JP2000133188A - Sample cooling holder of electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sample cooling holder such that once the sample cooling holder is attached to an electron microscope, the sample stage of the electron microscope can be positioned. SOLUTION: A heat exchanger 5 provided with a sample stage 8 and support 12 supporting the heat exchanger 5 are constantly pressed against the inner surface of a guard 13 by the action of bellows 6 provided in a first cooling line 4a through which a cryogen is supplied from a cryogen container to a heat exchanger 5 and in a second cooling line 4b through which the cryogen 1a subjected to heat exchange in the heat exchanger is recycled, the guard 13 having a pivot 15 attached thereto. Thus, once a sample cooling holder is attached to an electron microscope, the sample stage of the electron microscope can be positioned.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron microscope, and more particularly to a sample cooling holder suitable for cooling a sample to a very low temperature and observing the sample.

[0002]

2. Description of the Related Art In recent years, electron microscopes used for observing the surface of a base material have recently been used to observe the base material at a low temperature, triggered by the discovery of high-temperature superconductivity. I have. For this reason, the development of a holder for cooling a sample has been advanced.

[0003] Recently, in order to analyze the structure of a cell, a cell sample has been observed using a transmission electron microscope while being cooled to an extremely low temperature. As this conventional technology, "ANTI-DRIFT DEVICE FOR SIDE ENTRY ELE
CTORON MICROSCOPE SPECIMENHOLDER 』US Patent Numbe
As described in r4703181, there is disclosed an apparatus using a material having a large linear expansion coefficient so that the length L from the pivot to the sample table is constant even in a cooled state.

[0004]

A conventional sample cooling holder for an electron microscope is provided with a distance between a supporting member for holding the sample stage and the sample stage in order to eliminate thermal shrinkage caused when the sample stage is cooled. Focusing solely on the heat shrinkage of the support supporting the sample stage, there is no consideration. For this reason, when the sample stage was cooled, it was necessary to move the sample stage again in the direction of the support.

An object of the present invention is to provide a sample cooling holder which enables positioning of a sample stage of an electron microscope by only once attaching the sample cooling holder to the electron microscope.

[0006]

In order to achieve the above object, a feature of the sample cooling holder according to the present invention is that a guard provided with a pivot for positioning the focal point of a lens of an electron microscope on a sample stage is mounted. And a thermal expansion and contraction absorbing means provided in a cooling pipe for supplying and recovering the cryogen to a heat exchanger for cooling the sample stage.

Specifically, the present invention provides the following holder.

According to the present invention, a heat exchanger for cooling the sample stage is provided in a guard provided with a pivot for aligning the focal point of the lens of the electron microscope with the sample stage and supported by a support member. In a sample cooling holder of an electron microscope provided with a cooling pipe for supplying and recovering the cryogen from the cryogen container to be stored to the heat exchanger, a heat expansion / contraction absorbing means is provided on the heat exchanger side of the cooling pipe to provide the heat. A sample cooling holder for an electron microscope, characterized in that the cryogen is supplied to and recovered from an exchanger.

Preferably, the thermal expansion / contraction absorbing means is a bellows.

Preferably, the cooling pipe includes a first cooling pipe for supplying a cryogen and a second cooling pipe for recovering the cryogen, and the heat expansion / contraction absorbing means is provided on the heat exchanger side of each of the cooling pipes. A bellows is provided.

Preferably, a communication box is provided at the heat exchanger side end of the first and second cooling pipes, and the communication box is provided with a bellows as the heat expansion / contraction absorbing means.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a sample cooling holder for an electron microscope according to the present invention will be described below with reference to FIGS. 1 to 11, the same or equivalent parts are denoted by the same reference numerals.

FIG. 1 shows a cross section of the entire structure of a sample cooling holder according to one embodiment of the present invention. Reference numeral 1 denotes a cryogen container for storing a cryogen 1a such as liquid nitrogen or liquid helium.
An outer container 3 is provided on the outer periphery of the cryogen container 1. The outer container 3 is used as a vacuum container while maintaining the inside at a vacuum. The cryogen container 1 has an atmospheric pressure,
In order to store and hold the cryogen 1a having a sufficiently low saturation temperature, the outer peripheral surface of the cryogen container 1 is covered with a polymer film deposited with aluminum to shield radiant heat.

Reference numeral 2 denotes a shield for shielding radiant heat entering the cryogen container 1 from the external container 3 at room temperature. 2a is
A laminated heat insulating material wrapped around a shield, in which multiple polymer films on which aluminum is deposited are laminated.

4a is a heat exchanger 5 from the bottom plate of the cryogen container 1.
1 is a first cooling pipe for supplying the cryogen 1a to the first cooling pipe. 5
Is a heat exchanger made of a high heat conductive material such as copper. Further, the heat exchanger 5 is provided with a U-shaped flow path so that the cryogen 1a passes therethrough. Further, a second cooling pipe 4b is connected to the heat exchanger 5 so as to penetrate the outer container 3 so that the cryogen 1a or the evaporated gas is discharged into the atmosphere. Reference numeral 6 denotes a bellows to which the present invention is applied.

The liquid injection pipe 7 also functions as a pipe for discharging the gas from which the cryogen 1a has evaporated to the atmosphere. The injection pipe 7
A shield neck 3b thermally connected to the shield 2 is connected to a position about half the axial length of the shield 2. The shield neck 3b is cooled by the sensible heat of the vaporized gas inside the second cooling pipe 4b and exhibits an intermediate temperature between the room temperature and the temperature of the cryogen. Since the shield 2 is connected to the shield neck 3b, the temperature of the shield 2 also becomes an intermediate temperature.

Reference numeral 8 denotes a sample stage thermally connected to the heat exchanger 5, and 9 denotes a flow control valve connected to a liquid injection pipe. Reference numeral 10 denotes a discharge port for discharging evaporative gas generated when the liquid is stored in the cryogen container 1 into the atmosphere.
Is closed when accumulates. 11 is a heat shrinkage-reducing bellows.

FIG. 2 shows an enlarged cross section near the sample stage 8 in FIG. Reference numeral 12 denotes a support member for supporting the heat exchanger 5, which is one of members for determining the position of the sample stage. 13 is a room temperature guard. Reference numeral 14 denotes a flat screw for fixing the guard 13 after the guard 13 is assembled. Reference numeral 15 denotes a pivot for positioning the focus of the lens of the electron microscope on the sample stage. This pivot is always in contact with a pivot receiver (not shown) attached to the electron microscope.

Next, the operation of the sample cooling holder according to one embodiment of the present invention will be described. The purpose of the sample cooling holder is to keep the sample at a constant temperature for a long time. Moreover, the temperature is a low temperature of liquid nitrogen or liquid helium, which is about -200 or less.

In order to lower the temperature of the sample, the sample table 8
The coolant 1a is supplied to the inside of the heat exchanger 5 for cooling the refrigeration. The sample stage 8 can be obtained by processing a part of the heat exchanger 5 or by thermally connecting the sample stage 8 to the heat exchanger 5 by soldering or silver brazing.

In order to keep the temperature of the sample stage 8 as low as possible, the sample stage 8 and the heat exchanger must have a thermal conductivity of copper or the like in order to reduce the thermal resistance between the sample stage 8 and the heat exchanger 5. It is desirable to be formed of a material having a high hardness.

The method of supplying the cryogen 1a to the heat exchanger 5 is as follows.
The pressure inside the cryogen container 1 is made slightly higher than the atmospheric pressure by the flow control valve 9 in FIG. 1, and the cryogen 1a is supplied to the heat exchanger 5 by pumping.

When the flow control valve 9 is closed,
The cryogen 1a flows out of the discharge port 10 of the liquid injection pipe 7. This is because the internal pressure of the cryogen container 1 is increased more than necessary, and the effect of cooling the sample stage 8 is small, and the cryogen 1a is wasted. Therefore, to lower the temperature of the sample stage 8,
There is an optimal opening of the flow regulating valve 9.

In order to reduce the consumption of the cryogen 1a, the low-temperature cryogen container 1, the shield 2, the first and second cooling pipes 4a and 4b, the heat exchanger 5, the bellows 6 and the like are kept at a high vacuum. Is insulated.

Reference numeral 2b denotes a low-temperature shield which connects the shield 2 to the first and second cooling pipes 4a and 4b. The shield 2 and the first and second cooling pipes 4a and 4b Shows intermediate temperatures.

The thermal strain reducing bellows 11 is a low-temperature shield 2
b and the heat shrinkage due to the low temperature of the shield 2, the first
The second cooling pipes 4a and 4b are provided for the purpose of relieving the heat shrinkage and the heat distortion caused by the difference between the heat shrinkages.

The length L1 in FIG. 1 becomes shorter than the length L1 at room temperature due to thermal contraction caused by cooling. A bellows 6 is provided to recover the shortened length. Since the internal pressure of the bellows 6 is always higher than the atmospheric pressure, the length of the bellows 6 expands and contracts. The outside air of the bellows 6 is maintained in a vacuum state for heat insulation. Therefore, since the same situation occurs when an internal pressure of 1 atm is applied to the bellows 6, the bellows 6 extends in the longitudinal direction. This amount of elongation is determined by the number of peaks of the bellows 6 and the spring constant.

The bellows 6 includes first and second cooling pipes 4.
It may be a molded product integrated with the first and second cooling pipes 4a and 4b, or may be made of another material and assembled to the first and second cooling pipes 4a and 4b.

The bellows 6 has an outer diameter of 1 mm due to geometrical restrictions.
If you can only install the bellows 6, the bellows 6
It is desirable to manufacture by electrodeposition or electroforming. Also,
When the bellows 6 is manufactured by electrodeposition, the design is easy because the bellows 6 have almost the same properties as ordinary molded bellows.

Although the electroformed bellows 6 is usually made of nickel or a nickel alloy, it is preferable that the sample cooling holder of this embodiment is a non-magnetic material in order to utilize a magnetic field. Therefore, it is preferable to use copper or a copper alloy as the material of the bellows 6.

The length L 2 in FIG. 2 is the length from the tip of the pivot 15 to the center of the sample table 8. The length L2 is based on the position of the guard 13 which is fixed by the pressing force generated by the pressure difference between the inside and outside of the bellows 6 being transmitted to the heat exchanger 5, the supporting member 12 and the guard 13 so that they contact each other. Determined by the geometric dimensions of the support 12 and the heat exchanger 5.

FIG. 3 shows a cross section of the entire structure of a sample cooling holder according to another embodiment of the present invention. Reference numeral 16 denotes a nonmagnetic metal or polymer spring. 17 is a spring fixing plate for supporting the spring 16. The spring 16 is connected to the cooling pipe 4
The first cooling pipe 4a and the second cooling pipe 4b are installed in the internal space of the spiral spring 16 in a coaxial manner.

When the bellows 6 has too large a spring constant and the bellows 6 does not extend to a position shifted by thermal contraction during cooling, the spring 16 increases the pressing force by the spring force corresponding to the inability of the bellows to extend. Things. The pressing force of the spring 16 is applied to the heat exchanger 5 and the support 12.
Are transmitted to the guard 13 through the contact points, so that they are always in contact with each other.

Therefore, the heat exchanger 5, the support member 12 and the guard 13 can keep their contact with each other even when cooling is performed by the effect of the bellows 6 and the spring 16 or not.

FIG. 4 shows a cross section of the overall structure of a sample cooling holder according to still another embodiment of the present invention. In this embodiment,
By reducing the number of springs 16 of the sample cooling holder in FIG. 3 to one, the amount of heat entering the heat exchanger 5 from the guard 13 at room temperature due to the conduction heat of the springs 16 is reduced to half. By reducing the heat entering the heat exchanger 5, the effect of reducing the consumption of the cryogen 1a supplied to the heat exchanger 5 can be expected.

Further, by reducing the number of springs 16 from two to one, there is an effect that the consumption of liquid helium is reduced and the time during which the sample stage can be maintained at a low temperature is prolonged. 3 and 4 use a compression spring as the spring 16,
A tension spring may be provided on the support member 12 so that a hook (not shown) is provided on the guard 13 and the heat exchanger 5 to pull the sample table 8 to pull them.

FIG. 5 shows still another embodiment of the present invention.
A plate-like spring 16a is provided instead of the spring 16 in FIGS. This plate-shaped spring 16a has an advantage that it can be easily attached even in a narrow place, as compared with a spring-shaped spring.

FIG. 6 shows still another embodiment of the present invention.
The function of the bellows 6 shown in FIGS. 2 to 5 is performed by the bellows 18 for the heat exchanger which is also a communication box with the first and second cooling pipes 4a and 4b provided at the end of the heat exchanger 5. .
The reason for using the heat exchanger 5 is that the pressing force is proportional to the product of the pressure difference between the inside and outside of the bellows and the cross-sectional area of the bellows, so that the heat exchanger 5 larger than the first and second cooling pipes 4a and 4b is used. This is because a bellows having a large cross-sectional area can be applied and the pressing force increases. Also, a relatively large bellows has the advantage of good manufacturability.

FIG. 7 shows an AA cross section of FIG. Sample table 8
Since a flat surface has better work operability, it has a structure in which a cylindrical heat exchanger bellows 18 and a flat plate-shaped sample stand 8 are combined.

FIGS. 8 to 11 are for explaining the operation of the support member 12. FIG. At the position of the sample stage 8 in the axial direction, a flat screw 14 for attaching the support member 12 to the heat exchanger 5 is arranged. Since it is necessary to keep the length L2 of FIG. 8 constant at all times, the heat exchanger 5 and the support 12
The parts facing each other are provided with a certain gap.

The support member 12 shown in FIG. 8 is made of a composite material composed of unidirectional carbon fiber and epoxy resin. The carbon fiber itself has a characteristic that the linear expansion coefficient becomes negative when the temperature is lowered from room temperature to a low temperature, unlike ordinary polymer materials or metal materials. At a low temperature of 20K or less,
Lower thermal conductivity than epoxy material. This characteristic makes it possible to reduce the heat transmitted through the support member 12 and entering the sample stage 8.

The characteristics of the composite material, the sample stage 8 and the support 1
What is the arrangement of the flat screws for attaching 2 to the heat exchanger 5?
Even when the temperature of the sample stage 8 is lowered from room temperature to an extremely low temperature of 4.2 K, it is possible to keep the length of L2 in FIG. 8 unchanged. Further, the amount of heat that enters the sample table 8 or the heat exchanger 5 from the cover 13 through the support member 12 can be reduced.

FIG. 9 is an enlarged view of the support member 12, showing a carbon fiber-epoxy resin composite material which is alternately laminated. The oblique line in FIG. 9 indicates the direction of the unidirectional carbon fiber, and θ indicates the angle between the axial perpendicular and the unidirectional carbon fiber. 12a and 12b are both composites of unidirectional carbon fiber and epoxy resin, but the directions of the fibers are different.

The support member 12 comprises a carbon fiber-epoxy resin composite material 12a disposed at an angle of θ with respect to the perpendicular,
It is obtained by alternately laminating and solidifying carbon fiber-epoxy resin composite materials 12b arranged at an angle of (minus) θ.

FIG. 10 shows a unidirectional carbon fiber-epoxy resin composite material attached at an angle θ to a perpendicular to a main axis (in a direction in which a change in length due to a temperature change is minimized).

FIG. 11 is a diagram showing the relationship between the mounting direction θ of the carbon fiber of the composite material as shown in FIG. 10 and the expansion coefficient. The positive coefficient of expansion increases with increasing temperature,
A negative coefficient of expansion indicates that shrinking with increasing temperature. When the coefficient of expansion is 0, it indicates that the length does not change at all even when the temperature is increased. Therefore, if it is not desired to change the length L2 of FIG. 8 practically even at the time of cooling or heating, the expansion coefficient of the composite material constituting the support member 12 is 0 ±
^Preferably, it is 2.5 × 10 ⁻⁷ .

From FIG. 11, in the case of a carbon fiber epoxy resin composite material in which one direction of carbon fiber is aligned parallel to the main axis, -27 × 10 ^-7 It expands when cooled. When the angle θ formed with the main axis is 38 degrees, there is no heat shrinkage or elongation even when cooled. Therefore, when it is not desired to change the length L2 of FIG. 8 practically even during cooling or heating, the angle between the perpendicular of the main shaft and the carbon fiber is set to 3 degrees.
It is better to set to 8 ± 1 degrees.

Polyamide fibers are materials that have the property of elongating when cooled similarly to carbon fibers. Similarly, the effects of the present invention can be obtained by using a polyamide fiber instead of a carbon fiber.

The bellows 6 attached to the cooling pipe 4
Alternatively, the heat exchanger 5 on which the sample stage 8 is installed is pressed in the direction of the pivot 15 by the action of the bellows 18 for a heat exchanger, and the space between the mounting position of the sample stage 8 having a temperature change and the guard 13 at room temperature. Since the support member 12 does not thermally expand and contract, the distance L2 between the pivot 15 and the sample table 8 does not always change even when it is cooled. For this reason,
The position of the sample table 8 does not fluctuate, and the image of the electron microscope becomes clear. Further, since the material of the support member 12 is a composite material of carbon fiber epoxy resin, the heat conductivity is small, so that the consumption of the cryogen can be reduced.

[0050]

According to the present invention, the sample stage of the electron microscope can be positioned only by mounting the sample cooling holder on the electron microscope once, and the position of the sample stage can always be determined regardless of the cooling temperature change. Therefore, the image of the electron microscope can be sharpened.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of the overall configuration of a sample cooling holder according to one embodiment of the present invention.

FIG. 2 is an enlarged sectional view near a sample stage 8 in FIG.

FIG. 3 is a cross-sectional view of the entire configuration of a sample cooling holder according to another embodiment of the present invention.

FIG. 4 is a cross-sectional view of the entire configuration of a sample cooling holder according to still another embodiment of the present invention.

FIG. 5 is a cross-sectional view of the entire configuration of a sample cooling holder according to still another embodiment of the present invention.

FIG. 6 is a cross-sectional view of an overall configuration of a sample cooling holder according to still another embodiment of the present invention.

FIG. 7 is a sectional view taken along the line AA of FIG. 6;

FIG. 8 is a cross-sectional view of the vicinity of the support member of FIG.

FIG. 9 is an enlarged sectional view of the support member of the present invention.

FIG. 10 is a view for explaining directions of carbon fibers constituting the support of FIG. 9;

FIG. 11 is a diagram illustrating a relationship between an angle of a one-way carbon fiber prepreg and an expansion coefficient.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cryogen container, 2 ... Shield, 3 ... External container, 4a ... First cooling pipe, 4b ... Second cooling pipe, 5 ... Heat exchanger,
6 bellows, 7 injection tube, 8 sample stand, 11 heat-relaxation bellows, 12 support material, 13 guard, 14 flat screw, 15 pivot, 16 spring, 16a leaf spring,
17: spring fixing plate, 18: bellows for heat exchanger, θ: angle between carbon fiber and perpendicular to main shaft

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroyuki Kobayashi 882 Momo, Oaza-shi, Hitachinaka-shi, Ibaraki F-term in Hitachi Instruments Measuring Instruments Division (reference) 5C001 AA01 BB02 CC03

Claims (4)

[Claims] 1. A heat exchanger for cooling a sample stage is provided in a guard provided with a pivot for positioning a focal point of a lens of an electron microscope on the sample stage and supported by a support member, and stores a cryogen. In a sample cooling holder of an electron microscope provided with a cooling pipe for supplying and recovering the cryogen from a cryogen container to the heat exchanger, a heat expansion-contraction absorbing means is provided on the heat exchanger side of the cooling pipe, and the heat exchanger is provided. A sample cooling holder for an electron microscope, wherein the cryogen is supplied to and collected from the sample. 2. A sample cooling holder according to claim 1, wherein said thermal expansion / contraction absorbing means is a bellows. 3. The cooling pipe according to claim 1, wherein the cooling pipe comprises a first cooling pipe for supplying a cryogen and a second cooling pipe for recovering the cryogen, and the cooling pipe is provided on the heat exchanger side of each of the cooling pipes. A sample cooling holder for an electron microscope, wherein a bellows is provided as thermal expansion / contraction absorbing means. 4. A communication box according to claim 3, wherein a communication box is provided at the heat exchanger side end of said first and second cooling pipes, and said communication box is provided with a bellows as said heat expansion / contraction absorbing means. A sample cooling holder for an electron microscope.