A sers substrate based on double enhancement of graphite carbon material
The three-dimensional SERS substrate prepared by femtosecond laser and chemical wet etching technology solves the problems of complex processing and high cost of SERS substrate in the existing technology, realizes high sensitivity of trace substance detection, and has good repeatability and stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHINA UNIV OF PETROLEUM (EAST CHINA)
- Filing Date
- 2023-12-28
- Publication Date
- 2026-05-12
AI Technical Summary
Existing SERS substrates have complex processing techniques, high costs, and insufficient repeatability and stability, making it difficult to achieve highly sensitive trace substance detection.
A three-dimensional SERS substrate with chemical and physical enhancement was prepared by using femtosecond laser processing combined with chemical wet etching technology. By forming a graphite carbon crystal and silicon carbide composite structure on the PDMS surface, a pyramid array structure with high specific surface area was prepared by ablation of the PDMS substrate with femtosecond laser and electron beam evaporation of gold film.
It achieves a highly efficient and repeatable SERS substrate with good enhancement effect and stability, enabling sensitive detection of trace substances, simplifying the processing steps and reducing costs.
Smart Images
Figure CN117805021B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of femtosecond laser processing and micro-nano sensing. Specifically, this invention relates to a three-dimensional SERS substrate with chemical and physical enhancement for high-sensitivity SERS detection. Background Technology
[0002] Surface-enhanced Raman scattering (SERS) is a highly sensitive and high-resolution molecular recognition technique with significant applications in multiple fields. An ideal detection substrate must possess a high enhancement factor, long-term stability, and excellent reproducibility. SERS primarily employs two enhancement mechanisms: physical enhancement (EM) and chemical enhancement (CM), which significantly influence the Raman signal intensity. The physical enhancement mechanism depends on the optical excitation of surface plasmon resonances in the nanostructure "hot spots" on the SERS substrate, while the chemical enhancement mechanism arises from the electronic coupling between the absorbed molecules and the surface structure.
[0003] To date, a great deal of research has been conducted on these two mechanisms, and many methods for manufacturing nanostructures have been developed, including "top-down" processing methods such as electron beams, focused ion beams, and nanoimprinting, which use external high-energy beams to etch the material surface, and "bottom-up" processing methods such as hydrothermal methods, template methods, and chemical deposition, which utilize self-growth and reaction processes for self-assembly.
[0004] While each micro / nanofabrication technology has its own unique characteristics, most processes require multiple complex steps to construct uniform nanostructures, and suffer from drawbacks such as high processing costs and harsh processing conditions. Therefore, there is an urgent need to develop a novel SERS substrate with good enhancement effects, high repeatability, and stable properties for highly sensitive detection of trace targets.
[0005] In view of the above-mentioned shortcomings of the existing technology, the present invention is proposed. Summary of the Invention
[0006] To prepare a novel SERS substrate with good reinforcement, high repeatability, and stable properties, this invention utilizes the femtosecond laser processing method, which has advantages such as high processing precision, high flexibility, wide material applicability, and no need for a vacuum environment. It also combines chemical wet etching technology to prepare a pyramid array structure template with high repeatability and high specific surface area. A PDMS substrate array is prepared using a polymer rapid prototyping method. The surface of the PDMS array is roughened and modified using femtosecond laser to obtain a three-dimensional SERS substrate structure with both chemical and physical reinforcement.
[0007] To achieve the above objectives, the technical solution provided by the present invention is as follows:
[0008] A SERS substrate based on dual reinforcement of graphite carbon material, wherein the preparation steps of the SERS substrate include:
[0009] Step S1, polymer array preparation;
[0010] An inverted pyramid array structure is fabricated by etching on a pretreated silicon wafer using a chemical wet etching process.
[0011] Step S2: Fabrication of the substrate array using a rapid polymer method;
[0012] Using the silicon template prepared in step S1, a PDMS substrate array was fabricated using a rapid polymer method;
[0013] Step S3: Femtosecond laser ablation of the PDMS substrate.
[0014] The femtosecond laser direct writing method is used, which involves directly ablating the PDMS substrate with a femtosecond laser. The specific process is as follows:
[0015] Step S31: Using Pharos software, the femtosecond laser source is set to a repetition frequency of 2.5 kHz, an output wavelength of 1030 nm, and a line scan structure spacing of 0.03 mm, so that the surface structure can be completely processed.
[0016] In step S32, by adjusting the laser energy from 27mw to 42mw and the laser scanning speed from 10mm / s to 30mm / s, the femtosecond laser irradiates the PDMS surface, causing heat accumulation on the surface, thereby triggering a thermal effect and causing changes in the material properties.
[0017] In step S33, the femtosecond laser simultaneously damages the PDMS surface, creating a rough surface structure.
[0018] Step S34 completes the preparation of the SERS substrate based on dual reinforcement of graphite carbon materials.
[0019] Femtosecond laser irradiation of polydimethylsiloxane (PDMS) forms a composite structure of graphitic carbon crystals (GCs) and silicon carbide. During femtosecond laser processing, a thermal accumulation effect occurs on the material surface, and the polymer is decomposed into small hydrocarbon molecules through heat treatment. Under sufficient thermal energy, these small hydrocarbon molecules can be pyrolyzed to form GCs. If the heat is sufficient, degradation and pyrolysis occur simultaneously, allowing GCs to continue growing. GCs exhibit metal-like electrical conductivity, high adsorption capacity, and fluorescence quenching. Simultaneously, charge transfer between graphitic carbon and molecules leads to chemical reinforcement. After growth, the disordered stacking between graphitic carbon planes creates nanoscale gaps. Physical reinforcement is inversely proportional to the gap size, resulting in dual SERS reinforcement of the substrate.
[0020] It also includes step S4, electron beam evaporation;
[0021] To further improve the SERS signal, an electron beam evaporation deposition process was used to uniformly deposit a 50nm thick gold film on the PDMS array substrate after step S3.
[0022] Preferably, the pretreated silicon wafer refers to the surface of the material being processed using a femtosecond laser direct writing processing platform, wherein the material being processed is a crystalline phase with a 300nm SiO2 film. <100> The SiO2 film on the surface of the silicon wafer is selectively removed from the silicon wafer.
[0023] The processed silicon wafers are ultrasonically treated for 15 minutes, then rinsed with deionized water and air-dried.
[0024] Preferably, the specific process for preparing the inverted pyramid array structure by chemical wet etching is as follows:
[0025] Step S11, prepare 6 mol·L -1 Take 10.5 ml of potassium hydroxide solution and add 1 ml of isopropanol and 1 ml of deionized water. Use magnetic stirring to fully mix the etching solution to obtain the etching agent.
[0026] Step S12: Place the processed silicon wafer and etchant into a constant temperature magnetic stirrer at 60°C and 300 rpm for anisotropic wet etching for 120 min.
[0027] Step S13: Utilizing the different etching rates of silicon dioxide and silicon, the silicon dioxide film that was not removed by the femtosecond laser is used as a mask to prevent chemical wet etching. The area where the silicon dioxide film was removed is anisotropically etched, and the etchant performs chemical wet etching along the crystal phase of single-crystal silicon, thereby obtaining a pyramid pit array template, i.e., a silicon template with an inverted pyramid array structure.
[0028] Preferably, in step S2, the step of preparing the substrate array using the polymer rapid method includes:
[0029] In step S21, PDMS and curing agent are mixed in a ratio of 10:1;
[0030] Step S22: Stir for 2 minutes;
[0031] Step S23: Place the mixture in a vacuum pump to remove air bubbles;
[0032] Step S24: Slowly pour the PDMS mixed solution into the silicon template and heat it in a 70°C oven for 2 hours;
[0033] Step S25: After the PDMS has been cured, cut it and place the segmented PDMS substrate array in ethanol and clean it in an ultrasonic cleaner for 10 minutes.
[0034] Step S26: Obtain the PDMS substrate array.
[0035] Preferably, in step S3, the optimal parameters are controlled among five processing conditions by adjusting the laser power and scanning speed: laser power 20mw, scanning speed 10mm / s; or, laser power 30mw, scanning speed 10mm / s; or, laser power 40mw, scanning speed 10mm / s; or, laser power 40mm / s, scanning speed 20mm / s; or, laser power 40mw, scanning speed 30mm / s.
[0036] Preferably, the graphite carbon characterization method based on the SERS substrate with dual reinforcement of graphite carbon materials is as follows:
[0037] SERS substrates prepared under different processing conditions were placed on a Renishaw Raman test stage. The laser power was set to 1%, and the exposure time and number of exposures were 3 s and 2, respectively. The obtained data were processed using Wire 5.5 software to remove background and smooth all Raman spectra before obtaining the final SERS results. Among all the obtained Raman spectra, the results were obtained at 1350 and 1580 cm⁻¹. -1 The unique peaks corresponding to ID / IG of graphitic carbon were observed to indicate the formation of graphitic carbon; ID represents amorphous carbon, IG represents graphitized carbon, and the ratio of ID / IG is related to the degree of graphitization. The smaller the ratio of ID / IG, the higher the degree of graphitization of the material.
[0038] Compared with the prior art, the beneficial effects of the present invention are:
[0039] This invention proposes a novel dual-enhanced SERS substrate fabrication method. A pyramid array structure is fabricated using a femtosecond laser combined with chemical wet etching, efficiently obtaining inverted pyramid templates with uniform structure and high specific surface area. The PDMS substrate prepared by polymer molding exhibits reproducibility. Femtosecond laser pulse processing induces laser-induced modification of the PDMS polymer surface, simultaneously generating stacked GCs structures on the material surface. This results in a substrate with excellent enhancement effect, stable properties, and numerous 'hot spots,' overcoming the limitations of traditional substrates. This invention utilizes femtosecond laser pulse processing to fabricate a substrate with charge transfer chemical enhancement and localized plasmonic physical enhancement on the PDMS surface in a one-step process, further amplifying the Raman signal of the analyte and enabling sensitive detection of any type of trace substance, avoiding complex and redundant processing steps. The method of combining femtosecond laser processing and chemical wet etching is simple, allows for rapid and large-scale fabrication of SERS substrates, further improving substrate processing efficiency, and the selected substrate material is highly economical. The dual-enhanced SERS substrate prepared by this invention improves the SERS detection sensitivity and may inspire the detection of trace analytes, providing a feasible method for achieving highly sensitive SERS detection. Attached Figure Description
[0040] Figure 1 This is a flowchart illustrating the preparation process of the dual-reinforced substrate according to the present invention.
[0041] Figure 2 This is a structural parameter characterization diagram of the PDMS after molding according to the present invention;
[0042] Figure 3 This is a structural diagram of the PDMS of the present invention under different processing parameters;
[0043] Figure 4 SERS performance diagrams of the substrate under different processing parameters;
[0044] Figure 5 The SERS detection limit diagram of the substrate under optimal processing conditions;
[0045] Figure 6 Characterization diagrams of the graphitization degree of the substrate under different processing parameters. Detailed Implementation
[0046] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.
[0047] like Figure 1 As shown, the present invention proposes a SERS substrate based on dual reinforcement of graphite carbon material. The preparation steps of the SERS substrate include:
[0048] Step S1, polymer array preparation;
[0049] An inverted pyramid array structure is fabricated by etching on a pretreated silicon wafer using a chemical wet etching process.
[0050] Preferably, the pretreated silicon wafer refers to the surface of the material being processed using a femtosecond laser direct writing processing platform, wherein the material being processed is a crystalline phase with a 300nm SiO2 film. <100> The SiO2 film on the surface of the silicon wafer is selectively removed from the silicon wafer.
[0051] Using Pharos software, the femtosecond laser source was set to an output power of 50mW, an output frequency of 2.5kHz, and an output wavelength of 1030nm. Using EzCad2 software, a circle with a radius of 0.1mm was drawn, with a scan interval of 0.2mm (default 0.005mm for line filling the circle). The scan speed was set to 10mm / s. After setting these parameters, the processing command was entered.
[0052] The processed silicon wafers are ultrasonically treated for 15 minutes, then rinsed with deionized water and air-dried.
[0053] The specific process for preparing the inverted pyramid array structure using chemical wet etching is as follows:
[0054] Step S11, prepare 6 mol·L -1 Take 10.5 ml of potassium hydroxide solution and add 1 ml of isopropanol and 1 ml of deionized water. Use magnetic stirring to fully mix the etching solution to obtain the etching agent.
[0055] Step S12: Place the processed silicon wafer and etchant into a constant temperature magnetic stirrer at 60°C and 300 rpm for anisotropic wet etching for 120 min.
[0056] Step S13: Utilizing the different etching rates of silicon dioxide and silicon, the silicon dioxide film that was not removed by the femtosecond laser is used as a mask to prevent chemical wet etching. The area where the silicon dioxide film was removed is anisotropically etched, and the etchant performs chemical wet etching along the crystal phase of single-crystal silicon, thereby obtaining a pyramid pit array template, i.e., a silicon template with an inverted pyramid array structure.
[0057] Step S2: Fabrication of the substrate array using a rapid polymer method;
[0058] Using the silicon template prepared in step S1, a PDMS substrate array was fabricated using a rapid polymer method; Figure 2 This is a structural parameter characterization diagram of the PDMS after molding according to the present invention, combined with... Figure 2 The explanation is as follows:
[0059] In step S21, PDMS and curing agent are mixed in a ratio of 10:1;
[0060] Step S22: Stir for 2 minutes;
[0061] Step S23: Place the mixture in a vacuum pump to remove air bubbles;
[0062] Step S24: Slowly pour the PDMS mixed solution into the silicon template and heat it in a 70°C oven for 2 hours;
[0063] Step S25: After the PDMS has been cured, cut it and place the segmented PDMS substrate array in ethanol and clean it in an ultrasonic cleaner for 10 minutes.
[0064] Step S26: Obtain the PDMS substrate array.
[0065] Step S3: Femtosecond laser ablation of the PDMS substrate.
[0066] The femtosecond laser direct writing method is used, which involves directly ablating the PDMS substrate with a femtosecond laser. The specific process is as follows:
[0067] Step S31: Using Pharos software, the femtosecond laser source is set to a repetition frequency of 2.5 kHz, an output wavelength of 1030 nm, and a line scan structure spacing of 0.03 mm, so that the surface structure can be completely processed.
[0068] In step S32, by adjusting the laser energy from 27mw to 42mw and the laser scanning speed from 10mm / s to 30mm / s, the femtosecond laser irradiates the PDMS surface, causing heat accumulation on the surface, thereby triggering a thermal effect and causing changes in the material properties.
[0069] In step S33, the femtosecond laser simultaneously damages the PDMS surface, creating a rough surface structure. Figure 3 This is a structural diagram of the PDMS of the present invention under different processing parameters;
[0070] Step S34 completes the preparation of the SERS substrate based on dual reinforcement of graphite carbon materials.
[0071] Femtosecond laser irradiation of polydimethylsiloxane (PDMS) forms a composite structure of graphitic carbon crystals (GCs) and silicon carbide. During femtosecond laser processing, a thermal accumulation effect occurs on the material surface, and the polymer is decomposed into small hydrocarbon molecules through heat treatment. Under sufficient thermal energy, these small hydrocarbon molecules can be pyrolyzed to form GCs. If the heat is sufficient, degradation and pyrolysis occur simultaneously, and GCs continue to grow. GCs exhibit metal-like electrical conductivity, high adsorption capacity, and fluorescence quenching. Simultaneously, charge transfer between graphitic carbon and molecules leads to chemical reinforcement. After growth, the disordered stacking between graphitic carbon planes creates nanoscale gaps. Physical reinforcement is inversely proportional to the gap size, resulting in dual SERS reinforcement of the substrate.
[0072] It also includes step S4, electron beam evaporation;
[0073] To further improve the SERS signal, an electron beam evaporation deposition process was used to uniformly deposit a 50nm thick gold film on the PDMS array substrate after step S3.
[0074] Processing conditions optimization:
[0075] Preferably, in step S3, the optimal parameters are controlled among five processing conditions by adjusting the laser power and scanning speed: laser power 20mw, scanning speed 10mm / s; or, laser power 30mw, scanning speed 10mm / s; or, laser power 40mw, scanning speed 10mm / s; or, laser power 40mm / s, scanning speed 20mm / s; or, laser power 40mw, scanning speed 30mm / s.
[0076] For the processed substrate, the strength of the SERS signal is used to characterize the substrate performance under different processing conditions. The specific testing procedure is as follows:
[0077] (1) After the substrate is processed, place it in ethanol and put it in an ultrasonic cleaner for 15 minutes. Then rinse it thoroughly with deionized water to remove surface impurities and let it air dry naturally.
[0078] (2) Malachite green isothiocyanate (MGITC) was used as a Raman reporter molecule to test the effect of the substrate on SERS enhancement. 10 -7 mol·L -1 A concentrated MGITC solution was used to hydrophilically treat gold-plated PDMS array substrates under different processing conditions using a plasma cleaning agent. A brown centrifuge tube was then filled with the prepared 10% concentration of MGITC solution. -7 mol·L -1 A concentrated MGITC solution was used to immerse the hydrophilically treated substrate in the solution, followed by shaking and standing for 2 hours.
[0079] (3) Rinse the soaked substrate with deionized water and dry it thoroughly in the dark. SERS measurements were performed using a Renishaw Invia Raman microscope system with a 633nm laser, laser power set to 1%, integration time of 5s, and 3 integration cycles. Raman enhancement signals under different processing conditions were measured, and the measured signals were smoothed and baseline-removed. Data analysis yielded SERS enhancement spectra under different processing conditions, such as... Figure 4 As shown, the SERS enhancement signal is best when the laser power is 40mW and the scanning speed is 10mm / s. As the laser energy decreases and the scanning speed increases, the SERS enhancement signal gradually weakens. Conversely, as the laser energy increases and the scanning speed decreases, the SERS enhancement signal gradually increases. Based on ensuring substrate fabrication efficiency, a laser power of 40mW and a scanning speed of 10mm / s were ultimately determined to provide the optimal SERS enhancement signal.
[0080] SERS substrate detection limit
[0081] The above experimental results determined that a laser energy of 40 mW and a scanning speed of 10 mm / s were the optimal processing parameters, verifying the detection limit of the substrate, which is a crucial indicator for evaluating SERS performance. By configuring 10... -6 mol·L -1 Up to 10 -12 mol·L -1 The optimal processing parameters for gold plating were achieved by immersing the substrate in MGITC solutions of varying concentrations, shaking, and allowing it to stand for 2 hours. The substrate was then removed with tweezers, rinsed with deionized water to remove excess probe, and placed in a fume hood to air dry. The characteristic peak of MGITC was 1614 cm⁻¹. -1 The Raman scan band was set to 400 cm. -1 -1800 cm -1 A 633nm laser was used for excitation, with a designed excitation power of 1%, an integration time of 5s, and 3 integration cycles. After Raman detection, the detection data was smoothed and baseline-removed to obtain... Figure 5 Analysis of the results shows that our designed SERS-enhanced substrate can achieve 10 -11 mol·L -1 The detection limit is low, the substrate has good enhancement effect and excellent SERS enhanced detection line.
[0082] SERS-based graphite carbon characterization
[0083] SERS substrates prepared under different processing conditions were placed on a Renishaw Raman test stage. The laser power was set to 1%, and the exposure time and number of exposures were 3 s and 2, respectively. The obtained data were processed using Wire 5.5 software to remove background and smooth all Raman spectra before obtaining the final SERS results. Among all the obtained Raman spectra, the results were obtained at 1350 and 1580 cm⁻¹. -1 A unique peak corresponding to the ID / IG ratio of graphitic carbon was observed, indicating the formation of graphitic carbon. ID represents amorphous carbon, and IG represents graphitized carbon. The ID / IG ratio is related to the degree of graphitization; the smaller the ID / IG ratio, the higher the degree of graphitization of the material. Figure 6 It can be concluded that the substrate with the best Raman performance also has the highest degree of graphitization, which indirectly proves that chemical enhancement plays a key role in improving Raman signals.
[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A SERS substrate based on dual reinforcement of graphite carbon materials, characterized in that, The preparation steps of the SERS substrate include: Step S1, polymer array preparation; An inverted pyramid array structure is fabricated by etching on a pretreated silicon wafer using a chemical wet etching process. The specific process for preparing the inverted pyramid array structure using chemical wet etching is as follows: Step S11, prepare 6 mol·L -1 Take 10.5 ml of potassium hydroxide solution and add 1 ml of isopropanol and 1 ml of deionized water. Use magnetic stirring to fully mix the etching solution to obtain the etching agent. Step S12: Place the processed silicon wafer and etchant into a constant temperature magnetic stirrer at 60°C and 300 rpm for anisotropic wet etching for 120 min. Step S13: Utilizing the different etching rates of silicon dioxide and silicon, the silicon dioxide film that was not removed by the femtosecond laser is used as a mask to prevent chemical wet etching. The area where the silicon dioxide film was removed is anisotropically etched, and the etchant is chemically wet etched along the crystal phase of single-crystal silicon to obtain a pyramid pit array template, i.e., a silicon template with an inverted pyramid array structure. Step S2: Fabrication of the substrate array using a rapid polymer method; Using the silicon template prepared in step S1, a PDMS substrate array was fabricated using a rapid polymer method; In step S2, the rapid polymer method for preparing the substrate array includes: In step S21, PDMS and curing agent are mixed in a ratio of 10:1; Step S22: Stir for 2 minutes; Step S23: Place the mixture in a vacuum pump to remove air bubbles; Step S24: Slowly pour the PDMS mixed solution into the silicon template and heat it in a 70°C oven for 2 hours; Step S25: After the PDMS has been cured, cut it and place the segmented PDMS substrate array in ethanol and clean it in an ultrasonic cleaner for 10 minutes. Step S26: Obtain the PDMS substrate array; Step S3: Femtosecond laser ablation of the PDMS substrate; The femtosecond laser direct writing method is used, which involves directly ablating the PDMS substrate with a femtosecond laser. The specific process is as follows: Step S31: Using Pharos software, the femtosecond laser source is set to a repetition frequency of 2.5 kHz, an output wavelength of 1030 nm, and a line scan structure spacing of 0.03 mm, so that the surface structure can be completely processed. In step S32, by adjusting the laser energy from 27mw to 42mw and the laser scanning speed from 10mm / s to 30mm / s, the femtosecond laser irradiates the PDMS surface, causing heat accumulation on the surface, thereby triggering a thermal effect and causing changes in the material properties. In step S33, the femtosecond laser simultaneously damages the PDMS surface, creating a rough surface structure. Step S34 completes the preparation of the SERS substrate based on dual reinforcement of graphite carbon materials.
2. The SERS substrate based on dual reinforcement of graphite carbon material according to claim 1, characterized in that, It also includes step S4, electron beam evaporation; To further improve the SERS signal, an electron beam evaporation deposition process was used to uniformly deposit a 50nm thick gold film on the PDMS array substrate after step S3.
3. The SERS substrate based on dual reinforcement of graphite carbon material according to claim 1, characterized in that, The pre-treated silicon wafer refers to the surface of the material processed using a femtosecond laser direct writing processing platform, where the material is a crystalline phase with a 300nm SiO2 film. <100> The SiO2 film on the surface of the silicon wafer is selectively removed from the silicon wafer. The processed silicon wafers are ultrasonically treated for 15 minutes, then rinsed with deionized water and air-dried.
4. The SERS substrate based on dual reinforcement of graphite carbon material according to claim 1, characterized in that, In step S3, the optimal parameters are controlled within five processing conditions by adjusting the laser power and scanning speed: laser power 20mw, scanning speed 10mm / s; or, laser power 30mw, scanning speed 10mm / s; or, laser power 40mw, scanning speed 10mm / s; or, laser power 40mm / s, scanning speed 20mm / s; or, laser power 40mw, scanning speed 30mm / s.
5. The SERS substrate based on dual reinforcement of graphite carbon material according to claim 1, characterized in that, The method for characterizing graphite carbon on a SERS substrate reinforced with dual graphite carbon materials is as follows: SERS substrates prepared under different processing conditions were placed on a Renishaw Raman test stage. The laser power was set to 1%, and the exposure time and number of exposures were 3 s and 2, respectively. The obtained data were processed using Wire 5.5 software to remove background and smooth all Raman spectra before obtaining the final SERS results. Among all the obtained Raman spectra, the results were obtained at 1350 and 1580 cm⁻¹. -1 The unique peaks corresponding to ID / IG of graphitic carbon were observed to indicate the formation of graphitic carbon; ID represents amorphous carbon, IG represents graphitized carbon, and the ratio of ID / IG is related to the degree of graphitization. The smaller the ratio of ID / IG, the higher the degree of graphitization of the material.