Assessing dead time effects when attempting isotope ratio quantification by time-of-flight secondary ion mass spectrometry.

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is a quasi-non-destructive technique capable of analyzing the outer monolayers of a solid sample and detecting all elements of the periodic table and their isotopes. Its ability to analyze the outer monolayers resides in sputtering the sample surface with a low-dose primary ion gun, which, in turn, imposes the use of a detector capable of counting a single ion at a time. Consequently, the detector saturates when more than one ion arrives at the same time hindering the use of TOF-SIMS for quantification purposes such as isotope ratio estimation. Even though a simple Poisson-based correction is usually implemented in TOF-SIMS acquisition software to compensate the detector saturation effects, this correction is only valid up to a certain extent and can be unnoticed by the inexperienced user. This tutorial describes a methodology based on different practices reported in the literature for dealing with the detector saturation effects and assessing the validity limits of Poisson-based correction when attempting to use TOF-SIMS data for quantification purposes. As a practical example, a dried lithium hydroxide solution was analyzed by TOF-SIMS with the aim of estimating the 6Li/7Li isotope ratio. The approach presented here can be used by new TOF-SIMS users on their own data for understanding the effects of detector saturation, determine the validity limits of Poisson-based correction, and take into account important considerations when treating the data for quantification purposes.

Protonic Conduction in the BaNdInO4 Structure Achieved by Acceptor Doping.

The potential of calcium-doped layered perovskite compounds, BaNd1-x Ca x InO4-x/2 (where x is the excess Ca content), as protonic conductors was experimentally investigated. The acceptor-doped ceramics exhibit improved total conductivities that were 1-2 orders of magnitude higher than those of the pristine material, BaNdInO4. The highest total conductivity of 2.6 × 10-3 S cm-1 was obtained in the BaNd0.8Ca0.2InO3.90 sample at a temperature of 750 °C in air. Electrochemical impedance spectroscopy measurements of the x = 0.1 and x = 0.2 substituted samples showed higher total conductivity under humid environments than those measured in a dry environment over a large temperature range (250-750 °C). At 500 °C, the total conductivity of the 20% substituted sample in humid air (∼3% H2O) was 1.3 × 10-4 S cm-1. The incorporation of water vapor decreased the activation energies of the bulk conductivity of the BaNd0.8Ca0.2InO3.90 sample from 0.755(2) to 0.678(2) eV in air. The saturated BaNd0.8Ca0.2InO3.90 sample contained 2.2 mol % protonic defects, which caused an expansion in the lattice according to the high-temperature X-ray diffraction data. Combining the studies of the impedance behavior with four-probe DC conductivity measurements obtained in humid air, which showed a decrease in the resistance of the x = 0.2 sample, we conclude that experimental evidence indicates that BaNd1-x Ca x InO4-x/2 is a fast proton conductor.