JP2011053018A - Method and device for measuring potential in liquid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform microscale measurement of a surface potential of a material put in a liquid and its liquid-side potential structure affected by a state of the surface potential. <P>SOLUTION: A measuring object is set in the liquid (step S101), a cantilever is vibrated at a first frequency (step S104), and a DC potential and an AC potential of a second frequency different from the first frequency are superposed and applied to a probe provided on the cantilever (step S105). Next, the probe is made to approach the measuring object (step S108), and the probe is brought into contact with the measuring object by controlling the distance between the probe and the measuring object so that the amplitude of vibration of the first frequency is kept at a predetermined constant value (step S109). After that, the DC potential is controlled so as to make a vibration component of the second frequency zero, and a DC potential is measured when the vibration component of the second frequency is zero (step S110). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for measuring a potential on a surface of an object existing in a liquid and a potential of a liquid in the vicinity of the surface.

  For example, when an additive is added to the plating solution to control the thickness of the plating, or when there is an electrode in the liquid, such as certain types of batteries and capacitors, the substance (solid) present in the liquid There is a demand to measure and evaluate the potential structure on the liquid side affected by the surface potential state on a micro scale. For example, when evaluating the action of the additive in plating, the potential structure on the liquid side affected by the surface potential state of the plating object existing in the liquid in which the additive is added to the solvent is measured. When it is desired to evaluate the relationship between the battery electrolyte and the electrode, the potential structure on the liquid side affected by the surface potential state of the electrode existing in the liquid corresponding to the electrolyte is measured. Furthermore, when evaluating the dispersibility of a pigment or the like, the potential structure on the liquid side affected by the surface potential state of the pigment present in the liquid to which the dispersant or the like is added is measured.

  As a method for measuring the potential state of the surface of a substance present in a liquid, for example, there are an electrochemical method and a dynamic method using light scattering / flow (for example, zeta potential measurement). The potential states obtained by these methods are averaged over the entire surface and assume a perfect plane model or spherical model. For this reason, it is difficult to measure the potential state of the surface of the substance existing in the liquid and in the vicinity of the surface on the micro scale by the above-described method.

  Patent Document 1 discloses a scanning probe microscope that measures a surface shape of a sample and measures a potential potential in the surface shape. This scanning probe microscope applies a potential to the probe, detects a frequency shift amount due to the potential being applied to the probe, and integrates the detected frequency shift amount with a predetermined frequency. A signal in which the alternating potential signal is superimposed is used as a potential signal applied to the probe. At this time, the potential potential at the probe is obtained by performing servo control so that the detected frequency becomes zero.

JP 2005-283538 A (0017, 0063)

  By the way, the technique disclosed in Patent Document 1 measures the potential of a sample placed in air or in a vacuum, and measures the potential of a sample placed in a liquid or a liquid existing near the surface thereof. Not what you want. In addition, the technique disclosed in Patent Document 1 uses a change in vibration of the cantilever due to atomic force in a region where the probe does not touch the sample surface when detecting the sample surface. The potential on the surface of the sample is measured in a state that is not accurately captured. For this reason, in the technique disclosed in Patent Document 1, there is a risk that the measurement accuracy of the potential of the sample surface may be lowered.

  Further, the technique disclosed in Patent Document 1 detects a change in vibration of a cantilever due to an atomic force or electrostatic force acting on a probe by using a frequency shift amount of the vibration. However, since the resonance Q value of the vibration of the cantilever in the liquid is significantly lower than that in the atmosphere or vacuum, it is difficult to detect the frequency shift amount of the vibration of the cantilever in the liquid.

  Furthermore, in the technique disclosed in Patent Document 1, after detecting the sample surface, the probe attached to the cantilever is moved away by a predetermined amount, and then the predetermined amount toward the sample within a range not contacting the sample. Is moved by a predetermined step, and the potential is measured at each step. However, in this method, it is inevitable that the probe is charged by applying a potential to the probe. Further, the probe position may be shifted due to the thermal drift of the element used for the probe scanning, and the potential measurement accuracy may be lowered.

  As described above, the technique disclosed in Patent Document 1 is to measure the surface potential of a substance present in a liquid and the potential structure on the liquid side affected by the surface potential state of the substance on a microscale. There is room for improvement. The present invention has been made in view of the above, and a liquid potential measurement that can measure the surface potential of a substance placed in a liquid and the potential structure on the liquid side affected by the surface potential state on a micro scale. An object is to provide an apparatus and a liquid potential measurement method.

  In order to solve the above-described problems and achieve the object, the liquid potential measurement method according to the present invention is configured such that a cantilever having a probe on the free end side at a first frequency while a measurement target is held in a liquid. In the state where the probe is not in contact with the object to be measured, the probe is oscillated, and the probe is applied with a DC potential and an AC potential having a second frequency different from the first frequency. The vibration amplitude of the first frequency is detected, and then the probe is brought close to the measurement object while detecting the vibration amplitude of the first frequency, so that the vibration amplitude of the first frequency is kept at a predetermined constant value. The distance between the probe and the measurement object is controlled to determine that the probe and the measurement object are in contact when the vibration amplitude of the first frequency is maintained at the predetermined constant value. Judgment procedure, the probe and the measurement pair And the DC potential is controlled so that the vibration component of the second frequency becomes zero, and the DC potential when the vibration component of the second frequency becomes zero is determined. A surface potential measurement procedure to be obtained as a potential on the surface of the measurement object, a probe movement procedure for moving the probe to a position away from the measurement object, and at the position where the probe is separated from the measurement object, The direct-current potential is controlled so that the vibration component of the second frequency becomes zero, the direct-current potential when the vibration component of the second frequency becomes zero is obtained, and the potential is removed from the liquid And an in-liquid potential measurement procedure with a potential of

  As a desirable aspect of the present invention, in the submerged potential measurement method, the direct current potential when the vibration component of the second frequency becomes 0 at a position where the probe is away from the measurement target, and the probe The difference between the DC potential when the vibration component of the second frequency becomes 0 in a state where it is determined that the measurement object is in contact with the measurement object, and the liquid at the position where the probe is separated from the measurement object. A medium potential is preferable.

  As a desirable aspect of the present invention, in the liquid potential measurement method, when measuring two or more potentials in the liquid, the potential application procedure, the contact determination procedure, the surface potential measurement procedure, The probe moving procedure and the liquid potential measurement procedure are repeated, and the relationship between the potential in the liquid and the position of the potential is obtained from the measurement result of the potential at two or more points in the liquid. Using at least one of a linear function portion, an exponential function portion of the relationship, and a connecting portion of the linear function portion and the exponential function portion, and the thickness of the charge fixing layer in the liquid, and the liquid It is preferable to determine at least one of the effective thickness of the charge diffusion layer therein, the sign of the counter ion, and the excess or deficiency of the counter ion existing at the boundary between the charge fixing layer and the charge diffusion layer.

  In order to solve the above-described problems and achieve the object, an in-liquid potential measuring device according to the present invention includes a liquid holding means for holding a measurement object arranged in a liquid together with the liquid, and a free end side of the cantilever. Potential application for applying to the probe by superimposing a provided probe, vibration applying means for vibrating the cantilever at a first frequency, a DC potential, and an AC potential having a second frequency different from the first frequency Means, moving means for moving at least one of the probe and the measurement object in a direction in which the probe and the measurement object are separated from each other or in an approaching direction, and displacement detection means for detecting displacement of the cantilever A first vibration detecting means for detecting a vibration component of the first frequency from displacement information of the cantilever detected by the displacement detecting means, and the can detected by the displacement detecting means. Second vibration detection means for detecting a vibration component of the second frequency from lever displacement information, and the vibration amplitude of the first frequency detected by the first frequency detection means are maintained at a predetermined constant value. Position control means for controlling the distance between the probe and the measurement object; and potential control means for controlling the DC potential so that the vibration component of the second frequency detected by the second frequency detection means becomes zero. A surface detecting means for detecting a surface of the measurement object based on information representing a distance between the probe and the measurement object; and a potential on the surface of the measurement object and a potential in the liquid based on the DC potential. And a potential measuring means to be obtained.

  According to the present invention, the surface potential of a substance placed in a liquid and the potential structure on the liquid side affected by the surface potential state can be measured on a micro scale.

FIG. 1 is a configuration diagram of a liquid potential measuring apparatus according to the present embodiment. FIG. 2 is a flowchart showing the procedure of the liquid potential measuring method according to the present embodiment. FIG. 3A is an explanatory diagram of the liquid potential measuring method according to the present embodiment. FIG. 3-2 is an explanatory diagram of the liquid potential measuring method according to the present embodiment. FIG. 3C is an explanatory diagram of the liquid potential measuring method according to the present embodiment. FIG. 3-4 is an explanatory diagram of the liquid potential measuring method according to the present embodiment. FIG. 3-5 is an explanatory diagram of the liquid potential measuring method according to the present embodiment. FIG. 4A is a diagram illustrating a time change of an excitation signal output from the oscillator to the vibrator in order to vibrate the cantilever. FIG. 4B is a diagram illustrating a change with time of the potential applied to the probe. FIG. 4-3 is a diagram illustrating a potential signal indicating the displacement of the cantilever detected by the displacement detection device. FIG. 5A is an explanatory diagram of a method for determining contact between a probe and a measurement target. FIG. 5B is an explanatory diagram of a method for determining contact between the probe and the measurement target. FIG. 5C is an explanatory diagram of a method for determining contact between the probe and the measurement target. FIG. 6A is an explanatory diagram of a method for adjusting the DC potential applied to the probe. FIG. 6B is an explanatory diagram of a method for adjusting the DC potential applied to the probe. FIG. 6C is an explanatory diagram of a method for adjusting the DC potential applied to the probe. FIG. 7-1 is a diagram illustrating a relationship between the measured potential difference and the in-liquid measurement position information. FIG. 7-2 is a diagram illustrating a relationship between the measured potential difference and the in-liquid measurement position information. FIG. 7C is a diagram illustrating a relationship between the measured potential difference and in-liquid measurement position information. FIG. 8A is a schematic diagram illustrating the charge distribution in the measurement target surface and the liquid. FIG. 8-2 is a schematic diagram illustrating a charge distribution in the measurement target surface and the liquid. FIG. 8C is a schematic diagram illustrating the charge distribution in the measurement target surface and the liquid. FIG. 9A is a diagram illustrating a modification of the apparatus main body constituting the liquid potential measuring apparatus according to the present embodiment. FIG. 9-2 is a diagram illustrating a modification of the apparatus main body constituting the liquid potential measuring apparatus according to the present embodiment. FIG. 9-3 is a diagram illustrating a modification of the apparatus main body constituting the liquid potential measuring apparatus according to the present embodiment. FIG. 9-4 is a diagram illustrating a modification of the apparatus main body constituting the liquid potential measuring apparatus according to the present embodiment. FIG. 9-5 is a diagram illustrating a modification of the apparatus main body constituting the liquid potential measuring apparatus according to the present embodiment.

  Hereinafter, the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by the form (henceforth embodiment) for implementing the following invention. In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those in a so-called equivalent range.

  FIG. 1 is a configuration diagram of a liquid potential measuring apparatus according to the present embodiment. First, the liquid potential measuring apparatus according to the present embodiment will be described with reference to FIG. The liquid potential measuring apparatus 1 shown in FIG. 1 measures the potential on the surface of an object (measurement target) SA existing in the liquid and the potential of the liquid existing near the surface of the object. The in-liquid potential measuring device 1 is a kind of scanning probe microscope (SPM), and moves the probe 5 provided on the free end side of the cantilever 4 so as to trace the surface of the measurement target SA. The surface potential of the target SA and the potential of the liquid LI existing in the vicinity thereof are measured, or the surface state of the measurement target SA is detected.

  The liquid potential measuring device 1 includes a measuring device main body 100 and a measurement control device 50. The measuring device main body 100 includes a signal detection device 101 and an operation control / information detection system 102. The signal detection device 101 constituting the measurement device main body 100 is a stage 2, a liquid container 3 that is a liquid holding unit, a cantilever 4, a probe 5, a vibrator 6 that is a vibration applying unit, and a moving unit. And an XYZ scanning device 8.

  The stage 2 is a flat plate-like member, has a flat surface portion, and places a measurement target SA, which is a target for measuring an electric potential and a surface, on the flat surface portion. The liquid container 3 is attached to the stage 2 and holds the liquid LI in a space formed by the stage 2 and the liquid container 3. Further, at least a cantilever 4 having a probe 5 is disposed in the space of the liquid container 3. An opening 7 o is provided in the part (ceiling part) of the liquid container 3 facing the cantilever 4. The opening 7o is provided with a light transmission window 7 that transmits light.

  One end of the cantilever 4 is fixed to the XYZ scanning device 8 and the vibrator 6, and the unfixed end is a free end. A probe 5 is attached to the free end of the cantilever 4. The cantilever 4 is composed of an elastic body. The cantilever 4 is configured by, for example, silicon or a silicon nitride film or silicon oxide film formed on silicon. In the present embodiment, the cantilever 4 is made of silicon.

  The probe 5 can scan the measurement target region on the surface of the measurement target SA by causing the XYZ scanning device 8 to scan the cantilever 4 in the X direction or the Y direction. The probe 5 is made of at least a part of a conductive material (for example, a platinum sputtered film), is generated by an AC potential generator 21 and a DC potential generator 22 described later, and is added by an addition calculator 23. Is applied. With such a configuration, the probe 5 receives an atomic force and an electrostatic force with the measurement target SA. The probe 5 detects the surface shape and position of the measurement target SA, and measures the potential in the liquid on the surface of the measurement target SA and in the vicinity of the surface. In the present embodiment, since the position and potential are measured by the single probe 5 and cantilever 4, the measurement accuracy can be improved.

  The vibrator 6 is composed of a piezoelectric element (for example, a piezo element). The vibrator 6 applies a periodically changing force to the cantilever 4 to vibrate the cantilever 4 at a predetermined frequency. As a result, the probe 5 attached to the free end of the cantilever 4 vibrates at a frequency at which the cantilever 4 vibrates.

  The XYZ scanning device 8 includes a piezoelectric element (for example, a piezo element). In the present embodiment, the XYZ scanning device 8 is composed of, for example, three piezoelectric elements whose expansion and contraction directions are orthogonal to each other, and each piezoelectric element expands and contracts to move the cantilever 4 in the X, Y, and Z directions. Move. Here, the Z direction is a direction orthogonal to the plane portion of the stage 2, and the X direction and the Y direction are orthogonal to the Z direction. The X direction and the Y direction are orthogonal to each other. Of the piezoelectric elements constituting the XYZ scanning device 8, the one that moves the cantilever 4 in the Z direction corresponds to a moving means. That is, the moving means moves the probe 5 in a direction away from the measurement target SA or a direction approaching the measurement target SA by moving the cantilever 4 in a direction parallel to the Z direction.

  In the present embodiment, the probe 5 is moved by the XYZ scanning device 8 that is a moving unit, but the moving unit is not limited to the one that moves the probe 5. For example, the stage 2 on which the measurement target SA is placed may be moved in a direction away from the probe 5 or a direction approaching the probe 5. In other words, the moving means according to the present embodiment moves at least one of the probe 5 and the measurement target SA (or both) in a direction in which the probe 5 and the measurement target SA are separated or approached. That's fine.

  Next, the operation control / information detection system 102 will be described. The operation control / information detection system 102 includes a light emitting element 9, a light receiving element 10, a displacement detecting device 11, a first lock-in amplifier 12, a first vibration detector 13, an oscillator 14, a first FB circuit 15, a Z scanning driving device 16, An X scan drive device 17, a Y scan drive device 18, a second lock-in amplifier 19, a second vibration detector 20, an AC potential generation device 21, a DC potential generation device 22, an addition calculator 23, and a second FB circuit 24 are included. Composed. With these components, the operation control / information detection system 102 has a function of controlling the position of the cantilever 4 and the operation of the XYZ scanning device 8 and detecting the displacement of the cantilever 4.

  The oscillator 14 causes the vibrator 6 to vibrate at the first frequency by giving an excitation signal having a predetermined frequency (first frequency) to the vibrator 6 that vibrates the cantilever 4. As a result, the cantilever 4 vibrates at the first frequency. The first frequency is, for example, a frequency (fr) near the resonance frequency of the cantilever 4. The Z scanning driving device 16, the X scanning driving device 17, and the Y scanning driving device 18 operate the respective piezoelectric elements constituting the XYZ scanning device 8 to move the cantilever 4 in the X direction, the Y direction, and the Z direction. .

  The light emitting element 9, the light receiving element 10, and the displacement detection device 11 are displacement detection means that detects the displacement of the cantilever 4 (corresponding to the displacement of the probe 5) using an optical lever. The light emitting element 9 is, for example, a laser light emitting element, and irradiates light (laser light) LL toward the cantilever 4. The light LL is irradiated to the cantilever 4 through the light transmission window 7, is reflected by the cantilever 4, and enters the light receiving element 10. By providing the light transmission window 7 in the liquid container 3, the light LL can be irradiated to the cantilever 4 in the liquid container 3 and the reflected light can be received by the light receiving element 10.

  In the present embodiment, the light receiving element 10 is, for example, a four-divided photodiode, and includes four light receiving portions 10a, 10b, 10c, and 10d. When the cantilever 4 is stationary, the light LL reflected by the cantilever 4 is configured to irradiate the center of the light receiving element 10. At this time, each of the four light receiving units 10a, 10b, 10c, and 10d is irradiated with ¼ of the irradiation spot LS of the light LL.

  When the cantilever 4 vibrates, the cantilever 4 is periodically deformed. By this deformation, the angle of the light LL reflected by the cantilever 4 changes, and the position of the irradiation spot LS irradiated on the light receiving element 10 changes. Then, a difference arises in the photovoltaic power of each light-receiving part 10a, 10b, 10c, 10d. Since the difference in the photovoltaic power is correlated with the position of the irradiation spot LS that changes due to the deformation of the cantilever 4, the displacement due to the deformation of the cantilever 4 can be obtained based on the difference in the photovoltaic power. The displacement detection device 11 acquires a signal output from the light receiving element 10, that is, a signal corresponding to the photovoltaic power, and outputs a signal corresponding to the displacement of the cantilever 4 (displacement information of the cantilever 4). Here, the displacement detection means is not limited to the one using the optical lever described above. For example, the displacement of the cantilever 4 or the probe 5 may be detected by imaging the cantilever 4 or the probe 5 with an imaging means such as a camera and processing the output of the image.

  The first lock-in amplifier 12 and the first vibration detector 13 detect the first vibration component (more specifically, vibration amplitude) from the displacement information of the cantilever 4 detected by the displacement detector 11. It functions as a detection means. The first lock-in amplifier 12 acquires the excitation signal generated by the oscillator 14 as a reference signal, and acquires the displacement information of the cantilever 4 detected by the displacement detection device 11. The first lock-in amplifier 12 detects a vibration component having the same frequency as the reference signal from the displacement information of the cantilever 4 and outputs the detected vibration component to the first vibration detector 13. Accordingly, the first vibration detector 13 detects a vibration component having a frequency equal to the frequency of the reference signal, that is, the vibration signal (that is, the first frequency) from the displacement information of the cantilever 4 detected by the displacement detection device 11.

  The first FB (feedback) circuit 15 is a position control unit, and acquires the vibration component (vibration component of the first frequency) detected by the first vibration detector 13. Then, the first FB circuit 15 operates the XYZ scanning device 8 via the Z scanning drive device 16 so as to keep the vibration amplitude of the vibration component of the first frequency at a predetermined constant value, and the probe 5 and the measurement target SA. And control the distance. That is, the first FB circuit 15 feeds back the distance between the probe 5 and the measurement target SA so that the deviation between the vibration amplitude of the vibration component detected by the first vibration detector 13 and a predetermined constant value becomes zero. Control.

  The AC potential generator 21 generates an AC potential having a second frequency (fe) different from the frequency (first frequency fr) of the excitation signal for vibrating the cantilever 4. The DC potential generator 22 generates a DC potential having a predetermined magnitude. The addition computing unit 23 adds the AC potential generated by the AC potential generating device 21 and the DC potential generated by the DC potential generating device 22 and applies the sum to the probe 5. As described above, the AC potential generation device 21, the DC potential generation device 22, and the addition calculator 23 function as a potential application unit.

  The second lock-in amplifier 19 and the second vibration detector 20 detect the second vibration component (more specifically, vibration amplitude) from the displacement information of the cantilever 4 detected by the displacement detection device 11. It functions as a detection means. The second lock-in amplifier 19 acquires an AC potential signal generated by the AC potential generation device 21 as a reference signal, and acquires displacement information of the cantilever 4 detected by the displacement detection device 11. The second lock-in amplifier 19 detects from the displacement information of the cantilever 4 a frequency equal to the reference signal, that is, a vibration component having the second frequency, and outputs the vibration component to the second vibration detector 20. Accordingly, the second vibration detector 20 has a frequency equal to the frequency of the reference signal, that is, the AC potential generated by the AC potential generation device 21 (second frequency) from the displacement information of the cantilever 4 detected by the displacement detection device 11. Detect vibration components.

  The second FB (feedback) circuit 24 is a potential control unit, and acquires the vibration component (the vibration component of the second frequency) detected by the second vibration detector 20. The second FB circuit 24 controls (feedback control) the direct-current potential generated by the DC potential generation device 22 so that the vibration component becomes zero, more specifically, the vibration amplitude becomes zero. .

  Next, the measurement control device 50 will be described. The measurement control device 50 includes a processing unit 51, a storage unit 52, an input / output unit (I / O) 53, a drawing device 54, and an input device 55. The processing unit 51 and the storage unit 52 are connected via an input / output unit 53 and configured to exchange information with each other. The drawing device 54 and the input device 55 are connected to the input / output unit 53. Accordingly, the drawing device 54 acquires a control signal or the like from the processing unit 51 through the input / output unit 53, and the input device 55 inputs a command or the like to the processing unit 51 through the input / output unit 53.

  The processing unit 51 is configured by, for example, a CPU (Central Processing Unit). The storage unit 52 includes a primary storage device such as a RAM (Random Access Memory) and a ROM (Read Only Memory), and a secondary storage device such as a magnetic disk and a flash memory. The storage unit 52 stores a computer program for executing the liquid potential measurement method according to the present embodiment, and stores measurement results (potential and surface shape) obtained by the liquid potential measurement method according to the present embodiment. Save it.

  The processing unit 51 includes a control unit 51a, a surface detection unit 51b, a potential measurement unit 51c, and a position information acquisition unit 51d. The processing unit 51 reads the instruction code sequentially from the computer program for executing the submerged potential measurement method according to the present embodiment stored in the storage unit 52, and processes the control unit 51a and the surface detection. The function of the part 51b, the electric potential measurement part 51c, and the position information acquisition part 51d is implement | achieved.

  The control unit 51 a sends a control signal for operating a predetermined component of the signal detection device 101 constituting the measurement device main body 100 to a predetermined component of the operation control / information detection system 102 constituting the measurement device main body 100. Output. Accordingly, the control unit 51a controls the measurement apparatus main body 100. In addition, the control unit 51 a controls drawing on the drawing device 54 and generates a control signal based on a command input by the input device 55.

  The surface detection unit 51b is surface detection means, and detects that the probe 5 is in contact with the surface of the measurement target SA based on information representing the distance between the probe 5 and the measurement target SA. Detect the surface. The potential measuring unit 51c is a potential measuring unit, acquires a DC potential output from the DC potential generating device 22, and determines the potential on the surface of the measurement target SA and the potential in the liquid based on the DC potential. The position information acquisition unit 51d acquires the position information of the probe 5 in the Z direction from the Z scanning drive device 16, and stores the potential measured at the position where the position information is acquired and the position information in association with each other in the storage unit 52. To do.

  The drawing device 54 draws the surface potential or liquid potential of the measurement target SA, the surface shape of the measurement target SA, or the like obtained by measuring by the measurement device main body 100 and processing information by the measurement control device 50. Is. As the drawing device 54, for example, a display device such as a liquid crystal display or an image output device such as a printer or a plotter can be used. The input device 55 outputs to the processing unit 51 a command for operating the measurement device main body 100 and a command for causing the measurement device main body 100 to measure a potential and a shape. Next, the procedure of the liquid potential measuring method according to this embodiment will be described.

  FIG. 2 is a flowchart showing the procedure of the liquid potential measuring method according to the present embodiment. 3A to 3C are explanatory diagrams of the liquid potential measuring method according to the present embodiment. FIG. 4A is a diagram illustrating a time change of an excitation signal output from the oscillator to the vibrator in order to vibrate the cantilever. FIG. 4B is a diagram illustrating a change with time of the potential applied to the probe. FIG. 4-3 is a diagram illustrating a potential signal indicating the displacement of the cantilever detected by the displacement detection device. 5A to 5C are explanatory diagrams of a method for determining contact between the probe and the measurement target. 6A to 6C are explanatory diagrams of a method for adjusting the DC potential applied to the probe. The vertical axis in FIGS. 4-1 to 6-3 is the potential, and the horizontal axis is the time.

  The liquid potential measuring method according to the present embodiment can be realized by the liquid potential measuring apparatus 1 shown in FIG. In starting the measurement, first, in step S101, the measurement target SA is set on the stage 2. The measurement object SA is insulated or given a potential as necessary. Next, the process proceeds to step S102, and the liquid LI is filled in the liquid container 3. As the liquid LI, a liquid according to the purpose of evaluation is used. For example, when evaluating the action of an additive in plating, a liquid in which the additive is added to a solvent is used. When it is desired to evaluate the relationship between an electrolyte of a battery and an electrode, a liquid corresponding to the electrolyte is used. Is used. Further, when evaluating the dispersibility of a pigment or the like, a liquid obtained by adding a dispersant or the like to a solution containing the pigment is used.

  Next, it progresses to step S103 and the probe 5 is installed in the vicinity of measurement object SA. Here, the probe 5 and the cantilever 4 are arranged in the liquid container 3 filled with the liquid LI. When the installation of the probe 5 is completed, the process proceeds to step S104, and the cantilever 4 is vibrated by the vibrator 6. Here, regardless of the order of step S104 and step S105 to be described later, either may be executed first, or both steps may be executed simultaneously.

  In vibrating the cantilever 4 using the vibrator 6, for example, the input device 55 outputs a command (vibration start command) for vibrating the cantilever 4 to the measurement control device 50. Then, the control part 51a which comprises the process part 51 of the measurement control apparatus 50 acquires a vibration start command, and outputs the command which makes the vibrator | oscillator 6 output the vibration signal of 1st frequency fr to the oscillator 14. FIG. In response to this command, the oscillator 14 outputs an excitation signal Gr having the first frequency fr to the vibrator 6 as shown in FIG. 4A to vibrate the vibrator 6 at the first frequency fr. As a result, the cantilever 4 vibrates at the first frequency fr, and the probe 5 also vibrates at the first frequency fr. In the present embodiment, the first frequency fr is 50 kHz.

The excitation signal Gr [V] is expressed as in Expression (1). Further, the displacement amount (mechanical vibration displacement amount) Dr [nm] of the cantilever 4 that is vibrated by the vibrator 6 is expressed by the equation (2). Here, Gr0 is the amplitude [V] of the excitation signal (AC voltage) output from the oscillator 14, and Ar1 is the amplitude [nm] of the cantilever 4 that vibrates in the liquid by the vibrator 6.
Gr = Gr0 × sin (2 × π × fr × t) (1)
Dr = Ar1 × sin (2 × π × fr × t) (2)

Next, the process proceeds to step S105, and a potential is applied to the probe 5. Steps S104 and S105 correspond to a potential application procedure. In applying a potential to the probe 5, for example, the input device 55 outputs a command (potential application start command) for applying a potential to the probe 5 to the measurement control device 50. Then, the control unit 51a obtains a potential application start command, outputs a command to generate an AC potential of the second frequency fe to the AC potential generation device 21, and sends a command to generate a DC potential to the DC potential generation device 22. Output. In response to this command, as shown in FIG. 4B, the AC potential generation device 21 generates an AC potential Va [V] of the second frequency fe and outputs it to the addition calculator 23, and also generates a DC potential. The device 22 generates a DC potential Vd [V] and outputs it to the addition calculator 23. Thereby, the addition computing unit 23 applies a potential (probe applied potential) Vp [V] obtained by adding (superimposing) the AC potential Va and the DC potential Vd to the probe 5. The AC potential Va is expressed by equation (3), and the probe application potential Vp is expressed by equation (4). Here, Va0 is the amplitude [V] of the AC potential generated by the AC potential generation device 21. In the present embodiment, the second frequency fe is 17 kHz.
Va = Va0 × sin (2 × π × fe × t) (3)
Vp = Va0 × sin (2 × π × fe × t) + Vd (4)

The displacement amount (electrostatic force displacement amount) De [nm] of the cantilever 4 by the probe application potential Vp is as follows. First, the electrostatic force Fe [N] acting on the cantilever 4 by the probe application potential Vp is expressed as in Expression (5). Here, Vs is the potential [V] of the liquid LI existing near the surface of the measurement target SA or the probe 5, and C is near the probe 5 and the surface of the measurement target SA or the vicinity of the probe 5. Capacitance [F] between the existing liquid LI.
Fe = −1 / 2 × (∂C / ∂z) × (Vp−Vs) ² ... (5)

When Expression (5) is modified according to the trigonometric formula, Expression (5) is expressed as Expression (6).
Fe = −1 / 2 × (∂C / ∂z) × [{(Vd−Vs) ² + (Va0) ² } + 2 × Va0 × (Vd−Vs) × sin (2 × π × fe × t) − 1/2 × (Va0) ² × cos (2 × 2 × π × fe × t)] (6)

Formula (6) is expressed as Formula (7) using Fe0, Fe1, and Fe2. Here, Fe0 is the direct current component [N] in the first term on the right side of Equation (6), Fe1 is the amplitude [N] of the fe component in the second term on the right side of Equation (6), and Fe2 is the equation (6 ) Is the amplitude [N] of the 2 × fe component in the third term on the right side.
Fe = Fe0 + Fe1 × sin (2 × π × fe × t) + Fe2 × cos (2 × 2 × π × fe × t) (7)

Since the electrostatic force displacement amount De is sufficiently small, Hooke's law that the electrostatic force displacement amount De due to the electrostatic force Fe is proportional to Fe (De∝Fe) is approximately established. Therefore, the electrostatic force displacement amount De is expressed as in Expression (8). Here, Ae0, Ae1, and Ae2 in the equation (8) are respectively the DC component [nm] and the amplitude of the fe component [nm] of the electrostatic force displacement amount De due to the electrostatic force proportional to Fe0, Fe1, and Fe2 in the equation (7). ] 2 × fe component amplitude [nm].
De = Ae0 + Ae1 × sin (2 × π × fe × t) + Ae2 × cos (2 × 2 × π × fe × t) (8)

  When the cantilever 4 is vibrated by the vibrator 6 and the probe application potential Vp is applied to the probe 5, in the present embodiment, the control unit 51a irradiates the cantilever 4 with the light LL from the light emitting element 9, and The light LL reflected by the cantilever 4 is received by the light receiving element 10. Accordingly, the displacement detection device 11 detects the displacement (cantilever displacement amount) D of the cantilever 4.

The cantilever displacement amount D [nm] is obtained by superimposing the mechanical vibration displacement amount Dr by the vibrator 6 and the electrostatic force displacement amount De due to the electrostatic force caused by the probe applied potential Vp, as shown in Expression (9). It is expressed in
D = Dr + De = Ar1 × sin (2 × π × fr × t) + Ae0 + Ae1 × sin (2 × π × fe × t) + Ae2 × cos (2 × 2 × π × fe × t) (9)

Here, the displacement detection means (light emitting element 9, light receiving element 10, and displacement detecting device 11) using an optical lever system converts the electric signal output as a signal of the cantilever displacement amount D, that is, the displacement detecting device 11. Let E [V] be the signal output from. E is proportional to the cantilever displacement amount D (E∝D), and is expressed as in equation (10). Here, Er1, Ee0, Ee1, and Ee2 are the amplitude [V] of the fr component of the signal output from the displacement detection device 11 and proportional to the Ar1, Ae0, Ae1, and Ae2 of the equation (9), respectively, The amplitude [V], the amplitude [V] of the fe component, and the amplitude [V] of the 2 × fe component. Er is a signal [V] corresponding to the mechanical vibration displacement amount Dr of the signal E output from the displacement detection device 11, and Ee is a signal [V] corresponding to the electrostatic force displacement amount De. Er is the formula (11), and Ee is the formula (12). The signals E, Er, and Ee are as shown in FIG.
E = Er + Ee = Er1 × sin (2 × π × fr × t) + Ee0 + Ee1 × sin (2 × π × fe × t) + Ee2 × cos (2 × 2 × π × fe × t) (10)
Er = Er1 × sin (2 × π × fr × t) (11)
Ee = Ee0 + Ee1 × sin (2 × π × fe × t) + Ee2 × cos (2 × 2 × π × fe × t) (12)

  The first lock-in amplifier 12 detects the vibration component of the first frequency fr and outputs it to the first vibration detector 13. This output signal is Er in equation (11). The first vibration detector 13 outputs the vibration amplitude Er1 corresponding to the vibration amplitude Ar1 of the vibration component of the first frequency fr to the first FB circuit 15 from the signal acquired from the first lock-in amplifier 12. The second lock-in amplifier 19 detects the vibration component of the second frequency fe and outputs a corresponding signal to the second vibration detector 20. The signal output from the second lock-in amplifier 19 is the second term of Expression (12), that is, Ee1 × sin (2 × π × fe × t). The second vibration detector 20 detects the signal Ee1 corresponding to the vibration amplitude Ae1 of the vibration component of the second frequency fe from the signal acquired from the second lock-in amplifier 19 and outputs it to the second FB circuit 24. .

  When the cantilever 4 vibrates at the first frequency fr and the probe application potential Vp is applied to the probe 5, the process proceeds to step S106, and the probe 5 is moved to the measurement position. In moving the probe 5 to the measurement position of the measurement target SA, for example, the input device 55 outputs a command (measurement position movement command) for moving the probe 5 to the measurement position of the measurement target SA to the measurement control device 50. To do. Then, the control unit 51a obtains a measurement position movement command, and calculates a direction and a distance necessary for moving the probe 5 from the current position to the measurement position. Then, the control unit 51a generates a command for moving the probe 5 by the calculated distance in the calculated direction, and outputs the command to at least one of the X scanning drive device 17 and the Y scanning drive device 18. As a result, at least one of the X scan driving device 17 and the Y scan driving device 18 drives the XYZ scanning device 8 to move the cantilever 4 in the distance and direction corresponding to the measurement position movement command. Is moved to the measurement position.

  Next, it progresses to step S107 and the control part 51a sets the frequency | count n of measurement to 0. The measurement number n is the number of times of measuring the potential in the liquid separated from the surface of the measurement target SA at the same measurement position, and the value thereof is 1 or more. The number of times of measurement n may be determined in advance, or may be set for each type of measurement target SA or liquid LI, or for each measurement position. If the number of measurements n is set to 0, the process proceeds to step S108.

  In step S108, as shown in FIG. 3A, the probe 5 is brought close to the measurement target SA, and the surface of the measurement target SA is detected. In this case, the vibration amplitude of the first frequency fr is detected in a state where the probe 5 is not in contact with the measurement target SA, and then the probe 5 approaches the measurement target SA while detecting the vibration amplitude of the first frequency fr. Then, the surface of the measurement target SA is detected by controlling the distance between the probe 5 and the measurement target SA so that the vibration amplitude of the first frequency fr is maintained at a predetermined constant value.

  In order to make the probe 5 approach the measurement target SA, the control unit 51a generates a command for moving the probe 5 toward the measurement target SA and outputs the command to the Z scanning drive device 16. Thus, the Z scanning drive device 16 drives the XYZ scanning device 8 to move the cantilever 4 toward the measurement target SA, thereby bringing the probe 5 closer to the measurement target SA. Here, the control unit 51a measures the probe 5 based on, for example, a command (probe approach command) for causing the probe 5 to approach the measurement target SA, which is generated by the input device by input to the input device 55. The probe 5 is moved closer to the measurement target SA, or the probe 5 is moved closer to the measurement target SA with the end of step S107 as a trigger.

  Next, the process proceeds to step S109, and the surface of the measurement target SA is detected by the probe 5. Step S109 corresponds to a contact determination procedure. As illustrated in FIG. 3B, the surface of the measurement target SA can be detected by bringing the probe 5 into contact with the measurement target SA. First, the probe 5 is sufficiently separated from the surface of the measurement target SA. In this case, the cantilever 4 may move in the Z direction while vibrating without contacting the measurement target SA, or in the Z direction. May be stationary. As a result, the atomic force acting between the probe 5 and the measurement target SA can be ignored, and a signal corresponding to the vibration amplitude of the vibration component of the first frequency fr in that case is Er10 [V]. In this case, in Formula (11) described above, Er1 = Er10, and Formula (11) is Er = Er10 × sin (2 × π × fr × t). The time variation of Er is as shown in FIG. The first vibration detector 13 detects the vibration amplitude Er1 of the first frequency fr in a state where the probe 5 is not in contact with the measurement target SA. Then, the first FB circuit 15 acquires an electrical signal corresponding to the vibration amplitude Er1 of the vibration component of the first frequency fr output from the first vibration detector 13. While the first vibration detector 13 detects the vibration amplitude of the first frequency fr and the control unit 51a brings the probe 5 close to the measurement target SA, the first FB circuit 15 has the first frequency fr. The distance between the probe 5 and the measurement target SA is controlled so as to keep the vibration amplitude at a predetermined constant value.

  When the probe 5 and the measurement target SA approach each other until they periodically contact each other, the vibration amplitude Er1 of the vibration component of the first frequency fr is compared with the vibration amplitude Er10 when the probe 5 and the measurement target SA are not in contact with each other. Attenuates. That is, Er1 = α × Er10 <Er10 when an atomic force acts between the probe 5 and the measurement target SA. Here, α is the attenuation rate of the vibration amplitude of the vibration component of the first frequency fr due to the periodic contact between the probe 5 and the measurement target SA, and α <1.

  When the attenuation rate α maintains a predetermined value αc (0.8 in the present embodiment), the probe 5 and the measurement target SA are in periodic contact. That is, the distance Z between the probe 5 and the measurement target SA is zero. On the other hand, FIG. 5C shows the case where the attenuation rate α is smaller than the predetermined value αc (α1 <αc, Er1 = α1 × Er10). In this case, as a result of the vibration amplitude Er1 of the vibration component of the first frequency fr being attenuated excessively, the probe 5 and the measurement target SA are brought too close to each other.

  In the present embodiment, the first FB circuit 15 is configured so that the attenuation rate α maintains a predetermined value αc in the process in which the probe 5 approaches the measurement target SA, that is, the vibration amplitude of the vibration component of the first frequency fr. The distance Z between the probe 5 and the measurement target SA is controlled so that Er1 is kept at a predetermined constant value (αc × Er10). The first FB circuit 15 controls the distance between the probe 5 and the measurement target SA so that α = αc, that is, Er1 = αc × Er10. The time variation of Er at this time is as shown in FIG.

  The value of the attenuation rate α when the probe 5 and the measurement target SA are periodically in contact is determined in advance using, for example, experiments, simulations, or theoretical values. In an experiment, for example, the probe 5 is brought close to the measurement target SA while observing the potential of the measurement target SA in a state where the probe is connected to the ground and the measurement target SA is charged to a predetermined potential. When the potential of the measurement target SA becomes equal to the ground potential, it is determined that the probe 5 and the measurement target SA are in contact with each other, and the attenuation rate α at that time is set to the predetermined value, that is, the probe 5. And the value of the attenuation rate when the measurement object SA periodically contacts.

  The first FB circuit 15 operates the XYZ scanning device 8 via the Z scanning drive device 16 so that the deviation ΔEr1 [V] between the vibration amplitude Er1 obtained from the first vibration detector 13 and αc × Er10 becomes zero. The distance Z between the probe 5 and the measurement target SA is controlled. In this case, the deviation Δα between Er1 / Er10 and αc may be zero. The deviation ΔEr1 or the deviation Δα is information indicating the distance between the probe 5 and the measurement target SA. When the deviation ΔEr1 or the deviation Δα becomes 0, it can be determined that the probe 5 and the measurement target SA are periodically in contact with each other, so that the probe 5 has detected the surface of the measurement target SA.

  In step S109, the surface detection unit 51b of the measurement control device 50 acquires a signal of deviation ΔEr1 or deviation Δα from the first FB circuit 15, and when the deviation ΔEr1 or deviation Δα becomes 0, the probe 5 measures the measurement target. It determines with the surface of SA having been detected, and outputs the information to the positional information acquisition part 51d. Thereby, the surface of the measuring object SA is detected. As described above, the surface detection unit 51b detects the surface of the measurement target SA based on the information indicating the distance between the probe 5 and the measurement target SA. When the position information acquisition unit 51d of the measurement control device 50 acquires information that the surface of the measurement target SA has been detected from the surface detection unit 51b, the position of the probe 5 in the Z direction at that time from the Z scanning drive device 16. The position is set to 0, that is, the surface of the measurement target SA, and the information is stored in a predetermined area of the storage unit 52. Thereafter, the position information acquisition unit 51d outputs information indicating that the position of the probe 5 is stored in the storage unit 52 to the potential measurement unit 51c of the measurement control device 50 together with the address of the area in which the position information of the probe 5 is stored. To do.

  In this embodiment, when detecting the surface of the measurement target SA, the change in the vibration of the cantilever 4 due to the atomic force is used in a state where the probe 5 and the measurement target SA are periodically in contact with each other due to the vibration of the cantilever 4. The probe 5 and the measurement target SA come into contact with each other, so that the position of the surface of the measurement target SA can be accurately captured. Further, since the change in the vibration of the cantilever 4 due to the atomic force acting on the probe 5 is detected using the change in the vibration amplitude of the vibration, the liquid LI in which the resonance Q value of the vibration of the cantilever 4 is lowered. Among them, the change in vibration of the cantilever 4 can be detected with high accuracy. As a result, the potential measurement accuracy can be improved.

  Next, proceeding to step S110, the potential at the position of the probe 5 is determined from the DC potential Vd applied to the probe 5. Step S110 corresponds to a surface potential measurement procedure. As described above, the second vibration detector 20 detects the signal Ee1 corresponding to the vibration amplitude Ae1 of the vibration component of the second frequency fe from the signal acquired from the second lock-in amplifier 19, and sends it to the second FB circuit 24. Output. From the equations (6) to (9), it can be seen that the signal Ee1 detected and output by the second vibration detector 20 is proportional to (Vd−Vs) (Ee1∝ (Vd−Vs)). Therefore, Ee1 can be adjusted by adjusting the DC potential Vd generated by the DC potential generator 22. By setting Ee1 to 0, that is, by setting Vd = Vs, the second term on the right side of Expression (12) can be set to 0. That is, the vibration component of the second frequency fe can be set to zero.

  6A is a time change of a signal output from the second lock-in amplifier 19 when Vd> Vs, and FIG. 6-3 is a graph illustrating the change from the second lock-in amplifier 19 when Vd <Vs. It is a time change of the output signal. In either case, the signal output from the second lock-in amplifier 19 periodically changes with time. On the other hand, FIG. 6-2 shows the time change of the signal output from the second lock-in amplifier 19 when Vd = Vs. When Vd = Vs, the signal output from the second lock-in amplifier 19 is constant at 0 [V] regardless of time.

  Assuming that the direct-current potential Vd = Vd1z0 [V] at which Ee1 = 0, Ee1 = Vd1z0−Vs = 0. Here, since the surface of the measurement target SA is detected by the probe 5 in step S109, the probe 5 periodically contacts the surface of the measurement target SA. Therefore, Vs becomes a potential (surface potential) V0 (Z = 0) [V] on the surface (Z = 0) of the measurement target SA. That is, since Vd1z0-V0 (Z = 0) = 0, V0 (Z = 0) = Vd1z0. Thus, the DC potential Vd is adjusted so that Ee1 = 0, and the DC potential Vd when Ee1 = 0 is the potential at the position of the probe 5. Thereby, the potential at the position of the probe 5 can be measured.

  In step S110, the second FB circuit 24 acquires the signal Ee1 from the second vibration detector 20, and controls the DC potential Vd generated by the DC potential generator 22 so that the signal Ee1 becomes zero. That is, the second FB circuit 24 controls the DC potential Vd so that the vibration component of the second frequency fe detected by the second vibration detector 20 becomes zero. For example, the potential measurement unit 51c is triggered by the information output from the position information acquisition unit 51d to the effect that the position of the probe 5 is stored in the storage unit 52, that is, Ee1 = 0, that is, the second vibration detector 20 A DC potential Vd (= Vd1z0) generated by the DC potential generation device 22 when the output signal (potential signal) Ee1 becomes 0 is acquired from the DC potential generation device 22.

  The trigger for the potential measuring unit 51c to acquire the DC potential Vd generated by the DC potential generating device 22 is not limited to this, and may be a command from the input device 55, for example. Next, the potential measuring unit 51c determines the acquired DC potential Vd as the potential at the current position of the probe 5, in this example, the surface potential V0 (Z = 0). Thereafter, the potential measurement unit 51c reads the current position of the probe 5 from the address output from the position information acquisition unit 51d, and stores it in a predetermined area of the storage unit 52 in association with the determined potential. In the present embodiment, the change in the vibration of the cantilever 4 due to the electrostatic force acting on the probe 5 is detected by the change in the vibration amplitude of the vibration. Therefore, even in the liquid LI in which the resonance Q value of the vibration of the cantilever 4 decreases, the cantilever 4 It is possible to accurately detect a change in vibration.

  When the potential of the probe 5, that is, the potential of the liquid LI near the surface of the measurement target SA or the probe 5 is determined, the process proceeds to step S111. Step S111 corresponds to a probe moving procedure. In step S111, the control unit 51a measures the probe 5 by driving the XYZ scanning device 8 via the Z scanning drive device 16 and moving the cantilever 4 in the Z direction as shown in FIG. It is moved by a predetermined distance ΔZn + 1 from the surface of the target SA. That is, the probe 5 is separated from the surface of the measurement target SA by a predetermined distance ΔZn + 1. Accordingly, the probe 5 is arranged at a position away from the surface of the measurement target SA, and the potential measurement unit 51c measures the potential of the liquid LI at that position. At this stage, since n = 0, the predetermined distance is ΔZ1 [nm]. Here, the movement amount of the probe 5 in the Z direction may be set arbitrarily for each measurement, or may be the same movement amount. When the probe 5 that is in contact with the surface of the measurement target SA is moved from the measurement target SA, the control unit 51a stops the control of the distance between the probe 5 and the measurement target SA by the first FB circuit 15.

  When the probe 5 is moved from the surface of the measurement target SA by a predetermined distance ΔZ, in the present embodiment, the probe 5 is moved in the Z direction, that is, the direction orthogonal to the plane portion of the stage 2 shown in FIG. However, the moving direction of the probe 5 is not limited to this, and the direction having a predetermined angle with respect to the plane portion of the stage 2 may be set as the moving direction of the probe 5. In this case, if the moving distance of the probe 5 is L and the smaller one of the angles formed by the moving direction of the probe 5 and the plane portion of the stage 2 is β, a predetermined distance from the surface of the measurement target SA to the probe 5 is set. The distance ΔZn + 1 can be obtained by L × sin β.

  When the control unit 51a moves the probe 5 from the surface of the measurement target SA by a predetermined distance ΔZ1, the storage unit 52 stores the position information of the probe 5, that is, the information on the measurement position of the potential of the liquid LI to be measured. To a predetermined area. Thereafter, the position information acquisition unit 51d outputs information indicating that the position of the probe 5 is stored in the storage unit 52 to the potential measurement unit 51c of the measurement control device 50 together with the address of the area in which the position information of the probe 5 is stored. To do.

  When the probe 5 is moved by a predetermined distance ΔZ1 in the Z direction, the process proceeds to step S112, and the potential at the position of the probe 5 is determined from the DC potential Vd applied to the probe 5. Step S112 corresponds to a liquid potential measurement procedure. When the DC potential Vd = Vd1z1 [V] at which Ee1 = 0 is obtained at a position away from the surface of the measurement target SA by a predetermined distance ΔZ1, Ee1 = Vd1z1−Vs = 0. Therefore, Vs is a potential (liquid potential) V1 (Z = ΔZ1) [V] at a position (Z = ΔZ1) away from the surface of the measurement target SA by ΔZ1. That is, since Vd1z1-V1 (Z = ΔZ1) = 0, V1 (Z = ΔZ1) = Vd1z1.

  Electrochemical AFM or electrochemical STM can be used as a method for measuring the surface potential state on a micro scale. However, since these measure the potential through an electrochemical reaction that proceeds by passing a current between the probe and the measurement target, the true potential state of the measurement target surface is disturbed by the electrochemical reaction. Cannot be avoided. In addition, by measuring the potential difference between the probe immersed in the liquid and the measurement target without passing an electric current between the probe and the measurement target, the potential near the surface of the measurement target placed in the liquid is measured. Is measured, a potential difference exists between the probe and the measurement target. For this reason, the electric double layer is formed by moving liquid molecules or particles such as molecules, atoms, ions dissolved in the liquid to the probe or sample surface, eliminating the influence of potential difference in the electric double layer. Can not do it. On the other hand, in this embodiment, since the potential of the probe 5 is equal to the surroundings, the influence of the electric double layer due to the liquid polarization of the liquid LI existing in the vicinity of the probe 5 can be eliminated. Thereby, in this embodiment, the measurement accuracy of the surface potential of the measurement target SA and the liquid potential is improved.

  In step S112, the second FB circuit 24 acquires the signal Ee1 from the second vibration detector 20, and controls the DC potential Vd generated by the DC potential generator 22 so that the signal Ee1 becomes zero. That is, the second FB circuit 24 controls the DC potential Vd so that the vibration component of the second frequency fe detected by the second vibration detector 20 becomes zero. The potential measuring unit 51c is triggered by the information that the probe 5 has been moved from the surface of the measurement target SA by the predetermined distance ΔZ1, as a trigger, ie, a signal (potential signal) output by the second vibration detector 20 ) The DC potential Vd (= Vd1z1) generated by the DC potential generating device 22 when Ee1 becomes 0 is acquired from the DC potential generating device 22. The trigger for the potential measuring unit 51c to acquire the DC potential Vd generated by the DC potential generating device 22 is not limited to this, and may be a command from the input device 55, for example.

  Next, the potential measuring unit 51c converts the acquired DC potential Vd into the potential at the current position of the probe 5, in this example, the potential of the liquid LI at a position away from the surface of the measurement target SA by ΔZ1 (potential in liquid). Determine as V1. Thereafter, the potential measurement unit 51c reads the current position of the probe 5 from the address output from the position information acquisition unit 51d, and stores it in a predetermined area of the storage unit 52 in association with the determined potential. Next, the process proceeds to step S113, where the potential measuring unit 51c reads the liquid potential V1 (Z = ΔZ1) and the surface potential V0 (Z = 0) from the storage unit 52, and sets the liquid potential V1 (Z = ΔZ1). A potential difference ΔV1 [V] (= V1 (Z = ΔZ1) −V0 (Z = 0)) with respect to the surface potential V0 (Z = 0) is obtained, and the liquid potential V1 (in the Z direction) is determined in a predetermined region of the storage unit 52. Z = ΔZ1) is stored in association with the measured position information (in-liquid measured position information). As described above, in this embodiment, the potential structure and the like are evaluated using the potential difference ΔV1 between the liquid potential V1 (Z = ΔZ1) and the surface potential V0 (Z = 0). Evaluation is possible even when the value fluctuates. Note that the procedure for obtaining the potential difference ΔV1 in step S113 is not necessarily required, and the potential structure and the like may be evaluated using the liquid potential V1.

  When the in-liquid potential V1 (Z = ΔZ1) at a position away from the surface of the measurement target SA by ΔZ1 is measured and the potential difference ΔV1 is obtained, the process proceeds to step S114. In step S114, the control unit 51a adds 1 to the current measurement number n to obtain a new measurement number n. In this case, since n = 0 is set in step S107, the new measurement count n is 1. Next, it progresses to step S115 and the control part 51a determines whether the present measurement frequency n is equal to the predetermined predetermined measurement frequency nf set beforehand. The prescribed measurement number nf is the number of times of measuring the potential in the liquid LI.

  When it is determined No in step S115, that is, when the control unit 51a determines that n <nf, the process returns to step S108, and the procedure up to step S114 is executed to perform liquids at a plurality of different positions in the Z direction. The potential in LI is measured. In this case, as shown in FIG. 3-4, in step S108 and step S109, the probe 5 is again brought into contact with the surface of the measurement target SA to measure the surface potential, and then in step S111, the position is different from the previous time. The probe 5 is moved. Thus, whenever the electric potential in the liquid is measured at a position different from the previous time in the Z direction, the probe 5 can be prevented from being charged by bringing the probe 5 into contact with the surface of the measurement target SA. As a result, the measurement accuracy of the surface potential and the liquid potential is improved.

  In this embodiment, every time the potential in the liquid is measured at a position different from the previous time in the Z direction, the surface of the measurement target SA is also brought into contact with the potential in the liquid LI by bringing the probe 5 into contact with the surface of the measurement target SA. Detected every time As a result, the position of the probe 5 in the Z direction is detected every time the potential is measured, and is obtained with reference to the updated surface of the measurement target SA. As a result, even if a displacement of the position of the probe 5 occurs due to thermal drift of the piezoelectric element used in the XYZ scanning device 8 used for scanning the probe 5, the influence is minimized and the potential measurement accuracy is minimized. Can be suppressed.

  When the surface potential V0 (Z = 0) is determined in step S110, the process proceeds to step S111, and the control unit 51a drives the XYZ scanning device 8 via the Z scanning drive device 16 as shown in FIG. By moving 4 in the Z direction, the probe 5 is moved from the surface of the measurement target SA by a predetermined distance ΔZn + 1. In this case, since n = 1 in the previous step S114, the predetermined distance is ΔZ2. Thereby, the potential in the liquid LI can be measured at a position different from the previous time in the Z direction.

  Thereafter, in step S112, the potential V2 in the liquid LI is measured at a position away from the surface of the measurement target SA by ΔZ2, and a potential difference ΔV2 [V] (= V2 (Z = ΔZ2) −V0 (Z = 0)) is obtained. And it progresses to step S114 and the control part 51a adds 1 to the present measurement frequency n, and is set as the new measurement frequency n. In this case, since n = 1 is set in the previous step S114, the new number of measurements n is 2. Then, the process proceeds to step S115, where the control unit 51a determines whether or not the current measurement number n is equal to a preset predetermined measurement number nf, and repeats step S108 to step S115 until n = nf.

  In the present embodiment, as described above, after detecting the surface of the measurement target SA, the potential of the surface of the measurement target SA is measured, and then the probe 5 is moved away from the surface of the measurement target SA by a predetermined amount. The potential in the liquid LI is measured, and the difference from the potential on the surface of the measurement target SA immediately before is defined as the potential in the liquid LI. Thus, charging of the probe 5 can be avoided by contacting the probe 5 with the measurement target SA. Further, the potential and the position of the probe 5 are accurately measured by correcting the difference between the liquid potential and the surface potential of the measurement target SA and correcting the position of the probe 5 by detecting the surface of the measurement target SA. Can be controlled.

  When it determines with Yes at step S115, ie, when the control part 51a determines with n = nf, it progresses to step S116. In step S116, the control unit 51a determines whether or not to measure another position of the measurement target SA. When the other position is not measured (No at Step S116), the measurement of the potential ends, and the process proceeds to Step S117. When another position is measured (step S116, Yes), the process returns to step S106 and the subsequent procedure is executed.

  When measuring other positions, the control unit 51a uses the Z-scanning driving device 16, the X-scanning driving device 17, and the positional information of the measurement object SA at each position where the potential is measured, that is, the displacement amount of the XYZ scanning device 8, as follows. Acquired from the Y scanning drive device 18 and stored in a predetermined area of the storage unit 52 in association with the measured potential data. Note that the position information in the Z direction is on the surface of the measurement target SA. By measuring the potential at a plurality of positions, a plurality of pieces of position information of the measurement target SA can be obtained. And the surface shape of measurement object SA can be calculated | required from several positional information.

  7A to 7C are diagrams illustrating the relationship between the measured potential difference and the in-liquid measurement position information. 8A to 8C are schematic diagrams illustrating the charge distribution in the measurement target surface and the liquid. The charge distribution shown in FIG. 8A corresponds to the relationship between the potential difference shown in FIG. 7A and the measurement position information in liquid, and the charge distribution shown in FIG. 8B shows the potential difference shown in FIG. Corresponding to the relationship with the measurement position information, the charge distribution shown in FIG. 8C corresponds to the relationship between the potential difference and the in-liquid measurement position information shown in FIG. The horizontal axis of FIGS. 7-1 to 7-3 and FIGS. 8-1 to 8-3 is the distance from the surface of the measurement target SA, and 0 is the surface of the measurement target SA. Moreover, the vertical axis | shaft of FIGS. 7-1-FIGS. 7-3 is an electrical potential difference.

  In step S117, the control unit 51a reads out the potential difference ΔV [V] (here, the generic name of ΔV1, ΔV2,... ΔVnf) stored in the storage unit 52 and the in-liquid measurement position information, and the potential difference. The drawing device 54 of the measurement control device 50 shown in FIG. 1 draws the relationship between ΔV and in-liquid measurement position information. The result is as shown in FIGS. 7-1 to 7-3, for example. When the relationship between the potential difference ΔV and the measurement position information in the liquid is drawn, the process proceeds to step S118, and the charge distribution in the surface of the measurement target SA and the liquid LI is evaluated based on the drawn result. Table 1 shows the evaluation criteria. The charge distribution in the surface of the measurement target SA and in the liquid LI may be evaluated using the liquid potential U and the surface potential V0. In this case, the control unit 51a reads out the liquid potential U [V] (herein, the generic name of V1, V2,... Vnf) and the liquid measurement position information stored in the storage unit 52, The drawing device 54 of the measurement control device 50 shown in FIG. 1 draws the relationship between the liquid potential U and the liquid measurement position information.

  As shown in FIGS. 8A to 8C, the distance from the surface of the measurement target SA to the distance Zc is a layer called a charge fixing layer (reference numeral 40), and the region larger than the distance Zc is a charge diffusion layer ( This is a layer called 41). A charge (surface charge) 42 exists on the surface of the measurement target SA, and an ion (counter ion) 43 that forms a pair with the surface charge exists at the boundary between the charge fixing layer 40 and the charge diffusion layer 41. The counter ion 43 is an ion in the liquid LI and has a charge opposite to the surface charge 42. Further, as shown in FIGS. 7-1 to 7-3, in the charge fixing layer, the potential is linear, that is, changes according to a linear function of the distance from the surface to be measured, and in the charge diffusion layer, the potential is It changes according to the exponential function of the distance from the surface to be measured.

  As shown in Table 1, in this embodiment, a slope of a linear function portion (hereinafter referred to as a straight line portion) F1 (a portion indicated by A in FIG. 7-1), a straight line between the potential difference ΔV and the in-liquid measurement position information. The sign Sn of the counter ion and the excess / deficiency Bn of the counter ion with respect to the surface charge are evaluated according to the shape of the connection part (the part indicated by C in FIG. 7-1) between the part F1 and the exponential function part F2. Further, the thickness δFn [nm] of the charge fixing layer and the effective thickness (Debye length) δDn [nm] of the charge diffusion layer are obtained. The thickness δFn of the charge fixing layer is a distance Zc from the surface of the measurement target SA to the connection portion (portion indicated by C in FIG. 7-1) between the straight line portion F1 and the exponential function portion F2. The effective thickness of the charge diffusion layer is based on the connecting portion between the straight line portion F1 and the exponential function portion F2, and the potential difference ΔV1c [V] of the asymptotic line of the exponential function portion F2 at the connecting portion between the straight line portion F1 and the exponential function portion F2. ] Is a distance to a position that becomes 1 / e (e is the base of the natural number). Here, the straight line portion F1 is a portion where the potential changes according to a linear function of the distance from the measurement target surface (region up to the distance Zc in FIG. 7-1), and the exponential function portion F2 is the potential measured. It is a portion that changes according to an exponential function of the distance from the target surface. In addition, the linear part F1 should just be considered that the change with respect to the distance of the measured liquid potential is a linear function, and does not need to be a strict linear function. Similarly, the exponential function portion F2 is not necessarily a strict exponential function, as long as the change in the measured liquid potential with respect to the distance can be regarded as an exponential function.

  For example, in the example shown in FIG. 7A, the slope of the straight line portion F1 is positive, the shape of the connecting portion between the straight line portion F1 and the exponential function portion F2 is convex upward, and the straight line portion F1 and the exponential function portion The connecting portion with F2 is a polygonal line. For this reason, as shown in FIG. 8A, the charge distribution can be evaluated that the sign of the counter ion 43 is positive (that is, the surface charge 42 is negative) and the counter ion 43 is excessive with respect to the surface charge 42. . In the example shown in FIG. 7B, the slope of the straight line portion F1 is positive, the shape of the connecting portion between the straight line portion F1 and the exponential function portion F2 is convex downward, and the straight line portion F1 and the exponential function portion are The connecting portion with F2 is a polygonal line. Therefore, as shown in FIG. 8-2, the charge distribution is evaluated that the sign of the counter ion 43 is positive (that is, the surface charge 42 is negative) and the counter ion 43 is insufficient with respect to the surface charge 42. it can. In the example shown in FIG. 7C, the slope of the straight line portion F1 is positive, and the connecting portion between the straight line portion F1 and the exponential function portion F2 can be regarded as smooth. Therefore, as shown in FIG. 8C, the charge distribution is such that the sign of the counter ion 43 is positive (that is, the surface charge 42 is negative), and the counter ion 43 is not excessive or insufficient with respect to the surface charge 42. Can be evaluated. Here, when the potential is measured at a plurality of positions of the measurement target SA, the counter-ion sign Sn, the counter-ion excess / deficiency B1 with respect to the surface charge, the charge-fixing layer thickness δFn, and the charge diffusion layer effective thickness (Debye (Length) δDn is obtained for each position.

  That the connecting portion between the straight line portion F1 and the exponential function portion F2 is smooth means that the inclination of the tangent line of the exponential function portion F2 at the connecting portion is equal to the inclination of the straight line portion F1 or predetermined with respect to the inclination of the straight line portion F1. (For example, ± 5% of the inclination of the straight line portion F1). Further, that the connecting portion between the straight line portion F1 and the exponential function portion F2 is a polygonal line means that the inclination of the tangent line of the exponential function portion F2 at the connecting portion exceeds the predetermined range with respect to the inclination of the straight line portion F1. Say.

  In addition, when the electric potential is measured at a plurality of positions of the measurement target SA, a plurality of pieces of position information are obtained. Therefore, in step S117, the control unit 51a may draw the surface shape of the measurement target SA using these. In this case, the surface shape of the measurement target SA is drawn in three dimensions, and the potential difference ΔV in the vicinity of the surface of the measurement target SA is drawn in three dimensions (for example, equipotential difference lines) according to the surface shape of the measurement target SA. Further, the control unit 51a also sets the counter ion sign Sn, the counter ion excess / deficiency Bn with respect to the surface charge, the charge fixing layer thickness δFn, and the charge diffusion layer effective thickness (Debye length) δDn. You may make it draw in three dimensions according to the surface shape.

  As described above, the liquid potential measuring method and the liquid potential measuring apparatus 1 according to the present embodiment are liquids in the vicinity of the surface of the measurement target SA that are affected by the surface potential state of the measurement target SA installed in the liquid LI. The distance dependence of the potential in LI, that is, the potential structure can be measured on a micro scale to evaluate the charge distribution. And since the probe 5 contacts the surface of the measurement target SA, the liquid potential measurement method and the liquid potential measurement apparatus 1 according to the present embodiment can reliably capture the surface of the measurement target SA. Further, since the vibration amplitude of the vibration of the cantilever 4 is detected, a change in vibration of the cantilever 4 due to an atomic force or electrostatic force can be reliably detected in the liquid LI. Furthermore, when measuring a plurality of potentials in the Z direction, the probe 5 is brought into contact with the measurement target SA for each measurement, so that charging of the probe 5 can be avoided. As a result, the liquid potential measurement method and the liquid potential measurement apparatus 1 according to the present embodiment improve the measurement accuracy of the potential in the liquid LI in the vicinity of the surface of the measurement target SA, so that the potential structure can be grasped with high accuracy. . The method for realizing the liquid potential measurement method according to the present embodiment is not limited to the above-described method.

(Modification of the device body constituting the liquid potential measuring device)
FIGS. 9-1 to 9-5 are diagrams illustrating modifications of the apparatus main body constituting the liquid potential measuring apparatus according to the present embodiment. A signal detection device 101 a illustrated in FIG. 9A connects a direct current potential generator (DC) 30 between the measurement target SA placed on the stage 2 and the external ground GND. As a result, in the signal detection device 101a, the DC potential generator 30 applies a DC potential with the external ground GND as a reference to the measurement target SA in the liquid container 3.

  The signal detection device 101b illustrated in FIG. 9B insulates the measurement target SA placed on the stage 2 from the external ground GND. In the insulation method, the stage 2 and the liquid container 3 are made of an insulator. The signal detection device 101c illustrated in FIG. 9C connects the first DC potential generator (DC1) 31 between the measurement target SA placed on the stage 2 and the external ground GND. In addition, the electrode 33 is disposed at a position facing the measurement target SA via the liquid LI, and the second DC potential generator (DC2) 32 is connected between the measurement target SA and the electrode 33. As a result, the signal detection device 101c applies a DC potential with the external ground GND as a reference to the measurement target SA in the liquid container 3 by the first DC potential generator 31, and also by the second DC potential generator 32. A DC potential with reference to the electrode 33 is applied to the measurement target SA in the liquid container 3.

  The signal detection device 101d illustrated in FIG. 9D insulates the measurement target SA placed on the stage 2 from the external ground GND. Then, a DC potential generator (DC1) 30 is connected between the measurement target SA placed on the stage 2 and the electrode 33 disposed at a position facing the measurement target SA via the liquid LI. Thereby, in the signal detection device 101d, the DC potential generator 30 applies a DC potential with the electrode 33 as a reference to the measurement object SA in the liquid container 3.

  Here, like the signal detection device 101e shown in FIG. 9-5, the conductor 34 is provided on the whole or a part of the surface in contact with the liquid LI instead of the electrode 33 of the signal detection device 101d shown in FIG. 9-4. Thus, the light transmission window 7e is provided with conductivity. The light transmission window 7 e is provided in the liquid container 3. The conductor 34 is made of, for example, an ITO (Indium Tin Oxide) thin film that transmits light and has conductivity. The thin film of ITO can be formed by physical vapor deposition on the whole or part of the surface of the light transmission window 7e in contact with the liquid LI. In the signal detection device 101c shown in FIG. 9C, instead of the electrode 33, a light transmission window 7e in which the conductor 34 is provided on at least a part of the surface in contact with the liquid LI may be used.

  As described above, the liquid potential measuring device and the liquid potential measuring method according to the present invention have the potential of the surface of the measurement target placed in the liquid and the potential of the liquid existing at a position away from the surface of the measurement target. It is useful for measuring.

DESCRIPTION OF SYMBOLS 1 Submerged potential measuring device 2 Stage 3 Liquid container 4 Cantilever 5 Probe 6 Vibrator 7, 7e Light transmission window 8 XYZ scanning device 9 Light emitting element 10 Light receiving element 11 Displacement detector 12 First lock-in amplifier 13 First vibration detection 14 Oscillator 15 First FB circuit 16 Z scan driver 17 X scan driver 18 Y scan driver 19 Second lock-in amplifier 20 Second vibration detector 21 AC potential generator 22 DC potential generator 23 Addition calculator 24 Second 2FB circuit 40 charge fixed layer 41 charge diffusion layer 42 surface charge 43 counter ion 50 measurement control device 51 processing unit 51a control unit 51b surface detection unit 51c potential measurement unit 51d position information acquisition unit 52 storage unit 53 input / output unit 54 drawing device 55 Input device 100 Measuring device main body 101, 101a, 101b, 101c, 01d, 101e signal detection apparatus 102 operates the control-information detecting system

Claims (4)

While holding the measurement target in the liquid, the cantilever having the probe on the free end side is vibrated at the first frequency, and the probe has a DC potential and an AC potential having a second frequency different from the first frequency. A potential application procedure in which the voltage is superimposed and applied,
The vibration amplitude of the first frequency is detected in a state where the probe is not in contact with the measurement object, and then the probe is brought close to the measurement object while detecting the vibration amplitude of the first frequency, The distance between the probe and the measurement object is controlled so as to keep the vibration amplitude of the first frequency at a predetermined constant value, and when the vibration amplitude of the first frequency is kept at the predetermined constant value, A contact determination procedure for determining that the probe and the measurement object are in contact;
The DC potential is controlled so that the vibration component of the second frequency becomes zero in a state where it is determined that the probe and the measurement target are in contact, and the vibration component of the second frequency becomes zero. A surface potential measurement procedure for obtaining the direct current potential as a potential on the surface of the measurement object;
A probe moving procedure for moving the probe to a position away from the measurement object;
The direct-current potential is controlled so that the vibration component of the second frequency becomes zero at the position where the probe is away from the measurement target, and the vibration component of the second frequency becomes zero. A liquid potential measurement procedure in which a direct current potential is obtained and the potential is a potential in the liquid at the remote position;
A liquid potential measuring method comprising:   The direct current potential when the vibration component of the second frequency becomes 0 at a position where the probe is away from the measurement object and the probe and the measurement object are determined to be in contact with each other. 2. The liquid potential measuring method according to claim 1, wherein a difference from the direct current potential when a vibration component of two frequencies becomes 0 is a potential in the liquid at a position where the probe is away from the measurement target. . When measuring two or more potentials in the liquid, the potential application procedure, the contact determination procedure, the surface potential measurement procedure, the probe movement procedure, and the liquid potential measurement procedure are repeated,
From the measurement result of two or more potentials in the liquid, the relationship between the potential in the liquid and the position of the potential is obtained.
Using at least one of the linear function part of the relation, the exponential part of the relation, and the connecting part of the linear function part and the exponential function part, the thickness of the charge fixing layer in the liquid and 2. At least one of the effective thickness of the charge diffusion layer in the liquid, the sign of the counter ion, and the excess or deficiency of the counter ion existing at the boundary between the charge fixing layer and the charge diffusion layer is obtained. Or the liquid potential measuring method of 2 or 2. Liquid holding means for holding a measurement object arranged in the liquid together with the liquid;
A probe provided on the free end side of the cantilever;
Vibration applying means for vibrating the cantilever at a first frequency;
A potential applying means for applying a direct current potential and an alternating current potential of a second frequency different from the first frequency to the probe;
Moving means for moving at least one of the probe and the measurement object in a direction in which the probe and the measurement object are separated or in an approaching direction;
Displacement detecting means for detecting the displacement of the cantilever;
First vibration detection means for detecting a vibration component of the first frequency from displacement information of the cantilever detected by the displacement detection means;
Second vibration detection means for detecting a vibration component of the second frequency from displacement information of the cantilever detected by the displacement detection means;
Position control means for controlling the distance between the probe and the measurement object so as to keep the vibration amplitude of the first frequency detected by the first frequency detection means at a predetermined constant value;
Potential control means for controlling the DC potential so that the vibration component of the second frequency detected by the second frequency detection means becomes zero;
Surface detection means for detecting a surface of the measurement object based on information representing a distance between the probe and the measurement object;
A potential measuring means for obtaining a potential on the surface of the measurement object and a potential in the liquid based on the direct current potential;
An in-liquid potential measuring device comprising:

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