Patent Application
20240083753
The following information is provided to assist the reader in understanding technologies disclosed below and the environment in which such technologies may typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the technologies or the background thereof. The disclosure of all references cited herein are incorporated by reference.
Laser carbonization of polymers (for example, a polyimide) is an emerging technique that enables directly patterning conductive carbon electrodes for use in, for example, flexible devices, including supercapacitors and sensors. Lasers may be used to locally carbonize commercial polymers, such as polyimide, directly on flexible substrates. The “direct-write” approach of laser carbonization may provide a powerful alternative to printing technologies, which use nanocarbon-containing inks to print conducting electrodes of carbon nanotubes or graphene in flexible device fabrication. While laser-induced nanocarbon (LINC) patterns having a varying porous and fibrous morphologies have been demonstrated, the mechanisms underlying the formation of specific LINC morphologies are largely undetermined. An important challenge thus remains in determining the process-structure-property relationships for LINC formation to enable improved control of laser carbonization of polymers.
In one aspect, a method of producing a carbonized material includes applying a beam of electromagnetic radiation from a laser source to a polymeric substrate, varying the position of the beam to traverse over at least a portion of a surface of the polymeric substrate in a predetermined pattern, and controlling a fluence of the beam and speed of movement of the beam traversing over the at least a portion of the surface of the polymeric substrate as a function of position on the surface to one or more predefined levels of fluence and speed of movement of the beam to control at least one property of the produced carbonized material. Change in at least one of fluence as speed as well as a rate of change thereof may be independently controlled over a path of lasing. The fluence of the beam and speed of movement of the beam are controlled in a number of embodiments to the one or more predefined levels of fluence and speed of movement of the beam to achieve one or more predetermined transitions in the at least one property of the carbonized material at one or more predetermined positions on the surface of the polymeric substrate along a path of lasing. The one or more predetermined transitions in the at least one property of the carbonized material may include at least one of a transition in chemical composition, a transition in carbon atomic structure, or a transition in morphology. In a number of embodiments, the transition in chemical composition includes or is a transition in heteroatom content. In a number of embodiments, the transition in carbon atomic structure is or includes a transition to sp2-hybridized graphitic carbon. The produced carbonized material may be rich in graphene domains. Such graphene domains may be nanostructured graphene domains (for example, exhibiting porosity, anisotropic porosity, or a nanofiber structure or morphology).
The one or more predetermined transitions may be smooth transitions. Such transitions or gradients in one or more properties on a single substrate may be created via one or more gradients in fluence and/or speed along a path of lasing.
In a number of embodiments, the fluence of the beam is controlled to the one or more predefined levels of fluence by controlling a distance between a focus or waist of the beam and the surface of the polymeric substrate, by controlling optics of the laser source or by controlling power of the laser source. The fluence of the beam in a number of embodiments is controlled to the one or more predefined levels of fluence by controlling a distance between a focus or waist of the beam and the surface of the polymeric substrate. The distance between a focus or waist of the beam and the surface of the polymeric substrate may, for example, be controlled by a static variation in surface conformation of the polymeric substrate, by dynamically changing the position of the laser source during lasing, by dynamically changing the position of the polymeric substrate during lasing, or by combinations thereof. At least one of fluence of the beam or the speed of movement of the beam may be varied over the at least a portion of the surface of the polymeric substrate. At least one of fluence of the beam or the speed of movement of the beam may be held constant over the at least a portion of the surface of the polymeric substrate.
In a number of embodiments the one or more predetermined transitions in the at least one property of the carbonized material includes a one or more transitions in morphology. One or more thresholds levels of fluence for a given speed of movement of the beam associated with the one or more predetermined transitions may, for example, include a lower threshold corresponding to a transition from an isotropic porous morphology to an anisotropic cellular network and a higher threshold corresponding to (i) a transition from an anisotropic cellular network to aligned nanofibers or (ii) to a transition from an anisotropic cellular network to a porous ablated morphology. The fluence of the beam may be controlled over an area of the substrate to which the beam of electromagnetic radiation is applied to be between the lower threshold and the higher threshold to provide electrical conductivity over at least a portion of the area of the surface of the polymeric substrate.
In a number of embodiments, the method further includes creating a model of properties of the produced carbonize material as a function of at least one of (i) the speed of movement of the beam or (ii) the fluence of the beam or a variable upon which the fluence of the beam is dependent. The model of properties may also be determined as a function of beam focus and power input to the laser source.
In a number of embodiments, the one or more predetermined transitions (including fluence and/or speed associated therewith) are determined by traversing the laser source over at least one test polymeric substrate of the same polymeric material as the polymeric substrate which is inclined in orientation relative to the path of the laser source to create a continuous variation in fluence over the path of the laser source. In a number of embodiments, the one or more predetermined transitions are determined by traversing the laser source over at least one test polymeric substrate of the same polymeric material as the polymeric substrate which is inclined in orientation relative to the path of the laser source to create a continuous variation in fluence over the path of the laser source.
In another aspect, a system for producing a carbonized material includes a laser source configured to apply a beam of electromagnetic radiation from the laser source to a polymeric substrate, and a control system configured to vary the position of the beam to traverse over at least a portion of a surface of the polymeric substrate in a predetermined pattern and to control a fluence of the beam and speed of movement of the beam traversing over the at least a portion of the surface of the polymeric substrate as a function of position on the surface to one or more predefined levels of fluence and speed of movement of the beam to control at least one property of the produced carbonized material. In a number of embodiments, the control system is configured to control the fluence of the beam and the speed of movement of the beam to the one or more predefined levels of fluence and speed of movement of the beam to achieve one or more predetermined transitions in the at least one property of the carbonized material at one or more predetermined positions on the surface of the polymeric substrate along a path of lasing.
As described above, the one or more predetermined transitions in the at least one property of the carbonized material may include at least one of a transition in chemical composition, a transition in carbon atomic structure, or a transition in morphology. In a number of embodiments, the transition in chemical composition includes or is a transition in heteroatom content. In a number of embodiments, the transition in carbon atomic structure is or includes a transition to sp2-hybridized graphitic carbon. The produced carbonized material may be rich in graphene domains. Such graphene domains may be nanostructured graphene domains (for example, exhibiting porosity, anisotropic porosity, or a nanofiber structure or morphology).
The one or more predetermined transitions may be smooth transitions. Such transitions or gradients in one or more properties on a single substrate may be created via one or more gradients in fluence along a path of lasing.
In a number of embodiments, the control system is configured to control the fluence of the beam to the one or more predefined levels of fluence by controlling a distance between a focus or waist of the beam and a surface of the polymeric substrate, by controlling optics of the laser source, by controlling power of the laser source, or by combinations thereof. The control system is configured in a number of embodiments to control the fluence of the beam to the one or more predefined levels of fluence by controlling a distance between a focus or waist of the beam and a surface of the polymeric substrate. The distance between a focus or waist of the beam and the surface of the polymeric substrate may be controlled by a static variation in surface conformation of the polymeric substrate, by dynamically changing the position of the laser source during lasing. or by dynamically changing the position of the polymeric substrate during lasing.
The control system may be configured to vary at least one of fluence of the beam or the speed of movement of the beam over the at least a portion of the surface of the polymeric substrate. The control system may be configured to hold constant at least one of fluence of the beam or the speed of movement of the beam over the at least a portion of the surface of the polymeric substrate.
As described above, the one or more predetermined transitions in the at least one property of the carbonized material may include a one or more transitions in morphology. The one or more thresholds levels of fluence for a given speed of movement of the beam associated with the one or more predetermined transitions may, for example, include a lower threshold corresponding to a transition from an isotropic porous morphology to an anisotropic cellular network and a higher threshold corresponding to (i) a transition from an anisotropic cellular network to aligned nanofibers or (ii) to a transition from an anisotropic cellular network to a porous ablated morphology. The fluence of the beam may be controlled over an area of the substrate to which the beam of electromagnetic radiation is applied to be between the lower threshold and the higher threshold to provide electrical conductivity over at least a portion of the area of the surface of the polymeric substrate.
In a number of embodiments, the control system includes a processor system and a memory system in communicative connection with the processor system. The memory system includes an algorithm to control movement of the laser source. The memory system may further include a model of properties of the produced carbonize material as a function of at least one of (i) the speed of movement of the beam or (ii) the fluence of the beam or a variable upon which the fluence of the beam is dependent. The model of properties of the carbonized material may also be determined as a function of the beam focus and power input to the laser source.
In a number of embodiments, the one or more predetermined transitions (and associated fluence and/or speed) are determined by traversing the laser source over at least one test polymeric substrate of the same polymeric material as the polymeric substrate which is inclined in orientation relative to the path of the laser source to create a continuous variation in fluence over the path of the laser source. The one or more predetermined transitions may be determined by traversing the laser source over at least one test polymeric substrate of the same polymeric material as the polymeric substrate which is inclined in orientation relative to the path of the laser source to create a continuous variation in fluence over the path of the laser source.
In another aspect, a composition includes a carbonized material formed by a process as described herein. In that regard, the carbonized material is formed by applying a beam of electromagnetic radiation from a laser source to a polymeric substrate, varying the position of the beam to traverse over at least a portion of a surface of the polymeric substrate in a predetermined pattern, and controlling a fluence of the beam and speed of movement of the beam traversing over the at least a portion of the surface of the polymeric substrate as a function of position on the surface to one or more predefined levels of fluence and speed of movement of the beam to control at least one property of the carbonized material.
In a further aspect, devices include a composition hereof. Such devices may utilize properties of the compositions hereof such as electronic properties and/or physiochemical properties thereof. In a number of embodiments, such devices are electronic devices.
In still a further aspect, a composition includes a substrate including a path of laser-carbonized material wherein the path comprises a gradient in at least one property of the carbonized material along the path. In a number of embodiment, the path includes at least one of a gradient in chemical composition, a gradient in carbon atomic structure, or a gradient in morphology along the path. The gradient in chemical composition may include or be a gradient in heteroatom content. The carbonized material may include domains rich in graphene such as nanostructured graphene.
The path may, for example, include at least one of a transition or gradient in morphology. For example, the path may include a transition to a porous morphology. In a number of embodiment, the transition in morphology includes a transition from an isotropic porous morphology to an anisotropic cellular network, a transition from an anisotropic cellular network to aligned nanofibers or a transition from an anisotropic cellular network to a porous ablated morphology.
The path of laser-carbonized material may be created via traversing of a beam of electromagnetic energy over at least a portion of a polymeric precursor substrate and controlling the fluence and speed of movement of the beam of electromagnetic energy along the path.
The present devices, systems, methods and compositions], along with the attributes and attendant advantages thereof, will best be appreciated and understood in view of the following detailed description taken in conjunction with the accompanying drawings.
The present devices, systems, methods and compositions, along with the attributes and attendant advantages thereof, will best be appreciated and understood in view of the following description taken in conjunction with any accompanying drawings.
It will be readily understood that the components of embodiments hereof, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations in addition to the described example embodiments. Thus, the following more detailed description of the example embodiments, as represented in the figures, is not intended to limit the scope of the embodiments, as claimed, but is merely representative of example embodiments.
Reference throughout this specification to “one embodiment” or “an embodiment” (or the like) means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” or the like in various places throughout this specification are not necessarily all referring to the same embodiment.
Furthermore, described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments. One skilled in the relevant art will recognize, however, that the various embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, etcetera. In other instances, well known structures, materials, or operations are not shown or described in detail to avoid obfuscation.
As used herein and in the appended claims, the singular forms “a,” “an”, and “the” include plural references unless the context clearly dictates otherwise. Thus, for example, reference to “a laser source” includes a plurality of such laser sources and equivalents thereof known to those skilled in the art, and so forth, and reference to “the laser source” is a reference to one or more such laser sources and equivalents thereof known to those skilled in the art, and so forth. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, and each separate value as well as intermediate ranges are incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contraindicated by the text.
Determining, mapping, or modeling of laser conditions that lead to differences in physiochemical quantities or characteristics has largely yet to be accomplished in LINC grown on polymeric materials but is important in achieving controlled and repeatable LINC to produce patterns of predetermined properties, including, for example, morphological, chemical, and/or electrical properties. For example, it is desirable to identify transitional levels, values or thresholds in processing parameters resulting in changes in morphologies and/or other properties.
In a number of embodiments, devices, systems, and methods hereof provide an unprecedented capability to create compositions including patterns of graphene-based nanocarbon materials including nanofibers, branched networks and other nanoporous morphologies with spatial control of their morphology and properties through laser carbonization of substrate polymers. Many different polymers may be used in the devices, systems, and method hereof. A number of such polymers and other precursor materials, lasers suitable for use in connection therewith, and a general description of laser induced carbonization to form various graphene-based materials (that is, materials including graphene-rich domains), and a number of conditions for carbonization are, for example, summarized in U.S. Pat. Nos. 10,505,193, 11,014,816, 11,161,744, and U.S. Patent Application Publication Nos. 2019/0088420A1 and 2020/0112026A1, the disclosures of which are incorporated herein by reference.
The laser induced formation of nanocarbons is a superior alternative to top-down printing methods that are typically employed in fabricating flexible devices with functional nanocarbon materials. As opposed to the case of printing from ink or transfer printing methods, which require creating new inks for each type of nanocarbon to be printed, the devices, systems and method hereof can directly create different types of nanocarbons on different locations of the same surface easily by spatial control of laser fluence and speed of movement of the laser source.
It is important to understand the process-structure-property relationships for LINC formation. In that regard, to control LINC morphology, it is important to determine the laser condition (including, for example, wavelength, power, speed, pulse rate, etc.) that may be used to achieve a desired LINC morphology. Likewise, it is important to determine the manner in which morphology and chemical composition of LINCs affect their properties (for example, electrical conductivity, electrochemical behavior, etc.).
LINC is shown to be an attractive method to fabricate porous conductive electrodes directly on flexible substrates, which are required for a wide range of applications. As described above, as an alternative to printing technologies from nanocarbon inks, LINC formation is more scalable and less costly. Taken together, the results of studied hereof show that material properties such as resistivity can be tuned through morphology adjustment based on local control of laser fluence and speed of movement of the laser source. Accordingly, the variety of LINC morphologies achieved and the tunability of their properties make them superior to printing techniques that require the preparation of different nanocarbon inks for writing carbon-based electrodes with different morphologies and molecular structures on flexible substrates. Moreover the ability to control the spatial variation of morphologies and properties on the same substrate can be particularly useful in designing LINC for applications integrating high surface area nanocarbon electrodes with highly conductive and dense traces, such as for electrochemical applications.
In a number of embodiments, fluence and/or speed of the beam of electromagnetic radiation is varied over the pattern to create a transition in properties (for example, from one morphology to another). The fluence and/or speed of the beam (to, for example, create a spatial gradient therein) may be varied over the pattern to create a smooth transition or gradient in properties along the path of lasing as the beam traverses over the surface of the substrate. As used herein, the term “smooth transition” refers to a transition or gradient, without an abrupt change, from a carbonized material of one property (for example, morphology) to an adjacent carbonized material of another, different property (for example, morphology etc.). Such transitions are mechanically robust transitions without gaps or discontinuities between carbonized materials of adjacent, different properties (that is, for example, a continuous morphing from one morphology and an adjacent morphology). Such smooth transitions eliminate the need to create interfaces between, for example, one morphology and an adjacent morphology.
One or more models of one or more properties (for example, morphological, chemical, atomic structural, electrical and/or other properties, which may be interrelated) may be created as a function of the fluence (or of a variable upon which the fluence is dependent) and/or speed. In a number of embodiments, the model of a property such as morphology is determined as a function of beam focus (or a variable upon which fluence is dependent) and power input to the laser source as well as speed. Predetermined levels or thresholds of fluence and speed as well as models based thereon may, for example, be readily determined as described herein for a particular laser source, a particular wavelength of electromagnetic energy, a particular power input, a particular material, etc.
In a number of studies hereof (see
Studies hereof at a constant laser speed of, for example, 500 mm/s, illustrate methods, devices, and systems for lasing polymer films using representative polyimide films with spatially controlled gradients of optical energy flux. Combined with Gaussian beam modeling, the methods, devices, and systems hereof uniquely enable continuously sweeping different laser fluence values as a spatial map along the laser path. CO2 laser irradiation of the representative polymer polyimide demonstrated the direct formation of a variety of nanocarbons ranging from isotropic porous carbon, highly anisotropic cellular networks of graphitic carbon, and aligned carbon nanofibers. A fluence-based approach was developed to elucidate the process-structure-property relationships governing LINC formation for these morphologies. This is achieved by mathematically modeling the effect of degree of defocus on intensity distribution and fluence for a Gaussian laser beam. A methodology for creating fluence gradients on tilted polyimide films is also described. Importantly, two specific threshold values of fluence were identified as follows: the transition from isotropic porous morphology to anisotropic cellular networks (T1) at a fluence value of 12 J/cm2, second, the transition to aligned woolly nanofibers (T2) at a fluence value of 17 J/cm2. Moreover, anisotropic cellular networks were shown to have the highest electrical conductivity (≈5 S/cm) for the conditions studied (laser wavelength of 10.6 μm and scanning speed of 500 mm/s), due to the lateral connectivity and the high graphitic content. Hence, the models and results hereof provide insights into the physicochemical processes underlying LINC formation and enable generating a morphology diagram of laser processing parameters. Once again, anisotropic cellular networks are the most electrically conducting and have the highest quality sp2 carbon. On the other hand, the aligned woolly nanofiber morphology is electrically insulating along the length of the lased lines, although the woolly nanofiber morphology exhibits the highest degree of carbonization with the least heteroatom content. Such results provide new insights into the fluence-dependence of the physicochemical processes underlying LINC formation. Moreover, the methodology hereof enables generating a morphology diagram for LINC, which facilitates precise tunability of both the morphology and properties of LINC patterns, based on easy-to-control processing parameters, such as laser power and degree of beam defocusing.
A mapping of Z-values may, for example, be achieved by tilting a flat sample for monotonous fluence gradients, by designed surface topography that is machined (or otherwise formed to vary over the surface) before the laser carbonization process, by controlling the position of the laser source or by controlling the optics of the laser source which focus the beam. Fluence may also be controlled by altering power such as though pulse width modulation. The devises, systems, and methods hereof are capable of creating a variety of nanocarbons directly on, for example, the surface of a single flexible polymer film or substrate, such as a representative polyimide substrate, which makes such devices, systems, and methods attractive in, for example, functional flexible device manufacturing. The reason that changing Z-coordinate of the substrate surface enables creating spatial maps of laser fluence is that changing Z-values leads to controlling the degree of beam focus/defocus, which in turn controls the average fluence value on each point on the surface. As described above, control of focus/defocus may also be achieved optically. Hence, as the laser is rastered or scanned over a surface with spatially varying Z-coordinate, a spatially varying fluence map is generated, which enables creating fluence-dependent nanocarbon morphologies locally at each point of the surface. This ability to engineer spatial variations of morphology enables creating highly conducting traces of dense graphitic carbon that seamlessly morph into a high surface area nanoporous carbon for electrochemical electrodes, for example. Hence, the present methods, devices and systems can facilitate the fabrication of different types of flexible devices such as sensors, capacitors, and others.
Further insights into the fundamental mechanisms underlying the formation of LINC morphologies were gained in studies of lasing speed. In such studies, the approach of lasing individual electrodes on a tilted polyimide sheet as described above was used to allow scanning a continuum of laser fluence on the sample. Once again, such an approach is valuable for revealing discrete morphological transitions and mapping structural and chemical changes as a function of fluence. To investigate if morphological and structural transitions are energetically or kinetically driven, lines were lased at a fixed power and different speeds and the fluence values that drive these transitions were identified at the different speeds. In addition to the porous-to-cellular-networks and the cellular-network-to-woolly-fiber morphological transitions described above, a new ablation threshold was identified that occurs at low speeds (that is, v<300 mm/s under the conditions studied). This transition is characterized by ablation of the top surface and a hierarchical porosity with improved graphitization (D/G ratio of 0.64). Additionally, it was demonstrated that the fluence at which fibers form is highly speed dependent and that fibers form only at high speeds for the polyimide material studied (v>300 mm/s), in contrast with the other two transitions. For more in depth analysis, a methodology hereof was developed which integrates the experimental values with thermal finite element method (FEM) simulations of the tilted lasing. By logging the temperatures and temperature rates at the locations of the transitions, it was determined that the porous to cellular transition and the ablation transitions occur at a temperature around 3000° C. and 3100° C. respectively, which match temperatures of reported for polyimide graphitization and ablation of graphitic material. The determinations were further supported by Raman spectroscopy analysis which confirmed that graphitization occurs at the porous-to-cellular morphology transition with the appearance of the 2D peak and a marked drop in electrode resistivity. Additionally, the analysis revealed that the fiber formation transition occurs at temperature increase rate of ≈107° C./s. Without limitation to any mechanism, the fiber formation phenomenon may be due to the jetting of incompletely carbonized viscoelastic polymer (polyimide) as a result of the high rate of temperature increase and gas release. Such results provide insights into the kinetics of the physicochemical processes underlying LING formation and may be used in tailoring LINC material for various applications.
In a number of constant speed (v=500 mm/s) studies hereof, laser fluence gradients and beam defocus were leveraged to facilitate understanding LINC formation process by quantitatively correlating laser condition, the resulting LINC morphologies, and their varying physiochemical properties (for example, electrical conductivity). Additionally, methods, devices, and system of creating LINC materials with spatially varying morphologies and hence spatially varying properties are set forth. To investigate the effect of tuning fluence on morphology and properties, mathematical modeling of Gaussian laser beams was uniquely combined with two experimental approaches to control the local spread of the beam: 1) lasing individual lines on a tilted polyimide surface to achieve controlled gradients of fluence, and 2) lasing untilted samples at different degrees of defocusing for spatially uniform LINC lines. The first approach enables studying the evolution of nanoscale morphology and atomic structure continuously at different fluence values on the same polyimide film. Thus, one may precisely identify fluence thresholds for transition between different LINC morphologies owing to the resulting spatial map of fluence along a single LINC line in the tilted experiments. Based results of studies hereof, a model was developed for morphological evolution during laser carbonization that results in nanoporous structures, cellular networks, and woolly fibers at different fluence values, which enables delineating a clear morphology diagram. The results were correlated with electrical conductivity measurements to reveal the process-structure-property relationships governing the design of LINC materials with tunable and spatially varying properties.
LINCs form as a result of the local interaction of a laser beam with the surface of polyimide. As shown schematically in
The laser beam profile of the CW CO2 laser used in the above-described study is depicted in
As described above, to investigate the influence of beam intensity and fluence on polyimide carbonization, a gradient of fluence was created by lasing a tilted sample of polyimide.
The tilt angle controls how different points on the substrate along the laser path experience different fluence levels. A schematic of the system used in experiments hereof is shown in
Those skilled in the art will appreciate that electronic circuitry 100 of devices and systems hereof (whether tilted or untilted, and represented schematically by the arrows corresponding to beam motion in
The terms “electronic circuitry”, “circuitry” or “circuit,” as used herein include, but are not limited to, hardware, firmware, software, or combinations of each to perform a function(s) or an action(s). For example, based on a desired feature or need, a circuit may include a software-controlled microprocessor, discrete logic such as an application specific integrated circuit (ASIC), or other programmed logic device. A circuit may also be fully embodied as software. As used herein, “circuit” is considered synonymous with “logic.” The term “logic”, as used herein includes, but is not limited to, hardware, firmware, software, or combinations of each to perform a function(s) or an action(s), or to cause a function or action from another component. For example, based on a desired application or need, logic may include a software-controlled microprocessor, discrete logic such as an application specific integrated circuit (ASIC), or other programmed logic device. Logic may also be fully embodied as software.
The term “processor,” as used herein includes, but is not limited to, one or more of virtually any number of processor systems or stand-alone processors, such as microprocessors, microcontrollers, central processing units (CPUs), and digital signal processors (DSPs), in any combination. The processor may be associated with various other circuits that support operation of the processor, such as random-access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read only memory (EPROM), clocks, decoders, memory controllers, or interrupt controllers, etc. These support circuits may be internal or external to the processor or its associated electronic packaging. The support circuits are in operative communication with the processor. The support circuits are not necessarily shown separate from the processor in block diagrams or other drawings.
The term “controller,” as used herein includes, but is not limited to, any circuit or device that coordinates and controls the operation of one or more input and/or output devices. A controller may, for example, include a device having one or more processors, microprocessors, or central processing units capable of being programmed to perform functions.
The term “software,” as used herein includes, but is not limited to, one or more computer readable or executable instructions that cause a computer or other electronic device to perform functions, actions, or behave in a desired manner. The instructions may be embodied in various forms such as routines, algorithms, modules, or programs including separate applications or code from dynamically linked libraries. Software may also be implemented in various forms such as a stand-alone program, a function call, a servlet, an applet, instructions stored in a memory, part of an operating system or other type of executable instructions. It will be appreciated by one of ordinary skill in the art that the form of software is dependent on, for example, requirements of a desired application, the environment it runs on, or the desires of a designer/programmer or the like.
The samples hereof were lased at different powers ranging from P=11.7 W to P=30.7 W at a constant beam scanning velocity v=500 mm/s with the resulting lased lines shown in
More discrete transitions of LINC morphology along the lines are identified under both optical microscopy and scanning electron microscopy (SEM) imaging, as shown in
To correlate the observed morphologies from the tilted lasing experiment to the molecular structure of LINC, Raman spectroscopy mapping was carried out along the lased lines for two power values, P=11.7 W (does not have woolly fibers at the center of the line) and P=18.4 W (has woolly fibers at the center of the line), as shown in
The Raman spectra at points towards the edge of the lines prior to the formation of porous LINC display the characteristic peaks of polyimide at a Raman shift of 1395 cm−1, 1601 cm−1 and 1786 cm−1 associated with C—N—C axial vibration, imide ring vibration and C═O asymmetric ring respectively. The background signal due to polyimide fluorescence was removed. Moving along the line with increasing average fluence, the Raman peaks associated with polyimide disappear and the G and D bands characteristic of graphenic nanocarbon appear, indicating the progression of carbonization after T0. The observed spectra exhibit G and D peaks with large full width at half maximum (FWHM) and broadband band around the 2D peak. The spectra have the same shape along the lased line until a stark change in shape is observed beyond the T1 transition. In particular, a sharper well-defined 2D band appears, accompanied by a marked decrease in G and D peak FWHM (from 150 cm−1 to around 75 cm−1 for the G peak), as shown in
Similar analysis is performed for the lased line at P=18.4 W (
To gain more insight into the obtained LINC morphologies, untilted polyimide films were lased at different z values for the same power P=18.4 W to change the average fluence values. SEM images of the side view of the films along the direction of lasing are shown in
These transitions capture the evolution of LINC morphology with increasing average fluence values. A model of these fluence-dependent transitions is illustrated schematically in
Establishing that the LINC formation processes on the tilted and untilted samples are similar, at the same estimated fluence values, is important to generalize the results observed from the tilted experiments. The continuous nature of lasing across tilted samples could result in some dependence among the successive points along the lased path when compared with the lasing of flat untilted samples (at equivalent power, speed and z values). However, the equivalence between the tilted case and the untilted cases is demonstrated by three different approaches: analytical. numerical, and experimental as described below.
In the first, analytical approach it was shown that the energetics are equivalent, through average fluence calculations for both the tilted and untilted cases. However, equal fluence doesn't insure similar thermal response, because fluence represents the process energetics and not the kinetics. Hence, one needs to consider the time evolution of the temperature-dependent thermal diffusivity, phase transitions and laser material interactions.
To further elucidate the equivalence of laser heating across tilted and untilted samples, a 3D finite element model was developed with temperature-dependent material properties in ANSYS APDL finite element analysis software (available from ANSYS, Inc. of Canonsburg, Pennsylvania), to compare the temperatures (and rate of change of temperatures) experienced at similar levels of defocus for tilted and untilted polyimide at the same laser conditions. This technique has been used to model similar problems previously. The beam was modeled as a Gaussian distributed heat flux at the surface of the material. Polyimide carbonization was modeled through defined temperature-dependent material properties. The simulations show that the tilted and untilted lasing at similar laser conditions can be considered equivalent from both an energetic and kinetic perspective, supporting analytical calculations hereof. The differences in temperature values between the flat untilted and the tilted cases are within 3% at the same levels of beam defocus (z=0-6 mm). The result highlights the fact that equivalent fluence values lead to similar temperatures (for the same power and speed). It was also observed that for the same level of beam defocus, the difference between the rate of temperature increase for the flat untilted case and the titled case is less than 20%.
In light of the results discussed above energetic and kinetic equivalence in the cases of laser heating across tilted and untilted samples, the most important aspect of equivalence is the similarity of LINC morphologies obtained in both cases. Hence, it was confirmed that the LINC morphologies obtained in the case of flat untilted lasing experiments shown in
X-ray photoelectron spectroscopy (XPS) was used to characterize the fluence-dependent morphologies at several points along the lased lines (
Plotting the evolution of elemental composition as a function of fluence is more insightful than plotting these values as a function of power, because fluence is a quantity that is normalized to the spot area, which changes along the laser path in our tilted lasing experiments (that is, there is a gradient of fluence along the lines even though the power and speed are constant, as shown in
Multiple processes are involved in the formation of LINC, which depend on factors like laser wavelength, laser intensity, fluence, IR absorption of the material and type of polyimide. These inputs drive the temperature and heating rate in the polyimide and hence control the level of liquification, outgassing and carbonization that occur. This, in turn, affects the resulting morphology and molecular structure and hence the resulting properties. Chemical reactions also drive these processes like thermal dissociation and carbonization of the polyimide, solid-liquid phase transitions, plasma material interactions, melt expulsion and melt dynamics driven by Marangoni convection. In addition, the optical properties of the material can change, driving complex chain reactions, caused by the changing absorptivity of the material. Those processes can also depend on the gas environment and partial pressure. Moreover, they take place at different time scales, further complicating the phenomenon.
A number of noteworthy phenomena are observed in the studies hereof, which provide insight into the LINC formation process. For example, the transition to woolly fibers (T2) is clearly observed from the SEMs in
A better understanding of the chemical transformations that take place during these transitions can be built on previous pyrolysis research on the evolution and graphitization of different types of polyimide at temperatures up to 3000° C. Such studies are based on transmission electron microscopy (TEM), Raman spectroscopy, infrared spectroscopy, and outgassing observations at different temperatures. Such studies show that carbonization of polyimide films occurs over two steps. Initially at a temperature of 500° C. to 650° C. there is an abrupt weight decrease of the films accompanied by the release of large amounts of CO and CO2. This is followed by less weight loss and shrinkage due to evolution of small amounts of methane, hydrogen and nitrogen which can occur over a temperature range from 800° C. to above 1000° C. It has also been reported that nitrogen release continues in the second step of carbonization up to temperatures above 2000° C. and can be released abruptly. These findings further support the hypothesis that the morphology transitions observed (T1 and T2) are partly attributed to the rapid rate of gas released, especially when interacting with material jetting that can lead to the formation of nanofibers through rapid solidification of the jetted material. This mechanism of nanofiber formation is analogous to the fabrication of polymer nanofibers by electrospinning, albeit at much higher temperatures and more rapid heating/cooling rates.
The in situ polyimide pyrolysis studies were carried out using relatively low heating rates (≤30° C./min), compared to rapid temperature increase rates typical in laser irradiation. Hence, they do not necessarily represent the same reaction pathways taking place during laser heating of polyimide, which is an inherently non-equilibrium process in contrast to the quasi-equilibrium process of the slow heating. Structurally, TEM studies of the pyrolyzed polyimide have shown that the slowly carbonized polyimide exhibited turbostratic structure with nano-scale elongated pores from temperatures as low as 650° C. up to temperatures as high as 2450° C., beyond which the carbonized polyimide graphitized into high quality flat layers of graphitic carbon sheets comparable to pyrolytic carbon.
To further understand how the observed morphology transitions affect the properties of LINC, 15 mm LINC lines were lased at different z values and two power values, P=11.7 W and P=28.0 W in untilted configuration (ψ=0°). Using the two-point probe method, the resistance divided by line length (R/L) values are calculated from multiple resistance measurements at different lengths. First, the change in spot area as a function of z, according to the beam model is plotted in
Raman spectroscopy of these lines show a general inverse relationship between R/L values and the I(2D)/I(G) ratio. Indeed, we find that LINC with a well-defined and sharp 2D peak, exhibited the lowest resistivity. The average I(2D)/I(G) ratio starts at a value between 0.4-0.45 and increases for smaller spot size till a maximum value of around 0.53. Similar trends are observed in the I(G)/I(D) ratio where it reaches a maximum value of around 1.25. At higher power (P=28 W), R/L values are significantly smaller (
The I(2D)/I(G) ratio for P=28 W are generally similar to those obtained for P =11.7 W, with values between 0.42 at z=8 mm, and 0.49 at z=7 mm. Importantly, the disappearance of a sharp 2D peak at the onset of fiber formations (around z=3.8 mm) is accompanied by a drastic drop in conductivity. The conductivity of the LINC lased at P=28 W and v=500 mm/s is estimated to be around 5 S/cm, matching previously measured LINC conductivities, and superior to unannealed ink-jet-printed graphene. The resistivity could possibly be further increased by further optimizing the laser parameters such as speed or relasing.
Taken together, the electrical resistivity measurements hereof agree with the structural changes observed in the Raman spectra of
Two analytical approaches are typically used to understand how lasers interact with polymers. The first is the thermal approach, which focused on calculating the temperature rise in the material. The second is the fluence-based approach, which focuses on calculating the delivered laser energy in the material. Thermal models require estimating material properties of polyimide and LINC and are difficult to validate experimentally since it is difficult to measure the temperature at the laser spot; hence, they are generally more complex than fluence-based models. The devices, systems, and methods hereof provide a fluence-based approach for understanding LINC formation, based on Gaussian beam modeling, which is of a great utility from a manufacturing perspective. Though focus on lasing individual LINC lines in air, instead of areas formed by overlapping laser paths, the effect of multiple lasing of some regions on the surface is avoided. Multiple lasing greatly complicates the analysis and hinders extracting fundamental insights into the process-structure relationships for LING formation. Lasing lines also has an advantage over lasing individual spots, because one can circumvent laser power transient effects that are associated with laser ramping up when starting. By ignoring the initial portion of the lased LINC lines, one can ensure that steady state power is reached, when investigating the rest of the line or its end. In fact, when lasing our LINC lines it was sometimes observed that the initial spot has a drastically different morphology than the rest of the line, which is attributed to power transients in the laser.
In addition to elucidating the fluence-dependence of morphology, molecular structure, and electrical conductivity of LINC, the methodology hereof also enables generating maps of resulting morphologies as a function of accessible laser processing parameters (or ranges thereof), such as power and defocus, which can be easily controlled.
The studies discussed above show that when lasing individual lines with a spatially varying fluence gradient at a specific lasing speed (500 mm/s), discrete morphologies were observed, which were either of porous, cellular or fibrous nature. These morphologies were correlated to chemical and structural changes, and were observed at defined thresholds of fluence, confirming that an energetic approach to understand the process is valid at least at a fixed speed with different laser power values, despite the non-equilibrium nature of the process.
However, the same fluence value delivered at different values of speed can vary drastically in terms of temperature and temperature change with time, which can greatly affect the resulting morphology and carbonization. It is important to determine if morphologies of LINC be related to specific temperatures or temperature rates (that is, energetically controlled/limited or kinetically controlled/limited) Moreover, it is important to determine if the process energetics and kinetics influence the chemistry and gas release in process.
An approach similar to that described above was used to analyze laser nanocarbon formation through lasing lines with continuously varying laser fluence at different speeds to facilitate understanding the process kinetics. The resulting lines represent a map of a wide range of conditions, allowing precisely identifying morphological, structural and property changes. Through lasing at a fixed power and different speeds ranging from 100 mm/s to 500 mm/s at a power of 28 W, a more complete picture including process kinetics was determined.
Such an approach enables studying the evolution of nanoscale morphology and atomic structure continuously at different fluence values on the same polymeric (polyimide) film to investigate the influence of speed on morphology and structure. The experimental results were integrated with two energetic based approaches for estimating fluence (an area averaged fluence approach and a two-dimensional fluence model) to test whether a fluence-based approach can explain the results. Additionally, to get a deeper understanding of the process kinetics, the experimental results were integrated with thermal simulation results and the results correlate with process temperatures and temperature increase rates.
In a typical LINC process, a laser beam with power P is scanned across a polyimide sheet at a speed v with the sample surface at a distance z from the beam waist. In the varying speed studies hereof, the polyimide sheet was exposed to a spatial gradient of fluence by lasing a tilted sample of polyimide. This methodology enables different points on the linear lasing path to be exposed to different beam spots having different size and fluence. A schematic of the experimental setup, which is essentially the same as that of
The beam profile of the continuous CO2 laser (λ=10.6 μm) used for varying speed studies is once again depicted in
An example is shown in
The sample was lased at a constant power P=28 W at different beam speeds ranging between v=100 and v=500 mm/s, consisting of 11 lines as shown in
At slower speeds between v=270 and 100 mm/s, the T1 transition was observed with increasing fluence, however, with further increased fluence, a new, previously unreported transition was observed which is characterized with the gradual ablation of the cellular networks following the T1 transition. While ablated morphologies have been reported, the conditions governing their occurrence are not completely understood and are first reported in the present studies. The transition is demonstrated in
Using SEM and microscopy imaging, the locations of T1, T2 and T3 can be precisely identified along with the area averaged fluence values. These values can be used to investigate whether the occurrence of these thresholds is speed dependent and provide insight into the influence of process kinetics on the thresholds.
From SEM imaging of T3 in
MATLAB based edge detection techniques were used to detect the edge of ablations illustrated in the false-colored image in
To test the effect of T1 and T3 transition on resistivity, LINC electrodes were lased at flat conditions and their resistivity estimated from cross section area data at P=28 W and v=153 mm/s and v=270 mm/s and different defocusing values. The results are shown in
From the above analysis and experiments, a number of observations can be made. From the imaging it was observed that no fiber formations at speeds below v=300 mm/s. Additionally, it was observed that T1 is not strongly speed dependent at low speeds, in contrast with T2 which is speed dependent below v=500 mm/s indicating a kinetic influence. A new threshold for ablation of LINC along the lasing path was identified at low speeds starting at v=312 mm/s, revealing a hierarchical porosity with increased ablation. The fluence at ablation conditions is also identified revealing a speed dependence as well. It is clear that speed has a large influence on the LINC process due to the different kinetic conditions at equivalent fluence values. To get more insight into the influence of speed of the actual thermal kinetics, thermal FEM simulations of the tilted lasing were used. As set forth above, polymer lasing is a complex process with laser material interactions, phase and chemical transitions happening at different time scales and are extremely challenging to model accurately. The current model is significantly simplified. However, the model provides useful insight into the process kinetics. An objective of the model is to recreate the lasing conditions used in the experiments and identify the temperatures and temperature rates at points in the simulation corresponding to the locations of the experimentally identified thresholds.
A schematic of the model boundary conditions is shown in
The low speed dependence of maximum temperature for T1 (transition from porous to cellular networks) and T3 (Onset of ablation) indicates that these transitions are mainly controlled by temperature and not necessarily by temperature increase rate, implying energetic control at these conditions. To further elaborate on these results, those two transitions were correlated to two particular phenomenon: the graphitization of the polyimide (following carbonization) at T1 and the ablation of the formed graphite/graphene at T3. Previous studies have shown that graphitization of polyimide occurs at a temperature between 2500° C. and 3000° C. This would explain the appearance of the 2D peak at T1, which is associated with the onset of graphitization and the increase in degree of graphitic sheet stacking, and the observed drop in resistivity. This also explains the increased opacity observed under optical imaging. Additionally, ablation studies for graphite usually report that at a temperature of 3300° C. significant ablation is observed, even with CW laser-based heating studies. These temperature values are very close to the temperatures estimated by the simulations, and hence support the conclusions. The ablation is particularly clear at lower speeds due to the longer dwell times by the laser spot and the laser spot heat affected zone. Without limitation to any mechanism, this potentially explains why ablation is not apparent at speeds higher than 300 mm/s.
Alternatively, the results for the T2 transition (from cellular networks to woolly fibers). which show that the T2 transitions mainly occur at a rate around 0.8e7 and 1e7° C./s, suggest a temperature rate limited process at these conditions and illustrate the influence of kinetics on this transition. The transition to fibers has been suggested to be related to a number of phenomenon associated with the rapid rate of gas released, polyimide backbone bond stability and the mechanical properties of the polyimide.
To understand this transition and how it is different from the other transitions, it is useful to consider the physical phenomenon involved in the process leading to the jetting. Pore nucleation, pore growth due to reaction products, the viscoelastic nature of polyimide and the more brittle nature of graphitic materials. Typically, the phenomenon of jetting is studied and understood in terms of three dimensionless numbers: the Deborah number, Ohnesorge number and Weber number. Mckinley, G. H. Visco-Elasto-Capillary Thinning and Break-up of Complex Fluids. Rheol Rev. 2005, 3 (05), 1-48, the disclosure of which is incorporated herein by reference. The Deborah number is defined as the ratio of the characteristic relaxation time for a viscoelastic material (which typically decreases with increasing temperature) and the characteristic time scale for a process, which can be the time associated with the material response. Jones, T. J.; Reynolds, C. D.; Boothroyd, S. C. Fluid Dynamic Induced Break-up during Volcanic Eruptions. Nat. Commun. 2019, 10 (1), 3828. https://doi.org/10.1038/s41467-019-11750-4, 1-48, the disclosure of which is incorporated herein by reference. When the Deborah number is low, the material behaves more like a fluid. At a high Deborah number, the material demonstrates a more solid-like behavior. In the case of fiber formation, the response is driven by the rapid temperature increase (due to the shorter dwell times) and hence pressure increase in the pores due to the gases released during the process. At rapid temperature increases and higher gas release pressure, driven by a chemical reaction threshold which is likely governed by polyimide backbone stability, the Deborah number is likely to be very low. This is due to the shorter relaxation time of the polyimide and high pressure increase and release driven by the high temperature rates and short laser dwell times. At the low Deborah number and incomplete carbonization of the polyimide and gas release, the phase transitioning polyimide is likely to jet out, leading to fiber formations. The size and shape of the resulting jetting material are typically governed by the Ohnesorge number and Weber number. The Ohnesorge number represents the ratio between the viscous forces to inertial and surface tension forces. The Weber number represents the ratio between kinetic effects and surface tension effects for a droplet. These numbers, combined with other non-linear effects, decide whether the ejected material will form filaments/fibers or droplets as well as the size of the fibers. It is interesting that the LINC fibers exhibit filamentous shapes and interconnected webs with spherically shapes in between, which has also been observed in nonlinear viscosity jets seen with polymeric flows and sneeze jets. This phenomenon likely don't occur at the earlier transitions due to higher Deborah numbers, low gas release pressures and longer dwell times that graphitize the polyimide before the beam coincides with a point. If the dwell time is long and the heating rates are low, the material is likely to graphitize and lose its viscoelastic properties due to the phase change and hence no jetting would occur. This conclusion is further supported by the Raman spectrum of the nanocarbon fibers which are characterized by the disappearance of the 2D peak, indicating that the nanofibers are incompletely graphitized polyimide that are jetted prior to graphitization. Interestingly, this type of analysis have similarly been used to study jetting and fragmenting non-Newtonian fluids. Examples are the study volcanic magma bubble formation and fiber fragmentation, sneezing, ink jet printing, polymer fluids, some of which at certain conditions, can generate interconnected filaments like the nanofibers observed after the T2 transition in LINC.
Using a unique tilted lasing approach, insight was gained into the fundamentals of the process of laser induced carbonization of polyimide using continuous CO2 lasers. This unique methodology allowed identification the morphological transformations of LINC and correlating them with fluence values, Furthermore, the methodology allowed investigations of the effect of lasing speed, and hence process kinetics, on these morphological transitions. In addition to identifying how the fluence values at morphological transitions are affected by speed, a unique methodology to incorporate the experimental results with thermal simulations was developed to gain more insight on the process and identify whether a transition is energetically driven or kinetically driven. Using the simulation results combined with Raman and XPS analysis, it was determined that the two transitions, the transition from a porous to cellular morphology and the onset of ablation, are likely to reflect two physical phenomenon: the graphitization of polyimide and the ablation of the graphitized polyimide respectively. Those transitions are shown to be temperature dependent and the results agree with experimentally reported temperatures for such phenomenon. The cellular-to-fibrous networks transition was found to be mainly driven by the rate of temperature increase and it is proposed without limitation that it is the result of a decreased Deborah number combined with the rapid release of gas associated with the thermochemical stability of the polyimide. The resulting morphology is the result of the jetting of the incompletely carbonized polyimide, which acts like a non-Newtonian fluid jet which manifests with the formation of filaments and webs of nanocarbons.
LINC formation on polyimide. Polyimide tape (TAPECASE 2B, Cat. No. 15C616, tape thickness: 88.9 microns) was used as a substrate precursor for LINC formation experiments. To prepare for the experiments, the tape was place on silicon wafers, rinsed with acetone then Isopropyl alcohol for sample surface cleaning.
Direct laser irradiation on the polyimide sheets was conducted in air using a CO2 laser cutter/engraver system (Full Spectrum Laser Pro-Series 20×12, 1.5 inch focus lens) with 10.6 μm wavelength and 45 W power. The system allows tuning the power by controlling the laser current. We measure the laser power at different currents using a CO2 laser power meter (HLP-200, Changchun Laser Optoelectronics Technology Co., Ltd.). The beam radius was measured based on (1/e2) of the maximum intensity (wy, wx) at different distances (z) from the beam waist using the knife-edge method. Bilger, H. R.; Habib, T. Knife-Edge Scanning of an Astigmatic Gaussian Beam. Appl. Opt. 1985, 24 (5), 686, the disclosure of which is incorporate herein by reference. Using this technique, the beam radius at the beam waist (wox, woy), based on a Gaussian beam assumption, was determined to be 125.8 μm in the x-direction and 84 μm in the y-direction.
The laser objective lens is mounted on a motorized XY stage with a maximum speed of 500 mm/s in the X-direction. The beam spot size was controlled by adjusting the vertical distance (z) between the sample position and the beam waist; i.e. by moving the sample stage vertically with respect the objective lens. Laser power (P) was varied from 11.7 W to 30.7 W, and all experiments were performed at X-direction speed (v) of 500 mm/s and under ambient conditions.
In studies of lasing speed, lasing speed (v) was varied from 100 mm/s to 500 mm/s, and all experiments were performed at a power P=28 W and under ambient conditions.
Beam fluence model. The beam is modeled as a non-astigmatic elliptical Gaussian beam. The beam intensity is modeled using the following relationship (as illustrated in
where x and y are measured from beam center axis at distance z from the beam waist. Beam dimensions at defocusing level (z) are wx and wy (as illustrated in
Beam total power delivered at a spot with z vertical distance from the beam waist (estimated using thermopile measurements) is equal to the integration of the intensity over the laser spot in the horizontal plane (normal to the beam center axis), assuming complete absorption of the laser beam energy:
where wx and wy are the (1/e2) beam size.
This integration approximately gives the value of the maximum intensity:
where P is constant for different z's, however the wx and wy change.
The Gaussian beam size at different z values is estimated using the following equations (assuming the beam spot major and minor axis is aligned with the lasing direction x and y):
Where Mx2 and M2 are the beam quality factor for the x and y direction respectively, wox and Way are the beam waist dimensions (as illustrated in
The average flux Iav is estimated at a certain spot size for a laser power P, by averaging the intensity I(z) over the spot area A(z):
The average fluence F is then estimated using the following relationship:
F(z, v)=D(z, v)Iav(z)
where D(z,v) is the dwell time of the laser beam over a spot. The dwell time is estimated by dividing the beam length in the lasing direction x by the beam speed v.
The average fluence of the beam on a tilted surface is shown to be approximately equal to the untilted surface average fluence for our ranges of the tilting angle ψ.
The influence of speed on dwell time is shown in
2D Distribution of fluence model. The laser beam flux (I) is expressed at a point (x, y) at the laser beam focus and time (t) using scanning in the x-direction with speed (v) according to the following expression:
where P is the laser beam power, wox and woy is the beam waist size, v is the beam velocity and Lx is the lasing length in the x-direction.
To estimate the fluence at a point, the x and y-values are fixed at a point (xo,yo) and the flux is integrated over time using the following expression:
F(t)=∫0∞I(xo, yo, t)dt
If this value is estimated at different y-values perpendicular to the laser path, the fluence (F) delivered across the sample can be estimated due to a single laser path.
Characterization of LINC. SEM images of the LINC formations were taken on a Zeiss SIGMA VP Field emission scanning electron microscope. The samples were sputter coated with platinum and then imaged with a beam with an accelerating voltage of 2 kV. A XplorA Raman-AFM/TERS system microscope using 473-nm laser excitation at room temperature with a laser power of 25 mW was employed to obtain Raman spectra. XRD was conducted on a Bruker D8 Discover SRD X-ray diffractometer with Cu Kα radiation (A=1.54 Å). The LINC samples for XRD, were scratched from LINC lines. XPS analysis was performed using a Thermo Fisher ESCALAB 250 Xi XPS at a base pressure of 5e-9 Torr. All of the survey spectra were recorded in 1 eV step size. Elemental core spectra were recorded in 0.1 eV step sizes. All the spectra were corrected using C1s peaks (284.5 eV) as references. The resistance of the LINC lines were measured using a Keithley two-point probe meter (model: 2100, detection limit: 100 MO). LINC lines of lengths 15 mm are lased in the polyimide at different z values. Each value of z and power is replicated three times. A nickel paste (PELCO® Conductive Nickel Paint) was applied to the LINC lines at the measurement spots area for better contact with the probe terminals. The resistance at different lengths of LINC are measured and averaged from the three replications and used to estimate the R/L values for the LINC lines.
In variable speed studies, the resistivity of LINC are measured and averaged and the cross-sectional area is measured to estimate bulk resistivity. To identify the edge of onset of ablation, the local graph cut method in the image segmenter tool in MATLAB® was used.
Simulation of laser heating using ANSYS APDL. The laser heating of polyimide films was simulated in ANSYS APDL. In the simulations, the properties of polyimide were assumed to be temperature dependent to incorporate the influence of carbonization and graphitization. The model geometry of polyimide were defined as (thickness: 50 um, width: 1 mm, Length: 20 mm). Further details are presented in the supporting information.
The foregoing description and accompanying drawings set forth a number of representative embodiments at the present time. Various modifications, additions and alternative designs will, of course, become apparent to those skilled in the art in light of the foregoing teachings without departing from the scope hereof, which is indicated by the following claims rather than by the foregoing description. All changes and variations that fall within the meaning and range of equivalency of the claims are to be embraced within their scope.
This application claims benefit of U.S. Provisional Patent Application Ser. No. 63/140,463, filed Jan. 22, 2021, and U.S. Provisional Patent Application Ser. No. 63/285,365, filed Dec. 2, 2021, the disclosures of which are incorporated herein by reference.
This invention was made with government support under grant no. 2028580 awarded by the National Science Foundation. The government has certain rights in this invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2022/013459 | 1/24/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63140463 | Jan 2021 | US | |
| 63285365 | Dec 2021 | US |
