Magnetic Sector Secondary Ion Mass Spectrometry on FIB-SEM Instruments for Nanoscale Chemical Imaging.

The structural, morphological, and chemical characterization of samples is of utmost importance for a large number of scientific fields. Furthermore, this characterization very often needs to be performed in three dimensions and at length scales down to the nanometer. Therefore, there is a stringent necessity to develop appropriate instrumentational solutions to fulfill these needs. Here we report on the deployment of magnetic sector secondary ion mass spectrometry (SIMS) on a type of instrument widely used for such nanoscale investigations, namely, focused ion beam (FIB)-scanning electron microscopy (SEM) instruments. First, we present the layout of the FIB-SEM-SIMS instrument and address its performance by using specific test samples. The achieved performance can be summarized as follows: an overall secondary ion beam transmission above 40%, a mass resolving power (M/ΔM) of more than 400, a detectable mass range from 1 to 400 amu, a lateral resolution in two-dimensional (2D) chemical imaging mode of 15 nm, and a depth resolution of ∼4 nm at 3.0 keV of beam landing energy. Second, we show results (depth profiling, 2D imaging, three-dimensional imaging) obtained in a wide range of areas, such as battery research, photovoltaics, multilayered samples, and life science applications. We hereby highlight the system's versatile capability of conducting high-performance correlative studies in the fields of materials science and life sciences.

4D Surface Reconstructions to Study Microscale Structures and Functions in Soil Biogeochemistry.

The development of high-resolution microscopy and spectroscopy techniques has allowed the analysis of microscopic 3D objects in fields like nanotechnology and life and soil sciences. Soils have the ability to incorporate and store large amounts of organic carbon. To study this organic matter (OM) sequestration, it is essential to analyze its association with soil minerals at the relevant microaggregate scale. This has been previously studied in 2D. However, 3D surface representations would allow a variable angle and magnification analysis, providing detailed insight on their architecture. Here we illustrate a 4D surface reconstruction workflow able to locate preferential sites for OM deposition with respect to microaggregate topography. We used Helium Ion Microscopy to acquire overlapping Secondary Electron (SE) images to reconstruct the soil topography in 3D. Then we used nanoscale Secondary Ion Mass Spectrometry imaging to chemically differentiate between the OM and mineral constituents forming the microaggregates. This image was projected onto the 3D SE model to create a 4D surface reconstruction. Our results show that organo-mineral associations mainly form at medium curvatures while flat and highly curved surfaces are avoided. This method presents an important step forward to survey the 3D physical structure and chemical composition of microscale biogeochemical systems correlatively.

Health insurance benefit packages prioritized by low-income clients in India: three criteria to estimate effectiveness of choice.

We applied a decision tool for rationing choices, with a predetermined budget of about 11 US dollars per household per year, to identify priorities of poor people regarding health insurance benefits in India in late 2005. A total of 302 individuals, organized in 24 groups, participated from a number of villages and neighborhoods of towns in Karnataka and Maharashtra. Many individuals were illiterate, innumerate and without insurance experience. Involving clients in insurance package design is based on an implied assumption that people can make judicious rationing decisions. Judiciousness was assessed by examining the association between the frequency of choosing a package and its perceived effectiveness. Perceived effectiveness was evaluated by comparing respondents' choices to the costs registered in 2049 illness episodes among a comparable cohort, using three criteria: 'reimbursement' (reimbursement regardless of the absolute level of expenditure), 'fairness' (higher reimbursement rate for higher expenses) and 'catastrophic coverage' (insurance for catastrophic exposure). The most frequently chosen packages scored highly on all three criteria; thus, rationing choices were confirmed as judicious. Fully 88.4% of the respondents selected at least three of the following benefits: outpatient, inpatient, drugs and tests, with a clear preference to cover high aggregate costs regardless of their probability. The results show that involving prospective clients in benefit package design can be done without compromising the judiciousness of rationing choices, even with people who have low education, low-income and no previous experience in similar exercises.