We report a photolithographic method for the shape control of DNA hydrogels based on photo-activated self-assembly of Y-shaped DNA nanostructures (Y-motifs). To date, various methods to control the shape of DNA hydrogels have been developed to enhance the functions of the DNA hydrogel system. However, photolithographic production of shape-controlled DNA hydrogels formed through the self-assembly of DNA nanostructures without the use of radical polymerizations has never been demonstrated, although such a method is expected to be applied for the shape-control of DNA hydrogels encapsulating sensitive biomolecules, such as proteins. In this study, we used a photo-activated linker to initiate the self-assembly of Y-motifs, where the cross-linker DNA was at first inactive but was activated after UV light irradiation, resulting in the formation of shape-controlled DNA hydrogels only at the UV-exposed area produced by photomasks. We believe that this method will be applied for the construction of biohybrid machines, such as molecular robots and artificial cells that contain intelligent biomolecular devices, such as molecular sensors and computers.
The etching rate behavior of silicon dioxide (SiO 2 , fused silica) using chlorine trifluoride (ClF 3 ) gas is studied at substrate temperatures between 573 and 1273 K at atmospheric pressure in a horizontal cold-wall reactor. The etching rate increases with the ClF 3 gas concentration, and the overall reaction is recognized to be of the first order. The change of the etching rate with increasing substrate temperature is nonlinear, and the etching rate tends to approach a constant value at temperatures exceeding 1173 K. The overall rate constant is estimated by numerical calculation, taking into account the transport phenomena in the reactor, including the chemical reaction at the substrate surface. The activation energy obtained in this study is 45.8 kJ mol À1 , and the rate constant is consistent with the measured etching rate behavior. A reactor system in which there is minimum etching of the fused silica chamber by ClF 3 gas can be achieved using an IR lamp heating unit and a chamber cooling unit to maintain a sufficiently low temperature of the chamber wall.
The temperature gradient formed in a silicon-on-insulator (SOI) wafer during a flash lamp annealing process is calculated on the basis of the heat transport theory. The temperature of SOI wafer, having a 0.04-mm-thick active layer and a 0.1-mm-thick buried oxide (BOX) layer, is calculated. Within 1000 ms, the active layer surface reaches the maximum temperature higher than 1473 K. Because most of the heat is transported by conduction, a very large temperature gradient, such as 3 Â 10 7 K/m, is formed in the BOX layer owing to its very small heat conductivity. The radiant heat flux through the BOX layer is estimated to be significantly smaller than the conduction heat flux. From a series of calculations taking into account various thicknesses of the active layer and the BOX layer, a BOX layer thicker than 1 mm can significantly increase the active layer temperature.
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