Filament-less electron source

Abstract

To provide a Schottky emitter in which an operation temperature and a power consumption are reduced by heating the Schottky emitter by a resistance heating of an emitter itself.SOLUTION: Electron sources can include an electron source crystal 106 coupled in series between opposing electrically conductive supports to form an electrically conductive path, and electrical resistance of each of the electrically conductive supports is lower than electrical resistance of the electron source crystal 106. Electron source crystals 106 can include an emitting end 108 and opposing shank end 110, and the shank end 110 includes opposing leg portions 114a, 114b. Electrically conductive supports can include foil supports 104a, 104b spaced apart across a gap, and the opposing leg portions are attached respectively to the foil supports 104a, 104b such that the foil supports 104a, 104b are electrically connected to form the electrically conductive path.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The field is electron sources. [Background technology]

[0002] Electron microscopes and other precision measurement and imaging devices typically include a cathode electron source to generate an electron beam. Electron sources, such as Schottky emitters, typically include a filament that is heated with an electric current. The filament extends between two electrical contacts and is bent to form a symmetrical "A" shape. When an electric current is passed through the filament, the apex of the filament heats up rapidly, raising its temperature to over 1000 K. The electron emitter crystal (e.g., tungsten) <100> ) is attached to the apex of the bend and, by virtue of its attachment to the filament, receives the heat generated by the filament. During source operation, the filament is heated, an electrostatic potential is applied between the emitter crystal and the adjacent anode, and the work function of the emitting surface on the emitter crystal is lowered by the application of ZrO. The increased temperature and lowered work function cause a rapid increase in electron emission from the crystal tip, thereby generating the electron source beam.

[0003] Unfortunately, electron sources with wire filaments are inefficient when operated at high temperatures (1800 K for the Schottky example). All of the power required to maintain a high temperature at the emitting surface is generated in the wire filament and dissipated through emission and heat conduction. Operating materials at high temperatures creates various problems, including significant thermal expansion and excessive heat transfer to surrounding components. To reduce the operating power of the electron source, emission and heat conduction must be reduced. A typical solution to this problem is to modify the dimensions and material of the filament wire, but this solution is limited by the mechanical properties of the filament wire. Therefore, improved electron sources and related methods are needed. Summary of the Invention

[0004] According to one aspect of the disclosed technology, an electron source includes an electron source crystal coupled in series between opposing conductive supports to form a conductive path, the electrical resistance of each of the conductive supports being lower than the electrical resistance of the electron source crystal. In some examples, the electron source crystal includes an emitting end and opposing shank ends, the shank ends including opposing leg portions. In some examples, the conductive supports include foil supports spaced apart by a gap, each of the opposing leg portions attached to a respective foil support such that the foil supports are electrically connected to form the conductive path. In some examples, the conductive supports further include a base and a pair of electrical contacts extending from the base, with an end of each foil support opposite the gap attached to a respective electrical contact of the pair. In some examples, the foil supports extend outwardly perpendicular to the length direction from each leg portion. In some examples, the foil supports extend in a height direction parallel to the longitudinal direction of the electron source crystal by at least 10 times the thickness of the electron source crystal. In some examples, the foil supports have a thickness less than their respective length and height, and the thickness is less than twice the thickness of the electron source crystal. In some examples, the dimensions and material of the foil support are configured relative to the dimensions and material of the leg portion such that Joule heating generated in the leg portion primarily heats the emitting end to the emission temperature. In some examples, the foil support includes milled edges that face each other across the gap. In some examples, the foil support is made of tungsten, rhenium, hafnium, tantalum, molybdenum, or alloys thereof. Some examples include reservoirs of material configured to reduce the work function of the emitting surface located on the electron source crystal. In some examples, a gap separates at least a portion of the reservoirs. In some examples, the conductive support includes a wire member. In some examples, the conductive support includes a filament support.In some examples, the shank end includes a pair of lead surfaces configured to couple to respective conductive supports, and coupling of the crystal to the conductive supports allows current to flow from one lead out through the crystal to the other lead, thereby heating the crystal primarily from within the crystal rather than by thermal conduction from heat generated within the respective support members. Some examples include electron particle focusing systems that include any of the electron sources described herein.

[0005] In accordance with another aspect of the disclosed technique, an electron source includes an electron source crystal having an emitting end and an opposing shank end, the shank end being formed from a pair of opposing leg portions.

[0006] In accordance with a further aspect of the disclosed technique, an apparatus includes an electron source crystal and means for supporting the electron source crystal and generating Joule heat primarily within the crystal during operation.

[0007] According to a further aspect of the disclosed technology, a method of forming an electron source includes positioning an electron source crystal having an emitting end and an opposing shank end, and removing portions of an emitter through a portion of the shank end of the electron source crystal to form opposing crystal legs separated by a gap. In some examples, positioning the electron source crystal includes positioning the electron source crystal relative to a conductive support member, and the method can further include attaching the shank end of the electron source crystal to the conductive support member to form an emitter assembly, and removing portions of the emitter includes (i) removing portions of the emitter assembly through a portion of the shank end of the electron source crystal to form opposing crystal legs separated by a gap, and (ii) removing portions of the emitter assembly through a thickness and a height of the support member to form separate opposing supports spaced apart by the gap and connected across the gap through the opposing crystal legs. In some examples, attaching the shank end of the electron source crystal to the conductive support member includes spot welding the shank end of the electron source crystal to the conductive support member. In some examples, removing portions of the emitter includes laser milling the portions of the emitter. In some examples, removing portions of the emitter includes using a focused ion beam (FIB) to mill portions of the emitter. In some examples, prior to positioning the electron source crystal, attaching a conductive support member to a pair of electrical contacts extending from the base includes attaching the conductive support member to a pair of electrical contacts extending from the base. In some examples, positioning the electron source crystal relative to the conductive support member includes, with the conductive support member fixed, delineating a location on the support member corresponding to the alignment location of the electron source crystal. In some examples, delineating includes forming an optical mark or pattern on the conductive support member. In some examples, positioning a reservoir of material configured to lower the work function of the emitting surface on the electron source crystal. In some examples, removing portions of the emitter through a portion of the shank end of the electron source crystal to form opposing crystal legs separated by a gap includes removing a portion of the crystal where the reservoir of material is located. In some examples, the conductive support member includes a conductive foil strip.

[0008] The foregoing and other objects, features, and advantages of the disclosed technology will become more apparent from the following detailed description, which proceeds with reference to the accompanying drawings. [Brief explanation of the drawings]

[0009] [Figure 1A] FIG. 1 is a side view of the electron source assembly with a significant portion of the foil length removed to show the split-shank emitter feature. [Figure 1B] 1B is a side view of the electron source assembly of FIG. 1A, but enlarged to show the base and electrical contacts. [Figure 1C] FIG. 2 is a perspective view of the electron source assembly of FIGS. 1A-1C. [Figure 2] 1 is a flowchart of a method for fabricating an electron source assembly. [Figure 3] FIG. 1 is a side view of an electron particle focusing system. [Figure 4] FIG. 10 is a side view of another electron source assembly with a gap extending through the zirconium reservoir. [Figure 5] FIG. 10 is a side view of another electron source assembly with a foil support having a platform shape. [Figure 6] FIG. 2 is an electrical diagram of the electron source assembly. [Figure 7] FIG. 10 is a side view of another electron source assembly using a cut filament. [Figure 8] 8 is a microscope image of the exemplary electron source assembly shown in FIG. 7. DETAILED DESCRIPTION OF THE INVENTION

[0010] Schottky emitters are a type of electron source that uses both electrostatic potential and temperature to generate emission. The disclosed Schottky electron source example provides resistive heating of the crystal at the crystalline portion of the emitter crystal, rather than a conventional filament / wire that supports and heats the crystal. The disclosed examples also encompass other electron field emission sources, including cold electron sources (e.g., CFE, thermionic, nanowire, etc.). In various examples, such as the example shown in Figure 1A and other figures, the majority of heat generation occurs directly within the crystal, rather than being transferred to the crystal by the crystal support structure, which can provide various advantages, including improved thermomechanical stability of existing filament structures, lower power input and lower operating temperatures for suppressors, extractors, and insulators in close proximity to the electron source. Such improvements enable improved local vacuum environments, improved manufacturing reproducibility, reduced manufacturing steps (e.g., elimination of pyrometer measurements), and lower operating temperatures for crystal reservoirs (e.g., zirconium oxide), which can extend emitter lifetime.

[0011] In filament-based emitters, the primary purpose of the filament is to provide a source of thermal energy from Joule heating, enabling the tip to operate at high temperatures, such as 1800 K. While convenient, filaments require excessive operating power, cause significant thermal expansion, and are prone to thermomechanical drift. Furthermore, at such high temperatures, evaporation of the resistively heated filament can cause changes in filament temperature, worsening the mean time between failures. The disclosed examples allow current to be conducted through an electron source crystal (e.g., a field emitter crystal) with a higher resistance than the conductive paths into and out of the crystal, where the electron source crystal can be formed from a single crystal, a polycrystal, or a combination thereof. As used herein, the term "crystal" can refer to any type of electron emission source that can be attached to a filament or foil. A series connection can reduce dependency on the heat-generating capacity of the filament to heat the crystal to the appropriate operating emission temperature.

[0012] For example, in an A-shaped or other existing filament example, the filament can be severed at the crystal connection, forcing current through the crystal, causing most of the Joule heating normally provided by the filament rather than being generated in the crystal itself. Therefore, existing filament structures, such as wires, can continue to be used. Some disclosed examples also effectively eliminate the filament from the electron source structure. For example, a foil strip or other support structure can be used to replace the bent filament typically used in commercial electron sources. An example foil strip can be straight across the distance between the electrical contacts, and the emitter single crystal can be spot-welded to the foil strip. The emitter and foil strip can form an emitter assembly, which can be plasma- or laser-milled to create a split-emitter configuration.

[0013] In some instances, the emitter can be milled to create a split-emitter configuration (e.g., without a foil strip or other support structure). Using a single crystal of appropriate length, substantially all of the heating power is generated in the two crystal legs. When the single crystal is oriented along the optical axis for emission, substantially all of the thermal expansion of the emitter assembly is in that direction. The dimensions of the foil, single crystal, and milled section can be selected to limit the temperature of the foil and the support post to which the foil is attached.

[0014] 1A-1B illustrate an exemplary electron source assembly 100 including a foil strip 102 that has been laser milled to form first and second foil supports 104a, 104b. In a representative example, the electron source assembly 100 is a Schottky electron source assembly. In further examples, the electron source assembly may be a cold electron source assembly, a thermionic electron source assembly, a nanowire-based electron source assembly, or the like. The foil supports 104a, 104b can be made from a variety of materials, such as tungsten, rhenium, hafnium, tantalum, molybdenum, another metal, or a metal alloy. The selected material typically has a high melting point and can hold the electron source crystal 106 together, for example, via spot welding or laser welding attachment. Generally, the term "emitter" is used herein and can encompass a variety of electron-emitting electron source structures, including nanowires. The electron source crystal 106 includes a body 107 with an emitting end 108 and an opposing shank end 110. A crystal reservoir 109, for example, of zirconium oxide, is disposed in the body 107. The crystal 106 is disposed along an optical axis 111, which is typically aligned with the optical axis of an associated system in which the assembly 100 is installed, such as an electron microscope. The crystal 106 is conventionally a single crystal, such as tungsten, although other materials, such as rhenium, may alternatively be used, as described further below. The emitting end 108 includes an emitting surface 112 from which electrons are emitted. The emitting surface 112 is generally aligned with the optical axis 111, such that electrons are emitted from the emitting surface 112 in the direction of the optical axis 111. The shank end 110 includes a pair of crystal legs 114a, 114b facing each other across a gap 115. Crystal legs 114a, 114b meet at an apex 116 (top of FIG. 1 ) spaced apart from foil strip 102 such that foil supports 104a, 104b are not directly connected to one another, and gap 115 extends along the height (e.g., z-direction) of foil strip 102. The presence of gap 115 allows foil supports 104a, 104b to be electrically and mechanically coupled through crystal legs 114a, 114b and the unsplit portion of body 107 of crystal 106.In various examples, the gap can be about 0.1 μm, 1 μm, 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 40 μm, or more.

[0015] The foil supports 104a, 104b can have a small thickness, e.g., extending in the x-direction, which is in the plane of FIG. 1A, and a large height, e.g., extending in the z-direction, which is vertical in FIG. 1A. In some examples, the thickness can range from 10 μm to 100 μm, and the height can range from 0.5 mm to 10 mm, although other thicknesses and heights, including uniform and non-uniform ones, are possible. The height and thickness of the supports 104a, 104b near their attachment to the crystal legs 114a, 114b generally define the cross-sectional area of ​​the foil. The exemplary foil cross-sectional areas herein are typically larger than those of "A"-shaped cylindrical filament-based Schottky emitters. A larger foil cross-sectional area can provide more structural support for the electron source crystal 106. In a typical example, the foil height is large enough so that the ends of the crystal legs 114a, 114b do not extend beyond the lower edge 118 of the foil strip 102. The foil height can also be selected to be large enough to be manipulated with tweezers or other tools. In some instances, the foil support thickness is selected in relation to the selected foil material and machining parameters of the milling process used to form the gap 115. For example, some foil materials and milling processes can have a maximum material removal depth or a specific set of processed crystal legs, gaps, or foil support attributes. By way of example, attributes can include material burrs, splatter, thermally weakened zones, warping, localized melting and resolidification, etc. Laser milling has advantages over FIB milling in some cases, allowing for greater machining depths and therefore greater foil thicknesses.

[0016] Generally, the larger cross-sectional area of ​​the foil supports 104a, 104b (compared to a bent wire filament) provides lower electrical resistance. This advantageously allows a greater portion of Joule heating to occur in the crystal legs 114a, 114b rather than in the foil supports 104a, 104b. Therefore, the assembly 100 can be referred to as a filamentless electron source. Compared to an "A"-shaped filament-based emitter, Joule heating occurs only in the filament because substantially all of the current passes through the filament. When current flows and heats the filament, the emitter crystal heats only through conduction. In contrast to the split crystal legs 114a, 114b at the shank end 110, the current path forces the current to flow through the crystal legs 114a, 114b and the body 107, thereby reducing I 2 A significant portion of the R heating occurs within the crystal 106. As the length of the crystal legs 114a, 114b increases, the energy formed in the upper segment of the foil supports 104a, 104b also increases.

[0017] Furthermore, because the crystal legs 114a, 114b are formed by splitting the crystal 106, the cross-sectional area of ​​the crystal legs 114a, 114b is reduced by more than half. For example, the cross-sectional area of ​​each crystal leg of a split 0.127 mm (5 mil) diameter crystal is reduced by approximately 0.006 mm 2The resistance is less than 100 Ω. Because resistance is inversely proportional to area, splitting the crystal 106 and the corresponding reduction in the cross-sectional area of ​​the current path significantly increases the electrical resistance. Another significant advantage of the disclosed examples due to the higher resistance is the corresponding reduction in the supply current and therefore the power required to heat the emitter tip to operating temperature (e.g., 1800 K). While a single, bent-filament Schottky electron source may not consume significant power compared to other components of an electron microscope, large-scale industrial systems using arrays of electron sources can realize significant energy savings and reduced operating temperatures of adjacent components due to the low-power attributes of the disclosed examples using foil supports and split crystal legs. In some examples, additional energy savings are achieved through the increased resistance provided by a reduction in crystal diameter and the selection of a crystal material with higher resistance. For example, because area is proportional to the square of the diameter, a linear change in diameter results in a rapid increase in the resistance of the crystal legs. Example crystal diameters can include less than 5 mils, such as 4 mils, 3 mils, or less. In some examples, the crystal diameter can be greater than 5 mils, such as 6 mils, 8 mils, or more. In some instances, other materials having higher resistivity than tungsten, such as rhenium, may be used.

[0018] 1B-1C show the electron source assembly 100 attached to electrical contacts 120a, 120b. The electrical contacts 120a, 120b may be in the form of posts extending from a base 122, typically made of ceramic or another insulator. Foil supports 104a, 104b extend to the contacts 120a, 120b to define the length of the foil strip. In many examples, the electrical contacts 120a, 120b are radially symmetrically positioned on opposite sides of the center of the base 122, so that the emitter assembly 100 can be installed with the longitudinal extent of the emitting surface 112 and the electron source crystal 106 aligned with the optical axis 111 and the center of the base 122. In a typical example, one or more jigs can be used to position the crystal in a central position on the base 122. The aligned position of the electron source crystal 106 is typically radially offset from the center of the base 122 by less than 600 μm. In operation, a power source (not shown) is coupled to the contacts 120 a , 120 b to create a current through the foil supports 104 a , 104 b , the crystal legs 114 a , 114 b , and the crystal body 107 .

[0019] As discussed above, the use of conductive foil supports 104a, 104b eliminates the need for a cylindrical, bent filament. To heat the emitter tip to an operating temperature of 1800 K, a cylindrical, bent filament typically operates at 2000 K or higher. The high filament temperature also generates a significant amount of thermal expansion. Therefore, the placement of the filament relative to the electrical contacts, the placement or orientation of the crystal attached to the filament, or even slight asymmetries in the filament itself can result in various shifts in the X, Y, and / or Z directions, e.g., from 1 to about 10 μm or more in X and / or Y to about 40 μm in the Z direction, or depending on the angle relative to the Z direction. In the disclosed example, due to the primary amount of Joule heating generated within the crystal 106, the foil supports 104a, 104b can remove unwanted energy generated by conductively directing heat to the supports of the electrical contacts 120a, 120b. Joule heating is primarily within the crystal 106, and can include arrangements where the temperature within the crystal 106 is higher than the temperature of the foil supports 104a, 104b. Examples of temperature differences include 50K, 100K, 200K, 400K, etc. The dimensions of the foil supports 104a, 104b and the crystal 106 can also be selected to reduce power and thermal expansion. Preferably, the foil supports 104a, 104b remain below 1000K during operation, and the supports of the electrical contacts 120a, 120b are in the range of 450K to 700K, although other temperatures are possible.

[0020] Thus, the foil supports 104a, 104b generally remain substantially cooler with a corresponding reduction in thermal expansion compared to a heated "A" shaped bent filament. In a further example, one can hold a filament, such as a bent filament, and mill or machine the assembly to form split crystal legs to split the filament and provide sufficient electrical resistance in the crystal for the filament to generate Joule heating primarily within the crystal.

[0021] FIG. 2 illustrates an exemplary method 200 for fabricating an electron source assembly, such as a Schottky electron source assembly. At 202, a supported end of an electron source crystal is attached to a conductive foil strip to form an emitter assembly. For example, the crystal can be attached via welding, adhesive, or another process. At 204, a portion of the emitter assembly is removed, for example, by laser milling or FIB milling, to form a pair of opposing crystal legs on the supported end of the crystal and separate foil supports or other conductive supports. For example, the assembly can be performed by milling or machining a portion of the shank end of the electron source crystal to form a pair of opposing crystal legs separated by a gap. The milling or machining can be performed through the entire thickness of the foil strip, completely forming the gap. The removal typically continues along the entire height of the foil strip to form separate opposing foil supports spaced apart by a gap, resulting in an electrical connection across the gap between the supports via the opposing crystal legs. In some instances, an additional non-conductive base can be attached to the foil to provide additional structural support, and since the current path is through the crystal legs, no material needs to be removed to penetrate the non-conductive base. In further instances, the crystal can be held and opposing crystal leg portions removed without milling through a foil strip or forming a foil support. In such instances, a foil support or other conductive support can be subsequently attached, or the sectioned crystal can be secured to another structure.

[0022] In some examples, before attaching the electron source crystal to the foil strip at 202, the foil strip can be attached at 206, for example by spot welding, to a pair of electrical contacts on posts extending from the base. Attaching the foil strip to the contacts before attaching the electron source crystal to the foil strip can avoid additional folds and other stresses on the crystal associated with positioning and alignment after removal of the strip and emitter assembly. Furthermore, because the electron source crystal is not yet attached to the foil strip, the precision of aligning the foil strip when attaching it to the contacts can be reduced because the foil strip may lack the folds or vertices associated with the bent wire filament.

[0023] Before proceeding with attaching the electron source crystal to the conductive foil strip at 202, the electron source crystal can be carefully aligned to a center position on the foil strip that coincides with a center position on the base. For example, various jigs can be used on the crystal and / or the base and contacts to bring the crystal into an aligned position before attachment at 202. By attaching the crystal after the foil strip is attached and avoiding the use of a filament, additional steps associated with bent wire filaments, such as aligning the filament apex to the base and the crystal to the filament apex, can be avoided, resulting in a more accurately centered position. In some examples, a position can be delineated on the foil strip at 208 to place the electron source crystal in a center-aligned position. For example, optical alignment indicia, such as crosshairs, lines, or other optical shapes, can be projected onto the foil strip using, for example, an LED or laser, and the crystal can be positioned relative to the alignment indicia before attachment at 202. In some examples, the indicia can be a permanent mark, notch, groove, or the like. Once the position is delineated, the crystal can be attached to the foil at 202.

[0024] FIG. 3 illustrates an electron particle focusing system 300 including an electron emitter source 302, which can include any of the filamentless configurations described herein as an electron source assembly 304. The electron emitter source 302 typically includes a power supply and controller 306 coupled to the electron source assembly 304, which provides current for heating the crystal primarily within the crystal rather than supporting foil legs. In a typical example, the power supply and controller 306 may also be coupled to a cathode 308 and an anode 310, which provide potentials for increasing field emission from the electron emitter source crystal tip of the assembly 304. The electron beam generated by the electron emitter source 302 is then directed through a particle focusing column 312 to a sample 314 located in a sample chamber 316. In some examples, the system 300 may include a focused ion beam column 318 for directing ions toward the sample 314. Examples of the system 300 may include a transmission electron microscope, a scanning electron microscope, a scanning transmission electron microscope, and the like. Further examples may include critical dimension analysis systems (such as CD-SEMs), defect review systems, lithography systems, and the like.

[0025] 4 shows an exemplary electron source assembly 400 including an electron source crystal 402 having two legs 404a, 404b with respective portions secured to respective foil supports 406a, 406b. A crystal reservoir 408, such as zirconium, is disposed on the crystal 402 adjacent to the emitter tip 410. A gap 412 between the legs extends at least partially through the zirconium oxide reservoir 408.

[0026] 5 illustrates an exemplary electron source assembly 500 including an electron source crystal 502 having two crystal legs 504a, 504b attached to respective foil supports 506a, 506b. The foil supports 506a, 506b are attached to respective electrical contact posts 508a, 508b, which are secured to a base 510. The foil supports 506a, 506b can be formed from a foil strip by machining through the crystal 502 and the foil strip, forming the legs 504a, 504b through the same process. The foil strip can include a non-rectangular shape. The foil strip can include a platform section 512 to which the crystal 502 is secured prior to machining, and opposing leg members 514a, 514b that can be secured to the electrical contact posts 508a, 508b.

[0027] The figure shows an exemplary electron source assembly 600 including an electron source crystal 602 having a resistance R1 and conductive supports 604, 606 having respective resistances R2, R3, where R1 is also a low resistance. In a typical example, the electron source crystal 602 emits electrons in relation to the temperature of the crystal 602. An energy source 608 is coupled to contacts 610, 612 of the conductive supports 604, 606. Heat generated to raise the temperature of the crystal 602 is primarily formed within the crystal 602 by current flowing through the crystal 602 and its larger resistance R1 compared to the smaller resistances of R2, R3.

[0028] 7 is an example of an electron source assembly 700 including a filament 702 that has been cut by FIB milling to form opposing filament supports 704 a, 704 b. The assembly 700 includes an electron source crystal 706 that includes respective leg portions 708 a, 708 b that have been cut by FIB milling to form a gap 710. As current is forced to flow through the crystal 706, heat is generated primarily within the crystal 706, raising the crystal temperature for emission from the emitter tip 712 rather than through thermal conduction of heat resistively generated within the filament 702. FIG. 8 is a microscope image of an exemplary electron source crystal attached to a filament with a cut filament apex and a cut crystal shank.

[0029] As with the other examples above, splitting the emitter shank and directing current through the shank can localize the heating power within the crystal 706, e.g., near the tip 712, thereby causing the supporting hairpin filament 702 to cool by approximately 200 K compared to a typical emitter that does not include a serial electrical path through the crystal 706. In certain examples, including a split-shank configuration for the crystal 706 can result in less emission from the filament 702 and be more efficient due to the reduced temperature. Because the total heating power is reduced, heating of the suppressor and alumina base can also be reduced. Reduced heating reduces waste heat transfer to all surrounding emitter elements, reducing operating temperatures and outgassing rates, improving the vacuum environment of the electron source.

[0030] Various shapes of foil strips, filament wires, and other related supports can be used in various examples. In some examples, notches or other markings can be provided to indicate alignment for securing to electrical contacts or for securing crystal support ends or crystal legs. During operation, the foil support is typically heated to a lower temperature than the electron source crystal so that thermal expansion is attenuated or has minimal effect. In some examples, the foil strip can be triangular, for example, with vertices corresponding to the crystal locations. Because of reduced heating, even thermal expansion from a large triangular structure generally results in thermal expansion in the Z direction rather than the X or Y direction, if the foil cross-section and other characteristics lead to heating occurring primarily in the crystal. Rectangular strips configured to extend directly from contact to contact typically result in minimal Z-direction thermal expansion compared to other shapes, resulting in substantially less expansion compared to A-shaped filament-type emitters. Another advantage of the disclosed examples is that reduced X and Y shifts are accompanied by reduced Z-direction expansion.

[0031] General Considerations As used in this application and the claims, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. Additionally, the term "comprises" means "comprises." Furthermore, the term "coupled" does not exclude the presence of intermediate elements between the coupled items.

[0032] The systems, devices, and methods described herein should not be construed as limiting in any way. Instead, the present disclosure is directed to all novel and non-obvious features and aspects of the various disclosed embodiments, alone and in various combinations and subcombinations with one another. The disclosed systems, methods, and devices are not limited to any particular aspect or feature or combination thereof, nor do they require that any one or more particular advantages be present or problems be solved. While any theory of operation is for ease of explanation, the disclosed systems, methods, and devices are not limited to such theory of operation.

[0033] Although some operations of the disclosed methods are described in a particular order for convenience of presentation, it should be understood that this description style encompasses reordering unless a specific order is required by specific terminology described below. For example, operations described sequentially may, in some cases, be reordered or performed simultaneously. Moreover, for simplicity, the accompanying figures may not show the various ways in which the disclosed systems, methods, and apparatuses can be used with other systems, methods, and apparatuses. Additionally, this specification sometimes uses terms such as "generate" and "provide" to describe the disclosed methodologies. These terms are high-level abstractions of the actual operations that are performed. The actual operations that correspond to these terms will vary depending on the particular implementation and will be readily discernible to those skilled in the art.

[0034] In some instances, values, procedures, or devices are referred to as "lowest," "best," "smallest," etc. Such descriptions are intended to indicate that a selection from among many functional options may be made, and it will be understood that no such selection is necessarily better, lesser, or otherwise desirable than other options.

[0035] In view 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 representative and should not be construed as limiting the scope of the present disclosure. The alternatives specifically addressed in these sections are merely exemplary and do not constitute all possible alternatives to the embodiments described herein. For example, various components of the systems described herein may be combined in function and use. Accordingly, we claim all that comes within the scope of the following claims.

Claims

1. 1. An electron source comprising an electron source crystal coupled in series between opposing conductive supports to form a conductive path, the conductive supports each having an electrical resistance lower than the electrical resistance of the electron source crystal.

2. The electron source of claim 1 , wherein the electron source crystal includes an emitting end and an opposing shank end, the shank end including opposing leg portions.

3. 3. The electron source of claim 2, wherein the conductive supports include foil supports spaced apart by a gap, and each of the opposing leg portions is attached to a respective foil support such that the foil supports are electrically connected to form the conductive path.

4. With the base, 4. The electron source of claim 3, further comprising: a pair of electrical contacts extending from said base, an end of each foil support opposite said gap being attached to a respective electrical contact of said pair.

5. 4. The electron source of claim 3, wherein the foil supports extend lengthwise and perpendicularly outwardly from each leg portion.

6. 4. The electron source of claim 3, wherein the foil support extends in a height direction parallel to a longitudinal direction of the electron source crystal by at least 10 times the thickness of the electron source crystal.

7. 4. The electron source of claim 3, wherein the foil support has a thickness less than its length and height, the thickness being less than twice the thickness of the electron source crystal.

8. 4. The electron source of claim 3, wherein the dimensions and material of the foil support are configured relative to the dimensions and material of the leg portion such that the emitting end is heated to an emission temperature primarily by Joule heating generated in the leg portion.

9. The electron source of claim 3 , wherein the foil supports include milled edges facing each other across the gap.

10. 4. The electron source of claim 3, wherein the foil support is made of tungsten, rhenium, hafnium, tantalum, molybdenum, or alloys thereof.

11. 3. The electron source of claim 2, comprising a reservoir of material configured to lower the work function of an emitting surface located on the electron source crystal.

12. The electron source of claim 11 , wherein the gap separates at least some of the reservoirs.

13. The electron source of claim 2 , wherein the conductive support comprises a wire member.

14. 3. The electron source of claim 2, wherein the conductive support comprises a filament support.

15. 3. The electron source of claim 2, wherein the shank end includes a pair of lead surfaces configured to couple to respective conductive supports, and wherein coupling of the crystal to the conductive supports causes current to flow from one lead out through the crystal to the other lead, thereby heating the crystal primarily from within the crystal rather than by thermal conduction from heat generated within the respective support members.

16. 10. An electron particle focusing system comprising the electron source of claim 1.

17. 1. An electron source comprising an electron source crystal having an emitting end and an opposing shank end, the shank end being formed from a pair of opposing leg portions.

18. An electron source crystal having an emission end and an opposing shank end, the shank end being formed from a pair of opposing leg portions; means for supporting said electron source crystal and for generating Joule heat primarily within said crystal during operation.

Images