Graft copolymer-templated mesoporous TiO(2) films micropatterned with poly(ethylene glycol) hydrogel: novel platform for highly sensitive protein microarrays

In this study, we describe the use of organized mesoporous titanium oxide (TiO(2)) films as three-dimensional templates for protein microarrays with enhanced protein loading capacity and detection sensitivity. Multilayered mesoporous TiO(2) films with high porosity and good connectivity were synthesized using a graft copolymer consisting of a poly(vinyl chloride) (PVC) backbone and poly(oxyethylene methacrylate) (POEM) side chains as a structure-directing template. The average pore size and thickness of the TiO(2) films were 50-70 nm and 1.5 μm, respectively. Proteins were covalently immobilized onto mesoporous TiO(2) film via 3-aminopropyltriethoxysilane (APTES), and protein loading onto TiO(2) films was about four times greater than on planar glass substrates, which consequently improved the protein activity. Micropatterned mesoporous TiO(2) substrates were prepared by fabricating poly(ethylene glycol) (PEG) hydrogel microstructures on TiO(2) films using photolithography. Because of non-adhesiveness of PEG hydrogel towards proteins, proteins were selectively immobilized onto surface-modified mesoporous TiO(2) region, creating protein microarray. Specific binding assay between streptavidin/biotin and between PSA/anti-PSA demonstrated that the mesoporous TiO(2)-based protein microarrays yielded higher fluorescence signals and were more sensitive with lower detection limits than microarrays based on planar glass slides.     

Trap-assisted tunneling in Si-InAs nanowire heterojunction tunnel diodes

We report on the electrical characterization of one-sided p(+)-si/n-InAs nanowire heterojunction tunnel diodes to provide insight into the tunnel process occurring in this highly lattice mismatched material system. The lattice mismatch gives rise to dislocations at the interface as confirmed by electron microscopy. Despite this, a negative differential resistance with peak-to-valley current ratios of up to 2.4 at room temperature and with large current densities is observed, attesting to the very abrupt and high-quality interface. The presence of dislocations and other defects that increase the excess current is evident in the first and second derivative of the I-V characteristics as distinct peaks arising from trap-and phonon-assisted tunneling via the corresponding defect levels. We observe this assisted tunneling mainly in the forward direction and at low reverse bias but not at higher reverse biases because the band-to-band generation rates are peaked in the InAs, which is also confirmed by modeling. This indicates that most of the peaks are due to dislocations and defects in the immediate vicinity of the interface. Finally, we also demonstrate that these devices are very sensitive to electrical stress, in particular at room temperature, because of the extremely high electrical fields obtained at the abrupt junction even at low bias. The electrical stress induces additional defect levels in the band gap, which reduce the peak-to-valley current ratios.     

Transformable functional nanoscale building blocks with wafer-scale silicon nanowires

Through the fusion of electrostatics and mechanical dynamics, we demonstrate a transformable silicon nanowire (SiNW) field effect transistor (FET) through a wafer-scale top-down approach. By felicitously taking advantage of the proposed electrostatic SiNW-FET with mechanically movable SiNWs, all essential logic gates, including address decoders, can be monolithically integrated into a single device. The unification of various functional devices, such as pn-diodes, FETs, logic gates, and address decoders, can therefore eliminate the complex fabrication issues associated with nanoscale integration. These results represent a step toward the creation of multifunctional and flexible nanoelectronics.     

Imaging stacking order in few-layer graphene

Few-layer graphene (FLG) has been predicted to exist in various crystallographic stacking sequences, which can strongly influence the material's electronic properties. We demonstrate an accurate and efficient method to characterize stacking order in FLG using the distinctive features of the Raman 2D-mode. Raman imaging allows us to visualize directly the spatial distribution of Bernal (ABA) and rhombohedral (ABC) stacking in tri- and tetralayer graphene. We find that 15% of exfoliated graphene tri- and tetralayers is composed of micrometer-sized domains of rhombohedral stacking, rather than of usual Bernal stacking. These domains are stable and remain unchanged for temperatures exceeding 800 °C.     

Synthesis of LiFePO4 nanoparticles by solvothermal process using various polyol media and their electrochemical properties

Olivine structured LiFePO4 samples were synthesized by solvothermal process using various polyol media of ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG), and tetraethylene glycol (TTEG) without any heating as a post procedure. The X-ray diffraction patterns of the samples prepared in EG and DEG showed the crystalline peaks with well-fitted to the positions on the basis of an olivine type structure without any impurities. In order to determine the unit cell parameters, synchrotron powder XRD patterns were fitted with whole-pattern profile matching method using FULLPROF program. The obtained samples exhibited well dispersed nanoplate morphologies excepting for the sample prepared in EG. The samples prepared in EG, DEG, TEG, and TTEG showed the reversible capacity of 118, 167, 90, and 105 mAh/g at current density of 0.1 mA/cm2, respectively. Among them, the samples reacted in DEG and TTEG showed good performances at high rate of 16C with high capacities retention.     

Carbon contamination analysis and its effect on extreme ultra violet mask imaging performance using coherent scattering microscopy/in-situ accelerated contamination system

The coherent scattering microscopy/in-situ accelerated contamination system (CSM/ICS) is a developmental metrology tool designed to analyze the impact of carbon contamination on the imaging performance. It was installed at 11B EUVL beam-line of the Pohang Accelerator Laboratory (PAL). Monochromatized 13.5 nm wavelength beam with Mo/Si multilayer mirrors and zirconium filters was used. The CSM/ICS is composed of the CSM for measuring imaging properties and the ICS for implementing acceleration of carbon contamination. The CSM has been proposed as an actinic inspection technique that records the coherent diffraction pattern from the EUV mask and reconstructs its aerial image using a phase retrieval algorithm. To improve the CSM measurement accuracy, optical and electrical noises of main chamber were minimized. The background noise level measured by CCD camera was approximately 8.5 counts (3 sigma) when the EUV beam was off. Actinic CD measurement repeatability was <1 A (3 sigma) at 17.5 nm line and space pattern. The influence of carbon contamination on the imaging properties can be analyzed by transferring EUV mask to CSM imaging center position after executing carbon contamination without a fine alignment system. We also installed photodiode and ellipsometry for in-situ reflectivity and thickness measurement. This paper describes optical design and system performance observed during the first phase of integration, including CSM imaging performance and carbon contamination analysis results.     

Micro-contact printing of polydiacetylene liposomes using hydrophilic stamps

Micron-sized polydiacetylene (PDA) liposome patterns have been fabricated on titanium (Ti) substrates using a micro-contact printing (micro-CP) technique. Two types of stamps (PDMS and agarose) and inking methods ("soaking" and "dropping") are used for micro-CP, and we compare their effect on the morphology of the PDA patterns. The size and morphology of the patterned PDA liposomes are analysized by optical and fluorescence microscopies and atomic force microscopy (AFM). When the agarose stamp is inked by the "dropping" method, PDA patterns are most efficiently transferred to the Ti substrate. However, the thickness of the transferred PDA patterns is not homogeneous, with the edge of the transferred pattern being thicker than its center. In contrast, when the PDMS stamp is used for micro-CP, the center of the pattern is thicker than the edge. Red fluorescence patterns are readily obtained by heat treatment of the PDA-immobilized solid substrate. The intensity of the fluorescence of the samples is consistent with the results of optical microscopy and AFM experiments.     

Effect of sintering temperature on electrical characteristics of screen-printed Ag nanopaste on FR4 substrate

We investigated the feasibility of a printing technology for Ag circuit formation on a FR4 substrate. A conductive paste containing Ag nanoparticles (73 wt%) of 20-50 nm diameter was screen printed on an FR4 substrate and sintered under a sintering temperature ranging from 100 degrees C to 200 degrees C for 30 min. We carried out the thermal analysis of the Ag nanopaste to confirm the suitability of the set-up conditions. To investigate the sintering degree with various temperatures, fractured cross-sections were observed by field emission scanning electron microscopy (FESEM). For electrical characterization of the printed Ag circuit, a four-point probe method was used to measure the direct current (DC) resistivity, while a network analyzer and Cascade's probe system in the frequency range from 10 MHz to 20 GHz were used to measure the scattering parameters (S-parameter) of the sintered Ag conducting patterns. The resistivity under the application of a DC signal decreased as the temperature increased. The measured S-parameters indicated that the electrical losses decreased as the sintering temperature increased due to the interparticle neck formation after heat treatment at high temperatures.     

New blue phosphorescent iridium complexes containing phenylpyridine and triazole ligands: synthesis and luminescence studies

The synthesis and luminescence of iridium(III) complexes containing new phenylpyridine (C(see test for symbol)N) ligands, 4-Me-4'-F-ppy, 4-Me-4'-CF3-ppy and 4-OMe-4'-CF3-ppy, were studied. These ligands were designed for development of the blue light-emitting iridium complexes by introducing the electron-withdrawing group (F, CF3) and the electron-donating group (Me, OMe) at the para positions of the phenyl and pyridine ligand rings, respectively. As an ancillary ligand, trzl-CMe3 was employed where trzl-CMe3 represents 2-(5-tert-butyl-2H-1,2,4-triazol-3-yl)pyridine. The resulting iridium complexes, Ir(4-Me-4'-F-ppy)2(trzl-CMe3), Ir(4-OMe-4'-CF3-ppy)2 (trzl-CMe3) and Ir(4-Me-4'-CF3-ppy)2(trzl-CMe3) exhibited the blue emission at 472, 484 and 494 nm in CH2Cl2 solution, respectively. Ir(4-Me-4'-F-ppy)2(trzl-CMe3) showed the most hypsochromic shift in photoluminescence (PL) among the complexes prepared herein. In the electroluminescence (EL) spectra, Ir(4-Me-4'-F-ppy)2(trzl-CMe3) and Ir(4-Me-4'-CF3-ppy)2(trzI-CMe3) exhibited the luminescence peak at 437 nm and 496 nm, respectively. In the aspect of blue emission color purity, Ir(4-Me-4'-F-ppy)2(trzl-CMe3) had the CIE coordinates of (0.176, 0.143), very close to the saturated standard blue emission.