JP2005164292A - Probe for near field light scattering, and near field optical microscope using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a probe for near field light scattering having high photoelectric field intensifying efficiency. <P>SOLUTION: This probe includes a conical or pyramid-shaped probe main body 13a formed of a dielectric material and having a sharp tip portion; and a metal area 13c formed to cover one-directional side face of the probe main body 13a tip portion, or a spheroid-shaped metal area 13d formed to cover the tip portion of the probe main body 13a and having a major axis along an axial direction of the probe main body 13a. The degree of intensifying energy is thereby increased at a tip end of the probe. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a near-field light scattering probe for generating near-field light by local plasmon resonance, and more specifically, a near-field capable of increasing the enhancement efficiency of the photoelectric field of near-field light generated at the probe tip. The present invention relates to a light scattering probe.
The present invention also relates to a near-field optical microscope that performs optical measurement using a near-field scattering probe.

In recent years, the importance of measurement with a non-destructive high-resolution microscope has increased in a wide range of fields such as molecular biology and material analysis.
A general optical microscope is superior in that it allows non-destructive analysis of the shape, structure, and components of a sample in a relatively short period of time. Therefore, measurement with a size smaller than the wavelength of light could not be performed, and the spatial resolution was limited.

As a technique for solving this problem, a near-field optical microscope using a near-field probe capable of obtaining resolution higher than the resolution due to diffraction limit using near-field light has been developed, and its application is expected.
The basic principle of the near-field optical microscope is that the pointed tip of the near-field probe is brought close to the surface of the object to be measured and laser light is irradiated to scatter near-field light localized near the probe tip and convert it to propagating light. This makes it possible to measure at a high resolution below the wavelength of light.

FIG. 4 is a diagram showing the configuration of the near-field optical microscope.
The near-field optical microscope 10 includes a stage 11 on which the sample A is placed, a stage XY direction driving unit 12 for scanning the XY position of the sample on the stage by moving the stage 11 in the XY direction, and a tip near the measurement site. Is provided with a probe 13 (contact mode measurement) for scattering near-field light and a probe XYZ direction drive unit 14 for adjusting the XY direction and Z direction position of the probe 13.

  The stage 11 can irradiate the sample A with excitation laser light from below so that transmission measurement can be performed, and can emit near-field scattered light from the sample A below the stage 11. Yes.

  A microscope optical system including an objective lens 15 is provided below the stage 11. A half mirror 18 is attached below the objective lens 15, and the excitation light optical system E for irradiating the sample with laser light emitted from the laser light source 16 by the half mirror 18 and detection emitted from the sample A are detected. A detection light optical system P for detecting light is coupled.

  In the excitation light optical system E, a mask 17 having a ring-shaped window is provided in front of the laser light source 16, and laser light having a ring-shaped optical path passes through the mask 17 through the half mirror 18. The light incident on the objective lens 15 and refracted by the objective lens is adjusted so as to be condensed at the tip of the probe 13 at a total reflection critical angle or more.

  The detection light optical system P is adjusted so that the near-field light strongly scattered at the tip of the probe 13 is extracted as a parallel light beam by the objective lens 15 and guided to the detector 19 through the half mirror 18.

  The shape of the probe 13 that scatters near-field light can be roughly classified into a scattering type and an aperture type, and each has advantages and disadvantages. Therefore, when used in a near-field optical microscope, it is suitable for its measurement purpose. It is used properly. Among these, the scattering probe 13 is suitable for measurement with higher spatial resolution, for example, because it is easy to make a probe 13 having a sharp tip.

  As one form of the scattering probe, one using a scattering near-field probe based on silicon, silicon nitride, or the like is disclosed (for example, see Non-Patent Document 1). In the probe described in this document, the entire tip of an AFM (atomic force microscope) cantilever using a dielectric material such as silicon or silicon nitride as a substrate is covered with a silver deposition film (over the entire circumference). Yes.

  FIG. 3 is a cross-sectional view showing a conventional example of the tip portion of a typical scattering near-field probe. The probe 13 includes a probe main body 13a using silicon or silicon nitride as a base material and a metal member 13b covering the tip and the tip. This metal member 13b covers the entire periphery of the probe tip using a thin film forming technique such as vapor deposition.

  Then, when the tip of the probe 13 (cantilever) is brought into contact with the surface of the transparent sample and incident light having only an incident angle component equal to or greater than the total reflection critical angle is irradiated from the back side of the sample as shown in FIG. Near-field light that is strongly scattered at is generated. By detecting this near-field light, an optical image having a spatial resolution substantially equal to the probe tip diameter can be obtained.

N.Hayazawa et al., Optics Communication 183, p.333 (2000)

In the near-field optical microscope, it is desirable to increase the enhancement efficiency of the photoelectric field at the tip of the near-field light scattering probe in order to obtain a high signal intensity.
In particular, the shape of the metal member that causes local plasmon resonance should affect the signal intensity, but the optimum shape has not been considered in particular, and the metal member is made uniform by sharpening the tip shape. It has been believed that the shape of the coating is easy to concentrate the electric field.
In view of the above, an object of the present invention is to provide a near-field light scattering probe that can devise the shape of the probe tip and increase the photoelectric field enhancement efficiency at the probe tip.

  The near-field light scattering probe of the present invention made to solve the above problems is formed so as to cover a cone-shaped or pyramid-shaped probe body having a sharp tip portion and one side surface of the tip portion of the probe body. A metal region to be provided.

  In addition, another near-field light scattering probe of the present invention, which has been made to solve the above-described problems, includes a conical or pyramidal probe body formed of a dielectric material and having a sharp tip portion, and a tip portion of the probe body. And a spheroid-shaped metal region whose major axis direction is the axial direction of the probe main body.

  Further, the near-field optical microscope of the present invention, which has been made from another point of view, includes the above-described near-field light scattering probe of the present invention and excitation light that enters the excitation light for inducing local plasmon resonance toward the vicinity of the probe tip. An optical system and a detection light optical system for detecting detection light emitted from the probe tip are provided.

  We have devised various types of probes by trial and error and conducted computer simulations. In order to increase the energy enhancement strength, instead of using a metal member around the entire tip of the probe as in the past, close proximity It has been found that when the metal region is formed so as to cover the unidirectional side surface of the tip portion of the field light scattering probe body, the energy enhancement is increased.

  Further, it has been found that a spheroid-shaped metal region is formed in the tip portion of the probe body as a second shape that increases energy enhancement, and the major axis direction thereof is the axial direction of the probe body. It was.

  By using any one of these near-field light scattering probes for a near-field optical microscope, measurement with high signal intensity becomes possible.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The embodiment described below is merely an example, and modifications can be made without departing from the scope of the present invention.

FIG. 1 is a diagram showing a configuration of a near-field light scattering probe according to an embodiment of the present invention. As shown in FIG. 1, a metal region 13c is formed along one side surface of the probe body 13a. The tip of the probe in which the metal region 13c is formed is like the tip of a flathead screwdriver.
The radius of curvature of the tip of the probe body 13a may be 200 nm or less, more preferably about 20 to 100 nm.

  A dielectric material such as silicon or silicon nitride is used for the probe main body 13a. The metal region 13c can be formed by flying a metal substance from one direction toward the probe tip using a directional film forming technique such as vapor deposition or sputtering. Silver, gold, platinum and the like are preferable as the metal material.

FIG. 2 is a diagram showing a configuration of a near-field light scattering probe which is another embodiment of the present invention. As shown in FIG. 2, a spheroid-shaped metal region 13d is formed at the most distal portion of the probe body 13a. The major axis direction of the metal region 13d is the axial direction of the probe body 13a.
The metal region 13d needs to be processed with an accuracy of the order of several tens of nanometers, and a spheroidal metal region can be formed by focus ion beam processing after forming a metal film at the tip portion.

  Then, the near-field optical microscope shown in FIG. 4 is used as the near-field light scattering probe 13 shown in FIG. 1 or FIG.

Next, the result of computer simulation of the energy density distribution at the probe tip in the conventional example and the embodiment according to the present invention will be described.
In the computer simulation, Maxwell's equations were calculated by the FDTD method (Finite Difference Time Domain method). For the incident condition of the ring-shaped laser beam, the numerical value of the electromagnetic field obtained by Fresnel integration of a spherical wave (reference sphere) generated through the aberration lens is arranged as a boundary condition on the end face of the FDTD analysis region, Each latitude was divided into 20 parts.

  FIG. 5 is a diagram for explaining the calculated energy density distribution and energy enhancement for various probe tip shapes. FIG. 5 (a) shows the conventional example shown in FIG. 3, and FIG. 5 (b) shows FIG. 1) and FIG. 5C correspond to those of FIG. 2 (Example 2). FIG. 5D shows a case where there is no probe as a reference (that is, when there is no near-field light scattering).

  Assuming that the energy density without the probe is 1, it was 2.4 in the conventional example, 44 in the example 1, and 23 in the example 2.

  In both Example 1 and Example 2, the energy enhancement is significantly higher than the conventional example, and the emission intensity increases as the enhancement increases as shown in the figure.

The use of the near-field light scattering probe according to the present invention can be applied to near-field lithography, near-field processing and the like in addition to the near-field optical microscope.
Furthermore, even when used as Raman scattering spectroscopy, infrared absorption spectroscopy, fluorescence spectroscopy, or SHG microscope, it is possible to obtain a high optical signal amount by locally increasing the excitation light intensity by the photoelectric field enhancement effect of local plasmon resonance. Can be.

The block diagram of a near-field optical microscope. The figure which shows the structure of the probe for near-field light scattering which is one Example of this invention. The figure which shows the structure of the conventional probe for near-field light scattering. The figure which shows the structure of the probe for near-field light scattering which is another Example of this invention. The figure explaining the energy density distribution and energy increase intensity which were calculated about various probe tip shapes.

Explanation of symbols

10: Near-field optical microscope 11: Stage 12: Stage XY direction drive unit 13: Probe for near-field scattered light 13a: Probe body 13b to d: Metal region 14: Probe XYZ direction drive unit 15: Objective lens 16: Laser light source 17 : Mask 18: Half mirror 19: Detector

Claims (3)

Proximity comprising a conical or pyramidal probe body made of a dielectric material and having a sharp tip portion, and a metal region formed so as to cover one side surface of the tip portion of the probe body Field light scattering probe. A conical or pyramidal probe body formed of a dielectric material and having a sharp tip portion, and a spheroid-shaped metal formed so as to cover the tip portion of the probe body and whose major axis direction is the axial direction of the probe body And a near-field light scattering probe. The near-field light scattering probe according to claim 1, an excitation light optical system for injecting excitation light for inducing local plasmon resonance toward the vicinity of the probe tip, and the probe tip A near-field optical microscope comprising: a detection light optical system that detects detection light.

Images