WO2007132051A1

WO2007132051A1 - Material with fullerene-type structure, production method and applications thereof

Info

Publication number: WO2007132051A1
Application number: PCT/ES2007/070090
Authority: WO
Inventors: Manuel Camero Hernanz; Josephus Gerardus Buijnsters; Angel LANDA CÁNOVAS; Ignacio Jimenez Guerrero; Cristina GOMEZ-ALEIXANDRE FERNÁNDEZ; Raul GAGO FERNÁNDEZ
Original assignee: Consejo Superior De Investigaciones Científicas; Universidad Autónoma de Madrid
Priority date: 2006-05-12
Filing date: 2007-05-11
Publication date: 2007-11-22
Also published as: ES2301361A1; ES2301361B1

Abstract

The invention describes a carbon-based material with fullerene-type structure and more specifically consists of sp2 hybridization carbon partially hydrogenated up to an atomic content of 35%, preferably between 5 and 35%. The method for producing it is performed on a substrate at low temperature – between 25 and 300°C – using the plasma-assisted chemical vapour deposition (PACVD) technique, containing, within it, highly energized ions and applicable to non-heat-resistant materials covering a wide range of applications. These materials are useful for the production of, for example, mechanical or optical devices, magnetic means, aircraft wings, glasses and plastics or photodetectors.

Description

TITLE

FULERENE TYPE STRUCTURE MATERIAL, PROCEDURE FOR

MANUFACTURE AND ITS APPLICATIONS

SECTOR OF THE TECHNIQUE

The present invention falls within the Materials Technology sector, for its application in the Mechanical Technology sectors, both in the metal-mechanical transformation industry, and in mechanical devices that require low friction and wear and in Information Technology as magnetic media coating.

STATE OF THE TECHNIQUE:

The state of the art regarding carbon-based coatings comprises, on the one hand, classic diamond-type or DLC (diamond-like carbon) carbon coatings, which consist of a mixture of carbon atoms with trigonal and tetragonal coordination associated with their hybridizations sp ² and sp ³ , respectively, with a certain content of hydrogen atoms that saturate free bonds of carbon atoms. The physical properties of this type of coatings are directly associated with the sp ² / sp ³ fraction in the films, being those with high contents of sp ³ bonds, characteristic of the structure of the diamond, which show better mechanical properties (hardness greater than 10 GPa, wear coefficient lower than ICT ⁶ mm ³ / Nm) and optical transparency in ultraviolet-visible-infrared. However, coatings with high contents of sp ² bonds, typical of graphite have worse mechanical properties (hardness less than 10 GPa) and optical. Regarding the tribological behavior in different types of atmosphere, it is known that DLC coatings that do not contain hydrogen show better friction characteristics and wear in a humid atmosphere, while hydrogenated DLC layers have a better performance in a dry atmosphere. There are numerous articles and patents referring to conventional diamond carbon (DLC) layers and their abrasion resistant properties for application on optical substrates (1), magnetic media (2), aircraft wings (3), glass and plastics (4), or photodetectors (5).

On the other hand, since the 1990s, a new type of coatings with a structure of the fulerene type (FL) based on carbon nitride (CN _x ) (6) and carbon (C) (7), which do not contain hydrogen in their structure. The improvement in the tribomechanical properties of the FL layers is not related to the presence of a high fraction of sp ³ carbon hybrids, but to the curvature and cross-linking of the basal carbon planes with sp ² hybridization. FL coatings are amorphous, combining short-range fulerene type order with long-range lack of crystalline order. These materials have always been synthesized by physical vapor deposition techniques or PVD (physical vapor deposition), which require high substrate temperatures, of the order of 45O ⁰ C (8). Among the most commonly used physical techniques, it is interesting to mention: sputtering, sputtered laser deposition (PLD: pulsed laser deposition) (9) and modified arc methods (AJCA: Anodic Jet Carbon Are method) (10). These PVD methods of synthesis are complex and very directional, so it is not easy to apply them on large flat surfaces, or on three-dimensional pieces with complex shapes.

DESCRIPTION OF THE INVENTION Brief Description

An object of the invention is a material with a carbon-like structure in the form of a carbon coating, hereinafter, the fulerene material of the invention, consisting of carbon with partially hydrogenated sp ² hybridization to an atomic content of 35%, preferably between 5 and 35%.

A particular object is the rubber material of the invention which also comprises nitrogen to an atomic content of 35%.

Another object of the invention is a method for manufacturing the fullerene material of the invention on a substrate at low temperature, between 25 and 300 ⁰ C, using the technique of chemical vapor deposition assisted by plasma (PACVD), containing in Its sine is highly energetic ions and because it comprises the following stages: i) supply of the starting gases in the reactor at room temperature in a flow ratio "carbon precursor compound / activating gas" between 0.05 and 1 until reaching a pressure comprised between 10 ^{~ 4} and 50 Torr, ii) a decomposition reaction from a mixture of the carbon precursor compound, preferably a hydrocarbon, and a noble gas by applying an electromagnetic field, the frequency of which may vary in the 5 MHz range and 25 GHz, which produces the excitation of the noble gas as well as the activation, dissociation and ionization of the carbon precursor compound, and iü) a External energy supply to the carbon ions produced by ionization of the carbon precursor compound with energy values in the range 50-300 eV.

Another particular object is the process of the invention where step i) is carried out by a mixture of a carbon precursor compound, a noble gas and a nitrogen precursor.

Another particular object is the process of the invention where the carbon precursor compound is select among different hydrocarbons, such as: methane, ethylene and acetylene; where noble gas is selected from argon and neon; and where the nitrogen precursor is selected from molecular nitrogen or ammonia. Another particular object is the process of the invention where the energy supply of iii) is carried out by applying an electric polarization voltage to the substrate containing at least a temporary fraction of negative polarization, or by the incidence of laser radiation in the visible range-UV.

Finally, the object of the invention is the use of the process of the invention for the manufacture of materials, for example, mechanical, optical devices, magnetic media, aircraft wings, glasses and plastics or photodetectors.

Detailed description

The present invention is based on the fact that the inventors have observed that it is possible to obtain a material of the fulerene-like structure (FL) composed of carbon or partially hydrogenated carbon nitride, more specifically, composed mostly of carbon, with a moderate content between 5- 35% hydrogen, which gives them friction and wear properties that are not very dependent on atmospheric conditions, with a constant wear coefficient value of less than 5 x ICT ⁷ mm ³ / Nm over the entire range of relative humidity (Example 1 and 2).

In addition, this material with a fulerene-like structure (FL) consists of carbon atoms with sp ² hybridization partially hydrogenated, which produces the curvature of the formed graffiti planes. Optionally, they may contain nitrogen up to a maximum atomic percentage of 35% (Example 2). The interest of the material of the invention resides in that they are abrasion resistant coatings for any relative humidity value of the atmosphere because it combines the advantages of conventional diamond-type carbon (DLC) coatings and new carbonaceous materials with FL structure. In addition, the preparation method is particularly suitable for the growth of these layers due to the low temperature required, thus being compatible with a wide range of substrates and technological processes, and because it allows the homogeneous coating of three-dimensional pieces due to their non-directional character.

Therefore, an object of the invention is constituted by a material with a fleece-like structure in the form of a carbon coating, hereinafter referred to as a fleeting material of the invention, consisting of carbon with sp ² hybridization partially hydrogenated to an atomic content of 35%, preferably between 5 and 35%.

On the other hand, the present invention relates to a process for manufacturing the material of the invention in the form of continuous and uniform coatings, by means of the plasma-assisted vapor deposition (CVD) technique (PACVD), keeping the substrate at low temperature, between 25 and 300 ⁰ C, containing highly energetic ions, of at least 50 eV. To carry out said procedure, equipment such as that shown in Figure 1 has been used. More specifically, to obtain FL layers, the process of the invention consists in carrying out a decomposition or dissociation reaction of a precursor or supplier gas. of carbon atoms, for example a hydrocarbon, in a reaction chamber by applying an alternating electromagnetic field frequently in the range 5 MHz and 25 GHz, which results in the formation of a plasma. As a result of this process, plasma formed by electrons, ions and neutral species (atoms, molecules and radicals) is formed. Once the plasma is formed, the excitation of the noble gas takes place as well as the activation, dissociation and ionization of the hydrocarbon (and the excitation and dissociation of the nitrogen source in the case of carbon nitrides, see Example 2). The activation and subsequent dissociation and ionization of the hydrocarbon can occur either by collision of the hydrocarbon molecules with electrons present in the plasma or by inelastic collision with the excited activating species of the noble gas. The noble gas (argon or neon) can act as a diluent and as an activating gas for the hydrocarbon molecules. Likewise, in the case of the preparation of carbon nitride layers, the nitrogen atom supply gas (molecular nitrogen or ammonia) can also act as an activating gas for the hydrocarbon molecules.

The starting gases are fed into the reactor at room temperature in a "Hydrocarbon / activating gas" flow rate between 0.05 and 10 until reaching a pressure between 10 ^{~ 4} and 50 Torr. The working pressure depends on the type of precursor gas and the frequency of the electromagnetic field used to generate the plasma and can be adapted for each case by a person skilled in the art. During the process of preparing the FL layers, the presence of highly energetic ions is required to finally form the carbon-type carbon structures on the substrate. Therefore, an essential element of this invention is the method of supplying energy to the carbon ions produced by hydrocarbon ionization. Be You can use different systems to increase the energy of the carbon ions, such as the application of an electric polarization voltage to the substrate that contains at least a temporary fraction of negative polarization, or the incidence of laser radiation in the visible-UV range. The method that will be efficient for conductive substrates is the application of a continuous negative tension to the substrate during the layer preparation process, since it is homogeneous over the entire substrate. On insulating substrates it is necessary to apply an alternating voltage with a negative polarization component, a pulsed source with negative voltage pulses, or resort to excitation by visible UV-illumination. In this way, it is possible to obtain ions with energy greater than 50 eV from those generated in the plasma by ionization of the hydrocarbon molecules. The incidence of these ionic species carbonated with high energy leads to the formation of fulerene type structures in the deposit obtained. The value of the threshold bias voltage necessary for the stabilization of the FL layers depends on both the specific synthesis conditions and the type of precursor gases, working pressure, etc. In the case of the application of a negative tension to the substrate, it is also important to note that in addition to the increase in ion energy, plasma confinement occurs in the vicinity of the surface of the substrate to be coated. This fact favors the supply and transport of mass towards the surface of the substrate where the formation of the FL layer takes place, thus favoring the deposition process.

As a gaseous source, a mixture of a hydrocarbon (methane, ethylene, acetylene, or others) can be used as a supplier of carbon atoms and a noble gas (argon, neon, or others) as a diluent and activating gas. In the case of coatings also containing nitrogen in its structure, the addition of a nitrogen atom supply gas (molecular nitrogen or ammonia) to the gas mixture is necessary.

On the other hand, the manufacturing method described in the present invention, based on CVD techniques, has great advantages over PVD techniques because it allows deposits at quite high speeds and allows three-dimensional pieces to be homogeneously coated. So far, CVD techniques have been used to obtain carbon-based materials such as: (i) dense layers of diamond-type carbon (DLC), (ii) isolated carbon nanostructures, grown around catalyst metal particles (11, 12) and (iii) carbon powder with a fulerene type structure (13). However, until now it has never been possible to synthesize continuous and dense layers with a fulerene structure using CVD techniques.

Therefore, another object of the invention is a method for manufacturing the fullerene material of the invention on a substrate at low temperature, between 25 and 300 ⁰ C, using the technique of chemical vapor deposition assisted by plasma (PACVD ), containing within it highly energy ions and because it comprises the following steps: i) supply of the starting gases in the reactor at room temperature in a ratio of "carbon precursor compound / activating gas" flows between 0.05 and 1 to achieve a pressure between 10 ^{~ 4} and 50 Torr, ii) a decomposition reaction from a mixture of the carbon precursor compound, preferably a hydrocarbon, and a noble gas by applying an electromagnetic field, the frequency of which may vary in the 5 MHz and 25 GHz range, which produces the excitation of the noble gas as well as the activation, dissociation and ionization of the carbon precursor compound, and iii) an external energy supply to the carbon ions produced by ionization of the carbon precursor compound with energy values in the range 50-300 eV.

The relationship between flows established in the present invention, between 0.05 and 1, is a reflection of the general conditions for this type of reactions between these gases, with at least one activating gas molecule for each carbon precursor gas molecule.

In the application of the electromagnetic field of point ii) frequencies between a minimum of 5 MHz and 25 GHz can be included, reflecting the range of frequencies in which it is possible to achieve the dissociation and excitation of gases. Preferably, the 13.56 MHz and 2.45 GHz ISM bands are considered optimal for the application in the production of the material of the invention.

Another particular object is the process of the invention where the carbon precursor compound is selected from different hydrocarbons, such as: methane, ethylene and acetylene; where noble gas is selected from argon and neon; and where the nitrogen precursor is selected from molecular nitrogen or ammonia.

Another particular object is the process of the invention where the energy supply of iii) is carried out by applying an electric polarization voltage to the substrate containing at least a temporary fraction of negative polarization, or by the incidence of laser radiation in the visible range-UV. Another particular object is the process of the invention where the energy supply of iii) for a conductive substrate is carried out by applying a continuous negative voltage to the substrate during the layer preparation process.

Another particular object is the process of the invention where the energy supply of iii) for an insulating substrate is carried out by applying an alternating voltage with a negative polarization component, a pulsed source with negative voltage pulses, or by visible-UV lighting.

DESCRIPTION OF THE FIGURES

Figure 1.- Diagram of a PACVD reactor for the preparation of carbon-type (FL) carbon layers.

Figure 2.- Image of transmission electron microscopy (HRTEM) of a carbon layer with FL structure of the material of the invention. Figure 3.- XANES spectra of the coating of the material of the invention. The XANES spectra of the coating of the FL structure material of the invention obtained with the appropriate energy of the carbon ions are shown, compared to the spectrum of a conventional hydrogenated carbon layer without FL structure (not FL) obtained with carbon ions of insufficient energy to achieve the FL structure. In addition, the spectrum of the C60 fulerene is shown as a reference for the spectral characteristics. Figure 4.- Tribological properties (coefficients of friction and wear) of carbon coatings with FL structure compared to conventional carbon layers. The wear coefficient (abrasion resistance) and friction coefficient values for a series of partially hydrogenated carbon coatings produced with different carbon ion energy are shown. The tribological benefits of the coatings with FL structure object of this invention are perfectly distinguished, compared to those of conventional hydrogenated coatings without FL structure.

Figure 5.- Image of transmission electron microscopy (HRTEM) of a layer of carbon nitride with FL structure.

EXAMPLES OF REALIZATION

Example 1.- Manufacture of the carbon layers with FL structure of the invention.

In the first example, a carbon film with a FL-like structure and with a carbon content of 20% (atomic percentage) has been synthesized. A chemical vapor deposition equipment assisted by electron cyclotron resonance plasma (ECR-CVD) has been used (Figure 1). This equipment comprises, at least, an alternating current source with excitation frequency between 10 MHz and 2.45 GHz capable of activating the molecules or atoms present, a reaction chamber with controlled pressure in the range of 10 ^{~ 4} to 50 Torr, where the dissociation and ionization of the hydrocarbon and a substrate holder are placed where the piece to be coated is placed, with easy access for the application of the energy input method to the ionic species present in the plasma.

Two starting gases were used: methane hydrocarbon as carbon precursor gas in the film, and noble gas Argon as diluent and activating gas for hydrocarbon decomposition. The working pressure used was ICT ³ mbar, using an electromagnetic field at a frequency of 2.45 GHz with a plasma power of 200 W. The ratio of CH ₄ / Ar flows, used in the synthesis of FL carbon was 0, 43 The threshold energy of the plasma ions necessary to achieve stabilization of the FL structure was 100 eV, and it is important to note that this value varies with the ratio of gas flows used. During the growth process of FL carbon films using ECR-CVD, heating is not necessary, so the maximum temperature recorded during the process was always lower than 12O ⁰ C.

The composition, nanostructure and bond structure of the FL carbon films were analyzed using characterization techniques such as ion detection (ERDA), high resolution transmission electron microscopy (HRTEM) and X-ray absorption (XANES). The ERDA analysis of the films showed an atomic percentage of hydrogen below 35% while in films without FL structure this concentration is usually higher than 40%. The nanostructure of the material analyzed by HRTEM, indicated the presence of carbon atoms grouped in curved graffiti planes (Figure 2), confirming the formation of carbon films with a structure similar to that presented by the fulerene molecule, where the curvature is observed from the surface planes of the tank, and where the denomination of carbon-type carbon films (FL) is derived. On the other hand, XANES spectroscopy (Figure 3) indicates that FL carbon films show typical spectral characteristics of C60 fulerene, absent in films without FL structure.

The mechanical and tribological properties of the material obtained were studied by nanoindentation and pin-on-disk tests (using a WC / Co-6% hard metal ball on the coating), respectively. Young's hardness and modulus of the films with FL structure were 20 GPa and 150 GPa, while in films without FL structure they took values of 2 GPa and 20 GPa, respectively. The tribological properties of friction and abrasion resistance are shown in Figure 4 for a series of samples of materials without FL structure and with FL structure. A clear transition in the tribological properties was observed as a function of the energy of the ions. Thus, for the wear coefficient there is a transition from values greater than 5 x 10 ^{~ 5} mm ³ / Nm in non-FL layers, to values of the order of 1 x 10 ^{~ 7} mm ³ / Nm in the case of C layers with FL structure (8 x 10 ^{~ 8} - 2 x 10 ^{~ 7} mm ³ / Nm).

Example 2.- Manufacture of carbon nitride layers with FL structure.

In the second example, a third gas was added as a source of nitrogen to the hydrocarbon / noble gas mixture to obtain carbon nitride coatings. The C: N: H layers with FL structure were deposited in a CVD reactor with electron cyclotron resonance (ECR-CVD) using as an excitation source an electromagnetic field at a frequency of 2.45 GHz with a power of 210 W. a mixture of methane / argon / nitrogen with flow rates of 13 sccm / 20 sccm / 3 sccm, at a total pressure of 1.1-10 ^"2 Torr. A bias voltage was applied to the substrate of -200 V to achieve stabilization of the FL structure, a value that depends on the specific conditions of the gas mixture Under these conditions, the growth rate of the layers was 0.14 nm / s and the temperature remained below 14O ⁰ C.

As in Example 1, there is a threshold energy of the ions to achieve stabilization of the FL phase. A characterization similar to that described in the Example 1, with very similar results. The fulerene nanostructure is shown in the HRTEM photograph of Figure 5. The mechanical and tribological properties also improved substantially when the formation of the FL structure was achieved.

Bibliography

1.- Optically transparent, scratch-resistant, diamond-like carbon coatings, patent WO-00-56127. 2.- Recording media having protective overcoats of highly tetrahedral amorphous carbon and methods for their production. US-2003-148103.

3.- Wear resistant coatings to reduce ice adhesion on air foils, WO-2004-078873. 4.- Diamond-like Coal Coatings on Glass and Plastics for Added Hardness and Abrasion Resistance. US-2004-028906.

5.- Low Temperature Plasma Deposited Hydrogenated Amorphous Germanium Coal Abrasion Resistant Coatings. US-2005/0089686 and US-2004-043218.

6.- H. Sjδstrom, S. Stafsrδm, M. Boman, JE Sundgren, Superhard and Elastic Carbon Nitride Thin Films Having Fullerenelike Microstructure, PHYSICAL REVIEW LETTERS 75, 1336 (1995). 7.- I. Alexandrou, H. -J. Scheibe, CJ Kiely, AJ Papworth, GAJ Amaratunga, B. Schultrich, Carbon films with an sp ² network structure, PHYSICAL REVIEW B 60, 10903 (1999). Neidhardt, J; Czigany, Z; Hultman, L Superelastic fullerene ^¬ like carbon nitride coatings synthesised by reactive unbalanced magnetron sputtering, SURFACE ENGINEERING, 19, 299 (2003).

9.- Voevodin, AA; Jones, JG; Zabinski, JS; et al. Growth and structure of fullerene-like CNx thin films produced by pulsed laser ablation of graphite in nitrogen JOURNAL OF APPLIED PHYSICS, 92, 4980 (2002).

10.- I. Alexandrou, CJ. Kiely, A. J. Papworth, G. A. J. Amaratunga, Formation and subsequent inclusion of fullerene-like nanoparticles in nanocomposite carbon thin films CARBON 42, 1651 (2004).

11.- Lin, CC; Lo, PY; Lin, CH; et al. Structure and property features of the catalyst-assisted carbon nanostructures on Si wafer by catalyst ion implantation and ECR-CVD DIAMOND AND RELATED MATERIALS, 14, 778 (2005).

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Claims

1. Material with a rubber-like structure in the form of a carbon coating characterized in that it consists of carbon with sp ² hybridization partially hydrogenated to an atomic content of 35%, preferably between 5 and 35% of hydrogenated atoms incorporated in its structure.

2. Material according to claim 1 characterized in that it also contains nitrogen to an atomic content of 35%.

3. Process for manufacturing the material according to claims 1 and 2 characterized in that is carried on a substrate at low temperature, between 25 and 300 ⁰ C, using the technique of chemical vapor deposition assisted by plasma (PACVD), containing Highly energetic ions, and because it comprises the following stages: i) supply of the starting gases in the reactor at room temperature in a flow rate "compound precursor carbon / activating gas" between 0.05 and 1 until reaching a pressure between 10 ^{~ 4} and 50 Torr, ii) a decomposition reaction from a mixture of the carbon precursor compound, preferably a hydrocarbon, and a noble gas by applying an electromagnetic field, the frequency of which may vary in the range 5 MHz at 25 GHz, which produces the excitation of the noble gas as well as the activation, dissociation and ionization of the carbon precursor compound, and iii) ister of external energy to the carbon ions produced by ionization of the carbon precursor compound with energy values in the range 50-300 eV.

4. Method according to claim 3 characterized in that step i) is carried out by a mixture of a carbon precursor compound, a noble gas and a nitrogen precursor.

5. Method according to claims 3 and 4 characterized in that the carbon precursor compound is selected from different hydrocarbons, such as methane, ethylene and acetylene.

6. Method according to claims 3 and 4 characterized in that the noble gas is selected from argon and neon.

7. - Method according to claim 4 characterized in that the nitrogen precursor is selected from molecular nitrogen or ammonia.

8. Method according to claim 3 characterized in that the power supply of iii) can be carried out by applying an electrical polarization voltage to the substrate containing at least a temporary fraction of negative polarization, or by the incidence of laser radiation in the visible range-UV.

9. Method according to claim 3 characterized in that the energy supply of iii) for a conductive substrate is carried out by applying a continuous negative voltage to the substrate during the layer preparation process.

10. Method according to claim 3 characterized in that the power supply of iii) for an insulating substrate is carried out by applying an alternating voltage with a negative polarization component, a pulsed source with negative voltage pulses, or by lighting visible-UV.

11. The use of the method according to claims 3 to 10 for the manufacture of materials, for example, mechanical, optical devices, magnetic media, aircraft wings, glasses and plastics or photodetectors.