Infrared absorption in thin metallic films

(1)

lot-''t

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UNIVERSITY OF ADELAIDE

PHYSICS DEPARTMENT

THESIS FOR THE DEGREE OF MASTER OF SCIENCE

INFRARED ABSORPTION IN THIN METALLIC FILIUS

K.C.

Liddiard, B.Sc.

(Hons) Researcl'r

Scientist

Australian

Defence

Scientific

Service

WEAPONS RESEARCH ESTABLISHMENT, SALISBURY, ^SOUTH^AUSTRALIA

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1.

INTRODUCTION

2.

T}IERMAL PROPERTIES OF THIN METALLIC FILMS

2.L

Tt¡ernal

theory of a thin fihn infrared

absorber

2.L.7

Surface

radiation

loss

2.L,2

Absorbed

radiant

energy

2.I.3

Absorber geometry

2.t,4

The one-dimensional

heat

equation

2.2

Thermal capacitance

2.2.L Application to

composite

filns 2.2.2 Lateral

thermal conductance

2.3

Temperature

rise

due

to

absorbecl

radiation 2.3.I

Steady

state solution

2.3.2

Average tenperature

rise

2.3.3

Time dependent tenperature

rise 2,4

Thermal

rise

time

2,5

^Thermal^spread

2.6 Solution in

plane

polar

coordinates

2,6.L

Maximum temperature

rise

2.6.2

Temperature

rise

near

the

boundary

2.7

Therrnal

analysis of a typical thin film infrared

absorber

2.7.L

Considerations

in the selection of a suitable

absorber element

2.7.2 Incident infrared radiation

2.7,3

Temperature

rise for a

sna11

rectangular

absorber element

2.7.4

Temperature

rise for a large

absorber elenent

2.7.!

Absorbers

of circular

^area

3,

^OPTICATA}ID ELECTRICAL PROPERTIES OF TIIIN METALLIC FILMS

3.1 Introductory note

on radionetry

3.2

Electromagnetic

theory of the optical properties of

absorbing media

Page L 5

5- 6-

7

7- 8-

L0

10-

1L 72 1,2 -

73 74

14- 16- 17- 18- 19-

20

20-

No.

6 7

B

10

11

T3

1s 17

18 19 20

22

22-24 24-27 27-28 28-29

29

29-30

37-32

(3)

4

3.2.L

Absorption

in

netals

3.3

Thermal

radiation

sources

3.4 Infrared absorytion in thin metallic films

3.4.I

Dependence

of

absorption on angle

of

incidence

3.4.2 Influence of the plastic substrate film 3.4.3

^Double

netal film

3.5 Electrical

conduction

in thin netallic films

3.5.1

^Theory

of

conduction

in

continuous

netal filns

NUCLEATION AND GROWTH PROCESSES AND THE ^STRUCTUREOF THIN METALLIC FILNIS

4.t Introductory

concepts

4.t.1

Adsorption

of

vapour atons

4.1.2 Initial

nucleation

4,2

Observed

nucleation

and growth phenonena

4.2.1

Adatorn surface

mobility

and

film

aggloneration

4.2.2

The growth sequence

4.2,3 Filn structure

4.2,4

Substrate

transítion

temperatures

4.3 Electrical

çonduction

4.3.L Final filn

resistance

4.3.2

Aging

effects

4.3.3 Electrostatic

charge

effects

4.4 Selection of suitable netals for thin filn infrared

absorbers

4 .4

.7

^Gol

d fi

^lms

4.4.2 Platinun filns 4,4.3 Nickel filns 4.4,4 Alloy filns

PREPARATION OF METALLIC FILMS

5.1

Vacuun

coating unit

Page No.

32-34

34

35-36

37

37-39

59

39-40 40-43

4s

43

43-45 45-48

48

48-49 49-50 50-sl

51

-

^s3

53

53-54 54-56 s6-57

57

-

⁵⁹

59

59-60

60

60-61

61

6r-62

5

(4)

5,2

5.3

5.4

5.5 5.6 5.7 5.8 5.9

5.1.1 Anci1lary coating unit

Deposition

control

techniques

5.2,7 Film

resistance

5.2,2

Deposition

rate

and

film

^thickness

5.2.3

Chamber pressure

5,2.4

Deposition time Substrates

5. 5.

1

Resis tance measurement

5.3.2

^Thickness^monitor^sensing^head

5. 3.

3

Thickness measurenent

5.3.4 Infrared

measurements

5.3.5 Electron

nicroscopy

5.3.6

Measurement

of thernal

properties

5.3.7

Measurenent

of film resistance

^on

plastíc

^substrates

Preparation

of polyner filn

substrates

5.4.1

Ce11u1ose

nitrate 5.4.2 Polyvinyl

^formal

5.4,3 Polyúinyl chloride 5.4,4

Chlorinated ^PVC

5.4.5 Polyvinylidene chloride - acrylonitrite

^copolymer

5,4.6

Preparation

of sel.f-supporting filns

5.4.7

Selected polymer

films

Cleaning and

handling of

^substrates

Deposition

of gold films

Deposition

of

chroniun

filns

Deposition

of

nichrome

films

Deposi-tion

of nickel fílns

5.9.1 Filanent

vapour source deposition

62

62-63 63-64 64-65 65-66

66

66-67 67-68

68

68-69

69 69 70

70-71

7T 77

77-72

72 72

72-73 73-7s 75-76

76

76-77

77 77 78

(5)

5.9

,2 Electron

bearn dePosi

tiorr 6.

OPTICAL MEASUREMENT TECIINIQUTJS

6 .

1

Measurement

of

f i lm

thi

clllìcri; s

6.1.1

TolanskY

illterfcrolnct

^cl:

6.L.2

^Thicknessllìeasureìllclìts

6.2

lr{easurement

of s¡rectral

ab-sor:¡rf attce

6,2.I Infrared

spectropitotomctcr

6.2.2

Polyner substrates

6.2.3 Spectral

measurenlent:i

6.3

Measurement

of total

enrissivLty

6.3,I Emissivity

apparatus

7.

^{GOLD FILMS}

7.L Filn

^deposition

7.2 Electrical properties

ol" ^golcl

films

7.3 Infrared optical propertics of

¡¡oJ'd

films 8.

NICHROME FILMS

8.1

^Sone^reported

properties of

nicltrome

films 8.2 Film

deposition

8.3 Electrical properties of

nic.ltrome

films

8.4 Infrared optical properties of

^nichrome

films 9.

^NICKEL^FILMS

9.1 Film

deposition

9.2 Electrical properties of ni-ckel films

9.2.I Electrical conductivity of nickel filns 9.2,2 Electrical

^aging

9.3

Vacuum and oxidation

9.4

Stress

in nickel filns

9.5 Optical properties of nickel films

Page No.

78-81

8L 81,

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82-84

B5 85

85-87 87-88 88-90

90

90-93

93

93-94 94-96 96-97

97

97-98 98-99

99

-

¹⁰⁰

100

-

¹⁰¹

101

702

-

^I03

103

105

-

¹⁰⁴

10s

105

-

¹⁰⁸

r09 - Ltz

LT2

-

^7L4

(6)

L2.

L3,

11.5.5 Nickel

fifuns

11.6

Measurement

of

tenperature

rise lI.7

Summary

of thernal

properties

CONCLUSIONS ACKNOWLEDGEMENTS

LIST OF ^REFERENCES SYMBOL TABLE

LIST OF ^TABLES

1.

BULK THERIvIAL PROPERTIES OF SELECTED ABSORBER MATERIATS

2.

COMPUTED THERMAL PARAMETERS

3.

^SELECTED^POLYMER^FILMS

4.

SPECIMENS FOR TI]ERMAL MEASUREMENTS

5.

SI,JM},IARY OF THERMAL RISE TIME IvIEASUREMENTS

6.

^SI.JMMARYOF THERMAL SPREAD MEASUREMENTS

7.

TEMPERATURE RISE IUEASURENÍENTS

I'lo.

L4L

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^T44

L44

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L46

-

^t48

148 150

22 26 74

t28

135

t4I

t46

(7)

LIST OF F'IGUIìES

1.

Steady

state

ternperature

ri-se.

Selected

metallic

absorbers

2.

Tine dependent temperature

rise. lrlickel

absorber

3.

Time dependent average temperature

rise.

Selected

metallic

absorbers

4.

Time dependent temperature

rise.

Large area

nickel

absorber

5.

Steady

state

temperaturc

rise for rectangular

and

circular

absorber elements

6.

Blackbody

radiation for three selected

tenperatures

7, Infrared optical propcrties of a

thir"r

metallic film

8.

Dependence

of infrarecl optical propertics

on angle

of

incidence

9. Conductivity of thin filns

accordi-ng

to

Fuchs-Sondhierner theory

10.

Vacuum

coatjng unit

11.

Depositj-on

control

instrumentation

12. Monitor ci-rcuit

schematic

13.

Stibstrate arra:rgement

14.

Apparatus

for the preparation of

polyrner

films 15.

Electron beam

deposition

source

16.

Tolansky

nultiple

beam interferometer

17.

Tolarisky

fringe pattern

18. Infrared

spectrophotometer

19. Spectral

absorption

of collodion

substrates

20, Enis-sivity test

apparatus

2t,

Chart

recording of elnissivity

measutentent

22.

_Quartz

crystal monitor calibration f.or

_.qolcl

films 23. Emissivity of gold films

24.

_Quartz

crystal monitor calibration for

^nichrone

films 25.

Resistance

of

^nichrome

films

26.

_Quartz

crystal nonitor calibration for nicl<el films

27.

Resistance

of nickel films

on

glass

substratc-s

28.

Resistance

of nickel filns

on

collodion

stilrstrates

(8)

29. Enissivity of nickel

fil¡ns

30.

Absorptance and transmittance

of nickel fil¡ns 51. Structr¡re of

formvar substrates

32. Structure of collodion

substrates

33. Influence of coll.odion substrates in electron nicroscopy 54. Structr¡re of gold filrns

¹

55. Structt¡re of gold films

²

36. Structure of nichrone filns 37. Structure of nickel films

38. Stress in nickel filn on for¡nvar strbstrate

39.

Thermal

rise tine neasurement. Oscilloscope display 40. Thermal rise tine for a gold absorber filn

41.

Thernal

rise tine for

a

nickel

absorber

filn

42.

Steady

state

temperature

rise.

Gold absorber

film

43,

Steady

state

tenperature

rise. Nickel absorber filn

(9)

SUMMARY

This thesis

describes research

studies

on

the

absorption

of infrared radiation in thin metallic films. Thin films of nickel, gold

^{and a}

nickel-

chromium

alloy

welre vacuum deposited on

to freely-supported

^polymer^menbrane

substrates. It is

intended

that

these

films will

comprise

the radiation

receiver element

of ltigh

performance

infrared

detectors.

The research

is broadly divided into

two

nain

areas

of study.

^These

are the infrared optical properties of the

selected metal

filns,

^and^thermal

properties relevant to the

absorption process suçh as ternperature

rise,

thermal

rise tine

and

thernal

spread

in the

plane

of the fi1m.

^Tlretherrnal

characteris- tics are of

fundamental inportance

in

^infr¿rred

detector research,

because they determine

sensitivity,

^speed

of

response and

optical

^inage

quality.

The

first part of the thesis is

concerned

with a tl-reoretical

analysis

of the thernal

and

infrared optical properties of metallic

absorber

filns,

^and

includes a

resume

of nucleation

and growth phenomenon

in

^vacuumdeposited metal

fi1ns. This is

followed

by a description of

measurenent techniques and the

apparatus used

for the preparation of netal fi1ms,

curd

thcn a cletailed

^discussion

of experinental results. Careful

consideration was given

to the influence of

deposition

paraneters,

and

a

study was made

of the structure of the filns

^using

conventional

bright field electron nicroscopy. Finally, the

experimental

results are

conpared

with theoretical predictions.

In general,

good agreernent was found between

the theoretical

analysis and

the

measured

optical

and thermal

properties of the

selected

metal

absorber

filns. This

encouraging

result

enables

us to predict the nost suitable

metal, and

the

optirnurn

deposition paraneters, to satisfy specific

requirements

in infrared

detector

research.

(10)

I

herewith

state that this thesis

does

not contain

any

naterial

whictr has been accepted

for the award of any other degree or diplona in

any

University

and

that, to the best of

ny knowledge and

belief, the thesis contains no naterial previously published or hlritten by any other person, except when due referenco is nade in the text of the thesis.