C.-C. Hsu

Improved characteristics of organic light-emitting devicesby surface modification of nickel-doped indium tin oxide anode

This letter presents the optoelectrical performance of an organic light-emitting diode (OLED) through the elevation of indium tin oxide (ITO) anode work function by Ni co-sputter surface doping and additional O2 plasma treatment. The turn-on voltage of OLED devices can be reduced by 2.3V for Ni atomic concentration greater than 1.8% and by 2.7V for the additional O2 plasma treatment. Devices with Ni(2.6%)-doped and O2 plasma treated ITO anodes perform the highest luminance efficiency (0.91lm∕W), three times larger than undoped ITO (0.31lm∕W) at 250cd∕m2.

Second-harmonic green generation from two-dimensional χ(2) nonlinear photonic crystal with orthorhombic lattice structure

We report the synthesis of nonlinear photonic crystals (NPCs) with a periodical distribution of inverted χ(2) nonlinearity having an orthorhombic lattice structure on Z-cut congruent-grown lithium niobate (LiNbO3) substrate. The quasiphase-matching (QPM) mechanism of nonlinear wave interaction is examined by monitoring the far-field emission pattern of second-harmonic generation (SHG) as the NPC is pumped by a Nd:yttritium–aluminum–garnet laser beam. We observe (i) a series distribution of green SHG in a direction transverse to the fundamental beam, and (ii) an increase of phase-matching temperature in the SHG peak signal with the azimuth rotation angle in the x–y plane. These observations are ascribed to the high-order reciprocal lattice vectors assisted QPM–SHG process in a NPC that has a distribution of χ(2) nonlinearity with an orthorhombic crystal symmetry.

Wavelength tunability of second-harmonic generation from two-dimensional χ(2) nonlinear photonic crystals with a tetragonal lattice structure

The wavelength tunability of second-harmonic generation (SHG) in a two-dimensional nonlinear photonic crystal (2D NPC) on lithium niobate is examined by using a 1.55 μm-band optical parametric oscillator. We observed SHG signals that were generated off-axis from the fundamental pump beam and a multiple number of quasi-phase-matchable (QPM) wavelengths for a given crystal setting. The spacing between the phase-matched wavelengths increases with the azimuthal rotation angle (φ) in the x–y plane of the crystal. The peak intensity and propagation direction of the SHG signals are found to vary with the pump wavelength and crystal rotation angle. These observations are ascribed to a 2D distribution of high-order reciprocal lattice vectors Gmn(φ) and the corresponding χ(2)(Gmn) nonlinearities in 2D NPC having a tetragonal structural symmetry.

Ge-on-glass detectors

A single crystalline thin film of Ge on glass is fabricated using wafer bonding and smart cut. A simple metal-insulator-semiconductor detector is demonstrated for visible light and telecommunication wavelength. The implantation damage of separated Ge film bonded on glass is removed by chemical etching, and the surface roughness is reduced from 14to4nm. The defect removal reduces the dark current by a factor of 30 and increases the responsivity by a factor of 1.85 at visible wavelength. The responsivity of 0.27A∕W at 1.3μm wavelength for an unetched device does not increase after damage removal due to the decrease of the absorption layer thickness.

Mitigation of transverse domain growth in two-dimensional polarization switching of lithium niobate

This letter reports a charge control mechanism to mitigate the growth of transverse domain in the two-dimensional periodical polarization switching of Z-cut congruent-grown lithium niobate. This mechanism is established in a two-step procedure consisting of a first high temperature treatment followed by pulsed field poling. The ferroelectric χ(2) nonlinear photonic crystal thus formed exhibits a domain size as small as 3.3 μm and can emit an array of second harmonic green lasers when pumped by a Nd:yttritium–aluminum–garnet laser. These observations are ascribed to the (i) selective 180° domain nucleation underneath the oxidized electrode, and (ii) confinement of transverse domain motion to the positively charged boundary formed by the heat treatment.

Selective light emission from flexible organic light-emitting devices using a dot-nickel embedded indium tin oxide anode

This work demonstrates selective light emission from organic light-emitting diodes (OLEDs) with an Al/tris(8-hydroxyquinoline) aluminum N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1, 1′biphenyl-4, 4′-diamine/nickel-embedded indium tin oxide (ITO)/ polyethylene teraphythalate film structure. Embedding Ni in the surfaces of ITO anodes can reduce the OLED turn-on voltage by 2.3V, allowing the OLED to be selectively emitted. This approach based on Ni-embedded ITO approach can prevent crosstalks in passive OLED addressing because the lateral electric current is negligible outside the Ni-embedded area. It also reduces the roughness of the ITO surface by polishing. Therefore, this method can simultaneously improve the optoelectrical characteristics and increase the lifetime of an OLED device.

Differential gene expression between the porcine morula and blastocyst.

The survival and development of pre-implantation embryos are determinant factors affecting the outcome of animal reproduction. It is essential to transfer the expression of the genetic material from maternal sources, that is the ovum to the zygote before implantation to ensure successful development. Differentiation and transformation of blastomeres initiated during the morula and blastocyst stages is an important step of the embryonic development prior to implantation. We collected morula and early blastocyst samples from pure-bred Landrace pigs in vivo to study the differential gene expression patterns at these two stages. Total RNA was extracted from individual embryos and two rounds of amplification were employed. Two micrograms of antisense RNA, targets, were prepared and hybridized with each of four custom made oligo microarrays representing 24,000 porcine genes. The analyses of replicate hybridizations showed that among the 24,000 genes, 162 genes were expressed fivefold or greater in the morula compared to early blastocysts and 2126 genes were expressed fivefold or greater in early blastocysts compared to the morula. Of these differentially expressed genes, 1429 genes were functionally annotated with related human Gene Ontology terms. In addition to basic metabolic processes, genes related to signal transduction, transportation and cell differentiation were found in both stages and were up-regulated as embryo development proceeded. Real time polymerase chain reaction was utilized to quantify 12 genes differentially expressed in the 2 embryonic stages and validated the reliability of major evidences shown in microarrays. In conclusion, we have obtained a preliminary landscape of genes differentially expressed during the transition from morula to early blastocysts in pigs and showed a generally increased transcriptional activity, perhaps in preparation for implantation. Our results provide an opportunity to study the functions of these genes in relation to the development and survival of pre-implantation porcine embryos.

Dispersive QPM-SHG from /spl chi//sup (2)/ nonlinear photonic crystal LiNbO/sub 3/with tetragonal symmetry

We observe space dispersive, second harmonic green generations from a 2D QPM-periodically poled LiNbO/sub 3/ pumped by a Nd:YAG laser. The angular-tuning and phase-matching temperature analyses reveals a simultaneous quasi-phase-matching mechanism up to five reciprocal lattice vectors in the 2D /spl chi//sup (2)/ nonlinear photonic structure of tetragonal symmetry.

Two-dimensional polarization switching of lithium niobate

Summary form only given. We report a two-step oxidation and switching process on Z-cut congruent grown LiNbO/sub 3/. By employing the polarization-induced positive charge effect at the inverted surface domain boundary, we enable a 2D differential switching mechanism that can lead to the formation of a 2D, /spl chi//sup (2)/ nonlinear LiNbO/sub 3/ photonic crystal of arbitrary domain shape.