Sintered material and method for producing same, and electron source and device comprising same

Abstract

A method for manufacturing a sintered material, comprising iridium and cerium, includes the following steps: preparing a sintered body composed of iridium and cerium; and heating the sintered body at a temperature of 1400–1800°C for at least 0.5 hours in a gaseous environment with an oxygen partial pressure below 10⁻¹ Pa to obtain the sintered material. A sintered material composed of iridium and cerium, having a work function of 3.8 eV or less.

Description

Sintered Material, Method for Producing the Same, Electron Source, and Device Equipped with the Electron Source The present invention relates to a sintered material, a method for producing the same, an electron source, and a device equipped with the electron source. An emitter that emits electrons is used, for example, in an electron microscope and a semiconductor inspection device. The emitter includes an electron source and a heater that heats the electron source, and an emission current can be obtained by heating the electron source by energizing the heater. The electron source is composed of an electron emission material. Examples of the electron emission material include rare earth borides such as lanthanum boride (LaB 6 ), cerium boride (CeB 6 ), etc.; high melting point metals such as tungsten, tantalum, and hafnium, and their oxides, carbides, and nitrides. In recent years, research has been conducted on using a sintered body composed of iridium and cerium as an electron source (see Patent Documents 1 and 2). [Prior Art Documents] [Patent Documents] [Patent Document 1] Japanese Patent No. 6285254 [Patent Document 2] Japanese Patent No. 6805306 [Problems to be Solved by the Invention] The inventors of the present invention evaluated the performance of a sintered body composed of iridium and cerium as an electron source, and as a result, it was found that the work function of the above sintered body is large, and there is room for improvement in practical application as an electron source. One aspect of the present invention is made in view of the above problems, and an object thereof is to provide a sintered material composed of iridium and cerium and having a sufficiently small work function, and a method for producing the same. Another aspect of the present invention aims to provide an electron source composed of the above sintered material and a device equipped with the electron source. [Means for Solving the Problems] One aspect of the present invention relates to a method for producing a sintered material composed of iridium and cerium. The method for producing the sintered material includes the following steps: preparing a sintered body composed of iridium and cerium; and heat-treating the sintered body at a temperature of 1400 to 1800 °C for 0.5 hours or more in a low oxygen gas environment to obtain a sintered material. Furthermore, in the present invention, the "sintered body" means the state before the above heat treatment, and the "sintered material" means the state after the above heat treatment. In the above manufacturing method, by heat-treating a sintered body composed of iridium and cerium under predetermined conditions, a sintered material with a sufficiently small work function can be obtained. For example, even if the work function of the above sintered body is 4.1 to 4.3 eV, by undergoing the above heat treatment, a sintered material with a work function of 3.8 eV or less can be obtained. The mechanism by which the work function decreases due to heat treatment is not yet clear, but the inventors of the present invention speculate that the following are the main reasons: due to heat treatment, crystallization of the sintered body proceeds and crystals are formed, and metallic iridium precipitates on the surface of the crystals. As a result, a state in which metallic iridium is dispersed in islands on the surface of the sintered material or a layer of metallic iridium is formed so as to cover the entire surface of the crystals is achieved. The heat treatment is carried out in a low oxygen gas environment (a gas environment with an oxygen partial pressure of 10 -1 Pa or less). The above sintered body can be composed of at least one crystal phase selected from the group consisting of Ir 2 Ce crystal phase, Ir 3 Ce crystal phase, Ir 7 Ce 2 crystal phase and Ir 5 Ce crystal phase. In terms of the point that metallic iridium precipitates on the surface of the sintered material and an iridium region is easily formed, it is preferable that the composition of the sintered body is rich in iridium. Specifically, the sintered body is preferably composed of the Ir 7 Ce 2 crystal phase or the Ir 5 Ce crystal phase. The content of cerium relative to 100 parts by mass of the total mass of the sintered material produced from these sintered bodies can be 12.7 to 26.7 parts by mass. Another aspect of the present invention relates to a sintered material composed of iridium and cerium and having a work function of 3.8 eV or less. In one aspect, this sintered material includes a body portion composed of iridium and cerium, and an iridium region formed on the surface of the body portion. As described above, the sintered material that has undergone the above heat treatment has been crystallized. The degree of crystallization progress can be grasped by X-ray diffraction analysis (hereinafter referred to as XRD) targeting the surface of the sintered material. That is, in the spectrum obtained by XRD analysis targeting the surface of the sintered material, the full width at half maximum of the first peak at the position where the scattering angle 2θ is 47.6° can be 0.5 or less, and the full width at half maximum of the second peak at the position where the scattering angle 2θ is 55.5° can be 0.5 or less. Another aspect of the present invention relates to an electron source composed of the above sintered material. Another aspect of the present invention relates to a device including the above electron source. Examples of devices including an electron source include an electron microscope, a semiconductor manufacturing device, an inspection device, and a processing device. [Advantages of the Invention] According to one aspect of the present invention, a sintered material composed of iridium and cerium and having a sufficiently small work function, and a method for manufacturing the same can be provided. Further, according to another aspect of the present invention, an electron source composed of the above sintered material and a device including the electron source can be provided. Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the following embodiments. FIG. 1 is a plan view schematically showing a state in which an electron source according to the present embodiment is fixed to a filament. The electron source 1 is a wafer of a sintered material composed of iridium and cerium. The electron source 1 is fixed to the filament 2 at the joint portion 3. The joint portion 3 is located at the top of the filament 2 bent in a loop shape. Examples of devices including the electron source 1 include an electron microscope, a semiconductor manufacturing device, an inspection device, and a processing device. The electron source 1 emits electrons by being heated. The electron source 1 is heated by applying electricity to the filament 2. The electron source 1 has a substantially rectangular parallelepiped shape. The front end portion of the electron source 1 may be processed into a conical shape or a quadrangular pyramid shape. The shape of the electron source 1 is not particularly limited, and it may be processed into a desired shape by electric discharge machining or the like. The filament 2 heats the electron source 1 by being energized. The filament 2 may be, for example, a tungsten filament. Depending on the required performance, the tungsten filament may contain elements other than tungsten (for example, rhenium, aluminum, silicon, and potassium). The tungsten filament may also be doped with an alkali metal (for example, potassium) for stabilization. When the tungsten filament contains rhenium, the rhenium content in the tungsten filament may be, for example, 2 to 30 mass%, 2 to 10 mass%, or 2 to 5 mass%. Rhenium exhibits the effect of increasing the resistivity of the tungsten filament. The sintered material is composed of iridium and cerium as described above. The sintered material may contain at least one crystal phase selected from the group consisting of Ir 2 Ce crystal phase, Ir 3 Ce crystal phase, Ir 7 Ce 2 crystal phase, and Ir 5 Ce crystal phase. The total content of iridium and cerium may be 97 parts by mass or more, 98 parts by mass or more, or 99 parts by mass or more with respect to 100 parts by mass of the total mass of the sintered material. The sintered material may also be composed only of iridium, cerium, and unavoidable impurities. The content of iridium and the content of cerium can be appropriately set according to the type of crystal phase constituting the sintered material and the like. The content of iridium, relative to 100 parts by mass of the total mass of the sintered material, can be 73.3 parts by mass or more, 77 parts by mass or more, or 80 parts by mass or more, and can also be 87.3 parts by mass or less, 85 parts by mass or less, or 83 parts by mass or less. The content of cerium, relative to 100 parts by mass of the total mass of the sintered material, can be 12.7 parts by mass or more, 15 parts by mass or more, or 17 parts by mass or more, and can also be 26.7 parts by mass or less, 23 parts by mass or less, or 20 parts by mass or less. The work function of the sintered material is 3.8 eV or less, preferably 3.7 eV or less or 3.6 eV or less, and can also be 3.4 eV or less or 3.0 eV or less. By having the work function be 3.8 eV or less, even when the sintered material (electron source 1) is used under low vacuum conditions (for example, 10 -3 ~10 -6 Pa), a sufficiently large current density can be achieved. The lower limit value of the work function of the sintered material can also be, for example, 2.7 eV or more, 2.8 eV or more, 2.9 eV or more, 3.0 eV or more, 3.1 eV or more, 3.2 eV or more, or 3.3 eV or more. In the present invention, the work function means a value measured by ultraviolet photoelectron spectroscopy (UPS method) under the following conditions. Measurement sample: diameter 3 mm × length 2.5 mm [Heating conditions] Maximum heating temperature: 1550 °C Cumulative heating time: 78 hours (wherein the heating time at 1550 °C is 24 hours) [Ultraviolet photoelectron spectroscopy apparatus] Photon energy of ultraviolet light: 21.22 eV Bias voltage: -6 V Measurement area: center Energy resolution of the photoelectron analyzer: 0.025 eV Slot: 55 μm [Ion sputtering] As a pretreatment before measuring the work function and for removing contaminants on the outermost surface of the sample, ion sputtering was carried out under the following conditions. Ion type: argon ion Acceleration voltage: 1 kV Time: 20 to 100 seconds The sintered material can be obtained by heat-treating a sintered body composed of iridium and cerium in a low oxygen gas environment. That is, the manufacturing method of the sintered material includes the following steps: preparing a sintered body composed of iridium and cerium; and heat-treating the sintered body at a temperature of 1400 to 1800 °C for 0.5 hours or more in a low oxygen gas environment to obtain the sintered material. Here, the low oxygen gas environment means a gas environment in which the oxidation reaction of iridium and cerium does not proceed. Specifically, at an oxygen partial pressure of 10 -1 Pa or less, 10 -2 Pa or less, or 10 -3Pa or less, preferably 10 -4 Pa or less, more preferably 10 -5 Pa or less, even more preferably 5×10 -5 Pa or less, 4×10 -5 Pa or less, or 3×10 -5 It is only necessary to perform heat treatment of the sintered body in a gas of Pa or less. Such a low oxygen gas environment can be achieved by using an inert gas gas environment, or can be achieved by reducing the pressure in an air gas environment to preferably 10 -5 Pa or less, more preferably 10 -6 Pa or less. The crystal phase constituting the sintered body may be selected from the group consisting of Ir 2 Ce crystal phase, Ir 3 Ce crystal phase, Ir 7 Ce 2 crystal phase and Ir 5 At least one of the group consisting of Ce crystal phases, and in terms of the point that metallic iridium is precipitated on the surface of the sintered material and an iridium region is easily formed, it is preferably selected from the group consisting of Ir 7 Ce 2 crystal phase and Ir 5 At least one of the group consisting of Ce crystal phases. The total content of iridium and cerium, relative to 100 parts by mass of the total mass of the sintered body, may be 97 parts by mass or more, 98 parts by mass or more, or 99 parts by mass or more. The sintered body may also be composed only of iridium, cerium, and unavoidable impurities. The content of iridium and the content of cerium can be appropriately set according to the type of crystal phase constituting the sintered body, etc. The content of iridium, relative to 100 parts by mass of the total mass of the sintered body, may be 73.3 parts by mass or more, 77 parts by mass or more, or 80 parts by mass or more, and may also be 87.3 parts by mass or less, 85 parts by mass or less, or 83 parts by mass or less. The content of cerium, relative to 100 parts by mass of the total mass of the sintered body, may be 12.7 parts by mass or more, 15 parts by mass or more, or 17 parts by mass or more, and may also be 26.7 parts by mass or less, 23 parts by mass or less, or 20 parts by mass or less. In the spectrum (XRD spectrum) obtained by XRD analysis of the surface of this sintered body, for the peak portion derived from Ir, a peak portion (first peak portion) at a position where the scattering angle 2θ is 47.6° and a peak portion (second peak portion) at a position where the scattering angle 2θ is 55.5° can be observed. In this spectrum, the full width at half maximum of the first peak portion at a position where the scattering angle 2θ is 47.6° may also be greater than 0.5, 0.5 or more, or 0.55 or more. The upper limit value of the full width at half maximum of the first peak portion may be, for example, 0.55 or less. In this spectrum, the full width at half maximum of the second peak portion at a position where the scattering angle 2θ is 55.5° may also be greater than 0.5, 0.6 or more, or 0.65 or more. The upper limit value of the full width at half maximum of the second peak portion may be, for example, 0.69. Such a sintered body can be obtained, for example, by sintering a powder composed of iridium and cerium using a hot pressing method or a spark plasma sintering method (see Patent Documents 1 and 2). As described above, the temperature of the heat treatment for the sintered body is 1400 to 1800 °C, preferably 1400 to 1600 °C or 1500 to 1800 °C, and more preferably 1500 to 1600 °C. By the temperature being 1400 °C or higher, the effect of promoting crystallization can be exerted, and by being 1800 °C or lower, the effect of suppressing the dissolution of the material can be exerted. The time of the heat treatment is, as described above, 0.5 hours or more, and preferably may also be 1 hour or more, 2 hours or more, or 2.5 hours or more, 100 hours or more. By the time of the heat treatment being 0.5 hours or more, the effect of promoting crystallization can be exerted, and by the time of the heat treatment being 100 hours or more, the effect of precipitating iridium on the surface becomes easier to exert. The upper limit of the time of the heat treatment may be, for example, 240 hours or less. As described above, the work function of the sintered material after the above heat treatment is 3.8 eV or less. In contrast, the work function of the sintered body before the above heat treatment is, for example, 4.1 to 4.3 eV. The decrease in the work function caused by the heat treatment is presumably due to: the crystallization of the sintered body proceeds and crystals are formed, and metallic iridium precipitates on the surface of the crystals, resulting in a state where metallic iridium is dispersed in an island shape on the surface of the sintered material or a layer of metallic iridium is formed so as to cover the entire surface of the crystals. In the case where crystallization proceeds due to the above heat treatment, it can be confirmed by using the full width at half maximum (FWHM) of the peak from Ir in the XRD spectra for the surfaces of the sintered body and the sintered material before and after the heat treatment, respectively. Specifically, in one embodiment, the sintered body (before heat treatment) as described above shows a peak (first peak) with a FWHM greater than 0.5 at a scattering angle 2θ of 47.6° and a peak (second peak) with a FWHM greater than 0.5 at a scattering angle 2θ of 55.5°. In contrast, the sintered material (after heat treatment) can show a peak (first peak) with a FWHM of 0.5 or less at a scattering angle 2θ of 47.6° and a peak (second peak) with a FWHM of 0.5 or less at a scattering angle 2θ of 55.5°. In the spectrum obtained by XRD analysis of the surface of the sintered material, the FWHM of the first peak at a scattering angle 2θ of 47.6° is preferably 0.5 or less, more preferably 0.48 or less, 0.46 or less, 0.44 or less, 0.43 or less, or 0.42 or less, and may also be 0.39 or more, 0.40 or more, or 0.41 or more. In the spectrum obtained by XRD analysis of the surface of the sintered material, the FWHM of the second peak at a scattering angle 2θ of 55.5° is preferably 0.5 or less, more preferably 0.49 or less, and may also be 0.43 or more, 0.44 or more, or 0.45 or more. By the FWHM of the first peak and the second peak being below the upper limit value, the sintered material becomes likely to achieve a work function value small enough. Furthermore, in the state where the surface metal iridium of the sintered material is dispersed in an island shape, it can be observed by using EDX (Energy Dispersive X-ray) mapping analysis of the surface of the sintered body and EBSD (Electron Back Scatter Diffraction) analysis of the surface of the sintered material. That is, from such observations, it can be seen that in one embodiment, the sintered material can include a main body portion forming the core of the sintered material and an iridium region formed on the surface of the main body portion. The main body portion can be composed of iridium and cerium. The iridium region can be a region composed of iridium or a region not containing cerium. A plurality of iridium regions are scattered on the surface of the main body portion. The size of each iridium region (the maximum length of the straight line connecting two points on the outer periphery of one iridium region) can be, for example, 0.1 μm or more, 0.5 μm or more, or 1 μm or more, and may also be 30 μm or less, 20 μm or less, or 10 μm or less. [Examples] The present invention will be described more specifically based on examples below, but the present invention is not limited to the following examples. (Comparative Example 1) Directly use Ir as the main crystal phase 7 Ce 2 and also contains Ir 5 The crystalline phase of Ce and Ir 3 A sintered body of the crystalline phase of Ce (manufactured by Kobelco Research Institute, Inc.). FIG. 2 is an SEM image of the surface of the sintered body. FIG. 3 is an XRD spectrum of the surface of the sintered body. In the XRD spectrum, the ○ mark indicates the peak from Ir, and the □ mark indicates the peak from Ir 5 The peak of Ce, and the △ mark indicates the peak from Ir 7 Ce 2 The peak of, and the × mark indicates the peak from Ir 3 The peak of Ce (the same applies hereinafter). The full width at half maximum of the first peak at the position where the scattering angle 2θ is 47.6° is 0.543, and the full width at half maximum of the second peak at the position where the scattering angle 2θ is 55.5° is 0.690. Furthermore, in Comparative Example 1 and the following examples, an XRD spectrum was obtained using an XRD device manufactured by Rigaku Corporation, and the full width at half maximum was obtained using XRD analysis software (JADE, manufactured by MDI Corporation). Specifically, after background removal from the XRD spectrum, the full width at half maximum of each peak was obtained using the first peak and the second peak separated by peak fitting. Furthermore, Kα2 removal was not performed. Also, the work function of the above sintered body is 4.27 eV. Furthermore, in Comparative Example 1 and the following examples, a ultraviolet photoelectron spectroscopy device manufactured by Kratos analytical company was used to measure the work function. (Example 1) The sintered body used in Comparative Example 1 (a sintered body composed of the crystalline phase of Ir 7 Ce 2 manufactured by Kobelco Research Institute, Inc.) was placed in air at a reduced pressure of 10 -5 Pa (oxygen partial pressure: about 2×10 -6(Pa) It was heat-treated at 1750 °C for 3 hours to obtain a sintered material. Fig. 4 is an SEM image of the surface of the obtained sintered material. Fig. 5 is an XRD spectrum of the surface of the obtained sintered material. The full width at half maximum of the first peak at the position where the scattering angle 2θ is 47.6° is 0.415, and the full width at half maximum of the second peak at the position where the scattering angle 2θ is 55.5° is 0.489. The work function of the obtained sintered material is 3.67 eV. Also, with respect to 100 mass parts of the total mass of the obtained sintered material, the content of iridium is 82.8 mass parts and the content of cerium is 17.2 mass parts. (Example 2) The sintered body used in Comparative Example 1 (a sintered body composed of Ir 7 Ce 2 crystalline phase, manufactured by Kobelco Research Institute, Inc.) was heat-treated in air at a reduced pressure of 10 -5 Pa at 1600 °C for 80 hours to obtain a sintered material. Fig. 6 is an SEM image of the surface of the obtained sintered material. Fig. 7 is an XRD spectrum of the surface of the obtained sintered material. The full width at half maximum of the first peak at the position where the scattering angle 2θ is 47.6° is 0.429, and the full width at half maximum of the second peak at the position where the scattering angle 2θ is 55.5° is 0.457. The work function of the obtained sintered material is 3.52 eV. Also, with respect to 100 mass parts of the total mass of the obtained sintered material, the content of iridium is 82.8 mass parts and the content of cerium is 17.2 mass parts. Figs. 8(a) and 8(b) are images showing the results of EDX mapping analysis of the surface of the sintered body of Comparative Example 1. Fig. 8(a) is an image showing the distribution state of the Ce element, and Fig. 8(b) is an image showing the distribution state of the Ir element. From these images, it can be seen that the Ce element and the Ir element are distributed relatively uniformly on the surface of the sintered body of Comparative Example 1. Figs. 9(a) and 9(b) are images showing the results of EDX mapping analysis of the surface of the sintered material obtained in Example 1. Fig. 9(a) is an image showing the distribution state of the Ce element, and Fig. 9(b) is an image showing the distribution state of the Ir element. From these images, it can be seen that iridium regions R1 (bright regions in Fig. 9(b)) are scattered on the surface of the sintered material obtained in Example 1. Figs. 10(a) and 10(b) are images showing the results of EDX mapping analysis of the surface of the sintered material obtained in Example 2. Fig. 10(a) is an image showing the distribution state of the Ce element, and Fig. 10(b) is an image showing the distribution state of the Ir element. From these images, it can be seen that iridium regions R2 (bright regions in Fig. 10(b)) are scattered on the surface of the sintered material obtained in Example 2. In the sintered material of Example 1, the iridium region R1 is relatively uniformly dispersed. In contrast, the iridium region R2 in the sintered material of Example 2 appears to be unevenly distributed. Also, the size of the iridium region R2 in the sintered material of Example 2 appears to be larger than the size of the iridium region R1 in the sintered material of Example 1. Figures 11(a) and 11(b) are images showing the results of EBSD analysis of the surface of the sintered material obtained in Example 1. Figure 11(a) is an IQ (Image Quality) map of the surface of the sintered material obtained in Example 1, and Figure 11(b) is an image showing the Ir element and Ir 7 Ce 2 in the surface of the sintered material obtained in Example 1. From these images, it can be seen that Example 1 has a main body M1 (bright region in Figure 11(b)) composed of an Ir element and an Ir 7 Ce 2 crystalline phase, and an iridium region R1 (bright region in Figure 11(a)) dispersed in an island shape on the surface of the main body M1. It is speculated that the iridium region R1 is mainly composed of iridium elements. Figures 12(a) and 12(b) are images showing the results of EBSD analysis of the surface of the sintered material obtained in Example 2. Figure 12(a) is an IQ map of the surface of Example 2, and Figure 12(b) is an image showing the Ir element and Ir 7 Ce 2 in the surface of the sintered material obtained in Example 2. From these images, it can be seen that the sintered material obtained in Example 2 has a main body M2 (bright region in Figure 12(b)) composed of an Ir element and an Ir 7 Ce 2 crystalline phase, and an iridium region R2 (bright region in Figure 12(a)) dispersed in an island shape on the surface of the main body M2. It is speculated that the iridium region R2 is mainly composed of iridium elements. The iridium region R1 in the sintered material of Example 1 is relatively uniformly dispersed on the surface of the main body M1. In contrast, the iridium region R2 in the sintered material of Example 2 appears to be unevenly distributed on the surface of the main body M2. Also, the size of the iridium region R2 in the sintered material of Example 2 appears to be larger than the iridium region R1 in the sintered material of Example 1. (Example 3) The oxygen partial pressure during the heat treatment was changed to 10 -1Pa, and in the same manner as in Example 1, a sintered material was obtained. The work function of the obtained sintered material was 3.8 eV or less. The present invention relates to the following. [1] A method for manufacturing a sintered material, which is a method for manufacturing a sintered material composed of iridium and cerium, including the following steps: preparing a sintered body composed of iridium and cerium; and heat-treating the sintered body at a temperature of 1400 to 1800 °C for 0.5 hours or more in a gas environment with an oxygen partial pressure of 10 -1 Pa or less to obtain a sintered material. [2] The method for manufacturing a sintered material according to [1], wherein the sintered body is composed of at least one crystal phase selected from the group consisting of an Ir 2 Ce crystal phase, an Ir 3 Ce crystal phase, an Ir 7 Ce 2 crystal phase, and an Ir 5 Ce crystal phase. [3] The method for manufacturing a sintered material according to [1] or [2], wherein the work function of the sintered body is 4.1 to 4.3 eV. [4] A sintered material composed of iridium and cerium, and having a work function of 3.8 eV or less. [5] The sintered material according to [4], which includes a main body portion composed of iridium and cerium, and an iridium region formed on the surface of the main body portion. [6] The sintered material according to [4] or [5], wherein in the spectrum obtained by XRD analysis of the surface of the sintered material, a peak with a full width at half maximum of 0.5 or less is shown at a scattering angle 2θ of 47.6°. [7] The sintered material according to any one of [4] to [6], wherein in the spectrum obtained by XRD analysis of the surface of the sintered material, a peak with a full width at half maximum of 0.5 or less is shown at a scattering angle 2θ of 55.5°. [8] The sintered material according to any one of [4] to [7], wherein the content of cerium relative to 100 mass parts of the total mass of the sintered material is 12.7 to 26.7 mass parts. [9] An electron source composed of the sintered material according to any one of [4] to [8].

[10] A device including an electron source, which includes the electron source according to [9]. 1: Electron source 2: Filament 3: Joint portion M1, M2: Main body portion R1, R2: Iridium region [Fig. 1] Fig. 1 is a plan view schematically showing a state in which an electron source of an embodiment of the present invention is fixed to a filament. [Fig. 2] Fig. 2 is a scanning electron microscope (hereinafter referred to as SEM) image of the surface of the sintered body of Comparative Example 1. [Fig. 3] Fig. 3 is a spectrum obtained by XRD analysis of the surface of the sintered body of Comparative Example 1. [Fig. 4] Fig. 4 is an SEM image of the surface of the sintered material of Example 1. [Fig. 5] Fig. 5 is a spectrum obtained by XRD analysis of the surface of the sintered material of Example 1. [Fig. 6] Fig. 6 is an SEM image of the surface of the sintered material of Example 2. [Fig. 7] Fig. 7 is a spectrum obtained by XRD analysis of the surface of the sintered material of Example 2. [Fig. 8] Figs. 8(a) and 8(b) are images showing the mapping results of the surface of the sintered body of Comparative Example 1 by energy dispersive X-ray analysis (hereinafter referred to as EDX). [Fig. 9] Figs. 9(a) and 9(b) are images showing the mapping analysis results of the surface of the sintered material of Example 1 by EDX. [Fig. 10] Figs. 10(a) and 10(b) are images showing the mapping analysis results of the surface of the sintered material of Example 2 by EDX. [Fig. 11] Figs. 11(a) and 11(b) are images showing the analysis results of the surface of the sintered material of Example 1 by electron backscatter diffraction method (hereinafter referred to as EBSD). [Fig. 12] Figs. 12(a) and 12(b) are images showing the analysis results of the surface of the sintered material of Example 2 by EBSD. M1: Body part R1: Iridium region

Claims

1. A method for manufacturing a sintered material, comprising the following steps: preparing a sintered body composed of iridium and cerium; and heating the sintered body at a temperature of 1400 to 1800°C for at least 0.5 hours in a gaseous environment with an oxygen partial pressure of less than 10⁻¹ Pa, thereby precipitating metallic iridium on the surface of the sintered body to obtain the sintered material.

2. The method for manufacturing the sintered material as described in claim 1, wherein, The sintering system consists of at least one crystalline phase selected from the group consisting of Ir2Ce, Ir3Ce, Ir7Ce2, and Ir5Ce.

3. A method for manufacturing sintered materials as described in claim 1 or 2, wherein, The work function of the sintered body is 4.1–4.3 eV.

4. A sintered material composed of iridium and cerium, having a body portion composed of iridium and cerium and an iridium region formed on the surface of the body portion, and having a work function of 3.8 eV or less.

5. As in request item 4, of which, In the spectrum obtained by XRD analysis of the surface of the sintered material, a peak with a full width at half maximum (FWHM) of less than 0.5 is displayed at a scattering angle of 2θ of 47.6°.

6. As in request item 4, of which, In the spectrum obtained by XRD analysis of the surface of the sintered material, a peak with a full width at half maximum (FWHM) of less than 0.5 is displayed at a scattering angle of 2θ of 55.5°.

7. As in request item 4, of which, The content of cerium relative to 100 parts by mass of the sintered material is 12.7 to 26.7 parts by mass.

8. An electronic source comprising a sintered material as claimed in any one of claims 4 to 7.

9. An apparatus having an electronic source, comprising the electronic source as claimed in claim 8.

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