Ultrastiff, Strong, and Highly Thermally Conductive Crystalline Graphitic Films with Mixed Stacking Order

Abstract

A macroscopic film (2.5 cm × 2.5 cm) made by layer‐by‐layer assembly of 100 single‐layer polycrystalline graphene films is reported. The graphene layers are transferred and stacked one by one using a wet process that leads to layer defects and interstitial contamination. Heat‐treatment of the sample up to 2800 °C results in the removal of interstitial contaminants and the healing of graphene layer defects. The resulting stacked graphene sample is a freestanding film with near‐perfect in‐plane crystallinity but a mixed stacking order through the thickness, which separates it from all existing carbon materials. Macroscale tensile tests yields maximum values of 62 GPa for the Young's modulus and 0.70 GPa for the fracture strength, significantly higher than has been reported for any other macroscale carbon films; microscale tensile tests yield maximum values of 290 GPa for the Young's modulus and 5.8 GPa for the fracture strength. The measured in‐plane thermal conductivity is exceptionally high, 2292 ± 159 W m−1 K−1 while in‐plane electrical conductivity is 2.2 × 105 S m−1. The high performance of these films is attributed to the combination of the high in‐plane crystalline order and unique stacking configuration through the thickness.

Ultrahigh Strength and Modulus Graphene‐Based Hybrid Carbons with AB‐Stacked and Turbostratic Structures

“…The 2D band of graphite is indicative of the stacking sequence of the graphenes, and the symmetrical 2D bands observed in the rG-O and rG-O/PNE films suggest they have a turbostratic structure. [5,33] After the 3000 °C heat treatment, the 2D bands became asymmetric indicating that the high temperature caused AB stacking. [5,33] The asymmetric 2D bands can be deconvoluted into three Lorentzian peaks that can be used to estimate the amount of turbostratic and ABstacked regions (2D T at ≈2700 cm −1 for turbostratic and 2D 1 at ≈2680 cm −1 , and 2D 2 at ≈2720 cm −1 for AB stacking).…”

“…[5,33] After the 3000 °C heat treatment, the 2D bands became asymmetric indicating that the high temperature caused AB stacking. [5,33] The asymmetric 2D bands can be deconvoluted into three Lorentzian peaks that can be used to estimate the amount of turbostratic and ABstacked regions (2D T at ≈2700 cm −1 for turbostratic and 2D 1 at ≈2680 cm −1 , and 2D 2 at ≈2720 cm −1 for AB stacking). [5,34] In the case of the rG-O film, we observed almost no turbostratic character, but the rG-O/PNE film displayed a turbostratic content of ≈20% (Figure 2c).…”

“…[5,33] The asymmetric 2D bands can be deconvoluted into three Lorentzian peaks that can be used to estimate the amount of turbostratic and ABstacked regions (2D T at ≈2700 cm −1 for turbostratic and 2D 1 at ≈2680 cm −1 , and 2D 2 at ≈2720 cm −1 for AB stacking). [5,34] In the case of the rG-O film, we observed almost no turbostratic character, but the rG-O/PNE film displayed a turbostratic content of ≈20% (Figure 2c). The observed differences between the rG-O and rG-O/PNE films after the 3000 °C heat treatment (the presence of D and 2D T bands) are mainly due to the addition of PNE.…”

“…[3] If graphenes could be appropriately assembled at the macroscopic scale, a better performance than existing graphitic materials might be obtained. [5] Currently, the strengths of macroscopic graphene assemblies remain lower than the intrinsic strength of graphite. For example, the strengths of graphitic materials produced from graphene precursors reported to date are about 140 to 2200 MPa for fibers, [10][11][12] and about 40 to 660 MPa for films, [13][14][15][16] which are significantly lower than the in-plane strength of graphite (about 130 GPa).…”

Improving the Performance of Printable Carbon Electrodes by Femtosecond Laser Treatment

“…Now, heat treatment at very high temperatures (>2000 • C) is a stationary annealing process, in which heat diffuses throughout the film thickness. Temperature depth profile is constant, so that thermal energy uniformly "heals" defects (e.g., interstitials, stacking faults) of disordered carbon films, in this way increasing the inter-layer interaction between stacked layers [40]. Conversely, in case of fs-laser treatment, pulse duration is so short that heat diffusion is negligible, so that the temperature depth profile at the very end of the laser pulse is similar to the spatial distribution of the absorbed energy, i.e., sharply decreasing from the surface to the bulk.…”