Device for elementary analysis of a sample to be examined by laser-induced breakdown spectroscopy, comprising a sample holder

Abstract

The invention relates to a device for elementary analysis of a sample to be examined, the device comprising: - a base (1) that has a flat surface (10) and is intended to support a sample (2) to be examined; - a system (3) for generating a laser beam (30) intended to impact the sample (2) to be examined in a direction perpendicular to the flat surface (10) of the base (31), in order to generate a plasma (P) causing an optical emission (40); - means (4) for collecting the optical emission (40); - a sample holder (5) intended to rest on the base (1).

Description

Device for elementary analysis of a sample to be studied by optical emission spectrometry on plasma produced by laser, comprising a sample holder

[0001] The present invention relates to the field of high-resolution mapping and analysis of elements in solids.

[0002] More particularly, the invention relates, in particular but not exclusively, to a device for qualitative and quantitative analysis of the elementary chemical composition of a solid sample.

[0003] The invention can be applied in particular to the elemental analysis of hydrogen and oxygen by optical emission spectrometry on plasma produced by laser, in the field of the nuclear industry, or even the aeronautical or space industry.

[0004] In applications such as the characterization of devices subjected to radioactive sources, or the characterization of the aging capacity of devices used in particularly harsh environments, for example in aircraft or spacecraft, it may prove essential to carry out elemental analysis of metal samples.

[0005] More specifically, it may be necessary to be able to draw up a map of these elements within the sample analyzed. By mapping, we mean an identification of the elements making up the sample analyzed and, possibly, the distribution and the link between the different elements.

[0006] Such an analysis can be particularly useful in studies of metal embrittlement by hydrogen, or in studies of aging of fuel cladding in the presence of oxygen, or in studies of embrittlement of fuel cladding caused by the formation of hydrides, the latter promoting the propagation of cracks.

[0007] There are various known methods for mapping elements present in samples.

[0008] One of these methods is elemental analysis by optical emission spectrometry on laser-produced plasma, designated by the acronym "SEOPPL", a technique which is carried out in a natural atmosphere, also designated by the English acronym "LIBS" corresponding to the English expression "laser induced breakdown spectroscopy".

[0009] This method applies in particular to the in situ control and characterization of samples of parts to be analyzed.

[0010] A method and device for elementary analysis by optical emission spectrometry on plasma produced by laser is for example described by the patent document published under number WO 01 / 33202.

[0011] Such an analysis device comprises: - a base intended to support a sample to be studied; - a system for generating a laser beam intended to impact the sample to be studied in a direction perpendicular to the base, to generate a plasma generating an optical emission; - means for collecting the optical emission.

[0012] The laser beam generated by the generation system, after shaping by a shaping module, is applied to a sample to be studied via optical focusing means.

[0013] A plasma is then created at the impact of the laser beam on the sample to be studied, the plasma generating an optical emission to be analyzed to map the elements making up the sample studied.

[0014] The collection of the optical emission of the plasma is then carried out by the collection means.

[0015] The movement of the sample to be studied relative to the laser beam allows access to the distributions of the concentrations of the constituent elements of the surface of the sample, which makes it possible to establish elementary maps.

[0016] The device described in the aforementioned document comprises means for moving the sample to be analyzed.

[0017] The sample is more precisely placed to the nearest micrometer on a stage. This stage, for example motorized, allows micro-displacements to be made along two axes of direction.

[0018] The focus produced by the optical focusing means is a critical parameter. Indeed, this focus must be maintained throughout the analysis of the surface of the sample to be studied.

[0019] In the case where the surface to be analyzed of the sample is sufficiently flat (a surface being considered sufficiently flat if its relief does not present differences in height greater than the depth of field of the optical focusing means), and that the perfect perpendicularity of this surface is ensured in relation to the laser beam, then there is no focusing problem.

[0020] In the case where the surface of the sample is not flat, and / or this surface is not perfectly perpendicular to the laser beam, then an adjustment of the focus must be made as the analysis progresses.

[0021] A similar device is also known, described in the patent document published under the number WO 2016203163.

[0022] The device includes an autofocus system to compensate for such flatness and perpendicularity defects relative to the laser beam of the surface of the sample to be studied. To do this, the device uses a sensor that measures any flatness defects in the sample, as well as a motorization of the sample holder capable of orienting the sample holder according to the measured flatness defect.

[0023] This design solves the problem of the need to focus the laser beam, but inherently leads to an increase in the complexity of the device.

[0024] The invention aims in particular to overcome this drawback of the prior art.

[0025] More specifically, the invention aims to propose a device for elementary analysis of a sample to be studied, of the type previously described, which makes it possible to overcome defects in flatness and perpendicularity relative to the laser beam of the surface of the sample to be studied in a less complex manner than that proposed by the prior art.

[0026] This objective, as well as others which will appear subsequently, is achieved thanks to the invention which relates to a device for elementary analysis of a sample to be studied, the device comprising: a base having a flat surface and intended to support a sample to be studied; a system for generating a laser beam intended to impact the sample to be studied in a direction perpendicular to the flat surface of the base, to generate a plasma generating an optical emission; means for collecting the optical emission; characterized in that it comprises a sample holder comprising: a flat lower face intended to rest on a flat surface of the base; a cavity intended to receive the sample; at least one shoulder forming a bearing surface oriented towards the cavity, the bearing surface being inscribed in a plane parallel to the flat lower face of the sample holder;elastic return means configured to press the sample against the support surface; a cylindrical block having the cavity and the shoulder(s), a base having the flat lower face, and means for holding the block on the base, the holding means comprising two clamping jaws of the block each having a clamping surface whose generatrices extend perpendicular to the flat lower face.;

[0027] Thanks to the device according to the invention, the defects of flatness and perpendicularity as described above are overcome in a manner which is less complex than that proposed by the prior art (autofocus).

[0028] Indeed, the design of the device according to the invention makes it possible to guarantee that the surface of the sample to be studied extends perpendicular to the laser beam generated by the generation system of the device.

[0029] By means of the sample holder, the sample is pressed against the support surface and the surface of the sample then extends in the plane which is parallel to the flat lower face of the sample holder. In this way, and because the flat lower face of the sample holder rests on the flat surface of the base, the plane in which the face to be studied of the sample extends extends parallel to the flat surface of the base and thus perpendicular to the laser beam which, during operation of the device, extends perpendicular to the flat surface of the base.

[0030] By ensuring that the surface of the sample to be analyzed is pressed against the shoulder, there is no focusing problem when studying the surface of the sample to be studied. The sample holder of the device according to the invention forms a simple mechanical solution, and in particular simpler than that using autofocus.

[0031] The cylindrical block is for example obtained by precision machining.

[0032] This cylindrical block makes it possible to present faces extending, when integrating the sample holder into the device, parallel or perpendicular to the flat lower face of the sample holder, and to the flat surface of the base.

[0033] More precisely, the radially external surface of the block and more precisely the generatrices of this surface then extend perpendicular to the flat surface of the base while the bases of the cylinder extend parallel to the flat surface of the base.

[0034] Thanks to the two clamping jaws of the block, each of which has a clamping surface whose generatrices extend perpendicular to the flat lower face, it is ensured that these clamping jaws come into flat support against the radially external surface of the block during clamping, thereby guaranteeing that the clamping does not cause an angular tilting of the central axis of the cylindrical block relative to the flat surface of the base.

[0035] Conversely, tightening using a screw which would exert a point stress, perpendicular to the central axis of the cylindrical block, on the radially external surface of the cylindrical block, could cause such an offset distorting the measurement.

[0036] Preferably, the cylindrical block is cylindrical of revolution.

[0037] Advantageously, the shoulder takes an annular shape.

[0038] Such a shoulder makes it possible to form a continuous support surface on which the sample can be pressed.

[0039] According to an advantageous characteristic, the sample holder comprises a stop coupling to the block and forming a support for the elastic return means.

[0040] Thanks to such a stop separate from the block, the positioning of the sample in the block, then of the elastic return means, and finally of the stop are carried out in a simple manner, while helping to guarantee the correct positioning of the sample in relation to the axis of the laser beam.

[0041] Preferably, the elastic return means have at least two upper contact points intended to be in contact with the sample, and at least two lower contact points intended to be in support against the stop.

[0042] In this way, it is ensured that the support taken by the elastic return means against the stop, and the forces applied by the elastic return means are exerted in a regularly distributed manner to properly press the sample against the support surface formed by the shoulder.

[0043] According to an advantageous embodiment, the elastic return means take the form of a corrugated spring washer.

[0044] Such a wave spring washer is suitable for providing elastic return ensuring the sample is correctly pressed against the support surface.

[0045] Even more preferably, the spring washer has, in a side view, an S-shaped profile.

[0046] Such a spring washer perfectly ensures that the sample is properly pressed against the support surface.

[0047] The invention also relates to a method for elementary analysis of a sample to be studied by optical emission spectrometry on plasma produced by laser, comprising a step of preparing a sample and a step of positioning the sample on a base for its analysis, characterized in that the step of preparing a sample comprises a sub-step of forming by polishing on the sample a flat face to be studied, and in that the positioning step includes the use of a sample holder comprising: - a flat lower face intended to rest on the flat surface of the base; - a cavity intended to receive the sample; - at least one shoulder forming a bearing surface oriented towards the cavity, the bearing surface being inscribed in a plane parallel to the flat lower face of the sample holder;- elastic return means configured to press the sample against the support surface,- a cylindrical block having the cavity and the shoulder(s),- a base having the flat lower face, and means for holding the block on the base, the holding means comprising two clamping jaws of the block each having a clamping surface whose generatrices extend perpendicular to the flat lower face,and in that the positioning step comprises:- a sub-step of inserting the sample into the sample holder and positioning the flat face to be studied against a support surface of the sample holder lying in a plane parallel to a flat lower face of the sample holder intended to rest on a flat surface of the base;- a sub-step of adding elastic return means to press the flat face to be studied of the prepared sample against the support surface.;

[0048] The analysis method can be implemented by the device according to the aforementioned invention.

[0049] This analysis process guarantees the correct positioning of the sample in relation to the axis of the laser beam.

[0050] Other characteristics and advantages of the invention will appear more clearly on reading the following description of different preferred embodiments of the invention, given as illustrative and non-limiting examples, and the appended drawings among which:1a is a schematic representation seen from the side of a device for elementary analysis of a sample to be studied according to the invention, comprising in particular a sample holder resting on a base;1a is a schematic representation according to a cross-sectional view of the sample holder of a device according to the invention, the sample holder comprising a block receiving the sample, elastic return means and a stop making it possible to press the sample into the block, as well as a base and means for holding the block on the base;lais a schematic representation according to a cross-sectional view of the block receiving the sample and housing within it the elastic return means and the stop;lais a schematic representation in cross-section of the block alone;lais a schematic representation in cross-section of the stop;lais a schematic representation according to a profile view of the elastic return means taking in particular the form of a corrugated washer;lais a schematic representation seen from above of the sample holder illustrating in particular the means for holding the block on the base.;

[0051] With reference to the, a device for elementary analysis of a sample to be studied is represented.

[0052] The analysis device is of the type projecting a laser beam 30 onto a sample 2 to be studied to generate a plasma P generating an optical emission 40 intended to be collected and analyzed.

[0053] Still with reference to the, the device comprises:- a base 1 intended to support the sample 2 to be studied, the base 1 having a flat surface 10;- a system 3 for generating a laser beam 30 intended to impact the sample 2 to be studied, to generate a plasma P generating the optical emission 40;- means 4 for collecting the optical emission 40;- a sample holder 5 intended to carry the sample 2 to be studied above the base 1, the sample holder 5 resting on the base 1, and more precisely on the flat surface 10 of the base 1.

[0054] The system 3 for generating a laser beam 30 is configured to emit the laser beam 30 in a direction perpendicular to the flat surface 10 of the base 1.

[0055] The system 3 for generating a laser beam 30 comprises a source for generating a laser beam, means for shaping the laser beam, as well as optical means for focusing the laser beam.

[0056] The 3 generation system is configured so that the focusing of the laser beam 30 is adapted to the sample 2 to be studied.

[0057] This focus is defined in part by a depth of field within which the surface of the sample 2 to be studied impacted by the laser beam 30 must be located.

[0058] The means 4 for collecting the optical emission 40, for their part, comprise for example an optical fiber 41 oriented towards the plasma P, and positioned as close as possible to the plasma P to collect the optical emission 40.

[0059] The sample holder 5 is described in more detail below.

[0060] With reference to figures 2, 3 and 7, the sample holder 5 comprises:- a block 54;- a base 55;- means 56 for holding the block 54 on the base 55.

[0061] In a simplified design, the sample holder 5 comprises: - a flat lower face 50 intended to rest on the flat surface 10 of the base 1; - a cavity 51 intended to receive the sample 2; - a support surface 520 oriented towards the cavity, this support surface 520 being inscribed in a plane parallel to the flat lower face 50 of the sample holder 5; - elastic return means 53 configured to press the sample 2 against the support surface 520.

[0062] According to the present embodiments, the flat lower face 50 is presented by the base 55.

[0063] When the sample holder 5 is placed on the base 1, then the flat lower face 50 of the base 55 is in flat contact with the flat surface 10 of the base 1.

[0064] Cavity 51, intended to accommodate sample 2, is presented by block 54.

[0065] The sample holder 5 also comprises at least one shoulder 52 which forms the bearing surface 520.

[0066] The bearing surface 520 is in this case formed by a single shoulder 52.

[0067] This shoulder 52 is presented by the block 54 which is intended to accommodate the sample 2 in its cavity 51.

[0068] In this case, the shoulder 52 takes an annular shape. This shoulder 52 thus corresponds to an internal shoulder of the block 54 which is, according to the present embodiment, cylindrical, and more specifically cylindrical of revolution around a central axis.

[0069] The bearing surface 520 thus extends from a peripheral wall of the block 54 in the direction of the central axis of the cylindrical block 54 of revolution.

[0070] The cylindrical block 54 of revolution has:- a radially external surface 541;- a lower surface 540 fitting into one of the two bases corresponding to the cylindrical shape of revolution;- an upper surface 542 fitting into the other of the two bases of the cylindrical shape of revolution.

[0071] The cavity 51 opens onto the lower face 540.

[0072] Indeed, the block 54 has a light 543 centered on the upper surface 542, and opening into the cavity 51 to allow the laser beam 30 to impact the sample 2.

[0073] Being cylindrical, the generatrices of the radially external surface 541 all extend perpendicular to the lower face 540 and to the upper face 542.

[0074] Likewise, these generators extend perpendicular to a plane in which the support surface 520 is inscribed.

[0075] As functionally detailed below, block 54 includes an internal thread 544.

[0076] With reference to figures 2, 3 and 5, the sample holder 5 comprises a stop 57.

[0077] This stop 57 couples to the cylindrical block 54 and forms a support for the elastic return means 53. This stop 57 takes in particular an annular shape.

[0078] The stop 57 couples to the cylindrical block 54 by being screwed inside the cavity 51.

[0079] For this purpose, the stop 57 has an external thread 571 complementary to the internal thread 544.

[0080] The stop 57 and the block 54 are configured so that screwing the stop 57 into the cavity 51 brings an upper surface 570 of the stop 57 into a plane which is parallel to the plane in which the bearing surface 520 is inscribed.

[0081] In order for the block 54 and the stop 57 to have rigorously geometric shapes, and in particular to have faces and sides that fit into parallel or perpendicular planes, these two parts are manufactured by high-precision machining, or even by 3D printing.

[0082] With reference to figures 2, 3 and 6, the elastic return means 53 take the form of a corrugated spring washer.

[0083] More precisely, the spring washer has, according to a side view, an S-shaped profile.

[0084] Such a corrugated spring washer allows the elastic return means 53 to have at least two upper contact points 531, and in this case three upper contact points 531 intended to be in contact with the sample 2, and at least two lower contact points 532, and in this case three lower contact points 532 intended to be in contact against the stop 57, and more precisely against the upper surface 570 of the stop 57.

[0085] Due to the profile view of the, only two upper contact points 531 and two lower contact points 532 are visible, nevertheless, it can easily be understood that the washer has a third upper point 531 behind the upper point 531 located on the right part of the figure, and a third lower contact point 532 behind the lower contact point 532 located on the left part of the figure.

[0086] Now, with reference to Figures 2 and 7, the holding means 56 are described in more detail below.

[0087] These holding means 56 are fixed to the base 55. The holding means 56 comprise two jaws 561 for clamping the block 54.

[0088] Each jaw 561 has a clamping surface 562 whose generatrix or generatrices extend perpendicular to the flat lower face 50 presented by the base 55.

[0089] More precisely, the holding means 56 are configured so that the two clamping jaws 561 can be moved towards each other while maintaining the perpendicularity of the generatrices of the clamping surfaces 562 relative to the flat lower face 50.

[0090] For this purpose, and with more specific reference to the embodiment of the, the holding means 56 comprise a hinge 563 defining a pivot axis of one of the jaws relative to the other of the jaws 561 extending perpendicularly to the flat lower face 50. This pivot axis extends perpendicularly to the flat lower face 50. According to another preferred embodiment, not shown, the holding means 56 are made of an at least partially elastically deformable material and comprise a reduction in thickness in place of the hinge 563. In this way, the two jaws can be moved apart from each other to allow the insertion of the block 54.

[0091] In addition, the holding means 56 comprise a bolt 564 coupled to the two clamping jaws 561 to allow the two clamping jaws 561 to be brought closer to each other.

[0092] Such clamping means ensure that the block 54 is clamped in a position in which the central axis of the block 54 extends perpendicular to the planar underside 50.

[0093] The invention also comprises a method for elementary analysis of the sample 2 to be studied by optical emission spectrometry on plasma produced by laser.

[0094] This method comprises a step of preparing a sample 2, then a step of positioning the sample 2 on the base 1 for its analysis.

[0095] The step of preparing a sample 2 includes in particular the formation of the sample 2.

[0096] As schematically illustrated in Figures 2 and 3, sample 2 takes an essentially cylindrical shape of revolution.

[0097] For the purposes of analysis, the material to be analyzed corresponds, for example, to a metal strip included in a resin block designed so that the strip to be analyzed is flush with one of the bases of the resin block. This block forms sample 2 to be studied.

[0098] During the preparation step of sample 2, a sub-step of formation by polishing on sample 2 of a flat face to be studied is carried out.

[0099] For this purpose, the resin block is polished by bringing its base, on which the strip of material to be analyzed is flush, into contact with an abrasive surface.

[0100] Subsequently, the step of positioning sample 2 on base 1 for its analysis includes the use of sample holder 5 described previously.

[0101] This positioning step thus comprises: - a sub-step of inserting the sample 2 into the sample holder 5, and in particular of inserting the sample 2 into the cavity 31 of the block 54, and of positioning the flat face to be studied against the bearing surface 520 of the sample holder 5; - a sub-step of adding the elastic return means 53 to press the flat face to be studied of the sample 2 against the bearing surface 520.

[0102] Subsequently, of course, the stop 57 is screwed in such a way as to allow the elastic return means to bear against this stop 57 and to exert an elastic return force on the sample 2 to keep it pressed.

[0103] The block 54 is then positioned on the base 55 and clamped by the holding means 56.

[0104] Subsequently, the analysis by optical emission spectrometry on plasma produced by laser can be carried out, the sample holder 5 ensuring that the surface of the sample 2 to be analyzed is well positioned perpendicular to the laser beam 30, and the polishing ensuring that the surface state of the sample 2 to be analyzed does not have height differences located outside the depth of the focusing field of the generation system 3.

Claims

Device for elementary analysis of a sample to be studied, the device comprising: a base (1) having a flat surface (10) and intended to support a sample (2) to be studied; a system (3) for generating a laser beam (30) intended to impact the sample (2) to be studied in a direction perpendicular to the flat surface (10) of the base (31), to generate a plasma (P) generating an optical emission (40); means (4) for collecting the optical emission (40); characterized in that it comprises a sample holder (5) comprising: a flat lower face (50) intended to rest on the flat surface (10) of the base (1); a cavity (51) intended to receive the sample (2); at least one shoulder (52) forming a bearing surface (520) oriented towards the cavity (51), the bearing surface (520) being inscribed in a plane parallel to the flat lower face (50) of the sample holder (5);elastic return means (53) configured to press the sample (2) against the support surface (520), a cylindrical block (54) having the cavity (51) and the shoulder(s) (52), a base (55) having the flat lower face (50), and holding means (56) of the block (54) on the base (55), the holding means (56) comprising two jaws (561) for clamping the block (54) each having a clamping surface (562) whose generatrices extend perpendicular to the flat lower face (50).; Device according to the preceding claim, characterized in that the cylindrical block (54) is cylindrical of revolution. Device according to the preceding claim, characterized in that the shoulder (52) takes an annular shape. Device according to any one of the preceding claims, characterized in that the sample holder (5) comprises a stop (57) coupling to the block (54) and forming a support for the elastic return means (53). Device according to any one of the preceding claims, characterized in that the elastic return means (53) have at least two upper contact points (531) intended to be in contact with the sample (2), and at least two lower contact points (532) intended to be in support against the stop (57). Device according to any one of the preceding claims, characterized in that the elastic return means (53) take the form of a corrugated spring washer. Device according to claims 5 and 6, characterized in that the spring washer has, in a side view, an S-shaped profile. Method for elementary analysis of a sample (2) to be studied by optical emission spectrometry on plasma produced by laser, comprising a step of preparing a sample (2) and a step of positioning the sample (2) on a base (1) for its analysis, characterized in that the step of preparing a sample (2) comprises a sub-step of forming by polishing on the sample (2) a flat face to be studied, and in that the positioning step includes the use of a sample holder (5) comprising: a flat lower face (50) intended to rest on the flat surface (10) of the base (1); a cavity (51) intended to receive the sample (2); at least one shoulder (52) forming a bearing surface (520) oriented towards the cavity (51), the bearing surface (520) being inscribed in a plane parallel to the flat lower face (50) of the sample holder (5);elastic return means (53) configured to press the sample (2) against the bearing surface (520), a cylindrical block (54) having the cavity (51) and the shoulder(s) (52), a base (55) having the flat lower face (50), and holding means (56) of the block (54) on the base (55), the holding means (56) comprising two jaws (561) for clamping the block (54) each having a clamping surface (562) whose generatrices extend perpendicular to the flat lower face (50), and in that the positioning step comprises: a sub-step of inserting the sample (2) into the sample holder (5) and positioning the flat face to be studied against a bearing surface (520) of the sample holder (5) lying in a plane parallel to a flat lower face (50) of the sample holder (5) intended to rest on a flat surface (10) of the base (1);a sub-step of adding elastic return means (53) to press the flat face to be studied of the sample (2) against the support surface (520).;

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