Patent Number: 
Section: description

FIG. 1 is a cross-sectional view of a window 3 built up in two parts from a diamond foil 1 and a separate annular retaining element 2, wherein the foil 1 and the retaining element 2 are connected to one another by means of an adhesive or fusion layer 4. The diamond foil 1 has a thickness of up to 10 xcexcm and is transparent to an electron ray. The material of the retaining element 2 is characterized in that it is a temperature-resistant metal and has a linear thermal expansion coefficient whose value is preferably lower than 9xc3x9710xe2x88x926/K, i.e. similar or equal to the coefficient of expansion of the diamond. An example of this is molybdenum. It is also conceivable, however, that the foil transparent to electron rays is made of molybdenum and that the retaining element is manufactured from a material whose thermal expansion behavior matches that of molybdenum. It should be emphasized that the retaining element 2 did not take part in the actual manufacture of the diamond foil, acting as a carrier substrate, but that it was connected to the diamond foil only after the latter had been manufactured. The manufacture of thin diamond layers is known and takes place by means of gas deposition methods. The diamond foil is then fully divested of the carrier substrate on which it was depositedxe2x80x94for example, by etching or possibly by grinding away of the substratexe2x80x94and is connected to the retaining element 2 by its peripheral or edge regions, such that a transparent transmission zone 5 is created. The thin diamond layer 10 is provided with thickenings 16a,b,c acting as structural or reinforcement elements on its surface facing away from the retaining element 2 for mechanical stabilization of the thin diamond layer, as is shown for the embodiment in FIG. 2. Similar components have been given the same reference numerals as in FIG. 1. These thickenings 16a,b,c are also formed from diamond and in this embodiment extend parallel next to one another, which is more clearly shown in the plan view of FIG. 3. Embodiments with irregularly spaced thickenings are equally conceivable; and other geometries or patterns in which the thickenings are arranged are also possible. In the window shown in FIG. 2, the thickenings 16a,b,c have a triangular geometry. Their thickness does not come to the total thickness of the diamond foil, but it should be at least 10% of the total thickness of the foil. It is furthermore possible to provide both surfaces of the diamond foil with thickenings, or only the surface facing towards the retaining element. A balance should always be sought between the influence of a mechanical stabilization and sufficient areas of higher transparency acting as transmission zones for the electron ray. The thickenings may be added to the diamond foil, for example, through a suitable structuring of the CVD carrier substrate to be coated during the deposition process. It is also possible, however, to remove regions, for example by laser ablation or with an ion ray applied to a thicker foil, which regions will then form the subsequent regions transparent to electron rays. Besides the solution principle of a fixed connection through the use of an adhesion of fusion layer between the diamond foil and the retaining element of a material having a low linear thermal expansion coefficient, the solution principle of an integral window is proposed according to the invention, which window consists entirely of diamond. FIG. 4 is a cross-sectional view of such a window. The foil (300a) and the retaining element 300b in this embodiment form an integral whole, i.e. the window 300. A diamond plate having a thickness of more than 10 xcexcm, preferably of up to 1000 xcexcm, is used for this, which plate is thinned by laser or ion ablation down to a thickness which is transmissive to electrons over a surface area which corresponds to at least the diameter of the electron ray. This creates the actual window region 307 within the retaining element 300b. Besides this regular arrangement of the window region, the embodiment of FIG. 5, also made integrally from diamond, shows an irregularly thinned diamond plate, i.e. a transmission zone 308 reinforced with thickened portions 310a,b. The electron ray can pass through the regions 311a,b,c transparent to electron rays between the thickened portions. In the advantageous embodiment shown in FIG. 6, the thickened portions, i.e. the non-reduced regions 312a,b lie in the outermost region of the processed zone or transmission zone 309; the difference with the window of FIG. 5 is shown in dotted lines. With a sufficient stabilization, the actual transmission zone 309 still remains unaffected. It is clarified in the diagram of FIG. 7 that the windows with the proposed construction show a better pressure resistance than the known windows which are formed by a carrier substrate with a diamond foil provided in the deposition process. The bursting pressure is indicated as a measure for this. The thickness and the diameter indicate geometric values for the respective window. The diameter is understood to be the greatest longitudinal dimension of the window opening, i.e. of the transmission zone in cm here, corresponding, for example, to the diameter in circular openings, to the major axis of the ellipse in elliptical openings, and to the major side length in the case of rectangular openings. It is apparent that the window samples with less strongly adhering foils on silicon carrier substrates (triangles) became detached at a pressure of 3 to 4 bar. To achieve higher bursting pressures (dots), the diamond foil was fully removed from the carrier substrate, according to the invention, and fixedly connected to a separate retaining element or window frame from a material having a comparatively low linear thermal expansion coefficient by means of a separate connecting layer, or alternatively it was manufactured in one piece. The dotted line corresponds to the experimentally found limit value for the bursting pressure of the window, for which it holds that bursting pressure (bar)=1.3xc3x97[thickness(xcexcm)/diameter(cm)],  whereby a difference from the known relation xe2x80x83bursting pressure (bar)=1xc3x97[thickness(xcexcm)/diameter(cm)] was found. The window thickness in xcexcm should accordingly be greater than 0.7 times the product of diameter (cm) and pressure difference between the two sides of the window. FIG. 8 diagrammatically shows an X-ray device 20 operating by the LIMAX process, in which a window 3 according to the invention with its modifications described above may advantageously be used. The X-ray device is formed by the X-ray tube 21 and a liquid metal circulation system 22. The X-ray tube 21 is closed off by the window 3 in a vacuumtight manner. In the vacuum space of the X-ray tube 21, there is an electron source in the form of a cathode 23 which in the operational state emits an electron ray 24 which hits a liquid metal through the window 3, which metal is being passed over a steel plate. The liquid metal circulation system 22 is provided for this purpose, composed from a tubular duct system 25 in which the liquid metal is propelled by a pump 26 so as to flow past the outer side of the window 3 in a region 27. After passing through the region 27, it enters a heat exchanger 28 from which the generated heat is removed by means of a suitable cooling system. The interaction of the electrons passing through the window with the liquid metal generates X-ray radiation (i.e. the liquid metal acts as a target), which issues through the window 3 and an X-ray emission window 29 in the bulb 21 to the exterior. It is advisable to use a doped diamond, especially if the proposed windows are used in such X-ray devices, so as to prevent a charging of the window during operation by means of the conductivity, and thus to prevent a deflection, deceleration, or complete stoppage of the electron ray. Boron is suitable for a doping process so as to reduce the resistivity to less than 1000 xcexa9cm.