JP2607478B2 - Cryogenic sample cooling equipment for electron microscopes, etc. - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a cryogenic sample cooling apparatus used in combination with an apparatus for setting a sample in a vacuum vessel such as an electron microscope. The present invention is applicable not only to an electron microscope but also to a sample cooling device for cooling a sample to an extremely low temperature in an electron beam diffraction device, an ion scattering device, and a photoelectron spectroscopy device in which a sample is placed in a vacuum container. These are referred to as electron microscopes and the like.

[Related Art] As a device for cooling a sample such as an electron microscope, for example,
Journal of Electron Microscope 29 (1980) 346,
Alternatively, as described in electron microscope 10 (1975) 59, 5K
Several devices capable of cooling a sample to the following extremely low temperatures have been developed. These conventional devices cool the sample and the sample holder, using liquid helium as a coolant, and heat shield the sample, the sample holder, and the periphery of the liquid helium coolant container by surrounding the sample and the member cooled with liquid nitrogen as a coolant,
The heat conduction and heat radiation from the room temperature portion prevented the temperature of the sample and the sample holder from rising, and allowed the sample to be cooled to extremely low temperatures. Hereinafter, an apparatus having this structure is referred to as a single shield type. That is, the amount of heat flowing into the low-temperature portion due to heat conduction and heat radiation is reduced to about 100 K between the sample and the sample holder and the room temperature portion, because the lower the temperature of the high-temperature portion that contacts or opposes it, the smaller the amount. The liquid nitrogen cooling member is interposed to suppress the heat flowing into the liquid helium cooling member (the member thermally connected to the sample and the sample holder). However, even in this structure, the liquid nitrogen cooling member of 100 k or more and the liquid helium cooling member of several k come into contact or oppose with a large temperature difference of about one hundred degrees, and the amount of heat flowing into the liquid helium cooling member is It is hard to say that it is small enough. Therefore, in order to further complete the heat shield, the sample holder is provided inside the liquid nitrogen cooling member with a second liquid helium cooling member cooled by the liquid helium in the same container when the liquid helium cooling member is cooled. A device having a structure that covers the space has been developed. Hereinafter, an apparatus having this structure is referred to as a double shield type. In addition, when the high-temperature part and the low-temperature part are in contact with the inclusions interposed, the amount of heat flowing from the high-temperature part to the low-temperature part is proportional to the cross-sectional area of the inclusion and inversely proportional to the length. The cross-sectional area of the inclusion between the cooling member and the liquid nitrogen cooling member or between the liquid nitrogen cooling member and the main body at room temperature is made as small as possible, the length is sufficiently secured, and the heat to the low-temperature member is It is necessary to control the inflow. However, due to the limitation of the size of the sample chamber such as an electron microscope, in a conventional apparatus having a part contacting with a temperature difference of about one hundred degrees, an inclusion having a size large enough to satisfy this condition needs to be interposed between the low-temperature member and the high-temperature member. It was difficult to insert in between. For this reason, at present, the ultimate cooling temperature of the sample is considerably higher than the boiling point of helium 4.2 k. For the same reason, the liquid helium evaporation rate is high, and it is not easy to maintain the temperature for a long time by cooling the liquid helium storage container to a low temperature below the boiling point of helium by reducing the pressure in the liquid helium storage container.

[Problems to be solved by the invention]

In the above double heat shield type conventional apparatus, a refrigerant (liquid helium and liquid nitrogen) storage tank is installed in the sample chamber of the electron microscope. In this structure, not only is it difficult to reduce the size of the cooling stage, but also the vibration of the refrigerant storage tank caused by the boiling of the refrigerant is easily transmitted to the sample, which has the disadvantage that high-resolution observation of the sample becomes difficult.

When the sample is cooled to a very low temperature of about several K in a vacuum of an electron microscope or the like, the saturated vapor pressure of the residual gas becomes extremely low,
Residual gas condenses on the sample surface, causing sample contamination.
In order to prevent this, among the above-mentioned conventional cooling devices, in the single heat shield type, the liquid nitrogen cooling member is first cooled while the sample and the sample holder are kept at a high temperature of room temperature or higher. A procedure was adopted in which the residual gas was adsorbed, and then the sample and the sample holder were cooled with liquid helium. However, in this case, some of the water and hydrocarbons in the residual gaseous component are adsorbed on the part cooled to about 100 K with liquid nitrogen, thereby reducing the contamination of the sample. Residual gas components such as oxygen, nitrogen, hydrocarbons, and noble gases whose vapor pressure has not been sufficiently reduced are not adsorbed by the liquid nitrogen cooling member, and when the sample is cooled down to several K, they are adsorbed on the sample surface. Will be done. As described above, it was difficult to sufficiently prevent sample contamination with the single heat shield type apparatus. Further, even in the double heat shield type device, the liquid helium cooling member of the inner shield is cooled at the same time as the sample holder, so that the residual gas is adsorbed not only on the helium cooling member of the inner shield but also on the sample, and sample contamination is reduced. Not much reduced.

In the conventional sample cooling device, there is no device that can easily exchange the sample because the sample is surrounded by a single or double heat shield. That is, a complicated and large sample exchange mechanism was required, or the vacuum in the electron microscope was broken and the vicinity of the sample chamber was disassembled to exchange the sample, which required a great deal of labor.

An object of the present invention is to achieve a low cooling temperature of a sample, and
An object of the present invention is to provide a sample cooling device which can maintain the cryogenic temperature for a long time, can observe a sample at a high resolution, and has minimal sample contamination.

[Means for solving the problem]

In order to solve the above-mentioned problems, the periphery of a first cooling member cooled by liquid helium (a part of the sample stage that is in thermal contact with the sample and the sample holder) is cooled by liquid helium in another container. And two independent liquid helium storage containers (first and second liquid helium storage containers) installed outside the main body of the device such as the electron microscope body. ,
And a second liquid helium container) and a liquid nitrogen storage container to cool the three cooling members through three heat transfer members.

[Action]

Since the second cooling member is cooled by liquid helium like the first cooling member, the temperature difference from the sample can be suppressed to 10 degrees or less. Therefore, the amount of heat flowing into the sample and the sample holder can be significantly reduced as compared with the conventional apparatus. As a result, the ultimate cooling temperature can be further reduced. Further, the evaporation rate of liquid helium, which is the refrigerant of the first cooling member, can be extremely reduced. Furthermore, if the pressure of the first liquid helium container is reduced, the sample portion can be easily cooled to 4.2 K or less, and the heat inflow at this time can be kept sufficiently small. Since the refrigerant container is installed outside the main body of the apparatus such as the electron microscope and is not directly connected to the sample stage at a short distance, vibration of the refrigerant container due to boiling of the refrigerant or the like is not easily transmitted to the sample. Further, oxygen, nitrogen, hydrocarbons, and residual gas components such as rare gases, which are not adsorbed to the third cooling member cooled to the liquid nitrogen temperature, are adsorbed to the second cooling member cooled to the liquid helium temperature,
By cooling the first cooling member, it is possible to prevent the residual gas from being adsorbed on the sample and contaminated.

〔Example〕

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram when the present invention is incorporated in an electron microscope. The refrigerant container 1 is installed outside the mirror body and has a three-tank structure inside. That is, a liquid helium container 5 for cooling the sample and the sample holder in the sample stage 2 and the first cooling member, a liquid helium container 4 for cooling the second cooling member, and a liquid nitrogen container 3 for cooling the third cooling member. Consisting of
Each of them is thermally connected to each section of the sample stage through the heat transfer section 13. In addition, each of these three containers is thermally insulated.

FIG. 2 is a detailed sectional view of the heat transfer section 13 and the sample stage 2. In this figure, the electron beam
Pass through 8,52,29. The liquid helium container 5 is thermally connected to the heat transfer rod 42, and further includes a first cooling member (a heat transfer ring 39, a cylindrical silver thin film 36 bent into a corrugated shape, an inner cylinder 26), and a sample holder. 22 and sample 21 are cooled. The heat transfer rod 42 is covered by an inner shield heat transfer tube 43 that is thermally connected to the liquid helium container 4, and a second cooling member (second transfer member) that is thermally connected to the heat transfer tube 43. The heat ring 40, the inner shield first upper cap 45, the inner shield second upper cap 46, the cylindrical silver thin film 37, the intermediate cylinder 30, and the inner shield lower cap 27) cover the first cooling member. The inner shield tube 43 is further covered by an outer shield heat transfer tube 44 that is thermally connected to the liquid nitrogen container 3, and a third cooling member (a second cooling member) that is thermally connected to the outer shield heat transfer tube 44. The third heat transfer ring 41, the cylindrical silver thin film 38, the outer shield upper cap 47, the outer cylinder 31, and the outer shield lower cap 28) completely cover the second cooling member. The inner cylinder 26 and the intermediate cylinder 30 are connected via a cylindrical heat insulating tube 32. The intermediate cylinder 30, the outer cylinder 31, and the heat-insulating pipe 32 are connected via the same heat-insulating pipe 33. The outer cylinder 31 and the sample fine movement stage 35 are connected via an insulating tube 34 similar to the insulating tube 32. The cylindrical silver thin films 36, 37, and 38 have fine slits in the axial direction, and are further bent in a waveform and easily deformed elastically, so that vibrations that enter through the heat transfer section 13 and the like enter the sample holder 27. It is a structure that is difficult to be transmitted to. Such a sample is completely surrounded by a second cooling member cooled with liquid helium as a refrigerant, and a third cooling member cooled with liquid nitrogen as a refrigerant,
Not only is it thermally insulated, it is also thermally insulated from the electron microscope mirror at room temperature. Each part of these sample stages is thermally connected to a refrigerant container installed outside the mirror body by heat conduction. By employing this structure, the amount of heat and vibration flowing into the sample holder can be significantly reduced.

The sample is cooled in the following procedure. Sample 21 and sample holder
While keeping 22 above room temperature with a heater,
Liquid nitrogen is put into the liquid nitrogen container 3, the third cooling member is cooled, and water and a part of hydrocarbons in the residual gas in the vacuum in the electron microscope are adsorbed on the surface of the third cooling member. Next, liquid helium is charged into the liquid helium container 4, the second cooling member is cooled, and other residual gas components are adsorbed on the surface of the second cooling member. In this way, after making the vicinity of the sample a high vacuum, liquid helium is put into the liquid helium container 5 and the sample 21 is cooled through the first cooling member. If you take this step,
The contamination of the sample due to cooling can be significantly suppressed.

The sample holder 22 is carried to a position 60 through a hole opened in each thermal sold container by an external transport mechanism, and further,
The rotation introducer 50 rotates the cylinder 24 in which the gear 49 and the spiral groove 25 are cut, lowers the sample holder 22 along the spiral groove 25, and fixes the sample holder at the sample observation position 61. When the sample is taken out, the sample can be easily exchanged by following the reverse process.

〔The invention's effect〕

As described above, since the sample can be cooled stably to extremely low temperatures, it can be applied to an electron microscope or the like, and can perform experiments, observations, etc., without any particular hindrance, as compared with a sample at room temperature. .

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view when an embodiment of the present invention is incorporated in an electron microscope, and FIG. 2 is a heat transfer section 13 in FIG.
3 is a detailed vertical sectional view of the sample stage 2. FIG. DESCRIPTION OF SYMBOLS 1 ... Refrigerant container, 2 ... Sample stage, 3 ... Liquid nitrogen container, 4 ... Second liquid helium container, 5 ... First liquid helium container, 6 ... Electron gun, 7 ... Condenser lens,
8 ... Ion pump, 9 ... Objective lens, 10 ... Intermediate ...
… Intermediate lens, 11… Projection lens, 12 …… Film, 13
... heat transfer section, 21 ... sample, 22 ... sample holder, 23 ... guide cylinder, 24 ... spiral groove rotating cylinder, 25 ... spiral groove, 26 ...
Inner cylinder, 27… Inner shield lower cap, 28… Outer shield lower cap, 29… Electron beam passage hole, 30…
Inner cylinder, 31 ... Outer cylinder, 32,33,34 ... Cylindrical insulated tube, 35 ... Sample fine movement stage, 36,37,38 ... Wave cylindrical silver thin film, 39 ... First heat transfer ring, 40 …… Second heat transfer ring, 41 …… Third heat generation ring, 42 …… Heat transfer rod, 43 …… Inner shield heat transfer tube, 44 …… Outer shield heat transfer tube, 45 …… Inner shield first upper cap, 46 …… Inner shield second upper cap, 47 …… Outer shield upper cap, 48 …… Electron beam passage hole, 49 …… Gear, 50 …… Rotary introducer, 51 ……
Electron microscope body, 60: sample holder position when transported by the external transport mechanism, 61: sample holder position during sample observation.

Continuing from the front page (72) Inventor Nobuyuki Nagagabe 1-280 Higashi-Koigabo, Kokubunji City, Hitachi, Ltd.Basic Research Laboratories Co., Ltd. ) Inventor Shuji Hasegawa 1-280 Higashi Koigakubo, Kokubunji City Inside the Basic Research Laboratory, Hitachi, Ltd. (56) References JP-A-61-263036 (JP, A)

Claims (3)

(57) [Claims] 1. A first cooling member for cooling a sample or a sample holder disposed in a mirror body such as an electron microscope, a second cooling member having a shape substantially surrounding the first cooling member, and a second cooling member. A third cooling member having a shape substantially enclosing the first and second liquid helium containers and a liquid nitrogen container, which are independent from each other, and are provided outside the apparatus main body such as an electron microscope. And an electron microscope wherein the second liquid helium container and the liquid nitrogen container are connected to the first, second, and third cooling members by first, second, and third heat transfer members, respectively. Cryogenic sample cooling device for etc. 2. A patent comprising: a cylinder having a spiral groove disposed inside the first cooling member; and a transport mechanism for moving the sample holder up and down along the spiral groove of the cylinder. The cryogenic sample cooling device for an electron microscope or the like according to claim 1. 3. A cryogenic sample cooling apparatus for an electron microscope or the like according to claim 1, wherein said first liquid helium container is used under reduced pressure.