Turning clear water to any color at the touch of a button suggests an alchemist's wizardry, but Yadong Yin makes it a routine event in his materials chemistry lab. The feat by Yin, an assistant professor of chemistry at the University of California, Riverside, involves subjecting ordinary iron oxide particles - the kind that cover a floppy disk to record data - to a magnetic field. The magnet secures the particles in an array of photonic crystals. Those arrays can split light into various colors, and how they are arranged determines what colors are reflected. Yin's nanoparticles can self-assemble into colloidal crystals - with periodic structures analogous to their atomic or molecular counterparts—of any color. In other experiments similar crystals reflected light only with a fixed color, or wavelength. Yin's range of colors is a wide and fully reversible optical response to magnets. The applications fall into a category called optical microelectromechanical systems. "You could use the technique in any display where you need to change the color of the material with a magnet," Yin said. "You could make a board with that material, and on the back you would have electromagnets. As you vary the strength of the field, you will see different colors from the front." "We can produce one color at a time as we move the magnet over the solution," Yin said. And for his next feat, Yin hopes to apply fundamental chemistry to achieve these effects with different solvents. "Alcohol and mineral oil, for example, don't let us organize the colors in the same way," he said. "My research focus will address that issue, trying to put the materials in right order." The potential applications spin off in many directions, including making high-security documents with invisible photonic marks, fiber optics, sensors, or making inexpensive reflective displays useful on warning signs. It would work best in daylight, with refracted light, or with a light source in the dark, since it is all based on reflection. Very strong sunshine will provide the brightest colors. "You could put the particles on a bank note, embed them in the paper, and people would not see the color, but if you ran it over a magnet, it would appear as a security feature," Yin said. In China, where Yin was born on a farm in Jiangsu, near Shanghai, his family encouraged his science work. Although his parents had only an elementary school education, they recognized Yin's talents, and his usefulness. "They knew I liked to disassemble stuff as a child," he said. "Anything mechanical or electronic I would take apart, a radio, an old alarm clock. They were my playthings." Now, when he returns to China, his parents have a to-do list. "My dad is always waiting, keeping the things that were broken in my absence." In high school in Jiangsu, he chose chemistry when a teacher told him, "With chemistry, it is easier to find an industry job.'' Not true, he discovered. "And I didn't feel excited about chemistry then. At that point, we had no chance to do experiments." He won a place at the University of Science and Technology of China, in Hefei, Anhui Province, and received his B.S. and M.S. degrees in applied chemistry there, graduating a year early by hard work, he says, and went on to receive his Ph.D. at the University of Washington. At USTC, he managed not only to master the art of experiments but also to publish several papers. "In quite good journals," he adds. With that on his C.V., he sent an e-mail to his future adviser in Seattle and asked for a chance to study and work in his lab. "He said, O.K., come," Yin recalls. Yin was a postdoctoral researcher at UC Berkeley and then a staff scientist at the Lawrence Berkeley National Laboratory before joining UC Riverside in 2006. These days he enjoys telling old Chinese stories to his daughter Jessica. Her favorite is a classic from the 1500s about the monk who traveled west along the Silk Road to learn about Buddhism, with his disciples, one of them a wise monkey, and a dragon prince. They appear in different and amazing forms, and there's a fair amount of magic. But no rainbows in a drop of water. That's just chemistry.
Yadong Yin's Teaching Plans
Yin says his primary teaching goal will be to help build a strong nanomaterials program at the University of California, Riverside. "I will put a lot of attention on creating an interdisciplinary class, with many from other departments like physics, electrical engineering, chemical engineering and bioengineering," he said. The course will cover an interdisciplinary overview of all major aspects of nanoscale materials and their emerging applications. "The goal is for students to gain basic ideas they can carry into work in other fields," Yin said. Being able to tune in the brilliant colors obtained by the research in the Yin Laboratory should be a great motivator, he predicts. The graduate students will do research projects, and undergraduates and high-school students will work in the lab and will put ideas to use that they have learned from the textbooks. Yin hopes to solve a problem that he faced in China by not have an opportunity to take part in undergraduate research. "I got to the master's program and I didn't know what to do at first," he said. "I just had to get in and swim. Once you know what is important in the lab, the way people think, you can learn on your own." He also plans to continue collaboration with museums such as the Science Museum in London to present new ideas in science and technology, from emerging from his own group, on the museum's web site, in forms that will appeal to children