Scanning tunnelling/atomic force microscope combined with optical microscope

Abstract: This invention provides a compound type microscope which can observe the measurement sample(57) of an atomic force microscope (AFM) by means of an optical microscope. This compound type microscope is comprised of an optical microscope having an objective (61) and an observation optical system (62), a cantilever (53) having a reflecting surface and detecting an atomic force, an irradiating optical system (51,52,60) for applying a spotlight to the cantilver, detecting means (54) for detecting the displacement of reflected light caused by the displacement of the cantilever, and a sample stage (55) for placing a sample thereon. Also, a scanning tunnel type microscope (STM) having an interchangeable probe and an optical microscope having an objective may be disposed coaxially with each other so that the sample can be measured by the STM instead of by the AFM, and provision may further be made of an AFM having a cantilever, and said probe and the cantilever may be selectively disposed below the objective.

Description: This invention relates to a compound type microscope comprising a combination of a scanning tunnel type microscope (STM), an atomic force microscope (AFM) and an optical microscope. In recent years, there have been actively developed scanning tunnel type microscopes and atomic force microscopes in which a probe is brought close to the surface of a sample and scans the latter and a tunnel current or an atomic force acting between the probe and the sample is detected to thereby observe the minute structure of the surface of the sample. The principle of the operation of the atomic force microscope (hereinafter referred to as the AFM) will hereinafter be described briefly with reference to Figure 10 of the accompanying drawings. Light emitted from a light source 71 is condensed by a collimator lens 72, forms a spot on the reflecting surface of a cantilever 73 and is reflected thereby. This reflected light is received by a detector 74. A sample 75 is oscillated by a scanner 76 mounted on a Z stage 115a. The inclination of the cantilever 73 with respect to the sample 75 on a sample holder 77 caused by the atomic force is grapsed as a variation in the light receiving position on the detector 74. The variation in the light receiving position is converted into a variation in the relative distance between the sample 75 and the cantilever 73. The observation area of the AFM is determined by the oscillation range of the scanner 76 and is therefore as small as several µm. Accordingly, in order to investigate a particular point on a wide sample, it is necessary to move measuring points one after another and thus, a very long time has been required for observation. Even if an attempt is made to limit the measuring points in advance by an optical microscope or the like, as is known from EP-A-0 394 962, it has been very difficult in the prior-art AFM because the light source 71 and the detector 74 are deterrent. On the other hand, with regard to the prior-art scanning tunnel type microscope (hereinafter referred to as the STM), as shown in Figure 11 of the accompanying drawings, there has been developed a coaxial type scanning tunnel microscope of coaxial construction in which an STM scanner 116 is provided outside a visible optical system provided with the objective 112 of an optical microscope. In this microscope, an effort is made so that a sample 117 on a Z stage 115b can first be observed by means of the image pickup device 111 of the optical microscope and the position of a probe 114 fixed to the probe holder 113 of the STM can be confirmed to thereby specify a measuring point. Also, as shown in Figure 12 of the accompanying drawings, there has been proposed a coaxial type scanning tunnel microscope of the type disclosed in US-A-4 999 495 having an STM scanner 116 disposed in a through-hole in the objective 118 of an optical microscope having a through-hole. Also, the AFM and STM are very similar to each other in the control method and the algorithm of observation data obtainment and therefore, as shown in Figure 13 of the accompanying drawings, there has been developed an apparatus in which electrical control systems such as an I/V amplifier 119, a feedback circuit 120, a high voltage amplifier 121 and a display 122 are commonized. In this apparatus, only a detecting system and a driving system are changed over by switches 123 and 124, and the STM and AFM are selectively operated. As described above, in the prior-art AFM, the observation area is severl µm, and to find out a range of several µm from a wide area such as an organismic sample, it has been necessary to move measuring ranges of several µm one after another and find out a certain point of the target sample, and this has required a very long time. Also, in a coaxial type scanning tunnel microscope wherein the prior-art STM and an optical microscope are disposed coaxially with each other, a probe has been provided in the central portion of the optical microscope and therefore, it has been difficult in terms of space to dispose the light source of the AFM and a detector. It is an object of the present invention to provide a compound type microscope which can selectively use an AFM or an STM and which enables a sample for the AFM or the STM to be observed by means of an optical microscope. In accordance with the present invention a compound type microscope is constructed such that a scanning tunnel type microscope having an interchangeable probe and an optical microscope having an objective are disposed coaxially with each other and there is further provided an atomic force microscope having a cantilever and said probe and said cantilever are selectively disposed below said objective. The scanning tunnel type microscope having the interchangeable probe and the optical microscope having the objective are disposed coaxially with each other so that the axial direction of the probe and the axial direction of the objective may coincide with each other. Further, the atomic force microscope having the cantilever is disposed so that the cantilever may lie below the objective. Said probe and said cantilever are selectively disposed. Accordingly, when the AFM is used, the probe is removed and the cantilever is mounted, whereby the AFM and the optical microscope become usable, and the sample is observed by means of the optical microscope and the AFM observation is determined, whereafter the sample can be observed by means of the AFM. Also, when the STM is used, the cantilever is removed and the probe is mounted, whereby the sample can be observed by means of the STM and at the same time, the sample can be observed by means of the optical microscope. Now, in a compound type microscope provided with an STM or an AFM and an optical microscope, like the present invention, it is preferable that a predetermined positional relation be set between the probe of the STM or the tip of the cantilever of the AFM and the optical axis of the optical microscope. For example, in a compound type microscope comprising an STM and an optical microscope, the optical axis of the optical microscope and the axis of the probe of the STM are set on the same axis, whereby a sample and the probe of the STM can be observed in the same field of view. As a result, the alignment of the probe with the sample and the observation of the tip of the probe can be accomplished easily. Also, in a compound type microscope comprising an AFM and an optical microscope, the optical axis of the optical microscope and the tip of the cantilever of the AFM are made substantially coincident with each other, whereby it becomes possible to specify the observation area of the AFM on the sample. As a result, observation can be accomplished efficiently. However, mounting accuracy of the order of micron has been required of such setting and therefore, very difficult work has been involved. Particularly, when the AFM and the STM are selectively used as in the present embodiment, the mounting or dismounting of the cantilever of the AFM and the probe of the STM becomes necessary as previously described and therefore, it becomes necessary to adjust said positional relation and efficiency becomes very bad. So, in the optical microscope portion, provision is made of a photographing device for photographing at least a part of an image formed by the optical system of the optical microscope and making it into an observation image, and aligning means for moving this photographing device in a direction perpendicular to the direction of said optical axis. Accordingly, by the photographing device being moved in a direction perpendicular to the optical axis of the optical microscope, the image of the tip of the probe of the STM can be aligned with any position of said observation image. Also, in the same manner, the observation area of the AFM can be confirmed in the observation image of the optical microscope. Figure 1 shows the construction of the essential portions of a compound type microscope according to a third embodiment of the present invention when a cantilever for an AFM is mounted. Figure 2 shows the construction of the essential portions of the compound type microscope according to the third embodiment of the present invention when a probe for an STM is mounted. Figure 3 shows the construction of the essential portions of the basic apparatus of the compound type microscope according to the third embodiment of the present invention. Figure 4 shows the construction of the AFM unit of the compound type microscope according to the third embodiment of the present invention. Figure 5 is a partly cross-sectional view showing the essential portions of a compound type microscope according to a fourth embodiment of the present invention. Figure 6 is another cross-sectional view showing the essential portions of the compound type microscope according to the fourth embodiment of the present invention. Figure 7 is a schematic view showing the observation field and the tip of a probe in the compound type microscope according to the fourth embodiment of the present invention. Figure 8 is a partly cross-sectional view showing the structure of another example of the compound type microscope according to the fourth embodiment of the present invention. Figure 9 is a cross-sectional view showing the structure of another example of the compound type microscope according to the fourth embodiment of the present invention. Figure 10 shows the construction of a prior-art AFM. Figure 11 shows the construction of a prior-art STM. Figure 12 shows the construction of a prior-art STM. Figure 13 shows the construction of a prior-art apparatus in which an AFM and an STM are selectively used. Some embodiments of the present invention will hereinafter be described with reference to the drawings. A compound type microscope according to a first embodiment of the present invention will now be described with reference to Figures 1, 2, 3 and 5. Figure 1 shows the construction of the essential portions of the compound type microscope according to the present embodiment when a cantilever 13 for AFM is mounted. Figure 2 shows the construction of the essential portions of the compound type microscope when a probe for STM is mounted. Figure 3 shows the construction of the essential portions of the basic apparatus of the compound type microscope. Figure 5 shows the construction of the AFM unit of the compound type microscope. The compound type microscope according to the present embodiment is constructed by compounding an optical microscope comprised chiefly of an image pickup device 22 and an objective 21, an STM comprised chiefly of a scanner 18 for STM, a probe holder 20 and a probe 25, and an AFM comprised chiefly of a light source 11, a collimator lens 12a, an imaging lens 12b, a cantilever 13, a detector 14, a sample holder 15 for AFM, a scanner 16 for AFM and a Z stage 19. The objective 21 is formed with a through-hole 21a, in which a scanner 18 for STM is disposed. The scanner 18 for STM is engaged by the probe holder 20 on which the probe 25 is removably mountable. The light source 11 and collimator lens 12 for AFM are disposed obliquely with respect to the outside of the objective, and the detector 14 is disposed obliquely on the opposite side to the light source 11 so as to receive the reflected light from the cantilever 13. As shown in Figure 4, these are made into a unit which can be mounted and dismounted with respect to the basic apparatus shown in Figure 3. The Z stage 19 for bringing a sample 17 close to an area in which the atomic force of the sample 17 acts on the cantilever 13 is formed with a recess 19a, in which the scanner 16 for AFM is disposed. The scanner 16 for AFM oscillates the sample 17 on the sample holder 15. The operation when the observation of the AFM and the optical microscope is effected by means of the compound type microscope according to the present embodiment will now be described with reference to Figure 1. In this case, the scanner 18 for STM is disposed in the objective 21 of the optical microscope, but is not used during the AFM operation. The objective 21 and image pickup device 22 of the optical microscope are used both during the AFM operation and during the observation of the sample 17. Light emitted from the light source 11 is collimated by the collimator lens 12, whereafter it is stopped into a spot shape by an imaging lens, and is applied to the cantilever 13 for AFM disposed instead at a location whereat the probe for STM should be disposed, and the reflected light from the cantilever 13 is received by the detector 14. The sample 17 is placed on the sample holder 15 for AFM on the scanner 16 for AFM. At this time, the cantilever 13 and the sample 17 are on the focal plane of the objective 21 of the optical microscope and can be image-picked up by the image pickup device 22 and at the same time, can be observed. Any deviation from the focal plane caused by the working error or the like of the cantilever can always be adjusted to the focal plane by a mechanism (not shown) for vertically moving the objective 21. The operation when the observation of the STM and the optical microscope is effected by means of the compound type microscope according to the present embodiment will now be described with reference to Figure 2. In this case, the cantilever 13 is removed and the probe 25 for STM is mounted on the probe holder 20. The probe 25 is scanned by the scanner 18 for STM. The scanner 16 for AFM is embedded in the Z stage 19 and therefore, by placing a sample holder 26 for STM on the Z stage 19 and placing the sample 17 thereon, observation can be effected without any hindrance. Also, the scanner for AFM may be removed. Also, the light source 11, the collimator lens 12a, the imaging lens 12b and the detector 14 for AFM may be kept mounted without any hindrance being imparted to the observation of the STM and the optical microscope. Of course, they may be removed. During the observation of the STM, by the objective 21 being vertically moved, the focal plane thereof can be adjusted to the sample 17 and the tip of probe 25, and the sample can be image-picked up by the image pickup device 22 for observation. As described above, in the first embodiment of the present invention, the scanner 18 for STM is disposed in the through-hole 21a in the objective 21 of the optical microscope, and unless the probe 25 is mounted, space can be secured near the focus position of the optical microscope and thus, the cantilever for AFM can be disposed there. The control systems of the AFM and the STM are substantially the same and therefore can be used in common without being greatly changed. The scanner for AFM disposed in the recess formed in the Z stage 19 imparts no hindrance during the operation of the STM. A second embodiment of the present invention will now be described with reference to Figures 5 and 6. Figure 5 is a cross-sectional view showing portions of a compound type microscope according to the present embodiment, and shows a state in which a cantilever for AFM has been removed and a probe 214 for STM is mounted. On the lower portion of the compound type microscope according to the present embodiment, there are installed an object lens unit 217 comprising the objectives 217a and 217b of an optical microscope and a lens barrel 217c. The lens barrel 217c is fixed to the strut 218 of the optical microscope. A through-hole is formed in the central portion of the objective 217b, and a tube scanner 216 for STM is installed through this hole. This tube scanner 216 is mounted on the strut 219 of the STM. A probe holder 215 is mounted on the tip end of the tube scanner 216, and a probe 214 is fixed to the probe holder 215. The probe 214 is scanned by the tube scanner 216. In the upper portion of the compound type microscope, a photographing device 201 having a CCD image pickup element 202 therein is caused on the lens barrel 208 through a camera mount 204 and an aligning member 205 to photograph a portion of an image formed by the objective unit 217. The camera mount 204 of the photographing device 201 is fixed to the aligning member 205 by a screw 205a, and the aligning member 205 is slidable on the slide surface 208a of the lens barrel 208. That is, the slide surface 208a, the camera mount 204 and the aligning member 205 together constitute the connecting portion between the lens barrel 208 and the photographing device 201. Figure 6 is a cross-sectional view taken along line A-A of Figure 7. As shown in Figure 6, the aligning member 205 of the photographing device 201 has the force of a spring 206x imparted thereto by a jig 209x and is urged against a feed screw 207x provided on the opposite side, and is slidden in a direction x by the feeding of the feed screw 207x. Likewise, the aligning member 205 has the force of a spring 206y imparted thereto by a jig 209y and is urged against a feed screw 207y provided on the opposite side, and is slidden in a direction y by the feeding of the feed screw 207y. The objective unit 217 and the probe 214 are aligned so that the focus of the objective unit 217 may coincide with the tip end 214b of the probe 214. They are also aligned so that the optical axis of the objective unit 217 and the axis 214a of the probe 214 may substantially coincide with each other. The images of the tip end of the probe 214 and the surface of a sample by the objective unit 217 is formed on the image pickup surface 203 of the CCD image pickup element 202. The image formed by the objective unit 217 is larger than the image pickup area of the image pickup element 202, and the image pickup element 202 photographs a portion of the formed image, whereby the enlargement magnification of an observation image displayed is further increased. That portion of the formed image which has been photographed is picked up by the image pickup element 202, and is displayed as shown in Figure 7 by an image display device (not shown). In Figure 7, the image 213 of the surface of the sample and the image 211 of the tip end of the probe are reflected in an observation field 203a photographed by the image pickup element. The tip end 214b of the probe 214 scans a scanning range 212 by the tube scanner 216. Accordingly, when as shown in Figure 7, the tip end 214b of the probe 214 and the center 203b of the observation field 203a slightly deviate from each other, a part of the scanning range 212 of the probe 214 deviates from the observation field 203a, thus hindering the observation. In the present embodiment, when as shown in Figure 7, the scanning range 212 of the tip end 214b of the probe 214 deviates from the observation field 203a, the above-mentioned feed screws 207x and 207y are fed to thereby move the photographing device 201 in the directions x and y. The image pickup element 202 in the photographing device 201 is correspondingly moved and therefore, that portion of the formed image by the objective unit 217 which is picked up is changed, whereby the scanning range 212 of the tip end 214b of the probe 214 can be kept in the observation field 203a. Accordingly, in the compound type microscope according to the present embodiment, even if during the interchange of the probe 214, the axis of the probe 214 is not completely coincident with the optical axis 214a of the objective, the center 203b of the observation field and the image 211 of the tip end of the probe can be made coincident with each other by moving the photographing device 201 by the use of the feed screws 207x and 207y. Therefore, during the interchange of the probe, the operation of bringing the tip end of the probe to the center of the observation field which has heretofore been cumbersomely performed by shifting the probe can be accomplished easily by the use of the feed screws. Further, as shown in Figure 8, magnets 210x and 210y may be disposed in lieu of the springs 206, and the aligning member 205 may be connected to the feed screws 207 by the force with which the magnets 210x and 210y are attracted to the feed screws 207x and 207y. A cross-sectional view taken along line B-B of Figure 8 is shown in Figure 9. As shown in Figure 9, the magnet 210x disposed in the direction x of the aligning member 205 is attracted to the feed screw 207x, thereby connecting the aligning member 205 to the feed screw 207x in the direction x. Also, the magnet 210y disposed in the direction y of the aligning member 205 is attracted to the feed screw 207y, thereby connecting the aligning member 205 to the feed screw 207y in the direction y. Accordingly, by feeding the feed screw 207x and 207y, the photographing device 201 can be moved easily in the directions x and y. The magnets 210a and 210b of Figure 8 attract the aligning member 205 in a direction Z to thereby bring the photographing device 201 into intimate contact with the lens barrel 208 and present the tumble of the photographing device. In the other points, the construction of the present embodiment is similar to that of the second embodiment and therefore need not be described. Thus, according to the present embodiment, even if deviation occurs between the axis of the probe of the STM and the optical axis of the objective of the optical microscope, the image of the tip end of the probe can be easily aligned with the center of the observation field of the optical microscope. The relation between the probe of the STM and the observation field of the optical microscope has hitherto been described, and what has been described also holds true of the case of the AFM and the optical microscope. In the case of the AFM, the tip of the cantilever cannot be seen by means of the optical microscope, but if the positions of the tip of the cantilever and the optical axis of the objective of the optical microscope are suitably set, the area that is being observed by means of the AFM can be confirmed by the observation field of the optical microscope. Accordingly, when any deviation from said set value occurs to the positional relation between the cantilever of the AFM and the optical axis of the objective, the positional relation can be easily adjusted by the feed screws as previously described.

Claims: A compound type microscope in which a scanning tunnel type microscope having an interchangeable probe (25, 214) and an optical microscope having an objective (21, 217) are disposed coaxially with each other, said compound type microscope having an atomic force microscope having a cantilever (13), said probe (25) and said cantilever (13) being selectively disposed below said objective (21, 217) such that either the scanning type tunnel microscope or the atomic force microscope may be combined with the optical microscope. A compound type microscope according to claim 1, wherein said cantilever (13) has a reflecting surface and is able to be displaced in accordance with detected atomic force, the microscope further comprising an irradiating optical system (11, 12a, 12b) for irradiating said reflecting surface of said cantilever (13) with a spotlight and detection means (14) for receiving the reflected light of said spotlight applied to said reflecting surface of said cantilever (13) which is displaced by said atomic force to detect the amount of displacement, and wherein said irradiating optical system (11, 12a, 12b) is so disposed as to apply a spotlight from the outside of said optical microscope to said cantilever (13). A compound type microscope according to claim 1 or 2, further comprising: a photographic unit (201) for photographing at least a portion imaged by said optical microscope and making it into an observation image, and aligning means (205) for moving said photographic unit (201) in a direction perpendicular to the axial direction of said probe (214). A compound type microscope according to claim 3, wherein said optical microscope has: a lens barrel (208) formed with an opening portion (21a), a connecting portion (204, 205, 208a) for mounting said photographic unit (201) in said opening portion with a clearance which makes said photographic unit (201) movable in a direction perpendicular to the axial direction of said probe (214), and regulating means (206, 209, 207) provided in said opening portion for regulating said clearance and fixing said photographic unit (201). A compound type microscope according to claim 4, wherein said regulating means (206, 209, 207) fixes said photographic unit (201) at any position relative to said lens barrel (208) within the range of said clearance. A compound type microscope according to claim 4 or 5, wherein said regulating means (206, 209, 207) is provided around said opening portion, and has a feed screw portion (207) for moving on said photographic unit (201), and a spring portion (206) for urging said photographic unit (201) against said feed screw portion (207). A compound type microscope according to claim 4 or 5, wherein said regulating means (206, 209, 207) is provided around said opening portion, and has a feed screw portion for moving on said photographic unit, and a magnet for connecting said photographic unit to said feed screw portion.

Inventors: HIROYUKI MATSUSHIRO, MASATOSHI SUZUKI, TETSUJI ONUKI, HIROYUKI, MATSUSHIRO, MASATOSHI, SUZUKI, TETSUJI, ONUKI
Applicants: NIPPON KOGAKU KK, NIKON CORPORATION
Application year: 1992
Main classification: G01B7
IPC codes: G01N37, G01B7, H01J37, G01B21, G01Q30, G01Q20, G01Q60