DE102011005731B4 - Device for sample analysis by means of X-ray spectroscopy - Google Patents

Abstract

Device for analyzing a sample (1) by means of X-ray spectroscopy for elemental analysis and element qualification, comprising - a microscopic arrangement for observing the sample (1), wherein the sample region to be analyzed is located in the focal plane of a microscope objective (2), - an electron source (3) from which an electron beam (4) can be aligned with a region of the sample (1) selected by means of the microscopic arrangement, and - an X-ray detector (6) designed to detect the substance produced by the interaction of the electron beam (4) with the sample material X-radiation (5), wherein - the electron source (3) and the X-ray detector (6) are designed as a structural unit in the form of an analysis module (7), and wherein - the analysis module (7) together with the microscope objective (2) on an objective changer is arranged, or wherein - the analysis module (7) with a pivoting device (21) for pivoting in a Bere I between the microscope objective (2) and sample (1) is in communication, wherein the pivoting while maintaining the working distance between the microscope objective (2) and sample (1) or after increasing the distance between the microscope objective (2) and sample (1) can be realized, such that the objective changer or the pivoting device is designed for temporary positioning of the analysis module (7) in a working position in which the sample region to be analyzed is located in the electron beam (4) and at the same time in the reception region of the X-ray detector (6), wherein Shield (8) is provided, by which the electron source (3), the X-ray detector (6) and the sample area to be analyzed are hermetically separated from the surrounding free atmosphere and wherein a device for feeding the volume of space within the shield (8) a gas, preferably with helium, is present.

Description

The invention relates to a device for analyzing a sample by spectroscopic evaluation of X-radiation, which arises due to the interaction of an electron beam with the sample material. The invention is particularly suitable for elemental analysis and elemental qualification in materials microscopy, e.g. As in metallurgical samples or in the particle analysis.

Elemental analysis is a method for controlling the purity of organic and inorganic materials by determining the elements contained therein, such as carbon, hydrogen, nitrogen or sulfur. A distinction is made between qualitative elemental analysis, in which only the constituents are determined, and quantitative elemental analysis, in which the mass fractions of the found elements are determined.

According to the current state of the art, different methods are used for elemental analysis, such as EDX (energy dispersive X-ray spectroscopy), XRF (sequential X-ray fluorescence analysis) or photoluminescence.

All of these known methods have the disadvantage that they are used as independent methods and methods spatially separated from a light microscope. This leads to an interruption of the workflow, since the sample to be examined must be examined with a separate device, which is accompanied by a number of disadvantages, such as the repeated visit of the same sample site, preparation and introduction of the sample in a vacuum environment, in particular in the EDX analysis , Damage to the sample, etc.

In US Pat. No. 6,452,177 B1 For example, an electron beam-based material analysis system is described, which is particularly suitable for investigations under atmospheric pressure. Disadvantageously, no microscopic observation of the sample is possible with this system. Furthermore, the sample area where the material characterization takes place is relatively large with an analysis spot diameter> 100 μm, whereby closely spaced structures smaller than 100 μm can not be discriminated from each other.

In addition, there is no shielding for the X-radiation, and the time for a measurement is relatively large.

In JP 2007292476 A the integration of an X-ray source into a nosepiece is described. This design has the disadvantage that, in particular in XRF analyzes, the resolution of very small structures is not possible to the same extent as would be the case with EDX. In addition, the formation of the shield against X-radiation in this case is relatively expensive.

From the US 2008/0185509 A1 a device is known with which a sample can be analyzed by electron optics. In addition, it is possible to illuminate the sample with laser light or to detect the photons resulting from the particle bombardment.

In the US 2002/0053634 A1 An electron microscope is described, in which the focus position is determined by optics of light.

In the EP 0 849 765 A2 an ion beam system is described which operates under vacuum conditions. The blasting system and an electronic light-optical microscope are installed in a vacuum chamber. The workpiece is positioned by a displacement mechanism either over the shot-blasting system or over the microscope.

The DE 10 2009 041 993 A1 describes an observation and analysis device that allows a light-optical observation and an electron-optical analysis of the sample. A microscope objective, an electron beam source and an X-ray detector are independent assemblies. Optionally, these assemblies may be arranged in a nosepiece.

In the DE 100 07 650 C2 a light-optical microscope is described with an electron beam device. The electron beam device is integrated in the revolver of the microscope. If the electron beam device is pivoted in by means of the revolver over the sample, this can be excited by means of electron radiation.

Proceeding from this, the object of the invention is to develop a device for sample analysis by X-ray spectroscopy of the type described above so that the analysis of a sample can be made immediately after their microscopically enlarged representation and the analysis can be done with a compact module.

• – eine mikroskopische Anordnung zur Beobachtung der Probe, wobei sich der zu analysierende Probenbereich in der Fokusebene eines Mikroskopobjektivs befindet,
• – eine Elektronenquelle, von der ein Elektronenstrahl auf einen mittels der mikroskopischen Anordnung ausgewählten Bereich der Probe ausrichtbar ist, und
• – einen Röntgenstrahlen-Detektor, ausgebildet zur Detektion der durch die Wechselwirkung des Elektronenstrahls mit dem Probenmaterial entstehenden Röntgenstrahlung, wobei
• – die Elektronenquelle und der Röntgenstrahlen-Detektor als Baueinheit in Form eines Analysemoduls ausgebildet sind, und wobei
• – das Analysemodul gemeinsam mit dem Mikroskopobjektiv auf einem Objektivwechsler angeordnet ist, oder wobei
• – das Analysemodul mit einer Schwenkvorrichtung zum Einschwenken in einen Bereich zwischen Mikroskopobjektiv und Probe in Verbindung steht, wobei das Einschwenken unter Beibehaltung des Arbeitsabstandes zwischen Mikroskopobjektiv und Probe oder nach Vergrößerung des Abstandes zwischen Mikroskopobjektiv und Probe verwirklichbar ist, so dass der Objektivwechsler oder die Schwenkvorrichtung zum temporären Positionieren des Analysemoduls in einer Arbeitsposition, in der sich der zu analysierende Probenbereich im Elektronenstrahl und zugleich im Empfangsbereich des Röntgenstrahlen-Detektors befindet, ausgebildet ist, wobei

eine Abschirmung vorhanden ist, durch welche die Elektronenquelle, der Röntgenstrahlen-Detektor und der zu analysierende Probenbereich von der umgebenden freien Atmosphäre hermetisch getrennt sind und wobei eine Vorrichtung zum Beschicken des Raumvolumens innerhalb der Abschirmung mit einem Gas, vorzugsweise mit Helium, vorhanden ist.According to the invention, such a device comprises

• A microscopic arrangement for observing the sample, wherein the sample region to be analyzed is located in the focal plane of a microscope objective,
• An electron source, from which an electron beam to an electron microscope Arrangement selected region of the sample is alignable, and
• - An X-ray detector, designed to detect the resulting by the interaction of the electron beam with the sample material X-ray radiation, wherein
• - The electron source and the X-ray detector are designed as a unit in the form of an analysis module, and wherein
• - The analysis module is arranged together with the microscope objective on an objective changer, or wherein
• - The analysis module is connected to a pivoting device for pivoting into a region between the microscope objective and the sample, the pivoting while maintaining the working distance between microscope objective and sample or after increasing the distance between microscope objective and sample is feasible, so that the objective changer or the pivoting device for Temporary positioning of the analysis module in a working position in which the sample area to be analyzed in the electron beam and at the same time in the receiving area of the X-ray detector is formed, wherein

a shield is provided by which the electron source, the X-ray detector and the sample area to be analyzed are hermetically separated from the surrounding free atmosphere and wherein there is a device for feeding the volume of space within the shield with a gas, preferably helium.

In contrast to the prior art, it is possible with the device according to the invention to perform both the light microscopic and the electron beam excited examination, without a significant interruption of the workflow is required because of a change between two locally separate devices. In addition, higher throughput rates are possible when analyzing a series of samples.

Design features of the device according to the invention are specified in the claims 2 to 6.

With a laser-optical aiming beam in the visible wavelength range, a marking or calibration of the electron impact point on the specimen can be carried out in a simple manner. Alternatively, for the same purpose, a phosphorescent element may be provided for characterizing or calibrating the electron impact site.

It is particularly advantageous if one or more objectives associated with the light-microscopic arrangement are arranged together with the analysis module on an exchange device in order to be able to selectively exchange them with one another for the purpose of active use.

In a likewise advantageous embodiment of the invention, the area for visual observation of the sample by means of a light microscope arrangement on the one hand and the area for analysis of the sample with the analysis module on the other hand, although within the device according to the invention, but spatially separated from each other, as below with reference to an embodiment is explained in more detail.

The sample is advantageously surrounded by a gas under or near atmospheric pressure during analysis by the electron beam source and the X-ray detector.

With the device according to the invention, a microscopically small sample area can be analyzed in a spatially resolved manner, wherein a point analysis is possible within a few seconds due to the intended beam strengths.

The further advantages of the arrangement according to the invention, in addition to the possibility for direct sample analysis, are that the selection of the desired sample spot is possible directly in the light microscope image. With the optional automatic displacement of the sample relative to the electron source, the selected sample site can be centered under the electron source and the X-ray spectrum can be automatically recorded and evaluated.

Particularly advantageous is the compact design of the electron source and the X-ray detector in the form of the analysis module.

• – für den Arbeitsablauf bei der Materialmikroskopie aufgrund der kompletten Integration des Analysemoduls in einen Objektivrevolver ohne die Notwendigkeit, hierfür den Ort der Probe zu verändern. Dies bedeutet eine erhebliche Zeit- und Kostenersparnis bei der Analyse,
• – bezüglich des Messsignals und der Messzeit, da aufgrund der Ausführung in Form eines Analysemoduls der Abstand von Anregungsquelle und Detektor zur Probe auf ein Minimum von beispielsweise < 0.5 mm reduziert werden kann. Durch diesen sehr geringen Abstand werden eine effizientere Probenanregung und die Detektion von Röntgenquanten nahezu im gesamten Messraum erzielt. Dies geht einher mit einem deutlich verbesserten Messsignal-Rauschverhältnis und einer Verkürzung der Messzeit im Vergleich zu bekannten Verfahren.
• – hinsichtlich der lateralen Auflösung, da die Evakuierung des Messbereichs die Messung in Vakuumumgebung auf der Mikroskop-Plattform ermöglicht. Durch die Messung in Vakuumumgebung wird die Streuung der Elektronen reduziert, wodurch die laterale Ortsauflösung insbesondere bei der Analyse von Strukturen < 5 μm – im Gegensatz zur Messung in Helium-Atmosphäre – reduziert werden kann,
• – für die Justage, da aufgrund der festen Zuordnung der Komponenten innerhalb eines gemeinsamen Gehäuses der Aufwand bei der Justage der optischen Achsen von Lichtmikroskop und EDX-Analysemodul minimal ist,
• – für den Arbeitsablauf bei der EDX-Messung, da bei der lichtmikroskopischen Beobachtung der zu untersuchende Probenbereich mit dem Fadenkreuz im Okular zur Deckung gebracht wird. Das Fadenkreuz markiert die Stelle an der – nach Positionierung des EDX-Analysemoduls auf der optischen Achse durch Drehen des Objektivrevolvers oder Einschwenken in die optische Achse – die Elementanalyse erfolgt. Das Fadenkreuz entspricht dem Auftreffpunkt des Elektronenstrahls und damit dem Ort, an dem durch Elektronen-Materie-Wechselwirkung die materialspezifische Emission von Röntgenstrahlen erfolgt,
• – hinsichtlich einer automatisierten Helium-Spülung, indem beim Einschwenken des Analysemoduls ein Relais angesteuert und dadurch das Ventil der He-Zuleitung geöffnet wird. Durch den geringen Medien-Zufluss und die geringere Dichte von Helium verbleibt das Helium in dem Messvolumen des Analysemoduls und verdrängt die Luft, wodurch sich zugleich die Elektronen-Transparenz der anregenden Primärelektronen deutlich erhöht,
• – bezüglich einer optionalen Evakuierung des Messvolumens, indem die hermetische Verrieglung des Messvolumens über die Zuleitung auch die Evakuierung des Messvolumens ermöglicht,
• – ein vereinfachter Start der Messung: per Tastendruck erfolgt die Emission des Elektronenstrahls auf den mit dem Fadenkreuz markierten Probenbereich bei simultaner Detektion bzw. Integration der Röntgenquanten mit einem energiedispersiven Detektor,
• – in bezug auf die Abschirmung der Röntgenstrahlung durch die Kapselung des Messbereichs mit einem Teleskopgehäuse kann die bei der Messung erzeugte Röntgenstrahlung auf ein für den Benutzer ungefährliches Maß reduziert werden. Die Messung durch Anregung mit dem Primärelektronenstrahl ist nur möglich, wenn der Messbereich komplett gekapselt ist und der ideale Arbeitsabstand für einen bestmöglichen Fokus des anregenden Elektronenstrahls auf der Probe eingestellt ist. Der ideale Arbeitsabstand ist dann erreicht, wenn beispielsweise die Triggerschwelle für das Auslösen einer Schaltfunktion durch die relative Bewegung des Teleskopgehäuses ausgelöst wird,
• – aufgrund der räumlichen Trennung von Analysemodul und Mikroskopobjektiv, indem das Analysemodul anstelle des Mikroskopobjektivs in den optischen Strahlengang eingeschwenkt wird,
• – bei der Kalibrierung und Justage des einschwenkbaren Analysemoduls, da die optischen Achsen von Mikroskopobjektiv und Analysemodul deckungsgleich sind. Wenn das Fadenkreuz mittig und scharf abgebildet wird, z. B. mittels Autofokus-System mit Kantenauswertung, stimmt sowohl die Position als auch der Abstand für die EDX-Analyse zu der vorher mit dem Lichtmikroskop markierten Probenstelle.

Concrete advantages compared to the prior art continue to arise

• - For the process of material microscopy due to the complete integration of the analysis module in a nosepiece without the need to change the location of the sample. This means a considerable time and cost savings in the analysis,
• - With respect to the measurement signal and the measurement time, since due to the execution in the form of an analysis module, the distance from the excitation source and detector to the sample to a minimum, for example, <0.5 mm can be reduced. This very short distance results in more efficient sample excitation and the detection of X-ray quanta almost in the entire measurement space. This is accompanied by a significantly improved signal-to-noise ratio and a shortening of the measurement time in comparison to known methods.
• - in terms of lateral resolution, since the evacuation of the measuring range allows the measurement in a vacuum environment on the microscope platform. By measuring in a vacuum environment, the scattering of the electrons is reduced, whereby the lateral spatial resolution, in particular in the analysis of structures <5 microns - in contrast to the measurement in helium atmosphere - can be reduced,
• - For the adjustment, since due to the fixed assignment of the components within a common housing, the effort in the adjustment of the optical axes of light microscope and EDX analysis module is minimal,
• - For the workflow in the EDX measurement, as in light microscopic observation of the sample area to be examined is brought into line with the crosshairs in the eyepiece. The crosshair marks the point at which - after positioning the EDX analysis module on the optical axis by rotating the objective turret or swiveling into the optical axis - the element analysis takes place. The crosshair corresponds to the point of impact of the electron beam and thus to the location at which the material-specific emission of X-rays takes place by electron-matter interaction.
• - With regard to an automated helium flushing, by activating a relay during pivoting of the analysis module and thereby opening the valve of the He supply line. Due to the low media inflow and the lower density of helium, the helium remains in the measurement volume of the analysis module and displaces the air, which at the same time significantly increases the electron transparency of the exciting primary electrons,
• With regard to an optional evacuation of the measuring volume, in that the hermetic locking of the measuring volume via the supply line also enables the evacuation of the measuring volume,
• A simplified start of the measurement: at the touch of a button, the emission of the electron beam to the sample area marked with the crosshairs takes place with simultaneous detection or integration of the X-ray quanta with an energy-dispersive detector,
• With respect to the shielding of the X-radiation by the encapsulation of the measuring area with a telescope housing, the X-ray radiation generated during the measurement can be reduced to a level which is harmless to the user. The measurement by excitation with the primary electron beam is only possible if the measuring range is completely encapsulated and the ideal working distance is set for the best possible focus of the exciting electron beam on the sample. The ideal working distance is reached when, for example, the trigger threshold for triggering a switching function is triggered by the relative movement of the telescope housing,
• Due to the spatial separation of the analysis module and the microscope objective, in that the analysis module is pivoted into the optical beam path instead of the microscope objective,
• - during calibration and adjustment of the swivel-in analysis module, since the optical axes of the microscope objective and the analysis module are congruent. If the crosshairs are shown in the middle and sharp, z. B. by autofocus system with edge evaluation, both the position and the distance for the EDX analysis to the previously marked with the light microscope sample point.

The analysis device will be explained in more detail below with reference to exemplary embodiments. In the accompanying drawings show:

1 a variant embodiment of the device according to the invention with an analysis module, which has the form of a lens and is received in a nosepiece,

2 a variant embodiment of the device according to the invention, in which the analysis module is connected to a pivoting device for pivoting between a microscope objective and the sample,

3 3 shows a further embodiment variant of the device according to the invention with an analysis module in the outer form of an objective, but with an electron beam running concentrically to the optical axis of the objective;

4 an embodiment variant with means for the best possible focusing of the electron beam on the sample.

1 shows the basic structure of the device according to the invention with light microscopic observation option and direct sample analysis. For the sake of clarity, the light microscopic arrangement is used for the enlarged representation and optical evaluation of a sample 1 is provided, only a microscope objective 2 shown. Light microscopes and their beam paths are known and therefore require no further explanation at this point.

It can be seen in 1 an electron source 3 that has an electron beam 4 generated, to the test 1 is directed. Due to the interactions of the electron beam 4 with the sample 1 arises X-radiation 5 , which is characteristic of the chemical composition of the sample 1 within the interaction volume.

The case of electron irradiation from the sample 1 Outgoing X-ray emission comes with an X-ray detector 6 spectrally characterized. As an X-ray detector 6 For example, a cooled Si (Li) detector or a silicon drift detector can be used.

The reception direction of the X-ray detector 6 closes with the perpendicular to the surface of the sample 1 preferably angles as small as possible to maximize the detection efficiency, particularly with respect to light elements contained in the sample. This can be advantageous either the electron source 3 or the X-ray detector 6 in or close to the beam path of the microscope objective 2 the light microscopic arrangement are brought. The X-ray detector 6 is preferably arranged so that it detects as many X-ray quanta. For this purpose, it is brought as close as possible to the electron impact point, so that a large solid angle is detected.

In connection with the problem to be solved here is a compact electron source 3 suitable, which consists of an electron emitter and an electrode assembly for acceleration and focusing (not shown in the drawing). The electron energy is, for example,> 15 KeV.

To the electron beam 4 Compared to a scanning electron microscope, no such high demands are made. Thus, a beam width of a few micrometers is sufficient, since the spatial resolution, which is determined by the interaction volume, is usually not better due to the energy used for the analysis. In addition, the scattering of electrons in air immediately increases a relatively small beam diameter. Furthermore, the electron beam 4 also remain permanently aligned and does not necessarily have to be scanned over the sample 1 to be moved.

Inside the electron source 3 There is a vacuum, so that free electrons can be generated and focused under as few scattering processes as possible. The vacuum is generated by a multi-stage, for example, two-stage pumping system with the electron source 3 forms a unit and consists of a backing pump and a high vacuum pump (not shown in the drawing). The backing pump is at the bottom of the sample 1 facing the end of the electron source 3 connected, and there is a connection to the high vacuum pump, to the upper, the sample 1 opposite end of the electron source 3 connected. This creates a pressure gradient within the electron source unit, with the pressure falling from the lower to the upper end.

Pressure-limiting apertures within the pumping system allow the pressure gradient to be precisely adjusted. Consequently, the electron source is designed in such a way that the free electrons are generated in the upper region, which are then focused towards the lower end by means of electron optics (not shown) and there the electron source 3 leave.

According to the invention, the electron source 3 and the X-ray detector 6 as a unit in the form of an analysis module 7 educated. The analysis module 7 has here advantageously the outer shape of a lens housing and is with the microscope objective 2 , optionally also with other lenses, arranged on a lens changer.

Due to this configuration, it is possible in a simple manner, the analysis module 7 temporarily instead of the microscope objective 2 position so that the sample area to be analyzed in the electron beam 4 and at the same time in the reception area of the X-ray beam detector 6 located. This is the analysis module 7 relative to the sample 1 aligned, the electron beam 4 is aimed exactly at the sample area, the previously with the microscope objective located at this point 2 observed and selected as the result of this observation for material analysis. The microscope objective 2 has an optical axis 17 ,

The x-ray radiation 5 is using the X-ray detector 6 detected. The signal of the X-ray detector 6 It is applied to an evaluation unit (not shown) and is analyzed there by means of suitable software, according to which the element distribution in the irradiated sample area is visually displayed on a monitor or printed out.

The entire system is controlled by a central drive unit (not shown) which controls both the light microscopic device and receives and processes its data as well as with the electron source 3 and the X-ray detector 6 connected is.

Further, the analysis module 7 with a shield 8th coupled, which is exemplified here as a ring-shaped telescope housing and the radiation of the X-ray radiation 5 prevented to the outside.

The shield 8th is designed so that it can be measured by relative motion between sample before starting the sample analysis 1 and nosepiece is to close, preferably by lifting the sample 1 or the (not shown here) sample table on which the sample 1 is stored. The status of the shield 8th is detected by drive unit, and the electron source 3 will only be triggered if the closure is correct.

The device according to the invention is optional with a gas supply 9 equipped, in particular, for loading the volume within the shield 8th with helium is provided to cause a small scattering of the electrons. The supply takes place via a line 10 from a gas reservoir, not shown, through the shield 8th therethrough. Into the line 10 is a three-way valve 11 arranged, which in the in 1 shown switching position, the supply of gas into the volume within the shield 8th , in a second switching position via the line connection 12 on the other hand allows the evacuation of the volume. In this way, subsequent to the analysis, a rinse of the volume can take place. Is to the line connection 12 If necessary, a vacuum pump connected inside the shield 8th generates a negative pressure and the sample 1 be analyzed under this condition.

For the purpose of securely closing the shield 8th is a seal 13 provided here - adapted to the annular telescopic housing - is formed in the form of a sealing ring.

Furthermore, an electron-transparent membrane 16 present, through which focuses on the sample 1 directed electron beam 3 into the room or measuring volume within the shield 8th entry.

2 shows an embodiment of the device according to the invention, in which the analysis semodul 7 is coupled with a pivoting device. The pivoting device is for pivoting the analysis module 7 in the area between the microscope objective 2 and the sample 1 educated.

For the sake of clarity, for the same components, already based 1 have been explained in 2 again the same reference numerals. In this respect are out 2 again to the test 1 directed electron beam 4 , the X-radiation caused thereby 5 , an X-ray detector 6 , a shield here again in the form of a telescope housing 8th , a gas supply 9 , a lead 10 , a three-way valve 11 , a line connection 12 and a seal 13 seen.

In contrast to 1 Here is the X-ray detector 6 executed annular. It concentrically encloses a ring-shaped focussing device 15 for the electron beam 4 , Here is also an electron-transparent membrane 16 present, through which the entrance of the focused on the sample 1 directed electron beam 3 into the room or measuring volume within the shield 8th he follows.

The pivoting takes place by rotation about a parallel to the optical axis of the microscope objective 2 aligned axis of rotation 14 , depending on the design of the light microscope, either while maintaining the working distance between the microscope objective 2 and the sample 1 , or after increasing this distance, for example by lowering a (not shown) sample table on which the sample 1 is stored. In the pivoted state, the electron beam passes 4 Centric to extend the optical axis 17 of the microscope objective 2 , With the subsequent lifting of the sample table until it touches the seal 13 will the shield 8th closed and the analysis of the sample 1 will, as already shown 1 described, caused by a drive unit.

After analysis, rinse the volume inside the shield 8th and lowering the sample table with the sample 1 becomes the analysis module 7 swung out of the microscope beam path, so now again a microscope objective 2 be brought into the working position and the sample can be visually observed.

At the in 3 Again, the same reference numerals for the same components have been used as already in 1 and 2 , Here is the analysis module 7 - as already stated 1 described - performed in the form of a lens, together with other, not shown lenses arranged on a lens changer and can be pivoted to the place of these lenses. Unlike the execution after 1 Here again is the X-ray detector 6 designed in a ring shape and concentrically surrounds the likewise ring-shaped focusing device 15 for the electron beam 4 , He focuses on the sample 1 directed electron beam 4 occurs, comparable to 2 , also here by an electron-transparent membrane 16 through into the volume of space inside the shield 8th one.

Due to the vertical incidence of the electrons on the sample 1 Here, the distance between the electron source 3 and sample 1 be reduced to a minimum.

4 shows an embodiment variant for the best possible focusing of the electron beam 4 to the test 1 , Partly here is a shield 8th as shown in the embodiments according to 1 to 3 is used. Deviating from this, however, is in the direction of the optical axis 17 movable part of the shield 8th a photocell provided from a light source 18 , a retro reflector 19 and a photosensor 20 is formed. The focus of the electron beam 4 lies in a reference plane 21 caused by the position of the retroreflector 19 on the movable part of the shield 8th is defined. Thus, the reflector 19 in the direction of the optical axis 17 and thus relative to the frame fixedly arranged light source 18 and also the frame-fixed photosensor 20 displaceable.

When lifting the sample table in the direction of the optical axis 17 comes the sample table or - depending on the design of the sample - to rest against the lower, movable part of the telescopic shield 8th so with this part of the shielding 8th also the position of the retroreflector 19 relative to the light source 18 and the photosensor 20 is moved. The intensity of the retroreflector varies 19 received and to the photosensor 20 reflected light and thus the photosensor 20 output signal output. The sample is then in the best possible focus position when the output signal has reached its maximum.

In other words: Will the lower, movable part of the shield 8th moved upwards due to the telescopic design and the shield 8th compressed by this, the relative distance between the light source changes 18 and retroreflector 19 , At a predetermined displacement position, the light beam is reflected back a maximum. The case of the photosensor 20 emitted intensity signal is the indication that the electron beam 4 is optimally focused on the sample surface.

For a miniaturized version of an electron source, the following should be noted: In order to produce an electron beam with an energy of 30 KeV, a length of a simple electrode arrangement of <3 mm is sufficient. For example, free electrons can be generated in an electron emitter, which are then accelerated along the acceleration path and concentrated in a single lens before they exit through an aperture. In a very simplified embodiment can also be dispensed with the Einzelellinse by the electron beam is cut only through the aperture, but a lower current is to be accepted.

The focusing electron optics may, for example, consist of a layer system of conductive and insulating layers, wherein the conductive layers are set to different potentials, so that the free electrons are bundled, accelerated and focused by the resulting fields. The electron optics is further arranged to the exit opening of the electrons, which is a pressure-limiting aperture to the environment in the normal air pressure. The vacuum system within the electron source is a multi-stage vacuum system also with various pressure-limiting elements.

Claims (6)

Device for analyzing a sample ( 1 ) by means of X-ray spectroscopy for elemental analysis and element qualification, comprising - a microscopic arrangement for observing the sample ( 1 ), wherein the sample area to be analyzed in the focal plane of a microscope objective ( 2 ), - an electron source ( 3 ), from which an electron beam ( 4 ) to a region of the sample selected by the microscopic arrangement ( 1 ), and - an X-ray detector ( 6 ), designed to detect the interaction of the electron beam ( 4 ) with the sample material resulting X-radiation ( 5 ), wherein - the electron source ( 3 ) and the X-ray detector ( 6 ) as a structural unit in the form of an analysis module ( 7 ), and wherein - the analysis module ( 7 ) together with the microscope objective ( 2 ) is arranged on an objective changer, or wherein - the analysis module ( 7 ) with a pivoting device ( 21 ) for pivoting into a region between the microscope objective ( 2 ) and sample ( 1 ), wherein the pivoting while maintaining the working distance between the microscope objective ( 2 ) and sample ( 1 ) or after increasing the distance between the microscope objective ( 2 ) and sample ( 1 ) is realizable, so that the objective changer or the pivoting device for temporary positioning of the analysis module ( 7 ) in a working position in which the sample area to be analyzed in the electron beam ( 4 ) and at the same time in the reception area of the X-ray detector ( 6 is formed, wherein - a shield ( 8th ) is present, through which the electron source ( 3 ), the X-ray detector ( 6 ) and the sample region to be analyzed are hermetically separated from the surrounding free atmosphere, and wherein a device for feeding the volume of space within the shield ( 8th ) is present with a gas, preferably with helium. Device according to Claim 1, in which the electron beam ( 4 ) and centric to extend the optical axis ( 17 ) of the microscope objective ( 2 ), wherein when the analysis module is positioned or swiveled in ( 7 ) the focus of the electron beam ( 4 ) is located in the sample area to be analyzed. Device according to Claim 1 or 2, in which the entry of the electron beam ( 4 ) into the volume of space through an electron-transparent membrane ( 16 ) through. A device according to any one of claims 1 to 3, wherein there is a shield closure device and a control mechanism for safe closure with respect to the free atmosphere. Device according to one of claims 1 to 4, which with - a drive unit which generates control commands for the actuating devices, and - an evaluation unit, designed to analyze the spectrum of the X-radiation ( 5 ) Is provided. Device according to one of claims 1 to 5, which comprises means for the defined alignment of the electron beam ( 4 ) or the electron beam focus relative to the sample ( 1 ) by means of an optoelectronic arrangement, preferably consisting of a light source ( 18 ), which emits laser light in the visible wavelength range, and a photodetector arranged in the reception range of the laser light (US Pat. 20 ), having.

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