Molecular
Molecular Nano-Optics
Nano-Optics // Chemical
Chemical Imaging
Imaging Lab
Lab
Zee
ZeeHwan
HwanKim
Kim
Department
Departmentof
ofChemistry,
Chemistry,Korea
KoreaUniversity
University
Ultra-high resolution
Chemical Imaging:
Apertureless-NSOM
(IR, vis, FRET imaging
at < 10 nm resolution)
Mechanism of SERS
(Surface-enhanced
Raman scattering)
Tip-enhanced
nonlinear microscopy
Vibrational Circular Dichroism
vibrational chirality of
biomolecules
via SFG and CARS
Nano-Optics,
Scanning Microscopy,
Non-linear Spectroscopy
CARS microscopy:
In-vivo imaging of
intra-cellular
chemical transport
Single bio-molecule
Spectroscopy
Fourier Transform
Chemical Force Spectroscopy
Microscopy and Spectroscopy
Vibrational
Confocal
Electronic
Diffraction Limit
Chemical Information
FT-IR Microscopy
NSOM
Non-optical
100 µm
1 µm
AFM
10 nm
Spatial Resolution
1 nm
STM
1Å
Why
Whyisisititso
sodifficult
difficultto
tobuild
buildaaHigh-Resolution
High-ResolutionChemical
ChemicalMicroscope
Microscope??
Laser
(EM radiation)
AFM Tip
Tip-Enhanced Spectro-Microscopy,
(Apertureless NSOM, ANSOM)
Promises:
hv
-Resolution limited only by the tip-sharpness
-Wavelength-independent (UV to THz)
PZT
M
CCD camera
ND
M
E
PD
BS
Pinhole
λ/2
Objective
lens
AFM probe
Sample
M
xyz scanner
z
Pinhole
Optical
Isolator
Apertureless NSOM at Korea University
HeNe
HeNe Laser
laser
(632.8 nm)
y
x
AFM (topography)
ANSOM (optical)
InN
ANSOM:
Dielectric Mapping
GaN
• Identification of InN and GaN islands
Local refractive index change
n(InN) = 2.8
n(GaN) = 1.5
300 nm
• Local dielectric inhomogeneity in InN
islands:
Local crystal strain and defect?
Stacking fault?
GaN
InN
• Spatial resolution: better than 15 nm
100 nm
0
20
40
(n m)
60
- 1 .2
- 0 .8
-0 .4
L o g (In t e n s it y / I 0 )
Kim, Liu, and Leone J. Phys. Chem. B 109, 8203 (2005)
ANSOM:
Phase-Sensitive Plasmonic Field Imaging
Topography
y
100 nm
Ein
Au
Si
Field Distribution
Intensity
Phase
Local Field
z
x
Dipole Field
Simulation
Z
y
Kim and Leone, unpublished (2005)
ANSOM: Vibrational Imaging of monolayers
Kramers-Kronig Relation:
Absorption coefficient
∞
2ω n(ω ' ) − 1
k (ω ) =
dω '
2
2
∫
π 0 ω ' −ω
Refractive index
∞
2 ω ' k (ω ' )
n(ω ) = n∞ + ∫ 2 2 dω '
π 0 ω ' −ω
Liquid Condensed (LC)
ANSOM Contrast (arb. units)
3.0
ANSOM contrast
2.5
2.0
1.5
1.0
0.5
0.0
0.0
IR-transition
0.5
1.0
1.5
IR transition Frequency (arb. unit)
Liquid Expanded (LE)
2.0
ANSOM Imaging with
a Gold Nanoparticle antenna
Gold nanoparticle functionalized AFM tip
Gold coated tip
50 nm gold particle
Au
Sample
SEM image of the tip
100 nm
Au
Polymer coated SiO
•Test of fundamental assumptions in ANSOM
•Fabrication of alternative “optically active” probes