Scanning probe microscopy

Basic physical principles of scanning probe microscopy:

A common feature of all scanning probe microscopes (and defining their name) is the presence of a microscopic probe, which is brought into contact (not always mechanical contact) with the surface under study and, during scanning, moves over a certain area of ​​the surface of a given size.

The contact of the probe and the sample implies their interaction. Any one working interaction is selected. The nature of this chosen interaction determines whether the device belongs to one or another type within the family of probe microscopes. Surface information is retrieved by capturing (using a feedback system) or by detecting the interaction between the probe and the sample.

In a tunnel microscope, this interaction manifests itself in the flow of direct current in the tunnel contact. Atomic force microscopy is based on the interaction of a probe and a sample with forces of attraction or repulsion. We can mention such varieties of probe microscopes as a magnetic force microscope (the probe and the sample interact with magnetic forces), a near-field microscope (the optical properties of the sample are detected through a miniature aperture located in the near zone of the photon source), a polarizing force microscope (the sample interacts with conductive charged probe), etc.

Tunneling, atomic force probe microscopy, near field optical microscopy. Informative possibilities and spatial resolution.

Tunnel: The principle of operation of a tunneling microscope is based on the passage of an electron through a potential barrier, which is formed by a break in the electrical circuit - a small gap between the probing micropoint and the surface of the sample. The operation of the device is based on the well-known phenomenon of electron tunneling (tunneling effect). An electrical voltage is applied between the metal tip and the surface of the conductor under study (typical voltage values: from units of mV to V) and the tip is brought closer to the surface of the sample until a tunnel current appears. Stable images of many surfaces can be obtained with a tunneling current of 10-9 A, i.e. in 1 nA. In this case, the tip is close to the surface at a distance of fractions of a nanometer. To obtain an image of the surface, the metal tip is moved over the surface of the sample, maintaining a constant value of the tunneling current. In this case, the trajectory of the tip essentially coincides with the surface profile, the tip goes around the hills and traces the depressions. An important part of a scanning tunneling microscope is a mechanical manipulator, which ensures the movement of the probe over the surface with an accuracy of thousandths of a nanometer. Traditionally, a mechanical manipulator is made of a piezoceramic material.

Atomic power: In an atomic force microscope, the interaction is the force interaction between the probe and the sample. atomic resolution on conductive and non-conductive surfaces. In the case of studies of uncharged surfaces in a natural atmosphere (in air), the main contribution to the force interaction between the probe and the sample is made by: the repulsive forces caused by the mechanical contact of the extreme atoms of the probe and the sample, the van der Waals forces, as well as the capillary forces associated with the presence of the film adsorbate (water) on the sample surface.

The division of AFM according to the method of measuring and fixing the force interaction between the probe and the sample makes it possible to distinguish two main cases: contact atomic force microscopy and discontinuous contact AFM.

Near field optical microscopy: optical images with a longitudinal resolution of 50 nm. Provides better resolution than conventional optical microscope. Increasing the resolution of BOM is achieved by detecting the scattering of light from the object under study at distances smaller than the wavelength of light. If the probe (detector) of the near field microscope is equipped with a spatial scanning device, then such a device is called a near field scanning optical microscope. Such a microscope makes it possible to obtain raster images of surfaces and objects with a resolution below the diffraction limit.

If we take as a probe a miniature diaphragm with a hole of several nanometers - an aperture, then, in accordance with the laws of wave optics, visible light (with a wavelength of several hundred nanometers) penetrates into such a small hole, but not far, but at a distance comparable to the size holes. If a sample is placed within this distance, in the so-called "near field", the light scattered from it will be recorded. By moving the diaphragm in close proximity to the sample, as in a tunneling microscope, we obtain a raster image of the surface. Later, near-field microscopes were developed that did not use an aperture - apertureless SNOM.

The uniqueness of near-field optical microscopy compared to other scanning methods is that the image is built directly in the optical range, including visible light, but the resolution is many times higher than the resolution of traditional optical systems.

(An optical fiber with a miniature diaphragm is used as a probe. When scanning a sample, the manipulator moves the diaphragm near the surface. The radiation of the laser source, passing through the diaphragm, illuminates the surface under study. Scattered or re-emitted light is recorded in a microscope of this design. As a result of the fact that light scattering occurs in the near zone (at a distance from the emitting diaphragm less than the wavelength of light), it is possible to overcome the fundamental limitation of conventional optical microscopy in terms of resolution: surface details tens of nanometers in size become noticeable.)

Basic elements of a scanning probe microscope.

Cantilever, probe (for each microscopy its own), mechanical manipulator, laser, photodiode, feedback system. In simple terms: a probe, a movement system, a recording system.

Application in the study of nano-objects and linear measurements in the nanorange.

The most striking demonstrations of the possibilities of this experimental direction in the study of solid surfaces can be: the results of direct visualization of surface reconstruction, the manipulation of individual atoms to record information with a record density, the study of the local effect of surface defects on the band structure of the sample, etc.

The new possibilities of this direction in comparison with traditional methods of surface investigation make especially promising the use of probe microscopy (in particular, atomic force microscopy (AFM) for studying biological and organic materials. Significant progress has also been made on this path in recent years. In particular, with regard to to the research of nucleic acids, we can mention such results as the visualization of individual DNA molecules and the study of their conformational state in liquid media, the direct measurement of the interaction forces of complementary nucleotides, and the real-time visualization of the processes of interaction between DNA and proteins.

Karelian State Pedagogical University

Scanning probe microscopy

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Scanning probe microscope (SPM), its structure and principle of operation

Scanning probe microscopy (SPM)- one of the powerful modern methods for studying the morphology and local properties of the surface of a solid body with high spatial resolution

Despite the variety of types and applications of modern scanning microscopes, their operation is based on similar principles, and their designs differ little from each other. On fig. 1 shows a generalized scheme of a scanning probe microscope (SPM).

Fig.1 Generalized scheme of a scanning probe microscope (SPM).

The principle of its work is as follows. Using a coarse positioning system, the measuring probe is brought to the surface of the test sample. When the sample and probe approach at a distance of less than hundreds of nm, the probe begins to interact with the surface structures of the analyzed surface. The movement of the probe along the surface of the sample is carried out using a scanning device, which provides scanning of the surface with the probe needle. It is usually a piezoceramic tube with three pairs of separated electrodes applied to its surface. Under the action of stresses Ux and Uy applied to the piezotube, it bends, thereby ensuring the movement of the probe relative to the sample along the X and Y axes; under the action of stress Uz, it is compressed or stretched, which makes it possible to change the needle-sample distance.

The piezoelectric effect in crystals was discovered in 1880 by the brothers P. and J. Curie, who observed the appearance on the surface of plates cut with a certain orientation from a quartz crystal, electrostatic charges under the action of mechanical stresses. These charges are proportional to the mechanical stress, change sign with it, and disappear when it is removed.

The formation of electrostatic charges on the surface of a dielectric and the occurrence of electric polarization inside it as a result of mechanical stress is called the direct piezoelectric effect.

Along with the direct, there is an inverse piezoelectric effect, which consists in the fact that in a plate cut from a piezoelectric crystal, mechanical deformation occurs under the action of an electric field applied to it; moreover, the magnitude of mechanical deformation is proportional to the electric field strength. The piezoelectric effect is observed only in solid dielectrics, mainly crystalline ones. In structures that have a center of symmetry, no uniform deformation can disturb the internal equilibrium of the crystal lattice and, therefore, only 20 classes of crystals that lack a center of symmetry are piezoelectric. The absence of a center of symmetry is a necessary but not sufficient condition for the existence of the piezoelectric effect, and therefore not all acentric crystals have it.

The piezoelectric effect cannot be observed in solid amorphous and cryptocrystalline dielectrics. (Piezoelectrics - single crystals: Quartz. The piezoelectric properties of quartz are widely used in engineering to stabilize and filter radio frequencies, generate ultrasonic vibrations, and measure mechanical quantities. Tourmaline. The main advantage of tourmaline is the greater value of the partial coefficient compared to quartz. Due to this, and also because of the greater mechanical strength of tourmaline, it is possible to manufacture resonators for higher frequencies.

Currently, tourmaline is almost never used for the manufacture of piezoelectric resonators and has limited use for measuring hydrostatic pressure.

Rochelle salt. Rochelle salt piezoelectric elements were widely used in equipment operating in a relatively narrow temperature range, in particular, in pickups. However, at present they have been almost completely replaced by ceramic piezoelectric elements.

The probe position sensor continuously monitors the position of the probe relative to the sample and, through a feedback system, transmits data about it to a computer system that controls the movement of the scanner. To register the interaction forces of the probe with the surface, a method is usually used based on recording the deviation of the semiconductor laser beam reflected from the tip of the probe. In microscopes of this type, the reflected beam of light falls into the center of a two- or four-section photodiode connected in a differential circuit. The computer system serves, in addition to controlling the scanner, also for processing data from the probe, analyzing and displaying the results of surface examination.

As you can see, the structure of the microscope is quite simple. Of main interest is the interaction of the probe with the surface under study. It is the type of interaction used by a particular scanning probe microscope that determines its capabilities and scope. (slide) As the name implies, one of the main elements of a scanning probe microscope is a probe. A common feature of all scanning probe microscopes is the method of obtaining information about the properties of the surface under study. The microscopic probe approaches the surface until a balance of interactions of a certain nature is established between the probe and the sample, after which scanning is performed.

Scanning tunneling microscope (STM), its structure and principle of operation

The first SPM prototype was the scanning tunneling microscope (STM), invented in 1981. scientists of the IBM research laboratory in Zurich, Gerhard Binnig and Heinrich Röhrer. With its help, real images of surfaces with atomic resolution were obtained for the first time, in particular, a 7x7 reconstruction on a silicon surface (Fig. 2).

Fig.3 STM image of the surface of single-crystal silicon. Reconstruction 7 x 7

All currently known SPM methods can be conditionally divided into three main groups:

– scanning tunneling microscopy; STM uses a sharp conducting needle as a probe

If a bias voltage is applied between the tip and the sample, then when the tip of the needle approaches the sample at a distance of about 1 nm, a tunneling current arises between them, the magnitude of which depends on the distance "needle-sample", and the direction depends on the polarity of the voltage (Fig. 4). As the tip of the needle moves away from the surface under study, the tunneling current decreases, and as it approaches, it increases. Thus, using data on the tunneling current at a certain set of surface points, it is possible to construct an image of the surface topography.

Fig.4 Scheme of the occurrence of the tunneling current.

– atomic force microscopy; it registers changes in the force of attraction of the needle to the surface from point to point. The needle is located at the end of a cantilever beam (cantilever), which has a known rigidity and is capable of bending under the action of small van der Waals forces that arise between the surface under study and the tip of the tip. The deformation of the cantilever is recorded by the deflection of the laser beam incident on its rear surface, or by the piezoresistive effect that occurs in the cantilever itself during bending;

– near-field optical microscopy; in it, the probe is an optical waveguide (optical fiber), tapering at the end that faces the sample to a diameter less than the wavelength of light. In this case, the light wave does not leave the waveguide for a long distance, but only slightly “falls out” from its tip. A laser and a receiver of light reflected from the free end are installed at the other end of the waveguide. At a small distance between the surface under study and the tip of the probe, the amplitude and phase of the reflected light wave change, which is the signal used to construct a three-dimensional image of the surface.

Depending on the tunneling current or the distance between the needle and the surface, two modes of operation of the scanning tunneling microscope are possible. In the constant height mode, the tip of the needle moves in a horizontal plane above the sample, and the tunneling current changes depending on the distance to it (Fig. 5a). In this case, the information signal is the value of the tunneling current measured at each scanning point of the sample surface. Based on the obtained values ​​of the tunnel current, an image of the topography is constructed.

Rice. Fig. 5. STM operation scheme: a - in constant height mode; b - in direct current mode

In the constant current mode, the feedback system of the microscope ensures the constancy of the tunneling current by adjusting the "needle-sample" distance at each scanning point (Fig. 5b). It monitors changes in the tunnel current and controls the voltage applied to the scanner to compensate for these changes. In other words, as the current increases, the feedback system moves the probe away from the sample, and as it decreases, it brings it closer. In this mode, the image is built on the basis of data on the amount of vertical movement of the scanning device.

Both modes have their advantages and disadvantages. In constant height mode, you can get results faster, but only for relatively smooth surfaces. In constant current mode, irregular surfaces can be measured with high accuracy, but measurements take longer.

Having a high sensitivity, scanning tunneling microscopes have given humanity the opportunity to see the atoms of conductors and semiconductors. But due to design limitations, it is impossible to obtain an image of non-conductive materials on STM. In addition, for the high-quality operation of a tunneling microscope, a number of very strict conditions must be met, in particular, operation in a vacuum and special sample preparation. Thus, although it cannot be said that Binnig and Röhrer's first pancake turned out to be lumpy, the product came out a little damp.

Five years have passed and Gerhard Binning, together with Calvin Quayt and Christopher Gerber, invented a new type of microscope, which they called the atomic force microscope (AFM), for which in the same 1986. G. Binnig and H. Röhrer were awarded the Nobel Prize in Physics. The new microscope circumvented the limitations of its predecessor. Using AFM, it is possible to obtain images of the surface of both conductive and non-conductive materials with atomic resolution, moreover, under atmospheric conditions. An additional advantage of atomic force microscopes is the ability to visualize their electrical, magnetic, elastic, and other properties along with surface topography measurements.

Atomic force microscope (AFM), its structure and principle of operation

The most important component of ACM (Atomic Force Microscope) are scanning probes - cantilevers, the properties of the microscope directly depend on the properties of the cantilever.

The cantilever is a flexible beam (175x40x4 microns - averaged data) with a certain stiffness coefficient k(10-3 - 10 N/m), at the end of which there is a micro needle (Fig. 1). Range of radius of curvature R needle tip with the development of AFM changed from 100 to 5 nm. Obviously, with decreasing R The microscope allows you to obtain images with higher resolution. Needle point angle a is also an important characteristic of the probe, on which the image quality depends. a in various cantilevers varies from 200 to 700, it is not difficult to assume that the less a, the higher the quality of the resulting image.

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so to improve w0 the length of the cantilever (on which the stiffness coefficient depends) is on the order of several microns, and the mass does not exceed 10-10 kg. The resonant frequencies of various cantilevers range from 8 to 420 kHz.

The AFM scanning method is as follows (Figure 2) : the tip of the probe is above the surface of the sample, while the probe moves relative to the sample, like a beam in a cathode ray tube of a TV (line-by-line scanning). The laser beam directed at the surface of the probe (which bends in accordance with the landscape of the sample), reflected, hits the photodetector, which fixes the deflection of the beam. In this case, the deflection of the needle during scanning is caused by the interatomic interaction of the sample surface with its tip. With the help of computer processing of the photodetector signals, it is possible to obtain three-dimensional images of the surface of the sample under study.

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Rice. 8. Dependence of the strength of interatomic interaction on the distance between the tip and the sample

Forces of interaction of the probe with the surface are divided into short-range and long-range. Short-range forces arise at a distance of the order of 1-10 A when the electron shells of the atoms of the tip of the needle and the surface overlap, and rapidly decrease with increasing distance. Only a few atoms (in the limit one) of the tip of the needle enter into short-range interaction with surface atoms. When imaging a surface using this type of force, the AFM operates in contact mode.

There is a contact scanning mode, when the tip of the probe touches the surface of the sample, intermittent - the probe periodically touches the surface of the sample during scanning, and non-contact, when the probe is a few nanometers from the scanned surface (the latter scanning mode is rarely used, because the forces of interaction between the probe and the sample are practically hard to capture).

STM capabilities

STM was taught not only to distinguish between individual atoms, but also to determine their shape.
Many people have not yet fully realized the fact that scanning tunneling microscopes (STMs) are able to recognize individual atoms, as the next step has already been taken: now it has become possible to determine even forms individual atom in real space (more precisely, the form of distribution of electron density around the atomic nucleus).

Near-field optical microscope, its structure and principle of operation

Near-field optical microscopy; in it, the probe is an optical waveguide (optical fiber), tapering at the end that faces the sample to a diameter less than the wavelength of light. In this case, the light wave does not leave the waveguide for a long distance, but only slightly “falls out” from its tip. A laser and a receiver of light reflected from the free end are installed at the other end of the waveguide. At a small distance between the surface under study and the tip of the probe, the amplitude and phase of the reflected light wave change, which is the signal used to construct a three-dimensional image of the surface.

If you force light to pass through a diaphragm with a diameter of 50-100 nm and bring it closer to a distance of several tens of nanometers to the surface of the sample under study, then by moving such a “ ” across the surface from point to point (and having a sufficiently sensitive detector), you can investigate the optical properties of this sample in a local area corresponding to the hole size.

This is how a scanning near-field optical microscope (SNOM) works. The role of the hole (subwavelength diaphragm) is usually performed by an optical fiber, one end of which is pointed and covered with a thin layer of metal, everywhere except for a small area at the very tip of the tip (the diameter of the "dust-free" area is just 50-100 nm). From the other end, light from a laser enters such a light guide.

December 2005." href="/text/category/dekabrmz_2005_g_/" rel="bookmark">December 2005 and is one of the base laboratories of the Nanotechnology Department of the Faculty of Physics of the Russian State University. The laboratory has 4 sets of NanoEducator scanning probe microscopes, specially developed by the company NT-MDT (Zelenograd, Russia) for laboratory work... The devices are aimed at a student audience: they are fully controlled by a computer, have a simple and intuitive interface, animation support, and require a phased mastery of techniques.

Fig.10 Scanning Probe Microscopy Laboratory

The development of scanning probe microscopy served as the basis for the development of a new area of ​​nanotechnology - probe nanotechnology.

Literature

1. Binnig G., Rohrer H., Gerber Ch., Weibel E. 7 i 7 Reconstruction on Si(111) Resolved in Real Space, Phys. Rev. Lett. 1983 Vol. 50, No. 2. P. 120-123. This famous publication opened the era of STM.

2. http://www. *****/education/stsoros/1118.html

3. http://ru. wikipedia. org

4. http://www. *****/SPM-Techniques/Principles/aSNOM_techniques/Scanning_Plasmon_Near-field_Microscopy_mode94.html

5. http://scireg. *****.

6.http://www. *****/article_list. html

SCANNING PROBE MICROSCOPES: TYPES AND PRINCIPLE OF OPERATION

Kuvaytsev Alexander Vyacheslavovich
Dimitrovgrad Institute of Engineering and Technology Branch of the National Research Nuclear University "MEPhI"
student

annotation
This article describes the principle of operation of a probe microscope. This is a fundamentally new technology that can solve problems in such diverse areas as communications, biotechnology, microelectronics and energy. Nanotechnology in microscopy will significantly reduce the consumption of resources and will not put pressure on the environment, they will play a leading role in the life of mankind, as, for example, the computer has become an integral part of people's lives.

SCANNING PROBE MICROSCOPY: TYPES AND OPERATING PRINCIPLES

Kuvaytsev Aleksandr Vyacheslavovich
Dimitrovgrad Engineering and Technological Institute of the National Research Nuclear University MEPHI
student

Abstract
This article describes the principle of a probe microscope. It is a new technology that can solve problems in such diverse areas as communications, biotechnology, microelectronics and energy. Nanotechnology in microscopy will significantly reduce the consumption of resources and do not put pressure on the environment, they will play a leading role in human life, as, for example, the computer has become an integral part of people's lives.

In the 21st century, nanotechnologies are rapidly gaining popularity, which penetrate into all spheres of our life, but there would be no progress in them without new, experimental methods of research, one of the most informative is the method of scanning probe microscopy, which was invented and distributed by Nobel laureates in 1986 - Prof. Heinrich Rohrer and Dr. Gerd Binnig.

A real revolution took place in the world with the advent of methods for visualizing atoms. Groups of enthusiasts began to appear, designing their own devices. As a result, several successful solutions were obtained for visualizing the results of the interaction of the probe with the surface. Technologies for the production of probes with the necessary parameters were created.

So what is a probe microscope? First of all, this is the probe itself, which examines the surface of the sample; a system for moving the probe relative to the sample in two-dimensional or three-dimensional representation (moves along X-Y or X-Y-Z coordinates) is also necessary. All this is supplemented by a recording system that fixes the value of a function that depends on the distance from the probe to the sample. The registering system fixes and remembers the value of one of the coordinates.

The main types of scanning probe microscopes can be divided into 3 groups:

1. Scanning tunneling microscope - designed to measure the relief of conductive surfaces with high spatial resolution.
   In STM, a sharp metal needle is passed over the sample at a very short distance. When a small current is applied to the needle, a tunneling current arises between it and the sample, the value of which is recorded by the recording system. The needle is passed over the entire surface of the sample and captures the slightest change in the tunnel current, due to which a relief map of the sample surface emerges. The STM is the first of a class of scanning probe microscopes, the rest were developed later.
2. Scanning atomic force microscope - used to build the surface structure of the sample with a resolution up to atomic. Unlike STM, this microscope can be used to examine both conductive and non-conductive surfaces. Because of the ability to not only scan but also manipulate atoms, it is called power.
3. A near-field optical microscope is an "advanced" optical microscope that provides better resolution than a conventional optical microscope. An increase in the resolution of the BOM was achieved by capturing light from the object under study at distances smaller than the wavelength. If the probe of the microscope is equipped with a device for scanning the spatial field, then such a microscope is called a scanning optical microscope of the near field. Such a microscope makes it possible to obtain images of surfaces with very high resolution.

The image (Fig. 1) shows the simplest scheme of the probe microscope.

Figure 1. - Scheme of operation of a probe microscope

Its operation is based on the interaction of the sample surface with a probe, it can be a cantilever, a needle or an optical probe. With a small distance between the probe and the object of study, the actions of interaction forces, such as repulsion, attraction, etc., and the manifestation of effects, such as electron tunneling, can be recorded using registration tools. To detect these forces, very sensitive sensors are used that can detect the slightest changes. Piezo tubes or plane-parallel scanners are used as a coordinate scanning system to obtain a raster image.

The main technical difficulties in creating scanning probe microscopes include:

1. Ensuring mechanical integrity
2. Detectors must have maximum sensitivity
3. The end of the probe must have a minimum dimension
4. Create a sweep system
5. Ensuring the smoothness of the probe

Almost always, the image obtained by a scanning probe microscope is difficult to decipher due to distortions in obtaining results. As a rule, additional mathematical processing is required. For this, specialized software is used.

Currently, scanning probe and electron microscopy are used as complementary research methods due to a number of physical and technical features. Over the past years, the use of probe microscopy has made it possible to obtain unique scientific research in the fields of physics, chemistry and biology. The first microscopes were just devices - indicators that helped in research, and modern samples are full-fledged workstations, including up to 50 different research methods.

The main task of this advanced technique is to obtain scientific results, but the application of the capabilities of these devices in practice requires high qualifications from a specialist.

Study of piezoelectric microdisplacement scanners.

Objective: study of the physical and technical principles of ensuring microdisplacements of objects in scanning probe microscopy, implemented using piezoelectric scanners

Introduction

Scanning probe microscopy (SPM) is one of the powerful modern methods for studying the properties of a solid surface. At present, almost no research in the field of surface physics and microtechnologies is complete without the use of SPM methods.

The principles of scanning probe microscopy can be used as a basic basis for the development of technology for creating nanoscale solid-state structures (1 nm = 10 A). For the first time in the technological practice of creating man-made objects, the question of using the principles of atomic assembly in the manufacture of industrial products is raised. Such an approach opens up prospects for the implementation of devices containing a very limited number of individual atoms.

The scanning tunneling microscope (STM), the first of a family of probe microscopes, was invented in 1981 by Swiss scientists G. Binnig and G. Rohrer. In their work, they showed that this is a fairly simple and very effective way to study the surface with a high spatial resolution up to the atomic order. This technique gained real recognition after the visualization of the atomic structure of the surface of a number of materials and, in particular, the reconstructed silicon surface. In 1986, G. Binnig and G. Poper were awarded the Nobel Prize in Physics for the creation of the tunneling microscope. Following the tunneling microscope, an atomic force microscope (AFM), a magnetic force microscope (MSM), an electric force microscope (ESM), a near-field optical microscope (NOM) and many other devices with similar operating principles and called scanning probe microscopes.

1. General principles of operation of scanning probe microscopes

In scanning probe microscopes, the study of the microrelief and local properties of the surface is carried out using specially prepared needle-type probes. The radius of curvature of the working part of such probes (points) has dimensions of the order of ten nanometers. The characteristic distance between the probe and the sample surface in probe microscopes is 0.1 – 10 nm in order of magnitude.

The operation of probe microscopes is based on various types of physical interaction of the probe with the atoms of the sample surface. Thus, the operation of a tunneling microscope is based on the phenomenon of tunneling current flowing between a metal needle and a conducting sample; different types of force interaction underlie the operation of atomic force, magnetic force and electric force microscopes.

Let us consider the common features inherent in various probe microscopes. Let the interaction of the probe with the surface be characterized by some parameter R. If there is a sufficiently sharp and one-to-one dependence of the parameter R from the probe-sample distance P = P(z), then this parameter can be used to organize a feedback system (FS) that controls the distance between the probe and the sample. On fig. 1 schematically shows the general principle of organizing the feedback of a scanning probe microscope.

Rice. 1. Scheme of the feedback system of the probe microscope

Feedback system maintains parameter value R constant, equal to Ro set by the operator. If the probe-surface distance changes (for example, increases), then there is a change (increase) in the parameter R. In the OS system, a difference signal is formed that is proportional to the value. P= P - Po, which is amplified to the desired value and is fed to the actuating element of the IE. The actuating element processes this difference signal by moving the probe closer to the surface or moving it away until the difference signal becomes zero. In this way, the probe-sample distance can be maintained with high accuracy. In existing probe microscopes, the accuracy of keeping the probe-surface distance reaches ~0.01 Å. When the probe moves along the sample surface, the interaction parameter changes R, due to the surface topography. The OS system works out these changes, so that when the probe moves in the X,Y plane, the signal on the actuating element turns out to be proportional to the surface topography.

To obtain an SPM image, a specially organized process of scanning a sample is carried out. When scanning, the probe first moves over the sample along a certain line (line scanning), while the value of the signal on the actuating element, proportional to the surface topography, is recorded in the computer memory. Then the probe returns to the starting point and goes to the next scan line (frame scan), and the process is repeated again. The feedback signal recorded in this way during scanning is processed by a computer, and then the SPM image of the surface topography Z = f(x,y) constructed using computer graphics. Along with the study of the surface topography, probe microscopes make it possible to study various surface properties: mechanical, electrical, magnetic, optical, and many others.