Achim Walter Hassel

By employing a co‐sputtering technique, combinatorial thin film libraries in the Ti–Zr system are produced. The libraries have a compositional spread ranging from 40 to 70 at% Ti. The confocal geometry of the sputtering system is maintained for the production of all thin films. The microstructural and crystallographic properties are elucidated by energy dispersive X‐ray spectroscopy (EDX), X‐ray diffraction (XRD), and scanning electron microscopy (SEM) analysis. Furthermore, contact angle measurements and nanoindentations are performed to map the wettability, hardness, and elastic modulus of the alloy system. The electrochemical properties, i.e., the oxide film formation factor and the relative permittivity of anodically grown oxides on the parent metal alloys are determined. The measurements are performed in phosphate‐buffered saline in order to best simulate a biological environment. A linear shift in the properties is observed along the compositional gradient for the EDX, XRD, and SEM analysis. For all other sets of measurements deviations from the linear behavior, are observed around the 60 at% Ti concentrations. This coincides with the formation of a congruent alloy in bulk material. The observed changes however, deviated also from expectations for bulk alloys. The implications and potential for those alloys as implant material are discussed in the following.

Titanium anodic memristors were prepared in phosphate buffer (PB) and citrate buffer (CB) electrolytes. Studying their I-U sweeps, the memristors presented self-rectifying and volatile behaviors. Transmission electron microscopic analysis revealed crystalline protrusions inside a semi-crystalline Ti oxide. Grounded in this, a hybrid interfacial memristive switching mechanism relaying on partial filaments was proposed. Moreover, both analyzed memristor types demonstrated multilevel switching capabilities. The memristors anodized in the PB and CB showed high-to-low resistance ratios of 4 × 104 and 1.6 × 102, respectively. The observed (more than two order of magnitude) ratio improvement of the PB memristors suggests their better performance, in spite of their modestly high resistive state instabilities, attributed to the thermal stress caused by consecutive switching. The endurance and retention of both the PB and CB memristors was measured over up to 106 cycles, indicating very good lifetimes. Phosphate incorporation into the anodic oxide was confirmed by photoelectron spectroscopy analysis and was related to the improved memristive behavior of the PB sample. The presence of phosphate inside the memristively active layer modifies the availability of free O species (vacancies and ions) in the oxide. Taking all this into consideration, Ti anodic memristors anodized in PB are emphasized as candidates for neuromorphic computing.