Abstract

Bragg reflectors with widths down to 300 nm have been fabricated in porous silicon. This was achieved by irradiation of highly-doped p-type silicon with a focused beam of high-energy ions in a channeled alignment, in which the beam is aligned with a major crystallographic direction. The reflected colour is controllably tuned across the visible spectrum by varying the ion irradiated dose. The depth distribution of ion induced defects differs in channeled alignment compared to random beam alignment, resulting in the hole current during subsequent anodisation being more confined to narrower lateral regions, enabling different reflective wavelengths to be patterned on a sub-micron lateral scale. This work provides a means of producing high-density arrays of micron-size reflective colour pixels for uses in high-definition displays, and selectively tuning the wavelengths of porous silicon Fabry-Perot microcavities across the visible and infra-red ranges for optical communications and computing applications.

© 2007 Optical Society of America

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  1. G. Vincent, "Optical properties of porous silicon superlattices," Appl. Phys. Lett. 64, 2367-2369 (1994).
    [CrossRef]
  2. M. G. Berger, R. Arens-Fischer, M. Kruger, S. Billat, H. Luth, S. Hillbrich, W. Theiß, and P. Grosse, "Dielectric filters made of PS: advanced performance by oxidation and new layer structures," Thin Solid Films 297, 237-240 (1997).
    [CrossRef]
  3. M. Araki, H. Koyama, and N. Koshida, "Controlled electroluminescence spectra of porous silicon diodes with a vertical optical cavity," Appl. Phys. Lett. 69, 2956-2958 (1996).
    [CrossRef]
  4. L. Pavesi, "Porous silicon dielectric multilayers and microcavities," Riv. Nuovo Cimento 20, 1-78 (1997).
    [CrossRef]
  5. S. Nagata, C. Domoto, T. Nishimura, and K. Iwameji, "Single-mode optical waveguide fabricated by oxidization of selectively doped titanium porous silicon," Appl. Phys. Lett. 72, 2945-2947 (1998).
    [CrossRef]
  6. A. Birner, R. B. Wehrspohn, U. Gösele, and K. Busch, "Silicon-Based Photonic Crystals," Adv. Mater. 13, 377-388 (2001).
    [CrossRef]
  7. N. Savage, "Linking with light," IEEE Spectrum 39, 32-36 (2002).
    [CrossRef]
  8. V. Lehmann, Electrochemistry of Silicon (Wiley-VCH, Weinheim, Germany 2002).
    [CrossRef]
  9. D. Mangaiyarkarasi, M. B. H. Breese, Y. S. Ow, and C. Vijila, "Controlled blue-shift of the resonant wavelength in porous silicon microcavities using ion irradiation," Appl. Phys. Lett. 89, 021910-(1-3) (2006).
    [CrossRef]
  10. M. B. H. Breese, F. J. T. Champeaux, E. J. Teo, A. A. Bettiol, and D. Blackwood, "Hole transport through proton-irradiated p-type silicon wafers during electrochemical anodization," Phys. Rev. B 73, 035428 (2006).
    [CrossRef]
  11. D. S. Gemmell, "Channeling and related effects in the motion of charged particles through crystals" Rev. Mod. Phys. 46, 129-227 (1974).
    [CrossRef]
  12. L. C. Feldman, J. W. Mayer, S. T. Picraux, Materials Analysis by Ion Channeling (Acad. Press, New York, 1982).
  13. P. J. C. King, M. B. H. Breese, P. J. C. Smulders, P. R. Wilshaw and G. W. Grime, "The observation of a blocking to channeling transition for MeV protons at stacking faults in silicon. Phys. Rev. Lett. 74, 411-414 (1995).
    [CrossRef] [PubMed]
  14. M. B. H. Breese, P. J. C. King, P. J. C. Smulders, and G. W. Grime, "Dechanneling of MeV protons by 60º dislocations" Phys. Rev. B 51, 2742-2750 (1995).
    [CrossRef]
  15. M. B. H. Breese, D. N. Jamieson and P. J. C. King, Materials Analysis using a Nuclear Microprobe, (Wiley, New York, 1996).
  16. M. B. H. Breese, E. J. Teo, M. A. Rana, L. Huang, J. A. van Kan, F. Watt, and P. J. C. King, "Observation of many coherent oscillations for MeV protons transmitted through stacking faults," Phys. Rev. Lett. 92, 045503 (2004).
    [CrossRef] [PubMed]
  17. Ocean Optics http://www.oceanoptics.com/products/colorfilters.aspa>

2004

M. B. H. Breese, E. J. Teo, M. A. Rana, L. Huang, J. A. van Kan, F. Watt, and P. J. C. King, "Observation of many coherent oscillations for MeV protons transmitted through stacking faults," Phys. Rev. Lett. 92, 045503 (2004).
[CrossRef] [PubMed]

2002

N. Savage, "Linking with light," IEEE Spectrum 39, 32-36 (2002).
[CrossRef]

2001

A. Birner, R. B. Wehrspohn, U. Gösele, and K. Busch, "Silicon-Based Photonic Crystals," Adv. Mater. 13, 377-388 (2001).
[CrossRef]

1998

S. Nagata, C. Domoto, T. Nishimura, and K. Iwameji, "Single-mode optical waveguide fabricated by oxidization of selectively doped titanium porous silicon," Appl. Phys. Lett. 72, 2945-2947 (1998).
[CrossRef]

1997

M. G. Berger, R. Arens-Fischer, M. Kruger, S. Billat, H. Luth, S. Hillbrich, W. Theiß, and P. Grosse, "Dielectric filters made of PS: advanced performance by oxidation and new layer structures," Thin Solid Films 297, 237-240 (1997).
[CrossRef]

L. Pavesi, "Porous silicon dielectric multilayers and microcavities," Riv. Nuovo Cimento 20, 1-78 (1997).
[CrossRef]

1996

M. Araki, H. Koyama, and N. Koshida, "Controlled electroluminescence spectra of porous silicon diodes with a vertical optical cavity," Appl. Phys. Lett. 69, 2956-2958 (1996).
[CrossRef]

1995

P. J. C. King, M. B. H. Breese, P. J. C. Smulders, P. R. Wilshaw and G. W. Grime, "The observation of a blocking to channeling transition for MeV protons at stacking faults in silicon. Phys. Rev. Lett. 74, 411-414 (1995).
[CrossRef] [PubMed]

M. B. H. Breese, P. J. C. King, P. J. C. Smulders, and G. W. Grime, "Dechanneling of MeV protons by 60º dislocations" Phys. Rev. B 51, 2742-2750 (1995).
[CrossRef]

1994

G. Vincent, "Optical properties of porous silicon superlattices," Appl. Phys. Lett. 64, 2367-2369 (1994).
[CrossRef]

1974

D. S. Gemmell, "Channeling and related effects in the motion of charged particles through crystals" Rev. Mod. Phys. 46, 129-227 (1974).
[CrossRef]

Araki, M.

M. Araki, H. Koyama, and N. Koshida, "Controlled electroluminescence spectra of porous silicon diodes with a vertical optical cavity," Appl. Phys. Lett. 69, 2956-2958 (1996).
[CrossRef]

Arens-Fischer, R.

M. G. Berger, R. Arens-Fischer, M. Kruger, S. Billat, H. Luth, S. Hillbrich, W. Theiß, and P. Grosse, "Dielectric filters made of PS: advanced performance by oxidation and new layer structures," Thin Solid Films 297, 237-240 (1997).
[CrossRef]

Berger, M. G.

M. G. Berger, R. Arens-Fischer, M. Kruger, S. Billat, H. Luth, S. Hillbrich, W. Theiß, and P. Grosse, "Dielectric filters made of PS: advanced performance by oxidation and new layer structures," Thin Solid Films 297, 237-240 (1997).
[CrossRef]

Bettiol, A. A.

M. B. H. Breese, F. J. T. Champeaux, E. J. Teo, A. A. Bettiol, and D. Blackwood, "Hole transport through proton-irradiated p-type silicon wafers during electrochemical anodization," Phys. Rev. B 73, 035428 (2006).
[CrossRef]

Billat, S.

M. G. Berger, R. Arens-Fischer, M. Kruger, S. Billat, H. Luth, S. Hillbrich, W. Theiß, and P. Grosse, "Dielectric filters made of PS: advanced performance by oxidation and new layer structures," Thin Solid Films 297, 237-240 (1997).
[CrossRef]

Birner, A.

A. Birner, R. B. Wehrspohn, U. Gösele, and K. Busch, "Silicon-Based Photonic Crystals," Adv. Mater. 13, 377-388 (2001).
[CrossRef]

Blackwood, D.

M. B. H. Breese, F. J. T. Champeaux, E. J. Teo, A. A. Bettiol, and D. Blackwood, "Hole transport through proton-irradiated p-type silicon wafers during electrochemical anodization," Phys. Rev. B 73, 035428 (2006).
[CrossRef]

Breese, M. B. H.

M. B. H. Breese, E. J. Teo, M. A. Rana, L. Huang, J. A. van Kan, F. Watt, and P. J. C. King, "Observation of many coherent oscillations for MeV protons transmitted through stacking faults," Phys. Rev. Lett. 92, 045503 (2004).
[CrossRef] [PubMed]

M. B. H. Breese, P. J. C. King, P. J. C. Smulders, and G. W. Grime, "Dechanneling of MeV protons by 60º dislocations" Phys. Rev. B 51, 2742-2750 (1995).
[CrossRef]

P. J. C. King, M. B. H. Breese, P. J. C. Smulders, P. R. Wilshaw and G. W. Grime, "The observation of a blocking to channeling transition for MeV protons at stacking faults in silicon. Phys. Rev. Lett. 74, 411-414 (1995).
[CrossRef] [PubMed]

M. B. H. Breese, F. J. T. Champeaux, E. J. Teo, A. A. Bettiol, and D. Blackwood, "Hole transport through proton-irradiated p-type silicon wafers during electrochemical anodization," Phys. Rev. B 73, 035428 (2006).
[CrossRef]

D. Mangaiyarkarasi, M. B. H. Breese, Y. S. Ow, and C. Vijila, "Controlled blue-shift of the resonant wavelength in porous silicon microcavities using ion irradiation," Appl. Phys. Lett. 89, 021910-(1-3) (2006).
[CrossRef]

Busch, K.

A. Birner, R. B. Wehrspohn, U. Gösele, and K. Busch, "Silicon-Based Photonic Crystals," Adv. Mater. 13, 377-388 (2001).
[CrossRef]

Champeaux, F. J. T.

M. B. H. Breese, F. J. T. Champeaux, E. J. Teo, A. A. Bettiol, and D. Blackwood, "Hole transport through proton-irradiated p-type silicon wafers during electrochemical anodization," Phys. Rev. B 73, 035428 (2006).
[CrossRef]

Domoto, C.

S. Nagata, C. Domoto, T. Nishimura, and K. Iwameji, "Single-mode optical waveguide fabricated by oxidization of selectively doped titanium porous silicon," Appl. Phys. Lett. 72, 2945-2947 (1998).
[CrossRef]

Gemmell, D. S.

D. S. Gemmell, "Channeling and related effects in the motion of charged particles through crystals" Rev. Mod. Phys. 46, 129-227 (1974).
[CrossRef]

Gösele, U.

A. Birner, R. B. Wehrspohn, U. Gösele, and K. Busch, "Silicon-Based Photonic Crystals," Adv. Mater. 13, 377-388 (2001).
[CrossRef]

Grime, G. W.

P. J. C. King, M. B. H. Breese, P. J. C. Smulders, P. R. Wilshaw and G. W. Grime, "The observation of a blocking to channeling transition for MeV protons at stacking faults in silicon. Phys. Rev. Lett. 74, 411-414 (1995).
[CrossRef] [PubMed]

M. B. H. Breese, P. J. C. King, P. J. C. Smulders, and G. W. Grime, "Dechanneling of MeV protons by 60º dislocations" Phys. Rev. B 51, 2742-2750 (1995).
[CrossRef]

Grosse, P.

M. G. Berger, R. Arens-Fischer, M. Kruger, S. Billat, H. Luth, S. Hillbrich, W. Theiß, and P. Grosse, "Dielectric filters made of PS: advanced performance by oxidation and new layer structures," Thin Solid Films 297, 237-240 (1997).
[CrossRef]

Hillbrich, S.

M. G. Berger, R. Arens-Fischer, M. Kruger, S. Billat, H. Luth, S. Hillbrich, W. Theiß, and P. Grosse, "Dielectric filters made of PS: advanced performance by oxidation and new layer structures," Thin Solid Films 297, 237-240 (1997).
[CrossRef]

Huang, L.

M. B. H. Breese, E. J. Teo, M. A. Rana, L. Huang, J. A. van Kan, F. Watt, and P. J. C. King, "Observation of many coherent oscillations for MeV protons transmitted through stacking faults," Phys. Rev. Lett. 92, 045503 (2004).
[CrossRef] [PubMed]

Iwameji, K.

S. Nagata, C. Domoto, T. Nishimura, and K. Iwameji, "Single-mode optical waveguide fabricated by oxidization of selectively doped titanium porous silicon," Appl. Phys. Lett. 72, 2945-2947 (1998).
[CrossRef]

King, P. J. C.

M. B. H. Breese, E. J. Teo, M. A. Rana, L. Huang, J. A. van Kan, F. Watt, and P. J. C. King, "Observation of many coherent oscillations for MeV protons transmitted through stacking faults," Phys. Rev. Lett. 92, 045503 (2004).
[CrossRef] [PubMed]

M. B. H. Breese, P. J. C. King, P. J. C. Smulders, and G. W. Grime, "Dechanneling of MeV protons by 60º dislocations" Phys. Rev. B 51, 2742-2750 (1995).
[CrossRef]

P. J. C. King, M. B. H. Breese, P. J. C. Smulders, P. R. Wilshaw and G. W. Grime, "The observation of a blocking to channeling transition for MeV protons at stacking faults in silicon. Phys. Rev. Lett. 74, 411-414 (1995).
[CrossRef] [PubMed]

Koshida, N.

M. Araki, H. Koyama, and N. Koshida, "Controlled electroluminescence spectra of porous silicon diodes with a vertical optical cavity," Appl. Phys. Lett. 69, 2956-2958 (1996).
[CrossRef]

Koyama, H.

M. Araki, H. Koyama, and N. Koshida, "Controlled electroluminescence spectra of porous silicon diodes with a vertical optical cavity," Appl. Phys. Lett. 69, 2956-2958 (1996).
[CrossRef]

Kruger, M.

M. G. Berger, R. Arens-Fischer, M. Kruger, S. Billat, H. Luth, S. Hillbrich, W. Theiß, and P. Grosse, "Dielectric filters made of PS: advanced performance by oxidation and new layer structures," Thin Solid Films 297, 237-240 (1997).
[CrossRef]

Luth, H.

M. G. Berger, R. Arens-Fischer, M. Kruger, S. Billat, H. Luth, S. Hillbrich, W. Theiß, and P. Grosse, "Dielectric filters made of PS: advanced performance by oxidation and new layer structures," Thin Solid Films 297, 237-240 (1997).
[CrossRef]

Mangaiyarkarasi, D.

D. Mangaiyarkarasi, M. B. H. Breese, Y. S. Ow, and C. Vijila, "Controlled blue-shift of the resonant wavelength in porous silicon microcavities using ion irradiation," Appl. Phys. Lett. 89, 021910-(1-3) (2006).
[CrossRef]

Nagata, S.

S. Nagata, C. Domoto, T. Nishimura, and K. Iwameji, "Single-mode optical waveguide fabricated by oxidization of selectively doped titanium porous silicon," Appl. Phys. Lett. 72, 2945-2947 (1998).
[CrossRef]

Nishimura, T.

S. Nagata, C. Domoto, T. Nishimura, and K. Iwameji, "Single-mode optical waveguide fabricated by oxidization of selectively doped titanium porous silicon," Appl. Phys. Lett. 72, 2945-2947 (1998).
[CrossRef]

Ow, Y. S.

D. Mangaiyarkarasi, M. B. H. Breese, Y. S. Ow, and C. Vijila, "Controlled blue-shift of the resonant wavelength in porous silicon microcavities using ion irradiation," Appl. Phys. Lett. 89, 021910-(1-3) (2006).
[CrossRef]

Pavesi, L.

L. Pavesi, "Porous silicon dielectric multilayers and microcavities," Riv. Nuovo Cimento 20, 1-78 (1997).
[CrossRef]

Rana, M. A.

M. B. H. Breese, E. J. Teo, M. A. Rana, L. Huang, J. A. van Kan, F. Watt, and P. J. C. King, "Observation of many coherent oscillations for MeV protons transmitted through stacking faults," Phys. Rev. Lett. 92, 045503 (2004).
[CrossRef] [PubMed]

Savage, N.

N. Savage, "Linking with light," IEEE Spectrum 39, 32-36 (2002).
[CrossRef]

Smulders, P. J. C.

P. J. C. King, M. B. H. Breese, P. J. C. Smulders, P. R. Wilshaw and G. W. Grime, "The observation of a blocking to channeling transition for MeV protons at stacking faults in silicon. Phys. Rev. Lett. 74, 411-414 (1995).
[CrossRef] [PubMed]

M. B. H. Breese, P. J. C. King, P. J. C. Smulders, and G. W. Grime, "Dechanneling of MeV protons by 60º dislocations" Phys. Rev. B 51, 2742-2750 (1995).
[CrossRef]

Teo, E. J.

M. B. H. Breese, E. J. Teo, M. A. Rana, L. Huang, J. A. van Kan, F. Watt, and P. J. C. King, "Observation of many coherent oscillations for MeV protons transmitted through stacking faults," Phys. Rev. Lett. 92, 045503 (2004).
[CrossRef] [PubMed]

M. B. H. Breese, F. J. T. Champeaux, E. J. Teo, A. A. Bettiol, and D. Blackwood, "Hole transport through proton-irradiated p-type silicon wafers during electrochemical anodization," Phys. Rev. B 73, 035428 (2006).
[CrossRef]

Theiß, W.

M. G. Berger, R. Arens-Fischer, M. Kruger, S. Billat, H. Luth, S. Hillbrich, W. Theiß, and P. Grosse, "Dielectric filters made of PS: advanced performance by oxidation and new layer structures," Thin Solid Films 297, 237-240 (1997).
[CrossRef]

van Kan, J. A.

M. B. H. Breese, E. J. Teo, M. A. Rana, L. Huang, J. A. van Kan, F. Watt, and P. J. C. King, "Observation of many coherent oscillations for MeV protons transmitted through stacking faults," Phys. Rev. Lett. 92, 045503 (2004).
[CrossRef] [PubMed]

Vijila, C.

D. Mangaiyarkarasi, M. B. H. Breese, Y. S. Ow, and C. Vijila, "Controlled blue-shift of the resonant wavelength in porous silicon microcavities using ion irradiation," Appl. Phys. Lett. 89, 021910-(1-3) (2006).
[CrossRef]

Vincent, G.

G. Vincent, "Optical properties of porous silicon superlattices," Appl. Phys. Lett. 64, 2367-2369 (1994).
[CrossRef]

Watt, F.

M. B. H. Breese, E. J. Teo, M. A. Rana, L. Huang, J. A. van Kan, F. Watt, and P. J. C. King, "Observation of many coherent oscillations for MeV protons transmitted through stacking faults," Phys. Rev. Lett. 92, 045503 (2004).
[CrossRef] [PubMed]

Wehrspohn, R. B.

A. Birner, R. B. Wehrspohn, U. Gösele, and K. Busch, "Silicon-Based Photonic Crystals," Adv. Mater. 13, 377-388 (2001).
[CrossRef]

Wilshaw, P. R.

P. J. C. King, M. B. H. Breese, P. J. C. Smulders, P. R. Wilshaw and G. W. Grime, "The observation of a blocking to channeling transition for MeV protons at stacking faults in silicon. Phys. Rev. Lett. 74, 411-414 (1995).
[CrossRef] [PubMed]

Adv. Mater.

A. Birner, R. B. Wehrspohn, U. Gösele, and K. Busch, "Silicon-Based Photonic Crystals," Adv. Mater. 13, 377-388 (2001).
[CrossRef]

Appl. Phys. Lett.

G. Vincent, "Optical properties of porous silicon superlattices," Appl. Phys. Lett. 64, 2367-2369 (1994).
[CrossRef]

M. Araki, H. Koyama, and N. Koshida, "Controlled electroluminescence spectra of porous silicon diodes with a vertical optical cavity," Appl. Phys. Lett. 69, 2956-2958 (1996).
[CrossRef]

S. Nagata, C. Domoto, T. Nishimura, and K. Iwameji, "Single-mode optical waveguide fabricated by oxidization of selectively doped titanium porous silicon," Appl. Phys. Lett. 72, 2945-2947 (1998).
[CrossRef]

IEEE Spectrum

N. Savage, "Linking with light," IEEE Spectrum 39, 32-36 (2002).
[CrossRef]

Phys. Rev. B

M. B. H. Breese, P. J. C. King, P. J. C. Smulders, and G. W. Grime, "Dechanneling of MeV protons by 60º dislocations" Phys. Rev. B 51, 2742-2750 (1995).
[CrossRef]

Phys. Rev. Lett.

M. B. H. Breese, E. J. Teo, M. A. Rana, L. Huang, J. A. van Kan, F. Watt, and P. J. C. King, "Observation of many coherent oscillations for MeV protons transmitted through stacking faults," Phys. Rev. Lett. 92, 045503 (2004).
[CrossRef] [PubMed]

P. J. C. King, M. B. H. Breese, P. J. C. Smulders, P. R. Wilshaw and G. W. Grime, "The observation of a blocking to channeling transition for MeV protons at stacking faults in silicon. Phys. Rev. Lett. 74, 411-414 (1995).
[CrossRef] [PubMed]

Rev. Mod. Phys.

D. S. Gemmell, "Channeling and related effects in the motion of charged particles through crystals" Rev. Mod. Phys. 46, 129-227 (1974).
[CrossRef]

Riv. Nuovo Cimento

L. Pavesi, "Porous silicon dielectric multilayers and microcavities," Riv. Nuovo Cimento 20, 1-78 (1997).
[CrossRef]

Thin Solid Films

M. G. Berger, R. Arens-Fischer, M. Kruger, S. Billat, H. Luth, S. Hillbrich, W. Theiß, and P. Grosse, "Dielectric filters made of PS: advanced performance by oxidation and new layer structures," Thin Solid Films 297, 237-240 (1997).
[CrossRef]

Other

V. Lehmann, Electrochemistry of Silicon (Wiley-VCH, Weinheim, Germany 2002).
[CrossRef]

D. Mangaiyarkarasi, M. B. H. Breese, Y. S. Ow, and C. Vijila, "Controlled blue-shift of the resonant wavelength in porous silicon microcavities using ion irradiation," Appl. Phys. Lett. 89, 021910-(1-3) (2006).
[CrossRef]

M. B. H. Breese, F. J. T. Champeaux, E. J. Teo, A. A. Bettiol, and D. Blackwood, "Hole transport through proton-irradiated p-type silicon wafers during electrochemical anodization," Phys. Rev. B 73, 035428 (2006).
[CrossRef]

L. C. Feldman, J. W. Mayer, S. T. Picraux, Materials Analysis by Ion Channeling (Acad. Press, New York, 1982).

Ocean Optics http://www.oceanoptics.com/products/colorfilters.aspa>

M. B. H. Breese, D. N. Jamieson and P. J. C. King, Materials Analysis using a Nuclear Microprobe, (Wiley, New York, 1996).

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Figures (4)

Fig. 1.
Fig. 1.

(a). Peak reflected wavelength of porous silicon Bragg reflectors versus proton irradiation dose. The corresponding reflective colour is also shown. (b), (c), (d) respectively show optical images of the reflected light from 60 × 60 μm2 regions of porous silicon Bragg reflectors patterned with 10 μm and 2 μm wide colour pixels and 2 μm wide colour stripes.

Fig. 2.
Fig. 2.

(a). Cross-section SEM of the porous silicon Bragg reflector patterned with 2 μm wide lines in Fig. 1(d), from the region indicated by the dashed white line, with the unirradiated red background at the left side. (b) Linescan of recorded reflected intensity for red, green, blue from the 2 μm pixels in Fig. 1(c).

Fig. 3.
Fig. 3.

(a). Optical image of the reflected light from a region of a porous silicon Bragg reflector formed by irradiation with 1 μm wide lines in channeled alignment. A SEM image of the same region in which the porous silicon removed to show the surface profile is shown in the lower half. (b) Linescan of recorded reflected intensity for red, green, blue from the 1 μm wide irradiated lines in Fig. 3(a).

Fig 4.
Fig 4.

Different effects of channeled and random irradiation. (a) adjacent regions are irradiated with two different doses (lower dose to the left) with the wafer in random and channeled alignment. (b) during anodisation the hole currents flowing through the wafer are deflected round the irradiated regions. (c) shows the silicon surface remaining after anodisation, the Bragg reflecting layers are not shown, only the reflected colour. (d) SEM images of the surfaces of 1 μm wide irradiated lines in (left) random and (right) channeled irradiation.

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