Testing method for bending fracture mechanical properties of diamond self-supporting film micro cantilever beam

Abstract

The present invention provides a testing device and method for the bending and fracture mechanical properties of a diamond self-supporting film micro cantilever beam, comprising: depositing a diamond film on the surface of a single crystal silicon substrate, chemically etching the silicon substrate to obtain a self-supporting diamond film, and laser cutting to obtain a cantilever beam structure. During the test, the cantilever beam sample to be tested is first fixed on a displacement platform, and the three-coordinate displacement platform is adjusted under the observation of a microscope so that the pressure head is aligned with the free end of the micro cantilever beam. The pressure head is driven by controlling a piezoelectric ceramic actuator to load uniformly until the cantilever beam bends and breaks, and the real-time displacement and contact load data during the loading process are recorded to obtain a displacement-load curve. The present invention solves the difficult problem of testing the fracture mechanical properties of chemical vapor deposited diamond films with a relatively small thickness, and improves the deposition process of the diamond film by obtaining mechanical property parameters such as Young's modulus, fracture strength and fracture toughness of the diamond film, thereby improving its fracture strength and toughness.

Description

Technical Field

[0001] The invention relates to the technical field of superhard material testing, and in particular to a method for testing the bending fracture mechanical properties of a diamond self-supporting film micro cantilever beam. Background Art

[0002] CVD diamond films have excellent properties such as high hardness, high elastic modulus, extremely high thermal conductivity, good self-lubrication and chemical stability, which are very close to natural diamonds. They have broad application prospects in cutting tools, thermal management of high-power devices, micro-electromechanical devices, various optical windows and semiconductor fields. However, due to the uncertainty of defect size in polycrystalline diamond films, their fracture strength and toughness have large fluctuations. Therefore, it is of great significance to study how to optimize the fracture mechanical properties of polycrystalline diamond films, and accurately measuring the fracture mechanical properties of polycrystalline diamond films is the key to optimization.

[0003] Diamond film is a typical hard and brittle material. There are many factors that affect the feasibility and accuracy of its fracture mechanics performance testing, and film thickness is one of the most important factors. The shortcomings of the current research on the fracture mechanics properties of diamond films are mainly reflected in the following three aspects: (1) The conventional three-point or four-point bending method requires the thickness of the test sample to be more than 3 mm. However, the diamond film prepared by the CVD method is not a homogeneous material. Its properties will gradually change with the increase of film thickness, including the internal grain size and stress state, resulting in mechanical properties changing with the film. Therefore, the determination of the fracture mechanics properties under a specified film thickness cannot cover all aspects; (2) The fracture mechanics test results of hard and brittle materials often have a certain degree of randomness, so a large number of samples are required to obtain effective test results. The test samples used in conventional testing methods are large in size, which is obviously not economical for CVD diamond films with high deposition costs; (3) Since the cross-section of CVD diamond generally presents a columnar growth texture, the resistance encountered by the crack in the lateral and longitudinal extension of the film is quite different. Longitudinal extension is the main crack propagation mechanism during the fracture of diamond films. Traditional testing methods have only studied the toughness of the crack in the lateral extension mode, and no research has been conducted on the toughness of the crack in the longitudinal propagation mode.

[0004] The utility model patent with patent document CN209432578U discloses a test fixture for the mechanical properties of CVD diamond materials, the test fixture includes a first metal base, a second metal base, a first metal support rod, a second metal support rod and a top loading component, the first metal base and the second metal base are connected by the first metal support rod and the second metal support rod, and the top loading component is vertically arranged above the first metal base and the second metal base. The above scheme realizes the mechanical property test of small-sized diamond samples, which can not only solve the problem that the current diamond preparation technology is difficult to meet the national standard test bending strength sample size requirements, but also can complete the test by selecting the scraps on the large-sized diamond film, realize the evaluation of the mechanical properties of the entire diamond film, and save a large number of diamond film samples. However, the test sample size disclosed by this method is 1mm×2mm×10mm. Judging from the structure of the device and the sample size, this method is not suitable for the fracture mechanical property test of diamond films with a thickness of less than 1mm. In addition, the utility model does not involve the fracture toughness test of diamond films under the condition of longitudinal crack extension. Summary of the invention

[0005] In view of the defects in the prior art, the object of the present invention is to provide a method for testing the bending fracture mechanical properties of a diamond self-supporting film micro cantilever beam.

[0006] A method for testing the bending fracture mechanical properties of a diamond self-supporting film micro cantilever beam provided by the present invention comprises the following steps:

[0007] Sample acquisition steps: obtaining a diamond film microcantilever beam sample to be tested through diamond film deposition, chemical etching of silicon substrate, and laser cutting processes;

[0008] Adjustment and alignment steps: stick the diamond film micro cantilever beam sample to be tested on the fixture, fix the fixture on the three-axis displacement platform, and adjust the three-axis displacement platform so that the indenter is aligned with the free end of the micro cantilever beam sample;

[0009] Equipment installation steps: The indenter, contact load measuring instrument and piezoelectric ceramic actuator are connected in sequence, and the displacement of the piezoelectric ceramic actuator is controlled to drive the indenter to perform the fracture mechanics property test of the diamond film;

[0010] Performance test steps: The displacement and contact load of the piezoelectric ceramic actuator are collected through software to obtain the displacement-load curve. According to the system rigidity calibration results, the true deflection of the diamond film microcantilever beam sample and the Young's modulus, fracture strength and fracture toughness of the diamond film are calculated.

[0011] Preferably, in the sample acquisition step, the specific preparation process of the diamond film microcantilever beam sample includes:

[0012] Deposition step: roughening the surface of the single crystal silicon substrate with sandpaper and planting diamond powder, and depositing the diamond film by microwave plasma chemical vapor deposition or hot wire chemical vapor deposition;

[0013] Corrosion step: using a supersaturated potassium hydroxide solution to corrode the single crystal silicon substrate, and using a water bath to heat it during the process;

[0014] Sample preparation steps: A laser cutting machine is used to prepare the cantilever beam sample. First, the self-supporting diamond membrane is divided into sample pieces of set units. One side of the sample piece is pasted on the fixture using quick-drying glue, and the cantilever beam structure is cut.

[0015] Preferably, in the sample acquisition step, the micro cantilever beam obtained by laser cutting includes a micro cantilever beam without a cut and a micro cantilever beam with a single cut, wherein the micro cantilever beam without a cut is used for measuring Young's modulus and fracture strength, and the micro cantilever beam with a single cut is used for measuring fracture toughness.

[0016] Preferably, the single-sided cut cantilever beam is prefabricated with a laser cutting method, the laser power is 10W, the galvanometer movement speed is 20m / s, the reciprocating cutting is 4 times, and the cut depth is measured by the microscopic morphology of the cantilever beam fracture cut.

[0017] Preferably, in the adjustment and alignment step, the precise position of the indenter is determined by magnifying through two sets of optical microscopes, one on the x-axis and the other on the z-axis, wherein: the x-axis microscope is used to determine the effective length of the microcantilever; and the z-axis microscope is used to determine that the indenter is located at the center of the cantilever width.

[0018] Preferably, in the adjustment and alignment step, the position of the pressure head is adjusted by a three-coordinate displacement platform. After the pressure head is aligned with the center of the width of the cantilever beam, the displacement platform is slowly adjusted to move along the x-axis so that the pressure head and the cantilever beam are in contact. After observing the load information appearing on the software control interface, the pressure head is retracted until the load is 0.

[0019] Preferably, the pressure head is a Bosch pressure head.

[0020] Preferably, in the device installation step:

[0021] The maximum stroke of the piezoelectric ceramic actuator is 100μm, the minimum step length is 7nm, and the closed-loop control method is adopted with an accuracy of 0.05% FS;

[0022] The maximum range of the contact load measuring instrument is 1N, the sensitivity is 2.0±10%nN / mN, the working temperature is -20~50℃, and the limit overload is 200%FS;

[0023] The displacement mode of the pressure head is uniform motion, and the movement speed is 2μm / s.

[0024] Preferably, in the equipment installation step: the calibration process of the system rigidity is to align the indenter with the supported diamond film part at the bottom, drive the indenter to move, record the load-displacement curve, obtain the yield of the test system under the specified load, and the indenter displacement during the bending and fracture process of the cantilever beam minus the system yield under the current load is the true deflection of the cantilever beam.

[0025] Preferably, in the performance testing step, when the software collects the displacement and contact load of the piezoelectric ceramic actuator, the start of displacement of the actuator is used as the starting point of data recording time, and the relationship between displacement, load and time is established in the data table.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The method for testing the bending fracture mechanics properties of a diamond film micro cantilever beam proposed in the present invention solves the problem of testing the fracture mechanics properties of a diamond film with a relatively small thickness.

[0028] 2. The diamond self-supporting film micro-cantilever bending fracture mechanics performance testing system constructed by the present invention, combined with the preparation of uncut and single-sided cut diamond film micro-cantilever samples, can simultaneously measure the Young's modulus, fracture strength and fracture toughness of CVD diamond film materials.

[0029] 3. The diamond self-supporting film micro cantilever beam bending fracture mechanics performance testing method proposed in the present invention realizes the measurement of the fracture toughness of the diamond film when the crack propagates along the growth direction.

[0030] 4. The diamond self-supporting film micro cantilever beam bending fracture mechanics property testing method proposed in the present invention has relatively small requirements for the size of the test sample and has good economy for fracture mechanics property testing experiments of brittle materials that require a large amount of data support.

[0031] 5. The present invention meets the testing requirements of Young's modulus, fracture strength and fracture toughness of diamond films with a thickness of tens of microns. By obtaining the fracture mechanical properties of CVD diamond films, the deposition process of CVD diamond films is improved, which is of great significance for improving the application performance of CVD diamond films in various fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0033] Figure 1 This is a schematic diagram of the principle of testing the bending fracture mechanics properties of diamond self-supporting film microcantilever beam.

[0034] Figure 2 Schematic diagram of the calibration curve of system stiffness.

[0035] FIG3( a ) is a schematic diagram of the cantilever beam structure without cutouts and its relative position relationship with the pressure head.

[0036] Figure 3(b) is a schematic diagram of the single-side cut cantilever beam structure and its relative position relationship with the pressure head.

[0037] Figure 3(c) is the SEM image of the cantilever beam without cutouts.

[0038] Figure 4 Surface and cross-sectional microscopic images of five free-standing diamond films.

[0039] Figure 5(a) is a load-displacement curve of the uncut diamond film cantilever beam when the growth side is stretched.

[0040] Figure 5(b) is a load-displacement curve of the nucleation side of the uncut diamond film cantilever beam under tension.

[0041] Figure 6 Schematic diagram of the statistical results of Young's modulus of five diamond films.

[0042] Figure 7 Schematic diagram of the statistical results of the fracture strength of five free-standing diamond films.

[0043] Figure 8 Schematic diagram of the fracture toughness test results of single-layer nanodiamond and multi-layer composite diamond films.

[0044] The figure shows:

[0045] Bosch Indenter 1

[0046] Contact load measuring instrument 2

[0047] Piezoelectric Actuator3

[0048] Diamond self-supporting film microcantilever beam sample 4

[0049] Cantilever beam fixture 5

[0050] Three-coordinate displacement platform 6

[0051] Fixed system platform 7 DETAILED DESCRIPTION

[0052] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0053] like Figures 1 to 8As shown, a method for testing the bending fracture mechanical properties of a diamond self-supporting film micro cantilever beam provided by the present invention comprises the following steps:

[0054] S1, obtaining a diamond film micro cantilever beam sample to be tested through processes such as diamond film deposition, chemical etching of silicon substrate, and laser cutting;

[0055] S2, stick the diamond film micro cantilever to be tested on the fixture, fix the fixture on the three-coordinate displacement platform, adjust the displacement platform so that the pressure head is aligned with the free end of the micro cantilever;

[0056] S3, the indenter, the contact load measuring instrument and the piezoelectric ceramic actuator are connected in sequence, and the displacement of the piezoelectric ceramic actuator is controlled to drive the indenter to move, and the fracture mechanics property test of the diamond film is performed;

[0057] S4. The displacement and contact load of the piezoelectric ceramic actuator are collected through software to obtain the displacement-load curve. According to the system rigidity calibration results, the true deflection of the cantilever beam and the Young's modulus, fracture strength and fracture toughness of the diamond film are calculated.

[0058] Furthermore, in step S1, the specific preparation process of the diamond film cantilever beam includes:

[0059] Step S11, roughening the surface of the single crystal silicon substrate with sandpaper and planting diamond powder, and depositing a diamond film by microwave plasma chemical vapor deposition or hot wire chemical vapor deposition, with the preferred film thickness ranging from 30 to 300 μm;

[0060] Step S12, using a supersaturated potassium hydroxide solution to corrode the single crystal silicon substrate, and using a water bath to heat the substrate during the process, with the preferred heating temperature being 80° C.;

[0061] Step S13, using a laser cutting machine with a wavelength of 532nm to prepare a cantilever beam sample, firstly, the self-supporting diamond membrane is divided into 7mm×7mm samples, one side of the sample is pasted on the fixture with quick-drying glue, and then the cantilever beam structure is cut, the preferred laser power is 10W, the micro cantilever beam width is 160μm, and the length is 1000μm;

[0062] In step S1, the microscopic cantilever beam obtained by laser cutting includes two types: no cut and single-sided cut, wherein the former is used to measure Young's modulus and fracture strength, and the latter is used to measure fracture toughness. The single-sided cut cantilever beam is prefabricated with a laser cutting method, the preferred laser power is 10W, the galvanometer movement speed is 20m / s, the reciprocating cutting is 4 times, and the cut depth is measured by the microscopic morphology of the cantilever beam fracture cut.

[0063] Furthermore, in step S2, the preferred indenter is a Bosch indenter; the x-axis and z-axis optical microscopes are magnified 100 times to determine the precise position of the indenter, wherein the x-axis microscope is used to determine the effective length of the micro-cantilever, the effective length of the uncut cantilever is 900 μm, and the effective length of the single-sided cut cantilever is 700 μm, and the z-axis microscope is used to determine that the indenter is located at the center of the cantilever width; the indenter position is adjusted by a three-coordinate displacement platform, and after the indenter is aligned with the center of the cantilever width, the displacement platform is slowly adjusted to move along the x-axis to make the indenter contact with the cantilever, and after observing the load information appearing on the software control interface, the indenter is retracted until the load is 0. This is intended to avoid excessive idle travel of the indenter in the initial stage of the test.

[0064] Furthermore, in step S3, the maximum stroke of the piezoelectric ceramic actuator is 100μm, the minimum step length is 7nm, and a closed-loop control method is adopted with an accuracy of 0.05% FS; the maximum range of the contact load measuring instrument is 1N, the sensitivity is 2.0±10%nN / mN, the working temperature is -20~50℃, and the limit overload is 200%FS; the displacement mode of the indenter is uniform motion, and the movement speed is 2μm / s; the calibration process of the system rigidity is to align the indenter with the supported diamond film part at the bottom, drive the indenter to move, record the load-displacement curve, and obtain the yield of the test system under the specified load. The displacement of the indenter during the bending and fracture process of the cantilever beam minus the system yield under the current load is the true deflection of the cantilever beam.

[0065] Since the system rigidity during loading will cause errors in determining the true deflection of the cantilever beam, leading to errors in the calculation results of Young's modulus and fracture strength, it is necessary to calibrate the rigidity of the system to obtain the system yield under different contact loads.

[0066] In step S4, the calibration process of the system rigidity is to align the indenter with the diamond film part supported at the bottom, drive the indenter to move, record the load-displacement curve, and obtain the yield of the test system under different loads. The displacement of the indenter during the bending and fracture process of the cantilever beam minus the yield of the system under the current load is the true deflection (ω) of the cantilever beam. The calculation method is shown in formula (1-1):

[0067] ω=d-kF (1-1)

[0068] where k is the slope of the calibration curve (displacement / load) and F is the load magnitude.

[0069] In step S4, the test process of Young's modulus is to align the indenter with the free end of the uncut cantilever beam, drive the indenter to move to make the cantilever beam produce elastic deformation, collect contact load and displacement data during the loading process, and calculate the Young's modulus (E) of the diamond film. The calculation method is shown in formula (1-2):

[0070]

[0071] Where b is the cantilever width, l is the effective length of the uncut cantilever, and t is the diamond film thickness.

[0072] The dimensions of the uncut cantilever beam are: b = 160 μm, l = 900 μm, and t is measured by microscopic morphology of the fractured cross section of the cantilever beam.

[0073] In step S4, the fracture strength test process is to align the indenter with the free end of the uncut cantilever beam, drive the indenter to move until the cantilever beam breaks, collect the contact load and displacement data during the loading process, and calculate the fracture strength (σ F ), the calculation method is shown in formula (1-3):

[0074]

[0075] where F f is the breaking load of the cantilever beam.

[0076] In step S4, the fracture toughness test process is to align the indenter with the free end of the cantilever beam with a single edge cut, drive the indenter to move until the cantilever beam breaks, collect the load-displacement data during the loading process, and calculate the fracture toughness (K IC ), the calculation method is shown in formula (1-4):

[0077]

[0078] in is the dimensionless shape parameter of the cantilever beam with a single-sided notch, l0 is the effective length of the cantilever beam with a single-sided notch, specifically the distance from the contact point of the indenter to the notch, and c0 is the depth of the notch.

[0079] Preferably, in the size of the single-sided notched cantilever beam, l0=700 μm, and c0 is measured through the microscopic morphology of the fracture cross section of the single-sided notched cantilever beam.

[0080] In step S4, the test software has the functions of calibrating the load measuring instrument, controlling the displacement speed and stroke of the pressure head, adjusting the data collection time interval, etc., and displays the displacement-time curve, load-time curve, load-displacement curve and real-time load-displacement data on the main interface of the software. In the process of collecting the displacement and contact load of the piezoelectric ceramic actuator, the start of the actuator displacement is used as the starting point of the data recording time, and the relationship between the displacement and load and time is established in the data table.

[0081] More detailed description:

[0082] Embodiment 1:

[0083] The diamond self-supporting film micro cantilever beam bending fracture mechanical properties test system consists of four main parts: piezoelectric ceramic actuator and its closed-loop control power supply, contact load measuring instrument and its signal conversion method, x-axis and z-axis optical microscope and its display screen, micro cantilever beam fixture and three-coordinate displacement platform for adjusting its position.

[0084] The stiffness of the system will cause errors in the determination of the true deflection of the test specimen. Before all tests, the system stiffness needs to be calibrated.

[0085] The schematic diagram of the testing principle of the bending fracture mechanical properties of the diamond self-supporting film microcantilever beam is as follows: Figure 1 As shown, the yield of the test system mainly comes from the elastic deformation of the contact load measuring instrument.

[0086] During the system stiffness calibration process, the indenter is aligned with the diamond film supported at the bottom to control the loading and unloading of the indenter. The load-displacement curve obtained at this time is as follows: Figure 2 As shown, since the position of the pressure head does not change, the displacement data obtained in this process is actually the elastic deformation of the contact load measuring instrument.

[0087] The slope of the calibration curve is used to calculate the actual deflection of the cantilever beam specimen in subsequent tests.

[0088] Embodiment 2:

[0089] The Young's modulus and fracture strength of the diamond free-standing film under tensile stress were measured. At this time, an uncut cantilever beam was used as the sample, and the structure is shown in Figure 3(a).

[0090] Five diamond films with different structures were prepared on the surface of single crystal silicon using microwave plasma chemical vapor deposition technology. The surface and cross-sectional morphologies are shown in Figure 2. Figure 4 As shown, (mM) represents a single-layer micron diamond film, (mN) represents a single-layer nano diamond film, (2l) represents a micron / nano double-layer composite diamond film, (4l) represents a micron / nano four-layer composite diamond film, and (8l) represents a micron / nano eight-layer composite diamond film.

[0091] During the composite diamond film deposition process, the alternating deposition of micron diamond film and nano diamond film is achieved by periodically regulating the reaction gas pressure, carbon source concentration and nitrogen flow rate.

[0092] After the diamond film deposition is completed, the silicon substrate is removed by chemical etching to obtain a self-supporting diamond film. Specifically, the chemical etching solution is a potassium hydroxide aqueous solution with a supersaturated concentration. During the corrosion process, a water bath is used to heat the container containing the corrosion solution to 80°C. The thickness of the silicon substrate used in this experiment is 0.72mm, and the preferred corrosion time is about 24h.

[0093] Laser cutting is used to divide the diamond self-supporting film into 7mm×7mm square samples. The preferred laser power is 10W and the galvanometer movement speed is 20m / s. Quick-drying glue is used to stick the square sample into a special groove on the fixture. The growth side of the diamond film is exposed to the outside. The size of the groove is 7.5mm×5mm×1mm. Therefore, the fixed sample will have an area of ​​2mm×7mm at the bottom without support.

[0094] The micro-cantilever structure was prepared on the unsupported diamond film part by laser cutting. The preferred cutting power was 10 W, the galvanometer movement speed was 20 m / s, the width of the micro-cantilever was 160 μm, the length was 1000 μm, and the thickness was measured according to the cross-sectional morphology of the diamond film. The number of reciprocating motions of the galvanometer was adjusted according to the film thickness.

[0095] After the micro-cantilever structure is prepared, the fixture is fixed on the three-coordinate displacement platform with bolts, and the platform position is adjusted to align the Bosch indenter with the free end of the cantilever. First, the z-axis microscope in the system is used to determine that the indenter is located at the center of the cantilever width, and then the x-axis microscope is used to determine the distance between the contact position of the indenter and the cantilever and the root of the cantilever. The preferred distance is 900 μm.

[0096] To prevent excessive idle travel before the punch is loaded, the three-coordinate displacement platform is manually adjusted so that the punch moves along the x-direction and contacts the cantilever beam. Contact load is observed on the control program interface, and then the punch is slowly retracted until the load is zero.

[0097] The indenter movement mode is set to single step, the movement speed is 2 μm / s, and the stroke is set to 100 μm. After reaching the maximum displacement, the indenter immediately returns to the origin. The real-time displacement and contact load are recorded during the entire process of the indenter movement. The load-displacement curve is shown in Figure 5(a).

[0098] Formula (1-1) is used to calculate the true deflection of the cantilever beam, formula (1-2) is used to calculate the Young's modulus of the diamond film, and formula (1-3) is used to calculate the fracture strength of the diamond film. The statistical results of the Young's modulus and fracture strength of the five diamond films under tension on the growth side are shown in the figure. Figure 6 and Figure 7 shown.

[0099] Embodiment 3:

[0100] The Young's modulus and fracture strength of the diamond self-supporting film under tensile stress on the nucleation side are measured as described in Example 2, except that during the process of fixing the cantilever beam fixture, the growth side of the diamond film is exposed to the outside, that is, the nucleation side is subjected to tensile stress during the cantilever beam fracture process. The statistical results of the Young's modulus and fracture strength of the five diamond thick films under tensile stress on the nucleation side are as follows Figure 6and Figure 7 shown. Figure 6 The statistical results of Young's modulus of five diamond films are shown in Figure 2. The horizontal axis is marked as (sample name-loading side), g represents the tensile stress on the growth side, and n represents the tensile stress on the nucleation side. Figure 7 The statistical results of the fracture strength of five free-standing diamond films are shown in Figure 2. The horizontal axis is marked as (sample name-loading side), g represents the tensile stress on the growth side, and n represents the tensile stress on the nucleation side.

[0101] Embodiment 4:

[0102] The fracture toughness of single-layer nano- and multi-layer composite diamond films was measured using a single-edge notched cantilever beam as the specimen, as shown in Figure 3(b).

[0103] Using microwave plasma chemical vapor deposition technology, a single-layer nano- and eight-layer composite diamond thick film was prepared on the surface of single-crystal silicon. The surface and cross-sectional morphology are as follows: Figure 4 As shown, (mN) represents a single layer of nanodiamond film,

[0104] (8l) represents a micron / nano eight-layer composite diamond film.

[0105] In the composite diamond film, the alternating deposition of micron diamond film and nano diamond film is achieved by periodically regulating the reaction gas pressure, carbon source concentration and nitrogen flow rate.

[0106] After the diamond film deposition is completed, the silicon substrate is removed by chemical etching to obtain a self-supporting diamond film. Specifically, the chemical etching solution is a potassium hydroxide aqueous solution with a supersaturated concentration. During the corrosion process, a water bath is used to heat the container containing the corrosion solution to 80°C. The thickness of the silicon substrate used in this experiment is 0.72mm, and the preferred corrosion time is about 24h.

[0107] Laser cutting is used to divide the self-supporting diamond film into 7mm×7mm square samples. The preferred cutting power is 10W and the galvanometer movement speed is 20m / s. Quick-drying glue is used to fix the square sample to a special groove on the fixture. The growth side of the diamond film is exposed to the outside. The size of the groove is 7.5mm×5mm×1mm. Therefore, the fixed sample will have an area of ​​2mm×7mm at the bottom without support.

[0108] A single-sided incision micro-cantilever beam structure is prepared on an unsupported diamond film part by a laser cutting method. The preferred laser power is 10W, the galvanometer movement speed is 20m / s, the width of the micro-cantilever beam is 160μm, the length is 1000μm, the thickness is measured according to the cross-sectional morphology of the diamond film, and the number of reciprocating motions of the galvanometer is adjusted according to the film thickness. A single-sided incision is prefabricated at the root of the cantilever beam and prepared by a laser cutting method. The laser power is 10W, the galvanometer movement speed is 20m / s, the reciprocating cutting is performed 4 times, and the incision is 200μm away from the root of the cantilever beam.

[0109] After the micro-cantilever structure is prepared, the fixture is fixed on the three-coordinate displacement platform with bolts, and the platform position is adjusted to align the Bosch indenter with the free end of the cantilever. First, the z-axis microscope in the system is used to determine that the indenter is located at the center of the cantilever width, and then the x-axis microscope is used to determine the distance between the contact position of the indenter and the cantilever and the incision. The preferred distance is 700 μm.

[0110] To prevent excessive idle travel before the punch is loaded, the three-coordinate displacement platform is manually adjusted so that the punch moves along the x-direction and contacts the cantilever beam. Contact load is observed on the control program interface, and then the punch is slowly retracted until the load is zero.

[0111] The indenter movement mode is set to single step, the movement speed is 2μm / s, and the stroke is set to 100μm. After reaching the maximum displacement, the indenter immediately returns to the position origin. The real-time displacement and contact load are recorded during the entire process of the indenter movement.

[0112] The fracture cross section of the single-edge-notched cantilever beam was observed using a scanning electron microscope to accurately measure the depth of the prefabricated notch and the total thickness of the self-supporting membrane.

[0113] Formula (1-4) is used to calculate the fracture toughness of diamond self-supporting film. The statistical results of fracture toughness of single-layer nano- and multi-layer composite diamond thick films are as follows: Figure 8 shown.

[0114] Embodiment 5:

[0115] The fracture toughness of single-layer nano- and multi-layer composite diamond thick films is affected by the film thickness, as described in Example 4. The difference is that in the deposition process of the diamond thick film, the same deposition parameters as mN and 8l are used, but the deposition time is doubled. The two samples are named mN-2 and 8l-2, respectively. The fracture toughness statistical results are shown in Figure 8 shown.

[0116] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A method for testing the bending fracture mechanical properties of a diamond self-supporting film micro cantilever beam, characterized in that: The steps include: Sample acquisition steps: obtaining a diamond film microcantilever beam sample to be tested through diamond film deposition, chemical etching of silicon substrate, and laser cutting processes; Adjustment and alignment steps: stick the diamond film micro cantilever beam sample to be tested on the fixture, fix the fixture on the three-axis displacement platform, and adjust the three-axis displacement platform so that the indenter is aligned with the free end of the micro cantilever beam sample; Equipment installation steps: The indenter, contact load measuring instrument and piezoelectric ceramic actuator are connected in sequence, and the displacement of the piezoelectric ceramic actuator is controlled to drive the indenter to perform the fracture mechanics property test of the diamond film; Performance test steps: The displacement and contact load of the piezoelectric ceramic actuator are collected through software to obtain the displacement-load curve. According to the system rigidity calibration results, the true deflection of the diamond film microcantilever beam sample and the Young's modulus, fracture strength and fracture toughness of the diamond film are calculated; In the sample acquisition step, the micro cantilever beam obtained by laser cutting includes a micro cantilever beam without a cutout and a micro cantilever beam with a single cutout, wherein the micro cantilever beam without a cutout is used for measuring Young's modulus and fracture strength, and the micro cantilever beam with a single cutout is used for measuring fracture toughness; During the equipment installation steps: the calibration process of the system rigidity is to align the indenter with the supported diamond film at the bottom, drive the indenter to move, record the load-displacement curve, and obtain the yield of the test system under the specified load. The actual deflection of the cantilever beam is obtained by subtracting the system yield under the current load from the indenter displacement during the bending and fracture process of the cantilever beam.

2. The method for testing the bending fracture mechanical properties of a diamond self-supporting film micro cantilever beam according to claim 1, characterized in that: In the sample acquisition step, the specific preparation process of the diamond film microcantilever beam sample includes: Deposition step: roughening the surface of the single crystal silicon substrate with sandpaper and planting diamond powder, and depositing the diamond film by microwave plasma chemical vapor deposition or hot wire chemical vapor deposition; Corrosion step: using a supersaturated potassium hydroxide solution to corrode the single crystal silicon substrate, and using a water bath to heat it during the process; Sample preparation steps: A laser cutting machine is used to prepare the cantilever beam sample. First, the self-supporting diamond membrane is divided into sample pieces of set units. One side of the sample piece is pasted on the fixture using quick-drying glue, and the cantilever beam structure is cut.

3. The method for testing the bending fracture mechanical properties of a diamond self-supporting film micro cantilever beam according to claim 1, characterized in that: The single-sided incision cantilever beam was prefabricated by laser cutting method. The laser power was 10W, the galvanometer movement speed was 20m / s, the reciprocating cutting was 4 times, and the incision depth was measured by the microscopic morphology of the cantilever beam fracture incision.

4. The method for testing the bending fracture mechanical properties of a diamond self-supporting film micro cantilever beam according to claim 1, characterized in that: During the alignment step, the precise position of the indenter is determined by zooming in with two sets of optical microscopes, one on the x-axis and the other on the z-axis. The x-axis microscope is used to determine the effective length of the microcantilever, and the z-axis microscope is used to determine that the indenter is located at the center of the cantilever width.

5. The method for testing the bending fracture mechanical properties of a diamond self-supporting film micro cantilever beam according to claim 1, characterized in that: In the adjustment and alignment step, the position of the indenter is adjusted by the three-coordinate displacement platform. After the indenter is aligned with the center of the cantilever beam width, the displacement platform is slowly adjusted to move along the x-axis to make the indenter contact the cantilever beam. After observing the load information appearing on the software control interface, the indenter is retracted until the load is 0.

6. The method for testing the bending fracture mechanical properties of a diamond self-supporting film micro cantilever beam according to claim 1, characterized in that: The pressure head adopts a Bosch pressure head.

7. The method for testing the bending fracture mechanical properties of a diamond self-supporting film micro cantilever beam according to claim 1, characterized in that: During the device installation steps: The maximum stroke of the piezoelectric ceramic actuator is 100μm, the minimum step length is 7nm, and the closed-loop control method is adopted with an accuracy of 0.05% FS; The maximum range of the contact load measuring instrument is 1N, the sensitivity is 2.0±10%nN / mN, the working temperature is -20~50℃, and the limit overload is 200%FS; The displacement mode of the pressure head is uniform motion, and the movement speed is 2μm / s.

8. The method for testing the bending fracture mechanical properties of a diamond self-supporting film micro cantilever beam according to claim 1, characterized in that: In the performance test step, the software collects the displacement and contact load of the piezoelectric ceramic actuator. The start time of data recording is taken as the starting point when the actuator starts to move, and the relationship between displacement, load and time is established in the data table.

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