Eunho Lee

Water‐Free Transfer Method for CVD‐Grown Graphene and Its Application to Flexible Air‐Stable Graphene Transistors

Transferring graphene without water enables water-sensitive substrates to be used in graphene electronics. A polymeric bilayer (PMMA/PBU) is coated on graphene as a supporting layer for the water-free transfer process and as an excellent passivation layer that enhances device operation.

Facet‐Mediated Growth of High‐Quality Monolayer Graphene on Arbitrarily Rough Copper Surfaces

A synthetic approach for high-quality graphene on rough Cu surfaces via chemical vapor deposition is proposed. High-quality graphene is synthesized on rough Cu surfaces by inducing surface faceting of Cu surfaces prior to graphene growth. The electron mobility of synthesized graphene on the rough Cu surfaces is enhanced to 10 335 cm(2) V(-1) s(-1).

Direct Growth of Highly Stable Patterned Graphene on Dielectric Insulators using a Surface‐Adhered Solid Carbon Source

A novel method is described for the direct growth of patterned graphene on dielectric substrates by chemical vapor deposition (CVD) in the presence of Cu vapor and using a solid aromatic carbon source, 1,2,3,4-tetraphenylnapthalene (TPN), as the precursor. The UV/O3 treatment of the TPN film both crosslinks TPN and results in a strong interaction between the substrate and the TPN that prevents complete sublimation of the carbon source from the substrate during CVD. Substrate-adhered crosslinked TPN is successfully converted to graphene on the substrate without any organic contamination. The graphene synthesized by this method shows excellent mechanical and chemical stability. This process also enables the simultaneous patterning of graphene materials, which can thus be used as transparent electrodes for electronic devices. The proposed method for the synthesis directly on substrates of patterned graphene is expected to have wide applications in organic and soft hybrid electronics.

Enhanced sensitivity of a microfabricated resonator using a graphene-polystyrene bilayer membrane

A graphene layer was synthesized using chemical vapor deposition methods and a polystyrene solution was spin-cast onto the graphene film. The graphene-polystyrene bilayer membrane was attached between the two tines of a microfabricated quartz tuning fork (QTF). The modulus of the graphene-polystyrene bilayer was measured to be twice that of a pristine polystyrene membrane. Exposure of the membrane-coated QTF to ethanol vapor decreased the resonance frequency of the microresonator. The bilayer membrane-coated QTF produced a frequency change that was three times the change obtained using a polystyrene membrane-coated QTF, with a lower degree of degradation in the Q factor. The limit of detection of the bilayer membrane-coated QTF to ethanol vapor was determined to be 20u2009ppm.

Relationship between the dipole moment of self-assembled monolayers incorporated in graphene transistors and device electrical stabilities

Surface characteristics of the gate-dielectric layers in graphene field-effect transistors (FETs) critically affect the electrical properties of the devices. In this report, the effects of self-assembled monolayers (SAMs) on the electrical properties of graphene FETs were examined by using various SAM buffer layers with different end groups and alkyl chain lengths. Especially, the dipole moment of the SAMs affects the doping properties of graphene as well as field-effect mobility, hysteresis, and stability of graphene FETs. The type and magnitude of doping are dependent on the functional groups in SAMs: Electron withdrawing fluorine groups p-dope the graphene whereas electron donating amine groups n-dope the graphene. The electrical stabilities such as hysteresis and gate-bias instability are mainly governed by the magnitude of the dipole moment in SAMs. Hexamethyldisilazane treatment resulted in graphene FETs with the highest electrical stabilities, because of the short one aliphatic alkyl chain with a negligible dipole moment. In contrast, in graphene FETs with SAMs having a strong dipole moment, electrical stabilities deteriorated by the charge trapping in SAMs.