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1.
Nicholas P. McKay David L. Dettman Robert T. Downs Jonathan T. Overpeck 《Journal of Raman spectroscopy : JRS》2013,44(3):469-474
The potential for using Raman spectroscopy to measure stable oxygen isotope ratios (18O/16O) in carbonates is evaluated by measuring the Raman spectra and isotope ratios of a suite of 60 synthesized, 18O‐enriched calcite crystals ranging in composition from natural abundance (0.2 mole‐% 18O) to 1.2 mole‐% 18O. We determined the Raman‐inferred isotopic ratios (RRaman) by fitting curves to the ν1 symmetric stretching peak at 1086 cm−1 and the smaller satellite peak, associated with the ν1 stretching mode of singly substituted carbonate groups (C16O218O) at 1065 cm−1. The ratio of the two peak areas shows a 1:1 correspondence with the 18O/16O ratios derived from standard mass spectrometry methods, confirming that the relative intensities of the ν1 symmetric stretching peaks is a direct measure of the isotopic ratio in the carbonates. The 1‐sigma uncertainties of the RRaman values of the individual crystals were 0.00079 (384‰ PDB) and 0.00043 (210‰ PDB) for the four‐crystal sample means. This level of uncertainty is much too high to provide significant estimates of natural variability; however, there are multiple prospects for improving the accuracy and precision of the technique. Carbon isotope ratios in carbonates cannot be measured by our approach, but our results highlight the potential of Raman‐based isotope ratio measurement for C and other elements in minerals and organic compounds. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
2.
Ch. Schlechtriem U. Focken K. Becker 《Isotopes in environmental and health studies》2013,49(2):135-140
For many ecological applications of stable carbon isotope techniques, it is necessary to separate the lipid and lipid-free fractions. The effect of different lipid extraction methods on the isotope signature of the remaining lipid-free matter as well as the lipid fraction was tested. A hot extraction form of the Soxhlet method using petrol-ether was compared with two liquid-liquid extraction methods for lipid determination described by Bligh and Dyer and Smedes. Solid samples of fish and different natural food items were subjected to extraction and the carbon isotope ratios in lipid and lipid-free matter determined by IRMS. All methods were suitable for lipid extraction from all samples analysed here and did not cause biologically relevant differences (>1) in carbon isotopic ratios, except the Bligh and Dyer extraction method using chloroform which caused systematic errors for δ 13C when applied to diatoms. 相似文献
3.
Although most of them are relatively small, stable isotope deltas of naturally occurring substances are robust and enable workers in anthropology, atmospheric sciences, biology, chemistry, environmental sciences, food and drug authentication, forensic science, geochemistry, geology, oceanography, and paleoclimatology to study a variety of topics. Two fundamental processes explain the stable isotope deltas measured in most terrestrial systems: isotopic fractionation and isotope mixing. Isotopic fractionation is the result of equilibrium or kinetic physicochemical processes that fractionate isotopes because of small differences in physical or chemical properties of molecular species having different isotopes. It is shown that the mixing of radioactive and stable isotope end members can be modelled to provide information on many natural processes, including 14C abundances in the modern atmosphere and the stable hydrogen and oxygen isotopic compositions of the oceans during glacial and interglacial times. The calculation of mixing fractions using isotope balance equations with isotope deltas can be substantially in error when substances with high concentrations of heavy isotopes (e.g. 13C, 2H, and 18O ) are mixed. In such cases, calculations using mole fractions are preferred as they produce accurate mixing fractions. Isotope deltas are dimensionless quantities. In the International System of Units (SI), these quantities have the unit 1 and the usual list of prefixes is not applicable. To overcome traditional limitations with expressing orders of magnitude differences in isotope deltas, we propose the term urey (symbol Ur), after Harold C. Urey, for the unit 1. In such a manner, an isotope delta value expressed traditionally as?25 per mil can be written as?25 mUr (or?2.5 cUr or?0.25 dUr; the use of any SI prefix is possible). Likewise, very small isotopic differences often expressed in per meg ‘units’ are easily included (e.g. either+0.015 ‰ or+15 per meg can be written as+15 μUr. 相似文献
4.
Ryuichi Wada Tomoki Nakayama Tetsuya Hiyama Yasushi Fujiyoshi Naoyuki Kurita 《Isotopes in environmental and health studies》2017,53(6):646-659
Isotope ratios of carbon dioxide and water vapour in the near-surface air were continuously measured for one month in an urban area of the city of Nagoya in central Japan in September 2010 using laser spectroscopic techniques. During the passages of a typhoon and a stationary front in the observation period, remarkable changes in the isotope ratios of CO2 and water vapour were observed. The isotope ratios of both CO2 and water vapour decreased during the typhoon passage. The decreases can be attributed to the air coming from an industrial area and the rainout effects of the typhoon, respectively. During the passage of the stationary front, δ13C–CO2 and δ18O–CO2 increased, while δ2H–H2Ov and δ18O–H2Ov decreased. These changes can be attributed to the air coming from rural areas and the air surrounding the observational site changing from a subtropical air mass to a subpolar air mass during the passage of the stationary front. A clear relationship was observed between the isotopic CO2 and water vapour and the meteorological phenomena. Therefore, isotopic information of CO2 and H2Ov could be used as a tracer of meteorological information. 相似文献
5.
Zhiyuan Xiao Yanqing Yang Sheng Ouyang Zongde Kou Bin Huang Xian Luo 《Journal of Raman spectroscopy : JRS》2015,46(12):1225-1229
Phonon confinement effect and surface optical mode in SiC nanocrystal have been investigated through Raman spectroscopy. Considering high density of stacking faults in SiC grains, the correlation length of RWL (proposed by Richter, Wang, Li to explain phonon confinement in nano silicon) model is determined as a distance between nearby stacking faults. Thus, homogeneous region becomes thin slices in cylindrical SiC grains, which redefines weighting function. Effect of anisotropy of phonon dispersion curve is also analyzed during calculation. The additional 875‐cm−1 band is attributed to defects and amorphous SiC, which is confirmed by transmission electron microscopy. SiC grains are approximated as column array with grain boundary substances regarded as surrounding medium, which explains surface optical phonon mode at 915 cm−1. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
6.
The use of isotopic carbon dioxide lasers for determination of carbon (and oxygen) isotope ratios was first demonstrated in 1994. Since then a commercial device called LARA?, has been manufactured and used for Helicobacter pylori breath tests using 13C-labelled urea. The major advantages of the optogalvanic effect compared with other infrared absorption isotope ratio measurement techniques are its lack of optical background and its high sensitivity resulting from a signal gain proportional to laser power. Continuous normalisation using two cells, a standard and sample, lead to high accuracy as well as precision. Recent advances in continuous flow measurement of 13C/12C ratios of CO2 in air and extensions of the technique to 14C, which can be analysed as a stable isotope, are described. 相似文献
7.
A portable modular gas sensor for measuring the 13C/12C isotopic ratio in CO2 with a precision of 0.8‰(±1σ) was developed for volcanic gas emission studies. This sensor employed a difference frequency generation (DFG)-based spectroscopic
source operating at 4.35 μm (∼2300 cm-1) in combination with a dual-chamber gas absorption cell. Direct absorption spectroscopy using this specially designed cell
permitted rapid comparisons of isotopic ratios of a gas sample and a reference standard for appropriately selected CO2 absorption lines. Special attention was given to minimizing undesirable precision degrading effects, in particular temperature
and pressure fluctuations.
Received: 16 April 2002 / Revised version: 28 May 2002 / Published online: 21 August 2002
RID="*"
ID="*"Corresponding author. Fax: +1-713/5245237, E-mail: fkt@rice.edu 相似文献
8.
M.G. Donato G. Faggio M. Marinelli G. Messina E. Milani A. Paoletti S. Santangelo A. Tucciarone G. Verona Rinati 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(1):133-139
High quality synthetic diamonds were grown on single-crystal silicon by microwave plasma enhanced chemical vapour deposition
(CVD). A careful optimisation of both the experimental setup and the growth parameters was necessary before that the achievement
of the best results was made possible. The films were deposited using a CH4-H2 gas mixture at methane concentrations variable in the range 0.6-2.2%, while the substrate temperature was fixed at 750 °C. Raman spectroscopy and photoluminescence (PL) were utilised to monitor the quality of the deposited films and to study
the spatial distribution of defects, respectively. Micro-Raman analysis shows that linewidths of the diamond peak lower than
2.4 cm-1 can be easily measured at the growth surface, indicating that the crystalline quality of individual grains is comparable
to that of the best natural diamonds. The excellent phase purity of the diamond microcrystals at the growth surface is witnessed
by the complete absence of any non-diamond carbon feature and by a very weak luminescence background in the 1.6-2.4 eV spectral
range. A worsening of the quality of the diamond particles is found moving from the growth surface towards the film-substrate
interface. A photoluminescence feature at about 1.68 eV, commonly associated to Si impurities, is distinctly observed as the
exciting laser beam is focused close to the interface. A progressive degradation of the global quality of the films is found
with increasing methane concentration in the gas mixture, as witnessed by an increased PL background in the films grown at
higher methane concentrations.
Received 24 November 2000 相似文献
9.
Abstract In isotope geochemistry, natural differences in isotope abundance ratios of heavy elements (e.g. Sr, Nd, Pb) allow the use of specific isotopic signatures as tracers for these and genetically related elements. Examples of such applications in the field of anthropogeochemistry will be presented for lead and strontium. 相似文献
10.
Plant methoxyl groups of lignin and pectin have both distinct stable hydrogen isotope (δ2H) and carbon isotope (δ13C) values that can be used for studying environmental processes and for investigating the origin and authenticity of biomaterials. Up to now, the reported methods have been applied only to determine isotope values of the bulk plant methoxyl pool. In this work, we have applied several methods to distinguish between stable isotope ratios of methoxyl groups of pectin and the bulk plant methoxyl pool. Our results demonstrate that by applying alkaline hydrolysis to specifically cleave off the ester methyl moiety (pectin-like), we can distinguish δ2H and δ13C values of the pectin methoxyl pool from the bulk methoxyl pool. No measureable isotope discrimination was observed either during sample preparation or during analytical measurement. Furthermore, using this method, no major isotope difference in either the hydrogen or carbon isotope signature of the methoxyl groups of plant pectin and bulk matter from plant species such as leaves from trees, apples, carrots and potatoes was noted. We show the methanol released during alkaline hydrolysis of plant material and subsequently treated with hydriodic acid to be an excellent procedure to measure specifically and precisely the δ13C and δ2H isotope values of plant pectin-like methoxyl groups. This method is particularly advantageous when plant matter with a low methoxyl content has to be analysed. 相似文献
11.
Abstract The hippopotamus grazes nocturnally on land and resides in water during the day. Much of the ingested material must therefore be defecated directly into the aquatic system and can thus be considered an allochthonous resource available to aquatic consumers. The utility of stable isotope analyses of carbon and nitrogen to distinguish hippo faecal matter from other potential basal resources was tested at Lake Naivasha, Kenya. Hippopotami proved faithful to a short grass diet although supplementary grazing of aquatic macrophytes was observed. The typical isotopic ratios of C4 grasses ingested were not altered substantially by gut processes, and were clearly distinct from algal and aquatic macrophyte isotopic ratios. However, marginal plants such as Cyperus papyrus exhibit C4 ratios, and so the technique is suitable only for use in localities where ‘contamination’ from such sources is negligible. 相似文献
12.
A. A. Ezhevskii A. V. Soukhorukov D. V. Guseinov A. V. Gusev 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2010,4(3):432-436
An anisotropic EPR spectrum at T = 4 K was observed in silicon samples irradiated by phosphorus ions and subsequently annealed at 1000°C. Epitaxial silicon
layers with a natural isotope composition and enriched by 28Si isotope grown on a natural silicon wafer were investigated. The spectrum consisted of three lines corresponding to different
g-factor components: g
x
,g
y
, and g
z
. The central line was overlapped by the isotropic line coinciding by its g-factor with the line of the conduction electrons in silicon. The shape of the spectral lines indicated that the spectrum
was due to the paramagnetic centers which belong to the randomly oriented clusters with the anisotropic g-factor. The nature of the anisotropic EPR spectrum is due to the electrons localized on donors located in the strained phosphorous
clusters. The strains were caused by either incompletely annealed defects after the phosphorous implantation (E = 40 keV, D = 2 × 1014 cm−2, T
ann = 1000°C, 1 h) or phosphorous atoms in clusters. The distance between the components strongly depended on the temperature
and microwave power and decreased as they increased. 相似文献
13.
I. Tayasu F. Hyodo Y. Takematsu A. Sugimoto T. Inoue N. Kirtibutr 《Isotopes in environmental and health studies》2013,49(3):259-272
Abstract Nitrogen and carbon stable isotope ratios and uric acid concentrations in termites sampled from a dry evergreen forest in Thailand, were determined across three kinds of feeding habits. Feeding habits of Microcerotermes crassus, which is an abundant woodfeeder, and Dicuspiditermes makhamensis, a common soil-feeding termite, were confirmed by isotopic signatures. Lichen feeding termites (Hospitalitermes birmanicus, H. bicolor and H. ataramensis) were characterized by low δ15N values, suggesting that they assimilated nitrogen deposited from the atmosphere. There was also a significant difference in uric acid concentrations between termites representing different feeding habits. No significant relationships were found between uric acid concentrations and δ15N or δ13C in Hospitalitermes. However, δ15N values were correlated with C/N ratios in H. birmanicus, except in one colony of H. ataramensis. δ13C values in both species were negatively correlated with C/N ratios. 相似文献
14.
P.G. Sennikov A.V. Vodopyanov S.V. Golubev D.A. Mansfeld M.N. Drozdov Yu.N. Drozdov B.A. Andreev L.V. Gavrilenko D.A. Pryakhin V.I. Shashkin O.N. Godisov A.I. Glasunov A.Ju. Safonov H.-J. Pohl M.L.W. Thewalt P. Becker H. Riemann N.V. Abrosimov S. Valkiers 《Solid State Communications》2012,152(6):455-457
A new approach for producing high-purity silicon with isotopic enrichment of 28Si isotope is reported. The methods of centrifugal enrichment were modified to obtain the initial gaseous silicon tetrafluoride with a record-breaking enrichment of 0.99999664(11) with respect to 28Si. The effective conversion of silicon tetrafluoride into elementary silicon with minimal isotopic dilution was achieved in an electron cyclotron resonance discharge plasma, sustained by gyrotron microwave radiation with a frequency of 24 GHz. We have experimentally demonstrated the deposition of the layers of microcrystalline 28Si with enrichment of 0.999986 ± 0.000003, which is the best result at the present time. 相似文献
15.
A potentially useful scheme for photoselective isotope enrichment is presented. The selective laser excitation step is accomplished by utilizing the Stark effect to shift molecular transitions into resonance with laser frequencies. The method is demonstrated for isotope separation of 13C, 15N and 2H. Laser Stark spectroscopy can sensitively detect as few as 109 molecules in the optical path, thus the isotopic separation can be achieved from industrial sample mixtures containing natural abundances. A comparison of the isotopic enrichment efficiency using the present method of “exact” resonance and the previously used method of “near” resonance excitation is also given. 相似文献
16.
Boron isotopic enrichment is observed in the laser ablation of B4C target using nanosecond (ns) wide 532 nm laser beam of a Nd-YAG laser. B10/B11 ratio of 0.9 against the natural abundance of 0.25 is obtained at a laser power density of 8×108 W/cm2 (fluence of 6.4 J/cm2). The enrichment as a function of laser power density is demonstrated using a quadrupole mass spectrometer. Apart from higher
enrichment factor, only singly charged ions are found in the laser plume from the B4C target, in contrast to the multiply charged ions from the BN target reported in a recent report using femtosecond (fs) laser
pulses. This study indicates the possibility of using less expensive, widely used ns lasers, which can also yield a higher
throughput per pulse than a fs laser for isotope enrichment.
Received: 28 September 2001 / Accepted: 4 February 2002 / Published online: 3 June 2002
RID="*"
ID="*"Corresponding author. Fax: +91-4114/480-065, E-mail: mj@igcar.ernet.in 相似文献
17.
In SiC epilayers sp
3 C-H bond vibration bands were detected by infrared transmittance measurements. The absorption constants of the transmission peaks are related to the temperature at which the layers were grown and decrease with increasing growth temperature. The absorption centers vanish when the epilayer is removed or after annealing the sample at temperatures very much lower than the growth temperatures in a hydrogen-free atmosphere. These absorption centers are connected to hydrogen on silicon lattice sites. 相似文献
18.
Depending on the implantation temperature, the implantation of carbon ions into silicon at high doses results in the formation
of either amorphous SiCx or crystalline 3C-SiC precipitates. Various aspects of the precipitation behaviour observed, such as the impeded nucleation,
the limited growth and the resulting sensitivity to ballistic destruction are attributed to the large interfacial energy between
crystalline silicon and 3C-SiC. Periodically arranged amorphous SiCx nanoclusters, which are formed at lower temperatures, are shown to promote amorphisation by their surrounding stress field
and to represent sinks for silicon self-interstitials, which can be activated by annealing at 900 °C. By control of the depth
distribution of equally sized, oriented 3C-SiC precipitates formed at higher implantation temperatures, it is possible to
establish suitable starting conditions for the formation of buried homogeneous, single-crystalline 3C-SiC layers during a
post-implantation anneal. The properties of these ion-beam-synthesised SiC layers are described and attempts to combine them
with insulating and metallic layers are reviewed. A survey is given of the emerging applications of ion-beam-synthesised buried
SiC layers and microstructures in electronic, optical and micromechanical devices and as large-area SiC pseudosubstrates.
Received: 11 November 2002 / Accepted: 12 November 2002 / Published online: 4 April 2003
RID="*"
ID="*"Corresponding author. Fax: +49-821/598-3425, E-mail: lindner@physik.uni-augsburg.de 相似文献
19.
SiC reinforced copper composite coatings were prepared by electro-brush plating with micron-size silicon carbide (SiC) ranging from 1 to 5 μm on pure copper sheet in this paper. The micro-structural characterizations of SiC/Cu composite coatings were performed by optical microscope and Scanning Electron Microscope (SEM) coupled with spectrometer, to study co-deposition mechanism of SiC/Cu. It was found that there were three different patterns of SiC deposition in plating layers during electro-brush plating process, i.e. the particles could deposit inside copper grains, in grain boundaries, or in holes of the surface. To investigate deposition mechanism of each pattern, size of SiC and copper grains was compared. By comparison of size of copper grains and hard particles, SiC were either wrapped in copper grains or deposited in grain boundaries. Moreover, electro-brush plating layers at different brush velocities and current densities were obtained respectively, to analyze the microstructure evolution of the composite coatings. The hardness of plating layers was measured. The results indicated at the current density of 3 A/dm2, the SiC/Cu coating was compact with SiC content at a high level and the hardness reached a maximum. 相似文献
20.
M. Lee S. Moon M. Hatano C.P. Grigoropoulos 《Applied Physics A: Materials Science & Processing》2001,73(3):317-322
A new double laser recrystallization technique that can produce ultra-large direction- and location-controlled lateral grains
is presented. An excimer laser is combined with a pulse-modulated Ar+ laser to yield grains of tens of micrometers in size. The effect of different parameters on lateral grain growth is investigated.
These parameters include the time delay between the two lasers, the excimer-laser fluence, the Ar+-laser power and the pulse duration. The process has a wide process window and is insensitive to both the excimer-laser fluence
and the Ar+-laser power fluctuations. Preheating of the a-Si film with the Ar+ laser before firing the excimer laser is necessary for inducing lateral grain growth. The transient excimer-laser irradiation
is believed to generate nucleation sites for initiating the subsequent lateral grain growth. The surface roughness of the
recrystallized poly-Si is measured by atomic force microscopy.
Received: 14 September 2000 / Accepted: 24 February 2001 / Published online: 27 June 2001 相似文献