ABSTRACT
Silicon is one of the most important materials for modern electronics, telecom, and photovoltaic (PV) solar cells. With the rapidly expanding use of Si in the global economy, it would be highly desirable to reduce the overall use of Si material, especially to make the PVs more affordable and widely used as a renewable energy source. Here we report the first successful direction-guided, nano/microshaping of silicon, the intended direction of which is dictated by an applied magnetic field. Micrometer thin, massively parallel silicon sheets, very tall Si microneedles, zigzag bent Si nanowires, and tunnel drilling into Si substrates have all been demonstrated. The technique, utilizing narrow array of Au/Fe/Au trilayer etch lines, is particularly effective in producing only micrometer-thick Si sheets by rapid and inexpensive means with only 5 µm level slicing loss of Si material, thus practically eliminating the waste (and also the use) of Si material compared to the ~200 µm kerf loss per slicing and ~200 µm thick wafer in the typical saw-cut Si solar cell preparation. We expect that such nano/microshaping will enable a whole new family of novel Si geometries and exciting applications, including flexible Si circuits and highly antireflective zigzag nanowire coatings.
ABSTRACT
We report on the size-dependent transformation and geometrical modifications of periodically patterned Si templates by a combination of dry oxidation and chemical etching. Deep ultraviolet lithography patterned circular holes with diameters varying between 190 nm and 1 microm on Si wafers were oxidized at 1000 degrees C using dry oxygen for various durations, with selected samples chemically etched for oxide removal for additional alterations. An interesting phenomenon of a circular-to-square shape transformation of the holes was observed, which was particularly pronounced in the sub-200 nm regime. We tentatively attribute the change to the surface energy and geometry constraints in nanoscale patterns.
