Conductive atomic microscope

Abstract

Disclosed is a conductive atomic microscope in which the current flowing in a sample and a probe can be maintained constant by adjusting the voltage supplied to the sample on the basis of the current flowing in the probe. The conductive atomic microscope comprises: a voltage supply device for supplying voltage to a sample; a current detection device for detecting the current generated by the supplied voltage; and a controller for adjusting the voltage value supplied to the sample by the voltage supply device on the basis of the current value detected by the current detection device.

Description

Conductive atomic force microscope

[0001] The present invention relates to a conductive atomic force microscope, and more particularly, to a conductive atomic force microscope that scans the surface of a sample through a probe of a cantilever in contact with the sample surface.

[0002] An atomic force microscope (AFM) uses a probe to obtain surface information about a sample. An AFM consists of a probe tip and a cantilever connected to the tip. The cantilever is highly flexible, and the sharp probe tip, suspended from its tip, and the atomic repulsive forces acting on the sample surface, i.e., attractive and repulsive forces, cause the cantilever to bend. By measuring the degree of this bending through changes in the angle of reflection of a laser beam, surface information about the sample can be obtained.

[0003] Atomic force microscopy can be divided into contact mode and non-contact mode. The interatomic force between the probe and the sample changes from repulsion to van der Waals attraction as the distance between them increases. Contact mode AFM utilizes repulsion, while non-contact mode AFM utilizes attraction. The repulsion force used in contact mode is very small, on the order of 1 to 10 nN, but the cantilever to which the probe is attached is also very sensitive and bends with small changes in force. This angular displacement of the cantilever also bends the angle of the laser beam reflected from the upper surface of the cantilever. By measuring the angle of deflection of this laser beam with a position-sensitive photodiode (PSPD), it is possible to detect very small surface elevation changes. The cantilever is typically 100 μm long, 10 μm wide, and 1 μm thick, and its role is to amplify the minute interactions between the probe and the sample and transmit them to the macroscopic world. The probe attached to the end of the cantilever is typically 10 μm high and has a tip diameter of approximately 10 nm. Contact-mode AFM has the advantages of being relatively easy to operate and having a fast response time.

[0004] Contact-mode AFM includes conductive atomic force microscopy (C-AFM). C-AFM applies a voltage to a sample and / or probe and measures the current flowing through the sample due to the potential difference, thereby obtaining surface information about the sample.

[0005] Conventional conductive atomic force microscopes measure the IV characteristics of a sample by applying a constant voltage to the sample and / or probe. The IV characteristics include the resistance between the probe and sample and the threshold voltage.

[0006] However, as in a conventional conductive atomic force microscope, when a constant voltage is applied to the sample and / or probe while scanning the surface of the sample, there is a problem that the current flowing through the sample and / or probe may temporarily exceed the reference range, and the current exceeding the reference range may damage the sample and / or probe.

[0007] An object of the present invention to solve the above-described problems is to provide a conductive atomic force microscope capable of maintaining the current flowing through a sample and a probe constant by adjusting the voltage provided to the sample based on the current flowing through the probe.

[0008] In order to achieve the above-described object, a conductive atomic force microscope according to one embodiment of the present invention is a conductive atomic force microscope (C-AFM) that scans the surface of a sample by measuring a current flowing inside the sample through a tip of a cantilever, and the conductive atomic force microscope includes a voltage supply device that provides a voltage to the sample, a current detection device that detects a current generated by the provided voltage, and a controller that adjusts a voltage value provided to the sample by the voltage supply device based on a current value detected by the current detection device.

[0009] The above cantilever and the current detection device are connected by a conductor through which a current generated by the provided voltage flows, and a current amplifier that amplifies the current transmitted from the cantilever is installed on the conductor.

[0010] The above control device controls the voltage providing device based on the current value flowing in the conductor, thereby maintaining the current value flowing in the probe within a preset current value range.

[0011] The above control device controls the voltage providing device to lower the voltage provided to the sample when the current value detected by the current detection device exceeds a preset current value (set point current).

[0012] The above control device controls the voltage providing device to increase the voltage provided to the sample when the current value detected by the current detection device is less than a preset current value (set point current).

[0013] The above-described set point current is characterized by being 10 pA to 20 pA.

[0014] The above control device controls the voltage providing device to lower the voltage provided to the sample when the current value detected by the current detection device exceeds a preset breakdown limit current value.

[0015] The above control device lowers the voltage provided to the sample, and then, when the current value detected by the current detection device is less than the first current value, increases the voltage provided to the sample to the Max Voltage.

[0016] The control device increases the voltage provided to the sample to the Max Voltage, and when the current value detected by the current detection device exceeds the second current value, adjusts the voltage provided to the sample based on the current value detected by the current detection device.

[0017] According to the conductive atomic force microscope of the present invention, the current flowing through the sample can be maintained at a constant level, thereby preventing damage to the sample and probe caused by a current exceeding a reference range.

[0018] Figures 1 and 2 are block diagrams briefly showing each component of a conductive atomic microscope according to the present invention.

[0019] Figure 3 is a diagram showing the change in current value according to the voltage provided when measuring the surface of a sample using a conductive atomic force microscope.

[0020] Figure 4 is a drawing showing the change in current value according to a constant voltage applied when measuring the surface of a sample using a conductive atomic force microscope and the current flowing through the sample and probe being limited according to a preset current value (set point current).

[0021] FIG. 5 is a diagram showing IV graphs when the conductive atomic force microscope according to the present invention adjusts the voltage provided to the probe and / or sample based on the current flowing in the probe, cantilever, and wire.

[0022] Figure 6 is a diagram showing the breakdown characteristics of a conductive atomic force microscope and a constant current image of the critical voltage.

[0023] FIG. 7 is a drawing showing a current limit for protecting a sample and / or probe when a breakdown occurs in a conductive atomic force microscope according to the present invention.

[0024] Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. When designating components in each drawing, it should be noted that, where possible, identical components are given the same reference numerals, even if they appear in different drawings.

[0025] And when describing an embodiment of the present invention, if it is determined that a specific description of a related known configuration or function hinders understanding of the embodiment of the present invention, the detailed description is omitted.

[0026] Additionally, in describing components of embodiments of the present invention, terms such as first, second, A, B, (a), (b), etc. may be used. These terms are only intended to distinguish the components from other components, and the nature, order, or sequence of the components are not limited by the terms.

[0027] In this specification, the singular includes the plural unless specifically stated otherwise. The terms “comprises” and / or “comprising” as used herein do not exclude the presence or addition of one or more other components in addition to the components mentioned.

[0028] Hereinafter, the present invention will be described in more detail with reference to the attached drawings.

[0029]

[0030] Figures 1 and 2 are block diagrams briefly showing each configuration of a conductive atomic microscope (100) according to the present invention.

[0031] The conductive atomic force microscope (100, C-AFM, conductive-AFM) according to the present invention scans the surface of a sample (1) by measuring the current flowing inside the sample (1) through the probe (21, tip) of the cantilever (20, cantilever).

[0032] The conductive atomic microscope (100) according to the present invention, with reference to FIGS. 1 and 2, includes a voltage supply device (10), a cantilever (20), a current detection device (30), and a control device (40).

[0033] A voltage providing device (10) provides voltage to a sample (1) or a probe (21). As the voltage providing device (10) provides voltage to the sample (1) or the probe (21), a potential difference occurs between the sample (1) and the probe (21), and a current flows inside the sample (1) due to the potential difference.

[0034] The current detection device (30) detects and measures the current generated by the voltage provided to the sample (1) or the probe (21). The current detection device (30) detects and measures the current flowing inside the sample (1) according to the potential difference generated by the voltage provided by the voltage providing device (10).

[0035] The voltage providing device (10) can provide a direct current voltage to the sample (1) or the probe (21). When the voltage providing device (10) provides a direct current voltage to the sample (1) or the probe (21), a current flows through the sample (1) and the probe (21) due to a potential difference according to the direct current voltage, and the current detection device (30) detects and measures the current.

[0036] The current flowing inside the sample (1) flows along the probe (21) in contact with the sample (1) and the cantilever (20) connected to the probe (21). The current detection device (30) detects and measures the current flowing along the probe (21) and the cantilever (20).

[0037] The cantilever (20) and the current detection device (30) are connected by a conductor (33). The current flowing along the probe (21) and the cantilever (20) in contact with the sample (1) is transmitted and flows through the conductor (33). A current amplifier (31) is installed on the conductor (33) connecting the cantilever (20) and the current detection device (30). The current amplifier (31) amplifies a minute current signal of the pA to μA level flowing through the sample (1) and the cantilever (20).

[0038] The control device (40) receives the current value detected and measured by the current detection device (30) from the current detection device (30). The control device (40) controls the voltage providing device (10) based on the current value received from the current detection device (30). The control device (40) controls the voltage providing device (10) to adjust the voltage provided to the sample (1) and / or the probe (21).

[0039] The control device (40) controls the voltage providing device (10) based on the current value flowing in the conductor (33) detected and measured by the current detection device (30), thereby maintaining the current value flowing in the probe (21) within the set point current range.

[0040] The voltage providing device (10) can convert and adjust the voltage provided to the sample (1) and / or probe (21) according to the control signal of the control device (40) through a known voltage conversion means.

[0041] The voltage providing device (10) may include, as an example, a known transformer and rectifier to convert and regulate the voltage provided to the sample (1) and / or the probe (21). The voltage providing device (10) may convert the voltage through the transformer according to a control signal of the control device (40) and provide a stable voltage through the rectifier.

[0042] The voltage providing device (10) may include, as an example, a known variable resistance device to convert and regulate the voltage provided to the sample (1) and / or the probe (21). The voltage providing device (10) may regulate the output voltage by adjusting the voltage distribution through the variable resistance device controlled according to the control signal of the control device (40).

[0043]

[0044] FIG. 3 is a diagram showing changes in current values ​​according to the voltage applied when measuring the surface of a sample (1) using a conductive atomic force microscope (100). Specifically, (a) of FIG. 3 is a diagram showing changes in current values ​​when a constant voltage of 7 V is applied to the sample (1) and / or the probe (21), and (b) of FIG. 3 is a diagram showing changes in the applied voltage when the set point current is set to 10 pA.

[0045] When a conductive atomic force microscope (100) provides a constant voltage to the sample (1) and / or the probe (21) during surface measurement of the sample (1), an incident in which the leakage current suddenly increases may occur, as shown in (a) of FIG. 3. The conductive atomic force microscope (100) measures the current flowing inside the sample (1) through the probe (21) in contact with the surface of the sample (1).

[0046] On the surface of the sample (1), there are areas where current flows well and areas where current does not flow well, and when the probe (21) comes into contact with the area where current flows well, the leakage current may suddenly increase as described above. When the leakage current suddenly increases, the sample (1) and the probe (21) may be damaged by the leakage current.

[0047] In the conductive atomic force microscope (100) according to the present invention, as shown in (b) of FIG. 3, when the leakage current increases more than a preset current value (set point current), the control device (40) controls the voltage providing device (10) to lower the voltage provided to the sample (1) and / or the probe (21), thereby limiting the current flowing through the probe (21), the cantilever (20), and the wire (33) to less than a preset current value (set point current).

[0048]

[0049] FIG. 4 is a drawing showing the change in current value according to a constant voltage applied when measuring the surface of a sample (1) using a conductive atomic force microscope (100) and the current flowing through the sample (1) and the probe (21) being limited according to a preset current value (set point current).

[0050] In detail, (a) of FIG. 4 is a drawing showing the change in current value when a constant voltage of 7 V is provided to the sample (1) and / or the probe (21) and the current flowing through the sample (1) and the probe (21) is limited when the preset current value (set point current) is set to 10 pA, and (b) of FIG. 4 is a drawing showing the change in current value when a constant voltage of 7 V is provided to the sample (1) and / or the probe (21) and the current flowing through the sample (1) and the probe (21) is limited when the preset current value (set point current) is set to 10 pA, 15 pA, and 20 pA.

[0051] Referring to (a) and (b) of FIG. 4, when measuring the surface of a sample (1) by applying a constant voltage (7 V) to the sample (1) and / or probe (21) in the conventional conductive atomic force microscope method, a basic leakage current of about 10 pA exists, and a large leakage current or breakdown current, i.e., an overcurrent, occurs. As shown in (b) of FIG. 4, the overcurrent may be 50 pA or more.

[0052] On the other hand, when measuring the surface of the sample (1) by adjusting the voltage value while setting the set point current to 10 pA, 15 pA, and 20 pA, an overcurrent of 20 pA or more may not occur.

[0053] In particular, when measuring the surface of the sample (1) by adjusting the voltage value while setting the set point current to 20 pA (see (b) of Fig. 4), it can be seen that the current value distribution is similar to that when a constant voltage of 7 V is provided in the range of 0 to 20 pA of the current value, and that no overcurrent of 20 pA or more occurs.

[0054] Accordingly, the conductive atomic force microscope (100) according to the present invention may set the preset current value (set point current) at 10 pA to 20 pA when measuring the surface of the sample (1), and may preferably be set to 20 pA. However, the present invention is not limited thereto, and the preset current value may be changed to a preset current value that is similar to the current value distribution when a constant voltage is provided and does not cause an overcurrent exceeding a specific current value, depending on the type of the sample.

[0055]

[0056] FIG. 5 is a diagram showing IV graphs when a conductive atomic force microscope (100) according to the present invention adjusts the voltage provided to a sample (1) and / or a probe (21) based on the current flowing through the probe (21), cantilever (20), and wire (33).

[0057] Referring to (a) of FIG. 5, in the conductive atomic force microscope (100) according to the present invention, when measuring the surface of a sample (1) through a probe (21), a current detection device (30) measures and detects the current value flowing in the probe (21), the cantilever (20), and the conductor (33), and based on the measured and detected current value, a control device (40) adjusts the output voltage of the voltage supply device (10) to limit the occurrence of overcurrent.

[0058] Referring to (b) and (c) of FIG. 5, the conductive atomic force microscope (100) according to the present invention provides a constant voltage when the current value flowing through the probe (21), the cantilever (20), and the wire (33) is lower than a preset current value (set point current) (see section A of (b) of FIG. 5).

[0059] Thereafter, the conductive atomic microscope (100) controls the voltage providing device (10) to gradually lower the voltage provided to the sample (1) when the current value measured and detected by the current detection device (30) exceeds the preset current value (set point current) (see section B of (b) of FIG. 5). As the conductive atomic microscope (100) controls the voltage providing device (10) to gradually lower the voltage provided to the sample (1), the current value flowing to the probe (21) and the sample (1) is maintained within the preset current value (set point current) range so that the current value flowing to the probe (21) and the sample (1) does not exceed a certain range of the preset current value (set point current).

[0060] Thereafter, the conductive atomic microscope (100) controls the voltage providing device (10) to gradually increase the voltage provided to the sample (1) if the current value detected by the current detection device (30) is less than the preset current value (set point current) (see section C of (b) of FIG. 5). The conductive atomic microscope (100) controls the voltage providing device (10) to gradually increase the voltage provided to the sample (1), thereby maintaining the current value flowing through the probe (21) and the sample (1) within a certain range of the preset current value (set point current).

[0061] The conductive atomic force microscope (100) according to the present invention controls the voltage supply device (10) to gradually adjust the voltage when the current value flowing through the probe (21), cantilever (20) and wire (33) exceeds or falls below a preset current value (set point current), and it is preferable that the response speed at this time be approximately 1 ms.

[0062]

[0063] FIG. 6 is a drawing showing a constant current image of the breakdown characteristics and threshold voltage of a conductive atomic microscope (100), and FIG. 7 is a drawing showing a current limit for protecting a sample (1) and / or a probe (21) when a breakdown occurs in a conductive atomic microscope (100) according to the present invention.

[0064] In a conductive atomic microscope (100), the breakdown voltage is an important aspect as it can lead to malfunction or damage to the sample (1).

[0065] For example, as shown in FIG. 6, when a current exceeding a threshold value is generated in the sample (1) and / or the probe (21) and a breakdown occurs, the sample (1) and / or the probe (21) may be continuously damaged by repeated measurements using a conductive atomic force microscope (100).

[0066] The conductive atomic microscope (100) according to the present invention, as shown in FIG. 7, controls the voltage providing device (10) to lower the voltage provided to the sample (1) when the current value detected by the current detection device (30) exceeds a preset threshold value (breakdown current), thereby protecting the sample (1) and / or the probe (21) when a breakdown occurs.

[0067] Referring to (a) of FIG. 7, breakdown in a conductive atomic force microscope (100) may occur, for example, when the leakage current increases by more than 10 times per 1 V to 2 V.

[0068] The conductive atomic microscope (100) according to the present invention, as shown in (b) of FIG. 7, controls the voltage providing device (10) to rapidly lower the voltage provided to the sample (1) when the current value detected by the current detection device (30) exceeds a preset breakdown limit current value, thereby protecting the sample (1) and / or the probe (21) when a breakdown occurs.

[0069] In detail, referring to section (A) of Fig. 7 (b), the conductive atomic force microscope (100) according to the present invention provides a constant voltage to the sample (1) and / or the probe (21) when the current flowing through the probe (21), the cantilever (20), and the conductor (33) is below a preset leakage limit current value.

[0070] Referring to section (B) of Fig. 7 (b), in the conductive atomic force microscope (100) according to the present invention, when the current flowing through the probe (21), the cantilever (20), and the wire (33) is detected and measured to exceed a preset breakdown limit current value, the voltage providing device (10) immediately lowers the voltage provided to the sample (1) and / or the probe (21). In one embodiment, when the current flowing through the probe (21), the cantilever (20), and the wire (33) is detected and measured to exceed a preset breakdown limit current value, the voltage providing device (10) immediately lowers the voltage provided to the sample (1) and / or the probe (21), and the response speed at this time may be 1 ms or less.

[0071] The conductive atomic force microscope (100) according to the present invention detects and measures that the current flowing through the probe (21), the cantilever (20), and the wire (33) exceeds a preset breakdown limit current value, immediately lowers the voltage provided to the sample (1) and / or the probe (21), and then, when the current flowing through the probe (21), the cantilever (20), and the wire (33) is less than a first current value smaller than the leakage limit current, slowly increases the voltage provided to the sample (1) and / or the probe (21) until it is saturated at the max voltage. Here, the max voltage may be the same voltage as the constant voltage provided to the sample (1) and / or the probe (21) in the section (A) of Fig. 7 (b).

[0072] The conductive atomic force microscope (100) according to the present invention detects and measures that the current flowing through the probe (21), the cantilever (20), and the wire (33) is less than a first current value, and slowly increases the voltage provided to the sample (1) and / or the probe (21) until it is saturated with the Max Voltage, and then, as in section (C) of Fig. 7 (b), when the current flowing through the probe (21), the cantilever (20), and the wire (33) exceeds a second current value (Leakage Limit current), the control device (40) adjusts the voltage provided to the sample (1) and / or the probe (21) based on the current value flowing through the probe (21), the cantilever (20), and the wire (33). The control device (40) can slowly lower or maintain the voltage provided to the sample (1) and / or the probe (21) based on the current value flowing through the probe (21), cantilever (20) and wire (33).

[0073] The control device (40) slowly lowers or maintains the voltage provided to the sample (1) and / or the probe (21) based on the current value flowing through the probe (21), the cantilever (20), and the wire (33), thereby controlling the current value flowing through the probe (21), the cantilever (20), and the wire (33) to correspond to the leakage limit current value (second current value) (see section C of (b) of Fig. 7).

[0074] The conductive atomic force microscope (100) according to the present invention can protect the sample (1) and / or the probe (21) when a breakdown occurs by adjusting the voltage provided to the sample (1) and / or the probe (21) based on the current flowing in the probe (21), the cantilever (20), and the wire (33), as shown in (b) of FIG. 7.

[0075]

[0076] The scope of protection of the present invention is not limited to the description and expression of the embodiments explicitly described above. Furthermore, it should be noted that the scope of protection of the present invention may not be limited by obvious modifications or substitutions within the technical field to which the present invention pertains.

Claims

1. In a conductive atomic force microscope (C-AFM) that scans the surface of a sample by measuring the current flowing inside the sample through the tip of a cantilever, the conductive atomic force microscope, A voltage supply device that provides voltage to the above sample; A current detection device that detects the current generated by the voltage provided above; and A controller that adjusts the voltage value provided to the sample by the voltage providing device based on the current value detected by the current detection device; Conductive atomic force microscope, including.

2. In claim 1, The above cantilever and the current detection device are connected to a conductor through which a current generated by the provided voltage flows, A conductive atomic force microscope, wherein a current amplifier for amplifying the current transmitted from the cantilever is installed on the above conductor.

3. In claim 2, The above control device, A conductive atomic force microscope that controls the voltage supply device based on the current value flowing in the conductor, thereby maintaining the current value flowing in the probe within a preset current value range.

4. In claim 3, The above control device, A conductive atomic force microscope that controls the voltage providing device to lower the voltage provided to the sample when the current value detected by the current detection device exceeds a preset current value (set point current).

5. In claim 4, The above control device, A conductive atomic force microscope that controls the voltage providing device to increase the voltage provided to the sample when the current value detected by the current detection device is less than a preset current value (set point current).

6. In claim 5, A conductive atomic force microscope, characterized in that the set point current is 10 pA to 20 pA.

7. In claim 3, The above control device, A conductive atomic force microscope that controls the voltage supply device to lower the voltage provided to the sample when the current value detected by the current detection device exceeds a preset breakdown limit current value.

8. In claim 7, The above control device, A conductive atomic force microscope characterized in that, after lowering the voltage provided to the sample, if the current value detected by the current detection device is less than the first current value, the voltage provided to the sample is increased to the Max Voltage.

9. In claim 8, The above control device, A conductive atomic force microscope characterized in that, after increasing the voltage provided to the sample to the maximum voltage, if the current value detected by the current detection device exceeds the second current value, the voltage provided to the sample is adjusted based on the current value detected by the current detection device.

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