JP2016075525A - Method for preparing sample for observing particles with electron microscope and method for observing particles with electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a preparation method of an observation sample allowing particles with a specific average particle diameter which makes observation with an electron microscope difficult to be easily observed with the electron microscope, and a method for observing the particles with the electron microscope by using the observation sample.SOLUTION: Particles 1 whose average particle diameter is more than 100 nm and equal to or less than 100 μm are pressed together with tin 2, so that an observation sample having a part in which the particles 1 and the tin 2 contact with each other is prepared. The observation sample is observed with an electron microscope, so that the particles 1 are observed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a novel method for producing an observation sample for observing particles with an electron microscope, and also relates to a novel electron microscope observation method for particles using the measurement sample.

  In order to confirm the shape and internal structure of the powder sample (particles), observation with an electron microscope is performed.

  For example, in observation of particles with a transmission electron microscope (hereinafter referred to as TEM), the thickness of the observation target sample needs to be approximately 100 nm or less because an electron beam is transmitted. Therefore, a method of dispersing and fixing a powder sample on a sheet mesh having an organic thin film has been disclosed (see, for example, Patent Document 1). In this method, from the viewpoint of electron beam transparency, it was possible to observe only the end of the sample where the particle size of the powder sample was as small as 100 nm or less or thin enough to allow the electron beam to pass through.

  Further, in the observation of particles with a scanning electron microscope (hereinafter referred to as SEM), a method is generally used in which particles are dispersed on a conductive tape or a suitable sample stage and observed. In this method, the roughness of the particle surface and the particle size can be evaluated, but information inside the particle cannot be obtained.

  Therefore, thinning of the sample is necessary for TEM observation of particles having a particle size exceeding 100 nm, and processing for exposing the cross section is necessary for observation of the internal structure of the particles by SEM.

  In recent years, an ion etching apparatus (an apparatus that irradiates an ion beam) capable of processing a sample shape by irradiation with Ga ions or Ar ions has been developed and used for preparing a sample for observing a powder sample with an electron microscope. In preparation of a TEM observation sample of a powder sample, a focused ion beam processing apparatus (hereinafter referred to as an FIB apparatus) capable of thinning an arbitrary part of an object by irradiation with gallium (Ga) ions is used. There are many cases. In SEM observation of a powder sample, not only an FIB apparatus but also an ion milling apparatus that produces a smooth cross section by irradiation with argon (Ar) ions is used. In either sample preparation method, if the particle size is sufficiently large, for example, if the particle size exceeds 100 μm, one particle can be handled by itself, such as picking with a tweezers, so that sample preparation is possible in the same way as for inorganic bulk samples It is.

  On the other hand, in the case of particles that cannot be handled as single particles and have a particle size exceeding 100 nm, when these particles are directly observed with an electron microscope, an electron beam is not transmitted in TEM observation, and only surface shape is observed in SEM observation. I can't observe. Therefore, usually, the particles are mixed with a resin or the like to fix the particles, the mixture is processed by an ion etching apparatus, and the obtained workpiece is observed. The shape and internal structure of the particles can be observed by observing the processed product with an electron microscope.

  By the way, in order to improve performance such as heat resistance and water resistance, particles used in battery materials and semiconductor materials may be subjected to various treatments to form a surface treatment layer on the particle surface. . For the expression of the desired function, it is desirable that the surface treatment layer be uniform with a desired thickness, and it is important to evaluate the structure of the surface treatment layer in detail.

  In observing the structure of the surface treatment layer, in the sample preparation method for observation mixed with the above resin, if the surface treatment layer is organic, elution or peeling of the surface treatment layer occurs during curing in the resin. Thus, the thickness of the surface treatment layer could not be properly evaluated. Therefore, in the observation of particles whose surface is coated with an organic substance, a method for fixing the particles without affecting the structure of the surface treatment layer has been desired.

  On the other hand, a method of immobilizing particles with a material that is not an organic polymer material such as a resin and measuring the shape and cross section of the particles has been studied. Specifically, when analyzing particulate micrometeorites, a powder sample (particulate micrometeorite) and gold are pressed into contact with each other, processed by an FIB apparatus, and observed with a transmission electron microscope (TEM). The method is known (for example, refer nonpatent literature 1). According to this method, even if it is a meteorite (particle) whose component is unknown by using gold, alteration can be avoided and TEM observation can be performed. In addition, since metal is present near the powder sample, it is possible to omit a necessary conductive treatment before processing by the FIB apparatus, which is a very good sample preparation method.

  However, gold as an embedded metal is very expensive and difficult to use on a daily basis. Furthermore, since gold is a relatively hard metal at room temperature, it takes a lot of labor and time to prepare the sample, such as annealing, in order to press the micro meteorite (particles) into gold, and there is room for improvement. there were. Further, when annealing is performed, for example, particles surface-treated with organic matter may change the organic matter on the surface, and further improvement is necessary in terms of application to various particles. It was.

JP-A-2-262226

Takaaki Noguchi, Mineral-Water-Organic Interactions in the Early Solar System Early Evolution of Planetary and Life Origins August 22, 2014 Grinding Internet <URL: http://www-sys.eps.su-tokyo.ac.jp /~nagahara-kaken/members/noguchi/index.html>

  Therefore, an object of the present invention is to provide a method for preparing an observation sample that can easily observe particles having a specific particle diameter that have been difficult to observe with an electron microscope by a conventional method, and a method for observing the particles. Is to provide. In particular, a method for preparing an electron microscope observation sample in which the internal structure and the surface treatment layer are not damaged even if the particles are subjected to a surface treatment with an organic substance that easily undergoes structural destruction due to resin embedding, and an observation method for the particles And to provide.

In order to solve the above-mentioned problems, the present inventors have conducted intensive studies. As a result of searching for materials that are inexpensive and have good workability instead of gold, the present inventors have found that the above problems can be solved by using tin that is softer than gold at room temperature, and the present invention has been completed. It was.
That is, the first invention is a method for producing an observation sample that is produced for observing particles with an electron microscope, wherein the average particle diameter of the particles is more than 100 nm and not more than 100 μm. This is a method for producing an observation sample having a portion where the particles and tin are in contact with each other by pressure welding.

In 1st invention, when the said particle | grain is an inorganic particle, it can be used conveniently. Among them, when the surface of the particle is an inorganic particle coated with an organic substance, the particle can be observed without altering the organic substance on the surface (structural destruction or the like), which is a very useful method.
Furthermore, in the first invention, the observation sample includes a layer formed of the particles on tin, and the thickness of the thickest part of the layer is preferably 3 times or more the average particle diameter of the particles. . By doing so, the number of visual fields in which particles can be observed can be increased.

  In the first invention, an excellent effect is exhibited when the observation sample is obtained by irradiating an ion beam on a pressure-contacted material in which the particles are pressure-contacted on tin to expose a cross section. That is, since the particles are fixed on the tin, the observation sample cross section (particle cross section) can be easily exposed by the ion beam.

  2nd invention is the method of observing the sample for electron microscope observation produced with the method mentioned above with an electron microscope.

  According to the present invention, since the sample for observation is prepared by press-contacting the particle and tin, the particle can be easily fixed, so that the electron microscope can be easily observed. Specifically, in order to obtain an observation sample in pressure contact with tin even if the average particle diameter is over 100 nm and not more than 100 μm, the electron beam does not pass through and the internal structure cannot be observed when directly observing. The observation sample can be easily processed. For example, since the cross section of the observation sample can be easily exposed by irradiating an ion beam, observation of particles with an electron microscope is facilitated.

  Further, by using tin, even if the average particle diameter is more than 100 nm and not more than 100 μm and the particles are surface-treated with an organic substance, the internal structure and the surface treatment layer are not damaged, and can be easily observed with an electron microscope. A sample can be prepared. As a result, by measuring the electron microscope observation sample, not only the inside of the particle but also the structure of the surface treatment layer on the particle surface can be easily observed.

Conceptual diagram of a pressure welding object consisting of a powder sample and tin TEM photograph of AlN powder treated with lauryl phosphate (powder whose surface was treated with organic matter) measured in Example 1

  The present invention is a method for producing an observation sample prepared for observing particles with an electron microscope. And the average particle diameter of this particle | grain exceeds 100 nm and is 100 micrometers or less, and this invention produces the sample for observation which has the part which this particle | grain and tin contacted by press-contacting this particle | grain and tin. It is. And it is the method of observing the shape (surface state etc.) and internal structure of this particle | grain with an electron microscope by observing this observation sample with an electron microscope. Hereinafter, the present invention will be described in order.

(Particles to be measured)
In the present invention, the particles to be observed are those having an average particle diameter of more than 100 nm and 100 μm or less. Particles with an average particle diameter of more than 100 nm and not more than 100 μm cannot be observed with an electron microscope as they are, and there is a problem that the internal structure of the particles cannot be observed. Since it is difficult, the method of the present invention can be suitably applied. Therefore, more preferable particles to be observed are those having an average particle diameter of more than 100 nm and 50 μm or less. Furthermore, as a particle size suitable for the observation method, in order to perform SEM observation, since many particles can be observed, particles having an average particle size of more than 100 nm and 10 μm or less are preferable. In order to perform TEM observation, in consideration of the observation region of TEM observation, particles having an average particle diameter of 500 nm or more and 5 μm or less are preferable.

  In addition, in this invention, an average particle diameter means the spherical equivalent diameter (diameter) corresponding to the intermediate value of the particle size distribution (volume distribution) measured by the laser diffraction scattering method. The particle size distribution can be measured by the laser diffraction scattering method using a commercially available laser diffraction scattering type particle size distribution measuring device (for example, MT3300 manufactured by Nikkiso Co., Ltd.).

  In addition, the particle size distribution of the particles is sharp. For example, when the average particle size is R, particles satisfying a minimum particle size of 0.4R or more and a maximum particle size of 2.5R or less included in the sample. In the case of an object, the method of the present invention can be suitably employed. Particles having a particle size of 0.4R to 2.5R have a large gap between the particles when pressed with tin, so the surface state of the particles (including the surface state when the cross section is exposed) is observed. This is preferable because the field of view for doing so increases.

  The particles are not particularly limited as long as they satisfy the requirement that the average particle diameter is in the range of more than 100 nm and not more than 100 μm, and may be organic particles (powder) or inorganic particles (powder). Among these, inorganic particles whose surfaces are coated with an organic substance have a problem in embedding with a resin and are suitable as an object of the present invention. However, the tin particles are limited to those that are not integrated with the tin to be pressed.

  Examples of the inorganic particles include inorganic fillers mixed with the resin, and specific examples thereof include silica, alumina, group III nitride, talc, mica, calcium carbonate, and the like. Among them, the surface is organic, for example, alkyl sulfonic acid such as surfactant, alkyl phosphonic acid, alkyl phosphoric acid, alkyl ammonium, alkyl imidazolium and their salts, and silane coupling agents having organic groups. Things. In addition, the inorganic particles whose surfaces are coated with the organic material may satisfy an average particle diameter in the state of being coated with the organic material in a range of more than 100 nm and 100 μm or less.

(tin)
In the present invention, any tin can be used as long as it is commercially available for industrial use, but the higher the purity, the better. This is to prevent modification due to a chemical reaction between tin and powder. The specific purity is preferably 99.99% or more.

  Tin has an extremely soft Brinell hardness of 5.3 at room temperature, and can be brought into pressure contact with particles at a low pressure. Therefore, even if the particles themselves are easily broken or easily deformable organic particles / inorganic particles, fixation becomes easy, and it is easy to produce an observation sample for an electron microscope (for example, one whose cross section is exposed). Furthermore, even if the surface is an inorganic particle coated with an organic material, an observation sample for an electron microscope can be produced without deforming or altering the structure of the organic material layer.

  In addition, by press-contacting the particles and tin, tin is present in the vicinity of the particles, and the conductive treatment performed prior to processing by the FIB apparatus can be omitted. In addition, by preparing an electron microscope observation sample using tin, it is possible to omit the conductive treatment when observing the exposed cross section with an ion milling apparatus using an SEM. As a result, damage to the surface treatment layer that occurs during the conductive treatment using vapor deposition or the like can be eliminated.

  The shape of the tin that is pressed into contact with the particles is not particularly limited, but if the thickness of the tin before pressure welding is too thin, the resulting pressure contact is very thin and the operability is reduced. It is preferable to use what it has. For example, it is preferable to use a tin piece of about several mm cut from a tin ingot or spherical tin of about several mm in diameter. Specifically, it is preferable to use spherical tin having a diameter of 1 mm to 5 mm for pressure contact with the particles.

(Method of making pressure contact (sample for observation) by pressing particles and tin)
There is no particular limitation on the method for producing the press-contacted product by press-contacting the particles and tin. Specifically, it is sufficient that tin and particles are brought into contact with each other and pressure is applied to the contact object. Specifically, it is possible to use an apparatus that has a mechanism that applies pressure perpendicular to the contact object and that can be pressed by a smooth material that is harder than tin.

  Specific examples of the method for producing the press contact include the following methods. First, when using spherical tin, the surface of the tin is flattened in advance by, for example, a hydraulic press machine before pressure welding. Next, the particles are placed on the flattened tin, and at least a part of the particles is pushed into the tin again by a hydraulic press. The pressure at this time may be a pressure sufficient to push the particles into tin. Since tin is used, it is possible to produce a pressure contact with a small pressure. Note that, in this method, a pressure-contact material in which a part of the particles is in contact with the tin is used, but the pressure-contact material in which the particles are dispersed in the tin is prepared by pressure-bonding so that the tin and the particles are mixed. May be.

  The optimum pressure at the time of pressure welding may be appropriately determined so as to obtain a pressure welded material having a desired shape in consideration of the properties and shape of the target particles and ease of handling of the obtained pressure welded material. When pressed with excessive pressure, the pressed product becomes too thin, which not only makes handling difficult, but may cause damage to the surface treatment layer due to contact between powders. In addition, at the time of pressure welding, it is possible to soften tin by heating and press-contact within a range that does not affect the organic matter on the particle surface.

  The obtained pressure-contact material may be a mixture of tin and particles, but in order to observe the surface structure of the particles, it includes a layer formed from the particles on the tin, and is the thickest layer. It is preferable that the thickness of the portion is three times or more the average particle diameter of the particles. This press contact object can be produced by placing particles on tin and press contact. When the layer thickness of the thickest part of the particles formed on the tin is at least three times the average particle diameter of the particles, the number of measurement points with an electron microscope can be increased. In particular, since the layer has a gap, it becomes a pressure contact material that can be suitably applied when observing the surface of the particles. The upper limit of the particle layer thickness is 10 times the average particle diameter. When this upper limit is exceeded, the particles are liable to be detached from the pressure-contact material, and the operability tends to be lowered. In addition, the layer thickness formed from particle | grains can be confirmed by SEM observation or TEM observation. In addition, although this press-contact thing is explained in full detail below, when performing TEM observation, the protective layer which consists of tungsten, for example can also be formed on the layer formed from particle | grains.

(Method of processing the pressed object (method of preparing a sample for observation) and observation method with an electron microscope)
According to the shape of the press-contact material produced by the above method, it can be observed as it is with an SEM. However, the pressure contact object to be measured can be processed by the following method according to the electron microscope observation method to obtain an observation sample. For example, the surface state of the particles, the state of the interface between the surface and the inside, the internal structure, and the like can be observed by using a pressure contact object whose cross section is exposed by an ion beam as an observation sample.

  A case in which the TEM observation sample is manufactured using the FIB apparatus as the pressure contact object will be described. In this case, a known method can be applied, and the microsampling method is suitable for particles that are the measurement object of the present invention.

  Specifically, a surface deposition process (for example, tungsten deposition) is performed by an FIB apparatus at an arbitrary location on the surface of the pressure contact object, and a protective layer is first formed. The protective layer is subjected to a predetermined electron microscope observation sample preparation process while being processed. By doing so, a layer composed of particles and a protective layer (tungsten) for protecting against flare of an ion beam during processing can be obtained on the tin. The protective layer is not limited to tungsten, and any protective layer can be used as long as it has a composition different from that of the surface treatment layer applied to the surface of the particles.

  Next, the pressure-contacting material on which this protective layer is formed is irradiated with Ga ions to expose the cross-section of the pressure-contacting material and cut into a film thickness of about 100 nm to obtain an observation sample. The processing conditions at this time are not particularly limited, and known conditions can be employed. In this way, the layer made of particles contained in the obtained sample for electron microscope observation is in contact with only particles between the particles in contact with tin, particles in contact with a protective layer such as tungsten, and particles. Can be classified into no particle parts. Among these, in order to observe the internal structure of the particles, observation can be performed in any region. In order to observe the surface treatment layer on the surface of the particle, it is suitable to observe a portion that exists in the middle of the layer made of particles and is in contact only with the particles. In particular, by observing the gap formed when the particles come into contact with each other, the coated state can be confirmed even if the surface is an inorganic particle coated with an organic substance.

  Moreover, when observing the inorganic particle which coat | covered the organic substance on the surface, the kind of electron microscope can also be selected suitably according to the thickness of a surface treatment layer. For example, TEM observation is suitable when the film thickness is as thin as several tens of nm or less. At that time, when the difference in average atomic number between the particles and the surface treatment layer is large, observation with a Z contrast image obtained from STEM observation (scanning TEM) which is one of TEM observation methods is suitable. When the particles are crystalline, the particles and the surface treatment layer can be distinguished from each other by a lattice image obtained by TEM observation. In addition, the surface treatment layer can be visualized from secondary electron images, reflected electron images, X-rays generated by electron beam incidence, and intensity maps of electron beams that have lost specific energy due to interaction with the sample. .

  Although the above method is a method of observing by TEM, the observation sample obtained by the method of the present invention can also be used for SEM observation. For example, since the cross section of the particle can be exposed by exposing the cross section of the pressure contact object with an FIB apparatus or an ion milling apparatus, it can be applied to SEM observation. The method for obtaining an observation sample for SEM observation is not particularly limited, and generally known processing conditions may be employed.

  EXAMPLES Next, although an Example demonstrates this invention in detail, this invention is not limited to a following example.

Example 1
(Preparation of pressure contact)
As the particles to be observed, aluminum nitride (AlN) powder (particles) having an average particle diameter of 1000 nm, the surface of which was coated with a surfactant, dodecyl phosphoric acid, was used. The average particle size was determined as an intermediate value of the particle size distribution (volume distribution) by Nikkiso Co., Ltd. Microtrac HRA. As tin, spherical tin (particle diameter: 2.5 mm) having a purity of 99.9999% manufactured by Mitsuwa Chemicals Co., Ltd. was used.

  500 mg of spherical tin was set in a hydraulic molding machine TM-26 manufactured by Toho Machinery Co., Ltd., and the upper surface was smoothed, and then the AlN powder subjected to the surface treatment was sprinkled with 0.5 mg. The powder and tin were pressed together again with a hydraulic press molding machine (see FIG. 1). The thickness of the pressure contact itself was about 1 mm, and the thickest part of the particle layer was about 4 μm. During pressure welding, the pointer of the pressure gauge attached to the hydraulic press molding machine did not move. By doing so, a pressure contact object having a portion where tin and particles were in contact with each other was produced.

(Preparation of observation sample)
Next, in order to obtain a thin sample for TEM observation, an FIB apparatus (SMI SMI3050) was used.

  Based on the secondary ion microscope (SIM) image observed with the FIB apparatus, a tungsten protective film was formed using W (CO) 6 gas at an arbitrary position where the AlN powder was exposed on the surface of the pressure contact object. Thereafter, a piece of the pressed body was extracted using a microprobing system equipped in the FIB apparatus. One piece of the extracted pressure contact body was fixed to a nanomesh for TEM observation (manufactured by SII Nanotechnology) and processed into a thin piece.

  The flake processing was performed by irradiating Ga ions with an acceleration voltage of 30 kV using an FIB apparatus. In order to suppress damage to the sample, the objective aperture was adjusted so that the beam current value did not exceed 3 nA, and the section thickness was reduced to approximately 100 nm. In this way, a sample for electron microscope observation was produced.

(Electron microscope observation)
The obtained sample for observation was observed with a TEM apparatus (Tecnai F20 manufactured by FEI). Observation is a Z-contrast image obtained by STEM observation using a wide-angle annular dark field detector, which is one of the functions of the TEM apparatus. The result is shown in FIG.

  According to such a method, it was possible to easily observe the appearance of the AlN particles, particularly the vicinity of the surface. As shown in FIG. 2, a layer of organic matter (dodecyl phosphate) is observed on the surface of the AlN particles.

1 inorganic particles (AlN powder),
2 Tin

Claims (6)

  A method for preparing an observation sample prepared for observing particles with an electron microscope, wherein the particles have an average particle diameter of more than 100 nm and not more than 100 μm, and the particles and tin are pressed to contact the particles. A method for producing an observation sample having a portion in contact with tin.   The method according to claim 1, wherein the particles are inorganic particles. The method according to claim 1, wherein the particle is an inorganic particle having a surface coated with an organic substance.   4. The observation sample includes a layer formed of the particles on tin, and the thickness of the thickest portion of the layer is three times or more the average particle diameter of the particles. The method in any one of.   The method according to any one of claims 1 to 4, wherein the observation sample is obtained by irradiating an ion beam onto a pressure-contacted material in which the particles are pressure-contacted on tin to expose a cross section.   A method of observing the particles with an electron microscope by observing the observation sample produced by the method according to claim 1 with an electron microscope.

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