED 

0 DUAL BEAM, CH4 

A SINGLE BEAM, CH4 

n SPUTTERED+H~ 

- UNCOATED FUSED 

SILICA 

.2 .4 .6 .8 

NORMALIZED SPECULAR TRANSMRTANCE OF 

UNCOATED FUSED SILICA 

n 

Figure 9. - Protection that 0.1-p-thick DLC films deposited by 

various methods afforded fused silica after exposure to 100-pn 

Si02 particles at 27 mlsec. 

12 
...I-- ------_---- 55 

---- 

--- pm >:.x i.... I ,..... .~.x.~:.~~.:.:~.~~~~:.::~~: UNWATE D Zn S 

- - - SINGLE BEAM, CH 

------ He IMPLANTEDAT~x~O~~/C~~+ DLC 

--- He IMPLANTEDAT 2x1d7/cm2+ DLC 

Ih ---- SPUTTERED v) 

I I I I 1 30- 

0 2 4 6 a 10 

EXPOSURE TIME, min 

Figure IO. -Change In specular transmitlance at 10 pm due to total 

eroskn time for various surfaces of ZnS coated with DLC films. 

UNCOATED ZnSe 

------ He lMPLANTEDAT5x1016/cm2+ DLC 

--- He IMPLANTEDAT~x~O~~/C~~+ DLC 

80 

- - - - SPUlTERED !z 

E 

370 

&o E 

3 

w 

fa I040 

w 

B 

0 2 4 6 a 10 30 

EXPOSURE TIME. min 

Flguo 11. - Change In specular transmittanm at 10 pn due to total 

emslon tkne fw various surfaces of ZnSe coated with DLC films. 

13 
1. Report No. 2. Government Accession No. 

NASA TM- 102 1 1 1 

4. Title and Subtitle 

Diamondlke Carbon Proteciv Coatings for Optical Wndows

7. Author(s) 

Diane M. Swec and Michael J. Mirtch 

9. Performing Organization Name and Address 

Nationl Aeronautics and Space Adminstrao 

Lewis Resarch Centr 

Clevand, Ohio 4135-9 

3. Recipient's Catalog No. 

5. Report Date 

6. Performing Organization Code 

8. Performing Organization Report No. 

E-48 1 

10. Work Unit No. 

506-4 11 

12. Sponsoring Agency Name and Address 

13. Type of Report and Period Covered 

Technial Memorandu 

17. Key Words (Suggested by Author(s)) 

Diamondlke carbon films 

Ion beam depositn 

Infraed transmig windos 

Nationl Aeronautics and Space Adminstrao 

Washingto, D.C. 20546-01 

18. Distribution Statement 

Unclasifed - Unlimted 

Subject Cagory74 

14. Sponsoring Agency Code r------ 

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No of pages 

Unclasifed Unclasifed 14 

15. Supplementary Notes 

Prepad for the 198 Technial Symposia nAerospac Sensig poredby The Interaiol Society for

Optical Engier, Orlando, Florida, March 27-31, 198. 

22. Price' 

A03 

16. Abstract 

Diamondlke carbon (DLC) films wer deposit on infraed transmig optical windos a wer evalutd as 

proteciv coatings for thes windos exposd tparticle and rain erosin. The DLC films wer deposit on 

zinc selnid (ZnSe) and zinc sulfide (ZnS) by thre difernt ion beam methods: (1) sputer depositn from a 

carbon targe using an 8-cm argon ion source, (2) direct depositn by a 30-cm holw cathode ion source with 

hydrocabn gas in argon, and (3) dualbeam direct depositn by the 30-cm holw cathode ion source and an 

8-cm argon ion source. In an atemp to improve the adhernc of the DLC films on ZnSe and ZnS, ion beam 

cleanig, ion implanto with helium and neo ions, or sputer depositn of a thin, ion beam intermda 

coating was employd prio to depositn of the DLC film. The protecin tha the DLC films aforde the 

windos from particle and rain erosin was evalutd, along with the hydrogen conte, adhernc, intrsc 

stre, and infraed transmice of the films. Becaus of the elvatd stre levs in the ion beam sputerd 

DLC films and in those ion beam deposit with butane, films thicker than 0.1 pm and with god adhernc on 

ZnS and ZnSe could not be genratd. An intermda coating of germaniu sucefly aowedthe DLC films 

to remain adhernt to the optical windos a caused only neglib rduction in the specular transmice of 

the ZnS and ZnSe at 10 pm. Thes DLC films di not protec the optical windos from simulated pricle

erosin; howevr, they di improve the perfomance of ZnS exposd to rain erosin. 

*For sale by the National Technical Information Service, Springfield, Virginia 22161 NASA FORM 1626 OCT 86