High-density semiconductor nanorod arrays (NRAs) with one-dimensional (1D) structures have been extensively studied for their application in photonic and electronic devices. [1,2] Especially, 1D periodic NRAs of GaN, ZnO, and ZnS have attracted considerable interest in application to ultraviolet (UV) laser devices due to their direct wide bandgaps of DE g ³ 3.0 eV.[1±4] Among them, ZnO (DE g = 3.37 eV) is thought to be the most suitable material for UV laser devices because of its large exciton binding energy of 60 meV compared to the thermal energy (26 meV) of room temperature.[5]Recently, the room-temperature UV lasing emission from a directionally grown ZnO nanoarray was demonstrated with a threshold power density below 100 kW cm ±2. [1,6] Such NRAs with high-quality UV lasing properties were fabricated only by physical techniques like molecular beam epitaxy (MBE), metal±organic chemical vapor deposition (MOCVD), and gold-catalyzed vapor-phase transport (VPT) techniques; those are, however, expensive and energy consuming processes since they are operated under extreme conditions. [2,7,8] For example, the high-quality ZnO NRA with the best UV-lasing properties was realized by a gold-catalyzed VPT process at 925 C. [8] At this high temperature, however, one can hardly use a silicon (Si) wafer as a substrate, and it is necessary to use a sapphire (Al 2 O 3 ) wafer, even though the Si substrate would be advantageous in terms of easy transformation into electronic devices and low price. It is worth pointing out here that a perfectly and directionally grown ZnO NRA on a Si wafer has been rarely achieved due to the thermal instability of the Si substrate and the large lattice mismatch (~40 %) between the substrate and the ZnO NRA.[9±11]In the present study, a high-quality ZnO NRA was successfully grown on a Si wafer by a wet-chemical process at 95 C for 6 h, where the Si wafer was dip-coated with 4 nm sized ZnO nanoparticles as a buffer and seed layer prior to the crystal growth. To summarize the result in advance, we found that the product ZnO NRA's threshold power density of 70 kW cm ±2 is comparable to the lowest one of 40 kW cm ±2 determined for ZnO NRAs on Al 2 O 3 substrates.[1]ZnO nanoparticles as a starting precursor for the ZnO NRA were prepared according to the previously reported method.[12] As shown in Figure 1a, the particle size of monodispersed ZnO nanoparticles with quasi-spherical shape is determined to be approximately 4 nm. A single particle is observed in detail in the inset of Figure 1a, where the lattice distance between adjacent lattice planes is measured as 5.2 corresponding to the d-spacing between the (0001) planes. The surface image of the present ZnO NRA shows that the nanorod has a well-defined hexagonal plane with a homogeneous diameter of approximately 100 nm due to the uniform growth rate (Fig. 1b). The cross-sectional image in Figure 1c indicates that the nanorods with a uniform length of 1.5 lm are directionally and densely grown over the entire seeded surface of the Si wafer. In add...

Methylene blue-loaded gold nanorod@SiO2 (MB-GNR@SiO2) core@shell nanoparticles are synthesized for use in cancer imaging and photothermal/photodynamic dual therapy. For the preparation of GNR@SiO2 nanoparticles, we found that the silica coating rate of hexadecylcetyltrimethylammonium bromide (CTAB)-capped GNRs is much slower than that of PEGylated GNRs due to the densely coated CTAB bilayer. Encapsulated MB molecules have both monomer and dimer forms that result in an increase in the photosensitizing effect through different photochemical pathways. As a consequence of the excellent plasmonic properties of GNRs at near-infrared (NIR) light, the embedded MB molecules showed NIR light-induced SERS performance with a Raman enhancement factor of 3.0 × 1010, which is enough for the detection of a single cancer cell. Moreover, the MB-GNR@SiO2 nanoparticles exhibit a synergistic effect of photodynamic and photothermal therapies of cancer under single-wavelength NIR laser irradiation.

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The present work demonstrates that Cy5.5 conjugated Fe3O4/SiO2 core/shell nanoparticles could allow us to control movement of human natural killer cells (NK-92MI) by an external magnetic field. Required concentration of the nanoparticles for the cell manipulation is as low as ~20 μg Fe/mL. However, the relative ratio of the nanoparticles loaded NK-92MI cells infiltrated into the target tumor site is enhanced by 17-fold by applying magnetic field and their killing activity is still maintained as same as the NK-92MI cells without the nanoparticles. This approach allows us to open alternative clinical treatment with reduced toxicity of the nanoparticles and enhanced infiltration of immunology to the target site.

Hexagonal nanodisks of ZnO were fabricated by a solution process using ZnO nanoparticles and their cathodoluminescence characteristics were investigated. Monochromatic cathodoluminescence images showed that luminescence was spatially localized near the boundary of the nanodisk and spectral analysis in conjunction with the intensity profile consistently ascribed the spatial localization of luminescence to whispering-gallery-modelike-enhanced emission. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2174122͔With the successful demonstration of various nanostructures and increasing demand for integrable optoelectronic components with existing silicon technology, small-scale dielectric resonators applicable to photonic nanodevices with low-thresholds have gained importance because they can be used as low-power-consumption light sources in integrated circuits. Reducing the size of photonic devices, however, results in decrease of luminescence intensity in such a way that careful design of intensity enhancement mechanism should be introduced. For this reason, the whispering-gallery mode, which has been particularly utilized in applications to optical communication, has attracted much attention because it is a very efficient mechanism of luminescence enhancement even in small-scale resonators. 1-4 Since a top-down approach, such as lithography, has been among the best technological methods to fabricate tailored nanostructures appropriatue for specific research or application purposes, much effort has been made in order to fabricate nanoresonators via lithography to achieve low-threshold photonic nanodevices. There are, however, a few important generic problems in top-down fabrication of nanoresonators. There is unavoidable damage to films associated with lithographic etching process. An unwanted strain effect is also involved due to the limited choice of substrates to accommodate lattice misfit. In contrast, photonic nanodevices with bottom-up-based nanoscale resonant cavity employing whispering-gallery modes ͑WGMs͒ are very promising integrable components with high luminescence efficiency. More than that, a bottom-up approach typically does not depend on the choice of substrates, which is a major advantage in integration with current silicon technology.Due to direct and wide-band-gap characteristics with a large binding exciton energy, ZnO has drawn much attention for potential application to short-wavelength optoelectronic devices. In addition to single-crystalline ZnO thin films, ZnO nanowires and nanorods with perfect crystallinity were recently fabricated, and newly developed ZnO-based nanostructures demonstrated the possibility for nanoscale optoelectronic devices. [5][6][7] In contrast with one-dimensional nanostructures, such as nanorods, hexagonal nanodisk resonators employing WGMs have a smaller effective volume of gain medium, so that it is easier to fabricate compact photonic nanodevices. In addition, nanodisks are more confined to the surface of substrate and mechanical stability of nanodisks for pos...

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ZnO nanocoral reefs and nanofibers are synthesized on the glass substrate dip coated with ZnO seed with nanoparticles with an average size of 5 nm under a hydrothermal reaction. The ratios of length to diameter for the former and the latter are determined to be 100 and 1000, respectively. In addition, we found that a threshold power density for UV lasing action could be remarkably reduced from 40 kW/cm2 for the nanocoral reefs to 8 kW/cm2 for the nanofibers by increasing the cavity length of ZnO nanowires.

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