JP2006078219A - Measuring method of physical data using scanning probe microscope, cantilever and the scanning probe microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for continuously changing a spring constant, in order to realize a cantilever having optimum spring constant corresponding to the detection force. <P>SOLUTION: In the measuring method of physical data using a scanning probe microscope, the spring constant of the cantilever 1 of the scanning probe microscope is continuously changed to find out the optimum value of the spring constant most easily acquiring the physical property data of a measurement target. Further, the spring constant of the cantilever 1 is changed continuously to acquire viscoelastic data. Furthermore, the cantilever 1 is changed continuously to gain a focus curve. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for measuring physical property information using a scanning probe microscope (hereinafter abbreviated as SPM), a cantilever, and a scanning probe microscope, and more particularly, to a scanning probe microscope that obtains desired physical property information by changing a spring constant. The present invention relates to a method for measuring physical property information, a cantilever, and a scanning probe microscope.

  The scanning probe microscope is now an indispensable tool in nanotechnology not only as a device for obtaining fine surface shape information, but also as an analysis device for acquiring various physical property information and as a processing device for manipulation, etc. Yes.

  There are various scanning probe technologies. As a common technology, in the case of a probe microscope based on an XYZ direction high-precision scan and an atomic force microscope, a cantilever is used as a probe.

  The cantilever is appropriately selected depending on what physical property information is acquired or what scanning probe control is performed.

  For example, when evaluating the viscoelasticity of the sample surface, a cantilever having a spring constant corresponding to the viscoelasticity of the material is required.

  Now, there is a sample in which the material A and the material B are microphase-separated, and A is relatively soft.

  At this time, it is best to identify the difference between the viscoelasticity of the two materials by using a spring constant such that the material A is soft and the material B is hard.

  Even in cases where the adhesion force on the sample surface is evaluated using a force curve, a cantilever with a spring constant corresponding to the adhesion force is required. If the spring constant is too strong for the adhesion force, the adhesion force is measured. If it is too weak, the tip of the cantilever tip cannot be separated within the scanning range in the Z direction, and this makes it impossible to determine the adhesion force.

  Thus, the spring constant of the cantilever has an optimum value in relation to the detected force, and the spring constant greatly affects the S / N (Signal / Noise) ratio of the acquired physical property value.

  Until now, the spring constant of a cantilever has only one value unique to the cantilever.

  Among the commercially available products, there is one in which cantilevers having four types of spring constants with different lengths and widths are provided on one substrate (FIG. 11A).

Also in the Si single crystal probe, several cantilevers having a spring constant of around 0.01-50 N / m are prepared by changing the length or the like (FIG. 11B).
JP 2000-346784 A M. Radmacher, RWTillman, M. Fritz, HEGaub, "From Molecules to Cells: Imaging Soft Samples with the Atomic Force Microscope", Science 1992, 257, 1900-1905

  However, as a method of selecting an optimal spring constant when evaluating physical property information by SPM, in particular, viscoelasticity, surface adhesion force and adsorption force, among the cantilevers having individual spring constants. The cantilever with the most appropriate spring constant could only be selected.

  Accordingly, an object of the present invention is to realize a cantilever having an optimal spring constant corresponding to a detected force.

  As a means for solving the above problems, the present invention provides a method for measuring physical property information using a scanning probe microscope, wherein a cantilever is used as the scanning probe, and the spring constant of the cantilever is continuously changed. The optimum value of the spring constant at which the physical property information of the measurement object is most easily obtained is found, and desired physical property information is obtained by a spring having the spring constant.

  According to the present invention, it is possible to set an optimal spring constant according to the force to be detected, and it is possible to detect acquired information with a good S / N. In particular, viscoelasticity, adhesion force and adsorption force can be effectively evaluated.

  In addition, according to the present invention, it is possible to select an optimal spring constant in viscoelasticity, force curve, and phase imaging by continuously changing the spring constant, and measurement with good S / N is possible.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  The first method of changing the spring constant is a method of continuously changing the length of the cantilever arm of the cantilever 1. A cantilever is a cantilever beam.

  As shown in FIG. 1A, the present embodiment includes a cantilever 1, a jig 2, a jig 3, an adjustment mechanism 4, and a piezoelectric element 5.

  The jig 2 and the jig 3 are combined to form a cantilever holder.

  As shown in FIG. 1A, the spring constant is changed by sandwiching the cantilever 1 from above and below and adjusting the length of the arm portion of the cantilever 1 to be extended.

  The jigs to be sandwiched include a jig 2 that sandwiches the cantilever 1 from above and a jig 3 that sandwiches the cantilever 1 from below, and the jig 2 is provided with a piezoelectric element 5 for vibrating the cantilever 1.

  Further, an adjustment mechanism 4 that can adjust the relative positions of the jigs 2 and 3 and the cantilever 1 is provided, and the position of the fixed end of the cantilever 1 can be changed.

  FIG. 1B shows a scanning probe microscope using the cantilever 6.

  As shown in FIG. 1B, the scanning probe microscope of the present embodiment includes a cantilever 6, a laser 7, a photodetector 9, a piezo 10, a controller 12, and a display device 13.

  The laser light emitted from the laser 7 is reflected by the reflecting surface of the cantilever 6 provided with a spring constant variable mechanism, and the reflected light 8 is incident on the photodetector 9.

  The sample 11 can be displaced in the XYZ directions by the piezo 10.

  The controller 12 detects the signal from the photodetector 9 and controls the piezo 10.

  The longer the arm length of the cantilever that comes out of this jig, the smaller the spring constant, and the shorter the arm, the greater the length. The control amount of this signal is displayed on the display device 13.

  As described above, there is a sample in which the material A and the material B are microphase separated. When A is relatively soft, the A material is relatively soft and the B material is relatively hard. Using a visible spring constant best identifies the difference in viscoelasticity between the two.

  Here, the micro phase separation means a state in which two different types of polymers are not melted together and form respective regions with micro size.

  For example, it refers to a state in which the polymer A and the polymer B form an intricate state at the micro level while securing the respective regions, and form as a whole.

  For example, when materials with different mechanical properties, A and B, are microphase-separated, it is possible to obtain the most contrast in this material system by adjusting the spring constant by changing the length of the cantilever to acquire the viscoelastic image. Can be found.

  Even in phase imaging for contrasting the difference between the drive phase of the cantilever 1 and the actual vibration phase of the cantilever 1, an optimum contrast can be obtained by changing the spring constant by such a method.

  Similarly, in cases where the adhesion force of the sample surface is evaluated using a force curve, the spring constant corresponding to the detected adhesion force is determined by repeating the measurement of the force curve and the adjustment of the spring constant. be able to.

  Here, the force curve is a force curve obtained by plotting the displacement of the probe with respect to the distance between the sample and the probe in an AFM (atomic force microscope). From the amount of displacement of the probe, the magnitude of the force received by the probe is known.

  The second method of changing the spring constant is a method of changing the spring constant by applying a voltage to the piezoelectric layer formed on the cantilever of the cantilever 1 and changing the voltage.

  When a piezoelectric layer is formed on one of the upper and lower surfaces of the cantilever 1 (FIG. 2) and the sample surface is pushed in a state where the voltage is applied in the direction in which the cantilever 1 bends (opposite to the warping direction), the voltage is reduced. The spring constant is larger than when no voltage is applied.

  Further, the spring constant can be increased by forming two piezoelectric layers (FIG. 3) insulated from the cantilever 1 and applying a voltage with a polarity that cancels the displacement.

  Although the cantilever 1 is not displaced, the internal constant is applied to each piezoelectric layer, so that the spring constant becomes large.

  The higher the applied voltage, the greater the internal stress and the greater the spring constant.

  As shown in FIGS. 3A and 3C, the piezoelectric layer may be formed by forming two piezoelectric layers that are insulated from each other on either the upper or lower surface of the cantilever 14. It may be formed on the upper and lower surfaces of the cantilever 14 as shown in FIG.

  It is possible to change the spring constant by applying voltage in this way, and it is possible to measure the mechanical properties and adhesive force of the sample surface while changing the spring constant to achieve the best contrast detection. You can find a constant.

[Example]
The present invention will be further described with reference to examples.

Example 1
A sample obtained by laminating low-density polyethylene and high-density polyethylene was sliced in the cross-sectional direction with a microtome and fixed to a substrate.

  The height image of the surface was measured by tapping AFM, and viscoelastic imaging was simultaneously measured.

  Tapping AFM (Atomic Force Microscope) is one of the SPMs and is a method used mainly to measure uneven images on the surface of a sample. A cantilever is used as a probe, and this is vibrated at its resonance frequency. This is a technique of measuring the surface roughness image while intermittently contacting the sample surface.

  Viscoelasticity was measured by a method in which the cantilever was vibrated at the natural frequency of the cantilever holder and the amplitude when it was pushed into the sample was detected.

  Every time one screen was measured, the length of the cantilever arm was shortened by 5 μm and was shortened to 30 μm.

  As shown in FIG. 4, when the length of the cantilever is changed, the relative contrast between the low density polyethylene 20 and the high density polyethylene 21 changes, and the contrast becomes maximum when the length is shortened by 20 μm (FIG. 4 ( d)).

  By changing the length of the cantilever in this way, the spring constant can be changed and the spring constant appropriate for the sample can be adjusted.

(Example 2)
Piezoelectric films were formed on the upper and lower surfaces of the cantilever (FIG. 3B), and viscoelasticity image measurement of the sample similar to that in Example 1 was performed using the piezoelectric films.

  Scanning was performed by XY scanning with 256 lines, and viscoelastic image measurement was performed while applying DC voltages of the same polarity and the same value to the upper and lower piezoelectric films.

  Every 28 lines, the voltage was increased by 5V from 0 to 35V.

  Although the tapping AFM was used for the shape image, when measuring the shape, the voltage was applied to the piezoelectric film without applying a voltage, and the voltage was applied to the piezoelectric film only during viscoelasticity measurement.

  This is to keep the resonance frequency of the cantilever constant when measuring the shape.

  The measurement results are shown in FIG. As for the relative contrast of the high density polyethylene 23 with respect to the low density polyethylene 22, a viscoelastic image having the best contrast was obtained when the applied voltage was 20V.

  In the above embodiment, the piezoelectric layers are formed above and below the cantilever, but two piezoelectric layers may be formed on one surface of the cantilever with insulation.

  In this case, it is possible to continuously increase the spring constant without applying the apparent cantilever displacement by applying the same DC voltage having the opposite polarity.

  Furthermore, a single-layer piezoelectric film may be formed on either the upper or lower surface of the cantilever.

  By applying a voltage in the direction in which the cantilever bends, the force for pushing the probe tip onto the sample surface can be continuously increased.

(Example 3)
In Example 2 above, the spring constant that gives the best contrast is determined by measuring the displacement of the applied voltage vs. the cantilever (FIG. 6) in each of the regions where low density polyethylene and high density polyethylene are laminated. Can do.

  That is, in FIG. 6 showing the displacement of the applied voltage vs. the cantilever, the displacement of the low density polyethylene is 24 and that of the high density polyethylene is 25.

  The difference 26 of the displacement curve in each region is taken, and the applied voltage having the largest value is obtained.

  The applied voltage giving the peak value of the difference curve gives the maximum contrast in the viscoelastic image. In this case, it was about 20V.

  In this way, the optimum spring constant was determined, and the conditions under which the highest contrast could be measured were found.

Example 4
A part of the bulk sample obtained by heating and kneading polyester and styrene acrylic at 130 degrees was flattened with a microtome (analyzing the flattened part of the bulk sample, not the thinned sample).

  Viscoelasticity was measured by pressing the cantilever into the sample surface using the tapping AFM where the surface is intermittently brought into contact with the sample surface while vibrating the cantilever and the natural frequency of the cantilever holder.

  From the viscoelastic image of the 30 μm region, regions having two types of characteristics on the order of several microns were observed (FIG. 7).

  As in Example 1, the applied voltage was adjusted to adjust the spring constant that gives the best contrast.

  Next, after the scanning probe was positioned in the relatively elastic polyester region 27 and switched to the contact mode, the force curve was measured. When no voltage was applied, the tip of the probe was compared with the scanning stroke in the Z direction. Was not separated from the sample surface, and the force curve could not be measured (FIG. 8).

  Therefore, force curve measurement was repeated while applying a DC voltage to the two piezoelectric layers.

  When 10 V was applied, a force curve in which an adhesion force appeared was obtained (FIG. 9).

  When the force curve was measured under the same conditions in the polystyrene region 28 (FIG. 7) having relatively low elasticity, a force curve was obtained, which was about 1/5 of the adhesion force of the polyester region (FIG. 10).

It is a figure for demonstrating the cantilever provided with the mechanism which changes the spring constant by this invention, and the scanning probe microscope provided with the same. It is a figure for demonstrating forming a piezoelectric film in a cantilever and changing a spring constant by this invention. It is a figure for demonstrating forming a piezoelectric film in a cantilever and changing a spring constant by this invention. It is a figure for demonstrating the Example by this invention. It is a figure for demonstrating another Example by this invention. It is a figure for demonstrating another Example by this invention. It is a figure for demonstrating another Example by this invention. The force curve when the adhesion force is larger than the spring stress is shown. It is a figure for demonstrating another Example by this invention. It is a figure for demonstrating another Example by this invention. It is a figure for demonstrating a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cantilever 2 Jig which clamps cantilever 1 from the top 3 Jig which clamps cantilever 1 from the bottom 4 Adjustment mechanism which can adjust the relative position of jigs 2 and 3 and cantilever 5 Piezoelectric element 6 Cantilever which provided spring constant variable mechanism 7 Laser 8 Laser reflected light 9 Photo detector 10 Piezo 11 Sample 12 Controller 13 Display device 14 Cantilever substrate 15 One layer piezoelectric film provided on the upper surface of the cantilever 16 One layer piezoelectric film provided on the lower surface of the cantilever 17 Provided on the upper surface of the cantilever Two layers of piezoelectric films insulated from each other 18 Piezoelectric film provided on the upper and lower surfaces of the cantilever 19 Two layers of piezoelectric films insulated on the lower surface of the cantilever 20 Low density polyethylene region 21 High density polyethylene region 22 Low Density polyethylene region 23 High density poly Styrene region 24 low density polyethylene region cantilever displacement 25 high density polyethylene region cantilever displacement 26 24 25 difference 27 Polyethylene region 28 Polystyrene region 29 substrate 30 cantilever 31 substrate 32 cantilever with respect to the applied voltage with respect to applied voltage to the applied voltage

Claims (12)

In a method for measuring physical property information using a scanning probe microscope,
A cantilever is used as the scanning probe,
By continuously changing the spring constant of the cantilever,
Find the optimum value of the spring constant, which is the easiest to obtain physical property information of the measurement object,
A method of measuring physical property information using a scanning probe microscope, wherein desired physical property information is obtained by a spring having the spring constant. 2. A method for measuring physical property information using a scanning probe microscope according to claim 1, wherein the spring constant of the cantilever is continuously changed to obtain viscoelastic information of the measurement object. 2. The method for measuring physical property information using a scanning probe microscope according to claim 1, wherein a force curve is obtained by continuously changing a spring constant of the cantilever. 2. The method for measuring physical property information using a scanning probe microscope according to claim 1, wherein information indicating a phase of vibration of the cantilever is obtained by continuously changing a spring constant of the cantilever. 5. The method for measuring physical property information using a scanning probe microscope according to claim 1, wherein the spring constant is changed by changing a position of a fixed end of the cantilever. 6. The method of measuring physical property information using a scanning probe microscope according to claim 5, wherein a part of the cantilever is mechanically fixed to change the arm length of the cantilever. The scanning probe microscope according to any one of claims 1 to 5, wherein the spring constant is changed by applying a voltage to the piezoelectric layer formed on the cantilever and changing the voltage. Measuring method of physical property information. 8. The method for measuring physical property information using a scanning probe microscope according to claim 7, wherein a voltage is applied to the piezoelectric layer formed on the cantilever in a direction in which the cantilever bends (opposite to the warping direction). 9. The scanning according to claim 8, wherein a voltage and a voltage are applied to the two piezoelectric layers formed on the cantilever and insulated from each other so that the directions of displacement cancel each other, and the voltage is changed. A method for measuring physical property information using a probe microscope. The scanning probe microscope according to any one of claims 1 to 9,
A scanning probe microscope, wherein the cantilever is used as the scanning probe, and the scanning probe microscope is used in a method for measuring physical property information. A cantilever holder for a scanning probe microscope characterized in that a part of the cantilever is mechanically fixed and the arm length of the cantilever is changed. A scanning probe microscope comprising the cantilever holder according to claim 11.