Substrate that is electrically conductive on at least one of the faces of same provided with a stack of thin layers for growing carbon nanotubes (CNTs)

Abstract

The invention concerns a substrate that is electrical conductive on at least one of the faces of same, provided with a stack of thin layers comprising at least one layer of catalyst material suitable for accelerating the growth of carbon nanotubes, characterized in that the stack comprises the sequence of thin layers deposited in the following order on top of said at least one electrically conductive face of the substrate: a) optionally, a metal made from metal M or a layer of a metal alloy made from metal M or a graphene layer; b) a titanium layer (Ti); c) an aluminum layer (Al); d) a layer of catalyst material(s) for the growth of carbon nanotubes. The invention also concerns a functional substrate (6) comprising a substrate coated with a carbon nanotube (NTC) mat, a production method and the uses of such a functional substrate.

Claims

1. A substrate which is electrically conducting on at least one of its faces, provided with a stack of thin layers comprising at least one layer of catalyst material appropriate for accelerating the growth of carbon nanotubes, wherein the stack comprises the sequence of thin layers deposited in the following order above said at least one electrically conducting face of the substrate: a/ metal layer made of metal M or layer made of metal alloy based on the metal M or layer made of graphene; b/ titanium (Ti) layer; c/ aluminum (Al) layer; d/ layer of material(s) which are catalysts of the growth of carbon nanotubes.

2. The substrate as claimed in claim 1, being a bulk metal substrate.

3. The bulk metal substrate as claimed in claim 2, the metal of the substrate being chosen from copper (Cu), aluminum (Al), stainless steel, nickel (Ni) or platinum (Pt).

4. The substrate as claimed in claim 1, being a substrate coated with one or more thin electrically conducting layers forming said electrically conducting face.

5. The substrate as claimed in claim 4, the thin electrically conducting layers) being chosen from titanium nitride (TiN), tantalum nitride (TaN) or graphene.

6. The substrate as claimed in claim 4, being an electrically insulating substrate, such as a substrate made of silicon (Si) or made of silicon dioxide (SiO.sub.2).

7. The substrate as claimed in claim 1, the metal M of the metal layer deposited directly on the electrically conducting face of the substrate being chosen from iron (Fe), chromium (Cr), nickel (Ni), cobalt (Co) or palladium (Pd), and also from all the binary, ternary or quaternary alloys between these metals.

8. The substrate as claimed in claim 1, the material(s) which is(are) catalyst(s) of the growth of the carbon nanotubes (CNTs) of the layer of the top of the stack being chosen from iron (Fe), chromium (Cr), nickel (Ni), cobalt (Co) or palladium (Pd), and also from all the binary, ternary or quaternary alloys between these metals.

9. The substrate as claimed in claim 1, the layer deposited directly on the electrically conducting face of the substrate and the layer of material which is a catalyst of the growth of carbon nanotubes being composed of the same material.

10. The substrate as claimed in claim 1, the thickness of the layer deposited directly on the electrically conducting face of the substrate being between 1 and 20 nm.

11. The substrate as claimed in claim 1, the thickness of the Ti layer being between 2 and 10 nm.

12. The substrate as claimed in claim 1, the thickness of the Al layer being between 2 and 10 nm.

13. The substrate as claimed in claim 1, the thickness of the layer of materials which are catalysts of the growth of carbon nanotubes being between 0.2 and 5 nm.

14. The substrate as claimed in claim 1, the stack being as follows: bulk substrate made of copper or of aluminum/Fe/Ti/Al/Fe, the iron (Fe) layer directly in contact with the bulk substrate having a thickness of between 1 and 10 am.

15. The substrate as claimed in claim 1, the stack being as follows: bulk substrate made of stainless steel/Ti/Al/Fe.

16. The substrate as claimed in claim 1, the stack being as follows: substrate made of titanium nitride (TiN) or tantalum nitride (TaN) in the form of thin layers/Fe/Ti/Al/Fe, the iron (Fe) layer directly in contact with the substrate having a thickness of between 10 and 20 nm.

17. The substrate as claimed in claim 1, the stack being as follows: bulk substrate covered with one or more layers made of graphene/Fe/Ti/Al/Fe, the iron (Fe) layer directly in contact with the graphene having a thickness of between 1 and 10 nm.

18. A functional substrate comprising a substrate as claimed in claim 1 coated with a mat of carbon nanotubes (CNTs).

19. The functional substrate as claimed in claim 18, the CNTs density being greater than 10.sup.12/cm.sup.2, indeed even 10.sup.13/cm.sup.2.

20. A process for the preparation of a functional substrate as claimed in claim 18, according to which the following stages are carried out: preparation, by vacuum evaporation, of the stack of thin layers with the metal layer made of metal M or layer made of metal alloy based on the metal M or layer made of graphene (2), on the electrically conducting face of the substrate as claimed in claim 1; growth of mat of carbon nanotubes (CNTs) on the stack according to a chemical vapor deposition (CVD) technique, enhanced or not enhanced by plasma and activated or nonactivated by hot wires (Hot Wire CVD or HWCVD).

21. The process as claimed in claim 20, according to which, before carrying out the growth stage, the layer of catalyst materials is oxidized by means of an air plasma.

22. A substrate which is electrically conducting on at least one of its faces, provided with a stack of thin layers comprising at least one layer of catalyst material appropriate for accelerating the growth of carbon nanotubes, wherein the stack comprises the sequence of thin layers deposited in the following order above said at least one electrically conducting face of the substrate: b/ titanium (Ti) layer; c/ aluminum (Al) layer; d/ layer of materials which are catalysts of the growth of carbon nanotubes.

Description

DETAILED DESCRIPTION

(1) Other advantages and characteristics of the invention will emerge more clearly on reading the detailed description of implementational examples of the invention given by way of illustration and without limitation with reference to the following figures, among which:

(2) FIG. 1 is a diagrammatic view in transverse cross section of a substrate coated with a stack of thin layers according to the invention,

(3) FIG. 2 is an image taken with a scanning electron microscope (SEM) of a dense mat of CNTs on a substrate made of aluminum obtained by a CVD technique in accordance with the invention,

(4) FIG. 3A is an image taken by SEM of a dense mat of CNTs on a substrate made of aluminum obtained by a hot wire CVD (HWCVD) technique in accordance with the invention,

(5) FIG. 3B is an image taken by transmission electron microscopy (TEM) of a CNT on a substrate made of aluminum obtained by a hot wire CVD (HWCVD) technique in accordance with the invention,

(6) FIG. 4 is a diagrammatic view in transverse cross section of a substrate made of stainless steel coated with a stack of thin layers according to the invention,

(7) FIGS. 5A and 5B are images taken, respectively at 45 and in cross section, by SEM of a dense mat of CNTs on a substrate made of nickel supporting a stack of graphene layers, in accordance with the invention,

(8) FIGS. 6A to 6C are images taken at 45 by SEM of a dense mat of CNTs on a substrate made of SiO.sub.2 respectively supporting one, two and three graphene layers, in accordance with the invention,

(9) FIG. 6D is an image taken by TEM of a CNT on a substrate made of SiO.sub.2 supporting at least one graphene layer, in accordance with the invention.

(10) It is specified here that, for the sake, the different proportions between the thicknesses of materials have not been observed.

(11) It is specified that the unit of flow indicated below under the acronym sccm for standard cubic centimeters per minute corresponds to the unit of a flow rate of one cubic centimeter per minute under the conditions of temperature at 0 C. and of pressure at 101.325 kPa.

(12) It is specified that examples 1 to 6 are carried out in accordance with the invention and that the examples carried out according to the state of the art and given as comparative examples are not referenced but are each explained at the end of the description of an example in accordance with the invention.

(13) In all these examples, the successive depositions of the thin layers 3, 4, 5 and optionally 2 on the substrate 1 were carried out according to a vacuum evaporation technique in one and the same vacuum cycle. Very obviously, in the context of the invention, they may be carried out by any other technique which makes possible good control over the thicknesses of layers obtained.

Example 1

(14) This example 1 relates to the growth of dense mats of CNTs on an aluminum (Al) substrate 1. In this example 1, the substrate may be produced in the form of thin layer(s) or be composed of a bulk material made of Al. As aluminum passivates very rapidly in air, the thin layer 2 is composed of a fine layer of a metal M which may diffuse into the aluminum oxide, advantageously iron.

(15) The stages of the process for producing a dense mat of CNTs are as follows:

(16) Stage 1/: The substrate 1 made of Al is deoxidized in a bath of HF diluted to 0.1% for a period of time of 30 s.

(17) Stage 2/: The successive depositions of the thin layers 2, 3, 4 and 5 on the substrate 1 made of Al are subsequently carried out. Thus, after deposition of the stack, as shown in FIG. 1, the substrate 1 is respectively surmounted by a layer 2 made of iron, by a titanium layer 3, then by a layer 4 of aluminum and finally by a layer 5 made of iron as catalyst.

(18) The stack is thus of the type substrate made of Al/Fe/Ti/Al/Fe.

(19) The thickness in nanometers (nm) of each of the thin layers of the stack on the substrate 1 made of Al is shown in table 1 below.

(20) TABLE-US-00001 TABLE 1 THIN LAYER THICKNESS Fe (2) 1-10 nm, preferably equal to 2 nm Ti (3) 5 nm Al (4) less than 5 nm, preferably equal to 2 nm Fe (5) 1 nm

(21) Stage 3/: The growth of a mat of CNTs is carried out by a chemical vapor deposition (CVD) technique at 600 C. using a C.sub.2H.sub.2/H.sub.2/He gas mixture introduced into the CVD reactor in the following respective flow rates: 15 sccm/50 sccm/110 sccm.

(22) The other conditions of the CVD deposition are as follows: pressure of the gas mixture at 0.3 Torr; time for rise between ambient temperature and 600 C.: 15 minutes; duration of growth from 10 minutes to 1 hour, according to the desired height of CNT mat.

(23) It is specified here that this growth was carried out, after having oxidized the catalyst layer 5 beforehand, by means of a capacitive RF air plasma with a power of 70 W at a pressure of 0.3 Torr and for a period of time of 30 min.

(24) According to an advantageous application of this example 1, the growth of the CNTs can be carried out in vias with a diameter of 250 nm which are intended to emerge on lines of Al in order to produce interconnections in microelectronics: FIG. 2 clearly illustrates this growth of the CNTs between the vias.

(25) Example 1 according to the invention, which has just been described, makes it possible to obtain mats of CNTs with densities exceeding 10.sup.12/cm.sup.2.

(26) In addition, the electrical conduction between a mat 6 of CNTs and the Al substrate 1 obtained according to this example 1 is greatly increased with respect to the state of the art. In particular, the specific contact resistance obtained between the Al substrate 1 and a mat 6 of CNTs according to the invention is less than 310.sup.8 cm.sup.2.

(27) Thus, as comparative example, the electrical conduction obtained according to example 1 of the invention is increased by a factor at least equal to 3 with respect to a substrate made of Al either directly surmounted solely by a 1 nm layer of Fe or surmounted by a 10 nm layer made of Al, itself surmounted by a layer of 1 nm of Fe (stack: substrate made of Al/Al/Fe).

Example 2

(28) Stages 1/ and 2/ of example 1 are reproduced exactly. Only stage 3/ of growth of the CNTs is modified in the following way: no preliminary oxidation of the catalyst layer 5 (1 nm of Fe); hot filament CVD (HFCVD).

(29) It is specified that the gas mixture is identical to that of example 1 with the same flow rates, that the temperature of the HFCVD is approximately 450 C. and that the power of hot filaments applied is of the order of 450 W.

(30) Example 2 according to the invention, which has just been described, makes it possible to obtain mats of CNTs in the MWNT form, having a mean unit diameter of 6 nm, with on average six walls per CNT. The density of CNT walls obtained is greater than 10.sup.13/cm.sup.2.

(31) FIG. 3A shows a mat 6 of CNTs 60 in the MWNT form obtained according to example 2 of the invention, while FIG. 3B shows in detail the structure of a CNT also obtained according to example 2.

(32) In addition, electrical conduction between a mat 6 of CNTs and the Al substrate 1 obtained according to example 2 is greatly increased with respect to the state of the art.

(33) Thus, as comparative example, the electrical conduction obtained according to example 2 of the invention is increased by a factor of 10 to 100 with respect to a substrate made of Al directly surmounted solely by a layer of 1 nm of Fe and which the growth of CNTs was also activated by hot filaments (HFCVD).

Example 3

(34) This example 3 relates to the growth of dense mats of CNTs on a copper (cu) substrate 1. In this example 3, the substrate may be produced in the form of thin layer(s) or be composed of a bulk material made of Cu. As the titanium has the ability to readily diffuse into the copper, the thin layer 2 is composed of a fine layer of a metal M, advantageously iron, which makes it possible to prevent this diffusion phenomenon.

(35) The steps of the process for producing a dense mat of CNTs are as follows:

(36) Stage 1/: The successive depositions of the thin layers 2, 3, 4 and 5 on the substrate 1 made of Cu are subsequently carried out. Thus, after the deposition of the stack, as shown in FIG. 1, the substrate 1 is surmounted respectively by a layer 2 made of iron, by a titanium layer 3, then by a layer 4 made of aluminum and finally by a layer 5 made of iron as catalyst.

(37) The stack is thus of the type substrate made of Cu/Fe/Ti/Al/Fe.

(38) The thickness in nanometers (nm) of each of the thin layers of the stack on the substrate 1 made of Cu is shown in table 2 below.

(39) TABLE-US-00002 TABLE 2 THIN LAYER THICKNESS Fe (2) 1-10 nm, preferably equal to 2 nm Ti (3) 5 nm Al (4) less than 5 nm, preferably equal to 2 nm Fe (5) 1 nm

(40) The stack of layers 2 to 5 and the corresponding thicknesses are thus identical to those of examples 1 and 2.

(41) Stage 2/: The growth of a mat of CNTs is carried out according to the same technique with the same conditions as for example 1.

(42) Example 3 according to the invention, which has just been described, makes it possible to obtain mats of CNTs with growth on Cu according to a base growth mode.

(43) Thus, the mode of growth of the CNTs according to this example 3 of the invention is much better than that of tip growth type observed according to the state of the art on a substrate in Cu, in particular when use is made, as barrier layer, of a thin layer of titanium nitride (TiN) which results in growth in tip growth mode and thus in mats of CNTs having low densities.

(44) Alternatively, the Fe layer 2 directly deposited on the copper can be replaced with a Cr, Ni, Co or Pd layer of similar thickness or a graphene layer.

(45) This example 3 according to the invention may be applied in the same way to a substrate made of nickel (Ni) instead of a substrate made of copper.

Example 4

(46) This example 4 relates to the growth of dense mats of CNTs on a TiN substrate 1 in the form of thin layer(s). Due to the columnar structure of TiN in a thin layer, the majority of metals diffuse strongly into TiN. Thus, the thin layer 2 is in this instance composed of a fine layer of a metal M, advantageously iron, which is relatively thick, preferably a layer of 10 to 20 nm.

(47) The stages of the process for the preparation of a dense mat of CNTs are as follows:

(48) Stage 1/: The successive depositions of the thin layers 2, 3, 4 and 5 on the substrate 1 made of TiN are subsequently carried out. Thus, after deposition of the stack, as shown in FIG. 1, the substrate 1 is respectively surmounted by a layer 2 made of iron, by a titanium layer 3, then by a layer 4 made of aluminum and finally by a layer 5 made of iron as catalyst.

(49) The stack is thus of the type substrate made of TiN/Fe/Ti/Al/Fe.

(50) The thickness in nanometers (nm) of each of the thin layers of the stack on the substrate 1 made of TiN is shown in table 3 below.

(51) TABLE-US-00003 TABLE 3 THIN LAYER THICKNESS Fe (2) 10-20 nm, preferably equal to 20 nm Ti (3) 5 nm Al (4) less than 5 nm, preferably equal to 2 nm Fe (5) 1 nm

(52) Stage 2/: The growth of a mat of CNTs is carried out according to the same technique with the same conditions as for examples 1 and 3.

(53) Example 4 according to the invention, which has just been described, makes it possible to obtain mats of CNTs with growth on TiN according to a base growth mode.

(54) Alternatively, the Fe layer 2 deposited directly on TiN may be replaced with a Cr, Ni or Co layer of similar thickness.

(55) This example 4 according to the invention may be applied in the same way to a substrate made of tantalum nitride (TaN) instead of a substrate made of TiN.

Example 5

(56) This example 5 relates to the growth of dense mats of CNTs on a stainless steel substrate 1 in the form of a bulk material. Stainless steel is a material which does not form a native oxide and into which titanium does not diffuse to a great extent and does not form an alloy in the temperature range envisaged for the growth of CNTs by CVD. In this instance, it is possible to envisage dispensing with the thin layer 2.

(57) The stages of the process for the preparation of a dense mat of CNTs are as follows:

(58) Stage 1/: The successive depositions of the thin layers 3, 4 and 5 on the substrate 1 made of stainless steel are subsequently carried out. Thus, after deposition of the stack, as shown in FIG. 4, the substrate 1 is respectively surmounted with a titanium layer 3, then with a layer 4 made of aluminum and finally with a layer 5 made of iron as catalyst.

(59) The stack is thus of the type substrate made of stainless steel/Ti/Al/Fe.

(60) The thickness in nanometers (nm) of each of the thin layers of the stack on the substrate 1 made of stainless steel is shown in table 4 below.

(61) TABLE-US-00004 TABLE 4 THIN LAYER THICKNESS Ti (3) 5 nm Al (4) less than 5 nm, preferably equal to 2 nm Fe (5) 1 nm

(62) Stage 2/: The growth of a mat of CNTs is carried out according to the same technique with the same conditions as for examples 1, 3 and 4.

(63) Example 3 according to the invention, which has just been described, makes it possible to obtain mats of CNTs with growth on the stainless steel according to a base growth mode.

(64) In addition, the electrical conduction at the interface between a mat 6 of CNTs and the substrate 1 made of stainless steel obtained according to this example 5 is good.

Example 6

(65) This example 6 relates to the growth of dense mats of CNTs on a substrate 1, at least one face of which is made of graphene.

(66) The substrate 1 supporting the face made of graphene can be metallic, such as Cu, Ni or Pt. It may also be made of electrical insulating material, such as made of silicon (Si) or made of silicon dioxide (SiO.sub.2).

(67) The substrate 1 may support one or more layers of graphene constituting an electrically conducting face. Thus, a single layer of graphene or a stack of several layers of graphene, up to the graphene produced by exfoliation of highly oriented pyrolytic graphite (HOPG), may be concerned.

(68) The thin layer 2 is composed of a fine layer of a metal M, advantageously made of iron, which makes it possible to prevent the formation of alloy of titanium carbide type between the graphene and the titanium of layer 3.

(69) The stages of the process for preparation of a dense mat of CNTs are as follows:

(70) Stage 1/: The successive depositions of the thin layers 2, 3, 4 and 5 on the substrate supporting at least one graphene layer forming an electrically conducting face are subsequently carried out. Thus, after deposition of the stack, as shown in FIG. 1, the graphene 1 face is respectively surmounted by a layer 2 made of iron, by a titanium layer 3, then by a layer 4 made of aluminum, and finally, by a layer 5 made of iron as catalyst.

(71) The stack is thus of the type substrate with face made of graphene/Fe/Ti/Al/Fe.

(72) The stack of layers 2 to 5 and the corresponding thicknesses are identical to those of examples 1 to 3.

(73) Stage 2/: The growth of a mat of CNTs is carried out according to the same technique of hot filament CVD deposition with the same conditions of temperature and gas mixture with the respective flow rates as for example 2.

(74) The other conditions of the CVD deposition are as follows: pressure of the gas mixture is 0.3 Torr; time for rise between ambient temperature and 450 C.: 12 minutes; duration of growth from 10 to 30 minutes, depending on the desired height of CNT mat.

(75) Example 6 according to the invention with a substrate made of nickel supporting a stack of graphene layers makes it possible to obtain mats of CNTs with densities exceeding 10.sup.12/cm.sup.2.

(76) In addition, the electrical conduction between a mat 6 of CNTs and the substrate made of Ni supporting a stack of graphene layers which is obtained according to this example 6 is greatly increased with respect to the state of the art and is entirely comparable with that obtained between the mat 6 of CNTs and the substrate 1 made of Al of example 1 according to the invention.

(77) FIGS. 5A and 5B show a mat 6 of CNTs 60 in the MWNT form obtained according to example 6 of the invention with a substrate made of nickel supporting a stack of graphene layers.

(78) Example 6 according to the invention with a substrate made of SiO.sub.2 onto which one or more graphene layers is(are) transferred makes it possible to obtain mats of CNTs in the MWNT form having a mean unit diameter of 5 nm, with on average two or three walls per CNT. The density of CNT walls obtained is greater than 10.sup.12/cm.sup.2.

(79) FIGS. 6A to 6C show a mat 6 of CNTs 60 in the MWNT form obtained according to example 6 of the invention with a substrate made of SiO.sub.2 respectively supporting one graphene layer, two graphene layers or three graphene layers.

(80) FIG. 6D shows in detail a CNT obtained according to this example 6 with a substrate made of SiO.sub.2 supporting at least one graphene layer.

(81) The invention is not limited to the examples which have just been described; it is possible in particular to combine together characteristics of the examples illustrated within nonillustrated alternative forms.

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