Jin Gyeong Son

A Facile Route for Patterned Growth of Metal-Insulator Carbon Lateral Junction through One-Pot Synthesis

Precise graphene patterning is of critical importance for tailor-made and sophisticated two-dimensional nanoelectronic and optical devices. However, graphene-based heterostructures have been grown by delicate multistep chemical vapor deposition methods, limiting preparation of versatile heterostructures. Here, we report one-pot synthesis of graphene/amorphous carbon (a-C) heterostructures from a solid source of polystyrene via selective photo-cross-linking process. Graphene is successfully grown from neat polystyrene regions, while patterned cross-linked polystyrene regions turn into a-C because of a large difference in their thermal stability. Since the electrical resistance of a-C is at least 2 orders of magnitude higher than that for graphene, the charge transport in graphene/a-C heterostructure occurs through the graphene region. Measurement of the quantum Hall effect in graphene/a-C lateral heterostructures clearly confirms the reliable quality of graphene and well-defined graphene/a-C interface. The direct synthesis of patterned graphene from polymer pattern could be further exploited to prepare versatile heterostructures.

Nanoparticles inside nanodishes for plasmon excitations

We demonstrate a simple route to hybridize two different nanomaterials by using three-dimensional nanodishes that can serve as small plasmonic containers to host guest nanoparticles. The nanodishes were fabricated using nanoimprint lithography and oblique-angle film deposition, and the guest nanoparticles were drop-cast onto the host nanodishes. Based on the proposed method, colloidal Au nanoparticles were assembled inside the Au nanodishes in the form of a labyrinth. These Au nanoparticle–nanodish hybrids excited a strong surface plasmon resonance, as verified by a numerical simulation of the local field enhancement and by direct observation of both the enhanced Raman signals and photochemical reactions. Our results point to the potential of the nanodishes as a useful platform for combining diverse nanomaterials and their functionalities.

Electrochemical Release of Amine Molecules from Carbamate-Based, Electroactive Self-Assembled Monolayers

In this paper, carbamate-based self-assembled monolayers (SAMs) of alkanethiolates on gold were suggested as a versatile platform for release of amine-bearing molecules in response to the electrical signal. The designed SAMs underwent the electrochemical oxidation on the gold surface with simultaneous release of the amine molecules. The synthesis of the thiol compounds was achieved by coupling isocyanate-containing compounds with hydroquinone. The electroactive thiol was mixed with 11-mercaptoundecanol [HS(CH(2))(11)OH] to form a mixed monolayer, and cyclic votammetry was used for the characterization of the release behaviors. The mixed SAMs showed a first oxidation peak at +540 mV (versus Ag/AgCl reference electrode), indicating the irreversible conversion from carbamate to hydroquinone groups with simultaneous release of the amine molecules. The analysis of ToF-SIMS further indicated that the electrochemical reaction on the gold surface successfully released amine molecules.

Structural analysis of negative ions by postsource decay in time-of-flight secondary ion mass spectrometry

Phospholipids (PLs) are membrane lipids of living cells whose considerable role in biological membranes include protein sorting and regulation of biophysical properties and signaling pathways. PLs are classified by their head groups into phosphatidic acid, phosphatidylcholine (PC), phosphatidylglycerol, phosphatidylinositol (PI), phosphatidylserine (PS), and cardiolipin. Since PLs have varying ionization efficiencies, depending on their electron affinity, they can be detected at positive or negative ion modes so that PC and PS are generally detected as positive ions, and phosphatidylethanolamine and PI as negative ions. As a result, metabolite analyses in time-of-flight secondary ion mass spectrometry (ToF-SIMS) should be carried out by performing tandem mass spectrometry measurements at both ion modes to identify unknown PLs. For tandem mass spectrometry measurements in ToF-SIMS, a postsource decay (PSD)-like method was successfully applied to identify several lipids by using cholesterol as a model molec...