Patent Application
20130070905
The present invention relates to an X-ray waveguide formed of a core and a cladding, in particular, an X-ray waveguide whose core is such that a low electron density portion is provided in a high electron density portion.
As in the case of a conventional optical waveguide used in a visible light region or the like, a waveguide for an X-ray is of a configuration formed of a core and a cladding which surrounds the periphery of the core and has a smaller refractive index than that of the core, and is mainly used for obtaining an X-ray having a small beam size and a strong intensity. In the case of the waveguide for an X-ray, the X-ray is made incident on the waveguide at a small angle as compared with that of, for example, the waveguide for the visible light region because of the following reason. The refractive index of a substance for the X-ray is close to 1, and hence a difference in refractive index between the core and the cladding cannot be made very large. In addition, an allowance range for the incidence angle of the X-ray for forming a guided mode (coupling) to propagate an X-ray is narrow, and hence it has been necessary to perform precise axis adjustment by reducing the divergence angle of the incident X-ray.
F. Peiffer et al., Phys. Rev. B62, p. 16939 to 16943 discloses an X-ray waveguide using an artificial multilayer film as a core. Used in F. Peiffer et al., Phys. Rev. B62, p. 16939 to 16943 described above is an artificial multilayer film having unit structures obtained by alternately forming, on a substrate, a member formed of carbon having a low electron density (low electron density portion) and a member formed of nickel having a high electron density (high electron density portion) by magnetron sputtering. The X-ray waveguide has a lager allowance range for the incidence angle of an X-ray than that of an X-ray waveguide whose core is uniformly formed because X-rays localized in the laminated low electron density portions of the artificial multilayer film interact with each other. The allowance range for the incidence angle is large, and hence even X-rays that have diverged to some degree can be efficiently coupled. Accordingly, a transmitted X-ray having an additionally strong intensity can be obtained.
However, F. Peiffer et al., Phys. Rev. B62, p. 16939 to 16943 involves a problem to be solved. That is, in a guided mode, an X-ray propagates in the waveguide while most of the intensity of the X-ray converges on the low electron density portion. As the electron density of a material increases, the linear absorption coefficient of the material for an X-ray generally increases, though whether or not the coefficient increase depends on the atomic composition of the material. However, the transmitting performance of the artificial multilayer film disclosed in F. Peiffer et al., Phys. Rev. B62, p. 16939 to 16943 for an X-ray cannot help being limitative because carbon is used in the low electron density portion and hence the electron density of the portion is still high. In view of the foregoing, an X-ray waveguide using a material having a lower electron density than that of carbon in a low electron density portion has been requested.
The present invention has been made in view of such background art, and provides an X-ray waveguide having a high transmittance for an X-ray and a method of producing the waveguide by providing a core with a low electron density portion having a low electron density.
An aspect of the present invention is an X-ray waveguide including: a core for guiding an X-ray; and a cladding for confining the X-ray in the core, wherein: the core has a low electron density portion and a high electron density portion having a higher electron density than an electron density of the low electron density portion; the low electron density portion is provided in the high electron density portion; and the low electron density portion is formed of one of a pore and an organic substance. Further aspects of the present invention will become apparent from the following description of embodiments.
According to the present invention, there can be provided an X-ray waveguide having a high transmittance for an X-ray and a method of producing the waveguide by forming a low electron density portion used in a core from a pore or an organic substance.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.
An X-ray waveguide according to the present invention is an X-ray waveguide formed of a core and a cladding, and is characterized in that: the core is such that a low electron density portion having a low electron density is provided in a high electron density portion having a high electron density; and the low electron density portion is formed of a pore or an organic substance.
In particular, the waveguide is characterized in that: the core is formed of a laminating structure obtained by laminating unit structures in each of which the low electron density portion is provided in the high electron density portion in a certain direction; and the laminating direction of the unit structures of the laminating structure is a direction perpendicular to the propagating direction of an X-ray. Note that, the term “X-ray” as used in the present invention refers to electromagnetic waves in such a wavelength band that the refractive index real part of a substance is 1 or less. Specifically, the term “X-ray” as used in the present invention refers to electromagnetic waves each having a wavelength of 100 nm or less including extreme ultraviolet light (EUV light).
In addition, the core 14 is a laminating structure obtained by laminating unit structures 11 in each of which the low electron density portion 15 is provided in the high electron density portion 16 in a certain direction. As a result, the localization of an X-ray into the low electron density portion becomes significant, and hence an X-ray waveguide that provides an additionally strong transmitted X-ray can be provided.
The core 14 formed of a laminating structure is formed by laminating the unit structures 11. The unit structures 11 are each formed of the tubular or spherical low electron density portion 15 formed of a member having a low electron density that propagates an X-ray and the high electron density portion 16 formed of a member having a high electron density, and the low electron density portion is provided in the high electron density portion in the certain direction. A direction 19 is the certain direction in which the low electron density portion is provided. In addition, a laminating direction 18 of the unit structures 11 is a direction perpendicular to a propagating direction 17 of the X-ray.
Examples of the core 14 formed of the laminating structure of the present invention include films mainly formed of two structures.
The unit structures 11 are characterized in that their electron densities averaged with respect to a plane perpendicular to the laminating direction 18 repeatedly have a high density region and a low density region along the laminating direction 18. A size (laminating interval) in a direction parallel to the laminating direction 18 of the unit structures is not necessarily needed to be constant.
It is preferred that: the certain direction 19 in which the low electron density portions 15 of the unit structures 11 are provided be a direction parallel to the cladding 13; and the laminating direction 18 of the unit structures 11 be a direction perpendicular to the cladding 13. With the configuration, an X-ray can be preferably confined in the waveguide, and the X-ray can be localized in each low electron density portion. Accordingly, an X-ray waveguide that provides a strong transmitted X-ray can be provided.
In the present invention, as illustrated in
Two kinds of X-ray waveguides are available. The two kinds are such a one-dimensional confinement-type waveguide as illustrated in
With regard to the shape of the portion of the X-ray waveguide on which an X-ray is incident and a method of making the X-ray incident, any method may be adopted as long as the X-ray can be guided into the X-ray waveguide by the method. For example, configurations illustrated in
In the present invention, it is preferred that: the core be formed of an inorganic oxide-organic substance laminar structure; and the core be formed of a configuration obtained by laminating unit structures in each of which a laminar low electron density portion formed of the organic substance is provided in a high electron density portion formed of the inorganic oxide in a certain direction. The use of the laminar low electron density portions each formed of the organic substance in the core can provide an X-ray waveguide excellent in optical characteristics such as an incidence allowance angle on the X-ray waveguide and a high X-ray transmittance.
It is also preferred that: the core be formed of an inorganic oxide porous body; and the core be formed of a configuration obtained by laminating unit structures in each of which a tubular or spherical low electron density portion formed of a pore or an organic substance in the pore is provided in a high electron density portion formed of the inorganic oxide in a certain direction. The use of the tubular or spherical low electron density portions each formed of the pore or the organic substance in the core can provide an X-ray waveguide excellent in optical characteristics such as an X-ray transmittance.
The sectional shapes of the tubular low electron density portions are, for example, a circular shape, an elliptical shape, a quadrangular shape, and a polygonal shape. The core having the tubular low electron density portions is, for example, a porous silica, a porous titanium oxide, or a porous alumina. The core having the spherical low electron density portions is, for example, a hexagonal close-packed structure (reverse opal structure) formed of polystyrene spheres in the matrix of the high electron density portions in a self-assemble fashion or a mesoporous silica. Although the spherical structures are not needed to be completely spherical, an aspect ratio (shorter diameter of a pore section/longer diameter of the pore section) is preferably 0.30 or more.
As described above, in the present invention, the low electron density portions 15 are each formed of the pore or the organic substance. In the case of the core of
Examples of the organic substance include, for example, an amphipathic molecule typified by a surfactant or polymer, an alkyl chain moiety of a siloxane oligomer, an alkyl chain moiety of a silane coupling agent, and polymer particles. Examples of the surfactant include C12H25(OCH2CH2)4OH, C16H35(OCH2CH2)10OH, C18H37(OCH2CH2)10OH, a Tween 60 (Tokyo Chemical Industry Co., Ltd.), a Pluronic L121 (BASF), a Pluronic P123 (BASF), a Pluronic P65 (BASF), and a Pluronic P85 (BASF).
Table 1 shows an exemplary linear absorption coefficient as an index for the transmitting performance of a material used in each low electron density portion for an X-ray (12 keV). As can be seen from the table, the linear absorption coefficients of a pore and organic substances are smaller than that of carbon, and hence the pore and the organic substances each have higher transmitting performance than a conventional one.
It should be noted that the term “alkyl” refers to a portion (functional group) of a molecule formed of CnH2n+1. In the present invention, a material for the high electron density portion 16 has only to have a larger electron density than that of the low electron density portion 15, provided that as the abruptness of the change of a difference in electron density between the high electron density portion 16 and the low electron density portion 15 raises, the localization of X-rays into the low electron density portions 15 becomes more significant, and hence an X-ray waveguide that provides a strong transmitted X-ray can be provided. In addition, the high electron density portion is particularly preferably an inorganic oxide when a material having high unit structure property is produced by a self-assembly process to be described later. Examples of the inorganic oxide include silica, titanium oxide, and zirconium oxide.
In the X-ray waveguide of the present invention, the thickness of the high electron density portion 16 of the core 14 is preferably twice or less as large as the length by which the evanescent wave of an X-ray oozes toward the high electron density portion. An oozing length L of the evanescent wave of an X-ray to be used toward the high electron density portion 16 is represented by (Formula 1) described below. Under the condition, X-rays localized in the low electron density portions can preferably interact with each other, and hence a degenerated guided mode is formed. As a result, an X-ray waveguide having a large allowance range for the incidence angle of an X-ray can be provided.
L: The oozing length of an evanescent wave
λ: The wavelength of an X-ray
n1: The refractive index of the low electron density portion
n2: The refractive index of the high electron density portion
α: The incidence angle of the X-ray from the low electron density portion to the high electron density portion
In the present invention, the thickness of each of the claddings 12 and 13 is preferably equal to or larger than the oozing length L of the evanescent wave of an X-ray toward the cladding. When the thickness of each of the claddings is equal to or larger than the L, the X-ray is satisfactorily confined in the X-ray waveguide, and hence the loss of the intensity of the X-ray can be suppressed.
A method of producing an X-ray waveguide of the present invention is a method of producing an X-ray waveguide formed of a core and a cladding in which: the core is such that a low electron density portion having a low electron density that propagates an X-ray is provided in a high electron density portion having a high electron density; and the low electron density portion is formed of a pore or an organic substance, the method being characterized by including the steps of: preparing a substrate serving as a part of the cladding; forming the core on the surface of the substrate; and forming another part of the cladding on a part, or on the periphery, of the core.
The step of forming the core is preferably performed by a self-assembly process involving using a reaction liquid containing an organic substance.
In addition, when the X-ray waveguide of the present invention is a two-dimensional confinement-type waveguide, the waveguide is produced by the step of
The core of the X-ray waveguide of the present invention is preferably formed on a material for the cladding because the core is interposed between the claddings each, or surrounded with the cladding, having a smaller refractive index than that of the core. In the present invention, the surface portion of the substrate is preferably formed of the material for the cladding. When the substrate itself insufficiently functions as the cladding, the surface of the substrate needs to be treated. A method of treating the substrate is, for example, an oxidation treatment (formation of an oxide film) or film formation by sputtering or the like. Any such method can cause the surface layer of the substrate to function as the cladding. In addition, the treatment step may be performed before the step of forming the core on the substrate, or may be performed after the forming step.
A material having a smaller refractive index than that of the core, that is, having a larger electron density than that of the core is used as a material of which the cladding is formed, and examples of the material include an inorganic oxide and a heavy metal element. In the present invention, the core, which is not particularly limited, is preferably a core produced by a method based on a self-assembly process involving using a reaction liquid containing an organic substance. The core can be produced by employing a conventionally known method. For example, the core can be produced by employing a method (hydrothermal synthesis method) involving treating the surface of the substrate as the cladding through a chemical reaction caused by bringing a reaction liquid containing a surfactant, a precursor for a high electron density member, and an acid into contact with the surface and by holding the reaction liquid on the surface. Alternatively, the core can be produced by employing, for example, a method (sol-gel method) of forming the core upon evaporation of the solvent of the reaction liquid applied to the surface of the substrate by a method such as spin coating, dip coating, or capillary coating. Alternatively, the core can be produced by a sol-gel method involving applying, to the surface of the substrate, a reaction liquid containing an alkyl chain-containing siloxane oligomer or silane coupling agent. In any such method, a structure in which a large number of low electron density portions are provided in a high electron density portion can be produced at a time on the basis of self-assembly according to a wet process. Therefore, an X-ray waveguide can be produced with ease and at a low cost as compared with a method according to a dry process such as sputtering that has been conventionally employed.
The low electron density portions of the core produced here are each preferably an organic substance. Such non-laminar structure as illustrated in
In the case of the configuration using the non-laminar structure (
Any one of the conventionally known methods can be employed for the removal of the organic substance. For example, baking in an oxygen atmosphere, extraction with a solvent, or ozone oxidation can be employed. Although the baking step is generally employed, the extraction with a solvent or the ozone oxidation is preferably employed when the core, the substrate, the cladding formed on the surface of the substrate, and the like cannot be exposed to high temperatures.
In order that the two-dimensional confinement type waveguide of
Any method can be employed as a method of forming the cladding as long as the method enables the control of the thickness of the cladding and uniform formation of the cladding. For example, a dry process such as sputtering or vapor deposition, or a wet process such as a sol-gel method is applicable. When the cladding 12 must be partially formed upon, for example, production of an X-ray waveguide for oblique incidence of an X-ray illustrated in
In addition, the core of the X-ray waveguide of the present invention is produced by a method based on a self-assembly process, and a structure in which a large number of low electron density portions are provided in a high electron density portion can be produced at a time on the basis of self-assembly by one step. Therefore, an X-ray waveguide can be provided by a process simpler and quicker than a conventional one.
This example is an example in which a one-dimensional confinement-type X-ray waveguide using a laminar structure 54 of a configuration illustrated in each of
First, a silicon wafer 53 (30 mm×30 mm×0.5 mm) was prepared as a substrate, and its surface was cleaned in an ozone apparatus. Next, an alkyl chain-containing siloxane oligomer as a precursor for the laminar structure was synthesized. Decyltrichlorosilane (0.11 mol) was dissolved in diethyl ether (250 mL), and then a mixed solution was dropped while the resultant solution was vigorously stirred in an ice bath. The mixed solution is formed of tetrahydrofuran (350 mL), diethyl ether (365 mL), pure water (6.5 mL), and aniline (33.0 mL). After the mixture had been stirred for 2 hours, the precipitate was removed by filter filtration, and then hexane was added to the filtrate. After that, the solvent was evaporated. Thus, solid matter was obtained. After having been separated by suction filtration, the solid matter was sufficiently washed with cooled acetone and then dried in a vacuum. The solid matter after the drying was dissolved in tetrahydrofuran, and then the solution was subjected to 29Si-NMR measurement. As a result, it was confirmed that the solid matter was an alkyl chain-containing siloxane oligomer having the structure of C10H21Si(OSi(OMe)3)3.
The siloxane oligomer, tetramethoxysilane, tetrahydrofuran, pure water, and hydrochloric acid were mixed, and a molar ratio among them in the stated order was adjusted to 1.0:2.0:15:14:0.0050. Further, the solid content was dissolved by stirring. After a lapse of 2.5 hours, tetrahydrofuran was added to the solution, and then the molar ratio was adjusted to 1.0:2.0:60:14:0.0050. Thus, a reaction liquid was prepared.
The top of the silicon wafer 53 was coated with the reaction liquid solution by spin coating (5,000 rpm). The silicon wafer 53 after the spin coating was placed in a thermo-hygrostat at 20° C. and a humidity of 40%, and was then held for 1 day or longer. Thus, the core 54 was formed on the silicon wafer 53. The observation of the core 54 with an electron microscope confirmed that the core was the laminar structure illustrated in
In order that the peripheral portion of the silicon wafer 53 having the thickness distribution of the core 54 as a result of nonuniform application of the reaction liquid might be eliminated, the central portion of the silicon wafer 53 (20 mm×20 mm) was cut and taken out. Further, the top of the cut piece was masked with a metal mask made of aluminum, and then silica 52 as a cladding was formed only on the central portion of the core 54 (5.0 mm×5.0 mm) by magnetron sputtering so as to have a thickness of 300 nm. Further, a lead glass 56 (bottom face: 4.5 mm×4.5 mm, height: 6 mm) was bonded onto the silica 52 with a silver paste 55 so as to serve as a shielding material for a reflected X-ray and a direct beam that might inhibit the measurement of a transmitted X-ray 57. An X-ray waveguide was produced by the foregoing steps.
The characteristics of the produced X-ray waveguide were investigated with an X-ray microbeam (4 μm×4 μm, 12 keV). The position at which an X-ray was incident was aligned with the boundary of the portion where the silica 52 as the cladding was formed. Then, as illustrated in
The following facts were confirmed. The transmitted x-ray intensity for the incidence angle αi was as illustrated in
This example is an example in which a one-dimensional confinement-type X-ray waveguide using a non-laminar structure 54 of a configuration illustrated in each of
First, a silicon wafer 53 (35 mm×35 mm×0.5 mm) was prepared as a substrate, and its surface was cleaned in an ozone apparatus. A polyamic acid solution was applied by spin coating (2,000 rpm), and then the resultant was baked at 200° C. for 1 hour. Thus, a polyimide layer was formed. The presence of the polyimide film enables uniform formation of a core on the silicon wafer 53.
Next, a reaction liquid for the production of the core was prepared. 7.51 grams of C16H35(OCH2CH2)10OH (polyethylene oxide 10 hexadecyl ether) were stirred while being heated so as to be melted, and then 159.9 g of pure water and 26.5 mL of concentrated hydrochloric acid (36%) were added to the melt. The resultant solution was stirred for 1 hour or longer while its temperature was held at 80° C. After the solution had been cooled to 27° C., 2.24 mL of tetraethoxysilane was added to the solution, and then the mixture was stirred for 150 seconds. Thus, the reaction liquid was prepared.
The silicon wafer 53 was placed in a Teflon (registered trademark) container with its surface directed downward, and then the reaction liquid was poured into the container so that the substrate might be completely covered with the reaction liquid. Then, the Teflon (registered trademark) container was completely sealed. In this case, a quartz substrate (35 mm×35 mm×1.1 mm) was prepared, and the surface of the silicon wafer 53 was covered with the quartz substrate through a spacer. After that, the container was introduced into an oven at 80° C., and then the contents were subjected to a reaction for 5 days.
After that, the silicon wafer 53 taken out of the container was washed with ultrapure water and then air-dried. In order that the surfactant C16H35(OCH2CH2)10OH as an organic substance and the polyimide layer might be removed, the resultant was introduced into an electric furnace under an air atmosphere, and the temperature in the furnace was increased to 400° C. at 2° C. per minute. After having reached 400° C., the temperature was held at the value for 10 hours. After that, the temperature was decreased to room temperature at 2° C. per minute.
The core 54 was formed on the silicon wafer 53 by the foregoing steps. The observation of the core 54 with an electron microscope confirmed that the core was the non-laminar structure illustrated in
Further, the silica 52, the silver paste 55, and the lead glass 56 were placed by the same steps as those of Example 1. Thus, an X-ray waveguide was produced. The characteristics of the produced X-ray waveguide were investigated with an X-ray microbeam (4 μm×4 μm, 12 keV). The position at which an X-ray was incident was aligned with the boundary of the portion where the silica 52 as the cladding was formed. Then, as illustrated in
The following facts were confirmed. The transmitted x-ray intensity for the incidence angle αi was as illustrated in
This comparative example is an example in which a one-dimensional confinement-type X-ray waveguide using an artificial multilayer film whose low electron density portions are each carbon is produced and its X-ray propagation behavior is investigated.
First, a silicon wafer (20 mm×20 mm×0.5 mm) is prepared as a substrate, and its surface is cleaned in an ozone apparatus. Next, a nickel layer (20 nm) serving as a cladding is formed on the silicon wafer by magnetron sputtering. Further, seven layers each of carbon (45.7 nm) and nickel (2.5 nm) are alternately formed by magnetron sputtering to form an artificial multilayer film.
The top of the artificial multilayer film was masked with a metal mask made of aluminum, and then nickel as a cladding was formed only on the central portion of the artificial multilayer film (5.0 mm×5.0 mm) by magnetron sputtering so as to have a thickness of 20 nm. Further, a lead glass (bottom face: 4.5 mm×4.5 mm, height: 6 mm) is bonded onto the nickel with a silver paste so as to serve as a shielding material for a reflected X-ray and a direct beam that might inhibit the measurement of a transmitted X-ray 57. An X-ray waveguide is produced by the foregoing steps.
The characteristics of the produced X-ray waveguide are investigated with an X-ray microbeam (4 μm×4 μm, 12 keV). The position at which an X-ray is incident is aligned with the boundary of the portion where the nickel as the cladding is formed. Then, an X-ray microbeam is made incident on the X-ray waveguide. The optical path length by which the X-ray is guided at φi=0° out of the incidence angle of the X-ray is set to 5 mm. In addition, the αi is gradually increased from 0°, and then the intensities of the transmitted X-ray at different αi's are detected with a CCD camera and a photodiode connected to an X-ray image intensifier.
It is confirmed that the transmitted x-ray intensity for the incidence angle αi shows the maximum intensity (peak intensity) at αi=0.16° and a guided mode is formed at the angle. However, the intensity is about 50% of the peak intensity of Example 1.
The X-ray waveguide of the present invention is useful in, for example, the field of an analysis technology involving using an X-ray because the waveguide can provide an X-ray beam having a small beam size and a strong intensity.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2010-127336, filed Jun. 2, 2010, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-127336 | Jun 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/062153 | 5/20/2011 | WO | 00 | 11/28/2012 |
