JP2019074468A - Sample analysis method - Google Patents

Abstract

To provide a sample analysis method which allows for temporally analyzing a surface of a sample with high resolution using an electron beam device while introducing hydrogen into the sample.SOLUTION: A sample analysis method utilizes an electron beam device 100 configured to irradiate a surface 11a of a sample 11 with an electron beam and detect either or both of electrons and X-rays released from the surface 11a, and comprises steps of irradiating the surface 11a with the electron beam, and causing glow discharge between an electrode 16 provided inside the electron beam device 100 and the surface 11a, using the sample 11 as a negative electrode, while exposing the surface 11a to a hydrogen-containing ambience inside the electron beam device 100.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sample analysis method.

  In the development of high strength steels, hydrogen embrittlement, in which strength and toughness are degraded by hydrogen, has become a major problem. However, the material structural change related to hydrogen embrittlement is not clear, and it is desirable to perform observation over time while introducing hydrogen into steel in order to elucidate the mechanism of hydrogen embrittlement.

  Non-Patent Document 1 proposes a method of observing the shape of the surface of a test piece with an atomic force microscope (AFM) while performing electrolytic charging in an electrolytic solution.

A. Barnoush et al., Direct observation of hydrogen-enhanced plasticity in super duples stainless steel by means of in situ electrochemical methods, Scripta Materialia, 62 (2010) 242

  By the way, as a result of recent researches by the present inventors on hydrogen embrittlement of metal materials, it is possible that hydrogen which has penetrated into the material has an influence on strain distribution, phase transformation, dislocation movement, etc. caused by stress load. However, it has gradually become clear that it is the cause of hydrogen embrittlement.

  Along with this, it has become necessary to analyze temporal changes in the above-mentioned physical phenomenon when stress is applied while hydrogen is introduced into the material in high resolution and in a wide area. And, when analyzing these physical phenomena occurring in materials, an electron beam apparatus represented by a scanning electron microscope (SEM) is indispensable.

  That is, it has been recognized that it is necessary to analyze the surface of the material with high resolution using an electron beam apparatus while introducing hydrogen into the material and applying stress as necessary.

  Although the AFM used in Non-Patent Document 1 can analyze the surface shape of a material with high accuracy, it can not analyze strain distribution, phase transformation, dislocation motion, and the like. Further, in Non-Patent Document 1, it is impossible to apply the technique of Non-Patent Document 1 as it is to an electron beam apparatus maintained at a high degree of vacuum because electrolytic charging is performed in an electrolytic solution. Furthermore, the chemical reaction with the electrolytic solution may deteriorate the material surface, which is not preferable. In addition, loading of stresses during electrolytic charging is also not described.

  An object of the present invention is to provide a sample analysis method capable of analyzing the surface of a sample with high resolution and over time using an electron beam apparatus while introducing hydrogen into the sample.

  The present invention was made in order to solve the above-mentioned subject, and makes the following sample analysis methods a summary.

(1) An analysis method of a sample using an electron beam apparatus which injects an electron beam onto a surface of a sample at a predetermined acceleration voltage and detects at least one selected from electrons and X-rays emitted from the surface ,
Injecting the electron beam onto the surface;
Inside the electron beam apparatus, with the surface exposed to a hydrogen-containing atmosphere, the sample is used as a cathode, and glow discharge is generated between an electrode provided inside the electron beam apparatus and the surface Providing a process
Sample analysis method.

(2) In the step of generating the glow discharge, the voltage of the electrode with respect to the sample is 100 V or more and less than the predetermined acceleration voltage.
The sample analysis method as described in said (1).

(3) The partial pressure of hydrogen in the hydrogen-containing atmosphere is 1 Pa or more
The sample analysis method as described in said (1) or (2).

(4) the sample is a metal material,
The sample analysis method in any one of said (1) to (3).

(5) the energy of the electron beam is 200 eV or more
The sample analysis method in any one of said (1) to (4).

(6) The irradiation current of the electron beam is 10 pA or more
The sample analysis method in any one of said (1) to (5).

(7) further comprising the step of applying a stress to the sample,
The sample analysis method in any one of said (1) to (6).

  According to the present invention, it is possible to analyze the surface of a sample with high resolution and over time using an electron beam apparatus while introducing hydrogen into the sample.

It is a figure which shows schematic structure of the electron beam apparatus used for the sample-analysis method which concerns on one Embodiment of this invention. It is the figure which showed typically an example of the shape of the sample according to the stress to load. It is a figure which shows schematic structure of the electron beam apparatus used for the sample-analysis method which concerns on other embodiment of this invention. It is a figure for demonstrating the shape of a notch test piece. It is a figure which shows schematic structure of the electron beam apparatus used by the Example. It is a figure which shows the relationship of the tensile load and crack length which were loaded on the sample.

  A sample analysis method according to an embodiment of the present invention will be described with reference to FIG.

  FIG. 1 is a view showing a schematic configuration of an electron beam apparatus 100 used in a sample analysis method according to an embodiment of the present invention. The electron beam apparatus 100 includes, for example, an SEM.

  First, the structure of an electron beam apparatus 100 used in a sample analysis method according to an embodiment of the present invention will be described. As shown in FIG. 1, the inside of the electron beam apparatus 100 is divided into a sample chamber 10, an intermediate chamber 20 and an electron gun chamber 30.

  A vacuum exhaust unit 40 is provided in each of the sample chamber 10, the intermediate chamber 20, and the electron gun chamber 30. For example, a vacuum pump such as a turbo molecular pump, a diffusion pump, an ion pump, a titanium sublimation pump, an oil rotary pump, or a dry pump can be used as the vacuum evacuation unit 40.

  When analyzing a sample, the sample 11 is placed in the sample chamber 10. The type of sample 11 is a sample having conductivity. The shape of the sample 11 is not particularly limited as long as it can be placed in the sample chamber 10, such as a plate, a particle, or a rod. Moreover, according to the kind of stress given to the sample 11, it can process into a preferable shape. In the present embodiment, a metal material is used as the sample 11, and various stresses are applied to analyze the temporal change of the surface of the metal material when hydrogen embrittlement occurs.

  The sample chamber 10 is provided with a hydrogen supply unit 12 and a vacuum gauge 13 so that hydrogen gas can be supplied into the sample chamber 1 to a desired pressure. As the hydrogen supply unit 12, for example, a gas valve whose flow rate can be adjusted may be used. Further, as the vacuum gauge 13, a Pirani vacuum gauge, a diaphragm vacuum gauge or the like is used.

  Furthermore, the sample chamber 10 is provided with a detector 14. The detector 14 detects one or more selected from electrons and X-rays emitted from the surface 11 a when an electron beam is incident on the surface 11 a of the sample 11 at a predetermined acceleration voltage. Electrons include secondary electrons, reflected electrons, Auger electrons, and the like. Further, the detector 14 includes a secondary electron detector (SE detector), a backscattered electron detector (BSE detector), an electron backscattering diffraction detector (EBSD detector), a semiconductor detector (EDS detector), etc. Is included.

  Further, in the configuration shown in FIG. 1, the sample chamber 10 is further provided with a stress applying portion 15 for applying a stress to the sample 11. The type of stress applied to the sample 11 is not particularly limited, and may be any of tensile stress, compressive stress, bending stress, and torsional stress. FIG. 2: is the figure which showed typically an example of the shape of the sample according to the stress to load. For example, the shape may be a tensile test piece (FIG. 2a), a bending test piece (FIG. 2b), a cantilever test piece (FIG. 2c), a torsion test piece (FIG. 2d) or the like. The method of processing the sample 11 is also not particularly limited, and may be appropriately produced by machining, electrical discharge processing, focused ion beam processing, or the like. Furthermore, the sample 11 may be provided with a notch or a precrack in order to limit the area in which the crack occurs.

  Furthermore, an electrode 16 is provided inside the sample chamber 10. Then, glow discharge is generated between the electrode 16 and the surface 11 a of the sample 11 by applying a voltage so that the sample 11 becomes a cathode and the electrode 16 becomes an anode.

  The intermediate chamber 20 is in communication with the sample chamber 10 and the electron gun chamber 30 through the small holes 20a and 20b, respectively. By providing the intermediate chamber 20 between the sample chamber 10 and the electron gun chamber 30 and configuring a differential evacuation system, even if hydrogen gas is supplied into the sample chamber 10, the inside of the electron gun chamber 30 can be highly evacuated. It becomes possible to maintain. Although one intermediate chamber 20 is provided in the example illustrated in FIG. 1, a plurality of intermediate chambers 20 may be provided.

  In the electron gun chamber 30, an electron gun 31 for irradiating an electron beam is provided. The type of the electron gun 31 is not particularly limited, and, for example, a field emission type or filament type electron gun can be used. In the electron gun chamber 30, an electronic lens and a scanning coil (not shown) are provided, and the electron beam is scanned on the surface 11a of the sample 11 by controlling them.

  FIG. 3 is a view showing a schematic configuration of an electron beam apparatus 100 used in a sample analysis method according to another embodiment of the present invention. In the configuration shown in FIG. 3, the sample chamber 10 itself plays a role as the electrode 16 and generates glow discharge between the sample chamber 10 and the surface 11 a of the sample 11.

Next, a sample analysis method according to an embodiment of the present invention will be described by taking the configuration shown in FIG. 1 as an example. First, as shown in FIG. 1, in the sample chamber 10, the sample 11 is placed in a state in which stress can be applied by the stress applying unit 15. Then, the insides of the sample chamber 10, the intermediate chamber 20 and the electron gun chamber 30 are maintained in a high vacuum state. The degree of vacuum at this time is preferably 10 ⁻⁹ to 10 ⁻³ Pa.

  Thereafter, hydrogen is supplied into the sample chamber 10, and in a state where the surface 11a of the sample 11 is exposed to a hydrogen-containing atmosphere, the sample 11 is used as a cathode and glow discharge is generated between the electrode 16 and the surface 11a. As a result, plasma is generated and hydrogen in the atmosphere is ionized into hydrogen ions. Then, hydrogen ions in the plasma are electrically attracted to the surface 11a. As a result, even when the hydrogen partial pressure in the atmosphere is low, hydrogen is efficiently introduced into the sample from a wide range of the surface 11a.

  Next, an electron beam is incident on the surface 11a. Then, the surface shape, crystal orientation, element distribution, and the like of the sample 11 are analyzed by detecting at least one selected from electrons and X-rays emitted from the surface 11a.

  Subsequently, stress is applied to the sample 11. The method of applying stress is not particularly limited as described above. With hydrogen introduced into the sample from the surface 11a and with the electron beam incident on the surface 11a, stress is further applied, and by analyzing the sample surface, the presence or absence of a crack, the crack initiation point and the propagation path It becomes possible to evaluate etc. Furthermore, it is also possible to obtain a fracture toughness value or the like from the value of the applied stress.

  In the above example, although the electron beam is incident after the glow discharge is generated, the glow discharge may be generated in the state where the electron beam is incident. In addition, the glow discharge may be stopped during the surface analysis, or the surface analysis and the glow discharge may be alternately performed. Although reflected electrons and the like can be detected during glow discharge, secondary electrons with low energy can not be detected. Therefore, when it is desired to observe the secondary electron image, it is necessary to temporarily stop the glow discharge at the time of detection. Since stopping the glow discharge releases the introduced hydrogen, it is preferable to keep the sample at a low temperature in order to minimize the release of hydrogen.

  Furthermore, in the above example, although hydrogen is introduced into the sample and then stress is applied, the stress may be applied and then hydrogen may be introduced, or they may be performed simultaneously. Also, the stress application process may be omitted. The stress may be either fluctuating stress, cyclic stress or constant stress. For example, hydrogen may be introduced after applying a certain elastic stress, or stress may be continuously increased while introducing hydrogen, or hydrogen may be introduced while applying repeated elastic stress. It is also good.

  In order to generate glow discharge between the surface 11 a of the sample 11 and the electrode 16, the voltage of the electrode 16 with respect to the sample 11 is preferably 100 V or more. In order to efficiently introduce hydrogen into the sample, the above voltage is preferably 200 V or more.

  On the other hand, the electron beam decelerates under the influence of the negative voltage applied to the sample 11, and therefore, when the voltage is too high, the electron beam can not reach the surface 11a. Therefore, the voltage of the electrode 16 with respect to the sample 11 needs to be less than the acceleration voltage of the electron beam.

  Similarly, in order to introduce a sufficient amount of hydrogen into the sample, the hydrogen partial pressure in the hydrogen-containing atmosphere is preferably 1 Pa or more. The hydrogen partial pressure is more preferably 10 Pa or more, further preferably 50 Pa or more. On the other hand, if the hydrogen partial pressure is excessive, the electron beam may be scattered by hydrogen molecules, which may make it difficult to analyze the sample. Therefore, the hydrogen partial pressure is preferably 3 kPa or less, more preferably 1.5 kPa or less.

  In addition, if the energy of the electron beam is too low, not only the probability of scattering of the electron beam by hydrogen molecules will be high, but also the probe diameter of the electron beam may be large, and high resolution analysis results may not be obtained. Therefore, the energy of the electron beam is preferably 200 eV or more, and more preferably 1 keV or more.

  On the other hand, if the energy of the electron beam is too high, electrons emitted from the surface 11a of the sample 11 may be reduced, so the energy is preferably 50 keV or less, more preferably 30 keV or less.

  That is, the acceleration voltage of the electron beam is preferably 200 V or more, and more preferably 1 kV or more. The acceleration voltage is preferably 50 kV or less, more preferably 30 kV or less.

  Furthermore, if the irradiation current of the electron beam is low, the intensity of electrons or X-rays emitted from the surface 11 a of the sample 11 may be insufficient for detection. Therefore, the irradiation current of the electron beam is preferably 10 pA or more, and more preferably 100 pA or more.

  On the other hand, if the irradiation current of the electron beam is too high, the diameter of the probe of the electron beam becomes large, which may make it impossible to obtain high-resolution analysis results. Therefore, the irradiation current of the electron beam is preferably 1.5 μA or less, more preferably 10 nA or less.

  Further, in order to reduce the scattering by the hydrogen molecules of the electron beam incident on the surface 11a of the sample 11 and the electrons emitted from the surface 11a, it is desired to shorten the flight distance in their hydrogen-containing atmosphere . Therefore, it is preferable that the total flight distance from the small holes 20a of the intermediate chamber 20 through the surface 11a of the sample 11 to reach the detector 14 be 50 mm or less. The total flight distance can be brought into the above range by adjusting the arrangement of the sample 11 and the detector 14.

  EXAMPLES Hereinafter, the present invention will be more specifically described by way of examples, but the present invention is not limited to these examples.

Carbon on which gold fine particles of 20 nm diameter were deposited was used as a sample. The size of the gold-deposited surface of the sample is 4 mm × 4 mm. After placing this sample in the sample chamber in the SEM, the sample chamber is evacuated to 2 × 10 ⁻⁴ Pa, and then, hydrogen gas at a purity of 99.99% is gradually stepped up to a pressure of 3 kPa. It was introduced to the room. In the present example, the test was carried out in an electron beam apparatus having the configuration shown in FIG.

  A voltage of 250 V was applied between the sample chamber made of stainless steel and the sample so that the sample became a cathode. Then, at each pressure, it was measured whether gold particles could be imaged by the BSE detector. In addition, the flight distance of the electron from the small hole used as the entrance to a sample chamber of an electron beam to a BSE detector was 50 mm. In addition, a field emission type electron gun was used.

  Tables 1 to 3 show the measurement results when the pressure of hydrogen gas is 1 Pa, 500 Pa and 3 kPa. When electrons were scattered by hydrogen molecules and enough electrons could not reach the detector, the image was noisy. The data from which an image can be acquired and gold particles can be identified is indicated by "「 ". The data that could be acquired images but with a lot of noise is shown as “Δ”, and the data that could be acquired images but the spatial resolution was low and the gold particles could not be identified as “○”.

  As apparent from the results of Tables 1 to 3, even if the pressure of hydrogen gas was 3 kPa, an image could be obtained and gold particles of 20 nm diameter could be identified. Also, there was no influence of hydrogen gas on the scanning coil, and an image of a wide area of 2 mm × 2 mm could be obtained. As described above, it was confirmed that even when hydrogen gas is introduced into the sample chamber to 3 kPa and glow discharge is generated, the sample surface can be imaged with a high spatial resolution of 20 nm and a wide area of 2 mm × 2 mm.

  The SCM 435 steel having the chemical composition shown in Table 4 having a martensitic structure was used as a test material. The tensile strength of the test material is 1488 MPa. From the test material, a sample having the shape of a notched tensile test specimen as shown in FIG. 4 was taken, and the notched portion was mirror-polished with colloidal silica.

After placing the sample in a stress load device (tensile tester) in the sample chamber, the sample chamber is evacuated to 2 × 10 ⁻⁴ Pa, followed by hydrogen gas with a purity of 99.99%, or a purity of 99. 99% helium gas was introduced to a predetermined pressure of 500 Pa or less. In the present example, the test was carried out in an electron beam apparatus having the configuration shown in FIG.

  Then, a voltage of 250 V was applied between the sample chamber made of stainless steel and the sample so that the sample became a cathode, tensile stress was applied to the sample by stress control, and a hydrogen embrittlement crack was generated. . While stress was applied, the sample was scanned with an electron beam and a BSE detector imaged the notched portion of the sample every 30 seconds. The energy of the electron beam was 10 keV, and the irradiation current was 10 nA. The position of the detector and the type of the electron gun are the same as in the first embodiment.

  FIG. 6 shows the relationship between the tensile load applied to the sample and the crack length. The crack length is defined as the distance from the notch bottom to the crack tip. When cracks are found in both of the two notches in the sample, the total value of the crack lengths of the two cracks is shown. In hydrogen gas, cracks occurred at 1 Pa or more, and the crack length increased as the pressure of hydrogen gas increased. Also, the crack mainly propagated along the old γ grain boundary. When the pressure was less than 1 Pa, no crack occurred and the notch bottom was blunted. On the other hand, with helium gas, cracks did not occur at a pressure of 500 Pa or less.

  When a mixed gas of helium and hydrogen was introduced, a crack occurred if the partial pressure of hydrogen was 1 Pa or more. Also, no crack was generated simply by introducing hydrogen gas into the sample chamber without scanning the electron beam.

  As described above, dilute hydrogen gas is supplied into the sample chamber, a voltage is applied between the sample and the electrode (sample chamber) to generate glow discharge, stress is applied to the sample, and the sample surface is exposed to the electron beam. High-resolution and wide-area analysis of hydrogen embrittlement cracks that occur and propagate over time can be analyzed over time by introducing hydrogen into the sample by scanning with It was confirmed that it could be evaluated.

  According to the present invention, it is possible to analyze the surface of a sample with high resolution and over time using an electron beam apparatus while introducing hydrogen into the sample.

10. Sample chamber 11. Sample 11a. Surface 12. Hydrogen supply unit 13. Vacuum gauge 14. Detector 15. Stress loading section 16. Electrode 20. Intermediate room 20a, 20b. Small holes 30. Electron gun room 31. Electron gun 40. Vacuum exhaust unit 100. Electron beam equipment

Claims (7)

A method of analyzing a sample using an electron beam apparatus, comprising: irradiating a surface of a sample with an electron beam at a predetermined acceleration voltage; and detecting at least one selected from electrons and X-rays emitted from the surface,
Injecting the electron beam onto the surface;
Inside the electron beam apparatus, with the surface exposed to a hydrogen-containing atmosphere, the sample is used as a cathode, and glow discharge is generated between an electrode provided inside the electron beam apparatus and the surface Providing a process
Sample analysis method. In the step of generating the glow discharge, the voltage of the electrode with respect to the sample is set to 100 V or more and less than the predetermined acceleration voltage.
The sample analysis method according to claim 1. The partial pressure of hydrogen in the hydrogen-containing atmosphere is 1 Pa or more.
The sample analysis method according to claim 1 or 2. The sample is a metal material,
The sample analysis method according to any one of claims 1 to 3. The energy of the electron beam is 200 eV or more
The sample analysis method according to any one of claims 1 to 4. The irradiation current of the electron beam is 10 pA or more
The sample analysis method according to any one of claims 1 to 5. Further comprising applying a stress to the sample,
The sample analysis method according to any one of claims 1 to 6.

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