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1. WO2010004275 - SAMPLE HOLDER

Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

[ EN ]

SAMPLE HOLDER

The present invention relates to a sample holder and in particular, but not exclusively, to a sample holder in the form of a membrane structure for use in a method of analysis using high- energy radiation.

The term "high energy radiation" as used herein means radiation with an energy sufficient to penetrate and be transmitted through the sample under investigation. The high energy radiation may be either electromagnetic radiation for example x-ray radiation, or particle radiation for example electron radiation. When referring to electromagnetic radiation, the term "high energy radiation" means radiation with a photon energy in the range 4OeV to lOOkeV and in particular but not exclusively in the range 12OeV to 12keV (so-called "soft" x-rays). When referring to electron radiation, the term "high energy radiation" means electrons with an energy in the range lkeV to 50 MeV and in particular but not exclusively in the range 10keV to 20 MeV.

The sample holder is intended for use in methods of analysis that may include, for example, x-ray microscopy (XRM), x-ray fluorescence (XRF), time-of-flight spectroscopy (TFS) and accelerator mass spectroscopy (AMS), as well as microscopy analysis methods such as transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM).

It is known to provide a sample holder that comprises a silicon nitride membrane supported by a silicon frame. Such a sample holder is manufactured for example by Silson Limited of Blisworth, Northants, Great Britain. In a typical example as shown in Figure 1 , the frame is square with dimensions of 7.5mm x 7.5mm and a thickness of 0.2mm, with a square central window of dimensions 3mm x 3mm. The silicon nitride membrane is supported by the frame and has the same side dimensions and a thickness of 200nm. The membrane is transparent to x-rays and high energy particles. It can serve as a sample holder for a sample supported on the upper surface of the membrane, allowing analysis of the sample for example using x- rays or high energy particles that are transmitted through the window.

It is sometimes desirable to be able to conduct an analysis of a sample while subjecting the sample to one or more external influences, and/or to measure one or more other parameters of the sample while carrying out the analysis. For example, it may be desirable to subject the sample to an electric field, to measure its electrical conductivity, and/or to control or measure its temperature. It may also be desirable to contain a liquid sample on the membrane without allowing it to leak, or to control the flow of a liquid or gas sample across the membrane. Typically, to provide such facilities it is necessary to modify the equipment used to conduct the analysis. This may be costly and/or inconvenient.

It is an object of the present invention to provide a sample holder having additional functionality that allows one or more of the additional facilities identified above, or a number of other facilities, to be provided in a less costly and/or more convenient manner.

According to the present invention there is provided a sample holder for use in a method of analysis using selected high-energy radiation, the sample holder including a frame having a window, a membrane that extends across the window and has a surface for supporting a sample, said membrane being substantially transparent to the selected high-energy radiation, and a functional structure formed on the membrane, said functional structure providing additional functionality that allows selected parameters of a sample on the support surface to be measured and/or controlled.

Incorporating a functional structure on the membrane allows selected parameters of a sample to be measured and/or controlled without physically adapting the analysis instrument. This makes it much easier, and potentially cheaper, to measure additional parameters of the sample such as its temperature or electrical resistivity, or to subject the sample to external influences such as an electrical or magnetic field, or to control other parameters of the sample such as its temperature, other parameters that can be controlled include position and/or movement of the sample, particularly in the case of a fluid sample. The sample holder can be used in a method of analysis using various kinds of high-energy radiation (as defined above), including electromagnetic radiation (for example X-rays) and particle radiation (for example, electron radiation).

The functional structure may include one or more electrodes. The electrodes may extend at least partially across the window. The electrodes may be configured to generate an electric field. Alternatively, the electrodes may be configured for measuring the electrical resistivity of a sample.

The functional structure may include at least one electrically conductive element. The electrically conductive element may extend at least partially across the window. The electrically conductive element may be configured as a heating element, or a temperature sensing element, or as both a heating element and a temperature sensing element. The electrically conductive element may be configured to generate a magnetic field.

The functional structure may include a temperature-sensing element. The temperature- sensing element may comprise a thermocouple.

The functional structure may include a wall structure for containing a fluid sample (which may be in liquid, gas or gel form).

The functional structure may include a channel structure for controlling the flow of a fluid sample.

The functional structure may include a channel structure for controlling the flow of a fluid for heating or cooling a sample.

The sample holder may include a complementary sealing structure for sealing the channel structure.

The sample holder may comprise one or more than one of the aforesaid functional structures.

The functional structure may be formed on the membrane by deposition.

The functional structure may be formed on the support surface of the membrane.

The functional structure may be substantially co-planar with the support surface of the membrane.

The membrane may have an inner region that extends across the window and an outer region that is attached to the frame.

The membrane may be made from a very wide variety of materials according to the particular application for which the membrane is intended. Typically, the materials used include silicon nitride, silicon dioxide, silicon, boron carbide, diamond, various polymers and various metals.

Typical membrane thicknesses lie in the range IOnm to 20,000nm, but thicker and thinner membranes are not excluded.

The frame may be made of a material selected from the group comprising silicon, glasses, ceramics, plastics and metals.

Preferably, the sample holder is designed for use in a method of analysis using high-energy radiation, wherein the radiation comprises either electromagnetic radiation having a photon energy in the range 4OeV to 1 OOkeV, or particle radiation with a particle energy in the range lkeV to 50 MeV.

Various embodiments of the invention will now be described by way of example with reference to the accompanying drawings, wherein:

Figure Ia is sectional side view and figure Ib is a plan view of a prior art sample holder;

Figure 2 is a plan view of a sample holder according to a first embodiment of the invention having a co-planar electrode structure;

Figure 3 is a plan view of a sample holder according to a second embodiment of the invention having a co-planar heater/temperature-sensing element;

Figure 4 is a plan view of a sample holder according to a third embodiment of the invention having co-planar heater and temperature sensor elements;

Figure 5a is a plan view and figure 5b is a side sectional view of a sample holder according to a fourth embodiment of the invention having a seal ring for retaining a liquid sample and co-planar electrode structure;

Figure 6a is a plan view and figure 6b is a side sectional view of a sample holder according to a fifth embodiment of the invention having a channel system for a flowing fluid sample and co-planar electrode structure, figure 6c is a cross-sectional view of the same sample holder together with an upper sealing element, and figure 6d is a plan view of the sealing element; and

Figure 7a is a plan view and figure 7b is a side sectional view of a sample holder according to a sixth embodiment of the invention having a channel for a coolant or other fluid and a co- planar electrode structure.

The prior art sample holder shown in figures 1 a and 1 b consists of a silicon nitride membrane 2 supported by a silicon frame 4. The frame 4 is square with dimensions of 7.5mm x 7.5mm and a thickness of 0.2mm, and it has a square central window 6 of dimensions 3mm x 3mm. The silicon nitride membrane 2 is mounted on the frame 4 and has an inner portion 2a that extends across the window 6 and an outer portion 2b that is attached to the frame 4. The membrane 2 has the same side dimensions as the frame 4 and a thickness of 200nm. The membrane 2 is transparent to x-rays and high energy particles. The upper surface 8 of the membrane 2 provides a sample receiving surface, allowing analysis of a sample placed on that surface using x-rays or high energy particles that are transmitted through the window 6.

A sample holder according to a first embodiment of the invention is shown in figure 2. The basic structure of the sample holder is similar to the prior art sample holder shown in figures Ia and Ib, comprising a silicon nitride membrane 2 that is supported by a silicon frame 4. The membrane 2 has an inner portion 2a that extends across a window 6 in the frame, and an outer portion 2b that is attached to the frame 4. The dimensions of the membrane 2 and the frame 4 may for example be similar to those of the prior art sample holder described above.

The membrane 2 is provided on its upper sample-receiving surface 8 with a functional structure comprising two electrodes 10. In this example, each electrode 10 comprises two parallel elongate conductors, which are connected at one end to an electrical contact area 12. The conductive elements of the two electrodes are interleaved leaving only a small gap between them.

The electrodes 10 and the electrical contact areas 12 are formed by depositing an electrically conductive material on the upper surface 8 of the membrane 2. Various deposition methods maybe used including filament thermal evaporation, electron-beam evaporation, sputtering, electroless plating and electro-plating, or other deposition methods. Any suitable electrically conductive material may be used for the electrodes and the electrical contacts including, for example, aluminium, silver, gold or platinum. For example, a device as shown in figure 2 has been made employing electron-beam evaporated aluminium.

In use, electrical connection to the electrodes is made via the conducting contacts 12. The electrodes then may be used for example to apply a lateral electric field to a specimen on the sample holder, or to determine the electrical conductivity of a specimen.

A sample holder according to a second embodiment of the invention is shown in figure 3. The membrane 2 and the frame 4 are similar to those of the first embodiment shown in figure 2 and so will not be further described. In this embodiment the functional structure consists of an electrically conductive element 14 that extends across the window 6 and is connected at each end to a respective electrical contact area 16. In this case, the electrical element 14 includes a loop shape with a diameter of 1.5 mm, which surrounds the central region of the window 6. The element 14 and the contacts 16 are made of a suitable electrically conducting material by an appropriate deposition process, for example as described above in relation to figure 2.

In use, the element may be configured for use as a heating element, which allows ohmic heating by passing an electric current through the element. This may therefore be used for heating a specimen on the sample holder.

If required, the temperature of the sample area can be determined from the co-efficient of resistivity of the electrical element, using a four terminal Kelvin measurement to avoid contact and lead resistance errors.

Alternatively, the electrical element 14 may be used to generate an axial magnetic field passing through the middle of the window area. In this case, the choice of materials for the contacts and the conductive element may be different from those used for the heater/sensor structure in order to achieve an appropriate current level. The shape and dimensions of the structure may also be optimised to maximise the magnetic field produced.

A third embodiment of the invention is shown in figure 4. This is similar to the resistive heater structure shown in figure 3, but it includes in addition a thermocouple device 18 for sensing the temperature at the window of the sample holder. The thermocouple device 18 is connected to two additional electrical contact areas 20.

A fourth embodiment of the invention is shown in figures 5a and 5b. This device is similar to the first embodiment shown in figure 2, except that it also includes a functional structure comprising a circular wall 22 that is formed on the upper surface 8 of the membrane 2. The wall 22 surrounds the inner region of the membrane 2 that extends over the window 6. The wall thus defines with the membrane 2 a holder for a specimen in liquid or gel form.

In this example, the sample holder includes a pair of electrodes 10 and respective contact areas 12, which are similar to those shown in figure 2. It will however be appreciated that other functional structures, for example as shown in any other of the drawings filed herewith may alternatively be provided.

The wall 22 is preferably made of an electrically non-conductive material, for example a polymer such as an epoxy resin or a novolak resin, or a dielectric material. It can also be made of a metal, preferably with a non-conductive coating.

Figures 6a and 6b illustrate a fifth embodiment of the invention, in which the sample holder is provided with a number of channels that allow a fluid specimen to be mixed or circulated. In this example, the membrane 2 and the frame 4 are similar to those shown in figure 2, the membrane 2 supporting a pair of electrodes 10 with their associated contact areas 12. The channels 24 for directing the flow of the fluid specimen are formed by depositing an electrically non-conducting material 26 on specific areas of the upper surface of the membrane 2, so that the channels 24 are formed in the areas where the material 26 is not deposited. Any suitable material may be deposited including, for example, a photo- imageable polymer such as an epoxy-based photoresist. The channels 24 may be sealed by placing a second inverted sample holder 28, having a continuous layer of sealing material 30, on top of the first sample holder 32, as shown in figure 6c. The continuous layer of sealing material 30 may be considerably thinner that the sample holder 32 to minimise attenuation of the radiation or particle beam. Alternatively, a mirror image of similar channels 24 may also be formed in the second sample holder 28, as shown in figure 6d, to ensure there is no sealing material in the radiation path.

Figures 7a and 7b illustrate a sixth embodiment of the invention, which includes a channel for directing a temperature control fluid beneath the specimen. The channel 34 is formed between two blocks 36 of a suitable insulating material, for example a polymer. The channel can be sealed using a second sample holder, as described above and shown in figure 6c, or a mirror image version as shown in figure 7b. A suitable gas or liquid, for example helium gas, can be directed through the channel 34 in order to heat or cool the specimen.