Abstract:
Systems and methods are provided for interweaving carbon nanotubes. One embodiment comprises a layer of carbon nanotubes. The layer includes carbon nanotubes oriented in a first direction, as well as carbon nanotubes oriented in a second direction that crosses the first direction. The carbon nanotubes oriented in the second direction are interwoven through the carbon nanotubes oriented in the first direction.

Description:
FIELD 
       [0001]    The disclosure relates to the field of materials science, and in particular, to carbon nanotubes. 
       BACKGROUND 
       [0002]    Carbon nanotubes are resilient materials that are noted for their incredible strength and flexibility. However, carbon nanotubes are small (e.g., having a width on the order of nanometers), which makes it hard to harness their properties in products that are implemented on larger scales such as the meter scale. For example, carbon nanotubes may be bundled into large sheets/mats that use a binder to hold the nanotubes together. The strength of these mats is dependent upon the strength of the binder holding the nanotubes together. 
         [0003]    Since carbon nanotubes continue to exhibit extraordinary strength and other desirable properties, it remains desirable to develop materials that are capable of exhibiting a similar strength on the macroscopic level. 
       SUMMARY 
       [0004]    Embodiments described herein include sheets of carbon nanotubes that are woven together during fabrication. Because nanotubes traveling in different directions are interweaved into a unified layer, the nanotubes themselves are placed into shear and/or tension when forces are applied to the layer. Hence, the mode of failure for the layer does not result from the failure of a binding agent, but rather requires that the nanotubes themselves break. This makes the layer orders of magnitude stronger than prior materials utilizing carbon nanotubes, which is highly desirable. 
         [0005]    One embodiment is a method for selectively growing carbon nanotubes via a Chemical Vapor Deposition (CVD) process. The method includes aligning an electrical field in a first direction for a first set of carbon nanotubes, heating the first set of carbon nanotubes above a threshold temperature to trigger parallel growth of the first set of carbon nanotubes in the first direction via CVD, and repeatedly varying the first direction by adjusting the electrical field, causing the first set of carbon nanotubes to interweave into a second set of carbon nanotubes as growth continues. 
         [0006]    A further embodiment is a system for fabricating a sheet of interwoven carbon nanotubes. The system includes carbon nanotube catalysts that grow different sets of nanotubes, a heating system configured to emit light to heat the nanotubes, an electric field generator, and a controller. The controller is configured to operate the heating system to selectively heat individual sets in order to trigger carbon nanotube growth during Chemical Vapor Deposition (CVD), and to operate the electric field generator to generate an electrical field that points in a direction that varies during the growth of a set of carbon nanotubes, causing carbon nanotubes of the set to interweave other carbon nanotubes as growth continues. 
         [0007]    A further embodiment is a system for fabricating a sheet of interwoven carbon nanotubes. The system includes carbon nanotube catalysts that grow different chiralities of nanotubes, a lighting system, and an electric field generator. The system also includes a controller that is able to operate the lighting system to selectively heat individual chiralities in order to trigger carbon nanotube growth during Chemical Vapor Deposition (CVD), and to operate the electric field generator to generate an electrical field that points in a direction that varies during the growth of a chirality of carbon nanotubes, causing carbon nanotubes of the chirality to interweave other carbon nanotubes as growth continues. 
         [0008]    Another embodiment is a further system for fabricating a sheet of interwoven carbon nanotubes. The system includes a first substrate comprising carbon nanotube catalysts arranged on top of integrated heaters, and a second substrate oriented at a non-zero angle with respect to the first substrate. The second substrate includes carbon nanotube catalysts arranged on top of integrated heaters. The system further includes an electrical field generator. The system also includes a controller that is able to operate the integrated heaters to selectively heat a set of carbon nanotubes in order to catalyze growth during Chemical Vapor Deposition (CVD), and to operate the electric field generator to generate an electrical field that varies in direction during growth of the set of carbon nanotubes, causing the set of carbon nanotubes to interweave other carbon nanotubes as growth continues. 
         [0009]    Another embodiment is a material. The material includes a layer of carbon nanotubes. The layer includes carbon nanotubes oriented in a first direction. The layer also includes carbon nanotubes oriented in a second direction that crosses the first direction, and that are interwoven through the carbon nanotubes oriented in the first direction. 
         [0010]    Another embodiment is a further material. The material includes a first set of carbon nanotubes that comprise a first chirality and that are oriented in parallel, a second set of carbon nanotubes that comprise a second chirality and that form a first sinusoid intersecting the first set, and a third set of carbon nanotubes that comprise a third chirality and that form a second sinusoid intersecting the first set. The second sinusoid is shifted in phase from the first sinusoid. 
         [0011]    Other exemplary embodiments (e.g., methods and computer-readable media relating to the foregoing embodiments) may be described below. The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0012]    Some embodiments of the present disclosure are now described, by way of example only, and with reference to the accompanying drawings. The same reference number represents the same element or the same type of element on all drawings. 
           [0013]      FIG. 1  is a diagram illustrating an interweaved layer of carbon nanotubes in an exemplary embodiment. 
           [0014]      FIG. 2  is a block diagram illustrating a fabrication system for carbon nanotubes in an exemplary embodiment. 
           [0015]      FIG. 3  is a flowchart illustrating a method for growing carbon nanotubes into an interweaved layer in an exemplary embodiment. 
           [0016]      FIGS. 4-10  illustrate growth of an interweaved layer of carbon nanotubes in an exemplary embodiment. 
           [0017]      FIG. 11  is a diagram illustrating sinusoids formed by carbon nanotubes in an exemplary embodiment. 
           [0018]      FIG. 12  is a diagram illustrating excitation wavelengths and photoluminescence wavelengths for different chiralities of carbon nanotubes in an exemplary embodiment. 
           [0019]      FIG. 13  is a diagram illustrating substrates that utilize heaters in an exemplary embodiment. 
           [0020]      FIGS. 14-15  are diagrams illustrating a substrate capable of growing multiple layers of carbon nanotubes at once in an exemplary embodiment. 
           [0021]      FIGS. 16-17  are diagrams illustrating motion of an electric field generator about substrates for growing carbon nanotubes in an exemplary embodiment. 
           [0022]      FIG. 18  is a flow diagram of aircraft production and service methodology in an exemplary embodiment. 
           [0023]      FIG. 19  is a block diagram of an aircraft in an exemplary embodiment. 
       
    
    
     DESCRIPTION 
       [0024]    The figures and the following description illustrate specific exemplary embodiments of the disclosure. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the disclosure and are included within the scope of the disclosure. Furthermore, any examples described herein are intended to aid in understanding the principles of the disclosure, and are to be construed as being without limitation to such specifically recited examples and conditions. As a result, the disclosure is not limited to the specific embodiments or examples described below, but by the claims and their equivalents. 
         [0025]      FIG. 1  is a diagram illustrating an interweaved layer  100  of carbon nanotubes in an exemplary embodiment. In  FIG. 1 , nanotubes  110  running horizontally are interweaved with nanotubes  120  running vertically. When shear forces (S) are applied to layer  100 , those shear forces are borne by nanotubes  110 . This causes layer  100  to exhibit a high strength. That is, the strength of layer  100  results from the strength of the nanotubes that it is made from, in that the high strength is due to load being directly borne by the carbon nanotubes rather than a binder material. If the woven structure of layer  100  was not used, it would not be as strong. The following description and figures illustrate systems and methods for creating such interweaved layers of carbon nanotubes. 
         [0026]      FIG. 2  is a block diagram illustrating a fabrication system  200  for creating woven sheets of carbon nanotubes in an exemplary embodiment. Fabrication system  200  comprises any system capable of weaving carbon nanotubes together as those nanotubes are grown via Chemical Vapor Deposition (CVD) processes. In this embodiment, fabrication system  200  includes CVD chamber  290 , in which multiple substrates ( 210 ,  220 ) are placed. Substrate  210  includes catalysts  212  and  214 , and substrate  220  includes catalysts  216  and  218 . The catalysts ( 212 ,  214 ,  216 ,  218 ) facilitate carbon nanotube growth via CVD processes. In this embodiment, each catalyst corresponds with a different chirality of carbon nanotube. Thus, catalyst  212  grows chirality A, catalyst  214  grows chirality B, catalyst  216  grows chirality C, and catalyst  218  grows chirality D. As used herein, different “chiralities” of carbon nanotubes are carbon nanotubes that have distinct pairs of chiral numbers m and n, denoted as (n,m). These variables n and m characterize a nanotube by serving as unit vectors along different directions in a crystal lattice formed by a carbon nanotube. During fabrication, there may be many catalysts of each chirality, and catalysts of different chiralities may alternate with respect to each other when placed on the same substrate. 
         [0027]    Fabrication system  200  also includes systems that selectively trigger and direct growth from each of the catalysts ( 212 ,  214 ,  216 ,  218 ). That is, controller  230  may operate heating elements  241 - 244  in order to selectively heat individual catalysts to a threshold temperature that triggers CVD processes. Alternatively or additionally, controller  230  may operate lighting system  232  to apply light at wavelengths that energize and heat certain chiralities (e.g., A) without increasing the temperature of other chiralities (e.g., B, C, D) above a threshold temperature. Controller  230  may be implemented, for example, as custom circuitry, as a processor executing programmed instructions, or some combination thereof. 
         [0028]    As controller  230  selectively triggers the growth of individual catalysts (or sets of catalysts), controller  230  may operate one or more electric field sources ( 250 ,  270 ) in order to generate electrical fields. As carbon nanotube growth occurs within interior  251  of CVD chamber  290  to form layer  100 , the carbon nanotubes will grow parallel to the applied electrical fields. Controller  230  may further operate actuators (e.g.,  260 ,  280 ) in order change the direction of the electrical fields as growth continues (e.g., simultaneously with the growth of the carbon nanotubes, or in between growth phases before the carbon nanotubes have finished growing to their intended length). This may ensure that different chiralities and/or sets of nanotubes grow in different directions. 
         [0029]    By selectively growing different sets of nanotubes, and by controlling the direction of growth of each set of nanotubes via electric field sources  250  and  270 , controller  230  may interweave different carbon nanotubes together in any suitable pattern (e.g., a plain weave, a twill weave, a satin weave, etc.). This provides a substantial benefit by enhancing the strength of layers of materials that utilize carbon nanotubes. 
         [0030]    Illustrative details of the operation of fabrication system  200  will be discussed with regard to  FIG. 3 . Assume, for this embodiment, that catalysts A and B are arranged in an alternating/interspersed pattern on substrate  210  and that catalysts C and D are arranged in an alternating pattern on substrate  220  (e.g., as shown in  FIG. 4 ). The catalysts arranged on substrates  210  and  220  are substantially coplanar, and substrates  210  and  220  are separated by an angle θ (e.g., ninety degrees). 
         [0031]      FIG. 3  is a flowchart illustrating a method  300  for growing carbon nanotubes into an interweaved layer in an exemplary embodiment. The steps of method  300  are described with reference to fabrication system  200  of  FIG. 2 , but those skilled in the art will appreciate that method  300  may be performed in other systems. The steps of the flowcharts described herein are not all inclusive and may include other steps not shown. The steps described herein may also be performed in an alternative order. 
         [0032]    In order to initiate the process, controller  230  selects a set of carbon nanotubes to grow (step  302 ). In this case, nanotubes  213  having chirality A (which grow from catalysts  212 ) are chosen for growth, as shown in  FIG. 5 . As shown in  FIG. 5  and following figures, the size of individual carbon nanotubes has been substantially exaggerated in order to clarify in the weaving processes described herein. 
         [0033]    Controller  230  directs one or more actuators (e.g.,  280 ,  260 ) and/or electric field sources (e.g.,  250 ,  270 ) to align an electrical field in a desired direction of growth for the selected set of carbon nanotubes (step  304 ). In this case, the nanotubes will be grown upward along the page, and into the page as shown by the vectors illustrated in  FIG. 5 . Hence, controller  230  instructs actuators (e.g.,  280 ,  260 ) and/or electric field sources/generators (e.g.,  250 ,  270 ) to align an electrical field in the desired direction. 
         [0034]    With the electrical field aligned properly, nanotubes growing from catalysts  212  will grow in the expected direction. Thus, controller  230  directs elements of fabrication system  200  (e.g., heaters  241 - 244 , or lighting system  232 ) to heat catalysts  212  above a threshold temperature in order to trigger parallel nanotube growth in the desired direction via CVD processes (step  306 ). It should be noted that in embodiments which utilize a lighting system to apply heat, the lighting system heats carbon nanotubes, which transfer heat to their corresponding catalysts via conduction. Thus, as an initial step, it may be desirable to place substrates  210  and  220  into a heated oven to trigger a small amount of uniform growth at each of the catalysts, before utilizing the lighting system to heat individual chiralities. This ensures that there are carbon nanotubes for the lighting system to heat in step  306 . 
         [0035]    As used herein, the threshold temperature is a temperature at which growth continues at a non-negligible rate. While CVD processes may cause growth to occur for all carbon nanotubes at lower temperatures, the speed of this growth is orders of magnitude slower below a threshold temperature, and therefore not acceptable for fabrication purposes. For example, the threshold temperature may be selected to trigger growth in the range of several tens of microns per minute (e.g., a temperature of 650° C., 700° C., etc.). In one embodiment, the nanotubes are all kept at a temperature just below the threshold temperature (e.g., 20° C. below the threshold temperature), and then individual sets of nanotubes are heated above the threshold temperature to trigger growth at viable rates. Heating the first set of carbon nanotubes as shown in  FIG. 5  causes the carbon nanotubes  213  to grow upward and out of the page towards the reader. At each carbon nanotube  213 , carbon atoms are drawn out of the surrounding environment proximate to catalyst  212  at location  500 . These carbon atoms are added to the carbon nanotubes  213 , increasing their length in the direction of the electric field. 
         [0036]    As growth continues (e.g., before the carbon nanotubes have completed growing to their intended length, or during a period of time at which the carbon nanotubes are over the threshold temperature and actively growing), controller  230  changes the direction by altering the alignment of the electrical field (step  308 ). This changes the direction of growth for the carbon nanotubes, which causes the carbon nanotubes to interweave with another set of carbon nanotubes. As the direction of the electric field changes, the direction in which the carbon nanotubes grow also changes. In this manner, by oscillating the direction of the electric field as carbon nanotubes grow, the carbon nanotubes may form sinusoids along their length. 
         [0037]    Controller  230  may continue to trigger growth for different sets of carbon nanotubes, and change their direction of growth, in order to trigger interweaving of the different sets of carbon nanotubes (step  310 , returning to step  302 ). For example, as shown in  FIG. 6 , carbon nanotubes  215  (having chirality B) are grown from catalysts  214  upward and into the page away from the reader. Then carbon nanotubes  217  (having chirality C) are grown from catalysts  216  rightward and out of the page towards the reader as shown in  FIG. 7 , and carbon nanotubes  219  (having chirality D) are grown from catalysts  218  upward and out of the page towards the reader as shown in  FIG. 8 . Growth continues in this fashion in  FIGS. 9 and 10 , but the vertical component of growth for each set of nanotubes is periodically reversed/inverted/altered (e.g., in an oscillating fashion). This may be achieved by sweeping the electrical field back and forth through a repeating range of alignments. This results in layer  1000  exhibiting woven properties (because the nanotubes grow alternately upward and downward around each other as their growth continues). 
         [0038]      FIG. 11  is a side view of a portion of layer  1000  shown in  FIG. 10 . Specifically,  FIG. 11  is illustrated by view arrows  11  of  FIG. 10 . In  FIG. 11 , the lattice structure of individual carbon nanotubes is shown merely for the purpose of illustration and is not to scale.  FIG. 11  illustrates that carbon nanotubes  213  and  215  may be grown to form sinusoids that have the same amplitude and continue in the same direction, but are offset/shifted in phase from each other such that when carbon nanotube  213  reaches a peak, carbon nanotube  215  reaches a valley. Carbon nanotubes  217  and  219  also form sinusoids that are offset in phase, and travel in a direction that will cause them to interweave with nanotubes  213  and  215 . In one embodiment, catalysts for carbon nanotubes that are placed on the same substrate are separated from each other by a distance of several millimeters. The carbon nanotubes in this embodiment may also oscillate upward and downward during growth by an amplitude of several millimeters. That is, the amplitude of the sinusoids shown in  FIG. 11  may be several millimeters. While sinusoidal shapes are illustrated in  FIG. 11 , the techniques described herein are by no means limited to sinusoidal patterns nor to the length scales indicated. 
         [0039]      FIGS. 12-13  illustrate concepts and systems relating to selectively heating different sets and/or chiralities of nanotubes to facilitate the growth processes described above. Specifically,  FIG. 12  is a diagram illustrating excitation wavelengths/frequencies and photoluminescence wavelengths/frequencies for different chiralities of carbon nanotubes in an exemplary embodiment. This information may be utilized to operate lighting system  232  of  FIG. 2  to selectively heat (and thereby trigger the growth of) different chiralities of carbon nanotubes. Specifically, by emitting light at both the photoluminescence wavelength/frequency and the excitation wavelength/frequency of a specific chirality of nanotube, that chirality of nanotube may experience substantially more heating than other chiralities. Thus, by selectively operating lighting system  232  to apply multiple wavelengths of light at specific frequencies at the same time, controller  230  may selectively heat catalysts within fabrication system  200  to a temperature that triggers growth. 
         [0040]      FIG. 13  is a diagram illustrating substrates that utilize heaters ( 1310 ,  1320 ,  1330 ,  1340 ) to heat carbon nanotubes in an exemplary embodiment. In this embodiment, different chiralities of carbon nanotubes need not be used. Instead, the heaters may be selectively activated by controller  230  to trigger the growth of different sets of carbon nanotubes. These heaters ( 1310 ,  1320 ,  1330 ,  1340 ) may be integrated into substrates (e.g.,  210 ,  220 ) upon which the catalysts (e.g.,  212 ,  214 ,  216 ,  218 ) are arranged. For example, as shown in  FIG. 13 , heaters  1310  (for catalysts  212 ) are electrically coupled to activate by applying a differential voltage to wires P 1 , while heaters  1320  (for catalysts  214 ) are electrically coupled to activate by applying a differential voltage to wires P 2 . In a similar fashion, heaters  1330  (for catalysts  216 ) are electrically coupled to activate by applying a differential voltage to wires P 3 , while heaters  1340  (for catalysts  218 ) are electrically coupled to activate by applying a differential voltage to wires P 4 . 
         [0041]    The techniques described herein may also be applied in systems that allow for multiple layers of woven carbon nanotubes to be created at once. For example,  FIGS. 14-15  are diagrams illustrating a substrate  1410  capable of growing multiple layers of carbon nanotubes at once in an exemplary embodiment. In  FIG. 14 , a top view is shown of substrate  1410 .  FIG. 15  illustrates a front view of substrate  1410  indicated by view arrows  15 . As shown in  FIG. 15 , carbon nanotubes are grown from alternating locations A and B, in each of multiple layers  1510 ,  1520 , and  1530 . In this manner, fabrication may be performed efficiently as heating and electric fields may be applied to facilitate the growth of carbon nanotubes in multiple layers at once. 
         [0042]      FIGS. 16-17  are diagrams illustrating motion of an electric field generator  1610  about substrates for growing carbon nanotubes in an exemplary embodiment. Specifically,  FIG. 16  is a zoomed out view of  FIG. 5 , wherein substrates  210  and  220  are surrounded by a chassis,  1690  and  FIG. 17  is a front view indicated by view arrows  17  of  FIG. 16 . According to  FIGS. 16-17 , multiple electric field generators  1610  are placed on a rocking chassis  1690 . Generators  1610  are attached to chassis  1690  via support elements  1640 . Chassis  1690  rotates about axis  1650  in an oscillating fashion as growth occurs, causing electric field  1620  to change its orientation. As electric field  1620  changes orientation (e.g., by plus or minus five degrees of rotation about axis  1650 ), carbon nanotubes grown at substrate  220  change their orientation as they extend outward, resulting in the formation of sinusoidal carbon nanotubes. Similar mechanisms and systems may be utilized to generate varying electric fields that facilitate the growth of carbon nanotubes at substrate  210 . 
         [0043]    The rotation of chassis  1690  may be driven by any suitable mechanism, including form example linear actuator  1670 , attached to a support element  1640  via a securement point  1660 . 
       EXAMPLES 
       [0044]    Referring more particularly to the drawings, embodiments of the disclosure may be described in the context of an aircraft manufacturing and service method  1800  as shown in  FIG. 18  and an aircraft  1802  as shown in  FIG. 19 . During pre-production, exemplary method  1800  may include specification and design  1804  of the aircraft  1802  and material procurement  1806 . During production, component and subassembly manufacturing  1808  and system integration  1810  of the aircraft  1802  takes place. Thereafter, the aircraft  1802  may go through certification and delivery  1812  in order to be placed in service  1814 . While in service by a customer, the aircraft  1802  is scheduled for routine maintenance and service  1816  (which may also include modification, reconfiguration, refurbishment, and so on). 
         [0045]    Each of the processes of method  1800  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
         [0046]    As shown in  FIG. 19 , the aircraft  1802  produced by exemplary method  1800  may include an airframe  1818  with a plurality of systems  1820  and an interior  1822 . Examples of high-level systems  1820  include one or more of a propulsion system  1824 , an electrical system  1826 , a hydraulic system  1828 , and an environmental system  1830 . Any number of other systems may be included. Although an aerospace example is shown, the principles of the invention may be applied to other industries, such as the automotive industry. 
         [0047]    Apparatus and methods embodied herein may be employed during any one or more of the stages of the production and service method  1800 . For example, components or subassemblies corresponding to production stage  1808  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  1802  is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages  1808  and  1810 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  1802 . Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft  1802  is in service, for example and without limitation, to maintenance and service  1816 . For example, the techniques and systems described herein may be used for steps  1806 ,  1808 ,  1810 ,  1814 , and/or  1816 , and/or may be used for airframe  1818  and/or interior  1822 , or even any of propulsion  1824 , electrical  1826 , environmental  1830 , hydraulic  1828 , or systems  1820  in general. 
         [0048]    In one embodiment, layer  100  of  FIG. 1  comprises a portion of airframe  118  (e.g., a portion of a composite part utilized for a wing of an aircraft), and is manufactured during component and subassembly manufacturing  1808 . Layer  100  may be assembled together with other layers into a composite part for an aircraft in system integration  1810 , and then be utilized in service  1814  until wear renders the part unusable. Then, in maintenance and service  1816 , the part may be discarded and replaced with a newly manufactured part including a new layer  100 . 
         [0049]    Any of the various control elements shown in the figures or described herein may be implemented as hardware, software, firmware, or some combination of these. For example, an element may be implemented as dedicated hardware. Dedicated hardware elements may be referred to as “processors”, “controllers”, or some similar terminology. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. Moreover, explicit use of the term “processor” or “controller” should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor (DSP) hardware, a network processor, application specific integrated circuit (ASIC) or other circuitry, field programmable gate array (FPGA), read only memory (ROM) for storing software, random access memory (RAM), non-volatile storage, logic, or some other physical hardware component or module. 
         [0050]    Also, an element may be implemented as instructions executable by a processor or a computer to perform the functions of the element. Some examples of instructions are software, program code, and firmware. The instructions are operational when executed by the processor to direct the processor to perform the functions of the element. The instructions may be stored on storage devices that are readable by the processor. Some examples of the storage devices are digital or solid-state memories, magnetic storage media such as a magnetic disks and magnetic tapes, hard drives, or optically readable digital data storage media. 
         [0051]    Although specific embodiments are described herein, the scope of the disclosure is not limited to those specific embodiments. The scope of the disclosure is defined by the following claims and any equivalents thereof.