Cantilever array and scanning probe microscope including a sliding, guiding, and rotating mechanism

There are provided a cantilever array having a simple structure and being able to reliably detect a surface of a sample, a method for fabricating the same, a scanning probe microscope, a sliding apparatus of a guiding and rotating mechanism, a sensor, a homodyne laser interferometer, a laser Doppler interferometer having an optically exciting function for exciting a sample, each using the same, and a method for exciting cantilevers.The cantilever array includes a large number of compliant cantilevers (3) sliding on a surface (2) of a sample (1).

TECHNICAL FIELD

The present invention relates to a cantilever array having a single nano-sized mechanical oscillator or at least a million of nano-sized mechanical oscillators per square centimeter arranged in an array configuration, a method for fabricating the same, a scanning probe microscope, a sliding apparatus of a guiding and rotating mechanism, a sensor, a homodyne laser interferometer, a laser Doppler interferometer having an optically exciting function for exciting a sample, each using the same, and a method for exciting cantilevers.

BACKGROUND ART

The inventor has proposed a nanocantilever having a single nanometer-sized mechanical oscillator or at least a million of nano-sized mechanical oscillators per square centimeter arranged in an array configuration.

DISCLOSURE OF INVENTION

However, the proposed nanocantilever has a variety of problems in practical uses.

In order to further improve the nanocantilever, the present invention provides a scanning probe microscope in which probe nanometer-sized mechanical oscillators having natural frequencies of 1 MHz to 1 GHz are formed, for example, on an Si wafer by making use of a semiconductor processing technique, and a chip having the oscillators lying in contact with a sliding surface is disposed so as to provide a self-propelled probe; by providing each oscillator with a cantilever-shaped member, exerting a vibration on it, and propagating a surface acoustic wave, the surface acoustic wave having an amplitude of a few nm is amplified with a Q factor of the oscillator so as to improve efficiencies of an actuator and an optical modulator; or while the cantilever-shaped members are sliding on the surface of a sample, fine irregularities are detected as changes in luminance in accordance with reflecting states of light with which the surface is irradiated.

Also, its object is to provide a scanning probe microscope for obtaining an image from a change in vibration frequency and a sensor for measuring a substance or a mass, both by exciting each cantilever with light.

It is an object of the present invention to provide a cantilever array having a simple structure and being able to reliably detect a surface of a sample, a method for fabricating the same, a scanning probe microscope, a sliding apparatus of a guiding and rotating mechanism, a sensor, a homodyne laser interferometer, a laser Doppler interferometer having an optically exciting function for exciting a sample, each using the same, and a method for exciting cantilevers.

In order to achieve the above objects, according to the present invention,

[1] a cantilever array includes a large number of compliant cantilevers sliding on a surface of a sample,

[2] in the cantilever array set forth in [1], the cantilever array is densely disposed on the surface of the sample so as to propagate a surface acoustic wave in the sample,

[3] a cantilever array includes a plurality of cantilevers disposed so as to have respectively different natural frequencies,

[4] a method for fabricating a cantilever array includes the steps of: controlling a potential of each row of the cantilever array prepared from a single-crystal silicon so as to generate a high electric field between corresponding mutually opposing probes; and designating an orientation of a whisker crystal by using an electrophoresis in liquid or an electric field in gas so as to perform a growth control of the whisker crystal,

[5] in the method for fabricating a cantilever array set forth in [4], the whisker crystal is a carbon nanotube,

[6] a method for fabricating a cantilever array includes the steps of: disposing a flat electrode so as to face a surface of a single-crystal-silicon cantilever array; generating a concentrated electric field at the top of each probe; and growing needle crystals in the normal direction of a substrate,

[7] a scanning probe microscope is passively controlled such that each probe bears its share of the own weight of a chip having cantilevers and an external load, and a surface pressure of the probe lies within a certain range,

[8] a sliding apparatus of a guiding and rotating mechanism is passively controlled such that each probe bears its share of the own weight of a chip having cantilevers and an external load, and a surface pressure of the probe lies within a certain range,

[9] in a scanning probe microscope, fine irregularities of a sample corresponding to displacements of large number of cantilevers caused by an optical lever are detected as changes in luminance by an image capture apparatus,

[10] in a substance or mass sensor, fine irregularities of a sample corresponding to displacements of large number of cantilevers caused by an optical lever are detected as changes in luminance by an image capture apparatus,

[11] in a scanning probe microscope, cantilevers are irradiated with light and an interference luminance corresponding to a micro-cavity length between each cantilever, and a reference surface is observed by using an image capture apparatus,

[12] in a substance or mass sensor, cantilevers are irradiated with light, and an interference luminance corresponding to a micro-cavity length between each cantilever and a reference surface is observed by using an image capture apparatus,

[13] in a scanning probe microscope, fine irregularities of a sample corresponding to displacements of large number of cantilevers caused by an optical interferometer are detected as changes in luminance by an image capture apparatus,

[14] in the scanning probe microscope set forth in [13], a range of positions at which interference occurs is limited by using a low-coherent light source as a light source so as to reduce an affect of parasitic interference,

[15] in a substance or mass sensor, fine irregularities of a sample corresponding to displacements of large number of cantilevers caused by an optical interferometer are detected as changes in luminance by an image capture apparatus,

[16] in the substance or mass sensor set forth in [15], a range of positions at which interference occurs is limited by using a low-coherent light source as a light source so as to reduce an affect of parasitic interference,

[17] in a scanning probe microscope, a heterodyne laser Doppler meter is used for detecting a vibration of a cantilever,

[18] in a substance or mass sensor, a heterodyne laser Doppler meter is used for detecting a vibration of a cantilever,

[19] a scanning probe microscope includes an optical microscope coaxially disposed with a cantilever-detecting optical system,

[20] a substance or mass sensor includes an optical microscope coaxially disposed with a cantilever-detecting optical system,

[21] an optical-fiber homodyne laser interferometer includes a fine-cantilever-detecting optical system for positioning a fine cantilever at a laser spot,

[22] The optical-fiber homodyne laser interferometer set forth in [21] includes a fine-cantilever-detecting optical system for positioning the fine cantilever at a laser spot and an optical microscope coaxially disposed with the fine-cantilever-detecting optical system,

[23] in a laser Doppler interferometer having an optically exciting function for exciting a sample, the sample is irradiated with modulated light via a cantilever by using an output signal of the laser Doppler interferometer and a vibration of the sample is excited by the irradiation light so that the frequency characteristic and the mechanical characteristic of the sample are measured,

[24] in the laser Doppler interferometer having the optically exciting function for exciting a sample, set forth in [23], a self-excited loop including the laser Doppler interferometer is formed,

[25] in the laser Doppler interferometer having the optically exciting function for exciting a sample, set forth in [23], light is modulated by using a signal whose frequency is swept by a network analyzer, a vibration of the sample is excited by using the modulated light, and an output of the laser Doppler interferometer observing a vibration of the sample at the same time is connected to a signal input of the network analyzer so as to measure the frequency characteristic of the sample,

[26] in the laser Doppler interferometer having the optically exciting function for exciting a sample, set forth in [23], the light for vibration excitation is superimposed on measuring light of the laser Doppler interferometer so as to measure and excite a vibration with a single light path,

[27] in the laser Doppler interferometer having the optically exciting function for exciting a sample, set forth in [23], by realizing a self-excited vibration of the cantilever at its natural frequency, the interaction between the top of the cantilever and the sample and a change in mass accreted on the top of the cantilever are detected as a change in self-excited frequency or a change in amplitude or phase of self-excited vibrations,

[28] a method for exciting cantilevers includes the step of irradiating the rear surface of a substrate having a large number of cantilevers disposed thereon with light having a uniform quantity and a uniform wavelength so as to self-excite all cantilevers at respective natural frequencies thereof,

[29] a method for exciting cantilevers includes the step of irradiating the rear surface of a substrate having a large number of cantilevers disposed thereon with intensity-modulated light so as to bring the modulation frequency and the natural frequency of the cantilevers in agreement with each other,

[30] a method for exciting cantilevers includes the step of displacing a cantilever array itself or a physical object supported by the cantilever array by using a group of the cantilevers vibrating in the cantilever array,

[31] a method for exciting cantilevers includes the step of performing sensing or processing by using a group of the cantilevers vibrating in a cantilever array,

[32] a method for exciting cantilevers includes the step of irradiating a cantilever array with light having a uniform quantity so as to excite vibrations of the cantilevers and resultantly to cause clearances of air gaps to vary at a certain frequency so that quantities of reflected light and a transmitted light are modulated at the same frequency,

[33] a method for exciting cantilevers includes the step of irradiating a cantilever array formed by a group of cantilevers having respectively different natural frequencies with light having a uniform quantity so as to provide light modulated at a plurality of modulation frequencies as reflected light and/or transmitted light,

[34] a method for exciting cantilevers includes the step of irradiating a cantilever array with a light having a uniform quantity so as to generate traveling waves on the surfaces of the cantilevers and resultantly to modulate frequencies of reflected light and/or transmitted light, and

[35] a method for exciting cantilevers includes the step of irradiating a cantilever array formed by a group of cantilevers having respectively different natural frequencies with light having a uniform quantity so as to provide light having a plurality of frequencies as reflected light and/or transmitted light.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1is a diagrammatic view of a nanocantilever array according to a first embodiment of the present invention.

In this figure, with respect to reference numerals1to5,1denotes a sample (substrate),2denotes a sliding surface of the substrate1,3denotes a nanocantilever array,4denotes a large number of compliant nanocantilevers (oscillators), and5denotes sliding directions of the nanocantilever array3.

When the nanocantilever array3formed by the large number of compliant nanocantilevers4is activated in the sliding directions5, a condition under which the sliding surface2is very unlikely to provide a frictional condition is achieved.

FIG. 2is a diagrammatic view of a nanocantilever array according to a second embodiment of the present invention.

In this figure, with respect to reference numerals11to16,11denotes a sample (substrate),12denotes a surface of the substrate11,13denotes a nanocantilever array densely disposed on the surface12of the substrate11,14denotes cantilevers (oscillators),15denotes a propagating direction of a surface acoustic wave, and16denotes vibrating directions of the cantilevers14.

As shown in the figure, the cantilevers14are densely disposed on the surface12of the substrate11so as to propagate a surface acoustic wave in the substrate11. Since the nanocantilever array13has a Q factor of about 10,000 in vacuum, a surface acoustic wave having an amplitude of a few nm is amplified with Q factors of the cantilevers (oscillators)14.

Efficiencies of an actuator and an optical modulator can be improved by making use of the above phenomenon.

Meanwhile, the shape of the cantilever and symmetric and asymmetric properties thereof with respect to its supporting portion can be changed in accordance with its application.

FIG. 3is a diagrammatic view of a nanocantilever array according to a third embodiment of the present invention, having a structure in which cantilevers have respectively different natural frequencies.

In this figure, with respect to reference numerals references21to27,21denotes a sample (substrate),22denotes an upper surface of the substrate,23denotes a cantilever array,24A to24E denote cantilevers,25denotes probe masses,26denotes samples, and27denotes vibrating directions of the cantilevers.

In this embodiment, in the cantilever array23, the cantilevers24A to24E are formed so as to have respectively different natural frequencies. In other words, the cantilever24A has the highest natural frequency (small in probe mass) and the cantilever24E has the lowest natural frequency (large in probe mass). In order to make the natural frequencies of the cantilevers24A to24E different from each other, sizes of probes serving as masses of the corresponding cantilevers or lengths of the corresponding cantilevers are determined so as to differ from each other. In order to make the sizes of the probes different from each other, the thickness of a top silicon layer of an SOI substrate is previously designed so as to have a gradient. In order to make the lengths of the cantilevers different from each other, for example, a method for providing a gradient to pitches of a mask is available.

By fixing the specific samples26to the cantilever array23, a spectroscopy can be performed. In other words, any one of the cantilevers24A to24E having a natural frequency which is closest to a specific frequency characteristic of the samples26responds to the natural frequency and is detected in accordance with the vibration amplitude of the cantilever.

In the meantime, when a method for preparing cantilevers by using a single-crystal silicon is used, several millions to several hundred millions of cantilevers can be prepared by one operation on a chip having a few square centimeter.

Also, by disposing a large number of cantilevers in a frequency band over which an observation is performed, spectroscopy can be performed with a fine frequency spacing.

FIG. 4illustrates a cantilever array prepared from a single-crystal silicon, according to a fourth embodiment of the present invention, whereinFIG. 4(a) is a perspective view of the cantilever array andFIG. 4(b) is a magnified perspective view of the same.

In these figures, with respect to reference numerals31to36,31denotes a base substrate,32denotes a cantilever array,33denotes mutually opposing probes,34and35denote electrodes, and36denotes a power source.

A potential of each row of the cantilever array32prepared from a single-crystal silicon is controlled so as to generate a high electric field between the corresponding mutually opposing probes33. Thus, a growth control of a whisker crystal such as a carbon-nanotube while designating a growing orientation of the same by using an electrophoresis in liquid or an electric field in gas is possible.

Although it has been heretofore difficult to control growing spots and orientations of fine needle samples, by controlling a potential of each of mutually opposing rows of the cantilever array32, the above problem is solved. In addition, in the cantilever array32, several millions to several hundred millions of cantilevers can be prepared by one operation, whereby fine needle samples can be prepared by one operation. In the single-crystal-silicon cantilever array, a silicon and a silicon oxide layer of the base substrate31are electrically insulated from each other at each cantilever row. Accordingly, an external potential can be applied on each row through wires or by injecting an electric charge.

FIG. 5is an illustration of a method for growing a needle crystal according to a fifth embodiment of the present invention.

In this figure, with respect to reference numerals41to50,41denotes a chamber,42denotes a gas feed port,43denotes a gas discharge port,44denotes a substrate,45denotes an upper surface of the substrate44,46denotes a single-crystal-silicon cantilever array,47denotes needle-crystal growing spots,48denotes a flat electrode,49denotes an alternating-current power source, and50denotes lead wires.

The flat electrode48is disposed so as to face the single-crystal-silicon cantilever array46and a concentrated electric field is generated on the top of each probe so that needle crystals grow in the normal direction of the substrate44.

FIG. 6is a diagrammatic view of a self-propelled, scanning probe microscope according to a sixth embodiment of the present invention.

In this figure, with respect to reference numerals51to55,51denotes a sample,52denotes a sliding surface of the sample51,53denotes a probe (nanocantilever array),54denotes a large number of compliant nanocantilevers (oscillators), and55denotes sliding directions of the sample51.

This embodiment serves so as to construct a self-propelled, scanning probe microscope or a guiding mechanism, as also shown inFIG. 1, which is passively controlled such that each probe53bears its share of the own weight of a chip having the cantilevers54and such that a surface pressure of the probe53lies within a certain range. As a result, a self-propelled, scanning probe microscope scanning with a force of several tens of nN or less can be achieved without performing an active control in the normal direction of the probe.

A displacement measurement of the cantilevers54covers one, a few, or all of them of the cantilever array53.

In order to achieve a self-propelled type, a method with which a standing wave of light is generated between a substrate and the cantilevers54so as to cause each cantilever54to generate an isotropic vibration in the sliding directions55due to its structure is employed.

Alternatively, a method with which a surface acoustic wave is generated in the sample51or in the cantilever array53so as to displace the cantilever array53is available.

FIG. 7is a diagrammatic view of a scanning probe microscope, a substance sensor, or a mass sensor according to a seventh embodiment of the present invention.

In this figure, with respect to reference numerals60to70,61denotes a sample,62denotes a surface of the sample61,63denotes a probe (nanocantilever array),64denotes a large number of compliant nanocantilevers (oscillators),65denotes an antireflective film,66denotes a beam splitter or a half-mirror,67denotes optical-lever incident light,68denotes reflected light,69denotes an image-forming lens,70denotes an image capture apparatus (image pickup device) such as a CCD camera, and60denotes sliding directions of the sample61.

In this embodiment, when the optical-lever incident light67is incident on the probe63, displacements of the nanocantilevers64cause the reflected light68representing fine irregularities of the surface62of the sample61to be captured into the image capture apparatus70via the image-forming lens69.

More particularly, the cantilevers64are observed by using the image-forming lens69and the image capture apparatus70such as a CCD camera, and the cantilevers64are irradiated with the optical-lever incident light67. The reflected light68in accordance with a posture of each cantilever64is incident on the image capture apparatus70. Angular displacements of the cantilevers64allow the fine irregularities of the surface62of the sample61to be converted into changes in luminance in the image capture apparatus70such as a CCD camera.

By two-dimensionally scanning the sample61in a range sufficient to cover a pitch of the cantilevers64, the entire surface62of the sample61can be observed.

As mentioned above, the entire surface of a sample can be observed by using optical-lever incident light and a large number of cantilevers.

FIG. 8is a diagrammatic view of a scanning probe microscope, a substance sensor, or a mass sensor according to an eighth embodiment of the present invention.

In this figure, with respect to reference numerals71to80,71denotes a sample,72denotes a surface of the sample71,73denotes fine interference cavities of a probe (nanocantilever array),74denotes a large number of compliant nanocantilevers (oscillators),75denotes a reference surface,76denotes a beam splitter or a half-mirror,77denotes incident light,78denotes reflected light,79denotes an image-forming lens,80denotes an image capture apparatus (image pickup device) such as a CCD camera.

As shown in the figure, the cantilevers74are observed by using the image-forming lens79and the image capture apparatus80such as a CCD camera and are irradiated with light. An interference luminance in accordance with a micro-cavity length between each cantilever74and the reference surface75is incident on the image capture apparatus80.

As described above, by two-dimensionally scanning the sample71in a range sufficient to cover a pitch of the cantilevers74, the entire surface72of the sample71can be observed.

This embodiment serves to construct a scanning probe microscope, a substance sensor, or a mass sensor in which displacements of a large number of cantilevers are detected by an optical interferometer.

Also, according to a ninth embodiment of the present embodiment, when displacements of a large number of cantilevers are to be detected by an optical interferometer, in order to reduce interference caused by other than a light lever, a method for reducing an affect of parasitic interference by using a low-coherent light source such as an SLD (super-luminescent diode) or a white light source so as to limit a range of positions at which interference occurs is available.

FIG. 9is a diagrammatic view of a scanning force microscope, a substance sensor, or a mass sensor (first example) according to a tenth embodiment of the present invention, each using a heterodyne laser Doppler meter.

In this figure, with respect to reference numerals90to106,90denotes an optical fiber,91denotes a laser emitter,92denotes a quarter wave plate,93denotes a half-mirror,94denotes an objective lens,95denotes an XYZ piezo scanner,96denotes a sample,97denotes a cantilever,98denotes a mirror,99denotes an image-forming lens,100denotes an XY stage,101denotes an image capture apparatus (image pickup device) such as a CCD camera,102denotes an optical system unit,103denotes an XYZ positioning mechanism of the optical system unit102,104denotes an AFM base plate,105denotes a vacuum chamber partition, and106denotes a stage-supporting spring.

FIG. 10is a diagrammatic view of a scanning force microscope, a substance sensor, or a mass sensor (second example) according to an eleventh embodiment of the present invention, each using a heterodyne laser Doppler meter.

In this figure, with respect to reference numerals110to121,110denotes a vacuum chamber,111denotes an optical semiconductor device,112denotes an electrode,113denotes a lead wire for feeding an electric power to the electrode112,114denotes an XYZ piezo scanner of a sample,115denotes the sample,116denotes a cantilever,117denotes an objective lens,118denotes reflected light,119denotes an image-forming lens,120denotes an XY stage, and121denotes an image capture apparatus (image pickup device) such as a CCD camera.

FIG. 11is a diagrammatic view of a scanning force microscope, a substance sensor, or a mass sensor (third example) according to a twelfth embodiment of the present invention, each using a heterodyne laser Doppler meter.

In this figure, with respect to reference numerals122to132,122denotes a sample-preparing vacuum chamber,123to125denote rods for transporting a sample and a cantilever,126denotes an optical fiber,127denotes an optical system unit,128denotes a laser emitter,129denotes a beam splitter,130denotes the sample,131denotes the cantilever, and132denotes an image capture apparatus (image pickup device) such as a CCD camera.

FIG. 12is a diagrammatic view of a scanning force microscope, a substance sensor, or a mass sensor (fourth example) according to a thirteenth embodiment of the present invention, each using a heterodyne laser Doppler meter.

In this figure, with respect to reference numerals133to144,133denotes a sample-preparing vacuum chamber,134and135denote rods for transporting a sample and a cantilever,136denotes a sample-observing vacuum chamber,137denotes an optical fiber,138denotes a cantilever-detecting optical system,139denotes a laser-emitter XYZ stage,140denotes a laser Doppler emitter,141denotes a sample XYZ stage,142denotes the sample,143denotes the cantilever, and144denotes an image capture apparatus (image pickup device) such as a CCD camera.

As shown inFIGS. 9 to 12, a scanning force microscope, a substance sensor, or a mass sensor, each using a heterodyne laser Doppler meter, can be constructed. In other words, the heterodyne laser Doppler meter can be used for detecting a vibration of a cantilever.

In a widely-used optical lever mechanism, a detection limit of resolution decreases when a laser spot is made smaller. In a laser Doppler meter, the diameter of a laser spot can be decreased to an order of 1 micron, and also in principle, decreasing the spot diameter does not cause detection sensitivity to deteriorate as is the case in an optical lever meter.

In an optical lever mechanism or a homodyne interferometer, a higher frequency of a detection signal does not lead to an advantage in improving an S/N ratio except for reducing a 1/f noise. As opposed to the above, since a signal of a laser Doppler meter detects a Doppler effect, a signal intensity becomes higher as a speed or a vibration frequency of a measuring object becomes higher.

Thus, there is an advantage in that the laser Doppler meter can be used for detecting a vibration of a compact cantilever having a high natural frequency. In other words, by performing a heterodyne measurement, detection with a higher S/N ratio can be achieved.

The foregoing tenth to thirteenth embodiments are applicable to measuring a torsion of a cantilever, and applicable to measuring a vibration amplitude of a probe in a plane parallel to the surface of a sample by detecting a high natural frequency of a torsion of a hard cantilever.

FIG. 13is a diagrammatic view of a scanning force microscope, a substance sensor, or a mass sensor according to a fourteenth embodiment of the present invention, each having an optical microscope coaxially disposed with a cantilever-detecting optical system.

In this figure, with respect to reference numerals151to157,151denotes a laser emitter,152denotes a quarter wave plate,153denotes a dichroic mirror,154denotes an objective lens,155denotes a cantilever,156denotes an image-forming lens, and157denotes an image capture apparatus (image pickup device) such as a CCD camera.

As shown in the figure, by using a laser heterodyne interferometer, a laser homodyne interferometer, or an optical lever mechanism, each having an optical microscope coaxially disposed therewith, a laser spot can be positioned on a fine oscillator by using visual information of the optical microscope.

FIG. 14illustrates the structure of a cantilever-exciting apparatus according to a fifteenth embodiment of the present invention.

As shown in the figure, the structure in this embodiment is formed by excluding the image-forming lens156, the CCD157, and the dichroic mirror153from that in the foregoing fourteenth embodiment.

Next, sixteenth and seventeenth embodiments of the present invention will be described.

In a known optical-fiber-type interferometer, when a red laser having a wavelength of about 632 nm is used, a cut piece of an optical fiber having a core of 4 μm in diameter and a cladding of 125 μm in diameter is positioned away from a cantilever so as to perform a homodyne interference measurement. In this case, the following problems exist.

(1) When a sample smaller than 4 μm is irradiated with light, a large loss occurs.

(2) Since the cladding of 125 μm in diameter is large, a cantilever smaller than 100 μm causes a positional interference between the base of the cantilever and the cladding.

(3) Since reflected light generated due to a change in refractive index at an end surface of the optical fiber and sharing about 4% of the total quantity is used as reference light for performing the homodyne interference measurement, a signal intensity of interference is low.

(4) The distance between the cantilever and the optical fiber is not freely determined.

With a view of solving the above-mentioned problems, the following structure will be employed.

FIG. 15illustrates the structure of a fine-cantilever-use optical-fiber homodyne laser interferometer according to the sixteenth embodiment of the present invention.

In this figure, with respect to reference numerals160to169,160denotes an optical fiber,161denotes a first supporting member,162denotes a laser emitter,163denotes a beam splitter,164denotes a second supporting member,165denotes a mirror-positioning mechanism,166denotes a reference mirror,167denotes an objective lens,168denotes a cantilever-supporting member, and169denotes a cantilever.

By using the optical fiber160, light can be easily introduced into a vacuum or a low-temperature environment and optical measurement can be easily performed; in addition, a collimating lens (not shown), the beam splitter163, the reference mirror166, the objective lens167, and so forth are disposed at the measuring end portion of the optical fiber160, and a focal point of a micron-sized laser is formed at least 1 mm away from the objective lens.

With this arrangement, in comparison with a known method for directly facing the optical fiber core to the cantilever, measurement of a displacement or a vibration frequency of the micron-sized cantilever169becomes more possible, and interference measurement using reference light having a high intensity becomes more possible. Also, a higher signal-to-noise ratio is achieved, thereby providing increased degrees of spatial design freedom.

With this structure, all the foregoing problems (1) to (4) can be solved.

Also, when it is required to observe an image of a cantilever or a sample with a homodyne laser interferometer, a fine cantilever-use optical fiber is formed so as to have the following structure.

FIG. 16illustrates the structure of a fine-cantilever-use optical-fiber homodyne laser interferometer according to the seventeenth embodiment of the present invention, for observing an image of a cantilever or a sample.

In this figure, with respect to reference numerals170to181,170denotes an optical fiber,171denotes a laser emitter,172denotes a dichroic mirror,173denotes a first supporting member,174denotes a beam splitter,175denotes a second supporting member,176denotes a mirror-positioning mechanism,177denotes a reference mirror,178denotes an objective lens,179denotes a cantilever-supporting member,180denotes a cantilever, and181denotes a camera.

As shown in the figure, measuring light is introduced by using the dichroic mirror172, and an image is observed with the camera181by using the light transmitted through the dichroic mirror172.

With these methods, it is possible to vibrate the cantilever by modulating light having a different wavelength from that of the measuring light.

Next, an eighteenth embodiment of the present invention will be described.

Hitherto, a frequency which can be excited by a piezo element depends on the thickness of the element, a sonic speed and temperature in the element, the structure of the element, and so forth, and the piezo element has its own specific frequency characteristic. This problem is further prominent when a frequency to be excited becomes an order of MHz or higher.

For example, a vibration with a frequency up to a few MHz can be excited by a piezo element-with a thickness of 50 μm, having an electrode and an insulating plate bonded thereto, and, in a frequency range of higher than that, a vibration can be excited only at discrete frequencies.

Because of this problem, in the case of exciting a sample so as to vibrate in a frequency band of MHz or higher by using a piezo element or the like in order to measure the frequency characteristic of the sample, the frequency characteristic of the piezo element is superimposed on the frequency characteristic of the sample, thereby making it difficult or impossible to evaluate the frequency characteristic of the sample. In addition, as the frequency becomes higher, an error in a measured result becomes greater depending on a method for fixing the sample to the piezo element or quality of bonding the sample to the piezo element, thereby making it more difficult to evaluate the characteristic of the sample.

Likewise, in the case of exciting a force-detecting cantilever of a scanning probe microscope so as to vibrate by using a piezo element, when the natural frequency of the cantilever becomes higher in a frequency band of MHz or higher, it becomes more difficult to excite the cantilever. The possible cause for this problem is believed that an error in a measured result of the excitation characteristic of the cantilever occurs depending on a method for fixing the cantilever and the piezo element to each other, also in the case of exciting the cantilever. Also, in the case of exciting the cantilever in vacuum, it is required to dispose a vibration-exciting piezo element on the cantilever-supporting member and to carry out wiring to the piezo element, thereby making a product complicated.

The above problems cause the product to have deteriorated reliability and a deteriorated degree of vacuum, and make it difficult to magnify the scanning probe microscope and to heat the microscope at high temperature, for example.

In view of the foregoing circumstances, in this embodiment, there is provided a laser Doppler interferometer having an optically exciting function for exciting a sample, which allows the interferometer to perform a measurement in a high-frequency region and in a vacuum environment and to have a compact size and high reliability.

FIG. 17illustrates the structure of a measuring apparatus for measuring the characteristics of a sample according to an eighteenth embodiment of the present invention, using a laser Doppler interferometer having an optically exciting function for exciting the sample.

In this figure, the measuring apparatus for measuring the characteristics of the sample according to this embodiment is formed by an optically exciting unit200, a signal-processing unit300, a laser-Doppler interfering unit400, an AFM (atomic force microscope)-sample-stage controlling unit500, and a network analyzer600.

The optically exciting unit200is formed by a laser diode (LD) driver201, a laser diode (LD)202driven by the LD driver201, and a mirror203.

Also, the signal-processing unit300is formed by a first switch (sw1)301, a second switch (sw2)302, a digitaliser303, a phase shifter304, a filter305, and an amplifier306.

The laser-Doppler interfering unit400is formed by a He—Ne laser401, a first PBS (polarizing beam splitter)402, a second PBS403, an optical multiplexer404, a lens405, a polarization-maintaining fiber406, a sensor head (laser emitter)407(assembly of a lens, a λ/4 plate, and a lens), a nanocantilever408, a probe408A, a mirror409, an AOM (acousto-optic modulator)410, a λ/2 plate411, a third PBS412, a polarizer413, a photo diode414, a BPF (band-pass filter)415, amplifiers416,418, and423, digitalisers417and419, a delay line420, a DBM (double-balanced mixer)421, and a LPF (low-pass filter)422.

In addition, the AFM-sample-stage controlling unit500is formed by a DBM501connected to a LO (local oscillator), a controller502, a sample503, and a piezo element504of the sample503.

The network analyzer600has a signal input terminal601and an evaluation output terminal602.

Thus, in this embodiment, for example, output light of the laser diode (LD)202having a wavelength of 780 nm is superimposed on measuring light of a laser Doppler interferometer, emitted from the He—Ne (helium-neon) laser401and having a wavelength of 632 nm, and the superimposed light is introduced into the polarization-maintaining fiber406having a 4-μm core and is illuminated on the sample503via the laser emitter407and the nanocantilever408. The wavelengths are not limited to the above ones.

The following usages are possible depending on measuring methods.

(1) An output signal of the laser-Doppler interfering unit400is subjected to phase conversion, amplification, and if needed, filtering or digitalization, and the laser diode202having a wavelength of 780 nm is modulated by using the processed signal. With this process, the sample503can be self-excited at its natural frequency. In other words, by selecting a filter characteristic, a specific vibration mode can be excited, thereby producing a self-excited vibration of a three-dimensional structure serving as a sample having a size of an order of nanometers to microns.

Also, by irradiating the cantilever408serving as a force-detecting element of the scanning probe microscope with light, the cantilever408is self-excited, and a change in self-excited frequency allows the interaction between the probe408A disposed at the top of the cantilever408and the sample503or a change in mass to be detected.

(2) A signal whose frequency is swept by the network analyzer600is produced, and the laser diode202having a wavelength of 780 nm is modulated by using the signal. An output signal of the laser-Doppler interfering unit400is connected to the signal input terminal601of the network analyzer600. With this process, the frequency characteristic of the sample503can be measured by using the network analyzer600and the laser-Doppler interfering unit400having an optically exciting function.

Meanwhile, measuring light and vibration-exciting light may use a common optical system by superimposing them or may be illuminated on a sample by using respectively different optical paths.

Also, light generated by the LD202for exciting a vibration of the cantilever408is superimposed on the optical-measurement probe light401of the laser-Doppler interfering unit400. In this occasion, an output of a speed signal of the laser-Doppler interfering unit400is subjected to processing such as phase conversion, digitalization, and amplification, and light of a light source such as the laser diode202is modulated by using the signal or modulated at a frequency designated by an oscillator or at the swept frequency so that the light is used for excitation.

With the foregoing arrangement, a vibration specific to a measuring object to be measured by the laser Doppler interferometer is excited, whereby the frequency characteristic of the measuring object can be measured, and measurement or processing by making use of the vibration is possible.

Next, a nineteenth embodiment of the present invention will be described.

When the vibration characteristic of a sample is evaluated by a laser Doppler interferometer, it has been required to bond a piezo element to the sample so as to excite it, or to irradiate the sample with modulated light.

FIG. 18is a diagrammatic view of a measuring apparatus for measuring the frequency characteristic of a sample according to the nineteenth embodiment of the present invention.

In this figure, with respect to reference numerals701to706,701denotes a laser,702denotes a lens,703denotes a supporting portion of the lens,704denotes an interference cavity (air gap),705denotes a sample, and706denotes a sample-supporting portion.

In this embodiment, by using the laser701of a laser Doppler interferometer serving as measuring light having a uniform quantity, and the interference cavity704, one end of which is formed by the sample705, the sample705is excited at its natural frequency so that its amplitude, speed, and frequency are measured by using the laser Doppler interferometer.

When the sample705is to be irradiated with the measuring light of the laser Doppler interferometer, the measuring apparatus is arranged such that the sample705forms the interference cavity704together with a certain optical plane. When the interference cavity704becomes an integral multiple of a half wavelength of the laser Doppler interferometer, a vibration of the sample705occurs. The vibration has the same frequency as the natural frequency of the sample705. The vibration is measured by the laser Doppler interferometer.

By making use of this vibration function, a vibration of a sample can be excited without using modulated optical-excitation light.

A twentieth embodiment of the present invention will be described below.

When a three-dimensional nano-microstructure is used as a sensor or an actuator by vibrating it, a piezo element or a surface acoustic element has been used.

In the embodiment of the present invention, an exciting function using light is adapted to an oscillatory structure so as to perform actuation, processing, or sensing. Meanwhile, the following papers and so forth have revealed the fact that, when a part of a structure in which a standing wave of light is generated by interference is oscillatory, a self-excited vibration occurs or a vibration is generated by intensity-modulated light.

In recent years, since the silicon micromachine technology has allowed a cantilever array having a density of at least a million pieces per square centimeter to be prepared, it is expected to perform measurement, processing, actuation using the cantilever array. However, a method for exciting a specific group of cantilevers or all cantilevers in the cantilever array has not yet been established.

The following description is concerned about a method for adapting an excitation method by making use of optical excitation to a cantilever array and creation of a new function with the method. This will be described below one by one.

FIG. 19is an illustration of a method for exciting cantilevers according to the twentieth embodiment of the present invention.

In this figure, with respect to reference numerals800to804,800denotes a substrate,801denotes interference cavities,802denotes a plurality of cantilevers formed on the substrate800, each equipped with a probe and having the corresponding interference cavity801,803denotes a cantilever array formed by the cantilevers802, and804denotes laser light.

In this embodiment, a clearance (interference cavity length) of each interference cavity (air gap)801lying between the cantilever array803and the substrate800is determined so as to be an integral multiple of a wave length used for optical excitation, and the rear surface of the substrate800is irradiated with the laser light804serving as vibration-exciting light having a uniform quantity. Each cantilever802is self-excited by a standing wave of light lying in the corresponding interference cavity (air gap)801and by a change in the characteristic of the cantilever802. Even when the cantilevers802forming the cantilever array803do not have the same natural frequency, each cantilever802is self-excited at its natural frequency.

FIG. 20is an illustration of a method for exciting cantilevers according to a twenty first embodiment of the present invention.

In this figure, with respect to reference numerals800, and815to820,800denotes the substrate,815,816,817, and818denote cantilevers formed on the substrate800, equipped with respective probes and respectively having interference cavities811,812,813, and814,819denotes a cantilever array formed by the cantilevers815,816,817, and818, and820denotes laser light (wavelength λ) having a uniform quantity.

In this embodiment, in the cantilever array819, clearances of the interference cavities (air gaps) formed by the substrate800vary group by group of the cantilevers815to818. With this arrangement, a wavelength of vibration-exciting light can be determined so as to excite only an intended group of cantilevers.

FIG. 21is an illustration of a method for exciting cantilevers according to a twenty second embodiment of the present invention.

In this figure, with respect to reference numerals800, and832to834,800denotes the substrate,832denotes cantilevers formed on the substrate800, each equipped with a probe and having an interference cavity831,833denotes a cantilever array formed by the cantilevers832, and834denotes intensity-modulated laser light.

In this embodiment, the rear surface of the substrate800of the cantilever array833is irradiated with the laser light834serving as quantity-modulated, vibration-exciting light. The cantilevers832having a natural frequency in agreement with the frequency for the quantity-modulation are excited. With this arrangement, a specific group of cantilevers can be selectively excited.

FIG. 22is an illustration of a method for exciting cantilevers according to a twenty third embodiment of the present invention.

In this figure, with respect to reference numerals800, and842to847,800denotes the substrate,842denotes cantilevers formed on the substrate800, each equipped with a probe and having an interference cavity841,843denotes a cantilever array formed by the cantilevers842,844denotes laser light (wavelength λ) having a uniform intensity,845denotes a path of the top of each probe,846denotes a slider, and847denotes a displacing direction of the slider846.

In this embodiment, since the substrate800having the cantilevers842equipped with a million pieces of probes per square centimeter has its own weight of about 0.1 g, when all probes support the own weight, each probe bears its share of a load of 1 nN. When optical excitation is performed in such a state, vibrations of the cantilevers842are excited. When the optical excitation has an anisotropic property with which the top of each probe depicts an elliptical vibration, the substrate800having the cantilever array843moves in a direction parallel to the plane of the figure in accordance with the excitation of vibration.

Also, when the probes lie upwards, and the slider846serving as a physical object is placed on them, the slider846is displaced. The cantilever array is designed such that, when all probes come into contact with the slider846at the same time, a Q factor of the slider846decreases, and when sufficient oscillatory energy cannot be stored in the oscillators, the probes and the slider846less often come into contact with each other, for example, by making the heights of the probes uneven.

FIG. 23is an illustration of a method for exciting cantilevers according to a twenty fourth embodiment of the present invention.

In this figure, with respect to reference numerals800, and855to860,800denotes the substrate,855,856,857,858denote cantilevers formed on the substrate800and respectively having interference cavities851,852,853, and854(wherein855denotes a cantilever equipped with a reactive film a,856denotes a cantilever equipped with a reactive film b,857denotes a cantilever equipped with a reactive film c, and858denotes a cantilever equipped with a reactive film d),859denotes a cantilever array formed by these cantilevers, and860denotes laser light (wavelength λ) having a uniform quantity.

In this embodiment, a specific thin film is applied on the corresponding group of the cantilevers so as to react to a specific substance. In order to check existence of the specific substance, in accordance with the foregoing method, a vibration frequency or a wavelength of light with which vibrations of the group of the cantilevers are excited is determined. With this arrangement, measurement can be performed by using only a specific group of the cantilevers in the cantilever array859.

FIG. 24is an illustration of a method for exciting cantilevers according to a twenty fifth embodiment of the present invention.

In this figure, with respect to reference numerals800, and862to869,800denote the substrate,862to866denote cantilevers formed on the substrate800and having respective interference cavities861and respectively different natural frequencies,867denotes a cantilever array formed by these cantilevers,868denotes laser light (wavelength λ) having a uniform intensity with which the rear surface of the substrate800is irradiated, and869denotes a plurality of kinds of laser light (wavelength λ) having respectively different intensity-modulation frequencies.

In this embodiment, by irradiating the cantilever array867with the laser light868having a uniform intensity so as to excite vibrations of the cantilevers862to866, the clearance of each interference cavity861varies at a certain frequency so as to modulate the quantities of reflected light or transmitted light at the same frequency. When the cantilever array867formed by a group of the cantilevers having respectively different frequencies is irradiated with the laser light868having a uniform intensity, the light869modulated at the plurality of modulation frequencies can be obtained as reflected light or transmitted light.

FIG. 25is an illustration of a method for exciting cantilevers according to a twenty sixth embodiment of the present invention.

In this figure, with respect to reference numerals800, and872to880,800denote the substrate,872to876denote cantilevers formed on the substrate800and having respective interference cavities871and respectively different natural frequencies,877denotes a cantilever array formed by these cantilevers,878denotes laser light (wavelength λ) having a uniform intensity with which the rear surface of the substrate800is irradiated,879denotes incident light having a uniform wavelength with which the substrate800is irradiated obliquely from above, and880denotes five kinds of laser light (wavelengths λ1, λ2, λ3, λ4, λ5) having respectively different frequencies.

In this embodiment, the cantilever array877is irradiated with the laser light878having a uniform intensity so as to generate waves on the surface of the cantilever877so that a frequency of reflected light or transmitted light is modulated.

Meanwhile, the structure for generating photoacoustic modulation is not limited to the cantilevers and may include a oscillatory structure such as a both-ends-supported beam.

Meanwhile, the present invention is not limited to the foregoing embodiments, and since a variety of modifications are possible on the basis of the spirit of the present invention, these modifications shall not be excluded from the scope of the present invention.

As has bee described above in detail, according to the present invention, the following advantages are obtained.

(A) A simple structure can be achieved and a surface of a sample can be reliably detected on the order of nanometers.

(B) When activated in sliding directions by using a cantilever array formed by a large number of compliant cantilevers, a sliding surface is very unlikely to provide a frictional condition.

(C) By exerting vibrations and also propagating a surface acoustic wave, the surface acoustic wave having an amplitude of a few nm is amplified with Q factors of oscillators, whereby efficiencies of an actuator and an optical modulator can be improved.

(D) The entire surface of a sample can be observed by making use of optical-lever incident light and a large number of cantilevers.

(E) While cantilever-shaped members slide on the surface of a sample, fine irregularities can be detected as changes in luminance in accordance with reflecting states of light with which the surface is irradiated.

(F) A scanning probe microscope in which displacements of a large number of cantilevers are detected by an optical interferometer can be constructed.

(G) A scanning force microscope using a heterodyne laser Doppler meter can be constructed. That is, the heterodyne laser Doppler meter can be used for detecting a vibration of a cantilever.

(H) A laser spot can be positioned on a fine oscillator by using visual information of an optical microscope.

(I) The frequency characteristic of a three-dimensional structure as a sample can be accurately evaluated in a high-frequency band.

(J) By performing excitation and detection both with light, the mechanical part of a product can be simplified and miniaturized, accordingly improving reliability and cleanness of the product.

(K) By performing excitation and detection both with light, measurement can be achieved only by illuminating light on a sample, whereby a large number of samples can be evaluated with a high time efficiency.

(L) By performing excitation and detection both with light, a product has a simple and compact structure and high cleanness in a special environment such as in ultra-vacuum or at very low temperatures.

(M) When a sample is to be irradiated with measuring light of a laser Doppler interferometer, by disposing the sample so as to form an interference cavity with a certain optical plane, the sample is self-excited at its natural frequency, whereby an amplitude, a speed, and a frequency of the sample can be measured by using the laser Doppler interferometer.

(N) By adapting an excitation method by making use of optical excitation to a cantilever array, new functions such as actuation, substance selection, substance recognition, optical modulation and mass sensing can be created.

INDUSTRIAL APPLICABILITY

According to the present invention, a surface of a sample can be detected on the order of nanometers; efficiencies of an actuator and an optical modulator can be improved; fine irregularities can be detected as changes in luminance; a vibration of each cantilever can be detected; a large number of samples can be evaluated; by self-exciting a sample at its natural frequency, its amplitude, speed, and frequency can be measured; and actuation, substance selection, substance recognition, optical modulation and mass sensing can be performed. Also, the present invention is especially suitable for a measuring device and a sensor for measuring the characteristic of a sample.