Abstract: A non-evaporable getter 1 includes a mesh 3, a frame 2 which is attached to the mesh 3 and suppresses deformation of the mesh 3, and a powder-state getter material 4 which is surrounded by the mesh 3 and the frame 2, and whose particle size is larger than a mesh opening of the mesh 3.

Abstract: The present invention relates to a wheel polishing apparatus composed of a frame, motors, servo electric cylinders, a polishing head, guide rails and the like. A wheel is fixed onto the clamp on the platform, a motor I rotates the platform and the wheel via the main shaft, a motor II rotates the polishing head via the drive shaft; the canting servo electric cylinder can realize the relative movement of the polishing head along the contour line of the back cavity of the wheel via the canting guide rail, the horizontal servo electric cylinder can realize constant contact between the polishing head and the back cavity of the wheel via the horizontal guide rail. The invention can realize the function of automatically polishing the back cavity of the wheel, which has desirable effects and advanced process and high degree of automation, and is characterized by simple construction and low cost.

Abstract: A composite synthesis method and apparatus, a vaporizer for the composite synthesis apparatus, a vaporizer heater and a composite. In the composite synthesis apparatus using simultaneous vaporization, two or more vaporizers are heated by heaters such that samples vaporized by the vaporizers are supplied into a reactor to synthesize a composite. The apparatus and method may prepare multiple-metal or metal-carbon heterogeneous composites, and may be applied to various metal- and carbon-based adsorbents, absorbents, gas/liquid separation membranes and various catalyst processes. Further, the composite may be applied to various industrial fields through change in metal components or carbon structures.

Abstract: A cathode assembly is for use in a radiation generator and includes an ohmically heated cathode, and a support having formed therein a hole and a recess at least partially surrounding the hole. In addition, there is a mount coupled to the support. The mount includes a larger outer frame positioned within the recess, a smaller inner frame carrying the ohmically heated cathode and spaced apart from the larger outer frame, and a plurality of members coupling the smaller inner frame to the larger outer frame.

Abstract: Disclosed is a method for prediction of a film material such as a raw material for organic EL. In the method, a film material having an evaporation rate (V(%)) represented by the formula below can be predicted based on the values of the constant (Ko) and the activation energy (Ea). V=(Ko/P)×e?Ea/kT wherein Ko represents a constant (%·Torr), P represents a pressure (Torr), Ea represents an activation energy (eV), k represents a Boltzmann constant, and T represents an absolute temperature.

Abstract: An apparatus and method for producing electrons in a plasma flood gun is disclosed. The apparatus includes an indirectly heated cathode (IHC) which is contained within a pre-fabricated cartridge. This cartridge can be readily replaced in a plasma flood gun. In addition, the use of an IHC reduces the amount of contaminants that are injected into the workpiece or wafer.

Abstract: A dispenser cathode which comprises an emission surface, a reservoir for material releasing, when heated, work-function-lowering particles, and at least one passage for allowing diffusion of work-function-lowering particles from said reservoir to said emission surface, said emission surface comprising at least one emission area and at least one non-emission area covered with emission-suppressing material and surrounding each emission area, said non-emission area comprising at least one passage connecting said reservoir with said non-emission area and debouching within a diffusion length distance from an emission area for allowing diffusion of work-function-lowering particles from said reservoir to said emission area.

Abstract: A dispenser cathode which is comprises an emission surface, a reservoir for material releasing, when heated, work-function-lowering particles, and at least one passage for allowing diffusion of work-function-lowering particles from said reservoir to said emission surface, and emission surface comprising at least one emission area and at least one non-emission area covered with emission-suppressing material and surrounding each emission area, said non-emission area comprising at least one passage connecting said reservoir with said non-emission area and debouching within a diffusion length distance from an emission area for allowing diffusion of work-function-lowering particles from said reservoir to said emission area.

Abstract: It is described an emitter (26, 40) for X-ray tubes comprising: a flat foil with an emitting section (30, 46); and at least two electrically conductive fixing sections (31-34; 41-44); wherein the emitting section (30, 46) is unstructured.

Abstract: A dispenser cathode which comprises an emission surface, a reservoir for material releasing, when heated, work-function-lowering particles, and at least one passage for allowing diffusion of work-function-lowering particles from said reservoir to said emission surface, said emission surface comprising at least one emission area and at least one non-emission area covered with emission-suppressing material and surrounding each emission area, said non-emission area comprising at least one passage connecting said reservoir with said non-emission area and debouching within a diffusion length distance from an emission area for allowing diffusion of work-function-lowering particles from said reservoir to said emission area.

Abstract: To provide an electron source to be used for a surface analyzer such as a scanning or transmission electron microscope or an Auger electron spectroscope, or an electron beam lithography machine, particularly for a semiconductor wafer inspection apparatus such as a scanning electron microscope to be used at a low acceleration with an electron beam acceleration voltage of up to 1 kV, CD SEM or DR SEM. An electron source wherein a barium supplying source consisting of a complex oxide comprising barium oxide and an oxide of metal other than barium, is provided at a portion of a single crystal needle of tungsten or molybdenum.

Abstract: A porous cathode structure is fabricated from a plurality of wires which are placed in proximity to each other in elevated temperature and pressure for a sintering time. The sintering process produces the porous cathode structure which may be divided into a plurality of individual porous cathodes, one of which may be placed into a dispenser cathode support which includes a cavity for containing a work function reduction material such as BaO, CaO, and Al2O3. The work function reduction material migrates through the pores of the porous cathode from a work replenishment surface adjacent to the cavity of the dispenser cathode support to an emitting cathode surface, thereby providing a dispenser cathode which has a uniform work function and therefore a uniform electron emission.

Abstract: A cathode structure comprises a heater including a columnar ceramic body and a heating wire that is partially buried in the ceramic body, and a cathode unit disposed at a first end surface of the ceramic body. The heating wire leads out from a second end surface of the ceramic body.

Abstract: The invention relates to improving the efficiency of ion flow from an ion source, by reducing heat loss from the source both in the ion chamber of the ion source and its constituent parts (e.g. the electron source). This is achieved by lining the interior of the ion chamber and/or the exterior with heat reflective and/or heat insulating material and by formation of an indirectly heated cathode tube such that heat transfer along the tube and away from the ion chamber is restricted by the formation of slits in the tube. Efficiency of the ion source is further enhanced by impregnating and/or coating the front plate of the ion chamber with a material which comprises an element or compound thereof, the ions of which element are the same specie as those to be implanted into the substrate from the source thereof.

Abstract: A discharge electrode emitting electrons into a discharge gas, encompasses an emitter and current supply terminals configured to supply electric current to the emitter. The emitter embraces a wide bandgap semiconductor having at 300 K a bandgap of 2.2 eV or wider. Acceptor impurity atoms and donor impurity atoms being doped in the wide bandgap semiconductor, the activation energy of the donor impurity atoms being larger than the activation energy of the acceptor impurity atoms.

Abstract: A dispenser cathode which comprises an emission surface, a reservoir for material releasing, when heated, work-function-lowering particles, and at least one passage for allowing diffusion of work-function-lowering particles from said reservoir to said emission surface, said emission surface comprising at least one emission area and at least one non-emission area covered with emission-suppressing material and surrounding each emission area, said non-emission area comprising at least one passage connecting said reservoir with said non-emission area and debouching within a diffusion length distance from an emission area for allowing diffusion of work-function-lowering particles from said reservoir to said emission area.

Abstract: An oxide cathode for an electron tube and a method for manufacturing the oxide cathode are provided. In the oxide cathode including a sleeve for a heater, a metal substrate formed on the top of the sleeve, and an electron emission material layer coated on the metal substrate, the electron emission material layer is formed by coating a carbonate paste containing an alkaline earth metal carbonate, an organic blowing agent, and a vehicle on the metal substrate by screen printing, and thermally treating the coated carbonate paste. Picture quality degradation due to a Moire phenomenon is reduced by coating the carbonate paste by screen printing to provide an even cathode surface, and degradation of the cathode by Joule heat is reduced, thereby improving electron emission and lifespan characteristics of the cathode.

Abstract: The present invention relates to a cathode ray structure for a cathode ray tube, and more particularly, to a cathode structure for a cathode ray tube capable of maximizing thermal efficiency and minimizing power consumption.

Abstract: A cathode for an electron tube and a method of preparing the same are provided. The cathode includes a base metal and an electron emissive material layer attached to the base metal. A surface roughness, which is measured from the distance between a highest point and a lowest point of the surface of the electron emissive material layer, is controlled to be no greater than 8 ?m. By controlling the sizes of particles and pores constituting the electron emissive material layer to be uniform and controlling the density and porosity of the electron emissive material layer, the cathode is improved in compactness and surface evenness compared to a cathode prepared according to a spraying method. Accordingly, shrinking of the cathode during operation can be prevented, and the distance between the cathode and a G1 (first grid) electrode can be maintained uniform, so that the life of the cathode can be greatly extended, and a stable electron emission characteristic can be realized.

Abstract: A cathode sleeve structure for housing a heater. The cathode sleeve structure includes: a case member that is cylindrical and an end thereof is open; a plurality of supporting members that extend radially from vicinities of the end of the case member; and a linkage member that connects the plurality of supporting members. The case member, the plurality of supporting members, and the linkage member are formed as one piece.

Abstract: Body (1) formed from a porous matrix impregnated with an electron-emitting material, defined by external faces (11, 12, 13) that all have a roughness of less than 0.2 ?m. Because of this surface finish, the operation and the lifetime of the cathodes provided with such cathode emissive bodies are substantially improved.

Abstract: A magnetron capable of being efficiently assembled is provided. The magnetron includes a filament, a pair of shields, a pair of leads, a pair of connection plates, and a pair of terminal rods. The filament is coil-shaped. The shields are attached to both ends of the filament, respectively. The leads are attached to the shields at first ends of the leads, respectively. The connection plates are attached to second ends of the leads, respectively. The terminal rods are attached to the connection plates, respectively, to supply power to the leads through the connection plates, and have slender protrusions, which have sectional areas smaller than sectional areas of attachment portions of the terminal rods so that the terminal rods are attached to the connection plates with the slender protrusions passing through the connection plates.

Abstract: Cathode comprising a substrate (2) supporting a cathode emissive coating, comprising what is called an emissive central zone (12) and what is called a nonemissive peripheral zone (11); according to the invention: the average density and the emissive zone (12) is greater than that in said nonemissive zone (11), the average thickness in the emissive zone (12) is less than that in the nonemissive zone (11). In this way it is possible to significantly limit the drift in cut-off voltage, while still maintaining good maximum emission performance in DC mode and in pulse mode.

Abstract: An electron gun includes an electron emission cathode, a control electrode, and an extractor and the electron emission cathode is made of rare earth hexaboride. A tip of the electron emission cathode is located between the control electrode and the extractor, and the electron emission surface of the electron emission cathode is spherical or flat.

Abstract: An electron source has an anode and a cathode that is capable of being negatively biased relative to the anode, the cathode having an electron emitting portion and a cathode axis. An electromagnetic radiation source is adapted to generate an electromagnetic radiation beam to heat the cathode. A lens is adapted to direct the electromagnetic radiation beam onto the cathode, the lens having a lens axis that forms an acute angle with, or is substantially parallel to, the cathode axis of the electron emitting portion.

Abstract: A cathode with an improved work function, for use in a lithographic system, such as the SCALPEL™ system, which includes a buffer between a substrate and an emissive layer, where the buffer alters, randomizes, miniaturizes, and/or isolates the grain structure at a surface of the substrate to reduce the grain size, randomize crystal orientation and reduce the rate of crystal growth. The buffer layer may be a solid solution or a multiphase alloy. A method of making the cathode by depositing a buffer between a surface of the substrate and an emissive layer, where the deposited buffer alters, randomizes, miniaturizes, and/or isolates the grain structure at a surface of the substrate to reduce the grain size, randomize crystal orientation and reduce the rate of crystal growth.

Abstract: A nickel alloy for the manufacture of cathodes for cathode-ray tubes, comprises magnesium and aluminium in proportions chosen so as to allow good adhesion of an emissive oxide layer to the basis metal cap consisting of the alloy.

Abstract: The indirectly heated cathode structure includes a base metal having a thermal electron emitting material layer, a cylindrical sleeve holding the base metal at one end portion thereof and housing a heating heater in the inside thereof, an support having a large-diameter portion and g a small-diameter portion, and a cathode disc having a large-diameter portion at the leg-portion-side of the heating heater and having a small-diameter portion at the heater-main-portion side of the heating heater, wherein an outer surface of another end portion of the sleeve and an inner surface of the small-diameter portion of the support are fixed to each other, and an outer surface of the large-diameter portion of the support and an inner surface of the small-diameter portion of the cathode disc are fixed to each other.

Abstract: A metal cathode for an electron-emission device, and an indirectly heated cathode assembly employing the metal cathode where the metal cathode is formed of a quaternary alloy including 0.1-20% by weight barium (Ba), 0.1-20% by weight a metallic mobilizer facilitating Ba diffusion, a metal with a difference in atomic radius of at least 0.4 Angstrom from the atomic radius of platinum (Pt) or palladium (Pd), the metal being in the range of 0.01 to 30% by weight, and a balance of at least one of Pt and Pd. The metal cathode has a low operating temperature due to its reduced work function with improved current emission capability. The metal cathode can be used for a longer lifetime at high current density. Therefore, the metal cathode can be used effectively in electron-beam devices, such as a Braun tube or picture tube, satisfying larger size, longer life span, high definition, and high luminance requirements of the devices.

Abstract: An indirectly heated metal cathode for an electron tube includes a metal sleeve of an Mo material, a metal emitter disposed on the metal sleeve and including Pt or Pd as a main component; and a buffer layer between the metal sleeve and the metal emitter. The buffer layer prevents Mo, an element of the metal sleeve, from diffusing into the emitter during the operation of the metal cathode so that electron-emitting performance does not decrease rapidly with operating time due to an increase in a work function. Therefore, the metal cathode satisfies a long life span requirement for large scale and high definition electron tubes.

Abstract: The oxide cathode comprises a support and an oxide layer on the latter. It furthermore includes particles of a conducting material having a first end incorporated in the support and a second end lodged in the oxide layer, so as to constitute conducting bridges passing through an interface layer forming between the support and the oxide layer. The invention also relates to a process for manufacturing such a cathode. The conducting particles make it possible to improve the electrical conductivity of the cathode, both within the oxide layer and within the interface layer.

Abstract: An indirectly heated cathode for gas discharge tube C1 comprises a heater 1, a double coil 2, a plate member 3, and a metal oxide 10. An electrical insulating layer 4 is formed on the surface of heater 1. Heater 1 is disposed at the inner side of double coil 2. Plate member 3 is disposed along the length direction of double coil 2 at the inner side of double coil 2, which is to be the discharge surface side, and is electrically connected to double coil 2. Also, plate member 3 is grounded by being connected to the ground terminal of heater 1. Metal oxide 10 is held by double coil 2 and disposed to be in contact with plate member 3. Metal oxide 10 is in contact with double coil 2.

Abstract: Disclosed is a cathode in a cathode ray tube including a cathode sleeve having a heater inside, a base metal supported by the cathode sleeve so as to be formed at an upper end of the cathode sleeve, and an emission layer formed on the base metal, wherein the emission layer includes alkaline earth metal oxide and Y2O3-doped ThO2. The present invention enables to prevent the degradation of endurance of the cathode by carrying out the generation and extinction of free Ba stably.

Abstract: An electron gun also has a cathode for emitting electrons, a heater cap which contains a heater for applying the cathode with thermal energy for emitting electrons, a retainer for securing the cathode on the heater cap by clamping the peripheral edge of the cathode onto the heater cap, and a cylindrical Wehnelt supporter. The cylindrical Wehnelt supporter has a Wehnelt electrode for focusing an electron beam that is formed in such a shape that an average angle of the surface thereof with respect to an outermost shell of the electron beam matches a Pierce angle, and three or more heater cap supporters for securely supporting the heater cap at a position at which an electron emitting surface of the cathode and an opening formed through the wehnelt electrode satisfy a predetermined perveance.

Abstract: Cathode comprising a substrate (2) supporting a cathode emissive coating, comprising what is called an emissive central zone (12) and what is called a nonemissive peripheral zone (11); according to the invention:

Abstract: A cathode sleeve structure for housing a heater. The cathode sleeve structure comprises: a case member that is cylindrical and an end thereof is open; a plurality of supporting members that extend radially from vicinities of the end of the case member; and a linkage member that connects the plurality of supporting members. The case member, the plurality of supporting members, and the linkage member are formed as one piece.

Abstract: A cathode ray tube is provided with at least one oxide cathode including a cathode carrier with a cathode base of a cathode metal and a cathode coating of an electron-emitting material with oxide particles. The oxide particles contain an alkaline earth oxide selected from the group formed by the oxides of calcium, strontium, and barium, doped with an oxide doping in a quantity ranging from 120 to maximally 500 ppm of an oxide selected from the oxides of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. The electron-emitting material has an electric conductance of 3*10−3 &OHgr;−1 cm−1 to 12.5*10−3 &OHgr;−1 cm−1.

Abstract: A cathode ray tube has an electron gun including an indirectly heated cathode structure having a heater therein. The heater has a major heating portion formed of a spirally wound heating wire and two leg portions connected to opposite ends of the major heating portion. The two leg portions are welded to electrical conductors for applying voltages thereto at portions in the vicinity of open ends of the two leg portions, respectively, and the heater is covered with an insulating film except for the portions for welding. The two leg portions includes at least five layers of winding formed by spirally winding heating wires identical with the heating wire of the major heating portion, and the numbers of turns per unit length in each of the at least five layers of winding are smaller than a number of turns per unit length of the heating wire of the major heating portion.

Abstract: An electron tube cathode is disclosed, comprising a base, electron emissive material layers formed on the base and containing alkaline earth metal oxides including barium, and reducing metal layers interposed between the emissive material layers. The metal layers comprise at least one metal selected from W, Mo, Ta and Ti. The metal layers further comprise any one of rhenium, yttrium or a mixture thereof in the amount of 3 to 5 wt % thereof. The amount of the entire metal layer is 8 to 15 wt % of the entire emissive layer comprising the emissive material layers and the metal layers. The entire metal layer has a thickness of 3 to 5 &mgr;m. Each of the metal layers comprise at least one or more layers formed by means of a spraying method. The present invention provides advantages of enhancing emission characteristics and life characteristics of the cathode by increasing the amount of free Ba.

Abstract: In a cathode with an electron-emissive material layer formed on a base containing a reducing element, a relationship of 0.24≦B/A≦0.93 is satisfied, where A denotes a surface for layer formation of the base and B represents an area where the base and the electron-emissive material layer are in contact with each other. In addition, a relationship of 0.4≦D/C≦0.7 is satisfied, where C and D denote thicknesses of the base and the electron-emissive material layer, respectively. Thus, a cathode structure is provided in which sufficient electron emission can be obtained, a decrease in electron emission with the passage of time is not much during the operation, and variations in cut-off voltage are small.

Abstract: A cathode ray tube includes a phosphor screen and an electron gun. The electron gun includes an indirectly heated cathode structure and plural grid electrodes in axially spaced relationship. The cathode structure includes a base metal having an electron emissive material coating and a heater for heating the base metal. The heater includes a major heating portion having a spirally wound heating wire and leg portions disposed at ends of the major heating portion, and each of the leg portions includes a first multilayer winding portion having heating wires wound spirally in plural layers and a second multilayer winding portion disposed intermediate between the major heating portion and the first multilayer winding portion and having heating wires wound in plural layers.

Abstract: A metal cathode for an electron-emission device, and an indirectly heated cathode assembly employing the metal cathode where the metal cathode is formed of a quaternary alloy including 0.1-20% by weight barium (Ba), 0.1-20% by weight a metallic mobilizer facilitating Ba diffusion, a metal with a difference in atomic radius of at least 0.4 Angstrom from the atomic radius of platinum (Pt) or palladium (Pd), the metal being in the range of 0.01 to 30% by weight, and a balance of at least one of Pt and Pd. The metal cathode has a low operating temperature due to its reduced work function with improved current emission capability. The metal cathode can be used for a longer lifetime at high current density. Therefore, the metal cathode can be used effectively in electron-beam devices, such as a Braun tube or picture tube, satisfying larger size, longer life span, high definition, and high luminance requirements of the devices.

Abstract: Cold electrodes for gas discharges have an electrically conductive carrier material on which an emission coating is disposed. The photoelectric output work of the material of the emission coating is less than that of the carrier material or less than 5.6*10-19 joule/electron. The emission coating can, in particular, contain yttrium. The electrode preferably has the form of a hollow body and can be embedded in a glass body.

Abstract: An impregnated cathode whose initial electron emitting performance, lifetime property, and insulating property for an electron gun are excellent and that is suitable for mass production, and a method for manufacturing the same. In the impregnated cathode, the porosity of the sintered body of porous metal is continuously increased as the distance in the depth direction from an electron emitting face is increased. A pellet of sintered body of metal raw material has pores in it. The pores are filled with electron emitting material. The porosity is continuously increased as the distance in the depth direction from an electron emitting face is increased. Thus, since the discontinuity inside the pellet is not formed, a reaction generating free Ba continuously and smoothly proceeds on the entire pellet. In addition, since raw material powder having more than one kind of particle size is not necessary to be used, the manufacturing process can be simplified. Moreover, various functions such as lifetime property, etc.

Abstract: A cathode for use in an electron gun includes a base metal comprising Ni as a principal component and a two-layer electron emissive material disposed on the base metal. The inner layer is comprised of an alkaline earth metal oxide and 1-30 wt. % W and may further include 0.1-5 wt. % of a rare earth metal oxide. The outer layer is comprised of an alkaline earth metal oxide and may further include 0.1-5 wt. % of a rare earth metal oxide. The outer electron emissive layer provides stability for the cathode. In the degassing and activation process, W and Ni react at high temperatures to form a Ni4W fine crystal structure. An intermediate layer, such as Ba2SiO4, is dispersed in the Ni4W fine crystal structure in operation. Free barium is produced in reactions between the various cathode components to provide a high current density for the cathode. The normalized electron emission current value of the cathode does not decrease with use, even over extended periods of operation.

Abstract: A cathode ray tube has an electron gun including an indirectly heated cathode structure having a heater therein. The heater has a major heating portion formed of a spirally wound heating wire and two leg portions connected to opposite ends of the major heating portion. The two leg portions are welded to electrical conductors for applying voltages thereto at portions in the vicinity of open ends of the two leg portions, respectively, and the heater is covered with an insulating film except for the portions for welding. The two leg portions includes at least five layers of winding formed by spirally winding heating wires identical with the heating wire of the major heating portion, and the numbers of turns per unit length in each of the at least five layers of winding are smaller than a number of turns per unit length of the heating wire of the major heating portion.

Abstract: A cathode structure comprises a cylindrical metal sleeve having aperture portions at both ends, a base metal having an aperture portion on one end, which is fitted onto one of the aperture portions of the metal sleeve, and an electron-emitting layer, which is formed on a flat portion of an outside surface of the base metal. After an electron-emitting material is sprayed onto the base metal, its surface is mechanically flattened to form the electron-emitting layer. Thus, the planarity of the surface of the electron-emitting layer can be improved without deterioration of the electron emission characteristics and the moiré can be decreased without reduction of the resolution.

Abstract: An electric discharge tube or discharge lamp comprising a scandate dispenser cathode which is composed of a cathode body and a coating having an emissive surface, said cathode body including a matrix of at least one refractory metal and/or a refractory alloy and a barium compound which is in contact with the matrix material to supply barium to the emissive surface by means of a chemical reaction with said matrix material, and the coating containing one or more multilayers which may include a bottom layer of tungsten and/or a tungsten alloy, an intermediate layer of rhenium and/or a rhenium alloy and a top layer of scandium oxide, a mixture of scandium oxide and rare-earth metal oxides, a scandate and/or a scandium alloy, is characterized by a long service life and a high emission-current density.

Abstract: A cathode ray tube include phosphor screen and an electron gun. The electron gun includes an indirectly heated cathode structure and plural grid electrodes arranged in axially spaced relationship. The cathode structure includes a base metal having an electron emissive material coating and a heater for heating the base metal. The heater includes a major heating portion having a spirally wound heating wire and a pair of leg portions connected to opposite ends of the major heating portion. The major heating portion and an inner portion of each of the leg portions on a major-heating-portion side thereof are covered with an insulating coating, and the heater is welded to electrical conductors for applying a voltage thereto at an outer portion of each of the leg portions, the outer portion not being covered with the insulating coating.

Abstract: An indirectly heated cathode that can enhance the withstand voltage and the efficiency of radiating heat from a heater to a tubular sleeve, and a cathode ray tube using such a cathode. The indirectly heated cathode comprises a hot cathode emitting electrons at one end, and a tubular sleeve including a high melting point metal and having a heater inside. A thermal absorption layer is formed on the inside face of the tubular sleeve and the thermal absorption layer contains a boron compound.