Conductive transparent probe and probe control apparatus

A conductive transparent probe used in a probe control apparatus for adjusting a distance between the apex of the probe and a sample by vibrating the probe with an vibrator in a direction perpendicular to the axis of the probe is provided. The conductive transparent probe includes: an optical fiber having a taper part at one end; a conductive transparent film formed on the surface of the taper part; a first metal film formed on the surface of the optical fiber other than the taper part; wherein the conductive transparent film and the first metal film are electrically connected, and length and thickness of the first metal film are determined such that the conductive transparent probe vibrates while contacting with the vibrator.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a conductive transparent probe and a probe control apparatus. More particularly, the present invention relates to a conductive transparent probe used in a tunneling luminescence microscope, and a probe control apparatus for controlling a distance between the apex of a probe and a sample, wherein the tunneling luminescence microscope measures optical and electronic characteristics of a very small region of a size of the nanometer order by detecting luminescence caused by applying a probe current into the sample.

2. Description of the Related Art

As devices become small and technologies for utilizing characteristics of individual molecules develop, great demands have arisen for technologies for characteristic evaluation of a very small region of a size of the nanometer order in materials (to be referred to as a nano region hereinafter), and for technologies for optical and electronic characteristic measurement of individual molecules intrinsically having a size of the nanometer order. For realizing such measurement and evaluation, a tunneling luminescence microscope (to be referred to as a TL microscope hereinafter) is provided that enables detection and analysis of luminescence caused by applying a current from an apex of a sharpened probe to a sample. In addition, a probe that is transparent and has conductivity (to be referred to as a conductive transparent probe hereinafter) has been developed, wherein the conductive transparent probe applies a current from its apex into a sample, and at the same time, receives and collects luminescence from the apex, so that luminescence collection yield is improved. The conductive transparent probe is powerfully used for characteristic evaluation of a nano region. As effectiveness of the TL apparatus for characteristic evaluation of a nano region increases, it is demanded by users that the sample to be measured is not only a material having only a conductive region but also a material in which a nonconductive region or a highly resistive region is mixed with the conductive region.

In an apparatus (to be referred to as a probe microscope hereinafter) that measures a sample by bringing a probe extremely close to the surface of the sample, it is very important to properly control a very small distance (to be referred to as a gap hereinafter) between the apex of the probe and the surface of the sample. Therefore, generally, as for the probe microscope (for example, a scanning tunneling microscope (to be referred to as an STM, hereinafter)) that utilizes a tunneling current flowing between the probe and the sample for measurement, a method of detecting the tunneling current flowing between the probe and the sample is used for controlling the gap (this control method is called an STM control method hereinafter). The reason for using this method for realizing precision gap control is that the tunneling current is very sensitive to the gap.

However, the STM control method can be applied only to a sample of which the whole region is electronically conductive, and the STM control method cannot be applied to a sample in which a nonconductive region or a highly resistive region is mixed. Therefore, a TL apparatus that enables gap control without using the tunneling current is desperately desired, such that the TL apparatus can be applied to a sample in which a nonconductive region or a highly resistive region is mixed.

As a gap control method without using the tunneling current, there is a method for utilizing an atomic force such as attractive force and repulsive force between the apex of the probe and the sample. In this method, when the apex of the probe approaches very close to the surface of the sample, atomic force between the apex and the surface is detected, and the gap is adjusted such that the detected value becomes constant.

For feeding back the detected value for performing gap control, there is a method of using an optical lever and a soft probe of a cantilever shape.

In this case, a laser beam is used for detecting a very small displacement of the probe. However, since the laser beam is extremely stronger than a detected signal light used for observing the sample, there is a problem in that the SN ratio decreases when measuring weak luminescence caused by the tunneling current.

It is desirable to use a leaner probe made of an optical fiber in order to suppress optical transmission loss in the probe. However, it is difficult to use such a probe as the soft probe of a cantilever shape that is necessary for realizing an optical lever.

In addition, there is a method called a shear force gap control method. In the method, a linear probe perpendicular to the surface of the sample is vibrated in a direction perpendicular to a center axis of the probe, so that atomic force is detected by measuring amplitude of the probe vibrating at a specific frequency. In this method, when a voltage is applied between the apex of the probe and the sample for causing luminescence, a current flows into a sensor used for detecting the amplitude, so that a detected signal is disturbed and gap control becomes unstable. Therefore, there is a problem in that a voltage cannot be applied between the probe and the sample when the shear force gap control method is used.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a conductive transparent probe that is applicable to the shear force gap control method while the tunneling current can be applied to a very small region without decreasing luminescence collection yield. In addition, another object of the present invention is to provide a probe control apparatus for applying a voltage between the apex of the probe and a sample so as to apply a current from the apex of the probe to cause luminescence from the sample, wherein the probe control apparatus is applicable to a sample in which a nonconductive region or a highly resistive region is mixed with a conductive region, a conductive transparent probe can be used as a probe, and it is not necessary to use a laser beam that decreases the SN ratio when weak luminescence caused by tunneling current is measured.

The above-mentioned object is achieved by a conductive transparent probe used in a probe control apparatus for adjusting a distance between the apex of the conductive transparent probe and a sample by vibrating the conductive transparent probe with a vibrator in a direction perpendicular to the axis of the conductive transparent probe, the conductive transparent probe includes:

an optical fiber having a taper part at one end;

a conductive transparent film formed on the surface of the taper part;

a first metal film formed on the surface of the optical fiber other than the taper part;

wherein the conductive transparent film and the first metal film are electrically connected, and length and thickness of the first metal film are determined such that the conductive transparent probe vibrates while contacting with the vibrator.

According to the above-mentioned conductive transparent probe according to the present invention, shear force gap control can be performed without losing functions of applying a probe current and collecting luminescence, and measurement by using luminescence can be performed stably even for a sample in which a nonconductive region or a highly resistive region is mixed with a conductive region.

The above object is also achieved by a probe control apparatus including:

a probe that is straight and vertical with respect to a surface of a sample;

a vibrator for vibrating the probe in a direction perpendicular to a center axis of the probe;

an amplitude detection part for detecting an amplitude of the probe;

a part for controlling a distance between the apex of the probe and the sample by controlling the amplitude of the probe vibrating at a specific frequency to be a predetermined amplitude;

a voltage applying part for applying a voltage between the apex of the probe and the sample;

wherein the probe has optical transparency and electrical conductivity, and the probe is electrically insulated from the amplitude detection part.

According to the above-mentioned probe control apparatus according to the present invention, gap control between the probe and the sample can be performed stably even for a sample in which a nonconductive region or a highly resistive region is mixed with a conductive region, for which sample it is difficult to perform gap control by using probe current.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the present invention will be described with reference to figures.

In the embodiments, a probe control apparatus will be described first, and details of a conductive transparent probe applicable to the probe control apparatus will be described next.

FIG. 1shows a block diagram of the probe control apparatus of the present invention. As shown in the figure, the probe control apparatus of the present invention includes a probe1, a vibrator7, a power source for vibration9, a sensor10, a sensing signal processing circuit11, a sample position driving mechanism12, a control circuit13for the sample position driving mechanism, a probe bias power source14, a conductive holding plate15and a supporting structure16.

The apex of the linear probe1mounted perpendicular to the surface of the sample3is tapered to a point. The probe1is made of a linear optical fiber having optical transparency. A conductive film is applied on the periphery and the taper part of the optical fiber to provide conductivity, wherein the conductive film applied on the taper part is optically transparent for providing a luminescence collection ability. The probe1is held by the conductive holding plate15apart from the apex of the probe by 1-2 cm, so that the probe1is mounted on the supporting structure16.

The conductive holding plate15is connected to one end of the probe bias power supply14, and supplies a current from the probe bias power supply14to the probe1. The other end of the probe bias power supply14is connected to the sample3, so that a voltage applying mechanism for applying voltage between the apex of the probe1and the sample3is formed.

The vibrator7for vibrating the probe1in a direction perpendicular to the center axis of the probe1is provided on the supporting structure16. The vibrator7is connected to the power supply for vibration9, and pushes a point apart from the apex of the probe1by several millimeters via a sensor10that is an amplitude detection means, so that the probe1is vibrated in the direction parallel to the surface of the sample3.

The sensor10detects the amplitude of vibration of the probe1, and outputs a voltage value in proportion to a displacement amount (amplitude). The output from the sensor is transmitted to the sample position driving mechanism12via the sensing signal processing circuit11and the control circuit13.

The sample position driving mechanism12receives an output from the control circuit13, and moves the sample.

The sensing signal processing circuit11, the control circuit13and the sample position deriving mechanism12form a distance control means for controlling a distance (gap4) between the apex of the probe1and the sample3.

An insulator81electrically insulates the probe1from the sensor10, and an insulator82electrically insulates the sensor10from the vibrator7.

An operation of the probe control apparatus of the present invention is as follows.

The probe1is placed on the sensor10, and is vibrated by the sensor10in the direction perpendicular to the center axis of the probe1at a resonance frequency. The sensor10outputs a voltage corresponding to vibration of the probe1. At frequencies near the resonance frequency, if the frequency changes slightly, the amplitude of the probe1changes greatly. Thus, the amplitude of the probe1is monitored with the vibrator10for sensing at a frequency slightly apart from the resonance frequency. In this status, the apex of the probe1approaches the surface of the sample3(the operation for the probe1approaching the sample3is referred to as “approach”).

Even after starting the approach, while the gap4is so large that atomic force between the probe1and the sample3can be neglected, the probe1continues to vibrate at a constant frequency and a constant amplitude. Therefore, the amplitude of voltage output from the sensor10is constant, since the voltage change corresponds the vibration.

Next, when the probe1further approaches the surface of the sample3so closely that atomic force becomes large, the atomic force acts as a resistance (a shear force) to the vibration of the probe1, and the frequency changes. Therefore, the amplitude monitored by the sensor10changes. When the amplitude of the probe1changes, output voltage data of the sensor10also change. When the amplitude of the output voltage becomes a predetermined value, approach of the probe is stopped. After that, the gap4between the probe1and the surface of the sample is adjusted by performing feedback control such that the amplitude of the probe1is constant.

If a current flows to the sensor10from the probe1when applying a voltage between the apex of the probe1and the sample3, the detected signal output from the sensor10is disturbed and gap control becomes unstable. For preventing this signal disturbance, the insulator81is inserted between the probe1and the sensor10, so that they are electrically insulated.

The atomic force occurs irrespective of whether the sample3is conductive or nonconductive. Therefore, gap control between the probe1and the surface of the sample3can be performed even when the sample3includes both a conductive region and a nonconductive region or a highly resistive region. For example, when the probe1is placed above the nonconductive region of the sample3, the gap4between the probe1and the surface of the sample3is controlled properly by using atomic force although the probe current does not flow. When the probe1is placed above the conductive region of the sample3, gap control is performed by using the atomic force, and, in addition, tunneling current and luminescence caused by the current can be detected since the probe current can be applied.

That is, tunneling current and luminescence caused by the tunneling current can be measured even for a sample in which a nonconductive region or a highly resistive region is mixed with a conductive region, for which sample it is difficult to control the gap4by using the tunneling current. In addition, since detection of the gap4is performed by the sensor10so that a laser beam is not used, the SN ratio of the detected signal light is not lowered when measuring weak luminescence caused by the tunneling current. Therefore, measurement with a high SN ratio can be achieved.

In addition, since it is not necessary to use a soft probe of a cantilever shape, a probe made of a linear optical fiber applicable to forming a conductive transparent probe can be used.

Further, since the insulator81is inserted between the probe1and the sensor10so as to electrically insulate the sensor10from the probe1, current does not flow to the sensor10from the probe1even when a voltage is applied between the probe1and the sample3. Thus, the detected signal is not disturbed, so that gap control is performed stably.

FIGS. 2A and 2Bshow a relationship between an amplitude B-B′ of vibration of the apex of the probe1in the horizontal direction and a measurement target region A-A′ of the sample3.FIG. 2Ashows a relative position of the apex of the probe1and the sample3.FIG. 2Bshows a status in which the apex of the probe1moves sinusoidally with respect to the time axis.

In the probe control apparatus of the present invention, since the gap4is controlled by using the atomic force between the probe1and the sample3, it is necessary that the shear force caused by the atomic force acts on the probe1sufficiently. Therefore, it is difficult to lessen the horizontal amplitude B-B′ of the apex of the probe1to a value less than several tens of nanometers. Therefore, spatial resolution in measurement is limited by the amplitude B-B′.

In this embodiment, to avoid such limitation, the current applied to the sample3from the probe1is applied like a pulse in synchronization with the phase of vibration of the apex of the probe1. The timing for applying current can be synchronized with any phase. For example, in this embodiment, a pulse voltage is applied from the probe bias power source14while the apex of the probe1is located in the measurement target region A-A′ which is near the center O of the amplitude. Accordingly, even when the amplitude B-B′ of the apex of the probe1in the horizontal direction necessary for controlling the gap4is large, the spatial resolution of measurement by tunneling current and luminescence of the tunneling current can be intensified according to smallness of the measurement target region A-A′.

As mentioned above, according to the probe control apparatus of the present invention, the probe control apparatus is applicable to a sample in which a nonconductive region or a highly resistive region is mixed with a conductive region, and a conductive transparent probe can be used without using a laser beam, which lowers the SN ratio when measuring weak luminescence caused by tunneling current. In addition, a voltage can be applied between the apex of the probe and the sample for applying a current from the apex of the probe to the sample to cause luminescence.

Since the voltage applying mechanism applies a pulse voltage between the apex of the probe and the sample in synchronization with vibration of the probe, spatial resonance for measurement by using tunneling current and luminescence of the tunneling current can be intensified even if the amplitude of the apex of the probe in the horizontal direction necessary for controlling the gap is large.

Next, a conductive transparent probe applicable for use in the above-mentioned probe control apparatus will be described.

In order to perform gap control stably by the shear force gap control by using the above-mentioned probe control apparatus, it is necessary for the probe to have a smooth frequency-to-amplitude characteristic (represented by a curve indicating a relationship between frequency and amplitude) with few parasitic vibrations. For realizing this characteristic, it is necessary that the probe and the vibrator be integrated while vibrating, so that the probe vibrates by following faithfully the vibration of the vibrator. In order that the probe and the vibrator vibrate together, it is necessary that the probe has a moderate rigidity for keeping moderate contacting pressure between the probe and the vibrator, and that the probe has a moderate elasticity to vibrate stably. If the probe is so soft that contacting pressure between the probe and the vibrator is small, the probe vibrated by the vibrator jumps (amplitude of the probe exceeds that of the vibrator) from the vibrator, so that the probe does not vibrate together with the vibrator and does not follow faithfully the vibration of the vibrator, and parasitic vibration occurs. Thus, movement of the probe becomes unstable. If the probe is so rigid that the contact pressure is too large, the probe may be broken, or the probe cannot be vibrated at the desired amplitude, so that proper movement cannot be obtained.

However, a conventional probe used for STM is short, and a thick metal plating is applied on the surface of the probe for preventing mechanical vibration that may cause noise. Thus, rigidity of the probe is large, so that rigidity and elasticity are not proper for realizing shear force gap control. Therefore, the probe cannot be used for shear force gap control. Therefore, a conductive transparent probe is used as follows in the present invention.

FIG. 3shows a horizontal section of the first embodiment of the conductive transparent probe of the present invention.

The conductive transparent probe is made of an optical fiber21including a core22and a cladding23. A taper part25is provided in the optical fiber21, wherein the taper part25ranges within several hundred micrometers from one end opposed to a sample32in the optical fiber21, and the apex of the taper part25is sharpened to a size of the nanometer order. To provide conductivity and a luminescence collection function to the taper part25of the nonconductive optical fiber21, a conductive transparent film24having conductivity and transparency is applied on the surface of the taper part25. In addition, in order to provide conductivity to the optical fiber21, a first metal film26having conductivity is applied on the outer surface of the optical fiber21. The conductive transparent film24and the first metal film26are connected electrically.

Tunneling current is applied from the apex of the conductive transparent probe to the sample32, and luminescence caused by the tunneling current is collected from the apex of the same conductive transparent probe.

A part ranging from a point apart from the one end by a distance D to the other end of the optical fiber21is held by a conductive holding plate29formed by a metal plate, for example, so that the conductive transparent probe is mounted on the supporting structure31(refer to FIG.4). The conductive holding plate29is connected to a bias power source (not shown in the figure). Since the holding plate29contacts the first metal film26of the conductive transparent probe electrically, it has a function to provide a current to the conductive transparent probe.

The current from the bias power source is supplied to the apex of the conductive transparent probe via the first metal film26on the surface of the optical fiber21and the conductive transparent film24on the taper part25.

The conductive transparent probe is vibrated in a direction perpendicular to the axis of the optical fiber21by using a sensor28that pushes a point (vibration point) apart from the one end (apex) by a distance d (d<D, about several millimeters). The sensor28is attached to a vibrator30(FIG.4), and has a function to transmit vibration of the vibrator30to the conductive transparent probe and a function to detect vibration and amplitude of the conductive transparent probe. The sensor28is electrically insulated from the conductive transparent probe.

When the vibrator30operates, the conductive transparent probe vibrates at a frequency and an amplitude corresponding to those of a cantilever of a length D. In order to transmit vibration of the vibrator30to the apex of the conductive transparent probe faithfully, it is desirable to shorten the distance d. In addition, in order for the conductive transparent probe to vibrate easily, it is desirable to set the vibration point apart from the part where the conductive transparent probe is held, and to make the distance D as large as possible. According to an experiment, stable operation was obtained and the probe was easy to handle when the distance D was no less than 5 mm and the distance d was about 2-3 mm, wherein the distance D is almost the same as the length of the first metal film26from a part adjacent to the taper part25to the other end.

Next, operation of a shear force gap control system in which the conductive transparent probe of the present invention is implemented will be described.

FIG. 4shows a basic structure of the shear force gap control system in which the conductive transparent probe of the present invention is implemented. Although the shear force gap control system is similar to the probe control apparatus described by usingFIG. 1, the structure is simplified in the following embodiments since the conductive transparent probe is mainly described.

As shown in the figure, a part of the other end side of the conductive transparent probe is held by the conductive holding plate29. At this time, the conductive transparent probe is placed on the back side of the sensor28. Next, the conductive transparent probe is bent a little, and the conductive transparent probe is put on the sensor28such that a point a distance d apart from the apex of the conductive transparent probe is placed on the front of the sensor28. By elastic force caused by the bending, the conductive transparent probe and the sensor28contact each other with moderate contacting pressure.

Next, the conductive transparent probe is vibrated in a direction perpendicular to the axis of the optical fiber21(that is, parallel to the surface of the sample) at a specific frequency. The vibrated conductive transparent probe vibrates as a cantilever having a fixed end that is the part attached to the conductive holding plate29. The sensor28outputs a voltage corresponding to the amplitude of vibration of the conductive transparent probe.

While the conductive transparent probe is vibrated at a frequency slightly different from an Eigen frequency, when the frequency is changed slightly, the amplitude of the conductive transparent probe changes greatly. Thus, the conductive transparent probe is vibrated at a frequency slightly different from the Eigen frequency, and the amplitude is monitored by the sensor28.

When atomic force between the conductive transparent probe and the sample32becomes large as the conductive transparent probe approaches the sample32, the atomic force acts on the conductive transparent probe as a shear force in a direction perpendicular to the axis of the optical fiber21. The shear force acts as a resistance force against vibration of the conductive transparent probe vibrating as a cantilever. Thus, the frequency of the conductive transparent probe changes slightly so that the amplitude of the conductive transparent probe at a monitored frequency is changed. This change of the amplitude is detected as a change of output voltage of the sensor28. When the amplitude of the output voltage becomes a predetermined value, that is, when the shear force becomes a predetermined value, the approach of the conductive transparent probe to the sample32is stopped. After that, the gap between the conductive transparent probe and the sample32is controlled such that the amplitude of the conductive transparent probe at the monitored frequency is constant (that is, such that shear force is constant) while performing measurement. Accordingly, stable operation of an AFM (Atomic Force Microscope) can be obtained, wherein the AFM is a microscope performing the gap control by using atomic force (Yang et al. “Near-field differential scanning optical microscope with atomic force regulation”, Appl. Phys. Lett., 60(24), 15 Jun. 1992, for example, can be referred to for more information on conventional AFM).

Since the shear force gap control is stably performed irrespective of conductivity of the sample32, it becomes possible to realize a TL apparatus using the conductive transparent probe, that is applicable to a sample in which a nonconductive region or a highly resistive region is mixed with a conductive region.

For satisfying a contacting condition between the conductive transparent probe and the sensor28necessary for conducting stable shear force gap control, thickness and length of the first metal film26applied on the outer surface of the optical fiber21are adjusted, so that flexural rigidity of the conductive transparent probe is adjusted. As a material of the first metal film26, nickel, stainless steel and the like can be used, for example. However, any other material can be used as long as adhesive force between the material and the surface of the optical fiber21is strong and conductivity is high.

If the distance D from the end of the conductive transparent probe to the conductive holding plate29is equal to or less than several millimeters, the flexural rigidity of the optical fiber21becomes large. Therefore, there occurs a case in which the sensor28slides on the surface of the conductive transparent probe, so that vibrations of the vibrator30do not transfers to the optical fiber21faithfully.

When the thickness of the first metal film26of the outer surface of the optical fiber21is smaller than about 0.2 μm, the optical fiber21is easily broken by a slight shear force. In addition, if first metal film26is thin, electrical resistance from the holding plate29to the apex of the optical fiber21becomes large, so that it becomes difficult to supply a current to the apex of the optical fiber21. Therefore, a conductive transparent probe having a thin first metal film26is not practical.

On the other hand, if the thickness of the first metal film26is greater than 10 μm, rigidity of the conductive transparent probe becomes large, so that a large force is necessary for bending the conductive transparent probe. When bending the conductive transparent probe forcibly, plastic deformation occurs so that the shape does not return to its original shape. Therefore, the conductive transparent probe having a thick first metal film26is not applicable to the shear force gap control.

According to an experiment, when thickness of the first metal film26was 0.2-10 μm, the conductive transparent probe21had elasticity proper for shear force gap control, and good electrical conductivity, so that the conductive transparent probe had good characteristics for shear force gap control.

As mentioned above, when the length of the first metal film26from the part adjacent to the taper part25to the other end is equal to or greater than 5 mm, and thickness of the first metal film26is 0.2-10 μm, contacting pressure between the conductive transparent probe and the sensor28becomes a proper value, so that the conductive transparent probe vibrated by the sensor28does not jump from the sensor28. The conductive transparent probe integrates with the sensor28, and follows vibration of the sensor28faithfully. The movement of the conductive transparent probe does not become unstable due to parasitic vibration and the like. The conductive transparent probe is not too stiff and contact pressure is not too large. In addition, the conductive transparent probe does not break, and is oscillated at the desired amplitude. Thus, the conductive transparent probe operates properly.

Stress concentrates on a boundary part between a part performing bending vibration as a cantilever and a part held by the conductive holding plate29. Thus, the boundary part is easily broken. In addition, the optical fiber21may be distorted by pressure applied to the conductive transparent probe from the holding plate29for fixing the conductive transparent probe, so that there is a case that optical characteristics of the conductive transparent probe degrade.

In a second embodiment of the present invention shown inFIG. 5, a second metal film33is formed on the side of the other end of the conductive transparent probe, such that the optical fiber21is not distorted by a pressure applied to the optical fiber21from the holding plate29, wherein the thickness of the second metal film33is larger than that of the first metal film26. As a result of an experiment, it was found that the thickness of the second metal film33needed to be no less than 10 μm, and preferably no less than 50 μm. In this embodiment, if the thickness of metal film between the first metal film26and the second metal film33changes discontinuously, there is a possibility that the conductive transparent probe will be broken since stress concentrates on the part where the thickness changes discontinuously. Therefore, a transitional part34where thickness of metal film changes smoothly is provided between the first metal film26and the second metal film33. By adopting such a structure, the conductive transparent probe can be mounted firmly with reliability by the holding plate29without degrading optical characteristics of the conductive transparent probe. In addition, a conductive transparent probe that is hard to break by stress concentration can be realized.

FIG. 6is a section view of the third embodiment of the conductive transparent probe of the present invention. As shown in the figure, in this embodiment, the taper part25provided in one end part of the conductive transparent probe is covered with a material35through which light cannot pass, and a very small hole is provided at the apex of the taper part25opposed to the sample32. By adopting such a structure, it becomes possible to selectively collect only near optical fields in the tunneling current luminescence.

In the above-mentioned configuration of the probe control apparatus for controlling the gap by using shear force, vibration of the vibrator is applied to the conductive transparent probe via the sensor contacting the conductive transparent probe, and the sensor detects changes, due to atomic force, of amplitude of the conductive transparent probe. However, the configuration is not limited to this example. There is following another configuration of the gap control apparatus for using shear force. That is, instead of fixing the conductive transparent probe to the holding plate29, the conductive transparent probe can be fixed directly to the vibrator, and a laser beam is directed to the conductive transparent probe from the side direction of the conductive transparent probe, and, change of amplitude of the conductive transparent probe is detected by measuring the laser beam modulated by vibration of the conductive transparent probe. The conductive transparent probe can be applied to an apparatus for performing shear force gap control by such method using a laser beam.

As mentioned above, according to the conductive transparent probe, length and thickness of the first metal film from a part adjacent to the taper part to the other end are set to values such that the conductive transparent probe vibrates while integrating with the vibrator. Therefore, it becomes possible to realize a conductive transparent probe applicable to shear force gap control while tunneling current can be applied and luminescence collection yield is not degraded. Thus, the present invention produces the effect of enabling stable TL measurement for a sample in which a nonconductive region or a highly resistive region is mixed with a conductive region.

Especially, a conductive transparent probe having bending rigidity applicable to shear force gap control can be realized by setting the length of the first metal film to be no less than 5 mm, and setting the thickness of the first metal film to be 0.2-10 μm.

In addition, in the conductive transparent probe of the present invention, a second metal film is formed on an outer surface of the other end side, wherein thickness of the second metal film is no less than 10 μm, and the first metal film and the second metal film are connected by using a transitional part whose thickness changes continuously. Therefore, the conductive transparent probe can be held firmly with high reliability without degrading optical characteristics, and the conductive transparent probe is not broken even when bending stress concentrates on a part.

Further, in the conductive transparent probe, the taper part is covered by a material through which light cannot pass, and a very small hole is provided on the apex of the taper part covered by the material, wherein the diameter of the hole is smaller than a wavelength of a transmission light. Accordingly, only near optical fields can be collected.