An approach to the infrared study of materials by photothermal beam deflection spectroscopy

Materiuls Chemistry

and Physics,

AN APPROACH TO BEAM DEFLECTION

M.J.D.

LOW,

Department New York, Received

10 (1984)5 19.-528

THE INFRARED SPECTROSCOPY

C.MORTERRA

STUDY

519

OF

MATERIALS

BY

and A.G.SEVERDIA

of Chemistry, New York University, NY 10003 (U.S.A.) 12 January

PHOTOTHERMAL

1984;

accepted

31 January

4 Washington

Place,

1984

ABSTRACT

Infrared Fourier transform photothermal beam deflection spectroscopy (PBDS) is briefly outlined. It involves heating a surface by the photothermal effect, using infrared (IR) radiation from a scanning interferometer; energy is transferred to the gas above the surface and the resulting refractive index gradient in the gas is detected by observing the deflection of a laser beam grazing the solid's surface; the deflection is related to the IR radiation which is absorbed, so that the Fourier transform of the deflection signal results in the IR spectrum. PBDS is especially useful for materials which scatter and/or absorb IR radiation so extensively that conventional transmission/absorption techniques are not possible . A variety of examples of applications are given, including spectra of polymers, floor tile, polyester thread and fabric, leather, cellulose, paper, lichen and bone.

INTRODUCTION

Many

used

one

method, ways,

involves which

used

methods With

materials and there

scopy,

be characterized

the

more

latter,

by infrared

of doing

internal

involve

photoacoustic

absorptive

this.

(IR) spectro-

The most

widely

Transmission/Absorption

by using

extents,

recently, the

ways

conventional

may be modified

to smaller

and,

the

can

are several

emission

of

Other

or reflection

spectroscopy

properties

(T/A)

reflection.

(PAS) fll.

materials

probed

via the photothermal effect, i.e., the conversion --absorbed electromagnetic to thermal energy. Another new method IR Fourier scopy

transform

(PBDS).

(FT) photothermal

It is an off-shoot

of PAS

beam and

deflection detects

are of is

spectro-

the

0 Elsevier Sequoia/Printed in The

photo-

Netherlands

520 thermally-induced

ation

heating

of organic

with

emphasis

surface prove

and

being

reactions

It

will

with

destructive, which

samples,

solids

placed

the

on

no

examples

that

the

of

opaque

for

of

carbons

of

IR

12-41,

[5-81

and

should

applications

examination

structure

and/or

the examin-

objects

novel technique

some

changes

via the deflection

large

study this

noticed

are thick,

and

However,

useful;

be

a sample

to be useful

inorganic

[g-12].

to be widely

shown.

of gas over

beam. PBDS has been shown

of a light

or

highly

is

texture

are non-

of

the

described

in

scattering.

EXPERIMENTAL

The

instrumentation

detail will

be

components modulated

which heating

solid's

diameter 'mirage

IR

interferometer

(Fig.1). The

solid

the

An

useful.

scanning

and

effect'

beam

have

is new,

modulated

is focussed

by

onto

by

solid

absorbed

so

that

a

on the surface was

first

it to be the basis

scopic

technique:

the

of refractive laser

and

theoretical

DEFLECTION

Schematic

IR-FT-PBDS

POSlTlON

SENSOR

radiation a slight

2.5

mm

This deflection

or

a

et al. [151 who

and sensitive

d BEAM

to

a

of a flat

of the gas over

grazing

by Boccara

of a versatile

experimental

beam

is deflected.

described

lead

index

outline

through

by the

are

change

passage surface

caused

and

brief

the

effect

showed

Fig.1

been a very

photothermal

surface,

IR focus

techniques

as the technique

[13,14] but,

spectro-

treatments

have

521 been

described

processed

[16]. The deflection

as with

single-beam

PBD

'instrument emission

'black'

spectrum

The

spectra

minutes).

shown

The

scans

i.e.,

Note

the so

is

in a

influenced

by

of

the

by

ratioing

corrected

standard

and then

to result

variation

is

which

source S

istakento

in a pseudo

RESULTS

AND DISCUSSION

In order

to obtain

a flat

portion

ordinates

but

be

double-beam

are

'up,' bands

an IR-PBD

with

in

point

to pack

so that

spectra

are positive

to the

to

absorption

'down.'

all that

is neededisto (see Fig.11

to the probe powders

laser

Fe oxalates

beam

to

into a shallow

cup. One or two milligram Some

and

it is convenient

the material

is needed.

needed) 10 - 50

IR focus

With

(4, 2,

not about

contrast

to the

respect

of

displaced bands

spectrum

signal.

resolution

usually

periods

absorption

of a sample

photothermal

at 8 cm-'

available

point

it mechanically the

recorded

(measurement

that

bands

given

optimize

latter

to result

in %T, for which

spectra

adjust

1171

are

arbitrary

overlap.

abscissa,

bring

also and

were

resolutions - 2000

500

do not

The

So of a carbon

absorber

fi is measured

S/S,.

1 cm -'

using

and

signal

FT spectrometer,

S.

frequency,

the spectrum

a flat

and

spectrum

function' with

against

a conventional

results

of powder are shown

in

Fig.2.

The spectra needed

of Fe oxalates

and, as the spectrum

Fet2 compound the

could

literature,

FeC204.2H20 powders shown

were

pellet

the PBD spectra

Fig.2

Iron oxalates

recorded.

These also

T/A spectrum

containing

spectral

shows

the Fef3 show

features,

are a

of a KBr oxalate. the same but the

T/A spectrum

has the sloping

ground

distorts

which

of

and Fe2(C204f3.5H20

The two Fe+S spectra general

of the

not be found in

in Fig.2 , which

conventional

were

back-

spectral

522

features that is frequently found with spectra of solids, and the extent of the strong OH absorption in the PBD spectrum. involved

with obtaining

solid in a mortar

is not as clearly defined as

Note that the only the PBD spectrum

and placing

"sample

preparation"

was hand-grinding

the powder

the

in a cup. (The reason

the sample was ground is that the photothermal

signal increases

with decreasing particle size; also, grinding decreases specular reflection

in the case of crystalline materials.) Of greater is that the sample was not mixed with KBr (it has been

importance

reported that double decomposition reactions occur between alkali halides

and

oxalates

in pellets

[18])

so that

spectral

artifacts were avoided. Some results

obtained

with

relatively

shown in Fig.3. The Na polymethacrylate chunks:

a piece

of it was placed

simple materials

are

was in the form of clear

in position

and yielded

the

spectrum shown. The spectrum of the acid prepared from the salt is also shown ffor comparison, [19]). The acid was spectrum

indicate

see spectra 1102 and 1103 of ref.

in the form of a powder, absorptions

probably

The arrows caused

by

by the a SOi

contaminant introduced during manufacture. No sample preparation was needed with other materials, For example,

anodd-shaped piece

of floortilebetween

in size was placed in position and the well-structured

also.

1 and 2 cm spectrum

shown in Fig.4 was obtained. The sample proper is, of course, not

FLOOR TILE

! ~_ - -“No POLYMETHACRYLATE

>

1500

1000 cd

Fig.3 Spectra of polymers

Fig.4 Spectra of floor tiles

523 the

entire

beam

piece

which

is

about

1 mm.

portion

to

traversed

the

the

adjustment

should

be noticed there

and

a

simply,

holding

the

the

the

spot

larger

could

object

that

lay-out

will

mirror,

not

other

fit

posts

of the chamber.

be enlarged

must

depressed

It

so that,

to the size of the object

to be examined

i.e., areas

IR beams,

but

of the present

and the walls

area

of the object

10 x 10 x 5 cm,

focussing

of

i.e., the

in

to be

be accessible

beneath

the

to

surface

be examined.

Some

results

obtained

in Figs.

sewing

thread

threads the

to about

a width

size,

size

IR

in diameter

having

sample The

: the

surface

2.5 mm

beam

the

is examined.

is no limitation

the laser

shown

laser

only by the geometry

that

However,

about

define

micrometers,

examined.

on its

spot

probe

limited

area:

post

holding

principle,

the

which

is imposed

sampling

between

a portion

dimensions

is at present

limitation

cannot

by

These

but

a circular

of an object

itself

of

of tile

is focussed

5 and was

wound

lay side-by-side.

Another

different household

on a small After

sample

was

a

types

of materials

No.50

size

Al block

the assembly

the well-defined

spectrometer,

obtained.

with

6. Some

snippet

(a

so that was

spectrum of

POLYESTER

SEWING

THREAD

like

although

there

differences intensities. more

Fig.5,

in

SA/SB,

reflecting

composition

of

thread, obvious band

brought

the shown

The

in Fig.5 is

some

are

of

simply

stage.

relative

These

clearly

spectrum

was

of the

are in

fabric

nonfibrous

shown

that

in

made

sampling

spectrum

much

in place

and

which

the

resulting very

wound

in Fig.5 was

material

'polyurethane') on

the

'Ultrasuede'TM

fibers

'polyester'

placed

put

shown

suede-like

are

"polyester"

out

differential at

the top of

differences the

two

in the plastic

materials.

\I 2000

”

I

”

”

1500

I

IO00

”

I’

are

Spectra

of some

shown

in Fig.6.

Polyesters

The

products

shiny,

hard

cnf’

leather Fig.5

animal

covering

lady's belt

the

buckle

led to the top

of

a

spectrum:

524 the buckle, still attached belt, was placed

?ED GRAIN LEATHER

meter. mm2)

Small pieces of

suede

parchment

(about 15-20

leather

laid

to the

in the spectro-

on

and

the

of

spectro-

meter's sample platform led to the other

spectra

Differences

SUEDE LEATHER

readily

in

of the

Fiq.6.

spectra

are

observable,

e.g., differences in the relative intensities of the CH and OH bands, the absence of a strong band near 1800 cm -1 and the fairly strong band in the 3100-3000 parchment What ’ PARCHMENT

cm-l region in the

spectrum,

is important,

so on. is

that the spectra were obtained so easily

of

and,

destructively. Fig.6

and

however,

Leather

this

type

are

difficult

non-

course,

Soft materials

to

normally prepare

of

quite for

IR

study : specimens are usually thick and therefore opaque: converting them into fine powder so that

the

pellet

or mull

technique

can be

used

is extremely

difficult; and they cannot be dissolved without alteration. Fibrous materials which are opaque in thin layers, scatter IR radiation extensively,

and

are difficult

for

to prepare

IR study, are the subjects Figs.7

- 9. Pure

of

cellulose

fiber used for chromatography was tamped down to form a thin bed on the sampling The resulting in

Fig.7

cellulose remarkable. spectrum Fig.7

Cellulose

platform.

is

spectrum shown that of pure

and

not otherwise

Shown also is the

of 'Surgicel,' manu-

factured by Johnson & Johnson

525 1 PAPER onno 1577 iji

ij i TREATMENT OF PAPER WITH ETHYLENE OXIDE n

I

i 3000 zoo0 Fig.8 Modern paper

1000c Fig.9

in the form of threads woven for treating

Medieval paper

into a gauze-like fabric used

wounds. A single thread pulled from the fabric was

stretched over a ring; the spectrum shows the drastic effects of the

NO2 -treatment

material,

*.,

used

to convert

the large carbonyl

the

cellulose

starting

bands in the 1900-1800

region, loss of spectral detail below 1700

cm-l

cm-l, as well as the

great increase of the OH absorption. Spectra

of modern

paper

before

and

after

treatment

with

ethylene oxide are shown in Fig.8; pieces about 20 mm2 were used. Thetreatmentbrouyht

about a decline of the OHband

peaking near

3400 cm-' and an increase of the CH bands in the 3000-2700

cm-'

region. There is also a minor

change near 900 cm-', shown more

clearly

is a portion

in the insert,

which

of the differential

'pectrum 'AFTER/'BEFORE. Additional specimen;

spectra

of

paper

were

obtained

with

it was a 40 mm 2 piece of paper manufactured

The front surface

was white

and yielded

a spectrum

another in 1577.

almost

the

same as that of the modern paper shown in Fig.8. The back surface was

faintly

blueish

and

bore

a blue

'mold'

spot.

Spectra

of

different areas of the paper are shown in Fig.9: there are large and obvious differences attributable to the mold.

526 The results obtained Fig.10.

There

with some unusual

is some

interest

in the

samples

are shown in

IR remote

sensing

of

terrain, However, a sensor would 'see' not a signature similar to a spectrum

of a clean rock measured

of a rock

bearing

detritus,

plants

in the laboratory, and debris.

but that

Consequently,

spectral signatures are needed and, as part of such a study, some (about 3 x 5 x 2 cm) bearing patches of

weathered rock specimens lichen were examined. (SB) gave

the results

Red lichen shown

(SRf and greyish-black

in Fig.10. The

spectra,

lichen although

quite poor in quality

above 2000 cm-', are quite similar overall, but there are some minor differences shown more clearly in the insert, a segment of the differential spectrum. Fig.11 is also concerned with an unusual sample. The scalp of

a laboratory (about

rat was

removed

1 x 1.5 x 0.5 cm)

positioned

and the entire

was

in the spectrometer.

"AS IS" of Fig.11 resulted.

mounted

cleaned

on a small

The clearly

The spectrum

cranium

block

defined

is similar

and

spectrum to

others of bone i20] and not remarkable. The bone was then partly demineralizes by exposing it to a dilute citric acid solution for a short time. The treated specimen yielded the second spectrum of Fig.11; the drastic region,

decline

indicat .ing that

of the P-O bands

demineral .ization

in the 1000 cm-l had

RAT

occurred,

is

SKULL

DEMINERALIZED 3000

Fig.10

Lichen

Fig.11

Bone

2000

1000 cr

527 It should

obvious. hard

tissue

sectioning be

with

that

like bone and teeth but

is possible,

induced.

without

be noted

it

Yet,

altering

medical

is

them

is very

desirable

to the feasibility

and

to

or to study

examine

studies

of

comminution changes

such their

the effects of bone.

of such

for IR study

textural

e.g., to study

demineralization/remineralization point

difficult:

structural

grossly,

adhesives,

the preparation

specimens interaction

of diet

on the

The present

by the PBDS

or may

results

technique.

ACKNOWLEDGEMENT Support 268/83,

by

AR0

contract

and the donation

gratefully

DAAG29-83-K-0063,

of bone

samples

and

NATO

by R.Murphy,

grant

are

acknowledged.

REFERENCES 1

A.Rosencwaig, Photoacoustics Wiley, New York, 1980.

2

M.J.D,Low, M.Lacroix 35(1982)582.

and

A.G.Severdia,

3

M.J.D.Low, M.Lacroix 15(1982)57.

and

C.Morterra,

4

M.J.D.Low, M.Lacroix, 14(1982)16. C.Morterra M.J.D.Low

and and

and

C.Morterra

M.J.D.Low,

C.Morterra,

C.Morterra

and

M.J.D.Low,

C.Morterra

and

M.J.D.Low,

Photoacoustic

Appl.Spectrosc.

Spectrosc.Lett.

and

A.G.Severdia,

Spectrosc.Lett.

21(1983)275.

Carbon

21(1983)283.

,

Amer.Lab.

15(1982)689.

Carbon

Carbon

Spectroscopy,

in press.

M.J.D.Low, C.Morterra 15(1982)415.

and

A.G.Severdia,

Spectrosc.Lett.

10

M.J.D.Low, C.Morterra 29(1983)311.

and

A.G.Severdia,

J.Molec.Catal. -

11

M.J.D.Low, C.Morterra, A.G.Severdia Surface Sci. 13(1982)429.

and

M.Lacroix,

12

M.J.D.Low, C.Morterra, A.G.Severdia Symposium Series, in press.

and

J.M.D.Tacson,

13

M.J.D.Low, G.A.Parodi Instrum. 11(1981)265. --

14

M.J.D.Low

and

and

M.Lacroix,

M.Lacroix,

Infrared

Chem. ----

Phys.

Appl.

Biomed.

22(1982)139.

ACS

Environ.

528 15

A.C.Boccara, 36,130(1980).

D.Fournier

and

J.Badoz,

Appl.Phys.Lett.

16

A.C.Boccara, D.Fournier, W.Jackson and N.M.Amer,Opt.Lett.5, 377 (1980); D.Fournier, A.C.Boccara, N.M.Amer and R.Gerlach, &ml. Phys. Lett. 37, 519(1980); W.B.Jackson, N.M.Amer, ---A.C.zccara and D. Fournier, +pl.O@. 20, 1333(1981); A.C.Boccara and D. Fournier, Appl.Opt.20, D.Bebarre, 4281(1981).

17

M.J.D.Low and G.A.Parodi, M.J.D.Low, Spectrosc.Lett.

18

K.Kawakita, A.Ito and 83(1962)271.

19

Infrared Spectroscopy.Its Infrared Spectroscopy Committee, Use -in the Coatings Industry. Federation of Societies for Paint Technology, Philadelphia, 1960.

20

in Biochemistry, Biology F.S.Parker, Infrared Spectroscopy and Medicine, Plenum Press, New York, 1971, pp 497 ff. --

Spectrosc.Lett. in press.

O.Amakasu,

Nippon

13(1980)663;

Kagaku

Zasshi