Semiconductor nanowire building blocks: From flux line pinning to artificial photosynthesis
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My personal journey in nanowire research started with Professor Charles Lieber at Harvard University, where I investigated flux line pinning in high Tc superconductors using nanowires as pinning centers. More than 15 years later, I devote most of my efforts in studying these nanostructures for energy conversion and storage purposes. I would like to acknowledge the pioneering contribution of R.S. Wagner at Bell Laboratories. Much of our nanowire research today relies on the very powerful method developed by Wagner, known as the “vapor-liquid-solid process” (VLS).1 In 1964, Wagner described the VLS growth of silicon microand nanoscale wires or whiskers and pointed out that one of the catalysts that can be used is gold. Gold is often used today to grow silicon nanowires, as well as copper, nickel, and, more recently, aluminum. Wagner also noted that nanowires can grow into different cross directions. Over the past 10 years, there have
been thousands of papers on silicon nanowire growth, growth direction control, and the use of different catalysts and substrates, all based on Wagner’s original concept.2 Wagner’s work in the 1960s set the foundation for much of today’s nanowire research. My first nanowire experiments were in the early 1990s, when many of us were still working on high-Tc superconductors (HTSC). The subject of my PhD thesis was to find a way to introduce linear defects within high-temperature superconductors, in the hope of increasing the critical current density. Our approach was to introduce single-crystalline nanowires into a high-Tc cuprate superconductor to make a composite, to create stable linear tracks, and to increase the critical current density by “pinning” the flux lines.3 This work paralleled much of the work conducted at the time using fast ion irradiation to create linear defects within high-temperature superconductors. That was the start of my research in this very exciting area, and it
Peidong Yang, Departments of Chemistry, and Materials Science and Engineering, Lawrence Berkeley National Laboratory; [email protected] DOI: 10.1557/mrs.2012.200
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MRS BULLETIN • VOLUME 37 • SEPTEMBER 2012 • www.mrs.org/bulletin
© 2012 Materials Research Society
SEMICONDUCTOR NANOWIRE BUILDING BLOCKS: FROM FLUX LINE PINNING TO ARTIFICIAL PHOTOSYNTHESIS
was also the beginning of nanowire research in Lieber’s group. Shortly after, the landmark paper by Morales and Lieber (1998)4 introduced the laser ablation method for the growth of silicon nanowires, once again based on the VLS process. In this case, the vapor was generated using laser ablation. After that, there was significant research using VLS processes to grow semiconductor nanostructures of many different compositions. Many different vapor deposition methods were employed, including chemical vapor deposition (CVD) and several physical vapor deposition techniques. After joining the University of California, Figure 1. Nanowire nanolasers. (a) Schematic of an optically pumped nanowire laser Berkeley faculty in 1999, my first research cavity. (
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