Sho Fujii

Fabrication and Placement of a Ring Structure of Nanoparticles by a Laser-Induced Micronanobubble on a Gold Surface

We have developed a new fabrication method for a ring structure of assembled nanoparticles on a gold surface by the use of continuous Nd:YAG laser light. A micronanobubble on a gold surface, created by laser local heating, acts as a template for the formation of the ring structure. Both Marangoni convection flow and capillary flow around the micronanobubble are responsible for the driving force to assemble nanoparticles such as CdSe Q-dots into the ring structure from the solution. Because a single micronanobubble was generated by the Nd:YAG laser focusing point, the precise positioning of the ring structure was feasible directly on the gold surface, which makes it possible to fabricate various patterns of rings such as arrays and letters and even a double-ring structure without any photomasks or any templates.

Glycine Crystallization in Solution by CW Laser-Induced Microbubble on Gold Thin Film Surface

We have developed a novel laser-induced crystallization method utilizing local heat-induced bubble/water interface. Continuous laser beam of 1064 nm is focused on a gold nanoparticles thin film surface covered with glycine supersaturated aqueous solution. Light absorption of the film due to localized plasmon resonance caused local heating at the focal position and produced a single thermal vapor microbubble, which generated thermal gradient followed by convection flow around the bubble and eventually induced glycine crystallization and growth. The crystallization mechanism is discussed by considering gathering and accumulating molecules around the bubble/water interface assisted by convection flow and temperature jump.

Simultaneous Formation and Spatial Patterning of ZnO on ITO Surfaces by Local Laser-Induced Generation of Microbubbles in Aqueous Solutions of [Zn(NH3)4]2+

We demonstrate the simultaneous formation and spatial patterning of ZnO nanocrystals on an indium-tin oxide (ITO) surface upon local heating using a laser (1064 nm) and subsequent formation of microbubbles. Laser irradiation of an ITO surface in aqueous [Zn(NH3)4]2+ solution (1.0 × 10-2 M at pH 12.0) under an optical microscope produced ZnO nanocrystals, the presence of which was confirmed by X-ray diffraction analysis and Raman microspectroscopy. Scanning the focused laser beam over the ITO surface generated a spatial ZnO pattern (height: ∼60 nm, width: ∼1 μm) in the absence of a template or mask. The Marangoni convection generated in the vicinity of the microbubbles resulted in a rapid concentration/accumulation of [Zn(NH3)4]2+ around the microbubbles, which led to the formation of ZnO at the solid-bubble-solution three-phase contact line around the bubbles and thus afforded ZnO nanocrystals on the ITO surface upon local heating with a laser.

Observation of DNA pinning at laser focal point on Au surface and its application to single DNA nanowire and cross-wire formation

We report a new technique for fabricating a single DNA nanowire at a desired position in a sequential manner using the micronanobubble generated by laser local heating at the Au/water interface. In our previous report, we found the reversible pull-in/shrinkage of one end immobilized DNA strands near a Nd:YAG laser focal point on an Au surface. In further experiments, the pinning of DNA strands in the stretched state was observed on the Au surface only when the bubble has touched the free end of DNA. This pinning phenomenon was observed even on the alkane thiol modified Au surface as self-assembled monolayers (SAMs) such as hexanethiol, mercaptohexanol, and hexadecanethiol. However, no pinning was observed on the bovine serum albumin (BSA) modified surface. Since optical tweezers can manipulate a DNA modified bead (radius=1.87 μm), the bead was firstly fixed on a solid surface by being compressed with the optical tweezers, and the pulling and pinning of DNA on the bead were achieved. As a consequence, the laser local heating on the Au surface enables us to control the number and position of the one end immobilized DNA strands as DNA nanowires.

Zero-Magnetic-Field Splitting in the Excited Triplet States of Octahedral Hexanuclear Molybdenum(II) Clusters: [{Mo6X8}Y6]2– (X, Y = Cl, Br, I)

The temperature ( T) dependences of the emissions from the tetra- n-butylammonium salts of [{Mo6X8}Y6]2- (X, Y = Cl, Br, and I) in optically transparent polyethylene glycol dimethacrylate matrixes were studied in the T range of 3-300 K. [{Mo6Cl8}Y6]2-, [{Mo6Br8}Y6]2-, and [{Mo6I8}I6]2- showed the T-dependent emission characteristics similar to those of other hexanuclear Mo(II), Re(III), and W(II) clusters reported previously, while [{Mo6I8}Br6]2- and [{Mo6I8}Cl6]2- exhibited the emission properties different from those of other [{Mo6X8}Y6]2- clusters. The photophysical behavior of these clusters was explained by the excited triplet state spin-sublevel ( Φn, n = 1-4) model irrespective of the nature of X and Y. The zero-magnetic-field splitting energies between the lowest energy (Φ1) and the higher energy spin sublevels (Φ4 or Φ3) caused by the first- or second-order spin-orbit coupling, Δ E14 or Δ E13, were evaluated to be 620-870 or 50-99 cm-1, respectively. We found the linear correlation between the Δ E14 or Δ E13 value and the fourth power of the atomic number ( Z) of the inner halide X: Δ E14 or Δ E13 vs { Z(X)}4 (correlation coefficient: cc = ∼ 0.999). Furthermore, we also found the correlation between Δ E14 or Δ E13 and the 95Mo NMR chemical shift of the cluster. These findings gave very important insight into the spin-orbit coupling and zero-magnetic-field splitting in the excited triplet states of transition metal complexes.