Mechanically stable electron source

Abstract

To provide an electron source comprising an insulating base, a pair of conductive terminals, an insulating support member, a drift separation member, an emitter-cathode, and one or more heating elements.SOLUTION: Conductive terminals are exposed from a first surface of an insulating base. An insulating support member extends from the first surface of the insulating base. A drift isolation member is disposed at an end of the insulating support member remote from the insulating base. An emitter-cathode is coupled to the drift isolation member. One or more heating elements are coupled to the conductive terminals and the drift isolation member. Combination of the drift isolation member with the insulating support member can prevent stress-induced drift from impacting a position of the emitter-cathode, thereby improving mechanical stability of the electron source.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] The present disclosure relates generally to electron guns or electron sources, and more specifically to field emission guns (FEGs) or field emission sources with enhanced mechanical stability, for use in, for example, electron microscopes. CROSS-REFERENCE TO RELATED APPLICATIONS Summary of the Invention

[0002] Embodiments of the disclosed subject matter provide an electron source with enhanced mechanical stability and a method for making the same. In conventional electron sources, the heating element is spot welded at both ends to conductive terminals of an insulating base and directly to the emitter-cathode in the middle region. Mechanical stresses built up in the heating element or the corresponding spot welds are transferred to the emitter-cathode, causing drift in the emitter-cathode position over time. In some embodiments, the emitter-cathode and the heating element are instead indirectly coupled together through an intervening drift isolation member that is rigidly attached to the insulating base by an insulating support member. Alternatively, in some embodiments, the emitter-cathode is rigidly attached to the insulating base by an insulating support member and the heating element is directly coupled to the emitter-cathode near the junction between the emitter-cathode and the insulating support member. As a result, changes in the emitter-cathode position from stress-induced mechanical drift can be avoided or at least reduced, thereby resulting in a more mechanically stable electron source over time.

[0003] In one or more embodiments, the electron source can include an insulating base, a pair of conductive terminals, an insulating support member, a drift isolation member, an emitter-cathode, and one or more heating elements. The pair of conductive terminals can be exposed from a first surface of the insulating base. The insulating support member can extend from the first surface of the insulating base. The drift isolation member can be disposed at an end of the insulating support member remote from the insulating base. The emitter-cathode can be coupled to the drift isolation member. The one or more heating elements can be coupled to the conductive terminals and the drift isolation member.

[0004] In one or more embodiments, the electron source can include an insulating base, a pair of conductive terminals, an insulating support member, an emitter-cathode, and one or more heating elements. The pair of conductive terminals can be exposed from a first surface of the insulating base. The insulating support member can extend from the first surface of the insulating base. The emitter-cathode can be coupled to the insulating support member. The one or more heating elements can extend between and be coupled to the conductive terminals and the emitter-cathode. The one or more heating elements can be coupled to the emitter-cathode at one or more respective first locations substantially adjacent a junction between the emitter-cathode and the insulating support member.

[0005] In one or more embodiments, the electron source can include an insulating base, a pair of conductive terminals, an emitter-cathode, one or more heating elements coupled to at least the conductive terminals, and a means for isolating the emitter-cathode from mechanical drift.

[0006] In one or more embodiments, a method of fabricating an electron source can include bonding an insulating support member to an insulating base having a plurality of conductive terminals. The method can also include bonding a drift isolation member to the insulating support member. The method can further include bonding an emitter to the drift isolation member. The method can also include bonding one or more heating elements to the conductive terminals. The method can further include bonding one or more heating elements to the drift isolation member. The method can also include forming an emitter tip at an end of the emitter to form an emitter-cathode.

[0007] In one or more embodiments, a method of manufacturing an electron source can include bonding an insulating support member to an insulating base having a plurality of conductive terminals. The method can also include bonding an emitter to the insulating support member. The method can further include bonding one or more heating elements to the conductive terminals. The method can also include bonding one or more heating elements to the emitter at one or more first locations substantially adjacent a junction between the emitter and the insulating support member. The method can further include forming an emitter tip at an end of the emitter to form an emitter-cathode.

[0008] Any of the various innovations of the present disclosure can be used in combination or separately. This Summary is provided to introduce a selection of concepts in a simplified form that are further described in the Detailed Description below. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. The foregoing and other objects, features, and advantages of the disclosed technology will become apparent from the following Detailed Description, which proceeds with reference to the accompanying drawings. [Brief description of the drawings]

[0009] The following description proceeds with reference to the accompanying drawings, which are not necessarily drawn to scale. Where applicable, some elements may be simplified or not illustrated to help illustrate and explain the underlying functionality. Like reference numbers refer to like elements throughout the drawings.

[0010] [Figure 1A] 1A and 1B are perspective and top-down plan views of an electron source with a heating element directly coupled to the emitter-cathode. [Figure 1B] 1A and 1B are perspective and top-down plan views of an electron source with a heating element directly coupled to the emitter-cathode. [Figure 2A] FIG. 1 is a simplified schematic diagram illustrating a particular aspect of a mechanically stable electron source in which an emitter-cathode and a heating element are indirectly coupled together by an intervening drift isolation member, in accordance with one or more embodiments of the disclosed subject matter. [Figure 2B] FIG. 2 is a simplified schematic diagram illustrating certain aspects of another mechanically stable electron source in which the emitter-cathode is directly coupled to the heating element, in accordance with one or more embodiments of the disclosed subject matter. [Figure 3A] 1A and 1B are front and rear views, respectively, of a first exemplary electron source in accordance with one or more embodiments of the disclosed subject matter. [Figure 3B] 1A and 1B are front and rear views, respectively, of a first exemplary electron source in accordance with one or more embodiments of the disclosed subject matter. [Figure 3C] FIG. 4 is a detailed perspective view of the first exemplary electron source of FIGS. 3A-3B. [Figure 3D] FIG. 4 is a detailed perspective view of the first exemplary electron source of FIGS. 3A-3B. [Figure 3E] FIG. 4 is a simplified plan view showing the positional relationship between a heating element, a drift isolation member, an insulating support member, and an emitter-cathode in the first exemplary electron source of FIGS. 3A-3D. [Figure 3F] FIG. 13 is a simplified plan view showing the positional relationship between a heating element, a drift isolation member, an insulating support member, and an emitter-cathode in a modified example of the first exemplary electron source. [Figure 4A] 1A and 1B are front and rear views, respectively, of a second exemplary electron source in accordance with one or more embodiments of the disclosed subject matter. [Figure 4B] 1A and 1B are front and rear views, respectively, of a second exemplary electron source in accordance with one or more embodiments of the disclosed subject matter. [Figure 4C] FIG. 5 is a simplified perspective view of a drift isolation member employed in the second exemplary electron source of FIGS. 4A-4B. [Figure 4D] FIG. 4C is a detailed perspective view of the second exemplary electron source of FIGS. 4A-4B. [Figure 4E] FIG. 13 is a simplified plan view showing the positional relationship of a heating element, a drift isolation member, an insulating support member, and an emitter-cathode in a second exemplary electron source. [Figure 4F] 11A-11C are simplified cross-sectional views of variations of drift isolation members that can be used in either the first and second exemplary electron sources. [Figure 4G] FIG. 4F is a detailed perspective view of an electron source with a drift separator of FIG. 4F. [Figure 5A] 11A and 11B are front and rear views, respectively, of a third exemplary electron source in accordance with one or more embodiments of the disclosed subject matter. [Figure 5B] 11A and 11B are front and rear views, respectively, of a third exemplary electron source in accordance with one or more embodiments of the disclosed subject matter. [Figure 5C] FIG. 5C is a simplified perspective view of a drift isolation member employed in the third exemplary electron source of FIGS. 5A-5B. [Figure 5D] FIG. 5C is a detailed perspective view of the third exemplary electron source of FIGS. 5A-5B. [Figure 5E] FIG. 13 is a simplified plan view showing the positional relationship between a heating element, a drift isolation member, an insulating support member, and an emitter-cathode in a third exemplary electron source. [Figure 5F] FIG. 13 is a simplified side view of a variation of a drift isolation member that can be used in any of the first through third exemplary electron sources. [Figure 5G]FIG. 5C is a detailed perspective view illustrating a variation of the third exemplary electron source using the drift isolation member of FIG. 5F, in accordance with one or more embodiments of the disclosed subject matter. [Figure 5H] FIG. 5H is a simplified plan view showing the positional relationship between the heating element, drift isolation member, insulating support member, and emitter-cathode in the electron source of FIG. 5G. [Figure 6A] 11A-11C are front and rear views, respectively, of a fourth exemplary electron source in accordance with one or more embodiments of the disclosed subject matter. [Figure 6B] 11A-11C are front and rear views, respectively, of a fourth exemplary electron source in accordance with one or more embodiments of the disclosed subject matter. [Figure 6C] FIG. 7 is a detailed perspective view of the fourth exemplary electron source of FIGS. 6A-6B. [Figure 6D] FIG. 13 is a simplified plan view showing the positional relationship between a heating element, a drift isolation member, an insulating support member, and an emitter-cathode in a fourth exemplary electron source. [Figure 6E] FIG. 5F is a detailed side view illustrating a variation of the fourth exemplary electron source using the drift isolation member of FIG. 5F, in accordance with one or more embodiments of the disclosed subject matter. [Figure 6F] FIG. 6F is a simplified plan view showing the positional relationship between the heating element, drift isolation member, insulating support member, and emitter-cathode in the electron source of FIG. 6E. [Figure 6G] FIG. 5F is a detailed side view illustrating another variation of the fourth exemplary electron source that uses a variation of the drift isolation member of FIG. 5F, in accordance with one or more embodiments of the disclosed subject matter. [Figure 6H] FIG. 6H is a simplified plan view showing the positional relationship between the heating element, drift isolation member, insulating support member, and emitter-cathode in the electron source of FIG. 6G. [Figure 6I] FIG. 13 is a simplified perspective view of a variation using multiple drift isolation members for use in any of the first through fourth exemplary electron sources in accordance with one or more embodiments of the disclosed subject matter. [Figure 6J]FIG. 6C is a simplified plan view showing the positional relationships between the heating element, drift isolation member, insulating support member, and emitter-cathode in an electron source using the variation of FIG. 6I in accordance with one or more embodiments of the disclosed subject matter. [Figure 7A] FIG. 13 is a front view of a fifth exemplary electron source in accordance with one or more embodiments of the disclosed subject matter. [Figure 7B] FIG. 13 is a simplified plan view showing the positional relationship between a heating element, an insulating support member, and an emitter-cathode in a fifth exemplary electron source. [Figure 7C] FIG. 7C is a detailed perspective view of a variation of the fifth exemplary electron source of FIGS. 7A-7B. [Figure 8A] 11A and 11B are front and rear views, respectively, of a sixth exemplary electron source in accordance with one or more embodiments of the disclosed subject matter. [Figure 8B] 11A and 11B are front and rear views, respectively, of a sixth exemplary electron source in accordance with one or more embodiments of the disclosed subject matter. [Figure 8C] 8A-8B, in accordance with one or more embodiments of the disclosed subject matter. FIG. [Figure 9] FIG. 2 is a process flow diagram of an exemplary method for manufacturing an electron source in accordance with one or more embodiments of the disclosed subject matter. [Figure 10A] 1A and 1B are perspective and detailed perspective views, respectively, illustrating assembly of a drift isolation member in an exemplary manufacturing method, in accordance with one or more embodiments of the disclosed subject matter. [Figure 10B] 1A and 1B are perspective and detailed perspective views, respectively, illustrating assembly of a drift isolation member in an exemplary manufacturing method, in accordance with one or more embodiments of the disclosed subject matter. [Figure 10C] FIG. 11 is a detailed perspective view illustrating a variation of the assembly of the drift isolation member in accordance with one or more embodiments of the disclosed subject matter. [Figure 11A] 1A and 1B are perspective and detailed perspective views, respectively, illustrating assembly of an emitter in an exemplary manufacturing method, in accordance with one or more embodiments of the disclosed subject matter. [Figure 11B]1A and 1B are perspective and detailed perspective views, respectively, illustrating assembly of an emitter in an exemplary manufacturing method, in accordance with one or more embodiments of the disclosed subject matter. [Figure 12A] 1A and 1B are perspective and detailed perspective views, respectively, illustrating assembly of a heating element in an exemplary manufacturing method, in accordance with one or more embodiments of the disclosed subject matter. [Figure 12B] 1A and 1B are perspective and detailed perspective views, respectively, illustrating assembly of a heating element in an exemplary manufacturing method, in accordance with one or more embodiments of the disclosed subject matter. [Figure 13A] 1A and 1B are perspective and detailed perspective views, respectively, illustrating formation of an emitter tip in an exemplary manufacturing method in accordance with one or more embodiments of the disclosed subject matter. [Figure 13B] 1A and 1B are perspective and detailed perspective views, respectively, illustrating formation of an emitter tip in an exemplary manufacturing method in accordance with one or more embodiments of the disclosed subject matter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] General Considerations For the purpose of this description, certain aspects, advantages, and novel features of the disclosed embodiments are described herein. The disclosed methods and systems should not be construed as limiting in any manner. Rather, the present disclosure is directed to all novel and non-obvious aspects and aspects of the various disclosed embodiments, both alone and in various combinations and subcombinations with one another. The methods and systems are not limited to any particular aspect or feature, or combination thereof, and the disclosed embodiments do not require that any one or more particular advantages exist or problems be solved. Also, the techniques of any embodiment or example can be combined with any one or more of the techniques described in the other embodiments or examples. In light of the numerous possible embodiments to which the principles of the disclosed technology may be applied, it should be recognized that the illustrated embodiments are merely illustrative and should not be construed as limiting the scope of the disclosed technology.

[0012] Although some operations of the disclosed methods are described in a particular order for convenient presentation, it should be understood that this description style encompasses reordering, unless a particular order is required by specific terms described below. For example, operations described sequentially may in some cases be reordered or performed simultaneously. Furthermore, for simplicity, the accompanying drawings may not show the various ways in which the disclosed methods may be used with other methods. In addition, the description may use terms such as "provide" and "achieve" to describe the disclosed methods. These terms are high-level abstractions of actual operations that are performed. The actual operations that correspond to these terms may vary depending on the particular implementation and are readily discernible to those skilled in the art.

[0013] Disclosure of numerical ranges should be understood as referring to each discrete point within the range, including the endpoints, unless otherwise indicated. Unless otherwise indicated, all numerical values ​​expressing amounts of components, molecular weights, percentages, temperature, time, etc., used in the specification or claims should be understood as modified by the term "about". Thus, unless otherwise implied or expressly indicated, or unless the context is properly understood by those skilled in the art to have a more determinative configuration, the numerical parameters recited are approximations that may depend on the desired properties sought and / or detection limits under standard testing conditions / methods known to those skilled in the art. When directly and explicitly distinguishing the embodiments from the prior art discussed, the number of the embodiments is not approximate unless the word "about" is recited. Whenever "substantially", "approximately", "about", or similar words are expressly used in conjunction with a particular value, a variation of 10% or less of that value is intended, unless otherwise indicated.

[0014] Directions and other relative references may be used to facilitate discussion of the figures and principles herein, but are not intended to be limiting. For example, certain terms such as "inside," "outside," "upper," "lower," "internal," "external," "left," "right," "front," "rear," and the like may be used. These terms are used for clarity of explanation when dealing with relative relationships, where applicable, particularly with respect to the illustrated embodiments. However, these terms are not intended to imply absolute relationships, positions, and / or orientations. For example, with respect to an object, an "upper" portion can become a "lower" portion by simply flipping the object over. Nevertheless, it is still the same portion and the object remains the same.

[0015] As used herein, "comprising" means "including," and the singular forms "a" or "an" or "the" include plural references unless the context clearly dictates otherwise. The term "or" refers to a single element or a combination of two or more elements of stated alternative elements, unless the context clearly dictates otherwise.

[0016] Although there are alternatives for the various components, parameters, operating conditions, etc. described herein, this is not meant to imply that the alternatives are necessarily equivalent and / or will perform equally well, nor is it meant to imply that the alternatives are listed in order of preference unless otherwise stated. Any of the groups defined below may be substituted or not substituted unless otherwise stated.

[0017] Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, suitable methods and materials are described below. The materials, methods, and examples are illustrative only and are not intended to be limiting. Other features of the present disclosure will be apparent from the following detailed description and the appended claims.

[0018] Introduction Electron microscopes use electron beams to image or analyze objects. To generate the electron beam, the microscope uses an electron source, such as a field emission gun (FEG), which uses a sharply pointed Mueller-type emitter (e.g., emitter-cathode) held at a negative potential (e.g., several kilovolts) to cause field electron emission. Such emitter-cathode can be either cold cathode type (e.g., cold field (CF) emitter), Schottky type (e.g., coated to form a reservoir to reduce the work function of thermionic emission), or thermal field type (e.g., thermal field emitter (TFE)). For example, Figures 1A-1B show an example of a Schottky-type electron source 100 that can be used in an electron microscope. The electron source 100 includes an insulating base 102 (e.g., ceramic) with a pair of conductive terminals 104a, 104b (also referred to herein as posts) exposed from a top surface 102t of the base 102. A heating element 106 (also referred to herein as a heating filament) extends between and is coupled to the terminals 104a, 104b via respective spot welds 114a, 114b. An emitter-cathode 110 is coupled to a central region of the heating element 106 via a spot weld 112. The emitter-cathode 110 has a sharply pointed tip 110a at an opposite end of the emitter-cathode 110 from a base end 110b (also referred to herein as a tail end). Between the base end 110b and the tip 110a, the emitter-cathode 110 has a body region 110c of substantially constant diameter.

[0019] In the illustrated example, the emitter-cathode 110 includes a reservoir 124 coated on the body region 110c proximal to the tip 110a. However, if the emitter-cathode is constructed as a TFE or CF emitter, the reservoir 124 may be omitted. Additionally, in the illustrated example, the spot weld 112 is provided proximal to the base end 110b. However, the spot weld 112 may be located elsewhere along the body region 110c between the reservoir 124 and the base end 110b. Other attachment mechanisms (e.g., brazing, etc.) are possible instead of or in addition to spot welding.

[0020] However, it has been found that the electron source 100 develops mechanical instability over time. In particular, when the electron source 100 is operated, the position of the emitter-cathode 110 tends to drift over time, with the position change being greatest in the period immediately following initial installation of the emitter source. Thus, the electron beam generated by the emitter source 100 may initially be aligned with the optical axis of the microscope, but shortly after installation, the electron beam becomes misaligned (e.g., off-axis) due to mechanical drift of the emitter, thereby requiring realignment by an operator or technician. As the emitter-cathode 110 continues to drift during operation, additional repair operations may be required to realign the electron source 100 to compensate for such ongoing position changes.

[0021] 1A-1B, the inventors have discovered that mechanical stresses introduced during the manufacturing process build up in the heating element 106 and corresponding spot welds 112, 114a, and 114b. During operation of the electron source 100 in the electron microscope, the built up stresses are gradually released, thus moving the emitter-cathode 110 away from its initial aligned position.

[0022] Disclosed herein are electron sources with enhanced mechanical stability that can avoid or at least reduce stress-induced emitter-cathode position drift over time. In some embodiments, the electron source employs a separate structure that provides mechanical support to the emitter-cathode and does not rely solely on the heating element to provide such support. Thus, the functions of thermal heating and structural support can be separated and independently optimized. Furthermore, in some embodiments, the structure (e.g., material composition, dimensions, etc.) of the heating element is altered to further reduce the effect of any accumulated stress on the emitter-cathode position. Thus, after initial alignment when installed in an electron microscope, electron sources according to embodiments of the disclosed subject matter may remain substantially aligned with the optical axis of the microscope over time and do not require realignment, or at least less frequent alignment interventions, as would otherwise be the case.

[0023] For example, FIG. 2A illustrates certain aspects of a mechanically stable electron source 200 in accordance with one or more embodiments of the disclosed subject matter. The electron source 200 includes an emitter-cathode 210, an insulating base 202, and a pair of conductive terminals 204a, 204b (e.g., metal), which may be supported by or coupled to the insulating base 202, for example, via respective couplings 226a, 226b (e.g., brazed or soldered joints). When configured as a Schottky-type emitter, the emitter-cathode 210 may have a coating that forms a reservoir. For example, a Schottky-type emitter-cathode may be made of zirconium oxide (ZrO 2 The emitter-cathode 210 may be formed from tungsten (W) (and / or alloys thereof) with a TFE or CF emitter reservoir. Alternatively, when configured as a TFE or CF emitter, the emitter-cathode 210 may be formed without a coating or reservoir. For example, a TFE or CF emitter-cathode may be formed from single crystal tungsten (W).

[0024] The electron source 200 further includes one or more heating elements. In the example of Fig. 2A, the two heating elements 206a, 206b are respectively coupled to the conductive terminals 204a, 204b, for example, via respective couplings 214a, 214b (e.g., spot welds). However, it should be understood that instead, a single heating element can be provided, the heating element being coupled to opposite ends of the respective conductive terminals 204a, 204b via the couplings 214a, 214b.

[0025] The electron source 200 further includes an insulating support member 208, which may be supported by or coupled to the insulating base 202, for example, via a coupling 222 (e.g., a sintered joint). The insulating support member 208 and the insulating base 202 may each be formed from one or more ceramic materials, which may be the same or different for both. In general, the ceramic material is selected to have a relatively low thermal conductivity at the elevated temperatures generated during operation of the electron source 200. For example, the ceramic material may have a thermal conductivity of 10.0 W / mK or less at temperatures exceeding 1000° C. For example, in some embodiments, the insulating support member 208, the insulating base 202, or both, may be formed from aluminum oxide (Al 2 O 3 ) or Mullite (3Al 2 O 3 2SiO 2 or 2AlO 3 SiO 2 ). Other types of ceramic materials for the insulating support member 208, the insulating base 202, or both are possible according to one or more contemplated embodiments.

[0026] The electron source 200 also includes a drift isolation member 220 (e.g., metal or having a metal surface) supported by or coupled to an insulating support member 208, e.g., via a coupling 218 (e.g., a brazed or soldered joint). The emitter-cathode 210 of the electron source 200 can be supported by or coupled to the drift isolation member 220, e.g., via a coupling 212 (e.g., a spot weld). The heating elements 206a, 206b are also coupled to the drift isolation member 220, e.g., via respective couplings 216a, 216b (e.g., spot welds). Thus, the emitter-cathode 210 and the heating elements 206a, 206b are indirectly coupled to each other via the intervening drift isolation member 220. The insulating support member 208 rigidly connects the drift isolation member 220 to the insulating base 202, thereby providing support to the emitter-cathode 210. The combination of the drift isolation member 220 and the insulating support member 208, and their respective couplings thereto, act to isolate the emitter-cathode 210 from displacements induced by stresses (e.g., thermal expansion stresses, residual spot weld induced stresses, etc.) and may therefore be considered a mechanical drift isolation means 224.

[0027] In general, the drift separation member 220 can have a size larger than the heating elements 206a, 206b, the emitter-cathode 210, or both, but still small enough to avoid adverse effects on source thermal management by the heat sink. For example, the drift separation member 220 can have a maximum lateral dimension in a plane perpendicular to the extension direction of the emitter-cathode that is at least two times (e.g., three times or more) larger than the maximum diameter of the emitter-cathode. For example, if the drift separation member 220 is configured as a cylinder or semi-cylinder, the maximum lateral dimension includes its diameter. Thus, if the emitter-cathode 210 has a diameter of 50 μm to 500 μm, the drift separation member 220 has a diameter of at least 100 μm to 1 mm. Other exemplary shapes of the drift separation member 220 are also possible, and certain non-limiting examples are discussed in more detail below.

[0028] Additionally, in some embodiments, the drift isolation member 220 can be formed from a material that is stiffer (e.g., has a greater modulus of elasticity) than that of the heating elements 206a, 206b. For example, in some embodiments, the material forming the drift isolation member 220 has a modulus of elasticity of 400 GPa or more, while the material forming the heating elements 206a, 206b has a modulus of elasticity of 400 GPa or less, such as 200 GPa or less. The stiffer material of the drift isolation member 220, compared to the softer material of the heating elements 206a, 206b, can further isolate positional changes to the heating elements rather than affecting the emitter-cathode 210.

[0029] In some embodiments, the flexibility of the heating elements 206a, 206b can be further increased by modifying their size and / or shape. For example, the heating elements 206a, 206b can have a diameter (or maximum cross-sectional dimension in the case of a non-circular cross-section) of 10 mils (e.g., 250 μm) or less. In some embodiments, the heating elements 206a, 206b can have a diameter that is 5 mils (e.g., 127 μm) or less, e.g., 3 mils (e.g., 76 μm). In some embodiments, the heating elements 206a, 206b have a variable cross-sectional profile along their length, e.g., to increase the flexibility of the heating elements at positions away from the emitter-cathode 210. For example, the diameter of the heating elements welded to the conductive terminals can be reduced (e.g., by electrochemical etching, grinding, etc.) compared to the diameter of the heating elements welded to the drift isolation member.

[0030] In general, the material of the electron source 200 should also be selected to withstand the high temperatures generated during operation of the electron source 200, for example, by having a melting temperature substantially higher than 1800-2000K. For example, the conductive terminals may be formed from molybdenum (Mo), which has a melting temperature of about 2896K. In some embodiments, to reduce the current required to achieve a desired operating temperature (e.g., 1800K), the material forming the heating elements 206a, 206b may be selected to have a relatively high electrical resistivity. For example, the heating element material may have an electrical resistivity of at least 50 nΩ·m. In some embodiments, the electrical resistivity of the heating element may be at least 100 nΩ·m. In certain embodiments, for example, the drift isolation member 220 is formed from rhenium (Re), which has an elastic modulus of about 461 GPa and a melting temperature of about 3458K. In a particular embodiment, for example, the heating elements 206a, 206b are formed from tantalum (Ta), which has an elastic modulus of approximately 186 GPa, a melting temperature of approximately 3290 K, and an electrical resistivity of approximately 131 nΩ·m (at 20° C.).

[0031] Alternatively, in some embodiments, the emitter-cathode can be rigidly attached to an insulating base by an insulating support member, and the heating element can be directly coupled to the emitter-cathode. For example, FIG. 2B shows a particular embodiment of such a mechanically stable electron source 250. Similar to FIG. 2A, the electron source 250 includes an insulating base 202, conductive terminals 204a, 204b, heating elements 206a, 206b (or a single heating element), and an insulating support member 208. Details of such components and the coupling between them are the same as those described above for the electron source 200 of FIG. 2A and will not be repeated here. When configured as a Schottky-type emitter, the emitter-cathode 252 can have a coating forming a reservoir, for example, along a central portion 252c proximal to the emitter tip 252a. Alternatively, when configured as a TFE or CF emitter, the emitter-cathode 252 can be formed without a coating or reservoir.

[0032] 2A, however, the electron source 250 has an emitter-cathode 252 that is supported by or directly coupled to the insulating support member 208, for example, via a bond 258 (e.g., a brazed or soldered joint). In the illustrated example, a base end portion 252b of the emitter-cathode 252 is coupled to the insulating support member 208 (e.g., a top surface thereof). Thus, the emitter-cathode 252 extends axially away from the insulating support member 208, with its emitter tip 252a spaced from the insulating support member 208 and an intermediate central portion 252c (or body portion) separating the emitter tip 252a from the base end portion 252b (or tail end).

[0033] 2A, the heating elements 206a, 206b are directly bonded to the emitter-cathode 252 at the base end portion 252b, for example, via respective bonds 216a, 216b (e.g., spot welds) located near the junction between the emitter-cathode 252 and the insulating support member 208. As used herein, "near" refers to a portion of the heating element welded to the emitter-cathode that is no more than three heating element diameters away (less than 381 μm for a 127 μm diameter heating element) from the junction between the emitter-cathode and the insulating support member. Because the heating elements 206a, 206b are mounted near the rigid junction, rather than in the intermediate portion 252c, positional variations (e.g., due to accumulated stress or thermal expansion variations) introduced by the heating elements can be avoided or at least reduced. The combination of the base end portion 252b and the insulating support member 208, and their respective bonds thereto, act to isolate the emitter-cathode 252 from stress-induced displacements (e.g., thermal expansion stresses, residual spot weld stresses, stresses due to torsion during manufacturing, etc.) and may therefore be considered a mechanical drift isolation means 224.

[0034] To further isolate the location of the emitter-cathode 252 from the direct coupling of the heating elements 206a, 206b, in some embodiments, the base end portion 252b can be made more rigid than the remainder of the emitter-cathode 252, for example, by having an increased diameter compared to the central portion 252c. For example, the base end portion 252b can have a diameter that is at least two times larger (e.g., three times or more) than the diameter of the middle portion 252c of the emitter-cathode 252. Thus, if the middle portion 252c of the emitter-cathode 252 has a diameter of 50 μm to 500 μm, the base end portion 252b has a diameter of at least 100 μm to 1 mm.

[0035] Examples of electron sources 3A-3E show a first example of an electron source 300. The electron source 300 has a Schottky-type emitter-cathode 310 with a reservoir 324 (omitted if the emitter-cathode 310 is instead configured as a TFE or CF emitter), an insulating base 302, a pair of conductive terminals 304a, 304b, and a single heating element 306. The heating element 306 extends between the conductive terminals 304a, 304b and is coupled to the conductive terminals via respective spot welds 314a, 314b. In the illustrated example, the heating element 306 is coupled to the top surface of the terminals 304a, 304b. However, it is also possible that the heating element 306 could instead be coupled to the side of the terminals 304a, 304b, for example, in a manner similar to that shown in FIGS. 1A-1B.

[0036] The electron source 300 further comprises an insulating support member 308 and a drift isolation member 320. In the illustrated example, the insulating support member 308 is a cylindrical ceramic rod and the drift isolation member 320 is a semi-cylindrical metal rod. For example, the insulating support member 308 has a diameter D of about 0.8 mm. ISM As noted above, the drift separation member can have a maximum lateral dimension that is at least two times (e.g., at least three times) larger than the dimensions of the emitter-cathode 310, the heating element 306, or both. For example, the emitter-cathode 310 can have a diameter D of about 50-150 μm. EC and the heating element can have a diameter D of less than about 250 μm. HE Thus, the drift separation member 320 may have a diameter (or maximum lateral dimension), W, of, for example, about 0.3-0.5 mm. DIM Of course, these dimensions are intended to be exemplary only, and other sizes and dimensions are possible in accordance with one or more contemplated embodiments.

[0037] The insulating support member 308 is coupled at one end to the top surface 302t of the insulating base 302. The drift isolation member 320 is coupled (e.g., brazed) to the end of the insulating support member 308 opposite the insulating base 302 along the axial direction 326 of the emitter-cathode 310. Alternatively, in some embodiments, the insulating support member may be a cylindrical ceramic tube, such as the tube 350 of FIG. 3F. Instead of being coupled to the end of the insulating support member, an end portion of the drift isolation member 320 may be disposed in a central recess of the tube 350, or in a conduit 352, and the outer peripheral wall 320o may be coupled (e.g., brazed) to the inner peripheral wall 350i of the tube 350. The diameter of the conduit 352 may thus substantially match the diameter of the drift isolation member 320, e.g., about 0.3-0.5 mm. In either case, the drift isolation member 320 may be spaced apart from the drift isolation member 320 by a distance L of, e.g., about 1-2 mm. DIM The insulating support member may extend beyond the end of the insulating support member by only a distance of 10 mm. Again, these dimensions are for illustrative purposes only and other sizes and dimensions are possible in accordance with one or more contemplated embodiments.

[0038] Returning to FIGS. 3A-3E, the heating element 306 follows a generally arcuate U-shaped or V-shaped path between the conductive terminals 304a, 304b. The path shape (e.g., angle) and length of the heating element 306 can be varied to achieve a desired thermal profile. A central portion of the heating element 306 is coupled to the outer diameter side (e.g., curved side) of the drift isolation member 320 by a spot weld 316. The emitter-cathode 310 is coupled to the inner diameter side (e.g., flat side) of the drift isolation member 320 by a spot weld 312. Thus, the heating element 306 and the emitter-cathode 310 are disposed on opposite sides of the drift isolation member 320 and are indirectly coupled to each other via the intervening drift isolation member 320. In some embodiments, the spot weld 316 can be substantially adjacent to the insulating support member 308 along the axial direction 326 (e.g., such that the lower end of the heating element 306 that is welded to the drift isolation member 320 is within a diameter D of the heating element 306 from the upper surface of the insulating support member 308). HE3A), while spot weld 312 may be located approximately at the center of drift isolation member 320 along axial direction 326. Alternatively or additionally, spot weld 316 is closer to insulating support member 308 along axial direction 326 than spot weld 312 (e.g., spot weld 316 is between spot weld 312 and insulating support member 308).

[0039] 4A-4E show a second example of an electron source 400. The electron source 400 is identical to that of FIGS. 3A-3E, except that the drift isolation member 420 is a rectangular rod rather than a semi-cylindrical rod. As noted above, the drift isolation member 420 can have a maximum lateral dimension (e.g., the length of one side shown in FIG. 4E) that is at least two times (e.g., at least three times) larger than that of the emitter-cathode 310, the heating element 306, or both. A central portion of the heating element 306 is coupled to one side 420b of the drift isolation member 420 by a spot weld 416, and the emitter-cathode 310 is coupled to the opposite side 420a of the drift isolation member 420a by a spot weld 412. Thus, the heating element 306 and the emitter-cathode 310 are disposed on opposite sides of the drift isolation member 420 and are indirectly coupled to one another via the intervening drift isolation member 420. In some embodiments, spot weld 416 can be substantially adjacent to insulating support member 308 along axial direction 326, while spot weld 412 can be approximately centered on drift isolation member 420 along axial direction 326. Alternatively or additionally, spot weld 416 is closer to insulating support member 308 along axial direction 326 than spot weld 412 (e.g., spot weld 416 is between spot weld 412 and insulating support member 308).

[0040] FIG. 4F illustrates a drift isolation member 440 that can be used in place of the drift isolation member 320 of the electron source 300 of FIGS. 3A-3E or the drift isolation member 420 of the electron source 400 of FIGS. 4A-4E. FIG. 4G illustrates an electron source that uses the drift isolation member 440. The drift isolation member 440 is similar in shape and operation to the drift isolation member 320. However, the drift isolation member 440 includes an inner semi-cylindrical rod 442 formed from a ceramic and an outer coating 444 formed from a metal. In some embodiments, the rod 442 can be formed from the same ceramic as the insulating support member 308 and / or the insulating base 302, e.g., aluminum oxide or mullite.

[0041] In some embodiments, the outer coating 444 can be formed from a metal having a high stiffness (e.g., Re), as described in other ways above. However, in some embodiments, since the ceramic inner rod 442 already imbues the drift isolation member 440 with increased stiffness, the metal for the coating 444 can be selected to optimize other properties. For example, since the coating 444 provides a surface for bonding thereto (e.g., via spot welds 446) the emitter-cathode 310 and the heating element 306, the metal for the coating 444 can be selected to optimize or at least improve such bonding. Alternatively or additionally, the metal for the coating 444 can be selected to optimize or at least improve thermal radiation properties.

[0042] 5A-5E show a third example of an electron source 500. The electron source is the same as that of FIGS. 4A-4E, except that the drift isolation member 520 is a U-shaped bar instead of a rectangular bar. In particular, the drift isolation member 520 has a first longitudinal arm 520a, a second longitudinal arm 520b, and a lateral strut or crossbar 520c connecting the first and second longitudinal arms together. A gap 522 separates the first and second longitudinal arms from one another, the gap 522 being open at the end of the drift isolation member 520 opposite the crossbar 520c. When installed in the electron source 500, the first and second longitudinal arms 520a, 520b extend parallel to the axial direction 326, with the opening of the gap 522 facing the top surface of the insulating support member 308.

[0043] As in the previous example, the emitter-cathode 310 is coupled to one side of the drift isolation member 520 by spot welds 512. For example, the emitter-cathode 310 can be welded to a central portion of the crossbar 520c, as shown in Figures 5A, 5D, and 5E. The heating element 306 is also coupled to the drift isolation member 520 on the opposite side of the emitter-cathode 310, e.g., in a region substantially adjacent the insulating support member 308 along the axial direction 326. However, because the drift isolation member 520 has a gap 522 in the center of this region, the heating element 306 can instead be coupled to each of the longitudinal arms 520a, 520b, e.g., at spot welds 516a and 516b, as shown in Figure 5B. As described above, the drift isolation member 520 can have a maximum lateral dimension (e.g., the length or width of the crossbar 520c in FIG. 5E) that is at least two times (e.g., at least three times) larger than that of the emitter-cathode 310, the heating element 306, or both.

[0044] FIG. 5F illustrates a drift isolation member 540 that can be used in place of the drift isolation member 520 of the electron source 500 of FIGS. 5A-5E. FIGS. 5G-5H illustrate an electron source that uses the drift isolation member 540. The drift isolation member 540 has a pair of angled arms 540a, 540b that meet at a peak 540c, thereby forming a V-shape. A gap 542 separates the angled arms 540a, 540b from one another, with the gap 542 being open at an end of the drift isolation member 540 opposite the peak 540c. When installed in an electron source, the angled arms 540a, 540b extend in a direction that is transverse to the axial direction 326, such that the peak 540c coincides with the axial direction 326 at a location away from the insulating support member 308.

[0045] As in the previous example, the emitter-cathode 310 is bonded to one side of the drift isolation member 540 by a spot weld 552. For example, the emitter-cathode 310 can be welded to the peak 540c as shown in Figures 5G and 5H. The heating element 306 is also bonded to the drift isolation member 540 on the opposite side of the emitter-cathode 310, for example, in a region substantially adjacent the insulating support member 308 along the axial direction 326. However, since the drift isolation member 540 has a gap 542 at its center in this region, the heating element 306 can instead be bonded to each of the angled arms 540a, 540b. As noted above, the drift isolation member 540 can have a maximum lateral dimension (e.g., the length or width of the peak 540c in Figure 5H) that is at least two times (e.g., at least three times) larger than that of the emitter-cathode 310, the heating element 306, or both.

[0046] In some embodiments, the drift isolation member 540 can be formed from a metal having a high stiffness (e.g., Re), as otherwise described above. Alternatively, the drift isolation member 540 can be formed from the same material as the heating element 306. For example, both the heating element 306 and the drift isolation member 540 can be formed from tantalum filaments. In some embodiments, the drift isolation member 540 and the heating element 306 are both formed from metal filaments, but the heating element 306 is modified to be more flexible than the drift isolation member 540, for example, by having a smaller diameter and / or by reducing the diameter proximal to the conductive terminals 304a, 304b (e.g., at the spot welds 314a, 314b).

[0047] FIG. 5G further illustrates another optional variation of the electron source, in particular in which the emitter-cathode 310 is coupled to the drift isolation member at the central portion 310c (e.g., via spot weld 552) rather than at the base end portion 310b. Instead, the base end portion 310b is disposed proximate to the top surface 308t of the insulating support member 308, but separated therefrom by a narrow gap. Alternatively, in some embodiments, the base end portion 310b of the emitter-cathode 310 can be disposed in contact with the top surface 308t of the insulating support member 308. Alternatively, in some embodiments, the base end portion 310b of the emitter-cathode 310 can be coupled (e.g., brazed) to the top surface 308t of the insulating support member 308. Such an emitter-cathode configuration may be applied to any of the other electron source configurations described herein, including those of Figures 3A-3E, 4A-4G, 5A-5E, 6A-6J, and 8A-8B.

[0048] 6A-6D show a fourth example of an electron source 600. The electron source is identical to that of FIGS. 5A-5E, except that instead of a single heating element, two separate heating elements 606a, 606b are used. In particular, a first heating element 606a extends from conductive terminal 304a and is coupled thereto by spot weld 314a, and a second heating element 606b extends from conductive terminal 304b and is coupled thereto by spot weld 314b. In the illustrated example, each heating element 606a, 606b is coupled to a top surface of a respective one of terminals 304a, 304b. However, it is also possible that the heating elements are instead coupled to the sides of terminals 304a, 304b, for example, in a manner similar to that shown in FIGS. 1A-1B.

[0049] Heating element 606a follows a partial arcuate path from conductive terminal 304a to a sidewall of longitudinal arm 520a of drift isolation member 520, and heating element 606b follows another partial arcuate path from conductive terminal 304b to a sidewall of longitudinal arm 520b of drift isolation member 520 (e.g., a mirror image of heating element 606a about axial direction 326). Each heating element 606a, 606b is coupled to a corresponding sidewall of drift isolation member 520 by spot welds 616a, 616b, respectively. Alternatively, each heating element 606a, 606b can instead be coupled to a side of longitudinal arm 520a, 520b on the opposite side of emitter-cathode 310 in a manner similar to that described above for FIG. 5E. The provision of separate heating elements 606a, 606b (e.g., separated by gap 522 in drift isolation member 520) can result in improved thermal performance, at least as compared to the configurations of FIGS. 5A-5E. In some embodiments, the path shape (e.g., angle) and length of each heating element 606a, 606b can be varied to achieve a desired thermal profile. In general, however, it may be desirable to have the same shape and length for heating elements 606a, 606b to avoid asymmetries that may result in thermally induced stresses in drift isolation member 520.

[0050] 6E-6F show a variation of the electron source of FIGS. 6A-6D using the drift isolation member 540 of FIG. 5F instead of the drift isolation member 520. As in the previous example, the emitter-cathode 310 is coupled to one side of the drift isolation member 540 by spot welds 552. For example, the emitter-cathode 310 can be welded to the peak 540c as shown in FIGS. 6E and 6F. Additionally, each heating element 606a, 606b is coupled to a corresponding sidewall of the drift isolation member 540 by spot welds 618a, 618b, respectively. Alternatively, each heating element 606a, 606b can instead be coupled to the side of the angled arm 540a, 540b on the opposite side of the emitter-cathode 310 in a manner similar to that described above for FIG. 5H.

[0051] 6G-6H show a further variation in which the drift isolation member of FIG. 5F is extended beyond the top surface of the insulating support member. For example, the insulating support member 658 can have a pair of channels or recesses 660a, 660b in its top surface 658t. Similar to the drift isolation member 540, the drift isolation member 650 has a pair of angled arms 650a, 650b that meet at a peak 650c. The emitter-cathode 310 can be coupled to one side of the drift isolation member 650, for example at the peak 650c, by spot welds 652. Additionally, each heating element 606a, 606b can be coupled to a respective one of the arms 650a, 650b, for example via a respective spot weld 656a, 656b. In contrast to the previous example, however, each arm 650a, 650b has a lower end 652a, 652b that fits within a channel 660a, 660b of the insulating support member 658 so as to extend beyond the outer periphery of the insulating support member 658 below the insulating support member's upper surface 658t. In some embodiments, the drift isolation member 650 can be coupled to the insulating support member 658 by brazing the lower end 652a, 652b within the channel 660a, 660b. Thus, the spot welds 656a, 656b are kept farther away from the spot welds 654 of the emitter-cathode 310 and are further isolated by the bond to the insulating support member 658, which may provide further improvements in mechanical isolation and / or thermal performance for the resulting electron source.

[0052] 6I-6J show further variations of the isolation structure 670 using multiple drift isolation members 672a, 672b. For example, each drift isolation member 672a, 672b may be substantially identical to the drift isolation member 540 shown in FIG. 5F. However, one of the drift isolation members 672a, 672b may have a different size or shape compared to the other to allow the drift isolation members to be arranged in an orthogonal orientation, for example, as shown in FIGS. 6I-6J. Each of the drift isolation members 672a, 672b may be coupled to the insulating support member 308 (e.g., via brazing). Alternatively or additionally, the drift isolation members 672a, 672b may be coupled to one another, for example, by welding together proximal sections of their respective peaks. In some embodiments, the emitter-cathode 310 can be coupled to one or both of the drift isolation members 672a, 672b, for example, with the emitter-cathode 310 located at an inner corner formed by an orthogonal arrangement, as shown in Figure 6J. Such an isolation structure 670 can further improve the mechanical isolation of the emitter-cathode.

[0053] 7A-7B show a fifth example of an electron source 700. The electron source 700 includes a Schottky-type emitter-cathode 710 with a reservoir 324 (omitted if the emitter-cathode 310 is instead configured as a TFE or CF emitter), an insulating base 302, a pair of conductive terminals 304a, 304b, and a single heating element 306. The emitter-cathode 710 includes, along an axial direction 326, an emitter tip 710a, a base end portion 710b, and a central portion 710c between the emitter tip 710a and the base end portion 710b. The electron source 700 further includes an insulating support member 308 coupled at one end thereof to a top surface 302t of the insulating base 302. A base end portion 710 b of the emitter-cathode 710 is coupled (eg, brazed) along the axial direction 326 to the end of the insulating support member 308 opposite the insulating base 302 .

[0054] The heating element 306 extends between the conductive terminals 304a, 304b and is coupled to the conductive terminals via respective spot welds 314a, 314b. In the illustrated example, the heating element 306 is coupled to the top surface of the terminals 304a, 304b. However, it is also possible for the heating element 306 to be coupled to the side of the terminals 304a, 304b instead, for example, in a manner similar to that shown in FIGS. 1A-1B. The heating element 306 follows a generally arcuate U- or V-shaped path between the conductive terminals 304a, 304b. The path shape (e.g., angle) and length of the heating element 306 can be varied to achieve a desired thermal profile. A central portion of the heating element 306 is coupled to the base end portion 710b by spot welds 712.

[0055] Because the heating element 306 is directly coupled to the emitter-cathode 710, the emitter may be susceptible to mechanical drift. For additional stability, in some embodiments, the spot weld 712 may be substantially adjacent to the insulating support member 308 along the axial direction 326 (e.g., when the bottom end of the heating element 306 welded to the base end portion 710b is substantially adjacent to the diameter D of the heating element 306). HE (so as to be spaced from the top surface of the insulating support member 308 by a distance no greater than twice the distance between the reservoir 324 and the top surface of the insulating support member 308). Alternatively or additionally, the location of the spot weld 712 can be closer to the insulating support member 308 along the axial direction 326 than to the reservoir 324.

[0056] Further, in some embodiments, the base end portion 710b (or a sub-portion thereof) can have an enlarged diameter to increase its rigidity. The spot weld 712 is then placed within this enlarged diameter portion. For example, the base end portion 710b can have a diameter at least two times (e.g., at least three times) larger than the diameter of the intermediate portion 710c of the emitter-cathode 710, the heating element 306, or both. For example, the intermediate portion 710c of the emitter-cathode 710 can have a diameter of about 50-150 μm, and the heating element can have a diameter of less than about 250 μm. Thus, the base end portion 710b can have a diameter of about 0.5-0.8 mm, for example. Of course, these dimensions are intended to be exemplary only, and other sizes and dimensions are possible according to one or more contemplated embodiments. Alternatively, in some embodiments, placement of the spot weld 712 proximal to the joint between the emitter-cathode and the insulating support member 308 may be sufficient to avoid mechanical instability without further modification. Thus, in such embodiments, the emitter-cathode 310 may have a substantially constant diameter along its length, at least for the base end portion 310b and the intermediate portion 310c, as shown in FIG. 7C, for example.

[0057] 8A-8B show a sixth example of an electron source 800. The electron source is identical to that of FIGS. 6A-6D, except that the emitter-cathode 810 has a split configuration. In particular, the emitter-cathode 810 has an axially extending gap 802 that extends through the base end portion 810b and the middle portion 810c. The gap 802 may terminate before reaching the emitter tip 810a. As with the previous examples, the emitter-cathode 810 is coupled to the drift isolation member 520, in particular to the side of the crossbar 520c. For example, multiple spot welds 812a, 812b can be used on the opposite side of the base end portion 810b to couple the base end portion to the drift isolation member 520 while leaving the gap 802 open or exposed. Alternatively, a single spot weld can be used to bond base end portion 810b to the side of crossbar 520c in a manner similar to that described for Figures 5A-5E and 6A-6D. Alternatively, base end portion 810b can be bonded to the top surface of crossbar 520c by one or more spot welds, in which case gap 802 may be closed by contact with drift isolation member 520 otherwise. The split configuration of emitter-cathode 810 may further improve thermal performance.

[0058] FIG. 8C shows a variation 820 that uses drift isolation members 822a, 822b instead of the drift isolation member 520 in the electron source of FIGS. 8A-8B. The drift isolation members 822a, 822b may be mirror images of each other in the axial direction. The drift isolation members 822a, 822b may be separated by a gap 824 that may align with or at least overlap the axially extending gap 802 of the emitter-cathode 810. In essence, the drift isolation members 822a, 822b provide a shape similar to that of the drift isolation member 520, but are separated into separate components by the gap 824. Such a configuration may lead to further improvements in mechanical isolation and thermal performance.

[0059] Manufacturing Example 9 illustrates an exemplary method 900 for fabricating a mechanically stable electron source. Method 900 can begin at process block 902 by providing an insulating base with a conductive terminal. In some embodiments, providing process block 902 can include forming a suitable conduit in the insulating base (e.g., a ceramic base), inserting a conductive terminal (e.g., a metal post) in the conduit, and bonding (e.g., via brazing or soldering) the conductive terminal to the insulating base. In some embodiments, the conductive terminal is exposed from a top surface of the insulating base.

[0060] The method 900 may proceed to process block 904 where the insulating support member is coupled to the insulating base. For example, the insulating support member and insulating base may both be formed from ceramic, and one end of the insulating support member may be coupled (e.g., by sintering) to a top surface of the insulating base. Alternatively, in some embodiments, the insulating support member may be formed from the insulating base instead of a separate member being coupled to the insulating base. In such embodiments, the coupling at process block 904 is replaced with the formation of the insulating support member, for example, by etching or machining the top surface of the insulating base to form axially extending protrusions as the insulating support member. In some embodiments, the insulating support member 308 is formed or coupled to the insulating base 302 so as to extend further from its top surface than the conductive terminals 304a, 304b, for example, as shown in FIG. 10A.

[0061] The method 900 can proceed to process block 906 where the drift isolation member is bonded to the insulating support member. FIGS. 10A-10B show an exemplary bond between a drift isolation member 320 in the form of a semi-cylindrical metal rod and an insulating support member 308 in the form of a solid ceramic rod. For example, an axial end 320b of the drift isolation member 320 can be brazed to a top surface 308t of the insulating support member 308. Alternatively, in some embodiments, a recess 1002r can be formed in the insulating support member 1002, as shown in FIG. 10C, and an end of the drift isolation member 320 can be inserted into the recess 1002r. A circumferential surface 320s of the inserted end of the drift isolation member 320 can be brazed to a surface of the recess 1002r, while the remaining portion of the drift isolation member 320 protrudes above the top surface 1002t of the insulating support member 1002. Alternatively, in some embodiments, the insulating support member is constructed as a cylindrical tube, and the ends of the drift isolation members are disposed therein in a manner similar to that shown in FIG. 10C.

[0062] Returning to FIG. 9, the method 900 may proceed to process block 908 where the emitter-cathode is bonded to the drift isolation member. FIGS. 11A-11B illustrate an exemplary bonding of an emitter blank 1008 to a drift isolation member 320. For example, the emitter blank 1008 (also referred to herein simply as the emitter) may be placed on a flat side of a semi-cylindrical metal rod of the drift isolation member 320 and bonded thereto using one or more spot welds. For example, the emitter blank 1008 may include a single crystal rod of tungsten.

[0063] Returning to FIG. 9, the method 900 can proceed to process block 910 where one or more heating elements are coupled to conductive terminals, and process block 912 where the heating elements are coupled to the drift isolation member. FIGS. 12A-12B show exemplary coupling of the heating element 306 to the conductive terminals 304a, 304b and the drift isolation member 320. For example, the heating element 306 can be coupled at its respective ends to the conductive terminals 304a, 304b (e.g., to the top, side, or any other portion of the terminals 304a, 304b) via respective spot welds. For example, a central portion of the heating element 306 can be disposed on the rounded exterior of the semi-cylindrical metal rod of the drift isolation member 320 and coupled thereto using one or more spot welds. As discussed in detail above, the spot welds joining the heating element 306 to the drift isolation member 320 can be positioned substantially adjacent to the joint between the drift isolation member 320 and the insulating support member 308 (e.g., top surface 308t), while the spot welds joining the emitter blank 1008 to the drift isolation member 320 can be positioned along the axial direction, near the center of the drift isolation member 320.

[0064] In some embodiments, the heating element can be modified to have a variable diameter. For example, the ends of the heating element 306 that are bonded to the conductive terminals 304a, 304b can be reduced in diameter compared to the central portion that is bonded to the drift isolation member 320. The diameter of the ends of the heating element 306 can be reduced before or after bonding to the conductive terminals. For example, the diameter of the ends of the heating element 306 can be reduced by electrochemical etching or grinding. Other diameter reduction methods are possible according to one or more contemplated embodiments. Alternatively, the heating element 306 can be manufactured with a variable diameter (e.g., by wire drawing) instead of subjecting the heating element to post-manufacturing modifications.

[0065] Returning to FIG. 9, the method 900 may proceed to process block 914 where an emitter tip is formed at the end of the emitter blank. FIGS. 13A-13B illustrate an exemplary formation of an emitter tip of the emitter-cathode 310 from the emitter blank 1008. For example, the emitter blank 1008 may be etched to form a sharp emitter. In some embodiments, if the emitter-cathode is a Schottky type, the process block 914 may further include coating the emitter blank to form a reservoir. For example, the coating may include zirconium oxide. The reservoir may be located closer to the tip of the emitter-cathode than the spot weld that connects the heating element 306 to the drift isolation member. After process block 914, the resulting electron source is ready for use and the manufacturing method 900 may be complete.

[0066] Although process blocks 902-914 of method 900 are shown separately in FIG. 9, in some embodiments, the process blocks may be combined and performed together (concurrently or sequentially). Additionally, while FIG. 9 shows a particular order for blocks 902-914 of method 900, embodiments of the disclosed subject matter are not limited thereto. Indeed, in certain embodiments, the blocks may occur in a different order than shown, or simultaneously with other blocks. For example, bonding of the heating element to the drift isolation member in process block 912 may occur before bonding of the heating element to the conductive terminal in process block 910. In another example, formation of the emitter-cathode tip in process block 914 may occur before bonding of the emitter blank to the drift isolation member in process block 908. Thus, embodiments of the disclosed subject matter are not limited to the particular order shown in FIG. 9 and described above.

[0067] In a variation of the manufacturing method 900, process blocks 906, 908 can be omitted by directly bonding the emitter blank to the insulating support member, for example as shown in FIGS. 7A-7C. In such an embodiment, process block 912 can also be omitted by directly bonding the heating element to the emitter blank. However, to reduce the effect of any stress-induced variations from the heating element on the emitter-cathode position, the bonding of the heating element to the emitter blank is at a location substantially adjacent to the junction between the emitter blank and the insulating support member (e.g., at the top surface 308t). In some embodiments, process block 914 can further include forming the emitter blank to form an enlarged diameter end to which the heating element is bonded and / or to form a middle portion having a reduced diameter compared to the end. Alternatively, in some embodiments, the emitter blank can be formed with the enlarged diameter end prior to bonding the emitter blank to the insulating support member.

[0068] Additional Examples of the Disclosed Technology In view of the above implementations of the disclosed subject matter, the present application discloses additional examples in the sections listed below. It should be noted that a feature of a single section, or a combination of two or more features of that section, is also included in the disclosure of the present application, optionally in combination with one or more features of one or more additional sections and examples.

[0069] Item 1. An electron source, An insulating base; a pair of conductive terminals exposed from a first surface of the insulating base; an insulating support member extending from a first surface of the insulating base; a drift isolation member disposed at an end of the insulating support member remote from the insulating base; an emitter-cathode coupled to the drift isolation member; and one or more heating elements coupled to the conductive terminals and to the drift isolation member.

[0070] Item 2. The electron source of any item or example herein, particularly item 1, wherein the insulating base is formed from a first ceramic and / or the insulating support member is formed from a second ceramic.

[0071] Item 3. One or both of the first ceramic and the second ceramic is aluminum oxide (Al 2 O 3 ) or Mullite (3Al 2 O 3 2SiO 2 or 2Al 2 O 3 SiO 2 The electron source according to any of the clauses or examples herein, particularly clause 2, including

[0072] Item 4. The electron source of any one of the items or examples herein, particularly any one of items 1-3, wherein the insulating support member comprises a ceramic rod and the drift separation member is bonded to an axial end surface of the ceramic rod.

[0073] Item 5. The electron source according to any of the items or examples of this specification, particularly any one of items 1 to 3, wherein the insulating support member includes a ceramic tube, and at least a portion of the drift separation member is disposed within the ceramic tube and bonded to its inner circumferential surface.

[0074] Item 6. An electron source according to any item or example herein, particularly any one of items 1-5, wherein the emitter-cathode is welded to a first side of the drift isolation member and / or one or more heating elements are welded to a second side of the drift isolation member opposite the first side.

[0075] Clause 7. An electron source according to any clause or example herein, particularly any one of clauses 1-6, wherein the one or more heating elements are welded to the drift separation member at one or more respective first locations, and / or the emitter-cathode is welded to the drift separation member at a second location, and / or the one or more first locations are closer to the insulating support member along the axial direction of the emitter-cathode than the second location.

[0076] Item 8. The electron source of any item or example herein, particularly item 7, wherein the first location is substantially adjacent to a junction between the drift isolation member and the insulating support member.

[0077] Item 9. The electron source of any item or example herein, particularly any one of items 1-8, wherein the drift separation member comprises a first metal, and / or the heating element comprises a second metal, and / or the emitter-cathode comprises a third metal.

[0078] Item 10. The electron source of any item or example herein, especially item 9, wherein the drift isolation member comprises a ceramic member coated with the first metal.

[0079] Item 11. The electron source according to any one of the items or examples herein, particularly any one of items 9-10, wherein the first metal has a modulus of elasticity greater than the modulus of elasticity of the second metal.

[0080] Item 12. The electron source of any one of the items or examples herein, particularly any one of items 9 to 11, wherein the second metal has an electrical resistivity of more than 100 nΩ·m and / or an elastic modulus of less than 200 GPa, or the second metal has an electrical resistivity of more than 50 nΩ·m and / or an elastic modulus of less than 400 GPa.

[0081] Item 13. The electron source of any of the items or examples herein, particularly any one of items 9 to 12, wherein the first metal has an elastic modulus of at least 400 GPa.

[0082] Item 14. The electron source according to any one of the items or examples herein, in particular any one of items 9 to 13, wherein the first metal is rhenium (Re) and / or an alloy thereof, and / or the second metal is tantalum (Ta) and / or an alloy thereof, and / or the third metal is tungsten (W) and / or an alloy thereof.

[0083] Item 15. An electron source according to any of the items or examples herein, particularly any one of items 1 to 14, wherein the drift separation member has a maximum lateral dimension in a plane perpendicular to the extension direction of the emitter-cathode, and the maximum lateral dimension is at least twice as large as the maximum diameter of the emitter-cathode.

[0084] Item 16. The electron source of any of the items or examples herein, particularly any one of items 1 to 15, wherein the emitter-cathode is constructed as a Schottky emitter with a reservoir, the reservoir being positioned along the axial direction of the emitter-cathode closer to the tip of the emitter-cathode than the drift separation member.

[0085] Item 17. The reservoir is made of zirconium oxide (ZrO 2 20. The electron source according to any of the clauses or examples, particularly clause 16, of the present specification, comprising a coating of

[0086] Item 18. The electron source according to any item or example herein, particularly any one of items 1-15, wherein the emitter-cathode is constructed as a reservoir-less hot-field or cold-field emitter.

[0087] Item 19. The electron source of any of the items or examples herein, particularly any one of items 1-18, wherein one or more heating elements have a diameter of less than 127 μm (5 mils) or one or more heating elements have a diameter of less than 250 μm (10 mils).

[0088] Clause 20. The electron source of any clause or example herein, particularly any one of clauses 1-19, wherein the one or more heating elements have a first diameter proximate the conductive terminal and a second diameter proximate the drift isolation member, the first diameter being smaller than the second diameter.

[0089] Item 21. The electron source of any of the items or examples herein, particularly any one of items 1 to 20, wherein the drift separation member has a semi-cylindrical shape, and / or the emitter-cathode is bonded to a flat side of the semi-cylindrical shape, and / or one or more heating elements are bonded to a curved side of the semi-cylindrical shape.

[0090] Item 22. The electron source of any of the items or examples herein, particularly any one of items 1 to 20, wherein the drift separation member has a rectangular bar shape, and / or the emitter-cathode is coupled to one side of the rectangular bar shape, and / or one or more heating elements are coupled to an opposing side of the rectangular bar shape.

[0091] Clause 23. An electron source according to any clause or example herein, particularly any one of clauses 1-20, wherein the drift separation member has at least two arms separated by a gap, and / or the arms extend from an insulating support member along an axial direction of the emitter-cathode to a junction or strut spaced from the insulating support member, and / or the emitter-cathode is coupled to the drift separation member at a junction or strut, and / or one or more heating elements are coupled to the drift separation member of an arm.

[0092] Item 24. An electron source according to any item or example herein, particularly any one of items 1 to 23, wherein the emitter-cathode has an axially extending open gap extending from one end of the emitter-cathode proximate the drift separation member to an intermediate position spaced from the tip of the emitter-cathode.

[0093] Item 25. An electron source, An insulating base; a pair of conductive terminals exposed from a first surface of the insulating base; an insulating support member extending from a first surface of the insulating base; an emitter-cathode coupled to an insulating support member; one or more heating elements extending between and coupled to the conductive terminal and the emitter-cathode; An electron source, wherein one or more heating elements are coupled to the emitter-cathode at one or more respective first locations substantially adjacent a junction between the emitter-cathode and an insulating support member.

[0094] Clause 26. The electron source of any clause or example herein, particularly clause 25, wherein the emitter-cathode has a first diameter at a first position, and the emitter-cathode has a second diameter away from the first position and away from a tip of the emitter-cathode, the first diameter being greater than the second diameter.

[0095] Item 27. The electron source of any item or example herein, particularly item 26, wherein the first diameter is at least two times larger than the second diameter.

[0096] Item 28. The electron source of any one of the items or examples of this specification, particularly any one of items 25 to 27, wherein the insulating base is formed from a first ceramic and / or the insulating support member is formed from a second ceramic.

[0097] Item 29. One or both of the first ceramic and the second ceramic are aluminum oxide (Al 2 O 3 ) or Mullite (3Al 2 O 3 2SiO 2 or 2Al 2 O 3 SiO 2 29. The electron source according to any one of the paragraphs or examples herein, particularly any one of paragraphs 25 to 28, including

[0098] Item 30. The insulating support member includes a ceramic rod, and the emitter-cathode is bonded to an axial end surface of the ceramic rod; or The electron source according to any one of the paragraphs or examples herein, particularly paragraphs 25 to 29, wherein the insulating support member comprises a ceramic tube, and at least a portion of the emitter-cathode is disposed within the ceramic tube and bonded to its inner circumferential surface.

[0099] Item 31. The electron source according to any of the items or examples herein, particularly any one of items 25 to 30, wherein the heating element comprises a metal having an electrical resistivity of more than 100 nΩ·m and / or an elastic modulus of less than 200 GPa, or the heating element comprises a metal having an electrical resistivity of more than 50 nΩ·m and / or an elastic modulus of less than 400 GPa.

[0100] Item 32. The electron source according to any of the items or examples herein, particularly any one of items 25 to 31, wherein the heating element comprises tantalum (Ta) and / or an alloy thereof, and / or the emitter-cathode comprises tungsten (W) and / or an alloy thereof.

[0101] Clause 33. An electron source according to any clause or example herein, in particular any one of clauses 25 to 32, wherein the emitter-cathode is constructed as a Schottky emitter with a reservoir, the reservoir being positioned along the axial direction of the emitter-cathode closer to the tip of the emitter-cathode than the one or more first positions.

[0102] Item 34. The reservoir is made of zirconium oxide (ZrO 2 34. The electron source according to any of the clauses or examples herein, in particular clause 33, comprising a coating of

[0103] Item 35. The electron source according to any of the items or examples herein, particularly any one of items 25-32, wherein the emitter-cathode is constructed as a reservoir-less cold-field emitter.

[0104] Item 36. The electron source of any one of items or examples herein, particularly items 25-35, wherein one or more heating elements have a diameter of less than 127 μm (5 mils) or one or more heating elements have a diameter of less than 250 μm (10 mils).

[0105] Clause 37. The electron source of any clause or example herein, particularly any one of clauses 25-36, wherein the one or more heating elements have a first diameter proximal to the conductive terminal and a second diameter proximal to the one or more first locations, the first diameter being smaller than the second diameter.

[0106] Item 38. An electron source, An insulating base; A pair of conductive terminals; An emitter-cathode; one or more heating elements coupled to at least the conductive terminals; and means for isolating the emitter-cathode from mechanical drift.

[0107] Item 39. The electron source of any item or example herein, particularly item 38, wherein the insulating base comprises a ceramic.

[0108] Item 40. Ceramics made of aluminum oxide (Al 2 O 3 ) or Mullite (3Al 2 O 3 2SiO 2 or 2Al 2 O 3 SiO 2 39. The electron source according to any of the clauses or examples herein, particularly clause 39, including

[0109] Item 41. The electron source according to any of the items or examples herein, particularly any one of items 38 to 40, wherein the heating element comprises a metal having an electrical resistivity of more than 100 nΩ·m and / or an elastic modulus of less than 200 GPa, or the heating element comprises a metal having an electrical resistivity of more than 50 nΩ·m and / or an elastic modulus of less than 400 GPa.

[0110] Item 42. The electron source according to any of the items or examples herein, particularly any one of items 38 to 41, wherein the heating element comprises tantalum (Ta) and / or alloys thereof, and / or the emitter-cathode comprises tungsten (W) and / or alloys thereof.

[0111] Item 43. The electron source according to any of the items or examples herein, particularly any one of items 38-42, wherein the emitter-cathode is constructed as a Schottky emitter with a reservoir.

[0112] Item 44. The reservoir is made of zirconium oxide (ZrO 2 43. The electron source according to any of the clauses or examples herein, in particular clause 43, comprising a coating of

[0113] Item 45. The electron source according to any item or example herein, particularly any one of items 38-42, wherein the emitter-cathode is constructed as a reservoir-less cold-field emitter.

[0114] Item 46. The electron source of any one of items or examples herein, particularly items 38-45, wherein one or more heating elements have a diameter of less than 127 μm (5 mils) or one or more heating elements have a diameter of less than 250 μm (10 mils).

[0115] Clause 47. The electron source of any clause or example herein, particularly any one of clauses 38-46, wherein the one or more heating elements have a first diameter proximal to the conductive terminal and a second diameter proximal to the one or more first locations, the first diameter being smaller than the second diameter.

[0116] Item 48. A method for manufacturing an electron source, comprising: coupling an insulating support member to an insulating base having a plurality of conductive terminals; coupling the drift isolation member to an insulating support member; coupling an emitter to a drift isolation member; coupling one or more heating elements to conductive terminals; coupling one or more heating elements to a drift isolation member; forming an emitter tip at an end of the emitter to form an emitter-cathode.

[0117] Item 49. The method according to any of the items or examples herein, particularly item 48, wherein the method forms an electron source according to any of items 1 to 24 and 38 to 47.

[0118] Item 50. A method for manufacturing an electron source, comprising: coupling an insulating support member to an insulating base having a plurality of conductive terminals; coupling the emitter to an insulating support member; coupling one or more heating elements to conductive terminals; coupling one or more heating elements to the emitter at one or more first locations substantially adjacent a junction between the emitter and an insulating support member; forming an emitter tip at an end of the emitter to form an emitter-cathode.

[0119] Item 51. The method according to any of the items or examples herein, particularly item 50, wherein the method forms an electron source according to any of items 25 to 47.

[0120] Item 52. The method of any item or example herein, particularly any one of items 48-51, further comprising modifying one or more heating elements to have a variable diameter along their length.

[0121] Clause 53. The method of any clause or example herein, particularly any one of clauses 48-52, wherein forming the emitter tip comprises etching the emitter.

[0122] Clause 54. The method of any clause or example herein, particularly any one of clauses 48 to 53, wherein bonding the insulating support member to the insulating base comprises sintering, and / or bonding the drift isolation member to the insulating support member comprises brazing, and / or bonding the emitter to the drift isolation member comprises welding, and / or bonding the one or more heating elements to the conductive terminal comprises welding, and / or bonding the one or more heating elements to the drift isolation member comprises welding, and / or bonding the emitter to the insulating support member comprises brazing, and / or bonding the one or more heating elements to the emitter comprises welding.

[0123] Clause 55. The method of any clause or example herein, particularly any one of clauses 48 to 54, wherein the insulating support member is directly bonded to the insulating base (e.g., without a separate intervening member), and / or the drift isolation member is directly bonded to the insulating support member (e.g., without a separate intervening member), and / or the emitter is directly bonded to the drift isolation member (e.g., without a separate intervening member), and / or one or more heating elements are directly bonded to the drift isolation member (e.g., without a separate intervening member), and / or the emitter is directly bonded to the insulating support member (e.g., without a separate intervening member), and / or one or more heating elements are directly bonded to the emitter (e.g., without a separate intervening member).

[0124] Conclusion Any of the features shown or described with respect to Figures 2A-13B and paragraphs 1-55 can be combined with any of the others of Figures 2A-13B and paragraphs 1-55 to provide systems, methods, devices, and embodiments not otherwise shown or specifically described herein. For example, the split filament structure of emitter-cathode 810 of Figures 8A-8C can be used in place of emitter-cathode 310 of any of Figures 2A-7C and 11A-13B. Other combinations and variations are possible in accordance with one or more contemplated embodiments.

[0125] In light of the many possible embodiments to which the principles of the disclosed technology may be applied, it should be recognized that the illustrated embodiments are merely preferred examples and should not be construed as limiting the scope of the disclosed technology. Rather, the scope is defined by the following claims. We therefore claim all that falls within the scope of those claims.

Claims

1. 1. An electron source comprising: An insulating base; a pair of conductive terminals exposed from a first surface of the insulating base; an insulating support member extending from the first surface of the insulating base; a drift isolation member disposed at an end of the insulating support member remote from the insulating base; an emitter cathode coupled to the drift isolation member; one or more heating elements coupled to the conductive terminals and the drift isolation member; an electron source comprising:

2. the insulating base is formed from a first ceramic; the insulating support member is formed from a second ceramic; One or both of the first ceramic and the second ceramic are aluminum oxide (Al ２ O ３ ) or mullite (3Al ２ O ３ 2SiO ２ Or 2Al ２ O ３ SiO ２ ), 2. The electron source of claim 1.

3. the insulating support member comprises a ceramic rod and the drift isolation member is bonded to an axial end surface of the ceramic rod; or the insulating support member comprises a ceramic tube, and at least a portion of the drift isolation member is disposed within the ceramic tube and bonded to an inner circumferential surface thereof.

2. The electron source of claim 1.

4. the emitter-cathode is welded to a first side of the drift isolation member; the one or more heating elements are welded to a second side of the drift isolation member opposite the first side.

2. The electron source of claim 1.

5. the one or more heating elements are welded to the drift isolation member at one or more respective first locations; the emitter-cathode is welded to the drift isolation member at a second location; the one or more first locations are closer to the insulating support member along an axial direction of the emitter-cathode than the second locations; 2. The electron source of claim 1.

6. the first location is adjacent a junction between the drift isolation member and the insulating support member; 6. The electron source of claim 5.

7. the drift isolation member comprises a first metal, the heating element comprises a second metal, and the emitter-cathode comprises a third metal; 2. The electron source of claim 1.

8. the drift isolation member comprises a ceramic member coated with the first metal; 8. The electron source of claim 7.

9. the first metal has a greater elastic modulus than the second metal; the second metal has an electrical resistivity greater than 50 nΩ·m and an elastic modulus less than 400 GPa; The first metal has an elastic modulus of at least 400 GPa.

8. The electron source of claim 7.

10. The first metal is rhenium (Re) or an alloy thereof; the second metal is tantalum (Ta) or an alloy thereof; The third metal is tungsten (W) or an alloy thereof.

8. The electron source of claim 7.

11. the drift separation member has a maximum lateral dimension in a plane perpendicular to an extension direction of the emitter-cathode; said maximum lateral dimension being at least twice as large as said maximum diameter of said emitter-cathode; 2. The electron source of claim 1.

12. the emitter-cathode is constructed as a Schottky emitter with a reservoir; the reservoir is disposed along the axial direction of the emitter-cathode closer to the tip of the emitter-cathode than the drift separation member; or The emitter-cathode is constructed as a cold-field emitter without the reservoir; 2. The electron source of claim 1.

13. the one or more heating elements have a diameter of less than 250 μm (10 mils); 2. The electron source of claim 1.

14. the one or more heating elements have a first diameter proximate the conductive terminal and a second diameter proximate the drift isolation member; The first diameter is smaller than the second diameter.

2. The electron source of claim 1.

15. the drift separation member has a semi-cylindrical shape; The emitter cathode is bonded to the flat surface side of the semi-cylinder. The one or more heating elements are coupled to the curved side of the semi-cylindrical shape.

2. The electron source of claim 1.

16. The drift separation member has a rectangular rod shape, the emitter-cathode is coupled to one side of the rectangular bar; the one or more heating elements are coupled to opposing sides of the rectangular bar shape; 2. The electron source of claim 1.

17. the drift isolation member having at least two arms separated by a gap; the arms extend from the insulating support member along an axial direction of the emitter-cathode to a joint or strut spaced from the insulating support member; the emitter-cathode is coupled to the drift isolation member at the junction or the strut; the one or more heating elements are coupled to the drift isolation member at the arms; 2. The electron source of claim 1.

18. 1. An electron source comprising: An insulating base; a pair of conductive terminals exposed from a first surface of the insulating base; an insulating support member extending from the first surface of the insulating base; an emitter cathode coupled to the insulating support member; one or more heating elements extending between and coupled to the conductive terminal and the emitter-cathode; the one or more heating elements are coupled to the emitter-cathode at one or more respective first locations substantially adjacent a junction between the emitter-cathode and the insulating support member; electron source.

19. the emitter-cathode has a first diameter at the first location and a second diameter away from the first location; The first diameter is greater than the second diameter.

20. The electron source of claim 18.

20. The first diameter is at least two times larger than the second diameter; 20. The electron source of claim 19.

21. the insulating base is formed from a first ceramic; the insulating support member is formed from a second ceramic; One or both of the first ceramic and the second ceramic are aluminum oxide (Al ２ O ３ ) or mullite (3Al ２ O ３ 2SiO ２ Or 2Al ２ O ３ SiO ２ ), 20. The electron source of claim 18.

22. the insulating support member comprises a ceramic rod; and the emitter-cathode is bonded to an axial end surface of the ceramic rod; or the insulating support member comprises a ceramic tube; and At least a portion of the emitter-cathode is disposed within the ceramic tube and bonded to an inner circumferential surface of the ceramic tube.

20. The electron source of claim 18.

23. The heating element comprises a metal having an electrical resistivity of more than 50 nΩ·m and an elastic modulus of less than 400 GPa; 20. The electron source of claim 18.

24. The heating element comprises tantalum (Ta) or an alloy thereof; The emitter-cathode comprises tungsten (W) or an alloy thereof; 20. The electron source of claim 18.

25. the emitter-cathode is constructed as a Schottky emitter with a reservoir; the reservoir is disposed along an axial direction of the emitter-cathode closer to a tip of the emitter-cathode than the one or more first locations; or The emitter-cathode is constructed as a reservoir-less hot-field or cold-field emitter; 20. The electron source of claim 18.

26. the one or more heating elements have a first diameter proximate to the conductive terminal and a second diameter proximate to the one or more first locations; The first diameter is smaller than the second diameter.

20. The electron source of claim 18.

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