JP4021097B2 - Scanning near-field microscope - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides a micro light source that is an optical probe used in a scanning near-field microscope for the purpose of observing the shape of a solid surface in the nanometer region and measuring optical properties by irradiating or exciting the surface of the object to be measured. The present invention relates to a method for controlling the distance between a micro light source and a sample, and a scanning near-field microscope.
[0002]
[Prior art]
An aperture-type optical probe has been reported which is made by sharpening a glass capillary and an optical fiber and further coating the periphery with a metal ( US Patent 4469554, Dennis R. Turner , Japanese Patent Application Laid-Open No. 06-130302 (Genji Otsu), Japanese Patent Application Laid-Open No. 07-174542 ), a probe with a very sharp tip can be produced with the development of micromachining technology. It is now possible to obtain an optical image exceeding the resolution of the above with a scanning probe microscope.
[0003]
There has been proposed a scanning near-field microscope in which an evanescent wave is generated by totally reflecting illumination from the back surface of a sample using a prism or the like, and light is scattered by a probe having a very sharp tip (Japanese Patent Laid-Open No. Hei 6). -160719 Patent Publication No. (Otsu)).
A type of probe that converts the wavelength by modifying an organic dye at the probe tip has been reported (US Pat. No. 5,554,223, Patent 5105305, REBetzig US Pat. No. 5,547,024 Hillner).
[0004]
Also, it has been reported self-luminous type optical probe having a light emitting system inside the probe.
In addition, regarding a high-density memory having a device configuration combining STM and AFM, recording is performed by applying a voltage between the probe recording media in the STM configuration, and reproduction is performed by detecting the recording bit shape in the AFM configuration. Recording / reproducing apparatus to perform, recording / reproducing apparatus for controlling the probe position during recording and reproduction by applying the principle of AFM, and probe during recording and reproduction using deformation of an elastic body supporting the probe Proposals have also been made on recording / reproducing apparatuses that follow the surface of a recording medium (JP-A-1-245445 and JP-A-4-321955).
[0005]
[Problems to be solved by the invention]
However, the conventional aperture type fiber probe uses the waveguide portion to guide light from an external light source to a minute region of the sample. Therefore, an operation for coupling light to the fiber is necessary, and an operation for handling a fiber having a total length of about 1 m which is thin and easily broken is very complicated. In addition, a waveguide optical probe of the order of a cantilever manufactured by a semiconductor process has difficulty in coupling light from an external light source, and the leaked light has an adverse effect on observation with a scanning near-field microscope. In addition, since the probe itself has a low light throughput, the external light source requires a high-power and expensive laser. Further, if it is desired to use light of different wavelengths depending on the purpose, a laser light source capable of oscillating light of a necessary wavelength had to be prepared separately. The laser light source oscillates light with good monochromaticity, so in order to obtain light in a wide wavelength range, wavelength conversion using the nonlinear optical effect is necessary, but there is a wavelength limitation of light transmitted through the fiber itself. Therefore, the absorption measurement of the sample in the scanning near-field microscope could not be performed. Also, US Pat. No. 5,554,223, US Pat. No. 5,547,024 Hillner discloses a method of putting a luminescent material at the tip of the probe tip and illuminating the luminescent material by light excitation from an external light source. there were.
[0006]
Although electroluminescent mechanism towards emit light by the microscopic aperture point type has also been proposed, such as an organic EL element, there is a drawback that a small amount of light as a probe.
Therefore, in order to solve the above problem, the present invention aims to reduce the entire system and improve the operability as a scanning probe microscope and a recording / reproducing apparatus by not using an external light source.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, a first part of the present invention intends to emit light from a minute point of a medium by emitting ultrasonic waves from the outside of the resonator to the medium confined in the resonator. The size of the light emitting point can be controlled by selecting the shape of the resonator, the medium, and the irradiation power of the ultrasonic wave.
[0008]
By these things, sufficient light quantity is obtained, without requiring an external light source. Since the emission point spectrally extends from the ultraviolet region to the visible region, it is possible to perform spectroscopic measurement. Further, since the emission point reaches 5000K when the radiation light is converted into temperature, it can be used as a thermal microscope for imaging a minute region. In addition, since minute spot emission can be generated in the space in the resonator, the light source scans the surface of the object by remote control without touching the object.
[0009]
Since the distance between the sample and the probe is not the base part of the probe, the mechanical displacement of the probe is not detected, but the light scattered by the sample surface is detected and the amount of light is detected. Feedback is applied to the distance between the two so that they are constant. By selecting a medium to be used, light of different wavelengths or light in a wide wavelength range can be emitted, and absorption measurement in a scanning near-field microscope can be performed. The light intensity can be amplified by the power of the applied ultrasonic wave. Since light emission can be controlled by remote scanning, handling as a probe in a conventional SPM is completely different, and a scanning near-field microscope that can be handled as easily as an optical microscope is obtained.
[0010]
An optical system for condensing light on an external light source or an optical fiber is not required, and an inexpensive scanning near-field microscope system can be provided.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[Embodiment 1]
FIG. 1 is a configuration diagram showing a minute light emission point generating apparatus according to Embodiment 1 of the present invention. A resonator 2 having a spherical shape or a part of a spherical surface is filled with a medium 2 (gas or liquid) that induces light emission, and an ultrasonic transducer 3 is attached to the outside of the resonator toward the center. . In order to concentrate energy in as small an area as possible, it is preferable to install a plurality of ultrasonic transducers toward the resonance point in the resonator having a symmetrical shape, and they are arranged in a spatially symmetrical manner, and the number is limited. Absent.
[0012]
The case where H ₂ O is filled in the resonator will be further described. The ultrasonic wave emitted from the ultrasonic transducer is transmitted in a longitudinal wave in the medium, and the sound wave has a pressure, so that a high pressure part and a low pressure part are generated in the resonator. This temporal change in the pressure causes the gas dissolved in H ₂ O to be generated as bubbles (cavities). This bubble grows according to the period of sound pressure and instantaneously contracts and breaks. This is a phenomenon called cavitation (cavity phenomenon), and the inside of the cavity becomes a high temperature and high pressure state which is said to be several thousand degrees and several thousand atmospheres. In such a unique environment, a chemical reaction that does not normally occur can occur, and in the case of H ₂ O, it is liberated to H radical and OH radical under this environment. In the state where cavitation is occurring, when a stronger ultrasonic wave is irradiated, light emission 4 occurs when the bubbles contract. The reason for this is the emission 4 that occurs when the black body width due to heat generated by cavitation and OH radicals liberated by the heat are excited and de-excited by ultrasonic energy.
[0013]
Deliberately reducing the dissolved gas dissolved in water will reduce the number of cavitation bubbles. If the frequency of the sound wave is set to the resonance frequency of the system including the container and water, and the sound pressure is adjusted, only one bubble can be created in the water. The ultrasonic pressure and the buoyancy of the bubbles are balanced, and one bubble can be controlled in the water. When the sound pressure is gradually increased with respect to the bubbles, the bubbles emit light 4 with a sound pressure not less than a certain value and not more than a certain value. When temperature, sound pressure, and frequency satisfy the conditions that stabilize the bubble, the bubble repeats growth and collapse according to the cycle of the sound wave, and emits light every cycle. The resonance condition is about 25 kHz when a 100 ml flask is used, and it is necessary to supply a voltage of about 700 V to the ultrasonic transducer 3. The light emission time is extremely short, on the order of picoseconds. Therefore, when the light emission 4 obtained in this way is used, it is possible not only to perform imaging with a near-field microscope but also to perform time-resolved measurement.
[0014]
Further, since the emission spectrum of the micro light source extends to the ultraviolet region , it is possible to perform absorption measurement and transient absorption measurement using a near-field microscope, which has been impossible until now. The emission wavelength can be controlled to some extent by changing the medium, temperature, sound pressure, and frequency, and it has been confirmed that stable luminescence can be obtained even in a luminol (C ₈ H ₇ N ₃ O ₂ ) solution. ing.
[0015]
In addition, since the inside of the bubble is high temperature and high pressure, it can be used as a near-field thermal microscope or a recording / reproducing apparatus when considered as a minute heat source.
[Embodiment 2]
FIG. 2 is a schematic diagram showing a configuration example as a scanning near-field microscope according to the second embodiment of the present invention. The acoustic resonator may be a flask of about 100 ml or a beaker having a cylindrical shape. However, in order to use it as a near-field microscope, a sample inlet / outlet and a port for incorporating the piezoelectric element into the acoustic resonator 1 are required. . However, since a solution may be used as a medium, the port to be incorporated has a sealed structure. The figure shows an example in which two ultrasonic transducers are attached.
[0016]
Next, control of the distance between the micro light source 7 and the sample 8 will be described. In a normal scanning near-field microscope, a needle-like probe is used to detect the mechanical vibration and deflection of the needle-like part by some method in order to control the relative distance between the light emitted from the tip and the sample. Is going. Since the micro light source 4 of the present invention has a light source floating in the space, there is no equivalent to the needle-like portion that supports it. Since the minute light source 4 is driven at the resonance frequency and is obtained when the resonance condition of the resonator 1 is satisfied, the amount of light is reduced when the sample is completely in contact with the minute light source or the resonance condition is disturbed. Or the light emission disappears. If this is utilized, the distance between the micro light source 7 and the sample 8 can be known by condensing the light from the micro light source 7 with the lens 9 provided outside the transparent resonator 1 and monitoring the intensity. If feedback is applied so as to keep the monitored light quantity at a certain value, the Z distance between the micro light source 7 and the sample 8 can be controlled. Various conditions for obtaining light emission at a minute point are severe, but once a stable condition is found, light emission can be obtained stably. In order not to disturb the resonance conditions, the size of the sample stage placed on the PZT 10 is preferably about 5 mm.
[0017]
As is clear from the above explanation, when the needle-like part accidentally contacts the sample as in a normal scanning near-field microscope, there is no fear of mechanically destroying an expensive probe, which is called operability. In this respect, there is no need to replace the probe, which is simple.
The operation of the scanning near-field optical microscope will be described. In the case of using light emitted from the tip of a short needle as a probe as in a conventional scanning near-field optical microscope, the probe tip is vibrated perpendicularly to the sample by a vibrating means, and atoms acting between the probe tip and the sample surface The XYZ moving mechanism is used to detect the inter-force or other interaction-related force as a change in the vibration characteristics of the probe by the displacement detection means and to control the control means so as to keep the distance between the probe tip and the sample surface constant. The sample was scanned to measure the surface shape. This is known as DFM mode or tapping mode.
[0018]
Alternatively, the probe tip is brought close to the sample, and the atomic force acting between the probe tip and the sample surface or other interaction-related force is detected by the displacement detection means as a change in the probe deflection. The configuration was such that the surface shape was measured by scanning the sample with an XYZ moving mechanism while controlling with a control means so as to keep the distance between the surfaces of the sample constant. This is known as a contact mode.
[0019]
However, since the scanning near-field optical microscope using the micro light source probe of the present invention does not have a short needle portion, a method for detecting displacement as a change in vibration characteristics of the short needle portion or a displacement as a change in deflection of the short needle portion Is not used. As described above, the distance between the micro light source 7 and the sample 8 can be known by collecting the light from the micro light source 7 with the lens 9 provided outside the transparent resonator 1 and monitoring the intensity. The Z distance can be controlled by applying feedback so that the amount of light monitored is kept at a certain value.
[0020]
To observe in the same measurement mode as the DFM mode or tapping mode, the sample 8 side may be vibrated vertically with respect to the micro light source 7 by the PZT 10. As an excellent point in that case, when a short hand is used, it can only vibrate at the mechanical resonance frequency of the short hand, but the method of the present invention does not limit the frequency to be vibrated. However, when used in this mode, the intensity obtained by condensing with the lens 9 provided outside the resonator 1 also repeats the temporal intensity change, so the intensity monitored at the frequency at which the sample 8 is vibrated is measured. Lock-in detection is performed, and feedback is applied based on the change in signal strength as a result.
[0021]
[Embodiment 3]
FIG. 3 is a schematic diagram showing a near-field microscope of a reflective optical system according to Embodiment 3 of the present invention. In the configuration of FIG. 2, the configuration in which the micro light source 7 is observed on the transmission side with respect to the sample 8 is shown, but the components of the resonator 1 (the shape of the acoustic resonator and the arrangement of the ultrasonic transducers) are turned upside down. However, this can be realized by leaving only the objective lens 11 as it is. When trying to use as a recording / reproducing apparatus, there are many opaque media, and such an optical system is advantageous.
[0022]
In addition, chemical applications using ultra-high temperature / ultra-high pressure environment in bubbles and ultraviolet rays with strong light emission are possible.
[0023]
【The invention's effect】
The present invention is implemented in the form as described above, and has the following effects. An optical system that collects light on an external light source or optical fiber by using a probe of a scanning near-field optical microscope as a probe for a scanning near-field optical microscope instead of a conventional optical probe composed of a short needle. This eliminates the need to provide an inexpensive scanning near-field optical microscope system.
[0024]
In addition, since the minute light emission is not at the tip of the base like a short needle, the probe (short needle) itself is not destroyed, and the probe is not necessary to be replaced. Greatly improved. Light emission with a wide range of different wavelengths and wavelengths is obtained, it is a pulse light of about PS, and in the sense that minute point light emission can also be used as a heat source, absorption measurement, fluorescence measurement, time-resolved absorption measurement, time-resolved fluorescence measurement, It can be used for heat measurement, time-resolved heat measurement, and the like.
[0025]
Furthermore, it can be used for chemical applications using ultra-high temperature / ultra-high pressure environment and ultraviolet light with strong light emission, and can be used as chemical synthesis and optical processing technology.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a minute light emission point generating apparatus according to a first embodiment of the present invention.
FIG. 2 is a schematic diagram showing a configuration example as a scanning near-field microscope according to a second embodiment of the present invention.
FIG. 3 is a schematic diagram illustrating a configuration example of a reflection optical system according to a third embodiment of the present invention as a near-field microscope.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Resonator 2 Medium 3 Ultrasonic transducer 4 Light emission 5 Power supply 6 Controller 7 Micro light source 8 Sample 9 Lens 10 PZT
11 Objective lens

Claims (9)

In the scanning near-field microscope for observing the shape of the surface of the object to be measured and measuring optical properties by irradiating or exciting the surface of the object to be measured,
A resonator having a medium made of a gas or a liquid; and an ultrasonic wave generating transducer provided outside the resonator to generate an ultrasonic wave. The ultrasonic wave is applied to the medium enclosed in the resonator. A minute point emission generator that emits light from the medium by a cavity phenomenon at a resonance point in the resonator by irradiating;
The object to be measured provided in the resonator;
An optical system for condensing the emitted light generated in the medium, and a monitor for detecting the intensity of the collected light;
A moving mechanism that moves the object to be measured in the XY direction using a piezo element and scans it, and controls movement in the Z direction so that the emission intensity detected by the monitor is maintained at a predetermined value;
A scanning near-field microscope characterized by comprising:   The scanning near-field microscope according to claim 1, wherein the resonator is spherical or partly spherical.   The scanning near-field microscope according to claim 1, wherein the resonator has a symmetrical shape. The scanning near-field microscope according to claim 1, wherein the medium is H ₂ O or a luminol (C ₈ H ₇ N ₃ O ₂ ) solution.   2. The scanning near-field microscope according to claim 1, wherein the size and color of the light emission generated in the medium vary depending on the frequency and energy of the ultrasonic wave to be irradiated or the type of the medium.   The scanning near-field microscope according to claim 1, wherein the ultrasonic wave generating transducer is disposed at a spatially symmetrical position with respect to the resonator.   The scanning near-field microscope according to claim 1, wherein the optical system is a lens provided outside the resonator.   The scanning near-field microscope according to claim 1, wherein the optical system is an objective lens placed at a position close to the surface of the object to be measured.   The piezo element has a structure in which one objective lens can be accommodated therein, or a plurality of piezo elements have a structure in which an objective lens can be disposed between the piezo elements. The scanning near-field microscope according to claim 8.

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