Phone: þ82 2 2220 0501, Fax: þ82 2 2291 7395Liquid-phase pulsed laser ablation (LP-PLA) is a promising technique for the fabrication of various nanomaterials because this technique is very simple and it is easy to control the experimental parameters. This paper demonstrates the synthesis of phase-controlled iron oxide magnetic nanoparticles by laser ablation of a bulk a-Fe 2 O 3 target in the following liquid media: ethanol, D.I. water and acetone. Absorption spectra of the nanocolloidal solutions are measured by UV-Vis spectrophotometer. As-synthesized nanoparticles, extracted from the colloidal solutions, are characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscope (TEM) equipped with X-ray energy dispersive spectrometry (EDX) and a vibrating sample magnetometer (VSM) to discover crystallinity, phase structure, morphology, elemen-tal compositions and magnetic properties in detail. The experimental results showed that the type of target and the magnitude of laser power play important roles in controlling the uniformity of iron oxide phase in the final product nanoparticles. Laser ablation of the iron oxide target in ethanol and acetone yields crystalline maghemite (g-Fe 2 O 3 ) nanoparticles, while that in D.I. water yields amorphous hematite (a-Fe 2 O 3 ). Use of an iron oxide (a-Fe 2 O 3 ) target for PLA in all three solvents is able to prevent the formation of metal iron and wustite phases in the final product nanoparticles. Moreover, our nanoparticles obtained in all three solvents possess magnetic behaviour, particularly that obtained in acetone, which has better saturation magnetization than those in ethanol and D.I. water.

Vertically well-aligned ZnO nanowire (NW) arrays were synthesized directly on Si(100) substrate without any metal catalysts by conventional thermal evaporation. The effects of the substrate positions on the structures and properties of ZnO NW arrays were primarily discussed. The orientation and morphology of the resultant NWs were analyzed by using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The experimental results showed that the density and diameter of the ZnO NWs can be effectively controlled by changing the substrate position. The photoluminescence (PL) characteristics of the grown ZnO NW arrays show a sharp and strong ultraviolet (UV) emission at 380 nm and a very weak green emission at around 490 nm, indicating that the assynthesized NWs have outstanding optical properties with good crystalline quality and may have excellent application potential in optoelectronic devices.

Recently the preparation magnetic nanoparticles by a pulsed laser ablation in liquid has gained much attention because it is easy to control experimental parameters. Iron oxide magnetic nanoparticles have been prepared by a pulsed laser ablation of α-Fe 2 O 3 target in ethanol at different magnitude of laser energy of 1, 20, 40 and 80 mJ/pulse. It revealed that particle size increases with increasing laser energy. It could be concluded that 40 mJ/pulse is an optimum laser energy for the preparation of iron oxide nanoparticles with uniform size distribution. The nanoparticles are homogeneously dispersed in ethanol and their stability maintained for several months.

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Single and few-layer graphene nanosheets (GNs) have successfully synthesized by a modified Hummer's method followed by chemical reduction of exfoliated graphene oxide (GO) in the presence of hydrazine monohydrate. GO and GNs were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), X-ray diffractions (XRD), Raman spectroscopy, Transmission electron microscopy (TEM), Atomic force microscopy (AFM), Optical microscopy (OM) and by electrical conductivity measurements. The result showed that electrical conductivity of GNs was significantly improved, from 4.2 × 10 −4 S/m for GO to 12 S/m for GNs, possibly due to the removal of oxygencontaining functional group during chemical reduction. In addition, the NO 2 gas sensing characteristics of GNs are also discussed.

ZnO with different morphologies can be used various application depending on their shapes. Different morphologies of ZnO structures were synthesized by a catalysis-free thermal evaporation process. Their morphologies were dependent on the distance from the source to substrate on the same processing condition; in the result were products morphologies of the hollow, cage and star. Their shapes and crystalinity were evaluated by SEM and XRD, respectively. This work demonstrates what kind of growth factors would be involved in the final structure morphologies.

Vertically well-aligned ZnO nanowire (NW) arrays were synthesized directly on GaN/sapphire and Si substrate from Zn vapor deposition without catalysts. Experimental results showed that the number density, diameter, crystallinity and degree of the alignment of ZnO NWs depended strongly on both the substrate position and kind of the substrates used for the growth. The photoluminescence (PL) characteristics of the grown ZnO NW arrays exhibit a strong and sharp ultraviolet (UV) emission at 379 nm and a broad weak emission in the visible range, indicating that the obtained ZnO NWs have a high crystal quality with excellent optical properties. The as-grown ZnO NWs were characterized by using scanning electron microscopy (SEM), high resolution transmission electronic microscopy (HR-TEM), and X-ray diffraction (XRD).