Specimen transfer container for ion microprobe mass analyzer

Abstract

This invention is directed to a specimen holder for use with an ion microprobe mass analyzer. The specimen holder provides for the transfer of the specimen from an inert atmosphere to the analyzer without exposing the specimen to an atmosphere reactive therewith prior to analysis of the specimen.

Government Interests

The present invention relates generally to a specimen holder for housing a reactive and/or hygroscopic specimen in an ion microprobe analyzer, and more particularly to such a specimen holder for transferring the specimen from an inert atmosphere to the analyzer without exposing the specimen to a specimen-contaminating environment. This invention was made in the course of, or under, a contract with the United States Atomic Energy Commission.

Description

The ion microprobe mass analyzer has proven to be a valuable instrument for surface studies of many metallic materials and other substances such as semiconductors and geological specimens. In the operation of the ion microprobe a few layers of atoms are removed from the surface of the specimen by ion bombardment sputtering. As these atoms are removed they are simultaneously analyzed to determine the mass-to-charge ratio of the atoms.

In order to obtain an accurate analysis of the specimen surface, it is imperative that a specimen which is reactive and/or hygroscopic with atmospheric gases and substances be appropriately shielded from the atmosphere from the time it is mounted in the specimen holder through the specimen analysis. This shielding of the specimen from the atmosphere has limited the applicability of the analyzer since, by design, the sample-holding chamber in the analyzer is vented to atmosphere each time a specimen is placed in the chamber. Further, there has previously been a problem in transferring the specimen from an inert environment such as a dry box where the specimen is loaded in the specimen holder to the specimen-analyzing chamber in the analyzer without exposing the specimen to the atmosphere. Such exposures which result in reactions between the specimen and the atmosphere cause the analysis of the specimen to be inaccurate.

Accordingly, it is the primary aim or objective of the present invention to provide a specimen holder for use in an ion microprobe mass analyzer whereby the holder shields the specimen from reactive atmosphere constituents during transfer of the specimen from a specimen-loading chamber having an environment inert to the specimen into the specimen-analyzing chamber. The specimen holder also shields the specimen while it is in the analyzing chamber until the atmosphere containing reactants therein is evacuated. The specimen holder capable of accomplishing these goals comprises a housing having a receptacle at one end thereof for receiving a specimen container, sealing means at said end of the housing disposed about said receptacle, lid or cover means adapted to be disposed over said receptacle at said one end thereof in a contacting relationship with said sealing means, a passageway projecting into said housing so as to place the receptacle in registry with a source of vacuum for evacuating said receptacle and pulling said cover means against said sealing means for enclosing said receptacle, and valve means in registry with said passageway for selectively opening and closing the latter, with said cover means being affixed to said housing upon evacuation of said receptacle and closing of said passageway by said valve means.

Other and further objects of the invention will be obvious upon an understanding of the illustrative embodiment about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

A preferred embodiment of the invention has been chosen for the purpose of illustration and description. The preferred embodiment illustrated is not intended to be exhaustive or to limit the invention to the precise form disclosed. It is chosen and described in order to best explain the principles of the invention and their application in practical use to thereby enable others skilled in the art to best utilize the invention in various embodiments and modifications as are best adapted to the particular use contemplated.

In the accompanying drawings:

FIG. 1 is an exploded perspective view partially sectioned showing the specimen holder of the present invention;

FIG. 2 is a schematic plan view of the specimen chamber in the ion microprobe analyzer showing details of the mechanism employed for clamping and removing the lid from the specimen holder; and

FIG. 3 is an elevated view of the FIG. 2 structure showing further details of the specimen holder and the lid clamping mechanism.

Described generally, the present invention is directed to a specimen or sample holder for housing a specimen to be examined in an ion microprobe analyzer. The specimen holder provides for the transfer of the specimen from an inert environment where the specimen is placed in the holder to the specimen chamber in the analyzer where the specimen is analyzed without exposing the specimen to atmosphere, which exposure may introduce deleterious contaminants in the specimen due to reactions with the atmospheric gases and/or substances. The holder also provides for isolating the specimen from atmosphere in the specimen chamber of the analyzer until the specimen chamber is evacuated. These features are achieved by loading the specimen into the holder while the latter is in a dry box or other suitable inert environment, placing a lid on the holder over the specimen and then evacuating the internal cavities of the holder for clamping the lid against the holder. This vacuum is then maintained within the holder during the transfer and the evacuation of the specimen chamber in the analyzer. When the pressure in the analyzer is reduced to a value lower than that in the holder, the lid is released and a lid clamping mechanism holds the lid in place while the remainder of the specimen holder is rotated away.

Described more specifically and with reference to the accompanying drawings, the specimen holder of the present invention as generally shown at 10 comprises a cylindrical base portion 12 containing a centrally-disposed, cup-shaped recess or receptacle 14 extending to approximately the middle of the base portion and having a flat inner surface 15. A specimen-carrying block 16, which is of a cylindrical configuration of a diameter slightly less than the diameter of the receptacle 14, is adapted to be housed within the receptacle 14 in a loose-fitting, easily removable manner. This block 16 is, in turn, provided with a closed-end cavity 18 for receiving a specimen as generally indicated at 20. With the block 16 placed within the cavity 14, the upper surface 21 of the base portion is above the upper surface of the block 16. The upper surface 21 is essentially flat about the entire circumference defining this surface for receiving a lid or cover 22 which is of a cross section generally corresponding to the outer diameter of the base portion 12. With the specimen-carrying block 16 disposed within the receptacle 14, the lid 22 is placed on surface 21 and a vacuum is coupled to the base portion for evacuating the receptacle 14. This vacuum is applied by providing the base portion 12 with a throughgoing passageway 24 which is in registry with the lower surface 15 of the receptacle as shown. The communication with the receptacle through the passageway is selectively interrupted by a simple valve mechanism shown at 26 which is a threaded structure receivable in a threaded aperture 31 in the base portion and provided with longitudinally spaced-apart seals 28 and 30 for blocking the passageway 24 so as to maintain the interior of the receptacle at a pressure less than atmospheric pressure. To assure that the receptacle 14 can be adequately evacuated, the block 16 is provided with a plurality of throughgoing apertures such as the six shown at 32. Thus, with a vacuum being drawn from a suitable vacuum source (not shown) through passageway 32, the lid 22 is pulled against the surface 21 of the base portion. To assure that the lid is secured to the base portion by the differential pressure caused by the vacuum within the receptacle, a suitable seal such as an O-ring 34 is disposed in the surface 21 of the base portion about the receptacle 14.

With the specimen 20 loaded in the specimen holder and the lid clamped in place by evacuating the receptacle to a pressure in the range of 10 to 50 millitorrs, the specimen is transferred to the ion microprobe analyzer sample chamber generally shown at 37 in FIG. 2. This specimen chamber 37 is provided with a rotatable disc 39 which is provided with a number of receptacles 41 of a diameter sufficient for receiving the specimen holder 10. The specimen holder is disposed in a suitable receptacle 41 and the lid 22 of the specimen holder is fastened to a suitable lid clamping mechanism 43 for removing the lid when the pressure in the chamber is reduced to a pressure lower than that within receptacle 14 so as to release the clamping action provided by the aforementioned differential pressure. This lid clamping mechanism comprises a pivotable arm 45 having an elongated slot 47 therein for receiving a flange 49 on the lid 22. As shown, this flange 49 is off-set from the major portion of the lid but, if desired, this flange can be straight or disposed in any other satisfactory orientation. When the arm 45 is pivoted so that the flange 49 projects into the slot 47, a suitable lid-retaining mechanism, such as shown by screws 51, is activated to lock the lid in the clamping mechanism 43. A sliding key 52 held by screw 53 slides into a slot 54 in the pivotable arm 45 to hold the arm in position when the lid is clamped. With the lid properly clamped, the pressure within the ion microprobe specimen chamber is reduced to a pressure in the range of about 10.sup.-.sup.6 to 10.sup.-.sup.7 torr. Inasmuch as this pressure is less than the vacuum within the holder, the lid is released from the surface 21 of the specimen holder but held in place in the chamber 37 by the clamping mechanism 43. When this release becomes effective or any other suitable time thereafter, the disc 39 is selectively rotated to position the specimen in the proper location within the analyzer so as to undergo the desired testing.

In a typical operation of an ion microprobe analyzer using the specimen holder of the present invention, a sample of anhydrous lithium hydroxide (LiOH) was examined for water content. The LiOH powder was transferred from a sealed container to the cavity 18 in block 16 of the holder while in an argon-filled dry box containing less than 1.5 ppm water. The block 16 carrying the powder was then mounted in the receptacle of the holder and the lid 22 placed over the receptacle 18. The specimen holder was then evacuated to 5 .times. 10.sup.-.sup.2 torr pressure for securing and sealing the lid to the holder base 12. The mounted LiOH sample was then transferred in the vacuum atmosphere of the specimen holder to the ion microprobe sample chamber 37 where the lid was fastened to the lid clamping mechanism 43 by the screws 51. After the pressure in the instrument was reduced to 5 .times. 10.sup.-.sup.7 torr, the specimen holder was rotated from under the lid into the position required for examining the powder sample.

It will be seen that the present invention provides a relatively simple solution to the problems of specimen contamination as heretofore encountered since the sample or specimen holder readily provides for the transfer of the specimen from an inert atmosphere to the ion microprobe analyzer without the exposure of the specimen to the surrounding environment. This isolation of the specimen from the surrounding environment is maintained during the evacuation of the analyzer to assure that no air-borne contaminant contacts the specimen prior to analysis by the instrument.

As various changes may be made in the form, construction, and arrangement of the parts herein without departing from the spirit and scope of the invention and without sacrificing any of its advantages, it is to be understood that all matter herein is to be interpreted as illustrative and not in a limiting sense.

Claims

What is claimed is:

1. A specimen holder for use with an ion microprobe mass analyzer to provide for the transfer of a specimen to be analyzed from a specimen-loading facility to a specimen-analyzing chamber exhaustable to a predetermined pressure in said analyzer without exposing the specimen to an atmosphere reactive with the specimen, comprising an open housing having a receptacle at one end thereof for receiving a specimen container through the opening, sealing means at said open end of the housing disposed about said receptacle, removable lid means adapted to be disposed over said receptacle at said one end thereof in a contacting relationship with said sealing means, a passageway projecting into said housing in registry with said receptacle for placing said receptacle in communication with a source of vacuum to a pressure corresponding to said predetermined pressure for evacuating said receptacle and pulling said lid means against said sealing means for enclosing said receptacle, and valve means in registry with said passageway for selectively opening and closing said passageway, with said lid means being affixed to said housing upon evacuation of said receptacle and closing of said passageway by said valve means, whereby when said holder is positioned within the analyzer chamber and when said chamber is at said predetermined pressure, the cover is released from said contacting relationship with said sealing means so that the specimen may be analyzed.

2. The specimen holder claimed in claim 1, wherein said specimen container comprises a specimen-carrying block having a closed-end cavity therein for receiving the specimen, a plurality of apertures projecting through said block adjacent to said cavity, and wherein said block is disposed fully within said receptacle with said cavity opening towards said lid means and with said apertures projecting between said lid means and the innermost surface of said receptacle.

3. The specimen holder claimed in claim 2, wherein, in combination, lid clamping means are disposed within said specimen-analyzing chamber for receiving and securing said lid means to provide for selective displacement of said housing from said lid means.

4. The specimen holder claimed in claim 3, wherein said specimen-analyzing chamber has a rotatable disc disposed therein with said disc having a receptacle therein for receiving said specimen holder, said lid means has a flange projecting therefrom, said lid clamping means has a pivotable arm thereon having a slot therein for receiving said flange, and wherein clamping means project into said slot for securing said lid means to said arm.