JP2019082476A - Resin-embedded sample - Google Patents

Abstract

To maintain high resolution during observation by suppressing formation of contaminating deposit when irradiating a resin-embedded sample with an electron beam.SOLUTION: Provided is a resin-embedded sample comprised of an object under measurement embedded in a cured resin comprising a resin composition having a structural unit derived from a vinyl group-containing monomer and containing a depolymerizable resin which is depolymerized when its main chain is cut by heat.SELECTED DRAWING: Figure 1

Description

  The present invention relates to resin-embedded samples.

  In recent years, in the research and development of materials, in order to make the materials exhibit new properties, it has been performed to miniaturize the structure of the materials or to add functionality to the outermost surface of the materials. Under the present circumstances, in order to elucidate the expression mechanism of a characteristic, it is required to analyze the property of material in detail. As this analysis method, analysis with a transmission electron microscope is widely used because minute regions can be analyzed from various viewpoints.

  In the analysis by a transmission electron microscope, first, in order to fix an object to be measured, it is embedded in a resin to prepare a resin-embedded sample (see, for example, Patent Document 1). Next, using a microtome machining, a focused ion beam apparatus, an ion milling apparatus or the like, the resin-embedded sample is exfoliated to a thickness that allows transmission of an electron beam. For example, if the acceleration voltage is 200 kV, the thickness is thinned to 100 nm or less. Next, the exfoliated resin-embedded sample is introduced into a transmission electron microscope, and the sample is irradiated with an electron beam accelerated by a high voltage. Then, the form, composition, chemical state, and electronic state of the object to be measured can be analyzed by detecting the transmitted electron beam and the characteristic X-ray generated secondarily.

Unexamined-Japanese-Patent No. 2003-294594

  By the way, in a transmission electron microscope, when a resin-embedded sample is irradiated with an electron beam for a long time, carbon (carbon) deposits on the observation surface of the resin-embedded sample to cause contamination, and the electron image becomes unclear May be Carbon deposition is considered to be caused by hydrocarbon-based gas derived from an apparatus or sample, and when hydrocarbon-based gas irradiates an electron beam to a resin-embedded sample, an electron beam is generated. It gathers as a carbon source in the irradiated area, and deposits repeatedly and gradually accumulates, resulting in the formation of thick contaminated deposits. Such a contaminant deposit thickens the irradiation area of the electron beam in the resin-embedded sample, and reduces the electron beam transmitted through the resin-embedded sample. As a result, the amount of information decreases, the electronic image becomes unclear, and the resolution when observing the resin-embedded sample is greatly reduced.

  An object of the present invention is to provide a technique for suppressing formation of a contamination deposit and maintaining high resolution at the time of observation when the resin-embedded sample is irradiated with an electron beam.

The first aspect of the present invention is
A resin-embedded sample in which an object to be measured is embedded in a cured resin,
The resin cured sample is provided from a resin composition including a depolymerizable resin which contains a structural unit derived from a vinyl group-containing monomer and which is depolymerized by cutting off the main chain by heating. Ru.

A second aspect of the present invention relates to the resin-embedded sample of the first aspect,
The said depolymerizable resin is at least one of a thermosetting resin and a photocurable resin.

A third aspect of the present invention relates to the resin-embedded sample of the first or second aspect,
The said depolymerizable resin is at least one of a (meth) acrylic resin, a (meth) acrylic-modified epoxy resin, a fluorine resin and modified products thereof.

A fourth aspect of the present invention is the resin-embedded sample of any of the first to third aspects, wherein
The said depolymerizable resin is liquid at normal temperature.

A fifth aspect of the present invention relates to the resin-embedded sample of any of the first to fourth aspects, wherein
The cured resin has a heating loss of 1% or less as measured when the temperature is raised from room temperature to 200 ° C. at a temperature rising rate of 20 ° C./min.

A sixth aspect of the present invention is the resin-embedded sample of any of the first to fifth aspects, wherein
When the temperature of the cured resin is raised from room temperature to 200 ° C. at a heating rate of 20 ° C./min, the strength of the gas component of the mass-to-charge number ratio m / z = 41 or 42 detected by the mass spectrometer is It is 5 * 10 <^-11> or less per 1 mg of the said resin cured material.

A seventh aspect of the present invention is the resin-embedded sample of any of the first to sixth aspects, wherein
The cured resin product has a glass transition temperature of 80 ° C. or more and 200 ° C. or less, which is measured when the temperature is raised from room temperature to 200 ° C. at a temperature rising rate of 20 ° C./min.

An eighth aspect of the present invention is the resin-embedded sample of any of the first to seventh aspects, wherein
The cured resin has a pencil hardness of HB or more.

The ninth aspect of the present invention relates to the resin-embedded sample of any of the first to eighth aspects, wherein
The object to be measured is powdery.

A tenth aspect of the present invention is the resin-embedded sample of any of the first to ninth aspects, wherein
For transmission electron microscopy.

  According to the present invention, when the resin-embedded sample is irradiated with the electron beam, the formation of the contamination deposit can be suppressed, and the resolution at the time of observation can be maintained high.

It is a high angle annular dark-field image after irradiating an electron beam with respect to the sample of Example 1. FIG. It is a high angle annular dark-field image after irradiating an electron beam with respect to the sample of Example 2. FIG. It is a high angle annular dark-field image after irradiating an electron beam with respect to the sample of Example 3. FIG. It is a high angle annular dark-field image after irradiating an electron beam with respect to the sample of Example 4. FIG. It is a high angle annular dark-field image after irradiating an electron beam with respect to the sample of the comparative example 1. FIG. It is a high angle annular dark-field image after irradiating an electron beam with respect to the sample of the comparative example 2. FIG. It is a high angle annular dark-field image after irradiating an electron beam with respect to the sample of the comparative example 3. FIG.

  The inventor examined the cause of generation of hydrocarbon-based gas that forms a carbon-containing contaminant deposit. First, it is conceivable that hydrocarbon-based gas is adsorbed on the wall surface in the chamber or the processing surface of the resin-embedded sample and mixed in the chamber. Therefore, the inventor of the present invention bakes the inside of the chamber or the resin-embedded sample or applies a high vacuum to the inside of the chamber to reduce the contamination of the hydrocarbon-based gas into the chamber. The surface was irradiated with an electron beam and observed. However, it has been confirmed that the formation of the contaminant deposit can not be sufficiently suppressed, and the obtained electron image becomes unclear. On the other hand, when the type of resin constituting the resin-embedded sample was changed and examined, it was confirmed that the generation amount of the contaminated deposit fluctuates depending on the type of resin. From this, the hydrocarbon-based gas is derived from the resin of the resin-embedded sample rather than the contamination from the outside, and the hydrocarbon-based gas is generated by the decomposition of the resin in the resin-embedded sample It is guessed.

  The inventor further studied the decomposition of the resin, and the resin is not only deteriorated by the electron beam, but the electron beam staying without being able to pass through the resin-embedded sample is converted into heat, which heat It was thought that the decomposition was possible, and it was speculated that this decomposition product would be released as a hydrocarbon-based gas to form a contaminated deposit. Then, the present inventor paid attention to the form of the decomposition product of the resin, and examined the relationship between the molecular structure of the resin and the formation of the contaminated deposit. As a result, it was found that a resin containing a structural unit derived from a vinyl group-containing monomer and having a chemical structure derived from a vinyl group in its main chain is effective.

  However, it was found that the resin containing the above-mentioned structural unit also has a different thermal decomposition method, and the difference in the degree of formation of a contaminated deposit is different.

  Specifically, the thermal decomposition pattern is roughly classified into a main chain cleavage type in which the main chain is cut by heating and a main chain non-cleavage type in which the main chain is not cut. The main chain cleavage type is further classified into a depolymerization type in which the main chain is cleaved in order from the chain end, and a random decomposition type in which the main chain is cleaved at an arbitrary point according to the manner of end decomposition. On the other hand, the main chain non-cleavage type is classified into a side chain elimination type in which the side chain is eliminated and a main chain carbonization type in which the main chain is carbonized depending on the difference in reaction by heating.

Among the uncleaved main chain types, side-chain desorbed resins increase the contamination deposits because the main chain remains high molecular and tends to carbonize while the side chains are eliminated during thermal decomposition. It is easy to do. Examples of this resin include polyacrylic acid ester and polyvinyl alcohol, and resins having a chlorine group in the side chain.
Among the uncleaved main chain types, the carbonized resin of the main chain has the advantage that the chemical bond of the main chain is strong and thermal decomposition is difficult, but like the side chain detachment type, the side chain is more than the main chain cleavage and dissociation It is easy to increase the contaminating deposits, because it is easy to carbonize by the reaction of crosslinking and cyclization. Examples of this resin include polyacrylonitrile and phenol resin.
Among the main chain cleavage types, although the resin of random decomposition type is cut at the time of thermal decomposition to lower the molecular weight, it is randomly cut from the point where the chemical bond of the main chain is weak, and the polymer main chain is Contamination may be increased because residual carbonization may occur. Examples of this resin include polyethylene and polypropylene.
Among the main chain cleavage type resins, the depolymerization type resin is cleaved at the weak point of the chemical bond at the time of thermal decomposition, and monomers are sequentially separated from the cleavage point. Since the separated thermal decomposition product has a relatively low molecular weight, it is less likely to volatilize to become a carbon residue, and the formation of a contaminant deposit can be suppressed.

  From these facts, the present inventor has found that the formation of a contaminant deposit can be suppressed by using a resin that includes the above-mentioned structural unit and is cut in the main chain to be depolymerized in the resin-embedded sample. It came to create the present invention.

One Embodiment of the Present Invention
Hereinafter, as a resin-embedded sample according to one embodiment of the present invention, a resin-embedded sample for TEM to be used for a transmission electron microscope (TEM) will be described. In addition, the numerical range represented using "-" in this specification means the range which includes the numerical value described before and after "-" as a lower limit and an upper limit.

<Resin-embedded sample>
The resin-embedded sample of the present embodiment is formed by curing the resin after mixing the object to be measured and the resin composition, and is a sample in which the object to be measured is embedded in the cured resin.

  The object to be measured is not particularly limited. For example, a sample consisting of a metal, a metal compound or an inorganic compound can be used. In the present embodiment, since the position of the object to be measured can be fixed by resin embedding, the shape thereof is not particularly limited, and may be powder.

  A resin cured product contains a structural unit derived from a vinyl group-containing monomer, and cures a resin composition containing a depolymerizable resin whose main chain is cut and depolymerized by heating and, if necessary, other additives. It is formed.

The depolymerizable resin is a polymer obtained by reacting a polymerizable monomer containing a vinyl group-containing monomer, and when cured, contains a structural unit derived from the vinyl group-containing monomer and is derived from a vinyl group chemical structure _(-CH 2 -CH ₂ -) is a resin that has a in the main chain. The depolymerizable resin has a depolymerization property such that the main chain is cut at the position of the chemical structure derived from the vinyl group by heating, and thermal decomposition occurs.

  The depolymerizable resin is not particularly limited as long as it has depolymerization properties and can coat the object to be measured and fix the position of the object in the resin-embedded sample. For example, a thermosetting resin having depolymerization characteristics, a photocurable resin having depolymerization characteristics, and a thermoplastic resin having depolymerization characteristics can be used. Among these, it is preferable to use at least one of a thermosetting resin and a photocurable resin from the viewpoint of resin-embedding an object to be measured. Since these resins are liquid at normal temperature (for example, 23 ° C.) and have fluidity, they are excellent in the wrap around to the surface of the object to be measured, and improve the adhesion between the object to be measured and the cured resin. Also, the entrapment of air bubbles in the resin-embedded sample can be reduced.

  In addition, as the depolymerizable resin, a photocurable resin is more preferable because it does not require heating at the time of curing. When the depolymerizable resin is heated and cured, the object to be measured is also heated, and the object to be measured may be oxidized and degraded. In this respect, by using a photocurable resin as the depolymerizable resin, it is possible to suppress the oxidation of the object to be measured due to heating and maintain high analysis accuracy. In addition, since the curing reaction of the photocurable resin is more likely to progress than the thermosetting resin, and the uncured portion is less likely to remain, the formation of the contamination deposit due to the electron beam irradiation can be further reduced.

  In addition, as a thermosetting resin, both the normal temperature curable resin which a polymerization reaction advances also in room temperature environment, and the heat curable resin which a polymerization reaction advances by heating can be used. If the resin is a room temperature curable resin, heating is not required at the time of curing, so it is possible to suppress oxidation and deterioration of the object to be measured. On the other hand, in the case of a thermosetting resin, the curing reaction easily proceeds by heating, and the remaining of the unreacted material can be reduced compared to the thermosetting resin. Formation can be suppressed. Therefore, depending on the type of the object to be measured, such as using a thermosetting resin when the object to be measured does not easily deteriorate due to heat, and using a room temperature curable resin when it is easy to deteriorate due to heat. It is good to select the kind of resin as appropriate. As the heat-curable resin, a resin which is heat-cured at a temperature of 100 ° C. to 130 ° C. is preferable from the viewpoint of not deteriorating the object to be measured excessively.

  Specific examples of the depolymerizable resin include photopolymerizable (meth) acrylic resin, photopolymerizable or thermosetting (meth) acrylic-modified epoxy resin, thermosetting fluorine resin, and modified products thereof. It is preferred to use at least one.

The (meth) acrylic resin is a polymer mainly composed of (meth) acrylic acid ester, and has a main chain having a chemical structure (-CH ₂ -CH _2- ) derived from the vinyl group of (meth) acrylic acid ester. And have depolymerization properties. Examples of (meth) acrylic acid esters include methyl acrylate (MA), ethyl acrylate (EA), butyl acrylate (BA), methyl methacrylate (MMA), ethyl methacrylate (EMA), butyl methacrylate (BMA), 2-hydroxy Ethyl methacrylate (HEMA), benzyl methacrylate (BzMA), cyclohexyl methacrylate (CHMA), methacrylic acid (MAA), 2-ethylhexyl acrylate (HA), cyclohexyl acrylate CHA, diethylene glycol mono 2-ethylhexyl ether acrylate (M120), diethylene glycol mono Phenylether acrylate (M101A), lauryl acrylate (LA), lauryl methacrylate (LMA), isobol Use of acrylate (IBXA), isobornyl methacrylate (IBXMA), 2-phenoxyethyl acrylate (POA), tetrahydrofurfuryl acrylate (THFA), 2-hydroxypropyl acrylate (HPA), benzyl acrylate (BzA), etc. Can. One of these may be used alone, or two or more may be used in combination. Moreover, as a (meth) acrylic resin, you may use the modified body in which the epoxy resin, the urethane resin, etc. were added besides (meth) acrylic acid ester.

The (meth) acrylic-modified epoxy resin is an addition reaction product of (meth) acrylic acid ester and an epoxy resin, and is a resin having an epoxy group and a (meth) acrylic group in a chemical structure. The (meth) acrylic-modified epoxy resin has a chemical structure (-CH ₂ -CH _2- ) derived from the vinyl group of (meth) acrylic acid ester in the main chain, and has depolymerization properties.

  As an epoxy resin used as a raw material, for example, phenol novolac type, ortho cresol novolac type, cresol novolac type, dicyclopentadiene type, biphenyl type, fluorene bisphenol type, triazine type, naphthol type, naphthalene diol type, triphenylmethane type, For example, epoxy resins such as tetraphenyl type, bisphenol A type, bisphenol F type, bisphenol AD type, bisphenol S type, and trimethylolmethane type can be used. One of these compounds may be used alone, or two or more thereof may be used in combination.

  Moreover, as a (meth) acrylic acid ester added to an epoxy resin, what has an epoxy group can be used, for example, a glycidyl acrylate, a glycidyl methacrylate, etc. can be used, for example.

  As the fluorine resin, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or the like can be used. The monomer which comprises these has the fluorovinyl group by which one part or all part of hydrogen of a vinyl group was substituted by the fluorine, and has the depolymerization characteristic which depolymerizes by heating.

In the resin composition, a curing agent for curing the depolymerizable resin is blended.
When a (meth) acrylic resin is used as the depolymerizable resin, it is preferable to use a photopolymerization initiator for photocuring. As the photopolymerization initiator, a kind capable of absorbing the wavelength of the irradiation light may be appropriately selected, and examples thereof include photoradical polymerization initiators such as benzophenone type, thioxanthone type, acetophenone type, and acyl phosphine type. It is good to mix | blend about 1 mass%-10 mass% with respect to a (meth) acrylic resin. For example, cationic photopolymerization initiators such as allyldiazonium salts, diallyliodonium salts, and triallylsulfonium salts can also be used.
When a (meth) acrylic-modified epoxy resin is used as the depolymerizable resin, it is preferable to change the type of the curing agent to be blended according to the curing method of light curing or heat curing. For example, an amine-based curing agent, an imidazole-based curing agent, a phenol-based curing agent, an acid anhydride curing agent, an ultraviolet curing agent, and the like can be used. Specifically, amine compounds such as organic amine compounds and diamides, imidazole compounds such as 2-methylimidazole and 2-ethyl-4-methylimidazole, dihydric phenol compounds such as bisphenol A and bisphenol F, succinic anhydride, Acid anhydrides such as maleic anhydride, phthalic anhydride, trimellitic anhydride and pyromellitic anhydride, benzoins such as benzoin, benzoin methyl ether and benzoin ethyl ether, benzophenones such as α-hydroxyisobutylphenone and benzophenone Anthraquinones such as acetophenone, 9,10-anthraquinone, 1-chloroanthraquinone and the like can be used. Two or more of these may be used in combination as necessary. Among these, an imidazole-based curing agent is preferable because it is easy to adjust the glass transition temperature of the cured resin cured product.
In the case of using a fluorine resin as the depolymerizable resin, for example, polyisocyanate or the like can be used.

  The cured resin product has a weight loss on heating of 1% or less, which is measured when the temperature is raised from an ambient temperature to 200 ° C. at a heating rate of 20 ° C./min. preferable. That is, it is preferable to use a depolymerizable resin such that the heat loss of the cured resin becomes 1% or less. The heating loss represents the weight loss of the cured resin when the cured resin is heated in a predetermined heating pattern. According to the study of the present inventor, in the resin-embedded sample, in the case where the polymerization reaction of the depolymerizable resin is insufficient and a large amount of low molecular components and unreacted curing agent remain in the cured resin, electron By heating by radiation, these components are pyrolyzed to generate a hydrocarbon-based gas, which tends to form contaminant deposits. In this respect, by configuring the cured resin to have a heating loss of 1% or less, the curing reaction can be sufficiently performed to reduce the ratio of the low molecular component, the unreacted curing agent, etc. It is possible to suppress the generation of hydrocarbon gas due to

The mass of the cured resin is detected by the mass spectrometer among the gas components generated when the temperature is raised from room temperature to 200 ° C. at a temperature rising rate of 20 ° C./min in the mass spectrometer and reached 200 ° C. The strength of the gas component having a charge number ratio m / z = 41 or 42 is preferably 5 × 10 ⁻¹¹ or less per 1 mg of the cured resin, and more preferably 2 × 10 ⁻¹¹ or less. preferable.

Here, the knowledge which this inventor acquired about the intensity | strength of a gas component is demonstrated.
When the temperature of the cured resin is raised from room temperature to 200 ° C. by heating with a mass spectrometer, gas components such as a mass to charge ratio m / z = 15, 27, 30, 41, 42, 55 are detected. These gas components are hydrocarbon-based gases and are generated not only by thermal decomposition of the uncured product remaining in the cured resin, but also the cured resin itself is degraded, and the main chain and side of the resin It is also generated when the chain is broken and thermally decomposed. When these gas components are measured by a mass spectrometer, the amount of gas components generated can be determined as the intensity for each mass-to-charge ratio.
According to the study of the present inventor, it was confirmed that the smaller the amount of the gas component of m / z = 41 or 42 generated among the resin cured products, the less the formation of the contamination deposit. On the other hand, other gas components such as m / z = 15 may not have much correlation with the formation of the contaminated deposit, for example, because the contaminated deposit may be small although the amount is large. Was confirmed. From this, when the correlation between the strength of the gas component of m / z = 41 or 42 and the formation of the contamination deposit was further examined, the strength of the gas component of m / z = 41 or 42 was converted to unit weight (resin curing It was found that, according to the resin cured product having a ^{concentration} of 5 × 10 ⁻¹¹ or less per 1 mg of the substance, the generation of hydrocarbon-based gas can be reduced, and the formation of the contamination deposit can be further suppressed.

  The reason for converting the strength of the gas component to unit weight is that the strength of the gas component measured by the mass spectrometer fluctuates according to the weight of the cured resin. Specifically, the amount of the gas component detected by the mass spectrometer is determined as the intensity for each mass-to-charge ratio. The strength required at this time fluctuates according to the weight of the resin cured product so that it increases as the weight of the resin cured product increases. Therefore, in the present embodiment, by dividing the strength of the gas component to be measured by the weight of the cured resin, the amount of gas generation of the cured resin is specifically determined by the unit weight of the cured resin. It is determined as the strength per 1 mg of substance. Thereby, the influence of the fluctuation due to the weight of the cured resin can be cancelled.

  Further, the gas component having a mass-to-charge ratio m / z = 41 and the gas component 42 have, for example, the same charge, and exhibit gas components having different mass numbers depending on the difference in the number of hydrogen. Depending on the type of resin, gas components of m / z = 41 or 42 or both of them are generated, but when both gas components are generated, their respective strengths should be less than the above range.

  The cured resin product has a glass transition temperature (hereinafter also referred to as Tg) of 80 ° C. to 200 ° C., which is measured when the temperature is raised from room temperature to 200 ° C. at a temperature rising rate of 20 ° C./min. Is preferred. In other words, it is preferable to use a depolymerizable resin such that the Tg of the resin cured product is 80 ° C to 200 ° C. When the Tg of the cured resin is excessively low, the resin-embedded sample may be softened and deformed during electron beam irradiation, but the Tg of the cured resin may be 80 ° C. or higher to deform the resin-embedded sample. Can be maintained to maintain high resolution of the electronic image obtained by the measurement. In addition, if the Tg is excessively low, the hardness of the cured resin tends to be low. For example, when the resin-embedded sample is thin-processed by ion milling, unevenness is generated on the processing surface and desired smoothness is obtained. May not be obtained. In this regard, by setting the Tg to 80 ° C. or more, appropriate smoothness can be obtained at the time of processing. Furthermore, among the depolymerizable resins, resins that have a Tg of 80 ° C. or higher when cured have a higher degree of polymerization than resins below 80 ° C., and tend to be easily depolymerized by heating. On the other hand, when the Tg of the cured resin is excessively high, the fluidity of the depolymerizable resin forming the resin becomes low and it becomes difficult to embed the object under test, but the Tg should be 200 ° C. or less Thus, it is possible to select a depolymerizable resin having appropriate fluidity. As Tg of a resin cured material, 100 to 200 degreeC is more preferable, and 100 to 150 degreeC is further more preferable.

  The cured resin preferably has a pencil hardness of HB or more. According to the resin cured product having such hardness, when the resin-embedded sample is thin-processed by ion milling or the like, the occurrence of unevenness on the processed surface can be suppressed and appropriate smoothness can be realized. The resolution can be maintained high.

  Subsequently, preparation of a resin-embedded sample will be described. In the present embodiment, as an object to be measured, a metal powder which is easily oxidized by heating will be described as an example.

First, a metal powder is mixed with a resin composition containing a depolymerizable resin and an additive. At this time, as the depolymerizable resin, a photocurable resin having depolymerization properties and which does not require heating is used as an additive, and a photopolymerization initiator is used. As the depolymerizable resin, for the cured resin cured product, the strength of the gas component with a weight loss on heating of 1% or less and a mass to charge ratio m / z = 41 or 42 by mass spectrometry is 5 per 1 mg of the cured resin × ^{10 -11} or less, it is preferable to use a resin such as glass transition temperature Tg of 80 ° C. to 200 DEG ° C., or a pencil hardness of greater than or equal to HB. The concentration of the metal powder with respect to the resin composition is not particularly limited, but the metal powder may interfere with light irradiation to the resin, so the concentration may be such that the curing reaction can proceed appropriately.

Subsequently, the mixed mixture is formed into a film, and the formed product is irradiated with light. The wavelength of the irradiation light may be appropriately changed in accordance with the type of the photopolymerization initiator. For example, single-shot light having wavelengths near 250 nm, 365 nm, and 450 nm, or composite light including three wavelength ranges is emitted. As the irradiation conditions, for the irradiation light of 365 nm, for example, the intensity of the irradiation light may be 15 mW / cm ² as an output, the distance between the lamp of the irradiation device and the compact may be 10 cm, and the irradiation time may be 5 to 60 seconds. . The thickness of the formed body is not particularly limited as long as it can be sufficiently cured in the thickness direction, and may be appropriately changed according to the concentration of the metal powder. For example, when mixing a photocurable resin and metal powder by mass ratio 1: 1, it is good for the thickness of a molded object to be 0.1 mm-1 mm.

  The resin-embedded sample of the present embodiment can be obtained by curing the photocurable resin by light irradiation to form a cured resin.

  The obtained resin-embedded sample is exfoliated, for example, by ion milling or the like to be processed into a exfoliated sample for TEM.

  In addition, although the case where a photocurable resin and a photopolymerization initiator were included was demonstrated above as an example, it can also change into the combination of a thermosetting resin and a hardening | curing agent. For example, if the object to be measured is easily oxidized and degraded, it is preferable to use a resin composition containing a room-temperature curable resin and a curing agent (such as a two-component thermosetting epoxy resin). Also, for example, if the object to be measured does not deteriorate easily, it is preferable to heat and cure it in a range of about 100 ° C. to 130 ° C. using a resin composition containing a thermosetting resin and a curing agent.

<Effect according to the present embodiment>
According to this embodiment, one or more of the following effects can be obtained.

  In the present embodiment, the object to be measured is embedded with a resin composition containing a depolymerizable resin which contains a structural unit derived from a vinyl group-containing monomer and whose main chain is cut and depolymerized by heating, and is cured. , Constitute a resin-embedded sample. Even when the resin-embedded sample of the present embodiment is heated by irradiation with an electron beam, the depolymerizable resin constituting the cured resin product is a site where the chemical bond in the main chain is weak (chemistry derived from vinyl group) Cleavage at the location of the structure) and depolymerization by sequential separation of the monomers. And since the decomposition product generated by this depolymerization has a low molecular weight and is difficult to form carbon residue by electron beam, the formation of a contamination deposit is suppressed. Therefore, according to the resin-embedded sample of the present embodiment, since the formation of the contamination deposit can be suppressed when the electron beam is irradiated, the resolution of the electron image can be maintained high, and high resolution can be obtained. .

For example, polyethylene or polypropylene has a chemical structure derived from a vinyl group, but is a main chain cleavage-random decomposition type, and when heated, the chemical structure of the main chain is randomly selected from the weak chemical bond from the chemical structure. Since the polymer main chain tends to be cut off and carbonized, a contamination deposit is easily formed.
Also, for example, polyacrylates and polyvinyl alcohols are of the main chain non-cleavage-side chain elimination type, and from their chemical structure, while the side chains are eliminated during thermal decomposition, the main chain is a polymer. It is likely to remain in the form of carbonized and to form contaminated deposits.
Also, for example, polyacrylonitrile, phenol resin, and the like are of the main chain non-cleavage-main chain carbonization type, chemical bonds of the main chain tend to be strong due to their chemical structures, and side chains are released during thermal decomposition. Since the main chain is hard to be cut, it is carbonized to easily form a contaminated deposit.
For example, as resin which does not have a chemical structure derived from a vinyl group, condensation ester resin (polycarbonate, polyethylene terephthalate and polylactone etc.), condensation amide resin (nylon 6 and polyimide etc), ether resin (polyoxyethylene) And polydimethylsiloxanes) and diene resins (polybutadiene etc.), but they do not have the property of depolymerizing when heated, so they are easily carbonized to form a contaminated deposit.

Further, the depolymerizable resin is preferably at least one of a thermosetting resin and a photocurable resin having depolymerization properties.
Among the thermosetting resins, according to the room-temperature curable resin, since it is not necessary to heat for curing, it is possible to resin-embed an object to be measured which is oxidized by heating.
Among thermosetting resins, heat curing resins can accelerate the curing reaction, for example, by heating at about 100 ° C. to 130 ° C., so that the curing time can not only be shortened compared to room temperature curing resins, It is possible to suppress the remaining of the uncured portion and the unreacted curing agent, and to reduce the generation of hydrocarbon gas by electron beam irradiation. In addition, since the curing reaction easily proceeds, the hardness of the cured resin can be made higher than that of a room temperature curable resin.
According to the photocurable resin, there is no need to heat for curing, and the curing reaction proceeds more easily than the thermosetting resin, so the object to be measured is not limited, and contamination deposits by electron beam irradiation Can be suppressed.

  Further, specifically, the depolymerizable resin is preferably at least one of (meth) acrylic resin, (meth) acrylic-modified epoxy resin, fluorocarbon resin and modified products thereof. Among these, (meth) acrylic resins and (meth) acrylic-modified epoxy resins are more preferable because high hardness is obtained when they are cured.

  In addition, the depolymerizable resin is preferably liquid at normal temperature. By using a resin that is liquid at normal temperature, even if the object to be measured is powdery, the resin is made to wrap around the surface of the object to be measured, and the object to be measured is more reliably fixed in the cured resin. be able to.

  The cured resin preferably has a heating loss of 1% or less. Among the depolymerizable resins, according to the depolymerizable resin which makes the heating loss upon curing be 1% or less, unreacted monomers or uncured monomers when the resin cured product of the resin-embedded sample is constituted Since the remaining of the curing agent can be reduced, it is possible to suppress the generation of hydrocarbon-based gas due to electron beam irradiation and the formation of contamination deposits accompanying it.

When the temperature of the cured resin is raised from room temperature to 200 ° C. at a temperature rising rate of 20 ° C./min, the strength of the gas component of the mass to charge ratio m / z = 41 or 42 detected by the mass spectrometer is a resin It is preferable that it is 5 * 10 <^-11> or less per 1 mg of hardened | cured material. Among depolymerizable resins, depolymerizable such that the strength of the gas component of m / z = 41 or 42 detected when curing and mass spectrometry is 5 × 10 ⁻¹¹ or less in unit weight conversion According to the resin, by forming the cured resin product of the resin-embedded sample, even if the resin-embedded sample is heated by electron beam irradiation, the hydrocarbon-based gas is reduced and the contamination deposit is formed. Can be suppressed.

  The cured resin preferably has a glass transition temperature Tg of 80 ° C. to 200 ° C. Among the depolymerizable resins, according to the depolymerizable resin which has a Tg of 80 ° C. to 200 ° C. when cured, thermal deformation of the resin-embedded sample due to electron beam irradiation is suppressed, and a cured resin product is also obtained. The hardness of the above can be increased to form a smooth processed surface at the time of thin film processing.

  The cured resin preferably has a pencil hardness of HB or more. Among the depolymerizable resins, according to the depolymerizable resin having a pencil hardness of HB or more, when the resin-embedded sample is thin-processed by ion milling or the like, generation of irregularities on the processed surface is suppressed. Moderate smoothness can be realized, and the resolution of the electronic image can be maintained high.

  Hereinafter, the present invention will be described based on further detailed examples, but the present invention is not limited to these examples.

Example 1
In this example, in order to evaluate the resin component alone without the influence of the object to be measured, the resin composition is cured without mixing the object to be measured, and various evaluations are performed using the obtained resin cured product as a sample. Did.

(1) Preparation of sample Specifically, first, as a depolymerizable resin, prepare a (meth) acrylic modified epoxy resin which is an addition polymer of an epoxy resin containing bisphenol F and glycidyl acrylate, and as a cured product, 2 -A resin composition was prepared by mixing methylimidazole. The resin composition was uniformly applied at a thickness of 0.3 mm, and was cured by heating at 120 ° C. for 30 minutes in the air. Thus, a resin cured product as a sample was obtained. The (meth) acrylic-modified epoxy resin of Example 1 includes a structural unit derived from a vinyl group-containing monomer, and has a depolymerization property in which the main chain is cut and depolymerized by heating.

(2) Evaluation method of sample About the obtained resin cured product, heating loss, mass-to-charge ratio m / z = 15, 30, 41 generated amount of gas component, glass transition temperature Tg, hardness, by electron beam irradiation The formation of the contaminated deposit and the processing flaws were evaluated as shown below.

(Generation of gas component and heating loss)
The amount of loss on heating and the amount of gas component generation and the amount on heating loss due to the mass-to-charge ratio m / z = 15, 30, 41 are measured by a thermobalance (manufactured by Bruker AXS Co., Ltd.) as a mass spectrometer (Q-MS, Bruker AXS Co., Ltd.) is installed, and the temperature of the cured resin is raised from room temperature to 400 ° C. at a heating rate of 20 ° C./min, with a He flow rate of 150 cc / min. Measured by an analyzer. The strength per unit weight of each gas component was determined by dividing the measured strength by the weight of the sample [mg].

(Glass transition temperature Tg)
The glass transition temperature Tg is raised from room temperature to 200 ° C. at a temperature rising rate of 20 ° C./min and an argon flow rate of 150 cc / min with a differential thermal analyzer (DSC, manufactured by Netti Japan Co., Ltd.). It was warmed and measured by detecting a change in heat flow associated with heat absorption and heat absorption of the resin.

(hardness)
The hardness was determined on the surface hardness of the cured resin in accordance with “4.4 Scratch hardness (pencil method)” in JIS-K-5600 paint general test method. Specifically, using a pencil with a hardness of 6B to 9H manufactured by Mitsubishi Pencil Co., Ltd., the core is applied at an angle of 45 ° to the sample by a hand writing method, and 1 cm at a uniform speed while pressing strongly against the sample surface I pushed it out and scratched the surface. This was repeated five times, changing the location and checking the hardness of the scratched pencil.

(Contaminated sediments)
The formation of the contamination deposit is determined by first processing the cured resin into a sample for TEM, irradiating the sample with an electron beam, and confirming the presence or absence of the deposition of the contamination deposit in the area irradiated with the electron beam. did. Specifically, the obtained resin cured product is attached to a microtome, trimmed using a diamond knife, rough processing of the observation surface is performed, and then a focused ion processing apparatus (FIB, manufactured by Hitachi High-Technologies Corporation) is used It processed so that thickness might be set to 100 nm or less, and the thin sample for TEM was produced. Subsequently, this thin section sample for TEM is introduced into a transmission electron microscope ("JEM-ARM200F" manufactured by Nippon Denshi Co., Ltd.), and a high-angle annular dark-field image (High-Angle-Annular-Dark-Field) image (hereinafter HAADF) (Also called an image). The HAADF image is scanned with an electron beam at a magnification of × 1,000,000 and a pixel count of 1000 × 1000 for 30 seconds / frame against a thin sample for TEM with a transmission electron microscope, and then × 500, By scanning the electron beam at 30 seconds / frame with 1000 × 1000 pixels at a magnification of 000 and finally scanning the electron beam at 30 seconds / frame with 1000 × 1000 pixels at a × 100,000 magnification I got it.

(Machining scratch)
The processed flaws were confirmed by TEM when the cured resin was processed into a TEM sample.

(3) Evaluation Results The evaluation results for the samples of Example 1 are summarized in Table 1 below.
As shown in Table 1, in the sample of Example 1, the weight loss due to heating when heated up to 200 ° C. is 0.9%, and the mass-to-charge number ratio m / z generated when heated up to 200 ° C. It was confirmed that the gas component with = 41 has a unit weight conversion of 4 × 10 ⁻¹¹ , a glass transition temperature Tg of 120 ° C., and a hardness of 2H. Moreover, the HAADF image acquired from the sample of Example 1 is shown in FIG. According to FIG. 1, it is confirmed that the contrast is not significantly changed between the electron beam irradiated area (within the frame in the figure) and the unirradiated area of the electron beam, and the contamination deposit is present in the electron beam irradiated area. It turned out that it was not formed so much. That is, the sample of Example 1 has less generation of contamination deposits and high resolution at the time of observation.

(Example 2)
In Example 2, a (meth) acrylic resin which is a photocurable resin obtained by mixing methacrylic acid (MAA) and 2-ethylhexyl acrylate (HA) is prepared as a depolymerizable resin, and isopropylthioxanthone as a photopolymerization initiator Were mixed to prepare a resin composition. This resin composition was uniformly applied at a thickness of 0.3 mm, and was cured by exposure for 30 seconds with a wavelength of 365 nm and 15 mW / cm ² and an interval between the exposure light source and the object of 10 cm using a UV irradiation device. Thus, a resin cured product as a sample was obtained. The (meth) acrylic resin of Example 2 contains a structural unit derived from a vinyl group-containing monomer, and has a depolymerization property in which the main chain is cut and depolymerized by heating.

The sample of Example 2 was evaluated in the same manner as in Example 1. As a result, it was confirmed that the strength of the gas component with m / z = 41 was 1 × 10 ⁻¹³ and was 5 × 10 ⁻¹¹ or less. . Moreover, about the sample of Example 2, it was confirmed that there are no processing flaws, 0.3% of heat loss, glass transition temperature Tg is 90 degreeC, hardness is HB, and processing.
An HAADF image obtained from the sample of Example 2 is shown in FIG. According to FIG. 2, similarly to Example 1, it was confirmed that the contrast was not largely changed between the irradiated area and the unirradiated area of the electron beam, and the generation of the contamination deposit was small. In addition, since the photocurable resin is used as the depolymerizable resin when Example 2 is compared with Example 1, the remaining uncured material can be reduced compared to the case where a thermosetting resin is used. It was confirmed that the heating loss of the cured resin and the gas component of m / z = 41 can be reduced.

(Example 3)
In Example 3, a measurement target was mixed with the resin composition prepared in Example 2 to prepare a resin-embedded sample, and evaluation was performed in the same manner as in Example 1. Specifically, 50 mg of a positive electrode active material (LCO: average particle diameter 10 μm) for a lithium secondary battery as an object to be measured was mixed with 50 mg of a depolymerizable resin to prepare a resin composition. The resin composition was uniformly applied at a thickness of 0.15 mm, exposed to light and cured under the same conditions as in Example 2, and a sample (resin-embedded sample) was produced.

The sample of Example 3 was evaluated in the same manner as in Example 2. As a result, the strength of the gas component having a mass-to-charge number ratio m / z = 41 is 5 × 10 ⁻¹² and is 5 × 10 ⁻¹¹ or less. It was confirmed that there is. Moreover, about the sample of Example 3, it was confirmed that a heating loss is 0.7% and there is no process flaw. In Example 3, since the glass transition temperature Tg and the hardness change due to the presence of the object to be measured in the sample, these numerical values are not determined.
Moreover, the HAADF image acquired from the sample of Example 3 is shown in FIG. According to FIG. 3, as in Example 1, it was confirmed that the contrast was not significantly changed between the area irradiated with the electron beam and the area not irradiated with the electron beam, and the generation of the contamination deposit was small.

(Example 4)
In Example 4, a polyvinylidene fluoride (PVDF) was used as a depolymerizable resin, and a polyisocyanate was mixed as an additive to prepare a resin composition. The resin composition was allowed to cure in an environment of 150 ° C. for 2 hours to prepare a sample of Example 4. The polyvinylidene fluoride of Example 4 contains a structural unit derived from a vinyl group-containing monomer, and has a depolymerization property in which the main chain is cut and depolymerized by heating.

The sample of Example 4 is evaluated in the same manner as in Example 1. As a result, the strength of the gas component having a mass-to-charge number ratio m / z = 41 is 1 × 10 ⁻¹³ and 5 × 10 ⁻¹¹ or less. Was confirmed. Moreover, about the sample of Example 4, it was confirmed that heat-loss is 0.1%, glass transition temperature Tg is -40 degreeC, and hardness is 4B.
Moreover, the HAADF image acquired from the sample of Example 4 is shown in FIG. According to FIG. 4, similarly to Example 1, it was confirmed that the contrast was not significantly changed between the electron beam irradiated area and the non-irradiated area, and the generation of the contamination deposit was small. In Example 4, since the hardness of the resin cured product formed from the fluorocarbon resin was low, as shown in FIG. 4, processing flaws were confirmed on the processed surface of the TEM sample.

(Comparative example 1)
In Comparative Example 1, instead of a depolymerizable resin, an epoxy-modified polyimide resin obtained by adding bisphenol F to N-hydroxyethyl phthalate is used to mix a 2-methylimidazole system as a cured product to obtain a resin composition. Prepared. As in Example 1, this resin composition was cured by heating for 30 minutes at a temperature of 120 ° C. in the air to prepare a sample. The epoxy-modified polyimide resin of Comparative Example 1 has a condensation amide type structure, and belongs to the main chain non-cleavage-side chain release type.

The sample of Comparative Example 1 was evaluated in the same manner as Example 1. As a result, the strength of the gas component having a mass-to-charge number ratio m / z = 41 was 8 × 10 ⁻¹¹ and was larger than 5 × 10 ^−11. Was confirmed. Moreover, about the sample of the comparative example 1, it was confirmed that there are no processing flaws, 2.0% of heating loss, 240 degreeC of glass transition temperature Tg, hardness 2H.
Moreover, the HAADF image acquired from the sample of the comparative example 1 is shown in FIG. According to FIG. 5, it has been confirmed that the irradiation area of the electron beam is brighter than the non-irradiation area. In the HAADF image, the thicker the portion of the sample through which the electron beam passes, the larger the number of atoms interacting with the electron beam, and the brighter the observation. Therefore, in the sample of Comparative Example 1, it was confirmed that the electron beam irradiated area was thicker than the non-irradiated area, and the contamination deposit was formed thick in the electron beam irradiated area.

(Comparative example 2)
In Comparative Example 2, instead of the depolymerizable resin, a urethane-modified (meth) acrylic resin obtained by adding urethane acrylate (UA) to methacrylic acid (MAA) is mixed with benzyldimethyl ketal as a photopolymerization initiator. The resin composition was prepared. The resin composition was exposed to light and cured under the same conditions as in Example 2 to prepare a sample of Comparative Example 2. In addition, although the urethane modified (meth) acrylic resin of the comparative example 2 contains the structural unit derived from a vinyl group containing monomer, it belongs to a principal chain cleavage-random decomposition type.

The sample of Comparative Example 2 was evaluated in the same manner as Example 1. As a result, the strength of the gas component having a mass-to-charge number ratio m / z = 41 was 1 × 10 ⁻¹⁰ and was larger than 5 × 10 ^−11. Was confirmed. Moreover, about the sample of the comparative example 2, it was confirmed that there are 7% of heating loss, glass transition temperature Tg is 110 degreeC, hardness is HB, and a process flaw.
Moreover, the HAADF image acquired from the sample of the comparative example 2 is shown in FIG. According to FIG. 6, it was confirmed that the irradiated area of the electron beam was brighter than the non-irradiated area, and the contaminated deposit was formed thick, as in Comparative Example 1.

(Comparative example 3)
In Comparative Example 3, a resin composition was prepared by using polyester (PE) instead of the depolymerizable resin and mixing benzoyl peroxide as an organic peroxide as an additive. The resin composition was allowed to cure in an environment of 24 ° C. for 18 hours to prepare a sample of Comparative Example 3. In addition, although the polyester of the comparative example 3 contains the structural unit derived from a vinyl group containing monomer, it belongs to a principal chain cleavage-random decomposition type.

The sample of Comparative Example 3 was evaluated in the same manner as Example 1. As a result, the strength of the gas component having a mass-to-charge number ratio m / z = 41 was 3 × 10 ⁻¹⁰ and was larger than 5 × 10 ^−11. Was confirmed. Moreover, about the sample of Comparative Example 3, it was confirmed that the heat loss is 9%, the glass transition temperature Tg is 60 ° C., and the hardness is B. Moreover, it was confirmed that a processing flaw is slightly formed.
Moreover, the HAADF image acquired from the sample of the comparative example 3 is shown in FIG. According to FIG. 7, it was confirmed that the irradiated area of the electron beam was brighter than that of the non-irradiated area, and the contaminated deposit was formed thick as in Comparative Example 1.

As described above, contamination deposition when a resin-embedded sample is irradiated with an electron beam by using a depolymerizable resin having a chemical structure derived from a vinyl group in the main chain as a resin for embedding an object to be measured The formation of objects can be suppressed, and high resolution can be obtained.

Claims (10)

A resin-embedded sample in which an object to be measured is embedded in a cured resin,
The resin cured sample is formed from a resin composition containing a depolymerizable resin which contains a structural unit derived from a vinyl group-containing monomer and which is depolymerized by cutting the main chain by heating. The said depolymerizable resin is at least one of a thermosetting resin and a photocurable resin,
The resin-embedded sample according to claim 1. The said depolymerizable resin is at least one of a (meth) acrylic resin, a (meth) acrylic-modified epoxy resin, a fluorine resin, and their modified products,
The resin-embedded sample of Claim 1 or 2. The depolymerizable resin is liquid at normal temperature,
The resin-embedded sample of any one of Claims 1-3. The cured resin has a heating loss of 1% or less as measured when the temperature is raised from room temperature to 200 ° C. at a heating rate of 20 ° C./min.
The resin-embedded sample of any one of Claims 1-4. When the temperature of the cured resin is raised from room temperature to 200 ° C. at a heating rate of 20 ° C./min , the strength of the gas component of the mass-to-charge number ratio m / z = 41 or 42 detected by the mass spectrometer is 5 × 10 ⁻¹¹ or less per 1 mg of the cured resin .
The resin-embedded sample of any one of Claims 1-5. The cured resin has a glass transition temperature of 80 ° C. or more and 200 ° C. or less, which is measured when the temperature is raised from room temperature to 200 ° C. at a temperature rising rate of 20 ° C./min.
The resin-embedded sample of any one of Claims 1-6. The cured resin has a pencil hardness of HB or more.
The resin-embedded sample of any one of Claims 1-7. The object to be measured is in powder form,
The resin-embedded sample of any one of Claims 1-8. For transmission electron microscopy,
The resin-embedded sample of any one of Claims 1-9.