JP2016099220A - Scanning probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scanning probe microscope that can acquire a magnetic property and an electrical property by a single measurement at once in addition to a surface shape.SOLUTION: A scanning probe microscope includes: a three-dimensional movement mechanism 1 that varies a relative position of a sample 3 surface and a probe 6 tip in a Z direction connecting both of them and within an XY plane perpendicular thereto; force measurement means (data processing unit 31) that, while resonantly oscillating the probe 6 tip, measures an interatomic force which acts between the sample 3 surface and the probe 6 tip, and at least one force out of a magnetic force and an electrostatic force which act therebetween; and volume data acquisition means (data processing unit 31) that acquires volume data being three-dimensional data of the at least two forces, by repeating such an operation that measurements are conducted by the force measurement means while varying a distance between the sample 3 surface and the probe 6 tip within a prescribed range in the Z direction by the three-dimensional movement mechanism, and thereafter the same measurements are conducted after varying a position of both of them within the XY plane.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a scanning probe microscope, and more particularly to a novel scanning probe microscope that can grasp various characteristics of a sample in a multi-dimensional manner.

  The scanning probe microscope (SPM) detects the interaction between the probe tip and the sample surface while moving the probe P or sample S in a direction horizontal to the sample surface as shown in FIG. Originally, the shape of the sample surface is observed with high resolution. At this time, the distance between the tip of the probe and the sample surface is controlled by moving the probe P or sample S in a direction perpendicular to the sample surface so that the detected interaction (force) is constant. . That is, in normal SPM, the distance between the tip of the probe and the sample surface is controlled to be constant at a certain value, and in this state, the tip of the probe moves in the horizontal direction so as to trace the sample surface. As an interaction between the probe tip and the sample surface, atomic force is usually used. An atomic force microscope (AFM) observes the shape of the surface of a sample using atomic force.

  Other SPMs include Magnetic Force Microscope (MFM) and Electrostatic Force Microscope (EFM). In general, magnetic force and electrostatic force are far-distance forces compared to atomic forces. In these microscopes, the sample surface and the tip of the probe are observed after observing the shape of the sample surface at a short distance where the atomic force is dominant. A method is used in which information on magnetic force and electrostatic force is imaged by separating the tip of the probe and the sample surface by a certain distance.

  In these MFM and EFM, a method called dynamic mode is used. In the dynamic mode, the cantilever is excited in the vicinity of its mechanical resonance frequency, and physical property information on the sample surface is obtained from the change in the resonance state (Patent Documents 1, 2, etc.).

Special table 2001-522045 gazette Japanese Patent Laid-Open No. 05-026662

  Currently, research on various substances and samples is progressing, and we want to acquire the magnetic properties and electrical properties of one sample at a time, as well as the surface shape, and know the relationship between them. The demand is getting stronger. However, in order to meet such a demand with the conventional SPM, it was necessary to perform a complicated operation.

  For example, as described above, the sample is measured in the dynamic mode in MFM and EFM, but the distance over which the magnetic force and electrostatic force are applied varies depending on the sample. Therefore, the magnetic force and electrostatic force information can be effectively imaged. In order to do this, after measuring the surface shape with AFM first, the probe is lifted by a distance from which the atomic force or the magnetic force or electrostatic force is expected to reach. Measure the electrostatic force. However, depending on the type and state of the sample, the magnetic force or electrostatic force may not be correctly measured at the probe position, and in that case, the probe position needs to be changed again. In the conventional method, it was necessary to repeat trial and error in this way.

  The problem to be solved by the present invention is to provide a scanning probe microscope that can acquire not only the surface shape but also magnetic properties and electrical properties at a time in one measurement.

A scanning probe microscope according to the present invention made to solve the above problems is as follows.
a) a three-dimensional movement mechanism that changes the relative position of the sample surface and the tip of the probe in the Z direction connecting them and the XY plane perpendicular to the Z direction;
b) a force measuring means for measuring an atomic force and at least one of a magnetic force and an electrostatic force acting between the sample surface and the probe tip while causing the probe tip to resonate and vibrate;
c) The distance between the sample surface and the tip of the probe is measured by the force measuring means while changing the distance in the predetermined direction in the Z direction by the three-dimensional moving mechanism, and then the position of both is changed in the XY plane. And volume data acquisition means for acquiring volume data that is three-dimensional data of the at least two forces by repeating the same measurement operation.

  In the scanning probe microscope according to the present invention, first, the three-dimensional moving mechanism changes the distance within the predetermined range in the Z direction connecting the sample surface and the tip of the probe, and the force measuring means at each point between them is the atomic force. Measure at least one of magnetic and electrostatic forces. As a result, a curve representing this change in the Z direction of these at least two forces (this is called a “force curve”) is obtained.

  After obtaining the force curve data in the Z direction at one point on the sample surface, the 3D moving mechanism moves the sample surface and the tip of the probe relative to each other in the XY plane, and measures the same at another point. To collect force curve data at that point.

  If the force curve data in the Z direction is collected at each point on the sample surface in this way, finally three-dimensional volume data is obtained. Since this volume data represents the direct relationship between the interatomic force and at least one of the corresponding magnetic force and electrostatic force, the volume data shows the surface shape and physical properties of the sample. Can be obtained at once.

  In the scanning probe microscope according to the present invention, the force is measured at each point while the tip of the probe is resonantly oscillated. For this reason, not only the interatomic force but also other physical property information can be obtained from information on the excitation state (for example, frequency and phase) of the cantilever holding the probe.

  In the scanning probe microscope according to the present invention, the atomic force and at least one of the magnetic force and the electrostatic force are simultaneously measured by one measurement. It is possible to reconstruct the shape and physical property information of the sample surface at a position separated from the sample surface by an arbitrary distance, and repeat the measurement many times in order to search for an appropriate distance as in the past. There is no need.

  The volume data of the magnetic force or / and electrostatic force resulting from the physical properties of the surface of the sample obtained with the scanning probe microscope according to the present invention is the surface shape and its magnetic properties or / and It represents a direct relationship of electrical properties. This is expected to advance integrated research on the surface physical properties of samples.

Explanatory drawing which shows the mode of sample surface shape observation by a scanning probe microscope (SPM). The schematic block diagram of the principal part of the electrostatic force microscope which is one Example of the scanning probe microscope which concerns on this invention. The schematic block diagram of the cantilever excitation part in the said electrostatic force microscope. The schematic block diagram of the circumference | surroundings of a sample and a probe of the magnetic force microscope which is another Example of the scanning probe microscope which concerns on this invention. The flowchart of the operation | movement for volume data acquisition in the magnetic force microscope of an Example. The schematic explanatory drawing of the operation | movement for volume data acquisition in the magnetic force microscope of an Example. Explanatory drawing which represented the volume data obtained with the magnetic force microscope of an Example by the superimposition of a two-dimensional image.

  Hereinafter, an electrostatic force microscope which is one embodiment of a scanning probe microscope according to the present invention will be described with reference to the accompanying drawings. FIG. 2 is a schematic configuration diagram of a main part of the electrostatic force microscope, and FIG. 3 is a schematic configuration diagram of a cantilever excitation unit in the electrostatic force microscope.

  As shown in FIG. 2, the sample 3 to be observed is held on a sample holder 2 mounted on a scanner 1 having a substantially cylindrical shape. The scanner 1 includes an XY scanner that scans the sample 3 in two directions of X and Y orthogonal to each other, and a Z scanner that finely moves the sample 3 in the Z-axis direction orthogonal to the X-axis and Y-axis. The drive source is a piezoelectric element that is displaced by a voltage applied from the vertical position control unit 32. A cantilever 5 having a probe 6 at the tip is disposed above the sample 3, and the cantilever 5 is fixed to the cantilever holder so as to vibrate in the vertical direction.

  In order to detect the displacement of the cantilever 5 in the Z-axis direction, an optical displacement detector 10 including a laser light source 11, mirrors 12 and 13, and a photodetector 14 is provided above the cantilever 5. In the optical displacement detection unit 10, the laser light emitted from the laser light source 11 is reflected substantially vertically by the mirror 12 and is irradiated near the rear end of the cantilever 5. The cantilever 5 is made of silicon, silicon nitride, or the like, and a metal thin film such as gold (Au) or aluminum (Al) is formed on the front surface (the surface facing the sample 3) and the back surface by vapor deposition or the like. Thereby, the back surface of the cantilever 5 is a mirror surface, and the laser light irradiated from above is reflected with high efficiency. The reflected light from the back surface of the cantilever 5 is introduced into the photodetector 14 via the mirror 13. The photodetector 14 has a light receiving surface divided into a plurality (usually two) in the vibration direction (displacement direction, Z axis direction) of the cantilever 5, or the light receiving surface divided into four in the Z axis direction and the Y axis direction. Has a surface. When the cantilever 5 is displaced up and down, the ratio of the amount of light incident on the plurality of light receiving surfaces changes. Therefore, the amount of displacement of the cantilever 5 in the Z-axis direction can be calculated by processing a detection signal corresponding to the plurality of received light amounts. Can be calculated. The detection signal from the photodetector 14 is amplified and input to the amplitude / phase detection unit 30, and information about the amplitude / phase of the displacement of the cantilever 5 obtained there is provided to the data processing unit 31.

As shown in FIG. 3, the sample holder 2 is connected to the excitation voltage generator 21 via a DC component blocking capacitor 25, and one end is electrically connected to the metal thin film 5a on the front surface and back surface of the cantilever 5. The other end of the conductive lead portion 20 is connected to the ground potential (GND) of the microscope. The excitation voltage generator 21 includes a carrier wave generator 22, a modulated wave generator 23, and an amplitude modulator 24. The carrier wave generator 22 generates a sine wave voltage having a frequency f ₀ within a predetermined frequency range higher than the resonance frequency of the cantilever 5. Meanwhile, the modulation wave generator 23 is for generating a sine wave voltage of frequency f _m is desired to excite the cantilever 5 at a lower frequency than the carrier wave. The amplitude modulation unit 24 modulates the amplitude of the carrier wave according to the modulation wave waveform. Accordingly, the output of the amplitude modulation section 24, i.e. the excitation voltage applied to the sample holder 2 thereof envelope frequency at f ₀ are matched to the modulated waveform. Thereby, an excitation voltage is applied between the metal thin film 5 a on the front surface of the cantilever 5 and the sample 3. The capacitor 25 is for cutting off a large DC voltage generated when the excitation voltage generated by the excitation voltage generator 21 is switched.

  Further, the excitation voltage generation unit 21, the vertical position control unit 32, and the horizontal position control unit 33 are controlled by the main control unit 34, in order to set conditions, parameters, and the like necessary for measurement in the main control unit 34. An operation unit 35 and a display unit 36 for displaying measurement results are also connected.

Here, the electrostatic force acting on the cantilever 5 when the excitation voltage is applied between the metal thin film 5a on the front surface of the cantilever 5 and the sample 3 (hereinafter referred to as “probe-to-sample”) will be described.
Now, when a certain voltage V is applied between the probe and the sample, the electrostatic force F _esf between the probe and the sample is _expressed by the following equation (1). Here, C _ts is the capacitance between the probe and the sample, and z is the distance between the probe and the sample.
When a DC voltage V _DC and an amplitude modulation signal V _{AC, p-0} (an angular frequency ω _{0 of} a carrier wave and an angular frequency ω _m of a modulated wave) are applied between the probe and the sample, the applied voltage V _mod is the following ( It is expressed by equation (2).
Therefore, the electrostatic force F ^AM _esf between the probe and the sample when the voltage V _mod is applied between the probe and the sample is _expressed by the following equation (3).

As shown in the equation (3), the electrostatic force F ^AM _esf includes components of various frequencies including a direct current component, and one of them is a component of the angular frequency ω _m of the modulated wave. . That is, the cantilever 5 vibrates with the component of the angular frequency ω _m of the modulated wave due to the electrostatic force F ^AM _esf . For example, by detecting this specific frequency component with a lock-in amplifier or the like, the static electricity of only the angular frequency ω _m component is detected. It is possible to extract the force.

  The above is a detailed description of the electrostatic force microscope, but the magnetic force microscope is also different from the electrostatic force microscope of the above embodiment in that it measures the magnetic force between the probe and the sample, and other mechanisms, The principle is almost the same. In the case of a magnetic force microscope, for example, as shown in FIG. 4, if a magnetic field forming device 7 is provided around the sample 3 and the probe 6 and both are placed in the magnetic field, the sample 3 and the probe 6 are in the same manner as described above. The magnetic force acting between them can be measured.

  Next, FIGS. 5 and 6 show the concept of a scanning method in a magnetic force microscope (MFM) which is an embodiment of the present invention. In general SPM scanning, first, one line is scanned in the X direction at a high speed, and after the X scanning of one line is completed, the scanning is slightly shifted in the Y direction, and X scanning of one line is performed again. Fast scanning such as X scanning is called high-speed scanning, and slow scanning such as Y direction is called low-speed scanning.

  In the MFM of this embodiment, the direction of high-speed scanning and the direction of low-speed scanning are changed, and as shown in FIG. 6, high-speed scanning in the Z direction and low-speed scanning in the X direction are performed. Then, one high-speed scanning is the same as acquiring a force curve, and it is performed while changing the X coordinate.

More specifically, as shown in FIG. 5, first, excitation of the cantilever is started (step S1), and the tip of the probe is placed at a predetermined height Zmax (or the scanner is moved. The same applies hereinafter, S2). The frequency and / or phase change of the cantilever vibration is measured at that position (S3). Thereby, the electrostatic / magnetic interaction between the probe tip and the sample surface can be measured. Then, lowering the position of the probe tip in the Z direction by a small distance [Delta] Z (S4), the amplitude w of the oscillation of the cantilever is determined whether it is below a predetermined value w ₀ (S5). When w <w ₀ , it is determined that the tip of the probe is in contact with the sample surface, and the probe is moved in the X direction by a minute distance ΔX (S6). Then, the tip of the probe is raised to the height Zmax (S2), and thereafter the same measurement is repeated. When such a measurement is repeated and moved by a predetermined distance _Xmax in the X direction, the measurement is moved by a minute distance ΔY in the Y direction, and the same measurement is repeated (S7, S8, S9).

  By performing scanning in the ZX direction as described above, one two-dimensional image is obtained, and by subsequently acquiring such a two-dimensional image while changing the Y coordinate, the three-dimensional coordinate on the sample surface is obtained. Information can be acquired. This is called volume data. FIG. 7 shows how volume data is generated by superimposing two-dimensional images.

  In SPM, it is possible to capture not only one data but one data at one coordinate. That is, a plurality of volume data can be obtained with the same three-dimensional coordinates. Taking the MFM as an example, one of the volume data is atomic force, that is, surface shape data, and the other volume data is magnetic force data. Since the magnetic force also depends on the distance from the sample surface, in general MFM, the magnetic force is measured with the probe released to a distance where the interatomic force due to the shape does not reach, or the surface shape is stored in advance. Then, using the data, the magnetic force is measured while controlling the distance between the probe and the sample surface (lift mode). However, in the MFM of this embodiment, since the surface shape and magnetic force data are obtained at all XYZ coordinates, the Z where the distance between the probe and the sample surface is constant is extracted from the surface shape data. By applying to the magnetic force data, the same result as in the lift mode can be obtained. In addition, in the lift mode, only data at one distance can be obtained, whereas in the method of this patent, the Z coordinate extracted from the surface shape can be set to an arbitrary distance, so magnetic force images at various distances can be set. Can be reconstructed.

DESCRIPTION OF SYMBOLS 1 ... Scanner 2 ... Sample holder 3 ... Sample 5 ... Cantilever 5a ... Metal thin film 6 ... Probe 7 ... Magnetic field formation apparatus 10 ... Optical displacement detection part 11 ... Laser light source 12, 13 ... Mirror 14 ... Photo detector 20 ... Lead Unit 21 ... excitation voltage generation unit 22 ... carrier wave generation unit 23 ... modulation wave generation unit 24 ... amplitude modulation unit 25 ... capacitor 30 ... amplitude phase detection unit 31 ... data processing unit 32 ... vertical position control unit 33 ... horizontal position control unit 34 ... Main control part 35 ... Operation part 36 ... Display part

Claims (2)

a) a three-dimensional movement mechanism that changes the relative position of the sample surface and the tip of the probe in the Z direction connecting them and the XY plane perpendicular to the Z direction;
b) a force measuring means for measuring an atomic force and at least one of a magnetic force and an electrostatic force acting between the sample surface and the probe tip while causing the probe tip to resonate and vibrate;
c) The distance between the sample surface and the tip of the probe is measured by the force measuring means while changing the distance in the predetermined direction in the Z direction by the three-dimensional moving mechanism, and then the position of both is changed in the XY plane. A scanning probe microscope comprising: volume data acquisition means for acquiring volume data that is three-dimensional data of the at least two forces by repeating the same measurement operation.   The scanning probe microscope according to claim 1, wherein the force measuring unit measures an atomic force and a magnetic force.