Patent Number: 042232244
Section: description

DETAILED DESCRIPTION Referring now to the drawings, FIG. 1 shows a cross-section through an electron microscope perpendicular to the beam direction in the plane of the specimen holder. The housing, which can be evacuated, is identified by reference numeral 1. In this housing is located a specimen stage 2. This specimen stage is moved by two drive plungers 3 and 4 which pass through the wall of the housing in a vacuum-tight manner, in the plane defined by plungers 3 and 4. Between specimen stage 2 and plungers 3 and 4 is a positive force transmission which is maintained by a tension spring 5. Plunger 3 has a point 3a which engages a wedge-shaped depression provided in specimen stage 2. Plunger 4 is equipped with a roller 4a which rolls on a plane counter-surface of specimen stage 2. It should be noted, however, that any other cross feed can be used instead of this specimen stage drive. Specimen stage 2 has a conical opening 2a into which rod-shaped specimen holder 6 is inserted. For inserting and removing specimen holder 6, the wall of housing 1 is equipped at the proper point with a lock (not shown for the purpose of simplification). At its forward end, specimen holder 6 has an opening for a specimen. Reference numeral 8 identifies the bending line of the fundamental vibration of this rod-shaped, unilaterally supported specimen holder. The vibration antinode of this fundamental vibration is located at the free end of the specimen holder. However, since opening 7 for the specimen itself is located at this point, supplemental oscillator 10 cannot be mounted directly at the location of the vibration antinode. However, it is fastened in a holder 11 as close as possible to the specimen and therefore still in the region of large vibration amplitudes. FIG. 1a shows a cross-section through specimen holder 6 and supplemental oscillator 10 perpendicular to the plane of the drawing. As can be seen from this figure, specimen holder 6 has a rectangular-shaped cross-section. The two circular lines around holder 6 are projections of the inner and outer areas of the conical part of the holder seated in specimen stage 2. Specimen holder 6 includes a holder 11 for receiving the supplemental oscillator. In accordance with the shape of the cross-section of holder 6, supplemental oscillator 10 is also rectangular-shaped with the same sides ratio as specimen holder 6. This assures that the resonance frequencies of specimen holder 6 and supplemental oscillator 10 are approximately equal in the two preferred directions, i.e., along the two rectangle sides. FIG. 2 shows a cross-section through another embodiment of an electron microscope in the plane of the specimen holder. This microscope includes an annular-shaped adjustable specimen stage 2 including an aperture 2a for permitting the passage of a specimen holder 1 therethrough. The specimen holder 15 is rod-shaped, but contrary to the embodiment of the apparatus illustrated in FIG. 1, passes through the wall of housing 1 and is secured in this wall in a first support 16, shown simply as a sphere for the purpose of simplification. Besides support action, this sphere also has a sealing effect. The other end of specimen holder 15 has a point 15a which engages a correspondingly shaped conical depression in specimen stage 2. In the vicinity of first support 16, housing 1 is provided with a cylinder 17 which accommodates a compression spring 18. Due to this compression spring 18, positive force transmission always exists between point 15a of specimen holder 15 and the specimen stage. Cylinder 17 leads to a lock (not shown). Specimen holder 15 has a bore hole 19 at the point of the electron beam for receiving the specimen. Reference numeral 20 identifies the bending line of the fundamental vibration of the specimen holder in the plane of the section and perpendicular to the axis of the specimen holder. The base of a supplemental oscillator 21 is located at the point of the vibration antinode and consists of a block 22 screwed to the specimen holder 15 which receives supplemental oscillator 21. To receive block 22 and supplemental oscillator 21, specimen holder 15 is provided with a slot 23 in this region. FIG. 2a shows a cross-section through specimen holder 15 and supplemental oscillator 21 perpendicular to the plane of the drawing. The cross-section of holder 15 is circular in this embodiment and only the region of the slot deviates somewhat from this shape. Supplemental oscillator 21 mounted in block 22 also has a circular cross-section and consists of a bronze wire onto which a tube of polytetrafluoroethylene is shrunk. If specimen holder 15 is excited to resonance vibration, for example, by soil vibrations, then supplemental oscillator 21 also starts to vibrate. The polytetrafluoroethylene tube applied to the bronze wire is then deformed inelastically, i.e., energy is consumed, and supplemental oscillator 21 is damped thereby. The mass of supplemental oscillator 21 can be very small compared to the mass of specimen holder 15. With a fixed mass ratio .mu.=m.sub.Z /m.sub.S, optimum suppression of the interfering specimen holder vibration is obtained if the damping .phi.=(.mu./2(1+.mu.)).sup.1/2 and if at the same time the frequency ratio .alpha.=f.sub.Z /f.sub.S =1/(1+.mu.), where f.sub.Z represents the resonance frequency of the supplemental oscillator and f.sub.S the resonance frequency of the specimen holder. If, for example, .mu.=10.sup.-3 is set as the mass ratio, then an optimum damping .phi..sub.opt .apprxeq.0.02 and an optimum frequency ratio .alpha..sub.opt .apprxeq.0.999. The resonance frequency of the supplemental oscillator is therefore only 0.1% higher than that of the specimen holder. In the embodiments of the apparatus shown in FIGS. 1 and 2, two rod-shaped specimen holders 6 and 15, respectively, for laterally inserting a specimen into an electron microscope were shown. FIG. 3 shows an embodiment in which a specimen holder 25 is inserted into the specimen stage in the direction of the electron beam. Coupled by means of a slide ring, specimen stage 2 rests on the upper part of an objective pole piece 27. By means of plungers 3 and 4, of which only plunger 4 is visible in FIG. 3, as well as spring 5, the specimen stage is movable in the plane perpendicular to the electron beam. In this embodiment, a specimen cartridge with a conical upper part 25a and a tube 25b which extends to the point of maximum field strength in the pole piece gap serves as the specimen holder. Specimen 28 is fastened at that point. Conical part 25a of specimen holder 25 is connected to specimen stage 2 by friction and can therefore vibrate with the latter only in synchronism. Tube 25b, however, can be excited to vibrations which can lead to a change of position relative to the specimen stage and the objective pole piece 27. Reference numeral 29 identifies the flexing line of the first resonance frequency. The base of a bi-axial supplemental oscillator 30, which is connected to specimen holder 25 by means of a housing 31, is located approximately at the point of the vibration antinode, which means in this case, however, also at the point of specimen 28. FIG. 4 shows a section of a specimen holder which is of tubular design, at least in the portion shown. In the interior of tube 36 is disposed a tri-axial supplemental oscillator 37 which in this embodiment consists of a disc-shaped rubber mass 38, in the center of which a mass 39 is disposed so that it can vibrate. The latter mass may comprise brass or alloy steel. This tubular section of the specimen holder could be, for example, part of specimen holder 6 or part of specimen holder 15. The bi-axial vibration damper used in the embodiments shown in the drawings could then be eliminated. The reason it may be necessary under some conditions to employ a tri-axial vibration damper with such rod-shaped specimen holders although it can be assumed that the rod-shaped specimen holder itself is rigid in the rod direction, is that in the apparatus shown in FIG. 1, specimen stage 2 can vibrate in the direction of the rod-shaped specimen holder in such a manner that the ring diameter changes periodically in this direction, and in the embodiment shown in FIG. 2 rod 15 vibrates against rod point 15a, which can be considered as a spring. FIG. 5 shows an enlarged view of a rod-shaped supplemental oscillator 21 which consists of a spring wire 41 surrounded by a jacket of elastomer, for example, of polytetrafluoroethylene or synthetic rubber. FIG. 6 shows another embodiment of supplemental oscillator 21, which consists again of spring wire 41. In this embodiment, wire 41 is surrounded not only by a jacket 42 of elastomer, but also by a metal cylinder 43. A deformation of the elastomer between wire 41 and metal cylinder 43 occurs and thereby, vibration damping, when wire 41 vibrates. FIG. 7 shows a supplemental oscillator 50 which is fastened at one end to a holder 54. Supplemental oscillator 50 can be attached to a specimen holder by this holder and consists of a spring wire 51 which is surrounded over the larger part of its length by a jacket of any desired elastomer. The forward part of spring wire 51, which is not surrounded by jacket 52, has a thread onto which a nut 53 can be screwed. Nut 53 represents an additional weight which can be moved back and forth over a certain range along the length of supplemental oscillator 50. The resonance frequency of oscillator 50 can thereby be varied within certain limits and adapted to the resonance frequencies of the specimen holder more easily. The present invention is applicable not only to electron microscopes such as these described previously herein, but also to ion microscopes or to electron or ion diffraction apparatus. In addition to the different specimen holders shown in the various embodiments of the invention, the vibration damper of the invention can also be attached to the vibrating parts of a mechanical goniometer, such as is used, for example, in scanning surface microscopes as a specimen holder. The vibration damper of the invention can also be used for all parts in the interior of a charged-particle beam optical apparatus which are not frictionally coupled to the apparatus and can therefore be excited to vibrations of their own. By using additional supplemental oscillators, resonant vibrations of higher order can also be suppressed. In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense. What is claimed is: