TY - JOUR
T1 - Optical trapping of single nano-size particles using a plasmonic nanocavity
AU - Zhang, Jiachen
AU - Lu, Fanfan
AU - Zhang, Wending
AU - Yu, Weixing
AU - Zhu, Weiren
AU - Premaratne, Malin
AU - Mei, Ting
AU - Xiao, Fajun
AU - Zhao, Jianlin
PY - 2020/11
Y1 - 2020/11
N2 - Trapping and manipulating micro-size particles using optical tweezers has contributed to many breakthroughs in biology, materials science, and colloidal physics. However, it remains challenging to extend this technique to a few nanometers particles owing to the diffraction limit and the considerable Brownian motion of trapped nanoparticles. In this work, a nanometric optical tweezer is proposed by using a plasmonic nanocavity composed of the closely spaced silver coated fiber tip and gold film. It is found that the radial vector mode can produce a nano-sized near field with the electric-field intensity enhancement factor over 103 through exciting the plasmon gap mode in the nanocavity. By employing the Maxwell stress tensor formalism, we theoretically demonstrate that this nano-sized near field results in a sharp quasi-harmonic potential well, capable of stably trapping 2 nm quantum dots beneath the tip apex with the laser power as low as 3.7 mW. Further analysis reveals that our nanotweezers can stably work in a wide range of particle-to-tip distances, gap sizes, and operation wavelengths. We envision that our proposed nanometric optical tweezers could be compatible with the tip-enhanced Raman spectroscopy to allow simultaneously manipulating and characterizing single nanoparticles as well as nanoparticle interactions with high sensitivity.
AB - Trapping and manipulating micro-size particles using optical tweezers has contributed to many breakthroughs in biology, materials science, and colloidal physics. However, it remains challenging to extend this technique to a few nanometers particles owing to the diffraction limit and the considerable Brownian motion of trapped nanoparticles. In this work, a nanometric optical tweezer is proposed by using a plasmonic nanocavity composed of the closely spaced silver coated fiber tip and gold film. It is found that the radial vector mode can produce a nano-sized near field with the electric-field intensity enhancement factor over 103 through exciting the plasmon gap mode in the nanocavity. By employing the Maxwell stress tensor formalism, we theoretically demonstrate that this nano-sized near field results in a sharp quasi-harmonic potential well, capable of stably trapping 2 nm quantum dots beneath the tip apex with the laser power as low as 3.7 mW. Further analysis reveals that our nanotweezers can stably work in a wide range of particle-to-tip distances, gap sizes, and operation wavelengths. We envision that our proposed nanometric optical tweezers could be compatible with the tip-enhanced Raman spectroscopy to allow simultaneously manipulating and characterizing single nanoparticles as well as nanoparticle interactions with high sensitivity.
KW - optical trapping
KW - optical tweezer
KW - plasmonic nanofocusing
KW - radial vector mode
UR - http://www.scopus.com/inward/record.url?scp=85092061538&partnerID=8YFLogxK
U2 - 10.1088/1361-648X/abaead
DO - 10.1088/1361-648X/abaead
M3 - Article
C2 - 32870814
AN - SCOPUS:85092061538
SN - 0953-8984
VL - 32
JO - Journal of Physics: Condensed Matter
JF - Journal of Physics: Condensed Matter
IS - 47
M1 - 475301
ER -