Patent Application
20240246317
Not Applicable
Graphene is a single-layer sp2-hybridized 2D network of carbon atoms that conceptually serves as the basis of many important allotropes of carbon. It can be stacked to form 3D graphite, rolled to form 1D carbon nanotubes, and fused to form 0D fullerenes. Owing to its strongly delocalized electron configuration, graphene exhibits exceptional charge carrier mobility, thermal conductivity, mechanical strength, and chemical stability. However, like other nanomaterials, the properties of graphene depend on its size, atomic structure, and physical environment. Graphene and graphene-based materials have tailorable properties that can be exploited in a broad range of devices, including transistors, capacitors, electron field emitters, transparent conductors, sensors, catalysts, and drug delivery agents. Other 2D crystals, most notably boron nitride and molybdenum disulfide, have also been isolated.
Two-dimensional (2D) sp2-bonded carbon exists in the form of graphene, buckyballs and carbon nanotubes (CNTs). Graphene is “flat” or 2D, fullerenes (“Buckyballs”) are spherical or 0D, and CNTs are tubes in 1D. Forming these materials in a singular, regular, repeatable structure has not previously been achieved. Superstructures of these materials may provide very strong, light, highly thermally and electrically conductive structures. Attempts have been made to fabricate sp2-bonded sponges as shown in
The isolation of graphene via the mechanical exfoliation of graphite has sparked strong interest in two-dimensional (2D) layered materials. The properties of graphene include exceptional strength, and high electrical and thermal conductivity, while being lightweight, flexible and transparent. This opens the possibility of a wide range of potential applications, including high-speed transistors and sensors, barrier materials, solar cells, batteries, and composites.
Other classes of 2D materials of interest include transition metal dichalcogenide (TMDC) materials, hexagonal boron nitride (h-BN), as well as those based on Group 14 elements, such as silicene and germanene. The properties of these materials can range from semi-metallic, for example, NiTe2 and VSe2, to semiconducting, for example, WSe2 and MoS2, to insulating, for example, hexagonal boron nitride (h-BN).
Growth of regular 3D superstructures using sp2-bonded carbon may address the shortcomings of the flexible sp2 carbons for 3D applications given that hexagonally arranged carbon is strong, chemically inert, electrically and thermally conductive, and optically transparent. Such 3D superstructures may find used in many applications from packaging, thin optically transparent electrically conductive strong thin films, and many more.
When a carbon atom is attached to three groups (or, as in the case of graphene, three other carbon atoms) and so is involved in three σ bonds, it requires three orbitals in the hybrid set. This requires that it be sp2 hybridized.
An sp2-hybridized bond has 33% s and 67% p character. The three sp2 hybrid orbitals point towards the corners of a triangle at 120° to each other. Each sp2 hybrid is involved in a σ bond. The remaining p orbital forms the π bond. A carbon double bond may be viewed as a σ+π bond.
In one example, a microstructure comprises a plurality of interconnected units wherein the units are formed of graphene tubes. The graphene tubes that form the microstructure may be arranged in an ordered structure and form symmetric patterns that repeat along the principal directions of three-dimensional space. The microstructure may comprise a plurality of interconnected units including at least a first unit formed of first graphene tubes; and a second unit formed of second graphene tubes wherein one or more of the second graphene tubes are connected to one or more of the first graphene tubes.
A method of forming a graphene microstructure is disclosed herein which comprises: photo-initiating the polymerization of a monomer in a pattern of interconnected units to form a polymer microlattice; removing unpolymerized monomer; coating the polymer microlattice with a metal; removing the polymer microlattice to leave a metal microlattice; depositing graphitic carbon on the metal microlattice; converting the graphitic carbon to graphene; and removing the metal microlattice.
It has been found that an organic/inorganic superstructure may be used as a template for the formation of a 3D metal superstructure that may then be used to grow graphitic carbon on the surface of the metal. The template may be fabricated through a self-propagating photopolymer waveguide technique (see, e.g., Xiaoyu Zheng et. al., Ultralight, Ultrastiff Mechanical Metamaterials; Science 344 (2014) 1373-1377 and T. A. Schaedler, et al., Ultralight Metallic Microlattices; Science 334 (2011) 962-965) As illustrated schematically in
The present disclosure is of a “periodically structured” carbon nanostructure. The carbon nanostructures of the prior art are irregular and have much larger dimensions than those which may be achieved using the methodology disclosed herein.
The present process may be used to create a regular array, and the superstructure dimensions (unit) and structure may be optimized for strength, thermal and other fundamental properties.
There are several aspects of this procedure that are noteworthy:
The present process uses a polymeric structure as a template for such fabrication with the subsequent formation of a metal superstructure that may then be exposed to a hydrocarbon (e.g. methane, ethylene, acetylene, benzene) to form graphitic carbon, followed by etching of the metal from under the graphitic carbon using appropriate etchants such as, for example, FeCl3 or potassium permanganate.
Collimated UV light 12 through a photomask 14 or multi-photon lithography may be used in a photo-initiated polymerization to produce a polymer microlattice 18 comprised of a plurality of interconnected units. Exemplary polymers include polystyrene and poly(methyl methacrylate) (PMMA). Once polymerized in the desired pattern, the remaining un-polymerized monomer may be removed.
The polymer structure (polymer scaffold) may then be plated with a suitable metal using an electroless plating process.
Electroless nickel plating (EN) is an auto-catalytic chemical technique that may be used to deposit a layer of nickel-phosphorus or nickel-boron alloy on a solid workpiece, such as metal, plastic, or ceramic. The process relies on the presence of a reducing agent, for example hydrated sodium hypophosphite (NaPO2H2·H2O) which reacts with the metal ions to deposit metal. Alloys with different percentages of phosphorus, ranging from 2-5 (low phosphorus) to up to 11-14 (high phosphorus) are possible. The metallurgical properties of the alloys depend on the percentage of phosphorus.
Electroless plating has several advantages over electroplating. Free from flux-density and power supply issues, it provides an even deposit regardless of workpiece geometry, and with the proper pre-plate catalyst, may deposit on non-conductive surfaces. In contradistinction, electroplating can only be performed on electrically conductive substrates.
Before performing electroless plating, the material to be plated must be cleaned by a series of chemicals; this is known as the pre-treatment process. Failure to remove unwanted “soils” from the part's surface results in poor plating. Each pre-treatment chemical must be followed by water rinsing (normally two to three times) to remove chemicals that may adhere to the surface. De-greasing removes oils from surfaces, whereas acid cleaning removes scaling.
Activation may be done with an immersion into a sensitizer/activator solution—for example, a mixture of palladium chloride, tin chloride, and hydrochloric acid. In the case of non-metallic substrates, a proprietary solution is often used.
The pre-treatment required for the deposition of metals on a non-conductive surface usually consists of an initial surface preparation to render the substrate hydrophilic. Following this initial step, the surface may be activated by a solution of a noble metal, e.g., palladium chloride. Electroless bath formation varies with the activator. The substrate is then ready for electroless deposition.
The reaction is accomplished when hydrogen is released by a reducing agent, normally sodium hypophosphite (with the hydrogen leaving as a hydride ion) or thiourea, and oxidized, thus producing a negative charge on the surface of the part. The most common electroless plating method is electroless nickel plating, although silver, gold and copper layers can also be applied in this manner.
In principle, any hydrogen-based reducing agent can be used although the redox potential of the reducing half-cell must be high enough to overcome the energy barriers inherent in liquid chemistry. Electroless nickel plating most often employs hypophosphite as the reducer while plating of other metals like silver, gold and copper typically makes use of low-molecular-weight aldehydes.
A benefit of this approach is that the technique can be used to plate diverse shapes and types of surfaces.
As illustrated in
In an example, the growth of graphene on the metal tubes may be omitted to produce a mircolattice of interconnected metal tubes. A process for forming such a metal microstructure may comprise: photo-initiating the polymerization of a monomer in a pattern of interconnected units to form a polymer microlattice; removing unpolymerized monomer; coating the polymer microlattice with a metal; and removing the polymer microlattice to leave a microlattice of interconnected metal tubes in a pattern of interconnected units.
In another example, a metal/graphene microstructure of graphene-coated metal tubes in a pattern of interconnected units may be prepared by the process comprising the steps of: photo-initiating the polymerization of a monomer in a pattern of interconnected units to form a polymer microlattice; removing unpolymerized monomer; coating the polymer microlattice with a metal; removing the polymer microlattice to leave a metal microlattice; depositing graphitic carbon on the metal microlattice; and converting the graphitic carbon to graphene.
Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.
This application is a division of U.S. patent application Ser. No. 16/229,668, filed Dec. 21, 2018 which claims priority to U.S. Provisional Patent Application No. 62/611,347 filed on Dec. 28, 2017. This application is related to U.S. patent application Ser. No. 16/229,822, filed Dec. 21, 2018 which claims priority to U.S. Provisional Patent Application No. 62/611,483 filed on Dec. 28, 2017, and to U.S. patent application Ser. No. 16/230,070, filed Dec. 21, 2018 which claims priority to U.S. Provisional Patent Application No. 62/611,499 filed on Dec. 28, 2017, and to U.S. patent application Ser. No. 16/229,827, filed Dec. 21, 2018, and to U.S. patent application Ser. No. 16/229,971, filed Dec. 21, 2018 which claims priority to U.S. Provisional Patent Application No. 62/611,511 filed on Dec. 28, 2017, and to U.S. patent application Ser. No. 16/230,045 which claims priority to U.S. Provisional Patent Application No. 62/611,554 filed on Dec. 29, 2017, the contents of which are hereby incorporated by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| 62611347 | Dec 2017 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16229668 | Dec 2018 | US |
| Child | 18585500 | US |
