Patent Number: 055286461
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS The sample vessel illustrated in FIG. 6A and preferred as the first embodiment of the present invention is structured in the following procedures. The sample vessel is first configured as a pair of structures each of which consists of a silicon base plate 1 having an opening 1a or 1b and a thin film of diamond 2 integrated with the base plate 1. This structure is configured by forming, on one surface of the silicon base plate 1, the thin film of diamond 2 approximately 0.3 .mu.m thick, for example, by an evaporation-coating method and anisotropically etching a central portion of the base plate 1 from the side of the other surface thereof so as to form an opening to be used as an entrance window or an exit window including a central portion of the thin film of diamond 2. In the case of the first embodiment, a sample holding member accommodating space 4 is formed by bonding a spacer 3 which is made of a material containing silicon and has predetermined thickness to a surface of the thin film of diamond 2 of the one of the structures disposed on the side of the soft X-ray source by using a bonding agent containing silicon and disposing a metal mesh member 5 which is made of nickel wires having a diameter of approximately 0.3 mm at pitches of a 25 .mu.m for use as a sample holding member in contact with the thin film of diamond 2 as shown in FIG. 6B. By adequately dripping an aqueous solution over the metal mesh member 5 made of the nickel wires which is disposed in contact with the thin film of diamond 2 in the sample holding member accommodating space 4, a water film 6 which holds itself due to surface tension is easily formed in each unit mesh enclosed by the nickel wires 5a as shown in FIG. 6B and FIG. 6C. (The water film has free surfaces which are concave due to the surface tension as shown in FIG. 6C.) After setting a biological sample 7 into the water film 6, a surface of the thin film of diamond 2 of the other structure is cemented to the spacer 3 with the bonding agent so as to enclose the biological sample and the aqueous solution. The sample vessel thus obtained is effectively usable as a sample vessel which accommodates the biological sample to be subjected to microscopy with the vacuum enclosed type of X-ray microscopes. That is to say, the sample vessel preferred as the first embodiment of the present invention is capable of favorably limiting a shift of the biological sample 7 to be observed and remarkably facilitates observation of the sample since the sample vessel is configured so as to permit forming the water film 6 which holds itself due to the surface tension within each mesh enclosed by the nickel wires 5a, or within a limited narrow sample accommodating space, and sustains the biological sample in the water film 6. Further, this sample vessel has mechanical strength enhanced sufficiently to withstand bombardment with particles flying from the X-ray source and lowers the possibility of breakage due to pressure differences between both sides of the window of incidence, because the opening 1a which is the window of incidence of the soft X-rays is provided with the thin film of diamond 2 reinforced by the metal mesh member 5 made of nickel. Now, detailed description will be made of the sample holding member which is composed of the metal mesh member 5 and the thin film of diamond 2 used in the first embodiment. In FIG. 7A and FIG. 7B, the reference numeral 8 represents a ring-shaped holder which has an internal holding space 8b enclosed by an outer frame 8a and a central opening to be used as a transmission window 8C. Disposed in this holding space 8b is the metal mesh member 5 approximately 0.3 mm thick which is made of the metal wires braided in the mesh-like form and which is to be used as a sample holding member. By covering an upper surface of the metal mesh member 5 with the thin film of diamond 2 approximately 1 .mu.m thick, the thin film of diamond 2 which is reinforced with the metal mesh member 5 can be obtained. This thin film of diamond 2 is capable of withstanding a differential pressure on the order of 1 atmospheric pressure even when the thin film has, for example, an effective opening of several millimeters (6 mm in FIG. 7A). It is known that water molecules contained in aqueous solutions to be used in combination with biological samples have high polarization characteristics and the aqueous solutions form small angles of contact with substances other than organic compounds containing carbon, and are adsorbed sufficiently effectively to and by surfaces of the substances. Accordingly, a water film which holds itself due to the surface tension is formed in each of the meshes enclosed by the metal wires when the metal mesh member 5 is brought into contact with water. Therefore, the water film has curved surfaces and holds a biological sample after the metal mesh member 5 holding the thin film of diamond 2, the one shown in FIG. 7A in particular, is brought into contact with water and excessive water is wiped off. By utilizing this phenomenon, it is possible to hold an aqueous solution containing a sample to be observed, for example a biological sample, within a very narrow space of each mesh. Under the present circumstances, there is available no theoretical formula which defines the way in which an angle of contact .theta. with determines behavior of the water which is placed in the space enclosed by the metal wires of the mesh member. Therefore, let us approximate the space enclosed by the metal wires of the mesh member to a well-known cylindrical space which is shown in FIG. 8 and examine the angle of contact .theta. with the water film having the curved surfaces described above. When a radius of curvature of a curved surface S is represented by R and a diameter of the cylindrical space which corresponds to a pitch of meshes is designated by 2r, we obtain a relationship expressed by the following formula: EQU cos .theta.=r/R R used in this formula has a positive value when the curved surface S is concave as shown in FIG. 8 or a negative value when the curved surface S is convex. Accordingly, when the angle of contact .theta. with water is smaller than 90.degree., cos .theta. is larger than 0 and the curved surface S is concave, whereby a required water film is formed so as to hold a biological sample therein. When the angle of contact .theta. with water is equal or larger to or than 90.degree., on the other hand, it will be understood that cos .theta. is equal to or smaller than 0 and the curved surface S is convex or planar, whereby the required water film cannot be formed. That is to say, it is impossible to hold an aqueous solution containing a biological sample in each mesh when the angle of contact .theta. with water is equal to or larger than 90.degree.. Further, since the metal mesh member 5 for reinforcing and holding the thin film of diamond 2 can be braided at a minimum pitch on the order of 20 .mu.m, it is possible to enclose an aqueous solution containing a biological sample within a narrow space of a mesh measuring 20 .mu.m.times.20 .mu.m so that the biological sample can be easily observed continuously for a long time with no slight shift. Furthermore, since the metal mesh member 5 has an effect to reinforce the sample vessel 8 itself, the metal mesh member 5 makes it possible to manufacture X-ray windows which are strong and thin enough not to attenuate X-rays. As is understood from the foregoing description, the metal mesh member which is made of the nickel wires in the first embodiment may be made of other metals which are excellent in affinity with water, or still other materials which are excellent in affinity with water, for example, high molecular compounds such as acrylic resin, rayon and nylon or inorganic compounds containing silicon. Moreover, regarding the disposition of the metal mesh member in the space 4 for the biological sample 7 in the sample vessel V, the thin film of diamond 2 reinforced by the mesh member 5 may be disposed for the opening 1a to be used as the entrance window as described above and a thin film of silicon nitride may be disposed for the opening 1b to be used as the exit window, or vice versa. In the second embodiment of the present invention illustrated in FIG. 9A, a sample vessel V is formed by disposing, at a pitch of 100 .mu.m, a plurality of sample accommodating spaces 10 consisting of small openings measuring 50 .mu.m.times.50 .mu.m which are bored in a thin sample holding base plate 9 made of a copper sheet approximately 5 .mu.m thick and regularly arranged at a pitch of 100 .mu.m. By dripping an aqueous solution adequately into the sample accommodating spaces 10, it is possible to form water films 11 which can hold themselves due to the surface tension (free surfaces of the water films are held in curved conditions due to the surface tension in FIG. 9B) and sustain a biological sample 7 in each of the water films 11. The sample vessel V prepared as described above is usable with no modification as a sample vessel in particular for the atmosphere-open type X-ray microscopes without tightly sealing the water films 11, or with the water films 11 containing the biological samples 7 kept exposed to air, and under no restriction to postures of the biological samples. Accordingly, the sample vessel preferred as the second embodiment of the present invention is also capable of desirably restricting a shift of the biological samples 7 to be observed and facilitates microscopy of the samples since the sample vessel is configured so as to permit forming a water film 11 in each unit sample accommodating space 10 owing to the surface tension, and holding the biological sample 7 in this water film 11. FIG. 10A and FIG. 10B show a modification of the second embodiment of the present invention which is configured so as to have only one sample accommodating space 10. When a material of the sample holding base plate 9 as well as a size and depth (thickness of the base plate) of the accommodating space 10 is adequately selected, this modification also permits forming the water film 11 thinner than the base plate 9 and facilitates observation of a biological sample with no influence due to set posture of the sample vessel V. When the sample vessel preferred as the second embodiment is to be used with the vacuum enclosed type X-ray microscopes, it is sufficient to use the sample vessel V shown in FIG. 4 in a condition where it accommodates the sample holding base plate 9 and sustains the water films 11 containing the biological samples 7 as illustrated in FIG. 11 or to adopt a sample chamber 12 having openings 12a such as the entrance window and the exit window in a condition which where sustains water films 11 containing biological samples 7 in the sample holding spaces 10. Though the sample holding base plate is made of a copper sheet in the second embodiment described above, the sample holding base plate may be made of other metals excellent in affinity with water, or still other materials which similarly are excellent in affinity with water, for example, high molecular compounds such as acrylic resin, rayon and nylon, or inorganic compounds containing silicon. FIG. 13 illustrates the third embodiment of the sample vessel according to the present invention. The third embodiment is different from the first embodiment illustrated in FIG. 6A in that the sample vessel preferred as the third embodiment uses a thin film of silicon nitride 13 approximately 0.3 .mu.m thick formed on one surface of the silicon base plate 1 by CVD method and a thin film of aluminium 14 approximately 0.1 .mu.m thick is laminated over the thin film of silicon nitride 13 on the side of the opening of the entrance window 1a. The sample vessel preferred as the third embodiment can be manufactured in procedures described below. After forming the thin film of silicon nitride 13 as described above, portions to be used as an entrance window 1a and an exit window 1b are removed from the thin film of silicon nitride 1 so as to form a pair of structures consisting of a thin film of silicon nitride 13-silicon base plate 1 and a thin film of silicon nitride 13-silicon base plate 1 respectively. Further, aluminium is evaporation-coated so as to form a thin film of aluminium approximately 0.1 .mu.m thick over the thin film of silicon nitride 13 of the structure consisting of the thin film of silicon nitride 13-silicon base plate 1 which is disposed on the side of the entrance window 1a. After disposing a wetted biological sample in a portion corresponding to an internal space 4 in which the biological sample is to be enclosed, a spacer 3 is cemented to the integrated structures by using a bonding agent containing silicon. The end surfaces which are in parallel with the paper surface are sealed with a sealing agent containing silicon as the occasion demands. According to Japanese Patent Application No. Hei 4-58040, which was laid open on Oct. 12, 1993, as publication No. Hei 5-2647398 a thin film of aluminium 0.1 .mu.m thick exhibits transmittance of 0.53 for a ray having a wavelength of 39.81 .ANG.. Since the thin film of aluminium 0.1 .mu.m thick exhibits a transmittance of 2.3.times.10.sup.-7 for the visible ray, on the other hand, this thin film is usable as an ideal filter when solid detectors such as CCD's are used as detectors for X-ray microscopes. Since the sample vessel preferred as the third embodiment of the present invention has the exit window 1b (the window disposed on the side of the detector) which is transparent for the visible ray, the sample vessel permits observing biological samples with the visible ray. Though aluminium is evaporation-coated so as to form a thin film of aluminium approximately 0.1 .mu.m thick over the thin film of silicon nitride 13 of the integrated structure of the thin film of silicon nitride 13-silicon base plate 1 disposed on the side of the light source in the third embodiment, the coating metal is not limited to aluminium but may be any metal which reflects or absorbs the visible ray and ultraviolet ray, and allows transmission of X-rays. Though the sample vessel preferred as the third embodiment is structured by using the spacer 3 made of the material containing silicon, a material of the spacer is not limited to that containing silicon and may be any one of those which are not affected by vacuum.