WO2023143670A1

WO2023143670A1 - System and method for contactlessly ascertaining the electric potential of a sample

Info

Publication number: WO2023143670A1
Application number: PCT/DE2023/100056
Authority: WO
Inventors: Thomas Dittrich; Michael Franke
Original assignee: Helmholtz-Zentrum Berlin für Materialien und Energie Gesellschaft mit beschränkter Haftung
Priority date: 2022-01-26
Filing date: 2023-01-26
Publication date: 2023-08-03
Also published as: DE102022101772A1

Abstract

The invention relates to a system (100) for contactlessly ascertaining the electric potential of a sample (1). The system (100) - comprises an actuator unit (2) which is operatively connected to a bending body (3) along a first direction (11), wherein the bending body (3) is additionally operatively connected to a counter mass (4) which is resiliently or elastically suspended on the system (100), and the bending body (3) extends along an axis in a second direction (12) and has an electrode (5) which extends at least along the second direction (12), and - is designed such that the electrode (5) can be arranged opposite a sample (1) at a distance thereto along the first direction (11). The actuator unit (2) is designed to actuate the bending body (3) in order to produce a bending vibration about the axis with an adjustable frequency such that the distance between an arranged sample (1) and the electrode (5) varies over time by means of the bending vibration with the adjustable frequency such that an electric signal which varies over time can be detected in the electrode (5), said electric signal being used in order to ascertain the electric potential of the sample (1). The invention additionally relates to a method for contactlessly ascertaining the electric potential of the sample (1).

Description

System and method for non-contact determination of an electrical potential of a sample

Description:

The invention relates to a system and a method for contactless determination of an electrical potential of a sample.

Such a sample can be a semiconducting component, for example. For many modern semiconducting components, such as photodetectors or field effect transistors, the diffusion length of minority charge carriers is decisive for the performance of the component. In order to determine this diffusion length experimentally without damaging the component itself or the semiconductor material used, non-contact methods are generally used, in particular photoluminescence measurements or surface photovoltage measurements. In the latter, an electrode is brought close to the component whose diffusion length is to be examined in order to form an electric plate capacitor with it. An electrical potential is then induced in the component, for example by irradiation with suitable electromagnetic radiation. If the component and the electrode, which each form plates of the plate capacitor, are then moved relative to one another in such a way that the distance between the plates changes, a current that changes over time is induced in the electrode. This current can be controlled to zero by applying an electrical voltage, the electrical voltage being indicative of the electrical potential of the component.

For this purpose, an oscillating capacitor is known from DE 3438546 A1. In this oscillating capacitor, the movements of an oscillating electrode in relation to a stationary electrode are excited via a piezoceramic. The piezo ceramic is driven by an oscillator, which is followed by a controller, a compensation voltage generator, an integrator and a current-sensitive lock-in amplifier. The mean electrode distance between the oscillating electrode and the stationary electrode can be set with the controller. For this purpose, a DC voltage is superimposed by means of the controller on the AC voltage generated by the oscillator, which excites the oscillating electrode. However, since this oscillating capacitor can only determine changes in the electrical potential, it is only suitable for determining sufficiently low-frequency components of the electrical potential of the sample. In particular, the time-constant component of the electrical potential can be determined with this oscillating capacitor.

However, the circuit disclosed in DE 102019 117 989 B3 makes it possible to determine both the time-variable and the time-constant component of the electrical potential. However, the disadvantage remains that the Prior art known oscillating capacitors in relation to a mean electrode spacing ensures only relatively small deflections of the two electrodes to one another, because larger deflections ensure more significant changes in the measured variables indicative of the determination of the electrical potential. Furthermore, for these already low deflections, relatively high control powers are required for the actuator unit used in each case, so that they can contribute to an increased measurement error with corresponding electromagnetic interference fields, provided these act in the area between the electrodes.

Proceeding from this, the present invention is based on the object of providing a system and a method for contactless determination of the electrical potential of a sample, which is improved in each case with regard to the problems described above.

This object is achieved by a system having the features of claim 1 and a method having the steps of claim 12.

A first aspect of the invention relates to a system for contactless determination of an electrical potential of a sample, the system comprising an actuator unit which is operatively connected to a flexible body along a first direction. The flexible body is also operatively connected to a counterweight that is suspended resiliently or elastically with the system and extends along an axis in a second direction. The connection with at least the counterweight forms the suspension, also referred to as attachment of the bending body. The bending body is fastened in such a way that the ends lying in the direction of extension (along the axis) swing freely, i.e. the bending body is in particular not fastened at one end. In addition, the bending body has an electrode which extends at least along the second direction. The system is set up so that the electrode can be arranged in relation to a sample at a distance along the first direction. The actuator unit is designed to excite the bending body to a bending vibration with an adjustable frequency around the axis, so that the distance between an arranged sample and the electrode varies over time with the adjustable frequency due to the bending vibration, so that a time-varying electrical Signal can be detected, based on which the electrical potential of the sample can be determined. The bending vibration about the axis means a deflection perpendicular to this axis, the axis coinciding with the extension direction of the flexible body at rest.

The electrical potential, which can be determined by means of the system according to the invention, of the sample separate from the system can be both constant over time and variable over time Contain components, both components and their sum can be determined by the system.

The actuator unit is preferably designed and set up to generate vibrational energy and, in particular, to transmit it to the flexible body, so that the flexible body can be excited to perform a flexible vibration. Furthermore, the actuator unit is preferably operatively connected to the flexible body by a rigid connection, for example by a metal bolt. Such a connection advantageously achieves a strong, direct coupling between the actuator unit and the flexural body, so that at a given excitation amplitude, the actuator transfers the vibration energy generated in this way into the flexural body with almost no loss in order to excite the latter to flexural vibration. Furthermore, the excitation amplitude of the actuator can advantageously be kept low, so that correspondingly small electromagnetic stray fields, possibly generated by the actuator, which radiate into the area of the electrode and the sample and can contribute to a measurement error of the electrical potential of the sample to be determined, are advantageously minimized become. The actuator unit can excite the bending body to flexural vibration by pushing the bending body back and forth.

The bending body is also operatively connected to a spring-loaded or elastically suspended counterweight. In this case, the counterweight and the actuator unit are preferably rigid, for example via a metallic bolt, or also directly connected to one another. The counterweight itself, which can also include a housing or a sensor head surrounding the actuator unit at least in sections, is however suspended resiliently or elastically according to the invention. It can be suspended from the housing or from another part of the counterweight on the system. This resilient or elastic suspension leads to an intended impedance mismatch between the counterweight, which is preferably rigidly connected to the actuator unit, and an area surrounding the flexible body, to which the flexible body is connected in a resilient or elastic manner via bolts, actuator unit and counterweight. Due to the unavoidable mechanical connection or interaction between the flexible body and its environment, the latter removes part of the vibrational energy generated by the actuator unit from the flexible body, which is coupled out to the environment as energy dissipation. With the resilient/elastic suspension, it is advantageously achieved that the energy dissipation can be controlled in particular via an elasticity of the resilient/elastic suspension. In particular, the system can be configured by a suitable choice of counterweight, bending body and resilient/elastic suspension in such a way that the bending vibration with minimal excitation by the actuator unit and acceptable energy dissipation from the system causes a maximum deflection of the bending vibration of the Resulting in bending body. The counterweight can be suspended via a spring element, such as a spring, for example.

The electrode can be, for example, a substantially planar electrode, with one surface of the electrode being orientable substantially parallel to the sample and relative to it, so that the electrode forms a plate capacitor with the sample or a surface of the sample, with a first plate of the plate capacitor being formed by the electrode and a second plate of the plate capacitor is given by the sample. When the bending body flexes, a distance between the two plates is modulated over time, so that in particular a capacitance of the plate capacitor experiences a corresponding modulation over time. This can be used advantageously to determine the electrical potential of the sample.

The sample can include or be a metal or a semiconductor, for example.

It is noted that the sample is not a mandatory part of the claimed system, but merely serves as a reference to illustrate the operation of the system.

Advantageous refinements of this first aspect of the invention are specified in the corresponding dependent claims and are described below.

According to a first embodiment of the invention, the electrode is arranged in a region of a first antinode of the flexural body caused by the flexural oscillation. This area can in particular include an area of a maximum deflection of the flexible body relative to its rest position, which occurs during the bending vibration of the flexible body. In its rest position, the bending body extends essentially along said axis along the second direction. In this embodiment, the distance between the electrode and the sample is variable over the entire deflection of the flexure. A higher degree of accuracy in determining the electrical potential of the sample is thus advantageously achieved if the determination is based on a change in the capacitance of said plate capacitor over time.

According to a further embodiment of the invention, the actuator unit is operatively connected to the flexible body and the counterweight in a contact area, a vibration node of the flexible body that occurs when a bending vibration is present. The counterweight can be connected to the bending beam via the actuator unit. The contact area thus includes an area of minimal deflection of the flexible body during bending vibration about the axis, which also includes the node of vibration. A vibration node is the infinitesimally small area that is predetermined by the vibration behavior of the bending beam and in which there is no deflection during vibration. An excitation exclusively at this point (node) is not physically possible. In practice, however, excitation is always possible in the contact area, which has a finite size and which includes the vibration node. The contact area can also include a center of gravity of the bending body. The contact area is smaller than the extension of the bending body and in particular smaller than one tenth of the extension. The vibration node of the flexure shifts according to the mass distribution and the distribution of the elasticity of the flexure. In the case of a symmetrical bending body, for example, the vibration node lies in the middle of the bending body. The mass distribution of the flexible body can change due to components arranged on or on the flexible body.

In an advantageous embodiment, the actuator unit contains a piezo element. This is preferably provided and set up to generate the bending vibration of the bending body. The actuator unit is preferably arranged with the piezoelectric element in the contact area of the vibration node of the flexible body that occurs during bending vibration. Since the piezo element generates a relatively large force, especially when compared to electromagnetic actuators, with a relatively small deflection of the actuator, the piezo element develops an optimal coupling of the vibration energy generated into the bending body, especially when it is arranged in the said contact area, so that this is the case with low power of the piezo element is excited to flexural vibration with maximum deflection of the bending body. For example, the piezoelectric element can be arranged in the middle of the flexural body, so that when the flexural vibration is excited by the piezoelectric element, the flexural body is excited to perform a flexural vibration, in which the vibration node is in the area of the piezoelectric element, and the two ends of the flexural body each have an antinode in the event of a flexural vibration form with maximum deflection of the bending body. The electrode can then advantageously be attached to one of the two ends of the bending body, so that it experiences the maximum deflection during bending vibration.

In a further advantageous embodiment, the actuator unit contains an electromagnet which is provided and set up to generate the bending vibration of the bending body. Advantageously, the electromagnet or the actuator unit with the electromagnet is arranged in the area of the second antinode of the flexural body that occurs during flexural oscillation. Here, the electromagnet with its high deflection, in particular compared to a piezo element, advantageously develops the optimal transmission of the vibration energy generated by the actuator into the bending vibration with a relatively small force. In order to excite the bending body by means of the electromagnet, the bending body preferably has, at least in sections, ideally in the area of the second antinode, a magnetic material. The electrode is then preferably arranged on the first anti-node remote from the second anti-node, so that electromagnetic fields generated by the electromagnet radiate as weakly as possible into the area between the sample and the electrode, which could otherwise significantly contribute to the measurement error of the electrical potential of the sample.

According to a further embodiment of the invention, the actuator unit is arranged in the area of a second antinode of the flexural body, which occurs during flexural oscillation and is remote from the electrode. Analogously to the first antinode, the second antinode can describe a further area with maximum deflection of the bending body in relation to its rest position. The suspension of the bending body in the contact area, which includes the vibration node, remains unchanged and is not shifted in the direction of the vibration antinode.

In an advantageous embodiment, the counterweight has a mass that is 3 to 10 times that of the bending body. In order to keep the vibration energy generated by the actuator unit as completely as possible in the bending body, the counterweight must ideally be selected to be as large as possible. At the same time, the system should ideally not be too heavy and compact in terms of easy handling. If the counterweight is chosen to be 3 to 10 times as heavy as the bending body, the vibration quality of the system is sufficient to determine the electrical potential of the sample, while the energy dissipation from the system to the environment remains acceptable.

According to a further advantageous embodiment, the bending body is designed to be metallically conductive and is electrically connected to a predefined ground potential. This can be done, for example, via a conductor connected to the bending body. This measure prevents the bending body from becoming electrostatically charged, with corresponding interference fields contributing to the measurement error of the electrical potential of the sample if they act in the area between the electrode and the sample.

According to a further embodiment, the electrode is electrically insulated from the bending body. In this case, the electrode can be surrounded by a conductor element which is electrically insulated from the electrode, is conductive and runs all the way around, the conductor element in particular being electrically at ground potential, as corresponds to a next embodiment. For example, if it is a planar electrode, it can be surrounded laterally, ie within an extension plane of the electrode, by a circumferential conductor element, which can be configured as ring-like here. For example, the bending body can be 8 mm wide and the electrode can have a diameter of 5 mm. A corresponding opening or bore in the bending body can then be in the range of, for example, 6 mm to 6.5 mm. The electrode can be enclosed in this opening so that it is electrically isolated from the bending body and the conductor element. An annular shield of the electrode over the conductor element is then formed by the edge of the flexure. The conductor element and the bending body are both at ground potential and form a corresponding shield against external interference potentials.

In one embodiment of the invention, the system has an electronic circuit that is designed and set up to process an electrical signal from the electrode and to determine the electrical potential of the sample.

In particular, the electronic circuit can have a preamplifier of the electronic circuit which is arranged on the bending body and is electrically connected to the electrode on the input side and to a downstream part of the electronic circuit on the output side. This preamplifier is preferably designed, when the sample is arranged opposite the electrode, to pick up a particularly time-dependent voltage induced by the sample between the latter and the electrode, to pre-amplify it, and to provide it as a particularly time-dependent amplifier voltage on the output side at the downstream part of the electronic circuit.

Furthermore, the downstream part of the electronic circuit can have a rectifier which is electrically connected on the input side to an output of the preamplifier. This is preferably designed to rectify the time-dependent amplifier voltage, in particular with the aid of the adjustable frequency of the bending vibration, and to provide the output side of the rectifier as a DC voltage indicative of the time-constant component of the electrical potential at an output of the rectifier.

Furthermore, the downstream part of the electronic circuit can have a regulator that can be electrically connected to the output of the rectifier on the input side and to the sample on the output side. The regulator is preferably designed to compensate for the DC voltage present on the input side of the regulator with an inverse DC voltage, which is also indicative of the component of the electrical potential of the sample that is constant over time, and to provide it at an output of the regulator.

The downstream part of the electronic circuit can also have an adder electrically connected on the input side to the output of the preamplifier and to the output of the controller. The summer is preferably designed to the summing the time-dependent preamplifier voltage and the inverse DC voltage to form a sum voltage and providing this at a summator output.

In particular, the electrode is electrically insulated from the flexible body and attached to it, with the distance between the electrode and the flexible body, which is at ground potential, being as small as possible. The distance between the electrode and the sample is preferably significantly smaller than a lateral extension of the electrode even when the flexible body is in the rest position. For example, to be able to compensate for possible height differences of different types of samples or to regulate a measurement sensitivity given by the distance between the sample and the electrode in the rest position of the flexible body, the distance between the sample and the electrode is preferably adjustable by means of the displacement unit. The distance between the electrode and the sample is in particular between 0.05 mm and 0.5 mm. Furthermore, the lateral extent can be in the range of a few millimeters, such as 2 mm to 50 mm.

Furthermore, the system can have an optional electrically conductive sample holder, which is designed to receive the sample and to fix it to the sample holder. The sample holder can preferably be electrically connected to the electronic circuit. For example, the sample holder can be electrically at ground potential so that a time-dependent potential of the sample can be determined by means of the system. It is also provided that the sample holder can be electrically connected to a test signal generator to calibrate the time-dependent potential of the sample and/or to determine an electrical potential of the sample that is constant over time and in particular a potential of the sample that is constant over time and variable over time to a voltage source. In particular, for examining large samples with a sample surface that is larger than the surface of the electrode, the sample and the electrode can be shifted relative to one another by means of an optional shifting unit of the system.

In an advantageous embodiment, when a sample is placed opposite the electrode, an electrically insulating film is placed between the electrode and the sample. This makes it possible, in particular, for the electrode to be brought closer to the sample in such a way that the two are only separated from one another by the insulating film. Thus, if the film is chosen to be suitably thin, correspondingly small distances between sample and electrode are made possible without causing a short circuit between sample and electrode, which advantageously increases the capacitance of the plate capacitor made up of electrode and sample for determining the electrical potential of the sample. A dielectric constant of the plate capacitor can also advantageously be determined by the selection of the insulating film be adjusted, which in turn is also relevant for the capacitance of the plate capacitor.

In a further embodiment of the invention, the bending body has an opening along the second direction, so that when a sample is arranged opposite the electrode, the sample can be irradiated with electromagnetic radiation via the opening. Thus, an interaction process taking place in the sample between the radiation and the sample can be induced by the electromagnetic radiation, which in turn causes an electrical potential in the sample, so that this can be determined by the system.

According to one embodiment, the electrode is at least partially transparent to the electromagnetic radiation, so that when the electrode is positioned along an optical axis between the opening and the sample, the sample can continue to be irradiated with electromagnetic radiation. The sample can thus advantageously be irradiated with electromagnetic radiation through the electrode, which further simplifies the adjustment and handling of the system.

In one embodiment, the bending vibration of the bending body corresponds to a resonant frequency of the bending body, the resonant frequency being in the range from 500 Hz to 1000 Hz in particular. The resonant frequency is determined by the geometry and the materials of the bending body. If the bending vibration is operated at the resonant frequency of the bending body, maximum deflections of the bending body are advantageously achieved with minimal vibration energy generated by the actuator unit.

A high vibration quality is achieved by excitation with the resonance frequency of the bending body. A desired vibration amplitude of the bending body can thus be achieved with a very low excitation amplitude.

In one embodiment of the invention, when a sample is arranged opposite the electrode, the electrode and the sample are displaceable relative to one another by means of a displacement unit of the system. This is particularly advantageous when relatively large, in particular planar, samples are to be measured using the system, so that different areas of the sample can be measured by correspondingly displacing the electrode and the sample using the displacement unit. The sample or the electrode can be shifted relative to one another in such a way that a corresponding area of the sample is arranged opposite the electrode, so that the area of the sample forms a plate capacitor with the electrode of the system. Furthermore In particular, the distance between the sample and the electrode can advantageously be adjusted along the first direction by means of the displacement unit. This distance is decisive for the capacitance of the plate capacitor made up of sample and electrode, so that the capacitance of the plate capacitor, in particular a capacitance when the bending body is at rest, can be adjusted. The displacement unit can optionally be set up to displace the sample and electrode relative to one another in one, two and/or three spatial directions. In particular, the sample and the electrode can be displaced relative to one another in such a way that the sample remains stationary while the electrode is displaced relative to the sample by means of the displacement unit.

In a further embodiment of the system according to the invention, this has a vacuum chamber, in particular a high vacuum chamber or an ultra-high vacuum chamber. A vacuum chamber is designed in particular to support pressures of less than 300 hPa. In contrast to the vacuum chamber, a high-vacuum chamber is set up and designed to support pressures between 10 ^-8 to 10 ^-3 hPa. An ultra-high vacuum chamber, in turn, is designed and configured to support pressures between 10' ¹¹ hPa and 10' ⁸ hPa. In the following, only the vacuum chamber is referred to for better legibility. However, it is noted that the term 'vacuum chamber' can also refer to the high vacuum chamber or the ultra-high vacuum chamber, respectively. The vacuum chamber is preferably designed to accommodate at least the electrode and the sample that can be arranged opposite the electrode within the vacuum chamber, it being possible for the vacuum chamber to be at least partially evacuated when the sample is arranged opposite the electrode in the vacuum chamber. The system can thus be operated at an adjustable system pressure. In particular, partial evacuation can reduce the system pressure, for example compared to the atmospheric pressure of 1000 hPa, so that the bending vibration is exposed to a correspondingly reduced air resistance, which is advantageously reflected in a higher vibration quality of the system. The following applies: the higher the vacuum, the better the vibration quality.

A second aspect of the invention relates to a method for the non-contact determination of an electrical potential, in particular a time-dependent electrical potential of a sample using the system according to the invention or one of its embodiments, having at least the following steps: i) positioning the sample opposite the electrode, ii) by means of the actuator unit, excitation of the bending body to flexural vibration with the adjustable frequency around the axis, so that the distance between the sample and the electrode is changed by the flexural vibration with the adjustable frequency, iii) in particular with the adjustable frequency of the flexural vibration, clocked irradiation of the Sample with electromagnetic radiation, in particular via the opening, so that through an interaction process taking place in the sample between the sample and the electromagnetic radiation, an electrical voltage between the sample and the electrode is modulated in particular with the adjustable frequency of the bending vibration and is indicative of the particular time-dependent electrical potential of the sample is induced, iv) by means of the electronic circuit, processing the electrical signal of the electrode and determining the electrical potential of the sample.

In an advantageous embodiment, the processing of the electrical signal of the electrode and the detection of the electrical potential of the sample also has the following steps: i) using the preamplifier, preamplifying the voltage and providing the corresponding amplifier voltage at the output of the preamplifier, ii) using the rectifier , in particular with the aid of the adjustable frequency of the bending vibration, rectifying the amplifier voltage and providing the DC voltage at the output of the rectifier that is indicative of the component of the electric potential that is constant over time, iii) by means of the controller, regulating and compensating for the DC voltage applied to the controller on the input side by generating a die DC voltage compensating counter DC voltage, and providing the counter DC voltage at the output of the regulator, iv) by means of the adder, summing the indicative of the periodic and the time-constant component of the electrical potential amplifier voltage and the counter DC voltage, and providing the resulting sum voltage at the summator output.

Exemplary embodiments and further features and advantages of the invention are to be explained below with reference to the figures. Show it: Fig. 1 shows a first embodiment of the system according to the invention

determination of the electrical potential of a sample;

2 shows a second exemplary embodiment with a plan view of the electrode of the system, the electrode being electrically insulated from a peripheral conductor element;

figs 3a-d further embodiments of the system, with a symmetrical

Bending body with a central vibration node and a piezo element (Fig. 3a, third embodiment) and an additional electromagnet (Fig. 3b, fourth embodiment) as an actuator unit, an asymmetric bending body due to an opening in the bending body with a displacement corresponding to the change in the center of mass and the distribution of elasticity Oscillation nodes (Fig. 3c, fifth embodiment);

Fig. 4 shows a sixth embodiment of the system, wherein a

Preamplifier of the electronic circuit is attached to the bending body and

Fig. 5 is a circuit diagram of the system according to the invention and with the

System electrically connectable electronic circuit.

Fig. 1 shows a first exemplary embodiment of the system 100 according to the invention for determining an electrical potential of a sample 1.

The system 100 shown here comprises an elongate flexural body 3 which extends essentially along an axis along a second direction 12 . The flexible body 3 is operatively connected to an actuator unit 2 along a first direction 11 via a bolt 14 . The actuator unit 2 is also operatively connected to a counterweight 4 here. The bending body 3 can be made of metal, for example, preferably steel or stainless steel. The system 100 is shown here in a section within a plane spanned by the first and the second direction 11,12. In this section, an opening 8 of the bending body 3 along its axis is visible. An electrode 5 of the system 100 is arranged within this opening 8 and is electrically insulated from the bending body 3 but mechanically connected to it, the mechanical connection not being shown in this section. A wall of the opening 8 forms it a peripheral conductor element 7, which will be discussed further in the context of FIG.

Opposite the electrode 5 and in particular not necessarily a part of the system 100, as can be seen in FIG. For this purpose, the sample can first be irradiated with electromagnetic radiation via the opening 8 so that an electrical potential is induced in the sample 1 via an interaction process of the electromagnetic radiation and the sample 1 . In particular, the electrical potential can be modulated over time with a clocking of the electromagnetic radiation, so that the electrical potential also undergoes a time-dependent change that can be determined using the system 100 . The electrode 5 can be at least partially transparent to the electromagnetic radiation, so that the sample 1 can also be irradiated with electromagnetic radiation through the electrode 5, which considerably simplifies the adjustment effort for the irradiation.

The electromagnetic radiation can be, for example, electromagnetic waves, in particular electromagnetic waves with frequencies in the range from 1 THz to 30 PHz.

1 shows a snapshot of the flexible body 3 in which it is in its rest position and thus extends essentially along the second direction. According to the invention, however, the system 100 is designed in such a way that the actuator unit 2 can excite the flexural body 3 to perform a flexural oscillation about its axis. The bending vibration is indicated with arrows at the two ends of the bending body. In the first exemplary embodiment shown in FIG. 1, the actuator unit 2 is rigidly connected to the flexible body 3 at a contact area 6 via the bolt 14 for this purpose. The contact area 6 is located here in the middle of the bending body 3 and thus, with homogeneous mass distribution within the bending body 3, comprises a center of gravity of the bending body 3. In order to stimulate the bending body 3 to flexural vibration, the actuator unit 2 can move the bending body 3 along the first direction 11 push back and forth. So that the actuator unit 2 acts as much as possible on the center of gravity of the bending body 3, the bolt 14 can taper from the actuator unit 2 towards the bending body 3, in order to minimize the contact area 6 around the center of gravity.

Due to the inertia of the flexible body 3 , when the actuator unit 2 generates vibrational energy and transmits it to the flexible body 3 by means of the bolt 14 , a flexible vibration occurs around the axis of the flexible body 3 . By coupling the bending body 3 to the actuator unit 2 in the contact area 6, which is his Includes focus, there forms a vibration node 33 with minimal deflection of the bending body 3 compared to its rest position. On the other hand, a first and a second antinode 31, 32 with minimum mechanical impedance and maximum deflection of the flexible body 3 with respect to its rest position are formed at the two freely oscillating ends of the flexible body 3.

Advantageously, as shown in FIG. 1, when the actuator unit 2 is arranged in a contact area 6 in the area of the center of gravity of the flexible body 3, the actuator unit 2 is formed by a piezoelectric element. In comparison with an electromagnet, for example, this has the advantage of developing a large force with a small deflection of the actuator unit 2 so that the vibration energy generated by the actuator unit 2 can be optimally converted into the bending vibration of the bending body 3 . Due to the rigid connection between the actuator unit 2 and the bending body 3 via the bolt 14, the force of the actuator unit or the piezoelectric element is transmitted directly and almost without loss to the bending body. The actuator unit 2 or the piezo element is here surrounded by a housing 15 so that electrical interference fields emanating from the actuator unit 2 or the piezo element can be effectively shielded from the area between the sample 1 and the electrode 5 . For this purpose, the housing 15 is preferably connected electrically via a wire 9 to at least the bolt 9, the actuator unit 2 and the bending body 3 and is connected to the predefined ground potential.

On the other hand, the actuator unit 2 is operatively connected to a counterweight 4 here. According to the invention, the counterweight 4 is resiliently suspended, in the first exemplary embodiment shown here by means of elastic suspensions 10. Via the elastic suspensions 10, which can contain an elastomer, for example, the vibration energy generated by the actuator unit 2 can partially flow away, so that only a part of the vibration energy enters the Bending vibration of the bending body passes. This energy drain is unavoidable because of the connection and interaction of the bending body 3 with its surroundings. In FIG. 1, the environment of the bending body 3 is symbolized by a wall 13, which can be assumed to be significantly heavier than the bending body 3 and the counterweight 4 together. The wall 13 can be, for example, a wall 13 of a measurement chamber of the system 100, for example a vacuum chamber. With such a vacuum chamber, the area between sample 1 and electrode 4 can then be at least partially evacuated and the electrical potential of sample 1 can be determined under appropriate conditions. It is also or additionally conceivable that the wall 13 belongs to a displacement unit of the system 100 . by means of a Such a displacement unit can then be used to move the system 100 or the electrode 5 relative to the sample 1.

The resilient suspension via the counterweight 4 advantageously ensures that the energy dissipation of the vibrational energy and a vibration quality of the bending vibration can be adjusted via a degree of elasticity of the elastic suspension 10 . In particular, a suitable choice, in particular of the masses of bending body 3 and counterweight 4 and the connections between actuator unit 2 and bending body 3 and between actuator unit 2 and counterweight 4, can result in maximum deflection of antinodes 31, 32 with minimal vibration energy generated by actuator unit 2 and at an acceptable level Energy drain from the system 100 can be achieved. For this purpose, the mass of the counterweight 4 is preferably chosen to be 3 to 10 times as heavy as a total mass of the bending body 3 and the bolt 14 .

According to the law of conservation of momentum, the countermass 4 then performs mechanical oscillations of the same frequency as the bolt 14 and the bending body 3, but in the opposite direction and with a deflection that is 3 to 10 times less than the deflection of the bolt 14, depending on the mass ratios. The forces that the counterweight 4 exerts through its mechanical vibrations are the same as those that the bolt 14 exerts on the bending body 3 . Thus, the mechanical impedance of the counterweight 4 is also corresponding to the mass ratios by 3 to 10 times greater than that of the bolt 14. The elastic suspension 10 is preferably designed such that the counterweight 4, the actuator unit 2, the bolt 14 and the Vibration nodes 33 of the flexible body 3 remain sufficiently stationary along the first direction 11 so that only the antinodes 31 , 32 experience the greatest possible deflection along the first direction 11 . Due to the high impedance according to the mass ratios of the counterweight 4, which is moved only with minimal deflection but with great force, the counterweight 4, the actuator unit 2, the bolt and the bending body 3 are correspondingly withdrawn little vibrational energy. The vibration quality therefore remains advantageously high in the case of large deflections of the antinodes 31, 32, so that only low activation powers of the actuator unit 2 are required. For example, the system 100 can be operated with a piezo element at a few volts instead of with the otherwise usual drive voltages of the order of 100 volts. The correspondingly low control power thus advantageously ensures weaker interference fields which, if they couple into the area between sample 1 and electrode 5, can contribute to the measurement error of the electrical potential of sample 1. Due to the low control power, the thermal power loss of the piezo element, which is the square of its control voltage, remains advantageous and linearly related to a control frequency, advantageously low, so that it is possible to work even at high control frequencies up to the kHz range.

As can also be seen in FIG. 1, the electrode 5 is arranged on one of the two antinodes 31, 32 occurring during bending oscillations, in the first exemplary embodiment shown here on the first antinode 31. Of course, the electrode 5 can also be arranged on the second antinode 32, or else one electrode 5 each on an associated antinode 31, 32. Consequently, a distance along the first direction 11 between the sample 1 and the electrode 5 can be changed over almost the entire deflection of the antinode 31 in relation to the rest position of the flexible body 3 . The sample 1 and the electrode 5 thus each form a plate of a plate capacitor. The distance between the sample 1 and the electrode 5, which is decisive for a capacitance of the plate capacitor, during flexural oscillation of the flexural body 3 can advantageously be changed over the entire deflection of the antinode 31. An electrical potential induced in the sample 1 thus leads to correspondingly large changes in the capacitance, so that the electrical potential of the sample 1 can advantageously be determined more precisely by means of the system 100 .

In order to determine the electrical potential of the sample 1, the system 100 includes, in particular, an electronic circuit 20, which will be discussed separately in FIG. The electronic circuit 20 is electrically connected to the electrode 5 via a wire 9 so that a signal indicative of the electrical potential of the sample 1 can be passed on from the electrode 5 to the electronic circuit 20 via the wire 9 . For this purpose, the heavy wall 13 can have at least one bushing 16, via which the wire 9 is electrically connected to the electronic circuit 20. The wire 9 is preferably designed to be flexible, so that the flexural vibration of the flexible body 3 experiences as little additional damping as possible through the wire 9 .

The housing 15 can in particular be designed to be at least partially gas-tight, so that the actuator unit 2 can work within the housing 15 at a predetermined housing pressure. This housing pressure can then be independent of a pressure outside the housing 15, for example if the heavy wall 13 is part of a partially evacuatable vacuum chamber, so that the area outside the housing 15 but inside the heavy wall 13 can be partially evacuated. This is particularly advantageous if the actuator unit 2 includes a piezo element, since piezo elements are preferably used at a sufficient ambient pressure (e.g. at normal pressure, 1015 hPa) to prevent outgassing of the plastic components normally used on the piezo actuator (such as a casing of the piezo element ) and an associated one prevent vacuum deterioration. Furthermore, such a gas-tight housing 15 advantageously prevents components of the system 100, in particular the elastic suspension 10 and the actuator unit 2, from outgassing into the evacuatable area outside the housing 15. In particular, the connection between the bolt 14 and the housing 15 can be gas-tight and at the same time allow a movement of the bolt 14 caused by the actuator unit 2 relative to the housing 15 along the first direction 11 . This can be realized, for example, by means of a membrane or a bellows arranged between the bolt 14 and the housing 15 .

2 shows a second exemplary embodiment of the system 100 according to the invention, an electrode 5 arranged at one end of the flexible body 3 extending along the axis in the second direction 12 being visible in a plan view. The electrode 5 is enclosed in the flexible body 3 in such a way that a wall of the flexible body 3 surrounding the electrode 5 forms a circumferential conductor element 7 . Advantageously, the bending body 3 is electrically at the predefined ground potential, so that the circumferential conductor element 7 formed by the bending body 3 advantageously ensures at least partial shielding from interference fields, which would otherwise contribute more to a measurement error of the electrical potential of the sample 1. Sample 1, not shown here, is preferably arranged opposite electrode 5, so that sample 1 forms a plate capacitor with electrode 5.

In Figs. 3a-d further exemplary embodiments of the system 100 are shown. In all of the exemplary embodiments, the electrode 5 is preferably in the region of the first antinode 31 occurring during bending oscillation of the bending body 3. All of the exemplary embodiments shown in FIG.

3a shows a third exemplary embodiment of the system 100 with a symmetrical flexible body 3, which can be excited via its center of gravity in the middle of the flexible body 3 by the actuator unit 2 to flexural vibration. For this purpose, a piezoelectric element is preferably used as the actuator unit 2, which acts on a contact area 6 of the flexible body 3 via the bolt 14 in order to excite the latter to flexural vibration. This creates a first and a second antinode 31 , 32 , with the contact area 6 coinciding with a node 33 .

In the fourth exemplary embodiment of the system 100 illustrated in FIG. 3b, a symmetrical flexible body 3 is again visible, with an actuator unit 2 being arranged in the region of a second antinode 32 occurring during bending vibration. The actuator unit 2 is preferably designed here as an electromagnet, wherein the Bending body 3 in the region of the second antinode 32 is designed to be magnetic, in particular ferromagnetic, at least in sections, so that the electromagnet can introduce vibrational energy into the bending body 3 . Thus, the maximum deflection in the area of the antinodes 31, 32, in particular in the area of the first antinode 31 with the electrode 5, can advantageously be adjusted by means of an electromagnet. Here, too, the bending body 3 is suspended via the bolt 14 in the contact region of a vibration node 6 , 33 which occurs during bending vibration of the bending body 3 , and the bolt 14 is connected to the counterweight 4 .

In the fifth exemplary embodiment of the system 100 from FIG. 3 c , a flexible body 3 is shown, which has an opening 8 arranged in the region of the first antinode 31 . Due to the opening 8, the bending body 3 is no longer formed symmetrically with respect to its center of gravity. Accordingly, the contact area 6 of the flexible body 3 connected to the actuator unit 2 via the bolt 14 is advantageously shifted away from the opening 8 towards the center of gravity of this flexible body 3 that is correspondingly shifted in relation to the flexible body 3 from FIG. 3a along the second direction 12 . The flexural body 3 can thus also be excited to flexural vibration in an asymmetrical configuration via the contact region 6 that is displaced correspondingly to the vibration node 33 occurring during flexural vibration or to the center of gravity of the flexural body 3 .

Another sixth embodiment of the system 100 is shown in FIG. Here, a bending body 3 can be excited to flexural vibration in the area of the center of gravity of the bending body 3 via the actuator unit 2 , with the actuator unit 2 being firmly connected to the counterweight 4 on the other hand. In this exemplary embodiment, the counterweight 4 is rigidly connected to a housing 15 , which in turn is connected elastically to a wall 13 via an elastic suspension 10 . The wall 13 is assumed here to be significantly heavier than the bending body 3 , the bolt 14 , the actuator unit 2 , the counterweight 4 and the housing 15 . The housing 15 has a recess via which the actuator unit 2 is connected to the flexible body 3 via the bolt 14 . Thus, here the counterweight 4 and the housing 15, which is firmly connected to the counterweight 4, are suspended resiliently via the elastic suspension on the wall 13. The total mass of countermass 4 and housing 15 is preferably set at 3 to 10 times the mass of bending body 3, so that the bending vibration has a sufficiently high vibration quality and at the same time housing 15 and countermass 5, which form a sensor head, stay compact for ease of use.

Here, too, the bending body 3 has an opening 8 for light to enter via the electrode

5 to be able to carry out the electrical potential of the sample 1 with and without light. In addition in this case the electrode 5 is connected via a wire 9 to the input of a preamplifier 22 fastened here on the bending body 3 . This has the advantage that the wire 9 between the electrode 5 and the input of the preamplifier 22 can be selected to be correspondingly short in this exemplary embodiment, so that the unavoidable parasitic capacitance of the wire 9 caused by the wire 9 is correspondingly reduced. This has a positive effect on the amplification factor of the preamplifier 22 and thus the accuracy of the determination of the electrical potential of the sample 1. The preamplifier 22 forms a component of the electronic circuit 20, which is not shown here. The electronic circuit 20 for determining the electrical potential of the sample 1 will be discussed in more detail in FIG.

For the sixth exemplary embodiment considered here in FIG. 4, a flexible body 3 made of V2A steel with dimensions of 100×8×2 mm ³ with a resulting resonance frequency of 617 Hz can be used in particular. The excitation can take place, for example, in the vibration node 33 of the bending body 3 by means of a piezo element model PC4GQ, Thorlabs®. The bolt 14 between the bending body 3 and the piezoelectric element can be made of V2A steel and screwed tightly to the bending body 3, for example using at least one M1.6 screw, and in particular glued to the piezoelectric element, for example using a two-component adhesive. On the other side, the piezoelectric element can be glued to an iron block forming the counterweight 4 . The counterweight 4 can have a weight of 45 g, for example, and can in turn be screwed firmly to a housing 15, for example made of aluminum and measuring 52×38×31 mm ³ . Due to an electrical connection via a wire 9, the housing 15 is at the predefined ground potential of the bending body 3, the bolt 14, the actuator unit 2 and the counter-ground 4.

For a deflection of the antinodes 31, 32 of 50 pm in this exemplary embodiment when using a piezo element as the actuator unit 2, only a voltage of about 1 V is required, which corresponds to a deflection of the piezo element along the first direction 11 of only a few hundred nanometers. The resonance of the bending body 3 is so stable that the bending vibration can be excited, for example, by a signal generator connected to the piezoelectric element with an adjustable excitation frequency.

5 shows a circuit diagram of the electronic circuit 20 that can be connected to the system 100 according to the invention for determining the electronic potential of the sample 1. The flexible body 3 and the electrode 5 of the system 100 arranged on the flexible body 3 are particularly visible. The sample 1 and the electrode 5 form a plate capacitor. Furthermore, the sample 1 can be electrically connected, in particular short-circuited, to a sample holder (not shown here).

The electronic circuit 20 shown here can be used in particular in two variants, which can be set using a switch 28 . For this purpose, the sample 1 is electrically connected to the switch 28 via a conductor connection. The conductor connection may further include a capacitor 26 through which the sample 1 is grounded for high frequency.

If the switch 28 is set to the first switch position 28a, the sample is at the predefined ground potential. In this first variant, an electrical potential of the sample 1 that can be determined by the system 100 or the electronic circuit 20 can then first be induced in the sample 1, in particular by irradiating the sample 1 with electromagnetic radiation. The electromagnetic radiation can be modulated over time, in particular pulsed. The electromagnetic radiation can also be modulated with the frequency of the bending vibration, in particular the resonant frequency of the bending body 3 . The resulting at least partial synchronization between flexural vibration and irradiation makes it possible, in particular, to at least partially eliminate the dependency of the time-dependent electrical voltage on the distance between sample 1 and electrode 5, which advantageously leads to a reduced measurement error in the electrical potential of sample 1.

An electrical voltage is induced between the sample 1 and the electrode 5 by an interaction process between the electromagnetic radiation and the sample 1 . This electrical voltage can contain components of the electrical voltage that are constant over time as well as components of the electrical voltage that change over time, which are indicative of a potential of the sample 1 that is constant over time or a potential that changes over time. In this case, the electrical voltage refers to the predefined ground potential.

The electrode 5 is electrically connected to a preamplifier 22 which is designed to preamplify the electrical voltage and provide it preamplified as an amplifier voltage on the output side to a downstream part 21 of the electronic circuit 20 . The preamplifier 22 preferably contains an operational amplifier and an RC element, with the ohmic resistance of the RC element preferably being selected to be sufficiently high, for example 1 TQ. The capacitance of the RC element can be in the range from 0.1 pF to 1 pF, for example. Thus, characteristic time constants of the preamplifier 22 in the range of T=0.1 s to 1 s result from the product of the resistance and the capacitance of the RC element Voltage can not be chosen arbitrarily high, are only amplified by the preamplifier 22 time-varying electrical voltages above a cut-off frequency f = 1 / T. With the exemplary values of the RC element, this is f=1 Hz to 10 Hz is designed to detect the time-constant component of the electrical voltage or the time-constant electrical potential of the sample 1.

The time-varying components of the electrical voltage or the electrical potential of the sample 1, on the other hand, are preamplified by the preamplifier 22 and made available on the output side to the downstream part 21 as a time-dependent preamplifier voltage. An equalizer 29 can also be present here. The equalizer 29 is preferably designed to correct the time-dependent amplifier voltage by a correction factor such that a medium arranged between the sample 1 and the electrode 5 is taken into account. This medium, for example air, affects the corrected time-dependent amplifier voltage. This corrected, time-dependent amplifier voltage, which contains the said time-varying components of the electrical voltage or the electrical potential of the sample 1, is finally passed on to a summer 25.

In order to also be able to determine the time-varying components of the electrical voltage or the electric potential of the sample 1 below the cut-off frequency of the preamplifier 22, in particular their time-constant components, the downstream part 21 also has a rectifier 23. Here, use is made of the fact that the flexural vibration leads to a change over time in the component of the electrical potential of the sample 1, which is constant per se, as a result of the modulation of the distance between the electrode 5 and the sample 1. This change over time can be determined as a capacitance between sample 1 and electrode 5 modulated over time with the frequency of the flexural oscillation, in particular with the aid of rectifier 23 . The rectifier 23 is designed to rectify the constant component of the electrical voltage over time with the aid of the frequency of the bending vibration, in particular the resonant frequency of the bending beam 3, by synchronous rectification of the frequency of the bending vibration and the change in capacitance over time caused by the bending vibration and as a direct voltage am Provide output of the rectifier 23. The rectifier 23 is electrically connected to a regulator 24 at its output. The controller 24 can be designed as an integrating controller 24 and can compensate for the DC voltage present at the input of the controller 24 by generating and controlling a reverse DC voltage. The counter-DC voltage is consequently also indicative of the time-constant component of the electrical voltage or the electrical potential of the sample 1. The counter-DC voltage can also be passed on to an adder 25.

The adder 25 can finally form the sum of the two components by summing the time-variable and time-constant components of the electrical voltage or the electric potential of the sample 1 and provide it as a corresponding total voltage at an output of the adder 25 . This total voltage is indicative of the sum of the time-constant and time-varying components of the electrical signal of sample 1.

In the second variant, the switch 28 is in the second switch position 28b. Here the sample 1 is not at the predefined ground potential but is connected to a test signal generator 27 . A test signal, for example a test voltage which is constant over time or a test voltage which varies over time, in particular a periodic test voltage, can be generated by means of the test signal generator 27 and forwarded to the sample 1 . As described in the context of the first variant, this test voltage can then be determined by the system 100 or the electronic circuit 20 . This enables, in particular, a calibration of separately executable determinations of electrical potentials of sample 1 induced in the sample by means of electromagnetic radiation, for example.

Reference List

sample 1

actuator unit 2

bending body 3

counterweight 4

electrode 5

contact area 6

ladder element 7

Opening 8 electrical connection via a wire 9 elastic suspension 10

First direction 11

Second direction 12

Heavy wall 13

bolt 14

housing 15

implementation 16

circuit 20

Downstream part of circuit 21

preamp 22

rectifier 23

regulator 24

Summer 25

condenser 26

Test signal generator 27

switch 28

First switch position 28a

Second switch position 28b

equalizer 29

First antinode 31

Second antinode 32

Vibration node 33

system 100

Claims

patent claims

1. A system (100) for the contactless determination of an electrical potential of a sample (1), the system (100) comprising an actuator unit (2) which is operatively connected along a first direction (11) with a bending body (3), wherein the bending body (3) is also operatively connected to a counterweight (4) which is suspended resiliently or elastically with the system (100), extends along an axis along a second direction (12), and has an electrode (5) which extends at least along the second direction (12), is set up so that the electrode (5) can be arranged at a distance from a sample (1) along the first direction (11), and wherein the actuator unit (2) is designed to move the bending body (3) Excite a bending vibration with an adjustable frequency around the axis, so that the distance between an arranged sample (1) and the electrode (5) varies over time with the adjustable frequency due to the bending vibration, so that in the electrode (5) a time-varying electrical signal can be detected, on the basis of which the electrical potential of the sample (1) can be determined.

2. The system (100) according to claim 1, wherein the electrode (5) is arranged in a region of a first antinode (31) of the flexural body (3) caused by the flexural oscillation.

3. The system (100) according to claim 1 or 2, wherein the actuator unit (2) in a contact area (6) of a vibration node (33) of the bending body (3) occurring during bending vibration with the bending body (3) and the counterweight (4) is operatively connected.

4. The system (100) according to claim 1 or 2, wherein the actuator unit (2) is arranged in the region of a second antinode (32) of the flexural body (3) which occurs during flexural oscillation and is remote from the electrode (5).

5. The system (100) according to any one of the preceding claims, wherein the electrode (5) from the flexure (3) is electrically isolated.

6. The system (100) according to claim 5, characterized in that the electrode (5) from one of the electrode (5) electrically insulated, conductive and circumferential Conductor element (7) is surrounded, in particular wherein the conductor element (7) is electrically at a ground potential. The system (100) according to any one of the preceding claims, wherein the system (100) has an electronic circuit (20) which is designed and set up to process an electrical signal of the electrode (5) and the electrical potential of the sample ( 1) to determine. The system (100) according to any one of the preceding claims, wherein the flexure (3) has an opening (8) along its axis such that when the sample (1) is placed opposite the electrode (5), the sample (1) over the opening (8) can be irradiated with electromagnetic radiation. The system (100) of claim 8, wherein the electrode (5) is at least partially transparent to the electromagnetic radiation such that when the electrode (5) is positioned along an optical axis between the aperture (8) and the sample (1). , the sample (1) can still be irradiated with electromagnetic radiation. The system (100) according to any one of the preceding claims, wherein when the sample (1) is arranged opposite the electrode (5), the electrode (5) and the sample (1) are displaceable relative to one another by means of a displacement unit of the system (100). are. The system (100) according to any one of the preceding claims, further comprising a vacuum chamber, in particular a high vacuum chamber or an ultra-high vacuum chamber, which is designed to contain at least the electrode (5) and the sample (1) which can be arranged opposite the electrode (5) within the vacuum chamber record, wherein when the sample (1) is arranged opposite the electrode (5) in the vacuum chamber, the vacuum chamber can be at least partially evacuated. Method for the non-contact determination of an electrical potential, in particular a time-dependent electrical potential of a sample (1) using the system (100) according to one of the preceding claims, having at least the following steps: i) positioning the sample (1) opposite the electrode (5), ii) by means of the actuator unit (2), exciting the bending body (3) to flexure with the adjustable frequency around the axis, so that the distance between the sample (1) and the electrode (5) is changed by the flexural oscillation with the adjustable frequency, iii) in particular with the adjustable frequency of the bending vibration, pulsed irradiation of the sample (1) with electromagnetic radiation, in particular via the opening (8), so that an interaction process taking place in the sample (1) takes place between the sample (1) and the electromagnetic radiation an electrical voltage indicative of the electrical potential of the sample (1), modulated in particular with the adjustable frequency of the bending oscillation, is induced between the sample (1) and the electrode (5), iv) by means of the electronic circuit (20) according to claim 7, processing the electrical signal of the electrode (5) and determining the electrical potential of the sample (1).