Hyunjung Jung

Three-Dimensional Multilayered Nanostructures with Controlled Orientation of Microdomains from Cross-Linkable Block Copolymers

Three-dimensional (3D) nanostructures were obtained by the directed formation of multilayer block copolymer (BCP) thin films. The initial step in this strategy involves the assembly and cross-linking of cylinder-forming polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) BCP, in which 1.5 mol % of reactive azido (-N(3)) groups were randomly incorporated along the styrene backbone. Significantly, assembly of thin films of lamellar-forming BCPs on top of the underlying cross-linked cylindrical layer exhibited perpendicular orientations of microdomains between lamellae and cylinder layers. From the theoretical calculation of free energy in the multilayers, it was found that the nematic interactions between polymer chains at the interface play a critical role in the perpendicular orientation of lamellae on the cross-linked cylinder layers. Removal of the PMMA domains then affords nonsymmetrical nanostructures which illustrate the promise of this strategy for the design of well-defined 3D nanotemplates. It was also demonstrated that this structure can be effectively used to enhance the light extraction efficiency of GaN light-emitting diodes. Furthermore, we anticipate that such 3D nanotemplates can be applied to various areas, including advanced BCP nanolithography and responsive surface coating.

Microarray analysis of normal cervix, carcinoma in situ, and invasive cervical cancer: identification of candidate genes in pathogenesis of invasion in cervical cancer

The objective of this study was to identify genes that are related to pathogenesis of carcinoma in situ (CIS) to invasive cervical cancer with the use of oligonucleotide microarray and reverse transcription-polymerase chain reaction (RT-PCR). Each two cases of normal cervix, CIS, and invasive cervical cancer were investigated with DNA microarray technology. Differential gene expression profiles among them were analyzed. Expression levels of selected genes from the microarray results were confirmed by RT-PCR. The expressions of 15,286 genes were compared and 458 genes were upregulated or downregulated by twofold or more compared with each other group. Among 458 genes, 22 genes were upregulated and 40 genes were downregulated by twofold or more in invasive cervical cancer group compared with CIS group. RT-PCR analysis confirmed upregulation of 18 genes and downregulation of 5 genes in invasive cervical cancer group. RBP1, TFRC, SPP1, SAA1, ARHGAP8, and NDRG1, which were upregulated, and GATA3, PLAGL1, APOD, DUSP1, and CYR61, which were downregulated, were considered as candidate genes associated with invasion of cervical cancer.

Creating opal-templated continuous conducting polymer films with ultralow percolation thresholds using thermally stable nanoparticles

We propose a novel and robust strategy for creating continuous conducting polymer films with ultralow percolation thresholds using polymer-coated gold nanoparticles (Au NPs) as surfactant. Continuous poly(triphenylamine) (PTPA) films of high internal phase polymeric emulsions were fabricated using an assembly of cross-linked polystyrene (PS) colloidal particles as template. Polymer-coated Au NPs were designed to be thermally stable even above 200 °C and neutral to both the PS and PTPA phases. Therefore, the Au NPs localize at the PS/PTPA interface and function as surfactant to efficiently produce a continuous conducting PTPA polymer film with very low percolation thresholds. The volume fraction threshold for percolation of the PTPA phase with insulating PS colloids (as measured by electron microscopy and conductivity measurements) was found to be 0.20. In contrast, with the addition of an extremely low volume fraction (φ(p) = 0.35 vol %) of surfactant Au NPs, the volume fraction threshold for percolation of the PTPA phase was dramatically reduced to 0.05. The SEM and TEM measurements clearly demonstrated the formation of a continuous PTPA phase within the polyhedral phase of PS colloids. To elucidate the influence of the nanoparticle surfactant on the blend films, the morphology and conductivity of the blends at different PS colloid/PTPA volume ratios were carefully characterized as a function of the Au NP concentration. Our approach provides a methodology for a variety of applications that require a continuous phase for the transport of molecular species, ions, or electrons at low concentrations and a second phase for mechanical support or the conduction of a separate species.

GaN-Based Light-Emitting Diode With Three-Dimensional Silver Reflectors

We present a simple and robust method to fabricate three-dimensional Ag reflectors on GaN light-emitting diodes (LEDs) using SiO 2 nanospheres as the template. First, the hexagonal arrays of SiO2 nanosphere monolayer were spun-cast on a benzocyclobutene (BCB) layer, which was prepared on a sapphire surface. Then, the bottom half of the SiO2 nanospheres were embedded into the BCB layer after heating, resulting in arrays of ldquonano-lensesrdquo that were in the shape of convex hemispheres. The concave-shaped hemisphere arrays were produced by etching the SiO2 nanospheres with an HF solution. Ag was deposited onto both patterns, concave and convex hemispheres, resulting in the formation of three-dimensional Ag reflectors. From the electroluminescence measurements, these Ag reflectors, which contained either concave or convex hemisphere patterns, were found to enhance the light output of GaN LEDs by as much as 29%-33%.

Tuning photoluminescence of organic rubrene nanoparticles through a hydrothermal process

Light-emitting 5,6,11,12-tetraphenylnaphthacene (rubrene) nanoparticles (NPs) prepared by a reprecipitation method were treated hydrothermally. The diameters of hydrothermally treated rubrene NPs were changed from 100 nm to 2 μm, depending on hydrothermal temperature. Photoluminescence (PL) characteristics of rubrene NPs varied with hydrothermal temperatures. Luminescence of pristine rubrene NPs was yellow-orange, and it changed to blue as the hydrothermal temperature increased to 180°C. The light-emitting color distribution of the NPs was confirmed using confocal laser spectrum microscope. As the hydrothermal temperature increased from 110°C to 160°C, the blue light emission at 464 to approximately 516 nm from filtered-down NPs was enhanced by H-type aggregation. Filtered-up rubrene NPs treated at 170°C and 180°C exhibited blue luminescence due to the decrease of intermolecular excimer densities with the rapid increase in size. Variations in PL of hydrothermally treated rubrene NPs resulted from different size distributions of the NPs.