Exploitation of spontaneous formation of nano-structures through nonlinear chemical dynamics

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We have studied spontaneous formation of nano-structures through non-equilibrium nonlinear dynamics for the purpose of exploitation and establishment of a new method for nano-structuring, and obtained the following results : (1)Scratching of H-terminated vicinal Si(111) surfaces with Teflon tweezers in 40% NH_4F led to formation of nano-wires, mainly composed of carbon and fluorine. The successive etching of the Si(111) surfaces with the nano-wires in 40% NH_4F produced surprisingly well-ordered step structures on Si(111). (2)Immersion of H-terminated Si(111) surfaces in aqueous hydrogen halide (HX) solutions caused halogenation of the Si(111) surface (i.e. conversion of surface Si-H bonds to Si-X bonds). The reactions depended largely on experimental conditions such as the kind of hydrogen halide, the presence or absence of dissolved oxygen, and reaction time. (3)The immersion of H-terminated Si(111) in 7.1 M HI at 5℃ produced oriented nano-wires at the surface. High-resolution XPS measurements showed that the nano-wires were composed of silicon iodides or related compounds. The orientation of the nano-wires was explained to arise from the fact that the wires formation occurred under a surface-diffusion limited condition. (4)The shape and size of metal nano-particles could be regulated by photo and electric-field assisted chemical processes. (5)Photo-etching of TiO_2 (rutile) in aq. H_2SO_4 produced ordered rectangular nano-holes and grooves in the <001> direction. (6)The appearance mechanisms for a number of electrochemical oscillations and accompanying spatiotemporal patterns were revealed.