Thermodynamic approach to the quantitative interpretation of sputtered ion mass spectra

Andersen, C. A.; Hinthorne, James

doi:10.1021/ac60330a034

Cited by 424 publications

(81 citation statements)

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“…Even though the chemical compositions of silicate glasses are appreciably different from calcium carbonate, the decreasing trend with the ionization potential is similar. There may be some physical mechanism, such as the LTE model, 29 which can explain the relationship observed in Fig. 4, irrespective of the chemical compositions (matrix effect).…”

Section: Secondary-ion Yieldsmentioning

confidence: 98%

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Nano-SIMS Analysis of Mg, Sr, Ba and U in Natural Calcium Carbonate

et al. 2005

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IntroductionIn paleoclimate studies, valuable information, such as ancient ocean temperatures 1-3 and past alkalinity distributions, 4 can be derived from the study of minor (Mg and Sr) and trace (Ba and U) element concentrations in marine calcium carbonates. These effects are attributable to the fact that Mg, Sr and Ba are members of Group II in the periodic table, and all have very similar chemical and physical properties, including a stable 2+ oxidation state. However, they do not behave identically in nature, and their differences in behavior have significant implications in geochemistry.For example, laboratory experiments have shown that the partition coefficient of Mg 2+ into inorganic calcite correlates strongly with temperature. 5 Recent studies have revealed that the U/Ca ratios in corals could provide a temperature proxy comparable in accuracy to the Sr/Ca ratios. The mechanism may be ascribed to a recent study 7 showing that the uranyl ion (UO2 2+ ) substitutes easily for Ca 2+ in aragonite. In addition, the Ba/Ca ratio of biogenic carbonate has been used to reconstruct past alkalinity distributions in oceans. 4 There are several analytical methods that can be applied to measuring these elements at the ~50 µm scale in calcium carbonate, such as laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), secondary ion mass spectrometry (SIMS) and electron microprobe (EMP). Among them, the LA-ICP-MS method 8 has a number of advantages, such as being easy to operate, less expensive and having a smaller matrix effect than the SIMS method. 9 However, LA-ICP-MS consumes more sample (has worse depth resolution) and it is difficult to reduce the probe spot to <10 µm to achieve greater sensitivity. On the other hand, the advantages of the EMP method 10 are its relatively low cost and excellent spatial resolution (spot size ~3 µm) compared with the SIMS method, while the major drawback of the EMP is its relatively low sensitivity, whereby it is impossible to detect trace elements at the several 10s µmol/mol level.The most powerful tool for precise trace-element analysis of calcium carbonate is the SIMS method with its significant depth resolution.9 Recently, a Nano-SIMS NS50 ion microprobe with unparalleled lateral resolution up to 0.05 µm has been developed by Cameca 11 and mostly applied to the field of cosmochemistry, 12,13 with few geochemical applications thus far. 14,15 It is desirable to apply this new ion microprobe to the analysis of terrestrial samples with its high lateral resolution.In this work, minor (Mg and Sr) and trace (Ba and U) element analysis of natural calcium carbonate was carried out by using a Nano-SIMS NS50 instrument. Experimental details of the ion microprobe measurements at spot size of 5 -6 µm are given. We assessed the accuracy and precision of the analyses as compared with those determined by ICP-MS after chemical dissolution, and also those determined by LA-ICP-MS on the same samples measured by Nano-SIMS. We then applied this method to foraminifera, which are tiny ...

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Section: Secondary-ion Yieldsmentioning

confidence: 98%

“…Based on the local thermal equilibrium (LTE) model 29 as applied to secondary ion production by 16 O -ion bombardment, the following equation 30 is derived:…”

Section: Secondary-ion Yieldsmentioning

confidence: 99%

Nano-SIMS Analysis of Mg, Sr, Ba and U in Natural Calcium Carbonate

et al. 2005

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“…Probably the most well known is the method whose model assumes the plasma to be in local thermodynamic equilibrium (LTE). 1,2 In this method, the secondary ion yield is expressed using two parameters: the plasma temperature and the electron density. Their values must be obtained from the ion intensities of two elements included in the sample and whose concentrations are known (internal standards).…”

mentioning

confidence: 99%

Quantification Method Using the Inverse Velocity Dependence of Ion Intensities in Secondary Ion Mass Spectrometry: the High-Energy Method

Higashi¹,

Homma²

1998

ANAL. SCI.

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Secondary ion mass spectrometry (SIMS) is a highly effective analytical method for measuring in-depth and lateral concentration distributions of trace elements. However, the elemental sensitivity in SIMS is strongly influenced by not only the element species but also the surrounding matrix. That is, the elemental secondary ion yield varies by several orders of magnitude with the composition and/or chemical state of the matrix. This is called the matrix effect. The variation in the secondary ion yield cannot fully be explained by theories. For accurate quantification of an element in a sample, first a standard sample must be prepared that consists of the same matrix as the subject sample and that includes the same element at a concentration which is already known. Then the sensitivity factor of the element must be obtained by measuring the standard sample under the same experimental conditions as those for measuring the subject sample. However, a standard sample cannot always be prepared unless it is a sample whose matrix is usual and is a pure material such as Si or GaAs. Without a standard sample, the quantification method that employs sensitivity factors cannot be applied. Furthermore, an elemental sensitivity factor can fluctuate (sometimes by a factor of 2) due to experimental conditions such as the sample's position on the sample holder, unless the experimental setup is fixed when measuring both the standard and the analyzed samples.Besides this experimental method, various semi-theoretical quantification methods have been proposed although there is no theory that has succeeded in explaining secondary ion yields completely. Probably the most well known is the method whose model assumes the plasma to be in local thermodynamic equilibrium (LTE).1,2 In this method, the secondary ion yield is expressed using two parameters: the plasma temperature and the electron density. Their values must be obtained from the ion intensities of two elements included in the sample and whose concentrations are known (internal standards). That is, this method usually needs two internal standard elements. Moreover, the assumption of the presence of the LTE itself is difficult for most people to accept, because ion sputtering is not a phenomenon in equilibrium. Many other semi-theoretical methods are based on quantum-mechanical models.3 Of interest among them are the tunneling ionization model for ion emission from a metallic surface 4,5 and the bond-breaking model for ion emission from an ionic solid surface.6-8 They are acceptable phenomenologically and helpful for us in understanding negative ion emission by bombarding a cesium-covered surface with a Cs + beam, and positive ion emission by bombarding an oxidized surface with an O 2 + beam in actual SIMS measurements. The two models deal with different phenomena, but have a similarity in that the ionization probability is exponentially dependent on the time taken by a sputtered atom to pass through the characteristic distance for electron exchange and the time should be proportio...

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“…As opposed to elastic processes, inelastic collisions from projectile impacts can induce electronic excitation, resulting in the formation of localized heat (or what is defined as a thermal spike model) 30 . Sputtering of this nature is regarded as kinetically assisted potential sputtering, where the initial impact to generate the concerted, non-linear motion leading to emission contributes energy to generate the thermal spike [30][31] .…”

Section: Ion-solid Interaction Sputtering and Dependence On Size Andmentioning

confidence: 99%

“…Sputtering of this nature is regarded as kinetically assisted potential sputtering, where the initial impact to generate the concerted, non-linear motion leading to emission contributes energy to generate the thermal spike [30][31] . Factors influencing the occurrence of such elastic or inelastic collisions have been strongly correlated to the projectile cross-section, the energy per constituent distributed on the projectile upon impact (if considering clusters), and the molecular forces holding these projectiles together 32,33,20 .…”

Section: Ion-solid Interaction Sputtering and Dependence On Size Andmentioning

confidence: 99%

Development of a Primary Ion Column for Mass Spectrometry-Based Surface Analysis

Villacob¹

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Thermodynamic approach to the quantitative interpretation of sputtered ion mass spectra

Cited by 424 publications

References 20 publications

Nano-SIMS Analysis of Mg, Sr, Ba and U in Natural Calcium Carbonate

Nano-SIMS Analysis of Mg, Sr, Ba and U in Natural Calcium Carbonate

Quantification Method Using the Inverse Velocity Dependence of Ion Intensities in Secondary Ion Mass Spectrometry: the High-Energy Method

Development of a Primary Ion Column for Mass Spectrometry-Based Surface Analysis

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