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niform thin films composed of closely packed nanoparticles are important for applications such as nanoelectronics, light-emitting diodes, solar cells, and magnetic data storage. While electrostatically stabilized gold nanoparticles (Au-NPs) in water irreversibly aggregate, alkanethiolate-coated Au-NPs are very stable, and can be dried into a powder and subsequently re-dispersed in solvents without size change. Traditional methods for two-dimensional (2D) self-assembly of NPs coated with hydrophobic organic ligands include Langmuir-Blodgett deposition and spin-coating, although monolayer films prove difficult with the latter. Previously reported, however, were monolayer films prepared with a simple method for 2D self-assembly of dodecanethiol (DDT)coated Au-NPs at the air-toluene interface of an evaporating toluene droplet. Nevertheless, drawbacks are inherent in the modified Brust methods used to synthesize the Au-NPs, which include the
First operation of a Pr:YAlO3 microchip laser achieved at near-infrared wavelength
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icrochip lasers are monolithic solid-state lasers that use a small single crystal as the gain medium. Typically these crystals are composed of a host crystal doped with ions such as neodymium Nd3+ or praseodymium (III) Pr3+. In an effort to construct a laser that is both compact in size and operates at infrared laser wavelengths, M. Fibrich, H. Jelínková, and J. Šulcat of Czech Technical University in Prague and K. Nejezchleb and V. Škoda at Crytur Ltd. in Turnov created the first microchip praseodymium (III) yttrium aluminum oxide laser, YAlO3 (YAP), Pr:YAP. These materials are ideal for laser use due to good thermal and mechanical properties
slow Au-NP formation in toluene, and the difficulty in removing from the AuNPs the surfactant tetraoctylammonium bromide (TOAB), required to transfer gold ions from the aqueous phase to toluene. Recently, however, S.-K. Eah and co-researchers at Rensselaer Polytechnic Institute have developed a new, 10-min., TOAB-free method for synthesizing DDT-coated Au-NPs. The researchers have uploaded a three-minute demonstration video at http://www.youtube. com/watch?v=nqkwM9o1s-w. Eah and co-researchers reported in the May 18th issue of Langmuir (DOI: 10.1021/la100591h; p. 7410) that they synthesized Au-NPs in water by borohydride reduction. Phase transfer and coating with DDT was then performed by adding acetone to the aqueous AuNP mixture, and then adding hexane containing DDT. After vigorous shaking for 30 s, the DDT-coated Au-NPs were transferred to the hexane with all reaction byproducts remaining in the aqueous-acetone phase, making a product-cleanup step unnecessary. The researchers found that the lack of the normally used stabilizer molecules
was critical for the Au-NP phase transfer. By controlling reaction conditions, the researchers were able to precisely tune the Au-NP diameters in the range of 3.2–5.2 nm. The Au-NPs were indispersible in toluene and therefore selfassembled into a monolayer, closely packed film at the toluene-air interface of a toluene
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