Daniel Dillon Haas

Thermally controlled fluidic self-assembly

A novel approach for the fluidic self-assembly (FSA) of microparts in a multibatch process utilizing the thermal behavior of the carrier fluid as a means for selecting binding sites is presented. In the system studied, fluidic assembly takes place due to a capillary bridge between hexadecane deposited on a hydrophobic patch on a substrate and a hydrophobic surface on a micropart suspended in a carrier fluid. When desired, FSA of microparts is prevented by causing the surrounding carrier fluid to form a gel when heated, offering a method for directing self-assembly to sites that are not heated. It is shown that a suitable carrier fluid is 15 wt % Pluronic F127, which gels at about 40 degrees C when tested in the geometry used to demonstrate the concept. Experimental results demonstrating FSA and thermally controlled fluidic assembly (TCFSA) of plastic microparts dispersed in Pluronic F127 solution are presented. Potentially, TCFSA offers a general method for directed assembly as it relies on restricting the transport of microparts to a site rather than interfering with the fundamental attractive forces responsible for self-assembly.

Single-Mode Fiber Printheads And Scanline Interleaving For High-Resolution Laser Printing

A multiple-laser-diode printhead using a close-spaced array of single-mode optical fibers has been developed for large-format, high-resolution laser printing. This head avoids the output interaction problems of multiple-laser arrays on a single GaAs substrate, while providing small spots, close spacing, low noise, and a compact assembly. Each of the separately packaged laser diodes is controlled by current modulation, and its emission is coupled into the input end of a single-mode optical fiber. The array is made by mounting the fibers in a crystailographically etched set of parallel V-grooves in a silicon wafer. The fibers are specially prepared to allow close spacing. Single-mode fibers are desirable because their outputs can be imaged to give diffraction-limited spots. Close spacing of the multiple sources is desirable because the imaging lens utilizes a smaller field of view and requires less demagnification to give closely spaced scanlines. In order to further reduce the spot spacing to increase spot overlap, the writing head can be tilted with respect to the scanning direction, or the exposure tracks can be interleaved. Tilting requires appropriate pixel-data delays and tighter tolerances on the planarity of the array. A new and more convenient method of interleaving has been developed.