Abstract:
A method of forming an aperture in an optical fiber probe comprising the steps of sharpening the tip and bending the tip section of the optical fiber probe relative to a longitudinal axis, covering a portion of the probe with a metallic film, positioning the probe relative to a surface of a sample, effecting relative movement between the probe and the surface of the sample so that the probe is disposed in a region where an atomic force acts between the probe and the surface of the sample, measuring and monitoring a displacement of the probe resulting from the atomic force acting between the tip of the probe and the surface of the sample, using a pressing force from the atomic force to plastically deform or break the tip section of the probe to form an aperture in the tip section having a diameter obtained in accordance with a measured value of the displacement of the probe.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the invention 
     The present invention relates to an optical fiber probe and cantilever. having a microscopic aperture, used in a scanning near-field microscope, and to a method of forming this aperture. 
     2. Description of the Prior Art 
     An optical fiber probe of a scanning near-field microscope of the related art is manufactured using the type of method described below 
     (1) Tip sharpening step 
     {circle around (1)} Hot pulling method: heat is applied to the optical fiber probe, etc., and the optical fiber is pulled in an axial direction to sharpen the tip. 
     {circle around (2)} Etching method: the optical probe is immersed in etching fluid, and the tip is sharpened under predetermined etching conditions. 
     (2) Aperture forming step 
     {circle around (1)} Oblique vapor deposition method: an aperture section of the extreme tip section of the sharpened probe are left behind, and a metal is vapor deposited from an oblique direction so that sections other than the aperture are covered with a metallic film. 
     {circle around (2)} Pressing method: After a metallic film has been vapor deposited on a section including a tip section, the tip section is pressed against a sample surface to form an aperture. With this method, the probe is brought into contact with a detector surface made of silicon utilizing shear force, while carrying out distance regulation, and after contact the tip is broken using an external. impulsive force etc. while monitoring the detector output, until a desired output is obtained. 
     Also, in the case where a bent type optical fiber probe is processed, a bending step is carried out between the steps (1) and (2) described above. In the bending step laser light is applied to the sharpened probe, and the optical fiber is softened by the thermal effect. At this time, the probe is bent by a surface tension effect of the softened optical fiber material. 
     The manufacturing steps as described above are disclosed, for example, in the near-field nanophotonics handbook, 23-28 and 42-48, optronics society. Also, the method of forming an aperture by pressing an optical fiber probe is described in a “fiber probe aperture control method for near-field light microscope” by Teruyama and Saiki, 46 th  lectures of the applied physics association, 1030. 
     On the other hand, with a scanning near-field microscope, a cantilever with a microscopic aperture is also used (for example, H.Zhou, A.Midha, L.Bruchhaus, G.Mills, L.Donaldson, and J. M. R.Weaver: Novel SNOM/AFM Probes by combined Micromachining and Electron-Beam Nanolithography, Preliminary Proceedings of STM &#39;99, 459). A cantilever with a microscopic aperture has a cantilever section and a probe formed of a silicon nitride or silicon material using a semiconductor process, a microscopic aperture is provided in the probe tip, and the microscopic aperture is made into a through hole so that a beam is focused by an objective lens onto a rear surface of the cantilever, passed through the through holes and a laser beam is introduced. The tip section is also covered with a metallic film in the cantilever having a microscopic aperture. 
     However, with the aperture forming method of the related art, there are the following problems. 
     (1) In the case of the oblique vapor deposition method, in order to make an aperture with good reproducibility, it is necessary to optimize vapor deposition conditions. This optimization requires time, and also, in the case where the probe shape is altered, it is necessary to carry out the optimization again. Further, it is not possible to avoid variations in aperture diameter, even after optimization. Once the aperture have been formed, it is impossible to correct them and defective products must be discarded. 
     (2) In the case of the pressing method, light output is being monitored at the tome of forming the aperture, which means that thee is the advantage that a desired aperture can be obtained. However, with the method of the related art, it is difficult to regulate the pressing force, and fine adjustment of the aperture diameter is difficult. Because of this, it is often the case that the aperture diameter becomes bigger than a desired diameter because the pressing force is to large, or the tip is damaged and the shape of the aperture becomes elliptical. 
     In order to solve these problems in the related art, an object of the present invention is therefore to provide an optical fiber probe and a cantilever having a microscopic aperture, capable of obtaining an aperture of a desired diameter with good reproducibility, and finely adjusting a force for plastic deformation or breaking of a tip, and a method of forming this aperture. 
     SUMMARY OF THE INVENTION 
     In order to solve the foregoing problems in the conventional art, the optical fiber probe and cantilever with a microscopic aperture of the present invention includes means for bringing a probe tip and a sample close together or into contact with each other utilizing an atomic force or shear force acting between the optical fiber probe or the. probe tip of the cantilever with a microscopic aperture, or a tunnel current or evanescent light, regulating a force on the probe tip with a physical amount of any of these as a parameter, and forming an aperture of a desired diameter at the tip section by plastic deformation or breaking of the tip section of the probe using a force received from a sample surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of an apparatus for forming an aperture in a tip of a bent type optical fiber probe using a contact mode AFM regulation method, being a first embodiment of the present invention. 
     FIG. 2 is a schematic diagram of an apparatus for forming an aperture in a tip of a cantilever having a microscopic aperture using a dynamic mode AFM regulation method, being a second embodiment of the present invention. 
     FIG. 3 is a schematic diagram of an apparatus for forming an aperture in a tip of a straight type optical fiber probe using shear force regulation, being a third embodiment of the present invention. 
     FIG. 4 is a schematic diagram of an apparatus for forming an aperture in a tip of a straight type optical fiber probe using STM regulation, being a fourth embodiment of the present invention. 
     FIG. 5 is a schematic diagram of an apparatus for forming an aperture in a tip of a cantilever having a microscopic aperture using evanescent light regulation, being a fifth embodiment of the present invention. 
     FIG. 6 is a schematic diagram of an apparatus for forming an aperture in a tip of a straight type optical fiber probe using evanescent light regulation, being a sixth embodiment of the present invention. 
     FIG. 7 is a schematic diagram of an apparatus for forming an aperture in a tip of a bent type optical fiber probe using a contact mode AFM regulation method, while estimating aperture size using light microscopy or light intensity from the aperture, being a seventh embodiment of the present invention. 
     FIG. 8 is a force curve and a state diagram of contact mode ATM regulation. 
     FIG. 9 is a force curve of dynamic mode ATM regulation. 
     FIG. 10 is a force curve of shear force regulation. 
     FIG. 11 is a graph showing a relationship between probe—sample distance and current value for STM regulation. 
     FIG. 12 is a schematic diagram for describing an evanescent light regulation method. 
     FIG. 13 is a schematic diagram for describing an evanescent light regulation method. 
     FIG. 14 is a graph showing a relationship between probe—sample distance and evanescent light intensity for evanescent light regulation. 
     FIG. 15 is a schematic diagram for describing an optical fiber probe production method used in the present invention. 
     FIG. 16 is a schematic diagram for describing an cantilever production method used in the present invention. 
     FIG. 17 is a schematic diagram for describing an aperture forming method for a cantilever having a microscopic aperture used in the present invention. 
     FIG. 18 is a schematic diagram showing the angular relation between a longitudinal axis of the probe tip and a vertical axis extending from the surface of the sample. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The principal of the structure of and operation of the present invention will be described. 
     In the following, the principal of operation of regulating a force on the probe tip will be described for each parameter. 
     (1) When using atomic force (contact mode) 
     This method uses the principle of a contact mode atomic force microscope (hereafter referred to as a contact mode AFM) using a bent type optical fiber probe and a cantilever with a microscopic aperture. FIG.  8 ( a ) shows a force curve in the case of the probe and the sample being brought into contact with each other, and FIG.  8 ( b ) is a drawing showing conditions between the probe and the sample corresponding to numbers in the force curve of FIG.  8 ( a ). In FIG.  8 ( a ), the horizontal axis represents a distance the sample has moved, and if it moves to the left, the sample approaches the probe. The vertical axis represents an amount of bending of the cantilever, with the upper side being a cantilever repulsion force acting, and the lower side being a cantilever attraction force acting. 
     With a general contact mode AFM, an amount of bending of the cantilever is set, and a distance between the probe and the sample is feedback regulated so that the amount of bending is constant. The amount of bending is made to correspond to the force on the probe tip using hook&#39;s rule. Accordingly, by varying the bending amount parameter, as is clear from the force curve of FIG.  8 ( a ), the force on the probe tip inside a near field region where atomic force acts can be finely adjusted. 
     Here, if the sample is a planar surface and the probe tip is flexible and a sphere having a radius of curvature R, then a relationship between a contact surface area A of the probe tip and a pressing force F on the probe tip is established as A=KF 2/3  R 2/3  (K is a constant) using the Hertz theory of elastic contact. At this time, if the tip is subjected to plastic deformation or breaking, a microscopic aperture having an aperture surface area of about A are formed. That is, an aperture having a desired diameter are formed by the pressing force. 
     (2) When using atomic force (dynamic mode) 
     This method also uses the principle of a dynamic mode atomic force microscope (hereafter referred to as a dynamic mode AFM) using a bent type optical fiber probe and a cantilever with a microscopic aperture. FIG. 9 shows a force curve in the case of bringing a probe close to a sample while vibrating the probe in a vertical direction within a plane orthogonal to the sample surface. The horizontal axis represents a distance between the probe and the sample, and movement to the left is when the sample and the probe are brought close together. The vertical axis represents an vibration attenuation factor with respect to an initial vibration amount of the cantilever, and when this is 0 the cantilever maintains a freely oscillating state with no attenuation, and when it is enters the negative side an external force acts on the probe and attenuation occurs. Here, of external forces causing vibration attenuation, one having the highest contribution factor is an atomic force when the probe and the sample are moved apart, but is an intermittent contact force to the sample surface when the probe and the sample are moved closer together. 
     With a general dynamic mode AFM, the vibration attenuation factor is set, and the distance between the probe and the sample is feedback regulated so as to maintain vibration reduced by a constant amount from an initial vibration state. This attenuation factor corresponds to pressing force on the probe tip. Accordingly, by varying the attenuation factor parameters it is possible to finely adjust force on the probe tip within a near-field region where atomic force acts, as is clear from the force curve of FIG.  9 . 
     A microscopic aperture having a desired diameter is formed by subjecting the probe tip to plastic deformation or breaking with the pressing force on the probe tip. 
     With the dynamic AFM, it is also possible to take advantage of feedback using variation in phase of the cantilever, instead of the attenuation factor of the vibration. That is, if the distance between the probe and the sample is closed while exciting the cantilever at close to the resonant frequency, phase of vibration of the cantilever is varied by the external force acting on the probe tip. If the amount of variation in phase is set, it is possible to control the pressing force on the probe. tip in the same way as in when attenuation factor is a parameter, and as a result, an aperture having a desired diameter is formed by plastic deformation or breakage of the tip. 
     (3) When using shear force 
     This method is mainly used with straight type optical fiber probes. It is also possible to apply this method to bent type optical fiber probes and cantilevers with a microscopic aperture. Here, in the case of a straight type optical fiber probe, an amount of vibration of the probe is monitored, while in the case of a bent type optical fiber probe or a cantilever having a microscopic aperture a twisting angle is monitored. FIG. 10 shows a force curve in the case of bringing a probe and a sample together while vibrating the probe within a plane parallel to the sample surface. The horizontal axis represents a distance between the sample and the probe, with movement to the left being a condition of the probe and the sample approaching each other. The vertical axis represents a vibration attenuation factor compared to an initial vibration state of the optical fiber probe (or compared to vibration of the twisting angle in the case of a bent type optical fiber probe or a cantilever having a microscopic aperture), with 0 being a condition where a free vibration state is maintained and there is no vibration attenuation, while the negative side indicates that an external force is acting on the probe and vibration attenuation is occurring. Here, the external force causing vibration attenuation can be attributed to capillary force due to adsorbed water on the sample surface, frictional force between the probe and the sample, or an atomic force etc. 
     With shear force regulation, a vibration attenuation factor is set, and a distance between the probe and the sample is feedback controlled so that vibration is held at an amplitude attenuated by a fixed amount from an initial state of oscillation. This attenuation factor corresponds to force acting on the probe tip. Components of this force are a shear force acting in the direction of vibration, the vibration force, and a pressing force acting in the vertical direction. As clearly shown in the force curve of FIG. 10, by varying the attenuation factor parameter it becomes possible to finely adjust the shear force on the probe tip within a near field region where the shear force acts, and the pressing force is also varied by change in the distance between the sample and the probe. A microscopic aperture having a desired diameter is formed by plastic deformation or breakage of the probe tip using these forces. 
     In the case of shear force regulation, similarly to the dynamic mode AFM, instead of the vibration attenuation factor it is also possible to employ feedback using phase variation of the optical fiber probe or the cantilever having a microscopic aperture. Specifically, in the case of making a distance between the probe and the sample closer while exciting the optical fiber probe or the cantilever having a microscopic aperture close to the resonant frequency, phase of the vibration of the probe varies due to external force acting on the probe tip. If the amount of this phase variation is set, then similarly to the case where the attenuation factor is a parameter, it is possible to control the shear force and the pressing force on the probe tip, and as a result an aperture having a desired diameter is formed by plastic deformation or breakage of the tip. 
     (4) When using tunnel current 
     This method utilizes a scanning tunnel microscope (hereafter referred to as an STM) that uses straight type and bent type optical fiber probes having a conductive thin film formed on a tip and a cantilever having a microscopic aperture. FIG. 11 shows a relationship between a distance between a sample and a probe and a tunnel current value for conditions of a bias voltage applied between the probe and the sample. The horizontal axis represents the distance between the probe and the sample, with movement to the left indicating the probe and the sample being brought together. The vertical axis represents a tunnel current value. 
     With STM control, a tunnel current value is set, and a distance between the probe and the sample is regulated so that the tunnel current value is held constant. If the distance between the probe and the sample is closed with the tunnel current value as a parameter, pressing force is produced on the probe tip by the interaction of atomic force, an absorption layer of the sample surface, a contamination layer etc. This pressing force increases as the distance between the probe and the sample becomes closer. Accordingly, as shown clearly in FIG. 11, by varying the tunnel current value parameter, the probe and the sample are brought close together and it becomes possible to finely adjust a pressing force on the probe tip within a near field region where the tunnel current is effective. A microscopic aperture having a desired diameter is formed by plastic deformation or breakage of the tip with this pressing force. 
     (5) When using Evanescent light 
     This method is used with straight and bent type optical fiber probes, and with cantilevers having a microscopic aperture. Method of performing evanescent light regulation cab be classified into {circle around (1)} methods for forming evanescent light on the sample surface, and {circle around (2)} methods of forming evanescent light on the probe tip. 
     {circle around (1)} Methods for forming evanescent light on the sample side surface 
     As shown in FIG. 12, in the case where light  102  is injected from a reverse side of a transparent sample  101  formed from a prism under total reflection conditions, an evanescent field  103  is formed at the sample surface. If a probe  104  is bright close to this evanescent field, evanescent light is scattered and converted to propagated light. The evanescent light strength is dependent on the distance from the sample surface. FIG. 14 shown a relationship between a probe—sample distance and scattering light intensity at this time. In FIG. 14, the horizontal axis represents a distance between the probe and the sample, with movement to the right being the condition where the probe and the sample are brought closer together. As will be understood from FIG. 14, the light intensity increases as the sample surface is approached. Accordingly, regulation of the distance between the probe and the sample becomes possible using the intensity of light scattered at the probe tip. If fine adjustment of the distance between the probe and the sample is made possible, an aperture is formed by plastic deformation or breakage of the tip, similarly to the case for STM regulation. 
     {circle around (2)} methods of forming evanescent light on the probe tip 
     As shown in FIG. 13, an aperture  202  that is smaller than a desired aperture is formed in advance on a tip of a probe  201 , and if light  203  is introduced into the aperture and evanescent field is formed in the probe tip (namely, the size of the aperture is smaller than the wavelength). In this state, if the probe  201  and the sample  205  are brought closer together, evanescent light is scattered at the sample surface and converted to propagation light. The evanescent light intensity is dependent on the distance from the aperture, and as shown in FIG. 14, light intensity increases as the sample surface is approached. Accordingly, it becomes possible to regulate the distance between the probe and the sample using the intensity of light scattered at the probe tip. If fine adjustment of the distance between the probe and the sample is made possible, an aperture is formed by plastic deformation or breakage of the probe tip, similarly to the case for STM regulation. 
     In this method, in the state where the aperture is blocked off, after formation of an aperture by plastic deformation or breakage of the tip by bringing the probe into contact with the sample control is performed using the evanescent light from that aperture and it is possible to produce an aperture having the desired diameter. 
     Embodiments of the present invention will now be described in the following, based on the drawings. 
     FIG. 15 shows manufacturing processes up to before aperture formation using an optical fiber probe pressing method used in present invention. 
     {circle around (1)} Sharpening Process 
     Various methods have been proposed as processes for sharpening an optical fiber, but here a description will be given of a hot pulling method and an etching method as representative methods. 
     A optical fiber sharpening process using the hot pulling method is shown in FIG.  15 ( al ). In the case of the hot pulling method, a laser beam  302  of a CO2 laser or the like is converged on an optical fiber  301  with tension on the optical fiber  301 . At this time, energy of the laser light is converted to heat energy at converged section, and localized fusion occurs. At this time, if more tension continues to be applied from the two ends of the optical fiber, the optical fiber is stretched to a pencil shape and finally ruptures. The shape of the rupture surface and the taper angle are adjusted by the intensity of the laser beam irradiated and the irradiation surface area and magnitude of the tension. 
     Next, a description will be given of 2-phase etching, which is a typical example of a processes for sharpening using an etching method. As shown in FIG.  15 ( a   2 ), in the 2-phase etching process high concentration hydrofluoric acid solution  303  is used as etching fluid, and in order to prevent variations in concentration due to vaporization of the hydrofluoric acid, and to make the probe surface smooth at an interface, an organic solvent (heptane)  304  is deployed on the hydrofluoric acid solution, to give 2-phase conditions, and etching is carried out inside the hydrofluoric acid solution lower down than an interface between the two. The material of an optical fiber  305  is SiO 2  doped with GeO 2  for the core, and SiO 2  as the cladding. 
     A ratio of the etching rates of the core and the cladding is varied by varying the mixing ratio of the etching fluid (mixing ratio of NH4F(50 weight %):HF(50 weight %):H 2 O) at this time, making it possible to control the taper shape and thickness of the taper section. 
     The present invention is not limited to the above described hot pulling method and etching methods, and all generally used sharpening processes are included in the present invention. 
     {circle around (2)} Bending Process (Bent Type Only) 
     A bending process for a bent type optical fiber probe is shown in FIG.  15 ( b ). When making a bent type optical fiber probe, a laser beam  307  if a CO 2  laser or the like is condensed on the area around a tip of the sharpened optical fiber probe  306 . At the sections where the light is condensed SiO 2  is softened by the effect of heat energy, and the probe is bent by a difference in surface tension between the side where the laser beamed is condensed and the reverse side. 
     When the bent type probe is used in AFM control, laser light strikes a normal probe back face and displacement of the probe is detected using an optical lever method. In order to produce a reflection surface for this laser light, as shown in FIG.  15 ( c ), a rear surface  306   a  of the probe is mechanically ground by a grindstone  308 . 
     {circle around (3)} Film Attaching Process 
     In order to produce a microscopic aperture in the tip of an optical fiber probe with the method as shown in FIG.  15 ( d ), an Al film is vapor deposited. 
     The sharpened optical fiber  309  is fixed in a vacuum evaporator, and Al is vapor deposited. At this time, the angle of attaching the probe with respect to the vapor deposition source  310  is set so that Al is not vapor deposited in the tip section, and the optical fiber probe is rotated to vapor deposit Al to the circumference of the tip section. Since the tip aperture section will be extended by force in a subsequent process, it is not necessary to make the aperture properly at this stage, and as long as the size of the aperture is smaller than the desired aperture diameter, there is no problem if part or all of the aperture is blocked up with a metallic film. 
     Here, the metal used in film attaching is not limited to Al, and it is also possible to use a material such as Au or Cr etc. The film attaching method is also not limited to this method. 
     Next, manufacturing processes before formation of the aperture using a method of pressing the cantilever having a microscopic aperture will be shown. 
     {circle around (1)} Step of Manufacturing Cantilever with Probe Attached 
     Various methods are used for manufacturing a cantilever with a probe attached, but here an embodiment of a method of manufacturing a silicon nitride type cantilever, which is a typical example, will be described. 
     A method of manufacturing a silicon nitride film type cantilever used in the present invention is shown in FIG.  16 . As shown in FIG.  16 ( a ), a square cone shaped hole  401   a  defining the shape of a probe section of the cantilever is formed on a silicon substrate  402 . Next, as shown in FIG.  16 ( b ), a silicon nitride type film  402  for producing the cantilever and the probe section is deposited on the silicon substrate. Next, as shown in FIG.  16 ( c ), this silicon nitride film is formed into a cantilever pattern  403  by selective etching in the shape of the cantilever. As shown in FIG.  16 ( d ), a support section  404  is then connected to the end of the cantilever. Finally, as shown in FIG.  16 (e), the silicon substrate  401  is removed by etching and the cantilever is produced. 
     Besides this embodiment, as a cantilever it is also possible to use other forms of cantilever such as a cantilever made of a silicon film or a silicon oxide film, and all are included in the present invention 
     {circle around ( 2 )} Hole Drilling Process 
     Drilling of a hole in the cantilever  501  used in the present invention involves hanging the probe tip from a rear surface side of the cantilever, as shown in FIG.  17 ( a ), and forming a through hole  501   a  through the probe tip along a longitudinal axis thereof disposed generally orthogonal to a longitudinal axis of the cantilever  501  using a focussed ion beam (FIB)  502 . The hole diameter at this time can be any size, but in this embodiment the diameter is made φ100 nm. The hole drilling process is not limited to FIB processing, and the present invention also includes methods such as electron beam processing or laser processing. 
     {circle around ( 3 )} Film Attaching Process 
     As shown in FIG.  17 ( b ), the cantilever in which a hole has been drilled is fixed in a vacuum evaporator, and an Al film  504  is vapor deposited. An attachment angle of the cantilever  501  with respect to the evaporation source  503  at this time is set so that Al is not vapor deposited on the tip section. In the case of the cantilever also, similarly to the optical fiber probe, since the tip aperture is flared out in a subsequent process, there is no need to strictly manufacture the aperture, and as long as the size of the aperture is smaller than the desired aperture diameter, there is no problem if part or all of the aperture section is blocked up with metallic film. The metal used for film attachment is not limited to Al, and any material such as Au or Cr can be used. 
     Next, description will be given of a process of forming an aperture using a pressing method. 
     FIG. 1 is a schematic diagram of an apparatus for forming an aperture in a tip of a bent type optical fiber probe using a contact mode AFM, being a first embodiment of the present invention. 
     This apparatus comprises a coarse adjustment mechanism  3  for bringing a sample  2  close to a probe  1 , a Z fine adjustment mechanism  4   a  for finely adjusting a distance between the sample  2  and the probe  1 , an XY fine adjustment mechanism  4 b for scanning the sample  2  within a two-dimensional plane, a sample holder  5  for mounting a sample, a probe holder  5  for fixing the probe  1 , a displacement detection unit  6  for measuring an amount of displacement of the probe, and a control unit  7  for carrying out control of the overall system. Here, the coarse adjustment mechanism  3  uses a method for driving a feed screw with a motor, while the XY and Z fine adjustment mechanisms use a cylindrical piezoelectric element  4 . Also, displacement detection means applies a semiconductor laser  6   a  to a reflection surface  1   a  provided on a rear surface of the probe, and uses an optical head of an optical lever method for carrying out measurement of an amount of displacement of the probe using a four-piece detector  6   b.    
     In a state where an aperture section  1   b  of a bent type optical probe is pre-coated with an Al metal film and is almost completely blocked up, only a pin-hole that is smaller than the finally required fine aperture diameter (here φ50 nm) remains. 
     Using this apparatus, the sample  2  is brought closer to the probe  1  using the coarse adjustment mechanism  3  while monitoring an amount of bending of the bent type optical fiber probe  1 . The sample  2  is brought up to a region where an atomic acts between the probe  1  and the sample  2 , and if the amount of bending becomes a previously set amount the coarse adjustment mechanism  3  is stopped, and feedback is carried out using the Z fine adjustment mechanism  4   a  so that this amount of bending becomes constant. A pressing force received by the probe tip at an initial value for this amount of bending is a force that will not break the tip. After that, a bending amount parameter of the control unit is changed, and the distance between the sample and the probe is made gradually closer using the Z fine adjustment mechanism  4   a,  increasing the pressing force on the tip, thus breaking the tip and forming the aperture. In this embodiment, since a relationship between the aperture diameter and the bending amount is quantified in advance through experimentation, it is possible to form an aperture having any diameter by setting the bending amount. 
     The method of using the bending amount as a parameter in this method can also be applied to a cantilever having a microscopic aperture. 
     FIG. 2 is a schematic diagram of an apparatus for forming an aperture in a tip of a cantilever having a microscopic aperture using dynamic mode AFM, being a second embodiment of the present invention. 
     This apparatus comprises a coarse adjustment mechanism  3  for bringing a sample  11  close to a probe  10   a,  a Z fine adjustment mechanism  4   a  for finely adjusting a distance between the sample  11  and the probe  10   a,  an XY fine adjustment mechanism  4   b  for scanning the sample  1  within a two-dimensional plane, a sample holder  15  for mounting the sample  1 , a cantilever holder  13  having a piezoelectric element  12  for vibrating the cantilever attached, a vibration detection unit  6  for measuring an amount of vibration of the cantilever, and a control unit  14  for carrying out control of the overall system. Here, the coarse adjustment mechanism  3  uses a method for driving a feed screw with a motor, while the XY and Z fine adjustment mechanisms use a cylindrical piezoelectric element  4 . Also, vibration detection means applies a semiconductor laser  6   a  to a reflection surface  10   b  provided on a rear surface of the cantilever, and uses an optical head  6  of an optical lever method for carrying out measurement of an amount of vibration of the cantilever using a four-piece detector  6   b.    
     The cantilever having a microscopic aperture  10  has a hole formed in advance in the probe section by FIB processing, but the tip aperture section  10   c  is initially blocked up with an Al metallic film. 
     Using this apparatus, the cantilever  10  is vibrated at close to the resonant frequency and the sample  11  is brought closer to the probe  10   a  by the coarse adjustment mechanism  3  while monitoring an amount of vibration. The sample  11  is brought up to a region where an atomic acts between the probe  10   a  and the sample  11 , and if the vibration is attenuated to a previously set amount the coarse adjustment mechanism  3  is stopped, and feedback is carried out using the Z fine adjustment mechanism  4   a  so that this amount of vibration becomes constant. A pressing force received by the probe tip at an initial value for this amount of vibration is a force that will not break the tip. After that, a vibration attenuation factor parameter of the control unit  14  is changed, and the distance between the sample and the probe is made gradually closer using the Z fine adjustment mechanism  4   a,  increasing the pressing force on the tip, thus breaking the tip and forming the aperture. In this embodiment also, since a relationship between the aperture diameter and the vibration attenuation factor is quantified in advance through experimentation, it is possible to form an aperture having any diameter by setting the vibration attenuation factor. 
     In this embodiment, a vibration attenuation factor has been used as a parameter for controlling a distance between the probe and the sample, but it is also possible to consider a method of performing control using a variation in phase. 
     A control method using a dynamic mode AFMM can also be applied to a straight type optical fiber probe. 
     FIG. 3 is a schematic diagram of an apparatus for forming an aperture in a tip of a straight type optical fiber probe using shear force regulation, being a third embodiment of the present invention. 
     This apparatus comprises a coarse adjustment mechanism  3  for bringing a sample  21  close to a probe  20 , a Z fine adjustment mechanism  4   a  for finely adjusting a distance between the sample  21  and the probe  20 , an XY fine adjustment mechanism  4   b  for scanning the sample  21  within a two-dimensional plane, a sample holder  26  for mounting the sample, a probe holder  23  to which a piezoelectric element  22  for probe excitation is attached, a vibration detection unit  24  for measuring an amount of vibration of the probe  20 , and a control unit  25  for carrying out control of the overall system. Here, the coarse adjustment mechanism  3  uses a method for driving a feed screw with a motor, while the XY and Z fine adjustment mechanisms use a cylindrical piezoelectric element  4 . Also, the vibration detection means has the probe  20  fastened to piezoelectric body  24   a,  and employs a method for measuring vibration amount by converting variation in force acting on the probe tip to variation in an amount of electrical charge of the piezoelectric body. 
     In a state where an aperture section  20   a  of an optical fiber probe is pre-coated with an Al metallic film and is almost completely blocked up, only a pin-hole that is smaller than the finally required fine aperture diameter (here φ50 nm) remains. 
     Using this apparatus, the probe  20  is vibrated at close to the resonant frequency within a plane parallel to the sample, and the sample  21  is brought closer to the probe  20  by the coarse adjustment mechanism  3  while monitoring an amount of vibration. The sample  21  is brought up to a region where a shear force acts between the sample  21  and the probe  20 , and if the vibration is attenuated to a previously set amount the coarse adjustment mechanism  3  is stopped, and feedback is carried out using the Z fine adjustment mechanism  4   a  so that this amount of vibration becomes constant. A pressing force and shear force received by the probe tip at an initial value for this amount of vibration are forces that will not break the tip. After that, a vibration attenuation factor parameter of the control unit is changed, and the distance between the sample and the probe is made gradually closer using the Z fine adjustment mechanism  4   a,  increasing the pressing force and the shear force on the tip, thus breaking the tip and forming the aperture. In this embodiment also, since a relationship between the aperture diameter and the vibration attenuation factor is quantified in advance through experimentation, it is possible to form an aperture having any diameter by setting the vibration attenuation factor. 
     In this embodiment, a vibration attenuation factor has been used as a parameter for controlling a distance between the probe and the sample, but it is also possible to consider a method of performing control using a variation in phase. 
     As the method for detecting vibration amount, besides the piezoelectric method it is also possible to use a method for optically measuring vibration amount using a laser. 
     Also, shear force control is not limited to a straight type optical fiber probe, and can also be applied to a cantilever having a microscopic aperture or a bent type optical fiber probe. In such cases, the cantilever or bent type probe is twistingly vibrated so that the tip section of the cantilever or probe tip vibrates within a plane parallel to the sample. At this time, an amount of variation in the twisting angle is monitored using a force on the probe tip. This twisting angle corresponds to vibration amount in the case where a straight type optical fiber probe is used, and enables control of the distance between the probe and the sample. Accordingly, it is possible to form a microscopic aperture in the probe tip using the same principal as in the third embodiment. 
     FIG. 4 is a schematic diagram of an apparatus for forming an aperture in a tip of a straight type optical fiber probe using STM regulation, being a fourth embodiment of the present invention. 
     This apparatus comprises a coarse adjustment mechanism  3  for bringing a conductive sample  31  close to a probe  30 , a Z fine adjustment mechanism  4   a  for finely adjusting a distance between the sample  31  and the probe  30 , an XY fine adjustment mechanism  4   b  for scanning the sample  31  within a two-dimensional plane, a conductive sample holder  36  for fixing the conductive sample  31 , a probe holder  32  for fixing the sample, a voltage applying unit  33  for applying a bias voltage between the probe  30  and the sample  31 , current measuring means  34  for measuring a tunnel current flowing between the probe  30  and the sample  31 , and a control unit  35  for carrying out control of the overall system. Here, the coarse adjustment mechanism  3  uses a method for driving a feed screw with a motor, while the XY and Z fine adjustment mechanisms use a cylindrical piezoelectric element  4 . Also, the sample  31  is a Au coated glass to give a sample having conductivity, and the bias voltage is applied to the sample holder through the sample holder  36 . 
     The entire probe body, including the probe tip section, is coated in an Au metallic film, and the aperture section is almost completely blocked up. Since the probe itself is also covered with the conductive film, a tunnel current flows between the probe  30  and the sample  31  to bring the two together. 
     Using this apparatus, the sample  31  is brought closer to the probe  30  by the coarse adjustment mechanism  3  while monitoring an amount of current. The sample  31  is brought up to a region where a tunnel current flows between the sample  31  and the probe  30 , and if the tunnel current value becomes a previously set amount the coarse adjustment mechanism  3  is stopped, and feedback is carried out using the Z fine adjustment mechanism  4   a  so that this tunnel current value becomes constant. A pressing force received by the probe tip at an initial value for this tunnel current is a force that will not break the tip. After that, a tunnel current parameter of the control unit  35  is changed, and the distance between the sample  31  and the probe  30  is made gradually closer using the Z fine adjustment mechanism  4   a,  increasing the pressing force on the tip, thus breaking the tip and forming the aperture  30   a.  In this embodiment also, since a relationship between the aperture diameter and the tunnel current value is quantified in advance through experimentation, it is possible to form an aperture having any diameter by setting the tunnel current value. 
     A control method using STM can also be applied to a bent type optical fiber probe or a cantilever having a microscopic aperture having a conductive metal film formed on a tip. 
     FIG. 5 is a schematic diagram of an apparatus for forming an aperture in a tip of a cantilever having a microscopic aperture using evanescent light regulation, being a fifth embodiment of the present invention. 
     This apparatus comprises a coarse adjustment mechanism  3  for bringing a prism  41  used as a sample close to a probe  40   a,  a Z fine adjustment mechanism  4   a  for finely adjusting a distance between the prism  41  and the probe  40   a,  an XY fine adjustment mechanism  4   b  for scanning the prism  41  within a two-dimensional plane, a cantilever holder  42  for fixing a cantilever  40 , a laser optical system constructed so as to irradiate laser light under total reflection conditions from the underneath of the prism  41 , a light detection unit  44  for detecting the intensity of light scattered at the cantilever tip, and a control unit  45  for carrying out control of the overall system. Here, the coarse adjustment mechanism  3  uses a method for driving a feed screw with a motor, the XY and Z fine adjustment mechanisms use a cylindrical piezoelectric element  4 , and the light detection unit  44  uses a photomultiplier  44   a.    
     The cantilever having a microscopic aperture  40  has a through hole formed in advance in the probe section using FIB processing, but the tip aperture section  4   b  is initially blocked up by coating with an Al metallic film. 
     Using this apparatus, when forming the aperture, a laser beam is irradiated under total reflection conditions from underneath the prism  41  and an evanescent field is formed on the surface of the prism. Next, the prism  41  is brought closer to the probe  40   a  by the coarse adjustment mechanism  3 . If the probe  40   a  is brought up to an evanescent region evanescent light is scattered at the probe tip and converted to propagation light. This propagation light is converged by a converging lens  46  provided diagonally above the regions where the evanescent field is generated and light intensity is measured using a photomultiplier  44   a.  Since evanescent light intensity depends on the distance from the prism surface, if feedback is carried until the intensity of this scattered light becomes constant, it is possible to regulate the distance between the probe and the prism surface. If the scattered light intensity becomes a value set in advance, the coarse adjustment mechanism  3  is stopped, and feedback is carried out using the Z fine adjustment mechanism  4   a  so that this scattered light intensity becomes constant. A pressing force received by the probe tip at an initial value for this scattered light intensity is a force that will not break the tip. After that, a scattered light intensity parameter of the control unit is changed, and the distance between the probe  40   a  and the prism  41  is made gradually closer using the Z fine adjustment mechanism  4   a,  increasing the pressing force on the tip, thus breaking the tip and forming the aperture. In this embodiment also, since a relationship between the aperture diameter and the scattered light intensity is quantified in advance through experimentation, it is possible to form an aperture having any diameter by setting the scattered light intensity. 
     Control using evanescent light can also be applied to a bent type optical fiber probe or a straight type optical fiber probe. 
     It is also possible to consider a method in which scattered light detection is performed by converging light that has been converged at the probe tip at the probe aperture, and detecting the intensity of light propagated through the optical fiber at the end of the optical fiber. 
     FIG. 6 is a schematic diagram of an apparatus for forming an aperture in a tip of a straight type optical fiber probe using evanescent light regulation, being a sixth embodiment of the present invention. 
     This apparatus comprises a coarse adjustment mechanism  3  for bringing a sample  51  close to a probe  50 , a Z fine adjustment mechanism  4   a  for finely adjusting a distance between the sample  51  and the probe  50 , an XY fine adjustment mechanism  4   b  for scanning the sample  51  within a two-dimensional plane, a sample holder  56  for mounting a sample, a probe holder  52  for fixing the probe  50 , a laser optical system  53  for irradiating laser light to an optical fiber probe, a light detection unit  54  for detecting the intensity of scattered light, and a control unit  55  for carrying out control of the overall system. Here, the coarse adjustment mechanism  3  uses a method for driving a feed screw with a motor, the XY and Z fine adjustment mechanisms use a cylindrical piezoelectric element  4 , and the light detection unit  54  uses a photomultiplier  54   a.    
     In a state where an aperture section  50   a  of the optical fiber probe is pre-coated with an Al metallic film and is almost completely blocked up, only a pin-hole that is smaller than the finally required fine aperture diameter (here φ50 nm) remains. 
     Using this apparatus, when forming the aperture, a laser beam is converged by a converging lens  58 , is incoming from an end  50   b  of the optical fiber probe, and an evanescent field is formed in the vicinity of a microscopic aperture  50   a  provided in the probe tip. Next, the sample  51  is brought closer to the probe  50  by the coarse adjustment mechanism  3 . If the sample  51  approached the tip of the probe  50 , evanescent light is scattered at the sample surface and converted to propagation light. This propagation light is converged by a converging lens  57  provided diagonally above the probe tip, and light intensity is measured using the photomultiplier  54   a.  Since evanescent light intensity depends on the distance from the sample surface, if feedback is carried until the intensity of this scattered light becomes constant, it is possible to regulate the distance between the probe and the sample surface. If the scattered light intensity becomes a value set in advance, the coarse adjustment mechanism is stopped, and feedback is carried out using the Z fine adjustment mechanism  4   a  so that this scattered light intensity becomes constant. A pressing force received by the probe tip at an initial value for this scattered light intensity is a force that will not break the tip. After that, a scattered light intensity parameter of the control unit is changed, and the distance between the probe  50  and the sample  51  is made gradually closer using the Z fine adjustment mechanism  4   a,  increasing the pressing force on the tip, thus flaring the tip outwards and forming an aperture having a desired diameter. In this embodiment also, since a relationship between the aperture diameter and the scattered light intensity is quantified in advance through experimentation, it is possible to form an aperture having any diameter by setting the scattered light intensity. 
     This method is also applicable to a bent type optical fiber probe or a cantilever having a microscopic aperture. 
     FIG. 7 is a schematic diagram of an apparatus for forming an aperture in a tip of a bent type optical fiber probe using contact mode AFM regulation, while estimating aperture size using light microscopy or light intensity from the aperture, being a seventh embodiment of the present invention. 
     This apparatus comprises a coarse adjustment mechanism  3  for bringing a sample  61  close to a probe  60 , a Z fine adjustment mechanism  68   a  for finely adjusting a distance between the sample  61  and the probe  60 , an XY fine adjustment mechanism  68 b for scanning the sample within a two-dimensional plane, a sample holder  71  for mounting the sample, a probe holder  75  for fixing the probe  60 , a displacement detection unit  6  for measuring an amount of displacement of the probe, control unit  70  for controlling the overall system, and an inverting microscope  76  capable of observing a sample surface from a lower side of the sample. At this time, the sample  61  is observable by a CCD camera  63  through an optical system having an objective lens  62  of transparent glass arranged below the sample and comprising a mirror  72  totally reflecting an image of the probe tip  60   a,  an image lens  73  and a half mirror  64 , and a light path is divided into two by the half mirror  64  giving a structure capable of measuring light intensity using a photomultiplier  65 . Also, the Z fine adjustment mechanism  68   a  and the XY fine adjustment mechanism  68   b  used are made up of three cylindrical piezoelectric elements  68  arranged so as to surround the objective lens  62 , and the sample holder  71  provided on these cylindrical piezoelectric elements is caused to move by driving them in the same direction. 
     Using this apparatus, light of the laser optical system  69  is converged by the converging lens  74 , and is incident on the probe tip  60   b.  With the focal point of the objective lens  62  aligned with the sample surface by a focussing mechanism  66 , the sample  61  is brought close to the probe  60  by the coarse adjustment mechanism  3 , and if it reaches a region where an atomic force acts, the aperture shape is observed n a monitor  67  using the image of the CCD camera  63 . At the same time, evanescent light formed at the probe tip  60   a  scatters at the sample surface, light that has passed through the sample  61  is converged by the objective lens  62  and light intensity is measured using the photomultiplier  65 . An amount of bending of the probe at this time is measured by an optical head  6  using an optical lever method, and with the amount of bending as a parameter the amount of bending is increased further by the control unit  70  while performing feedback using the Z fine adjustment mechanism  68   a,  and if a pressing force of the probe tip increases the tip aperture  60   a  is flared outwards by plastic deformation or breakage. The aperture diameter at this time can be estimated by monitoring light leaking out from the tip using the image of the CCF camera, or by measuring light intensity the photomultiplier  65 , and the bending amount is increased until an aperture of a desired diameter are obtained. This method is not limited to the case of making the bending amount a parameter, and can also be applied to other distance regulating methods. It can also be applied to a straight type optical fiber probe. 
     FIG. 18 is a schematic view showing a preferred angular relation between a longitudinal axis A of a probe tip  600  and a vertical axis B extending from the surface of a sample  700  in the methods of forming an aperture in the optical fiber probe according to the foregoing embodiments of the present invention. Preferably, the longitudinal axis A is inclined less than 45° from the vertical axis B. 
     It is also possible to make an aperture for a cantilever using the previously described methods, taking light intensity using the image from a CCD camera or a photomultiplier as a criterion. In this case, introduction of laser light involves an objective lens arranged on an upper side of the cantilever, and light is converged in an aperture opened in the cantilever from a rear surface. It is also possible to apply a method where a light waveguide is formed on the cantilever, laser light is coupled into the light waveguide at an optical fiber or an objective lens, and light is guided into the aperture. 
     As described above the present invention brings a probe tip and a sample close together or into contact with each other using an atomic force or a shear force acting between the probe tip of an optical fiber probe or a cantilever having a microscopic aperture, or tunnel current or evanescent light, controls a force acting on the tip with one of these physical amounts as a parameter, and forms an aperture in the optical fiber probe or cantilever having a microscopic aperture using means for subjecting the probe tip to plastic deformation or breakage using a force from the sample surface to make an aperture of a desired diameter in the tip section. 
     By using this type of method, it is no longer necessary to optimize vapor deposition conditions as was the case when forming an aperture through vapor deposition in the related art, and even if the type or shape of optical fiber probe or cantilever having a microscopic aperture is varied it is possible to form an aperture with good reproducibility. Also, it is possible to correct the aperture diameter after aperture formation. 
     Still further, in the case of forming an aperture by pressing the probe of an optical fiber probe or cantilever having a microscopic aperture against a sample, it is possible to adjust the pressing force more finely than in the related art, and problems such as the aperture diameter being too large and the shape of the aperture becoming elliptical can be alleviated, and it is possible to easily form the aperture.