A sample structure and its manufacturing method, and incident space angle calibration method

Abstract

The present application provides a sample structure and a method for making it, and a method for calibrating the spatial angle of incidence, wherein the sample structure includes a substrate, a metal film located on the substrate, and a nanostructure located inside or on the metal film. The sample structure is simple, and the manufacturing method is simple, but the near-field light field distribution generated under the irradiation of oblique incident light can be detected by SNOM, and has a good response to the spatial angle of incident light, and can be used for SNOM near-field light field imaging, and then the spatial angle component of the incident light is inferred from the measurement results of the SNOM near-field light field imaging, thereby realizing the calibration of the spatial angle of the incident light of the SNOM device. The calibration method is simple and easy, and the sample structure preparation process is simple. It can be used as a standard sample to calibrate the spatial angle of incident light of scattered scanning near-field optical microscopes of different manufacturers or laboratories. It has a wide range of applications and can be mass-produced.

Description

Technical Field

[0001] The invention belongs to the technical field of nano-optical measurement, and in particular relates to a sample structure and a manufacturing method thereof, and an incident space angle calibration method. Background Art

[0002] Scattering Scanning Near-field Optical Microscopy (s-SNOM) is an optical super-resolution microscopy technology based on scanning probes, which is mainly used to characterize the near-field light field distribution in the micro-region (micrometer-nanometer level) on the sample. The basic principle is: use the AFM probe to focus the laser beam to illuminate a nanoscale enhanced near-field signal area near the needle tip. When the needle tip approaches the sample surface, due to the differences in the dielectric properties of different materials, the near-field optical information will change accordingly. By analyzing the collected scattered signals through background suppression technology, the near-field light field imaging of the sample surface can be obtained. This technology breaks through the diffraction limit of the traditional optical imaging mechanism and can scan and image the nanoscale near-field optical information on the sample surface. It is an important measurement tool in the development of nanoscience and technology.

[0003] During SNOM near-field light field imaging measurement, a laser beam needs to be irradiated in the contact area between the probe tip and the sample as an excitation light source to achieve the excitation and detection of the near-field light field on the sample surface. For scattering SNOM systems, lasers are mostly incident at an angle in three-dimensional space, and their incident angles are related to the SNOM optical path structure, sample requirements and other measurement conditions. The near-field signal of the sample is usually very sensitive to the spatial angle of the incident light, and may even directly affect the distribution of the near-field light intensity and phase. Therefore, correctly calibrating the spatial angle of the incident light is of great significance for calibrating and analyzing SNOM measurement results. However, since the SNOM optical path system is usually more complex and has a compact spatial structure, there is a lack of effective means to directly measure and accurately calibrate the spatial angle of the incident light. Summary of the invention

[0004] In view of this, the present invention provides a sample structure and a manufacturing method thereof, and an incident spatial angle calibration method to solve the problem in the prior art that there is a lack of effective means for directly measuring and accurately calibrating the spatial angle of incident light.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A sample structure is used in a scanning near-field optical microscope in a reflective illumination mode, and the sample structure comprises:

[0007] substrate;

[0008] a metal film disposed on a substrate;

[0009] A nanostructure is located in or on the metal film.

[0010] Preferably, the nanostructure is a nano single slit located in the metal film and penetrating the metal film, a nano groove located in the metal film and not penetrating the metal film; or a nano boss located on the metal film.

[0011] Preferably, when the nanostructure is a single nanoslit located in the metal film, the length of the single nanoslit is 10 μm-500 μm, including endpoint values; the width of the single nanoslit is 100 nm-1 μm, including endpoint values.

[0012] Preferably, the length of the single nano-slit is 20 μm-40 μm, including the endpoint values; the width of the single nano-slit is 100 nm-200 nm, including the endpoint values.

[0013] Preferably, the metal film is made of gold, silver or copper.

[0014] Preferably, the thickness of the metal film is 10 nm-500 nm, including end points.

[0015] Preferably, the substrate is made of a silicon wafer or a quartz wafer.

[0016] The present invention also provides a method for preparing a sample structure, comprising:

[0017] providing a substrate;

[0018] forming a metal film layer on the surface of the substrate;

[0019] The metal film layer is processed to form a nanostructure.

[0020] Preferably, forming a metal film layer on the surface of the substrate specifically includes:

[0021] Depositing a metal film layer on the surface of the cleaned substrate;

[0022] The deposition method includes magnetron sputtering coating, vacuum thermal evaporation coating, or electron beam evaporation coating.

[0023] In addition, the present invention also provides a method for calibrating the spatial angle of incident light of a scattered scanning near-field optical microscope, which is characterized by comprising:

[0024] Providing a sample structure, wherein the sample structure is the sample structure described above, and the sample structure includes a nanostructure;

[0025] irradiating the nanostructure on the sample structure with tilted polarized light to generate surface plasmons;

[0026] Obtaining the interference fringe period of the surface plasmon;

[0027] The angle between the incident light and the normal direction of the surface of the sample structure is calculated to determine the spatial angle of the incident light.

[0028] Through the above technical solution, it can be known that the sample structure provided by the present invention includes a substrate, a metal film located on the substrate, and a nanostructure located inside or on the metal film. The sample structure is simple and the manufacturing method is simple, but the near-field light field distribution generated under the irradiation of oblique incident light can be detected by SNOM, and has a good response to the spatial angle of the incident light, and can be used for SNOM near-field light field imaging, and then the spatial angle component of the incident light is inferred from the SNOM near-field light field imaging measurement results, thereby realizing the calibration of the spatial angle of the incident light of the SNOM device. The calibration method is simple and easy, and the sample structure preparation process is simple. In the incident light spatial angle calibration method provided by the present invention, the generation of the near-field interference fringes (near-field light field distribution) required for calculation is only related to the incident angle, the incident light wavelength, and the material properties of the sample itself, and is unrelated to the specific optical path, signal detection method, detection element model performance, etc. of the SNOM system used. Therefore, the sample structure provided by the present invention can be used as a standard sample to calibrate the incident light spatial angle of scattered scanning near-field optical microscopes (especially SNOM systems with reflective illumination) of different manufacturers or laboratories. It has a wide range of applications and can be mass-produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0030] Figure 1 A schematic diagram of a sample structure provided by an embodiment of the present invention;

[0031] Figure 2 A flow chart of a sample structure manufacturing method provided by an embodiment of the present invention;

[0032] Figure 3 A flow chart of a method for calibrating the spatial angle of incident light in a scattered scanning near-field optical microscope provided in an embodiment of the present invention;

[0033] Figure 4 This is the SEM image of the actual processed nano single slit;

[0034] Figure 5 and Figure 6A schematic diagram showing the spatial angle of incident light provided by an embodiment of the present invention;

[0035] Figure 7 Schematic diagram of the sample structure actually processed;

[0036] Figure 8 and Fig. 9 These are the SNOM near-field optical imaging measurement results of two nanoslits with different orientations. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The sample structure provided by the present invention is used to calibrate the incident light angle of a scattered SNOM system, especially a sample structure of a SNOM system with a reflective illumination mode, that is, used in the field of calibration technology of the spatial angle of the incident light of the SNOM, such as Figure 1 As shown, Figure 1 A schematic diagram of a sample structure provided in an embodiment of the present invention, wherein the sample structure comprises:

[0039] Substrate 2;

[0040] A metal film 1 located on a substrate 2;

[0041] The nanostructure 4 is located in or on the metal film 1 .

[0042] It should be noted that the specific material of the substrate is not limited in this embodiment, and the substrate is required to be hard, supportive, smooth, non-conductive, and easy to plate metal film. The substrate can be a silicon wafer, a quartz wafer, or a similar hard substrate with a smooth surface.

[0043] In this embodiment, the material of the metal film is not limited, wherein the metal film is a metal that can generate surface plasmons (SPPs) at the wavelength of the incident light, such as gold, silver, copper, etc. The film thickness is 10nm-500nm, including the end value. For the visible light band, such as incident light with a wavelength of 633nm, considering factors such as SPPs excitation efficiency and film stability, preferably, the metal film is a gold film, and preferably, the film thickness is 50nm-100nm, including the end value.

[0044] In this embodiment, the nanostructure is a micro-nanostructure that can efficiently generate SPPs under incident laser irradiation. The size of the nanostructure matches the wavelength of the incident laser and meets the conditions for generating SPPs. In this embodiment, the specific shape of the nanostructure is not limited. The nanostructure located on the metal film can be a nano-groove or nano-wire structure obtained by etching the metal film; it can also be a nanostructure formed on the metal film by other processes, such as nano-steps or protrusions.

[0045] That is, the nanostructure is a nano single slit located in the metal film and penetrating the metal film, a nano groove located in the metal film and not penetrating the metal film; or a nano platform located on the metal film.

[0046] From the perspective of convenience in calculation and analysis, in this embodiment, preferably, the nanostructure is a nano single slit structure that penetrates the metal film. The length of the nano single slit is 10 μm-500 μm, the width is 100 nm-1 μm, and the depth is greater than or equal to the thickness of the metal film. Considering the convenience of finding and measuring under the microscope field of view and the ease of processing, it is preferably 20 μm-40 μm long and 100 nm-200 nm wide. The above numerical ranges all include the endpoint values.

[0047] Based on the above sample structure, this embodiment also provides a method for making the above sample structure, such as Figure 2 As shown, the sample structure manufacturing method includes:

[0048] S101: providing a substrate;

[0049] S102: forming a metal thin film layer on the surface of the substrate;

[0050] S103: Processing the metal film layer to form a nanostructure.

[0051] Specifically, the manufacturing method includes: depositing a desired metal film on a clean substrate surface by magnetron sputtering coating, vacuum thermal evaporation coating, or electron beam evaporation coating, and then using focused ion beam etching or etching equipment with similar functions to process the desired micro-nano structure, such as a nano single slit structure, on the surface of the metal film.

[0052] The sample structure and sample structure manufacturing method provided in the embodiments of the present invention can be used as standard samples to calibrate the incident light angle of scattered scanning near-field optical microscopes of different manufacturers and models due to their simple sample structure and relatively simple preparation process. They have a wide range of applications and can be mass-produced.

[0053] Based on the same inventive concept, the present invention also provides a method for calibrating the spatial angle of incident light in a scattered scanning near-field optical microscope, such as Figure 3 As shown, Figure 3 A flow chart of a method for calibrating the spatial angle of incident light in a scattered scanning near-field optical microscope provided in an embodiment of the present invention, wherein the calibration method comprises:

[0054] S201: providing a sample structure, wherein the sample structure is the sample structure described in the above embodiment, and the sample structure includes a nanostructure;

[0055] The specific form of the nanostructure is not limited in this embodiment. Regardless of nanogrooves, nanopeaks, nanosteps, or nanoprotrusions, as long as they are linear one-dimensional structures, they can generate interference fringe periods for calculation and calibration.

[0056] S202: irradiating the nanostructure on the sample structure with tilted polarized light to generate surface plasmons;

[0057] S203: Acquire the interference fringe period of the surface plasmon;

[0058] S204: Calculate the angle between the incident light and the normal direction of the surface of the sample structure to determine the spatial angle of the incident light.

[0059] That is, the incident light spatial angle calibration method of the scattered scanning near-field optical microscope provided in the embodiment of the present invention is based on the sample structure provided in the above embodiment, see Figure 1 , an AFM probe 5 is used to generate an incident laser beam 3 to irradiate the nanostructure 4 on the sample; the specific structure of the nanostructure 4 is not limited in this embodiment, and the following takes a single nanoslit as an example to illustrate the specific steps of the spatial angle calibration method of the incident light of the scattered scanning near-field optical microscope provided in the embodiment of the present invention. Figure 4 , Figure 4 This is the SEM image of the actual processed nano single slit.

[0060] like Figure 5 and Figure 6 As shown, the spatial angle of the incident light can be expressed by θ and Indicates that θ is the angle between the incident light and the normal direction of the sample surface. is the angle between the normal line of the nanoslit and the incident plane.

[0061] To facilitate measurement, a series of fixed angle deviations can be machined on the sample. Arranged nano-slits, such as Figure 7As shown in , in actual use, any two of the nano-slits can be selected for measurement. Since a coordinate system needs to be set up for subsequent calculations, and the nano-slit is placed in a horizontal or vertical position, it can be used as a reference coordinate. Therefore, the calculated spatial angle of the incident light can be simplified to avoid further conversion of coordinates. Preferably, in this embodiment, one of the two selected slits is placed in a horizontal or vertical position within the plane where the sample surface is located. The distance between adjacent slits is 50μm-200μm to ensure that the generated SPPs do not interfere with each other.

[0062] Nano-single slit structures (or similar micro-nano structures such as nano-grooves, steps, etc.) can efficiently excite SPPs under oblique p-polarized light irradiation, and its wavelength is:

[0063]

[0064] Where λ0 is the wavelength of incident light, ε d is the dielectric constant of the medium (ε for air d =1), ε m is the complex dielectric constant of the metal.

[0065] The SPPs generated by the nano single slit propagate to both sides of the single slit, and interfere with the SPPs excited by the probe tip to form interference fringes. Since the propagation direction of the SPPs on both sides of the single slit is different from the direction of the probe exciting the SPPs, the interference fringes generated on both sides of the single slit have different periods, which can be expressed by the following formula:

[0066]

[0067]

[0068] where Λ - is the interference fringe period on one side of the incident light of the nanoslit, Λ + is the interference fringe period on the other side. θ is the angle between the incident light and the normal direction of the sample surface. is the angle between the normal line of the nanoslit and the incident plane. Together they determine the spatial angle of the incident light. In a certain SNOM optical path system, for different nanoslits, θ is the same. It is related to the placement direction of the single seam.

[0069] Therefore, if we measure two different directions (the angle between them is known to be The interference fringe period of a single nanoslit on the incident light side Then we can calculate And the value of θ:

[0070] in

[0071] or

[0072] From this, the spatial angle of the incident light can be determined.

[0073] Taking the SNOM measurement of a 633nm wavelength laser light source as an example, gold is selected as the metal coating material of the sample to be tested, the film thickness is 60nm, and the substrate is a silicon wafer. The length of the processed nano single slit is 20μm, the width is 200nm, and the depth is 60nm. The wavelength of SPPs on the gold film is λ SPP =604nm.

[0074] Two single slits were selected for SNOM near-field optical imaging measurement, one of which (slit 1) was placed vertically in the plane of the sample surface, and the other (slit 2) was placed at an angle of 25° to it. The measurement results are shown in Figure 2. Figure 8 and Fig. 9 As shown, Figure 8 and Fig. 9 The SNOM near-field optical imaging measurement results of two nano-slits with different orientations (angle deviation 25°) (the scanning direction is perpendicular to the single slit direction). Calculated θ = 57°, That is, the angle between the incident light and the normal direction of the sample surface is 57°, and the angle between the incident light and the normal direction of the nanoslit slit 1 (that is, the horizontal direction in the plane where the sample surface is located) is 39°, thereby determining the spatial angle of the incident light.

[0075] The incident light spatial angle calibration method of the scattered scanning near-field optical microscope provided in the embodiment of the present invention is based on the sample structure described in the above embodiment. The incident light angle component is inferred from the SNOM near-field light field imaging measurement results, thereby realizing the calibration of the incident light spatial angle of the SNOM device.

[0076] It should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0077] It should also be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that an article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such article or device. In the absence of further restrictions, the elements defined by the sentence "comprising a ..." do not exclude the existence of other identical elements in the article or device including the above elements.

[0078] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A sample structure, characterized in that: The method is applied to calibrate the spatial angle of incident light in a scanning near-field optical microscope in a reflective illumination mode. The sample structure includes: Substrate; the material of the substrate is a silicon wafer or a quartz wafer; A metal film located on a substrate; the thickness of the metal film is 10nm-500nm, including endpoint values; a nanostructure located in or on the metal film; the nanostructure is a single nanoslit located in the metal film and penetrating the metal film, a nanogroove located in the metal film and not penetrating the metal film; or a nano-boss located on the metal film; when the nanostructure is a single nanoslit located in the metal film, the length of the single nanoslit is 10μm-500μm, including endpoint values; the width of the single nanoslit is 100nm-1μm, including endpoint values.

2. The sample structure according to claim 1, characterized in that: The length of the single nano-slit is 20 μm-40 μm, including the endpoint values; the width of the single nano-slit is 100 nm-200 nm, including the endpoint values.

3. The sample structure according to claim 1, characterized in that: The material of the metal film is gold, silver or copper.

4. A method for calibrating the spatial angle of incident light of a scattered scanning near-field optical microscope, characterized in that: include: Providing a sample structure, wherein the sample structure is the sample structure according to any one of claims 1 to 3, and the sample structure comprises a nanostructure; irradiating the nanostructure on the sample structure with tilted polarized light to generate surface plasmons; Obtaining the interference fringe period of the surface plasmon; The angle between the incident light and the normal direction of the surface of the sample structure is calculated to determine the spatial angle of the incident light.

Images