Nano-reactions at solid surfaces by an atomic force microscope with a molecular-recognition cantilever

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1. Using an atomic force microscope, we attempted to control the photochemical reactions in nanometer-scale. The photocatalytic decomposition of the stearic-acid film was selectively accelerated at the TiO_2surface where a positive voltage of 10 V was applied under ultraviolet illumination. The spatial resolution of the photocatalytic decomposition was estimated to be 30 nm or less from patterns of stearic-acid films. The AFM-assisted photocatalysis can be explained in terms of the accumulation of photogenerated holes at the TiO_2 surface by applying an electric field. It was found that the AFM-assisted photocatalysis was applicable to oxidation reactions of organic compounds in nano-meter scale.2. We developed a new technique to transcribe nano-patterns produced by AFM assisted lithography. The photocatalysts films of TiO_2, SnO_2, Nb_2O_5, Ga_2O_3 were prepared at room temperature by a RF sputtering technique. These oxide films are amorphous with flat surfaces. In particular, amorpho … More us TiO_2 films prepared at a higher pressure of 2x10^<-2> Torr exhibited the highest photocatalytic activity in these oxide films. We demonstrated that these amorphous TiO_2 films have the photocatalytic ability comparable to that of crystalline one. The high photocatalytic activity may be ascribed to the formation of nano-crystals of TiO_2. The amorphous TiO_2 films, which are in contact with self-assembled membranes of octyl-trichlorosilane (OTS) deposited on Si wafers, decomposed completely OTS films into CO_2 and H_2O within 5 min. The patterns of TiO_2 films were transcribed in part to OTS-SAMs within 30 s, but the resultant patterns are unclear. The suppression of lateral diffusion of reactive species are required to realize photocatalytic lithography.3. SAMs of dodecanethiol and aminothiophenol are formed on cantilevers coated with Au. Current vs. voltage characteristics were measured between Au substrates and these cantilevers modified with SAMs. Drastic differences in current vs. voltage characteristics were found between dodecanethiol and aminothiophenol SAMs: distinct current flow at a small bias voltage for aminothiophenol SAMs. In complex impedance plots, the aminothiophenol SAMs gave rise to small real part of impedance corresponding ac conductance at a frequency less than 5 Hz. Single strand DNA with 60 bases was immobilized to aminothiophenol SAMs deposited on Au substrate. In AFM topographs, there were a large number of networks of DNA because of its polymerization. The cantilever modified with aminophiophenol SAMs leads to no meaningful maps of ac conductivity with respect to the DNA networks. Major reason is the response time of the ac conductivity is too long to draw the map in area of 100 nm x 100 nm. Less