Generation and Measurement of Surface Plasmon Coupled Emission

Kathleen Hamilton

Defense of the Masters ThesisUniversity of New Hampshire

June 15th, 2007

•SPCE signals have been measured with novel material sets

•A compact apparatus has been constructed to measure these signals

•Depending on step size, a full 180º scan can be completed in < 5 minutes

•Reproducible scans can be made with resolutions up to 0.5˚

2

Main Results

Outline

•Introduction

•Sample Preparation

•Apparatus Design and Construction

•Results

•Conclusions and Future Work

3

Introduction

•Fluorescence

•Surface Plasmons

•Surface Plasmon Resonance (SPR)

•Surface Plasmon Coupled Emission (SPCE)

4

Fluorescence

S0

S1

hν hν′

• Process of light emission from a molecule

• Repeatable

• Emission wavelength is characteristic of the dye

• Emission is isotropic

green: excitationred: emission

black: non-radiative processes5

Surface Plasmons

•Oscillations of surface electrons in a metal

•Act as a wave propagating along interface

•Decay rapidly into the metal volume

•Can be used to transfer energy through thin films

6

Surface Plasmon Resonance (SPR)

•Absorption of incident energy into surface plasmons

•Prism is rotated, reflectance is measured as a function of 7

Excitation of SPR through a glass prism, incident on a silver film (grey) and dielectric overlayer (pink)

•Describe reflection/transmission of light at dielectric and metal surfaces

•Boundary Conditions:

•Tangential E continuous

•Tangential B continuous

•Wave phases are equal

•Used to identify SPR angle

Fresnel Equations

8

Four phase Fresnel Equations

dm

d1

prism

air

•Affected by

•Thickness of silver films

•Thickness of dielectric overlayer

•Wavelength of incident light

9

m

2

1

0

Calculated SPR curves for Ag films

Films of thickness: 0 nm (blue), 50 nm (black), 20 nm (red), 80 nm (green), 100 nm (lt. blue)

curves calculated using four-phase Fresnel programs from the research group of Robert M. Corn: http://unicorn.ps.uci.edu/calculations/fresnel/fcform.html 1

0

Effect of Dielectric Layer Thickness on SPR Angle

SPR curves with dielectric overlayer thicknesses of: 5 nm (blue), 10 nm (black), 20 nm (red), 50 nm (green), 100 nm (lt. blue)

curves calculated using four-phase Fresnel programs from the research group of Robert M. Corn: http://unicorn.ps.uci.edu/calculations/fresnel/fcform.html 1

1

Effects of Wavelength on SPR angle

Calculated SPR curves for wavelengths: 532 nm (black), 550 nm (blue), 575 nm (red), 600 nm (green), 660 nm (lt. blue)

curves calculated using four-phase Fresnel programs from the research group of Robert M. Corn: http://unicorn.ps.uci.edu/calculations/fresnel/fcform.html 1

2

SPCE•“Inverse” process to SPR

•SPCE uses surface plasmons for emission at wavelength dependent angles

•Fluorescing molecules above a metal will induce plasmons in the metal

•Plasmons will couple to photons via glass interface

13

Methods of Generation

SPCE

θSPCE θSPCE

θE

Left: Reverse Kretschmann configuration (RK)Right: Kretschmann configuration (KR)

14

SPCE generation with the RK configuration

•Incident light excites fluorescence

•Fluorescing molecules induce plasmons on metal surface

•Plasmons are coupled to photons at glass interface

•Resulting light is emitted at angles determined by plasmon wavenumber 1

5

Outline

•Introduction

•Sample Preparation

•Apparatus Design and Construction

•Results

•Conclusions and Future Work

16

Sample Preparation

Aga

b

glass

dye

a: adhesion layer b: passivation layer

•Two Components

•Thin films deposited by sputtering

•Thin fluorescent dye deposited by spin coating

17

Sputter Deposition• Physical vapor deposition• Deposition under vacuum reduced impurities in films• Rotation of substrate creates films of uniform thickness• Reactive gas sputtering creates material for passivation layer1

8

Thin Film StacksMaterial Material

SetSetAdhesion Adhesion

LayerLayer ThicknessThickness Ag Ag ThicknessThickness

PassivatioPassivation Layern Layer ThicknessThickness

AlSi/Ag/AlSi-N

AlSi 2 nm 34.1 nmAlSi-N

(15% N2)10 nm

AlSI/Ag/AlSi-N

AlSi 2 nm 50 nmAlSi-N

(15% N2)10 nm

Si/Ag/Si-O(x)

Si 1 nm 50 nmSi-O(x) (5% O2)

10 nm

Si/Ag/Si-O(x)

Si 1 nm 50 nmSi-O(x) (5% O2)

20 nm

Si/Ag/Si-O(x)

Si 1 nm 50 nmSi-O(x)

(10% O2)20 nm

19

Spin Coating

•Small volume of dye deposited on substrate

•Rotated at high speeds (2200-3000 rpm)

•Result is thin, uniform coating

20

Outline

•Introduction

•Sample Preparation

•Apparatus Design and Construction

•Results

•Conclusions and Future Work

21

Apparatus Design and Construction

•Three Mechanical Components

•Excitation

•Rotation

•Detection

•Computer Interface and Control

22

•Excitation with 5 mW laser ( = 532 nm)

•Driven by 2.85 V (DC)

•Beam divergence < 0.069º

23

• Rotational motion is driven by a stepper motor

• Step resolution: 0.0281º

• Accuracy: <1º

• Repeatability: < 0.1º

24

Fluorescence detection made by a photomultiplier

Wavelength filter

200 m aperture

PMT

amplifier

Amplifier is needed to convert PMT output from current to voltage

25

•Data acquisition module (DAQ) converts analog PMT signal to digital

•DAQ signal is read by LabVIEW program

•DAQ also controls voltage applied to the PMT

Computer Control

26

•Four part LabVIEW program

•PMT Voltage Specified

•Motor sent to home position

•Step size and number of steps specified

•Motor advances and DAQ signal is read on alternate iterations

•Angle and DAQ signal are written to file

27

Data from LabVIEW is imported to Matlab, plotted and fitted with Gaussian curves

28

Theta (deg.)

Outline

•Introduction

•Sample Preparation

•Apparatus Design and Construction

•Results

•Conclusions and Future Work

29

•SPCE has been qualitatively observed from different material sets

•SPCE has been measured from different material sets

•SPCE signals have been measured with 4 different film stacks, made from 3 different material sets

•Depending on step size, a full 180º scan can be completed in < 5 minutes

Results

30

SPCE Measurement

QuickTime™ and aMotion JPEG OpenDML decompressor

are needed to see this picture.

31

First detected SPCE signal

32

Theta (deg.)

Sig

nal In

ten

sity

(V

)

•Scans begin at 0˚ and traces out an angle

•Peaks are measured in the regions: < 90˚ and > 90˚

0 90

180

Geometry of an SPCE scan

Repeated scans with increasing PMT voltage: 0.79 V (green), 0.81 V (blue), 0.84 V (black), 0.84

V (red)34

Sig

nal In

ten

sity

(V

)

Theta (deg.)

5 repeated scans at 0.84 V

Run SPCE SPCE

01 57.8 ± 1.4

122.8 ± 0.3

02 58.3 ± 0.6

122.7 ± 0.2

03 56.6 ± 1.6

124 ± 0.9

04 58.0 ± 1.1

122.9 ± 0.8

05 57.7 ± 1.0

123.2 ± 0.3

First (red), second (blue), third (black), fourth (green), fifth (magenta)

35

Theta (deg.)

Sig

nal In

ten

sity

(V

)

3 scans at 0.84 V

Scan SPCE SPCE

01 67.9 ± 11.9

118.7 ± 0.4

02 64.2 ± 6.2

118.7 ± 0.3

03 63.8 ± 5.3

118.3 ± 0.2

36

Theta (deg.)

Sig

nal In

ten

sity

(V

)

•Angular Reproducibility

•High uncertainty in fits due to poor fitting of small peaks

•Variant peaks at same voltage

•Altering the voltage of consecutive scans led to uniformity

Repeated Scan Characteristics

37

Tests of Si/Ag/Si-O(x) (5% O2)

Scans with PMT voltages: 0.75 V (blue), 0.79 V (green), 0.84 V (red), 0.84 V (black)

Run SPCE SPCE

0.75V 68.4 ± 0.2

127.1 ± 0.8

0.79V 69.5 ± 0.2

129.9 ± 0.6

0.83V 64.2 ± 0.2

124.9 ± 0.5

0.84V 66.2 ± 0.2

126.4 ± 0.4

38

Theta (deg.)

Sig

nal In

ten

sity

(V

)

Tests of Si/Ag/Si-O(x) (10% O2)

Scan SPCE SPCE

0.75 V 47.4 ± 2.2 105.3 ± 5.4

0.81 V 53.3 ± 0.7 112.9 ± 2.3

0.84 V 55.2 ± 1.3 115.1 ± 2.1

PMT Voltages: 0.75 V (black), 0.81 V (red), 0.84 V (blue)

39

Theta (deg.)

Sig

nal In

ten

sity

(V

)

Higher Resolution Scans

•Previous scans were made with step sizes of 1.0º

•Scans were made with smaller step sizes, 0.75º, 0.5º, 0.25º, 0.2º, 0.1º

•Step sizes > 0.5º show similar angular reproducibility as the 1.0º step size scans

•Step sizes < 0.5º show poor angular reproducibility

40

Smaller Step Scans

Left: Step sizes of 1.0º (red), and 0.5º (black)Right: Step sizes of 0.1˚ (black), 0.15˚ (blue), and 0.2˚ (red)

41

Theta (deg.) Theta (deg.)

Sig

nal In

ten

sity

(V

)

Sig

nal In

ten

sity

(V

)

Reverse Scans•Second LabVIEW program written

•Program will execute two scans in two directions

•First scan will be done in clockwise direction

•Second scan will be done in counter-clockwise direction

•Reversed direction scans were done to check angular reproducibility

42

Clockwise and Counter-clockwise scans at 1.0º step size

Run SPCE SPCE

CW 67.3 ± 0.1 136 ± 0.3

CCW 68.2 ± 0.3 136 ± 0.3

Clockwise (red) and counterclockwise (black) SPCE scans with 1˚ step size.

43

Sig

nal In

ten

sity

(V

)

Theta (deg.)

Clockwise and Counter-clockwise scans at 0.2º step size

Run SPCE

CW 48.2 ± 0.1

CCW 56.1 ± 0.1

Clockwise (red) and counterclockwise (black) scans with step size of 0.2˚44

Theta (deg.)

Sig

nal In

ten

sity

(V

)

Outline

•Introduction

•Sample Preparation

•Apparatus Design and Construction

•Results

•Conclusions and Future Work

45

Conclusions and Future Work

•SPCE can be generated with many different material sets

•Adhesion/Passivation materials may affect fluorescence intensities

•Scans with step sizes >0.5˚ are reproducible

•Fluorescent dye quality

•Symmetry of peaks46

Acknowledgments • Thanks to the current and former members of Jim

Harper’s group: Amanda Brown, Don Carlson, Derya Deniz, Dana Filoti and Anne-Marie Shover

• Thanks to the current and former members of Tom Laue’s group: Brett Austin, Sue Chase, and Kari Hartmen for their help in early design of the apparatus and fluorescent dye preparation

• Thanks to Rudolf Seitz of the Chemistry Department for access to the spin coater

• Thanks to Rob Cinq-Mars of the UNH Instrumentation Center for help in LabVIEW programming and stepper motor operation

• Thanks to Ignacy and Zygmunt Gryczynski of the University of North Texas

• Thanks to the thesis committee members: Professors Tom Laue, Olof Echt and James Harper

47

SupportThis thesis was financially supported in part by NIH Grant 1-R33CA14460-

01

48

Tests of AlSi/Ag/AlSi-N (15% N2)

Scan SPCE SPCE

0.75 V 50.8 ± 1.0 108 ± 1.8

0.79 V 48.3 ± 0.8 106.2 ± 1.9

0.81 V 54.4 ± 0.5 114.1 ± 1.1

0.83 V 50.0 ± 0.3 111.9 ± 0.9

0.85 V 54.3 ± 0.3 117.5 ± 1.7

Scans with PMT voltage: 0.75 V (red), 0.79 V (green), 0.81 V (grey),

0.84 V (blue), 0.84 V (black)50

Scans of Si/Ag/Si-O(x) (5% O2), 20nm thick passivation layer

PMT voltages 0.75 V (green), 0.77 V (blue), 0.84 V (red) and 0.84 V (black).

Run SPCE SPCE

0.75 V 48.5 ± 0.5 109.4 ± 1.0

0.77 V 52.2 ± 0.4 116.9 ± 4.7

0.83 V 51.7 ± 1.4 110.5 ± 3.5

0.85 V 54.8 ± 1.4 113.7 ± 1.0

Fluorescence Spectrum

plot from Molecular Probes: http://probes.invitrogen.com/servlets/spectra?fileid=6393ph8

•Semi-transparent and highly reflective slides

•AlSi/Ag/AlSi-N

•Si/Ag/Si-O(x) (5% O2)

•Highly transparent and semi-reflective slides

•Si/Ag/Si-O(x) (10% O2)

53

Theta (deg.)Theta (deg.)

Sig

nal In

ten

sity

(V

)

Sig

nal In

ten

sity

(V

)

Signal Attenuation as films erode

Left: Dye layer newly depositedRight: 18 hours later

Sample: Si/Ag/SiO(x) (5% oxygen)