Conductive Atomic Microscope

Abstract

A conductive atomic microscope is disclosed that can maintain a constant current flowing through the sample and the probe by adjusting the voltage supplied to the sample based on the current flowing through the probe. The conductive atomic microscope includes a voltage supply device that supplies voltage to the sample, a current detection device that detects the current generated by the supplied voltage, and a controller that adjusts the voltage supplied by the voltage supply device to the sample based on the current value detected by the current detection device.

Description

Technical Field

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

Background Art

[0002] An atomic force microscope (AFM) obtains surface information of a sample using a probe. The atomic force microscope includes a probe (Tip) and a cantilever connected to the probe. The cantilever has a property of being easily bent, and the atomic repulsive force acting on the sharp probe attached to its end and the sample surface, that is, the attractive and repulsive forces cause the cantilever to bend, and the surface information of the sample can be obtained by measuring the degree of the bend through the change in the reflection angle of the laser light.

[0003] Atomic force microscopes can be divided into contact mode and non-contact mode. The interatomic force between the probe and the sample changes from a repulsive force to a van der Waals attractive force as the distance between them increases. Contact mode AFMs utilize the repulsive force, while non-contact mode AFMs utilize the attractive force. The magnitude of the repulsive force used in contact mode is very small, about 1 to 10 nN, but the cantilever to which the probe is attached is also very sensitive and will bend with even small changes in force. The angular displacement of the cantilever that occurs at this time also causes the angle of the laser beam reflected from the upper surface of the cantilever to bend, and by measuring the deflection angle of this laser beam with a PSPD (position-sensitive photodiode), it becomes possible to detect very small changes in surface height. The cantilever is usually about 100 μm long, 10 μm wide, and 1 μm thick, and plays the role of amplifying the minute interactions between the probe and the sample and transmitting 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 about 10 nm. Contact-mode AFM has the advantage of being relatively easy to operate and having a fast response speed.

[0004] Contact-mode AFM includes conductive atomic microscopy (C-AFM). Conductive atomic microscopy obtains surface information of a sample by applying a voltage to the sample and / or probe and measuring the current flowing inside the sample by the potential difference.

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

[0006] However, when scanning the surface of a sample, as in conventional conductive atomic microscopes, a constant voltage is applied to the sample and / or probe. In such cases, the current flowing through the sample and / or probe may temporarily exceed a reference range, and this excess current can damage the sample and / or probe. [Overview of the project] [Problems that the invention aims to solve]

[0007] The objective of the present invention to solve the above-mentioned problems is to provide a conductive atomic microscope that can maintain a constant current flowing through the sample and the probe by adjusting the voltage supplied to the sample based on the current flowing through the probe. [Means for solving the problem]

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

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

[0010] The control device controls the voltage supply device based on the current value flowing through the conductor to maintain the current value flowing through the probe within a previously set range. When the current value detected by the current detection device exceeds a previously set current value (set point current), the control device controls the voltage supply device to lower the voltage supplied to the sample.

[0011] If the current value detected by the current detection device is less than a previously set current value (set point current), the control device controls the voltage supply device to increase the voltage supplied to the sample.

[0012] The aforementioned set point current is characterized by being between 10 pA and 20 pA. When the current value detected by the current detection device exceeds a previously set breakdown limit current value, the control device controls the voltage supply device to lower the voltage supplied to the sample.

[0013] After lowering the voltage supplied to the sample, the control device raises the voltage supplied to the sample to the maximum voltage (Max Voltage) if the current value detected by the current detection device is less than the first current value.

[0014] After the control device increases the voltage supplied to the sample to the maximum voltage (Max Voltage), if the current value detected by the current detection device exceeds the second current value, the control device adjusts the voltage supplied to the sample based on the current value detected by the current detection device. [Effects of the Invention]

[0015] The conductive atomic microscope of the present invention makes it possible to maintain a constant current flowing through the sample, thereby preventing damage to the sample and probe caused by currents exceeding a reference range. [Brief explanation of the drawing]

[0016] [Figure 1] This is a simplified block diagram showing the various components of the conductive atomic microscope according to the present invention. [Figure 2] This is a simplified block diagram showing the various components of the conductive atomic microscope according to the present invention. [Figure 3] This figure shows the change in current value due to the supplied voltage during surface measurement of a sample using a conductive atomic microscope. [Figure 4] This figure shows how the current flowing through the sample and probe is limited by the change in current value due to a constant supply voltage and a pre-set current value (set point current) during surface measurement of a sample using a conductive atomic microscope. [Figure 5] This figure shows an IV graph of the voltage adjustment provided to the probe and / or sample by the conductive atomic microscope according to the present invention, based on the current flowing through the probe, cantilever, and conductor. [Figure 6] This figure shows the breakdown characteristics and constant current image of the critical voltage of a conductive atomic microscope. [Figure 7] This figure shows the current limit for protecting the sample and / or probe when a breakdown occurs in the conductive atomic microscope according to the present invention. [Modes for carrying out the invention]

[0017] Hereinafter, some embodiments of the present invention will be described in detail with reference to illustrative drawings. When assigning reference numerals to the components in each figure, it should be noted that, as far as possible, the same component will have the same reference numeral when shown in other drawings.

[0018] Furthermore, in describing embodiments of the present invention, if a specific description of a related known configuration or function is deemed to hinder understanding of the embodiments of the present invention, such detailed description will be omitted.

[0019] In addition, when describing the components of the embodiments of the present invention, terms such as first, second, A, B, (a), (b), etc. can be used. Such terms are only for distinguishing the components from other components, and the essence, order or sequence of the corresponding components are not limited by such terms.

[0020] In this specification, the singular form includes the plural form unless otherwise specified in the text. "Including" and / or "comprising" used in the specification do not exclude the existence or addition of one or more other components in addition to the components mentioned.

[0021] Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 and FIG. 2 are block diagrams briefly showing the components of the conductive atomic microscope 100 according to the present invention.

[0022] The conductive atomic microscope 100 (C-AFM, conductive-AFM) according to the present invention scans the surface of the sample 1 by measuring the current flowing inside the sample 1 through the probe 21 (tip) of the cantilever 20.

[0023] As shown in FIGS. 1 and 2, the conductive atomic microscope 100 according to the present invention includes a voltage supply device 10 (Voltage Supply), a cantilever 20, a current detection device 30 (Current Detection Device), and a control device 40 (Controller).

[0024] The voltage supply device 10 provides a voltage to the sample 1 or the probe 21. By providing a voltage to the sample 1 or the probe 21 by the voltage supply device 10, a potential difference is generated between the sample 1 and the probe 21, and a current flows inside the sample 1 due to the potential difference.

[0025] The current detection device 30 detects and measures the current generated by the voltage supplied to the sample 1 or probe 21. The current detection device 30 detects and measures the current flowing inside the sample 1 based on the potential difference generated by the voltage supplied by the voltage supply device 10.

[0026] The voltage supply device 10 can supply a DC voltage to the sample 1 or the probe 21. When the voltage supply device 10 supplies a DC voltage to the sample 1 or the probe 21, a current flows between the sample 1 and the probe 21 due to the potential difference caused by that DC voltage, and the current detection device 30 detects and measures that current.

[0027] The current flowing inside sample 1 flows along the probe 21 in contact with 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.

[0028] The cantilever 20 and the current detection device 30 are connected by a conductor 33. The current flowing through the probe 21 in contact with the sample 1 and along the cantilever 20 is transmitted to the conductor 33. A current amplifier 31 is provided on the conductor 33 connecting the cantilever 20 and the current detection device 30. The current amplifier 31 amplifies the minute current signals in the pA to μA range flowing through the sample 1 and the cantilever 20, etc.

[0029] The control device 40 receives the current value detected and measured by the current detection device 30. The control device 40 controls the voltage supply device 10 based on the current value received from the current detection device 30. The control device 40 controls the voltage supply device 10 to adjust the voltage supplied to sample 1 and / or probe 21.

[0030] The control device 40 controls the voltage supply device 10 based on the current value flowing through the conductor 33 detected and measured by the current detection device 30, to maintain the current value flowing through the probe 21 within the range of a previously set current value (set point current).

[0031] The voltage supply device 10 can convert and adjust the voltage supplied to sample 1 and / or probe 21 by control signals of the control device 40 through known voltage conversion means. The voltage supply device 10 may, in one embodiment, include known transformers and rectifiers to convert and regulate the voltage supplied to sample 1 and / or probe 21. The voltage supply device 10 can convert the voltage through a transformer and provide a stable voltage through a rectifier based on the control signal of the control device 40.

[0032] The voltage supply device 10 may, in one embodiment, include a known variable resistor to convert and adjust the voltage supplied to sample 1 and / or probe 21. The voltage supply device 10 can adjust the output voltage by adjusting the voltage distribution through a variable resistor controlled by a control signal of the control device 40.

[0033] Figure 3 shows the change in current value due to the supplied voltage during surface measurement of sample 1 through the conductive atomic microscope 100. Specifically, Figure 3(a) shows the change in current value when a constant voltage of 7V is supplied to sample 1 and / or probe 21, and Figure 3(b) shows the change in supplied voltage when the set point current is set to 10pA.

[0034] When the conductive atomic microscope 100 applies a constant voltage to sample 1 and / or probe 21 during surface measurement of sample 1, an event may occur in which the leakage current suddenly increases, as shown in Figure 3(a). The conductive atomic microscope 100 measures the current flowing through the interior of sample 1 through the probe 21 in contact with the surface of sample 1.

[0035] The surface of sample 1 has areas where current flows well and areas where it does not. When the probe 21 comes into contact with an area where current flows well, the leakage current may suddenly increase, as described above. If the leakage current suddenly increases, sample 1 and the probe 21 may be damaged by that leakage current.

[0036] As shown in Figure 3(b), the conductive atomic microscope 100 according to the present invention limits the current flowing through the probe 21, cantilever 20, and conductor 33 to a set point current or less by controlling the voltage supply device 10 to lower the voltage supplied to the sample 1 and / or probe 21 when the leakage current increases above a set point current.

[0037] Figure 4 shows how the current flowing through sample 1 and probe 21 is limited by the change in current value due to a constant supply voltage and a pre-set current value (set point current) during surface measurement of sample 1 through a conductive atomic microscope 100.

[0038] More specifically, Figure 4(a) shows the change in current value when a constant voltage of 7V is provided to sample 1 and / or probe 21, and how the current flowing through sample 1 and probe 21 is limited when the set point current is set to 10pA. Figure 4(b) shows the change in current value when a constant voltage of 7V is provided to sample 1 and / or probe 21, and how the current flowing through sample 1 and probe 21 is limited when the set point current is set to 10pA, 15pA, and 20pA.

[0039] Referring to Figures 4(a) and 4(b), in the conventional conductive atomic microscope method, i.e., when a constant voltage (7V) is applied to sample 1 and / or probe 21 to measure the surface of sample 1, a basic leakage current of around 10 pA exists, and a large leakage current or breakdown current, i.e., an overcurrent, occurs. In this case, the overcurrent can exceed 50 pA, as shown in Figure 4(b).

[0040] In contrast, when measuring the surface of Sample 1 by adjusting the voltage value with the set point current set to 10 pA, 15 pA, and 20 pA, it is possible that an overcurrent of 20 pA or more will not occur.

[0041] In particular, when measuring the surface of Sample 1 by adjusting the voltage value with the set point current set to 20 pA (see Figure 4(b)), the current distribution is similar to that when a constant voltage of 7 V is provided in the current range of 0 to 20 pA, and it can be seen that no overcurrents exceeding 20 pA occur.

[0042] Therefore, when measuring the surface of sample 1, the conductive atomic microscope 100 according to the present invention may have a set point current of 10 pA to 20 pA, preferably set to 20 pA. However, it is not limited to this, and the set point current may be changed depending on the type of sample, that is, to a set point current that is similar to the current distribution when a constant voltage is provided and does not cause overcurrents exceeding a specific current value.

[0043] Figure 5 shows an IV graph of the voltage adjustment provided to sample 1 and / or probe 21 by the conductive atomic microscope 100 according to the present invention, based on the current flowing through the probe 21, cantilever 20, and conductor 33.

[0044] Referring to Figure 5(a), when the conductive atomic microscope 100 according to the present invention measures the surface of the sample 1 through the probe 21, the current detection device 30 measures and detects the current value flowing through the probe 21, the cantilever 20, and the conductor 33, and the control device 40 adjusts the output voltage of the voltage supply device 10 based on the measured and detected current value to limit the occurrence of overcurrent.

[0045] Referring to Figures 5(b) and 5(c), the conductive atomic microscope 100 according to the present invention provides a constant voltage when the current flowing through the probe 21, cantilever 20, and conductor 33 is less than or equal to a set point current (see section A in Figure 5(b)).

[0046] Thereafter, when the current value measured and detected by the current detection device 30 exceeds a set point current, the conductive atomic microscope 100 controls the voltage supply device 10 to gradually lower the voltage supplied to the sample 1 (see section B in Figure 5(b)). By controlling the voltage supply device 10 to gradually lower the voltage supplied to the sample 1, the conductive atomic microscope 100 maintains the current value flowing through the probe 21 and the sample 1 within the range of the set point current, so that the current value flowing through the probe 21 and the sample 1 does not exceed a certain range of the set point current.

[0047] Thereafter, if the current value detected by the current detection device 30 is less than a previously set current value (set point current), the conductive atomic microscope 100 controls the voltage supply device 10 to gradually increase the voltage supplied to the sample 1 (see section C in Figure 5(b)). By controlling the voltage supply device 10 to gradually increase the voltage supplied to the sample 1, the conductive atomic microscope 100 maintains the current value flowing through the probe 21 and the sample 1 within a certain range of the previously set current value (set point current).

[0048] In the conductive atomic microscope 100 according to the present invention, when the current value flowing through the probe 21, cantilever 20, and conductor 33 exceeds or falls below a previously set current value (set point current), the voltage supply device 10 is controlled to gradually adjust the voltage, and it is preferable that the reaction rate at this time is about 1 ms.

[0049] Figure 6 shows a constant current image of the breakdown characteristics and critical voltage of the conductive atomic microscope 100, and Figure 7 shows the current limit for protecting sample 1 and / or probe 21 when breakdown occurs in the conductive atomic microscope 100 according to the present invention.

[0050] In the conductive atomic microscope 100, the breakdown voltage is an important aspect as it can lead to malfunction or damage to sample 1.

[0051] For example, as shown in Figure 6, if a current exceeding a critical value is generated in sample 1 and / or probe 21, causing breakdown, repeated measurements through the conductive atomic microscope 100 may cause sustained damage to sample 1 and / or probe 21.

[0052] As shown in Figure 7, the conductive atomic microscope 100 according to the present invention protects sample 1 and / or probe 21 when a breakdown occurs by controlling the voltage supply device 10 to reduce the voltage supplied to sample 1 when the current value detected by the current detection device 30 exceeds a pre-set critical value (breakdown current).

[0053] Referring to Figure 7(a), in the conductive atomic microscope 100, breakdown may occur, for example, when the leakage current increases by more than 10 times per 1V to 2V.

[0054] As shown in Figure 7(b), the conductive atomic microscope 100 according to the present invention protects sample 1 and / or probe 21 when a breakdown occurs by controlling the voltage supply device 10 to rapidly reduce the voltage supplied to sample 1 when the current value detected by the current detection device 30 exceeds a pre-set breakdown limit current value.

[0055] In detail, the conductive atomic microscope 100 according to the present invention, referring to section (A) of Figure 7(b), provides a constant voltage to sample 1 and / or probe 21 when the current flowing through the probe 21, cantilever 20 and conductor 33 is less than or equal to a pre-set leakage limit current value.

[0056] Referring to section (B) of Figure 7(b), in the conductive atomic microscope 100 according to the present invention, if the current flowing through the probe 21, cantilever 20, and conductor 33 is detected and measured to exceed a pre-set breakdown limit current value, the voltage supply device 10 immediately reduces the voltage supplied to sample 1 and / or probe 21. In one embodiment, if the current flowing through the probe 21, cantilever 20, and conductor 33 is detected and measured to exceed a pre-set breakdown limit current value, the voltage supply device 10 immediately reduces the voltage supplied to sample 1 and / or probe 21, and the reaction rate at this time may be 1 ms or less.

[0057] The conductive atomic microscope 100 according to the present invention detects and measures that the current flowing through the probe 21, cantilever 20, and conductor 33 exceeds a pre-set breakdown limit current value, and immediately reduces the voltage supplied to sample 1 and / or probe 21. If the current flowing through the probe 21, cantilever 20, and conductor 33 is less than a first current value which is less than the leakage limit current, the voltage supplied to sample 1 and / or probe 21 is slowly increased until it saturates at the maximum voltage. Here, the maximum voltage may be the same voltage as the constant voltage supplied to sample 1 and / or probe 21 in section (A) of Figure 7(b).

[0058] In the conductive atomic microscope 100 according to the present invention, when the current flowing through the probe 21, cantilever 20, and conductor 33 is detected and measured to be less than a first current value, the voltage supplied to sample 1 and / or probe 21 is slowly increased until it is saturated at the maximum voltage (Max Voltage). Then, as shown in section (C) of Figure 7(b), if the current flowing through the probe 21, cantilever 20, and conductor 33 exceeds a second current value (Leakage Limit current), the control device 40 adjusts the voltage supplied to sample 1 and / or probe 21 based on the current value flowing through the probe 21, cantilever 20, and conductor 33. When the control device 40 adjusts the voltage supplied to sample 1 and / or probe 21 based on the current value flowing through the probe 21, cantilever 20, and conductor 33, it can slowly decrease or maintain that voltage.

[0059] The control device 40 slowly lowers or maintains the voltage supplied to sample 1 and / or probe 21 based on the current values ​​flowing through the probe 21, cantilever 20, and conductor 33, so that the current values ​​flowing through the probe 21, cantilever 20, and conductor 33 correspond to the leakage limit current value (second current value) (see section C in Figure 7(b)).

[0060] The conductive atomic 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 supplied to the sample 1 and / or the probe 21 based on the current flowing through the probe 21, the cantilever 20 and the conductor 33, as shown in Figure 7(b).

[0061] The scope of protection of the present invention is not limited to the descriptions and expressions of the embodiments explicitly described above. Furthermore, it should be reiterated that the scope of protection of the present invention is not limited by obvious modifications or substitutions in the art to which the present invention pertains.

Claims

1. In a conductive atomic microscope (C-AFM) that scans the surface of a sample by measuring the electric current flowing inside the sample through a cantilever tip, the conductive atomic microscope is: A voltage supply device that provides voltage to the aforementioned sample; A current detection device for detecting the current generated by the aforementioned provided voltage; and A control device that adjusts the voltage value that the voltage supply device provides to the sample based on the current value detected by the current detection device; A conductive atomic microscope, including [a specific type of microscope].

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

3. The control device is The conductive atomic microscope according to claim 2, wherein the voltage supply device is controlled based on the current value flowing through the conductor to maintain the current value flowing through the probe within a previously set range.

4. The control device is The conductive atomic microscope according to claim 3, wherein when the current value detected by the current detection device exceeds a previously set current value (set point current), the voltage supply device is controlled to lower the voltage supplied to the sample.

5. The control device is The conductive atomic microscope according to claim 4, wherein if the current value detected by the current detection device is less than a previously set current value (set point current), the voltage supply device is controlled to increase the voltage supplied to the sample.

6. The conductive atomic microscope according to claim 5, characterized in that the previously set current value (set point current) is 10 pA to 20 pA.

7. The control device is The conductive atomic microscope according to claim 3, wherein when the current value detected by the current detection device exceeds a previously set breakdown limit current value, the voltage supply device is controlled to lower the voltage supplied to the sample.

8. The control device is The conductive atomic microscope according to claim 7, characterized in that, after lowering the voltage supplied to the sample, if the current value detected by the current detection device is less than a first current value, the voltage supplied to the sample is raised to the maximum voltage (Max Voltage).

9. The control device is The conductive atomic microscope according to claim 8, characterized in that, after raising the voltage supplied to the sample to the maximum voltage (Max Voltage), if the current value detected by the current detection device exceeds the second current value, the voltage supplied to the sample is adjusted based on the current value detected by the current detection device.

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