Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu,...
-
Upload
arturo-mepham -
Category
Documents
-
view
224 -
download
3
Transcript of Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu,...
![Page 1: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/1.jpg)
![Page 2: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/2.jpg)
Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a N
oncentrosymmetric Crystal
Wei-Tao Liu, Y. Ron Shen
Physics Department,
University of California at Berkeley
![Page 3: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/3.jpg)
Optical Spectroscopy Techniques for Probing Phonons
IR Raman
SFS
For bulk and surface phonons
![Page 4: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/4.jpg)
Bulk phonons Bulk structure
Surface phonons Surface structure
Microscopic surface phonons
different from
Fuchs-Kliwer surface phonon-polaritons (Re -1)
![Page 5: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/5.jpg)
Existing Techniques To Probe Surface Phonons
• He scattering: Often limited to < 30 meV
• EELS: Difficult for insulating crystalsOften probing surface phonon-
polaritons
• Infrared-visible sum-frequency spectroscopy
![Page 6: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/6.jpg)
(2)1 2 1 2
(2)(2) (2)
(2)
(2)
( ) : ( ) ( )
( )
0 in media with inversion symmetry
0 at surfaces or interfaces
S
BS
B
S
P E E
i k
�
�
�
�
(2) 21 2
(2) (2)
2
ˆ ˆ ˆ |e : |
qNR
q q q
SFG e e
A
i
�
As 2 q, or el,
SFG is resonantly enhanced,
Spectroscopic information.
1
2
1
2
2
1
SF
SF
Sum-Frequency Spectroscopy
Measurements with different polarization combinations independent (2)ijk
![Page 7: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/7.jpg)
1, 0.2 -2
2, 0.42 -10 s
s
To detectorand computer
Experimental Setup
![Page 8: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/8.jpg)
Surface Phonons of Diamond (111)(A Centrosymmetric Crystal)
Raman spectrum
SFG spectrum
Pandey model
(cm-1)
Ra
ma
n S
ign
al
IRSF Vis
![Page 9: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/9.jpg)
Surface Phonons of Noncentrosymmetric Crystals
(21 out of 32 crystallographic point groups are non-centrosymmetric)
(2) 21 2
(2)(2) (2)
ˆ ˆ ˆ |e : |
( )BS
SFG e e
i k
�
�
SF output is overwhelmed by bulk contribution unless can be suppressed,
Achievable with selective sample geometry and input/output polarization combination
(2)B
Basic Idea: Surface and Bulk have different structural symmetry.
![Page 10: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/10.jpg)
Si
OSi-OH
Si-O-Si
Example: Quartz(0001)(relevant in many areas of science and Technology)
D3 point group
[0001]
Side view Front view
![Page 11: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/11.jpg)
)2(,
)2(,
)2(,
)2(, babBbbaBabbBaaaB )2(
,)2(
, bacBabcB
)2(,
)2(, bcaBacbB )2(
,)2(
, cbaBcabB
Bulk and Surface Nonlinear Susceptibilities of Quartz(0001)
4 Nonvanishing elements of bulk nonlinear susceptibilities:
3 Nonvanishing elements of surface nonlinear susceptibilities for the (0001) surface:
)2(,cccS )2(
,)2(
, bbcSaacS
)2(,
)2(,
)2(,
)2(, cbbScaaSbcbSacaS
W.T.Liu, Y.R.Shen, PRL (2008)
![Page 12: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/12.jpg)
(2) (2) (2), , ,[ cos3 / ]SSP eff S aac B aaaC i k
(2) (2) (2) (2), 1 , 2 , 3 , cos3 /PPP eff S aaz S ccc B aaaC C C k
2)2()( effIRvisSFS
SF Output from (0001) –Quartz with SSP and PPP Polarization Combinations
Bulk contribution dominates unless ~ 0
![Page 13: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/13.jpg)
SF Phonon Spectra of Quartz
![Page 14: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/14.jpg)
750 800 1000 1100 1200 1300
0
1
2
3
4
5
I SF
G (
a. u
.)
Wavenumbers (cm-1)
x5
0
30
6090
120
150
180
210
240270
300
330
Properties of bulk -quartz
D3 point group
SF signal from bulk -quartz can be suppre
ssed at certain sample orietations.
![Page 15: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/15.jpg)
Surface modes observed with bulk signal suppressed.
-Quartz (0001) surface: vibration modes
2)2()2(BulkSurfaceSSPI
)2(Surface Isotropic
)2(Bulk )3cos(
Surface and bulk signals are separable
W.-T. Liu and Y. R. Shen, PRL 101, 016101 (2008)
![Page 16: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/16.jpg)
Si-OH
Si-O-Si
Mode assignment: OTS titration
…
Si-OH
![Page 17: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/17.jpg)
850 900 950 1000 1050
1
2
3
4
Wavenumbers (cm-1)
Hydrated surface Baked @ 100C Rehydrated
I SS
P (
arb
. u
nit)
SiOH+SiOH SiOSi+H2O
Effect of Baking
![Page 18: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/18.jpg)
500C baking disrupts the ordered surface lattice structures
Irreversible surface structural change
SF I
nten
sity
Quartz
Fused Silica
• After baking at 500C
• Rehydroxylated
• After boiled in water
![Page 19: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/19.jpg)
Boiling
S. Yanina et al., Geochimica 70, 1113 (2006)
Deteriorated LEEDpatterns after 500C
F. Bart et al., Surf. Sci 311, L671 (1994)
![Page 20: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/20.jpg)
T. Goumans et al., PCCP 9, 2146 (2007)
Surface structure: Si-O-Si bonding geometry
Bulk
Si-O-Si stretch @ 795 cm-1
Si-O-Si = 143.7o
Surface
Si-O-Si stretch @ 870 cm-1
Si-O-Si ~ 130o
Si-O-Si ~ 120o-135o
![Page 21: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/21.jpg)
• Max 30o on partly hydrated -quartz (0001);
• Silanol groups has a broader distribution on fuse
d silica.
Surface structure: Si-OH orientation
Bulk terminated surface
Partially hydrated
![Page 22: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/22.jpg)
• Surface vibrations of non-cen
trosymmetric crystals can be
obtained with SFG;
• Example: -quartz (0001)
980 cm-1: Si-OH stretch
880 cm-1: (strained) Si-O-Si vi
bration;
Si-OH
Si-O-Si
Summary
![Page 23: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/23.jpg)
Probing Bulk Phonons
Infrared spectroscopy IR active modes
Raman spectroscopy Raman active modes
SF spectroscopy IR and Raman active modes
For quartz, only E(TO) modes are both IR and Raman active – 3 out of 11 existing phonon modes between 700 and 1300 cm-1
![Page 24: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/24.jpg)
750 800 1000 1100 1200 1300
0
1
2
3
4
5
I SF
G (
a. u
.)
Wavenumbers (cm-1)
x5
0
30
6090
120
150
180
210
240270
300
330
Raman spectrum
SF spectrum
![Page 25: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/25.jpg)
Sum-Frequency Spectroscopy on Bulk Phonons of Quartz
![Page 26: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/26.jpg)
Three-fold Symmetry from Bulk SFVS
![Page 27: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/27.jpg)
(2) 2,
(2) (2) (2) 21 , 2 , 3 ,
(2) (2) (2) 21 , 2 , 3 ,
,(2) (2), ,
| sin 3 |
| sin 3 |
| sin 3 |
( )
SSS B aaa
SPP B aaa B bca B abc
PSP B aaa B cba B abc
q ijkB ijk NR ijk
q IR q q
S A
S B B B
S C C C
A
i
![Page 28: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/28.jpg)
Fitting of the experimental results yields
q = 795, 1064, 1160 cm-1
and the corresponding nonvanishing
Aq,aaa , Aq,bca Aq,cab , Aq,bca = 0, (2)
, 0NR ijk
,
,
,
1
/ Raman polarizability ratio
ij kq ijk
q q q
q bca bc aa
q aaa q q
AQ Q
A
A Q Q
![Page 29: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/29.jpg)
SF Spectroscopy for Bulk Phonons
• Complementary to IR and Raman spectroscopy:Identify modes both IR and Raman activeSimple spectrum.
• One fixed beam geometry is often sufficient to characterize the detected modes, such as Raman polarizability ratio.
• Reflected SF signal comes from a surface layer thickness of reduced wavelength.
![Page 30: Sum-Frequency Spectroscopy on Bulk and Surface Phonons of a Noncentrosymmetric Crystal Wei-Tao Liu, Y. Ron Shen Physics Department, University of California.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649cbb5503460f9498337c/html5/thumbnails/30.jpg)
IR-visible sum-frequency spectroscopy can be used to probe bulk phonons of crystals,
complementary to IR and Raman spectroscopy.
It can also be an effective tool to probe surface phonons of crystals with or without inversion
symmetry.