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  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
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  • C01P2004/13—Nanotubes

Definitions

• the present invention relates to the growth of nanotubes (NTs).
• the present invention is derived from a series of experiments designed and conducted using the principles of the previous patent application, TREKANG.
• the present invention represents a major simplification over the TREKANG concept in that there are no wavides. Wavides were conceived to deliver the energy that stimulates growth to the feedlayer in the vicinity of the catpar. The current experiments prove that wavides are not necessary.
• NT growth is accomplished by energizing feedatoms in a feedlayer to migrate to a growth site or catpar of the NT. Simply put, this is not a chemical vapor deposition (CVD) technology as the atmosphere of the chemical reactor is an ineratmo.
• CVD chemical vapor deposition
• CVD chemical vapor deposition
• the CVD process involves a carbon bearing gas as a constituent of the atmosphere in a reaction chamber. Some of these gas molecules react with a catpar in the chamber and if the temperature, partial gas pressure and many other parameters are correct, a carbon atom from a gas molecule transitions onto the surface of the catpar and a CNT will grow out of the catpar.
• This process is quite popular because the CVD process, in general, has proven to be extremely useful, over many decades, in many other endeavors including semiconductor microcircuit fabrication.
• this technology is used for CNT growth.
• the first drawback is that although initial growth of the CNTs is quite rapid, the growth quickly slows to a crawl and for all intents and purposes stops. Breakthroughs have been made that allow the growth to continue perceptibly, albeit slowly, but a second problem comes into play.
• the already formed CNTs are immersed in an environment of hot, carbon bearing gasses. Reactions continue on the surface of the CNTs that create
• substrates upon which CNTs are grown can be many different substances, the most common substrate is silicon, in part because of the decades of experience with it in the semiconductor industry. Silicon was thought to be impervious to catalyst elements, but in CNT fabrication it has been found that at least some catalyst materials can diffuse into the silicon layer. Thus the effective size of the catpar gets smaller and can become incapable of supporting CNT growth. Other substrates may be porous to catalyst materials as well.
• a method of fabricating a long carbon nanotube yarn includes the following steps: (1) providing a flat and smooth substrate; (2) depositing a catalyst on the substrate; (3) positioning the substrate with the catalyst in a furnace; (4) heating the furnace to a
• predetermined temperature (5) supplying a mixture of carbon containing gas and protecting gas into the furnace; (6) controlling a difference between the local temperature of the catalyst and the furnace temperature to be at least 50. degree. C; (7) controlling the partial pressure of the carbon containing gas to be less than 0.2; (8) growing a number of carbon nanotubes on the substrate such that a carbon nanotube array is formed on the substrate; and (9) drawing out a bundle of carbon nanotubes from the carbon nanotube array such that a carbon nanotube yarn is formed.
• U.S. Patent # 8,206,674 describes a growth technique for boron nitride nanotubes (BNNTs). From the abstract: Boron nitride nanotubes are prepared by a process which includes: (a) creating a source of boron vapor; (b) mixing the boron vapor with nitrogen gas so that a mixture of boron vapor and nitrogen gas is present at a nucleation site, which is a surface, the nitrogen gas being provided at a pressure elevated above atmospheric, e.g., from greater than about 2 atmospheres up to about 250 atmospheres; and (c) harvesting boron nitride nanotubes, which are formed at the nucleation site.
• a method of production of carbon nanoparticles comprises the steps of: providing on substrate particles a transition metal compound which is decomposable to yield the transition metal under conditions permitting carbon nanoparticle formation, contacting a gaseous carbon source with the substrate particles, before, during or after said contacting step, decomposing the transition metal compound to yield the transition metal on the substrate particles, forming carbon nanoparticles by decomposition of the carbon source catalyzed by the transition metal, and collecting the carbon nanoparticles formed.
• the technique described in the previous paragraph is the technique in which the catalyst is dispersed into the carbon-bearing gas flow of the reactor. It produces CNTs of up to approximately 0.5 mm in length. The CNTs appear as smoke and can be drawn off continuously. However, the technology has been unable to grow long, highq CNTs.
• U.S. Patent #8,926,934 describes a laser-assisted CVD CNT growth process.
• a method for growing an array of carbon nanotubes includes the steps of: (a) providing a substrate; (b) forming a catalyst film on the substrate, the catalyst film including carbonaceous material; (c) introducing a mixture of a carrier gas and a carbon source gas flowing across the catalyst film; (d) focusing a laser beam on the catalyst film to locally heat the catalyst to a predetermined reaction temperature; and (e) growing an array of the carbon nanotubes from the substrate.
• the present invention is a technology for growing NTs by liberating feedatoms so that the free atoms can migrate to a growth site or catpar of the NT. Simply put, this is a non-CVD process: there is no hot, carbon bearing gas.
• One embodiment, shown in figure 1, is to fabricate a substrate with a feedlayer of feedatoms on its front side and a layer of catalyst over the front side of the feedlayer. Emrad incident upon the bottom of the substrate propagates to the feedstock layer and liberates feedatoms that migrate to a growth site or catpar where an NT is growing. The free atoms are incorporated into the growing NT.
• the parameters of the emrad and substrate properties can be used to ensure that the feedatoms are liberated and migrate to a growth site or catpar with the appropriate energy to grow an NT.
• Figure 1 illustrates schematically the embodiment of the present invention in which the NTs grow directly out of the catalyst layer.
• Figure 2 illustrates schematically the embodiment of the best mode present invention in which the NTs grow directly out of catpars.
• Figure 3 illustrates schematically the embodiment of the present invention in which the NTs grow directly out of catpars and the feedlayer has been replaced with a feedvoir replenished by a retun.
• Figure 4 illustrates schematically the basic experimental setup for most of the experiments that have been carried out at the present time.
• Figure 5 illustrates schematically the broadtip assembly embodiment of the present invention.
• Figure 6 illustrates schematically a close view of a portion of the broadtip substrate assembly embodiment of the present invention.
• Figure 7 illustrates schematically the broadtip assembly mounted to the articulated arm and motion stage in operation according to the present invention.
• Figure 8 illustrates schematically an industrial application embodiment of the present invention wherein a laser delivers energy to substrate assemblies that continuously grow CNTs.
• Figure 9 illustrates schematically the tratip from the TREKANG patent application.
• BNNT - When used herein shall refer to a boron nitride nanotube.
• Broadtip system - When used herein shall refer to a NT growth system comprising a broadtip assembly mounted to an articulated arm which is itself mounted to a motion stage. This system grows NTs from the broadtip substrate assembly and deposits them onto an adjacent "target surface". The motion of the broadtip assembly across the adjacent target surface enables patterned three dimensional deposition of NTs. Broadtips are analogous to tratips but are larger with many catalyst particles. Because of their size emrad is used to deliver the energy to the feedlayer instead of plasmons. See figures 5, 6 and 7. [029] Broadtip assembly - When used herein shall refer to a subsystem comprising a broadtip substrate assembly mated to an emrad source and packaged to be mounted to an articulated arm for use in a broadtip system. See figures 5 and 7.
• Broadtip substrate assembly When used herein shall refer to a substrate assembly subsystem configured to be integrated into a broadtip assembly and used in a broadtip system. See figures 5 and 6.
• Catpar - When used herein shall refer to a volume of catalyst material, wherein the size, shape and elemental constituents are appropriate for growing a nanotube: a catalyst particle.
• the catalyst may contain one or more elemental constituents.
• CNT - When used herein shall refer to a carbon nanotube.
• Emrad - When used herein shall refer to electromagnetic radiation, however generated and of appropriate wavelength, to stimulate CNT growth within the technique being described.
• Feedatom - When used herein shall refer to an atom or molecule that is a chemical constituent of a nanotube: the atomic feedstock of a nanotube.
• Feedlayer - When used herein shall refer to a layer of nanotube feedstock atoms (feedatoms) that may comprise other constituents such as catalyst material.
• Feedvoir - When used herein shall refer to a reservoir of nanotube feedstock atoms (feedatoms) that may contain other constituents such as catalyst material.
• Growth site - When used herein shall refer to a position on a catalyst layer where a nanotube grows out of the surface. In the case of nanotube growth at a growth site, the catalyst layer has not been annealed so catpars have not formed.
• Highq - When used herein shall refer to nearly defect free: high quality.
• a highq NT is a nanotube that is nearly pristine, perfect and defect free. As such its tensile strength and electrical properties are maximal.
• Ineratmo - When used herein shall refer to the inert, gaseous atmosphere in a
• CNT growth chamber an inert atmosphere. If the sides of the substrate are isolated then it refers to the atmosphere on the nanotube growth side (front side) of the substrate.
• This "inert” atmosphere generally is made up of inert gasses. However, if partial pressures of other gasses, including ones introduced to react with NTs, catpars and/or free carbon, are introduced into the atmosphere during the growth process, the term interatmo still applies.
• Migrate - When used herein shall refer to the process or processes by which a feedatom travels from a feedlayer or feedvoir to a growth site or catpar after being energized. Migrate is a more general form of trek that encompasses trekking to a growth site as well as a catpar.
• NT - When used herein shall refer to a nanotube.
• Plasmon - When used herein shall refer to a quantum of plasma oscillation.
• electromagnetic energy can be transformed at a surface into plasmons capable of propagating the energy through a medium.
• Retun - When used herein shall refer to a replenishment tunnel or other structure in a substrate or wavide that facilitates the replenishment of feedatoms, catalyst material, and/or other materials for nanotube growth.
• Figure 3 illustrates a notional retun.
• Substrate assembly When used herein shall refer to a subsystem
• a substrate comprising a substrate, a feedlayer deposited onto the front side of the substrate and one of two catalyst configurations, either a catalyst layer or catpars, arranged on the front side of the feedlayer.
• Tratip - When used herein shall refer to a traveling micro or nanoscale platform or tip.
• a nanotube is grown from a catpar attached to the end of the tratip, a moveable platform.
• the platform or tip is a part of a cantilever or other support structure that facilitates the movement of the nanoscale nanotube growing system.
• the nanotube may be grown vertically, horizontally or at an angle to enable structured nanotube growths to be fabricated.
• a tratip is analogous to the sensing tip of an atomic force microscope which is attached to a cantilever.
• Figure 9 illustrates a tratip.
• the tratip could be stationary and the target surface or volume, upon which the nanotube growth is being deposited, could be mobile.
• Trek - When used herein shall refer to the process or processes by which a feedatom travels from a feedlayer or feedvoir to a catpar after being energized. Trekking is the verb form of trek.
• Wavide - When used herein shall refer to a waveguide through a substrate that transports energy in the form of emrad or plasmons.
• FIG. 2 illustrates the best mode contemplated by the inventor of Free Atom Nanotube Growth according to the present invention.
• the embodiment in figure 2 has an array of catpars arranged on the front side of the carbon feedlayer.
• the feedlayer has been located on the front side of quartz substrate.
• Emrad in the form of laser radiation is incident from the front side of the substrate assembly.
• the laser photons liberate some carbon feedatoms from the feedlayer and some of these free atoms migrate to the catpars.
• At the catpar some of the carbon atoms are incorporated into the growing CNT.
• the system shown in figure 1 grows CNTs.
• Emrad in the form of laser radiation, incident on the bottom of the substrate propagates through the substrate that is transparent to the emrad.
• the emrad propagates to the feedlayer. All or most of the emrad energy is absorbed in the feedlayer. This energy liberates some of the carbon feedatoms in the feedlayer to migrate (shown by the arrow) through the very thin iron catalyst layer to the growth site growing a CNT.
• the feedatoms are transported to the growth site with an optimal energy for becoming a part of the CNT growing from the catpar.
• the atmosphere in the chemical reactor where CNT growth is occurring is an ineratmo.
• the interatmo environment also decreases or eliminates amorphous carbon build up on the catpars. Additionally, the ineratmo decreases or eliminates damage to growing CNTs from unwanted chemical reaction on their surfaces because the hot carbon gas environment of CVD has been eliminated.
• Ostwald ripening a thermodynamic process that results in small catpars generally losing catalyst atoms to larger catpars. As Ostwald ripening occurs, more catpars stop growing CNTs because the either become too large or too small to sustain CNT growth. The low temperature synthesis possible with the present invention decreases the rate of Ostwald ripening.
• FIG. 3 illustrates the feedvoir embodiment of the current invention which comprises a feedvoir sitting between the catpar and substrate instead of a feedlayer.
• One of the feedvoirs in figure 3 illustrates a retun through the substrate for replenishing the feedatoms, catalyst material and/or other materials for NT growth.
• This reservoir would most probably be off the substrate on which the NTs are growing. In this way, continuous NT growth may be accomplished, especially in the case of industrial- scale growth in a manufacturing environment.
• feedlayers and feedvoirs are not limited to containing only feedatoms.
• Catalyst or other materials that are found to be beneficial for the growth of NTs can be added to the feedatoms in the feedlayers or feedvoirs. These materials could be layered or otherwise arranged with feedatoms in the feedlayers or feedvoirs to be liberated at different stages of the growth process.
• Figure 9 illustrates the tratip embodiment of the TREKANG patent application comprising a catpar residing on a tratip.
• the tratip can grow the NT while on the move, enabling growth of an NT in three dimensions. Such capability enables NTs to be deposited on an adjacent target surface in patterns.
• the next embodiment of the present invention is analogous to the tratip.
• the broadtip system comprises the broadtip assembly; broadtip substrate assembly; the articulating arm; and the motion stage that together facilitate the three dimensional motion.
• the broadtip system is a large tratip.
• the scale of the broadtip substrate assembly is tens to thousands of growth sites or catpars instead of one catpar in the case of a tratip.
• the broadtip substrate assembly is so large plasmons are not required to couple energy to its feedlayer or feedvoir.
• the broadtip assembly is mounted onto an articulated arm and motion stage that facilitates three dimensional motion across an adjacent target surface upon which the broadtip system deposits nanotubes that are growing from the broadtip substrate assembly.
• the emrad energizing nanotube growth from a broadtip substrate assembly may propagate from the back side of the broadtip substrate assembly, may be incorporated into the broadtip substrate assembly, or propagate from the front side through a transparent adjacent target surface onto the broadtip substrate assembly.
• the three dimensional growth pattern may be controlled by manipulating the emrad intensity, emrad pattern on the broadtip substrate assembly and by turning the emrad source on and off.
• the substrate assembly is made by coating on the front side a thick feedlayer
• the substrate used for the experiments was flat and smooth, the substrate may be contoured to concentrate the catalyst and position the catpar. Even in the case of no annealing to form catpars, a roughened or contoured substrate would create more growth sites in the form of irregularities in the otherwise smooth catalyst layer.
• the substrate assembly properties can be used to tune the amount of energy delivered to the feedlayer or feedvoir. These properties include the substrate contour, thickness and material properties such as transparency.
• nanotubes such as silicon (SI), boron nitride (BN), aluminum nitride
• AIN gallium nitride
• GN gallium nitride
• the feedlayer composition would need to be modified to provide the proper feedatoms.
• the emrad wavelength range would be required to energize the feedatoms to migrate. Two emrad sources of differing wavelength ranges can be used to energize two species of feedatoms.
• the emrad may be generated by laser, LED, fluorescent lamp or incandescent lamp.
• emrad sources would be external to the substrate.
• these sources could be fabricated as a part of the substrate.
• an optical amplifier may be fabricated separately or as part of the substrate to amplify an emrad source.
• Requirements for the emrad source include possessing a wavelength or wavelength range absorbed by the feedlayer, and, once absorbed, imparting enough energy to the absorbing feedatoms to free them to migrate. These free atoms would then form NTs at the growth site or catpar.
• the wavelength of this emrad should be as short as possible and still fit other criteria such as the required laser power, cost and safety of carrying out the experiment.
• a laser of 405 nm wavelength and a 365 nm LED lamp were chosen for the experiments.
• a feature of the present invention is that NT growth may be paused or ceased by stopping the emrad. This could allow the fine tuning of NT length or a way to accurately begin and end different stages of NT growth in a multi-stage growth scenario.
• the feedatoms for NT growth do not come from the atmospheric gasses; the constituent gasses, pressure and temperature of the atmosphere can be adjusted to optimize NT growth.
• the ineratmo gasses may be circulated, filtered, exchanged, monitored and/or changed to facilitate control of the ineratmo constituents, temperature and pressure, thereby maintaining an optimal atmosphere in the reaction chamber.
• the ineratmo can be altered during growth process as required to continue growth, change NT characteristics, and functionalize NTs.
• Real time diagnostic measurements may be employed to measure and control the growth and functionalization of NTs. These diagnostics include the NT growth rate and structure; catalyst temperatures, pressures and compositions; feedatom transport; and ineratmo compositions, temperatures and pressures.
• Free Atom Nanotube Growth technology may be adapted to grow assemblages of atoms thereby forming molecules, structures, shapes and machines in an accurate and controlled manner. These assemblages formation processes may or may not require a catalyst to facilitate the formation of the assemblage.
• FIG. 1 is a schematic illustration of the experimental configuration for most experiments.
• a two-inch diameter, 6 mm thick quartz disc was used as the substrate.
• a 140 nm layer of carbon was sputtered onto the front surface of the substrate to form a feedlayer with carbon feedatoms.
• the sputtered carbon forms an amorphous carbon layer.
• On the front side of the of the carbon feedlayer a 2 - 3 nm layer of iron was sputtered.
• the iron is a catalyst for carbon nanotube growth.
• the iron layer completes the substrate assembly that consists of the substrate and its carbon and iron layers.
• the emrad that enters from the bottom of the picture and traverses the quartz substrate is mostly absorbed in the carbon layer.
• FIG. 2 is a schematic illustration of another experimental configuration which is the best mode of the present invention as conceived by the inventor.
• One difference in figure 2 from figure 1 is that the catalyst layer has been annealed to form catpars.
• the second difference is that the emrad, laser radiation in most experiments, is incident from the front side of the substrate assembly. Carbon nanotubes have been grown from catpars in some of the experiments. Most experiments have been carried out with the radiation incident from the front side of the substrate assembly because the insertion and extraction of the assembly is simpler when the front side is toward the emrad source. However experiments have shown NT growth from emrad illuminating either side of the quartz substrate.
• Figure 4 illustrates schematically the basic experimental configuration.
• the substrate can be mounted on the substrate mount with either the front side or back side facing the laser or lamp. Not shown in figure 4 are the heaters and thermocouples that are attached to the substrate mount.
• Carbon nanotubes were grown with the substrate at ambient temperature and 200 C; argon gas pressures ranging from 50 to 200 Torr; irradiances of a few to tens of milliwatts per square centimeter; and wavelengths of 405 and 365 nm radiation. Experiments are continuing to map out the NT growth parameter space.
• the Free Atom Nanotube Growth technology will enable researchers to grow large amounts of long, highq NTs thereby stimulating research into the properties of the NTs and the macroscopic assemblages formed using these materials.
• these properties include very high tensile strength, high thermal conductivity, for some chiralities low conductivity and the ability to sustain very high electrical current densities, and for other chiralities semiconductor properties.
• interesting properties include high tensile strength, high thermal conductivity, low electrical conductivity and neutron absorption based upon the presence of boron. Indeed, the long, highq NTs may reveal properties and applications that are not possible with the currently available NTs.
• the long, highq nanotubes can be used to construct: 1) enhanced strength structures; 2) enhanced conductivity conductors, wires, microscale and nanoscale integrated circuits, microscale and nanoscale transistors, diodes, gates, switches, resistors, capacitors, single sensors and arrays; 3) receivers, rectennas or electromagnetic radiation emitting structures; 4) surface geometries to promote or prevent biological growth; 5) surfaces with special optical, reflective, interference or diffractive properties; 6) surfaces to promote or prevent chemical reactions; 7) structures with certain material properties including strength, hardness, flexibility, density, porosity, etc.; and 8) surfaces that emit particles such as electrons under electrical stimulation (field emission).
• the method for FANG nanotube growth would comprise the steps of: 1) preparing a substrate including modifying its surface to have a desired roughness and contouring; 2) laying down a feedlayer onto the substrate; 3) completing a substrate assembly by laying down a thin film of catalyst on the surface of the feedlayer; 4) forming catpars from the thin catalyst film by annealing; 5) installing the assembly in a reaction chamber and sealing the chamber; 6) replacing the atmosphere in the reaction chamber with an ineratmo; 7) adjusting the temperature of the substrate assembly and the pressure of the ineratmo; 8) starting the emrad source to energize feedatoms to migrate to growth sites or catpars; and 9) operating the system for the time interval to achieve the desired NT growth results.
• a FANG broadtip system nanotube growth would comprise the steps of: 1) preparing a substrate for a broadtip substrate assembly including proper sizing and modifying its surface to have a desired roughness and contouring; 2) laying down a feedlayer onto the broadtip substrate; 3) completing the broadtip substrate assembly by laying down a thin film of catalyst on the surface of the feedlayer; 4) forming catpars from the thin catalyst film; 5) installing the broadtip substrate into a broadtip assembly; 6) attach the broadtip assembly to an articulated arm; 7) finish a broadtip system construction by attaching the articulated arm to a motion stage; 8) install a target surface upon which a pattern of nanotubes is to be deposited into a reaction chamber; 9) installing the broadtip system into the reaction chamber including connecting electrical leads and sealing the chamber; 10) replacing the atmosphere in the reaction chamber with an ineratmo; 11) adjusting the temperature of the broadtip substrate assembly and the pressure of the ineratmo and 12) initiating an automatic NT
• step 4 can be eliminated in both of the preceding procedures.
• Figure 8 illustrates schematically this vision.
• Figure 8 shows the side view inside a reaction chamber.
• Five assemblies each consisting of a substrate with catpars arranged on it sitting above a laser. In between is a lens that transports the photons from the laser to the backside of the substrate.
• Above the front surface of the five substrates is a "draw bar harvester".
• the bar moves down, attaches to the growing NT surface and then rises in cadence with the growth.
• an industrial laser cuts the NTs off, above the substrate assembly level.
• the bar then transports the harvested NTs out of the reaction chamber to a processing location. Another bar moves in and acquires the tops of the growing NTs and the process continues.
• FIG. 7 is an overhead view of another embodiment of an industrial process for the Free Atom Nanotube Growth Technology, in this case a broadtip system.
• the broadtip assembly to which the articulated arm attaches, which in turn is attached to a motion stage moves the broadtip assembly in three dimensions.
• the broadtip assembly also rotates in two axes.
• Two raised platforms and a sloped surface on the drawing facilitate the vertical NT and NT bridge structure features.
• the varied forms of the patterns of NTs deposited on the surface illustrate the potential capabilities of this system as envisioned by the inventor. [081] Achieving industrial-scale manufacturing of long, highq NTs means that these materials will become increasingly plentiful and inexpensive.
• CNTs In the case of CNTs, with their remarkable tensile strength and electrical properties, new ways of building existing commodities will be developed and new products will be invented using the superior material properties.
• CNT high strength material possibly exceeding in tensile strength all existing materials by an order of magnitude or more, will revolutionize life on Earth.
• CNT electrical components created at the nanometer scale lengths will enable smaller, lower power integrated circuits and will transform human society.
• the most extreme example of the benefits may be that high strength CNTs will enable the Space Elevator, thereby opening the resources of space to civilization in the form of enhanced Earth observation, space-based solar power, asteroid mining, planetary defense and colonization of the moons and planets of our solar system!

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