JPS587022B2 - Capsule device for electron microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a capsule device (atmospheric gas sample chamber) for an electron microscope.

Generally, samples observed with an electron microscope are placed in a vacuum.

However, in recent years, techniques have been developed to observe samples in special environments such as high temperatures, low temperatures, and atmospheric gases.

As a result, two methods have been developed for the atmospheric gas sample chamber (usually called a capsule): one with a thin film window, and the other with a differential pumping system using partition walls with pinholes in multiple stages. has been done.

However, these capsules have the following problems.

That is, when observing a sample with a size of about 1 micron, which is the object of electron microscopy, in a gas atmosphere, the purity of the gas used is an extremely important issue.

Particularly when observing changes in phenomena while heating a sample in an atmospheric gas, the influence of even a small amount of impure gas cannot be ignored in many cases.

Furthermore, even when the highest purity gas is used, if other gases remain in the sample chamber, these residual gases will affect the measurement.

On the other hand, the vacuum gauge in the electron microscope currently in general use is usually installed directly above the main diffusion pump.
Even if it shows x10-6 Torr, the actual degree of vacuum in the sample chamber is about IXIO-5 Torr.

Therefore, conventionally, when introducing high-purity gas, a so-called gas cleaning method has been used in which gas introduction and exhaust are repeated several times, but it has not been possible to actually measure the cleanliness.

Therefore, there was a problem with the accuracy of the results when observing the sample.

The present invention solves the problems of the prior art, and is characterized by directly measuring the cleanliness in a capsule using the differential pumping method described above.

As a result, it is possible to observe gas reactions with much higher reliability than before.

That is, the present invention is characterized in that an ion pump for measuring the partial pressure of defective residual gas is installed together with a vacuum gauge in the capsule chamber into which the sample is charged. Focusing on sensitivity, the inside of the capsule is cleaned with a rare gas such as argon, and the amount of residual gas other than the rare gas is detected.

The gist of the present invention will be explained below with reference to the drawings.

FIG. 1 is a schematic longitudinal side view of the apparatus of the present invention, in which 1 is a mirror body, 2 is an objective lens pole piece that accommodates a sample 3, and perforated partition walls 4 and 5 are provided above and below the pole piece.

Furthermore, on the side of this pole piece 2, an ion pump 6 for partial pressure measurement, a hole communicating with a vacuum gauge 7, a hole for sample insertion, a sample fine movement mechanism 8, a heating device, a heating mechanism 9 such as a thermocouple, an objective lens diaphragm, and a liquid A plurality of holes are provided for communication with auxiliary devices such as a nitrogen trap 10 and a vacuum exhaust system 11 dedicated to the capsule chamber.

Others 12 and 13 are perforated partition walls provided in the condenser lens 14 section, 15 is a vacuum gauge provided in the main exhaust system, and 16 is a vacuum gauge provided in the electron gun section.

Note that numbers 16, 15, and 7 each use an ionization gauge.

To observe the sample 3, the sample 3 is housed in the pole piece 2, and the interior of the mirror body 1 is evacuated.

The degree of vacuum measured by the vacuum gauge 15 is IX10=Tor
Even at r, the degree of vacuum inside pole piece 2 remains 1×10-4
It is about Torr.

However, in the present invention, the ion pump 6 is installed inside the pole piece 2, and the pumping capacity of the pump 6 varies depending on the type of gas, and is particularly poor for rare gases.

The indicated value of the degree of vacuum shows the same value as the vacuum gauge 7 for air, nitrogen, etc., but is hardly felt for rare gases.

For example, when atmospheric pressure air is exhausted, it shows the same value as ionization gauge 7, but when argon gas is introduced into the pole piece with IXIO-5 Torr and then exhausted, ionization gauge 7 shows 1 x 10-5 Torr. The indicated value of the ion pump 6 is 1×10 −7 Torr.

This can be considered to mean that the residual gas other than argon gas in the pole piece 2 is about 1×10 −7 Torr.

The proof is shown below. A thin film sample of eutectoid steel has a pearlite structure on the entire surface, but this can be removed using a normal vacuum (IXIO
-5 Torr) to 900°C and cooled, pro-eutectoid ferrite is formed in about half the area.

This is because decarburization occurred due to oxygen remaining in the sample chamber (capsule).

However, as mentioned above, the ion pump 6 cleaned with argon
When the eutectoid steel thin film is similarly cooled from 900° C. with the indicated value of IXIO-7 Torr (7 indicates IXIO-5 Torr), the decarburized portion becomes 5% or less.

As is clear from this result, the indicated value of the ion pump 6 indicates the partial pressure of the residual gas.

By installing an ion pump in the sample chamber in this way, it is possible to detect the amount of residual gas after cleaning with a rare gas such as argon, so after confirming this condition, you can introduce the desired gas to ensure high reliability. Gas reaction experiments can be performed.

In addition, when performing an experiment with a high gas concentration using the apparatus of the present invention, it is necessary to create a small capsule within the pole piece 2 and charge the sample into the capsule.

However, in experiments using a gas as low as IXIO-2 Torr, this small capsule can be omitted.

As explained above, the device of the present invention can detect residual gas using an ion pump in an electron microscope that performs a low-pressure gas reaction in a vacuum, and can prevent the residual gas from affecting observation, so it is extremely effective.

[Brief explanation of the drawing]

FIG. 1 is a schematic longitudinal cross-sectional side view of the apparatus of the present invention, and FIG. 2 is a cross-sectional plan view thereof. 1... Mirror body, 2... Objective lens pole piece, 3... Sample, 4, 5... Perforated partition, 6...・Ion pump for partial pressure measurement, 7...
...Vacuum gauge, 8...Specimen fine movement mechanism, 9...
... Heating mechanism, 10 ... Vacuum exhaust system liquid nitrogen trap, 12, 13 ... Perforated partition wall, 14 ...
... Condenser lens, 15 ... Vacuum gauge provided in the main exhaust system, 16 ... Vacuum gauge provided in the electron gun section.

Claims (1)

[Claims] 1. A capsule device for an electron microscope characterized in that an ion pump for measuring the partial pressure of defective residual gas is installed together with a vacuum gauge in the capsule chamber into which a sample is loaded.