Papers by Keyword: Secondary Ion Mass Spectrometry

Abstract: Lithium-silicon compounds are promising materials as negative electrodes in Li-ion-batteries. The diffusion of Li in electrode materials is important for charging/discharging rates, maximum specific capacity and possible side reactions. In order to further the development of novel negative electrode materials for lithium-ion batteries, understanding the basic principles of atomic transport is of high importance. Thin Li_xSi films were investigated, which were produced by reactive ion-beam co-sputtering of segmented elemental Li and Si targets. Li tracer self-diffusion experiments were done on Li_xSi|⁶Li_xSi heterostructures and ⁶Li and ⁷Li isotopes depth profiles were analysed by secondary ion mass spectrometry before and after annealing. Diffusivities were extracted by comparing the experimental depth profiles to analytical solutions of the diffusion equation. The diffusivities for low Li concentrations x < 0.1 in Li_xSi follow the Arrhenius law between 140 and 325 °C with an activation energy of 1.4 eV. A trap-limited diffusion mechanism is suggested, comparable to hydrogen diffusion in hydrogenated amorphous silicon. In contrast, for x ≈ 0.4 complete isotope interdiffusion is observed directly after deposition at room temperature. These results indicate a significant acceleration of diffusion with increasing Li content as suggested in literature by theoretical calculations [1].

Abstract: This article presents a review on Li diffusion in lithium containing metal oxide compounds. The focus is on the investigation of solid state diffusion by tracer methods. In contrast to experiments with Nuclear Magnetic Resonance Spectroscopy and Impedance Spectroscopy, only a limited number of tracer based experiments can be found in the literature. Possible reasons are discussed. Measurements on the system Li-Nb-O are given in detail, while additional results on other Li-M-O (M = Al, Si, Mn, Ti) systems are also presented. The review is completed by a brief survey of the experimental methods in use.

Abstract: Self-diffusion in thin nanocrystalline Pt films was investigated using secondary ion mass spectrometry. Our experiments are motivated by recent investigations on stress relaxation where self-diffusion of Pt is supposed to play an important role, especially at temperatures below 250 °C and annealing times of a few hours. For the diffusion experiments, double layers of ^natPt/¹⁹⁴Pt were deposited on oxidized silicon wafers using ion beam sputtering. At 180 °C no significant diffusion induced broadening of the profiles could be observed even after an annealing time of 64 h. However, the concentration of ¹⁹⁵Pt in the top layer decreases slightly after an annealing time of 16 h and remains constant for higher annealing times. At 600 °C a broadening of the profiles was observed after an annealing time of 5 minutes. From our results we conclude that at 180 °C only atoms in the grain boundaries are mobile. After about 16 h the isotopes in the grain boundaries are completely interdiffused. From the change of the ¹⁹⁵Pt concentration in the top layer we estimate the amount of grain boundary phase in the Pt films to be about 5 %. The broadening of the profile after annealing at 600 °C is attributed to bulk diffusion.

Abstract: The diffusion of lithium in amorphous lithium niobate layers is studied as a function of temperature between 293 and 423 K. About 800 nm thick amorphous ⁷LiNbO₃ layers were deposited on sapphire substrates by ion-beam sputtering. As a tracer source about 20 nm thin ⁶LiNbO₃ layers were sputtered on top. Isotope depth profile analysis is done by secondary ion mass spectrometry. Compared are amorphous samples which show a ratio of Li : Nb < 1 (Li-poor) and of Li : Nb > 1 (Li-rich) close to the stoichiometric composition of Li : Nb = 1 for crystalline LiNbO₃. The results reveal that the diffusivities of both types of samples obey the Arrhenius law with an activation enthalpy of 0.70 eV and 0.83 eV, respectively. The diffusivities of the sample containing a higher amount of Li are lower by a factor of about two to ten. This demonstrates that variation of the Li content in amorphous samples over the stability range of the crystalline LiNbO₃ phase has only a modest influence on diffusivities and activation enthalpies.

Abstract: The effect of high intensity pulsed beam (HIPB) of accelerated carbon ions on zirconia ceramics of the 97ZrO₂-3Y₂O₃ (in mol %) composition is investigated. The parameters of the ion beam are as follows: the energy of the accelerated ions is 200 keV, pulse duration is 100 ns, pulse current density equal to 40 and 150 A/cm². It was revealed that ions treatment of ceramics leads to melting of the subsurface layer. In this area, the grains are elongated towards the surface. Upon treatment of ceramics by accelerated ions with the pulse energy density equal to 3 J/cm² (fluence ≥ 9.4•10¹⁵ cm^–2), formation of zirconia cubic phases up to 30 mass % is observed. The size of coherent-scattering region X-rays of the grains of the c-ZrO2 phase is 15–20 nm. The analysis of the elemental composition of the irradiated surface layers by secondary ion mass spectrometry (SIMS) method makes possible to conclude that formation of high concentration of non-stoichiometric oxygen vacancies under ion treatment is the main cause of the cubic phase stabilization in zirconia.

Abstract: The effect of the surface preparation in samarium doped semiconducting barium titanate [(Ba_1-xSm_x)TiO₃] ceramics with (Ba, Sm)/Ti ratio of 1.000 was studied by means of isotope tracer technique using a secondary ion mass spectrometer. The surfaces of specimens were prepared with the chemical mechanical polishing (CMP) with colloidal silica slurry or the mechanical polishing (MP) with diamond paste. The oxygen diffusion coefficients obtained in the CMP samples were small compared to those in the mechanical polished samples. This fact suggests that the surface prepared with CMP has less oxygen defect concentration. Moreover, it was also indicated that high temperature treatment over 1000 °C is required for annihilation of defects formed by MP. The oxygen diffusion study used CMP sample brings the useful information on the oxygen defect chemistry in Sm doped BaTiO₃.

Abstract: Li diffusion is investigated in Li₂O-deficient, (110) oriented LiNbO₃ single crystals in the temperature range between 523 and 673 K by secondary ion mass spectrometry. A thin layer of ion-beam sputtered isotope enriched ⁶LiNbO₃ was used as a tracer source, which allows one to study pure isotope interdiffusion. The diffusivities coincide with those of (001) oriented single crystals and follow the Arrhenius law with an activation enthalpy of 1.33 eV. The results prove the existence of a three-dimensional diffusion mechanism.

Abstract: We investigated lithium self-diffusion in amorphous and single crystalline lithium niobate at low temperatures of 323, 423 and 623 K. The diffusivity was studied by secondary ion mass spectrometry (SIMS), using ion beam sputtered ⁶LiNbO₃ as a tracer source. Our intention was to get information how structural disorder influences ionic diffusivity, while chemical composition remains unchanged. The results indicate an increase of the Li diffusivity by about eight orders of magnitude in the amorphous state.