Infrared Analysis of Thin Multilayered Polymer Film Using Cantilever Enhanced Photoacoustic Detector
Kaori Watanabe and Fumiko Hiwatashi
Systems Engineering Inc. www.systems-eng.co.jp info@systems-eng.co.jp
Introduction

PAS Sampling Depth

Polymer thin film is used in...

Sample• Structural material• Adhesive

Multilayered films for hybrid and novel functions• Paint and printing

0x

ΔT ∝ βI = βI0exp(−x/β)

ΔTs = ΔTexp(−x/μ) ∝ βI0exp(−x/β−x/μ) ≈ βI0exp(−x/μ)• Vibrational spectroscopy -> definitive molecular information0» PAS: Non-destructive (little sample preparation), depth-profilingxµ: “PAS Sampling Depth”• Cantilever and laser interferrometer based detector

PA intensity / arb. units

k: Thermal conductivity [W cm-1 K-1]

V: Mirror velocity [cm s-1]

ρ: Density [kg cm-3]

ν: Infrared wavenumber [cm-1]

Results and Discussion

S/N = 13

2000

-1

1000

Layered sheets of food wrap
PE, PVC, PVDC; 10 um each

Photoacoustic Spectroscopy (PAS)

Mirror velocity V = 5 kHz = 0.32 cm s-1

1740
PVC
PA Intensity / arb. units

4.

HeatPE
PVC
PVDC1/e» THz, IR, NIR, UV-Vis etc.

Estimated
Sampling
Depth

Heat generated at depth eµ can be detected
Generated heat decays to 1/e2 at surface

ΔT/eΔT/e2
0µeµx×e
4000

3500

30002500• Non-destructive» Irregular shaped, small, or opaque sample etc.

“PASSampling
Depth”ΔTPAS advantage• Versatile

Estimated factor
i.e., A ≈ e

4. Thermal expansion of surrounding gas detected• Depth-profiling400» 4.6A < 12.5 μm < 6.4A

Layered film

2. Absorbed energy partially transformed into heat• Highly sensitive600

2.6 < A < 2.7

1.

3. Heat diffuses back to sample surface

800• 605 cm-1 peak: Observed at 20 kHz, not observed at 40 kHz

PE 10 μm
PVC 10 μm
PVDC 10 μm

Photoacoustic spectroscopy

2.

1000

» 3.4A < 12.5 μm < 4.8A

1. PAS spectrum of multilayered film

wavenumber / cm

3.

1200
-1
wavenumber / cm

• 1080 cm-1 peak: Observed at 10 kHz, not observed at 20 kHz

Conventioanl 1scan

3000

1400

» 3.8A < 12.5 μm < 5.3A

S/N = 137

4000

1600

• 1775 cm-1 peak: Observed at 10 kHz, not observed at 20 kHz

C: Specific heat [J kg-1 K-1]

Sample: PE

1800

Estimation of accurate samping depth Aμ (A: factor)

α: Thermal diffusivity α = k/ρC [cm2 s-1] ω: Angular modulation frequency ω = 2πVν• Ten times more sensitive than(non-radiating relaxation)

1775
PI

2000

Generated heat decays to 1/e

PAS with cantilever detector

1080
PI

μ: Thermal diffusion length µ = 2α / ωNovel PAS detector (GASERA; booth 555)

1. Sample absorbs incident light-1

40 kHz (2.53 cm s )Heat generated at position x• XPS, SSIMS, SPM, XRD etc.

• Determination of accurate sampling depth of-1

10 kHz (0.63 cm s )Heat diffused from position x to the sample surface

PA301 1scan605
PI-1(0.32 cm s )-1

Surface analysis• Infrared PAS analysis of multilayered films

5 kHz

20 kHz (1.26 cm s )• Biomaterial

This study-1

I = I0exp(−βx) (β: Absorption coefficient)

Depth profiling analysis is necessary

traditional acoustic microphone

PI 50 μm

2.5 kHz (0.16 cm s )Photoacoustic / arb. units

nm to μm ordered polymer structure

Teflon® FEP 12.5 μm

Kapton® 300F929

Light intensity at position xI0• Electronic device

Multilayered polyimide film

Incident light beam irradiated onto sample

Sealed sample chamber
Gas

2. PAS spectrum of multilayered film, various mirror velocity

2000-1
wavenumber / cm

1500

1000

1740 cm-1 peak of PVC observed
Sampling depth > 10 μm↔

PAS sampling depth μ = 7.6 μm

Photoacoustic signal observed beyond μ500

Conclusion
Photoacoustic signal can be detected beyond PAS sampling depth μ.
Accurate sampling depth is estimated to be ~eμ, where the generated
signal decays to 1/e2 upon reaching the sample surface.