Hard brittle material densification detection method based on near field optical amplitude and phase analysis

Abstract

The application discloses a kind of hard brittle material densification detection methods based on near-field optical amplitude and phase analysis, first determine the scanning parameter of sample, then using scanning near-field optical microscopy system obtains the near-field amplitude or phase of hard brittle material sample, directly obtains the corresponding relationship between near-field amplitude or phase and densification rate, and then obtains the densification rate at different positions.The application is imaged by collecting and analyzing the optical signal of the sample surface scattered by the probe with the detector, so the resolution of the imaging mainly depends on the manufacturing accuracy of the probe tip, and the radius of curvature of the tip of the probe is on the order of 10 nm, which exceeds the classical diffraction limit, so high-precision detection can be achieved.Because the optical signal of the sample surface is analyzed, the sample surface will not be damaged, and non-destructive testing of densification can be achieved.The higher test efficiency effectively solves the problem of low test efficiency and the long-time scanning sample thermal drift caused thereby.

Description

Technical Field

[0001] The present invention relates to the field of near-field optical microscopes and optical element defect detection, and in particular to a method for detecting the densification of hard and brittle materials based on near-field optical amplitude and phase analysis. Background Art

[0002] Fused quartz is a prime example of a hard and brittle material. Due to its exceptional properties, including high hardness, high optical transmittance, and excellent thermal stability, it is widely used in optical devices such as laser inertial confinement fusion (ICF), lasers, and photolithography machines. These extreme applications place high demands on hard and brittle materials, and manufacturing components that meet these requirements often requires multiple ultra-precision machining steps. However, due to the inherent physical properties of hard and brittle materials, they are susceptible to localized densification at the surface and subsurface levels under the influence of external forces during these machining processes. This densification can reduce mechanical properties such as hardness and Poisson's ratio; it can also lead to differential absorption from the base material, compromising optical performance. Consequently, when applied to high impact loads or where optical performance is critical, densification can shorten the service life of hard and brittle components, significantly impacting the overall system lifespan.

[0003] Currently, there are many mainstream methods for detecting localized densification in hard and brittle materials. For example, Raman spectroscopy is the primary method for evaluating the densification rate in fused silica, a hard and brittle material. However, the accuracy of Raman spectroscopy in assessing the densification rate is significantly limited. The first major limitation is the resolution of Raman spectroscopy measurements. In addition to other factors such as the sample, the resolution of the instrument depends on the wavelength of the laser beam, the microscope objective lens that focuses the laser beam on the sample and collects Raman scattering. Under the test conditions of current mainstream equipment, the lateral diameter of the focused beam spot can be controlled to the micron level. The range of localized densification is also on the micron level. This means that the interval between each Raman spectral data point is difficult to control, which directly affects the measurement resolution. Furthermore, obtaining a two-dimensional Raman image of the sample can lead to measurement inaccuracies. The second major limitation is long scanning times and low scanning efficiency. This is because fused silica, as an amorphous non-metallic oxide, has less pronounced Raman scattering than other materials. Therefore, obtaining Raman spectral data at an accurate measurement location requires a long measurement time. As the single-point measurement time increases, not only will the total image scanning time be greatly extended to several hours, but it will also aggravate mechanical drift and thermal drift, affecting measurement accuracy.

[0004] Therefore, the use of current existing technologies for densification detection is often limited, and it is necessary to find a new optical microscopy-based method to detect the densification of hard and brittle materials. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a hard and brittle material densification detection method based on near-field optical amplitude and phase analysis, which can improve the accuracy and efficiency of hard and brittle material densification detection.

[0006] The technical solutions of the present invention are as follows:

[0007] A method for detecting the densification of hard and brittle materials based on near-field optical amplitude and phase analysis comprises the following steps:

[0008] Step 1: Pre-densification is performed by nanoindentation to form a nanoindentation area on the surface of the hard and brittle material with an indentation load of 100 to 500 mN.

[0009] Step 2: Use a nano-infrared spectroscopy system to perform infrared absorption tests on different positions of the nanoindentation area to obtain a nano-infrared spectrum, and determine that the excitation light wavelength that produces the highest peak intensity is the optimal nano-infrared absorption peak.

[0010] Step 3: Using a scattering scanning near-field optical microscope system, the nanoindentation area is scanned over the entire range using infrared light of a wave number corresponding to the optimal nano-infrared absorption peak to obtain near-field optical amplitude and phase scanning images of the nanoindentation area.

[0011] Step 4: Extract data from the near-field amplitude and phase scanning images of the indentation area to obtain the variation pattern of the near-field amplitude and phase at different positions of the indentation and the substrate; determine the correspondence between amplitude and phase and densification by exploring the changes in near-field amplitude and phase corresponding to different densification rates.

[0012] Step 5: Calculate the densification rate at different positions in the nanoindentation area based on the corresponding relationship between the near-field amplitude and phase and the densification and the variation law of the near-field phase in the nanoindentation area.

[0013] Furthermore, the nanoindentation area in step 1 is prefabricated using a standard Berkovich indenter, and the load is directly controlled by the nanoindenter.

[0014] Furthermore, in step 2, the nano-infrared spectroscopy system detects the thermal expansion of the local sample surface caused by the absorption of infrared radiation through the tip. The nano-infrared spectroscopy system includes an atomic force microscope device and an optical device. The tip of the probe of the atomic force microscope device is coated with gold, and the radius of curvature of the tip of the probe is 20-40nm. The probe operates in contact mode when performing nano-infrared spectroscopy scanning. The light source of the optical device is a tunable quantum cascade laser, and the harmonic adjustment range of the quantum cascade laser is 940-1900cm -1 .

[0015] Furthermore, the area size of the full-range image scan in step three is determined according to the size of the nanoindentation, ensuring that the scanned image simultaneously contains the nanoindentation and the surrounding substrate area of ​​appropriate size. The scattering scanning near-field optical microscopy system collects and analyzes the sample near-field signal scattered by the probe through the MCT detector to perform near-field optical imaging. The scattering scanning near-field optical microscopy system includes an atomic force microscope device and a near-field optical device. The probe of the atomic force microscope device operates in tapping mode when performing near-field optical imaging. The tip curvature radius of the probe is 20-40nm. The light source of the near-field optical device is a tunable quantum cascade laser or a CO2 laser. According to the optimal nano-infrared absorption peak of the incident light of the sample obtained in step two, a laser containing the wave number corresponding to the optimal nano-infrared absorption peak is selected. The MCT detector is a mercury cadmium telluride detector, which is suitable for optical detection in the infrared field. The reference signal of the near-field amplitude and phase selects the signal of the non-densified area in the substrate area for reference.

[0016] Furthermore, the variation law of the near-field amplitude and phase at different positions described in step four is the variation law from the substrate area to the indentation center. The correspondence between the near-field phase and densification is jointly established by the first principles and dipole model methods. The specific method is to calculate and obtain the dielectric constant of the hard and brittle material model with different densification rates by the first principles. Further, the calculated dielectric constant information is substituted into the dipole model for solution to obtain the near-field amplitude and phase. The parameters in the dipole model are directly determined according to the relevant parameters during the experiment. The dipole model is a point dipole model or a finite dipole model. By comparing the near-field amplitude or phase obtained by experiment and calculation, it is determined that the scattered scanning near-field optical microscopy system signal that directly reflects the densification rate is an amplitude signal or a phase signal. Then the correspondence between the densification rate and the near-field amplitude or phase is established. The corresponding relationship is compared by comparing the near-field amplitude or phase obtained through experiment and calculation, and then fitting is performed between the densification rate and the near-field amplitude or phase. The fitting relationship varies according to the different change relationships between the obtained densification rate and the near-field amplitude or phase.

[0017] Furthermore, in step five, the correspondence between the near-field phase and densification is used to substitute the near-field phase at different indentation positions to inversely calculate the densification rate at the corresponding position.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The present invention can first determine the scanning parameters of the sample, and then use a scanning near-field optical microscopy system to obtain the near-field amplitude or phase of the hard and brittle material sample, directly obtain the corresponding relationship between the near-field amplitude or phase and the densification rate, and then obtain the densification rate at different positions.

[0020] 2. The present invention uses a detector to collect and analyze optical signals scattered by the probe from the sample surface for imaging. Therefore, the imaging resolution depends primarily on the manufacturing precision of the probe tip. The radius of curvature of the probe tip is on the order of 10 nm, exceeding the classical diffraction resolution limit, enabling high-precision detection. Furthermore, because the optical signals from the sample surface are analyzed, the surface is not damaged, enabling compact, nondestructive testing.

[0021] 3. This invention significantly improves testing efficiency. Specifically, compared to approximately 12 hours required to obtain a 10μm×10μm Raman spectroscopy image at a 32×32 resolution, this invention achieves a 10μm×10μm image at a 128×128 resolution in approximately 20 minutes. This higher testing efficiency effectively addresses the issues of low testing efficiency and the resulting thermal drift of samples from long-term scanning. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the morphology of the nanoindentation area of ​​the hard and brittle material fused quartz.

[0023] Figure 2 Nano-infrared spectra at different positions in the nanoindentation area of ​​hard and brittle material fused quartz.

[0024] Figure 3 This is the near-field optical phase image of the nanoindentation region of the hard and brittle material fused silica.

[0025] Figure 4 is the changing trend of the near-field phase at different positions.

[0026] Figure 5 These are the densification rate results at different indentation positions under multiple different loads obtained according to an embodiment of the present invention.

[0027] Figure 6 The densification rates at different indentation positions obtained according to the embodiment of the present invention are compared with those in the literature. DETAILED DESCRIPTION

[0028] To make the objectives, technical solutions, and advantages of the present invention more clear, the following will provide a more complete description of the present invention with reference to the accompanying drawings and embodiments. It should be understood that the embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. All other embodiments obtained by persons of ordinary skill in the art without creative effort are intended to fall within the scope of protection of the present invention.

[0029] Example 1:

[0030] This embodiment is used to illustrate a method for detecting the densification of fused quartz, a hard and brittle material.

[0031] Step 1: pre-densification of the hard and brittle material surface by nanoindentation, with an indentation load of 100 to 500 mN, preferably 100 to 250 mN.

[0032] The morphology of the indentation is shown in FIG. Figure 1 As shown, the indentation load was 250 mN. The surface topography of the sample was acquired using an atomic force microscope (AFM) with a probe radius of curvature of approximately 20 nm. During the topography scan, the AFM operated in tapping mode, with a sampling frequency of 1 Hz and a resolution of 256 × 256 pixels.

[0033] Step 2: Use a nano-infrared spectroscopy system to perform infrared absorption tests on different positions of the nanoindentation area determined in step 1 to obtain a nano-infrared spectrum, and determine that the excitation light wavelength that produces the highest peak intensity is the optimal nano-infrared absorption peak.

[0034] The nano-infrared spectroscopy system includes an atomic force microscope (AFM) and an optical device. The AFM probe is a gold-coated probe tip with a radius of curvature of approximately 20 nm. The probe operates in contact mode during nano-infrared spectroscopy. The optical device's light source is a tunable quantum cascade laser (QCL) with a tunable wavenumber range of 940 to 1900 cm -1 .like Figure 2 As shown, the nano-infrared spectra of the samples were obtained at different positions of the indentation, with a wave number range of 940 to 1250 cm -1 , scanning resolution 2cm -1 From the nano-infrared spectrum data at different positions, it can be seen that when the excitation light wave number is 1070cm -1 When the nano-infrared optical absorption of fused quartz is the most obvious, the spectral peak intensity reaches the highest, so the optimal nano-infrared absorption peak is determined to be 1070cm -1 .

[0035] Step 3: Use the optimal nano-infrared absorption peak determined in Step 2 to perform a scattering scanning near-field optical microscopy scan. Scan the entire nanoindentation area determined in Step 1 to obtain near-field optical amplitude and phase results for that area. The reference signals for the near-field amplitude and phase signals are selected from the non-densified area of ​​the substrate.

[0036] Figure 3The image shows the near-field phase of the indentation. The scanned image size is 20×20μm, the scanned image resolution is 256×256, and the scanning sampling frequency is 0.1Hz. The atomic force microscope (AFM) apparatus is the same system as the AFM apparatus used for nano-infrared spectroscopy. The probe operates in tapping mode during near-field optical imaging. The light source of the near-field optical apparatus is a tunable quantum cascade laser or a CO2 laser. The MCT detector is a mercury cadmium telluride (MCT) detector.

[0037] Step 4. Data extraction is performed on the near-field amplitude and phase scanning images of the indentation area obtained in step 3 to obtain the variation pattern of the near-field amplitude and phase at different positions such as the indentation and the substrate; by exploring the near-field amplitude and phase changes corresponding to different densification rates, the correspondence between amplitude, phase and densification is determined. The specific method is to calculate and obtain the dielectric constant of different densification rate models through first principles. Furthermore, the calculated dielectric constant information is substituted into the dipole model for solution to obtain the near-field amplitude and phase. The parameters in the dipole model can be directly determined according to the relevant parameters during the experiment. The dipole model is a point dipole model or a finite dipole model. The near-field amplitude or phase calculated by the dipole model is compared with the near-field amplitude or phase obtained by the experiment to determine that the scattering scanning near-field optical microscopy system signal that directly reflects the densification rate is a phase signal.

[0038] like Figure 4 As shown, the near-field phase edge Figure 3 The trend of the white line is shown in the figure. It can be seen from the figure that the near-field phase of the substrate remains basically unchanged, while in the inner area of ​​the indentation, as the topography gradually decreases, the phase also gradually decreases, which is caused by the continuous deepening of the densification rate.

[0039] The correspondence between the near-field phase and densification is established by combining the first principles and dipole model methods. The correspondence between the near-field phase and densification is:

[0040]

[0041] Where D is the densification rate, The corresponding relationship is primarily based on a comparison of experimentally and calculated near-field phases, determining that the fitting relationship between the densification rate of direct fused silica and the near-field phase signal is a quadratic polynomial fit. This fitting relationship is then performed between the densification rate and the near-field phase. The fitting relationship varies depending on the different responses of different test materials to s-SNOM.

[0042] Step 5: Calculate the densification rates at different positions in the indentation area based on the correspondence between the near-field phase and densification determined in step 4 and the variation pattern of the near-field phase in the indentation area.

[0043] like Figure 5 As shown, according to the correspondence between the near-field phase and densification in step four, the densification rates of the indentations at different positions from the center of the indentation to the edge of the indentation with three different loads of 500mN, 300mN, and 250mN were calculated. The densification rate is highest at the center of the indentation and gradually decreases with increasing distance from the center of the indentation. At the same time, the densification rate obtained by the detection method of the present invention is compared with the densification rate in the literature (Raman spectroscopic measurements and imaging on sub-newton Berkovich and spherical imprints in fused silica, Journal of Non-Crystalline Solids 2024) to verify the correctness of the densification results obtained by the method of the present invention. The comparison results are shown in Figure 2. Figure 6 As shown in the results, it can be seen that the densification rate calculated according to the present invention is in good agreement with that in the literature, which verifies the correctness of the invention.

[0044] The present invention is not limited to this embodiment, and any equivalent concepts or modifications within the technical scope disclosed by the present invention are included in the protection scope of the present invention.

Claims

1. A method for detecting the densification of hard and brittle materials based on near-field optical amplitude and phase analysis, characterized by: The steps include: Step 1: pre-densification by nanoindentation, forming a nanoindentation area on the surface of the hard and brittle material with an indentation load of 100 to 500 mN; Step 2: Using a nano-infrared spectroscopy system to perform infrared absorption tests on different positions of the nano-indentation area to obtain a nano-infrared spectrum, and determining that the excitation light wavelength with the highest peak intensity is the optimal nano-infrared absorption peak; Step 3: Using a scattering scanning near-field optical microscope system, a full-range image scan of the nanoindentation area is performed using infrared light of a wave number corresponding to the optimal nano-infrared absorption peak to obtain near-field optical amplitude and phase scanning images of the nanoindentation area. Step 4: extract data from the near-field amplitude and phase scanning images of the indentation area to obtain the variation patterns of the near-field amplitude and phase at different positions of the indentation and the substrate; determine the corresponding relationship between amplitude and phase and densification by exploring the changes in near-field amplitude and phase corresponding to different densification rates; Step 5: Calculate the densification rate at different positions in the nanoindentation area based on the corresponding relationship between the near-field amplitude and phase and the densification and the variation law of the near-field phase in the nanoindentation area.

2. The method for detecting densification of hard and brittle materials based on near-field optical amplitude and phase analysis according to claim 1, characterized in that: The nanoindentation area in step 1 is prefabricated using a standard Berkovich indenter, and the load is directly controlled by the nanoindenter.

3. The method for detecting densification of hard and brittle materials based on near-field optical amplitude and phase analysis according to claim 1, characterized in that: In step 2, the nano-infrared spectroscopy system detects thermal expansion of the local sample surface caused by absorption of infrared radiation through a tip; the nano-infrared spectroscopy system includes an atomic force microscope device and an optical device; the tip of the probe of the atomic force microscope device is coated with gold, and the radius of curvature of the tip of the probe is 20-40nm; the probe operates in contact mode when performing nano-infrared spectroscopy scanning; the light source of the optical device is a tunable quantum cascade laser, and the harmonic adjustment range of the quantum cascade laser is 940-1900cm -1 .

4. The method for detecting densification of hard and brittle materials based on near-field optical amplitude and phase analysis according to claim 1, characterized in that: The size of the area for the full-range image scan in step three is determined according to the size of the nanoindentation to ensure that the scanned image simultaneously includes the nanoindentation and the surrounding substrate area of ​​appropriate size; the scattering scanning near-field optical microscopy system collects and analyzes the sample near-field signal scattered by the probe through the MCT detector to perform near-field optical imaging; the scattering scanning near-field optical microscopy system includes an atomic force microscope device and a near-field optical device; the probe of the atomic force microscope device operates in tapping mode when performing near-field optical imaging; the tip curvature radius of the probe is 20-40nm; the light source of the near-field optical device is a tunable quantum cascade laser or a CO2 laser, and according to the optimal nano-infrared absorption peak of the incident light of the sample obtained in step two, a laser with a wave number corresponding to the optimal nano-infrared absorption peak is selected; the MCT detector is a mercury cadmium telluride detector, which is suitable for optical detection in the infrared field; the reference signal of the near-field amplitude and phase selects the signal of the non-densified area in the substrate area for reference.

5. The method for detecting densification of hard and brittle materials based on near-field optical amplitude and phase analysis according to claim 1, characterized in that: The variation law of the near-field amplitude and phase at different positions described in step 4 is the variation law from the substrate area to the indentation center; the correspondence between the near-field phase and densification is jointly established by the first principles and dipole model methods; the specific method is to calculate and obtain the dielectric constant of the hard and brittle material model with different densification rates by the first principles; further, the calculated dielectric constant information is substituted into the dipole model for solution to obtain the near-field amplitude and phase; the parameters in the dipole model are directly determined according to the relevant parameters during the experiment; the dipole model is a point dipole model or a finite dipole model; by comparing the near-field amplitude or phase obtained by experiment and calculation, it is determined that the scattered scanning near-field optical microscopy system signal that directly reflects the densification rate is an amplitude signal or a phase signal; then the correspondence between the densification rate and the near-field amplitude or phase is established; the correspondence is compared by comparing the near-field amplitude or phase obtained by experiment and calculation, and then the densification rate and the near-field amplitude or phase are fitted, and the fitting relationship is different according to the different change relationship between the obtained densification rate and the near-field amplitude or phase.

6. The method for detecting densification of hard and brittle materials based on near-field optical amplitude and phase analysis according to claim 1, characterized in that: In step five, the correspondence between the near-field phase and densification is used to substitute the near-field phase at different indentation positions to inversely calculate the densification rate at the corresponding position.

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