Tectonometamorphic evolution of the Åreskutan Nappe-Caledonian history revealed by SIMS U–Pb zircon geochronology

Secondary ionization mass spectrometry (SIMS) U–Pb dating of zircons from the Åreskutan Nappe in the central part of the Seve Nappe Complex of western central Jämtland provides new constraints on the timing of granulite–amphibolite-facies metamorphism and tectonic stacking of the nappe during the Caledonian orogeny. Peak-temperature metamorphism in garnet migmatites is constrained to c. 442 ± 4 Ma, very similar to the ages of leucogranites at 442 ± 3 and 441 ± 4 Ma. Within a migmatitic amphibolite, felsic segregations crystallized at 436 ± 2 Ma. Pegmatites, cross-cutting the dominant Caledonian foliation in the Nappe, yield 428 ± 4 and 430 ± 3 Ma ages. The detrital zircon cores in the migmatites and leucogranites provide evidence of Late Palaeoproterozoic, Mesoproterozoic to Early Neoproterozoic source terranes for the metasedimentary rocks. The formation of the ductile and hot Seve migmatites, with their inverted metamorphism and thinning towards the hinterland, can be explained by an extrusion model in which the allochthon stayed ductile for a period of at least 10 million years during cooling from peak-temperature metamorphism early in the Silurian. In our model, Baltica–Laurentia collision occurred in the Late Ordovician–earliest Silurian, with emplacement of the nappes far on to the Baltoscandian platform during the Silurian and early Devonian, Scandian Orogeny lasting until c. 390 Ma.

Surface studies on uranium monocarbide using XPS and SIMS

The air-exposed surfaces of sintered and are-melted UC samples were examined by XPS and SIMS. XPS results indicate that the surface is covered with a very thin layer of UO2 mixed with free carbon, which would have formed along with the oxide during the reaction between UC and oxygen or moisture. From the SIMS depth profile of oxygen, the thickness of the oxide layer is found to be approximately 10 nm. The SIMS oxygen images of the surface as a function of etching time reveal that the surface of UC consists of a top layer of adsorbed moisture/oxygen; this contamination layer is followed by a layer containing uranium oxide, uranium hydroxide and free carbon and then grain boundary oxide and finally bulk UC. The behaviour of sintered and are-melted samples is similar.

Influence of carbide particles on the dynamic recrystallization of as-cast 304 stainless steel: a study using secondary ion mass spectrometric (SIMS) analysis

The domain of dynamic recrystallization (DRX) in as-cast 304 stainless steel material occurs at higher temperatures (1250 degrees C) and lower strain rates (0.001 s(-1)) than in wrought 304 stainless steel (1100 degrees C and 0.01 s(-1)). The above result has been explained earlier on the basis of a simple theoretical DRX model involving the rate of nucleation versus rate of grain boundary migration. The present investigation is aimed at examining experimentally the influence of carbide particles on the DRX of ascast 304 using secondary ion mass spectrometric (SIMS) analysis. Isothermal compression tests at a constant true strain rate have been performed on wrought 304 and as-cast 304 materials in the temperature and strain rate ranges of 1000 to 1250 degrees C and 0.001 to 1 s(-1) respectively. The SIMS analysis carried out on the deformed samples revealed that the large carbides present in the as-cast 304 material strongly influence the DRX process. In as-cast 304 material, the presence of large carbide particles in the microstructure shifts the DRX domain to higher temperature and lower strain rate in comparison with wrought 304 material.

Two new species of Brachystelma Sims (Apocynaceae: Asclepiadoideae-Ceropegieae) from the Western Ghats of India

Two new species of Brachystelma: B. mahajanii Kambale & S. R. Yadav from Ebbanad, Nilgiri District, Tamil Nadu and B. vartakii Kambale & S. R. Yadav from Periya, Kasargod District, Kerala are described and illustrated.

Spatial determination of gold catalyst residue used in the production of ZnO nanowires by SIMS depth profiling analysis

In this paper we demonstrate how secondary ion mass spectrometry (SIMS) can be applied to ZnO nanowire structures for gold catalyst residue determination. Gold plays a significant role in determining the structural properties of such nanowires, with the location of the gold after growth being a strong indicator of the growth mechanism. For the material investigated here, we find that the gold remains at the substrate-nanowire interface. This was not anticipated as the usual growth mechanism associated with catalyst growth is of a vapour-liquid-solid (VLS) type. The results presented here favour a vapour-solid (VS) growth mechanism instead. Copyright © 2007 John Wiley & Sons, Ltd.

A STUDY OF THE COMPOSITION DISTRIBUTION AT THE TI/AL2O3 INTERFACE USING THE MCS(+)-SIMS TECHNIQUE

In this article, the MCs(+)-SIMS technique has been used to characterize Ti/Al2O3 metal/insulator interfaces. Our experiment shows that by detecting MCs(+) secondary ions, the matrix and interface effects are reduced, and good depth profiles have been obtained. The experimental result also shows that with the increase of the annealing temperature (RT, 300 degrees C, 600 degrees C, 850 degrees C), the interface gets broadened gradually, indicating diffusion and reaction take place at the interface, and the interface reaction is enhanced with the increase in annealing temperature. When the temperature increases, the AlCs+ signal forms two plateaus in the Ti layer, indicating Al from the decomposition of Al2O3 diffuses into the Ti layer and exists as two new forms (phases). Also, with the increase of the annealing temperature, oxygen diffuses into the Ti layer gradually, and makes the O signal in the Ti layer increase significantly in the 850 degrees C annealed sample.

四极SIMS对AlxGa1-xAs中Si的定量分析

讨论了用MIQ-156四极SIMS仪器对Al_xGa_(1-x)As中Si进行定量分析的实验方法,考察了测量结果的重复性及x变化时Si RSF的变化规律,在IMS-4f SIMS仪器上进行了对比测试,用Cs~+源对~(29)Si的原子检测限达到4×10~(15)cm~(-3).

GaAs中氧的SIMS相对灵敏度因子的测定

介绍了用离子注入标样测定GaAs中氧的SIMS相对灵敏度因子的方法,并将实验数据进行离子计数-浓度,溅射时间-深度转换后求得的特征值(C_(max)、R_p、ΔR_p)等与理论计算值进行比较,二者符合较好,其中C_(max)的SIMS测量值同LSS理论计算值和Monte Carlo模拟计算值之间的平均偏差分别为9％和27％。最后,对几种GaAs基的材料和器件进行氧的定量分析,获得了有益的结果。

用四极型SIMS对砷化镓中硅定量分析的研究

GaAs中Si的定量分析是典型的SIMS分析课题,有明确的应用背景。对影响SIMS定量分析的一些基本因素进行了实验研究,用O_2~+源和Cs~+源对均匀掺硅和离子注入硅GaAs样品进行了定量分析,考察了实验的稳定性。