Research

Research Thrust 1: Functional Nanomaterials

Carbon Nanomaterials - Graphene

Graphene possesses unprecedented mechanical- and electrical- properties, which potentially benefit high performance, flexible optoelectronic devices (e.g., flexible conductor, transistor) and a variety of energy storage systems (e.g., thermoelectrics, supercapacitor). In NL, we prepare various types of graphene processed by different methods (e.g., CVD, mechanical/chemical exfoliation from graphite) and characterize their electrical and mechanical properties in systematic correlation with their physical structures and chemical doping concentrations.

Nature 2006, 442, 282-286.

Nanocrystal Quantum Dots

Nanocrystal quantum dots exhibit exceptional optical properties, such as broad absorbance, narrow emission, facile bandgap tunability and high photoluminescent quantum yields. In addition, they possess extensive process capabilities amenable to solution based processing methods. In NL, we develop novel synthesis to manipulate the internal structure of nanocrystal quantum dots and characterize their optical properties (e.g., exciton dynamics, spectral window & bandwidth). Our research aims at versatile engineering of optical properties of nanocrystal quantum dots for their use in light-emitting devices, optically & electrically pumped lasers, photovoltaic devices and biological labels.

Visible Quantum Dots

Research Thrust 2: Engineered Nanohybrids & Nanostructures

Metal Photonics & Plasmonics

We pursue efficient engineering of light via metal structures and development of improved fabrication methods for the metal structures. Micro- and nanostructures of a metal allow us to manipulate surface plasmon polaritons (SPPs) – coupled photon-electron waves propagating along a metal-dielectric interface. Since SPPs are able to contain both characteristics of light and charge, exploiting SPPs can lead to novel optical behaviors, for example, concentration of light below the optical diffraction limit, generating large electric-field enhancements in confined regions. This unique characteristics of SPPs have opened up new opportunities for photonic and plasmonic applications such as surface-enhanced spectroscopy, subwavelength waveguides, optical antennas, and solar cells. [J. H. Park et al., ACS Appl. Mater. Interfaces 2013, 5, 9701-9708]

Block Copolymer Patterning

In microelectronic device manufacturing, a feature half-pitch of ~ 22 nm represents the limit of conventional photolithographic methods. Alternative approaches for forming sub-22 nm features, such as electron beam lithography and extreme UV lithography, have some critical drawbacks in terms of cost and throughput. In contrast, block copolymer microphase separation spontaneously generates microdomains with period of <10 nm and above, and thin films of block copolymers can therefore be used to form nanoscale patterns over a large area with low cost in a fast process. Thus, our research group have studied block copolymers for potential applications in nanolithography and device fabrication.

3D Nanocarbon Hybrids

3D nanocarbon-based hybrid structures, made of 2D graphene or 1D nanotubes, could substantially benefit diverse energy conversion/storage applications due to their excellent charge carrier transport properties and catalytic characteristics. However, the construction of 3D nanocarbon hybrids in a desired architecture still remains a challenge. In NL, we focus on the rational design of 3D nanocarbon hybrids to engineer their electrical or electrochemical properties for photovoltaic devices, supercapacitors, ion-batteries, and thermopower generators.

Research Thrust 3: Electronic & Energy Conversion Applications

Stretchable Transparent Conductors

Soft electronics is considered as a key technology that will have broad impact over the society. One critical hurdle for the advancement and commercialization of soft electronics is the development of stretchable transparent conductors. In NL, we strive to understand the science behind stretchable transparent conductors under strain and aim to fabricate devices, such as, stretchable solar cells and touch screens through applying morphologically engineered nanohybrid composites of transparent elastomers and conductive nanomaterials (e.g., graphene, CNT and metal nanowires).

High-Performance, Low-Cost, Reformable Thermoelectrics

Thermoelectrics, which utilize Seebeck and Peltier effect, have received great interests for use in various energy conversion systems. Generally, conventional inorganic semiconductors exhibit high thermoelectric performance, Figure of merits (ZT), but they have daunting drawbacks, such as element scarcity, high production cost, and poor processibility. In NL, we rationally design organic-inorganic nanohybrid systems, which synergistically exploit the high thermoelectric performance from inorganic semiconductors and the extensive processibility, the structural flexibility and the mechanical strength from conductive carbon based nanomaterials.

Graphene Superlattice for NanoElectronics

Graphene is of great interest for electronic devices because of its extraordinary properties, including high mobility, high electrical/thermal conductivity and high transparency, from an atomically-thin two- dimensional material. However, the intrinsic zero bandgap makes it very difficult to achieve the high on/off current ratio required from field-effect transistors useful in digital electronics and high thermal conductivity deteriorates to use as a thermoelectric materials. In order to overcome this hurdle, NLstudies the patterning of graphene into superlattice structures with sub-10 nm periods as a strategy to open the bandgap and lower the thermal conductivity due to quantum confinement and phonon scattering.

Graphene based Energy Storage Devices

Since the graphene was isolated as a freestanding form, intense interest has been incurred to utilize its electrochemical properties. In NL, we investigate the electrochemical properties of graphene based nanocomposites and arrays to implement them into a variety of electrochemical devices including super capacitors or batteries.