This invention relates electrical contacts, and in particular to electrical contacts of the type that may also form a vacuum seal between the rotating part of, for example, a cylindrical rotating magnetron sputtering device, and a static mount therefor.

In the context of this disclosure, the term "magnetron sputtering device" shall be understood to include, but not be limited to, a cylindrical magnetron sputtering, arc, laser ablation or any other plasma source where the target, target elements, electrodes, anode or cathode elements of the construction of such device are enabled to rotate in-vacuum at the same time as power is transmitted.

This invention relates to the rotational device on a cylindrical magnetron sputtering, arc, laser ablation or any other plasma source where the target, target elements, electrodes, anode or cathode elements of the construction of such device are enabled to rotate in- vacuum at the same time as power is transmitted.

The power is transmitted from an essentially static element on the atmosphere side into the vacuum side.

The power can be transmitted via electric current, electric field variations, electromagnetic wave or any combination of such power modes. The power could be transmitted on an essentially constant mode or on an essentially alternating mode, such as sinusoidal, pulsed or pulse packages. This invention also relates to the use of such rotational device for the rotation of a target, electrodes or coating elements requiring a dynamic power transmission contact and dynamic seal. This disclosure also relates to the use of the invention in vacuum plasma technology where a plasma discharge, or any other appropriate source of energy such as arcs, laser, which can be applied to the target or in its vicinity would produce suitable coating deposition or plasma treatment on components of different nature.

This invention also relates but not exclusively to the use of the device in sputtering, magnetron sputtering, arc, plasma polymerisation, laser ablation and plasma etching, PECVD. This invention also relates to the use of such devices and control during non-reactive and reactive processes, with or without feedback and plasma process control.

This invention also relates to the arrangement of these devices as a singularity or a plurality of units.

This invention also relates to the use of these devices in different power modes such as DC, DC pulsed, multi-pulsed power packages, RF, AC, AC dual, HIPIMS, microwave or any other powering mode in order to generate a plasma, such as sputtering plasma, plasma arc, electron beam evaporation, plasma polymerization plasma, plasma treatment or any other plasma generated for the purpose of a process, for example, and not exclusively, as a deposition process or surface treatment process.

BACKGROUND ART

Since the advent of rotatable cylindrical magnetron sputtering sources [SHATTERPROOF GLASS CORPORATION, US4356073, 26 ^th Feb 1982] the use of dynamic seals on the rotating cylindrical target has been a common feature across this sector of the industry. A key component for the effective functionality of the device is the ability for the device to transmit electrical power across a moving interface (rotating power transmission). The power transmission from an essentially static electrical contact to the essentially rotating element presents limitations due to the nature of rotating electrical contacts. Current state of the art [BEKAE T ADVANCED COATINGS, US2008/0087541, 17 ^th Aprt 2008] is based on either graphite or bronze brush electrical contact technology.

Known solutions, involving brush electrode contacts, present limitations in the contact asperity surface. Usually, those contacts are immersed in water and surface electrochemical reactions affect the efficacy of the power transmission. Some types of very high frequency transmission are limited because of the power loss at the contact, and by formation of wear debris. Furthermore, the transmission of very high-currents can severely limit the durability of the dynamic electrical contact.

A need therefore exists for a solution to one or more of the above problems, and/or an alternative to known brush electrical contacts. A need also exists for improvements in and relating to the operation and performance of a rotating electrical contact, especially in a plasma process involving a rotating target, electrode or coating element.

SUMMARY OF THE INVENTION

Various possible objects of the invention include those set forth in the following non- exhaustive list: to overcome some of the limitations on the current limit and power loss associated with using known static/dynamic contacts; to enhance high frequency power transmission by providing a low-impedance contact; and to obtain a low leak rate from vacuum to atmosphere in a vacuum apparatus incorporating the present invention.

Various aspects of the invention are set forth in the appended claims.

According to a first aspect of the invention, there is provided a (suitably brushless) electrical contact adapted, in use, to provide an electrical connection across a dynamic interface between a first static part and a second dynamic part, the electrical contact comprising a liquid retained and interposed between the static and dynamic parts, the liquid comprising a high electrical conductivity liquid. Preferably, the high-conductivity liquid comprises a liquid metal or a liquid alloy, that is to say, a metal or alloy that is in a liquid state at operating temperatures, which are typically temperatures of around, or greater than, 20 degrees Centigrade.

Suitably, the liquid metal comprises any one or more of the group comprising: Ga (Gallium); Gallium alloy; Gain (Gallium-Indium alloy); GalnSn (Gallium-Indium-Tin alloy); an GalnSnZn (Gallium-Indium-Tin-Zinc alloy).

Because the high electrical conductivity liquid (e.g. liquid metal) is interposed between the static and dynamic parts, it can form an effective, low-resistance pathway for the transmission of electrical power between the static and dynamic parts.

The high electrical conductivity liquid suitably presents a low friction between the static and dynamic parts. This is advantageous because it provides a lower-friction alternative to a known brush contact arrangement whereby the brush makes contact with, and exhibits a finite drag, on the dynamic part. By using a liquid in place of a brush, friction is reduced, and in certain cases, the liquid may act as a lubricant also lowering the friction (and hence drag and/or wear) between the static and dynamic parts.

Because the high electrical conductivity liquid is retained between the static and dynamic parts, it can form a seal therebetween.

Retention of the high electrical conductivity liquid can be accomplished in a variety of ways, for example, by annular seals (e.g. O-ring seals) between the static and dynamic parts. However, the provision of separate mechanical seals is preferably avoided because such seals tend to increase the rolling resistance between the static and dynamic parts. Accordingly, in a preferred embodiment of the invention, the high electrical conductivity liquid is retained by exploiting its surface tension properties, which is a particularly effective means where the high electrical conductivity liquid comprises liquid metal. Specifically, in suitable embodiments of the invention, the static part comprises a tube, which at least partially surrounds, and which rotatably receives, a tubular dynamic part. In this situation, the interior surface of the static part and the exterior surface of the dynamic part comprises aligned (in use) complementary recesses, that together form an annular cavity between the static and the dynamic part. Preferably, the interior shape and configuration, and in particular, the radii of curvature of the recesses are selected to interact with the high electrical conductivity liquid in a way that causes the high electrical conductivity liquid to be retained in the annular cavity by its surface tension. Therefore, provided any gap between the static and dynamic part is small enough, escape of the high electrical conductivity liquid via the gap is effectively inhibited or prevented. Further, because the high electrical conductivity liquid "fills" the annular cavity, it effectively covers, blocks or closes-off any such gap, thereby inhibiting or preventing the transduction of gases from one side of the high electrical conductivity liquid "fill" to the other.

In other embodiments of the invention, either or both of the static and dynamic parts comprise a flange, which flange or flanges are axially offset relative to one another and which are immersed/submerged in the high electrical conductivity liquid. The provision of flanges can be particularly beneficial because, for a small increase in volume of material of each part, they can greatly increase the surface area of the static and dynamic parts that are in contact with the high electrical conductivity liquid, thereby improving the power transmission characteristics of the contact.

In certain embodiments of the invention, the static part comprises one or more radially-inwardly-extending flanges. In certain embodiments of the invention, the dynamic part comprises one or more radially-outwardly-extending flanges. The flange or flanges of the static part may be axially offset from the flange of flanges of the dynamic part. In a preferred embodiment of the invention, however, the static and dynamic parts each comprise a plurality of respective flanges, which are interdigitated. The annular cavity described above, where provided, is suitably in fluid communication with an expansion volume or reservoir for the high electrical conductivity liquid. A portion of the expansion volume or reservoir is suitably filled with an inert gas, or is at least partially evacuated (filled with a vacuum).

The provision of an expansion volume suitably enables the high electrical conductivity liquid to expand isobarically, for example under thermal expansion or contraction. This configuration reduces the likelihood of the high electrical conductivity liquid "clamping" the dynamic part to the static part (or vice-versa) under thermal expansion.

The provision of a reservoir suitably enables there to be an excess of high electrical conductivity liquid to fill the annular cavity. This configuration may help to safeguard against the annular cavity "running dry" in the event of gradual leakage, loss or evaporation of high electrical conductivity liquid from the annular cavity.

The use of the high electrical conductivity liquid to form a seal enables the electrical power to be transmitted from an essentially static element on an atmosphere side of the apparatus in which it is installed into the vacuum side (i.e. the dynamic part located at least partially within the vacuum side of the apparatus in which it is installed).

The electrical power can be transmitted via electric current, electric field variations, electromagnetic wave or any combination of such power modes. The power could be transmitted on an essentially constant mode or on an essentially alternating mode, such as sinusoidal, pulsed or pulse packages.

In certain embodiments, the invention relates to the use of such a contact in a rotational device for the rotation of a target, electrodes or coating elements requiring a dynamic power transmission contact and dynamic seal.

This invention is particularly suitable for use in vacuum plasma technology where a plasma discharge, or any other appropriate source of energy such as arcs, laser, which can be applied to the target or in its vicinity would produce suitable coating deposition or plasma treatment on components of different nature.

This invention also relates, but not exclusively, to the use of the contact/device in sputtering, magnetron sputtering, arc, plasma polymerisation, laser ablation and plasma etching, PECVD. This invention also relates to the use of such devices and control during non- reactive and reactive processes, with or without feedback and plasma process control.

This invention also relates to the arrangement of these contacts/devices as a singularity or a plurality of units.

This invention also relates to the use of these contacts/devices in different power modes such as DC, DC pulsed, multi-pulsed power packages, F, AC, AC dual, HIPIMS, microwave or any other powering mode in order to generate a plasma, such as sputtering plasma, plasma arc, electron beam evaporation, plasma polymerization plasma, plasma treatment or any other plasma generated for the purpose of a process, for example, and not exclusively, as a deposition process or surface treatment process.

According to another aspect of the invention, there is provided an essentially cylindrical, although not exclusively, target and backing tube assembly (or target assembly) are able to rotate by appropriate driving mechanism. The power transmission from an essentially static atmospheric contact point may be carried via a dynamic electrical contact via a liquid element presenting a high electrical conductivity and low friction. The preferred liquid element is essentially a liquid metal which composes of Gallium and or Gallium alloys such as those based (or though not exclusively) on Gain, GalnSn, GalnSnZn alloys for example.

An additional sealing surface could be provided incorporating extremely low vapour pressures of the liquid elements which enhances the vacuum quality achievable by these rotating seals. A plurality of electrical contact elements and seal elements could be provided in order to maximise the power capability and sealing characteristics of the contact/device.

In one of the embodiments of the present invention, the target and backing tube assembly rotates via an appropriate engagement to a drive mechanism while the power is transmitted via the electrical liquid contact elements.

The present invention also relates to the use of the device in vacuum coating and or treatment technology where for example plasma discharge, or any other appropriate source of energy form such as arcs, laser, which can be applied to the target or in its vicinity would produce suitable coating deposition or suitable plasma treatment on components of different nature.

In particular, although not exclusively, the present invention also relates to the use of this device in conjunction with a suitable magnetic field provided by a magnetic array so that the unit could be used as a magnetron sputter source as the magnetic field over the target surface together with the biasing of the target provides a magnetron effect and under adequate conditions of rarefied vacuum atmosphere a plasma discharge can be established. The discharge producing in this case suitable vacuum treatment such as sputtering deposition, plasma etching, plasma treatment, plasma polymerisation, PECVD and other plasma treatment and process methods.

The present invention may be characterised, although not exclusively, by providing a dynamic vacuum seal with helium leak rates on the order of lE-10 mbar l/s.

The present invention may be characterized by an end block that is provided with water coolant and electric power with rotating or static contacts.

The present invention could comprise of single or a plurality of electrical contacts using elements of the present invention.

The present invention could comprise of single or a plurality of vacuum seals using elements of the present invention. This invention also relates to the use of such devices and control during non-reactive and reactive processes, with or without feedback plasma process control.

The present invention also relates to the speed of rotation of the cylindrical target, from zero (static) to any rotational speed whether it is constant, complex or variable.

The present invention also relates to the use of these devices in different operation modes such as DC, DC pulsed, AC, HIPIMS (High Power Impulse Magnetron Sputtering), MPPS (Modulated Pulsed Power Sputtering), RF, microwave and any combination of power delivery or pulse power package.

The present invention, by improving the vacuum quality, may also improve the coating product operation and final coating quality.

The present invention may relate to the use of in plasma processes such as arc, sputtering, magnetron sputtering, plasma polymerisation, plasma etching, PECVD with or without magnetic array.

The present invention may also relate to the use of laser ablation or laser guided arc techniques.

The present invention may also relate to a single device or any arrangement of any number of these contacts/devices.

The present invention may also relate to single sources used with a passive or active anode.

The present invention may also relate to the use of these devices in dual magnetron sputtering.

The present invention may also relate to reactive and non reactive sputtering, arc or magnetron sputtering processes.

The present invention may also relate to substrates that may or may not be biased. The present invention may relate to any application of this contact/device in web, glass, display, decorative and batch coaters. The present invention may also relate to the use of any number of these contacts/devices with any type of feedback control, such as rotation speed control, plasma emission monitoring control, target impedance control, partial pressure of reactive and non reactive species control, power control, power mode control, etc.

The present invention may also relate to any target construction suitable to be constructed, assembled on to and driven in the device of this invention.

Embodiments of the invention will now be described, by way of example only, with reference to the following figures in which:

Figure 1 is a cross-section of a known brush arrangement as described by US2008/0087541;

Figure 2 contains two exploded views excerpted from prior art document US2008/0087541;

Figure 3 is a simplified, schematic cross-section of a first embodiment of a brushless contact in accordance with the invention;

Figure 4 is a simplified, schematic cross-section of a second embodiment of a brushless contact in accordance with the invention;

Figure 5 is a simplified, schematic cross-section of a third embodiment of a brushless contact in accordance with the invention;

Figure 6 shows a partial longitudinal section of a sputtering apparatus incorporating brushless electrical contacts in accordance with the present invention;

Figure 7 shows a longitudinal section of a possible option for the brushless contact of the present invention;

Figure 8 is a view of the main rotating element 8 and 16 with extended electrical contact elements 13 (dynamic) and 12 (static);

Figure 9 shows a partial cross section view of the seal/contact element 14; and

Figure 10 is a vapour pressure curve for gallium. With regard to Figure 1, the original reference signs above 100 have been kept for ease of reference with the original document. New reference signs l-8b have been assigned for ease of cross-referencing to this disclosure. With regard to Figure 2, the original reference signs above 200 (for Fig 2a) and above 300 (for Fig 2b) have been kept for ease of reference with the original document. New reference signs 3,4, 4a have been assigned for ease of cross-referencing to this disclosure.

With regard to Figures 1 & 2 of the drawings, the essential static assembly 1 on the atmospheric side of the device depicted in Figure 1 is connected to the rotating element 2 (target assembly) which rotates around an axis of rotation 8b. Besides the rotation transmission; the electrical transmission between the static atmospheric contact 3 and the dynamic-rotating contact assembly 4 are fundamental for the effective operation of such device.

Referring to Figure 2, in the known device, the static atmospheric electrical contact 3 connects to a dynamic rotating electrical contact assembly 4, in which brush contact elements 4a are sprung against a cavity of the static element 3 in order to transmit the electrical power between the static and the dynamic elements. The nature of the contact is such that typically the electrodes are immersed in a coolant media, making the electrical contact more stable, but with higher impedance and being more prone to electrochemical corrosion effects during operation.

Referring now to the invention, in Figure 3, a generally tubular static electrical contact assembly 5-6 supports a rotating element 8 nested within the static electrical contact assembly 5-6. The rotating element (dynamic part) 8 is mounted for relatively free rotation within the static electrical contact assembly 5-6 (static part) about a longitudinal axis of rotation, designated 8b in the drawings. Relative axial displacement of the static part 5, 6 and the dynamic part 8 is inhibited in a known manner by thrust bearings or the like, a detailed description of which is not necessary for this disclosure.

The static part 5, 6 and the dynamic part 8 are electrically coupled to one another by a quantity of high electrical conductivity liquid 7, for example, liquid Gallium or a liquid Gallium alloy, which is retained by complementary grooves 6a, 8a formed in the interior and exterior surfaces, respectively, of the static 5, 6 and dynamic parts 8.

The high electrical conductivity liquid 7 thus maintains electrical contact and a low- friction interface between the static 5, 6 and dynamic parts 8.

Typically, high electrical conductivity liquids such as Gallium and/or Gallium alloys such as those based (or though not exclusively) on Gain, GalnSn, GalnSnZn alloys for example, have a high surface tension, and so to form a good electrical connection between the high electrical conductivity liquid 7 and the static 5, 6 and dynamic parts 8, the grooves 6a, 8a should be shaped so as to provide adequate contact area and rounded features with appropriate radii of curvature. In the illustrated embodiments, both the static part 6 and the dynamic part 8 contain features such as 6a and 8a for that purpose, that is to say, having a radius of curvature adapted to enable the high electrical conductivity liquid to "wet" them properly, as well as to "bridge" whatever small gap there may be between the static 6 and dynamic 8 parts.

Electrical contact is desired all around the rotation contact of 8, so in the cross section that could visualised by zone 11, taking the general form of a flattened toroidal cavity formed by the recesses in the static part 6 and the dynamic part 8.

In the embodiment shown in Figure 3, the cavity 11 communicates with an overflow cavity, which is partially filled by the high electrical conductivity liquid 7. The overflow cavity expands to zone 9 allowing thermal expansion of the liquid contact 7. Essentially, the liquid electrical element 7 9 high electrical conductivity liquid 7) should be kept in protective atmosphere 10, which is preferably vacuum, which favours ease of thermal expansion of the high electrical conductivity liquid 7. This protective atmosphere will provide stability to the liquid electrical contact 7 as the formation of surface oxides is restricted.

Suitable materials for constructing elements 5-6 and 8 could be varied, although the preferred material may be stainless steel. It is also possible to have conducting materials of different natures, such as copper, with surface treatments in order to decrease the chemical reactivity with high electrical conductivity liquid 7. The chemical selection of all the elements should be such that electrochemical reactions either by the chemical nature of elements or by the induced voltages on elements 5-8 do not produce detrimental reactions such as oxidation of materials. In addition, the low impedance nature of the electrical contact between static 5, 6, dynamic 8 and liquid 7 elements prevents or inhibits potentially harmful electrochemical reactions on the electrical contacts, thereby improving the stability of the contact during operation.

Figure 4 shows a schematic cross section of a variation of the brushless contact of the present invention described above in relation to Figure 3, in which there is a static electrical contact assembly 5-6 that connects electrically to the rotating element 8, which is able to rotate around the axis of rotation 8b while maintaining electrical contact and low friction. The dynamic electrical contact is achieved via a high electrical conductivity liquid 7 (liquid element 7) presenting a high electrical conductivity. The preferred liquid element would be a liquid metal which composes of Gallium and or Gallium alloys such as those based (or though not exclusively) on Gain, GalnSn, GalnSnZn alloys for example. Typically the liquid metals have a high surface tension and adequate contact area and rounded features with appropriate radius need to be inserted. Both the static part 6 and dynamic part 8 should contain features such as 6a and 8a for that purpose. The electrical contact is desired all around the rotation contact of 8, so in the cross section that could visualised by zone 11. The details of the arrangement of Figure 4, i.e. the expansion zone 9, protective atmosphere 10, materials of construction, surface treatments, etc. are as described above, and therefore do not require repetition other than to say that the same considerations apply to the embodiment of Figure 4 as they do to the embodiment of Figure 3.

In addition, however, the embodiment of Figure 4 further shows conductor elements

12 (i.e. ribs, flanges and the like, which extending into the high electrical conductivity liquid 7) which increase the surface area contact between the static element 5 and the liquid element 7. This favours the transmission of electrical current because it greatly increases the surface area of the static part in contact with the high electrical conductivity liquid 7. In addition, the lower current density produces a lower voltage differential between the elements 5, 6, 8, creating a lower probability of electrochemical reactions.

Figure 5 shows a schematic cross-section of the brushless contact of the present invention, in which the static electrical contact assembly 5-6 connects electrically to the rotating element 8, which is able to rotate around the axis of rotation 8b while maintaining electrical contact and low friction. The dynamic electrical contact is achieved via a liquid element 7 presenting a high electrical conductivity. The preferred liquid element would be a liquid metal which composes of Gallium and or Gallium alloys such as those based (or though not exclusively) on Gain, GalnSn, GalnSnZn alloys for example. Typically the liquid metals have a high surface tension and adequate contact area and rounded features with appropriate radius need to be inserted.

Both the static element 6 and dynamic element 8 should contain features such as 6a and 8a for that purpose. The electrical contact is desired all around the rotation contact of 8, so in the cross section that could visualised by zone 11.

The details of the arrangement of the embodiment shown in Figure 5, i.e. the expansion zone 9, protective atmosphere 10, materials of construction, surface treatments, etc. are as described above, and therefore do not require repetition other than to say that the same considerations apply to the embodiment of Figure 5 as they do to the embodiment of Figure 3.

In addition, however, the embodiment of Figure 5 further shows conductor elements 12, 13, which are metal ribs, flanges and the like, which extend into the high electrical conductivity liquid 7, and which increase the surface area contact between the static part 5 and the liquid 7; and between the dynamic part 8 and the liquid 7. As can be seen, the conductor elements 12, 13 are axially offset relative to one another, and are interdigitated, that is to say, alternating along the axis of rotation 8b between static part 5 conductor elements 12 and dynamic part 8 conductor elements 13. This configuration further favours the transmission of electrical current because it greatly increases the surface area of the static part in contact with the high electrical conductivity liquid 7. In addition, the lower current density produces a lower voltage differential between the elements 5, 6, 8, creating a lower probability of electrochemical reactions.

Figure 6 shows a partial longitudinal section of a sputtering apparatus incorporating electrical contacts in accordance with the present invention. The essential static assembly 1 on the atmospheric side is connected to the rotating element 2 (target assembly) which rotates around an axis of rotation 8b. Besides the rotation transmission, the electrical transmission between the static contacts 5, 12 and the dynamic-rotating contact assembly 8. Dynamic elements 13, 16, and 2 rotate around the axis of rotation 8b while maintaining a low-friction, electrical contact with the static parts via the high electrical conductivity liquid 7. Elements 13 and 2 have been described by reference to the preceding Figures, and are not further described herein to avoid unnecessary repetition.

Part 16 is an extension of dynamic element between the contact zone of 8 and the target assembly 2. The present invention presents a second feature of seal/contact 14. This feature seals the vacuum side, where elements 2 and 16 are located, from the atmosphere side, while maintaining a rotating contact. Details of this element 14 and a leak check point 15 are shown and described further with reference to Figure 9.

Figure 7 shows a longitudinal section of a possible option for the contact of the present invention, in which the static electrical contact assembly 6 connects electrically to the rotating element 8, which is able to rotate around the axis of rotation 8b while maintaining a low-friction electrical contact by virtue of the high electrical conductivity liquid 7. The dynamic electrical contact is achieved via a liquid element, which is omitted from Figure 7 for clarity. Both the static element 6 and dynamic element 8 contain conductor elements, such as 12 and 13 which increase the surface area of contact between the static element 5 and the liquid 7; and between the rotating element 8 and the liquid element 7. Rotating element 8 connects to element 16 which extends the driving rotating motion and the electrical power into the vacuum area. Adequate sealing elements 17a-17b keep the liquid electrical contact in a protective atmosphere, preventing deterioration of the electrical dynamic contact during operation.

Figure 8 is a view of the main rotating element 8 and 16 with extended electrical contact elements 13 (dynamic) and 12 (static). The rotating elements are able to rotate around the axis of rotation 8b while maintaining electrical contact, low friction and sealing. Design features of elements 12 and 13 allow breaking through any surface oxide that could be formed on the liquid electrical contact element, enhancing the electrical conductivity of the device. The zone where an additional sealing is provided 14a is also indicated. This zone could accommodate both sealing between vacuum and atmosphere and additional electrical contact, which stabilises power transmission.

Figure 9 shows a partial cross-sectional view of the seal/contact element 14. The surface contact area 14a seals against seals located in zones 14b-14c. Bearing /seal elements 14d-14e give necessary stability to the main sealing elements 14b-14c. Element 15 provides isolation from atmosphere and a leak check point for the seal. Seal elements 14b-14c could also be made out of a liquid contact with low vapour pressure, as for example described with reference to Figure 10 below.

In this case, the element 15 serves as refilling and vacuum or atmosphere protective control of the liquid seal. The preferred option would be to have a liquid seal that is also electrically conductive and presents low friction and also has an extremely low vapour pressure, in that way creating a very high efficiency vacuum seal with levels of helium leak rate below lE-10 mbar l/s. The electrical conductive nature of such seal also allows additional electrical contact point on this element which can stabilise the power transmission over long rotating elements as those seen in Figure 8.

Finally, Figure 10 is a vapour pressure curve for gallium, one of the possible liquid contacts 7 of the present invention. This material has an extremely low vapour pressure while maintaining the liquid form (in the case of pure gallium >30 degrees Centigrade), which enables the use of these materials in order to have a sealing feature maintaining very low levels of vacuum helium leak rates < lE-10 mbar. l/s. This constitutes a 100-fold improvement on the known state of the art dynamic seals, which are only able to guarantee levels <1Ε-8 mbar l/s, due to the nature of the lip seal contacts.

The invention is not restricted to the details of the foregoing embodiments, which are merely exemplary of the invention. In particular, any shapes, dimensions, materials or properties, whether express or implied are illustrative only, and are not restrictive of the scope of the invention.