Analysis of Sn-Bi Solders: X-ray Micro Computed Tomography Imaging and Microstructure Characterization in Relation to Properties and Liquid Phase Healing Potential.

This work provides an analysis of X-ray micro computed tomography data of Sn-xBi solders with x = 20, 30, 35, 47, 58 wt.% Bi. The eutectic thickness, fraction of eutectic and primary phase are analyzed. Furthermore, the 3D data is evaluated by means of morphology parameters, such as, shape complexity, flatness, elongation and mean intercept length tensor. The investigated alloys are categorized in three groups based on their morphology, which are described as "complex dominant", "complex- equiaxed" and "mixed". The mechanical behavior of Sn-Bi alloys in the semi-solid configuration and the correlation with microstructural parameters are discussed. A varying degree of geometric anisotropy of the investigated alloys is found through the mean intercept length tensor. Representative volume element models for finite element simulations (RVE-FEM) are created from tomography data of each alloy to analyze a correlation of geometric and elastic anisotropy. The simulations reveal an elastic isotropic behavior due to the small difference of elastic constants of primary and eutectic phase. A discussion of properties in the semi-solid state and liquid phase healing is provided.

Enabling luminescence decay time-based sensing using integrated organic photodiodes.

The use of organic photodiodes (OPDs) for measuring phosphorescent lifetimes of optochemical oxygen sensors is described. Phosphorescent indicators with lifetimes ranging from ∼5 to 60 µs have been studied using light-emitting diodes as the excitation source and organic photodiodes integrated into the sensor substrate for detection. A measurement system using an adjusted electronic circuitry to detect photocurrents in the nanoampere range is presented. The response behaviour of the organic photodiodes has been characterized, and it was found that a forward (positive) bias had to be applied in order to decrease the response time of the OPDs to a range suitable for phosphorescence decay time measurements. A modulation cutoff frequency of ∼100 kHz has been determined, corresponding to a response time of the organic photodiodes of 1.6 µs. Two sensor dyes have been characterized regarding their lifetimes upon exposure to 0-20% oxygen, and it was shown that results comparable to literature data and inorganic photodetectors can be achieved.

Diffusion of Ag into organic semiconducting materials: a combined analytical study using transmission electron microscopy and X-ray reflectivity.

This study shows that the morphology of organic/metal interfaces strongly depends on process parameters and the involved materials. The interface between organic n-type blocking layer materials and the top Ag cathode within an organic photodiode was investigated. Ag was deposited on either amorphous tris-8-hydroxyquinolinato-aluminum (Alq(3)) or crystalline 4,7-diphenyl-1,10-phenanthroline (Bphen) using different deposition techniques such as electron beam deposition, ion beam sputtering, and vacuum thermal evaporation at various deposition rates. The interfaces were studied by transmission electron microscopy and X-ray reflectivity. It was found that Bphen does not show any Ag diffusion no matter which deposition technique was used, whereas the Ag diffusion into Alq(3) depends on the deposition technique and the deposition rate. The highest amount of Ag diffusion into Alq(3) occurred by using thermal vacuum deposition at low deposition rates.

Filter-free integrated sensor array based on luminescence and absorbance measurements using ring-shaped organic photodiodes.

An optical waveguiding sensor array featuring monolithically integrated organic photodiodes as integrated photo-detector, which simplifies the readout system by minimizing the required parts, is presented. The necessity of any optical filters becomes redundant due to the proposed platform geometry, which discriminates between excitation light and sensing signal. The sensor array is capable of measuring luminescence or absorption, and both sensing geometries are based on the identical substrate. It is demonstrated that background light is virtually non-existent. All sensing and waveguide layers, as well as in- and out-coupling elements are assembled by conventional screen-printing techniques. Organic photodiodes are integrated by layer-by-layer vacuum deposition onto glass or common polymer foils. The universal and simple applicability of this sensor chip is demonstrated by sensing schemes for four different analytes. Relative humidity, oxygen, and carbon dioxide are measured in gas phase using luminescence-based sensor schemes; the latter two analytes are also measured by absorbance-based sensor schemes. Furthermore, oxygen and pH in aqueous media were enabled. The consistency of calibration characteristics extending over different sensor chips is verified.