Ferroelectric optical tunnel scanning microscope tip and preparation method thereof

Abstract

The invention discloses a tip of a ferroelectric optical tunnel scanning microscope. The tip is prepared from a ferroelectric material. The needle tip is divided into a left part and a right part which are symmetrical, the polarization directions of the left part and the right part are opposite, and a tail-to-tail or head-to-head polarized positive domain and negative domain are prepared on the needle tip; the length of the needle tip is 100-10mm, the width of the needle tip is less than or equal to 100mu m, the thickness of the needle tip is less than or equal to 100mu m, and a grating is processed on the side wall of one domain of the needle tip. The invention also provides a preparation method of the advantage ferroelectric optical tunnel scanning microscope needle tip. The needle point is used for the optical scanning tunneling microscope, traditional optical surface information can be obtained, electromagnetic force action information can also be obtained according to ferroelectric characteristics, and therefore a domain wall structure can be better detected.

Description

Technical Field

[0001] This invention relates to the field of optical measurement technology, specifically to a ferroelectric optical tunneling scanning microscope tip and its preparation method. Background Technology

[0002] Semiconductor etching technology requires the use of various microscopes for process measurements, including atomic force microscopy (AFM), electron microscopy, scanning tunneling microscopy, and the more recently developed optical scanning tunneling microscopy.

[0003] With the advancement of optical integration technology, the demand for optical scanning tunneling microscopy (OSM) is increasing. Currently, OSM is used to measure the phase of waveguide evanescent waves. OSM is based on electron scanning tunneling microscopy, but uses an optical fiber tip instead of a metal tip and photonic tunneling instead of electron tunneling to measure the optical properties of microstructures.

[0004] Currently, with the rise of ferroelectric materials such as lithium niobate in the field of microfabrication, research on domain walls of these materials is gradually increasing. For example, Chinese Patent Application No. 202011438154.0, entitled "Semiconductor Structure of Lithium Niobate and its Preparation Method," discloses a semiconductor domain wall composed of reverse-polarized ferroelectric domains. Due to the different polarization directions, the surface of ferroelectric domains generates charges through pyroelectric effects, and the direction of the charges is related to the polarization direction. The domain wall is very thin, less than 1 nm, and generally does not have a geometric protrusion structure, only optical and electrical properties, making it difficult to detect using AFM. Summary of the Invention

[0005] The technical problem to be solved by this invention is: how to design an optical tunneling scanning microscope tip made of ferroelectric materials so that it can measure the domain wall morphology of ferroelectric materials.

[0006] The primary objective of this invention is to provide a ferroelectric optical tunneling scanning microscope tip; the technical solution adopted is as follows: A ferroelectric optical tunneling scanning microscope tip is disclosed, wherein the tip is made of ferroelectric material; the tip is divided into two symmetrical left and right parts with opposite polarization directions; positive and negative domains with tail-to-tail or head-to-head polarization are prepared on the tip; the tip length is 100 μm to 10 mm, the tip width is less than or equal to 100 μm, the tip thickness is less than or equal to 100 μm, and a grating is fabricated on the sidewall of one domain of the tip.

[0007] In a further preferred embodiment of the technical solution of the present invention, the ferroelectric material is lithium niobate, lithium tantalate, or potassium titanium oxyphosphate.

[0008] In a further preferred embodiment of the technical solution of the present invention, the inclined surface of the tip of the needle forms an angle of 5° to 45° with the vertical surface.

[0009] In a further preferred embodiment of the technical solution of the present invention, the tip of the needle tip is connected to a bare optical fiber, and the bare optical fiber is connected to an external optical instrument.

[0010] The second objective of this invention is to provide a method for preparing the tip of a ferroelectric optical tunneling scanning microscope; the technical solution adopted is as follows: A method for preparing a tip for a ferroelectric optical tunneling scanning microscope includes the following steps: Step 1: Prepare a thin film of lithium niobate of a certain thickness; Step 2: Prepare positive and negative domains with opposite polarization directions, either tail-to-tail or head-to-head, on the thin film lithium niobate from Step 1. Step 3: Fabricate a needle tip on the thin film lithium niobate from Step 2; Step 4: Fabricate a grating along the length direction on the sidewall of one of the domains; Step 5: Heat and apply vibration to detach the processed needle tip from the substrate.

[0011] In a further preferred embodiment of the technical solution of the present invention, in step 1, a thin film lithium niobate with a thickness of 10 μm is prepared by implantation stripping or grinding.

[0012] In a further preferred embodiment of the technical solution of the present invention, in step 2, positive and negative domains with opposite polarization directions are prepared on thin film lithium niobate by room temperature electric field polarization or laser induction.

[0013] In a further preferred embodiment of the technical solution of the present invention, in step 3, the tip is fabricated on the thin film lithium niobate by ion beam etching or photolithography.

[0014] In a further preferred embodiment of the technical solution of the present invention, in step 4, a grating is fabricated along the length direction on the sidewall of a domain of the needle tip using ion beam etching or photolithography. The function of the grating is to amplify the displacement by selecting an appropriate wavelength and grating constant, which can be as high as tens to hundreds of times, effectively detecting the minute displacement of the needle tip.

[0015] The beneficial effects of this invention compared to the prior art are: The present invention provides a ferroelectric optical tunneling scanning microscope tip for use in optical scanning tunneling microscopes. It can not only obtain traditional optical surface information, but also obtain electromagnetic force information based on ferroelectric properties, thereby better detecting domain wall structures. Attached Figure Description

[0016] Figure 1This is a three-dimensional schematic diagram of the tip of the ferroelectric optical tunneling scanning microscope of the present invention; Figure 2 This is a front view of the tip of the ferroelectric optical tunneling scanning microscope of the present invention; Figure 3 This is a schematic diagram showing the tip of the ferroelectric optical tunneling scanning microscope suspended above the ferroelectric material to be tested in this embodiment. Figure 4 for Figure 3 A three-dimensional schematic diagram; Figure 5 This is a schematic diagram of the displacement of the ferroelectric optical tunneling scanning microscope tip when it is above the domain wall of the ferroelectric material to be tested, according to this embodiment. Figure 6 This is a schematic diagram of the measurement results of the domain wall morphology of the ferroelectric material under test obtained by the tip of the ferroelectric optical tunneling scanning microscope in this embodiment. Wherein: 1-domain wall of the ferroelectric material to be tested, 2-positive domain, 3-negative domain, 4-grating, 5-tip of the needle tip, 6-ferroelectric material to be tested. Detailed Implementation

[0017] The technical solution of the present invention will be described in detail below, but the scope of protection of the present invention is not limited to the embodiments described.

[0018] To make the content of this invention clearer and easier to understand, the following description is in conjunction with the appendix. Figure 1 - Appendix Figure 6 The specific implementation methods will be further described below.

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] like Figure 1 and 2 As shown, this embodiment is a ferroelectric optical tunneling scanning microscope tip, which is used in optical scanning tunneling microscopes.

[0021] The ferroelectric optical tunneling scanning microscope tip of this embodiment is made of ferroelectric material; ferroelectric materials are known to those skilled in the art, including lithium niobate, lithium tantalate, or potassium titanium oxyphosphate, etc. Lithium niobate is preferably used as the ferroelectric optical tunneling scanning microscope tip of this embodiment.

[0022] like Figure 1As shown, the needle tip in this embodiment is divided into two mirror-symmetrical parts, with opposite polarization directions. The needle tip length is 100μm-10mm, preferably 500μm; the needle tip width is less than or equal to 100μm, preferably 10μm; the needle tip thickness is less than or equal to 100μm, preferably 10μm; and the bevel of the tip portion forms an angle of 5° to 45° with the vertical plane, preferably 15°.

[0023] like Figure 2 As shown, the needle tip is divided into two parts, left and right, with opposite polarization directions: the left part is polarized to the left, and the right part is polarized to the right.

[0024] like Figure 2 As shown, positive and negative domains with tail-to-tail or head-to-head polarization are prepared on the needle tip. A grating is fabricated on the sidewall of one of the domains at the needle tip. The function of the grating is to produce a magnification effect on the displacement by selecting an appropriate wavelength and grating constant. This magnification effect can be as high as tens to hundreds of times, effectively detecting the tiny displacement of the needle tip.

[0025] like Figure 1 As shown in this embodiment, the preparation method of the tip of the ferroelectric optical tunneling scanning microscope includes the following steps: Step 1: Prepare a 10 μm thick thin film of lithium niobate by implantation-exfoliation or grinding methods; Step 2: Prepare positive and negative domains with opposite polarization directions, either tail-to-tail or head-to-head, on thin-film lithium niobate by room temperature electric field polarization or laser-induced method; Step 3: The required needle tip is fabricated on the thin lithium niobate film in Step 2 by ion beam etching or photolithography. In this embodiment, the preferred dimensions are: needle tip length of 500 μm, needle tip width of 10 μm, needle tip thickness of 10 μm, and the angle between the bevel and the vertical plane of the tip tip is 15°. Step 4: Using ion beam etching or photolithography, a grating is fabricated along the length direction on the sidewall of a domain at the tip; Step 5: Heat and apply vibration to detach the processed needle tip from the substrate.

[0026] In the preparation method of this embodiment, the injection-peeling or grinding methods mentioned in step 1 are all preparation methods of this material known to those skilled in the art.

[0027] In the preparation method of this embodiment, the room temperature electric field polarization or laser-induced method mentioned in step 2 are conventional microfabrication processes known to those skilled in the art. Those skilled in the art know that positive domain 2 and negative domain 3 are polarized tail-to-tail or head-to-head.

[0028] In the preparation method of this embodiment, the ion beam etching or photolithography method mentioned in step 4 is a conventional microfabrication process known to those skilled in the art.

[0029] like Figure 3 As shown, in this embodiment, the tip of the needle is bonded to the bare optical fiber at its tip during use. Preferably, the bare optical fiber has a diameter of 10 μm and a core diameter of 5 μm, allowing light to be transmitted through the core. The length of the bare optical fiber is 10 mm to 100 mm, preferably 50 mm. This bare optical fiber is used to connect optical instruments such as photodetectors and spectrometers.

[0030] like Figure 3 and 4 As shown, when detecting the domain wall morphology of the ferroelectric material 6 to be tested, the tip of this embodiment is suspended above the domain wall 1 of the ferroelectric material to be tested, and the distance between the tip and the domain wall 1 is controlled by a three-dimensional displacement platform and a piezoelectric ceramic. Specifically, the tip of this embodiment is mounted on an optical scanning tunneling microscope, and a piezoelectric ceramic is mounted on the optical scanning tunneling microscope. The movement of the piezoelectric ceramic drives the movement of the tip to adjust the distance between the tip and the domain wall of the ferroelectric material.

[0031] Optical scanning tunneling microscopes and the installation of piezoelectric ceramics on optical scanning tunneling microscopes are technologies known to those skilled in the art.

[0032] like Figure 3 As shown, because the ferroelectric domains on both sides of the domain wall at the needle tip have opposite polarization directions, the surface of the ferroelectric material under test has opposite charge distributions. Specifically, the left side has an upward polarization direction and a positive surface charge, while the right side has a downward polarization direction and a negative surface charge.

[0033] In this embodiment, tail-to-tail polarized positive domains 2 and negative domains 3 are prepared on the needle tip using a laser-induced method. Because the needle tip is tail-to-tail polarized, the surface of the tip portion 5 carries a positive charge. Figure 3 As shown, when the needle tip is in the domain on the right side of the ferroelectric material to be tested (the needle tip is not at the domain wall), the right side surface of the ferroelectric material to be tested is negatively charged and is subject to Coulomb attraction. The forces on both sides are balanced, and the needle tip does not produce displacement.

[0034] The closer the needle tip is to the domain wall of the ferroelectric material being tested, the more Coulomb repulsion from the opposite charge on the other side of the domain wall will be felt, resulting in a displacement to one side. When the needle tip is exactly above the domain wall of the ferroelectric material being tested, there is Coulomb repulsion on the left and Coulomb attraction on the right, resulting in the maximum displacement to one side.

[0035] The aforementioned displacement can be used as one of the parameters for measuring the domain wall position. The displacement can be quantified using the following formula. According to formula (1), the additional charge generated at the needle tip... The relationship between the surface area A of the needle tip, the pyroelectric coefficient P, and the temperature change ΔT is as follows: (1)

[0036] The pyroelectric coefficient of lithium niobate materials The lateral area A is calculated based on the specific needle tip shape, and the temperature change ΔT is set to a range of 20℃-30℃ to calculate the additional charge generated. The stress and deformation of the needle tip were calculated using finite element software such as ANSYS, with a maximum displacement of 343 nm. Figure 5 As shown. This displacement is obtained by reflecting the laser light source on the grating at the tip of the needle through the light source.

[0037] Increasing the temperature change range ΔT, for example, to 20℃-70℃, can yield a larger displacement.

[0038] The laser source in the aforementioned optical scanning tunneling microscope serves several purposes: (1) Light source of optical scanning tunneling microscope. The wavelength of the light source is in the visible-mid-infrared band. It is directly irradiated onto the upper surface of the sample and simultaneously irradiated from below the sample, and the output is achieved through evanescent wave coupling. The laser on the upper surface of the sample enters the above-mentioned needle tip through reflection and scattering, and the reflection and scattering characteristics of the sample surface can be measured; the laser irradiating from below the sample can measure waveguide transmission, refractive index change and other characteristics through evanescent wave coupling.

[0039] (2) Heating light source that generates temperature change ΔT. The laser on the surface of the sample is partially absorbed by the needle tip and the sample, generating heat and temperature change, triggering pyroelectric effect and generating surface charge.

[0040] (3) Laser for measuring needle tip displacement. The laser beam on the surface of the sample to be tested is partially reflected by the grating on the needle tip. The displacement of the needle tip is calculated based on the change in the reflection angle. The function of the grating is to amplify the displacement by selecting an appropriate wavelength and grating constant. This amplification can be as high as tens to hundreds of times, effectively detecting the minute displacement of the needle tip.

[0041] Specific application examples: The tip in this embodiment can simultaneously perform optical scanning tunneling measurements and domain wall position measurements. First, the sample under test has positive and negative domains distributed along the X-direction with a period of 10 μm, and exhibits undulations due to processing errors. Using the above method, based on the displacement of the ferroelectric tip, measurements can be performed as follows: Figure 6 The black curve shown has the highest signal above the domain walls of the sample under test; simultaneously, as measured by evanescent wave, ... Figure 6The gray curves shown indicate that the surface closer to the needle tip has a high evanescent wave coupling strength, and vice versa, thus revealing the surface undulations.

[0042] The ferroelectric optical tunneling scanning microscope tip of this embodiment, used in optical scanning tunneling microscopes, can not only obtain traditional optical surface information, but also obtain electromagnetic force information based on ferroelectric properties, thereby better detecting domain wall structures.

[0043] The above embodiments are merely illustrative of the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solutions based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A ferroelectric optical tunneling scanning microscope tip, characterized in that, The tip is made of ferroelectric material; the tip is divided into two symmetrical parts, left and right, with opposite polarization directions; positive and negative domains with tail-to-tail or head-to-head polarization are prepared on the tip; the tip length is 100μm~10mm, the tip width is less than or equal to 100μm, the tip thickness is less than or equal to 100μm, and a grating is fabricated on the sidewall of one domain of the tip.

2. The ferroelectric optical tunneling scanning microscope tip according to claim 1, characterized in that, The ferroelectric material is lithium niobate, lithium tantalate, or potassium titanium oxyphosphate.

3. The ferroelectric optical tunneling scanning microscope tip according to claim 1, characterized in that, The bevel of the tip of the needle forms an angle of 5° to 45° with the vertical plane.

4. The ferroelectric optical tunneling scanning microscope tip according to claim 1, characterized in that, The tip of the needle is connected to a bare optical fiber, which in turn connects to external optical instruments.

5. The method for preparing the tip of a ferroelectric optical tunneling scanning microscope according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Prepare a thin film of lithium niobate of a certain thickness; Step 2: Prepare positive and negative domains with opposite polarization directions, either tail-to-tail or head-to-head, on the thin film lithium niobate from Step 1. Step 3: Fabricate a needle tip on the thin film lithium niobate from Step 2; Step 4: Fabricate a grating along the length direction on the sidewall of one of the domains; Step 5: Heat and apply vibration to detach the processed needle tip from the substrate.

6. The preparation method according to claim 5, characterized in that, In step 1, thin-film lithium niobate with a thickness of 10 μm is prepared by implantation-exfoliation or grinding methods.

7. The preparation method according to claim 5, characterized in that, In step 2, positive and negative domains with opposite polarization directions are prepared on thin-film lithium niobate by room temperature electric field polarization or laser induction.

8. The preparation method according to claim 5, characterized in that, In step 3, the tip is fabricated on the thin film lithium niobate by ion beam etching or photolithography.

9. The preparation method according to claim 5, characterized in that, In step 4, a grating is fabricated along the length direction on the sidewall of a domain at the tip using ion beam etching or photolithography.

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