US2508317A - Electronic microscope - Google Patents

Description

y 1950 A. VERHOEFF 2,508,317

ELECTRONIC MICROSCOPE Filed May '7, 1948 ADIZMNUJ WERHOEW IN VEN TOR.

A TTOR/VE Y Patented May 16, 1950 ELECTRONIC MICROSCOPE Adrianusverhoeff, Eindhoven, Netherlands, as-

signor to Hartford National Bank and Trust Company, Hartford, Conn, as trustee Application May 7, 1948, Serial No. 25,611 In the Netherlands July 8, 1947 3 Claims.

This invention relates to an electronic microscope comprising a lock device for the introduction of the object to be reproduced into the beam of rays. It is common practice to house the object in a space which communicates through two narrow, diametrically-provided apertures for the passage of the beam of rays with the evacuated space of the microscope.

If the object is to be replaced by another, these apertures are first closed to prevent air from penetrating into the vacuous space. Upon changing the object it is desirable that as little air as possible is allowed to leak in and the change is carried out rapidly and by simple manipulations.

In a known form of construction the object holder is arranged in a space recessed in a body which exhibits rotational symmetry and which body is passed through the wall of the discharge tube in an air-tight manner. This body exactly fits in a tube, one end of which is closed and the wall of which exhibits the two said apertures for the passage of the beam of rays. Turning the body causes the apertures to be closed, whilst the object space is then brought into communication with a channel through which the object may be led to the exterior. Prior to the establishment of the communication with the vacuous space, the supply of air from the outside is shut-off, so that the amount of air that is to be evacuated by the pump is restricted to the contents of the object space.

It is furthermore known to shape the rotary body in the form of a tube, one end of which is closed, the admission of air being prevented in that the object holder closes the tube when the object is located in the beam of rays. The object holder cannot be removed until the apertures through which the object space and the vacuous space communicate with one another are closed by turning the tube.

The fit surfaces which have to ensure, in the known devices, the air-tight closure of the rotary member in the wall of the tube require accurate working which takes up much time. In order to improve this closure, a thin layer of fat is often applied to the fit surfaces. This involves the disadvantage that, upon turning the tube, the edges of the apertures scrape a small amount of fat from the opposite surface, these fat particles constituting insulating surfaces which may be electrically charged. The resulting field may provoke a variation in the direction of the electron movement, in the beam of rays and lead to disturbances in the image. True, it has previously been suggested, to close the apertures by valves of re- 2 silient material, but wear and tear of the valves may result in the edges of the apertures being soiled, which has the same harmful effect.

The object of the invention is to obviate the said disadvantages. In the electronic microscope according to the invention the object is supported by a holder which closes, in a vacuum-tight manner, the space which houses the object and which communicates with the vacuous space through two diametrical apertures, for the passage of the beam of rays. According to the invention, the object holder displaces a movable member which, subsequent to the removal of the holder, brings about the air-tight closure of the object space.

In one of the known devices precautions have been taken to prevent the object from being removed while the object space still communicates with the vacuous space. This is not required in the microscope according to the inven tion, so that material simplification of the construction is rendered possible.

The invention will now be explained more fully with reference to the accompanying drawing in which Fig. 1 is a sectional view of the lock device, the object being in a position in which the electron beam is capable of passing through it, whereas Fig. 2 shows the same device the object holder being withdrawn to such extent that the object space is precisely closed.

The part of the discharge tube adjacent the lock device has a cylindrical metal wall I, which constitutes the upright edge of a circular metal plate 2, by which the vacuous space of the microscope is divided into two parts. The plate is provided with aperture 3 to allow the passage of the electron beam. The plate has furthermore provided in it two diametrically opposite channels 4 and 5, the channel 5 being larger in diameter than the channel 4. The former extends beyond the aperture 3.

The bore 4 contains the object holder 6, one end of which is provided with a handle or knob l, to enable it to be shifted to and fro and turned. In the aperture 4 a perforated and threaded plug 8 is secured to the wall of the tube and presses against a ring 9 of resilient material, which thus embraces the object holder hermetically.

With its other end, to which, in addition, the object is secured, theobject holder 6 forces a member ID, housed in the space 5 so as to be slidable against a guide bush [4, so as to allow the electron beam to strike the object through the aperture 3. Upon removing the object holder, this member is displaced under the action of the pressure of a. spring l3, in the direction of the object holder 6 until it engages the edges of the channel 4, thus closing the aperture thereof in an air-tight manner.

In Fig. 2 this closure has just been effected. The object holder 6 is now adapted to be entirely removed without air being permitted to leak in through the aperture 4. If then, the object holder is introduced through the channel 4, the air contained therein will escape to the exterior through a groove ll provided in the surface of the object holder. This groove does not extend throughout the length of the holder. The instant when the object holder engages the member It), the end of the groove has passed the resilient ring 9 and the outlet of air is shut off. Then the channel 4 and the groove ll still contain a. small amount of air at the end of the object holder, this air flowing into the vacuous space when the object holder 6 is moved on, However, this amount of air may be extremely small. The holder is moved to such an extent that the closing member abuts against the guide bush [4, which is secured to the screw cap 52, with which the channel 5 is closed. During this movement the pressure of the spring [3 is required to be surmounted.

Turning the screw cap 8 permits the pressure of the resilient ring 9 upon the object holder 6 to be increased at will and hence the frictional resistance of the object holder to be caused to exceed the pressure of the spring, so that there need be no risk of the object holder being displaced by the spring pressure exerted. By adjusting the screw cap l2 it may be ensured that, in the inward position of the closing member, the object occupies the correct position in the beam of rays.

The correct position of the object with respect to the direction of passage of the beam of rays be checked externally by providing a mark on the knob I.

What I claim is:

1. In an electron microscope, a lock device for the introduction of an object into the field of said microscope, said lock device having means including opposing wall portions enclosing a, first vacuous and a second vacuous space, a plate member extending transversely between the said opposing wall portions and interposed between said first vacuous space and the said second vacuous space and having an aperture connecting the said vacuous spaces, one wall portion and the plate member having internal surface means defining .a passage therethrough which passage also extends transversely to the said wall portions and forms with the said aperture in said plate member an object space, an object holder in said passage and slidably'engaging the surface means thereof and hermetically sealing the said object space: from the exterior of the said lock device inthe operative position of the said objectholder, a plug member, means supporting said plug member in said passage and in compressive relation withsaid object holder in the operative position of said object holder whereby upon removal of said object holder the said plug member is moved tossed the said aperture. V

2. In an electron microscope, a look device for 4 the introduction of an object into the field of said microscope, said lock device having means including opposing wall portions enclosing a first vacuous and a second vacuous space, a plate member extending transversely between the said opposing wall portions and interposed between said first vacuous space and the said second vacuous space and having an aperture connecting the said vacuous spaces, one wall portion and the plate member having internal surface means defining a passage therethrough which assage also extends transversely to the said wall portions and forms with the said aperture in said plate member an object space, abutment means defining one end of said object space, an object holder in said passage and slidably engaging the surface means thereof and hermetically sealing the said object space from the exterior of the said lock device in the operative position of the said object holder, a plug member, means supporting the said plug member in said passage and in compressive relation with said object holder in the operative position of said object holder whereby upon removal of said object holder the said plug member is moved to seal the said aperture at the said abutment means.

3. In an electron microscope, a lock device for the introduction of an object into the field of said microscope, said lock device having means including opposing wall portions enclosing a first vacuous and a second vacuous space, a plate member extending transversely between the said opposing wall portions and interposed between said first vacuous space and the said second vacuous space and having an aperture connecting the said vacuous spaces, one wall portion and the plate member having internal surface means defining a passage therethrough which passage also extends transversely to the said wall portions and forms with the said aperture in said plate member an object space, outwardly tapering abutment surface portions of said internal surface means defining onev end of said object space, an object holder in said passage and slidably engaging the surface means thereof and hermetically sealing the said object space from the exterior of the said lock device in the operative position of the said object holder, a plug member, means supporting the said plug member in said passage and in compressive relation with said object holder in the operative position of said object holder whereby upon removal of said object holder the said plug member is moved to seal the said aperture at said outwardly tapering abutment surface portions.

ADRIANUS VERHOEFF.

EEFERENiJES CITED The following references are of record in the file of this patent:

UNITED STATES PA I.d.NTS

Number Name Date 2,264,209 Krause Nov. 25, 1941 2,254,210 Krause Nov. 25, 1941 2,272,843 Hillier Feb. 10, 1942

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