JPS6063866A - Objective lens movable diaphragm device of electron microscope - Google Patents

Abstract

PURPOSE:To obtain an optimum angular aperture on the back side focal surface of each of a high resolving power lens mode and an extremely low power lens mode by arranging a plurality of objective lens movable diaphragms in the upper and lower sides, along an optical axis, of each corresponding lens mode. CONSTITUTION:A sample 2 set in a sample holder 1 is fixed in an optical axis within an objective lens comprising an upper magnetic pole 3 and a lower magnetic pole 4. A movable diaphragm 6 having a plurality of stop holes 5 with different diameters is arranged in a lens space between the upper and lower magnetic poles. A movable diaphragm 9 having a plurality of stop holes 8 with different diameters is arranged in a through hole 7 installed in the lower magnetic pole 4. The back side focal surface in a high resolving power lens mode exists in the lens space, and an optimum angular aperture to obtain good contrast with small stop holes 5 is selected using the movable diaphragm 6. The back side focal surface in an extremely low power lens mode exists in the lower magnetic pole 4, and an optimum angular aperture to obtain good contrast with stop holes 8 is selected using te movable diaphragm 9.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a movable aperture of an objective lens of an electron microscope, etc.
In particular, the present invention relates to an objective lens movable diaphragm device suitable for obtaining an optimal aperture angle in high resolution lens mode and extremely low magnification lens mode.

[Background of the invention]

In order to optimally set the aperture angle related to image contrast, etc., the objective aperture of an electron microscope generally has 3 to 4 different aperture diameters (20 mμφ to 100 mμφ) in the lens gap between the upper and lower magnetic poles of the objective lens. A movable diaphragm device equipped with a diaphragm device is installed, and when examining the microscope, the user selects one of these depending on the magnification, zoom mode, etc., and uses it under optimal conditions.

However, with this method, when the focal lengths of the objective lenses are significantly different, such as the high-resolution lens mode and the extremely low magnification lens mode, in one of the lens modes (mainly the high-resolution lens mode), the rear focal plane is Since the lens is equipped with a movable aperture device, it is possible to set the optimum aperture angle with a small aperture diameter to obtain a good conotrast without cutting the field of view, but this is difficult in the other lens mode.

Roughly speaking, there is a utility model registration No. 873672 that allows fine adjustment of the aperture angle, but this is based on a single aperture plate (with multiple aperture holes) that moves up and down to finely adjust the aperture angle. Even with the movable diaphragm device 1, it is impossible to set the diaphragm hole to obtain the optimum aperture angle and obtain good contrast without cutting the field of view by placing the optimum diaphragm hole in the rear focal plane outside the lens gap. Can not.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a complete objective lens movable diaphragm device for an electron microscope, etc., which can obtain an appropriate aperture angle at the rear focal plane in each of the high-resolution lens mode and extremely low magnification lens mode.

[Overview of the invention] The present invention corresponds to each lens mode of high resolution lens mode and extremely low magnification lens mode, and by arranging a plurality of objective lens movable diaphragms v above and below along the optical axis,
The objective is to obtain an appropriate aperture angle at the rear focal plane of each of the high-resolution lens mode and ultra-low magnification lens mode.

[Embodiments of the invention]

Examples of the present invention will be described below.

An embodiment of the present invention is shown in FIGS. 1 and 2. FIG.

In the figure, a sample 2 loaded in a sample holder 1 is mounted on the optical axis within an objective lens composed of an upper magnetic pole 3 and a lower magnetic pole 4. In the lens gap between the upper and lower magnetic poles of the objective lens, there are a plurality of aperture holes 5 (from 10 mμφ to
A movable aperture 6 with a diameter of 70 mμφ) is provided. Furthermore, a movable aperture 9 having a plurality of different aperture holes (8tlOmμφ to 70mμφ) is installed in the through hole 7 provided in the lower magnetic pole 4.

Next, the operation of this embodiment will be explained.

FIG. 1 shows the state of the high-resolution lens mode. This j! 6, the objective lens is strongly excited fIN/v'fi〉1
In 6), the focal length of the objective lens is 2 mm or less. Therefore, the back focal plane in this lens mode is the lens gap (
By using the movable diaphragm 6 mounted near the rear focal plane, it is possible to select the optimum aperture angle to obtain good contrast with the small aperture 5. .

Is Figure 2 in extremely low magnification lens mode? The objective lens shown is weakly excited (IN/V''PJ < i o ) and the focal length of the objective lens is set to 8 or more. Therefore, the rear focal plane in this lens mode is outside the lens gap and inside the lower magnetic pole 4. In this case, it is difficult to select the optimum aperture angle for the aperture 5 of the movable diaphragm 6 if the quad of the field of view is included, so the By using the movable diaphragm 9 in the through hole 7 provided in this manner, it is possible to select the optimum aperture angle for obtaining good contrast with the small aperture 8.

Therefore, according to this embodiment, in the configuration of the present invention in which a plurality of movable apertures are all arranged up and down along the optical axis, corresponding to the rear focal plane of each lens mode, the movable aperture V + By using this, you can set the optimal aperture angle to obtain good contrast without cutting the field of view.
The practical effects are extremely large.

Furthermore, according to this embodiment, the movable diaphragm 6 and the movable diaphragm 9 can be easily attached and detached alternately in conjunction with the lens mode changeover switch that changes the excitation condition of the objective lens, which improves operability during microscopy. is also effective.

In addition, if the utility model (873, 672)'Th is used as a movable diaphragm device placed up and down corresponding to each lens mode, the aperture angle corresponding to the accelerating voltage sample can be finely adjusted in each lens mode. Needless to say, it is possible and moreover, it is effective.

〔Effect of the invention〕

As described above, according to the present invention, an appropriate aperture angle can be obtained at the rear focal plane in each of the high resolution lens mode and the extremely low magnification lens mode.

[Brief explanation of drawings]

FIG. 1 is a high resolution lens mode diagram showing an embodiment of the present invention, and FIG. 2 is an extremely low magnification lens mode diagram.

Claims (1)

[Claims] 1. In an objective lens consisting of an upper magnetic pole and a lower magnetic pole, in which a sample loaded in a sample holder is attached to the optical axis and has multiple lens modes, a An objective lens movable aperture device for an electron microscope, etc., characterized by having a plurality of movable apertures located above and below.