To shorten the wait for the 14th ThGOT and the 6th Optics Colloquium we would like to give you a small foretaste of our numerous exciting technical presentations in the coming weeks.
Non-destructive characterization of coatings and surfaces using laser-acoustic surface waves
Volker Weihnacht, Fraunhofer Institute for Material and Beam Technology IWS, Dresden
Up to now, the measurement of mechanical surface and layer properties has often been limited to indenting methods for hardness or Young's modulus measurement or cross-section preparation of a surface segment with subsequent analysis. The laser-acoustic investigation of surfaces and coatings using surface waves offers a promising alternative or supplement to this. It is based on sound wave excitation with a pulsed laser and velocity measurement of the waves as a function of their frequency.
The spectrum obtained provides a great deal of information about the surface and layer properties, which can be determined directly via a suitable fit model. In the best case, both the Young's modulus, the density and the layer thickness can be determined from the measurement curve. The method is extraordinarily sensitive; even layers a few nanometers thick can be measured accurately. By adapting the sensor technology, it is possible to characterize not only thin layers but also thick layers down to the millimeter range. In addition to measuring the classic layer properties, the detection of defects such as pores and microcracks often plays a role here.
This talk will be presented in SESSION C: NEW MEASUREMENT METHODS IN SURFACE ENGINEERING on March 13, 2019 at 1:30 pm.
Non-destructive test for the analysis of defects in thin barrier layers
Mariagrazia Troia, University of Stuttgart - Institute of Interfacial Process Engineering and Plasma Technology (IGVP), Stuttgart, Germany
The effectiveness of barrier coatings against oxygen used for food packaging and encapsulation of sensitive electronic devices are severely limited by point micro- and submicrometric defects. A new nondestructive test was developed and optimized to determine the density, origin, and effect on the oxygen transmission rate of such defects in films generated by plasma enhanced chemical vapor deposition (PECVD). Thin films serving as oxygen barrier layers were deposited on thin, flexible PET films using an electron cyclotron resonance (ECR) plasma and a gas mixture of hexamethyldisilazane (HMDSN) and oxygen. The ECR plasma is generated by microwaves with a frequency of 2.45 GHz.
To analyze the defects, the coated sample is placed in a test cell between a pure CO2 atmosphere and a saturated lime water solution. The CO2 molecules preferentially penetrate the defects in the barrier layers and cause the precipitation of calcium carbonate crystals on the top side of the defects, i.e., the side with the lime water solution. Real-time analysis was performed using an optical microscope placed on the transparent top of the cell. Markers placed on the sample were used to determine the position of the crystals and the underlying defects, which were then examined in more detail using a scanning electron microscope (SEM).
This talk will be presented in SESSION C: NEW MEASUREMENT METHODS IN SURFACE ENGINEERING on March 13, 2019 at 1:50 pm.