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Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 23 — Nov. 18, 2013
  • pp: 28334–28343
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Stability of EUV multilayer coatings to low energy alpha particles bombardment

M. Nardello, Paola Zuppella, V. Polito, Alain Jody Corso, Sara Zuccon, and M.G. Pelizzo  »View Author Affiliations


Optics Express, Vol. 21, Issue 23, pp. 28334-28343 (2013)
http://dx.doi.org/10.1364/OE.21.028334


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Abstract

Future solar missions will investigate the Sun from very close distances and optical components are constantly exposed to low energy ions irradiation. In this work we present the results of a new experiment related to low energy alpha particles bombardments on Mo/Si multilayer optical coatings. Different multilayer samples, with and without a protecting capping layer, have been exposed to low energy alpha particles (4keV), fixing the ions fluency and varying the time of exposure in order to change the total dose accumulated. The experimental parameters have been selected considering the potential application of the coatings to future solar missions. Results show that the physical processes occurred at the uppermost interfaces can strongly damage the structure.

© 2013 Optical Society of America

1. Introduction

The space science program of the European Space Agency foresees several key missions to explore the innermost regions of Solar system and to address the main scientific objectives established in the Cosmic Vision 2015-2025 plan. Among many ambitious projects, Solar Orbiter (SOLO) has been selected as a M-class mission: it is a Sun-observing satellite which will approach the star at the closest distance ever reached (0.28 AU at the perihelion) providing observations with unprecedented temporal and spatial resolution. The Solar Orbiter spacecraft will operate in a very harsh environment, which can cause severe degradation to space instrumentation. All the instruments on board will be exposed to high stress environmental agents, with effects on their functioning and performances which are very difficult to predict [1

1. ESA, “Solar Orbiter environmental specification - Issue 3.0” (2010).

].

Many solar UV and EUV instruments have suffered significant performance degradation after deployment in space, due to several contamination sources. In particular, low energy particles fluxes from the solar wind plasma (mainly electrons, protons and alpha particles) contribute to the degradation of optical materials, causing the physical alteration of the surface and roughening the surface profile. The most severe degrading effects on the instrumental performance is the change of reflectance of mirrors and their scattering increase [2

2. U. Schule, “The cleanliness control program for the SUMER/SOHO experiment” in UV and X-ray Spectroscopy of Laboratory and Astrophysical Plasma, Silver E. & Kahn S. eds. (Cambridge University Press, 1993), pp. 373–382.

].

In this work we present a continuation of such experiment, in which the effect of solar wind low energy alpha particles bombardment on nanostructured optical coatings is studied. The ion implantation has been carried out at the Ion beam Center in the Forschungzentrum Dresden-Rossendorf (FZD). Small samples of selected multilayer coatings have been exposed to alpha particles fluxes and their optical performances being verified prior and after the experimental sessions. The total doses accumulated during the irradiation sessions are equivalent to those taken in 1, 2 and 4 years (nominal science phase is 3.6 years) of SOLO mission.

2. Material and methods

The solar wind is an outflow of completely ionized gas originating from the solar corona and expanding outwards the interplanetary regions, carrying the solar magnetic field along with it. It mainly consists of ionized hydrogen (electrons and protons) with an admixture of about 8% of alpha particles (He2+) and trace amounts of heavy ions such as O+6 and Fe+10.The ions velocity and density can be much variable. The solar wind can be as slow as about 300 km/s and faster than 750 km/s, but it typically travels at about 400 km/s. The ions of the quiet solar wind carry considerable kinetic energy, typically around 1 keV for protons and 4 keV for the alpha particles, and are considered to be one of the most long-term sources of degradation to surface materials. More severe but transient disturbances can be caused by energetic particles events as coronal mass ejection, which have not been considered in this analysis. The effects of high energy particles on EUV multilayer coatings have been investigated elsewhere [11

11. A. D. Rousseau, D. L. Windt, B. Winter, L. Harra, H. Lamoureux, and F. Eriksson, “Stability of EUV multilayers to long-term heating, and to energetic protons and neutrons, for extreme solar missions,” Proc. SPIE 5900, 590004 (2005). [CrossRef]

].

The solar wind parameters at 1AU are reported in Table 1

Table 1. Solar wind parameters from models at 1 AU

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, according to the last issue of the ESA Solar Orbiter Environmental Specifications document [1

1. ESA, “Solar Orbiter environmental specification - Issue 3.0” (2010).

].

By considering the scaling factors and the values of density and speed, it is thus possible to estimate the total number of He2 + received by the spacecraft for unit area A (in this context indicated as “dose”) at every spacecraft position r(t) and their sum over one or several orbital periods T (total dose computed by Eq. (1)).

TotalDose(1orbit)=t0TFlux(t)dt=t0Tdensityscaling_factor(r(t))speed(t)dt
(1)

The alpha particles doses per unit area are then shown in Fig. 2
Fig. 2 Total number of alpha particles per unit area received by the satellite over half orbit, from the perihelion to the aphelion.
, as a function of the spacecraft distance from the Sun during half orbital period.

By integrating the relationship above over 4 years of Solar Orbiter science phase duration (nominal 3.6 years for launch in 2017) and over intermediate steps (1 and 2 years), the total experimental doses can be estimated. According to the facility experimental availability, a flux of 1.5·1011 s−1cm−2 has been fixed for all the irradiation sessions while the duration has been varied in order to account for the established total doses. The irradiation sessions lasted about 5 hours for 1 year (session A, total dose 2.6·1015 #He2+ /cm2), 10 hours for 2 years (session B, total dose 5.2·1015 #He2+ /cm2) and 20 hours for 4 years (session C, total dose 1.1·1016 #He2+ /cm2) equivalent doses respectively.

The optical coatings selected for the experimental investigation are periodic Mo/Si multilayer (named REF), REF with Ir/Mo capping layer (named CL1), REF with Ir/Si capping layer (named CL2) [12

12. A. J. Corso, P. Zuppella, P. Nicolosi, D. L. Windt, E. Gullikson, and M. G. Pelizzo, “Capped Mo/Si multilayers with improved performance at 30.4 nm for future solar missions,” Opt. Express 19(15), 13963–13973 (2011). [CrossRef] [PubMed]

, 13

13. M. G. Pelizzo, M. Suman, G. Monaco, P. Nicolosi, and D. L. Windt, “High performance EUV multilayer structures insensitive to capping layer optical parameters,” Opt. Express 16(19), 15228–15237 (2008). [CrossRef] [PubMed]

], and periodic Ir/Si multilayer [14

14. P. Zuppella, G. Monaco, A. J. Corso, P. Nicolosi, D. L. Windt, V. Bello, G. Mattei, and M. G. Pelizzo, “Iridium/silicon multilayers for extreme ultraviolet applications in the 20-35 nm wavelength range,” Opt. Lett. 36(7), 1203–1205 (2011). [CrossRef] [PubMed]

], deposited on a Si(100) substrate by magnetron sputtering [15

15. J. D. Torre, J. L. Bocquet, Y. Limoge, J. P. Crocombette, E. Adam, G. Martin, T. Baron, P. Rivallin, and P. Mur, “Study of self-limiting oxidation of silicon nanoclusters by atomistic simulations,” J. Appl. Phys. 92(2), 1084 (2002). [CrossRef]

] by RXO LLC, USA. The parameters of the ML structures have been optimized for a peak of reflectivity at 30.4 nm at angle of incidence of 5° (Tables 2

Table 2. Parameters of the Mo/Si periodic multilayer tuned at 30.4 nm. d is the period, Γ is the layer thickness ratio and N is the number of layers.

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4

Table 4. Parameters of the Ir/Si periodic multilayer tuned at 30.4 nm. d is the period, Γ is the layer thickness ratio and N is the number of layers.

table-icon
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).

Table 3. Capping layers structure parameters selected for the Mo/Si multilayer

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The ion implantation experiment has been performed at Forschungszentrum Dresden-Rossendorf (Germany, ex Helmholtz-Zentrum Dresden-Rossendorf) in the Low Energy Implanter (LEI) facility (Fig. 3
Fig. 3 The LEI facility at Forschungszentrum Dresden-Rossendorf and the samples accommodated in the support of LEI.
), within the EU Integrating Activity SPIRIT. The experimental details (doses, fluxes, durations and energies) are reported in Table 5

Table 5. Ion implantation experiment details.

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.

The vacuum level has been constantly lower than 10−8 mbar, and the temperature inside the chamber has been kept within 27-29 °C. The samples have been allocated in a dedicated support and placed perpendicularly to the alpha particles flux. The ion currents have been integrated over time in order to monitor the total dose established.

Reflectivity measurements at 5° incidence angle in the 25–35 nm spectral range have been performed prior and after irradiation at the Bending Magnet for Emission Absorption and Reflectivity (BEAR) beamline at ELETTRA Synchrotron (Trieste, Italy) [16

16. G. Naletto, M. G. Pelizzo, G. Tondello, S. Nannarone, and A. Giglia, “The monochromator for the synchrotron radiation beamline X-MOSS at ELETTRA,” SPIE Proc. 4145, 105 (2001). [CrossRef]

], using a 0.9 polarized beam. A witness sample has been also measured in order to avoid bias in the results due to possible aging effects on multilayer performances.

The morphology of the samples, both irradiated and not irradiated, has been characterized by using Atomic Force Microscope operating in non-contact mode (XE-70, Park System), to verify a possible increase of the superficial roughness due to the ion bombardment as well as presence of contaminants.

3. Results and discussion

The reflectance of the multilayer structures before and after implantation as measured at the synchrotron facility are reported in Fig. 4
Fig. 4 Reflectance measurements of the structures REF (a), CL1 (b), CL2 (c) and Ir/Si (d) before and after low energy alpha particles implantation experiment.
. A non-irradiated witness sample has also been re-measured to verify possible degradation due to natural aging of the structures; no degradation in time was observed in any of the samples.

All the coatings show a degradation in reflectance, even though the multilayer protected by an Ir/Mo capping layer have a higher resistance with respect to alpha particles bombardment (Table 6

Table 6. Peak reflectance of the multilayer structure before and after alpha particles implantation sessions and reflectance percentage drops.

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). The same was observed in the experiment with protons, such that we can conclude that Ir/Mo capping layer offers a great protection against solar wind ions.

The roughness of the film surfaces has been verified by AFM before and after implantation; no increase in roughness was found in any of the samples. For example, in Fig. 5
Fig. 5 AFM image taken on a Mo/Si REF sample prior (a) and after (b) alpha particle implantation
the AFM image taken before and after implantation is shown for the case of Mo/Si multilayer, which shows the most important degradation in reflectance among the coatings. Nevertheless, the images show no evident changes in the surface morphology, so that the degradation cannot be attributed to an increasing of the roughness on the top last layer.

The fact that there is a drop in reflectance without a variation of the shape of the curve and of the peak wavelength suggests that there is an increase of inter-diffusion at interfaces. In order to infer a possible explanation of the physical phenomena simulations of collision dynamics with SRIM/TRIM software were performed [17

17. http://www.srim.org/ - consulted on August 2013.

, 18

18. J. F. Ziegler and J. P. Biersack, SRIM - The Stopping and Range of Ions in Solids (Pergamon Press., 1985).

]. The multilayer model was built inside the software which performs Montecarlo simulations of elastic scattering interaction between the incident ions and the target structure atoms. Ions’ energy of 4keV has been specified and a statistics of 99999 incident ions has been used. The results of the simulations are the position of the incident ions inside the multilayer structure (Fig. 6
Fig. 6 Stopping range of He ions in the multilayer as a function of depth from top surface. The cases of REF and CL1 samples are shown; CL2 case is very similar to the case CL1.
) and of the scattered atoms of the target (Fig. 7
Fig. 7 Density of atoms of the target material displaced from their original position as a function of the multilayer depth per unit of ion flux. The case of REF sample is shown. Dashed lines represent the original position of the interfaces assumed ideally smooth.
). Such simulation results confirm the presence of inter-diffusion at the interfaces of first layers.

To estimate the inter-diffusion amount in the different samples, we have considered the atom distribution curve at each single interface, for all the atom species. In order to obtain a comparison model for the different multilayers, the right side of the normalized curve has been fitted with a Boltzmann function shown in Eq. (2).
y=a2+a1a21+exx0d
(2)
and the parameter σ = √d/2 has been used to estimate the degree of inter-diffusion. The σ values obtained for the different Mo/Si multilayers have been plotted as function of the depth from multilayer top surface in order to understand the different performances of the coatings.

4. Conclusion

For the first time multilayer coatings for high EUV reflectance have been irradiated by low energy (4 keV) alpha particles to verify their stability over time in Sun close heliosphere. Optical characterization of the sample prior and after the experiment shows that bombardment can strongly damage the nanostructures. All samples show a change in reflectivity, which has been demonstrated to be more dramatic in case of a standard uncapped Si/Mo multilayer and Ir/Si multilayers. For high He + doses, Ir/Mo capping layer seems able to protect the Mo/Si structure underneath. This is probably due to the barrier offered by the combination of the metal layers of Ir and Mo, so that the increase of their thicknesses would probably ensure even a greater protection. Nevertheless, the design of such capping layer on top of Mo/Si combine together the highest efficiency at 30.4 nm and a good stability both to proton and to alpha particle bombardment, and therefore should be considered as a preferred candidate for potential space mission instrumentations.

Acknowledgments.

The authors thank: Dr. Fineschi and Prof. E. Antonucci, PI of METIS on board of Solar Orbiter; Dr. A. Giglia and Prof. S. Nannarone for measurement at ELETTRA-BEAR beamline; the SPIRIT technical and administrative staff of the Forschungszentrum Dresden-Rossendorf for support during ion implantation experiment; Mewael G. Sertsu of University of Padova for his assistance during ion implantation experiment. This work has been performed with the financial support of the Italian Space Agency (ASI/INAF/015/07/0 and ASI/INAF/Solar Orbiter) and of the Cassa di Risparmio di Padova e Rovigo (CARIPARO) Foundation-Bandi di Eccellenza 2009/2010. This work has been supported by the European Community as an Integrating Activity “Support of Public and Industrial Research Using Ion Beam Technology (SPIRIT)” under EC contract no. 227012.

References and links

1.

ESA, “Solar Orbiter environmental specification - Issue 3.0” (2010).

2.

U. Schule, “The cleanliness control program for the SUMER/SOHO experiment” in UV and X-ray Spectroscopy of Laboratory and Astrophysical Plasma, Silver E. & Kahn S. eds. (Cambridge University Press, 1993), pp. 373–382.

3.

M. G. Pelizzo, A. J. Corso, P. Zuppella, D. L. Windt, G. Mattei, and P. Nicolosi, “Stability of extreme ultraviolet multilayer coatings to low energy proton bombardment,” Opt. Express 19(16), 14838–14844 (2011). [CrossRef] [PubMed]

4.

E. Antonucci, S. Fineschi, G. Naletto, M. Romoli, D. Spadaro, G. Nicolini, P. Nicolosi, L. Abbo, V. Andretta, A. Bemporad, F. Auchère, A. Berlicki, R. Bruno, G. Capobianco, A. Ciaravella, G. Crescenzio, V. Da Deppo, R. D'Amicis, M. Focardi, F. Frassetto, P. Heinzel, P. L. Lamy, F. Landini, G. Massone, M. A. Malvezzi, J. D. Moses, M. Pancrazzi, M. G. Pelizzo, L. Poletto, U. H. Schühle, S. K. Solanki, D. Telloni, L. Teriaca, and M. Uslenghi, “Multi Element Telescope for Imaging and Spectroscopy (METIS) coronagraph for the Solar Orbiter mission,” Proc. SPIE 8443, 844309 (2012). [CrossRef]

5.

S. Fineschi, E. Antonucci, G. Naletto, M. Romoli, D. Spadaro, G. Nicolini, P. Nicolosi, L. Abbo, V. Andretta, A. Bemporad, F. Auchère, A. Berlicki, R. Bruno, G. Capobianco, A. Ciaravella, G. Crescenzio, V. Da Deppo, R. D'Amicis, M. Focardi, F. Frassetto, P. Heinzel, P. L. Lamy, F. Landini, G. Massone, M. A. Malvezzi, J. D. Moses, M. Pancrazzi, M. G. Pelizzo, L. Poletto, U. H. Schühle, S. K. Solanki, D. Telloni, L. Teriaca, and M. Uslenghi, “METIS: a novel coronagraph design for the Solar Orbiter mission,” Proc. SPIE 8443, 84433H (2012). [CrossRef]

6.

M. G. Pelizzo, D. Gardiol, P. Nicolosi, A. Patelli, and V. Rigato, “Design, deposition, and characterization of multilayer coatings for the ultraviolet and visible-light coronagraphic imager,” Appl. Opt. 43(13), 2661–2669 (2004). [CrossRef] [PubMed]

7.

J. P. Halain, P. Rochus, E. Renotte, T. Appourchaux, D. Berghmans, L. Harra, U. Schuhle, W. Schmutz, F. Auchere, A. Zhukov, C. Dumesnil, F. Delmotte, T. Kennedy, R. Mercier, D. Pfiffner, L. Rossi, J. Tandy, A. BenMoussa, and P. Smith, “The EUI instrument on board the Solar Orbiter mission: from breadboard and prototypes to instrument model validation,” SPIE Proc. 8443, 844307 (2012). [CrossRef]

8.

M. H. Hu, K. Le Guen, J. M. André, P. Jonnard, E. Meltchakov, F. Delmotte, and A. Galtayries, “Structural properties of Al/Mo/SiC multilayers with high reflectivity for extreme ultraviolet light,” Opt. Express 18(19), 20019–20028 (2010). [CrossRef] [PubMed]

9.

R. Soufli, M. Fernandez-Perea, S.L. Baker, J.C. Robinson, J. Alameda, and C.C. Walton, “Spontaneously intermixed Al-Mg barriers enable corrosion-resistant Mg/SiC multilayer coatings,” Appl. Phys. Lett. 101(4), 043111 (2012).

10.

A.S. Kuznetsov, M.A. Gleeson, and F. Bijkerk, “Hydrogen-induced blistering mechanisms in thin film coatings,” J. Phys. Condens. Matter 24(5), 052203 (2012).

11.

A. D. Rousseau, D. L. Windt, B. Winter, L. Harra, H. Lamoureux, and F. Eriksson, “Stability of EUV multilayers to long-term heating, and to energetic protons and neutrons, for extreme solar missions,” Proc. SPIE 5900, 590004 (2005). [CrossRef]

12.

A. J. Corso, P. Zuppella, P. Nicolosi, D. L. Windt, E. Gullikson, and M. G. Pelizzo, “Capped Mo/Si multilayers with improved performance at 30.4 nm for future solar missions,” Opt. Express 19(15), 13963–13973 (2011). [CrossRef] [PubMed]

13.

M. G. Pelizzo, M. Suman, G. Monaco, P. Nicolosi, and D. L. Windt, “High performance EUV multilayer structures insensitive to capping layer optical parameters,” Opt. Express 16(19), 15228–15237 (2008). [CrossRef] [PubMed]

14.

P. Zuppella, G. Monaco, A. J. Corso, P. Nicolosi, D. L. Windt, V. Bello, G. Mattei, and M. G. Pelizzo, “Iridium/silicon multilayers for extreme ultraviolet applications in the 20-35 nm wavelength range,” Opt. Lett. 36(7), 1203–1205 (2011). [CrossRef] [PubMed]

15.

J. D. Torre, J. L. Bocquet, Y. Limoge, J. P. Crocombette, E. Adam, G. Martin, T. Baron, P. Rivallin, and P. Mur, “Study of self-limiting oxidation of silicon nanoclusters by atomistic simulations,” J. Appl. Phys. 92(2), 1084 (2002). [CrossRef]

16.

G. Naletto, M. G. Pelizzo, G. Tondello, S. Nannarone, and A. Giglia, “The monochromator for the synchrotron radiation beamline X-MOSS at ELETTRA,” SPIE Proc. 4145, 105 (2001). [CrossRef]

17.

http://www.srim.org/ - consulted on August 2013.

18.

J. F. Ziegler and J. P. Biersack, SRIM - The Stopping and Range of Ions in Solids (Pergamon Press., 1985).

OCIS Codes
(230.4170) Optical devices : Multilayers
(260.7200) Physical optics : Ultraviolet, extreme
(350.1820) Other areas of optics : Damage
(350.4990) Other areas of optics : Particles
(350.6090) Other areas of optics : Space optics

ToC Category:
Thin Films

History
Original Manuscript: August 30, 2013
Manuscript Accepted: October 10, 2013
Published: November 11, 2013

Citation
M. Nardello, Paola Zuppella, V. Polito, Alain Jody Corso, Sara Zuccon, and M.G. Pelizzo, "Stability of EUV multilayer coatings to low energy alpha particles bombardment," Opt. Express 21, 28334-28343 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-23-28334


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References

  1. ESA, “Solar Orbiter environmental specification - Issue 3.0” (2010).
  2. U. Schule, “The cleanliness control program for the SUMER/SOHO experiment” in UV and X-ray Spectroscopy of Laboratory and Astrophysical Plasma, Silver E. & Kahn S. eds. (Cambridge University Press, 1993), pp. 373–382.
  3. M. G. Pelizzo, A. J. Corso, P. Zuppella, D. L. Windt, G. Mattei, and P. Nicolosi, “Stability of extreme ultraviolet multilayer coatings to low energy proton bombardment,” Opt. Express19(16), 14838–14844 (2011). [CrossRef] [PubMed]
  4. E. Antonucci, S. Fineschi, G. Naletto, M. Romoli, D. Spadaro, G. Nicolini, P. Nicolosi, L. Abbo, V. Andretta, A. Bemporad, F. Auchère, A. Berlicki, R. Bruno, G. Capobianco, A. Ciaravella, G. Crescenzio, V. Da Deppo, R. D'Amicis, M. Focardi, F. Frassetto, P. Heinzel, P. L. Lamy, F. Landini, G. Massone, M. A. Malvezzi, J. D. Moses, M. Pancrazzi, M. G. Pelizzo, L. Poletto, U. H. Schühle, S. K. Solanki, D. Telloni, L. Teriaca, and M. Uslenghi, “Multi Element Telescope for Imaging and Spectroscopy (METIS) coronagraph for the Solar Orbiter mission,” Proc. SPIE8443, 844309 (2012). [CrossRef]
  5. S. Fineschi, E. Antonucci, G. Naletto, M. Romoli, D. Spadaro, G. Nicolini, P. Nicolosi, L. Abbo, V. Andretta, A. Bemporad, F. Auchère, A. Berlicki, R. Bruno, G. Capobianco, A. Ciaravella, G. Crescenzio, V. Da Deppo, R. D'Amicis, M. Focardi, F. Frassetto, P. Heinzel, P. L. Lamy, F. Landini, G. Massone, M. A. Malvezzi, J. D. Moses, M. Pancrazzi, M. G. Pelizzo, L. Poletto, U. H. Schühle, S. K. Solanki, D. Telloni, L. Teriaca, and M. Uslenghi, “METIS: a novel coronagraph design for the Solar Orbiter mission,” Proc. SPIE8443, 84433H (2012). [CrossRef]
  6. M. G. Pelizzo, D. Gardiol, P. Nicolosi, A. Patelli, and V. Rigato, “Design, deposition, and characterization of multilayer coatings for the ultraviolet and visible-light coronagraphic imager,” Appl. Opt.43(13), 2661–2669 (2004). [CrossRef] [PubMed]
  7. J. P. Halain, P. Rochus, E. Renotte, T. Appourchaux, D. Berghmans, L. Harra, U. Schuhle, W. Schmutz, F. Auchere, A. Zhukov, C. Dumesnil, F. Delmotte, T. Kennedy, R. Mercier, D. Pfiffner, L. Rossi, J. Tandy, A. BenMoussa, and P. Smith, “The EUI instrument on board the Solar Orbiter mission: from breadboard and prototypes to instrument model validation,” SPIE Proc. 8443, 844307 (2012). [CrossRef]
  8. M. H. Hu, K. Le Guen, J. M. André, P. Jonnard, E. Meltchakov, F. Delmotte, and A. Galtayries, “Structural properties of Al/Mo/SiC multilayers with high reflectivity for extreme ultraviolet light,” Opt. Express18(19), 20019–20028 (2010). [CrossRef] [PubMed]
  9. R. Soufli, M. Fernandez-Perea, S.L. Baker, J.C. Robinson, J. Alameda, and C.C. Walton, “Spontaneously intermixed Al-Mg barriers enable corrosion-resistant Mg/SiC multilayer coatings,” Appl. Phys. Lett.101(4), 043111 (2012).
  10. A.S. Kuznetsov, M.A. Gleeson, and F. Bijkerk, “Hydrogen-induced blistering mechanisms in thin film coatings,” J. Phys. Condens. Matter24(5), 052203 (2012).
  11. A. D. Rousseau, D. L. Windt, B. Winter, L. Harra, H. Lamoureux, and F. Eriksson, “Stability of EUV multilayers to long-term heating, and to energetic protons and neutrons, for extreme solar missions,” Proc. SPIE5900, 590004 (2005). [CrossRef]
  12. A. J. Corso, P. Zuppella, P. Nicolosi, D. L. Windt, E. Gullikson, and M. G. Pelizzo, “Capped Mo/Si multilayers with improved performance at 30.4 nm for future solar missions,” Opt. Express19(15), 13963–13973 (2011). [CrossRef] [PubMed]
  13. M. G. Pelizzo, M. Suman, G. Monaco, P. Nicolosi, and D. L. Windt, “High performance EUV multilayer structures insensitive to capping layer optical parameters,” Opt. Express16(19), 15228–15237 (2008). [CrossRef] [PubMed]
  14. P. Zuppella, G. Monaco, A. J. Corso, P. Nicolosi, D. L. Windt, V. Bello, G. Mattei, and M. G. Pelizzo, “Iridium/silicon multilayers for extreme ultraviolet applications in the 20-35 nm wavelength range,” Opt. Lett.36(7), 1203–1205 (2011). [CrossRef] [PubMed]
  15. J. D. Torre, J. L. Bocquet, Y. Limoge, J. P. Crocombette, E. Adam, G. Martin, T. Baron, P. Rivallin, and P. Mur, “Study of self-limiting oxidation of silicon nanoclusters by atomistic simulations,” J. Appl. Phys.92(2), 1084 (2002). [CrossRef]
  16. G. Naletto, M. G. Pelizzo, G. Tondello, S. Nannarone, and A. Giglia, “The monochromator for the synchrotron radiation beamline X-MOSS at ELETTRA,” SPIE Proc. 4145, 105 (2001). [CrossRef]
  17. http://www.srim.org/ - consulted on August 2013.
  18. J. F. Ziegler and J. P. Biersack, SRIM - The Stopping and Range of Ions in Solids (Pergamon Press., 1985).

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