Crystalline Colloidal Array
Optical Devices
Sanford A. Asher
Dept. of Chemistry
University of Pittsburgh
Pittsburgh, PA 15260
412-624-8570
asher@pitt.edu
Sanford A. Asher, Department of Chemistry
CRYSTALLINE COLLOIDAL SELF-ASSEMBLY:
MOTIF
FOR
CREATING SUBMICRON
PERIODIC SMART MATERIALS
Sanford A. Asher, Department of Chemistry
Outline
ƒ CCA and PCCA Photonic Crystal
Fabrication
ƒ Nanosecond Photonic Crystal Switches
ƒ Hydrogel Volume Phase Transition
Refractive Index Switching
– Thermally activated
– Chemically activated
– Photochemically activated
Crystalline Colloidal Arrays Self-Assembly
z fabricated from monodisperse, highly charged colloidal particles
Dialysis /
Ion Exchange
Resin
- + ++ - + +- - -+ +
- ++-- +-+
+ -+
+
+
- -- - +++ +
- - + - +
+
+
Self-assembly
FCC
~ 1013 spheres/cm3
-+- - +
+
+
+--+
+ - - +
+- +
+
+
-
- - +
-- --+
- +
++ +-
-- - +
-+ - - +
+
-
++ -+
- - - + - - - -+
- - -- - + - +
+
- - +- -- +
- - ---+ - - +
-- -+ -- +
+ -- - -+ +
- +- +
- ++
-+ +
+
+
+
++ -- - -+
-+
+ + -+ - -- - +
- - -- - - + - - ++
- - +-- - +
++ - - +
-+
+-
-- -- +
+ - - +
+-
- - - -+
-- + +-+ -+
-- --- + +
-- -+
+
- - +- +
+ -+
- -+ - +
-+- - +
Crystalline Colloidal Array
z spacing dependent only upon
particle number density and
crystalline structure
Holtz, Asher et al J. Am. Chem. Soc. 1994, 116, 4497
Polystyrene Colloid Synthesis:
EMULSION POLYMERIZATION
Preparing ~ 100 nm Polystyrene Colloids
160 ml Water
60 ml Styrene (monomer)
2.00 g MA-80-1 (surfactant)
2.90 g COPS -1 (ionic co-monomer) 2.00 g Divinyl Benzene (crosslinker)
0.20 g Sodium Bicarbonate (buffer)
0.70 g Ammonium Persulfate (initiator)
Polymerize at 70oC for 3 hrs.
Temperature
Controller
N2
R•
Long polymer chain
TEM of polystyrene spheres
+
- -
+
N2
Surfactant
+
H2O
R•
Water
Reese, Asher et al J. Colloid Interface Sci. 2000, 232, 76
What Drives CCA Self-Assembly?
+
+
SO3- H H -O3S
H+ -O S
3
H+
-O
SO3-+
3S
H
-O
r
H+
+
SO3- H
SO3- +H
3S
2
κa
2
⎤ e − κr
Z e ⎡ e
U (r ) =
ε ⎢⎣ 1 + κ a ⎥⎦ r
2
U
2a
Negatively charged particle
Sphere Radius
Medium Dielectric Constant
Interaction Potential Energy
2
4
π
e
(n p Z + ni )
κ2 =
ε kB T
1
κ
Ionic Impurities
Particle concentration Shear boundary
Debye layer thickness
(in pure water ) ~ 700 nm
r
Sanford A. Asher, Department of Chemistry
+
Bragg Diffraction
λ0
+
+
- - - - - ------- - - +
+
+
+
- - - - - ------ - - -+
θB
+
- - --------- - - --
+
d ~ 200 nm
+
+
- - - - - ------- - -+
+
- - - - - ------- - +
- - - - - -----+ - - - --
+
d
-- - - - ----- +
---- - -
+
(111) FCC CCA
- - - - - ---------- - -+
+
+
+
+
+
+
- - - - - -------- - -- +
+
- - - - - ------- - - -+
-- - - - ------- - +
+
- - - - - -------- - - -- +
+
- - - - - ------ -+ --
mλo = 2ndsin θ
+
λ0 = wavelength of diffracted light
n = refractive index of system
d = interplanar spacing in crystal
θB = Bragg glancing angle
Diffracted Intensity, ID
+
+
+
- - - - - --------- - --
+
500
600
700
Wavelength / nm
800
All Light Diffracted-Finite Widths-Top Hat Profiles
Diffraction Phenomena of Photonic Crystals
* Kinematic Diffraction
x-rays: Atomic & Molecular Lattice
wimpy scattering
little attenuation
each layer contributes similarly
*
Dynamical Diffraction
strong scattering
must consider coupled
incident and diffracted wave
*
Theoretical Foundation Based on Work in
1930-1940
W.H. Zachariasen, The Theory of X-ray Diffraction
in Crystals, Wiley, 1945.
3-D Photonic Bandgap Crystals-for much larger modulations of
refractive index
Dynamical Bragg Diffraction From Crystalline Colloidal Arrays, P. A. Rundquist, P.
Photinos, S. Jagannathan, and S. A. Asher, J. Chem. Phys. 91, 4932-4941 (1989).
Ultra Efficient
Diffraction
0
91 nm PS CCA
- Log T
2
100 μm = 400 layers
4
6
8
10
0
200
400
600
800
1000
Number of fcc (111) layers
FCC Crystal
B
A
Stacking of
closest-packed
layers:
C
HCP: ABABABAB…
FCC: ABCABCABC…
FCC Twin: ABCABCBACBA…
Twin Planes
Lamellar
FCC Twin: ABCABCBACBACBABCABC…
σ polarization
3
W
- log10 T
2.5
L U
K
2
1.5
X
L
X
1
U
.5
0
400
600
800
1000 1200 1400
Wavelength (nm)
CCA in the middle: ABCABC layers.
Reciprical lattice and unit cell.
Sanford A. Asher, Department of Chemistry
Incident light
(0-20)
(-220)
(-200)
Diffracted intensity ratio
Dependence of Diffraction Efficiency on
Number of Stacking Faults Along 111
(200)/(111)
(220)/(111)
(311)/(111)
0.5
0.4
0.3
0.2
0.1
0
0
5
10
15
% stacking faults
20
Conclusions
• Diffraction from FCC 111 planes
independent of stacking faults
• Diffraction from higher Miller index planes
severely attenuated by stacking faults
• Stacking faults increase with particle
spacing
• Stacking faults will be the major difficulty
for fabricating 3-D photonic bandgap
materials
Crystalline Colloidal Array Optical
Devices
•Passive Spectral Bandpass Reject Filter
0
EXP: Raman Spectroscopy
-log T
rejecting Rayleigh
line, Δλ = 5 nm
-7
λ
Sanford A. Asher, Department of Chemistry
First Photonic Crystal Patent
Photonic Crystals
Have Revolutionary
Applications in Areas
Such as Optics,
Optical Computing
and Communications.
Crystalline Colloidal Array
Tunable Optical Devices
•Refractive index thermal nonlinearities
•Hydrogel volume phase transitions
•Photochemically accuated lattice
alterations
Sanford A. Asher, Department of Chemistry
Optical Limiter and Switch
Low Intensity
?
100% Transmission
High Intensity
?
No Transmission
Concept for Creating Nonlinear Optical Switch
Low intensity illumination :
CCA
100% transmission
index matched (np = nm)
High intensity illumination causes the sphere refractive index
to mismatch that of the medium - Bragg diffraction occurs.
CCA
no transmission
index mismatched (np ≠nm)
Transmission Through CCA as a Function
of the Refractive Index Between the
Spheres and the Medium
Nanosecond Photothermal
Dynamics in Colloidal Suspension
R. Kesavamoorthy, M. S. Super,
and S. A. Asher,
J. Appl. Phys. 71, 1116-1123
(1992).
Nanosecond Photothermal Dynamics in Colloidal Suspension
R. Kesavamoorthy, M. S. Super, and S. A. Asher,
J. Appl. Phys. 71, 1116-1123 (1992).
Refractive Index Dependence on Temperature
Photothermal Effect:
Δn = (dn/dT) · ΔT
Example: PMMA,
dn/dT = -1.1 X 10-4 / 0° C
×
Requirements:
(1) To index match the particles to the
aqueous medium (nH2O = 1.33), we
need to use a low refractive index
polymer to synthesize the particles.
(2) We need to chemically bond a dye
to the particles in order to prepare
transparent, absorbing CCA.
(
CH2
CH
C
)n
O
OCH2CF2CF2CF3
Trans mis s ion S pec tra of P FB MA Pol ymerize d CC A at Di fferen t
Me diu m Re frac ti ve In de x
1.4
1.4
1.2
np > nm = 1.437
1.0
Extinction
Extinction, -log(It/I0)
1.2
1.0
0.8
0.8
0.6
0.4
0.2
0.0
1.34 1.36 1.38 1.40 1.42 1.44 1.46
med iu m refractive in dex, nm
0.6
0.4
np > nm = 1.333
0.2
0
500
550
600
650
700
750
Wave le ngth / nm
A ~ ( n p /n m )2 - 1
800
Dyed PFBMA CCA Hydrogel
Covalently attached absorbing dye to the CCA in the hydrogel.
Extinction
1.0
dye absorption band
0.8
0.6
diffraction band
0.4
0.2
0
400 450 500 550 600 650 700 750 800
Wavelength (nm)
PCCA Fabrication
+
- - +- - -+ - - +
+---- - - --- - ++
+
+- - --- - +- - - + +- - --- - +-- - - - -+
-- - ++ - - -- +
-+ -+ - --- - +-- -+
+
- - -- - - - -- + - -- - - -- +
-- --- +
+
+
+
- -- - + - - +- -+ -+--+
+
+
- -- +- - +- - -- - - - -+- -- -- - -- - ++
- - -- +
+
- -+- --- - --+ -- -- - -- - --+
-+ - - + +- - - --+ - -- - -+
+ --- --- -+
+
+
+
-+ - - +
- - +- - - - --- - - - --- - +- - - -+
+
+- --- - +- - - + +- - --- - - +- - - -+
-- - ++ - - -- +
- + --- -+- - - + - -- - ++
- - -- - - - -- + - -- - - -- +
-- --- +
+
+
+
- -- - + - -- -+
+- -+ +-+ - -- - +
- -- - ++- - -- - -- -- - - - -+- - - +- - -- +
+
+- -+- --- - --+ -- -- -- --- +- - -- - -+ - - + +- - - --+ - - -+
+ --- -+- - - +-
Acrylamide
Bisacrylamide
Photopolymerize
+
Self Assembly Motif for Creating Submicron Periodic Materials. Polymerized
Crystalline Colloidal Arrays,
S. A. Asher, J. Holtz, L. Liu, and Z. Wu, J. Am. Chem. Soc. 116, 4997-4998 (1994).
+
Extinction
Experimental Set-up For
Measuring Optical
Switching Nonlinearity
n0 Medium index
532 nm
Pump
beam
cylinder with DMSO/water
shutter
lens
Probe beam
594
beam splitter
nm D1
(reference signal)
CCA hydrogel sample
D2
(diffraction signal)
Optical Switching of Dyed PCCA
2.4
Tg = 62 0C
Ron / Roff
2.2
2.0
1.8
Nsec Switchable Polymerized
Crystalline Colloidal Array
Bragg Diffracting Materials
1.6
1.4
1.2
G. Pan, R. Kesavamoorthy, and
S. A. Asher
1.0
0.8
0.6
0.4
0
0.5
1.0
1.5
2.0
2.5
3.0
Incident Pump Beam Energy (mJ)
nm (1.390) > np (1.386) , dyed PCCA
nm (1.382) < np , dyed PCCA
nm (1.388) > np , undyed PCCA
J. Am. Chem. Soc. 120, 65256530 (1998).
Dependence of Nonlinear Effect on Probe Delay Time
Ron/Roff at Tg
3.0
Nsec Switchable Polymerized
Crystalline Colloidal Array
Bragg Diffracting Materials
2.5
G. Pan, R. Kesavamoorthy,
and S. A. Asher
2.0
J. Am. Chem. Soc. 120, 65256530 (1998).
1.5
1.0
-4
-2
0
2
4
6
Probe delay time / ns
8
Conclusions
• Observed nsec photothermal switching
• Problem low efficiency (<10%) /!
• Stay Tuned: Inefficiency results from
temperature dependence of diffraction λ
• Switching should be 99 + %
Crystalline Colloidal Array
Tunable Optical Devices
Refractive index thermal nonlinearities
•Hydrogel volume phase transitions
•Photochemically accuated lattice
alterations
Sanford A. Asher, Department of Chemistry
Poly(N-isopropylacrylamide) : T Dependent ΔGMIX
Poly(N-isopropylacrylamide)
(PNIPAM) undergoes a
reversible phase transition
when heated above 32.1 oC.
This coil-globule transition is
analogous to a liquid-vapor
phase transition. The recipe
and synthesis conditions
determine the extent of volume
changes and whether they are
continuous or discontinuous.
Chemical Structure of NIPAM
N
O
Thermally Switchable Periodicities from Novel Mesocopically Ordered Materials
J. M. Weissman, H. B. Sunkara, A. S. Tse , and S. A. Asher
Science 274, 959-960 (1996).
Extinction (-log I/Io)
2
40 oC
1.5
40 oC
1
10 oC
0.5
10 oC
0
400
450
500
550
600
Wavelength (nm)
Optical switching from PNIPAM CCA
Sanford A. Asher, Department of Chemistry
Sanford A. Asher, Department of Chemistry
Unfortunately system does not switch quicklyCCA disorders!
NIPAM CCA Lightly Polymerized into PCCA
Hydrogel
Matrix
Monomer
Crosslinker
Initiator
UV
Polymerization
PNIPAM
Colloid
“Nanogel Nanosecond Photonic Crystal Optical Switching,”
C. Reese, A. Mikhonin, M. Kamenjicki, A. Tikhonov and S.A. Asher
J. Am. Chem. Soc., 126, 1493-1496 (2004).
1.4
3
10 C
15 C
20 C
25 C
28 C
30 C
32 C
34 C
37 C
40 C
45 C
A b s o rb a n c e
2.5
2
1.5
1
A b so rb an ce at 716 n m
1.2
1
0.8
40oC
0.6
0.4
0.2
5
10
15
20
25
30
35
40
45
Temperature / C
20oC
0.5
0
200
300
400
500
600
50
PNIPAM
Colloid
700
Wavelength / nm
800
900
1000
Time Dependence of Diffraction Changes after 3 nsec T-jump
− Δ log T
1.5
4 ms
.3
0.48 m s
.2
0.3 m s
54 μ s
.1
1
− log T
.4
56 0
600
64 0
W avelen gt h / nm
680
24 μ s
9 μs
1.5 μ s
1 μs
.5
800 n s
600 n s
300 n s
0
100 n s
400
500
600
W avelength / nm
700
0
1
− Log T
605 nm
0.1
τ1 ≈ 870 ns (26%)
τ2 ≈ 19 μs
Kinetics
(24%)
τ3 ≈ 130 μs (50%)
0.01
0
40
80
120
Delay time / μs
− Log T
1
375 nm
0.1
τ1 ≈ 1.2 μs
(28%)
τ2 ≈ 21 μs
(11%)
τ3 ≈ 147 μs (61%)
0.01
0
40
80
Delay time / μs
120
NSec Individual Sphere Volume Phase Transitions
0.0 8
0.0 7
ΔOD
.15
0.0 6
60 0 nm
0.0 5
τ ≈ 1 20 n s
0
1
D e la y tim e / μs
1500 μsec
1000 μsec
200 μsec
20 μsec
2.5 μsec
0.4 μsec
0.3 μsec
0.2 μsec
0.1 μsec
0 μsec
2
.1
.05
400
450
500
550
600
Wavelength / nm
650
Fast Kinetic Transmission Changes in
PNIPAM Photonic Crystals.
• Heating pulse: 3 ns duration, 1.9 μm, ~1.3
mJ/pulse
• T-jump ~ 23°C → 30°C ± 2°C, IR spot
diameter ~ 200 – 300 μm
• Transient absorption probed by temporally
delayed 120 ns “white-light” pulse
Crystalline Colloidal Array
Tunable Optical Devices
•Refractive index thermal nonlinearities
•Hydrogel volume phase transitions
•Photochemically accuated lattice
alterations
PHOTORESPONSIVE
POLYMERIZED CRYSTALLINE COLLOIDAL ARRAYS
AS A PHOTOSWITCHABLE DEVICE
Marta Kamenjicki, Igor K. Lednev, Sanford A. Asher
N
N
Department of Chemistry
University of Pittsburgh
Pittsburgh, PA 15260
Photochemically Controlled Photonic Crystals, M. Kamenjicki, I. Lednev, A. Mikhonin, R.
Kesavamoorthy and S.A. Asher, Advanced Functional Materials, 13, 774-780 (2003).
λ2
λ1
λ1
UV
H2N-R
Vis, Δ
R=
N
OH
N
O
HO
N
O
O
CH2 CH CH 2
O
N
H
OH
N
N
Trans -
PCCA
PCPCCA
N
N
OH
O
H
O
HO
Cis -
PCPCCA
HO
AZOBENZENE PHOTOISOMERIZATION
9.0 Å
5.3 Å
UV
N
N
N
N
VIS,
180°
60°
Trans-azobenzene
Cis-azobenzene
• reversible photochromism in fluids and solids
• isomerization results in changes of
1) absorption spectrum
2) dipole moment
3) geometrical conformation
Azobenzene (water solution) Dynamics Under
UV and Vis Light
1.0
Dark
H 2N
OH
N
Absorbance
N
O
20 sec. 488 nm
(50 mW)
OH
0.5
UV
N
N
N
N
Vis,
1 min 365 nm
(12 mW)
1 cm quartz cell
0.0
200
300
400
500
Wavelength /nm
600
700
Peak position /a.u.
Azobenzene Functionalized PCCA Dynamics
Under UV and Vis Light
0.8
UV
UV VisUV
Vis
A ( 340 nm)
-log T
Time
0.4
UV
0.8
0.6
Vis
Time
0
350
450
550
Wavelength /nm
650
750
a)
.8
.8
.6
.6
.4
.4
.2
Speed
0
360
400
440
480
Wavelength /nm
520
0
.8
.8
.6
.6
.4
.4
.2
Limit?
.2
t = 0.3 μs
0
360
.2
t = 102.3 μs
400
440
480
Wavelength /nm
520
0
360
400
.6
.6
.4
.4
0
360
b)
.2
400
440
480
Wavelength /nm
520
0
440
480
Wavelength /nm
0s
15 s
36 s
66 s
120 s
-log
T
.6
.4
.2
Fig. 11
360
380
400
420 440 460 480
Wavelength /nm
520
t = 6155.8 μs
.8
0
520
t = 302.3 μs
440
400
480
Wavelength /nm
.8
t = 2002.3 μs
400
440
480
Wavelength /nm
360
.8
.2
360
t = 5.3 μs
500
520
540
520
Optical Switching
• Use of Laser Heating to Drive Hydrogel
Volume Phase Transition
• Use of Photochemistry to Drive Hydrogel
Volume Phase Transition
• Use of Thermal Refractive Index
Mismatch to Control DiffractionInefficiency due to dynamic diffraction
wavelenght shift-stay tuned
FUTURE WORK
• Optimize these sensors to combine
hydrogel volume phase transition with
thermal heating by nsec pulses
• Available Δn > 0.15 !
• Decrease characteristic size of switching
materials.
Acknowledgements
Asher Research Group Members
$: NIH, NCI, NASA and NSF