Holder for a cantilever for atomic force microscopy and atomic force microscope

Abstract

The invention relates to a holder unit for a cantilever (202) for an atomic force microscope comprising a holder (200) having a connecting portion (210) configured to be connected to an atomic force microscope, particularly to a head (100) of an atomic force microscope, and a retaining portion (220) configured to retain a cantilever (202) in a desired orientation. Further, the invention relates to an atomic force microscope configured to receive the connecting portion (220) of the holder (200), a method of manufacture of the holder (200) and a method for automatic connection of the holder (200) to the atomic force microscope.

Description

[0001] Holder for a cantilever for atomic force microscopy and atomic force microscope

[0002] Description

[0003] The invention relates to a holder unit for holding a cantilever for atomic force microscopy (particularly force spectroscopy), particularly a holder unit for retaining a chip, to which the cantilever is attached. Furthermore, the invention relates to an atomic force microscope.

[0004] Besides other applications, atomic force microscopy has been used to determine mechanical parameters of samples, such as their stiffness. For example, AFM can be used to determine the stiffness of biological tissue samples to distinguish between healthy tissue and cancer (WO 2012 / 076729). Due to their small size (typically in the pm region), cantilevers for atomic force microscopes are typically attached to larger structures, such as silicon chips, which are mounted to a holder of the atomic force microscope. Cantilevers have a limited lifetime and must be changed during longer series of experiments. However, using systems according to the prior art, mounting a new cantilever (e.g. attaching a new cantilever chip to a holder) is tedious and time-consuming and must be performed manually by trained users.

[0005] Therefore, the objective of the present invention is to provide a holder unit, and an atomic force microscope (hereafter also designated “AFM”) allowing an easy change of the cantilever, which is particularly performed automatically.

[0006] A first aspect of the invention relates to a holder unit for holding a cantilever for an atomic force microscope, wherein the holder unit comprises a holder comprising a connecting portion configured to be connected to the atomic force microscope, particularly to a head of the atomic force microscope, wherein the holder further comprises a retaining portion configured to retain the cantilever, particularly in a desired orientation.

[0007] A cantilever within the meaning of the present specification is a flexible elongated body which comprises a tip for contacting a sample, in particular to obtain a stiffness measurement of the sample by determining a force curve (force acting on the cantilever vs. position of the cantilever).

[0008] In certain embodiments of the present invention, the holder unit further comprises the cantilever, wherein the cantilever is retained by the retaining portion of the holder.

[0009] In certain embodiments, the retaining portion is configured to retain a chip, wherein the cantilever is attached to the chip. In particular, the holder unit comprises the chip, wherein the chip is retained by the retaining portion. Furthermore, in particular, the holder unit can comprise the cantilever wherein the cantilever is attached to the chip.

[0010] In certain embodiments, the chip is permanently fixed, e.g. glued, to the holder. If the chip is glued to the holder by means of adhesive, the retaining portion of the holder can comprise a notch arranged at a connection area between the chip and the holder, such that the adhesive can be absorbed by the notch. This measure avoids an uncontrolled flow of adhesive, particularly into areas of a beam path of a light beam for detecting a deflection of the cantilever as disclosed herein.

[0011] In certain embodiments, the cantilever is permanently fixed, e.g. glued, to the chip.

[0012] Alternatively, the retaining portion can comprise a recess such as a blind hole or a through- hole, wherein the chip is retained in the recess of the retaining portion, particularly by means of a snap-in connection or plug-in connection. This measure allows for repeated attachment and detachment of one and the same chip on the retaining portion.

[0013] In the context of the present specification, the term “chip” designates a substantially planar, flat body. The chip may be formed, e.g., from silicon or similar materials. A chip may comprise one cantilever or a plurality of cantilevers, e.g., four cantilevers arranged at opposite sides of the chip. The cantilever or cantilevers may be glued to the chip.

[0014] To change the cantilever, the chip is typically not removed from the holder according to the invention, but the holder is removed from the atomic force microscope along with the chip and is replaced by a new holder, to which a new chip with a new cantilever has particularly been pre-attached.

[0015] In certain embodiments, the connecting portion is configured to be at least partially inserted into a slot of the atomic force microscope, particularly a slot of a head of the atomic force microscope. This improves positioning of the holder on the AFM.

[0016] In certain embodiments, the connecting portion comprises a connecting surface configured to be engaged by a clamping element of the atomic force microscope to clamp the holder to the atomic force microscope. Clamping provides a means of reversibly attaching the holder to the AFM, particularly automatically.

[0017] In certain embodiments, the holder comprises or consists of an optically clear material. In this manner, a light beam used to determine the deflection of the cantilever can travel through the holder without being absorbed or reflected.

[0018] In the context of the present specification, the term “optically clear” describes a material which is transparent to visible light.

[0019] In certain embodiments, the optically clear material comprises a refractive index above 1 ,333. For example, the holder may be formed from an optically clear plastic material, or an optically clear polymer, or an optically clear non-glass material.

[0020] In certain embodiments, the holder is manufactured from a single piece of material. In certain embodiments, the retaining portion extends along a longitudinal axis from a first end which is adjacent to the connecting portion to a second end configured to retain the cantilever.

[0021] In certain embodiments, an area of the retaining portion perpendicular to the longitudinal axis is larger at the first end than at the second end. This particularly avoids unwanted collisions between the holder and the sample.

[0022] In certain embodiments, the first end of the retaining portion comprises a smaller area perpendicular to the longitudinal axis than the connecting portion.

[0023] In certain embodiments, the retaining portion is frustum-shaped. In certain embodiments, the retaining portion is shaped as a frustum of a rectangular pyramid. Therein, in particular, a base of the frustum forms a connecting portion or is connected to a connecting portion and a tip of the frustum forms the retaining portion or, in particular, a retaining surface of the retaining portion.

[0024] In particular, the area of the retaining portion perpendicular to the longitudinal axis decreases from the first end, where said (cross-sectional) area is smaller or equal to 228 mm2, to the second end, where said area (e.g. the area of the retaining surface) is smaller or equal to 63 mm2. Furthermore, in a preferred embodiment, the retaining portion comprises a length along the longitudinal axis from the first end to the second end that is larger or equal to 15 mm.

[0025] In certain embodiments, the retaining portion comprises a retaining surface configured to retain the cantilever, particularly configured to retain the chip to which the cantilever is attached.

[0026] In certain embodiments, the retaining surface comprises a first section, particularly having a planar surface, and a second section, particularly having a planar surface, separated by an edge, wherein the first section extends at an angle 0°<a<90°, particularly 5°<a<85°, more particularly 10°<a<80°, even more particularly 20°<a<70°, most particularly 30°<a<60°, with respect to the second section. This angle allows the cantilever to be oriented centrally on the retaining surface while being able to freely contact the sample without obstruction by the holder.

[0027] In certain embodiments, the holder, particularly the retaining portion, is hollow. In certain embodiments, the holder forms a cavity and an opening leading into the cavity. In particular, the retaining portion forms the cavity and / or the connecting portion comprises the opening. This is advantageous particularly during manufacturing of the holder, because injection molding of such a holder is faster compared to a solid retaining portion. Furthermore, the hollow retaining portion reduces the weight of the holder.

[0028] In certain embodiments, the cavity is frustum shaped, particularly shaped as a frustum of a rectangular pyramid. Therein, in particular, the holder is also frustum shaped, more particularly shaped as a frustum of a rectangular pyramid Thereby, the inner contours of the cavity particularly resemble the outer contours of the holder, which allows to achieve sufficient mechanical stability of the holder while using a minimum of material.

[0029] In certain embodiments, the cavity formed by the holder is configured to receive a transparent body of the atomic force microscope when the holder is connected to the atomic force microscope. The transparent body is formed from an optically clear material. In certain embodiments the transparent body is formed from a glass material. In certain embodiments, the material of the transparent body comprises a refractive index which is greater than the refractive index of air. In certain embodiments, the material of the transparent body comprises a refractive index which is greater than the refractive index of the material of the holder. In certain embodiments, the transparent body comprises a refractive index of 1 ,6 to 2,2, more particularly about 1 ,9.

[0030] In particular, in case a transparent body is provided, the light beam used to determine the deflection of the cantilever, particularly a free end of the cantilever travels through the transparent body and the transparent holder onto the cantilever and the light beam reflected from the cantilever travels back through the transparent holder and the transparent body onto a mirror which guides the reflected light beam onto a photodetector, e.g., a photodiode, to determine the deflection of the cantilever. The free end of the cantilever can be formed resulting from a mechanical fastening of the cantilever on the holder unit, wherein the free end of the cantilever is an end section of the cantilever distant from its mechanical fastening to the holder unit, particularly to the retaining portion of the holder unit. The transparent body improves the stability of the transparent body-holder assembly, such that the holder can be made longer in the z-direction (when attached to the atomic force microscope), while saving material of the holder, the holder particularly being a single-use consumable which is replaced after a series of measurements. In addition, in case the material transparent body comprises a higher refractive index than air, this allows the optics of the AFM system to be built more compactly, since the measuring light beam from the light source towards the cantilever and the reflected light beam from the cantilever to the mirror and photodiode travels through the transparent body instead of an air-filled cavity of the holder.

[0031] In certain embodiments, the cavity comprises a shape matching the shape of the transparent body. In other words, the transparent body forms a positive, and the cavity of the holder forms a corresponding negative. Thereby, the volume of air between the holder and the transparent body is minimized, and the holder and the transparent body jointly form a continuous body, which improves the accuracy of the measuring light beam and the reflected light beam used for detection of cantilever deflection.

[0032] In certain embodiments, the shape of the cavity (and particularly also the transparent body) is rotationally asymmetric in respect of a rotation around the longitudinal axis (extending the z- direction when the holder is connected to the AFM head). E.g., the cavity and the transparent body have a cross-sectional shape perpendicular to the longitudinal axis, which is not circular. This results in an alignment of the holder into a desired orientation when the holder is placed on the transparent body, e.g., during automatic loading of a new holder with attached cantilever chip onto the AFM head.

[0033] In certain embodiments, the cavity (and particularly also the transparent body) tapers along the longitudinal axis in a direction from the first end of the holder towards the second end of the holder. This further improves alignment and positioning of the holder when the holder is placed on the transparent body.

[0034] In certain embodiments, the cavity (and particularly also the transparent body) is frustum shaped, particularly shaped as a frustum of a rectangular pyramid.

[0035] In certain embodiments, the holder, particularly, the connecting portion, comprises a groove, wherein the groove is configured to receive an aligning element of the atomic force microscope upon connection of the holder, particularly the connecting portion to the atomic force microscope, particularly the head (particularly upon insertion of the connecting portion into the slot), in particular such that the holder is aligned into a desired position, more particularly centered, on the atomic force microscope, particularly the head.

[0036] In certain embodiments, the holder, particularly the connecting portion, comprises a plurality of grooves, wherein each groove is configured to receive a respective aligning element of the atomic force microscope, particularly the head upon connection of the holder, particularly the connecting portion to the atomic force microscope, particularly the head (particularly upon insertion of the connecting portion into the slot), in particular such that the holder is aligned into a desired position, more particularly centered, on the atomic force microscope, particularly the head.

[0037] In particular, the at least one groove comprises a cross-section (wherein the cross section can be one of: tapering, circular (e.g. hemispherical), triangular), such that the holder unit can be centered on the atomic force microscope, particularly on the head by receiving an aligning element, wherein the aligning element can be a pin and / or can comprise a portion of a sphere, particularly a hemisphere.

[0038] In certain embodiments, the holder, particularly the connecting portion, comprises a protrusion, wherein the protrusion is configured to engage, particularly insert into, a notch of the atomic force microscope, particularly the head, upon connection of the holder, particularly the connecting portion to the atomic force microscope, particularly the head (particularly upon insertion of the connecting portion into the slot), in particular such that the holder is aligned into a desired position, more particularly centered on the atomic force microscope. In certain embodiments, the holder, particularly the connecting portion comprises a plurality of protrusions, wherein each protrusion is configured to engage, particularly insert into, a respective notch of the atomic force microscope, particularly the head, upon connection of the holder, particularly the connecting portion to the atomic force microscope, particularly the head (particularly upon insertion of the connecting portion into the slot), in particular such that the holder is aligned into a desired position, more particularly centered on the atomic force microscope.

[0039] As already introduced above, the holder unit can comprise the holder and a cantilever for an atomic force microscope, wherein the cantilever is retained by the retaining portion of the holder.

[0040] In certain embodiments, the holder unit comprises a chip, to which the cantilever is attached, wherein the chip is retained by the retaining portion of the holder. In particular, the chip is permanently attached, e.g., glued, to the retaining portion. This advantageously allows to exchange the cantilever quickly and easily (and particularly automatically) by exchanging the entire holder with the pre-attached cantilever chip.

[0041] A further second aspect of the invention relates to an atomic force microscope, particularly adapted for force spectroscopy measurement, configured to receive the connecting portion of the holder according to the first aspect of the invention to connect the holder to the atomic force microscope, particularly to a head of the atomic force microscope.

[0042] In certain embodiments, the atomic force microscope comprises a slot configured to at least partially receive the connecting portion of the holder to connect the holder to the atomic force microscope, particularly to a head of the atomic force microscope.

[0043] In certain embodiments, the atomic force microscope comprises a head, in other words a part which is movable in respect of a sample, in particular such that the cantilever is approached on the sample. E.g., in a stiffness measurement of the sample, the head with the holder and the attached cantilever is moved towards the sample, such that the cantilever, particularly the free end of the cantilever indents the sample and the head is subsequently moved away from the sample, wherein the deflection of the cantilever is measured to obtain the force acting on the cantilever, from which the stiffness of the sample can be determined.

[0044] In certain embodiments, the atomic force microscope comprises an actuator configured to move the head along the longitudinal axis.

[0045] In certain embodiments, the atomic force microscope comprises a light source for generating light and focusing optics configured to focus the light and direct a first light beam along a longitudinal axis onto the cantilever. In certain embodiments, the atomic force microscope comprises a mirror configured to receive a second light beam reflected by the cantilever and reflect the second light beam, thereby forming a third light beam.

[0046] In certain embodiments, the atomic force microscope comprises a detector configured to detect a position of the third light beam reflected by the mirror configured to generate a deflection signal indicating a deflection of the cantilever along the longitudinal axis based on the detected position of the third light beam.

[0047] When a spring constant of the cantilever is known, a force can be determined from the deflection signal and the spring constant. Thereby, a force curve (position of the cantilever vs. force) of a sample can be generated, and the stiffness of the sample can be determined from the force curve.

[0048] In certain embodiments, the atomic force microscope, particularly the head, comprises a through-hole arranged in the slot, particularly wherein the through-hole is configured such that the first light beam (from the light source) is able to pass through the through-hole onto the holder and / or such that the second light beam (reflected by the cantilever) is able to pass through the through-hole onto the detector (directly or via the mirror).

[0049] In certain embodiments, the atomic force microscope, particularly the head, comprises at least one clamping element configured to clamp the holder to the atomic force microscope, particularly in a clamping position, wherein (particularly in the clamping position), the clamping element is configured to engage the connecting portion, particularly the connecting surface of the connecting portion, of the holder when the holder is received in the slot.

[0050] In certain embodiments, the atomic force microscope comprises at least one spring configured to bias the clamping element into the clamping position.

[0051] In certain embodiments, the atomic force microscope comprises at least one pivoting member, particularly a bolt or an axle, wherein the pivoting member is pivotably received in a bearing comprised by the atomic force microscope, wherein the pivoting member is connected to the clamping element, such that the clamping element is configured to be moved between the clamping position and an open position by pivoting the pivoting member in the bearing. In the open position, the holder is insertable into and / or removable from the slot of the atomic force microscope.

[0052] In certain embodiments, the atomic force microscope comprises a lever, wherein the pivoting member is connected to the lever.

[0053] In certain embodiments, the atomic force microscope further comprises a bar which is movable between a first position and a second position, wherein the bar is configured to engage the lever in the second position, thereby pivoting the pivoting member to bias the clamping element from the clamping position to the open position,

[0054] In certain embodiments, the atomic force microscopy comprises plurality of levers, wherein a respective pivoting member is connected to each lever.

[0055] In certain embodiments, the atomic force microscope comprises a linear motor configured to move the bar between the first position and the second position.

[0056] In certain embodiments, the bar comprises a pin configured to engage a hole of a connecting lever, wherein the connecting lever is connected to a mirror axis, wherein the atomic force microscope comprises a mirror configured to reflect a light beam reflected by the cantilever onto a detector of the atomic force microscope, wherein the mirror is connected to the mirror axis, such that the mirror can be tilted by pivoting the mirror axis. In this manner, the mirror may be tilted by the same linear actuator used to actuate the clamping mechanism.

[0057] In certain embodiments, the atomic force microscope, particularly the head, comprises a transparent body configured to insert into a cavity formed by the holder when the holder is connected to the atomic force microscope, particularly the head. The transparent body is formed from an optically clear material. In certain embodiments the transparent body is formed from a glass material. In certain embodiments, the material of the transparent body comprises a refractive index which is greater than the refractive index of air. In certain embodiments, the material of the transparent body comprises a refractive index which is greater than the refractive index of the material of the holder. In certain embodiments, the transparent body comprises a refractive index of 1 ,6 to 2,2, more particularly about 1 ,9.

[0058] In certain embodiments, the transparent body comprises a first end connected to the atomic force microscope, particularly the head, and a second end protruding from the atomic force microscope, particularly the head, along the longitudinal axis (particularly in a vertical, z- direction).

[0059] The transparent body improves the stability of the transparent body-holder assembly, such that the holder can be made longer in the z-direction (when attached to the atomic force microscope), while saving material of the holder, the holder particularly being a single-use consumable which is replaced after a series of measurements. In addition, in case the material transparent body comprises a higher refractive index than air, this allows the optics of the AFM system to be built more compactly, since the measuring light beam from the light source towards the cantilever and the reflected light beam from the cantilever to the mirror and photodiode travels through the transparent body instead of an air-filled cavity of the holder.

[0060] In certain embodiments, the transparent body comprises a shape matching the shape of the cavity of the holder. In other words, the transparent body forms a positive, and the cavity of the holder forms a corresponding negative. Thereby, the volume of air between the holder and the transparent body is minimized, and the holder and the transparent body jointly form a continuous body, which improves the accuracy of the measuring light beam and the reflected light beam used for detection of cantilever deflection.

[0061] In certain embodiments, the shape of the transparent body (and particularly also the cavity of the holder) is rotationally asymmetric in respect of a rotation around the longitudinal axis (extending the z-direction when the holder is connected to the AFM head). E.g., the transparent body (and particularly also the cavity) have a cross-sectional shape perpendicular to the longitudinal axis, which is not circular. This results in an alignment of the holder into a desired orientation when the holder is placed on the transparent body, e.g. during automatic loading of a new holder with attached cantilever chip onto the AFM head.

[0062] In certain embodiments, the transparent body tapers along the longitudinal axis in a direction from the first end of the transparent body towards the second end of the transparent body. This further improves alignment and positioning of the holder when the holder is placed on the transparent body.

[0063] In certain embodiments, the transparent body is arranged in the slot of the atomic force microscope, particularly the head.

[0064] In certain embodiments, the cavity (and particularly also the transparent body) is frustum shaped, particularly shaped as a frustum of a rectangular pyramid.

[0065] In certain embodiments, the atomic force microscope, particularly the head, comprises an aligning element configured to engage a groove of the holder, particularly of the connecting portion, upon connection of the holder, particularly the connecting portion, to the atomic force microscope, particularly the head (particularly upon insertion of the connecting portion into the slot of the atomic force microscope), in particular such that the holder is aligned into a desired position, more particularly centered, on the atomic force microscope, particularly the head.

[0066] In certain embodiments, the atomic force microscope, particularly the head, comprises a plurality of aligning elements, wherein each aligning element is configured to engage a respective groove of the holder, particularly of the connecting portion, upon connection of the holder, particularly the connecting portion, to the atomic force microscope (particularly upon insertion of the connecting portion into the slot), in particular such that the holder is centered on the atomic force microscope.

[0067] In certain embodiments, the aligning element is a half sphere.

[0068] In certain embodiments, the aligning element is arranged in the slot.

[0069] In certain embodiments, the atomic force microscope, particularly the head, comprises a notch configured to receive a protrusion of the holder, particularly of the connecting portion, upon connection of the holder, particularly the connecting portion, to the atomic force microscope, particularly the head (particularly upon insertion of the connecting portion into the slot), in particular such that the holder is aligned into a desired position, more particularly centered, on the atomic force microscope.

[0070] In certain embodiments, the atomic force microscope, particularly the head, comprises a plurality of notches, wherein each notch is configured to receive a respective protrusion of the connecting portion of the holder upon connection of the connecting portion to the atomic force microscope (particularly upon insertion of the connecting portion into the slot of the atomic force microscope), in particular such that the holder is centered on the atomic force microscope.

[0071] In certain embodiments, the notch or the plurality of notches is / are arranged in the slot.

[0072] In certain embodiments, the atomic force microscope comprises the holder unit according to the first aspect of the invention.

[0073] A third aspect of the invention relates to a method of manufacture of the holder unit according to the first aspect of the invention, wherein the holder is formed by injection molding. Therein, in particular, the retaining portion is hollow, wherein more particularly the connecting portion comprises an opening into a cavity formed by the (hollow) retaining portion.

[0074] A fourth aspect of the invention relates to a method for automatic connection of the holder according to the first aspect of the invention to the atomic force microscope according to the second aspect of the invention, wherein the holder is provided in a receiving position, and wherein the atomic force microscope, particularly the head, is automatically moved, particularly lowered, towards the receiving position, and wherein the holder is automatically connected to the atomic force microscope, particularly to the head of the atomic force microscope.

[0075] In certain embodiments, the at least one clamping element is brought in the open position in the receiving position or prior to reaching the receiving position.

[0076] In certain embodiments, the holder is automatically connected to the atomic force microscope by automatically moving the at least one clamping element into the clamping position.

[0077] Wherever alternatives for single separable features are laid out herein as “embodiments”, it is to be understood that such alternatives may be combined freely to form discrete embodiments of the invention disclosed herein.

[0078] In the following, embodiments as well as further features and advantages of the present invention are described with reference to the Figures, wherein

[0079] Fig. 1A,B show a holder unit according to an embodiment of the invention; Fig. 2 shows a front view of a part of a head of an atomic force microscope to which the holder according to the invention is connected;

[0080] Fig. 3 shows a side view of the part of the head and the holder depicted in Fig. 2;

[0081] Fig. 4 shows a bottom view of the head of the atomic force microscope with a slot for inserting the holder;

[0082] Fig. 5 shows a bottom view of the head of the atomic force microscope with the holder inserted in the slot;

[0083] Fig. 6 shows a cut-away view of the head of the atomic force microscope;

[0084] Fig. 7 shows a transparent body as part of an atomic force microscope according to an embodiment of the invention;

[0085] Fig. 8 shows an anchoring plate for anchoring a transparent body to a head of an atomic force microscope according to an embodiment of the invention;

[0086] Fig. 9 shows a side view of the head of the atomic force microscope with a holder connected to the head; and

[0087] Figs. 10A,B show an optical path of light emitted from a light source and reflected from the cantilever and a mirror towards a detector (Fig. 10a), wherein a transparent body is arranged in the holder unit shown in Fig. 10b.

[0088] Fig. 1 A and Fig. 1 B are different views of an embodiment of a holder unit comprising a holder 200 according to the invention, showing the holder 200 from different perspectives.

[0089] The holder 200 comprises a connecting portion 210 and a retaining portion 220. The retaining portion 220 comprises a retaining surface 223, to which a chip 201 , e.g., a silicon chip, comprising at least one cantilever 202 is preferably permanently attached, for instance by gluing. The connecting portion 210 is configured to be inserted into a slot 106 of a head 100 of an atomic force microscope (see Fig. 4 and Fig. 5) to clamp the holder 200 to the head 100.

[0090] The connecting portion 210 is ring-shaped and comprises a cylindrical geometry with a circular cross-section perpendicular to the longitudinal axis L, which forms the central cylinder axis. In particular, when the holder 200 is connected to a head 100 of an atomic force microscope, the entire retaining portion 210 is inserted into a slot 106 of the head 100 (see Fig. 5).

[0091] The connecting portion 210 further forms two connecting surfaces 211 which are configured to be engaged by clamping elements 122 of the head 100 of the atomic force microscope to clamp the holder 200 to the head 100 (see Fig. 5). As best seen in Fig. 1 B, the connecting portion 210 comprises three grooves 213 formed on a bottom surface of the connecting portion 210, which are equally spaced around the circumference of the connecting portion 210, that is at angles of 120° around the circumference. The grooves 213 have a round shape (or other shapes as described herein) and are configured to receive corresponding aligning elements 108, e.g., ceramic hemispheres, of the head 100, which are arranged in the slot 106 of the head 100 (see Fig. 4), thereby aligning, particularly centering, the holder 200 in the slot 106. Furthermore, it is also envisioned within the scope of this disclosure that the connecting portion 210 of the holder 200 comprises a plurality of protrusions instead of the grooves 213, which insert into corresponding notches adjacent the slot 106 of the AFM head 100 (not shown) to align, particularly center, the holder 200 on the AFM head 100.

[0092] The retaining portion 220 of the holder 200 extends from a first end 221 to a second end 222. The retaining portion 220 tapers from the first end 221 towards the second end 222 which facilitates insertion, particularly automatic insertion, of the holder 200 into the slot 106 of the AFM head 100.

[0093] As can be best observed from Fig. 1 A, the retaining surface 223 at the second end 222 of the retaining portion 220 comprises a first section 224 and a second section 225 separated by an edge 226. Thereby, the first section 224 and the second section 225 are arranged at an angle relative to each other, wherein the angle is larger than 0° and smaller than 90°. The chip 201 comprising the cantilever 202 is attached to the first section 224 of the retaining surface 223. Due to the angle between the first section 224 and the second section 225, a cantilever 202 comprising a tip 203 attached at an end of the chip 201 oriented towards the edge 226 is not obstructed by the retaining portion 220 and is free to contact a sample. Particularly, the chip 201 can be bonded to the retaining surface 223 (particularly to the first section 224) by means of an adhesive. Alternatively, the chip 201 can also be mechanically connected to the retaining portion 220 by engaging in a recess that can be formed e.g. in the first section 224. For this the first section 224 may protrude past the second section 225.

[0094] As best seen in Fig. 1 B, the retaining portion 220 of the holder 200 is hollow and forms a cavity 227 which is accessible through an opening 212 of the connecting portion 210, which simplifies the manufacturing of the holder 200, for example by injection molding. Furthermore, the cavity 227 is adapted to accommodate a transparent body 130 of the AFM head 100 according to an embodiment as described in Fig. 7.

[0095] Fig 2 shows a front view and Fig. 3 shows a side view of the holder 200 arranged in said slot 106 of the head 100.

[0096] Fig. 4 shows a bottom view of the head 100 of the atomic force microscope according to an embodiment of the invention comprising a circular slot 106 for insertion of the connecting part 210 of the holder 200 and a circular through-hole 107 arranged centrally in the slot 106. Three aligning elements 108 formed by ceramic hemispheres are arranged in the slot 106 around the circumference of the through-hole 107 to align and particularly center the holder 200 when the holder 200 is inserted in the slot 106. The edge around the slot 106 may additionally be tapered to allow easy insertion of the holder 200.

[0097] The through-hole 107 is configured to allow passage of a light beam from a light source of the atomic force microscope through the optically clear holder 200 onto the cantilever 202 on the chip 201 retained by the holder 200 and allow passage of the reflected light beam from the cantilever 202 onto a mirror disposed in the head 100, which reflects the light beam towards a detector (e.g., a photodiode), such that the deflection of the cantilever 202 can be determined by the detector.

[0098] Fig. 5 shows the holder 200 according to the invention inserted into the slot 106 of the head 100 of the atomic force microscope. The holder 200 is held in a clamping position by two clamping elements 122 arranged on opposite sides of the slot 106 which engage the connecting surfaces 211 of the holder 200 to fix the holder 200 in the slot 106. Furthermore, the clamping elements 122 are connected to pivoting members 123 (e.g. rods) which are pivotably mounted in bearings 124. One end of each pivoting member 123 is further connected to a lever 125. The levers 125 each comprise a stump 125a configured to attach a spring, such as a leaf spring, to bias the clamping elements 122 into the clamping position shown in Fig. 5. The levers 125 extend from the outside of the head 100 shown in Fig. 5 to the inside of the head 100 shown in Fig. 6, such that the levers 125 can be operated by a bar 119 arranged inside the head 100.

[0099] The levers 125 are shown from the inside of the head 100 in Fig. 6. As illustrated in Fig. 6, the head 100 further comprises said bar 119 which is configured to be moved along a longitudinal axis L, e.g. by a linear motor. When the bar 119 is moved down from the position displayed in Fig. 6, the bar 119 engages the levers 125 and pushes the levers 125 against the force of the springs into a downward position (the left lever 125 is displayed in the downward position in Fig. 6). In turn, the pivoting member 123 is pivoted and thereby forces the clamping elements 122 in an open position (not shown), where the holder 200 can be inserted into the slot 106 or removed from the slot 106, particularly automatically.

[0100] According to further embodiment of the atomic force microscope, the head 100 may comprise a mirror pivotably coupled to a mirror axis 114a (see Fig. 6), wherein a connecting lever 121 is connected to the mirror axis 114a. The connecting lever 121 further comprises a hole 121a, e.g. an oblong hole, into which a pin 120 connected to or integrally formed with the bar 119 is inserted. When the bar 119 is moved linearly along the longitudinal axis L, the pin 120 moves inside the hole 121a and thereby pivots the connecting lever 121 around the mirror axis 114a leading to a pivoting motion of the mirror about the mirror axis 114a. In this manner, pivoting of the mirror and opening of the clamping elements 122 to insert or remove the holder 200 can be realized by a single linear motor of the head 100, which reduces the size, weight and complexity of the head 100.

[0101] Fig. 7 shows a view of a transparent body 130 made from an optically clear material configured to be inserted into the cavity 227 formed by the holder 200 when the holder 200 is connected to the AFM head 100, e.g. by clamping as described above.

[0102] The transparent body 130 extends along the longitudinal axis L (which particularly runs in the vertical direction during use of the AFM when the transparent body 130 is installed on the AFM head 100) from a first end 131 to a second end 132. A base portion 134 of the transparent body 130 having a cuboid shape is formed at the first end 131 , wherein the base portion 134 comprises two tabs 133 formed at opposing lateral ends of the base portion 134. A protruding portion 135 having the shape of a frustum of a rectangular pyramid extends from the base portion 134 along the longitudinal axis L towards the second end 132. The protruding portion 135 is adapted to be inserted into the cavity 227 formed by the holder 200 when the holder 200 is connected to the AFM head (see Fig. 9). This improves the structural integrity of the holder 200 head 100 assembly and the optically clear transparent body 130 is transparent to light travelling between the cantilever 202 and measuring optics inside the AFM head which are used to measure cantilever 202 deflection, particularly during force spectroscopy measurements.

[0103] Fig. 8 shows a perspective view of an anchoring plate 140 configured to mount the transparent body 130 shown in Fig. 7 to the head 100. The anchoring plate 140 has the shape of a circular disc with a central rectangular cutout 141 and three circular holes 142 spaced at equal distances around the circumference of the anchoring plate 140. The holes 142 are configured to receive screws or bolts to fix the anchoring plate 140 on the AFM head 100. The cutout 141 is configured such that the protruding portion 135 of the transparent body 130 fits through the cutout 141. The tabs 133 of the transparent body 130 are particularly clamped between the anchoring plate 140 and another component of the head 100, e.g. a ring, for receiving the holder 200 on a bottom end of the AFM head 100 (see Fig. 9).

[0104] As depicted in Fig. 9, the holder 200 described above may be inserted in the slot 106 of the head 100, while the transparent body 140 inserts into the cavity 227 of the holder 200. The holder 200 may then be clamped in the slot 106 unit by clamping elements 122 which engage with the connecting surface 211 as described above. Optionally, similar to the embodiment shown in Fig. 4 and Fig. 5, the holder 200 may be aligned by protrusions 108 arranged in the slot 106 inserting in the grooves 213 of the connecting part 210 of the holder 200 or alternatively by protrusions on the connecting part 210 of the holder 200 inserting into notches in the slot 106 (not shown).

[0105] In particular, the cavity 227 of the holder 200 comprises the same shape as the protruding portion 135 of the transparent body, such that almost no air-filled space occurs between the holder 200 and the transparent body 130 which improves the optical properties of the system. The fit between the cavity 227 and the protruding portion 135 may also advantageously align the holder 200, particularly during automatic exchange of the holder 200 to obtain the correct positioning of the holder 200 and the cantilever 202 attached thereto.

[0106] Fig. 9 further shows a temperature sensor 150 (e.g. an infrared sensor) connected to a bottom end of the head 100 of the AFM. This sensor 150 is arranged in close distance to a sample during force spectroscopy measurement and can be advantageously used to obtain the temperature of the sample in real time during a measurement.

[0107] Fig. 10A schematically depicts an optical path of light emitted from a light source 105 and detected by a detector 113. The light is emitted from the light source 105 as a first light beam B1 towards the cantilever 202 held by the holder 200. From the cantilever 202, particularly from a top surface of the cantilever 202 facing the light source 105, the light is reflected as a second light beam B2 towards a mirror 112, which can be rotated by means of a mirror drive 114b. From the mirror 112, the light is finally reflected as a third light beam B3 towards the detector 113, which may be a 4-quadrant photodiode. The optical path can be changed by moving the light source 105 with respect to the cantilever 202 using a cross table with first, second and third light source linear drives along the x-y- and the z-direction, respectively. Additionally, the photodetector 113 can be moved along the x-direction, i.e., outside the drawing plane shown in Fig. 10A, by means of a detector linear drive. The deflection of the cantilever 202 is indicative of the distance between the tip 203 of the cantilever 202 and a sample 3 arranged on a sample stage 300.

[0108] Fig. 10A also schematically indicates a first linear drive 101 with a coarse linear motor 101a and a fine linear motor 101b for moving the cantilever 202 held by the holder 200 along a first longitudinal axis L1 as well as a second linear drive 102 with a coarse linear motor 102a and a fine linear motor 102b for moving the cantilever 202 held by the holder 200 along a second longitudinal axis L2. Additionally, the sample stage 300 can be moved by a third linear drive 103 comprising a coarse linear motor 103a and a fine linear motor 103b along a third longitudinal axis L3.

[0109] Fig. 10B shows an embodiment, wherein the holder 200 is configured to receive a transparent body 130. The transparent body 130 is formed from an optically clear material, such as a glass material. In particular, the material of the transparent body comprises a refractive index which is greater than the refractive index of air. In certain embodiments, the material of the transparent body comprises a refractive index which is greater than the refractive index of the material of the holder. For example, the transparent body comprises a refractive index of 1.6 to 2.2, more particularly about 1.9.

[0110] In case a transparent body 130 is provided, the light beam used to determine the deflection of the free end of the cantilever 202 travels through the transparent body 130 and onto the cantilever 202 and the light beam reflected from the cantilever 202 travels towards the mirror 112 through the transparent body 130. At the interfaces of the transparent body 130, the light is refracted. The transparent body 130 improves the stability of an assembly formed by the transparent body 130 and the holder 200, such that the holder 200 can be made longer in the z-direction, which simplifies the handling of the holder 200. In addition, in case the material of the transparent body comprises a higher refractive index than air, this allows the optics of the atomic force microscope 1 to be built more compactly, since the refraction of the light beam at the transparent body 130 allows to refract the light beam towards the mirror 112, whereas in the case without the transparent body 130 the light has to be guided from the cantilever 202 to the mirror entirely due to the reflection of the cantilever 202, which requires a rather bulky shape of the holder 200, as can be understood from comparing the holders 200 of Fig. 10A and 10B.

[0111] List of reference signs

Claims

Claims1. A holder unit for holding a cantilever (202) for an atomic force microscope, the holder unit comprising a holder (200) comprising a connecting portion (210) configured to be connected to an atomic force microscope, particularly to a head (100) of an atomic force microscope, and a retaining portion (220) configured to retain a cantilever (202) in a desired orientation, wherein particularly the holder unit comprises the cantilever (202) retained by the retaining portion (220).

2. The holder unit according to claim 1 , wherein the retaining portion (220) is configured to retain a chip (201) to which the cantilever (202) is attached or attachable, wherein particularly the holder unit comprises the chip (201), wherein the chip (201) is retained by the retaining portion (220).

3. The holder unit according to claim 1 or 2, wherein the connecting portion (210) is configured to be at least partially inserted into a slot (106) of the atomic force microscope, particularly into a slot (106) of the head (100) of the atomic force microscope, wherein particularly the connecting portion (210) comprises a connecting surface (211) configured to be engaged by a clamping element (122) of the atomic force microscope to clamp the holder (200) to the atomic force microscope.

4. The holder unit according to one of the preceding claims, wherein the holder (200) comprises or consists of an optically clear material.

5. The holder unit according to one of the preceding claims, wherein the retaining portion (220) extends along a longitudinal axis (L) from a first end (221), which is adjacent to the connecting portion (210), to a second end (222) configured to retain the cantilever (202), wherein an area of the retaining portion (220) perpendicular to the longitudinal axis (L) is larger at the first end (221) than at the second end (222), wherein particularly the first end (221) of the retaining portion (220) comprises a smaller area perpendicular to the longitudinal axis (L) than the connecting portion (210).

6. The holder unit according to claim 5, wherein the area of the retaining portion perpendicular to the longitudinal axis decreases from the first end, where said area is smaller or equal to 228 mm2, to the second end, where said area is smaller or equal to 63 mm2.

7. The holder unit according to one of the preceding claims, wherein the retaining portion (220) comprises a retaining surface (223) configured to retain the cantilever (202), particularly the chip (201) to which the cantilever (202) is attached, wherein particularly the retaining surface (223) comprises a first section (224) and a second section (225) separated by an edge (226), wherein particularly the first section (224) extends at anangle a with respect to the second section (225), wherein 0°<a<90°, particularly 5°<a<85°.

8. The holder unit according to one of the preceding claims, wherein the retaining portion (220) is hollow, wherein particularly the connecting portion (210) comprises an opening (212) into a cavity (227) formed by the retaining portion (220), wherein particularly the cavity (227) formed by the holder (200) is configured to receive a transparent body (130) of the atomic force microscope when the holder (200) is connected to the atomic force microscope, wherein particularly the cavity (227) comprises a shape matching the shape of the transparent body (130).

9. The holder unit according to one of the preceding claims, wherein a. the connecting portion (210) comprises at least one groove (213), particularly a plurality of grooves (213), wherein the at least one groove (213) is configured to receive an aligning element (108) of the atomic force microscope, particularly of the head (100), upon connection of the connecting portion (210) to the atomic force microscope, particularly to the head (100), in particular such that the holder (200) is centered on the atomic force microscope, particularly on the head (100), and / or b. the connecting portion (210) comprises at least one protrusion, particularly a plurality of protrusions, wherein the protrusion is configured to engage, particularly to be inserted into, a notch of the atomic force microscope, particularly of the head (100), upon connection of the connecting portion (210) to the atomic force microscope, particularly to the head (100), in particular such that the holder (200) is centered on the atomic force microscope, particularly on the head (100).

10. The holder unit according to one of the claims 4 to 9, wherein the optically clear material comprises or consists of one of the following materials: a plastic material, a polymer, a non-glass material.

11. The holder unit according to claim 9 or 10, wherein the at least one groove (213) comprises a cross-section, such that the holder unit can be centered on the atomic force microscope, particularly on the head (100) by receiving an aligning element (108) in the at least one groove (213), wherein particularly the cross-section is one of tapering, circular, triangular, and wherein particularly the aligning element (108) comprises a portion of a sphere, particularly a hemisphere.

12. The holder unit according to one of the claims 2 to 11 , wherein the chip (201) is retained by the retaining portion (220) by means of adhesive.

13. The holder unit according to one of the claims 2 to 11 , wherein the retaining portion (220) comprises a recess, particularly in form of a blind hole or a through-hole, and wherein the chip (201) is retained in the recess of the retaining portion (220), particularly by means of a snap-in connection or a plug-in connection.

14. An atomic force microscope comprising a holder unit according to one of the claims 1 to 13, wherein particularly the atomic force microscope comprises a slot (106) configured to receive the connecting portion (210).

15. The atomic force microscope according to claim 14, wherein the atomic force microscope comprises at least one clamping element (122) configured to clamp the holder (200) to the atomic force microscope in a clamping position, wherein in the clamping position, the clamping element (122) is configured to engage the connecting portion (210), particularly the connecting surface (211) of the connecting portion (210) of the holder (200), when the holder (200) is received in the slot (106), wherein particularly the atomic force microscope comprises at least one spring configured to bias the clamping element (122) into the clamping position.

16. The atomic force microscope according to claim 14 or 15, wherein the atomic force microscope comprises at least one pivoting member (123), particularly a bolt or an axle, wherein the pivoting member (123) is pivotably received in a bearing (124) comprised by the atomic force microscope, wherein the pivoting member (123) is connected to the clamping element (122), such that the clamping element (122) is configured to be moved between the clamping position and an open position, in which the holder (200) is insertable into and / or removable from the slot (106) of the atomic force microscope, by pivoting the pivoting member (123) in the bearing (124).

17. The atomic force microscope according to claim 16, wherein the atomic force microscope comprises at least one lever (125), wherein the pivoting member (123) is connected to the lever (125), wherein particularly the atomic force microscope further comprises a bar (119) which is movable between a first position and a second position, wherein the bar (119) is configured to engage the lever (125) in the second position, thereby pivoting the pivoting member (123) to bias the clamping element (122) from the clamping position to the open position, wherein particularly the atomic force microscope comprises a linear motor configured to move the bar (119) between the first position and the second position, wherein particularly the bar (119) comprises a pin (120) configured to engage a hole (121a) of a connecting lever (121), wherein the connecting lever (121) is connected to a mirror axis (114a), wherein the atomic force microscope comprises a mirror configured to reflect a light beam reflected by the cantilever (202) onto a detector of the atomic force microscope, wherein the mirror isconnected to the mirror axis (114a), such that the mirror can be tilted by pivoting the mirror axis (114a).

18. The atomic force microscope according to one of the claims 14 to 17, wherein a. the atomic force microscope comprises at least one aligning element (108), particularly a half sphere, particularly arranged in the slot (106), configured to engage a groove (213) of the connecting portion (210) of the holder (200) upon connection of the connecting portion (210) to the atomic force microscope, in particular such that the holder (200) is centered on the atomic force microscope, and / or b. the atomic force microscope comprises at least one groove, particularly arranged in the slot (106), configured to receive a protrusion of the connecting portion (210) of the holder (200) upon connection of the connecting portion (210) to the atomic force microscope, in particular such that the holder (200) is centered on the atomic force microscope.

19. The atomic force microscope according to one the claims 14 to 18, wherein said atomic force microscope, particularly said head (100), comprises a transparent body (130) formed from an optically clear material, wherein said transparent body (130) is configured to be inserted into a cavity (227) formed by the holder (200) when the holder (200) is connected to the atomic force microscope, particularly to the head (100), wherein particularly the transparent body (130) comprises a shape matching the shape of the cavity (227).

20. A method for automatic connection of the holder (200) according to one of the claims 1 to 13 to the atomic force microscope according to one of the claims 14 to 19, wherein the holder (200) is provided in a receiving position, and wherein the atomic force microscope, particularly the head (100), is automatically moved towards the receiving position, particularly in the open position of the at least one clamping element (122), and wherein the holder (200) is automatically connected to the atomic force microscope, particularly by automatically moving the at least one clamping element (122) into the clamping position.

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