High resolution ultrasonic interferometry for quantitative nondestructive characterization of interfacial adhesion in multilayer (metal/polymer/metal) composites Abstract-We describe an ultrasonic method for the quantitative and nondestructive characterization of interfacial adhesion. Near an interface, such as polymer/metal, there exists a thin interfacial boundary layer at the nm length scale where the polymer may have properties different from those of the bulk polymer. On the other hand, ultrasonics measures linear mechanical properties of materials on a length scale which is that of the wavelength, usually in the range of several µm. Hence, it is usually stated that standard ultrasonic techniques cannot probe interfaces effectively. Here, we report on an ultrasonic interferometry technique that is built around metal/polymer/metal structures and that exhibits high sensitivity to interfacial properties, even at usual ultrasonic wavelengths. A rigorous mathematical model for the ultrasonic response of multilayered media that accounts for viscoelasticity is presented. Results of numerical calculations point out scaling features for interfacial properties in terms of specific stiffness S. We describe our technique and illustrate some experimental results on sample multilayers where interfacial adhesion properties were modified through chemical action on the metal substrates. We show that the measurements confirm the predictions from the model. In particular, it is suggested that adhesion is not a shear-related problem only, but that extensional forces are also important. Finally, we discuss our results in relation to other techniques for characterizing confined molecular systems. This work is meant to be openended, leading to applications for nondestructive evaluation and also to perspectives in the field of fundamentals of adhesion.
Though most objections to the use of selenium are largely unfounded (lag and ghosting effects, low DQE), the high bias voltage associated with the thick layer of selenium required to have an acceptable x-ray absorption in radiography and fluoroscopy applications, may have some practical inconvenience.The purpose of this study was to evaluate the pertinence of a solution using a thin coplanar selenium layer, as a photosensitive converter requiring only a few tens of volts of bias, associated with a thick columnar coating of sodium doped cesium iodide scintillator.It will be shown that CsI(Na) can be evaporated with a very uniform needle-like morphology on amorphous selenium structures, the later showing no evidence of thermal recristallization. Photoluminescence characterization of this scintillator material shows a light emission peak centered at 420 nm as expected, which matches the sensitivity spectrum of selenium. Preliminary sensitivity measurements give a signal in the range of 2000 pC/cm2/mR for 4OOi-CsI, with no reflector present.The thin selenium layers deposited display low dark currents of less than 130 pA/cm2 at an electric field of 10 volts per micron.Work in progress will be presented including the scintillator (x-ray absorption, sensitivity and emission), the thin selenium photosensor as well as the coupled structure characteristics.
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