A method of nanoscale subsurface infrared imaging

Abstract

The application discloses a method for nanoscale subsurface infrared imaging, which adopts a photoinduced force microscope to perform infrared imaging on a subsurface structure of a surface of a phonon material. The nanoscale infrared imaging of the structure in the subsurface is realized by using the signal of the surface of the phonon material.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of infrared spectrum and imaging, and particularly relates to a method for nanoscale subsurface infrared contrast imaging. BACKGROUND

[0002] The subsurface of a material refers to the part below the surface, and current researches on subsurface imaging mainly focus on the detection of subsurface defects of optical elements, which are divided into destructive detection and non-destructive detection. Compared with the destructive detection method, the non-destructive method is more rapid and efficient.

[0003] In the prior art, the non-destructive subsurface detection methods include confocal microscopy, total internal reflection microscopy and the like. Although these technologies can achieve higher resolution than traditional methods, the resolution thereof can only achieve micrometer level. In the prior art, there is still lack of a method for nanoscale subsurface detection and imaging.

[0004] Atomic force microscopy technology can provide nanoscale structural information of the surface of nanomaterials. However, for the information of the subsurface of nanomaterials coated in a specific matrix or the heterogeneity inside the nanomaterials, it is difficult to achieve by measuring the interaction force between the atomic force microscope probe and the sample surface. SUMMARY

[0005] In view of the above problems in the prior art, the present application provides a method for nanoscale infrared subsurface imaging. The method is suitable for the subsurface imaging of the surface and the subsurface, and can be used to characterize the morphology, structure and chemical composition of the nanoscale structure in the subsurface, and is expected to be applied to the infrared subsurface imaging analysis of the nanoscale structure in the subsurface.

[0006] To achieve the above object, the present application adopts the following technical solution:

[0007] A method for nanoscale subsurface infrared imaging, which adopts a light-induced force microscope to perform infrared imaging on a subsurface structure having a surface of phonon material.

[0008] Preferably, the infrared imaging is at the phonon absorption wavelength of the phonon material. At the phonon absorption wavelength, the phonon plasmon resonance absorption excited by the light-induced force microscope needle tip or the bulk absorption signal of the phonon material is imaged. Among them, the area of the subsurface defect or other structure at the subsurface forms an infrared image with a contrast difference from the background without the above structure, and the contrast is affected by the thickness, refractive index, etc. of the imaging object. The subsurface defect is a structure such as a crack on the subsurface of the material that is integrated with the surface phonon material, and the other structure at the subsurface is a non-integrated attached structure or a protruding integrated structure at the subsurface, such as a nanomaterial, DNA, and organic framework material at the subsurface.

[0009] Preferably, the phonon material is one of mica, quartz, boron nitride, silicon nitride, silicon dioxide, aluminum oxide, molybdenum trioxide, or silicon carbide.

[0010] Preferably, the phonon material is mica, and the phonon absorption wavelength is 1200 cm -1 -870 cm -1 .

[0011] Preferably, the phonon material is quartz, and the phonon absorption wavelength is 1240 cm -1 -950 cm -1 .

[0012] Preferably, the phonon material is boron nitride, and the phonon absorption wavelength is 1600 cm -1 -1300 cm -1 .

[0013] Preferably, the phonon material is silicon nitride, and the phonon absorption wavelength is 1893 cm -1 -700 cm -1 .

[0014] Preferably, the phonon material is silicon dioxide, and the phonon absorption wavelength is 1250 cm -1 -800 cm -1 .

[0015] Preferably, the phonon material is aluminum oxide, and the phonon absorption wavelength is 2000 cm -1 -650 cm -1 .

[0016] Preferably, the phonon material is molybdenum trioxide, and the phonon absorption wavelength is 1000 cm -1 -400 cm -1 .

[0017] Preferably, the phonon material is silicon carbide, and the phonon absorption wavelength is 1064 cm -1 625 cm -1 .

[0018] The thickness of the surface of the phonon material is 0-50 nm.

[0019] Preferably, the surface of the phonon material is flat. The phonon material with a flat surface can have a uniform background infrared signal.

[0020] Preferably, the subsurface structure is a solid, a defect, or a liquid. For non-integrated subsurface structures, both solids and liquids can be imaged with high resolution by the method of the present application.

[0021] Preferably, the subsurface structure is a polymer, DNA, an organic framework material, or a two-dimensional material.

[0022] Preferably, the thickness or depth of the subsurface structure is 0-2000 nm. The method of the present application can be used to image subsurface structures of any thickness or depth, and is particularly suitable for imaging nanostructures with a thickness or depth of less than 10 nm. For structures with a thickness or depth of less than 10 nm, existing methods are difficult to use, and the present application fills the technical gap in subsurface infrared imaging.

[0023] The present application uses an atomic force microscope tip to focus infrared light, and then detects the induced force generated by the interaction between the subsurface material and the infrared light, thereby achieving the acquisition of nanoscale infrared spectral information, and has the following beneficial effects:

[0024] 1. The present application uses the surface of a phonon material as an imaging substrate, which can ensure that the substrate has a high infrared optical signal. In addition, a flat substrate can have a uniform background infrared signal.

[0025] 2. The present application uses the phonon crystal absorption signal and its significant light response to achieve high-sensitivity imaging.

[0026] 3. Due to the use of phonon crystal signal imaging strategy, the method of the present application can achieve subsurface infrared imaging of non-integrated structures with weak or no infrared absorption.

[0027] 4. The present application can change the type and thickness of the phonon material surface to obtain high-efficiency infrared enhancement effect according to the need for signal enhancement at different wavelengths (such as obtaining the highest enhancement factor).

[0028] 5. The present application has a horizontal resolution of 10 nm. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 This is a schematic diagram of the experimental method of the present invention. In order to show the sub-surface nanostructure, the phonon material surface is not drawn completely.

[0030] Figure 2 This is the infrared spectral imaging obtained in Example 1. a is the atomic force microscope topography imaging of the silicon nitride top surface, b is the nano-infrared imaging performed on the silicon nitride top surface using the phonon exciton resonance absorption signal (negative mode) of the silicon nitride, c is the nano-infrared imaging performed on the silicon nitride top surface using the bulk absorption signal (positive mode) of the silicon nitride phonon material, and d is the imaging at a wavelength without any absorption.

[0031] Figure 3 This is the infrared spectral imaging obtained in Example 2. Figure a is the atomic force microscope topography imaging of the silicon nitride top surface, b is the nano-infrared imaging performed on the silicon nitride top surface using the phonon exciton resonance absorption signal (positive mode) of the silicon nitride, and c is the nano-infrared imaging performed on the silicon nitride top surface using the bulk absorption signal (negative mode) of the phonon material.

[0032] Figure 4 This is the infrared spectral imaging obtained in Example 3. A is the atomic force microscope topography imaging of the silicon nitride top surface, B is the nano-infrared imaging performed on the silicon nitride top surface using the phonon exciton resonance absorption signal (positive mode) of the silicon nitride, and C is the nano-infrared imaging performed on the silicon nitride top surface using the bulk absorption signal (negative mode) of the silicon nitride phonon material.

[0033] Figure 5 This is the infrared spectrum imaging obtained in Example 4. Figure a is the atomic force microscope topography imaging of the silicon nitride top surface, and figures b and c are the direct mode (forward mode) and sideband mode (forward mode) nano-infrared imaging of the silicon nitride top surface using the silicon nitride phonon exciton resonance absorption signal, respectively.

[0034] Figure 6 This is the infrared spectral imaging obtained in Example 5. A is the atomic force microscope topography imaging of the silicon nitride top surface, B is the nano-infrared imaging performed on the silicon nitride top surface using the phonon exciton resonance absorption signal (positive mode) of the silicon nitride, and C is the nano-infrared imaging performed on the silicon nitride top surface using the bulk absorption signal (negative mode) of the silicon nitride phonon material.

[0035] Figure 7 This is the infrared spectral imaging obtained in Example 6. Figure a is the atomic force microscope topography imaging of the silicon nitride top surface, b is the nano-infrared imaging performed on the silicon nitride top surface using the phonon exciton resonance absorption signal (positive mode) of the silicon nitride, and c is the nano-infrared imaging performed on the silicon nitride top surface using the bulk absorption signal (negative mode) of the silicon nitride phonon material.

[0036] Figure 8 is the infrared spectral imaging obtained from Example 7. Wherein a is the atomic force microscope topography imaging of the top surface of the silicon nitride, b is the nano-infrared imaging using the phonon polariton resonance absorption signal (positive mode) of the silicon nitride on the top surface of the silicon nitride, c is the nano-infrared imaging using the bulk absorption signal (negative mode) of the phonon material of the silicon nitride on the top surface of the silicon nitride.

[0037] Figure 9 is the infrared spectral imaging obtained from Example 8. Wherein a is the atomic force microscope topography imaging of the top surface of the silicon nitride, b is the nano-infrared imaging using the phonon polariton resonance absorption signal (positive mode) of the silicon nitride on the top surface of the silicon nitride, c is the nano-infrared imaging using the bulk absorption signal (negative mode) of the phonon material of the silicon nitride on the top surface of the silicon nitride. DETAILED DESCRIPTION

[0038] The experimental method as shown in Figure 1 is adopted, and the subsurface nanostructure is arranged below the surface of the phonon material and below the AFM probe.

[0039] Example 1

[0040] In this example, the surface of the phonon material is silicon nitride with a thickness of 50 nm, and the structure to be imaged is a silicon wafer with a thickness of hundreds of microns below the surface of the silicon nitride. The light-induced force microscope is used, and the nano-infrared imaging is performed using the sideband detection mode of the probe in the tapping mode. The imaging and spectral scanning are performed at different wavelengths.

[0041] The results are shown in Figure 2 , wherein a is the atomic force microscope topography imaging of the top surface of the silicon nitride, b is the nano-infrared imaging using the phonon polariton resonance absorption signal (negative mode) of the silicon nitride on the top surface of the silicon nitride, c is the nano-infrared imaging using the bulk absorption signal (positive mode) of the phonon material of the silicon nitride on the top surface of the silicon nitride, and d is the imaging at a wavelength without any absorption. As can be seen, when the atomic force microscope imaging is used, the top surface of the silicon nitride is relatively flat, and only the wrinkles pulled out by the bottom silicon wafer are present, so no signal of the silicon wafer below the silicon nitride is observed except for the wrinkles. When the nano-infrared imaging is performed using the phonon polariton resonance absorption or the bulk absorption signal of the phonon material of the silicon nitride, the silicon wafer below the subsurface can be successfully observed in the positive mode (the structure to be imaged is bright, and the phonon surface signal is dark) and the negative mode (the structure to be imaged is dark, and the phonon surface signal is bright).

[0042] This example shows that under the strategy of using the surface of the phonon material as the imaging substrate, the super-resolution infrared imaging of the material without infrared absorption can be realized, and the imaging thickness can be less than 50 nm.

[0043] Example 2

[0044] In this example, the surface of the phononic material is silicon nitride with a thickness of 50 nm, and the structure to be imaged is a polystyrene microsphere with a diameter of 4 microns underneath the surface of the silicon nitride. Using a photoinduced force microscope, nanometer infrared imaging is performed using the sideband detection mode of the probe in tapping mode, and imaging and spectral scanning are performed at different wavelengths.

[0045] The results are shown in FIG. 2, in which a is the atomic force microscope topography imaging of the upper surface of the silicon nitride, b is the nanometer infrared imaging using the phonon polariton resonance absorption signal (positive mode) of the silicon nitride on the upper surface of the silicon nitride, and c is the nanometer infrared imaging using the bulk absorption signal (negative mode) of the phononic material of the silicon nitride on the upper surface of the silicon nitride. As can be seen, when atomic force microscope imaging is used, since the upper surface of the silicon nitride is not undulating, the polystyrene sample signal at the bottom of the silicon nitride is not observed. When nanometer infrared imaging is performed using the phonon polariton resonance absorption of the silicon nitride or the bulk absorption signal of the phononic material, the distribution of the polystyrene microsphere under the subsurface is successfully observed. Figure 3 This example shows that under the strategy of using a phononic material surface as an imaging substrate, high-molecular super-resolution subsurface infrared imaging can be achieved.

[0046] Example 3

[0047] In this example, the surface of the phononic material is silicon nitride with a thickness of 50 nm, and the structure to be imaged is a silicon wafer with a thickness of several hundred microns underneath the surface of the silicon nitride, with a closely arranged array of polystyrene microspheres with a diameter of 4 microns at the edge. Using a photoinduced force microscope, nanometer infrared imaging is performed using the sideband detection mode of the probe in tapping mode, and imaging and spectral scanning are performed at different wavelengths.

[0048] The results are shown in FIG. 3, in which a is the atomic force microscope topography imaging of the upper surface of the silicon nitride, b is the nanometer infrared imaging using the phonon polariton resonance absorption signal (positive mode) of the silicon nitride on the upper surface of the silicon nitride, and c is the nanometer infrared imaging using the bulk absorption signal (negative mode) of the phononic material of the silicon nitride on the upper surface of the silicon nitride. As can be seen, when atomic force microscope imaging is used, since the upper surface of the silicon nitride is relatively flat, with only slight wrinkles at the edge pulled out by the bottom silicon wafer and the microspheres, the sample signal at the bottom of the silicon nitride is not observed except for the wrinkles. When nanometer infrared imaging is performed using the phonon polariton resonance absorption of the silicon nitride or the bulk absorption signal of the phononic material, the distribution of the silicon wafer and the polystyrene microspheres under the subsurface is successfully observed.

[0049] Figure 4

[0050] ​​This embodiment shows that super-resolution infrared imaging of materials without infrared absorption can be achieved under the strategy of using the surface of the phononic material as the imaging substrate.

[0051] Example 4

[0052] In this example, the phononic material surface is 50 nm thick silicon nitride, and the structure to be imaged is a 200 nm diameter polystyrene microsphere beneath the silicon nitride surface. Using optically induced force microscopy (IIFM), both tapping mode sideband detection and direct mode nano-infrared imaging were used to image and spectrally scan the polystyrene microspheres at different wavelengths.

[0053] The results are as follows Figure 5 Figure 1 shows the topography of the silicon nitride surface imaged using atomic force microscopy (AFM), while B and C show direct (forward) and sideband (forward) nano-infrared imaging of the silicon nitride surface using the silicon nitride phonon exciton resonance absorption signal. As can be seen, the AFM imaging method does not detect any signal from the bottom of the silicon nitride due to the smooth surface of the silicon nitride surface. However, using the silicon nitride phonon exciton resonance absorption signal for nano-infrared imaging reveals the distribution of microspheres on the subsurface using both sideband and direct modes.

[0054] This embodiment shows that under the strategy of using the surface of the phononic material as the imaging substrate, super-resolution infrared imaging can be performed using the sideband mode or the direct mode with a resolution better than 100 nm.

[0055] Example 5

[0056] In this example, the phononic material surface is 10 nm thick silicon nitride, and the structure to be imaged is a 4-micron diameter polystyrene microsphere beneath the silicon nitride surface. Using an optically induced force microscope (IIFM) with tapping mode and sideband detection, nano-infrared imaging of the polystyrene microspheres was performed at different wavelengths, including imaging and spectral scanning.

[0057] The results are as follows Figure 6 As shown in the figure, a is an atomic force microscope topography image of the silicon nitride top surface, b is a nano-infrared image of the silicon nitride top surface using the silicon nitride phonon exciton resonance absorption signal (positive mode), and c is a nano-infrared image of the silicon nitride top surface using the silicon nitride phonon material bulk absorption signal (negative mode). It can be seen that when using atomic force microscope imaging, the silicon nitride top surface is relatively flat, with only wrinkles caused by the microspheres at the bottom. Therefore, apart from the wrinkles, no signal from the polystyrene at the bottom of the silicon nitride is observed. Nano-infrared imaging using the silicon nitride phonon exciton resonance absorption or the phonon material bulk absorption signal reveals the distribution of the subsurface microspheres.

[0058] This embodiment demonstrates that high-molecular super-resolution subsurface infrared imaging can be achieved by using the surface of a phononic material as an imaging substrate.

[0059] Example 6

[0060] In this example, the imaging substrate is 10 nm thick silicon nitride. The sample is a silicon wafer several hundred microns thick, with a dense array of 4-micron diameter polystyrene microspheres at its edge. Nanoscale infrared imaging is performed using a light-induced force microscope (LIFM) with sideband detection in tapping mode. The sample is imaged and spectrally scanned at different wavelengths.

[0061] The results are as follows Figure 7 As shown in the figure, a is an atomic force microscope topography image of the silicon nitride top surface, b is a nano-infrared image of the silicon nitride top surface using the silicon nitride phonon exciton resonance absorption signal (positive mode), and c is a nano-infrared image of the silicon nitride top surface using the silicon nitride phonon material bulk absorption signal (negative mode). It can be seen that when using atomic force microscope imaging, the silicon nitride top surface is relatively flat, with only wrinkles caused by the pull of the bottom silicon wafer. Therefore, apart from the wrinkles, no signal from the microspheres or silicon wafer at the bottom of the silicon nitride is observed. Nano-infrared imaging using the silicon nitride phonon exciton resonance absorption or the phonon material bulk absorption signal reveals the distribution of the silicon wafer and polystyrene microspheres on the subsurface.

[0062] This embodiment shows that super-resolution infrared imaging of materials without infrared absorption can be achieved under the strategy of using the surface of the phononic material as the imaging substrate.

[0063] Example 7

[0064] In this example, the phononic material surface is silicon nitride with a thickness of 10 nm. The structure to be imaged is a polystyrene microsphere with a diameter of 200 nm beneath the silicon nitride surface. Using an optically induced force microscope (IIFM) with tapping mode and sideband detection, nano-infrared imaging of the polystyrene microspheres was performed at different wavelengths, including imaging and spectral scanning.

[0065] The results are as follows Figure 8As shown in the figure, a is an atomic force microscope topography image of the silicon nitride top surface, b is a nano-infrared image of the silicon nitride top surface using the silicon nitride phonon exciton resonance absorption signal (positive mode), and c is a nano-infrared image of the silicon nitride top surface using the silicon nitride phonon material bulk absorption signal (negative mode). It can be seen that when using atomic force microscope imaging, the silicon nitride top surface is relatively flat, with only wrinkles caused by the microspheres at the bottom. Therefore, apart from the wrinkles, no microsphere signal at the bottom of the silicon nitride is observed. Nano-infrared imaging using phonon exciton resonance absorption or the phonon material bulk absorption signal can observe the distribution of the subsurface microspheres.

[0066] This example demonstrates that, using the phononic material surface as an imaging substrate, sideband mode can be used for super-resolution infrared imaging with a resolution better than 20 nm.

[0067] Example 8

[0068] In this example, the phononic material surface is 10 nm thick silicon nitride, and the structure to be imaged is a 100 nm long and 50 nm wide gold nanorod beneath the silicon nitride surface. Using a light-induced force microscope (PIFM) with tapping mode and sideband detection, nano-infrared imaging of the gold nanorods was performed at different wavelengths, including imaging and spectral scanning.

[0069] The results are as follows Figure 9 Figures (a) and (b) show the atomic force microscope topography of the silicon nitride top surface, (c) the nano-infrared imaging of the silicon nitride top surface using the silicon nitride phonon exciton resonance absorption signal (positive mode), and (d) the nano-infrared imaging of the silicon nitride top surface using the bulk absorption signal of the silicon nitride phonon material (negative mode). As can be seen, the atomic force microscope imaging does not detect the gold nanorods at the bottom of the silicon nitride due to the presence of wrinkles on the top surface. The nano-infrared imaging of the silicon nitride top surface using the silicon nitride phonon exciton resonance absorption signal (positive mode) and (d) the nano-infrared imaging of the silicon nitride top surface using the bulk absorption signal of the silicon nitride phonon material (negative mode) reveal the subsurface distribution of the gold nanorods.

[0070] This embodiment shows that under the strategy of using the surface of the phononic material as the imaging substrate, subsurface spatial resolution better than 20 nm can be achieved, and super-resolution infrared imaging of metal materials can be achieved.

Claims

1. A method for nanoscale subsurface infrared imaging, characterized in that: The method adopts a light-induced force microscope to perform infrared imaging on a subsurface structure having a phononic material surface, wherein the infrared imaging is performed at a phonon absorption wavelength of the phononic material.

2. The method according to claim 1, characterized in that The phonon material is one of mica, quartz, boron nitride, silicon nitride, silicon dioxide, aluminum oxide, molybdenum trioxide or silicon carbide.

3. The method according to claim 1, wherein The phonon material is mica, and the phonon absorption wave number is 1200 cm -1 ~870 cm -1 The phonon material is quartz, and the phonon absorption wave number is 1240 cm -1 ~950 cm -1 The phonon material is boron nitride, and the phonon absorption wave number is 1600 cm -1 ~1300 cm -1 The phonon material is silicon nitride, and the phonon absorption wave number is 1893 cm -1 ~700 cm -1 The phonon material is silicon dioxide, and the phonon absorption wave number is 1250 cm -1 ~800 cm -1 The phonon material is aluminum oxide, and the phonon absorption wave number is 2000 cm -1 ~650 cm -1 The phonon material is molybdenum trioxide, and the phonon absorption wave number is 1000 cm -1 ~400 cm -1 The phonon material is silicon carbide, and the phonon absorption wave number is 1064 cm -1 ~625 cm -1 .

4. The method according to claim 1, wherein The thickness of the surface of the phonon material is 0-50 nm.

5. The method according to claim 1, wherein The surface of the phononic material is flat.

6. The method according to claim 1, characterized in that The subsurface structure is solid or liquid.

7. The method according to claim 1, characterized in that The subsurface structures are defects.

8. The method according to claim 1, characterized in that The subsurface structure is a polymer, DNA, an organic framework material or a two-dimensional material.

9. The method according to claim 1, wherein The thickness or depth of the subsurface structure is less than 2000 nm.

10. The method according to claim 9, wherein The thickness or depth of the subsurface structure is less than 10 nm.

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