Near-Field Plasmonic Probe with Super Resolution and High Throughput and Signal-to-Noise Ratio

Significance 

Near-field scanning optical microscopy (NSOM) technique has been widely used to satisfy the increasing demand for spatially resolving objects, especially at the nanoscale level. NSOM enables the user to observe the light-matter interaction beyond the diffraction limit thus leading to better spectroscopic analysis, optical imaging and chemical identification. Furthermore, it can be operated in a vacuum environment and hence does not require the presence of a medium.

Presently, two main types of NSOM commonly used are the aperture type and the scattering type. The former uses a tiny aperture connected to the tip apex of atomic force microscope probe whereby the size of the aperture determines the optical resolution. On the hand, there is no aperture in the NSOM scattering type. Instead, it consists of a sharp tip probe made of metal or semiconductor materials. The scattering type has better optical resolutions as compared to the aperture type.

However, these two types of NSOM still experience challenges that limit their workability. For example, the interference experienced between the scattered light and the illuminated light samples causes disturbances that lead to inaccurate measurements. Today, several approaches have been put forward towards the realization of NSOM that is capable of providing better optical throughput, signal to noise ration and spatial resolution beyond that provided by the aperture tips and scattered tips.

Researchers at National Tsing Hua University in Taiwan led by Professor Ta-Jen Yen developed a high efficiency plasmonic near-field scanning optical microscopy, with the aim of enhancing signal-to-noise ratio, resolution and throughput. The design is also capable of supporting Fabry-Perot resonance and radially polarized excitation for the focusing modes. Their research work is published in the journal, Nano Letters.

Ruei-Han Jiang and colleagues observed that the developed plasmonic tip outperformed the conventional NSOM aperture and scattering tips. For instance, it produced a topographic and optical resolution of 10nm, the throughput of 3.28% and a signal-noise ratio of 18.2.

The plasmonic tip (p-tip) was able to efficiently interfere with the surface plasmon polaritons (SPP) at the apex tip due to the presence of the subwavelength annular gratings on the facet of the tip. This shows that the p-tip can be used as a simplification of the conventional NSOM scattering tip by expanding its measurements and also eliminating the complex convolution and high-order analysis. Additionally, the high signal to noise ratio obtained in the experiment is attributed to the interference and propagation of the surface waves through plasmonic lens characterization.

Considering the fact that the p-tip can offer a near-background-free p-NSOM measurement, the authors are optimistic that it can be employed in various applications such as nanolithography, near-field optics and tip-enhanced spectroscopy among other several applications.

 

Near-Field Plasmonic Probe with Super Resolution and High Throughput and Signal-to-Noise Ratio. Advances in Engineering

 

About the author

Han Ruei Jiang received B.S. in materials science and engineering from National Tsing Hua University, Taiwan, in 2011. Since 2012, she started the Ph.D. program under the supervision of Dr. Ta Jen Yen in the department of materials science and engineering from National Tsing Hua University, Taiwan. Her research interests include near-field spectroscopy and microscopy (SNOM), nano-fabrication, and plasmonics.

About the author

Chi Chen received B.S. and M.S. degrees in chemistry from National Taiwan University. In 2009, she obtained the Ph.D. degree at University of California-Irvine and achieved optical imaging of single molecules with 1 Ångstrom resolution by a low-temperature UHV STM. She then joined RIKEN as the postdoctoral associate focused at tip-enhanced Raman spectroscopy and successfully pushed the optical resolution down to 1.7 nm. Since 2013, she started her independent research career in Academia Sinica as an assistant research fellow. Her research interests include near-field spectroscopy and microscopy (SNOM), Tip-enhanced Raman spectroscopy (TERS), Instrumentation to combine optics with an AFM/STM, and the applications to study single molecules and nanomaterials.

About the author

Ding-Zheng Lin received his B.S. degree from Department of Mechanical Engineering National Taiwan University, Taiwan, in 2001 and his M.S. and Ph.D. degrees from the Institute of Applied Mechanics, National Taiwan University, Taiwan, in 2003 and 2007, respectively. From 2008 to 2018, he was a researcher at Industrial Technology Research Institute, Taiwan. He has published 27 journal papers as well as 26 conference papers and got 22 granted patents. His research interests are in the fields of nano-optics, nanofabrication, plasmonic devices, optical biosensing, scanning near-field optical microscopy (SNOM), surface enhanced Raman spectroscopy (SERS), Localized surface plasmon resonance (LSPR) and biometric recognition techniques.

About the author

He-Chun Chou received B.S. and M.S. degrees in chemistry from National Taiwan University and then obtained the Ph.D. degree at University of Texas at Austin. Now he is a post-doctoral research associate under the supervision of Dr. Chi Chen in the Research Center of Applied Sciences, Academia Sinica.

About the author

Jen-You Chu is a research supervisor of Microstructure and characterization department in the Material and Chemical Research Laboratories at the Industrial Technology Research Institute (ITRI, Taiwan). His research interests are at the surface and interface analysis, nanophotonics, and advanced microscopy. His Ph.D. is in physics with surface science. In the ITRI, he studies surface characterization techniques, like the probe engineering of atomic force microscope and near-field optical microscopy about 15 years. His works are the characterization of nano-material and help company solving the problem in material development.

About the author

Ta-Jen Yen received his M.S. degree from National Taiwan University in 1995. After working for military and ASUSTek computer Inc. for 5 years, Dr. Yen returned school in 2000 and obtained his Ph. D. degree from University of California at Los Angeles in 2005. Currently, Dr. Yen is a professor and a Vice President for Global Affairs at National Tsing Hua University, Taiwan.

Reference

Jiang, R., Chen, C., Lin, D., Chou, H., Chu, J., & Yen, T. (2018). Near-Field Plasmonic Probe with Super Resolution and High Throughput and Signal-to-Noise Ratio. Nano Letters, 18(2), 881-885.

Go To Nano Letters

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