Advanced Materials Optical Diagnostics group Nonlinear Optics with Nanostructured TiO ² A.GALAS and V.GAYVORONSKY Institute of Physics NASU, pr. Nauki 46, 03028 Kiev, Ukraine; E-mail: [email protected] ; Tel: (380) 44 265 08 14 JASS’04 , S.-Petersburg, Russia, 28 March - 7 April 2004
25
Embed
Advanced Materials Optical Diagnostics group Nonlinear Optics with Nanostructured TiO ² A.GALAS and V.GAYVORONSKY Institute of Physics NASU, pr. Nauki.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
AdvancedMaterialsOpticalDiagnostics group
Nonlinear Optics with Nanostructured TiO²
A.GALAS and V.GAYVORONSKY
Institute of Physics NASU, pr. Nauki 46, 03028 Kiev, Ukraine; E-mail: [email protected] ; Tel: (380) 44 265 08 14
JASS’04 , S.-Petersburg, Russia, 28 March - 7 April 2004
AMOD group members
From left to right:A.Galas, E.Shepelyavy, V.Kalicev, V.Gayvoronsky
F.KochTechnical University of Munich, Physics Department E16, 85748
Garching, Germany
In collaboration with
V.TimoshenkoMoscow State University, Physics Department, 119992 Moscow, Russia
Outline
1. Introduction
2. Samples characterization • Sol-gel synthesis• Structural characterization• Optical and electron properties
3. Nonlinear optical (NLO) monitoring of anatase nanoparticles
• NLO refraction and absorption• Giant NLO response ((3) ~ 10-5 esu)• Monitoring of photocatalytic activity with NLO response
4. Conclusions
Porous TiO2 applications:
• - dye-sensitized solar cells
• (Graetzel cell) low cost, high efficiency, exceptional stability
Nanoparticle TiO2 layers on glass substrate were prepared in Institute of Surface Chemistry NASU (Kiev) with film drawing from viscous solution (precursor). The precursor was prepared with sol-gel technique using Titanium(IV) isopropoxide, acetic acid, -terpineol (to control viscosity). Polyethylenе glycol with molecular weights 300 (PEG 300) and 1000 (PEG 1000) were used as pore and complexing agents.
The drawing layers on glass substrate were treated 1 hour at 5000 C. Multilayer films are annealed at the same conditions after each layer deposition. Thicknesses 100 – 1000 nm, porosity 34-39%
XRD -TiO2 layers contain nanocrystals of only single phase – anatase TEM – nanoparticle mean diameter 16 nm (distribution 5 - 30 nm)
H. I. Elim et.al., Applied Physics Letters 28 (2003) 2691-2693
S - sample, A – the beam attenuator, L – focusing lens with focal length f, Sp – beam splitters, D – diaphragm in the far field, P1, P2
and P3 – photodiodes, r – transverse coordinate.Dashed line – laser beam propagation without a sampleSolid line - focused by a sample beam
Setup for the laser beam selfaction effect research
f
Sp
Sp
SDLAr
P3
P2P1
f
Sp
Sp
DLAr
P3
P2P1
Total transmittance and normalized on-axis transmittance in far field
77
78
79
80
81
0 20 40 60 80 10071
72
73
74
75
double layer
single layer
Tot
al tr
ansm
ittan
ce, %
Laser Intensity, MW/cm2
0 20 40 60 80 1001.00
1.02
1.04
1.06
1.08
1.10
On-
axis
tran
smitt
ance
, arb
.un.
single layer
Laser Intensity, MW/cm2
double layer
Single layer d = 180 nmDouble layer d = 360 nm
p= 40 ps
Giant NLO Response
(3) ~ 2 ·10-5 esu
of TiO2(1000) films versus input laser intensity at =1064 nm.
Giant NLO Response
WHY Giant ?Bulk TiO2 - (3) ~ 10-11 esu
Thin TiO2 films - (3) ~ 10-9 esu
Our nanoparticle TiO2 films - (3) ~10-5 esu
(3) ~ 10-5 esu
Total transmittance and normalized on-axis transmittance in far field.
77
78
79
80
81
1 10 100
62
64
66
68
70
TiO2(1000)
TiO2(300)
Tot
al tr
ansm
ittan
ce, %
Laser Intensity, MW/cm2
1 10 1001.0
1.1
1.2
1.3
1.4
1.5
TiO2(1000)
TiO2(300)
On-
axis
tran
smitt
ance
, arb
.un.
Laser Intensity, MW/cm2
TiO2(1000) (3) ~ 2 ·10-5 esu
TiO2(300) (3) ~ 6 ·10-5 esu
Giant NLO Response
TiO2(1000) d = 360 nmTiO2(300) d = 240 nm
p= 40 ps
of TiO2(1000) and TiO2(300) films versus input laser intensity at =1064 nm
200 300 400 500 6000.0
0.5
1.0
1.5
2.0
2.5
initial
5 hours
2 hours
Op
tica
l De
nsi
ty
, nm0 50 100 150 200 250 300 350
0.0
0.2
0.4
0.6
0.8
1.0= 524 nm
Standard P-25
TiO2(1000)
TiO2(300)
OD
/OD
0
t, min
TiO2 + h h+ + e (1)R6G + h R6G* (2)
R6G* +TiO2 R6G+ +TiO2(e-) (3)
Photocatalytic activity of the anatase films
R6G water solution absorption spectra for different UV dose in TiO2 presense
Dynamics of R6G photodestruction with UV light due to the presence of TiO2 films.
R6G* + O2 R6G+ + O-2 (4)
TiO2(e-) + O2 TiO2 + O-2 (5)
R6G++O-2
destruction products (6)
Destruction of Rhodamine (R6G):
Energy band structure of nanoporous anatase.
0
1
2
3
4
180 fs << p=40 ps < 100 ps
electronslocalized
delocalized
ST-ST
ST-DT relaxation ~100 ps
CB-ST relaxation ~180 fs
Hole trapping
TPA
EF
HoleTrap (HT)
DeepTrap (DT)
ShallowTrap (ST)
Conduction Band (CB)
Valence Band (VB)
Ene
rgy,
eV
Laser quantum 1.17 eV, pulse duration~ 40 ps
Schematic diagram of possible water dissociation mechanisms on the vacancy defected TiO2(110) surfaces. Dissociation at a vacancy would result in two equivalent OH groups.
Dark atoms are Ti cations, lighter atoms are in-plane O anions. Models for water and OH are represented with covalent radii.
Physisorbtion of H2O
Chemisorbtion of H2O
Photoemission spectra (h = 35 eV, normal emission) from the valence band region of a sputtered and UHV - annealed, clean TiO2(1 1 0) surface.
U. Diebold / Surface Science Reports 48 (2003) 5-229
Defect state and molecular orbitals of adsorbed H2O
Size distribution in anatase nanoparticle films
0 5 10 15 20 25 30 350
5
10
15
20
Par
ticle
s nu
mbe
r
particle size, nm0 5 10 15 20 25 30
0
5
10
15
20
Par
ticle
s nu
mbe
rparticle size, nm
5%
TiO2(1000) TiO2(300)
(3) ~2·10-5esu (3) ~6·10-5esu
Photocatalytic activity (reference P-25 =1)
1.34
Photocatalytic activity (reference P-25 =1)
2.72
ConclusionsElectron and optical properties (refraction index, absorption, optical band gap) of nanoparticle anatase films slightly vary for the samples prepared with different comlexing agents