JPH11271337A - Optical probe, its manufacture, and scanning-type probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical probe for preventing the output of light from a fiber from being attenuated greatly by exposing only the flatly machined core part of the tip part of an optical probe with a fine opening. SOLUTION: An optical fiber 1 consists of a clad part 3 whose refractive index differs from that of a core part 2 for propagating light, a tip part 4 of an optical probe is in nm size and only the flatly and finely machine core part of the tip part 4 of the optical probe is exposed, and those other than the end part is covered with a metal film 5. A material for reflecting light such as golf, platinum, aluminum, chromium, and nickel is used for the metal film 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for a scanning probe microscope for observing the shape of a solid surface in a nanometer region and measuring optical properties by irradiating or exciting a surface of an object to be measured. The present invention relates to an optical probe, an optical probe manufacturing method, and a scanning probe microscope.

[0002]

2. Description of the Related Art An aperture-type optical probe has been reported in which a glass capillary and an optical fiber are sharpened to produce a probe. With the development of micromachining technology, a probe having a very sharp tip can be produced. Obtaining an optical image that exceeds the resolution of an optical microscope can now be realized with a scanning probe microscope.

[0003]

However, the problem with the optical probe having the small aperture is that the intensity of the evanescent field at the small aperture is reduced by a factor of 1 / 1/1 from 10,000
This is a point that it is greatly reduced to 000000. This hinders optical observation of the sample at a high S / N ratio and optical processing / writing at a fast scan. In order to solve this, when trying to produce a nanometer-sized flat at the tip of the probe, strictness is required for the processing conditions, and as a result, there is a problem that the tip shape varies.

[0004]

According to the present invention, in order to solve the above-mentioned problems, the tip of an optical probe is flatly processed to a nanometer size. If the diameter of the core for guiding the light in the fiber is smaller than the wavelength of the light, the light can only pass through a tunnel phenomenon. Therefore, it is a shape that is not practically suitable to make the tip end thin and long. In order to increase the output of light from the optical probe, the taper angle is increased, the length of the core that is narrower than the wavelength of the light used is shortened, and a flat shape of nanometer size is at the tip It is advantageous. On the other hand, in the process of manufacturing an optical probe, in order to stably produce the tip shape with good reproducibility, the etching process that preferentially reduces the core of the fiber and the etching process that sharpens the outer shape of the fiber are combined. Was made possible.

[0005] Among these optical probe manufacturing processes, the etching process for preferentially reducing the core of the fiber involves a mixing ratio of hydrofluoric acid and ammonium fluoride of 1: 2.
(<2) is used as an etching solution. In the etching step for sharpening the fiber, hydrofluoric acid is used as an etchant. In this case, the fiber clad portion is preferentially etched. The structure of the etching solution is a two-layer structure in which a solution having a lower specific gravity than these etching solutions and not mixed and reacted with each other is superposed on the above-mentioned solution containing hydrofluoric acid as a main component.

Further, as a replacement step of the step of sharpening the tip of the optical probe, a step of applying a tension while heating the fiber by a heating means and performing a tensile break is performed.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of an optical probe according to a first embodiment of the present invention. The optical fiber 1 includes a core portion 2 for transmitting light and a clad portion 3 having a different refractive index. The tip portion of the optical probe is finely flattened to have a nanometer size, and the outside is covered with a metal film 5 except for the tip portion 4. As the metal film 5, a material that reflects light, such as gold, platinum, aluminum, chromium, and nickel, is used.

FIG. 2 is a view showing the shape near the tip of an optical probe according to a second embodiment of the present invention. FIG. 2 (A)
As shown in the figure, the shape near the tip is straight,
It can be hook-shaped as shown in FIG. The straight-shaped optical probe is mounted on a near-field microscope that vibrates the tip of the optical probe horizontally with respect to the sample surface. The hook-shaped optical probe is mounted on a near-field microscope of a type in which the tip of the optical probe is vibrated perpendicularly to the sample surface and a type in which the tip is brought into contact with the sample surface.

The outer diameter 8 of the front end portion 6 can be formed in a step-like shape smaller than the outer shape of the rear end portion 7, thereby reducing the spring elasticity of the optical probe and observing a soft sample surface. Suitable for. FIG.
(A) and (B) show an optical probe 14 of a third embodiment of the present invention in which the outer diameter is reduced stepwise and a part of a manufacturing process thereof, in which a fiber is immersed in an etching solution. Is represented. FIG. 3A shows a step of forming a concave portion 12 in the core portion 2 of the fiber. Optical fiber 1
About 1 cm to 10 cm of the end of the resin, the coating of the synthetic resin is removed and the surface is cleaned. The end face is cut flat by cleavage, and 0.5 mm to 50 mm from the end of the optical fiber 1.
The mm part is inserted into the etching solution.

The etching solution comprises a first solution layer 10 containing hydrofluoric acid as a main component and a second solution layer having a specific gravity smaller than that of the first solution layer and not reacting with and mixing with the first solution layer. 9 is composed of two layers. As the first solution layer 10, a mixed solution (HF: NH 3 F) of a 40% concentration aqueous hydrofluoric acid solution and a 50% concentration ammonium fluoride is used.
= 1: 2 (<2)). As the second solution layer 9, an organic solvent such as hexane, heptane, and octane, and oils and fats such as mineral oil, vegetable oil, and chemically synthesized oil are used. Other solutions which do not react and mix with each other or with the solution layer 10 can also be used.

FIG. 3B shows an etching step for forming a tapered portion 13 near the tip of the fiber. In this case, a 40% concentration aqueous solution of hydrofluoric acid is used as the first solution layer 11, and the second solution layer 9 is the same as that shown in FIG. Etching is performed at the interface between the first solution layer and the second solution layer. This sharpening process is based on Denn
isR. Turner et al. (US 4,469,55)
4). Since the hydrofluoric acid solution has high volatility, there are problems that the concentration gradually changes and that the influence on the human body and the environment is great. The two-layer structure of the hydrofluoric acid solution and the organic solution layer has an effect of preventing volatilization and suppressing hydrofluoric acid released to the atmosphere.

FIG. 3B shows the step of sharpening by chemical etching, but the sharpening can also be performed by a heating and stretching method. FIG. 3C shows the process. While heating the tip of the probe,
Stretch the fiber to both ends and sharpen. As a heating means, a method of condensing and applying a carbon dioxide gas laser beam, a method of passing an optical fiber through the center of a platinum wire wound in a coil shape, and flowing an electric current to the platinum wire to heat it can be used.

When the tip 4 of the sharpened optical probe manufactured by heat drawing is flattened as shown in FIG.
(A) The same steps as those shown in (B) are performed. In this case, it is structurally different that the fiber core portion 2 has a tapered shape due to the sharpening of the tip portion 4 due to the method of heating and stretching. FIGS. 4 and 5 which illustrate detailed steps in FIGS. 4 and 5 show a part of the manufacturing process of an optical probe according to a fourth embodiment of the present invention. FIG. 4A shows a state in which the end face of the fiber is cleaved flat.
This is immersed in the etching solution shown in FIG. Then, as shown in FIG. 4B, the core portion 2 of the fiber is preferentially etched, so that the concave portion 12 can be formed on the end face. Subsequently, the clad portion 3 can be preferentially etched by immersing in the etching solution shown in FIG. 3B, so that the tapered portion 13 as shown in FIG. By making the tip portion tapered once the core portion 2 is recessed once, it is easy to control the etching time for flattening the tip portion 4, so that it has a flatness of nanometer size as shown in FIG. An optical probe can be manufactured with good reproducibility.

FIG. 5 shows a part of the manufacturing process of an optical probe according to a fifth embodiment of the present invention. FIG. 5A shows a fiber end face that has been cut into a tapered shape by the heat drawing method. When this is immersed in the etching solution shown in FIG. 3 (a), as shown in FIG.
Is preferentially etched, so that the recess 1
2 can be produced. Subsequently, the clad portion 3 can be preferentially etched by immersing it in the etching solution shown in FIG. 3B, so that the tapered portion 13 shown in FIG.
Can be produced. In this case, since the tapered shape of the tip is formed in the first heat drawing step, it is not necessary to perform etching at the interface between the two etchants as shown in FIG. You can put it on. By forming the tapered shape at the tip after the core portion 2 is recessed once, it is easy to control the etching time for flattening the tip, so that light having a flatness of nanometer size as shown in FIG. Probes can be produced with good reproducibility.

FIG. 6 shows a part of the manufacturing process of an optical probe according to a sixth embodiment of the present invention. FIG. 9 is a cross-sectional view illustrating a step of depositing a metal film 5 on a portion of the optical fiber formed in the previous step except for a tip 4. As a method of depositing the metal film 5, a thin film deposition method having anisotropy such as vacuum evaporation or sputtering is used, and the thickness is selected in the range of 20 nm to 1000 nm. The deposition direction is behind the tip as shown by the arrow in FIG. 6, and the angle A is selected in the range of 20 degrees to 90 degrees. The size of the tip 4 is the size of the flattened tip 4 of the optical fiber, the thickness of the metal film 5,
It can be changed by the deposition angle.

FIGS. 4, 5, and 6 show the steps of manufacturing the linear light propagation body probe shown in FIG. 1A.
It is also possible to manufacture the hook-shaped light propagation body probe shown in FIG. The functions and effects of the optical probe manufacturing method are as follows.
Figures 4-5, except that the probe tip is shaped like a hook
There is no difference from the operation and effect of the method for manufacturing the light propagation body probe shown in the sixth embodiment.

FIG. 7 shows an example of a scanning probe microscope equipped with an optical probe according to a seventh embodiment of the present invention.
The hook-shaped optical probe 22 shown in the second embodiment of FIG.
At the rear end 7, it is installed on a bimorph 15 which is a vibration means,
The tip of the optical probe 22 is oscillated vertically with respect to the sample 16, and an atomic force or other force acting between the tip of the optical probe 22 and the surface of the sample 16 is subjected to the vibration characteristic of the optical probe 22. Displacement detection means 17 as a change
And X is controlled by the control means 18 so that the distance between the tip of the optical probe 22 and the surface of the sample 17 is kept constant.
In this configuration, the sample is scanned by the YZ movement mechanism 19 to measure the surface shape. At the same time, the light from the optical property measurement light source 21 is introduced into the optical probe 22, the sample 16 is irradiated with light from the tip 4 of the tip of the optical probe 22, and the sample 16 is detected by the optical property measurement light detection means 20, so The optical characteristics are measured.

FIG. 7 shows a transmission type configuration for detecting the measurement light on the back surface of the sample 16, but a reflection type configuration for detecting the measurement light on the sample surface or a configuration for detecting the light with the optical probe 22 is also possible. It is. Although an optical lever is usually used as the displacement detecting means 17, the displacement detecting means 17 becomes unnecessary by using an optical probe having a piezoelectric body. FIG. 7 shows the device configuration for vibrating the optical probe 22, but it is also possible to perform the measurement as a contact mode AFM by not vibrating the bimorph 15 or using a device configuration not using the bimorph 15.

Further, by providing these devices with a reservoir for a reservoir so that the probe and the sample are held in the liquid, measurement in the liquid can be performed. Although the optical probe 22 has been described above, this probe can be used as a probe dedicated to the AFM. In this case, the metal film 5 is not required, and the tip can be made sharper. As the probe material, optical fiber, glass fiber, thin metal wire, or the like can be used. A feature of using the AFM probe as an AFM probe is that, especially in a mode in which the probe is vibrated in a liquid to detect an atomic force, the conventional AFM probe has a plate structure, so that the influence of the viscosity of the liquid and the disturbance vibration transmitted through the liquid are reduced. Although it is affected, it exhibits extremely stable resonance characteristics and can be measured stably.

[0020]

As described above, according to the optical probe and the method of manufacturing the optical probe according to the present invention, the intensity of the evanescent field at the minute aperture is reduced by the incident light in the conventional optical probe utilizing the optical near-field effect. In contrast to the light that has been greatly attenuated, light that enhances the intensity of the evanescent field formed in the minute opening by processing the tip of the optical probe with the minute opening flat at nanometer size. It becomes possible to provide a probe,
Scanning probe microscope observation with a high N ratio has become possible. As a result, the application range of fluorescence image observation, Raman spectroscopy of minute regions, and time-resolved spectroscopy can be greatly expanded. In the application to memory, the writing speed could be improved. This process can improve the productivity of producing probes with good reproducibility.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an optical probe of the present invention.

FIG. 2 is a diagram showing the vicinity of the tip of the optical probe of the present invention.

FIG. 3 is a diagram showing an etching and heat drawing step of the optical probe of the present invention.

FIG. 4 is a view showing a manufacturing process of the optical probe of the present invention.

FIG. 5 is a view showing a manufacturing process of the optical probe of the present invention.

FIG. 6 is a view showing a film forming process of the optical probe of the present invention.

FIG. 7 is a diagram showing an example in which the optical probe of the present invention is mounted on a near-field microscope.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical fiber 2 ... Core part 3 ... Cladding part 4 ... Tip part 5 ... Metal film 6 ... Tip front part 7 ... Tip rear part 8 ... Outer diameter 9. ··· Second solution layer 10 ··· First solution layer 11 ··· First solution layer 12 ··· Indented portion 13 ··· Tapered portion 14 ··· Step-shaped light with reduced outer diameter Probe 15 Bimorph 16 Sample 17 Displacement detecting means 18 Control means 19 XYZ moving mechanism 20 Optical property measuring light detecting means 21 Optical property measuring light source 22 ... Optical probe

Claims (11)

[Claims] 1. An optical probe in which the vicinity of the tip of an optical fiber composed of a core part and a clad part is tapered and the end part functions as an optical aperture, and only the core part whose end part is flat is exposed. An optical probe, wherein a portion other than an end portion is covered with a metal film. 2. The optical probe according to claim 1, wherein the optical probe has a straight shape. 3. The optical probe according to claim 1, wherein the optical probe has a hook shape. 4. The optical probe according to claim 1, wherein the outer diameter of the optical probe in the vicinity of the tip is thinned in a step shape. 5. An optical probe manufacturing method, comprising: a step of preferentially etching a core of a fiber and a step of sharpening a tip of the fiber in the optical probe to flatten the shape of the tip of the core. Method. 6. The optical probe includes a step of heating and thermally breaking the core, a step of preferentially etching the core, and a step of flattening the shape of the core tip by a step of sharpening the tip of the fiber. A method for manufacturing an optical probe, comprising: 7. The optical probe according to claim 5, wherein the etching solution used in the step of preferentially etching the core portion of the optical probe is a mixed solution of hydrofluoric acid and ammonium fluoride. Production method. 8. The distance between the tip of the probe and the surface of the sample or medium to be measured is determined by the operating distance at which an atomic force or other interaction-related force acts between the tip of the probe and the surface. In a scanning probe microscope that scans the sample surface by two-dimensional scanning means and controls the probe along the shape of the surface by control means to measure the sample shape in a state where the probe is brought close to the inside of the probe. Vibrating means for vibrating the tip and the surface relatively horizontally or vertically, displacement detecting means for detecting displacement of the probe, and the tip of the probe based on a detection signal output by the detecting means. A control means for keeping the distance between the surfaces constant, and at least an optical probe according to claims 1 to 4. Scanning probe microscope. 9. The distance between the tip of the probe and the surface of the sample or medium to be measured is determined by the working distance at which an atomic force or other interaction-related force acts between the tip of the probe and the surface. In a state in which the probe is brought close to the inside, the sample surface is scanned by two-dimensional scanning means, and the probe is controlled along the shape of the surface by the control means. In a scanning probe microscope that performs light detection and simultaneously measures a sample shape and two-dimensional optical information, a vibration unit that vibrates the tip and the surface of the probe relatively horizontally or vertically, and displaces the probe. Displacement detecting means for detecting, and a control means for maintaining a constant distance between the tip of the probe and the surface based on a detection signal output by the detecting means. A scanning probe microscope having a step and at least the probe according to claim 1. 10. The distance between the tip of the probe and the surface of the sample or medium to be measured is determined by the working distance at which an atomic force or other interaction force acts between the tip of the probe and the surface. In a state of being close to the inside, while scanning the sample surface by two-dimensional scanning means, controlling the probe along the shape of the surface by control means, in a scanning probe microscope to measure the sample shape, A displacement detection unit for detecting the displacement of the probe, and a control unit for keeping a distance between the tip of the probe and the surface constant based on a detection signal output by the detection unit, and at least from claim 1 A scanning probe microscope comprising the probe according to 4. 11. The distance between the tip of the probe and the surface of the sample or medium to be measured is determined by the operating distance at which an atomic force or other interaction-related force acts between the tip of the probe and the surface. In a state in which the probe is brought close to the inside, the sample surface is scanned by two-dimensional scanning means, and the probe is controlled along the shape of the surface by the control means. In a scanning probe microscope that performs light detection and simultaneously measures a sample shape and two-dimensional optical information, a displacement detection unit that detects displacement of the probe, and a tip of the probe based on a detection signal output by the detection unit. And control means for keeping the distance between the probe and the surface constant; and torsion detecting means for detecting the torsion of the probe, and at least claim A scanning probe microscope comprising the probe according to any one of claims 1 to 4.