Patent Application
20180179629
The present invention is generally related to apparatus and methods for high volume production of films on large-sized thin metal foils, and, in particular, to high volume production of graphene and carbon nanotubes (CNTS) on large-sized thin foils using chemical vapor deposition (CVD) or atomic layer deposition (ALD).
In conventional chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes, shown in
For samples that are stiff enough to be suspended, such as the wafers used in the semiconductor industry, it is common to use fixtures with rails 207, as shown in
In applications where the substrate is thin or stiffness low (e.g., a metal foil), and where there is a need to have thin film deposited on both sides of the foil, the most common approach is to use a rolled substrate.
For applications where the substrate is thin and not stiff and where there is a need to have a thin film deposited on both sides of a foil, an alternate approach is to roll up a foil substrate 405 and insert it into the CVD chamber 401 in the form of a tube oven, as schematically shown in
Embodiments of the invention allow nanomaterials to be grown in a gas deposition process on one or more foils using one or more gas permeable separators. The gas deposition process may be CVD, but it may instead be ALD. Each separate gas permeable separator may be placed in physical contact with one or at most two of the one or more foils. The one or more foils may be stacked with one or more of the gas permeable separators. For clarification, stacked means that a first gas permeable separator is physically set or placed on top of a first foil, and a second foil is physically set or placed on top of the first separator, followed by a second separator that is placed on top of the second foil, and so on, until the desired number of foils and separators are prepared. The nanomaterial may be graphene, carbon nanotubes, graphite, graphene flakes, graphene oxide, reduced graphene oxide, graphene nanoribbons, and others. The one or more foils may already have a nanomaterial grown thereon before growth of another nanomaterial thereon. The one or more gas permeable separators may each be a quartz fiber filter, have a thickness preferably of 0.38 mm to 1.0 mm, and may be flexible. The gas permeable separators preferably may have pores with a pore size of 0.1 microns to 10.0 microns.
Embodiments of the invention may instead include a foil rolled with a gas permeable separator in physical contact with the foil. Such embodiments may have a rolled foil pitch of 0.38 mm or less, such as 0.1 mm. In addition, a stack of multiple foils and separators may also be rolled together, in accordance with other embodiments of the invention. The foil(s) and gas permeable separator(s) may be rolled such that the gas permeable separator(s) is (are) compressed. The compression ratio depends on the porosity of the separator, where a higher porosity separator, having more voids, may be compressed more than a separator with lower porosity, having fewer voids.
Other embodiments of the invention may instead include a metal foam rolled upon itself such that adjacent rolled portions are physically touching, and the foam acts as both the substrate on which a nanomaterial is formed and the gas permeable separator, and where a nanomaterial may be formed anywhere on the surfaces of the foam exposed to the process gases.
This application claims the benefit of U.S. Provisional Application No. 62/184,806, filed Jun. 25, 2015, which is incorporated by reference herein in its entirety.
Apparatus and methods for deposition of a thin film on the surface(s) of large-sized metal foil(s) (also referred to as sheets) using gas deposition, such as CVD or ALD processes are described herein, in accordance with embodiments of the invention. The thin film gas deposition process is for growth of nanomaterials, nonlimiting examples of which include graphene, carbon nanotubes, hybrid nanomaterial comprising carbon nanotubes grown directly on graphene or other carbon-based nanomaterials. The apparatus for thin film deposition may include a stack of multiple sheets which are separated by gas permeable material(s), a CVD or ALD chamber in which the CVD or ALD deposition takes place, and a control system to control the process parameters, such as gas flow and temperature.
A quartz fiber filter having a thickness from 0.38 mm to 1.00 mm is an exemplary flexible gas permeable separator. Such a separator has been used for high temperature sampling of acidic gases and for air pollution analysis, and typically have a maximum operating temperature of 1000 C. Thinner quartz fiber filters are also contemplated. The typical pore size in a quartz filter is 2 μm, but pore sizes ranging from 0.1 μm to 10 μm are also contemplated. The typical diameter of a quartz fiber from a quartz filter is in the range of 0.1 to 10 μm.
A metal foam material may also be used as an exemplary gas permeable separator. Typically, Cu or Ni foam has a thickness of 1.6 mm and pores sizes in the range of 20 to 60 μm. Other exemplary metal foams include stainless steel and aluminum. A metal foam separator preferably is not used when the material of the foam is catalytic to the formation of the nanomaterial meant to be fabricated in the CVD process.
Exemplary rigid or stiff gas permeable materials include porous alumina, porous zirconia, and porous titania filters that are also used for gas or liquid filtration. Other exemplary rigid permeable separators include quartz filter disks, otherwise known as quartz sintered disks or quartz fritted disks or quartz frits. Sintered or fritted disks typically are made from fusing quartz granules together, and have an average pore size ranging from 10 to 500 μm, depending on the porosity grade of the filter.
Exemplary foil or sheet samples may be any materials suitable for CVD or ALD processes, including but not limited to, Cu and Ni foils having thicknesses ranging from 0.1 μm to 100 μm. More preferably, thin metal foils having a thickness range from 9 μm to 35 μm are suitable for these processes. Extremely thin metal foil samples that cannot easily be suspended on rails and stacked in multiple layers may be used in accordance with embodiments of the invention. For example, a 9 μm thick Cu foil tends to soften and lose stiffness when exposed to high temperatures close to 1000 C, and therefore cannot easily be suspended on rails. Yet, such a metal foil may be used in embodiments of the invention.
There is no fundamental or little limitation on the size or dimensions of the foil that the gas permeable material may support. For example, a 100 mm wide Cu foil with length of 1 to 2 m may easily be supported by a gas permeable separator with the same or similar size for stacking in multiple layers with such foils, in accordance with an embodiment of the invention. It is mainly the size of the CVD chamber that may limit the dimensions of the foil. This is true even though rail suspension generally is particularly difficult for foil samples having a width or length 10 mm or larger. And it is true even though rail-supported suspension is not generally mechanically stable, as vibration may cause adjacent foil layers to contact each other or change the gap(s) between them.
It should be noted that the foil itself may already have nanomaterial(s) deposited on it before further nanomaterial(s) is (are) deposited on it thereafter, in accordance with other embodiments of the invention. For example, a Ni foil already having graphene grown on it that is covered with a CNT catalyst material may be used to grow nanomaterial(s), such as CNTs, on the graphene.
Besides Cu and Ni foil, other materials may be used for growth of nanomaterials thereon. For example, as mentioned above, a foam, such as Cu foam or Ni foam, may be used in accordance with embodiments of the invention. Typically, Ni and Cu foams are 0.08 mm to 1.6 mm thick. The foam material may be used with additional gas permeable separator(s), such as quartz filter(s). Or the foam may be used without any gas permeable separator(s) because the foam material is itself gas permeable, having the porosity to enable gas flow and heat transfer, and function as a substrate for the growth of the nanomaterial. In this case, the samples of foam are just physically stacked on top of each other, and graphene or CNT growth may take place on the surfaces of each sample of the foam. The surface of a foam is understood to be the total surface area of the foam material that can be exposed to the process gases in the process chamber. It should be noted that the foam itself, just as for the foil, may already have nanomaterial(s) deposited on it before further nanomaterial(s) is (are) deposited on it thereafter, in accordance with other embodiments of the invention. For example, a Ni foam already having graphene grown on it that is covered with a CNT catalyst material may be used to grow nanomaterial(s), such as CNTs, on the graphene.
Other carbon-based materials that may be used as a foil on which CNTs may be grown include, but are not limited to, graphite, graphene flakes, graphene oxide, reduced graphene oxide, and graphene nanoribbons. The material of the foil may also be in the form of a thin filter morphology.
The gas permeable separator also does not need to be a single discrete continuous piece of material as long as the discrete pieces can support the foil and provide mechanical stability, in accordance with other embodiments of the invention. Moreover, the gas permeable separator or multiple separators may only be a fraction of size of the two major dimensions, i.e. length and width, of the foil supported. Exemplary embodiments include a separator that is 1/10th or 1/100th the length or width of the foil it supports. One exemplary embodiment includes three gas permeable separators per each foil stably holding each foil, although each such separator is much smaller in length or in width compared to each foil. Other exemplary embodiments include a different number of separators per each foil than three stably holding each foil. The shape of each of the multiple separators may be long rectangles positioned parallel to the axis of a tube CVD chamber or positioned perpendicular to the axis of a tube CVD chamber, or placed in any optimized position for separating the thin foils using a minimum number and position of separators, as would be understood by a person of ordinary skill in the art. The major determinant is to have the multiple separators spaced close enough to prevent the foil from touching a neighboring foil in the stack. The spacing of the discrete separators will depend on the thickness of the foil; thinner foil will require closer discrete separator spacing. For example, a 10 cm long and 9 μm thick foil may be separated by using two discrete separators that are 0.5 cm long, 1.0 cm wide, matching the width of the foil, and are spaced 5 cm apart.
Referring again to
A CVD system, such as described with respect to
For the purpose of growing a hybrid graphene (G)-carbon nanotube (CNT) material, which is described in published PCT patent application (WO 2013/119295 A1), incorporated herein by reference in its entirety, the graphene-coated Cu or Ni foils are coated with a thin layer of a catalyst incorporating iron and alumina or aluminum to help aid the fabrication of CNTs. The catalyst layer may instead be cobalt or nickel. In this process of fabricating the hybrid G-CNT material, the CNTs will only grow on the areas where the catalyst is deposited. If the catalyst is deposited only on the top side of the graphene, the CVD process will produce growth of CNTs on the top side of the graphene. Depending on the CVD growth process, the grown CNTs may be single-walled CNTs, double-walled CNTs, multi-walled CNTs, or their combinations. Also, depending on the CVD growth process, the grown CNTs may be vertically aligned CNTs, bundles of CNTs grown together, or randomly aligned CNTs. The CNTs may be from a few microns to a few hundreds of microns in length, and their length may be controlled by the duration of the CVD process.
When a fiber filter separator is used in a CVD process traces of the separator fiber may be found mixed with the nanomaterial as a pollutant. Typically, traces of tens of quartz fibers per cm2 of nanomaterial may be found after a quartz separator is removed. For many applications, such as the use of a CNT film as an anode in a lithium ion battery, the traces of quarts fiber are inert to the battery electrolyte and will not alter the performance of the battery. For other applications, such as the use of a graphene film as an anode in a lithium-ion battery or an electrode for a display apparatus, the traces of quartz fiber may be wiped off with the help of compressed dry nitrogen gas or by rinsing the foil with graphene in a liquid cleansing solution.
One advantage of using a gas permeable separator(s) is that it (they) increases (increase) the density of the CNT film in units of mg/cm2 as compared to the density of a CNT film grown without the use of a gas permeable separator(s). The separator may slow down the flow of process gases near the CNT catalyst, such that slower gas flow may enable more catalytic particles to nucleate, resulting in the growth of a denser CNT film. In one example, the CNT density on a sample grown without the use of a gas permeable separator was less than 1 mg/cm2 as opposed to a density between 1-2 mg/cm2 for a CNT film grown with a gas permeable separator. By using gas permeable separators, CNT films with densities of 4 mg/cm2 or larger are possible.
The coating of the CNT catalyst on the graphene may be unpatterned or patterned. In unpatterned catalyst deposition, large continuous surfaces or the entire side of a sample are coated with the catalyst using one of the common deposition methods, which include thermal evaporation, e-beam or ion-beam evaporation, sputtering, CVD deposition, ALD deposition, wet chemical deposition, or wet electrochemical deposition. During a CVD process the CNTs will grow where the catalyst is available. In patterned deposition, the graphene is lithographically patterned on the entire side of the sample or on a section of the sample using standard lithography processes well known in the semiconductor industry arts. In patterned deposition, during a CVD process, the CNT film will grow only where the catalyst is available on the patterned graphene regions.
The graphene does not have to be grown by a CVD process, but instead may be deposited by submersion of graphene flakes in a solution that promotes the deposition of the graphene flakes on the Cu or Ni foils. The graphene may be a graphene oxide that is converted to graphene before or after the deposition on the foil. The graphene layers grown by CVD may be a single layer or a few layers of graphene, or they may be multilayers of graphene. In accordance with other embodiments, the graphene may also be substituted by graphite.
The CNT catalyst, nonlimiting examples of which include iron, cobalt, nickel and their alloys, aluminum and alumina, may be deposited on the foil(s) in the form of a thin film(s). Processes, such as thermal evaporation, e-beam evaporation, sputtering, and CVD deposition of organometallic precursors, may be used to produce the catalyst films, in accordance with embodiments of the invention. Other ways of depositing the CNT catalyst film(s) on the foil(s) include wet catalyst deposition, such as electrochemical deposition, drop casting, spin coating, doctor blade coating, dip coating, Langmuir-Blodgett coating, and spray coating, in accordance with other embodiments of the invention.
Other nanomaterials or structures, such as nanowires, may be grown or fabricated using the teachings described herein, in accordance with embodiments of the invention. Nonlimiting examples of such nanowires include silicon, germanium, ZnO, and TiO2 nanowires.
The gas permeable separators described herein may be used for CVD growth of CNTs directly, without graphene or graphite, on substrates other than Cu and Ni foils, in accordance with embodiments of the invention. For example, the substrate may be a stainless steel foil coated with a CNT catalyst that enables CNTs to be grown on the surface of the stainless steel foil. Or the CNTs may be grown instead on stainless steel mesh, silicon, and silicon oxide wafers, to name a few common substrates on which CNTs are known to grow after the substrate is coated with a CNT catalyst.
After a single use in helping to grow nanomaterials, the quartz-based gas permeable separators will be slightly coated with carbon-based contamination, as is typical for any quartz-based tube or fixture used in a CVD or ALD process. Nevertheless, the gas permeable separators may be used multiple times without affecting the growth of the graphene or CNTs. This is because the quartz-based gas permeable separators may be cleaned easily by heating a stack of empty separators (i.e., with no foils in the stack) for 30 minutes in air at high temperature, such as 600 C to 900 C. Alternatively, the quartz-based gas permeable separators may be cleaned by soaking them in acid, such as HCl, for 1 hour or more, rinsing them with deionized (DI) water, and drying them in air at a lower temperature, such as 100 C to 200 C.
The gas permeable separator 1106 also would need to be flexible enough to be able to roll it. If the separator is not flexible or is rigid, only strips or pieces of the separator may be used to roll the thin foil, in accordance with embodiments of the invention. Without using a gas permeable separator(s) it would be very difficult to roll a thin metal foil into a spiral that has a small gap where the foil would not contact itself or has a uniform or constant gap over the diameter of the roll. In addition, a thin metal foil without separator support may not have enough mechanical stability to keep the gap between the rolled foil uniform or constant.
Considering the 0.38 mm thick gas permeable separator 1106 and 0.02 mm thick foil 1105 rolled assembly 1107 described above, for a tube furnace with 6 inches inner radius 1108, core 1104 with radius 1109 of 1 inch, determined by the minimum bend radius, and tube length that can fit 1 m long foil, the total width of the foil that can fit in the CVD or ALD system is 180 m, or 180 m2 for 1 m long foil. The minimum bend radius is determined by the smallest bending of the foil and separator that does not alter the structure of the separator and does not produce stress in the foil that will cause a wrinkling of the nanomaterial after the roll is unwound, as would be understood by a person of ordinary skill in the art. The processing of such a large-sized foil width per single batch of a CVD or ALD process will result in a high volume manufacturing capability, producing, for example, the 180 m2 of graphene on a foil in 3-5 minutes, and therefore will lower manufacturing costs for growing the nanomaterials per unit area. Prior art systems may not achieve such a large production capacity and avoid higher manufacturing costs.
Although some of the discussion above relates to compression of the separators, the CNT films may also be compressed in a post growth process. Specifically, a stack of multiple foils and separators may be removed from the CVD or ALD chamber and the CNT film of each of the multiple-stacked foils may be simultaneously compressed to increase the volumetric density of the CNT film grown on each foil and in the stack as a group, in accordance with embodiments of the invention. In one exemplary embodiment shown in
Compression of the nanomaterial 1709 may be performed directly, after the stack 1712 of foils 1705 and separators 1706 is removed from the CVD or ALD chamber, with the help of rigid and smooth (e.g., stainless steel or Teflon) plates 1707 and 1708 being moved toward each other under the urging of a press or clamping mechanism (not shown in
Additional processes may be performed on a compressed stack, such as high temperature water vapor-based or oxygen-based purification of the CNTs in the stack for the purpose of removing any defects on the CNTs and/or removing amorphous carbon from the CNT film. Additional CVD coating or similar processes may also be performed on the stack after it is compressed. In addition, the stack of compressed CNTs on the foils may also be submerged into liquids for additional processing, such as drop-cast deposition or electrodeposition of reduced metal oxides for Li-ion battery electrodes, or pre-lithiation of an anode for Li-ion battery electrodes.
Embodiments of the invention have applications, including but not limited to, high volume production using CVD tools in the semiconductor industry, and high volume production of nanomaterials, such as graphene and carbon nanotubes for batteries, such as Li-ion batteries, and for supercapacitors, structural materials, displays and touch screens, biological scaffolds, and sensors.
The specific embodiments described above are merely exemplary, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular embodiments or forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.
This application is a National Stage of International Application No. PCT/US2016/039217, filed Jun. 24, 2016, which claims the benefit of U.S. Provisional Application No. 62/184,806, filed Jun. 25, 2015.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2016/039217 | 6/24/2016 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62184806 | Jun 2015 | US |
