Abstract

The motion of the probe tip in a near-field scanning optical microscope, dithered by vibration of a tuning fork, can modulate the reflection signal from the sample surface not only at the fundamental dithering frequency but also at its second harmonic. By lock-in amplification of these modulated signals, enhanced optical images are obtained, even with an uncoated fiber probe. In particular, accurate optical images with higher resolution are obtained when the second-harmonic signal is detected, which results from the parametric modulation of the tip–sample separation at the double frequency of the horizontal dithering motion of the tip. Using a DVD ROM with a track pitch of 0.74 µm as a test sample, we observed that the sharp edges around the pits are clearly resolved with the second-harmonic signals and obtained enhanced resolution of 70 nm full width at half-maximum.

© 2000 Optical Society of America

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References

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  1. D. W. Pohl, W. Denk, and M. Lanz, Appl. Phys. Lett. 44, 651 (1984).
    [CrossRef]
  2. E. Betzig, M. Isaacson, and A. Lewis, Appl. Phys. Lett. 51, 2088 (1987).
    [CrossRef]
  3. K. Karrai and R. D. Grober, Appl. Phys. Lett. 66, 1842 (1995).
    [CrossRef]
  4. T. Pangarubuan, K. Yamada, S. Jiang, H. Ohsawa, and M. Ohtsu, Jpn. J. Appl. Phys. 31, L1302 (1992).
    [CrossRef]
  5. S. K. Eah, J. H. Park, and W. Jhe, in Technical Digest of the Fifth International Conference on Near-Field Optics (Japan Society of Applied Physics, Tokyo, 1998), p. 163.
  6. E. Betzig, P. L. Finn, and J. S. Weiner, Appl. Phys. Lett. 60, 2484 (1992).
    [CrossRef]
  7. V. Sandoghdar, S. Wegscheider, G. Krausch, and J. Mlynek, J. Appl. Phys. 31, 2499 (1997).
    [CrossRef]

1997 (1)

V. Sandoghdar, S. Wegscheider, G. Krausch, and J. Mlynek, J. Appl. Phys. 31, 2499 (1997).
[CrossRef]

1995 (1)

K. Karrai and R. D. Grober, Appl. Phys. Lett. 66, 1842 (1995).
[CrossRef]

1992 (2)

T. Pangarubuan, K. Yamada, S. Jiang, H. Ohsawa, and M. Ohtsu, Jpn. J. Appl. Phys. 31, L1302 (1992).
[CrossRef]

E. Betzig, P. L. Finn, and J. S. Weiner, Appl. Phys. Lett. 60, 2484 (1992).
[CrossRef]

1987 (1)

E. Betzig, M. Isaacson, and A. Lewis, Appl. Phys. Lett. 51, 2088 (1987).
[CrossRef]

1984 (1)

D. W. Pohl, W. Denk, and M. Lanz, Appl. Phys. Lett. 44, 651 (1984).
[CrossRef]

Betzig, E.

E. Betzig, P. L. Finn, and J. S. Weiner, Appl. Phys. Lett. 60, 2484 (1992).
[CrossRef]

E. Betzig, M. Isaacson, and A. Lewis, Appl. Phys. Lett. 51, 2088 (1987).
[CrossRef]

Denk, W.

D. W. Pohl, W. Denk, and M. Lanz, Appl. Phys. Lett. 44, 651 (1984).
[CrossRef]

Eah, S. K.

S. K. Eah, J. H. Park, and W. Jhe, in Technical Digest of the Fifth International Conference on Near-Field Optics (Japan Society of Applied Physics, Tokyo, 1998), p. 163.

Finn, P. L.

E. Betzig, P. L. Finn, and J. S. Weiner, Appl. Phys. Lett. 60, 2484 (1992).
[CrossRef]

Grober, R. D.

K. Karrai and R. D. Grober, Appl. Phys. Lett. 66, 1842 (1995).
[CrossRef]

Isaacson, M.

E. Betzig, M. Isaacson, and A. Lewis, Appl. Phys. Lett. 51, 2088 (1987).
[CrossRef]

Jhe, W.

S. K. Eah, J. H. Park, and W. Jhe, in Technical Digest of the Fifth International Conference on Near-Field Optics (Japan Society of Applied Physics, Tokyo, 1998), p. 163.

Jiang, S.

T. Pangarubuan, K. Yamada, S. Jiang, H. Ohsawa, and M. Ohtsu, Jpn. J. Appl. Phys. 31, L1302 (1992).
[CrossRef]

Karrai, K.

K. Karrai and R. D. Grober, Appl. Phys. Lett. 66, 1842 (1995).
[CrossRef]

Krausch, G.

V. Sandoghdar, S. Wegscheider, G. Krausch, and J. Mlynek, J. Appl. Phys. 31, 2499 (1997).
[CrossRef]

Lanz, M.

D. W. Pohl, W. Denk, and M. Lanz, Appl. Phys. Lett. 44, 651 (1984).
[CrossRef]

Lewis, A.

E. Betzig, M. Isaacson, and A. Lewis, Appl. Phys. Lett. 51, 2088 (1987).
[CrossRef]

Mlynek, J.

V. Sandoghdar, S. Wegscheider, G. Krausch, and J. Mlynek, J. Appl. Phys. 31, 2499 (1997).
[CrossRef]

Ohsawa, H.

T. Pangarubuan, K. Yamada, S. Jiang, H. Ohsawa, and M. Ohtsu, Jpn. J. Appl. Phys. 31, L1302 (1992).
[CrossRef]

Ohtsu, M.

T. Pangarubuan, K. Yamada, S. Jiang, H. Ohsawa, and M. Ohtsu, Jpn. J. Appl. Phys. 31, L1302 (1992).
[CrossRef]

Pangarubuan, T.

T. Pangarubuan, K. Yamada, S. Jiang, H. Ohsawa, and M. Ohtsu, Jpn. J. Appl. Phys. 31, L1302 (1992).
[CrossRef]

Park, J. H.

S. K. Eah, J. H. Park, and W. Jhe, in Technical Digest of the Fifth International Conference on Near-Field Optics (Japan Society of Applied Physics, Tokyo, 1998), p. 163.

Pohl, D. W.

D. W. Pohl, W. Denk, and M. Lanz, Appl. Phys. Lett. 44, 651 (1984).
[CrossRef]

Sandoghdar, V.

V. Sandoghdar, S. Wegscheider, G. Krausch, and J. Mlynek, J. Appl. Phys. 31, 2499 (1997).
[CrossRef]

Wegscheider, S.

V. Sandoghdar, S. Wegscheider, G. Krausch, and J. Mlynek, J. Appl. Phys. 31, 2499 (1997).
[CrossRef]

Weiner, J. S.

E. Betzig, P. L. Finn, and J. S. Weiner, Appl. Phys. Lett. 60, 2484 (1992).
[CrossRef]

Yamada, K.

T. Pangarubuan, K. Yamada, S. Jiang, H. Ohsawa, and M. Ohtsu, Jpn. J. Appl. Phys. 31, L1302 (1992).
[CrossRef]

Appl. Phys. Lett. (4)

D. W. Pohl, W. Denk, and M. Lanz, Appl. Phys. Lett. 44, 651 (1984).
[CrossRef]

E. Betzig, M. Isaacson, and A. Lewis, Appl. Phys. Lett. 51, 2088 (1987).
[CrossRef]

K. Karrai and R. D. Grober, Appl. Phys. Lett. 66, 1842 (1995).
[CrossRef]

E. Betzig, P. L. Finn, and J. S. Weiner, Appl. Phys. Lett. 60, 2484 (1992).
[CrossRef]

J. Appl. Phys. (1)

V. Sandoghdar, S. Wegscheider, G. Krausch, and J. Mlynek, J. Appl. Phys. 31, 2499 (1997).
[CrossRef]

Jpn. J. Appl. Phys. (1)

T. Pangarubuan, K. Yamada, S. Jiang, H. Ohsawa, and M. Ohtsu, Jpn. J. Appl. Phys. 31, L1302 (1992).
[CrossRef]

Other (1)

S. K. Eah, J. H. Park, and W. Jhe, in Technical Digest of the Fifth International Conference on Near-Field Optics (Japan Society of Applied Physics, Tokyo, 1998), p. 163.

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Figures (6)

Fig. 1
Fig. 1

Schematic diagram of the two independent, oscillating motions of the fiber tip glued to a tuning fork.

Fig. 2
Fig. 2

Schematic diagram of the NSOM system: PZT, piezoelectric transducer.

Fig. 3
Fig. 3

Scanning-electron microscope images of a DVD ROM sample: (a) top view, (b) oblique view.

Fig. 4
Fig. 4

Optical images of a DVD ROM obtained by three reflection-signal detection schemes: (a) without lock-in-amplification, (b) with first-harmonic lock-in-amplification, and (c) with second-harmonic lock-in-amplification. The scan area is 4 µm×4 µm.

Fig. 5
Fig. 5

Phase-dependent output maps from (a) the x and (b) the y channels of LIA-2 in first-harmonic lock-in-detection. Light and dark areas represent the relative out-of-phase optical signals reflected from the two slanted sides of each pit, which results in the canceled-out signals near midpoints around each pit shown in Fig. 4(b). Note that the brightness represents the relative optical phase information, not topographic information.

Fig. 6
Fig. 6

Top, highly magnified second-harmonic optical image; bottom, plot of the cross-sectional profile along the white bar in the top figure.

Equations (3)

Equations on this page are rendered with MathJax. Learn more.

θ=θ0 sinωt+ϕ0.
x=L sin θ,  z=L cos θ.
xLθ=Lθ0 sinωt,  zL1-12θ2=L1-θ024+θ024 cos2ωt.

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