Papers by Author: Johann Michler

Abstract: The measuring of internal stress has not only a great scientific aspect, but is particularly important for nondestructive description of component or products in industry. It is expected that exceeding of local mechanical limits in the material can have catastrophic consequences. In this paper is mapped the deformation field of amorphous material under the nanoindenter tip using diffraction in Debye-Scherrer geometry. Using the FEM analysis, it was modeled the deformation field in such material. There is a great match in between measured and calculated data. The result is pointing out on large limits of internal stresses measuring by conventional standard methods.

Abstract: We report a simple synthetic route based on electroless deposition (galvanic displacement) and natural lithography to synthesize organized Au nanoparticles (NPs). We will study the influence of different experimental parameters (time, temperature, pH and additives) on the synthetic process. We show for the first time the formation of organized extended domains of Au nanorings using gelatin as an additive. A wide range of applications can be envisaged for these nanostructures, as for instance chemical- and bio-sensors using the SERS effect.

Abstract: This study was triggered by our experience on electrophoretic deposition (EPD) with different suspension systems showing evidence of a particle concentration threshold, below which no deposit was formed. In this study, the role of particle concentration in the mechanism of EPD was investigated with a model system, consisting of isopropanol suspensions with TiO2 nanosized particles (d50 = 130 nm). The investigated concentration range was 0.01 - 0.4 vol% TiO2. Constant voltage EPD tests with variable particle concentration were performed for 1 min under different applied voltages (25 - 300 V corresponding to 62.5 - 750 V/cm). A longer deposition time (30 min) was tested for a lower concentration value (0.003 vol% TiO2). The deposition process was evaluated in situ by means of the current measured during EPD. The deposits obtained were characterized by weight and profile measurements and scanning electron microscope (SEM). The results confirmed the finding of a lower limit value of particle concentration, determining a threshold in the formation of an EPD coating. Above this threshold, proportionality between deposited mass and particle concentration was observed, in agreement with the equation of Hamaker. Below this threshold, the proportionality was lost with evidence of a lack of coating formation. A possible interpretation for this experimental finding was provided.