Jun 7, 2012
FIB mills single-nanowire plasmonic gratings
Periodic patterns, such as gratings, have been widely used for manipulating electromagnetic fields in metallic nanostructures by coupling light with surface plasmon polaritons (SPPs). So far, most of the plasmonic gratings are fabricated on a two-dimensional surface with transversal sizes much larger than the wavelength of light, which limits the miniaturization of not just SPP gratings, but also functional SPP circuits and devices that use wavelength-selective gratings for applications such as sensing and signal processing.
To realize the full potential of ultra-tight field confinement of plasmonic nanostructures, scientists from Zhejiang University and Peking University, China, have demonstrated one-dimensional single-nanowire plasmonic gratings, which are extremely compact.
Using a focused-ion-beam (FIB) milling technique with a 30 keV 1 pA Ga+ ion beam, the group has successfully inscribed high-quality Bragg gratings on a 290 nm diameter gold nanowire. The grating structures are 30 nm deep and 390 nm wide, and are spaced at 780 nm intervals over a total length of 15 µm.
By evanescent coupling with fibre tapers for SPP excitation and signal collection, the tiny grating exhibits evident grating effects for the propagation of plasmons in the nanowire around the 1.5 µm wavelength for optical communication.
A grating length of around 10 µm is required, which is several orders of magnitude smaller than traditional Bragg gratings, such as fibre Bragg gratings. The Bragg wavelength can be adjusted by changing the periodicity of the grating. The grating effects in the single nanowire design are sensitive to parameters such as grating depth, width and length.
Thanks to their deep-subwavelength diameters and highly uniform geometries, the one-dimensional plasmonic gratings are promising structures for wavelength-selective manipulation of SPP and light in a miniature package. The components could serve as highly compact functional elements in a variety of applications, such as nanoscale optical sensing and interconnection.
More information can be found in the journal Nanotechnology.
About the author
The study was conducted by teams from the State Key Laboratory of Modern Optical Instrumentation, Department of Optical Engineering at the Zhejiang University and the State Key Laboratory for Mesoscopic Physics at Peking University. Xining Zhang is a PhD student at Zhejiang University. She performed the optical experiments. Zhe Ma, a postdoc at Zhejiang University, Rui Luo, a PhD student at Peking University, and Ying Gu, an associate professor in Peking University, performed the theoretical calculations and simulation. Chao Meng and Xiaoqin Wu, PhD students at Zhejiang University, synthesized and characterized the gold nanowires. Limin Tong of Zhejiang University and Prof. Qihuang Gong of Peking University analysed the results.