RU2380195C1 - Method for production of metal or semiconductor nanoparticles deposited on carrier - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention is related to methods for production of nanoparticles and may be used in processes of application of highly efficient catalytic nanocoatings. Method includes melting and dispersion of melt material, supply of produced liquid drops of this material in plasma, cooling of liquid nanoparticles formed in plasma till they harden, and depositing of produced hard nanoparticles onto carrier. At the same time values of plasma parametres are selected based on the following ratios:

where T_e is electronic temperature of plasma, eV, n_e is electronic density of plasma, m^-3, α is coefficient of surface tension of dispersed melt material, n/m, R and r - maximum and minimum values of liquid drops radius, m; L is specific size of plasma, m.

EFFECT: possibility to use independent ratios for selection of plasma parametres and accounting of dispersed material properties, increased efficiency of nanoparticles production process.

3 cl, 2 dwg

Description

The invention relates to the field of nanotechnology, in particular to technologies for producing nanostructured materials and their deposition on various carriers (substrates, substrates) in accordance with the field of application, and can be used in applying highly efficient catalytic nanocoatings.

It is known that nanostructures with a surface density of particles of at least 10 ¹² cm ^-2 are also promising for creating highly efficient nanoelectronic devices, such as ultrafast switches, ultra-miniature memory cells, etc. In these areas, the efficiency of using nanostructured (sub) monolayer coatings substantially depends on the surface density (packing) of the nanoparticles, which in turn depends on their size and dispersion value.

The fundamental difference between nanostructured materials and macromaterials is that in the former the number of surface atoms is commensurate with the number of atoms in the volume, and the radius of curvature of the surface is comparable to the lattice constant. In this case, an exchange of electrons is possible both between surface atoms and with substrate atoms, which ensures high catalytic activity of nanocatalytic coatings. This is especially true when creating highly efficient catalysts based on platinum group metals for electrodes of hydrogen fuel cells. In addition, the catalytic properties of some materials dramatically depend on particle sizes. Thus, gold nanoparticles with a size of less than 5 nm have unique catalytic properties and can be effectively used to catalyze the reaction of producing hydrogen from carbon monoxide and water vapor in compact reactors at ordinary temperature directly in the engine exhaust system (DAThompson, Using gold nanoparticles for catalysis, Nanotoday, v. 2, No.4 (2007), 40-43).

Known methods for producing nanoparticles can be divided into two main groups in accordance with the physics of processes: synthesis from atoms, clusters, complex radicals and molecules; dispersion of macromaterials.

Among the former, both physical (thermal evaporation and condensation, ion sputtering) and chemical (for example, gas-phase chemical reactions, water heating reactions, sol-gel method, etc.) are widely used. However, chemical methods have some limitations. Thus, gas-phase and water-heating chemical reactions require a low reaction temperature with a potentially low cost of production, but are not able to produce high-quality nanomaterials and are not suitable for mass production. The sol-gel method also gives a low cost of production, but the nanoproduction is contaminated with reagents. Spray pyrolysis creates large or agglomerated particles.

Physical methods can also be described as intense. These primarily include methods using thermal plasma. The main types of thermal plasma: high-power plasma jets, electric arc discharges, laser and electron-beam plasma, plasma of a high-frequency (radio-frequency) induction discharge.

The specificity of the proposed method, including both the production of high-quality nanoparticles and the application of a close-packed, including monolayer, coating of such particles on a carrier, significantly limits the list of acceptable methods. Thus, the preparation of particles with a diameter of several nanometers and a narrow dispersion by synthesis methods in thermal plasma is substantially hindered by coagulation of particles.

A device for implementing a method for producing nanoparticles based on the synthesis of metal nanopowders in an electric arc plasma (Zhqiang Wei et al., Efficient preparation for Ni nanopowder by anodic arc plasma, Mater. Lett. 60 (2006), 766-770), which includes vacuum chamber, gas inlet system, power supply system, plasma generator with high-frequency initiator, vacuum pump, water-cooled cylindrical collector, water-cooled copper crucible with a diameter of 20 mm mounted on an insulated stand and connected to a power source (as an e). A tungsten rod with a diameter of 10 mm is used as a cathode. Changing the interelectrode distance allows you to vary the temperature in the crucible. The initial pressure in the chamber is 10 ^-3 Pa, working ~ 10 ³ Pa. The electric arc is ignited using the RF initiator. Ionized gas flows out of the nozzle, forming a plasma jet flowing out to the anode. Metal atoms detach from its surface when the kinetic energy of a plasma jet exceeds the surface energy of a metal in a crucible. An area of supersaturated vapor forms above the evaporation zone. The generation of nanoparticles and their size distribution are determined by the process of homogeneous nucleation (condensation) in a supersaturated pair. The primary particles in the synthesis process are nuclei (crystallization). These nanometer-sized particles are in a suspended state, so their movement and growth can be described as Brownian coagulation. In the process of growth, in addition to the mechanism of adsorption by the initial nuclei of atoms, the particle size can also increase by fusion in collisions of nuclei and clusters. In plants of this type, to limit the growth of particle sizes, they are as quickly as possible removed from the synthesis zone using neutral gas flows.

This device is in basic details typical for the implementation of highly productive technologies for the synthesis of nanopowders by condensation methods.

The disadvantage of this method is the low quality of the particles (average diameter of about 60 nm with a dispersion of 20-100 nm, specific surface area of about 15 m ² / g) due to the difficulty of controlling their coagulation, making it impossible to use them for applying highly effective catalytic coatings in nanoelectronic devices.

Methods using electrodispersion of liquid droplets are based on the phenomenon of the occurrence of Rayleigh (capillary) instability of a droplet of size R relative to the division process when its electric charge reaches a certain critical value Q _cr = 8π (ε ₀ αR ³ ) ^1/2 , where α is the surface melt tension (A.I. Grigoriev, S.O. Shiryaeva, Patterns of the Rayleigh decay of a charged drop, ZhTF, vol. 61, issue 3 (1991), p. 19). It is characteristic that daughter drops are initially unstable, so the fission process is cascading in nature. It is also important that such a process stops at a certain stage (d _min ≈ 8 · 10 ^-7 εα ^-3 ) when particles lose their charge due to field emission (Kozhevin VM et al., J. Vac. Sci. Technol. In 18 (2000) , 1402). For most metals, this corresponds to a particle size of several nanometers with a fairly narrow size distribution width, which makes the electrodispersion method extremely promising for the production of highly dispersed metal nanoparticles. In a plasma, macroparticles and, in particular, droplets, as a rule, acquire a negative charge due to collisions with electrons having much greater mobility than ions. The magnitude of this charge is determined by the magnitude of the floating potential and depends on the plasma parameters.

A known method of producing nanoparticles (patent RU 2265076, IPC С23С 4/00, B01J 2/02, B22F 9/00, published November 27, 2005, bull. No. 33), which includes dispersing the material by applying to the tip cathode of a conductive material with a radius the curvature of the tip is not more than 10 μm of the electric field with a field strength at the tip of the tip of not less than 10 ⁷ V / cm, feeding the obtained liquid droplets of this material into an electric discharge plasma with a pulse duration of at least 10 μs generated in an inert gas at a pressure of 10 ^-3 - 10 ^-1 Pa between electrodes at potentials difference of at least 2 kV and simultaneous exposure to a magnetic field of at least 600 Gs normal to said electric field creating the said plasma, cooling in liquid gas of the nanoparticles formed in the said plasma to solidify and applying the obtained solid nanoparticles to the carrier, the parameters of which plasma satisfy the relations:

;

;

;

;

,

,

where R and r are respectively the maximum and minimum radii of the liquid droplets supplied to the plasma, m;

- радиус Дебая, м;

- Debye radius, m;

T _e is the electron temperature of the plasma, eV;

n _e is the plasma density, m ^-3 ;

τ _d is the time of flight of liquid droplets through the plasma, s;

τ _p - plasma lifetime, s;

T _m is the melting temperature of the conductive material, K;

L is the characteristic distance at which the plasma pressure decreases e times, m

As the conductive material, metal or a semiconductor may be used.

As the inert gas, any known inert gas can be used.

The application of the obtained nanoparticles to the carrier can be carried out in an electric field, the intensity vector of which is directed at an angle to the direction of motion of the nanoparticles. The deposition of nanoparticles on a carrier can be carried out in an inhomogeneous electric field.

The simultaneous fulfillment of the conditions given in the formula of the ratios ensures cascade fission of all the initial liquid droplets of material supplied to the plasma and the rapid cooling of the formed nanometer liquid droplets (final fission products), such that, as a result, the solid nanoparticles deposited on the substrate have an amorphous structure. Fulfillment of these conditions makes it possible to reproducely form monodisperse structures consisting of amorphous nanoparticles with a variable, including extremely high, packing density.

In an example implementation of the method, it is assumed that under the conditions stated in claim 1 of the formula, the electron density of the interelectrode discharge plasma will be 10 ¹⁰ -10 ¹¹ cm ^-3 and, in accordance with the first ratio, the electron temperature values must exceed 500 eV, which should be achieved (by the opinion of the authors of this method) with a potential difference between the electrodes of a quasi-stationary discharge of at least 2 kV. In order for droplets of all sizes to charge up to the value of a floating potential, i.e. in order to satisfy the second ratio at the above electron density, the distance between the electrodes should be selected in accordance with the inert gas pressure (about 5 cm).

In order for the formed nanoparticles to have an amorphous structure that impedes their coalescence, their abrupt (10 ⁷ K / s) cooling during solidification is necessary. Since the plasma lifetime is sufficiently large, the third relation should be satisfied by the choice of parameter L. In this case, the value of this parameter is close to the size of the hole in the anode and should be no more than 1 cm.

Further, nanometer-sized particles are separated from larger particles by selecting the diameter of the annular anode on which the substrate is mounted. The potential difference between the annular anode on which the substrates are mounted and the additional cathode is selected so that amorphous particles of nanometer sizes are directed by the electric field onto the substrate, and the trajectories of larger particles are not disturbed.

The disadvantage of this method is that the plasma parameters cannot be independently estimated from the first two conditions given, since they both include the Debye radius R _D , the value of which is just a function of the sought parameters T _e and n _e . The possibility of achieving the required level of electron temperature T _e ≥500 eV (indicated in the implementation example) in an electrode discharge plasma by application of a potential difference of at least 2 kV without indicating the discharge power cannot be estimated. In addition, the patent does not discuss a method for renewing a 10 μm tip cathode, which makes it difficult to achieve process continuity.

As a prototype of the claimed invention, a method for producing nanoparticles is selected (patent RU 2242532, IPC С23С 4/00, publ. 12/20/2004, bull. No. 35), which includes dispersing the molten material, feeding the obtained liquid droplets of this material into a plasma formed in an inert gas at a pressure of 10 ^-1 -10 ^-4 Pa, cooling in an inert gas of liquid nanoparticles formed in the aforementioned plasma to solidify and applying the resulting solid nanoparticles to the carrier, while the plasma parameters satisfy the relations:

;

;

;

;

where R and r are respectively the maximum and minimum radii of the liquid droplets supplied to the plasma, m;

- радиус Дебая, м;

- Debye radius, m;

T _e is the electron temperature of the plasma, eV;

n _e is the plasma density, m ^-3 ;

τ _d is the time of flight of liquid droplets through the plasma, s;

τ _p - plasma lifetime, s;

T _m is the melting temperature of the conductive material, K;

L is the characteristic distance at which the plasma pressure decreases e times, m

Mentioned material may be metal, semiconductor, metal oxide. The application of the said nanoparticles to the carrier is carried out in an electric field, the intensity vector of which is directed at an angle to the direction of motion of the nanoparticles. Mentioned nanoparticles can be deposited on a carrier in an inhomogeneous electric field.

In other additional paragraphs, 2 specific methods of electrodispersion are claimed: based on laser ablation of the macromaterial (clause 7) and in the electrode electric discharge (clause 8).

In claim 7, the dispersion of the molten material and the delivery of the obtained liquid droplets into the said plasma is carried out by laser ablation of a target from the said material in an inert gas atmosphere at a pressure of 10 ^-4 -10 ^{-2 -2} Pa by radiation from a pulsed-periodic YAG: Nd ³⁺ laser operating on a length waves of 1.06 μm, having a pulse duration of at least 20 ns, a leading edge of the pulse of less than 5 ns and a pulse repetition rate of at least 10 Hz, while the laser power density on said target is set to at least 10 ⁹ W / cm ² .

The essence of the method according to claim 7 is as follows. Irradiation of the target surface with a repetitively pulsed laser leads to the melting and evaporation of the surface layer. As a result of optical breakdown, a plasma zone with a thickness L≥100 μm is formed above the surface of the molten metal. Under the influence of plasma pressure, the liquid layer becomes unstable, which leads to the ejection of liquid droplets with a diameter of from 1 μm to 100 nm. These drops fall into the above plasma, are charged to a critical value, which is the threshold for the development of capillary (Rayleigh) instability of a liquid drop that causes its division (A.I. Grigoriev, S.O. Shiryaeva, Patterns of Rayleigh decay of a charged drop, ZhTF, 1991 t. 61, issue 3, p. 19). The parameters of this plasma must satisfy the first and second relations simultaneously to ensure cascade division of drops of all sizes (from R to r) in the plasma. With the above irradiation parameters, the density n _e and the electron temperature T _{e of the} plasma should be 10 ¹⁸ cm ^-3 and 30 eV, respectively. The fulfillment of the third relation should provide subsequent rapid (at least 10 ⁷ K / s) cooling of the droplets in the peripheral plasma, which should rapidly expand and cool in a time shorter than the time of cooling the particle to the melting temperature (i.e., when radiation losses are not compensated by the flow energy from plasma), which is necessary for the amorphization of their structure. According to the calculations of the inventors under the above conditions, a plasma lifetime of about 1 μs, a nanoparticle speed of about 3 · 10 ⁴ cm / s and a melting point of 1350-1730 K (for copper and nickel) the third ratio is satisfied. This effect allows one to significantly limit the increase in the size of nanoparticles due to their coalescence.

The method according to claim 8, based on the electrodispersion of a material in an electrode discharge, is described in the above analogue (patent RU 2265076).

The disadvantages of the prototype include the lack of independent relationships for a reasonable choice of plasma parameters, namely, electron temperature T _e and plasma density n _e , since in two relations for evaluating these parameters there is a value of the Debye screening radius R _D , which itself is a function of the desired parameters. The high cost of equipment and low productivity of laser dispersion (p. 7) makes it difficult to commercialize the method and coating nanoparticles on carriers with a large area (> 10 ² cm ^-2 ). There is no description of the method for renewing 10 μm of the tip cathode, that is, achieving a continuous mode of operation with a long service life of the device for implementing the method of claim 8. In addition, the possibility of achieving the required level of electron temperature T _e ≥500 eV (indicated in the implementation example) in an electrode discharge plasma by applying a potential difference of at least 2 kV without indicating the discharge power cannot be estimated.

The objective of the invention is to provide a method for producing nanoparticles by electrodispersing liquid macrodrops in a plasma, in which the electron temperature and density in the aforementioned plasma are determined from independent ratios that take into account the properties of the dispersible material, the implementation of which ensures that droplets of the charge reach critical values of the development of Rayleigh instability, leading to cascade fission and nanostructuring of liquid droplets in the aforementioned plasma, as well as adayuschego large values of performance and service life of the apparatus for implementing the inventive method.

The essence of the invention lies in a method for producing nanoparticles deposited on a carrier, including melting and dispersing the molten material, the introduction of liquid droplets of this material into the plasma, cooling the liquid nanoparticles formed in the specified plasma until they solidify, and the deposition of solid nanoparticles on the carrier. In this method according to the claimed invention, the values of the electron temperature and electron density of the plasma are selected from independent ratios that take into account the properties of the dispersible material:

where T _e is the electron temperature of the plasma, eV;

n _e is the electron density of the plasma, m ^-3 ;

α is the coefficient of surface tension of the dispersible molten material, n / m;

R, r - maximum and minimum values of the radius of liquid macrodrops, m;

L is the characteristic plasma size, defined as the distance at which the plasma pressure drops "e" times, where "e" is the base of the natural logarithm, m

In particular cases of the implementation of the proposed method, the dispersion of a liquid material, the cooling of liquid nanoparticles until they solidify occurs in the plasma of the cathode spots of a vacuum (p≤10 ^-1 Pa) electric arc discharge with a voltage of at least 10 V and a discharge current between the cathode and anode of at least 10 A, however, the temperature of the cathode electrode can be set above the melting temperature of the cathode material.

In the proposed method, in contrast to the prototype, the parameters used for the electrodispersion of liquid plasma droplets are selected on the basis of two independent conditions (1) - (2), which explicitly take into account the properties of the dispersible material (a is the surface tension coefficient of the metal melt) and ensure the charge of all drops to the threshold of cascade fission during the passage of the distance L in the plasma. Plasma can be created by any of the known methods, provided that its parameters satisfy conditions (1) - (2).

It is known that plasma particles acquire a charge as a result of collisions with electrons (M.A. Olevanov et al., Coagulation Rate of Dust Particles in a Low-Temperature Plasma, ZhTF vol. 73, issue 10 (2003), p. 51). The authors of the claimed invention on the basis of calculating the plasma electron energy required to overcome the Coulomb barrier corresponding to the critical charge of the droplets (A.I. Grigoriev, S.O. Shiryaeva, Patterns of the Rayleigh decay of a charged drop, ZhTF, 1991 vol. 61, issue 3, p. 19) of the largest size R, the condition is formulated for the minimum level of the electron temperature of the plasma (1) taking into account the properties of a particular dispersible material.

The independent condition (2) for the product of the electron density and the characteristic plasma size L, which is necessary for the macroparticle to accumulate the smallest size r of charge is greater than the critical level during collisions with electrons during its passage in the plasma, is formulated taking into account the mean velocity V _d ~ 10 ² m / s (Schuike, T. and Anders A., Velocity distribution of carbon nanoparticles generated by pulsed vacuum arcs. Plasma Sources Sci. Technol. 8 (1999), 567).

Condition (1) corresponds to the electron temperature T _e ≥20 eV for nickel droplets ~ 10 ^-7 m in size. The level of the product of the electron density and the characteristic plasma size should be n _e L≥2 · 10 ¹⁴ m ^-2 . The fulfillment of these conditions is possible using a wide range of known methods for generating plasma.

The method proposed in items 2 and 3 uses a specific method for generating the aforementioned plasma, namely, the use of plasma from a cathode vacuum arc, which consists mainly of ionized and excited particles of the cathode material. A characteristic property of the cathode vacuum arc is the concentration of the discharge current in the cathode spots, where the current density and power, plasma density and pressure can reach 100 MA / cm ² and 10 ⁹ W / cm ² , 10 ²⁰ cm ^-3 and 10 ¹⁰ Pa, respectively ( A.Anders, Metal plasma immersion ion implantation and deposition: a review. Science & Coatings Technol. V.93 (1997), pp158-167) due to the small size of the spots (~ 10 μm) and the duration of their existence (~ 10 ^-7 from). The formation of cathode spots is a consequence of explosive electron emission from microinhomogeneities (geometric and structural) of the cathode surface. It is characteristic that cathode spots moving randomly or under the influence of an external magnetic field form craters with diameters in the range of several tens of microns, which are largely a result of the ejection (splashing) of material melted under the influence of plasma pressure and serving in this case as sources of liquid macrodrops with mainly in the range of about 0.1-1 μm (A. Anders, The fractal nature of vacuum arc cathode spots, IEEE Trans. Plasma Sci. v. 33, No.5 (2005), 1456-1464). Considering that the number of such macrodrops ejected from each anode spot can reach 10 ⁵ (I.G. Kesaev, Cathodic processes of an electric arc, Nauka, M. 1968, p. 35), and the frequency of formation of cathode spots up to 10 ⁷ s ^-1 , droplet ejection performance can be up to 10 ¹¹ s ^-1 (Cao Qin and S. Coulombe, Organic layer-coated metal nanoparticles prepared by a combined arc evaporation / condensation and plasma polymerization process, Plasma Sources Sci. Technol 16 (2007), 240- 249). This value is 4-5 orders of magnitude higher than the performance of laser dispersion (at a repetition rate of about 10 Hz). The performance of ejection of macrodrops can be increased by increasing the temperature of the cathode, including equal to and higher than the melting temperature of its material, that is, using a liquid metal cathode.

Due to the extremely high values of the power density in the cathode spot, the dense erosion plasma of the cathode spot into which macrodrops fly into has a rather high temperature, therefore it is completely ionized and contains not only once but also repeatedly ionized ions (I.A. Krinberg, Dependence of ion charge on current strength in stationary and pulsed vacuum discharges.Letters in ZhTF, v.27, issue 2 (2001), 9-16). In this erosive plasma of a microflare of a cathode spot, which has characteristic dimensions of the order of the diameter of the formed crater (~ 10 μm), macrodrops are charged due to collisions with electrons (M.A. Olevanov et al., Coagulation Rate of Dust Particles in a Low Temperature Plasma, ZhTF t.73, issue 10 (2003), p. 51). Typical values of cathode spot plasma density n _e > 10 ²⁴ m ^-3 (A. Anders, Metal plasma immersion ion implantation and deposition: a review, Science & Coatings Technol v.93 (1997), pp158-167) significantly exceed the minimum level by condition (2) n _e > 10 ¹⁹ -10 ²⁰ m ^-3 , therefore, the charge acquired by macrodrops during movement in the plasma of the cathode spot will significantly exceed the critical level. Taking into account that during the decay of droplets having a charge 10 times larger than critical, there is a sharp increase (almost 3 orders of magnitude) of secondary droplets and a decrease in their characteristic sizes (A.I. Grigoryev, S.O. Shiryaeva, Patterns of Rayleigh decay of charged drops, ZhTF, 1991 vol. 61, issue 3, p. 19), the productivity of the generation of nanoparticles in the plasma of the cathode spot increases, respectively. The electron energy level of about 20 eV in the plasma of the cathode spot corresponds to modern ideas about the processes in such devices (A. Anders, The fractal nature of vacuum arc cathode spots, IEEE Trans. Plasma Sci. V. 33, No.5 (2005), 1456 -1464). Thus, under conditions typical of a vacuum arc (voltage of at least 10 V, the discharge current between the cathode and anode of at least 10 A) in the plasma of the cathode spot of a vacuum arc, conditions (1) - (2) of cascade fission of liquid droplets of material are realized, leading to their nanostructuring.

An estimate of the propagation time of a cooling wave inside 10-nm particles by the authors gives values not exceeding 10 ^-9 s; therefore, the cooling rate of such nanoparticles is determined by the cooling rate of the plasma of the cathode spot, i.e., its lifetime. The plasma cooling rate, in turn, is determined mainly by radiation losses and plasma expansion. For plasma of cathode spots, which is the product of the ionization of metal vapors of materials with a high charge number Z, radiation losses make a significant contribution to the rapid cooling of the plasma, which ultimately limits the lifetime of the plasma of the cathode spot to 10 ^-7 -10 ^-8 s (A.Anders, Metal plasma immersion ion implantation and deposition: a review, Science & Coatings Technol v. 93 (1997), pp158-167). The above values of the lifetime of an individual cathode spot indicate that under these conditions there is a cooling rate of nanodroplets of at least 10 ⁷ K / s, which is sufficient for amorphization of the material during solidification of the nanoparticles.

The proposed method has greater manufacturability and reduced energy consumption per unit of production compared to the proposed specific methods for implementing the prototype formula in paragraphs 7 and 8, since the total generation time of nanodroplets is a statistical superposition of such processes in separate spontaneously (or under the influence of a magnetic field) cathode spots moving along the cathode surface. This continuous renewal of the cathode spots ensures uniform cathode erosion, and consequently, the resource of its operation and the device as a whole increases. Although the process of formation of nanoparticles in the plasma of a single cathode spot is purely pulsed (τ _p ~ 10 ^-7 s), in general, the operation mode of the device for implementing the inventive method can be characterized as a high-performance stationary process with a continuous operation resource determined by the cathode material reserve (100 hours and more).

EFFECT: invention allows reproducibly forming monodisperse structures from amorphous metal nanoparticles, semiconductors with high performance and long service life of the device based on the use of electrodispersion of liquid droplets in a dense plasma of cathode spots of a cathode electric arc.

The inventive method for producing nanoparticles is illustrated by a design drawing of a plasma electrodispersion device that implements the inventive method for producing nanoparticles using a vacuum arc discharge as a source of plasma and macrodrops (Figure 1), as well as a drawing illustrating the process of electrodispersion of liquid droplets of material in a cathode spot plasma (Fig. 2).

The device includes a vacuum electric arc plasma source with a cathode 1 and anode 2 connected to a constant (or pulsed) voltage source 3, a solenoid 4 capable of creating a magnetic field in the cathode zone, a vacuum chamber 5 with a residual pressure of less than 10 ^-1 Pa, in which the carrier 6 on an insulating stand 7, which directs the flow of solid nanoparticles 8.

The inventive method is as follows. After the chamber 5 has been evacuated, a constant voltage source 3 with a value of at least 10 V (depending on the cathode material and the residual pressure in the chamber) is connected to the cathode 1 and anode 2 of the plasma arc source, while the discharge current between the cathode 1 and anode 2 is not set less than 10 A. Melting of the material and its dispersion into macrodrops occurs in the crater of the cathode spot. The resulting droplets enter the dense erosion plasma of the cathode spot with parameters satisfying relations (1) - (2). As a result, all droplets with sizes from r to R are charged due to collisions with electrons at least to the critical value of the onset of their cascade fission during their passage in the plasma of the cathode spot. The resulting nanoparticles are cooled to solidify in the rapidly expanding plasma of the cathode spot and in the plasma of the interelectrode discharge over a period of about 10 ^-7 s, which leads to amorphization of their structure.

Next, the nanoparticles are sent to the carrier 6 with a positive potential with or without the use of known methods for separating them by size (electrostatic or electromagnetic separators).

The magnitude of the discharge current determines the performance of the device, which can also be increased by increasing the cathode temperature, including equal to and higher than the melting temperature of its material. The geometry of the cathode can be different (planar, cylindrical, hollow cathode, liquid metal cathode, etc.). As the conductive material, metal or a semiconductor may be used.

Figure 2 represents on an enlarged scale a portion of the cathode surface layer and illustrates the above-described processes of ejection of macrodrops from a cathode spot crater and their electrodispersion in a cathode spot plasma. Here 1 is the cathode, 9 is the layer of molten material, 10 is the plasma of the cathode spot, 11 are macrodrops, 8 are nanoparticles.

Given the significant increase in the number of droplets after electrodispersion in the plasma of the cathode spot, the use of this method is able to provide a density of nanoparticles on the carrier of ~ 10 ¹² cm ^-2 required to create highly efficient nanoelectronic devices. The productivity of obtaining nanoparticles is easily scaled by the magnitude of the discharge current, which makes it possible to vary over a wide range the area of the treated surface of the carrier.

Thus, the inventive method provides for obtaining nanoscale amorphous spherical particles with a narrow dispersion with high performance and efficiency.

Claims (3)

1. A method of producing metal or semiconductor nanoparticles deposited on a carrier, including melting and dispersing the molten material, feeding the obtained liquid droplets of this material to the plasma, cooling the liquid nanoparticles formed in the plasma before they solidify, depositing the obtained solid nanoparticles on a carrier, characterized in that values of plasma parameters are selected based on the following relationships:

,
where T _e is the electron temperature of the plasma, eV;
n _e is the electron density of the plasma, m ^-3 ;
α is the coefficient of surface tension of the dispersible molten material, n / m;
R and r are the maximum and minimum values of the radius of liquid macrodrops, m;
L is the characteristic plasma size, m 2. The method according to claim 1, characterized in that the dispersion of the liquid material is carried out in the plasma of the cathode spots of a vacuum electric arc discharge, and the cooling of liquid nanoparticles before their solidification is carried out in the plasma of the cathode spots and the interelectrode plasma of a vacuum electric arc discharge at a voltage of at least 10 V and discharge the current between the cathode and the anode is at least 10 A. 3. The method according to claim 2, characterized in that the cathode temperature is set above the melting temperature of its material.

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