A hexagonal-close-packed (hcp), hierarchical amorphous TiO2 nanocolumn array was fabricated by pulsed laser deposition (PLD) using a PS colloidal monolayer as a template under a high pressure (6.7 Pa) of background oxygen gas. The formation mechanism was investigated, and a model of multidirection glancing deposition was proposed to explain the formation process. This strategy can be extended to the fabrication of similar structures using different materials. Interestingly, this nanostructured array could be transferred to almost any substrate, avoiding restriction of substrate types in fabrication of nanocolumn arrays, which is helpful in the design and creation of nanodevices on various desired substrates. This hierarchical nanocolumn array exhibits excellent superamphiphilicity with both water and oil contact angles of 0 degrees, without further UV irradiation. More importantly, the amorphous TiO2 nanocolumn array demonstrates better performance in photocatalytic activity than an anatase nanocolumn array due to its large surface area and special microstructures, suggesting that the surface area of the TiO2 is preferable to its crystal structure for enhancing photocatalytic activity. The combination of superamphiphilicity and photocatalytic activity gives the surface an excellent self-cleaning effect.

ZnO nanoparticles were prepared by laser ablation of a zinc metal plate in a liquid environment using different surfactant (cationic, anionic, amphoteric, and nonionic) solutions. The nanoparticles were obtained in deionized water and in all surfactant solutions except the anionic surfactant solution. The average particle size and the standard deviation of particle size decreased with increasing amphoteric and nonionic surfactant concentrations. With the increase of the amphoteric surfactant concentration, the intensity of the defect emission caused by oxygen vacancies of ZnO rapidly decreased, while the exciton emission intensity increased. This indicates that anionic oxygen in the amphoteric surfactant molecules effectively occupied the oxygen vacancy sites at the ZnO nanoparticle surface due to charge matching with the positively charged ZnO nanoparticles.

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When a fluorescent compound shows unique optical properties, an elucidation of the mechanism may lead to an important development of novel sensing strategies. A helical 3,3′-di-tert-butylsalen-zinc(II) complex, [Zn 2 L 1 2 ], has a red-shifted fluorescence as compared to that of [ZnL 2 2 ], a half-structured mononuclear complex of [Zn 2 L 1 2 ]; in addition, [Zn 2 L 1 2 ] exhibits a fluorescence color change from green to light blue under external stimulations. We investigated the origins of these phenomena by spectroscopy, fluorescence lifetime measurement, fluorescence microscopy, X-ray powder diffraction, and X-ray singlecrystal analysis. From the experimental data, we concluded that intramolecular and intermolecular π-π interactions are critical elements that determine the shifts of the fluorescence to a longer wavelength.

This is the second in a series of three papers examining nanomaterial formation in laser ablation in liquids (LAL). Here we study the effect of the laser wavelength and fluence on the mass yield and size distribution of nanoparticles prepared by laser ablation of a platinum target immersed in water. For all wavelengths tested, laser fluences in the range of 10–70J∕cm2 resulted in spheroidal, nonagglomerated platinum nanoparticles with sizes ranging from 1to30nm. Nanoparticle size distributions are found to be composed of two modes that are attributed to thermal vaporization and explosive boiling mechanisms. The peak of the smaller size mode remains nearly constant at 3nm for all laser conditions, which is suggested to be due to the strong confinement of the vapor plume by the liquid. The larger size mode peaks in the range of 5–15nm with a population that is strongly dependent on the laser parameters. It is concluded that changes in the mean size reported in many earlier studies on LAL of metal targets are a result of the relative quantity of nanoparticles from each mechanism rather than direct control over the ablation process. Additionally, it was observed that the yield of platinum nanoparticles was significantly larger for 1064nm wavelength at fluences greater than 10J∕cm2. The maximum ablation rate was approximately 4.4mg∕h, with an estimated ablation and collection efficiency of 0.9μg∕J. Dependence of the mass yield on wavelength and fluence is seen to be dependent primarily on the extent of the explosive mechanism.

A hierarchical TiO(2) ordered hemispherical particle array with hexagonal-non-close-packed (hncp) tops is prepared by pulsed laser deposition (PLD) using a polystyrene colloidal monolayer as a template. Compared with conventional lithography, the route presented has the advantage of low cost for producing hncp nanostructured arrays. This hierarchical particle array exhibits excellent superhydrophilicity with a water contact angle of 0 degrees without further UV irradiation. The superhydrophilic property originates from oxygen defects or vacancies on the surface of the TiO(2) nanoparticles produced by PLD and the increased roughness of the hierarchical particle arrays. More importantly, this property is very stable for half a year and could be used in self-cleaning surfaces and microfluidic devices.

In order to examine whether intratracheal instillation studies can be useful for determining the harmful effect of nanoparticles, we performed inhalation and intratracheal instillation studies using samples of the same nanoparticles. Nickel oxide nanoparticles (NiO) and titanium dioxide nanoparticles (TiO2) were used as chemicals with high and low toxicities, respectively. In the intratracheal instillation study, rats were exposed to 0.2 or 1 mg of NiO or TiO2. Cell analysis and chemokines in bronchoalveolar lavage fluid (BALF) were analyzed from 3 days to 6 months following the single intratracheal instillation. In the inhalation study, rats were exposed to inhaled NiO or TiO2 (1.65, 1.84 mg/m(3), respectively) for 4 weeks. The same endpoints were examined from 3 days to 3 months after the end of exposure. Inhalation of NiO induced an increase in the number of neutrophils in BALF and concentrations of cytokine-induced neutrophil chemoattractant (CINC)-1, CINC-2 and heme oxygenase (HO)-1. Intratracheal instillation of NiO induced persistent inflammation and upregulation of these cytokines was observed in the rats. However, inhalation of TiO2 did not induce pulmonary inflammation, and intratracheal instillation of TiO2 transiently induced an increase in the number of neutrophils in BALF and the concentrations of CINC-1, CINC-2 and HO-1. Taken together, a difference in pulmonary inflammation was observed between the high and low toxicity nanomaterials in the intratracheal instillation studies, as in the inhalation studies, suggesting that intratracheal instillation studies may be useful for ranking the harmful effects of nanoparticles.

This is the first in a series of three papers aimed at better understanding the processes that lead to nanomaterial formation during laser ablation of solid targets in liquids. Here we study the variation of the target surface morphology versus laser fluence and wavelength in order to suggest an ablation mechanism. A key finding is that an explosive ablation mechanism is prominent for a wide range of laser fluences for all wavelengths tested. Interestingly, however, ultraviolet (355nm) and infrared (1064nm) wavelengths show characteristically different explosive behaviors. In the infrared case, numerous large craters with diameters around 20μm form at localized points within the laser irradiated area. In contrast, ultraviolet ablation results in a striking transition to nanoscale surface roughness across the entire irradiated area. This texture is attributed to spinodal decomposition at the molten target surface. We propose that the wavelength and fluence dependence of the ablation craters can be explained by the amount of energy absorbed in the target. The consequences of the ablation mechanism for nanomaterial synthesis are discussed.