RU2259607C1 - Device for electrostatic excitation of cantilever in scanning probing microscopy - Google Patents

Abstract

FIELD: microscopy.

SUBSTANCE: device has cantilever holder with cantilever, including base with flexible beam, source of excitation of oscillations of flexible beam relatively to standard, block for supporting position of flexible beam, second electrode. On flexible beam first and second electric-conductive areas are formed. Areas are separated by layer of dielectric and are actually a first electrode. First electrode is positioned with possible interaction with second electrode. Cantilever oscillations excitation source is made in form of first electrostatic drive. Electrostatic drive is connected to first electrode.

EFFECT: broader functional capabilities.

1 cl, 6 dwg

Description

The invention relates to the field of scanning probe microscopy, which studies the topography and surface properties of objects, such as magnetic, electrical, thermophysical, elastic, etc. It can be used to excite mechanical vibrations of the probe (cantilever) in scanning probe microscopes (SPM).

A known ultrasonic scanning probe microscope [1] with a device for excitation of cantilever oscillations, containing a cantilever holder with a cantilever, including a base with a flexible beam, at the end of which a tip is fixed, as well as a source of vibration excitation of the flexible beam relative to the sample, made in the form of an ultrasonic emitter (UI) conjugated to the sample. In this case, liquid layers are located between the MI and the sample.

The first disadvantage of this device is that it does not use the adjustment of the position of the tip of the cantilever probe normal to the surface of the sample.

The second disadvantage is the impossibility of oscillations of the flexible cantilever beam around its longitudinal axis.

The third disadvantage is associated with the limited frequency characteristics of the MD. All these shortcomings narrow the functionality of ultrasonic SPM.

In addition, in the known device, temperature drifts of the position of the sample relative to the tip of the probe are possible, associated with heating the ID and the placement of liquid layers to provide acoustic contact between the ID and the sample.

It should be noted that heating the MI and the location of the liquid layers can also constrict the functionality of the device. For example, when heated, the choice of the studied materials is limited, such as thermolabile biological samples, materials with a high coefficient of thermal expansion, etc.

The specified device is selected as a prototype of the proposed solution.

The technical result of the invention is to expand the functionality of the device.

The specified technical result is achieved by the fact that in the device for electrostatic excitation of cantilever oscillations in scanning probe microscopy, comprising a cantilever holder with a cantilever including a base with a flexible beam, and also a source of vibration excitation of the flexible beam relative to the sample, a block for maintaining the position of the flexible beam and a second electrode are introduced, on the flexible cantilever beam, the first and second electrically conductive regions with individual connection are formed, separated by a dielectric layer and constituting a first electrode arranged to interact with the second electrode, and the cantilever oscillation excitation source is made in the form of a first electrostatic drive connected to the first electrode, which is used as two electrically conductive regions, and to the second electrode.

There is an option in which the unit for maintaining the position of the flexible beam is made in the form of a second electrostatic drive, consisting of a constant voltage source, the first end connected to the first electrode, and the second end to the second electrode.

There is also an option in which the first electrostatic drive is made in the form of a source of alternating electric voltage, the first end connected to the first electrode, which use two electrically conductive areas, and the second end to the second electrode.

In addition, it is possible to use as a second electrode a sample made of an electrically conductive material, or an electrically conductive plate having a diffusely reflecting surface on the side opposite to the cantilever and mounted on the cantilever holder.

It is also possible to perform the first electrostatic drive in the form of a source of paraphase alternating voltage, the first end connected to the first electrically conductive region of the first electrode, the second end to the second electrically conductive region of the first electrode, and the third end to the second electrode.

It is also advisable to perform the first electrostatic drive in the form of a combination of an alternating voltage source and a paraphase alternating voltage source, while the alternating voltage source is connected to the first and second electrodes, and the paraphase alternating voltage source is connected by the first end to the first electrically conductive region of the first electrode , the second end with the second electrically conductive region of the first electrode, and the third end with the second th electrode.

Figure 1 shows a diagram of a device for electrostatic excitation of cantilever oscillations in scanning probe microscopy in general form.

Figure 2 shows the cantilever (bottom view).

Figure 3 shows a diagram of the connection of electric voltage sources to the cantilever and an electrically conductive sample.

Figure 4 shows a diagram of the connection of electric voltage sources to the cantilever and the electrically conductive plate.

Figure 5 shows a variant of connecting a paraphase alternating voltage source to two electrically conductive regions on a flexible cantilever beam.

Figure 6 shows an embodiment of the first electrostatic drive in the form of a combination of an alternating voltage source and a paraphase alternating voltage source.

The device for electrostatic excitation of cantilever oscillations in scanning probe microscopy contains a cantilever holder 1 (Fig. 1) with a cantilever 2, including a base 3 with a flexible beam 4, the tip 5 is fixed at its end. The holder 1 can be mounted, for example, on the SZM piezoscanner (not shown). In this case, the cantilever 2 is connected with the first electrode (see below) to the oscillation source 6 (the first electrostatic drive) of the flexible beam 4 relative to the second electrode 7 and the position support unit 8 of the flexible beam 4. The first 9 is formed on the flexible beam 4 of the cantilever 2 (Fig. 2) and the second 10 electrically conductive areas with individual connections to the electronic units 6 and 8, separated by a dielectric layer 11 and representing the first electrode located with the possibility of interaction with the second electrode 7. Block 8 can be performed ene as a second electrostatic actuator composed of DC voltage source connected to the first and second electrodes. The description of SPM, piezoscanners and cantilevers is described in detail in [2, 3].

The first electrostatic drive 6 may consist of a source 12 (Fig. 3) of alternating voltage connected to the first electrode, which is used as two electrically conductive regions 9 and 10 (Fig. 2), and to a second electrode, which can be used sample 13 (figure 3) made of an electrically conductive material.

The position maintenance block 8 (FIG. 1) of the flexible beam 4 can be made in the form of a second electrostatic drive, consisting of a constant voltage source 14 (FIG. 3), also connected to the first (regions 9 and 10) and the second (sample 13) electrodes.

There is an option in which an electrically conductive plate 15 (FIG. 4) is used as the second electrode, mounted on the cantilever holder 1 with the possibility of interaction with the cantilever 2. This option is used if the sample 16 is made of dielectric material. In this case, the plate 15 may have an adjustment movement of a relatively flexible beam 4, carried out by bending the plate 15 and moving in the gaps of the fastener when secured with screws (not shown). It is also possible to fix the plate 15 by means of glue, solder, etc.

On the holder of the cantilever 1 is fixed a spring grip 17 containing two isolated from one another current leads arranged with the possibility of electrical interaction with electrically conductive regions 9 and 10.

The plate 15 and the spring grip 17 can be made, for example, of beryllium bronze and mounted on the cantilever holder 1 through insulators (not shown), or the cantilever holder 1 must be made of insulating material. The size of the plate 15 should be such that there is optical access to the flexible beam 4 from the side of its free end. For example, with the length of the flexible beam 4 equal to 100 μm, the length of the plate 15 may be of the order of 50 μm. Moreover, its width may slightly exceed the width of the flexible beam 4, which will allow this object to be more visible in an optical microscope. The plate 15 from the side opposite the cantilever may have a diffusely reflecting surface, which will allow for preliminary signal tuning on it with a greater degree of accuracy.

There is an option where the first electrostatic drive is made in the form of a source of paraphase alternating voltage 18 (Fig. 5), connected by the first and second ends to the first 9 and second 10 conductive regions with individual leads, and the third end to the second electrode 7.

There is also an option in which the first electrostatic drive 6 (Fig. 1) is made in the form of a combination of an alternating voltage source 12 (Fig. 6) and a paraphase alternating voltage source 18, while the alternating voltage source 12 is connected to the first ( areas 9 and 10) and the second (7) electrodes, and the source of the paraphase alternating voltage 18, the first end is connected to the first conductive region 9 of the first electrode, the second end to the second conductive region 10 of the first electrode and the third end - to the second electrode 7. In Figures 5 and 6 as electrode 7 can be used as electrically conductive pattern 13 (Figure 3) and the electroconductive plate 15 (Figure 4).

The device operates as follows. The cantilever 2 is fixed using a spring grip 17 on the holder 1, ensuring their electrical connections. Using the unit for maintaining the 8 position of the flexible beam 4, set its desired initial position in the Z coordinate. Alternating voltage from the first electrostatic drive 6 (Fig. 1 and Fig. 2) is applied to the first electrode in the form of two electrically conductive regions 9 and 10 separated by a dielectric layer 11, and to the second electrode 7. In this case, due to the electrostatic interaction between them, mechanical vibrations of the flexible beam 4 of the cantilever 2 are excited, which makes it possible to analyze the surface in a non-contact mode. For more details, see the operation of the device in [2, 3].

When the device shown in FIG. 3 is functioning, the sample 13 must be made of an electrically conductive material. Using a source of constant electric voltage 14 and electrostatic interaction forces, the position of the flexible beam 4 relative to the sample 13 is pre-set at the coordinate Z. When applying alternating potentials between the sample 13 and the flexible beam 4 with the first electrode, electrostatic forces of attraction and repulsion arise. Accordingly, in this case, mechanical vibrations of the flexible beam 4 can be excited.

The specifics of the operation of the device depicted in figure 4, is that during operation, an adjustment movement of the plate 15 relative to the cantilever 2 is possible in order to optimize the force effects between them. In this case, using electrostatic interaction, similar to that described above, the flexible beams 4 are vibrated and pre-positioned relative to the sample 16.

In order not to damage the flexible beam 4 of the cantilever 2 during the adjustment of the plate 15, a cantilever simulator in the form of a spring made, for example, of beryllium bronze and repeating the geometric shape of the flexible cantilever beam can be used. The installation process of the cantilever 2 is as follows. Take the base 3 of the cantilever 2 with tweezers and set it in such a way that one part of the base 3 rests on the cantilever holder 1, and the other on the plate 15. After that, the base 3 is moved towards the spring grip 17 and put under it. After that, the base 3 is fixed on the holder 1, which allows its further movement to be carried out without fear of damaging the flexible plate 4.

The alignment process of the plate 15 can occur as follows. The cantilever holder 1 with a cantilever simulator and plate 15 is mounted in an optical microscope and the size between them is set from 10 to 100 μm by folding the plate 15. The cantilever holder 1 with plate 15 thus prepared is installed in the SPM and then the cantilever 2 with flexible beam 4 is inserted .

The use cases of the device described above make it possible to study the surface of a sample in a noncontact mode, see, for example, [4].

The operation of the device depicted in Fig. 5 consists in alternately supplying potentials from the source 18 to the electrically conductive regions 9 and 10, which, when electrostatically interacted with the electrode 7, causes the flexible beam 4 to swing around its axis (O-O) in the direction B. In this case, it is possible to study the friction force of the surface of the sample in the spot measurement zone, to manipulate the medium, etc.

In the device depicted in Fig.6, the two described measurement methods are combined.

The introduction of a block for maintaining the position of the flexible beam allows you to select the preliminary bending of the flexible beam, which increases the Z-range of scanning probe microscopy.

The formation on the flexible cantilever beam of the first and second electrically conductive regions individually connected, separated by a dielectric layer and representing the first electrode located with the possibility of interaction with the second electrode, allows the cantilevers to be monitored at the manufacturing stage to correct, for example, the areas of the electrically conductive regions. In addition, it becomes possible to eliminate the parasitic vibrations of the cantilever beam around the longitudinal axis arising as a result of errors in the performance of the conductive layers. This can be done by individually connecting the electrically conductive areas to additional electronic units (not shown).

The implementation of the oscillation source of the flexible cantilever beam in the form of a first electrostatic drive connected to the first and second electrodes, allows to reduce the thermal load on the structure, which increases the possible choice of the studied materials.

The above extends the functionality of the device while maintaining accuracy characteristics.

The use of a sample of electrically conductive material as the second electrode simplifies the design of the device.

The implementation of the second electrode in the form of an electrically conductive plate mounted on the cantilever holder allows you to adjust the distance between it and the flexible cantilever beam, which increases the ability to adjust the force effects on the cantilever and extends the functionality of the device. The implementation of the electrically conductive plate with a diffusely reflecting surface from the side opposite the cantilever allows you to observe the shape and size of the laser beam directed to the flexible beam of the cantilever when setting up the SPM. This makes it possible to simplify the SPM tuning procedure.

The implementation of the first electrostatic drive in the form of a source of paraphase alternating voltage, the first end connected to the first conductive region of the first electrode, the second end to the second conductive region of the first electrode, and the third end to the second electrode, allows vibrations of the flexible cantilever beam around the longitudinal axis, which also extends the functionality of the device.

The implementation of the first electrostatic drive in the form of a combination of an alternating voltage source and a paraphase alternating voltage source makes it possible to combine the described methods for studying the surface of samples.

LITERATURE

1. US patent No. 5675075, G 01 B 5/28, 1997

2. Probe microscopy for biology and medicine. V.A. Bykov et al. Sensory Systems, Volume 12, No. 1, 1998, pp. 99-121.

3. Scanning tunneling and atomic force microscopy in surface electrochemistry. A.I. Danilov. Advances in Chemistry, 64 (8), 1995, pp. 818-833.

4. A positive decision on the application No.20031289 of 05/13/02

Claims (7)

1. Device for electrostatic excitation of cantilever oscillations in scanning probe microscopy, comprising a cantilever holder with a cantilever including a base with a flexible beam, and also a source of vibration excitation of the flexible beam relative to the sample, characterized in that a block for maintaining the position of the flexible beam on the flexible beam is inserted into it cantilever, the first and second electrically conductive regions with individual connection are formed, separated by a dielectric layer and representing the first electrode, located ny to interact with the second electrode, and the source of excitation of the cantilever oscillation is formed as a first electrostatic actuator connected to the first and second electrodes. 2. The device for electrostatic excitation of cantilever oscillations in scanning probe microscopy according to claim 1, characterized in that the positioning unit of the flexible beam is made in the form of a second electrostatic drive consisting of a constant voltage source, the first end connected to the first electrode, and the second end to to the second electrode. 3. The device for electrostatic excitation of cantilever oscillations in scanning probe microscopy according to claim 1, characterized in that the first electrostatic drive is made in the form of a source of alternating electric voltage, the first end connected to the first electrode, which use two electrically conductive regions, and the second end to the second electrode. 4. The device for electrostatic excitation of cantilever oscillations in scanning probe microscopy according to claim 1 or 3, characterized in that a sample made of an electrically conductive material is used as the second electrode. 5. The device for electrostatic excitation of cantilever oscillations in scanning probe microscopy according to claim 1 or 3, characterized in that the second electrode is an electrically conductive plate having a diffusely reflecting surface on the side opposite to the cantilever and mounted on the cantilever holder. 6. The device for electrostatic excitation of cantilever oscillations in scanning probe microscopy according to claim 1, characterized in that the first electrostatic drive is made as a source of paraphase alternating voltage, the first end connected to the first electrically conductive region of the first electrode, the second end to the second electrically conductive region of the first electrode, and the third end with the second electrode. 7. The device for electrostatic excitation of cantilever oscillations in scanning probe microscopy according to claim 1, characterized in that the first electrostatic drive is made in the form of a combination of an alternating voltage source and a paraphase alternating voltage source, while the alternating voltage source is connected to the first and second electrodes and the source of the paraphase alternating voltage is connected by the first end to the first electrically conductive region of the first elec electrode, the second end to the second electrically conductive region of the first electrode, and the third end to the second electrode.

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