Abstract

Cr–Ti multilayers with ultrashort periods of 1.392.04nm have been grown for the first time as highly reflective, soft-x-ray multilayer, near-normal incidence mirrors for transition radiation and Čherenkov radiation x-ray sources based on the Ti–2p absorption edge at E=452eV(λ=2.74nm). Hard, as well as soft, x-ay reflectivity and transmission electron microscopy were used to characterize the nanostructure of the mirrors. To achieve minimal accumulated roughness, improved interface flatness, and to avoid intermixing at the interfaces, each individual layer was engineered by use of a two-stage ion assistance process during magnetron sputter deposition: The first 0.3nm of each Ti and Cr layer was grown without ion assistance, and the remaining 0.390.72nm of the layers were grown with high ion–neutral flux ratios Φ˙ (ΦTi=3.3,ΦCr=2.2) and a low energy Eion(ETi=23.7andECr=21.2), ion assistance. A maximum soft-x-ray reflectivity of R=2.1% at near-normal incidence (78.8°) was achieved for a multilayer mirror containing 100 bilayers with a modulation period of 1.379nm and a layer thickness ratio of Γ=0.5. For a polarizing multilayer mirror with 150 bilayers designed for operation at the Brewster angle, 45°, an extinction ratio, Rs/Rp, of 266 was achieved with an absolute reflectivity of R=4.3%.

© 2006 Optical Society of America

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  1. W. Knulst, O. J. Luiten, M. J. van der Wiel, and J. Verhoeven, "Tabletop soft x-ray source based on 5-10 MeV LINACs," in Proceedings of the Seventh European Particle Accelerator Conference (Austrian Academy of Sciences, 2000), pp. 2609-2611.
  2. H.-Ch. Mertins, F. Schäfers, H. Grimmer, D. Clemens, P. Böni, and M. Horisberger, "W/C, W/Ti, Ni/Ti, and Ni/V multilayers for the soft-x-ray range: experimental investigation with synchrotron radiation," Appl. Opt. 37, 1873-1882 (1998).
    [CrossRef]
  3. E. Spiller, Multilayer Optics for Soft X Rays (Plenum, 1986).
  4. D. L. Windt, "IMD: software for modeling the optical properties of multilayer films," Comput. Phys. 12, 360-370 (1998).
    [CrossRef]
  5. B. L. Henke, E. M. Gullikson, and J. C. Davis, "X ray interactions: photoabsorption, scattering, transmission and reflection at E= 50-30000 eV, Z = 1-92," At. Data Nucl. Data Tables 54, 181-342, (1993).
    [CrossRef]
  6. D. T. Atwood, Soft X Rays and Extreme Ultraviolet Radiation (Cambridge University Press, 1999), pp. 55-95.
  7. M. Yamamoto and T. Namioka, "Layer-by-layer design method of soft x ray multilayers," Appl. Opt. 31, 1622-1630 (1992).
    [CrossRef] [PubMed]
  8. F. Eriksson, "Soft x ray multilayer mirrors," Ph.D. dissertation (Thin Film Physics Division, IFM, Linköping University, Sweden, 2004).
  9. C. Engström, T. Berlind, J. Birch, L. Hultman, I. P. Ivanov, S. R. Kirkpatrick, and S. Rohde, "Design, plasma studies, and ion assisted thin film growth in an unbalanced dual target magnetron sputtering system with a solenoid coil," Vacuum 56, 107-113 (2000).
    [CrossRef]
  10. F. Eriksson, G. A. Johansson, H. M. Hertz, and J. Birch, "Enhanced soft x ray reflectivity of Cr/Sc multilayers by ion-assisted sputter deposition," Opt. Eng. 41, 2903-2909 (2002).
    [CrossRef]
  11. J. Als-Nielsen and D. McMorrow, Elements of Modern X Ray Physics (Wiley, 2001), Chap. 1, pp. 24-26.
  12. J. M. Freitag and B. M. Clemens, "Nonspecular x ray reflectivity study of roughness scaling in Si/Mo Multilayers," J. Appl. Phys. , 89, 1101-1107 (2001).
    [CrossRef]
  13. H. M. Hertz, G. A. Johansson, H. Stollberg, J. de Groot, O. Hemberg, A. Holmberg, S. Rehbein, P. Jansson, F. Eriksson, and J. Birch, "Table-top x ray microscopy: sources, optics and applications," J. Phys. IV 104, 115-119 (2003).

2003 (1)

H. M. Hertz, G. A. Johansson, H. Stollberg, J. de Groot, O. Hemberg, A. Holmberg, S. Rehbein, P. Jansson, F. Eriksson, and J. Birch, "Table-top x ray microscopy: sources, optics and applications," J. Phys. IV 104, 115-119 (2003).

2002 (1)

F. Eriksson, G. A. Johansson, H. M. Hertz, and J. Birch, "Enhanced soft x ray reflectivity of Cr/Sc multilayers by ion-assisted sputter deposition," Opt. Eng. 41, 2903-2909 (2002).
[CrossRef]

2001 (1)

J. M. Freitag and B. M. Clemens, "Nonspecular x ray reflectivity study of roughness scaling in Si/Mo Multilayers," J. Appl. Phys. , 89, 1101-1107 (2001).
[CrossRef]

2000 (1)

C. Engström, T. Berlind, J. Birch, L. Hultman, I. P. Ivanov, S. R. Kirkpatrick, and S. Rohde, "Design, plasma studies, and ion assisted thin film growth in an unbalanced dual target magnetron sputtering system with a solenoid coil," Vacuum 56, 107-113 (2000).
[CrossRef]

1998 (2)

H.-Ch. Mertins, F. Schäfers, H. Grimmer, D. Clemens, P. Böni, and M. Horisberger, "W/C, W/Ti, Ni/Ti, and Ni/V multilayers for the soft-x-ray range: experimental investigation with synchrotron radiation," Appl. Opt. 37, 1873-1882 (1998).
[CrossRef]

D. L. Windt, "IMD: software for modeling the optical properties of multilayer films," Comput. Phys. 12, 360-370 (1998).
[CrossRef]

1993 (1)

B. L. Henke, E. M. Gullikson, and J. C. Davis, "X ray interactions: photoabsorption, scattering, transmission and reflection at E= 50-30000 eV, Z = 1-92," At. Data Nucl. Data Tables 54, 181-342, (1993).
[CrossRef]

1992 (1)

M. Yamamoto and T. Namioka, "Layer-by-layer design method of soft x ray multilayers," Appl. Opt. 31, 1622-1630 (1992).
[CrossRef] [PubMed]

Als-Nielsen, J.

J. Als-Nielsen and D. McMorrow, Elements of Modern X Ray Physics (Wiley, 2001), Chap. 1, pp. 24-26.

Atwood, D.

D. T. Atwood, Soft X Rays and Extreme Ultraviolet Radiation (Cambridge University Press, 1999), pp. 55-95.

Berlind, T.

C. Engström, T. Berlind, J. Birch, L. Hultman, I. P. Ivanov, S. R. Kirkpatrick, and S. Rohde, "Design, plasma studies, and ion assisted thin film growth in an unbalanced dual target magnetron sputtering system with a solenoid coil," Vacuum 56, 107-113 (2000).
[CrossRef]

Birch, J.

H. M. Hertz, G. A. Johansson, H. Stollberg, J. de Groot, O. Hemberg, A. Holmberg, S. Rehbein, P. Jansson, F. Eriksson, and J. Birch, "Table-top x ray microscopy: sources, optics and applications," J. Phys. IV 104, 115-119 (2003).

F. Eriksson, G. A. Johansson, H. M. Hertz, and J. Birch, "Enhanced soft x ray reflectivity of Cr/Sc multilayers by ion-assisted sputter deposition," Opt. Eng. 41, 2903-2909 (2002).
[CrossRef]

C. Engström, T. Berlind, J. Birch, L. Hultman, I. P. Ivanov, S. R. Kirkpatrick, and S. Rohde, "Design, plasma studies, and ion assisted thin film growth in an unbalanced dual target magnetron sputtering system with a solenoid coil," Vacuum 56, 107-113 (2000).
[CrossRef]

Böni, P.

H.-Ch. Mertins, F. Schäfers, H. Grimmer, D. Clemens, P. Böni, and M. Horisberger, "W/C, W/Ti, Ni/Ti, and Ni/V multilayers for the soft-x-ray range: experimental investigation with synchrotron radiation," Appl. Opt. 37, 1873-1882 (1998).
[CrossRef]

Clemens, B. M.

J. M. Freitag and B. M. Clemens, "Nonspecular x ray reflectivity study of roughness scaling in Si/Mo Multilayers," J. Appl. Phys. , 89, 1101-1107 (2001).
[CrossRef]

Clemens, D.

H.-Ch. Mertins, F. Schäfers, H. Grimmer, D. Clemens, P. Böni, and M. Horisberger, "W/C, W/Ti, Ni/Ti, and Ni/V multilayers for the soft-x-ray range: experimental investigation with synchrotron radiation," Appl. Opt. 37, 1873-1882 (1998).
[CrossRef]

Davis, J. C.

B. L. Henke, E. M. Gullikson, and J. C. Davis, "X ray interactions: photoabsorption, scattering, transmission and reflection at E= 50-30000 eV, Z = 1-92," At. Data Nucl. Data Tables 54, 181-342, (1993).
[CrossRef]

de Groot, J.

H. M. Hertz, G. A. Johansson, H. Stollberg, J. de Groot, O. Hemberg, A. Holmberg, S. Rehbein, P. Jansson, F. Eriksson, and J. Birch, "Table-top x ray microscopy: sources, optics and applications," J. Phys. IV 104, 115-119 (2003).

Engström, C.

C. Engström, T. Berlind, J. Birch, L. Hultman, I. P. Ivanov, S. R. Kirkpatrick, and S. Rohde, "Design, plasma studies, and ion assisted thin film growth in an unbalanced dual target magnetron sputtering system with a solenoid coil," Vacuum 56, 107-113 (2000).
[CrossRef]

Eriksson, F.

H. M. Hertz, G. A. Johansson, H. Stollberg, J. de Groot, O. Hemberg, A. Holmberg, S. Rehbein, P. Jansson, F. Eriksson, and J. Birch, "Table-top x ray microscopy: sources, optics and applications," J. Phys. IV 104, 115-119 (2003).

F. Eriksson, G. A. Johansson, H. M. Hertz, and J. Birch, "Enhanced soft x ray reflectivity of Cr/Sc multilayers by ion-assisted sputter deposition," Opt. Eng. 41, 2903-2909 (2002).
[CrossRef]

F. Eriksson, "Soft x ray multilayer mirrors," Ph.D. dissertation (Thin Film Physics Division, IFM, Linköping University, Sweden, 2004).

Freitag, J. M.

J. M. Freitag and B. M. Clemens, "Nonspecular x ray reflectivity study of roughness scaling in Si/Mo Multilayers," J. Appl. Phys. , 89, 1101-1107 (2001).
[CrossRef]

Grimmer, H.

H.-Ch. Mertins, F. Schäfers, H. Grimmer, D. Clemens, P. Böni, and M. Horisberger, "W/C, W/Ti, Ni/Ti, and Ni/V multilayers for the soft-x-ray range: experimental investigation with synchrotron radiation," Appl. Opt. 37, 1873-1882 (1998).
[CrossRef]

Gullikson, E. M.

B. L. Henke, E. M. Gullikson, and J. C. Davis, "X ray interactions: photoabsorption, scattering, transmission and reflection at E= 50-30000 eV, Z = 1-92," At. Data Nucl. Data Tables 54, 181-342, (1993).
[CrossRef]

Hemberg, O.

H. M. Hertz, G. A. Johansson, H. Stollberg, J. de Groot, O. Hemberg, A. Holmberg, S. Rehbein, P. Jansson, F. Eriksson, and J. Birch, "Table-top x ray microscopy: sources, optics and applications," J. Phys. IV 104, 115-119 (2003).

Henke, B. L.

B. L. Henke, E. M. Gullikson, and J. C. Davis, "X ray interactions: photoabsorption, scattering, transmission and reflection at E= 50-30000 eV, Z = 1-92," At. Data Nucl. Data Tables 54, 181-342, (1993).
[CrossRef]

Hertz, H. M.

H. M. Hertz, G. A. Johansson, H. Stollberg, J. de Groot, O. Hemberg, A. Holmberg, S. Rehbein, P. Jansson, F. Eriksson, and J. Birch, "Table-top x ray microscopy: sources, optics and applications," J. Phys. IV 104, 115-119 (2003).

F. Eriksson, G. A. Johansson, H. M. Hertz, and J. Birch, "Enhanced soft x ray reflectivity of Cr/Sc multilayers by ion-assisted sputter deposition," Opt. Eng. 41, 2903-2909 (2002).
[CrossRef]

Holmberg, A.

H. M. Hertz, G. A. Johansson, H. Stollberg, J. de Groot, O. Hemberg, A. Holmberg, S. Rehbein, P. Jansson, F. Eriksson, and J. Birch, "Table-top x ray microscopy: sources, optics and applications," J. Phys. IV 104, 115-119 (2003).

Horisberger, M.

H.-Ch. Mertins, F. Schäfers, H. Grimmer, D. Clemens, P. Böni, and M. Horisberger, "W/C, W/Ti, Ni/Ti, and Ni/V multilayers for the soft-x-ray range: experimental investigation with synchrotron radiation," Appl. Opt. 37, 1873-1882 (1998).
[CrossRef]

Hultman, L.

C. Engström, T. Berlind, J. Birch, L. Hultman, I. P. Ivanov, S. R. Kirkpatrick, and S. Rohde, "Design, plasma studies, and ion assisted thin film growth in an unbalanced dual target magnetron sputtering system with a solenoid coil," Vacuum 56, 107-113 (2000).
[CrossRef]

Ivanov, I. P.

C. Engström, T. Berlind, J. Birch, L. Hultman, I. P. Ivanov, S. R. Kirkpatrick, and S. Rohde, "Design, plasma studies, and ion assisted thin film growth in an unbalanced dual target magnetron sputtering system with a solenoid coil," Vacuum 56, 107-113 (2000).
[CrossRef]

Jansson, P.

H. M. Hertz, G. A. Johansson, H. Stollberg, J. de Groot, O. Hemberg, A. Holmberg, S. Rehbein, P. Jansson, F. Eriksson, and J. Birch, "Table-top x ray microscopy: sources, optics and applications," J. Phys. IV 104, 115-119 (2003).

Johansson, G. A.

H. M. Hertz, G. A. Johansson, H. Stollberg, J. de Groot, O. Hemberg, A. Holmberg, S. Rehbein, P. Jansson, F. Eriksson, and J. Birch, "Table-top x ray microscopy: sources, optics and applications," J. Phys. IV 104, 115-119 (2003).

F. Eriksson, G. A. Johansson, H. M. Hertz, and J. Birch, "Enhanced soft x ray reflectivity of Cr/Sc multilayers by ion-assisted sputter deposition," Opt. Eng. 41, 2903-2909 (2002).
[CrossRef]

Kirkpatrick, S. R.

C. Engström, T. Berlind, J. Birch, L. Hultman, I. P. Ivanov, S. R. Kirkpatrick, and S. Rohde, "Design, plasma studies, and ion assisted thin film growth in an unbalanced dual target magnetron sputtering system with a solenoid coil," Vacuum 56, 107-113 (2000).
[CrossRef]

Knulst, W.

W. Knulst, O. J. Luiten, M. J. van der Wiel, and J. Verhoeven, "Tabletop soft x-ray source based on 5-10 MeV LINACs," in Proceedings of the Seventh European Particle Accelerator Conference (Austrian Academy of Sciences, 2000), pp. 2609-2611.

Luiten, O. J.

W. Knulst, O. J. Luiten, M. J. van der Wiel, and J. Verhoeven, "Tabletop soft x-ray source based on 5-10 MeV LINACs," in Proceedings of the Seventh European Particle Accelerator Conference (Austrian Academy of Sciences, 2000), pp. 2609-2611.

McMorrow, D.

J. Als-Nielsen and D. McMorrow, Elements of Modern X Ray Physics (Wiley, 2001), Chap. 1, pp. 24-26.

Mertins, H.-Ch.

H.-Ch. Mertins, F. Schäfers, H. Grimmer, D. Clemens, P. Böni, and M. Horisberger, "W/C, W/Ti, Ni/Ti, and Ni/V multilayers for the soft-x-ray range: experimental investigation with synchrotron radiation," Appl. Opt. 37, 1873-1882 (1998).
[CrossRef]

Namioka, T.

M. Yamamoto and T. Namioka, "Layer-by-layer design method of soft x ray multilayers," Appl. Opt. 31, 1622-1630 (1992).
[CrossRef] [PubMed]

Rehbein, S.

H. M. Hertz, G. A. Johansson, H. Stollberg, J. de Groot, O. Hemberg, A. Holmberg, S. Rehbein, P. Jansson, F. Eriksson, and J. Birch, "Table-top x ray microscopy: sources, optics and applications," J. Phys. IV 104, 115-119 (2003).

Rohde, S.

C. Engström, T. Berlind, J. Birch, L. Hultman, I. P. Ivanov, S. R. Kirkpatrick, and S. Rohde, "Design, plasma studies, and ion assisted thin film growth in an unbalanced dual target magnetron sputtering system with a solenoid coil," Vacuum 56, 107-113 (2000).
[CrossRef]

Schäfers, F.

H.-Ch. Mertins, F. Schäfers, H. Grimmer, D. Clemens, P. Böni, and M. Horisberger, "W/C, W/Ti, Ni/Ti, and Ni/V multilayers for the soft-x-ray range: experimental investigation with synchrotron radiation," Appl. Opt. 37, 1873-1882 (1998).
[CrossRef]

Spiller, E.

E. Spiller, Multilayer Optics for Soft X Rays (Plenum, 1986).

Stollberg, H.

H. M. Hertz, G. A. Johansson, H. Stollberg, J. de Groot, O. Hemberg, A. Holmberg, S. Rehbein, P. Jansson, F. Eriksson, and J. Birch, "Table-top x ray microscopy: sources, optics and applications," J. Phys. IV 104, 115-119 (2003).

van der Wiel, M. J.

W. Knulst, O. J. Luiten, M. J. van der Wiel, and J. Verhoeven, "Tabletop soft x-ray source based on 5-10 MeV LINACs," in Proceedings of the Seventh European Particle Accelerator Conference (Austrian Academy of Sciences, 2000), pp. 2609-2611.

Verhoeven, J.

W. Knulst, O. J. Luiten, M. J. van der Wiel, and J. Verhoeven, "Tabletop soft x-ray source based on 5-10 MeV LINACs," in Proceedings of the Seventh European Particle Accelerator Conference (Austrian Academy of Sciences, 2000), pp. 2609-2611.

Windt, D. L.

D. L. Windt, "IMD: software for modeling the optical properties of multilayer films," Comput. Phys. 12, 360-370 (1998).
[CrossRef]

Yamamoto, M.

M. Yamamoto and T. Namioka, "Layer-by-layer design method of soft x ray multilayers," Appl. Opt. 31, 1622-1630 (1992).
[CrossRef] [PubMed]

Appl. Opt. (2)

H.-Ch. Mertins, F. Schäfers, H. Grimmer, D. Clemens, P. Böni, and M. Horisberger, "W/C, W/Ti, Ni/Ti, and Ni/V multilayers for the soft-x-ray range: experimental investigation with synchrotron radiation," Appl. Opt. 37, 1873-1882 (1998).
[CrossRef]

M. Yamamoto and T. Namioka, "Layer-by-layer design method of soft x ray multilayers," Appl. Opt. 31, 1622-1630 (1992).
[CrossRef] [PubMed]

At. Data Nucl. Data Tables (1)

B. L. Henke, E. M. Gullikson, and J. C. Davis, "X ray interactions: photoabsorption, scattering, transmission and reflection at E= 50-30000 eV, Z = 1-92," At. Data Nucl. Data Tables 54, 181-342, (1993).
[CrossRef]

Comput. Phys. (1)

D. L. Windt, "IMD: software for modeling the optical properties of multilayer films," Comput. Phys. 12, 360-370 (1998).
[CrossRef]

J. Appl. Phys. (1)

J. M. Freitag and B. M. Clemens, "Nonspecular x ray reflectivity study of roughness scaling in Si/Mo Multilayers," J. Appl. Phys. , 89, 1101-1107 (2001).
[CrossRef]

J. Phys. IV (1)

H. M. Hertz, G. A. Johansson, H. Stollberg, J. de Groot, O. Hemberg, A. Holmberg, S. Rehbein, P. Jansson, F. Eriksson, and J. Birch, "Table-top x ray microscopy: sources, optics and applications," J. Phys. IV 104, 115-119 (2003).

Opt. Eng. (1)

F. Eriksson, G. A. Johansson, H. M. Hertz, and J. Birch, "Enhanced soft x ray reflectivity of Cr/Sc multilayers by ion-assisted sputter deposition," Opt. Eng. 41, 2903-2909 (2002).
[CrossRef]

Vacuum (1)

C. Engström, T. Berlind, J. Birch, L. Hultman, I. P. Ivanov, S. R. Kirkpatrick, and S. Rohde, "Design, plasma studies, and ion assisted thin film growth in an unbalanced dual target magnetron sputtering system with a solenoid coil," Vacuum 56, 107-113 (2000).
[CrossRef]

Other (5)

J. Als-Nielsen and D. McMorrow, Elements of Modern X Ray Physics (Wiley, 2001), Chap. 1, pp. 24-26.

W. Knulst, O. J. Luiten, M. J. van der Wiel, and J. Verhoeven, "Tabletop soft x-ray source based on 5-10 MeV LINACs," in Proceedings of the Seventh European Particle Accelerator Conference (Austrian Academy of Sciences, 2000), pp. 2609-2611.

E. Spiller, Multilayer Optics for Soft X Rays (Plenum, 1986).

D. T. Atwood, Soft X Rays and Extreme Ultraviolet Radiation (Cambridge University Press, 1999), pp. 55-95.

F. Eriksson, "Soft x ray multilayer mirrors," Ph.D. dissertation (Thin Film Physics Division, IFM, Linköping University, Sweden, 2004).

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Figures (7)

Fig. 1
Fig. 1

Potential ion energy versus growth diagram for a single bilayer of a Cr–Ti ML with a modulation period of 1.38 nm . Initial, d ( initial ) , and final, d ( final ) , thicknesses of individual Ti and Cr layers are labeled together with ion energies in the corresponding regions.

Fig. 2
Fig. 2

Hard-x-ray reflectivity as a function of grazing incidence angle 2 θ for a Cr–Ti multilayer with N = 100 periods. The presence of distinct interference fringes is magnified in the figure. The individual layer thicknesses and the average interface width obtained by simulations are given. The simulation was shifted vertically for clarity.

Fig. 3
Fig. 3

Reflectivity of a Cr–Ti ML close to normal incidence. The peak reflectivity is 2.1 % , and from simulations we found an average interface width of 0.33 nm .

Fig. 4
Fig. 4

Cross-sectional HRTEM micrograph of a Cr–Ti ML containing 100 bilayers with a nominal period of Λ = 1.39 nm .

Fig. 5
Fig. 5

Reflectivity comparison of a series of MLs, with a different number of bilayers of N = 20 , 50 , 100 , and 200 at two probing wavelengths.

Fig. 6
Fig. 6

(a) Soft-x-ray diffuse-scattering measurements at the first Bragg peak at near-normal incidence for a ML series with different bilayers. Reflectivity is plotted on a log scale and was shifted vertically for clarity. (b) Roughness profile in terms of simulated interface width (solid curve) and ratio of diffuse-to-specular integrated intensities (dotted curve) as a function of bilayers N.

Fig. 7
Fig. 7

Soft-x-ray reflectivity measurements of a ML that contains 150 bilayers intended for use at the Brewster angle. Both in-plane and out-of-plane polarization reflectance is shown.

Equations (3)

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R = ( Δ δ ) 2 + ( Δ β ) 2 4 .
Φ = j i j n = I i M ρ N A υ A p r q ,
E i o n = q | V p V s | ,

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