The present application is related generally to x-ray windows.
X-ray windows can be used for enclosing an x-ray source or detection device. The window can be used to separate ambient air from a vacuum within the enclosure while allowing passage of x-rays through the window.
X-ray windows can be made of a thin film. It can be desirable to minimize attenuation of the x-rays (especially with low energy x-rays), thus it can be desirable that the film is made of a material and thickness that will result in minimal attenuation of the x-rays. Thinner films attenuate x-rays less than thick films. The film cannot be too thin;
however, or the film may sag or break. A sagging film can result in cracking of corrosion resistant coatings. A broken film can allow air to enter the enclosure, often destroying the functionality of the device. Thus it can be desirable to have a film that is made of a material that will have sufficient strength to avoid breaking or sagging, but also as thin as possible for minimizing attenuation of x-rays.
X-ray windows are often used with x-ray detectors. In order to avoid contamination of an x-ray spectra from a sample being measured, it can be desirable that x-rays impinging on the x-ray detector are only emitted from the source to be measured. Unfortunately, x-ray windows can also fluoresce and thus emit x-rays that can cause contamination lines in the x-ray spectra. Contamination of the x-ray spectra caused by low atomic number elements is usually less problematic than contamination caused by higher atomic number elements. It can be desirable therefore that the window and support structure be made of materials with as low of an atomic number as possible in order to minimize this noise.
Information relevant to attempts to address these problems can be found in U.S. Pat. No. 5,090,046.
It has been recognized that it would be advantageous to have an x-ray window that is strong, minimizes attenuation of x-rays, and minimizes x-ray spectra contamination. The present invention is directed to an x-ray window that satisfies these needs.
In one embodiment, the x-ray window includes an aluminum layer disposed between a first amorphous carbon layer and a second amorphous carbon layer. In another embodiment, the x-ray window includes a stack of thin film layers including an aluminum layer, a polymer layer, and an amorphous carbon layer. The above embodiments can be hermetically sealed to an enclosure having a hollow center. The amorphous carbon layer can be disposed as the farthest layer away from the hollow center.
As used herein, the term amorphous carbon means an allotrope of carbon that lacks crystalline structure and includes both sp3 (tetrahedral or diamond-like) bonds and sp2 (trigonal or graphitic) bonds.
Hydrogenated amorphous carbon means an amorphous carbon in which some of the carbon atoms are bonded to hydrogen atoms.
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Use of polymer layer(s) can be beneficial for providing structural strength to the window. Aluminum layer(s) can provide improved gas impermeability to the window. Amorphous carbon layer(s) can provide corrosion resistance. These materials have fairly low atomic numbers, thus minimizing x-ray spectra contamination.
The aluminum layer(s) can be substantially pure aluminum, or can include other elements. For example, a mass percent of aluminum in the aluminum layer(s) can be at least 80% in one embodiment, at least 95% in another embodiment, or at least 99% in another embodiment. In the various embodiments described herein, the aluminum layer(s) can have various thicknesses. For example, the aluminum layer(s) can have a thickness of between 10 to 30 nanometers in one embodiment, or a thickness of between 10 to 60 nanometers in another embodiment.
The amorphous carbon layer(s) can comprise only carbon, or substantially only carbon, in one embodiment. The amorphous carbon layer(s) can have various percentages of carbon. For example, a mass percent of carbon in the amorphous carbon layer(s) can be at least 80% in one embodiment, at least 95% in another embodiment, or at least 99% in another embodiment.
Hybridization of carbon in the amorphous carbon layer(s) can include both sp3 hybridization and sp2 hybridization in various relative percentages. For example, the percent sp3 hybridization can be between 5% and 25% in one embodiment, between 15% and 25% in another embodiment, between 5% and 15% in another embodiment, or less than 25% in another embodiment. The percent sp2 hybridization can be between 75% and 95% in one embodiment, between 85% and 95% in another embodiment, between 85% and 95% in another embodiment, or greater than 75% in another embodiment.
The amorphous carbon layer(s) can be hydrogenated amorphous carbon layer(s) in another embodiment. Hydrogen inside the amorphous carbon matrix can help to stabilize the sp3 carbon atoms and can improve the cohesiveness of the layer. There can be many different percentages of atomic percent of hydrogen in the hydrogenated amorphous carbon layer. For example, an atomic percent of hydrogen in the hydrogenated amorphous carbon layer can be between 50% and 70% in one embodiment, between 25% and 51% in another embodiment, between 14% and 26% in another embodiment, between 5% and 15% in another embodiment, between 1% and 10% in another embodiment, or between 0.1% and 2% in another embodiment.
The amorphous carbon layers can have various thicknesses. For example, the amorphous carbon layer(s), including hydrogenated amorphous carbon layer(s), can have a thickness of between 5 to 25 nanometers in one embodiment, or a thickness of between 1 to 25 nanometers in another embodiment.
The polymer layer(s) can have various mass percentages of polymer. For example, a mass percent of polymer in the polymer layer(s) can be at least 80% in one embodiment, at least 95% in another embodiment, or at least 99% in another embodiment. The term “mass percent of polymer” means percent by mass in the layer that are elements of the polymer selected, such as carbon and hydrogen, and possibly other elements, depending on the polymer selected. The polymer layer can consist of only polymer in one embodiment, or can include other elements or molecules in another embodiment.
The polymer layer(s) can have various thicknesses. For example, and the polymer layer can have a thickness of between 150 to 300 nanometers.
The polymer can be or can include a polyimide. Polyimide can be useful due to its high strength and high temperature resistance as compared with many other polymers.
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The enclosure 83 can be made of various materials, but titanium may be preferable due to a good match of the film's coefficient of thermal expansion and titanium's coefficient of thermal expansion. The titanium can be substantially pure titanium, with minimal other elements, in one embodiment. Alternatively, the titanium can include a certain percent of other elements. For example, the titanium can have a mass percent of greater than 99% in one embodiment, greater than 90% in another embodiment, or less or equal to 90% in another embodiment. The film 80 may be attached to the enclosure 83 by an adhesive, such as an epoxy.
The inner layer 81 can be a polymer layer 22 disposed between two aluminum layers 21a-b, as shown in
An alternative to amorphous carbon layer(s) is use of HMDS (hexamethyldisilazane) layer(s). HMDS is an organosilicon compound with the molecular formula [(CH3)3Si]2NH. Thus, amorphous carbon layer(s) may be replaced with HMDS layer(s) in any location in this document. Either amorphous carbon or HMDS can serve as a corrosion barrier. HMDS may be spin cast or vapor deposited. For vapor deposition, a vacuum can be used but isn't required.
The aluminum layer can be evaporation deposited. The aluminum layer and/or the amorphous carbon layer can be sputter deposited. Evaporation might be selected due to lower cost. Sputter might be selected due to improved ability to control film structure and adhesion.
Amorphous carbon layers have been successfully deposited by magnetron reactive gas sputtering with the following parameters and process:
The various amorphous carbon and aluminum window films described herein can be attached to a support structure, such as a silicon or a carbon composite support structure. The support structure can provide additional support and can allow the window film to be made thinner and/or span larger distances. The window films can be attached to support structures, such as a carbon composite support structure for example, by a suitable adhesive, such as an epoxy, cyanoacrylate, or polyurethane.
Priority is claimed to U.S. Provisional Patent Application Ser. Nos. 61/663,173, filed on Jun. 22, 2012; and 61/655,764, filed on Jun. 5, 2012; which are hereby incorporated herein by reference in their entirety.
Number | Date | Country | |
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61663173 | Jun 2012 | US | |
61655764 | Jun 2012 | US |