Cation Mass Research Articles

Work function shifts and variations of ionization probabilities occurring during SIMS analyses using an in situ deposition of Cs0

Abstract To optimize the advantageous quantification technique consisting in analyzing MCs x + clusters, the Laboratoire d'Analyse des Materiaux (LAM) has developed the Cation Mass Spectrometer (CMS), a new instrument specially dedicated to performing this kind of analysis. To further enhance the potential of this instrument, we have developed a column that delivers a collimated and adjustable stream of neutral Cs atoms to be deposited on the surface of the sample while this one is being analyzed by SIMS. As this configuration permits a successful decoupling of the sputtering and Cs introduction processes by avoiding the constraints imposed by an energetic Cs + ion bombardment, it becomes possible to optimize simultaneously the sensitivity of the analysis, by carefully adjusting the Cs concentration to its optimum value, and the depth resolution of the analysis, by choosing adequate primary bombardment conditions. For the present paper, we have performed in situ measurements of the produced variations of the sample's work function, which are a typical concomitant of alkali metal deposition, by recording successive energy distributions of secondary Cs + ions sputtered from three different samples (Al, Si, Ni). The work function shifts detected by using this method can subsequently be used to explain the variations of the ionization probability of secondary Cs found in a previous study of MCs x + cluster analysis based upon the described technique. In this respect, we find curves which are typical for what one would expect considering the electron-tunneling model and this theoretical prediction is thus corroborated by our experimental results.

Cation Mass Spectrometer (CMS): recent developments for quantitative analyses of positive and negative secondary ions

The Cation Mass Spectrometer (CMS) has been developed in our laboratory to perform quantitative measurements with an optimal sensitivity and excellent depth and lateral resolution. For positive secondary ions, the MCs x + mode has been used to circumvent the problems linked to the matrix effect by decoupling the Cs surface concentration from the sputtering conditions, so that an optimal Cs surface concentration is guaranteed and permits one to obtain high sensitivity. Similarly, flooding the sample surface with Cs lowers the work function and permits high useful yields for negative secondary ions. To obtain these performances, a patented neutral Cs deposition column is used for Cs surface concentration control in combination with a surface ionisation Cs + gun for the sputtering of depth profiles or a Ga + LMIS for imaging.

Optimization of SIMS analyses performed in the MC sx+ mode by using an in situ deposition of C s

In order to optimize the advantageous quantification technique consisting in analyzing MCs x + clusters, we used the new Cs 0 column installed on the Cation Mass Spectrometer (CMS) and introduced an analysis technique consisting of an ion bombardment accompanied by a simultaneous deposition of Cs 0 at the surface of the sample. This experimental technique permits a successful decoupling of the sputtering and Cs introduction processes by avoiding the constraints imposed by an energetic Cs + ion bombardment. In order to investigate numerous aspects of the mentioned analytical technique, analyses were performed on three different samples (Al, Si, Ni) using a Ga + ion bombardment. In this paper, we will present an overview of the obtained results. We will deal in particular with the Cs concentrations reached during the analyses and the behavior of the measured MCs x + signals. We show in this context that the values of the Cs concentration and of the useful yields only depend on the ratio between the erosion and deposition rates, but not on the individual values of these two rates.

Optimization of SIMS analyses performed in the MCs x+ mode by using an in situ deposition of neutral Cs

To optimize the advantageous quantification technique consisting in analyzing MCs x + clusters, the Laboratoire d'Analyse des Matériaux (LAM) has developed the Cation Mass Spectrometer (CMS), a new instrument specially dedicated to perform this kind of analysis. To further enhance the potential of this instrument, we have developed a column that delivers a collimated and adjustable stream of neutral Cs atoms to be deposited on the surface of the sample while this one is being analyzed. Using this new column, it was possible to introduce an analysis technique consisting of an X y+ ion bombardment (where `X' stands for any element excepting Cs) accompanied by a simultaneous deposition of Cs 0 at the surface of the sample. This experimental technique permits a successful decoupling of the sputtering and Cs introduction processes by avoiding the constraints imposed by an energetic Cs + ion bombardment. As a consequence, it becomes possible to optimize simultaneously the sensitivity of the analysis, by carefully adjusting the Cs concentration to its optimum value, and the depth resolution of the analysis, by choosing adequate primary bombardment conditions. In this paper, we investigate numerous aspects of the mentioned analytical technique by using a Ga + ion bombardment and by performing analyses on three different samples (Al, Si, Ni). We study in detail the behavior of the measured MCs x + signals as well as of the corresponding useful yields. In this context, the observed evolutions are discussed in terms of ionization probabilities, number of available atoms participating in the formation mechanisms and recombination probabilities. We show in particular that the useful yields only depend on the ratio between the erosion and deposition rates, but not on the individual values of these two rates.

On the use of the 16O( 4He, 4He) 16O resonance for the evaluation of radiation damage in oxides

This paper deals with the evaluation of the radiation damage induced in the various sublattices of oxide single crystals submitted to irradiation with energetic ions. The study is focused on the depth distribution of the disorder (disorder profile) and the variation of the disorder as a function of the ion fluence (disordering kinetics). More specifically we discuss the pertinence of the use of the standard RBS or of the 16O( 4He, 4He) 16O resonance at 3.04 MeV for the study of the anionic sublattice in oxides with different cation masses. The experimental results obtained on several binary oxides indicate that the RBS mode is better suited for the study of oxides with low cation mass (e.g. SiO 2), whereas the resonant mode is more adapted to the study of oxides with high cation mass (e.g. UO 2). In the medium mass region (illustrated by ZrO 2), either the RBS or the resonant modes can be used depending whether the disorder profile or the disordering kinetics are evaluated.

The effects of alkali cation mass and radii on the density of alkali germanate and alkali germano-phosphate glasses

A quantitative density model for alkali germanate and alkali germano-phosphate glasses has been developed based on Raman spectra and density data. The model demonstrates that for lighter/smaller cations such as lithium and sodium, the transition from 4- to 3-membered GeO 4 rings is the prominent structural change responsible for changes in the density trends with increasing alkali oxide concentrations. For the heavier/larger cations such as potassium and rubidium, the 4- to 3-membered ring transition remains important but other factors must be considered. These include increases in density due to additional mass of the alkali oxides and decreases in density due to depolymerization of the glass network. The model shows that these combined factors can account for the ‘germanate anomaly’ noted in these glasses.

In situ deposition of neutral Cs for Secondary Ion Mass Spectrometry

The Cation Mass Spectrometer (CMS) is a new instrument allowing to optimize the advantageous quantification technique consisting in analyzing MCsx+ clusters. To further enhance the potential of this instrument, we have developed a column that delivers a collimated and adjustable stream of neutral Cs atoms to be deposited on the surface of the sample while this one is being analyzed by Secondary Ion Mass Spectrometry (SIMS). Using this new column, it was possible to introduce an analysis technique consisting of a Xy+ ion bombardment (where X stands for any element except Cs) accompanied by a simultaneous deposition of Cs0 at the surface of the sample. This experimental technique permits a successful decoupling of the sputtering and Cs introduction processes by avoiding the constraints imposed by an energetic Cs+ ion bombardment. As a consequence, it becomes possible to optimize simultaneously the sensitivity of the analysis, by carefully adjusting the Cs concentration to its optimum value, and the depth resolution of the analysis, by choosing adequate primary bombardment conditions. In this paper, we will first describe the new Cs0 column and outline its performances. In a second part, we will focus on the analytical aspect and study the ability to vary the Cs concentration over a complete and continuous range. Experiments using a Ga+ primary bombardment show in particular that the Cs concentration produced during analyses performed with the mentioned technique only depends on the characteristics of the analyzed material and the ratio between the erosion and deposition rates, but not on the individual values of these two rates.

The structure of alkali germanophosphate glasses by Raman spectroscopy

A series of alkali germanophosphate glasses ((R 2O) x (GeO 2:P 2O 5) 1− x where R=Na, K and Rb) with variable GeO 2:P 2O 5 ratios (8:1, 6:1, 4:1 and 2:1) have been investigated using Raman spectroscopy. The glass network may be treated as being made up of separate germanate and phosphate components. Addition of alkali cations indicates that the alkalis preferentially modify the phosphate part of the network. Network depolymerization occurs by formation of Q 2 and Q 1 PO 4 tetrahedra. At high Ge:P ratios the glasses exhibit a density anomaly. The anomaly is attributed to the formation of small three-membered GeO 4 rings. However, alkali cation size and mass are contributing factors to the shape of the density anomaly in the K 2O and Rb 2O containing glasses. Depolymerization of the 2:1 alkali germanophosphate glasses is predominantly by formation of Q 2 PO 4 tetrahedra. At low Ge:P ratios (2:1) density trends are linear. No ring transition is observed in these glasses. Furthermore, the presence of [5]Ge cannot be ruled out, but if present, does not play a major role in generating a ‘germanate anomaly’.

Useful yields of MCs x+ clusters: a cesium concentration-dependent study on the Cation Mass Spectrometer (CMS)

To optimize the advantageous quantification technique consisting in analyzing MCs x + clusters, the Laboratoire d’Analyse des Matériaux (LAM) has developed a new instrument specially dedicated to performing this kind of analysis. The Cation Mass Spectrometer (CMS) instrument leads to high MCs x + useful yields by allowing to reach an optimum value of the stationary Cs surface concentration, which is known to be a very critical parameter in MCs x + analysis due to its strong influence on the probability of secondary Cs + ionization. The present work focuses on the potential of the CMS instrument to vary the stationary Cs concentration over a large range and the benefits concerning the MCs x + useful yields resulting from this possibility. Analyses were performed on three different samples (Al, Si, Ni) while modifying the impact angle of the primary Cs + beam and in the Cs +–Ga + cobombardment mode. These techniques are shown to be complementary with respect to the covered ranges of cesium concentrations resulting in a complete range going from quasi 0 to some 30%. The observed variations of the useful yields are discussed in terms of the stationary Cs concentration produced during the analysis and the consequent variations of the Cs + ionization probability provoked by work function shifts which were determined by in-situ measurements. A comparison between the performances of the CMS and those of classic Cameca instruments shows, depending on the element, useful yield enhancements up to a factor 90 mainly due to work function conditions resulting in high Cs + ionization probabilities.

Thermal conductivity of ceramics in the ZrO2-GdO1.5system

Low thermal conductivity ceramics in the ZrO2–GdO1.5 system have potential in structural (refractories, thermal barrier coatings, thermal protection) and nuclear applications. To that end, the thermal conductivities of hot-pressed xGdO1.5 ·(1 – x)ZrO2 (where x = 0.05, 0.15, 0.31, 0.50, 0.62, 0.75, 0.89, and 1.00) solid solutions were measured, for the first time, as a function of temperature in the range 25 to 700 °C. On the ZrO2-rich side, the thermal conductivity first decreased rapidly with increasing concentration of GdO1.5 and then reached a plateau. On the GdO1.5-rich side, the decrease in the thermal conductivity with increasing concentration of ZrO2 was less pronounced. The thermal conductivity was less sensitive to the composition with increasing temperature. The thermal conductivity of pyrochlore Gd2Zr2O7 (x = 0.5) was higher than that of surrounding compositions at all temperatures. A semiempirical phonon-scattering theory was used to analyze the experimental thermal conductivity data. In the case of pure ZrO2 and GdO1.5, the dependence of the thermal conductivity to the absolute temperature (T) was less than 1/T. Therefore, the minimum thermal conductivity theory was applied, which better described the temperature dependence of the thermal conductivity of pure ZrO2 and GdO1.5. In the case of solid solutions, phonon scattering by cation mass fluctuations and additional scattering by oxygen vacancies on the ZrO2-rich side and by gadolinium vacancies on the GdO1.5-side seemed to account for the composition and temperature dependence of the thermal conductivity.

Cation Mass Spectrometer: towards an optimisation of MCs x+ cluster analysis

The Cation Mass Spectrometer (CMS) should lead to high MCs x + useful yields by allowing to reach an optimum value of the stationary Cs surface concentration, which is known to be a very critical parameter in MCs x + analysis due to its strong influence on the probability of secondary Cs + ionisation. For the present work, variations of the Cs concentration were obtained by modifying the impact angle of the primary Cs + beam and by bombarding the sample simultaneously with Cs + and Ga + beams. Results show that these techniques allow to cover a large and continuous range of Cs surface concentrations and to reach an optimisation of the MCs x + useful yields (enhancements up to a factor 100 compared to Cameca 4f and 6f instruments) mainly due to work function conditions resulting in high Cs + ionisation probabilities.

Low-energy excitation in CsPbX 3 (X=Cl, Br)

Inelastic neutron scattering measurements of a powder specimen of anion conducting superionic conductor CsPbCl 3 were performed at 30, 100, 200 and 300 K by the time-of-flight (TOF) spectrometer. A low-lying dispersionless excitation near 1.8 meV was observed in the inelastic scattering spectra of CsPbCl 3. The value of the low-energy excitation is almost independent of temperature. A low-lying dispersionless excitation near 1.8 meV was also observed in anion conducting superionic conductor CsPbBr 3 by the inelastic neutron scattering measurements. The results suggest that the presence of the low-lying dispersionless excitation would be related to the mass of heavy cations in CsPbX 3 (X=Cl, Br).

Ab initio quantum mechanical modeling of infrared vibrational frequencies of the OH group in dioctahedral phyllosilicates. Part II: Main physical factors governing the OH vibrations

The physical factors responsible for the variability observed in OH infrared (IR) fundamentals in dioctahedral phyllosilicates, due to octahedral substitution of Al3+ by Mg2+, Fe2+, and Fe3+, are discussed here. The data analyzed consist of experimental frequencies as well as frequencies modeled using Density Functional Theory (DFT) calculations. The charge of the octahedral cations surrounding the OH is one of the main factors affecting both the OH stretch and the in-plane bend; cationic electronegativity and ionic radius play important roles in the stretch and bend modes, respectively. The mass of the octahedral cations does not affect the OH fundamental vibrations. The nature of the octahedral cations alone can explain most of the variability observed in the OH in-plane bend, making this fundamental vibration the most suitable for assessing octahedral composition. Discrepancies between modeled and experimental OH stretch frequencies indicate the existence of other factors governing this fundamental vibration. Further DFT calculations indicate that apical O atoms of the tetrahedral sheet with unsatisfied charges due to octahedral and/or tetrahedral substitutions can explain these discrepancies. The modeling results are utilized to predict the frequency of the OH stretch and in-plane-bend combination band that occurs near 4545 cm−1 (2.2 μm) in phyllosilicates. This band can be observed in imaging spectrometer data, allowing for the detection and analysis of phyllosilicates and other minerals in large natural systems. The modeling results confirm that the variability observed in the combination band of dioctahedral phyllosilicates reflects octahedral and, to a certain degree, tetrahedral composition, but not interlayer composition.

Bond valence analysis of transport pathways in RMC models of fast ion conducting glasses

The bond valence method is applied to analyze local structure models from reverse Monte Carlo (RMC) fits to diffraction data. While our earlier studies demonstrated that for a wide range of silver ion conducting glasses both absolute value and activation energy of the ionic conductivity may be predicted from the volume fraction of regions with a sufficiently low valence mismatch for the silver ion, this investigation focuses on the precautions that have to be considered in a generalization of the bond valence approach to ionic conductors with various types of mobile ions and especially to alkali-metal ion conducting glasses. The separate structure conductivity correlations observed for each mobile cation can be combined to a unified empirical relationship by employing the square root of the cation mass as a scaling factor.

Cation Mass Dependence of the Nearly Constant Dielectric Loss in Alkali Triborate Glasses

Electrical ac conductivity measurements on alkali triborate glasses ( M2O x 3B2O3, M = Li, Na, K, and Rb) were performed at temperatures down to 8 K and frequencies up to 1 GHz. All samples show a nearly constant dielectric loss (NCL), at the limit of high frequencies and/or low temperatures. The magnitude of the NCL is found to decrease as m(-1/3) with increasing alkali ion mass m. This quantitative result for the NCL, closely related to the mean-square displacement of ions, indicates that the origin of the NCL might be related to vibrational relaxation of the ions in the anharmonic potentials that cage them, and the cage is decaying very slowly with time.

Heavy ion irradiation effects of brannerite-type ceramics

Brannerite, UTi 2O 6, occurs in polyphase Ti-based, crystalline ceramics that are under development for plutonium immobilization. In order to investigate radiation effects caused by α-decay events of Pu, a 1 MeV Kr + irradiation on UTi 2O 6, ThTi 2O 6, CeTi 2O 6 and a more complex material, composed of Ca-containing brannerite and pyrochlore, was performed over a temperature range of 25–1020 K. The ion irradiation-induced crystalline-to-amorphous transformation was observed in all brannerite samples. The critical amorphization temperatures of the different brannerite compositions are: 970 K, UTi 2O 6; 990 K, ThTi 2O 6; 1020 K, CeTi 2O 6. The systematic increase in radiation resistance from Ce-, Th- to U-brannerite is related to the difference of mean atomic mass of A-site cation in the structure. As compared with the pyrochlore structure-type, brannerite phases are more susceptible to ion irradiation-induced amorphization. The effects of structure and chemical compositions on radiation resistance of brannerite-type and pyrochlore-type ceramics are discussed.

Bond valence analysis of ion transport in reverse Monte Carlo models of mixed alkali glasses

ABSTRACTAn analysis of RMC structure models of ion conducting glasses in terms of our bond softness sensitive bond-valence method enables us to identify the conduction pathways for a mobile ion as regions of sufficiently low valence mismatch. The strong correlation between the volume fraction F of the “infinite pathway cluster” and the transport properties yields a prediction of both the absolute value and activation energy of the dc ionic conductivities directly from the structural models. Separate correlations for various types of mobile cations can be unified by employing the square root of the cation mass as a scaling factor. From the application of this procedure to RMC models of mixed alkali glasses, the mixed alkali effect, i.e. the extreme drop of the ionic conductivity when a fraction of the mobile ions is substituted by another type of mobile ions may be attributed mainly to the blocking of conduction pathways by unlike cations. The high efficiency of the blocking can be explained by the reduced fractal dimension of the pathways on the length scale of individual ion transport steps.

Amorphization and recrystallization of the ABO 3 oxides

Single crystals of the ABO 3 phases CaTiO 3, SrTiO 3, BaTiO 3, LiNbO 3, KNbO 3, LiTaO 3, and KTaO 3 were irradiated by 800 keV Kr +, Xe +, or Ne + ions over the temperature range from 20 to 1100 K. The critical amorphization temperature, T c, above which radiation-induced amorphization does not occur varied from approximately ∼450 K for the titanate compositions to more than 850 K for the tantalates. While the absolute ranking of increasing critical amorphization temperatures could not be explained by any simple physical parameter associated with the ABO 3 oxides, within each chemical group defined by the B-site cation (i.e., within the titanates, niobates, and tantalates), T c tends to increase with increasing mass of the A-site cation. T c was lower for the Ne + irradiations as compared to Kr +, but it was approximately the same for the irradiations with Kr + or Xe +. Thermal recrystallization experiments were performed on the ion-beam-amorphized thin sections in situ in the transmission electron microscope (TEM). In the high vacuum environment of the microscope, the titanates recrystallized epitaxially from the thick areas of the TEM specimens at temperatures of 800–850 K. The niobates and tantalates did not recrystallize epitaxially, but instead, new crystals nucleated and grew in the amorphous region in the temperature range 825–925 K. These new crystallites apparently retain some `memory' of the original crystal orientation prior to ion-beam amorphization.

FT-IR and Raman Spectroscopic Characterization of the Major Oilfield Sulfate Scale Forming Minerals

Sulfate minerals commonly form in the oilfield environment due to secondary recovery operations. Two essential tools for identification of these minerals are Fourier transform infrared (FT-IR) and Raman spectroscopies. In this paper, a comprehensive database of the FT-IR and Raman spectra of these minerals has been composed. The symmetry of the sulfate tetrahedra in the various sulfate molecules has been assigned from observation of the vibrational degeneracy. Force constant calculations show that cation mass and polarizability are the dominant influences upon sulfate symmetry. Studies of the vibrational peak positions have demonstrated a direct relationship between properties of the associated sulfate cation and the positions of both the infrared and Raman v1 and v3 vibrations. The major influences were found to be cation electronegativity, cation mass, and cation ionic radius. These observations were confirmed from force constant calculations. It has been concluded that both FT-IR and Raman spectroscopies are valid techniques for identification of oilfield scale minerals. Raman spectroscopy is particularly useful as it can be applied to aqueous systems and the in situ measurements of scale formation.

Useful yields of MCs + and MCs 2+ clusters: a comparative study between the Cameca IMS 4f and the Cation Mass Spectrometer

The useful yields of MCs + and MCs 2 + clusters strongly depend on the stationary cesium surface concentration c Cs incorporated in the specimen during the primary bombardment. The Cation Mass Spectrometer (CMS) has been designed to reach high MCs x + useful yields by allowing an optimization of c Cs in an instrument providing a high transmission via a high extraction field and a magnetic sector spectrometer. For this purpose the CMS instrument has been equipped by several newly developed features, among which figures a sample stage and adapted collection optics allowing variations of the impact angle of the primary beam on the specimen at a constant primary energy. These variations of the incidence angle imply changes of the sputtering yield Y, which determines the Cs surface concentration according to c Cs = 1/(1 + Y). In this paper, we will study the improvement of secondary yields obtained on the CMS, in comparison with a classical Cameca IMS 4f, by making use of precisely this possibility to vary the sputtering yield. On both machines, analyses were performed on six different elements (B, F, Mg, S, As, and In) implanted in silicon samples. The observed variations of the useful yields are discussed in terms of the stationary cesium surface concentration incorporated in the specimen during the primary bombardment. Depending on the element, useful yield enhancements ranging from a factor 7 to a factor 80 can be observed between the CMS and the Cameca IMS 4f. This finding can be explained by the fact that the CMS allows to reach lower stationary Cs surface concentrations, which are close to the optimum value for the investigated samples.