Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2000-12-19
2004-07-27
Luu, Thanh X. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C073S105000
Reexamination Certificate
active
06768095
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a near-field optical probe for observing, measuring and forming optical characteristics in a microscopic region of a sample, and a manufacturing method for the same.
At present, in the scanning near-field microscope (hereinafter, abbreviated as SNOM), an optical medium having a microscopic aperture in a sharpened tip is used as a probe. The tip and microscopic aperture is approached to a measured sample to a distance of less than a wavelength of light to measure an optical characteristic and shape of the sample with resolution. In this apparatus, a linear optical fiber probe vertically held to a sample at a tip is horizontally vibrated with respect to a sample surface. The detection of change in vibration amplitude caused by a shearing force acting between the sample surface and the probe tip is made by illuminating laser light to the probe tip and detecting a change of a shade thereof. The distance between the probe tip and the sample surface is held constant by moving the sample by a fine movement mechanism in a manner of making amplitude constant. From a signal intensity inputted to the fine movement mechanism, a surface shape is detected and a sample optical characteristic is measured. Such apparatus is proposed.
A scanning-type near-field atomic microscope has also been proposed which uses an optical fiber probe formed in a hook form as a cantilever for an atomic force microscope (hereinafter, abbreviated as AFM) to illuminate laser light to a sample from a tip of the optical fiber probe simultaneous with AFM operation to detect a surface shape and measure a sample optical characteristic (Japanese Patent Laid-open No. 174542/1995).
FIG. 16
is a structural view showing a conventional optical fiber probe. This optical fiber probe uses an optical fiber
501
covered at a periphery by a metal film coating
502
. A probe needle portion
503
is sharpened and has an aperture
504
at a tip of the probe needle portion
503
.
On the other hand, in the AFM utilized as shape observing means for microscopic regions, a silicon or silicon-nitride micro-cantilever manufactured by a silicon process is broadly utilized. The micro-cantilever used in the AFM has a feature in mechanical characteristic such as in spring constant and resonant frequency because of high resonant frequency, good mass producibility and less variation in shape. By forming a microscopic aperture in a tip of the micro-cantilever used in AFM, as shown in
FIG. 17
, a probe for SNOM is known which is formed by a tip
505
, a lever
506
, a base
507
, microscopic aperture
508
and a shade film
509
(S. Munster et al., Novel micromachined cantilever sensors for scanning near-field optical microscopy, Journal of Microscopy, vol. 186, pp17-22, 1997). Here, a tip
505
and a lever
506
are formed of silicon nitride or silicon. By incidence of light on the SNOM probe as shown at Light in
FIG. 17
, near-field light can be illuminated from the microscopic aperture
508
.
However, the optical fiber probe shown in
FIG. 16
is poor in mass producibility because of manual manufacture one by one. Also, because the optical fiber
501
is used as a light-propagating member, the difference in propagation characteristic by wavelength is great and difficult in use for spectroscopic analysis.
Although the SNOM probe shown in
FIG. 17
is easy to mass-produce by a silicon process, foreign matter including dust in air readily intrudes into a recess in a tip portion. Accordingly, there has been a problem that near-field light illuminated from the microscopic aperture is not stabilized in intensity. Further, where the tip in position is formed at a tip of the cantilever, a spot of incident light is off the cantilever during introduction of light into the microscopic aperture. When detecting an optical signal from a sample by the microscopic aperture, optical signals at other than the tip end are detected. consequently, there has been a problem that the optical image of SNOM is worsened in optical-image S/N ration. Further, because the tip is formed using mold formed of anisotropic etching of silicon, the tip at an end angle is fixed as
70
degrees. Accordingly, there has been a problem that the near-field light illuminated from the microscopic aperture cannot be increased in intensity. Further, the lever
506
and the tip
505
are structured of a material small in reflectivity relative to a wavelength of incident light or the light detected by the microscopic aperture. In the NOM probe shown in
FIG. 17
, because the structural material of them is in an optical path, the intensity of incident light or detection light attenuates due to reflection upon the structural material. There has been a problem that the near-field light illuminated from the microscopic aperture
508
and the light detected by the microscopic aperture
508
are decreased in intensity.
Therefore, this invention has been made in view of the above, and it is an object to provide a near-field optical probe having a cantilever for SNOM to illuminate and/or detect light through a microscopic aperture, which is excellent in mass-producibility and evenness, capable of obtaining an intensity of stable near-field light without intrusion of foreign matter to a tip portion, improves optical-image S/N ratio by shading leak light and capable of obtaining great near-field light intensity, and a method for manufacturing same.
SUMMARY OF THE INVENTION
Therefore, the present invention has a structure, in a near-field optical probe for observing and measuring optical information in a microscopic region of a sample by generating and/or detecting near-field light, comprising: a cantilever; a base for supporting the cantilever; a tip in the form of a conical or pyramidal formed on the cantilever in a surface opposite to a surface of the base; a microscopic aperture formed in an end of the tip; a shade film formed on the surface of the cantilever opposite to the surface of the base and on a surface of the tip excepting the microscopic aperture; wherein the tip and the cantilever are formed using a transparent material high in transmissivity for a wavelength of light to be generated and/or detected in the microscopic aperture, the tip being filled with the transparent material. Accordingly, the near-field optical probe can illuminate near-field light to the sample by introducing light to the microscopic aperture and/or detect optical information in a microscopic region of a sample by the microscopic aperture.
Also, because the tip is filled with a transparent material, foreign matters will not intrude into the tip, enabling illumination and/or detection of near-field light with stable intensity. Furthermore, because the refractive index of the transparent member is greater than a refractive index of air, it is possible to increase the amount of near-field light passing through the microscopic aperture.
Also, the transparent material forming the tip and the transparent material forming the cantilever are structurally formed of a same transparent material. Accordingly, because there is no reflection between the tip and the cantilever, light incidence on the microscopic aperture and optical information detection from the microscopic aperture can be made with efficiency. Also, because the transparent material can be formed at one time in the manufacture process, the manufacturing method is facilitated. Furthermore, the transparent material is structurally silicon dioxide. Because silicon dioxide is one of the materials having high transmissivity in a visible portion of light, generation and detection of near-field light can be made with efficiency. Also, because silicon dioxide is a material generally used in the silicon process, it is favorable in control of form and mass producibility.
Also, the tip and the cantilever are structurally formed of transparent materials different in optical characteristic. Accordingly, if for example the cantilever is formed of silicon dioxide and the tip of diamond, the mechanical characteristic of th
Ichihara Susumu
Kasama Nobuyuki
Kato Kenji
Mitsuoka Yasuyuki
Niwa Takashi
Adams & Wilks
Luu Thanh X.
Seiko Instruments R & D Center Inc.
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