Direct Growth of Wafer-Scale, Transparent, p-Type Reduced-Graphene-Oxide-like Thin Films by Pulsed Laser Deposition

Abstract

Reduced graphene oxide (rGO) has attracted significant interest in an array of applications ranging from flexible optoelectronics, energy storage, sensing, and very recently as membranes for water purification. Many of these applications require a reproducible, scalable process for the growth of large-area films of high optical and electronic quality. In this work, we report a one-step scalable method for the growth of reduced-graphene-oxide-like (rGO-like) thin films via pulsed laser deposition (PLD) of sp2 carbon in an oxidizing environment. By deploying an appropriate laser beam scanning technique, we are able to deposit wafer-scale uniform rGO-like thin films with ultrasmooth surfaces (roughness <1 nm). Further, in situ control of the growth environment during the PLD process allows us to tailor its hybrid sp2–sp3 electronic structure. This enables us to control its intrinsic optoelectronic properties and helps us achieve some of the lowest extinction coefficients and refractive index values (0.358 and 1.715, respectively, at 2.236 eV) as compared to chemically grown rGO films. Additionally, the transparency and conductivity metrics of our PLD grown thin films are superior to other p-type rGO films and conducting oxides. Unlike chemical methods, our growth technique is devoid of catalysts and is carried out at lower process temperatures. This would enable the integration of these thin films with a wide range of material heterostructures via direct growth.

Controllable Synthesis of Wafer‐Scale Graphene Films: Challenges, Status, and Perspectives

“…[ 1 ] Nevertheless, only a few solutions, including epitaxial growth on SiC, chemical reduction of graphite oxide, and chemical vapor deposition (CVD), enable the preparation of wafer‐scale graphene films. [ 21,32,33 ] As for the epitaxial growth on SiC, graphene is obtained from certain crystallographic planes by thermal decomposition of bulk SiC substrate at an elevated temperature typically above 1400 °C. [ 34 ] Graphene layers are formed by the rearrangement of carbon atoms and the sublimation of silicon atoms, owing to the higher vapor pressure of silicon compared to carbon.…”

“…[ 35 ] Meanwhile, reduced graphene oxide (rGO) could also fulfill wafer‐scale films affording high uniformity. [ 33,36–38 ] Recently, Juvaid et al. reported the synthesis rGO films on target substrates by pulsed laser deposition (PLD), as depicted in Figure 2d.…”

“…reported the synthesis rGO films on target substrates by pulsed laser deposition (PLD), as depicted in Figure 2d. [ 33 ] A 4‐in. wafer can be attained (Figure 2e), which is featured by smooth surface, high transparency, and excellent uniformity (evaluated by Raman spectroscopy in Figure 2f).…”

“…wafer can be attained (Figure 2e), which is featured by smooth surface, high transparency, and excellent uniformity (evaluated by Raman spectroscopy in Figure 2f). [ 33 ] Despite these advances, the process of chemical oxidation introduces a large number of defects in the crystalline structure of rGO, resulting in marked decline in the electrical and thermal properties. [ 12 ]…”

“…(d–f) Reproduced with permission. [ 33 ] Copyright 2020, American Chemical Society. g) An optical image of a 6‐in.…”