Sae Mi Lee

Anti‐Solvent Derived Non‐Stacked Reduced Graphene Oxide for High Performance Supercapacitors

An anti-solvent for graphene oxide (GO), hexane, is introduced to increase the surface area and the pore volume of the non-stacked GO/reduced GO 3D structure and allows the formation of a highly crumpled non-stacked GO powder, which clearly shows ideal supercapacitor behavior.

Photo-switchable molecular monolayer anchored between highly transparent and flexible graphene electrodes

A molecular ultra-thin film (for example, a molecular monolayer) with graphene electrodes would allow for the realization of superior stable, transparent and flexible electronics. A realistic prospect regarding the use of graphene in two-terminal molecular electronic devices is to fabricate a chemically stable, optically transparent, mechanically flexible and molecularly compatible junction. Here we report on a novel photo-switchable molecular monolayer, one side chemically and the other side physically anchored between the two graphene electrodes. The photo-switchable organic molecules specified with an electrophilic group are chemically self-assembled into a monolayer on the graphene bottom electrode, while the other end is physically contacted to the graphene top electrode; this arrangement provides excellent stability for a highly transparent and flexible molecular monolayer device with a high device yield due to soft contacts at the top electrode interface. Thus, the transparent graphene electrodes allow stable molecular photo-switching due to photo-induced changes in the molecular conformational length.

Highly hydrophilic and insulating fluorinated reduced graphene oxide

A facile method for the synthesis of highly fluorinated reduced graphene oxide from graphene oxide using BF3-OEt2 solution and alkylthiol/alkylamine on the Gram scale has been described using a detailed mechanism. The maximum fluorination was as high as 38 wt% and the fluorinated reduced graphene oxide produced has great wettability and high insulating properties.

Voltage‐Controlled Nonvolatile Molecular Memory of an Azobenzene Monolayer through Solution‐Processed Reduced Graphene Oxide Contacts

The solution-processed fabrication of an azobenzene (ABC10) monolayer-based nonvolatile memory device on a reduced graphene oxide (rGO) electrode is successfully accomplished. Trans--cis isomerizations of ABC10 between two rGO electrodes in a crossbar device are controlled by applied voltage. An rGO soft-contact top electrode plays an important role in the conformational-change-dependent conductance switching process of an ABC10 monolayer.

Hybrid windshield-glass heater for commercial vehicles fabricated via enhanced electrostatic interactions among a substrate, silver nanowires, and an over-coating layer

We introduce a transparent windshield-glass heater produced via transparent electrodes using silver nanowire (AgNW) networks for conventional use in the automobile industry. A high-quality conducting hybrid film is deposited on a plasma-treated glass substrate by spraying AgNWs, immersing the sprayed product in positively charged adhesive polymer solution, and then spraying negatively charged graphene oxide (GO) and a silane layer as an over-coating layer (OCL).The results of heating tests conducted after adhesion tests show that the sheet resistance changes with the application of polymer glue. Surprisingly, the transmittance of the film with the GO OCL is higher than that of the film without the GO OCL. Heating and defrosting tests are carefully conducted via infrared (IR) monitoring. Adhesive-polymer-treated and GO-protected AgNW transparent glass heaters exhibit the best performance with low sheet resistance; thus, through strong electrostatic interaction among the substrate, adhesive layer, and OCL, our AgNW hybrid glass heater can reach the target temperature with a standard vehicle voltage of 12 V in a short period of time.

Tunable Sub-nanopores of Graphene Flake Interlayers with Conductive Molecular Linkers for Supercapacitors

Although there are numerous reports of high performance supercapacitors with porous graphene, there are few reports to control the interlayer gap between graphene sheets with conductive molecular linkers (or molecular pillars) through a π-conjugated chemical carbon-carbon bond that can maintain high conductivity, which can explain the enhanced capacitive effect of supercapacitor mechanism about accessibility of electrolyte ions. For this, we designed molecularly gap-controlled reduced graphene oxides (rGOs) via diazotization of three different phenyl, biphenyl, and para-terphenyl bis-diazonium salts (BD1-3). The graphene interlayer sub-nanopores of rGO-BD1-3 are 0.49, 0.7, and 0.96 nm, respectively. Surprisingly, the rGO-BD2 0.7 nm gap shows the highest capacitance in 1 M TEABF4 having 0.68 nm size of cation and 6 M KOH having 0.6 nm size of hydrated cation. The maximum energy density and power density of the rGO-BD2 were 129.67 W h kg(-1) and 30.3 kW kg(-1), respectively, demonstrating clearly that the optimized sub-nanopore of the rGO-BDs corresponding to the electrolyte ion size resulted in the best capacitive performance.

Changes in major charge transport by molecular spatial orientation in graphene channel field effect transistors

Changes in major charge transport of graphene channel transistors in terms of the spatial orientation of adsorbed functional molecules were demonstrated. In contrast to the horizontally (physically) bound molecules, the vertically (chemically) bound molecules did not change major charge carriers of graphene channels, revealing the molecular orientation-dependent doping effects.

Catalyst-free bottom-up growth of graphene nanofeatures along with molecular templates on dielectric substrates

Synthesis of graphene nanostructures has been investigated to provide outstanding properties for various applications. Herein, we report molecular thin film-assisted growth of graphene into nanofeatures such as nanoribbons and nanoporous sheets along with a predetermined molecular orientation on dielectric substrates without metal catalysts. A Langmuir-Blodgett (LB) method was used for the formation of the molecularly patterned SiO2 substrates with ferric stearate layers, which acted as a template for the directional growth of the polypyrrole graphene precursor. The nanofeatures of the graphene were determined by the number of ferric stearate layers (e.g., nanoribbons from multiple layers and nanoporous sheets from a single layer). The graphene nanoribbons (GNRs) containing pyrrolic N enriched edges exhibited a p-type semiconducting behavior, whereas the nanoporous graphene sheets containing inhomogeneous pores and graphitic N enriched basal planes exhibited the typical electronic transport of nitrogen-doped graphene. Our approaches provide two central methods for graphene synthesis such as bottom-up and direct processes for the future development of graphene nanoelectronics.