JP4544150B2 - Near-field optical probe - Google Patents

Description

  The present invention relates to a near-field optical probe that can be used for surface analysis and the like.

  Near-field spectroscopy (infrared, Raman, fluorescence) effective for surface nanochemical structural analysis is characterized by high spatial resolution. Specifically, as shown in FIG. 7, when infrared light IR is irradiated toward the probe tip 100, near-field light is generated from the probe tip 100 in a range smaller than the irradiation light wavelength. By irradiating the sample 200 with this and spectroscopically analyzing the reflected light R from the sample with a detector, scattering-type near-field spectroscopic analysis becomes possible. Near-field spectroscopic analysis is very useful in that a more precise surface analysis is possible.

  However, actually, as shown in FIG. 8, the reflected light R from the sample 200 cannot be detected efficiently on the side surface of the probe tip 100 irradiated with the infrared light IR due to irregular reflection of the irradiated light. Therefore, it is said that it is difficult to obtain the theoretical resolution. This becomes more prominent as the probe tip diameter increases, as shown in FIG. 9, and the error from the actual measurement value increases.

Therefore, it has been proposed to improve the spatial resolution by sharpening the probe (see, for example, Patent Documents 1 and 2). However, even if an attempt is made to improve the spatial resolution only by sharpening the probe, although some improvement is seen, the spatial resolution as the theoretical value still cannot be obtained.
JP 2004-163147 A JP 2005-189108 A

  An object of the present invention is to solve the above-described conventional problems. That is, an object of the present invention is to provide a near-field optical probe capable of realizing a spatial resolution close to a theoretical value.

  As a result of intensive studies to solve the above problems, the present inventors have considered that the following phenomenon is the cause of failure to obtain a spatial resolution close to the theoretical value. In other words, the near-field infrared spectroscopy employs a scattering system that irradiates light to the probe tip from an external light source, so that the irradiated light is reflected by the side of the probe and hits the sample surface near the probe tip. I guessed that the spatial resolution would decrease. And based on this guess, the present inventors came up with the following this invention, and discovered that the said subject could be solved.

That is, the present invention provides a scattered near-field light characterized in that a metal coat layer is formed on the core portion at the tip, and nanoholes or nanogrooves are formed in the metal coat layer on the side surface other than the top portion at the tip. It is a probe.

  When the infrared light irradiated on the side surface reaches the nanohole or nanogroove on the metal coating layer, the infrared light is reflected and scattered by the nanohole or nanogroove. The reflected / scattered infrared light does not reach the sample surface near the probe tip. As a result, a decrease in spatial resolution is suppressed, and a spatial resolution close to the theoretical value can be realized.

  In particular, since the infrared light hitting the nanogroove top (convex portion) propagates through the top as evanescent light and is converted into near-field light at the probe tip, the near-field light generation efficiency can be further improved.

  According to the near-field optical probe of the present invention, a spatial resolution close to the theoretical value can be realized.

  Hereinafter, the near-field optical probe of the present invention will be described by dividing it into first to third embodiments.

[First Embodiment]
In the scattering near-field optical probe according to the first embodiment, a metal coat layer is formed on the core portion at the tip, and nanoholes or nanogrooves are formed on the metal coat layer on the side surface other than the top portion at the tip . Here, the “tip” refers to the end of the near-field optical probe, or from the position where the diameter or width decreases in the tip direction (direction toward the analysis sample) to the end (second and third embodiments described later). The same applies to.

As the material for the core, SiO ₂ can be used. The metal coat layer is preferably a metal containing at least one selected from the group consisting of Fe, Cr, Al, Ni, Au, Pt, and Ag. The thickness of the metal coat layer is preferably 50 to 500 nm. The metal coat layer can be formed by a vacuum deposition method or the like.

  FIG. 1 shows a near-field optical probe in which nanoholes are formed in a metal coat layer. At the tip of the near-field optical probe, a plurality of nanoholes 14 are formed in the metal coat layer 12 formed in the core 10. The infrared light applied to the nanohole 14 is repeatedly reflected and scattered on the curved surface of the nanohole 14, and does not reach the sample surface near the probe tip. As a result, a decrease in spatial resolution is suppressed, and a spatial resolution close to the theoretical value can be realized.

  The shape of the opening of the nanohole 14 is not particularly limited. The average equivalent circle diameter X at the opening of the nanohole 14 is preferably 1/10 to 1/2 (or 10 nm to 2 μm) of the near-field optical probe tip curvature diameter D. The average depth Y of the nanoholes 14 is preferably 1/20 to 1/4 (or 5 nm to 1 μm) of the average equivalent circle diameter X in the opening.

  Moreover, it is preferable that the area ratio of the nanohole 14 calculated | required by following formula (1) is 5 to 80%. In the following formula (1), n is the number of nanoholes 14, and L is the length of the tip in the axial direction.

Formula (1): Area ratio = nX ² / 4DL

  The average equivalent circle diameter, nanogroove width, average depth, and area ratio, which will be described later, may be measured by observing a portion to be measured with an SEM (scanning electron microscope) from directly above and taking the magnification into consideration. Such nanoholes can be formed by irradiating an electron beam or a (femtosecond) laser.

  FIG. 2 shows a near-field optical probe in which nanogrooves 16 are formed on the metal coat layer 12 formed on the core portion 10. A spiral nano groove 16 is formed at the tip of the near-field optical probe. By forming the nanogroove 16, the same effect as when nanoholes are provided can be obtained. In addition, since the infrared light hitting the top of the nanogroove (convex portion) propagates through the top as evanescent light and is converted to near-field light at the probe tip, the near-field light generation efficiency can be further improved.

  The average width Z of the nanogroove 16 is preferably 1/20 to 1/2 (or 5 nm to 1 μm) of the near-field optical probe tip curvature diameter D. The average depth is preferably 1/40 to 1/4 (or 2 nm to 1 μm) of the near-field optical probe tip curvature diameter D.

  The nanogroove can be formed by irradiating an electron beam or a (femtosecond) laser while rotating around the axis of the near-field optical probe.

  In FIG. 2, the nanogroove 16 is formed in a spiral shape, but a plurality of nanogrooves 16 may be provided concentrically. Such a configuration is significant in that the nanogroove 16 can be easily formed.

  As shown in FIG. 3, the cross-sectional shapes of the nanoholes and nanogrooves are various, such as a polygonal shape such as a semicircle (FIG. 3A), a V-shape (FIG. 3C), and a quadrangle (FIG. 3B). However, in consideration of further improving the reflection / scattering efficiency of the nanohole or nanogroove, at least as shown in FIGS. 3D and 3E, the depth direction is larger than the opening. It is preferable to have a shape having a large-diameter portion whose diameter increases toward.

[Second Embodiment]
In the near-field optical probe according to the second embodiment, a metal sphere is provided at the tip, and the shape of the cross-section in the width direction of the tip of the near-field light probe is circular or flat.

  Since the metal sphere provided at the tip is in an isolated state from the entire probe, the influence of infrared light reflection from the side surface can be ignored. As a result, a decrease in spatial resolution is suppressed, and a spatial resolution close to the theoretical value can be realized. In addition, it is possible to simultaneously ensure high resolution and probe stability (strength) during scanning in one direction. Also, a resolution close to that of a metal sphere can be obtained.

  The material of the metal sphere is a metal containing at least one selected from the group consisting of Fe, Cu, Al, Ni, Au, Pt, and Ag in consideration of its reflectance and dielectric constant. preferable. The diameter of the metal sphere is preferably 50 nm to 500 nm.

  FIG. 4 shows an example in which the shape of the cross section in the width direction at the tip of the near-field optical probe is circular. A metal ball 22 is provided at the tip (end) of the near-field optical probe 20. The near-field optical probe 20 is preferably a multi-walled carbon nanotube in consideration of the fact that it is significant to use a probe having a small cross-sectional area with respect to the irradiation light and the point that it retains good rigidity. In order to provide the multi-walled carbon nanotube with the metal sphere, a method of condensing the metal at one end while centrifugally rotating the carbon nanotube in metal vapor may be adopted.

  FIG. 5 shows an example in which the shape of the cross section in the width direction at the tip of the near-field optical probe is a flat shape. FIG. 5A is a front view of the tip of the near-field optical probe, and FIG. 5B is a side view of the tip of the near-field optical probe. A metal ball 22 is provided on the flat tip hold portion 30 which is the tip of the near-field optical probe shown in FIG.

  As a material of the flat chip hold part 30 shown in FIG. 5, it is preferable that it is a metal containing at least 1 sort (s) selected from the group which consists of Al, Cu, and Fe. The cross-sectional shape may be an ellipse or a polygon such as a triangle or a trapezoid as long as the aspect ratio of the cross-section is high.

  The flat tip hold part 30 can be formed by press working. The material and diameter of the metal sphere and the method for providing the metal sphere are the same as the example of the near-field optical probe described in FIG.

[Third Embodiment]
As shown in FIG. 5, the near-field optical probe according to the third embodiment further includes an infrared inactive medium in the core part 40 at the tip where the first metal coat layer (not shown) is formed. The medium layer 42 is formed so that the diameter of the medium layer 42 increases toward the tip (end), and then the diameter of the medium layer 42 further decreases toward the tip (end). Is formed. As shown in FIG. 6, the tip of the near-field optical probe slightly protrudes from the surface of the infrared inactive medium. The upper part of the infrared inactive medium surface is not covered with metal by the second metal coat layer 44 and forms a concave surface. When measuring an actual sample, infrared rays IR are irradiated not on the most advanced part but on the concave part.

  The infrared light IR irradiated on the concave surface is transmitted through the medium layer 42. The transmitted infrared light IR is reflected and scattered by the core portion, but the reflected and scattered infrared light is reflected by the second metal coat layer 44 provided outside the medium layer 42 formed on the more distal end side. It is blocked to prevent infrared light from reaching the vicinity of the probe tip. As a result, a decrease in spatial resolution is suppressed, and a spatial resolution close to the theoretical value can be realized.

  In addition, since the blocked infrared light is effectively sent to the probe tip, the infrared light is converted into near-field light with high efficiency. As a result, the generation efficiency of near-field light can be further improved.

As the core portion 40 at the tip on which the first metal coat layer (not shown) is formed, a SiO ₂ fiber coated with a metal containing at least one of Au, Ag, Cr, Al, Pt, and Fe Can be used.

  Examples of the infrared inactive material constituting the infrared inactive medium include KBr, TaBr (KRS-5), ZnSe, Ge, and CaF. The average thickness of the medium layer is preferably not less than about 5 times the average width of the probe.

  The near-field optical probe of the present invention as described above can be used as a probe for a spectroscopic analysis apparatus or an optical recording apparatus, but is particularly preferably applied to a spectroscopic analysis apparatus. Examples of the analyzer include the devices described in JP-A-2005-227160, JP-A-2003-294618, and JP-A-2001-330546.

It is a partial front view which shows an example of the 1st Embodiment of this invention. It is a partial front view which shows the other example of the 1st Embodiment of this invention. It is a fragmentary sectional view which shows the cross-sectional shape of a nanohole or a nanogroove. It is a partial front view which shows an example of the 2nd Embodiment of this invention. It is a figure which shows the other example of the 2nd Embodiment of this invention, (A) is a partial front view, (B) is a partial side view. It is a fragmentary sectional view showing an example of a 3rd embodiment of the present invention. It is explanatory drawing explaining the mechanism of a scattering type near-field spectral analysis. It is explanatory drawing explaining a problem by the mechanism of a scattering type near field spectroscopy analysis. It is a figure which shows the relationship between the real spatial resolution and probe tip diameter in a scattering type near field spectroscopy analysis.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,40 ... Core part 12 ... Metal coating layer 14 ... Nanohole 16 ... Nanogroove 20 ... Near field optical probe 22 ... Metal ball 30 ... Flat tip hold part 42- .... Medium layer 44 ... Second metal coat layer 100 ... Probe tip 200 ... Sample D ... Curvature diameter X ... Average equivalent circle diameter Y ... Average depth Z ... Average width IR ・ ・ ・ Infrared light R ・ ・ ・ Reflected light

Claims (1)

A scattering near-field optical probe, characterized in that a metal coat layer is formed on a core portion at the tip, and nanoholes or nanogrooves are formed on the metal coat layer on the side surface other than the top portion at the tip .

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