Carbon nanostructured materials and methods for forming carbon nanostructured materials

Abstract

The present disclosure relates to methods for depositing vertically oriented carbon nanowalls (CNWs) using non-equilibrium gases such as gaseous plasma. Methods are disclosed for rapid deposition of uniformly distributed nanowalls on large surfaces of substrates using ablation of bulk carbon materials by reactive gaseous species, formation of oxidized carbon-containing gaseous molecules, ionization of said molecules and interacting said molecules, neutral or positively charged, with a substrate. The CNWs prepared are useful in different applications such as fuel cells, lithium ion batteries, photovoltaic devices and sensors of specific gaseous molecules.

Claims

1. A method for depositing a layer of CNWs on a substrate using a CO cycle, the method comprising: providing a carbon-containing precursor material in condensed form in the reaction chamber; providing an oxygen-containing atmosphere in the reaction chamber; forming a plasma discharge in the oxygen-containing atmosphere in the reaction chamber; wherein CO molecules in the plasma discharge interact with the carbon-containing precursor material to form CO.sub.xO.sub.y molecules, the CO.sub.xO.sub.y molecules diffusing to the substrate and decomposing at the substrate to form CO molecules and carbon, the carbon building up CNWs.

2. A method according to claim 1 wherein the CO molecules formed at the substrate by decomposition of the CO.sub.xO.sub.y molecules subsequently diffuse to the carbon-containing precursor material to form further CO.sub.xO.sub.y molecules.

3. A method according to claim 1 wherein at least some of the C.sub.xO.sub.y gaseous molecules are charged, thereby being accelerated in a sheath between the plasma and the substrate before interacting with the substrate, thereby promoting the formation of CNWs.

4. A method according to claim 1 wherein x>y.

5. A method according to claim 1 wherein x≥2.

6. A method according to claim 1 wherein y≥1.

7. A method according to claim 1 wherein the substrate is heated to a temperature in the range 100-1500° C.

8. A method according to claim 1 wherein the substrate is heated to a temperature in the range 700-1000° C.

9. A method according to claim 1 wherein the carbon-containing precursor material is heated to a temperature greater than 100° C.

10. A method according to claim 1 wherein the carbon-containing precursor material is heated to a temperature greater than 300° C.

11. A method according to claim 1 wherein the pressure in reaction chamber during deposition of CNWs is between 1 and 100 Pa.

12. A method according to claim 1 wherein the oxygen-containing atmosphere in the reaction chamber is free of hydrogen-containing gas.

13. A method according to claim 1 wherein the growth rate of the CNWs is more than 1 nm/sec.

14. A method according to claim 1 wherein the growth rate of the CNWs is at least 10 nm/sec.

15. A method for depositing a layer of CNWs on a substrate, the method comprising: providing an atmosphere containing CO.sub.xO.sub.y molecules in a reaction chamber; providing a substrate in the reaction chamber; forming a plasma discharge in the atmosphere containing CO.sub.xO.sub.y molecules in the reaction chamber; wherein CO.sub.xO.sub.y molecules diffuse to the substrate and decompose at the substrate to form CO molecules and carbon, the carbon building up CNWs.

Description

SUMMARY OF THE FIGURES

(1) Embodiments and experiments illustrating the principles of the present disclosure will now be discussed with reference to the accompanying figures in which:

(2) FIG. 1 shows a schematic of the CO cycle. The CO molecules diffuse in the gas phase until they reach the surface of a carbon-containing material. The CO molecules interact with the carbon-containing material causing formation of volatile C.sub.xO.sub.y molecules. The C.sub.xO.sub.y gaseous molecules formed on the surface of carbon-containing material diffuse in the gas phase until they reach the surface of the heated substrate. The C.sub.xO.sub.y gaseous molecules interact with the heated substrate. The C.sub.xO.sub.y gaseous molecules decompose on the heated substrate causing growth of the CNWs and formation of CO molecules. The CO molecules released from the heated substrate diffuse in the gas phase until they reach the surface of a carbon-containing material. It is considered that both CO and CO.sub.xO.sub.y molecules are partially ionized.

(3) FIG. 2 shows a further schematic of the CO cycle. A CO molecule 1 (neutral or ionized) interacts with a carbon-containing precursor material 2 and on the surface 3 of the carbon-containing precursor material 2 causes formation of a CO.sub.xO.sub.y gaseous molecule 4. The C.sub.xO.sub.y gaseous molecule follows diffusion path 5 and eventually reaches the surface 6 of the heated substrate 7. The CO.sub.xO.sub.y gaseous molecule 4 decomposes on the surface 6 of the heated substrate and releases one or more CO molecules 1. The CO molecule 1 follows its diffusion path 8 and eventually interacts with the surface 3 of the carbon-containing precursor material 2 to form a CO.sub.xO.sub.y gaseous molecule.

(4) FIG. 3 shows an SEM image of CNWs deposited on a heated substrate using an embodiment of the present disclosure.

(5) FIG. 4 shows an image of a water droplet on the surface of CNWs deposited on a heated substrate using an embodiment of the present disclosure.

(6) FIG. 5 shows a schematic of the setup suitable for growing CNWs according to Example 1.

(7) FIG. 6 shows the thickness of the CNWs versus treatment time according to Example 1.

(8) FIG. 7 shows a schematic of the setup suitable for growing CNWs according to Example 2.

(9) The reference numerals used in the drawings are as follows: 1 CO molecule (neutral or ionized) 2 Carbon-containing material 3 The surface of the carbon-containing material 4 CO.sub.xO.sub.y gaseous molecule (neutral or ionized) 5 Diffusion path of C.sub.xO.sub.y 6 The surface of the heated substrate 7 Heated substrate 8 Diffusion path of CO 9 Reaction chamber 10 Two-stage rotary vacuum pump 11 Gate valve 12 High-pressure container with oxygen-containing gas 13 Leak valve 14 Radio-frequency generator 15 Antenna 16 Graphite block 17 Sample 18 Duct used for pumping the reaction chamber 19 Duct used for leaking the oxygen-containing gas into the reaction chamber 20 Duct used for placing a holder with carbon-containing material into the reaction chamber 21 Holder with carbon-containing material 22 Duct used for placing the holder with substrate into the reaction chamber 23 Holder with substrate

DETAILED DESCRIPTION

(10) Aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

(11) The present disclosure relates to methods of depositing CNWs by contacting a substrate with C.sub.xO.sub.y gaseous molecules. In preferred embodiments of the present disclosure, the source of said C.sub.xO.sub.y gaseous molecules is a carbon-containing precursor material. Said carbon-containing precursor material is left to interact with CO molecules (neutral or ionized), that arrive to its surface from the gas phase. The interaction of said CO molecules with said carbon-containing precursor material causes formation of said CO.sub.xO.sub.y gaseous molecules. The CO.sub.xO.sub.y gaseous molecules desorb from the surface of the said carbon-containing precursor material, enter the gas phase and diffuse in the gas phase until they reach the substrate. When the said substrate is heated to elevated temperature the said CO.sub.xO.sub.y gaseous molecules (neutral or ionized), decompose to carbon atoms or carbon clusters and CO molecules on the surface of said substrate. The C atoms or clusters build CNWs on the surface of said substrate while the CO molecules desorb from the surface of said substrate, enter the gas phase, diffuse in the gas phase and eventually reach the surface of said carbon-containing precursor material. The carbon-containing precursor material is left to interact with said CO molecules that arrive to its surface from the gas phase. The interaction of said CO molecules with said carbon-containing material causes formation of said CO.sub.xO.sub.y gaseous molecules. This process shall be called the “CO cycle”. In the CO cycle said CO molecules serve as a medium for ablation of said carbon-containing material to form said CO.sub.xO.sub.y gaseous molecules. The CO.sub.xO.sub.y gaseous molecules serve as building material for growth of CNWs. The growth of CNWs is a consequence of decomposition of said CO.sub.xO.sub.y gaseous molecules on the surface of said substrate.

(12) “CO cycle”, within the context of the present disclosure, shall be understood as a procedure that involves: interaction of CO molecules with a carbon-containing precursor material, preferably graphite; said interaction leading to formation of CO.sub.xO.sub.y gaseous molecules; said C.sub.xO.sub.y gaseous molecules diffusing in the gas phase until they reach and interact with a substrate; said interaction between said CO.sub.xO.sub.y gaseous molecules and said substrate causing decomposition of said C.sub.xO.sub.y gaseous molecules; said thermal decomposition of said CO.sub.xO.sub.y gaseous molecules leading to growth of CNWs on the surface of said substrate; said thermal decomposition of said CO.sub.xO.sub.y gaseous molecules also leading to formation of CO molecules on the surface of said substrate.

(13) The “CO cycle”, within the context of the present disclosure, is schematically presented in FIGS. 1 and 2.

(14) “Carbon-containing precursor material”, within the context of the present disclosure, shall be understood as any condensed material (e.g. solid or liquid material) containing carbon atoms. “Carbon-containing precursor material” may for example be pure (or substantially pure) carbon in any form including but not limited to graphite, highly oriented pyrolytic graphite, soot, CNWs, fullerenes, carbon black; or any type of polymer including fluorinated, nitrated and oxidized polymers; or any type of hydrocarbons including those in liquid state at room temperature such as ketones, alcohols, lipids and the like.

(15) “C.sub.xO.sub.y gaseous molecules”, within the context of the present disclosure, may be any molecule that contains at least two carbon atoms (i.e. x≥2) and at least one oxygen atom (i.e. y≥1), the number of carbon atoms being larger than the number of oxygen atoms (i.e. x>y). “C.sub.xO.sub.y gaseous molecules” should preferably have suitable stability at room temperature and suitable instability at elevated temperature. The list of “CO.sub.xO.sub.y gaseous molecules”, within the context of the present disclosure, includes but is not limited to molecules such as C.sub.xO where x is any integer from 2 to about 1000 including C.sub.4O, C.sub.6O, C.sub.7O; C.sub.xO.sub.2, where x is any integer from 3 to about 1000, etc.

(16) “Substrate”, within the context of the present disclosure, may be any solid material including metals and alloys, semi-conductors, metal oxides, nitrides and carbides including ceramics and glasses, polymers and other forms of carbon-based materials.

(17) “CNW” materials, within the context of the present disclosure, shall be understood as carbon-containing structures that have the thickness up to about 100 nm, height between about 100 nm and 100,000 nm and extend from the surface of a substrate. CNW materials, within the context of the present disclosure, shall be understood also as dense structures of thickness up to about 100 nm oriented randomly on a substrate forming a network. CNW materials, within the context of the present disclosure, shall be understood to be composed predominantly of carbon but may also contain other elements including hydrogen, fluorine, nitrogen, oxygen or metal atoms. The structure of CNW, within the context of the present disclosure, shall be understood rich in graphene sheets but may contain also other types of carbon. Such a structure allows for a very large surface as compared to smooth carbon materials but still benefits from superior electrical and chemical properties of graphene.

(18) In preferred embodiments, the CNWs are synthesized using the CO cycle. It is found that, using this approach, rapid synthesis of CNWs is possible on a wide range of solid substrates and the growth rate is superior to synthesis procedures known to the present inventors at the time of writing.

(19) CNW materials are promising for mass application in cases where graphene properties are favorable and large surface-to-mass ratios are required. The known techniques, briefly presented above, suffer from low deposition rates—typically of the order of 1 nm/s. The low deposition rates of current techniques are due to the synthesis procedure which is based on the deposition of carbon from CH.sub.x radicals. The radicals are formed either in gaseous plasma or using hot wires. The pressure inside the processing chamber limits the density of CH.sub.x radicals in plasma: if the pressure is too high, gas phase agglomeration of CH.sub.x radicals occurs and the resultant C.sub.xH.sub.y clusters that adsorb on the substrate surface do not allow for formation of CNWs but rather a thin film of hydrogenated carbon. Another drawback of current techniques is a need for continuous supply of carbon-containing materials (in most techniques hydrocarbons) upon growth of CNWs. Yet another drawback of current techniques is the need for hydrogen, which, in atomic form, serves for enhancing the quality of deposited CNWs. The present disclosure addresses these shortcomings of current techniques by substantially increasing the growth rate without losing the superior graphene-like structure of the CNWs. The growth rate is enhanced using CO.sub.xO.sub.y gaseous molecules as the carbon source and the synthesis procedure is highly controllable, without the need to provide a continuous supply of precursors into the reaction chamber. Furthermore, no hydrogen is used in the methods of the present disclosure.

(20) In the methods of the present disclosure, C.sub.xO.sub.y gaseous molecules are applied as a building material for CNWs. The C.sub.xO.sub.y gaseous molecules are rarely referred to in literature. The commonly known gaseous molecules containing only C and O are carbon monoxide (CO), carbon dioxide (CO.sub.2), tricarbon dioxide (C.sub.3O.sub.2) and pentacarbon dioxide (C.sub.5O.sub.2). These molecules are gaseous at room temperature but inherently unstable when the number of carbon atoms is more than 3. Graphene oxides are another type of C.sub.xO.sub.y gaseous molecules. They may contain several hexagonal carbon rings terminated by oxygen atoms (often epoxy bond) or OH radicals. The graphene oxides are solid and rather stable at room temperature. Under non-equilibrium conditions and upon interacting oxygen with a carbon-containing material a variety of CO.sub.xO.sub.y gaseous molecules are created.

(21) Many C.sub.xO.sub.y gaseous molecules are unstable and decompose spontaneously. The decomposition rate depends on the temperature. As a general rule, the decomposition rate increases with increasing temperature. Many C.sub.xO.sub.y gaseous molecules will decompose slowly at room temperature but very fast at elevated temperatures. The preferred embodiments of the present disclosure take advantage of the temperature dependence of the decomposition rate of CO.sub.xO.sub.y gaseous molecules. In preferred embodiments, the entire reaction chamber is kept at room or only slightly above room temperature in order to prevent substantial loss of CO.sub.xO.sub.y gaseous molecules by thermal decomposition at the walls of the reaction chamber or at other parts of the reaction chamber. The substrate, however, is preferably kept at higher temperature in order to facilitate rapid thermal decomposition of CO.sub.xO.sub.y gaseous molecules on its surface.

(22) Thermal decomposition of carbon-containing gaseous molecules by itself does not necessarily assure the required CNW arrangement of carbon atoms on a substrate surface. As will be understood, carbon usually grows in many other forms than CNWs. The CNWs are considered to grow preferentially due to simultaneous interaction of positively charged C.sub.xO.sub.y gaseous molecules with the substrate. The positively charged ions are accelerated in the sheath between gaseous plasma and the substrate and gain energy of the order of 10 eV just before interacting with the substrate. This energy is beneficial since it allows for proper arrangement of carbon atoms on the substrate; said carbon atoms arrange in the form of CNWs.

(23) The method may include the step of ablation of the carbon-containing precursor material placed in the reaction chamber. The ablation rate of carbon-containing precursor material depends on the temperature of the material. In a preferred embodiment the carbon-containing precursor material is heated to a rather high temperature in order to assure for rapid ablation of carbon-containing precursor material. The carbon-containing precursor material, in the preferred embodiments, is ablated by reactive plasma species, in particular by interaction of CO molecules with said carbon-containing precursor material. The CO molecules can be neutral or positively charged. The neutral CO molecules in gaseous plasma become vibrationally excited, thereby increasing the ablation rate of the carbon-containing material. The ablation of the carbon-containing material, in accordance with the preferred embodiments, results in the formation of CO.sub.xO.sub.y gaseous molecules on the surface of said carbon-containing material, said CO.sub.xO.sub.y gaseous molecules desorb from the surface of said carbon-containing material.

(24) Another parameter that is considered to have an impact on the CO cycle according to the present disclosure is the gas purity. Without wishing to be bound by theory, it is assumed that gases other than oxygen-containing, if present, would likewise react with the carbon-containing precursor material, e.g. at its surface, upon exposure to oxygen-containing gas. Therefore, in the preferred embodiments, the oxygen-containing gas is in contact with the carbon-containing material at a relatively high level of purity, e.g. at 90%, 95%, 99% or 99.9% molar concentration of the oxygen-containing gas in the reaction gas. For this purpose, the treatment chamber is first evacuated to a relatively low pressure in order to remove other gases from the reaction chamber, and only then the oxygen-containing gas is added to the chamber. A treatment chamber is thus first evacuated by an appropriate vacuum pump. The pressure in the processing chamber after evacuation is preferably equal to or below 10 Pa, even more preferred equal to or below 1 Pa. After a successful evacuation, the treatment chamber is filled with the oxygen-containing gas to a (higher) pressure of e.g., 1,000 Pa, or 100 Pa, or 10 Pa. This is lower than atmospheric pressure. Such a moderate pressure was found advantageous in terms of the affinity between oxygen-containing gas and carbon-containing material. The use of a vacuum chamber is therefore advantageous for assuring high purity of oxygen-containing gas, and for assuring appropriate pressure in order to make suitable use of the CO cycle.

(25) The optimal duration of processing depends on the treatment parameters, such as the temperatures of both carbon-containing material and the substrate, plasma parameters (which in turn depend on discharge parameters) and the pressure of oxygen-containing gas.

(26) The CNW deposition rate increases with increasing temperature of carbon-containing precursor material. At a carbon-containing precursor material temperature of about 300° C. a satisfactory ablation rate can be achieved. Further increase of the carbon-containing precursor material's temperature results in higher ablation rates.

(27) Higher ablation rates in turn cause an increase of the CNW deposition rate. In one experiment, the temperature of carbon-containing material was about 800° C., and deposition rates of about 100 nm/s were achieved.

(28) The temperature of the substrate plays a role. The deposition rate of CNWs on the substrate is found to be low when the substrate's temperature is about 100° C. and increases with increasing temperature. At a substrate temperature of about 400° C., a higher CNW deposition rate can be achieved. A further increase of the substrate temperature results in increasing CNW deposition rate. In one experiment, the temperature of the substrate was about 1000° C., and deposition rates of about 100 nm/s were achieved.

(29) In the preferred embodiments, the pressure of oxygen-containing gas is between 1 and 100 Pa. Operating in this range allows for reliable ignition and sustenance of plasma in the reaction chamber by various electrical discharges. In preferred embodiments plasma is sustained by a high-frequency electrodeless discharge. A suitable frequency is between 0.1 MHz and 10 GHz. Such electrodeless coupling is beneficial since the sputtering of material facing plasma is suppressed. Preferably, a discharge is powered by a standard high frequency generator operating at radio frequency (13.56, 27.12 MHz, or any other harmonic of 13.56 MHz) or microwave frequency (e.g. 2.45 GHz). The power of the discharge generator should be high enough to sustain gaseous plasma in the processing chamber. The suitable range of generator power depends on the volume of the reaction chamber and the pressure of the oxygen-containing gas. Typically, a larger volume and higher pressure will require a higher discharge power. In one experiment, the pressure of oxygen-containing gas was 30 Pa, the volume of dense plasma was about 1 liter and the discharge power was 800 W.

(30) Preferably, the contact time of the heated substrate with the CO.sub.xO.sub.y gaseous molecules is between 0.1 s and 1000 s. In further preferred embodiments the treatment time is between 1 s and 100 s. This preferred treatment time allows for optimal CNW deposition efficiency at the preferred pressure and the preferred temperature of carbon-containing material and the preferred temperature of substrate, according to the present disclosure. Preferably, the temperature of the substrate during treatment is between 700 and 1000° C. At lower temperature, the treatment time needed for optimal CNW deposition becomes too large, while at higher temperature the CNW may become degraded so that desired properties of the CNWs may be lost. This is particularly true at temperatures above about 1500° C., or even 2000° C. where deposition of carbon in other morphological or structural forms is observed.

(31) The following treatment parameters have shown to be particularly advantageous: pressure of 30 Pa, discharge power of 800 W, generator frequency of 13.56 MHz, the temperature of the carbon-containing precursor material 800° C., substrate temperature 1000° C. and the volume of intense gaseous plasma 1 liter.

(32) Some preferred embodiments of the present disclosure shall now be described with reference to the following non-limiting examples.

Example 1

(33) CNWs were deposited onto titanium substrate according to the process schematically presented in FIGS. 1 and 2. The pressure upon contacting the (titanium) substrate heated to about 1000° C. with the oxygen-containing gas (in this case, pure carbon dioxide) was 30 Pa, the frequency of the discharge generator was 13.56 MHz and the temperature of the carbon-containing material was 800° C. The treatment time was 20 s.

(34) The CNW deposited on the titanium substrate was imaged with a scanning electron microscope (SEM). FIG. 3 represents an SEM image of a typical product. The deposited CNW coating has a super-hydrophobic character. An image of a water drop on the surface of the CNW coating is presented in FIG. 4.

(35) The experimental set up for this example is shown schematically in FIG. 5. The reaction chamber 9 is made from borosilicate glass and is equipped with a two-stage rotary vacuum pump 10. There is a gate valve 11 for separating the vacuum pump 10 from the reaction chamber 9. The oxygen-containing gas was carbon dioxide stored in a high-pressure container 12 separated from the reaction chamber 9 with a leak valve 13. Gaseous plasma is generated in the reaction chamber by a radio-frequency generator 14 operating at the frequency of 13.56 MHz and with the output power of 800 W. The generator is coupled with gaseous plasma via an antenna 15. Carbon-containing precursor material, a piece of graphite 16 in this case, and the sample 17 were placed in the same reaction chamber 9, adjacent each other.

(36) The reaction chamber 9 was first evacuated to a pressure below 1 Pa by the vacuum pump 10. Then, the pump was separated from the reaction chamber 9 by closing the gate valve 11. Carbon dioxide from the high-pressure container 12 was leaked into the evacuated reaction chamber 9 using the leak valve 13 until a pressure of 30 Pa was reached in the reaction chamber 9. When the pressure of 30 Pa was reached, the leak valve was closed. Then, plasma was created inside the reaction chamber 9 using the RF generator 14. Both the graphite block 16 and the sample 17 were heated inside the reaction chamber 9 due to power dissipated into plasma by the RF generator 14 so no external heating was applied in this Example 1. The density of positively charged ions was of the order of 10.sup.18 m.sup.−3.

(37) The treatment time in this example was varied and the thickness of the CNWs was measured for each treatment time. The thickness of the CNWs versus the treatment time is shown in FIG. 6.

Example 2

(38) Example 2 discloses a configuration suitable for the synthesis of CO.sub.xO.sub.y gaseous molecules. The setup shown in FIG. 5 was modified in order to allow for independent exposure of carbon-containing precursor material and heated substrate to gaseous plasma. Altogether, the experimental setup is similar to the one in FIG. 5 for Example 1, except for the arrangement of the reaction chamber 9. The reaction chamber 9 used in Example 2 is schematically shown in FIG. 7. The reaction chamber 9 is equipped with several ducts. Duct 18 is used for pumping the reaction chamber 9. Duct 19 is used for leaking the oxygen-containing gas into the reaction chamber 9. Duct 20 is used for placing a holder with carbon-containing precursor material 21 into the reaction chamber 9. The holder with carbon-containing precursor material 21 is movable so it is either placed in the duct 20 or placed inside the reaction chamber (dashed position in FIG. 7). The holder with carbon-containing precursor material 21 may be externally heated using any suitable method including but not limited to resistive heating, inductive heating or irradiation with photons, electrons or ions.

(39) The holder with carbon-containing precursor material 21 was mounted in the position inside the duct 20. The reaction chamber 9 was first evacuated to pressure below 1 Pa by the vacuum pump 10. Then, the pump was separated from the reaction chamber 9 by closing the gate valve 11. Carbon dioxide from the high-pressure container 12 was leaked into the evacuated reaction chamber 9 using the leak valve 13 until a pressure of 30 Pa was reached in the reaction chamber 9. When the pressure of 30 Pa was reached, the leak valve 13 was closed. Then plasma was created inside the reaction chamber 9 using the RF generator 14. The holder with carbon-containing material 21 was moved from the position inside the duct 20 into the center of the reaction chamber 9. The position of the holder with carbon-containing material 21 in the center of the reaction chamber 9 is marked in FIG. 7 with dashed line. Plasma inside the reaction chamber 9 was characterized by optical spectroscopy. The spectrum of the plasma in reaction chamber was dominated by atomic oxygen lines as long as the holder with carbon-containing material 21 was mounted in the position of the duct 20. The ratio between oxygen line at 777 nm and the most intensive line of C.sub.2 band was about 7, as long as the holder with carbon-containing material 21 was mounted in the position inside the duct 20. When the holder with carbon-containing material 21 was moved from the position inside the duct 20 into the center of the reaction chamber 9—dashed position in FIG. 7—the ratio between oxygen line at 777 nm and the most intensive line of C.sub.2 band dropped to 0.5 within a second, indicating bonding of oxygen to stable C.sub.xO.sub.y gaseous molecules. The method disclosed in Example 2, therefore enables synthesis of stable C.sub.xO.sub.y gaseous molecules, which are considered to be beneficial for growth of CNWs.

Example 3

(40) Example 3 discloses a configuration suitable for synthesis of CNWs from CO.sub.xO.sub.y gaseous molecules. The setup shown schematically in FIG. 5 was modified in order to allow for independent exposure of carbon-containing material and heated substrate to gaseous plasma. The reaction chamber 9 useful for Example 3 is shown for the relevant details schematically in FIG. 7. The reaction chamber 9 is equipped with several ducts. Duct 18 is used for pumping the reaction chamber 9. Duct 19 is used for leaking the oxygen-containing gas into the reaction chamber 9. Duct 20 is used for placing the holder with carbon-containing material 21 into the reaction chamber 9. Duct 22 is used for placing the holder with substrate 23 into the reaction chamber 9. The holder with substrate 23 is movable so it is either placed inside the duct 22 or inside the reaction chamber (dashed position in FIG. 7). The holder with substrate 23 may be externally heated using any method including but not limited to resistive heating, inductive heating or irradiation with photons, electrons or ions.

(41) The holder with substrate 23 was mounted in the position of the duct 22. The C.sub.xO.sub.y gaseous molecules were synthesized according to the procedure disclosed in Example 2. When the C.sub.xO.sub.y gaseous molecules were created in the reaction chamber, the discharge was turned off, and the holder with carbon-containing material 21 was moved to the position inside the duct 20. Such configuration with the discharge turned off was kept for several minutes. Then, the holder with the substrate 23 was moved to the dashed position inside the reaction chamber 9, as shown in FIG. 7, and the discharge was turned on. As soon as the discharge was turned on and the holder with the substrate 23, at the dashed position in FIG. 7, heated to the elevated temperature of 500° C., CNWs started growing on the holder with the substrate 23 at the growth rate of almost 100 nm per second, similar as in Example 1.

(42) The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the aspects of the disclosed embodiments in diverse forms thereof.

(43) While the present disclosure has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the present disclosure set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the present disclosure.

(44) For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

(45) Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

(46) Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

(47) It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example ±10%.

REFERENCES

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