Scanning noise microscope

Abstract

To provide a scanning noise microscope capable of measuring at both low temperatures and a room temperature.SOLUTION: There is provided a scanning noise microscope comprising a sample stage whose sample position is adjustable, a probe support unit for supporting a probe and capable of adjusting the position of the probe and bringing the tip of the probe close to the surface of the sample, an objective lens, and an optical detector capable of detecting a terahertz wave focused by the objective lens, the scanning noise microscope measuring a passive near-field signal obtained by scattering the near-field light of the sample itself at the tip of the probe. The optical detector is disposed in a first chamber, and the sample stage, the probe support unit, and the objective lens are disposed in a second chamber, with the first and second chambers constituted to be capable of controlling the temperature independently.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a scanning noise microscope (SNoiM), and more particularly to a scanning noise microscope that can be used both at low and room temperatures. [Background technology]

[0002] Conventionally, in the field of optical measurement technology, there has been a problem in that the resolution of geometric microscopes cannot exceed the wavelength. A scattering-type scanning near-field optical microscope (s-SNOM) achieves a resolution far exceeding the wavelength by using active measurement, which focuses excitation light on a probe and measures the scattered light generated by the near-field effect.

[0003] On the other hand, a light detection device called CSIP (Charge Sensitive Infrared Phototransistor) is used to detect the emission light generated by the sample itself at the nanoscale without using an external light source. A measurement method using a passive near-field microscope that uses a detector has been realized. By using such a passive near-field microscope, it is possible to directly measure, for example, terahertz waves (wavelength 10 μm to 1 mm), which are light or electromagnetic waves in the region between infrared and microwaves emitted from the molecular motion and photon vibration of the sample itself, making it possible to observe the state of biological reactions in cells and the state of gold nanoparticle catalytic reactions.

[0004] The operation of the CSIP photodetector requires a low vacuum temperature. Non-Patent Document 1 discloses a scanning noise microscope in which the entire device is placed in a chamber and maintained at a low temperature (4.2 K) and a vacuum. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Lin, K.-T.; Weng, Q.; Kim, S.; Komiyama, S.; Kajihara, Y. Development of a Cryogenic Passive-Scattering-Type near-Field Optical Microscopy System. Rev. Sci. Instrum. 2023, 94, 023701 Summary of the Invention [Problem to be solved by the invention]

[0006] In the device of Non-Patent Document 1, the entire device is kept at a low temperature and in a vacuum, but when replacing the sample or the probe, the entire device returns to room temperature and atmospheric pressure. In order to perform measurements again, cooling and decompression are required again, which takes time and effort. For example, when performing preliminary measurements to select a high-quality probe, the probe needs to be replaced, which takes a huge amount of time.

[0007] An object of the present disclosure is to provide a scanning noise microscope that is capable of measurement at both low and room temperatures and that allows easy replacement of samples and probes. [Means for solving the problem]

[0008] The first aspect of the present invention is a sample stage capable of adjusting the position of the sample; a probe support unit that supports a probe and is capable of adjusting a position of the probe to bring a tip of the probe close to a surface of the sample; An objective lens; a photodetector capable of detecting the terahertz wave collected by the objective lens; A scanning noise microscope for measuring a passive near-field signal obtained by scattering near-field light of the sample itself at the tip of the probe, the photodetector is disposed within the first chamber; the sample stage, the probe support, and the objective lens are disposed in a second chamber; The first chamber and the second chamber are configured to be capable of independent temperature control. The scanning noise microscope is characterized by the above.

[0009] According to this embodiment, the temperatures of the first and second chambers can be controlled independently, making it possible to measure a sample at room temperature (high temperature), and also to maintain the photodetector at a low temperature even if the second chamber reaches room temperature when replacing the sample or probe.

[0010] This aspect further includes a refrigerant container for accommodating a refrigerant, and a cooling rod extending from the refrigerant container is vacuum insulated in the second chamber. For example, the sample stage may be placed on a cooling plate and be in thermal contact with the cooling rod via a metal wire connecting the cooling plate.

[0011] In this aspect, the cooling plate and a lens shield surrounding the objective lens may be in thermal contact with each other. For example, the cooling plate and the lens shield may be in thermal contact with each other via a metal wire connecting the sample stage and the lens shield.

[0012] This aspect may further include a shielding portion that covers the sample and the objective lens to block background radiation. The shielding portion can prevent background radiation from entering a detector, enabling highly accurate measurement.

[0013] This aspect may further include a shielding unit opening / closing mechanism that moves the shielding unit to switch between a shielded state and a non-shielded state. By switching the shielding unit to the non-shielded state, it is possible to observe the appearance of the sample or for alignment.

[0014] This aspect may further include a detection unit position adjustment unit capable of moving the detection unit including the photodetector in the first chamber relative to the second chamber. For example, the detector unit position adjustment mechanism may include an X-axis operation gear, a Y-axis operation gear, and a Z-axis operation gear for moving the detector unit in the X-axis direction, the Y-axis operation gear, and the Z-axis direction, respectively, a moving gear that can be moved to a position meshing with the X-axis operation gear, the Y-axis operation gear, and the Z-axis operation gear, respectively, and an operation rod that moves and rotates the moving gear. Such a position adjustment mechanism allows the position adjustment while maintaining the photodetector at a low temperature, enabling efficient measurement. Effect of the Invention

[0015] According to the present disclosure, a single scanning noise microscope can be used to perform measurements at both low and room temperatures, and samples and probes can be easily replaced. [Brief description of the drawings]

[0016] [Figure 1] 1 is a diagram showing a schematic configuration of a scanning noise microscope according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing a cooling structure of an AFM chamber in an embodiment. [Diagram 3] 1A and 1B are diagrams illustrating a background radiation blocking portion according to an embodiment. [Figure 4] 5A and 5B are diagrams illustrating a position adjustment mechanism for a photodetector in the embodiment. [Diagram 5] 5A and 5B are diagrams illustrating a position adjustment mechanism for a photodetector in the embodiment. [Figure 6] 11 is a graph showing a cooling retention time of the AFM system in the present embodiment. [Figure 7] 1A and 1B are diagrams showing the results of far-field measurement using a scanning noise microscope according to the present embodiment. [Figure 8] 1A and 1B are diagrams showing the results of near-field measurement using a scanning noise microscope according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, the embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto. The components of the embodiments described below can be combined as appropriate.

[0018] The scanning noise microscope (SNoiM) according to this embodiment is a passive near-field optical microscope that measures near-field light (evanescent waves) emitted by the sample itself by scattering them at the tip of a probe, without irradiating the sample or probe with light. A photodetector capable of detecting terahertz waves is used to detect the near-field optical signal, and this photodetector needs to be cooled to about 5K or less to operate.

[0019] This embodiment is similar to the microscope according to the prior art (Non-Patent Document 1) in that it is a scanning noise microscope. However, the prior art scanning noise microscope is only capable of low-temperature measurement in a vacuum, and the entire device is cooled. The scanning noise microscope according to this embodiment improves on the scanning noise microscope according to the prior art in the following respects.

[0020] The scanning noise microscope according to this embodiment allows measurements not only at low vacuum temperatures but also at room temperature. Also, the sample and the probe can be replaced while the detector is kept at a low temperature. Since the probe can be replaced while the detector is kept at a low temperature and measurements can be performed at room temperature, measurements in which the probe is replaced can be performed multiple times in a short period of time. Therefore, a high-quality probe can be selected quickly.

[0021] In this embodiment, the detector and the AFM system are placed in different chambers and their temperatures can be controlled independently, which allows room temperature measurement while the detector is kept at a low temperature. When the chambers are separated in this way, the problem arises of how to cool the AFM system including the sample. Another problem arises of extending the low temperature retention time. Furthermore, as the chamber becomes narrower, alignment of the detector and the optical system becomes difficult, and this point also needs to be considered. The scanning noise microscope according to this embodiment allows measurements at room temperature by placing the detector and the AFM system in different chambers, and also solves these problems.

[0022] Fig. 1 is a diagram showing a schematic configuration of a scanning noise microscope according to this embodiment. As shown in Fig. 1, the scanning noise microscope has a configuration in which a detector chamber 100 including a photodetector 111 and an AFM chamber 200 including an AFM system are installed on a vibration isolation table 400. The photodetector 111 in the detector chamber 100 and the AFM system in the AFM chamber 200 can be independently temperature controlled. The detector chamber 100 and the AFM chamber 200 correspond to the first chamber and the second chamber, respectively, in the present invention.

[0023] The detector unit 110 is disposed in the cooling shield 120 of the detector chamber 100. The detector unit 110 includes a photodetector 111, a lens 112, and a pinhole 113. The photodetector 111, the lens 112, and the pinhole 113, together with the objective lens 226, constitute a confocal microscope. The photodetector 111 can detect terahertz light collected by the objective lens 226. The photodetector 111 is, for example, a CSIP detector, and has a detectable wavelength of about 8 to 20 μm and an operating temperature of liquid helium temperature, i.e., about 4.2 K. Therefore, the inside of the cooling shield 120 is kept at about 4.2 K by a refrigerator (not shown). The detector chamber 100 includes a first heat retention tank at the liquid helium temperature (about 4.2 K) and a second heat retention tank at the liquid nitrogen temperature (about 77 K). The detector chamber 100 also includes: The vacuum is maintained by a vacuum device (not shown).

[0024] Furthermore, the detector unit 110 can be moved in the X, Y and Z directions by a detector unit position adjustment mechanism 130, enabling alignment of the photodetector 111 with the objective lens 226. Note that position adjustment by the detector unit position adjustment mechanism 130 can be performed while the photodetector 111 is maintained at an extremely low temperature. Details of the detector unit position adjustment mechanism 130 will be described later.

[0025] An AFM system is installed in the AFM chamber 200. The AFM system includes a sample stage 220, a driving unit 221, a probe support unit 222, and a probe 223. The sample stage 220 can place a sample 224 thereon, and can adjust the position of the sample 224 in the XY directions. The probe 223 is attached to the tip of the probe support unit 222. The probe support unit 222 supports the probe 223, and is driven in the XYZ directions by the driving unit 221 to adjust the position of the probe 223, and can bring the tip of the probe 223 close to the surface of the sample 224. In this way, a three-dimensional image of the sample 224 is obtained by imaging the sample 224 while scanning or sweeping the probe 223 relative to the sample 224.

[0026] The AFM system can be set to a low temperature using a cooling mechanism, and can be evacuated using a vacuum device (not shown).

[0027] The AFM system is placed on a cooling plate 210 and surrounded by a cooling shield 211 and a shutter 212. The cooling shield 211 and the shutter 212 are made of aluminum, which has good thermal conductivity and can shield background radiation at room temperature (300K). The shutter 212 can be moved up and down along a lens shield 227 surrounding an objective lens 226 by a shutter opening / closing mechanism 213, and can be switched between a shielded state and a non-shielded state. Note that FIG. 1 shows the shutter 212 in a closed state. Details of the shutter opening / closing mechanism 213 will be described later. Note that the shutter 212 and the shutter opening / closing mechanism 213 correspond to the shielding section and the shielding section opening / closing mechanism of the present invention, respectively.

[0028] When the shutter 212 is closed, the inside is kept at a low temperature by the cooling plate 210, the cooling shield 211, the shutter 212, and the lens shield 227. The AFM system is cooled by a coolant (liquid nitrogen) contained in a coolant container 300. FIG. 2 is a diagram showing the cooling structure of the AFM chamber 200. A copper rod 301 for cooling, which contacts the bottom of the coolant container 300, extends into the AFM chamber 200, and a copper wire 302 provided at the tip of the copper rod 301 is connected to the cooling plate 210. This thermal contact keeps the AFM system at the liquid nitrogen temperature (about 77K). In addition, a part of the AFM system and the lens shield 227 are in thermal contact with each other by the copper wire 225, and the objective lens 226 is also cooled. In FIG. 1, the copper wire 302 is connected to the driving unit 221, but it may be connected to other parts such as the cooling plate 210 or the sample stage 220. Although copper is used as the material for the rods and wires, other metals with good electrical conductivity may be used.

[0029] The state of the sample 224 in the AFM chamber can be observed by a microscope 228 equipped with a CCD camera.

[0030] The opening and closing of the shutter 212 will be described with reference to FIG. 3. The shutter 212 can move up and down, and FIG. 3 shows both a state 212A in which the shutter 212 is located at the bottom end and a state 212B in which the shutter 212 is located at the top end. When the shutter 212 is in the bottom end position, the shutter 212 is in contact with the cooling shield 211, and the inside of the AFM system is shielded from background radiation. On the other hand, when the shutter 212 is in the top end position, light from the AFM system can be seen through the opening on the top surface of the cooling shield 211. The system can be accessed and observed.

[0031] The shutter opening / closing mechanism 213 is generally composed of a shutter operating rod 401, a magpie gear 402, a magpie gear 403, a connecting member 404, and a feed screw 405. The connecting member 404 is connected to the shutter 212, and the internal thread of the connecting member 404 meshes with the feed screw 405, so that the shutter 212 moves up and down as the feed screw 405 rotates. When adjusting the position of the shutter 212, the shutter operating rod 401 engaged with the shaft of the magpie gear 402 is rotated to rotate the magpie gear 402. The magpie gear 402 meshes with the magpie gear 403, so that the magpie gear 403 and the feed screw 405 rotate as the magpie gear 402 rotates. In this way, the shutter operating rod 401 can adjust the vertical position of the shutter 212.

[0032] Next, the detector unit position adjustment mechanism 130 of the detector unit 110 will be described with reference to Fig. 4 and Fig. 5. Fig. 4(A) is a bottom view of the detector unit position adjustment mechanism 130, Fig. 4(B) is a cross-sectional view taken along line AA in Fig. 4(A), and Fig. 5 is a side view of the detector unit position adjustment mechanism as viewed from a direction parallel to the axis of the operating rod.

[0033] The detector unit position adjustment mechanism 130 is generally composed of an operating rod 501, a moving gear 503, an X-axis operating gear 505, a Y-axis operating gear 506, and a Z-axis operating gear 507. The X-axis operating gear 505, the Y-axis operating gear 506, and the Z-axis operating gear 507 move the detector unit 110 in the X-axis, Y-axis, and Z-axis directions by rotating, respectively. The operating rod 501 penetrates the cooling shield 120 from the outside of the detector chamber 100. Note that the operating rod 501 is the only member that penetrates the cooling shield 120. The operating rod 501 has an operating rod chuck 502 engaged with a moving gear chuck 504. The moving gear 503 can be moved by the operating rod 501 to a position where it meshes with each of the X-axis operating gear 505, the Y-axis operating gear 506, and the Z-axis operating gear 507. The position of the detector unit 110 in the X-axis, Y-axis, and Z-axis directions can be adjusted by using the operating rod 501 to move the movable gear 503 to a position where it meshes with a desired operating gear and then rotating it. In consideration of the cooling performance of the detector unit 110, it is preferable to provide fewer through holes in the cooling shield 120. According to the detector unit position adjustment mechanism 130 of this embodiment, it is only necessary to provide one through hole for the operating rod 501.

[0034] The scanning noise microscope according to this embodiment has two chambers, a detector chamber 100 and an AFM chamber 200, and the temperature and vacuum of each chamber can be controlled independently. Therefore, according to this embodiment, a single scanning noise microscope can be used to observe a sample at atmospheric pressure and room temperature, in a vacuum and room temperature, and in a vacuum and at a low temperature. In addition, after a preliminary measurement is performed at atmospheric pressure and room temperature to select a high-quality probe, it is possible to perform measurements at a low temperature and / or in a vacuum in a short time using the selected probe.

[0035] In this embodiment, the detector chamber 100 is cooled by a refrigerator, and the AFM chamber 200 is cooled by liquid nitrogen. The AFM chamber 200 can be kept at a low temperature for 30 hours or more, which is longer than the conventional method. Figure 6 is a diagram showing the cooling effect of the AFM chamber 200 according to this embodiment. The changes in temperature of the shutter (radiation shield), copper wire 302, and copper rod 301 after the coolant container 300 is filled with liquid nitrogen are shown as graphs 601, 602, and 603, respectively. As can be seen from this experiment, a low temperature of approximately 100K can be maintained for 30 hours or more.

[0036] 7(A) and 7(B) show the results of far-field image observation at room temperature (300 K) and low temperature (110 K) using the scanning noise microscope according to this embodiment. Image 701 is an optical image of a sample observed at room temperature. The sample is placed on a SiO2 substrate. The sample includes an Au electrode and a NiCr wire. Image 702 is a far-field image at room temperature with no current applied to the sample, and image 703 is a far-field image at room temperature with a current of 4.7 mA applied to the sample. Similarly, image 704 is an optical image of the same sample observed at low temperature. Image 705 is a far-field image at low temperature with no current applied to the sample, and image 706 is a far-field image at low temperature with a current of 9 A applied to the sample.

[0037] FIG. 8 shows the results of observation of near-field signals at room temperature (300 K) and low temperature (110 K) using the scanning noise microscope according to this embodiment. FIG. 8(A) shows a profile 803 of the near-field signal (left axis) and a profile 804 of the sample height (right axis) when a sample 801 is scanned at the position indicated by the arrow 802 with a current of 11 mA applied to the sample at room temperature. Similarly, FIG. 8(B) shows the results of measurement at low temperature for the same sample 801. 805 is a profile of the near-field signal when a current of 12 mA is applied to the sample 801, 806 is a profile of the near-field signal when no current is applied, and 807 is a profile of the sample height. In FIG. 8(A) and FIG. 8(B), the positions corresponding to the NiCr thin wire are highlighted in the background. FIG. 8(C) shows the sample 801, which is a 3.3 μm wide NiCr thin wire provided on a SiO2 substrate. Fig. 8(C) shows an optical image 811, a far-field image 812, and a near-field image 813 of the sample 801. Fig. 8(D) is a diagram showing the tip height dependency (attenuation characteristic) of the near-field signal. Image 813 is an image showing the near-field signal obtained by two-dimensionally scanning the sample 801. As described above, it can be seen that this embodiment makes it possible to measure hot electrons in the sample 801 with nanometer resolution.

[0038] In this embodiment, the openable and closable shutter 212 can be closed to keep the AFM system at a low temperature and block 300K background radiation, which is a problem when performing low-temperature measurements.

[0039] In addition, the detector unit position adjustment mechanism 130 of the detector unit 110 allows alignment of the detector unit 110 and the optical system. Conventionally, it was difficult to adjust the position of the detector, so it was necessary to repeat the process of performing a temporary adjustment at room temperature, then cooling and checking the results, which made measurements inefficient. The detector unit position adjustment mechanism 130 according to this embodiment can operate even at extremely low temperatures, allowing precise alignment in the operating state.

[0040] The present disclosure is not limited to the above-described embodiment, and various modifications are possible based on the spirit of the present disclosure, and these modifications are also included in the scope of the present disclosure. [Industrial Applicability]

[0041] The present disclosure can be applied to the measurement of near-field light generated by a material itself, that is, the measurement of electron temperature or the state of motion of electrons. [Explanation of symbols]

[0042] 100: detector chamber, 110: detector unit, 111: photodetector, 112: lens, 113: pinhole, 120: cooling shield 200: AFM chamber, 210: cooling plate, 211: cooling shield, 222: probe support, 223: probe, 224: sample, 225: copper wire, 226: objective lens, 227: lens shield 300: refrigerant container, 301: copper rod, 302: copper wire

Claims

1. a sample stage capable of adjusting the position of the sample; a probe support unit that supports a probe and is capable of adjusting a position of the probe to bring a tip of the probe close to a surface of the sample; An objective lens; a photodetector capable of detecting the terahertz wave collected by the objective lens; A scanning noise microscope for measuring a passive near-field signal obtained by scattering near-field light of the sample itself at the tip of the probe, the photodetector is disposed within the first chamber; the sample stage, the probe support, and the objective lens are disposed in a second chamber; The first chamber and the second chamber are configured to be capable of independent temperature control.

1. A scanning noise microscope comprising:

2. Further comprising a refrigerant container for containing a refrigerant; The sample stage is disposed on a cooling plate; A cooling rod extending from the refrigerant vessel is in thermal contact with the cooling plate.

2. A scanning noise microscope according to claim 1.

3. The cooling rod and the cooling plate are in thermal contact with each other through a metal wire.

3. A scanning noise microscope according to claim 2.

4. The cooling plate is in thermal contact with a lens shield that surrounds the objective lens.

3. A scanning noise microscope according to claim 2.

5. The cooling plate and the lens shield are in thermal contact with each other through a metal wire connecting the sample stage and the lens shield.

5. A scanning noise microscope according to claim 4.

6. Further comprising a shielding portion for covering the sample and the objective lens and blocking background radiation.

2. A scanning noise microscope according to claim 1.

7. Further comprising a shielding part opening / closing mechanism that moves the shielding part and switches between a shielded state and a non-shielded state.

7. A scanning noise microscope according to claim 6.

8. a detector unit position adjustment mechanism that can move a detector unit including the photodetector in the first chamber relative to the second chamber; 2. A scanning noise microscope according to claim 1.

9. The detector unit position adjustment mechanism includes: an X-axis operating gear, a Y-axis operating gear, and a Z-axis operating gear for moving the detector unit in an X-axis direction, a Y-axis direction, and a Z-axis direction, respectively; a movable gear that is movable to a position where it meshes with each of the X-axis operation gear, the Y-axis operation gear, and the Z-axis operation gear; An operating rod for moving and rotating the moving gear; 9. The scanning noise microscope of claim 8, comprising:

Images