Subsequent Secondary Ion Mass Spectrometry Research Articles

An Acid-Based Method for Highly Effective Baddeleyite Separation from Gram-Sized Mafic Rocks.

Dating mafic igneous rocks (silica-undersaturated) is difficult for the lack of suitable minerals such as zircons (ZrSiO4) commonly found in the sialic rocks such as granites. In this regard, baddeleyite (ZrO2) has been long recognized as the most important mineral to serve as a geochronometer for dating silica-undersaturated igneous rocks. However, separating baddeleyite is difficult due to its small grain size, typical tabular morphology, and low abundance in samples. The standard water-based separation technique requires kilogram-sized samples and usually has a very low recovery rate. In this study, a new separation method based on the different solubilities of the minerals within HF + HCl + HNO3 reagents was developed to achieve a high recovery of baddeleyite. With ∼19 g of diabase powder, the new method recovers 150–160 baddeleyite grains of 10–100 μm length and 4–50 μm width, an order of magnitude improvement over the water-based separation method, which typically recovers 11–12 similarly sized baddeleyite grains out of the ∼19 g sample. Subsequent secondary ion mass spectrometry U–Pb analyses demonstrate that the baddeleyite grains recovered by the new separation method keep the U–Pb system closed, indicating no Pb loss during acid treatment. Thus, this new method enables the most efficient baddeleyite recovery from gram-sized rocks and is anticipated to greatly contribute to the geochronological study of silica-unsaturated mafic rocks.

Investigation of NH3 input partial pressure for N-polarity InGaN growth on GaN substrates by tri-halide vapor phase epitaxy

The influence of NH3 input partial pressure on N-polarity InGaN grown by tri-halide vapor phase epitaxy was investigated. It was found that surface morphology, solid composition and optical properties were affected by NH3 input partial pressure. As shown in thermodynamic analyses, the indium content increased due to an increase in the driving force for InN deposition caused by increased NH3 input partial pressure. In addition, the deep level emission around 2.1 eV in photoluminescence measurements drastically decreased at higher NH3 input partial pressures. Ab initio calculations and subsequent secondary ion mass spectrometry measurements suggested the reduction of metal-vacancies and/or carbon impurity incorporation in the InGaN layers.

Oxygen Ion Conduction in Bulk and Grain Boundaries of Nominally Donor‐Doped Lead Zirconate Titanate (PZT): A Combined Impedance and Tracer Diffusion Study

Oxygen ion conduction in Nd3+‐doped Pb(ZrxTi1−x)O3 (PZT) was investigated by impedance spectroscopy and 18O‐tracer diffusion with subsequent secondary ion mass spectrometry (SIMS) analysis. Ion blocking electrodes lead to a second relaxation feature in impedance spectra at temperatures above 600°C. This allowed analysis of ionic and electronic partial conductivities. Between 600°C and 700°C those are in the same order of magnitude (10−5–10−4 S/cm) though very differently activated (2.4 eV vs. 1.2 eV for ions and electron holes, respectively). Oxygen tracer experiments showed that ion transport mainly takes place along grain boundaries with partly very high local ionic conductivities. Numerical analysis of the tracer profiles, including a near‐surface space charge zone, revealed bulk and grain‐boundary diffusion coefficients. Calculation of an effective ionic conductivity from these diffusion coefficients showed good agreement with conductivity values determined from impedance measurements. Based on these data oxygen vacancy concentrations in grain boundary and bulk could be estimated. Annealing at high temperatures caused a decrease in the grain‐boundary ionic conductivity and onset of additional defect chemical processes near the surface, most probably due to cation diffusion.

(Invited) Stability and Defect Chemistry of High-Temperature Piezoelectric Single Crystals

Piezoelectric single crystals of the langasite family exhibit piezoelectrically excited bulk acoustic waves up to temperatures of about 1400 °C. Therefore, the materials show the potential to be operated as resonant microbalance at extremely high temperatures. Such piezoelectric transducers enable, for example, film deposition monitoring or gas sensing by determination of atmosphere dependent mass changes of thin films already deposited on the resonators. Further, langasite based surface acoustic wave devices are increasingly operated at elevated temperatures. Consequently, the stability and operation limits of these crystals need to be determined and correlated with the transport kinetics of the constitutive elements and of dopants. In this work, the high-temperature stability of the piezoelectric single crystals CTGS (Ca3TaGa3Si2O14) and LGS (La3Ga5SiO14) is reviewed and related to their defect chemistry and the atomistic transport processes occurring in the crystals. First, the resonance frequency of CTGS and LGS bulk acoustic devices is determined up to temperatures as close as possible to their ultimate operation limit which is the melting point. The figure shows the relative frequency shift in comparison to common piezoelectric crystals such as quartz. It is obvious that the maximum operation temperature of langasite type crystals exceeds that of quartz significantly. The diffusion coefficients of oxygen and hydrogenous species follow from tracer diffusion runs and subsequent secondary ion mass spectrometry as well as optical absorption spectroscopy. The electrical conductivity is determined by impedance spectroscopy as function of temperature, oxygen partial pressure and crystal orientation. Key issues limiting the high-temperature operation are the evaporation of gallium, the formation of oxygen vacancies and the incorporation of hydrogen. For example, a dominant role of hydrogen is observed in hydrogenous atmospheres since the diffusion coefficient of hydrogenous species is orders of magnitude higher than that of oxygen. Further, the loss mechanisms are correlated with the transport kinetics. Its effect on the electromechanical properties such as mechanical stiffness, piezoelectric and dielectric constant, effective viscosity and electrical conductivity is evaluated. Thereby, the electromechanical properties are extracted from resonance spectra using a one-dimensional physical model. The viscoelastic damping in langasite, expressed as viscosity, governs the total loss up to about 650 °C. Between 400 and 650 °C, the temperature dependence of the property can be described by a single activation energy. Above about 600 °C, the electrical conductivity impacts the total loss noticeable. In contrast, the loss in CTGS is virtually not affected be the conductivity. In addition, the damping of the piezoelectric devices is determined by monitoring the amplitude of the displacement by laser vibrometry. Comparing CTGS and LGS, the former shows significantly lower losses at high temperatures which is caused to some extent by its fully ordered structure. Finally, application relevant aspects such as use of piezoelectric resonators are briefly presented. One example is the determination of thermodynamic properties of thin films. Figure 1

Correlated imaging with C60-SIMS and confocal Raman microscopy: Visualization of cell-scale molecular distributions in bacterial biofilms.

Secondary ion mass spectrometry (SIMS) and confocal Raman microscopy (CRM) are combined to analyze the chemical composition of cultured Pseudomonas aeruginosa biofilms, providing complementary chemical information for multiple analytes within the sample. Precise spatial correlation between SIMS and CRM images is achieved by applying a chemical microdroplet array to the sample surface which is used to navigate the sample, relocate regions of interest, and align image data. CRM is then employed to nondestructively detect broad molecular constituent classes—including proteins, carbohydrates, and, for the first time, quinolone signaling molecules—in Pseudomonas-derived biofilms. Subsequent SIMS imaging at the same location detects quinolone distributions in excellent agreement with the CRM, discerns multiple quinolone species which differ slightly in mass, resolves subtle differences in their distributions, and resolves ambiguous compound assignments from CRM by determining specific molecular identities via in situ tandem MS.

Secondary ion mass spectrometry combined with alpha track detection for isotope abundance ratio analysis of individual uranium-bearing particles

Secondary ion mass spectrometry (SIMS) was used in combination with alpha track detection for the efficient analysis of uranium-bearing particles with higher (235)U abundances in environmental samples. A polycarbonate film containing particles was prepared and placed in contact with a CR-39 plastic detector. After exposure for 28 days, the detector was etched in a NaOH solution and each uranium-bearing particle was identified through observation of the alpha tracks recorded in the detector. A portion of the film containing each uranium-bearing particle was cut out and put onto a glassy carbon planchet. The films on the planchet were decomposed through plasma ashing for subsequent uranium abundance ratio analysis with SIMS. The alpha track-SIMS analysis of 10 uranium-bearing particles in a sample taken from a nuclear facility enabled n((235)U)/n((238)U) abundance ratios in the range 0.0072-0.25 to be detected, which were significantly higher than those obtained by SIMS without alpha track detection. The duration of the whole analytical process for analysis of 10 particles was about 32 days. The detection efficiency was calculated to be 27.1±6.5%, based on the analysis of the particles in uranium reference materials. The detection limits, defined as the diameter of the particle which produces alpha tracks more than one for a 28-days exposure, were estimated to be 0.8, 0.9, 1.1, 2.1 and 3.0 μm for the particles having the same uranium abundance ratios with NBL CRM U850, U500, U350, U050 and U010 reference materials, respectively. The use of alpha track detection for subsequent SIMS analysis is an inexpensive and an efficient way to measure uranium-bearing particles with higher (235)U abundances.

Defect chemistry based design of monolithic langasite structures for high temperature sensors

High temperature stable piezoelectric crystals open a wide range of new sensor applications due to the ability to monitor environmentally dependent mechanical properties of sensor films deposited onto piezoelectric resonators. An understanding of the defect chemistry of piezoelectric single crystals like langasite (La3Ga5SiO14) aids in establishing their application limits and enables the creation of monolithic structures by appropriate doping. Key defect chemical properties of langasite are outlined with respect to dopants which increase the electrical conductivity or lower the electromechanical losses. We focus here on electronic and ionic transport in heavily Sr-doped langasite since spatially localized doping can be used to create monolithic electrodes. The total electrical conductivity (impedance measurements), the transport of oxygen and dopants (diffusion runs using stable tracers and subsequent secondary ion mass spectrometry) as well as the electromechanical properties (network analysis) are correlated. Strontium doped areas exhibit an increased conductivity by about 4 orders of magnitude, largely governed by oxygen ions. For demonstration of the concept, langasite bulk acoustic wave resonators with Sr-doped monolithic electrodes are operated up to 800°C. The resonator quality factors are found to be sufficiently high to use such resonators as high sensitivity sensors.

Study of the oxygen incorporation and diffusion in Sr(Ti 0.65Fe 0.35)O 3 ceramics

For applications in high temperature fast conductometric gas sensors and oxygen membranes, several mixed conductors show promising features. In particular, acceptor-doped strontium titanate (STO) has been widely investigated for an application as a fast conductometric oxygen sensor. By a B-site substitution with 35% iron, the resulting ceramic solid solution SrTi 0.65Fe 0.35O 3 (STF35) exhibits a temperature-independent conductivity, an ideal prerequisite for a gas sensor. In the presented study, the oxygen tracer exchange behavior and the tracer diffusion of dense ceramic STF35 bulks have been investigated in the temperature range between 600 and 900 °C by means of 18O 2 tracer exchange experiments and subsequent secondary ion mass spectrometry (SIMS), resulting in the determination of k* and D* values, respectively. Furthermore, by coating the samples with a thin alkaline earth metal oxide layer (CaO), a significantly enhanced oxygen surface exchange reaction was observed. These findings are in good agreement with previous results on STO single crystals.

Surface Kinetics of Oxygen Incorporation into SrTiO3

Effective surface rate constants for oxygen incorporation have been determined for single-crystal Fe-doped from chemical relaxation experiments, by in situ, spatially resolved optical absorption spectroscopy, and from tracer exchange experiments, by subsequent secondary ion mass spectrometry analysis. Experiments were carried out as a function of temperature, oxygen partial pressure, and dopant concentration. The effect of various metal films (Pt, Ag, Cr) and metal oxide films and on the surface reaction kinetics was also investigated. The implications of the results with regard to the mechanisms of chemical and tracer incorporation into are discussed. © 2002 The Electrochemical Society. All rights reserved.

Determination of hydrogen solubility in oxide ceramics by using SIMS analyses

Hydrogen solubility in oxide ceramics was evaluated by annealing in D2O-containing atmosphere and subsequent secondary ion mass spectrometry (SIMS). A good proportional relation was obtained between the relative intensity of deuterium ion in SIMS and literature data of hydrogen solubility for YSZ and Sr(Yb)CeO3−δ. The hydrogen solubility in CeO2 and rare-earth doped ceria (Ce0.8M0.2O1.9, M=Y, La, Nd, Sm, Gd, Yb) was evaluated. The hydrogen solubility in ceria dramatically increased by rare earth substitution, and it depended on the lattice parameter of Ce0.8M0.2O1.9.

SiC Dopant Incorporation Control Using Site-Competition CVD

The use of site-competition epitaxy, which is based on intentional variation of the Si/C ratio during epitaxy, has now been reproduced in numerous national and international laboratories. Presented in this paper is a summary of the site-competition technique as a comparison of controlled doping on C-face 6H-SiC(0001-) versus Si-face 6H-SiC(0001) substrates for phosphorous (P), aluminum (Al), boron (B), and nitrogen (N). Also reported herein is the detection of hydrogen in boron-doped CVD SiC epilayers and hydrogen-passivation of the boron-acceptors. Results from low temperature photoluminescence (LTPL) spectroscopy indicate that the hydrogen content increased as the C–V measured net hole concentration increased. Secondary ion mass spectrometry (SIMS) analysis revealed that the boron and the hydrogen incorporation both increased as the Si/C ratio was sequentially decreased within the CVD reactor during epilayer growth. Boron-doped epilayers that were annealed at 1700 °C in argon no longer exhibited hydrogen-related LTPL lines, and subsequent SIMS analysis confirmed the outdiffusion of hydrogen from the boron-doped SiC epilayers. The C–V measured net hole concentration for the B-doped epitaxial layers increased more than threefold as a result of the 1700 °C anneal, which is consistent with hydrogen passivation of the boron-acceptors. For N-doped epitaxy, N incorporation into C-sites is favored on the Si-face whereas N incorporation into the Si-site is apparently the preferred lattice site on the C-face. Both P and N exhibit preferred incorporation on the C-face while Al and B incorporation is more efficient on the Si-face.

Application of ion-beam-analysis techniques to the study of irradiation damage in zirconium alloys

Ion-beam-analysis techniques are being used to provide an understanding of the nature of collision cascades, irradiation-induced phase changes, lattice location of solute atoms and defect-solute atom interactions in various zirconium alloys. In zirconium intermetallic compounds, such as Zr 3Fe, Zr 2Fe, ZrFe 2, and Zr 3(Fe x ,Ni 1 − x ), electron and ion irradiations have been used to obtain detailed information on the crystalline-to-amorphous transformation occurring during the irradiation. Transmission-electron-microscopy (TEM) observations have provided information on the nature of the damage produced in individual cascades, the critical dose required for amorphization, and the critical temperature for amorphization. In a study on the electron-energy dependence of amorphization in Zr 3Fe, Zr 2Fe and ZrCr 2 in situ high-voltage-electron-microscope investigations were combined with high-energy forward-elastic-recoil measurements to yield information on the threshold displacement energies for Zr and Fe or Cr in these lattices, as well as the role of secondary displacements of lattice atoms by recoil impurities (C,O) at low electron energies. In Zr implanted with 56Fe ions and subsequently bombarded with 40Ar ions at 723 K, subsequent secondary-ion-mass-spectrometry (SIMS) analyses were used to monitor the effect of irradiation on the migration of Fe in the Zr lattice. In addition, ion-channeling investigations have been used to determine the lattice sites of solute atoms in Zr as well as the details of the interaction between the solute atoms and the irradiation-produced defects.

Hydrogen incorporation in boron-doped 6H-SiC CVD epilayers produced using site-competition epitaxy

We report on the initial investigations of using site-competition epitaxy to control boron incorporation in chemical vapor deposition (CVD) 6H-SiC epilayers. Also reported herein is the detection of hydrogen in boron-doped CVD SiC epilayers and hydrogen-passivation of the boron-acceptors. Results from low temperature photoluminescence (LTPL) spectroscopy indicate that the hydrogen content increased as the capacitance-voltage (C-V) measured net hole concentration increased. Secondary ion mass spectrometry (SIMS) analysis revealed that the boron and the hydrogen incorporation both increased as the Si/ C ratio was sequentially decreased within the CVD reactor during epilayer growth. Epilayers that were annealed at 1700°C in argon no longer exhibited hydrogen-related LTPL lines, and subsequent SIMS analysis confirmed the outdiffusion of hydrogen from the boron-doped SiC epilayers. The C-V measured net hole concentration increased more than threefold as a result of thel700°C anneal, which is consistent with hydrogen passivation of the boron-acceptors. However, boron related LTPL lines were not observed before or after the 1700°C anneal.

Crystalline state information from secondary ion mass spectrometry

Secondary ion mass spectrometry (SIMS) is used to study boron-doped silicon [100] wafers with a surface amorphous layer caused by the implantation of arsenic. When certain instrumental conditions are used, sample charging is observed at a depth of 1400 Å, corresponding to the end of the amorphous layer. The same sample was then regrown using rapid thermal annealing. In the subsequent SIMS analysis, the charging occurs at 2600 Å depth, corresponding to the p-n junction. Therefore, the depth of the rectifying barrier is strongly affected by the crystalline state of the sample, and the use of SIMS for obtaining information about the crystalline state in ion-implanted p-n materials is demonstrated.