Depth profiling and standardization from the back side of a sample for accurate analyses: Emphasis on quantifying low-fluence, shallow implants in diamond-like carbon.

RATIONALE: Back-side thinning of wafers is used to eliminate issues with transient sputtering when analyzing near-surface element distributions. Precise and accurate calibrated implants are created by including a standard reference material during the implantation. Combining these methods allows accurate analysis of low-fluence, shallow features even if matrix effects are a concern. METHODS: Implanted Na (<2.0 × 1011 ions/cm2 , peaking <50 nm) in diamond-like carbon (DLC) film on silicon (solar wind returned by NASA's Genesis mission) was prepared for measurement as follows. Implanted surfaces of samples were epoxied to wafers and back-side-thinned using physical or chemical methods. Thinned samples were then implanted with reference ions for accurate quantification of the solar wind implant. Analyses used a CAMECA IMS 7f-GEO SIMS in depth-profiling mode. RESULTS: Back-side-implanted reference ions reduced the need to change sample mounts or stage position and could be spatially separated from the solar wind implant even when measuring monoisotopic ions. Matrix effects in DLC were mitigated and the need to find an identical piece of DLC for a reference implant was eliminated. Accuracy was only limited by the back-side technique itself. CONCLUSIONS: Combining back-side depth profiling with back-side-implanted internal standards aides quantification of shallow mono- and polyisotopic implants. This technique helps mitigate matrix effects and keeps measurement conditions consistent. Depth profile acquisition times are longer, but if sample matrices are homogeneous, procedural changes can decrease measurement times.

Oxygen isotopic composition of an enstatite ribbon of probable cometary origin.

Filamentary enstatite crystals are found in interplanetary dust particles (IDPs) of likely cometary origin but are very rare or absent in meteorites. Crystallographic characteristics of filamentary enstatites indicate that they condensed directly from vapor. We measured the O isotopic composition of an enstatite ribbon from a giant cluster IDP to be δ18O = 25 ± 55, δ17O = -19 ± 129, Δ17O = -32 ± 134 (2σ errors), which is inconsistent at the 2σ level with the composition of the Sun inferred from the Genesis solar wind measurements. The particle's O isotopic composition, consistent with the terrestrial composition, implies that it condensed from a gas of nonsolar O isotopic composition, possibly as a result of vaporization of disk region enriched in 16O-depleted solids. The relative scarcity of filamentary enstatite in asteroids compared to comets implies either that this crystal condensed from dust vaporized in situ in the outer solar system where comets formed or it condensed in the inner solar system and was subsequently transported outward to the comet-forming region.

Q-gases in a late-forming refractory interplanetary dust particle: A link to comet Wild 2.

We report the structure, chemical composition, O, Al-Mg, He, and Ne isotope systematics of an interplanetary dust particle, "Manchanito". These analyses indicate that Manchanito solidified as refractory glass (with oxidized Fe but reduced Ti) in a chondrule-like formation environment more than 3.2 Myr after CAIs, after which it was exposed to Q-like noble gases in the dissipating solar nebula. Manchanito's He and Ne isotopic composition and concentrations are similar to those measured in samples of comet Wild 2, from which we infer that Manchanito's parent body was a comet. We propose that after formation and exposure to Q-like gases, Manchanito was transported to the outer Solar System where it came into contact with organics and volatile ices on its cometary parent body. Manchanito provides additional evidence that cometary solids have been subjected to energetic processing and large-scale transport in a wide range of environments in the Solar System.

Identification of Large Isotope Anomalies in Quartz by Infrared Spectroscopy.

We report an infrared (IR) spectroscopic technique to detect quartz grains with large isotope anomalies. We synthesized isotopically doped quartz and used Fourier transform infrared spectroscopy (FT-IR) in two different instruments: a traditional far-field instrument and a neaSpec nanoFT-IR, to quantify the shift in the peak of the Si-O stretch near 780 cm-1 as a function of isotope composition, and the uncertainty in this shift. From these measurements, we estimated the minimum detectable isotope anomaly using FT-IR. The described technique can be used to nondestructively detect very small (30 nm) presolar grains. In particular, supernova grains, which can have very large isotope anomalies, are detectable by this method.

Modeling the Raman spectrum of graphitic material in rock samples with fluorescence backgrounds: accuracy of fitting and uncertainty estimation.

We propose a robust technique called Savitzky-Golay second-derivative (SGSD) fitting for modeling the in situ Raman spectrum of graphitic materials in rock samples such as carbonaceous chondrite meteorites. In contrast to non-derivative techniques, with assumed locally linear or nth-order polynomial fluorescence backgrounds, SGSD produces consistently good fits of spectra with variable background fluorescence of any slowly varying form, without fitting or subtracting the background. In combination with a Monte Carlo technique, SGSD calculates Raman parameters (such as peak width and intensity) with robust uncertainties. To explain why SGSD fitting is more accurate, we compare how different background subtraction techniques model the background fluorescence with the wide and overlapping peaks present in a real Raman spectrum of carbonaceous material. Then, the utility of SGSD is demonstrated with a set of real and simulated data compared to commonly used linear background techniques. Researchers may find the SGSD technique useful if their spectra contain intense background interference with unknown functional form or wide overlapping peaks, and when the uncertainty of the spectral data is not well understood.