Multielectrode Arrays at Wafer-Level for Miniaturized Sensors Applications: Electrochemical Growth of Ag/AgCl Reference Electrodes.

In this study, a range of miniaturized Ag/AgCl reference electrodes with various layouts were successfully fabricated on wafer-level silicon-based substrates with metallic intermediate layers by precisely controlling the electrochemical deposition of Ag, followed by electrochemical chlorination of the deposited Ag layer. The structure, as well as the chemical composition of the electrode, were characterized with SEM & EDS. The results showed that the chlorination is very sensitive to the applied electric field and background solution. Potentiostatic chlorination, in combination with an adjusted mushroom-shaped Ag sealing deposition, enabled the formation of electrochemical usable Ag/AgCl layers. The stability of the electrodes was tested using open circuit potential (OCP) measurement. The results showed that the reference electrodes stayed stable for 300 s under 3 M KCl solution. The first stage study showed that the stability of the Ag/AgCl reference electrode in a chip highly depends on chip size design, chlorination conditions, and a further protection layer.

In-operando photoelectron spectroscopy for batteries: Set-up using pristine thin film cathode and first results on NaxCoO2.

A model all-solid-state battery cell with a thin film NaxCoO2 cathode was assembled under ultra-high vacuum conditions and cycled inside the vacuum chamber, using a dedicated sample holder. We present in-operando x-ray photoelectron spectroscopy measurements of a NaxCoO2 cathode at different charging states. During battery operation, the change in sodium content, the change in cobalt oxidation state, and the evolution of the O1s and VB emissions could be monitored. Comparison with a conventional post-mortem analysis technique showed that the new measurement technique produces comparable results regarding the oxidation state of the transition metal, but sodium and oxygen results show differences due to cathode/electrolyte interfacial reactions for conventional analysis. By using surface layer-free samples in the presented techniques, we could circumvent such reactions and obtain reliable spectra for the pure bulk-like active cathode material.

Toward an Understanding of Thin-Film Transistor Performance in Solution-Processed Amorphous Zinc Tin Oxide (ZTO) Thin Films.

Amorphous zinc tin oxide (ZTO) thin films are accessible by a molecular precursor approach using mononuclear zinc(II) and tin(II) compounds with methoxyiminopropionic acid ligands. Solution processing of two precursor solutions containing a mixture of zinc and tin(II)-methoxyiminopropinato complexes results in the formation of smooth homogeneous thin films, which upon calcination are converted into the desired semiconducting amorphous ZTO thin films. ZTO films integrated within a field-effect transistor (FET) device exhibit an active semiconducting behavior in the temperature range between 250 and 400 °C, giving an increased performance, with mobility values between µ = 0.03 and 5.5 cm2/V s, with on/off ratios increasing from 105 to 108 when going from 250 to 400 °C. Herein, our main emphasis, however, was on an improved understanding of the material transformation pathway from weak to high performance of the semiconductor in a solution-processed FET as a function of the processing temperature. We have correlated this with the chemical composition and defects states within the microstructure of the obtained ZTO thin film via photoelectron spectroscopy (X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy), Auger electron spectroscopy, electron paramagnetic resonance spectroscopy, atomic force microscopy, and photoluminescence investigations. The critical factor observed for the improved performance within this ZTO material could be attributed to a higher tin concentration, wherein the contributions of point defects arising from the tin oxide within the final amorphous ZTO material play the dominant role in governing the transistor performance.