Sample holder for electron microscopy

The apparatus is for use with an electron microscope, a sample, a source of high pressure gas and a vacuum pump system. The apparatus includes a holder part a body part and a Joule-Thomson refrigerator. The holder part is adapted to receive the sample and adapted to present the sample to the microscope for inspection in use. The body part defines a cavity, the cavity being evacuated by the vacuum pump system for use. The refrigerator is disposed within the cavity and thermally-coupled to the holder part, the refrigerator being coupled in use to the source of high pressure gas to maintain the sample at about a predetermined temperature.

FIELD

The invention relates to the field of electron microscopy.

BACKGROUND

In the field of electron microscopy, it is known to cool a sample by thermally coupling a supply of liquid nitrogen to the receptacle in which the sample is housed.

SUMMARY

Forming one aspect of the invention is apparatus for use with an electron microscope, a sample, a source of high pressure gas and a vacuum pump system, the apparatus comprising: a holder part adapted to receive the sample and adapted to present the sample to the microscope for inspection in use; a body part defining a cavity, the cavity being evacuated by the vacuum pump system for use; and a Joule-Thomson refrigerator disposed within the cavity and thermally-coupled to the holder part, the refrigerator being coupled in use to the source of high pressure gas to maintain the sample at about a predetermined temperature.

According to another aspect, the holder part can comprise a sampling end, the sampling end being adapted to receive the sample.

According to another aspect, the apparatus can further comprise a conductor, the refrigerator being thermally-coupled to the sampling end by the conductor.

According to another aspect, the conductor can be flexible.

According to another aspect, the body part can be releasably coupled to the holder part and coupled to the refrigerator, the conductor being sized and dimensioned to permit, if the body part and the holder part are separated and operatively positioned, connection of the conductor to one or more of the body part and the holder part.

According to another aspect, the apparatus can further comprise a screw-operated lamp operatively connected to the refrigerator and adapted to permit said connection of the conductor.

According to another aspect, the holder part can comprise an insulator having a passage and constructed of thermally insulating material, the refrigerator and the sampling end being thermally coupled via the passage.

Advantages, features and characteristics of the invention will become apparent upon review of the following detailed description with reference to the appended drawings, the latter being briefly described hereinafter.

DETAILED DESCRIPTION

An embodiment20of the invention: is shown inFIGS. 1-6; will be understood to be used with an electron microscope, a sample, a source of high pressure nitrogen gas and a vacuum pump system; and will be seen to include a holder part22, a body part24and a refrigeration part26.

Holder Part

The holder part22will be seen to include a rod28, an insulator23, a casing30, a shaft seal32, a flange seal34and a plurality of bolts36.

The rod28is oxygen-free copper and has a sampling end38, a terminal end40and a central portion42. The sampling end38has defined therein three recesses44adapted to suit standard 3 mm diameter copper meshes. The terminal end40is provided with threads46. The central portion42extends from the sampling end38to the terminal end40and includes a frustoconical portion48and an externally threaded portion50, the threaded portion50being intermediate the frustoconical portion48and the terminal end40.

The insulator29is constructed of thermally insulating material and has: a passage, more particularly, a central bore52in which the rod28is positioned such that the sampling end38protrudes therefrom; a threaded central portion54in receipt of the threaded portion50of rod28; a frustoconical mouth56sealingly receiving the frustoconical portion48of the rod28; and a flanged end58through which protrudes the threaded terminal end40of the rod and which has throughbores60defined therethrough.

The casing30is hollow and has: the sampling end38protruding through one end; a peripheral groove62; and a flanged end64. The flanged end64has a recess66defined therein, throughbores68defined therethrough and threaded sockets70defined therein, the recess66being in receipt of the flanged end58of the insulator.

The shaft seal2is an O-ring disposed in the peripheral groove62.

The flange seal34is an O-ring disposed between the flanged end58of the insulator and the flanged end64of the casing to provide for a hermetic seal therebetween.

The bolts36pass through the throughbores f the insulator and n the threaded sockets70of the casing to rigidly connect the same.

Body Part

The body part24incudes a shell72, a plurality of bolts74and a body seal76.

The shell72is tubular and defines a port78with a shut-off valve79and a central cavity80with opposed apertures8Z each bounded by a rim84having threaded sockets86defined therein, one of the rims having a depression88therein.

The body seal76is an o-ring that hem t seals the rim to the flanged end64of the casing.

Refrigeration Part

The refrigeration part26includes a refrigeration mechanism90, a clamp92, a flexible con r94, a joint96, an end seal98and a plurality of bolts100.

The refrigeration mechanism90is a Joule-Thomson refrigerator: having extending therefrom a plurality of connections102; terminating in a cooling plate104; operating at 125 bar nitrogen; and having a flanged end106having defined therethrough a plurality of throughbores108, the flanged end being disposed in the depression88and the cooling plate being disposed in the cavity80.

The clamp92includes a pair of plates1143,112, a bolt114, a nut116and a member118. The plates110,112are secured to the member118in spaced relation to one another and are in gripping, thermally communication relation to the cooling plate104. One of the plates110has a bore120therethrough. The bolt114passes through the bore110to the nut116.

The flexible conductor94is a length of soft braid of copper sandwiched at one end between the bolt114and the plate110.

The joint96is a bolt to which the flexible conductor extends and is securely connected in thermally conductive relation thereto, the joint96being threadingly connected to the terminal end40of the rod28.

The end seal99is disposed between the flanged end108of the refrigerator a the rim84of the shell72and provides a hermetic seal therebetween.

The bolts100pass through the throughbores108into threaded sockets86and securely connect the refrigerator90to rim84of the shell72.

Cryogenic Use

In cryogenic use (not shown), the gas supply is coupled to the connections102to provide high pressure gas to the refrigerator to produce the cooling necessary to maintain cryogenic conditions of the specimen. The necessary vacuum environment in the cavity [<10−6bar] is attained by connecting port78to a vacuum pump system. (it will be understood that the vacuum pump system need not necessarily be connected or in operation when refrigerator is working; the chamber80can be isolated from the vacuum pump system via shut off valve79).

Experimental

Scanning tunneling microscopy images of a sample positioned on the cooling plate104of a Joule-Thomson refrigerator90showed sub-nanometer resolution, thereby demonstrates minimal vibration in the longitudinal direction. This is probative of the utility of the Joule-Thomson refrigerator in the present context when coupled with a conductor adapted to resist translation of vibration, at least in the transverse direction.

Advantages

Persons of ordinary skill will readily appreciate that the foregoing structure provides significant advantages, including: no temperature drift associated with evaporation of liquid nitrogen in a Dewar flask, no vibration associated with liquid nitrogen bubbles; no limitations upon rotation/angle of the sample; relatively fast cool-down and warm up time [<15 min]; and relatively low cost operation.

Variants

The rod can be sealed to the insulator, for example, by an o-ring122, as shown inFIG. 7andFIG. 8.

The bolts coupling the casing to the insulator can also be omitted, as indicated byFIG. 9.

The terminal end of the rod can be provided with an internal, rather than an external thread, to permit connection of the conductor with a bolt124, as indicated byFIG. 10. The conductor could also be soldered or glued at each, end, as shown inFIG. 11.

Further variations are possible.

For example, whereas a copper rod is specified, other materials, such as aluminum, silver, etc., can be employed.

Further, whereas a seal between the rod and insulator is provided by the threaded connection therebetween and the frustoconical interface, other seals, such as glue, epoxy, etc. are possible.

The insulator could be any non-magnetic and low thermal conductivity material, such as Inconel, Ti6Al4V, poly-paraphenylene-terephthalamide, polyimide, polyamide, polyamide-imides, polytetrafluoroethylene, etc. The insulator could also take other forms, need not include a cylindrical bore in close-fitting relation to the rod and need not be formed entirely cut of low thermal conductivity material.

Of course, whereas the holder part is specified to receive 3 mm copper meshes, the holder part could be modified to accept other supports; and it could also have less or more than three recesses.

Gases other than nitrogen can be used, such as argon, methane, etc. Gas mixtures can also be used, as can gas at pressures other than 125 bar.

The conductor need not be braided, need not be copper and need not be completely or partially flexible.

The shell need not be tubular.

The rod and refrigerator could be oriented at any angle.

The apparatus can be used at temperatures other than cryogenic, temperatures as low as about 10K can be achieved with a Joule-Thomson refrigerator and heating is also possible in relatively high temperature conditions by the use of electrical connections, i.e up to about 500K.

The holder part and body part need not be separate and could be constructed integrally.

Whereas a vacuum pump system is mentioned, it will be understood that this term should be understood to encompass any structure capable of functioning in the manner of a vacuum pump to evacuate the chamber and need not even include a pump.

Accordingly, the invention will be understood to be limited only by the accompanying purposively construed.