Quantifying Moisture Penetration in Encapsulated Devices by Heavy Water Mass Spectrometry: A Standard Moisture Leak Using Poly(ether-ether-ketone)

Moisture penetration into active biomedical implants such as the bionic ear and eye is a major problem in healthcare since surgery is required to replace devices affected by corrosion. Existing methods for measuring moisture leak rates such as the commercially available dynamic relative humidity method are not sufficiently sensitive to guarantee security against moisture penetration. Helium leak detection is highly sensitive but is challenged by the unknown relation to the moisture leak rate because of mixed flow modes involving liquid water. A standard moisture leak traceable to fundamental units is not currently available, preventing direct comparison of moisture and helium leak rates in the same device. Here, we demonstrate a practical calibrated moisture leak based on the stable polymer poly(ether-ether-ketone), for calibrating heavy water mass spectrometry. Using biomedical test structures from manufactured encapsulations, we show that in the majority of cases, calibrated measurements of molar moisture leak rates exceed the helium leak rate, especially for very small and large leaks. Comparison with theory shows that LaPlace pressure is the driving force for the enhanced moisture flows. We recommend that the compliance limit for helium testing in biomedical devices be reduced by one order of magnitude.

Impurity Tracking Enables Enhanced Control and Reproducibility of Hybrid Perovskite Vapor Deposition

Metal halide perovskite semiconductors have the potential to enable low-cost, flexible, and efficient solar cells for a wide range of applications. Physical vapor deposition by co-evaporation of precursors is a method that results in very smooth and pinhole-free perovskite thin films and allows excellent control over film thickness and composition. However, for a deposition method to become industrially scalable, reproducible process control and high device yields are essential. Unfortunately, to date, the control and reproducibility of evaporating organic precursors such as methylammonium iodide (MAI) have proved extremely challenging. We show that the established method of controlling the evaporation rate of MAI with quartz microbalances (QMBs) is critically sensitive to the concentration of the impurities MAH2PO3 and MAH2PO2 that are usually present in MAI after synthesis. Therefore, controlling the deposition rate of MAI with QMBs is unreliable since the concentration of such impurities typically varies from one batch of MAI to another and even during the course of a deposition. However once reliable control of MAI deposition is achieved, we find that the presence of precursor impurities during perovskite deposition does not degrade the solar cell performance. Our results indicate that as long as precursor deposition rates are well controlled, physical vapor deposition will allow high solar cell device yields even if the purity of precursors changes from one run to another.

Rapid Hydrophilization of Model Polyurethane/Urea (PURPEG) Polymer Scaffolds Using Oxygen Plasma Treatment

Polyurethane/urea copolymers based on poly(ethylene glycol) (PURPEG) were exposed to weakly ionized, highly reactive low-pressure oxygen plasma to improve their sorption kinetics. The plasma was sustained with an inductively coupled radiofrequency generator operating at various power levels in either E-mode (up to the forward power of 300 W) or H-mode (above 500 W). The treatments that used H-mode caused nearly instant thermal degradation of the polymer samples. The density of the charged particles in E-mode was on the order of 10¹⁶ m⁻³, which prevented material destruction upon plasma treatment, but the density of neutral O-atoms in the ground state was on the order of 10²¹ m⁻³. The evolution of plasma characteristics during sample treatment in E-mode was determined by optical emission spectroscopy; surface modifications were determined by water adsorption kinetics and X-ray photoelectron spectroscopy; and etching intensity was determined by residual gas analysis. The results showed moderate surface functionalization with hydroxyl and carboxyl/ester groups, weak etching at a rate of several nm/s, rather slow activation down to a water contact angle of 30° and an ability to rapidly absorb water.