JPH09281122A - Near-field optical microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make an ultrahigh resolution observation possible regardless of a sample to be conductive or non-conductive by providing a vibration means for vibrating probe tip in the direction perpendicular to the probe axis and a control means for monitoring the probe vibration and controlling the position in the probe axis direction, on the opposite side of the probe tip end. SOLUTION: A metal probe 3 is fixed to a bimorph cell 4 to which a variable frequency oscillator 7 is connected and with this oscillator 7, alternating current voltage is impressed to the element 4 to finely vibrate the probe 3. A means to monitor this fine vibration of the probe 3 and to feedback-control the position of the probe 3 in Z-axis direction of the probe 3 is constituted of a photodetector 13 consisting of a laser diode 10, lens 11 and 12, a half split photodiode and an amplifier, a program installed in a computer 6 to input the output of the photodetector 13 and give a specific controlling output to a Z-axis piezostage 5, and its interface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention inserts a probe into a near field (near field) where an evanescent field generated on the surface of the sample exists, and scans the sample or the probe to obtain optical information on the sample surface. The present invention relates to a near-field optical microscope apparatus capable of super-resolution observation of various information including.

[0002]

2. Description of the Related Art Near-field scanning optical microscopes (NSOM: Near-field Scanning Optical M
icroscope) is the refractive index distribution, absorption coefficient distribution,
It enables super-resolution observation of optical information such as fluorescent substance distribution. The principle of super-resolution in this microscope is to extract high wave number information contained in the evanescent field generated on the sample surface.

Since the evanescent field is localized on the surface of the sample and cannot propagate in space, it was impossible to measure it with a conventional optical microscope. However, the development of a new technique made this measurement possible, and the evanescent field became As a method of measuring the components, firstly, a method of setting a minute aperture in the evanescent field and diffracting the evanescent field in this minute aperture to convert it into propagating light has been proposed. Alternatively, a method has been proposed in which the light is scattered by metal (or metal) and converted into propagating light for measurement. The latter method is disclosed, for example, in Japanese Patent Application No. 4-286046 (JP-A-6-13784).
7).

In the former method of diffracting an evanescent field with a minute aperture and converting it into propagating light, it has been proposed to use a micropipette or an optical fiber as a probe. After sharpening, this probe is provided with a metal coating on the periphery and a minute opening is provided at the tip. The feature of this probe is that diffracted light from a minute aperture is guided inside the probe and measured. Therefore, it is possible to prevent mixing of noise components other than the scattered light from the tip of the probe. However, there is a major drawback that the signal light that is being propagated is absorbed by the coated metal thin film and the S / N is lowered.

On the other hand, a scattering probe NSOM using a dielectric needle or a metal needle with a sharp tip as a scatterer
Then, the scattered light from the tip is detected by an external focusing system without being guided in the probe. In this method, since the wave is not guided inside the probe, there is no absorption during the waveguiding by the metal thin film, and especially when the probe material is metal (metal probe NSOM), the scattering efficiency is much higher than that of the dielectric probe. It is expensive and has a high spatial resolution.

When the evanescent field is measured with the metal probe NSOM, the evanescent field includes the shape and optical information of the sample surface. Therefore, in order to extract only the optical information of the sample, the probe must be removed from the sample surface. It is necessary to control and scan to the position of nm. However, it is very difficult to control the probe tip to a position of several nm from the sample surface.

Therefore, in the metal probe NSOM having the above-mentioned advantageous characteristics, the fact that the probe has conductivity is utilized to make use of the scanning tunneling microscope (STM: Scanning).
Tunneling Microscope) (Satoshi Kawata, Yasushi Inoue: Near-field optical scanning microscope, electron microscope, Vol. 28, No. 2, pp. 137-1)
40 (1993)). In the form combined with this STM control, while keeping the distance between the probe and the sample constant,
It is possible to scan with a metal probe, and an optical image in which the influence of the shape of the sample surface is eliminated is obtained. It has been reported that the super-resolution observation of optical images of magneto-optical discs, rat cardiomyocytes, etc. was successfully performed using this.

[0008]

However, in combination with STM control, a tunnel current must be passed between the probe and the sample, so that a sample having conductivity, a sample coated with a metal thin film, and a conductive substrate can be used. The problem is that the sample itself is constrained by the fact that the sample must be made with a very thin thickness of nanometers or less. (Before observation, it is necessary to give conductivity to a non-conductive sample. Therefore, there is a problem that it cannot be applied to in vivo observation of the surface of a dielectric crystal or biological tissue. Also in the device, ST that handles ultra-small current called tunnel current
The addition of equipment for M control (which also requires auxiliary equipment mainly related to thermal phenomena such as cooling and amplification) leads to an increase in the size of the device and also increases the cost of the device. However, there is also a problem in using the device that a normal technician cannot handle it easily because it is very difficult to handle unless he is skilled in the operation.

[0009]

SUMMARY OF THE INVENTION Therefore, the first object of the present invention is to provide a near-field optical microscope apparatus that enables super-resolution observation of a sample regardless of whether the sample is conductive or non-conductive. It is a second object of the present invention to provide a near-field optical microscope apparatus that can be handled easily and easily by a general engineer without using a special technique.

[0010]

In the near-field optical microscope according to the present invention, a probe having a sharp tip made of a dielectric or metal is inserted into an evanescent field generated on the surface of a sample. Then, the evanescent field is converted into propagating light and the propagating light is detected while scanning the probe or the sample, in a near-field optical microscope capable of observing information on the surface portion of the sample, with the tip of the probe. On the opposite side, a probe exciting means for vibrating the tip of the probe in a direction orthogonal to the axis of the probe is provided, and a control means for monitoring the vibration of the probe and performing feedback control of the axial position of the probe is provided. This is a basic feature. Preferably, the input signal in the feedback control of the control means is a signal of the amplitude of the vibration of the probe. Then, depending on the probe used, it is preferable to vibrate the probe excitation means at the resonance frequency of the probe. Further, preferably, the input signal in the feedback control of the control means is a signal of a phase difference with respect to an excitation reference phase in the vibration of the probe. The near-field optical microscope according to the present invention feeds back the probe height so that the height of the probe is kept constant and the height of the probe is kept constant and / or the amplitude of the probe vibration is constant. A constant distance mode for two-dimensionally scanning the sample while controlling the distance between the probe and the sample surface to be constant is provided.

[0011]

The probe exciting means vibrates the tip of the probe in the direction orthogonal to the axis of the probe. The control unit controls the position of the probe in the axial direction by monitoring the vibration of the probe and utilizing the shear force generated between the probe and the sample. This eliminates the influence of the shape of the surface of the sample regardless of the conductivity of the sample (for example, in vivo observation of a biological sample) and removes optical information (for example, refractive index distribution, absorptance distribution, fluorescent substance distribution). , Etc., super-resolution observation is possible, and the system is basically small and does not need to be large, and there is no operational difficulty that requires skill (exciting the probe,
Therefore, super-resolution observation can be performed easily and easily.

[0012]

[Principle of Distance Control by Share Force] First, the principle of distance control by share force, which is the principle background of the present invention, will be described below. For example,
When controlling the probe-sample distance control using the shear force generated between the probe and sample when the "metal" probe is vibrated, the probe used in the target near-field optical microscope is a thin needle. It has a resonance frequency corresponding to the length, diameter, and bending rigidity of the probe as well as the vibration of. When a forced displacement at the resonance frequency of the probe is applied laterally above the probe, the probe tip is an open end, so that the probe vibrates at the same frequency as the forced displacement frequency.

The probe is brought close to the sample surface while being vibrated. It is said that water molecules are very thinly adsorbed on the surface of the substance existing in the atmosphere to form an adsorption layer (liquid layer). Therefore, when the tip of the probe enters the adsorption layer on the sample surface, the viscous damping force of the adsorption layer on the sample surface acts and the resonance frequency changes. As the distance between the probe and the sample decreases, the length of the probe that comes into contact with the adsorption layer increases, and the viscous damping coefficient increases accordingly. Therefore, the amplitude of the probe vibration is reduced, and the phase difference between the forced periodic vibration and the probe vibration changes.

Here, changes in the amplitude and the phase difference are detected and fed back so that the amplitude or the phase difference is constant, and the height of the probe is controlled. Then, when the probe or the sample is two-dimensionally scanned, the probe traces the sample surface while keeping a constant distance from the sample. Therefore, similarly to the STM and AFM, it is possible to observe the shear force image of the spatial distribution on the surface of the sample. Since a microscope capable of observing a shear force image does not require the conductivity of the sample as in the case of the AFM, an insulating sample can also be observed.

The lateral vibration model of the probe is analyzed.
The probe approaches the sample surface, and the viscous damping acts due to the adsorption layer on the sample surface. Let's replace this with the model in Figure 1 using a spring and dashpot.

Consider a vibration system in which a viscous damping force acts. The spring constant of the spring S is k. All damping forces shall be given by the dashpot D. Dashpot D
The damping force is -c (dx / dt), where c is the viscous damping coefficient of, and acts in the direction opposite to the direction in which the mass m of the mass M moves. Also, the forced periodic displacement Psinwt is the upper end U of the spring.
Therefore, a force of kPsinwt acts on the mass m of the mass body M. Therefore, the equation of motion of mass m is

[0016]

[Equation 1] And rewriting the above equation,

[0017]

[Equation 2] here,

[0018]

(Equation 3) And p indicates the natural frequency when there is no damping.
The solution of the equation (2-2) is a general solution when the right side is 0,
It is given as the sum of special solutions. The general solution when the right side is 0 is

[0019]

(Equation 4) There are various methods to obtain the specific solution of this equation, but it is assumed that the forced displacement causes a vibration having the same frequency as that of the method. However, since the viscous damping force acts, unlike the case where the viscous damping force does not act, it is considered that the displacement that occurs is delayed in phase from the forced displacement. Therefore, the resulting displacement is

[0020]

(Equation 5) far. A and β are undetermined constants,

[0021]

(Equation 6) And rewriting formula (2-5),

[0022]

(Equation 7) Becomes From this, when U and V are calculated,

[0023]

(Equation 8) Becomes Therefore, the solution of equation (2-2) is

[0024]

[Equation 9] Becomes

In the equation (2-9), C and D are obtained from the initial condition, but the first term on the right side is a term representing the natural vibration and is attenuated and disappears with time. However, the term of forced vibration caused by forced displacement continues to be steady vibration. Since only the forced vibration is a problem here, only the forced vibration term is considered without considering the natural vibration term.

From equations (2-5) to (2-7), the forced vibration is

[0027]

(Equation 10) Becomes However, when ζ = μ / p, ζ represents a damping ratio.

The amplitude A and the phase delay β of the displacement caused by the forced displacement can be expressed by a function of ω. Magnification α (= A
/ P) is plotted on the vertical axis and ω / p is plotted on the horizontal axis. When the amplitude-frequency characteristics are illustrated, the frequency response curve of FIG. 2 is obtained. From FIG. 2, the magnification approaches 1 as the frequency of forced displacement becomes lower than the undamped natural frequency of the system, that is, as ω becomes smaller than p. Therefore, the amplitude A of the forced vibration
It can be seen that is equal to the amplitude P of the forced displacement. On the other hand, when ω becomes larger than p, the magnification becomes smaller than 1. When ω is smaller or larger than p, the response curve converges to a constant value regardless of the value of ζ. It has the same characteristics as the response curve without damping. As .omega. approaches p, the magnification rapidly increases and becomes a resonance state. this is,
In equation (2-10), (δA / δ (ω / p)) = 0,

[0029]

[Equation 11] Occurs when the value is

[0030]

(Equation 12) It is. The resonance frequency ω / 2π at this time is called a displacement resonance frequency. From the equation (2-11), the extreme value is at ω / p = 0 when ζ = 1 / √2, and the extreme value does not exist when ζ> 1 / √2.

FIG. 3 shows the relationship between β and ω / p in the equation (2-10) and the phase-frequency response curve. β is the phase difference between the forced displacement and the generated displacement as described above. (2-
From equation (10), when ω <p, tan β is positive and β <90 °,
When ω> p, tan β is negative and β <90 °. Regardless of the value of ζ, β = 90 ° when ω = p, β when ω >> p
= 180 °. Especially when the value of ζ is small, the phase changes rapidly near the resonance point.

Qualitatively summarizing the above analysis results,
As the probe approaches the sample surface, the amplitude of the vibration decreases and the phase shifts with respect to the vibration.When the vibration is applied at the resonance frequency, the probe is affected by the viscous resistance on the sample surface and the amplitude changes greatly. Regarding the phase, the resonance frequency does not change at all, and a slight shift from the resonance point causes a large change.

[0033]

[Embodiment] Therefore, in an embodiment of the present invention, based on the above analysis results, a near-end metal probe using a sharp-pointed metal probe that has higher light utilization efficiency and higher spatial resolution than a dielectric material can be used. The field optical microscope will be described below.

FIG. 4 shows a schematic system configuration of the near-field optical microscope apparatus of one embodiment. 1 is an XY biaxial piezo stage on which the sample 2 is mounted, 3 is a metal probe as a scatterer for inserting the tip into the evanescent field, 4 is the side opposite to the tip 3p of the metal probe 3 (in this case, the upper part of the probe) ) Provided as a probe excitation means, a bimorph type piezo element 5 is a Z axis for precisely driving the structure of the metal probe 3 and the bimorph type piezo element 4 in the height direction or in the axial direction of the metal probe 3, that is, the Z axis direction. The piezo stage, the Z-axis piezo stage 5 and the XY two-axis piezo stage 1 are respectively controlled via an interface based on program means built in the computer 6. Further, an alternating voltage is applied from the oscillator 7 to the bimorph type piezo element 4 provided above the metal probe 3.

The means for monitoring the minute vibrations of the metal probe 3 and performing feedback control of the probe position in the axial direction of the probe, that is, the Z-axis direction, is laser diode 10, lens 11, lens 12, in this embodiment.
It is configured to include a photodetector 13 including a two-divided photodiode and an amplifier, and a program built in the computer 6 for inputting the output of the photodetector 13 and giving a predetermined control output to the Z-axis piezo stage 5, and its interface.

More specifically, the material of the metal probe 3 is platinum iridium (PtIr), which is widely used for the probe of the metal probe NSOM. PtIr has no decrease in scattered light rate due to oxidation, is soft, and has excellent workability. Wrapping film sheet (alumina, # 15000, particle size 0.3μ)
m, Sumitomo 3M), and sharpened by mechanical polishing.

In order to make the metal probe 3 vibrate slightly,
The probe is fixed to the bimorph type piezo element 4, and this piezo element 4 has a variable frequency oscillator (WA
VETEKMODEL162, frequency 0.3 mHz to 30 MHz) is connected, and an alternating voltage (to 10 V) is applied to the bimorph type piezo element 4 by this oscillator. As shown in FIG. 5, the bimorph type piezo element 4 has a structure in which two thin plates of piezoelectric ceramic elements are bonded together with a metal elastic plate as a center electrode. By applying a voltage,
As shown in FIG. 6B, one side extends and the other side contracts, so that a bending displacement occurs according to the waveform of the applied voltage. The bending displacement is used to vibrate the metal probe 3, and the tip of the probe is slightly vibrated in the direction orthogonal to the axial direction of the probe.

In order to measure the minute vibration of the metal probe 3, a laser diode 10 (Panas) having a wavelength of 674 nm is used as a light source.
onic LN9R05N, maximum output 5mW) is used, and the detector is split into two photodiodes 13 (Hamamatsu Photonics S2721-0
2, element gap 5 μm) is used. Amplitude of probe vibration is A / D conversion board (Interface AZI-3503)
Through computer 6 (PC-9801RA).

For controlling the height of the probe and the Z-axis, a high-precision piezo stage 5 (Queensgate) with a built-in capacitance type sensor is used.
Instruments DPT / AX100, accuracy 1.5 nm), which was controlled by computer 6 through RS-232C. For scanning the sample 2 side, a high-precision 2-axis piezo stage 1 (Physik Instrumen) with a built-in capacitance type sensor is used.
te P-915.583) was used. The piezo stage can be controlled from a computer via a D / A conversion board (Interface AZI-35
03).

A method for measuring minute vibrations of the metal probe 3 will be described. A laser beam focused by a lens 11 (NA is 0.615) illuminates the vicinity of the tip of the probe, and the probe image is illuminated by a single lens 12 (f = 50.2mm), and imaging is performed on the boundary line of the photodiode. In this system, the tip of the probe was vibrated and the intensity difference between the two detection surfaces of the two-divided photodetector 13 was measured to generate a waveform representing a minute vibration of the probe.

Now, with the above configuration, first, the resonance frequency of the probe was measured. In metal probe, by utilizing the resonance phenomenon of vibration,
That is, the optical or electrical sensitivity can be increased.

In the measurement, an AC voltage was applied from the oscillator 7 to the bimorph type piezo element 4 with the probe separated from the sample, and the metal probe 3 was vibrated. And
While observing the output waveform of the photodetector 13 with an oscilloscope, the applied AC voltage was kept constant, the frequency was changed, and the amplitude was measured.

The results are shown in FIG. The peak amplitude of the probe vibration was 4706 Hz. The resonance frequency is
Depending on the length, diameter, bending rigidity, etc. of the probe, the longer the length and the smaller the diameter, the higher the resonance frequency. When the same measurement was performed with multiple probes,
The resonance frequency was in the range of about 1 kHz to 10 kHz.

Further, when the applied voltage to the bimorph type piezo element 4 was lowered, the amplitude of the probe vibration was also reduced in proportion thereto.

Next, the relationship between the probe-sample distance and the amplitude was examined. While vibrating the probe at the resonance frequency,
The amplitude change was examined when the sample was brought close to the sample surface. Sample 2
A slide glass was used for. The amplitude of the probe vibration was measured while changing the distance between the probe and the sample by 1 nm.

The results are shown in FIG. The horizontal axis is the probe
The distance between the samples and the vertical axis indicate the amplitude of probe vibration. Figure 7
It can be seen that the amplitude of the probe vibration decreases as the probe approaches the sample, and the amplitude is proportional to the probe-sample distance. Moreover, the slope of the amplitude with respect to the distance between the probe and the sample is constant regardless of the voltage applied to the bimorph type piezo element. Therefore, it can be seen that the distance where the amplitude is affected is proportional to the initial value of the amplitude of the probe vibration.

Based on the above preliminary measurement, the shear force image on the surface of the sample was observed using the apparatus system of this example. Sample 2 is a magneto-optical disk substrate (M
O) was used. FIG. 8 shows the structure of this magneto-optical disk substrate. The magneto-optical disk substrate is made of glass (refractive index 1.5)
The grooves with a width of about 500 nm and a depth of 40 nm are lined up at 1.6 μm intervals.

FIG. 9 shows a shear force image of the magneto-optical disk substrate. The height of the metal probe 3 was kept constant and the sample 2 was scanned (constant height mode). The scanning range is 5 μm × 5 μm, and the scanning pitch is 100 nm × 100 nm. That is, it is a scan of 50 × 50 points. The voltage applied to the piezo element 4 at this time was 3 V, and the resonance frequency of the probe was 4656 Hz. The vibration direction of the probe is shown in Fig. 4.
Is parallel to the direction in which the grooves of the magneto-optical disk extend. As can be seen from FIG. 9, it can be observed that the grooves are periodically arranged at intervals of 1.6 μm. Note that FIG. 10 shows a cross section of FIG. 9. In addition, as a supplementary note, in the constant height mode, the position of the metal probe 3 in the Z-axis direction is fixed, but in order to select a height that does not collide with the surface of the sample 2 prior to actual scanning,
An appropriate scanning point is selected (about 20 points), feedback control of probe vibration is performed, and the distance from the sample surface is measured.

Next, the height of the probe is feedback-controlled from the computer 6 in real time so that the amplitude of the probe vibration is constant, the distance between the probe and the sample surface is kept constant, and the sample 2 is scanned and measured. (Constant distance mode).

FIG. 11 shows the measured shear force image. Sample 2 is a magneto-optical disk substrate that is exactly the same as the constant height mode. Scan range is 5μm x 5μ
m, the scan pitch is 100 nm × 100 nm. The voltage applied to the piezo element 4 at this time was 3 V, and the resonance frequency of the probe was 4656 Hz. The probe-sample distance was fixed at 20 nm. The vibration direction of the probe is the horizontal direction in FIG. 4 and is parallel to the direction of the groove of the magneto-optical disk. It can be clearly seen from FIG. 11 that the grooves are periodically arranged at intervals of 1.6 μm. Further, FIG. 12 shows a cross section of FIG. 11. The depth of the groove is about 30 nm, and it can be seen that it substantially matches the sample structure of FIG.

Considering the results of the above-mentioned examples, when the probe is slightly vibrated at the resonance frequency and brought close to the sample surface, its amplitude in the vicinity of the sample decreases in proportion to the distance between the probe and the sample. Further, the slope of the amplitude with respect to the distance between the probe and the sample is the same regardless of the initial value of the amplitude of the probe vibration. It is considered that this is because the probe and the sample are not vertical but are tilted, and thus contact the sample surface when the probe vibrates. Therefore, it is considered that as the amplitude of the probe vibration increases, the distance over which the amplitude changes becomes longer.

At any applied voltage, the probe-
Since the slope of the amplitude is equal to the distance between the samples, the amount of change in the amplitude when the position of the probe changes is also equal. Therefore, the distance accuracy determined by the S / N of the signal was the same at any voltage, which was 3 nm. The larger the applied voltage is, the easier the measurement becomes, but the in-plane resolution is lowered due to the increase in the amplitude of the probe vibration. Therefore, it is considered preferable to reduce the amplitude of probe vibration as much as possible.

Next, comparing and considering the constant height mode and the constant distance mode, in the constant height mode, the dynamic range in the height direction is determined by the initial value of the amplitude of the probe vibration, so that the range is narrow. The range will be exceeded due to the inclination of. In order to widen the dynamic range, it is necessary to increase the amplitude of the probe vibration, but if the amplitude of the probe vibration is increased, the spatial resolution decreases. On the other hand, in the constant distance mode, since the probe position is controlled by feedback, the dynamic range in the height direction is the same as the dynamic range of the piezo in the height direction. Therefore, the dynamic range becomes wider than that in the constant height mode. Further, since the amplitude of the probe vibration can be reduced as much as it can be detected, the spatial resolution can be improved as compared with the constant height mode. From these points,
It can be seen that the measurement in the constant distance mode is superior.

In the above embodiment, the amplitude signal is used for the feedback control by monitoring the probe vibration, but the phase difference of the probe vibration with respect to the phase of the reference vibration applied to the exciting means may be used. Is obvious as in the above-described vibration model analysis, and a phase difference can be detected and feedback controlled. At this time, as shown in FIG. 3, the resonance frequency cannot be used, and a frequency slightly deviated from the resonance frequency is used.

For the light scattering NSOM probe, whichever dielectric or metal is used,
In addition to providing an optical system for collecting scattered light, a probe having a detection unit capable of directly photoelectrically converting scattered light at the tip or the tip of the probe may be used. It can be arranged and operated in the same manner as in the example.

[0056]

According to the present invention, the influence of the sample surface can be eliminated without performing STM control, and only the optical information can be observed by super-resolution. Super-resolution observation can be performed without any special preliminary operation even in biological cell tissues, etc.
(In vivo observation is possible), and further, there is an effect that this is remarkably improved in terms of easiness of operation of the device while maintaining the miniaturization of the device.

[Brief description of drawings]

FIG. 1 is a diagram showing a vibration model of a probe.

FIG. 2 is a diagram showing amplitude-frequency characteristics.

FIG. 3 is a diagram showing a phase-frequency characteristic.

FIG. 4 is an illustrative view of a main part of an embodiment of the present invention.

FIG. 5 is an operation explanatory view of a bimorph type piezo element which is one of the excitation means, and FIG. 5A shows the case where V = 0 and FIG.
Is an explanatory diagram when V ≠ 0.

FIG. 6 is a diagram showing a relationship between applied frequency and amplitude of a used probe.

FIG. 7 is a diagram showing a relationship between a distance between probed sample surfaces and amplitude.

FIG. 8: Sample structure of magneto-optical disk substrate used for observation
It is a figure which shows (cross section).

FIG. 9 is a photograph replacing a drawing showing a shear force image on the surface of a magneto-optical disk substrate when operated in a constant height mode.

10 is a diagram showing a profile in one section of the image of FIG.

FIG. 11 is a photograph replacing a drawing showing a shear force image on the surface of a magneto-optical disk substrate when operated in a constant distance mode.

12 is a diagram showing a profile in one section of the image of FIG.

[Explanation of symbols]

 1 XY Y-axis piezo stage 2 Sample 3 Metal probe 4 Bimorph type piezo element 5 Z-axis piezo stage 6 Computer 7 Oscillator 10 Laser diode 11, 12 lens 13 Two-division photo detector

Claims (5)

[Claims] 1. A probe having a sharp tip made of a dielectric or metal is inserted into an evanescent field generated on the surface of a sample, the evanescent field is converted into propagating light, and the propagating light is converted into the probe or the sample. In a near-field optical microscope capable of detecting information while scanning and observing information on the surface portion of the sample, a probe excitation for vibrating the tip of the probe in a direction orthogonal to the axis of the probe on the side opposite to the tip of the probe. The near-field optical microscope apparatus is provided with a control means for monitoring the vibration of the probe and performing feedback control of the axial position of the probe. 2. The near-field optical microscope apparatus according to claim 1, wherein the input signal in the feedback control of the control means is a signal of the amplitude of the vibration of the probe. 3. The near-field optical microscope apparatus according to claim 1, wherein the input signal in the feedback control of the control means is a phase difference with respect to an excitation reference phase in the vibration of the probe. 4. The probe excitation means is vibrated at the resonance frequency of the probe according to the probe used.
The near-field optical microscope apparatus according to claim 1 or 2. 5. The probe and the sample are controlled by feedback control of the height of the probe so that the height of the probe is kept constant and the sample is two-dimensionally scanned in a constant height mode and / or the amplitude of probe vibration is constant. The near-field optical microscope according to any one of claims 1 to 4, further comprising a constant distance mode in which a sample is two-dimensionally scanned while maintaining a constant distance between the surfaces.