Abstract
Optical antennas have been widely used for sensitive photodetection, efficient light emission, high resolution imaging, and biochemical sensing because of their ability to capture and focus light energy beyond the diffraction limit. However, widespread application of optical antennas has been limited due to lack of appropriate methods for uniform and large area fabrication of antennas as well as difficulty in achieving an efficient design with small mode volume (gap spacing < 10nm). Here, we present a novel optical antenna design, arch-dipole antenna, with optimal radiation efficiency and small mode volume, 5 nm gap spacing, fabricated by CMOS-compatible deep-UV spacer lithography. We demonstrate strong surface-enhanced Raman spectroscopy (SERS) signal with an enhancement factor exceeding 108 from the arch-dipole antenna array, which is two orders of magnitude stronger than that from the standard dipole antenna array fabricated by e-beam lithography. Since the antenna gap spacing, the critical dimension of the antenna, can be defined by deep-UV lithography, efficient optical antenna arrays with nanometer-scale gap can be mass-produced using current CMOS technology.
Highlights
IntroductionOptical antennas [1,2,3,4] have been widely used for a variety of applications such as sensitive photodetection [5,6], enhanced light emission [7,8,9,10], high resolution imaging [11,12], heatassisted magnetic recording [13], and surface-enhanced Raman spectroscopy (SERS) [14,15,16] since they can capture and focus propagating electromagnetic energy into sub-diffractionlimited area, and vice versa
We demonstrate a novel optical antenna design, arch-dipole antenna, with 5 nm gap spacing fabricated by CMOS process
We introduce a new antenna design, arch-dipole antenna, which can be reproducibly fabricated with uniform gap spacing below 10 nm
Summary
Optical antennas [1,2,3,4] have been widely used for a variety of applications such as sensitive photodetection [5,6], enhanced light emission [7,8,9,10], high resolution imaging [11,12], heatassisted magnetic recording [13], and surface-enhanced Raman spectroscopy (SERS) [14,15,16] since they can capture and focus propagating electromagnetic energy into sub-diffractionlimited area, and vice versa. The antenna performance of focusing localized optical energy or enhancing the emitter efficiency critically depends on the small (a few nanometers-scale) high field region such as the antenna feed gap [15,17], which can be achieved by focused ion-beam (FIB) and electron beam (e-beam) but with poor uniformity and reproducibility for critical dimensions below 10 nm and limited fabrication area. Since the fin layer is deposited by atomic layer deposition (ALD), the thickness of the fin can be precisely controlled with sub-nm accuracy and good reproducibility In this design, the optimum fin height is chosen to control the radiation of the arch-dipole antenna, which enables matched radiation and absorption quality factors for the maximum field enhancement [21]. The SERS enhancement factor measured from the arch-dipole antenna array is two orders of magnitude greater than that from a typical dipole antenna array fabricated by e-beam lithography
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