Strain measuring device and method for measuring mechanical strain

Abstract

The strain measurement device 100 for measuring mechanical strains in a sample 1 comprises a sample holder device 10 arranged to accommodate the sample 1 to be investigated, an indenter device 20 comprising an indenter tip 21 and an actuator stage 22 supporting the indenter tip 21, the actuator stage 22 being adapted to apply a load axis z via the indenter tip 21 in an indentation zone 2 of the sample 1 accommodated by the sample holder device 10 when the sample holder device 10 is in a load application position. 1 an indenter device 20 arranged to apply a localized mechanical load along an imaging axis z 2 a confocal Raman microscope device 30 arranged to collect at least one Raman spectrum in an indentation zone 2 of the sample 1, and a calculation device 40 arranged to calculate at least one strain parameter based on the at least one Raman spectrum, the sample holder device 10, the indenter device 20 and the confocal Raman microscope device 30 being arranged such that the confocal Raman microscope device 30 is able to collect the at least one Raman spectrum while the sample holder device 10 is in a load application position, the indenter device 20 and the confocal Raman microscope device 30 being aligned with a load axis z of the actuator stage 22. 1 and the imaging axis z of the confocal Raman microscope device 30. 2 Furthermore, a strain measurement method for measuring the mechanical strain in the sample 1 will be described.

Description

Technical Field

[0001] The present invention relates to a strain measuring device configured to measure mechanical strain in a sample, particularly a laser-transparent sample. Further, the present invention relates to a strain measuring method for measuring mechanical strain in a sample. The strain measurement is based on a combination of confocal Raman spectroscopy and indentation. The use of the present invention is available, for example, in the fields of materials science and materials research.

Background Art

[0002] In this specification, references are made to the following prior art that illustrates the technical background and related art of the invention. [1] A.M. Korsunsky, Chapter 8 - Residual Stress "Measurement", A Teaching Essay on Residual Stresses and Eigenstrains (edited by Korsunsky AM), Butterworth-Heinemann (2017) [2] W. Ecker et al., "Nanoscale evolution of stress concentrations and crack morphology in multilayered CrN coating during indentation, Experiment and simulation (Nanoscale changes in stress concentration and crack morphology in multilayer CrN coatings during indentation: experiments and simulations)", Materials & Design, Vol. 188, p. 108478 (2020) [3]A.J.G. Lunt, "A review of micro-scale focused ion beam milling and digital image correlation analysis for residual stress evaluation and error estimation", Surface and Coatings Technology, Vol. 283, pp. 373 - 388 (2015) [4]C. Gammer et al., "Measurement of local strain", MRS Bulletin, Vol. 44(6), pp. 459 - 464 (2019) [5]J. Gim et al., "Nanoscale deformation mechanics reveal resilience in nacre of Pinna nobilis shell", Nat Commun, Vol. 10, p. 4822 (2019) [6]A. Zeilinger et al., "In-situ Observation of Cross-Sectional Microstructural Changes and Stress Distributions in Fracturing TiN Thin Film during Nanoindentation", Scientific Reports, Vol. 6, p. 22670 (2016) [7]P. Manimunda et al., "Chem. Commun.", Vol. 55, pp. 9200 - 9203 (2019) [8]H.C. Loh et al., "Commun Mater", Vol. 1, p. 77 (2020) [9]Y.B. Gerbig et al., "In-situ Raman spectroscopic measurements of the deformation region in indented glasses", JOURNAL OF NON-CRYSTALLINE SOLIDS, Vol. 530, p. 119828 (2019)

[10] WO 96 / 10737 A1

[11] RU 2 680 853 C1

[12] WO 97 / 03346 A1

[13] JP 2017 146294 A

[14] KR 101 783 541 B1

[0003] Localized stress often affects the performance or failure of solid materials. Therefore, studying the development of localized stress is an essential element for understanding the mechanical response of materials. Localized stress is determined by the applied stress, residual stress, and their interaction. The applied stress can be measured and controlled, but residual stress is essentially difficult to detect, control, or suppress. Over the past few decades, several techniques have been developed to evaluate internal strain or stress.

[0004] Microscale focused ion beam milling and digital image correlation analysis are destructive techniques that provide direct measurement of residual strain on the sample surface. However, this technique is limited to the evaluation of residual strain and is not applicable to the induced contact strain in the presence of an external contact load. In addition, mechanical milling ultimately destroys the region of interest. Furthermore, the digital image correlation method cannot provide volume information and is limited to the surface area.

[0005] As non-destructive techniques, transmission electron diffraction techniques and microscopy techniques can determine localized lattice strains with high spatial resolution up to several nanometers (see, for example, [4, 5]). However, in the case of transmission electron microscopy (TEM), a relatively thin specimen is required, which is a drawback because the specimen has a given thickness and the resolution must be evaluated with respect to volume so that the strain value is single-valued. The strain relaxation effect may be induced during specimen preparation, and free edge effects may be introduced during in-situ mechanical loading. In addition, the field of view of the TEM method is limited to several microns, and 3D property evaluation is not supported by this technique.

[0006] Microfocus X-ray diffraction is another known technique for real-time measurement of strain / stress with micron-sized probing resolution [1]. However, this technique requires complex measurement techniques such as advanced synchrotron beamlines, and like electron diffraction techniques, X-ray diffraction has its own drawbacks regarding the preparation of specimens with limited sizes, and the free surface of the specimen may induce or relax the residual stress / strain in the specimen [1, 2]. In this case too, the applied mechanical load may cause excessive deformation at the free end of the specimen. As a result, the data collected from the irradiated volume contains information from the deformation at the specimen end, inevitably leading to measurement errors. Finally, in the transmission concept of X-ray diffraction measurement, information is obtained from the irradiated volume rather than point-by-point data. Therefore, with this technique, depth-direction analysis along the irradiation axis cannot be performed, and only a single strain value can be obtained from the volume.

[0007] Raman spectroscopy can examine the molecular energy characteristics of Raman-active materials. In addition to its ability to evaluate the structural material properties, this technique is also used for the measurement of mechanical strain / stress. Such strain affects the frequency of molecular vibrations and, as a result, influences the Raman spectrum through changes in peak position and width. Therefore, information regarding the magnitude of mechanical strain / stress can be obtained by measuring the position and / or width of the vibrational bands of a strained sample and comparing it with the unstrained state (reference state) of the sample. In contrast to diffraction techniques, confocal Raman spectroscopy can perform depth profiling within the penetration depth of the material. This penetration depth is a function of the laser wavelength and the absorption coefficient of the sample and can range from several millimeters in the case of a laser-transparent material. Thus, depending on the sample thickness, generation and propagation of strain / stress fields are possible even in the absence of free / cut ends.

[0008] Known protocols for investigating loaded / indented samples include post-indentation Raman spectroscopy and off-axis Raman spectroscopy under an applied load. In post-indentation Raman spectroscopy, first, the sample is indented and the residual impression is scanned after indentation. As an example, an integrated indentation setup has been proposed in [7], where a translation stage moves the sample from the indentation station to another measurement station (optical position) connected to a Raman spectrometer via an optical fiber cable. However, with this method, real-time measurements cannot be performed. Also, since the elastic response (induced elastic strain) recovers as soon as the load on the sample is removed, the elastic response cannot be studied.

[0009] On the other hand, in off-axis Raman spectroscopy under a loaded state (see, for example, [9] to

[14] ), Raman spectroscopy is used while a load is applied to the sample. However, when the incident laser is made to coincide off-axis in the loaded state, in-line scanning cannot be performed below the load application spot (that is, measurement in the sample volume is impossible), which means that the calculation of the strain tensor becomes more complicated. Furthermore, in an available in-situ Raman indentation setup including off-axis characterization of the sample, a part of the induced strain field is in the shadow of the indenter and thus not accessible to the Raman microscope. In addition, since the intensity of the vibration band varies depending on the probing direction, the tilt angle of the setup brings further complexity to data analysis. Off-axis Raman spectroscopy has been performed on tensile / compressed samples (not indented samples) [8]. However, since strain also disperses when the load application disperses, this technique cannot study the generation of strain in the loaded area (structural materials such as bioceramics have no correlation with the microstructural tissues of samples that may play an important role in the generation of concentrated stress / strain).

[0010] In summary, the conventional evaluation of localized stress in the loaded state has been very difficult because it is necessary to combine the following two important aspects. The first is the ability to "time-resolve" the interaction between the strain / stress field generated in the loaded state and the possible residual strain / stress. Therefore, destructive techniques cannot meet this requirement. For this reason, only non-destructive strain / stress measurement techniques, for example, those based on diffraction measurement, remain as practical options. The second is the ability to probe "localized" strain / strain with sub-micron resolution. Therefore, synchrotron X-ray microdiffraction, transmission electron diffraction and microscopy, and confocal Raman microscopy [1, 2] remain as the only applicable techniques for time-resolved measurement of localized strain / stress under contact load. However, due to physical constraints, none of these techniques have been able to perform three-dimensional mapping of the induced contact strain / stress field in known configurations so far.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Non-Patent Documents

[0012]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Non-Patent Document 6

Non-Patent Document 7

Non-Patent Document 8

Non-Patent Document 9

Summary of the Invention

Problems to be Solved by the Invention

[0013] An object of the present invention is to provide an improved strain measuring device and / or strain measuring method for measuring mechanical strain in a sample, which can avoid the limitations and drawbacks of conventional techniques. In particular, the strain measuring device and / or method can perform real-time three-dimensional mapping and avoid limitations caused by time offset and / or orientation offset.

Means for Solving the Problems

[0014] This object is solved by a strain measuring device and / or strain measuring method comprising the features of the independent claims. Advantageous embodiments and uses of the present invention are defined in the dependent claims.

[0015] According to a first general aspect of the present invention, the above object is solved by a strain measuring device configured to measure mechanical strain in a sample, the strain measuring device including a sample holder device arranged to accommodate the sample to be investigated, and a indenter device including an indenter tip and an actuator stage supporting the indenter tip, the actuator stage being arranged to apply a localized mechanical load along a load axis through the indenter tip in a penetration zone of the sample accommodated by the sample holder device when the sample holder device is in a load application position, the indenter device, a confocal Raman microscope device having an imaging axis and arranged to collect at least one Raman spectrum in the penetration zone of the sample, and a calculation device arranged to calculate at least one strain parameter based on the at least one Raman spectrum.

[0016] According to the device of the present invention, the sample holder device, the indenter device, and the confocal Raman microscope device are arranged such that the confocal Raman microscope device can collect at least one Raman spectrum while the sample holder device is in the load application position. Further, according to the present invention, the indenter device and the confocal Raman microscope device are arranged such that the load axis (penetration direction) of the actuator stage coincides with the imaging axis of the confocal Raman microscope device.

[0017] According to a second general aspect of the present invention, the above object is solved by a strain measurement method for measuring mechanical strain in a sample, the method comprising the steps of placing the sample to be investigated on a sample holder device; applying a localized mechanical load to the sample using a indenter device comprising an indenter tip and an actuator stage supporting the indenter tip, the mechanical load being applied along the load axis through the indenter tip using the actuator stage in the indentation zone of the sample when the sample holder device is in the load application position; collecting at least one Raman spectrum using a confocal Raman microscope device having an imaging axis in the indentation zone of the sample; and calculating at least one strain parameter based on the at least one Raman spectrum.

[0018] According to the method of the present invention, at least one Raman spectrum is collected while the sample holder device is in the load application position. Further, according to the present invention, the indenter device and the confocal Raman microscope device are arranged such that the load axis of the actuator stage coincides with the imaging axis of the confocal Raman microscope device. Preferably, the strain measurement method according to the second general aspect of the present invention or an embodiment thereof is carried out using the strain measurement device according to the first general aspect of the present invention or an embodiment thereof.

[0019] The term "strain measurement" refers to determining strain, which is a measure of the deformation of a material under the influence of a force, particularly an external force. The deformation results in a change in the molecular vibration frequency of the material. In elastic deformation, the induced strain and stress are correlated. Thus, the strain measurement device and method of the present invention can also be regarded as a stress measurement device and method for measuring mechanical stress in a sample, in which case at least one stress parameter is obtained by correlation with changes in the peak width and / or position of the collected Raman spectrum.

[0020] Providing a sample holder device at the load application position includes arranging the sample holder device and the indenter device such that the indenter tip can contact and press against the sample on the sample holder device by the indentation of the indenter tip. Preferably, the sample holder device and the indenter device have fixed positions relative to each other such that the sample holder device is at the load application position throughout the strain measurement. The sample holder device preferably comprises a support platform with a surface on which the sample is placed. The support platform has sufficient mechanical stability to withstand any forces generated by the application of a localized mechanical load to the sample by the indenter tip. The support platform is preferably configured to allow probe light for collecting at least one Raman spectrum to pass through holes (windows) in the platform to directly expose a self - supporting (thick) transmissive sample or by using a transmissive backplate to support a thin sample (< 1 mm). Particularly preferably, the sample holder, in particular its support platform, has concentric windows mounted upside down under a confocal Raman microscope device.

[0021] The actuator stage of the indenter device is preferably fixedly arranged relative to the sample holder device and is configured to shift the indenter tip along a linear shift axis perpendicular to the surface of the support platform, in particular relative to the sample holder device and preferably relative to the sample accommodated by the sample holder device. Particularly preferably, the actuator stage comprises a piezoelectric actuator and a transducer, which has advantages with respect to the amount and time control of the applied load. Advantageously, the actuator stage may be configured to insert the indenter tip with a resolution step size of at least 5 nm. The indenter tip is made of a non - deformable material, such as a hard ceramic like diamond.

[0022] By shifting the indenter tip towards the sample holder device, particularly its support platform, the indenter tip contacts and presses against the sample, and as a result, a mechanical load is applied to the sample. By shifting in the opposite direction, the load can be reduced to zero (release of the sample). Due to the tip shape of the indenter tip, the direct application of the load is localized in the point-shaped contact section between the indenter tip and the sample. The contact section provides an indentation zone, and the load axis (the axis applying force to the sample) is the shift axis of the indenter tip.

[0023] A confocal Raman microscope device generally includes a light source device such as a laser light source for generating excitation light, an imaging optical system for directing the excitation light towards the sample, focusing the excitation light at a selectable sample depth, and collecting Raman scattered light from the sample, and a detector device for spectral decomposition for detecting the Raman scattered light, for example, a spectrometer. The imaging optical system may be configured to relay the excitation light in free space and / or an optical waveguide.

[0024] The imaging axis (exploration direction) is provided according to the direction in which the sample is irradiated by the imaging optical system. The imaging axis coincides with the load axis, that is, preferably both axes are the same or parallel with a distance at the location where the load is applied, and as a result, the influence of the distance on the obtained measurement results is negligible. The coinciding axis can be provided by adjusting at least one of the imaging optical system and the actuator stage. Preferably, the imaging axis is perpendicular to the surface of the support platform, particularly perpendicular to the surface of the sample disposed on the support platform.

[0025] The calculation device for calculating at least one strain parameter includes a computer circuit and is optionally included in the control device of the strain measuring device.

[0026] The arrangement of the present invention of the sample holder device, the indenter device, and the confocal Raman microscope device includes setting the sample holder device and / or the indenter device such that the sample holder device is in the load application position, i.e., such that the advancing indenter tip can contact the sample. At the same time, the arrangement of the present invention of the sample holder device, the indenter device, and the confocal Raman microscope device includes setting the sample holder device and / or the confocal Raman microscope device such that the imaging optical system directs the excitation light towards the sample on the support platform, in particular towards the indentation zone of the sample, and can collect Raman scattered light from the sample, in particular from the indentation zone of the sample. Advantageously, at least one Raman spectrum can be collected when the sample holder device is in the load application position, in particular when the sample placed on the sample holder device can be subjected to a localized mechanical load, for example a static load or a dynamically varying load.

[0027] In contrast to the prior art (e.g., [7]), the technique of the present invention aligns the indentation direction (load axis) with the Raman microscope (imaging axis on the same straight line), co-localizes the load application spot and the contact zone, and as a result, can determine the amount (single value) of the induced contact strain / stress under elastic-inelastic deformation, and optionally a 1D, 2D, or 3D distribution. The change in the molecular vibration band in the indentation zone of the sample is measured by Raman spectroscopy with improved accuracy. In particular, according to the present invention, in a Raman active material, preferably in a laser-transparent and / or sufficiently thin material, the induced contact strain / stress field with sub-micron spatial resolution can be loaded and measured in real time. Advantageously, the arrangement of the present invention of the indenter device and the confocal Raman microscope device in which the load axis and the imaging axis coincide eliminates the limitations of off-axis techniques (e.g., [8]). Furthermore, due to the arrangement of the present invention of the confocal Raman microscope device, at least one Raman spectrum can be collected during and / or after the application of the load without moving the sample, and as a result, strain measurements are accurately performed in the indentation zone. In particular, the recovery of the sample can be measured during the decrease of the load.

[0028] According to a preferred embodiment of the present invention, the sample holder device, the indenter device, and the confocal Raman microscope device are arranged such that the confocal Raman microscope device can collect at least one Raman spectrum simultaneously with the application of a localized mechanical load. Regarding this method, at least one Raman spectrum is preferably collected simultaneously with the step of applying a localized mechanical load, that is, during the application of the load. Advantageously, at least one strain parameter is estimated without being affected by the relaxation process after the load application. Alternatively, or in addition, at least one Raman spectrum may be collected before and / or after applying the localized mechanical load.

[0029] According to a particularly preferred embodiment of the present invention, the indenter device, particularly at least its indenter tip, and the confocal Raman microscope device, particularly at least a part of its imaging optical system, are arranged such that a localized mechanical load can be applied at a loading spot on the first side of the sample, and at least one Raman spectrum can be collected in the indentation zone, particularly at a loading spot from the second side opposite the sample. They are arranged on the opposite sides of the sample holder device, particularly on the opposite sides of the support platform of the sample holder device. Regarding this method, the localized mechanical load is preferably applied at a loading spot on the first side of the sample, and at least one Raman spectrum is collected in the indentation zone, particularly at a loading spot from the second side opposite the sample. Advantageously, sufficient space is obtained by arranging the indenter and the confocal Raman microscope device (or its components) opposite each other.

[0030] Applying a load and collecting Raman scattered light from the opposite side preferably includes providing a perpendicular orientation of the load axis and the imaging axis, applying the load from above along the direction of gravity, and collecting at least one Raman spectrum from below the support platform. Alternatively, applying the load from below parallel to the direction of gravity and collecting at least one Raman spectrum from above the support platform may be provided.

[0031] According to a further preferred embodiment of the present invention, the sample holder device is provided with a translation stage arranged to adjust the x-y position of the sample holder device in a plane perpendicular to the imaging axis of the confocal Raman microscope device. For the present method, the x-y position of the sample holder device is preferably adjusted in a plane perpendicular to the imaging axis. Advantageously, the translation stage facilitates the adjustment of the sample with respect to the load axis and the imaging axis, and thus two-dimensional (in a plane parallel to the surface of the support platform) or three-dimensional scanning measurements can be performed by operating the translation stage.

[0032] Another particular advantage of the present invention results when the confocal Raman microscope device is configured to collect multiple Raman spectra in a time-resolved manner, for example, when the relaxation properties of the sample can be investigated. Alternatively, or in addition, mapping of the sample within a range including the indentation zone may be provided. Advantageously, this mapping function provides additional reference information regarding the sample in regions with little or even no strain. To map the sample, an optical scanner device may be provided that is arranged to continuously focus the excitation light at different locations inside and / or outside the indentation zone.

[0033] According to a further advantageous embodiment of the present invention, the indenter device comprises a load cell connected to the actuator stage and arranged to measure the mechanical load applied to the sample. Regarding the method, the mechanical load applied to the sample can be measured using a load cell connected to the actuator stage. Advantageously, the load cell can be used to determine the correlation between at least one Raman spectrum and / or at least one strain parameter collected and the amount of load applied to the sample. Furthermore, the load cell can be used for load control and / or the load can be applied according to a predetermined time function, and thus at least one strain parameter can be calculated according to a given test protocol.

[0034] Advantageously, various features of the indenter tip are available to improve strain measurement. Preferably, the indenter tip has a distal contact section that is exposed for contact with the sample and has a dimension of less than 1 μm. Alternatively, larger dimensions, for example in the range of 1 μm to 1 mm, or up to 3 mm, or even up to 5 mm are possible. The small dimension of the contact section can improve the application of high external pressure and position-resolved measurements in an advantageous manner. Alternatively, or in addition, the indenter tip may be replaceable. Thus, it may be easier to adapt the measurement setup to a particular sample. Alternatively, or in addition, the indenter tip may be a diamond tip. Since diamond has high hardness, measurements of almost all materials of interest are possible. Furthermore, the indenter tip material may include, for example, zirconia, sapphire, ruby, or tungsten carbide. Alternatively, or in addition, the indenter tip may be a conical spherical tip. The conical spherical shape has advantages for homogeneous load application and the generation of strain in the sample. Alternatively, the indenter tip may have a tip shape with a cube corner or Berkovich shape to further localize stress concentration or partially deform the sample in a non-elastic manner. Furthermore, the tip shape may include, for example, a Vickers shape or a flat punch shape.

[0035] The tip can be changed to attach one of different tip shapes and / or materials. The tip dimensions and contact radius can be varied as well. In practice, the tip is selected according to measurement conditions, such as sample size, sample hardness, or sample structure. For example, the conical spherical tip may have a radius in the range of 300 nm to several millimeters, while the cube corner may have a tip dimension of about 70 - 100 nm, and the Berkovich tip may have a tip dimension of about 120 nm.

[0036] The features disclosed in the context of the strain measurement device and its embodiments also represent preferred features of the strain measurement method of the present invention and its embodiments. The foregoing aspects and the preferred features of the present invention, particularly the configuration of the device, and the features regarding the dimensions and configurations of the individual components described in relation to the device are also applicable to the method. The preferred embodiments, variations, and features of the present invention described above can be combined with each other as necessary.

[0037] Further advantages and details of the present invention are described below with reference to the accompanying drawings, which are schematically shown below.

Brief Description of the Drawings

[0038]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Best Mode for Carrying Out the Invention

[0039] Hereinafter, embodiments of the present invention will be described with reference to, in particular, the arrangement of a sample holder device, a indenter device, and a confocal Raman microscope device of an in-situ strain measurement apparatus, and their operations. The present invention is preferably implemented using, for example, a known confocal Raman microscope for strain measurement. Therefore, details of the confocal Raman microscope, available control methods thereof, and available methods for Raman signal acquisition will not be described as long as they are known from the prior art.

[0040] Calculating at least one strain parameter is preferably performed based on at least one collected Raman spectrum and at least one measured amount of load, such as in the calculation in conventional Raman-based strain measurement. In particular, this includes signal evaluation of at least one Raman spectrum, correlating features of at least one Raman spectrum, such as band peak position and / or band width and / or changes thereof, with the amount of deformation, e.g., the penetration of the indenter tip, and analytically or numerically calculating at least one stress or strain parameter from the amount of load and the amount of deformation. Calculating at least one stress or strain parameter may include calculating a single stress or strain parameter, such as a localized strain, as a single value, or calculating a plurality of stress or strain parameters as a map and / or a time function.

[0041] Generally, the sample includes a solid Raman active material such as ceramic or plastic. In an exemplary manner, reference is made to a plate-shaped sample, which is preferably transparent at the wavelength range of a confocal Raman microscope, particularly at the probe light wavelength of its light source, and at the Raman scattered light wavelength. The wavelength range of the confocal Raman microscope is, for example, about 400 nm to 1.5 μm. The transparent sample has a thickness in the range of, for example, 10 μm (supported by a laser-transparent backplate such as quartz) to 5 mm (self-supporting). It should be noted that optical transparency is not an essential feature of the sample. In the case of no optical transparency, strain measurements may be limited to thin samples (such as tooth enamel) having a thickness in the range of, for example, 10 μm to 100 μm.

[0042] Figure 1 schematically shows a side view of an embodiment of a strain measurement device 100 for measuring mechanical strain in sample 1. This strain measurement device 100 includes a sample holder device 10, a piezoresistive device 20 having a piezoresistive tip 21 and an actuator stage 22, a confocal Raman microscope 30, and a calculation device 40 included in a control device 50 such as, for example, a control computer. The load axis z of the piezoresistive device 20, particularly its piezoresistive tip 21 1 and the imaging axis z of the confocal Raman microscope 30 2 extend along a common perpendicular z-axis. The sample holder device 10 is adapted to place the sample in a plane perpendicular to the load axis and the imaging axis, particularly in a horizontal x-y plane. Figure 2 additionally shows a preferred translation stage 60 for adjusting the positions of the sample holder device 10 and the piezoresistive device 20 relative to the confocal Raman microscope device 30 and / or for scanning the sample for sample map measurement (see Figure 4). Details of the sample holder device 10 are shown in the top view of Figure 3.

[0043] The sample holder device 10 includes a support platform 11 extending in a horizontal x-y plane for accommodating the sample 1. The support platform 11 is attached to a support plate 13 via four support columns 12 (see FIGS. 1 and 3). Preferably, the support platform 11 includes an adjustable sample holder frame 14 having a central laser exploration window 15 for transmitting probe light and for collecting at least one Raman spectrum. The sample 1 can be fixed to the surface of the sample holder frame 14. The position of the sample holder frame 14 in the x-y plane can be adjusted via the sample adjustment knob 16. When the sample 1 is placed on the sample holder frame 14, the sample holder device 10 is in the load application position, and the clamped sample 1 will touch the indenter tip (from the bottom surface) and will be exposed to light / laser (from the upper side). The sample adjustment knob 16 is provided to determine the position of the sample 1 with respect to the load axis z 1 and the imaging axis z 2 is provided. The scanning operation of the sample in the x-y plane may be provided by the translation stage 60. Thus, the contact zone / area on the sample 1 can be scanned through the optical / laser exploration window 15 by operating the translation stage 60 in the x-y plane, and the measurement depth in the sample 1 can be scanned by operating the translation stage 60 in the z direction and / or by shifting the focus of the confocal Raman microscope device 30 along the z axis.

[0044] The indenter device 20 includes an indenter tip portion 21, an actuator stage 22, and a load cell 23. The indenter tip portion 21 has, for example, a conical spherical rigid tip section 21A (see FIG. 4) made of diamond and a tip support body section 21B. With this setup, different indenter tip portions having different sizes and shapes, which are adapted to form and apply different stress fields, can be exchanged. The actuator stage 22 is supported by the support plate 13 and / or the translation stage 60 and is a piezoelectric actuator that can apply indentation with a minimum step size of, for example, 5 nm and a maximum applied load of, for example, 20 N. The load cell 23 is disposed between the actuator stage 22 and the tip support body section 21B to measure the load applied to the sample 1. In particular, the load cell 23 may have a reading resolution of, for example, 0.01 N and a maximum load of, for example, 20 N, and the load cell 23 is connected to the shank of the piezoelectric actuator. The load cell 23 is connected to a control device 50 for analyzing the load cell output and optionally providing loop control of the actuator stage 22 in response to the load cell output.

[0045] The confocal Raman microscope 30 preferably includes a microscope body 34 (schematically shown in FIG. 2) having an attenuation vibration microscope base plate 35 made of, for example, granite, which is provided with a light source device 31, an imaging optical system 32, and a detector device 33. The light source device 31 is, for example, a laser (λ = 488 nm, 532 nm, 633 nm, or 785 nm). The detector device 33 is connected to a calculation device 40. The confocal Raman microscope 30 is, for example, a confocal Raman microscope (such as WITec Alpha 300R from Germany's Bittner etc.). Preferably, the confocal Raman microscope 30 is provided with a conventional confocal microscope imaging section that enables microscopic imaging for visually monitoring the sample.

[0046] The translation stage 60 is for supporting the sample holder device 10, for adjusting the position of the sample holder device 10 within the x - y plane, and for the load axis z of the indenter tip portion 211 It is fixedly arranged on the microscope base plate 35 for adjustment. Further, the translation stage 60 is configured to adjust the position of the sample holder device 10 along the z-direction, that is, to adjust the focal position of the confocal Raman microscope 30 in the sample 1 along the z-direction. This adjustment can be carried out by an electric actuator and / or a manually driven micrometer screw gauge 61.

[0047] The indenter device 20 is mounted upside down under the confocal Raman microscope 30 with the sample 1 sandwiched therebetween to apply a given load (applied by the indentation of the indenter tip 21) to the sample 1 (see FIG. 1). The load induces a change in the vibration band of the Raman signal, particularly in at least one Raman spectrum of the sample collected by the confocal Raman microscope 30. This change is filtered and mapped, and the induced elastic strain / stress of the sample 1 is evaluated by the calculation device 40. The indenter device 20 and the confocal Raman microscope 30 are arranged such that 1 the load axis z 2 coincides with the imaging axis z. Therefore, the confocal Raman microscope device 30 can collect at least one interference-free Raman spectrum even while the sample holder device 10 is at the load application position and even during load application.

[0048] As an alternative to the illustrated embodiment, the confocal Raman microscope 30 can also be mounted upside down under the indenter device 20 with the sample 1 sandwiched therebetween, reversing the arrangement of the indenter device 20 and the confocal Raman microscope 30, or the coincident load axis and imaging axis can be inclined relative to the vertical z-axis.

[0049] In the strain measurement according to the present invention, the strain measuring device 100 preferably operates as follows. Prior to strain measurement, the x-y position of the indenter tip 21 can be adjusted using the micrometer screw gauge 61 of the translation stage 60 (see FIG. 2). After attaching the sample 1 to the support platform 11 of the sample holder device 10, the region of interest (ROI) can be selected using the sample adjustment knob 16 while monitoring the sample 1 in the microscope imaging section of the confocal Raman microscope device 30. Thereafter, the position of the sample can be fixed using the sample holder grip screw 17 (see FIG. 3). As a preliminary reference measurement, the vibration band of the molecular structure of the sample in the unloaded state can be obtained using the confocal Raman microscope 30 before indentation. The characteristics of the vibration band can be used as a reference for subsequent strain measurements.

[0050] The strain measurement includes applying a localized mechanical load to the sample 1 using the indenter tip 21 of the indenter device 20. The indenter tip 21 is inserted until contact with the sample 1 is achieved and the indentation zone 2 is formed (see FIG. 4). Further insertion of the indenter tip 21 applies a load to the sample 1, resulting in elastic and / or inelastic deformation being induced in the indentation zone 2, i.e., the direct contact zone and the adjacent region of the sample 1.

[0051] Furthermore, strain measurement includes the step of collecting at least one Raman spectrum in the indentation zone 2 using a confocal Raman microscope device 30. Simultaneously with the application of the load, at least one Raman spectrum is collected using the confocal Raman microscope device 30. Calculating at least one strain parameter from at least one Raman spectrum includes, for example, filtering at least one collected Raman spectrum of the explored zone for a selected peak position and / or band width and correlating it with the indentation data (load, penetration, and / or contact shape) using a calculation device 40. The correlation between the characteristics of at least one Raman spectrum and the induced strain / stress results in at least one strain parameter to be obtained.

[0052] By collecting and evaluating a single spectrum, a zero-dimensional map of the sample is obtained, resulting in a single strain value (see Fig. 4A). Preferably, a plurality of Raman spectra are collected while operating the translation stage 60 to scan the indentation zone 2 to obtain the vibrational bands of the molecular structure of the sample 1 inside and / or around the indentation zone 2 with a local resolution. Thus, a one-dimensional, two-dimensional, or three-dimensional map of the sample can be obtained, as schematically illustrated by the line scan, area scan, and volume scan in Figs. 4B to 4D. The line scan in Fig. 4B preferably provides a depth-wise analysis of the strain in the sample. Alternatively, other directions of the line scan can also be set. In addition, the mapping shown in Figs. 4A to 4D can be performed with a time resolution, for example, by repeated collection and evaluation of the Raman spectra.

[0053] In summary, to perform time-resolved three-dimensional mapping of localized strain / stress using a confocal Raman microscope 30, two main elements are combined. First, a sharp micro- or nano-indentor (indentor tip 21) with a controllable indentation or load forms a localized contact stress field. This task cannot be achieved with conventional micro-tensile or bending testing machines because the applied stress field is not localized and / or the laser for scanning the stress / strain zone is not fully accessible. Second, the confocal Raman microscope 30 and the calculation device 40 provide at least one strain parameter, preferably with a spatial resolution for mapping the indentation area. By combining the Raman microscope device 30 with a translation stage 60, sub-micron scan resolution is advantageously provided in the x, y, and z directions.

[0054] Optionally, the exploration spatial resolution can be improved by selecting an objective lens of an imaging optical system 32 with a larger numerical aperture (NA) and a laser with a shorter wavelength (λ). Thus, for example, by using a 532 nm laser of the light source device 31 and an objective lens with NA = 0.9, the spatial resolution (0.61 * λ / NA) can be reduced to 360 nm. In addition, in order to detect changes in the vibration band of the sample 1 exposed to an external force, the detector device 33 of the confocal Raman microscope 30 is preferably provided with a spectrometer having a high resolution of Raman shift (≦1 cm -1 )). This resolution can be adjusted, for example, by selecting a high grating number (>1800 g / mm) and a large focal length (>300 mm) accessible with available confocal Raman microscopes.

[0055] As an example, by using a piezoelectric actuator of the actuator stage 22 through a diamond tip having a known shape to apply and control the indentation of the indentor tip 21 and recording the resulting load using a load cell 23, the applied Hertzian contact stress σ and indentation strain ε at the contact point can be obtained from the following formula. [Number] In the formula, P is the load, a is the contact radius, R is the radius of the indenter tip 21, and h is the applied contact depth (penetration into Sample 1). By collecting the Raman spectrum from the loaded Sample 1 and comparing it with the spectrum in the unloaded state, any change in the vibration band can be achieved, and this change can be used to correlate the induced peak shift with the applied contact stress. In particular, the contact stress can be calculated by the above formula based on the measured load, the known radius, and the contact depth derived from the induced peak shift.

[0056] The application of the present invention is not limited to the determination of the Hertz contact stress as a strain parameter. Instead, any correlation between the applied force or pressure and the change in the vibration band of the Raman active material can be calculated, particularly in real-time and / or time-resolved mode.

[0057] The inventors conducted a series of point measurements, area scans, and 3D mappings (stack of area scans to obtain volume data) on geological fluorapatite samples (1 mm thick) under different contact loads using the strain measurement device 100 and method of the present invention in a field test, and investigated the induced strain / stress and Raman peak shift. As an example, FIG. 5 illustrates the results of performing an in-situ Raman indentation test in point measurement mode while gradually increasing the load (0 to 170 g). According to FIG. 5A, the extracted Raman peak of the phosphate group of fluorapatite at the contact point of the indentation zone shows changes in peak position and width. FIG. 5B shows the measured load depending on the applied penetration of the indenter tip 21. The linear behavior of the extracted load-penetration curve indicates the elastic response of the sample. Therefore, the correlation between the Raman peak change (induced peak shift) and the applied penetration (contact depth) can be obtained as shown in FIG. 5C. This correlation is used to calculate the strain parameter (Hertz contact stress). 1 The extracted Raman peak of the vibration band shows changes in peak position and width. FIG. 5B shows the measured load depending on the applied penetration of the indenter tip 21. The linear behavior of the extracted load-penetration curve indicates the elastic response of the sample. Therefore, the correlation between the Raman peak change (induced peak shift) and the applied penetration (contact depth) can be obtained as shown in FIG. 5C. This correlation is used to calculate the strain parameter (Hertz contact stress).

[0058]

[0058] In further tests, as shown in Fig. 6, in-situ Raman indentation in the mapping (3D) mode under a constant load of 1 N or 1.45 N made it possible to evaluate the characteristics of the stress distribution around the indentation zone and / or at different depths of the fluorapatite sample. Figs. 6A and 6B show the spatial distributions of the indentation stress and indentation strain in the sample under the action of the indenter tip with a radius of 125 μm, while Fig. 6C shows a cross-sectional view of the sample in plane i.

[0059] Furthermore, using the in-situ function of this method and performing a load scan cycle revealed the changes in mechanical strain in the calcite sample (Fig. 7). In this study, a series of images at the same location on the x-y plane (2D scan) were processed at defined applied contact loads P = 84 mN, P = 147 mN, and P = 0 (scan after removing the 147 mN load), which respectively represent the elastic (1), elastic-inelastic (2), and residual strain (3) states.

[0060]

[0058] The features of the invention disclosed in the above description of the specification, the drawings, and the claims may be important, either individually, in combination, or in sub-combinations, in the implementation of the invention in various embodiments. The present invention is not limited to the preferred embodiments described above. Rather, multiple variations and derivatives using the inventive concept are also possible and are included within the scope of protection. In addition, the present invention also claims protection for the subject matter and features of the dependent claims, independently of the features and claims referred to by the dependent claims.

Claims

1. A strain measuring device (100) configured to measure mechanical strain in a sample (1), a sample holder device (10) arranged to accommodate the sample (1) to be investigated, A probe device (20) including a probe tip portion (21) and an actuator stage (22) that supports the probe tip portion (21), wherein the actuator stage (22) is configured to apply a localized mechanical load along a load axis (z １ ), through the probe tip portion (21), in a press-fitting zone (2) of the sample (1) accommodated by the sample holder device (10) when the sample holder device (10) is at a load application position. The probe device (20) is arranged as such. Imaging axis (z ２ ) and a confocal Raman microscope device (30) arranged to collect at least one Raman spectrum in the indentation zone (2) of the sample (1). and a calculation device (40) arranged to calculate at least one strain parameter based on the at least one Raman spectrum, wherein the sample holder device (10), the indenter device (20), and the confocal Raman microscope device (30) are arranged such that the confocal Raman microscope device (30) can collect the at least one Raman spectrum while the sample holder device (10) is in the load application position, The piezoelectric device (20) and the confocal Raman microscope device (30) are arranged such that the load axis (z １ of the actuator stage (22) coincides with the imaging axis (z ２ ) of the confocal Raman microscope device (30). A strain measurement device (100).

2. The strain measuring device according to claim 1, wherein the sample holder device (10), the indenter device (20), and the confocal Raman microscope device (30) are arranged such that the confocal Raman microscope device (30) can collect the at least one Raman spectrum simultaneously with the application of the localized mechanical load.

3. The strain measuring device according to claim 1 or 2, wherein the indenter device (20) and the confocal Raman microscope device (30) are arranged such that the localized mechanical load can be applied at a load application spot on a first side of the sample (1), and the at least one Raman spectrum can be collected in the indentation zone (2), particularly at the load application spot from a second side opposite to the sample (1).

4. The sample holder device (10) is provided with a translation stage (60) arranged to adjust the x-y position of the sample holder device (10) in a plane perpendicular to the imaging axis (z ２ ) of the confocal Raman microscope device (30). The strain measuring device according to any one of claims 1 to 3.

5. The strain measuring device according to any one of claims 1 to 4, wherein the confocal Raman microscope device (30) is configured to perform at least one of time-resolved collection of a plurality of Raman spectra and mapping of the sample (1) within a range including the indentation zone (2).

6. characterized in that the indenter tip (21) has a distal contact section exposed for contacting the sample (1), characterized in that the indenter tip (21) is replaceable, characterized in that the indenter tip (21) is a diamond tip, a sapphire tip, or a ruby tip, characterized in that the indenter tip (21) is a conical spherical tip, and The strain measuring device according to any one of claims 1 to 5, including at least one of the features that the tip portion (21) of the indenter has a tip shape including a cube corner, or a Berkovich shape, or a Vickers shape, or a flat punch shape.

7. The feature that the actuator stage (22) includes a piezoelectric actuator and a transducer, The feature that the indenter device (20) includes a load cell (23) connected to the actuator stage (22), and the load cell (23) is arranged to measure the mechanical load applied to the sample (1), and The strain measuring device according to any one of claims 1 to 6, including at least one of the features that the sample holder device (10) has a concentric window attached upside down under the confocal Raman microscope device (30).

8. A strain measuring method for measuring mechanical strain in a sample (1), comprising: placing the sample (1) to be investigated on a sample holder device (10); A step of applying a localized mechanical load to the sample (1) using a probe device (20) including a probe tip portion (21) and an actuator stage (22) that supports the probe tip portion (21), wherein the mechanical load is applied through the probe tip portion (21) using the actuator stage (22) in a press-in zone (2) of the sample (1) when the sample holder device (10) is at a load application position, along a load axis (z １ ) and the step is applied along the In the indentation zone (2) of the sample (1), at least one Raman spectrum is collected using a confocal Raman microscope device (30) having an imaging axis (z ２ ). calculating at least one strain parameter based on the at least one Raman spectrum, wherein the at least one Raman spectrum is collected while the sample holder device (10) is at the load application position, The piezoelectric device (20) and the confocal Raman microscope device (30) are such that the load axis (z １ ) of the actuator stage (22) and the imaging axis (z ２ ) of the confocal Raman microscope device (30) are arranged to coincide with each other. A strain measurement method.

9. The strain measuring method according to claim 8, wherein the at least one Raman spectrum is collected simultaneously with the step of applying the localized mechanical load.

10. The strain measuring method according to claim 8 or 9, wherein the at least one Raman spectrum is collected before and / or after the step of applying the localized mechanical load.

11. The localized mechanical load is applied at a load application spot on a first side of the sample (1), and the at least one Raman spectrum is collected in the indentation zone (2), particularly at the load application spot from a second side opposite to the sample (1). The strain measuring method according to any one of claims 8 to 10.

12. The strain measuring method according to any one of claims 8 to 11, including adjusting the x-y position of the sample holder device (10) in a plane perpendicular to the imaging axis of the confocal Raman microscope device (30).

13. Collecting a plurality of Raman spectra in a time-resolved manner, and Mapping, preferably three-dimensionally mapping, the sample (1) within the range including the indentation zone (2), the strain measurement method according to any one of claims 8 to 12, including at least one of the above.

14. The strain measurement method according to any one of claims 8 to 13, further comprising measuring the mechanical load applied to the sample (1) using a load cell (23) connected to the actuator stage (22).

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