Optical antennas are widely used in surface-enhanced Ramon spectroscopy (SERS) because of their ability to focus light in sub-diffraction-limited area, resulting in strong field enhancement. The field enhancement depends critically on the gap spacing of optical antennas. Current nanofabrication techniques such as focused ion beam milling and electron beam lithography are limited by poor uniformity and reproducibility as the dimension decreases below 10 nm, making it difficult to fabricate optical antennas with well-defined sub-10 nm gap spacing. In this project, we report on the design and demonstration of new optical antennas with uniform sub-5nm gap spacing. Using deep-UV spacer lithography, the antenna gap is defined by a thin dielectric layer whose thickness is precisely controlled by atomic layer deposition (ALD). We have fabricated arch-dipole antennas with 5-nm gap spacing. Strong SERS signals from trans-1,2-bis (4-pyridyl) ethylene (BPE) molecules have been measured from the antennas, with an enhancement factor exceeding 10^8. The resonance characteristics and the excitation polarization dependence of the SERS signal confirm the observed SERS enhancement is resulted from the antennas. Since the proposed new antennas can be made by deep UV lithography, uniform SERS substrates with sub-5nm gaps can be mass produced in existing Si CMOS foundries.
Project end date: 01/29/13