Examination of mechanical stability and gas sensor application of (As2S3)100-x(AgI)x chalcogenide glasses

K. Kolev1*, T. Petkova1, C. Popov2

1 Institute of Electrochemistry and Energy Systems (IEES), Bulgarian Academy of Sciences2 Institute of Nanostructure Technologies and Analytics (INA), University of Kassel, Germany

INA

inlet

Ana

lyte

1

MFC-3

MFC-2

MFC-1

Flow Chamber

sensor

PC

outlet

Mass-flow controllers

Ana

lyte

2

valv

es

carrier gas

Electronics acquisition

card

EXPERIMENTAL SET–UP

SORPTION PROPERTIES

CONCLUSIONS

The surface and morphology analysis of the thin films shows that films are uniform, homogeneous, featureless and smooth both on surface and in depth

The magnitude and the sign of the stress are functions of the film composition and structure as well as of the mechanical and thermomechanical properties.

The bigger tensile stress of the samples with 5 % at. AgI can be related to initial incorporation of atoms with larger atomic radius into As2S3 pyramidal structure.

As AgI amount increases Ag atoms occupy the microvoids and thus the glass density enhances and the structure stabilizes. This densification and stabilization of the structure leads to weakening of the tensile stress and change in the sign of the mechanical stress to compressive in the samples with 25 and 30 % at. of AgI.

Resonating cantilevers functionalized with amorphous (As2S3)90(AgI)10 film were exposed to vapors of different analytes, including water, VOC and ammonia, in order to study the sorption properties of the chalcogenide coating.

The highest sensitivity was observed towards acetone, the analyte with one of the highest molecular weight and with the lowest dipole moment among the tested analytes.

The sensor acted primarily as a microbalance distinguishing the vapors by the difference in their molecular weight with physisorption as main mechanism.

The short response and recovery times together with the linear increase of the response signals with the analyte concentration make the investigated As-S-Ag films a promising candidate for gas sensitive elements.

MOTIVATION Development of new transduction principles in the sensoric technique

Search for new sensitive materials

New sensors with improved sensitivity, selectivity and reliability

Different functionalization layers for diverse gases

Electronic Sensor

Cantilever sensors – a miniature version of a microbalance

Fabrication process – complementary metal-oxide-semiconductor (CMOS) technology

Integration of transducer, actuator and read-out in one unit

Decrease of the resonance frequency with addition of mass, i.e. by sorption of gas molecules

CANTILEVER–BASED

CHEMICAL GAS SENSORS

22

21

2

11

4 K

m

K – spring constant of the cantilever

1 – resonance frequency before exposure

2 – resonance frequency after exposure

ACKNOWLEDGMENTS

The authors gratefully acknowledge the financial support of the European Social Fund (Program “Development of human resources”) under

contract BG051PO001/07/3.3-02/58/17.06.2008).

Stoney's equation:

- film stressd - film thicknessESi - Young's modulus of the substrate - Poisson's ratio of the substrate

D - thickness of the substrateR - curvature radius of the bending

L, h - length and deflection of the cantilever beam

dR

DESi 1)1(6

2

RL2 h2

2 h

D

Dcant

L

dh

cantilever, deflection determinedby optical microscopy

Focus on frame Focus on beam

hh

tens ile com pressive

7mm

1 6 m m

16mm

4m m

4 m m2 m m

8 m m

5 m m

6 m m4 m m

3 m m

8 .5 m m

4.6mm

56

74

12

3

THEORETICAL BASIS of

STRESS INVESTIGATION

SURFACE and MORPHOLOGY

STRESS MEASUREMENTS