JP6975415B2 - Sample cooling device - Google Patents

Description

The present invention relates to a sample cooling device, and relates to a cooling device capable of cooling to an extremely low temperature under an ultra-high vacuum.

Low temperature experiments on solid surfaces are carried out for various purposes, and cryogens are appropriately selected according to the purposes. Then, the minimum temperature reached on the sample surface is determined according to the type of the cryogen and the structure / mechanism for holding the sample (hereinafter referred to as "sample holding mechanism"). One of the purposes of low temperature experiments is to freeze-condensate gaseous molecules at room temperature and solidify them. By solidifying gas molecules in this way, experiments on various basic physical properties become possible. Since most gas molecules freeze and condense at an extremely low temperature of 20K, 20K can be regarded as one of the indicators of the minimum temperature reached in the low temperature generation technology.

Liquid helium is used as the cryogen to obtain the minimum temperature reached below 20 K. The boiling point of helium-4 is 4.2K at normal pressure, and if a helium flow path is provided near the sample, a low temperature close to 4K can be obtained. Non-Patent Document 1 describes an ultra-high vacuum sample cooling transfer mechanism capable of cooling up to 12.5 K using liquid helium. Non-Patent Document 2 describes a low temperature cooling technique of 1 K or less by ^{a 3 He refrigerator system.} Patent Document 3 describes an ultra-high vacuum sample cooling transfer mechanism using liquid helium that can be cooled to 150 K. Non-Patent Document 6 describes an ultra-high vacuum sample cooling mechanism capable of cooling to 1 mK or less by Joule-Thomson expansion using liquid helium. Patent Document 1 describes a biaxial moving mechanism capable of cooling up to 25 K using liquid helium. Patent Document 2 describes a moving mechanism capable of cooling up to 20 K using liquid helium, and a radiation shield. In addition, some ultra-high vacuum (UHV) cooling sample manipulators using liquid helium as a cryogen are already on the market. However, liquid helium is expensive, and as a result, the running cost of the experiment is high.

Another method of obtaining cryogenic temperatures is a closed-cycle helium refrigerator. As a liquid helium-free refrigerator, Non-Patent Document 3 describes a liquid helium-free ultra-high vacuum sample cooling transfer mechanism capable of cooling to about 50 K. Non-Patent Document 4 describes a cryogen-free ultra-high vacuum sample cooling mechanism using a pulse tube refrigerator, but the mechanism is such that the beam cannot enter or exit. Non-Patent Document 5 describes an ultra-high vacuum sample cooling transfer mechanism capable of cooling up to 40 K using a Gift-McMahon (hereinafter referred to as GM) refrigerator. The GM refrigerator is a typical liquid helium-free refrigerator that is relatively inexpensive, and is a device that uses helium gas as a working fluid and lowers the temperature by a refrigeration cycle that uses adiabatic expansion (simon expansion) of gas. .. With a GM refrigerator, a low temperature of about 4K can be easily obtained. As described above, since the minimum temperature reached by the closed-cycle helium refrigerator is 4K or less, the sample can be cooled by thermally contacting the minimum temperature portion (cold end) with the sample. By using this method, it is not necessary to use liquid helium as a refrigerant, so that the above-mentioned cost problem is greatly improved. However, in this method, the operation of the sample holding mechanism is limited. That is, in the conventional sample holding mechanism using a closed cycle helium refrigerator, in order to cool the sample to an extremely low temperature, it is necessary to improve the thermal contact between the cold end and the sample, and for this reason, the sample is used. It is virtually impossible to rotate in the in-plane direction. Therefore, for example, it is difficult to exert various actions on freeze-condensed substances (for example, gas molecules) at extremely low temperatures at different angles, and it cannot be said that they are easy to use for structural analysis of the sample surface, for example.

In Non-Patent Document 7, a refrigerator with a refrigerator that can be easily attached and detached, a sample insulation mechanism with excellent heat conduction at low temperatures, a filament for electronic shock heating, and an open / close type having a slit for injecting and emitting a beam. The results of experiments using a manipulator constructed from a heat shield, a sample holder that can be taken in and out of a UHV, a Si diode temperature sensor, and the like are described. Further, in Patent Document 4, it is possible to cool the sample to less than 7.2K in an ultra-high vacuum, irradiate the surface of the sample with various beams from outside the device, and measure the reflected beam and the emitted beam from the surface outside the device. The surface observation sample cooling device is disclosed in order to provide a surface observation sample cooling device and a surface observation device capable of exchanging samples without breaking the vacuum. In Patent Document 5, an internal heat conductive wire cable that can be twisted and bent, and an external heat conductive wire that can be twisted and bent via a heat insulating element on the outside of the heat control film with a heat control thin film coated on the outer surface thereof. Disclosed is a heat conductive member in which cables are laminated and the outer surface thereof is coated with a heat control thin film to reduce the influence of radiation.

Here, charged particles such as an ion beam are often used for structural analysis of the sample surface. Specifically, for example, an ion beam is incident on the sample and the scattered ion intensity is measured as a function of the rotation angle in the in-plane direction of the sample to determine the atomic position on the surface. As described above, in the structural analysis of the surface, it is important to rotate the sample in the in-plane direction.

Adding a mechanism for rotating the sample in the in-plane direction to the sample holding mechanism leads to an increase in heat inflow to the sample. This is because heat inflow from the atmosphere side to the sample is unavoidable in order to introduce the movement required for in-plane rotation from the atmosphere. In fact, no sample holding mechanism using a closed-cycle helium refrigerator has been realized so far, in which the minimum temperature reached is 20 K or less and the sample can be rotated in the in-plane direction. Therefore, it is difficult to apply a sample cooling device using a closed-cycle helium refrigerator to structural analysis.

Japanese Unexamined Patent Publication No. 2004-10989 Japanese Unexamined Patent Publication No. 2004-103274 U.S. Pat. No. 4,516,435 Japanese Unexamined Patent Publication No. 2015-05592 Japanese Unexamined Patent Publication No. 2004-245790

Aiura et al. , Rev. Sci. Instrument. 74 (2003) 3177 Yoshihiro Koike, Taiyo Nippon Sanso Technical Report, 24 (2005) 60 Franzen, Kollias, El-Batanony, Rev. Sci. Instrument. 63 (1992) 4227 Pellicione et al. , Rev. Sci. Instrument. 84 (2013) 033703 J. Phys. E: Sci. Instrument. 17 (1984) 22 Zhang et al. , Rev. Sci. Instrument. 82 (2011) 103702 Taku Suzuki, Shunichi Hishida, Physical Society of Japan Summary 2013 Autumn Meeting 26p PSA-28

An object of the present invention is to provide a sample cooling device using a relatively inexpensive liquid helium-free refrigerator, in which the minimum temperature reached is sufficiently low and the sample can be rotated in the in-plane direction.

In the sample cooling device according to the embodiment of the present invention using the liquid helium-free closed cycle helium refrigerator, it was attached to the cold end of the closed cycle helium refrigerator so as to minimize the heat inflow from the outside to the sample. Provide a sample holding mechanism. This makes it possible to rotate the sample in the in-plane direction with high accuracy while the minimum temperature reached is sufficiently low without using liquid helium. The sample holding mechanism is rotatably attached to a heat shielding body made of a heat shielding wall, a heat transfer member surrounded by the heat shielding body, a sample holding portion that can be attached to and detached from the heat transfer member, and a sample holding portion. Can include sample stages, and so on. The sample stage can rotate while holding the sample.

As a closed-cycle helium refrigerator, for example, in a device that combines a GM refrigerator and a sample transfer mechanism, the heat shielding design of the sample transfer mechanism and the cooling performance of the GM refrigerator are sufficiently improved to move the sample in the in-plane direction. Make it rotatable.

For example, as a cold end at the tip of the refrigerator head of a closed-cycle helium refrigerator, a refrigerator alone that can obtain a minimum temperature of about 4K can be used. This low temperature can be transmitted to the sample holder via the intermediate rod. In addition, the intrusion of radiant heat into the sample stage holding the intermediate rod and sample holder should be minimized by the radius tube (for example, made of gold-plated oxygen-free copper) and the radius shield cover (for example, made of gold-plated oxygen-free copper). Can be done.

More specifically, the following can be provided.
(1) The closed cycle refrigerator, the heat transfer means attached to the cold end of the closed cycle refrigerator, the shield means for blocking external radiation to the heat transfer means, and the heat transfer means thermally. In a sample cooling device comprising a sample holding means for contacting and rotatably holding a sample in a specific plane, and a vacuum chamber capable of holding the heat transfer means, shielding means, and sample holding means in a vacuum. ,
The sample holding means includes a rotating member that can rotate in the specific plane, a receiving means that rotatably receives the rotating member, and at least the vacuum chamber, a shielding means, or a transmission means that holds the sample held by the rotating member. It engages with a highly thermally conductive electrically insulating member that can be electrically insulated from the thermal means and electrically insulatingly engages with the rotating member to transmit rotational motion in the specific plane. Includes a passive rotating means that is rotated by receiving a rotational driving force from the outside of the sample holding means.
The sample cooling device is further flexible, thermally connected to the heat transfer means and in close contact with the electrically insulating member, allowing heat transfer from the electrically insulating member to the heat transfer means. A sample cooling device including a heat transfer joint and an external driving means for engaging and driving the passive rotating means.
(2) The sample cooling device according to (1) above, wherein the closed cycle refrigerator includes a GM refrigerator.
(3) The sample cooling device according to (1) or (2) above, wherein the heat transfer means includes a heat transfer rod.
(4) The sample cooling device according to any one of (1) to (3) above, wherein the shielding means includes a radiation tube.
(5) The sample cooling device according to any one of (1) to (4) above, wherein the rotating member includes a sample stage.
(6) The sample cooling device according to any one of (1) to (5) above, wherein the receiving means includes a bearing.
(7) The sample cooling device according to any one of (1) to (6) above, wherein the high thermal conductive electrical insulating member includes a sapphire plate.
(8) The passive rotating means is coupled to a shaft common to the rotating member via an electrically insulating material, and engages with an engaging convex portion or a concave portion of the external driving means. The sample cooling device according to any one of (1) to (7) above, which is a transmission member capable of transmitting a driving force.
(9) The sample cooling device according to any one of (1) to (8) above, wherein the flexible heat transfer joint includes a copper braided wire.
(10) The sample cooling device according to any one of (1) to (9) above, wherein the external drive means includes a drive shaft.
(11) The sample cooling device according to any one of (1) to (10) above, wherein the vacuum chamber is provided with a heater for baking as needed.
(12) The sample cooling according to any one of (1) to (11) above, further comprising an apparatus moving mechanism and capable of moving the sample holding means to an appropriate position in the vacuum chamber. Device (13) The sample holding means is provided at the tip of the heat transfer means, and the shield means includes a radiation tube for covering the heat transfer means and a radiation shield cover for covering the sample holding means. The sample cooling device according to any one of (1) to (12) above.
(14) The sample cooling device according to (13) above, wherein the radiation shield cover includes a shutter having an opening for exposing at least a part of the sample.
(15) The shutter is rotatably attached to the radiation shield cover by a hinge, and the opening / closing drive shaft extends a driving force from the outside of the vacuum chamber along the outside of the radiation tube. The sample cooling device according to (14) above, wherein the shutter is rotated by the hinge so as to open and close.
(16) The GM refrigerator includes a cylindrical first stage extending from the head portion and a cylindrical second stage extending from the end portion of the first stage, and the first stage has a larger diameter than the second stage. The shield means is attached to the end of the first stage outside the second stage, the heat transfer means extending from the tip of the second stage is rod-shaped, and the shield means has the heat transfer means. The sample cooling device according to (2) above, wherein the heat transfer means is covered in order to shield the radiation from the outside.
(17) The external drive means includes a drive shaft, which extends along the outside of the shield means and passes through at least one bearing fixed to the outside of the shield means. The sample cooling device according to any one of (1) to (12).
(18) The sample cooling device according to (17) above, wherein the drive shaft is connected by at least one universal joint.
(19) The sample cooling device according to (18) above, wherein the drive shaft is driven by a drive device outside the vacuum chamber.
(20) The sample cooling device according to any one of (1) to (19) above, further comprising a vacuum pump.

Here, the refrigerator generally refers to a device that takes heat from an object, cools it below the ambient temperature (freezing), and dissipates the heat to the atmosphere. There are steam compression chillers, absorption chillers, air insulation chillers, Joule-Thomson effect chillers, and Sterling cycle chillers depending on the cooling ultimate temperature and cooling method. The Stirling refrigerator is a refrigerator that uses a Stirling cycle. If a machine having the same structure as a Stirling engine is driven by an energy source other than the engine body such as an electric motor, the engine has a temperature difference, so the low temperature side can be used as a cooler. This is a Stirling refrigerator (or Stirling cooler). A working fluid is required inside the refrigerator for the refrigerator, but helium is often used as the working fluid for obtaining extremely low temperature. Also, the closed cycle may mean a cycle in which the working fluid circulates inside the system to perform conversion between thermal energy and work. On the other hand, there is an open cycle. The closed cycle refrigerator may mean a device that generates a low temperature by using the cycle as described above, and the closed cycle helium refrigerator uses helium as a working fluid and the working fluid is a refrigerator. It can mean a device that circulates inside and cools (freezes) by performing heat energy and conversion between work. In addition to the structure of the Stirling refrigerator, the Gifford McMahon refrigerator has a rotary valve linked to the displacer, and by using this valve to switch the pipeline in a circular manner, the cooling performance is improved. (Giford-McMahon cooler, abbreviated as GM refrigerator). Further, the cold end described above can mean a low temperature side end of a Stirling refrigerator (for example, a closed cycle helium refrigerator, a GM refrigerator, etc.).

The heat transfer means described above can mean a means for transferring heat, and may include a medium for transferring heat (including a solid and / or a fluid containing a liquid or a gas, a structure or a composite such as a heat pipe). Can mean. For example, a heat transfer member may be included. The heat transfer member may include a heat transfer rod. For these, solids having high conductivity at extremely low temperatures can be used. This heat transfer means can transfer low temperature farther (that is, absorb (or take away) heat from a distance) from the attached cold end, and the transfer direction can be the longitudinal direction. The closer to the cold end, the easier it is to lower the temperature, but in order to exert various actions on the sample, it is preferable that the temperature is separated by an amount that can avoid interference with the cold end. On the other hand, if it is too far away, the minimum temperature reached tends to be high. Such heat transfer means may include two or more parallel passages (or conductors). The heat transfer means preferably one that can easily transfer heat in the longitudinal direction. For example, a metal intermediate rod or the like can have one end face attached to the cold end of a closed cycle helium refrigerator so that the heat at the other end can be transferred to the cold end side. Here, the term "metal" may include, for example, the case where an intermediate rod is formed by using copper, a copper alloy, oxygen-free copper, or the like as a material. Here, it is preferable that the heat transfer means is attached to the cold end by a method having high heat transfer. When the end faces of the cold end and the end faces of the heat transfer means are butt-joined, the heat transfer property increases as the true contact area of both end faces increases, so that the flatness of both end faces is high and the surface roughness is small. Further, by sandwiching and pressing a thin plate made of oxygen-free copper or the like having high plastic deformation between both end faces, the plastically deformed copper or the like enters the gap between both end faces and comes into contact with each other, thereby improving the heat transfer coefficient. You can also do it. Since the cold end side becomes extremely cold, it is higher than the ambient temperature (for example, room temperature, first stage, etc.), and the heat transfer means has a longitudinal side surface facing the ambient environment and has a high thermal conductivity. It has a side temperature that is approximately equal to the temperature at its center. Radiant energy seen from the surrounding environment with visible light or the like, that is, radiant energy due to light or heat, is easily incident on the heat transfer means from the environmental object. Therefore, it is preferable to prevent it from being seen by environmental objects by means of shielding. The shielding means may include a heat shield wall or a heat shield that can be cooler than the surrounding environment. It may also include a radiation tube. It may include a low temperature radiation tube consisting of a heat shield wall and / or a heat shield. When the heat transfer means is covered with such a shield means, the incident heat energy becomes small, which is preferable. Such a radiation tube is made of a metal, which is a material that is sufficiently cooled by contact with the first stage and whose low temperature is easily transmitted in the longitudinal direction, particularly copper, aluminum, iron, and stainless steel. Is preferable. Since the energy entering from the environment is mainly provided by ultraviolet rays, visible light, and infrared rays and far infrared rays, such materials are highly opaque and can efficiently shield them.

The sample holding means described above may include a sample holding portion. The sample holder can hold the sample and allow the sample to rotate in a particular plane. The sample holding portion can keep the temperature of the sample sufficiently low, and can make the sample electrically float from the housing or the like. The sample holding portion may include a rotating member, a receiving means, a high thermal conductive electrical insulating member, and a passive rotating means. The rotating member may include a sample stage, which may include a sample (sample) holder for holding the sample. The particular surface may include the surface of the sample. The rotating member may come into contact with the cold member so that the sample can be cooled. The receiving means receives a rotating member so that the sample can rotate in the predetermined plane. The receiving means can include bearings and can include roller bearings and / or ball bearings. For example, solid-lubricated bearings are preferred because they are used in vacuum. The bearing can allow the rotating member to easily rotate with respect to the fixing member such as the housing. It is preferable that the sample is electrically insulated from a fixing member such as a housing. For example, the receiving means such as a bearing may be made of an insulating material. Further, a high thermal conductive electrical insulating member can be used on the rotating member side of the receiving means. Examples of the material having high thermal conductivity and electrical insulation include ceramics, and in particular, diamond, cubic boron nitride, aluminum oxide, aluminum nitride and the like can be used. For example, the high thermal conductive electrical insulating member may include a ceramic member, a diamond member, a cubic boron nitride member, an aluminum oxide member, an aluminum nitride member, and the like. It has a shape in which high thermal conductivity and electrical insulation function, and can include a thin film shape, a plate shape, a rod shape, a cylindrical shape, and the like. Aluminum oxide is preferably used because of the ease of forming the bulk member. In particular, single crystal aluminum oxide (eg, sapphire) can be used. For example, a sapphire plate can be included. It is not preferable to dispose a driving device for rotating the rotating member in the vicinity of the sample holding means because an unnecessary inflow of heat and maintenance of a clean vacuum state may be difficult. Therefore, the rotating member is rotated by the passive rotating means that receives the rotational driving force transmitted from the driving means outside the sample holding means (for example, the outside of the vacuum chamber). The passive rotating means may rotate in substantially the same direction as the rotation of the rotating member. When the rotational driving force is transmitted by a wire or the like extending along the longitudinal direction of the heat transfer means, it is considered that the rotational axis is often substantially perpendicular to the rotational axis of rotation in the predetermined plane. Therefore, it is preferable to provide a mechanism for changing the direction of the rotational driving force by, for example, about 90 degrees. Such a mechanism may include a transmission member capable of transmitting the driving force by having an engaging convex portion or an engaging concave portion corresponding to the driving side and the passive side, respectively. Such transmission members include spur gears, bevel gears, crown gears, worm gears (eg, a combination mechanism of screw gears (worms) and spiral gears (worm wheels)), belts or timing belts and pulleys, or sprockets. A roller chain or the like may be included. The structure, shape, material, etc. are appropriately changed, modified, and prepared according to the sample to be measured. Since the sample cooling device according to the embodiment of the present invention often uses a plate-shaped sample, the structure, shape, and material of the sample holder should be selected according to the plate-shaped sample. In particular, if the surface is irradiated with an electron beam, radiation, or other light to analyze the spectrum of the reflected radiation or light, a sample holder that makes it easy to expose the surface to the surface is considered preferable. ..

The highly thermally conductive electrical insulating member is an electrically insulating member having high thermal conductivity, and for example, insulating ceramics and the like are preferably used as the material thereof. For example, a sapphire plate can be included. The flexible heat transfer joint described above may mean a joint capable of transferring heat between at least two members, and may mean a conduit or conductor of heat. This heat transfer joint is flexible and can be flexibly deformed. For example, at least two members connected by the heat transfer joint may be deformable so flexibly that they can easily move relative to each other. Specifically, when tension acts between two members (for example, an electrically insulating member and a heat transfer means), it may be possible to change from a bent state to a taut state. Alternatively, the heat transfer joint can be bent or twisted due to relative movement such as rotation of at least one of the two members in a bent state. Such a heat transfer joint may include a bundle (including a twisted one) of thin wires made of a material having high thermal conductivity. The thin wire is preferably one that can be easily deformed such as bent. For example, a thin wire made of oxygen-free copper can be included. For example, copper braided wire may be included. The external drive means can include a rigid wire, a wire, or the like capable of transmitting a torsional force, and may include, for example, a drive shaft including a final shaft. It may also include an engaging mechanism such as a gear including a bevel gear attached to the tip of a drive shaft or the like. And, in the case of a rigid shaft, the direction of the drive shaft can be changed by using a particularly flexible coupling (for example, a universal joint). Further, such an external drive means may be subjected to a torsional force by a motor or the like arranged inside or outside the vacuum chamber. The motor may include a servo motor or a stepping motor, and may further include an encoder. When the motor is located outside the vacuum chamber, a joint capable of transmitting a force such as a torsional force from the outside to the inside of the vacuum chamber can be provided. For example, a ferrofluidic seal can directly penetrate the drive shaft inside and outside the vacuum chamber while maintaining a vacuum. In order to achieve a clean ultra-high vacuum, it is also possible to use a joint such as a magnet coupling that does not have a shaft that penetrates inside and outside.

Further, since charged particles or the like from the filament provided on the back side of the sample may hit the front surface (or the back surface), the potential of the sample and / or the sample holder is made higher (or lower) than that of the vacuum chamber or the like. Is preferred. Therefore, it is preferable that the sample and / or the sample holder is electrically insulated from the vacuum chamber or the like. On the other hand, since the sample and / or the sample holder is rotatably provided in the plane, it is preferable that the sample and / or the sample holder is electrically insulated from the rotation mechanism or, together with the rotation mechanism, from the vacuum chamber or the like. On the other hand, in order to realize a low temperature, it is preferable to adhere to a heat absorbing member (for example, a heat transfer means including an intermediate rod or the like). In order to obtain such properties, ceramics that are heat conductive materials but are electrically insulating, particularly aluminum oxide (for example, polycrystalline aluminum oxide or single crystal aluminum oxide such as sapphire) can be interposed. .. Further, since the series of operations is performed in a high vacuum, it is preferable that no organic component is mixed. Therefore, it is difficult to use oil, grease, or the like for the sliding portion between the rotating member and the non-rotating member that supports the rotating member. Therefore, it is preferable to use a material whose surface is coated with a solid lubricant such as molybdenum disulfide (for example, stainless steel to which molybdenum disulfide is adhered by sputtering). The vacuum chamber may be equipped with a heater for baking in order to achieve a high vacuum.

The device movement mechanism described above may include an XY stage and a Z stage capable of moving in the Z-axis direction perpendicular to them (xyz stage). In order to facilitate the movement by such a moving mechanism, a bellows can be further provided.

In order to have the above configuration, the sample cooling device according to the embodiment of the present invention cools the sample to, for example, 30K or less, 20K or less, or 15K or less without using liquid helium, and yet the sample is cooled. It has become possible to rotate in the in-plane direction with high accuracy. Such rotations include, for example, clockwise, ± 10 degrees or more, ± 30 degrees or more, ± 50 degrees or more, ± 70 degrees or more, or ± 90 degrees or more. Examples thereof include 10 degrees or more, 30 degrees or more, 50 degrees or more, 70 degrees or more, 90 degrees or more in any of 0 to + or-. .. In addition to this, the device can meet various specifications often required when applied to experimental studies of solid surfaces.

It is a schematic schematic diagram of the sample cooling apparatus which is an Example of this invention. It is a cut-out perspective view which shows the sample cooling apparatus which is an Example of this invention. It is a perspective view from the front around the sample stage which constitutes the sample holding mechanism of the sample cooling apparatus which is an Example of this invention. It is a perspective view from the back around the sample stage which constitutes the sample holding mechanism of the sample cooling apparatus which is an Example of this invention. It is an exploded perspective view which shows the detail of a sample holder and its surroundings. It is a perspective view which shows the sample holder and the sample transfer used for the transfer. It is a perspective view which shows the sample holder and another sample transfer used for the transfer thereof. It is a schematic perspective view which shows the outline of the boat member which attached the sample holding mechanism such as a sample stage. It is a schematic front view which shows the outline of the boat member which attached the sample holding mechanism such as a sample stage. It is a schematic AA sectional view which shows the outline of the boat member which attached the sample holding mechanism such as a sample stage. It is schematic cross-sectional view which shows the outline of the boat member which attached the sample holding mechanism such as the sample stage which concerns on another Example. It is a schematic cross-sectional view which shows the outline of the boat member which attached the sample holding mechanism such as the sample stage which concerns on still another Example. FIG. 11 is a schematic cross-sectional view showing an outline of a boat member equipped with a sample holding mechanism such as a sample stage according to an embodiment of FIG. 11, and a part of a copper braided wire which is a heat transfer joint is cut to show a cross section. It is a schematic diagram. It is the schematic sectional drawing of the copper braided wire corresponding to the heat transfer joint in one Example. It is a graph which shows the temperature change of the thermal conductivity of copper and sapphire at an extremely low temperature. It is a front view which shows the radical tube which contains the GM refrigerator head of a sample cooling apparatus, the intermediate rod connected to it, and the like. It is a side view which shows the radical tube which contains the GM refrigerator head of a sample cooling apparatus, the intermediate rod connected to it, and the like. It is a top view which shows the radical tube which contains the GM refrigerator head of a sample cooling apparatus, the intermediate rod connected to it, and the like. It is a perspective view which shows the radical tube which contains the GM refrigerator head of a sample cooling apparatus, the intermediate rod connected to it, and the like. It is an enlarged perspective view of a sample part. It is a perspective view which shows the radical tube which contains the intermediate rod and the like connected to the GM refrigerator head of a sample cooling apparatus. It is an image perspective view which shows the drive transmission path along the outer surface of the radiation tube which contains the intermediate rod which is connected to the GM refrigerator head of a sample cooling apparatus. FIG. 3 is a partial cross-sectional perspective view showing a radiation tube including a GM refrigerator head of a sample cooling device attached from above the device moving mechanism and an intermediate rod connected to the head of the sample cooling device in another embodiment. FIG. 3 is a partial cross-sectional side view showing a radiation tube including a GM refrigerator head of a sample cooling device attached from above the device moving mechanism and an intermediate rod connected to the head of the sample cooling device in another embodiment. It is a photograph from the front showing the open state of the radiation shield cover. It is a photograph from the front showing the closed state of the radiation shield cover. It is a graph which shows the relationship between the elapsed time from the start of cooling, and the temperature of an intermediate rod part and a sample stage. It is a graph which shows the relationship between the in-plane rotation angle of a sample, and the temperature of an intermediate rod part and a sample stage part. It is a graph which shows the relationship of the temperature in the tantalum sample and the intermediate rod part in the sample heating test using the sample cooling apparatus in the Example of this invention.

Hereinafter, examples of the present invention will be described with reference to the drawings, but the scope of the present invention is not limited.

[Example 1]
FIG. 1 is a schematic view showing an example of a cooling device according to an embodiment of the present invention. The sample cooling device 10 of the present invention includes a GM refrigerator head 12, a tube 14 for supplying helium gas to the head 12, a tube 16 for discharging helium gas from the head 12, and a helium gas compressor 18 for compressing helium gas. , A device moving mechanism 20 under the head 12 of the GM refrigerator, a flange 22 for operably connecting the moving mechanism in the tank of the device moving mechanism 20 from outside the tank, and a baking heater 24 as needed. A head 12 of a GM refrigerator equipped with a vacuum tank system including a removable vacuum tank 26 (the front side is transparent in FIG. 1), a vacuum pump 30 connected by a valve 28, and a first stage 32. Intermediate rod 36 connected to the lower end of the second stage (cold end) 34 at the tip of the A sample holding system comprising a sample holding system and a sample transfer mechanism 44 having a gate valve 42 whose height is adjusted to the sample portion 40 at the lower portion of the vacuum chamber 26 are included. The sample transfer mechanism 44 includes a sample transfer device 48 connected by a magnet coupling to an operation unit 46 that can be operated from the outside of the vacuum chamber exhausted by the vacuum pump 49. The GM refrigerator is a relatively inexpensive liquid helium-free refrigerator, and a commercially available one can be used. The device moving mechanism 20 has an XY stage 20a fixed to the flange 22 in a direction other than the height direction (horizontal direction or XY direction), and an intermediate flange fixing the frame of the XY stage in the height direction (Z direction). The Z-axis adjusting mechanism 20b and the bellows 20c that enable movement in the XY and Z directions are provided. As a result, the position of the sample unit 40 in the vacuum chamber 26 can be finely adjusted. As the vacuum pumps 30 and 49, for example, commercially available turbo molecular pumps can be used. The magnetic levitation type is preferable.

FIG. 2 shows a perspective view including a partially cut-out cross section of a sample cooling device (excluding a compressor connected to a GM refrigerator head) according to one embodiment of the present invention. The head 12 of the GM refrigerator schematically shown in FIG. 1 has a structure in which a cool storage device that cannot withstand a high temperature of 100 ° C. or higher can be easily attached and detached. By removing the head 12 of this GM refrigerator, baking at about 200 ° C. can be performed, and as a result, an ultra-high vacuum ( ^10-8 Pa or less) can be obtained. In the second stage (cold end) 34 at the tip of the GM refrigerator head 12, the minimum temperature reached of about 4K can be obtained by the refrigerator alone. This low temperature is finally transmitted to the sample holder 50 via the intermediate rod 36. Further, the intrusion of radiant heat into the intermediate rod 36 and the sample stage 52 is minimized by the gold-plated oxygen-free copper radiation tube 38 and the radiation shield cover (described later) connected to the first stage 32. A rotary introducer 100 including a stepping motor 107 is provided.

The sample holding mechanism arranged in the sample unit 40 is a device moving mechanism 20 composed of an xyz stage capable of moving in the xyz direction and a rotating stage capable of rotating operation via an intermediate rod 36 and a GM refrigerator head 12. It is connected so that the sample can be moved in any direction in the vacuum chamber 26 (see FIG. 1) without breaking the vacuum. This makes it possible to adjust the sample position required for structural analysis.

3 and 4 show a detailed frontal perspective view and a back perspective view of the sample stage 52 around the sample stage 52, which is installed at the tip of the intermediate rod 36 and constitutes the sample holding mechanism arranged in the sample portion 40. Each is shown. Further, FIG. 5 is an exploded perspective view showing details of the molybdenum sample holder 50 and its surroundings. 6A and 6B are perspective views showing the sample holder 50 and the sample transfer 62 (two types) used for transporting the sample holder 50. The thin plate-shaped sample 56 may be fixed by being sandwiched between the rear plate 58 of the sample holder 50 and the sample holder 50, or may be welded to the opening of the rear plate 58. At this time, the rear plate 58 and the sample holder 50 can be fastened by the split bolt 59. The sample holder 50 is fixed to the sample stage 52. At that time, the holder screw 60 (see FIG. 3) is used to bring the sample holder 50 and the sample stage 52 into close contact with each other. That is, by rotating the holder screw 60, a pressing force is applied between the sample holder 50 and the sample stage 52, and good heat conduction and / or heat transfer is obtained. The sample transfer 62 of FIG. 6A or 6B is used to rotate the holder screw 60. The sample transfer 62 includes a sample transfer jig 64, and is also used when the sample holder 50 is installed or removed from the sample stage 52. That is, the sample holder 50 has a structure that can be inserted and removed from the sample stage 52 in the longitudinal direction thereof, and can be combined with a magnet feedthrough or the like (for example, a mechanism by the sample transfer device 48 and the operation unit 46) to hold the sample holder. The sample can be exchanged in an ultra-high vacuum by grasping the protrusion 51 on the lower end side of the 50. When removing the sample holder 50 from the sample stage 52, the holder screw 60 described above is loosened by using the sample transfer 62. By doing so, the sample holder 50 can be easily removed. The sample stage 52 is installed so as to rotate in synchronization with the in-plane rotation gear 66, and by rotating the in-plane rotation gear 66, the sample rotates in the in-plane direction while keeping the sample at an extremely low temperature. Can be done. At this time, in order to avoid interference with the frame of the opening 122 (see FIG. 20), the cut lower surface 65 may be provided as shown in FIG. 6B.

The sample stage 52 and the intermediate rod 36 may be connected via an electrical and thermal connection in which the top surface 77 of the boat member 76 is in close contact with the lower end surface of the intermediate rod 36, where here is a sapphire plate. It is electrically isolated by interposing 86. Therefore, it is possible to apply a high voltage of about 1 kV to the high voltage application terminal 70 on the sample stage 52. Further, since the tungsten (W) filament 72 for thermionic emission is installed behind the sample holder 50, the tungsten filament wiring 74 to the W filament 72 is energized while applying a positive high voltage to the sample stage 52. By doing so, the sample can be heated to 1000 K or more. The sapphire plate 86 has good heat conduction at extremely low temperatures, but has a property that it is difficult to transfer heat at high temperatures. Therefore, in the vicinity of the minimum reached temperature, the sample temperature is substantially the same as the temperature of the second stage 34, but the temperature of the sample 56 can be selectively increased during heating. Cooling of the sample 56 via the intermediate rod 36 is performed by utilizing the heat conduction of the copper braided wire 80 whose one end is in close contact with the deck 78 of the boat member 76 having the top surface 77 which is in close contact with the intermediate rod 36. .. The other end of the copper braided wire 80 is in close contact with the sapphire plate 86. The copper braid 80 is flexible and long enough to allow the sample stage 52 to rotate in-plane 90 degrees clockwise and counterclockwise with the sapphire plate 86. In the basic state of FIG. 3, it is in a state of being bent in the space inside the radiation cover, which will be described later. The temperature of the sapphire plate 86 is measured by a temperature sensor 82 arranged at the same rotational position as the other end.

7, 8 and 9 are a schematic perspective view, a schematic front view, and a schematic AA showing an outline of a boat member 76 equipped with a sample holding mechanism such as a sample stage 52 arranged in the sample unit 40. It is a cross-sectional view. The sample stage 52 shown in these figures is in a state of being rotated 90 degrees counterclockwise from the basic state shown in FIG. 3, and the sample holder 50 is substantially pulled out from the sample stage 52. .. The sample stage 52 includes an upper cover 84 and a sapphire plate 86, and a holder screw 60 is attached to a lower lower base material 68 via an inclined portion 84a matching the inclined portions 50a on both sides of the inserted sample holder 50. , Pressed through an insulator for electrical insulation. A circular opening is provided in the center of the lower base material 68 and the sapphire plate 86, and a bearing 88 such as a roller bearing is provided on the outside (the edge of the lower base material 68 defining the opening) along the opening. Supports the pressing force. The end of the holder screw 60 on the lower base material 68 side is fixed to the boat member 76, but is fastened with a nut 90. The lower base material 68 rotates together with the hollow cylindrical shaft 92 by engaging with the convex portion of the end portion of the hollow cylindrical shaft 92 on the plate side. The hollow cylindrical shaft 92 is fixed to the inner peripheral surface of the in-plane rotation gear 66 and rotates in synchronization with the in-plane rotation gear 66. The in-plane rotation gear 66 engages with the bevel gear 96 at the tip of the final shaft 94, and the final shaft 94 is transmitted from the in-plane rotation rotation introducer 100 via the coupling 93 (see FIG. 3). When rotated by the rotation of, the in-plane rotation gear 66 finally rotates, and the sample stage 52 rotates in the in-plane.

FIG. 10 is a schematic cross-sectional view showing an outline of the boat member 76 in another embodiment. Similarly, the sample stage 52 is in a state of being rotated 90 degrees counterclockwise, and the sample holder 50 is in a state of being pulled out from the sample stage 52. The sample stage 52 includes an upper cover 84 and a sapphire plate 86, and is inserted in the lower side of the drawing via an inclined portion 84a matching the inclined portions 50a on both sides of the sample holder 50 to be inserted. It is pressed against the lower base material 68 of the above by the holder screw 60 via the insulator 61. A circular opening is provided in the center of the lower base material 68 and the sapphire plate 86 to define the inner diameter of the hollow cylindrical shaft 92. The hollow cylindrical shaft 92 is rotatably supported by a bearing 88, such as a ball bearing. The end of the holder screw 60 on the lower base material 68 side is fixed to the lower surface of the lower base material 68, but is fastened with a nut 90. The sapphire plate 86 rotates with the hollow cylindrical shaft 92. The hollow cylindrical shaft 92 is provided with an in-plane rotation gear 66 on the other end side. The in-plane rotation gear 66 engages with the bevel gear 96 at the tip of the final shaft 94, and the final shaft 94 passes through a plurality of universal joints 98 (see FIG. 18) to introduce an in-plane rotation rotation introducer. When rotated by rotation from 100, the in-plane rotation gear 66 finally rotates, and the sample stage 52 rotates in-plane.

FIG. 11 is a schematic cross-sectional view showing an outline of the boat member 76 in still another embodiment, in which the tungsten filament 72 and the like are omitted from FIG. Similarly, the sample stage 52 is in a state of being rotated 90 degrees counterclockwise, and a state in which the sample holder 50 is fixed to the sample stage 52. The sample stage 52 includes an upper cover 84 and a sapphire plate 86, and the inserted sample holder 50 is pressed against the sapphire plate 86 via the inclined portions 84a matching the inclined portions 50a on both sides thereof. The sapphire plate 86 is pressed against the lower lower base material 68 including the backup base material 85 that closely supports the sapphire plate 86 by the holder screw 60 via the insulator 61. When inserting or removing the sample holder 50 in a vacuum, the holder screw 60 is loosened and slightly thin on the upper end side of the sample holder 50 (the end opposite to the lower end where the protrusion 51 is located). Coupled with the tapered shape so as to be narrow in width, it is easy to insert the sample holder 50 (with or without the sample 56 attached to the opening). Then, when the degree of insertion becomes high, the upper cover 84 that can be moved upward in the drawing is pushed up due to the loosened holder screw 60. Next, by tightening the holder screw 60 using the sample transfer device 48, the pressing force against the sapphire plate 86 on the lower side of the sample holder 50 is increased and the adhesion is improved. As a result, the temperatures of the sample holder 50 and the sample 56 can be lowered more quickly to reach a lower temperature. FIG. 12 is a schematic cross-sectional view obtained by rotating the schematic vertical cross-sectional view of the boat member 76 of FIG. 11 by 90 degrees. The sapphire plate 86 is provided with a sample holder 50 and a copper braided wire terminal 81 separated from each other in a state of being pressed against the surface 81a by the holder screw 60 and the fastening screw 81b, respectively. Although sapphire is electrically insulating, it has high thermal conductivity, so that electricity does not flow between the sample holder 50 and the copper braided wire terminal 81, but heat flows sufficiently. On the other hand, since copper has good conductivity and good thermal conductivity, the copper braided wire 80 is connected from the copper braided wire terminal 81 to which the heat transferability between the fine wires is improved by crimping the copper braided wire or the like. It is expected that sufficient electricity and heat will flow through the intermediate rod 36 to which the boat portion 76 and its top surface 77 are in close contact. FIG. 13 shows a cross section 80a of the copper braided wire 80. Further, FIG. 14 shows a graph showing the temperature dependence of the thermal conductivity of copper and sapphire, especially in the extremely low temperature region. As can be seen from this figure, sapphire exhibits a very high thermal conductivity between 10K and 100K, and copper also exhibits a very high thermal conductivity in a similar range. Therefore, the temperature sensor 82 can indicate a sufficiently low temperature. In general, heat transfer between at least two members that perform relative movement such as rotation involves a bearing or the like in order to facilitate relative movement, so that the contact area is small and the heat transfer coefficient is small. Become. Therefore, it is preferable to connect the two with a heat conduction tube or a heat conductor to realize a heat conduction path of another route. However, with a highly rigid metal tube or metal rod, it is difficult for them to move relative to each other. Therefore, connect both with a flexible heat conduction tube or heat conductor to secure another route of heat conduction. Examples of such a flexible heat conductive tube or heat conductor include those obtained by twisting a fine metal wire such as copper, and one example thereof is the copper braided wire 80 described above. As shown in FIG. 13, each thin wire 80b has almost the same thickness and is twisted so as to be in contact with each other. And bending are performed freely. For example, the diameter of each thin wire is preferably about 1 mm or less. If more flexibility is desired, it is preferably about 0.5 mm or less. Further, if a flexible one is desired, it is preferably about 0.1 mm or less. If a more flexible one is desired, it is preferably about 0.04 mm or less. If it is too thin, it will be inconvenient to handle, so it is preferably about 0.0001 mm or more. It is preferably about 0.01 mm or more. It is preferably made of oxygen-free copper having high thermal conductivity. Therefore, if sufficient deflection is provided to ensure the maximum distance between the two due to relative movement, sufficient heat conduction can be ensured without hindering the movement of the sample stage 52.

15A, 15B, and 15C, and 16A and 16B include a GM refrigerator head 12 attached from above the device moving mechanism 20 and an intermediate rod and the like 36 connected to the GM refrigerator head 12, as shown in the schematic diagram of FIG. It is a front view, a side view, and a top view which show the radiation tube 38 and the like, and is also the perspective view seen from above and the partial perspective view which enlarged the vicinity of the sample part. 17 and 18 are a perspective view and an image perspective view showing a part of the drive transmission path along the outside of the radiation tube 38 including a part of the GM refrigerator head 12 and an intermediate rod connected to the part, and the like. .. 19A and 19B are a front view and a perspective view showing a partial contact section showing a radiation tube 38 and the like including a GM refrigerator head 12 and an intermediate rod 36 and the like connected to the GM refrigerator head 12. In one embodiment, a rotation introducer 100 for in-plane rotation, a rotation introducer 108 for a radiation shield cover, a current introduction terminal 110 for a temperature sensor and a low temperature control heater, and a sample high voltage application terminal 112 are provided. In the GM refrigerator head 12, the tube for supplying / discharging helium gas and the compressor are omitted. The device moving mechanism 20 arranged under the GM refrigerator head 12 includes an in-plane rotation introducer 100 including a stepping motor 107, a rotation shield cover rotation introducer 108, a temperature sensor, and a current introduction for a low temperature control heater. The terminal 110 and the sample high voltage application terminal 112 are provided. As described above, the rotation of the stepping motor 107 is transmitted to the final shaft 94 in the vacuum chamber 26 by the in-plane rotation introduction device 100, and the bevel gear 96, the in-plane rotation gear 66, and the sample stage 52 are rotated. Can be made to. The temperature sensor and the current introduction terminal 110 for the low temperature control heater are independently connected to the temperature sensor and the low temperature control heater 114 (see FIG. 3) arranged in the vacuum chamber 26 including the temperature sensor 82 described above. Further, the sample high voltage application terminal 112 is used to apply a positive high voltage to the sample stage 52 described above, and to pass a current through the tungsten filament wiring 74 in order to energize the tungsten filament 72. used. The radius tube 38 covering the intermediate rod 36 extends downward from the first stage 32, but the drive shaft 104 from the in-plane rotation introducer 100 crawls on the outside of the radius tube 38 and then from the middle. Get inside. Further, the drive shaft 116 from the rotation shield cover rotation introducer 108 including the stepping motor 107 extends along the outer surface of the radius tube 38. The radiation shield cover 118 is arranged at the position of the sample unit 40. The radiation shield cover 118 has a tube shape with a slightly enlarged diameter connected from the radiation tube 38 on the radiation tube 38 via the connection portion 120. The back side thereof has a semi-cylindrical semi-square prism shape having a long square cross section so as to include a sample holding mechanism contained therein. After the lower half of the radiation shield cover 118, the front portion is cut off so that the cylinder is vertically split in half on the front side, and the long square opening 122 is formed substantially vertically in the front view. A frame defining the edge of the opening 122 is formed, and the frame is provided with an upper frame 136 and a lower frame 138, which are vertically wide shutter receiving surfaces, so as to face each other substantially vertically. Inside the opening 122, the sample stage 52 shown in FIGS. 3 and 4 is exposed. FIG. 18 is an image perspective view showing a drive transmission path to the final shaft 94 via the drive shaft 104 and the coupling 93 in another embodiment. A drive shaft 104 rotatably fixed by a bearing 102 along the outside of the radiation tube 38 is shown. This rotation can be given manually, but it is preferable to give it by the stepping motor 107 because it is superior in quantitativeness.

19A and 19B are a partial cross-sectional perspective view and a partial cross-sectional view showing a radiation tube including a GM refrigerator head of a sample cooling device attached from above the device moving mechanism and an intermediate rod connected to the GM refrigerator head in another embodiment. It is a side view. As described above, it can be seen that the copper braided wire 80 is in a bent state in the space inside the radiation cover. As a result, even if the sample stage 52 rotates in-plane by 90 degrees clockwise and counterclockwise together with the sapphire plate 86, the copper braided wire 80 can handle it. Further, as shown in FIG. 18, the drive shaft 104 along the outside of the radius tube 38 enters the radius tube 38 via the universal joint 98 from the middle, and the drive shaft 104 that transmits the rotational driving force is Connected to the coupling 93 shown in FIGS. 3 and 4, the rotational driving force is transmitted to the final shaft 94.

20 and 21 are photographs from the front showing the (a) open state and (b) closed state of the radiation shield cover 118, respectively. In FIG. 20, the drive shaft 116 and the rotary bearing 124 described above are fixed to the left side of the radius shield cover 118, and the shutter of the radius shield cover is rotatably fixed by the hinge 126 (hereinafter referred to as “shutter”). The drive shaft 116 engages so that the "shutter") 128 can be opened and closed. The shutter 128 includes a hinge-side bent portion 130, a front portion 133 including an upper plate 140 and a lower plate 142 that define a slit 134 extending laterally (horizontally) at the center of the height thereof, and a clasp-side bent portion 132. The hinge-side bent portion 130 and the clasp-side bent portion 132 extend slightly to the front side from the hinge portion and then bend at approximately 90 degrees so as to cover the sample stage 52 at a slight distance to form the front surface of the front portion 133. do. The back side of the upper plate 140 and the lower plate 142 comes into contact with the front side of the upper frame 136 and the lower frame 138 of the frame of the opening 122, and cooling of the upper plate 140 and the lower plate 142 is promoted. In order for the sample holder 50 to slide sideways and be taken out from the opening 122, it is preferable that the surface of the sapphire plate 86 on which the sample holder 50 is pressed protrudes toward the front side of the right horizontal frame 144 of the opening 122. Since the holder screw 60 or the like that fastens the sample stage 52 to the sapphire plate 86 protrudes from the slit 134, it does not interfere with the shutter 128. The drive shaft 116 directly drives the hinge 126 to which the rotary bearing 124 is fixed, but if necessary, a damping mechanism may be provided to generate higher torque. By opening the shutter 128 in this way, the sample can be exchanged without breaking the vacuum.

In the above, the shutter 128 is opened and closed by using the rotation introducer 108 for the radiation shield cover, but the sample holder 50 is driven in a direction substantially perpendicular to the longitudinal direction of the vacuum chamber 26 for attaching and detaching the sample holder 50. You will need it. In order to realize this drive, the sample stage 52 or the boat member 76 or the radius tube 38 extends in the direction perpendicular to the longitudinal direction of the sample stage 52 or the boat member 76 or the radius tube 38 (or the sample stage 52 or the boat member 76 or the radius tube 38 extends in the vertical direction. Therefore, the relative movement is realized in the horizontal direction, which is the direction perpendicular to it. In such a case, a sample transfer mechanism 44 attached to the side surface of the vacuum chamber 26 as shown in FIG. 1 can be provided. Since the vacuum chamber 26 is fixed to the intermediate rod 36 and the sample stage 52 via the flange 22, the relative position with respect to the sample stage 52 can be specified and fixed with reference to this. Further, since a sufficient moving distance can be taken in the horizontal direction, the sample holder 50 can be inserted and removed using the sample transfer device 48 or the sample transfer 62 as shown in FIGS. 1 and 6A and 6B. By opening the shutter 128, the sample stage 52 can be exposed from the long square opening 122, the holder screw 60 can be loosened, the sample holder 50 can be pulled out, and then the rear plate 58 to which the sample 56 is fixed can be pulled out. ..

Further, even when the shutter 128 is closed, the sample 56 is exposed from the slit 134, so that the surface of the sample 56 can be irradiated with an electron beam, an electromagnetic wave, or the like, if necessary. Alternatively, it is also possible to detect the reflected light or the scattered light of the light irradiated on the surface of the sample 56.

[Experimental example]
The following confirmation experiment was performed by the sample cooling device 10 shown in FIG. The GM refrigerator of the sample cooling device 10 at room temperature was switched on, and cooling was started as a preliminary test without attaching a sample. As a result, FIG. 22 shows the relationship between the elapsed time from the start of cooling and the temperatures of the intermediate rod 36 and the sample stage 52. In this graph, each temperature of the intermediate rod 36 and the sample stage 52 measured by the silicon diode temperature sensor and the elapsed time from the start of cooling are shown. Within 4 hours after the start of cooling, the temperatures of the intermediate rod 36 and the sample stage 52 began to show constant values, and it can be said that they reached their respective minimum temperatures. The minimum temperature reached for the second stage 34 at this time was 10.0 K.

As described above, after the minimum temperature reached is once shown in the no-load state, the stepping motor 107 of the in-plane rotation introducer 100 is driven, and the sample stage 52 is in-plane from 0 degrees to 90 degrees clockwise. Rotated. The rotation speed at this time was about 8.6 degrees / minute. FIG. 23 shows a graph plotting the temperatures of the intermediate rod 36 and the sample stage 52 with respect to the in-plane rotation angle of the sample (the basic state is 0 degree) at this time. As can be seen from this figure, the temperature of the intermediate rod 36 seemed to gradually increase while showing a peak-like appearance in some places, but did not exceed 7.5 K. On the other hand, the temperature of the sample stage 52 also seems to gradually increase while showing peaks in some places, but it can be seen that the temperature was kept below 15 K.

Next, polycrystalline tantalum was attached to the sample holder 50 as a sample, and as described above, once the minimum temperature was reached, electron impact heating was started. This electronic shock heating was performed by applying a voltage of 650 to 1000 V to the sample and energizing the tungsten filament with a current of 5 to 9 A. As a result, an emission current of 0 to 40 mA was obtained. FIG. 24 shows the results of examining the temperatures near the sample, the second stage, the sample stage, the intermediate rod, and the braided wire during the electron impact heating. The temperatures of the polycrystalline tantalum and the intermediate rod in this sample heating test are shown. It is a graph which showed the time-dependent change of. By adjusting the energization current of the tungsten filament and the voltage applied to the sample during heating, it is shown that the temperature of the sample is continuously variable in the range of 1375 K or less. On the other hand, the intermediate rod was kept below 200K even during heating. Therefore, it can be seen that there is no heat damage to the refrigerator head. Incidentally, when the acceleration voltage was 1000 V and the emission current was 37.3 mA, a sample temperature of 1375 K was obtained.

Next, after once showing the minimum reached temperature in the no-load state as described above, the stepping motor of the in-plane rotation introducer is driven, and the sample stage is set in the in-plane clockwise or counterclockwise by 10 degrees. After rotating the sample at 45 degrees and 90 degrees, the deviation from the initial angle was investigated when the sample was rotated in the opposite direction by the same angle. The driven angle was measured using a rotary encoder attached to the stepping motor, and the actual sample stage angle was measured using a laser autocollimator. Table 1 summarizes the evaluation results of the rotation accuracy in the in-plane direction. It can be seen that the angle deviation was within 0.5 degrees in all experiments.

As described above, in the sample cooling device of the present invention, a sample holding mechanism attached to the cold end of the closed cycle helium refrigerator is designed and manufactured so as to minimize the heat inflow from the outside to the sample. This made it possible to cool the sample to 15 K or less without using liquid helium, and to rotate the sample in the in-plane direction with high accuracy. In addition to this, the device meets the following specifications often required when applied to experimental studies of solid surfaces.
(1) Withstand baking at about 200 ° C and ^{obtain an ultra-high vacuum (10-8} Pa or less).
(2) The sample can be exchanged without breaking the vacuum.
(3) Various beams can be incident and emitted for surface observation.
(4) The sample shall be electrically insulated so that the sample current of the beam can be measured.
(5) To clean the surface of the sample, it is possible to heat 1000K or more by electronic shock heating.
(6) The minimum temperature reached on the sample surface is 15K or less.
(6) The sample can be rotated in the in-plane direction within a range of ± 90 degrees with an accuracy of 0.5 degrees or less.

Although the GM refrigerator was used as the refrigerator in the examples so far, the same can be achieved by attaching the heat shield, heat transfer rod (intermediate rod), etc. of this technology to the cold end of other types of refrigerators. It should be understood that a sample cooling transfer device can be constructed.

10 Sample cooling device 12 GM refrigerator head 14 Tube for supplying helium gas 16 Tube for discharging helium gas 18 Helium gas compressor 20 Device moving mechanism 20a XYZ stage 20b Rotating stage 22 23 Flange 24 Baking heater 26 Vacuum tank 28 Valve 30 49 Vacuum pump 32 First stage 34 Second stage (cold end)
36 Intermediate rod 38 Radiation tube 40 Sample part 42 Gate valve 44 Sample transfer mechanism 46 Operation part 48 Sample transfer device 50 Sample holder 52 Sample stage 56 Sample 58 Rear plate 59 Slicing bolt 60 Holder screw 61 碍 62 Sample transfer 64 Sample transfer Gear 66 In-plane rotation gear 68 Lower base material 70 High voltage application terminal 72 Tungsten (W) filament 74 Tungsten filament wiring 76 Boat member 77 Top surface 78 Deck 80 Copper braided wire 81 Copper braided wire terminal 82 Temperature sensor 84 Top Cover 85 Backup Base Material 86 Sapphire Plate 88 Bearing 90 Nut 92 Hollow Cylindrical Shaft 93 Coupling 94 Final Shaft 96 Head Gear 98 Universal Joint 100 In-plane Rotation Introducer 102 Bearing 104 Drive Shaft 107 Stepping Motor 108 Radiation Shield Cover Rotation introducer 110 Temperature sensor and current introduction terminal for low temperature control heater 112 Sample high voltage application terminal 114 Low temperature control heater 116 Drive shaft 118 Radiation shield cover 120 Connection part 122 Long square opening 124 Rotating bearing 126 Hinge 128 Radi Bearing cover part Shutter 130 Hing side bending part 132 Clasp side bending part 133 Front part 134 Slit 136 Upper frame 138 Lower frame 140 Upper plate 142 Lower plate 144 Right horizontal frame

Claims (20)

With a closed cycle helium refrigerator,
A heat transfer means attached to the cold end of the closed cycle helium refrigerator,
A shielding means that should block external radiation to the heat transfer means,
A sample holding means that thermally contacts the heat transfer means and rotatably holds the sample in a specific plane.
A vacuum chamber capable of maintaining the heat transfer means, the shielding means, and the sample holding means in a vacuum,
In a sample cooling device equipped with
The sample holding means is
A rotating member that can rotate in the specific plane, and
A receiving means that rotatably receives the rotating member,
A highly thermally conductive electrically insulating member capable of electrically insulating the sample held by the rotating member from at least the vacuum chamber or the shielding means or the heat transfer means, and
A passive rotating means that electrically engages with the rotating member to transmit a rotational motion in the specific plane and is rotated by receiving a rotational driving force from the outside of the sample holding means.
Including
Further, where the rotating member is in close contact with the surface of the electrically insulating member, it is thermally connected to the heat transfer means, and its end is brought into close contact with the surface of the electrically insulating member from the rotating member. It is flexible so that heat can be transferred to the heat transfer means via the electrically insulating member, and the rotating member can be rotated in-plane up to 90 degrees clockwise and counterclockwise so that the sample can be exchanged. A heat transfer joint with sufficient length, and
An external driving means that engages with and drives the passive rotating means,
Sample cooling device including. The sample cooling device according to claim 1, wherein the closed-cycle helium refrigerator includes a GM refrigerator. The sample cooling device according to claim 1 or 2, wherein the heat transfer means includes a heat transfer rod, and the shield means includes a radiation tube. The sample cooling device according to any one of claims 1 to 3, wherein the rotating member includes a sample stage, and the receiving means includes a bearing. The sample cooling device according to any one of claims 1 to 4, wherein the high thermal conductive electrical insulating member includes a sapphire plate. The sample cooling device according to any one of claims 1 to 5, wherein the sample holding means includes a filament for thermionic emission. The passive rotating means is coupled to a shaft common to the rotating member via an electrically insulating material, and engages with an engaging convex portion or a concave portion of the external driving means to exert a driving force. The sample cooling device according to any one of claims 1 to 6, wherein the sample cooling device is a transmission member capable of transmitting. The sample cooling device according to any one of claims 1 to 6, wherein the flexible heat transfer joint includes a copper braided wire. Further, a device moving mechanism is provided, and the sample holding means can be moved to an appropriate position in the vacuum chamber.
The sample cooling device according to any one of claims 1 to 8, wherein the vacuum chamber is provided with a heater for baking as needed. The sample holding means is provided at the tip of the heat transfer means.
The sample cooling device according to any one of claims 1 to 9, wherein the shielding means includes a radiation shield cover that covers the sample holding means. The sample cooling device according to any one of claims 1 to 10, wherein the rotating member includes a sample holder and a holder screw, and the sample holder and the sample stage are brought into close contact with each other by rotating the holder screw. The sample cooling device according to claim 10 , wherein the radiation shield cover includes a shutter having an opening for exposing at least a part of the sample. The shutter is rotatably attached to the radiation shield cover by a hinge.
13. The sample cooling device described. The GM refrigerator includes a cylindrical first stage extending from the head portion and a cylindrical second stage extending from the end portion of the first stage.
The first stage has a larger diameter than the second stage and
The shielding means is attached to the end of the first stage outside the second stage.
The heat transfer means extending from the tip of the second stage has a rod shape.
The sample cooling device according to claim 2, wherein the shielding means covers the heat transfer means in order to shield the heat transfer means from external radiation. The vacuum chamber comprises a sample transfer mechanism that is height-matched to the sample holding means and is connected via a gate valve.
The sample cooling device according to any one of claims 1 to 14, wherein the sample transfer mechanism can exchange samples without breaking the vacuum by rotating the rotating member. The sample cooling device according to claim 15, wherein the sample transfer mechanism includes a sample transfer jig. The external drive means includes a drive shaft.
The sample cooling device according to any one of claims 1 to 16, wherein the drive shaft extends along the outside of the shield means and passes through at least one bearing fixed to the outside of the shield means. The sample cooling device according to claim 17, wherein the drive shaft is connected by at least one universal joint. The sample cooling device according to claim 18, wherein the drive shaft is driven by a drive device outside the vacuum chamber. The sample cooling device according to any one of claims 1 to 19, further comprising a vacuum pump.

Images