RO135074A2 - Method for operating a cluster source based on magnetron sputtering and gas aggregation, in low temperature plasma jet mode - Google Patents

Abstract

The invention relates to a method for operating a cluster source based on magnetron sputtering in combination with the inert gas aggregation of the atoms generated in the magnetron discharge. According to the invention, the method consists in generating a plasma jet which emerges together with the clusters from a cluster source and enters a collecting enclosure to which the cluster source is attached. By this method, by injecting a reactive gas into the plasma jet, immediately after its exit from the cluster source, the chemical state of the surface of the resulting nanoparticles is modified, during their movement towards a substrate placed in the collecting chamber. The plasma jet obtained by this method is characterized by a low temperature, which allows the deposition of nanoparticles with the modified surface on materials susceptible to thermal degradation, such as, for example, polymers.

Description

DESCRIPTION OF THE INVENTION

FIELD OF THE INVENTION

This invention relates to a new mode of operation of a cluster source based on magnetron spraying in combination with the aggregation in inert gas of the ejected atoms from the magnetron target. The new operating regime consists in generating a plasma jet that emerges from the cluster source and enters the cluster collection enclosure; in the classic mode of operation the plasma jet is absent. Both modes of operation of the cluster source allow the obtaining of nanoparticles. This aspect is demonstrated in this invention for tungsten nanoparticles and its compounds synthesized in the plasma jet regime. The main advantage of the plasma jet mode over the conventional mode of operation is that the chemical state of the surface of the metal nanoparticles obtained in the cluster source can be easily modified by injecting the corresponding reactive gases into the plasma jet. Also, the temperature of the plasma jet is reduced, which allows the deposition of nanoparticles on temperature sensitive materials (such as polymers).

The basis of the invention

The invention is closely related to the field of nanoparticle synthesis using plasma (gas discharges). It combines two plasma-based devices: i) cluster sources based on magnetron spraying and inert gas aggregation of vapors obtained by magnetron scattering; and ii) plasma jet sources.

Nanoparticles have gained special attention in recent decades in both academia and technology. This interest is mainly due to the special properties (such as optical, electrical, magnetic, chemical or antibacterial) that nanoparticles possess. For this reason, nanoparticles from various materials have already begun to be used in various fields (eg medicine), being integrated into various technological devices but also into new materials (eg for catalysis and photocatalysis).

There are currently a variety of methods for producing nanoparticles, both chemical and physical. The latter, especially those based on electric discharges in gases (plasma), are highlighted by the chemical purity of the synthesized nanoparticles.

Among the sources of nanoparticles (nanoclusters) that use electric discharges in gas are those based on magnetron spraying combined with gas aggregation, which were originally developed in the 1990s by H. Haberland (Zeitschrift Fur Phys. D Atoms, Mol. Chist ., 20,413, 1991).

From a constructive point of view, the nanoparticle production installations that use cluster sources consist of two vacuum enclosures, one that houses the cluster source and one that acts as a collection chamber; the two enclosures communicate with each other through an orifice (cluster source nozzle).

Nanoparticles are produced in the vacuum chamber of the cluster source (also called the aggregation chamber) by aggregation from atoms obtained by spraying the surface of a target consisting of the material of interest.

The spraying takes place after the bombardment of the target with energy ions produced in magnetron type plasma, which is generated in an inert gas (usually argon, but not only). The pulverized atoms in the target, moving away from the substrate, reach a cooled area of the aggregation chamber, where their partial pressure becomes supersaturated due to the decrease in temperature. This facilitates the nucleation of the nanoparticles: thus, after the collision of the pulverized atoms in the target with those of the working gas, metal-metal dimers result in the case of homogeneous nucleation. These atomic nuclei continue to adhere to pulverized atoms in the target, leading to the formation of nanoparticles in the target material.

The process of forming nanoparticles takes place simultaneously with their movement to the outlet of the cluster source, due to entrainment by the inert gas stream. This results in a bundle of nanoparticles that emerges due to the flow of gas from the source of clusters in the collection chamber. By placing a substrate in the path of the gas flow, the nanoparticles produced in the cluster source will be collected on it.

In the classical mode of operation of the plasma cluster source it is confined inside it.

Another technological tool based on gas discharges (plasma), with various technological applications, is represented by plasma jet sources.

There are various types of plasma jets, classified according to specific criteria, the most common being plasma temperature (high or low temperature) or working pressure (low pressure or atmospheric pressure).

Plasma jets have various technological applications, some of them being:

i) Modification of surface chemistry by exposing them to a jet of plasma produced in a gas that is chemically reactive with the material of the surface to be processed;

ii) Synthesis of nanomaterials (such as carbon, nanofibers and carbon nanowires) following the injection of chemical precursors (such as acetylene) into the jet;

iii) Synthesis of nanoparticles (such as metallic ones) following melting and evaporation of the discharge electrodes.

iv) Coating by plasma-spray process;

v) Metal processing (cutting and welding) using high temperature plasma jets using electric arc.

The present invention provides a particle source that uses a cluster source based on magnetron spraying and inert gas aggregation that operates in a plasma jet regime, as well as its possible applications.

The plasma jet is obtained under specific operating conditions of the cluster source. These allow the plasma to expand from the aggregation source of the cluster source into the collection enclosure to which the source is attached.

Cluster sources based on magnetron spraying and inert gas aggregation are versatile and are widely used for the production of nanoparticles (both metallic and polymer).

However, this type of cluster sources encounters difficulties in the production of nanoparticles from metal compounds (oxides, nitrides, carbides, etc.).

If it is intended to obtain nanoparticles directly from a target of a metal compound, their production is obstructed primarily by the very low plasma spray efficiency of the metal compounds compared to that metal.

If it is intended to obtain nanoparticles by reactive magnetron spraying (using a metal target and introducing a reactive gas into the aggregation chamber - for example N2 or O2 to obtain nanoparticles of nitrides or metal oxides), the magnetron spraying process becomes difficult to be controlled due to the particularities of this type of process (one of them being the possible poisoning of the target and the drastic reduction of the spray efficiency of the target).

The invention offers the possibility to modify the chemical nature of the nanoparticles by introducing the reactive gas at the exit of the cluster source, in the plasma jet. The change in the chemical state of the nanoparticles takes place during their transport to the substrate.

The invention provides the possibility of depositing nanoparticles on temperature sensitive substrates (such as polymers) because the plasma jet from the cluster source produces a negligible heating of the substrate. The possible application in this case is the development of biosensors.

Several works present the production of nanometric materials (nanoparticles or nanostructures) using cluster sources based on magnetron spraying and inert gas condensation on the one hand, and using plasma jets on the other hand.

So:

US 00614505A discloses a method of producing Al nanoparticle layers based on magnetron spraying, with their subsequent use in quantum tunneling devices. The device is essentially a source of nanoparticles based on magnetron spraying and inert gas condensation, namely He. The oxidation on the surface of the nanoparticles is performed by the residual water vapor residues in the He tank. Plasma is confined inside the nanoparticle source.

A method of producing amorphous and crystalline Si nanoparticles using a nanocluster source based on magnetron spraying and gas aggregation in a mixture of Ar and H2 is also known from US patent 20110209987A1. The latter prevents the oxidation of the Si target and reduces the surface tension of the nanoparticles produced. Plasma is confined inside the nanoparticle source.

EP 0522842A1 is also known regarding a plasma torch which generates a plasma jet intended for the coating of substrates with synthetic diamond, using as working gas a gas containing carbon.

EP3206728A1 is also known regarding a method of increasing vertical carbon nanoperets on medically implantable devices, using a low pressure plasma jet.

DE 10031002Al is also known regarding the modification of the chemical state (oxidation or nitriding) of a surface (metallic or carbon) using a low pressure plasma beam.

Gunnarsson R. and co-authors (J. Nanopart. Res., 17, 353, 2015) reported the synthesis of titanium oxide nanoparticles having controlled size and stoichiometry, using a cavitation discharge that expands into a vacuum chamber.

Lazea-Stoyanova A. and co-authors (Dig. J. Nanomater. Bios., 9, 3, 2014) reported the production of metal nanoparticles (Cu or W) using a plasma jet at atmospheric pressure.

Choukourov A. et al. (Beilstein J. Nanotechnol., 8, 2002-2014, 2017) reported changing the surface chemical status of Ag nanoparticles generated with a cluster source based on magnetron spraying and gas aggregation using a plasma discharge in the deposition (or collection) chamber, positioned between the cluster source nozzle and the substrate.

RO 135074 A2,

Ag nanoparticles change their surface chemistry as they pass through this plasma. The magnetron plasma is confined inside the nanoparticle source and does not expand in the aggregation chamber, being completely independent of the plasma in the collection chamber.

Brief presentation of the figures

Figure 1 shows a schematic longitudinal sectional view of the cluster source based on magnetron discharge and inert gas condensation, exemplified for the plasma jet regime.

Figure 2 shows an image of the plasma jet and the substrate. The image shows the deposit obtained on a substrate placed inside the deposit.

Figure 3 shows the scanning electron microscopy (SEM) image of the nanoparticles deposited on the substrate in jet mode, with O2 injected into the plasma jet, at the exit of the cluster source.

Figure 4 shows the spectrum of X-ray photoelectrons (XPS) recorded in the W4f area on the nanoparticle sample deposited in jet mode, with O2 injected into the plasma jet, at the exit of the cluster source.

The definition of terms in general the technical terms or phrases that appear in this text are used as such, being common to people who have skills in technologies related to plasma and nanoparticle synthesis; for a better understanding of them definitions have been selected, as follows.

Plasma: refers to an ionized gaseous medium containing free charge carriers (electrons and ions) and excited neutral particles (atoms, molecules, radicals). Due to the presence of charge-free carriers, plasma is conductive, has a high degree of interaction between its constituents and, in addition, responds to the action of electric and magnetic fields. Moreover, due to the chemical and physical interaction of excited atoms, molecules, radicals, ions, electrons, photons with surfaces, their chemical and physical properties change.

Plasma jet: A directional plasma stream ejected from a plasma-producing device or object, such as a plasma torch, star, etc.

Spraying a target in plasma: the ejection of atoms from a material (called a target, usually in the shape of a disk) following the bombardment of the target with ions produced in plasma (usually of a neutral gas, such as, but not limited to, Ar ⁺ ). After spraying the target, atoms are obtained from the target material that can be directed to an object (substrate) to form a thin film (deposition, coating) on its surface. This process is widely used for the functional coating of various thin film surfaces. However, the method is also used to obtain atomic clusters, by condensing vapors.

Magnetron: device that combines strong electric and magnetic fields to confine plasma in the vicinity of the target; in this way the spray rate of the target is increased.

Condensation: reverse process of vaporization, involving the change of the state of aggregation from gaseous to liquid or solid state.

Clusters: in physics means small, multiatomic particles.

Nanoparticles: particles with dimensions between 1 and 100 nm.

Source of clusters (nanoparticles): a device that produces nanoparticles based on physical or chemical processes, or a combination thereof. Nanoparticles can be produced by two strategies: "from large to small" and "from small to large". The first strategy involves mechanical methods of reducing the size of macroscopic materials (grinding). The second strategy involved the aggregation of atoms produced by some method. In the present invention the second strategy is used, the atoms being produced by magnetron spraying and their aggregation being achieved by condensing them into an inert gas stream.

Detailed presentation of the invention

The object of the invention is the method of operating in low temperature plasma jet mode of a cluster source based on magnetron spraying and gas aggregation and its use for the synthesis of nanoparticles with chemically modified surface.

Fig. 1 shows schematically in cross section a cluster source based on magnetron spraying and gas aggregation. It consists of a vacuum chamber (1) in which a magnetron spray plasma source (2) is provided axially provided with a target (4); In the approach presented here the target is metallic, from W, but it can be from any other material. The enclosure of the cluster source has on the opposite side of the target an axially placed hole (7) which communicates with the deposition enclosure (10). The region between the target and the outlet is called the aggregation area (6). In this area, which is cooled (5), the nanoparticles grow by condensing the vapors scattered from the target. The substrate (9), on which the nanoparticles are deposited, is positioned in the deposition chamber. This is a metal plate but can also be made of glass, silicon, or temperature sensitive material (such as a polymer foil). The working gases are introduced into the process in a controlled manner, at a constant flow, so that the pressure in the aggregation chamber is an order of magnitude larger than in the deposition chamber. The working gas from the cluster source (3) is Ar (but can be any other inert gas suitable for the magnetron scattering process, such as Kr). It has multiple roles: it supports the electric discharge, contributes to the nucleation process and drives the nanoparticles to the deposition chamber. The reactive gas (12) is introduced in a controlled manner into the deposition chamber, in the immediate vicinity of the outlet. The working gases are discharged with a vacuum system (11) attached to the storage chamber.

Under typical operating conditions, the magnetron discharge plasma is limited inside the cluster source, near the target and extending to a greater or lesser extent in the aggregation area. Under these conditions, the nanoparticles are ejected from the cluster source through the outlet through a bundle of nanoparticles.

Under certain experimental conditions, when the thickness of the spatial load of the wall becomes smaller or comparable to the diameter of the outlet of the cluster source, the plasma expands outside the cluster source, in the form of a plasma jet.

The plasma jet formed is exemplified by the photo image shown in Fig.2. This figure shows the outlet of the cluster source (6), the plasma jet (8), the reactive gas injection tube (12) and the substrate (9), on which the material deposited by the plasma jet is identified.

The thickness of the spatial load blanket on the wall is a decreasing function of the power applied to the discharge and the pressure, so that for very small diameters of the outlet the plasma transfer cannot be achieved, the cluster source not being able to work in plasma jet mode.

In the specific working configurations of a cluster source, an optimal diameter is identified for which the cluster source can work both in the classical regime and in the plasma jet regime. The transition between the two modes is made for a specific value of the target-orifice distance, given that the power applied to the discharge and the working pressure have a constant value.

The deposition of nanoparticles in the plasma jet regime is demonstrated here using a target of W and as working gases Ar (in the cluster source) and O2 (in the plasma jet, in order to oxidize the surface of the nanoparticles).

In Figs. 3 shows the SEM scanning electron microscopy image of the nanoparticles deposited on the substrate; the size of the nanoparticles is between 20 and 40 nm.

Elemental analysis of the sample surface deposited under these experimental conditions was performed by X-ray photoelectron (XPS) spectroscopy. FIG. 4 shows the high resolution XPS spectrum in the W4f area. The presence of the two maximums assigned WO3 and the two maximums assigned W metallic is noticed in this spectrum. Since the X-ray penetration depth is a maximum of 20 nm in the XPS technique and the nanoparticle size is between 20 and 40 nm, the XPS spectrum of Figs. 4 suggests that the nanoparticles were efficiently oxidized (some completely and others with an oxide shell, their core remaining metallic).

The temperature of the substrates exposed to the plasma jet did not exceed 60 ° C during deposition. Tests of deposition of metallic W nanoparticles on PET (polyethylene terephthalate) substrate showed that after exposure of the substrate to the plasma jet it retains its integrity.

The objects of the invention are:

Operation of cluster sources based on magnetron spraying and inert gas aggregation in the plasma jet regime, and application of this operating regime for the synthesis of chemically modified surface particles.

Claims (3)

CLAIMS: 1. Operating mode of the cluster source based on magnetron spraying and aggregation in inert gas, namely the plasma jet mode, characterized in that, under specific operating conditions of the plasma source, for which the thickness of the spatial load layer on the wall is smaller than the outlet diameter of the cluster source, the plasma expands outside the source, in the deposition chamber, in the form of a plasma jet. Method for modifying the chemical nature of the surface of nanoparticles generated according to claim 1, characterized in that reactive gas is injected into the plasma jet evolving in the deposition chamber and the chemical nature of the surface of the nanoparticles changes due to their interaction with reactive plasma. during their movement through the collection chamber to the substrate. The method of depositing the generated nanoparticles according to claim 1, characterized in that, due to the low temperature of the plasma jet, the substrate used is not damaged although it is sensitive to destruction with temperature.