electrostatic self assembled films for photonics ph d defense

Second-Order Nonlinear Optical Characteristicsof

Nanoscale Self-Assembled Multilayer Films

J. R. HeflinR. M. DavisH. W. GibsonG. IndebetouwH. Marand

Ph. D. Thesis Defense

by

Patrick J. Neyman

June 16, 2004© Patrick Neyman: patrickneyman.com

Preface

• This presentation is a combination of my Ph. D. defense presentation and supplemental slides for further clarification

• The supplemental slides are those which I developed for conference presentations

Thank you for watching-Patrick Neyman

© Patrick Neyman: patrickneyman.com

Nonlinear Optics (NLO) Introduction Device Applications using NLO Molecules Measurment Techniques Molecules for NLO Applications ISAM Film Properties Thick ISAM Films Absorption of Second Harmonic Hybrid Covalent / Ionic Fabrication Method Thermal Stability Temporal Stability Electro-Optic Coefficient Measurement

Outline


Linear (classical) Optics• Optical electric field induces polarization of the molecules

• Induced polarization is linearly proportional to the electric field

moleculardipole moment:

macroscopicpolarization field:

• The index of refraction of a material is given by:

n 1 4

• At high intensities, the linear relationship between & no longer holds


Nonlinear Optics (NLO)• The polarization may be expanded in a Taylor series:

• For an anisotropic medium, the polarization field is given by:

and the dipole moment is given by:

N

S

O

OHN

O O-

Na+

OH

n

N


Second-Order NLO Applications

• When both an optical and a dc field are applied along one axis:

P(2)(t) = {Ecos(t) + E0}2

= {½E2 cos(2t) + 2EE0 cos(t) + ½E

2 + E02}

• Three different modes of oscillation:

½E2 cos(2t) Second Harmonic Generation (SHG)

2EE0 cos(t) Electro-Optic Effect (n)

½E2 + E0

2 Optical Rectification

Consider applied optical and DC fields with amplitudes E and E0


Noncentrosymmetry Required for Second-Order NLO Response

• The second-order polarization field strength is given by:

• If the medium is centrosymmetric, it must possess inversion symmetry, which means the following relationship must hold:

which suggests that

• These relations can hold only when (2) = 0



Outline


Second-Order NLO Applications

(1) (2)0

2 (2)0 0

4

1 4 8

8

D E P

E E E

n E E E

• For polarization at frequency (1) (2)02P E E E

the displacement field is

2 (2) (2)0 0 0 00

48 on E n E n En

• Refractive index is dependent upon the applied electric field strength


Application Requirements• Sufficient asymmetry and conjugation along z-axis

– measured as r33 or

• Target film thickness = 1 m

• Thermal stability

• Temporal stability

(2)zzz



Outline


Experimental Apparatus


Beam Propagation in Sample


Longitudinal Intensity Profile of Fundamental Beam

• SHG intensity scan of the beam along the z-axis at focus• Beam travels ~ 1.7 mm within the sample• The “focus length” is ~ 3.7 mm.

0

50

100

150

200

250

300

350

-5000 -4000 -3000 -2000 -1000 0 1000 2000 3000 4000 5000

Z-position (microns)

SH

G In

ten

sit

y (

a. u

.)


Spatial Intensity Profile of Fundamental Beam

• Intensity scan in the x-y plane at the focus of a f = 450 mm

• The beam waist radius is approximately 50 m.

Signal

020

4060

80100

120140 0

2040

6080

100120

140

0

50

100

150

200

250

300

350

HorizontalVertical

p-pol'n relative to samples, 25 um pinhole

Vertical, y (m) Horizontal, x (m)

x84-plane at peak of Beam Profile of p-polarized 1064nm fundamentalRank 1 Eqn 8001 [UDF 1] y=Gauss Int(a,b,c)

r2=0.97271377 DF Adj r2=0.97015569 FitStdErr=19.717266 Fstat=588.20068

a=320.02648 b=65.984203

c=44.377731

0 50 100 150Y Position (micron)

0

50

100

150

200

250

300

350F

unda

men

tal I

nten

sity

= waste radius (m)

y68-plane at peak of Beam Profile of p-polarized 1064nm fundamentalRank 1 Eqn 8001 [UDF 1] y=Gauss Int(a,b,c)

r2=0.97376778 DF Adj r2=0.97130851 FitStdErr=18.921379 Fstat=612.49748

a=317.41407 b=83.817783

c=53.477767

0 50 100 150X Position (micron)

0

50

100

150

200

250

300

350F

unda

men

tal I

nten

sity

= waste radius (m)


• Maker fringe equation:

• For films with l<<lc:

• For a reference film compared to quartz:

• For a film compared to the reference:

Quartz Measurement

(2) 2 2 22 ( ) sin

2c effc

lI l I

l

(2) 22 ( )

2 effI l

(2), , 2 ,

(2), 2 ,

2eff std c quartz std

eff quartz std quartz

l I

l I

(2), 2 ,

(2), 2 ,

eff ISAM ref ISAM

eff ref ISAM ref

l I

l I


Interference Fringe Pattern

0

100

200

300

400

500

600

700

800

900

0 10 20 30 40 50 60 70 80 90

Angle (degrees)

SH

G In

ten

sity

(a.

u.)

• Signal increases with increased incident angle below 60 due to

– decreased reflective loss of the p-polarized light

– increased path length

– increased coupling with the (2) tensor

(2) 2 2 22 ( ) sin

2c effc

lI l I

l

2cll k

122

2

cos

sin1

glass

glassglass

tl

tn

lc =

21 m,

typical for glass


2 22

2

1cot csc 3cot

2

p p

s p

Iarc

I

(2)2

(2)2cotzzz

zxx

(2)2 22

(2)2

csc 3cotp p

zzzs p

zxx

I

I

Tilt Angle Measurements

0

100

200

300

400

500

600

700

-100 -80

-60

-40

-20 0 20 40 60 80 100

Polarizer Angle

I(2

)



Outline


Organic Chromophores

154DEA-TCVAB

133DMA-DCVS

52DMA-NS

47Disperse Red 1

37NB-DMAA

12DMNA

0 (10-30 cm5/esu)StructureChromophore

N

H3C

H3C

NO2

N

H3C

H3C

CN

NC

H

N

H3CH2C

H3CH2C

N

N

CN

NC

H

N

H3C

H3C NO2

N

H3CH2C

H3CH2C

N

NO2N

N

H3C

H3C

N

NO2

• long conjugation length

• strong electron donors and acceptors

• diametric positioning of donors and acceptors

To have large molecular second order NLO responses (), organic molecules need:

N is number density

F is local field factor

is tilt angle away from polar axis

(2) 3cosNF

where:


Chromophores for NLOPoly S-119

NHON

S OOO-

SO

OHN

Na+

N

SO

OHN

O O-Na+

OH

N

Procion Red MX-5B

N

N

SO

O

O

O

O OS

OHN

N N

NH

Cl

Cl

Na

Na

Procion Brown MX-GRN

NN

N N

N Cl

Cl

HNHO3S

H3C

CH3

HO3S

SO3HHN

n n

PCBS

Poly S-119

Procion Red

PCBS

Procion Brown

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

Ab

sorb

ance

(P

roci

on

Red

&

P

roci

on

Bro

wn

)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Ab

sorb

ance

(P

oly

S-1

19

&

P

CB

S)

300 400 500 600 700 800 900 1000 1100

Wavelength (nm)

• Note that some chromophores absorb the second-harmonic (532 nm)

• This can be a significant effect in thick films© Patrick Neyman: patrickneyman.com

Polymers for ISAM Films

• NLO active polyanions: PCBS, Poly S-119• NLO inactive polycation: PAH


Polymers for ISAM Films

PAHPoly S-119

• Nine repeat units of Poly S-119, nineteen of PAH

• Modeled in vacuo using ChemDraw 3D



Outline


ISAM Films

• C∞ symmetry

• Formation time < 45 sec• Layer thickness ~ 1-10 nm

• Homogeneous• Physically robust

• Temporal stability: 6+ yr• Thermal stability: >150 C


ISAM Film Formation

• Immersion in oppositely charged aqueous solutions• May repeat indefinitely• Structural control at molecular level

G. Decher et al.

Makromol. Chem., Makromol. Symp. 46, 321 (1991);

Thin Solid Films 210/211, 831 (1992).


• Interfaces are “fuzzy” rather than discrete resulting in a periodically varying density of each material

• Interpenetration may occur over several monolayers

ISAM Film Formation


Second Harmonic Intensity (I2) Scales

Quadratically Fundamental Intensity (I)120

100

80

60

40

20

0

I

(arb

. uni

ts)

10008006004002000

I(arb. units)

• (ISAM) (quartz)

J. R. Heflin et al.

SPIE Proc. 3147, 10 (1997);

App. Phys. Lett. 74, 495 (1999).


• In general: , for l << lc , as here:

• Chromophore orientation same for all layers

Quadratic Growth of SHG with Film Thickness

8

6

4

2

0

(I

)1/2

(arb

. uni

ts)

120100806040200

Number of Bilayers

J. R. Heflin et al.

SPIE Proc. 3147, 10 (1997);

App. Phys. Lett. 74, 495 (1999).

(2) 22 ( )

2 effI l (2) 2 2

2 ( ) sin2c eff

c

lI l

l


• Regions of potential about an ionic endgroup with radius a, from the Debye-Hückel approximation, may be written as

where the Debye length --1 is the distance at which is reduced by 1/e, and is given by

Effect of Solution Counter Ion Concentration


Thickness Controlled by Solution Parameters

• Constant deposition per bilayer• Thickness controlled by pH or NaCl (~1 – 10 nm)


Consistency Along Surface

0.05.0

10.015.0

20.025.0

30.035.0

30.035.0

40.045.0

50.055.0

60.0

0

100

200

300

400

500

Incident Angle

PCBS / PAH Reference Standard, Consistency Scan

SHG (a. u.)

x-position (mm)

• Interference fringe data taken for 35 mm along the length of the film, at 0.5 mm intervals

• For timeliness, each datum was averaged over 10 counts, which is reflected in the roughness of the “surface”

• The signal remains constant along the length of the slide

-4

-2

0

2

4

0.0

5.0

10.0

15.0

20.0

25.0

0

1000

2000

3000

4000

3046ee DS FS SHG Maxima Map

SHG peak at ~51degrees

Horizontal, x (mm)

Vertical, y (mm)F ro n t (fro sted ) s id e

Y

X

Z

0 2 424 m m--y =

Targ e tS a feL im its

O b v io u sE v ap o ra tio nR eg io n

2 -4 m m

2 -4 m m

1 5 -2 5 m m

F ro stedR eg io n

• New technique using Mathematica 4.0 for analysis of several fringe data files to produce map of surface

• Complete surface map may be obtained in minutes rather than hours

• Prior to multi-axis stage control, mapping would take several weeks

• (different sample than that in example of previous technique)© Patrick Neyman: patrickneyman.com

Variation of Inactive Polycation pH

• Quadratic growth of SHG with film thickness• Increased cation pH increases anion layer thickness• Increased cation pH increases SHG

05

101520253035404550

0 10 20 30 40

Number of Bilayers

Sq

uar

e R

oo

t o

f S

HG

(a.

u.)

PCBS / PAH, pH = 7 / 10

PCBS / PAH, pH = 7 / 7


Variation of Inactive Polycation pH

• Increased pH dramatically increases bilayer thickness

• (2) decreases due to increased thickness, despite:– Increased SHG

– Decreased tilt angle

PAH pH

Tilt Angle

Bilayer Thickness

(nm)

(2) (10-9 esu)

10 37 9.2 0.33

7 65 0.21 3.1 0

500

1000

1500

2000

2500

3000

3500

4000

Polarization Angle

SH

G (

a.u

.)

PCBS / PAH; pH = 7 / 10; 20 bl

0

100

200

300

400

500

600

700

800

Polarization Angle

SH

G (

a.u

.)

PCBS / PAH; pH = 7 / 7; 20 bl


Impact of Choice of Polycation

• PCBS with Poly(L-Lysine) or PDDA in place of PAH• Chromophore deposition per bilayer constant for each film

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 10 20 30 40

Number of Bilayers

Ab

sorb

ance

at

362

nm

PCBS / PDDA, pH = 7 / 7PCBS / PDDA, pH = 7 / 10PCBS / PLL, pH = 7 / 7

0

1

2

3

4

5

6

7

8

0 10 20 30 40

Number of BilayersS

qu

are

Ro

ot

of

SH

G (

a.u

.)

PCBS / PDDA, pH = 7 / 7PCBS / PDDA, pH = 7 / 10 PCBS / PLL, pH = 7 / 7

• Some cations fail to exhibit bulk SHG


Thermal Stability

Heat to Hold for 150 °C 18 hours

Cool toroomtemp


Thermal Stability


• Chromophore degradation accounts for loss in SHG after heating well beyond Tg

0.0

0.2

0.4

0.6

0.8

1.0

300

500

700

900

1100

Wavelength (nm)

Abs

orba

nce

(a.u

.)

Final Initial

Thermal Stability


SHG Recovery Independent of Humidity

• Identical samples heated to 150 degrees to draw out moisture• No difference in second harmonic intensity between cooling in

nitrogen environment or cooling in air

0 5 10 15 20 25

0

50

100

150

0.0

0.2

0.4

0.6

0.8

1.0

2

Squ

are

Roo

t of

SH

G

Tem

pera

ture

(de

gree

s C

)

Elapsed Time, Cooling Cycle (hours)

SR(SHG), air cooled SR(SHG), N2 cooled Temp., air cooled Temp., N2 cooled


Interface Effects

• The susceptibilities asymptotically approach a true value for the film

• Surface SHG and the lack of interpenetration for the first few layers causes the susceptibility to be artificially inflated

• The artificial inflation becomes negligible as film thickness is increased

0

1

2

3

4

5

6

0 10 20 30 40 50

# Bilayers

chi(

2), p

H 1

0 (n

ano

esu

)

0

10

20

30

40

50

60

70

80

90

chi(

2), p

H 7

(n

ano

esu

)

chi(2) pH 10 chi(2)zzz (65) pH 10

chi(2) pH 7 chi(2)zzz (37) pH 7


• The susceptibilities asymptotically approach a true value for the film

• Surface SHG and the lack of interpenetration for the first few layers causes the susceptibility to be artificially inflated

• The artificial inflation becomes negligible as film thickness is increased

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40

Number of Bilayers

, pH

7 /

10 (

nano

esu

)

0

20

40

60

80

100

120

140

160

180

200

, pH

7 /

7 (n

ano

esu)

PCBS / PAH, pH = 7 / 10

PCBS / PAH, pH = 7 / 7

Interface Effects


Interface Effects

• One NLO bilayer of PCBS / PAH

• Variation of the number of buffer bilayers (PMMA / PAH) between NLO bilayer and substrate

0

5

10

15

20

25

30

35

0 1 2 3 4 5

Number of Buffer Bilayers

SH

G (

a.u

.)


Interface Effects


• 20 buffer layers (PMMA / PAH) between glass and film

• Varying number of buffer bilayers between film and air

0

5

10

15

20

25

30

35

40

45

0 2 4 6 8

Number of Buffer monolayers

SH

G (

a.u

.)


0

5

10

15

20

25

30

35

0 1 2 3 4 5

Number of Buffer Bilayers

SH

G (

a.u

.)

Interface Effects

• 5 buffer bilayers each side of NLO ISAM film versus no buffer layers

• “Artificially inflated” SHG at low number of layers due to effects at film-glass and film-air interfaces

0

5

10

15

20

25

0 2 4 6 8 10

Number of Bilayers

Sq

ua

re R

oo

t o

f S

HG

(a

.u.)

5 buffer bilayers at each interface No buffer layers


• Variation of the number of buffer bilayers (PMMA / PAH) between NLO bilayer and substrate


“Capping” Effect

• Capped: outer layer is NLO inactive material (PAH)

• Drop in SHG due to “capping” effect, where outermost chromophores are pulled away from the preferred direction

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0 5 10 15 20

Number of Bilayers

SH

G (

a.u

.)

SHI (UnCapped) SHI (Capped)



Outline


Thick ISAM Films: 250-bl PCBS

• Absorbance @ 362 nm is effective thickness

• Thickness at 1.30 Absorbance is 580 ± 20 nm• = 1.1×10-10 esu(2) (1064nm)eff

y = 121.61x + 16.692

0

20

40

60

80

100

120

140

160

180

200

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4Absorbance @ 362 nm

Sq

ua

re R

oo

t o

f S

HG

(a

.u.)


SHG Intensity, SHG-Absorbing

a) Non-SHG-absorbing film, lc = 1 m (red, solid line), Film with lc = 1 m and a2 = 5.0 m-1 (blue, dotted line)

b) Non-absorbing approximation (green, long-dashed)

SHG-Absorbing approximation(purple, short-dashed)

0.5 1 1.5 2

0.1

0.2

0.3

0.4

0.5

0.6

0.2 0.4 0.6 0.8 1

0.1

0.2

0.3

0.4

0.5

0.6

(a) (b)

Thickness (m)

Squa

re R

oot o

f I 2

(

a.u.

)

Squa

re R

oot o

f I 2

(

a.u.

)

Thickness (m)

2/ 2 212

2 , 2 2

1 2 1

2

l l

abs

e e k lI

k

22 ,0I l


SHG Absorption

• Non-SHG-absorbing film, lc = 10 m (red, solid line), Film with lc = 10 m and a2 = 0.1 m-1 (blue, dotted line)

• Absorption may hinder prediction of electro-optic response at telecommunication wavelengths

20 40 60 80

10

20

30

40

I 2 (

a. u

.)

Thickness (m)


SHG Conversion Efficiency

• Non-SHG-absorbing film (red, solid line), Film with 1.0 absorbance at the SHG wavelength (blue, dashed line)

• Absorption may hinder prediction of electro-optic response at telecommunication wavelengths

2 4 6 8 10

1

2

3

4

5SHG Conversion Efficiency (%)

kL/2


SHG Conversion Efficiency

0.5 1 1.5 2 2.5 3

50

100

150

200

250

SHG Conversion Efficiency (%)

kL/2

• Non-SHG-absorbing film (red, solid line), Film with 1.0 absorbance at the SHG wavelength (blue, dashed line)

• Thin, mildly-absorbing films may be accurately characterized


Thick ISAM Films: 200-bl Poly S-119

• 1064-nm data follows expected curve for the exhibited SHG absorbance

• Absorbance @ 480 nm is effective thickness (2.5 ~ 750 nm)• Correction obtained via Excel using approximation:

where

0

20

40

60

80

100

120

0 0.5 1 1.5 2 2.5

Absorbance @ 480 nm

Sq

ua

re R

oo

t o

f S

HG

(a

.u.)

Corrected

Original

2

2 22 2 2 2 2 2 22 ,0 2 , 2 , 2 ,2

1010 ln 10

2

AA

abs c abs c c absI I l I l l A I

21 10 2 10A A

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

350 400 450 500 550 600 650Wavelength (nm)

Ab

so

rba

nc

e


Thick ISAM Films: 200-bl Poly S-119

• 1064-nm data follows expected curve for the exhibited SHG absorbance

• 1200-nm data unaffected by SHG absorption

• Absorbance @ 480 nm is effective thickness

• Thickness at 2.53 Absorbance is 745 ± 30 nm

• = 5.8×10-10 esu, = 3.3×10-10 esu (2) (1064nm)eff (2) (1200nm)eff

y = 24.562x + 8.6709

y = 42.678x + 9.0972

0

10

20

30

40

50

60

70

80

90

100

0 0.5 1 1.5 2 2.5Absorbance @ 480 nm

Sq

ua

re R

oo

t o

f S

HG

(a

.u.)

1064 nm

1200 nm

for 1064 fit

Linear (for1064 fit)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

350 400 450 500 550 600 650Wavelength (nm)

Ab

so

rba

nc

e


Shortcoming of Polymer-Polymer Films

• (2) should not vary with film thickness• Not all chromophores contribute to SHG


Summary of Polymer-Polymer Films• Thickness grows linearly with number of bilayers

• Thickness > 750 nm achievable

• SHG grows quadratically with number of bilayers

• Increased counterion concentration results in

– Increased SHG per bilayer

– Increased thickness per bilayer

– Decreased (2)

Increase in thickness outweighs increase in SHG More loopy polymer conformation results in

– Increased chromophore adsorption into “fuzzy” interfaces

– Increased thickness of each monolayer

– Decreased net polar order



Outline


Incorporation of Monomer Chromophores

• Chromophores between layers of PAH• Significant reduction in film thickness• Significant increase in net polar order

Polymer Chromophore Monomer Chromophore


Hybrid Ionic / Covalent Assembly

• Triazine covalently bonds with non-protonated amines

• Covalent bonding occurs above pKa of PAH (~9)

• Ionic bonding of sulfonates with protonated amines below pKa


Resonantly Enhanced (2)

• SHG measured at various wavelengths in absorbing region of Procion Red

• Normalized absorbance spectrum shown as green line• (2) expected to increase with increased absorbance

0.0

0.2

0.4

0.6

0.8

1.0

420 440 460 480 500 520 540 560 580 600 620

Wavelength (nm)

No

rma

lize

d S

qu

are

Ro

ot

SH

G (

a.u

.)


Procion Red pH Variation

• PAH layer thickness increases as pH is increased above pKa

• Interpenetration increases with pH due to electrostatic screening

• Reactivity of PR triazine with PAH amine increases with pH

PR pH

PAH pH

Bilayer Thickness

(nm)

10.5 10 4.3

10.5 7 0.52

7 7 0.55

10.5 4.5 0.34

7 4.5 <0.30.00

0.05

0.10

0.15

0.20

0 10 20 30

Number of Bilayers

Abs

orba

nce

at 5

23 n

m

pH 10.5 / 10

pH 10.5 / 7

pH 7 / 7

pH 10.5 / 4.5

pH 7 / 4.5

PR / PAH

0

10

20

30

40

50

60

70

80

0 10 20 30

Number of Bilayers

Squ

are

Roo

t of S

HG

(a.

u.)

pH 10.5 / 10

pH 10.5 / 7

pH 10.5 / 4.5

PR / PAH

• Growth of SHG with number bilayers indicates bulk (2) effect• PAH pH 10: (2)

zzz 0.510-9 e.s.u.PAH pH 7, 4.5: (2)

zzz 1.110-9 e.s.u. 0.6 (2)zzz (quartz)

• Procion Red has low molecular hyperpolarizability

• Minimal reactivity of PR triazine with PAH amine below pKa

• No bulk polar order observed (only interface effects)

• Increase in absorption with film thickness due to ionic bonding

Angew. Chem. 41 (2002), p3236

PR pH

PAH pH

Bilayer Thickness

(nm)

10.5 10 4.3

10.5 7 0.52

10.5 4.5 0.34

PR pH

PAH pH

Bilayer Thickness

(nm)

7 7 0.55

7 4.5 <0.30

1

2

3

4

5

6

7

8

0 10 20 30

Number of Bilayers

Squ

are

Roo

t of S

HG

(a.u

.)

pH 7 / 7

pH 7 / 4.5


Procion Red Structure

• Procion Red MX-5B



Procion Brown Structure

• Procion Brown MX-GRN



Procion Brown NaCl Variation

• Procion Brown / PAH at pH 10.5 / 7

• Peak absorbance grows linearly with number of bilayers

• Addition of NaCl increases amount of adsorbed chromophores

y = 0.004x - 0.001

y = 0.0029x + 0.0005

y = 0.0022x - 0.0025

y = 0.0014x - 0.0027

y = 0.001x - 0.002

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0 5 10 15 20 25 30

Number of Bilayers

Ab

so

rba

nc

e @

46

0 n

m1.0M NaCl

0.50M NaCl

0.25M NaCl

0.10M NaCl

No NaCl



• SHG grows quadratically with number of bilayers

• Addition of NaCl increases SHG

y = 6.2204x + 0.3155

y = 5.5446x + 2.7696

y = 4.27x + 1.5767

y = 1.9003x + 5.482

y = 1.2042x + 4.5033

0

20

40

60

80

100

120

140

160

180

200

0 5 10 15 20 25 30Number of Bilayers

Sq

ua

re R

oo

t S

HG

(a

.u.)

1.00M NaCl

0.50M NaCl

0.25M NaCl

0.10M NaCl

No NaCl



• Maximum benefit of NaCl in 0.25 - 0.50 M region

0

1

2

3

4

5

6

7

0 0.2 0.4 0.6 0.8 1NaCl (Molar Concentration)

Sq

ua

re R

oo

t S

HG

/ B

ilay

er

(a.u

.)

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

0.0035

0.0040

0.0045

46

0-n

m A

bs

orb

an

ce

/ B

ilay

er

SRSHG / Bilayer

Absorbance / Bilayer



• Tilt angle measured relative to substrate normal (z-direction)

• 0.50 M yields best chromophore orientation

0

5

10

15

20

25

30

35

40

45

50

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

NaCl Molarity (M)

Tilt

An

gle

(d

eg

rees

)



NaCl (M)

peak Abs per bilayer± 0.0003

Bilayerthickness

(nm)±0.05 nm

/ bl(a.u.)± 5%

refractiveindex @532 nm

Tilt Angle± 4º, 1º

(10-9 esu)± 10%

(10-9 esu)± 12%, 10%

0 0.0010 0.26 1.2 1.56 42.8º 17 30

0.10 0.0014 0.38 1.9 1.71 40.8º 19 41

0.25 0.0022 0.74 4.3 1.85 39.1º 22 56

0.50 0.0029 0.95 5.5 1.77 38.3º 22 56

1.00 0.0040 1.32 6.2 1.81 39.2º 18 45

2I

(2)eff (2)

zzz

• 0.50 M NaCl yields best susceptibility and thickness

• No change in chromophore concentration above 0.25 M

• 0.50 M and 0.0 M chosen for comparison studies

0.0000

0.00050.0010

0.00150.0020

0.00250.0030

0.00350.0040

0.0045

0.00 0.25 0.50 0.75 1.00NaCl Concentration (M)

Ab

sorb

an

ce /

nm


Rendition of Adsorption Surface

• Mixture of both covalent bonding possibilities for Procion Brown

• Increased NaCl → Increased contour -- like surface of spaghetti

• Decreased average tilt angle due to physical restriction

• Contraction of network further restricts chromophores© Patrick Neyman: patrickneyman.com


Outline


Thermal Stability: Procion Brown (0.5 M NaCl)

• Heat to 85 °C, hold for 36 hours

• Heat to 150 °C, hold for 24 hours

• SHG reduced with temperature -- no permanent loss of SHG© Patrick Neyman: patrickneyman.com

Thermal Stability: Procion Brown (0.0 M NaCl)

• 0.0 M NaCl Procion Brown stable at 85 °C, not at 150 °C

• Loss in SHG does not correspond with loss in absorbance

• Reorientation of the chromophores away from preferred direction© Patrick Neyman: patrickneyman.com

Thermal Stability: Procion Red

• 0.0 M NaCl Procion Red not stable at 100 °C

• 40% Loss in SHG , 7% loss in absorbance

• Reorientation of the chromophores away from preferred direction© Patrick Neyman: patrickneyman.com

Thermal Stability: Poly S-119

• Poly S-119 stable at 150 °C C. Figura, Ph. D. Thesis, VA Tech (1999)

• Loss in SHG above 150 °C corresponds with loss in absorbance

• Temperature-dependent reduction of SHG below 150 °C investigated by temperature dependence of absorbance

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 1 2 3 4 5 6 7Time (hours)

Ab

so

rba

nc

e @

48

0 n

m

0

50

100

150

200

250

300

350

400

450

Te

mp

era

ture

(C

)

Abs @ 480 nm

Temp (°C)

Squ

are

Roo

t of S

HG

(a

.u.)

Tem

pera

ture

(de

gree

s C

)

0

50

100

150

200

250

0 20 40 60 80 100

0.0

0.2

0.4

0.8

1.0

0.6

Temperature

SHG

Elapsed Time (hours)



• Temperature-dependent loss of absorbance corresponds withtrans-to-cis isomerization Langmuir 15 (1), (1999), p193-201.

• Trans-to-cis isomerization results in reduced conjugation

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

400 420 440 460 480 500 520

Wavelength (nm)

Ab

so

rba

nc

e

24

55

102

153

203

T



• Trans-to-cis isomerization induced by UV exposure in right-hand figure Langmuir 15 (1), (1999), p193-201.

• In both cases: UV absorbance increases visible absorbance decreases

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

400 420 440 460 480 500 520

Wavelength (nm)

Ab

so

rba

nc

e

24

55

102

153

203

T

exposure time



Outline


• Poly S-119 remains stable after >6.5 years

• PCBS remains stable after ~1.5 years

0.00.10.20.30.40.50.60.70.80.91.01.1

1400 1600 1800 2000 2200 2400Time (days)

Sq

ua

re R

oo

t S

HG

(a

.u.)

Poly S-119/PAH Reference Standard, 68 bl

Measured with quartz

0.00.10.20.30.40.50.60.70.80.91.01.1

0 100 200 300 400 500 600Time (days)

Sq

ua

re R

oo

t S

HG

(a

.u.)

PCBS/PAH: pH 7/10, 30 bl

PCBS/PAH: pH 7/7, 30 bl

Temporal Stability: Poly S-119, PCBS


Temporal Stability: Procion Red

• Procion Red films exhibit decrease in polar order

0.00.10.20.30.40.50.60.70.80.91.01.1

0 100 200 300 400 500 600

Time (days)

Sq

ua

re R

oo

t S

HG

(a

.u.)

P-Red/PAH: pH 7/10, 25 blP-Red/PAH: pH 10.5/7, 20 bl


Temporal Stability: Procion Brown

• 0.5 M NaCl remains stable after >420 days

• 0.0 M NaCl exhibits increase in net polar order

0.00.10.20.30.40.50.60.70.80.91.01.11.21.3

0 100 200 300 400 500Time (days)

Sq

ua

re R

oo

t S

HG

(a

.u.)

P-Brown/PAH: pH 10.5/7, 30 bl, 0.5M NaCl

P-Brown/PAH: pH 10.5/7, 30 bl, No NaCl



Outline


Electro-Optic MeasurementsAl electrode

ISAMfilm

ITO Glasssubstrate

Polarizer Analyzer

Babinet-Soleil

V

• Teng and Man electro-optic measurement(Appl. Phys. Lett. 56, 1734 (1990))

• 1 kHz ac voltage between ITO and Al modulates s- and p-polarized refractive indices through r33 and r13, varying phase between s- and p-polarizations

• Modulation of intensity through crossed analyzer detected by lock-in amplifier

• 50-bilayer Procion Brown/PAH films with 0.5 M ionic strength have r33 1/2 that of lithium niobate (30 pm/V)

Film Device r33 – r13 (pm/V) r33 (pm/V) Tilt Angle

0.5 M NaCl(not soaked)

1 8.6 14.341.9º

2 7.0 11.8

0.5 M NaCl(soaked)

1 8.2 14.242.5º

2 8.2 14.2

0.0 M NaCl(not soaked)

1 1.9 3.945.6º

2 2.0 4.3


Conclusions

Thickness: 750 nm film thickness achievedQuadratic scaling of SHG with thickness

Thermal Stability: Procion Brown stable at 150 °C for 24 hoursafter holding at 85 °C for 36 hours

Temporal Stability: No loss in Procion Brown SHG after 420 days

Electro-OpticProperties: r33 of Procion Brown is ½ that of lithium niobate

Significant Milestones Toward Application Requirements


Acknowledgments

J. R. Heflin, Chair

R. M. DavisH. W. GibsonG. IndebetouwH. Marand

Presented to the committee on June 16, 2004

• VPI Chemistry– H. W. Gibson– H. Wang

• VPI Chem-Eng– R. M. Davis– K. E. Van Cott

• VPI Physics– J. R. Heflin– C. Brands– C. Figura

• Luna Innovations– D. Marciu– M. Miller


electrostatic self assembled films for photonics ph d defense

Technology

patrick neyman patrick

sample patrick neyman

monolayers patrick neyman

l150 c patrick neyman

order nlo applications

e cos t

isam quartz

harmonic intensity