Mode evolution and nanofocusing of grating-coupled surface plasmon polaritons on metallic tip

We present a detailed analysis on mode evolution of gratingcoupled surface plasmonic polaritons （SPPs） on a conical metal tip based on the guidedwave theory. The eigenvalue equations for SPPs modes are discussed, revealing that cylindrical metal waveguides only support TM01 and HEm1 surface modes. During propagation on the metal tip, the gratingcoupled SPPs are converted to HE31, HE21, HE11 and TM01 successively, and these modes are sequentially cut off except TM01. The TM01 mode further propagates with drastically increasing effective mode index and is converted to localized surface plasmons （LSPs） at the tip apex, which is responsible for plasmonic nanofocusing. The gapmode plasmons can be excited with the focusing TM01 mode by approaching a metal substrate to the tip apex, resulting in further enhanced electric field and reduced size of the plasmonic focus.

Silica nanocone array as a template for fabricating a plasmon induced hot electron photodetector

Plasmon induced hot electrons have attracted a great deal of interest as a novel route for photodetection and lightenergy harvesting. Herein, we report a hot electron photodetector in which a large array of nanocones deposited sequentially with aluminum, titanium dioxide, and gold films can be integrated functionally with nanophotonics and microelectronics. The device exhibits a strong photoelectric response at around 620 nm with a responsivity of 180 μA/W under short-circuit conditions with a significant increase under 1 V reverse bias to 360 μA/W. The increase in responsivity and a red shift in the peak value with increasing bias voltage indicate that the bias causes an increase in the hot electron tunneling effect. Our approach will be advantageous for the implementation of the proposed architecture on a vast variety of integrated optoelectronic devices.

Azimuthal vector beam exciting silver triangular nanoprisms for increasing the performance of surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy(SERS)with high-sensitivity performance is a very necessary detection technology.Here,we present a method for increasing the performance of SERS based on silver triangular nanoprism arrays(ATNAs)vertically excited via a focused azimuthal vector beam(AVB).The ATNA substrates with different structural parameters are prepared based on the traditional self-assembled and modified film lift-off technique.Based on a theoretical model established adopting the structural parameters of the ATNA substrates,theoretical simulation results show that AVB excitation can achieve greater electric-field enhancement than linearly polarized beam(LPB)excitation.Experimental result indicates that SERS sensitivity obtained via AVB excitation is 10^-13M(1 M=1 mol/L)using rhodamine 6 G(R6 G)as the target analyte,which is 2 orders of magnitude lower than that of LPB excitation(10^-11M).Meanwhile,the uniformity and reproducibility of the ATNA substrates are examined using Raman mapping and batch-to-batch measurement,respectively,and the Raman enhancement factor is calculated to be^3.3×10^7.This method of vector light field excitation may be used to improve the SERS performance of the substrates in fields of ultra-sensitive Raman detection.