You may think that your cleanroom should be clean, but a serendipitous bit of grime that interfered with an experiment at Princeton University could lead to the production of cheaper, higher-quality LEDs. The accident occurred in the lab of Stephen Y. Chou, a professor of electrical engineering, during the imprinting of polymer-based diodes. Where a speck of dust had prevented contact between the mask and the polymer, a regular structure had grown, creating a photonic bandgap material: rows of pillars less than 1 µm high. Further experiments showed that the size and distribution of the pillars depend on the gap between the mask and the developing surface, which could enable manufacturers to tailor the material to their needs. The technique may find its initial application in the manufacture of computer monitors. Because fine control of the height and distribution of the pillars is possible, the colors emitted by the LED, which are determined by microcavities formed in the polymer, can be made to range from blue to red. Instead of manufacturing each color with different light-emitting materials, the entire range of colors could be produced with one material by controlling the height and distribution of the pillars. Further, a display made with the process would be much sharper than those now on the market, because each pixel would be a composite of many pillars acting as a group of tiny dots, rather than a monolithic block. The researchers are completing research on the application of the technique to LED manufacturing and expect to publish their results soon. Other potential applications include controlling the manufacture of integrated circuits and sorting DNA fragments based on their size. Princeton has applied for US and international patents on the process, which the researchers call lithographically induced self-assembly.