Abstract:
An observation and analysis unit that magnifies an image of a sample and further accomplishes the evaluation and analysis thereof. The observation and analysis unit includes a light-microscopic device designed for the magnified imaging and optical evaluation of the sample and a sample analyzer that analyzes selected regions of the sample. The sample analyzer includes an electron source from which an electron beam can be directed to a region of the sample selected by use of the light-microscopic device. The sample analyzer further includes an X-ray detector designed to detect X-ray radiation generated by the interaction of the electron beam with the sample material. The unit further includes an actuation and evaluation unit that generates control commands for the light-microscopic device and the electron source and spectrally analyzes the X-ray radiation.

Description:
PRIORITY CLAIM 
     The present application is a National Phase entry of PCT Application No. PCT/EP2010/062169, filed Aug. 20, 2010, which claims priority from German Application Number 102009041993.4, filed Sep. 18, 2009, the disclosures of which are hereby incorporated by reference herein in their entirety. 
     FIELD OF THE INVENTION 
     The invention relates to an observation and analysis unit provided with means for the magnified imaging of a sample and with means for the evaluation and analysis thereof. 
     BACKGROUND 
     Observation devices suitable for the magnified imaging and optical evaluation of samples are actually known in the form of light microscopes. With light microscopes, a resolving power is achieved that is about 1000 times that of the human eye. In addition to this relatively high resolution, it is necessary in many light-microscopical examinations to carry out a detailed analysis of the chemical element composition of particular regions of the sample, identified by means of the light microscope, e.g., in order to characterize undesirable inclusions in metallurgical samples. 
     In the prior art, such detailed analyses are, as a rule, carried out with a scanning electron microscope, which, in imaging the sample surface by means of secondary electrons, yields an even substantially higher resolution of better than 1 nanometer (nm). In chemical analyses by X-ray spectroscopy with the scanning electron microscope, however, the best possible resolution is within a range of 0.5 to 2 micrometers (μm) and is determined by the volume of interaction of the electron beam with the sample. 
     For examining one and the same sample, thus, it is necessary to change from one instrument to another, which involves a considerable interruption of the work flow, as the examination of the sample in the scanning electron microscope takes place in a vacuum, for which reason the sample taken from the light microscope first has to be brought into a vacuum through a lock, after which the sample region of interest has be found again in the scanning electron microscope and positioned. 
     Added to this may be waiting time for the availability of a scanning electron microscope, and furthermore there is the risk of the sample getting damaged during transfer between the instruments. Moreover, a scanning electron microscope is a relatively expensive investment, the technical capabilities of which are required to a limited extent only, if at all, for solving the problem mentioned above, i.e. the analysis of a chemical element composition after light-microscopical examination. 
     U.S. Pat. No. 6,452,177, for example, describes an electron-beam-based material analysis system which is suitable especially for examinations under atmospheric pressure. This system has the drawback that it is unfit for microscopical observation of the sample. Moreover, the sample region in which the material is to characterized is dot-shaped and relatively large, i.e. &gt;100 μm; there is no shielding against the X-ray radiation, and the time required for a measurement is relatively long. Another drawback is that the electrons escape from the vacuum of the electron source to the surrounding atmosphere through an electron-transparent membrane. This leads to increased scattering, which is a disadvantage especially for examinations at high resolution. Furthermore, the electron scattering produces X-ray radiation, which is superimposed on the signal measured of the sample, thus degrading the quality of the measurement signal. 
     SUMMARY OF THE INVENTION 
     Departing from this, the invention addresses the problem of creating an observation and analysis unit with which an analysis of a sample by electron-beam excitation can be accomplished immediately after or during its light-microscopically magnified imaging. 
     According to the invention, such an observation and analysis unit comprises
         a light-microscopical device designed for the magnified imaging and optical evaluation of a sample,   means for the analysis of selected regions of the sample, provided with an electron source from which an electron beam can be directed to a region of the sample selected by means of the light-microscopic device, and with an X-ray detector designed to detect the X-ray radiation generated by the interaction of the electron beam with the sample material, and   an actuation and evaluation unit which generates control commands for the light-microscopic device, the electron source and/or sample positioning, and spectrally analyzes the X-ray radiation.       

     In contrast to prior art, the unit according to the invention permits both the light-microscopical and the electron-beam-excited examination to be carried out without requiring an interruption of the work flow because of any changing between two physically separated instruments. As an added advantage, X-ray analysis with the invented unit, unlike analysis with a scanning electron microscope, does not need a vacuum environment, because the sample is examined in air or in the presence of some other gas. Moreover, higher throughput rates are possible when a series of samples are to be analyzed. During analysis by application of electron beam source and X-ray detector, the sample is surrounded by some gas below or near atmospheric pressure. 
     In an example embodiment, the invented observation and analysis unit is provided with control means for moving the sample relatively to the observation ray path of the light-microscopical unit, the electron beam and/or the X-ray detector. The control means are connected to the actuation and evaluation unit, so that control commands for position changes can be generated and issued either on the basis of arbitrary specifications or as a function of the result of observation and/or analysis. 
     To prevent any hazard due to unwanted propagation of the X-rays, a shielding means that is opaque to X-rays can be provided. Furthermore, a shutter or filter may be provided which blocks the ray path of the light-microscopical unit to the X-rays at least when the electron source is in switched-on state. 
     It is also feasible and within the scope of the invention that the shielding means is gas-tight and that an arrangement for feeding some gas, preferably helium, into the space between sample and electron source is provided. 
     Feeding gas into the space between sample and electron source is feasible and advantageous also independent of the design of a shielding means. 
     Furthermore, the observation and analysis unit should be provided with means for focusing the electron beam on the selected region of the sample. In that respect, a tubule may be provided between the electron source and the sample, through which the electron beam is guided to the sample. Preferably, a device for varying the distance between the sample surface and the electron beam outlet port of the tubule is provided. 
     To enable the electron beam to be targeted at the sample in a straightforward way, a light beam, preferably a laser beam, run parallel to the direction of the electron beam and is visible to the operator of the observation and analysis unit. With such a—preferably laser-optical—targeting beam in the visible wavelength range, the spot of impact of the electrons on the sample can easily be marked or calibrated. Alternatively, for the same purpose, a phosphorescent element can be provided for marking or calibrating the spot of electron impact. 
     It is of particular advantage if one or several objectives allocated to the light-microscopical unit are arranged, together with the electron source and/or the X-ray detector, on a change-over device by means of which they can be interchanged and selected for active use. In another favorable embodiment of the invention, the area for visual observation of the sample by means of the light-microscopical unit on the one hand, and the area for analysis of the sample by means of the electron beam and the X-ray detector on the other hand, may be arranged within the observation and analysis unit, but physically separated from one another. 
     In a special embodiment of the invention, a light microscope is provided with
         an electron source, from which an electron beam is directed at the sample in addition to, or as an alternative to, the illumination ray path coming from the objective of the light microscope,   an X-ray detector, which detects the X-ray radiation generated on account of the interaction of the electron beam with the sample, and,   arranged downstream of the X-ray detector, an evaluation device which spectrally analyzes the X-ray radiation.       

     Here again, during analysis by means of the electron beam source and the X-ray detector, the sample is surrounded by some gas below or near atmospheric pressure. 
     It is to be understood that the subject matter of the invention includes all technically equivalent means and their operating relationships. This includes, for example, means for the analysis of selected regions of the sample by means of ions that, emitted by an ion source, are used to excite the sample substance instead of excitation by electrons. 
     Another example is examination of the luminescence generated in the sample by the electron beam, using a luminescence detector operating via the light microscope, or a separate detector. 
     With the invented observation and analysis unit, a microscopically small, spatially resolved sample region can be analyzed, with a spot analysis being possible within a few seconds thanks to the radiant intensities provided. 
     Further advantages of the invented arrangement, in addition to the capability of direct sample analysis at the light microscope ray path, are given by the fact that selection of the desired sample region is possible directly in the light microscope image. By means of the optional shifting of the sample relative to the electron source, the sample region selected can be centered under the electron source, and the X-ray spectrum can be recorded and evaluated automatically. 
     It is possible advantageously to achieve a compact design of the electron source and the X-ray detector and to implement scanning of the sample and/or the electron beam, whether for mapping or for increasing the spatial resolution by means of deconvolution. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Below, the invention will be explained in greater detail with reference to exemplary embodiments. In the accompanying drawings, 
         FIG. 1  depicts the design principle of the invented observation and analysis unit, 
         FIG. 2  is an extended view of the design principle of the invented observation and analysis unit following  FIG. 1 , 
         FIG. 3  depicts an example embodiment based on the design principle according to  FIG. 1 , 
         FIG. 4  is a flow chart depicting the example of process sequence in the observation and analysis of a sample with the invented unit, 
         FIG. 5  is a Monte Carlo simulation of the interactions of an electron beam with a sample, 
         FIG. 6  depicts an embodiment with a device for the adjustment of the electron beam relative to the sample, 
         FIG. 7  depicts an example embodiment in which the electron source is of miniaturized design and can be integrated into a revolving objective nosepiece, 
         FIG. 8  depicts a miniaturized electron source to be installed into a revolving objective nosepiece, with its external interfaces, 
         FIG. 9  depicts an embodiment in which the sample can, by means of a slide, be transferred from an area of the light-microscopical unit to a separate area for X-ray analysis, 
         FIG. 10  depicts, supplementary to  FIG. 9 , the setting of the distance between the sample surface and the electron beam outlet port by means of laser triangulation. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows the design principle of the invented observation and analysis unit with a facility for light-microscopical observation, and subsequent direct sample analysis. For the sake of clarity, only one microscope objective  2  of the light-microscopical unit provided for the magnified imaging and optical evaluation of a sample  1  is shown. As mentioned in the beginning, light microscopes and their ray paths are known and need no further explanation here. 
     In  FIG. 1  one can see an electron source  3 , which generates an electron beam  4  that can be directed at the sample  1  below the microscope objective  2 . On account of the interactions of the electron beam  4  with the sample  1 , X-ray radiation  5  is generated that is characteristic of the chemical composition of the sample  1  within the interaction volume. 
     The X-ray radiation emitted by the sample  1  under electron irradiation is spectrally characterized by an X-ray detector  6 . The X-ray detector  6  employed may be a cooled Si(Li) detector or a silicon drift detector as commonly used in electron microscopes. 
     The detecting direction of the X-ray detector  6  preferably forms the smallest possible angle with the line normal to the surface of the sample  1  in order to maximize the detection efficiency especially as far as light elements contained in the sample are concerned. For this purpose, it is advantageous to arrange either the electron source  3  or the X-ray detector  6  in or near the ray path of the microscope objective  2  of the light-microscopical unit. The X-ray detector  6  is preferably arranged in such a way that it captures as many X-ray quanta as possible. For this purpose, it is placed as close as possible to the electron impact site, so that a large solid angle is captured. 
     In connection with the problem to be solved, a compact electron source  3  is suited, which consists of an electron emitter and an electrode arrangement for acceleration and focusing (not shown in the drawing). The electron energy is, e.g., &gt;15 keV. 
     The requirements the electron beam  4  must satisfy are less exacting than those to be met by a scanning electron microscope. For example, a beam width of a few micrometers (μm) is absolutely sufficient, because, due to the energy used for analysis, the spatial resolution, which is determined by the interaction volume, is not any better as a rule. Moreover, a relatively small beam diameter gets immediately enlarged as the electrons are scattered in air. Furthermore, the electron beam  4  may remain permanently aligned and need not be moved across the sample  1  in a scanning mode. 
     Within the electron source  3  there is a vacuum, so that free electrons can be generated and focused with the fewest possible scatter processes. The vacuum is generated by a multi-stage, e.g., two-stage pump system, which forms a unit with the electron source  3  and consists of a backing vacuum pump and a high-vacuum pump (not shown on the drawing). The backing vacuum pump is connected to the lower end of the electron source  3 , which faces the sample  1 , and there is connection to the high-vacuum pump, which is connected to the upper end of the electron source  3 , which faces away from the sample  1 . In this way, a pressure gradient is produced within the electron source unit, with the pressure decreasing from the lower to the upper end. 
     Placement of pressure-limiting apertures within the pump system, the pressure gradient can be precisely adapted. As a consequence, the electron source is configured in such a way that the free electrons are generated in the upper area and then focused by means of an electron lens system (not shown) towards the lower end, where they leave the electron source  3  through a suitable device, e.g., through a tubule  7 . 
     At the outlet port of the tubule  7 , a pressure-limiting aperture is provided, so that the sample  1  can be analyzed under ambient pressure. The pressure-limiting aperture may consist of several stages. To improve the efficiency of the pump system, the tubule  7  may be of a tapered design. 
     The distance between the sample  1  and the electron outlet port at the tubule  7  may be, e.g., &lt;0.5 mm. To minimize this distance, the tubule  7  itself or the entire electron beam unit may be arranged so as to be movable towards the sample  1 . Optionally, controlling this distance may be provided by mechanical contact between sample  1  and tubule  7 . In case of conductive samples  1 , this distance can be determined and controlled on the basis of an electric resistance or impedance measurement. 
     The electron beam  4  is directed at a selected region within the field of view of the microscope objective  2 , so that the electrons hit the sample in this region. On collision of the electrons with the atoms of the sample material, electrons are knocked out of the inner shells of the atoms. Such a state is unstable, which is why the missing electrons are immediately replaced by electrons richer in energy from higher orbitals. The energy difference is liberated in the form of X-ray quanta. The X-ray radiation  5  generated thereby is characteristic of the transitions and the respective atoms, and thus, for the elements existing in the sample region. 
     This X-ray radiation  5  is detected by the X-ray detector  6 . As shown in  FIG. 2 , the signal of the X-ray detector  6  is applied to an actuation and evaluation unit  8 , where it is evaluated and can be analyzed, e.g., by use of suitable software, whereupon the element distribution in the sample region irradiated is visually displayed on a monitor or printed out. 
     The entire system is supervised by a central computing unit  9 , which can control the light-microscopical unit and receive and process its data, and which is, via the actuation and evaluation unit  8 , is connected with the electron source  3 , the X-ray detector  6  and the drives of a movable sample stage  10 , which carries the sample  1 . It is thus possible to operate the observation and analysis unit by use of a single software program. 
     Furthermore, as shown symbolically in  FIG. 3 , the unit consisting of the microscope objective  2 , the electron source  3  and the X-ray detector  6  may be enclosed by a shielding  11 , which shields the X-ray radiation  5  off from the outside. 
     The shielding  11  may, for example, be permanently installed, in which case it prevents X-ray radiation  5  from leaking out at any time without being actuated, so that the electron source  3  can be actuated at any time without danger. Alternatively, the shielding  11  may be designed in such a way that it has to be manually closed every time before a sample analysis. In this case, the status of the shielding  11  is detected by the actuation and evaluation unit  8 , and the electron source  3  is actuated only if manual closure has been carried out correctly. As an alternative, it is also feasible that the shielding  11  be controlled by actuation and evaluation unit  8 , so that closure is effected automatically before the electron source  3  is switched on. In this version, the atmospheric pressure within the shielding  11  is maintained. 
     In this connection, the observation and analysis unit can be provided with a gas feeding means in addition, which makes it possible to flood the area between sample  1  and electron source  3  with a gas, which causes a decrease in the scattering of the electrons while retaining the atmospheric pressure. Gases having atomic numbers lower than nitrogen and oxygen, the main constituent elements of air, are especially suitable for that purpose. Helium, for example, is a particularly preferable gas; being a noble gas, it is harmless and chemically low-reactive. To minimize gas consumption, the outer confinement by the shielding  11 , which should be dimensioned as small as possible, can be sealed so that only the least possible amount of gas can leak out. 
     In this embodiment, the possibility of visual light-microscopical observation exists until immediately before the electron source  3  is switched on. As soon as the electron source  3  is switched on, a shutter  12 , controlled by the actuation and evaluation unit  8 , occludes the optical ray path to protect the user against the X-ray radiation  5 . Alternatively, the shutter  12  can be replaced with a permanently installed X-ray protective glass, so that light-microscopical observation need not be interrupted at any time. 
       FIG. 4  shows the sequence of processes in direct sample observation by use of the light-microscopical unit. The flow chart makes a difference between measurement in a single spot (solid-line connections) and measurement within a certain region (broken-line connections), for example, along a line or within an area. Therefore, the sequence of processes starts with selecting between the two ways. Measurement in a region consists of measurements of several individual spots. Because of the finite resolution, a spot measurement actually means a measurement in a region of several micrometers (μm), resulting from the dissipation volume of the electron beam  4 . Nevertheless, this is regarded as a spot measurement here. A measurement across a region of several spots is given if the electron beam  3  has to be positioned from one spot on the sample to another, necessitating a relative movement between the two spots. 
     For measurement in a spot, the spot in which the element analysis is to be carried out, is selected in the light-microscopical image after or during its being recorded. This may be done, e.g., by clicking on the spot in the image with a mouse pointer displayed by the software. Once the measurement spot has been identified, the sample  1  is automatically positioned by movement of the sample stage  10  so that the spot to be measured on the sample  1  is at the focus of the electron beam  4 . With positioning accomplished, the electron source  3  is automatically activated by the actuation and evaluation unit  8 , and the electron beam  4  is directed at the selected sample detail. 
     The characteristic X-ray radiation  5  produced in this place is detected by the X-ray detector  6  and read out via the actuation and evaluation unit  8 . By means of the software, the spectrum measured is automatically analyzed, and the exact element composition in the measurement spot selected is output as a result. The time from selecting up to the output of the result essentially depends on the beam current and the sensitivity of the X-ray detector  6 ; at maximum, it amounts to several seconds. 
     In a measurement in a larger region consisting of several measuring spots, at first individual measuring spots in this region are identified that are to be moved to in succession. A list of these spots is created in the computing unit  9 . Thereupon, the electron beam  4  is automatically positioned to the first spot of the list, and the measurement is carried out as described above, so as to obtain the element composition in this spot. The procedure is then repeated for all spots that make up the measuring region. When all measuring spots have thus been processed, the spatial distribution of elements is displayed as a result. This can be accomplished, e.g., by a colored or other graphic overlay on the light-microscopical image. 
       FIG. 5  shows a Monte Carlo simulation of the interactions of an electron beam  4  of 30 keV energy and 1 μm beam diameter in air at an atmospheric pressure of 1 bar and a density of 1.293 kg/m 3  with the sample  1 . After a path length of 500 μm, 97% of the electrons have lost less than 1 keV of energy, thus still having sufficient energy left to excite X-ray emission in a sample  1  placed below it. To be sure, the beam diameter increases due to scattering at the air molecules, but it still is less than 50 μm. By local feeding of helium instead of air into the space between the electron outlet port and the sample  1 , scattering can be reduced and, thus, a smaller beam diameter be achieved. 
     Supplementing  FIG. 3 ,  FIG. 6  shows an embodiment provided with a device for adjusting the electron beam  4  relative to the sample  1 . For this purpose, a laser beam  13  is used, which marks the desired electron impact site on the sample  1 . Generated by a laser diode  14 , the laser beam  13  is coupled into an optical fiber  16  via an optical coupling system  15 , the said optical fiber preferably being run above the tubule  7 . At the end of the optical fiber  16  there is a microlens  17  for focusing the laser beam  13 . The optical fiber  16  is connected with the tubule  7  by holders  18 . This arrangement is adjusted in such a way that, with a minimum focal spot of the laser beam  13  on the sample  1 , the electron impact site is visibly marked. A prior initial adjustment of the laser beam  13  relative to the electron source  3  can be done by means of a phosphorescent screen (not shown on the drawing), which also renders the electron impact site visible. 
       FIG. 7  shows another example embodiment, in which the electron source  3  is miniaturized to such an extent that it can be integrated into a revolving objective nosepiece  19  of the light-microscopical unit. In the revolving objective nosepiece  19 , the electron source  3  is located in place of one of several microscope objectives  2 . 
     In this case, X-ray analysis of the sample  1  simultaneously with light-microscopical observation is not possible, though, but the fast possible change-over between microscope objectives  2  and electron source  3  by the precise rotation of the revolving objective nosepiece  19  is not a disadvantage in that respect. An advantage is that the electron beam  4  hits the sample surface at a right angle, so that shading effects are avoided. Also, lateral positioning of the electron beam  4  does not depend on the distance between the electron source  3  and the sample  1  here, so that the electron source  3  needs to be adjusted only once, i.e. during installation. 
     The electron source  3  can be fixed to the revolving objective nosepiece  19  either directly or via a suitable adapter; for example, it may be provided with a matching thread so that it can be screwed right into the revolving objective nosepiece  19 . The actuation and evaluation unit  8  and the vacuum pumps are located outside the revolving objective nosepiece  19  and are connected with the electron source  3  via supply lines for power supply, control signals and vacuum. 
     In the view presented by  FIG. 7 , the microscope objective  2  is inactive and laterally moved out of action, as are other microscope objectives  2  (not shown), whereas the electron source  3  is in working position. The X-ray detector  6  arranged on a side can be activated in this configuration. If, however, a microscope objective  2  instead of the electron source  3  is brought into the working position by a turn of the revolving objective nosepiece  19 , both the electron source  3  and the X-ray detector  6  are switched to an inactive state. 
     Furthermore, during element analysis, the X-ray radiation  5  can optionally be screened towards the outside, as already explained in the context of  FIG. 3 . 
     The miniaturized electron source  3  to be integrated into a revolving objective nosepiece  19  is shown in  FIG. 8 . The external interfaces provided comprise a hose  20  for vacuum connection and electrical feed lines  21  for power supply and actuation of the electron source  3  and the electron lens system if provided. Individual components of the electron source  3  and of the electron lens system, which have to be very compact because of the limited space available, may be fabricated in a miniaturized manner in a microsystem technology known as MEMS (microelectromechanical system) technology. 
     To generate an electron beam having an energy of 30 keV, a simple electrode arrangement with an overall length of &lt;3 mm is sufficient. For example, one uses an electron emitter to generate free electrons, which are then accelerated along the acceleration section and concentrated in a single lens before they exit through the aperture. In a highly simplified embodiment, one can do without the single lens and merely have the electron beam cut off by the aperture, although one has to put up with a lower current in this case. 
     The electron lens system may consist, e.g., of a system of conductive and insulating layers, with different potentials being applied to the conductive layers, so that the free electrons are concentrated, accelerated and focused by the fields generated. Further, the electron lens system is arranged towards the outlet port of the electrons, which constitutes a pressure-limiting aperture relative to the normal atmospheric pressure environment. The vacuum system within this electron source unit is not shown in detail here, but, as explained above, ideally it is a multi-stage vacuum system also provided with various pressure-limiting elements. 
     Optionally, also the X-ray detector  6  can be fitted in the revolving objective nosepiece  19  in place of a microscope objective  2  immediately next to the electron source unit. In this case, positioning the electron source automatically also positions the X-ray detector  6 , and no extra means for lateral fixing of the X-ray detector  6  is required. 
       FIG. 9  shows an embodiment in which the sample  1  can be moved out of the area of the microscope objective  2  by a slide  22  and transferred to a separate area for X-ray analysis. With this it is also possible to position the electron source  3  to a place vertically above the sample  1 ; in this case, the size and weight of the electron source  3  are less restricted than they are in the example according to  FIG. 8 . 
     Another advantage is that the light-microscopical unit, or at least the microscope objective  2 , need not be integrated within the shielding  11 . Nevertheless, the area for X-ray analysis is firmly joined directly to the light-microscopical unit. The slide  22  ensures fast transfer. Due to a fixed moving distance of the slide  22 , which corresponds to the distance between microscope objective  2  and electron source  3 , it is ensured that the detail of the sample  1  observed through the microscope objective  2  is identical to the detail analyzed in the area for X-ray analysis. Fast covering of the moving distance is made possible by suitable mechanical or electrically controlled stops. In addition to the one-dimensional movement of the slide, the arrangement can, as described above, comprise a sample stage  10 , on which the slide moving device is permanently mounted, and which permits traveling to any position on the sample, whereas the slide device permits precise transfer of the sample positions traveled to. 
     The shielding  11  of the area for X-ray analysis is designed in such a way that, by means of a closing plate  23  fitted to the slide  22 , it is closed automatically as soon as the sample  1  is in the measuring area. 
     Supplementing  FIG. 9 ,  FIG. 10  shows how the working distance between the sample  1  and the electron outlet port can be set by means of laser triangulation. For this purpose, a laser source  24  is arranged and adjusted in such a way that a laser beam  25  hits the electron impact site at the desired working distance. The laser spot is detected by a CCD sensor  27  via an optical imaging system  26 . After sample transfer, a movement of the electron source  3  relative to the sample  1  is released by the signals of the CCD-Sensors  27 , and the desired working distance is set. 
       FIG. 10  also shows a possible position of the X-ray detector  6 . Preferably, however, the X-ray detector  6  occupies a position outside the drawing plane, e.g., normal to it, in order to leave sufficient space for providing the triangulation device. 
     LIST OF REFERENCE NUMBERS 
     
         
           1  sample 
           2  microscope objective 
           3  electron source 
           4  electron beam 
           5  X-ray radiation 
           6  X-ray detector 
           7  tubule 
           8  actuation and evaluation unit 
           9  computing unit 
           10  sample stage 
           11  shielding 
           12  shutter 
           13  laser beam 
           14  laser diode 
           15  optical coupling system 
           16  optical fiber 
           17  microlens 
           18  holders 
           19  revolving objective nosepiece 
           20  hose 
           21  supply lines 
           22  slide 
           23  closing plate 
           24  laser source 
           25  laser beam 
           26  optical imaging system 
           27  CCD sensor