WO1999015886A1

WO1999015886A1 - Sample holder device

Info

Publication number: WO1999015886A1
Application number: PCT/GB1998/002878
Authority: WO
Inventors: Richard Edward Palmer; Peter Georg Laitenberger; Jens Schmidt
Original assignee: The University Of Birmingham
Priority date: 1997-09-24
Filing date: 1998-09-24
Publication date: 1999-04-01
Also published as: GB9720220D0

Abstract

A sample holder device comprises a sample holder (10) and a support (12) which receives and supports the sample holder (10). A hollow body (16) of the sample holder (10) has an abutment surface (24) for engagement with a corresponding abutment surface (50) of the support (12) and is internally screw-threaded for engagement of a correspondingly screw-threaded sleeve (32) on the support (12). The axis of screw-threading on said sleeve (32) extends perpendicularly to the abutment surface (24) on the body (16). The sample holder (10) has an end wall (18) defining a sample-receiving surface to which a sample (S) can be secured by clamps (20). The sample holder (10) is rotatable about the axis of screw-threading to engage the screw-threaded formation thereon with the screw-threaded sleeve (32) on the support (12) so that the sample holder (10) can be detachably secured to the support (12) with the abutment surfaces in mutual engagement.

Description

SAMPLE HOLDER DEVICE

This invention relates to a sample holder device for holding a sample in a vacuum chamber, particularly an ultra high vacuum (UHV) chamber.

The preparation of clean surfaces for surface science experiments in a UHV chamber almost always involves heating of the sample to temperatures of several hundred degrees above room temperature. On the other hand, cooling to low temperatures is also often desirable in order to be able to investigate low-temperature surface phenomena. An increasing number of investigations also rely on the transfer of samples into the UHV chamber. The sample is usually attached to a magnetic transfer rod of a transfer device and, after introduction into the UHV chamber, brought into place for experimental analysis using the transfer device.

H-J Druin et al, Rev. Sci. Instru, 60(6), June, 1989, pages 1 167-1 168 disclose a sample holder device in which a mobile sample holder has an upper planar surface to which the sample is clamped and also has a pair of lower spaced ramp surfaces and an end wall. The end wall has a central aperture therethrough whose axis extends parallel to and below the upper planar surface and between the ramp surfaces. The mobile sample holder is engageable with a support (or fixed sample holder) having corresponding ramp surfaces and an end wall with an internally screw- threaded fixing hole therein. A separate mounting screw is engaged in the central aperture in the mobile sample holder and has a screw-threaded shank which is engaged in the screw-threaded fixed hole in the support. The head of the screw is engageable with a screwdriver bit provided on a carrier mounted on the end of a rotatable and slidable transfer rod. The carrier has a pair of pins which extend forwardly of the rod to engage detachably in small apertures in the end wall on either side of the central aperture in the mobile sample holder. In this way, the mobile sample holder is mounted on the carrier for movement into engagement with the fixed sample holder, and rotation of the magnetic rod can be effected to engage the screw with the screw-threaded fixed hole in the fixed sample holder whereby the two holders can be clamped together with their ramp surfaces in mutual engagement.

The sample is heated by a heating filament which extends upwardly between the ramp surfaces to terminate just below the upper planar surface where the sample is carried. However, such a sample holding device is not particularly suitable for use in electron spectroscopy experiments (in particular high resolution electron energy loss spectroscopy - HREELS) in a UHV chamber using non-magnetic, high temperature resistant materials where there is a small scattering chamber which permits only the insertion of holders of about 20-25mm width in the plane of the sample.

It is therefore an object of the present invention to provide a sample holder device which can be of a more compact design.

According to the present invention, there is provided a sample holder device comprising a sample holder and a support adapted to receive and support the sample holder; wherein (a) the sample holder comprises a body having (i) an abutment surface for engagement with a corresponding abutment surface of the support, (ii) a screw-threaded formation for engagement with a corresponding screw-threaded formation on the support, the axis of screw-threading on said formation extending perpendicularly to the abutment surface on the body, and (iii) a sample- receiving surface (preferably defined by an end wall of the body opposite to the abutment surface) adapted to receive a sample; (b) means are provided for securing the sample to the sample-receiving surface; and (c) the sample holder is rotatable about the axis of screw-threading to engage the screw-threaded formation thereon with the screw-threaded formation on the support so that the sample holder can be detachably secured to the support with the abutment surfaces in mutual engagement.

Such an arrangement can be made very compact laterally of the axis of screw-engagement and a very effective thermal connection between the sample holder and the support can be obtained via the mutually engaging screw-threaded formations and the mutually engaging abutment surfaces.

Depending upon its intended use, the sample holder device may be formed of non-magnetic, high temperature resistant materials.

To increase the axial compactness of the device, it is particularly preferred for the screw-threaded formation on the sample holder to be of the female- type and the screw-threaded formation on the support to be of the male- type. With such an arrangement, the male-type screw-threaded formation on the support can be provided on a sleeve which is engageable within the sample holder.

An electron source such as a filament may be located within the sleeve so that the source can be positioned, in use, very close to the sample.

It is preferred for the sleeve to be lined with a dielectric material, for example an alumina tube, which is capable of charging up during heating and of focusing the electron beam from the source onto the sample, whereby to prevent direct bombardment of the support and sample holder. Isolated electrical contact means may be provided between the support and the sample holder to enable temperature measurements to be made with a thermocouple which is to be positioned adjacent the sample in use.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing, in which:- Fig 1 is a perspective view of a sample holder device according to the present invention shown together with a transfer fork for transferring a sample carried on a sample holder of the device into a UHV chamber, and Fig 2 is a part-sectional side view of the device of Fig 1.

Referring now to the drawings, the sample holder device comprises a sample holder indicated generally by reference numeral 10, and a support 12. Also shown in Fig 1 is a transfer fork 14 of a device for transferring the sample holder 10 carrying a sample S into a UHV chamber (not shown) in which the support 12 is fixedly mounted in use.

In this particular embodiment, the UHV chamber forms part of a multi- chamber UHV system equipped with facilities for Auger electron spectroscopy, X-ray photoelectron spectroscopy, low energy electron diffraction and HREELS and has been used successfully to investigate growth of C₆₀ films on silicon surfaces.

The sample holder 10 comprises an internally screw-threaded hollow cup- shaped body 16 having an end wall 18 with a window 19 therein. The hollow body 16 is formed of tantalum to prevent it from siezing on the support 12 which is formed of molybdenum. The outer surface of the end wall 18 forms a sample-receiving surface against which the sample S is clamped by clamping plates 20 held by screws 22 engaging in internally screw-threaded bores in the end wall 18. The clamp plates 20 are formed of molybdenum. As can be seen from Fig 2, the sample S is positioned over the window 19. At the opposite end of the hollow body 16 to the end wall 18, a rim around the internally screw-threaded recess defines an abutment surface 24 which is polished to provide a smooth surface lying in a plane exactly perpendicular to the axis of the screw-threading in the body 16.

A pair of mounting screws 26 are mounted on the upper side of the body 16 and carry respective beryllium-copper contact springs 28 which are electrically isolated from the screw 26 and the body 16 by way of alumina isolating washers 29. The sides of the body 16 have flats thereon (see Fig. 1 ) to reduce the width of the sample holder 10 to a minimum.

The support 12 comprises a stepped plate 30 having a laterally projecting sleeve 32 formed integrally therewith and extending laterally of the plate 30. The sleeve 32 is externally screw-threaded for engagement with the internal screw-threading in the hollow cup-shaped body 16. The interior of the sleeve 32 is lined with an alumina tube 34. A filament 36 is mounted within the sleeve 32 and terminates just short of the free end of the sleeve 32.

The stepped plate 30 carries a pair of beryllium-copper contact plates 38. The contact plates 38 are mounted on the stepped plate 30 via respective pairs of mounting screws 30 fitted with electrically insulating alumina washers 42. That region of the stepped plate 30 which is remote from the sleeve 32 is coupled to a supporting carrier 46 in the form of a copper cooling block. Coupling is effected through the intermediary of a thin sapphire plate 48. The carrier 46, in use, is cooled with liquid nitrogen and the sapphire plate 48 acts as a thermal switch. When cooling of the sample S is required, the carrier 46 is cooled with liquid nitrogen and this renders the sapphire plate 48 thermally conductive so that cooling of the sample S can rapidly take place. In contrast, under high temperature conditions, the sapphire plate 48 acts as a thermal barrier. In both cases, the sapphire plate 48 is an electrical insulator.

The surface of the plate 30 which surrounds the sleeve 32 and which faces the abutment surface 24 is accurately machined and polished so as to define an abutment surface 50 which is accurately perpendicular to the axis of the screw-threading on the sleeve 32.

Referring now to Fig 1 , the transfer fork 14 is mounted on the inner end of an elongate rod 60 (only partly shown) which is slidably and rotatably mounted relative to the UHV chamber (not shown). The transfer fork 14 comprises a first circular flange 62 fixedly mounted on the end of the rod 60 and a second circular flange 64 which is slidably mounted on three support posts 66 extending from the first flange 62. Springs 68 are mounted on the posts 66 and serve to bias the flange 64 resilently away from the flange 62 against retaining nuts 69 on the posts 66. The movable flange 64 carries a pair of spaced support pins 70. The pins 70 are disposed mutually diametrically relative to the axis of rotation of the rod 60 and are engageable in respective bores 72 in the body 16 of the sample holder 10. In this particular embodiment, the pins 70 are standard 2mm gold-coated beryllium-copper pins used for electrical connections. When disposed in the bores 72, the pins 70 serve to hold the hollow body 16 and sample S securely on the transfer fork 14 whilst at the same time allowing easy insertion and retraction of the fork 14. The spring loading of the flange 64 relative to the flange 62 permits some lateral movement of the sample holder 10 relative to the support 12 during fixing so that exact alignment of the sample holder 10 with the support 12 is not an essential requirement. This transfer fork device allows convenient and simple transfer of samples of dimensions up to 10 x 12mm² with only visual alignment between the support 12 and the rod 60.

In use, it is to be appreciated that the sample S is first attached to the sample holder 10 outside the UHV chamber. The sample holder 10, with the sample S attached, is then mounted on the transfer fork 14 when the latter is outside the UHV chamber. The rod 60 is then extended so as to transfer the sample holder 10 into the UHV chamber until it abuts against the sleeve 32 of the support 12. Rotation of the rod 60 then causes rotation of the sample holder 10 and engagement of the internal screw- threading in the body 16 with the externally screw-threaded sleeve 32. Rotation is continued until the abutment surfaces 24 and 50 are brought into mutual engagement. These surfaces 24 and 50 are accurately machined and polished so that they come into full and close contact when the hollow body 16 is in the correct angular orientation relative to the support 12. This means that the sample S is correctly orientated relative to the filament 36 and the contact springs 28 are properly engaged with the respective contact plates 38.

Because of the closely engaging abutment surfaces 24 and 50 and because of the screw-engagement between the sample holder 10 and the support 12, a very good thermal contact is ensured. The polishing of the abutment surfaces 24 and 50 serves to reduce the temperature across this junction.

The sample S, which is positioned over the circular aperture in the end wall 18, is heated by electron bombardment from the filament 36 which is located within the sleeve 32 directly behind the window 19. The sample holder 10 and sample S are biased together for heating to typically 1 kV. The alumina tube 34 around the filament 36 charges up during heating and focuses the electron beam through the window 19 against the sample S so that direct bombardment of the support 12 and sample holder 10 is avoided. The contact springs 28 and contact plates 38 serve to enable a thermocouple (not shown) positioned near to the sample S to be connected to monitoring equipment (not shown) whereby the temperature of the sample S can be monitored.

It will be appreciated that, during operation, the transfer fork 14 is disengaged from the sample holder 10 and is removed from the UHV chamber by retraction of the rod 60.

The performance of the above-described device has been tested by measuring the temperature with thermocouples directly attached to the support 12 and the sample holder 10 and use of an optical pyrometer on a silicon sample S, for low and high temperatures, respectively. In low temperature studies, by cooling the carrier 46 with liquid nitrogen, a temperature of 85K was reached on the sample holder 10 in only 20 minutes, with only a negligible temperature drop across the junction between the sample holder 10 and the support 12. In high temperature studiesd, the silicon sample S has been heated up to temperatures of 1200°C with about 60W heating power. Temperatures as high as 1400°C can be reached easily. The sample S can be maintained at temperatures of 500 to 600°C (heating power 10W) in a steady state regime in which the temperature of the carrier 46 connected to the liquid nitrogen reservoir levels out at about 200°C without liquid nitrogen cooling of the reservoir.

Claims

1. A sample holder device comprising a sample holder (10) and a support (12) adapted to receive and support the sample holder (10); wherein (a) the sample holder (10) comprises a body (16) having (i) an abutment surface (24) for engagement with a corresponding abutment surface (50) of the support (12), (ii) a screw-threaded formation for engagement with a corresponding screw-threaded formation (32) on the support (12), the axis of screw-threading on said formation (32) extending perpendicularly to the abutment surface (24) on the body (16), and (iii) a sample-receiving surface adapted to receive a sample (S); (b) means (20) are provided for securing the sample (S) to the sample-receiving surface; and (c) the sample holder (10) is rotatable about the axis of screw- threading to engage the screw-threaded formation thereon with the screw- threaded formation (32) on the support (12) so that the sample holder (10) can be detachably secured to the support (12) with the abutment surfaces in mutual engagement.

2. A device as claimed in claim 1 , wherein the sample-receiving surface on the body (16) defined by an end wall (18) of the body (16) opposite to the abutment surface (24).

3. A device as claimed in claim 1 or 2, wherein the screw-threaded formation on the sample holder (10) is of the female-type and the screw- threaded formation (32) on the support (12) is of the male-type.

4. A device as claimed in any preceding claim, wherein the screw- threaded formation on the support (12) is an externally screw-threaded sleeve (32) and an electron source (36) is located within the sleeve (32).

5. A device as claimed in claim 4, wherein the sleeve (32) is lined with a dielectric material which is capable of charging up during heating and of focusing an electron beam from the source (36) onto the sample (S), whereby to prevent direct bombardment of the support (12) and sample holder (10).

6. A device as claimed in any preceding claim, wherein isolated electrical contact means (28,38) are provided between the support (12) and the sample holder (10) to enable temperature measurements.