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Multifunctional Particles for Multifunctional Particles for Crystalline Colloidal Array Crystalline Colloidal Array
Sophisticated Photonic Crystals Sophisticated Photonic Crystals Optical DevicesOptical Devices
Sanford A. AsherSanford A. AsherDept. of ChemistryDept. of Chemistry
University of PittsburghUniversity of PittsburghPittsburgh, PA 15260Pittsburgh, PA 15260
412412--624624--85708570asher@pitt.eduasher@pitt.edu
Sanford A. Asher, Department of Chemistry
CRYSTALLINE COLLOIDAL SELF-ASSEMBLY:
MOTIF
FOR
CREATING SUBMICRON
PERIODIC SMART MATERIALS
OutlineOutlineCCA and PCCA Photonic Crystal CCA and PCCA Photonic Crystal
FabricationFabricationSpatial Control of Electromagnetic Spatial Control of Electromagnetic
Field Maxima Ag@SiOField Maxima Ag@SiO22
Magnetically Controlled CCAMagnetically Controlled CCA–– SuperparamagneticSuperparamagnetic CCACCA–– FerrFerroomagnetic CCAmagnetic CCA☺☺ Nothing@PSNothing@PS--Hollow Sphere CCAHollow Sphere CCA
Sanford A. Asher, Department of Chemistry
Holtz, Asher et al J. Am. Chem. Soc. 1994, 116, 4497
Crystalline Colloidal Arrays Self-Assemblyfabricated from monodisperse, highly charged colloidal particles
~ 1013 spheres/cm3
spacing dependent only upon particle number density and crystalline structure
-
Dialysis /Ion Exchange Resin
Self-assembly
Crystalline Colloidal Array
FCC--
----
- --
+
-
--
---
- --
+
--
---- -- -
--
--- ---
--
--- -
-
--
---
- --
-
--
---
- --
--
---- --
++
--
-
--
--
-
---
-----
--
---
- --
--
---
- --
--
---
- --
--
---
- --
--
-
-
-
--
++
+
++ + +
+
+
+
+
++ +
+
+
+
++
+
+
+
++
+
+
++
+
+
+
+
+
+
+ +
++
+
++
+
++
+ +
--
---- --
+
++
+
--
---- --
+ +
+
++
+
+
+
+
+
+
+
+ +
++
+
+
+
++ +
+
+
+
- ---
--
--
--
---- --+
+
--
--- --+
+
--
---- --+
+
+
+--
--- --+
---
-- -- ++
+
+
+
+
+
+
+
+
++
+
+-
-
--
-+
+
+
+
+
+
-
---
----
-+
+-
- -
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.
Polystyrene Colloid Synthesis:EMULSION POLYMERIZATION
TEM of polystyrene spheres
Reese, Asher et al J. Colloid Interface Sci. 2000, 232, 76
Temperature ControllerN2
N2
H2O
-
Long polymer chain
Surfactant
Water
-
--
++
+
R•
R•
What Drives CCA Self-Assembly?
Medium Dielectric Constant
re
aeeZrU
ra κκ
κε
−
⎥⎦
⎤⎢⎣
⎡+
=222
1)(
Interaction Potential Energy
Sphere Radius
Ionic Impurities
( )ipB
nZnTk
e+=
επκ
22 4
Particle concentration
2ar
U
r
H+ SO3-
-O3SH+
+H H+
H+
-O3S-O3S
-O3S SO3-SO3
-
SO3-
+H
+H
+H
Shear boundary
Negatively charged particle
Debye layer thickness
nmwaterpurein 700~)(1κ
Sanford A. Asher, Department of Chemistry
mλ = 2nd sin θm = order of diffraction
λ = diffracted wavelengthn = refractive index of system
d = spacing between diffracting planesθ = Bragg glancing angle
Crystalline Colloidal Array
--
---- --
--
---
- --
--
---- --
--
---
- --
--
---
- --
--
---- --
--
---- --
--
---
- ----
---
- --
--
---- --
--
---- --
--
---
- ----
---
- --
--
---
- ----
---- --
--
---
- --
--
---
- --
--
---- --
--
---- --
--
---
- --
--
---- --
--
---- --
--
---- --
--
---- --
--
---
- -- --
---- --
--
---
- --
--
---- --
--
---- --
--
---
- --
+
+
++
+
++
+
+++
+
++
++
++
++
+
+
+
+
++
+
+
+
+
+
++
+
+
+
+
+
+
+
+ + ++
++
+ +
+
++
+
+ +
d θλ
Bragg Diffraction
Diff
ract
ed In
tens
ity, I
D
500 600 700 800Wavelength / nm
d ~ 200 nm
+
- - - - --------- -- - -
-
-
---
--
- - - - ------------ -
-
-
---
--+ + +
λ0
- - - - -------------
-
-
---
--- - - - ---
--------- -
-
-
---
--
- - - - ------------ -
-
-
---
--- - - - ---
--------- -
-
-
---
--
- - - - -------------
-
-
---
--
- - - - ------------ -
-
-
---
--
- - - - -------------
-
-
---
--
- - - - -------------
-
-
---
--
- - - - ------------ -
-
-
---
--- - - - ---
--------- -
-
-
---
--
- - - - -------------
-
-
---
--
- - - - ------------ -
-
-
---
--
+
+
++
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
dθB
mλo = 2ndsin θ
(111) FCC CCA
λ0 = wavelength of diffracted light n = refractive index of systemd = interplanar spacing in crystalθB = Bragg glancing angle
All Light Diffracted-Finite Widths-Top Hat Profiles
Bandgap, Δλ↔Δθ
Diffraction Phenomena of Photonic Crystals
* Kinematic Diffractionx-rays: Atomic & Molecular Latticewimpy scatteringlittle attenuationeach layer contributes similarly
* Dynamical Diffractionstrong scatteringmust consider coupledincident and diffracted wave
* Theoretical Foundation Based on Work in1930-1940
W.H. Zachariasen, The Theory of X-ray Diffractionin 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
0 200 400 600 800 1000
0
2
4
6
8
10
-Log
T91 nm PS CCA
100 μm = 400 layers
Number of fcc (111) layers
Britney Spears Britney Spears Photonic Crystal Site
It is a little known fact, that Ms Spears is an expert in semiconductor physics. Not content with just singing and acting, she will guide you in the fundamentals of the vital laser components that have made it possible to hear her super music in a digital format.
BandgapBandgap causes standing wave where at the causes standing wave where at the edges the electric field maxima occur within edges the electric field maxima occur within
the high and low refractive index layersthe high and low refractive index layers
Low refractive index layers
High refractive index layers
Incident
Diffracted
Opportunity to spacially tune electric field maximum to
region of high optical
nonlinearities!
100 nm
The monodisperse SiO2 spheres show a homogeneous incorporation of Ag quantum dot inclusions. dsphere=78+5.4 nm, dAg=3-8 nm.
. “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).
(EtO)4Si
+ H2O +
AgNO3
hν
SiO2
Ag QD
Ag@SiO2
A
B
C
Can Easily Vary Loading and Sizes
300 400 500 600 7000.0
0.5
1.0
1.5
2.0
(b)
(c)
(d)43
8 nm
(e)
(a)
Ext
inct
ion,
-log
(I/I 0)
Wavelength, nm
Figure 11
random dispersion in water
Refractive index matched
Ag QD Plasmon Resonance in Random Dispersion of Ag@SiO2
mλ=2ndsinθ
200 300 400 500 600 7000.0
0.5
1.0
1.5
2.0
2.5
3.0
307
nm28
8 nm
266
nm253
nm23
5 nm
220
nm21
0 nm
605
nm
565
nm
521
nm49
0 nm
457
nm
425
nm40
3 nm
Ext
inct
ion,
-log
I/I 0
Wavelength/nm
fcc CCA
Ag@SiO2 CCA Diffraction as a Function of Lattice Spacing
Plasmon Resonance
200 300 400 500 600 700 8000.00
0.25
0.50
0.75
1.00
1.25
1.50
392
nm
565
nm
490
nm
425
nm
Ext
inct
ion,
-log
I/I0
Wavelength/nm
Refractive Index Matched Random Dispersion PlasmonResonance
Dependence of Plasmon Resonance Extinction on Bragg Condition
Increased plasmonabsorption
Decreased plasmonabsorption
Electromagnetic standing wave produced by incident and diffracted light
Spatial Concentration of Electromagnetic Field
Photonic Crystal
StandingWave
Bormann Effect
200 300 400 500 6000.0
0.2
0.4
0.6
0.8
1.0
1.2
408
nm
Ext
inct
ion,
-log
I/I0
Wavelength, nm
Dependence of Plasmon Resonance Extinction on CCA Ordering
Refractive Index Matched Random Dispersion PlasmonResonance
λo/n = λinFor λ at red edge of bandgap electric field maximum occurs in water!
In water Layer
In Ag@SiO2 Layer
SiO2
Ag quantum dot
nav = ΦAg nAg + (1-Φ) nwBut on red edge of plasmonresonance nAg < 0, thus, nav < nw!
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).
100 nm
TEM Picture of CdS@SiO2 Composite 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
Sanford A. Asher, Department of Chemistry
Nothing@PSNothing@PS--Hollow Sphere CCAHollow Sphere CCA
FeCl2.4H2OFeCl3.6H2O
NH3.H2OStrong stirring Black
precipitateSonicate the precipitate in 1 M TMAOH solution
Magnetic colloid
Oleic Acid/ SDBS Sonication
Surface modified magnetic colloid
StMMA NaSSH2O
70 0CAPS5hr Emulsion
polymerization
Brown latexMagnetic separation
APS: Ammonium PersulfateMMA: Methyl MethacrylateNaSS: Sodium Styrene Sulfonate St: StyreneSDS: Sodium Dodecyl SulfonateTMAOH: Tetramethylammonium Hydroxide
Synthesis of Monodisperse Charged Superparagnetic Particles
Iron Oxide Polystyrene-iron oxide composite
~ 10 nm ~ 135 nm, polydispersity 7.5%Ferrite content 17 wt%
-50 -40 -30 -20 -10 0 10 20 30 40 50
-80
-60
-40
-20
0
20
40
60
80σ
/ em
u/g
H / KOe
nanosize iron oxidePSt-iron oxide composite particles
Magnetic Properties of Superparamagnetic Particles
Magnetic Force on a Magnetic Moment
F p H dHdx
L p H dHdx
L
F pL dHdx
F m dHdx
= + − +
=
=
( ) ( )2 2
m=pL : magnetic moment
dHdx : spatial derivative of magnetic field strength
p+p- H
---
---
----
---
-
Magnetic force at different position:Fm= (dM/dH•H+M) •dH/dL
M is the magnet moment of each particle
Repulsive force between a pair of particles, Fe=πεζ2κae-κh
ε is the dielectric constant, ζ is the zeta potential of a particle, κ is the reciprocal double-layer thickness, a is the radius of the particles, and h is the interparticle distance .
In magnetic fieldNo magnetic field
---
---
-
---
---
----
---
-
---
---
-
Part 2: Self-assembly of Superparamagnetic Particles
6 5 4 3 2 1140
160
180
200
220
240FC
C 1
11 p
lane
spa
cing
/ nm
dH/dL / KOe/cm
350 400 450 500 550 6000
2
4
6
8
10
12
14
16
L ( mm) (Left to right)2,3,4,5,6,7,8,9,10,11
Rel
ativ
e D
iffra
ctio
n In
tens
ity
wavelength (nm)
L
magnet
sampleCCD fiber
Effect of external magnetic field on lattice constantSelf-assembly of Superparamagnetic Particles
Effect of External Magnetic Field on Lattice Constant
400 500 600 700 800 9000
2
4
6
8
10
12
14
16
18 L H dH/dL 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 of magnet 911
Rel
ativ
e In
tens
ity (a
.u.)
Wavelength / nm
0 1 2 3 4 5
850
860
870
880
890
900
910
920
Diff
ract
ion
peak
/ nm
dH/dL / KOe/cm
L
magnet
sample
CCD fiber
Effect of external magnetic field on self-assemblyEffect of external magnetic field on self-assembly
2 4 6 8 10 121
2
3
4
5
6
7
Effective surface charge
1.5 C/cm2
1.4 1.3 1.2 magnetic force
F /
10-1
1 dyn
es
Distance from magnet / mm
Comparison of Electrostatic and Magnetic Force
Charge renormalization Zeff= Z/4
μ
deionization
NaCl added
More NaCl added
Red shift
Blue shift
Blue shift
Color Change of CCA in magnetic field
H
In magnetic field, CCA color changes with ionic strength.
Magnetic field induced assembly in NaCl solution
0 1 2 3 4
160
180
200
220
240
FCC
(111
) pla
ne s
pcai
ng /
nm
NaCl concentration / mM
350 400 450 500 550 600 650 7000
2
4
6
NaCl Concentration (From left to right)4.0mM, 2.0mM, 1.0mM, 0.67mM, 0.33 mM,0.16 mM, 0mM
Rel
ativ
e in
tens
ity
wavelength (nm)
Magnetic field induced assembly in organic polar solvents
20 30 40 50 60 70 80
140
160
180
200
220
FCC
(111
) pla
ne s
paci
ngs
/ nm
dieletric constant of medium
400 500 6000
10
20
30
40
50From left to rightEthanol, Methanol, Acetonitrile, Ethylene Glycol, DMSO, water
Rel
ativ
e In
tens
ity
wavelength (nm)
Magnetic Response of PCCA
0 30 60 90 120 150 180776
780
784
788
Remove magnetImpose magnet
Bra
gg d
iffra
ctio
n pe
ak /
nm
Time / mins
740 760 780 800 820 840 8600.0
0.3
0.6
0.9
1.2
1.5
1.8 before removing magnet
time after removing magnet (mins) 0 15 30 45 60
Rel
ativ
e re
flect
ion
Inte
nsity
Wavelength /nm
740 760 780 800 820 840 860
0.4
0.8
1.2
1.6
2.0 before imposing magnet
Time after imposing magnet (mins) 0 15 30 45 60 75
Rel
ativ
e R
efle
ctio
n In
tens
ity
Wavelength / nm
CCD
magnet
CCD
RemoveImpose
CoCl2.4H2OFeCl3.6H2O
NH3.H2OStrong stirring Black
precipitateSonicate the precipitate in 1 M TMAOH solution
Magnetic colloid
Oleic Acid/ SDBS Sonication
Surface modified magnetic colloid
StMMA NaSSH2O
70 0CAPS5hr Emulsion
polymerization
Brown latexMagnetic separation
APS: Ammonium PersulfateMMA: Methyl MethacrylateNaSS: Sodium Styrene Sulfonate St: StyreneSDS: Sodium Dodecyl SulfonateTMAOH: Tetramethylammonium Hydroxide
Synthesis of Ferromagnetic Charged Magnetic Particles
Co2
+Fe
2+
Ferromagnetic Composite Particles
~ 123 nm, ~ 14 wt% Cobalt Ferrite
-2000 -1500 -1000 -500 0 500 1000 1500 2000-1.0
-0.5
0.0
0.5
1.0
Dispersed in deionized water
Dried Powder
Red
uced
Mag
netiz
atio
n (M
/Ms)
H / Oe
Magnetic Behavior of ferromagnetic particles in powder and dispersion
H H
A B
Gold nanocrystals
External magnetic field controlled orientation of single ferromagnetic particles
Mag
netic
fiel
d H
2
H1
Incident Light
Diffractedlight
CCD
H2
H1
Incident Light
CCD
×
Diff
ract
ed L
ight
Inte
ntsi
ty
Response of ferromagnetic PCCA to oscillating magnetic field
λ= 2 n d sinθ
543.5 nm
CCD
H
CCD
+ H
- H
500 600 700 8000
2
4
6
8
10
12H /Oe
90 65553322130
Rel
ativ
e D
iffra
ctio
n In
tens
ity (a
.u.)
Wavelength /nm
External magnetic field controlled orientation of magnetic photonic crystals
H1
+ H2
- H2H1
H2
Incident Light
Diffractedlight×
0.5 1.0 1.5
1.6
2.0
2.4
2.8 1 Hz 4 HZ
Rel
ativ
e In
tens
ity /a
.u.
Time / sec
0 50 100 150 200 250 3001.5
1.8
2.1 10 Hz 60 Hz
Rel
ativ
e In
tens
ity
Time /ms
-1.0 -0.5 0.0 0.5 1.0 1.5 2.00.2
0.4
0.6
0.8
1.0
Rel
ativ
e am
plitu
de /a
.u.
log( f /Hz)
Magnetic Response Frequency Dependence of Magnetooptical Fluid
SN
Front View
SN
CCD Fiber Optic
Top View
Optical Switch Controlled by weak magnetic field
water
S NN S
500 600 700
1
2
3
4
5
6
Rel
ativ
e In
tens
ity (a
.u.)
-20 Oe -9 Oe +9 Oe +20 Oe
Rel
ativ
e In
tens
ity (a
.u.)
Wavelength /nm-120 -90 -60 -30 0 30 60 90 120
1
2
3
4
5
6
686 nm 549 nm
H / Oe
Optical Switch Fabricated with Ferromagnetic PCCA
Patterning SurfacesUsing 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
0 5 10 15 200
2
4
6
8
10
12
14
16
18
20
-50
0
50
100
150
200
250
300
350
μm
nm
Position Defined Assembly of Ferromagnetic Particles
ys0915.018: Height
0 2 4 6 8 100
1
2
3
4
5
6
7
8
9
10
-50
0
50
100
150
200
250
300
350
Position Defined Assembly of Ferromagnetic Particles
Outline
• CCA and PCCA Photonic Crystal Fabrication
• Spatial Control of Electromagnetic Field Maxima Ag@SiO2
• Magnetically Controlled CCA– Superparamagnetic CCA– Ferromagnetic CCA
Sanford A. Asher, Department of Chemistry
Nothing@PSNothing@PS--Hollow Sphere CCAHollow 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
400 600 800 10000
1
2
3
4 275 nm Silica 275/379nm Silica@PSt 379 nm Hollow PSt
Rel
ativ
e D
iffra
ctio
n In
tens
ity /a
.u.
Wavelength /nm
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
400 600 800 1000 12000
1
2
3
4E
xtin
ctio
n /a
u.
Wavelength /nm400 500 600 700 800 900
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Rel
ativ
e In
tens
ity /
au.
Wavelength /nm
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
AcknowledgementsAcknowledgements
Asher Research Group Members
$: NIH, NCI, NASA and NSF
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