In this paper, the evolution of lead zirconate titanate (PZT) capacitor leakage current mechanism as a function of dielectric thickness has been investigated. It has been pointed out that PZT leakage current switches from Schottky to Poole–Frenkel conduction mechanisms as PZT thickness decreases. The leakage current evolution seems to be dependant on the presence of a dead layer at metal/PZT interface. The dead layer thickness is estimated at about 40 nm. The switch from an interface limited conduction mode to a bulk limited mode can be attributed to the presence of a higher defect concentration in the dead layer in comparison with PZT bulk.
Aims: To develop a new type of microbiological Reference Materials (RMs), displaying long‐term stability at room temperature. The purpose was to produce and validate two batches of RMs for the enumeration of Bacillus cereus and Clostridium perfringens.
Methods and Results: The RMs were based on spores of B. cereus and Cl. perfringens, adsorbed on calcium carbonate pellets. Two batches of 1000 units were manufactured and validated in compliance with ISO guide 35. After verification of their homogeneity, the stability of the ‘RM‐B. cereus’ and ‘RM‐Cl. perfringens’ batches was proven during at least 36 and 9 months, respectively, at room temperature. The validation study was completed by international collaborative trial involving 12 laboratories, allowing the validation of the assigned values.
Conclusions: The methodology developed in this work enabled to produce easy‐to‐handle and cost‐effective RMs, displaying an unprecedented stability at room temperature, a good homogeneity and a precise and validated assigned value.
Significance and Impact of the Study: This study revealed new paths for the development of stable microbiological RMs. Overcoming the intrinsic instability of the living cells makes it possible to produce valuable tools for the quality assurance of microbiology laboratories.
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