Phonon energy dispersions in graphene. e) Raman spectra of pristine (top) and defected (bottom) graphene. Similar to (c), the left side of the dashed line is the uncoated region. e) Raman spectra of the marked points in (d). f and g) SEM images of (f) 2-layer and (g) 3-layer PAA (BTDA-PDA) LB film after annealing at 1050 oC on SiO2/Si, showing the boundary lines of the uncoated and coated regions.. a) Optical image of graphene as synthesized from monolayer BTDA-PDA; the material contains approximately 7.2% vacancies. Proposed mechanism of graphene growth on copper substrates from different polymer precursors. a) Change in weight as a function of temperature.
Growth of bilayer graphene using copper deposition. a) Skema (b) SEM and (c) Raman spectra of bilayer graphene growth. Raman spectra after heat treatment of PVbd at 800 oC on each substrate depending on the cooling rate.
Characteristics and Importance of graphene
Applications of graphene
Introduction: Research background for graphene growth using polymer sources by chemical vapor deposition. Graphene is a two-dimensional, one-atom thick and honeycomb-shaped crystalline carbon film, an allotrope of carbon. Overview of applications of graphene in various sectors ranging from conductive inks to chemical sensors, light-emitting devices, composites, energy, touch panels and high-frequency electronics13.
Nanomedicine, which uses nanotechnology for treatment, diagnosis and monitoring, offers drug delivery systems, imaging agents and combines the diagnostic process with therapy. Graphene's properties, which are large surface area, chemical purity and the possibility of functionalization, offer opportunities for nanomedicine.
An optical analysis of graphene by Raman spectroscopy
Electrons, phonons and Raman spectra of graphene (a) Electronic Brillouin zones of graphene (black hexagons), Brillouin zone with the first phonon (red diamond) and electron dispersion scheme (Dirac cones). Phonon energy distributions in graphene. e) Raman spectra of intact (top) and defected (bottom) graphene16. Also, the intensity of the 2D peak is very large because the scattering undergoes a double resonance, at Κ and Κ'.
Development of synthetic method of graphene based on chemical vapor deposition (CVD)
Synthesis of graphene on Cu using gas source
Synthesis of graphene using solid precursor as a carbon source and its growth mechanism 7
Top inset, IDS–VDS properties as a function of VG; VG changes from 0 V (bottom) to 240 V (top). Bottom inset, SEM (JEOL-6500 microscope) image of this device where the PMMA-derived graphene is perpendicular to the Pt leads. During the transfer process of catalytic metal to arbitrary substrates, not only unwanted damage such as impurities and defect will be made, but also additional expenses and time are required.
Increasing the size of graphene crystals, controlling the layer number and stacking order, and handling the doping level are another major challenge for graphene growth. Finally, from a cost perspective, graphene growth at low temperature is preferred. Since the growth process is carried out at high temperatures, it is expensive and consumes a lot of energy.
Advantages of using a polymer as a graphene precursor
Conversion of Ultrathin Polyimide Film to Graphene and Study on Conversion Mechanism
Experimental section
- Synthesis and sample preparation
- LB assembly
- Conversion reaction
- Characterization
To prepare multilayer coated films of PAAs, 15 minute delays were used after each layer of film was deposited. Afterwards, the PAA salt-coated Cu substrate was dried in an oven thermostat at 80 oC for 1 h to evaporate the remaining solvent. To prepare an LB film of PMMA, a 0.1% of a chlorobenzene solution of PMMA (MicroChem Corp., 950 PMMA C4, 4% in chlorobenzene) was used; all other steps were unchanged.
The sample was then cooled from the oven and transferred to a SiO2 (300 nm)/Si substrate by etching with ammonia persulfate (0.1 M) solution. Optical imaging was obtained using an Axio.A1 scope (Carl Zeiss) and SEM images were obtained with an S-4800 instrument (Hitachi). Raman spectra were measured using an Alpha 300s micro Raman spectrometer (WITec) equipped with a 532 nm laser.
The NMR spectra were recorded using an Ascend 400 MHz spectrometer (Bruker) using DMSO-d6 as the solvent.
Results and discussion
To investigate the thermal stabilities of the PIs, the weight change during the thermal annealing process was monitored by thermogravimetric analysis (TGA) at a heating rate of 100 °C/min (up to a maximum of 1000 °C). The high thermal stabilities of the PIs are widely known and such materials have been used in a wide range of applications54. The thickness of the PAA monolayers was determined to be ∼1 nm by AFM (see Table S1).
The sharp peaks of the G and 2D bands and the high 2D/G ratio (2.25) measured in the respective Raman spectra (Fig. 8(d)) suggested to us that the PI-GR (BTDA-PDA) product was indeed monolayer graphene. . The lack of a D-band in the Raman spectrum of the product was also consistent with the formation of a defect-free surface. In comparison, graphene grown from a monolayer of PMMA (PMMA-GR) showed strong D and G bands and a very weak 2D band, results indicative of the incomplete formation of graphene 16, 56.
First, BTDA-PDA-derived PAA films were prepared on SiO2/Si substrates (instead of Cu foils) and then heated to elevated temperatures. To determine whether there is a dependence of the conversion on the thickness of the PI film, a series of PI and PMMA LB films with different thicknesses (1, 2, 3 or 5 layers) were independently prepared on separate Cu substrates (Table S1). Figures 11(a) and 11(b) showed that monolayers and bilayers of PAA resulted in the formation of high-quality graphene, while the use of three or five layers of PAA as precursors resulted in the formation of defective graphene.
The left and right sides of the dashed line are uncoated and coated areas with BTDA-PDA, respectively. As noted in the TGA results described above, approx. 50% of the original amount of PAA remains after heating the material to 1,000 °C. As shown in Figure 14, inspection of the temperature-dependent Raman spectra recorded for BTDA-PDA on Cu foils revealed that the size of the graphitic domains (crystallites) increased during the carbonization process, consistent with the mechanism described above.
On the other hand, thicker PAA films (i.e., those composed of three or five layers) may not have resulted in the formation of high-quality graphene after annealing because the upper regimes of carbonized materials were not in contact with the Cu surface and therefore less likely to undergo structural rearrangement. Finally, we discuss how the quality of PI-GR products depends on the type of PI precursor used.
Conclusion
However, the deposited copper is much thinner than the copper foil and therefore evaporated during the 1050 oC heat treatment. Although we experimented through many factors such as reaction temperature, Cu deposition thickness, reaction time, and so on, we finally could not make uniform bilayer graphene. From the Raman spectra shown in figure 8(d) , we concluded that the PI-GRs grown from the BTDA-based PIs were of higher quality than those prepared from the PMDA-based PIs is.
It is known that BTDA-based PIs and PMDA-based PIs have different glass transition temperatures (Tg 280 ~ 320 °C for the former and 400 ~ 420 °C for the latter), but similar decomposition temperature (Td 500 °C). The relatively wide temperature range between the Tg and the Td displayed by the BTDA-based PIs may have allowed sufficient rearrangement during the heat treatment and resulted in the formation of a well-ordered structure. Similarly, the small temperature window between the Tg and the Td exhibited by the PMDA-based PIs was insufficient to allow proper realignment.
In support of this conclusion, annealing PMDA-based PIs at 450 oC improved the quality of the formed graphene (see Figure 16). Formation of graphene from (b) PAA and (c) PMMA according to the corresponding temperature of the graph shown above. The integrated intensity ratio, ID/IG, was used to determine the in-plane crystallite size La (nm) using the Tuinstra-Koenig relationship [1].
At 1,050 oC, a significant D peak could not be detected, preventing the calculation of the corresponding crystallite size.
Growth of Graphene at Low Temperature by Using Ultrathin Poly Vinyl butadiyne Thin Film
Experimental section
The TGA data in Figure 19(b) and (d) show how much polymer remains after heat treatment at 800 oC. It is also believed that the TMS group plays a role in retaining the polymer so that the polymer does not solidify and maintains its position during the early stage of the heat treatment. During the heat treatment process, parameters observed to control graphene quality include temperature, treatment time, polymer film types and thickness, substrate, gas type and amount, polymer oxidation, polymer film thickness, and cooling rate. .
Platinum acted as a good catalyst for the decomposition of the precursor material into smaller building units, which are essential for the synthesis of graphene and for the arrangement of carbon moieties into the graphite domain with a high diffusion coefficient. In Figure 20, the Raman spectra shown represented the results of heat treatment at 800 oC for 1 hour and cooling by adjusting the cooling rate. Oxidative treatment of poly(vinyl acetylene) before the carbonization step strongly affects the pyrolysis of the polymer63.
They identified and confirmed the formation of the functional groups -C=O and -O-H by IR spectroscopy. We also check the formation of functional groups such as C=O (1720) and benzene ring (1600) by IR after heat treatment at 200 oC with oxygen in the atmosphere. But when heat treated at 200 oC and atmospheric pressure, the amount of carbon remaining is relatively small.
We did a control experiment adjusting the pressure of 0.2 torr using Ar gas and the pump, but the D/G peak intensity ratio is about 1.6, the result of which is similar to the case of heat treatment at atmospheric pressure at 200 oC. It is also expected to be graphitized by heat treatment through the cycling and carbonization process. Kaburagi, Y.; Hishiyama, Y., Highly crystallized graphite films prepared by high-temperature heat treatment from carbonized aromatic polyimide films.
C.; Flandrois, S.; Daulan, C.; Saadaoui, H., AFM and STM studies of the carbonization and graphitization of polyimide films. Choi, J.-H.; Li, Z.; Cui, P.; Fan, X.; Zhang, H.; Zeng, C.; Zhang, Z., Drastic reduction in the growth temperature of graphene on copper by increased London dispersion force.
