JP5904751B2 - Scanning probe microscope and phase adjustment method thereof - Google Patents

Description

  The present invention relates to a scanning probe microscope.

  A scanning probe microscope (SPM) is a general term for a scanning microscope that acquires information on the surface of a sample while scanning a mechanical probe and displays the mapping. The SPM includes a scanning tunneling microscope (STM), an atomic force microscope (AFM), a scanning magnetic force microscope (MFM), a scanning near-field light microscope (SNOM), and the like.

  AFM is the most widely used SPM, and cantilever with a mechanical probe at its free end, optical displacement sensor that detects the displacement of the cantilever, and relative scanning of the mechanical probe and the sample. A scanning mechanism is provided as a main element. Since the optical displacement sensor has a simple configuration and high detection sensitivity, an optical lever type optical displacement sensor is most widely used. This optical lever type optical displacement sensor irradiates a light beam with a diameter of several μm to several tens of μm on the cantilever, and changes the reflection direction of the reflected light according to the change of the cantilever warp by using a two-part optical detector or the like By capturing it, an electrical signal reflecting the operation of the mechanical probe at the free end of the cantilever is output. In the AFM, the relative position between the mechanical probe and the sample is set to XY while the relative distance between the mechanical probe and the sample is controlled in the Z direction so that the output of the optical displacement sensor becomes constant by the scanning mechanism. By scanning in the direction, the uneven state of the sample surface is mapped and displayed on a computer monitor.

  AFM often employs a method (AC mode) in which a cantilever is vibrated and an interaction between a sample and a probe is detected from its vibration characteristics. This is because there is an advantage that the force acting between the sample and the probe can be kept weak compared to the normal method (called contact mode). In this AC mode AFM, the vibration of the cantilever caused by the interaction between the sample and the probe, that is, one of amplitude change or phase change of the displacement is detected, and the surface shape of the sample is measured based on the detection result. .

  Japanese Patent Application Laid-Open No. 2008-232984 discloses one such AC mode AFM.

  In the AC mode AFM, the interaction between the sample and the probe often detects a change in vibration state (amplitude change or phase change) in a repulsive region, and an image is formed based on the change. The amplitude of the cantilever displacement decreases as the repulsive force between the sample and the probe increases. The phase of the cantilever displacement advances as the repulsion increases.

  When considering the detection sensitivity, the amount of change in the amplitude of the displacement of the cantilever is the largest in the vicinity of the resonance frequency of the cantilever. For this reason, in the AM method (amplitude modulation method) that is controlled based on the change in amplitude of the displacement of the cantilever, the vibration frequency of the cantilever is set in the vicinity of the resonance frequency of the cantilever. Also in the PM method (phase modulation method) that is controlled based on the change in the phase of the displacement of the cantilever, the detection sensitivity is highest near the resonance frequency of the cantilever.

  A change in phase of the displacement of the cantilever, that is, a phase difference generated due to the contact between the sample and the probe is detected by a phase detection circuit such as a lock-in amplifier. This phase detection circuit outputs A cos φ as a phase signal. Here, A is the amplitude of the displacement signal of the cantilever, and φ is the phase difference between the displacement signal of the cantilever and a synchronization signal (sometimes referred to as a reference signal) synchronized with the excitation signal.

JP 2008-232984 A

  However, the conventional AC mode AFM as disclosed in Japanese Patent Application Laid-Open No. 2008-232984 has the following problems.

  The phase difference φ between the displacement signal of the cantilever and the synchronization signal synchronized with the excitation signal has a certain value even if the sample and the probe are not in contact. First, since the cantilever is vibrated at its mechanical resonance frequency, a phase difference of π / 2 is surely generated between the displacement signal and the synchronization signal. In addition, the frequency at which the cantilever vibrates changes due to individual differences in the mechanical resonance frequency of the cantilever, and it is unpredictable due to the mechanical vibration characteristics of the piezoelectric element that vibrates the cantilever and the holder that holds the cantilever. A phase difference will occur. That is, the phase difference between the displacement signal of the cantilever and the synchronization signal synchronized with the excitation signal has an unpredictable initial value of the phase difference even when the sample and the probe are not in contact. The phase signal Acosφ has a signal change amount with respect to a change in φ, that is, a detection sensitivity, depending on the initial value of φ. As a result, in the conventional AC mode AFM, the detection sensitivity changes every time the cantilever is replaced.

  The present invention has been made in view of such problems, and an object thereof is to provide a scanning probe microscope capable of easily correcting a change in detection sensitivity of phase detection that occurs every time a cantilever is replaced. It is.

A scanning probe microscope according to the present invention includes a cantilever having a probe at a free end, a scanning unit that relatively moves the probe and the sample three-dimensionally, and an addition that vibrates the cantilever based on an excitation signal. A vibration detection unit, a displacement detection unit that detects displacement of the cantilever and outputs a displacement signal representing the displacement, and a phase detection unit that generates a phase signal including information on a phase difference between the excitation signal and the displacement signal. It has. The phase detection unit includes a phase adjustment unit that gives the phase difference a phase offset that cancels an initial phase difference that exists when the probe and the sample are not in contact with each other. The scanning probe microscope further includes an input unit for inputting the phase offset information and a phase display unit for displaying the phase signal. The phase adjustment unit gives the phase offset to the phase difference in accordance with the information input by the input unit.

  ADVANTAGE OF THE INVENTION According to this invention, the scanning probe microscope which can correct | amend easily the change of the detection sensitivity of the phase detection which arises whenever replacement | exchange of a cantilever is provided.

The structure of the scanning probe microscope of 1st embodiment is shown. The signal flow in the signal processing part of FIG. 1 is shown. The signal flow in the signal processing part of Drawing 1 by the modification of a first embodiment is shown. -A graph showing the relationship between Asin φ and φ. The structure of the scanning probe microscope of 2nd embodiment is shown. The structure of the scanning probe microscope of 3rd embodiment is shown. 7 shows a signal flow in the signal processing unit of FIG. 6.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<First embodiment>
The configuration of the scanning probe microscope of the present embodiment is shown in FIG. As shown in FIG. 1, the scanning probe microscope has a cantilever 12 having a probe 11 at a free end. The cantilever 12 can be held by the holder 13 so as to face the sample 19.

  The scanning probe microscope also has a displacement detector 15 that detects the displacement of the cantilever 12 and outputs a displacement signal representing the displacement. The displacement detection unit 15 includes an optical lever type optical displacement sensor, and receives a laser light source 16 that irradiates a laser beam focused on the back surface of the cantilever 12 and a laser beam reflected from the back surface of the cantilever 12. The division detector 17 and an operational amplifier 18 that generates a displacement signal of the cantilever 12 from the output of the division detector 17 are configured.

  The scanning probe microscope also has a vibration unit 14 that vibrates the cantilever 12 based on the vibration signal. The vibration part 14 is provided in the holder 13, for example. The vibration unit 14 is made of, for example, a piezoelectric element, and can vibrate the cantilever 12 with a predetermined amplitude at a frequency near its mechanical resonance frequency.

  The scanning probe microscope also includes a scanning unit 20 that relatively moves the sample 19 and the probe 11 in three dimensions. The scanning unit 20 includes a Z scanner 21 and an XY scanner 22. The Z scanner 21 is disposed on the XY scanner 22, and the sample 19 can be placed on the Z scanner 21 via a sample table (not shown). The Z scanner 21 is driven by a Z driver 23 and can move the sample 19 in the Z direction with respect to the probe 11. The XY scanner 22 is driven by an XY driver 24 and can move the sample 19 in the XY direction with respect to the probe 11.

  The scanning probe microscope also includes a controller 25 that controls the Z driver 23 and the XY driver 24, and a host computer 28 that forms an image of the surface of the sample 19. The controller 25 can generate an XY scanning signal for two-dimensionally scanning the probe 11 along the surface of the sample 19 and a Z control signal for controlling the distance between the probe 11 and the sample 19. . The controller 25 selects one of an amplitude signal and a phase signal, which will be described later, and supplies the selected control signal to the Z control unit 27. The Z control unit 27 generates a Z control signal based on the signal supplied from the selection unit 26. have. The host computer 28 can form an image of the surface of the sample 19 using the XY scanning signal and the Z control signal generated by the controller 25. The host computer 28 has an input unit 29 for inputting and setting phase offset information, which will be described later.

  The scanning probe microscope also includes a signal processing unit 30 that supplies an excitation signal to the excitation unit 14 and generates an amplitude signal and a phase signal from the displacement signal output from the displacement detection unit 15. The signal processing unit 30 includes a signal generator 31, an amplitude detection unit 32, an amplitude display unit 33, a phase detection unit 34, and a phase display unit 36.

  The signal generator 31 outputs an excitation signal that vibrates the cantilever 12 with a predetermined amplitude at a frequency near its mechanical resonance frequency, for example. The signal generator 31 also outputs a synchronization signal synchronized with the excitation signal to the phase detection unit 34. This synchronization signal can be composed of, for example, a square wave signal (logic signal) having the same frequency and the same phase as the excitation signal.

  The amplitude detection unit 32 generates an amplitude signal representing the amplitude of the displacement signal of the cantilever 12 supplied from the displacement detection unit 15, and outputs this to the amplitude display unit 33 and the controller 25.

  The amplitude display unit 33 can display the amplitude signal supplied from the amplitude detection unit 32. The amplitude display unit 33 can be configured by a display that displays a voltage value of a signal such as a digital meter, an analog meter, or an oscilloscope. For example, the amplitude display unit 33 displays the value of the amplitude signal, that is, the amplitude value. The amplitude display unit 33 can be replaced by a monitor of the host computer 28.

  The phase detection unit 34 generates a phase signal including information on the phase difference between the displacement signal of the cantilever 12 supplied from the displacement detection unit 15 and the synchronization signal supplied from the signal generator 31, and generates the phase signal as a phase display unit 36. Output to the controller 25. Since the synchronization signal and the excitation signal have the same frequency and phase, the phase difference between the displacement signal and the synchronization signal is equivalent to the phase difference between the displacement signal and the excitation signal.

  The phase detection unit 34 includes a phase adjustment unit 35 that can adjust the phase of the synchronization signal supplied from the signal generator 31. The phase adjustment unit 35 can give a predetermined phase offset indicated by the phase offset command supplied from the controller 25 to the phase of the synchronization signal. In other words, the phase adjustment unit 35 can give a predetermined phase offset to the phase difference between the displacement signal and the synchronization signal. The phase detector 34 generates and outputs a phase signal including information on the phase difference between the synchronization signal to which the phase offset is given and the displacement signal. The phase difference between the synchronization signal to which the phase offset is given and the displacement signal is equivalent to the phase difference given to the phase difference between the displacement signal and the synchronization signal. The predetermined phase offset is input and set by the input unit 29 of the host computer 28 so as to cancel the initial phase difference existing when the probe 11 and the sample 19 are not in contact with each other. That is, the phase adjustment unit 35 gives a phase offset for canceling the initial phase difference to the phase difference between the displacement signal and the synchronization signal.

  The phase display unit 36 can display the phase signal supplied from the phase detection unit 34. The phase display unit 36 may be configured by a display that displays a voltage value of a signal such as a digital meter, an analog meter, or an oscilloscope. The phase display unit 36 displays the value of the phase signal, for example. The phase display unit 36 can be replaced with a monitor of the host computer 28.

  Here, a signal flow in the signal processing unit 30 will be described with reference to FIG.

Let the vibration signal be A ₀ sin ω ₀ t. Here, A ₀ is the amplitude of the vibration signal, ω ₀ is the angular frequency of the vibration signal, and t is time. ω ₀ has a value approximately equal to 2π · f _{0 where} the resonance frequency of the cantilever 12 is f ₀ .

The synchronization signal is, for example, a square wave signal having the same frequency (that is, angular frequency ω ₀ ) and the same phase as the excitation signal.

The displacement signal of the cantilever 12 is set as Asin (ω ₀ t + φ ₀ + φ). Here, A is the amplitude of the displacement signal, φ ₀ is the initial phase difference of the displacement signal that exists when the probe 11 and the sample 19 are not in contact, and φ is that the probe 11 and the sample 19 are in contact with each other. The phase difference of the displacement signal generated due to the above. When the probe 11 and the sample 19 are not in contact, φ is zero.

The amplitude detector 32 detects the amplitude A of the displacement signal Asin (ω ₀ t + φ ₀ + φ) of the cantilever 12 and outputs an amplitude signal A representing the amplitude.

The phase adjustment unit 35 gives the phase offset ψ ₀ to the phase of the synchronization signal based on the phase offset command. That is, the phase adjustment unit 35 shifts the phase of the synchronization signal by ψ ₀ . This is equivalent to giving a phase offset −φ ₀ to the phase difference between the displacement signal of the cantilever 12 and the synchronization signal (ie, the excitation signal). The phase detector 34 receives a phase signal Acos (φ ₀ + φ−ψ ₀ ) including information on the phase difference between the displacement signal Asin (ω ₀ t + φ ₀ + φ) of the cantilever 12 and the synchronization signal given the phase offset ψ _0. Generate and output.

  Next, the phase adjustment procedure will be described.

In a state where the probe 11 and the sample 19 are not in contact with each other, first, an excitation signal A ₀ sin ω ₀ t is output from the signal generator 31. At the same time, the signal generator 31 outputs a square wave signal having the same frequency (angular frequency ω ₀ ) as that of the excitation signal.

Next, the input unit 29 of the host computer 28 inputs and sets the phase offset ψ ₀ to be given to the synchronization signal. The phase offset ψ ₀ set at this time may be an arbitrary value. The phase adjustment unit 35 shifts the phase of the synchronization signal by ψ ₀ based on the phase offset command. The phase detector 34 receives a phase signal Acos (φ ₀ + φ−ψ ₀ ) including information on the phase difference between the displacement signal Asin (ω ₀ t + φ ₀ + φ) of the cantilever 12 and the synchronization signal given the phase offset ψ _0. Generate and output. The phase display unit 36 displays the value of the phase signal Acos (φ ₀ + φ−ψ ₀ ). Here, φ is 0 in the current state where the probe 11 and the sample 19 are not in contact. Therefore, the phase display unit 36 displays the value of Acos (φ ₀ −ψ ₀ ).

Then, while monitoring the value of Acos displayed in the phase distribution display section 36 (φ ₀ -ψ _0), as the value of Acos (φ ₀ -ψ ₀₎ becomes a maximum value, that is A, the host computer 28 The input unit 29 adjusts the phase offset ψ ₀ . As a result, the phase offset ψ ₀ is set equal to φ ₀ . In other words, the initial phase difference φ ₀ is canceled.

  After this adjustment, the phase signal including information on the phase difference φ output from the phase detector 34 is Acos φ.

As described above, according to the scanning probe microscope and the phase adjustment method of the present embodiment, the initial phase difference φ ₀ existing in a state where the probe 11 and the sample 19 are not in contact can be easily canceled. In other words, a change in detection sensitivity of phase detection that occurs each time the cantilever 12 is replaced can be easily corrected. As a result, it is possible to detect a phase signal including information on the phase difference φ generated due to the contact between the probe 11 and the sample 19 with good reproducibility.

[Modification]
The phase adjustment procedure described above may be modified as described below. The phase adjustment procedure of this modification will be described with reference to FIG. 3, members denoted by the same reference numerals as those shown in FIG. 1 are similar members, and detailed description thereof is omitted.

In a state where the probe 11 and the sample 19 are not in contact with each other, first, an excitation signal A ₀ sin ω ₀ t is output from the signal generator 31. At the same time, the signal generator 31 outputs a square wave signal having the same frequency (angular frequency ω ₀ ) as that of the excitation signal.

  First, the following is performed as <first step>.

At the input unit 29 of the host computer 28, the phase offset ψ ₀ to be given to the synchronization signal is input and set. The phase offset ψ ₀ set at this time may be an arbitrary value. The phase adjustment unit 35 shifts the phase of the synchronization signal by ψ ₀ based on the phase offset command. The phase detector 34 receives a phase signal Acos (φ ₀ + φ−ψ ₀ ) including information on the phase difference between the displacement signal Asin (ω ₀ t + φ ₀ + φ) of the cantilever 12 and the synchronization signal given the phase offset ψ _0. Generate and output. The phase display unit 36 displays the value of the phase signal Acos (φ ₀ + φ−ψ ₀ ). Here, φ is 0 in the current state where the probe 11 and the sample 19 are not in contact. Therefore, the phase display unit 36 displays the value of Acos (φ ₀ −ψ ₀ ).

Then, while monitoring the values of Acos displayed in the phase distribution display section 36 (φ ₀ -ψ _0), as the value of Acos (φ ₀ -ψ ₀₎ becomes a maximum value, that is A, the host computer 28 The input unit 29 adjusts the phase offset ψ ₀ . As a result, the phase offset ψ ₀ is set equal to φ ₀ . After this adjustment, the phase signal including information on the phase difference φ output from the phase detector 34 is Acos φ.

  Next, the following is performed as the <second step>.

In the input unit 29 of the host computer 28, a new phase offset equal to a value obtained by adding −π / 2 to ψ ₀ (= φ ₀ ) is newly input and set instead of the previous phase offset ψ ₀ . That is, the input unit 29 of the host computer 28, changes the phase offset giving the synchronizing signal from the [psi ₀ to (φ ₀ -π / 2). The phase adjustment unit 35 shifts the phase of the synchronization signal by (φ ₀ −π / 2) = (φ ₀ −π / 2) based on the phase offset command. The phase detection unit 34 includes a phase signal Acos (φ including information on the phase difference between the displacement signal Asin (ω ₀ t + φ ₀ + φ) of the cantilever 12 and the phase offset of (φ ₀ −π / 2). ₀ + φ−φ ₀ + π / 2) = A cos (φ + π / 2) = − A sin φ is generated and output. This is because the phase adjustment unit 35 shifts the phase of the synchronization signal by (φ ₀ −π / 2), whereby the phase difference (φ ₀ + φ) between the displacement signal of the cantilever 12 and the synchronization signal (that is, the excitation signal). Therefore, the second phase offset (−φ ₀ + π / 2) is given.

  FIG. 4 is a graph showing the relationship between -Asin φ and φ. As can be seen from this graph, −Asin φ changes most sensitively to changes in the phase shift amount φ when φ = 0. For this reason, it can be said that the phase difference φ generated due to the contact between the probe 11 and the sample 19 can be detected most efficiently.

As described above, according to the modified example of the scanning probe microscope and the phase adjustment method of the present embodiment, the initial phase difference φ ₀ that exists when the probe 11 and the sample 19 are not in contact can be canceled. In other words, a change in detection sensitivity of phase detection that occurs each time the cantilever 12 is replaced can be easily corrected. In addition to this, the phase difference φ generated due to the contact between the probe 11 and the sample 19 can be detected efficiently. As a result, the phase difference φ generated due to the contact between the probe 11 and the sample 19 can be detected with high sensitivity and good reproducibility.

<Second embodiment>
The scanning probe microscope of the present embodiment is the same as the scanning probe microscope of the first embodiment except that the configuration of the signal processing unit is different. Therefore, here, description will be given with emphasis on the configuration and operation of the signal processing unit of the present embodiment.

  FIG. 5 shows the configuration of the scanning probe microscope of the present embodiment. In FIG. 5, members denoted by the same reference numerals as those shown in FIG. 1 are similar members, and detailed description thereof is omitted.

  As shown in FIG. 5, the signal processing unit 40 in the scanning probe microscope of the present embodiment replaces the phase display unit 36 of the signal processing unit 30 in the scanning probe microscope of the first embodiment with a division unit 41 and a phase. The display unit 42 is provided.

  The division unit 41 divides the phase signal supplied from the phase detection unit 34 by the amplitude signal supplied from the amplitude detection unit 32, and generates and outputs a division signal representing the result.

  The phase display unit 42 can display the division signal supplied from the division unit 41. The phase display unit 42 can be configured by a display that displays a voltage value of a signal such as a digital meter, an analog meter, or an oscilloscope. The phase display unit 42 displays the value of the phase signal, for example. The phase display unit 42 can be replaced with a monitor of the host computer 28.

  Here, the flow of signals in the signal processing unit 40 will be described.

As in the first embodiment, the excitation signal is set to A ₀ sin ω ₀ t. Here, A ₀ is the amplitude of the vibration signal, ω ₀ is the angular frequency of the vibration signal, and t is time. ω ₀ has a value approximately equal to 2π · f _{0 where} the resonance frequency of the cantilever 12 is f ₀ .

The synchronization signal is, for example, a square wave signal having the same frequency (that is, angular frequency ω ₀ ) and the same phase as the excitation signal.

The displacement signal of the cantilever 12 is set as Asin (ω ₀ t + φ ₀ + φ). Here, A is the amplitude of the displacement signal, φ ₀ is the initial phase difference of the displacement signal that exists when the probe 11 and the sample 19 are not in contact, and φ is that the probe 11 and the sample 19 are in contact with each other. The phase difference of the displacement signal generated due to the above. When the probe 11 and the sample 19 are not in contact, φ is zero.

The amplitude detector 32 detects the amplitude A of the displacement signal Asin (ω ₀ t + φ ₀ + φ) of the cantilever 12 and outputs an amplitude signal A representing the amplitude.

The phase adjustment unit 35 shifts the phase of the synchronization signal by ψ ₀ based on the phase offset command. The phase detector 34 receives a phase signal Acos (φ ₀ + φ−ψ ₀ ) including information on the phase difference between the displacement signal Asin (ω ₀ t + φ ₀ + φ) of the cantilever 12 and the synchronization signal given the phase offset ψ _0. Generate and output.

The division unit 41 generates and outputs a division signal cos (φ ₀ + φ−φ ₀ ) representing the result of dividing the phase signal A cos (φ ₀ + φ−φ ₀ ) by the amplitude signal A. The phase display unit 42 displays the value of the division signal cos (φ ₀ + φ−ψ ₀ ).

  Next, the phase adjustment procedure will be described.

In a state where the probe 11 and the sample 19 are not in contact with each other, first, an excitation signal Asinω ₀ t is output from the signal generator 31. At the same time, the signal generator 31 outputs a square wave signal having the same frequency (angular frequency ω ₀ ) as that of the excitation signal.

Next, the input unit 29 of the host computer 28 inputs and sets the phase offset ψ ₀ to be given to the synchronization signal. The phase offset ψ ₀ set at this time may be an arbitrary value. The phase adjustment unit 35 shifts the phase of the synchronization signal by ψ ₀ based on the phase offset command. The phase detector 34 receives a phase signal Acos (φ ₀ + φ−ψ ₀ ) including information on the phase difference between the displacement signal Asin (ω ₀ t + φ ₀ + φ) of the cantilever 12 and the synchronization signal given the phase offset ψ _0. Generate and output. The division unit 41 generates and outputs a division signal cos (φ ₀ + φ−φ ₀ ) obtained by dividing the phase signal A cos (φ ₀ + φ−φ ₀ ) by the amplitude signal A. The phase display unit 42 displays the value of the division signal cos (φ ₀ + φ−ψ ₀ ). Here, φ is 0 in the current state where the probe 11 and the sample 19 are not in contact. Therefore, the phase display unit 42 displays the value of cos (φ ₀ −φ ₀ ).

Then, while monitoring the value of cos displayed in the phase distribution display section 42 (φ ₀ -ψ _0), as the value of cos (φ ₀ -ψ ₀₎ becomes a maximum value, ie 1, the host computer 28 The input unit 29 adjusts the phase offset ψ ₀ . As a result, the phase offset ψ ₀ is set equal to φ ₀ . In other words, the initial phase difference φ ₀ is canceled.

  After this adjustment, the phase signal including information on the phase difference φ output from the phase detector 34 is Acos φ. The division signal displayed on the phase display unit 42 is cosφ.

As described above, according to the scanning probe microscope and the phase adjustment method of the present embodiment, adjustment is performed so that the value of cos (φ ₀ + φ−φ ₀ ) is 1, so that adjustment can be performed intuitively and accuracy is improved. Also goes up. That is, it is possible to cancel the initial phase difference φ ₀ that exists accurately and easily in a state where the probe 11 and the sample 19 are not in contact with each other.

<Third embodiment>
The scanning probe microscope of the present embodiment is the same as the scanning probe microscope of the first embodiment except that the configuration of the signal processing unit is different. Therefore, here, description will be given with emphasis on the configuration and operation of the signal processing unit of the present embodiment.

  FIG. 6 shows the configuration of the scanning probe microscope of the present embodiment. In FIG. 6, members denoted by the same reference numerals as those shown in FIG. 1 are similar members, and detailed description thereof is omitted.

  As shown in FIG. 6, the signal processing unit 50 in the scanning probe microscope of the present embodiment includes each component of the signal processing unit 30 in the first embodiment, that is, a signal generator 31, an amplitude detection unit 32, and an amplitude display unit 33. In addition to the phase detection unit 34 and the phase display unit 36, a phase detection unit 51 is provided. In the first embodiment, the phase signal output from the phase detection unit 34 is supplied to the phase display unit 36 and the controller 25. However, in this embodiment, the phase signal output from the phase detection unit 34 is a phase signal. Although supplied to the display unit 36, it is not supplied to the controller 25. Instead, the phase signal output from the phase detection unit 51 is supplied to the controller 25.

  The phase detection unit 51 includes a phase adjustment unit 52 that can adjust the phase of the synchronization signal supplied from the signal generator 31. The phase adjustment unit 52 can give a predetermined phase offset indicated by the phase offset command supplied from the controller 25 supplied from the controller 25 to the phase of the synchronization signal. In other words, the phase adjustment unit 52 can give a phase offset to the phase difference between the displacement signal and the synchronization signal. The phase detection unit 51 generates and outputs a phase signal including information on the phase difference between the synchronization signal to which the phase offset is given by the phase adjustment unit 52 and the displacement signal.

The phase adjustment unit 52 shifts the phase of the synchronization signal supplied from the signal generator 31 by a predetermined amount. The phase adjustment unit 52 gives a phase offset equal to a value obtained by adding −π / 2 to the phase offset ψ ₀ indicated by the phase offset command to the synchronization signal, and is different from the phase adjustment unit 35 in this respect. . That is, the predetermined amount is “phase offset instructed by the phase offset command” + “− π / 2”.

  The phase detection unit 51 generates a phase signal including information on the phase difference between the displacement signal of the cantilever 12 supplied from the displacement detection unit 15 and the synchronization signal to which the phase offset is given by the phase adjustment unit 52. Output to the controller 25.

  Further, the phase detection unit 34 generates a phase signal including information on a phase difference between the displacement signal of the cantilever 12 supplied from the displacement detection unit 15 and the synchronization signal to which the phase offset is given by the phase adjustment unit 35, This is output to the phase display unit 36.

  As described above, in the scanning probe microscope of the present embodiment, the phase signal supplied to the controller 25 and the phase signal supplied to the phase display unit 36 are independent by the phase detection unit 51 and the phase detection unit 34, respectively. Generated.

  Here, a signal flow in the signal processing unit 50 will be described with reference to FIG.

As in the first embodiment, the excitation signal is set to A ₀ sin ω ₀ t. Here, A ₀ is the amplitude of the vibration signal, ω ₀ is the angular frequency of the vibration signal, and t is time. ω ₀ has a value approximately equal to 2π · f _{0 where} the resonance frequency of the cantilever 12 is f ₀ .

The synchronization signal is, for example, a square wave signal having the same frequency (that is, angular frequency ω ₀ ) and the same phase as the excitation signal.

The displacement signal of the cantilever 12 is set as Asin (ω ₀ t + φ ₀ + φ). Here, A is the amplitude of the displacement signal, φ ₀ is the initial phase difference of the displacement signal that exists when the probe 11 and the sample 19 are not in contact, and φ is that the probe 11 and the sample 19 are in contact with each other. The phase difference of the displacement signal generated due to the above. When the probe 11 and the sample 19 are not in contact, φ is zero.

The amplitude detector 32 detects the amplitude A of the displacement signal Asin (ω ₀ t + φ ₀ + φ) of the cantilever 12 and outputs an amplitude signal A representing the amplitude.

The phase adjustment unit 35 shifts the phase of the synchronization signal by ψ ₀ based on the phase offset command. The phase detector 34 receives a phase signal Acos (φ ₀ + φ−ψ ₀ ) including information on the phase difference between the displacement signal Asin (ω ₀ t + φ ₀ + φ) of the cantilever 12 and the synchronization signal given the phase offset ψ _0. Generate and output. The phase display unit 36 displays the value of the phase signal Acos (φ ₀ + φ−ψ ₀ ).

The phase adjustment unit 52 gives a phase offset equal to a value obtained by adding −π / 2 to the phase offset ψ ₀ to the phase of the synchronization signal. That is, the phase adjustment unit 52 shifts the phase of the synchronization signal by ψ ₀ −π / 2. The phase detection unit 51 includes a phase signal Acos (φ ₀ + φ including information on a phase difference between the displacement signal Asin (ω ₀ t + φ ₀ + φ) of the cantilever 12 and a synchronization signal to which a phase offset of ψ ₀ −π / 2 is given. −φ ₀ + π / 2) = − A sin (φ ₀ + φ−φ ₀ ) is generated and output to the controller 25.

  Next, the phase adjustment procedure will be described.

In a state where the probe 11 and the sample 19 are not in contact with each other, first, an excitation signal A ₀ sin ω ₀ t is output from the signal generator 31. At the same time, the signal generator 31 outputs a square wave signal having the same frequency (angular frequency ω ₀ ) as that of the excitation signal.

Next, the input unit 29 of the host computer 28 inputs and sets the phase offset ψ ₀ to be given to the synchronization signal. The phase offset ψ ₀ set at this time may be an arbitrary value. The phase adjustment unit 35 shifts the phase of the synchronization signal by ψ ₀ based on the phase offset command. The phase detector 34 receives a phase signal Acos (φ ₀ + φ−ψ ₀ ) including information on the phase difference between the displacement signal Asin (ω ₀ t + φ ₀ + φ) of the cantilever 12 and the synchronization signal given the phase offset ψ _0. Generate and output. The phase display unit 36 displays the value of the phase signal Acos (φ ₀ + φ−ψ ₀ ). Here, φ is 0 in the current state where the probe 11 and the sample 19 are not in contact. Therefore, the phase display unit 36 displays the value of Acos (φ ₀ −ψ ₀ ).

Then, while monitoring the value of Acos displayed in the phase distribution display section 36 (φ ₀ -ψ _0), as the value of Acos (φ ₀ -ψ ₀₎ becomes a maximum value, that is A, the host computer 28 The input unit 29 adjusts the phase offset ψ ₀ . As a result, the phase offset ψ ₀ is set equal to φ ₀ . In other words, the initial phase difference φ ₀ is canceled.

The phase adjustment unit 52 gives a phase offset equal to a value obtained by adding −π / 2 to the phase offset ψ ₀ to the phase of the synchronization signal. That is, the phase adjustment unit 52 shifts the phase of the synchronization signal by ψ ₀ −π / 2. Phase detector 51, the displacement signal _{Asin (ω 0 t + φ 0} + φ) and ψ ₀ -π / 2 phase signal Acos including information of the phase difference between the synchronizing signal is phase offset given (φ ₀ + _{φ-ψ 0} + Π / 2) = − A sin (φ ₀ + φ−φ ₀ ) is generated and output to the controller 25. In Adjusted phase offset [psi ₀ as described above, since the phase offset [psi ₀ is set equal to phi _0, the phase signal including the information of the phase difference phi which is output from the phase detector 51 becomes -Asinφ .

  As shown in FIG. 4, −Asinφ changes most sensitively to changes in the phase shift amount φ when φ = 0. Therefore, the phase difference φ generated due to the contact between the probe 11 and the sample 19 can be detected most efficiently.

As described above, in the scanning probe microscope and the phase adjustment method of the present embodiment, the initial phase difference φ ₀ that exists when the probe 11 and the sample 19 are not in contact can be canceled. In other words, a change in detection sensitivity of phase detection that occurs each time the cantilever 12 is replaced can be easily corrected. In addition to this, it is possible to detect the phase difference φ generated due to the contact between the probe 11 and the sample 19 with high sensitivity. As a result, the phase difference φ generated due to the contact between the probe 11 and the sample 19 can be detected with high sensitivity and good reproducibility.

  This advantage of the present embodiment is common to the modification of the first embodiment, but in order to achieve this, the modification of the first embodiment requires two steps, whereas this advantage is In the embodiment, only one step is required.

Furthermore, the division type shown in FIG. 5 of the second embodiment is provided in the scanning probe microscope of this embodiment, and the division signal that is the result of dividing the phase signal output from the phase detection unit 34 by the amplitude signal is monitored. In other words, if the combination of the present embodiment and the second embodiment is performed, the adjustment can be performed intuitively and the accuracy is improved. That is, the initial phase difference φ ₀ that exists when the probe 11 and the sample 19 are not in contact can be easily and accurately canceled.

  The embodiments of the present invention have been described above with reference to the drawings. However, the present invention is not limited to these embodiments, and various modifications and changes can be made without departing from the scope of the present invention. Also good.

DESCRIPTION OF SYMBOLS 11 ... Probe, 12 ... Cantilever, 13 ... Holder, 14 ... Excitation part, 15 ... Displacement detection part, 16 ... Laser light source, 17 ... Divided detector, 18 ... Operation amplifier, 19 ... Sample, 20 ... Scanning part, 21 ... Z scanner, 22 ... XY scanner, 23 ... Z driver, 24 ... XY driver, 25 ... Controller, 26 ... Selection unit, 27 ... Z control unit, 28 ... Host computer, 29 ... Input unit, 30 ... Signal processing unit, DESCRIPTION OF SYMBOLS 31 ... Signal generator, 32 ... Amplitude detection part, 33 ... Amplitude display part, 34 ... Phase detection part, 35 ... Phase adjustment part, 36 ... Phase display part, 40 ... Signal processing part, 41 ... Division part, 42 ... Phase Display unit 50... Signal processing unit 51... Phase detection unit 52.

Claims (10)

A cantilever with a probe at the free end,
A scanning unit that relatively moves the probe and the sample three-dimensionally;
An excitation unit that vibrates the cantilever based on an excitation signal;
A displacement detector that detects the displacement of the cantilever and outputs a displacement signal representing the displacement;
A phase detection unit that generates a phase signal including information on a phase difference between the excitation signal and the displacement signal;
The phase detection unit includes a phase adjustment unit that gives the phase difference a phase offset that cancels an initial phase difference existing when the probe and the sample are not in contact with each other .
An input unit for inputting information of the phase offset;
A phase display unit for displaying the phase signal;
The phase adjustment unit is a scanning probe microscope that gives the phase offset to the phase difference in accordance with the information input by the input unit . A cantilever with a probe at the free end,
A scanning unit that relatively moves the probe and the sample three-dimensionally;
An excitation unit that vibrates the cantilever based on an excitation signal;
A displacement detector that detects the displacement of the cantilever and outputs a displacement signal representing the displacement;
A phase detection unit that generates a phase signal including information on a phase difference between the excitation signal and the displacement signal;
The phase detection unit includes a phase adjustment unit that gives the phase difference a phase offset that cancels an initial phase difference existing when the probe and the sample are not in contact with each other .
An amplitude detector that generates an amplitude signal representing the amplitude of the displacement signal;
An amplitude display for displaying the amplitude signal;
An input unit for inputting information of the phase offset;
A division unit for generating a division signal obtained by dividing the phase signal by the amplitude signal;
A scanning probe microscope comprising a phase display unit for displaying the division signal . A second phase detector that generates second phase information including the phase difference information;
The second phase detection unit includes a second phase adjustment unit that gives the phase difference a second phase offset equal to a value obtained by adding + π / 2 to the phase offset according to the information input by the input unit. has, scanning probe microscope according to claim 1 or claim 2. Oscillating a cantilever having a probe at a free end based on an excitation signal;
Scanning the probe along the surface of the sample;
Detecting the displacement of the cantilever and outputting a displacement signal representing the displacement;
Generating a phase signal including information on a phase difference between the excitation signal and the displacement signal;
Providing the phase difference with a phase offset that cancels an initial phase difference existing in a state where the probe and the sample are not in contact with each other, and
The step of providing the phase offset includes a step of adjusting the phase offset while monitoring the phase signal, and a phase adjustment method for a scanning probe microscope. The phase signal is Acos (φ ₀ + φ−ψ ₀ ), where A is the amplitude of the displacement signal, φ ₀ is the initial phase difference, −ψ ₀ is the phase offset, and φ is the probe. And the phase difference of the displacement signal generated due to the contact of the sample,
The step of adjusting the phase offset, in the state (φ = 0) to the said probe and the sample is not in contact, the value of Acos (φ ₀ -ψ ₀₎ to adjust the phase offset such that the maximum The phase adjustment method for a scanning probe microscope according to claim 4 . A second phase signal different from the phase offset is applied to the phase difference to generate a second phase signal that changes sensitively to the phase difference generated due to contact between the probe and the sample. The phase adjustment method for a scanning probe microscope according to claim 4 , further comprising a step of: The phase signal is Acos (φ ₀ + φ−ψ ₀ ), where A is the amplitude of the displacement signal, φ ₀ is the initial phase difference, −ψ ₀ is the phase offset, and φ is the probe. And the phase difference of the displacement signal generated due to the contact of the sample,
In the step of adjusting the phase offset, in the state where the probe and the sample are not in contact (φ = 0), first, the phase offset is set so that the value of A cos (φ ₀ −ψ ₀ ) becomes maximum. Adjust
The phase adjustment method for a scanning probe microscope according to claim 6 , wherein the second phase offset is equal to −ψ ₀ + π / 2. Oscillating a cantilever having a probe at a free end based on an excitation signal;
Scanning the probe along the surface of the sample;
Detecting the displacement of the cantilever and outputting a displacement signal representing the displacement;
Generating a phase signal including information on a phase difference between the excitation signal and the displacement signal;
Providing the phase difference with a phase offset that cancels an initial phase difference existing in a state where the probe and the sample are not in contact with each other, and
The phase signal is Acos (φ ₀ + φ−ψ ₀ ), where A is the amplitude of the displacement signal, φ ₀ is the initial phase difference, −ψ ₀ is the phase offset, and φ is the probe. And the phase difference of the displacement signal generated due to the contact of the sample,
Generating an amplitude signal representing the amplitude A of the displacement signal;
Generating a division signal cos (φ ₀ + φ−ψ ₀ ) obtained by dividing the phase signal by the amplitude signal ;
Step of providing the phase offset in the state (φ = 0) to the said probe and the sample is not in contact, while monitoring the value of _{cos (φ 0 -ψ 0),} cos (φ 0 -ψ 0) A method for adjusting a phase of a scanning probe microscope , comprising a step of adjusting the phase offset so that a value of 1 becomes 1 . A second phase signal different from the phase offset is applied to the phase difference to generate a second phase signal that changes sensitively to the phase difference generated due to contact between the probe and the sample. The phase adjustment method for a scanning probe microscope according to claim 8 , further comprising a step of: The second phase offset ψ ₀ is adjusted to be equal to the initial phase difference φ ₀ , the second phase offset is equal to −ψ ₀ + π / 2, and the second phase signal is Acos (φ ₀ The phase adjustment method for a scanning probe microscope according to claim 6 or 9 , wherein + φ−ψ ₀ + π / 2) = − Asinφ.

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