Patterning processing method for inducing graphene on PDMS (Polydimethylsiloxane) by femtosecond laser

Abstract

The invention discloses a patterning processing method for inducing graphene on PDMS (Polydimethylsiloxane) by femtosecond laser. The patterning processing method comprises the following steps: preparing a PDMS film; cleaning the surface of the PDMS film by adopting an organic solvent; focusing femtosecond laser on the surface of the PDMS film, and inducing to generate graphene; wherein the femtosecond laser adopts low repetition frequency. And the LIG is prepared on the surface of the PDMS by the low-repetition-frequency femtosecond laser.

Description

Technical Field

[0001] This application relates to the technical field of graphene, and specifically relates to a patterning processing method for inducing graphene on PDMS using femtosecond laser. Background Art

[0002] Polydimethylsiloxane (PDMS) is a non-toxic and transparent silicone material, with characteristics of chemical stability, cold and heat resistance. At the same time, due to its high elasticity and biocompatibility caused by its low Young's modulus, it is widely used in flexible electronics, optoelectronic devices, biomedical sensing, microfluidics and other fields, and has the advantages of simple and fast manufacturing methods and low material costs.

[0003] However, due to the characteristics of low conductivity of the polymer itself, PDMS is often only used as a flexible substrate or surface encapsulation. Existing technologies generally broaden the application fields of PDMS by surface modification or incorporation of special materials such as noble metals and graphene.

[0004] However, the processes of surface modification of PDMS or incorporation of graphene often require complex processing steps or strict experimental environments, which greatly weakens its extensive commercial value. Therefore, it is particularly important to prepare graphene nanomaterials by a simple and fast method and achieve modifiable processing of patterning.

[0005] Currently, the process of femtosecond laser-induced graphene uses laser pulses with a high repetition rate (63 MHz), and its mechanism is usually explained as the thermal effect accumulation generated by the extremely short time interval between multiple laser pulses at a high repetition rate, resulting in a sharp increase in the temperature at the laser action position and generating graphitization. This not only limits the selection of femtosecond laser light sources, but also has limitations in the explanation of the principle of femtosecond laser-induced graphene. Summary of the Invention

[0006] Volume Number: 230288CI

[0007] In order to solve the above deficiencies in the art, this application proposes a new mechanism for femtosecond laser-induced graphene, that is, the thermal accumulation effect of multiple laser pulses is not the key to achieving graphitization, and the thermal effect generated by a single pulse can also achieve graphitization. At the same time, the key to achieving graphitization is that the thermal effect of femtosecond laser is greater than its material removal effect.

[0008] According to one aspect of this application, there is provided a patterning processing method for inducing graphene on PDMS using femtosecond laser, including:

[0009] Preparing a PDMS thin film;

[0010] Cleaning the surface of the PDMS thin film with an organic solvent;

[0011] Focus the femtosecond laser on the surface of the PDMS film to induce the generation of graphene;

[0012] Among them, the femtosecond laser uses a low repetition rate.

[0013] According to some embodiments of the present application, preparing the PDMS film includes:

[0014] Mix the elastomer of PDMS and the curing agent evenly and pour them into a mold for thermal curing.

[0015] According to some embodiments of the present application, the low repetition rate is 50 kHz - 1 MHz.

[0016] According to some embodiments of the present application, the weight ratio of the elastomer of PDMS to the curing agent is (8 - 12):1; the curing temperature is 50 - 80 °C; the curing time is 1 - 3 h.

[0017] According to some embodiments of the present application, using a femtosecond laser to focus on the PDMS surface to induce the generation of graphene includes:

[0018] Place the cleaned PDMS film on the processing platform and use a femtosecond fiber laser and a near-infrared objective lens for processing.

[0019] According to some embodiments of the present application, the wavelength range of the femtosecond fiber laser is 1030 nm ± 5 nm; the near-infrared objective lens is a 10-fold near-infrared objective lens with a numerical aperture of 0.3.

[0020] According to some embodiments of the present application, it further includes: performing Raman characterization on the sample.

[0021] Volume number: 230288CI

[0022] Compared with the prior art, the present application at least includes the following beneficial effects:

[0023] The present application provides a patterning processing method for inducing graphene on PDMS using a femtosecond laser, realizing the preparation of LIG on the surface of PDMS with a low repetition rate femtosecond laser.

[0024] The present application further explores the mechanism of preparing LIG with a femtosecond laser. By adjusting the repetition frequency and scanning speed of the femtosecond laser, the present application finds that a high repetition rate laser is not a necessary condition for realizing the grapheneization of PDMS, and a low repetition rate femtosecond laser dominated by the thermal effect of a single pulse can also realize the preparation of LIG on PDMS.

[0025] Combined with the "cold processing" characteristics of femtosecond lasers themselves, this application proposes a new mechanism for fabricating LIG on PDMS using femtosecond lasers, that is, the thermal effect of femtosecond lasers being greater than the ablation effect of femtosecond lasers is the key to realizing LIG.

[0026] This application also uses characterization methods such as Raman spectroscopy and transmission electron microscopy to prove that LIG fabricated using low-repetition-rate femtosecond lasers has high crystallinity and few-layer characteristics. Realizing the patterned fabrication of FsLIG on PDMS, it can be foreseen that this technology has good application prospects in flexible electronic devices and terahertz devices for metamaterials. Brief Description of the Drawings

[0027] Figure 1 It is a flowchart of the patterned processing of inducing graphene on PDMS in the exemplary embodiments of this application using femtosecond lasers.

[0028] Figure 2 It is a Raman detection diagram of different positions of a line structure.

[0029] Figure 3 It is a Raman spectrum of Raman detection of line structures processed at different repetition rates.

[0030] Figure 4 It is an SEM image of FsLIG in this application.

[0031] Figure 5 It is a TEM image of the edge of FsLIG in this application.

[0032] Figure 6 It is an SEM image of the patterned fabrication of FsLIG in this application. Detailed Description of the Embodiments

[0033] Volume number: 230288CI

[0034] Next, the technical solutions of this application will be clearly and completely described in combination with the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, rather than all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative efforts fall within the scope of protection of this application.

[0035] It should be particularly noted that similar replacements and modifications made to this application are obvious to those skilled in the art, and they are all considered to be included in this application. Relevant personnel can obviously make changes or appropriate alterations and combinations to the methods and applications described herein without departing from the content, spirit, and scope of this application to implement and apply the technology of this application. Obviously, the described embodiments are only part of the embodiments of this application, rather than all of them.

[0036] Unless otherwise specified, the conditions of this application are carried out according to conventional conditions or the conditions recommended by the manufacturer. For the raw materials or excipients used, as well as the reagents or instruments used, if the manufacturer is not specified, they are all conventional products that can be obtained through commercial purchase.

[0037] The following is a detailed description of this application.

[0038] Laser Induced Graphene (LIG) is different from the strictly monolayer or few-layer quasi-two-dimensional sp2 carbon lattice materials. Instead, it is a three-dimensional porous nano-carbon material. Its principle is to break the chemical bonds of the carbon precursor through the thermal effect of the laser and cause its recombination to form a graphene structure.

[0039] Since its porous structure and defect density are related to the laser parameters, by adjusting various parameters of the processing laser (such as wavelength, power, repetition frequency, etc.), the structure and properties of LIG can be optimized, and new possibilities are provided for the further doping and functionalization of LIG.

[0040] Therefore, although LIG does not have the excellent properties comparable to perfect graphene, its other characteristics, such as simple process, high production efficiency, adjustable performance, etc., still have great research value. It is an effective means to overcome the bottleneck of traditional technology and realize the efficient production of graphene-based devices and their functional modification.

[0041] At the same time, the femtosecond laser direct writing technology (Femtosecond Laser Direct Writing, FsLDW) Volume number: 230288CI

[0042] is one of the research focuses in the field of advanced special processing and manufacturing, with advantages such as maskless, non-contact, wide material applicability, and low processing environment requirements.

[0043] By adjusting the processing parameters through the interaction between the femtosecond laser and the material, the processing of structures and the regulation of properties at the micron, sub-micron, even nano-scale or cross-scale can be achieved. Therefore, using femtosecond laser-induced graphene (Femtosecond Laser Induce Graphene, FsLIG) to prepare graphene in flexible polymer plastics or green materials mainly composed of lignocellulose has great prospects for future applications in the directions of graphene-based flexible electronic devices and metamaterials.

[0044] Currently, Shuichiro Hayashi et al. have achieved highly crystalline graphene materials in PDMS using femtosecond lasers. They employed the laser focusing and scanning method to prepare a linear structure of graphene on the PDMS surface using the thermal accumulation effect of high-repetition-frequency (63 MHz) laser pulses, and studied the influence of preparation parameters on the size of the modified area. The prepared wire structure was analyzed by Raman spectroscopy and transmission electron microscopy (TEM) to determine the material formed by laser irradiation. By analyzing different positions on the surface and cross-section of the modified area, the uniformity of the formed material was evaluated, and conductivity measurements were performed on the structure to discuss the influence of the formed material on the conductivity of the fabricated structure.

[0045] The prior art believes that the heat accumulation generated by high-repetition-frequency lasers is the key to forming LIG. Most discussions on the "formation mechanism of FsLIG" are limited to the influence of laser thermal effects, and there are limitations in the selection of femtosecond laser light sources and the explanation of the principle of femtosecond laser-induced graphene.

[0046] However, this application has conducted a more in-depth study on the formation mechanism of FsLIG, discussed the formation of LIG from high repetition frequencies (1 MHz) to low repetition frequencies (10 kHz), achieved the preparation of high-quality graphene under a large repetition frequency span, and further proposed a new mechanism for FsLIG, that is, the thermal effect of femtosecond laser pulses is greater than the ablation effect of laser pulses, which is the key to forming and retaining LIG.

[0047] This application proposes a new mechanism for femtosecond laser-induced graphene, that is, a high-repetition-frequency laser is not a necessary condition for realizing PDMS grapheneization. A low-repetition-frequency femtosecond laser dominated by the thermal effect of a single pulse can also achieve the preparation of LIG on PDMS. At the same time, the thermal effect of the femtosecond laser being greater than its ablation effect on the material is the key to realizing grapheneization. We have achieved the preparation of highly crystalline few-layer graphene at a low repetition frequency (50 kHz), studied the influence of LIG morphology by scanning electron microscope (SEM), and verified it using Raman detection and transmission electron microscope (TEM). Finally, patterned processing of femtosecond laser-induced graphene on PDMS was realized.

[0048] A method for patterned processing of femtosecond laser-induced graphene on PDMS:

[0049] Completely mix the elastomer and curing agent of PDMS at a weight ratio of 8:1, pour it into a circular mold, and thermally cure it at 70 °C for 2 h, and perform surface cleaning with 99.5% alcohol.

[0050] Place the cleaned PDMS film on a three-dimensional processing platform and process it using a high-power femtosecond fiber laser with a central wavelength of 1030 nm and a 10× near-infrared objective lens with a numerical aperture (NA) of 0.3;

[0051] Use a confocal Raman spectroscopy analysis imaging instrument to perform Raman characterization on the sample. The laser wavelength is 532 nm, and the focusing objective lens is a 10× objective lens;

[0052] Use TEM (JEOL JEM 2100F, Japan) to perform nanoscale characterization on the prepared structure.

[0053] According to some embodiments of the present application, the elastomer is poly(dimethyl-methylvinylsiloxane) and a trace amount of platinum catalyst; the curing agent is a prepolymer with vinyl side chains and poly(dimethyl-methylhydrogenosiloxane). Crosslinking and curing are achieved through the hydrosilylation reaction of vinyl and silicon-hydrogen bonds.

[0054] Examples

[0055] Completely mix the elastomer and curing agent of PDMS (Dow Corning DC184, USA) in a weight ratio of 8:1, pour them into a circular mold, and thermally cure at 70 °C for 2 h. Then, perform surface cleaning using 99.5% alcohol;

[0056] Place the cleaned PDMS film on a three-dimensional processing platform and use a high-power femtosecond fiber laser with a central wavelength of 1030 nm (Yili Technology, China) and a 10× near-infrared objective lens with a numerical aperture (NA) of 0.3

[0057] times (M Plan Apo NIR, Mitutoyo, Japan) for processing;

[0058] Use a confocal Raman spectroscopy analysis imaging instrument (Nanobase, Korea) to perform Raman characterization on the sample. The laser wavelength is 532 nm, and the focusing objective lens is a 10× objective lens. Use TEM (JEOL JEM 2100F, Japan) to perform nanoscale characterization on the prepared structure.

[0059] Experimental Examples

[0060] The Raman spectrum of graphene generally has three obvious characteristic peaks, among which:

[0061] The D peak is located at about 1350 cm-1 and is usually used to characterize the number of defects in graphene;

[0062] The G peak is located at around 1580 cm-1 and is formed by the in-plane vibration of sp2 carbon atoms. As the number of graphene layers increases, the position of the G peak will have a red shift of about 1 / n.

[0063] The 2D peak caused by the second-order lattice vibration appears at 2700 cm-1 and is used to characterize the number of graphene layers and the degree of crystallinity.

[0064] 1. High-repetition-rate Raman spectroscopy detection

[0065] To understand the formation process of LIG in PDMS, the Raman spectra of different positions of the line structure were first detected. Raman characterization was carried out on different positions of the prepared line structure under the parameters of a repetition frequency of 1 MHz, a power of 400 mW, and a scanning speed of 0.5 mm / s (as Figure 2 ):

[0066] Figure 2 It is a Raman detection diagram of different positions of the line structure. Among them, (a) is the surface schematic diagram of each position, with a laser power of 200 mw, a repetition frequency of 1 MHz, and a scanning speed of 1 mm / s; (b) is the Raman spectrum of each position. The colors at different positions correspond to the colors in the Raman spectrum. The scale bar is 50 μm.

[0067] It can be observed that few-layer graphene with high crystallinity and low defects (ID / IG < 1, I2D / IG = 0.95) is generated at the groove at the direct position of the laser spot (i.e., at A). This is mainly because the photothermal effect brought by the direct laser irradiation causes PDMS to carbonize and form LIG. As the distance from the center position increases, due to the Gaussian characteristics of the laser beam, the photothermal effect of the laser decreases, and the thermal effect generated by the direct laser irradiation rapidly weakens. However, due to the thermal diffusion effect, the thermal effect accumulated by the laser pulse also causes the structure around the groove to be graphitized (i.e., at B and C). However, as the distance from the center position increases, its crystallinity decreases (the 2D peak gradually decreases) and the number of defects significantly increases (the intensity of the D peak increases), and finally, due to the thermal effect not being sufficient to cause the degradation of PDMS, the modification of PDMS cannot be achieved at the edge (i.e., at D), as

[0068] shown in Figure 2 (b), the bottom gray line is the Raman spectrum of PDMS, and the double-peak structure near 2900 cm-1 is the symmetric and asymmetric vibrations of CH3, which are generally considered to originate from the methyl groups contained in PDMS.

[0069] 2. Low-repetition-rate Raman spectroscopy detection

[0070] The Raman spectra of the line structures prepared at other repetition frequencies (10 kHz, 50 kHz, 100 kHz, 500 kHz) were studied.

[0071] Different from the preparation of LIG on PDMS reported in current literature, which shows the formation of LIG at high repetition rates (63 MHz), this application discovers that even at low repetition rates (50 kHz), the formation of LIG can still be detected. At parameters of 50 kHz and 2 mm / s, the time interval between adjacent pulses is much greater than the dissipation time of the thermal effect of a single pulse (the time required for the thermal field generated by each femtosecond laser pulse to decay is a few microseconds). Therefore, the thermal accumulation effect between multiple pulses is basically 0. According to the corresponding Raman spectrum, IG / ID < 1 and I2D / IG = 0.63 can be calculated. This indicates that even low-repetition-rate laser processing dominated by the thermal effect of a single pulse can still achieve the preparation of high-quality LIG.

[0072] Figure 3 To perform Raman detection on the line structures processed at different repetition rates:

[0073] (a) Raman spectra of structures processed at different scanning speeds with a power of 300 mw at a repetition rate of 10 kHz;

[0074] (b) Raman spectra of structures processed after increasing the repetition rate to 50 kHz.

[0075] In addition, by comparing Figure 3 (a) and (b), it can be found that at parameters of 10 kHz and 0.1 mm / s, the time interval of each laser pulse is already less than that at parameters of 50 kHz and 1 mm / s. At the same time, at the same power, the intensity of the energy of each pulse at 10 kHz parameters is also higher than that at 50 kHz.

[0076] That is, at parameters of 10 kHz and 0.1 mm / s, both the thermal effect of a single pulse and the thermal accumulation effect formed by the superposition of multiple pulses are stronger than those at parameters of 50 kHz and 1 mm / s. However, no obvious 2D peak is detected in the line structures processed under the former conditions.

[0077] Considering the "cold processing" characteristics generated by the interaction between pulses with high photon energy and materials at low repetition rates, the material in direct contact with the laser will form a high-temperature and high-pressure plasma state: Volume No. 230288CI

[0078] and rapidly detach from the substrate in the form of ejection, resulting in the originally generated LIG being excited into a plasma state by subsequent high-energy pulses and removed. Therefore, LIG cannot be detected at extremely low repetition rates (such as 10 kHz).

[0079] Therefore, this application proposes a new theory that the key to realizing LIG with ultrashort pulsed lasers is that the thermal effect of the laser is greater than the ablation effect of the laser. By adjusting various parameters of the laser, such as the repetition frequency, power, and scanning speed, the thermal effect at the irradiated site is sufficient to achieve LIG, while the ablation effect of the laser should be minimized to retain the generated LIG.

[0080] 3. Cross-section thickness morphology and surface morphology analysis by scanning electron microscope

[0081] Figure 4 SEM images of FsLIG are as follows:

[0082] (a) shows the cross-section characterization, demonstrating the layered structure of LIG and PDMS, with a scale bar of 100 μm;

[0083] (b) is an enlarged image of (a), with a scale bar of 20 μm;

[0084] (c) shows the surface characterization, presenting a granular bulging structure on the LIG surface, with a scale bar of 20 μm.

[0085] (d) is an enlarged image of (c), with a scale bar of 4 μm.

[0086] The cross-section thickness morphology and surface morphology of LIG were studied using a scanning electron microscope. Figure 4 (a) shows the cross-section morphology of LIG under a laser repetition frequency of 1 MHz, a laser power of 60 mW, and a scanning speed of 1 mm / s. The layered structure of LIG and PDMS can be clearly observed. Figure 4 (b) is Figure 4 the enlarged morphology of (a), where the thickness of LIG is approximately 43 μm, and the internal structure shows a porous chip-like stacked structure, mainly due to the material plasma eruption caused by femtosecond laser. Figure 4 (c) shows the surface morphology characterization of the structure, where the laser direct writing part on the LIG surface has a granular bulging structure, and the spaced part of the processing line has a porous structure, which is Figure 4 more clearly shown in (d).

[0087] 4. Transmission electron microscope analysis of sub-micron scale structures

[0088] Figure 5 TEM images of the FsLIG edge are as follows:

[0089] (a) TEM image taken at the edge of the LIG sample, with a scale bar of 20 nm;

[0090] (b) is an enlarged image of the red box area in (a), showing few-layer characteristics and a wavy layered structure, volume number: 230288CI

[0091] Scale bar is 5 nm;

[0092] (c) is an enlarged image of the orange area in the field of view of (b), showing the few-layer characteristics and wavy wrinkled edges of LIG. The scale bar is 2 nm.

[0093] (d) is an enlarged image of the green area in the field of view of (b), showing the ultra-polycrystalline nature of LIG. The scale bar is 0.5 nm.

[0094] Figure 5 (a) is an image of LIG stacked in sheets, and the enlarged image of the red marked area is shown in Figure 5 As shown in (b), lattice fringes with a spacing of about 0.34 nm can be observed, which corresponds to the (002) plane of the graphite material, consistent with the Raman results, indicating the formation of LIG. In addition, a wavy stacking structure can be observed at the edge of LIG. Since each layer of graphene corresponds to a dark line in the lattice image of the high-resolution TEM, by observing Figure 5 In the high-resolution lattice image of the wavy stacked structure in (c), we can clearly see the phenomenon of 3-5 dark lines stacking (indicated by the red dotted lines in Figure (c)), that is, the formed LIG is a few-layer graphene, which is consistent with the result of I2D / IG calculated by Raman spectroscopy in the previous article. Figure 5 (d) Figure 5 The enlarged image of the green box in (b) shows that LIG prepared on PDMS also has ultra-polycrystalline characteristics, indicating its potential in catalytic and electrochemical applications.

[0095] 5. Preparation of complex patterns on PDMS surface

[0096] Figure 6 Preparation for patterning of FsLIG:

[0097] (a) is an interdigitated pattern;

[0098] (b) is a spiral pattern;

[0099] (c) is a periodic pattern of dense teeth;

[0100] (d) The periodic structure of the hexagonal star-shaped hole pattern, the scale bar is 50 μm.

[0101] In order to explore the application prospects of FsLIG, we used laser parameters with a repetition frequency of 1 MHz and a laser power of 60 mW to fabricate complex patterns on the PDMS surface, such as Figure 6(a) and (b) show the preparation of interdigital patterns and spiral patterns, with the minimum line spacing reaching about 10 μm and the line width reaching about 70 μm. This demonstrates the application prospect of the FsLIG technology in the preparation of microcapacitors and microelectrodes, volume number: 230288CI. In addition, we have also achieved the periodic patterning of FsLIG, Figure 6 (c) and (d) are the periodic patterns of serrated teeth and hexagonal stars respectively, and it can be preliminarily predicted the application potential of this technology in metamaterial terahertz devices and other aspects.

[0102] The description of the above embodiments is only used to help understand the method and its core idea of the present application. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A patterning processing method for femtosecond laser-induced graphene on PDMS, characterized in that, Including: Preparing a PDMS film; Cleaning the surface of the PDMS film with an organic solvent; Focusing femtosecond laser on the surface of the PDMS film to induce the generation of graphene; Wherein, the femtosecond laser uses a low repetition rate.

2. The method according to claim 1, wherein Preparing the PDMS film includes: Mixing the elastomer of PDMS and the curing agent evenly and then pouring them into a mold for thermal curing.

3. The method according to claim 2, wherein The low repetition rate is 50 kHz - 1 MHz.

4. The method according to claim 3, wherein The weight ratio of the elastomer of PDMS to the curing agent is (8 - 12):1; the curing temperature is 50 - 80 °C; the curing time is 1 - 3 h.

5. The method according to claim 1, wherein Focusing femtosecond laser on the surface of PDMS to induce the generation of graphene includes: Placing the cleaned PDMS film on a processing platform and processing it with a femtosecond fiber laser and a near-infrared objective lens.

6. The method according to claim 5, characterized in that, The wavelength range of the femtosecond fiber laser is 1030 nm ± 5 nm; the near-infrared objective lens is a 10-fold near-infrared objective lens with a numerical aperture of 0.

3.

7. The method according to claim 1, wherein Also including: Performing Raman characterization on the sample.

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