Vibration-free cryogenic cooling

Abstract

To provide a device and a method for vibration-free cryogenic cooling, suitable for transmission electron microscopes (TEM) and other analytical instruments.SOLUTION: A device includes a thermal reservoir adapted to be positioned outside a sample chamber, and a longitudinal member extending from the thermal reservoir into the sample chamber and flexibly couplable to a sample holder within the sample chamber.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates to cryogenic cooling of analytical instruments. [Background technology]

[0002] As scientific frontiers advance, analytical instruments must meet increasingly stringent requirements. A new generation of analytical applications requires long measurement times of 10 hours or more, cryogenic sample temperatures below 77 K, temperature stability greater than 1 K, and sub-nanometer position stability. In addition, samples can be in very dense environments. Current approaches cannot meet such stringent requirements or operating conditions. Therefore, there remains a need for improved techniques for cooling samples within analytical instruments. Summary of the Invention

[0003] Briefly, the disclosed technology provides vibration-free cryogenic cooling suitable for transmission electron microscopes (TEMs) and other analytical instruments. By way of example, a thermal battery can include a cryocooler, a thermal switch, a thermal refrigeration reservoir, and a cold finger. The thermal reservoir can be mounted outside the sample chamber. The cold finger can provide thermal coupling between the reservoir and a sample holder within the sample chamber. The temperature of the sample holder or sample can be regulated by a heater or a series variable thermal resistor. The operational phase includes cooling the reservoir, decoupling the cryocooler from the reservoir, and passive vibration-free thermal energy extraction from the sample to the reservoir with temperature regulation. Embodiments can provide a 12-hour stand time with the sample temperature maintained at 20 K±0.1 K, with correspondingly longer stand times at higher sample temperatures. The operational phase can be repeated periodically for even longer analytical studies.

[0004] In a first aspect, the disclosed technology can be implemented as an apparatus having a thermal reservoir positioned outside a sample chamber and a longitudinal member extending from the thermal reservoir into the sample chamber, the longitudinal member being flexibly couplable to a sample holder within the sample chamber.

[0005] In some examples, the thermal reservoir can be configured to passively extract thermal energy from the sample holder to maintain the temperature of the sample holder within a predetermined operating temperature range for at least a predetermined period of time. The apparatus can further include a heater thermally coupled to the sample holder, a temperature sensor thermally coupled to the sample holder, and a controller coupled to receive a signal from the temperature sensor and drive the heater. The heater can be configured to actively supply thermal energy to the sample holder to regulate the temperature of the sample holder. The thermal energy can flow from the sample holder to the thermal reservoir along a first path defined by the longitudinal member. The apparatus can also include a thermal resistor positioned on the first path to increase the thermal resistance between the thermal reservoir and the heater. The disclosed technology can be implemented as a thermal battery incorporating the above-described apparatus, along with a cryocooler and a thermal switch coupling the cryocooler to the thermal reservoir.

[0006] In additional examples, thermal energy from the sample to the thermal reservoir can flow along a first path, and the device can include a separate component with variable thermal resistance disposed on the first path and configured to control the flow of thermal energy along the first path. In some examples, the separate component can be a passive temperature regulator, and in other examples, the device can include a controller coupled to the separate component and configured to control the separate component. The device can include a separate thermal mass disposed within the sample chamber and thermally coupled to the longitudinal member and / or the sample holder. The predetermined period can be in the range of 2 to 30 hours. The sample temperature setpoint for the operating temperature range can be 10 K to 50 K, with a tolerance of 10 mK to 3 K.

[0007] In a further example, the thermal reservoir can include a primary thermal reservoir (wherein the longitudinal member is a first longitudinal member coupled to the primary thermal reservoir), a secondary thermal reservoir positioned outside the sample chamber, and a second longitudinal member extending from the secondary thermal reservoir into the sample chamber. The second longitudinal member can be coupled to a thermal shield near the sample holder. The secondary thermal reservoir can be configured to passively extract thermal energy from the thermal shield. The device can include a cryocooler in thermal contact with the secondary thermal reservoir and coupled to the primary reservoir through a thermal switch. The device can be configured to passively extract thermal energy from the sample holder to the primary reservoir when the thermal switch is open. The secondary thermal reservoir can surround the primary reservoir, and the second member can be annularly disposed around the first member. The secondary thermal reservoir can incorporate copper or a copper alloy. The primary thermal reservoir can incorporate erbium or an erbium alloy. The disclosed technology can be implemented as a system incorporating any of the above-described devices and incorporating a transmission electron microscope (TEM) incorporating a sample chamber and sample holder.

[0008] In a second aspect, the disclosed technology can be implemented as a method for controlling the temperature of a sample in a sample chamber. A thermal reservoir positioned outside the sample chamber is filled. After the thermal reservoir reaches a target setpoint, filling is stopped. The thermal reservoir is thermally coupled to the sample through a longitudinal member. The flow of thermal energy to or from the sample is adjusted to regulate the temperature of the sample.

[0009] In some examples, the regulating can include activating a heater in response to a signal indicative of the temperature in the sample chamber. The regulating can be performed at least in part by a variable series thermal resistor. The regulating can include activating the variable series thermal resistor from a controller in response to a signal indicative of the temperature in the sample chamber. The filling can be performed by a cryocooler. The stopping can include turning off the cryocooler and changing the state of a thermal switch coupling the cryocooler to the thermal reservoir from a closed state to an open state. In a further example, the thermal reservoir can be partially or fully refilled after a predetermined period of time.

[0010] In another aspect, the disclosed technology can be implemented as a system incorporating a transmission electron microscope (TEM), a sample holder, and a regulated thermal cell. The TEM includes an electron source, a focusing lens, a sample chamber, an objective lens, and an imaging device. The sample holder is disposed within the sample chamber. The regulated thermal cell includes a thermal reservoir disposed outside the sample chamber, a thermal strap connecting the thermal reservoir to the sample holder, and a temperature regulator. The temperature regulator is configured to control the flow of thermal energy from the sample holder to the thermal reservoir to regulate the sample temperature.

[0011] In some examples, the system can be configured to maintain a stable cryogenic temperature of the sample in the sample holder for 6 consecutive hours, where the stable cryogenic temperature has (i) a temperature change of 200 mK or less at a temperature setpoint in the range of 20-80 K, (ii) a sample displacement of 1 nm / min or less, and (iii) a vibration of 1 pm rms or less in the 1-2000 Hz band.

[0012] In a further example, the system can include a sample shield disposed within the sample chamber, the thermal strap can be a first strap, and the regulated thermal battery further includes a secondary reservoir, first and second cryocooler stages, first and second thermal switches, and a second strap coupling the secondary reservoir to the sample shield. The first thermal switch can be coupled between the first cryocooler stage and the secondary reservoir. The first cryocooler stage can be configured to charge the secondary reservoir with the first thermal switch in a closed state. The second thermal switch can be coupled between the second cryocooler and the thermal reservoir. The second cryocooler can be configured to charge the thermal reservoir with the second thermal switch in a closed state.

[0013] The foregoing and other objects, features, and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram of a first exemplary system in which the disclosed technology can be deployed. [Figure 2A] FIG. 1 illustrates a second exemplary system in which the disclosed techniques can be deployed. [Figure 2B] FIG. 1 illustrates a second exemplary system in which the disclosed techniques can be deployed. [Figure 3] 1 is a cross-sectional view of an exemplary device according to the disclosed technology in an analytical instrument environment. [Figure 4] 1 is a chart illustrating the specific heat capacity of exemplary materials at cryogenic temperatures. [Figure 5] FIG. 1 is a cross-sectional view of an exemplary sample chamber coupled to a thermal reservoir in accordance with the disclosed technology. [Figure 6] 1 is a flowchart of a first exemplary method of operating a thermal battery in accordance with the disclosed technology. [Figure 7] FIG. 1 is a diagram of a first apparatus in accordance with the disclosed technology. [Figure 8] 10 is a chart illustrating sample holder displacement in an example configuration in which the disclosed technology can be deployed. [Figure 9] 10 is a set of charts illustrating the displacement of a sample holder with various thermal masses coupled to the sample holder, in accordance with an example of the disclosed technology. [Figure 10] 1 is a schematic diagram illustrating temperature regulation according to an example of the disclosed technology; [Figure 11] 10A-10C are schematic diagrams illustrating temperature regulation according to further examples of the disclosed technology. [Figure 12] FIG. 1 is a diagram of a first exemplary thermal switch usable with the disclosed technology. [Figure 13] FIG. 10 is a diagram of a second exemplary thermal switch in accordance with the disclosed technology. [Figure 14] 1 illustrates a generalized example of a suitable computing environment in which the described embodiments, techniques, and techniques relating to beam focusing can be implemented. DETAILED DESCRIPTION OF THE INVENTION

[0015] Introduction Advances in electron microscopes, 3D reconstruction software, and computing power have made it possible to accurately image and reconstruct objects 100 nm or smaller. Areas of particular interest include biology, where research related to viruses, including the novel coronavirus, is planned, and materials science, where nanotechnology continues to develop new structures and novel compositions. For high resolution, minimizing sample vibrations can be desirable. Traditional techniques using liquid nitrogen or liquid helium reservoirs suffer from vibrations caused by boiling liquids. Furthermore, as the size of sample particles increases, the number of images required increases, resulting in longer study times. At the same time, the sample stability required for accurate reconstruction becomes more demanding. In some applications, atomic motion at 77 K is sufficient to impair image resolution or sample stability. Additionally, radiation damage to samples can impair image quality during the long imaging times used for ultra-high resolution imaging, and such radiation damage can be reduced at lower temperatures. Therefore, maintaining a stable, low temperature of 20 K or below, free from external vibrations, for periods of 6 to 12 hours or longer is crucial. The disclosed technology addresses this need. Atomic motion can be kept to amplitudes of 1-10 pm, or less than the size of most atoms.

[0016] The examples described below implement a solid-state thermal reservoir to provide vibration-free cooling with long stand times. Furthermore, cyclic operation can be supported to continue the study of a single sample over a series of stand times. That is, if the thermal reservoir warms up and can no longer maintain the sample at a particular temperature setpoint (e.g., 20 K), the analytical study can be paused while the thermal reservoir is refilled. Thus, with a 12-hour stand time and a 6-hour refill time in a single cycle, the disclosed embodiments can be repeatedly cycled for long-term studies lasting 100 hours, 1000 hours, or even longer, with an operating duty cycle exceeding 60%. With a 6-hour stand time and a 6-hour refill time, long-term operation with a duty cycle of approximately 50% can be achieved.

[0017] Another feature of some of the examples described below is temperature regulation. Without regulation, gradual warming of the reservoir can shift the equilibrium temperature of the sample holder and sample beyond the design specifications. Temperature regulation can be implemented as active regulation using a heater to compensate for the monotonic decrease in thermal energy flow during stand time as the reservoir warms and the temperature difference between the sample and reservoir decreases. In another example, a variable thermal resistor in the cooling path can provide temperature regulation without introducing excess heat, reducing the flow of thermal energy from the sample to the reservoir when the temperature difference between the samples is large.

[0018] Various workflows can be implemented for 3D image reconstruction studies. In the single particle workflow, the sample can contain many identical copies of the object with a distribution of orientations. A survey scan can find candidate objects at each orientation, and by appropriately selecting the candidate objects, images can be acquired at various object rotations. The images can be reconstructed together to determine the 3D structure of the object.

[0019] In a tomography workflow, a single copy of the object can be placed in the sample volume and its orientation can be determined if it is not already known. This object can be thinned, for example by focused ion beam milling (FIB), to obtain a sample suitable for TEM imaging. In a TEM, the sample holder can be used to gradually tilt the sample, allowing images to be acquired at various orientations. In a single particle workflow, the images can be reconstructed to determine the 3D structure of the object.

[0020] term The usage and meaning of all terms cited in this section apply throughout this disclosure unless expressly indicated otherwise or to the contrary in context. The following terms are expanded to their associated word forms:

[0021] In the context of cooling, "active" cooling is performed by a machine with one or more moving parts, such as a compressor or a cryocooler with one or more pistons. In some examples of the disclosed technology, active cooling can be used to fill a thermal reservoir. In contrast, "passive" cooling is performed without moving parts. In examples of the disclosed technology, the thermal reservoir, once filled, can provide passive cooling to the sample and other devices in the sample chamber, i.e., with any cryocoolers turned off. In a common example, active cooling can release heat from the cooled sample to a sink at a higher temperature than the sample, while passive cooling can absorb heat from the cooled sample in a sink at a lower temperature than the sample. The presence of ancillary moving components, such as a copper blade that can move with the sample holder, does not prevent its characterization as passive cooling, since the movement of the copper blade does not perform the cooling. In the context of temperature regulation, "passive" regulation is performed by a device with no input control signal. A variable thermal resistor may have a thermal resistance that changes depending on its temperature or the temperature of its immediate surroundings, but it does not have a control signal and may be a passive regulator. In contrast, "active" regulation is performed by a device that has an input control signal. In some examples of the disclosed technology, a heater or controlled variable thermal resistor may be used for active temperature regulation, for example, in a servo loop. Analog or digital control, including pulse width modulation (PWM), pulse frequency modulation (PFM), or other techniques, may be used. Considering the entire servo loop as a device does not preclude classification as an active regulator, since internal components (e.g., heaters) within the servo loop have input control signals. In some examples of the disclosed technology, passive cooling and active regulation may coexist.

[0022] The term "annular" refers to a ring-shaped object having the general form of a torus, and extends to hollow cylinders. The presence of additional holes, such as screw holes, or wire mesh cylinders, such as Kellem® Cord Grips (Hubbell Inc., Shelton, CT), does not prevent such an object from being described as annular.

[0023] A "controller" is an electronic device that can couple to a load or actuator to change a physical parameter. Some controllers can include a microprocessor that is programmable to execute machine-readable instructions. The description of a computing device herein is generally applicable to such controllers. Such controllers can include additional electronic circuitry, such as filters and amplifiers. Other controllers can include analog circuitry, such as filters and amplifiers, without a microprocessor.

[0024] A "cryocooler" is a refrigerator that provides cooling at very low temperatures. A typical cryocooler may include a compressor, an expander, one or more heat exchangers, and may include one or more pistons. Common types of cryocoolers include the Gifford-McMahon type, the Linde-Hampson type, the pulse tube type, and the Stirling type.

[0025] The term "cryogenic" refers to temperatures below 100 K, equipment or processes operating at temperatures below 100 K, or material properties or parameters below 100 K. Materials may be characterized by terms (such as "metallic" or "conductive") that refer to the general properties of such materials at room temperature and not necessarily according to their properties at cryogenic temperatures.

[0026] A "discrete component" is a device that can be distinguished from its surroundings based on material properties, labeling, or packaging. In some examples, a thermal resistor can be integrated into the cold finger. The thermal resistor can have a thermal conductivity that is different from that of the adjacent copper rod and can be a separate component within the cold finger structure.

[0027] An "electron microscope" is a type of analytical instrument in which a sample is irradiated with an electron beam, and the resulting particles or electromagnetic radiation are used to form an image. A scanning electron microscope (SEM) images reflected, secondary, or backscattered particles or radiation from the sample surface onto which the electron beam is incident. Because the beam interactions detected by an SEM occur at or near this surface, an SEM can operate on samples of any thickness. In contrast, a transmission electron microscope (TEM) images transmitted electrons (including scattered electrons). TEMs operate on samples approximately 10–150 nm thick and can be mounted on a grid for mechanical support and thermal conductivity, which can be held in a sample holder. While TEMs can provide magnifications of over 50 million, SEM magnifications are typically limited to approximately 2 million. The sample chamber in a high-performance TEM can be small and crowded. Equipment that can be accommodated in an SEM sample chamber often cannot fit inside a TEM sample chamber. A typical size for a TEM sample chamber is about 60 mm in diameter and 35 mm in height, while an SEM sample chamber can be 5-10 times larger in each dimension, or about 100-1000 times larger. For the purposes of this disclosure, a scanning transmission electron microscope (STEM) that performs transmitted electron imaging is considered a TEM.

[0028] A "heater" is a device that converts electrical energy into thermal energy.

[0029] A "longitudinal member" is a solid object having a length greater than three times its cross-sectional (transverse) dimension. Some longitudinal members of interest in this disclosure are cold fingers, which may take the form of copper rods or tubes and may have one or more embedded devices, such as thermal resistors. While some longitudinal members are rigid, this is not required; longitudinal members may include flexible structures such as wires, multi-strand wire bundles, wire braids, foils, ribbons, or other sheet forms; hinges, pin joints, or other linking elements; helical, corrugated, or other spring-like structures. In particular, longitudinal members may include one or more rigid components and one or more flexible components. A longitudinal member may be formed as a group of attached longitudinal members. The term "strap" is generally synonymous with "longitudinal member" and extends to objects and assemblies of various structures. A "thermal strap" is a strap that provides thermal coupling or thermal energy flow along its length or between devices at its ends.

[0030] Terms such as "operating [attribute]" (e.g., "operating conditions" or "operating temperature") refer to the value of the [attribute] during the stand time of the disclosed embodiments, typically when the thermal reservoir is providing passive cooling to the sample and the sample is in a condition suitable for the analytical procedure.

[0031] The term "regulating" refers to maintaining a parameter (the "regulated parameter") within a predetermined tolerance. A "regulator" is a device or combination of devices configured to regulate a parameter of interest. In examples, a regulator can (i) sense a first parameter, (ii) control a second parameter, and (iii) achieve regulation of a third parameter. In various examples, some of the first, second, and third parameters may be the same or all may be different. In some disclosed examples, a servo loop senses the temperature of the bridge (the first parameter) and thereby controls the current to the heater (the second parameter) to regulate the temperature of the sample (the third parameter). In other disclosed examples, a passive variable thermal resistor regulates the temperature of a remote sample (the third parameter) in response to its instantaneous temperature (the first parameter) by changing its thermal resistance (the second parameter).

[0032] A "sample" is a physical object that can be the subject of an analytical procedure using a TEM or other analytical instrument. The sample can be held or moved by a "sample holder," which in some instances can be a multi-surface gripper. The sample and sample holder can be placed within a "sample chamber" for purposes of imaging, analysis, or related process operations. Within the sample chamber, a "shield" (sometimes called a "cryobox") provides a thermal shield to reduce radiative heat transfer between the sample and nearby warm components and also helps protect the sample from contaminants.

[0033] A "sensor" is a device that has an electrical property or generates an electrical signal, the value of which is indicative of a physical parameter. Some sensors of interest in this disclosure are temperature sensors.

[0034] c p The "specific heat capacity", denoted by , is the amount of heat energy required to raise the temperature of a unit mass of a given material at a constant pressure. This amount is expressed as a function of its mass (in this case, c p An exemplary unit of is Jkg-1 K -1 ) or volume (in this case, c p An exemplary unit of is Jcm -3 K -1 )

[0035] A "stand time" is a continuous time interval during which the target operating conditions of the system can be met. In an example of the disclosed technology, the thermal battery can maintain the sample at a temperature setpoint within a predetermined tolerance for the stand time. The target operating conditions can include additional requirements such as temperature or position fluctuations or deviations.

[0036] A "thermal battery" is a system that includes a thermal reservoir, a means for charging the thermal reservoir, and a facility (such as a port or cold finger) for delivering thermal energy (hot or cold air) to a load. The load itself is not part of the thermal battery.

[0037] "Thermal conductivity" is an intensive property of a material that indicates the ratio of thermal energy flow density (e.g., power per cross-sectional area) to the temperature gradient in the direction of thermal energy flow (e.g., temperature change per length). A device of a given material and dimension can have a "thermal conductance" (the ratio of thermal energy flow (power) to temperature difference) and a "thermal resistance" (the reciprocal of thermal conductance). Such a device can be called a "thermal resistor."

[0038] "Thermal energy" refers to both "cold" and "hot," with cold provided to an object being an alternative description of heat removed from the object, and cold removed from an object being an alternative description of heat provided to the object. Thermal energy can be delivered to and stored in thermal reservoir materials, and energy can be extracted from such materials. Thermal energy can be specified in J, kWh, Btu, or similar units. "Thermal energy flow" (or simply "flow") refers to the rate of thermal energy transfer, has the dimension of power, and can be expressed in W, Btu / hr, or similar units. Thermal energy flow can be positive or negative. For convenience, such flow is often described in the conventional sense (i.e., the direction in which thermal energy flows), but the use of words such as "extract" or "deliver" is not limiting, and such descriptions can also extend to flow in the opposite direction.

[0039] A "thermal reservoir" is a continuous mass of material that can be configured to accept, store, and deliver thermal energy. Some examples herein implement the thermal reservoir using a solid block of metal, but this is not required. In various examples, a liquid, a solid-liquid combination, a solid pellet in a carrier medium, or a liquid capsule can also be used. A cryogenic thermal reservoir is "filled" by cooling, such as by a mechanical cryocooler or from another thermal reservoir, and "discharged" by warming, such as when cold is stored in the thermal reservoir and the thermal reservoir is used to extract thermal energy from a sample chamber.

[0040] A "variable thermal resistor" is a thermal resistor whose thermal resistance can change over time, either spontaneously (e.g., due to changes in the ambient temperature in the thermal resistor's immediate vicinity) or in response to an external control input.

[0041] First Exemplary System FIG. 1 is a diagram 100 of a first exemplary system in which a regulated thermoelectric cell 130 provides cooling to a sample holder 123 within a transmission electron microscope (TEM) 110.

[0042] Within the TEM 110, an electron beam may be generated by an electron source 112. The beam may be focused by a focusing lens 114 onto a sample location within a sample chamber 120. A sample 126 may be held by a sample holder 123 positioned within the sample chamber 120. The illustrated system may be used to image or analyze the sample 126, although the dotted outline indicates that the sample itself is not part of the illustrated system. After passing through the sample 126, the transmitted electron beam may be focused by an objective lens 116 onto an imaging plane of an imager 118.

[0043] The regulated thermal battery 130 can be coupled to the TEM 110, and in particular to the sample holder 123 within the sample chamber 120. The battery 130 can include a thermal reservoir 133 disposed outside the sample chamber 120. A thermal strap 136 can be coupled between the sample holder 123 and the reservoir 133 to provide heat exchange between the sample holder 123 and the reservoir 133. Additionally, the battery 130 can include a temperature regulator 139. The regulator 139 can control the flow of thermal energy between the reservoir 133 and the sample holder 123 (and thereby to or from the sample 126) to regulate the temperature of the sample holder (and, therefore, the temperature of the sample).

[0044] Numerous extensions or variations of the illustrated system can be implemented within the scope of the disclosed technology. In some examples, the TEM 110 can be a scanning transmission electron microscope (STEM), and in other examples, the TEM 110 can be replaced by other analytical or process equipment with similar performance requirements. An example illustrated system can provide a stand time of 12 hours (or ranges of 2-50, 4-30, 6-20, 8-15, or 12-24 hours) at a temperature setpoint of 20 K (or adjustable over ranges covering 4-77 K, 10-50 K, or 15-30 K, or 20-80 K, 30-50 K, or 25-80 K), with a temperature change of up to 200 mK (or ranges of 50-1,000 mK, 100-500 mK, or 150-250 mK) over this stand time. Additionally, sample displacement can be kept below 1 nm / min (or below 0.5 nm / min if the cooling system contributes a maximum of about 0.2 nm / min, or in the ranges of 0.1-10 nm / min, 0.2-5 nm / min, or 0.5-2 nm / min), and vibrations can be limited to a maximum of 1 pm rms (or in the ranges of 0.1-10 pm rms, 0.2-5 pm rms, or 0.5-2 pm rms) over a frequency range of 1-2000 Hz (or 0.1-20000 Hz, 0.2-10000 Hz, 0.5-5000 Hz, 2-1000 Hz, 5-500 Hz, 10-200 Hz, or 50-100 Hz).

[0045] Thermal reservoir 133 can include a solid thermal reservoir with no moving parts, such as one or more blocks of a solid metal, such as erbium, another rare earth element, tin, or a combination thereof. Cooling can be achieved by the flow of thermal energy from sample holder 123 to reservoir 133 through strap 136, resulting in gradual warming of reservoir 133 over stand time. In a further example, battery 130 can include one or more additional thermal reservoirs arranged as a substantially concentric volume shell around the immediately preceding reservoir. Battery 130 can include one or more cryocoolers and thermal switches, as described herein.

[0046] Because the sample holder 123 can be movable, but the thermal reservoir 133 can be mounted immovably due to its mass, the strap 136 can be configured to flexibly couple with the sample holder 123. In some examples, the strap 136 can include a rigid portion (such as a copper rod) and a flexible portion (such as a copper braid). The curved right portion of the strap 136 is generally the curved or flexible portion of the strap 136.

[0047] In various examples, the temperature regulator 139 may be a servo-controlled heater, a servo-controlled series regulator, or a passive series regulator, or any combination of such devices. The regulator 139 may be variously attached to the other illustrated components. In some examples, the regulator 139 may be coupled to the heat strap 136; in other examples, the regulator 139 may be integrated into the heat strap 136; and in further examples, the regulator 139 may be independently coupled to the sample holder 123. While the temperature regulator 139 is shown positioned within the chamber 120, this is not required; in other examples, the regulator 139 may be located near the reservoir 133 or outside the chamber 120. In further examples, the temperature regulator 139 may be distributed among multiple components. For example, a passive regulator can be positioned proximate the interface between the reservoir 133 and the strap 136, an active series throttle can be installed at an intermediate position along the strap 136, and / or an active heater device can be installed within the sample chamber 123 in various combinations. In other examples, the thermal reservoir 133 can include a non-metallic solid, liquid, gas, or composite material in various combinations. For example, the reservoir 133 can include a solid pellet immersed in a fluid or a closed cell filled with a fluid.

[0048] Second Exemplary System 2A and 2B are diagrams 200 and 201 illustrating a second exemplary system in which the disclosed technology can be deployed. Figure 2A shows a general view of a TEM column 210 with an attached thermal battery 230, and Figure 2B shows a partial view of the thermal battery 230 coupled to a sample chamber 220.

[0049] Starting with FIG. 2A, table 240 is attached to frame 244 by vibration isolation mounts 242. Table 240, in turn, supports the entire TEM column 210 and thermocell 230. As illustrated, duct 256 provides high-voltage cables to the electron gun and accelerator 258. Focusing assembly 218 and probe corrector 216 can deliver the focused electron beam to specimen chamber 220, which is also coupled to thermocell 230. The electron beam transmitted through specimen chamber 220 passes through image corrector 214 and onto camera 252. Partially hidden behind thermocell 230 is specimen loading subsystem 254, which is coupled to specimen chamber 220.

[0050] Turning to Figure 2B, the thermal battery 230 and sample chamber 220 are shown as mirror images of their relative orientation in Figure 2A. Inside the housing 233, a secondary thermal reservoir surrounds the primary thermal reservoir; this is not visible in Figure 2B; port 236 surrounds an annular cold finger that couples the thermal reservoir to structures within the sample chamber 220. Cryocoolers 264, 266 provide controlled cooling to the thermal reservoir within the housing 230 and can be disconnected from the reservoir by a thermal switch located within the housing 262. Also visible in Figure 2B is the automated sample loader 224, which provides a load to the opposing sample stage (not shown in Figure 2B).

[0051] First Exemplary Apparatus FIG. 3 is a cross-sectional view 300 of an exemplary apparatus according to the disclosed technology in an analytical instrument environment. The right side of FIG. 3 is a partial cross-sectional view of an analytical instrument, such as an electron microscope, having a central (beam) axis 315. Collection optics 314 and objective optics 312 are disposed on either side of a sample chamber 320, within which a sample holder 323 can hold a sample 326 within an internal shielded volume defined by a shield 329. Magnetic pole pieces 313, 311 create a magnetic field between the collection 314 and objective optics 312, which can severely limit the space available for components and equipment within or near the sample holder 323. For ease of illustration, the beam aperture has been omitted from FIG. 3.

[0052] The left side of Figure 3 shows a cross-sectional view of a thermal battery according to the disclosed technology. Primary thermal reservoir 333 is surrounded by secondary thermal reservoir 343 within vacuum chamber 376. Column 331 supports reservoir 333 within reservoir 343, column 341 supports reservoir 343 within vacuum chamber 376, and column 371 represents mechanical support for vacuum chamber 376 from the table, frame, or footing of the analytical instrument. Above reservoirs 333 and 343, secondary cryocooler 364 provides cooling to secondary reservoir 343 and primary cryocooler 354 through thermally conductive cap 363. Thermal switch 362 can be in an on (closed) state when secondary reservoir 343 is filling and can be switched to an off (open) state when cryocooler 364 is switched off during instrument stand time, reducing heat loss as portions of the thermal battery warm up at different rates. Primary cryocooler 354 provides cooling to primary reservoir 333 through thermal switch 352. Similar to switch 362, switch 352 can be in an on or closed state when primary reservoir 333 is filling, and can be switched to an off or open state when cryocooler 354 is switched off during stand time of the device, reducing heat loss as portions of the thermal battery warm up at different rates.

[0053] Turning to the coupling of reservoirs 333, 343 to components within sample chamber 320, longitudinal member 336 (sometimes referred to as the inner cold finger) can extract heat from sample holder 323 to primary reservoir 333, while longitudinal member 346 (sometimes referred to as the outer cold finger) can extract heat from shield 329 to secondary reservoir 343. Members 336, 346 can have a cylindrical shape about a common axis 335 and can be separated from each other and from main vacuum chambers 376, 372 by joints 378. In an example, joint 378 can have a serpentine or corrugated cross-section to reduce heat leakage. In the illustrated example, members 336, 346 can be rigid and can be flexibly coupled to sample holder 326 and shield 329, respectively, by links 337, 347. The shield 329 can act as a heat shield to reduce radiative heat transfer to the sample 326 and can also provide protection against stray contaminants (from warmer regions of the vacuum chamber 372) reaching the sample 326. Similarly, the longitudinal member 346 can act as a heat shield surrounding the longitudinal member 336. The vacuum within the chambers 376, 372 can provide thermal insulation and reduce heat leakage to the reservoirs 343, 333 and the shield 329, the sample holder 333, or the sample 326.

[0054] Also shown in FIG. 3 are thermal resistor 381, heater 383, and thermal mass 385.

[0055] During the stand time, without compensation or regulation, the reservoir 333 may become warmer as it extracts thermal energy from the sample 326, causing the flow of thermal energy to the reservoir 333 to decrease, causing the sample 326 to also become warmer. Therefore, compensation or regulation may be included to maintain the temperature of the sample 326 or sample holder 323 constant over the stand time despite the primary reservoir 333 gradually warming. In various examples, the heater 383 may be adjusted to maintain a constant temperature of the sample 326 or sample holder 323 as the reservoir 333 becomes warmer. To illustrate in terms of energy flow, if the unregulated heat flow from the sample holder 323 to the reservoir 333 decreases from 3 W to 1 W over the stand time, the temperature regulated heater 383 may provide approximately 2 W to the reservoir 333 at the beginning of the stand time and decrease to approximately 0 W at the end of the stand time. In this way, heat extraction from the sample holder 323 can be maintained constant at approximately 1 W over the stand time, consistent with a constant equilibrium temperature of the sample 326 or sample holder 323.

[0056] Additionally, a thermal resistor 381 can be inserted into the member 336 to partially decouple the reservoir 333 from the heater 383. The thermal resistor 381 can be selected to optimize the stand time for given operating conditions and a given thermal capacity of the reservoir 333. If the resistance of the resistor 381 is too small, the heater 383 may generate more heat, which can significantly shorten the stand time. If the resistance of the resistor 381 is too large, a larger temperature difference between the sample holder 323 and the reservoir 333 may be required to extract the desired thermal energy flow from the sample holder 323. Therefore, the temperature range of the thermal reservoir 333 that can maintain the temperature of the sample holder 323 may be reduced, which also leads to a shortened stand time. In these cases, an optimal resistance value for the thermal resistor 381 can be selected to maximize the stand time.

[0057] Finally, Figure 3 shows a thermal mass 385 coupled to the heat flow path from sample holder 323 to reservoir 333. Thermal mass 385 can reduce temperature and position fluctuations in sample holder 323, as described further herein. However, mass 385 is an optional feature. Depending on the design requirements and exact operating parameters, in some instances, the thermal mass of member 336 can provide sufficient damping without auxiliary mass 385. In other instances, damping of temperature or position fluctuations may not be necessary.

[0058] Various implementations of the flexible thermally conductive links 337, 347 can be used. In some examples, a copper wire braid can be used to provide high thermal conductivity with low vibration transmission, while in other examples, an untwisted bundle of copper filaments can be used to provide low stiffness (high flexibility). For example, link 347 can be implemented as a copper braid, and link 337 can be implemented as a filament bundle. In one example, a filament bundle having 2000 copper filaments, each 25 μm in diameter, can be used.

[0059] Exemplary Operating Parameters Specifically, a complete thermal battery is described with reference to Figure 3 above and Figure 5 below. The described system is for illustrative purposes only, and many variations can be made, such as omitting listed components, including additional components, modifying values, etc. All values ​​are approximate.

[0060] 1.Design requirements In this example, the design requirements are to maintain the sample temperature at a setpoint of 20 K with a stability of ±0.1 K and a stand time of 12 hours. Additional requirements are that the thermal cell contribute to misalignment not exceeding 0.2 nm / min, vibration not exceeding 1 pm rms over the frequency band 0.5-5000 Hz, and a fill time not exceeding 6 hours. By extension, the temperature setpoint can be selected at any value in the range 20-80 K.

[0061] 2. Thermal reservoir The battery may incorporate an inner reservoir 333 incorporating 100 kg of erbium, which is charged (cooled) to 6 K and discharged (warmed) to 15 K over stand times. An outer reservoir 343 may surround the inner reservoir and incorporate 100 kg of copper. The outer reservoir 343 may provide a heat shield for the inner reservoir 333 and its associated cold finger 336, and may also cool the heat shield 329 within the sample chamber through its own cold finger 346.

[0062] 3.Primary cooling Primary cooling can be provided by a cryocooler 364, such as a model PT420 (CryoMech Inc., Syracuse, NY), operating between room temperature (hot side) and 50 K (secondary reservoir, cold side). A second cryocooler 354 can provide cooling from 65 K (hot side, secondary reservoir) to 6 K (cold side, primary reservoir). The cryocoolers 354, 364 can be shut off during stand time to eliminate sources of mechanical vibration. Each cryocooler 354, 364 can be decoupled from its cold-side load by a respective thermal switch 352, 362 to reduce heat leakage and extend stand time. Commercially available gas switches (Chase Research Cryogenics Ltd., Neepsend, Sheffield, UK) or a dedicated hybrid switch design can be used.

[0063] 4. Overall dimensions Excluding the cold finger, the battery mass is 330 kg, height is 1.1 m, and diameter is 0.35 m.

[0064] 5. Cooling performance For a typical system design, recharge can be completed in 5 hours, starting with the inner and outer reservoirs at 15K and 65K, respectively. An initial charge of the entire battery from an initial state of 295K can be completed in 24 hours. Various designs offer recharge times of 3-6 hours, 2-10 hours, or 1-24 hours.

[0065] 6. Cold Finger Each reservoir 333, 343 can be coupled to a respective component within the sample chamber by a cold finger 336, 346. The cold finger 346 for the outer reservoir 343 can be a copper tube with a rigid attachment to the heat shield 329 (sometimes referred to as a cryobox) within the sample chamber 320. The cold finger 336, 536 for the inner reservoir 333 can be an assembly including a solid copper rod extending into the sample chamber and (optionally) further inside the heat shield 329, 521, and a bridge 586 within the heat shield volume extending from one side of the sample holder 323, 523 to the other. Each end of the bridge can be flexibly coupled to the sample holder by a copper braid or wire bundle 337, 537. The cold fingers 333, 343 can be coaxial.

[0066] 7.Temperature control The temperature sensor 582 and heaters 383, 583 can be mounted on a bridge 586 and driven by a servo loop (Figure 10). The servo control can be used to regulate the sample temperature.

[0067] 8.Temperature fluctuation damping For instant designs, the inner cold finger can provide sufficient thermal mass to damp temperature and displacement fluctuations and meet corresponding requirements. In other designs, a 10-100 g erbium mass 385 (Figure 9) can be incorporated into the bridge 586.

[0068] Specific Heat Capacity of Example Materials 4 is a chart 400 illustrating the specific heat capacity of an exemplary material at cryogenic temperatures. p is plotted on the vertical axis and temperature is plotted on the horizontal axis. The chart covers the range from 100 K to near absolute zero. Chart 400 shows solid lines 411-416 for lead, copper, stainless steel, erbium, neodymium, and tin, respectively. Dashed line 417 is shown for erbium-nickel alloy.

[0069] In the first embodiment, the amount of energy that can be absorbed as the reservoir warms up is multiplied by an amount ΔT, the specific heat capacity c p For this reason, certain examples of the disclosed technology use materials such as erbium, lead, or neodymium for the primary thermal reservoir, all of which have significantly higher C in the region of interest between 5 and 20 K than more common materials such as copper, lead, or even tin. p Erbium may be chosen in certain instances due to a combination of considerations including ease of handling, regulatory issues, and availability. By comparison, a secondary reservoir designed to warm to 50-65 K during stand time may be in a different regime, where copper or stainless steel c relative to erbium is preferred. p The shortage (approximately 30%) can be offset based on handling or availability considerations.

[0070] In a second embodiment, the chart 400 shows a change in c as the temperature approaches zero. p This illustrates that the temperature change ΔT for a given amount of thermal energy ΔQ in an object of volume V is ΔT = ΔQ / (c p ·V), this temperature change ΔT is given by temperature and c p can increase significantly as approaches zero. The implication of this phenomenon is that small variations in heat flow can manifest as large variations in temperature and accompanying variations in position due to thermal expansion or contraction. This can make precise temperature regulation difficult, as will be discussed further herein.

[0071] In a third aspect, chart 400 illustrates the non-monotonic behavior for certain materials, particularly erbium-nickel alloys and erbium, but to a lesser extent neodymium. This behavior is associated with the phase transitions of the respective materials. p The peak in the graph of can be applied to achieve increased thermal energy storage based on the energy of a phase transition (known in some contexts as latent heat).

[0072] Second Exemplary Apparatus FIG. 5 illustrates a cross-sectional view 500 of an exemplary sample chamber coupled to a thermal reservoir according to the disclosed technology. A cryobox 521 resides within the sample chamber (not shown). In some examples, the sample chamber can form a vacuum enclosure. A sample holder 523 can hold a sample (not shown) at the origin 505 (the center of the cryobox 521 on the beam axis), and the sample can be imaged or analyzed by a beam traveling in a direction perpendicular to the drawing page. The sample holder 523 can be coupled to a stage 524 by thermal insulation 525. An autoloader 550 can deliver samples to the stage 524 and receive samples from the stage 524 after the analysis procedure is complete. The stage 524 can provide translational or rotational adjustment of the sample during analysis. A longitudinal member (cold finger) 536 can extract thermal energy from the sample holder 523 to a reservoir (not shown). In this example, cold finger 536 includes bridge 586, and two flexible braids 537 provide thermal coupling between sample holder 523 and member 536. Braids 537 can be sized to allow a full range of movement for sample holder 523 as it moves between its imaging position (as shown) and the autoloader.

[0073] Also shown in FIG. 5 is a heater 583 and a temperature sensor 582 that can be used for temperature regulation, as described herein. In this example, the heater 583 is mounted on the bridge 586 so that it is positioned symmetrically relative to the blade 537, but this is not required, and other locations for the heater 583 can be used. In some examples, the heater 582 can be mounted on the main support of the cold finger 536. A thermal resistor 581 can provide partial isolation between the heater 582 and the thermal reservoir. Similarly, the temperature sensor 582 can be variously mounted on the sample holder 523 (either close to the sample or far from the sample) or on the translation stage. In some examples, a bridge-mounted sensor can be used with calibration applied to compensate for steady-state or dynamic temperature differences between the bridge 586 and the sample held in the sample holder 523.

[0074] In some instances, it may be desirable to maintain the sample holder at a high voltage relative to the vacuum vessel and member 536. In such instances, a high voltage insulator 539 may be incorporated into the thermal path between the sample holder 523 and the cold finger 536, as shown.

[0075] Exemplary Methods FIG. 6 is a flowchart 600 of a first exemplary method of operating a thermal battery to control the temperature of a sample or sample holder in a sample chamber. At process block 610, a thermal reservoir can be filled. For example, the thermal reservoir can be filled using a cryocooler. The thermal reservoir can be located outside the sample chamber in which the sample is held. At process block 620, filling can be stopped when a setpoint is reached. In some examples, the setpoint can be a target temperature for the thermal reservoir, and in other examples, the setpoint can be a target temperature within the sample chamber. In a further example, the setpoint can be a predetermined time period for the filling operation.

[0076] At process block 630, the thermal reservoir can be thermally coupled to the sample through the longitudinal member. In some examples, this action can be performed by the sample holder receiving the sample from an autoloader (e.g., similar to 550) after the reservoir has been filled. In other examples, this action can be performed before block 610 if the sample has already been loaded into the sample chamber. In other examples, a thermal switch can be provided between the thermal reservoir and the sample holder. The thermal switch can be opened during filling or thermal cycling of the thermal reservoir and closed at process block 630 before performing an analytical procedure on the sample.

[0077] Thermal energy can then be extracted from the sample through the longitudinal members to the thermal reservoir during stand time. Because the filling is stopped, the sample can be maintained at a low temperature operating point without mechanical vibration by passively extracting thermal energy to the thermal reservoir. In block 640, the flow of thermal energy can be adjusted to regulate the sample temperature.

[0078] Numerous variations and extensions of the disclosed method can be implemented. In some examples, temperature regulation can be maintained for a predetermined stand time. At the expiration of the stand time, the method can return to block 610 for another cycle of recharging the thermal reservoir, stopping the charging, and passively extracting thermal energy for another stand time. This cycle can be repeated any number of times.

[0079] In an additional example, the regulating can be performed by driving a heater in response to a signal indicative of the temperature in the sample chamber. In a further example, the regulating can be performed, at least in part, by an in-line temperature regulator. The in-line temperature regulator can be a variable thermal resistor in the thermal flow path between the sample holder and the thermal reservoir. In some examples, the variable thermal resistor can be actively controlled. In some embodiments, duty cycle control (e.g., pulse width modulation (PWM)) between binary states having two different thermal resistance values ​​can be used, while other embodiments can use continuous analog control. For example, some materials have thermal conductivities that depend on an applied magnetic field.

[0080] In another example, the variable thermal resistor can be a passive device whose thermal resistance decreases as the thermal reservoir warms during stand time to present a net thermal resistance that decreases proportionally to the temperature difference between the sample holder and the thermal reservoir, so that heat flow is substantially constant, within a predetermined tolerance, over the temperature swing of the thermal reservoir.

[0081] Third Exemplary Apparatus 7 is a diagram 700 of a first apparatus coupled to a sample holder within a sample chamber in accordance with the disclosed technology. The apparatus includes a thermal reservoir 730 positioned outside the sample chamber 720 and a longitudinal member 734 extending from the reservoir 730 into the sample chamber 720. The member 734 can be flexibly coupled to the sample holder 723 within the chamber 720. In some examples, the flexible coupling can be provided by a flexible member 737 that is different from the member 734. The flexible member 737 can be a twisted or braided copper wire. A sample 726 can be held within the sample holder 723.

[0082] Numerous variations and extensions can be implemented within the scope of the disclosed technology. The thermal reservoir 730 can be configured to passively extract thermal energy from the sample holder 723 to regulate the temperature of the sample holder 723 within a predetermined operating range, at least for a predetermined stand time. The thermal reservoir 730 can include a primary thermal reservoir coupled to the sample holder 723 by member 734, as well as a secondary thermal reservoir also located outside the sample chamber 720. The apparatus can also include a second longitudinal member thermally coupling the second reservoir to a heat shield within the sample chamber 720. Thus, the second reservoir can be configured to passively extract thermal energy from the heat shield. The second longitudinal member can be annularly disposed around the first longitudinal member 734. The second reservoir can be annularly disposed around the primary reservoir. The primary reservoir can include erbium, an erbium alloy, another rare earth metal or alloy, or tin. In other examples, fluids or other solid materials can be used. The secondary reservoir can include tin, copper, stainless steel, lead, or a rare earth metal or alloy. The apparatus can further include a cryocooler in thermal contact with the secondary thermal reservoir and coupled to the primary reservoir through a thermal switch. The apparatus can be configured to passively extract thermal energy from the sample holder to the primary reservoir with the thermal switch open and the cryocooler turned off. The disclosed technology can be implemented as a system including the above-described apparatus in conjunction with a TEM. The sample chamber 720 and sample holder 723 can be part of a TEM.

[0083] The apparatus can also include a heater and a temperature sensor, each thermally coupled to the sample holder 723, and a controller configured to receive a signal from the temperature sensor and drive the heater. The heater can be configured to actively provide thermal energy to the sample holder 723 to regulate the temperature of the sample holder 723. The thermal energy can flow from the sample holder 723 to the thermal reservoir 730 along a first path defined by the longitudinal member 734. The apparatus can also include a separate thermal resistor positioned on the first path between the heater and the reservoir 730. The thermal resistor can have a thermal conductivity higher than the average thermal conductivity of the member 734. In a further example, the apparatus can include a variable thermal resistor on the first path. The variable thermal resistor can be configured to control the flow of thermal energy along the first path to assist in regulating the temperature of the sample holder. In some examples, the variable thermal resistor can be a passive temperature regulator, and in other examples, the variable thermal resistor can be actively controlled. The apparatus can include a controller configured to control the variable thermal resistor based on, for example, a signal indicative of the temperature within the sample chamber. In a further example, the apparatus can include a separate thermal mass disposed within the sample chamber and thermally coupled to the longitudinal member 734 or the sample holder 723.

[0084] Various modes of series regulation can be implemented. A switch-mode regulator can switch the series resistor between a high and a low thermal resistance state to maintain (i) a constant average thermal energy flow and (ii) a constant sample temperature. Alternatively, an analog regulator can vary the continuously variable resistance via an analog feedback loop or a PID servo controller to maintain a substantially constant thermal energy flow and a constant sample temperature. Furthermore, a passive regulator can have a temperature-dependent thermal resistance that matches the operating temperature, the thermal impedance of a given embodiment, and the precise location of the variable thermal resistor within the heat flow path so that as the thermal reservoir warms, the thermal resistance decreases so that the thermal energy flow can be maintained substantially constant for all values ​​of reservoir temperature within its temperature swing. Finally, regulators can be combined. For example, if a passive regulator cannot maintain the required sample temperature stability, a passive regulator can be combined with an active regulator. The presence of a passive regulator can significantly reduce the heating power required by the active regulator. Less excess heat is introduced into the system, allowing for longer stand times or the use of smaller, lighter thermal reservoirs.

[0085] The instrument can be configured to provide stand times ranging from 2 to 30 hours with temperature set points of 10 to 50 K. Sample temperatures can be maintained within an operating range having a span of 10 mK to 3 K.

[0086] Exemplary displacements under cryogenic conditions 8 is a chart 800 illustrating specimen holder displacement in an exemplary configuration in which the disclosed technology can be deployed. A specimen holder in the form of a gripper (similar to 523 in FIG. 5) can experience displacement fluctuations due to its thermal expansion coefficient in the presence of temperature fluctuations. As described herein in the context of FIG. 4, thermal fluctuations can become unacceptably large at very low temperatures due to a decrease in specific heat capacity.

[0087] In chart 800, the quantity plotted on the vertical axis is the change in gripper tip displacement over a 10-second interval. Time is plotted along the horizontal axis. Line 810 was measured at 77 K and shows a displacement well below ±20 pm. Shaded area 820 was measured at a gripper temperature of 17 K and shows a displacement excursion typically exceeding ±150 pm for the same apparatus as line 810. The design goal 850 of ±85 pm of maximum 10-second displacement change is easily met at 77 K, but may not be met at 17 K for the measured configuration.

[0088] Example Displacement with Damping Figure 9 is a set of charts 901-903 illustrating the displacement of a specimen holder with various thermal masses coupled to it. In these charts, the specimen holder was a gripper tip similar to 523 in Figure 5, with an operating temperature of 17 K, and the thermal mass was erbium. The thermal mass was attached to a bridge in a location similar to heater 583 in Figure 5, with a thermal resistance between the thermal mass and the bridge of 50 K / W. As in Figure 8, the change in gripper tip displacement over 10-second intervals is plotted on the vertical axis, and time is plotted along the horizontal axis. Other values ​​of thermal resistance can be used, such as approximately 10 K / W, or in the range of 2 K / W to 200 K / W, or typically 5 K / W to 100 K / W, or 10 K / W to 50 K / W.

[0089] Three series of simulations were performed with different thermal masses (similar to 385 in Figure 3) and 1-second moving average filters. Trace 910 shows measurements without erbium loading. Thus, the difference between traces 910 and 920 is due to the moving average filter, and this difference is only about 15%. Trace 920 shows a simulation with a 10g erbium thermal mass, and trace 930 is a simulation with a 100g erbium thermal mass. The 10g erbium loading appears effective, reducing displacement by more than 50% compared to trace 910, although displacement can exceed the target specification of 950. The 100g erbium loading reduces displacement by about 90%, and the resulting displacement remains less than ±20pm, well below the design target of ±85pm of 950.

[0090] First Exemplary Temperature Regulation Circuit FIG. 10 is a schematic diagram 1000 illustrating temperature regulation according to an example of the disclosed technology. For an assembly incorporating a reservoir, cold finger, and sample holder similar to those described in the context of FIG. 3 or 5, the heat transfer and thermal behavior are represented by a thermal model. The components of the thermal model are shown in FIG. 10 using similar electrical components. In particular, the thermal mass can be represented by an electrical capacitor (with one terminal connected to electrical ground), and the thermal resistance can be represented by an electrical resistance.

[0091] Thermal resistor 1081 represents a partially insulated thermal resistor similar to 381 in FIG. 3. Capacitors 1033, 1086 represent respective portions of the longitudinal member on the reservoir side and sample side of thermal resistor 1081. In particular, thermal mass 1086 may include a bridge similar to 586 in FIG. 5. Capacitor 1030 represents the thermal mass of the primary thermal reservoir similar to 333 in FIG. 3. Capacitor 1023 represents the thermal mass of the sample holder and optionally a typical sample, coupled to mass 1086 by thermal resistor 1037, which represents two braids similar to 537 in FIG. 5. In this configuration, heater 1083 and temperature sensor 1082 may be mounted between thermal resistor 1081 and braid 1037 on a longitudinal heat transfer member (similar to 336 in FIG. 3), which in some examples includes a bridge (similar to the configuration shown in FIG. 5). The dashed lines around components 1082, 1083, 1086 indicate the collocation or close thermal coupling between these three components.

[0092] Reference signal 1051 provides the temperature setpoint and is summed with a temperature signal from sensor 1082 at node 1053 and signed as shown. The error signal is input to PID controller 1055, the output of which drives heater 1083. Components 1082, 1053, 1055, 1083 form a programmable control loop based on analysis and design requirements of the thermal circuit shown in FIG. 10, as is well known in the art.

[0093] Second Exemplary Temperature Regulation Circuit FIG. 11 is a schematic diagram 1100 illustrating temperature regulation according to a further example of the disclosed technology. FIG. 11 uses the same electrical representation of the thermal model as FIG. 10. Components 1123, 1130, 1133, 1137, 1181, and 1186 are similar to their correspondingly numbered counterparts in FIG. 10 and will not be described further. However, the configuration of FIG. 11 includes an additional thermal mass, represented by capacitor 1185, similar to 385 in FIG. 3. In this configuration, temperature sensor 1182 and heater 1183 are mounted on or near thermal mass 1185, as indicated by the dashed outline around these three components. Additionally, component 1187 represents the thermal resistance between damping mass 1185 and bridge 1186. The servo loop formed by components 1182, 1151, 1153, 1155, and 1183 is similar to the servo loop of FIG. 10 and will not be described further. (However, the specific PID configuration of controller 1155 may differ from that of controller 1055 because each thermal circuit is different.)

[0094] First Exemplary Thermal Switch 12 is a diagram of a first exemplary thermal switch 1200. The switch 1200 can be configured to thermally couple or isolate the cold head 1261 from the hot head 1263. In some examples, the switch 1200 can implement switch 352 of FIG. 3, where the primary reservoir 333 is the cold head 1261 and the cryocooler 354 is the hot head 1263. In other examples, the switch 1200 can implement switch 362 of FIG. 3, where the secondary reservoir 343 is the cold head 1261 and the cap 363 is the hot head 1263.

[0095] The cold and hot heads 1261, 1263 can be mechanically attached by a sleeve 1265, which can be formed from a low thermal conductivity material, such as stainless steel. Operation of the switch 1200 can be achieved by introducing or removing gas into the interstitial space 1273 between the cold head 1261 and the hot head 1263. In some examples, a heater-activated getter 1267 can operate the switch 1200. When the getter 1267 cools, gas can be expelled from the interstitial space 1273 and gas piping 1271, and the switch 1200 assumes an off (open) state with high thermal resistance between the cold head 1261 and the hot head 1263. Conversely, when the getter 1267 warms, gas is released through the piping 1271 into the interstitial space 1273, and the switch 1200 transitions to an on (closed) state with low thermal resistance between the cold head 1261 and the hot head 1263.

[0096] Second Exemplary Thermal Switch FIG. 13 is a simplified diagram of a second exemplary thermal switch 1300 in accordance with the disclosed technology. Similar to the switch 1200 of FIG. 12, the switch 1300 can be configured to thermally couple or isolate the cold head 1361 from the hot head 1363. A duct 1371 connects the interstitial space 1373 to a gas reservoir 1367. Operation of the switch 1300 can be performed by a combination of mechanical action to make or break mechanical contact at the contact surface 1381 and gas operation to introduce or remove gas from the interstitial space 1373. The gas operation can be similar to the operation of the getter 1267 and will not be described further. The mechanical action can be translation to bring the cold heads 1361, 1363 into contact, and pressure is applied to the surface 1381 to establish a thermal conduction path between the cold head 1361 and the hot head 1363, turning the switch on. Reverse action can separate the cold heads 1361, 1363, leaving any solid conduction path between the cold head 1361 and the hot head 1363 in a state of high thermal resistance.

[0097] The gas and mechanical actions can be performed simultaneously or sequentially. When switch 1300 is in the on state, there can be mechanical contact at surface 1381 and gas conduction across interstitial space 1373. When switch 1300 is in the off state, there can be mechanical separation at surface 1381 and interstitial space 1373 can be evacuated.

[0098] The combination of mechanical and gas action in the hybrid switch 1300 offers advantages over purely mechanical or purely gas switches. Purely gas switches may require a very large surface area of ​​interstitial space to provide high thermal conductivity. In contrast, hybrid switches provide a large share of their on-state conductance through mechanical contact, significantly reducing the area required for gas switch components. Purely mechanical switches can experience unstable thermal conductivity due to tribological issues in a vacuum. The presence of a gas medium in the hybrid switch mitigates these issues. The hybrid switch 1300 can meet a field lifespan of more than 10 years and allows for field replacement of components. Therefore, the hybrid switch 1300 can be used in a thermal battery configuration for a TEM with a 12-hour stand time.

[0099] Example Problems and Solutions In some instances, the problem of providing vibration-free cooling to a sample in a small or crowded environment can be solved by providing a solid thermal reservoir outside the sample chamber, which can be coupled to the sample holder by a cold finger that penetrates into the sample chamber. A machine such as a cryocooler can be turned off after the thermal reservoir is filled.

[0100] In some instances, the problem of thermal coupling to a movable sample holder can be solved by flexibly coupling the cold finger to the sample holder. Copper braid, multi-strand stranded wire, or one or more layers of metal foil can be used as flexible couplings.

[0101] In some instances, the problem of regulating the temperature of the sample as the thermal reservoir warms can be solved by incorporating a temperature regulator to compensate for the decrease in heat flow into the thermal reservoir as it warms.

[0102] In some examples, the temperature regulator may be a heater that is controlled to maintain a substantially constant temperature of the sample even as the reservoir warms up. The power of the heater may be controlled based on a signal indicative of the sample temperature or another temperature within the sample chamber.

[0103] In some examples, the temperature regulator may be a variable thermal resistor in or in series with the cold finger. The variable thermal resistor may be a passive device whose thermal resistance varies with temperature. Alternatively, the variable thermal resistor may be a device whose thermal resistance can be controlled by an externally applied signal, such as an electrical or magnetic signal.

[0104] In some instances, the problem of thermal fluctuations or thermally induced positional variations can be solved by introducing a thermal mass close to and thermally coupled to the sample holder. A 10-100 g block of erbium can be used.

[0105] In various examples, any one or more of the above problems can be solved by a suitable combination of the above solutions. In other examples, the above problems can be combined with other problems not listed, or the above solutions can be modified or combined with other solutions not listed.

[0106] Generalized Computer Environment 14 illustrates a generalized example of a suitable computing system 1400 in which the described examples, techniques, and technologies for operating a thermal battery can be implemented. The computing system 1400 is not intended to suggest limitations on the scope of use or functionality of the present disclosure, as the innovations may be implemented in a variety of general-purpose or special-purpose computing systems. The computing system 1400 can control or monitor a thermal battery, including cryocoolers, thermal switches, servo-controlled temperature regulators, or their interfaces with analytical instruments or sample processing systems.

[0107] Referring to FIG. 14, a computing environment 1410 includes one or more processing units 1422 and memory 1424. In FIG. 14, this basic configuration 1420 is included within the dashed line. The processing unit 1422 can execute computer-executable instructions for control or data acquisition, etc., as described herein. The processing unit 1422 may be a general-purpose central processing unit (CPU), a processor in an application-specific integrated circuit (ASIC), or any other type of processor. In a multiprocessing system, multiple processing units execute computer-executable instructions to increase processing power. The computing environment 1410 may also include a graphics processing unit or inter-processing unit 1430. The tangible memory 1424 may be volatile memory (e.g., registers, cache, or RAM), non-volatile memory (e.g., ROM, EEPROM, or flash memory), or some combination thereof, accessible by the processing units 1422, 1430. Memory 1424 stores software 1480, in the form of computer-executable instructions suitable for execution by processing units 1422, 1430, that implements one or more innovations described herein. For example, software 1480 can include software 1481 for controlling a thermal cell, software 1482 for servo control, software 1483 for a console interface, software 1484 for monitoring the status of a thermal cell, a sample, or a temperature regulator, software 1485 for interfacing with a coupled analytical instrument (e.g., a TEM), or other software 1486 (including control of a sample stage or loading mechanism). The inset shown for software 1480 in storage 1440 is equally applicable to software 1480 elsewhere in FIG. 14 . Memory 1424 can also store control parameters, calibration data, measurement data, or database data. Memory 1424 can also store configuration and operational data.

[0108] Computing system 1410 may have additional functionality, such as one or more storage devices 1440, input devices 1450, output devices 1460, or communication ports 1470. An interconnection mechanism (not shown), such as a bus, controller, or network, interconnects the components of computing environment 1410. Typically, operating system software (not shown) provides an operating environment for other software executing in computing environment 1410 and coordinates the operation of the components of computing environment 1410.

[0109] Tangible storage 1440 may be removable or non-removable and includes magnetic disks, magnetic tapes or cassettes, CD-ROMs, DVDs, or any other medium that can be used to store information in a non-transitory manner and that can be accessed within computing environment 1410. Storage 1440 stores instructions (including instructions and / or data) for software 1480 that implements one or more innovations described herein. Storage 1440 may also store control parameters, measurement data, reference data, calibration data, configuration data, sample data, or other databases or data structures.

[0110] The input devices 1450 may be mechanical, touch-sensitive, or proximity-sensitive input devices such as a keyboard, mouse, pen, touchscreen, or trackball, a voice input device, a scanning device, or another device that provides input to the computing environment 1410. The output devices 1460 may be a display, printer, speakers, an optical disk writer, or another device that provides output from the computing environment 1410. The input or output may also be communicated to remote devices by a network connection via the communications port 1470.

[0111] The communications port 1470 enables communication over a communications medium to another computing entity. The communications medium conveys information such as computer-executable instructions, audio or video input or output, or other data in a modulated data signal. A modulated data signal is a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, the communications medium may use an electrical, optical, RF, acoustic, or other carrier.

[0112] A data acquisition system can be integrated into the computing environment 1410 as an input device 1450 or coupled to a communication port 1470 and can include an analog-to-digital converter or a connection to an instrumentation bus. An instrumentation control system can be integrated into the computing environment 1410 as an output device 1460 or coupled to a communication port 1470 and can include a digital-to-analog converter, a switch, or a connection to an instrumentation bus.

[0113] In some examples, the computer system 1400 may also include a computing cloud 1490 upon which instructions implementing all or a portion of the disclosed techniques are executed. Any combination of the memory 1424, the storage 1440, and the computing cloud 1490 may be used to store software instructions and data for the disclosed techniques.

[0114] The innovations may be described in the general context of computer-executable instructions, such as those contained in program modules, being executed in a computing system on a target real or virtual processor. Generally, program modules or components include routines, programs, libraries, objects, classes, components, data structures, etc. that perform particular tasks or implement particular data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. The computer-executable instructions of the program modules may be executed in local or distributed computing systems.

[0115] The terms "computing system," "computing environment," and "computing device" are used interchangeably herein. Unless the context clearly dictates, none of the terms imply any limitation on the type of computing system, computing environment, or computing device. In general, a computing system, computing environment, or computing device may be local or distributed, and may include any combination of dedicated hardware and / or general-purpose hardware and / or virtualized hardware, along with software that implements the functionality described herein.

[0116] General Considerations As used in this application and in the claims, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. Additionally, the term "include" means "comprise." Furthermore, the term "coupled" does not exclude the presence of intermediate elements between the coupled items. Furthermore, as used herein, the terms "or" and "and / or" refer to any one item or combination of items within that phrase.

[0117] The systems, methods, and apparatus 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 each other. The disclosed systems, methods, and apparatus 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. Furthermore, techniques from any example can be combined with techniques described in any one or more of the other examples. While any theory of operation is provided for ease of explanation, the disclosed systems, methods, and apparatus are not limited to such theory of operation.

[0118] 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. Furthermore, 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, the description may use terms such as "filling," "producing," "providing," or "regulating" to describe the disclosed methods. 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 specific implementation and will be readily discernible to those skilled in the art.

[0119] In some instances, values, procedures, or devices are referred to as "minimum," "best," "maximum," "optimum," "extreme," etc. It will be understood that such descriptions are intended to indicate that a selection from a few options or many options is possible, and that such selections are not necessarily smaller, better, less favorable, or otherwise preferable to other options not considered. Positional terms such as "top," "bottom," "left," and "right" are used solely for convenience of description.

[0120] Any theories of operation, scientific principles, or other theoretical explanations presented herein with respect to the devices or methods of the present disclosure are provided for purposes of better understanding and are not intended to limit the scope, and the devices and methods in the appended claims are not limited to devices and methods that function in a manner described by such theories of operation.

[0121] Any of the disclosed methods can be controlled or implemented by computer-executable instructions or computer program products stored on one or more computer-readable storage media, such as tangible, non-transitory computer-readable storage media, and executed on a computing device (e.g., any available computing device, including a tablet, smartphone, or other mobile device that includes computing hardware). A tangible computer-readable storage medium is any available tangible medium that can be accessed within a computing environment (e.g., one or more optical media disks, such as a DVD or CD, a volatile memory component (such as DRAM or SRAM), or a non-volatile memory component (such as flash memory or a hard drive)). By way of example, with reference to FIG. 14 , a computer-readable storage medium includes memory 1424 and storage 1440. 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 (e.g., 1470).

[0122] Any of the computer-executable instructions for implementing the disclosed technology, as well as any data created and used during the practice of the disclosed embodiments, can be stored on one or more computer-readable storage media. The computer-executable instructions can be, for example, a dedicated software application, or part of a software application accessed or downloaded via a web browser or other software application (such as a remote computing application). Such software can be executed, for example, on a single local computer (e.g., any suitable commercially available computer) or in a networked environment using one or more networked computers (e.g., via the Internet, a wide area network, a local area network, a client-server network, a cloud computing network, or other such network).

[0123] For clarity, only selected aspects of software-based implementations are described. Other details well known in the art are omitted. For example, it should be understood that the disclosed technology is not limited to any particular computer language or program. For example, the disclosed technology can be implemented in software written in Adobe Flash, C, C++, C#, Curl, Dart, Fortran, Java, JavaScript, Julia, Lisp, Matlab, Octave, Perl, Python, Qt, R, Ruby, SAS, SPSS, SQL, WebAssembly, any derivatives thereof, or any other suitable programming language, or in some examples, a markup language such as HTML or XML, or any combination of suitable languages, libraries, and packages. Similarly, the disclosed technology is not limited to a particular computer or hardware type. Specific details of suitable computers and hardware are well known and need not be described in detail in this disclosure.

[0124] Additionally, any of the software-based embodiments (e.g., including computer-executable instructions for causing a computer to perform any of the disclosed methods) may be uploaded, downloaded, sideloaded, or remotely accessed through suitable communications means, including, for example, the Internet, the World Wide Web, an intranet, a software application, cable (including fiber optic cable), magnetic communications, electromagnetic communications (including RF, microwave, infrared, and optical communications), electronic communications, or other such communications means.

[0125] 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 preferred examples of the disclosed subject matter and should not be construed as limiting the scope of the claims. Rather, the scope of the claimed subject matter is defined by the following claims. We therefore claim all that comes within the scope and spirit of those claims.

Claims

1. 1. An apparatus comprising: a solid block of metal adapted to be placed outside the sample chamber and forming a cryogenic primary thermal reservoir; a secondary thermal reservoir surrounding the primary thermal reservoir and having a first opening; a first support column supporting the primary thermal reservoir within the secondary thermal reservoir; a thermally conductive cap disposed over the first opening; a series arrangement of a primary cryocooler and a first thermal switch coupling the cap to the primary thermal reservoir through the first opening; a second thermal switch coupling the cap to the secondary thermal reservoir; a vacuum chamber surrounding the secondary thermal reservoir and having a second opening; a secondary cryocooler having a hot side at room temperature and a cold side coupled to the cap and adapted to cool the cap through the second opening; a second support column supporting the secondary thermal reservoir within the vacuum chamber; a longitudinal member extending from the primary thermal reservoir to the sample chamber and flexibly couplable to a sample holder within the sample chamber; a sleeve extending from the secondary thermal reservoir to the sample chamber and flexibly connectable to a heat shield surrounding the sample holder, the longitudinal member and the sleeve being coaxial; a coupling that couples the sleeve to the vacuum chamber and the longitudinal member; a thermal resistor and heater disposed within the longitudinal member; An apparatus comprising:

2. 10. The apparatus of claim 1, wherein the primary thermal reservoir is configured to passively extract thermal energy from the sample holder to maintain the temperature of the sample holder within a predetermined operating temperature range for at least a predetermined period of time.

3. moreover, a temperature sensor thermally coupled to the sample holder; a controller coupled to receive a signal from the temperature sensor and to activate the heater; Equipped with The apparatus of claim 2 , wherein the heater is configured to actively supply thermal energy to the sample holder to regulate a temperature of the sample holder.

4. the thermal energy flows along the longitudinal member from the sample holder to the primary thermal reservoir; The apparatus of claim 2 , wherein the thermal resistor comprises a variable thermal resistor configured to control the flow of thermal energy along the longitudinal member.

5. The apparatus of claim 4 , further comprising a controller coupled to the thermal resistor and configured to control the thermal resistor.

6. The apparatus of claim 2 , further comprising a separate thermal mass disposed within the sample chamber and thermally coupled to the longitudinal member and / or the sample holder.

7. The apparatus of claim 4 , wherein the thermal resistor is a passive temperature regulator.

8. 3. The apparatus of claim 2, wherein the predetermined time period ranges from 2 to 30 hours, and the predetermined operating temperature range has a sample temperature setpoint between 10 K and 50 K and a tolerance between 10 mK and 3 K.

9. 10. The apparatus of claim 1, wherein the apparatus is configured to passively extract thermal energy from the sample holder to the primary thermal reservoir with the first thermal switch in an open state.

10. The apparatus of claim 1 , wherein the secondary thermal reservoir comprises copper or a copper alloy.

11. The apparatus of claim 1 , wherein the primary thermal reservoir comprises erbium or an erbium alloy.

12. 1. A system comprising: A transmission electron microscope, electron source, Condenser lens, a sample chamber; Objective lens, and imaging device, a transmission electron microscope having a sample holder disposed within the sample chamber; A regulated thermal battery, comprising: a solid block of metal positioned outside the sample chamber and configured to form a cryogenic primary thermal reservoir; a secondary thermal reservoir surrounding the primary thermal reservoir and having a first opening; a first support column supporting the primary thermal reservoir within the secondary thermal reservoir; a thermally conductive cap disposed over the first opening; a series arrangement of a primary cryocooler and a first thermal switch coupling the cap to the primary thermal reservoir through the first opening; a second thermal switch coupling the cap to the secondary thermal reservoir; a vacuum chamber surrounding the secondary thermal reservoir and having a second opening; a secondary cryocooler having a hot side at room temperature and a cold side coupled to the cap and configured to cool the cap through the second opening; a second support column supporting the secondary thermal reservoir within the vacuum chamber; a longitudinal member extending from the primary thermal reservoir to the sample chamber and flexibly couplable to the sample holder; a sleeve extending from the secondary thermal reservoir to the sample chamber and flexibly connectable to a heat shield surrounding the sample holder, the longitudinal member and the sleeve being coaxial; a coupling that couples the sleeve to the vacuum chamber and the longitudinal member; and a thermal resistor and a heater disposed within the longitudinal member; a regulated thermal battery having A system having:

13. the system is configured to maintain a stable cryogenic temperature of the sample in the sample holder for six consecutive hours; The stable cryogenic temperature state is a temperature change of less than 200 mK with the temperature set point in the range between 20 K and 80 K; a displacement of the sample of 1 nm / min or less; and Vibrations of less than 1 pm rms over the 1 to 2000 Hz band, The system of claim 12 , comprising:

14. the secondary cryocooler is configured to charge the secondary thermal reservoir with the second thermal switch closed; The system of claim 12 , wherein the primary cryocooler is configured to charge the primary thermal reservoir with the first thermal switch closed.

15. 1. A method of cryogenic conditioning comprising: controlling the flow of thermal energy through a longitudinal member coupled between a cryogenic primary thermal reservoir and a sample chamber, the longitudinal member incorporating a thermal resistor and a heater, the longitudinal member being flexibly coupleable to a sample holder in the sample chamber, the primary thermal reservoir comprising a solid block of metal positioned outside the sample chamber and supported by a first post inside a secondary thermal reservoir having a first opening; extracting thermal energy from a heat shield surrounding the sample holder to the secondary thermal reservoir via a sleeve coaxial with the longitudinal member, the sleeve being flexibly coupleable to the heat shield; extracting thermal energy from the primary thermal reservoir through the first opening to a cap disposed over the first opening via a series arrangement of a first cryocooler and a first thermal switch; extracting thermal energy from the cap and the secondary thermal reservoir through a second opening in a vacuum chamber surrounding the secondary thermal reservoir with a second cryocooler having a hot side at room temperature and a cold side coupled to the cap, the cap further being coupled to the secondary thermal reservoir through a second thermal switch; and the secondary thermal reservoir is supported by a second support within the vacuum chamber; The method wherein the sleeve is coupled to the vacuum chamber and the longitudinal member by a joint.

16. controlling the flow of thermal energy is performed by the first and second thermal switches being in an open state; 16. The method of claim 15, wherein extracting thermal energy from the primary thermal reservoir, the cap, and the secondary thermal reservoir is performed by the first and second thermal switches in a closed state.

17. 16. The method of claim 15, further comprising activating the heater in response to a signal indicative of a temperature within the sample chamber.

18. the thermal resistor is a variable thermal resistor; 16. The method of claim 15, further comprising activating the variable thermal resistor in response to a signal indicative of a temperature within the sample chamber.

19. the first cryocooler has a compressor and an expander; The method may further include, after the primary thermal reservoir reaches a target setpoint: shutting down the first cryocooler to reduce mechanical vibrations; changing the state of the first thermal switch from a closed state to an open state; 16. The method of claim 15, comprising:

20. 16. The method of claim 15, further comprising at least partially recharging the primary thermal reservoir after performing the step of controlling the flow of thermal energy for a predetermined period of time.

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