We fabricated a highly oxidized large-scale graphene platform using chemical vapor deposition (CVD) and UV/ozone-based oxidation methods. This platform offers a large-scale surface-enhanced Raman scattering (SERS) substrate with large chemical enhancement in SERS and reproducible SERS signals over a centimeter-scale graphene surface. After UV-induced ozone generation, ozone molecules were reacted with graphene to produce oxygen-containing groups on graphene and induced the p-type doping of the graphene. These modifications introduced the structural disorder and defects on the graphene surface and resulted in a large chemical mechanism-based signal enhancement from Raman dye molecules [rhodamine B (RhB), rhodamine 6G (R6G), and crystal violet (CV) in this case] on graphene. Importantly, the enhancement factors were increased from ∼10(3) before ozone treatment to ∼10(4), which is the largest chemical enhancement factor ever on graphene, after 5 min ozone treatment due to both high oxidation and p-doping effects on graphene surface. Over a centimeter-scale area of this UV/ozone-oxidized graphene substrate, strong SERS signals were repeatedly and reproducibly detected. In a UV/ozone-based micropattern, UV/ozone-treated areas were highly Raman-active while nontreated areas displayed very weak Raman signals.

We have devised a method to optimize the performance of organic field-effect transistors (OFETs) by controlling the work functions of graphene electrodes by functionalizing the surface of SiO2 substrates with self-assembled monolayers (SAMs). The electron-donating NH2-terminated SAMs induce strong n-doping in graphene, whereas the CH3-terminated SAMs neutralize the p-doping induced by SiO2 substrates, resulting in considerable changes in the work functions of graphene electrodes. This approach was successfully utilized to optimize electrical properties of graphene field-effect transistors and organic electronic devices using graphene electrodes. Considering the patternability and robustness of SAMs, this method would find numerous applications in graphene-based organic electronics and optoelectronic devices such as organic light-emitting diodes and organic photovoltaic devices.

Selective n-type doping of graphene is developed by utilizing patternable gold nanoparticles functionalized with photoreactive cinnamate moieties. The gold nanoparticles can be regularly patterned on the graphene by UV-induced cross-linking of cinnamate, which provides a convenient method to control the optical and electrical properties of graphene site-specifically. The strong n-type doping of graphene covered with the patterned gold nanoparticles was confirmed by Raman, X-ray photoelectron spectroscopy, and electron transport measurements. We believe that our method would find numerous applications in the area of graphene-based optoelectronics including light-emitting devices, solar cells, and optical sensors.

We report a photo and field (PF)-induced doping of a graphene-heterostructure field-effect transistor (graphene HFET) using a double-layered gate insulator consisting of narrow-bandgap insulator (NGI) and widebandgap insulator (WGI). The PF-induced doping in the graphene HFETs with variable NGIs (hafnium oxide, silicon nitride, and hexagonal boron nitride) are investigated, and consequently we reveal that this rewritable/erasable doping behavior is not limited to specific insulating materials, but unexceptionally accomplished when a step-like vertical band diagram, that is graphene/NGI/WGI, is fulfilled in the device. We clearly verify that this doping is originated from PF-induced charge transfer between graphene and defects at the NGI/WGI interface, and then the polarized charges at the NGI/WGI interface pretend to be "remote dopants", shifting Dirac voltage of the device. The remote dopant is highly stable in the dark due to the presence of the adjacent insulators providing enormous energy barriers, but can be efficiently tuned by the modulation of the gate bias and incident photon energy. Because the PF-induced doping mechanism is not limited by specific materials that is still hard to be synthesized as a large scale, the graphene HFET memory devices can be patterned with a large scale using practical fabrication processes, appealing to industrial applications.