Highly Efficient Excitation of Surface Plasmons Using a Si Gable Tip

Abstract

Fabrication method: Figure S1 shows the steps for fabricating the gabled Si tip SPP excitation device. To fabricate the sample, we first obtained a <100> Si wafer and grew 300 nm of SiO2 by thermal oxidation (18 mins in the Bruce technologies oxidation furnace at the Toronto Nano-fabrication Center-TNFC). Then we cleaved a small piece of sample from the oxidized Si wafer. As the next step, we made patterns of 500 nm wide lines and 200 m square pads of ma-N 2400 negative resist on top of the oxidized Si sample using Vistec E-beam lithography unit. Next, we etched the oxide layer using deep reactive ion etching using an Oxford Instruments PlasmaPro Estrelas100 DRIE System unit at the TNFC facilities. After that, we wet-etched the oxide masked Si sample in 45% KOH solution for 7 mins at 80 0 C temperature to create the gabled Si tip structures. The height of the gable tip after the wet etch was measured to be 6 m. Next, we deposited a thick (more than 6 m) PECVD oxide on top of the Sample containing the Si tip, using an Oxford Instruments PlasmaLab System 100 PECVD unit. Then we planarized the top surface of the deposited PECVD oxide using chemical mechanical polishing (CMP). The CMP of the top surface was carried out until the top oxide thickness was reduced to the approximate height of the tip of the Si chimney tip. Further CMP was not carried out to avoid destruction of the Si tip. We also polished the bottom surface of the sample (rough Si) for reducing the defused reflection while coupling light from the bottom. As the next step, we patterned negative resist (ma-N 2400) on the oxide surface for metal deposition and grating fabrication by lift off using the same electron beam lithographic system at TNFC. We used the 200 m square Si marker pads for alignment of the resist patterns for proper positioning of the grating. Then we deposited gold on top of the patterned resist using a Datacomp Electronics TES12D Thermal Evaporator and carried out lift off to fabricate the grating. In the sample layout, hence in the fabricated sample as well the 1 st grating was 10 microns away from the tip of the Si chimney. We fabricated several other gratings at varying distances from the Si tip to monitor the decay of the excited surface plasmon polariton as mentioned in the manuscript. Figure S2 shows the layout of the fabricated sample with the little opening for

Directional excitation of surface plasmon using multi-mode interference in an aperture

“…However, the resulting SP radiates away from the hole in every direction, which diminishes its usefulness for many applications. Unidirectional and local excitation of SP has been an active area of research, and many schemes have been proposed to achieve this goal including: gratings, multiple coherent beams, partially filled or asymmetric holes [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] . However, these approaches suffer from a number of limitations including complicated geometries and narrow bandwidth.…”