Download - Laboratoire de Physique des Interfaces et des Couches Minces (LPICM) CNRS, Ecole Polytechnique
Laboratoire de Physique des Interfaces et des Couches Minces (LPICM)
CNRS, Ecole Polytechnique
91128 Palaiseau
France
Gennaro Picardi
Polarization properties of oblique incidence
Tip enhanced Raman spectroscopy
Experimental set-up
Raman (HORIBA JY)SPM (PSIA) Optical coupling
Piezos x, y
Piezo z
MicroscopeLaser
Grating
Notch filter
Detector
Half-wave plate
Analyzer
Confocal Raman
Feedback control
Oblique back-scattering configuration
Side illumination of the tip
STM Au tip etching
1-2 min
Electrochemical etching of a gold wire (0.125 mm) in a solution of 1:1 ethanol and conc. HCl (37%).
Applied Voltage: ~2.4 V
7-8 minBreak of the tip(circuit closes)
Rtip = 20-30 nm
L. Billot, L. Berguiga, M.L. de la Chapelle, Y. Gilbert and R. Bachelot; Eur. Phys. J. Appl. Phys. 31 (2005) 139B. Pettinger, B. Ren, G. Picardi, R. Schuster and G. Ertl; Rev. Sci. Instrum. 75 (4) (2004) 837
Anodic oxidation(passivation)
AuOHe-
Au dissolution
H+, 2 Cl-
DisproportionCl-
½ e-, Cl-
AuCl4-
AuCl2- + H20
Au deposition
H20, Cl-
Au*-Cl-
Au*-H20
Oscillatory electrodissolution of gold
Passiveregion
Activeregion
Au electrodissolution in HCl is diffusion limited
Z.L. Li,T.H. Wu, Z.J. Niu, W. Huang, H.D. Nie ; Electrochem. Comm. 6 (2004) 44
X. Wang, Z. Liu, H. Zhang, X. Wang, Z. Xie, D. Wu, B. Ren and Z. Tian; Appl. Phys. Lett. 91 (2007) 101105
Brilliant Cresyl Blue
on Au (111)
Au tip(oblique incidence)
585 cm-1 exc 633 nm
20 s
D1 filter
STM-TERS on dyes
400 600 800 1000 1200 1400 1600
0
50
100
150
200
Ram
an i
nte
nsi
ty (
a. u
.)
Raman shift ( cm-1 )
G. Picardi, Q. Nguyen, J. Schreiber and R. Ossikovski, Europ. Phys. J. Appl. Phys. in press (2007)
TERS for structured materials nano-characterization
W.X. Sun and Z.X. ShenNear-field scanning Raman microscopy using apertureless probes
J. Raman spectrosc. 2003; 34: 668-676
Micro-Raman Spectroscopy provide mapping of stresses in Si structures ( well defined Raman shift due to strain )
3700 nm
Near-field Raman mapping at 521 cm-1 ( Si-Si )
(using aperture-less probe)
380 nm300 nm
Introducing polarized TERS
(p) - pol
no analyzer analyzer at 90°
« … polarization of the ligth scattered by the particle will differ from the polarization of the incident light. The light partly depolarized by the particle then inelastically scatters with the optical phonon in Si thereby producing allowed Raman signal. The allowed Si Raman signal should be associated with a local area around the particle. »
V. Poborchii, T. Tada and T. Kanayama, Jpn. J. Appl. Phys. 44 (2005)
(p) - pol
Half-wave plate
AnalyzerSample
incident light-tip interaction
scattered light- tip interaction
Incident light Scattered light
Polarization control may become an important parameter in the TERS experiment
I. The tip modifies the polarization state of the incident and scattered radiation.
II. The far field signal can be reduced by using an analyzer.
Polarization control in TERS
Rj : Raman tensor of j-phonon
ei : incident polarization state (polarizer P)
es : scattered polarization state (analyzer A)
The scattered intensity depends on the polarization states ei, es as well as on the sample orientation S
Raman intensity
000
00d
0d0
R
0d0
d00
000
R
00d
000
d00
R 321
Sample orientation S
Analyzer
n
ie
se
Polarizer
j
2
ijTs e . R .eI
Calculation of the scattered intensity in the far field
Far field: experimental verification
Calculation of the scattered intensity in the far field
The sample orientation (or azimuth) S modulates the scattered intensity.
(100) c-Si (111) c-Si
P || A
P ┴ A
Sample orientation S (deg) Sample orientation S (deg)
Inte
nsi
ty (
arb
. un
.)
Inte
nsi
ty (
arb
. un
.)
The tip-enhancement tensor A describes the field enhancing and polarization properties of the tip
a and b : tip-dependent TERS parameters
The tip tensor A transforms the sample Raman tensor R to an effective scattering tensor R’
Far field (tip withdrawn): R (R : Raman polarizability tensor)
Near field (light-tip intaction): R’ = AT R A (A : tip-enhancement tensor)
Total field (tip in contact): Far field + Near field
(the tip-enhancement tensor)
Calculation of the scattered intensity in the near field
b00
0b0
00a
A
R. Ossikovski, Q. Nguyen and G. Picardi, Phys. Rev. B 75, 045412 (2007)
NH4F etched Si (111)
NC-AFM STM
(b) Etch-pit initiation by dissolved oxygen on terraces of Si (111)C.P. Wade and C.E.D. ChidseyAppl. Phys. Lett. 71 (12) 1997
Ut = -1.5 V
It = 50 pA
Pt/Ir tip
Ut = -1.0 V
It = 100 pA
Au tip
750 nm
Opticalmicroscope
10 m
TERS on Si(111) with polarization control (I)
Raman intensity of the 1st order Si phonon peak ( 521 cm-1 ) tip down tip up
a : b = 1.6 : 1
Analyzer fixed at 90°
a : b = 5.5 : 1
= 20° = 71°
20
40
60
80
100
120
140
0 20 40 60 802.4
2.8
3.2
3.6
4.0
4.4
480 500 520 540 5600
30
60
90
120
150
Inte
nsit
y (c
ps) (b)
(d)
Con
tras
t
Incident polarization (deg)
Raman shift (cm-1)
0 20 40 60 80
2.0
2.4
2.8
3.2
20
30
40
50
60
70
80
Con
tras
t
Incident polarization (deg)
Inte
nsit
y (c
ps)
(c)
(a)
( s ) ( p ) ( p ) ( s )
Tip #1 Tip #2
G. Picardi, Q. Nguyen, J. Schreiber and R. Ossikovski, Appl. Spectr. 61 (12), 2007
Oblique incidence: p - polarization or s - polarization ?
400 600 800 1000 1200 1400
20
40
60
80
100
120
Ram
an in
tens
ity
(a.u
.)
Raman shift (cm-1)
400 600 800 1000 1200 1400
20
40
60
80
100
120
Ram
an in
tens
ity
(a.u
.)
Raman shift (cm-1)
(with p-pol ) (with s-pol )
Higher intensity with incident (p) polarizationbut strong TERS also with incident (s) light
BCB on Au (111)No analyzer
Tip #2
G. Picardi, Q. Nguyen, J. Schreiber and R. Ossikovski, Appl. Spectr. 61 (12), 2007
Influence of the incident polarization in TERS ( I )
( p ) – polarization (in-plane) of the incident electric field
EFE up to 35
EFE up to 10
( s ) – polarization (out-of-plane) of the incident electric field
‘ Understanding TERS ’
A. L. Demming, F. Festy and D. RichardsJ. Chem. Phys. 122, 1847 (2005)
‘ Finite Element simulations of TERS ’
A. Downes, D. Salter and A. ElfickJ. Phys. Chem. B 110, 6692 (2006)
Influence of the incident polarization in TERS ( II )
1. Overall higher field enhancement with p – polarized excitation,
but field enhancement also with s – polarized ligth.
Near-field Raman spectra of SWCNT measured under p- and s- polarization conditions.
Polarization measuraments in TERS applied to SWCNTY. Saito, H. Hayazawa, H. Kataura, T. Murakami, T. Tsukagoshi, Y. Inouye and S. Kawata
Chem. Phys. Lett. 410, 136 (2005)
2 bis.
2. With p – polarized light illumination also enhancement of the field
component in the substrate plane (i.e. out of the plane of incidence).
With s – polarized light illumination also enhancement of the field
component normal to the substrate plane (i.e. in the plane of incidence).
Cross polarization effect(depolarized enhancement)3.
Imaging should be (?) different.
S. Foteinopoulou, J. P. Vigneron and C. VandenbemOpt. Expr. 15, 4253 (2007)
‘Under p - pol or s - pol light illumination the charge is differently
concentrated.’
Far field artifacts when TERS probing bulk samples
‘ The (tip in) contact signal may include a component that is unrelated to the plasmon resonance enhancement due to reflection and scattering from the tip … leading to additional unlocalized Raman signal.’
‘ … significant enhancement of Raman scattering from silicon substrates can be achieved without a field enhancement effect by plasmon resonces. Pure laser deflection and near field scattering cause similar effects which are difficult to distinguish.’
C. Georgi, M. Hecker and E. Zschech, Appl. Phys. Lett. 90, 171102 (2007).
N. Lee, R. D. Hartschuh, D. Methani, …and A. P. Sokolov , J. Raman Spectrosc. 38, 789 (2007).
ACKNOWLEDGEMENTS
Quang Nguyen
Razvigor Ossikovski
Bernard Drevillon(LPICM director)