Magnetic Sector Secondary Ion Mass Research Articles

Deployment of Magnetic Sector Secondary Ion Mass Spectrometry Technology on Focused Ion Beam Instruments: From the Initial Concept Idea to the Analytical Add-On System

Deployment of Magnetic Sector Secondary Ion Mass Spectrometry Technology on Focused Ion Beam Instruments: From the Initial Concept Idea to the Analytical Add-On System

Toward Operando Structural, Chemical, and Electrochemical Analyses of Solid-State Batteries Using Correlative Secondary Ion Mass Spectrometry Imaging.

The global transition from fossil fuels to green energy underpins the need for efficient and reliable energy storage systems. Advanced analysis and characterization of battery materials is not only important to understand fundamental battery properties but also crucial for their continued development. A deep understanding of these systems is often difficult to obtain through only pre- and/or post-mortem analyses, with the full complexity of a battery being hidden in its operational state. Thus, we have developed an operando methodology to analyze solid-state batteries (SSBs) structurally as well as chemically before, during, and after cycling. The approach is based on a specially designed sample holder, which enables a variety of electrochemical experiments. Since the entire workflow is performed within a single focused ion beam scanning electron microscope equipped with an in-house developed magnetic sector secondary ion mass spectrometer, we are able to pause the cycling at any time, perform analysis, and then continue cycling. Microstructural analysis is performed via secondary electron imaging, and the chemical mapping is performed using the secondary ion mass spectrometer. In this proof-of-concept study, we were able to identify dendrites in a short-circuited symmetric cell and to chemically map dendritic structures. While this methodology focuses on SSBs, the approach can directly be adapted to different battery systems and beyond. Our technique clearly has an advantage over many alternatives for battery analysis as no transfer of samples between instruments is needed and a correlation between the microstructure, chemical composition, and electrochemical performance is obtained directly.

Correlative High-Resolution Imaging of Iron Uptake in Lung Macrophages.

Detection of iron at the subcellular level in order to gain insights into its transport, storage, and therapeutic prospects to prevent cytotoxic effects of excessive iron accumulation is still a challenge. Nanoscale magnetic sector secondary ion mass spectrometry (SIMS) is an excellent candidate for subcellular mapping of elements in cells since it provides high secondary ion collection efficiency and transmission, coupled with high-lateral-resolution capabilities enabled by nanoscale primary ion beams. In this study, we developed correlative methodologies that implement SIMS high-resolution imaging technologies to study accumulation and determine subcellular localization of iron in alveolar macrophages. We employed transmission electron microscopy (TEM) and backscattered electron (BSE) microscopy to obtain structural information and high-resolution analytical tools, NanoSIMS and helium ion microscopy-SIMS (HIM-SIMS) to trace the chemical signature of iron. Chemical information from NanoSIMS was correlated with TEM data, while high-spatial-resolution ion maps from HIM-SIMS analysis were correlated with BSE structural information of the cell. NanoSIMS revealed that iron is accumulating within mitochondria, and both NanoSIMS and HIM-SIMS showed accumulation of iron in electrolucent compartments such as vacuoles, lysosomes, and lipid droplets. This study provides insights into iron metabolism at the subcellular level and has future potential in finding therapeutics to reduce the cytotoxic effects of excessive iron loading.

Magnetic Sector Secondary Ion Mass Spectrometry on FIB-SEM Instruments for Nanoscale Chemical Imaging.

The structural, morphological, and chemical characterization of samples is of utmost importance for a large number of scientific fields. Furthermore, this characterization very often needs to be performed in three dimensions and at length scales down to the nanometer. Therefore, there is a stringent necessity to develop appropriate instrumentational solutions to fulfill these needs. Here we report on the deployment of magnetic sector secondary ion mass spectrometry (SIMS) on a type of instrument widely used for such nanoscale investigations, namely, focused ion beam (FIB)–scanning electron microscopy (SEM) instruments. First, we present the layout of the FIB-SEM-SIMS instrument and address its performance by using specific test samples. The achieved performance can be summarized as follows: an overall secondary ion beam transmission above 40%, a mass resolving power (M/ΔM) of more than 400, a detectable mass range from 1 to 400 amu, a lateral resolution in two-dimensional (2D) chemical imaging mode of 15 nm, and a depth resolution of ∼4 nm at 3.0 keV of beam landing energy. Second, we show results (depth profiling, 2D imaging, three-dimensional imaging) obtained in a wide range of areas, such as battery research, photovoltaics, multilayered samples, and life science applications. We hereby highlight the system’s versatile capability of conducting high-performance correlative studies in the fields of materials science and life sciences.

Surface Passivation and Detrimental Heat-Induced Diffusion Effects in RbF-Treated Cu(In,Ga)Se2 Solar Cell Absorbers.

Alkali postdeposition treatments of Cu(In,Ga)Se2 absorbers with KF, RbF, and CsF have led to remarkable efficiency improvements for chalcopyrite thin film solar cells. However, the effect of such treatments on the electronic properties and defect physics of the chalcopyrite absorber surfaces are not yet fully understood. In this work, we use scanning tunneling spectroscopy and X-ray photoelectron spectroscopy to compare the surface defect electronic properties and chemical composition of RbF-treated and nontreated absorbers. We find that the RbF treatment is effective in passivating electronic defect levels at the surface by preventing surface oxidation. Our X-ray photoelectron spectroscopy (XPS) data points to the presence of chemisorbed Rb on the surface with a bonding configuration similar to that of a RbInSe2 bulk compound. Yet, a quantitative analysis indicates Rb coverage in the submonolayer regime, which is likely causing the surface passivation. Furthermore, ab initio calculations confirm that RbF-treated surfaces are less prone to oxidation (in the form of Ga, In, and Se oxides) than bare chalcopyrite surfaces. In addition, elemental diffusion of Rb along with Na, Cu, and Ga is found to occur when the samples are annealed under ultrahigh vacuum conditions. Magnetic sector secondary ion mass spectrometry measurements indicate that there is a homogeneous spatial distribution of Rb on the surface both before and after annealing, albeit with an increased concentration at the surface after heat treatment. Depth-resolved magnetic sector secondary ion mass spectrometry measurements show that Rb diffusion within the bulk occurs predominantly along grain boundaries. Scanning tunneling and XPS measurements after subsequent annealing steps demonstrate that the Rb accumulation at the surface leads to the formation of metallic Rb phases, involving a significant increase of electronic defect levels and/or surface dipole formation. These results strongly suggest a deterioration of the absorber-window interface because of increased recombination losses after the heat-induced diffusion of Rb toward the interface.

Comparison of quantitative analyses using SIMS, atom probe tomography, and femtosecond laser ablation inductively coupled plasma mass spectrometry with Si1−XGeX and Fe1−X NiX binary alloys

Due to their electrical and physical properties, Si1−XGeX materials are widely used in microelectronic devices. In particular, the Ge component found within Si1−XGeX compounds is important for enhancing carrier mobility and altering the lattice constant of metal-oxide-semiconductor field-effect transistors. In this study, magnetic sector secondary ion mass spectrometry (magnetic sector SIMS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to determine the accurate concentrations of major compositions present within binary alloy samples. However, quantitative SIMS analysis is limited by the matrix effect, which influences the sputter yield of an element in a compound and alters the secondary ionization yields. Quantitative deviations that were due to the matrix effect were reduced by using Cs cluster ions (MCs+ and MCs2+) instead of elemental ions; the SIMS results using the elements were, therefore, compared with those using MCs+ and MCs2+ cluster ions. In the case of Fe1−XNiX alloys that have a less matrix effect compared to Si1−XGeX alloys, both the Cs primary ion beam (Cs+) and an oxygen primary ion beam (O2+) were used to measure the Fe1−XNiX compositions. The quantitative results from the two different primary ion beams were then compared to understand the ionization process. Deviations in the quantitative values gained with the O2+ beam were lower than those obtained using the Cs+ primary ions, meaning that using oxygen as the primary ion improves the accuracy in quantifying Fe1−XNiX compounds. Other reliable tools for analysis such as atom probe tomography and femtosecond laser ablation inductively coupled plasma mass spectrometry were also used in the quantitative analysis, with results that were consistent with the most accurate results obtained using magnetic sector SIMS and ToF-SIMS.

Chip-SIP: Stable Isotope Probing Analyzed with rRNA-Targeted Microarrays and NanoSIMS.

Chip-SIP is a stable isotope probing (SIP) method for linking microbial identity and function in mixed communities and is capable of analyzing multiple isotopes (13C, 15N, and 18O) simultaneously. This method uses a high-density microarray to separate taxon-specific 16S (or 18S) rRNA genes and a high sensitivity magnetic sector secondary ion mass spectrometer (SIMS) to determine the relative isotope incorporation of the rRNA at each probe location. Using a maskless array synthesizer (MAS), we synthesize multiple unique sequences to target hundreds of taxa at the ribosomal operational taxonomic unit (OTU) level on an array surface, and then analyze it with a NanoSIMS 50, using its high-spatial resolution imaging capability to generate isotope ratios for individual probes. The Chip-SIP method has been used in diverse systems, including surface marine and estuarine water, rhizosphere, and peat soils, to quantify taxon-specific relative incorporation of different substrates in complex microbial communities. Depending on the hypothesis and experimental design, Chip-SIP allows the user to compare the same community incorporating different substrates, different communities incorporating the same substrate(s), or quantify how a community responds to treatment effects, such as temperature or nutrient concentrations.

Quantitative Analysis and Band Gap Determination for CIGS Absorber Layers Using Surface Techniques.

Recently, Cu(InXGa(1−X))Se2 (CIGS) absorber layers have been extensively studied by many research groups for thin-film solar cell technology. CIGS material is particularly promising due to its exceptionally high absorption coefficient and large band gap range, which is adjustable as a function of alloy stoichiometry. To enhance the conversion performance of CIGS solar cells, understanding the CIGS structure and composition is a crucial challenge. We conducted a quantitative study to determine the bulk composition of the major elements such as Cu, In, Ga, and Se of four different CIGS photovoltaic cells. The compositional information was obtained by X-ray fluorescence (XRF), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and femtosecond laser ablation inductively coupled plasma mass spectrometry (fs-LA-ICP-MS). Then, the XRF concentration ratio was compared with the intensity ratio of fs-LA-ICP-MS to investigate the potential of accurate and rapid analysis using the fs-LA-ICP-MS technique. In contrast to the bulk information, the surface techniques can supply detailed information about the chemical composition across the depth profile. Here, elemental depth distributions of CIGS thin films were investigated using magnetic sector secondary ion mass spectrometry (SIMS) and Auger electron spectroscopy (AES). The atomic distributions of four different CIGS absorber layers exhibited a good agreement although they were obtained using two different surface instruments, AES and SIMS. Comparative analysis results of different CIGS absorber layers using SIMS, AES, and fs-LA-ICP-MS provide us with the appropriate technique for the information of accurate composition in a rapid analysis time. Thanks to a simple approach using the Ga/(In + Ga) ratio, the optical band gap energy of the Cu(InXGa(1−X))Se2 quaternary layer was monitored in the entire CIGS layer. The elemental distribution and the band gap determination were then used to elucidate their relationship to the corresponding CIGS cell efficiency result.

Evaluation of the use of magnetic sector secondary ion mass spectrometry to investigate 14C distribution in Magnox reactor core graphite

AbstractLarge quantities of irradiated graphite will arise from the decommissioning of the UK's Magnox power stations. Irradiated graphite contains 14C as well as other longer lived radionuclides (e.g. 36Cl). The potential use of magnetic sector secondary ion mass spectrometry (MS-SIMS) to examine the distribution of the 14C within trepanned graphite samples from a Magnox nuclear power station has been investigated. This work indicates that the methodology proposed has the potential to be used to analyse irradiated graphite samples with preliminary results highlighting a possible 14C enrichment in the carbonaceous deposit found on a channel wall sample. 14C concentrations in samples without this deposit were below the limits of detection of the instrument. The methodology used for these determinations ensured that possible mass interferences between 14C species and oxygen-bearing or nitrogen-bearing species were eliminated from the analysis. Future work will utilize the methodology proposed in this work on a larger number of samples.

Chemical characterization of III–V heterostructures in 3D architecture

Future nanoelectronic devices will integrate ultra-thin multilayers of various materials in 3D architecture. The depth and lateral resolution become critical for the analysis of the chemical composition of such materials. 2D composition depth profiling with high resolution for arrays of III–V trenches has been studied using magnetic sector secondary ion mass spectrometry. The averaged SIMS profiles were compared with 3D reconstructions of individual trenches containing confined InGaAs layers using higher spatial techniques: time-of-flight secondary ion mass spectrometry and atom probe tomography.

Improved understanding of an electron beam charge compensation method for magnetic sector secondary ion mass spectrometer analysis of insulators

Good charge compensation has historically been difficult to achieve for secondary ion mass spectrometry positive secondary ion depth profile analysis of highly insulating samples using a magnetic sector secondary ion mass spectrometer. A new charge compensation method has been developed utilizing an adjacent electron beam approach. A combination of computational simulation and quantitative characterization of the charge compensation phenomenon was used to elucidate the underlying mechanisms of this charge compensation technique with the goal of further improving this method. Results of this approach show that a low intensity electron shower consisting of secondary and backscattered electrons resulting from the impact of the primary electron beam with elements in the electron beam flight path may be responsible for charge compensation. It is also determined that the charge compensation provided by the adjacent impact technique can be further improved to provide better profile stability, higher mass resolution, and higher detection sensitivity by removing the conductive metal coating immediately adjacent to the sputtered area. Analysis of electron beam sensitive materials is also possible using this improved method.

Dynamic SIMS analysis of cryo-prepared biological and geological specimens

The modification of a dynamic magnetic sector secondary ion mass spectrometry (SIMS) instrument to permit the analysis of frozen biological and geological samples is described. The SIMS instrument used for this study combines SIMS analysis with the generation of ion-induced secondary electron images, allowing direct superposition of the SIMS image onto the image of cellular structures. Secondary ion maps have been acquired with sub-micron resolution, permitting the characterisation of sub-cellular elemental distributions in plant cells and human fibroblast cells, as well as the distribution of chemical impurities at grain boundaries in polar ice samples. This cryo-preparation technique clearly extends the applicability of SIMS analysis to a wide range of samples.

Sputtering with polyatomic ions: revisiting kinetic energy distributions of secondary ions

A new more accurate data processing procedure for calibration of kinetic energies of secondary ions measured in magnetic sector secondary ion mass spectrometers has been developed. The procedure was applied to reprocessing of raw data from previously published measurements of kinetic energy spectra of secondary atomic and cluster ions sputtered from Ta by 6 keV/atom Au −, Au 2 − and Au 3 − projectiles. Absolute energies of the sputtered Ta n + ions were determined more accurately, which permitted a fairer comparison of energy spectra for the same secondary ions measured under bombardment with different primary ions. Most probable and mean energies were determined for the sputtered ions, and their energy spectra were converted into distributions over inverse velocities. The reprocessed experimental results revealed strong differences between results for atomic and diatomic ions and those for larger cluster ions (consisting of more than seven atoms). In particular, the comparison of atomic and polyatomic bombardment showed that there are strong differences between atomic and diatomic sputtered species, while there were almost no changes between larger sputtered clusters. Results are discussed in terms of observed enhancements under polyatomic ion bombardment for the total sputtering efficiency and the ionization of sputtered species.

Comparison of secondary ion mass spectroscopy analysis of ultrashallow phosphorus using Cs+, O2+, and CsC6− primary ion beams

It is well known that reducing the work function of the sample surface using Cs+ ions increases the negative ion yield of phosphorus. It is also well known that a shallow primary beam implantation depth (RP) is required for achieving high depth resolution during the analysis of ultrashallow implant profiles. The combination of the opposite polarities of the positive Cs+ primary ion beam and the negatively biased sample (the combination most often used for P analysis using magnetic sector secondary ion mass spectroscopy) unfortunately accelerates the Cs+ ions towards the sample thus limiting the degree to which the primary ion impact energy can be reduced [R. Loesing, G. M. Guryanov, J. L. Hunter, and D. P. Griffis, J. Vac. Sci. Technol. B 18, 509 (2000)]. A low primary ion beam impact energy and high impact angle, both of which result in lower RP, can be obtained using a negatively charged cluster ion such as CsC6− (Peabody negative ion source) impacting on a negatively biased sample [G. Gillen, L. King, B. Freibaum, R. Lareau, and J. Bennett, in Secondary Ion Mass Spectrometry, SIMS XII, edited by A. Benninghoven et al. (Elsevier, Amsterdam, 2000), p. 279; R. Loesing, G. M. Guryanov, and D. P. Griffis, in Proceedings of the 13th Annual SIMS Workshop, Lake Tahoe, 2000, p. 36]. If, however, Cs is not required to improve secondary ion yield, a low energy O2+ primary beam impacting on a positively biased sample can be used [I. M. Abdelrehim, T. H. Büyüklimanli, S. P. Smith, and C. W. Magee, in Secondary Ion Mass Spectrometry SIMS XII, edited by A. Benninghoven (Elsevier, Amsterdam, 2000), p. 279; S. P. Smith, C. J. Hitzman, and C. W. Magee, in Secondary Ion Mass Spectrometry, SIMS XI, edited by G. Gillen (Wiley, Chichester, 1998), p. 277]. In this case, the reduction in sensitivity for P due to the loss of the negative ion yield enhancing Cs can be partly compensated by flooding the sample surface with oxygen. In this study Cs+, CsC6−, and O2+ primary ions are compared for depth profiling of ultrashallow phosphorus in Si in terms of decay length, sensitivity, and crater bottom roughness.

Use of an SF5+ polyatomic primary ion beam for ultrashallow depth profiling on an ion microscope secondary ion mass spectroscopy instrument

A magnetic sector secondary ion mass spectrometry (SIMS) instrument has been fitted with a modified hot filament duoplasmatron ion source for generation of SF5+ primary ion beams for SIMS depth profiling applications. The SF5+ primary ion beam has been evaluated by depth profiling of several low energy boron ion implants, boron delta-doped structures and a Ni/Cr metal multilayer depth profiling standard reference material. Using 3.0 keV impact SF5+ bombardment at a 52° impact angle with oxygen flooding gives a trailing edge decay length (1/e) for the boron implants and delta-doped layers of 1.3 nm. Under the same conditions, O2+ bombardment gives a trailing edge decay length (1/e) of 2.3 nm. The use of the SF5+ beam without oxygen flooding gives a substantial increase in decay length that is related to the formation of ripples as determined by atomic force microscopy. In the case of the Ni/Cr reference material, a significant reduction in sputter-induced topography is observed with SF5+ bombardment.

Preliminary evaluation of an SF5+ polyatomic primary ion beam for analysis of organic thin films by secondary ion mass spectrometry.

Organic vapor deposited thin films of pure biomolecules, polymer films and biomolecules dispersed in gelatin and biological tissue have been analyzed in a magnetic sector secondary ion mass spectrometer using an SF5+ primary ion beam at keV impact energies. In comparison to Ar+ bombardment under identical conditions, bombardment with SF5+ gives a 10 to 50 fold enhancement in the secondary ion yields for characteristic molecular ions. The SF5+ primary ion beam can be focussed to a small spot allowing molecular ion images to be obtained at micrometer spatial resolution with enhanced sensitivity. More importantly, the decay in molecular ion signal as a function of primary ion dose commonly observed in SIMS using monoatomic primary ions is either eliminated or greatly reduced, allowing molecular depth profiles to be obtained of organic thin films. By continuing to sample intact molecules as sputtering proceeds into the sample, the total number of detected characteristic secondary ions is increased by as much as a factor of approximately 700 for SF5+ bombardment as compared to Ar+ bombardment under identical analytical conditions. This effect is thought to be a result of the high erosion rate and the low penetration depth inherent in the use of a polyatomic primary projectile.

Surface metal contamination during ion implantation: Comparison of measurements by secondary ion mass spectroscopy, total reflection x-ray fluorescence spectrometry, and vapor phase decomposition used in conjunction with graphite furnace atomic absorption spectrometry and inductively coupled plasma mass spectrometry

Among the many challenges being addressed by manufacturers and users of ion implanters is the reduction of contamination of wafers during implantation by metals such as Al, Fe, Cr, Na, Cu, Mo, and W. Reproducible and accurate measurement of this near-surface contamination is equally challenging for analytical techniques and analysts. For this study As+ and BF+2 implants were made into Si wafers to study sources of metals contamination and to provide samples to be analyzed by a variety of techniques for comparison of their analytical strengths and weaknesses. Analytical techniques chosen for evaluation were quadrupole and magnetic sector secondary ion mass spectrometry, total reflection x-ray fluorescence spectrometry, and vapor phase decomposition used in conjunction with both graphite furnace atomic absorption spectrometry and inductively coupled plasma mass spectrometry.