Cold field emitter assembly

Abstract

The invention relates to a cold field emitter assembly. Apparatuses and methods are disclosed for a mechanically stable, long-life cold field emitter assembly compatible with ultra-high vacuum and intermittent high temperature flash. And the metal adapter is welded between the hexaboride electrode and the metal filament. Some embodiments use a tungsten filament, a tantalum adapter, and a LaB6 microrod electrode having a nanorod emitter tip. Other material combinations and also use in an electron source for an electron microscope are disclosed. In various variations, the adapter is deposited onto the filament, and then the electrode is welded to the adapter.

Description

Technical Field

[0001] This disclosure relates to electronic sources. Background Technology

[0002] Cold field emission electron sources operating at or near room temperature offer higher brightness, better beam coherence, greater positional stability, and longer lifetime compared to sources operating at high temperatures, making them highly attractive for use in high-resolution electron microscopy, such as S / TEM, SEM, and other applications. Lanthanum hexaboride (“LaB6”) is a refractory ceramic with good electrical conductivity and a low work function. LaB6 cold field emitters have been demonstrated to achieve high brightness at approximately 10⁻⁶ Hz. -10 LaB6 can emit stably under moderate vacuum and shows great potential as a next-generation cold field emission source. However, material incompatibility between LaB6 and commonly used emitter support materials can lead to erosion over time. Some conventional methods to overcome this problem involve bonding LaB6 to the support using graphite paste, without direct contact between LaB6 and the support. However, the presence of large amounts of graphite paste can form trapped gas reservoirs, making it difficult to operate the source in ultra-high vacuum and potentially contaminating the LaB6 emitter during operation. Therefore, improved techniques are needed to achieve efficient and stable operation of LaB6 cold field sources over a long lifespan. Summary of the Invention

[0003] In short, examples of the disclosed technology employ an adapter to couple the electrode to a supporting filament. A corresponding molten band bonds the adapter to both the electrode and the filament. Inventively, a LaB6 electrode can be attached to a tungsten filament via a tantalum adapter; however, other materials and combinations can be used. The molten band can be formed by spot welding or laser welding without filler material to obtain an emitter assembly with mechanical stability and compatibility with ultra-high vacuum.

[0004] In other examples, welding can be used to form a molten band between the adapter and the electrode, and another technique can be used to assemble the adapter and the filament. Examplely, a tantalum adapter can be formed by deposition onto the filament.

[0005] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with reference to the accompanying drawings. Attached Figure Description

[0006] Figures 1A to 1B An image of an electron microscope and its electron source, which are examples of applications of the disclosed techniques.

[0007] Figure 2 is an image of a conventional transmitter structure.

[0008] Figures 3A to 3BThis is a SEM image of a LaB6 electrode with nanorod tips, which can be incorporated into an example of the disclosed technology.

[0009] Figure 4 This is a cross-sectional view of an example transmitter structure based on the disclosed technology.

[0010] Figures 5 to 6 These are photomicrographs of an example transmitter structure based on the disclosed technology.

[0011] Figures 7 to 10 This is a diagram of an example transmitter structure based on the disclosed technology.

[0012] Figure 11 This is a flowchart of a first example method based on the disclosed technology.

[0013] Figure 12 This is a flowchart of a second example method based on the disclosed technology.

[0014] Figure 13 This is a diagram showing an example setup of a spot welding assembly based on the transmitter structure of the disclosed technology.

[0015] Figure 14 This is a diagram showing an example setup of a laser welding assembly based on the emitter structure of the disclosed technology. Detailed Implementation

[0016] Introduction

[0017] Electron microscopes are widely used for materials and equipment analysis, and also for biological research. Various configurations are used, including SEM, TEM, and STEM. In all these configurations, an electron beam is generated by an electron source and delivered to the sample. Electron sources typically utilize thermionic emission, Schottky emission, or cold field emission. Cold field emission offers advantages such as higher brightness, lower energy diffusion, better coherence, and longer lifetime, primarily due to its low-temperature (≤300K) operation and its role as a smaller dummy source compared to other emitter types. Electron energy diffusion of approximately 0.2 eV to 0.3 eV and >10 eV can be achieved from cold field emitters. 9 A / (sr.m 2 The actual brightness (in .V). Cold field emission sources typically have electrodes with a tip (called an "emitter") having a lateral amplitude of a few nanometers to hundreds of nanometers, at which electrons can be emitted under the influence of an externally applied electric field.

[0018] Lanthanum hexaboride (LaB6) is an attractive material for cold field emitters due to its low work function, high conductivity, and, in particular, proven ability to operate at around 10⁻⁶ Ω·cm. -10Stable cold emission in a moderate vacuum. As a ceramic material, LaB6 can be fabricated into nanorod tips and can withstand high temperatures. Other rare-earth hexaborides can also be used.

[0019] However, considerations of material compatibility, vacuum compatibility, and mechanical stability negatively impact performance. Note that while cold field emitters can be operated at room temperature for electron microscopy, they are often cleaned in situ by resistively heating the emitter assembly (also known as "thermal flashing"). For efficient heating, it is desirable to mount the emitter electrodes directly onto the filament. Tungsten, with its high melting point, is a common material for emitter filaments; it can be generated and withstand temperatures exceeding 2000°C without causing mechanical problems.

[0020] However, tungsten and LaB6 do not bond well directly. The joint between tungsten and LaB6 is susceptible to corrosion and atomic migration (especially at high cleaning temperatures), which can lead to mechanical drift or joint failure.

[0021] Some examples of the disclosed technology use adapters made of tantalum to couple filaments (e.g., tungsten) to electrodes (e.g., LaB6). Tantalum offers good compatibility with LaB6 and has a low joint degradation rate. As a metal, tantalum is vacuum compatible and can be welded to tungsten and LaB6 without filler. Like LaB6 and tungsten, tantalum has a high melting point. Therefore, the welded assembly of the tungsten filament, tantalum adapter, and LaB6 filament can withstand high temperatures and support ultra-high vacuums with low outgassing (e.g., below 4 × 10⁻⁶). -10 It can provide excellent mechanical stability under cyclic thermal flash evaporation in the range of 600K to 2200K.

[0022] The material choices described above are exemplary. Other combinations of materials may be similarly implemented. For example, the filament material may include a tungsten alloy, rhenium, or a rhenium alloy. The adapter material may include tantalum or a tantalum alloy. The electrode material may include other hexaborides. Other filament, adapter, or electrode materials may also be used in the disclosed technology. In variations, tungsten alloy filament materials may be used to selectively control filament resistivity, mechanical filament strength, or weld reliability.

[0023] Figures 1A to 1BThis is a diagram of an electron microscope 100 and an electron source, exemplifying the application of the disclosed techniques. An electron source 111, electron optics 121, and a sample 131 are positioned along axis 105. Source 111 generates an electron beam 115, which is shaped and delivered to the sample 131 by optics 121. Detector 141 detects the transmitted electrons, for example, in a TEM or STEM configuration, while detector 142 detects secondary particles, for example, in a SEM configuration. Sample 131 is not part of the illustrated electron microscope and is shown in dashed outline. Furthermore, a given electron microscope may have only one detector, either detector 141 or 142.

[0024] Figure 1B This is a schematic diagram of an electronic source 102 that can be incorporated into the disclosed technology. (The diagram is as follows...) Figure 1B The electron source 111 is shown in the diagram.

[0025] The transmitter 130 can be mounted to the filament 110 using any of the techniques described herein. For the sake of simplicity, Figure 1B Details of the adapter and various transmitters are omitted. The transmitter 130 can be combined with the anodes 150 and 160 to generate an electron beam 115 along the centerline 105. The centerline 105 passes through the apertures 152 and 162 of the extraction anode 150 and the acceleration anode 160, respectively.

[0026] The electron source 102 may be coupled with at least four electrical terminals 141 to 144. A power supply 172 may be coupled to terminals 141 to 142 to drive current through the filament 110 for thermal regulation of the electron source 102. A power supply 173 may apply an extraction voltage V1 between the emitter 130 (coupled to terminal 142) and terminal 143 of the extraction anode 150. A power supply 176 may apply acceleration voltages V2–V1 between the extraction anode 150 and terminal 144 of the acceleration anode 160.

[0027] Figure 2 is an image 200 of a conventional emitter structure before tip formation. Dimensions are according to scale 202. Since graphite is unsuitable for soldering, a drop of water-based graphite paste 220 is applied to bond with the filament 210, and the electrode 230 is attached to the graphite paste 220 to form the emitter assembly. A significant amount of water-based graphite paste 220 may be required to support the mass of the electrode 230, which, as shown, has a thickness ≥50 μm and a length >1.2 mm. Graphite has good material compatibility with LaB6. However, as water evaporates from the paste 220 during room temperature curing, pumping, baking, and emitter flash evaporation, trapped cavities can remain. These cavities can continue to release gas over time, degrading the vacuum conditions around the electron source and leading to emitter contamination. The disclosed technique completely removes the graphite paste, thereby providing improved performance.

[0028] Figures 3A to 3BSEM images 301 and 302 show an example LaB6 electrode with nanorod tips that can be incorporated into the disclosed emitter assembly. The illustrated electrode has a microrod structure with nanorod emitter tips. The diameter of the illustrated electrode decreases incrementally (layer-by-layer) from about 100 μm to about 80 nm. The microrods can be shaped, for example, using a focused ion beam (FIB) tool by ion milling to form the nanorod tips.

[0029] First, a roughly square microrod with a diameter of about 100 μm (see example...) Figure 7 The microrods 740 can form a first level, which can be tapered at its distal end, as in... Figure 3A This is seen in the shoulder 311. The second layer 312 can be a microrod segment with a diameter of about 5 μm and a length of about 30 μm, wherein another shoulder leads to the tip 310 of the nanorod, which is seen in... Figure 3B This is illustrated in more detail below. In this example, the tip 310 has a third nanorod level 313 and a fourth nanorod level 314. As illustrated, level 313 has a length of approximately 1.6 μm and a diameter of approximately 500 nm, and level 314 has a diameter of approximately 80 nm and a length of approximately 1.27 μm. Furthermore, as shown, level 314 has a pointed tip. In this example, the tip radius is approximately 10 nm.

[0030] the term

[0031] An "adapter" is a physical component that couples two other components. In some of the disclosed examples, the adapter is tantalum or a tantalum alloy and is used to couple the filament to the electron electrode in the electron emitter assembly.

[0032] The term "atomic percentage" (or "at%)" refers to the percentage of atoms of a particular element or group of elements in a given device or material. Therefore, atomic percentage can apply to a single element, such as boron; a series of elements in the periodic table, such as rare earth elements or lanthanides; a group of elements, such as halogens; a portion of the periodic table, such as transition metals; or another specific group of elements. A similar term, "weight percentage" (or "wt%)," refers to the percentage of a particular element or group of elements by weight.

[0033] As a verb, "clamp" refers to the action of holding two physical objects together by reversibly applying force. Welding, soldering, and gluing are irreversible (requiring different unrelated actions for assembly and disassembly) and are not considered clamping actions. As a noun, "clamp" is a device that reversibly applies force to two physical objects to hold them together.

[0034] As a noun, "current" refers to "electrical current," that is, a stream of charged particles. While current can sometimes flow through wiring or other conductive materials, this is not required. An electron beam is an example of current flowing in a vacuum.

[0035] The term "cylindrical" describes an elongated object ("cylinder") with a uniform cross-sectional shape over a length at least three times the maximum lateral amplitude (referred to as the "diameter") of its cross-sectional shape. A "wire" is a conductive cylinder. While some cylindrical objects described herein have a generally circular cross-section, this is not a requirement. For example, various microrods or nanorods shown herein have square cross-sections and are also cylinders. Rectangular microrod cylinders (e.g., 50 μm × 100 μm cross-sections) may also be used. The length of the cylinder can be measured along its "axis," which is the line connecting the centroids of continuous cross-sections. The axis does not have to be straight: the cylinder (e.g., filament 110) may have bends. The requirement for a uniform cross-sectional shape means that the diameter and cross-sectional area vary by a maximum of 1.5 times over the required length. However, a cylinder may have twists about its axis while maintaining a uniform cross-sectional shape. Some electrodes of interest herein (see...) Figures 3A to 3B It may have segmented cylindrical sections, for example, connected by conical sections that may not be cylindrical.

[0036] As a verb, “deposition” refers to the act of attaching particulate material as a layer onto a physical object. In some examples, this action can be achieved through physical vapor deposition or chemical vapor deposition, sputtering, plating, or powder-based additive manufacturing. Since lamination, winding, or welding apply bulk material (rather than particulate material) to a physical object, they are not considered as performing deposition.

[0037] An electric field is the manifestation of electrical energy stored in a volume, thereby exerting a force on the charges within or at the boundaries of that volume. Typically, applying a voltage between two objects generates an electric field in the region between them. Electric fields can also exist in the propagation of electromagnetic energy (such as laser beams).

[0038] An "electrode" is a conductive object through which charged particles travel between a vacuum, a gas, or another fluid. While electrodes can often be metal, this is not a requirement. In the disclosed examples, the focus is on a LaB6 electrode used as a field emission source for electrons.

[0039] An “electron emitter” (or simply “emitter”) is a device that can be used as an electron source in an electron microscope or other equipment. The device is considered an electron emitter even if it does not actually emit electrons. Electron emitters are typically operated via cold field emission or thermionic emission and Schottky emission. In cold field emission, electrons are drawn away from the emitter by a strong electric field (e.g., at room temperature or below 200°C). In thermionic emission and Schottky emission, electrons acquire sufficient energy, both thermally and electrically, to overcome the work function of the electrode material and thus escape from the electrode. As used herein, the terms emitter and electron emitter can refer to the portion of an electrode from which electron emission occurs (e.g., 314), the electrode can be an entire object in which the emitter can be formed, and “emitter structure” or “emitter assembly” can refer to the electrode with one or more other objects (e.g., filaments or adapters; see [link to documentation]). Figure 4 The assembly includes an unfinished assembly without nanorod emitter tips.

[0040] A "filament" is a conductive device that can convert electrical energy (such as an electric current flowing through it) into heat. The device is considered a filament even if it does not actually generate heat.

[0041] A “melting zone” is the region at the boundary between two welded objects that contains material from the two objects being mixed together. Therefore, if the two objects have different compositions, the local material composition within the melting zone can differ from the composition of either object.

[0042] "Placement" refers to the action of integrating one object into an assembly of multiple objects.

[0043] "Microrods" are elongated structures with a maximum lateral dimension ranging from 1 μm to 500 μm. "Nanorods" are elongated structures with a maximum lateral dimension ranging from 1 nm to 1000 nm. Some electrodes of interest in this paper are microrods with nanorod tips. Some microrods and nanorods described herein are, for example, cylinders with square or rectangular cross-sections, but this is not a requirement.

[0044] The term "pulse" refers to a waveform that has a finite time amplitude and is continuous within that amplitude, has an average value within that amplitude, and crosses that average value exactly twice (e.g., once on the rise and once on the fall). For example, an electric current, laser energy, or other form of energy can be applied as a pulse.

[0045] A "terminal" is an attachment point for an electrical component. Voltage or current signals can flow to and from the electrical component through this terminal.

[0046] "Thickness" refers to the longitudinal dimension of an object in the direction of current flow, energy flow, or the application of clamping force.

[0047] As a verb, “welding” refers to the act of joining two physical objects by applying energy to melt adjacent portions of two objects, thereby joining them together after the molten portions cool and solidify. The molten materials of the two objects may mix to form a molten band. Brazing and welding are not considered welding because they do not melt portions of the two objects. Welding can be performed with or without filler material, the latter being referred to as “spontaneous.” Some examples of the disclosed techniques use light energy to induce melting, such as “laser welding.” Other examples use electrical energy to induce melting, such as “spot welding.” Both laser welding and spot welding can be spontaneous. As a noun, “welded portion” refers to the area of ​​the welded objects that is in a molten state during the welding operation. At least a portion of the welded portion can be a molten band. Welded portions formed by spot welding or laser welding are respectively referred to as “spot welded portions” or “laser welded portions.” In some examples, the energy deposited in a single welding operation can be distributed over the boundaries of multiple objects, thereby enabling the simultaneous welding of multiple pairs of objects.

[0048] As a verb, "winding" refers to the action of bending a sheet-like object around another object to at least the extent that the sheet-like object contacts itself. In some of the disclosed examples, the adapter may be implemented as a foil wound around a filament.

[0049] Example transmitter structure

[0050] Figure 4 This is a cross-sectional view 400 of an example structure according to the disclosed technology. In this structure, the adapter 420 can be coupled to the filament 410 via a first molten band 415 and to the emitter electrode 430 via a second molten band 425. The material of the adapter 420 can have superior interfacial properties relative to one or both of the filament 410 and the electrode 430, and can avoid the problems of erosion or mechanical instability in direct electrode-filament joints. Furthermore, the joint in the form of a molten band (the characteristics of welding) provides a structure compatible with ultra-high vacuum and without the gas release problems associated with some other forms of joints.

[0051] In some examples, the filament 410 may contain at least 50 at%, 80 at%, or 90 at% of tungsten, rhenium, or a tungsten-rhenium alloy. The portion of the filament 410 adjacent to the first molten band 415 may be a cylindrical wiring having a maximum lateral amplitude in the range of 25 μm to 500 μm.

[0052] The filament 410 and the adapter 420 may have different material compositions. The adapter 420 may contain at least 80 at%, 90 at%, 95 at%, 98 at%, or 99 at% tantalum. A generally flat embodiment of the adapter 420 (see example...) Figures 9 to 10It can have a thickness ranging from 1 μm to 500 μm, 5 μm to 100 μm, 25 μm to 125 μm, 10 μm to 50 μm, or 20 μm to 30 μm. Other adapters 420 (see example) Figures 7 to 8 It may have a distance between the centroid of the first melt zone 415 and the centroid of the second melt zone 425, which is within either of these ranges.

[0053] Electrode 430 may contain at least 60 at%, 80 at%, or 85 at% boron. Electrode 430 may contain hexaboride materials, such as rare earth hexaborides, lanthanide hexaborides, or particularly LaB6. The portion of electrode 430 adjacent to the second molten zone 425 may be a fine rod extending to the tip of a nanorod at the distal end of electrode 430. Arrow 432 illustrates the distal and proximal directions of electrode 430 relative to the illustrated emitter assembly.

[0054] The combination of tungsten filament, tantalum foil adapter, and LaB6 electrode offers the unique advantages of tungsten's rigidity, tantalum's material compatibility, and LaB6's low work function. This combination is solderable, and all components can withstand very high temperatures of 2000°C and above. Emitter tips with negligible position drift under cyclic thermal flash at ≤2200K are obtained.

[0055] The first molten band 415 may comprise a blend of a first material (e.g., tungsten) for the filament (e.g., 410) and a second material (e.g., tantalum) for the adapter (e.g., 420). The second molten band 425 may comprise a blend of the second material (e.g., tantalum) for the adapter (e.g., 420) and a third material (e.g., LaB6) for the electrode (e.g., 430). The first molten band 415 or the second molten band 425 may be a welded section, such as spot welding or laser welding. Given that the molten bands may have different compositions from any of the joined objects, the molten bands may be different components of an assembled structure.

[0056] Similar to Figure 1B The 102 electron source can combine with Figure 4The structure is as follows. Electron emission can occur at the (distal) tip of electrode 430, which is thus the emitter (similar to 130). Typically, an electron beam (115) can be emitted along the orientation of the centerline (105) of the tip. The electron source may additionally include an extraction anode (150) having an aperture (152) through which the centerline of the tip passes. Applying an extraction voltage (V1) between the structure (tip) and the extraction anode can create a sufficiently strong electric field at the tip to draw electrons away from the tip toward the extraction anode. An accelerating anode (160) may be positioned downstream of the extraction anode and also has an aperture (162) through which the centerline of the tip passes. The voltage difference (V2–V1) between the extraction anode and the accelerating anode can create an electric field that causes the emitted electrons to pass through the aperture of the extraction anode and be further accelerated toward the accelerating anode, and then through the aperture of the accelerating anode toward the target (131).

[0057] The electron source may be combined with at least four electrical terminals (141 to 144) through which voltage or current can be applied to operate the electron source, including (i) current passing through the filament (110), (ii) extraction voltage applied to the extraction anode relative to the emitter structure, and (iii) acceleration voltage applied to the acceleration anode relative to the extraction anode.

[0058] In addition, combined with Figure 4 The structure of this electron source itself can be placed in conjunction with... Figure 1A In electron microscopes similar to those used in electron microscopes.

[0059] Figures 5 to 6 These are photomicrographs 500 and 600 of the example transmitter structure with corresponding scales 502 and 602. Figure 5 In this process, a tungsten filament 510 has a generally circular cross-section and is wound together with a tantalum foil adapter 530. The filament 510 and the foil 530 can be welded together to form a molten band (similar to...). Figure 4 (415), the molten zone in Figure 5 The molten band (425) between the electrode 540 and the foil 530 is not visible. The LaB6 electrode 540 can be welded to the foil 530. Although some evidence of melting can be seen in the contact area 554, most of the molten band (425) between the electrode 540 and the foil 530 is hidden beneath the electrode 540. The electrode 540 has a tip 542 that can emit electrons under the influence of an applied external electric field. In variations, other material compositions can be used for the filament 510, foil 530, or electrode 540 disclosed herein.

[0060] Figure 6 Another example transmitter assembly is shown. Figure 5 The electrode 540 is mounted symmetrically with respect to the two arms of the filament 510, while Figure 6The electrode 640 is mounted asymmetrically relative to the two arms of the filament 610. Specifically, the tantalum sleeve adapter 630 has an elongated cross-section. When the filament 610 and sleeve 630 are folded, a generally flat surface exists, facilitating the mounting of the electrode 640 on this surface. The filament 610, sleeve adapter 630, and electrode 640 may have... Figure 5 The material composition is similar to that of other materials or components. Within the contact area 654, the edge portion of the molten band between the electrode 640 and the sleeve 630 can be seen. Figure 6 In the middle, the emitter tip has not yet been formed at the distal end 643 of electrode 640.

[0061] Figures 7 to 10 Figures 700, 800, 900, and 1000 show alternative transmitter structures. Figure 7 In this process, the filament 720 is welded to the adapter 730. The upper portion of the adapter 730 may be a hollow cylinder into which the electrode 740 can be inserted. Clamping force and / or welding energy may be applied in the direction indicated by arrow 752 to connect the electrode 740 to the adapter 730. The hollow cylindrical shape of the adapter 730 can constrain the orientation of the electrode 740, which can facilitate fixation during assembly.

[0062] Figure 8 A variation of the adapter 830 is shown, where the upper portion has a through slot into which the electrode 840 can be mounted. The filament 820 and the force / energy arrow 852 are similar in their configuration. Figure 7 The corresponding counterpart in the diagram will not be described further. The slotted shape of the adapter 830 allows external access to the interface between the adapter 830 and the electrode 840, which can facilitate laser welding, for example, using a laser beam oriented at an angle relative to arrow 852.

[0063] Figures 7 to 8 The diagram illustrates a transmitter structure in which the adapter connectors for the filament and electrodes are spaced apart from or not collinear with each other, and in which the adapter-filament connector and adapter-electrode connector can be formed separately. In contrast, Figures 9 to 10 The transmitter structure is shown in which the adapter-wire connector and the adapter-electrode connector are adjacent or collinear, thus allowing the two connectors to be formed in a single welding operation.

[0064] exist Figure 9In this assembly, adapter 930 is formed around filament 920. Electrode 940, adapter 930, and filament 920 can be clamped together by a force applied in direction 952 to form an assembly. This facilitates the formation of adapter-filament and adapter-electrode molten bands in a single spot welding operation, allowing current to flow through the assembly in the direction indicated by either arrow 952. Alternatively, such an assembly can be welded by laser welding, optionally repositioning the laser between multiple welded sections.

[0065] Figure 10 Example of a variation. In Figure 9 In the middle, the adapter 930 extends substantially along the length of the filament 920 (or more than 50% of the length of the filament), while... Figure 10 In this configuration, adapter 1030 extends along a relatively small portion (or less than 50% of the length) of filament 1020. The longer sleeve of adapter 930 facilitates manufacturing and clamping for welding and further protects the surface of filament 920 from degradation at high temperatures. Conversely, a shorter sleeve of adapter 1030 is more economical and avoids vacuum problems caused by residual cavitation between sleeve 1030 and filament 1020. The straight filament segment 1020 facilitates winding with tantalum foil.

[0066] Although arrows 952 and 1052 indicate a single welding operation for forming the adapter-wire connector and adapter-electrode connector, this is not a requirement, and as... Figures 7 to 8 Similarly, adapter-filament connectors and adapter-electrode connectors can be formed in separate operations. For example, tantalum sleeves 930 and 1030 can be clamped around filaments 920 and 1020 and then soldered to a sub-assembly, followed by electrodes 940 and 1040 being clamped to the sub-assembly and soldered to adapters 930 and 1030. Alternatively, sleeves 930 and 1030 can be formed by deposition on filaments 920 and 1020 before electrodes 940 and 1040 are soldered to them.

[0067] Electrode 740 is shown to have a square facet at its distal end (e.g., at the top of Figure 700, away from adapter 730). Nanorods or pointed tips may be formed after assembling the illustrated structure, but this is not required, and in other examples, emitter tips may be formed on electrode 730 before assembling the illustrated structure. Similar considerations apply to electrodes 840, 940, and 1040.

[0068] The embodiments shown herein are exemplary, and many other configurations can be implemented within the scope of the disclosed technology. For example, the laminated assembly may include a continuous layer of filament-adapter-electrode-adapter-filament. That is, the two outer layers may form support arms, and the adapter layer provides material compatibility between the electrode and the two filament arms. The entire laminated assembly can be spot-welded in a single welding operation.

[0069] First example method

[0070] Figure 11 This is a flowchart 1100 of a first example method according to the disclosed technology. This method can be used to form... Figure 4 A transmitter assembly similar to or a variant of the transmitter assembly.

[0071] At process block 1110, an adapter (similar to 420) can be attached to the filament (410). At process block 1120, the adapter can be clamped to the electrode (430), and at process block 1130, the adapter can be soldered to the electrode.

[0072] Many variations and extensions of this method can be implemented within the scope of the disclosed technology, some of which are... Figure 4 , Figure 12 Or as described in the context elsewhere in this document. The adapter may contain tantalum or a tantalum alloy. The electrodes may contain rare earth hexaborides.

[0073] Attachment of box 1110 can be performed in various ways. To form a molten band (similar to 415), the filament and adapter can be clamped together and welded. In some examples, the filament, adapter, and electrode can all be clamped together before any welding action is performed. Two welding actions can be performed as a single operation. One or both welding actions can be performed by electric spot welding or by laser welding. Either welding action or both welding actions can be performed by a single transient energy pulse delivered to the clamped object, or by performing both welding actions together, to avoid damage caused by a second energy pulse while the interface between the clamped objects is in a molten state.

[0074] As an alternative to clamping and welding, a deposition process can be used to form the adapter and attach it to the filament. Examples include chemical vapor deposition (CVD) or sputtering.

[0075] Example method extension

[0076] Figure 12 This is a flowchart 1200 of a second example method that exemplifies an extension of the first method. These extensions may be applied individually or in any combination, or may be applied in variations.

[0077] At process block 1230, a transmitter assembly incorporating the filament, adapter, and electrodes can be fabricated. As indicated by the dotted line, it can be used... Figure 11 The method execution box 1230 is used, but this is not required.

[0078] In the first extension, the adapter can be wound around the filament at frame 1210 before the assembly is formed at frame 1230.

[0079] Then, as Figures 3A to 3B As illustrated, the cold field emitter may have nanorod tips (310, 311) incorporated at the distal ends of the microrod electrodes. In a different example of the second extension, the nanorod tip may be implemented at box 1220A prior to assembling the emitter structure at box 1230, or alternatively, at box 1220B after the emitter structure has been assembled. Box 1220B is shown in dashed outline to indicate that it is an alternative to box 1220A.

[0080] As a third extension, at box 1240, the emitter assembly can be placed in an electron microscope; and as another extension, at box 1250, an electric field can be generated at the electrode tip to extract electrons from the electrode and generate an electron beam.

[0081] Welding example

[0082] Figure 13 Figure 1300 shows an example setup of the spot welding assembly of the transmitter assembly. As shown, the filament 1310, adapter 1320, and electrode 1330 are aligned and held between welding terminals 1341 and 1342. The clamping force is kept to a minimum to mitigate the risk of electrode 1330 breaking. One or both of terminals 1341 and 1342 may be spring-loaded. Power supply 1350 drives current 1352 in the circuit through wiring 1345 and 1346, terminals 1341 and 1342, and aligned devices 1310, 1320, and 1330, thereby forming a connection with... Figure 4 Similar molten bands as 415 and 425. Illustratively, terminal 1341 may be a plate on which assembly 1360 is supported, while terminal 1342 may be in the form of a pointed probe tip. Advantages of spot welding include single-setup operation of clamping and energy delivery, concentrated energy delivery at the interface to be welded (which can have high contact resistance), minimal path required for welding equipment (only two wires), and avoidance of filler material.

[0083] Numerous variations and extensions are possible within the scope of the disclosed technology. Current 1352 can flow in opposite directions. Clamping and spot welding operations can be performed only on adapter 1320 and electrode 1330, or only on adapter 1320 and filament 1330. In the example, welding can be performed by delivering 1J to 10J of electrical energy (often 3J to 6J) to assembly 1360 in a current pulse with a duration of 50ms to 500ms (or approximately 150ms) and a full-width half-maximum of 10ms to 200ms (or approximately 40ms).

[0084] Figure 14 Figure 1400 shows an example configuration of a laser welding emitter assembly according to the disclosed technology. As shown, the filament 1410, adapter 1420, and electrode 1430 can be clamped together (clamp not shown) as an assembly 1460. A laser beam can be guided to selected areas of the assembly from different orientations, as illustrated by arrows 1451 and 1452. The deposited laser energy melts the adjacent portions of the adapter 1420 and electrode 1430, thereby forming a... Figure 4 A similar molten band as 425. Similarly, the deposited laser energy melts the adjacent portion of adapter 1420 and filament 1410, thereby forming a molten band similar to 415. Advantages of laser welding include the ability to focus energy delivery at specific points, reduced clamping forces due to non-contact energy delivery, reduced risk of mechanical damage to assembly 1460, and avoidance of filler material.

[0085] Numerous variations and extensions are possible within the scope of the disclosed technology. In different examples, laser energy can be continuously scanned over the area where it will be deposited; or laser energy can be deposited at one, two, or more discrete points to induce localized melting and the formation of molten bands. The amount of energy deposited can be similar to that used for spot welding. One or more lasers can be used.

[0086] Additional Examples

[0087] The following are other embodiments of the disclosed technology.

[0088] Example 1 is a structure comprising: a filament; an adapter; a first molten strip coupling the filament to the adapter; an electrode; and a second molten strip coupling the electrode to the adapter.

[0089] Example 2 includes the subject matter described in Example 1, and further specifies that the filament contains at least 50 at% tungsten.

[0090] Example 3 includes the subject matter according to Example 1, and further specifies that the filament contains at least 50 at% rhenium.

[0091] Example 4 includes the subject matter according to any one of Examples 1 to 3, and further specifies that the total atomic percentage of tungsten and rhenium in the filament is at least 50%.

[0092] Example 5 includes the subject matter according to any one of Examples 1 to 4, and further specifies that: the filament comprises a cylindrical wiring adjacent to the first molten band, the cylindrical wiring having a diameter in the range of 25 μm to 500 μm and a length at least three times its diameter.

[0093] Example 6 includes the subject matter according to any one of Examples 1 to 5, and further specifies that the first molten strip comprises a blend of a first material of the filament and a second material of the adapter.

[0094] Example 7 includes the subject matter according to any one of Examples 1 to 6, and further specifies that the first molten band is at least a portion of the weld.

[0095] Example 8 includes the subject matter according to any one of Examples 1 to 7, and further specifies that the filament and the adapter have different material compositions.

[0096] Example 9 includes the subject matter according to any one of Examples 1 to 8, and further specifies that the adapter contains at least 90 at% tantalum.

[0097] Example 10 includes the subject matter according to any one of Examples 1 to 9, and further specifies that the adapter has a thickness in the range of 1 μm to 500 μm.

[0098] Example 11 includes the subject matter according to any one of Examples 1 to 10, and further specifies that the second molten band comprises a mixture of the first material of the electrode and the second material of the adapter.

[0099] Example 12 includes the subject matter according to any one of Examples 1 to 11, and further specifies that the second molten band is at least a portion of the weld.

[0100] Example 13 includes the subject matter according to any one of Examples 1 to 12, and further specifies that the electrode contains at least 60 at% boron.

[0101] Example 14 includes the subject matter according to any one of Examples 1 to 13, and further specifies that the electrode comprises a hexaboride material.

[0102] Example 15 includes the subject matter according to any one of Examples 1 to 14, and further specifies that the electrode comprises a rare earth hexaboride material.

[0103] Example 16 includes the subject matter described in Example 15, and further specifies that the electrode comprises lanthanum hexaboride.

[0104] Example 17 includes the subject matter according to any one of Examples 1 to 16, and further specifies that the electrode comprises: a microrod adjacent to the second molten band; and a nanorod tip located at a distal end.

[0105] Example 18 is an electron source comprising a structure according to any one of Examples 1 to 17, the structure having an emitter formed at the tip of the electrode; an extraction anode having a first aperture around the centerline of the emitter; an acceleration anode having a second aperture around the centerline of the emitter; and at least four electrical terminals configured to receive power to: drive current through the filament; apply an extraction voltage to the extraction anode; and apply an acceleration voltage to the acceleration anode.

[0106] Example 19 is an electron microscope that includes an electron source according to Example 18.

[0107] Example 20 is a method comprising: attaching an adapter to a filament; clamping the adapter to an electrode; and welding the adapter to the electrode.

[0108] Example 21 includes the subject matter described in Example 20, and further specifies that: the adapter comprises tantalum or a tantalum alloy; and the electrode comprises a rare earth hexaboride.

[0109] Example 22 includes the subject matter according to any one of Examples 20 to 21, and further specifies that the attachment includes: clamping the filament to the adapter; and welding the filament to the adapter.

[0110] Example 23 includes the subject matter according to Example 22, and further includes: wrapping the adapter around the filament before clamping the filament.

[0111] Example 24 includes the subject matter according to any one of Examples 22 to 23, and further specifies that, prior to performing any one of the welding actions, the two clamping actions clamp the filament, the adapter, and the electrode together.

[0112] Example 25 includes the subject matter according to any one of Examples 22 to 24, and further specifies that the two welding actions are performed as a single operation.

[0113] Example 26 includes the subject matter according to any one of Examples 22 to 25, and further specifies that at least one of the welding actions is electric spot welding.

[0114] Example 27 includes the subject matter according to any one of Examples 22 to 26, and further specifies that at least one of the welding actions is laser welding.

[0115] Example 28 includes the subject matter according to any one of Examples 22 to 27, and further specifies that at least one welding action in the welding action includes delivering a single energy pulse.

[0116] Example 29 includes the subject matter according to any one of Examples 20 to 28, and further includes forming a nanorod tip at the distal end of the electrode after welding the electrode.

[0117] Example 30 includes the subject matter according to any one of Examples 20 to 28, and further includes forming a nanorod tip at the distal end of the electrode prior to welding the electrode.

[0118] Example 31 includes the subject matter according to any one of Examples 20 to 30, and further specifies that the attachment includes depositing the adapter onto the filament.

[0119] Example 32 is a process comprising: forming an emitter assembly by means of the method described in Example 20; forming a nanorod tip at the distal end of the electrode before or after the welding action; and placing the emitter assembly in an electron microscope via the nanorod tip.

[0120] Example 33 includes the subject matter described in Example 32, and further includes: generating an electric field at the tip of the electrode to generate an electron beam in the electron microscope.

[0121] Example 34 is a structure comprising: a filament having a first material composition; a rare earth hexaboride electrode comprising: a microrod adjacent to a second molten band; a nanorod tip located at a distal end; an adapter having a thickness in the range of 5 μm to 100 μm; a second material composition having at least 80 at% tantalum, the second material composition being different from the first material composition; a first molten band coupling the filament to the adapter; and a second molten band coupling the electrode to the adapter.

[0122] Example 35 is an electron microscope that includes a cold field emission electron source, the cold field emission electron source including the structure described in Example 34.

[0123] General considerations

[0124] As used herein and in the claims, the singular forms “a,” “an,” and “the” include the plural forms unless the context clearly indicates otherwise. Additionally, the term “comprising” means “including.” Furthermore, the term “coupled” does not exclude the existence of intermediate elements between coupled items. Moreover, as used herein, the terms “or” and “and / or” mean any combination of one or more of the phrases. Terms connected by “or” or “and / or” need not be mutually exclusive.

[0125] The systems, methods, and apparatuses described herein should not be construed as limiting in any way. Rather, this disclosure relates to all novel and non-obvious features and aspects of the various disclosed embodiments, whether individually or in various combinations and sub-combinations formed with each other. The disclosed systems, methods, and apparatuses are not limited to any particular aspect or feature or combination thereof, nor are they required to possess any one or more particular advantages or problems solved. Techniques from any example may be combined with one or more of the techniques described in any other example. Any operational theory is provided for ease of interpretation, but the disclosed systems, methods, and apparatuses are not limited to such operational theory.

[0126] Although some of the methods disclosed are described in a specific order for ease of presentation, it should be understood that this descriptive approach includes rearrangement unless the specific language described below requires a particular order. For example, operations described sequentially may be rearranged or performed simultaneously in some cases. Furthermore, for simplicity, the accompanying drawings may not show the various ways in which the disclosed systems, methods, and apparatus can be combined with other systems, methods, and apparatus. Additionally, this description sometimes uses terms such as “accelerate,” “acquire,” “attach,” “analyze,” “apply,” “clamp,” “clean,” “configure,” “deliver,” “deposit,” “determine,” “guide,” “drive,” “form,” “melt,” “generate,” “indicate,” “place,” “mill,” “get,” “provide,” “receive,” “scan,” “transfer,” “use,” or “weld” to describe the disclosed techniques. These terms are high-level abstractions of the actual operations performed. The actual operations corresponding to these terms may vary depending on the specific implementation and are readily discernible by those skilled in the art who possess the knowledge of this disclosure.

[0127] In some examples, values, processes, or devices may be referred to as “lowest,” “best,” “maximum,” “optimal,” “extreme,” etc. It will be understood that such descriptions are intended to indicate that a choice can be made among several or many alternatives, and that such a choice is not necessarily better, smaller, or otherwise preferred than other unconsidered alternatives.

[0128] The operational theories, scientific principles, or other theoretical descriptions of the devices or methods referred to herein are provided for the purpose of better understanding and are not intended to be limiting in scope. The devices and methods in the appended claims are not limited to those that operate in a manner described by such operational theories.

[0129] Any of the disclosed methods can be controlled or implemented as a computer-executable instruction or computer program product stored on one or more computer-readable storage media (e.g., tangible, non-transitory computer-readable storage media) and executed on a computing device (e.g., any available computing device, including tablets, smartphones, or other mobile devices containing computing hardware). A tangible computer-readable storage medium is any available tangible medium that can be accessed in a computing environment (e.g., one or more optical media such as a DVD or CD, a volatile memory component (e.g., DRAM or SRAM), or a non-volatile memory component (e.g., flash memory or hard disk drive)). Computer-readable storage media include memories and storage devices. The terms "computer-readable medium" or "computer-readable storage medium" do not include signals and carrier waves. Additionally, the terms "computer-readable medium" or "computer-readable storage medium" do not include communication ports.

[0130] Any of the computer-executable instructions used to implement the disclosed technology, and any data created and used during the implementation of the disclosed embodiments, may be stored on one or more computer-readable storage media. The computer-executable instructions may be, for example, part of a dedicated software application or a software application accessed or downloaded via a web browser or other software application (e.g., a remote computing application). Such software may be executed using one or more networked computers, for example on a single local computer (e.g., any suitable commercially available computer) or in a networked environment (e.g., via the Internet, a wide area network, a local area network, a client-server network, a cloud computing network, or other such networks).

[0131] The disclosed technology is not limited to any particular computer or hardware type. Certain details of suitable computers and hardware are well known and do not need to be elaborated in this disclosure.

[0132] Given that the principles of the disclosed subject matter can be applied to many possible embodiments, it should be recognized that the illustrated embodiments are merely preferred examples of the disclosed subject matter and should not be considered as limiting the scope of the claims. Specifically, the scope of the claimed subject matter is defined by the appended claims. Therefore, we claim protection for all contents falling within the substance and spirit of these claims.

Claims

1. A structure comprising: fine filaments; adapter; A first molten strip couples the filament to the adapter; electrode; and A second molten band couples the electrode to the adapter.

2. The structure according to claim 1, wherein: The total atomic percentage of tungsten and rhenium in the filament is at least 50%.

3. The structure according to claim 1, wherein: The first molten band comprises a mixture of the first material of the filament and the second material of the adapter.

4. The structure according to claim 1, wherein: The adapter contains at least 90% tantalum atoms.

5. The structure according to claim 1, wherein: The second molten zone contains a mixture of the first material of the electrode and the second material of the adapter.

6. The structure according to claim 1, wherein: The electrode contains a rare earth hexaboride material.

7. The structure according to claim 1, wherein the electrode comprises: Microrods, wherein the microrods are adjacent to the second molten zone; and Nanorod tip, the nanorod tip being located at the distal end.

8. An electron source, the electron source comprising: The structure according to claim 1, wherein the structure has an emitter formed at the tip of the electrode; Extraction anode, the extraction anode having a first pore around the centerline of the transmitter; An accelerating anode having a second pore around the centerline of the transmitter; At least four electrical terminals, said at least four electrical terminals being configured to receive power to: A driving current passes through the filament; An extraction voltage is applied to the extraction anode; as well as An accelerating voltage is applied to the accelerating anode.

9. An electron microscope, said electron microscope comprising: The electronic source according to claim 8.

10. A method, the method comprising: Attach the adapter to the filament; Clamp the adapter to the electrodes; as well as The adapter is welded to the electrode.

11. The method of claim 10, wherein: The adapter comprises tantalum or a tantalum alloy; and The electrode contains rare earth hexaborides.

12. The method of claim 10, wherein the attachment comprises: The filament is clamped to the adapter; as well as The filament is welded to the adapter.

13. The method according to claim 12, further comprising: The adapter is wound around the filament before clamping it.

14. The method according to claim 12, wherein: The two welding actions are performed as a single operation.

15. The method according to claim 12, wherein: At least one of the welding actions is electric spot welding.

16. The method of claim 12, wherein: At least one of the welding actions is laser welding.

17. The method according to claim 12, wherein: At least one of the welding actions includes delivering a single energy pulse.

18. The method according to claim 10, further comprising: After the electrode is welded, a nanorod tip is formed at the distal end of the electrode.

19. The method according to claim 10, further comprising: Nanorod tips are formed at the distal end of the electrode before welding.

20. The method of claim 10, wherein the attachment comprises: The adapter is deposited onto the filament.

21. A process comprising: The transmitter assembly is formed by the method according to claim 10; Nanorod tips are formed at the distal end of the electrode before or after the welding action; as well as The emitter assembly was placed in an electron microscope through the tip of the nanorod.

22. The process according to claim 21, further comprising: An electric field is generated at the tip of the electrode to produce an electron beam in the electron microscope.

23. A structure comprising: A filament having a first material composition; Rare earth hexaboride electrode, wherein the rare earth hexaboride electrode comprises: Microrods, said microrods being adjacent to the second molten zone; and Nanorod tip, the nanorod tip being located at the distal end; and An adapter, the adapter having: Thickness in the range of 5μm to 100μm; and A second material composition having at least 80 at% tantalum, the second material composition being different from the first material composition; A first molten strip, which couples the filament to the adapter; and The second molten strip couples the electrode to the adapter.

24. An electron microscope, said electron microscope comprising: A cold field emission electron source, the cold field emission electron source comprising the structure according to claim 23.

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