Atomic force microscope with optional replaceable fluid cell

Abstract: An atomic force microscope which is readily useable for researchers for its intended use without extensive lost time for setup and repair. The probe (10,20) used therein is a cantilevered optical lever which imparts surface information in a gentle and reliable manner by reflecting an incident laser beam (24). The probe is carried by a replaceable probe-carrying module (48) which is factory set up and merely inserted and fine tuned by the user. The probe-carrying module also includes the provision for forming a fluid cell (124) around the probe. Fluid can be inserted into and/or be circulated through the fluid cell through incorporated tubes (126,128) in the probe-carrying module. Electrodes (164) are also provided in the fluid cell for various uses including real-time studies of electro-chemical operations taking place in the fluid cell. The piezoelectric scan tube (32) employed includes a voltage shield (60) to prevent scanning voltages to the tube from affecting data readings. Samples (14) are easily mounted, replaced, and horizontally adjusted using a sample stage (58) which is magnetically attached to the top of the scan tube. Calibration tools are provided to make initial set up and fine tuning of the microscope a simple and straightforward operation requiring little or no technical talent.

Description: Background of the Invention : This invention relates to scanning microscopes used for imaging the topography of surfaces and, more particularly, to an atomic force microscope having extended use capabilities. The family of scanning probe microscopes that have been introduced to the scientific community of recent years is broadening the frontiers of microscopy. As typified by the greatly simplified general example of Figures 1 and 2, these microscopes scan a sharp probe 10 over the surface 12 of a sample 14 to obtain surface contours, in some cases actually down to the atomic scale. The probe 10 may be affixed to a scanning mechanism and moved in a scan pattern over the surface 12 or alternately (and equally effectively because of the small sizes involved) the probe 10 may be stationary with the sample 14 mounted on a scanning mechanism that moves the surface 12 across the probe 10 in a scanning pattern. The tip 16 of the probe 10 rides over the surface 12 as the probe 10 is moved across it. As the tip 16 follows the topography of the surface 12, the probe 10 moves up and down as indicated by the bi-directional arrow 18. This up and down movement of the probe 10 is sensed to develop a signal which is indicative of the z directional component of the 3-dimensional surface 12. Early atomic force microscopes (AFMs) mounted the probe 10 to a wire and electrically sensed the movement of the wire the probe tip 16 moved over the surface 12. Recent prior art AFMs employ technology developed in the microelectronics art as depicted in Figure 1. It should be noted that drawings figures herein are not to scale as the probe 10 and its tip 16 (typically of a diamond material) are extremely small so as to be useful at the near-atomic level. If the drawings were drawn to scale, these components would not be visible. In fact, when working with AFMs, these components are not visible to the naked eye and must be viewed with an optical microscope. As will be seen shortly, this is a source of some of the problems which are solved by this invention. As depicted in Figure 1, recent prior art AFMs have the probe 10 extending outward from the forward edge of a substrate 20 with the probe 10 being formed thereat by manufacturing techniques which are not critical to the present invention. It is sufficient to point out that the probe 10 is typically in the form of an arm extending outward from the substrate 20 with the diamond tip 16 attached at the end of the arm. Also, the probe 10 is extremely small and extremely fragile. The substrate 20 is typically adhesively attached to the bottom and extending outward from the forward edge of a large steel block 22 mounted to the surrounding structure. Where the probe 10 and sample 14 are conductive, the position of the probe 10 as a result of the deflection caused by the surface 12 during the scanning process can be sensed electrically. Where non-conductive samples are to be scanned, the prior art literature suggests bouncing a laser beam 24 off the probe 10 to be sensed by a photoelectric sensor 26. As depicted in Figure 2, as the probe 10 deflects up and down, the reflection angle of the laser beam 24 is changed. It is this change in reflection angle that is sensed by the photoelectric sensor 26, which then outputs an electrical signal related to the angle (by way of the beam of light striking a detecting surface), and thereby the z directional component of the probe 10. Regardless of the probe positional sensing method employed (electrical or laser light), there are a number of problems associated with the prior art AFMs as typified by the simplified drawings of Figures 1 and 2. As depicted in Figure 2, the surface 12 of a sample 14 has a thin (i.e. molecular level) coating of water 28 thereon. Often, the small, lightweight tip 16 of the probe 10 is "sucked" into the surface 12 against the miniscule resilient biasing force of the probe 10 by the capillary action of this coating of water 28. This, of course, can seriously damage the tip 16 to the point of making it non-useful for its intended purpose, Further on the negative side, the coating of water 28 is not sufficient to provide any lubricating with respect to the tip 16 sliding over the surface 12. As a result, frictional wear of the tip 16 is a serious problem causing the tip 16 to wear off quickly to the point of making it non-useful for its intended purpose. Also, with some sample materials the tip 16 may dig into and damage the sample surface 12 rather than sliding over it to provide useful information. Additionally, the scanning action is accomplished by the application of fairly high voltages to a scanning member. With the steel mounting block 22 in close proximity as depicted in Figure 1, these voltages can be attracted to the steel block 22 and, in the process, affect the probe 10 thereby introducing false data into the output stream. The type of environment and class of persons who are and will be using AFMs in the future also adds to the problems of this extremely useful and potentially powerful device. Typically, the user is a researcher working on various projects in a laboratory environment. He/she is not interested in having to "play" with the AFM to get it to produce workable results. In its present configuration as depicted by the drawings of Figures 1 and 2, it is difficult of set up for scanning. It is easy to break the tip 16 from the probe 10 and/or the probe 10 from the substrate 20. Replacing the probe/tip assembly is a major undertaking; and, because of the problems described above, the life expectancy of the probe/tip is extremely short. Moreover, the sample 14 is glued to the top of a piezoelectric scanning tube (not shown in Figures 1 or 2) which provides the scanning action by moving the sample with respect to the stationary probe 10 (which must remain fixed in position to have the laser beam 24 reflect from it for detection purposes). Thus, once placed, the sample 14 is impossible to move (so as to change the scanning point) and difficult to change. Positioning the tip 16 of the probe 10 on the surface 12 of the sample 14 is difficult at best and virtually impossible in some cases. In short, while AFMs are moving into a commercial stage of development, the products which are available in the prior art are not the efficient, easy to use laboratury aids that the users thereof desire and need. Wherefore, it is a general object of the present invention to provide an AFM system which is easy to set up, calibrate, and use in the typical laboratory environment by the typical laboratory worker. It is a principal object of the present invention to provide an AFM system in which the probe-tip resist frictional wear. It is still a principal object of the present invention to provide an AFM system in which the probe/tip are not subjected to the capillary forces of water coating the surface of the sample. It is yet a principal object of the present invention to provide an AFM system in which the probe/tip slide easily over the sample surface and resist digging into softer samples and damaging them thereby providing a gentler and more reliable operation. These objects are obtained with the privisions of claims 1 and 16. It must be remarked, however, that using a scanning tunneling microscope on a sample immersed in a drop of liquid is described in a paper "Semiconductor topography in aqueous environements: tunneling microscopy of chemomechamnically polished (001) GaAs" by Sonnenfeld et al, in Applied Physics letters, vol.50, n°24, June 15,1987, New York, USA, p.1742-1744. It is a further object of the present invention to provide an AFM system in which the probe-tip are contained in an easily replaceable module which is recyclable by the AFM supplier. It is a still further object of the present invention to provide an AFM system having calibration/setup tools included therewith which make the setting up of the AFM a simple and straightforward task. It is another object of the present invention to provide an AFM system in which the sample is held by a removeable and adjustable member which allows the position of the sample to be changed in situ and allows a new sample to be installed easily and quickly without destruction of previous samples. It is also an object of the present invention to provide an AFM system in which the steel mounting block of the prior art is removed without affecting the stability of the probe and tip. Description of the Drawings : Figure 1 is a simplified drawing of a prior art atomic force microscope showing the probe as mounted to a substrate carried by a large steel block being detected by a laser beam being reflected therefrom. Figure 2 is an enlarged drawing of the tip of the probe of Figure 1 showing the movement of the tip over the surface of a sample and how the reflection angle of the laser beam is changed as a result of deflection of the probe. Figure 3 is a partially cutaway side view of an atomic force microscope according to the present invention. Figure 4 is an enlarged cutaway side view of the sample-holding block of the atomic force microscope of Figure 3 showing how the supporting screws thereof are calibrated to a proper height. Figure 5 is an enlarged cutaway side view of the sample-holding block of Figure 4 mounted on the base portion of the atomic force microscope of Figure 3 showing how the supporting screws thereof are calibrated to place the probe tip at a proper height. Figure 6 is an enlarged cutaway side view of the probe and tip of a non-preferred embodiment of the present invention in which the scanning takes place within a fluid drop. Figure 7 is a bottom view of the probe-carrying module of the present invention in its preferred embodiment. Figure 8 is a cutaway view of the probe-carrying module of Figure 7 in the plane VIII-VIII. Figure 9 is a simplified drawing depicting a prior art three point support/adjustment technique as employed in the present invention. Figure 10 is a side view of a calibration tool employed in the AFM system of the present invention to make the probe-carrying module position the probe tip exactly in its proper position when the probe-carrying module is inserted into the sample-holding block of Figure 4. Figure 11 is a bottom view of the calibration tool of Figure 10. Figure 12 is a drawing depicting the use of the calibration tool of Figures 10 and 11. Figure 13 is a partially cutaway side view of the top of a piezoelectric scanning tube employing the voltage shield and the removeable/slideable stage of the present invention in a first embodiment. Figure 14 is a detailed drawing of the preferred holding and adjusting mechanism for the photoelectric sensor employed in the present invention. Figure 15 is a partially cutaway side view of the top of a piezoelectric scanning tube employing the voltage shield and the removeable/slideable stage of the present invention in an alternate embodiment. Figure 16 is a top view of the preferred probe configuration of the present invention. Figure 17 is a front view of the probe of Figure 16. Figure 18 is a drawing of an optional removeable but non-transparent probe-carrying module without fluid cell potential that may be employed in the present invention. Description of the Preferred Embodiment : The essential elements of an AFM 28 according to the present invention in its preferred embodiment are depicted in the cutaway side view of Figure 3. There is a base 30 which, as in the typical prior art AFM, is shock mounted in some manner. A piezoelectric scan tube 32 is mounted extending perpendicularly upward from the base 30. The scan tube 32 is of a conventional design well known in the art whereby by the application of z-, y-, and z-directional scan voltages to the wires 34, the top end 36 of the tube 32 can be moved horizontally in two orthogonal directions and vertically to provide x and y scanning as well as fine probe positioning in the z direction to the atomic level. A sample-holding block 38 is supported on the tips of three adjusting screws 40 threaded through the base 30 employing a hole/slot/surface contact and alignment technique which is well known in the art, to be addressed in greater detail later herein. As can be seen, the scan tube 32 extends through a bore 42 in the bottom 44 of the sample-holding block 38 so that the top end 36 thereof is within a chamber 46 within the sample-holding block 38. A probe-carrying module 48 is disposed within the chamber 46 and supported on the tips of three adjusting screws 50 threaded through the bottom 44 employing a special application of the above-mentioned hole/slot/surface contact and alignment technique, which will also be addressed in greater detail later herein. The probe-carrying module 48, as will be seen shortly, provides the solution to several major problems of prior art AFMs as described above. The probe-carrying module 48 is of a transparent material having parallel, planar top and bottom surfaces, 52, 54, respectively. In order of preference, the probe-carrying module 48 can be made of quartz, glass, or a plastic such as polycarbonate. The substrate 20 having the probe 10 mounted thereto is glued to the bottom surface 54 within an O-ring 56 also glued to the bottom surface 54. As will be described in further detail shortly, this arrangement can be employed to place the probe 10 within a fluid cell which can exist between the bottom surface 54 and the sample 14 within the O-ring 56. That, of course, eliminates the capillary attraction problem described above and provides a low friction/lubricating environment wherein even soft tissue samples, and the like, can be scanned without damage thereto. As will be noted, the steel block 22 of the prior art has been eliminated, as desired. The probe tip 16 is automatically aligned with respect to the laser beam 24 in a manner to be described shortly. Perhaps most important, the probe-carrying module 48 can be removed and replaced quickly, accurately, and easily if and when the probe/tip become broken and/or worn. The used module 48 can then be returned to the factory for the installation of a new probe 10 under the proper conditions. The sample 14 is attached to the top of a removeable sample stage 58. Thus, a particular sample 14 can be attached easily to the stage 58 at a bench location away from the AFM 28. If desired, a particular sample can be removed temporarily and then be reinserted at a later time. Additionally, the sample stage 58 is magnetically attached to a ferromagnetic electrical interference shield 60 carried by the top end 36 of the scan tube 32. The shield 60 prevents electrical interference from the scan voltages applied to the tube 32 and, additionally, the magnetic attachment of the sample stage 58 thereto permits the stage 58 (and attached sample 14) to be slid horizontally in the x and y directions to place the desired area for scanning under the probe tip 16. The top of the sample holding block 38 has a flat stage area 62 thereon which is parallel to the bottom 44. A bore 64 extends perpendicularly from the stage area 62 into the chamber 46 generally concentrically about a point on the probe-carrying module 48 where the tip 16 of the probe 10 is to be located. A laser beam source 66 is carried by a rectangular holding member 68 magnetically attached to the stage area 62 for horizontal sliding movement thereon. The laser beam 24 from the source 66, therefore, shines down the bore 64 to strike the probe 10 from whence it is angularly reflected up bore 70 to strike the detecting surface 72 of a photoelectric sensor 26 (of a type well known in the art which individually forms no part of the novelty of this invention). The sensor 26 is adjustably held in a micro detector adjustor 74. In presently tested embodiments of this invention, the source 66 of the laser beam 24 is a holder gripping one end of an optic fiber which has the laser beam 24 from a commercial laser device input thereto at the opposite end to prevent heat buildup from the laser device in the area of the probe 10 and associated apparatus. A preferred source 66 would include a laser-emitting diode located within the source 66 itself. The horizontal position of the holding member 68 is fine-adjusted in the x and y directions (to place the laser beam 24 exactly on the probe 10 for optimum reflection) by means of a pair of orthogonally oriented micro laser adjustors 76. Having thus described the present invention and its various components and aspects in a general manner, the various point of novelty will now be addressed in greater detail. The sample holding block 38 and the method of setting the adjusting screws 50 is depicted in the enlarged drawing of Figure 4. As can be seen from this figure, there are micro laser adjustors 76 oriented at 90° to one another. Each adjustor 76 comprises a vertical member 78 extending upward from the sample holding block 38 adjacent the stage area 62. A leaf spring member 80 extends upward along the inner surface of the vertical member 78 from a point of attachment thereto at 82. A magnetic probe 84 extends outward towards the stage area 62 from a point just above the point of attachment 82. An adjusting screw 86 is threaded through the vertical member 78 into contact with the leaf spring member 80 near the top of the vertical member 78. Note that the adjusting screws 86 have a large diameter turning wheel 88 on the outer end thereof whereby the adjusting screws 86 can be turned easily a fraction of a rotation when horizontally adjusting the position of the holding member 68 on the stage area 62. Note also that there is a large mechanical advantage from the positioning of the adjusting screw 86 on the leaf spring member 80 with respect to the magnetic probe 84 and the point of attachment 82. As a result, turning the wheel 88 (which can be accomplished easily and smoothly because of the mechanical advantages provided) will result in a very small horizontal movement of the holding member 68, which is desirable in order to be able to accurately accomplish the final positioning of the laser beam 24 on the probe 10. As depicted in detail in Figure 14, the preferred micro detector adjustor 74 comprises a U-shaped slider member 90 magnetically adhering to the sliding surface 92 of the sample holding block 38, which is perpendicular to the bore 70. The sensor 26 is held within the sideward-facing U of the slider member 90 by a holder 148 having an area 150 therein sized to the contours of the sensor 26. Both the holder 148 and the slider member 90 are held to the sliding surface 92 by magnets 116. The slider member 90 is moved up and down by the adjusting screw 94 which is threaded through the slider member 90 between the webs 96 in the sample holding block 38 provided for the purpose. The holder 148 is moved sideways by the adjusting screw 152 threaded through the bottom of the U of the slider member 90. The position of the adjusting screws 50 (and thereby the position of the probe-carrying module 48 when inserted into the chamber 46) can be set using a calibration blank 98 and height gauge 100 as shown. The height gauge 100 is inserted into the bore 42 and the calibration blank 98 is positioned on the adjusting screws 50. The screws 50 are then raised and/or lowered, as appropriate, until the calibration blank 98 is just resting evenly on the flat top surface of the height gauge 100. At that point, the screws 50 are set to a height such that when the probe-carrying module 48 is positioned on the screws, the probe tip 16 will be at the desired (and anticipated) probe height as shown. The adjusting screws 40 must also be set to a proper height to support the probe-carrying module 48 at a point where the sample surface of a mounted sample to be scanned will be at the probe level anticipated by the calibration procedure just described with respect to Figure 4. This is accomplished using the calibration tool 102 in the manner depicted in Figure 5. Calibration tool 102 comprises a yoke 104 having a bottom 106 configured exactly like the bottom 44 of the sample holding block 38, including a bore 42′ for the scan tube 32 to pass through. It should be noted that, as will be seen from a description contained hereinafter, while the adjusting screws 50 of the sample holding block 38 need be adjusted only rarely, the adjusting screws 40 will need to be adjusted whenever the sample 14 is changed. This is because the sample 14 is glued to the sample stage 58 and the height of the sample surface may change significantly from one sample to the next, at least in the sizes being considered in the operation of the AFM 28. The calibration tool 102 also has a short focal length calibration microscope 108 positioned perpendicularly to be above the sample surface 12 when the calibration tool 102 is mounted on the adjusting screws 40. The focal length of the calibration microscope 108 is chosen such as to focus exactly at the plane the probe tip 16 will be in. To properly adjust the adjusting screws 40, the sample 14 is mounted on the scan tube 20 and the calibration tool 102 positioned as shown in Figure 5. While viewing through the calibration microscope 102, the adjusting screws 40 are used to move the calibration tool 102 up and down until the entire surface 12 of the sample 14 is in focus. At that point, the adjusting screws 40 are properly set. Because of the short focal length employed, the surface 12, when completely in focus, is also parallel to the scanning action of the probe 10. Before continuing with the setup and calibration aspects of the present invention, attention is directed to Figures 13 and 15 which are directly related to the last described aspects of this invention. As mentioned earlier, the scanning movement of the piezoelectric scan tube 32 is affected by the application of voltages (which can be in the 100 volt range) to electrodes 110 on the exterior and interior surfaces of the tube 32, which is made of a piezoelectric material. Independently of the attracting potential of the steel block 22 (which has been removed in the preferred embodiment of this invention), the inventors herein have observed (and proved) that the scanning voltages employed to move the scan tube 32 can still adversely affect the probe 10. To solve this problem, a disk shaped voltage shield 112 is attached to the top end 36 of the tube 32. Since the shield 112 must be electrically conductive, it is attached to the top end 36 of the tube 32 with an insulating adhesive 114. The voltage shield 112 is then physically connected to a ground potential. Optionally, it can be connected to a fixed voltage potential which is available. The adjustability and removability aspects of the sample stage 58 can be accomplished in two ways as depicted in Figures 13 and 15, respectively. In the embodiment of Figure 13, the voltage shield 112 is of a ferro-magnetic material and the sample stage 58 has a magnet 116 mounted therein. In the embodiment of Figure 15, the voltage shield 112 has a magnet 116 mounted concentrically therein and the sample stage 58 is of a ferro-magnetic material. Accordingly, in either embodiment the voltage shield 112 not only shields against the effects of stray voltages reaching the probe 10; but, additionally, provides a surface on the top end 36 of the scan tube 32 onto which the removeable sample stage 58 having a sample 14 glued thereto can be magnetically attached. Accordingly, while the sample 14 is positioned on the tube 32 and as part of the adjustment of the adjusting screws 40 as described with respect to Figure 5, the sample stage 58 can be slid horizontally in both the x and y directions to place an area of interest under the probe to be scanned thereby. The problems of capillary action and friction in soft samples as well as the providing of the gentler and more reliable operation will now be addressed. An important aspect of the AFM 28 of this invention is the inclusion of a unique probe design which is, in fact, a microfabricated cantilever with an optical lever as shown in Figures 16 and 17. The probe 10 comprises a pair of V-shaped arms 154 formed on the bottom forward edge of the supporting substrate 20 by microfabrication techniques well known in the microelectronics art which, per se, form no part of this invention. The arms 154 are, therefore, cantilevered out from the bottom forward edge of the substrate 20. Because of the nature of the materials employed in such microfabrication, the cantilevered arms 154 deflect easily (i.e. their self biasing force is practically non-existent). Because such microfabricated materials have a very smooth surface, they inherently reflect the laser beam 24, thus forming the desired optical lever. The actual contacting tip 16 is made of diamond and separately attached where the two arms 154 join to form the "V". The problems of capillary action and friction in soft samples can be solved in the AFM 28 of this invention by optionally having the probe 10 and area of the sample being scanned immersed in a fluid bath. In a non-preferred embodiment, this novel aspect of the present invention can be accomplished in the manner shown in Figure 6. This approach was employed in early tested embodiments of the present invention; but, has been superceded by the apparatus to be described shortly. As will be noted, this embodiment employs the prior art technique of having the probe 10 mounted on a substrate 20 which, in turn, is mounted to a steel block 22, or the like, carried by the base portion of the AFM. To provide the fluid bath, a clear cover glass 118 is attached to the top of the substrate 20 extending outward over the probe 10. A drop of fluid 120 (such as de-ionized water) is then injected with a syringe into the area surrounding the probe 10 defined by the cover glass 118, the sample surface 12, and the edge of the substrate 20, where it adheres by capillary action and surface tension. The laser beam 24 passes through the cover glass 118 and fluid 120 to the probe 10 from which it is reflected to pass back through the fluid 120 and cover glass 118. Any minor refraction will remain constant and can be accounted for by adjusting the position of the photoelectric sensor 26. Other than being associated with the non-replaceable, steel block mounted probe 10, the only other problem with this embodiment is that the life of the drop of fluid 120 is limited due to evaporation. The probe-carrying module 48 shown in detail in Figures 7 and 8 solves many of the problems associated with the prior art while, when desired or needed, optionally providing the novel fluid cell environment of this invention and is, therefore, the preferred approach. Each probe-carrying module 48 is assembled and calibrated (in the manner to be described shortly) at the factory. As mentioned earlier, if the probe 10 wears out or breaks off, the researcher merely installs a new probe-carrying module 48 and sends the broken one back to the factory for recycling. The probe-carrying module 48 has an angled area 122 (approximately 10°) cut into the bottom surface 54 into which the probe carrying substrate 20 is glued. The probe 10 and substrate 20 are surrounded by an O-ring 56 which is also adhesively attached to the bottom surface 54. When the O-ring 56 is positioned on the surface 12 of the sample 10 as shown in Figure 8, a fluid cell 124 is formed between the bottom surface 54 and the sample surface 12 within the O-ring 56. Inlet and outlet tubes 126, 128 are formed into the material of the probe-carrying module 48 communicating with the fluid cell 124 and the exterior of the module 48. Fluid 120 can be injected (or even circulated if applicable) through the tubes 126, 128. The evaporation problem is, therefore, eliminated. It should be noted that where the fluid cell is not needed, the optional probe-carrying module 48 of Figure 18 can be employed. In this case, the probe-carrying module 48' is of metal or plastic and, as with the above-described version, has an angled area 122 (approximately 10°) cut into the bottom surface 54 into which the probe carrying substrate 20 is glued. A bore 156 through the probe-carrying module 48' from the top surface 52 to the bottom surface 54 aligned with the probe 10 is provided to allow the laser beam 24 to pass through the probe-carrying module 48', strike the probe 10, and be reflected therefrom to the photoelectric sensor 26. Returning to the above-described preferred probe-carrying module 48 containing the fluid cell, in addition to providing the benefits described with respect to eliminating the capillary attraction affect on the probe 10 and the reduction of friction in soft samples, the fluid cell can also be employed for electro-chemical purposes, and the like. To this end, in the preferred embodiment of this invention three additional tubes 158, 160, and 162 are formed into the material of the probe-carrying module 48 communicating with the fluid cell 124 and the exterior of the module 48. Each of the tubes contains an electrode 164 extending between the fluid cell 124 on one end and the exterior of the module 48 on the other, at which point electrical connection can be made thereto. As will readily be appreciated by those skilled in the art, such an arrangement has many uses. For example, samples could be "pinned down" to substrates electrically by applying a voltage between one or more of the electrodes 164 in the fluid cell (containing the sample) and the voltage shield 112. The presence of the three electrodes 164 (i.e. a working electrode, a reference electrode, and an auxiliary electrode) make possible a wide range of electro-chemical studies such as plating, corrosion, and electrostripping within the real-time environment of the AFM 28. The prior art hole/slot/support system employed in the invention and mentioned earlier is depicted in simplified form in Figure 9. Three points, of course, define a plane as is a well known mathematical fact just as the fact that two points define a straight line. A simpler example is the three legged stool, which will never wobble like its four legged cousin. Thus, in complex apparatus such as the AFM 28 wherein stability of the components therein with respect to one another, the use of a three point support system is a logical approach. To provide accuracy of placement with adjustability, the hole/slot/support technique of Figure 9 is commonly employed. The surface to be supported has a straight slot 130 formed therein at a first general point of support. A hole 132 is formed into the surface in longitudinal alignment with the slot 130 at a second, but specific, point of support. The surface to be supported is placed on three supports by first placing one support into the slot 130. The one support is then slid within the slot as required and the article rotated as needed to allow a second of the three supports to be inserted into the hole 132. Two points of support have thus been established. As two points define a line, the two support points only allow rotation of the surface to be supported about the support points in the hole 132 and slot 130. The surface to be supported is then lower (i.e. rotated about the line defined by the first two support points) until the surface to be supported is resting on the third of the three supports. This supporting technique will repeatedly result in the same positioning of the surface to be supported on the three supports, While the above-described prior art three point support system is used throughout the AFM 28, a novel approach thereto is used to pre-calibrate the probe-carrying modules 48 at the factory so that when one is inserted into the chamber 46 to be supported by the adjusting screws 50, the probe tip 16 will be placed in approximate accurate alignment with the nominal position of the laser beam 24. As can be seen from the drawing of Figure 7 the bottom surface 54 of the probe-carrying module 48 has only a slot 130 formed therein. The "hole" 132 is provided according to the calibration technique shown in Figures 10-12. At the factory, after the substrate 20 with the probe 10 attached is affixed to the angled area 122, the calibration tool 134 of Figures 10 and 11 is employed to position a washer 136 so that the hole in the center of the washer 136 is the hole 132′ which receives the second of the adjusting screws 50. The calibration tool 134 has a horizontal base 138 with three pins 140 extending downward therefrom perpendicular to the base 138 and spaced in the same triangular shape as the three adjusting screws 50. A microscope 142 is vertically fit into a bore 144 through the base 138 which has the same relationship to the pins 140 that the bore 64 has to the adjusting screws 50. Crosshairs 146 within the microscope 142 cross in the approximate position of the laser beam 24 within the bore 64. With the probe-carrying module 48 lying on its top surface 52, one pin 140 is inserted in the slot 130. A washer 136 is placed on the bottom surface 54 and another of the pins 140 is inserted into the hole 132′ thereof and then placed on the bottom surface 54 along with the third pin 140. The calibration tool 134 is then slid over the bottom surface 54 to place the probe tip 16 in the center of the crosshairs 146. The washer 136 is then glued to the bottom surface 54 by the application of a fast-drying glue. That completes the calibration procedure as the hole 132′ is now fixed so as to place the probe tip 16 in the proper position when the probe-carrying module 48 is used in an AFM 28. After insertion of the probe-carrying module 48 into the chamber 46, the micro laser adjustors 76 are then used to precisely place the laser beam 24 on the probe 10 for optimum reflection. Simultaneously, the micro detector adjustor 76 is used to optimally position the photoelectric sensor 26. Thus, the AFM 28 of this invention can be placed into service for useful work quickly and easily without undue expense of time and without the need for a high degree of technical training. If the procedures as set forth above are followed, the probe 10 is virtually unbreakable as a result of the setup procedure; and, when the probe 10 does wear out or break, it is quickly and easily replaced.

Claims: An atomic force microscope (28) for determining a characteristic of a sample (14), comprising : a probe (10) adapted to scan said sample ; scanning means (32) for causing relative scanning movement between said probe and said sample ; sensing means (26, 66) for sensing a position of said probe ; and characterized by a fluid body (120) in communication with said sample and in which said probe is immersed in contact with said sample so that during said relative scanning movement capillary attraction between said probe and said sample, caused by a surface film formed on said sample due to exposure to ambient atmosphere, is reduced. Atomic force microscope according to claim 1, characterized in that said probe (10) includes a probe tip (16) disposed on a lever immersed in the fluid body. Atomic force microscope according to claim 1, characterized by : a rigid cover plate (52) disposed on a top surface of said fluid body (120) to define a fluid cell (124) between said cover plate and said sample. Atomic force microscope according to claim 3, characterized in that : said rigid cover plate (52) comprises an optically transparent material ; and said sensing means (26, 66) comprises optical means (26) for sensing a vertical movement of said probe by means of light (24) applied to said probe through said rigid cover plate. Atomic force microscope according to claim 1, characterized by : means for exchanging fluid (126, 128) within said fluid body. Atomic force microscope according to claim 1, 3, 4 or 5, characterized in that it comprises : two or more electrodes (164) in contact with said fluid body for performig an electrochemical reaction. Atomic force microscope according to claim 1, 3, 4, 5 or 6, characterized in that the said scanning means comprises : a scanner (32) ; and a conductive shield element (60) at a fixed potentiel disposed between said probe and said scanner for electrically shielding said probe from said scanner. Atomic force microscope according to any one of the preceding claims, characterized in that it comprises : a removable probe module (48) on which said probe is fixedly mounted at a selected location. Atomic force microscope according to any one of the preceding claims, characterized in that it comprises : a slidably movable and removable sample support (58) releasably coupled to said scanning means and on which said sample is mounted. Atomic force microscope according to any one of the preceding claims, characterized in that it comprises : a support (38) on which said deflection detection system and said probe are mounted ; and means mounted on said support (74, 76) for adjusting positioning of said sensing means. Atomic force microscope according to claim 8, characterized by : a probe module support (134) mechanically coupled to said probe module (48) during operation of said atomic force microscope and having a predetermined spatial arrangement (130, 132, 140) with said sensing means so that when said probe module is mechanically coupled to said probe module support, said probe is in substantial alignment with said sensing means. The atomic force microscope according to claim 9 further comprising : magnetic means (116) magnetically mechanically coupling said sample support to said scanning means. Atomic force microscope according to any one of the preceding claims, characterized in that : said sensing means comprises a light beam source (66) and a light beam detector (26) ; and said adjusting means (74, 76) comprises means for adjusting positioning of at least one of said light beam source and said light beam detector so that a light beam output by said source and reflected of said probe is incident on said detector. Atomic force microscope according to claim 7, wherein said scanner comprises a piezoelectric tube (32) and said conductive shield is mounted on a distal end of said tube between said tube and said probe. Process for operating an atomic force microscope in which a relative scanning movement is produced between a sample (14) and a tip (16) of a lever mounted probe (10) by a scanning means (32) and a deflection of said lever mounted probe is detected by a deflection detection system (26, 66), characterized by the steps of : providing a fluid body (120) in communication with the surface (12) of the sample ; immersing said lever mounted probe in said fluid body to reduce capillary attraction, caused by a surface film formed on said sample due to exposure to ambient atmosphere, between the lever mounted probe and the sample ; and producing said relative scanning movement between said probe and said sample while said lever mounted probe is immersed in said fluid body. Process according to claim 15, comprising : placing two or more electrodes (164) in contact with said fluid body ; and applying a voltage across said electrodes during said scanning step to produce an electrochemical reaction in said fluid. Process according to claim 15, wherein said step of providing a fluid body comprises : providing a fluid body including water. Process according to claims 15, 16 or 17) comprising : disposing a rigid cover plate (52) on a top surface of said fluid body to define a fluid cell between said cover plate and said sample. Process according to claim 18, comprising : said disposing step comprising disposing an optically transparent rigid cover plate on the top surface of said fluid body ; and sensing a vertical movement of said probe by means of light applied to said probe through said optically transparent rigid cover plate.

Inventors: DRAKE BARNEY, HANSMA PAUL K, DRAKE, BARNEY, HANSMA, PAUL K.
Applicants: UNIV CALIFORNIA, THE REGENTS OF THE UNIVERSITY OF CALIFORNIA
Application year: 1990
Main classification: G01B7
IPC codes: H01J37, G01B21, G01B7, G01L5, G01N37, G01B11, B01L7, G01Q60