Multifunctional Particles for
Crystalline Colloidal Array
Sophisticated Photonic Crystals
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
CCA and PCCA Photonic Crystal
Fabrication
Spatial Control of Electromagnetic
Field Maxima Ag@SiO2
Magnetically Controlled CCA
–
Superparamagnetic CCA
–
Ferromagnetic CCA
☺ Nothing@PS-Hollow Sphere CCA
Crystalline Colloidal Arrays Self-Assembly
fabricated from monodisperse, highly charged colloidal particles
Dialysis /
Ion Exchange
Resin
- + ++ - + +- - -+ +
- ++-- +-+
+ -+
+
+
- -- - +++ +
- - + - +
+
+
Self-assembly
FCC
~ 1013 spheres/cm3
-+- - +
+
+
+--+
+ - - +
+- +
+
+
-
- - +
-- --+
- +
++ +-
-- - +
-+ - - +
-
+
++ -+
- - - + - - - -+
- - -- - + - +
+
- - +- -- +
- - ---+ - - +
-- -+ -- +
+ -- - -+ +
- +- +
- ++
-+ +
+
+
+
++ -- - -+
-+
+ + -+ - -- - +
- - -- - - + - - ++
- - +-- - +
++ - - +
-+
+-
-- -- +
+ - - +
+-
- - - -+
-- + +-+ -+
-- --- + +
-- -+
+
- - +- +
+ -+
- -+ - +
-+- - +
Crystalline Colloidal Array
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
Ionic Impurities
Particle concentration Shear boundary
Debye layer thickness
1
κ
(in pure water ) ~ 700 nm
r
Sanford A. Asher, Department of Chemistry
Crystalline
Colloidal Array
λ
d
θ
- - +- - -+ - +
+
+-- -- -- -- - --- - - -- ++
- - --- - +- - --- +- -- +
+
-- -- - + -- - - +- - - -- - +- - ++
- -+- - - + + - -- - +- + - - -- -- - - -- +- - - -- + - -- - - --- -+
- + - + -- -- -+ -- -- +
+ +- -- +-- - + -- - - - ---+- +- ++
-- - - - -- - - + -- - -- - -- + +- -- +-- +- - -- -+-- +
- --- +- --- - - - -- - -+ - - + - - - --+ - +
+ --- --- -+ - -+
+
+
+
mλ = 2nd sin θ
m = order of diffraction
λ = diffracted wavelength
n = refractive index of system
d = spacing between diffracting planes
θ = Bragg glancing angle
+
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
Bandgap,
Δλ↔Δθ
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
Britney Spears
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Spears Photonic Crystal Site
It is a little known fact, that Ms Spears is an expert in
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Bandgap causes standing wave where at the
edges the electric field maxima occur within
the high and low refractive index layers
High refractive index
layers
Opportunity to
spacially tune
electric field
maximum to
region of high
optical
nonlinearities!
Incident
Diffracted
Low refractive index layers
Ag@SiO2
100 nm
(EtO)4Si
+ H2O +
AgNO3
hν
Ag QD
The monodisperse SiO2 spheres show a homogeneous incorporation of Ag quantum dot
inclusions. dsphere=78+5.4 nm, dAg=3-8 nm.
SiO2
. “Photochemical Incorporation of Silver Quantum Dots in
Monodisperse Silica Colloids for Photonic Crystal Applications,” W.
Wang and S. A. Asher, J. Am. Chem. Soc., 123, 12528-12535 (2001).
Can Easily Vary Loading and Sizes
A
B
C
Ag QD Plasmon Resonance in Random
Dispersion of Ag@SiO2
2.0
438 nm
(a)
Extinction, -log(I/I0)
1.5
1.0
(b)
random dispersion
in water
(c)
0.5
(d)
Refractive index
matched
(e)
0.0
300
400
500
Wavelength, nm
Figure 11
600
700
fcc CCA
mλ=2ndsinθ
605 nm
565 nm
0.5
521 nm
1.0
490 nm
288 nm
307 nm
1.5
457 nm
2.0
Plasmon Resonance
253 nm
266 nm
Extinction, -logI/I
0
2.5
403 nm
425 nm
220 nm
235 nm
3.0
210 nm
Ag@SiO2 CCA Diffraction as a Function of
Lattice Spacing
0.0
200
300
400
500
Wavelength/nm
600
700
1.50
490 nm
425 nm
Dependence of Plasmon Resonance Extinction on Bragg
Condition
1.00
565 nm
Extinction, -logI/I0
392 nm
1.25
0.75
0.50
0.25
Refractive
Index Matched
0.00
Random
200
Dispersion
Plasmon
Resonance
300
400
500
600
Wavelength/nm
700
800
Spatial Concentration of Electromagnetic Field
Increased plasmon
absorption
Decreased plasmon
absorption
Standing
Wave
Photonic
Crystal
Electromagnetic standing wave produced by
incident and diffracted light
Bormann Effect
Dependence of Plasmon Resonance
Extinction on CCA Ordering
408 nm
1.2
Refractive
Index
Matched
Random
Dispersion
Plasmon
Resonance
Extinction, -logI/I0
1.0
0.8
λo/n = λin
For λ at red edge of
bandgap electric
field maximum
occurs in water!
0.6
0.4
In water Layer
0.2
In Ag@SiO2 Layer
0.0
200
300
400
Wavelength, nm
500
600
Ag quantum dot
nav = Φ
SiO2
nAg + (1-Φ) nw
But on red edge of plasmon
resonance nAg < 0, thus, nav < nw!
Ag
Electric Field is Localized
• Increased nonlinear optical responses
• Increased linear optical responses
• Recent Example: Increased Absorbance
of Dyes Towards Longer Wavelengths in
Solar Cells-dramatically increased
efficiencies:Tom Mallouk, Penn State
• Method for increasing refractive index
contrast
Other Examples of Complex
Particles
•
•
•
•
•
CdS@SiO2
CdS cores within SiO2 Spheres
CdS shells around SiO2 cores
Concentric CdS and SiO2 shells
Synthesized during microemulsion
condensation of (EtO)4Si
"Preparation and Properties of Tailored Morphology, Monodisperse Colloidal Silica-Cadmium
Sulfide Nanocomposites",
S.-Y. Chang, L. Liu, and S. A. Asher, J. Am. Chem. Soc. 116, 6739-6744 (1994).
"Creation of Templated Complex Topological Morphologies in Colloidal Silica",
S.-Y. Chang, L. Liu, and S. A. Asher, J. Am. Chem. Soc. 116, 6745-6747 (1994).
Sanford A. Asher, Department of Chemistry
100 nm
TEM Picture of CdS@SiO 2 Compos ite Nanoparticles
Sanford A. Asher, Department of Chemistry
Outline
• CCA and PCCA Photonic Crystal
Fabrication
• Spatial Control of Electromagnetic
Field Maxima Ag@SiO2
• Magnetically Controlled CCA
– Superparamagnetic CCA
– Ferromagnetic CCA
Nothing@PS-Hollow Sphere CCA
Synthesis of Monodisperse Charged Superparagnetic Particles
FeCl2.4H2O
FeCl3.6H2O
NH3.H2O
Strong stirring
Sonicate the
precipitate in 1 M
TMAOH solution
Surface modified
magnetic colloid
Magnetic colloid
St
MMA
NaSS
H2O
Oleic Acid/ SDBS
Sonication
5hr Emulsion
polymerization
Black
precipitate
70 0C
APS
Brown latex
APS: Ammonium Persulfate
MMA: Methyl Methacrylate
NaSS: Sodium Styrene Sulfonate
St:
Styrene
SDS: Sodium Dodecyl Sulfonate
TMAOH: Tetramethylammonium Hydroxide
Magnetic
separation
Iron Oxide
~ 10 nm
Polystyrene-iron oxide composite
~ 135 nm, polydispersity 7.5%
Ferrite content 17 wt%
Magnetic Properties of Superparamagnetic Particles
80
60
40
nanosize iron oxide
PSt-iron oxide composite particles
σ / emu/g
20
0
-50
-40
-30
-20
-10
0
10
-20
-40
-60
-80
H / KOe
20
30
40
50
Magnetic Force on a Magnetic Moment
-p
+p
H
dH L
dH L
F = p( H +
) − p( H +
)
dx 2
dx 2
dH
F = pL
dx
dH
F=m
dx
m=pL : magnetic moment
dH
dx
: spatial derivative of magnetic field strength
No magnetic field
In magnetic field
- - - - --
- - - - --
- - - - - - - -- - - --
Repulsive force between a pair of particles,
Fe=πεζ2κae-κh
- - - - - - -- - - --
Magnetic force at different position:
Fm= (dM/dH•H+M) •dH/dL
ε is the dielectric constant, ζ is the zeta potential of a particle,
M is the magnet moment of each particle
κ is the reciprocal double-layer thickness,
a is the radius of the particles, and h is the interparticle distance .
Part 2: Self-assembly of Superparamagnetic Particles
Self-assembly of Superparamagnetic Particles
Effect of External
Magnetic
Field
Lattice
Constant
Effect of external
magnetic
field on
on lattice
constant
240
16
220
200
Relative Diffraction Intensity
FCC 111 plane spacing / nm
14
L ( mm) (Left to right)
2,3,4,5,6,7,8,9,10,11
12
10
8
6
4
2
180
0
350
400
450
500
550
600
wavelength (nm)
L
160
CCD fiber
sample
magnet
140
6
5
4
3
dH/dL / KOe/cm
2
1
Effect of external magnetic field on self-assembly
Effect of external magnetic field on self-assembly
18
16
12
10
8
6
4
L
CCD fiber
sample
magnet
910
Diffraction peak / nm
Relative Intensity (a.u.)
14
L
H
d H/d L primary peak
mm kOe KOe/cm
nm
3
3.57
4.69
850
5
2.75
3.56
866
7
2.13
2.71
871
11 1.29
1.56
888
14 0.91
1.03
899
19 0.54
0.51
904
in absence
911
920 of magnet
900
890
880
870
860
850
2
0
400
0
1
2
3
4
5
dH/dL / KOe/cm
500
600
700
Wavelength / nm
800
900
Comparison of Electrostatic and Magnetic Force
7
Effective surface charge
1.5 μ C/cm
1.4
1.3
1.2
magnetic force
2
5
4
F / 10
-11
dynes
6
3
2
1
2
4
6
8
10
Distance from magnet / mm
Charge renormalization Zeff= Z/4
12
Color Change of CCA in magnetic field
deionization
Red shift
Blue shift
NaCl added
H
More NaCl added
Blue shift
In magnetic field, CCA color changes with ionic strength.
Magnetic field induced assembly in NaCl solution
6
220
Relative intensity
FCC (111) plane spcaing / nm
240
200
180
NaCl Concentration (From left to right)
4.0mM, 2.0mM, 1.0mM, 0.67mM, 0.33 mM,0.16 mM, 0mM
4
2
0
350
400
450
500
550
600
650
700
wavelength (nm)
160
0
1
2
NaCl concentration / mM
3
4
Magnetic field induced assembly in organic polar solvents
50
40
Relative Intensity
FCC (111) plane spacings / nm
220
From left to right
Ethanol, M ethanol, Acetonitrile, Ethylene Glycol, DM SO, water
200
30
20
10
180
0
400
500
600
wavelength (nm )
160
140
20
30
40
50
60
70
dieletric constant of medium
80
Magnetic Response of PCCA
788
before imposing magnet
Time after imposing magnet (mins)
0
15
30
45
60
75
Relative Reflection Intensity
784
1.6
1.2
CCD
0.8
magnet
0.4
740
760
780
800
820
1.8
860
840
Wavelength / nm
780
776
0
30
60
Impose
CCD
1.2
0.9
0.6
0.3
0.0
740
Impose magnet
before removing magnet
time after removing magnet (mins)
0
15
30
45
60
1.5
Relative reflection Intensity
Bragg diffraction peak / nm
2.0
760
780
800
820
840
860
Wavelength /nm
Remove magnet
90
Time / mins
120
150
180
Remove
Synthesis of Ferromagnetic Charged Magnetic Particles
Co2+
Fe2+
CoCl2.4H2O
FeCl3.6H2O
NH3.H2O
Strong stirring
Sonicate the
precipitate in 1 M
TMAOH solution
Surface modified
magnetic colloid
Magnetic colloid
St
MMA
NaSS
H2O
Oleic Acid/ SDBS
Sonication
5hr Emulsion
polymerization
Black
precipitate
70 0C
APS
Brown latex
APS: Ammonium Persulfate
MMA: Methyl Methacrylate
NaSS: Sodium Styrene Sulfonate
St:
Styrene
SDS: Sodium Dodecyl Sulfonate
TMAOH: Tetramethylammonium Hydroxide
Magnetic
separation
Ferromagnetic Composite Particles
~ 123 nm, ~ 14 wt% Cobalt Ferrite
Reduced Magnetization (M/Ms)
Magnetic Behavior of ferromagnetic particles in powder and
dispersion
1.0
0.5
Dispersed in
deionized water
Dried Powder
0.0
-0.5
-1.0
-2000
-1500
-1000
-500
0
H / Oe
500
1000
1500
2000
External magnetic field controlled orientation of single ferromagnetic particles
A
B
Gold nanocrystals
H
H
H1
H2
Magnetic field H2
×
Diffracted Light Intentsity
Response of ferromagnetic PCCA to oscillating magnetic field
CCD
543.5 nm Incident
Light
Diffracted
λ= 2 n d sinθ
light
Relative Diffraction Intensity (a.u.)
12
10
8
6
External magnetic field controlled orientation
of magnetic photonic crystals
H /Oe
90
65
55
33
22
13
0
CCD
CCD
+H
-H
4
H
2
0
500
600
700
Wavelength /nm
800
Incident
Light
2.4
2.0
1.6
0.5
2.1
1.0
Time / sec
1.5
+ H2
Relative Intensity
10 Hz
60 Hz
- H2
1.8
1.5
0
Diffracted
light
×
Relative Intensity /a.u.
1 Hz
4 HZ
2.8
H1
H1
H2
50
100
150 200
Time /ms
250
300
Relative amplitude /a.u.
Magnetic Response Frequency
Dependence of Magnetooptical Fluid
1.0
0.8
0.6
0.4
0.2
-1.0 -0.5 0.0 0.5 1.0
log( f /Hz)
1.5
2.0
Optical Switch Controlled by weak magnetic field
CCD Fiber Optic
N
S
N
S
water
Front View
Top View
Optical Switch Fabricated with Ferromagnetic PCCA
6
-20 Oe
-9 Oe
+9 Oe
+20 Oe
Relative Intensity (a.u.)
5
5
4
686 nm
549 nm
4
3
3
N
S
S
2
N
2
1
1
500
600
700
Wavelength /nm
-120 -90 -60 -30
0
30
H / Oe
60
90 120
Relative Intensity (a.u.)
6
Patterning Surfaces
Using Paramagnetic
Colloids
S. Asher, X. Xu and G. Walker,
Dept. of Chemistry, University of
Pittsburgh and Prof. Gary Friedman,
Dept. of Electrical Engineering,
Drexel University
Position Defined Assembly of Ferromagnetic Particles
20
18
16
350 nm
14
300
250
12
200
10
150
8
100
50
6
0
4
-50
2
0
0
5
10
15
20
μm
Position Defined Assembly of Ferromagnetic Particles
ys0915.018: Height
10
9
8
350
7
300
250
6
200
5
150
4
100
50
3
0
2
-50
1
0
0
2
4
6
8
10
Sanford A. Asher, Department of Chemistry
Outline
• CCA and PCCA Photonic Crystal
Fabrication
• Spatial Control of Electromagnetic
Field Maxima Ag@SiO2
• Magnetically Controlled CCA
– Superparamagnetic CCA
– Ferromagnetic CCA
Nothing@PS-Hollow Sphere CCA
Nothing@Polystyrene Spheres
• Synthesize SiO2 cores
• Using emulsion polymerization synthesize
PS shell
• Etch out SiO2 cores with HF
• Fill Hollow Cores with reagent
• Introduce Reactants in Medium to diffuse
into core and react to fill shell voids
Relative Diffraction Intensity /a.u.
4
3
275 nm Silica
275/379nm Silica@PSt
379 nm Hollow PSt
2
1
0
400
600
800
Wavelength /nm
1000
ferrite
Fabrication of particles with complex morphology. ~ 203 nm MPS modified silica particles A were first coated with a
~43 nm copolymer shell to give core-shell particles B (~289 nm). Particles B were further coated with a ~ 17 nm
silica shell to produce particles C (~ 323 nm). Particles C were further coated with ~ an additional ~42 nm PS shell
to produce composite particles D (~407 nm). When the composite particles D react with HF, polymeric particles E
with concentric shells were produced. When the polymer component in the composite particles D is removed by
calcination silica particles F occur
Magnetic composite particles (25 wt%) self-assemble into CCA.
1st order diffraction 1007nm, 2nd order diffraction at 511 nm
3.5
4
Extinction /au.
3
2.5
2.0
2
1.5
1.0
1
0.5
0
400 600 800 1000 1200
Wavelength /nm
400 500 600 700 800 900
Wavelength /nm
0.0
Relative Intensity /au.
3.0
Conclusions
• Possible to make complex particles
• The photonic crystal structure allows
localization of electromagnetic fields on
colloidal particles
• Important new phenomena
• Future bright for new phenomena and new
devices
Acknowledgements
Asher Research Group Members
$: NIH, NCI, NASA and NSF