Transcript Slide 1
Examination of mechanical stability and gas sensor application of (As2S3)100-x(AgI)x chalcogenide glasses INA K. Kolev1*, T. Petkova1, C. Popov2 1 2 Institute of Electrochemistry and Energy Systems (IEES), Bulgarian Academy of Sciences Institute of Nanostructure Technologies and Analytics (INA), University of Kassel, Germany EXPERIMENTAL SET–UP MOTIVATION Development of new transduction principles in the sensoric technique Search for new sensitive materials New sensors with improved sensitivity, selectivity and reliability MFC-1 Flow Chamber Electronic Sensor Analyte 1 MFC-2 carrier gas Different functionalization layers for diverse gases sensor inlet Electronics acquisition card valves Analyte 2 MFC-3 Mass-flow controllers outlet PC SORPTION PROPERTIES Fabrication process – complementary metal-oxidesemiconductor (CMOS) technology 64.480 64.475 64.470 25 % 8% 17 % 33 % 64.465 Water Methanol Isopropanol Acetone 64.460 64.455 54 % 64.450 0 Integration of transducer, actuator and read-out in one unit 7 14 21 28 35 42 49 56 63 64.490 water methanol ethanol isopropanol acetone ammonia 20 15 Resonance frequency, kHz Cantilever sensors – a miniature version of a microbalance Resonance frequency shift, Hz Resonance frequency, kHz CANTILEVER–BASED CHEMICAL GAS SENSORS 25 64.485 10 5 acetone in 64.475 64.470 64.465 0 70 0 10 20 30 40 50 10 20 30 40 50 100 120 Response time, s 60 Concentration, vol% Resonance frequency, kHz Decrease of the resonance frequency with addition of mass, i.e. by sorption of gas molecules THEORETICAL BASIS of STRESS INVESTIGATION K – spring constant of the cantilever 64.485 64.480 64.475 acetone out 64.470 64.465 64.460 1 – resonance frequency before exposure 0 16mm 20 40 60 80 Response time, s 16mm 8mm 4.6mm 5mm 3mm 4mm 4mm 2mm 6mm 123 5 67 4 2 – resonance frequency after exposure 8.5mm 4mm STRESS MEASUREMENTS 7mm 150 Stoney's equation: s D2 ESi 6 (1 ) R 1 d Initial stress Stress after 3 Months relaxation Focus on frame Mechanical Stress, MPa SURFACE and MORPHOLOGY 64.480 64.460 0 Time, min K 1 1 2 m 2 2 4 1 2 64.485 Focus on beam s - film stress d - film thickness ESi - Young's modulus of the substrate - Poisson's ratio of the substrate D - thickness of the substrate R - curvature radius of the bending L2 + h2 R 2h L, h - length and deflection of the cantilever beam cantilever, deflection determined by optical microscopy h h compressive tensile d tensile stress 0 compressive stress -50 -100 -150 5 10 15 20 25 30 AgI content, % D h 50 0 Dcant L 100 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 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). 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.