Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
2000-05-15
2002-10-22
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C250S306000
Reexamination Certificate
active
06469288
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-135821, filed May 17, 1999; No. 11-163482, filed Jun. 10, 1999; No. 11-354417, filed Dec. 14, 1999; and No. 2000-121198, filed Apr. 21, 2000, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a near field optical microscope and a probe for the near field optical microscope which detect light scattered by a probe entering into a near field to obtain information concerning the surface of a sample.
A scanning probe microscope (SPM) is a generic name of an apparatus in which, when a probe is set 1 &mgr;m or less close to a sample surface, the probe is let scan in the X- and Y-directions or X-, Y-, and Z-directions while detecting a correlative effect caused between both the probe and the sample surface, thereby to carry out two-dimensional mapping of the correlative effect. For example, scanning probe microscopes include a scanning tunneling microscope (STM), an atomic force microscope (AFM), a magnetic force microscope (MFM), and a scanning near-field optical microscope (SNOM).
Among them, developments of the SNOM as an optical microscope having a resolution which exceeds the diffraction limit by detecting near field light formed near a sample has been eagerly promoted after the later half of 1980s to achieve application use for fluorescence measurement of a bionic sample, evaluation of an element (various characteristic evaluations of dielectric light guide paths, measurement of light emission spectrums of semiconductor quantum dots, evaluation of various characteristics of semiconductor laser, etc.).
The SNOM is basically an apparatus which sets a sharp probe near a sample with light illuminated thereon and detects a field (near field) of light near the sample.
The U.S. Pat. No. 5,272,330 granted to Bezig et al. on Dec. 21, 1993 discloses a SNOM in which light is introduced to a probe having a narrowed top end, thereby to generate a field of light localized near a very small opening at the top end of the probe, and this is brought into contact with a sample, to illuminate a very small part of the sample. Transmitted light is detected by an optical detector provided below the sample, and two-dimensional mapping of an intensity of transmitted light is carried out.
The SNOM uses a rod-like probe such as an optical fiber or glass rod which has a top end processed to be narrow or a crystalline probe.
A rod-like probe covered with a metal film except the top end thereof has already been commercially available as an improved type of the probe.
An apparatus using this probe has an improved resolution in the lateral direction in comparison with an apparatus using a probe not coated with metal.
Meanwhile, the AFM has been most widely spread as an apparatus for obtaining topography information of the sample surface among SPMs.
The AFM detects a displacement of a cantilever which shifts in accordance with a force acting on a probe when the prove supported on the top end of the cantilever is set near a sample surface, for example, by an optical displacement sensor, thereby to obtain indirectly information concerning concaves and convexes of the sample surface.
One of the AFMS is disclosed in the Japanese Patent Application KOKAI Publication No. 62-130302.
The technique of measuring concaves and convexes on a sample by detecting a correlative force between the sample and the top end of the probe is utilized for other SPM apparatuses and is used as a means for carrying out so-called regulation.
N. F. van Hulst et al. has proposed a new SNOM which uses an AFM cantilever made of silicon nitride and detects optical information of a sample while measuring concaves and convexes of the sample by AFM measurement, in “Appl. Phs. Lett. 62(5)”, P. 461 (1993).
In this apparatus, the sample is set on an internal total reflection prism and the sample is illuminated with a He-Ne laser beam from the total reflection prism side, so the sample is excited and an evanescent optical field is formed near the sample surface.
Subsequently, a probe supported on the top end of the cantilever is inserted in the evanescent optical field, and evanescent light as a localized wave is converted into scattered light as a propagation wave. A part of this light is propagated inside a silicon-nitride-made probe which is substantially transparent with respect to the He-Ne laser beam and passes to the back side of the cantilever.
This light is condensed by a lens provided above the cantilever and enters into a photomultiplier tube through a pinhole provided at a position conjugate with the top end of the probe with respect to the lens. A SNOM signal is outputted from the photomultiplier tube.
While detecting this SNOM signal, displacement of the cantilever is measured by an optical displacement detection sensor. For example, a piezoelectric scanner is subjected to feedback control such that the displacement is maintained at a regulated constant value.
Accordingly, during one scanning, SNOM measurement is carried out based on a scanning signal and a SNOM signal and AFM measurement is carried out based on a scanning signal and a feedback control signal.
In the SNOM of an aperture type disclosed by Betzig et al., the probe should be subjected to metal coating to obtain a high resolution in the lateral direction.
However, it is not easy to manufacture uniformly a large quantity of probes each having an opening at the top end and coated with metal
A resolution exceeding a resolution which can be realized by an ordinary optical microscope is required for a SNOM which is expected to have a super resolution. To realize the super resolution, the diameter of the opening at the top end of the probe must be 0.1 &mgr;m or less or preferably 0.05 &mgr;m or less.
An opening having a diameter of these values is very difficult to prepare with excellent reproductivity.
In addition, since the amount of light which enters into the probe through the opening decreases in proportion to square of the radius of the opening, the light amount to be detected is reduced so that the S/N ratio is deteriorated, if the opening diameter is reduced for the purpose of improving the resolution of an SNOM image in the lateral direction. Thus, there is a problem of trade-off.
Hence, a proposal has been made for a new SNOM (scattering-type) SNOM which uses a feature that high-diffraction dielectric material or metal strongly scatters near-field light without forming an opening at the top end of the probe.
In this SNOM, no opening is required at the top end of the probe so that there is not the problem of trade-off and the difficulty of forming the opening.
Kawata et al. disclose a scattering-type SNOM in the Japanese Patent Application KOKAI Publication No. 6-137847.
In this SNOM, the evanescent light formed on the sample surface is scattered by a needle-like probe and is thereby converted into propagation light. This propagation light, i.e., scattered light is detected by a condenser lens and a photodetector provided in a side of the probe, and optical information is obtained, based on a detection signal thereof.
Further, Kawata et al. disclose an apparatus in which a metal probe of the STM is used as its probe and propagation light generated due to scattering of evanescent light generated on the sample surface by the top end of the metal prove is observed from the lateral side of the sample and probe while controlling the distance between a sample and the probe by the STM, so STM observation and SNOM observation can be achieved, in “DAI-42-KAI NIHON OHYOH BUTSURIGAKU KANKEI RENGOH KOENKAI (preliminary report compilation No. 3, page 916, March 1995)”.
Also, Kawada et al. further reports that the SNOM observation can be achieved even by multiple scattering of propagation light entering obliquely from the upside of the sample, between the top end of a metal probe and a sample, in place of the evanescent light, in “DAI-43-KAI NIHON OHYOH
Sasaki Hiroko
Sasaki Yasuo
Le Que T.
Olympus Optcial Co., Ltd.
Scully Scott Murphy & Presser
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