KR102468350B1 - A ciliated graphene composite, the method for manufacturing the same, and a triboelectric nanogenerator comprising the same - Google Patents

Abstract

In the present specification, a porous graphene structure; and a plurality of graphene cilia spaced apart from each other on the surface of the porous graphene structure.

Description

Ciliary graphene composite, manufacturing method thereof, and triboelectric nanogenerator including the same

Disclosed herein is a ciliary graphene composite, a method for preparing the same, and a triboelectric nanogenerator including the same.

Due to the development of wearable electronic devices and the emergence of flexible electronic devices, there is an increasing demand for a power supply capable of supplying stable energy thereto. Accordingly, research on triboelectric nanogenerators using a surface charge induction method generated from friction between different materials is being continuously conducted.

The concept of generating electrical energy using surplus power generated by the human body or nature is attracting attention as a next-generation power supply because it does not require periodic charging. In addition, since it can be manufactured using various materials, it is easy to manufacture a power supply having flexibility suitable for wearable devices.

Currently, graphene has been studied as a representative candidate material for triboelectric nanogenerators due to its high electron mobility, thermal stability, flexibility, and chemical stability.

However, conventional graphene synthesis methods, chemical vapor deposition, and mechanical exfoliation methods require high-temperature processes and sensitive synthesis conditions, and have disadvantages in that large-area synthesis is difficult. In addition, synthesized graphene requires additional processes such as transfer or patterning for application to desired fields. Contamination and material defects generated in this process significantly degrade the excellent properties of the material, limiting desired applications.

Additionally, processes such as surface modification and chemical structure modification are required to improve triboelectric efficiency. This limits the application of graphene as a triboelectric nanogenerator.

Accordingly, there is an increasing need for a technique for forming a graphene-based composite having a ciliary structure using a local annealing method and applying it to a nanogenerator.

One aspect of the present invention is to provide graphene with a three-dimensional structure that can be rapidly synthesized in a large area and can be synthesized and patterned at the same time by applying a laser-induced synthesis method rather than a conventional graphene synthesis method, thereby providing disadvantages of conventional synthesis methods. want to complement

In addition, it is intended to increase the efficiency of the triboelectric nanogenerator without additional surface modification, chemical structure modification, etc., and to minimize the time required for fabrication compared to the existing graphene-based triboelectric nanogenerator.

In one embodiment according to the present invention to achieve the above object, a porous graphene structure; and a plurality of graphene cilia spaced apart from each other on the surface of the porous graphene structure.

In one embodiment, the plurality of graphene cilia may be vertically aligned on a porous graphene structure.

In one embodiment, the graphene may be laser induced graphene oxide.

In one embodiment, the graphene cilia may have a length of 100 μm or more.

In one embodiment, the ratio of the peak intensity (I _D ) in the range of 1300 to 1400 cm ^-1 and the peak intensity (I _G ) in the range of 1500 to 1600 cm ^-1 measured in the Raman spectroscopy spectrum I _D /I _G is 0.8 to You can have it with 1.1.

In one embodiment, the ciliary graphene composite may have an a-axis crystal size (L _a ) calculated by Equation 1 of 10 - 20 nm.

[Equation 1]

L _a = (2.4Х10 ^-10 )×λ _l ⁴ ×(I _G /I _D )

Here, λ _l is the wavelength of the Raman laser, I _G is the intensity of the G peak, and I _D is the intensity of the D peak in the Raman spectroscopic spectrum.

In one embodiment, the ciliary graphene composite may include pyrrolic nitrogen and graphitic nitrogen structures.

In one embodiment, the ciliary graphene composite may have an oxygen (O) content of 5% or less and a nitrogen (N) content of 1% or more based on X-ray photoelectron spectroscopy (XPS) analysis.

In one embodiment, the ciliary graphene composite may have a graphitic nitrogen content of 1% or more based on X-ray photoelectron spectroscopy (XPS) analysis.

In another embodiment according to the present invention, irradiating a laser on the graphene precursor material along the laser irradiation path; including, forming a laser spot at the intersection of the laser irradiation path and the graphene precursor material, an island A method for preparing a model graphene composite is provided.

In one embodiment, adjusting the diameter of the laser spot by adjusting the working distance (WD) in the z-axis direction based on the focal plane located on the irradiation path; may further include.

In one embodiment, the power and scan speed of the laser may have specific fixed values.

In one embodiment, the power density of the laser may be 10 to 100 W/mm ² .

In another embodiment of the present invention, a triboelectric active layer comprising the above-described ciliary graphene composite; and a counter material layer disposed to face the ciliary graphene composite.

In one embodiment, the counter material may include one or more of PMMA, PET, acrylics, LIGs, PDMS, PVC, and PTFE.

In one embodiment, a spacer separating the triboelectroactive layer and the counter material layer may be further included.

In one embodiment of the present invention, graphene with a three-dimensional structure was fabricated using a laser-induced synthesis method capable of rapid, large-area synthesis and patterning at the same time, and was applied to a triboelectric nanogenerator.

Laser-induced graphene synthesized according to this method has high conductivity, thermal stability, and flexibility, so it can extremely compensate for the disadvantages of existing graphene synthesis methods.

In addition, it has the advantage that the process of surface modification and chemical structure modification to increase triboelectric efficiency can be solved at once through a single-step synthesis process, which reduces the time required for production compared to the existing graphene-based triboelectric nanogenerator. can be extremely minimized.

Accordingly, the triboelectric nanogenerator according to the embodiment of the present invention has the potential to be applied to various application fields such as wearable electronic touch sensors, flexible touch pads, and human motion monitoring.

1A shows a schematic diagram of a single step synthesis of LIG according to an embodiment of the present invention.
Figure 1b shows an SEM image illustrating the nanostructured morphology of the LIG surface as a function of the working distance.
1C shows a SEM image of a cross-section of a LIG according to an embodiment of the present invention.
Fig. 1d shows the trend of the size of the laser spot as a function of the working distance.
FIG. 1e is a graph showing a comparison of laser power density and sheet resistance according to working distance. FIG. 2a shows Raman spectra of LIGs having various nanostructures.
Figure 2b is a Raman spectrum of LIGs according to an embodiment of the present invention, showing the results of plotting the D and G peaks with a 5-peak model.
Figure 2c shows a graph showing the trend of the crystal size of LIG according to the morphology of the nanostructure.
Figure 2d is a graph showing the comparison of the ratio of carbon, nitrogen, and oxygen atoms by X-ray photoelectron spectroscopy (XPS) analysis of the LIG manufactured by varying the working distance according to an embodiment of the present invention.
Figure 2e shows the results of X-ray photoelectron spectroscopy (XPS) analysis of LIGs according to an embodiment of the present invention.
2F shows the deconvolved N1s core level spectrum of LIGs according to an embodiment of the present invention.
Figure 2g shows the deconvolved N1s core level spectrum of LIGs according to an embodiment of the present invention.
2H shows a UPS spectrum around the secondary electron critical region of LIGs according to an embodiment of the present invention.
2i shows an energy band diagram at the LIG/PMMA interface.
3A shows a schematic diagram of a LIG-based TENG according to an embodiment of the present invention.
3B is an analysis result obtained by inducing surface charge by performing a contact/separation motion on the surface charge potential of LIG and dielectric material candidates according to an embodiment of the present invention.
3C shows a schematic diagram of an operating mechanism of a TENG based on LF-LIG to which LIG is applied according to an embodiment of the present invention.
3D shows electrical output signals according to press/release operations of counter material candidate materials.
Figure 4a shows the electrical energy generation results of LIG-TENG applying three types of nanostructures.
Figure 4b shows the average voltage and current values of the generated LF-LIG TENG as a function of load resistance.
Figure 4c compares the output power density according to the load resistance in the LIG-TENG applied with three types of nanostructures.
4D shows the result of comparing the electrical output performance when the counter material is changed in the LF-LIG based TENG to which the LIG according to the embodiment of the present invention is applied.
Figure 4e shows the results of performing a cycle stability test of the LF-LIG TENG according to an embodiment of the present invention.
Figure 4f shows a schematic diagram of a power supply circuit to which the LF-LIG TENG is applied according to an embodiment of the present invention.
Figure 4g shows the capacitor charging test results of LIG-TENG with three types of nanostructures applied.
5A shows a schematic diagram of a laser-induced graphene-based touch sensor in accordance with an implementation of the present invention.
5B shows a result of measuring the output performance of a single pixel to confirm the operability of the laser-induced graphene-based touch sensor according to an embodiment of the present invention.
5C shows results of measuring electrical signals output by various finger touch events in the laser-induced graphene-based touch sensor according to an embodiment of the present invention.
FIG. 5D shows an image represented by mapping a drag motion to a response according to a signal generation sequence in each pixel.
5E shows a real-time output signal for each pixel of a 4x4 matrix, a drag direction, etc. as a result of performing a continuous drag operation in a laser-induced graphene-based touch sensor according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in more detail.

The embodiments of the present invention disclosed in the text are illustrated for purposes of explanation only, and the embodiments of the present invention may be implemented in various forms and should not be construed as being limited to the embodiments described in the text. .

The present invention can have various changes and can have various forms, the embodiments are not intended to limit the present invention to a specific disclosed form, and all changes, equivalents or substitutes included in the spirit and technical scope of the present invention It will be understood to include.

Singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, the terms "include" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that the presence or addition of numbers, steps, operations, components, parts, or combinations thereof is not precluded.

Ciliary graphene composite

In order to solve the problem as described above, in one embodiment according to the present invention, the porous graphene structure; and a plurality of graphene cilia spaced apart from each other on the surface of the porous graphene structure.

In an exemplary embodiment, the plurality of graphene cilia may be vertically aligned on a porous graphene structure. Specifically, a plurality of vertically aligned nanofibers may have a structure completely covering the surface. This structure can increase the surface area of the composite, improve the sheet resistance, and increase the triboelectric efficiency.

In an exemplary embodiment, the graphene may be laser induced graphene oxide. Such laser-induced graphene oxide may be derived from a graphene precursor material such as PI.

In an exemplary embodiment, in the case of a graphene composite having a ciliary shape including graphene cilia, the contact area may be increased, which may be advantageous for triboelectric power generation. Therefore, as the length of the graphene cilia increases, the contact area may significantly increase, and at this time, the effect of generating triboelectricity may increase rapidly. On the other hand, when the structure of the graphene composite is close to planar or the length of graphene cilia is short, there may be a disadvantage in the contact area, and thus the effect of generating triboelectricity may be reduced.

Specifically, the graphene cilia may have a length of 100 μm or more. When the length of the graphene cilia is less than 100 μm, triboelectric efficiency may be reduced due to a decrease in surface area. On the other hand, the composite may exhibit a D peak of about 1350 cm ^-1 , a G peak of about 1580 cm ^-1 , and a 2D peak of about 2700 cm ^-1 measured in a Raman spectroscopy spectrum, from which the presence of graphic carbon can be confirmed. have.

In an exemplary embodiment, the ratio of the peak intensity (I _D ) in the range D of 1300 to 1400 cm ⁻¹ and the peak intensity G in the range 1500 to 1600 cm ⁻¹ (I _G ) measured in the Raman spectroscopy spectrum, I _D /I _G may have in the range of 0.7 to 1.1, for example, may be 0.8 or more, 0.9 or more, or 1.0 or more, and may be in the range of 0.7 to 0.8 or 1.03 to 1.05. Specifically, it may range from 0.7 to 1.05 in the case of the ciliary graphene composite, from 0.7 to 0.8 if the length of the graphene cilia is less than 100 μm, and if the length of the graphene cilia is greater than 100 μm (eg, 250 μm). or more), and may have an I _D /I _G value range from 1.03 to 1.05. For example, the composite may have a wider D peak and a G peak as the cilia length increases, and accordingly, the I _D /I _G ratio gradually increases, for example, from 0.5 (LIG) to 1.05 (LF-LIG). can do.

In an exemplary embodiment, the ciliary graphene composite may have an a-axis crystal size (L _a ) calculated by Equation 1 of 10 - 20 nm.

[Equation 1]

L _a = (2.4Х10 ^-10 )×λ _l ⁴ ×(I _G /I _D )

Here, λ _l is the wavelength of the Raman laser, I _G is the intensity of the G peak, and I _D is the intensity of the D peak in the Raman spectroscopic spectrum. As the graphene ciliary structure is strengthened, additional defect activation sites may occur, which may cause a decrease in the I _G / _ID peak ratio. In this case, the calculated a-axis crystal size may also decrease together. This difference in crystallite size may be caused by interstitial doping of heteroatoms as well as effects due to amorphous carbon such as stacking faults and lattice symmetry breaking.

In addition, the ciliary graphene composite may include one or more structures of pyridinic nitrogen (Pyridinic N), pyrrolic nitrogen (Pyrrolic N), and graphitic nitrogen (Graphitic N) structures.

In an exemplary embodiment, when the porous graphene structure predominates in the composite, it may contain a large number of oxygen-related functional groups and have a small amount (~0.4%) nitrogen content, which is mostly present at pyrrolic positions (0.32%). However, as the graphene ciliary structure is strengthened, it may have a graphene structure in which oxygen content is low but more than half of the total nitrogen content (~2%) is present in the graphitized position (1.04%).

Specifically, in the case of graphene (LIG), which does not have a graphene ciliary structure and has a porous graphene structure, the content of pyridinic N, pyrrolic N, and graphitic nitrogen may have a nitrogen content as low as about 0.4%, with 0.023%, 0.32%, and 0.04%, respectively. As the graphene cilia structure is strengthened, for example, in the case of the composite (SF-LIG) in which the length of the graphene cilia is less than 100 μm, the contents of pyridinic nitrogen, pyrrolic nitrogen, and graphic nitrogen are respectively 0.008%, 0.77%, and 0.77%, respectively. and 0.21% for a total nitrogen content of about 1.0%. In the case of the composite (LF-LIG) in which the length of the graphene cilia is greater than 100 μm (preferably greater than 250 μm), the graphene nitrogen structure is further strengthened, and the contents of pyridinic nitrogen, pyrrolic nitrogen, and graphic nitrogen are 0.16%, 0.71%, and 1.04%, respectively, for a total nitrogen content of about 2.0%. Accordingly, the ciliary graphene composite may have a graphitic nitrogen content of 1% or more based on X-ray photoelectron spectroscopy (XPS) analysis, and may have excellent triboelectric efficiency.

For example, the ciliary graphene composite may have an oxygen (O) content of 5% or less and a nitrogen (N) content of 1% or more or a nitrogen (N) content of 2% or more based on X-ray photoelectron spectroscopy (XPS) analysis. can In the case of having such a low oxygen content and a high nitrogen content, a graphitic nitrogen structure can be developed and excellent triboelectric efficiency can be obtained. In particular, in the case of the graphene ciliary structure-reinforced composite, the conductivity may be lower than that of the case where the porous graphene structure predominates, but may contain a large number of graphene nitrogen components and have a low work function (Φ = 4.62 eV). , improved triboelectric charging efficiency can be obtained.

Manufacturing method of ciliary graphene composite

In another embodiment according to the present invention, irradiating a laser on the graphene precursor material along the laser irradiation path; including, forming a laser spot at the intersection of the laser irradiation path and the graphene precursor material, an island A method for preparing a model graphene composite is provided.

First, a graphene precursor material may be prepared, and the graphene precursor material may have various shapes. For example, the graphene oxide precursor material may have the form of a sheet, film, thin film, pellet, powder, block, monolith block, composite, component, electronic circuit board, or flexible substrate or rigid substrate. It is not limited.

In addition, the graphene precursor material is polyimide, polyetherimide, polyetherketone, polyethylene terephthalate, polyethylene naphthalate, fluorinated ethylene propylene, perfluoroalkoxy alkane, Teflon, polystyrene, polycarbonate, polyethylene, polyvinyl alcohol , poly (methyl methacrylate), acrylonitrile butadiene styrene, and may be at least one selected from the group consisting of poly (acrylonitrile), but is not limited thereto.

In an exemplary embodiment, a focusing lens may be positioned on the irradiation path. A laser passing through a focusing lens may have a conical energy distribution, and laser process parameters such as a laser spot size, overlapping area, and power density may be controlled by adjusting a working distance.

In an exemplary embodiment, adjusting the diameter of the laser spot by adjusting the working distance (WD) in the z-axis direction based on the focal plane located on the irradiation path; may further include. Specifically, the diameter of the laser spot can be minimized at the focal plane (WD=0), and a defocus effect can be obtained by moving in (+) and (-) directions in the z-axis direction based on the focal plane. In this way, when the focus of the laser is defocused, the size of the laser spot may increase.

In an exemplary embodiment, the power and scan speed of the laser may have certain fixed values. That is, laser process parameters such as laser spot size, overlapping area, and power density may be controlled by fixing the laser power and scan speed to specific values and then adjusting the working distance of a substrate such as a graphene precursor material.

In an exemplary embodiment, the power density of the laser may be 10-100 W/mm ² . Preferably, the power density of the laser may be 40-80 W/mm ² or 60-80 W/mm ² . When the laser power density is less than 10 W/mm ² , porous graphene may be formed instead of a fibrous structure, and when it exceeds 100 W/mm ² , the fiber structure may be collapsed. In particular, when having a laser power density of 60 W/mm ² or more, a graphitic nitrogen structure can be developed and excellent triboelectric efficiency can be obtained.

triboelectric nanogenerator

In another embodiment of the present invention, a triboelectric active layer comprising the above-described ciliary graphene composite; and a counter material layer disposed to face the ciliary graphene composite. A triboelectric nanogenerator (TENG) is provided. An external force is applied to the triboelectric active layer or the counter material layer, and triboelectricity may be induced therethrough.

In an exemplary embodiment, the ciliary graphene composite may serve not only as an electrode for directly collecting generated charges, but also as an active layer for inducing triboelectricity by contacting the counter material.

In one embodiment, the counter material may include one or more of PMMA, PET, acrylics, LIGs, PDMS, PVC, and PTFE. Each of the counter materials may have a unique charge potential value, and as a result, characteristics of a triboelectric output signal generated when in contact with the LIG may vary. Preferably, the counter material may include PMMA, PET, or acrylic, and, for example, PMMA may have optimal output performance.

In one embodiment, a spacer separating the triboelectroactive layer and the counter material layer may be further included.

Example

Hereinafter, the configuration and effects of the present invention will be described in more detail by way of examples. However, these examples are provided only for illustrative purposes to aid understanding of the present invention, and the scope and scope of the present invention are not limited by the following examples.

Example 1: Laser Induced Graphene (LIG) Fabrication

Laser-induced graphene was prepared on the surface of a commercial polyimide film (PI, Isoflex, thickness: 150 μm) by irradiating a 9.3 μm CO 2 continuous laser (30 W) mounted on an XLS 10 MWH (Universal Laser System).

The laser scan speed and laser power were fixed at 5mm/s and 220mW, respectively, and the laser spot size and power density were controlled by controlling the working distance (WD) from the focal plane (WD=0mm) to ±0.9~1.2mm. Adjusted. The laser spot diameter at the focal plane was 0.003 mm ² , and the effective laser power density for each working distance condition was calculated by measuring the laser power on the sample surface with a power meter (Coherent).

On the other hand, Figure 1a shows a schematic diagram of the single-step synthesis of LIG in Example 1. Since the laser passing through the focusing lens has a conical energy distribution, it is possible to precisely control laser process parameters such as laser spot size, overlapping area, and power density by adjusting the working distance. The size of the laser spot on the PI film is minimized on the focal plane, and when the PI film is moved in the (+) and (-) directions in the z-axis direction based on the focal plane, the size of the laser spot is larger due to the defocus effect. will lose

Experimental Example 1: Laser Induced Graphene (LIG) Analysis

SEM analysis

The laser-induced graphene of Example 1 has a unique nanostructure, which is related to the separation of individual laser pulses. The nanostructure of the prepared laser-induced graphene was analyzed with a scanning electron microscope (SEM, APERO, FEI).

The surface morphology of each type of LIG was characterized by SEM as shown in Fig. 1b. The left image of FIG. 1B is a LIG manufactured with a working distance of 1.2 mm, and it can be seen that it has a flat surface composed of only a porous structure ('LIG'). This structure corresponds to a structure similar to a conventional LIG.

By adjusting the working distance, as the PI film approaches the focal plane, it has a vertically arranged ciliary structure on top of the porous structure ('SF-LIG'). When the PI film is placed on the focal plane (WD = 0) by further adjusting the working distance, it can be seen that when the substrate is placed on the focal plane, numerous vertically aligned nanofibers with a length of several hundred micrometers completely cover the surface ( 'LF-LIG').

Such a nanostructure can be confirmed as a cross-sectional image in FIG. 1c. In the cross-sectional SEM image, it can be seen that the surface has a structure composed of graphene fibers and a porous conductive LIG is formed below it.

Laser spot size analysis

As confirmed through SEM analysis, it was confirmed that the structure of graphene changes depending on the working distance. The effective laser spot size and laser power density according to the working distance were investigated to identify the main factors determining the shape change. The working distance was controlled by adjusting the stage height (−0.9 mm≤WD≤+1.2 mm) of the PI film while keeping the laser power (220 mW) and scan speed (5 mm/s) constant. The effective laser spot size was measured by the line width of the LIG formed on the PI by laser irradiation.

Figure 1d shows the trend of the size of the laser spot according to the working distance, and schematically shows the structure of the LIG accordingly. In addition, the power density was calculated from the measurement information and is shown in Fig. 1e.

The laser spot area at the focal point is minimized (~0.003mm ² ), and at this time, the laser power irradiated per unit has a maximum value of about 70W/mm ² . As such, when the PI substrate is located on the focal plane (WD = 0mm), the fiber LF-LIG nanostructures with a surface morphology dominated by G were synthesized.

When the focus is defocused by adjusting the working distance in the z-axis direction, it has a laser spot size of 0.01 to 0.02 mm ² , which is about 3 to 6 times larger than the laser spot size in the focal plane, and the laser power density at this time is 23 ~ 10 W/mm ² , which is approximately 2.5 to 7 times lower.

That is, a large amount of energy per unit area can be irradiated to a narrow area near the focal plane. However, when the absolute value of the working distance increases, the size of the laser spot increases, but the focus is defocused and the amount of energy per unit area on the substrate decreases. Therefore, synthesis at a low power density (less than 15 W/mm ² ) induces a general porous LIG structure, while the surface structure can be controlled by adjusting the working distance to have a power density of 65 to 70 W/mm ² . .

sheet resistance analysis

The sheet resistance characteristics of the sheets of the three types of LIGs described above were evaluated through 4-point probe measurement. Sheet resistance was measured with an automatic sheet resistance meter (ARMS-600).

As can be seen in Figure 1e, it can be seen that the structure composed only of porous LIG has excellent conductivity (RLIG: 31.57 ± 6.59 Ω/sq). However, the resistances of the 'SF-LIG' and 'LF-LIG' samples were measured to be 50.63±1.76 and 78.87±2.30 Ω/sq, respectively, showing a tendency to increase compared to the porous LIG structure.

This can be interpreted that the LIG forming the entangled network structure acts as a more favorable current path for charge transport than the SF-LIG and LF-LIG having a one-dimensional vertically aligned fiber structure. The surface structure and sheet resistance uniformity of each synthesized LIG can be confirmed in Table 1 below.

Sample # Height (μm) Sheet Resistance (Ω/sq) - LIG SF-LIG LF-LIG LIG SF-LIG LF-LIG One 7 98 292 33.48 52.49 76.15 2 6 114 283 42.08 52.77 77.79 3 5 111 264 27.43 50.39 78.69 4 6 90 264 28.90 50.97 77.99 5 7 91 256 26.65 48.72 81.44 6 5 96 298 24.84 48.42 76.05 7 8 96 278 34.24 48.38 82.82 8 5 98 259 32.56 49.88 77.33 9 6 102 288 23.49 51.50 81.29 10 5 104 294 42.06 52.81 79.11 Average 6 100 277.6 31.57 50.63 78.87 Standard Deviation ±1.1 ±7.87 ±15.68 ±6.59 ±1.76 ±2.30

Raman spectrum

Material crystallinity characteristics were analyzed by Raman spectroscopy (Lab Ram GR, Horiba, 514 nm) in the range of 1,000 to 3,000 cm ^-1 .

Figure 2a shows the Raman spectra of LIGs with various nanostructures. All LIG nanostructures show three main peaks: a D peak of ~1350 cm ^-1 , a G peak of ~1580 cm ^-1 , and a 2D peak of ~2700 cm ^-1 in the Raman spectrum in the range of 1,000 to 3,000 cm ^-1 . Through this, it is possible to confirm the presence of graphic carbon in the manufactured LIG.

The general LIGs synthesized in the out-of-focus region with working distances of -0.9 mm and 1.2 mm show low D peak intensities and high G and 2D peak intensities. In addition, as the working distance approaches the focal plane to form a fiber structure (SF-LIG and LF-LIG), the D and G peaks broaden, and accordingly, the I _G /I _D ratio is observed to decrease gradually. do.

The change in the Raman peak can be explained as an effect due to the different power densities of the irradiated lasers in the synthesis of each LIG.

When the D and G peaks are plotted with a 5-peak model for more specific causal analysis, the Raman spectrum of LIG displays sharp D and G peaks with low intensity of the D′ peak, whereas the D* and D** peaks are shown in Fig. 2b. Not observed as clearly as indicated. On the other hand, in the fibrous structure, it has clear D* and D** peaks and high D peak intensity, which is due to the breakdown of lattice symmetry (D' related) in the fibrous structure, as well as amorphous carbon (D*) and stacking faults. This means that more defects due to (D**) are included than in the LIG structure.

Crystal size analysis

The crystal size was analyzed to confirm the detailed characteristics of LIG. The a-axis crystal size (La) of each LIG was calculated using the intensity ratio of the G peak and the D peak as a variable using Equation 1 below.

[Equation 1]

L _a = (2.4Х10 ^-10 )×λ _l ⁴ ×(I _G /I _D )

Here, λ _l is the wavelength of the Raman laser (λ _l =514 nm).

As shown in Fig. 2c, the crystallite size of LIG showed a clear trend depending on the morphology of the nanostructure. In the case of porous LIG ('LIG'), a crystallite size larger than the fibrous structure at ~32 nm was induced. As the working distance decreased and the fibrous structure was created, additional activation sites were generated, and the peak ratio of I _G / _ID gradually decreased from 1.83 to 0.95. This means that the crystal size of the LF-LIG sample was minimized to 16 nm, half of that of the LIG sample. The difference in crystallite size is caused by interstitial doping of heteroatoms as well as effects caused by amorphous carbon such as stacking faults and lattice symmetry breaking, as analyzed by Raman spectroscopy.

XPS analysis

The ratio of carbon, nitrogen and oxygen atoms was analyzed by X-ray photoelectron spectroscopy (K-alpha).

As a result of analyzing the content of the three major atoms (carbon, oxygen, and nitrogen) of LIG, it was confirmed that the elemental composition ratio changed according to the change in the shape of the LIG nanostructure, as shown in Fig. 2d.

First, it was confirmed that the carbon content in each nanostructure was similar at about 93%.

However, there is a difference in the relative ratio of oxygen and nitrogen content. N and O elements have been reported to be self-supplied during LIG synthesis as PI substrates with abundant C–O, C=O, and C–N bonds are thermally decomposed (Fig. 2e).

A high oxygen content (5.4–7.35%) was detected in LIG, which decreased in the presence of a fibrous structure and was therefore minimized in LF-LIG, showing a value of 4.1%. In contrast, it was confirmed that the nitrogen content tended to gradually increase as the fiber type became richer.

Figure 2f shows deconvoluted N1s core-level XPS spectra depending on the morphology. While pyrrolic N dominates in LIG, the graphitic N ratio increases with the formation of a fibrous structure, which means that the high-intensity nitrogen peak in LF-LIG originates from the graphitic N composition.

The detailed carbon (C1s), oxygen (O1s), and nitrogen (N1s) core level peaks for each LIG are shown in Fig. 2g. Through this, it was confirmed that LIG contains a number of oxygen-related functional groups and a small amount of nitrogen of less than 2% is located in pyrrolic. It was confirmed that LF-LIG has a lower oxygen content than LIG, but has a relatively large amount of nitrogen atoms present mostly at graphite positions.

On the other hand, although such N element doping tends to improve the graphene carrier concentration, it can be seen in Fig. 1e that the conductivity of LF-LIG is lower than that of LIG, which means that the vertically oriented conductive fibers This is because the conductivity of the LF-LIG is limited by a structure that is unfavorable to charge transport in the direction.

work function analysis

The compositional change as a function of the work function of the LIG was calculated based on the analysis of ultraviolet photoelectron spectroscopy (UPS) (Escalab 250Xi, He 21.2 eV).

Figure 2h shows the UPS spectrum around the secondary electron critical region of each LIG sample. For more accurate analysis, the work function was calculated by the equation WF = hv - (E _cutoff - E _fermi ) after correcting the location of the Fermi level using a gold film.

As a result, as expected, it was confirmed that the work function of LIG containing oxygen was 5.08±0.06 eV, slightly higher than that of undoped pure graphene.

According to a prior report, since oxygen-containing functional groups such as carbonyl, epoxy, and hydroxyl groups tend to withdraw electrons from graphene, oxygen-containing LIGs may have a higher work function due to the doping effect. More importantly, when the fiber structure became dominant, the work function value decreased to 4.62 ± 0.03 eV. Considering the XPS results in Fig. 2f together, the graphical N component of LF-LIG with 5 valence electrons It appears to reduce the work function by electrons because it prefers to transfer electrons to surrounding carbon atoms.

Based on these experimental results, as shown in FIG. 2i, it is possible to predict the transfer effect of triboelectricity when LIGs having various surface structures come into contact with polymer materials. When a counter material with a low Fermi level is assumed as such a polymer material, LF-LIG can generate a larger work function difference than other nanostructures and can effectively exchange a large number of charges with the polymer.

Example 2: Fabrication of laser-induced graphene-based triboelectric nanogenerators (TENGs)

The LIG of the example was prepared on a PI film of 60 × 60 mm in size. During the LIG manufacturing process, the LIG formed a flexible film with a curved structure by the heat induced by the irradiated laser. In addition, a contact layer having a double-layer structure was prepared by laminating copper electrodes with PMMA, PET, acrylic, PI, PDMS, PVC, and PTFE as triboelectric counter materials, respectively.

The prepared flexible film and the contact layer were fixed to the acrylic substrate, the two triboelectric layers were fixed to the acrylic substrate and fixed with two PI films (70x40mm) to form a space between the two layers, and the alligator clip was placed on the opposite layer of LIG and copper. Triboelectric nanogenerators (TENGs) were fabricated by fixing them to electrodes and forming a path through which charges could be transferred to a measurement system.

A schematic diagram of the fabricated LIG-based TENG is shown in Fig. 3a. TENG consists of three main parts (namely, LIG/PI, counter material/Cu/substrate, and spacer). In this structure, LIG serves as an electrode to directly collect the generated charge as well as an active layer in contact with the counter material. also plays the role of

Experimental Example 2: Performance Analysis of Triboelectric Nano Generators (TENGs)

The triboelectric nanogenerators (TENGs) prepared in Example 2 were mounted in the vibrator chamber to apply a uniform frequency and pressure, and the press/release frequency and pressure were interlocked composed of a function generator (Agilent 33220A) and a power amplifier (Labworks). controlled precisely by the system. Output voltage performance was measured with an oscilloscope (Tektronix, DPO 5204B).

The surface charge potential of dielectric material candidates (PMMA, PET, acrylic, LIGs, PDMS, PVC, PTFE) and LIG were analyzed by inducing surface charge by performing contact/separation motions using a charge electrometer.

As shown in Fig. 3b, compared to PI, PMMA, PET, acrylic, LIG, SF-LIG and LF-LIG showed positive and negative charge values of 1.05, 0.77, 0.41, 0.15, 0.09 and 0.04 kV, respectively. In particular, values of -0.55, -0.68, and -0.83 kV were induced in PDMS, PVC, and PTFE, respectively, and when comparing the relative charge potentials between LIGs, it can be seen that more negative charge potentials are induced by the fiber structure.

To further verify this, the trend of the output signal was observed to confirm the relative charging polarity of the LIG with respect to the counter material. Figure 3d shows the triboelectric series of counter materials used, classified from left to right in the order of triboelectric electrification through contact and materials having characteristics of being prone to negative electric charges when generated.

The operating mechanism of the TENG is shown in Fig. 3c. Specifically, the counter material contacts the TENG in a pressing and releasing operation, and as a result, frictional charges are transferred, and thus (+) and (-) output voltage signals are sequentially generated. . At this time, a negative voltage signal indicates the current flow from the counter material side to the LIG, and a positive voltage signal indicates the current flow from the LIG to the counter material side of the electrode. As a result, LIG-based TENGs using PTFE, PDMS, PVC or PI counter materials showed that a negative output signal was first generated in the push step followed by a positive signal in the release step. Conversely, when acrylic, PET, or PMMA is applied as a counter material, a positive output signal occurs before a negative output signal, indicating that the LIG conducts electricity through the cathode when in contact.

Therefore, LF-LIG/PMMA can be selected as an optimal combination due to the high roughness and low work function of LF-LIG and the large charge potential difference between them.

Meanwhile, the electric energy generation results of three types of LIG-TENG according to the nanostructure of the LIG are shown in FIG. 4a. To measure the difference in electrical output performance, the same vibration force of 130 N and vibration frequency of 1 Hz were applied to each TENG using an electrodynamic shaker.

The voltage generated by the porous LIG-based TENG was 19.6 V, and it was confirmed that the performance greatly improved as the nanostructure changed to a fibrous structure. Specifically, the output voltages of SF-LIG and LF-LIG-based TENGs were 75.6V and 180.8V, respectively, which were 385% and 922% higher than those of LIG-based TENGs, respectively.

Therefore, the LIG having a rough surface due to the nanofiber structure increases the contact area and increases the surface charge density, and thus can produce higher output performance.

The load resistance depends on the measured output performance at 10 ⁵ ~10 ¹⁰ Ω, and the load resistance of the entire circuit was increased by connecting a ceramic resistor in series on the breadboard, and the LED (2.5 ~ 3.2V) was connected to a bridge rectifier (2A). , 1000V) was measured by connecting in series with the TENG device. The average voltage and current values of the LF-LIG TENG generated as a function of the load resistance are shown in FIG. 4B.

According to Ohm's Law, it is observed that as the load resistance range increases from 10 ⁵ to 10 ¹⁰ Ω, the voltage increases and the current decreases (0 to 180 V and 30 to 0 μA, respectively). From this trend, it can be confirmed that the voltage and current crossing point occurs at 5×10 ⁶ Ω.

Next, in order to evaluate the accurate performance of the LIG-based TENG, the output power was calculated by applying the formula of power density = V I/A. Here, V and I are the output voltage and current respectively and A is the active contact area.

As the voltage increases and the current decreases with the load resistance, the peak power output of each TENG is located at a resistance of 5 × 10 ⁶ Ω. As can be seen in Figure 4c, the maximum output power value of LF-LIG TENG is 512mW/m ² , which is 5 times and 130 times higher than SF-LIG TENG (98mW/m ² ) and LIG TENG (3.9mW/m ² ), respectively. confirmed that The property improvement effect in this LF-LIG was the same even when other polymers commonly used as counter materials such as acrylic and PET were applied (FIG. 4d).

On the other hand, since the performance is deteriorated due to wear of the contact surface, the mechanical durability of the TENG is an important factor for generating a uniform electrical energy value in repetitive press/release operations. To confirm the electrical output performance durability of the TENG, the cycle stability test of the LF-LIG TENG was performed up to 10 ⁴ cycles at a vibration frequency of 1 Hz and a force of 130 N. As a result, the initial value was maintained even after 10 ⁴ cycles, and no significant change was observed in the output performance.

as in Fig. 4e. To further prove the efficiency of this LIG TENG, a capacitor charging test was performed by fabricating a circuit (Fig. 4f). Here, LIG, SF-LIG and LF-LIG TENG were used as power supplies and the generated electrical energy was rectified to charge a 100 nF capacitor at 1 Hz oscillation frequency.

In Fig. 4g, LIG and SF-LIG TENG achieve potential values of about 3V and 4V in 150 seconds, respectively, indicating that the capacitor is not fully charged. On the other hand, the LF-LIG TENG achieved a saturation potential value of 7V within 90 seconds by supplying enough electrical energy to fully charge the capacitor. Therefore, it can be seen that the LF-LIG TENG has an excellent electrical energy harvesting ability compared to other LIG TENGs.

Example 3: Fabrication of a laser-induced graphene-based touch sensor

In the same manner as in Example 1, a triboelectric touch sensor system was fabricated by direct patterning on the PI film. 10×10 mm ² LF-LIG pixels were directly patterned on the PI film in the focal plane (WD=0 mm) and synthesized in a 4×4 array.

Each pixel was connected to the synthesized LIG at a working distance of -0.9 mm, and a copper wire was attached to the end of each LIG electrode. The upper triboelectric layer (ie, PMMA) was fabricated with a size of 10 × 10 mm ² , and an acrylic spacer with a thickness of 0.5 mm was placed between the PI substrate and the PMMA.

As shown in Fig. 5a, a 4 × 4 matrix of square LF-LIG arrays was synthesized on a PI substrate connected to LIG electrodes fabricated by a defocusing method. In particular, LF-LIG was utilized as an active layer due to its high triboelectric properties, and the conductive electrode of this sensor system adopted LIG to obtain low resistance characteristics. A flexible acrylic spacer with a thickness of 0.5 mm was fixed to the PI substrate, and a PMMA layer of a 4 × 4 matrix as a counter material was placed on the spacer.

Experimental Example 3: Laser-induced graphene-based touch sensor performance analysis

An electrometer (Keithley 6514) measured the output signal of the touch sensor according to actions such as single touch, double touch, multi-touch and drag events.

First, the output performance of a single pixel was measured to confirm the operability of this touch sensor system. The output signal sensed by the electrometer is shown in Figure 5b. As a result, uniform output voltage and current signals with values of 7.5V and 0.2μA, respectively, were generated from repetitive finger touch events. Specifically, between the LF-LIG and the PMMA pixel, a (+) signal was generated as an output signal of the triboelectric charge in a finger touch operation, whereas a (-) signal was generated by a finger touch release operation.

In Fig. 5c, each pixel/electrode is connected with an electrometer and output electrical signals are measured at various finger touch events. Consisting of a PMMA/LF-LIG triboelectric layer and a LIG electrode, each pixel is numbered (row, column). For example, (3,2) represents the pixel located in row 3 and column 2 of a 4x4 matrix.

Next, three types of touch events, i.e., single, double, and multi-touch events, were performed in the sensor system. In the case of a single touch on a (3,2) pixel, a 7.5V output signal was observed at that pixel in the mapping picture. In addition, when (3,2) and (2,3) pixels are double-touched at the same time, a distinct response was observed in the corresponding pixel, and a response signal with a weak intensity of 3.2V was measured in an adjacent pixel. Therefore, this multi-touch operation can also be recognized through the mapping picture in the present sensor system. In addition, when three pixels of (4,1), (3,3), and (1,4) were touched, a clear response was also observed in the corresponding pixel.

In FIG. 5D , arrows indicate dragging motions in various directions. First, the finger was placed at (1,1) and dragged along the arrow. A mapping picture was then obtained showing distinct responses according to the order of signal generation at each pixel. These mapping figures were obtained from the real-time output voltage signal of each pixel shown in FIG. 5e. The direction of dragging can also be recognized from such mapping values and real-time output signals. Therefore, this triboelectric type touch sensor system can be applied not only to energy harvesting devices but also to writing/drawing sensor systems with very sensitive sensitivity.

Therefore, the triboelectric nanogenerator according to the embodiment of the present invention has the potential to be applied to various application fields such as wearable electronic touch sensors, flexible touch pads, and human motion monitoring.

The embodiments of the present invention described above should not be construed as limiting the technical spirit of the present invention. The protection scope of the present invention is limited only by the matters described in the claims, and those skilled in the art can improve and change the technical idea of the present invention in various forms. Therefore, these improvements and modifications will fall within the protection scope of the present invention as long as they are obvious to those skilled in the art.

Claims (16)

porous graphene structure; and a plurality of graphene cilia formed spaced apart from each other on the surface of the porous graphene structure.
An island having a ratio I _D /I _G of the range peak intensity (I _D ) and the range peak intensity (I _G ) of 1500 to 1600 cm ^-1 measured in the Raman spectroscopy spectrum from 0.8 to 1.1 ^. Model graphene composites. According to claim 1,
The plurality of graphene cilia are vertically aligned on a porous graphene structure, a ciliary graphene composite. According to claim 1,
The graphene is a laser-induced graphene oxide, a ciliary graphene composite. According to claim 1,
The graphene cilia have a length of 100 μm or more, the ciliary graphene composite. delete According to claim 1,
The ciliary graphene composite has an a-axis crystal size (L _a ) calculated by Equation 1 of 10 - 20 nm.
[Equation 1]
L _a = (2.4Х10 ^-10 )×λ _l ⁴ ×(I _G /I _D )
Here, λ _l is the wavelength of the Raman laser, I _G is the intensity of the G peak, and I _D is the intensity of the D peak in the Raman spectroscopic spectrum. According to claim 1,
The ciliary graphene composite includes a pyridinic nitrogen, pyrrolic nitrogen, and graphitic nitrogen structure. According to claim 1,
The ciliated graphene composite has an oxygen (O) content of 5% or less and a nitrogen (N) content of 1% or more based on X-ray photoelectron spectroscopy (XPS) analysis. According to claim 7,
The ciliated graphene composite has a graphitic nitrogen content of 1% or more based on X-ray photoelectron spectroscopy (XPS) analysis. As a method for producing a ciliary graphene composite,
Including; irradiating a laser onto the graphene precursor material along the laser irradiation path,
Forming a laser spot at an intersection of the laser irradiation path and the graphene precursor material,
The ciliary graphene composite has a ratio of I _D /I _G between peak intensity (I _D ) in the range of 1300 to 1400 cm ^-1 and peak intensity (I _G ) in the range of 1500 to 1600 cm ^-1 measured in the Raman spectroscopy spectrum. A method for producing a ciliated graphene composite having a ratio of 0.8 to 1.1. According to claim 10,
Adjusting the diameter of the laser spot by adjusting the working distance (WD) in the z-axis direction based on the focal plane located on the irradiation path; further comprising a ciliary graphene composite manufacturing method. According to claim 10,
The power and scan speed of the laser have a specific fixed value, ciliary graphene composite manufacturing method. According to claim 10,
The power density of the laser is 10 to 100 W / mm ² , Ciliary graphene composite manufacturing method. a triboelectric active layer comprising the ciliary graphene composite according to any one of claims 1 to 4 and 6 to 9; and
A triboelectric nanogenerator comprising a; counter material layer disposed to face the ciliary graphene composite. According to claim 14,
The triboelectric nanogenerator, wherein the counter material includes one or more of PMMA, PET, acrylic, LIGs, PDMS, PVC, and PTFE. According to claim 14,
A triboelectric nanogenerator further comprising a spacer spaced apart from the triboelectric active layer and the counter material layer.

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