WO1997030570A1

WO1997030570A1 - Device for preparing a plasma and use of said device for preparing a plasma

Info

Publication number: WO1997030570A1
Application number: PCT/DE1997/000214
Authority: WO
Inventors: Horst Schmidt-Böcking; Karl-Heinz Gericke; Anselm Tobias Haas; Michael Lock; Volker Dangendorf; Angela Demian
Original assignee: Schmidt Boecking Horst; Gericke Karl Heinz; Anselm Tobias Haas; Michael Lock; Volker Dangendorf; Angela Demian
Priority date: 1996-02-13
Filing date: 1997-02-04
Publication date: 1997-08-21
Also published as: DE19605226A1; DE19605226C2

Abstract

The invention relates to a process for preparing a plasma in which the plasma is produced by interaction of free electrons with other particles. The plasma is produced in the form of a plasma sheet while free electrons with an electrical field intensity of this kind are produced, said plasma sheet being produced by cold emission without special ambient conditions such as high temperature from a solid structure, in particular metal. The electrical field intensity causing the emission is set up by the geometry of the electrode structure, in particular for electrode structures of several nm to mm, to be locally limited. Many locally limited electrical fields are attached to each other substantially in one plane.

Description

DESCRIPTION

Device for producing a plasma and use of the device for producing a plasma

The present invention relates to a device for producing a plasma according to claim 1 and the use of such a device according to claims 6 to 11.

Such a method is already known to the applicants, in which free electrons of sufficient energy interact with other particles such as molecules, atoms, solids, ions or radicals and thereby generate the plasma.

It is known from DE 36 05 735 to generate a plasma in which electrons are emitted from a metal tip to which an electric field of a certain size is applied. Electrons can be emitted from this metal tip even at ambient pressure and ambient temperature if the electric field strength is sufficiently large. Furthermore, it is described that the point-emitted electrons can be influenced in their energy, for example, by corresponding electric fields after the emission.

From the Patent Abstracts of Japan, JP-OS 07142192, it is known to assemble several plasmas in order to obtain a flat plasma. Nothing is described there about the shape of the individual plasmas and the generation of these individual plasmas.

In contrast, the invention proposes a device according to claim 1, by means of which a flat plasma can be generated.

The area is defined by the electrodes and in particular their mechanical attachment. Due to the sharp edges of the electrodes, electrons can escape at these edges, which in comparison to the point-like emergence of electrons from a tip already results in a significantly larger spatial expansion. The fact that several pairs of electrodes can be present means that a flat plasma can be generated. Individual parameters of the plasma can advantageously be set precisely by setting a corresponding electric field strength. By means of the device according to claim 1, a plasma can be produced in a simple manner, the production of which does not require any particular demands on the environmental conditions. Due to the sufficiently large electrical field strength generated by the electrical voltage that is applied to the electrode pairs, the plasma can be produced in particular under ambient conditions such as normal air pressure and room temperature. Another advantage over other known methods for producing a plasma is that a large plasma area is created without the need to generate a large-volume plasma.

In the case of such a large-volume plasma, by means of which a plasma with a comparatively large surface area has hitherto been generated, usually only the edge region can be used in industrial application.

These known application methods are e.g. cleaning, etching and vapor deposition of surfaces, cutting materials, generating light in lamps, plasma screens, applications in gas phase chemistry in the more general sense and the like.

A large plasma edge is essential for these applications. In the known prior art, this leads to a comparatively large-volume plasma, in which correspondingly high temperatures can then occur in the interior, which can then again lead to undesirable reactions.

For the generation of the plasma according to the prior art, precisely defined conditions with regard to pressure and temperature are also necessary. Furthermore, in the case of a large-volume plasma, rapid adjustability, for example with regard to the ion density and the ion transport, is ruled out in practice. In any case, this is not possible with short time constants and precise local resolution.

In contrast, the device according to claim 1 can be used to produce a plasma which is precisely defined with regard to its spatial extent and with regard to the components contained in it and their temperature distribution. This plasma area can at the same time have sufficient expansion for a large number of applications. In particular, in the case of such a plasma, the ratio of the plasma surface to the plasma volume can be selected as desired, ie can also be selected as large as desired. By means of the device according to claim 1, locally limited plasmas can be integrated into a large plasma area. Due to the possibility of the small and at the same time controllable expansion of the plasma in one direction, the plasma can be brought as close as possible to objects which are to be processed or changed by means of this plasma.

By designing the device according to claim 2, the plasma as a whole can be adapted to different applications. The individual plasma surfaces can differ in their composition and temperature distribution. If, for example, a gas flows through these plasma areas, this gas can be processed one after the other with different plasmas.

The device according to claim 3 is particularly easy to manufacture.

It can be used in the device according to claim 4 that the plasma can be adjusted with both temporal and local accuracy via the electric field strength. Depending on the application of the plasma, for example, the result, such as the rate of a certain chemical conversion of starting materials, can be monitored as a measured variable. This measured variable can be compared with a reference variable. In the event of a deviation, the electrical field strength is then adjusted so that the measured variable approximates the reference variable. It is advantageous that this regulation is possible with a very short time constant. The electric field strength can be varied in the order of nanoseconds.

With the design of the device according to claim 5, a locally different formation of the plasma can be achieved in a targeted manner in the plasma area.

Claims 6 to 11 show advantageous applications of the device. When used according to claim 10, a spectral adjustability results from the use of a certain gas.

An exemplary embodiment of the invention is shown in the drawing. It shows:

1: a device for generating a plasma,

Fig. 2: another device for generating a plasma in a section in

Side view, 3: the device according to FIG. 2 in plan view,

4: a device for producing a three-dimensional plasma and

5: another representation of the device according to FIG. 4.

1 shows a side view of a device with which a plasma according to the invention can be generated. 103 electrodes 101 and 102 face each other on a surface.

These electrodes are advantageously produced using microstructure technology or nanostructure technology. As an alternative to this production of a device, it is also conceivable to print a plastic film accordingly, for example with an aluminum film. It will only be possible to achieve a lower resolution with regard to the electrode spacings, but because of its low cost, such a production method is particularly suitable for applications in mass production. In manufacturing processes using microstructure technology or nanostructure technology, the electrode spacing depends on the wavelength of the radiation with which this structure is generated. If this structure is generated, for example, with light in the visible range, this results in a distance of the electrodes in the order of the wavelength of visible light, i.e. of a few 100 nm. By using radiation of a shorter wavelength, correspondingly smaller electrode spacings and thus correspondingly greater field strengths can be achieved with lower electrical voltages.

These electrodes 101 and 102 advantageously have a sharp edge 104 on their upper side. When a voltage is applied between the electrodes 101 and 102, an electrical field 105 is created between these electrodes. The sharp edge 104 then creates a particularly large electrical field 105 of almost atomic orders of magnitude on the upper side of the electrodes 101, 102, which facilitates the exit of electrons 106 from the electrode 101. In this case, a voltage which is negative in relation to the electrode 102 is applied to the electrode 101.

The structure of these electrodes 101, 102 is applied to materials such as glass or plastic film by means of already known technology, for example lithographic processes. Depending on the manufacturing process, this results in the distance between the electrodes 101 and 102, which has a significant influence on the electric field strength. Due to the rectangular etchable electrode structures, ie the sharp edges 104 of the electrodes 101 and 102 on their upper side, field strengths of such a magnitude are achieved even at comparatively low voltages that electrons 106 are emitted. It is also possible to obtain a cold emission of electrons 106 from the cold electrode 101 of the electrode 101 designed as a solid-state electrode.

To generate the field strengths, the electrodes 101 and 102 are then connected with direct or alternating voltages of the order of magnitude of a few 100 V, as is known from microelectronics. The electric field 105 can then be varied in the order of ns by voltages of this order of magnitude. This makes it possible to control or regulate the plasma with a rapidly variable manipulated variable. Overall, there is a control or regulation with a very short time constant.

The electrons 106 are then accelerated as free electrons in the strong electric fields 105 and generate ions or radicals by impact ionization with the surrounding atoms or molecules of the surrounding gas atmosphere. The resulting microplasma between the electrodes 101 and 102 can be switched through appropriate wiring, i.e. Applying voltage to electrodes 101 and 102 can be switched on and off quickly.

A plasma can therefore be produced under these conditions under standard ambient conditions, i.e. Normal pressure, room temperature and without pre-ionization. At the same time, the plasma has a small extent perpendicular to the electric field lines, so that the ions can be easily extracted with pulsed electric fields and applied to other adjacent surfaces.

When using a plasma generated with the device, for example, a gas can flow in the direction of arrow 107 over the surface and thereby interact with the plasma, which is formed in particular on the upper side of electrodes 101 and 102. It is also conceivable to bring this surface close to the top of a solid to be processed by means of the plasma. Another direction of flow of a gas can be formed substantially perpendicular to the plane of the paper.

FIG. 2 shows a further embodiment of a cathode 101 and an associated anode 102, by means of which a plasma can be generated. Anode 102 and cathode 101 be attached to a plastic film 103. The electric field 105 forms again between the electrodes 101 and 102 when an electrical voltage is applied. By means of a corresponding manufacturing process, the electrodes 101 and 102 again have a sharp edge 104 on the top. If the plastic film 103 acting as a carrier has holes 202, the gas can flow in the direction of arrow 201 if the number of holes 202 is sufficiently large. The gas then flows vertically through the plasma surface. Fig. 2 shows the device in a section in side view, in which the holes 202 are just visible.

The illustration according to FIG. 3 shows the device according to FIG. 2 in a top view. The cathode 101 is again provided with the reference number 101. The plastic film 103 is penetrated by holes 202. These holes 202 lead to a honeycomb structure of the plastic film 103, so that there is still a mechanical connection of the electrodes and the gas can still flow vertically through the plasma surface.

In the devices described so far, the gas could only interact with a plasma surface. Appropriate wiring of the individual electrodes in the area allows the plasma to be designed differently within the area.

However, it is also possible to allow the gas to flow vertically through the plasma area and to provide several of these plasma areas one behind the other in the direction of flow of the gas.

A procedure for producing such a plasma, which can be regulated and / or controlled in three dimensions, is given by the so-called LIGA technology. Using this technique, it is possible to produce a corresponding electrode structure in three dimensions. (LIGA = lithography, electroforming, molding, described for example in W. Ehrfeld, H. Lehr: Radiation, Physics ND Chemistry 45 (3), 349-365 1995)). If an electrode structure is thus produced in this method in such a way that electrodes are always sufficiently close together and are correspondingly sharp-edged, corresponding three-dimensional plasma fields can be generated.

An example of this is given by the illustration according to FIGS. 4 and 5.

4 shows a side view of an arrangement of electrodes 101 and 102, which in turn have correspondingly sharp edges 104 at the corners. These electrodes are held by supporting walls (for example made of plastic) at a defined distance held. The electrical field 105 then arises again between the electrodes. The gas flows through corresponding holes in the direction of arrow 401. The gas then flows through a plurality of plasma surfaces.

5 shows a top view of the device according to FIG. 4. The electrodes 101 and 102 are again held by a carrier made of plastic 103, which, however, must again have holes 202 so that the gas can flow through the plasma surfaces.

The production takes place, for example, in such a way that metallic electrodes are introduced into a solid plastic block. Using LIGA technology, the corresponding structure with the sharp edges of the electrodes is then worked out.

One possible application of plasmas produced in this way is, for example, in the chemistry of the gas phase. The electrons in the plasma have high energy and are therefore able to break practically any electronic bond. The kinetic energy of the electrons can be set comparatively precisely, so that the energy can be adjusted to stimulate certain reactions. The energy of the electrons can be varied within an energy range of a few 10 eV. The primary electron acts like a dynamically induced catalyst, which is available for further reactions unused even after the reaction. Although the electron gas is extremely hot and can break practically any chemical bond, the gas atoms or molecules remain practically at the ambient temperature of the reactor vessel. This means that chemical reaction zones can be created with the plasma, which practically have two separately selectable temperatures for reaction stage 1 (e.g. dissociation of the starting molecules) and for reaction stage 2 (synthesis of the end products).

The plasmas therefore allow a completely new type of gas phase chemistry. In environmental protection, e.g. Cold burns induced by electron impact reduce dioxins and nitrogen oxides. Higher nitrogen oxides can also be separated into nitrogen and oxygen.

It is also possible to cold-synthesize materials that could previously only be implemented in a comparatively cumbersome manner at very high temperatures. For example, a conversion of methane into ethyne, ethene and ethane is possible. Conversion of ethane to ethyne can also be considered. Further conceivable possible applications are briefly outlined below. For example, in a noble gas atmosphere, noble gas ions or excited noble gas atoms can be generated in a very thin layer directly on the surface to be treated. Due to their high ionization energy, the generated noble gas ions can etch away any dirt on the surface or parts of the surface and after the etching reaction are available as neutral noble gas atoms for subsequent reactions again in a completely environmentally friendly manner. Because of the good controllability of the plasma, the surface treatment can be carried out locally in a very targeted manner.

Surfaces can also be steamed. Because of the good controllability of the plasma, an application in printing and writing systems is conceivable, since the plasma can also be generated under standard thermodynamic conditions.

Claims

PATENT CLAIMS

1. Device for generating a two-dimensional plasma surface formed by a plurality of microplasmas at ambient temperature, with the following further features: on a surface (103) there are mechanically connected electrodes (101,

102), the electrodes (101, 102) have a sharp edge (104) on their upper side, in each case two of the electrodes (101, 102) lie on the surface (103) at a distance of the order of a few nm to mm and an electric voltage can be applied to each of the opposing pairs of electrodes, so that electrons are cold emitted from the edge of one electrode (101) and accelerated in such a way that a micro-plasma is formed between the two electrodes by impact ionization.

2. Device according to claim 1, characterized in that several surfaces of electrodes are provided, so that a three-dimensional plasma is formed.

3. Device according to one of claims 1 or 2, characterized in that the electrodes are produced by means of micro or nanostructure technology.

4. Device according to one of claims 1 to 3, characterized in that the microplasmas can be controlled or regulated by changing the voltage with a time constant in the range of nanoseconds.

5. The device according to claim 4, characterized in that the plasma can be set locally differently in the control or regulation.

6. Use of the device according to one of the preceding claims in a catalytic converter for exhaust gas purification.

7. Use of the device according to one of claims 1 to 5 for the synthesis of complex chemical compounds from simple basic components such as for example for the production of higher hydrocarbons from methane.

8. Use of the device according to one of claims 1 to 5 for cleaning and / or etching of surfaces.

9. Use of the device according to one of claims 1 to 5 for vapor deposition and / or printing on surfaces.

10. Use of the device according to one of claims 1 to 5 as a large-area spectral light source and / or spectral lamp.

11. Use of the device according to one of claims 1 to 5 as a flat screen.