Transmission of Light through Dielectric-Filled Nanoapertures

By: Samuel Chan Zhuo Ying Wu

St. John’s University, August, 2009

Mentor: Dr. Xu

• Motivation

• Introduction to Dielectric-filled Nanoapertures

• Previous Results

• Current Work

• Conclusion

Motivation: The Diffraction Limit

a. The Image of a Point Source

b. The Illumination Profile

• Point spread Function (PSF) depends on numerical aperture and wavelength. • Typical PSF (NA~1, 780 nm):1 micron by 0.5 microns.

Motivation: Break the Diffraction Limit

Resolution ~ ..

61.0

Metal-coated fiber

R. C. Dunn, Chem. Rev. 99, 2891 (1999).

resolution: /5

Objective lens

Focal volume

Excitation volume

Metal tip

Laser illumination

E. J. Sanchez et al., Phys. Rev. Lett. 82, 4014 (1999).

resolution: /10

N. Fang et al., Science 308, 534-537 (2005).

resolution: /4

Schematic of Light Transmission through an Aperture

Metal

Substrate

Illumination

simulation

3-D finite element methodwith perfectly matched layer B.C.

A finite element method (FEM) software package for various physics and engineering applications, especially coupled phenomena, or multiphysics.

COMSOL Multiphysics RF Module

Previous Results: Resonant Transmission

Au

Fused Silica

Illumination

a-Si Film thickness: 200 nm = 810 nm

ph

ase

shif

tFabry-Perot Interferometer

Fabry-Perot Resonances inside Waveguide

phase shift = 2 phase shift = 420

0 n

m

55 nm 105 nm

Black arrows: electric field directions-5 -4 -3 -2 -1 0 1 2

)||/|log(| 20

2 EE

H. Xu et al., Opt. Commun. 282, 1467-1471 (2009).

Current Work: Transmission through ZnO-filled nanoapertures in silver

Ag

Fused Silica

Illumination

ZnO Film thickness: 100 nm = 488 nm

Previous work:

silicon-filled aperture in gold

nSi: 3.882-0.099*inAu: 0.157-4.991*i

Current work:

ZnO-filled aperture in silver

nZnO: 2.06nAg: 0.131-2.81*i

Transmission through ZnO-filled nanoapertures in silver

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

0 20 40 60 80 100 120 140 160 180 200Diameter (nm)

Nor

mal

ized

Tra

nsm

issi

on

Hole depth: 200 nm

Phase = 0

Transmission through ZnO-filled nanoapertures in silver with various thickness

0.00

0.50

1.00

1.50

2.00

2.50

3.00

0 20 40 60 80 100 120 140 160 180 200

60nm

100nm

130nm

160nm

Diameter (nm)

Nor

mal

ized

Tra

nsm

issi

on

Application: Nanoscopic Near-field Probe

30 nm

Aluminumcoating

Si

SiO2

Illumination at 488 nm

-4 -3 -2 -1 0 1

)||/|log(| 20

2 EE

core

metal

tapered fiber

Enhancement in near-field intensity ~1000 times by silicon filling!

Conclusion

• Transmission resonance peaks were found at aperture diameter of around 40 nm for ZnO-filled nanoapertures with normalized transmission of ~ 100%.

•ZnO-filled nanoapertures may be useful for optical scanning probe devices that yield resolution of less than /10.

AcknowledgementsDr. Huizhong Xu

St. John’s University and staff

Dr. Sat Bhattacharya

Harlem Children Society

All of you!!