DE102013005173C5 - Measuring device and method for detecting a pulse distribution of charged particles - Google Patents

Abstract

A measuring device (100) adapted to detect a pulse distribution of an ensemble (1) of charged particles, comprising: - an electron optical imaging device (10) having an electron optical axis (OA), the electron optical imaging device (10) comprising an objective lens device (11) which is arranged to generate a pulse image (3) of the x and y components of the momentum vectors of the particles perpendicular to the electron optical axis (OA), - an energy analyzer adapted for energy resolved imaging of the ensemble (1), and - a detector means (30) adapted to receive the impulse image of the ensemble (1), the x and y components of the impulse vectors of the particles being detectable by coordinates of the particles in the impulse image, characterized in that the energy analyzer comprises a drift device (20) which is arranged to be traversed by the particles of the ensemble (1) with a time of flight - which depends on the z-component of the momentum vectors of the particles parallel to the electron optical axis (OA), - the detector means (30) for the time-resolved recording of the pulse image of the ensemble (1) is set, wherein the z-components of the momentum vectors of the particles by the time of flight in the drift device (20) can be detected, and the electron-optical imaging device (10) further comprises: - a first telescope optics (12) for spatially generating a first real space intermediate image (4) of the ensemble (1) of the particles fixed position - a variable and perpendicular to the electron optical axis (OA) adjustable first aperture (13) adapted to define a field of view of the measuring device (100), wherein by the adjustable first aperture (13) a selection of position and Size of a sample area reaching the image is made possible, and- a retarding optics (14), which adjust the beam energy of the Particle to the potential of the drift device (20) is arranged, wherein the retarding optics (14) is arranged to decelerate the ensemble of the particles (1) and with respect to its image magnification and pulse image scaling to the drift device (20) and at least five, along the Electron-optical axis (OA) arranged Retardierungsoptik segments (141), with which the input and output side focal lengths of the retarding optics (14) are independently adjustable.

Description

The invention relates to a measuring device for detecting a pulse distribution of a set of charged particles, for. B. from a sample to be examined, is set up. In particular, the invention relates to a parallel imaging time-of-flight microscope for the simultaneous detection of the momentum and energy distribution of the ensemble of charged particles with optional spin filtering. The invention also relates to a method for detecting the momentum distribution of the charged particle ensembles. Applications of the invention are given in particular in investigations on solid surfaces by means of photoelectron emission.

The state of an electron is quantum mechanically completely defined by its momentum and spin degrees of freedom, which z. B. in the form of the three Cartesian components of each of the polar momentum vector (k _x , k _y , k _z ) and the axial spin vector (s _x , s _y , s _z ) can be represented. In special cases, only a subset of these six parameters is nonzero. This applies z. For a monoenergetic, unidirectional and fully polarized electron beam, in which only two parameters are different from zero. In elementary processes, such as electron scattering or photoemission, however, generally arise electron ensembles, which have a characteristic three-dimensional momentum and spin distribution. To fully characterize such processes, the three components of the momentum vector must be measured if there is no spin-dependent interaction. In the case of a spin-dependent interaction, the spin degree of freedom must additionally be determined, which in many cases ( z , The photoemission from ferromagnetic samples with unidirectional spin alignment) is characterized by a component.

It is well known that the momentum distribution of an ensemble of charged particles, e.g. As in photoelectron spectroscopy, to measure with an energy-dispersive spectrometer. Conventional energy dispersive spectrometers detect photoelectrons only in a limited angular range over a sample surface. The measurement of a full pulse distribution, which in the case of the photoelectrons represents a direct image of the electronic band structure in the pulse space, therefore requires a mutual pivoting of the sample and the spectrometer and a sequential measurement at different pivoting positions. The measurement with conventional energy-dispersive spectrometers is therefore a very time-consuming and error-prone procedure.

A significant improvement is achieved by applying a two-dimensional momentum distribution through an imaging dispersive spectrometer 100 ' according to 10 (Prior art) is detected (see Krömker et al. in "Rev. Sci. Instrum. "Vol. 79, 2008, pp. 053702-1 to 053702-7 ). The imaging spectrometer 100 ' comprises an electron-optical imaging device 10 ' for generating a pulse image of the x and y components (k _x , k _y ) of the momentum vectors of the electrons perpendicular to the optical axis ( z Axis), an energy analyzer 20 ' for the energy-resolved imaging of the electrons and a detector device 30 ' is arranged to receive the pulse image of the electrons. The energy analyzer 20 ' comprises an imaging energy filter in the form of a hemispherical spectrometer. The hemispherical spectrometer is constructed with two mutually offset, hemispherical electrodes, each of which can be traversed simultaneously by particles exclusively with a selected energy. The energy filter allows that with the spectrometer 100 ' a lateral momentum distribution at the selected energy can be detected simultaneously. The measurement of a full momentum distribution, however, requires that the lateral momentum distribution in the energy region of interest be measured sequentially in small steps (ie, with small energy increments).

Thus, sequential acquisition at different angles and / or at different energies is required for all spectrometer types described so far. With these methods, the acquisition of the entire momentum distribution of charged particles, in particular electrons, in the half space over a solid sample is very time consuming.

DE 10 2005 045 622 B4 discloses an arrangement for analyzing electron spin polarization with a parallel imaging electron microscope. The arrangement comprises a polarization-sensitive scattering target in an electron-optical beam path and a spatially resolving detector or an arrangement of a plurality of detectors for detecting the scattered electrons. The conventional technique is not designed for parallel energy selective measurements.

Out US Pat. No. 6,737,647 B2 An arrangement is known for imaging the particle ensemble pulsed emitted by a sample on a detector with a round-lens optical system. A part of the round lens optics is controllable so that the speed or trajectory of the particles is influenced and chromatic and / or spherical errors of the image are reduced.

The conventional technique is not designed for parallel measurements of particle pulses.

In the publications of G. Schönhense et al. ("Surface Science", Vol. 480, 2001, pp. 180-187) and H. Spiecker et al. ("Nuclear Instruments and Methods in Physics Research A", Vol. 406, 1998, p. 499-506) Photoelectron emission microscopes are described which have time-of-flight drift paths for an energy-resolved imaging of photoelectrons in spatial space. To achieve sufficient spatial resolution, the objective lenses of the described microscopes are equipped with aperture stops with which the pulse distribution of the detected particles is restricted. An energy-resolved imaging of electron ensembles in the momentum space is not possible with these microscopes.

Another photoelectron emission microscope with energy resolution is from M. Kotsugi et al. ("Review of Scientific Instruments", Vol. 74, 2003, pp. 2754-2758) described. Out DE 10 2010 010 981 A1 For example, an electron-optical analysis arrangement for analyzing the electron spin polarization of electrons is known.

The object of the invention is to provide an improved measuring device for detecting a pulse distribution of a charged particle ensemble, with which disadvantages of conventional techniques are avoided. In particular, the measuring device should enable the measurement of a full pulse distribution of the particles with reduced expenditure of time, improved energy resolution and / or improved reliability. The object of the invention is also to provide an improved method for detecting a pulse distribution of a charged particle ensemble, with which disadvantages of conventional techniques are avoided.

These objects are achieved by a measuring device or a method having the features of the independent claims. Advantageous embodiments and applications of the invention will become apparent from the dependent claims.

According to a first general aspect of the invention, the stated object is achieved by a measuring device which is used to detect a pulse distribution of an ensemble of charged particles, such. B. electrons, ions or positrons, in particular from a sample to be examined, is arranged and comprises an electron-optical imaging device, an energy analyzer and a detector device. The electron-optical imaging device has an objective lens device which is set up to generate a pulse image (reciprocal image) of the x and y components of the momentum vectors of the particles perpendicular to an electron-optical axis (hereinafter referred to as optical axis) of the measuring device, in particular the electron-optical imaging device is. The reciprocal image is not limited by an aperture stop. The energy analyzer is configured for an energy resolved mapping of the ensemble of particles. The detector device is adapted to receive the pulse image of the ensemble of particles, wherein the x and y components of the momentum vectors of the particles can be detected by coordinates of the particles in the momentum pattern.

According to the invention, the energy analyzer comprises a drift device which is arranged to be traversed by the particles of the ensemble with a time of flight which is parallel to the optical axis of the component of the momentum vectors of the particles ( z Component of the momentum vectors of the particles). In contrast to the energy analyzer conventionally used, the drift device advantageously does not constitute an energy filter with which particles with energies deviating from a specific interval are deflected out of the imaging beam path. Rather, an energy-resolved image is achieved by all the particles that are to be examined and are generated, for example, on a sample, depending on their energy successively through the drift path of the drift device and arrive at the end of the drift device. The limitation of the conventional technique to the sequential measurement in narrow energy intervals is overcome.

Furthermore, according to the invention, the detector device is set up for a time-resolved recording of the pulse image of the ensemble of charged particles. Therefore, with the detector device, the time of flight of all particles in the drift device can be measured. The time of flight is determined by the z-components of the momentum vectors of the particles due to the function of the drift means. Advantageously, therefore, together with the x and y components of the momentum vectors of the particles from the coordinates of the particles in the momentum image, all x, y and z components of the momentum vectors of the particles can be detected by the detector device in a common measurement operation. The measuring time and the error rate of the measurement, as they occur in the conventional sequential measurements are reduced. The energy resolution of the measurement is improved over conventional techniques.

According to a second general aspect of the invention, said object is achieved by a method for detecting a momentum distribution of a charged particle ensemble, such as e.g. As electrons, ions or positrons, which are generated on a sample examined, z. B. emerge from the surface of the sample. Preferably, the method according to the invention is carried out with the measuring device according to the first general aspect of the invention. The method comprises generating a pulse image of the particles with an objective lens device of an electron-optical imaging device, wherein the pulse pattern comprises the x and y components of the momentum vectors of the particles in a reciprocal plane of the objective lens device perpendicular to an optical axis of the electron optical imaging device. Furthermore, the method comprises energy resolved imaging of the ensemble with drift means traversed by the ensemble particles with a time of flight dependent on the z component of the momentum vectors of the particles parallel to the optical axis.

Furthermore, the method comprises a time-resolved recording of the pulse image of the ensemble with a detector device, wherein the x- and y-components of the momentum vectors of the particles by coordinates of the particles in the pulse image and the z-components of the momentum vectors of the charged particles as a function of the time of flight in the drift device are detected. Preferably, the position of the reciprocal plane of the objective lens device is achromatic, so that this plane does not move spatially with changed particle energy.

The measuring device according to the invention, hereinafter also referred to as "time-of-flight pulse microscope", and the method according to the invention avoid the loss of detection efficiency associated with conventional sequential detection in that all three Cartesian components of the pulse vector are detected simultaneously with high precision. In this case, for each detected particle, two pulse components (k _x , k _y ) are represented by the electron-optical imaging device, in particular an imaging electron-optical column, which can be constructed as in an electron microscope. This corresponds to the enlarged image of the reciprocal image plane. The third pulse component (k _z ) is detected by measuring the time of flight of the charged particle through the low-energy drift path of the drift device integrated into the column. This can be z. B. in the investigation of electrons in the energy interval of interest with a width of several electron volts all three pulse components of each emitted charged particle without losses in the half space on a solid sample detect.

An essential advantage of the time-of-flight pulse microscope is that, in contrast to conventional high-resolution electron microscopy, no aperture stop is placed in the reciprocal image plane (crossover) of the objective lens device, since the particle distribution in this reciprocal plane is being imaged. In contrast to conventional time-of-flight spectrometers, the k-parallel field of view can always be constant, the scaling factor constant, and the k-resolution constant. With sufficiently small starting energy of the particles, the acceptance angle range is unlimited. In particular, even at high starting energies, a constant field of view of approximately one to two Brillouin zones of typical single-crystal surfaces in the momentum space can always be imaged. This is particularly advantageous in a high energy photoelectron spectroscopy (HAXPES) application. In general, the spherical aberration is minimized for the application of the pulse mapping in order to simulate the largest possible field of view in the momentum space at the same time.

Advantageously, the energy selective measurement can be done at fixed settings, i. without geometric variation of the observation angle and without passing through voltages. The method requires a time structure (time pattern) which is impressed on the particle ensemble during the generation and / or during the imaging of the charged particles. The time structure of the particle ensemble is z. B. in the investigation of solid surfaces by a time structure of the exciting radiation. Advantageously, this time structure is available both for low-energy laser sources and for synchrotron radiation sources for exciting photoelectrons on solid surfaces.

A further advantage of the invention is that when using a matched electron optics with exclusively electrostatic elements, the time-of-flight pulse microscope is basically suitable for analyzing the momentum distribution of all types of charged particles, in particular of electrons, ions or positrons.

The gain in measurement efficiency can be estimated from available quantities. With time-of-flight technology, an energy resolution of 10 meV can be achieved without much effort, see eg BPS Kirchmann et al. in "Appl. Phys. A. "Vol. 91, 2008, pp. 211-217 , Electron-optical simulations show that without aberration correction an energy interval of about 10% of the drift energy can be used simultaneously. For an assumed drift energy of 30 eV, a permissible interval of about 3 eV results. At a detector-side time resolution of 200 ps and a drift path of the drift device of 800 mm, this results in an energy resolution of 30 meV, see, for. B. A. Oelsner et al. in "Rev. Sci. Instrum. "Vol. 72, No. 10, 2001, p. 3968 , Thus, about 100 energy intervals can be detected simultaneously.

A great practical advantage of the measuring device according to the invention is its size. While z. B. a conventional imaging dispersive electron spectrometer occupies a volume of more than 1 m ³ , the measuring device according to the invention in the form of a linear column with Diameter of 150 mm and a length in the range of 1 m can be realized.

A particular advantage of the method according to the invention is that it is possible to study processes in which two electrons with different energies are generated simultaneously, which can be detected in coincidence, even if their energy and direction of the momentum vector are different. Another advantage lies in the possibility of reducing the radiation exposure of the examined sample by orders of magnitude. Furthermore, the method is particularly well suited to investigate ultrafast dynamic processes. For example, a fast excitation signal (photon or field pulse) can be synchronized with the sample signal over a variable time delay to perform so-called pump-probe experiments. To increase the resolution, a conventional aberration correction (mirror, multipole) or dynamic aberration correction is also possible.

According to the invention, the electron-optical imaging device comprises a first telescope optics, which is set up to produce a first real-space intermediate image (first Gaussian intermediate image) of the ensemble of particles with a spatially fixed position, a variable and adjustable perpendicular to the optical axis first aperture (Aperture, aperture stop), which is set up to define a field of view of the measuring device, and a retarding optics, which is adapted to adapt the beam energy of the particles to the potential of the drift device.

With the first telescope optics, the first intermediate image is advantageously produced in a spatially fixed plane, wherein a definition of the position and size of the sample region reaching the image is made possible by the adjustable first diaphragm. Furthermore, with the adjustable first aperture, to increase the pulse resolution, the size of the source volume on the sample in the first intermediate image along the optical axis can be limited and defined.

Advantageously, the ensemble can be braked with the retarding optics and adjusted with respect to its image magnification and pulse image scaling to the drift device. The retarding optics is set up to adjust the entry conditions into the flight time path into energy and angular divergence. The adaptation comprises, in particular, provision of an intermediate pulse image of the ensemble at the beginning of the drift device and a common z-component pulse shift of all particles for adaptation to the potential in the drift device.

According to a further preferred embodiment of the invention, a second telescope optics is provided, with which a telescopic beam path is provided by the drift device to the detector device. The second telescope optics advantageously makes it possible to focus a further intermediate impulse image of the ensemble on the detector device, so that the time-resolved recording of the impulse image of the ensemble can be improved.

Preferably, the objective lens device comprises an extractor electrode arranged to generate an extractor field relative to the sample and along the optical axis has a thickness of at least half the diameter of the electrode aperture (bore diameter), wherein within the extractor along the optical axis a portion having a In comparison to the extractor field reduced field strength is formed. Advantageously, with the said thickness of the extractor electrode is achieved that an undesirable field penetration of the downstream electrodes is avoided and the particles in the extractor field, the desired acceleration energy, for. B. 20 keV, for A-minimization minimization and to minimize the field curvature reach.

According to a particularly preferred embodiment of the invention, the extractor electrode comprises a plurality of extractor electrode segments, which are distributed around the optical axis in the azimuthal direction. The extractor electrode segments provide the ability to create a non-rotationally symmetric extractor field and to generate a beam correction. The beam correction is particularly advantageous if the optical axis is not aligned perpendicular to the surface of the examined sample, but the surface is tilted relative to the optical axis. If a manipulator is missing for sample tilting or has only a limited operating range, different voltages can be applied to the extractor electrode segments to achieve the beam correction. The quality of the beam correction increases with the number of extractor electrode segments. In practice, it has proved to be advantageous if the extractor electrode comprises at least four, in particular at least eight extractor electrode segments.

According to a further embodiment of the invention, the retarding optics comprises at least five retarding optical segments arranged along the optical axis, with which input and output focal lengths of the retarding optics can be set independently of one another. For this purpose, depending on the voltages of the retarding optical segments, the location of the electrostatic lens effect within the Retardation optics are moved. Advantageously, the retarding optics segments allow the beam energy of the particles to be adapted to the potential of the drift device independently of the potential of the upstream upstream electrodes.

Advantageously, the invention offers the possibility of carrying out a spin-dependent imaging of the ensemble of the charged particles. The measuring device may be equipped according to a variant of the invention with an adjustable Spinfiltereinrichtung. The spin filter device is preferably arranged immediately before the low-energy drift path. By spin filtering, in addition to the momentum components of the particles, a component of the spin polarization vector can be determined. It is of particular advantage that the value of the energy-dependent asymmetry function S (E) of the particles is exactly known at the same time by the time of flight in the drift device, which considerably facilitates the data evaluation. The gain in measurement efficiency is particularly high in the inventive method with the spin filter device, since conventional techniques typically use a single-channel spin detector. In contrast, it has already been demonstrated that with an imaging spin filter 3800 Points of a lateral electron distribution can be displayed simultaneously, see, for example, FIG. BC Ink et al. in "Appl. Phys. Lett. "Vol. 99, 2011, p. 032505 ,

Preferably, the spin filter device is configured for spin filtering as in DE 10 2005 045 622 B4 is described. Therefore, according to a preferred variant of the invention, the spin filter device comprises a spin filter crystal, which is rotatable relative to the optical axis of the measuring device. The spin filter crystal is preferably arranged between the electron-optical imaging device and the drift device, particularly preferably immediately in front of the drift device. Alternatively or additionally, the spin filter device is preferably arranged such that there is a real or reciprocal image plane of the electron-optical imaging device on the spin filter crystal of the spin filter device.

Particularly preferably, the rotatability is provided by at least one of three degrees of freedom, which is a rotation for setting a polar angle θ relative to the upstream optical axis (angle of incidence on the spin filter crystal), a rotation about an azimuthal angle Φ around the surface normal of the spin filter crystal and a rotation about a crystal orientation angle α the orientation about the optical axis located upstream. The polar angle θ may in particular be 45 °, so that there is a 90 ° reflection on the spin filter crystal.

According to a further embodiment of the invention, an adaptation lens group may be arranged between the spin filter device and the drift device such that the scattering energy of the spin filter device and the kinetic energy of the particles in the drift device are independently adjustable.

If, according to a further advantageous variant of the invention, a second diaphragm is arranged in the drift device, diffusely scattered particles can advantageously be collected. The second aperture is z. As an image aperture at the location of an intermediate image in the drift path, which serves the elimination of secondary electrons, if they arise during the diffraction process in the spin filter crystal and can lead to an inelastic background in the diffraction patterns.

According to a particularly preferred embodiment of the invention, the measuring device comprises a chopper with which an ensemble of charged particles according to a predetermined time structure (time function of the particle stream) is modulated to allow the time-resolved recording of the pulse image even in the case of a temporally continuous Ensembles. With the chopper means parts of the continuous particle beam are so hidden before entering the drift path that a measurement of the time of flight of the passing particles is possible. The chopper device advantageously enables the application of the invention even in the generation of a continuous ensemble of charged particles, e.g. For example, when the charged particles are emitted from the sample due to a non-time-domain process and, in particular, the source for exciting the charged particles emanating from the sample does not have an inherent time structure. The chopper means and the detector means are synchronized to provide the time-resolved recording of the impulse image of the charged particle ensemble in dependence upon the time structure introduced with the chopper means.

Preferably, the chopper means comprises an aperture stop and a deflection optics arranged in the retarding optics or between the retarding optics and the drift means. The deflection optics is set up for a high-frequency excitation of an electric deflection field, with the z. B. is a continuous ensemble of charged particles according to the predetermined time structure modulated. Advantageously, various variants of deflection optics are possible, the z. B. a multipole arrangement, and / or comprise two antisymmetric deflectors and lens groups on both sides of the aperture stop, and / or integrated into the retarding optics of the electron-optical imaging device or at the output are arranged. In particular, the multipole arrangement can have advantages in reducing aberrations. The aperture diaphragm is preferably the above-mentioned second diaphragm.

In the following, further advantages of the invention are summarized. A method is provided for loss-free representation of the full impulse distribution of a particle ensemble, in particular electron ensembles, on a 2D (display-like) 2D detector in which the x and y components of the impulse vector of a detected particle are determined by the coordinate of its impingement point on the detector and the z-component is measured by its time of flight in a low-energy drift path in the electron-optical lens system. In particular, it is possible to measure the energy of the particle by its time of flight in the low-energy drift path. The particle beam can be braked over several stages and adjusted in terms of its image magnification and pulse image scaling. To increase the pulse resolution, the size of the swelling volume on the examined sample can be limited and defined by the variable and laterally adjustable first aperture in a Gaussian image in the electron-optical column.

• 1: eine schematische Querschnittsansicht einer ersten Ausführungsform der erfindungsgemäßen Messvorrichtung;
• 2: schematische Querschnittsansichten verschiedener Varianten einer Objektivlinseneinrichtung der erfindungsgemäßen Messvorrichtung;
• 3 und 4: schematische Querschnittsansichten weiterer Ausführungsformen der erfindungsgemäßen Messvorrichtung mit einer Spinfilterung;
• 5 bis 8: weitere Varianten der erfindungsgemäßen Messvorrichtung mit einer Spinfilterung;
• 9: schematische Querschnittsansicht weiterer Ausführungsformen der erfindungsgemäßen Messvorrichtung mit einer Choppereinrichtung; und
• 10: eine schematische Illustration eines herkömmlichen abbildenden Spektrometers.

Further details and advantages of the invention will become apparent from the following description of the accompanying drawings. Show it:

• 1 a schematic cross-sectional view of a first embodiment of the measuring device according to the invention;
• 2 : schematic cross-sectional views of different variants of an objective lens device of the measuring device according to the invention;
• 3 and 4 : schematic cross-sectional views of further embodiments of the measuring device according to the invention with a spin filtering;
• 5 to 8th : further variants of the measuring device according to the invention with a spin filtering;
• 9 : schematic cross-sectional view of further embodiments of the measuring device according to the invention with a chopper device; and
• 10 : A schematic illustration of a conventional imaging spectrometer.

In the following description of preferred embodiments of the invention, reference will be made, by way of example, to a measuring device for the detection of electrons emitted from a surface of a sample to be examined. It is emphasized that the implementation of the invention is not limited to this example, but is also possible in the measurement of other charged particles. The parts of the measuring device and steps of the method, in particular with regard to the measurement of the pulse components of the charged particles, will be described. The measuring device, in particular the electrodes and the fields generated therewith, can be determined by the person skilled in the art using simulation and design techniques which are known per se, eg. B. from electron microscopy, designed to provide the function of the measuring device according to the invention.

1 shows a first embodiment of the measuring device according to the invention 100 in the form of a time-of-flight impulse microscope based on a linear electron-optical column with a plurality of lens groups and a low-energy drift path in front of the image detector. In this embodiment of the measuring device 100 no spin filter is provided.

The measuring device 100 comprises an electron-optical imaging device 10 with an optical axis OA which extends in the z-direction. The electron-optical imaging device 10 includes an objective lens device 11 , a first telescope optics 12 , a variable first aperture 13 with a perpendicular to the optical axis OA adjustable aperture, and a retarding optics 14 with several, along the optical axis OA arranged Retardierungsoptik segments 141 , The objective lens device 11 is constructed with three electrodes, which is an extractor electrode 111 , a focus electrode 112 and an electron optical column 113 include. Further details of the objective lens device 11 be down with respect to 2 described.

Furthermore, the measuring device comprises 100 a drift device 20 with a drift path 21 along the optical axis OA , The length of the drift path 21 is z. B. 80 cm. The drift device 20 can be a section of the optical axis OA include, which is not limited by any electrode, or it may have the shape of a hollow cylindrical electrode, in its field-free interior, the drift path 21 is formed. The drift device 20 works as an energy analyzer because it is traversed by charged particles with an energy-dependent time of flight, without the particle position in a plane perpendicular to the optical axis OA and therefore an energy resolved image of the particles downstream of the drift path 21 allows.

For the time-resolved recording of a pulse image of an ensemble 1 (in 1 dotted marked) of charged particles, the measuring device 100 one arranged in the optical axis A second telescope optics 50 and a detector device 30 on. The detector device 30 that z. B. comprises a multi-channel plate detector or a semiconductor image detector is for an image recording with a characteristic time resolution of z. B. 150 ps, see A. Oelsner et al. in "Journal of Electron Spectroscopy and Related Phenomena" Vol. 137-140, 2004, pp. 757-761 ,

In a method for detecting a pulse distribution of an ensemble 1 of photoelectrons from an examined sample 2 will be out of the sample 2 triggered photoelectrons in one with the extractor electrode 111 generated extractor field to an energy of z. B. 20 keV accelerates. The thickness of the extractor electrode 111 along the optical axis OA is z. B. 2 mm, while the bore diameter in the extractor electrode 111 z , B. 4 mm. Subsequently, the photoelectrons are passed through the focus electrode 112 so in the electron optical column 113 imaged that in a first reciprocal plane 3 gives a high-resolution image of the lateral momentum distribution of the triggered photoelectrons (first pulse image). Coordinates of the particles in the radial direction (see arrow r ) the x and y components of the momentum vectors of the particles. The location of the reciprocal level 3 (Diffraction plane) is achromatic, ie the first reciprocal plane 3 spatially does not shift with variation of the electron energy. With the first telescope optics 12 is in a first intermediate image plane 4 produces a Gaussian image, its size and position by varying the first aperture 13 (Field of view) can be selected. Inside the retarding optics 14 there is a second pulse image 5 , With the retarding optics 14 becomes a second intermediate image in a second intermediate image plane 22 at the beginning of the drift route 21 the drift device 20 generates and adjusts the energy of the beam to the desired drift energy.

In the drift track 21 the drift device 20 the electron beam is dispersed with respect to its kinetic energy, so that at the end of the drift path 21 a time-of-flight distribution of the electrons is formed according to the kinetic energies. With the second telescope optics 50 a telescopic beam path is generated, so that a third pulse image (image of the pulse distribution) on the detector device 30 is focused. With the detector device 30 becomes the impulse image of the ensemble 1 the photoelectrons are recorded in a time-resolved manner, the z-components of the momentum vectors of the particles being parallel to the optical axis OA by the time of flight in the drift facility 20 be recorded.

The 2A to 2D show schematic sketches of several variants of Objektivlinseneinrichtungen 11 based on planar electrodes ( 2A) , conically shaped electrodes ( 2 B) or back-turned electrodes to increase the field strength and reduce the focal length ( 2C) , In all cases, the diameter of the three electrodes decreases 111 to 113 down the beam gradually. The variant according to 2 B has advantages in a measuring geometry, in which an excitation beam 7 obliquely on the surface of the sample 2 incident. In the variant according to 2C is the extractor electrode 111 so back-turned that in the area behind the extractor electrode 111 gives the highest possible field strength. This advantageously results in an increase in the pulse resolution. The design of electron lenses with minimized aberrations is z. B. from M. Szilagyi et al. in "Appl. Phys. Lett. "Vol. 49, no. 13, 1986, p. 767 ; M. Szilagyi et al. "J. Vac. Sci. Technol. "Vol. A 5 (2), 1987, p. 273 ; or M. Szilagyi et al. in "J. Vac. Sci. Technol. "Vol. B 6 (3), 1988, p. 953 described.

2D 11 illustrates, in a schematic plan view along the optical axis, an objective lens device 11 according to an axially symmetric type, e.g. B. from the 2A to 2C wherein one or more of the electrodes 111 to 113 , in particular the extractor electrode 111 , are replaced by a non-rotationally symmetric multipole arrangement. In the variant according to 2D Thus, instead of round lenses multipole elements with variable potentials u ₁ to u _n be applied to the objective lens device 11 integrated. This embodiment enables a correction of the beam position already in the objective lens device 11 , This is advantageous to reduce aberrations caused by misalignment of the reciprocal plane 3 of the first pulse image (see 1 ), which is not limited by an aperture stop, could be caused in the subsequent lens groups.

The 3 and 4 show schematic representations of the measuring device according to the invention 100 for time-of-flight pulse microscopy with an integrated imaging spin filter device 40 , The measuring device 100 is with the components 10 . 20 . 30 and 50 constructed as above with respect to the 1 and 2 has been described. According to 3 contains the spin filter device 40 a spin filter crystal 41 , whose crystal surface is oriented for a spin-dependent reflection with a deflection of 90 ° during 4 the general case of scattering around a freely selectable polar angle θ shows. In the in the 3 and 4 shown embodiments is on or in the vicinity of the spin filter crystal 41 an intermediate image and on the detector device 30 a pulse image (reciprocal image). The energy of the photoelectrons in the drift path 21 the drift device 20 is identical to the scattering energy at the spin filter crystal 41 ,

The spin filter device 40 includes the spin filter crystal 41 and an actuator (not shown) with which the spin filter crystal 41 is rotatable and displaceable with respect to all three spatial directions. The spinfilter crystal 41 is in or near the plane of the second intermediate image (see reference numeral 22 in 1 ) and can be adjusted with the actuator with respect to position and angle coordinates. Optionally, the spin filter crystal 41 be moved out of the beam path with the adjusting device to a non-spin filtered image in the straight direction (according to 1 ).

The following rotations of the spin filter crystal 41 are provided individually or in combination. A first spin of the spin filter crystal 41 around one of three spatial axes is the rotation for adjusting the polar angle θ relative to the optical axis OA the upstream electrodes. The polar angle θ denotes the angle between the z-direction before and the z'-direction after the spin filter crystal 41 , According to 3 is the polar angle θ 45 °, so that the 90 ° reflection shown at the spin filter crystal 41 results.

Furthermore, a rotation about a surface normal of the spin filter crystal 41 possible. This rotation determines the azimuthal angle Φ , With variation of the azimuthal angle Φ the scattering condition of the low energy electron diffraction is changed so that the spin asymmetry can be greatly varied. These dependencies of intensity and spin asymmetry on the azimuthal angle Φ (also called rotation diagrams) are z. B. from J. Kirscher and R. Feder in Phys. Rev. Lett., Vol. 42, No. 15, 1979, p. 1008 , described.

Another rotation, the crystal orientation angle α defined, can be around the upstream optical axis OA (z-direction). With variation of the crystal orientation angle α the quantization direction of the spin analysis of the spin polarization vector can be determined P change. The spin polarization vector P is always perpendicular to the spreading plane. By changing the crystal orientation angle α from 0 ° to 90 °, both transverse spin polarization components of the incident electron beam can be analyzed. By changing the crystal orientation angle α from 0 ° to 180 ° (and analogously from 90 ° to 270 °), the spinasymmetry can be reversed. In this way, it is advantageously possible to eliminate apparatus asymmetries in spin-dependent diffraction.

The 5 and 6 show further variants of the measuring device according to the invention 100 for time of flight impulse microscopy with the components 10 . 20 . 30 and 50 and the integrated imaging spin filter device 40 , In addition, there is an adjustment lens group 60 between the spin filter device 40 and the drift device 20 arranged. The adjustment lens group 60 allows independent variation of the scattering energy at the spin filter crystal 41 and the kinetic energy (drift energy) when entering the low-energy drift path 21 the drift device 20 , The adjustment lens group 60 forms an asymmetrical single lens (immersion lens), which is immediately behind the spin filter crystal 41 is inserted in the beam path.

Optionally, the impulse distribution ( 6 ) or the image plane ( 5 ) in the plane of the spin filter crystal 41 be placed. So is in the in 5 Case shown a second reciprocal level 5 with the second pulse pattern as in the embodiment of 1 in the retarding optics 14 positioned. The adjustment lens group 60 is only weakly excited and serves to adapt the beam energy of the particles from the scattering energy to the drift energy. Both energies are typically in the range of 20-80 eV. In the in 6 In the case shown, the second pulse image emerged from the interior of the retarding optics 14 on the spin filter crystal 41 postponed. In this case, the adjustment lens group is 60 more excited, so that behind this the second intermediate image plane 22 lies with the second intermediate image.

On the detector device 30 will in both cases the 5 and 6 focused on a pulse image. A second aperture 23 at the location of the second intermediate image plane 22 serves the elimination of secondary electrons, which in the diffraction process in the spin filter crystal 41 can arise and lead to an inelastic background in the diffraction patterns (for clarity, the second aperture 23 and the second intermediate image plane 22 shown next to each other).

According to 6 additionally illustrates by way of example that immediately before the drift device 20 an electron-optical chopper device 70 can be inserted in the beam path. Because the second aperture 23 allows the electron beam to pass only on the optical axis, a time structure of the imaged electron beam is generated with this arrangement. The function of the chopper device 70 will be below with reference to the 9A to 9D described in more detail.

The 7 and 8th show further variants of the measuring device according to the invention 100 with the components 10 . 20 . 30 and 40 , wherein a real image on the image detector of the detector device 30 is shown. So shows 7 the mode in which on the image detector of the detector device 30 instead of the impulse image, a real space image (Gaussian image) is focused. This mode of operation is advantageous for analyzing the analyzed sample area in the Set real space. For this mode, the first aperture 13 be opened so that an extended field of view for determining the area to be analyzed is displayed. The desired image area can then be adjusted by means of the lateral adjustment of the sample 2 in the radial direction ( r Direction) and then by retracting a small first aperture 13 to be selected. On the spinfilter crystal 41 can either be a pulse picture ( 7 ) or an intermediate image ( 8th ).

Alternatively, the image of a real image on the image detector of the detector device can be 30 by a changed excitation of the electron-optical imaging device 10 and the retarding optics 14 reach by putting in the plane of the first aperture 13 a pulse image is focused.

In generating the charged particles with an excitation source with no time structure, a continuous ensemble of the charged particles is created. Also in this case, pulsed operation can be achieved by placing it in a suitable position within the measuring device 100 a chopper device 70 with a deflecting optics (chopper, electrostatic chopper) is inserted. In the 9A to 9D Variants of the invention are illustrated in which with the chopper 70 an ensemble of charged particles is modulated according to a predetermined time function. The current of the charged particles is modulated time-dependent. The processing of the time-resolved pulse image of the ensemble of charged particles takes place in consideration of the time function, so that as a result the z-components of the pulses can be determined as in the case of an inherently pulsed ensemble of charged particles.

The chopper device 70 includes z. B. two parallel plates or a multipole element, which (not shown) are driven by an electric pulse generator or by a high-frequency power source. The excitation frequency of the chopper device 70 is dependent on the desired time interval with the detector device 30 to be picked up pulse-shaped pulse images. For example, a frequency of 10 MHz results in a distance of the individual pulses of 100 ns. The amplitude of the high frequency and the hole size of the second aperture 23 (see below) can be tuned to each other to give pulses of 1 ns in length. This corresponds to a pulse duty factor of 1: 100, ie the intensity is reduced by 2 orders of magnitude compared to operation without a time structure. For common laboratory sources without time structure, z. B. intensive noble gas discharge lamps, this loss is tolerable, since a total of the method of the invention by the parallel angle and energy detection enables an efficiency gain of 6 orders of magnitude.

The chopper device 70 Optionally, near the Gaussian image at the beginning of the drift path of the drift device 20 ( 9A) or near the second reciprocal image plane in the interior ( 9B) or behind the retarding optics 14 ( 9C) be arranged. For eliminating aberrations due to beam deflection by the chopper device 70 an antisymmetric tandem arrangement with two choppers can be exploited ( 9D) , If the chopper 70 in the retarding optics 14 ( 9B) integrated, the beam deflection through the chopper 70 in the second reciprocal level 5 take place the second pulse image.

For independent choice of the energy of the electron beam in the area of the chopper device 70 and in the low-energy drift route 21 the drift device 20 can be an adaptation lens group 60 use, as in the 9C and 9D is shown. According to 9C is the chopper device 70 at the exit of the retarding optics 14 arranged to avoid aberrations, the second reciprocal level 5 is moved so that they are at the place of the chopper 70 lies and a Gaussian intermediate image at the second aperture 23 with the help of the adaptation lens group 60 is produced.

When using a signal with z. B. 10 MHz repetition rate and 1 ns pulse length, the energy and length of the drift path can be adjusted so that the interval of 100 ns between the successive pulses for the time of flight dispersion is fully utilized. By selecting a bias voltage on the sample 2 and the choice of operating voltages of the electron optical imaging device 10 and the retarding optics 14 can be achieved that electrons are effectively suppressed with energies below a minimum energy. This is advantageous if it is to be avoided that particularly low-energy electrons with flight times> 100 ns can pass through the drift path. Such electrons would lead to a background in the measurement signal, since they can no longer be clearly correlated with the time structure of the source.

In the tandem arrangement according to 9D includes the chopper device 70 two antisymmetric deflection optics 71 . 72 which help to reduce aberrations with lens groups 73 . 74 on both sides of the second aperture 23 interact, being in the middle of both deflection optics 71 . 72 each a second and third reciprocal level 5 . 6 lies.

The features of the invention disclosed in the foregoing description, drawings and claims may be significant to the realization of the invention in its various forms both individually and in combination.

LIST OF REFERENCE NUMBERS

100, 100 '

measuring device

1

Ensemble of charged particles

2

sample

3

first reciprocal level

4

first intermediate image plane

5

second reciprocal level

6

third reciprocal level

7

excitation beam

10, 10 '

Electron-optical imaging device

11

Object lens means

111

extractor

112

focus electrode

113

Electron-optical column

12

first telescope optics

13

first aperture

14

Retardierungsoptik

141

Retardierungsoptik segments

20

drift facility

20 '

energy analyzer

21

drift

22

second intermediate image plane

23

second aperture

30, 30 '

detector device

40

Spin filter device

41

Spin filter crystal

50

second telescope optics

60

Matching lens group

70

chopper equipment

71, 72

scanning optics

73, 74

lens groups

OA, OA '

optical axes

θ

polar angle

Φ

azimuthal

α

Crystal orientation angle

P

Spin polarization vector

u ₁ , u ₂ ... u _N

Potentials of the electrodes

r, r '

radial coordinates

z, z '

Axialkoordinaten

Claims (21)

A measuring device (100) adapted to detect a pulse distribution of an ensemble (1) of charged particles, comprising: - an electron optical imaging device (10) having an electron optical axis (OA), the electron optical imaging device (10) comprising an objective lens device (11) which is arranged to generate a pulse image (3) of the x and y components of the momentum vectors of the particles perpendicular to the electron optical axis (OA), - an energy analyzer adapted for energy resolved imaging of the ensemble (1), and - a detector means (30) arranged to receive the impulse image of the ensemble (1), the x and y components of the impulse vectors of the particles being detectable by coordinates of the particles in the impulse image, characterized in that - the energy analyzer comprises a drift device (20) which is arranged to pass through the particles of the ensemble (1) with a time of flight are dependent on the z-component of the momentum vectors of the particles parallel to the electron optical axis (OA), - the detector means (30) for time-resolved recording of the pulse image of the ensemble (1) is set, wherein the z-components of the momentum vectors of the particles by the time of flight in the drift device (20) can be detected, and - the electron-optical imaging device (10) further comprises: - a first telescope optical system (12), which generates a first real space intermediate image (4) of the ensemble (1) of the particles spatially fixed position - a variable and perpendicular to the electron optical axis (OA) adjustable first aperture (13) adapted to define a field of view of the measuring device (100), wherein by the adjustable first aperture (13) a selection of position and Size of a sample area reaching the image is made possible, and - a Retardierungsoptik (14), which is used to adjust the beams the retarding optics (14) is arranged to decelerate the ensemble of the particles (1) and adapt them to the drift device (20) with respect to its image magnification and pulse image scaling, and at least five, along the electron-optical axis (OA) arranged Retardierungsoptik segments (141), with which input and Output-side focal lengths of the retarding optics (14) are independently adjustable. A measuring device (100) adapted to detect a pulse distribution of an ensemble (1) of charged particles, comprising: - an electron optical imaging device (10) having an electron optical axis (OA), the electron optical imaging device (10) comprising an objective lens device (11) which is arranged to generate a pulse image (3) of the x and y components of the momentum vectors of the particles perpendicular to the electron optical axis (OA), - an energy analyzer adapted for energy resolved imaging of the ensemble (1), and - a detector means (30) arranged to receive the impulse image of the ensemble (1), the x and y components of the impulse vectors of the particles being detectable by coordinates of the particles in the impulse image, characterized in that - the energy analyzer comprises a drift device (20) which is arranged to pass through the particles of the ensemble (1) with a time of flight are dependent on the z-component of the momentum vectors of the particles parallel to the electron optical axis (OA), - the detector means (30) for time-resolved recording of the pulse image of the ensemble (1) is set, wherein the z-components of the momentum vectors of the particles by the time of flight in the drift device (20) can be detected, - the electron-optical imaging device (10) further comprises: - a first telescope optics (12) for generating a first real space intermediate image (4) of the ensemble (1) of the particles with a spatially fixed Position is set up, - a variable and perpendicular to the electron optical axis (OA) adjustable first aperture (13), which is adapted to define a field of view of the measuring device (100), wherein the adjustable first aperture (13) a selection of position and size a sample region reaching the image is made possible, and - a retarding optics (14), which is used to adapt the beam energy e of the particles is set to the potential of the drift device (20), wherein the retarding optics (14) is arranged to decelerate the ensemble of the particles (1) and to adapt it to the drift device (20) with respect to its image magnification and pulse image scaling, and wherein an imaging, adjustable Spinfiltereinrichtung (40) is provided, which is arranged for spin-dependent imaging of the ensemble (1). A measuring device (100) adapted to detect a pulse distribution of an ensemble (1) of charged particles, comprising: - an electron optical imaging device (10) having an electron optical axis (OA), the electron optical imaging device (10) comprising an objective lens device (11) which is arranged to generate a pulse image (3) of the x and y components of the momentum vectors of the particles perpendicular to the electron optical axis (OA), - an energy analyzer adapted for energy resolved imaging of the ensemble (1), and - a detector means (30) arranged to receive the impulse image of the ensemble (1), the x and y components of the impulse vectors of the particles being detectable by coordinates of the particles in the impulse image, characterized in that - the energy analyzer comprises a drift device (20) which is arranged to pass through the particles of the ensemble (1) with a time of flight are dependent on the z-component of the momentum vectors of the particles parallel to the electron optical axis (OA), - the detector means (30) for time-resolved recording of the pulse image of the ensemble (1) is set, wherein the z-components of the momentum vectors of the particles by the time of flight in the drift device (20) can be detected, - the electron-optical imaging device (10) further comprises: - a first telescope optics (12) for generating a first real space intermediate image (4) of the ensemble (1) of the particles with a spatially fixed Position is set up, - a variable and perpendicular to the electron optical axis (OA) adjustable first aperture (13), which is adapted to define a field of view of the measuring device (100), wherein the adjustable first aperture (13) a selection of position and size a sample region reaching the image is made possible, and - a retarding optics (14), which is used to adapt the beam energy e of the particles is set to the potential of the drift device (20), wherein the retarding optics (14) is arranged to decelerate the ensemble of the particles (1) and to adapt it to the drift device (20) with respect to its image magnification and pulse image scaling, and wherein a chopper means (70) is provided, with which a continuous ensemble is modulated according to a predetermined time structure to allow the time-resolved recording of the pulse image of the ensemble (1) of charged particles. Measuring device according to one of the preceding claims, comprising - A second telescope optics (50), which is adapted to generate a telescopic beam path from the drift device (20) to the detector device (30). Measuring device according to one of the preceding claims, in which - the objective lens device (11) has an extractor electrode (111) which is used to generate a Extractor array is arranged and has a thickness of at least half the bore diameter. Measuring device according to Claim 5 in which - the extractor electrode (111) comprises a plurality of extractor-electrode segments (u ₁ , ..., u _N ) distributed around the electron-optical axis (OA) in the azimuthal direction. Measuring device according to one of Claims 2 to 6 in which - the retarding optics (14) has at least five retarding optical segments (141) arranged along the electron-optical axis (OA), with which the input and output focal lengths of the retarding optics (14) can be set independently of one another. Measuring device according to one of Claims 1 or 3 comprising - an imaging, adjustable spin filter means (40) adapted for spin dependent imaging of the ensemble (1). Measuring device according to Claim 8 in which the spin filter device (40) comprises a spin filter crystal (41) which is rotatable relative to the electron optical axis (OA), between the electron optical imaging device (10) and the drift device (20), in particular directly in front of the drift device ( 20), and / or - is arranged so that a real or reciprocal image plane of the electron-optical imaging device (10) lies on the spin filter device (40). Measuring device according to one of Claims 2 or 8th in that - between the spin filter device (40) and the drift device (20) an adaptation lens group (60) is arranged so that the scattering energy of the spin filter device (40) and the kinetic energy of the particles in the drift device (20) are independently adjustable are. Measuring device according to one of the preceding claims, in which - In the drift device (20) an aperture (22) is arranged, can be collected with the diffuse scattered particles. Measuring device according to one of Claims 1 or 2 comprising - chopper means (70) for modulating a continuous ensemble according to a predetermined time structure to enable the time resolved recording of the burst image of the charged particle ensemble (1). Measuring device according to Claim 3 or 12 in which - the chopper device (70) comprises an aperture diaphragm (23) and a deflection optics (71-72) arranged in the electron optical imaging device (10) or between the electron optical imaging device (10) and the drift device (20) in that a continuous ensemble (1) can be modulated in accordance with the predetermined time structure by high-frequency excitation of the deflection optics (71-72). Measuring device according to Claim 13 in which the deflection optics (71-72) comprises - a multipole arrangement, - two antisymmetric deflectors (71, 72) and lens groups (73, 74) on both sides of the aperture stop (23), the antisymmetric deflectors (71, 72) for eliminating aberrations by the beam deflection in the lens groups (73, 74) of the chopper device (70), and / or - integrated in the retarding optics (14) or arranged at the output thereof. Method for detecting a pulse distribution of an ensemble (1) of charged particles from a sample (2), comprising the steps of: - generating a pulse image (3) of the particles with an objective lens device (11) of an electron-optical imaging device (10), wherein the pulse image ( 3) in a reciprocal plane of the objective lens device (11) comprises the x- and y-components of the momentum vectors of the particles perpendicular to an electron-optical axis (OA) of the electron-optical imaging device (10), - energy-resolved imaging of the ensemble (1) with an energy analyzer, - Recording of the pulse image of the ensemble (1) with a detector device (30), wherein the x and y components of the momentum vectors of the particles are detected by coordinates of the particles in the pulse image, characterized in that - the energy analyzer comprises a drift device (20) , which is traversed by the particles of the ensemble (1) with a time of flight from the zK Component of the momentum vectors of the particles parallel to the electron optical axis (OA) depends, and - the pulse image of the ensemble (1) with the detector means (30) is recorded with time resolution, wherein the z-components of the momentum vectors of the charged particles by the time of flight in the drift device (20) are detected, wherein - with a first telescope optics (12) a first real space intermediate image (4) of the ensemble (1) of the particles is generated with a spatially fixed position, - with a variable and perpendicular to the electron optical axis (OA) adjustable first Aperture (13), which is set up to define a visual field of the measuring device (100), the position and size with a retarding optics (14), the beam energy of the particles is adapted to the potential of the drift device (20), the ensemble (1) of the particles braked and with respect to its image magnification and pulse image scaling to the Driftinrichtung (20) is adapted, wherein the retarding optics (14) at least five along the electron-optical axis (OA) arranged Retardierungsoptik segments (141), with which input and output side focal lengths of the retarding optics (14) are independently adjustable. Method for detecting a pulse distribution of an ensemble (1) of charged particles from a sample (2), comprising the steps of: - generating a pulse image (3) of the particles with an objective lens device (11) of an electron-optical imaging device (10), wherein the pulse image ( 3) in a reciprocal plane of the objective lens device (11) comprises the x- and y-components of the momentum vectors of the particles perpendicular to an electron-optical axis (OA) of the electron-optical imaging device (10), - energy-resolved imaging of the ensemble (1) with an energy analyzer, - Recording of the pulse image of the ensemble (1) with a detector device (30), wherein the x and y components of the momentum vectors of the particles are detected by coordinates of the particles in the pulse image, characterized in that - the energy analyzer comprises a drift device (20) , which is traversed by the particles of the ensemble (1) with a time of flight from the zK Component of the momentum vectors of the particles parallel to the electron optical axis (OA) depends, and - the pulse image of the ensemble (1) with the detector means (30) is recorded with time resolution, wherein the z-components of the momentum vectors of the charged particles by the time of flight in the drift device (20) are detected, wherein - with a first telescope optics (12) a first real space intermediate image (4) of the ensemble (1) of the particles is generated with a spatially fixed position, - with a variable and perpendicular to the electron optical axis (OA) adjustable first diaphragm (13), which is set up to define a visual field of the measuring device (100), the position and size of a sample region to be imaged are selected, - the radiation energy of the particles is limited to the potential of the drift device (20) with a retarding optical system (14) is adjusted, whereby the ensemble (1) of the particles is decelerated and with respect to its image magnification and Imp ulsbild scaling is adapted to the drift device (20), and - a spin-dependent image of the ensemble (1) with an imaging, adjustable spin filter device (40). Method for detecting a pulse distribution of an ensemble (1) of charged particles from a sample (2), comprising the steps of: - generating a pulse image (3) of the particles with an objective lens device (11) of an electron-optical imaging device (10), wherein the pulse image ( 3) in a reciprocal plane of the objective lens device (11) comprises the x- and y-components of the momentum vectors of the particles perpendicular to an electron-optical axis (OA) of the electron-optical imaging device (10), - energy-resolved imaging of the ensemble (1) with an energy analyzer, - Recording of the pulse image of the ensemble (1) with a detector device (30), wherein the x and y components of the momentum vectors of the particles are detected by coordinates of the particles in the pulse image, characterized in that - the energy analyzer comprises a drift device (20) , which is traversed by the particles of the ensemble (1) with a time of flight from the zK Component of the momentum vectors of the particles parallel to the electron optical axis (OA) depends, and - the pulse image of the ensemble (1) with the detector means (30) is recorded with time resolution, wherein the z-components of the momentum vectors of the charged particles by the time of flight in the drift device (20) are detected, wherein - with a first telescope optics (12) a first real space intermediate image (4) of the ensemble (1) of the particles is generated with a spatially fixed position, - with a variable and perpendicular to the electron optical axis (OA) adjustable first Aperture (13), which is set up to define a field of view of the measuring device (100), the position and size of a sample region to be imaged are selected, - the retardation optics (14) are used to match the beam energy of the particles to the potential of the drift device (20) in which the ensemble (1) of the particles is decelerated and with respect to its image magnification and Impulsbi ld-scaling is adapted to the drift device (20), and - a modulation of a continuous ensemble according to a predetermined time structure with a chopper (70) and a time-resolved recording of the pulse image of the ensemble (1) after passing through the drift device (20). Method according to one of Claims 15 to 16 in which - to increase the pulse resolution, the size of the swelling volume on the sample (2) through the variable and perpendicular to the electron optical axis (OA) adjustable aperture (13) in a Gaussian 'see Intermediate image along the optical axis (OA) is limited and defined. Method according to one of Claims 15 or 17 , with the step - spin-dependent imaging of the ensemble (1) with an imaging, adjustable spin filter device (40). Method according to Claim 16 or 19 in which - by varying a crystal orientation angle α (rotation about the incident beam), the quantization direction of the spin filtering is changed and / or by varying an azimuthal angle Φ (rotation about the surface normal of the spin filter crystal) the contrast of the spin filtering is changed. Method according to one of Claims 15 to 16 comprising the steps of - modulating a continuous ensemble (1) according to a predetermined time structure with a chopper means (70), and - time resolved recording of the burst image of the ensemble (1) after passing through the drift means (20).

Images