AFRL-AFOSR-JP-TR-2016-0090 A Study of Material and Optical Properties of Nano Diamond Wires

This Korea-USA collaborative project, sponsored by AOARD for 2 years (April 18, 2013 April 17, 2015), “A study of material and optical properties of nano diamond wires (AOARD134085)”, aspired to find a way to synthesize a new form of carbon, crystalline diamond nanowires, and then to characterize them for device applications in nanophotonics, nanoelectronics, and quantum information processing. Reproducible synthesis of the crystalline diamond nanowires has proven to be extraordinarily challenging, to us as well as to the field in general. Our lab has so far had the only reported success. However, if a method is successfully developed with reproducibility, it would bring yet another new member into the family of carbon allotropes, this time on the sp side. It would also generate new insights into the phases, stability, and functionalization of diamond altered under nanoscale confinement, and pave way for a broad range of applications in nanoelectronics and nanophotonics, e.g., quantum information processing. Enabled by the AOARD support, the Korean-US collaborative team has taken on this challenge to investigate the feasibility of reproducible growth of diamond nanowires during the period of performance. As a result, progresses have been made on techniques for improving the reproducibility of diamond nanowires and the unexpected discovery of yet another new carbon allotrope – graphite nanowires. Specifically, the concept of catalyst engineering was proposed and tested with successes to provide ultrasmall (sub-5-nm) noble metals or iron-family catalysts and to support sufficiently high capillary pressure (> 4 GPa) associated with the small diameter during atmospheric chemical vaporliquid-solid (VLS) growth of diamond nanowires. In addition to the catalyst engineering, painstaking efforts have been made for careful optimization of growth parameters, such as temperature, time, and gas flow ratios. Such modifications and numerous experimental growth trials resulted in the growth of carbon nanowires from the high melting point Pt catalyst, ultrathin iron-family catalysts, and the NiFe multilayered (or alloy) catalysts. It also led to the unexpected discovery of crystalline graphite nanowires from the ultrasmall iron-family catalysts. These findings will significantly improve the reproducibility of crystalline carbon wires and lay a foundation for those wires to be integrated into emerging optoelectronic devices. Due to the ending of the WCU program at the host institution – SNU, the project was transitioned after two years along with the PI-role to Professor N-M Hwang at SNU whose group has been collaborating with us on this front for a few years. The pursuit, however, continues just the same in the new setting.